OPERATION
OF
ASTEWATER
TREATMENT
Volume III
A
Field
Study
Training
Program
ENVIRONMENTAL PROTECTION AGENCY .
• OFFICE OF WATER PROGRAMS •
DIVISION OF MANPOWER AND TRAINING •
-------
Environmental Protection Agency Review Notice
This training manual has been reviewed by the Office of Water Program
Operations, U.S. Environmental Protection Agency, and approved for publi-
cation. Approval does not signify that the contents necessarily reflect the
views and policies of the Environmental Protection Agency. Mention of trade
names or commercial products does not constitute endorsement or recom-
mendation for use by the Environmental Protection Agency, California State
University, Sacramento, California Water Pollution Control Association, au-
thors of the chapters or project reviewers and directors.
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OPERATION OF WASTEWATER
TREATMENT PLANTS
Second Edition
Volume III
A Field Study Training Program
prepared by
California State University, Sacramento
(formerly Sacramento State College)
Department of Civil Engineering
in cooperation with the
California Water Pollution Control Association
*****************************************************
Kenneth D. Kerri, Project Director
Bill B. Dendy, Co-Director
John Brady, Consultant and Co-Director
William Crooks, Consultant
for the
Environmental Protection Agency
Office of Water Program Operations
Municipal Permits and Operations Division
First Edition, Technical Training Grant No. 5TT1-WP-16-03 (1970)
Second Edition, Grant No. T900690010
1960
i
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NOTICE
This manual is revised and updated before each printing based on com-
ments from persons using the manual.
First printing, 1971
5,000
Second printing, 1972
7,000
Third printing, 1973
9,000
Fourth printing, 1974
6,000
Fifth printing, 1975
4,000
Sixth printing, 1977
11,000
Seventh printing, 1979
4,000
SECOND EDITION, Volume III
First printing, 1980 7,000
Copyright © 1980 by
Foundation o1 California State University, Sacramento
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PREFACE TO THE SECOND EDITION
VOLUME III
Volume III is a continuation of Volumes I and II. Volume I emphasized the knowledge and skills needed by new
operators and the operators of smaller treatment plants. Volume II stressed information needed by operators of
larger conventional treatment plants and by operators in supervisory and management positions. Volume III con-
tains information for operators with advanced waste treatment processes, complex solids handling and disposal
facilities, and industrial wastes to treat.
Topics covered in Volume III include the identification of the source and control of odors. The chapter on activated
sludge deals with the use of pure oxygen and alternative operational strategies. Most of the available processes for
treating and disposing of solids are covered in this volume. Advanced treatment processes to remove solids and
nutrients from the secondary effluents of conventional treatment plants are covered in considerable detail from the
viewpoint of the operator. Special chapters include the maintenance and troubleshooting of instruments and support
system equipment. Industrial waste treatment is discussed on the basis of treating strictly industrial wastes or
treating wastewater containing both domestic and industrial wastes. A special feature of this volume is numerous
case histories illustrating how various industries treat wastes and also reclaim and recycle treated wastewater.
You may wish to concentrate your studies on those chapters that pertain to your plant. Upon successful comple-
tion of this entire volume, you will have gained a broad knowledge of the entire wastewater treatment and reclama-
tion field.
For information on:
1. Uses of this manual,
2. Instructions to participants in home-study course, and
3. Summary of procedure,
please refer to Volume I.
Kenneth D. Kerri
John Brady
1980
iii
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OPERATION OF WASTEWATER TREATMENT PLANTS
VOLUME III, SECOND EDITION
Chapter Topic Page
20 Odor Control 1
21 Activated Sludge
(Pure Oxygen and Operational Control Alternatives) 31
22 Solids Handling and Disposal 119
23 Solids Removal from Secondary Effluents 281
24 Phosphorus Removal 353
25 Wastewater Reclamation 381
26 Instrumentation 421
27 Industrial Waste Monitoring 479
28 Industrial Waste Treatment 531
29 Support Systems 705
Final Examination 799
Glossary 813
Index 845
TECHNICAL CONSULTANTS, FIRST EDITION
William Garber Frank Phillips
George Gardner Warren Prentice
Carl Nagel Ralph Stowell
Joe Nagano Larry Trumbull
TECHNICAL CONSULTANTS, SECOND EDITION
George Gardner Carl Nagel
Larry Hannah Al Petrasek
Mike Mulbarger
iv
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COURSE OUTLINE
VOLUME I, SECOND EDITION
Chapter Topic
1 The Treatment Plant Operator
2 Why Treat Wastes?
3 Wastewater Treatment Facilities
4 Racks, Screens, Comminutors and Grit Removal
5 Sedimentation and Flotation
6 Trickling Filters
7 Rotating Biological Contactors
8 Activated Sludge
(Package Plants and Oxidation Ditches)
9 Waste Treatment Ponds
10 Disinfection and Chlorination
Final Examination
Glossary
Index
VOLUME II, SECOND EDITION
11 Activated Sludge
(Conventional Activated Sludge Plants)
12 Sludge Digestion and Solids Handling
13 Effluent Disposal
14 Plant Safety and Good Housekeeping
15 Maintenance
16 Laboratory Procedures and Chemistry
17 Basic Arithmetic and Treatment Plant Problems
18 Analysis and Presentation of Data
19 Records and Report Writing
Final Examination
Glossary
Index
v
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CHAPTER 20
ODOR CONTROL
by
Tom Ikesaki
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2 Treatment Plants
TABLE OF CONTENTS
Chapter 20. Odor Control
Page
OBJECTIVES 4
GLOSSARY 5
20.0 Need for Odor Control 7
20.1 Odor Generation 7
20.10 Biological Generation of Odors 7
20.11 Hydrogen Transfer Schemes 7
20.12 Hydrogen Sulfide Generation 8
20.2 Odor Identification and Measurement 8
20.3 Odor Complaints 11
20.4 Solutions to Odor Problems 12
20.40 Chemical Treatment of Odors in Wastewater 12
20.400 Chlorination 12
20.401 Hydrogen Peroxide 12
20.402 Oxygen 14
20.403 Ozone 14
20.404 Chromate 14
20.405 Metallic Ions 14
20.406 Nitrate Compounds 14
20.407 pH Control (Continuous) 14
20.408 pH Control (Shock Treatment) 14
20.41 Biological Odor Reduction Towers 14
20.410 Odor Reduction Tower Parts 14
20.411 Odor Reduction Tower Loading Rates 16
20.412 Start Up 16
20.413 Odor Reduction Tower Monitoring 16
20.42 Treatment of Odors in Air 17
20.43 Masking, Modification and Counteraction 17
20.44 Combustion 17
20.45 Absorption 17
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Odor Control 3
20.46 Chemical Scrubber Units for Foul Air Treatment 17
20.460 Major Components 20
20.461 Starting Procedure 20
20.462 Shut-Down Procedure 22
20.463 Operational Checks and Maintenance 22
20.47 Absorption 22
20.470 Process Description 23
20.471 Start-Up 23
20.472 Shut Down 23
20.473 Operational Checks 24
20.48 Ozonization 24
20.49 Good Housekeeping 24
20.5 Troubleshooting Odor Problems 25
20.6 Review of Plans and Specifications 27
20.7 Additional Reading 27
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4 Treatment Plants
OBJECTIVES
Chapter 20. ODOR CONTROL
Following completion of Chapter 20, you should be able to
do the following:
1. Determine the source and cause of odors,
2. Respond to odor complaints, and
3. Solve odor problems.
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Odor Control 5
GLOSSARY
Chapter 20. ODOR CONTROL
ABSORPTION (ab-SORP-shun) ABSORPTION
Taking in or soaking up of one substance into the body of another by molecular or chemical action (as tree roots absorb dissolved
nutrients in the soil).
ADSORPTION (add-SORP-shun) ADSORPTION
The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another substance.
BENZENE BENZENE
An aromatic hydrocarbon (C6Hg) which is a colorless, volatile, flammable liquid. Benzene is obtained chiefly from coal tar and is
used as a solvent for resins and fats and in the manufacture of dyes.
ELECTROLYTE (ELECT-tro-LIGHT) ELECTROLYTE
A substance which dissociates (separates) into two or more ions when it is dissolved in water.
ELECTROLYTIC PROCESS (ELECT-tro-LIT-ick) ELECTROLYTIC PROCESS
A process that causes the decomposition of a chemical compound by the use of electricity.
INDOLE (IN-dole) INDOLE
An organic compound (C8H7N) containing nitrogen which has an ammonia odor.
MERCAPTANS (mer-CAP-tans) MERCAPTANS
Compounds containing sulfur which have an extremely offensive skunk odor.
ODOR PANEL ODOR PANEL
A group of people used to measure odors.
OLFACTOMETER (ol-FACK-tom-meter) OLFACTOMETER
A device used to measure odors in the field by diluting odors with odor-free air.
OXIDATION (ox-i-DAY-shun) OXIDATION
Oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. In wastewater
treatment, organic matter is oxidized to more stable substances. The opposite of REDUCTION.
OXIDATION-REDUCTION POTENTIAL OXIDATION-REDUCTION POTENTIAL
The electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element
(the reductant) and used as a qualitative measure of the state of oxidation in wastewater treatment systems.
OXIDIZED ORGAN ICS OXIDIZED ORGANICS
Organic materials that have been broken down in a biological process. Examples of these materials are carbohydrates and proteins
that are broken down to simple sugars.
OZONIZATION (O-zoe-nie-ZAY-shun) OZONIZATION
The application of ozone to water, wastewater, or air, generally for the purposes of disinfection or odor control.
PHENOL (FEE-noll) PHENOL
An organic compound that is a derivative of benzene.
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6 Treatment Plants
REDUCTION (re-DUCK-shun) REDUCTION
Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic
conditions in wastewater, sulfate compounds or elemental suflur are reduced to odor-producing hydrogen sulfide (H2S) or the
sulfide ion (S~2). The opposite of OXIDATION.
SKATOLE (SKATE-tole) SKATOLE
An organic compound (C9H9N) containing nitrogen which has a fecal odor.
STRIPPED ODORS STRIPPED ODORS
Odors that are released from a liquid by bubbling air through the liquid or by allowing the liquid to be sprayed and/or tumbled over
media.
THRESHOLD ODOR THRESHOLD ODOR
The minimum odor of a sample (gas or water) that can just be detected after successive odorless (gas or water) dilutions.
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Odor Control 7
CHAPTER 20. ODOR CONTROL
20.0 NEED FOR ODOR CONTROL
Odor control in wastewater collection systems and at
wastewater treatment plants is becoming very important. With
the increased demand for housing, collection systems are
being extended farther and farther away from the treatment
plant. Longer collection systems create longer flow times to
reach the treatment plant. Increased travel times cause the
wastewater to become septic and thus cause odor and corro-
sion problems in collection systems and treatment plants. To
complicate matters the larger buffer areas around wastewater
treatment plants have all but disappeared. Land values and
increased population have made it impossible to continue to
have large buffer areas around most plants. As homes and
businesses become neighbors to existing plants, what was a
minor odor problem now becomes a major problem. No longer
can even the smallest trace of odor exist without complaints
from neighbors. Thus, preventing the emission of odors has
become a prime operating consideration.
20.1 ODOR GENERATION
In order to control odors more effectively, an understanding
of odor generation is needed. Understanding the problem and
the causes will lead to a more effective solution.
20.10 Biological Generation of Odors
The principal source of odor generation is a result of the
production of inorganic (no or one carbon in formula, HZS) and
organic (more than one carbon in formula, C8H7N) gases by
microorganisms in the collection system and treatment pro-
cesses. Odors also may be produced when odor-containing or
odor-generating materials are discharged into the collection
system by industries and businesses.
The main concerns of operators are the inorganic gases
HYDROGEN SULFIDE (H2S) and AMMONIA (NH;,). These
two gases give off the most offensive odors. As little as 0.5 ppb
(parts of gas per billion parts of air) of either of these gases can
be detected by the human nose and cause odor complaints.
Hydrogen sulfide has an extremely offensive smell and has the
odor produced by rotten eggs. Ammonia has a very sharp,
pungent smell and also is very offensive. Other inorganic
gases found in wastewater treatment plants are: carbon
dioxide (C02), methane (CH4), nitrogen (Nz), oxygen (02),
and hydrogen (H2). Normally found in nature, these gases are
the products of normal respiration and biological activity of
plants and animals and are not odorous.
Organic gases usually are formed in the collection system
and in the treatment plant by the anaerobic decomposition of
nitrogen and sulfur compounds. Organic gases also can derive
their odors from industrial sources. Examples of organic gases
found around treatment plants are MERCAPTANS,1 INDOLE,2
and SKATOLE.3 These odorous compounds contain nitrogen-
and sulfure-bearing organic compounds.
In the normal biological oxidation of organic matter, the mi-
croorganisms remove hydrogen atoms from the organic com-
pounds. In the process, the microorganisms use the bound
sources of oxygen to gain energy. The hydrogen atoms are
then transferred through a series of reactions that are some-
times called "hydrogen transfer" or "dehydrogenation."
20.11 Hydrogen Transfer Schemes
The following reactions illustrate the role of the hydrogen
atom in the formation of both odorless and odorous com-
pounds or end products.
Hydrogen
Acceptor
AEROBIC REACTION
Hydrogen
Atoms
Added
4 H+
End
Product
Molecular
Oxygen
ANAEROBIC REACTIONS
2 NO31 + 12 H4
Nitrate
C02
Carbon
Dioxide
SOj2
Sulfate
Oxidized
Organics4
8 H+
10 H4
n H+
2 H20
Water
(Odorless)
N + 6 H,0
Nitrogen Gas
(Odorless)
CH, + H20
Methane <3as
(Relatively odorless)
H2S + 4 H,0
Hydrogen Sulfide
(Odorous)
Lower Organics
(Odorous)
Gas
The order in which microorganisms break down compounds
containing oxygen in nature is: molecular oxygen (free dis-
solved oxygen), nitrate, sulfate, oxidized organics, and carbon
dioxide.
1 Mercaptans (mer-CAP-tans). Compounds containing sulfur which have an extremely offensive skunk odor.
2 Indole (IN-dole). An organic compound (CaH7N) containing nitrogen which has an ammonia odor.
3Skatole (SKATE-tole). An organic compound (C^H^N) containing nitrogen which has a fecal odor.
4 Oxidized Organics. Organic materials that have been broken down in a biological process. Examples of these materials are carbohydrates
and proteins that are broken down to simple sugars.
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8 Treatment Plants
There are some organisms that pan only use molecular oxy-
gen and cannot use the other forms. These microorganisms
are called "strictly aerobic microorganisms." "Facultative mi-
croorganisms" can use molecular oxygen and combined (or
bound) sources of oxygen such as nitrate. Still others, "strictly
anaerobic microorganisms," can only use bound sources such
as nitrate.
Q
20.12 Hydrogen Sulfide Generation
The main cause of most odors in wastewater systems is
hydrogen sulfide. Hydrogen sulfide can be detected by the
human nose in very low concentrations. This gas has a very
characteristic rotten egg odor. The conditions which lead to
hydrogen sulfide production also are conditions which produce
other odors and other problems. These problems include dan-
gers from explosive gas mixtures and hazards to the respira-
tory system to persons working in confined or close spaces
and corrosion or deterioration of concrete sewer structures
(such as pipelines and manholes). For these reasons, special
attention is given to hydrogen sulfide generation.
The most common source of sulfide in wastewater is biologi-
cal activity in the collection sewer or treatment plant. Sulfide
compounds can develop in the natural breakdown of sulfur-
bearing organic compounds. The source for the breakdown is
protein that is discharged in wastes in the forms of undigested
amino acids as part of feces and in urine as part of the unstable
urea protein. This natural breakdown accounts for only a minor
portion of all the sulfide compounds in the system. The major
part of odor-producing sulfide results from the breakdown of
inorganic sulfur compounds.
The principal sulfur compound found in wastewaters is sul-
fate. Sulfate compounds find their way into wastewaters from
the public water supply and from industrial sources. The pres-
ence or absence of oxygen establishes whether or not hydro-
gen sulfide will exist. When dissolved oxygen is present, the
sulfate ions will remain as sulfate. If the wastewater does not
contain dissolved oxygen, the biological breakdown will reduce
sulfate to sulfide, using the oxygen in the sulfate compound for
energy to break down organic matter. Although sulfate and all
essential elements may be present, sulfide is not produced in
all wastewater systems. The pH of the wastewater is an impor-
tant condition. Hydrogen sulfide is extremely pH dependent.
Sulfide can exist in wastewater in three forms depending on
the pH: S~2 ion, HS~ ion, or H2S gas. When sulfide is in an
ionic form, it is in solution so that it cannot escape as a gas.
Odors are formed and released when sulfide is in the gaseous
form (H2S). The pH of the solution has to be below pH 7.5 in
order for hydrogen sulfide gas to escape. At a pH below 5, all
sulfide is present in the gaseous H2S form and most of it can
be released from wastewater to cause odor, corrosion, explo-
sive conditions and respiratory problems.
SULFIDE FORMS (also see Fig. 20.1)
hydrogen
sulfide
(H2S) gas
H,S, 50%
HS~, 50%
HS-
ion
100%
S 2
ion
100%
below pH
of 5
neutral
pH of 7
pH of
9
above pH
of 10
The temperature of the system is an important factor that
must be considered, because the rate of bacterial metabolism
is related to temperature. Areas where the temperature is nor-
mally above 65°F (18°C) have more problems than those with
lower temperatures. Hydrogen sulfide generation is the
greatest at temperatures around 85°F (30°C) and above.
Figure 20.2 shows the sulfur cycle. The arrows indicate all
the ways sulfide can be produced in collection systems and
treatment plants.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 28.
20.OA Why is wastewater tending to become more septic
and thus causing odor and corrosion problems?
20.1 A How are odors produced?
20.1B What are the main inorganic gases of concern to
operators?
20.1C What is the order in which microorganisms break
down compounds containing oxygen in nature?
20.1 D What is the major source of inorganic odor-producing
sulfate compounds found in collection systems and
treatment plants?
20.1E Hydrogen sulfide causes problems at what pH range?
20.2 ODOR IDENTIFICATION AND MEASUREMENT
In order to control odors effectively, the operator should
know where odors originate and the cause. Odor detection in
the past has been very unscientific because it relied on the
human sense of smell. While our noses are more sensitive
than most instruments or detection devices, each person has a
different tolerance level for various odors. Occasionally what
smells good to one individual smells bad to another.
Odors can be detected by the use of lead-acetate strips to
reveal the presence of hydrogen sulfide. Gas detection de-
vices can be used to detect the presence of specific gases that
cause odors. Today odors can be measured by the use of an
OLFACTOMETER5 or an ODOR PANEL.6 The olfactometer
can measure odors in the field by diluting the odors with odor-
5 Olfactometer (ol-FACK-tom-meter). A device used to measure odors in the field by diluting odors with odor-free air. Reference, Metcalf &
Eddy, Inc., WASTEWATER ENGINEERING TREATMENT, DISPOSAL, REUSE, McGraw-Hill, New York, 1979.
6 Odor Panel. A group of people used to measure odors. Procedures for measuring odors by the use of a group of people are designated
D1391-57 by the American Society for Testing Materials, Philadelphia, Pennsylvania.
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Odor Control 9
100
80
60
40
20
0
11
10
9
P"
Fig. 20.1 Effect of pH on hydrogen sulfide-sulfide
equilibrium
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5
WA6T&
OB6ANIC
MATTER
OC6ANIC
V9
co.
SULFITE-1
<90^'
^4
*«Z
gfclO
3£>p
[4UUPAT6
4q4."
<^AWT
P<20T£lN
OI26ANJIC
<=>
<#
/7g. 20.2 Sulfur cycle
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Odor Control 11
free air. The number of dilutions required to reduce an odor to
its minimum THRESHOLD ODOR7 concentration provides a
quantitative measure of the concentration of strength of an
odor. The results are reproducible within reasonable levels.
Certain types of odors have significant effects on people and
animals. These odors have a major health and economic im-
pact on those affected. For these reasons, the identification of
odors is important. Once the odor has been identified, the
solutions can be studied. Unfortunately for us, different noses
are sensitive to different odors and the sensitivity of individual
noses varies from day to day.
The following are some facts that can help in odor classifica-
tion:
1. All individuals have a sense of smell,
2. Individuals respond differently to the same odor,
3. Some odors are objectionable and others are pleasant,
4. Odors travel great distances with the direction of the wind,
5. Small concentrations of odors can be offensive,
6. Similar compounds do not have the same odor, and
7. The human nose rapidly becomes fatigued (insensitive) to
odors.
The best that most operators can do when recording odors is
to classify the odor in some reasonable fashion. Sometimes a
person not working in a plant will have to identify odors be-
cause an operator's nose can become insensitive. Usually the
smells or odors can be classified into the following groups:
Table 20.1 summarizes the odors we can detect from vari-
ous substances and the threshold odor concentration, the level
at which our nose first detects an odor.
TABLE 20.1 ODOR CHARACTERISTICS"
Skunk,
Rotten cabbage,
Ammonia,
Fecal,
Rotten egg, and
Decayed flesh.
With this information the operator can begin attacking the
source of the problem. Skunk odors are frequently organic
gases that contain sulfur compounds. These odors are usually
from mercaptans. Rotten cabbage odors come from organic
compounds with sulfur compounds attached. Usually the or-
ganic compound associated with this smell is dimethyl sulfide.
Fishy smells are organic compounds that have nitrogen com-
pounds attached. Dimethyl amine is a typical compound pro-
ducing such a smell. Ammonia odors come from organic com-
pounds with nitrogen attached. Indole is such a compound.
Fecal odors are derived from skatole, which is an organic
compound with nitrogen attached. Rotten egg odors are from
the hydrogen sulfide molecule. The smell of decayed flesh
comes from diamines which are another ammonia-type com-
pound.
All of these compounds are similar, but they all smell differ-
ent. Once the odors are identified, the source may be con-
trolled and possibly eliminated. Solutions to odor problems are
different if there are mixtures of odors because different com-
pounds are involved.
SUBSTANCE
REMARKS
TYPICALb
THRESHOLD
ODOR, ppm
ALKYL MERCAPTAN
VERY DISAGREEABLE, GARLIC-LIKE
0.00005
AMMONIA
SHARP, PUNGENT
0.037
BENZYL MERCAPTAN
UNPLEASANT
0.00019
CHLORINE
PUNGENT, IRRITATING
0.010
CHLOROPHENOL
MEDICINAL
0.00018
CROTYL MERCAPTAN
SKUNK
0.000029
DIPHENYL SULFIDE
UNPLEASANT
0.000048
ETHYL MERCAPTAN
ODOR OF DECAYED CABBAGE
0.00019
ETHYL SULFIDE
NAUSEATING
0.00025
HYDROGEN SULFIDE
ROTTEN EGG
0.0011
METHYL MERCAPTAN
DECAYED CABBAGE
0.0011
METHYL SULFIDE
DECAYED VEGETABLE
0.0011
PYRIDINE
DISAGREEABLE, IRRITATING
0.0037
SKATOLE
FECAL, NAUSEATING
0.0012
SULFUR DIOXIDE
PUNGENT, IRRITATING
0.009
THIOCRESOL
RANCID, SKUNK-LIKE
0.0001
THIOPHENOL
PUTRID
0.000062
a MOP 11, Chapter 27, "Odor Control," Water Pollution Federation,
Washington, D.C., 1976.
b Various references will list slightly different threshold odor concen-
trations.
20.3 ODOR COMPLAINTS
Periodically all wastewater treatment plants will cause some
odor. These will be detected by the public and must be handled
by the operator. All complaints should be answered promptly
and courteously. The public pays for your services and indi-
rectly is your boss.
NEVER APPROACH A HOME WITH A NEGATIVE
ATTITUDE.
Beginning a conversation with a negative attitude will quickly
upset the public. Even if you can't detect the odor when you
answer a complaint, that does not mean that the odor was not
there or is not there now. Your nose may not be as sensitive as
the nose of the person filing the complaint. Also, your nose
may be accustomed to the smell and no longer be able to
detect the offensive odor.
The greatest complication develops if you do not properly
handle the problem. If the public unites against the plant and
becomes very odor conscious, even the slightest odor can
cause an uproar. Remember that the person filing the com-
plaint called because of a problem. You must be a diplomatic
7 Threshold Odor. The minimum odor of a sample (gas or water) that can just be detected after successive odorless (gas or water) dilutions.
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12 Treatment Plants
listener. Invite those who have complained to visit the plant
and offer them a tour. While you are showing them around the
plant, they may indicate to you where the odor that is bothering
them is the strongest. This information may help you identify
and control the cause of the odor problem.
Whenever an odor complaint is investigated, a record should
be made of the visit and the important facts recorded (Fig.
20.3). Investigations in the neighborhood near the location of
an odor complaint can be very helpful. Odors can be coming
from a nearby sewer, storm drain, trash pile, home plumbing
problem, or dead animal. If an odor complaint is repeated and
the source cannot be located, consider sending personnel to
the site during the time of day when odors are a problem to
determine the source.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 28.
20.2A How can odors be measured?
20.2B List as many groups or types of odors or smells as you
can recall.
20.3A Never approach a person who has an odor complaint
with a attitude.
20.3B When investigating an odor complaint, why might you
be unable to detect an odor that is disturbing to the
person complaining?
20.4 SOLUTIONS TO ODOR PROBLEMS
In order to solve any odor problem, a good systematic prob-
lem analysis is essential. The following steps indicate the pro-
cedure to follow when attempting to solve odor problems.
1. Make an on-site inspection and investigation of the problem
areas.
2. Attempt to identify the source or cause of the problem.
3. Review plant housekeeping.
4. Review plant operations.
5. Review plant performance.
6. Evaluate plant performance.
7. Review engineering or design features of the plant.
8. List and review all solutions to the problem.
9. Put into practice the best possible solution.
Solving the problem may create complications including new
odors and operating problems. Many times the odor is pro-
duced by a number of different gases in combination. When
this happens, a single solution may not be the answer. Chemi-
cals which counter the highest odor may cause other odors
which are even more offensive. Solutions to odor problems
may substantially increase operating and chemical costs.
Often the solution will not be a textbook answer, but a combi-
nation of solutions developed by trial and error and technical
aid from others.
To solve odor problems, try to identify the source and correct
the problem when the odors are being produced. Solutions
consist of preventing the development of anaerobic conditions
and/or retarding or stopping the activity of organisms which
produce odors under anaerobic conditions.
20.40 Chemical Treatment of Odors in Wastewater
20.400 Chlorlnatlon
Chlorination is one of the oldest and most effective methods
used for odor control. Chlorine is used in the disinfection pro-
cess and is readily available at the wastewater treatment plant.
Because of this availability, chlorine is frequently used to con-
trol odors. Chlorine is a very reactive chemical and, therefore,
oxidizes many compounds in wastewater. The reaction be-
tween chlorine and hydrogen sulfide and ammonia has been
studied by many researchers.
The reaction between chlorine and hydrogen sulfide is:
H2S + 4 Cl2 + 4 HzO -> H2S04 + 8 HCI
The reaction of ammonia with chlorine is:
NH2CI + HCI (monochloramine, NH2CI)
NHCI2 + HCI (dichloramine, NHCI2)
NHCI2 + Cl2 -~ NCI3 + HCI (trichloramine, NCIj)
NH3 + Cl2
NH2CI + Cl2
The most important role that chlorine plays in controlling
odors is to inhibit the growth of odor-causing microorganisms.
This control requires less chemical than trying to oxidize the
odor once formed. This means that the chlorine should be
added in the collection system ahead of the plant.
Odors are not always removed by the use of chlorine. The
reaction of chlorine with certain chemicals can cause a more
odorous gas. One example is the reaction of chlorine with
PHENOL8 to form chlorophenol, a medicinal-smelling sub-
stance.
Sodium hypochlorite has been used like chlorine to control
odors. The chemical reactions with other substances are very
similar.
Experience has shown that a 12 to 1 dose of chlorine to
dissolved sulfide (12 mg/L chlorine per each 1 mg/L sulfide) is
needed to control the generation of hydrogen sulfide in sewers.
Do not determine the chlorine dose on the basis of the concen-
tration of H2S in the sewer atmosphere.
20.401 Hydrogen Peroxide
For a number of years, hydrogen peroxide (H202) has been
used as an oxidant to control odors. Hydrogen peroxide reacts
in three possible ways to control odors.
1. Oxidant action:
Oxidizes the compound to a nonodor-
ous state. An example of this is the
conversion of hydrogen sulfide to sul-
fate compounds.
H,0 + sulfate com-
H2S +
h2o2
pounds
In actual practice a dose of 2:1 to 4:1
of H202
to S" is needed for control.
2. Oxygen producing: Acts to prevent the formation of odor
compounds. This is accomplished by
keeping the system aerobic.
3. Bactericidal to the Kills the bacteria that produce odors,
sulfate-reducing Without biological activity, odors will
bacteria: not be generated. This high a dose of
H202 is probably not economically
feasible.
8 Phenol (FEE-noll). An organic compound that is a derivative of benzene.
-------
Odor Control 13
Date
. Name of investigator
Location
Person filing complaint
Address
Phone number
Date and time complaint occurred
Nature of complaint
INVESTIGATION:
Date and time of investigation __
Strength of odor
1 . No odor
2 . Faint
3 . Noticeable
4 . Definite
5 . Strong
6. Overwhelmingly strong
Wind direction
1. North wind
2. South wind
3 . East wind
4 . West wind
5. No wind
Description of odor
1. Ammonia
2. Decayed Cabbage
3. Feca)
4 . Fistiy
5. Gate
6. Medicinal
7. Rotten Egg
8 . Skunk
9. Other
1.
2.
3.
4
5.
Strength of wind
- Quiet
_ Mild
- Gusty
_ Strong
_ Very strong
Try to comment on whether odor occurs during any specific time of the day, day of the week, or weather conditions.
Comments:
Reviewed by: Date
(Chief Operator)
Corrective Action:
Fig. 20.3 Odor complaint form
-------
14 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 28.
20.4A Outline the systematic steps you would follow to solve
an odor problem.
20.4B What is the most important role that chlorine plays in
controlling odors?
20.4C What are the three possible ways hydrogen peroxide
reacts to control odors?
20.402 Oxygen
Oxygen has been used with a great deal of success. The
most common practice with oxygen is to use air to aerate the
wastewater and try to keep the wastewater aerobic. The trans-
fer of oxygen to the wastewater will increase its OXIDATION-
REDUCTION POTENTIAL9 (ORP) and thus reduce the forma-
tion of odorous gases. With increased ORP, the sulfate ion is
not used as an oxygen source, so the odor is reduced.
Up-stream aeration will cause hydrogen sulfide to be
stripped out (carried out by the air) of the liquid, if it is present,
and thus reduce the release of odors at the plant when water
flows over weirs or other locations of high turbulence.
STRIPPED ODORS10 may be collected from above the sur-
face where aeration takes place and be treated. If these odors
are not properly handled, localized corrosion and odor prob-
lems can result.
20.403 Ozone
Ozone is a powerful oxidizing agent that effectively removes
odors. Ozone has limited use because an effective concentra-
tion may be too costly to use at large treatment plants. Ozone
works well when used to remove odors from air collected over
sources of odors (Section 20.48).
An advantage of ozone is the fact that there are no known
deaths resulting from the use of ozone. Ozone can cause irrita-
tion of your nose and throat at a concentration of 0.1 ppm, but
your nose can smell ozone around 0.01 to 0.02 ppm. Another
advantage of ozone is that you can manufacture what you
need at the plant site and do not have to handle bulky contain-
ers. Ozone is not available in containers because it is relatively
unstable and cannot be stored.
20.404 Chromate
Chromate compounds can effectively inhibit the sulfate re-
duction to sulfide. However, this method introduces heavy
metals into the sludge and wastewater, and this may cause an
even more offensive odor. Heavy metals, such as chromate,
cause serious toxic conditions that limit their usefulness.
20.405 Metallic Ions
Certain metallic ions (mainly zinc) have been used to form
precipitates with sulfide compounds. These precipitates are
insoluble and have a toxic effect on biological processes such
as sludge digestion. Therefore, this process has its limitations.
20.406 Nitrate Compounds
The first chemicals used in the anaerobic breakdown are
nitrate ions. If enough nitrate ions are present, the sulfate ions
will not be broken down. The cost of this type of treatment to
halt hydrogen sulfide production is very high and, at present, is
not practical.
20.407 pH Control (Continuous)
Increasing the pH of the wastewater is an effective odor
control method for hydrogen sulfide. By increasing the pH
above 9, biological slimes and sludge growth are inhibited.
This, in turn, halts sulfide production. Also, any sulfide present
will be in the form of the HS- ion or S-2 ion, rather than as H2S
gas which is formed and released at low pH values.
20.408 pH Control (Shock Treatment)
Short term, high pH (greater than 12.5) slug dosing with
sodium hydroxide (NaOH) is effective in controlling sulfide
generation for periods of up to a month or more depending on
temperature and sewer conditions. Care must be exercised in
selecting the length of dosing so that downstream treatment
plant biological systems will not be seriously impaired.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 28.
20.4D How is oxygen used to control odors?
20.4E What is a limitation of using metallic ions to precipitate
sulfide?
20.4F How can pH adjustment control odors from hydrogen
sulfide?
20.41 Biological Odor Reduction Towers (ORT)
(Fig. 20.4)
An odor removal tower is essentially a deep bed trickling
filter that is lightly loaded to produce a nitrifying biological
zoogleal mass on the filter media. Foul air and off gases from
the treatment plant process system are captured and piped
into the bottom of the odor removal tower. As this odorous air
passes up through the filter media, the odors may be oxidized
to an acceptable odor level and discharged to the atmosphere
at the top of the tower. The odor reduction tower (ORT) has
two flow streams, one liquid to maintain the biomass on the
media and also the air flow carrying the odors.
20.410 Odor Reduction Tower Parts
LIQUID STREAM
1. Filter Media. Usually plastic media is used to provide sur-
face area for the biological slimes or biomass to attach
themselves. The filter media bed depth may range from
twenty to thirty feet (6 to 9 m) in depth.
9 Oxidation-Reduction Potential. The electrical potential required to transfer electrons from one compound or element (the oxidant) to
another compound or element (the reductant) and used as a qualitative measure of the state of oxidation in wastewater treatment systems.
10 Stripped Odors. Odors that are released from a liquid by bubbling air through the liquid or by allowing the liquid to be sprayed and lor
tumbled over media.
-------
Odor Control 15
GRATING
ORT SPRAY
DISTRIBUTION ROOM
FLUSHING COCK
TREATED
WASTEWATER
SPRAY NOZZLE
FILTER MEDIA
sss
'—FOUL AIR
FOUL AIR
DISTRIBUTION
DIFFUSER
ORT SUMP
ORT CIRCULATION
PUMP 2
•ORT CIRCULATION
PUMP 1
Fig. 20.4 Biological odor reduction tower (ORT)
(Permission of Sacramento Area Consultants)
-------
16 Treatment Plants
2. Filter Sump. A tank at the bottom of the filter where the
applied liquid (primary or secondary effluents) is collected
to be pumped back over the filter media to sustain the
biomass.
3. Sump Overflow. An outlet weir that prevents the filter
sump from filling too high and returns the overflow back to
the plant headworks.
4. Filter Feed Pump. A pump that recycles secondary
effluent from the treatment plant to the top of the filter, This
water is applied through spray nozzles to the filter bed. The
filter feed may be secondary effluent or a blend of second-
ary and primary effluent. This blend is essential to maintain
the proper BOD loading on the filter to support the biomass
in a nitrifying stage.
5. Spray Nozzles. Nozzles placed over the top of the filter
media to assure an even distribution over the filter of the
recirculated effluent. These spray nozzles perform the
same function as the rotating distributor arm on a trickling
filter.
AIR STREAM
1. Supply Fans (Blowers). Fans that transport foul air and off
gases from the treatment plant process units through ducts
and pipes to diffusers at the bottom of the odor reduction
tower.
2. Mist Eliminator. A device located at the top of the odor
reduction tower above the filter bed. This device separates
as much moisture as possible from the gas stream before it
enters the exhaust fan of the odor reduction tower to be
discharged to the atmosphere.
3. Tower Exhaust Fan. This fan pulls air from the filter bed
and tower column and discharges scrubbed air to the at-
mosphere.
20.411 Odor Reduction Tower Loading Rates
Recommended loading rates to maintain a nitrifying biomass
are summarized in Table 20.2. Odor reduction towers operated
in accordance with Table 20.2 should use secondary effluent
and a single pass operation. There are two advantages to this
method of operation. One, plugging of the spray heads is
minimized by using secondary rather than primary effluent.
Two, a single pass operation prevents buildup of sulfuric acid
(HjSO^ which could eventually corrode the structure and
equipment. The pH must be maintained above 6.0. Caustic
soda can be added to the feed water if necessary to increase
the pH.
TABLE 20.2. ODOR REDUCTION TOWER LOADING
Organic Loading
Hydraulic Loading
Foul Air Application
Average Air Velocity
Maximum Feed
Water Recirculation
RATES
= 0.5 lbs BOD/day/cu yd media
(0.3 kg BOD/day/cu m media)
= 2.3 to 3.0 GPM/sq ft media surface
(1.6 to 2.0 Usec/sq m media surface)
= 125 CFM/sq ft media surface
(0.63 cu m air/sec/sq m media surface)
= 150 ft/min
(46 m/min)
= 7:1
20.412 Startup
1. Check to determine if all items such as hatches, grates, and
duct work are secure.
2. Check sump for debris and dirt. Wash down the sump and
inspect the overflow line.
3. Check filter spray heads for operation and position of flush-
ing valves. Flushing valves should be closed.
4. Check drain lines from mist eliminators. They should be
free of obstructions and the drain valves should be closed.
5. Inspect condition of supply and discharge fans. These fans
should rotate freely and have the proper lubricants and belt
tension.
6. Fill sump with effluent to the proper level. Regulate supply
flow to the sump to make up for the small amount being
returned to the plant through the overflow box.
7. Start recirculation pump which supplies water to the filter
media sprinklers. Examine sprinkler operation and water
distribution patterns on the top of the filter bed. Clean any
nozzles that are plugged or restricted.
8. Start tower discharge and supply fans. Note that the tower
will not remove odors from the gas stream until a biomass is
established on the filter media. The fans do not have to run
until the biomass is established. Some air must be venti-
lated through the filter bed during start up.
20.413 Odor Reduction Tower Monitoring
DAILY
1. Check operation of fans and pumps.
2. Drain mist eliminators.
3. Check for proper sump level and make up water feed sup-
ply.
4. Measure pH of sump feed recirculation water to the filter.
Do not allow the pH to drop below 6.0. If the pH is too low,
either increase the make up water addition rate (increase
sump overflow rate) or raise pH by the addition of caustic
soda. Water with a low pH can cause corrosion damage.
WEEKLY
1. Measure BOD loading across filter surface.
2. Check spray nozzle distribution pattern. The supply fan
may have to be turned off during this check.
3. Lubricate fans and pumps.
QUARTERLY
1. Inspect sump for silt and debris. Supply fan and recircula-
tion pump may have to be turned off during this inspection.
ANNUALLY
Take odor reduction tower out of service.
1. Check and clean spray nozzles and distribution lines.
2. Check air ducts, plenums, fan housings, diffusers and mist
separators for corrosion. Clean and paint as required.
3. Clean sump.
4. Flush filter media. Inspect media for fit (secureness) and
deterioration of media, grates, valves, and other appurte-
nances.
-------
Odor Control 17
QUESTIONS
Write your answers in a notebook and then compare your-
answers with those on page 29.
2Q.4G How are off gases and foul air treated in a biological
odor reduction tower?
20.4H How \s toe fitter feed spread over the media?
20.41 Why should the pH of the spray water not be allowed
to drop below 6.0?
20.4J How can the pH of the spray water be increased if the
pH becomes too low?
20.42 Treatment of Odors in Air
The practice of treating air containing odors from a treatment
process may be more economical than treating the wastewa-
ter. This type of odor control is becoming more and more popu-
lar. The methods of controlling odors in air include masking
and counteraction (counter masking), combustion, absorption,
adsorption, and OZONIZATION .n
20.43 Masking, Modification and Counteraction
Odor masking has been used with limited success for many
years. Odor masking is accomplished by taking the odorous
compound and mixing it with a control agent. The masking
agent or chemical has a stronger and supposedly more pleas-
ant odor quality which, when mixed with the odorous com-
pound, results in a more pleasant odor than the odorous com-
pound.
"Counteraction" is tine control of odors by adding nonocior-
producing reactive chemicals to the odor by spraying the air
over the odor-pTodueirg area.
Caution must be exercised when considering the application
of masking chemicals because they are usually chlorinated
BENZENE12 compounds. These compounds may be undesir-
able from an environmental stand point.
20.44 Combustion
Industry has been removing odorous gases by combustion
for years. The problem witti using combustion to remove odors
from a wastewater treatment plant is that the concentrations of
odors in the gases are extremely low and the combustibility of
the gases is so low that fuel costs are high.
The Key to the process is temperature. It has been reported
that the best temperature is greater than 1500°F (820°C). If
insufficient temperatures are used and incomplete combustion
occurs, odors that are not completely oxidized can be more
obnoxious than the original odor.
20.45 Absorption
"Absorption" is the process in which the odorous compo-
nents are removed from a gas by being taken in or soaked up
by a chemical solution.
Odors may be absorbed through a process called 'scrub-
bing." This process is one of the most economical methods
used today. The odorous compound is absorbed into a solu-
tion, either through solubility or chemical absorption. Odors
may be scrubbed with chemicals such as potassium perman-
ganate, sodium hypochlorite, caustic soda, and chlorine
dioxide.
The air stream must be brought into contact with the absorb-
ing compound Usually air is movec through duels to a scrub-
bing unit A scrubbing unit is a device that provides for the
contact o? the air and scrubbing compound. This device may
be a simple spray chamber, packed tower, or any similar unit.
Spray chambers usually are not as effective as other methods
due to the short contact time. Contact time is achieved through
the use of packed media towers or tray towers (Fig. 20.5).
Regardless of the chemical used, the arrangement of the
units is very similar. Some of the odorous gases removed by a
hypochlorite process are hydrogen sulfide, mercaptans, sulfur
dioxide, ammonia, and organic gases. Absorption using this
method (hypochlorite) is very rapid. Unfortunately, alt odorous
gases are not removed by this method or by the same chemi-
cals.
A brine solution absorption system is shown in Figure 20.6.
Salt is dissolved in water in the brine tank. This brine solution
flows inio the recycle tank. The soluton is pumped from the
recycle tank directly over the media or to electrolytic cells. As
the brine solution passes through e'ectrolytic cells oxidizing
agents are formed and this solution is sprayed over the media.
When this solution comes in contact with odorous gases as it
flows over the media, the odorous gases are oxidized to form
less objectionable gases. Odorous air may flow horizontally
through the media (Fig. 20.5) or vertically through the media in
a column. This system has been used successfully to reduce
odors significantly from organically overloaded plastic-media
trickling filters.
20.46 Chemical Scrubber Units for Foul Air Treatment
This absorption process removes odors from gases pro-
duced at various treatment processes and locations in a treat-
ment plant. Odors are removed by ELECTROLYTIC PRO-
CESSES13 which generate oxidizers that destroy or convert
odors into harmless, nonodorous gases. The system works
very similar to the old radio-vacuum tubes by an anode-
cathode assembly.
The anode-cathode assembly is the key in the scrubber sys-
tem, and the heart of the assembly is the anode. Each assem-
bly is activated when the rectifier transfers electrons from the
anode (leaving it positively charged) and forces them on the
cathode making it negatively charged. Raising the voltage
causes an excess of electrons on the cathode to seek a means
of reaching the electron deficient anode. Electrons on the
cathode will use any available means to cross the gap between
the two surfaces.
Should pure water fill the void between the anode and
cathode, only a few electrons would escape to the anode. If,
however, soluble salts are present, the conductivity o( the
water is immensely increased. As the electrons flow across the
gap, they chemically convert the salt to sodium hypochlorite
and disassociate some water into oxygen and hydrogen.
As the concentration of soluble salts increases, electron flow
resistance diminishes. Subsequently, less voltage is required
to force the transfer of electrons from the cathode to the anode;
and the chemical changes occurring to the dissolved salts are
increased.
11 Ozcnization (O-zoe-nie-ZAY-shun). 7he application of ozone to water, wastewater, or air, generally for the purposes of disinfection or odor
control.
12 Benzene. An aromatic hydrocarbon (C eHs) which is a colorless, volatile, flammable liquid. Benzene is obtained chiefly trom coal tar and is
used as a solvent for resins and fats and in the manufacture of dyes.
13 Electrolytic Process (ELECT-tro-UT-ick). A process that causes the decomposition of a chemical compound by the use of electricity.
-------
Treatment Plants
LIQUID
SPRAY
TK * 7K 7K * 7K 7R ^
ODOROUS
PACKED MEDIA
>/OR TRAYS f)
CLEAN
AIR
LIQUID SPRAY AND
ODOR COMPOUNDS
TO TREATMENT
Fig. 20.5 Packed media tower or tray tower for odor removal
by absorption.
-------
Odor Control
MIST
SPRAY
ODOR-FREE
DISCHARGE
MEDIA
RECYCLE
TANK
PUMP
WATER
CELL
UNIT
SALT
BRINE
TANK
ODOROUS
GASES
Fig. 20.6 Brine solution absorption system
(Permission of PEPCON)
-------
20 Treatment Plants
Chemical reactions occur at both the anode the cathode.
Reactions at the cathode result primarily in the decomposition
of water into hydrogen and the hydroxy I ion, whereas the fol-
lowing oxidative reactions occur simultaneously at the anode:
1. Oxidation of chloride to hypochlorite.
2. Formation of other highly oxidative species; namely ozone,
singlet oxygen, and peroxides.
3. Electrolysis of water to produce normal gaseous oxygen.
All of these reactions, at both the anode and cathode sur-
faces, are completely dependent upon the amounts of soluble
salts in the circulation stream, and of course, on the output of
the rectifier.
20.460 Major Components
For convenience, the major components of this type of odor
control unit are summarized under the following headings:
Brine Distribution System. Consists of a separate tank and
metering equipment for converting sodium chloride crystals
(common salt) into a brine solution. A measurable quantity of
the prepared brine is overflowed into the scrubber basin to
form the desired concentration of ELECTROLYTE.14
Cell Recycle System. Comprised of an electrically driven
non-corrosive, magnetic pump and associated piping for trans-
ferring the solution from the scrubber basin throuqh the cells
and then to the scrubbing tower where the solution returns to
the basin by gravity.
Electrolytic Unit. Consists of anode-cathode assemblies that
are activated through the application of DC power. For simplic-
ity and readability the word CELL will be interchanged with the
phrase ANODE-CATHODE ASSEMBLY throughout the re-
mainder of this section.
Fresh Water System. Composed of an incoming line for
supplying fresh water to the brine tank and the scrubbing tow-
er.
Rectifier. Comprised of the electrical unit used in converting
AC power to DC power.
Scrubbing System. Comprised of non-corrosive recycle
pump, vertical tower, a set of spray nozzles, a packing bed and
a collection basin.
20.461 Starting Procedure
The scrubber system is designed so that sodium chloride
(salt) is converted to hypochlorite in the electrolytic cells (Fig.
20.7) at the rate required to produce the oxidant for destruction
or conversion of odorous compounds in the absorption scrub-
ber. The hypochlorite is regenerated after the oxidation of H2S
and other odorous materials. Salt makeup, therefore, is only
that required to replace physical losses of chlorine compounds
(mainly salt) from the system.
If available, use either a high quality rock salt, one that does
not contain an appreciable amount of impurities, or the type of
salt recommended for water softeners. Do not use finely granu-
lated table salt as it has a tendency to compact and dissolve
slowly.
1. Place about 200 pounds (91 kg) of salt in the brine tank
and replenish periodically in order to keep at least 12
inches (30.5 cm) of salt in the tank.
2. Fill the remaining portion of the brine tank with an external
source of water.
3. Use an external source to fill the scrubber basin with suffi-
cient water to completely cover both pump intake nozzles.
To this quantity of water add about 20 pounds (9 kg) of the
same type of salt as was used in filling the brine tank. As a
result, an initial source of electrolyte is made available.
4. For achieving an optimum conversion of brine into hypo-
chlorite with the use of the cells after stability has been
achieved, the solution in the scrubber basin should con-
tain 30 grams per liter of sodium chloride. Laboratory
analyses are required for accurately determining the
grams per liter of sodium chloride in solution.
5. Whenever the quantities and types of oxidizable impurities
contained within the air stream are not known, refer to
Table 20.3 for operating guidelines to determine the op-
timum level of operation for a 12,000 CFM (5.66 cu m/sec)
scrubber.
6. In reference to Table 20.3, the initial operation of the unit
should begin at an estimated level of 5 ppm of hydrogen
sulfide within the air stream. This suggests setting the
brine tank flowmeter at 50 milliliters per minute.
7. Open the valve in the cell pump intake line. Place the cell
pump discharge valve in the % open position.
TABLE 20.3 OPERATING GUIDELINES FOR A CHEMICAL SCRUBBER
H2S,
ppm
HjS, lbs
per day8
NaCI, lbs
per day®
Fresh Water to Brine Tank
Fresh water
through tower
spray nozzles
in gallons
per day"
Total overflow
from scrubber
basin in gallons
per day15
Gals,
per dayb
Milliliters
per minute
1
1.28
7.7
3.7
9.7
9.1
12.8
2
3.56
15.4
7.4
19.4
18.2
25.6
5
6.40
38.5
18.5
48.7
45.5
64
10
12.8
77
37
97.2
91
128
20
25.6
154
74
197.3
182
256
a lbs/day x 0.454 = kg/day
b gals/day x 3.785 = LI day
14 Electrolyte (ELECT-tro-LIGHT). A substance which dissociates (separates) into two or more ions when it is dissolved in water.
-------
MANOMETER
NOZZLE
PRESSURE
SWITCH
<+)
FLOW
METER
RECTIFIER
SALT
(-)
CELL UNIT
MANOMETER
3 ASSEMBLIES
NOZZLE
GAS
INLET
WATER
SITE
GLASS
CELL CIRC. PUMP
SPARE
OVERFLOW
TOWER CIRC. PUMP
PRINT; TANK
SCRUBBER TOWER
o
fig- 20.7 Chemical scrubber system
(Permission of PEPCON) q
a
o
o
o
3
IO
-------
22 Treatment Plants
8. Push the pump start button on the face of the rectifier. The
cell pump will begin circulating the solution in the scrubber
basin through the cells. Operate the pump for more than a
minute before pushing the rectifier control switch to "ON."
Flow through the cells can be regulated by adjusting the
pump discharge valve. Open the discharge valve about %
of its full capacity to insure the magnetic pump does not
become overloaded.
CAUTION: Since the pump works on a magnetic principle
and there is little head pressure between the basin and the
pump, it may be necessary to momentarily close the dis-
charge valve when starting. Thus the pump creates inter-
nal pressure and orients itself magnetically, resulting in
almost immediate circulation as the valve is slowly
reopened to the % position.
9. Check and determine that the rectifier current control
switch is at zero. As previously mentioned, allow the pump
to operate more than a minute before pushing the rectifier
control switch to "ON." SOLUTION MUST BE FLOWING
THROUGH THE CELLS BEFORE POWER IS APPLIED.
Flow of solution is easily determined by checking the vinyl
discharge hoses on the cells. Start the rectifier and then
turn the current control switch slowly until the desired
operating level is achieved. At the assumed 5 ppm of H2S
within the air stream, set the rectifier at about 500 amps.
Adjustments, if necessary, can then be made up or down
in 50 amp increments.
CAUTION: Follow manufacturer's instructions regarding
rectifier operation. Do not exceed either the amperage or
voltage limits.
10. Open both the intake and discharge valves on the scrub-
ber recycle pump.
11. Start the scrubber recycle pump.
12. After operation has started, should an undesirable odor be
detectable near the treatment site, the operator should
first increase the output of the rectifier by about 50 amps.
After about two hours, check and determine whether or
not the increase in power was sufficient to eliminate the
undesirable odor. If not, increase the output by another 50
amps and continue this procedure until the undesirable
odor is eliminated. Similarly, if a hypochlorite odor (smell
of household bleach) is detectable near the treatment site
and the gas stream is otherwise odor free, DECREASE the
rectifier setting in 50 amp increments until the hypochlorite
odor disappears.
CAUTION: Do not exceed manufacturer's maximum levels
of amperage or voltage under any circumstance.
13. Under the assumed operating level of 5 ppm of H2S in the
gas stream, add approximately 46 gallons (174 liters) of
fresh water through the spray nozzles at the top of the
tower each day. In order to achieve this desired daily level
of overflow from the scrubber basin without hindering the
operator's schedule, the fresh water spray valve on the
spray line to the upper tower section should be completely
opened once each 8-hour shift. During each opening the
operator will want to overflow about 16 gallons (61 liters)
of water from the scrubber basin.
This quantity of water is easily determined by collecting
the overflow in a container of known quantity. For exam-
ple, if 2 gallons (7.6 liters) are collected per minute, then it
can be assumed 16 gallons (61 liters) will overflow the
scrubber basin in 8 minutes.
14. Generally two days of continuous operation are necessary
to remove any fluctuation that may occur. In other words,
this period of time can be looked upon as the break-in
period.
20.462 Shut-Down Procedures
1. Turn the current control knob on the rectifier to zero.
2. Push the "Pump Stop" button on the rectifier panel. Both
the pump and the rectifier are simultaneously turned off
when this button is pushed.
3. Turn the main rectifier switch to the "OFF" position.
4. Stop the scrubber recycle pump.
5. Shut the flowmeter valve off, if the unit is to be off for more
than two hours.
20.463 Operational Checks and Maintenance
This unit requires minimum operator attention; however,
several routine checks should be accomplished each day, es-
pecially during the initial operating period. The following items
can be performed while the system is operating:
1. Keep the vertical hole in the exposed end of each anode
filled with silicone oil during the first six weeks of operation.
More than likely, the addition of oil will be required once
each week during the six-week interval. Use the oil supplied
by the manufacturer for servicing the anodes.
2. Once each week for the first six weeks, check for loose nuts
on the bus bar and bus bar pieces, and for loose banks
around the tops of the cells. Tighten any connections that
are loose.
3. Once each day check for the presence of gas bubbles in the
vinyl (plastic) discharge tube at the top of each cell. Gas
bubbles in the discharge stream reveal the cell is function-
ing properly and conversely a lack of bubbles suggests the
cell is inoperative.
4. Once each day the operator should feel the outside surface
of the copper cathode to determine if the assembly is
operating at a comparative temperature to the other as-
semblies and the last daily inspection.
5. 'If a cell should feel warm, in fact, hot enough to cause an
immediate withdrawal of your hand, the condition more than
likely reveals a plugged or shorted assembly.
6. A noticeable increase (2 or more Volts) in the output of the
rectifier may signify an increase of electrical resistance
within the cells. Resistance of this type can result from the
formation of a scale-like deposit on the inner walls of the
cathode.
Should an increase in DC voltage ever occur and be
noticeable for a period of a day, then the operator can as-
sume a deposit has formed on the cathodes. Cathode scale
can be easily removed by flushing the system with dilute
nitric acid.
Most of the material in this section is reproduced with the
permission of PEPCON.
20.47 Adsorption
"Adsorption" is the process in which the odorous compo-
nents are removed from a gas through adherence to a solid
surface (Fig. 20.8). The attractive force holding the gaseous
molecule at the surface may be either physical (physical ad-
-------
sorption) or chemical (chemisorption). Any adsorption process
should include a solid with an extremely large capability to
adsorb gases. Activated carbon is such a solid.
Activated carbon is a highly porous material. Adsorption
takes place upon the walls of the pores within activated car-
bon. Due to the nonpolar nature of its surface, activated carbon
has the ability to adsorb organic and some inorganic materials
in preference to water vapor. The materials and amounts ad-
sorbed are dependent upon the physical and chemical makeup
of the compound. Adsorption is affected by the molecular
weight and boiling point of a compound. Higher molecular
weight compounds are usually more strongly adsorbed than
lower ones. Activated carbon will adsorb most organics that
have molecular weights over 45 and boiling points over 41 °F
(5°C). Also, activated carbon can be manufactured from sev-
eral different materials which have considerable variation in
their adsorption characteristics.
Activated carbon is an effective means for controlling odors
from all areas of the system, such as primary sedimentation
and trickling filtration. Odorous air is collected and directed
through activated carbon beds where the odor-causing organic
gases and some inorganic gases (hydrogen sulfide) are re-
moved from the air and adsorbed on the carbon.
20.470 Process Description
The process consists of a foul-air collection system, ducting,
blowers, and activated carbon beds. Foul-air containing odors
from various sources in the treatment plant are collected and
removed from the air as the odorous air passes through the
activated carbon beds. The activated carbon beds consist of
several feet of granular activated carbon (Fig. 20.8).
Odor Control 23
20.471 Start-Up
Inform operating personnel of intent to start blowers.
1. Make sure that the air blower motor electrical switches are
off and tagged out.
2. Check to be sure that the blower rotates freely.
3. Make sure all covers are properly in place and are secure.
4. Unlock electrical switches at the main power control center
for the blower motor. Turn on electrical power for the
blower.
5. Observe blower to make sure it is operating properly.
6. Check carbon bed for air flow.
7. After initial start up, measure air flow above carbon beds
with a probe and record the velocity.
20.472 Shut Down
1. Turn electrical power off at blower. If for short duration, this
is good enough but it should be tagged. For long duration,
turn power off at main power switch and tag and lock out.
2. Inform all operating personnel of status of activated carbon
units.
3. If shut down is of a long duration, carbon units should be
washed with clean water.
ODOR-FREE
DISCHARGE
ACTIVATED CARBON
ODOROUS
GASES
Fig. 20.8 Activated carbon adsorption process
-------
24 Treatment Plants
20.473 Operational Checks
DAILY
1. Inspect operation of air blower and motor.
2. Check air flow through the carbon bed.
WEEKLY
1. Measure air flow on the discharge side of the carbon bed
with a velocity meter (like the ones used to measure air flow
in air conditioning ducts). Compare against initial readings.
If the air flow is low, the activated carbon is becoming
plugged. To unplug the carbon, shut down the blower and
spray water over the top of the bed for one hour. Put the unit
back in service and recheck the air flow above the carbon
bed.
QUARTERLY
1. Measure H2S levels in the air at various depths in the acti-
vated carbon.
Draw off samples and use an H2S gas detector. If H2S
levels are found almost all the way through the activated
carbon bed, this is an indication that the bed may fail soon.
Usually activated carbon beds will regenerate themselves
during periods when the odor levels are low.
If an activated carbon bed fails, consult your supplier for
assistance regarding the regeneration or replacement of
the activated carbon.
NOTE
1. After activated carbon has been in service for a long period
of time and then taken out of service, the carbon may
develop a grey appearance. This grey appearance is usu-
ally caused by salts which form crystals when the activated
carbon drys out. These crystals will cause a grey color, but
the activated carbon will still be black.
20.48 Ozonization
Ozonization is an oxidation process (Fig. 20.9). Ozone is a
powerful oxidant and can effectively oxidize odor-causing
compounds to less objectionable forms. Air is collected from
the sources and directed into a mixing chamber where this
odorous air is mixed with ozone. The odorous air is oxidized,
and the odors are eliminated. Ozone, being relatively unstable,
must be manufactured on site.
Successful treatment of odors with ozone depends on the
type of odor, intensity or strength of odor, flow rate of odorous
air to be treated, and the size of the ozone contact chamber.
The longer the contact time, the more effective the treatment.
Therefore, control of the ozonization process is achieved by
regulating the speed or number of suction fans. Fifteen sec-
onds is considered the minimum mixing and contact time for
effective treatment of odors.
20.49 Good Housekeeping
The best solution to odor problems is to prevent odors from
ever developing. This can be achieved by good housekeeping.
Regularly clean all baffles, weirs, troughs, diversion boxes,
channels and all exposed clarifier mechanisms where scum
and solids could accumulate and decompose. Cleaning is ac-
complished by the use of deck brushes with long handles and
hosing with a high velocity jet of water. These efforts will help
you keep odor problems from becoming a serious public issue.
EXHAUST
DUCTED FROM GRIT
CHAMBER
SUCTION
FANS
OZONE DIFFUSER-
ALUMINUM BAFFLE
DUCTED FROM
HEADWORKS
Fig. 20.9 Ozone contact chamber
-------
Odor Control
20.5 TROUBLESHOOTING ODOR PROBLEMS
PLANT AREA ODOR PROBLEMS
Influent
Headworks
H2S odor
Organic odor
H2S odor
Organic odor
Primary sedimentation
H2S odor
Biological system
Activated sludge
Organic odor
Biological filter
H2S odor
Decayed organic
odor (ammonia, fishy,
rotten cabbage)
POSSIBLE SOLUTIONS*
Chemical addition.
Air stream treatment.15
Chemical addition.
Air stream treatment.b
Correct faulty plant
operation.
Chemical addition at
headworks.
Air stream treatment.
Remove sludge faster.6
Chemical addition.
Cover tanks, vent
odors and treat.
Eliminate short-
circuiting in aeration
chamber.6
Prevent sludge deposits
from developing.
Air stream treatment.
Chemical addition (H202
in the liquid prior to
the filter).
Provide even air dis-
tribution to the filter
to avoid anaerobic areas."
Clean filter vents and
underdrain system.
Correct any design
deficiencies.
Correct any design
problems. Chemical
addition (H202, Cl2, or
N03~). Air stream
treatment.
a Each solution listed may be applied to all odor problems in the plant area where the problem is occurring.
b Investigate industrial waste sources as a possible cause of the problem if this item appears to be the correct solution.
-------
Treatment Plants
20.5 TROUBLESHOOTING ODOR PROBLEMS, (Continued)
PLANT AREA ODOR PROBLEMS
Biological system (continued)
Secondary sedimentation Organic odor
Inorganic odor
Anaerobic digestion
Decaying organic
odor
Inorganic odor
Sludge handling
Drying beds Decaying organic
odor
POSSIBLE SOLUTIONS8
Correct design problem.
Increase removal rate
of sludge.
Reduce turbulence that is
causing stripping of
odor.
Increase air in aeration
systems.
Improve operations.
Light waste gas burner
if not lit.
Correct leaking water
seal on floating-cover-
type digester.
Fixed cover digesters:
a. Add water to water
seal, and
b. Seal cracks in roof.
Floating cover digesters:
a. Correct leaking
water seal, and
b. Lower cover until suf-
ficient seal around
outside is obtained.
Gas equipment:
Find and correct leaks
around valves, flame
assembly, sample wells
and access hatch.
Look for sources and correct
around pop-off valves, vents,
drain lines and piping.
Check digester opeation.
Chemical addition
(Countermasking, Masking).
Check opeations of
digester.
Review operations such
as withdrawal rate from
digester.
Each solution listed may be applicable to all odor problems in the plant area where the problem is occurring.
-------
Odor Control 27
20.5 TROUBLESHOOTING ODOR PROBLEMS, (Continued)
PLANT AREA ODOR PROBLEMS POSSIBLE SOLUTIONS*
Check operations.
Check operations at
digester area.
Remove solids from area.
Improve housekeeping.
Air stream treatment.
Check operations.
Check operations at
digesters.
Improve housekeeping.
Treatment of odors in
air removed from
centrifuge area.
Review operations.
Develop an aerobic
layer on the surface.
Check operations.
Review operational data.
Chemical addition.
Check mixing.
Lower dosage rate.
Check diffuser.
Look for chlorine leaks.
Remove sludge deposits
in chamber.
Source control.
Improve housekeeping.
8 Each solution listed may be applicable to all odor problems in the plant area where the problem is occurring.
20.6 REVIEW OF PLANS AND SPECIFICATIONS
Odor control facilities require a careful review of the plans
and specifications similar to the review given other treatment
processes.
1. When clarifiers and other large tanks and areas are en-
closed to control odors, be sure provisions are made to lift
covers over tanks for inspection and maintenance pur-
poses. Movable cranes or hoists are helpful.
2. Hydrogen sulfide gas combines with moisture to form sul-
furic acid which is very corrosive. All concrete must be pro-
tected from corrosion. All pipes, vents, screens, grates,
support systems, and other materials exposed to odorous
air must be made of corrosion resistant materials.
3. Be sure provisions are made for ventilation of enclosed
spaces with fresh air before anyone enters enclosed
spaces for any reason. Equipment and instruments must be
available to detect hydrogen sulfide, explosive conditions
and an oxygen deficiency in enclosed atmospheres before
entry.
Biological system (continued)
Vacuum filters or
Filter presses
Organic odor
Centrifuges
Organic odor
Sludge retention
basins
Ponds or lagoons
Organic odor
Inorganic odor
Ammonia odor
Disinfection
Chlorine smell
Ammonia odor
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 29.
20.4K How can odors in air be treated?
20.4L What is a solid that is used in an adsorption process to
remove odors from air?
20.4M When operating a chemical scrubber unit using a brine
solution, how would you determine if the rectifier out-
put is set properly or is set too high or too low?
20.7 ADDITIONAL READING
1. MOP 11, Chapter 27* "Odor Control."
2. "Ozonization of Septic Odors at a Pretreatment Facility."
Water Pollution Control Federation, Deeds & Data, July,
1977, p. D-1.
* Depends on edition.
-------
28 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
Chapter 20. ODOR CONTROL
Work these discussion and review questions before continu-
ing with the Objective Test. The purpose of these questions is
to indicate to you how well you understand the material in the
lesson. Write the answers to these questions in your notebook.
1. How would you determine the source and cause of odors
and a solution to the problem?
2. How should an odor complaint be handled?
3. What can happen if an odor complaint is handled improp-
erly?
4. How can odorous gases be treated?
5. What would you do if persons living near your treatment
plant complained of a chlorine smell?
PLEASE WORK THE OBJECTIVE TEST NEXT.
SUGGESTED ANSWERS
Chapter 20. ODOR CONTROL
Answers to questions on page 8.
20.0A Wastewater is tending to become more septic, and
thus causing odor and corrosion problems, because
collection systems are being extended farther and
farther away from treatment plants.
20.1 A The principal source of odor generation is from the
production of inorganic and organic gases by mi-
croorganisms. Odors also may be produced when
odor-containing or odor-generating materials are dis-
charged into the collection system by industries and
businesses.
20.1 B The main inorganic gases of concern to operators are
hydrogen sulfide (H2S) and ammonia (NHj).
20.1C The order in which microorganisms utilize oxygen in
nature is: molecular oxygen (free dissolved oxygen),
nitrate, sulfate, oxidized organics, and carbon dioxide.
20.1D The major source of inorganic odor-producing sulfate
compounds found in collection systems and treatment
plants is sulfate compounds from the public water
supply and from industrial sources.
20.1E Hydrogen sulfide causes problems at lower or acidic
pH ranges. At a pH below 5, all sulfide is present in the
gaseous H2S form and most of it can be released from
wastewater to cause odor, corrosion, explosive condi-
tions and respiratory problems.
Answers to questions on page 12.
20.2A Odors can be measured by the use of an olfactometer.
20.2B Usually smells can be classified into the following
groups:
1. Ammonia 5. Garlic
2. Decayed cabbage 6. Medicinal
3. Fecal 7. Rotten egg
4. Fishy 8. Skunk
20.3A Never approach a person who has an odor complaint
with a negative attitude.
20.3B Vou might not be able to detect an odor disturbing a
person complaining because:
1. Your nose may not be as sensitive as the nose of
the person complaining, and
2. Your nose may be accustomed to the smell, and
may no longer be able to detect the offensive odor.
Answers to questions on page 14.
20.4A Systematic steps to follow to solve an odor problem
include:
1. Review plant operations,
2. Review plant performance,
3. Evaluate plant performance,
4. Review engineering or design features of the plant,
5. Make an on-site inspection and investigation of the
problem areas,
6. Attempt to identify the source or cause of the prob-
lem,
7. List and review all solutions to the problem, and
8. Put into practice the best possible solution.
¦20.4B The most important role that chlorine plays in control-
ling odors is to inhibit the growth of odor-causing mi-
croorganisms.
20.4C Three possible ways hydrogen peroxide reacts to con-
trol odors are (1) oxidant action, (2) oxygen producing,
and (3) bactericidal to the sulfate-reducing bacteria.
Answers to questions on page 14.
20.4D Oxygen is used to control odors by aerating wastewa-
ter and attempting to keep it aerobic. Also, aeration
can strip odors out of wastewater.
20.4E A limitation of using metallic ions to precipitate sulfide
is the toxic effect on biological processes such as di-
gestion.
20.4F Odors can be controlled by increasing the pH. At pH
levels above 9.0, biological slimes and sludge growths
are inhibited. Also, any sulfide present will be in the
form of HS~ ion or S-2 ion, rather than as HzS gas
which is formed and released at low pH values.
-------
Odor Control 29
Answers to questions on page 17.
20.4G Off-gases and foul air are treated in a biological odor
reduction tower by passing up through the filter media
where the odors are oxidized to an acceptable odor
level.
20.4H The filter feed is spread over the media by the use of
spray nozzles.
20.41 The pH of the spray water should not be allowed to
drop below 6.0 because the water will cause corrosion
damage.
20.4J The pH of the spray water can be increased by the
addition of caustic soda.
Answers to questions on page 27.
20.4K Odors in air can be treated by masking and counterac-
tion, combustion, absorption, adsorption and ozoniza-
tion. Perhaps the best treatment is to prevent odors
from forming.
20.4L Activated carbon is a solid that is used to remove
odors from air by the adsorption process.
20.4M If the rectifier output is set too high, a hypochlorite
odor (smell of household bleach) is detectable. If the
output is set too low, an undesirable odor is detecta-
ble. No odors are detectable if the rectifier is set prop-
erly.
OBJECTIVE TEST
Chapter 20. ODOR CONTROL
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one correct answer to each question.
1. The reaction of chlorine to control odors with certain chem-
icals can produce a more odorous gas.
1. True
2. False
2. Ozonization is an oxidation process using ozone.
1. True
2. False
3. Activated carbon will not remove hydrogen sulfide from
odorous air.
1. True
2. False
4. Good housekeeping is not an effective means of control-
ling odors.
1. True
2. False
5. Operators do not have to worry about odor complaints.
1. True
2. False
6. Adsorption is the taking in or soaking up of one substance
into the body of another substance.
1. True
2. False
7. An olfactometer is a device used to measure odors.
1. True
2. False
8. Gas bubbles in the discharge tube at the top of each cell in
a chemical scrubber reveal that the cell is functioning
properly and conversely a lack of bubbles suggests the
cell is inoperative.
1. True
2. False
9. If a cell in a chemical scrubber feels hot enough to cause
an immediate withdrawal of your hand, the condition re-
veals that everything is functioning properly.
1. True
2. False
10. In a biological odor reduction tower, odors will not be re-
moved from the gas stream until a biomass is established
on the filter media.
1. True
2. False
11. What is the order in which microorganisms break down
compounds containing oxygen in nature?
1. Carbon dioxide, nitrate and sulfate
2. Carbon dioxide, sulfate and nitrate
3. Nitrate, carbon dioxide and sulfate
4. Nitrate, sulfate and carbon dioxide
5. Sulfate, nitrate and carbon dioxide
12. Hydrogen sulfide causes the most serious problems at
what pH range?
1. Less than 5
2. 5 to 7
3. 7, neutral
4. 7 to 9
5. Greater than 9
-------
30 Treatment Plants
13. Always approach a person with an odor complaint with
a(n) attitude (select best answer).
1. Impatient
2. Negative
3. Official
4. Positive
5. Superior
14. Odors in AIR can be treated by
1. Absorption.
2. Adsorption.
3. Metallic ions.
4. Ozonization.
5. pH adjustment.
15. Low air flow readings indicate that an activated carbon
bed is becoming plugged. The proper procedure to unplug
the bed is to
1. Dose the bed with acid.
2. Rake the surface of the bed.
3. Remove the activated carbon and replace it.
4. Spray water over the top of the bed.
5. Wash the bed with a high pressure spray.
16. Which type(s) of salt may be used for salt makeup in a
chemical scrubber system?
1. Brine salt
2. High quality rock salt
3. Pharmaceutical salt
4. Table salt
5. Water softener salt
17. Smells or odors usually can be classified into which of the
following groups?
1. Ammonia
2. Fecal
3. Pig
4. Skunk
5. Swamp
18. Steps followed (not in order) in procedures used when
attempting to solve odor problems include
1. Evaluation of plant performance.
2. Examination of engineering or design features of plant.
3. Identification of source or cause of problem.
4. On-site inspection and investigation of the problem
areas.
5. Review of plant housekeeping.
END OF OBJECTIVE TEST
-------
CHAPTER 21
ACTIVATED SLUDGE
Volume I, Chapter 8
Package Plants and Oxidation Ditches
Volume II, Chapter 11
Operation of Conventional Activated Sludge Plants
Volume III, Chapter 21
Pure Oxygen Plants and Operational Control Options
by
Ross Gudgel
and
Larry Peterson
-------
32 Treatment Plants
TABLE OF CONTENTS
Chapter 21. Activated Sludge
Volume III. Pure Oxygen Plants and Operational Control Options
Page
OBJECTIVES 36
GLOSSARY 37
LESSON 1
21.0 Advanced Topics on the Activated Sludge Process 43
21.1 Pure Oxygen 43
21.10 Description of Pure Oxygen Systems 43
21.11 PSA (Pressure Swing Absorption) Oxygen Generating System 47
21.12 Cryogenic Air Separation Method 47
21.13 Process and System Control 50
21.14 System Start-Up 50
21.15 Control Guidelines 50
21.16 Process Safety 51
21.17 Operator Safety 51
21.18 Pure Oxygen System Maintenance 52
21.19 Acknowledgment 52
LESSON 2
21.2 Return Activated Sludge 53
21.20 Purpose of Returning Activated Sludge 53
21.21 Return Activated Sludge Control 53
21.210 Constant RAS Flow Rate Control 53
21.211 Constant Percentage RAS Flow Rate Control 53
21.212 Comparison of Both RAS Control Approaches 53
21.22 Methods of RAS Flow Rate Control 55
21.220 Sludge Blanket Depth 55
21.221 Settleability Approach 55
21.222 SVI Approach 57
21.23 Return Rates with Separate Sludge Re-Aeration 57
21.24 Acknowledgment 58
-------
Activated Sludge 33
LESSON 3
21.3 Waste Activated Sludge 59
21.30 Purpose of Wasting Activated Sludge 59
21.31 Methods of Wasting Activated Sludge 60
21.310 Sludge Age Control 60
21.311 F/M Control 61
21.312 MCRT Control 63
21.313 Volatile Solids Inventory 64
21.314 MLVSS Control 65
21.32 Microscopic Examination 65
21.33 The Al West Method 66
21.34 Summary of RAS and WAS Rates 68
21.35 Acknowledgment 68
LESSON 4
21.4 Treatment of Both Municipal and Industrial Wastes 69
21.40 Monitoring Industrial Waste Discharges 69
21.400 Establishing a Monitoring System 69
21.401 Automatic Monitoring Units 70
21.41 Common Industrial Wastes 70
21.42 Effects of Industrial Wastes on the Treatment Plant Unit Processes 70
21.43 Operational Strategy 71
21.430 Need for a Strategy 71
21.431 Recognition of a Toxic Waste Load 71
21.432 Operational Strategy for Toxic Wastes 71
21.433 Recognition of a High Organic Waste Load 71
21.434 Operational Strategy for High Organic Waste Loads 72
21.5 Industrial Waste Treatment 72
21.50 Need to Treat Industrial Wastes 72
21.51 Characterization of Influent Wastes 72
21.52 Common Industrial Wastewater Variables 72
21.520 Flow 72
21.521 pH 73
21.522 BOD and Suspended Solids 73
21.523 COD 73
21.524 Nutrients 73
21.525 Toxicity 73
-------
34 Treatment Plants
21.53 Flow and Pre-Treatment Considerations 73
21.530 Flow Segregation 74
21.531 Flow Control 74
21.532 Screening 74
21.533 Grit, Soil, Grease and Oil Removal 74
21.534 Central Pre-Treatment Facilities 74
21.535 Start-Up or Restart of an Industrial Activated Sludge Process 76
21.54 Operational Considerations (Activated Sludge) 77
21.540 Neutralization 77
21.541 Nutrients 77
21.542 Daily System Observations 78
21.543 Return Activated Sludge 78
21.544 Waste Activated Sludge 78
21.545 Clarification 78
21.55 Pulp and Paper Mill Wastes 79
21.550 Need for Record Keeping 79
21.551 Wastes Discharged to the Plant Collection System 79
21.552 Variables Associated with the Treatment of Paper Mill Wastes 80
21.553 Start-Up and Shutdown Procedures 81
21.554 Management of Shutdowns and Start-Ups 81
21.555 The Periodic-Feeding (Step-Feed) Technique for Process Start-up
of Activated Sludge Systems 82
21.556 Operation of a Municipal Plant Receiving Paper Mill Wastewater 85
21.557 Acknowledgments 85
21.56 Brewery Wastewaters 85
21.560 Operational Strategy 85
21.561 Sources and Characteristics of Brewery Wastewater 86
21.562 Brewery Wastewater Treatment Plant Tour 86
21.563 Nutrient Addition 88
21.564 Aeration Basin Flow Scheme 89
21.565 Activated Sludge System Operation 89
21.566 Sludge Wasting 92
21.567 Filamentous Organisms 93
21.568 Laboratory Testing 95
21.569 Record Keeping 95
-------
Activated Sludge 35
21.57 Food Processing Wastes 95
21.570 Treatment of Artichoke Wastewater 95
21.571 Pilot Project 95
21.572 Daily Operational Procedures 97
21.573 Treatment of Dairy Wastes 97
21.574 Operation 97
21.575 Plant Effluent 99
21.576 Operational Techniques for Upgrading Effluent 99
21.58 Petroleum Refinery Wastes 99
21.580 Refinery Wastewater Characteristics 99
21.581 Activated Sludge Process 99
21.582 Frequency of Sampling and Lab Tests 99
21.583 Operational Procedures 99
21.584 Response to Sulfide Shock Load 99
21.585 Correcting Excessive Phenols 101
21.586 Treating Ammonia 101
21.59 Summary and Acknowledgments 101
21.590 Summary 101
21.591 Acknowledgments 101
21.6 Effluent Nitrification 101
21.60 Need for Effluent Nitrification 101
21.61 Nitrogen Removal Methods 101
21.610 Ammonia-Stripping 101
21.611 Ion Exchange 101
21.612 Breakpoint Chlorination 102
21.62 Biological Nitrification 102
21.63 Factors Affecting Biological Nitrification 102
21.64 Rising Sludge and the Nitrification Process 105
21.65 Acknowledgments 1°5
21.7 Review of Plans and Specifications — Pure Oxygen Activated Sludge Systems 105
21.70 Need to be Familiar with System 105
21.71 Physical Layout 105
21.72 Oxygen Generation Equipment 106
21.73 Reactors (Aeration Tanks) 106
21.74 Safety and Instrumentation 106
21.75 Preventive Maintenance 106
21.8 Metric Calculations 107
21.80 Conversion Factors 107
21.81 Problem Solutions 107
-------
OBJECTIVES
Chapter 21. ACTIVATED SLUDGE
Volume III. Pure Oxygen Plants and Operational Control Options
Following completion of Chapter 21, you should be able to:
1. Safely operate and maintain a pure oxygen activated
sludge plant,
2. Review the plans and specifications for a pure oxygen sys-
tem,
3. Describe the various methods of determining return sludge
and waste sludge rates and select the best method for your
plant,
4. Operate an activated sludge process that must treat both
municipal and industrial wastes,
5. Operate an activated sludge process that must treat strictly
an industrial waste, and
6. Operate an activated sludge process to produce a nitrified
effluent.
-------
Activated Sludge 37
GLOSSARY
Chapter 21. ACTIVATED SLUDGE
ABSORPTION (ab-SORP-shun) ABSORPTION
Taking in or soaking up of one substance into the body of another by molecular or chemical action (as tree roots absorb dissolved
nutrients in the soil).
ACTIVATED SLUDGE (ACK-ta-VATE-ed sluj) ACTIVATED SLUDGE
Sludge particles produced in raw or settled wastewater (primary effluent) by the growth of organisms (including zoogleal bacteria) in
aeration tanks in the presence of dissolved oxygen. The term "activated" comes from the fact that the particles are teeming with
bacteria, fungi, and protozoa. Activated sludge is different from primary sludge in that the sludge particles contain many living
organisms which can feed on the incoming wastewater.
ACTIVATED SLUDGE PROCESS (ACK-ta-VATE-ed sluj) ACTIVATED SLUDGE PROCESS
A biological wastewater treatment process which speeds up the decomposition of wastes in the wastewater being treated. Activated
sludge is added to wastewater and the mixture (mixed liquor) is aerated and agitated. After some time in the aeration tank, the
activated sludge is allowed to settle out by sedimentation and is disposed of (wasted) or reused (returned to the aeration tank) as
needed. The remaining wastewater then undergoes more treatment.
ADSORPTION (add-SORP-shun) ADSORPTION
The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another substance.
AERATION LIQUOR (air-A-shun) AERATION LIQUOR
Mixed liquor. The contents of the aeration tank including living organisms and material carried into the tank by either untreated
wastewater or primary effluent.
AERATION TANK (air-A-shun) AERATION TANK
The tank where raw or settled wastewater is mixed with return sludge and aerated. The same as aeration bay, aerator, or reactor.
AEROBES AEROBES
Bacteria that must have molecular (dissolved) oxygen (DO) to survive.
AEROBIC DIGESTION (AIR-O-bick) AEROBIC DIGESTION
The breakdown of wastes by microorganisms in the presence of dissolved oxygen. Waste sludge is placed in a large aerated tank
where aerobic microorganisms decompose the organic matter in the sludge. This is an extension of the activated sludge process.
AGGLOMERATION (a-GLOM-er-A-shun) AGGLOMERATION
The growing or coming together of small scattered particles into larger floes or particles which settle rapidly. Also see FLOC.
AIR LIFT AIR LIFT
A special type of pump. This device consists of a vertical riser pipe submerged in the wastewater or sludge to be pumped.
Compressed air is injected into a tail piece at the bottom of the pipe. Fine air bubbles mix with the wastewater or sludge to form a
mixture lighter than the surrounding water which causes the mixture to rise in the discharge pipe to the outlet. An air-lift pump works
similar to the center stand in a percolator coffee pot.
ALIQUOT (AL-li-kwot) ALIQUOT
Portion of a sample.
AMBIENT TEMPERATURE (AM-bee-ent) AMBIENT TEMPERATURE
Temperature of the surroundings.
ANAEROBES ANAEROBES
Bacteria that do not need molecular (dissolved) oxygen (DO) to survive.
-------
38 Treatment Plants
BACTERIAL CULTURE (back-TEAR-e-al) BACTERIAL CULTURE
In the case of activated sludge, the bacterial culture refers to the group of bacteria classed as AEROBES, and facultative organisms,
which covers a wide range of organisms. Most treatment processes in the United States grow facultative organisms which utilize the
carbonaceous (carbon compounds) BOD. Facultative organisms can live when oxygen resources are low. When "nitrification" is
required, the nitrifying organisms are OBLIGATE AEROBES (require oxygen) and must have at least 0.5 mgIL of dissolved oxygen
throughout the whole system to function properly.
BATCH PROCESS BATCH PROCESS
A treatment process in which a tank or reactor is filled, the water is treated, and the tank is emptied. The tank may then be filled and
the process repeated.
BENCH SCALE ANALYSIS BENCH SCALE ANALYSIS
A method of studying different ways of treating wastewater and solids on a small scale in a laboratory.
BIOMASS (BUY-o-MASS) BIOMASS
A mass or clump of living organisms feeding on the wastes in wastewater, dead organisms and other debris. This mass may be
formed for, or function as, the protection against predators and storage of food supplies. Also see ZOOGLEAL MASS.
BULKING (BULK-ing) BULKING
Clouds of billowing sludge that occur throughout secondary clarifiers and sludge thickeners when the sludge becomes too light and
will not settle properly.
CATHODIC PROTECTION (ca-THOD-ick) CATHODIC PROTECTION
An electrical system for prevention of rust, corrosion, and pitting of steel and iron surfaces in contact with water, wastewater or soil.
CILIATES (SILLY-ates) CILIATES
A class of protozoans distinguished by short hairs on all or part of their bodies.
COAGULATION (ko-AGG-you-LAY-shun) COAGULATION
The use of chemicals that cause very fine particles to clump together into larger particles. This makes it easier to separate the solids
from the liquids by settling, skimming, and draining or filtering.
COMPOSITE (PROPORTIONAL) SAMPLE (com-POZ-it) COMPOSITE (PROPORTIONAL) SAMPLE
A composite sample is a collection of individual samples obtained at regular intervals, usually every one or two hours during a
24-hour time span. Each individual sample is combined with the others in proportion to the flow when the sample was collected. The
resulting mixture (composite sample) forms a representative sample and is analyzed to determine the average conditions during the
sampling period.
CONING (CONE-ing) CONING
Development of a cone-shaped flow of liquid, like a whirlpool, through sludge. This can occur in a sludge hopper during sludge
withdrawal when the sludge becomes too thick. Part of the sludge remains in place while liquid rather than sludge flows out of the
hopper. Also called "coring."
CONTACT STABILIZATION CONTACT STABILIZATION
Contact stabilization is a modification of the conventional activated sludge process. In contact stabilization, two aeration tanks are
used. One tank is for separate re-aeration of the return sludge for at least four hours before it is permitted to flow into the other
aeration tank to be mixed with the primary effluent requiring treatment.
CRYOGENIC (cry-o-JEN-nick) CRYOGENIC
Low temperature.
DENITRIFICATION DENITRIFICATION
A condition that occurs when nitrite or nitrate ions are reduced to nitrogen gas and bubbles are formed as a result of this process.
The bubbles attach to the biological floes and float the floes to the surface of the secondary clarifiers. This condition is often the
cause of rising sludge observed in secondary clarifiers.
DIFFUSED-AIR AERATION DIFFUSED-AIR AERATION
A diffused air activated sludge plant takes air, compresses it, and then discharges the air below the water surface of the aerator
through some type of air diffusion device.
DIFFUSER DIFFUSER
A device (porous plate, tube, bag) used to break the air stream from the blower system into fine bubbles in an aeration tank or
reactor.
-------
Activated Sludge 39
DISSOLVED OXYGEN DISSOLVED OXYGEN
Molecular oxygen dissolved in water or wastewater, usually abbreviated DO.
ENDOGENOUS (en-DODGE-en-us) ENDOGENOUS
A reduced level of respiration (breathing) in which organisms break down compounds within their own cells to produce the oxygen
they need.
F/M RATIO F/M RATIO
Food to microorganism ratio. A measure of food provided to bacteria in an aeration tank.
Food _ BOD, lbs/day
Microorganisms MLVSS, lbs
_ Flow, MGD x BOD, mg/L x 8.34 lbs/gal
Volume, MG x MLVSS, mg/L x 8.34 lbs/gal
or = BOD, kg/day
MLVSS, kg
FACULTATIVE (FACK-ul-TAY-tive) FACULTATIVE
Facultative bacteria can use either molecular (dissolved) oxygen or oxygen obtained from food materials such as sulfate or nitrate
ions. In other words, facultative bacteria can live under aerobic or anaerobic conditions.
FILAMENTOUS BACTERIA (FILL-a-MEN-tuss) FILAMENTOUS BACTERIA
Organisms that grow in a thread or filamentous form. Common types are thiothrix and actinomyces.
FLIGHTS FLIGHTS
Scraper boards, made from redwood or other rot-resistant woods or plastic, used to collect and move settled sludge or floating
scum.
FLOC FLOC
Groups or clumps of bacteria that have come together and formed a cluster. Found in aeration tanks and secondary clarifiers.
FLOCCULATION (FLOCK-you-LAY-shun) FLOCCULATION
The gathering together of fine particles to form larger particles.
FOOD/MICROORGANISM RATIO FOOD/MICROORGANISM RATIO
Food to microorganism ratio. A measure of food provided to bacteria in an aeration tank.
Food _ BOD, lbs/day
Microorganisms MLVSS, lbs
_ Flow, MGD x BOD, mg/L x 8.34 lbs/gal
Volume, MG x MLVSS, mg/L x 8.34 lbs/gal
or _ BOD, kg/day
MLVSS, kg
Commonly abbreviated F/M Ratio.
HEADER HEADER
A large pipe to which the ends of a series of smaller pipes are connected. Also called a "manifold."
INTERFACE INTERFACE
The common boundary layer between two fluids such as a gas (air) and a liquid (water) or a liquid (water) and another liquid (oil).
MCRT MCRT
Mean Cell Residence Time, days. An expression of the average time that a microorganism will spend in the activated sludge
process.
MCRT days = Solids in Activated Sludge Process, lbs
Solids Removed from Process, lbs/day
MLSS MLSS
Mixed Liquor Suspended Solids, mg/L. Suspended solids in the mixed liquor of an aeration tank.
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40 Treatment Plants
MLVSS MLVSS
Mixed Liquor Volatile Suspended Solids, mgIL. The organic or volatile suspended solids in the mixed liquor of an aeration tank. This
volatile portion is used as a measure or indication of the microorganisms present.
MANIFOLD MANIFOLD
A large pipe to which the ends of a series of smaller pipes are connected. Also called a "header."
MEAN CELL RESIDENCE TIME (MCRT) MEAN CELL RESIDENCE TIME (MCRT)
An expression of the average time that a microorganism will spend in the activated sludge process.
MCRT days = Solids in Activated Sludge Process, lbs
Solids Removed from Process, lbs/day
MECHANICAL AERATION MECHANICAL AERATION
The use of machinery to mix air and water so that oxygen can be absorbed into the water. Some examples are: paddle wheels,
mixers, or rotating brushes to agitate the surface of an aeration tank; pumps to create fountains; and pumps to discharge water
down a series of steps forming falls or cascades.
MICROORGANISMS (micro-ORGAN-is-ums) MICROORGANISMS
Very small organisms that can be seen only through a microscope. Some microorganisms use the wastes in wastewater for food
and thus remove or alter much of the undesirable matter.
MIXED LIQUOR MIXED LIQUOR
When the activated sludge in an aeration tank is mixed with primary effluent or the raw wastewater and return sludge, this mixture is
then referred to as mixed liquor as long as it is in the aeration tank. Mixed liquor also may refer to the contents of mixed aerobic or
anaerobic digesters.
MIXED LIQUOR SUSPENDED SOLIDS (MLSS) MIXED LIQUOR SUSPENDED SOLIDS (MLSS)
Suspended solids in the mixed liquor of an aeration tank.
MIXED LIQUOR VOLATILE SUSPENDED SOLIDS MIXED LIQUOR VOLATILE SUSPENDED SOLIDS
(MLVSS) (MLVSS)
The organic or volatile suspended solids in the mixed liquor of an aeration tank. This volatile portion is used as a measure or
indication of the microorganisms present.
MOVING AVERAGE MOVING AVERAGE
To calculate the moving average for the last 7 days, add up the values for the last 7 days and divide by 7. Each day add the most
recent day to the sum of values and subtract the oldest value. By using the 7-day moving average, each day of the week is always
represented in the calculations.
NITRIFICATION (NYE-tri-fi-KAY-shun) NITRIFICATION
A process in which bacteria change the ammonia and organic nitrogen in wastewater into oxidized nitrogen (usually nitrate). The
second-stage BOD is sometimes referred to as the "nitrification stage" (first-stage BOD is called the "carbonaceous stage").
OXIDATION (ox-i-DAY-shun) OXIDATION
Oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. In wastewater
treatment, organic matter is oxidized to more stable substances. The opposite of REDUCTION.
POLYELECTROLYTE (POLY-electro-light) POLYELECTROLYTE
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polyelectrolytes may be of
biological origih or derived from starch products, cellulose derivatives, and alignates. Synthetic polyelectrolytes consist of simple
substances that have been made into complex, high-molecular-weight substances. Often called a "polymer."
POLYMER (POLY-mer) POLYMER
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polymers may be of biological
origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polymers consist of simple substances that
have been made into complex, high-molecular-weight substances. Often called a "polyelectrolyte."
PROTOZOA (pro-toe-ZOE-ah) PROTOZOA
A group of microscopic animals (usually single-celled) that sometimes cluster into colonies.
PURGE PURGE
To remove a gas or vapor from a vessel, reactor, or confined space.
-------
Activated Sludge 41
RAS RAS
Return Activated Sludge, mgIL. Settled activated sludge that is collected in the secondary clarifier and returned to the aeration basin
to mix with incoming raw or primary settled wastewater.
REDUCTION (re-DUCK-shun) REDUCTION
Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic
conditions in wastewater, sulfate compounds or elemental sulfur is reduced to odor-producing hydrogen sulfide (H2S) or Ihe sulfide
ion (S-2). The opposite of OXIDATION.
RETURN ACTIVATED SLUDGE (RAS) RETURN ACTIVATED SLUDGE (RAS)
Settled activated sludge that is collected in the secondary clarifier and returned to the aeration basin to mix with incoming raw or
primary settled wastewater.
RISING SLUDGE RISING SLUDGE
Rising sludge occurs in the secondary clarifiers of activated sludge plants when the sludge settles to the bottom of the clarifier, is
compacted, and then starts to rise to the surface, usually as a result of denitrification.
ROTIFERS (ROE-ti-fers) ROTIFERS
Microscopic animals characterized by short hairs on their front end.
SECCHI DISC (SECK-key) SECCHI DISC
A flat, white disc lowered into the water by a rope until it is just barely visible. At this point, the depth of the disc from the water
surface is the recorded secchi disc reading.
SEIZING SEIZING
Seizing occurs when an engine overheats and a component expands to the point where the engine will not run. Also called
"freezing."
SEPTIC (SEP-tick) SEPTIC
This condition is produced by anaerobic bacteria. If severe, the wastewater turns black, gives off foul odors, contains little or no
dissolved oxygen and creates a heavy oxygen demand.
SHOCK LOAD SHOCK LOAD
The arrival at a plant of a waste which is toxic to organisms in sufficient quantity or strength to cause operating problems. Possible
problems include odors and solids in the effluent. Organic or hydraulic overloads can cause a shock load.
SLUDGE AGE SLUDGE AGE
A measure of the length of time a particle of suspended solids has been undergoing aeration in the activated sludge process.
Sludge Age, = Suspended Solids Under Aeration, lbs or kg
daVs Suspended Solids Added, lbs/day or kg/day
SLUDGE DENSITY INDEX (SDI) SLUDGE DENSITY INDEX (SDI)
This test is used in a way similar to the Sludge Volume Index (SVI) to indicate the settleability of a sludge in a secondary clarifier or
effluent. SDI = 100/SVI. Also see SLUDGE VOLUME INDEX (SVI).
SLUDGE VOLUME INDEX (SVI) SLUDGE VOLUME INDEX (SVI)
This is a test used to indicate the settling ability of activated sludge (aeration solids) in the secondary clarifier. The test is a measure
of the volume of sludge compared to its weight. Allow the sludge sample from the aeration tank to settle for 30 minutes. Then
calculate SVI by dividing the volume (ml) of wet settled sludge by the weight (mg) of the sludge after it has been dried. Sludge with
an SVI of one hundred or greater will not settle as readily as desirable because it is as light as or lighter than water.
SVI = Wet Settled Sludge, ml x 1000
Dried Sludge Solids, mg
STABILIZED WASTE STABILIZED WASTE
A waste that has been treated or decomposed to the extent that, if discharged or released, its rate and state of decomposition would
be such that the waste would not cause a nuisance or odors.
STEP-FEED AERATION STEP-FEED AERATION
Step-feed aeration is a modification of the conventional activated sludge process. In step aeration, primary effluent enters the
aeration tank at several points along the length of the tank, rather than all of the primary effluent entering at the beginning or head of
the tank and flowing through the entire tank.
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42 Treatment Plants
STRIPPED GASES STRIPPED GASES
Gases that are released from a liquid by bubbling air through the liquid or by allowing the liquid to be sprayed or tumbled over media.
SUPERNATANT (sue-per-NAY-tent) SUPERNATANT
Liquid removed from settled sludge. Supernatant commonly refers to the liquid between the sludge on the bottom and the scum on
the surface of an anaerobic digester. This liquid is usually returned to the influent wet well or to the primary clarifier.
TOC TOC
Total Organic Carbon. TOC measures the amount of organic carbon in water.
TURBIDITY METER TURBIDITY METER
An instrument for measuring the amount of particles suspended in water. Precise measurements are made by measuring how light
is scattered by the suspended particles. The normal measuring range is 0 to 100 and is expressed as Nephelometric Turbidity Units
(NTU's).
VOLUTE (vol-LOOT) VOLUTE
The spiral-shaped casing which surrounds a pump, blower, or turbine impeller and collects the liquid or gas discharged by the
impeller.
WAS WAS
Waste Activated Sludge, mgIL. The excess growth of microorganisms which must be removed from the process to keep the
biological system in balance.
WASTE ACTIVATED SLUDGE (WAS) WASTE ACTIVATED SLUDGE (WAS)
The excess growth of microorganisms which must be removed from the process to keep the biological system in balance.
ZOOGLEAL MASS (ZOE-glee-al) ZOOGLEAL MASS
Jelly-like masses of bacteria found in both the trickling filter and activated sludge processes. These masses may be formed for or
function as the protection against predators and for storage of food supplies. Also see BIOMASS.
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Activated Sludge 43
CHAPTER 21. ACTIVATED SLUDGE
Volume III. Pure Oxygen Plants and Operational Control Options
(Lesson 1 of 4 Lessons)
NOTE: Review Volume I, Chapter 8, and Volume II, Chapter
11, before starting Volume III.
21.0 ADVANCED TOPICS ON THE ACTIVATED SLUDGE
PROCESS
Research and operational experience are gradually reveal-
ing how the activated sludge process treats wastes and how to
control the process. One objective of this chapter is to provide
operators with a better understanding of the factors that can
upset an activated sludge process and how to control the pro-
cess to produce a high quality effluent. Pure oxygen systems
dissolve oxygen into wastewater with a high efficiency for use
by microorganisms treating the wastes. This allows the use of
smaller aeration (reactor) tanks than air activated sludge sys-
tems. Operators need greater skill and knowledge to operate
pure oxygen systems than conventional systems.
Operation of either pure oxygen or conventional aeration
activated sludge processes is very complex. The quality of
your plant's effluent depends on the characteristics of the
plant's influent flows and wastes, as well as how the actual
process is controlled. Two very important factors are:
1. RETURN ACTIVATED SLUDGE (RAS) RATE, and
2. WASTE ACTIVATED SLUDGE (WAS) RATE.
Several methods have been developed to help operators
select the proper rates. This chapter reviews some of these
methods and their advantages and limitations. You must re-
member that each of these factors affects the others and the
impact on all process variables must be considered before
changing one variable.
Some NPDES permits require the removal of ammonia from
plant effluents. Biological nitrification (converting ammonium
(NH4+) to nitrate (N03~) is the most effective way to remove
ammonia unless total nitrogen removal is necessary. If total
nitrogen removal is required, biological nitrification is the first
step of the biological nitrification-denitrification approach to nit-
rogen removal. The biological nitrification process is an exten-
sion of the activated sludge process and is operated on the
basis of the same concepts.
Industrial wastes are becoming more common in many
municipal wastewaters. Whether you operate an activated
sludge plant in a small town or a large city, you must know how
to treat the industrial wastes that may be present with your
municipal wastewaters. Many industries pretreat their own
wastewaters before discharge to municipal collection systems
while other industries treat all of their wastewaters rather than
discharge into municipal collection systems. Whether you are
treating strictly industrial wastewaters or a mixture of industrial
and municipal wastewaters, this chapter will provide you with
the information you need to know to safely treat these different
types of wastewaters using the activated sludge process.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 112.
21.OA Why are pure oxygen systems used instead of con-
ventional aeration methods?
21.OB What treatment process can be used to remove am-
monium (NH4+) from wastewater, but not total nitro-
gen?
21.1 PURE OXYGEN
21.10 Description of Pure Oxygen Systems
The pure oxygen system (Fig. 21.1) is a modification of the
activated sludge process (Fig. 21.2). The main difference is the
method of supplying dissolved oxygen to the activated sludge
process. In other activated sludge processes, air is com-
pressed and released under water to produce an air-water
INTERFACE1 that transfers oxygen into the water (dissolved
oxygen). If compressed air is not used, surface aerators agi-
tate the water surface to drive air into the water (dissolved
oxygen) to obtain the oxygen transfer. In the pure oxygen sys-
tem, the only real differences are that pure oxygen rather than
air is released below the surface or driven into the water by
means of surface aerators and the aerators are covered.
In the pure oxygen system, oxygen is first separated from
the air to produce relatively high-purity oxygen (90 to 98 per-
cent oxygen). Pure oxygen is applied to the wastewater as a
source of oxygen for the microorganisms treating the wastes.
As with forced-air activated sludge systems, the pure oxygen
must be driven into the water. This is accomplished by a dif-
fuser mechanism or by mechanical agitation consisting of
TURBULENT MIXERS2 and surface aerators. The agitators
also supply the energy to mix the reactor (aeration tank) con-
tents to distribute the waste food (measured as BOD or COD)
to the activated sludge microorganisms in the mixed liquor
suspended solids (MLSS) and to prevent buildup of MLSS
deposits in the reactor.
The pure oxygen reactors are staged (divided into two to five
sections by baffles as shown in the three-stage system on Fig.
21.3) and are completely covered to provide a gas-tight enclo-
sure. The wastewater, return sludge, and oxygen are fed into
the first stage. The mixed liquor and atmosphere above it flow
in the same direction from the first stage to the last.
11nterface. The common boundary layer between two fluids such as a gas (air) and a liquid (water) or a liquid (water) and another liquid (oil).
2 Turbulent Mixers. Devices that mix air bubbles and water and cause turbulence to dissolve oxygen in water.
-------
OXYGEN
PRODUCTION
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PLANT 1
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PRETREATMENT
THICKENER
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PRIMARY
CLARIFICATION
RETURN
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SLUDGE (RAS)
THICKENED
SLUDGE
SUPERNATANT
ANAEROBIC
DIGESTER
(PRIMARY)
ANAEROBIC
DIGESTER
(SECONDARY)
SOLIDS
DEWATERING
PURE OXYGEN REACTORS
VENT
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5
»
3
-------
Activated Sludge 45
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FEED-
TREATED
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RETURN ACTIVATED SLUDGE
WASTE ACTIVATED SLUDGE
Fig. 21.3 Schematic diagram of pure oxygen system with surface aerators
(3 stages shown)
(Permission of Union Carbide Corporation)
-------
Activated Sludge 47
When pure oxygen is driven into the water, it behaves similar
to air and the bubbles rise to the water surface. During this rise
to the surface, only a small portion of the oxygen is absorbed
into the mixed liquor. Covering the reactor and sealing it from
the outside atmosphere allows the oxygen that is not dissolved
into the water (mixed liquor) to be used again. This contained
gas over the water is still relatively high in oxygen concentra-
tion, the main contamination consisting of carbon dioxide gas
given off by the respiration (breathing) of the activated sludge
microorganisms and the nitrogen stripped from the incoming
wastewater. The number of stages and the methods of contact-
ing the liquid and oxygen vary from one system to another. In
one type of design, the oxygen-rich gas that accumulates in
the space between the mixed liquor water surface and the roof
of the reactor is removed, compressed, and recycled back to
the diffuser of the reactor. In another type of design, surface
aerators are used to drive the oxygen-rich gas into the water.
In deep reactors (40 feet or 12 m), the surface aerator device
may also be equipped with an extended shaft and submerged
impeller to keep the tank contents well mixed. A third type of
design incorporates both submerged diffusers and surface
aeration. Some reactors vent the excess oxygen along with the
carbon dioxide. Uncovered reactors skim the surface sludge
for wasting.
In all types of design, a valve opens automatically and ad-
mits more pure oxygen to the first-stage reactor whenever suf-
ficient oxygen is removed from the gas space of the first-stage
reactor to drop the pressure below the required 1 to 4 inches (2
to 10 cm) of water column pressure. This constantly re-
plenishes the oxygen supply and the pressure is sufficient to
force gas movement through the succeeding stages. This
pressure prevents air from leaking into the reactors, diluting
the oxygen concentration and possibly creating an explosive
mixture. Oxygen leaking from a reactor can create an explo-
sive condition on the roof or around the reactor. Potentially
explosive conditions inside the reactor from a mixture of hy-
drocarbons and oxygen are avoided by an automatically acti-
vated analysis and purge system.
In each of the succeeding stages, the gas above the mixed
liquid in that stage is reinjected into the mixed liquor of the
same stage (by compressor or surface aerator). As the
oxygen-rich gas passes from one stage to the next, the oxygen
is used by the activated sludge microorganisms and the at-
mosphere becomes more and more diluted by the carbon
dioxide produced by the organisms and nitrogen STRIPPED3
from solution. The last stage in the reacter is equipped with a
roof vent controlled by a valve mechanism that is called an
oxygen vent valve. This valve vents gas from the last stage to
the atmosphere and is normally set to vent gas when the oxy-
gen concentration drops below 50 percent. As gas is vented
from the last stage, more pure oxygen is released into the first
stage to maintain the desired 1 to 4 inches (2 to 10 cm) of
water column pressure.
Two methods are commonly used to produce pure oxygen.
One is the Pressure Swing Absorption (PSA) Oxygen Generat-
ing System and the other is the CRYOGENIC4 Air Separation
Method.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 112.
21.1A Why are the pure oxygen reactors staged?
21.1B How is the pure oxygen diluted as it passes from one
stage to the next stage?
21.11 PSA (Pressure Swing Absorption) Oxygen
Generating System (Fig. 21.4)
The PSA Oxygen Generating Systems are usually installed
in smaller plants. They take air from the atmosphere and com-
press it to 30 to 60 psi (2 to 4 kg/sq cm) and cool the com-
pressed air in a water-cooled heat exchanger called an after
cooler. The after cooler condenses and removes the moisture
from the air stream. Next the air passes through an adsorbent
vessel filled with a molecular sieve. Under pressure, this
molecular sieve has the ability to adsorb nitrogen and other
impurities from the atmospheric air, thus allowing the remain-
ing pure oxygen to be used in the reactor. While one adsorber
vessel is separating air into oxygen and nitrogen, the other two
vessels are in various stages of desorption (or cleanup). The
cleanup cycle consists of depressurizing and PURGING5 with
some product oxygen. The last step involves pressurizing with
compressed air before going back on stream. During this pro-
cess, product oxygen is flowing continuously to the activated
sludge plant.
The PSA unit can be turned down to 25 percent of its rated
oxygen throughout without a significant loss of efficiency.
Compressor and valve maintenance can be scheduled so as
not to have more than one or two days of downtime per year by
the use of multiple compressors. A backup tank of liquid pro-
vides oxygen after evaporation to handle peak loads or
downtime oxygen demand. The switching valves are selected
on the basis of their ability to withstand very severe conditions
over long periods of time.
21.12 Cryogenic Air Separation Method (Fig. 21.5)
Oxygen produced by the cryogenic air separation method
uses low temperature (cryogenic) or refrigeration principles to
separate oxygen from air. Air is filtered, compressed, cooled to
remove moisture, and then routed to the cold box or "cryo"
plant tower. These towers are heavily insulated to conserve
energy by minimizing heat leaks or losses. In Fig. 21.5 all the
items contained in the dash-lined box are located in the "cryo"
plant tower.
The reversing heat exchanger primarily removes carbon
dioxide and water. This heat exchanger has two directional gas
flows; one of air going into the tower and the other of nitrogen
being exhausted to the atmosphere. As the flowing air re-
moves carbon dioxide and water, ice will form in the heat ex-
changer and restrict the air flow through the heat exchanger.
After several minutes of operation, a valve is activated that
interchanges the gas stream flows by reversing the direction of
flow. The nitrogen exhaust is routed through the inlet air pas-
3 Stripped Gases. Gases that are released from a liquid by bubbling air through the liquid or by allowing the liquid to be sprayed or tumbled
over media.
4 Cryogenic (cry-o-JEN-nick). Low temperature.
5 Purge. To remove a gas or vapor from a vessel, reactor or confined space.
-------
Treatment Plants
30-60 PSI
AFTER-
COOLER
FEED
AIR
COOLING
WATER
r \
PRODUCT
OXYGEN
VAPORIZER
ADSORBER
ADSORBER
ADSORBER
LIQUID
OXYGEN
STORAGE
WASTE
NITROGEN
PRESSURE SWING ADSORPTION UNIT
Fig. 21.4 Flow diagram of a three-bed PSA (Pressure Swing Adsorption) oxygen generating system
(Permission of Union Carbide Corporation)
-------
Activated Sludge
LIQUID
OXYGEN
STORAGE
WASTE N
UPPER
COLUMN
TURBINE
MAIN
CON-
.DENSER
AND GEL
TRAP
FROM
SUPER
HEATER
> VAPORIZER
WASTE N
>
1 PRODUCT
LIQUID
OXYGEN
TO
STORAGE
OXYGEN
GAS
«tV.UV
SURGE TANK
AFTER
COOLER
SUCTION
FILTER
LOWER
COLUMN
GEL1.:
TRAP
REVERSING HEAT EXCHANGER
AIR
COMPRESSOR
COLD BOX
Fig.21.5 Flow diagram of a cryogenic oxygen generating system
(Permisftlon of Union Carbide Corporation)
-------
50 Treatment Plants
sage and thaws the partially blocked passages. A small portion
of the water and carbon dioxide leave as tiny ice particles. The
inlet air then travels through the previous nitrogen exhaust side
until once again the ice builds up in the passage. Again the
valve is activated and switches the routes of the two gas flows.
This cycle usually varies from five to twenty minutes depending
on the system. The exiting pure oxygen is also heat exchanged
against the incoming air. In this case, however, the passages
are never switched. This allows the oxygen to remain at high
purity (about 98 percent pure oxygen).
A silica gel trap absorbs any remaining moisture that may
have gotten past the reversing heat exchanger. Trace hydro-
carbons are also picked up by the gel trap. The clean, cold air
is liquified and separated into oxygen and nitrogen by frac-
tional distillation in a two column arrangement. The lower high
pressure column produces pure liquid nitrogen to use as reflux
(flow back) in the low pressure upper column. Nitrogen, the
most volatile component of air, is taken from the top of the
upper column. Pure oxygen, the less volatile component, is
taken from near the bottom of the upper column. A 98 percent
purity oxygen stream is sent to the activated sludge process
after heat exchange against the incoming air to recover its
refrigeration (cool incoming air). Refrigeration to run the pro-
cess comes from expanding a portion of the cooled and
cleaned incoming air through an expansion turbine before it
enters the upper column.
Approximately three percent of the capacity of the oxygen
plant is available as liquid oxygen. This liquid can be used to
keep the stored liquid oxygen backup tank full and ready to
supply oxygen during peak loads or plant start-up.
To start an AMBIENT TEMPERATURE6 cryogenic plant pro-
ducing oxygen without liquid oxygen requires about three to
five days. If liquid oxygen is available, a few hours is all that is
required to place the plant in production. The oxygen produc-
tion rate of a plant is determined by the oxygen demand in the
activated sludge plant. As less production is required, the oxy-
gen plant air compressors are partially unloaded.
Cryogenic plants are usually shut down once a year for ap-
proximately five to seven days for maintenance. During this
period the gel traps are warmed to drive off moisture and hy-
drocarbons. By the use of multiple compressors and opera-
tional maintenance thaws, this downtime can be reduced to
two or three days per year. During downtime, oxygen vapor-
ized from the backup liquid oxygen storage tank is used.
Sometimes in larger plants more than one oxygen producing
facility is supplied to minimize the use of backup liquid oxygen.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 112.
21.1C What two methods are commonly used to produce
pure oxygen?
21.1D What does cryogenic mean?
21.1E How often and for how long are cryogenic plants shut
down for maintenance?
21.13 Process and System Control
Pure oxygen systems may be used to supply oxygen to any
of the activated sludge process modes — conventional, step-
feed, complete mix or contact stabilization.
21.14 System Start-Up
Pure oxygen system start-up is basically much the same as
starting conventional air systems. Individual components and
starting procedures are usually outlined in the O&M manual or
the manufacturer's literature. Take special care with the reac-
tor because flow and organic loadings must be determined
prior to start-up. Overloading or underloading may cause prob-
lems. Careful review of design data usually provides sufficient
information to initially start the system. After start-up, the sys-
tem is "fine tuned" to prevailing conditions in the wastewater.
21.15 Control Guidelines
1. REACTOR VENT GAS — A mixture of unused oxygen
(about 5 to 10 percent of the oxygen supplied), inert gases
and carbon dioxide is continually discharged from the last
stage of the reactor. The vent purity, or percentage of oxy-
gen contained in the mixture of gases, is an indicator of
oxygen use efficiency. A low oxygen purity reading (25 per-
cent or below) indicates that sufficient oxygen is not present
and adequate BOD removal may not be accomplished. A
high purity reading (50 percent or higher) indicates that too
much oxygen is being wasted with the by-product gases. A
manually controlled vent valve is adjusted to control vent
purity. If purity is low, the valve could be opened further and
closed down if purity is high. In normal operation (after
start-up), "fine tuning" of this setting usually is not changed
unless there is a drastic change in either the quantity or
strength of the wastewater entering the plant.
2. REACTOR GAS SPACE PRESSURE — Gas space pres-
sure is set by controlling the vent rate in the last stage. This
will automatically establish the pressure level throughout
the reactor. Gas pressure will vary to some extent within the
reactor, dropping as more oxygen is vented and rising as
venting is decreased or consumption is reduced. Pressure
is usually preset at two inches (5 cm) water column in the
first stage and the system will automatically feed oxygen at
the required rates to maintain this condition. However, dur-
ing high loading periods, the operator can increase oxygen
transfer and production by increasing the pressure set point
from 2 to 4 inches (5 to 10 cm) of water column, providing
the vent valve setting is not changed. Relief valves on the
first and last stage of each reactor prevent over-
pressurization. Similarly, during periods of unloading, a
vacuum release provided by these same valves prevents a
negative pressure.
3. DISSOLVED OXYGEN — A dissolved oxygen probe is
sometimes located in the diversion box prior to the second-
ary clarifer or in the last stage of the reactor. It indicates the
amount of DO in the mixed liquor. Typical oxygen systems
usually operate with a DO range of 4 to 10 mgIL of dis-
solved oxygen. If the organic load increases over an ex-
tended period which would tend to drop the dissolved oxy-
gen level below 4 mg/L, the operator should adjust the vent
valve to a more open position which will increase oxygen
production. Above a DO of 10 mg/L, the amount of oxygen
being produced could be decreased if this is anticipated to
be a long-term condition.
By measuring and monitoring these control guidelines, the
operator can establish the most efficient treatment method on
the basis of plant performance and experience. Operation of
the secondary clarifiers, return rates, wasting rates and other
control guidelines, are much the same for the pure oxygen
system as they are for the conventional air activated sludge
system.
8 Ambient Temperature (Am-bee-ent). Temperature of the surroundings¦
-------
Activated Sludge 51
21.16 Process Safety
Potentially explosive or flammable conditions can be present
when pure oxygen gas is mixed with any hydrocarbon such as
gasoline, fuel oil and lubricating oils. In addition to normal
safety devices found on motors, compressors, electrical com-
ponents and control mechanisms, the pure oxygen system
uses safety devices to ensure process safety when working
with oxygen gas. These safety devices are:
1. L.E.L (LOWER EXPLOSIVE LIMIT COMBUSTIBLE GAS
DETECTOR) — Indicates potential explosive conditions
within the reactor, and analyzes samples collected from the
first and last stage of each train in the reactor. Readings are
made based on all components being analyzed as propane.
If a hydrocarbon spill gets through the primary treatment
system without being diverted and causes a reading of
more than 25 percent of the L.E.L., an alarm will sound. The
product valve from the oxygen system will shut down and
air will automatically be directed to the reactor gas space to
PURGE7 the system. The purge will continue until normal
readings are obtained. If the spill is so large that the L.E.L.
continues to rise to the 50 percent level, in addition to an
alarm sounding, an electrical restart of the purge blower will
occur. The mixers will shut down to stop hydrocarbon strip-
ping and they cannot be restarted until readings below the
10 percent L.E.L. are obtained.
No electrical work is ever installed below the roof nor are
there any metal-to-metal contact potentials present. The
mixers pass through the roof through a water seal. This
eliminates the potential for sparks and a source of ignition.
By eliminating sources of ignition and any chance of ignita-
ble mixtures, the chances of an explosion become virtually
zero. To date the safety record at activated sludge plants
using pure oxygen has been excellent. Also, having a deck
(roof) over the reactor provides a safe and easily accessible
place for maintenance work and further minimizes the
chances of having accidents.
One way to help prevent explosive conditions from
developing is to install a Lower Explosive Limit (L.E.L.)
Combustible Gas Detector in the plant headworks. This de-
tector should trigger an alarm whenever hydrocarbons
reach the headworks so action can be taken to prevent
hydrocarbons from reaching reactors containing pure oxy-
gen. Wastewater containing hydrocarbons can be diverted
to emergency holding ponds if available.
2. LIQUID OXYGEN (STORAGE TANK) LOW TEMPERA-
TURE ALARM — Provides an alarm and shutdown of the
liquid storage system in the event heated water recircula-
tion within the vaporizer reaches a low temperature level. A
temperature monitor measures temperature levels of the
oxygen gas and if the vapor falls below -10 degrees
Fahrenheit (~23°C), an alarm will sound on the instrument
panel. At an indication of -20 degrees Fahrenheit (-29°C),
the liquid system will shut down until the temperature re-
turns to normal conditions, but must be manually reset.
3. EMERGENCY TRIP SWTICH — In the event that any other
unsafe condition should arise within the compressor sys-
tem, liquid oxygen system or electrical panels, an
emergency trip switch may be manually pulled. When
pulled, the entire oxygen system shuts down and must be
reset manually and each major piece of equipment re-
started. This safety switch is not commonly used. It is only
used as a last resort if safety systems fail or a major prob-
lem exists within the system which threatens the well being
and the safety of personnel. This switch is usually located
away from a source of danger. As with any treatment plant,
the operator must follow safety precautions established by
the manufacturers and design engineers. Caution and
warning signs should be posted in areas where danger is
present.
21.17 Operator Safety
Special safety rules must be applied when operating and
maintaining pure oxygen systems because of the unique prop-
erties of high purity oxygen. Cold liquid oxygen (LOX) can
cause skin burns. Always wear rubber gloves and protective
clothing when taking liquid oxygen samples from columns.
This is the only time operators need to handle liquid oxygen.
Pure oxygen supports and accelerates combustion more
readily than air. Therefore, all types of hydrocarbons and other
flammable materials must be kept from mixing with the oxygen.
The following precautions are intended to eliminate the possi-
bility of combustion and explosions.
1. Special non-hydrocarbon lubricants as specified by the
manufacturer should be used for equipment in contact with
oxygen.
2. Tools and equipment must be specially designed to be
compatible for use in oxygen service.
3. Flammable materials must be kept far away from oxygen
systems and storage tanks.
4. Grease and oil must be removed from tools and equipment
by the use of a solvent such as chloroethane.
5. Smoking and open flames are prohibited near oxygen sys-
tems and storage tanks.
Liquid oxygen is delivered by specially designed trucks and
transferred by specially trained technicians. Therefore, the
chances of liquid oxygen spills are remote. If a liquid oxygen
spill occurs, the liquid could saturate a combustible material
and this material could ignite or explode. Ignition can be
caused by hot objects, open flames, glowing cigarettes, em-
bers, sparks, or impact such as might be caused by striking
with a hammer, dropping a tool or scuffing with your heel.
Typical combustible materials that are dangerous when satu-
rated with spilled liquid oxygen include asphalt in black top
pavements, humus in soil, oil or grease on concrete floors or
pavements, articles of clothing, or ANY OTHER SUBSTANCE
THAT WILL BURN IN AIR. Any equipment involving liquid oxy-
gen should be constructed on a concrete pad to avoid the
potential of soaking a black top surface with liquid oxygen.
Every possible effort must be made to prevent the spillage of
liquid oxygen. If a spill does occur, the following procedures
must be followed:
1. No one may set foot in any area still showing frost marks
from an oxygen spill.
2. The affected area must be roped off as soon as possible.
When rope, barricades and signs are not immediately
available, someone must stay at the area to warn other
persons of the hazard.
3. No tank car or truck movements are allowed over an area
still showing frost marks from an oxygen spill.
These procedures apply to any oxygen spillage on any sur-
face, including cement, gravel, black top, or dirt either inside
buildings or outdoors. A10 ONE IS ALLOWED TO STEP ON
ANY AREAS WHERE FROST MARKS EXIST FROM A SPILL.
7 Purge. Remove pure oxygen from the reactors and attempt to dilute hydrocarbon vapors to below the explosive limit.
-------
52 Treatment Plants
21.18 Pure Oxygen System Maintenance
Maintenance of a pure oxygen production system is spe-
cialized for the specific equipment. However, this equipment is
similar to the equipment found in other types of activated
sludge plants, including air compressors, valves and instru-
ments. Manufacturers commonly aid the operator during
start-up with training sessions and field work. A maintenance
contract with the supplier can be used to provide the technical
services needed. As with any large scale production system,
equipment preventive maintenance ensures proper operation
and greater efficiency.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 112.
21.1F What special measures are used to control pure oxy-
gen systems?
21.1G How can hydrocarbons be detected before they reach
the reactor?
21.19 Acknowledgment
This section was reviewed by Mr. R.W. Hirsch. The authors
thank Mr. Hirsch for his many helpful comments and sugges-
tions.
fend, of 120?o\a\
on
ACfivAtep t&uQM
Please answer the discussion and review questions before
continuing with Lesson 2.
DISCUSSION AND REVIEW QUESTIONS
(Lesson J of 4 Lessons)
Chapter 21. ACTIVATED SLUDGE
At the end of each lesson in this chapter you will find some
discussion and review questions that you should answer be-
fore continuing. The purpose of these questions is to indicate
to you how well you understand the material in this lesson.
Write the answers to these questions in your notebook before
continuing.
1. Why does the pure oxygen process normally use covered
reactors?
2. How is pure oxygen separated from impurities and other
gases in the PSA system?
3. What safety hazards might an operator encounter when
working around a pure oxygen system?
4. What safety systems are found around pure oxygen sys-
tems to protect operators and equipment?
-------
CHAPTER 21. ACTIVATED SLUDGE
(Lesson 2 of 4 Lessons)
Activated Sludge 53
NOTE: The next two lessons, Section 21.2, Return Activated
Sludge, and Section 21.3, Waste Activated Sludge, are
provided to familiarize you with different ways to control
both the pure oxygen and air activated sludge pro-
cesses. YOU, the operator, will have to determine
which ways will work best for your plant. Once a particu-
lar procedure is selected, EVERY OPERATOR ON
EVERY SHIFT MUST FOLLOW THE SAME PROCE-
DURE. If the procedure does not produce satisfactory
results, then new procedures must be developed and
tested for everyone to follow.
Abbreviations used in this section include:
1. MLSS, Mixed Liquor Suspended Solids, mg/L.
2. MLVSS, Mixed Liquor Volatile Suspended Solids, mg/L.
3. RAS, Return Activated Sludge, mg/L.
4. F/M, Food to Microorganism Ratio, lbs BOD or COD added
per day per lb of MLVSS or kg/day per kg MLVSS.
5. Q, Flow, MGD or cu m/sec.
21.2 RETURN ACTIVATED SLUDGE
21.20 Purpose of Returning Activated Sludge
To operate the activated sludge process efficiently, a prop-
erty settling mixed liquor must be achieved and maintained.
The mixed liquor suspended solids (MLSS) are settled in a
clarifier and then returned to the aeration tank as the Return
Activated Sludge (RAS) (Fig. 21.6). The RAS makes it possible
for the microorganisms to be in the treatment system longer
than the flowing wastewater. For conventional activated sludge
operations, the RAS flow is generally about 20 to 40 percent of
the incoming wastewater flow. CHANGES IN THE ACTIVATED
SLUDGE QUALITY WILL REQUIRE DIFFERENT RAS FLOW
RATES DUE TO SETTLING CHARACTERISTICS OF THE
SLUDGE. Table 21.1 shows typical ranges of RAS flow rates
for some activated sludge process variations.
21.21 Return Activated Sludge Control
Two basic approaches that can be used to control the RAS
flow rate are based on the following:
1. Controlling the RAS flow rate independently from the in-
fluent flow; and
2. Controlling the RAS flow rate as a constant percentage of
the influent flow.
21.210 Constant RAS Flow Rate Control
Setting the RAS at a constant flow rate that is independent of
the aeration tank influent wastewater flow rate results in a
continuously changing MLSS concentration. The MLSS will be
at a minimum during peak influent flows and at a maximum
during low influent flows. This occurs because the MLSS are
flowing into the clarifier at a higher rate during peak flow when
they are being removed at a constant rate. Similarly, at
minimum influent flow rates, the MLSS are returned to the
aeration tank at a higher rate than they are flowing into the
clarifier. The aeration tank and the secondary clarifier must be
TABLE 21.1 A GUIDE TO TYPICAL RAS FLOW RATE
PERCENTAGES"
Type of Activated Sludge RAS Flow Rate at Percent of Incoming
Proceaa Waatewater Flow to Aeration Tank
Minimum
Maximum
Standard Rate
15
75
Carbonaceous Stage of Separate
Stage Nitrification
15
75
Step-Feed Aeration
15
75
Contact Stabilization
50
150
Extended Aeration
50
150
Nitrification State of Separate
Stage Nitrification
50
200
'RECOMMENDED STANDARDS FOR SEWAGE WORKS (10
STATE STANDARDS), Great Lakes-Upper Mississippi River Board
of State Sanitary Engineers, 1978 Edition, published by Health Edu-
cation Service, Post Office Box 7126, Albany, New York 12224.
Price, $1.75 plus 48« for shipping and handling charges.
looked at as a system in which the MLSS are stored in the
aeration tank during minimum wastewater flow and then trans-
ferred to the clarifier as the wastewater flows initially increase.
In essence, the clarifier has a constantly changing depth of
sludge blanket as the MLSS moves from the aeration tank to
the clarifier and vice versa. The advantage of using this ap-
proach is simplicity, because it minimizes the amount of effort
for control. This approach is especially effective for small
plants with limited flexibility.
21.211 Constant Percentage RAS Flow Rate Control
The second approach to controlling RAS flow rates requires
a programmed method for maintaining a constant percentage
of RAS flow to the aeration tank influent wastewater flow rate.
The program may consist of an automatic flow-measurement
device, a programmed system, or frequent manual adjust-
ments. The programmed method is theoretically designed to
keep the MLSS more constant through high and low flow
periods.
21.212 Comparison of Both RAS Control Approaches
The advantages of the constant RAS flow approach are the
following:
1. Simplicity.
2. Maximum solids loading on the clarifier occurs at the start ol
peak flow periods.
3. Requires less operational time.
The advantages of the constant percentage RAS flow ap-
proach are the following:
1. Variations in the MLSS concentration are reduced and the
F/M ratio varies less.
2. The MLSS will remain in the clarifier for shorter time periods
which may reduce the possibility of denitrification in the
clarifier.
-------
s
3
DIGESTER
[(SECONDARY)
SOLIDS
THICKENER
PRIMARY
CLARIFIER
SECONDARY
CLARIFIER
AERATION
TANK
PRETREATMENT
CHLORINE
CONTACT
SOLIDS
DEWATERING
DRY SOLIDS
SOLIDS WASTING WITH A GRAVITY OR FLOATATION THICKENER
Fig. 21.6 Return and waste activated sludge flow diagram
-------
Activated Sludge 55
A limitation of using the constant flow approach is that the
F/M ratio is constantly changing. The range of F/M fluctuation
due to short-term variations in the MLSS (because of hydraulic
loading) is generally small enough so that no significant prob-
lems arise.
The most significant limitation of the constant percentage
flow approach is that the clarifier is subjected to maximum
hydraulic loading when the reactor contains the maximum
amount of sludge. This may result in solids washout with the
secondary effluent.
In general, it appears that most activated sludge operations
perform well and require less attention when the constant RAS
flow rate approach is used. In many plants it is much simpler
for the operator to let the MLSS fluctuate, as long as adequate
treatment can be maintained. Larger, more complex plants
may have to vary the RAS to keep the MLSS close to the target
value. Activated sludge plants with flows of 10 MGD (37,850 cu
m/day) or less often experience large hydraulic surges and
performance of these plants will benefit the most from the use
of the constant RAS flow rate approach.
Procedures for monitoring and maintaining RAS flow rates
are presented in Table 21.2. The operator may develop de-
tailed standard operating procedures for treatment plants by
using this table.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 112.
21,2A What words do the letters in the following abbrevia-
tions represent?
1. MLSS 3. RAS
2. MLVSS 4. F/M
21.2B What are the two basic approaches that can be used
to control the RAS flow rate?
21.22 Methods of RAS Flow Rate Control
For either RAS flow rate control approach discussed above,
there are a number of techniques which may be used to set the
rate of sludge return flow. The most commonly used tech-
niques are listed below:
1. Monitoring the depth of the sludge blanket.
2. Settleability approach, and
3. SVI approach.
21.220 Sludge Blanket Depth
Monitoring the depth of the sludge blanket in the clarifier is
the most direct method available for determining the RAS flow
rate. The sludge blanket depth and uniformity may be checked
by any of the following methods:
1. A series of air lift pumps mounted within the clarifier at
various depths;
2. Gravity flow tubes located at various depths;
3. Electronic sludge level detector (a light source and photo-
electric cell attached to a graduated handle or drop cord.
The photo-electric cell actuates a buzzer when in contact
with the sludge);
4. Sight glass finder (a graduated pipe with a light source and
sight glass attached to the lower end);
5. Plexiglass core sampler; and
6. Some type of portable pumping unit with a graduated suc-
tion pipe or hose (siphon).
The blanket depth should be kept from one to three feet (0.3
to 1 m) as measured from the clarifier bottom at the sidewall.
The operator must check the blanket depth on a routine basis,
making adjustments in the RAS to control the blanket depth.
If it is observed that the depth of the sludge blanket is in-
creasing, however, an increase in the RAS flow can only solve
the problem on a short-term basis. Increases in sludge blanket
depth may result from having too much activated sludge in the
treatment system, and/or because of a poorly settling sludge.
Long-term corrections must be made that will improve the set-
tling characteristics of the sludge or remove the excess solids
from the treatment system. If the sludge is settling poorly, in-
creasing the RAS flow may even cause more problems by
further increasing the flow through the clarifier. If the sludge is
settling poorly due to bulking, the environmental conditions for
the microorganisms must be improved. If there is too much
activated sludge in the treatment system, the excess sludge
must be wasted.
Measurements of the sludge blanket depth in the clarifier
should be made at the same time each day. The best time to
make these measurements is during the period of maximum
daily flow because the clarifier is operating under the highest
solids loading rate. The sludge blanket should be measured
daily, and adjustments to the RAS rate can be made as neces-
sary. Adjustments in the RAS flow rate should only be needed
occasionally if the activated sludge process is operating prop-
erly.
An additional advantage of monitoring the sludge blanket
depth is that problems, such as improperly operating sludge
collection equipment, will be observed due to irregularities in
the blanket depth. A plugged pickup on a clarifier sludge collec-
tion system would cause sludge depth to increase in the area
of the pickup and decrease in the areas where the properly
operating pickups are located. These irregularities in sludge
blanket depth are easily monitored by measuring profiles of
blanket depth across the clarifier.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 112.
21,2C The sludge blanket depth should be kept to less than
what portion or fraction of the clarifier sidewall water
depth?
21.2D When should the sludge blanket depth be measured
and why?
21.221 Settleability Approach
Another method of calculating the RAS flow rate is based on
the results of the 60-minute settling test. Settleability is defined
as the percentage of volume occupied by the sludge after set-
tling for 60 minutes. Test is run on a sample collected from the
aeration basin effluent.
EXAMPLE
Determine the return activated sludge (RAS) flow as a per-
centage of the influent flow and in MGD when the influent flow
is 7.5 MGD (28,390 cu m/day) and the sludge settling volume
(SV) in 60 minutes is 275 mlIL.
Known Unknown
Intl. Flow, MGD = 7.5 MGD 1. RAS Flow as a Percent
of Infl. Flow, %
SI Set Vol. (SV). ml IL = 275 mlIL 2. RAS Flow, MGD
-------
56 Treatment Plants
TABLE 21.2 STANDARD OPERATING PROCEDURES FOR RAS CONTROL
PROCESS
RAS
CONTROL
METHOD
MODE OF
OPERATION
WHAT TO
CHECK
FREQUENCY
OF
ADJUSTMENT
WHEN TO
CHECK
CONDITION
PROBABLE
CAUSE
RESPONSE
Complete
Mix or
Plug Flow
Constant Flow
Manual
Sludge Blanket
Daily
Every 8 Hours
High
Satisfactory
Low
Low RAS Rate
High RAS Rate
Increase Return
Continued Monitoring
Decrease Return
Constant %
of Influent
Flow
Manual
% of Jnfluent
Flow
2 Hrs
Every 2 Hrs
High
Satisfactory
Low
Variations
in Daily
Influent
Flow
Adjust to Desired
% of fnfluent Flow
Sludge Blanket
Daily
Every 8 Hrs
High
Satisfactory
Low
% of Flow
Too Low
% ol Flow
Too High
Increase % of Flow
Continue Monitoring
Decrease % of Flow
Constant %
of Influent
Row
Automatic
Sludge Blanket
Daily
Every 8 Hrs
High
Satisfactory
Low
% of Flow
Too Low
% of Flow
Too High
Increase % of Flow
Continue Monitoring
Decrease % of Flow
Control by
Sludge
Blanket
Level
Automatic
Sludge Blanket
Daily
Every 8 Hrs
High or Low
Satisfactofy
Controller
Malfunction
Fix Controller or
Manually Adjusl
Accordingly
Continue Monitoring
Reaeration
or
Contact
Stabili-
zation
Constant %
of Flow
Automatic
Ratio of
MLSS/RASgs
(Centrifuge
Test)
Every 2 Hrs
Every 2 Hrs
High Ratio
Satisfactory
Low Ratio
Return Too
High
Return too
Low
Decrease Return
Continue Monitoring
Increase Return
1. Calculate RAS flow as a % of influent flow. The settleability method assumes that measurements made
with a laboratory settling cylinder will accurately reflect the
settling in a clarifier. This assumption will seldom (if ever) be
true because of the effects of the cylinder walls and the quies-
cent (still or lack of turbulence) nature of the liquid in the cylin-
der. Some operators have found that gently stirring (1-2 rpm)
the sludge during the settling test reduces these problems.
" This is a factor for converting MGD to GPM.
2. Calculate RAS Row, MGD.
RAS Flow, MGD = RAS Flow, decimal x Jnfl. Flow, MGD
= 0.38 x 7.5 MGD
= 2.8 MGD x 694 GPM/MGD*
= 1,945 GPM
RAS Flow, % = SV, mlIL x 100%
1,000 ml/i - SV, mlIL
= 275 ml/L x 1QQ%
1,000 ml IL - 275 ml/1
= 275 ml/L x 1QQ%
725 ml IL
= 38% of influent flow rate
-------
Activated Sludge 57
Another way to calculate the RAS flow as a percentage of
the influent flow is by using the chart in Fig. 21.7 below. First,
locate the SV value (from the 30-minute sludge settling test —
275 ml/L) on the bottom scale. Draw a vertical line up to the
curve and a horizontal line from that point to the left vertical
axis. This value (38%) is the RAS flow as a percentage of the
influent flow. To find the RAS flow in MGD, multiply the R/Q
value (0.38) by Q (7.5 MGD).
60
0
1111 1II 11
O \73
SV x
1000 - SV
100%
11 11 1 1 1 1 I
1 M 1 11 i I I
i
y\
/ ~
' 1
1
-------
58 Treatment Plants
TABLE 21.3 EFFECTS OF CHANGES ON RETURN SLUDGE AERATION TIME (RSAT)
PROCESS CONTROL GUIDELINES
CHANGE MADE
EFFECT ON SVI
EFFECT ON NITRIFICATION
Increase
Decrease
Increase
Decrease
Step Change
Increase RSAT
*
*
Decrease RSAT
*
*
Return Sludge Flow
Increase
*
*
Decrease
*
*
Process Air Rate
-------
Activated Sludge 59
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 4 Lessons)
Chapter 21. ACTIVATED SLUDGE
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 2.
5. What are the advantages of the constant RAS flow ap-
proach and the constant percentage RAS flow approach?
6. Different RAS flow rates will be required as the result of
what two activated sludge conditions?
7. What is the difference between the method of RAS control
and the rate of RAS control?
8. Why is the following statement true and how can this prob-
lem be corrected on a long-term basis? If you observe that
the depth of the sludge blanket is increasing, an increase in
the RAS flow can only solve the problem on a short-term
basis.
CHAPTER 21. ACTIVATED SLUDGE
(Lesson 3 of 4 Lessons)
Abbreviations used in this section include:
1. RAS, Return Activated Sludge
2. WAS, Waste Activated Sludge
3. MCRT, Mean Cell Residence Time
4. MLVSS, Mixed Liquor Volatile Suspended Solids
21.3 WASTE ACTIVATED SLUDGE
21.30 Purpose of Wasting Activated Sludge
One of the most important controls of the activated sludge
process is the amount of activated sludge that is wasted. The
amount of waste activated sludge (WAS) removed from the
process affects all of the following items:
1. Effluent quality,
2. Growth rate of the microorganisms,
3. Oxygen consumption,
4. Mixed liquor settleability,
5. Nutrient quantities needed,
6. Occurrence of foaming/frothing, and
7. Possibility of nitrifying.
The objective of wasting activated sludge is to maintain a
balance between the microorganisms under aeration and the
amount of incoming food as measured by the COD or BOD
test. When microorganisms remove BOD from wastewater, the
amount of activated sludge increases (microorganisms
grow and multiply). The rate at which these microorganisms
grow is called the growth rate and is defined as the increase in
the amount of activated sludge that takes place in one day.
The objective of sludge wasting is to remove just the amount of
microorganisms that grow in excess of the microorganism
death rate. When this is done, the amount of activated sludge
formed by the microorganism growth is just balanced by that
which is removed from the process. This allows the total
amount of activated sludge in the process to remain somewhat
constant. This condition is called "steady-state" and is a desir-
able condition for operation. However, "steady-state" can only
be approximated because of the variations in the nature and
quantity of the food supply (BOD) and of the microorganism
population. The objective of process control is to approach a
particular "steady-state" by controlling any one or a combina-
tion of the following control guidelines.
1. Sludge Age
2. F/M or Food to Microorganism Ratio
3. MCRT, Mean Cell Residence Time
4. Volatile Solids Inventory
5. MLVSS Concentration
The best mode of process control will produce a high quality
effluent which meets NPDES permit requirements with consis-
tent treatment results at a minimal cost.
Wasting of the activated sludge (Fig. 21.6, page 54) is usu-
ally achieved by removing a portion of the RAS flow. The waste
activated sludge is either pumped to thickening or dewatering
facilities and then to a digester or incinerator, or to the primary
-------
60 Treatment Plants
clarifiers where it is pumped to a digester with the raw sludge.
Procedures for making WAS adjustments are presented in
Table 21.4 which the operator may use to develop standard
operating procedures for a treatment plant.
An alternate method for wasting sludge is taking it from the
mixed liquor in the aeration tank. There are much higher con-
centrations of suspended matter in the RAS than there are in
the mixed liquor. Therefore, when wasting is practiced from the
aeration tank, larger sludge handling facilities are required.
Wasting from the RAS takes advantage of the gravity settling
and thickening of the sludge that occurs in the secondary
clarifier. However, wasting from the aeration tank has the ad-
vantage of not wasting excessive amounts of sludge since a
large quantity of mixed liquor is involved. The extra security of
wasting from the aeration tank should not be underestimated.
Unfortunately, many plants do not have the flexibility to waste
from the aeration tank nor are there sufficient sludge handling
facilities to handle the more dilute sludge.
21.31 Methods of Sludge Wasting
Wasting of the activated sludge can be accomplished on an
intermittent or continuous basis. The intermittent wasting of
sludge means that wasting is conducted on a batch basis from
day to day.
21.310 Sludge Age Control
Sludge age is a measure of the length of time a particle of
suspended solids has been undergoing aeration in the acti-
vated sludge process. As you can see in this formula for cal-
culating sludge age, it is based on a ratio between the solids in
the aeration tank and the solids in the incoming wastewater.
Sludge Age,_ Suspended Solid9 Under Aeration, lbs or kg
days Suspended Solids Added, lbs/day or kg/day
Using sludge age as a control technique, the operator
wastes just enough sludge to maintain the sludge age which
produces the best quality effluent. In most activated sludge
plants, sludge age ranges from 3 to 8 days. Difficulties are
commonly experienced using the sludge age control technique
when the BOD or COD to solids ratio in the wastewater
changes. This is because sludge age is based on the assump-
tion that the BOD (or COD)/solids ratio is fairly constant. By
realizing that the BOD or COD to solids ratio does change and
adjusting the sludge age when the ratio changes, the sludge
age is a useful process control technique. Calculate the sludge
age as shown in the following example.
EXAMPLE
Determine the sludge age for an activated sludge plant with
an influent flow of 7.5 MGD (28,390 cu m/day). The primary
effluent suspended solids concentration is 100 mgIL. Two aer-
ation tanks have a volume of 0.6 MG (2,270 cu m) each and a
mixed liquor suspended solids (MLSS) concentration of 2,200
mgIL.
Known
Infl. Flow, MGD
Prim. Effl. SS, mgIL
Tank Vol., MG
MLSS, mgIL
No. of tanks
Unknown
= 7.5 MGD Sludge Age, days
= 100 mgIL
= 0.6 MG/tank
= 2,200 mgIL
= 2 tanks
TABLE 21.4 STANDARD OPERATING PROCEDURES FOR WAS CONTROL
METHOD OF
CONTROL
PROCESS
OPERATION
WHAT TO
CHECK
WHEN TO
CHECK
CALCULATIONS
FREQUENCY OF
ADJUSTMENT
CONDITIONS
PROBABLE
CAUSE
RESPONSE*
F/M
HIGH RATE
CONVENTIONAL
RATE
EXTENDED
AERATION
MLVSS&
INFLUENT
COD
DAILY
F/M BASED ON-
7 DAY AVG. COD
7 DAY AVG. MLVSS
DAILY
ACTUAL F/M:
HIGH
SATISFACTORY
LOW
EXCESSIVE
WASTING
INSUFFICIENT
WASTING
REDUCE WAS
INCREA8E
WAS
MLVSS
HIQH RATE
CONVENTIONAL
RATE
EXTENDED
AERATION.
MLVSS&
INFLUENT
COD OR
BOD
DAILY
VOLATILE
SOLIDS
INVENTORY
DAILY
ACTUAL
MLVSS:
HIGH
SATISFACTORY
LOW
INSUFFICIENT
WASTING
EXCESSIVE
WASTING
INCREASE
WAS
REDUCE WAS
MCRT
HIQH RATE
CONVENTIONAL
RATE
EXTENDED
AERATION
MLSS.
WMmi
DAILY
7 DAY AVQb
SOLIDS INVENTORY
7 DAY AVERAGE*' OF
SOUD8 IN WAS
7 DAY AVERAGE" OF
SOLIDS IN EFFLUENT
DAILY
ACTUAL MCRT:
HIGH
SATISFACTORY
LOW
INSUFFICIENT
WA8TING
EXCESSIVE
WA8TING
INCREASE
WAS
REDUCE WAS
8LUDQE
AGE
HIGH RATE
CONVENTIONAL
RATE
EXTENDED
AERATION
INFLUENT
S8.&MLSS
DAILY
7 DAY AVG OF
SS INVENTORY &
SS IN INFLUENT
DAILY
ACTUAL SA:
HIGH
SATISFACTORY
LOW
INSUFFICIENT
WASTING
EXCESSIVE
WASTING
INCREA8E
WAS
REDUCE WAS
' . n niwv w uwnimw hi« n»w
P"wtou» WA8 rate, TNa to neceeeary to enow tha procees to
When calculating the MCRT, determine the deeired MCRT <7 day*)
i. However, when IncraMlng or decreasing dally WAS rata*, any ohangaa should not exceed 10 to 15 percent of the
stabilize.
and use the moving average for the number ot day* (7 days) In (he desired MCRT.
-------
Activated Sludge 61
Sludge Age, days
Solids under aeration, lbs
Solids added, lbs/day
3. Add the current WAS flow to the additional WAS flow, MGD.
1. Calculate the solids under aeration, lbs.
No. TanK Vol, , .
Solids under = Tanksx MG/tank x MLSS, mg/i. x 8.34 lbs/gal
aeration, lbs = 2 tanks x 0 6 MG/tank x 2200 mg/L x 8.34 lbs/gal
= 22,000 lbs
2. Calculate the solids added, lbs/day
Solids added, = Infl. Flow, MGD x Prim. Effl. SS, mg/L x 8.34 lbs/gal
lbs/day _ 7 5 MG0 x 100 mg/f. x 8.34 lbs/gal
- 6,255 lbs/day
3. Determine sludge age, days.
Sludge Age, = Solids under aeration, lbs
days Solids added, lbs/day
_ 22,000 lbs
6,255 lbs/day
¦ 3.5 days
Calculate the waste activated sludge (WAS) flow rate using
the sludge age control technique as shown in the following
example.
EXAMPLE
Determine the waste activated sludge (WAS) flow rate in
MGD for an activated sludge plant that adds 6,255 lbs (2,837
kg) of solids per day (from previous problem). The solids under
aeration are 33,075 pounds (15,000 kg), the return activated
sludge (RAS) suspended solids concentration Is 0,300 mg/L
and the desired sludge age is 5 days. Current sludge waste
rate Is 4,455 lbs (2,020 kg) per day.
Known
Solids Added, lbs/day
Solids Aerated, lbs
RAS Susp. Sol., mg/L
Unknown
= 6,255 lbs/day WAS Flow, MGD
= 33,075 lbs
* 8,300 mg/L
Desired Sludge Age, days = 5 days
Current WAS Rate, lbs/day = 4,455 toe/day
1. Calculate the desired pounds of solids under aeration
(MLSS) for the desired sludge age of 5 days.
Desired Solids - Solids Added, lbs/day * Sludge Age, days
under aeration,
lbs » ®£55 lbs/day x 5 days
-31,275 lbs
2. Calculate the additional WAS flow, MGD, to maintain the
desired sludge age.
Additional SolldsAerated, a* ¦ Desired Solids. tbe
WAS FLOW, MOD " ras Susp. Sol., tnfl!L x B.34 lbs/flat
_ 33,075 lbs-31,275 lbs
6,300 mg/L* x 8.34 Ibe/flal
-1.800 lbs removed per day"
52,542
« o,034 MGD"* x 694 GPWMGD
-24 GPM
* Remember that mg/L to the same as tbsfMJt*
** Removean addWonal 1,800 ibs duftog•
"• Hth® actual son^uw^iiWBtlonarsttW
Total WAS
Flow, MGD
Current WAS
Flow, MGD
Solids Wasted, lbs/day
+ Additional WAS
Flow, MGD
_+ Flow, MGD
RAS Susp. Sol,, mg/t x e.34 lbs/gal
4.455 lbs/day + 0 034
6,300 mg/L x 8.34 lbs/gal
0.085 MGD + 0.034 MGD
0.119 MGD x 694 GPM/MGD
82 GPM
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 113.
21.3A What is the objective of wasting activated sludge?
21.3B How is wasting of the excess activated sludge usually
achieved?
21.3C Calculate the waste activated sludge (WAS) flow rate
in MGD and GPM for an activated sludge plant that
adds 4,750 lbs of solids per day. The solids under
aeration are 41,100 pounds and the return activated
sludge (RAS) suspended solids concentration is 5,800
mg/L. The desired sludge age is 8 days.
21.311 F/M Control
F/M control is used to ensure that the activated sludge pro-
cess is being loaded at a rate that the microorganisms In the
mixed liquor volatile suspended solids (MLVSS) are able to
use most of the food simply in the wastewater being treated. If
too much or too little food is applied for the amount of mi-
croorganisms, operating problems may occur and the effluent
quality may drop.
There are four facts thatshould be remembered regarding
the F/M methpd of control:
1. The food concentration Is estimated with the COD (or BOD)
tests. The oxygen demand tests provide crude but reliable
approximations of the actual amount of food removed by
the microorganisms.
2. The amount of food (COD or BOD) applied is important to
calculate the P/M.
3. Thequanfty of microorganisms can fee represented by the
quantity of MLVSS. Ideally, the living or active mi-
croorganisms would aimpiy becounted, but this is not feas-
ible, 8nd stucUee, have shown $®| the MLVSS is a good
nin the
leduot your current wasting rate.
-------
62 Treatment Plants
4. Operation by or calculations of the F/M should not be on the
basis of daily tests because flows and organic concentra-
tions can vary widely on a day-to-day basis. One way to
handle these variations is to calculate the F/M based on a
seven-day MOVING AVERAGE9 of food (COD, BOD, or
TOC), flow and microorganisms (MLSS).
The range of organic loadings of activated sludge plants is
described by the F/M. Different ranges of organic loadings are
necessary for conventional, extended aeration, and high rate
types of activated sludge systems. These ranges have been
shown to produce activated sludge that settles well.
Table 21.5 presents the ranges of F/M that have been used
successfully with the three loading conditions. The F/M values
shown are expressed in terms of BOD, COD, and Total Or-
ganic Carbon, (TOC). The TOC is an additional means of es-
timating organic loading. The values indicated are guidelines
for process control, and they should not be thought of as
minimums or maximums.
TABLE 21.5 TYPICAL RANGES FOR F/M LOADINGS
BOD
COD<1>
TOC<2>
Conventional
AS Range
F/M
0.1 to 0.5
0.06 to 0.3
0.25 to 1.5
Extended
Aeration
F/M
0.05 to 0.1
0.03 to 0.06
0.1 to 0.25
High-Rate
Range
F/M
0.5 to 2.5
0.3 to 1.5
1.5 to 6.0
(1) Assumes BOD/COD tor settled wastewaters = 0.6
(2) Assumes BOD/TOC for settled wastewaters = 2.5
The F/M is calculated from the amount of COD or BOD applied
each day and from the solids inventory in the aeration tank.
EXAMPLE
Determine the food to microorganism (F/M) ratio for an acti-
vated sludge plant with a COD of 100 mgIL applied to the
aeration tank, an influent flow of 7.5 MGD (28,390 cu m/day)
and 33,075 lbs (15,000 kg) of solids under aeration. Seventy
percent of the MLSS are volatile matter. All knowns are
seven-day moving averages.
Known Unknown
Infl. Flow, MGD = 7.5 MGD F/M, lbs COD/day/lb MLVSS
COD, mg//. = 100 mgIL
Solids under aeration, = 33,075 lbs
lbs
MLSS VM, % = 70%
1. Calculate the food to microorganism ratio.
F/M,
1 lb COD/day = Flow, MGD x COD, mg/l x 8.34 lbs/gal
lb MLVSS Solids Solids under aeration, lbs x VM portion
_ 7.5 MGD x 100 mgIL x 8.34 lbs/gal
33,075 lbs x 0.70
= 6,255 lbs COD/day
23.150 lbs MLVSS
= 0.27 lbs COD/day/lb MLVSS
The determination of WAS flow rates using F/M control
technique is calculated in the same manner as for the sludge
age technique. However, the solids inventory for the aeration
tank can be more logically determined based on the COD or
BOD concentration of the wastewater to be treated when using
the F/M for process control. This procedure is shown in the
following calculations.
EXAMPLE
Determine the desired waste activated sludge (WAS) flow
rate using the F/M control technique. The influent flow is 7.5
MGD (28,390 cu m/day), total aeration tank volume is 1.2 MG
(4,542 cu m), COD to aeration tank is 100 mgIL, the mixed-
liquor suspended solids (MLSS) are 3,300 mgIL and 70 per-
cent volatile matter, the RAS suspended solids are 6,300 mgIL
and the desired food to microorganism (F/M) ratio is 0.29.
Current WAS flow rate is 0.085 MGD.
Known
Infl. Flow, MGD
Tank Vol., MG
COD, mg IL
MLSS, mg IL
MLSS VM, %
RAS Susp. Sol., mg IL
Desired F/M,
lbs COD/day
lb MLVSS
Current WAS, MGD
= 7.5 MGD
= 1.2 MG
= 100 mg IL
= 3,300 mg IL
= 70%
= 6,300 mg IL
_ n ,Q lbs COD/day
lb MLVSS
= 0.085 MGD
Unknown
WAS Flow, MGD
1. Determine COD applied in pounds per day.
COD, lbs/day = Flow, MGD x COD, mgIL x 8.34 lbs/gal
= 7.5 MGD x 100 mg IL x 8.34 lbs/gal
= 6,255 lbs COD/day
2. Determine the desired pounds of MLVSS.
Desired MLVSS, =
lbs
COD applied, lbs/day
F/M, lbs COD/day/lb MLVSS
6,255 lbs COD/day
0.29 lbs COD/day/lb MLVSS
= 21,569 lbs MLVSS
3. Determine the desired pounds MLSS.
Desired MLSS, lbs = Desired MLVSS, lbs
MLSS VM portion
= 21,569 lbs
0.70
= 30,813 lbs
4. Determine actual MLSS pounds under aeration.
Actual MLSS, lbs = Tank Vol., MG x MLSS, mgIL x 8.34 lbs/gal
= 1.2 MG X 3,300 mg IL x 8.34 lbs/gal
= 33,026 lbs
9 Moving Average. To calculate the moving average for the food for the last 7 days, add up the COD values for the last 7 days and divide by 7.
Each day add the most recent day to the sum of values and subtract the oldest value. By using the 7-day moving average, each day of the
week is always represented in the calculations.
-------
Activated Sludge 63
5. Calculate the additional WAS flow, MGD, to maintain the
desired food to microorganism (F/M) ratio.
Additional WAS = Solids Aerated, lbs • Desired Solids, lbs
Flow, MGD RAS Susp. Sol., mg!L x 8.34 lbs/gal
33,026 lbs - 30,813 lbs
TABLE 21.6 MCRT NEEDED TO PRODUCE A NITRIFIED
EFFLUENT AS RELATED TO THE TEMPERATURE
6,300 mg//.* x 8.34 lbs/gal
_ 2,213 lbs removed per day**
52,542
= 0.042 MGD*** x 694 GPM/MGD
= 29 GPM
* Remember that mgIL is the same as Ibs/M lbs.
** Remove 2,213 lbs during a 24-hour period.
*** If the actual solids under aeration are less than the desired solids,
reduce or stop your current wasting rate.
6. Calculate the total WAS flow in MGD and GPM.
Total WAS Flow, = Current WAS + Additional WAS
MGD Flow, MGD Flow, MGD
= 0.085 MGD + 0.042 MGD
= 0.127 MGD x 694 GPM/MGD
= 88 GPM
The F/M control technique for sludge wasting is best used in
conjunction with the MCRT control technique. Control to a de-
sired MCRT is achieved by wasting an amount of the aeration
tank solids inventory which in turn fixes or provides an F/M
ratio.
21.312 MCRT Control
By using the MCRT, the operator can control the organic
loading (F/M). In addition, the operator can calculate the
amount of activated sludge that should be wasted in a logical
manner.
Basically, the MCRT expresses the average time that a mi-
croorganism will spend in the activated sludge process. The
MCRT value should be selected to provide the best effluent
quality. This value should correspond to the F/M loading for
which the process is designed. For example, a process de-
signed to operate at conventional F/M loading rates may not
produce a high quality effluent if it is operating at a low MCRT
because the F/M may be too high for its design. Therefore you
must find the best MCRT for your process by relating it to the
F/M as well as the effluent COD, BOD, and suspended solids
concentrations.
The MCRT also determines the type of microorganisms that
predominate in the activated sludge because it has a direct
influence on the degree of nitrification which may occur in the
process. A plant operated at a longer MCRT of 15 to 20 days
will generally produce a nitrified effluent. A plant operating with
an MCRT of 5 to 10 days may not produce a nitrified effluent
unless wastewater temperatures are unusually high (above
77°F or 25°C). Table 21.6 presents the typical range of MCRT
values that will enable nitrification at various wastewater tem-
peratures. MCRTs below the values listed in Table 21.6 are
also possible under more optimum conditions, similarly, under
less favorable conditions a higher MCRT may be required. The
determination of a correct MCRT is only the first of many con-
siderations found in operating an activated sludge plant to
achieve nitrification. Nevertheless, the values shown have
been used successfully to produce nitrified effluents at numer-
ous plants where ammonia removal is required from the
effluent, but not total nitrogen removal.
Temperature, °C
10
15
20
25
30
MCRT, Days
30
20
15
10
7
As stated earlier, MCRT expresses the average time that a
microorganism spends in the activated sludge process. The
MCRT and the WAS flow rate for maintaining a desired MCRT
are shown in the following example.
EXAMPLE
Determine the waste activated sludge (WAS) flow rate using
the MCRT technique. The influent flow is 7.5 MGD (28,390 cu
m/day), total aeration tank volume is 1.2 MG (4,542 cu m),
mixed liquor suspended solids (MLSS) are 3,300 mgIL, RAS
suspended solids are 6,300 mg/L, effluent suspended solids
are 15 mgIL, and the desired mean cell residence time (MCRT)
is 8 days.
Known
Infl. Flow, MGD
Tank Vol., MG
MLSS, mgIL
RAS SS, mg/L
Effl. SS, mg/L
= 7.5 MGD
= 1.2 MG
= 3,300 mg IL
= 6,300 mg/L
= 15 mg/L
Unknown
WAS Flow, MGD
Desired MCRT, days = 8 days
MCRT,"
days
Suspended Solids in Aerator, lbs
Susp. Sol. Wasted, lbs/day + Susp. Sol. in Elf I., lbs/day
Determine suspended solids in aerator in pounds.
SS in = (Aerator, MG) x MLSS, mg/L x 8.34 lbs/gal
= 1.2 MG x 3,300 mg/L x 8.34 lbs/gal
= 33,036 lbs
Aerator,
lbs
2. Determine suspended solids lost in effluent in pounds per
day.
SS lost in = Intl. Flow, MGD x Effl. SS, mg/L x 8.34 lbs/gal
effl.,
lbs/day
= 7.5 MGD x 15 mg/L x 8.34 lbs/day
= 938 lbs/day
3. Determine the desired suspended solids wasted in pounds
per day.
SS in Aerator, lbs
MCRT, days =
SS Wasted, =
lbs/day
SS wasted, lbs/day + SS in Effl., lbs/day
SS in Aerator, lbs - SS in Effl., lbs/day
MCRT, days
33,026 lbs - 938 lbs/day
8 days
4,128 lbs/day - 938 lbs/day
3,190 lbs/day
'NOTE: Some operators use volatile suspended solids instead of
suspended solids.
MCRT may be calculated three different ways:
1. SS in Aerator, lbs,
2. SS in Aerators and Secondary Clarlfiers, lbs, and
3. SS in Aerators and Secondary Sludge Blankets, lbs.
-------
64 Treatment Plants
4. Determine the waste activated sludge (WAS) flow rate,
MGD.
SS Wasted, = WAS Flow, MGD x RAS SS, mgIL x 8.34 lbs/gal
lbs/day
WAS Flow, = SS Wasted, lbs/day
MGD RAS SS, mg IL x 8.34 lbs/gal
3,190 lbs/day
6,300 mgIL x 8.34 lbs/gal
= 0.06 MGD x 694 GPM/MGD
= 42 GPM
This means that for the next 8 days, approximately 60,000
gallons per day should be wasted from the RAS system. How-
ever, the WAS flow rate should be determined and adjusted
daily to maintain the desired MCRT.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 113.
21.3D What four facts should be remembered regarding the
F/M method of control?
21,3E Calculate the desired pounds of MLSS if the desired
F/M ratio is 0.30 lbs COD/day/lb MLVSS if 7,000 lbs of
COD per day are added and the volatile matter is 70
percent of the MLSS.
21,3F What does the Mean Cell Residence Time (MCRT)
represent?
MQ fOUZ UWP
(256A(2PIM£
21.313 Volatile Solids Inventory
If wasting is done from the RAS, the operator must measure
the volatile suspended matter in the RAS to obtain average
concentrations. If the volatile content in the RAS suspended
solids concentration is decreasing, the WAS flow rate must be
increased proportionally to waste the proper amount of volatile
suspended solids. Similarly, if there is an increase in the RAS
volatile content, the WAS flow rate must be decreased propor-
tionally to avoid losing or wasting too many microorganisms.
Using volatile suspended solids values to control the WAS flow
will take care of this problem.
When continuous wasting is practiced, the operator should
check the RAS volatile suspended solids at least once every
shift and make the appropriate WAS flow adjustment.
EXAMPLE
An activated sludge plant is currently wasting 0.05 MGD (35
GPM or 2.18 L/sec). The return activated sludge (RAS) volatile
suspended solids (VSS) on day 1 are 6,000 mg/L and on day 2
(the next day) the RAS VSS are 7,500 mg IL. Determine the
adjusted waste activated sludge (WAS) rate based on the in-
crease in return activated sludge (RAS) volatile suspended
solids (VSS) from 6,000 to 7,500 mg/L.
Known
WAS Flow, MGD
RAS VSS, mg/L
(day 1)
RAS VSS, mg/L
(day 2)
Unknown
• 0.05 MGD Adjusted WAS Flow, MGD
6,000 mg/L
7,500 mg/L
1. Calculate the adjusted waste activated sludge (WAS) flow
in MGD and GPM.
Arii WAS Flow = RAS VSS for day 1 • m9/L * WAS Flow, MGD
A* WAS Flo*. RASVSSforday2 mg/L
= 6,000 mg/L x 0.05 MGD
7,500 mg/L
= 0.04 MGD x 694 GPM/MGD
= 28 GPM
When intermittent wasting is practiced, the operator must
check the RAS volatile suspended solids to calculate the nec-
essary WAS flow. In addition, this calculation must be
readjusted for the reduced time of wasting.
EXAMPLE
In the previous example, the waste activated sludge pump-
ing (WAS) period is 4 hours per day and the calculated WAS
flow was 0.04 MGD or 28 GPM (1.75 L/sec). Calculate the
WAS flow.
Unknown
WAS Flow, MGD for 4
hour/day wasting period
Known
WAS Flow, MGD = 0.04 MGD
Wasting Time, hr/day = 4 hrs/day
1. Determine the WAS flow for a 4 hour-day wasting period.
New WAS flow, MGD = WAS Flow, MGD x 24 hr/day
4 hours of wasting/day
= 0.04 MGD x 24 hr/daV
4 hr/day
= 0.24 MGD x 694 GPM/MGD
= 167 GPM
The operator would repeat the WAS flow calculation for each
wasting period to take into account the RAS volatile sus-
pended solids variations.
Intermittent wasting of sludge has the advantage that less
variation in the suspended matter concentration will occur dur-
ing the wasting period, and the amount of sludge wasted will
be more accurately known. The disadvantages of intermittent
wasting are that the sludge handling facilities in the treatment
plant may be loaded at a higher hydraulic loading rate and that
the activated sludge process is out of balance for a period of
time until the microorganisms regrow to replace those wasted
over the shorter period of time. Intermittent wasting usually is
not practiced in plants treating more than 10 MGD (37,800 cu
m/day).
In using either of these methods for wasting, the operator
does not have complete control of the amount of activated
sludge wasted due to the solids lost in the effluent. This "wast-
ing" of activated sludge in the effluent must be accounted for
with any method of process control or the system will always
be slightly out of balance. The loss of activated sludge in the
effluent generally accounts for less than five percent of the
total solids that need to be wasted; however, it is necessary to
be aware of this loss and to be able to take it into account by
the methods shown in Section 21.312, "MCRT Control." The
need for taking into account the solids lost in the effluent is
especially important if one encounters situations where large
concentrations of suspended solids are washed out in the sec-
ondary effluent, as in the case of sludge bulking.
Proper control of the WAS will produce a high quality effluent
with mininum operational difficulties.
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Activated Sludge 65
21.314 MLVSS Control
This technique for process control is used by many
operators because it is simple to understand and involves a
minimum amount of laboratory control. The MLVSS control
technique usually produces good quality effluent as long as the
incoming wastewater characteristics are fairly constant with
minimal variations in influent flow rates.
With this technique, the operator tries to maintain a constant
MLVSS concentration in the aeration tank to treat the incoming
wastewater organic load. To put it in simple terms, if it is found
that a MLVSS concentration of 2,000 mg/L produces a good
quality effluent, the operator must waste sludge from the pro-
cess to maintain that concentration. More sludge is wasted
until the desired level is reached again.
The laboratory control tests and operational data involved in
using this technique include the following:
1. MLVSS Concentration
2. RAS Volatile Suspended Solids Concentration
3. Influent Wastewater Flow Rate
4. Volume of Aeration Tank
Whether a new plant is being started or the operation of an
existing plant is being checked, this control technique is used
to indicate when activated sludge should be wasted. In most
cases it is not the most reliable technique because it ignores
process variables such as F/M and microorganism growth rate
necessary for maintaining optimum system balance. When
operational problems occur, the operator is unable to make
rational process adjustments due to the lack of process control
data.
The control technique is implemented by choosing an
MLVSS concentration which produces the highest quality
effluent while maintaining a stable and economical operation.
WAS flow rates are determined as follows:
EXAMPLE
A 1.2 MG (4,542 cu m) aeration tank has a mixed liquor
suspended solids (MLSS) concentration of 3,300 mg/L. The
return activated sludge (RAS) suspended solids concentration
is 6,300 mg/L. The volatile portion of both suspended solids is
70 percent. Experience has shown that the desired mixed liq-
uor volatile suspended solids (MLVSS) in the aeration tank is
approximately 21,250 pounds (9,639 kg). Determine the de-
sired waste activated sludge (WAS) flow rate if the current
WAS flow rate is 0.15 MGD.
Known
Tank Vol., MG
MLSS, mg/L
RAS SS, mg/L =
Volatile Portion
Desired MLVSS, lbs =
Current WAS Flow, =
MGD
1.2 MG
3,300 mg/L
6,300 mg/L
0.70
21,250 lbs
0.15 MGD
Unknown
Desired WAS Flow, MGD
1. Determine mixed liquor volatile suspended solids (MLVSS)
under aeration in pounds.
Actual MLVSS, = Tank Vol., MG x MLSS, mg/L x Volatile x 8.34 lbs/gal
lbs = 1.2 MG x 3,300 mg/L x 0.70 x 8.34 lbs/gal
= 23,120 lbs
2. Determine the pounds of volatile solids to be wasted.
Amt. Wasted, = Actual MLVSS, lbs - Desired MLVSS, lbs
lbs = 23,120 lbs - 21,250 lbs
= 1,870 lbs to be wasted per day
3. Determine the additional waste activated sludge (WAS)
flow rate in MGD and GPM.
Amt. Wasted, = WAS Flow, MGD x RAS SS, mg/L x Vol. x 8.34 lbs/gal
lbs/day
or Amount Wasted, lbs/day
WAS Flow, MGD =
RAS SS, mg/L * Volatile x 8.34 lbs/gal
1,870 lbs/day
6,300 mg/L x 0.70 x 8.34 lbs/gal
= 0.05 MGD x 694 GPM/MGD
= 35 GPM
4. Determine the desired WAS flow rate in MGD and GPM.
Desired WAS = Current WAS . Additional WAS
Flow, MGD Flow, MGD Flow, MGD
= 0.15 MGD + 0.05 MGD
= 0.20 MGD x 694 GPM/MGD
= 140 GPM
21.32 Microscopic Examination
Some operators use a microscope to examine the mi-
croorganisms in the mixed liquor for an indication of the condi-
tion of the activated sludge treatment process. The majority of
the BOD is removed by common zoogleal microorganisms.
The microorganisms that are important indicators in the acti-
vated sludge process are the PROTOZOA10 and ROTIFERS11.
The protozoa eat the bacteria and help produce a clear
effluent. The presence of rotifers is an indication of a stable
effluent. If excessive FILAMENTOUS BACTERIA12 are ob-
served, you usually can expect an activated sludge that settles
poorly.
If most of the microorganisms in the mixed liquor suspended
solids are protozoa (ciliates) and rotifers, you can expect a
good settling activated sludge. By using the proper return acti-
vated sludge (RAS), waste activated sludge (WAS), and aera-
tion rates, you can produce an effluent with a BOD of less than
10 mg/L.
Apparently some filamentous bacteria are good, but too
many are bad. Filamentous bacteria can form a network or
backbone upon which activated sludge floe can gather and
form an excellent settling floe. If the filaments become exces-
sive, a bridging mechanism forms which prevents the activated
sludge from flocking or gathering together. If the floe cannot
come in contact with each other, sufficient particle mass will
not be produced to achieve a good settling floe.
10 Protozoa (pro-toe-ZOE-ah). A group of microscopic animals (usually single-celled) that sometimes cluster Into colonies.
11 Rotifers (ROE-ti-fers). Microscopic animals characterized by short hairs on their front end.
11 Filamentous Bacteria (FILL-a-MEN-tus). Organisms that grow in a thread or filamentous form. Common types are thiothrix and ac-
tlnomyces.
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66 Treatment Plants
Three groups of protozoa are important to the operator of an
activated sludge process.
1. Amoeboids
2. Flagellates
3. Ciliates
AMOEBOIDS (Fig. 21.8)
Look for amoeboids in the mixed liquor suspended solids
floe during start-up periods or when the process is recovering
from an upset condition.
Fig. 21.8 Amoeboids
FLAGELLATES (Fig. 21.9)
Flagellates are usually found with a light, dispersed, strag-
gler floe, a low population of microorganisms, and a high or-
ganic (BOD) load. With a high organic (BOD) load, other mi-
croorganisms will start to thrive, a more dense sludge floe will
develop, and the flagellate population will decrease.
Fig. 21.11 Stalked ciliates
Free swimming ciliates are usually present when there is a
large number of bacteria in the activated sludge. These or-
ganisms feed on bacteria and help produce a clear effluent.
They are associated with a good degree of treatment.
Stalked ciliates are usually present when the free swimming
ciliates are unable to compete for the available food. A large
number of stalked ciliates and rotifers (Fig. 21.12) will indicate
a stable and efficiently operating activated sludge process.
u
i
Fig. 21.9 Flagellates
CILIATES
Ciliates are usually found in large numbers when the acti-
vated sludge is in a fair to good setting condition. Ciliates are
classified into two basic groups, free swimming ciliates (Fig.
21.10) and stalked ciliates (Fig. 21.11).
Fig. 21.10 Free swimming ciliates
Fig. 21.12 Rotifers
The types of microorganisms and the numbers of mi-
croorganisms can be used as a guide in making activated
sludge process control adjustments. Figure 21.13 can help you
determine whether the mean cell residence time (MCRT)
should be increased or decreased. A decline in mi-
croorganisms, especially ciliates, is frequently a warning of a
poorly settling sludge. If a relatively large number of
amoeboids arid flagellates are observed, try increasing the
MCRT. If the numbers of microorganisms are relatively low
with rotifers predominating and you have a pin floe, try de-
creasing the MCRT.
These observations can allow an operator to detect a
change in organic loading or in level of a toxic chemical before
the activated sludge process becomes upset. The changes in
type and number of microorganisms should be compared with
observations of the settling characteristics of the mixed liquor
suspended solids in the 60-minute settleability test and with
the calculated food to microorganism ratio.
In summary, large numbers of ciliates and rotifers are an
indication of a stable activated sludge process that will produce
a high quality effluent.
Major portions of this section were taken from PROCESS
CONTROL MANUAL FOR AEROBIC BIOLOGICAL WASTE-
WATER TREATMENT FACILITIES, Municipal Operations
Branch, Office of Water Program Operations, U. S. Environ-
mental Protection Agency, Washington, D, C. 20460.
-------
H
U
Z
<
3
2
8
U
OS
D.
W
>
U
OJ
STRAGGLERS
GOOD SETTLING
FREE SWIM.
C1L1ATES
FLAGELLATES
AMOEBOIDS
ROTIFERS
STALKED
CILIATES
FREE
SWIMMING
CILIATES
FLAGELLATES
AMOEBOIDS
ROTIFERS
STALKED
CILIATES
FREE
SWIMMING
CILIATES
FLAGELLATES
AMOEBOIDS
PIN FLOC
NEMATODES
ROTIFERS
STALKED
CILIATES
&
FREE
SWIMMING
CILIATES
FLAGELLATES
AMOEBOIDS
NEMATODES
ROTIFERS
STA LKED
CILIATES
FREE SWIM.
CILIATES
FLAGELLATES
AMOEBOIDS
Fig. 21.13 Relative number of microorganisms vs. sludge quality
-------
68 Treatment Plants
21.33 The Al West Method
Sections 21.2, "Return Activated Sludge" and 21.3, "Waste
Activated Sludge" have outlined various methods operators
use to "control" their activated sludge process. Mr. West has
correctly observed that the activated sludge "process is NOT
controlled by attempting to achieve PRECONCEIVED levels of
INDIVIDUAL variables such as, mixed liquor sludge concentra-
tion, mean cell residence time and food to microorganism
ratios. CONTROL tests such as, final clarifier sludge blanket
depth determinations, mixed liquor and return sludge concen-
trations (by centrifuge) and sludge settleability are used to de-
fine sludge quality and process status and to determine pro-
cess adjustments." Mr. West worked continuously to develop
better ways for operators to control the activated sludge pro-
cess. For the most recent procedures, contact:
Operational Technology Branch
U. S. Environmental Protection Agency
National Training & Operational Technology Center
Cincinnati, Ohio 45268
21.34 Summary on RAS and WAS Rates
How should you operate your activated sludge process?
Only you can answer this question. In Chapters 8 and 11, we
outlined what we consider are simple and direct procedures for
operating package plants, oxidation ditches and conventional
activated sludge plants. In Chapter 21, various alternative
methods were outlined on how to control the activated sludge
process.
What counts is the effluent quality from your activated
sludge plant. The effluent quality is influenced by influent
characteristics and conditions in the aeration tank and sec-
ondary clarifier. Observe these characteristics and conditions;
you must be alert for any change and make appropriate ad-
justments to control the activated sludge process. EVERY
OPERATOR ON EVERY SHIFT MUST FOLLOW THE SAME
PROCEDURES. TRY NOT TO ADJUST YOUR RAS AND IMS
RATES BY MORE THAN 10 OR 15 PERCENT FROM ONE
DAY TO THE NEXT DAY. SELECT A METHOD YOU UNDER-
STAND, RECORD AND ANALYZE DATA, STICK WITH YOUR
METHOD AND YOU CAN MAKE IT WORK TO PRODUCE A
GOOD EFFLUENT.
21.35 Acknowledgment
Major portions of Section 21.3 were adapted from PRO-
CESS CONTROL MANUAL FOR AEROBIC BIOLOGICAL
WASTEWATER TREATMENT FACILITIES, Municipal Opera-
tions Branch, Office of Water Program Operations, U. S. En-
vironmental Protection Agency, Washington, D. C. 20460.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 113.
21.3G Which microorganisms are important indicators in the
activated sludge process?
21.3H In the Al West method, what important activated
sludge control tests are used to define sludge quality
and process status?
6-Hcl of \~2£ho\A $ .of 4
ACfiVAfgP
Please answer the discussion and review questions before
continuing with Lesson 4.
-------
Activated Sludge 69
DISCUSSION AND REVIEW QUESTIONS
(Lesson 3 of 4 Lessons)
Chapter 21. ACTIVATED SLUDGE
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 2.
9. What items are affected by the amount of waste activated
sludge (WAS) removed from the process?
10. How will you know when you have established the best
mode of process control for your plant?
11. What is the basis for the F/M method of controlling the
activated sludge process?
12. How would you adjust the MCRT to produce a nitrified
effluent?
13. What are the advantages and limitations of intermittent
wasting of activated sludge?
14. How would you select the RAS and WAS rates for your
activated sludge plant?
wmat?
CHAPTER 21. ACTIVATED SLUDGE
(Lesson 4 of 4 Lessons)
21.4 TREATMENT OF BOTH MUNICIPAL AND
INDUSTRIAL WASTES
21.40 Monitoring Industrial Waste Discharges (Also see
Chapter 27, "Monitoring Industrial Wastes.")
Industrial manufacturing processes of most types generate
some waste materials. These waste materials take the form of
liquid, gaseous or solid residuals. In most cases, the deliberate
and indiscriminate disposal of these waste materials to the
collection system will have a deteriorating effect upon the acti-
vated sludge process and possible detrimental effects on the
treatment plant effluent receiving waters.
As discussed in Chapter 11, Section 11.011, you should
become acquainted with the various industrial facilities in your
area to determine what, if any, adverse impact they may create
on your activated sludge process.
21.400 Establishing a Monitoring System
Regulations at both state and federal levels usually require
that industrial waste monitoring be established as an important
part of an industrial waste control and treatment system.
An industrial waste monitoring program is valuable for the
following reasons:
1. To assure regulatory agencies of industrial compliance with
discharge requirements and implementation schedules set
forth in the discharge permit,
2. To maintain sufficient control of treatment plant operations
to prevent NPDES permit violations, and
3. To gather necessary data for the future design and opera-
tion of the treatment plant.
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70 Treatment Plants
In establishing a monitoring program, one of the first tasks
should be an examination of the wastewater characteristics of
each industry that discharges to the collection system. Aware-
ness of the specific types of harmful waste materials that may
enter the collection system will help you prepare a monitoring
program to protect the treatment plant and receiving waters.
Some industries pretreat wastewaters before discharge to
the collection system to recover valuable materials, to reduce
sewer-service charges, and to keep undesirable constituents
out of the sewers and treatment plant. However, if undesirable
constituents are known to be present in the municipal waste-
water stream, pretreatment of the industrial wastewater portion
must be enforced to reduce the constituents to acceptable
levels. Proper monitoring at the site of an industrial wastewater
pretreatment plant is essential. Additionally, if it is likely that an
accidental spill or unlawful discharge may escape pretreat-
ment and enter the collection system, a sophisticated monitor-
ing system should be installed at your treatment plant. The
reasons for wastewater monitoring at the treatment plant itself
include establishing a last point of measurement of certain
problem constituents before entering the unit processes so
that the operator can start corrective operational measures
where possible.
21.401 Automatic Monitoring Units
Automatic monitoring of several wastewater characteristics
has been a dependable method of alerting the operator to
abnormal influent wastewater conditions. Numerous water
quality indicators are used for operational controls, yet the
number of water quality indicators that can be automatically
measured without difficulty is limited. Therefore, it is essential
that the operator also rely on the appearance and odor of the
influent wastewater as part of the monitoring program at the
treatment plant.
Some of the more common monitoring devices include:
1. Flow measuring,
2. pH monitoring,
3. Oxidation potential monitoring (conductivity),
4. Suspended solids monitoring,
5. DO monitoring,
6. Wastewater samplers, and
7. Gas-phase hydrocarbon analyzer.
Normally, data is recorded on a strip chart recorder; how-
ever, other equipment, such as pumps or valves may be acti-
vated by these monitoring devices. The monitoring systems
should also be combined with an alarm system that will give
the operator warning when a high concentration of an undesir-
able water quality indicator reaches the monitoring station.
21.41 Common Industrial Wastes
Reduction and/or elimination of harmful waste constituents
from industrial discharges may be controlled by enforcing your
municipal sewer ordinance. Several objectionable industrial
waste constituents and the possible effects of each waste are
discussed below.
1. Flammable Oils. Examples of flammable oils are crude
gasoline, benzene, naphtha, fuel oil, and mineral oil. These
substances are not soluble and tend to collect in pools, thus
creating potential explosive conditions. When methane gas
is mixed with flammable oils, a very powerful explosion may
result.
2. Toxic Gases. Toxic gases such as hydrogen sulfide (H2S),
methane (ChU), and hydrogen cyanide (HCN) are often
present or may be formed in industrial discharges. Waste-
water with high quantities of sulfate can cause problems in
anaerobic decomposition, due to the formation of H2S.
Also, cyanide combines with acid wastes to form the ex-
tremely toxic gas, HCN.
3. Oils and Greases. A municipal plant generally does not
have facilities for the removal of significant quantities of oils
and grease. Pretreatment of wastewater may be desirable
to reduce the total concentration of oils and grease (hexane
extractables). In general, emulsified oils and greases of
vegetable and animal origin are biodegradable and can be
successfully treated by a properly designed municipal
treatment facility. However, oils and greases of mineral ori-
gin may cause problems and these are the constituents
generally requiring pretreatment.
4. Settleable Solids. Settleable solids cause obstructions in
the sewer system by settling and accumulating. At places
where wastewater accumulates, anaerobic decomposition
may take place, producing undesirable products, such as
hydrogen sulfide and methane.
High settleable solids concentrations may overload the
capacity of the treatment plant.
5. Acids or Alkalies. Acids or alkalies are both corrosive and
may also interfere with biological treatment. Even neutral
sulfate salts may cause corrosion, since the sulfate can be
biologically reduced to sulfide and then oxidized to sulfuric
acid.
6. Heavy Metals. Heavy metals may be toxic to biological
treatment systems or to aquatic life in the receiving water
and may adversely affect downstream potable water
supplies.
7. Cyanides. Cyanides are toxic to bacteria and may cause
hazardous gases in the sewer.
8. Organic Toxicants. Pesticides and other extremely toxic
substances in wastewater are objectionable except in very
small concentrations. Even if the biological treatment sys-
tems are not altered by higher concentrations, toxicants
may still damage receiving surface water quality.
21.42 Effects of Industrial Wastes on the Treatment Plant
Unit Processes
When undesirable industrial constituents enter the municipal
waste stream, certain adverse effects on common unit treat-
ment processes can be expected. For example, acids and cor-
rosive materials would damage the conveyance system of
pipes and pumps. Dangerous gases and explosive materials
create hazards to plant personnel. Other constituents, such as
heavy metals or toxic organics, may actually inhibit or kill the
microorganisms at the treatment plant.
Some of the more common adverse effects that industrial
waste constituents have on unit processes are listed below.
A. Sewer System
1. Corrosion caused by acids
2. Clogging due to fats and waxes
3. Hydraulic overload by discharge of cooling waters
4. Potential explosion danger with gasolines and other
fuels
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Activated Sludge 71
B. Grit Channels
1. Overloading with high grit concentrations
2. Increased organic content of grit
3. Intermittent flow reduces removal efficiency
C. Screens and Comminutors
1. Overload with excess solids
2. Excessive wear on comminutor cutting surfaces by
hard materials
D. Clarifiers
1. Fluctuating hydraulic loadings reduce removal efficien-
cies
2. Scum problems from excessive quantities of oils
3. Impaired effluent quality caused by finely divided sus-
pended solids
4. Excessive sludge quantities with high suspended sol-
ids concentrations
E. Sludge Digesters
1. Negative effects on sludge digestion caused by inor-
ganic solids
2. Overload caused by excessive solids
3. Increased scum layers caused by excessive organic
solids
4. pH problems from an industrial wastewater with a high
sugar content
5. Toxicants
F. Activated Sludge
1. Deterioration in quality with transient loading
2. Excessive carbohydrate concentrations can cause
bulking or poorly settling sludge
3. Toxicants
4. Foaming problems
21.43 Operational Strategy
21.430 Need for a Strategy
Adverse effects to the activated sludge process can be sig-
nificantly reduced if the operator has a plan of operation or an
operational strategy ready to implement when adverse indus-
trial constituents enter the treatment plant.
This section will discuss the observations and corrective ac-
tions (operational strategy) taken at a typical activated sludge
plant when (1) a toxic waste (cyanide), and (2) a high BOD
waste (milk) enter the treatment plant mixed with the domestic
wastewater.
This typical plant monitors the influent pH and the aeration
tank DO. These are the only two water quality indicators that
are monitored continuously. The operators at this plant rely
heavily on sight and smell observations of the influent waste-
water, aeration tank mixed liquor, and the secondary effluent
as the first indicators of shock or overload conditions at the
plant. These observations allow the proper corrective actions
to be implemented before significant damage to the activated
sludge process occurs.
Our typical treatment plant is designed to operate in the
contact stabilization modification of the activated sludge pro-
cess. This mode of operation is very desirable when industrial
waste constituents that are harmful to the organisms in acti-
vated sludge may occur unexpectedly in the treatment plant
influent. The advantage of operating in this mode is discussed
in Chapter 11, Section 11.91.
The average operating data
Peak influent flow
Raw wastewater COO
Primary effluent feed to the
aeration tanks
Aeration contact basin F/M
DO through the system
Sludge aeration time
Ammonia oxidation
Secondary effluent nitrate
Secondary effluent SS
Air-to-flow ratio
HAS flow rate control
for our typical plant is as follows:
: 17.0 MGD
: 400 to 450 mg/L
: Three-point step feed
: 0.5 to 0.8 lbs COD/day/lb MLVSS
0.05 to 5.0 mg/L
7 to 12 hours to keep most of the
biomass under aeration
30 to 50 percent
0.3 to 1.5 mg/L
5 to 10 mg/L (varies with the
waste)
1.8 to 2.5 cu ft/gal
Flow paced and allow "zero"
sludge blanket in the secondary
clarifier
21.431 Recognition of a Toxic Waste Load
In our sample plant, the first indication of a toxic waste load
within the treatment plant is recognized by observing the aera-
tion basin DO recording device. As the toxic load moves into
and through the aeration basin, the DO residual will increase
significantly. A DO increase without an air input increase indi-
cates that the toxic waste load is killing the microorganisms in
the aeration tank, thus reducing the oxygen uptake (respira-
tion) by the microorganisms.
A second indication of a toxic waste reaching the plant may
be observed in the secondary clarifier effluent. The effluent will
begin to exhibit floe carry-over (an indication of cell death). The
degree of carry-over will depend on the substance and quantity
of the toxic waste.
When a toxic substance is known to have entered the treat-
ment plant, the operator should make every effort to obtain a
sample of the wastewater and have the sample analyzed as
soon as possible to determine the toxic constituents. A record
of these upset conditions and the constituents involved is very
important so that if uncontrollable problems develop at the
treatment plant, the records can be reviewed in an attempt to
determine the input source.
21.432 Operational Strategy for Toxic Wastes
The operator's primary mission in the case of toxic wastes is
to save the activated sludge system.
When the operator in our sample plant recognizes a toxic
waste condition, the RAS flow is reduced significantly to keep
as many of the bacteria affected by the toxic waste in the
secondary clarifiers. The operator then significantly increases
the WAS flow to purge the activated sludge process of the toxic
waste and the sick or dead microorganisms. Additionally,
every attempt is made to process the toxic waste flow through
the plant as fast as possible to reduce contamination of other
unit processes such as anaerobic or aerobic digesters.
The toxic waste processing time through our typical plant
may vary from 30 minutes to 2 hours.
21.433 Recognition of a High Organic Waste Load
The first indication of a high organic waste load within the
treatment plant is recognized by observing the aeration basin
DO recording device. As the high organic load moves into and
-------
72 Treatment Plants
through the aeration basin, the DO residual will decrease sig-
nificantly. A DO decrease without an air input decrease indi-
cates that the high organic waste load is too great for the
available microorganisms to properly assimilate and
metabolize the waste (food to microorganism ratio is out of
balance because of a greater BOD (food)).
If the high organic waste load is significant, the nutrient con-
tent of the municipal waste may be inadequate for proper
biological activity. Therefore, nitrogen and phosphorus can be
added on the basis of a total carbon measurement of the in-
fluent wastestream to ensure adequate amounts of these nu-
trients.
The quantity of nitrogen and phosphorus required for a
waste can be estimated from the quantity of sludge produced
per day. The pounds of nitrogen required per day will be about
10 percent of the volatile solids (dry weight) produced each
day. The phosphorus requirement will be one-fifth of the nitro-
gen requirement. The amounts of nitrogen and phosphorus
added daily are equal to the differences between the quantity
required and the quantity in the wastes.
Additional Nitrogen, = Nitrogen Required, - Nitrogen in Wastes,
lbs/day lbs/day lbs/day
A second indication of high organic waste reaching the plant
may be observed in the secondary clarifier effluent. The
effluent will become more turbid (less clear) indicating that the
waste flow has not been adequately treated.
The sampling and analysis recommended in Section 21.401
should also be implemented in this situation.
21.434 Operational Strategy for High Organic Waste
Loads
The operator's primary mission in the case of high organic
loads is to improve the microorganism treatment efficiency.
Upon recognizing a high organic waste load condition, the
RAS flow must be significantly increased to provide more mi-
croorganisms to the aeration contact basin to adequately treat
the high organic waste. The rate of RAS increase must be
accomplished gradually so that both design hydraulic and sol-
ids loading rates for the secondary clarifiers are not exceeded.
In addition, every attempt should be made to increase the air
or oxygen input to maintain proper DO levels in the aeration
basins. If appropriate, nitrogen and phosphorus should be
added to provide the additional nutrients needed by the mi-
croorganisms.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 113.
21.4A Why is an industrial waste monitoring program valu-
able for the operator of an activated sludge plant?
21,4B List five common wastewater monitoring devices.
21.4C What would you do if a high organic waste load en-
tered your activated sludge plant?
21:5 INDUSTRIAL WASTE TREATMENT
21.50 Need to Treat Industrial Wastes
As the operator of an industrial wastewater treatment plant,
it Is your responsibility to ensure that required sewer-use stan-
dards or effluent quality standards are achieved in order that
the production system may remain on-line. Because of tighter
restrictions on the quality of industrial wastewater that can be
discharged to municipal sewer systems or receiving streams,
your industrial facility may be required to pretreat the industrial
process wastewaters. This pretreatment can be costly, but
failure to properly pretreat these wastewaters may result in
excessive sewer use fees and treatment charges, in severe
fines for violations and possible production shutdowns. Many
industries are finding it more economical to build, operate and
maintain their own treatment facilities than to pay for pretreat-
ment and use of municipal treatment plants.
This section will provide you with information necessary to
increase your process awareness and alert you to precautions
required in operating your activated sludge industrial wastewa-
ter treatment plant.
Although there is a wide variety of applications of the acti-
vated sludge process to industrial wastewater treatment in op-
eration today, this section will concentrate on some typical
plants which treat wastes from fruit and vegetable processing,
paper product manufacturing, and petroleum refining.
21.51 Characterization of Influent Wastes
The character of the wastewater is dependent on the particu-
lar production process and the way it is operated. The first step
to successful operation of your treatment plant is to charac-
terize the wastewaters through various analyses. These
characteristics describe the concentrations or amounts of
wastes in the wastewaters and include BOD, total suspended
solids, settleable solids, COD, pH, DO, temperature, total sol-
ids, dissolved solids, chloride, nitrogen, and phosphorus.
These pollutants are often used to determine the fees paid by
industry for use of municipal collection systems and treatment
plants. Other pollutants that are measured include toxic sub-
stances such as arsenic, zinc and copper. Toxic substances
usually must be pretreated by industry. The procedures for
measuring the concentrations or amounts of these wastes are
outlined in Chapter 16, "Laboratory Procedures and Chemis-
try."
Another important characteristic of the wastewater being
treated is the flow. Flow rate should be described in terms of
the daily average and also the fluctuations. Because many
industrial facilities do not generate consistent waste flows and
constituents over a 24-hour day or 7-day week, you must de-
termine when the variations can be expected and operate your
activated sludge process in a manner that anticipates these
variables and does not allow these fluctuations to cause a
deterioration of the quality of the plant effluent. Effective
sewer-use ordinances require that industry notify the operator
of a municipal treatment plant whenever a significant acciden-
tal discharge (spill or dump) or process failure might upset a
treatment plant. By warning the operator of the volume and
nature of the discharge, provisions can be made to handle the
waste when it reaches the plant. Process supervisors should
notify the operators of their industrial wastewater treatment
plants when a potentially harmful spill or dump occurs.
21.52 Common Industrial Wastewater Variables
21.520 Flow
Flow measurements are a basic requirement at every treat-
ment plant. Recorded flow data are essential because these
records allow you to establish correct operating guidelines
(loadings) and determine if your treatment plant is properly
sized to process the hydraulic loads.
In many industrial production facilities, the wastewater flows
are generally higher during the day-shift hours of Monday
through Friday. Significant flow reductions may be anticipated
in the evening hours with possible "zero" flow conditions dur-
ing weekends, holidays, and annual production maintenance
shutdown periods.
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Activated Sludge 73
In cases where flows to your treatment plant approach or
exceed the hydraulic design capacity, every effort should be
taken to implement a production facility pollution abatement
program to reduce water consumption and minimize waste
generation through proper management of processing and
production operations.
21.521 pH
The pH of production facility wastewaters may vary from 2.5
to 13.0 depending upon the production being processed and
the type of operations conducted within the facility. Natural
waters generally have pH values between 6.5 and 8.0.
If the wastewater pH varies greatly from neutral (7.0), the
wastewater should be adjusted (neutralized). Neutralization
may be accomplished in a tank of sufficient detention time
(15-20 minutes). Sulfuric acid (to lower pH) or caustic (to in-
crease pH) addition to the waste stream may be controlled with
pH probes and controllers for rough and fine pH adjustment.
21.522 BOD and Suspended Solids
The BOD test is the rate of oxygen uptake from the wastewa-
ter by microorganisms in biochemical reactions. These mi-
croorganisms are converting the waste materials to carbon
dioxide, water and inorganic nitrogen compounds. The oxygen
demand is related to the rate of increase in microorganism
activity resulting from the presence of food (organic wastes)
and nutrients. Microorganism activity may be hindered in some
industrial wastes due to the presence of toxic wastes. Indus-
trial wastewaters may contain levels of BOD from 500 to
10,000 mg/L
Suspended solids information may be used to determine the
quantity of solids which will require removal in the activated
sludge treatment system. Typical suspended solids concentra-
tions for industrial wastewaters vary from 125 mg/L to 3,000
mg/L
For any waste, the concentrations of pollutants can be
readily reduced by simply using more water, but the increase in
volume will result in the same number of total pounds of pollut-
ants. The organic load, consisting of both BOD and suspended
solids, can onJy be effectively reduced by reductions in pounds
of pollutants generated at production facility sources.
21.523 COD
Chemical oxygen demand (COD) is an alternative to
biochemical oxygen demand (BOD) for measuring the pollu-
tional strength of wastewaters. When considering the use of
COD for measuring the strength of wastewater, you must bear
in mind that the BOD and COD tests involve separate and
distinct reactions. Chemical oxidation measures the presence
of carbon and hydrogen, but not amino nitrogen in organic
materials. Furthermore, the COD test does not differentiate
between biologically stable and unstable compounds. For
example, cellulose is measured by chemical oxidation, but is
not measured biochemically under aerobic conditions.
The primary disadvantage of the COD test is its susceptibil-
ity to interference by chloride. Thus, wastewaters containing
HIGH salt concentrations, such as brine, cannot be readily
analyzed without modification.
21.524 Nutrients
Aside from carbonaceous organic matter (which is meas-
ured largely as BOD), the nutrients required for reproduction of
microorganisms are nitrogen (N) and phosphorus (P). In
unusual cases, other elements may also be critical. These
other essential nutrients include iron, calcium, magnesium,
potassium, cobalt, and molybdenum. Since many production
facility wastewaters are deficient in nutrients for biological
treatment, nutrients can be added to optimize your biological
wastewater treatment system efficiency.
The amount of these nutrients required for a treatment pro-
cess depends both on the age of the microorganisms and the
numbers of cells generated (growth rate) during the reduction
of BOD. A BOD/nitrogen/phosphorus ratio of 100:5:1 is usually
adequate. However, high-rate systems with no available nitro-
gen or phosphorus in the wastewater may require a ratio of
100:10:2. Ratios lower than 100:5:1 may be adequate for aer-
ated ponds and systems with a very long sludge age. All nut-
rients need to be in a soluble form to be used by the mi-
croorganisms.
21.525 Toxicity
The most common causes of wastewater toxicity are exces-
sive amounts of free ammonia, residual chlorine, detergents,
paints, solvents, and biocides. Other wastes that can upset
microorganisms include heavy metals, chlorinated hydrocar-
bons, petroleum products, acids, bases (caustics) and tem-
perature changes. These toxic materials can enter the waste-
water stream through indiscriminate dumping, improper han-
dling of toxic materials, leaking vessels and pipes, or acciden-
tal spills.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 114.
21.50A List three types of industries whose wastes could be
treated by an activated sludge plant.
21.51A What factors influence the character of industrial
wastewaters?
21,52A How would you attempt to solve a hydraulic overload-
ing problem at an industrial wastewater treatment
plant?
21.52B How can the pH of an industrial wastewater be ad-
justed (1) upwards, and (2) downwards?
21.52C Chemical oxidation (COD) measures the presence of
(1) and (2) but not (3) in
organic materials.
21.52D List the three major nutrients required by mi-
croorganisms and four other elements that might be
critical.
21.52E What are the most common causes or kinds of toxic-
ity in industrial wastewaters?
21.53 Flow and Pre-Treatment Considerations
Because industrial wastewater characteristics may change
significantly over a given period of time, a program for sam-
pling, testing, and measuring the flow is essential.
Variations in production activity will change wastewater
characteristics. Samples should be collected during each
operating shift and during different stages of the finished prod-
uct and raw product runs. Flows should be monitored continu-
ously, even during cleanup and on weekends.
Daily or seasonal shutdown and start-up of a processing/
production facility usually causes wastewater characteristics to
vary greatly. This variation often causes problems in a treat-
ment system. Biological treatment systems perform best on a
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74 Treatment Plants
uniform supply of a given source of food (BOD). If the food
supply changes greatly, the biological process may not be able
to adjust to the change. The impact of frequent shutdowns and
start-ups on a treatment system should be carefully evaluated.
Flow regulation procedures using holding tanks may be nec-
essary to smooth out the flows (see Section 21.531, "Flow
Control").
21.530 Flow Segregation
Considerable treatment cost savings may be achieved by
processing only the wastewaters that contain pollutant materi-
als in quantities exceeding the limits set forth in your local,
state, or federal discharge permit. Consider classifying the
processing/production facilities wastewaters into three
categories (i.e., low strength BOD, medium strength BOD, and
high strength BOD). You may find that it is possible to reuse
the low strength BOD waters for cleanup purposes or dispose
of it by discharge directly to a sanitary sewer system, by spray
on fields, or by irrigation of pasture land.
Treatment of the medium strength BOD wastewaters (usu-
ally resulting from cleanup) may be possible by using a screen
system to remove large solids and then processing the waste-
water through an air flotation unit, plate and frame filter press
or similar device. Since only 30 to 40 percent BOD and sus-
pended solids reductions may be obtained from this treatment
method, the dewatering process effluent (low in BOD/SS) may
then be routed to the activated sludge system and will aid in
diluting the high strength BOD wastewaters.
21.531 Flow Control
If your treatment plant experiences wide flow variations,
these variations often cause problems in a treatment system.
Depending on the daily operating mode of the processing/
production facility, variations in instantaneous flow can be from
very small to very great (a maximum of ten times the
minimum). Each facility is obviously different, but large varia-
tions in flow may be smoothed with a surge or storage tank of
about 10 to 20 percent of the total daily flow volume. Settling of
solids will be a significant problem in a tank of this size, so that
tank must either be mixed or some means must be provided for
solids removal.
Control measures for water use in the process/production
facility should be implemented. One of the most important
methods of water use reduction is a complete and comprehen-
sive training program of everyone involved in process/
production. Additionally, roof gutters, downspouts, and facility
storm drains may discharge to the treatment plant. These
should be relocated and/or rerouted to appropriate drainage
systems to eliminate charges for treating this water.
21.532 Screening
Discrete waste solids (such as trimmings, rejects, corn meal,
and pulp) are effectively separated from the wastewater flow
by various types of screens. Screening has many objectives
including recovery of useful solid by-products; a first-stage
primary treatment operation; or pretreatment for discharge to a
municipal wastewater treatment system.
Screens should be located as close as possible to the
process/production producing the waste. The longer the solids
are in contact with water and the rougher the flow is handled
(more turbulent), the more material will pass through the
screens and the more the solids will become dissolved.
21.533 Grit, Soil, Grease, and Oil Removal
Fruit and vegetable, meat and fish, paper, and petroleum
processing/production introduce large amounts of grit, soil
grease and oil to the waste stream. This material will acceler-
ate equipment wear, settle in pipelines, accumulate in the
treatment system, and create odors if not removed.
An aerated tank or lagoon can be provided to remove these
wastes from the waste stream. This aeration system is usually
designed to pre-aerate the wastewater while it aids the release
of free and emulsified grease for surface collection. Addi-
tionally, separation and settling of grit, soil, and oil sludge are
accomplished.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 114.
21.53A How often should samples from industrial wastewa-
ters be collected?
21.53B How can large variations in flow be reduced?
21.53C What kinds of waste solids can be effectively re-
moved by various types of screens?
21.53D Why should screens be located as close as possible
to the process/production producing the waste?
21.534 Central Pre-Treatment Facilities
Microorganisms that treat wastes in the activated sludge
process will not work unless they are provided a suitable envi-
ronment and are properly acclimated (adjusted to the wastes).
A suitable environment may be provided by treating undesir-
able or toxic constituents in industrial wastes at the source
where they are produced or at a central pretreatment facility
(Figure 21.14).
Frequently the most economical method of treating toxic or
undesirable wastes is at the source. If possible, do not allow
these wastes to enter the plant wastewater or if they do, treat
the waste in as concentrated form as possible, before it be-
comes diluted with other wastewaters. Source pre-treatment is
appropriate for extreme pH levels, inert suspended solids, oil,
grease or toxic materials (such as heavy metals).
Figure 21.14 shows a typical industrial pretreatment facility.
The processes and the order of treatment will depend on both
the type of industry and waste constituents. The first process is
pH adjustment. Many manufacturing processes produce either
high or low pH waste streams on either a continuous or batch
basis. If source pretreatment does not reduce these pH varia-
tions to within acceptable ranges, central pH control facilities
must adjust the wastewater pH to near neutral levels. Neu-
tralization chemicals may be added and mixed in pipelines or
in neutralization tanks. Figure 21.14 shows the pH adjustment
process before the equalization tank. Some plants adjust the
pH after the equalization tank. Location of the neutralization
process depends on the type of industry and type of wastes
being treated. See Chapter 28, "Industrial Waste Treatment,"
Section 28.3, "Neutralization," for more details.
Industry frequently uses special screens and microscreens
to remove floatable and settleable solids instead of using pri-
mary clarifiers. These coarse or large solids are usually re-
moved before the flow equalization tank. Removing these sol-
ids now will reduce unnecessary clogging and wear on
downstream pipes, pumps, aerators and clarifier mechanisms.
Also this process will help avoid odor problems that could
develop from the settling out of solids in the equalization and
emergency basins. For more information see Section 28.2,
-------
r
CENTRAL PRETREATMENT
~i
PRETREATMENT
NUTRIENT
ADDITION
-A
BASE ACID
CENTRAL
WASTEWATER
COLLECTION
SYSTEM
MANUAL OR
AUTOMATIC
DIVERSION
PH
ADJUSTMENT
COARSE
SOLIDS
REMOVAL
h3po4
EQUALIZA-
TION TANK
COOLING
TOWER
EMERGENCY
TANK
TO
SECONDARY
TREATMENT
J
Fig. 21.14 Control of the influent hydraulic and organic
loading to the secondary biological treatment process
-------
76 Treatment Plants
"Screening and Microscreens," in Chapter 28, "Industrial
Waste Treatment."
Biological treatment processes work best if they receive fair-
ly constant hydraulic and organic loadings. Equalization and
emergency tanks are used by industry to store peak loads for
release and treatment during periods of low loadings. Fluctu-
ating flows (hydraulic loads) are usually smoothed out by allow-
ing all wastewater to flow into the equalization tank and by
pumping the wastewater to be treated out of the equalization
tank at a constant flow rate. Variations in organic loadings are
smoothed out by mixing the wastewater flowing into the
equalization tank with the water already in the tank. By the use
of effective mixing (such as with propellers, stirrers or aera-
tion), the organic content of the wastewater in the equalization
tank can be kept fairly constant, thus providing a constant
organic load to the activated sludge process.
Emergency basins or storage tanks are usually kept empty
or almost empty so that there is plenty of room to store any
process spills or wastewater diverted when treatment pro-
cesses are upset. Wastewater may be diverted automatically
on the basis of signals from continuous monitoring equipment
(total organic carbon, pH, or conductivity analyzers). Also di-
version can be done manually based on results from continu-
ous analyzers, grab samplers, or from a verbal warning of
upset conditions from process operating personnel.
Generally, continuous monitoring and automatic diversion is
the ideal approach for detection and isolation of process up-
sets. Unfortunately, continuous monitoring produces some se-
vere operational problems in the form of sampling system and
analyzer difficulties. Solids can plug the sampling lines and the
analyzers may require considerable maintenance. To avoid
these problems, some plants rely on the analysis of grab sam-
ples and notification by process operators when spills occur.
Whether you use continuous monitoring or grab samples to
detect spills and undesirable influent conditions, you must pro-
tect your biological treatment processes from unsuitable condi-
tions.
Frequently industrial wastewaters lack the proper amounts
of nutrients for proper microorganism growth and reproduction
in the activated sludge process. The major nutrients of concern
are nitrogen and phosphorus. Other nutrients such as calcium,
magnesium, sodium, potassium, iron, chloride, and sulfur are
needed by the microorganisms, but sufficient quantities are
usually found in most process waters.
Nitrogen and phosphorus are needed for biological growth
and reproduction in quantities approximated by a BODs : N : P
ratio of 100:5:1 or a COD : N : P ratio of 150:5:1. If the nitrogen
or phosphorus levels in the wastewater being treated are less
than the values indicated by these ratios, more nitrogen can be
added in the form of ammonia (usually as 30 percent aqueous)
and phosphorus as phosphoric acid (usually as 75 percent
aqueous). When these nutrients must be added, they are me-
tered into the wastewater from the equalization tank or recycle
sludge streams before the aeration tank. The additions are
based on the difference between the desired amount and the
actual amount in the wastewater being treated.
When the wastewater being treated has been heated by a
production process, the water may have to be cooled before
biological treatment, especially during the warmer summer
months. Biological activity and treatment effectiveness usually
drops rapidly at water temperatures above 99°F (37°C). Cool-
ing towers are sometimes installed where heated discharges
can cause problems. Usually a portion of the influent flow, or in
extreme cases, the entire influent flow, is directed over the
cooling towers during the warmest summer months. Proper
operation of these towers allows sufficient evaporative cooling
for control of the aeration basin temperature.
Sometimes sufficient water cooling will occur from aeration
in the equalization and aeration basins. Mechanical aerators
can be especially effective. Diffused air aeration systems,
however, can increase the temperature by 5 to 7°F (3 to 4°C)
because of the hot air from the blowers. If excessive cooling is
caused by surface aerators in the cold winter months, shut
down the aerators (if possible) or add heat by using heat ex-
changers or steam.
Troubleshooting problems in central pretreatment facilities
are similar to other treatment processes. If a spill occurs with a
high initial oxygen demand, mechanical aerators may not be
able to supply enough oxygen to maintain a minimum dis-
solved oxygen (0.5 mg/L) in the equalizing basin. When this
happens, the basin may become septic and give off undesir-
able odors. If the aerators cannot deliver more oxygen, addi-
tional oxygen may be provided in the form of hydrogen
peroxide.
Another possible problem with mechanical floating aerators
is excessive cooling of the wastewater during cold winter
months. If the water temperature becomes too low, the activity
of the activated sludge organisms and the performance of the
secondary clarifier may be reduced greatly. A partial solution to
this problem is to shut off some of the aerators completely or to
shut off all of the aerators periodically. You must keep the
contents of the equalizing basin well mixed to avoid surges of
waste organic loads or solids settling on the bottom of the
basin. If a proper schedule is developed for turning the
aerators on and off, you can provide sufficient mixing and keep
the heat lost from the surface of the basin low.
If the aerators fail, carefully monitor the flows from the
equalizing basin to the aeration tank using continuous ana-
lyzers or frequent grab samples. If the variation in organic
loading, hydraulic loading or temperatures becomes much
greater than normal, divert all or some of the flow to the
emergency basin. When the aerators are returned to opera-
tion, the flow to the aeration basin should be increased gradu-
ally to avoid shocking the biological system.
When the nutrient flow stops, try to get the flow back on line
as soon as possible. If the nutrient flow can be restarted in 24
hours or less, feed nutrients at twice the normal rate for the
same period of time that the nutrient flow was off. If the nutrient
flow will be off for more than 24 hours, try adding nutrients from
bags such as agricultural or garden fertilizers.
21.535 Start-Up or Restart of an Industrial Activated
Sludge Process
Once the wastewater has been properly pretreated and
ready for the activated sludge process, the activated sludge
biological culture must be ready to treat the wastes. Whether
you are starting a new activated sludge process or trying to get
an existing process back on line after the culture has been
wiped out by a toxic waste, the procedures to develop a new
activated sludge culture are similar.
New activated sludge cultures are started by obtaining
"seed activated sludge" or activated sludge microorganisms
from either a nearby municipal or industrial wastewater treat-
ment plant. The amount of seed activated sludge needed de-
pends on the hydraulic and organic loadings on your treatment
plant. The greater the load, the more tank trucks of activated
sludge seed will be needed.
Once the activated sludge seed has been added to the aera-
tion basin, the level of the water in the aeration basin is usually
maintained just below the overflow level. The aeration system
-------
Activated Sludge 77
is in operation. You want to increase the population of acti-
vated sludge microorganisms. This is accomplished by feeding
the "bugs" a solution they can eat quickly and use efficiently
for building more microorganism cells. The most common
chemical feed is sodium acetate. These microorganisms also
require nutrients for fast and healthy growth. The key elements
are nitrogen and phosphorus. They also must be provided in
the form of chemicals added to the wastewater. Usually am-
monium sulfate and potassium dibasic phosphate (available in
a dry form in bag quantities) are used because they are rela-
tively pure and can provide an adequate buffer for pH control in
the aeration basin. These chemicals are easily dissolved in
small amounts of water.
Start-up procedures will vary with each industrial waste
treatment plant. Usually the chemicals are added to achieve a
ratio of COD : N : P of 150:5:1 or BOD : N : P of 100:5:1.
Chemicals are added on a batch basis directly to the aeration
basin (or indirectly through pump wells) until the mi-
croorganisms multiply to approach a MLSS level of 2,000
mg/L. Usually enough sodium acetate (food) is added in a
batch to allow the bugs to feed for one to three days. Between
batch feedings, periodic analyses of the aeration basin con-
tents will indicate the rate at which the bugs are consuming the
organic materials (oxygen uptake rate readings and filtered
COD or TOC analyses) and the rate of growth of the bugs
(MLSS analyses). These measurements will indicate the tim-
ing for future batch feedings. Experience indicates that you
usually have to feed chemicals for about one week to produce
a flocculating sludge.
Once a MLSS level of over 2,000 mg/L has been reached,
the industrial wastewater may be introduced into the aeration
basin. THIS STEP MUST BE VERY GRADUAL Pump approx-
imately 10 percent of the total industrial waste flow from the
equalizing basin. Chemical feeding should be continuous if at
all possible. This procedure allows the activated sludge mi-
croorganisms to slowly adapt or become acclimated to the
industrial wastes so the wastes will not shock the delicate
growth patterns of the activated sludge microorganisms.
Periodically take samples from the aeration basin in order to
monitor the degree of biological growth and removal of organic
wastes (oxygen uptake rate, MLSS, and filtered COD). After
two or three days, if the monitoring results are favorable (i.e.,
high COD removal, MLSS increasing, oxygen uptake rates
steady), the industrial waste flow input can be increased (20 to
25 percent of the total flow) and the chemical feed (food) can
be reduced by a similar amount. Also, at this time, the perma-
nent nutrient feed system (if any) should be started to assure
an adequate supply of nitrogen and phosphorus.
This procedure is followed until all of the industrial wastewa-
ter flow (with no chemical feed) is being fed to the activated
sludge process. The time for the acclimation process to be
complete will vary with the industrial wastes being treated, but
usually two to three weeks are required. Once the activated
sludge process starts to generate excess activated sludge
above the desired MLSS level, sludge wasting should be
started to control the MLSS.
Portions of this section were taken from BACKGROUND
DOCUMENT, DU PONT ACTIVATED SLUDGE TREATMENT.
Permission to use the material in these two sections is sin-
cerely appreciated.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 114.
21.53E In general, where is the most economical location to
treat toxic wastes?
21.53F Why do some industries require a waste pretreat-
ment facility?
21.53G Why does industry use screens to remove coarse
solids?
21.53H How can variations or fluctuations in influent organic
loadings be smoothed out before the aeration basin?
21.531 What chemicals are used to provide nutrients in the
form of nitrogen and phosphorus?
21.53J Where would you obtain a "seed activated sludge" to
get an existing activated sludge process back on line
after being wiped out by a toxic waste?
21.53K Why must industrial wastes be added gradually to
the aeration basin initially?
21.54 Operational Considerations (Activated Sludge)
The following discussion will center on specific operational
problems experienced at various industrial wastewater treat-
ment plants. Corrective action methods are also presented.
21.540 Neutralization
pH control systems may be installed to treat various
process/production wastewaters. pH adjustment of this nature
is usually done as a pretreatment process. However, lime,
alum, and iron salts may be used in a pre-secondary chemical
clarification process. In this case it is necessary to provide
additional pH adjustment facilities to neutralize the normally
high pH effluent (8.5 to 11.0) from the chemical clarification
process. Abnormally high wastewater pH will result in loss of
activated sludge system efficiency and cause settling prob-
lems in the secondary clarifier. A consistently alkaline waste
(high pH) can be neutralized by using carbon dioxide (CO2).
Boiler stack gas and a compressor delivery system could be a
source of carbon dioxide.
If a high pH wastewater is a problem because you use lime,
alum or iron salts as a settling aid, consider the use of poly-
mers instead.
If the pH is too low (acid), the pH can be increased by the
addition of lime (Ca(OH)2) or caustic soda (Na OH). The acti-
vated sludge process usually operates satisfactorily in a pH
range from 6.5 to 8.0.
21.541 Nutrients
Nutrients, especially nitrogen and phosphorus, can be criti-
cal in the performance of the activated sludge system. The
exact point at which nutrients become critical depends on your
type of treatment process and how you operate it.
Remember that all applied nutrients must be in a soluble
form to be used by the microorganisms. The addition of nutri-
ents should be accomplished at a point where the incoming
wastewater is highly mixed, preferably in the aeration basin.
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78 Treatment Plants
The quantity of nutrients added to the treatment system
should be based on the desired BOD reduction and the
amount of the nutrient deficiencies. The amount of nitrogen
and phosphorus required to treat a waste can be estimated
from the quantity of sludge produced per day. The pounds of
nitrogen required per day is equal to 10 percent of the volatile
solids (on a dry weight basis) produced each day. Phosphorus
requirements are one-fifth the nitrogen requirements. The
amount of nutrients which have to be added each day is de-
termined by the difference between the quantity required and
the quantity available in the wastes.
Typical supplemental nitrogen is provided by using aqueous
ammonia or anhydrous ammonia. Supplemental phosphorus
is provided by using dissolved triple superphosphate, phos-
phate fertilizer, or phosphoric acid (a waste acid from alumi-
num bright dipping facilities).
When the supply of nitrogen and phosphorus from the
wastewater is below that required by the microorganisms in
your biological treatment process for extended periods of time,
filamentous organisms may begin to predominate and cause
sludge bulking in the secondary clarifier.
21.542 Dally System Observations
Daily observations of the bacterial population must be made
to observe developing system changes and stress conditions
so that proper action may be taken before overall treatment
efficiency is affected. Under normal conditions, the bacterial
population is composed primarily of small bacteria with large
numbers of stalked ciliates and many free swimming ciliates
and rotifers (Section 21.32). The presence of these higher
forms gives you the indication that the process is operating
properly. The following conditions have been found to cause
the disappearance of the higher forms.
1. DO levels below 3.0 to 4.0 mg/L: With a high mixed liquor
solids, it is possible that the oxygen transfer efficiency is
impaired at lower DO concentrations. Additionally, fila-
mentous growth may predominate.
2. High organic loadings: When the process is in the dis-
persed growth phase, it has been observed that the higher
forms do not compete as well as the simpler bacterial
forms.
3. Toxic substances or nutrient deficiencies: These conditions
will affect the growth and maintenance of the higher forms.
4. pH control: If the pH control system is not operating prop-
erly to adjust the pH to near neutral, ciliates and rotifers will
not adapt to pH fluctuations and will disappear.
21.543 Return Activated Sludge (RAS)
In most cases the RAS values for industrial waste treatment
systems are the same as for municipal systems as discussed
in Section 21.2. However, some systems experience a sludge
with low compacting characteristics (high SVI). This is usually,
yet not always, the result of conditions shown in Section 21.23,
Table 21.3, on page 58.
21.544 Waste Activated Sludge (WAS)
An activated sludge plant, operating at a high rate (or low
sludge age) will produce 0.5 to 1.0 pounds of microorganisms
for each pound of BOD removed. In addition to the production
of up to 0.5 pounds of microorganisms per pound of BOD
removed, added sludge results from the non-biodegradable
suspended solids, both volatile and nonvolatile, in the influent
to secondary treatment. Consequently, it is common for the
total secondary sludge production to be 0.8 to 1.0 pounds per
pound of BOD removed. Sludge from secondary treatment
systems is still biologically active and will putrefy. This can
cause an intolerable odor. If the sludge contains no domestic
wastes, it may be possible to spread and dry the sludge quickly
on a disposal site or agricultural land, and then plow it into the
soil.
Secondary sludge is difficult to dewater as compared with
primary sludge. Raw, undigested secondary sludge has a total
solids content of only one-half to one percent in air systems
and one to three percent in pure oxygen systems. In addition,
the cellular matter in the sludge is only fifteen percent solids!
Unless the cell membranes are ruptured, microorganisms
cannot be dewatered to greater than ten percent solids. Cells
can be ruptured by heating or slow freezing although natural
freezing can be used in some climates.
An alternate method of handling WAS from a treatment sys-
tem that operates seasonally is to divert WAS to a lagoon. At
the end of the season, the solids from the lagoon are periodi-
cally returned to the aeration system for "complete" oxidation
during the off-season period.
21.545 Clarification
In industrial waste treatment systems, sludge settling often
is significantly affected by influent characteristics variations. As
a result of these variations, the settling characteristics of the
sludge are extremely critical. Therefore, clarification rates of
less than 400 gpd/sq ft (16 cu m per day/sq m) may be neces-
sary to obtain proper operation.
If you observe a gradual decrease in percent solids removal
over a period of time, this reduction may be the result of grit
and silt accumulation in the aeration basin. The grit and silt are
not carried out in the effluent, remain in the basin, and reduce
aeration volume and detention time. A higher volatile content
of the sludge would be indicative of this condition. A lower
volatile content would occur only if the aeration basin's con-
tents are well mixed. In this case there should be no settling
nor accumulation of grit and silt.
If this condition exists, make every attempt to increase the
efficiency of your grit removal process. If you do not have grit
removal facilities, make every effort to increase the mixing in
the aeration system to prevent the settling of solids in "blind" or
"dead" areas (typically corners). If none of the above control
methods are available to you, consider cleaning your aeration
basins on a yearly basis if necessary. If you operate a munici-
pal treatment facility and find grit and silt are coming from an
industrial source, make the industry remove the grit and silt by
pretreatment methods. Industry should not be allowed to dump
this material into a sewer.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 114.
21.54A Where should nutrients be added to a wastewater?
21.54B List some typical sources of supplemental nitrogen
and phosphorus.
21.54C What factors or conditions have been found to cause
the disappearance of higher forms of mi-
croorganisms from the activated sludge process?
21.54D What items could cause a GRADUAL DECREASE in
percent solids removal from an activated sludge pro-
cess over a period of time?
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Activated Sludge 79
NOTICE
The following Sections, 21.55 through 21.58, were prepared
by the operators of actual industrial wastewater treatment
plants. These operators have described procedures they use
to treat industrial wastes by the activated sludge process. Vou
must remember that there are many types of industries and
that the waste flows and constituents will be different at every
treatment plant. The intent of the following sections is to pro-
vide you with ideas that might work for your industrial waste
treatment activated sludge plant.
21.55 Pulp and Paper Mill Wastes by James J. McKeown
Industrial wastewater treatment plants are designed in much
the same manner as municipal plants; however, there are
some important differences in treating pulp and paper mill
wastes. Before any waste stream can be treated, both the
average and range of fluctuations of flows and waste con-
stituents must be measured, recorded and analyzed.
21.550 Need for Record Keeping
The format for record keeping will usually be prepared by the
environmental control supervisor. There are three basic rea-
sons for keeping accurate records.
The first reason is to keep a history which helps troubleshoot
problems which arise. Each entry onto the log sheet is made at
the frequency needed to help locate trouble. Even so, the
operator needs to be alert for trends which occur in between
the log entries. Most log sheets call for pertinent remarks and
the operator should make use of this column to note unusual
conditions or to simply enter "all's well." Your record will be
read by the person relieving you in order to pick up the opera-
tion. You know the things most helpful to you when starting a
shift and it's simply a matter of doing likewise for your relief.
The second reason has to do with accounting for the opera-
tion of the plant during appropriate times, such as, weekly or
monthly. If the operator should fail to make an entry and must
estimate a value, the value should be footnoted accordingly.
Failure to enter even routine data may prevent a calculation
from being made. Serious mechanical problems or chronic
symptoms of future problems should also be noted so the work
orders can be issued to correct the problem.
The last reason is that records are legal documents which
will protect the company from unjust claims. In other words, the
company may have to prove that its operations were normal
during a certain time period. The only way this can be accom-
plished is by use of the actual operating data. Therefore, it is
very important to keep accurate records. Don't forget that all
recorder charts are also a part of the official record. You may
be asked to make notations on these charts as part of the
accounting procedure and it's usually a good idea to initial the
note. Another good idea is to make a note on your log sheet
each time you mark the recorder chart.
21.551 Wastes Discharged to the Plant Collection System
In most industrial systems, departments or small networks of
sewers are monitored individually. The control of wastewater in
these networks is often the responsibility of production per-
sonnel. Experienced production personnel know that certain
conditions in their area will result in abnormal discharges to the
sewer. With proper communications between operating and
waste treatment plant personnel, an alarm can be sounded
either before or right after a spill actually happens. A quick
phone call will allow emergency measures to be implemented
in time to prevent operating problems. Everyone must encour-
age the necessary communications to give waste treatment
personnel all the advance notice they need to properly operate
the plant.
Several key sewers may be monitored continuously. In such
a system the wastewater treatment plant operator can usually
read the recorders to see if all the sewers contain normal quan-
tities of wastewater. The use of centralized instrument panels
both in the mill production area as well as the treatment plant
will allow confirmation of a particular condition.
Operators should understand the reason why each water
quality indicator is being monitored and if necessary, how the
sensor works. In highly automated systems, the operator may
use instrumentation personnel in order to maintain the proper
calibration and operation of each sensor. However, even in this
case, a basic understanding of the instrument or electrode is
useful.
The most common control sensors which are used in pulp
and paper mills are conductivity, flow, pH and turbidity. Special
situations may be monitored to determine temperature, color,
sodium, COD, TOC, or TOD. Oxygen respiration may also be
monitored to detect overloads or spills. Continuous bioassays
may be required at certain installations and DO is used to
control aeration in activated sludge plants. Treatment plant
personnel should be aware ol the meaning of changes in the
values of each water quality indicator at each sampling point.
The operator should be familiar with certain mill waste flow
and constituent recorder patterns (variations) which are likely
to occur in each sewer, so that appropriate control actions can
be initiated. For example, a modest increase in conductivity
accompanied by a low pH indicates that acid is probably being
discharged into the mill sewer. However, if both conductivity
and pH are quite high, then an organic discharge containing
black liquor is the likely event. Further, if flow measurement is
available, the operator should be able to determine the poten-
tial severity of the discharge. The operator should know what
combinations of readings to look for and what actions are nec-
essary in each case to control the situation. Many mills use
continuous recorders with signal alarms to alert the operators
that a particular sewer is exceeding its normal limit. However,
whether communication is automatic or by person to person
contact, most situations have a history of occurrence and can
be properly handled using predetermined control measures.
If a spill is detected by the sensor system, the operator
should be able to verify the spill. A phone call to the mill oper-
ating area may be sufficient to learn how long the event is likely
to continue. With this information, a decision can then be made
on the procedures to use to control the spill. Industrial control
systems often use emergency storage tanks or spill ponds
which can be filled quickly to protect the treatment plant.
Knowledge about the nature and duration of an emergency
upset is a necessity for proper management of reserve storage
capacity. These diverted wastes can later be bled into the
treament plant at controlled rates.
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80 Treatment Plants
21.552 Variables Associated with the Treatment of Paper
Mill Wastes
NUTRIENT CONTROL
The wastewater usually does not have enough nitrogen and
phosphorus to support bacteriological growth. Thus, facilities
are often installed to add these nutrients to the wastewater
before biological treatment. The proper amounts of these nut-
rients must be added because too little or too much may create
problems. The operators should be familiar with their nutrient
feeding systems and in cold climates, the temperatures at
which certain nutrient chemicals will freeze. Many wastewaters
only require nitrogen addition because there is enough phos-
phorus in the wastewater as a result of boiler water corrosion
control and cleaning operations.
Experience with BOD removal at the lowest possible nutrient
addition rates will allow the operator to properly control the
addition rate. Soluble ammonia nitrogen and phosphorus gen-
erally need not exceed 0.5 and 0.25 mgIL, respectively, in the
final effluent. Many systems are providing adequate treatment
at effluent concentrations of 20 to 50 percent of these values. If
final effluent nutrient values are considerably lower than these
values, then additional nutrients may be necessary.
FOAM CONTROL
Another additive in pulp mill wastewater systems is a de-
foamer. Some pulp mill effluents foam because the wood
soaps are not fully captured in either the tall oil or recovery
systems. The chemicals which cause foams are oxidized dur-
ing biological treatment. However, if foaming isn't controlled in
the biological plant while treatment is taking place, a variety of
problems may result, including frothing of mixed liquor solids
thereby removing these solids (organisms) from the system.
Foam can also engulf and shortout motors and other electrical
equipment. Also, foam will cause certain level recorders to
misinterpret the true liquid level and this can be troublesome if
flow measurement is affected. Foam may also cause an air
pollution problem, especially if it dries and becomes
windborne.
Foam is generally controlled by water sprays or dosing with
an antifoam chemical. The object of either approach is to
cause an uneven distribution of surface tension in the foam.
The spray also provides a physical impact which busts the
foam and creates channels for subsequent drainage through
the foam.
Defoaming chemicals are very expensive and their applica-
tions should be carefully controlled. The delivery system can
be by overhead spray or by using the aerator to distribute the
chemical into its own spray. Either system has been used with
success in the paper industry. Most paper mills use metering
pumps to feed defoamer. The chemical is added continuously
at a predetermined rate. If foam volume increases, the chemi-
cal dose is increased for a short period of time and then re-
duced to the baseline again. Excessive use of defoamers may
also place an added oxygen demand on the system which is
undesirable. Automatic systems respond to conductivity or
photoelectric sensors. When the foam reaches the sensor, the
defoamer chemical is applied in steps until the foam recedes
below the sensor. Chemical suppliers will gladly recommend
procedures which reflect their experience.
pH CONTROL
The plant may be equipped with a neutralization system
where acid or caustic is added prior to the mixed liquor tank.
Most facilities add these chemicals prior to the primary
clarifiers. However, some plants bypass the clarifiers with large
volumes of bleach plant wastes and, in this case, pH adjust-
ment is accomplished in a blend tank where bypassed wastes
join primary effluent.
Hydrated lime, Ca(OH)2, and caustic, NaOH are two of the
common alkaline solutions used to increase pH while sulfuric
acid, H2SO4, is the common acid solution. Control of pH varia-
tions is probably more important than the actual pH value.
However, most mills have a high and low pH target value which
must not be exceeded and pH should be adjusted to fall within
this range.
Most pH control systems are automatic and are based upon
pH and flow sensors placed downstream from the blending
point. Acid and caustic make up requires that the operators
follow prescribed safety rules because of the danger involved
in handling these concentrated chemicals.
PRODUCT RELATED SITUATIONS
Treatment of pulp and paper mill wastewaters is similar in
many ways to the treatment of municipal wastes. The ma-
chinery is identical in many cases. However, the operator who
worked in a municipal plant will quickly become aware of some
additional differences which depend on the type of pulp and
paper being produced. These differences are reviewed here.
The paper industry has several types of pulp mills and man-
ufactures a large number of grades of paper. To a large extent
the waste treatment systems operations will reflect the particu-
lar mix of pulp and paper being made each shift. Thus, a
knowledge of which grades are being produced can be an
important factor in the operation of the plant. We cannot cover
all of these product related differences in this section. How-
ever, the topics of flow, settleable solids, color, and odor can
be discussed in general terms.
1. FIBER — The paper industry manufactures products made
primarily of cellulose. The cellulose must be treated in the
mill in a variety of ways which include cleaning, blending,
refining, screening, bleaching, trimming, and drying. In
many of these operations, the cellulose is pumped from one
unit process to another. In order to efficiently process the
cellulose into paper, the fibers must be separated (diluted)
for some unit processes and matted (molded) for others.
The result is that the cellulose is contacted with large quan-
tities of water at various points in the process.
This water is later removed from the cellulose and much
of it is reused. The recycle system in a paper mill actually
retains 3 to 10 times the amount of water sewered. The
paper industry is continually looking for new ways to reuse
much of this water. In many cases, the mill uses internal
treatment to renovate these waters before reuse in showers
or for stock dilution.
Also, the effluents are generally treated within the mill
before being discharged to the sewer. Most of the usable
fiber is scalped from the water by a variety of savealls. The
savealls may be screens, filters of various sorts, dissolved
air flotation units, or mechanical clarifiers. See Chapter 28,
"Industrial Waste Treatment," for details on these pro-
cesses.
When the recycle system is working properly, the treat-
ment plant receives moderate quantities of water containing
the fine cellulose particles and dirt which have been delib-
erately separated from the paper. However, when the recy-
cle system is out of balance, large quantities of water and
cellulose may be sent to the sewer.
Most of these cellulose fibers settle readily and will clog
screens and impair the passage of effluent if adequate mix-
ing or dilution isn't maintained in the sewers. Further, when
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Activated Sludge 81
the fibers reach the primary clarifier, they settle readily and
increase the load on the rakes. Most clarifiers are designed
to handle this load without overloading, but the sludge re-
moval rate is usually increased to keep the torque in con-
trol.
2. FLOW — Large quantities of extra water may also accom-
pany these abnormal fiber discharges. Again, the size of
the plant should be adequate to handle these surges. How-
ever, the operation may require adjustment of chemical
feed and use of standby pumps after hydraulic surges have
reached the plant.
Further, most paper mills operate around the clock. Thus,
flows are fairly constant and don't decrease during the night
as happens with the flow to municipal plants.
3. SETTLEABILITY — If the paper plant contains a pulp mill,
some further differences may be evident. The pulping of
wood separates a number of chemicals from the fiber.
These chemicals are believed to cause higher SVI levels in
biological sludges produced during treatment. In the case of
treating 100 percent pulp mill effluent, secondary clarifiers
are designed with overflow rates lower than systems pro-
cessing only domestic wastes in order to accomodate this
slower settling floe. Also, the final effluent may contain
slightly higher suspended solids concentrations where 100
percent pulp mill wastes are being treated.
4. COLOR AND TURBIDITY — The chemicals extracted from
wood are colored very much like swamp water which con-
tains vegetative extracts. Thus, the wastewater will gener-
ally appear yellowbrown. A wastewater can be clear in
terms of suspended solids, although it is still colored by
dissolved solids. Wastewater with a dissolved color will
change in color with changes in pH as well as mill opera-
tions.
Certain papermills use dyes or pigments to color the fi-
bers. Tissue paper, construction paper, and a variety of
specialty products are examples of grades which are col-
ored. The wastewater associated with these grades will
also be colored. Mills with one paper machine produce
effluents which change in color every time that the pa-
permaker changes the dye. However, the color change isn't
as noticeable in effluents from mills with many paper ma-
chines because the colors blend toward neutral and often
appear gray. Most dyes are oxidized and thus disappear
during biological treatment.
Mills making filled grades or using starch will produce
waters which appear white. Starch will usually degrade in
biological treatment and the cloudiness and turbidity will
disappear during treatment. Some mills use titanium
dioxide and talc to fill the paper sheet. These very fine white
particles have high refractive powers and may not be com-
pletely removed during treatment. Thus, the final effluent
will contain white solids. Also, the return activated sludge
may appear white because it contains large quantities of
these inorganic pigments.
5. ODOR — The odor of the water discharged from a pulp mill
will reflect the chemicals used and produced in the pulping
process. In most cases, these odors are associated with
gases which were captured in the process water back in the
mill. When these waters arrive at the treatment plant and
are aerated, the gases are stripped from the wastewater.
The extent to which these gases are present in the waste-
water depends on the pulping process and the extent to
which the waters are stripped of gas prior to discharge to
the sewer.
EMERGENCY SYSTEMS
The plant probably has some emergency features which are
seldom used. Industrial systems must be able to be started up
and shut down in accordance with production variations. In
many cases, these are planned far enough in advance to turn
down or shut down the plant in an efficient manner. However,
occasionally, because of an equipment failure at the plant,
personnel have to respond quickly by employing seldom used
facilities. The operators should run through periodic drills
which simulate their reactions to these emergencies so there
will be no delay when a real emergency occurs. Examples of
seldom used facilities are standby pumps, diversion valves,
spill tanks and lagoons as well as feed tanks used to supply
organic load to build up an activated sludge culture prior to
plant start-up. Further, spill tanks should normally be operated
empty so their capacity is available during an emergency. After
the tanks are used to scalp a spill, they should be emptied
(usually gradually) at a rate which will allow the plant to treat
the wastewater adequately. However, the goal should be to
empty them as quickly as possible because the plant is sus-
ceptible to upset if another spill should occur which is larger
than the reserve spill capacity. The spill tank is often used to
store the waste for use during the shutdown period.
21.553 Start-Up and Shutdown Procedures
The paper industry has occasion to shut down and start-up
an activated sludge plant for several reasons. Holidays, main-
tenance (preventative and emergency), process upsets,
strikes, and scheduled production reductions may require that
the activated sludge plant be turned down or shut down. The
procedures for shutdown and subsequent start-up vary with
the nature and duration of the shutdown, as well as the
weather expected during the shutdown.
For short shutdowns a set of action plans must be developed
to alleviate potential problems in line with some interim goals.
The goals must be selected prior to each planned shutdown.
21.554 Management of Shutdowns and Start-Ups
by W. A. Ebertiardt
WHY MANAGE SHUTDOWNS AND START-UP?
The performance of an activated sludge plant improves with
increasing stability in influent loadings (waste composition and
volume) and environmental conditions (pH, temperature, DO).
Typically, as the steady-state condition is lost, discharges of
suspended solids and BOD increase. Also of significance,
once lost, the favorable performance associated with steady-
state operation is not quickly regained.
Shutdown/start-up conditions have a high potential for pro-
ducing a loss of biological equilibrium or steady-state. In addi-
tion, shutdowns/start-ups increase the risks of personal injury
and produce abnormally high operating costs due to the new or
unusual conditions typically experienced.
As an operator, it is your responsibility to the environment,
your employer, and yourself to prevent or minimize the poten-
tial adverse impacts of a shutdown/start-up. To adequately
meet your responsibilities, you must carefully manage the situ-
ation.
WHAT IS A SHUTDOWNISTART-UP?
Shutdown/start-up is a situation whereby the normal waste-
water feed is interrupted, or, one or more of the activated
sludge support systems (such as aeration) malfunctions. The
result is that the biological process is prone to lose equilibrium.
Typical circumstances surrounding a shutdown/start-up are:
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82
Treatment Plants
A. Interruption of Normal Feed
1. Manufacturing interruptions (weekends, holidays, an-
nual shutdown, equipment failures)
2. Manufacturing abnormalities (spills, process changes
or tests, product changes)
3. Feed support loss (failure of a feed pump)
B. Interruption of Biological Support Systems
1. Mechanical failures or planned outages (recirculation
pumps, aerator, chemical feed pump)
2. Runout of a chemical (nutrient, neutralization, polymer)
HOW CAN I MANAGE SHUTDOWNSISTART-UPS?
To successfully manage shutdowns/start-ups, you must
have OBJECTIVES and GOALS, and a PLAN FOR IM-
PLEMENTATION.
1. OBJECTIVES AND GOALS — Several basic objectives to
be accomplished during shutdowns/start-ups are:
1. Maintain satisfactory/legal process performance,
2. No personal injuries, and
3. Maintain least cost for satisfactory performance.
For each objective, specific goals must be established.
Table 21.7 provides some suggested goals. For example,
one goal toward achieving the process performance objec-
tive is to maintain a constant F/M ratio. This would prevent
one or more of the potential problems cited for failure to
control or change the ratio.
YOU must customize the suggested objectives and goals to
your operation.
2. PLANNING — The shutdown/start-up plan is a strategy to
accomplish your selected goals. The plan is necessary for
both scheduled and sudden occurrences. The plan may be
formally typed in a manual or written in a log book. This plan
should include the specific activities and associated timing
and responsibilities necessary to overcome all identified
barriers to accomplishing each goal. For example, the
shutdown might involve discontinuance of wastewater from
manufacturing — a barrier to maintaining a constant F/M
ratio. Your plan might call for storage of wastewater in a
basin in advance of the shutdown with provision to pump it
to the process during the outage (holding wastewater in a
basin at all times might be a continuing plan to cover un-
scheduled losses of process wastewater). Finally, your
plan, as applicable, must be coordinated with other waste-
water treatment AND manufacturing activities.
3. IMPLEMENTATION — Successful implementation of your
plan requires:
a. COMMUNICATIONS with involved and affected per-
sonnel and organizations before and during implemen-
tation,
b. DISCIPLINED EXECUTION of the planned action
steps,
c. EVALUATION OF RESULTS during execution with ap-
propriate plan adjustments, and
d. CRITIQUE of results and performance after the incident
with emphasis on learning for future improvement.
4. SUMMARY — The benefits of well managed shutdowns/
start-ups include satisfactory and legal performance, fewer
injuries, and reduced costs. To manage an interruption, you
must identify its occurrence (actual or potential) and ag-
gressively act to minimize its consequences. Success will
follow if objectives and goals are established, plans are
developed to achieve them, and plan implementation is
coordinated, disciplined, and flexible.
21.555 The Periodic-Feeding (Step-Feed) Technique for
Process Start-Up of Activated Sludge Systems13
by R.S. Dorr
NEED FOR EFFECTIVE START-UP PROCEDURES
Activated sludge biological treatment systems are being
constructed in many locations across the country by pulp and
paper mills. Process start-up of these high rate biological sys-
tems presents a complex problem. The plants currently in op-
eration across the country prove that given enough time and
attention these systems can be successfully started up. Time,
however, is costly and often limited when dealing with dis-
charge permit deadlines.
DEVELOPMENT OF THE START-UP PROCEDURE
The periodic-feeding technique which has been developed
for the start-up of pulp and paper mill activated sludge systems
is based upon the biological growth kinetics and physical mi-
crobiological concepts which govern the biological treatment
process. Several statements are crucial to the development of
this start-up procedure and are summarized below:
1. The concentration of microorganisms in the system influent
(the mill sewer) is insignificant in comparison to concentra-
tions found in domestic collection systems.
2. There exists a critical minimum mean cell residence time
(MCRT) below which the system cannot function and the
microorganisms cannot establish themselves.
3. The degree of flocculation of the microorganisms is influ-
enced by the food-to-microorganisms ratio (F/M). At very
high values of F/M, microorganisms are completely dis-
persed and will not settle, rendering the secondary clarifiers
nonfunctional.
4. If the secondary clarifiers are for some reason nonfunc-
tional, the mean cell residence time is equal to the hydraulic
retention time of the aeration basins.
5. Increasing the food (soluble BOD) to a bacterial population
beyond certain limits, does not necessarily increase the
rate of population growth.
In view of these facts, a process start-up procedure should
provide a means of controlling the food-to-microorganism ratio
and/or the mean cell residence time to prevent dispersal and
washout of whatever bacteria may be initially present in the
system. Neither the soluble BOO concentration in the system
influent nor the amount of bacteria in the system can normally
be controlled during a process start-up.14 The hydraulic load-
13 This section was taken from "Development and Testing of the Step-Feed Technique for the Process Start-Up of Activated Sludge Systems "
by R.S. Dorr, PROCEEDINGS OF THE 1976 NCASI NORTHEAST REGIONAL MEETING," NCASI Special Report No. 77-03, May 1977.
NOTE: The original paper referred to this procedure as STEP-FEED, but this section uses the term PERIODIC-FEEDING to avoid confusion
with the step-feed activated sludge process.
14 As an exception, bacteria from another similar activated sludge plant may be Introduced by "massive seeding" techniques Involving many
truckloads of thickened sludge.
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Activated Sludge 83
TABLE 21.7 GOALS FOR SHUTDOWNS/START-UPS
Goals
Potential Problems
Action Plans
1. Maintain constant food charac-
teristics
2. Maintain constant food/microor-
ganisms (F/M)
3. Maintain nutrient balance (N, P,
metals)
4. Maintain environment constant
(temperature, pH, DO)
Solids in effluent
SVI increase
Low BOD removal
Lost activated sludge organisms
Solids in effluent
SVI increase
Solids in effluent
Bulking
Low BOD removal which persists
Solids in effluent
Low BOD removal
5. Maintain hydraulic loading con-
trol
6. Necessary equipment functional
7. Complete required maintenance
on schedule
8. No personnel injuries
9. Cost optimization
10. Protect receiving stream
11. Meet permit requirements
Hydraulic surges
Flows during periods requiring a "dry
outage"
Sludge recycle imbalances
Power outage (light, equipment)
Instrument air outage (valve posi-
tioning)
Less than optimum performance
after start-up
Production downtime for subsequent
repair
Lack of safety equipment
Difficult environment (no lighting)
Abnormal (non-routine) tasks
Inadequate staffing
Shutdown extension due to
— Inadequate staffing
Undertaking necessary work
Provision of unnecessary equipment
(generator for aerators)
Spills
Inadequate treatment
Inadequate performance and/or dis-
charge monitoring
Normal waste
— Store prior to shutdown
— Feed during shutdown
Abnormal wastes
— Minimize
— Bypass to storage for equalization
Pre-Shutdown
— Store waste
— Lower MLSS
During Shutdown
— Feed stored waste
— Reduce or stop wasting
Assure in advance
— Adequate supply of nutrients
— Provisions for addition of nutrients
Optimize aeration for
— DO
— Heat retention in winter
— Heat loss in summer
Introduce heat during prolonged winter usage
Assure in advance
— Supply of neutralization chemicals
— Provision for addition of chemicals or store
pre-neutralized waste
Plan together with manufacturing people
Use of surge/storage basins
Closed valve motivation
Gradual increase in loading at start-up
Advance provisions
— Standby generators
— Instrument air override
— Use storage basins
Critical path planning
Maximum prework
Avoid shutdown items
Individual job safety
— Analyses with appropriate follow-up
— Safety training program
Question shutdown needs
Complete planning
Comprehensive planning
Meet all goals in this table
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84 Treatment Plants
ing rate, however, can be regulated. This is the basis of the
start-up procedure described in this section.
Assume a waste stream of 10 MGD and 100 mg/L soluble
BOD were to be treated in an activated sludge plant designed
to have a hydraulic retention time of six hours. Flow is intro-
duced to the system along with normal amounts of nitrogen
and phosphorus required, and aerators and recycle pumps are
started. After the six hours of flow required to fill the basins and
clarifiers, the following conditions exist:
1. The soluble BOD level throughout the system is 100 mg/L.
2. The amount of bacteria present is very small, existing only
in the form of "seed."
3. The value of F/M is very high, and therefore the bacteria are
totally dispersed.
At this point, the flow through the system could be allowed to
continue at 10 MGD; however, this might be disadvantageous
for two reasons. The "seed" microorganisms cannot possibly
consume a very significant portion of the soluble BOD during
the six hours in which it would pass through the system. In-
deed, it may take several days under very similar conditions to
consume the 100 mg/L in a BOD bottle. There is no reason to
believe that the reaction will take place any faster inside the
aeration basin. Therefore, constantly feeding the system a
fresh supply of wastewater containing 100 mg/L soluble BOD
provides no real advantage.
Additionally, since the bacteria are dispersed, 10 MGD of
water containing whatever concentration of microorganisms
that exist in the system would be flushed over the effluent weir
of the secondary clarifier. This loss must be made up for by the
rate of growth of the bacterial population. The six hour resi-
dence time could be at or below the minimum mean cell resi-
dence time required for growth; therefore, washout of any
bacterial growth will occur. In any case, it would put the mi-
croorganisms to an extreme handicap in establishing them-
selves.
In this start-up procedure, the influent flow is shut off. The
water within the plant is then recirculated between the second-
ary clarifiers and the aeration basins. With this method, the
mean cell residence time may be made as long as necessary
simply be retaining the entire mass of microorganisms within
the system. The bacteria proceed to consume the soluble BOD
present and subsequently increase in concentration, rapidly
lowering the F/M value. Eventually, the energy level drops to a
point where the bacteria begin to flocculate and the amount of
food remaining becomes a limiting factor in further growth.
Now is the time to introduce more food to the microorganism
population. Again, it might be disadvantageous to feed the full
10 MGD flow through the system for the same reasons stated
previously. The flow instead is introduced at a gradually in-
creasing rate, thus gradually accelerating the rate of introduc-
tion of available food to match the growing concentration of
microorganisms. In terms of the food-to-microorganism ratio,
"F" might be matched to an ever increasing "M" in a way to
maintain a value of F/M that would neither inhibit the growth
rate nor disperse the bacteria. As an additional advantage, a
reduced rate of feed would produce a lower overflow rate in the
secondary clarifiers, making them more efficient than normally
possible. This fact could be used as justification for allowing
higher than normal F/M values during the low flow portions of
the start-up.
The value of F/M could ideally be held constant or gradually
decreased by carefully regulating the flow rate through the
plant. Practically, however, this is not possible due to uncer-
tainties in the actual soluble BOD concentration in the waste
stream and also because the flows cannot usually be regulated
with any precision. Much more feasible from an operating
standpoint would be to keep the value of F/M within a range
that would eventually narrow down to the optimum when the
system is started. The feed could be increased in a periodic
step-wise manner as long as the period steps did not cause the
F/M to exceed a "safe" level.
Although bacteria are the primary motivators in stabilizing
the organic wastes, other types of microorganisms play an
important role in an activated sludge system. More complex
single cell organisms called protozoa act as scavengers de-
vouring dispersed bacteria producing a highly clarified effluent.
These protozoa also serve as useful indicators of the overall
condition of the system. Because of their greater complexity
and size, they are more sensitive to changes in their environ-
ment and can be more easily observed under a typical com-
pound microscope.
The usefulness of microscopic indicators in this type of
start-up scheme is obvious. Following each periodic (step) in-
crease in feed to the system, the value of F/M will rapidly pass
from a high level to one near the normal optimum. Timing the
next periodic (step) increase is critical both to the viability of the
microbial population and to the overall start-up time require-
ments. The F/M value may be guessed at based on measured
MLVSS and either estimated BOD loads or rapid tests that
approximate BOD such as COD to TOC analysis. These lab
tests are very important during start-up; however, only by mi-
croscopic inspection can the system's energy level be im-
mediately and directly confirmed. In addition, this observation
may detect nutrient deficiency, low pH, low dissolved oxygen
levels and other problems hindering most start-ups. The dis-
covery by microscope of one of these defects is independent of
plant instruments that may be as yet inaccurately calibrated or
laboratory tests with which the technician is unfamiliar.
Besides producing a rapid and controlled growth of active
microorganisms, the periodic (step)-feed procedure has sev-
eral other virtues. Using this procedure, a full, active population
may be grown from even the smallest amount of seed or-
ganisms. A bucket of activated sludge from another plant will
contain all the types of microorganisms necessary to start a
system and may be used if it is uncertain that they exist nor-
mally in the mill wastewater. This small population of mi-
croorganisms, when introduced during the zero-flow step, will
proliferate and stabilize the F/M value within a matter of sev-
eral days.
The periodic (step)-feed method minimizes the possibility of
sudden kills of the active bacteria mass. The microbial popula-
tion is extremely fragile during the early stages of its develop-
ment, but it is also during this time that most of the wastewater
flow bypasses the system. This effect reduces the possibility
that a slug of toxic, inhibitory or high strength organic material
in the waste stream could fill the system to a concentration that
would endanger its growth.
Finally, there is no period of "population stabilization" after
the target MLVSS level is attained using the periodic (step)-
feed method. Often in the start-up of an activated sludge sys-
tem by other methods, the types of microorganizms present in
the system when the target is reached are not the same ones
that will predominate during the normal operation. This is be-
cause the population produced by using these methods devel-
ops under conditions, such as the energy level, that are far
removed from those prevalent after the target is reached. A
considerable length of time may be required for a turn-over of
the types of microorganisms represented in the population.
Plant performance can be expected to be somewhat less than
optimum during this period. By gradually "zeroing in" on the
-------
Activated Sludge 85
optimum F/M value, the periodic (step)-feed technique culti-
vates a highly diverse population of microorganisms which are
more adequately suited for survival during normal operation.
21.556 Operation of a Municipal Plant Receiving Paper
Mill Wastewater by Anthony A. Leotta and W.A.
Hopsecger
Operating experience described in this section were ob-
tained from a treatment plant with present day domestic flows
averaging from 2.0 to 2.5 MGD (7,570 to 9,460 cu m/day) and
paper mill flows from 0.3 to 0.5 MGD (1,135 to 1,890 cu
m/day). Paper mill wastewater averages 600 mgIL suspended
solids and 250 mg/L BOD. Domestic wastewater is relatively
weak and averages 75 mg IL suspended solids and 50 mgIL
BOD.
Nutrient deficiencies are experienced at this plant. Urea is
introduced into the aeration tanks to provide a concentration of
5 mg/L at the head of the aeration tank. Another satisfactory
approach to solving the nitrogen deficiency is to bypass a por-
tion (10 to 20 percent) of the primary influent directly to the
aeration tanks. Nutrients which are usually removed by pri-
mary treatment are diverted to the aeration tanks to satisfy the1
nitrogen deficiency.
Mixed liquor suspended solids are adjusted to 2,500 mg/L.
Experience seems to indicate that paper waste is difficult to
consume by microorganisms and therefore may require more
microorganisms than in most domestic treatment plants to do
the job.
DO levels in the aeration tank are maintained between 2 and
3 mg/L throughout the entire tank. Too much air (over 3 mg/L)
results in a breaking up of the floe and a resultant decrease in
settleability. Too little air results in a loss of beneficial activated
sludge bacteria and could result in an undesirable explosion of
filamentous growths.
Optimum return activated sludge (RAS) flows range from 40
to 50 percent, depending on flow and secondary clarifier condi-
tions. Return rates of 20 to 25 percent do not maintain the
proper MLSS in aeration. Rates in excess of 50 percent cause
an increase in overflow rates which result in bulking sludge
flowing over the clarifier weirs.
Depending upon the type of solids in the return sludge, the
wasting schedule is reduced during the autumn and winter
season in order to maintain higher MLSS in aeration. Since
microorganisms become less active (sluggish) in colder tem-
peratures, MLSS are raised to about 3,000 mg/L during the
colder seasons. Closer control of MLSS vs. suspended solids
in return sludge is required during the colder season. Experi-
ence has shown that the ratio between MLSS and return
sludge suspended solids should be about 3. In other words,
with the best range of MLSS from 2,000 to 3,000 mg/L, sus-
pended solids in the return sludge should be maintained be-
tween 6,000 to 9,000 mg/L. Wasting schedules are calculated
to maintain this ratio.
The operating guidelines are summarized as follows:
1. F/M ratio <1.0
2. SVI around 200
3. MLSS of 2,500 mg/L (warm weather)
4. MLVSS, 70 percent of MLSS
5. DO, 2 to 3 mg/L throughout aeration tank
6. Return activated sludge rate, 40 to 50 percent
7. Return activated sludge suspended solids, 7,500 mg/L
8. MLSS/RAS SS, 3
21.557 Acknowledgments
Authors in this section on how to treat pulp and paper mill
wastes included James J. McKeown, W.A. Eberhardt, R.S.
Dorr, Anthony A. Leotta and W.A. Hopsecger. Reviewers of
this section included Al Brosig, Anthony A. Leotta, Larry Metz-
ger, David B. Buckley, Ray Pepin and W.A. Eberhardt.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 114.
21.55A Why must accurate records be kept?
21,55B Why should the effluent from a pulp and paper mill
activated sludge process contain around 0.5 mg/L
ammonia nitrogen and 0.25 mg/L phosphorus?
21.55C Under what conditions might the paper industry shut
down an activated sludge process?
21,55D Why is the periodic feeding (step-feed) technique for
process start-up of activated sludge systems effec-
tive?
21.56 Brewery Wastewaters by Clifford J. Bruell
21.560 Operational Strategy
In brewery wastewater treatment plants, as in other food or
industrial treatment plants, there exists the potential of tre-
mendous fluctuations within influent wastewater characteris-
tics. This is especially true with respect to the organic content
of the influent. A brewery wastewater treatment plant that re-
ceives an organic load of 25,000 pounds (11,000 kg) of BOD
on one day may experience an organic loading of 50,000
pounds (22,000 kg) of BOD (or more) the following day. Eco-
nomically it is impossible to design, construct and operate a
wastewater treatment plant that will as a matter of routine, treat
highly fluctuating loads or the entire potential, load from an
industrial plant. Therefore, a multifaceted waste load monitor-
ing program to CONTROL the source of the wastewaters and
to CAPTURE FOR REUSE valuable raw materials is essential.
Due to the nature of brewery operations and the characteris-
tics of brewery wastewater, MOST BREWERY WASTEWATER
TREATMENT PLANTS ARE SMALL WASTEWATER TREAT-
MENT PLANTS THAT DO THE WORK OF LARGE WASTE-
WATER TREATMENT PLANTS. Therefore, a tight, well orga-
nized operation is imperative in order to meet NPDES permit
goals. The various operational strategies described in this sec-
tion are examples of what has worked best at a typical plant.
These methods are NOT THE ONLY WA Y to get the job done.
Careful experimentation (where only one variable at a time is
changed) is necessary to determine the best operating
methods at every individual treatment plant. There is no substi-
tute for experience and every operator has experience. The
key to successful operation is using existing experience and to
build on that foundation with new, well documented experi-
ence.
-------
86 Treatment Plants
21.561 Sources of Characteristics of Brewery Wastewater
SOURCES OF BREWERY WASTEWATER
In the brewing industry, as in other food processing indus-
tries, there is always some minimal loss of raw materials. Brew-
ing ingredients such as malted barley, rice, starch, hops and
yeast often become part of the wastewater. Raw material
losses can be controlled by the use of capture systems and
recycle loops; however, it is inevitable that some portion of this
material will become waste. The malting of barley requires
large volumes of water which flushes from the grain concen-
trated organic materials throughout the malting process. To
maintain sanitary conditions within a food plant, large volumes
of cleaning solutions are required. These soapy solutions, that
often have a high pH (caustic soda) and their associated rinse
water, also become part of the brewery wastewater stream. A
small portion of the product, BEER and brewery by-products
(brewers yeast) are very concentrated (organically), and can
enter the waste stream. On occasion, lubricating oils or other
maintenance or utility materials (ammonia, glycol coolant,
acids) may accidentally enter the sewer line. Together these
items are the sources of brewery wastewater.
CHARACTERISTICS OF BREWERY WASTEWATER
Brewery wastewater that contains starches, sugars and al-
cohol can be characterized as organically strong. This means
that the wastewater may often exert a BOD of 1,200 mgIL or
greater (municipal wastewater often has a BOD of 200 mg/L).
Much of this BOD is "soluble" or "dissolved" and only 10 to 15
percent of this BOD can be removed by primary clarification.
Therefore, ahighlyefficientsecondary treatment process,
such as activated sludge, is necessary to successfully treat
brewery waste. Nutrients such as nitrogen and phosphorus are
often considered to be deficient within brewery wastewater.
Textbook data often states that the ratio of BOD:Nitro-
gen: Phosphorus that is necessary to produce desirable acti-
vated sludge microorganisms is 100 pounds BOD: 5 pounds N:
1 pound P, within the influent to the aeration basins. If waste-
water has a very high BOD, due to starches and sugars, then
the nitrogen and phosphorus levels considered NORMAL in
municipal wastewater would be deficient when compared to
the BOD in brewery wastewater. If cleaning solutions (acids
and caustics) are released rapidly to a brewery wastewater
treatment plant (instead of being slowly metered), drastic pH
fluctuations within the influent will result. This pH fluctuation
(pH 4 to 10) can cause operational problems if the influent is
not neutralized.
21.562 Brewery Wastewater Treatment Plant Tour
OVERALL PICTURE
A typical brewery wastewater treatment plant flow layout is
shown on Figure 21.15. Typical data has been included to give
you the "feel" of the relative operating conditions of this plant.
To provide you ,with an overall picture of the plant, let's take a
WALKING TOUR of the plant shown on Figure 21.15. At each
location try to picture the equipment that would be seen and
the process that is taking place. USE YOUR EXISTING
KNOWLEDGE OF WASTEWATER TREATMENT AND TRY TO
RELATE IT TO THIS BREWERY WASTEWATER TREATMENT
PROCESS. Also, much of the other information within the re-
mainder of this section on brewery wastewater treatment will
be somewhat specific to the typical brewery wastewater treat-
ment plant described.
PRETREATMENT OF WASTEWATER
To begin the tour let us start at the headworks of the plant. At
this point the flow from various portions of the brewery, which
is collected by a massive network of piping, valves, floor drains
and sumps, is delivered to the wastewater treatment plant via a
lift station and several gravity lines. An influent flow of 3.0 MGD
(11,350 cu m/day) containing 1,200 mg/L BOD (30,000 lbs or
13,600 kg/day) and 250 mg/L SS (6,000 lbs or 2,700 kg/day)
would be an average loading to this plant. The first step of the
treatment process is bar screening. At this brewery the au-
tomatically raked bar screen removes can lids, cans, glass,
pieces of wood, rags and balls of "grain and keg wax" that form
within the sewer lines. Immediately following the bar screening
step is the GRIT REMOVAL CHAMBER or grit channel. Grit at
a brewery wastewater treatment plant consists of malted bar-
ley and hops. Depending on what raw materials are used,
grains such as corn grits or rice might also be captured within a
grit chamber. These brewing materials are readily settled and
removed from the waste stream. Therefore, this grit material
has some limited reuse value, an example of this would be as a
compost mix additive. Estimation of the volumes of grit that are
generated at various breweries is very difficult because these
volumes would depend on whether malting was being done on
site and the efficiency of the recapture systems. At this brew-
ery between 0.5 to 1.0 cubic yards of grit per MG (0.1 to 0.2
LI cu m) of flow is generated.
A useful operational aid within the area of the bar screen is
an in-line continuous monitoring pH meter. A meter at this
location, with a low and high pH alarm, can alert an operator of
POTENTIAL pH PROBLEMS long before they BECOME
PROBLEMS. The magnitude of a pH fluctuation and the dura-
tion can alert an operator of the severity of the problem. An
automatic/manual acid addition system is used to meter
(pump) concentrated H2SO4 to neutralize caustic cleaning so-
lutions. An additional recording pH meter is used to control/
monitor the acid addition. At this brewery the acid addition step
is done within the grit chamber area; however, a more desir-
able addition and monitoring point would be downstream of the
surge tank or primary clarifier. Other brewers have success-
fully used automatic caustic addition systems (50 percent
NaOH via pump) to neutralize acid spills. If an automatic caus-
tic addition system is not present, stores of caustic materials
such as lime or NaOH should be kept on hand for emergency
situations (large acid spills).
After grit removal the influent wastewater stream enters a
0.5 MG (2,100 cu m) surge tank. Brewer production is often a
batch process. A good example of this is the malting process.
When a malting tank is drained of liquid within the "steeping
out" process, this can exert an immediate high hydraulic load
(8 MGD (30,000 cu m/day) flow rate) upon the wastewater
treatment plant. The surge tank is used to catch this peak
hydraulic load and then the waste can be metered to the plant
at a controlled rate. Pumping from the surge tank at a con-
trolled rate of flow eliminates shock loadings to the aeration
basins and prevents disturbing the sludge blanket within all of
the plant clarifiers. Another function of the surge tank is dilution
of high strength organic wastes within the influent. Beer has a
very high BOD that can exceed 200,000 mg/L. If an accidental
beer spill occurred, consisting of 10 to 100 Bbls of beer (31
gallons/Bbl), this would be considered a major overload situa-
tion. A load of this magnitude, unchecked, could cause a plant
process failure. However, when a surge tank is used, dilution
will occur within the tank and the entire waste load is ME~
TERED into the aeration system. When the waste material then
enters the aeration system at a slightly elevated organic con-
centration (rather than greatly elevated), it is possible to meet
dissolved oxygen requirements and to form a desirable
biomass. Tofacilitate mixing and dilution several floatino
aerators are used. These units rise and fall (float) just as the
tank level does. These mixers achieve a small degree of pro-
aeration. Oils and grease, within the waste stream, are also
"conditioned" by the mixing action of the surge tank. These
-------
5-15% BOD REMOVAL
10-60% SS REMOVAL
INFLUENT: 3.0 MGD
1,200 MG/L BOD = 30,000 LB/DAY
250 MG/L SS = 6,000 LB/DAY
PRIMARY SLUDGE
o-?<
CLARIFIER
SURGE TANK
550,000 GAL
FILTER
ALTERNATE DRYING
SYSTEM
INTAKE
pH MONITOR
BAR SCREEN
AND
GRIT CHAMBER
LANDFILL
20% SOLIDS
PRIMARY CLARIFIER EFFLUENT
HOLDING
D.A.F. THICKENED
SLUDGE
#1 = 700 SQ. FL COMB. - 1,850
#2 = 1,150 SQ. FT. COMB. = SQ. FT
SINGLE
CELL
D.A.F. EFFLUENT
#1 FLOTATOR
PROTEIN
*2 FLOTATOR
WASTE SLUDGE
SLUDGE
DRYING
PLANT
SECONDARY
CLARIFIER
14,800 SQ. FT.
2 TANKS
CHLORINE
CONTACT
CHAMBER
EFFLUENT
CHLORINE
CONTACT
Vi RETURN SLUDGE
REAERATION
CONTACT
-\
r
J
AERATION
12 AERATION TANKS
3.63 MG VOLUME
SLUDGE FLOW
WATER FLOW
EFFLUENT-
<20 MG/lSS
20 MG/L BOD
Fig. 21.15 Flow schematic of brewery wastewater treatment plant
-------
88 Treatment Plants
materials become slightly coagulated which results in an in-
creased removal efficiency of floating oil and grease (F.O.G.)
within the primary clarifier.
The control of the surge tank level is a manual operation
controlled by the operator (level alarms and overflow provi-
sions are present). Periodically the operator checks the surge
tank level and adjusts the rate of waste pumping to maintain a
desired level. From the surge tank the waste is pumped into
the primary clarifier.
PRIMARY CLARIFIER
The primary clarification step typically removes 10 to 60 per-
cent of the influent suspended solids. However, because bre-
wery waste has a highly soluble organic content, a smaller
amount of BOD removal is achieved at this point. A 5 to 15
percent BOD removal is typically obtained; this fact also indi-
cates that only a small amount of BOD is associated with the
solids removed here. Though oil and grease are not a major
portion of the influent stream, some is skimmed from the pri-
mary clarifier surface along with small amounts of yeast, hops
and grain hulls that tend to float within the primary clarifier.
Sludge solids concentrations of materials removed from the
primary clarifier typically range from 3 to 5 percent solids.
Sludge blanket depths are measured periodically. Sludge
pumping frequency and the rate of removal (pumping rate) are
adjusted to maintain a minimum sludge blanket depth within
the clarifier without causing "coning."
21.563 Nutrient Addition
Brewery wastewater is usually nutrient deficient. Most brew-
ery wastewaters have a deficiency in both nitrogen and phos-
phorus. To supplement nitrogen, ammonia gas (or liquid) can
be metered into the primary clarifier effluent. Some brewery
wastewater treatment plants use phosphoric acid, H3PO„, as
an additional source of phosphorus. At the brewery wastewa-
ter treatment plant under examination here, adequate quan-
tities of phosphorus are present within the influent. This is due
to the fact that phosphorus is derived from both malting by-
products and phosphorus based cleaning solutions. However,
within this plant, nitrogen is deficient.
A desirable organic strength to nutrient ratio is 100 pounds
BOD: 5 pounds N: 1 pound P. In order to calculate the quan-
tities of nutrient addition required it is first necessary to have
some estimate of organic strength of the waste. To run a 5-day
BOD test as an estimate of organic strength is impractical
because it takes too long! This is especially true if nutrient
addition rates have to be adjusted on a DAILY basis. There-
fore, analysis such as chemical oxygen demand (COD) or total
organic carbon (TOC) is necessary to provide relatively quick
results. These tests can be run within several hours and a BOD
value can be calculated once a BOD:COD or BOD:TOC ratio
has been established. As an indication of the amount of nitro-
gen that is already present within the influent, NH3-N analysis
is performed on'a 24-hour composite sample of the primary
clarifier effluent. This same sample is used for other analyses
such as TOC analysis. As an estimate of nitrogen content,
NH3-N analysis is used because it is easier to run than T.K.N.
(Total Kjeldal Nitrogen) analysis. This usually ends up in a shift
in the BOD:N ratio FROM 100 pounds BOD:5 pounds N
(T.K.N.) TO 100 pounds BOD:2 pounds NH3-N. (This is true
because in this wastewater the ratio of 5 pounds T.K.N.:2
pounds NH3-N holds true.) The same philosophy applies to
phosphorus analysis (it is easier to run ortho-P analysis than
total-P analysis).
An example of NH3-N addition calculation sheet is provided
(see the sample calculation}. The basic principles of the addi-
tion procedure is to
1. Estimate the organic strength of the waste (via a quick
method such as TOC).
2. Estimate the amount of nutrient already present (via a quick
method such as NH3-N).
3. Estimate the supplemental amount of nutrient required.
The sample calculation procedure is designed to allow addi-
tion of the nutrient on a continuous basis for 24 hours. Also,
when the plant effluent analysis reveals 1.0 mg/Z. or greater
residual of the nutrient that is being supplemented, this is an
indication that the addition quantity is sufficient. If the residual
is far above or below the 1.0 mg/Z. concentration, the addition
ratio should be adjusted accordingly.
NUTRIENT ADDITION SAMPLE CALCULATION
Sample Data: Item
Data
Primary Effluent, 24-hour
Composite Total Organic
Carbon (TOC)
554
mg/Z.
BOD:TOC Ratio
2.2:1
Calculated Sample BOD
2.2 x 554 mg/Z.
1,219
mg//L
Estimated Flow for the
Next 24 hours
3.3
MGD
Final Effluent, 24-hour Composite
NHj-N Concentration
0.88
mg/Z.
Primary Effluent, 24-hour
Composite NH3-N Concentration
8.36
mg/Z.
SAMPLE AMMONIA ADDITION CALCULATIONS
1. Estimate the present day's BOD loading in pounds of BOD
per day.
BOD Loading, = R MGD x Est BOD mgiL x 8.34 lbs/gal
lbs/day a
= 3.3 MGD x 1,219 mg/Z_ x 8.34 lbs/gal
= 33,549 lbs BOD/day
2. Calculate the amount of ammonia (NH3-N) required in
pounds per day. Assume an ammonia requirement of 2
pounds NH3 per 100 pounds BOD.
N13 ^equire(j' = BOD, lbs/day x NH3-N, lbs
lbs/day —
BOD, lbs
_ oo lbs BOD y 2 lbs NH3-N
day 100 lbs BOD
= 671 lbs NHj-N/day
3. Estimate the ammonia (NH3-N) supplied to the aeration ba-
sins in the primary clarifier effluent.
^Supplied. = Rovv MQD x NHa.N mg/L x 8 34 |bs/ga(
= 3.3 MGD x 8.36 mg/Z. x 8.34 lbs/gal
= 230 lbs NHj-N/day
4. Determine the amount of ammonia (NH3-N) that must be
added to the primary effluent.
^Vbs^da 641 = NH3 Ret)uirec1' 'bs/day - NH3 Supplied, lbs/day
= 671 lbs/day - 230 lbs/day
= 441 lbs NHj-N/day
NOTE: Effluent NH3-N concentration is 0.88 mg/L which is a
satisfactory (possibly a little high) level.
-------
Activated Sludge 89
5. Calculate the rotameter setting. The rotameter constant is
5.45 lbs NH3-N for a 24-hour period for each one percent.
Rotameter _ NH3-N Added, lbs/day
Setting, % " 5 45 !bs NH3-N/day/%
= 441 lbs NHj-N/day
5.45 lbs NHj-N/day/%
= 81%
21.564 Aeration Basin Flow Scheme
Immediately after nutrient addition, the primary clarifier
effluent enters the first aeration basin or "contact cell." The
wastewater is highly bio-oxidizable and combined with the re-
turn sludge (which has been re-aerated) they exert an im-
mediate high oxygen demand upon the aeration system. Fig-
ure 21.16, the Simplified Aeration Basin Flow Schematic, is a
clear overview of the activated sludge system. The fresh waste
is distributed throughout the basin and mixed with return
sludge from the adjacent "Return Sludge Reaeration" cell. To-
gether, the return sludge and fresh waste travel in a "plug flow"
pattern through the nine (9) aeration cells (0.303 MG or 1,150
cu m each) in a serpentine fashion. Assuming an average flow
of 3.0 to 3.5 MGD (11,350 to 13,250 cu m/day) and a 35
percent return sludge pumping rate, aeration time is approxi-
mately 14 to 16 hours. The mixed liquor leaving the final aera-
tion cell is split and distributed to the two secondary clarifiers.
The activated sludge mixed liquor is next separated from the
final effluent within the secondary clarifier. The sludge or-
ganisms settle within the quiescent (calm) clarifier and are
removed from the bottom of the tank while the clear effluent
overflows the tank weirs. From the secondary clarifier the sec-
ondary effluent passes through a chlorine contact chamber
and is chlorinated. If necessary the final effluent is dechlori-
nated with sodium bisulfide before discharge to the receiving
waters. A small portion of the return sludge is continuously
wasted. Return sludge that is not wasted enters the return
sludge re-aeration basins. Flow of the return sludge within the
re-aeration system is also in a "plug flow" pattern. Return
sludge within the re-aeration phase is allowed to "rest" for 18
to 20 hours before re-entering the contact cell of the aeration
system. The trip of a sludge particle that makes the complete
loop from the contact cell, through the entire aeration and re-
aeration system and back to the contact cell, could take 32 to
36 hours under the previously described operating conditions.
21.565 Activated Sludge System Operation
Brewery wastewaters, as well as many other food process-
ing wastewaters, are highly bio-oxidizable. This means that
when activated sludge organisms come in contact with the
fresh wastewater, the organisms will immediately start to use
the wastewater as a food source. When this happens there is a
sudden demand for oxygen by the sludge organisms. Dis-
solved oxygen (DO) uptake rates in excess of 200 mg Oj/hrIL
may occur. The aeration basin DO levels might even drop to
0.5 mgIL or less. Some believe that when DO levels greater
than 5.0 mg IL are NOT maintained, this will promote the
growth of filamentous organisms. This is just one possible
cause of filamentous growth. Filamentous organisms are often
cited as a possible cause of sludge "bulking." To avoid DO
level sags within the first aeration basin or "contact cell," and
the associated possibility of sludge "bulking," several design
modifications have been made to the basin.
The Contact Cell Aeration Mode is shown within Figure
21.17. This is an enlarged view of the first aeration basin that
receives the primary effluent. The view shown here represents
what would be seen if you were looking down into a nearly
empty aeration basin. A jet-type aeration system that uses
Venturi nozzles is the type of aeration system used. Two large
submerged basin recirculation pumps collect mixed liquor and
pump it into the "liquid" header. Air or oxygen is metered into
the "gas" header. When the "liquid" and "gas" pass through
the aeration Venturi nozzles simultaneously, a jet action oc-
curs and the gas becomes impinged within the liquid. These
aeration basins are not covered. This type of jet aeration sys-
tem is used within all aeration basins and the capability of
using air OR oxygen within all of the "gas" headers exists. In
most basins where DO requirements can be met with air, stan-
dard aeration blowers are used to supply air and satisfy oxy-
gen demands. However, in the contact cell where DO de-
mands are high, oxygen is necessary (pure oxygen is more
effective than air because air is only 21 percent 02). The oxy-
gen is first vaporized from liquid and then metered into the
"gas" header within the contact cell. When oxygen is used
within the header, NO AIR is used simultaneously. Within the
"contact cell" special modifications direct the raw primary
clarifier effluent and the return activated sludge from the last
reaeration basin to within the immediate vicinity of the sub-
merged pump's suction. This is accomplished by piping and
duct work that are equipped with flow metering devices. This
modification enables the fresh re-aerated return sludge and
wastewater to be mixed and quickly distributed throughout the
contact cell. With the aid of oxygen, it is possible to maintain
minimum DO levels. An on-line DO meter and lab meter are
used to monitor the basin and frequent oxygen flow rate ad-
justments are made. Following "contact" the mixed liquor
moves to the aeration basin on the right (in a plug flow fashion)
through a submerged flow control gate. The "plug flow" mode
of aeration basin flow is used because this type of basin flow
(rather than "complete mix") has also been cited as being
instrumental in the PREVENTION of the growth of filamentous
organisms or dispersed growth. Also, this particular aeration
scheme has been the most successful mode at this plant for
obtaining the required 20/20 BOD/SS effluent.15
Aeration basin MLSS levels are run at various levels be-
tween 2,000 to 2,800 mgIL (85 percent VSS). Many factors
dictate the exact MLSS level that is maintained. An example of
this is influent organic loading. When very low ogranic loadings
occur to the aeration basins, a relatively low MLSS should be
maintained to prevent an excessive sludge age from develop-
ing. The inverse relationship is also true to a certain degree.
Temperature is another factor that greatly influences the MLSS
level that should be maintained. The activity (ability to remove
carbon) of the sludge organisms within the biomass is highly
temperature dependent. An increase in basin temperature of
only 10°C (i.e. an increase from 20°C to 30°C) can DOUBLE
the activity of the biomass. Therefore, during periods of higher
summer temperatures, a lighter biomass MLSS can achieve
the same organic removals as twice (2x) the biomass under
winter operating conditions (temperatures). As the sludge or-
ganisms increase their activity as a result of warmer basin
temperatures, they also increase the quantities of oxygen re-
quired. This means that at high MLSS levels and high basin
temperatures, it is often difficult to maintain satisfactory DO
levels within the aeration basins. When this happens and aera-
tion capabilities cannot be increased, it often becomes neces-
sary to trim back the MLSS levels until minimum DO levels are
achieved again.
The suspended solids levels maintained within the return
sludge re-aeration basins often range from 6,000 to 10,000
mgIL. This concentration depends on the settling characteris-
15 Art effluent with less than 20 mgl L of both BOD and suspended solids.
-------
8
SURGE TANK
INFLUENT
PRIMARY CLARIFIER EFFLUENT
PRIMARY
CLARIFIER
3
®
3
p*
2
o>
mm
-f-H—f-
CONTACT BASIN
I
I
-
-
—
WASTE
-I >• SLUDGE
i
l
J_ RETURN SLUDGE
I \ PUMPING
I
LIQUID OXYGEN STORAGE
(2) SECONDARY
CLARIFIERS
X
FINAL
EFFLUENT
Fig. 21.16 Simplified aeration basin flow schematic
-------
RETURN
ACTIVATED
SLUDGE f
OXYGEN GAS FEED
I I BASIN 1U
RECIRCULATION
AERATION JET
FLOW PATTERN
(TYPICAL)
PUMP
PRIMARY
EFFLUENT
BASIN FLOW
PRIMARY
EFFLUENT CONTACT CELL AERATION MODE
(TOP VIEW)
Fig. 21.17 Contact cell aeration mode (top view)
-------
92 Treatment Plants
tics of the sludge and the operation of the secondary clarifiers.
Return sludge rates are adjusted to maintain a sludge blanket
between 12 to 18 inches deep (30 to 45 cm) within the sec-
ondary clarifier. Numerous blanket depth measurements (with
a "thief" type sampler) are made to control the blanket depth.
The goal is NOT to build a DEEP blanket (that leaves sludge
within the clarifiers for a long period of time) OR to pump the
blanket levels TOO LOW and then pump only dilute sludge into
the return sludge re-aeration basins. An on-line suspended
solids meter is used to monitor return sludge suspended solids
levels and to aid with this determination. Also, grab samples of
the secondary clarifier influent are taken frequently to measure
sludge settling rates and sludge volume indices (SVIs). Once
again, just as the relationship between temperature and basin
DO levels dictates maximum MLSS levels, the settling charac-
teristics of the sludge within the secondary clarifier may also
dictate the maximum MLSS level that can be maintained under
aeration. To control clarifier sludge blanket depth, return
sludge pumping rates can be increased only to a certain point
(about 50 percent), and after that further increases in return
rates are not beneficial. This is because the additional return
that is pumped back through the re-aeration and aeration sys-
tem ultimately comes back into the clarifier and causes a high
hydraulic loading. This increased hydraulic loading into the
clarifier can cause the characteristically light fluffy sludge to
become stirred up and possibly bulk. If the sludge settling
characteristics are poor (high SVI) and increasing return
sludge pumping rates do not control sludge blanket depths,
again MLSS levels must be trimmed back.
Other commonly used activated sludge operational control
factors such as the food to microorganisms ratio (F/M), mean
cell residence time (MCRT) and sludge age, are very difficult to
us as the SOLE determining factor to direct sludge wasting on
a day to day basis. These factors can be very useful as plant
design figures or they can be used to determine desirable
operating ranges. However, to calculate these factors and ad-
just sludge wasting rates or to attempt to adjust MLSS levels
on a daily basis "shooting" at a specific F/M SET POINT be-
comes impossible. When highly fluctuating organic loads enter
a plant it is very difficult to waste or build MLSS rapidly enough
(within 24 hours) to meet a specific set point. Instead, select a
proper MLSS level SET POINT which actually results in an
F/M, MCRT or sludge age value that floats in the vicinity of
what would approximate a desirable "factor" range! In reality
there are many interrelated and independent factors that influ-
ence plant operation. These factors include basin DO levels
that can be maintained, sludge settling characteristics, effluent
quality and many other factors dictate what MLSS level can be
maintained. This proper MLSS level must be determined ex-
perimentally by SLOWLY adjusting the MLSS level together
with careful observation of plant behavior. Ultimately a proper
MLSS SET POINT can be determined and used to control
sludge wasting activities. However, you must realize that this
"proper MLSS set point" may have to be adjusted when in-
fluent characteristics change and when seasonal changes oc-
cur.
As previously described, all sludge that is not wasted flows
into the re-aeration portion of the plant. There are numerous
benefits from return sludge re-aeration. A list of some of the
advantages is as follows:
1. Basic math indicates that if nine aeration basins are main-
tained at a MLSS of 2,000 mgIL, then the addition of only
three return sludge re-aeration basins ( ALL basins equal
0.303 MG or 1,150 cu m) at a SS level of 6,000 mg/L (return
sludge concentration) will DOUBLE the available biomass
within the activated sludge system. (9 aeration x 2,000
mg/L = 3 re-aeration x 6,000 mg/L or double initial capac-
ity.)
2. During periods of high organic loading, the re-aeration
phase allows adequate "rest" time for the sludge or-
ganisms to metabolize adsorbed and absorbed BOD.
3. If a poison or toxic substance should enter the plant (heavy
metals, pH or temperature shift) only a small portion of the
biomass will be destroyed. The plant can recover quickly
and be back on line within a short period of time (again
achieving satisfactory BOD removal).
4. The "rest" period within re-aeration seems to condition the
sludge so that it will readily accept new influent loading and
consistently obtain high BOD removals (+98 percent).
21.566 Sludge Wasting
An example of a sludge wasting calculation is included. The
major basis of the calculation is that sludge wasting will be
done continuously for a 24-hour period with the GOAL being a
desired MLSS "SET POINT." Every 24 hours all of the data is
reviewed and a new sludge wasting rate is implemented.
The following illustrates the wasting formula calculation. As
a quick indication of influent organic strength, a total organic
carbon (TOC) measurement is used to project BOD loading.
SAMPLE DATA: Item
Data
Final Aeration Cell MLSS
Primary Effluent, 24-hour Composite
Sample, TOC
Desired MLSS set point
Return Sludge (waste) SS
Estimated Flow for the Next
24 hours
2,420 mg/L
554 mg/L
2,200 mg/L
7,160 mg/L
3.3 MGD
Volumes and Assumptions
1. Volume of each aeration cell 0.3 MG.
2. Nine aeration cells, total aeration volume 2.7 MG.
3. Solids in secondary clarifiers are equal to 15 percent of the
solids within the aeration basins.
4. MLSS of final aeration basin is representative of the MLSS
of all the aeration basins. 9 x final aeration basin MLSS =
total aeration solids.
5. Yield factor = 0.5 lbs MLSS solids produced/lb BOD re-
moved.
6. Estimate primary effluent flow from recent records and ac-
tual flow data for first 8 to 10 hours of the day. Take into
consideration whether the sludge wasting system is in op-
eration.
7. Conversion factor = Yield x BOD:TOC ratio
1.1 = 0.5 x 2.2
SAMPLE WASTING FORMULA CALCULATIONS
1. Calculate the solids in the system in pounds. Since solids in
the secondary clarifiers are 15 percent of the solids in the
aeration basins, multiply the solids in the aeration basins by
1.15.
Final Aeration x8.34jbs_xUs
Solids in _ Aeration
System, lbs Volume, MG " Cell MLSS, mg/L ga!
= 2.7 M Gal x 2420 mg/L x 8.34 lbs/gal x 1.15
= 62,668 lbs
-------
Activated Sludge 93
2. Estimate the solids produced in the system in pounds per
day. Assume 1.1 pounds of solids are produced per pound
of TOC.
Solids = 1.1 lbs solids/day x T0C ,bs/d
Produced, 1 |b TOC/day
lbs/day 7
= 1.1 x Flow, MGD x TOC, mgILx 8.34 lbs/gal
= 1.1 x 3.3 MGD x 554 mg//. x 8.34 lbs/gal
= 16,772 lbs solids/day
3. Determine the desired pounds of solids in the system based
on a MLSS set point of 2,200 mg/L Assume solids in the
secondary clarifiers are 15 percent of the solids in the aera-
tion basins (multiply by 1.15).
Desired
Solids in
System,
lbs
Aeration
MLSS Set
Volume, MG Point, mg/L
x 8.34 !!?!_ x 1.15
gal
= 2.7 M Gal x 2,200 mg/L x 8.34 lbs/gal x 1.15
= 56,971 lbs
4. Calculate the sludge wasting amount in pounds per day.
Sludge (Solids in - Desired Solids) + Solids Produced,
Wasting _ System, lbs in System, lbs lbs/day
lbs/day* Waste During 1 day
(62,668 lbs - 56,971 lbs) + 16772
1 day
= 5,697 lbs/day + 16,772 lbs/day
= 22,469 lbs/day
lbs
day
NOTE: If the sludge wasting rate is negative, the MLSS is too
low. Reduce the existing wasting rate by 10 to 15
percent. Some operators shut off the waste when
negative values are obtained, but many operators try
to avoid drastic changes in wasting rates by adjusting
the existing wasting rate up or down by no more than
10 to 15 percent each day.
5. Determine the sludge wasting rate in MGD and GPM.
Sludge
Wasting
Rate, MGD
Sludge
Wasting
Rate, GPM
Sludge Wasting Amount, lbs/day
Waste Sludge SS, mg/L x 8.34 lbs/gal
= 22,469 lbs/day
7,160 mg/L x 8.34 lbs/gal
= 0.376 M gal/day
= 376,000 gal/day
1,440 min/day
261 GPM
Waste sludge is first pre-thickened in dissolved air flotation
(D.A.F.) units and mixed with primary sludge in the sludge
holding tanks. Water is evaporated from the separated
sludge mixture within the sludge drying plant and the product
is currently marketed as a high vitamin B-12, high protein,
animal feed supplement.
One last item that should be covered along with aeration
basin control is the subject of aeration basin foam. At all
times foam is present on the basin surfaces. Foam is a natu-
ral part of the biomass. A dark, greasy looking foam is the
sign of an old sludge age while a white, clear foam is indica-
tive of a young sludge age. Large quantities of foam can
sometimes cause operational problems if the foam does not
stay within the basins. Excessive foam can be caused by
large quantities of detergents within the waste stream or
some brewery materials such as yeast. Control of this foam
can be achieved by: (1) decreasing air flow to the aerators,
(2) by the use of chemical surfactants, or (3) by water sprays
aimed to physically collapse the foam. A novel approach to
foam control involves overflowing the aeration basin into a
small side basin, letting the foam collapse and then wasting
this foaming material from the plant.
21.567 Filamentous Organisms
Within brewery wastewater treatment plants, often the
number one operational problem is the control of filamentous
organisms (Fig. 21.18). Often sludge "bulking" is related to a
filamentous bacteria by the name of SPHAEROTILUS NA-
TANS. To blame all sludge bulking on this ONE type of fila-
mentous organism is a misconception. In reality there are
about 10 different types of filamentous organisms that can
become predominant within BREWERY activated sludge and
cause sludge settling problems. To a certain degree there is
a relationship between the different filamentous organisms
and specific operating conditions. Therefore, in some cases,
if the type of filamentous organism can be identified, the
causative operating condition can also be determined and
rectified. However, this approach is usually not practical. To
begin with, specific filamentous organism identification re-
quires 500X - 1 ,OOOX power microscope. Also, even if the
specific filament can be identified, the literature relating fila-
ment type to causative condition is somewhat limited.
A more successful approach to filamentous organisms
management, as reported within the literature is described as
follows: (It should be noted that only SOME of the techniques
described have been used at the plant described here.)
1. Determine if filamentous organisms are the true culprit. This
can usually be done by examining a sludge sample with a
relatively inexpensive microscope. The filamentous or-
ganisms look like fine "hairs" or "wires" extending out of the
sludge floe particles or they can be found in the liquor float-
ing free. Some filaments are always present, but if they
appear to be 20 percent of the biomass or more, they could
be causing settling problems.
2. A "short term" corrective step is often necessary to halt
immediate "bulking." Many process adjustments can be
done to bring the filaments under control:
a. Careful polymer or chemical (FeCI3) dosage to prevent
SS loss within the secondary clarifiers.
b. Excessive sludge wasting to remove filamentous or-
ganisms from the system.
c. Chemical dosage of the return sludge with oxidants
such as H-O, (0.1 lb H202/1 lb. VSS) or Cl2 (3 to 5 lbs
Clj/1000 lbs VSS).
3. Develop a "long-term" control program to correct opera-
tional problems and to prevent the recurrence of filamen-
tous organisms. A list of common causes of filamentous
"bulking" is as follows:
a. Low DO levels within aeration basins and secondary
clarifiers (this is often a RESULT of a high F/M ratio,
although the F:M ratio alone is not necessarily the prob-
lem).
-------
94 Treatment Plants
1. Typical brewery activated
sludge, few filaments
2. Brewery activated sludge, some
filaments
3. Typical highly filamentous sludge
Fig. 21.18 Filamentous organisms (100 x magnification)
-------
Activated Sludge 95
b. A lack of adequate nutrients (nitrogen or phosphorus)
or trace minerals within the influent.
c. The presence of high levels of sulfur within the influent.
d. Low F/M levels within aeration system (less than 0.2).
e. Large fluctuations within the plant influent organic load-
ing.
Many of these problems can be overcome by implementing
operational changes and by engineering design changes. At
the wastewater treatment plant under examination here, many
changes have been made to control the growth of filamentous
organisms. Experimentation has revealed that the dissolved
oxygen concentration (DO) is the most influential factor that
affects filamentous organism growth within this plant. Since
some filamentous organisms are often desirable (to maintain
floe structure), a desired DO LEVEL SET POINT is used to
ADJUST FILAMENT CONCENTRATIONS. Over a long period
of time, experience has shown that filamentous organism con-
centrations can be adjusted by adjusting "contact" cell DO
levels. AN INCREASED DO LEVEL (5 to 10 mg/L) will yield A
DECREASE IN FILAMENTOUS ORGANISMS. A DE-
CREASED DO LEVEL (1 to 3 mg/L) will result in an IN-
CREASED NUMBER OF FILAMENTOUS ORGANISMS.
21.568 Laboratory Testing
Only a small portion of the testing within a brewery wastewa-
ter treatment plant is devoted to "permit" monitoring require-
ments. The majority of the laboratory time is spent obtaining
test data that is required to assist in making process control
adjustments. Numerous MLSS measurements are made to
evaluate sludge wasting needs and sludge settling characteris-
tics. Plant loading data is updated daily by the use of Total
Organic Carbon (TOC) analysis. Nutrient concentrations are
measured at several locations within the plant to assist with
nutrient addition calculations. Both 24-hour composite sam-
ples and grab samples are used to obtain representative data.
Microphotographs (Fig. 21.18) of sludge samples from several
locations within the aeration system serve as a permanent
record of microorganism diversity and relative filamentous or-
ganism concentrations. Many additional quantitative and qual-
itative tests are performed and the results are recorded. This
data, along with numerous other measurements and evalua-
tions recorded throughout the wastewater treatment plant
serve as the basis for mapping out operational control
strategies and are indispensable.
21.569 Record Keeping
Every wastewater treatment plant is different and requires
different types of testing and record keeping. There is no sub-
stitute for well organized laboratory data and operational log
sheets. The extreme value of this information cannot be over
emphasized. Well recorded data can serve as a quick update
to an operator coming on shift or it may be graphed, charted, or
tabulated to indicate more clearly overall trends. Proper use
and analysis of records have allowed the operators of plants
treating brewery wastes to produce a high quality effluent.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 115.
21.56A Why are primary clarifiers not very effective in remov-
ing BOD from brewery wastes?
21.56B Where are nutrients added and how are nutrients
added when treating brewery wastes?
21.56C What factors influence the MLSS level in the aeration
basins?
21.56D How is the sludge wasting rate determined?
21.56E How can filamentous "bulking" be controlled in acti-
vated sludge plants treating brewery wastes?
21.57 Food Processing Wastes
This section discusses how to treat wastewaters from two
different types of food processing wastes. Treatment of ar-
tichoke wastewater and dairy wastes are presented by two
operators who actually treat these wastes on a day-to-day
basis. Almost all of the foods we eat (fruits, vegetables, fish,
meats, dairy products) produce wastewaters when they are
processed for consumption. Treatment of these wastewaters
may be unique for each food, but the basic principles of pre-
treating the wastewater to produce an environment suitable for
activated sludge treatment are similar.
21.570 Treatment of Artichoke Wastewater by Peter Luthi
Processing of artichokes in California is a year round opera-
tion with a major peak during the months of March, April and
May and a minor peak in September, October and November.
The fact that some wastewater is generated all year round
makes the operation of an activated sludge system possible at
this pretreatment facility (Fig. 21.19). The effluents from the
activated sludge plant which treats high strength wastewater,
the flotation unit which treats medium strength wastewater,
and cooling water with a low BOD load are all discharged into
the sewer for final treatment by the municipal wastewater
treatment plant.
Wastewaters from the artichoke processing plant are segre-
gated according to BOD strength and only the highest BOD
portion of the wastewater is treated by the activated sludge
system (Fig. 21.19). Primary objectives of the activated sludge
treatment process are to:
1. Treat the high strength (high BOD) waste to acceptable
levels with a minimum of input (energy, labor, dollars) and a
minimum of waste sludge produced, and
2. Produce a treated effluent that is discharged to a municipal
treatment plant that meets the following discharge limits:
a. BOD <500 mg/L,
b. Suspended solids <500 mg/L, and
c. pH within a range of 6 to 9.
BOD strength of the wastewater treated varies between
1,000 and 15,000 mg/L with a pH of around 4.5 (from the use
of vinegar and citric acid in the process). Volume of high
strength BOD water ranges from 1,500 gal/week to 15,000
gal/week (5.7 to 57 cu m/week) during the peak season^
21.571 Pilot Project
The unusually high and widely fluctuating BOD levels of the
waste required that the feasibility of an activated sludge sys-
tem be studied on a pilot project. An activated sludge system
-------
96 Treatment Plants
pH AND NUTRIENTS (N&P)
ADJUSTMENT
I
HIGH
i-iuluING
TANK
ACTIVATED
SLUDGE
TANK
WASTE WATER
PUMP
DILUTION
WATER FOR
HIGH STRENGTH
WASH
MEDIUM
STRENGTH
WASTE-
WATER
ARTICHOKE
PROCESSING
PLANT
FLOTATION
UNIT
CLARIFIER
LESS THAN
500 mg/l BOO
500 mg/| ss
pH 6-pH 9
OIL AND SUSPENDED
SOLIDS
OIL
COOLING WATER
(LOW BODs LOAD)
MUNICIPAL
WASTE WATER
TREATMENT
PLANT
Fig. 21.19 Artichoke activated sludge pretreatment facility
-------
Activated Sludge 97
with extended aeration using mean cell residence times up to
15 days was chosen. As much as 90 to 95 percent BOD re-
moval could be achieved if the influent BOD was kept below
6,000 mg/L Higher influent BODs resulted in lower effluent
quality. Medium strength wastewater is therefore used to dilute
the influent.
To accumulate some operating data during the pilot project,
the following analyses were performed on a daily basis:
1. Influent and effluent COD and suspended solids,
2. Mixed liquor suspended solids,
3. pH of influent, mixed liquor and effluent,
4. Dissolved oxygen, and
5. SVI
COD rather than BOD was chosen for its relatively easy and
fast analysis. A graph showing 15-day moving average influent
COD, mixed liquor, suspended solids, moving F/M ratio,
effluent COD and suspended solids was drawn and kept up
daily to find the best operating guidelines. Fifteen-day moving
averages for influent COD and F/M ratio were computed to
reduce the effect of fluctuating daily results.
21.572 Daily Operational Procedures
Through trial and error, and after several upsets over a
nine-month period, it was readily visible from the graph and
data accumulated that acceptable results (less than 500 mg/L
BOD and suspended solids) were obtainable when the F/M
ratio was kept between 0.08 to 0.28 pounds BOD/day/pound
MLVSS.
Daily influent and effluent COD and pH, mixed liquor and
effluent suspended solids analyses are performed. Also, de-
terming the SVI on a daily basis is helpful in detecting changes
in the settling characteristics of the activated sludge. Sludge
volume indeces were, however, generally higher than data
given in literature for municipal treatment plants.
Nutrients (N and P, in the form of ammonium phosphate
fertilizer) were initially added in batches on a daily basis. Mow-
ever, a continuous addition directly into the in-feed line used
later on proved much more reliable and provided for a
smoother operation. Lack of sufficient nutrients was responsi-
ble for bad settling characteristics in several cases. If the SVI
increases and lack of nutrients is suspected, a look at the
sludge under the microscope should be taken. The presence
of filamentous bacteria will confirm the suspicion. Sufficient
amounts of nutrients proved to be quite important and upsets
caused by their lack took a long time to remedy. No provision
for chlorinating the return sludge exists. No adverse effects
were observed by the addition of too much nitrogen and phos-
phorus.
To keep influent COD concentration as steady as possible
on a day-to-day basis, dilution with medium strength wastewa-
ter is used when needed.
The fluctuating concentrations of the influent COD make it
necessary to keep the DO level in the aerator between 4.0 and
6.0 mg/L. Rapid changes occur sometimes and can drop DO
levels to as low as 2.0 mg/L in a matter of hours. Therefore,
keeping levels at 4.0 to 6.0 mg/L assures that the DO does not
drop below the critical 2.0 mg/L
Effluent pH monitoring shows that when effluent pH drops
below 6.5 it is necessary to adjust the influent pH to between
5.5 and 6.5. This is done with granular sodium hydroxide
added to the holding tank. At times of low feed rates, however,
the system is able to tolerate the normal influent pH of 4.2 to
4.8 and only occasionally are adjustments necessary.
Influent levels vary from 4,300 gal/day to 8,600 gal/day (16
to 32 cu m/day). Levels higher than 8,600 gal/day (32 cu
m/day) produce turbulence in the clarifiers with accompanying
solids loss in the effluent. Mixed liquorsolids vary from 3,000 to
4,500 mg/L. Influent volume is the most important variable
used to control the system. By increasing or reducing the vol-
ume, the F/M ratio can be increased or decreased more
gradually or kept at one level when influent COD concentration
changes. In anticipation of heavy production times and coincid-
ing larger amounts of wastewater, mixed liquor solids are al-
lowed to build up to 4,500 mg/L and the F/M ratio increases
which allows treatment of larger volumes with higher concen-
trations of COD. Sludge must now be wasted on a daily basis
to keep the aerator solids level (MLSS) at 4,500 mg/L. Waste
sludge is disposed of on land.
Immediately following heavy production, sludge is wasted at
an increased rate to reduce mixed liquor solids to 3,000 mg/L
to avoid starvation of the system now that COD concentration
and waste volume are dropping. During times of low produc-
tion the F/M ratio is reduced to around 0.08 lbs BOD/day/lb
MLVSS. At this level of subsistence, when influent BOD level
and feed rate are at their lowest, the effluent produced is of a
lower quality. More solids than usual are being carried away
with the effluent and sludge wasting only has to be done on an
occasional basis. However, the primary objectives of reducing
effluent BOD and suspended solids levels below 500 mg/L can
still be achieved.
21.573 Treatment of Dairy Wastes by Ralph L. Robbins, Jr.
Dairy wastes can be treated by the various modes of the
activated sludge process. Many dairy waste treatment plants
have the designed flexibility to 1reat by either:
1. Extended aeration,
2. Contact stabilization, or
3. Step-feed aeration.
On the basis of actual operating experience and analysis of
influent, plant and effluent samples, the extended aeration
mode appears to work best for some plants.
21.574 Plant Influent
Dairy wastewaters are comprised of production materials
such as lactose, calcium lactate and protein hydrolysates. The
sanitary facilities at many plants are separate from the indus-
trial dairy wastes and do not enter the wastewater stream to
the treatment facility. Thus chlorination of the effluent is not
necessary. The influent averages a BOD loading of 3,000 lbs
per day (1,360 kg/day} and a total solids level of approximately
3,500 lbs per day (1,590 kg/day). The treatment facility (Fig.
21.20) operates throughout the entire year with little change of
temperature in the aeration tanks. The effluent temperature
does not fall below 60°F (15°C) year round, thus providing tor a
stable operation all year.
-------
98 Treatment Plants
RAW WASTEWATER INFLUENT
DESIGN:
420,000+ GPD
3750 LB/DAY BOD5
VACUUM
FILTER
BLOG.
HYDROGEN
O O CK
PEROXIDE
O O
1
SPILL
CONTROL
PROJECT
CONT.
BLOG.
PLANT EFFLUENT
DESIGN:
420,000+GPD
< 75 LB/DAY BODg
P-
SETTLING
TANK
#1
SETTLING
TANK
#2
MIXED LIQUORS
FLOW
AERATION
TANK
4,000 CF
FLOW
CONTINUOUS
RETURN
SLUDGE
(VARIABLE —
ABOUT
1.5 X AVERAGE
INFLUENT)*
ID
SETTLING
TANK
#3
SLUDGE
HOLDING
TANK
•WASTE SLUDGE
(OCCASIONAL)
Fig. 21.20 Dairy waste activated sludge treatment facility
-------
Activated Sludge 99
21.575 Operation
Aeration tanks may be operated in the extended aeration
mode. Some dairy wastes require at least 18 hours aeration
time in the tanks. Up to 80 percent of the BOD load can be
reduced in the first tank with the other two tanks treating the
remaining 20 percent. For this reason the diffuser capability in
the first tank should be twice that of the other two tanks.
The mixed liquor suspended solids level in the aeration
tanks are kept at a high level of 1 percent or 10,000 mgIL. This
high level of MLSS is necessary to prevent process upsets
caused by shock organic loadings. Extra air capacity is neces-
sary in case of shock organic loadings in order to keep aeration
tank DO levels between 2 to 6 mg IL.
Settling tank detention times can be as long as 8 hours.
Activated sludge is recirculated to the aeration tanks at a rate
of 1V2 to 2 times the plant influent rate.
Vacuum filters are used to dewater the sludge. Lime and
ferric chloride are added for flocculation of the waste sludge
before filtering. The sludge cake runs from 20 to 30 percent dry
solids. The waste sludge cake is disposed of at a sanitary
landfill site.
21.576 Plant Effluent
Plant effluent is monitored daily by plant personnel. Analyt-
ically the BOD, SS, COD, phosphorus, nitrate, nitrite and total
nitrogen are monitored.
21.577 Operational Techniques for Upgrading Effluent
Problems can develop with milk protein breakdown. The ad-
dition of 50 mg IL of anhydrous ammonia can produce a com-
plete breakdown of milk protein in the aeration tanks. Activated
carbon can help in many areas, including odor control, removal
of phosphate, media for extra bacteria growth in the aeration
tanks and an aid in flocculation and settling in the clarifiers.
A fermentor can be used to grow commercial bacteria for
injection into aeration tanks during times of bacteria kill due to
shock loadings from major spills in the production area. In-
stallation of a system for the addition of hydrogen peroxide for
odor control and additional oxygen during times of shock load-
ings can be helpful.
A spill control system which diverts major spills into a pre-
treatment holding tank for pH adjustment and pre-aeration be-
fore being blended into the main aeration tanks can be used if
there is adequate warning.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 115.
21.57A How are high strength artichoke waste influents
(BOD >6,000 mg IL) adjusted before being treated
by the activated sludge process?
21.57B Why were 15-day moving averages computed and
plotted for artichoke influent COD and F/M ratio?
21.57C What chemical can be used to provide nutrients for
the treatment of artichoke wastes?
21.57D Why might the chlorination of the effluent from a dairy
waste treatment plant not be necessary?
21.57E Why are high levels of MLSS (10,000 mgIL) kept in
aeration tanks that treat dairy wastes?
21.58 Petroleum Refinery Wastes by Cal Davis
21.580 Refinery Wastewater Characteristics
Three main compounds, ammonia, phenols and sulfide, are
found in petroleum refining wastewater and can be treated
very effectively by the activated sludge process.
Influent flows can vary both in rate and contaminant concen-
tration, very rapidly and without notice. Waste treatment plants
with holding ponds can control hydraulic loadings, but not al-
ways BOD loadings. To some extent hydraulic loading can be
used to control BOD loading with the MLVSS remaining con-
stant in the aeration basin. In the event of a shock load, a
hydraulic loading change would be the first corrective step.
21.581 Activated Sludge Process
Understanding and monitoring the activated sludge process
is important in treating petroleum refining wastewater. Recog-
nizing that each plant operates differently, most petroleum
treatment activated sludge units (Fig. 21.21) operate on ex-
tended aeration mode with MCRTs up to 30 days in order to
maintain the nitrification population necessary to oxidize am-
monia. The minimum MCRT for good nitrification seems to be
20 days.
21.582 Frequency of Sampling and Lab Teats
Wastewater from a refinery can change in flow rate and
waste concentration very suddenly. Certain tests must be run
each shift while others can be run daily. Tests that need to be
run each shift at the treatment plant include DOs, temperature,
pH, sulfide, phenols, ammonia, and 30-minute settleability.
During upset conditions these tests need to be run at least
twice a shift. Tests that need to be run each day include TOC
or COD, BOD, MLTSS, MLVSS, recycle sludge TSS, am-
monia, phenols, pH, P04 and oil.
21.583 Operational Procedures
When you come on duty after a shift change, visually inspect
the activated sludge process, and review the log book and lab
sheet for any changes in influent rates or concentrations.
Check the following items: hydraulic loading, DOs, aeration
basin, MLTSS and MLVSS, pH, temperature of influent, sludge
recycle rate and clarifier loading. For comparison purposes
measure sludge settleability and also calculate the SVI and
F/M ratio. Under normal conditions DOs are 1.5 to 2.0 mgIL,
pH from 6.8 to 7.0, and phenols, ammonia and sulfide are nil.
21.584 Response to Sulfide Shock Load
If a check of the activated sludge system shows DOs less
than 0.5 mg/L, pH of 5.6, aeration basin turning a light color,
and phenols showing in effluent, then a sulfide shock is indi-
cated. Testing may show no phenols in influent stream since
-------
PH ADJUSTMENT
PHOSPHORIC
ACID
DISSOLVED
OXYGEN
MONITOR
EFFLUENT
QUALITY: (MG/U
TOO 30
NH3 2
PHENOL OIL
OIL AND GREASE NIL
PH 6-7
TSS 30
O
o
fit
»-*
3
A
3
ja
to
3
V)
EFFLUENT
TO RECEIVING
STREAM
MECHANICAL
AERATOR
- ^ MECHANICAL
CI M 1J SLUDGE SKIMMER
AERATION
BASIN
SLUDGE
DISPOSAL
AIR
DISTRIBUTION
HEADEH
CLARIFICATION
BASIN
V//////////.
AIR BLOWER
SLUDGE
TO
DISPOSAL
FEED
QUALITY: fMG/L)
TOC 100
NH3 6
PHENOL 20
OIL ANO GREASE 8
PH 9-10
SLUDGE RECYCLE
PUMP (3)
OPERATING PARAMETERS
FEED FROM SLUDGE RETENTION TIME — 30-35 DAYS
CHEMICAL SLUDGE VOLUME INDEX — 50-70
FLOCCULATION FOOD TO MICRO RATIO — 0.1 lb. TOC/DAY
lb. MLVSS
Fig. 21.21 Refinery waste activated sludge process
-------
Activated Sludge 101
sulfide tends to mask or interfere with the phenol test. To cor-
rect this problem, the hydraulic loading needs to be reduced
until DOs are above 1.5 mg/L and soda ash should be added to
the aeration basin to bring the pH above 6.2 in order to re-
activate the phenol eaters. If phenols in the effluent are near
your NPDES limit, adding hydrogen peroxide (H202) can be
beneficial.
21.585 Correcting Excessive Phenols
Phenols in excess may pose more of a problem with odor
and in extreme cases of phenol shock, microbes will stop work-
ing and DOs will increase to the saturation limit. To correct this
problem, a decrease in hydraulic loading is necessary and if
phenols in the effluent are near the NPDES limit, the addition
of H202 will help to oxidize the phenols.
21.586 Treating Ammonia
Ammonia can be very troublesome since it is related directly
to fish toxicity. Ammonia can be difficult to biologically treat
because it is difficult to cultivate nitrifying organisms to de-
grade ammonia. Besides the free ammonia, two other problem
compounds that can show up in petroleum refining wastewater
are monoethanolamine (MEA) and thiocyanate. Both of these
compounds are biologically degraded to ammonia. Lab results
must be checked each shift for an indication of a potential
increase in ammonia and the maintaining of an MCRT or envi-
ronment that is conducive to cultivating nitrifying bacteria.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 115.
21.58A What are the three main petroleum refinery waste
compounds that can be treated by the activated
sludge process?
21.58B Why are MCRTs as high as 30 days necessary to
treat petroleum refinery wastes?
21.58C How can a shock load of phenols be treated?
21.59 Summary and Acknowledgments
21.590 Summary
The basic treatment unit in the activated sludge process is a
biological reactor (aerated basin or pond). This reactor pro-
vides an environment for the conversion of soluble organic
material into insoluble microorganism cells. The subsequent
unit is a secondary clarifier or pond where the cells are allowed
to settle. The settled cells, or sludge, may be either returned to
the aeration system, wasted from the system, or stored. As the
result of biological growth, large volumes of organic solids are
generated in secondary treatment processes.
Although several different activated sludge systems are
used to provide secondary treatment (See Sections 11.05 and
11.9) for industrial, domestic, and domestic-industrial waste-
waters, the control strategies and/or operating guidelines are
essentially the same.
This section has described conditions unique to the treat-
ment of industrial wastewater. Control of your activated sludge
system will be enhanced by using the information for the oper-
ation and control of your plant contained in various sections of
Chapters 8,11, and 21.
21.591 Acknowledgments
Portions of Section 21.50 through 21.54 were taken from
"Pollution Abatement in the Fruit and Vegetable Industry (Vol-
umes 1, 2, and 3), EPA Technology Transfer Seminar Publica-
tion, U. S. Environmental Protection Agency, Center for En-
vironmental Research Information, 26 West St. Clair Street,
Cincinnati, Ohio 45268.
The representatives of industry who prepared these sections
on how to treat industrial wastes are sincerely thanked. With-
out the contributions from James J. McKeown, Clifford J.
Bruell, Peter Luthi, Ralph L. Robbins, Jr., and Cal Davis, this
section would not have appeared in this manual.
21.6 EFFLUENT NITRIFICATION
21.60 Need for Effluent Nitrification
Many activated sludge processes are designed to attain a
high degree of nitrification. The degree of nitrification that must
be attained is dictated by the maximum allowable limit of am-
monia nitrogen discharged with the final effluent. This limit is
usually governed by the NPDES permit issued by state or
federal regulatory agencies.
Nitrogenous compounds discharged from wastewater
treatment plants can have several harmful effects. These im-
pacts include ammonia toxicity to fish life, reduction of chlorine
disinfection efficiency, an increase in the dissolved oxygen de-
pletion in receiving waters, adverse public health effects
(mainly groundwater), and a reduction in the suitability for re-
use.
Nitrogen concentrations in raw municipal wastewaters gen-
erally range from 15 to 50 mg/L, of which approximately 60
percent is ammonia-nitrogen, 40 percent is organic nitrogen,
and a negligible amount (one percent) is nitrite and nitrate-
nitrogen.
21.61 Nitrogen Removal Methods
Ammonia nitrogen can be reduced in concentration or re-
moved from wastewater by several processes. These pro-
cesses can be divided into two broad categories: physical-
chemical methods and biological methods.
This section is devoted mainly to biological nitrification. A
brief discussion of some physical-chemical nitrogen removal
methods also is included.
21.610 Ammonia-stripping
The ammonia nitrogen which is present in wastewater dur-
ing conventional biological treatment can be removed by a
physical process called desorption (stripping). Simply stated,
the wastewater is first made very alkaline by adding lime, and
the ammonia is then induced to leave the water phase and
enter the gas phase where it is released to the atmosphere. To
accomplish this stripping, the wastewater is contacted with a
sufficient quantity of ammonia-free air. This contacting with air
is done in a slat-filled tower very similar to those used by
industry to cool water.
21.611 Ion Exchange
This nitrogen removal process involves passing ammonia-
laden wastewater through a series of columns packed with a
material called clinoptiiolite. The ammonium ion adheres to or
is absorbed by the clinoptiiolite. When the first column in a
series loses its ammonia adsorptive capacity, it is removed
-------
102 Treatment Plants
from the treatment scheme and washed with limewater. This
step converts the captured ammonium ions to ammonia gas,
which is then released to the atmosphere by contacting heated
air with the wastewater stream, in much the same manner as
described under ammonia stripping.
21.612 Breakpoint Chlorination
Breakpoint chlorination (superchlorination) for nitrogen re-
moval is accomplished by adding chlorine to the wastewater in
an amount sufficient to oxidize ammonia-nitrogen to nitrogen
gas. After sufficient chlorine has been added to oxidize the
organic matter and other readily oxidizable substances pre-
sent, a stepwise reaction of chlorine with ammonium takes
place.This may be the simplest nitrogen removal process, yet it
has some disadvantages. In practice, approximately 10 mg/L
of chlorine is required for every 1 mgJL of ammonia-nitrogen. In
addition, acidity produced by the reaction must be neutralized
by the addition of caustic soda or lime which add greatly to the
total dissolved solids in the wastewater.
21.62 Biological Nitrification
The nitrogen present in wastewater predominates as am-
monia and organic nitrogen. As the organic matter in the
wastewater decomposes, a portion of the organic nitrogen is
converted to ammonia nitrogen. When the wastewater is suffi-
ciently aerated, the nitrite forming bacteria (nitrosomonas) will
oxidize the ammonia-nitrogen to nitrite-nitrogen. The nitrate
forming bacteria (nitrobacter) then oxidize the nitrite-nitrogen
to nitrate-nitrogen. Nitrate represents the final form of nitrogen
resulting from the oxidation of nitrogenous compounds in the
wastewater. The wastewater nitrogen cycle is shown in Figure
21.22.
21.63 Factors Affecting Biological Nitrification
Because of current ammonia removal requirements and an-
ticipation of future "complete nitrogen removal" requirements,
you may be required to operate such an activated sludge plant.
If you are operating a plant of this type, there are seven princi-
pal control guidelines that you must consider to maintain the.
nitrification process at optimum performance levels:
1. Dissolved oxygen,
2. pH,
3. Wastewater temperature,
4. Nitrogenous food,
5. Detention time,
6. MCRT, F/M, or sludge age, and
7. Toxic materials.
Each of these guidelines must be properly controlled for the
successful operation of a biological nitrification process.
1. Dissolved Oxygen (DO)
Nitrification exerts a substantial oxygen requirement.
Each pound of ammonium-nitrogen that is nitrified requires
approximately 4.6 pounds of oxygen (4.6 kg 02/kg
NH+-N).
Nitrification appears to be uninhibited at DO concentra-
tions of 1 mgIL or more. To insure adequate nitrification, the
DO in the aeration tank must usually be maintained be-
tween 1.0 to 4.0 mgIL under average loading conditions.
This will include a reasonable DO safety factor. Under peak
loading, the DO may fall off somewhat, yet should never fall
below 1.0 mg/L.
The oxygen requirement may be calculated as shown in
the following example.
EXAMPLE
Determine the oxygen requirements for the effluent from a
10 MGD activated sludge plant with an average five-day BOD
of 30 mg/L and an average ammonium-nitrogen concentration
of 15 mg/L.
Known Unknown
Flow, MGD = 10 MGD Oxygen Requirement, lbs/day
BOD, mg/L = 30 mg/L
NH4+-N, mg/L =15 mg/L
1. Calculate the ammonium-nitrogen load in pounds per day.
NH^-N Load, = Flow, MGD x NH4-N, mg/L x 8.34 lbs/gal
Ibs/day = 1Q MQD >; 15 mg/L x g 34 ,bs/ga|
= 1,251 lbs NH4-N/day
2. Calculate the BOD load in pounds per day.
BOD, lbs/day = Flow, MGD x BOD, mg/L x 8.34 lbs/gal
= 10 MGD x 30 mg/L x 8.34 lbs/gal
= 2,502 lbs BOD/day
3. Calculate the ammonium-nitrogen oxygen requirement
(pounds per day of oxygen to oxidize ammonia (NH3) to
nitrate (N03).
Oxygen, lbs/day = NH4+-N,J^!-x 4.6 lbs Oxygen
(NH4+-N) day lbNH4+-N
= 1251lbs NH4_N x 4,6 lbs °*ygen
day lb NH4+-N
= 5,755 lbs Oxygen/day
4. Calculate the BOD oxygen requirement.
Oxygen, lbs/day = BOD.J^- x 1-5 lb» Oxygen
(BOD) day lb BOD
_ 2502 '^s BOD x 1.5 lbs Oxygen
day lb BOD
= 3,753 lbs Oxygen/day
5. Calculate the total oxygen requirement to properly oxidize
ammonium nitrogen (NH4+ -N) and biochemical oxygen
demand (BOD).
Total Oxygen = Oxygen, lbs/day + Oxygen, lbs/day
Requirement, (NH4 -N) (BOD)
lbs/day = 5 755 |bs/day + 3,753 ibs/day
= 9,508 Ibs/day
Because the rate of nitrification will vary significantly with
temperature and pH, compensation must be made for these
variations. During the summer months, the following
methods can be used to match the oxygen requirement to
your plant's oxygen capability. These methods attempt to
provide more oxygen for nitrification while trying to reduce
other oxygen demands.
a. Reduce the aeration system MLSS concentration.
b. Reduce the wastewater pH by reducing chemical addition
(if used).
c. Reduce the number of tanks in service while increasing
oxygen supply to the tanks remaining in service.
-------
Activated Sludge 103
AMMONIA
NlWWNWj
]£>(%ANI4
WiTl206gW-HHs]
3
a
I
S!
o
|!
1
AlMCbPHECl^
MiTCO^EN,
Nlfl2ATe
KrrCU^N, NO?
MiTCO&eN.MO^
Fig. 21.22 Wastewater nitrogen cycle
-------
104 Treatment Plants
2. pH
In many wastewaters, there is insufficient alkalinity ini-
tially present to leave a sufficient residual for buffering the
wastewater during the nitrification process. The signifi-
cance of pH depression in the process is that nitrification
rates are rapidly depressed as the pH is reduced below 7.0.
Because of the effect of pH on nitrification rate, it is espe-
cially important that there be sufficient alkalinity in the
wastewater to balance the acid produced by nitrification. A
pH of between 7.5 and 8.5 is considered optimal. Approxi-
mately 7.2 pounds of alkalinity are destroyed per pound
(7.2 kg/kg) of ammonia-nitrogen (NHs-N) oxidized. Caustic
or lime addition may be required to supplement moderately
alkaline wastewaters.
If it becomes necessary to add chemicals (preferably
lime) for pH adjustment, the required quantities of chemical
will vary with wastewater temperature, MLVSS concentra-
tion, influent ammonia-nitrogen concentration and the natu-
ral alkalinity of the wastewater. As the oxidation of
ammonia-nitrogen to nitrate-nitrogen destroys approxi-
mately 7.2 pounds of alkalinity per pound (7.2 kg/kg) of
ammonia-nitrogen, this loss of alkalinity must be added to
the chemical quantity calculated for pH adjustment. For op-
eration under the most adverse temperature and pH condi-
tions, sufficient lime must be added initially to raise the pH
into the desired range, and then 5.4 pounds of hydrated
lime per pound (5.4 kg/kg) of ammonia-nitrogen will be re-
quired to maintain the pH. Sufficient alkalinity should be
provided to leave a residual of 30 to 50 mg/L after complete
nitrification.
3. Temperature
The optimum wastewater temperature range is between
60 to 95 degrees F (15 to 35°C) for good nitrification opera-
tion. Nitrification is inhibited at low wastewater tempera-
tures and up to five times as much detention time may be
needed to accomplish "complete nitrification" in the winter
as is needed in the summer. The growth rate of nitrifying
bacteria increases as the wastewater temperature in-
creases and conversely it decreases as the wastewater
temperature decreases. Since there is no control over the
wastewater temperature, operating compensationsfor
slower winter growth rates are necessary. Increasing the
MLVSS concentration, the MCRT, and adjusting the pH to
favorable levels can be expected to provide substantial, if
not "complete," oxidation of ammonia-nitrogen com-
pounds. Under summer conditions, operation will be possi-
ble at less favorable pH levels and lower MLVSS concentra-
tions.
4. Nitrogenous Food
The growth rate of nitrifying bacteria (nitrosomonas and
nitrobacter) is affected very little by the organic load applied
to the aeration system. However, the population of the nit-
rifying bacteria will be limited by the amount of nitrogenous
food available in the wastewater. Organic nitrogen and
phosphorus-containing compounds as well as many trace
elements are essential to the growth of microorganisms in
the aeration system. The generally recommended ratio of
five-day BOD to nitrogen to phosphorus for domestic waste
is 100:5:1. Laboratory nitrogen determination (TKN) and
phosphorus determination analysis should be performed so
that you may add the supplemental phosphorus nutrient if
necessary. Phosphorus in the form of phosphate fertilizer
may be added and adjusted according to the five-day BOD
level and the TKN concentration in the wastewater.
5. Detention Time
The time required for nitrification is directly proportional to
the amount of nitrifiers present in the system. Because the
rate of oxidation of ammonia-nitrogen is essentially linear or
constant, short-circuiting must be prevented. The aeration
tank configuration should insure that flow through the tank
follows the plug-flow mixing model as closely as possible
and provides a minimum detention time of approximately
4.0 hours. Single-pass tanks may be modified and divided
into a series of three compartments with ports between
them to preclude short-circuiting. Not all of the various mod-
ifications to the activated sludge process are appropriate for
nitrification applications, although some see use only where
partial ammonia removal is required.
6. MCRT, F/M, or Sludge Age
To achieve the desired degree of nitrification, the MCRT
must be long enough (usually 4 days plus) to allow the
nitrifying bacteria sufficient time to grow. Since the nitrifying
bacteria grow much more slowly than the bacteria using the
carbonaceous compounds, it is possible to waste the nitrify-
ing bacteria from the system at a higher rate than their
growth rate. In simpler terms, this means that nitrification in
plants can be maintained only when the rate of growth of
nitrifying bacteria is rapid enough to replace organisms lost
through sludge wasting. When these bacteria can no longer
keep pace, the ability to nitrify decreases and may stop.
When reviewing the performance of your activated
sludge process for the selection of an optimum F/M ratio,
MCRT or sludge age, oxygen requirements for bacteria
using the carbonaceous compounds should be considered
along with nitrification requirements. These guidelines
should be selected to provide the degree of nitrification re-
quired by the discharge permit. If the ammonia-nitrogen
limit is being exceeded, the MCRT or sludge age should be
increased. Increasing these guidelines will increase the
MLVSS and consequently decrease the F/M ratio. With the
other conditions (discussed above) constant, a definite rela-
tionship will exist between the weight ratio of the
ammonia-nitrogen oxidized per day to the MLVSS under
aeration.
The growth of cell mass from the oxidation of ammonia is
about 0.05 lbs per lb (0.05 kg/kg) of ammonia-nitrogen
oxidized. As a result, the degree of nitrification will have
little effect on the net sludge yield and WAS rates.
7. Toxic Materials
Various types of toxic materials which will inhibit the nit-
rification process (in concentrations greater than those indi-
cated) are shown below.
a. Halogen-substituted phenolic compounds, 0.0 mg/L
b. Thiorea and thiorea derivatives, 0.0 mg/L.
c. Halogenated solvents, 0.0 mg/L.
d. Heavy metals, 10 to 20 mg/L.
e. Cyanides and all compounds from which hydrocyanic
acid is liberated on acidification, 1 to 2 mg/L.
f. Phenol and cresol, 20 mg/L.
Pretreatment alternatives provide a degree of removal of
the toxicants present in raw wastewater. However, the
types of toxicants removed by each pretreatment stage
vary among the alternatives. Chemical primary treatment
can be used where toxicity from heavy metals is the major
problem. Lime primary treatment is one of the most effec-
-------
Activated Sludge 105
tive processes for removal of a wide range of metals. Chem-
ical treatment is usually not effective for removal of organic
toxicants, unless it is coupled with a carbon adsorption step
such as in a physical-chemical treatment sequence.
When materials toxic to nitrifiers are present in the raw
wastewater on a regular basis, the pretreatment technique
most suitable for their removal can be used in the plant to
safeguard the nitrifying population. The determination of the
most suitable pretreatment process application may be ini-
tially developed based on BENCH SCALE ANALYSIS15 to
screen alternatives.
The particular pretreatment technique that is effective
may also indicate the type of toxicant that is interfering with
nitrification and may permit identification and elimination of
the source. Subsequent specific analysis can then be run in
the identified category of compounds. If the toxicants can-
not be eliminated by a source control program, often a pilot
study of the process identified by the bench scale tests can
be justified to confirm the process selection.
21.64 Rising Sludge and the Nitrification Process
Rising sludge caused by unwanted denitrification in the
clarifiers may occasionally plague your nitrification operation.
Denitrification occurs because the facultative heterotrophic or-
ganisms in the biological sludge in the clarifier accomplish nit-
rate reduction by what is known as a process of nitrate dissimi-
lation. In this process, nitrate and nitrite replace oxygen in the
respiratory process of the organisms under oxygen-deficient
conditions. This nitrate dissimilation allows bubbles of nitrogen
gas and carbon dioxide to adhere to the sludge floe surface
resulting in rising sludge.
The degree of stabilization of the sludge in the aeration tank
(depending on detention time and DO) also has a profound
effect on denitrification in the clarifier. Clarifier sludges contain-
ing partially oxidized or unoxidized organics float more readily
than well oxidized sludges. Wastewater temperature is also
important as it affects the rate of denitrification and therefore
affects the rate of gas and bubble formation (depends on warm
temperatures and denitrification rates).
Some considerations for good clarifier operation to preclude
denitrification in the clarifier are discussed in the following sec-
tions.
1. The settled sludge must be quickly removed from the
clarifier to minimize the occurrence and duration of
oxygen-deficient conditions. The RAS rate may be propor-
tioned with the aerator influent flow to maintain an essen-
tially "zero" sludge blanket in the clarifier.
2. Since the nitrification sludge is lighter and does not com-
pact as well as carbonaceous sludges, sludges with low
SVI values are preferable. They can be withdrawn from the
clarifier faster. Since the saturation level of nitrogen is
greater in deep tanks than laboratory cylinders, bubbles will
form and sludges will float faster in the laboratory than in
the field.
3. There is a minimum concentration of nitrate-nitrogen below
which there is insufficient nitrogen to cause rising sludge. In
weak wastewaters or for those plants in which nitrification is
suppressed, rising sludge will not occur.
4. A drop in wastewater temperature will reduce denitrification
rates and may render rising sludge a problem only under
warmer wastewater conditions.
21.65 Acknowledgments
Major portions of Section 21.6 were taken from PROCESS
CONTROL MANUAL FOR AEROBIC BIOLOGICAL WASTE-
WATER TREATMENT FACILITIES, Municipal Operations
Branch, Office of Water Program Operations, U. S. Environ-
mental Protection Agency, Washington, D. C. 20460, NIT-
RIFICATION AND DENITRIFICATION FACILITIES, WASTE-
WATER TREATMENT, EPA Technology Transfer Publication,
U. S. Environmental Protection Agency, Center for Environ-
mental Research Information, 26 West St. Clair Street, Cincin-
nati, Ohio 45268, and PROCESS DESIGN MANUAL, NITRO-
GEN CONTROL, U. S. Environmental Protection Agency, Cen-
ter for Environmental Research Information, 26 West St. Clair
Street, Cincinnati, Ohio 45268.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 115.
21.6A List the harmful effects that could result from the dis-
charge of nitrogenous compounds from wastewater
treatment plants.
21.6B What are the principal control guidelines for biological
nitrification?
21,6C How can you control rising sludge that results from
unwanted denitrification?
21.7 REVIEW OF PLANS AND SPECIFICATIONS —
PURE OXYGEN ACTIVATED SLUDGE SYSTEMS
21.70 Need to be Familiar with System
The operational staff that reviews the plans and specifi-
cations for a pure oxygen plant should be very familiar with the
activated sludge process. A tour through an existing pure oxy-
gen system would be extremely helpful. Specific questions re-
garding the operation and maintenance of the facility can be
answered by manufacturers or other treatment plant personnel
whose systems use pure oxygen. Also, sources of industrial
waste discharges should be identified and investigated for
possible toxic wastes, heavy load contributions, and seasonal
fluctuations. Be sure your plant has the capacity and flexibility
to treat all industrial wastes.
After plans are submitted, the operation and maintenance
staff should review all areas of the plans and specifications
with special attention directed towards:
1. Physical plant layout,
2. Oxygen generation equipment,
3. Reactor basins (aeration tanks),
4. Oxygen safety and process instrumentation, and
5. Preventive maintenance program.
21.71 Physical Layout
The pure oxygen generation system should be located near
the plant maintenance facilities. If this is not possible, an area
within the system should be included. This will be an aid during
major maintenance on the facility. Major pieces of equipment
should be easily accessible. A crane or other lifting devices
should be provided to lift large pieces of equipment during
ie Bench scale analysis. A method of studying different ways of treating wastewater and solids on a small scale in a laboratory.
-------
106 Treatment Plants
major overhauls. Road access and loading facilities should
also be provided. Sources of noise and vibrations should also
be considered. Most equipment in oxygen production systems
produce noise similar to air blower systems and, if not properly
installed, could produce vibrations which could be transferred
through walls or structures adjacent to such facilities. In offices
or laboratories, noise considerations should also be reviewed,
especially in plants where housing areas are near the oxygen
generation site. Silencers are typically provided with the gen-
eration equipment. The overall layout of the system should
also allow for expansion of the wastewater treatment plant and
oxygen production facilities.
21.72 Oxygen Generation Equipment
If the oxygen generation equipment is located within a build-
ing, it should be well ventilated. In areas of extremely hot tem-
peratures, vent fans on the roof would be of benefit. A heating
system is normally not required if the lowest temperature does
not remain below freezing for long periods of time. The com-
pressor equipment generates sufficient heat which can heat
the building. Systems located in the open must be designed to
operate during the most severe weather conditions.
Individual equipment suppliers recommended by the design
engineer should be contacted for specific answers to the in-
stallation of compressors, valve skids or oxygen storage
facilities. Start-up controls, instrumentation, and safety devices
should be carefully reviewed. A vibration shutdown system on
compressors should be included. Prior to actual start-up, the
manufacturer should run each compressor and check the
equipment for proper operation, including excessive vibration.
When everything operates in an acceptable manner, calibrate
and set vibration monitor to shut down the equipment if exces-
sive vibration develops. This monitor insures proper operation
and protection of the equipment. If a separate water cooling
system is provided, the water used should be treated to avoid
scaling and corrosion of the units.
A specific cleaning requirement should be specified in the
plans and specs which would include oxygen pipe lines, sam-
ple lines, valve skids and other equipment to insure equipment
protection during start-up. Contamination from dirt, grease,
and welding slag should never be allowed in a pure oxygen
atmosphere. The specifications should include a requirement
that equipment manufacturers be present during the start-up
and provide a training program to the operations staff. A rec-
ommended spare parts list and source of suppliers or vendors
should be provided.
Major oxygen feed lines, valves, sample tubing and electri-
cal systems must be tagged and indicated in the "as built"
drawings and instruction booklets. Specialized drawings and
instruction booklets must include detailed descriptions on pre-
ventive maintenance, safety and operation instructions. At
least four (4) copies should be provided. Any modification dur-
ing start-up should be indicated in these manuals.
21.73 Reactors (Aeration Tanks)
The location of the reactor should be reviewed with consid-
eration for future expansion. Reactors located above normal
ground elevation should have facilities provided to remove
equipment located on the deck. Oxygen reactors are usually
completely covered and access to each basin must be pro-
vided through a sealed and air-tight lid or locking manhole.
Gas sampling lines or other conduits can be installed within the
deck. If they are located on the deck, they should be protected
and indicated by safety signs to avoid a tripping hazard.
The deck should be a rough surface such as broomed con-
crete. A completely smooth deck is a slipping hazard if water is
allowed to collect. Warning signs should be provided at each
entrance to indicate the presence of oxygen and that no smok-
ing or open flames are allowed. A well lighted deck is helpful
for night shift operators.
Interior metal such as weir plates, mixer blades and valves
should be constructed of stainless steel, carbon steel, or
coated carbon steel as dictated by the specific sen/ice. A good
protective coating should also be provided over any surfaces
that may corrode. Control valves should have position indi-
cators and be located in such a manner that preventive main-
tenance may be performed without draining the reactor.
Equipment on the reactor should be tagged with equipment
numbers corresponding to electrical control panel facilities.
21.74 Safety and Instrumentation
Operator safety and process safety are both very important
in pure oxygen systems. Safety signs, belt guards, tempera-
ture shutdown switches and overload protection devices
should be provided and indicated in the specifications by the
engineer. A system "emergency trip switch" station should be
provided and located away from major electrical controls. If
tripped during a major mechanical or electrical equipment fail-
ure, the entire oxygen operation shuts down without endanger-
ing personnel or equipment.
The specifications should include a requirement that the
equipment supplier provide a training class to instruct person-
nel on operation, maintenance, and safety hazards involved in
the pure oxygen generation and waste treatment process.
Process control involves major instrumentation and control
systems. Preventive maintenance on such systems is ex-
tremely technical in nature and should be completely under-
stood before maintenance personnel attempt to maintain such
systems. The design engineer can provide the necessary
background to ensure proper training.
One major area of concern is instrumentation sample tubing
and heat trace lines. These systems are the main control and
safety equipment functions of the entire system. To avoid
costly errors, the manufacturer or equipment supplier should
be consulted. If sample lines for lower explosive limit (L.E.L.) or
system pressure sensing control lines are incorrectly installed,
the entire operation could fail. If they must be installed under
roadways, they should be protected within rigid, sealed conduit
to prevent being crushed or kinked.
21.75 Preventive Maintenance
Most specifications would not include specific requirements
for preventive maintenance. The system design should give
consideration to the staff size and experience needs of the
system. The design engineer could direct key personnel to-
wards the needs of the system and requirements. Manufactur-
ers can provide maintenance contracts which provide preven-
tive maintenance as well as major tune-ups. Spare parts can
be included but can be purchased separately. The cost of such
contracts depends on the needs of the system and the options
involved.
of \&&o\a 4 o$4r
on
ACtfVAlEP
Please work the discussion and review questions next.
-------
Activated Sludge 107
DISCUSSION AND REVIEW QUESTIONS
(Lesson 4 of 4 Lessons)
Chapter 21. ACTIVATED SLUDGE
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 3.
15. Why would an operator want to monitor the influent to a
wastewater treatment plant?
16. How can undesirable constituents be detected in a plant
influent in addition to the use of automatic monitoring
units?
17. Why should an operational strategy be developed before a
toxic waste is discovered in the influent to a plant?
18. Why do some industries pretreat industrial process
wastewaters?
19. Why does the operator of an industrial waste treatment
plant have to know the flow and waste characteristics of
the wastewater being treated?
20. How do toxic materials enter the waste stream?
21. Why should grit, soil, grease and oil be removed from the
waste stream?
22. How can the amount of nutrients to be added each day be
determined?
23. How does ammonia stripping remove nitrogen from
wastewater?
24. How is the nitrification process influenced by tempera-
ture?
25. How would you handle materials toxic to a nitrification
process?
Please work the objective test next.
21.8 METRIC CALCULATIONS
This section contains the solutions to all problems in this
chapter using metric calculations.
21.80 Conversion Factors
ft x 0.3048
m x 3.281
lb x 0.454
kg x 2.205
gal x 3.785
liter x 0.264
MGD x 3785
cu m/day x 0.000264
GPM x 0.063
Usee x 15.85
1000 L
1 L
21.81 Problem Solutions
FROM SECTION 21.310 SLUDGE AGE CONTROL
1. Calculate the sludge age in days.
Known Unknown
Infl. Flow, cu m/day = 28,000 cu m/day Sludge Age, days
Prim. Effl. SS, mgIL = 100 mgIL
Tank Vol., cum = 2300 cu m
MLSS, mgIL = 2200 mg/L
No. of tanks = 2 tanks
Sludge Age, days = Solids under aeration, kg
Solids added, kg/day
a. Determine the solids under aeration in kilograms.
Solids under = No. x Tank Vol., x MLSSrng x 1 kg
aeration, kg Tanks cum/lank L 1 000,000 mg
x 1,0001
1 cu m
= 2 tanks x 2300 cum * 2300 m? x 1 *9
tank L 1,000,000 mg
x 1.000 L
1 cu m
= 10,120 kg
b. Calculate the solids added in kilograms per day.
Solids added, _ Intt. Flow x Pri. Etf. ss, x 1 kg x 1,000 L
kg/day CU m/day mg IL 1 goo,000 mg 1 cu m
= 3« nnncu m x 100!!!? x 1 k9 x 1000 L
day L 1,000,000 mg 1 cu m
= 2,BOO kg/day
c. Determine the sludge age in days.
Sludge Age, _ Solids under aeration, kg
days Solids added, kg/day
= 10,120 kg
2,800 kg/day
= 3.6 days
= m
= ft
= kg
= lb
= liters
= gal
= cu m/day
= MGD
= LI sec
= GPM
= 1 cu m
= 1 kg
-------
108 Treatment Plants
2. Calculate the waste activated sludge (WAS) flow rate using
the sludge age control technique.
Known
Solids Added, kg/day
Solids Aerated, kg
RAS Susp. Sol., mg/L
Desired Sludge Age, days
Unknown
= 2,800 kg/day WAS Flow, cu m/day
= 15,000 kg
= 6,300 mg/L
= 5 days
Current WAS Rate, kg/day = 2000 kg/day
a. Calculate the desired kilograms of solids under aera-
tion (MLSS) for the desired sludge age of 5 days.
Desired solids = Solids Added, kg/day x Sludge Age, days
under aeration,
kg = 2,800 kg/day x 5 days
= 14,000 kg
b. Calculate the additional WAS flow, cu m/day, to main-
tain the desired sludge age.
Solids Aerated, kg - Desired Solids, kg
WAS Flow,
cu m/day
RAS Susp. Sol., mgIL
1,000,000 mg 1 cu m
1 kg
1,000 L
= (15,000 kg - 14,000 kg) 1,000,000 mg
6,300 mg/L
1 cu m
1 kg
1,000 L
1,000 kg/day*
1,000,000 mg
1 kg
1 cu m
1,000 L
6,300 mg/L
= 159 cu m/day
* Remove an additional 1,000 kg during a 24-hour period.
c. Determine the total WAS flow in cubic meters per day.
Total WAS
Flow,
cu m/day
Current WAS, cu m/day + Additional WAS, cu m/day
_ Current WAS, kg/day
RAS SS. mg/L
1.000,000 mg
1 kg
1 cu m
159 1
1,000 L
day
_ 2,000 kg/day
6,300 mg/L
cu m
day
1,000,000 mg
1 kg
1,000 L
day
159
= 477 cu m/day
= 5.5 liters/sec
day
1,000L
1 cu m
1 day
86,400 sec
FROM SECTION 21.311 FIM CONTROL
1. Determine the food to microorganism (F/M) ratio for an acti-
vated sludge plant.
Known Unknown
Infl. Flow, cu m/day = 28,000 cu m/day
COD, mg/L = 100 mg/L
Solids Under Aeration, = 15,000 kg
kg
MLSS VM, % = 70%
F/M, kg COD/day/
kg MLVSS
a. Calculate the food to microorganism ratio.
F/M k9 COD/day
kg MLVSS
Flow, cum _ COD,rug x 1kg 1,000 L
day L 1,000,000 mg i cum
Solids Under Aeration, kg * VM portion
28,000 cum x 100 mg 1kg 1,000 i.
day t- 1,000,000 mg 1 cu m
15,000 kg x 0.70
2,800 kg COD/day
10,500 kg MLVSS
= 0 27 kg COD/day/kg MLVSS
2. Determine the desired waste activated sludge (WAS) flow
rate using the F/M control technique.
Known
Infl. Flow, cu m/day
Tank Vol., cu m
COD, mg/L
MLSS, mg/L
MLSS VM, %
RAS Susp. Sol., mg/L
Desired F/M,
kg COD/day
Unknown
= 28,000 cu m/day WAS Flow, cu m/day
= 4,600 cu m
= 100 mg/L
= 3,300 mg/L
= 70%
= 6,300 mg/L
= 0 2g kg COD/day
kg MLVSS
kg MLVSS
Current WAS, cu m/day = 320 cu m/day
a. Determine COD applied in kilograms per dav.
COD, kg/day = Flow, cu m x COD,!?? x J k9
day L 1,000,000 mg
= 28,000 cu m
day
= 2,800 kg/day
100 H!£ :
L
1,000 L
1 cu m
1,000 L
1,000,000 mg 1 cum
1 kg
b. Calculate the desired kilograms of MLVSS.
Desired MLVSS,
kg
COD Applied, kg/day
F/M, kg COD/day/kg MLVSS
2,800 kg COD/day
0.29 kg COD/day/kg MLVSS
9,655 kg MLVSS
C.
Determine the desired kilograms of MLSS.
Desired MLVSS,= Desired MLVSS, kg
kg MLSS VM portion
= 9,655 kg
0.70
= 13,793 kg
d. Determine the actual kilograms of MLSS under aera-
tion.
Actual MLSS,
Kg
Tank Vol.,
cu m
x MLSS, JUi
L
1 kg
= 4,600 cu m x 3,300
= 15.160 kg
mg
x 1.000Z.
1,000,000 mg 1 cu m
1 kg v 1,000 L
1,000,000 mg 1 cu m
-------
Activated Sludge 109
e. Calculate the additional WAS flow in cubic meters per
day to maintain the desired F/M ratio.
Additional _ (Solids Aerated, kg Desired Solids, kg)
RAS SusP S°'" m*IL
1,000,000 mg 1 cu m
1 kg 1,000 L
_ (15,580 kg - 13,793 kg) x 1,000,000 mg x 1 cu m
6,300 mgIL 1kg 1,000 L
_ 1,787 kg/day* x 1,000,000 mg x 1 cu m
6,300 mg IL 1kg 1,000 L
— 284 cu m/day
Remove an additional 1,787 kg during a 24-hour period.
f. Calculate the total WAS flow in cubic meters per day
and liters per second.
Total WAS
Flow,
cu m/day
_ Current WAS Flow, + Additional WAS Flow,
cu m/day cu m/day
= 320 cu m/day + 284 cu m/day
= 604 cu m/day x 1 'Q00 L x 1 6aV
1 cu m 86,400 sec
= 7.0 liters/sec
FROM SECTION 21.312 MCRT CONTROL
1. Determine the waste activated sludge (WAS) flow rate
using the MCRT technique.
Known
Inft. Flow, cu m/day
Tank Vol., cu m
MLSS, mgIL
RAS SS, mgIL
Effl. SS, mgIL
Unknown
= 28,000 cu m/day WAS Flow, cu m/day
= 4,600 cu m
= 3,300 mg IL
= 6,300 mg/*.
15 mg IL
Desired MCRT, days = 8 days
MCRT days = Suspended Solids in Aerator, kg
Susp. Sol. wasted, kg/day + Susp. Sol. in Effl., kg/day
a. Determine suspended solids in total secondary system
in kilograms.
SS in Sec. _ Aerator Vol., x MLSS, x 1 kg x 1,000 L
System, kg cu m mg IL 1 qoo.OOO mg 1 cum
= 4,600 cu m x 3,300 mg/L x 1*0 x 1'000*-
1,000,000 mg 1 cu m
= 15,180 kg
b. Determine suspended solids lost in effluent in kilograms
per day.
SS lost in _ Infl. Flow x Effl. SS, * 1 kg x 1,000 L
cum/day mgIL 1,000,000 mg 1 cum
Effl.,
kg/day
= nnn cu m * is m9 v 1 k9 v 1,000 L
day L 1,000,000 mg 1 cu m
= 420 kg/day
c. Determine the desired suspended solids wasted in kilo-
grams per day.
MCRT, days
SS in Aerator, kg
SS Wasted, kg/day + SS in Effl., kg/day
SS Wasted, = SS in Aerator, kg -SS in Effl., kg/day
kg/day MCRT, days
= 15,180 kg - 420 kg/day
8 days
= 1,898 kg/day - 420 kg/day
= 1,478 kg/day
d. Determine the waste activated sludge (WAS) flow rate in
cubic meters per day.
SS Wasted, _ WAS Flow, x RAg ss x 1 x 1.000 L
kg/day cu m/day L 1 Ooo,000 mg 1 cu m
WAS Flow, SS Wasted, kg/day
cu m/day
1 kg
1,000 L
RAS SS, mg )
L 1.000,000 mg 1 cu m
1,478 kg/day
1 kg
1,000 L
6,300 mg x
L 1,000,000 mg 1 cum
235 cu m/day x 1'000 L x 1 day
1 cu m 86,400 sec
2.7 liters/sec
FROM SECTION 21.313 VOLATILE SOLIDS INVENTORY
1. Determine the adjusted waste activated sludge pumping
rate based on changes in the return activated sludge vol-
atile suspended solids concentration.
Known Unknown
WAS Flow, cu m/day = 190 cu m/day Adjusted WAS Flow,
Llsec = 2.20 Usee cu m/day
RAS VSS, mgIL = 6,000 mg/L Adjusted WAS Flow,
(day 1) 1/sec
RAS VSS, mgIL = 7,500 mg IL
(day 2)
a. Calculate the adjusted waste activated sludge (WAS)
flow in cu m/day and liters/sec.
Adj. WAS = RAS VSS for day 1, mgIL x WAS Flow, cu m/day
Flow,
cu m/day
RAS VSS for day 2, mgIL
_ 6,000 mg//. x 190 cu m/day
7,500 mg/L
= 152cu m/day
Adj. WAS RAS VSS for day 1, mg/L x WAS Flow, Llsec
L/sec RAS VSS ,or day 2' mg/L
_. 6,000 mg/L x 2.20 L/sec
7,500 mg/L
= 1.76 liters/sec
2. Determine the adjusted waste activated sludge pumping
rate based on a pumping period of four hours.
Known Unknown
WAS Flow, cu m/day = 160 cum/day WAS Flow, cu m/day for
Wasting Time, hr/day = 4 hrs/day 4 hours/day wasting
period
-------
110 Treatment Plants
a. Calculate the WAS flow for a four hour per day wasting
period.
New WAS = WAS Flow, x 24 hr/day
Flow cu m/day wasting Period, hr/day
cu m/day
160
cum 24 hr/day
day 4 hr/day
= 960 cu m/day
FROM SECTION 21.314 MLVSS Control
1. Determine the desired waste activated sludge (WAS) flow
based on the MLVSS control method.
Known
Tank Vol., cu m
MLSS, mgIL
RAS SS, mgIL
Volatile Portion
= 4,600 cu m
= 3,300 mg/L
= 6,300 mg/L
= 0.70
Unknown
Desired WAS Flow,
cu m/day
Desired MLVSS, kg = 9,650 kg
Current WAS Flow, = 550 cu m/day
cu m/day
a. Determine mixed liquor volatile suspended solids
(MLVSS) under aeration in kilograms.
Actual
MLVSS, kg
Tank Vol.. x MLSS,
cu m mg/L
1 k9 _ x 1-P9PJ-
1,000,000 mg 1 cu m
3,300 -mQ-
L
0.70
1 kg
1,000 J.
.1,000,000 mg 1 cu m
10,626 kg
b. Determine the kilograms of volatile solids to be wasted.
Amount = Actual MLVSS, kg - Desired MLVSS, kg
Wasted, kg = 1Q 626 kg _ g 65Q kg
= 976 kg to be wasted per day
c. Determine the additional waste activated sludge (WAS)
flow in cubic meters per day.
Ar"°un' . = WAS f'ow' X RAS SS, mg/L x Volatile
Wasted, cu m/day
kg/day
1 kg
1,000 L
1,000,000 mg 1 cu m
WAS Flow, _ Amount Wasted, kg/day x 1,000,000 mg x 1 cu m
cum/day ras SS, mg/L x Volatile 1kg 1,000 L
= 6,300 mg/L x 0.70 x 1'000'000 mg x 1 cu m
1 kg 1,000 L
= 221 cu m/day
d. Determine the desired WAS flow in cubic meters per
day.
Desired WAS _ Current WAS, + Additional WAS
Flow, — 'J~"
cu m/day
cu m/day cu m/day
= 550 cu m/day + 221 cu m/day
771 cu m/day x 1'000f- x
1 day
1 cu m 86,400 sec
FROM SECTION 21.563 NUTRIENT ADDITION
SAMPLE AMMONIA ADDITION CALCULATIONS
Known Unknown
Primary Effluent, 24-hour = 554 mg/L NH3 Added, kg/day
Composite Total Organic
Carbon (TOC) Rotameter Setting, %
BOD: TOC Ratio = 2.2:1
Calculated Sample BOD = 1,219 mg/L
2.2 x 554 mg/L
Estimated Flow for the
Next 24 hours
Final Effluent, 24-hour
Composite NH3-N
Concentration
= 12,500 cu m/day
= 0.88 mg/L
= 8.36 mg/L
Primary Effluent,
24-hour Composite
NHj-N Concentration
1. Estimate the present day's BOD loading in kilograms of
BOD per day.
BOD Loading, = Row cu m x BQD mg
kg/day ' day l
1 kg
1000 i
1,000,000 mg 1 cu m
1 kg
1000 L
= 12,500 x 1,219™.? >
day L 1,000,000 mg 1 cu m
= 15,238 kg/day
2. Calculate the amount of ammonia (NH3-N) required in kilo-
grams per day. Assume an ammonia requirement of 2 kg of
ammonia per 100 kg of BOD.
NH3 Required = BQD kg/day x NH3-N, kg
kg/day BOD, kg
15,238 kg/day x
305 kg/day
2 kg NH3-N
100 kg BOD
8.9 liters/sec
3. Estimate the ammonia (NH3-N) supplied to the aeration ba-
sins in the primary clarifier effluent.
NH3 Supplied, _ Row JCUJ" x MHj mg V 1 *<9 v IQOOJ^
kg/day ' day 3' L 1,000,000 mg 1 cu m
= 12,500X 8.36 1!? x 1 ^9 x 1000 L
day L 1,000,000 mg 1 cu m
= 104 kg NH3-N/day
4. Determine the amount of ammonia (NH3-N) that must be
added to the primary effluent.
^kg/day^ = ^ec'u'red' k9/day - NH3 Supplied, kg/day
= 305 kg/day - 104 kg/day
= 201 kg NH3-N/day
NOTE: Effluent NH3-N concentration is 0.88 mg/L which is a satisfac-
tory (possibly a little high) level.
5. Calculate the rotameter setting. The rotameter constant is
2.5 kg NHj-N for a 24-hour period for each one percent.
Rotameter _ NH3-N Added, kg/day
Setting, % 2.5 kg NH3-N/day/%
= 201 kg NH3-N/day
2.5 kg NH3-N/day/%
= 80%
-------
Activated Sludge 111
FROM SECTION 21.566 SLUDGE WASTING
SAMPLE WASTING FORMULA CALCULATIONS
Known
Final Aeration Cell MLSS, mgIL = 2,420 mg/L
Primary Effluent 24-hour Composite = 554 mg/L
Sample, TOC, mg IL
Desired MLSS Set Point, mg//.
Return Sludge (Waste) SS, mg IL
Estimated Flow for the Next 24-hours,
cu m/day
= 2,200 mg/L
= 7,160 mg/L
= 12,500 cu m/day
Volumes and Assumptions
1. Volume of each aeration cell 1,150 cu m
2. Nine aeration cells, total aeration volume 10,350 cu m
3. Solids in secondary clarifiers are equal to 15 percent of the
solids within the aeration basins.
4. MLSS of final aeration basin is representative of the MLSS
of all the aeration basins. 9 x final aeration basin MLSS =
total aeration solids.
5. Yield factor = 0.5 kg MLSS solids produced per kg BOD
removed.
6. Estimate primary effluent flow from recent records and ac-
tual flow data for first 8 to 10 hours of the day. Take into
consideration whether the sludge wasting system is in op-
eration.
7. Conversion factor = Yield x BOD:TOC ratio
1.1 = 0.5 x 2.2
CALCULATIONS
1. Calculate the solids in the system in kilograms. Since solids
in the secondary clarifiers are 15 percent of the solids in the
aeration basins, multiply the solids in the aeration basins by
1.15.
Solids in
System, kg
Aeration
Final Aeration
Volume, cu m Cell MLSS, mg/L
1 Kg
1000 L
x 1.15
¦ 10,350 cu m x 2420 -!!!i *
L 1.000,000 mg
' 28,800 kg
1,000,000 mg 1 cu m
1kg 1000 L
-x 1.15
2. Estimate the solids produced in the system in kilograms per
day. Assume 1.1 kilograms of solids are produced per kilo-
gram of TOC.
1.1 kg Solids/day
L x TOC, kg/day
1 kg TOC/day
Solid*
Produced,
kg/day
• 1.1 x Flow, 01 m x TOC, mgIL x -
day
' 1.1 x 12,500 (*ifn x 554 ^x.
1 kg
10001
1,000,000 mg 1 cu m
1 kg 1000L
day
1,000,000 mg 1 cu m
¦ 7,610 kg/day
3. Determine the desired kilograms of solids in the system
based on a MLSS set point of 2,200 mg/L. Assume solids in
the secondary clarifiers are 15 percent of the solids in the
aeration basins (multiply by 1.15).
Qatlrrl ^ Aeration MLSS Set
9oNds in "" Volume, cu m Point, mglL
8y«wm, kg
1 kg
> 10,350 cu m x 2.200
¦ 26,185 kg
mg
1000 L
1,000,000 mg 1 cu m
1kg 1000 L v
1,000,000 mg 1 cu m
4. Calculate the sludge wasting amount in kilograms per day.
(Solids in _ Desired Solids) + Solids Produced,
Sludge _ System, kg in System, kg kg/day
Amount, Waste During 1 Day
kg/day
(28,800 kg - 26,185) + 7,618 kg
1 day
= 2615 kg/day + 7,618 kg/day
= 10,233 kg/day
day
5. Calculate the sludge wasting rate in cubic meters per day.
Sludge Wasting
Sludge _ Amount, kg/day 1,000,000 mg 1 cu m
Wasting Rate, ~ ... . . x x
cu m/day w¥?e 1 k8
1000 L
SS, mg/L
10,233 kg/day 1,000,000 mg 1 cu m
7,160 mgIL 1kg 1000 L
¦¦ 1,430 cu m/day
FROM SECTION 21.63 FACTORS AFFECTING BIOLOGI-
CAL NITRIFICATION
1. Determine the oxygen requirements in kilograms per day.
Known Unknown
Flow, cu m/day = 40,000 cu m/day Oxygen Requirement, kg/day
BOD, mg/L = 30 mg/L
NH+-N, mg/L = 15 mg/L
a. Calculate the ammonium-nitrogen load in kilograms per
day.
NH4 -N Load,
kg/day
cum „„+ „ mg
¦ Flow, x NH4 -N, —
Day
cu m . _ mg
= 40,000 x 15 1
day L
¦ 600 kg/day
1 kg
1.0001.
L 1,000,000 mg 1 cu m
1 kg 1.0001.
1.000,000 mg I cum
b. Calculate the BOD load in kilograms per day.
BOD. kft'day
cu m ___
= Flow, x BOD
day
cu m
= 40,000
day
= 1,200 kg/day
_mg
L
1 kg
1,000,000 mg
aoJUfl V 1*0
1,0001
1 cu m
1,000 L
1,000,000 mg 1 cu m
c. Calculate the ammonium-nitrogen oxygen requirement
(kilograms per day of oxygen to oxidize ammonia (NH3)
to nitrate (NO3)).
Oxygen, ^ nh + -n kg v 4.6 kg Oxygen
(1$-% ' ' "1
= 600 kg NH+-N X 4 6 k9 Oxygen
day kg NH^"-N
= 2,760 kg Oxygen/day
d. Calculate the BOD oxygen requirement.
Oxygen,
kg/day
(BOD)
= BOD, x 1-5 kg Oxygen
day
kg BOD
= 1,200 k9 600 x 15 k9 Oxygen
day kg BOD
= 1,800 kg Oxygen/day
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112 Treatment Plants
e. Calculate the total oxygen requirement to properly
oxidize ammonium-nitrogen (NH^-N) and biochemical
oxygen demand (BOD).
/>
CZ7
Total Oxygen
Requirement,
kg/day
Oxygen, kg/day , Oxygen, kg/day
(NH„+-N) (BOD)
2,760 kg/day + 1,800 kg/day
4,560 kg/day
cm
SUGGESTED ANSWERS
Chapter 21. ACTIVATED SLUDGE
Volume III. Pure Oxygen Plants and Operational Control Options
Answers to questions on page 43.
21.OA Pure oxygen systems dissolve oxygen with a higher
efficiency for use by microorganisms treating the
wastes. This allows the use of smaller reactor tanks
than air activated sludge tanks. The sludge produced
has improved settleability and dewaterability.
21.OB Biological nitrification can remove ammonia from
wastewater by converting it to nitrate.
Answers to questions on page 47.
21.1 A Pure oxygen reactors are staged to increase the effi-
ciency of the use of oxygen.
21.1B As the pure oxygen flows from one stage to the next
stage, the oxygen is diluted by the carbon dioxide pro-
duced by the microorganisms and the nitrogen
stripped from the wastewater being treated.
Answers to questions on page 50.
21.1C The two methods commonly used to produce pure
oxygen are:
1. Pressure Swing Adsorption (PSA) Oxygen Gen-
erating System;
and
2. Cryogenic Air Separation Method.
21.1D Cryogenics means very low temperature.
21.1 E Cryogenic plants are usually shut down once a year
for approximately five to seven days for maintenance.
Answers to questions on page 52.
21.1F Special measurements used to control pure oxygen
systems include:
1. Reactor vent gas;
2. Reactor gas space pressure; and
3. Dissolved oxygen.
21.1G Hydrocarbons can be detected before they reach the
reactor by installing an L.E.L. detector in the plant
headworks.
END OF ANSWERS TO QUESTIONS IN LESSON 1
Answers to questions on page 55.
21.2A 1. MLSS, Mixed Liquor Suspended Solids.
2. MLVSS, Mixed Liquor Volatile Suspended Solids.
3. RAS, Return Activated Sludge.
4. F/M, Food to Microorganism Ratio.
21,2B The two basic approaches that can be used to control
the RAS flow rate are:
1. Controlling the RAS flow rate independently from
the influent flow; and
2. Controlling the RAS flow rate as a constant per-
centage of influent flow.
Answers to questions on page 55.
21,2C The sludge blanket depth should be kept to one to
three feet (0.3 to 1 m) as measured from the clarifier
bottom at the sidewall.
21.2D The sludge blanket depth should be measured at the
same time every day during the period of maximum
flow and highest solids loading rate.
Answers to questions on page 58.
21.2E Techniques used to determine the rate of RAS flow
include:
1. Monitoring the depth of the sludge blanket;
2. Settleability approach; and
3. SVI approach.
21,2F Sludge is allowed to settle 30 minutes in the settleabil-
ity test.
21.2G Known Unknown
Infl. Flow, MGD = 4 MGD RAS Flow MGD
SI. Set. Vol (SV), mlIL = 250 mlIL
1. Calculate RAS flow as a percent of influent flow.
RAS Flow, % = SV, ml IL x 100%
1,000 mlIL - SV, ml IL
= 250 ml/l x 1QQ%
1,000 mlIL - 250 ml IL
= 250 ml IL x 1QQ%
750 ml/*.
= 33% of influent flow rate
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Activated Sludge 113
2. Calculate RAS flow, MGD.
= RAS Flow, decimal x Infl. Flow, MGD
= 0.33 x 4 MGD
= 1.33 MGD
RAS Flow,
MGD
Answers to questions on page 61.
21.3A The objective of wasting activated sludge is to main-
tain a balance between the microorganisms and the
amount of food as measured by the COD or BOD test.
21,3B Wasting of the excess activated sludge is usually
achieved by removing a portion of the RAS flow.
Sometimes wasting is directly from the MLSS in the
aeration tank.
21.3C Known
Solids Added, lbs/day
Solids Aerated, lbs
RAS Susp. Sol., mg/L
Desired Sludge Age, days
Unknown
= 4,750 lbs/day WAS Flow,
= 41,100 lbs MGD and GPM
= 5,800 mg/L
= 8 days
1. Calculate the desired solids under aeration for the
desired sludge age of 8 days.
Desired Solids, = Solids Addsd, lbs/day x Sludge Age. clays
lbs
= 4,750 lbs/day
= 38.000 lbs
8 days
21.3E Known Unknown
F/Mi lbs COD/day ^ 0.30 lbs COD/day MLSS, lbs
lb MLVSS lb MLVSS
= 7,000 lbs COD/day
COD added,
lbs/day
Volatile portion
= 0.70
1. Determine the desired pounds of MLVSS.
Desired MLVSS, lbs = COD applied, lbs/day
F/M, lbs COD/day/lb MLVSS
= 7,000 lbs COD/day
0.30 lbs COD/day/lb MLVSS
= 23,333 lbs MLVSS
2. Determine the desired lbs MLSS.
Desired MLSS, lbs
= Desired MLVSS, lbs
MLSS VM portion
= 23,333 lbs MLVSS
0.70
= 33,333 lbs
21.3F The MCRT expresses the average time a mi-
croorganism spends in the activated sludge process.
Answers to questions on page 68.
21 3G The microorganisms that are important indicators in
the activated sludge process are the protozoa and
rotifers.
21.3H Important activated sludge control tests that are used
to define sludge quality and process status include
final clarifier sludge blanket depth, mixed liquor and
return sludge concentrations, and sludge settleability.
END OF ANSWERS TO QUESTIONS IN LESSON 3
2. Calculate the WAS flow, MGD and GPM to main-
tain the desired sludge age.
Solids Aerated, lbs - Oe6ired Solids, lbs*
WAS Flow, MGD =
RAS Susp. Sol., mg/L x 8.34 lbs/gal
_ (41,100 lbs - 38,000 lbs)/day
6,800 mg/L x 8.34 lbs/gal
= 0.064 MGD x 694 GPM/MGD
= 45 GPM
* Difference represents solids wasted in pounds
per day.
Answers to questions on page 64.
21.3D Four facts that should be remembered regarding the
F/M method of control.
1. The food concentration is estimated by the COD or
BOD tests.
2. The amount of food (COD or BOD) applied is im-
portant to calculate the F/M.
3. The quantity of microorganisms can be repre-
sented by the quantity of MLVSS.
4. The data obtained to calculate the F/M should be
based on the seven-day moving average.
Answers to questions on page 72.
21.4A An industrial waste monitoring program is valuable for
the operator of an activated sludge plant for the follow-
ing reasons:
1. To maintain sufficient control of treatment plant op-
erations to prevent NPDES permit violations; and
2. To gather necessary data for the future design and
operation of the treatment plant.
21.4B Common wastewater monitoring devices include:
1. Flow measuring;
2. pH monitoring;
3. Oxidation potential monitoring;
4. Suspended solids monitoring;
5. DO monitoring; and
6. Wastewater samplers.
21,4C If a high organic waste load enters your plant:
1. Gradually increase the RAS flow;
2. Increase the air input to the aeration tanks; and
3. Add nutrients if necessary.
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114 Treatment Plants
Answers to questions on page 73.
21.50A Types of industries whose wastes could be treated
by an activated sludge plant include:
1. Fruit and vegetable processing,
2. Meat and fish processing,
3. Paper product manufacturing, and
4. Petroleum refining.
21.51A The character of industrial wastewater is dependent
on the particular production process and the way it is
operated.
21.52A One approach to solving a hydraulic overloading
problem is to reduce water consumption and
minimize waste generation through proper manage-
ment of processing arid production operations.
21.52B The pH of an industrial wastewater can be adjusted
(1) upwards by the addition of caustic, and (2) down-
wards by the addition of sulfuric acid.
21.52C Chemical oxidation (COD) measures the presence of
(1) CARBON and (2) HYDROGEN, but not (3)
AMINO NITROGEN in organic materials.
21.52D The three major nutrients are carbonaceous organic
matter (measured by BOD test), nitrogen (N) and
phosphorus (P). Other elements that might be critical
include iron, calcium, magnesium, potassium, cobalt,
and molybdenum.
21.52E The most common causes or kinds of toxicity in in-
dustrial wastewaters include excessive amounts of
free ammonia, residual chlorine, detergents, paints,
solvents, and biocides.
Answers to questions on page 74.
21.53A Samples from industrial wastewaters should be col-
lected during each operating shift and during differ-
ent stages of the finished-product and raw-product
runs.
21.53B Large variations in flow can be reduced or smoothed
out by routing the flows through a surge or storage
tank.
21.53C Discrete waste solids (such as trimmings, rejects,
corn meal and pulp) are effectively separated from
the wastewater flow by various types of screens.
21.53D Screens should be located as close as possible to
the process/production producing the waste. The
longer the solids are in contact with water and the
rougher the flow is handled (more turbulent), the
more material will pass through the screens and the
more the solids will become dissolved.
Answers.to questions on page 77.
21.53E Generally the most economical location to treat toxic
wastes is at the source. If possible, do not allow toxic
wastes to enter the plant wastewater.
21 53F Industrial waste pretreatment facilities are necessary
to treat industrial wastes so they can be treated by
the activated sludge process. Pretreatment involves
pH adjustment, coarse solids removal, flow equaliza-
tion, nutrient addition and cooling.
21.53G Screens are used to remove coarse solids to reduce
unnecessary clogging and wear on downstream
pipes, pumps, aerators and clarifier mechanisms.
Also this process will help avoid odor problems that
could develop from the settling out of solids in the
equalization and emergency basins.
21.53H Organic loadings can be smoothed out by the use of
an equalizing tank and also by keeping the contents
of the tank well mixed.
21.531 Nitrogen is supplied in the form of ammonia (usually
as 30 percent aqueous) and phosphorus as phos-
phoric acid (usually as 75 percent aqueous).
21.53J "Seed activated sludge" may be obtained from either
a nearby municipal or industrial wastewater treat-
ment plant.
21.53K Initially industrial wastes must be added gradually to
the aeration basin to allow time for the activated
sludge microorganisms to adapt or become accli-
mated to the wastes.
Answers to questions on page 78.
21.54A Nutrients should be added to wastewater at a point
where the incoming wastewater is highly mixed and
preferably in the aeration basin.
21.54B Supplemental nitrogen can be provided by aqueous
ammonia or anhydrous ammonia. Supplemental
phosphorus can be provided by dissolved triple
superphosphate, phosphate fertilizer, or phosphoric
acid.
21.54C Factors or conditions that have been found to cause
the disappearance of higher forms of mi-
croorganisms from the activated sludge process in-
clude:
1. DO levels below 3 to 4 mgIL,
2. High organic loadings,
3. Toxic substances or nutrient deficiencies, and
4. pH control.
21.54D A gradual decrease in percent solids removal from
an activated sludge process over a period of time
may be the result of grit and silt accumulation in the
aeration basin which was not carried out in the
effluent and remained in the basin, thus resulting in
reduced aeration volume and detention time.
Answers to questions on page 85.
21.55A Accurate records must be kept for the following rea-
sons:
1. To help troubleshoot problems which arise,
2. To account for the operation of the plant during
appropriate times, and
3. To serve as legal documents which will protect
the company from unjust claims.
21,55B Effluent from a pulp and paper mill activated sludge
process should contain some nutrients. If low levels
of nutrients are present, a nutrient deficiency could
exist in the process.
21.55C The paper industry might shut down an activated
sludge process during holidays, maintenance (pre-
ventive and emergency), process upsets, strikes,
and scheduled production reductions.
21.55D The periodic feeding (step-feed) technique for pro-
cess start-up of activated sludge systems is effective
because it allows organisms time to consume the
available food (waste). When they are ready for more
food, more is added. This procedure encourages
rapid microorganism reproduction.
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Activated Sludge 115
Answers to questions on page 95.
21.56A Primary clarifiers are not very effective in removing
BOD because most of the BOD is "soluble" or "dis-
solved" and can't be removed by sedimentation.
21.56B Nutrients can be metered into the primary clarifier
effluent. To supplement nitrogen, ammonia gas (or
liquid) can be added. Phosphoric acid (H?P04) can
be used as a source of phosphorus. Sufficient phos-
phorus may be present in the influent from malting
by-products and phosphorus based cleaning solu-
tions.
21.56C The MLSS level in aeration basins is influenced by:
1. Influent organic loading, and
2. Temperature.
21.56D The sludge wasting rate is adjusted in an attempt to
regulate the actual MLSS in the aeration basins as
close as practical to the desired MLSS "set point."
21.56E Filamentous "bulking" can be controlled by:
1. Proper DO levels in aeration basins,
2. Providing sufficient nutrients (nitrogen and phos-
phorus) and trace minerals,
3. Proper F/M ratios, and
4. Minimizing large fluctuations or influent organic
loadings.
Answers to questions on page 99.
21.57A High strength artichoke waste influents (BOD >
6,000 mg/L) are diluted with medium strength
wastewater to produce an influent BOD of less than
6,000 mg/L before treatment by the activated sludge
process.
21.57B Fifteen-day moving averages were computed
and plotted for artichoke influent COD and F/M ratio
to reduce the effect of fluctuating daily results.
21.57E High levels of MLSS are necessary to prevent pro-
cess upsets caused by shock organic loadings.
Answers to questions on page 101.
21.58A The three main petroleum refinery waste compounds
that can be treated by the activated sludge process
are ammonia, phenols, and sulfide.
21.58B MCRTs as high as 30 days are necessary to treat
petroleum refinery wastes in order to maintain the
nitrification population necessary to oxidize am-
monia.
21.58C A shock load of phenols can be treated by decreas-
ing the hydraulic loading. Hydrogen peroxide can be
used to help oxidize phenols in the effluent.
Answers to questions on page 105.
21.6A Harmful effects that could result from the discharge of
nitrogenous compounds include:
1. Ammonia toxicity to fish life,
2. Reduction in effectiveness of chlorine disinfection
efficiency,
3. Increase in DO depletion of receiving waters,
4. Adverse public health impact on ground water, and
5. Reduction of suitability of water for reuse.
21,6B The principal control guidelines for biological nitrifica-
tion are:
1. DO,
2. pH,
3. Wastewater temperature,
4. Nitrogenous food,
5. Detention time,
6. MCRT, F/M or sludge age, and
7. Toxic materials.
21.6C Rising sludge resulting from unwanted denitrification
can be controlled by:
1. Returning settled sludge as quickly as possible and
maintaining essentially "zero" sludge blanket in the
clarifier-, and
2. Maintain sludges with low SVI values.
21.57C Ammonium phosphate can be used to provide both
nitrogen and phosphorus for the treatment of ar-
tichoke wastes.
21.57D If domestic or sanitary wastes are not treated by a
dairy waste treatment plant, effluent chlorination may
not be necessary.
END OF ANSWERS TO QUESTIONS IN LESSON 4
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116 Treatment Plants
OBJECTIVE TEST
Chapter 21. ACTIVATED SLUDGE
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one correct answer to each question.
1. As oxygen rises through the mixed liquor to the surface of
a reactor, most of the oxygen is absorbed into the mixed
liquor.
1. True
2. False
2. Pure oxygen systems may be used to supply oxygen to
any of the activated sludge process modes — conven-
tional, step feed, complete mix or contact stabilization.
1. True
2. False
3. Operation of the secondary clarifiers, return sludge rates,
and wasting rates are much the same for pure oxygen
systems as they are for conventional air-activated sludge
systems.
1. True
2. False
4. Monitoring the depth of the sludge blanket in the clarifier is
the most direct method available for determining the RAS
flow rate.
1. True
2. False
5. A limitation of using the constant flow RAS approach is
that the F/M ratio remains constant.
1. True
2. False
6. The objective of wasting activated sludge is to maintain a
balance between the microorganisms under aeration and
the amount of incoming food.
1. True
2. False
7. Wasting of activated sludge must be accomplished on a
continuous basis.
1. True
2. False
8. The character (constituent) of industrial wastewaters de-
pends on the particular production process and the way
the process is operated.
1. True
2. False
9. All nutrients need to be in a soluble form to be used by the
microorganisms in a biological treatment process.
1. True
2. False
10. An advantage of biological treatment processes is that the
microorganisms can easily adjust to great fluctuations of
flows and wastes (BOD).
1. True
2. False
11. When should the oxygen vent valve on the last reactor be
opened?
1. When the combined carbon dioxide and nitrogen con-
centrations reach an excess of 55 percent for an ex-
tended period
2. When the Lower Explosive Limit (L.E.L.) is above 20
percent
3. When the methane concentration is above 65 percent
4. When the oxygen concentration drops below 45 per-
cent for an extended period
5. When the oxygen concentration drops below 75 per-
cent for an extended period.
12. How is oxygen provided to the reactor while a cryogenic
unit is shut down for maintenance?
1. By a standby cryogenic unit
2. By another parallel cryogenic unit
3. By surface aerators
4. By the use of liquid oxygen from storage tanks
5. By using algae to produce oxygen by photosynthesis
13. Methods use to determine the RAS flow rate include
1. Mixed liquor volatile suspended solids approach.
2. Monitoring the depth of the sludge blanket.
3. Organic loading.
4. SVI approach.
5. Settleab lity approach.
14. How can the sludge blanket depth be measured in the
secondary clarifier?
1. By looking over side of clarifier and reading depth
markings on wall
2. By lowering a surveyor's rod until the end disappears in
the blanket
3. By using a sight glass finder
4. By using an electronic sludge level detector
5. By using sonar
15. The amount of waste activated sludge (WAS) removed
from the process affects which of the following items?
1. Effluent quality
2. Growth rate of microorganisms
3. Mixed liquor settleability
4. Occurrence of foaming/frothing
5. Oxygen consumption
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Activated Sludge 117
16. When activated sludge is wasted on a continuous basis,
the operator should check the return activated sludge vol-
atile suspended solids at least
1. Every two hours.
2. Every four hours.
3. Once every shift.
4. Every other day.
5. Once a week.
17. Why do industries pretreat wastewaters before discharg-
ing to the collection system?
1. To impress the public
2. To keep undesirable constituents out of the sewers
3. To recover valuable materials
4. To reduce sewer-service charges
5. To train operators
18. What types of industrial wastes could inhibit the activity of
microorganisms in a treatment plant?
1. Heavy metals
2. Low pH wastewaters
3. Methanol
4. Organic materials
5. Toxic wastes
19. How can a toxic waste be discovered in a treatment plant?
1. Decrease in aerator DO
2. Decrease in secondary effluent floe
3. Increase in aerator DO
4. Increase in plant inflow
5. Increase in secondary effluent floe
20. The primary disadvantage of the COD test is its suscepta-
bility to interference by
1. Amino nitrogen.
2. Borate.
3. Chloride.
4. Iron.
5. Sulfide.
21. How can ammonia nitrogen be removed from wastewa-
ter?
1. Ammonia stripping
2. Biological nitrification
3. Breakpoint chlorination
4. Ion exchange
5. Pressure filtration
22. What is the minimum recommended DO in an aeration
tank for biological nitrification?
1. 0.5 mgIL
2. 1.0 mgIL
3. 1.5 mgIL
4. 2.0 mgIL
5. 4.0 mg/L
23. How does breakpoint chlorination remove ammonia?
1. By breaking down ammonia
2. By oxidizing ammonia-nitrogen to nitrogen gas
3. By producing alkalinity conditions
4. By removing the nitrifying bacteria
5. By using up the oxygen
24. Procedures used for shutdown and subsequent start-up of
activated sludge processes treating industrial wastes vary
with the
1. Crew available for shutdown.
2. Duration of shutdown.
3. Microorganisms (MLVSS) in aeration basin.
4. Nature of shutdown.
5. Weather expected during shutdown.
25. Important objectives that should be accomplished during
shut-downs and start-ups include
1. Conform with legal requirements (NPDES Permit) for
plant effluent.
2. Delay subsequent start-up as long as possible.
3. Maintain satisfactory process performance.
4. No personal injuries.
5. Treat wastes at a minimum cost for satisfactory per-
formance.
26. Possible techniques for controlling filamentous organisms
in an industrial activated sludge process include
1. Dosage of return sludge with oxidants such as hydro-
gen peroxide or chlorine.
2. Lower DO levels in aeration basins so filamentous or-
ganisms cannot breathe or respire.
3. Lower F/M level to starve filamentous organisms.
4. Reduce nutrients essential for filamentous growth.
5. Stop sludge wasting to allow activated sludge or-
ganisms to gain control.
27. Petroleum refinery wastes that can be treated by the acti-
vated sludge process include
1. Ammonia
2. Chloride
3. Iron
4. Phenols
5. Sulfide
28. What is the return activated sludge (RAS) flow in GPM
when the influent flow is 2 MGD, the mixed liquor sus-
pended solids (MLSS) are 2,200 mg/L, and the RAS sus-
pended solids are 8,100 mg/L?
1. 0.55 GPM
2. 0.75 GPM
3. 1.875 GPM
4. 375 GPM
5. 520 GPM
29. What is the return activated sludge (RAS) flow in GPM
when the influent flow is 2.5 MGD and the sludge settling
volume (SV) in 30 minutes is 290 ml/L?
1. 0.725 GPM
2. 1.025 GPM
3. 505 GPM
4. 710 GPM
5. 1,945 GPM
30. An aeration tank has a volume of 1.4 million gallons. The
MLSS is 2,400 mgIL and the volatile portion is 0.75. The
mixed liquor volatile suspended solids (MLVSS) under
aeration is
1. 17,194 lbs.
2. 21,017 lbs.
3. 23,120 lbs.
4. 28,022 lbs.
5. 30,940 lbs.
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118 Treatment Plants
31. Calculate the total waste activated sludge (WAS) flow rate
in GPM for a plant that adds 3,560 lbs of solids per day.
There are 22,470 lbs of solids in the aerator, the RAS
suspended solids concentration is 7,100 mgIL, and the
current WAS flow is 0.02 MGD. The desired sludge age is
6 days.
1. 0 GPM, stop wasting
2. 13 GPM
3. 15 GPM
4. 27 GPM
5. 29 GPM
32. Calculate the desired MLSS if the desired F/M ratio is 0.20
lbs COD/day/lb MLVSS, and if 5,000 lbs of COD per day
are added, the volatile portion of the solids in the aeration
tank is 0.70 and the tank volume is 1.8 MG.
1. 2,000 mgIL
2. 2,100 mgIL
3. 2,200 mgIL
4. 2,300 mgIL
5. 2,400 mg/L
33. Calculate the ammonia (NH3-N) that must be added in
pounds per day to treat an industrial wastewater. Influent
flows are 2.5 MGD and primary effluent TOC is 487 mg/L
with a BOD:TOC ratio of 2.1:1. Primary effluent NH3-N
concentration is 5.61 mg/L. Two pounds of NH3-N are
required for every 100 pounds of BOD treated. Select the
closest answer.
1. 100 lbs NH3-N/day
2. 200 lbs NHg-N/day
3. 300 lbs NH3-N/day
4. 400 lbs NH3-N/day
5. 450 lbs NH3 N/day
END OF OBJECTIVE TEST
-------
CHAPTER 22
SLUDGE HANDLING AND DISPOSAL
by
Liberato D. Tortorici
and
James F. Stahl
(With Special sections by Richard Best and William Anderson)
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120 Treatment Plants
TABLE OF CONTENTS
Chapter 22. Sludge Handling and Disposal
Page
OBJECTIVES 127
GLOSSARY 128
LESSON 1
22.0 Need for Sludge Handling and Disposal 131
22.00 Sludge Types and Characteristics 131
22.01 Sludge Quantities 131
22.010 Primary Sludge Production 131
22.011 Secondary Sludge Production 133
22.02 Sludge Volumes 134
22.03 Sludge Handling Alternatives 134
22.1 Thickening 135
22.10 Purpose of Sludge Thickening 135
22.11 Gravity Thickening 135
22.110 Factors Affecting Gravity Thickeners 137
22.111 Operating Guidelines 138
22.1110 Hydraulic and Solids Loadings 138
22.1111 Sludge Detention Time 138
22.112 Normal Operating Procedures 139
22.113 Typical Performance 139
22.114 Troubleshooting 140
22.1140 Liquid Surface 140
22.1141 Thickened Sludge Concentration
22.12 Dissolved Air Flotation Thickeners 144
22.120 Factors Affecting Dissolved Air Flotation 144
22.121 Operating Guidelines 146
22.1210 Solids and Hydraulic Loadings 140
22.1211 Air to Solids (A/S) Ratio
22.1212 Recycle Rate and Sludge Blanket
22.122 Normal Operating Procedures
-------
Solids Disposal 121
22.123 Typical Performance 148
22.124 Troubleshooting 149
22.13 Centrifuge Thickeners 150
22.130 Factors Affecting Centrifuge Thickeners 150
22.131 Operating Guidelines 155
22.1310 Hydraulic and Solids Loadings 155
22.1311 Bowl Speed 156
22.1312 Feed Time 156
22.1313 Differential Scroll Speed and Pool Depth 156
22.1314 Nozzle Size and Number 156
22.132 Normal Operating Procedures 157
22.133 Typical Performance 157
22.134 Troubleshooting 161
22.1340 Basket Centrifuge 161
22.1341 Scroll Centrifuge 161
22.1342 Disc-Nozzle Centrifuge 161
22.14 Thickening Summary 162
LESSON 2
22.2 Stabilization 163
22.20 Purpose of Stabilization 163
22.21 Anaerobic Digestion 163
22.22 Aerobic Digestion 163
22.220 Factors Affecting Aerobic Digestion 164
22.221 Operating Guidelines 164
22.2210 Digestion Time 164
22.2211 Digestion Temperature 165
22.2212 Volatile Solids Loading 165
22.2213 Air Requirements and Dissolved Oxygen 166
22.222 Normal Operating Procedures 166
22.223 Typical Performance 167
22.224 Troubleshooting
22.2240 Dissolved Oxygen and Oxygen Uptake 168
22.2241 Foaming
22.2242 Loadings 168
22.23 Chemical Stabilization 170
22.230 Lime Stabilization 170
22.231 Normal Operating Procedures 171
22.232 Troubleshooting 171
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122 Treatment Plants
22.233 Chlorine Stabilization 171
22.234 Normal Operating Procedures 171
LESSON 3
22.3 Conditioning 173
22.30 Purpose of Conditioning 173
22.31 Chemical Conditioning 173
22.310 Chemical Requirements 173
22.311 Chemical Solution Preparation 178
22.312 Chemical Addition 178
22.313 Typical Chemical Requirements 178
22.314 Troubleshooting 179
22.32 Thermal Conditioning 179
22.320 Factors Affecting Thermal Conditioning 180
22.321 Operating Guidelines 180
22.322 Normal Operating Procedures 181
22.323 Typical Performance 181
22.324 Troubleshooting 181
22.3240 Reactor Temperature 181
22.3241 Reactor Pressure 181
22.3242 Heat Exchanger Pressure Differential 182
22.3243 Sludge Dewaterability 182
22.33 Wet Oxidation 182
22.330 Factors Affecting Wet Oxidation 184
22.331 Typical Performance 184
22.34 Elutriation 184
22.340 Process Description 184
22.341 Operating Guidelines 184
LESSON 4
22.4 Dewatering 186
22.40 Purpose of Dewatering 186
22.41 Pressure Filtration 186
22.410 Plate and Frame Filter Press 186
22.4100 Factors Affecting Pressure Filtration Performance 186
22.4101 Operating Guidelines 186
22.4102 Operating Procedures 188
22.4103 Typical Performance 189
22.4104 Troubleshooting 189
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Solids Disposal 123
22.411 Belt Filter Press 190
22.4110 Factors Affecting Belt Pressure Filtration 190
22.4111 Operating Guidelines 190
22.4112 Normal Operating Procedure 192
22.4113 Typical Performance 193
22.4114 Troubleshooting 193
22.412 Vacuum Filtration 193
22.4120 Factors Affecting Vacuum Filtration 194
22.4121 Operating Guidelines 198
22.4122 Normal Operating Procedures 199
22.4123 Typical Performance 199
22.4124 Troubleshooting 199
22.42 Centrifugation 200
22.420 Process Description 200
22.421 Typical Performance 200
22.43 Sand Drying Beds
22.430 Factors Affecting Sand Drying Beds 201
22.431 Operating Guidelines 201
22.432 Normal Operating Procedures 202
22.433 Typical Performance 203
22.434 Troubleshooting 203
22.44 Surfaced Sludge Drying Beds 203
22.440 Need for Surfaced Drying Beds 203
22.441 Layout of Surfaced Drying Beds 203
22.442 Operation 206
22.443 Cleaning the Drying Bed 206
22.45 Dewatering Summary 207
lesson 5
22.5 Volume Reduction 207
22.50 Purpose of Volume Reduction 207
22.51 Composting
22.510 Factors Affecting Composting 208
22.511 Normal Operating Procedure 211
22.512 Typical Performance
22.513 Troubleshooting 212
22.52 Mechanical Drying
22.520 Factors Affecting Mechanical Drying 213
22.521 Normal Operation and Performance 214
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124 Treatment Plants
22.53 Sludge Incineration by Richard Best 214
22.530 Process Description 214
22.531 Furnace Description 214
22.5310 Furnace Refractory 214
22.5311 Center Shaft 221
22.5312 Shaft Drive 221
22.5313 Top and Lower Bearings 221
22.5314 Furnace Off-Gas System 221
22.5315 Burner System 226
22.532 Controls and Instrumentation 227
22.533 MHF Operations 227
22.5330 Furnace Zones 227
22.5331 Auxiliary Fuel 227
22.5332 Air Flow 229
22.5333 Combustion 230
22.5334 Air Flow and Evaporation 230
22.5335 Recommended Furnace Operating Ranges 230
22.5336 Alarm Systems 230
22.5337 Burnouts 232
22.534 General Operational Procedures (Start-up, Normal Operation and Shutdown) 232
22.535 Common Operating Problems (Troubleshooting) 233
22.5350 Smoke 233
22.5351 Clinkering 233
22.5352 Inability to Stabilize Burn 233
22.536 Safety 233
22.54 Facultative Sludge Storage Lagoons 234
22.6 Land Disposal of Wastewater Solids by Bill Anderson 234
22.60 Need for Land Disposal 234
22.61 Regulatory Constraints 234
22.610 Regulation of Sludge Disposal 234
22.611 Regulation of Sludge Reuse in Agriculture 234
22.62 Disposal Options 239
22.620 Digested Sludge — Dewatered 239
Storage 239
Transportation 239
22.6200 Sanitary Landfill Disposal 239
Landfill Moisture Adsorption Capacity 239
Placement of Sludge in a Landfill 239
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Solids Disposal 125
22.6201 On-Site Dedicated Land Disposal (DLD) 239
Placement of Sludge Cake in a Dedicated Land Disposal Site 239
Trenching 239
Landfilling 240
Incorporation into Surface Soils 240
22.6202 Agricultural Reclamation 240
Application Rate 240
Method of Application 240
22.621 Stabilized Sludge — Liquid Process 241
Storage 241
Transportation 241
22.6210 High-Rate Dedicated Land Disposal 241
Rate of Application 241
Disposal Techniques 241
1. Ridge and Furrow 241
2. Flooding 241
3. Subsurface Injection 242
Site Layouts 242
System Operational Criteria 242
Equipment Needs 242
22.6211 Agricultural Reclamation 242
Application Rate 244
Method of Application 244
1. Subsurface Injection 244
2. Ridge and Furrow Controlled Flooding 244
3. Sludge Mixed with Irrigation Water 244
22.6212 Permanent Lagoons 244
22.622 Disposal of Reduced Volume Sludge 244
22.6220 Composting 244
22.6221 Mechanical Drying 244
22.6222 Incinerator Ash 244
22.6223 Utilization Options 247
22.623 Screenings, Grit and Scum * 247
22.6230 Dewatered Screenings and Grit 247
22.6231 Dewatered Scum 247
22.6232 Dewatered Raw Sludge 247
.63 Environmental Controls (Monitoring) 247
22.630 Odors 247
22.631 Sludge/Dedicated Land Disposal Soils 247
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126 Treatment Plants
22.632 Groundwater 248
22.633 Surface Water Monitoring 248
22.634 Public Health Vectors 248
22.64 Acknowledgment 248
22.7 Review of Plans and Specifications 249
22.8 Metric Calculations 250
22.80 Conversion Factors 250
22.81 Problem Solutions 250
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OBJECTIVES
Chapter 22 SLUDGE HANDLING AND DISPOSAL
Categories of sludge handling and disposal processes con-
tained in this chapter include thickening, stabilization, condi-
tioning, dewatering, volume reduction and land disposal. Fol-
lowing completion of Chapter 22, you should be able to do the
following with regard to the processes in these sludge handling
and disposal categories:
1. Explain the purposes of the processes,
2. Properly start up, operate, shut down, and maintain these
processes,
3. Develop operating procedures and strategies for both nor-
mal and abnormal operating conditions,
4. Identify potential safety hazards and conduct duties using
safe procedures,
5. Troubleshoot when a process does not function properly,
and
6. Review plans and specifications for the processes.
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128 Treatment Plants
GLOSSARY
Chapter 22. SOLIDS HANDLING AND DISPOSAL
ANAEROBIC (AN-air-O-bick) ANAEROBIC
A condition in which "free" or dissolved oxygen is NOT present in the aquatic environment.
ASPIRATE (ASS-per-RATE) ASPIRATE
Use of a hydraulic device (aspirator or eductor) to create a negative pressure (suction) by forcing a liquid through a restriction, such
as a Venturi. An aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump; sometimes used instead
of a sump pump.
BAFFLE BAFFLE
A flat board or plate, deflector, guide or similar device constructed or placed in flowing water, wastewater, or slurry systems to cause
more uniform flow velocities, to absorb energy, and to divert, guide, or agitate liquids.
BLIND BLIND
A condition that occurs on the filtering medium of a microscreen or a vacuum filter when the holes or spaces in the media become
clogged or sealed off due to a buildup of grease or the material being filtered.
BOUND WATER BOUND WATER
Water contained within the cell mass of sludges or strongly held on the surface of colloidal particles.
BULKING (BULK-ing) BULKING
Clouds of billowing sludge that occur throughout secondary clarifiers and sludge thickeners when the sludge becomes too light and
will not settle properly.
CAVITATION (CAV-i-TAY-shun) CAVITATION
The formation and collapse of a gas pocket or bubble on the blade of an impeller. The collapse of this gas pocket or bubble drives
water into the impeller with a terrific force that can cause pitting on the impeller surface.
CENTRATE CENTRATE
The water leaving a centrifuge after most of the solids have been removed.
CENTRIFUGE CENTRIFUGE
A mechanical devicie that uses centrifugal or rotational forces to separate solids from liquids.
COAGULATION (co-AGG-you-LAY-shun) COAGULATION
The use of chemicals that cause very fine particles to clump together into larger particles. This makes it easier to seoarate the solids
from the liquids by settling, skimming, draining, or filtering. p
CONING (CONE-ing) CONING
Development of a cone-shaped flow of liquid, like a whirlpool, through sludge. This can occur in a sludge hoooer durina sludae
withdrawal when the sludge becomes too thick. Part of the sludge remains in place while liquid rather than sludae flows out ofthe
hopper. Also called "coring." a
DENITRIFICATION DENITRIFICATION
A condition that occurs when nitrite or nitrate ions are reduced to nitrogen gas and bubbles are formed as a result of this nrrv*»«
The bubbles attach to the biological floes and float the floes to the surface of the secondary clarifiers or gravity thickeners
DENSITY (DEN-sit-tee) DENSITY
A measure of how heavy a substance (solid, liquid, or gas) is for its size. Density is expressed in terms of weight per unit volume
that Is, grams per cubic centimeter or pounds per cubic foot. The density of water (at 4°C or 39°F) is 1.0 aram Der cubic centimeter or
about 62.4 pounds per cubic foot. ' 8 m p CUDIC cemimeter or
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Solids Disposal 129
DEWATERABLE DEWATERABLE
This is a property of a sluge related to the ability to separate the liquid portion from the solid, with or without chemical conditioning. A
material is considered dewaterable if water will readily drain from it. Generally raw sludge dewatering is more difficult than water
removal from digested sludge.
EDUCTOR (e-DUCK-tor) EDUCTOR
A hydraulic device used to create a negative pressure (suction) by forcing a liquid through a restriction, such as a Venturi. An
eductor or aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump; sometimes used instead of a
suction pump.
ELUTRIATION (e-LOO-tree-A-shun) ELUTRIATION
The washing of digested sludge in plant effluent. The objective is to remove (wash out) fine particulates and/or the alkalinity in
sludge. This process reduces the demand for conditioning chemicals and improves settling or filtering characteristics of the solids.
ENDOGENOUS (en-DODGE-en-us) ENDOGENOUS
A reduced level of respiration (breathing) in which organisms break down compounds within their own cells to produce the oxygen
they need.
FILAMENTOUS ORGANISMS (FILL-a-MEN-tuss) FILAMENTOUS ORGANISMS
Organisms that grow in a thread or filamentous form. Common types are thiothrix and actinomyces.
FLOCCULATION (FLOCK-you-LAY-shun) FLOCCULATION
The gathering together of fine particles to form larger particles.
GASIFICATION (GAS-i-fi-KAY-shun) GASIFICATION
The conversion of soluble and suspended organic materials into gas during anaerobic decomposition. In anaerobic sludge digest-
ers, this gas is collected for fuel or disposed of using the waste gas burner.
GROWTH RATE, Y GROWTH RATE, Y
An experimentally determined constant to estimate the unit growth rate of bacteria while degrading organic wastes.
INCINERATION INCINERATION
The conversion of dewatered sludge cake by combustion (burning) to ash, carbon dioxide, and water vapor.
INORGANIC WASTE INORGANIC WASTE
Waste material such as sand, salt, iron, calcium, and other mineral materials which are only slightly affected by the action of
organisms. Inorganic wastes are chemical substances of mineral origin; whereas organic wastes are chemical substances usually
of animal or vegetable origin. Also see NONVOLATILE MATTER.
NITRIFYING BACTERIA NITRIFYING BACTERIA
Bacteria that change the ammonia and organic nitrogen in wastewater into oxidized nitrogen (usually nitrate).
NONVOLATILE MATTER NONVOLATILE MATTER
Material such as sand, salt, iron, calcium, and other mineral materials which are only slightly affected by the action of organisms.
Volatile materials are chemical substances usually of animal or vegetable origin. Also see INORGANIC WASTE.
POLYELECTROLYTE (POLY-electro-light) POLYELECTROLYTE
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polyelectrolytes may be of
biological origin or derived from starch products, cellulose derivatives, and alignate8. Synthetic polyelectrolytes consist of simple
substances that have been made into complex, high-molecular-weight substances. Often called a "polymer."
POLYMER (POLY-mer) POLYMER
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polymers may be of biological
origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polymers consist of simple substances that
have been made into complex, high-molecular-weight substances. Often caled a "polyelectrolyte."
POLYSACCHARIDE (polly-SAC-a-ride) POLYSACCHARIDE
A carbohydrate such as starch, insulin or cellulose.
PRECOAT PRECOAT
Application of a free-draining, non-cohesive material such as diatomaceous earth to a filtering media. Precoating reduces the
frequency of media washing and facilitates cake discharge.
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130 Treatment Plants
PROTEINACEOUS (PRO-ten-NAY-shus)
Materials containing proteins which are organic compounds containing nitrogen.
PROTEINACEOUS
PUG MILL
PUG MILL
A mechanical device with rotating paddles or blades that is used to mix and blend different materials togehter.
PUTRESCIBLE (pew-TRES-uh-bull)
PUTRESCIBLE
Material that will decompose under anaerobic conditions and produce nuisance odors.
RABBLING RABBLING
The process of moving or plowing the material inside a furnace by using the center shaft and rabble arms.
RISING SLUDGE RISING SLUDGE
Rising sludge occurs when sludge settles to the bottom of the thickener, is compacted, and then starts to rise to the surface, usually
as a result of denitrification.
SCFM SCFM
Cubic Feet of air per Minute at Standard conditions of temperature, pressure, and humidity.
SECONDARY TREATMENT SECONDARY TREATMENT
A wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the
water being treated. Usually the process follows primary treatment by sedimentation. The process commonly is a type of biological
treatment process followed by secondary clarifiers that allow the solids to settle out of the water being treated.
SEPTICITY (sep-TIS-it-tee) SEPTICITY
Septicity is the condition in which organic matter decomposes to form foul-smelling products associated with the absence of free
oxygen. If severe, the wastewater turns black, gives off foul odors, contains little or no dissolved oxygen and creates a heavy oxygen
demand.
SHORT-CIRCUITING SHORT-CIRCUITING
A condition that occurs in tanks or ponds when some of the water or wastewater travels faster than the rest of the flowing water.
SLUDGE-VOLUME RATIO (SVR) SLUGE-VOLUME RATIO (SVR)
The volume of sludge blanket divided by the daily volume of sludge pumped from the thickener.
SLURRY (SLUR-e) SLURRY
A thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry).
SPECIFIC GRAVITY SPECIFIC GRAVITY
Weight of a particle or substance in relation to the weight of water. Water has a specific gravity of 1.000 at 4°C (or 39°F). Wastewater
particles usually have a specific gravity of 0.5 to 2.5.
STABILIZATION STABILIZATION
Conversion to a form that resists change. Organic material is stabilized by bacteria which convert the material to gases and other
relatively inert substances. Stabilized organic material generally will not give off obnoxious odors.
THERMOPHILIC BACTERIA (thermo-FILL-lik) THERMOPHILIC BACTERIA
Hot temperature bacteria. A group of bacteria that grow and thrive in temperatures above 113°F (45°C). The optimum temperature
range for these bacteria in anaerobic decomposition is 120°F (49°C) to 130°F (57°C).
VECTOR VECTOR
An insect or other organism capable of transmitting germs or other agents of disease.
VOLATILE MATTER (VOL-a-till) VOLATILE MATTER
Matter in water, wastewater, or other liquids that is lost on ignition of the dry solids at 550°C.
Y, GROWTH RATE
An experimentally determined constant to estimate the unit
growth rate of bacteria while degrading organic wastes.
Y, GROWTH RATE
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Solids Disposal 131
CHAPTER 22. SLUDGE HANDLING AND DISPOSAL
(Lesson 1 of 5 Lessons)
22.0 NEED FOR SLUDGE HANDLING AND DISPOSAL
22.00 Sludge Types and Characteristics
The solids removed in wastewater treatment plants result in
waste streams such as grit, screenings, scum (floatable mate-
rials) and sludge (Figure 22.1). Sludge is by far the largest in
volume and the handling and disposal of these residual solids
represents one of the most challenging problems wastewater
treatment plant operators must solve. The problems of dealing
with sludge are complicated by the facts that (1) sludge is
composed largely of the substances responsible for the offen-
sive character of untreated wastewater, (2) only a small portion
of the sludge is solid matter and (3) the response of similar-
type sludges to various handling techniques differs from one
treatment plant to the next plant. Waste activated sludge
(WAS) produces the greatest volume of sludge and sludge
disposal problems confronting operators today.
Some general statements can be made about the reaction of
similar sludge types to a specific unit process, but the operator
should be aware that the exact response of a particular sludge
depends on the plant location and on a large number of vari-
ables.
This chapter is designed to familiarize the operator with (1)
the general characteristics of wastewater treatment plant
sludges, (2) the unit processes used to effectively handle
sludge, and (3) the operating guidelines necessary for suc-
cessful unit process performance.
Basically two types of sludge are produced at any SEC-
ONDARY WASTEWATER TREATMENT FACILITY: They are
classified as primary and secondary sludges.
Primary sludge includes all those solids which settle to the
bottom of the primary sedimentation tank and are removed
from the waste stream. On a very general basis, primary
sludge solids are usually fairly coarse and fibrous, have SPE-
CIFIC GRAVITIES2 or DENSITIES3 significantly greater than
that of water and are composed of 60 to 80 percent VOLATILE
(organic) MATTER* The remaining 20 to 40 percent of the
sludge solids are classified as NONVOLATILE (inorganic)
MATTER?
Secondary sludge is generated as a by-product of biological
degradation of organic wastes in the secondary biological (ac-
tivated sludge and trickling filter) treatment processes. As bac-
teria feed on and degrade organic matter, new bacteria cells
are produced. In order to maintain the desired quantity or popu-
lation of bacteria within the biological treatment system, some
of these new bacteria cells have to be removed from the pro-
cess stream. Usually these bacteria cells are removed in the
secondary clarifier. The biological solids or bacteria cells that
are removed are termed secondary sludge. On a very general
basis, secondary sludges are more flocculant than primary
sludge solids, less fibrous, have specific gravities closer to that
of water and consist of 75 to 80 percent volatile (organic) mat-
ter and 20 to 25 percent nonvolatile (inorganic) material.
22.01 Sludge Quantities
The daily quantity of primary and secbndary sludges re-
moved will vary from one treatment plant to the next plant.
Before sludge handling equipment can be designed, pur-
chased and installed, estimates have to be made to determine
the daily quantity of sludge removed from the system. Although
the design and installation of such equipment is the engineer's
responsibility, the operator should be aware of how engineers
make these estimates.
22.010 Primary Sludge Production
The quantity of primary sludge generated depends on: (1)
the influent wastewater flow, (2) the concentration of influent
settleable suspended solids, and (3) the EFFICIENCY8 of the
primary sedimentation basin. The estimation of primary sludge
production is Illustrated in the following example.
EXAMPLE 1. PRIMARY SLUDGE PRODUCTION
Given: The influent flow to a primary clarifier is 1.5 MGD. The
Influent suspended solids concentration is 350 mgIL.
The effluent suspended solids concentration from the
primary clarifier is 150 mgIL.
Find: 1. The total pounds of suspended solids entering the
plant per day (lbs SS/day).
1 Secondary Wastewater Treatment Facility. A wastewater treatment facility used to convert dissolved or suspended materials Into a form
more readily separated from the water being treated. Usually the facility followsprimary treatment by sedimentation. The facility commonly Is
a type of biological treatment process followed by secondary clartfiers that allow the solids to settle out of the water being treated.
Specific Gravity. Weight of a particle or substance In relation to the weight of water. Water has a specific gravity of 1.000 at 4 C (or
2 Specific Gravity. Weight of a particle
Wastewater particles usually have a specific gravity of 0.5 to 2.5.
(or 39aF).
Density. A measure of how heavy a substance (solid, liquid, or gas) Is for Its size. Is expressed In terms of weight per unit volume,
that Is, grams per cubic centimeter or pounds per cubic foot. The density of water (at 4 C or 39 F) Is 1.0 gram per cubic centimeter or about
62.4 pounds per cubic foot,
4 Volatile Matter. Matter In water, wastewater, or other liquids that is lost on Ignition of the drysollds at 55Q*C,
5 Nonvolatile Matter. Material such as sand, salt, Iron, calcium and other mineral materials which an only slightly affected by the action of
organisms. Volatile materials are chemical substances usually of animal or vegetable origin.
(Inf. Susp. Solids, mglL - Effl. Susp. Sol., mgIL) 100%
Infi. Susp. SoHds, mgIL
Efficiency, %>
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132 Treatment Plants
TREATMENT ?&OC&&o FUNCTlOW
peer0£ArAi£A/r
emoves £&are.&t 60/./0S
K/US PA7?JO<*£A//d SACTEB/A
Fig. 22.1 Typical flow diagram of a wastewater treatment plant
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Solids Disposal 133
2. The total pounds of suspended solids leaving the
primary clarifier with the primary effluent (lbs SSI
day).
3. The total pounds of dry (no moisture present)
sludge solids produced per day.
Solution:
Known
Unknown
Flow, MGD = 1.5 MGD 1. Dry SS entering plant,
lbs/day
Inf. SS, mgIL = 350 mgIL 2. Dry SS leaving primary
clarifier, lbs/day
Effl. SS, mgIL = 150 mg IL 3. Dry sludge solids produced,
lbs/day
1. Calculate the amount of dry influent suspended solids, lbs/
day.
Infl Susp Sol, = Flow, MGD x Susp Sol, mg IL x 8.34 lbs/gal
lbs/day = 1 5 MGD x 350 mg/L x 8.34 lbs/gal
= 4379 lbs/day
2. Calculate the amount of dry suspended solids leaving the
primary clarifier, lbs/day.
Prim. Clar. Effl. , ,
Susp. Sol, = Flow, MGD x Susp Sol, mgIL x 8.34 lbs/gal
lbs/day = 1 5 MGD x 150 x a.34 lbs/gal
= 1877 lbs/day
3. Calculate the amount of dry primary sludge produced, lbs/
day.
Primary Sludge, „ |nf Sus So! lb8/day. Eff, Susp Soi, lbs/day
lbs/day
= 4379 lbs/day -1877 lbs/day
2502 lbs/day
OR
Primary Sludge, = Flow, MGD x (In SS, mgIL - Ef SS, mgIL)
lbs/day x 8.34 lbs/day
= 1.5 MGD x (350 mgIL -150 mg/L)
x 8.34 lbs/gal
- 2502 lbs/day
NOTE All answers are in terms of pounds of dry solids per
day.
22.011 Secondary Sludge Production
The daily quantity of sludge produced is dependent on (1)
the influent flow to the biological or secondary system, (2) the
influent organic load to the biological system, (3) the efficiency
of the biological system in removing organic matter, and (4) the
growth rate, Y, of the bacteria within the system. The determi-
nation of secondary sludge production is rather complicated
due to the mathematics and variables involved. The rate of
biological growth, Y, is highly dependent on such variables as
temperature, nutrient balances, the amount of oxygen supplied
to the system, the ratio between the amount of food supplied
(BOD) and the mass or quantity of biological cells developed
within the system, detention time and other factors. A detailed
discussion of the estimation of growth rates and sludge pro-
duction is beyond the scope of this chapter. A general rule of
thumb that operators may use to estimate secondary sludge
production is that for every pound of organic matter (soluble
5-day BOD) used by the bacteria cells, approximately 0.30 to
0.70 pounds of new bacteria cells are produced and have to be
taken out of the system. The following example illustrates the
estimation of secondary sludge production.
EXAMPLE 2. SECONDARY SLUDGE PRODUCTION
Given: The primary effluent organic content, as measured by
the 5-day BOD test, to a secondary treatment facility is
200 mg/L. The secondary effluent 5-day BOD is 30
mg/L The bacteria growth rate, Y, is 0.50 lbs SS/lb
BOD removed and the flow rate, Q, is 1.5 MGD.
NOTE: The secondary influent flow in your plant may be dif-
ferent than the actual plant effuent flow due to in-plant
recycle uses of effluent and/or secondary system
streams.
Find: 1. The total pounds of BOD entering the secondary
system per day.
2. The total pounds of BOD leaving the secondary
system with the effluent per day.
3. The total pounds of BOD removed per day by the
secondary system.
4. The total dry pounds of secondary sludge produced
per day by the secondary system.
Solution:
Known Unknown
Flow, MGD =1.5 MGD 1. BOD Entering, lbs/day
Infl. BOD, mg/L = 200 mg/L 2. BOD Leaving, lbs/day
Effl. BOD, mg/L = 30 mg/L 3. BOD Removed, lbs/day
Y, lbs SI Sol Prod _ 0.50 lbs SI Sol 4. Sludge Prod., lbs/day
lb BOD Rem lb BOD
1. Determine the 5-day BOD entering the secondary system,
lbs BOD/day.
Entering BOD, = Flow, MGD x BOD, mg/L x 8.34 lbs/gal
lbs BOD/day „ 15 MQD x 200 mg/L x 8 34 |bs/ga,
- 2502 lbs BOD/day
2. Determine the 5-day BOD leaving the secondary system,
lbs BOD/day.
Leaving BOD, - Flow, MGD x BOD, mg/L x 8.34 Iba/gal
lbs BOD/day „ 15 MQD x 30 mg/L x 8 34 |b8/ga|
- 375 lbs BOD/day
3. Determine the 5-day BOD removed from the secondary
system, lbs BOD/day.
Bod Removed, - Entering BOD, - Leaving BOO,
lbs BOD/day lbs BOD/day lbs BOD/day
= 2502 lbs BOD/day - 375 lbs BOD/day
» 2127 lbs BOD/day
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134 Treatment Plants
OR
BOD Removed, = Flow, MGD x (In BOD, mg/L - Ef BOD, mg/Z.)
lbs BOD/day x 8.34 lbs/gal
= 1.5 MGD x (200 mg/Z. - 30 mg/Z_) x 8.34 lbs/gal
= 2127 lbs BOD/day
Likewise, if the secondary sludge from Example 2 is with-
drawn from the secondary clarifier at a sludge solids concen-
tration (% SI Sol) of 1.0 percent, the daily volume of sludge
would be determined as follows:
Solution:
4. Determine the secondary sludge produced in terms of
pounds of dry sludge solids per day.
Known
Unknown
Sludge Produced,
lbs dry solids/day
BOD Removed, x Y,lbs SI So1 Prod/day
lbs BOD/day lbs BOD Rem/day
2127 lbs BOD/day ' 0 50 lbs Sl So' day
1 lb BOD/day
1064 lbs dry sludge solids/day
22.02 Sludge Volumes
Examples 1 and 2 illustrated how to estimate the quantity or
pounds of primary and secondary sludge solids, respectively.
The total volume or gallons of primary and secondary sludges
are equally as important for sizing sludge handling equipment.
Sludge volumes in gallons are determined by the sludge solids
content (% SS) and the pounds of solids in a sludge sample
according to the following equation:
Sludge Volume, gal = _ Sludge Quantity, lbs dry solids
8.34 lbs/gal x Sludge Solids, %/100%
If the primary sludge from Example 2 is withdrawn from the
primary clarifier at a sludge solids concentration (% SI Sol) of 5
percent, the daily volume of sludge would be determined as
follows:
Solution:
Known
Unknown
Primary Sludge Quantity = 2502 lbs/day Primary Sludge Volume,
lbs/day gal/day
Sludge Solids, % = 5%
Determine the daily primary sludge volume in gallons per
day.
Primary Sludge Volume, _ Sludge Quantity, lbs dry solids/day
gal/day 8 34 |bs/ga| x Sludge Solids, %/lO0%
2502 lbs/day
8.34 lbs/gal x 5%/100%
2502
8.34 x 0.05
= 6,000 gal/day
Secondary Sludge = 1064 lbs/day Secondary Sludge Volume,
Quantity, lbs/day gal/day
Sludge Solids, % = 1.0%
Determine the daily secondary sludge volume in gallons per
day.
Secondary Sludge = Sludge Quantity, lbs dry solids/day
Volume, gal/day g |bs/ga.l x Sludge Solids, %/100%
1064 lbs/day
8.34 lbs/gal x 1.0%/100%
= 12,758 gal/day
22.03 Sludge Handling Alternatives
Depending on the type and quantity of sludge produced, a
variety of unit processes and overall sludge handling systems
can be established to process the sludge. The schematic dia-
gram presented in Table 22.1 illustrates these sludge process-
ing alternatives. The remainder of this chapter will be divided
into separate lessons on thickening, stabilization, conditioning,
dewatering, volume reduction, and ultimate disposal of solids.'
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 263.
22.OA List the two types and general characteristics of
sludges that are produced at a typical wastewater
treatment facility.
22.0B List the variables that govern the quantity of primary
sludge production.
22.0C Determine the daily quantity (lbs/day) of primary
sludge produced for the following conditions: (1) in-
fluent flow of 2.0 MGD, (2) influent suspended solids
of 200 mg/L, and (3) primary effluent suspended sol-
ids of 120 mg/L
22.0D List the variables that influence the production of sec-
ondary sludges.
OBJECTIVE
SPECIFIC
PROCESSES
THICKENING
Remove water
from the sludge
mass
1. Gravity
2. Flotation
3. Centrifugation
TABLE 22.1 SLUDGE PROCESSING ALTERNATIVES
TYPE OF ALTERNATIVE
STABILIZATION CONDITIONING DEWATERING VOLUME REDUCTION
Convert odor-
causing portion
of sludge solids
to nonodorous
end products
1. Digestion
2. Thermal
3. Chemical
Pretreatment of
sludge to facili-
tate removal of
water in sub-
sequent treat-
ment processes
1. Chemical
2. Thermal
3. Elutriation
Reduce sludge
moisture and
volume to allow
economical dis-
posal
1. Filtration
2. Centrifugation
3. Drying Beds
Reduction of sludge
mass prior to ulti-
mate disposal
1. Drying
2. Incineration
3. Composting
DISPOSAL
Ultimate disposal
1. Land
2. Ocean
3. Air
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Solids Disposal 135
22.0E Estimate the daily quantity of secondary sludge pro-
duced for the following conditions: (1) influent flow of
2.0 MGD, (2) influent BOD to the secondary system of
180 mg/L and effluent from the secondary system of
30 mg/L and (3) growth rate coefficient, Y, of 0.50
pounds of solids per pound of BOD removed.
22.0F For the conditions given in problem 22.0C, estimate
the daily volume (gal/day) of primary sludge if it is
withdrawn from the primary clarifier at a sludge solids
concentration of 4.0 percent.
22.1 THICKENING
22.10 Purpose of Sludge Thickening
Settled solids removed from the bottom of the primary
clarifier (primary sludge) and settled biological solids removed
from the bottom of secondary clarifiers (secondary sludge)
contain Jarge volumes of water. Typically, primary sludge con-
tains approximately 95 to 97 percent water. For every pound of
primary solids, there are 20 to 30 pounds of water and for
every pound of secondary solids approximately 50 to 150
pounds of water are incorporated in the sludge mass. If some
of the water is not removed from the sludge mass, the size of
subsequent sludge handling equipment (digester, mechanical
dewatering equipment, pumps) have to be larger to handle the
greater volumes and this would obviously increase equipment
costs.
Concentration or thickening is usually the first step in a
sludge processing system following initial separation of solids
by sedimentation from the wastewater being treated.
Maximum sfudge thickening should always be attempted in the
sedimentation tank before using a separate sludge thickener.
THE PRIMARY FUNCTION OF SLUDGE THICKENING IS TO
REDUCE THE SLUDGE VOLUME TO BE HANDLED IN SUB-
SEQUENT PROCESSES. The advantages normally as-
sociated with sludge thickening include: (1) improved digester
performance due to a smaller volume of sludge, (2) construc-
tion cost savings for new digestion facilities due to smaller
sludge volumes treated, and (3) a reduction in digester heating
requirements because less water has to be heated. Also re-
duced sludge volumes result in smaller facilities for storing,
blending, dewatering and incinerating or disposing of the
sludge. The following example illustrates the reduction in
sludge volume when a sludge is thickened.
EXAMPLE 3.
Given: A primary sludge is withdrawn from a primary clarifier
at a sludge solids concentration of 3.0 percent. The
volume of sludge withdrawn is 2,000 gallons per day.
Find: 1. The amount of primary sludge solids withdrawn in
pounds per day.
2. If the sludge is concentrated (thickened) to 5.0 per-
cent sludge solids, find the new sludge volume.
Solution:
Known Unknown
Sludge Solids, % =3.0% 1. Amount of Dry Sludge,
lbs/day
Sludge Vol, gal/day = 2000 gal/day 2. Thickened Sludge Vol-
ume, gal/day
1. Determine the amount of primary dry sludge withdrawn in
pounds per day.
Dry Sludge Solids, = RhlHnc Vn, gal x 8.34 lbs x SI Sol, %
lbs/day day gal " 100%"
— 2000 x x 3.0%
day gal 100%
= 500 lbs/day
2. Calculate the new thickened sludge volume in gallons per
day.
Sludge Volume, = Dry Sludge Solids, lbs/day
gal/
-------
SCUM /
SCHARGE
SAFETY
RAILING
DRIVE
"assembly
fi
A
effluent
WEIR
SCUM
baffle
WATER
LEVEL^y
1=3—
INFLUENT LNE
SLUDGE
RAKE
SLUDGE
HOPPER
SLUDGE
WITHDRAWAL
Fig. 22.2 Gravity thickener
-------
Solids Disposal 137
The Inlet or distribution assembly usually consists of a circu-
lar steel skirt or BAFFLE7 which originates above the water
surface and extends downward approximately 2 to 3 feet (0.6
to 0.9 m) below the water surface. The sludge to be thickened
enters the assembly, flows downward under the steel skirt and
through the tank where the solids settle to the bottom. The inlet
assembly provides for an even distribution of sludge through-
out the tank and reduces the possibility of SHORT-
CIRCUITING8 to the effluent end of the thickener.
The sludge rake provides for movement of the settled (thick-
ening) sludge. As the rake slowly rotates, the settled solids are
moved to the center of the tank where they are deposited in a
sludge hopper. The tank bottom is usually sloped towards the
center to facilitate the movement of sludge to the collection
point. Typically, sludge pumps include centrifugal recessed-
impeller-type pumps or positive displacement progressive-
cavity-type pumps.
The vertical steel member (pickets) that are usually mounted
on the sludge rake assembly provide for gentle stirring or floc-
culation of the settled sludge as the rake rotates. This gentle
stirring action serves two purposes. Trapped gases in the
sludge are released to prevent RISING9 of the solids. Also,
stirring prevents the accumulation of a large volume of solids
floating on the thickener surface that must be removed as
scum and will create nuisance and odor problems.
The effluent or thickener overflow flows over a continuous
weir located on the periphery (outside) of the thickener. The
outlet works usually include an effluent baffle to retain floating
debris and a scum scraper and collection system to remove
these floatables.
22.110 Factors Affecting Gravity Thickeners
The successful operation of gravity thickeners is dependent
on the following factors; (1) type of sludge, (2) age of the feed
sludge, (3) sludge temperature, (4) sludge blanket depth, (5)
solids and hydraulic detention times and (6) solids and hydrau-
lic loadings. The first three factors deal with the characteristics
of the influent sludge while the remaining three factors deal
with operational controls.
Both the type and age of sludge to be thickened can have
pronounced effects on the overall performance of gravity
thickeners. Fresh primary sludge usually can be concentrated
to the highest degree. If the primary sludge is septic or allowed
logo ANAEROBIC,10 hydrogen sulfide (H2S), methane (Ct-L),
and carbon dioxide (C02) gases may be produced (GASIFI-
CATION11)- If gas is produced, it will attach to sludge particles
and carry these solids to the surface. The net effect(s) of gas
production due to anaerobic conditions will be reduced thick-
ener efficiency and lower solids concentration.
Secondary sludges are not as well suited for gravity thicken-
ing as primary sludge. Secondary sludges contain large quan-
tities of BOUND WATER12 which makes the sludge less dense
than primary sludge solids. Biological solids are composed of
approximately 85 to 90 percent water by weight within the cell
mass. The water contained within the cell wall is referred to as
"bound water."
cr
The fact that biological solids contain large volumes of cell
water and are often smaller or finer in size than primary sludge
solids makes them harder to separate by gravity concentration.
The age of the secondary sludge also plays an important role
in the efficiency of gravity thickening processes. In the acti-
vated sludge process, ammonia is converted to nitrite and ni-
trate according to the following equations:
Ammonia (NH3) + Oxygen -» Nitrite (N02~) + HsO
Nitrite (N02~) + Oxygen Nitrate (N03~)
The conversion of ammonia to nitrite and then nitrate is
termed "nitrification." This conversion will occur if sufficient
oxygen and aeration time are alloted in the activated sludge
process to permit the buildup of NITRIFYING BACTERIA.13
In the solids-liquid separation section (secondary sedimen-
tation) of activated sludge wastewater treatment plants, the
available oxygen in the settled sludge may be depleted to the
point where no dissolved oxygen remains. If the sludge is held
too long in the final clarifier or gravity thickener and the dis-
solved oxygen concentration decreases to zero, the nitrate can
be converted to nitrogen gas. The conversion of nitrate to ni-
trogen gas is termed DENITRIFICATION.14 Rising bubbles of
nitrogen gas due to denitrification will carry settled solids to the
surface of secondary clarifiers or gravity thickeners and will
adversely affect process performance. Another problem occa-
sionally encountered with activated sludge processes is
"sludge bulking." If sufficient oxygen is not available in the
aeration basin or nutrient imbalances are present, FILA-
MENTOUS ORGANISMS15 may grow in the aeration basins.
The predominance of these organisms will decrease the
settleability of activated sludge and it will not settle as readily in
the secondary clarifiers or compact to its highest degree in
gravity thickeners. Greater compaction can be achieved by the
addition of chemicals.
7 Baffle. A flat board or plate, deflector, guide or similar device constructed or placed in flowing water, wastewater, or slurry systems to
cause more uniform flow velocities, to absorb energy, and to divert, guide, or agitate liquids.
• Short-Circuiting. A condition that occurs in tanks or ponds when some of the water or wastewater travels faster than the rest of the flowing
water.
• Rising Sludge. Rising sludge occurs when sludge settles to the bottom of the thickener, is compacted, and then starts to rise to the
surface, usually as a result of denitrilication.
to Anaerobic (AN-air-O-bick). A condition in which "free" or dissolved oxygen is NOT present in the aquatic environment.
11 Gasification (GAS-i-tl-KAY-shun). The conversion of soluble and suspended organic materials into gas during anaerobic decomposition.
In anaerobic sludge digesters, this gas is collected for fuel or disposed of using the waste gas burner.
,2 Bound Water. Water contained within the cell mass of sludges or strongly held on the surface of colloidal particles.
n Nitrifying Bacteria. Bacteria that change the ammonia and organic nitrogen in wastewater Into oxidized nitrogen (usually nitrate).
14 Denitrification. A condition that occurs when nitrite or nitrate ions are reduced to nitrogen gas and bubbles are formed as a result of this
process. The bubbles attach to the biological floes and float the floes to the surface of the secondary clarifiers or gravity thickeners.
is Filamentous Organisms (FILL-a-MEN-tuss). Organisms that grow in a thread or filamentous form. Common types are thlothrix and ac-
tfnomyces.
-------
138 Treatment Plants
Another sludge characteristic which affects the degree of
thickening is the temperature of the sludge. As the temperature
of the sludge (primary or secondary) increases, the rate of
biological activity is increased and the sludge tends to gasify
and rise at a faster rate. During summertime (warm weather)
operation, the settled sludge has to be removed at a faster rate
from the thickener than during wintertime operation. When the
sludge temperature is lower during the winter, biological activ-
ity and gas production proceed at a slower rate.
Solids and hydraulic retention times and loadings are dis-
cussed in the next section which reviews operating guidelines.
22.111 Operating Guidelines
The size of gravity thickeners is determined and designed by
engineers. THE OPERATOR CONTROLS THE SOLIDS RE-
TENTION TIME WITHIN THE THICKENER AND REACHES
PEAK PERFORMANCE BY CONTROLUNG THE SPEED OF
THE SLUDGE COLLECTION MECHANISM (IF POSSIBLE),
ADJUSTING THE SLUDGE WITHDRAWAL RATE AND CON-
TROLUNG THE SLUDGE BLANKET DEPTH. Successful op-
eration of gravity concentrators requires that the operator be
able to calculate applied loading rates and sludge detention
time, and be aware of the available controls.
22.1110 Hydraulic and Solids Loadings. The hydraulic sur-
face loading or overflow rate is defined as the total number of
gallons applied per square foot of thickener water surface area
per day (gpd/sq ft). To calculate hydraulic surface loading, first
determine the total water surface area in square feet. Then
divide the number of gallons applied per day by the surface
area (sq ft). The gallons applied usually include more than just
the sludge pumped, because it is better to keep a good high
flow of fresh liquid entering the thickener to prevent septic
conditions and odors from developing. To accomplish this
higher flow, secondary effluent is usually blended with the
sludge feed to the thickener. Typical hydraulic loading rates
are from 400 to 800 gpd/sq ft (16 to 32 cu m per day/sq m). For
a very thin mixture or for waste activated sludge (WAS) only,
hydraulic loading rates of 100 to 200 gpd/sq ft (4 to 8 cu m per
day/sq m) would be appropriate.
EXAMPLE 4
Given: A 20-foot diameter gravity thickener is used to thicken
20 GPM of primary sludge. 80 GPM of secondary
effluent is blended with the raw sludge to prevent septic
conditions and odors.
Find: The hydraulic surface loading applied to the gravity
thickener.
Solution:
Known
Thickener Diameter, ft = 20 feet
Sludge Flow, (3PM = 20 GPM
Blend Flow, GPM = 80 GPM
Total Flow, GPM = 100 GPM
Unknown
Hydraulic Surface Loading,
gpd/sq ft
Determine the flow in gallons per day and the water surface
area in square feet. Calculate the hydraulic surface loading in
gallons per day (gpd) per square foot.
Hydraulic Surface - ToUI How, gsl/mln x 60 mln/hr x 24 hr/dsy
Loading, gpd/sq ft 1 x (Diameter, ft)'
100 gstfmln x 60 mln/hr x 24 tit/flay
, 144,000 gpd
314 sq ft
¦ 460 gpd/sq ft
Z x (20 ft)'
4
The solids loading is defined as the total number of pounds
of solids applied per square foot of thickener surface area per
day. To calculate the solids loading, first find the total surface
area (sq ft) of the thickener. Next, using the flow rate and solids
concentration, calculate the total pounds of solids applied per
day. Finally, divide the total solids (lbs/day) by the total surface
area (sq ft) to find the solids loading. The proper operating
solids loading will vary with the type of sludge. Typical values
are discussed in Section 22.113, "Typical Performance."
EXAMPLE 5
Given: A 45-foot diameter gravity thickener is used to thicken
100 GPM of primary sludge. The primary sludge is
applied to the thickener at an initial sludge solids con-
centration of 3.5 percent.
Find: The solids loading (S.L.) applied to the gravity thickener
in lbs/day per sq ft.
Solution:
Known Unknown
Thickener Diameter, ft = 45 feet Solids Loading,
Sludge Flow, GPM = 100 GPM lbs/day/sq ft
Sludge Solids, % = 3.5%
Determine the solids applied to the thickener in pounds per
day.
Solids = Flow, gpd x 8.34 lbs/gal x Solids' %
Applied, 100%
lbs/day
= 100 gal/min x 1440 min/day x 8.34 lbs/gal
X 3-5%
100%
= 42,034 lbs/day
Calculate the solids loading.
Solids Loading, _ Solids Applied, lbs/day
'bs/day/sq ft Surface Area, sq ft
_ 42,034 lbs/day
1 (45 ft)2
4
= 26 lbs/day/sq ft
22.1111 Sludge Detention Time. The sludge detention time
is defined as the length of time the solids remain in the gravity
thickener. This time is based on the amount of solids applied,
the depth and concentration of the sludge blanket, and the
quantity of solids removed from the bottom of the thickener.
The operator has the ability to CONTROL THE SOUDS DE-
TENTION TIME AND THE DEGREE OF THICKENING TO
SOME EXTENT BY CONTROLUNG THE DEPTH OF THE
SLUDGE BLANKET. If the blanket is maintained at too high a
level and the solids detention time is excessive, gasification
may develop with subsequent rising sludge and deterioration
of effluent quality. The actual response of a particular sludge to
gravity thickening depends on the treatment plant. Trial and
error procedures usually determine the best operation. To aid
the operator in controlling the detention time of the solids in the
thickener, the sludge-volume ratio (SVR) term is used. SVR is
defined as the volume of the sludge blanket divided by the
daily volume of sludge pumped from the thickener. This term Is
a relative measure of the average detention time of solids in
the thickener and is calculated in days. Typical SVR values are
between 0.5 and 2.0 days. The higher SVRs are desirable for a
maximum sludge concentration; however, to guard against
gasification, the lower SVR values are maintained during warm
weather.
-------
Solids Disposal 139
22.112 Normal Operating Procedures
Typically, the flow through the thickener is continuous and
should be controlled to be as constant as possible. Monitoring
of the influent, effluent and concentrated sludge streams
should be done at least once per shift and should include
collection of samples for later laboratory analysis.
Under normal operating conditions, water at the surface
should be relatively CLEAR and free from solids and gas bub-
bles. The sludge blanket depth is usually kept around 5 to 8
feet (1.5 to 2.4 m). The speed of the sludge collectors should
be fast enough to allow the settled solids to move towards the
sludge collection pump. The bottom sludge collectors should
not be operated at speeds that will disrupt the settled solids
and cause them to float to the surface. Sludge withdrawal rates
should be sufficient to maintain a constant blanket level.
Normal start-up and shutdown procedures for placing a
thickener in or out of service are outlined below.
Start-Up
— Turn on the sludge collectors and scum collection equip-
ment.
— Activate chemical conditioning systems, if used.
— Open all appropriate inlet valves.
— Turn on and adjust, if possible, the influent sludge pump.
— Check the sludge blanket depth.
— Open all appropriate sludge withdrawal valves.
— Set the sludge pump in the automatic "ON" position.
— Routinely check the blanket depth and thickened sludge
concentration and adjust the withdrawal rate as required.
The thickener should be operated continuously. However, if
the thickener is not operated as a continuous process and daily
or frequent shutdowns are required, the following procedures
should be followed:
Shutdown
— Turn off the influent sludge pump and close appropriate inlet
valves.
— Turn off the chemical addition equipment, if chemical condi-
tioning is used.
— Allow the scum collection and sludge collection removal
systems to operate until the water surface is free of floating
material and settled sludge has been removed from the
thickener bottom.
— Turn off the scum collection, sludge collection and sludge
withdrawal equipment.
— Hose down and clean up the area as required.
22.113 Typical Performance
Typical loadings and thickener output concentrations for var-
ious sludge types are summarized in Table 22.2. Note that the
data presented in Table 22.2 is generalized and the actual
response of a particular sludge at a particular plant may vary
significantly.
TABLE 22.2 OPERATIONAL AND PERFORMANCE
GUIDELINES FOR GRAVITY THICKENERS
Solids Loading,
Thickened
Sludge Type
Ibs/day/sq ft*
Sludge, %
Separate
Primary
20-30
8-10
Activated Sludge
5-8
2-4
Trickling Filter
8-10
7-9
Combined
Primary & Act. SI.
6-12
4-9
Primary & Trickling
10-20
7-9
Filter
• Ibs/day/sq ft x 4.883 = kg/day/sq m
In order to rate the performance of gravity thickeners, the
operator must be familiar with the calculations required to de-
termine process efficiency.
The efficiency of any process in removing a particular con-
stituent is determined by the following equation:
Efficiency, % = ('"fluent-Effluent) x 100„/o
Influent
In the case of gravity thickeners, suspended or sludge solids
removal is a key performance factor. One of the goals of the
operator should be to remove as much of the influent solids as
possible. Usually the supernatant or overflow from the thick-
ener is returned to the plant headworks. If the solids concentra-
tion in this stream is high, then you are recirculating solids and
can end up "chasing your tail" (having to treat more and more
solids). The following example shows how to calculate sludge
solids removal efficiency for a gravity thickener.
EXAMPLE 6
Given: A gravity thickener receives 20 GPM of primary sludge
at a concentration of 3.0 percent sludge solids (30,000
mg/L). The effluent from the thickener contains 0.15
percent (1500 mg/L) of sludge solids.
Find: The efficiency in removing sludge solids.
Solution:
Unknown
Thickener Efficiency, %
= 20 GPM
Known
Gravity Thickener
Flow, GPM
(Primary Sludge)
Infl SS, %
Infl SS, mg/L
Effl SS, %
Effl SS, mg/L
= 3.0%
= 30,000 mgIL
= 0.15%
= 1,500 mg/L
Determine the thickener efficiency in removing sludge sol-
ids.
Efficiency, % = (
-------
140 Treatment Plants
the effectiveness of the thickener in concentrating the sludge.
The concentration factor (cf) is determined by the following
equation:
„ ...../ (l Thickened Sludge Cone., %
Concentration factor (cf) = 2 :—
Influent Sludge, Cone. %
The following example illustrates the use of the above equa-
tion.
EXAMPLE 7
Given: A primary sludge with a concentration of 3.0 percent
sludge solids is thickened to a concentration of 7.0 per-
cent sludge solids.
Find: The concentration factor (cf).
Solution:
Known Unknown
Primary Sludge Cone., % = 3.0% Concentration Factor
Thickened Sludge = 7.0%
Cone., %
Concentration = Thickened Sludge Concentration, %
Fac,or Influent Sludge Concentration, %
_ 7.0% Sludge Solids
3.0% Sludge Solids
= 2.33
The concentration factor determined above means that the
influent sludge was thickened to a concentration 2.33 times its
initial concentration. For primary sludges, the operator should
achieve concentration factors of 2.0 or higher. Concentration
factors for secondary sludges should be 3.0 or greater.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 264.
22.11A List the main components of gravity thickeners.
22.11B Discuss the function of the inlet baffle, sludge rakes,
and vertical pickets.
22.11C Discuss how the age of sludge may affect gravity
concentration of primary and waste activated
sludges.
22.11D How does sludge temperature affect the efficiency of
gravity thickeners and what measure should be
taken during summertime operation to reduce gas
production and rising sludge.
22.11E Determine the hydraulic surface (gpd/sq ft) and sol-
ids loading (Ibs/day/sq ft) to a 30-ft diameter gravity
thickener if 60 GPM of primary sludge at an initial
suspended solids concentration of 3.0 percent
sludge are applied.
22.11F A gravity thickener is used to concentrate 40 GPM of
waste activated sludge at a concentration of 0.9%
(9,000 mgIL). The underflow sludge is withdrawn at 3
percent and the effluent suspended solids concentra-
tion is 1,800 mgIL. Determine the suspended solids
removal efficiency (%) and the concentration factor.
22.114 Troubleshooting
VISUAL INSPECTION OF MOST WASTEWATER TREAT-
MENT UNIT PROCESSES COUPLED WITH AN UNDER-
STANDING OF THE EXPECTED RESULTS (COMPARE DE-
SIGN VALUES WITH OPERATING CRITERIA) FROM GOOD
PERFORMANCE ARE THE KEYS TO SUCCESSFUL OPER-
ATION. More often than not, the operator is made aware of
equipment malfunctions and/or decreases in process effi-
ciency by observing such items as liquid surfaces and effluent
quality and also being aware of uncharacteristic odors. Enough
emphasis cannot be placed on the OPERATOR'S AWARE-
NESS and ability to RECOGNIZE SIGNS OF TROUBLE. In
most instances, the experienced operator has the ability to
ward off major operational problems and to maintain efficient
operation by careful inspection and operational adjustments.
The specific areas of concern regarding gravity thickeners
are: (1) surface and overflow quality, and (2) sludge blanket
depth and thickened sludge concentrations.
22.1140 Liquid Surface. As previously discussed, the over-
flow or effluent should be relatively clear (less than 500 mg/L
suspended solids) and the liquid surface should be free of gas
bubbles. If the operator notices an excessively high carryover
of suspended solids, attention should immediately focus on the
hydraulic loading and signs of gasification. If gas bubbles are
evident at the tank surface, the problem may be caused by an
excessive sludge detention time and subsequent gasification.
The action(s) to be taken should include a determination of
sludge blanket depth and a visual estimate of the thickened
solids concentration. If the problem is related to an excessive
sludge retention time, the thickened sludge concentration will
be thicker than normal and the depth of the sludge blanket will
be higher than usual.
To correct the problem, the operator should increase the
rate of sludge withdrawal from the bottom of the thickener or
lower the feed rate, if possible. Once a change of this nature is
made, the operator should periodically check the condition of
the effluent and the thickened (underflow) solids so as not to
completely remove the sludge blanket and drastically reduce
the thickened sludge concentration.
If the sludge blanket depth and solids concentrations are not
high enough to be considered for causes of gasification, the
operator should investigate the speed of the sludge collectors
and the influent characteristics. Sludge collection equipment
may be equipped with a variable speed mechanism. If the
scrapers are operating at too low of a speed, gasification may
develop because pickets are not stirring the sludge and releas-
ing the gas. Another common cause of gasing in gravity thick-
eners is the age of the influent sludge. If the sludge is held too
long in the primary and/or secondary clarifiers, it may be well
on its way to releasing gas before it enters the thickener. If
gasing in the thickener cannot be attributed to operation of the
thickener, the operator should observe the influent sludge and
adjust the rate of sludge to the thickener. Secondary effluent
can be recirculated to the thickener to freshen the influent
sludge.
If poor effluent quality cannot be attributed to gasification,
the problem may be the result of malfunctions in chemicai
conditioning equipment or increased hydraulic loadings.
Chemical conditioning will be covered in Section 22.31, but the
operator should be aware that chemical underdosing or over-
dosing can lead to equipment inefficiencies and should inspect
the chemical addition equipment. Hydraulic loadings in excess
of design values also may lead to solids carryover and de-
creased efficiency. The operator should check the rate of
sludge pumping to the thickener, determine the hydraulic load-
ing according to the calculations presented in Example 4 and
adjust the thickener feed rate for successful operation.
Coagulating chemicals may be used if the effluent quality
needs improvement.
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Solids Disposal 141
22.1141 Thickened Sludge Concentration. Even if the
thickener appears to be operating effectively as evidenced by
the lack of gas on the surface and solids carryover with the
effluent, the operator should periodically check the thickened
sludge concentration and the blanket depth. The main objec-
tive of sludge thickening is to produce as concentrated a
sludge as possible to effect volume reductions and cost sav-
ings in subsequent processes. If the thickened sludge concen-
tration is not as thick as desired, the operator should check the
blanket depth before making any adjustment to the withdrawal
rate. On occasion, sludge in primary sedimentation tanks and
gravity thickeners can become very thick and resistant to
pumping. If this happens, a "hole" (CONING,6) can develop in
the blanket and liquid from above the blanket can be pulled
through the pump. Lowering the rate of sludge withdrawal
would increase the amount of solids at the bottom of the thick-
ener and eventually result in SEPTICITY17 and rising sludge. A
hole (cone) in the sludge blanket (indicated by a low thickened
sludge concentration and a high blanket level) can best be
corrected by: (1) lowering the flow to the affected thickener, (2)
increasing the speed of the collectors to keep the sludge at the
point of withdrawal, and (3) increasing the rate of thickened
sludge pumping. If both the blanket and the thickened sludge
solids concentrations are low, the operator should lower the
rate of sludge withdrawal in accordance with the calculations
outlined below.
With time and experience, the opeator should be able to
roughly estimate the concentration of the influent and thick-
ened sludges. This ability to "eyeball" concentrations coupled
with previous performance data should enable the operator to
control withdrawal rates.
EXAMPLE 8
Given: A 40-foot diameter by 10-foot SWD (Side Water Depth)
gravity thickener is used to concentrate 100 GPM of
primary sludge. The primary sludge enters the thick-
ener at approximately 3.5 percent based on the previ-
ous week's data. The sludge is withdrawn from the bot-
tom of the thickener at 40 GPM at a concentration of 7.0
percent. The thickener effluent has a suspended solids
concentration of 700 mg/L and the sludge blanket is 3
feet thick.
Find: 1. The sludge detention time in hours.
2. If the present influent and effluent conditions are
maintained, will the sludge blanket increase or de-
crease in depth?
3. What changes should be made if a higher concen-
tration of underflow (thickened sludge) solids is de-
sired?
4. What changes would stop gasification? How would
these changes affect thickened sludge concentra-
tions?
Solution:
Known
Gravity Thickener
Diameter, ft
Side Water Depth, ft
Flow In, GPM
(Primary sludge)
Sludge Out, GPM
Primary Sludge
Cone., %
Sludge Out Cone., % = 7.0%
Thickener Effluent
Susp Sol, mg/L
40 feet
10 feet
100 GPM
¦ 40 GPM
3.5%
Unknown
1. Sludge - Volume Ratio,
days
2. Will sludge blanket in-
crease or decrease?
3. What changes would in-
crease underflow sludge
concentrations?
4. What changes would stop
gasification? How would
these changes affect thick-
ened sludge concentra-
tions?
% =
700 mg/L
0.07%
Sludge Blanket, ft =3 feet
1. Calculate the Sludge - Volume Ratio (SVR) in days.
a. Determine the sludge blanket volume in gallons.
Sludge Blanket = tt x (Diameter x Blanket, ft x748 9al
Volume, gal 4 Cu ft
= 1 x (40 ft)2 x 3 ft x 7 48 gal
4 cu ft
= 28,200 gallons
b. Determine the sludge pumped in gallons per day.
Sludge Pumped, = Slud Qut QPM x 1440
gal/day a day
= 4n 9al x id4n m'n
min day
= 57,600 gal/day
18 Coning (CONE-ing). Development of a cone-shaped flow of liquid, like a whirlpool, through sludge. This can occur in a sludge hopper
during sludge withdrawal when the sludge becomes too thick. Part of the sludge remains In place while liquid rather than sludge flows out of
the hopper. Also called "coring."
17 Septicity (sep-TIS-it-tee). Septicity is the condition in which organic matter decomposes to form foul-smelling products associated with the
absence of free oxygen. If severe, the wastewater turns black, gives off foul odors, contains little or no dissolved oxygen and creates a heavy
oxygen demand.
-------
*42
c. Calculate the Stodge - Volume Ratio (SVR) in days.
SVR dnyc = S8*
Sludge f utriped, gal/day
= 29,200^
57,MO fit/day
= 0.5 days
2. Will the sludge blanket increase or decrease? If the quantity
of solids entering the thickener is greater than tfie quantity
leaving the thickener, then the blanket depth will increase. If
the quantity of solids entering the thickener is less than the
quantity leaving the thickener, the blanket thickness will
decrease. The solution to this problem is based on mass
balance calculations, as shown below:
a. Determine the pounds of sludge solids entering the
thickener daily.
S'und.9® Solids = Flow In, GPM x 1440 Hill x 8.34 x Sl ln' T°
Entering, d , 100o/o
lbs/day 1 a
= mn 9al v 1440 m!n * ft a* lbs x 3'5%
min
day
gal 100%
= 42,034 lbs/day
b. Determine the pounds of sludge solids withdrawn in the
thickener underflow daily.
SWithdrawnd8 = Sludfle 0ut' GPM x 1440 — x 8 34 — x Sl °Ul %
lbs/day ' day gal 100%
= 40 X 1440 X 8.34 x 7 0%
min day
= 33,627 lbs/day
gal 100%
c. Determine the pounds of solids lost in the thickener
effluent daily.
S^Lost in = Row GPM x 1440 x 8.34 !^i x Effl %
Effl, lbs/day day ga, 100%
= (100 GPM-40 GPM) x 1440 x 8.34 x °_07%
day gal 100%
= 60 5?[x 1440™? x 8.34 !^i x °-07%
min day gal 100%
= 504 lbs/day
d. Determine total pounds of solids removed daily.
Solids Out, _ Sludge Solids , Solids Lost in
lbs/day Withdrawn, lbs/day Effl, lbs/day
= 33,627 lbs/day + 504 lbs/day
= 34,131 lbs/day
e. Compare the sludge solids in with the solids out.
aE1SS^k"-42-M4'""tt'
lbs/day
Solids Out, - m
lbs/day -34,131 lbs/day
Therefore, since the solids entering (42,034 lbs/day)
are greater than the solids out (34,131 lbs/day), the
sludge blanket will increase in depth.
3. What changes would increase the thickened sludge con-
centration? Higher thickened sludge solids concentration
will normally result if the depth of the sludge blanket is
increased. To increase the blanket depth, the flow rate of
the thickened sludge should be decreased somewhat. The
thickened sludge is at a rate of 40 GPM AND THE RATE
SHOULD HOT BE CHANGED AT MCHEUEMTS O*
GREATER THAN 20 PERCENT WHEN STEADY STATE.
CONDITIONS EXIST. DRASTIC CHANGES SHOULD BE
AVOtDED and a doee watch sheutd be kept over the dept)
of the blanket after such changes are made. To increase
the sludge blanket depth and the thickened sludge concen-
tration, the sludge withdrawal rate should be decreased to
approximately 40 GPM - (40 GPM x 20%/100%) = 40
GPM - 8.0 GPM = 32 GPM.
Another approach to regulating the sludge blanket depth
is to sound (measure) the depth of the sludge blanket In
general, if the depth is greater than 7 feet (2.1 m), increase
the underflow withdrawal rate and if the depth is less than 5
feet (1.5 m), decrease the withdrawal rate.
4. What changes would stop gasification? How would these
changes affect thickened sludge concentrations?
If gasification develops as a result of excessive sludge
retention times, the rate of the sludge withdrawal should be
increased so as to lower the sludge blanket depth with sub-
sequent lowering of the sludge retention time. The net ef-
fect on thickener performance will be a decrease in thick-
ened sludge concentration and a possible improvement in
effluent quality. Another alternative may be to recirculate
secondary effluent to freshen the sludge.
EXAMPLE 9
Given: The thickener from Example 8 has just been restarted
following routine maintenance shutdown. The influent
concentration is "eyeballed" at approximately 3.0 per-
cent sludge solids. The influent flow is 150 gpm and the
sludge withdrawal pump is set at 15 gpm. After a few
hours of continuous operation, the sludge blanket depth
is measured and found to be 2 feet thick. The underflow
concentration is estimated to be approximately 6 per-
cent.
Find: Should the operator increase, decrease, or maintain
the current rate of withdrawal?
Solution:
Known
Known information from Example 8
Infl SI Cone, %
Infl Flow, GPM
Sludge Withdrawal
Pump, GPM
= 3.0% SI Sol
= 150 GPM
= 15 GPM
= 2 ft
Unknown
Should rate of sludge
withdrawal be increased,
decreased, or not
changed?
Sludge Blanket
Depth, ft
Thickened SI Cone, % = 6.0% SI Sol
1. Calculate the sludge solids entering in pounds per minute.
Solids Entering, _ ,n|t F)ow GPM x 0 34 Ibs^ x SI Sol In, %
Ibs/min gai 100%
= 150 gal/min x 8.34 lbs/gal x 3.0%/100%
= 37.5 Ibs/min
2. Calculate the sludge solids leaving the thickener in pounds
per minute.
Solids Withdrawn, = Underf|0Wi GPM x 8.34 lbs x Unfl Sl- %
•bs/min gal 100%'
- 15?!Lx8.34!5!.x6^%
min
7.5 Ibs/min
gal 100%
-------
Solids Disposal 143
The number of pounds exiting with the effluent can be ne-
glected if the effluent is clear (less than 500 mg/L suspended
solids) and little solids carryover is observed.
Based on the visual estimations of sludge concentration and
the above calculations, sludge is being stored at the rate of
30.0 Ibs/min (lbs enter-lbs exit). The sludge blanket depth is 2
feet but let us assume typical operation for this thickener indi-
cates that a blanket depth of 5 feet can be maintained. The
operator should therefore determine the time required to fill the
thickener with 3 additional feet of sludge at the present condi-
tions. The calculations are shown below.
Storage
Time, min
Storage 62.4 lbs v Unfl SI %
Volume, cu ft
cu ft
100%
Sludge Storage Rate, Ibs/min
w x (40 ft)2 x 3 ft x 62.4 lbs x 6.0%
cu ft
100%
30 Ibs/min
Storage
Time, hrs
= 470 min
„ 470 miri
60 min/hr
7.8 hours
If the unit is left as is, the blanket will reach a depth of 5 feet
in approximately 8 hours. However, at the end of the 8 hours,
the operator will again have to adjust the withdrawal rate to
avoid even greater buildup of sludge blanket. Drastic changes
in withdrawal rates are not desirable and can be avoided by
making a slight adjustment at the start of the 8-hour period.
This adjustment should be made based on the ratio of volume
stored to total storage volume as shown below.
Sludge Storage _ (Stored Sludge Height, ft) y Solids Entering,
Rate, Ibs/min ~ Total Storage Height, ft ,bs/min
= 11.
5 ft
x 37.5 Ibs/min
We, therefore, want to store solids at a rate of 15 Ibs/min
instead of the current 30 Ibs/min. To obtain this storage rate,
the desired sludge withdrawal rate must be determined in
pounds per minute.
Sludge Withdrawal _ Solids Entering, _ Sludge storage
Rate, Ibs/min Ibs/min Rate, Ibs/min
= 37.5 Ibs/min
= 22.5 Ibs/min
15 Ibs/min
The sludge withdrawal pumping rate must be increased in
order to remove underflow solids at a rate of 22.5 pounds per
minute.
Sludge Withdrawal
Pumping Rate, GPM
Sludge Withdrawal, Ibs/min
8.34 lbs/gal x Unfl SI, %/100%
22.5 Ibs/min
8.34 lbs/gal x 6.0%
100%
= 45 GPM
= 15 Ibs/min
The sludge withdrawal pumping rate should therefore be
increased from 15 GPM to 45 GPM at this time. This change
represents a 200 percent increase in withdrawal rate which is
substantially greater than the 20 percent change outlined in
Example 8. In Example 8, the thickener was operating under
steady state (lbs in = lbs out) conditions and under such condi-
tions the withdrawal rate should not be changed by increments
greater than 20 percent. For this example, the thickener is not
at steady state and the formulas outlined above should govern
the withdrawal rate changes. Approximately 4 hours after the
above change is made the operator should re-check the blan-
ket depth, sludge concentrations and effluent quality, rerun the
above calculation and change the withdrawal rate, if required.
Table 22.3 summarizes the operational problems that may
develop and lists the corrective measures that might correct
such problems.
Operational Problem
TABLE 22.3 TROUBLESHOOTING GRAVITY THICKENERS
Possible Causes Check or Monitor Possible Solutions
Liquid level clear but sludge
1. a.
Gasification
1. a.
Sludge blanket and sludge
1. a.
rising and solids carry-over
b.
Septic feed
detention
c.
Blanket disturbances
b.
Characteristics of feed
b.
d.
Chemical inefficiencies
c.
Sludge collector speed
e.
Excessive loadings
d.
Chemical equipment
c.
e.
Hydraulic flow rate
d.
2. Thin (dilute) underflow sludge
and clear effluent
3. Thin (dilute) underflow sludge,
liquid level clear but sludge
rising with solids carryover
4. Thin (dilute) underflow sludge,
liquid surface laden with solids
and solids carryover
a. Low blanket
b. Sludge withdrawal rate too
high
a. Collector speed too low or
inoperative
b. Hole or cone in sludge
blanket
a. Hydraulic loading high
b. Chemical system inopera-
tive
2. a. Blanket level 2.a.
drawal rate
Increase slud
from clarifier
rate
e. Lower flow if possible
Decrease sludge withdrawal
rate
3. a. Collector mechanism and 3. a.
speed
b. Blanket level b.
a. Loadings. Influent sludge 4. a.
b. Chemical equipment b.
Turn on and/or increase
collector speed
Increase collector speed
and increase withdrawal
rate
Lower influent sludge flow
Increase chemical rate
* If solids carryover is caused by gasification, increase collector speed.
-------
144 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 264 and 265.
22.11G Why should the operator make routine visual checks
on gravity thickeners as well as any other equip-
ment?
22.11H What is the meaning of the term "hole" in the blanket
and how can it be corrected?
22.111 A gravity thickener has been operating successfully.
On a routine check the operator notices that solids
are rising to the surface. List the possible causes
and outline the procedures the operator should fol-
low to correct the problem(s).
22.12 Dissolved Air Flotation Thickeners
The objective of flotation thickening is to separate solids
from the liquid phase in an upward direction by attaching air
bubbles to particles of suspended solids. Four general
methods of flotation are commonly employed. These include:
1. Dispersed air flotation where bubbles are generated by
mixers or diffused aerators.
2. Biological flotation where gases formed by biological activ-
ity are used to float solids.
3. Dissolved air (vacuum) flotation where water is aerated at
atmospheric pressure and released under a vacuum.
4. Dissolved air (pressure) flotation where air is put into solu-
tion under pressure and released at atmospheric pressure.
Flotation by dissolved air (pressure) is the most commonly
used procedure for wastewater sludges and will be the topic of
discussion in this section. Flotation units may be either rectan-
gular or circular in design. The dissolved air system employs
either a compressed air supply or an ASPIRATOR-TYPE18 air
injection assembly to obtain a pressurized air-water solution.
The key components of dissolved air flotation thickener (DAF)
units, as shown in Figure 22.3, are (1) air injection equipment,
(2) agitated or unagitated pressurized retention tank, (3) recy-
cle pump, (4) inlet or distribution assembly, (5) sludge scrap-
ers, and (6) an effluent baffle.
The sludge to be thickened is either introduced to the unit at
the bottom through a distribution box and blended with a pre-
pressurized effluent stream or the influent stream is saturated
with air, pressurized, and then released to the inlet distribution
assembly. Total waste stream pressurization may shear floccu-
lent type sludges and seriously reduce process efficiency. Di-
rect saturation and pressurization of the sludge stream is not
the preferred mode of operation where primary sludges are to
be thickened. Primary sludges often contain stringy material
that can clog or "rag-up" the aeration equipment in a pres-
surized retention tank. Flotation thickening of excess biological
solids may use air saturation and pressurization of the waste
stream with less possibility of clogging the air addition and
dissolution equipment.
The preferred mode of operation from a maintenance stand-
point is the use of a recycle stream to serve as the air carrying
medium. Referring again to Figure 22.3, the operation of dis-
solved air flotation (DAF) units which incorporate recycle tech-
niques are as follows. A recycled primary or secondary effluent
stream is introduced into a retention tank to dissolve air into the
liquid. The retention tank is maintained at a pressure of 45 to
70 psig (3.2 to 4.9 kg/sq cm). Compressed air is either intro-
duced into the retention tank directly or at some point upstream
of the retention tank or an aspirator assembly is used to draw
air into the stream.
The pressurized air saturated liquid then flows to the distri-
bution or inlet assembly and is released at atmospheric pres-
sure through a back pressure-relief valve. The decrease in
pressure causes the air to come out of solution in the form of
thousands of minute air bubbles. These bubbles make contact
with the influent sludge solids in the distribution box and attach
to the solids causing them to rise to the surface. These concen-
trated solids are then removed from the surface. An effluent
baffle is provided to keep the floated solids from going into the
effluent. The effluent baffle extends approximately 2 to 3
inches (5.0 to 7.5 cm) above the water surface and 12 to 18
inches (0.3 to 0.45 m) below the surface. Clarified effluent
flows under the baffle and leaves the unit through an effluent
weir. If air is introduced or aspirated upstream of the retention
tank, it is usually done on the suction side of the recycle pump
to use the pump as a driving force for dissolving air into the
liquid. The main disadvantage associated with introducing air
to the suction side of pumps is the possibility of pump CAVITA-
TION'19 and the subsequent loss of pump capacity. Systems
that add compressed air directly to the retention tank com-
monly use a float control mechanism to maintain a desired
air-liquid balance. A sight glass should be provided to periodi-
cally check the level of the air-liquid interface because if the
float mechanisms fail, the retention tank may either fill com-
pletely with liquid or with air. In either case, the net effect will be
a drastic reduction in flotation efficiency.
22.120 Factors Affecting Dissolved Air Flotation
The performance of dissolved air flotation units depends on
(1) type of sludge, (2) age of the feed sludge, (3) solids and
hydraulic loading, (4) air to solids (A/S) ratio, (5) recycle rate,
and (6) sludge blanket depth.
As is the case with gravity thickeners, the type and age of
sludge applied to flotation thickeners will affect the overall per-
formance. Primary sludges are generally heavier than excess
18 Aspirate (ASS-per-RATE), Use of a hydraulic device (aspirator or eductor) to create a negative pressure (suction) by forcing a liquid
through a restriction, such as a Venturi. An aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump;
sometimes used instead of a sump pump.
19 Cavitation (CAV-i-TAY-shun). The formation and collapse of a gas pocket or bubble on the blade of an impeller. The collapse of this gas
pocket or bubble drives water into the impeller with a terrific force that can cause pitting on the impeller surface.
-------
Solids Disposal 145
SLUDGE
REMOVAL —
MECHANISM
EFFLUENT.
floated
sludge
DISCHARGE
RECYCLE
FLOW
POLYMER FEED
RECYCLE FLOW
FEED SLUDGE
INFLUENT
DISTRIBUTION
BOX
BOTTOM
SLUDGE
COLLECTOR
EFFLUENT
FLOTATION UNIT
rOU
RECIRCULATION
PUMP
AIR
FEED
THICKENED
SLUDGE
DISCHARGE
FEED
SLUDGE
AIR SATURATION TANK
RE-AERATION
PUMP
RECYCLE
FLOW
Fig. 22.3 Dissolved air flotation thickener
-------
146 Treatment Plants
biological sludges and are not as easy to treat by flotation
concentration. If enough air is introduced to float the sludge
mass, the majority of the primary sludge solids will float to the
surface and be removed by the skimming mechanisms. Gritty
or heavy primary sludge particles will settle and be deposited
on the floor of the flotation unit and provisions should be made
to remove these settled solids. If a flotation unit is used for
primary sludge thickening, the flotation cell is usually equipped
with sludge scrapers to push the settled solids to a collection
hopper for periodic removal. Problems will arise when concen-
trating primary sludges or combinations of primary sludge and
waste activated sludge if the flotation chamber is not equipped
with bottom sludge scrapers and sludge removal equipment.
Solids buildup will result in a decrease in flotation volume and a
reduction in thickener efficiency.
Excess biological sludges are easier to treat by flotation
thickening than primary sludges because they are generally
lighter and thus easier to float. Bottom sludge scrapers should
still be incorporated in the design of units used solely for biolog-
ical sludge because a small fraction of solids will settle. These
settled solids will eventually become anaerobic and rise due to
gasification. If these solids are deposited at the effluent end of
the unit, solids may be carried under the effluent baffle and exit
the unit with the effluent.
Sludge age usually does not affect flotation performance as
drastically as it affects gravity concentrators. A relatively old
sludge has a natural tendency to float due to gasification and
this natural buoyancy will have little or no negative effect on the
operation of flotation thickeners. However, rising sludge does
create problems in primary and final sedimentation processes
and should be avoided by controlling the sludge withdrawal
rate from these unit processes.
Solids and hydraulic loadings, A/S (air to solids) ratios, recy-
cle rate and sludge blanket depth are normal operational
guidelines and are discussed in the following paragraphs.
22.121 Operating Guidelines
The size of dissolved air flotation units is determined by the
engineers who design them. The operator has control over A/S
ratio, recycle rate and the blanket thickness and can optimize
performance by properly adjusting these variables. Before dis-
cussing the control variables, the operator should be familiar
with determining applied loading rates.
22.1210 Solids and Hydraulic Loadings. Solids and hydrau-
lic loadings for flotation units are based on the same calcula-
tions used to determine loading rates for gravity thickeners. If
either the solids or hydraulic loading becomes excessive,
effluent quality declines and thickened sludge concentrations
are reduced. The following example shows how to calculate
loading rates.
EXAMPLE 10
Given: A dissolved air flotation unit receives 100 gpm of waste
activated sludge with a suspended solids concentration
of 8,000 mg/L. The rectangular flotation unit is 40 feet
long and 15 feet wide.
Find: The hydraulic loading (gpm/sq ft) and solids loading
(Ibs/hr/sq ft).
Solution:
Known Unknown
Flow, GPM = 100 GPM 1. Hydraulic Loading, gpm/sq ft
Sus Sol, mg/L = 8000 mg/L 2. Solids Loading, Ibs/hr/sq ft
= 0.8%
Flotation Unit
Length = 40 ft
Width = 15 ft
1. Determine the hydraulic loading, gpm/sq ft.
Hydraulic Loading, _ Flow, GPM
gpm/sq ft Liquid Surface Area, sq ft
_ 100 gal/min
40 ft x 15 ft
_ 100 gal/min
600 sq ft
= 0.2 gpm/sq ft
2. Determine the solids loading, Ibs/hr/sq ft.
Flow, GPM x 60min x 8.34 lbs x SS, %
Solids Loading, = hr gal 100%
Ibs/hr/sq ft Liquid Surface Area, sq ft
100 gal x 60 min x 8.34 lbs x 0.8%
min hr gal 100%
40 ft x 15 ft
400 Ibs/hr
600 sq ft
= 0.67 Ibs/hr/sq ft
22.1211 Air to Solids (A/S) Ratio. The QUANTITY OF AIR
INTRODUCED and dissolved into the recycle or waste stream
IS CRITICAL to the operation of flotation thickeners. Enough
air has to be added and dissolved to float the sludge solids.
The most effective method of accomplishing this is to introduce
air into a pressurized retention tank along with the waste
stream to be thickened or along with a portion of the thickener
effluent stream. Air also can be dissolved in primary or sec-
ondary effluent, thus avoiding solids spin around in the DAF
unit. MIXING OF THE RETENTION TANK CONTENTS
SHOULD ALSO BE USED TO INCREASE THE AMOUNT OF
AIR THAT CAN BE PUT INTO SOLUTION. In unmixed pres-
sure retention tanks, only about 50 percent of the injected air
will dissolve while 90 percent saturation can be obtained by
vigorous agitation of the tank contents. As previously dis-
cussed, following a short detention time in the pressurized
retention tank, the saturated-air-liquid stream is pumped to the
inlet side of the flotation unit where it enters a distribution as-
sembly via a back pressure-relief valve. The release of the
saturated air stream to atmospheric pressure causes the air to
come out of solution in the form of very small bubbles.
Thousands of these minute bubbles attach to particles of sus-
pended solids allowing the solids to float to the surface, con-
centrate and be removed by the sludge skimming mechanism.
The more air you have dissolved in the retention tank, the
greater the number of minute air bubbles that will be released
in the distribution assembly. And, the more bubbles you pro-
duce in the distribution assembly, the more efficient your oper-
ation will be.
The amount of air supplied to the unit is usually controlled by
an air rotameter and compressor assembly which are activated
by a liquid level indicator in the retention tank. THE MOST
IMPORTANT OPERATIONAL CONCERN IS TO INSURE
-------
Solids Disposal 147
THAT THE AIR ROTAMETER, COMPRESSOR AND THE
FLOAT MECHANISM TO ACTUATE AIR INJECTION ARE IN
PROPER WORKING ORDER.
The quantity of air applied to the system is determined accord-
ing to the following calculations.
EXAMPLE 11
Given: An air rotameter and compressor provide for 10 cubic
feet per min (SCFM)20 of air to be injected into a
pressurized retention tank.
Find: The pounds of air applied to the unit per hour (tbs/hr).
Solution:
Known Unknown
Air Flow, SCFM = 10 SCFM Air Applied, Ibs/hr
Calculate the air applied in pounds of air per hour.
^APplied- = Air Flow,_Ell x 60 mjn x 0.075 lb air
lbs/hr min hr ou ft air
= 10 cu ft x 6(* min x 0.075-
Ib
min
45 Ibs/hr
hr
cu ft
NOTE: The conversion factor of 0.075 pounds of air per cubic
foot of air will change with temperature and elevation or
barometric pressure.
The ratio between air supplied and the quantity of solids
applied to the flotation unit is then the air-to-solids (A/S) ratio.
The following example illustrates the determination of air/solids
(A/S) ratio.
EXAMPLE 12
Given: A dissolved air flotation unit receives 100 gpm of waste
activated sludge at a concentration of 9000 mg/L (0.9%
solids). Air is supplied at a rate of 5.0 cu ft/min.
Find: The air-to-solids (A/S) ratio.
Solution:
Known
Solids Flow, GPM = 100 GPM
SI Cone, mg/t
= 9000 mg/L
= 0.9% Solids
Unknown
Air-to-Solids (A/S)
Ratio
Air, cu ft/min = 5.0 cu ft/min
Calculate the air-to-solids (A/S) ratio.
Air, lbs _ Air, cu ft/min x 0.075 Ibs/cu ft
Solids, lbs Solids, GPM x 8.34 lbs x SI Cone, %
gal 100%
_ 6.0 cu ft/min x 0.075 Ibs/cu fl
100 gal x 8,34 lbs y 0.9%
min gal 100%
= 0 375 lb8 alf
7.5 lbs solids
= 0.05 lbs air/lb solids
22.1212 Recycle Rate and Sludge Blanket. Both the rate of
effluent recycle and the thickness of the sludge blanket are
operational controls available to optimize DAF performance.
Typically, the recycle rates of 100 to 200 percent are used. A
recycle rate of 100 percent means that for every gallon of
influent sludge there is one (1) gallon of DAF effluent recycled
to the DAF inlet works.
The following example illustrates the determination of recy-
cle rate.
EXAMPLE 13
Given: A dissolved air flotation unit receives waste activated
sludge flow of 50 GPM. The recycle rate is set at 75
GPM.
Find: Percentage of recycle.
Solution:
Unknown
Percentage of recycle.
Known
Waste Flow, GPM = 50 GPM
Recycle Flow, GPM = 75 GPM
Calculate the percentage of recycle.
Recycle, %= Recycle Flow, GPM x 10Q%
Waste Flow, GPM
= 75 GPM x 100%
50 GPM
= 150%
The optimum recycle rate for a particular unit will vary from
one treatment plant to the next and it is impossible to define
that rate tor every application. The important point is that the
recycle stream carries the air to the inlet of the unit. Obviously,
as the rate of recycle increases, the potential to carry more air
to the inlet also increases. The term "potential" is used here
because the recycle rate and the quantity of air dissolved and
released in the inlet assembly are dependent on one another
by virtue of what happens in the retention tank. DAF recycle
pumps are usually centrifugal pumps which means that as the
pressure upstream (retention tank) increases, the output (flow)
decreases. Therefore, the rate of recycle is directly dependent
on the pressure maintained within the retention tank. As stated
previously, retention tank pressures of 45 to 70 psi (3.2 to 4.9
kg/sq cm) are commonly used. As the pressure within the re-
tention tank is increased or decreased by closing or opening
the back pressure-relief valve, the recycle rate will decrease or
increase. The optimum recycle rate and retention tank pres-
sure are usually determined by experimentation.
The thickness of the floating sludge blanket can be varied by
mcreasfng or decreasing the speed of the surface sludge
scrapers. Increasing the sludge scrapers speed usually tends
to thin out the floated sludge while decreasing the scrapers
speed will generally result in a more concentrated sludge.
22.122 Normal Operating Procedures
Typically, the flow through the thickener is continuous and
should be set as constant as possible. Monitoring of the in-
fluent, effluent, and float sludge streams should be done at
least once per shift and composite samples should be taken for
later laboratory analysis.
Under normal operating conditions, the effluent stream
should be relatively free of solids (less than 100 mg/L sus-
pended solids) and will resemble secondary effluent. The float
solids will have a consistency resembling that of cottage
cheese. The depth of the float solids should extend approxi-
mately 6 to 8 inches (15 to 20 cm) below the surface. The
20 SCFM. Cubic Feet of air per Minute at Standard conditions of temperature, pressure and humidify.
-------
148 Treatment Plants
surface farthest from the float solids collection and the dis-
charge point should be scraped clean of floating solids with
each pass of the sludge collection scrapers. If the sludge blan-
ket is allowed to build up (too thick) and drop too far below the
surface, thickened (floated) solids will be carried under the
effluent baffle and contaminate the effluent.
Normal start-up and shutdown procedures are outlined be-
low:
Start-Up
— Open the inlet and discharge valves on the recycle pump
and turn on the recycle pump only when thickener is full.
— Adjust the retention tank pressure to the desired pressure
(45 to 70 psig or 3.2 to 4.9 kg/sq cm) by opening or closing the
pressure regulating valve.
— Open the inlet and discharge valves on the re-aeration
pump and turn on the re-aeration pump. If a mechanical mixer
is used instead of a re-aeration pump, turn on the mixer in the
retention tank. Mixing in the retention tank may be accom-
plished by methods other than the use of mechanical mixers.
— Open the appropriate air injection valves and turn on the air
compressor.
— Open the appropriate chemical addition valves and turn on
the chemical pump if chemicals are used.
— Open the inlet and discharge valves on the sludge feed
pump and start the feed pump.
— Allow floated sludge mat to build up, then .turn on sludge
collection scrapers.
If the thickener is not operated in a continuous mode and
daily or frequent shutdowns are required, the following proce-
dures should be followed:
Shutdown
— Turn off the sludge inlet pump and close the appropriate
valves.
— Turn off the chemical pump and close appropriate valves.
— Turn on the fresh water supply to the unit AND ALLOW IT
TO RUN ON FRESH WATER UNTIL THE SURFACE IS FREE
OF FLOATING SLUDGE.
— Turn off the air compressor and close appropriate air
valves.
— Turn off the re-aeration and recycle pumps and close ap-
propriate valves.
— Turn off the sludge collectors.
— Hose do\Vn and clean up as required.
22.123 Typical Performance
Typical operating guidelines as well as thickened sludge
concentration and suspended solids removals for waste acti-
vated sludge are presented in Table 22.4.
TABLE 22.4 OPERATIONAL AND PERFORMANCE
GUIDELINES FOR FLOTATION THICKENERS
Without With
Polymer Addition Polymer Addition
Solids Loading,
Ibs/hr/sq ft*
0.4 - 1
1 - 2
Hydraulic Loading,
GPM/sq ft**
0.5 - 1.5
0.5 - 2.0
Recycle, %
100 - 200
100 - 200
Air/Solids, lb/lb
0.01 - 0.10
0.01 - 0.10
Minimum Influent Solids
Concentration, mg IL
5000
5000
Float Solids Concen-
tration, %
2 - 4
3-5
Solids Recovery, %
50 - 90
90-98
* Ibs/hr/sq ft x 4.883 = kg/hr/sq m
** GPM/sq ft x 0.679 = Llseclsq m
The determination of solids recovery in the operation of the
DAF unit is based on laboratory analysis and the following
calculations.
EXAMPLE 14
Given: A 100-foot diameter dissolved air flotation unit receives
750 GPM of waste activated sludge at a concentration
of 0.75% (7500 mgIL) sludge solids. The effluent con-
tains 50 mg//. of suspended solids. The float or thick-
ened sludge is at a concentration of 3.3 percent.
Find: The solids removal efficiency (%) and the concentration
factor (cf).
Solution:
Known Unknown
Dissolved Air Flotation Unit 1. Solids Removal Efficiency, %
Infl Solids, mgIL = 7500 mg IL 2. Concentration Factor (cf)
or = 0.75%
Effl Solids, mg IL = 50 mg IL
Effl Sludge, % = 3.3%
(Thickened Sludge)
-------
Solids Disposal 149
1. Determine the solids removal efficiency, %.
Solids Removal = (Inf Solids, mg/L - Effl Solids, mg/L) 100%
E,flclency' % Infl Solids, mg/L
(7500 mg/L - 50 mg/L) 100%
7500 mg/L
= 99.3%
2. Calculate the concentration factor (cf) for the thickened
sludge.
Concentration _ Thickened Sludge Concentration, %
Factor, (cf) Effluent Sludge Concentration, %
= 3.3%
0.75%
= 4.4
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 265 and 266.
22.12A List the main components of dissolved air flotation
(DAF) systems.
22.12B Discuss the function of the distribution box, the re-
tention tank and the effluent battle.
22.12C Why should a sight glass be provided on the reten-
tion tank?
22.12D List the factors that affect the performance of DAF
thickeners.
22.12E What effect does sludge age have on DAF thicken-
ers?
22.12F Determine the hydraulic loading (gpd/sq ft) for a
20-foot diameter DAF unit. The influent flow is 100
GPM.
22.12G For the above problem, determine the solids load-
ing, A/S ratio and recycle flow rate (GPM), if the
influent sludge has a suspended solids concentra-
tion of 0.75% (7500 mg/L), and is supplied at a rate
of 2.5 cu ft/min. Air is supplied at a rate of 0.75 cu
ft/min and a recycle ratio of 100 percent is required.
22.12H Determine the suspended solids removal efficiency
(%) and the concentration factor (cf) if a DAF unit
receives an influent sludge at 1.0 percent (10,000
mg/L) suspended solids. The effluent is at 50 mg/L
suspended solids and the float or thickened sludge is
at a concentration of 3.8 percent.
22.124 Troubleshooting
VISUAL INSPECTION of the dissolved air flotation unit in
conjunction with a working knowledge of the operating tech-
niques is the operator's biggest asset in assuring efficient op-
eration. The specific areas that the operator should be con-
cerned with are: (1) effluent quality, and (2) thickened sludge
(float) characteristics. The effluent from DAF units should be
relatively clear (less than 100 mg/L suspended solids). Well
operated units should produce effluents equivalent in appear-
ance to secondary clarifier effluent. If an unusually high
amount of suspended solids are exiting the unit with the
effluent, the problem may be related to: (1) sludge blanket
thickness, (2) chemical conditioning, (3) A/S ratio, (4) recycle
rate, (5) solids and/or hydraulic loading or any combination of
the above.
If the float solids appear to be well flocculated and concen-
trated (resembling cottage cheese), the speed of the sludge
scrapers should be increased. Poor effluent quality in conjunc-
tion with a concentrated float sludge usually results from allow-
ing the sludge blanket to develop too far below the surface.
When this happens, the undermost portions of the blanket will
break off and be carried under the effluent baffle. Increasing
the sludge collector speed will result in a decrease in blanket
thickness and prevent solids from flowing under the baffle.
If the scrapers are already operating at full speed and the
blanket level is below the effluent baffle, the unit is probably
overloaded with regard to solids. In this case, the influent flow
rate and concentration should be checked and the flow rate
should be decreased, if possible.
High solids carryover with the effluent, in conjunction with
lower than normal float solids concentrations, usually indicate
that problems exist with the air system, chemical conditioning
system and/or the loading rates. The operator should sys-
tematically check the retention tank pressure and sight glass,
the recycle pump, the air compressor assembly, the re-
aeration pump, the chemical conditioning equipment, and the
influent flow.
Equipment malfunctions are quickly revealed by checking
the retention tank pressure and the sight glass. Higher than
desired pressures will result in decreased recycle rates and the
back pressure-relief valve should be opened somewhat to de-
crease the pressure and increase the recycle rate. Lower than
normal pressures will result in higher recycle rates. In this
case, the pressure-relief valve should be closed somewhat to
decrease the recycle rate, and allow more time for air to dis-
solve in the retention tank.
Malfunctions in the retention tank liquid level indicator and
air compressor activation assembly will also cause drastic de-
creases in flotation efficiency. The liquid level rated on the
sight glass is the best indicator of this problem.
If the liquid level in the retention tank is lower or higher than
normal, either the float mechanism to activate the air inlet valve
or control is malfunctioning or the air compressor and solenoid
valves are not operating correctly. If the liquid level in the reten-
tion tank is not at the desired level, the operator should shut
the DAF unit off, open the hatch on the retention tank, and
clean the liquid level indicator probes.
If everything (air, recycle, and retention pressure) seems to
be in proper order, but the DAF effluent is still high in solids and
the float solids are at a low concentration, the operator should
check the retention tank mixer (re-aeration pump), the chemi-
cal conditioning system and the loading rates.
If chemical conditioners are used, they must be prepared
properly and applied at the desired dosage. Chemical condi-
tioning is covered in Section 22.3. The operator should be fully
aware that proper operation of the chemical conditioning sys-
tem will not only greatly help the performance of the DAF, but it
should be carefully watched and calibrated because of the high
cost of chemicals.
if all the equipment is operating properly and the problem
still exists, the operator should check the hydraulic and solids
loading according to Example 10 and adjust flow rates as re-
quired.
Table 22.5 summarizes problems that may arise and the
corrective measures that might be taken.
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150 Treatment Plants
TABLE 22.5 TROUBLESHOOTING DISSOLVED AIR FLOTATION
Operational Problem
1. Solids carryover with effluent
but good float concentration
2. Good effluent quality but float
sludge thin (dilute)
3. Poor effluent quality and thin
(dilute) float sludge
Possible Causes
1. Float blanket too thick
2. Float blanket too thin
3.a. A/S low
b. Pressure too low or too high
c. Recycle pump inoperative
d. Re-aeration pump inoperative
e. Chemical addition inadequate
f. Loading excessive
QUESTION
Write your answer in a notebook and then compare your
answer with the answer on page 266.
22.121 On a routine check of a dissolved air flotation unit,
the operator notices high suspended solids in the
effluent and a thinner than normal sludge. DISCUSS
the possible causes and solution to the problem.
22.13 Centrifuge Thickeners
Centrifugal thickening of wastewater sludge results from
sedimentation and high centrifugal forces. Sludge is fed at a
constant feed rate to a rotating bowl. Solids are separated from
the liquid phase by virtue of the centrifugal forces and are
forced to the bowl wall and compacted. The liquid and fine
soiids (CENTRATE)21 exit the unit through the effluent line.
Three centrifuge designs are commonly installed today.
They are (1) basket centrifuges, (2) scroll centrifuges, and (3)
disc-nozzle type centrifuges. The mechanical operation of the
three centrifuges varies significantly and separate descriptions
of each will follow.
BASKET CENTRIFUGE. The basket centrifuge is a solid
bowl which rotates along a vertical axis and operates in a batch
manner. A schematic of a typical basket centrifuge is shown in
Figure 22.4. Feed material is transported by a pipe through the
top and is introduced at the bottom of the unit. This sludge is
accelerated radially outward to the basket wall by centrifugal
force. Cake continually builds up within the basket until the
quality of the centrate, which overflows a weir at the top of the
unit, begins to deteriorate. At that point, feed to the unit is
stopped and a nozzle skimmer enters the bowl to remove the
innermost and wettest portion of the retained solids. The inner
solids are generally too wet for conveyor belt transport through
the system. Upon completion of the skimming sequence,
which takes about one-half minute, deceleration of the bowl
takes place followed by knife or plow insertion. As the knife
moves toward the bowl wall, retained solids are scraped out
and fall through the bottom of the basket for conveyance to a
discharge point as cake. Upon retraction of the knife, the solids
discharge cycle is completed.
When basket centrifuges are used as thickening devices,
full-depth skimming is commonly practiced with the nozzle
skimmer while the basket is revolving at full speed, and the
deceleration and knife insertion sequences are eliminated from
the operation.
SCROLL CENTRIFUGE. The scroll centrifuge is a solid bowl
which rotates along a horizontal axis and operates in a con-
tinuous manner. A schematic of this type of centrifuge is shown
in Figures 22.5 and 22.6. The newest design in scroll cen-
Check or Monitor
1 .a. Right speed
b. Solids loading
2.a. Flight speed
b. Solids loading
3.a. —Air rate
—Compressor
b. Pressure gage
c. Pressure gage and pump
d. Pump pressure
e. Chemical system
1. Loading rates
Possible Solutions
1 .a. Increase flight speed
b. Lower flow rate to unit if pos-
sible
2.a. Decrease flight speed
b. Increase flow rate if possible
3.a. -Increase air input
-Repair and/or turn on com-
pressor
b. Open or close valve
c. Turn on recycle pump
d. Turn on re-aeration pump
e. Increase chemical dosage
f. Lower flow rate
trifuges is a tapered bowl which employs an inner scroll to
evenly distribute the feed sludge. Sludge is fed to the unit
through a stationary tube along the center line of the inner
screw which accelerates the sludge and minimizes turbulence.
Sludge passes through ports in the inner conveyor shaft and is
distributed to the periphery (outer edge) of the bowl. Solids
settled through the liquid pool in the separating chamber are
compacted by centrifugal force against the bowl and are con-
veyed by the outer screw conveyor to the discharge point.
Separated liquid (centrate) is discharged continuously over an
adjustable weir.
DISC-NOZZLE CENTRIFUGE. The disc-nozzle centrifuge is
a solid bowl which rotates along a vertical axis and operates in
a continuous manner. A schematic of the centrifuge is shown
in Figure 22.7. Feed material is introduced at the top of the unit
and flows through a set of some 50 conical discs which are
used for stratification (separation into layers) of the waste
stream to be clarified. The discs are fitted quite closely to-
gether and centrifugal force is applied to the relatively thin film
of liquor and solids between the discs. This force throws the
denser solid material to the wall of the centrifuge bowl where it
is subjected to additional centrifugal force and concentrated
before it is discharged through nozzles located on the
periphery. Clear liquid continuously flows over a weir at the top
of the bowl and exits via the centrate line. The bowl is equipped
with twelve nozzle openings, but various numbers and sizes of
discharge nozzles can be used depending on feed liquor
characteristics and the desired results. The number and size of
discharge nozzles used directly controls final sludge concen-
tration for any given feed condition.
22.130 Factors Affecting Centrifuge Thickeners
The performance of centrifugal thickeners depends on (1)
type of sludge, (2) age of the feed sludge, (3) solids and hy-
draulic loading, (4) bowl speed and resulting gravitational ("g")
forces, (5) pool depth and differential scroll speed for scroll
centrifuges and (6) size and number of nozzles for disc cen-
trifuges.
Centrifuges are not commonly used to thicken primary
sludges because each of the three designs have sludge inlet
assemblies that are highly subject to clogging. For this reason,
there will be no discussion of centrifugal thickening of primary
sludge.
Secondary sludges are more suited to centrifugal thickening
because of their lack of stringy and bulky material and the
potential for plugging is minimal. Centrifuges are less affected
2, Centrate. 'jhe'water leaving a centrifuge after most of the solids have been removed.
-------
SeMi ttapMal 191
SLUDGE
FEED
POLYMER
SKIMMINGS
j
KNIFE
CAKE
Fig. 22.4 Basket Centrifuge
-------
in
IS}
SOLIDS
SOLIDS
NNER SCREW CONVEYOR
DRIVE
GEAR
SLUDGE
FEED
DRYING
SEPARATION
SCREW CONVEYOR -
msmm
n
CENTRIFUGE FRAME
POLYMER
FEED
i
!
^ I j
SLUDGE
] CENTRATE
SLUDGE CAKE
°» ?I L
Mi.
SLUDGE CAKE
DISCHARGE
CENTRATE
DISCHARGE
-------
Fig. 22.6 Photo of scroll centrifuge
(Permission of Dorr-Oliver Incorporated)
-------
154 Treatment Plants
SLUDGE
- FEED
CENTRATE
DISCHARGE
SLUDGE
DISCHARGE
RECYCLE
Fig- 22.7 Disc centrifuge
-------
Solids Disposal 155
by sludge characteristics such as age of sludge and bulking or
rising conditions due to the high centrifugal forces developed.
Usually, centrifugal forces of 600 to 1400 "g's" or 600 to 1400
times the force of gravity are developed and fluctuations in
sludge thickening characteristics can generally be overcome.
However, in all cases, if the sludge is fresh and exhibits good
settling characteristics, it would more readily be thickened than
an old sludge. Every attempt should be made, regardless of
the thickening system used, to feed a consistent and fresh
sludge to the thickening facility. Solids and hydraulic loading,
bowl speed, differential scroll speed, and nozzle sizes will be
discussed in the following paragraphs.
22.131 Operating Guidelines
The physical size and number of centrifugal thickeners
needed depends on the anticipated sludge volume and its de-
watering properties. For a specific plant, the operator usually
has a variety of operational controls to optimize centrifuge per-
formance. Prior to a discussion of these control strategies, the
operator should be familiar with determining hydraulic and sol-
ids loadings.
22.1310 Hydraulic and Solids Loadings. Unlike gravity and
flotation thickeners, the loading rates for centrifuges are not
related to unit areas (gpm/sq ft or gpd/sq ft). The accepted
loading unit terminology for centrifuge loadings are gal/hr/unit
or Ibs/hr/unit. This type of terminology is used because of the
various sizes available from different manufacturers and the
variations in design from one unit to the next unit.
The loading rates of scroll centrifuges and disc centrifuges
are straightforward and illustrated in the following sample cal-
culations.
EXAMPLE 15
Given: A scroll centrifuge was selected to thicken 120,000
GPD of waste activated sludge with an initial sludge
solids (SS) concentration of 0.80 percent (8,000 mg/L).
Find: 1. The hydraulic load (gal/hr).
2. The solids load (lb SS/hr).
Solution:
Known
Scroll Centrifuge
Flow, GPD
= 120,000 GPD
Unknown
1. Hydraulic Load,
gal/hr
2. Solids Load,
lbs SI Sol/hr
Sludge Solids, mgIL= 8,000 mg/L
, % = 0.80%
1. Determine the hydraulic load in gallons per hour.
Hydraulic Load, = Flow' GPP
gal/hr 24 hr/day
= 120,000 gal/day
24 hr/day
= 5,000 gal/hr
2. Calculate the solids load in pounds of sludge solids per
hour.
Solids Load, = Flow, gal/hr x 8.34 lbs y SI Sol, %
lbs/hr gaT 100%
= 5000 gd x 8.34 |bs x 0.80%
hr gal 100%
= 334 Ibs/hr
These same calculations would apply for disc-nozzle cen-
trifuges. The determination of loading rates for basket cen-
trifuges is more complicated because they operate in a batch
manner and the down time required to remove the thickened
solids must be incorporated in the loading calculation as fol-
lows.
EXAMPLE 16
Given: A basket centrifuge is fed 50 GPM of waste activated
sludge at a sludge solids concentration of 0.8%. The
basket run time is 20 minutes for the unit to fill com-
pletely with solids. After the unit is full, the solids are
skimmed out. The skimming operation takes 11/2 min-
utes.
Find: 1. Hydraulic Load (gal/hr)
2. Solids Load (Ibs/hr)
Solution:
Known
Basket Centrifuge
Flow, GPM = 50 GPM
Sludge Solids, % = 0.8%
Run Time, min = 20 min
Skimming Time, min = 1.5 min
Unknown
1. Hydraulic Load, gal/hr
2. Solids Load, Ibs/hr
1. Determine the hydraulic load in gallons per hour.
Hydraulic = Flow, gal x Run Time, min
Load,
gal/hr
(Run Time, min + Skm Time, min)
x 60 min
hr
= 50 gal x 20 min y 60 min
min (20 min + 1.5 min) hr
= 2,790 gal/hr
If the unit were fed continuously at a rate of 50 GPM, the
hydraulic loading rate would be 3,000 gal/hr (50 gal/min x
60 min/hr).
2. Calculate the solids load in pounds of sludge solids per
hour.
Solids Load, = Flow, gal x 8.34 lt» x SI Sol, %
Ibs/hr
hr
100%
0.8%
= 2790 gal^ x 8.34 lbs x
hr gal 100%
= 186 Ibs/hr
-------
156 Treatment Plants
22.1311 Bowl Speed. Regardless of the type of centrifuge
(basket, scroll, or disc) used, increasing the bowl speed (RPM)
will result in higher gravitational forces and thicker sludge con-
centration. This is because gravitational forces are directly
proportional to the bowl diameter and revolutions per minute.
For a given machine, the bowl diameter is fixed and cannot be
changed. If more or less "g" force is desired, the bowl speed
should be increased or decreased but IN NO INAY SHOULD
THE BOWL BE OPERATED AT SPEEDS OUT OF THE MAN-
UFACTURER'S RECOMMENDED RANGE. Operation out of
the recommended range can lead to bearing failures and
costly repairs.
22.1312 Feed Time. This section deals with the basket-
type batch operated centrifuges only. The actual feed time (run
time) for basket centrifuges will depend on the influent sludge
solids concentration (% SS), the flow rate (GPM), and the av-
erage concentration of the solids retained in the basket. The
solids storage volume within a basket is fixed. If the feed is
shut off prior to filling the storage area with solids, the portion of
retained sludge farthest from the basket wall will be extremely
wet. The net effect of not filling the basket completely with
solids is an overall decrease in the cake solids concentration
because large volumes of water are carried out during the
skimming sequence.
Conversely, if the feed time exceeds the time required to fill
the storage area with solids, the effluent quality will decrease
drastically after the bowl is full. This is because once the bas-
ket is filled with solids, no more storage area is available for
additional incoming solids.
The following example illustrates the feed time required to fill
a 48-inch diameter basket centrifuge with concentrated solids.
ALL 48-INCH DIAMETER BASKETS HAVE SOUDS STOR-
AGE VOLUMES OF APPROXIMATELY 16 CUBIC FEET.
EXAMPLE 7
Given: A 48-inch diameter basket is used to thicken waste
activated sludge at a concentration of 0.75 percent
sludge solids. The applied flow rate is 50 GPM and the
average concentration of solids within the basket is 7.0
percent.
Find: The time required to fill the storage volume with thick-
ened sludge.
Solution:
Known Unknown
48-inch diameter basket centrifuge 1. Time required to fill
storage volume, min
Flow, GPM, = 50 GPM
Infl Solids, % = 0.75%
Basket Solids, % = 7.0%
Solids Storage Vol, = 16 cu ft
cu ft
1. Calculate the amount of stored solids in pounds.
Solids, lbs _ Storage Vol, cu ft x 62.4 lbs y Bkt Sol, %
cu ft 100%
16 cu ft x 62.4 lbs x 7.0%
cu ft 100%
= 70 lbs
Therefore, under these conditions the centrifuge could
store 70 pounds of dry solids.
2. Determine the time required to fill the storage volume or the
feed time in minutes.
Feed time, _ Stored Solids, lbs
min Flow, GPM x 8.34 lbs x |nf Soi7%
gal 100%
= 70 lbs
50 gal x 8.34 lbs x 0.75%
min gal 100%
= 70 lbs
3.13 Ibs/min
= 22 minutes
For the conditions given in the above example, feed times
less than 22 minutes will result in wetter discharge solids and
feed times greater than 22 minutes will result in poorer effluent
quality.
22.1313 Differential Scroll Speed and Pool Depth. This
section deals with scroll-type centrifuges only. In addition to
being able to adjust the bowl speed, the operator can adjust
the differential or relative scroll speed and the liquid depth
(pool) within the bowl. As previously discussed, scroll cen-
trifuges have an inner screw (scroll) which rotates at a different
speed than the bowl. The difference between the bowl speed
and the speed of the inner screw is termed the "differential"
(relative) scroll speed. As the differential scroll speed is in-
creased, the solids that are compacted on the bowl wall are
conveyed out of the centrifuge at a faster rate, resulting in a
decrease in the concentration of these solids. Lower concen-
trations result because as the solids are moved out at a faster
rate, they are subjected to centrifugal forces for shorter periods
of time. Likewise, as the relative scroll speed is decreased, the
solids at the bowl wall are moved out at a slower rate and are
more compact because they are subjected to the centrifugal
forces for longer times.
The liquid depth (pool depth) within the bowl can be varied
by adjusting and/or changing the effluent weirs. As the bowl
depth is increased, the effluent quality will also increase be-
cause the liquid level and consequently the hydraulic detention
time within the bowl increases. Longer retention times result in
increased suspended solids capture because these solids
have a better opportunity to be thrown to the bowl wall. Con-
versely, as the pool depth decreases, the suspended solids
removal and effluent quality also decrease due to shorter de-
tention times within the bowl. However, in regard to cake sol-
ids, changing the pool depth has just the opposite effect. As
the pool depth is increased, solids recovery increases but the
cake solids get wetter. As the pool depth is decreased and
solids recovery decreases, the cake solids get dryer. Thus the
operator must adjust the pool depth to get the recovery and
cake solids desired, realizing that a high recovery will usually
result in the wettest cakes, while dry cakes are normally ac-
companied with lower solids recovery.
22.1314 Nozzle Size and Number. This section deals only
with disc-nozzle type centrifuges. The degree of sludge thick-
ening can be controlled somewhat by increasing or decreas-
ing both the number of nozzles and nozzle openings. Nozzles
are located at the periphery (outer edge) of the disc centrifuge
bowl and are used to discharge the thickened sludge from the
unit. If the size of the nozzles is increased, the dryness of the
compacted sludge will decrease because the sludge will exit
-------
Solids Disposal 157
the unit at a faster rate and will not concentrate to its highest
degree. This principle is much like that of the scroll speed
where increasing differential scroll speeds result in wetter
sludge. If the nozzle openings are reduced and/or the number
of nozzles is decreased, the sludge will remain subjected to
centrifugal forces for longer times and will dry or become
thicker.
22.132 Normal Operating Procedures
Typically, the flow through centrifuges is continuous and
should be set as constant as possible. Even though the basket
centrifuge is a batch process, the flow rate during the feeding
time should be as constant as possible. Routine monitoring of
the influent, effluent, and thickened sludge streams should be
done at least once per shift and samples collected for pertinent
solids analysis. Normal start-up and shutdown procedures for
the three centrifuge types varies and each is outlined below.
BASKET CENTRIFUGE
— Retract the skimmer and plow.
— Turn on the drive motor.
— When the centrifuge reaches approximately 80 percent full
speed, open appropriate chemical and sludge inlet valves and
turn on the pumps.
— When the centrate "breaks" (high solids in effluent), turn off
the sludge and chemical pumps.
— While the machine is operating at full speed, activate the
skimmer to advance towards the wall and remove solids.
— If full-depth skimming cannot be used (sludge is too thick),
retract the skimmer and push and deceleration button.
— When the bowl is rotating at approximately 50 to 70 RPM,
activate the plow.
— After all the solids are removed, retract the plow, accelerate
the bowl and proceed as above.
For any prolonged machine shutdown, fresh water should be
pumped into the bowl while the knife is inserted to clean the
wall. Following clean-out, the knife is retracted and the drive
motor turned off.
SCROLL CENTRIFUGE
— Turn on drive motor.
— When the bowl is at full speed, open appropriate chemical
and sludge valves and turn on the respective pumps.
— Adjust differential (relative) scroll speed as required.
— Flush centrifuge after each use to prevent solids from cak-
ing on inside of bowl.
For prolonged machine shutdown, the feed and chemical
pumps are turned off and fresh water is introduced into the unit
for approximately 20 to 30 minutes. The drive motor is then
turned off.
DISC NOZZLE CENTRIFUGE
— Turn on drive motor.
— Activate the pre-screens.
— When the unit is at full speed, open appropriate chemical
and sludge valves and turn on the respective pumps.
For prolonged machine shutdown, the feed and chemical
pumps are turned off and water is introduced into the cen-
trifuge for 20 to 30 minutes. The main drive motor is then
turned off.
22.133 Typical Performance
Typical operating guidelines as well as thickened sludge
concentrations and sludge solids removals for various types
are presented in Table 22.6.
TABLE 22.6 OPERATIONAL AND PERFORMANCE
GUIDELINES FOR CENTRIFUGAL THICKENERS
TREATING WASTE ACTIVATED SLUDGE
Thickened Solids
Sludge, % Recovery, %
9- 10 70- 90
5-7 80- 90
5 - 5.5 90 +
Centrifuge Capacity, Feed
Type GPM* Solids, %
Basket 33 - 70 0.7
Scroll 75- 100 0.4 - 0.7
Disc 30- 150 0.7- 1.0
* GPM x 0.063 = Lis
The variations in solids loading are due to the many different
sizes of centrifuges available from various manufacturers. The
performance data reflect no chemical conditioning prior to cen-
trifugation. The addition of polymers normally improves the
recovery of suspended solids much more than the recovery of
cake solids. For example, look at the solids recovery and cake
solids vs polymer dosage curves for both a basket and scroll
centrifuge shown in Figures 22.8, 22.9, 22.10, and 22.11. For
the basket centrifuge, it can be seen that with no polymer
addition, the thickened sludge solids were 4.5 percent and the
suspended solids recovery was 75 percent. At a polymer dos-
age of approximately 5 lbs/ton (2.5 gm/kg), the thickened
sludge solids were increased to 6 percent and the solids re-
covery leveled off at 95 percent. For the scroll centrifuge, the
thickened sludge solids remained fairly constant at 7 percent
regardless of the polymer dosage. However, with no polymer
addition, the solids recovery was at 25 percent and could not
reach 90 percent until the polymer dosage exceeded 11 lbs/ton
(5.5 gm/kg). In all, the operator must realize that when using
polymers, a great deal of experimentation and "tinkering" with
both the dosage and point of application must be done to ob-
tain the best results and minimize chemical costs. A more
detailed discussion of the basics of chemical conditioning will
be presented in Section 22.31.
The determination of centrifuge performance is based on
laboratory solids analysis and the following calculations.
EXAMPLE 18
Given: A 22-inch diameter by 60-inch long scroll centrifuge is
used to thicken 80 GPM of waste activated sludge
(WAS). The WAS has an initial sludge solids concentra-
tion of 0.80 percent (8,000 mg/L). The centrifuge
effluent (centrate) has a sludge solids concentration of
0.20 percent (2,000 mg/L).
-------
SYMBOL
~
—
SLUDGE TYPE
WASTE ACTIVATED
BOWL DIAMETER
48 in
BOWL SPEED—RPM
1400
—
FEED RATE,gpm
50
FEED,% SS
1.35
SVI, ml/g
177
—
012345678
POLYMER DOSAGE, lbs/ton
Fig. 22.8 Cake solids from basket centrifuge thickening
POLYMER DOSAGE, lbs/ton
Fig. 22.9 Suspended solids recovery from basket centrifuge
thickening
-------
Solids Disposal 159
CO
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O
CO
P
o
UJ
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UJ
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o
o
UJ
oc
CO
o
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z
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Q-
CO
3
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10
9
8
7
6
5
4
3
2
I
0
I I
I I I I I
I I I I
1 1
A
A
A
ft
~
—
SLUDGE TYPE
WASTE ACTIVATED
MACHINE SIZE,cm
81x254
FEED RATE, gpm
70-90
BOWL SPEED, rpm
1280
POOL DEPTH
MAX.
—
—
I I
I I I I I
1 1 1 1
1 1
100,
8
POLYMER DOSAGE, lbs/ton
Fig. 22,10 Cake solids from scroll centrifuge thickening
10 II 12
POLYMER DOSAGE,lbs/ton
Fig. 22.11 Suspended solids recovery from scroll centrifuge
thickening
-------
160 Treatment Plants
Unknown
Sludge Solids Removal
Efficiency, %
Find: The sludge solids removal efficiency.
Solution:
Known
22-inch diameter by 60-inch long
scroll centrifuge
Flow, GPM = 80 GPM
Infl SS, % = 0,80%
, mg/L = 8,000 mgIL
Effl SS, % = 0.20%
, mg IL = 2,000 mg//L
Determine the sludge solids removal efficiency as a percent.
(Infl SS, % - Effl SS, %) x 100%
Efficiency, %
Infl SS, %
(0.80% - 0.20%) x 100%
0.80%
0.60 x 100%
0.8
= 75%
The determination of thickened sludge concentrations (%
TS) for scroll and disc centrifuges is based on collecting thick-
ened sludge samples and analyzing for total solids content (%
TS) according to procedures outlined in Chapter 16. The de-
termination of thickened sludge concentrations of basket cen-
trifuges is more complicated because samples of the skimmed
portions and the knifed portion of the retained solids have to be
collected, analyzed, and the composite (average solids) have
to be calculated based on the relative quantity of skimmed and
knifed solids.
EXAMPLE 19
Given: A 48-inch diameter basket centrifuge with a total sludge
storage volume of 16 cu ft (120 gal) is used to thicken
WAS at an initial suspended solids concentration of
0.80% (8,000 mg IL). Approximately 13 cu ft of solids in
the basket bowl were skimmed out and the average
total solids concentration of the skimmed portion was
determined to be 4.0 percent thickened sludge (TS).
The remaining 3 cu ft was removed by inserting the
knife (plow) and the average concentration of these
solids was 7.5 percent total solids.
Find: The average (composite) total solids concentration of
the thickened sludge removed from the basket.
Solution:
Known
48-inch diameter basket centrifuge
Storage Volume, cu ft = 16 cu ft
, gal
Unknown
Average Total Thickened
Sludge Solids Removed, %
Infl SI Sol, %
, mg/L
Skimmed Volume, cu ft =
Skimmed SI, %
Knife Volume, cu ft
Knife Solids, %
120 gal
0.80%
8,000 mg/L
13 cu ft
4.0%
3 cu ft
7.5%
Calculate the average thickened sludge solids as a percent.
Thickened _ Sk Vol, cu ft x Sk SI, % + Kn Vol, cu ft x Kn Sol, %
Sludge' % Sk Vol, cu ft + Kn Vol, cu ft
_ 13 cu ft x 4.0% + 3 cu ft x 7.5%
13 cu ft + 3 cu ft
_ 52 + 22.5
16
¦ 4.66%
You must realize that this mathematical calculation assumes
perfect mixing of the skimmed and knifed solids. In actual prac-
tice, perfect mixing is very difficult to achieve.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 266 and 267.
22.13A List the three centrifuge types. Which ones are con-
tinuous and which operate in a batch (intermittent
feed) mode?
22.13B List the factors that affect centrifugal thickening.
22.13C Why are centrifuges not commonly used to thicken
primary sludges?
22.13D Determine the solids and hydraulic loading for a 20-
inch by 62-inch scroll centrifuge. The feed rate is 30
gpm and the influent solids concentration is 1.1 per-
cent (11,000 mg/L) suspended solids.
22.13E Determine the hydraulic and solids loading for a 48-
inch diameter basket centrifuge. The feed rate is 40
gpm, the feed time is 25 minutes and 3 minutes are
required to receive the solids and restart the feed.
The influent solids concentration is 1.1 percent.
22.13F How does differential scroll speed affect perform-
ance of scroll centrifuges?
22.13G A 20-inch disc centrifuge receives 25 gpm of waste
activated sludge with a suspended solids concentra-
tion of 0.65 percent. The effluent (centrate) contains
0.03 percent SS (300 mg/L) and the thickened
sludge concentration is 4.9 percent. Determine the
percent efficiency and the concentration factor (cf).
-------
Solids Disposal 161
22.134 Troubleshooting
Since the operating characteristics of the three centrifuges
are quite different, the operating problems and corrective
measures also are different. Each of the centrifuges will be
discussed for troubleshooting and it should be remembered
that CLOSE VISUAL MONITORING IS THE OPERATOR'S
BEST INDICATION OF OPERATIONAL PROBLEMS.
22.1340 Basket Centrifuge. The operator should be con-
cerned with the concentration of the thickened excess biologi-
cal sludges. The entire volume of stored sludge can usually be
skimmed out without having to use the deceleration and knife
insertion sequences when chemical conditioners are not used.
If you notice that the initial skimmings (stored solids farthest
from basket wall) contain large quantities of relatively clear
water, check the feed time and/or the influent sludge flow. Start
feed times and/or low flows will result in only partial filling of the
storage volume. If the storage volume is not completely filled
with solids prior to discharge, the sludge will be thinner than
desired because of dilution with the water discharged. The
operator should monitor the centrate quality with time for one
complete run, then adjust (increase) the feed time and/or flow
rate so that the centrate quality "breaks" when the feed se-
quence is finished. Conversely, if the thickened sludge concen-
trations appear to be in a desirable range but the overall cen-
trate quality is poor, the operator should monitor the effluent for
one complete run and adjust (decrease) the feed time and/or
sludge flow rate. If the feed time and/or sludge flow exceeds
the time required to fill the storage volume, the majority of the
solids entering the unit beyond the "break" point will exit with
the centrate.
If POLYMERS22 are added for conditioning, the net effect
will be an increase in feed time, suspended solids recovery
and thickened sludge concentrations. If the conditions de-
scribed above are evident, the operator should check the
polymer addition system in addition to procedures mentioned.
The use of polymers may also pose an additional problem
because the sludge will thicken to a higher degree and the
skimmer may not be able to travel all the way to the basket
wall. The skimmer will usually proceed towards the wall until it
encounters sludge in excess of approximately 6 percent thick-
ened sludge (TS). At this concentration, thickened biological
sludges are usually not fluid enough to flow through the skim-
mer and flow through downstream piping. To remove the re-
maining stored solids, the deceleration and knife insertion se-
quence must be used. The problems that may arise could be
plugging of the skimmer if it proceeds too far into the thickened
sludge, or wet and sloppy discharged solids upon deceleration
and knife insertion if the skimmer does not proceed far enough
into the sludge. The distance that the skimmer travels is ad-
justable by set screws on the skimming mechanism. This dis-
tance of travel should be set by monitoring a few runs and
adjusting as required to obtain a firm and conveyable knifed
sludge.
Another problem which may develop with the use of baskets
is vibration failures due to plugging of the feed parts and/or
uneven solids distribution. This problem usually develops only
when dewatering primary sludges and will be discussed in
Section 22.4.
22.1341 Scroll Centrifuge. The operational controls for
scroll centrifuges on a day-to-day basis usually include relative
scroll speed, pool depth, sludge flow, and chemical condition-
ing when used. Unless the centrifuge is equipped with a hy-
draulic backdrive, the bowl speed cannot be changed without
changing the belt sheaves. In addition, once the optimum bowl
speed has been determined and set, there is usually no point
in changing it for a given sludge. The same can be said regard-
ing the pool depth because maximum pool depths are com-
monly used when thickening sludges. This is because in thick-
ening processes it is usually desirable to recover as much of
the influent sludge solids as possible.
The performance breakdowns that are commonly encoun-
tered are deteriorations in centrate quality and decreases in
discharge or cake total solids concentrations. For any given
centrifuge, there are upper limits for hydraulic and solids load-
ings. If these limits are exceeded, both the centrate and cake
solids will fall below the desired range. If the centrifuge is oper-
ated within its loading limits, the most common problem is a
decrease in centrate quality and/or cake dryness. When this
problem is evident by visual observation, the operator should
adjust the relative scroll speed, monitor the centrate and cake,
and readjust the relative scroll speed until the desired results
are achieved. If the centrate quality is poor but the cake is
within a desired range, increasing the relative scroll speed
should result in a cleaner centrate. As the scroll speed is in-
creased, the centrifuged solids are conveyed out at a faster
rate and the solids are not given the opportunity to entirely fill
the bowl and flow over the effluent weir. To achieve good
solids recovery, polymers are usually required when thickening
biological solids via scroll centrifugation unless the centrifuge
is operated well below its loading capacities. Thickened biolog-
ical solids are plastic in nature and tend to slip within the bowl
as the screw or scroll conveyor tries to move them out. In order
to successfully move these solids out of the centrifuge and
produce a desirable centrate, polymers are often required. The
operator should, therefore, check the polymer conditioning
equipment in conjunction with relative scroll speed to optimize
centrate quality and thickened sludge concentrations.
22.1342 Disc-Nozzle Centrifuge. Disc-nozzle centrifuges
are higher speed units and usually develop centrifugal forces
in excess of 3,000 "g's." Because of these high "g" forces,
suspended solids recoveries are almost always in excess of 90
percent. Centrate quality usually poses no operational con-
cerns unless the thickened sludge is not adequately removed.
The solids will eventually build up and contaminate the cen-
trate. If this happens, the size and/or number of the discharge
nozzles should be increased to facilitate sludge discharge. On
a day-to-day basis, the nozzles do not have to be changed and
the operator should check the hydraulic flow rate if the centrate
contains a high amount of suspended solids. Operating at load-
ings in excess of the recommended range will almost always
result in less than optimum performance.
One of the major mechanical problems associated with
disc-nozzle centrifugation is plugging of the nozzles because
of the relatively small openings (0.07 to 0.08 inch or 1.75 to
2.00 mm). When this occurs, pre-screening of the sludge has
to be incorporated into the process sequence. Unless the
sludge is adequately screened, the nozzles will continuously
plug and interrupt operation of the unit. Plugging will be evident
by excessive machine vibrations due to an uneven distribution
of solids along with bowl wall. All centrifuges are equipped with
vibration switches for automatic shutoff in the event of exces-
sive vibration. If a nozzle becomes plugged, the operator
should disassemble the bowl assembly and remove and clean
the nozzles prior to restarting the centrifuge.
22 Polymer (POLY-mer). A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polymers may be
of biological origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polymers consist of simple substances
that have been made into complex, high-molecular-weight substances. Often called a "poiyelectrolyte."
-------
162 Treatment Plants
Table 22.7 lists operational problems that may develop and corrective measures the operator may take.
TABLE 22.7 TROUBLESHOOTING CENTRIFUGAL THICKENERS
Possible Causes Check or Monitor Possible Solutions
Operational Problem
Basket
1. Cenlrate quality good but dis-
charge solids dilute
2. Centrate quality poor during
the end of the run, but dis-
charge solids o.k.
3. Centrate quality poor and dis-
charge solids dilute
4. Vibrations
Scroll
1. Centrate quality good but dis-
charge solids dilute
2. Centrate poor but discharge
solids o.k.
3. Centrate poor and discharge
solids dilute
Disc-Nozzle
1. Centrate good but discharge
solids dilute
2. Centrate poor but discharge
solids o.k.
3. Vibrations
1 .a. Feed time too short
b. Flow rate too low
2.a. Feed time too long
b. Flow rate too high
c. Incorrect chemical dose
3.a. High loadings
b. Insufficient chemicals
4.a. Mechanical malfunctions
such as bearings, drive unit,
or base support
b. Plugged leed port
1.a. Scroll speed too high
b. Pool depth too high
2.a. Scroll speed too slow
b. Hydraulic load too high
c. Pool depth too low
d. Incorrect chemical dose
3.a. Bowl speed too low
b. Loading too high
c. Chemical inefficiencies
d. Scroll speed and pool depth
not optimum
1 .a. Size and number of nozzles
too large
2.a. Size and number of nozzles
too large
b. Hydraulic load too high
3.a. Mechanical malfunctions
such as bearings, drive unit,
or base support
b. Plugged nozzle
1 .a. Time for centrate to break
b. Sludge flow rate
2.a. Time for centrate to break
b. Sludge flow rate
c. Chemical system
3.a. Flow rate and break time
b. Chemical system
4.a. Inspect ail mechanical
equipment
1.a. Scroll rpm
b. Pool depth
2.a. Scroll rpm
b. Flow rate
c. Pool setting
d. Chemical system
3.a. Bowl rpm
b. Flow rate
c. Chemical system
d. Scroll rpm and pool depth
1.a. Nozzles
2.a. Nozzles
b. Flow rate
3.a. Inspect all mechanical
equipment
b. Nozzle
1.a. Increase feed time
b. Increase flow rate
2.a. Lower feed time
b. Lower flow rate
c. Increase chemical dosage
3.a. Lower flow rate
b. Increase chemical dosage
4.a. Mechanical repairs
b. Unplug as required
1.a. Decrease scroll speed
b. Lower pool depth
2.a. Increase scroll speed
b. Decrease flow
c. Increase pool
d. Increase chemical dosage
3.a. Increase bowl speed
b. Decrease flow rate
c. Increase chemical dosage
d. Vary scroll speed and pool
depth
1.a. Decrease number and/or
size of nozzles
2.a. Increase number and/or noz-
zle size
b. Decrease flow rate
3.a. Mechanical repairs
b. Unplug as required
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 267.
22.13H
22.131
A scroll centrifuge is used to thicken waste activated
sludge. On a routine check, the operator notices a
poor centrate quality. The discharge solids are good.
What should the operator check and what action
should be taken?
How can the concentration of thickened sludge be
increased from a disc centrifuge and how can the
changes affect centrate quality?
22.14 Thickening Summary
The successful operation of any thickening device is depen-
dent on the operator's knowledge of the operating guidelines,
the consistency of the influent sludge, maintaining loading
rates within the recommended and design values, and when
used, effective polymer addition.
For optimum operation of subsequent sludge processes
(stabilization, dewatering), the thickener should be operated so
as to produce as thick a sludge as possible with maximum
sludge solids recovery.
eup of ls&ou i
amp
O&PC^AL
\
-------
Solids Disposal 163
DISCUSSION AND REVIEW QUESTIONS
Chapter 22. SLUDGE HANDLING AND DISPOSAL
(Lesson 1 of 5 Lessons)
At the end of each lesson in this chapter you will find some
discussion and review questions that you should work before
continuing. The purpose of these questions is to indicate to you
how well you understand the material in the lesson. Write the
answers to these questions in your notebook before continu-
ing.
1. Why is the handling and disposal of sludge such a compli-
cated problem?
2. List the major types of alternatives available for processing
sludges.
3. What are the advantages normally associated with sludge
thickening?
4. How does temperature affect the operation of gravity thick-
eners?
5. The performance of dissolved air flotation thickeners de-
pends upon what factors?
6. What is the most important operational concern when
operating a dissolved air flotation thickener?
7. What is the best way for an operator to detect operational
problems in a centrifuge?
CHAPTER 22. SLUDGE
(Lesson 2
22.2 STABILIZATION23
22.20 Purpose of Sludge Stabilization
Prior to the disposal of wastewater treatment plant sludges,
federal, state and local regulatory agencies require that they
be stabilized. Stabilization converts the volatile (organic) or
odor-causing portion of the sludge solids to nonodorous end
products, prevents the breeding of insects upon disposal and
reduces the pathogenic (disease carrying) bacteria content.
Unit processes commonly used for stabilization of wastewa-
ter sludges include: (1) anaerobic digestion, (2) aerobic diges-
tion, and (3) chemical treatment.
Anaerobic digestion has been explained in great detail in
Chapter 12, "Sludge Digestion and Solids Handling," and only
a brief review of the process will follow. The remainder of this
section will discuss aerobic digestion and chemical treatment.
22.21 Anaerobic Digestion
The most widely used method of sludge stabilization is
anaerobic digestion, in which decomposition of organic matter
is performed by microorganisms in the absence of oxygen.
Anaerobic digestion is a complex biochemical process in which
several groups of anaerobic and facultative (survive with or
without oxygen) organisms break down organic matter. This
process can be considered a two-phase process; in the first
phase, facultative acid-forming organisms convert complex or-
ganic matter to volatile (organic) adds. In the second phase,
anaerobic methane-forming organisms convert the acids to
odorless end products of methane gas and carbon dioxide.
The performance of anaerobic digesters in converting vol-
atile (organic) matter to methane and carbon dioxide depends
on (1) sludge type, (2) digestion time, (3) digestion tempera-
ture, and (4) mixing. In general, as the concentration of sludge
solids fed to anaerobic digesters increases, the performance
ANDLING AND DISPOSAL
5 Lessons)
or efficiency in converting volatile sludge solids also increases
due to lower sludge volumes and longer digestion times. In
addition, the methane-forming bacteria are highly sensitive to
temperature changes and anaerobic digesters are usually
heated to maintain temperatures of 94 to 97°F (34 to 36°C). If
the temperature falls below this range and/or if the digestion
time falls below 15 days, the digester may become upset and
require close monitoring and attention. Refer to Chapter 12,
"Sludge Digestion and Solids Handling," for a detailed discus-
sion of operating procedures and corrective measures re-
quired during upset conditions.
22.22 Aerobic Digestion
Aerobic digestion involves the conversion of organic sludge
solids to odorless end products of carbon dioxide and water by
aerobic microorganisms. This process essentially evolved
from the extended-aeration version of the activated sludge
process, and may be used for either primary sludge, second-
ary sludge, or mixtures of the two types of sludges.
Sludge to be stabilized is delivered to the aerobic digester on
a continuous or an intermittent basis. A few aerobic digesters
are operated on a batch basis. Figure 22.12 shows a typical
aerobic digestion process in a schematic fashion. When oper-
ated in a continuous mode, thickened sludge is fed continu-
ously to the digester inlet. The digester is equipped with blow-
ers and air diffusion equipment to supply oxygen to the system
and to provide for mixing of the digester contents. Digested
sludge continuously exits through an effluent line and is either
pumped directly to dewatering facilities or may flow to a gravity
thickener prior to dewatering. The use of thickening equipment
following digestion is to concentrate the sludge and reduce the
hydraulic loadings on subsequent dewatering equipment. The
overflow (effluent) from the thickener is usually pumped back
to the plant headworks for more treatment. The underflow (sol-
ids) from the thickener is pumped to the dewatering facilities. If
thickeners are not used, the digested sludge is pumped di-
rectly to the dewatering facilities.
» stabilization. Conversion to a form that resists change. Organic material Is stabilized by bacteria which convert the material to gases and
other relatively Inert substances. Stabilized organic material generally will not give off obnoxious odors.
-------
164 Treatment Plants
FLOATING SURFACE
/~~ AERATOR
CLARIFIED
RAW SLUDGE
EFFLUENT
AEROBIC DIGESTER
SLUDGE TO
RETURN SLUDGE
DISPOSAL
Fig. 22.12 Aerobic sludge digestion process
In the intermittent or batch mode of operation, the digester
receives thickened sludge for a portion of the day. After the
digester is fed, the blowers and air diffusion equipment remain
in operation until approximately 2 to 3 hours before the next
feeding. At 2 to 3 hours before the next feeding, the blowers
are turned off and the digester contents are allowed to settle
for approximately V/2 to 2V2 hours. A portion of the settled
solids are then withdrawn and pumped to sludge dewatering
facilities. A portion of the supernatant (top) liquor is also with-
drawn for either recycle to the plant influent or further treatment
with the plant secondary effluent. The blowers are then turned
on and thickened sludge is again pumped to the aerobic di-
gester to replace the volume of sludge withdrawn. From an
operations standpoint, the continuous mode of feeding is pre-
ferred because it tends to minimize operator attention and to
reduce associated operational costs.
22.220 Factors Affecting Aerobic Digestion
The operation and performance of aerobic digesters are af-
fected by many variables. These include: (1) sludge type, (2)
digestion time, (3) digestion temperatures, (4) volatile solids
loading, (5) quantity of air supplied, and (6) dissolved oxygen
(DO) concentrations within the digester.
The sludge type deals with the influent characteristics of the
waste stream to be stabilized. The operator has little, if any,
control over the chemical and biological make-up of the in-
fluent sludge. As stated earlier, aerobic digestion may be used
for either primary sludge, secondary sludge, or mixtures of the
two. The process has found its widest application with sec-
ondary sludges. Secondary sludges are composed primarily of
biological cells that are produced in the activated sludge and/or
trickling filter processes as a by-product of degrading organic
matter. In simplified terms, by the time secondary sludges
leave the biological treatment process, settle in final clarifiers,
concentrate in sludge thickening units, and are delivered to
aerobic digesters, the quantity of available food (organic mat-
ter) is substantially reduced. In the absence of an external food
source, these microorganisms enter the ENDOGENOUS24 or
death phase of their life cycle. When no food is available (en-
dogenous phase), the biomass begins to self-metabolize
(self-destruct), which results in a conversion of the biomass to
end products of carbon dioxide and water and a net decrease
in the sludge mass.
When primary sludge is introduced to an aerobic digester,
food becomes available to the microorganisms. In the pres-
ence of an external food source (the primary sludge), the
biomass will convert the food to end products of carbon dioxide
and water and will function in the growth phase of their life
cycle until the food supply is exhausted. During this growth
phase, the biomass will reproduce resulting in a net increase in
the sludge mass. Aerobic digestion times are long enough to
allow the food to be depleted and the biomass to eventually
enter the endogenous or death phase. The main drawback to
aerobically digesting primary sludge is that more air has to be
supplied to maintain a desirable DO level because the bacteria
are more active when food is available.
Digestion time, temperature, volatile solids loading and air
supply are considered operational controls and are discussed
below.
22.221 Operating Guidelines
22.2210 Digestion Time. In general, as the digestion time is
increased, the efficiency or effectiveness of aerobic digesters
in achieving the goals of stabilization is also increased. The
24 Endogenous (en-DODGE-en-us). A reduced level of respiration (breathing) in which organisms break down compounds within their own
cells to produce the oxygen they need.
-------
Solids Disposal 165
physical size of aerobic digesters is determined by engineers
and the operator has no control over the digester volume.after
it is constructed. The operator does have control over the di-
gestion time by controlling the degree of sludge thickening
prior to digestion. The digestion time is directly proportional to
the thickened sludge flow according to the following equation:
Flow, GPD = Flow at 2.5% SS, GPD x SS, %
SS, %
_ 10,000 GPD x 2.5%
DIGESTION TIME, days
DIGESTER VOLUME, gal
SLUDGE FLOW, gal/day
As the flow to the digester increases, the time of digestion
decreases; as the flow decreases, the digestion time in-
creases. The following example illustrates the effect of sludge
concentration and the resulting sludge volume on digestion
time.
EXAMPLE 20
Given: A 40-foot diameter by 10-foot side-wall-depth (SWD)
aerobic digester receives 10,000 GPD of thickened
secondary sludge. The thickened sludge concentration
is 2.5 percent (25,000 mg/L) sludge solids (total sol-
ids).
Find: 1. The time of digestion.
2. What effect thickening the sludge to 3.5 percent
sludge solids will have on digester performance.
Unknown
Digestion Time, days
Effect of Increasing
Sludge Solids to 3.5%
Solution:
Known
Aerobic Digester
Diameter, ft = 40 ft
Depth (SWD), ft = 10 ft
Flow, GPD = 10,000 GPD
Thickened
Sludge, % = 2.5% Sludge Solids
mg/L = 25,000 mg/L.
1. Calculate the digestion time in days.
a. Calculate the digester volume.
Volume, gal _ 7t x (Diameter, ft)2 x SWD, ft x 7.48 gal
4 cu ft
= _rt_ x (40 ft)2 x 10 ft x 7.4B gal
4 cu ft
= 94,000 gal (approximate)
b. Determine the digestion time in days.
Digestion = Digester Volume, gallons
Time, days " Row, GPD
= 94,000 gal
10,000 gal/day
= 9.4 days
NOTE: The digestion time in days based on the solids in the
digester is more important than the hydraulic digestion
time.
Digestion Time, days
(solids)
Digester Solids, lbs
Sludge Wasted, lbs/day
2. Determine the effect of increasing the sludge solids from
2.5 percent to 3.5 percent sludge solids. The total sludge
volume pumped to the aerobic digester will be decreased
and the digestion time will be increased. Calculate the new
digestion time in days.
a. Determine the new flow to the aerobic digester in gallons
per day.
3.5%
= 7,143 GPD
b. Calculate the new digestion time.
Digestion _ Digester Volume, gallons
Time, days Row, GPD
94,000 gal
7,143 gal/day
= 13.2 days
The overall impact of thickening the sludge to 3.5 percent
sludge solids is an increase in digestion time and a potential
increase in digester efficiency.
The above example illustrates the need to THICKEN
SLUDGE AS MUCH AS POSSIBLE PRIOR TO STABILIZA-
TION TO OBTAIN MAXIMUM DIGESTION TIMES.
22.2211 Digestion Temperature. Aerobic digestion, like the
activated sludge process, depends on groups of mi-
croorganisms performing specific functions. These mi-
croorganisms, as every living creature, require favorable envi-
ronments to function properly. An important environmental
condition is the maintenance of desirable temperatures. As the
temperature of the system decreases, the rate of biological
activity atso decreases. In the case of aerobic digestion, a
decrease in biological activity will result in a decreased rate of
destruction of the biomass and the potential for unstabilized
sludge exiting the digester. Desirable aerobic digestion tem-
peratures are approximately 65 to 80°F (18 to 27°C) and in
colder climates, provisions may have to be made to heat the
digester to maintain temperatures in the above range, tn addi-
tion, if aerobic digesters are fabricated with steel and erected
above ground, sufficient insulation should be provided to pre-
vent excess heat loss and reduce heating costs. Actual tem-
peratures in aerobic digesters depend on the temperature and
volume of sludge fed to the digester and also the temperature
of the air coming from the blowers to the digester.
22.2212 Volatile Solids Loading. Volatile sludge solids
loading is an estimate of the quantity of organic matter applied
to the digester. Procedures for calculating sludge solids con-
centration are outlined in Chapter 16, "Laboratory Procedures
and Chemistry." The optimum volatile solids loading for
aerobic digestion (and anaerobic digestion) depends on the
treatment plant and is generally determined by pilot and/or full
scale experimentation. In general, volatile sludge solids (VSS)
loadings for effective aerobic stabilization vary from 0.07 lb
VSS/day/cu ft to 0.20 lb VSS/day/cu ft, depending on the tem-
perature and type of sludge.
The operator should be familiar with the calculations re-
quired to determine volatile suspended solids loading rates.
The following example outlines these calculations and it should
be noted that the determination of volatile sludge solids loading
is identical for aerobic and anaerobic stabilization processes.
EXAMPLE 21
Given: A 40-foot diameter by 10-foot SWD aerobic digester
receives 7,140 GPD of secondary sludge. The thick-
ened secondary sludge is at a concentration of 3.5 per-
cent sludge solids and is 75 percent volatile matter.
Find: The volatile sludge solids loading (lb VSS/day/cu ft).
-------
166 Treatment Plants
Unknown
Volatile Sludge Solids
Loading, lb VSS/day/cu ft
Solution:
Known
Aerobic Digester
Diameter, tt = 40 ft
Depth (SWD), ft = 10 ft
Flow, GPD =7,140 GPD
Sludge Solids, % = 3.5%
Volatile Matter, % = 75%
Calculate the volatile sludge solids (VSS) loading in pounds
of VSS per day per cubic foot of aerobic digester.
a. Determine the digester volume in cubic feet.
Volume, cu ft = 1 x (Diameter. «>* * DePth.
4
= 7T X (40 ft)2 X 10 ft
4
= 12,566 cu ft
b. Calculate the volatile sludge solids (VSS) loading in
pounds of VSS per day per cubic foot.
VSS Loading, _ VSS Added, lbs/day
lbs VSS/ Digester Volume, cu ft
day/cu ft
Flow, GPD x 8.34 lbs x SS, % x VM, %
gal
100%
100%
7,140-
Digester Volume, cu ft
x 8.34.
75%
day
gal 100% 100%
12,566 cu ft
= 1,563 lbs VSS/day
12,566 cu ft
= 0.12 lbs VSS/day/cu ft
The VSS loading is affected by the concentration and vol-
ume of sludge introduced into the digester. In general, the
volatile portion of a sludge from a particular plant will not vary
from day to day. If the digestion capacity is fixed, the daily
sludge flow in combination with the degree of thickening will
determine the VSS loading.
22.2213 Air Requirements and Dissolved Oxygen. Oxygen
is supplied to the sludge by using air diffusers or mechanical
aerators. Air requirements are usually expressed as cfm air/
1000 cu ft of aerobic digester capacity for diffuser systems,
and as horsepower per 1,000 cubic feet for mechanical
aerators. Air requirements also are expressed as 1.5 to 2
pounds of oxygen per pound of volatile sludge solids de-
stroyed. The air requirements are governed by a desire to keep
the digester solids in suspension (well mixed) and to maintain
a dissolved oxygen (DO) concentration of 1 to 2 mg/L within
the digester.
Depending on the sludge type, temperature, and concentra-
tion and the activity of biomass within the digester, the quantity
of air required to maintain a residual DO of 1 to 2 mg/L will
vary. Obviously, as the concentration and/or activity increases,
more air is required to satisfy the oxygen requirements of the
biomass. The residual DO is a measure of the quantity of
oxygen supplied beyond that used by the biomass. For exam-
ple, if the biomass requires 3.0 mg/L of oxygen and 5.0 mg/L
are supplied via the blowers or mechanical aerators, then 2.0
mg/L of oxygen are left over. The quantity left over is called the
residual DO. The residual DO within the digester should al-
ways be greater than 1.0 mg/L. If the digester DO falls below
1.0 mg/L, FILAMENTOUS ORGANISMS25 may grow. Fila-
mentous organisms are undesirable because they can lead to
sludge bulking and/or foaming which will negatively affect di-
gester operation.
Typical air rates required to maintain a residual DO of 1.0 to
2.0 mg/L are discussed in Section 22.223, "Typical Perform-
ance." You should realize that values in any book are esti-
mates and that the exact air supply requirements are usually
determined in the plant by experimentation. The following
example illustrates the determination of air rates for aerobic
digesters.
EXAMPLE 22
Given: A pilot-scale digestion study showed that 0.040 CFM of
air was required per cu ft of digestion capacity to satisfy
the biomass oxygen requirements. Based on these pilot
studies, a full-scale digester with dimensions of 100 ft
long by 25 ft wide by 10 ft SWD has been constructed.
Find: The quantity of air (CFM) to be delivered to the full-
scale digester.
Solution:
Known
Aerobic Digester
Air Required,
CFM/cu ft
Length, ft
Width, ft
SWD, ft
Unknown
Air Rate, CFM
= 0 040 CFM air
cu ft digester
= 100 ft
= 25 ft
= 10ft
Determine the rate of air that must be delivered to the
aerobic digester in cubic feet of air per minute (CFM).
a. Calculate the digester volume in cubic feet.
Digester = Length, ft x Width, ft x SWD, ft
Volume, cu ft = 100 ft x 25 ft x 10 ft
= 25,000 cu ft
b. Determine the rate of air that must be supplied in CFM.
Air Rate, CFM = Aif Requj![gd- CFM air x Djg Vq| cu
cu ft Digester
= 0 040 CFM aifx 25,000 cu ft
cu ft digester
= 1,000 CFM air
22.222 Normal Operating Procedures
The sludge feed to aerobic digesters should be as continu-
ous and consistent as possible. This is best achieved by
proper operation of the sludge thickening facilities and by
pumping the thickest possible sludge. Aerobic digesters
should be routinely checked at least once per shift and com-
posite samples of the influent and effluent should be collected
daily for laboratory analysis. Daily laboratory analysis on the
influent and effluent streams should include suspended solids,
percent volatile matter, and ph measurements. Alkalinity, total
and soluble COD, ammonia-nitrogen, nitrite and nitrate should
be determined on the influent and effluent weekly. In addition
to these laboratory analyses, the residual dissolved oxygen
(DO) in the digester should be measured at least once per
shift. Digester temperature should be measured daily.
2S Filamentous Organisms (FILL-a-MEN-tuss). Organisms that grow in a thread or filamentous form. Common types are thiothrtx and ac-
tinomyces.
-------
Solids Disposal 167
Digester temperature measurements are straightforward
and simply involve the use of a thermometer. The determina-
tion of dissolved oxygen (DO) in the digester and oxygen (02)
uptake rates require the use of a membrane-type electrode
commonly called a DO probe. Membrane electrode instru-
ments are commercially available in some variety and it is
impossible to formulate detailed operational instructions that
would apply to every instrument. Calibration procedures and
readout are included in manufacturer's instructions and they
should be followed exactly to obtain the guaranteed precision
and accuracy.
Residual DO in the digester can simply be measured by
lowering the probe into the digester, gently raising and lower-
ing the probe approximately 6 to 12 inches (15 to 30 cm) and
recording the readout measurement after the readout has sta-
bilized. Depending on the instrument readout measurement
and the temperature of the digester, the DO can be determined
in mg/L with the aid of charts supplied by the electrode manu-
facturer. DO measurements should be obtained from at least 3
points within the digester to obtain an average dissolved oxy-
gen concentration. These measurements should be obtained
at the influent and effluent ends of the digester and approxi-
mately midway along the length of the digester.
Oxygen uptake measurements are an indication of the activ-
ity of the aerobic digester biomass. Accurate OXYGEN (02)
UPTAKE MEASUREMENTS are of importance to the operator
because they will readily indicate IF THE PROCESS IS FUNC-
TIONING PROPERLY OR IF UPSET CONDITIONS EXIST.
Oxygen uptake measurement requires the use of a sealed
container into which a DO probe and a mixer can be inserted to
measure the oxygen concentration with time. Approximately
one liter of digested sludge should be collected in a wide-
mouth container, the top sealed and the container vigorously
mixed. Vigorous mixing will saturate the sample with oxygen.
Following approximately 1/2 to 1 minute of mixing, the oxygen-
saturated sample is placed into the oxygen uptake container,
the DO probe inserted and the mixer turned on. The DO con-
centrations are then recorded with time for 10 to 15 minutes or
until zero DO is recorded. The uptake measurement is then
calculated according to the following equation:
Oxygen Uptake,
mg/L/hr
(DO,, mg/L - D02, mg/L) x 60 min
(Time2, min - Time,, min)
hr
The following example illustrates the determination of 02
uptake:
EXAMPLE 23
Given: An operator measures the dissolved oxygen (DO) con-
centration with time on an air-saturated sample taken
from an aerobic digester. The following measurements
were recorded:
Time
D.O. (mg/L)
0 Min
7.1
1 Min
6.0
2 Min
5.2
3 Min
4.5
4 Min
3.9
5 Min
3.2
Find: The oxygen uptake in mg/L/hr.
Solution:
Known
Aerobic Digester
DO Measurements with Time
for an Air-Saturated Sample
Unknown
Oxygen Uptake, mg/L/hr
Calculate the oxygen uptake for the air-saturated sample
from an aerobic digester in mg/L/hr. Generally the 2-minute
DO reading is used in order to allow the DO probe and the
sample time to stabilize. The 5-minute DO reading also is used
in the calculation.
Oxygen Uptake,
mg/L/hr
(DO,, mg/L - P02, mg/L) x 60 min
(Time2, min - Time,, min) hr
(5.2 mg/L - 3.2 mg/L) x 60 min
(5 min - 2 min)
2.0 mg/L x 60 min
3 min
40 mg/L/hr
hr
hr
If the uptake measurement and residual DO measurements
are significantly different than those values usually measured,
the operator should be aware that something may be wrong
(see Section 22.2240). Change in oxygen uptake rates could
indicate the presence of substances capable of inhibiting the
activities of the organisms treating the sludge.
Like a well-operated activated sludge system, a well-
operated aerobic digester should be relatively free of odors.
The surface will contain a small accumulation of foam due to
the turbulence created by the diffusers or mechanical aerators
and the operator should be aware of changes in the physical
appearance of the system. The operator soon comes to think
of an aerobic digester as a living organism. The organisms
thrive and enjoy good health or become upset and refuse to
function properly. By combining careful observation with expe-
rience, you may determine what is happening and what ad-
justments, if any, are required. Section 22.224 deals with
troubleshooting.
22.223 Typical Performance
Table 22.8 shows typical operating guidelines for aerobic
digestion and includes a summary of performance to be ex-
pected.
TABLE 22.8 OPERATIONAL AND PERFORMANCE
GUIDELINES FOR AEROBIC DIGESTION
Digestion
. Time,
"3?
Air Rata VSS
Destruction,
Diffused Air, Mechanical. VSS toad, %
CFM/cuft* HP/1000 cu ft® lb VSS/day/cu ft®
Primary
Secondary
15-20
10-15
0.015-0.06
0.015-0.04
0.05-1.25
0.05-1.25
.08-.20
.08-.20
25-50
25-40
a CFM/cu ft x 1.0 - Cu M/min/Cu M
b HP/1000 cu ft X 26.34 = W/cu m
clb VSS/day/cu ft x 10.02 - kg/day/cu m
The efficiency of aerobic digesters is usually measured by
the quantity of suspended and volatile (sludge) solids con-
verted to end products of COz and H20.
The following example illustrates how to calculate the effi-
ciency of aerobic digesters.
EXAMPLE 24
Given: An aerobic digester receives 9,000 GPD of secondary
sludge at a concentration of 3.6 percent sludge solids
(SS) and 74 percent volatile solids (matter). The di-
gester effluent is at a concentration of 2.6 percent
sludge solids and 64 percent volatile matter.
Find: 1. Pounds of sludge solids (SS) and pounds of volatile
sludge solids (VSS) entering the digester.
2. Pounds of sludge solids and pounds of volatile
sludge solids exiting the digester.
3. Efficiency of digester in destroying sludge solids, %.
-------
168 Treatment Plants
4. Efficiency of digester in destroying volatile sludge
solids, %.
Solution:
Known
Aerobic Digester
Flow, GPD = 9,000 GPD
Sludge Solids In, % = 3.6%
Volatile Solids In, % = 74%
Sludge Solids Out, % = 2.6%
Volatile Solids Out, % = 64%
Unknown
1. Sludge, Solids, In,
lbs/day
Volatile Solids In,
lbs/day
2. Sludge Solids Out,
lbs/day
Volatile Solids Out,
lbs/day
3. Sludge Solids Re-
moval Eff, %
4. Volatile Solids Re-
moval Eff, %
1. Determine the sludge solids and volatile solids entering the
aerobic digester in pounds per day.
Sludge Solids
Entering, lbs/day
= Flow, GPD x 8.34 !!?i x SS ln' %
gal 100%
= 9,000 9?Lx 8.34 !^1 x 3 6%
day gal 100%
= 2,702 lbs SS/day
= Sludge Solids, x VSS' %
day 100%
__ ^ 702 x 74%
day 100%
= 2,000 lbs VSS/day
2. Determine the sludge solids and volatile solids exiting the
aerobic digester in pounds per day.
Volatile Solids
Entering, lbs/day
Sludge Solids
Exiting, lbs/day
= Flow, GPD x 8.34 !^i x SS 0ut' %
gal 100%
= 9,000 55L x 8.34 x 2-6%
day gal 100%
= 1,952 lbs SS/day
= Sludge Solids, x vss %
day 100%
= 1,952 lbs ss x 64%
day 100%
= 1,249 lbs VSS/day
3. Calculate the efficiency of the sludge solids destruction as a
percent.
Volatile Solids
Exiting, lbs/day
SS Destruction
Efficiency, %
(SS Entering, lbs/day - SS Exiling, lbs/day) * 100%
SS Entering, lbs/day
(2702 lbs SS/day - 1952 lbs SS/day) x 100%
2702 lbs SS/day
27.8%
4. Calculate the efficiency of the volatile sludge solids destruc-
tion as a percent.
(VSS Entering, - VSS Exiting,) x 100%
VSS Destruction _ lbs/day lbs/day
Efficiency, % VSS Entering, lbs/day
(2,000 lbs VSS/day -1249 lbs VSS/day) x 100%
2,000 lbs VSS/day
= 37.6%
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 267 and 268.
22.20A What are the goals of stabilization?
22.20B List the unit processes commonly used for stabiliza-
tion.
22.21A Explain the two-step process of anaerobic digestion.
22.22A Briefly explain the aerobic digestion process.
22.22B Why is continuous feeding of aerobic digesters pre-
ferred over batch draw-and-fill systems?
22.22C List the factors affecting aerobic digestion.
22.22D Briefly explain why aerobic digestion is more suitable
for treating secondary sludges than treating primary
sludges.
22.22E How can an operator control the digestion time?
22.22F A digester with an active volume of 140,000 cubic
feet receives 110,000 gpd of primary sludge. What is
the digestion time (days)?
22.22G If the sludge from problem 22.22F is thickened from
2.7 percent to 3.5 percent, what will happen to the
digestion time?
22.22H How does temperature affect aerobic digester per-
formance?
22.221 An aerobic digester with dimensions of 120 ft in
length, 25 feet wide, and 11 feet SWD receives
24,000 gpd of secondary sludge at a concentration
of 3.1 percent and 73 percent volatile matter. What
is the digestion time (days) and the VSS loading
(Ibs/day/cu ft)?
22.22J Why should the DO in aerobic digesters be main-
tained at concentrations greater than 1.0 mg/L?
22.22K Explain how the DO level is determined in aerobic
digesters.
22.22L Determine the 02 uptake rate for the following field
measurements:
Time (min)
0
1
2
3
4
5
6
DO (mg/L)
6.3
5.1
4.2
3.4
2.6
1.8
1.0
22.22M A 1,000,000 gallon aerobic digester receives 91,000
gpd of primary sludge at a concentration of 5.1 per-
cent SS and 76 percent volatile matter. The digester
effluent is at a concentration of 3.7 percent SS and
67 percent volatile matter. Determine the digestion
time (days), VSS loading (Ibs/day/cu ft) and percent
VSS destruction.
22.224 Troubleshooting
Aerobic digesters, like all biological systems, are subject to
upsets. These upsets may result from equipment malfunctions,
changes in the influent characteristics and/or operation out of
the range of recommended operating guidelines.
-------
Solids Disposal 169
Even before sample analyses are available from the labora-
tory, the operator may become aware of process inefficiencies
by careful observation of the physical appearance of the di-
gested sludge and routine monitoring of the residual dissolved
oxygen.
22.2240 Dissolved Oxygen and Oxygen Uptake. After an
aerobic digester reaches steady state, that is, the concentra-
tion of solids within the digester is fairly constant, the 02 uptake
rate and residual DO should be relatively constant from day to
day. If the residual DO increases significantly, the operator
should be aware that either the air rate is excessive or the 02
uptake rate and activity of the biomass has decreased. The 02
uptake should be checked immediately. If the 02 uptake is in
the range normally encountered, then the biomass is function-
ing properly and the increase in DO is most likely due to high
air rates to the digester. The operator should check the air rate
and adjust as required to maintain a DO of 1 to 2 mg/L. Exces-
sive air rates are not desired because they may cause high
turbulence within the digester which may adversely affect
sludge settleability and may lead to foaming problems. If the
02 uptake rate is significantly lower than normal, the operator
should be aware that something may be inhibiting the biomass.
The operator should check the temperature and pH of the
digester contents. A significant decrease in the temperature or
pH will reduce the activity of the biomass. If the temperature is
low, the operator should try to determine what could have
caused the drop in temperature and how the temperature can
be returned to the normal operating range. If the pH is signifi-
cantly lower than normal (6.8 to 7.3), the operator may have to
add caustic or lime for pH adjustment. A decline in the pH may
be caused by nitrification in the digester or by changes in the
influent sludge characteristics. If the decline is caused by nitri-
fication, the decrease in pH will be gradual over about a week's
time. A review of the daily pH measurements will indicate
whether the decline was gradual or not. If nitrification is the
cause of a decrease in pH, the operator may lower the air rate
somewhat and/or decrease the hydraulic detention time
somewhat to suppress the growth of nitrifying bacteria. In any
case, the pH should not be allowed to drop below 6.0. If the pH
is below or close to 6.0, the operator should take immediate
action to neutralize the digester contents. The safest and
easiest way to determine the quantity of lime (Ca(OH)2) or
caustic (NaOH) to be added is to conduct jar tests (see page
175, JAR TEST PROCEDURE) on the digested sludge accord-
ing to the following example.
EXAMPLE 25
Given: The pH of an aerobic digester has declined to 6.1. The
operator wishes to raise the pH to 7.0 with the addition
of sodium hydroxide.
Find: How much caustic must be added if the digester vol-
ume is 100,000 gallons.
Procedure: The operator should run jar tests on the digested
sludge and determine how much must be added to a 1
liter sample to raise the pH to 7.0. ASSUME the
operator determines that 20 mg OF CAUSTIC added to
1 LITER of sludge raises the pH to 7.0. The quantity that
must be added to the full-scale plant must be calculated
according to the following solution.
Jar Test Results,
Caustic Added,
mg/L
= 20 mg NaOH/i.
Solution:
Known
Aerobic Digester
pH down to
Up pH to
Digester Vol, gal
= 6.1
= 7.0
= 100,000 gal
Unknown
Amount of Caustic
(NaOH) to be added,
lbs
Determine the amount of caustic (NaOH) to be added in
pounds.
Caustic Added, NaOH to Jar, mg x Dig Vol, gal x 3.78 Ugal
Sludge Sample Vol, L x 454 gm/lb x 1000 mg/gm
20 mg x 100,000 gal x 3.78 L/gal
1 L x 454 gm/lb x 1000 mg/gm
= 16.7 lbs NaOH
If a significant rise in DO along with a decrease of 02 uptake
is definitely not being caused by low temperatures or low pH,
the operator should check the sludge flow and volatile sludge
solids loading to the digester during the previous seven days.
Excessive sludge flows will reduce the time of digestion and
may increase the volatile sludge solids loading to the point
where the digester is operating out of the recommended range
of operation. The operator should adjust the flows and volatile
sludge solids loading so as to operate within the range nor-
mally used for good operation.
The discussion thus far has dealt with a residual DO higher
than normal, but the reverse may be noted. If the DO drops
significantly, the operator should check the air rate and adjust
as required to increase the residual DO to 1.0 to 2.0 mg/L If
higher than normal 02 uptake rates are also noted, the
operator should be aware that the volatile sludge solids loading
rate to the digester may be higher than normal. As long as
sufficient air capacity exists to meet air requirements at higher
loading rates, the system can still operate but the operator
should still check critical operating guidelines such as tempera-
ture, pH, and digestion time. If low DO exists and the blower is
operating at full capacity, the operator should decrease the
flow and loading to the digester or obtain additional blower
capacity if the loadings cannot be decreased.
22.2241 Foaming. Aerobic digesters often develop foaming
problems. If excessive foam develops, the operator should
check the air rate and residual DO. If the DO is high and the
remaining critical factors (02 uptake, pH, temperature) are
satisfactory, the problem may be related to excessive turbu-
lence. In this case, you should lower the air rate. If the DO is
low, the operator should increase the air rate and observe a
sample of digested sludge under a microscope. Low DO en-
courages filamentous growth. If filamentous growths are ob-
served, the problem may be related solely to DO and the pre-
dominance of filamentous growths. On occasion, foaming will
develop even with high DO. If this occurs, the problem may be
related to influent characteristics and the operator should add
defoaming agents to the digester to suppress the foam. Foam-
ing in biological systems can be caused by a variety of condi-
tions and generally indicates a rather complex problem. If the
procedures given in this section will not cure a foaming prob-
lem, a consultant may be helpful.
22.2242 Loadings. Both the digestion time as governed by
the hydraulic flow rate (GPD) and the volatile sludge solids
loading (lbs VSS/day/cu ft) should be maintained in the ranges
summarized in Table 22.8 (page 167). Operation outside of the
recommended range may lead to decreased digester effi-
ciency. A review of daily influent and effluent pounds of volatile
sludge solids will indicate whether or not the digester is effi-
ciently converting volatile (organic) matter to stabilized end
products. A decrease in volatile suspended solids destruction
should indicate to the operator that either digestion times are
too short or volatile sludge solids loadings are too high.
Table 22.9 summarizes operational problems that may be
encountered and corrective measures that might be taken.
-------
TABLE 22.9 TROUBLESHOOTING AEROBIC DIGESTERS
Possible Causes Check or Monitor
170 Treatment Plants
Operational Problem
1. High residual DO and normal
uptake rate
2. High residual DO and low up-
take rate
1. High air rates
2. a. Low digester temperature
b. Low digester pH
c. VSS loading too high or too
low
d. Digestion time too high or
too low
e. Toxicity
1. Air rate
2. a. Temperature and heating
equipment
b. pH. Check for nitrification
c. Flow rate and feed concen-
tration
d. Flow rate
e. Toxic trace constituents in
the influent sludge
Possible Solutions
1. Lower air rate
2. a. Increase temp.
b. Neutralize pH. Lower air
rate & digestion time
c. Adjust to obtain recom-
mended loading
d. Adjust to obtain recom-
mended detention time
e. Control of industrial waste
discharges
3. Foaming
3. a. Filamentous growth
b. Excessive turbulence
3. a. Residual DO and mi- 3. a.
croscopic exam
b. Air rate and residual DO
Increase air rate. Add de-
foamant
b. Lower air rale. Add de-
foamant
4. Reduced VSS destruction
5. Poor settling sludge
4. a. Low digestion time
b. High VSS Loading
c. Low temperature
d. Low DO
e. LowpH
f. Toxicity
5. Digestion time too high or too
low
4. a. Flow & concentration of
feed
b. Same as 4. a.
c. Temperature
d. DO
e. pH
f. Toxic trace constituents in
the influent sludge
5. Flow rate and solids wasting
4. a. Decrease flow
b. Decrease flow
c. Adjust temperature
d. Increase air rate
e. Neutralize pH
f. Control industrial waste
discharges
5. Run jar test to determine op-
timum dosage of alum, lime or
polymer
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 268 and 269.
22.22N What routine checks can the operator make to indi-
cate aerobic digestion process inefficiencies?
22.220 A 15,000 gallon aerobic digester has been operating
successfully with a sludge flow of 1000 GPD. The
influent sludge is normally at a concentration of 3.6
percent with a volatile content of 74 percent. The
operator determines the residual DO in the digester
to be 4.0 mg/Z.. Normally the digester operates at a
DO of 1.5 mg/L. What should the operator do?
22.22P List the potential causes of foaming and the correc-
tive measures that should be taken.
22.23 Chemical Stabilization
Sludges which are not biologically digested or thermally sta-
bilized can be made stable by the addition of large dosages of
lime or chlorine. THE ADDITION OF LIME OR CHLORINE to
sludge to prepare it for ultimate disposal IS NOT A COMMON
PRACTICE. Chemical addition is usually considered to be a
TEMPORARY STABILIZATION PROCESS and finds applica-
tion at overloaded plants or at plants experiencing stabilization
facility upsets. The main drawback to chemical stabilization is
the cost associated with the large quantities of chemical re-
quired.
22.230 Uma Stabilization
Lime stabilization is accomplished by adding sufficient quan-
tities of time to the sludge to raise the pH to 11.5 to 12.0.
Estimated dosages to achieve a pH of 11.5 to 12.0 are gener-
ally 200 to 220 pounds of lime per ton for primary sludge solids
(100 to 110 grams of lime per kg of solids). Waste activated
sludge (WAS) will require doses from 400 to 800 pounds of
lime per ton of sludge solids (200 to 400 grams of lime per kg of
solids). An indication of the quantity required for a medium-size
wastewater treatment plant is given in the following example.
EXAMPLE 26
Given: A 3.0 MGD secondary treatment plant produces 3,400
lbs/day of primary solids and 1,700 lbs/day of second-
ary sludge solids. Lime stabilization requires the addi-
tion of 210 lbs/ton to raise the pH to 12.0.
Find: The lbs of lime required per day.
Solution:
Known Unknown
Secondary Treatment Plant Lime Required, lbs/day
Flow, MGD = 3.0 MGD
Prim Sol, lbs/day = 3,400 lbs/day
Sec Sol, lbs/day = 1,700 lbs/day
To increase pH to 12.0, = 210 lbs lime
add lime, lbs/ton ton S| Sol
Calculate the amount of lime required in pounds of lime per
day.
Lime Req'd.
lbs/day
_ Dose, lbs lime y Sludge, lbs/day
Ton Sludge
210 lbs lime
2000 lbs/ton
x (3400 lbs/day + 1700 lbs/day)
Ton Sludge
= 536 lbs lime/day
200 lbs/ton
An important consideration and drawback of lime stabiliza-
tion is that the sludge mass is not reduced as with other stabili-
zation processes (digestion, oxidation). In fact, the addition of
lime adds to the overall quantity of solids that must be ulti-
mately disposed.
-------
22.231 Normal Operating Procedures
Lime as it arrives from the supplier in powder form cannot be
added directly to sludge. The powdered lime must be made
into a SLURRY26 with the addition of water prior to blending
with the sludge. Slurry concentrations (lb lime/gal water) are
discussed in Section 22.3, "Conditioning." A lime stabilization
system must incorporate the use of a slurry or mixing tank to
mix the lime with water; a slurry transfer pump and a sludge
mixing tank to mix the sludge and lime slurry. The process may
be either continuous or batch and the slurry-sludge mixing tank
must be of sufficient size to allow the mixture to remain at least
30 minutes at a pH of 11.5 to 12.0 before disposal. The pH of
the slurry-sludge mixture should be measured either manually
or automatically to ensure proper pH adjustment. The process
of lime stabilization produces an unfavorable environment and
destroys pathogenic and nonpathogenic bacteria. If the pH is
not adjusted to the above range, the goals of stabilization will
not be achieved.
22.232 Troubleshooting
The usual problem that is encountered with lime stabilization
is improper pH adjustment and subsequent disposal of unsta-
bilized sludge. Routine pH measurements on the slurry-sludge
mixer will inform the operator of process inefficiencies. If the
pH is lower than desired, the operator should check the slurry
tank, slurry transfer pump and the flow and concentration of
solids to the sluriy sludge mixing tank. If an insufficient amount
of lime was slurried or the slurry transfer pump is inoperative,
the desired pH rise will not be acheived. If the lime slurry
equipment and accessories are operating properly, the
operator should check the flow rate and solids concentration to
the mix tank. If either the flow or concentration is higher than
normal, the total pounds of sludge solids also will be higher. In
this case, the operator should increase the rate of flow of the
lime slurrry to the mixing tank until the desired pH is obtained.
22.223 Chlorine Stabilization
Chlorine stabilization is accomplished by adding sufficient
quantities of chlorine to the sludge to kill pathogenic and non-
pathogenic organisms. Estimated dosages to achieve disinfec-
tion are generally 100 to 300 lbs chlorine/ton of sludge solids
Solids Disposal 171
(50 to 150 gm chlorine/kg sludge solids). Waste activated
sludge (WAS) requires higher doses than primary sludge. As is
the case with lime stabilization, there is very little reduction of
the sludge mass with chlorine stabilization. Therefore, the
quantity of solids that remain for ultimate disposal are signifi-
cantly greater than with digestion processes. The addition of
the large quantities of chlorine required for stabilization will
result in an acidic (pH < 3.5) sludge and neutralization with
lime or caustic may be required prior to dewatering due to the
corrosive condition of the mixture.
22.234 Normal Operating Procedures
Sludge to be treated enters the chlorine-sludge retention
tank (Fig. 22.13) through a feed or recirculation pump. The
retention tank is normally operated at a pressure of 35 to 45
psig (2.5 to 3.2 kg/sq cm) and detention times of 10 to 15
minutes. After leaving the reactor, the flow splits with about 10
percent discharged for further solids processing and 90 per-
cent passing through an eductor and recycled back to the reac-
tor. The passage of the sludge through the eductor creates a
vacuum which causes the chlorine gas to move from the
chlorine supply container into the sludge line.
Chlorine stabilization systems are completely automated
with shutdown switches in the event of equipment malfunc-
tions. The operator should refer to manufacturer's literature for
routine operating procedures and troubleshooting techniques.
In general, since these systems are fully automated, the
operator need only be concerned with maintaining desired
flows, replenishing chlorine supplies as needed, adjusting the
chlorine addition rate, and checking equipment operation ac-
cording to manufacturer's recommendations.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 269.
22.23A List two chemicals used to stabilize sludges.
22.23B What are two major limitations of using chemicals to
stabilize sludges?
22.23C Under what circumstances are chemicals most often
used to stabilize sludges?
euP0Fl£443K)2
OKJ '
Guxooe UAJ0W.I
AkiC
28 Slurry (SLUR-e). A thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry)
-------
OXIDIZED
SLUDGE
RECYCLED OXIDIZED SLUDGE
PLUS CHLORINE
CHLORINE
INFLUENT SLUDGE
PUMP
EDUCTOR
PRESSURIZED
CHLORINATED SLUDGE
RETENTION TANK
Fig. 22.13 Sludge stabilization with chlorine
-------
Solids Disposal 173
DISCUSSION AND REVIEW QUESTIONS
Chapter 22. SLUDGE HANDLING AND DISPOSAL
(Lesson 2 of 5 Lessons)
Write the answers to these questions in your notebook be-
fore continuing. The problem numbering continues from Les-
son 1.
8. Why do wastewater treatment plant sludges have to be
stabilized before disposal?
9. What variables affect the operation and performance of
aerobic digesters?
10. What laboratory tests should be performed on aerobic di-
gester influent and effluent samples?
11. What factors could upset an aerobic digester?
12. What problems are commonly encountered with the lime
stabilization process?
CHAPTER 22. SLUDGE HANDLING AND DISPOSAL
(Lesson 3 of 5 Lessons)
22.3 CONDITIONING
22.30 Purpose of Conditioning
Conditioning is defined as the pretreatment of sludge to
facilitate the removal of water in subsequent treatment pro-
cesses. Solid particles in sludge usually require conditioning
because they are fine in particle size, hydrated (combined with
water) and may carry an electrostatic charge. Sludge condi-
tioning reduces mutually repelling electrostatic charges on
suspended sludge particles, decreases the ability of biological
sludges to entrain (hold) water and promotes COAGULA-
TION27 (gathering together) of the sludge solids. Sludge condi-
tioning methods include: (1) chemical treatment, (2) thermal
treatment, (3) wet oxidation, (4) ELUTRIATION28 and (5)
others such as freezing, electrical treatment and ultrasonic
treatment. Of these, only chemical treatment, elutriation, ther-
mal treatment and wet oxidation are practiced on a full-scale
basis and the following discussion will focus on these four
methods only.
22.31 Chemical Conditioning
The most commonly used chemical(s) for sludge condition-
ing is ferric chloride either alone or in combination with lime. In
recent years, a group of synthetic organic chemicals, known as
POLYELECTROLYTES29 or polymers, have been developed
and their use is rapidly gaining popularity and acceptance.
Polymers are usually classified in three general types: anionic,
cationic, or nonionic. Anionic polymers have a negative charge
and are normally used as coagulant aids with positively
charged alum and ferric chloride. Cationic polymers are posi-
tively charged and can serve as the sole coagulant or in com-
bination with an inorganic coagulant such as alum. The use of
cationic polymers is most common in sludge dewatering.
Nonionic polymers are normally comprised of equal portions of
cationic and anionic polymers, and have a charge that can vary
with the pH of the solution. Nonionic, anionic and cationic
polymers are all used as a coagulant aid. A seasonal fluctua-
tion has been noted in chemical conditioning requirements so
that many plants can successfully condition using cationic
polymers during the summer and anionic polymers during the
winter.
A detailed review of the chemistry involved when chemicals
are used for conditioning is beyond the scope of this chapter.
Essentially, the addition of chemicals reduces natural repelling
forces and allows the solids to come together (coagulate) and
gather (FLOCCULATE)30 into a heavier solid mass.
The optimum chemical(s) type and dosage for a particular
sludge is highly dependent on the characteristics of that
sludge. Calculation of chemical requirements is usually based
on ON-SITE EXPERIMENTATION and TRIAL AND ERROR
PROCEDURES. This is because sludge types and characteris-
tics vary from one treatment plant to the next and there is no
one chemical or dosage that can be applied to all plants and
sludges.
22.310 Chemical Requirements
In selection of chemical types and the determination of
chemical requirements, it is important that the operator be very
familiar with the selection procedures and be able to compare
the efficiency and cost of one product or chemical with other
products.
27 Coagulation (co-AGG-you-LAY-shun). The use of chemicals that cause very fine particles to clump together into larger particles. This
makes it easier to separate the solids from the liquids by settling, skimming, draining, or filtering.
28 Elutriation (e-LOO-tree-A-shun). The washing of digested sludge in plant effluent. The objective is to remove (wash out) fine particulates
and lor the alkalinity in sludge. This process reduces the demand for conditioning chemicals and improves settling or filtering characteristics
of the solids.
29 Polyelectrolyte (POLY-electro-iight). A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural
polyelectrolytes may be of biological origin or derived from starch products, cellulose derivatives, and alignates. Synthetic poiyelectrolytes
consist of simple substances that have been made into complex, high-molecular-weight substances. Often called a "polymer."
30 Flocculation (FLOCK-you-LAY-shun). The gathering together of fine particles to form larger particles.
-------
174 Treatment Plants
Chemical requirements are usually determined by prelimi-
nary laboratory-scale "jar tests" (page 175) followed by pilot or
full-scale trial experiments.
Jar tests are effective in indicating the RELATIVE quantity of
chemical(s) required, but should be followed by on-site dewa-
tering experiments to more accurately determine the required
chemical dosage.
Chemicals are available in either liquid or solid (powder,
crystals) form and the best way to equate one product to the
next is to express the quantity required (lbs) per unit (tons) of
dry sludge solids. The quantity required per unit of dry sludge
solids (lb/ton) can then be multiplied by the chemical cost per
pound ($/lb) to give you the cost in dollars per ton ($/ton) of
sludge processed for each type of chemical.
EXAMPLE 27
Given: Jar tests indicate that a waste activated sludge flow of
30,000 GPD with a solids concentration of 1.5 percent
sludge solids will require 18 pounds per day of Polymer
A or 165 pounds per day of Polymer B for successful
gravity thickening. Polymer A is a dry product and costs
$2.00 per dry pound. Polymer B is a liquid product and
costs $0.21 per liquid pound.
Find: 1. The polymer dosage in pounds polymer/ton of solids
for Polymer A and Polymer B.
2. The unit cost in $/ton.
Solution:
Known
Jar Tests on Waste Activated Sludge
Flow, GPD = 30,000 GPD
SI Sol, % =1.5%
c. Calculate the dosage for Polymer B in liquid pounds of
polymer per ton of sludge solids.
Unknown
1. Polymer dosage in lbs
polymer per ton of sol-
ids for both Polymer A
and B.
Polymer A, lbs/day
Polymer B, lbs/day
Polymer A, $/lb
Polymer B, $/lb
= 18 lbs/day
= 165 lbs/day
= $2.00/dry lb
= $0.21/liquid lb
2. Unit cost in dollars per
ton for both Polymer A
and B.
1. Determine the polymer dosage in pounds of polymer per
ton of sludge for both Polymer A and B.
a. Calculate the tons of dry sludge solids per day treated
by the polymers.
Flow, GPD x 8.34 lbs x SI Sol, %
Sludge, = gal 100%
tons/day 2000 lbs/ton
30,000 gal x 8.34 lbs x 1.5%
_ day gal 100%
2,000 lbs/ton
= 1.88 tons/day
b. Calculate the dosage for Polymer A in dry pounds of
polymer per ton of sludge solids.
Polymer A Dose, = Amount of Polymer A, lbs/day
lbs polymer Sludge, tons/day
ton sludge ^ 18 lbs Polymer A/day
1.88 tons/day
= 96 lbs dry Polymer A/ton sludge
Polymer B Dose,
lbs polymer
ton sludge
Amount of Polymer B, lbs/day
Sludge, tons/day
_ 165 lbs Polymer B/day
1.88 tons/day
= 88 lbs liquid Polymer B/ton sludge
2. Determine the unit cost in dollars per ton for both Polymer A
and B.
a. Calculate the unit cost for Polymer A in dollars of
polymer per ton of sludge solids treated.
Unit Cost, $/ton = Dose, lbs polymer x Polymer Cost, J_
ton sludge lb
9.6 lbs polymer x $2.00
ton sludge lb polymer
= $19.20/ton of sludge
b. Calculate the unit cost for Polymer B in dollars of
polymer per ton of sludge solids treated.
Unit cost, $/ton = Dose,lbs Po|ymer x Polymer Cost,
ton sludge lb
_ 88 lbs polymer x $0.21
ton sludge lb polymer
= $18.50/ton ot sludge
This example illustrates the need to equate polymers on a
cost per ton of solids ($/ton) basis rather than on a pound of
product per ton of solids (lb/ton) basis. Even though more
pounds of Product B were required, it yielded a lower cost than
Product A.
Successful jar test and pilot or full-scale chemical addition
requires that the chemicals be "prepared" prior to application.
Liquid and powder or crystal polymers and lime must be mixed
with water prior to using as a sludge conditioner. Ferric
chloride can be added directly to sludge as it arrives in either
bulk tanks or 55-gallon drums.
Typically, dry polymers are mixed with water to produce a
solution strength of 0.05 to 0.25 percent. Liquid polymers are
usually diluted to 1 to 10 percent polymer solutions as product,
while lime is mixed to create 5 to 30 percent lime solutions.
THESE SOLUTION STRENGTHS ARE ALL BASED ON THE
RATIO OF PRODUCT WEIGHT TO THE WEIGHT OF WATER.
Sample calculations to determine the pounds of product re-
quired per gallon of solution are illustrated below:
EXAMPLE 28
Given: Twenty five gallons of a 0.1 percent polymer solution Is
to be prepared by an operator at a wastewater treat-
ment plant.
Find: The pounds of dry polymer to be added to the 25 gal-
lons of water.
Solution:
Known
Volume of Solution, gal = 25 gal
Polymer Solution, % =0.1 %
Unknown
Dry Polymer Added, lbs
-------
Solids Disposal 175
Determine the pounds of dry polymer 1o be added by setting
up the problem as a proportion.
Polymer Solution, % = Dry Polymer, lbs
100% Vol of Sol, gal x 8.34 lbs/gal
0.1% _ Dry Polymer, lbs
100% 25 gal x 8.34 lbs/gal
Rearrange the terms in the above equation and solve for the
pounds of dry polymer.
Dry Polymer, lbs = 25 gal x 8.34 lbs/gal x °-1%
100%
= 0.21 lbs of Dry Polymer
In the above example, if 0.21 lbs of dry Polymer are mixed
with 25 gallons of water, the solution strength would be 0.10
percent.
EXAMPLE 29
Given: Six pounds of dry polymer are added to 480 gallons of
water.
Find: The strength of the polymer solution.
Solution:
Known Unknown
Volume of Solution, gal = 480 gal Strength of Polymer
Solution, %
Dry Polymer Added, lbs = 6 lbs
Calculate the strength of the polymer solution as a percent.
Polymer Solution, % = Dry Polymer Added, lbs * 100%
Vol of Sol, gal x 8.34 lbs/gal
_ 6 lbs polymer x 100 %
480 gal x 8.34 lbs/gal
= 0.15%
EXAMPLE 30
Given: A lime solution is prepared by adding 250 pounds of
lime to 100 gallons of water.
Find: The strength of the lime solution as a percent.
Solution:
Known Unknown
Lime Solution Strength of Lime Solution, %
Lime Dose, lbs = 250 lbs
Water Volume, gal = 100 gal
Calculate the strength of the lime solution as a percent.
Lime Solution, % = Dry Lime Dose, lbs x 100%
Volume of Water, gal x 8.34 lbs/gal
_ 250 lbs lime x 100%
100 gal water x 8.34 lbs/gal
= 30%
EXAMPLE 31
Given: Five gallons of a liquid polymer are added to 395 gal-
lons of water.
Find: The strength of the polymer solution as a percent.
Solution:
Known Unknown
Liquid Polymer, gal = 5 gal Strength of Polymer
Solution, %
Volume Water, gal = 395 gal
Calculate the strength of the polymer solution as a percent.
Polymer _ Liquid Polymer, gal x 8.34 lbs/gal x 100%
Solution, % Total Volume, gal x 8.34 lbs/gat
_ 5 gal x 8.34 lbs/gal x 100%
(395 gal + 5 gal) x 8.34 lbs/gal
= 1.25%
The procedures for jar tests are outlined below and again, it
should be noted that these tests only indicate the relative effec-
tiveness of sludge conditioners. JAR TESTS SHOULD BE
FOLLOWED BY PILOT OR FULL-SCALE TESTS TO DETER-
MINE THE EXACT CHEMICAL REQUIREMENTS.
JAR TEST PROCEDURE
1. Collect approximately one (1) gallon (approximately 4 liters)
of a representative sample of sludge to be tested.
2. Prepare chemical solutions according to the manufacturer's
recommendation. Only a small amount of chemical solution
is needed for the jar test as compared with actual doses for
wastewater being treated.
3. Save approximately V2 liter of the sludge sample for the
sludge solids determination.
4. Fill a 1-liter beaker up to the 1-liter mark with the sludge to
be tested.
5. Pipet a portion of the prepared chemical solution into the
beaker containing the sludge. Polymer dosages should be
increased by increments of 5 lbs/ton (2.5 gm/kg) or less for
dry polymers, 25 lbs/ton (12.5 gm/kg) or less for liquid
polymers, 100 lbs/ton (50 gm/kg) or less for ferric chloride
and 200 lbs/ton (100 gm/kg) or less for lime.
6. After the chemical is placed in the beaker containing the
sludge sample, the entire contents should be poured
SLOWLY into a second 1-liter beaker and then poured
slowly back to the original 1-liter beaker. This slow pouring
action allows the chemical to mix with the sludge and
coagulate and flocculate the sludge solids. If the chemical is
effective, large floe particles will develop and free water will
be observed. If the floe does not develop, add another por-
tion of the chemical solution and slowly pour from one
beaker to next. Continue adding portions of the chemical
followed by gentle pouring until floe formation and clear
water or a supernatant are observed.
7. Instead of pouring the chemical and sludge sample back
and forth from one beaker to another, a stirring apparatus
can be used as described in Chapter 23, Section 23.130,
"Jar Test." The chemical mixing, flocculation, and settling
conditions used in the jar test should be similar to the actual
conditions in the treatment plant in order to obtain realistic
results.
8. Record the volume of chemical solution required for floe
formation.
9. After the solids analysis is performed on the initial sludge
sample, determine the chemical dosage and associated
costs.
The following example illustrates the incremental procedure
and calculations for jar testing.
-------
176 Treatment Plants
EXAMPLE 32
Given: A 1-gallon (4 liter) sample of digested primary sludge is
to be collected and jar tests run using Polymer A, a dry
polymer, and Polymer B, a liquid product. A 1/2-liter
sample of the digested sludge was analyzed for sus-
pended solids concentration. The sludge solids concen-
tration was found to be 2 percent (20,000 mg/L).
Find: The quantity and approximate cost of Polymer A and
Polymer B required.
Polymer Preparation: The solution to this problem is a series of
jar tests. The first step is to prepare the polymer solu-
tions. Polymer A is a dry polymer, therefore, mix a 0.05
to 0.25 percent solution. For jar tests, a 0.1 percent
solution is desirable. Approximately 1 liter of solution
should be prepared. The quantity of dry polymer to be
added to 1 liter of water is determined based on the
calculation in Example 29.
Solution:
Known
Jar Tests Run on
Polymers A and B
Sludge Solids, % = 2 %
mg/L = 20,000 mgIL
Polymer A is a dry powder
0.05 to 0.25 percent solution
Polymer B is a liquid mix
1 to 10 percent solution
1 liter _
Unknown
Quantity and Cost of Polymer
A and Polymer B.
1 liter =
0.265 gal
3.78 LI gal
To dose the jars, prepare 1 liter of a 0.10 percent solution of
the dry polymer.
Dry Polymer = Volume, gal x 8.34 lbs/gal x Solution, /»
100%
= 1 L x 0.265 gal x 8.34 lbs x 0.10%
L gal 100%
= 0.0022 lbs of dry polymer
Convert the dose in pounds to grams.
Dry Polymer, = 0.0022 lbs x 454 grams/lbs
grams
= 1.00 grams
OR
Calculate the polymer dose in grams directly,
Dry Polymer, = volume, L x
grams
1000 gm x Solution, %
100%
= 1 i y 1000 gm x 0.10%
L 100%
= 1.00 grams
Therefore, 1.00 gram of dry polymer mixed with 1 liter of
water will produce 0.10 percent polymer solution.
To dose the jars, prepare 1 liter of a 2.5 percent solution of
the liquid polymer.
Liquid Polymer, _ ^ Solution %
gal
Volume, gal x
= 1 L x
0.265 gal
100%
, 2-5%
100%
Convert the dose in gallons to milliliters.
Liquid Polymer, = g.0065 gal x 3780 ml
ml gal
= 25 ml
OR
Calculate the liquid polymer dose in milliliters directly,
Liquid Polymer, _ volume /_ x 1000 ml x Solution, %
ml ' L 100%
= 1 L x 1000 ml x 2.5%
100%
= 25 ml
Determine the amount of water to be mixed with the liquid
polymer.
Volume Water, = Total Volume, ml - Liquid Polymer, ml
ml = 1000 ml - 25 ml
= 975 ml
Therefore, 25 ml of liquid polymer mixed with 975 ml of water
will produce a 2.5 percent solution.
Following polymer preparation, the jar tests should be con-
ducted and the results recorded according to the following for-
mat:
Polymer
Sludge Type
Type
Product
Form
%
Solution
ml
Added
Observation
Dig. Primary
A
dry
0.10
15
No floe formed
Dig. Primary
A
dry
0.10
30
Small floe formed
Dig. Primary
A
dry
0.10
50
Large floe and
clear supernatant
Dig. Primary
B
liquid
2.5
15
No floe formed
Dig. Primary
B
liquid
2.5
30
Small floe formed
Dig. Primary
B
liquid
2.5
50
Large floe and
clear supernatant
Based on the amount of polymer added and the observa-
tions made for the above tests, approximately 50 ml of Polymer
Solution A and 50 ml of Polymer Solution B are required to
coagulate and flocculate the solids. The dosage (lb/ton) can
then be calculated as follows:
POLYMER A (DRY)
Determine the dosage of Polymer A in pounds of polymer
per ton of sludge solids treated.
Sol, % v Polymer, ml 1 gal 8.34 lbs 2000 lbs
(Added) 378Q m|
Dosage, lbs = 100%
ton SI Vol, L
gal ton
1 gal x 8.34 lbs x SI Sol, %
3.78 L gal 100%
By cancelling out similar terms, the equation can be reduced
to:
Dosage,
= 0.0065 gal
lbs _ Sol, % x Polymer Added, ml x 2
ton SI Vol, L x SI Sol, %
= 0.10 x 50 x 2
1.0 x 2.0
= 5 lbs dry Polymer/ton sludge solids
-------
Solids Disposal 177
POLYMER B (LIQUID)
Dosage,
lbs Sot, % x Polymer Added, ml x 2
ton
SI Vol, L x SI So!, %
2.5 x 50 x 2
1.0 x 2.0
= 125 lbs liquid Polymer/ton sludge solids
Calculate the cost per ton to use Polymer A if the dry Polymer
costs $2.00 per pound.
Cost,
$ _ 5 lbs Polymer x $2.00
ton ton sludge solids lb Polymer
= $10/ton sludge solids
Calculate the cost per ton to use Polymer B if the liquid
Polymer costs $0.21 per pound.
Cost ® = 125 lbs Polymer x $0.21
ton ton sludge solids lb Polymer
= $26.25/ton sludge solids
Based on these jar tests, Polymer A would cost about one
half as much as Polymer B.
Following jar test experiments, the polymer or any other
chemical should be evaluated on pilot or full-scale equipment.
The determination of polymer dosages is identical to calcula-
tions used for the jar test examples except that larger values of
chemical and sludge are used. The following example illus-
trates the calculation ori a full-scale basis.
EXAMPLE 33
Given: A waste activated sludge flow of 200 gpm at 0.90 per-
cent (9000 mgIL) solids is to be conditioned with 20
gpm of a 0.05 percent dry polymer solution.
Find: The pounds of dry polymer to be mixed with 5000 gal-
lons of water to produce a 0.05 percent solution and the
resulting dosage in lbs/ton.
Solution:
Known
Waste Activated Sludge
Sludge Flow, GPM = 200 GPM
SI Sol, % = 0.90%
, mg/i. = 9,000 mgIL
Polymer Flow, GPM = 20 GPM
Polymer Solution, % = 0.05%
Unknown
1. Pounds of dry polymer
to be mixed with 5000
gallons to produce a
0.05 percent polymer
solution.
2. Dosage in pounds
polymer per ton of
sludge solids.
1. Determine the pounds of dry polymer to be mixed with
5,000 gallons to produce a 0.05 percent polymer solution.
Dry Polymer _ Polymer Sol, % x Vol, gal x 8.34 lbs/gal
Required, lbs —
= 0.05% x 5000 gal x8.34 lbs
100% gal
= 20.9 lbs
2. Calculate the dosage in pounds of polymer per ton of
sludge solids.
lbs
ton
Sol, % x Polymer Added, GPM 2000 lbs
SI Flow, GPM x SI Sol, %
0.05% x 20 GPM v 2000 lbs
ton
200 GPM x 0.9%
11 1 lbs polymer
ton
ton sludge solids
An extensive amount of time and discussion was devoted to
the determination of chemical solution requirements and chem-
ical dosages because many times the proper amount(s) of
chemicals are not added in routine operation. In order to chem-
ically condition sludge at the required dosage, the operator
must be able to determine the quantity to be prepared and
added to the sludge.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 269 and 270.
22.30A Why do solid particles present in sludge usually re-
quire conditioning?
22.30B List the different types of conditioning methods avail-
able.
22.31 A Briefly explain how chemical addition conditions
sludge.
22.31 B Explain why chemical types and dosage require-
ments vary from plant to plant.
22.31 C Briefly explain how chemical requirements are de-
termined for a particular sludge.
22.31 D Three pounds of dry polymer are added to 360 gal-
lons of water. What is the solution strength of the
mixture?
22.31 E Ten pounds of lime are added to 100 gallons of wa-
ter. What is the solution strength of the mixture?
22.31 F Ten gallons of liquid polymer are added to 790 gal-
lons of water. What is the solution strength of the
mixture?
22.31 G Five gallons of commercially available ferric chloride
is added to 50 gallons of water. What is the solution
strength of the mixture?
22.31 H A jar test has been conducted on digested primary
sludge. The sludge has a concentration of 3.0 per-
cent SS (30,000 mgIL) and 60 ml of a 0.15 percent
solution of polymer was required to flocculate the
sludge. Determine the polymer dosage in lbs/ton and
the cost in $/ton if the polymer costs $1.50/lb.
22.311 A polymer solution of 2.5 percent is prepared from a
liquid polymer and added at a rate of 3 GPM to a
sludge flow of 30 GPM. The sludge has a solids con-
tent of 4 percent sludge solids. Determine the dos-
age (lbs/ton) and the cost ($/ton) if the liquid polymer
costs $.20/!b.
-------
178 Treatment Plants
22.311 Chemical Solution Preparation
ONE OF THE KEYS TO SUCCESSFUL CHEMICAL CON-
DITIONING IS THE PREPARATION OF THE CHEMICAL SO-
LUTION. Depending on the solution strength to be made, the
proper amount (lbs) of dry polymer or lime must first be
weighed out and then added to a predetermined amount of
water and mixed. THE WEIGHING CONTAINER SHOULD BE
DRY, AND THE DRUMS OR BULK STORAGE TANKS OF
DRY CHEMICALS SHOULD NOT BE ALLOWED TO ABSORB
MOISTURE. If these chemicals are stored in a dry place, there
should be no problems with handling and transferring to a
weighing container. If the chemicals absorb moisture or be-
come wet, balls or cakes of chemicals will form and prevent
easy handling and transferring.
If the quantity of chemical used exceeds approximately 25 to
50 lbs per day (11 to 22 kg/day), automatic chemical feed
systems are commonly used. Such equipment usually includes
a storage hopper to hold bulk supplies of the chemical and a
screw conveyor system to measure out and transfer the dry
chemical to the mixing chamber. These automatic systems are
usually activated by liquid-level indicators in the mixing tank.
When the liquid level falls below the bottom probe, a signal is
automatically sent and water is delivered to the mix tank. After
the water level reaches a predetermined point, a second signal
activates the screw conveyor system and dry chemical is de-
livered to the tank. The length of time the screw feeder is
operated depends on the number of pounds per minute the
feeder can deliver to the mix tank, the solution desired, and the
volume of the mix tank. The most common problems encoun-
tered with automatic feed systems are plugging of the screw
conveyor and the build up of chemicals at the discharge side of
the screw. These problems can usually be traced back to pre-
mature wetting of the chemicals by water sprays coming from
the mix tanks or from not having a water tight storage and feed
system. If moisture can be prevented from entering the storage
hopper and screw conveyor, smooth operation should result.
Lime is somewhat easier to put into solution than dry polymers.
Automatic dry polymer feed systems are sometimes equipped
with wetting mechanisms to prewet the polymer as it falls into
the mix tank. If the polymer is not properly wet as it falls into the
mix tank, a poor mix will result and will be evident by balls or
"fish eyes" of undissolved polymer in the tank. Another method
of mixing dry polymers is to use an aspirator or EDUCTOR31 to
put the dry polymer into solution.
For smaller systems requiring less than 25 to 50 lbs/day (11
to 22 kg/day), manual batching can successfully be used. The
procedure to prepare and apply batch chemicals manually is
as follows:
1. Weigh out the desired quantity of dry product in a dry con-
tainer.
2. Partially fill the mix tank with water until the impellers on the
mixer are submerged.
3. Turn on the mixer.
4. Add the premeasured dry product to the mix tank. Lime can
be poured directly into the tank. Dry polymers have to be
added through an eductor for wetting purposes.
5. Fill the tank to the desired level.
6. Allow tank contents to mix thoroughly before use to suffi-
ciently "cure" the solution.
7. Turn off the mixer.
The curing or mixing time after the dry chemical has been
added to the tank should be 45 to 60 minutes for polymers and
approximately 30 minutes for lime. If adequate mixing times
are not allowed for curing, the chemical will not be as effective
as it should be because it will not fully dissolve and chemical
requirements for successful conditioning will increase.
The preparation of chemical solutions from liquid polymers
and liquid ferric chloride is not as difficult as for dry polymers
and lime because these liquids go into solution more rapidly
and prewetting is not required.
Automatic batching systems are commonly used for han-
dling quantities in excess of 55 gallons/day (208 liters/day) of
product. These systems incorporate the use of bulk storage
tanks, bulk solution transfer pumps and mixing tanks. Manual
preparation incorporates the same procedures outlined for dry
chemicals except that eductors are not used and the curing
time can usually be reduced to approximately 20 to 30 min-
utes.
After the chemicals are cured, they can either be pumped to
another tank or pumped to the sludge stream to be con-
ditioned. The use of a second holding tank provides for a mix
tank to be available at any time to prepare another batch of
chemicals. Both the mix tank and transfer tank, if used, should
be covered and protected from the sun's rays and extreme
heat. Covering of the tanks should prevent foreign material
from entering and possibly clogging equipment. When poly-
mers are used, covering should be mandatory because the
ultraviolet sun rays deteriorate the polymer molecules and can
rapidly decrease the effectiveness of the solution. The same is
true if the tank contents are allowed to approach temperatures
of 120 to 130°F (49 to 54°C). At these temperatures, the
polymer molecules can be broken down and the effectiveness
of the solution deteriorates. To ensure protection against ul-
traviolet rays and extreme heat, all chemical tanks should be
covered and insulated or painted white to reflect heat.
22.312 Chemical Addition
Once the chemical has been prepared and the approximate
dosage and addition rate determined, the solution can be
added to the sludge for conditioning. The point(s) of application
for the different chemicals will vary and is dependent on the
chemical type and the specific mechanical equipment (DAF,
centrifuges) used. In general, polymers are added directly into
the feed assemblies of the various equipment types. Polymers
should not be added to the suction side of sludge feed pumps
because the shearing forces through such pumps tend to
shear any floe formation. After conferring with the equipment
and polymer manufacturers, application points for polymers
should be determined by field experimentation. The use of lime
and ferric chloride generally requires a blending tank to mix
these chemicals with the sludge prior to dewatering. Lime and
ferric chloride are generally not used for DAF thickening or
centrifugation. Their use is usually limited to gravity thickening
and vacuum and pressure filtration. Again, application points
and blending requirements can best be determined by field
experimentation and discussions with the equipment and
chemical manufacturers.
22.313 Typical Chemical Requirements
Table 22.10 summarizes typical chemical dosages required
for various sludge types. Remember that the actual chemical
requirements vary not only with the actual sludge, but also with
the dewatering device. The optimum chemical dosage(s) is
usually determined by on-site experimentation.
31 Eductor (e-DUCK-tor). A hydraulic device used to create a negative pressure (suction) by forcing a liquid through a restriction, such as a
Venturi. An eductor or aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump; sometimes used instead of
a suction pump.
-------
Solids Disposal 179
TABLE 22.10 TYPICAL CHEMICAL CONDITIONING
REQUIREMENTS*
Ferric
Sludge Type
Chloride,
lbs/tonb
Lime,
lbs/tonb
Polymer,
lbs/tonb
Primary
20-
40
120-
200
4
-24
Primary, WAS
30-
50
140 -
180
10
- 20
WAS
80-
200
-
4
-30
Digested Primary
30-
100
300 -
600
5
-40
Digested Primary and WAS
30 -
200
300 -
600
15
- 50
Digested WAS
80-
200
300-
600
15
-40
Digested Elutriated Primary
40-
80
-
10
Digested Elutriated Primary
and WAS
40 -
80
-
15
- 30
aSLUDGE PROCESSING AND DISPOSAL A STATE OF THE ART
REVIEW, LA/OMA Project, County Sanitation Districts of Los
Angeles County, Whittier, California, April 1977.
b Expressed as pounds of chemical/ton of dry sludge solids,
lbs/ton x 0.5 = gm of chemical/kg of dry sludge solids.
22.314 Troubleshooting
If decreases in thickening and/or dewatering equipment per-
formance cannot be traced to equipment malfunctions, then
the operator should check the chemical mixing (preparation)
and addition equipment. With automatic feeding systems, the
operator should check (1) the level of dry product in the stor-
age hopper and replenish if necessary, (2) the screw conveyor
and unplug if necessary, (3) the quality of the solution (are
there large balls of undissolved chemical?), and (4) the chemi-
cal addition pump. Many times these chemical pumps are al-
lowed to run dry due to inoperative level indicators and shut off
mechanisms. If pumps are run dry, the interior components
may wear and the pump will not deliver at its rated capacity.
The operator should recalibrate the chemical feed pump and
repair if necessary, because the pump may be the only means
of measuring the chemical feed rate. The best indication of a
failure in the chemical preparation and/or the chemical feed
rate is to run a jar test on the sludge with a laboratory prepared
batch of the chemical. If these jar tests indicate substantially
less polymer than that supposedly added at full scale, there is
usually a problem with the quality of the full-scale solution or
the application rate.
Table 22.11 summarizes the problems that may arise during
chemical conditioning and the action that might be taken.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 270.
22.31 J Why should dry chemicals be kept in a dry place?
22.31 K What is the purpose of wetting dry polymers?
22.31 L Outline the procedures to prepare a batch solution of
dry and liquid chemicals.
22.31 M Why is curing time important?
22.31 N Why should chemical tanks be covered?
22.310 Why are polymers generally not added to the suction
side of sludge pumps?
22.31 P Outline the areas to be checked if sludge thickening
or dewatering inefficiencies cannot be traced back to
equipment failures.
22.32 Thermal Conditioning
Wastewater sludges, and biological sludges in particular,
may have large quantities of bound water associated with
them. The cell mass of biological sludges contains water along
with other soluble and particulate matter. Outside the cell wall
is a gelatinous sheath (cover) composed of PROTEINACE-
OUS32 and POLYSACCHARIDE33 material along with an addi-
tional quantity of water referred to as "bound water." Subject-
ing these sludge particles to extreme heat at elevated pres-
sures hydrolizes (decomposes) the surrounding sheath and
bursts the cell wall allowing bound water to escape. The net
effect of releasing the cell water is a substantial increase in the
dewaterability of the sludge.
When used for conditioning, thermal treatment facilities are
usually operated in the heat treatment or low pressure wet
oxidation (LPO) modes. The process descriptions for heat
treatment and LPO conditioning are basically identical to that
for the wet oxidation process outlined in Section 22.33. The
major differences are that (1) air is not introduced into the
reactor for heat treatment conditioning and only a limited or
small quantity of air is introduced for LPO conditioning and (2)
the reactor temperatures are lower than those sustained for
wet oxidation. Reactor temperatures for heat treatment and
LPO conditioning are typically 350°F to 400°F (177°C to 204°C)
with reactor detention times of 20 to 40 minutes.
TABLE 22.11 TROUBLESHOOTING CHEMICAL CONDITIONING PROCESSES
Problem Possible Causes Check or Monitor Possible Solutions
Effluent quality and/or sludge
concentrations from thickening or
dewatering equipment deteriorat-
ing
1. Poor solution mixture
2. Chemical dosage inadequate
1 a. Automatic feed system
1 b. Mixer operation
1c. Run jar test on sludge with a
fresh laboratory solution of
chemical
2. Chemical feed pump opera-
tion.
1a. Fill storage hoppers and
batch tanks
1b. Allow for adequate curing
time
1 c. Batch a new supply of chem-
icals
2. Turn on pump, open appropri-
ate valves. Calibrate pump
and increase rate or solution
strength of the chemical.
32 Protelnaceous (PRO-ten-NAY-shus). Materials containing proteins which are organic compounds containing nitrogen.
33 Polysaccharide (polly-SAC-a-rlde). A carbohydrate such as starch, insulin or cellulose.
-------
180 Treatment Plants
22.320 Factors Affecting Thermal Conditioning
The performance and efficiency of thermal conditioning sys-
tems are dependent on: (1) the concentration and consistency
of the influent sludge, (2) reactor detention times, and (3) reac-
tor temperature and pressure. For conditioning purposes, the
introduction of relatively small quantities of air (LPO) results in
little, if any, difference in sludge dewaterability. The advantage
usually associated with adding air is a reduction in fuel re-
quirements because of increased thermal efficiencies within
the reactor. This potential fuel savings may be offset by the
power requirements needed to supply the air. For all practical
purposes, however, heat treatment and LPO conditioning will
be regarded as equivalent in this discussion.
The solids concentration of the influent sludge will have sig-
nificant effects on the overall heating requirements and the
reactor detention times. The physical size of thermal condition-
ing systems is based on hydraulic and solids loadings. If the
concentration of the influent sludge decreases significantly, the
volume of water pumped to the reactors will increase. This will
cause a decrease in the detention time within the reactor and
an increase in the heating requirements due to the increased
water volume. The following example illustrates the effect(s)
that sludge concentration has on operation of thermal systems.
EXAMPLE 34
Given: A thermal conditioning system is designed to process
200 GPM of waste activated sludge at a concentration
of 3.5 percent. The thermal reactor has a volume of
8,000 gallons.
Find: 1. The reactor detention time under design conditions.
2. The reactor detention time if the sludge enters at a
concentration of 2.5 percent.
3. The effect of reduced concentration on heat re-
quirements.
Solution:
Detention _ Reactor Volume, gal
Time, min
Known
Thermal Conditioning System
Treat Waste Activated Sludge
WAS Flow, GPM = 200 GPM
Reactor Vol, gal = 8000 gal
Sludge Solids, % = 3.5%
Unknown
1. Reactor Detention Time
2. Reactor Detention Time if
Solids at 2.5%
3. Effect of 2.5% Solids on
Heat Requirements
1. Calculate the reactor detention time in minutes.
Detention = Reactor Volume, gal
Time, min Row GPM
8000 gallons
200 gal/min
= 40 min
2. Calculate the reactor detention time if the sludge solids
concentration drops from 3.5% to 2.5%. A reduction in sol-
ids concentration causes an increase in WAS flow.
New Flow, = Q|d F)ow GPM x Old SI Sol, %
GPM New SI Sol, %
= 200 GPM x
= 280 GPM
3.5%
2.5%
Flow, GPM
_ 8000 gallons
280 gal/min
= 29 min
3. What is the effect on heat requirements of a decrease in
WAS concentration from 3.5% to 2.5% sludge solids?
A specific amount of heat is required to raise a volume of
water from one temperature level to the desired level. If the
volume of water increases (as it will when WAS concentration
drops to 2.5% sludge solids), the amount of heat required to
raise the temperature of the increased volume of water also
increases.
In the above example, the reactor detention time decreased
from 40 minutes to 29 minutes when the sludge concentration
decreased from 3.5 to 2.5 percent. This is not necessarily de-
sirable. In general, as the reactor detention time increases
from 20 to 40 minutes, the dewaterability of the sludge also
increases somewhat and it is important to CONSISTENTLY
PUMP A THICKENED SLUDGE to the thermal unit to ensure
effective and efficient operation.
The temperature and pressure within the reactor also con-
tributes to the degree of conditioning obtainable. As the reactor
temperature is increased from 350 to 400°F (177 to 204°C), the
general trend is an increase in the dewaterability of the con-
ditioned sludge. Pressures are increased with temperature to
prevent sludge from boiling so these two factors are dependent
on each other.
22.321 Operating Guidelines
The key operating guidelines that the operator has some
control over on a day-to-day basis are: (1) inlet sludge flow, (2)
reactor temperature and detention time, and (3) sludge with-
drawal from the decant tank.
As discussed, the inlet sludge flow and reactor detention
time are dictated by the concentration of the thickened feed
sludge and the total pounds of solids processed. If the operator
maintains a consistently thick feed by closely monitoring and
operating the thickening equipment, the sludge inlet volume
will be minimized, reactor detention times will be maximized,
and optimum thermal conditioning should result. The control of
reactor temperature between the normal range of 350 to 400°F
(177 to 204°C) will depend on how the sludge dewaters in
subsequent dewatering facilities. In general, the sludge de-
waters better following conditioning at higher temperatures but
the temperature should be maintained so as to achieve the
desired dewatering results. The degree of dewatering required
will vary from one treatment plant to the next and the operator
should maintain operating temperatures according to the de-
waterability desired and achieved. If it is found that a reactor
temperature of 350°F (177°C) provides sufficient conditioning
to satisfy the dewatering requirements, the operator should not
increase the conditioning temperature. If on the other hand, a
temperature of 350°F (177°C) is not adequate from a dewater-
ing standpoint, the operator should increase the reactor tem-
perature. Any decisions to vary reactor temperatures and/or
pressures should be based on consultation between the
operator and supervisors.
The operator also has the ability to control the concentration
of the underflow solids from the decant tank by controlling the
rate of sludge withdrawal. The decant tank is a gravity thick-
-------
Solids Disposal 181
ener arid the same operating procedures outlined in Section
22.1 should be applied in operating the decant tank. In most
instances, gasification is not a problem in thermal conditioning
decant tanks because of the lack of biological activity. The high
temperatures sustained in the thermal reactors should sterilize
the sludge and biological activity with subsequent gas produc-
tion should not occur.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 270.
22.32A Briefly explain how thermal conditioning improves
the dewaterability of sludge.
22.32B List the factors that affect thermal conditioning.
22.32C Determine the reactor detention time for a reactor
volume of 1,000 gallons and a sludge flow of 33 GPM
with a concentration of 4.0%.
22.32D If the sludge concentration from problem 22.32C de-
creases to 2.5%, determine the reactor detention
time assuming the same total pounds are processed.
22.32E Briefly discuss the operating controls available to op-
timize thermal conditioning facilities.
22.32F Why is gasification not usually a problem with gravity
thickening of thermally treated sludge?
22.322 Normal Operating Procedures
Thermal conditioning units can be operated in the continu-
ous or batch modes. Continuous operation is the preferred
mode because energy is not wasted in allowing the heat ex-
changer and reactor contents to cool down and be heated back
to the desired temperature each day when operated as a batch
process.
Under the batch operation mode the following steps should
be followed:
1. Fill the reactor and heat exchangers with water if the water
is drained after the previous day's shutdown.
2. Turn on the boiler make-up water pump and open valve to
the steam boiler.
3. Open the required steam valves to the thermal reactor and
start the boiler.
4. After the reactor has reached its desired operating tempera-
ture, open the sludge inlet and outlet valves.
5. Turn on the sludge grinder and the stirring mechanism in
the decant (gravity thickener) tank.
6. Turn on the vent fan from the decant tank and activate the
appropriate odor-control equipment.
7. Turn on sludge feed pump. If LPO conditioning is used, turn
on air compressor.
The above procedures should be followed in reverse for
shutdown operation. For continuous operation, these proce-
dures are followed whenever the operation is interrupted for
mechanical or routine shutdowns.
Whether operating in the continuous or batch mode, fuel
levels for the steam generating system should be routinely
checked and replenished as required and daily records of the
pressure drop across the heat exchangers should be kept. The
heat exchangers are subject to clogging due to the formation of
scale. Periodic acid flushings are therefore required to remove
these deposits and to unplug the heat exchangers. The best
indication of scaling and the time at which an acid flushing
should be conducted is the pressure drop across the heat
exchangers. Pressure drop is determined by measuring the
pressures at the heat exchanger inlet and outlet and calculat-
ing the pressure differential (Ap) according to the following
equation:
Ap = P outlet - P inlet
When the pressure difference (Ap) reaches a certain mag-
nitude, the system should be taken out of service and an acid
flushing should be done. The pressure drop at which an acid
flushing is required is determined by the manufacturer and in
no case should the pressure differential be allowed to develop
beyond the manufacturer's recommended figure. Routine
and/or periodically required acid flushings should be con-
ducted according to the manufacturer's procedure.
22.323 Typical Performance
Typical operating guidelines are presented in Table 22.12.
The overall evaluation of thermal performance is based on
subsequent mechanical dewatering of the conditioned sludge.
Performance data for various conditioning and dewatering
schemes will be presented in Section 22.4. The degree of
dewatering obtainable is indicated in Table 22.12 from a qual-
itative standpoint.
TABLE 22.12 DEGREE OF DEWATERING FROM
VARIOUS SLUDGE TYPES
Reactor
Sludge Type
Thermal
Mode
°F»
PSK3b
Detention
Time,
Mln
Dewafertblffty
Primary
LPO or HT
350-400
350-400
20-60
Excellent
Secondary
LPO or HT
350-400
350-400
20-60
Good-Excellent
Dig. Primary
LPO or HT
350-400
350-400
20-60
Good-Excellent
Dig. Primary
LPO or HT
350-400
350-400
20-60
Good
& Secondary
a (°F - 32°F) x 5/9 = °C
b psi x 0.07 = kg/sq cm
22.324 Troubleshooting
Thermal conditioning systems are high temperature and
high pressure processes and incorporate the use of sophisti-
cated instrumentation and mechanical equipment. All of the
mechanical, electrical, and performance difficulties that might
arise cannot be summarized in this section. In the event of
complicated mechanical and/or electrical malfunctions, the
operator should not attempt to locate and/or to correct these
problems without the assistance of qualified mechanics, elec-
tricians, or instrument personnel. The following discussion will
be limited to malfunctions typically encountered on a day-to-
day basis.
22.3240 Reactor Temperature. If the reactor temperature
cannot be maintained at the desired temperature, the operator
should check: (1) the fuel supply to the steam boiler, (2) tem-
perature sensor and boiler accuator assembly, and (3) boiler
make-up water supply. If the boiler fuel system and make-up
water supply are adequate but the reactor temperature fluc-
tuates significantly, the problem may be related to instrumenta-
tion malfunctions and the operator should seek the assistance
of qualified electricians or instrumentation personnel.
22.3241 Reactor Pressure. If the high pressure feed pump
is inoperative, the desired pressure will not be maintained. The
usual problem with the feed pump is loss of prime due to a plug
on the suction side or clogging of the sludge guide. Loss of'
prime will result in low or no flow through the system.
-------
182 Treatment Plants
22.3242 Heat Exchanger Pressure Differential. Increases
in the pressure drop across the heal exchangers indicates the
buildup of scale. In the event of an excessive pressure drop,
the operalor should schedule a shutdown and acid flush the
system according to the manufacturer's recommended proce-
dure.
22.3243 Sludge Dewaterability. A decrease in the de-
waterability of the thermally conditioned sludge may be attrib-
uted to operational difficulties with the specific dewatering
equipment and/or the maintenance of less than optimum ther-
mal conditioning criteria. If the deterioration in dewaterability
cannot be attributed to dewatering equipment inefficiencies,
the operator should check: (1) the flow rate through the thermal
system, (2) reactor temperature, and (3) operation of the de-
cant (gravity) thickener.
An increase in the flow rate due to introducing a thin feed
sludge will result in decreased reactor detention times and
possible decreases in dewaterability.
If the problem is attributed to low reactor detention times, the
operator should check and optimize the sludge thickening
equipment. Decreases in reactor temperatures will also result
in inferior dewatering characteristics and the operator should
check and adjust the temperature as required.
The operation of the decant tank will also affect dewaterabil-
ity. In general, the operator should provide for as thick a decant
underflow sludge as possible to the dewatering facility. This is
controlled by monitoring and controlling the underflow sludge
withdrawal rate. Be careful that the sludge does not become so
heavy that it cannot be moved out of the decant tank. Decant
stirring plows should be operated continuously. Operation of
the decant tank should follow the same procedures outlined for
gravity thickeners.
Table 22.13 summarizes operational problems that might be
encountered and criteria that should be checked.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 270 and 271.
22.32G Why is continuous operation o1 a heat treatment unit
desirable?
22.32H Outline the start-up and shutdown procedures for a
heat treatment unit.
22.321 Why should a Jog be kept on the pressure drop
across the heat exchangers and what action should
be taken to correct excessive pressure drops?
22.32J Over the course of a week, the dewaterability of a
thermally conditioned sludge decreases drastically.
What operating criteria should be checked and what
corrective measures can be taken?
22.33 Wet Oxidation
Wet oxidation is a thermal treatment process that stabilizes
organic matter and results in a net reduction in the sludge
mass and a total destruction of pathogenic organisms.
Three modes of wet oxidation exist: low-pressure wet oxida-
tion (LPO), intermediate-pressure wet oxidation (IPO), and
high pressure wet oxidation (HPO). Figure 22.14 is a schemat-
ic of the process. Sludge to be processed is first passed
through a grinder to reduce the particle size of the sludge
solids and thereby reduce the potential for clogging inside the
wet oxidation unit. The sludge may then be pumped to the
oxidation unit by a high-pressure positive-displacement pump
along with air which is supplied by an air compressor. A high-
pressure feed pump is used to produce and maintain required
pressures in the oxidation unit. Sludge and air are then passed
through heat exchangers and delivered to the thermal reactor.
Stabilization takes place within the reactor. The stabilized
sludge leaving the reactor is cooled in the heat exchangers
against the entering cold sludge and then released to a decant
(gravity) thickener for separation and compaction of the stabi-
lized sludge solids. Off gases from the decant tank are vented
to gas scrubbers and carbon adsorbers or to a catalytic com-
bustion unit for odor control. Overflow from the decant tank
may be returned to the plant headworks while the underflow
(thickened) solids are pumped to subsequent dewatering units.
The decant tank overflow may require additional treatment
prior to recycling to the plant headworks. Heat is added to the
reactor from an external source, usually a steam generator, to
maintain desired reactor temperatures.
Under LPO conditions, feed sludge is reacted with approxi-
mately 15 SCF34 air/lb solids (0.94 SCM35 air/kg solids), while
temperatures around 400°F (204°C) and pressures of 400 psig
(28 kg/sq cm) are maintained. IPO treatment requires the addi-
tion of approximately 45 SCF air/lb solids (2.81 SCM air/kg
TABLE 22.13 TROUBLESHOOTING THERMAL CONDITIONING PROCESSES
Problem
Possible Causes
Check or Monitor
Possible Solution
1. Reactor temperature not
maintained
2. Reactor pressure not main-
tained
1 a. Fuel exhausted
b. Temperature sensor and ac-
tuators inoperative
c. Make-up water supply in-
adequate
2a. Feed pump inoperative
3. Heat exchanger Ap excessive 3a. Scaling
4. Reduction in sludge de-
waterability
4a. Low temperature
b. Low detention time
c. Poor operation of decant
1a. Fuel supply and fuel lines
b. Instrumentation
c. Water supply
2a. Grinder, pump suction and
discharge valve and sludge
supply
3a.
Inlel arid outlet pressures
3a.
4a.
Reactor temperature
4a.
b.
Sludge flow
b.
c.
Thickness of blanket and
c.
sludge concentration
1a. Replenish
b. Clean and repair or replace
c. Replenish
2a. Unplug grinder and pump
suction. Open suction and
discharge valves. Provide
thickened sludge.
3a. Acid Hush exchangers
Thicken feed sludge
Thicken underflow sludge
34 SCF. Standard cubic feet of air at standard conditions of temperature, pressure and humidity.
34 SCM. Standard cubic meters of air at standard conditions of temperature, pressure and humidity.
-------
SLUDGE
STORAGE
REACTOR
HEAT
EXCHANGER
GRINDER
SLUDGE PUMP
AIR
BOILER
BOILER
FEED
WATER
STEAM
AIR COMPRESSOR
GASES TO
ATMOSPHERE
GASES TO ODOR
CONTROL SYSTEM
ODOR CONTROL SYSTEM
WATER SCRUBBERS
SIDESTREAM LIQUID
TO TREATMENT
ACTIVATED
CARBON
SOLIDS
SEPARATION
_i Q U ID STREAMS
TC TREATVENT
VAPOR- l IQUID
SEPARATOR
THICKENED SLUDGE
TO DE WATERING
Fig. 22.14 Wet-air oxidation system
-------
184 Treatment Plants
solids) and reactor temperatures and pressures of 450°F
(232°C) and 500 to 600 psig (35 to 42 kg/sq cm), respectively.
Under HPO conditions, feed sludge is reacted with approxi-
mately 100 SCF air/lb solids (6.24 SCM air/kg solids) while
reactor temperatures and pressures approximate SOOT
(260°C) and 1,000 to 1,500 psig (70 to 105 kg/sq cm), respec-
tively. For each of the three modes of wet oxidation, reactor
detention times usually vary from 20 to 40 minutes.
22.230 Factors Affecting Wet Oxidation
The performance and efficiency of wet oxidation units are
dependent on: (1) the concentration and consistency of the
feed sludge, (2) reactor detention time, (3) reactor temperature
and pressure, and (4) quantity of air supplied.
The effects of feed sludge, reactor temperature and pres-
sure, and reactor detention times are covered in Section 22.32,
"Thermal Conditioning." The major difference between wet
oxidation and thermal conditioning is that air is introduced for
wet oxidation. As wet oxidation progresses from the LPO to
HPO mode of operation, the degree of oxidation or conversion
of the sludge solids to volatile gases also increases. Thus, an
increase in oxidation is due primarily to reacting the sludge
with greater quantities of oxygen at elevated temperatures and
pressures.
The OPERATING CRITERIA, NORMAL OPERATING
PROCEDURE and TROUBLESHOOTING are the same as
those discussed in Section 22.3 (22.321, 22.322, and 22.323)
for thermal conditioning except that reactor temperatures and
pressures are higher for IPO and HPO. In addition, the quantity
of air supplied (SCF per pound of sludge solids) is also higher
for IPO and HPO when compared to thermal conditioning.
22.331 Typical Performance
Typical operating guidelines and the degree of oxidation for
the three modes of wet oxidation are presented in Table 22.14.
TABLE 22.14 OPERATIONAL AND PERFORMANCE
GUIDELINES FOR WET OXIDATION UNITS
Reactor
Detention
Air,
SCF/lb
Solids'
% Reduction
Mode of Time,
Operation °F" PSIG15 Min
Total
Solids
vss
Total
COD
LPO 350-400 350- 400 20-60
15
20-25
25-40
25-40
IPO 450 500- 600 20-60
45
30-50
40-60
40-60
HPO 500 1000-1500 20-60
100
70-75
75-85
75-85
«(°F - 32°F) x 5/9 = °C
b psi x 0.07 = kg/sq cm
C SCF/lb X 0.0624 = SCM/kg
In addition to reducing the sludge mass and total COD, wet
oxidation should generally result in sterilization (total destruc-
tion of pathogenic and nonpathogenic organisms) of the
sludge because of the elevated temperatures and the reactor
detention times used. The thermally oxidized sludge which is
thickened and withdrawn from the bottom of the decant tank
usually exhibits excellent dewatering characteristics as will be
discussed in Section 22.4, "Dewatering."
One of the main drawbacks of wet oxidation or thermal con-
ditioning is the production of noxious odors and high-strength
liquid side-streams. The odors closely resemble that of burned
plastic and are produced by volatilizing or converting the or-
ganics in the sludge to complex organic gases. The production
of odors requires that the off gases from the decant tank be
deodorized prior to atmospheric discharge. Therefore, thermal
treatment systems must be equipped with gas scrubbers and
carbon adsorbers or catalytic combustion units. The operator
should become familiar with the operation and maintenance of
the air pollution control equipment by reviewing the manufac-
turer's literature.
The liquid sidestream's (decant tank overflow and dewater-
ing equipment) effluents are extremely high in soluble organics
and the operator should be aware that recycling these liquids
to the treatment plant headworks may result in operational
problems in secondary treatment processes. If problems
develop because of the recycling of thermal liquors, separate
aerobic or anaerobic treatment may be required.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 271.
22.33A Explain the differences between LPO, IPO, and
HPO.
22.33B List the factors affecting wet oxidation.
22.33C Why is air pollution control equipment required on
thermal treatment units?
22.34 Elutriation
22.340 Process Description
Elutriation is basically a washing process which may not
actually improve the dewatering characteristics of digested
sludge, but does reduce chemical conditioning requirements.
The reduction in chemical conditioning requirements has been
related to a reduction in sludge alkalinity and subsequent re-
duction in lime requirements for pH adjustment. While dilution
of digested sludge with fresh water and/or plant effluent results
in a dilution and an apparent reduction in alkalinity, THE
MAJOR REASON FOR IMPROVED DEWATERABILITY IS
MOST PROBABLY THE RESULT OF WASHING OUT OF
FINE, DIFFICULT TO DEWATER SOLIDS.
As discussed in Section 22.0, fine, low density solids have
large surface areas with possibly high electrostatic charges
and are more difficult to dewater than larger and coarser sol-
ids. If these fine solids are taken out of the sludge mass, the
remaining sludge solids would naturally be easier to dewater.
The problem with elutriation is that the fine solids removed
from the sludge stream are recycled back to the plant head-
works. Sometimes these fine solids may pass through the
plant and leave in the plant effluent.
Various case histories testify to the fact that elutriation low-
ers chemical demands and improves dewaterability, but as
much as 50 percent of the digested solids may be lost to the
plant effluent with the elutriation effluent (elutriate). The loss of
these fine solids into the plant effluent will deteriorate the
effluent quality while recycling to the plant headworks gener-
ally results in operational problems due to the buildup of fine
solids throughout the system.
In general, elutriation is not a preferred or efficient method of
sludge conditioning in light of the ever increasing federal, state,
and local effluent discharge requirements.
22.341 Operating Guidelines
The simplest and most common method of elutriation is the
single-stage method which uses a single contact between the
solids and elutriating liquid (elutriate). In this system, the
sludge and elutriant make contact in an elutriating tank and are
vigorously mixed for 30 to 60 seconds. The mixer is then
-------
turned off and the contents allowed to settle from 4 to 24 hours
under batch operation, or the contents are delivered to a grav-
ity thickening tank under continuous operation. After the
sludge and elutriant are vigorously mixed and settled or deliv-
ered to a gravity thickener, the operation becomes one of grav-
ity thickening and the reader should refer to Section 22.1 for
operating strategies.
Solids Disposal 185
QUESTION
Write your answer in a notebook and then compare your
answer with the one on page 271.
22.34A How does elutriation improve the dewaterability of
sludge? Discuss the problems associated with the
process.
DISCUSSION AND REVIEW QUESTIONS
Chapter 22. SLUDGE HANDLING AND DISPOSAL
(Lesson 3 of 5 Lessons)
Write the answers to these questions in your notebook be-
fore continuing. The problem numbering continues from Les-
son 2.
13. How is the optimum type of chemical and dose to condi-
tion a particular sludge determined? Why?
14. What are the most common problems encountered with
automatic dry chemical feed systems? List the cause of
each problem.
15. How would you attempt to identify the cause of a decrease
in the performance of sludge thickening or dewatering
processes when the problems appear to be with the chem-
ical conditioning facilities?
16. List the types of problems typically encountered on a day-
to-day basis with a thermal conditioning system.
17. How are odors controlled from thermal treatment sys-
tems?
-------
186 Treatment Plants
CHAPTER 22. SLUDGE
(Lesson 4
22.4 DEWATERING
22.40 Purpose of Dewatering
Following stabilization, wastewater sludges can be ulti-
mately disposed of by a variety of methods or they can be
dewatered prior to further processing and/or ultimate disposal.
In general, it is more economical to dewater sludge followed by
disposal than it is to pump or haul liquid sludge to disposal
sites. The primary objective of dewatering is to reduce sludge
moisture and consequently sludge volume to a degree that will
allow for economical disposal. Unit processes most often used
for dewatering are: (1) pressure filtration, (2) vacuum filtration,
(3) centrifugation, and (4) sand drying beds.
22.41 Pressure Filtration
Basically, there are two types of pressure filtration systems
used for sludge dewatering. These are: (1) plate and frame
filter press, and (2) belt filter press. The operating mechanics
of these two filter press types are totally different and each will
be discussed.
22.410 Plate and Frame Filter Press
The plate and frame filter press operates in a batch manner
and consists of vertical plates which are held rigidly in a frame
and pressed together. A schematic diagram of a typical plate
section is shown in Figure 22.15. Sludge is fed into the press
through feed holes along the length of the press. A filter cloth is
mounted on the face of each individual plate. As filtration pro-
ceeds, water (filtrate) passes through the fibers of the cloth, is
collected in drainage ports provided at the bottom of each
press chamber and is discharged. Sludge solids are retained
on the filter cloths and are allowed to build up until the cavities
between the plates are completely filled with solids (cake). As
the cake builds up between the plates, the resistance to flow
increases because the water has to pass through a thicker
layer of compacted solids. As the cake builds up and the re-
sistance increases, the volume of sludge fed to the filter and
consequently the volume of filtrate decreases. When the fil-
trate flow is near zero, the feed is shut off and the plates are
disengaged. As the plates are pulled away from each other,
the retained cakes are discharged by gravity and fall into a
hopper or conveyor. The diaphragm press or variable volume
type filter presses have expandable membranes on the plate
faces to further dewater the cake and to ease cake removal.
After the cakes are discharged, the plates are pulled back
together and the feed restarted.
22.4100 Factors Affecting Pressure Filtration Perform-
ance. The degree of dewatering and sludge solids removal
efficiency are affected by: (1) sludge type, (2) conditioning, (3)
ANDLING AND DISPOSAL
5 Lessons)
filter pressure, (4) filtration time, (5) solids loadings, (6) filter
cloth type, and (7) PRECOAT36.
Both the sludge type and conditioning methods used will
drastically affect the operation and performance of filter press-
es. PRIMARY SLUDGES DEWATER MORE READILY AND
REQUIRE LESS CHEMICAL CONDITIONERS THAN SEC-
ONDARY SLUDGES. Chemicals used to condition sludge prior
to plate and frame filtration generally are lime or ferric chloride.
As the quantity of chemical conditioners increases, the dry-
ness of the discharged cake solids and the sludge solids re-
moval also increase. As discussed in Section 22.3, the op-
timum chemical dosages are determined by jar-test experi-
ments followed by pilot or full-scale tests. Experience has
shown that various combinations of lime, ferric chloride, ash
and/or polymer can be used to condition sludge prior to plate
and frame filtration. If the chemical dosages are less than op-
timum, the performance of the filter press also will be less than
optimum. Thermal conditioning or wet oxidation of wastewater
sludges followed by gravity thickening yields a readily dewa-
terable sludge. The operating criteria maintained in the thermal
conditioning system will have definite effects on sludge de-
waterability. As discussed in Section 22.32, the thermal condi-
tioning system should be operated so as to obtain the desired
degree of dewatering by pressure filtration. The operating
criteria and their effects on filter performance are discussed
below.
22.4101 Operating Guidelines. The operator has the ability
to control filter press performance to a certain degree by con-
trolling the pressure, time of filtration and the solids loading.
Selection of a particular type of filter cloth for a specific sludge
is generally done by pilot or full-scale testing with various cloth
types. Once a filter cloth is selected and installed, the operator
must control the frequency and duration of media cleaning.
PRESSURE
The feed to filter presses is initiated at low pressure and high
flow rates. As the cake builds up and the resistance to flow
increases, a pneumatically or hydraulically driven positive dis-
placement feed pump provides increasing pressure as the flow
drops off. Generally, the initial pressure is maintained at ap-
proximately 25 psi (1.75 kg/sq cm) for 5 to 10 minutes then
increased at intervals approximating 5 psi/min (0.35 kg/sq
cm/min) until the terminal operating pressure is reached. Final
operating pressures usually vary from 100 to 225 psi (7.0 to
15.8 kg/sq cm) depending on the manufacturer of the press.
Some presses are designed to operate at 100 to 125 psi (7.0 to
8.8 kg/sq cm). In general, higher pressures should result in
somewhat drier discharge by forcing more water from the
sludge mass. The most effective pressure for a particular
sludge is determined by experimentation and the operator
96 Precoat. Application of a free-draining, noncohesive material such as diatomaceous earth to a filtering media. Precoating reduces the
frequency of media washing and facilitates cake discharge.
-------
Solids Disposal 187
TRAVELING END
FIXED END
OPERATING HANDLE
botonobloo
]—Oo^ELECTRIC
MOTOR AND —
CLOSING GEAR
FILTER CLOTHS
FIXED END
SLUDGE
CAKE
SLUDGE IN
FILTRATE
DRAIN HOLES'
Fig. 22.15 Plate and frame filter press
-------
188 Treatment Plants
should be aware that increased cake dryness may result from
increased operating pressures. For some sludges, particularly
secondary sludge, the reverse might happen. That is, as the
pressure is increased, the sludge retained on the filtering
media may compress to a higher degree and reduce the poros-
ity (openings) of the sludge cake that is formed. If the openings
in the sludge formation are reduced, fine low-density solids
,may be captured and incorporated in the sludge cake. The
inclusion of fine solids generally results in wetter cakes be-
cause these solids have large surface areas and relatively
large quantities of water associated with them.
FILTRATION TIME AND SOLIDS LOADING
The time of filtration is actually controlled by the physical
size of the filter and solids loading rate applied. As discussed,
when the cavities between the plates are filled with solids and
the filtrate flow is almost zero, the filtering sequence is com-
plete. Obviously, for a given cavity volume, the filtration time
will vary as the solids loading rate and the dewaterability vary.
If the time of filtration is not adequate to completely fill the plate
cavities with dewatered solids, large volumes of water will be
discharged when the plates are disengaged and the cakes
discharged. The operator should control filtration time based
on the filtrate flow rate. If on the other hand, the filtration time
exceeds the time required to fill the cavity volume, the cakes
will be firm and dry upon discharge but the quantity of solids
processed per hour or per day (solids loading) will decrease.
The solids loading is determined by dividing the pounds of
solids applied per hour by the surface area of the plates. Since
filter presses are batch systems, time is lost in disengaging the
plates, discharging.the cakes and re-engaging the plates prior
to restarting the feed pump. The incorporation of down time
into the solids loading equation results in a net filter yield. The
following example illustrates the determination of solids load-
ing and net filter yield.
EXAMPLE 35
Given: A particular filter press with a plate surface area of 100
sq ft is used to dewater digested primary sludge. The
digested sludge is at a concentration of 3.0 percent
sludge solids. The filtration time is 2 hours and the total
volume of sludge processed is 700 gallons. The time
required to discharge the cakes and restart the feed is
20 minutes.
Find: 1. The solids loading (Ibs/hr/sq ft).
2. The net filter yield (Ibs/hr/sq ft).
3. If the feed solids concentration decreased to 2 per-
cent sludge solids and the filtration time remained at
2 hours, what problems might develop?
Solids Loading,
Ibs/hr/sq ft
Solution:
Known
Plate Area, sq ft
SI Sol, %
Filtration Time, hrs
100 sq ft
3.0%
2 hrs
Sludge Volume, gal = 700 gal
Discharge and = 20 min
Restart, min
Unknown
1. Solids Loading, Ibs/hr/sq ft
2. Net Filter Yield,
Ibs/hr/sq ft
3. If solids drop to 2% SI Sol,
what problems might
develop?
1. Calculate the solids loading in pounds per hour per square
foot.
SI Vol, gal x 8.34 lbs x SI Sol, %
gal 100%
Filt. Time, hr x Area, sq ft
700 gal x 8.34 lbs x 3.0%
gal 100%
2 hr x 100 sq ft
0.88 Ibs/hr/sq ft
2. Calculate net filter yield in pounds per hour per square toot.
Net Filter
Yield,
Ibs/hr/sq ft
Loading, Ibs/hr x Filt Time, min
; sq ft
Filt Time, min + Down Time, min
0.88 Ibs/hr/sq ft x 120 min
120 min + 20 min
= 0.75 Ibs/hr/sq ft
3. What would happen if the feed concentration decreased to
2 percent sludge solids?
If the feed solids concentration decreases to 2 percent
sludge solids, the cake MAY be wetter upon discharge if the
filtration time is not increased. The operator should check the
filtrate flow and adjust the filtration time so that the filtrate flow
is near zero when the feed pump is turned oft.
FILTER CLOTH AND PRECOAT
The selection of a particular cloth type is done by experi-
mentation in conjunction with the manufacturer's recom-
mendation. Once a cloth is selected and installed, the operator
must determine the frequency of media cleaning by inspecting
the condition of the cloth and monitoring filter performance.
After repeated use, the cloth media may BLIND37 and ad-
versely affect filter performance. If the cloth is clogged, water
will not drain as readily and the discharged cakes will be wet
and sloppy upon release from the plates. Also, as the cloth
becomes clogged, a longer time will be required to dry the
cake. Some presses are furnished with media washing equip-
ment and the media can be cleaned in place. If a washing
system is not furnished with the press, the operator will have to
remove the filter cloths, wash them according to the manufac-
turer's recommended procedure, then re-install them. To re-
duce the frequency of media washing and to facilitate cake
discharge, a precoat may be applied before each batch is
loaded for filtering. Precoating is an optimal operation and
uses a free-draining, non-cohesive material such as
diatomaceous earth (a fine siliceous earth consisting mainly of
the skeletal remains of diatoms). This is made into a slurry and
is applied to the filter so as to leave a thin layer on the filter
cloth. When the sludge is applied, the precoat material pre-
vents the sludge solids from sticking to the filter cloth. The net
effect is that when the filter press is opened, the cake will
readily discharge and solids remaining on the cloth will be
minimized. The operator can improve operation and perform-
ance of filter presses by using precoats; however, precoating
adds to the solids load to be disposed of.
22.4102 Normal Operating Procedure. The specific opera-
tion of different pressure filters will vary somewhat, but the
basic operational procedures are similar. The filtration cycle
can be divided into various steps: (1) preparation of precoat
and chemical conditioners, (2) chemical conditioner and
sludge mixing, (3) precoat application, (4) sludge application,
and (5) cake discharge.
37 Blind. A condition that occurs on the filtering medium of a microscreen or a vacuum filter when the holes or spaces in the media become
clogged or sealed off due to a buildup of grease or the material being filtered.
-------
Solids Disposal 189
The procedures for normal operation are outlined below:
1. Slurry (add water to) the precoat mix in a separate precoat
tank.
2. Slurry the lime, if used, in a separate lime slurry tank.
3. Transfer the lime to a separate tank containing the sludge
to be filtered and provide gentle stirring. Add the appropri-
ate quantity of ferric chloride, if used. Usually either lime or
ferric chloride is used as a chemical conditioner.
4. Apply the precoat material to the filter.
5. Introduce the conditioned sludge to the filter.
6. When the filtrate flow decreases to near zero, turn off the
feed pump.
7. Disengage and open the press for cake discharge.
8. Close the press and repeat the above procedures.
Full-scale filter press installations are generally automated
or semi-automated so as to reduce operator attention. Even
with fully automated systems, the operator should routinely
check the operation of the various equipment and should make
adjustments as required.
22.4103 Typical Performance. Operating guidelines, con-
ditioner requirements, and filter press performance for various
sludge types are summarized in Table 22.15. Note that when
thermal conditioning is used, precoat material and chemical
conditioners are often not required.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 271.
22.40A What are the primary objectives of sludge dewater-
ing?
22.40B What unit processes are most commonly used for
sludge dewatering?
22.41 A Why does the flow through plate and frame filter
presses decrease with filtration time?
22.41 B List the factors that affect pressure filtration perform-
ance.
22.41 C Increasing the operating pressure might result in wet-
ter cakes. Why?
22.41 D How should the time of filtration be controlled?
22.41 E What purpose does precoating serve?
22.41 F List the NORMAL operation procedures for filter
presses.
22.41 G The typical performance data presented in Table
22.15 indicates that secondary sludges do not dewa-
ter as readily as primary sludges. Why is this so?
22.4104 Troubleshooting. The operator should be
concerned with the characteristics of the cakes discharged at
the end of the filtration cycle. Generally, filter presses consis-
tently produce excellent effluents (filtrate) unless the filtering
media is torn or not properly installed. Routine monitoring of
both the filtrate and cake is required for continued successful
operation.
Depending on the operation and performance of filter press-
es, the discharge cakes will be: (1) firm and dry throughout, (2)
firm and dry at the outer sections with wet and sloppy inner
sections, or (3) wet and sloppy throughout.
A firm and dry cake indicates good filter press operation and
no adjustments are necessary. If the cakes are firm and dry at
the ends but are composed of liquid centers, the operator
should check filtration time and chemical dosages. The filtra-
tion time should be checked by monitoring the filtrate flow on a
subsequent filter run. If the filtration time is not adequate, the
cavities between the plates will not fill completely with solids
and the innermost portions of the cakes will be wet. The
operator should increase the filtration time so as to obtain near
zero filtration flow at the end of the feed cycle. If the cakes are
wet throughout, either the filtration time should be increased if
necessary or the pressure should be monitored during a sub-
sequent run. If the desired pressure is not being developed,
the operator should check the condition and operation of the
high-pressure feed pump and the condition and installation of
the filter cloths. A tear in the filtering media or misalignment of
the cloths will cause a lot of the sludge to pass through the filter
without building up between the plates, and will usually result
in poor effluent quality. The operator also should check to de-
termine if the poor effluent quality is related to a clogged or
dirty filter cloth. If the pressure is as desired and the filtrate
quality is good, inconsistent and wet cakes could develop from
a low chemical dosage. The operator should check all aspects
of the chemical conditioning system and adjust the chemical
dosage to achieve the desired degree of dewatering.
If precoats are used to aid in discharge of the dewatered
solids, the operator should check the precoat system if rela-
tively large quantities of solids remain on the filter cloths upon
discharge.
Table 22.16 summarizes potential operational problems and
corrective measures to assist in maintaining effective filter
press dewatering.
TABLE 22.15 TYPICAL PERFORMANCE OF PLATE AND FRAME FILTER PRESS
Sludge Type
Chemical Conditioners
Lime (lb/ton)a or FeCI3 (lb/ton)1
Thermal
Treat.
Pressure,
psigb
Yield,
Ibs/hr/sq ft«
Cake
Solids,
% TSd
Solids
Recovery, %
Primary
100-200
100 - 200
—
100-200
0.5-1.0
40-50
90-99
Primary
—
—
LPO
100-200
0.5-1.2
40-50
90-99
Secondary
200 - 500
100-400
—
100-200
0.1 - 0.3
20-30
90-99
Secondary
—
—
LPO
100-200
0.1 - 0.4
20-40
90-99
Dig. Primary
100-400
100-200
—
100-200
0.5-1.0
40-50
90-99
Dig. Primary
—
—
LPO
100-200
0.5-1.0
40-50
90-99
Dig. Primary
200 - 600
100-400
—
100-200
0.1 -0.3
20-30
90-99
Dig. Secondary
200 - 600
100-400
—
100-200
0.1-0.3
20-30
90-99
Dig. Secondary
—
LPO
100-200
0.1 - 0.4
20-30
90-99
¦lb chemical/ton dry solids, lbs/ton x 0.5 = gm chemical/kg dry solids
bpsi x 0.07 = kg/hr/sq m
clbs/hr/sq ft x 4,883 = kg/hr/sq m
^Thickened sludge
-------
190 Treatment Plants
TABLE 22.16 TROUBLESHOOTING PLATE AND FRAME FILTER PRESSES
Operational Problem
1. Inner portions of
cakes wet and
sloppy upon
discharge
Possible Causes
1 a. Low filtration
time
b. Low pressure
c. Chemical
inefficiencies
2. Cakes wet
throughout
2a. Low filtration
time
b. Low pressure
c. Chemical
inefficiencies
3. Solids remain on
cloth upon discharge
3a. Precoat
inefficiencies
Check or Monitor
1a. Filtrate flow for
an entire run
b. Pressure
developed
c. Chemical dosages
2a. Filtration flow
b. Pressure developed.
Check media for
tears or
misalignment
c. Chemical equipment
and dosage
3a. Precoat application
and dosage
Possible Solutions
1a. Increase filtration
time
b. Repair and/or unplug
feed pump. Align
filter media
c. Increase chemical
dosage
2a. Increase filtration
time
b. Repair feed pump.
Replace and/or
realign media
c. Increase chemical
dosage
3a. Increase precoat
dosage
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 271.
22.41 H What measures should be taken if the discharge
cakes from a filter press are wet throughout?
22.411 Why do solids occasionally cling to the filtering media
when the cakes are discharged?
22.411 Belt Filter Press
Belt filter presses operate in a continuous manner and con-
sist of two endless belts that travel over a series of rollers.
Variations in belt filter designs are available from different
manufacturers, but the basic principles are the same for all belt
filters. A schematic of a typical belt filter press is presented in
Figure 22.16. Sludge to be dewatered is pre-conditioned, usu-
ally with polymers, then applied to the free-water drainage
zone of the filter belt. This portion of the belt is so named
because it allows for most of the free water to drain through the
filter and to be collected in a trough on the underside of the
belt. The main differences between different brandname filter
types are the method of introducing and mixing chemicals with
the sludge and the type of drainage zone used. Some presses
use in-line polymer mixing where the polymer is added directly
to the feed line and mixed with sludge by passing the flow
through a Venturi-type restriction to create mild turbulence.
With this type of chemical mixing system, the conditioned
sludge is applied to a horizontal "drainage zone" as shown in
Figure 22.16.
Mixing chambers also can be used to ensure adequate
polymer and sludge contact. Such chambers are cylindrical in
design and slowly rotate to allow the polymer to mix with the
sludge. Mixing chambers simply replace the Venturi-type re-
striction for creating mild turbulence. When the conditioned
sludge moves out of the mix chamber, it can be applied directly
to a horizontal drainage zone as discussed above or it can be
delivered to a cylindrical "reactor chamber." The reactor
chamber replaces the horizontal drainage zone and consists of
a screen around the outside edge of the chamber which allows
most of the free water to drain out.
Regardless of the polymer mixing and "drainage zone" de-
watering used, the partially dewatered solids are carried to a
point on the unit where they are trapped between two endless
belts and further dewatered as they travel over a series of
perforated and unperforated rollers. This zone is known as the
"press" or "dewatering zone." In this zone, the entrapped sol-
ids are subjected to shearing forces as they proceed over the
rollers. Water is forced from between the belts and collected in
filtrate trays while the retained solids are scraped from the two
belts when they separate at the discharge end of the press.
The two endless belts then travel through respective washing
chambers for the removal of fine solids to decrease the possi-
bility of plugging.
22.4110 Factors Affecting Belt Pressure Filtration. The abil-
ity of belt filter presses to dewater sludge and to remove sus-
pended solids is dependent on: (1) sludge type, (2) condition-
ing, (3) belt tension or pressure, (4) belt speed, (5) hydraulic
loading, and (6) belt type.
Sludge type, consistency of the feed, and chemical condi-
tioning will affect the performance of belt filters. Polymers are
generally used for chemical conditioning in conjunction with
belt filter operations. Polymer dosages must be optimized to
ensure optimum dewatering. Unlike plate and frame filter
presses which can consistently handle secondary sludge if
properly conditioned with chemicals, the belt filter might not be
able to handle secondary or waste activated sludges consis-
tently. Even with adequate polymer addition to flocculate and
to cause a separation of solids from the liquid, the belt press
might not be suitable for dewatering secondary sludges. Sec-
ondary sludges generally lack fibrous materials and exhibit a
plastic or jello-like nature. When these sludges are trapped
between the two belts and pressure is applied by the rollers,
they tend to slip towards the belt sides and eventually squeeze
out from between the belts. The net effects are that these
solids contaminate the effluent by falling into the filtrate trays'
and continued housekeeping is required. If this problem is evi-
dent, primary sludge may have to be blended with the second-
ary sludge to add fibrous material necessary to contain the
sludge between the belts. This procedure has produced sludge
cakes in the range of 24 to 26 percent solids with the use of
polymers.
The operating guidelines available to vary the degree of de-
watering are discussed below.
22.4111 Operating Guidelines. A well-operated belt filter
press should result in a high degree of dewatering provided the
operator is aware of the important operating controls.
-------
HIGH PRESSURE
PRESSING ZONE
SLUDGE CAKE
TO DISPOSAL
BELT WASH
FREE WATER
DRAINAGE ZONE
o
BELT
WASH
CHEMICALLY
CONDITIONED
SLUDGE
LOW PRESSURE
PRESSING ZONE
PERFORATED
"press ROLLER
BELT GUIL-E AND
TENSION ROLLER
\ BELT GUIDE AND
j TENSION ROLLER
PERFORATED
p R E S S ROLLER
Fig. 22.16 Belt filter press
-------
192 Treatment Plants
BELT TENSION PRESSURE
The operator can increase or decrease the pressure applied
to the sludge by adjusting the tension rollers to take up slack
on the two endless belts. As the belt tension is increased, more
water is generally squeezed from the belt resulting in drier
cakes. The pressure variations available on each manufactur-
er's belt press are different and the operator should consult the
manufacturer's literature to determine the range of operating
pressures. Although pressure increases usually result in drier
cakes, some undesirable conditions may develop as a result of
increasing the tension between the belts. These are: (1) sludge
may be forced from between the belts due to increased shear
forces, or (2) sludge may be forced through the belt. Both of
these conditions will result in filtrate contamination and in-
creased housekeeping requirements. The optimum operating
pressure should be selected by the operator so as to produce
the driest cake possible while containing the sludge between
the belts.
BELT SPEED AND HYDRAULIC LOADING
The belt speed can be varied from approximately 2 to 10
feet/minute (0.6 to 3 m/min). The speed at which the belt
should be operated depends on the sludge flow rate to the belt
and the concentration of the influent sludge. Since most of the
water associated with the sludge is removed in the drainage
zone, sufficient belt area has to be provided to allow the water
to drain. As the belt speed is increased, the rate of belt area
contacting the influent sludge also increases and allows for
greater volumes of water to drain from the sludge. If the belt
area is not sufficient enough to allow the free water to drain, a
"washing out" of the belt will occur. Washing out means that
large quantities of free water unable to be released in the
drainage zone will travel to the dewatering zone and flow out
from between the belts and drastically reduce effluent quality.
The belt speed should be controlled so that the sludge deliv-
ered to the dewatering zone has a minimum amount of free
water. The experienced operator will be able to optimize belt
speed by observing the dryness of the solids delivered to the
dewatering zone. Obviously, as the concentration of influent
sludge increases, less water is associated with the sludge
mass and reduced belt speeds can be used. THE IDEAL
OPERATING BELT SPEED IS THE SLOWEST THE
OPERATOR CAN MAINTAIN WITHOUT" WASHING OUT"
THE BELT. As the belt speed decreases, cake dryness in-
creases because the sludge is subjected to pressure and
shearing forces for longer periods of time.
Hydraulic loadings are based on the flow rate applied per
unit of belt width. Belt presses range in width from approxi-
mately 1.5 feet to 7.0 feet (0.45 to 2.1 m). Manufacturers gen-
erally recommend loadings of 10 to 25 GPM per foot (180 to
450 cu m/day/m) of belt width. The ideal loading for a particular
belt press and a specific sludge should be determined on the
basis of dewatering performance and consistency of operation.
If a belt press is operated close to the upper hydraulic limit,
frequent "washing out" may result due to slight variations in
sludge characteristics and/or chemical dosages. An example
for the calculation of the hydraulic loading follows.
EXAMPLE 36
Given: A 6-foot-wide belt press receives 100 GPM of primary
sludge at a concentration of 5 percent.
Find: The hydraulic loading, GPM/ft
Solution:
Known Unknown
Belt Filter Press Hydraulic Loading, GPM/ft
Belt Width, ft = 6 ft
Flow, GPM = 100 GPM
SI Sol, % = 5%
Determine the hydraulic loading in gallons per minute per foot.
Hydraulic = Flow' GPM
Loading, Belt Width, ft
GPM/ft = 100 GPM
6 ft
= 16.7 GPM/ft
BELT TYPE
Belts are available in a variety of materials (nylon, polypro-
pylene), each with various porosities. Porosity is a measure of
fiber openings. As the porosity increases, the resistance to
flow decreases and larger volumes of water are able to be
drained. If the porosity (fiber openings) is too large, sludge
solids may pass through the belt and result in poor filtrate
quality. If the porosity is too low, the belt may blind or plug
which will produce frequent "washouts." The right belt for a
particular application is determined by experimentation in con-
junction with manufacturer's recommendations. After a belt is
selected and installed, the operator should provide for
adequate belt cleaning by maintaining the belt-washing
equipment in proper working condition and by adjusting the
washwater volume as required.
22.4412 Normal Operating Procedure. The operation of dif-
ferent belt filters will vary somewhat, but the following proce-
dures will be applicable for most cases:
1. Prepare an adequate supply of an appropriate polymer
solution.
2. Turn on the washwater sprays and the belt drive.
3. Adjust the belt speed to its maximum setting and allow the
washwater to wet the entire belt.
4. Turn on the mix drum and reactor drum if applicable.
5. Open appropriate sludge and polymer valves.
6. Turn on the polymer pump and adjust the polymer rate as
required to achieve the desired dosage.
7. Turn on the sludge feed pump.
8. Lower the belt speed as low as possible without running
the risk of "washing out."
9. Adjust the belt tension as required.
10. Turn on the dewatered sludge conveyor.
-------
Solids Disposal 193
The operator should routinely check the operation of the belt
press and make adjustments as required to produce a dry cake
and good filtrate quality.
22.4113 Typical Performance. Operating guidelines,
polymer requirements, and typical performance data are pre-
sented in Table 22.17.
TABLE 22.17 TYPICAL PERFORMANCE OF BELT
PRESS FILTRATION UNITS
Sludge Type
Primary
Secondary
Dig. Primary
Dig. Secondary
Polymer,
lbs/ton^
4- 8
9-20
4- 8
15-30
Cake.
% TS°
25-35
17-20
25-30
17-20
SS Recovery, Hyd. Load,
% GPM/ftc
95-99 10-25
90-99 5- 15
95-99 10-25
90 - 99 5- 15
a lb of dry polymer/ton dry sludge solids.
polymer/kg dry sludge solids
b Thickened sludge
C GPM/ft X 0.207 = Llseclm
lbs/ton x 0.5 = gm
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 272.
22.41 J What purpose does the drainage zone serve?
22.41 K What is the function of mix chambers used on some
belt presses?
22.41 L What is the purpose of reactor chambers used on
some belt presses?
22.41 M Describe the function of the "press" or "dewatering
zone."
22.41 N List the factors affecting belt filter performance.
22.410 What problems might be expected when using a belt
press to dewater secondary sludge?
22.41 P How does pressure affect belt press operation?
22.41 Q Explain how low belt speed affects belt press per-
formance.
22.41 R What does the term "washing out" mean?
22.41 S What is the ideal belt speed?
22.41 T How does belt type affect belt press performance
and what problem may develop if the porosity is too
low?
22.4114 Troubleshooting. A close watch over belt press
operation in combination with field experience should enable
the operator to optimize performance. In addition to mechan-
ical reliability and maintenance, the operator should be con-
cerned with the filtrate quality and dryness of the dewatered
sludge. The most frequent problem encountered with belt
presses is "washing out." Usually this problem is indicated by
large volumes of water carrying onto the dewatering zone and
overrunning the sides of the belt. When this happens the
operator should check: (1) the polymer dosage, (2) adequate
mixing in reactor, (3) hydraulic loading, (4) drum speed, (5) belt
speed, and (6) belt washing equipment.
If the polymer dosage is too low, the solids will not flocculate
and free water will not be released from the sludge mass. If the
polymer dosage is adequate as evidenced by large floe parti-
cles and free water, the operator should increase the belt
speed so as to provide more belt surface area for drainage. If
the belt is already at its maximum setting, the operator should
check the flow rate to the press and reduce it if the rate is
higher than normal. If the polymer dosage, belt speed, and
hydraulic loading are set properly but "washing out" still per-
sists, the problem may be related to blinding of the filter media.
The operator should check the appearance of the belts as they
leave their respective washing chambers. If the belts appear to
be dirtier than normal, the operator should increase the wash-
water rate and turn off the polymer and feed pumps and allow
the belts to be washed until they are clean. Belt blinding often
develops because of polymer overdosing. If too much polymer
is added, the belts can become coated with a film of excess
chemical which will prevent drainage and result in "washing
out" of the belt. The operator should check the polymer addi-
tion rate and adjust the rate as required so as not to grossly
overdose the sludge.
Poor effluent quality will generally result from "washing out"
or from sludge being forced either through or from the sides of
the belt. If sludge is forced from the belts, the operator should
check the belt tension and condition of the belts. Again, if the
belts are dirty and water is prevented from draining, the sludge
and water will squeeze from the belt side when they are sub-
jected to pressure in the dewatering zone. The operator can
reduce belt tension somewhat and clean the belts to eliminate
the problem.
If the unit is working as expected, that is the sludge is con-
tained between the belts and filtrate quality is good but the
discharge cakes are not as dry as desired, the operator can
reduce the belt speed and/or increase the tension somewhat to
achieve drier cakes. After a change in belt speed is made, the
operator should observe the operation for at least 15 minutes
to make certain that a "wash out" will not occur.
Table 22.18 summarizes typical operational problems and
corrective measures that could be taken to optimize belt press
performance.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 272.
22.41 U What steps should the operator take if "washing out"
of the belt develops.
22.41V How can blinding of the belt be corrected?
22.412 Vacuum Filtration
A vacuum filter consists of a rotating drum which continu-
ously passes through a trough or pan containing the sludge to
be dewatered. A typical rotary-drum vacuum filter is shown in
Figures 22.17 and 22.18, with an operation schematic in Fig-
ure 22.19. The cylindrical drum, which is covered with some
type of cloth media, is submerged about 20 to 40 percent in the
trough. The trough is usually equipped with an agitator to keep
the chemically conditioned sludge well mixed and to keep
sludge from settling in the trough. The filter drum is divided into
compartments. In sequence, each compartment is subject to
vacuums ranging from 15 to 30 inches (38 to 75 cm) of mer-
cury. As the vacuum is applied to the compartment of the drum
submerged in the trough, sludge is picked up on the filter
media and a sludge mat is formed. This is known as the "mat
formation" or "sludge pick-up zone." As the drum rotates out of
the trough, the vacuum is decreased slightly and water is
sucked from the sludge mat, through the filter media and dis-
charged through internal pipes to a drainage system. This is
known as the "drying zone" of the cycle. Just prior to the point
where the media separates from the drum, the vacuum is re-
duced to zero. The dewatered solids remaining on the filter
media are then discharged to a sludge hopper or conveyor via
-------
194 Treatment Plants
scrapers or discharge rollers. The cloth then reunites with the
drum and is reintroduced into the sludge trough for another
cycle.
22.4120 Factors Afecting Vacuum Filtration. The following
factors can have pronounced effects on the operation and per-
formance of vacuum filters: (1) sludge type, (2) conditioning,
(3) applied vacuum, (4) drum speed or cycle time, (5) depth of
submergence, and (6) media type and condition.
The sludge type and the conditioning methods used will
drastically affect filter operation. In general, STRAIGHT
(ONLY) SECONDARY SLUDGES (DIGESTED OR UNDI-
GESTED) ARE NOT EASILY DEWATERED BY VACUUM
FILTRATION because they do not dewater enough to readily
discharge from the belt; however, THERMALLY CON-
DITIONED secondary sludges can be effectively dewatered
with a vacuum filter. Even with extremely high dosages of lime
and ferric chloride, secondary sludges that have not been
thermally conditioned will generally not dewater effectively.
Such sludges usually require blending with primary sludges
prior to vacuum filtration for successful dewatering.
Operational Problem
1. Washing out of belt
2. Poor filtrate quality.
3. Cake solids too wet.
TABLE 22.18 TROUBLESHOOTING BELT FILTER PRESS
Possible Cause Check or Monitor
1 a. Polymer dosage
insufficient
b. Hydraulic load too
high
c. Belt speed too low
d. Belt blinding
2a. Washing out
b. Sludge squeezed
from belt
3a. Belt speed too high
b. Belt tension too low
1b. Polymer flow rate
and solution
b. Sludge flow
rate
c. Belt speed
d. Washing equipment and
polymer overdosage
2a. Same as 1
b. Belt tension
Washing equipment
Possible Solution
3a.
b.
Belt speed
Belt tension
1a. Increase dose
rate
b. Lower flow
c. Increase speed
d. Increase wash water
rate. Turn off sludge and
polymer and clean belts.
Reduce polymer if
overdosing
2a. Same as 1
b. Decrease tension.
Wash the belt
3a. Reduce belt speed
b. Increase belt tension
-------
Fig. 22.17 Vacuum filter
(Permission of Eimco)
-------
AUTOMATIC VALVE
SLUDGE POOL
AIR AND
FILTRATE
LINE
AIR BLOW-BA CK LINE-
CLOTH CAULKING STRIPS
CLOTH MEDIA
DRUM
FILTRATE PIPING
SLUDGE AGITATOR
CAKE SCRAPER
SLUDGE CAKE TO
DISPOSAL
-SLUDGE FEED
Fig. 22.18 Rotary drum vacuum filter
-------
SLUDGE
" POOL
CLOTH MEDIA
MIXER
POLYMER FEED
CAKE SCRAPER
CAKE
DRYING
\ AREA
SLUDGE FEED
DISCHARGE
AREA
SLUDGE CAKE
TO DISPOSAL "
PICK-UP
AREA
CONVEYOR BELT
•VAT
Fig. 22.19 Vacuum filter operating schematic
-------
198 Treatment Plants
As discussed in Section 22.3, sludge conditioning must be
optimized to achieve the desired degree of dewatering regard-
less of the sludge type and type of dewatering equipment
used. To ensure successful vacuum filtration, the operator
should follow the procedures outlined in Section 22.3 to condi-
tion and prepare the sludge for dewatering. The vacuum filter
operating guidelines and their effects on filter performance are
discussed below.
22.4121 Operating Guidelines. The applied vacuum will af-
fect the degree and rate of sludge pick-up in the "formation
zone" and will affect the quantity of water withdrawn from the
sludge in the drying zone. In general, reduced vacuums will
result in wetter cakes and less than optimum discharge charac-
teristics. The operator should attempt to maintain AS HIGH A
VACUUM AS POSSIBLE to obtain high degrees of dewater-
ing.
The drum speed or the time required to make one complete
cycle also controls the degree of dewatering. Typically, cycle
times vary from 2 to 6 minutes and THE LOWER THE CYCLE
TIME THE HIGHER THE DEGREE OF DEWATERING. Cycle
time as controlled by drum speed affects sludge dewatering in
two ways. First, it controls the rate of sludge pick-up and the
thickness of the sludge mat in the "formation zone," and sec-
ond, it controls the length of time the sludge remains in the
"drying zone." As the cycle time is increased, the opportunity
to pick up sludge from the trough and the time the sludge mat
is subjected to a vacuum in the "drying zone" are increased.
This generally results in drier cakes and improved discharge
characteristics. The operator should maintain as low a drum
speed as possible to obtain the highest degree of dewatering.
The cycle time is dependent on the solids loading or net filter
yield and the minimum speed that can be used depends on the
filter area and the quantity of sludge to be processed. Obvi-
ously, if the number and/or size of the filters is not adequate to
handle the entire sludge load at the lowest drum speed, the
operator will have to maintain higher drum speeds. In addition
to controlling the degree of dewatering, the drum speed also
controls the net filter loading. As the drum speed increases, the
net filter loading and the total quantity of sludge processed per
day increases. The following example illustrates the determi-
nation of filter loading and filter yield.
EXAMPLE 37
Given: A 6-foot diameter by 10-foot long vacuum filter with a
total surface area of 188 sq ft (n x 6 foot x 10 foot)
dewaters 4,500 lbs/day of primary sludge solids. The
filter is operated for 7 hours per day at a drum cycle
time of 3 minutes and produces a dewatered sludge of
25 percent thickened sludge (TS) with 95 percent solids
recovery.
Find: The filter loading in Ibs/hr/sq ft and filter yield in lbs/hr/
sq fit.
Solution:
Known Unknown
Vacuum Filter
Diameter, ft
Length, ft
Surface Area,
sq ft.
SI Sol Loading,
lbs/day
Filter Operation
hrs/day
Drum Cycle Time,
min
Dewatered Sludge Sol, %
Solids Recovery, %
Calculate the filter loading in pounds per hour per square
foot.
Filter Loading, = SI Sol Loading, lbs/day
Ibs/hr/sq ft Fil Operation, hrs/day x Area, sq ft
4500 lbs/day
7 hrs/day x 188 sq ft
= 3.4 Ibs/hr/sq ft
Calculate the filter yield in pounds per hour per square foot.
SI Sol Loading, lbs x Recov, %
Filter Yield, = ^ 100%
Ibs/hr/sq ft Fil Op, hr/day x Area, sq ft
4500 lbs x 95%
day 100%
7 hr/day x 188 sq ft
= 3.2 Ibs/hr/sq ft
EXAMPLE 38
Given: Based on previous experimentation with the filter and
sludge from Example 37, the operator knows that lower-
ing the drum cycle to 2 minutes will produce a 30 per-
cent dewatered sludge with 95 percent solids capture
or recovery, but the filter yield will decrease to 1.7 lbsI
hr/sq ft.
Find: The time the filter must be operated to process 4,500
pounds of primary sludge solids.
Solution:
Known
Information given in Example 37
If drum cycle time reduced to 2 min,
Dewatered SI Sol, % = 30%
Solids Recovery, % = 95%
Filter Yield
Ibs/hr/sq ft =1.7 Ibs/hr/sq ft
Calculate the time the filter must be operated to process
4,500 pounds per day of primary sludge solids.
SI Sol Loading, lbs x Recov, %
Filter Yield, _ day 100%
Ibs/hr/sq ft pu Qp hr/day x Area, sq ft
Rearrange the terms.
SI Sol Loading, lbs x Recov, %
Filter Opera- _ day 100%
tion, hr/day Fj| yield, ibs/hr x Area, sq ft
sq ft
4500 lbs_ x 95%
= day 100%
1.7 Ibs/hr x 188sqft
sqft
= 13.4 hours/day
Therefore, the filter must be operated for 13.4 hours per day
to produce a dewatered sludge cake of 30 percent solids when
using a 2-minute cycle time.
The exact response (filter yield and dewatered sludge as
'percent sludge solids) of a particular sludge depends on the
treatment plant. Experimentation is required to determine the
filter yields and degrees of dewatering at different cycle times.
= 6ft
= 10 ft
= 188 sq ft
= 4500 lbs/day
= 7 hrs/day
= 3 min
= 25%
= 95%
1. Filter Loading,
Ibs/hr/sq ft
2. Filter Yield,
Ibs/hr/sq ft
Unknown
Time filter must be
operated in hours
per day
-------
Solids Disposal 199
The depth of submergence of the drum within the trough
affects the formation of the sludge mat on the media. In gen-
eral, as the depth of submergence increases, more sludge
solids are picked up and filter yields may increase somewhat.
The depth of submergence should always be within the manu-
facturer's recommended range. In addition, the liquid level in
the trough should never be maintained below a level which will
cause a loss in vacuum. If the liquid level in the trough is too
low, air will be pulled Into the vacuum compartments and will
result in a loss of vacuum and a subsequent loss of mat forma-
tion and sludge dewatering.
The material of construction for the filter media is selected
based on experimentation with various cloth types. As the
porosity (openings) of the media increases, the ability to cap-
ture suspended solids decreases because fine, low-density
solids can pass directly through the media. Regardless of the
type and size of media selected for a particular application, the
operator must ensure adequate media cleaning via the wash-
water zone. If the media blinds with fine solids or chemical
coatings, sludge will not be picked up in the trough (vat) in the
sludge blanket formation zone and the vacuum filter will be-
come inoperable.
22.4122 Normal Operating Procedure. The specific opera-
tion of a particular vacuum will vary somewhat, but the follow-
ing procedures will be applicable for most operations:
1. Prepare chemicals in appropriate chemical tanks.
2. Transfer lime, if used, to a mixing tank to provide contact
with the sludge and/or add the required amount of ferric
chloride, if used.
3. Turn on the filter drum and the washwater to wet the entire
belt.
4. Pull up tension.
5. Fill the trough to the operating level with the conditioned
sludge.
6. Turn on the sludge mixer in the trough.
7. Turn on the vacuum pumps and filtrate pumps.
8. Adjust the drum speed and vacuum until the desired results
are achieved.
Whenever the unit is shut down, the cloth should be thor-
oughly cleaned to reduce the possibility of plugging during
subsequent operation. After shutdown, release cloth tension.
22.4123 Typical Performance. Table 22.19 summarizes
typical vacuum filter operation and performance criteria for var-
ious sludge types.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 272.
22.41 W What purpose does the agitator or mixer in the trough
serve?
22.41 X Explain what happens in the "mat formation" and
"drying zones."
22.41V Why does the filter media pass through a washing
zone?
22.412 List the factors that affect vacuum filtration.
22.41AA What vacuum should the operator maintain?
22.41 AB Explain how cycle time or drum speed affects vac-
uum filter dewatering.
22.41 AC Determine the FILTER YIELD (Ibs/hr/sq ft) for a vac-
uum filter with a surface area of 300 sq ft. Digested
sludge is applied at a rate of 75 GPM with a sus-
pended solids concentration of 4.7 percent. The filter
recovers 93 percent of the applied suspended solids.
22.41 AD How does the porosity of the filter media affect vac-
uum filter performance?
22.4124 Troubleshooting. Successful vacuum filtration will
result in a relatively clear filtrate and a relatively thick sludge
mat that will readily discharge from the filter media. The most
common problems that develop with vacuum filters are deterio-
rations in filtrate quality and wet cakes that are difficult to dis-
charge from the belt.
If the filtrate quality is noted to contain more than the usual
amount of solids, the operator should check the vacuum and
TABLE 22.19 TYPICAL PERFORMANCE OF VACUUM FILTERS
Sludge Type
Primary
Primary and
Trickling
Filter
Primary and
Air-Act.
Digested
Primary
and Tr.
Filter
Digested
Primary
& Air-Act.
Lime,
lbs/ton*
50-150
200-600
FeCI,,
lbs/ton*
25-50
Thermal
Conditioning
LPO
LPO
LPO
LPO
Vacuum,
In. Hgb
15-30
15-30
15-30
15-30
15-30
15-30
Cycle,
Mln.
2-6
2-6
2-6
2-6
2-6
2-6
Yield,
lbs Sol/hr/sq ft6
4-12
4-8
4-5
4-8
4-5
4-5
a lbs of chemical/ton of dry sludge solids, lbs/ton x 0.5 = gm of chemical/kg of dry sludge solids
" in. Hg x 2.54 = cm Hg
c lbs solids/hr/sq ft x 4.883 = kg/hr/sq m
d Thickened sludge
Cake.
%TS»
24-40
30-45
25-40
25-35
25-40
25-30
Solids
Recovery, %
85-95
35-95
85-95
85-95
85-95
85-90
-------
200 Treatment Plants
the condition of the filter media. The filter media can easily
move out of alignment and often work their way free of the
drum. If this happens, a proper seal will not develop between
the media and drum and unfiltered sludge will be sucked from
the trough and contaminate the filtrate. If the seal is broken
between the media and drum, a loss of vacuum will develop
when the unsealed point on the drum is subjected to a vacuum.
The operator should check the vacuum gages for losses of
vacuum and realign the filter media as required. If the filter
media (cloth blanket) is misaligned, this is a major repair job
and will require the unit to be shut down. A tear in the filter
media will have the same effect as misalignment and the
operator should repair or replace the media if it is defective.
A substantial reduction in cake dryness and/or discharge or
filtrate characteristic will result from (1) inadequate chemical
conditioning, (2) cycle times too low (drum speed too fast), or
(3) media blinding. The operator should check the condition of
media and increase the washwater rate, or turn off the sludge
feed and wash the belt if it is laden with solids as it exits the
washing zone. A clogged media will usually develop when poor
mat formation occurs in the pick-up zone. Whatever solids are
picked up will not effectively drain in the drying zone and a wet
cake will develop.
If the media is clean and a good seal is developed, a de-
crease in sludge dryness and discharge characteristics could
result from high drum speeds or improper conditioning. If pos-
sible, the drum speed should be lowered to afford more drying
time, and the chemical mixing and addition system should be
checked for malfunctions. The operator should also be aware
that drastic changes in the influent sludge characteristics could
affect the chemical dosage and the degree of dewatering. If the
influent sludge appears to be thicker than normal, the operator
must increase the rate of chemical addition to match the in-
crease in influent solids.
Table 22.20 summarizes the most common operational
problems and the usual corrective measures taken to maintain
good vacuum filter dewatering.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 272 and 273.
22.41 AE What can cause a loss in vacuum and how will such
a loss affect filter performance?
22.41 AF If the sludge is not picked up in the mat formation
zone, what should the operator do?
22.41 AG How can the operator increase cake dryness?
22.42 Centrifugation
22.420 Process Description
Centrifuge designs for dewatering sludge include batch-
operated basket centrifuges and continuous-flow scroll cen-
trifuges. Factors affecting centrifugation, operating criteria and
troubleshooting were described in detail in the thickening sec-
tion (22.1) of this manual. The reader should refer to Section
22.1 for a review of the mechanics of centrifugation. The main
differences between centrifugal thickening and centrifugal de-
watering are that the concentration of feed sludge is somewhat
higher for dewatering than for thickening, and that a drier cake
is the usual goal for dewatering. The operator may therefore
have to maintain a higher differential (relative) scroll speed
when dewatering because of the higher solids loading, but the
principles of centrifugation remain the same as previously dis-
cussed.
22.421 Typical Performance
Table 22.21 summarizes typical centrifuge operating criteria,
conditioning requirements, and performance data for various
sludge types.
Usually, the physical size of the centrifuge will govern the
maximum through put for a particular sludge and, in general,
the exact response of a particular sludge depends on the
treatment plant.
Troubleshooting techniques for basket and scroll centrifuge
dewatering are identical to those already outlined in Section
22.1.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 273.
22.42A Why are higher scroll speeds usually required to de-
water sludges as compared to sludge thickening?
22.42B A scroll centrifuge is used to dewater 60 GPM of
digested primary sludge at a concentration of 3.0
percent sludge solids. A liquid polymer is used for
conditioning. The polymer solution is 2.5 percent and
2 GPM are added to the sludge stream. What is the
hydraulic loading (GPH), the solids loading (lb SS/hr)
and the polymer dosage (lb liq/ton)?
22.42C A 48-inch diameter basket centrifuge is used to de-
water 50 GPM of digested primary sludge. The feed
is at a concentration of 2.7 percent sludge solids and
TABLE 22.20 TROUBLESHOOTING VACUUM FILTERS
Operational Problem
1. Loss of Vacuum
2. Poor filtrate quality
Possible Causes
4. Poor mat formation
1. a. Filter media misaligned
b. Tear in filter media
c. Trough empty
d. Vacuum pumps inopera-
tive
2. a. Same as 1a and 1b
b. Insufficient conditioning
3. Wet cake and poor discharge 3.
a. Same as 1
b. Drum speed too high
c. Insufficient conditioning
4. a. Same as 1, 2, and 3
b. Clogged media
Check or Monitor
1. a. Media alignment
b. Media condition
c. Level in trough
d. Operation of vacuum
pumps
2. a. Same as 1a and 1b
b. Conditioning system
3. a. Same as 1
b. Drum speed
c. Conditioning system
4. a. Same as 1, 2 and 3
b. Media condition
Possible Solution
1. a. Realign media
b. Repair/replace media
c. Fill trough
d. Repair and/or turn on
pumps
2. a. Same as 1a and 1b
b. Increase dosage or degree
of conditioning
3. a. Same as 1
b. Lower drum speed
c. Increase dosage or degree
of conditioning
4. a. Same as 1, 2, and 3
b. Clean media
-------
Solids Disposal 201
polymers are added to achieve 95 percent sus-
pended solids recovery. The average concentration
of solids stored within the basket is 23 percent. The
feed time is automatically set at 17 minutes. Is the
feed time too long, too short, or OK? Assume the
basket has a solids storage capacity of 16 cubic feet.
22.42D A basket centrifuge is used to dewater digested sec-
ondary sludge. On a routine check, the operator
notices that the centrate quality is poor but the dis-
charge solids are dry. What should the operator
check and what action should be taken to produce a
clean centrate?
22.43 Sand Drying Beds
The use of sand drying beds to dewater wastewater sludges
is usually limited to small or medium-sized plants (less than 5
MGD or 19,000 cu m/day) because of land restrictions. Drying
beds usually consist of 4 to 9 inches (10 to 23 cm) of sand
placed over 8 to 20 inches (20 to 50 cm) of graded gravel or
stone. Sludge is placed on the beds in 12 to 18 inch (30 to 45
cm) layers and allowed to dewater by drainage through the
sludge mass and supporting sand, and by evaporation from
the surface exposed to the atmosphere. An underdrain system
composed of a lateral network of perforated pipes or trenches
can be used to collect the filtrate for subsequent recycle to the
plant headworks. After drying, the dewatered sludge is re-
moved by manual shoveling (forks) for further processing or
ultimate disposal. Sludge drying beds are usually not used for
sludges that have been stabilized or conditioned by wet oxida-
tion because of the odorous nature of thermally heated sludge.
22.430 Factors Affecting Sand Drying Beds
The design, use, and performance of drying beds are af-
fected by many factors. These include (1) sludge type, (2)
conditioning, (3) climatic conditions, (4) sludge application
rates and depths, and (5) dewatered sludge removal tech-
niques.
As is the case with mechanical dewatering devices, the type
of sludge applied and the effectiveness of chemical condition-
ers can determine the degree of dewatering and the operation
of the beds. Since the majority of dewatering is by drainage
through the support sand, the sludge has to be adequately
conditioned to flocculate the sludge solids and release free
water. Care must be taken to prevent chemical overdosing for
two reasons, (1) media (sand) blinding with unattached
polymer may develop, and (2) large floe particles that settle too
rapidly may also blind the media. Whatever the mechanism for
blinding, the net result will be the same. The liquid portion of
the sludge will be unable to drain through the bed and dewater-
ing will be by evaporation only. The time required to evaporate
water is substantially greater than the time required to remove
water by a combination of evaporation and drainage.
Chemical requirements, pre-screening requirements, and
the response of sludges to sand drying operations are gener-
ally determined by laboratory, pilot and/or full-scale experi-
mentations.
Climatic conditions are very important to an efficient sand
drying bed operation. After all the water that can be removed
by drainage is complete, evaporation is the only mechanism
available for further dewatering. As climatic conditions vary
from inclement and humid to dry and arid, so does the rate of
evaporation and consequently the time required to achieve the
desired degree of dewatering. In wet or cold climates, the sand
beds are usually covered with greenhouse-types of enclosures
to protect the drying sludge from rain and to reduce the drying
period during cold weather. Such enclosures should be well
ventilated to promote evaporation. They also can serve to con-
trol odors and insects.
The operator has little, if any, control over the sludge type
and characteristics, no control over climatic conditions and
physical size of the sand beds, but can control, to some extent,
the depth of sludge application and dewatered sludge removal
techniques.
22.431 Operating Guidelines
The physical size of sand drying beds is based on the
amount of sludge to be dried each year. In general, sand beds
are loaded at rates of 10 to 35 lbs of sludge solids/yr/sq ft (50 to
TABLE 22.21 TYPICAL PERFORMANCE OF CENTRIFUGES
Conditioning
Sludge Type
Centrifuge
Type
Polymer,
Ibe/ton*
Thermal
Flow,
GPM»
Solid* Load,
Ibs/hrc
Cake,
%TS<*
Solide
Recovery, %
Primary
Scroll
0-5
20-150
200-1500
25-35
30-95
Primary
Scroll
0-5
LPO
20-150
200-1500
25-40
50-95
Secondary
Scroll
0-15
—
20-150
100-700
6-9
30-95
Secondary
Scroll
0-7
LPO
20-150
100-700
20-30
70-95
Secondary
Basket
0-10
—
20-70
70-350
6-9
50-95
Secondary
Basket
0-4
LPO
20-70
70-350
20-30
70-95
Dig. Pri.
Scroll
0-15
—
20-150
200-1500
20-25
30-95
Dig. Pri.
Scroll
0-5
LPO
20-150
200-1500
20-30
70-95
Dig. Pri.
Basket
0-15
—
35-50
200-500
20-25
70-95
Dig. Sec.
Scroll
0-40
—
20-150
200-1500
6-12
30-95
Dig. Com.®
Scroll
0-20
—
20-150
200-1500
10-25
30-95
Dig. Com.®
Basket
0-20
—
35-50
200-500
10-20
50-95
a lbs of dry polymer/ton of dry sludge solids, lbs/ton x 0.5 = gm of polymer/kg of dry sludge solids
b GPM x 5.45 = cu m/day
c Ibs/hr X 0.454 = kg/hr
d Thickened Sludge
• Digested Primary + Digested Combined
-------
202 Treatment Plants
170 kg/yr/sq m) for open drying beds and 20 to 45 lbs of sludge
solids/yr/sq ft (100 to 220 kg/yr/sq m) for covered drying beds.
Obviously, as the loading rate decreases, the time required to
dewater the sludge decreases as does the potential for blind-
ing of the bed. The operator should control loading rates ac-
cording to the total area of bed available and the estimated
quantity of sludge production. The operator should also pro-
vide for a standby capacity of 10 percent additional area, if
possible, to meet unexpected increases in sludge loads and to
allow for down time for operational problems. If sufficient bed
area is not available to allow for standby capacity, auxiliary
mechanical dewatering equipment or liquid sludge haulers
should be available for emergency situations.
EXAMPLE 39
Given: An operator at a treatment plant has two sand beds
available for dewatering experiments. Each bed has
dimensions of 200 feet long by 25 feet wide. Sludge is
applied to Bed A to a depth of 3 inches and to Bed B to
a depth of 9 inches. Bed A requires six (6) days to dry
and one (1) day to remove the sludge for another appli-
cation. Bed B requires 21 days to dry and one (1) day to
remove the sludge for another application. The applied
sludge is at a concentration 3 percent sludge solids.
Find: 1. The total gallons and lbs of sludge applied per appli-
cation for Bed A and Bed B.
2. The loading rates (Ibs/yr/sq ft) for Bed A and Bed B
assuming repeated applications are made on each
bed with no operational or maintenance down time.
3. Which application depth should be used.
BED B
Sludge Applied,
gal/application
Sludge Applied,
lbs/application
_ L, ft x W, ft x D, in/apl x 7.48 gal
12 in/ft cu ft
= 200 ft x 25 ft x 9 in/apl x 7.48 gal
12 in/ft cu ft
= 28,050 gal/application
= SI Appl, gal x 8.34 lbs x SI Sol, %
apl gal 100%
_ 28,050 gal X 8.34 lbs x 3.0%
apl gal 100%
= 7,018 lbs/application
2. Determine the loading rates for the sludge applied in
pounds per year per square foot for both Beds A and B.
BED A
Loading Rate, = Sl APP'- lbs/aP' x 365 daVs/yr
Ibs/yr/sq ft L, ft x w, ft x Cycle, days/apt
_ 2340 Ibs/apl x 365 days/yr
200 ft x 25 ft x (6 days + 1 day)/apl
= 24.4 Ibs/yr/sq ft
BED B
Loading Rate, = Sl AppL lbs/aP' x 365 daVs/y
Ibs/yr/sq ft L, ft x W, fl x Cycle, days/apl
7018 Ibs/apl x 365 days/yr
200 ft x 25 ft x (21 days + 1 day)/apl
= 23.3 Ibs/yr/sq ft
= 200 ft
= 25 ft
= 3 in (Bed A)
= 9 in (Bed B)
Unknown
1. Sludge Applied,
gallons/application and
pounds/application for both
Beds A and B.
2. Loading Rates, Ibs/yr/sq ft for
both Beds A and B.
3. Which application depth
should be used?
Solution:
Known
Two Sand Beds
Length, ft
Width
SI Depth, in
SI Depth, in
Drying Time
Bed A, days = 6 days
Bed B, days = 21 days
Sludge Removal,
days = 1 day
Sludge
Solids, % = 3%
1. Determine the sludge applied in gallons per application and
pounds per application for both Beds A and B.
BED A
Sludge Applied, = L, ft x W, ft x D, in/apl x 7.48 gal
gal/application 12jn/ft cuft
_ 200 ft x 25 ft x 3 in/apl x 7.8 gal
cu ft
12 in/ft
= 9,350 gal/application
Sludge Applied, _ SI Appl, gal x 8.34 lbs x SI Sol, %
lbs/application ga| 100%
9,350 gal x 8.34 lbs x 3.0%
apl gal 100%
= 2,340 lbs/application
3. Which application depth should be used?
Based on the data given and the above analysis, there is no
substantial difference in the amount of solids that can be
applied per year for application depths of 3 inches and 9
inches. The operator should choose the 9-inch application be-
cause it will result in less operator time. A 3-inch application
would require the operator to refill and possibly remove solids
every 7 days while a 9-inch application will require operator
attention every 22 days.
The preceding example ONLY illustrates the calculations
necessary to determine loading rates and it should NOT be
misinterpreted that high application depths are more efficient
than low application depths as a result of these calculations.
The operator should go through the above analysis for a par-
ticular sludge and specific data to determine the optimum
depth of application. Usually, greater depths of digested
sludge are applied and the drying times are longer than used in
this example.
Sludge removal from sand drying beds should be done so as
to remove as little of the sand media as possible and care
should be taken to avoid compacting the sand bed. Heavy
equipment should not be allowed on the bed. Provisions
should be made to remove dewatered sludge by surface
scrapers or collectors that are mounted on the vertical walls of
the bed or on the access road between the beds. Compaction
of the bed will result in reduced drainage rates, longer drying
times and may increase the potential for plugging.
22.432 Normal Operating Procedures
The sludge should be applied to the bed as evenly as possi-
ble and should be done with minimal upsetting of the bed
surface. This is best accomplished by applying the sludge
through an inlet distribution assembly which may consist of
-------
Solids Disposal 203
troughs and weirs to apply the sludge evenly and with as little
turbulence as possible. Be sure to flush the sludge out of the
pipe and leave one end open for any gas produced by
anaerobic decomposition to escape. Some operators make a
large two-wheel "pizza cutter" out of disc harrows, or a tine-
type drag device, either of which is dragged across the sludge
as soon as it begins to "fetch up." This promotes cracking
along these lines which allows operators to fork out easily
handled sized pieces of dried sludge. Remove the sludge from
the bed when it reaches a dryness that will allow for easy
removal. Scrape and smooth the surface of the bed with a rake
to prepare the drying bed for more sludge.
22.433 Typical Performance
Table 22.22 summarizes typical operating guidelines and
performance data for sand drying of wastewater sludges.
The final concentration to which the sludge can be dried is
dependent on the climatic conditions and time the sludge re-
mains in the bed after the majority of water has drained
through the sand. In general, the sludge is dried to the point
where it can easily be removed from the bed. If the sludge is
removed when it is relatively wet and sticking to the bed sur-
face, large quantities of sand also will be removed.
TABLE 22.22 TYPICAL PERFORMANCE OF SAND BEDS
Loading, lb SS/eq ft*
Sludge Type
Digested Primary
Digested Secondary
Digested Combined
Open Bed Covered Bed
20-35
10-20
10-25
20-45
10-25
10-35
Cake,
% TSb
30-70
30-50
30-70
Solids
Recovery, %
95-99
95-99
95-99
alb/sq ft x 4.883 = kg/sq m
^Thickened sludge
Sand bed operations are more of an art than a science be-
cause of the large number of uncontrolled variables. Even
though sand beds are a common method of sludge dewater-
ing, it is difficult to list typical operation and performance data
with a reasonable degree of certainty.
22.434 Troubleshooting
Sand drying beds are relatively simple to operate and the
only problem that appears to develop at most installations is
plugging of the media (sand) surface. When sludge is applied,
the majority of water should drain within the first 3 to 10 days
after the application. If poor drainage is evident by small filtrate
quantities and a slow rate of drop of the liquid surface, the
operator can assume the media is plugged. If sufficient area or
standby capacity is available, the affected bed(s) should be
allowed to dry by evaporation. After the sludge is dried and
removed, the operator should rake the surface of the bed and
might remove the upper 2 to 3 inches (5 to 8 cm) of sand and
replenish with fresh sand if excessive blinding is evident. If
sufficient capacity is not available to allow time for the sludge in
the affected bed to dry by evaporation, the operator should
pump the sludge out of the bed and clear or replace the upper
layer of sand.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 273 and 274.
22.43A Why are sand drying beds not commonly used for
wet oxidized sludges?
22.43B List the factors that affect sand drying bed perform-
ance.
22.43C Why should overdosing with chemicals, particularly
polymer, be avoided?
22.43D Why might primary sludge from the bottom of digest-
ers require pre-screening?
22.43E Why are drying beds sometimes covered?
22.43F A 150-foot long by 30-foot wide sand drying bed is
loaded at 15 Ibs/yr/sq ft. One application of sludge is
made per month (12 applications per year). Deter-
mine the depth (in) of each application if the sludge
has a concentration of 3.0 percent sludge solids.
22.43G How should an operator determine the most desir-
able depth of sludge to be applied to sand beds?
22.43H Why should sand bed compaction be avoided?
22.431 Why should the sand bed surface be raked after
sludge is removed?
22.43J What determines the final concentration to which
sludge is dewatered on sand beds?
22.43K What is the major problem that is encountered when
operating sand drying beds?
22.44 Surfaced Sludge Drying Beds
22.440 Need for Surfaced Drying Beds
Sludge drying beds using gravel and sand with an under-
lying pipe system for bed drainage have a limitation of manual
cleaning with forks or shovels to remove the dried sludge.
Equipment such as tractors with front end loaders cannot be
used to remove dry sludge from sand beds because the
equipment would break the pipe underdrains, compact the
sand bed, or mix the sand and gravel layers. Some operators
lay planks or mats on the sand bed surface to distribute the
weight of cleaning equipment. After the sludge removal opera-
tion is complete, the operator simply removes the planks or
mats leaving the sand bed undisturbed. Surfaced drying beds
of either blacktop or concrete have been used to facilitate
easier sludge removal by the use of skip loaders. One advan-
tage of a surfaced bed is the ability to speed up sludge drying.
22.441 Layout of Surfaced Drying Beds (Fig. 22.20)
Surfaced drying beds are designed to allow the use of me-
chanical sludge removal equipment. Other design consid-
erations include the application of digested sludge to be dried
and the drainage of water released from the sludge being
dried. Drying beds are rectangularly shaped with widths of 40
to 50 feet (12 to 15 m) and lengths of 100 to 200 feet (30 to 6
m). A two-foot high retaining wall around the outside of the bed
contains the sludge.
The actual size of a drying bed depends on the sludge pro-
duced by the treatment plant. A plant with small flows, less
than 2 MGD (7,570 cu m/day), and with secondary treatment
may require only four 40 by 100 feet (12 by 30 m) drying beds
for sludge handling purposes. However, a 10 MGD (37,850 cu
m/day) plant with activated sludge and no solids thickening
processes before sludge digestion may require 20 drying beds
50 by 200 feet (15 by 60 m) to provide adequate sludge han-
dling capabilities. The drying beds are usually sized so that
one bed can be filled with sludge from the digesters to an
18-inch (45 cm) sludge depth in an eight-hour period.
The drying bed is provided with a 4-inch (100 mm) or 6-inch
(150 mm) drain line down the center of the bed and 18 inches
(45 cm) to 30 inches (75 cm) below the surface of the drying
bed. The drain line is either a perforated pipe or a pipe with
pulled joints (space between joints) (Fig. 22.21). The trench in
-------
204 Treatment Plants
TO HEADWORKS
=1
DRAIN VALVE
SLUDGE FEED FROM DIGESTERS
STOP LOGS
7
A
EQUIPMENT
ENTRANCE
i >
n\?
3-
STOP LOGS
SLUDGE
INLET
VALVE
PAVED AREA
SLOPING TO
DRAIN PIPE
DRAIN MEDIA
(SAND & GRAVEL)
DRAIN PIPE
6*-
CLEANOUT
EXTENDING TO
GROUND SURFACE
Fig. 22.20 Surfaced sludge drying bed (top view)
-------
Solids Disposal 205
HEADER BOARDS 2" X 8"
PAVEMENT
12-16"
* ' / • # • ' *i
SAND
LAST 6 INCHES
GRAVEL
ARM
PERFORATED-
PULLED JOINT
£
£
llCS
i
DRAIN PIPE
1
n:
2
JOINT OPENED - COVERED WITH FELT PAPER
TO PREVENT GRAVEL FROM ENTERING
Fig. 22.21 Drainage details
-------
206 Treatment Plants
which the drain pipe is placed is filled with gravel and sand that
serve as a media to filter solids out of the drainage water.
The drying bed drain pipe to the plant headworks is
equipped with a valve outside of the bed for isolation of the
drying bed. At the other end (high end) of the drain pipe, the
line is extended to the ground surface (grade) and a cleanout is
installed to allow cleaning of the drain line. Digested sludge is
usually applied to the drying bed through a six-inch (150 mm)
sludge feed line with a control valve or a box arrangement as
shown in Figure 22.20.
Equipment access to the bed is through a 12-foot (3.6 m)
opening in the end wall. The opening is closed off with 2 x
12-inch (5 x 30 cm) planks (stop logs) to seal the opening
when the drying bed is being filled and in use.
22.442 Operation
When placing a sludge drying bed into operation the follow-
ing tasks should be performed:
1. Remove the drain line cleanout on the bed to be filled and
flush the drain line with water.
2. Close the valve on the drain line discharge after flushing the
drain line.
3. If the drain media is filled with gravel only, fill the drain line
and filter area with water until the gravel is flooded. This will
prevent sludge from entering the voids (empty spaces) in
the gravel over the drain line during filling of the drying bed.
Beds with gravel and an overlying sand upper layer do not
require Hooding before filling with digested sludge. How-
ever, the sand layer should be loosened and raked level
before applying sludge to the drying bed. After flooding the
drain media, make sure the cleanout cap is replaced and
secured.
4. Install the 2 x 12-inch (5 x 30 cm) stop logs in the equip-
ment entrance opening to the bed. To seal the ends where
the stop logs fit into the wall slot, use rags or burlap sacks
wrapped around each end of the stop log and along the
bottom of the stop log next to the paving. Sealing is neces-
sary to prevent sludge leaking from the bed during the filling
operation and the first days of drying. Sand or soil also may
be used to form a small dam to prevent leaking. If the drying
bed being filled has a gate for entrance to an adjacent bed
that is not to be filled, seal the stop logs in this gate to
prevent leakage.
WARNING: NEVER SMOKE NEAR A SLUDGE DRYING
BED THAT IS BEING FILLED OR HAS BEEN
FILLED RECENTLY BECAUSE THE GASES
FROM THE SLUDGE COULD FORM AN EX-
PLOSIVE MIXTURE.
5. Select the digester that sludge is to be withdrawn from and
close feed valves to all drying beds except to the drying bed
to be filled. Start sludge flowing from the digester to the
drying bed by opening the proper valves.
Control the sludge feed to the drying bed at the drying
bed inlet valve. This allows you to observe the flow of
sludge and rate of sludge application. The sludge should
not be applied too fast to the bed because it may cause
coning in the digester. When coning occurs, only the sludge
will be drawn which will greatly extend the drying time. Eight
to 12 hours may be required to fill a bed 40 by 100 feet (12
by 30 m) 18 inches (45 cm) deep at the side wall with
sludge having a 6 to 8 percent solids content.
Samples should be taken of the applied sludge thirty
minutes after the start of the filling by placing 100 to 200 ml
of sludge in a 1,000 ml beaker. An additional 100 to 200 ml
sample is placed in the same beaker every hour thereafter
while filling the drying bed. Always use the same size sam-
ple. Upon completion of filling the bed, the 1,000 ml beaker
should be full of sludge from samples taken during the filling
time.
When the bed is filled to the desired level (usually 6 to 18
inches (15 to 45 cm) deep at the side walls), close the
sludge feed valve at the digester. If no more sludge is to be
withdrawn for at least a week, the sludge line should be
cleared of sludge and flushed with water to prevent plug-
ging of the line. Always leave the valve open at the filled
drying bed, or another empty drying bed, to prevent gas
from building up in the line and damaging the pipes, valves,
or fittings.
6. Dewatering the drying bed. Mix the contents in the 1,000 ml
sample beaker. Remove a 200 to 300 ml portion for labora-
tory analysis. Leave the remaining portion of sludge and the
beaker sitting on the wall of the sludge drying bed. If the
wastewater plant is staffed for 24-hour operation, an
operator should check the beaker every four hours looking
for signs of water-sludge separation.
Water-sludge separation usually occurs in 12 to 24 hours
after the sludge has been applied to the drying bed. The
sludge will rise to the surface leaving a 10 to 40 percent
portion by volume of water under the sludge. When this
occurs, the drying bed drain line valve is partially opened to
drain off the water from the drying bed. The sample beaker
can then be returned to the laboratory. The water-sludge
separation will not continue for more than several hours
because the sludge will resettle to the bottom. If the sludge
resettles, a large percentage of the water will move back
into the sludge or to the surface of the sludge in pools.
These pools will take a considerable amount of time to
evaporate from the sludge. To hasten sludge drying, open
the drain valve when the sludge sample shows that the
water-sludge separation has occurred. This procedure has
reduced the sludge volume in a drying bed by as much as
30 percent during the first day of drying.
Sludge drying may be further hastened after a crust has
formed on the sludge surface and has started to crack. Mix
or break down the sludge by driving equipment through the
drying bed to expose new sludge to surface evaporation.
22.443 Cleaning the Drying Bed
When the sludge on the bed has dried, the stop logs are
removed and a tractor equipped with a front bucket (skip
loader) is used to scoop up the sludge and remove it from the
drying bed. The equipment operator should not drive on or
across the drain trench because it will damage the trench or
the drain pipe.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 274.
22.44A What is a limitation of using sand drying beds?
22.44B How would you start to fill a surfaced drying bed that
has gravel only in the drainage trench?
22.44C What should be done when water-sludge separation
is observed in a beaker containing digested sludge
that is sitting on the wall of the sludge drying bed?
-------
Solids Disposal 207
22.45 Dewatering Summary
Successful dewatering requires that (1) the operator be very
familiar with the operation of the particular dewatering de-
vice(s) used, (2) sludge conditioning be optimum, and (3) the
influent sludge be as thick and consistent as possible.
QUESTION
Write your answer in a notebook and then compare your
answer with the one on page 274.
22.45A How can an operator have a successful sludge de-
watering program?
of oft? L,e<&>owv
MANPuiu&fc cw
-------
208 Treatment Plants
by the action of THERMOPHILIC38 facultative aerobic mi-
croorganisms to sanitary, nuisance-free, humus-like material.
Composting is a biological process and requires that a suitable
environment be established and maintained to ensure the sur-
vival and health of this group of bacteria. In order to create a
suitable environment, several criteria must be met.
First, composting of wastewater sludges requires that these
sludges be blended with previously composted material or
bulking agents such as sawdust, straw or wood shavings. This
blending process should produce a fairly uniform, porous struc-
ture in the composting material to improve aeration. The bulk-
ing material also provides control of the initial moisture content.
Second, aeration must be sufficient to maintain aerobic condi-
tions in the composting material. Third, proper moisture con-
tent and temperatures must be maintained. Microorganisms
require moisture to function, but too much moisture can cause
the process to become anaerobic and/or reduce the compost-
ing temperature below that which is suitable for the bacteria.
Composting generally falls into two categories: (1) windrow
and (2) mechanical. The most common method of sludge
composting is by windrow operation (Figure 22.22) and will be
the only one discussed here. Mechanical composters are rela-
tively untried on wastewater sludges and sufficient data do not
currently exist for accurate evaluation and reliable operating
procedures.
Windrow composting is generally limited to digested sludge
and consists of collecting dewatered digested sludge, mixing it
with previously composted material or bulking agents, and
forming windrow piles. Typical windrow stack (pile) dimensions
and spacing between stacks are shown in Figure 22.23. Spe-
cialized machinery such as "Flow-Boy"-type trailers can form
windrows and at the same time mix dewatered sludge with
compost material or bulking agents.
The initial moisture content of the blend of the dewatered
sludge and bulking agents or compost should be approxi-
mately 45 to 65 percent moisture. After formation of the wind-
rows, the stacks should be turned once or twice daily during
the first five days to begin the compost action and to ensure a
uniform mixture. Thereafter, the windrows should be turned
anywhere from once per day to once a week to provide aera-
tion and to encourage drying by exposing the compost material
to the atmosphere. After the process is complete, the compost
product must be loaded onto trucks for disposal and/or recy-
cling. This can be accomplished by a variety of equipment
including skip loaders and specially designed compost load-
ers.
Chemically stabilized and wet oxidized sludges are gener-
ally not suited for compost operations. Chemical stabilization
produces environments that are unsuitable for microorganism
survival and usually will not support the life of composting bac-
teria unless the sludges are neutralized and favorable condi-
tions exist. Sludge that has been stabilized by wet oxidation
can be composted, but noxious odors will more than likely
develop in and around the compost operation. Unless provi-
sions are made to house the compost area and scrub the
exhaust gases, a severe lowering of air quality could develop
and lead to numerous odor complaints.
22.510 Factors Affecting Composting
The time required to complete the composting process and
the efficiency of the operation depend on many factors. These
include: (1) sludge type, (2) initial moisture content and uni-
formity of the mixture, (3) frequency of aeration or window
turning (4) climatic conditions, and (5) desired moisture con-
tent of the final product.
The type of digested sludge to be treated in a compost facil-
ity can drastically affect performance and operation. Primary
and secondary sludges can be treated by compost processes,
but the plastic nature of dewatered secondary sludge and in-
creased moisture content make them more difficult to compost
than primary sludge. The difficulties arise with secondary
sludge because greater efforts have to be put into mixing with
compost material or bulking agents to produce an evenly
blended, porous mixture. Dewatered secondary sludges tend
to clump together and form "balls" when they are blended with
compost material. The balls that are formed within the win-
drows readily dry on the outer surface but remain moist on the
inside. Occasionally, this creates anaerobic conditions leading
to odor production and a lower composting temperature. The
problem is further complicated when large quantities of
polymer are used in the dewatering step because of the sticky
nature of polymers.
The initial moisture content and homogeneity (evenness) of
the mixture are important considerations in starting the com-
post process. These factors depend on sludge type, use of
polymers as discussed above, and the effectiveness of the
blending operation.
The quantity of compost product that must be blended with
dewatered sludge to produce an initial moisture of 45 to 65
percent depends on the concentration of the dewatered sludge
and the moisture content of the recycled compost material.
The following examples show how to calculate the amount of
compost required for blending purposes.
EXAMPLE 40
'Given: A 5 MGD plant produces 4,100 lbs/day of dewatered
digested primary sludge. The dewatered sludge is at a
concentration of 30 percent thickened sludge (TS).
Final compost product at the plant has a moisture con-
tent of 30 percent.
Find: The total pounds of compost that must be blended with
the dewatered sludge to produce a moisture content of
the mixture of 50 percent.
Solution:
Known
Flow, MGD
= 5 MGD
Sludge, lbs/day = 4100 lbs/day
(dewatered digested
primary sludge)
Dewatered SI Sol, % = 30% Solids
Unknown
Pounds of compost
blended daily with
dewatered sludge to
produce a mix-
ture with 50 percent
moisture content.
Final compost, %
= 30% moisture
(70% solids)
38 Thermophilic (thermo-FILL-lik). Hot temperature bacteria. A group of bacteria that grow and thrive in temperatures above 113°F (4S"C).
¦ The optimum temperature range for these bacteria in anaerobic decomposition is 120°F (49°C) to 135°F (57°).
-------
Solids Disposal 209
Fig. 22.22 Windrow composting
-------
Fig. 22.23 Windrow stack dimensions and spacing between stacks
-------
Solids Disposal 211
Determine the moisture content of the dewatered sludge.
Sludge
Moisture, %
100% - Dewaterd SI Sol, %
= 100% - 30%
70% moisture
Calculate the pounds of compost that must be blended daily
with the dewatered sludge to produce a mixture with 50 per-
cent moisture content.
Sludge, lbs/day x SI Moist, % + Comp lbs/day x C Moist, %
Sludge, lbs/day + Compost, lbs/day
Mixture
Moisture,e
Rearranging terms:
Compost,
lbs/day '
Sludge, lbs/day x SI M, % - Sludge, lbs/day x Mix M, %
Mix M, % - Comp M, %
4100 lbs/day x 70% - 4100 lbs/day x 50%
50% - 30%
4100 lbs/day <70% - 50%)
50% - 30%
= 4100 lbs/day
EXAMPLE 41
Given: A 5 MGD plant produces 2700 lbs/day of dewatered
digested secondary sludge. The dewatered sludge is at
a concentration of 17 percent thickened sludge. Final
compost product is at a moisture content of 30 percent.
Find: The total pounds of compost that must be recycled to
produce an initial mixture moisture of 50%.
Solution:
Known
Flow, MGD
= 5 MGD
= 2700 lbs/day
= 17% solids
= 30% moisture
Unknown
Pounds per day of
compost to produce
an initial mixture
of 50%.
Sludge, lbs/day
(dewatered digested
secondary sludge)
Dewatered Sludge, %
Final Compost, %
Calculate the pounds per day of compost that must be recy-
cled to produce an initial mixture moisture of 50 percent.
Sludge
Moisture, %
= 100% - Dewatered SI Sol, %
= 100% - 17%
= 83%
Compost, _ Sludge, lbs/day x SI M, % - Sludge, lbs/day x Mix M, %
Ibs^day ~
Mix M, % - Comp M, %
2700 x 83% - 2700 lbS x 50%
day
day
2700 lbs/day
50% - 30%
(03% - 50%)
<50% - 30%)
= 4455 lbs/day
The preceeding examples illustrate the effect the degree of
sludge dewatering has on the quantity of compost that must be
recycled to obtain the desired initial moisture content of the
mixture. Even though fewer pounds of secondary sludge were
produced (Example 41), more pounds of compost had to be
recycled than for the primary sludge because of the differences
in the degree of dewatering obtained.
The frequency of aeration or turning of the stacks is deter-
mined by trial and error. Obviously, the stacks should be
turned frequently enough to prevent anaerobic conditions but
not so frequently that excessive heat loss occurs. If the stacks
are turned too often, excessive heat will be released and the
temperature may drop to a point where it is unfavorable for the
thermophilic composting bacteria. To optimize the frequency of
turning requires close monitoring of the windrows for various
turning frequencies. If the frequency of turning is not optimized
as evidenced by anaerobic conditions or low temperatures, the
time required to complete the process will increase.
Climatic conditions play an important role in compost opera-
tions. Wet and cold climates generally require longer compost-
ing times than hot and arid regions. Wet weather is particularly
damaging to windrow composting because the piles can be-
come soaked and lose heat and the area generally becomes
inaccessible to heavy equipment.
The desired final moisture content of compost product af-
fects the time of composting because longer times are required
for higher degrees of drying. In general, a well operated wind-
row compost facility can dry siudge from an initial moisture
content of approximately 60 percent to a moisture content of
30 percent in about 15 to 20 days and to a final moisture of 20
percent in approximately 20 to 30 days. The final moisture
content at which the compost process is stopped depends on
whether the material is used as a fertilizer base, and/or the
economics of hauling the compost to final disposal.
22.511 Normal Operating Procedure
The required steps for successful composting are generally
the same from one operation to the next, although the
mechanisms for blending sludge with bulking agents or com-
post material and the method of aeration might vary depending
on the type of equipment used. The procedures for successful
composting are listed below:
1. Dewater sludge to the highest degree economically practi-
cal.
2. Blend dewatered sludge with recycled compost or bulking
agents to produce a homogeneous (even blended) mixture
with a moisture of 45 to 65 percent.
3. Form the windrow piles and turn (aerate) once or twice daily
for the first 4 to 5 days after windrow formation.
-------
212 Treatment Plants
4. Turn the piles approximately once every two days to once a
week to maintain temperatures (130 to 140°F or 55 to 60°C)
and until the process is complete. The temperature of the
piles should be routinely monitored during this period.
5. Load the compost onto trucks for disposal and/or recycle
purposes.
22.512 Typical Performance
Typical performance and operational data for windrow com-
posting operations are summarized in Table 22.23. Since
climatic conditions play an important role in windrow compost-
ing, the data should be viewed with caution because it reflects
summertime operation. During wet weather periods and in cold
climates, the composting time may double or triple those pre-
sented in Table 22.23.
A higher ratio of blend material and longer compost times for
secondary sludge are usually required because dewatered
secondary sludges are commonly wetter than dewatered pri-
mary sludges. As a result, it is more difficult to produce a
homogeneous blend when secondary sludges are composted.
TABLE 22.23 TYPICAL PERFORMANCE OF WINDROW
COMPOSTING
Sludge Blend Material Initial Max Compost Final Compost
Type* Ratio, (lb/lb)b Moisture, (%) Temp, (°F)C Moisture, (%) Time, (days)
Primary 0.5:1 - 1:1 45 - 65 130 - 140 30-25 8 - 15
Secondary 1:1 - 1.5:1 45 - 65 130- 140 30- 25 15 - 25
a Sludge is digested and dewatered.
b Assuming compost product is used for blending. Ratio is lb Compost/lb Sludge or kg
Compost/kg Sludge.
c (°F - 32) x 5/9 = °C.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 274 and 275.
22.50A What is the distinction between drying and incinera-
tion? What category does composting fall into and
why?
22.51 A Why does a suitable environment need to be estab-
lished in compost piles?
22.51 B Why are chemically stabilized and wet-oxidized
sludges generally not composted?
22.51 C List the criteria necessary to create a suitable com-
post environment.
22.51 D List the factors that affect compost operations.
22.51 E Explain why secondary sludges are not as easy to
compost as primary sludges. Include a discussion of
the "balling" phenomenon.
22.51 F A medium-size wastewater treatment plant produces
4700 lbs/day of dewatered digested primary sludge
with a solids concentration of 27 percent and 3300
lbs/day of dewatered secondary sludge with a solids
concentration of 15 percent. The sludges are
blended together and then composted in windrows.
Determine the total pounds of compost that must be
recycled and blended with the combined sludge to
produce a moisture of 60 percent. The final compost
product of the plant has a moisture content of 30
percent.
22.51 G List the operational procedures required for windrow
composting.
22.51 H Why does the data presented in Table 22.23 indicate
longer compost times for secondary sludge?
22.513 Troubleshooting
Windrow composting is a relatively simple and cost-effective
method to further reduce and stabilize the sludge, but difficul-
ties can arise which will render the process ineffective and
troublesome. Barring climatic conditions, which the operator
has no control over but should plan for, the most common
problems that arise are anaerobic conditions and reductions in
compost temperatures.
Anaerobic conditions can prevail if the initial moisture con-
tent is greater than the optimum range (45% to 65%), the
stacks are not turned frequently enough, and/or balling occurs.
If anaerobic conditions develop, the operator should increase
the frequency of aeration and inspect the pile for balling. If
balling is not evident and a uniform mixture exists, then more
frequent turning should correct the problem. If balling is evident
and a non-homogeneous mixture exists, increasing the fre-
quency of turning may result in a decrease in the compost
temperature. The operator should monitor the temperature and
turn the stacks frequently enough to reduce the anaerobic
odors while maintaining thermophilic temperatures.
As discussed earlier, balling will occur if the dewatered
sludge is too wet and/or polymer over-dosing occur. The
operator should optimize the performance of the dewatering
facilities to eliminate future compost problems. If balling is not
evident and piles are turned frequently, anaerobic conditions
might develop if the moisture content of the stack is too high.
This condition will usually result in corresponding reduced
composting temperatures and can generally be traced back to
not blending enough compost or bulking agents with the
sludge prior to windrow formation. The stack will eventually
recover from too much moisture but if the odors are severe, the
operator might remix the stack with a sufficient quantity of
bulking agents or compost to bring the windrow to a desirable
moisture content.
Temperature decreases can be caused by high moisture
contents or too much aeration or turning. If the pile is
homogeneous and the moisture content is within the optimum
range, the operator should reduce the frequency of turning to
maintain thermophilic temperatures.
Table 22.24 summarizes usual operational problems and
corrective measures that may alleviate or eliminate inefficien-
cies.
-------
Solids Disposal 213
TABLE 22.24 TROUBLESHOOTING WINDROW COMPOSTING
Operational Problem Possible Causes Check or Monitor Possible Solutions
Anaerobic conditions
1.a.
Aeration frequency
1.a.
Frequency of
1.a.
Increase aeration
too low
aeration and stack
frequency
b.
Stack moisture too
temperature
b.
Blend additional
high
b.
Stack moisture and
compost or bulking
c.
Balling
temperature
agents
c.
See 3
c.
See 3
Low compost
2.a.
Aeration frequency
2.a.
Frequency of
2.a.
Decrease aeration
temperatures
too high
aeration and stack
frequency
b.
Stack moisture
moisture
b.
Blend additional
c.
Balling
b.
Stack moisture
compost or bulking
c.
See 3
agents
c.
See 3
Sludge balling
3.a.
Dewatered sludge
3.a.
Dewatering facility
3.a.
Increase cake
too wet
b.
Dewatering facility
dryness
b.
Polymer over-
c.
Blending operation
b.
Reduce polymer
dosing
dosage
c.
Ineffective blending
c.
Improve blending
operations
22.52 Mechanical Drying
Mechanical heat drying is a dehydration process that re-
moves water from sludge without combustion of the solid ma-
terial. Mechanical drying is either direct or indirect. In an indi-
rect drier, steam fills the outer shell of a rotating cylinder.
Sludge circulates through the inner compartment and is dried
by the heat from the steam. Direct driers use the direct contact
of sludge with preheated gases.
The most common types of driers include direct and indirect
rotary driers and modified multiple-hearth incinerators. Other
mechanical driers include flash driers, atomized-spray driers,
and fluidized-bed driers. Only the direct and indirect driers will
be discussed here. Drying by modified multiple hearth in-
cinerators will be discussed in Section 22.53 of this section.
Rotary driers or rotary kilns consist of a horizontal cylindrical
steel shell with flights (mixing blades) projecting from the inside
wall of the shell. A typical rotary drier is shown in Section
22.53, Figure 22.27. The basic difference between direct and
indirect rotary driers is that indirect driers are equipped with a
jacketed hollow through which steam is passed while hot
gases are passed directly through the drier for direct drying.
In both cases, the dewatered sludge is blended with previ-
ously dried material and continuously fed into the drier. The
cylindrical drum rotates about 5 to 8 rpm and the inlet end is
slightly higher than the discharge end. As the drier rotates, the
flights projecting from the shell wall elevate, tumble, and mix
the material (like a clothes drier) to provide frequent contact by
tumbling the wetted sludge. The rotation of the drier drum
causes the sludge to fall off the walls of the drum near the top
or crown portion of the kiln. As the sludge falls it becomes drier
and is conveyed towards the outlet end of the drum. Also, the
speed of rotation of the drum will affect the moisture content of
the sludge being dried.
Blending of the sludge with dried product is generally prac-
ticed to improve the conveying characteristics of the sludge
and to reduce the potential for balling. This blending of wet
sludge with a previously dried sludge is accomplished in a
PUG MILL.39 As is the case with compost operations, the
sludge may clump together and form balls that readily dry on
the outer surface but remain wet on the inside if the blending is
not done properly.
22.520 Factors Affecting Mechanical Drying
The degree of drying obtained and the efficiency of rotary
driers depend on: (1) sludge type, (2) sludge detention within
the drier, (3) temperature, and (4) moisture content and ratio of
wet-to-dry sludge before being fed to the rotating kiln.
39 Pug Mill. A mechanical device with rotating paddles or blades that is used to mix and blend different materials together.
-------
214 Treatment Plants
Secondary sludges have a greater tendency to ball and con-
tain more water than primary sludges. Secondary sludges are,
therefore, not as well suited to mechanical drying operations
as primary sludges. Obviously, any sludge should be dewa-
tered to the highest degree possible by centrifuges, filter
presses, or vacuum filters to reduce the volume of water deliv-
ered to the drier and to facilitate the drying process.
The length of time the sludge remains in the drier and the
temperature of the drying gas will affect the degree of drying
obtained. As drying time and temperature increase, the mois-
ture content of the dried product will decrease. Drying time is
governed by the size of the drier, the quantity of sludge applied
and the speed of the drum. As the speed increases, the drying
time decreases because the sludge is picked up and tumbled
towards the outlet at a faster rate. To increase the drying time,
the operator should lower the drum speed and/or reduce the
quantity of sludge applied, if possible. The operator should be
aware that as the drum speed is reduced to increase the drying
time, the frequency of contact between wetted sludge particles
and the drying medium will also decrease.
A fine line exists between operating the drum at a speed to
maximize drying time while still providing frequent contact be-
tween wet sludge particles and hot gases or heated surfaces.
Trial and error procedures should afford the operator the best
opportunity to maximize the drum speed.
22.521 Normal Operation and Performance
Operational data on heat driers is scarce since the process
is not routinely used at the present time. The use of mechan-
ical driers is uncommon because this is a very expensive pro-
cess principally due to large energy demands.
Due to this relative lack of operating data, it is virtually im-
possible to list typical performance and operating data or to
outline specific operational procedures. In general, the sludge
to be dried should be dewatered to the highest degree possi-
ble, blended with previously dried material to produce a
homogeneous structure and adequately mixed or tumbled
within the drier to maximize contact with the drying medium
(gases or heated surfaces) and to minimize sludge balling.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 275.
22.52A Distinguish between direct and indirect drying.
22.52B Would the multiple-hearth furnace be categorized as
a direct or indirect drier? Why?
22.52C What purpose do the flights installed on rotary driers
serve?
22.52D Why is sludge blended with previously dried material
prior to rotary drying?
22.52E Why should sludge be dewatered to its maximum
degree prior to mechanical drying or incineration?
22.52F What affect does drum speed have on rotary drier
performance?
22.53 Sludge Incineration by Richard Best
22.530 Process Description
Sludge incineration is defined as the conversion of dewa-
tered cake by combustion to ash, carbon dioxide, and water
vapor. As a result of incineration, the volume of sludge is signif-
icantly reduced (up to 90 percent by weight). This reduction in
volume is caused by the evaporation of the water in the cake
and the conversion of the volatile matter in the cake to carbon
dioxide and water. The only material remaining after the incin-
eration of a cake is some ash and the inert matter in the cake.
The most common type of sludge incinerator is the
multiple-hearth furnace (MHF) (Fig. 22.24) and will be the only
process discussed in detail in this section. Other incineration
designs include fluidized-bed reactors (Figs. 22.25 and 22.26)
and rotary kilns (Fig. 22.27).
Rotary kilns may be used to either dry or incinerate sludge.
They also have been used for refuse incineration and ore pro-
cessing. In Figure 22.27 a storage bin is located on the lower
left to hold the sludge for processing. The clam shell bucket
loads the sludge into the feed hopper. A conveyor moves the
sludge to the inlet hopper to the rotary kiln. Inside the kiln the
sludge is either dried or incinerated. Dried sludge or ash is
removed from the kiln into the hopper in front of the operator.
Hot gases flow through the scrubber on the right to remove
the particulate matter suspended in the gases. The stack in the
middle right serves as an emergency bypass stack in case of
system failure. Behind the stack is a clarifier that is used for
ash separation in liquid ash systems.
The MHF, in its simplest form, is a refractory-lined (high
temperature endurance bricks) steel cylinder equipped with a
centralized shaft and runners (Fig. 22.24). Inside the MHF
there are a number of levels called hearths. A center shaft
passes through the center of the hearths. Arms are attached to
this center shaft. Plows are attached to each arm which are
called rabble teeth. The hearths are "sprung" arches and are
not connected to the center shaft.
During incineration, sludge cake enters the top of the fur-
nace and is moved back and forth across the hearths by the
rabble teeth. The cake drops alternatingly on each hearth
through an outer drop opening and then through a center drop
and works its way down through the hearths. As the cake
reaches the edge of one hearth it drops to the hearth below
until it reaches ignition temperature and burns. Ash remaining
after the sludge is burned is then rabbled (moved across the
hearths) until it reaches the bottom of the MHF and has been
cooled.
22.531 Furnace Description
Before attempting to understand the operation of an MHF,
the purpose of the various parts of the furnace must be under-
stood.
22.5310 Furnace Refractory. The furnace shell is insulated
to prevent the loss of heat into the atmosphere and to protect
the equipment and workers from the high temperatures found
within the furnace. The outer steel shell is protected from the
internal heat by 9 to 13 inches (23 to 33 cm) of refractory (brick
resistant to high temperature) on the inside.
The hearths or levels within the furnace are actually self-
supported arches. The weight of the arches or the thrust is
transmitted to the outside shell. The hearths are made of a
specially shaped refractory brick with castable insulation
poured into the odd-shaped spaces.
Figures 22.28 and 22.29 illustrate the two different types of
hearths installed within the MHF. The hearths on which the
cake drops to the next lower hearth from the center are called
"in" hearths. The hearths on which the cake drops through
holes on the outside of the furnace are called "out" hearths.
-------
Solids Disposal 215
o
HEATED AIR
INLET
DRIED SLUDGE
TO DISPOSAL
DRYING
ZONE ~
DEWATERED SLUDGE
INLET
COOLING ZONE
RABBLE ARM AT
EACH HEARTH
HEATED AIR
OUTLET
SHAFT COOLING
AIR FAN
RABBLE ARM
DRIVE
Fig. 22.24 Multiple-hearth furnace used as a sludge dryer
-------
WASTE SLUDGE STORAGE TANKS
IO
o>
re
u
3
re
D
0)
3
-------
Solids Disposal 217
SIGHT GLASS
EXHAUST
PREHEAT BURNER
THERMOCOUPLE
PRESSURE TAP
f—SLUDGE INLET
ACCESS DOOR
FLUIDIZING AIR
Fig. 22.26 Fluidized-bed reactor
(Permission of Don-Oliver Incorporated)
-------
Fig. 22.27 Rotary kiln
(Permission of Envirotech)
-------
SHAFT
-------
SHAFT
LUTE
CAP
PLAN VIEW
WALL
BRICK
DROP
HOLE
CURB
BRICK
HEARTH
BRICK
DROP
HOLE
OUTSIDE SHELL
to
to
o
n>
r*
3
»
3
0)
3
INSULATING BLOCK
CASTABLE
INSULATION
SKEW
BLOCK
CASTABLE
INSULATION
-OUTSIDE SHELL
SIDE VIEW
Fig. 22.29 Out hearth
-------
Solids Disposal 221
Out hearths (those hearths where the cake moves to the
outside edge of the hearth) have a circular cap ringing the
center shaft at the hearth/shaft meeting point. This is known as
the lute cap (Fig. 22.30). The purpose of this cap is to prevent
air and sludge from passing through the shaft opening rather
than through the drop holes.
The holes around the outside of the hearth are called "drop
holes." The sludge cake passes to the next lower or in hearth
(those hearths where the waste material moves toward the
inside of the furnace) through these drop holes.
When the furnace is in operation, cake enters the furnace
through a counterbalanced flap gate installed to prevent the
escape of gasses from the furnace and to limit the flow of cold
air into the top of the furnace.
Once the cake goes through the flap gate, it drops onto the
top hearth of the furnace. This is called "hearth No. 1." At this
point, the cake begins to be moved through the furnace by
action of the rabble teeth (Figure 22.30). This process is called
"rabbling."
Rabbling is a term used to describe the process of moving or
plowing the material inside a furnace by using the center shaft
and rabble arms. Rabbling forms spiral ridges of cake on each
hearth which aids with the drying and burning of the cake. The
surface area of these ridges varies with the side slope of the
cake (or the slope of the sides of the furrows). This angle may
vary widely from 20 degrees up to 60 degrees. Rabbling, in
addition to exposing the wet sludge cake surface to the furnace
gases, helps to break up large cake particles which increases
the surface area of the sludge available for drying.
Because of the ridges formed by rabbling, the surface area
of cake exposed to the hot gases is considerably greater than
the hearth area provided. During rabbling the cake falls
through the in hearth and the out hearth ports and the
counter-current flow of hot gases over the cake decreases the
drying time.
22.5311 Center Shaft. The rotating shaft to which the rab-
ble arms and teeth are attached is called the "center shaft."
The center shaft has seals at the top and bottom called "sand
seals" (Fig. 22.31). These are stationary cups partially filled
with sand that surround the shaft. A cylindrical steel ring is
attached to the shaft and extends down into the sand to form
the seal. At the bottom of the shaft, the sand cup is attached to
the shaft and rotates while the steel ring is fixed to the furnace
bottom. These seals are very effective if properly maintained.
They prevent the escape of heat and gases from the furnace
and the entrance of air at these points. Gases escaping from
the furnace could cause potential air pollution problems. Un-
planned entrance of air can cause draft changes and false
furnace conditions which will reflect on the control panel in-
struments. These seals also allow for the differential expansion
and contraction of the furnace body due to changes in temper-
ature.
Due to the extremely high temperatures within the MHF, the
center shaft and the rabble arms are hollow. This allows a fan,
installed at the bottom of the furnace, to blow cool air (ambient
air) through the center shaft and rabble arms while the furnace
is in operation (Figures 22.30 and 22.32). This fan is called the
cooling air fan. The hot air exhausted at the top of the furnace
from the shaft is called cooling air.
Depending on the furnace design, the cooling air can either
be returned to the burning zone of the MHF or vented to the
atmosphere.
22.5312 Shaft Drive. The center-shaft drive mechanism on
an MHF is usually a combination of an electric variable-speed
drive and an independent gear reducer. Occasionally hydraulic
drives are used instead of electric variable-speed drives. Con-
nected to the output shaft of the gear reducer is a pinion gear
which drives the large bevel or bell gear attached to the bottom
of the furnace shaft.
22.5313 Top and Lower Bearing. Each MHF manufac-
turer uses its own bearing design for the top and lower shaft
bearings. The operational principles are the same for all manu-
facturers.
The lower bearing supports the entire weight of the center
shaft. In a larger furnace this could be 60,000 pounds (27,240
kg) or more. The top bearing maintains shaft alignment. The
shaft rotates within the bearing and the bearing housing main-
tains alignment.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 275.
22.53A What is sludge incineration?
22.53B What is the refractory?
22.53C What are rabble arms and rabble teeth?
22.53D The lute cap serves what purpose?
22.53E What is the purpose of the sand seal?
22.5314 Furnace Off-Gas System (Fig. 22.33). As the
sludge cake is incinerated, hot air and gases must be vented
from the MHF. To vent these gases, almost all incinerators are
equipped with an emergency by-pass damper located on the
top of the MHF. The function of the by-pass damper is to vent
the furnace gases to the atmosphere during emergency condi-
tions. This device protects equipment and operating person-
nel.
CYCLONE SEPARATOR. Under normal operation of the
MHF, the furnace gases are vented into the off-gas system. As
the gases leave the furnace, the first unit that the gases may
enter is the cyclone separator.
Hot furnace gases which have fly ash and solid particles in
suspension are drawn through the furnace into the cyclone by
the induction draft (I.D.) fan. The cyclone is constructed so that
the gas flow sets up a separating current. This current causes
the fly ash and heavy particles to settle out into the cyclone bin
at the bottom. The cyclone bin has a flap gate which dumps the
ash into the recycle screw. The recycle screw returns the fly
ash and heavy particles to the furnace on a middle hearth. This
material is then carried out with the ash. A vibrator assists in
keeping the fly ash and particles moving downward in the cy-
clone bin. The hot gas and finer particles are drawn up out of
the cyclone and move on to the precooler.
PRECOOLER. The precooler is a section of furnace exhaust
ducting in which water is sprayed to cool the furnace exhaust
gases to saturation temperature and to wet the small particles
of light ash (particulate matter). The precooler lowers the tem-
perature of the exhaust to a point where it prevents damage to
the rest of the off-gas system components.
VENTURI SCRUBBER. Immediately below the precooler is
a constant or variable throat Venturi scrubber. The Venturi
scrubber is provided to clean the particulate matter from the
cooled furnace gases. Water is sprayed into the top of the
Venturi for even distribution.
-------
222 Treatment Plants
CASTABLE
SHAFT
COVERING
INSULATION
SHAFT HOLDING PIN
FIRE BRICK
RABBLE
ARM
HOLDING
PIN K
RABBLE
-TEETH
'/'Y// y ' r /,
DROP
HOLES
LUTE CAP
OUT HEARTH
FURNACE SHELL
SHAFT
Fig. 22.30 Action of rabble arm and rabble teeth
-------
Solids Disposal 223
HEARTH
t»a
-4-
SAND
SEAL
* SHAFT
BOTTOM
Fig. 22.31 Lower sand seal schematic
-------
224 Treatment Plants
WWW
RABBLE
ARMS FOR
THIS HALF
OF FURNACE
NOT SHOWN
<
I
tn
ui
o
<
Z
cc
D
u.
s \ \ s s
HI-TEMP
ALARM
TO ATMOSPHERE
X
EXCESS HOT AIR
www\
HTH 1 ^
AMBIENT AIR
HTH 2
HTH 3
L
HTH 4
RABBLE ARM
3
k\WW\
HTH 5
HTH 6
X
^ V. ^ ^ ^
-c
HI
LO
O
X
\
DAMPERS
(INTER-LOCKED)
PRESSURE SWITCH
I
in
Ui
V)
<
O
H
co
D
<
X
X
LU
UJ
O
<
z
cc
3
u.
Z
<
u.
1
cc
Fig. 22.32 Shaft cooling air system for a six-hearth furnace
-------
TEMP.
WATER
i-PRE-COOLER
ATMOSPHERE
BYPASS STACK DRAFT SWITCH
EMERGENCY
BYPASS
DAMPER
\\\\\\//////A—IDEMISTER
OXYGEN
SAMPLE POINT
DRAFT
GAGE
CYCLONE
FLY ASH
' I I II I I
¦¦ I I I I I I
WATER
SPRAY
I.D
DAMPER
OUT HEARTH
PRES
~TEMP.
CYCLONE
BIN
BURNER
_[] PRES.
IN HEARTH
I I 1 I I 1 I I
WATER /
VENTURI
VARIABLE
K L>
CONTROL
cm
THROAT
c
FLY ASH
TRAYJ
WATER
RECYCLE SCREW
v i \/1 v •»/ • :
MAIAIX!/
AIR
PORT
cm
BURNER
~CD
PRES.
\ SMALL
I* DOORS
FURNACE
COMBUSTION
AIR FAN
EXHAUST
STACK
IMPINGEMENT
PLATES
— WATER
SPRAY
SCRUBBER
DRAIN
Fig. 22.33 Furnace off-gas system
-------
226 Treatment Plants
The water and gases are mixed and accelerated in an ad-
justable, narrow Venturi throat. As the gases re-expand in the
exit portion of the Venturi, the water is split into tiny droplets in
which the particulate matter is entrapped and removed from
the gas stream.
The ducting directly below the Venturi scrubber usually
makes a sharp bend. Because of the high air speed, the water
droplets with their collected particulate matter cannot make the
turn and run into the bottom of the ducting. From there, the
water and particulate matter flow to a drain. Following the Ven-
turi scrubber there is usually an impingement scrubber.
IMPINGEMENT SCRUBBER (Fig. 22.34). The impinge-
ment scrubber consists of three sections:
1. The impingement baffles,
2. The lower sprays, and
3. The mist eliminator.
CLEAN GAS
OUTLET
MIST ELIMINATOR
STAGE
PLATE WATER
IMPINGEMENT
BAFFLE
PLATE
STAGES 4
SPRAYS
u7 J "\\l/77 " "
DIRTY GAS ^
INLET
SCRUBBER WATER
DISCHARGE
Fig. 22.34 Impingement scrubber
The impingement plates are level, flat stainless steel plates
with thousands of tiny holes in them. The gas is drawn up
through the perforated impingement plates which have water
continually flowing across them. As the gas passes through the
holes, it collects water droplets while leaving any remaining
particles trapped in the flowing water due to impingement ac-
tion of the bars just above the perforations. The particle and
water slurry overflows the plates, is collected in the bottom of
the scrubber and is drained out. The gas carrying water drop-
lets is drawn up into the mist eliminator.
The fixed-bladed mist eliminator directs the gas stream to
the side of the scrubber shell where the droplets collect by
centrifugal action. The collected droplets drain back down to
the impingement plate section for reuse. The remaining cool,
clean gas is drawn out the top of the scrubber by the induced
draft (I.D.) fan.
INDUCED DRAFT (I.D.) FAN AND DAMPER. The I.D. fan
provides the suction or draft necessary to vent the furnace
gases and pull them through the off-gas system. Since the
quantity of these gases varies with the quantity and type of
cake burned in the MHF, a damper is installed immediately
before the I.D. fan. This damper is used to regulate the suction
or draft within the MHF.
ASH HANDLING SYSTEM. Ash is the inorganic material left
after the sludge cake is burned. This material is disposed of in
a variety of methods depending on the MHF installation. The
two most common are wet and dry ash systems which we will
discuss briefly. Other types of ash systems include pneuma-
tic ash transport, ash classification and ash eductors.
The wet ash system is the simplest of all ash handling sys-
tems. The ash drops out of the MHF into a mix tank where
effluent water is continuously added. This produces an ash
slurry which is pumped to an ash lagoon. The ash settles out in
the lagoon and the water is returned to the front end for treat-
ment. The ash is left to dry and ultimately removed from the
lagoon for disposal.
In the dry ash system, the ash drops from the MHF onto an
ash screw conveyor. This screw conveyor carries the ash to a
bucket elevator. The bucket elevator transports the ash to a
storage bin where it awaits disposal.
At the bottom of the storage bin is the ash conditioner. This
is a screw conveyor equipped with a series of water sprays.
The water sprays wet the ash so it does not create dust or blow
off a truck during transport.
22.5315 Burner System. Burners are provided on an MHF
to supply the necessary heat to ignite the sludge. Prior to dis-
cussing the burner system, it is important to understand com-
bustion. In order for any combustion to occur, the three ingre-
dients of the fire triangle (Figure 22.35) must be present.
FUEL
A I R
T EMPERATURE
Fig. 22.35 Fire triangle
For complete combustion to occur, there must be a specific
ratio between the amount of fuel and the amount of air. The
burner system described here is manufactured by the North
American Manufacturing Company. This type of system is
common to all burner systems supplied on MHF's although
component names may be different.
-------
Solids Disposal 227
COMBUSTION AIR FAN. This fan supplies the filtered
burner/combustion air for the burner system.
OIL PUMPS. Positive displacement pumps supply oil to the
burners (except for natural gas burners).
SAFETY VALVES. Electric solenoid valves are used to stop
the fuel flow during a burner shutdown.
PRESSURE REGULATORS. Standard pressure regulators
,are used to control the fuel pressure.
AIR-FUEL RATIO REGULATOR. A pressure regulator that
maintains a specific ratio between fuel and air.
COMBUSTION-AIR CONTROL VALVE. A butterfly valve
that governs the flow of combustion air to the burner.
FLOW-LIMITING VALVE. A metering valve that allows a
specific flow of combustion air to the burner.
FUEL MHF burners are fired by a variety of fuels. Natural
gas, number 2 fuel oil, and heavy oil. The fuel and air are
regulated to the proper pressure and injected into the burner.
At this point the fuel/air mixture is ignited by the pilot and the
resulting flame is sensed by the ultra-violet scanner which sig-
nals the burner control station that a flame-safe condition
exists.
The temperature and firing rate of the burner is then con-
trolled by the temperature indicator controller (T.I.C.).
22.532 Controls and Instrumentation
Usually, multiple hearth furnaces are equipped with the fol-
lowing controls to maintain temperature, draft, and oxygen.
LOW DRAFT SWITCH. This switch shuts down the MHF in
the event of an unsafe draft condition.
DRAFT CONTROLLER/INDICATOR. This is a controller that
opens and closes the induced draft damper in order to main-
tain the draft within the MHF.
OXYGEN ANALYZER/CONTROLLER. This instrument
measures the percent oxygen in the stack gas which is an
indication of complete combustion. In some cases a controller
is attached to this instrument to control the oxygen level in the
furnace by regulating the combustion air.
TEMPERATURE INDICATOR CONTROLLER (T.I.C.). This
instrument controls the burner firing rate and the hearth tem-
perature.
TEMPERATURE RECORDING CHART. A strip recorder
used to record the temperatures throughout the furnace.
SCRUBBER DIFFERENTIAL-PRESSURE INDICATOR. An
instrument which indicates the pressure difference across the
scrubber. This pressure difference is the main operating vari-
able on the Venturi scrubbers.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 275.
22.53F List the parts of the furnace off-gas system and the
purpose of each part.
22.53G Why do multiple-hearth furnaces contain burners?
22.53H What three ingredients are necessary for combus-
tion to occur?
22.533 MHF Operations
Operation of an MHF requires a person knowledgeable
enough in furnace theory and operations to keep the fire burn-
ing in the desired location and prevent damage to the equip-
ment. But more important, a furnace operator must be able to
look at the instruments, fire, and feed and be able to predict
what is going to happen. The operator makes the necessary
changes to maintain a stable burn and the most efficient bum
possible. The objective of an operator is to operate the furnace
at design conditions and to keep operating costs to an absolute
minimum.
22.5330 Furnace Zones. The furnace is generally consid-
ered to be separated into three distinct zones, drying, combus-
tion, and cooling. None of these zones are confined to any
specific hearth or hearths, but will always be in this order. The
area of each zone is determined by actual conditions in the
furnace.
The furnace zones are as follows:
1. THE DRYING ZONE. In this area, generally the top one-
fourth of the furnace, the sludge is exposed to high temper-
atures while being continuously turned over by the rabble
teeth. The constant turning over of the sludge exposes
more surface area to the high temperature gases flowing
over the cake surface and increases the rate at which mois-
ture is driven out of the wet sludge. The wetter the cake
entering the furnace and the greater the feed rate, the more
hearths will be in the drying zone.
2. THE COMBUSTION ZONE. Ideally this zone is where the
actual burning of the volatile materials in the sludge takes
place. Usually the combustion zone will be confined to only
one hearth. Ideally, the actual burning should occur approx-
imately at the midpoint of an out hearth (Figure 22.36). At
this location, all gases given off in the final stages of the
drying process, just prior to ignition, will be destroyed. This
happens since they must pass through the flame, with very
high temperatures, as the flame goes through the drop hole
around the shaft.
3. THE COOLING ZONE OR AIR PREHEAT ZONE is where
the ash is cooled. Any remaining carbon in the sludge is
burned off here before the ash falls into the ash hopper. At
the same time as the ash passes down the furnace, the air
admitted through the air ports, slide doors or shaft return-air
duct is flowing over the hot ash and being preheated.
22.5331 Auxiliary Fuel. The amount of fuel used will de-
pend on several factors:
1. Conditions in the furnace.
Items such as shaft speed, number of slide doors, air
ports open, or forced air ducted to the furnace, and the
amount of shaft cooling air being returned to the furnace
influence conditions in the furnace.
Air for proper combustion should be added low in the
furnace. This allows the cool ambient air to pick up a great
amount of heat as it passes across the hot ash and also
cools the ash before disposal.
If air is added in the fire zone or above it, incoming air will be
much cooler and will serve to cool the air where it enters the
furnace. This will cause more fuel consumption. Air should be
added at or above the fire ONLY when absolutely necessary to
reduce the temperature or quench the fire.
-------
228 Treatment Plants
W
WET SLUDGE
OUT HEARTH
HOT GASSES
lh\
FLAMES
LUTE
, PARTIALLY DRY
I i SLUDGE FALLING
PARTIALLY DRY SLUDGE
HEATED AIR
ASH AND COALS
ASH AND BURNING
COALS DROPPING
Fig. 22.36 Flames in middle of an out hearth
-------
Solids Disposal 229
2. The moisture content of the sludge feed to the furnace.
The drier the cake being fed to the furnace, the less fuel
will be required to dry the sludge to maintain a good burn.
Ideally, the MOISTURE content of the furnace feed should
not exceed 75 percent. Every bit of moisture entering the
furnace requires a great deal of fuel to be consumed in the
process of evaporation.
3. The volatile content of the solids in the sludge feed.
The higher the percent volatile material, the less fuel will
be required. Assuming, of course, a reasonable percent
solids in the sludge.
4. Cake feed rate.
A constant cake feed rate coupled with the above men-
tioned items helps to reduce the quantity of fuel required.
22.5332 Air Flow. The draft or vacuum in the furnace is the
direct cause of all air flow within the MHF. The draft within the
furnace is caused by the induced draft fan and by the convec-
tion flow caused by the temperature differentials between the
interior of the furnace and the atmosphere. Convection flows
also explain why there is a draft within the MHF when the
induced draft fan is off and the by-pass damper is open.
AIR
HOT
BURNER
Fig. 22.37 Convection air flow in an MHF
Convection air flow develops in the MHF as a result of air
being heated by the burners in the MHF (Figure 22.37). The air
flow within an MHF is from the bottom to the top. The flow
occurs because as the air in the MHF is heated and rises, it
creates a vacuum in the bottom of the furnace. This vacuum
causes cooler, outside air to flow into the bottom of the furnace
where the air is heated and rises. The term used to describe
this process is called "convection flow" and "draft" is the
measurement of the negative pressure or vacuum created by
this flow.
The draft in the furnace is measured either in tenths of
inches or millimeters of water column. Relating this height of
column to pounds per square inch or kilograms per square
centimeter, you must remember that 1 foot (304.8 mm) of
water column is equal to 0.434 psi (0.0305 kg/sq cm). There-
fore, one inch (25.4 mm) of water column equals 0.0378 psi
(0.00266 kg/sq cm) and one tenth of one inch (2.54 mm) water
column equals .0038 psi (0.00027 kg/sq cm). A very small
pressure.
We want only enough air in the furnace to allow for the
complete combustion of the volatile matter in the sludge cake.
Therefore, we must control the draft within the furnace care-
fully. The normal range of draft within the MHF is from 0.05 to
0.2.inches (1.3 to 5.1 mm) of water.
In the multiple-hearth furnace it is extremely important to
remember that an excess amount of air must be available at
all times. This excess air assures that all volatiles (combusti-
bles) can contact sufficient oxygen to insure complete combus-
tion. If there is inadequate oxygen present, there will be in-
complete combustion, which means smoke. Smoke indicates
unburned hydrocarbons. While remembering that the human
eye cannot detect the ultra-violet spectrum of the flames, a
visual inspection of the burning zone can give a good indica-
tion of the amount of excess air present.
1. A darker flame, ending in a curlicue of smoke, with a dull
smokey atmosphere means there is a lack of air (volatile
hydrocarbons are carbonizing).
2. A bright, sharp flame indicates excess air, but not how
much. Decrease the amount of excess air which will de-
crease the amount of fuel being burned, AS LONG as the
stack plume does not become smokey, black, light blue, or
brownish.
3. Short blue flames on the lower hearths indicate burning of
fixed carbon which means there is adequate excess air.
There are two ways of getting excess air into the furnace.
These are:
1. By evenly opening the smaller doors and possibly the big
doors a little on the BOTTOM HEARTH, or opening the
dampers of the air ducts, the incoming air rushes over the
hot ash and is preheated while the ash is being cooled.
2. Opening the center shaft cooling air return damper allows
the hot air to be returned if the furnace is so equipped.
Since air is approximately 21 percent oxygen, an oxygen
content of about 8 to 12 percent in the furnace gas indicates
that adequate excess air has been added to insure complete
combustion.
The oxygen analyzer is the operator's tool for determining
the excess air in the furnace. Drawing samples from the
exhaust after the induced draft (I.D.) fan and using the
analyzer determines the amount of oxygen remaining after
combustion. The oxygen analysis is sent to the panel for the
operator's reaction. Fluctuation in the oxygen is an indication
-------
230 Treatment Plants
of change in the furnace. A rapidly decreasing excess oxygen
usually means that the fire is growing and is removing the
excess oxygen. This is a common occurrence during a burn-
out.
An increasingly excess oxygen reading can mean a reduc-
tion in fire. By adding air above the fire, a false indication of
excess oxygen will be given. Since it is a false reading, a visual
inspection of the burn for smoke should be made until the air
above the fire can be removed.
General rules for excess oxygen change are summarized as
follows:
O2 Change
Increase O2
Decrease O2
Cause
-Decreasing fire and/or
increasing air above
fire zone.
Increasing fire
and temperatures.
The oxygen demand of the furnace changes with the amount
of combustion going on inside the furnace. Too much cool air is
a waste of fuel and too little air causes smoke. Control must be
maintained to provide the proper amount of air to fit the de-
mands of the furnace.
22.5333 Combustion. Combustion is a chemical reaction
which requires oxygen, fuel, and heat. In the furnace, air pro-
vides oxygen, the primary fuel is sludge, and the heat comes
from the burning sludge. Fuel is burned as an auxiliary fuel in
the burners to help provide the heat needed to burn the sludge
and to preheat the furnace to combustion temperatures.
22.5334 Air Flow and Evaporation. Above the fire the fur-
nace has wet, cold sludge in it. As the hot, dry air and combus-
tion gases pass over the upper hearths, the heat is transferred
to the sludge. At the same time the moisture in the sludge is
evaporated, the dry gases pick up the moisture and carry it out
of the furnace.
Return shaft cooling air (Figure 22.38) is the usable by-
product of the center shaft cooling air. The main shaft is dou-
blewalled and cast in sections. The sections have a tubular
inner duct called a "cold air tube." The annular (ring shaped)
space between the inner tube and the outer shaft wall serves
as a passageway for hot air and is referred to as the hot air
compartment. The central shaft and rabble arms are cooled by
air supplied at a fixed quantity and pressure from a blower
which discharges air through a housing into the bottom of the
shaft.
Two or more rabble arms are held in shaft sockets above
each hearth where the cold air tube as well as the outer shaft
wall provide support. Each rabble arm has a central tube which
conducts the cold air from the cold air tube to the extreme end
of the rabble arm (Figs. 22.30 and 22.32). From there, the air
goes through the outer air space in the arm, back toward the
shaft and through the openings into the hot air compartments.
Unused heated cooling air may be returned to the atmosphere
by other means depending on the design.
The hot air compartment may be vented to atmosphere or
the hot shaft air may be returned to the furnace for combustion
purposes. Shaft return air is sent below the normal burn zone
but still above the final ash cooling hearth.
6UOUIV MOT A/MAXl/Vl^M
T£Mf^ATl4££ OF t7ZO°FCZQO0c)
When the preheated shaft cooling air is not required for fur-
nace operation, it is vented to the induced draft stack. This hot
air will prevent "stream" plume formation. As it exits the fur-
nace at the top of the center shaft, the operator may direct the
path of this heated air. By means of two mechanically linked
dampers (called proportional dampers), the operator at the
main control panel directs the heated air out into the atmos-
phere or back to the furnace as hot air return.
Hot air return should be used with some discretion. The hot
air return can: (1) provide a fast source of air (oxygen) within
the furnace; (2) use less fuel to heat the air; (3) reduce smok-
ing; or (4) increase the drying rate of sludge. Returning too
great a volume has the disadvantages of blowing "fly ash" as
well as "dumping" the return air into the furnace at one point
rather than distributing it evenly around the hearths. Re-
member that as the air passes over the hot coals, some of the
oxygen is being removed before it gets to the fire.
22.5335 Recommended Furnace Operating Ranges.
Table 22.25 summarizes the general temperature and pres-
sure ranges maintained on the various hearths when burning
wastewater sludge.
TABLE 22.25 MHF OPERATING RANGES
Location Range Optimum
Hearth #1 (Gas Exit) 700 to 1,000°Fa As low as possible
Burning Hearth 1,300 to 1,700°Fa 1,600°Fa
Bottom Hearth 200 to 800°Fa 200°Fa or
As low as possible
Scrubber Inlet 100 to 300°Fa 150°Fa
Furnace Draft
Furnace Oxygen
0.05 to 0.2
inches6 of water
8 to 12 percent
0.1 inchb of water
10 percent
a (°F - 32)5/9 = °C
b inches x 25.4 = millimeters
22.5336 Alarm Systems. Almost all MHFs are equipped
with an alarm system because of the speed at which the sys-
tem will react to changes. The alarm system informs the
operator of abnormal conditions. The operator should react to
an alarm as follows:
1. Understand what malfunction is causing the alarm before
pressing the acknowledge button. Many times a group of
alarms will go off at one time. Find the alarm that is
downstream from the rest of the alarms (for example, the
ash bin is downstream from the center shaft).
2. Press the reset button to see if the alarm conditions still
exist.
3. Try to restart the equipment that caused the alarm at the
location of the equipment rather than from an alarm panel.
DO NOT FORCE IT TO RUN! If it starts, restart all equip-
ment that was shut down by the alarm. Press reset button.
4. If it does not start, make a brief visual inspection of the
malfunctioning equipment.
5. Make a decision as to whether or not you can safely correct
the problem.
6. Return to the panel and furnace and check the conditions. If
you can fix the problem, you still must control the furnace. If
you cannot fix the problem, bum out the remaining sludge
or maintain as stable a condition as possible. If you must
burn out the remaining sludge, try to control the burnout
temperature.
-------
Solids Disposal
i
SAND
SEAL
SHAFT
BOTTOM
GLAND
—I AIR
HOUSING
COOLING AIR
M.
^ ¦ BEARING
Fig. 22.38 Shaft cooling air return system
-------
232 Treatment Plants
22.5337 Burnouts. A burnout occurs when the sludge feed
has been stopped and the fire continues to burn. Eventually,
the final quantity of sludge is dry enough to burn and does.
This final rapid burning of the last sludge can cause high tem-
peratures in the furnace that can potentially cause damage to
the furnace and its related equipment. Operators must control
the burnout temperatures. The ideal burnout is to have only a
100 degree Fahrenheit (55 degree Celsius) increase in any
hearth temperature during a burnout. This requires concentra-
tion by the operator on the furnace's changing conditions: fire
position, sludge remaining in the furnace, shaft speed, tem-
peratures, excess oxygen, burner settings, and the ability to be
smarter than the furnace by anticipating the fire's next move
long before it happens. This way the operator makes adjust-
ments which limit the fire's final burnout.
The operator may choose to increase the shaft speed in1
preparation for the burnout. The purpose is to move the last
sludge lower in the furnace before it burns. This results in
keeping the high temperatures away from the top of the fur-
nace. The operator must be careful not to allow unburned
sludge to pass through the furnace. The high shaft speed will
also generate a higher furnace temperature because of the
increased rate at which fresh fuel is available to the fire.
There are three basic adjustments that control the fire during
a burnout:
1. Opening doors at or just above the fire,
2. Stopping and restarting the shaft or changing the shaft
speed, and
3. Reducing or shutting off burners.
1. Opening doors. By opening the doors, a large volume of
cold air enters the furnace. This replaces the heat needed
for combustion and cools the fire. The draft must be main-
tained (.07 to .2 inches or 1.8 to 5 mm water column) by
opening the induced draft damper. To prevent an induced
draft fan overload, air ports and doors below the fire and the
hot air return can be closed to reduce the total air flow. The
air flow removed from underneath can now be added di-
rectly at the fire for combustion and also above the fire
where it will have a cooling effect.
Cooling air will only provide short-term control. The fire
will eventually generate more heat than can be compen-
sated by cooling air. Another control must be used
QUICKLY.
2. Stopping the center shaft. Stopping the center shaft will
remove the fresh fuel for the fire which will cause the fire to
die down. By starting and stopping the shaft, the operator
controls the amount of fuel available for the fire to burn. The
shaft should be stopped no longer than three minutes.
When it is started again, a low shaft speed (0.4 to 0.7 rpm)
will help control the fire by turning over the fresh sludge at a
slower rate. When the temperature rises again, the shaft is
stopped again. This procedure is continued until the fire
does not cause a high temperature jump. Once the temper-
ature starts to drop with the shaft running, close up the
furnace doors to control the temperature change. Once the
fire has burned out completely, the operator can switch
from induced draft to natural draft to control the tempera-
ture.
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3. Reducing or shutting off the burners. During a burnout, the
sludge needs little or no heat from the burners. Once the
fire starts to increase the temperatures, reduce and then
shut off the burners. This will provide two advantages:
1. Temperatures will be reduced, and
2. Gases from the burner will be removed. This missing
gas volume can be replaced by cooling air above the
fire.
Once the temperature starts to fall, the burners can be relit to
control the dropping temperatures.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 276.
22.531 List the three distinct zones in a furnace.
22.53J List the factors that influence the amount of fuel re-
quired.
22.53K What three factors are essential for combustion and
what is the source of each factor?
22.53L Shaft speed adjustment may be required as a result
of changes in what factors?
22.53M What is a burnout?
22.534 General Operational Procedures (Start-Up,
Normal Operation, and Shutdown)
MHF operational procedures are based on consideration of
the interrelationships between air flow, shaft speed, and tem-
perature.
The first step in starting an MHF is to set the water flows to
the scrubbers and then start the induction draft (I.D.) fan. Once
the I.D. fan is at the operational speed, you then want to set
your I.D. damper to maintain the desired draft (0.1 inch or 2.54
mm water column). At this point you begin the "purge cycle"
(removing unwanted gases from the furnace). The purge cycle
is usually controlled by a timer and will last from 3 to 10 min-
utes. At the end of the purge cycle (usually indicated by a panel
light), you start the shaft cooling air fan, the combustion air fan,
the ash system, and the center shaft. You are now ready to
start heating up the MHF.
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The first step in the warm-up of an MHF is to light the pilot
lights on the bottom hearth. The temperature is then brought
up to 200°F (93°C). DO NOT allow the temperature to exceed
200°F (93°C) at any point in the furnace. Hold the temperature
at 200°F (93°C) until the refractory is dry and warm. To check
this, open the door of the MHF and observe the refractory
where it meets the steel shell. The refractory and the shell
MUST be dry. If it is dry, carefully feel the refractory where it
joins the shell. The refractory at this point should be warm to
the touch. The time required for the dry-out/warm-up varies
depending on how long the furnace has been out of sen/ice. If
the temperature of the hearth never dropped below 200°F
(93°C), the dry-out/warm-up will not be required, but if the MHF
-------
Solids Disposal 233
has been off line for an extended period of time, the dry-out/
warm-up may take from several days to a week. If there is any
question as to whether the furnace is dry or warm, LET THE
FURNACE WARM-UP for an additional period of time. Re-
member this is one of the most critical periods in MHF opera-
tion.
Once the refractory is warm, the operator may proceed to
heat up the unit at a rate of 50°F/hr (28°C/hr). This rate of
temperature increase must be maintained carefully, even at
the expense of adding air for cooling.
Once the temperature on a given hearth reaches 1,000°F
(540°C) THAT HEARTH'S temperature may be raised at a rate
of 100°F/hr (56°C/hr). This procedure is followed until the burn-
ing zone of the furnace reaches 1,600°F (870°C) at which point
the feed to the furnace may be started.
NOTE: The same rate of temperature losses apply when the
furnace is taken out of service. Drop the temperature at
a rate of 10OT/hr (56°C/hr) to 1,000°F (540°C) and then
lower the temperature at 50°F/hr (28°C/hr) when the
temperature is below 1,000°F (540°C).
When feed is introduced to the furnace, the temperatures
will initially drop. This is due to the cooling effect of the wet
cake. Once the cake reaches the burning zone, however, the
cake should start to burn and the temperature profile will even
out. Once this profile is established, the profile should be main-
tained within a 200°F (110°C) range. The burn is then main-
tained by use of the shaft speed, return air, and the burners.
The sludge cake has a very high heating value (approxi-
mately 10,000 BTU/lb volatile solids or 23,260 kilojoules/kg
volatile solids). In many cases the volatile content of the sludge
cake is high enough that the cake will burn without the addi-
tional heat input from the burners. This condition is called an
autogenous (aw-TAW-jen-us) burn. To achieve this condition,
the sludge cake must generally exceed 25 percent total solids
and 70 percent total volatile solids. To maintain an autogenous
burn condition, a constant steady-state sludge feed is manda-
tory. An autogenous burn represents the most economical
mode of MHF operation.
Even when an autogenous burn cannot be established, fuel
usage is affected by the heat released by the burning volatile
material in the sludge cake. The MHF should be operated on a
continuous basis when the unit is in operation to take advan-
tage of the heat from the burning sludge. Remember that all
the fuel used to maintain the temperatrue on a furnace at a
standby mode represents money added to the total cost of
solids disposal.
Another benefit of continuous operation is an increase in
refractory life. As the MHF is cycled up and down in tempera-
ture, the refractory expands and contracts with the tempera-
ture changes. As this expansion and contraction occurs, the
joints between the hearth bricks open and close. As these
joints open, ash falls into the joint. When the MHF is later
reheated, the surrounding brick expands and compresses the
ash and a tremendous pressure is exerted on the brick. This
process occurs repeatedly until the brick finally breaks.
Ultimately there is a trade-off between fuel cost to maintain
furnace temperatures and the cost of refractory repair. As a
general rule, MHF operation is most economical when sched-
uled on as nearly a continuous a basis as possible.
22.535 Common Operating Problems (Troubleshooting)
22.5350 Smoke. The most common cause of smoke or air
emissions from an MHF is low oxygen content. This means
there is insufficient oxygen in the furnace to completely burn
the hydrocarbons. The solution to this problem is to add air to
the furnace.
Air may be added to the furnace through the doors, air ducts,
or through the use of the shaft cooling air return. Just as impor-
tant as the excess air is where you add the air. Air generally
should be added at or below the fire.
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22.5351 Clinkering. Many times hard, rock-like clinkers will
form within the furnace. If this situation is allowed to continue,
the clinkers may grow to a point where the drop holes plug and
the rabble teeth become blinded (plugged). The solution to
clinkering lies in understanding how a clinker is formed.
A clinker is nothing more than melted ash that has cooled.
The only temperatures in the furnace high enough to melt the
ash are the actual flame temperatures of the burners and the
flame from the burning sludge. However, the sludge flame
temperature is rarely high enough. Therefore, as a general
rule, the solution to clinkering lies in distributing the burner
input into the MHF. An example of this would be running
burners on separate hearths at lower firing rates.
If this does not correct the problem, it will be necessary to
reduce the feed rate to the furnace and have the cake
analyzed for mineral content and for excessive levels of
polyelectrolyte.
22.5352 Inability to Stabilize Burn. If you cannot stabilize
the burn, the first place to look for a problem is your feed cake.
The MHF loading must be constant with little or no change in
moisture or volatile content.
If the feed is constant, then the operator may be making
other process changes too quickly. The ultimate effect of any
process change to a furnace will show-up one hour after the
change was made. Therefore, make one change at a time and
WAIT for the results.
22.536 Safety
An MHF has several safety considerations above those in
the rest of the treatment plant. These considerations all revolve
around the fact that the MHF uses high temperatures to de-
stroy the solids. Therefore, TREAT EVERYTHING AS IF IT
WERE HOT!
Anytime you are in the furnace area, wear protective clothing
including heavy leather gloves, face shield, hard hat, long
sleeve shirt and long pants.
Never wear synthetic fabrics. The heat from the furnace can
cause synthetic fabrics to ignite and act like napalm on your
skin. Wear clothing made of cotton.
Never look directly into a furnace door when the furnace is in
operation. Always approach the door from an angle and look in
at an angle.
A furnace, when out of operation, is a confined space. Treat
it accordingly, checking the atmosphere before entering for
toxic gases (hydrogen sulfide), explosive conditions, and an
oxygen deficient atmosphere.
Always check the temperature of the ash bed before entry.
Though the furnace may be cold, the ash bed may still be
several hundred degrees under the surface.
Always lock out the main fuel control valve and the control
power prior to furnace entry.
Check and verify the operation of all safety controls and
interlocks on a regular basis.
-------
234 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 276.
22.53N At what rate of temperature increase do you bring a
cold furnace up to temperature?
22.530 What is an autogenous burn?
22.53P Why is it desirable to operate an MHF on a continu-
ous basis?
22.53Q What is the cause of smoke from an MHF and how
can this problem be corrected?
22.53R What protective clothing should be worn when in the
furnace area?
r
22.54 Facultative Sludge Storage Lagoons
Facultative sludge storage lagoons can serve three very im-
portant purposes:
1. Volume reduction. Volatile solids can be reduced by 45
percent and solids concentrations can be increased from
two percent up to eight percent or more. Sludge concentra-
tions as high as 25 percent solids have been obtained in the
bottom layers of some lagoons.
2. Storage buffer. Storage is frequently required when sludge
production is continuous and land disposal is affected by
changing seasonal conditions.
3. Further stabilization. Anaerobically digested sludge is
further stabilized in the storage lagoon by continued
anaerobic biological activity.
Facultative sludge storage lagoons vary in depth from 10 to
16 feet (3 to 5 m). Surface areas are based on solids loadings
of 20 to 50 pounds of volatile sludge solids per day per 1000
square feet of surface area (0.1 to 0.25 kg VSS per day per
square meter). Surface aerators are commonly used to main-
tain aerobic conditions near the surface in order to avoid odor
problems.
There should be enough lagoons to allow each lagoon to be
out of service for approximately six months. Stabilized and
thickened sludge can be removed from the basins using a mud
pump mounted on a floating platform.
QUESTION
Write your answer in a notebook and then compare your
answer with the one on page 276.
22.54A List three purposes of facultative sludge storage la-
goons.
22.6 LAND DISPOSAL OF WASTEWATER SOLIDS (by
William Anderson)
22.60 Need for Land Disposal
The alternatives for land disposal and/or utilization of
wastewater solids are shown in Figures 22.39, 22.40 and
22.41. The alternatives for sludge are placed in either of two
categories based on the process used after stabilization (di-
gestion or chemical stabilization); (1) dewatering to about 20 to
30 percent solids, or (2) concentration during liquid storage to
6 percent solids.
Disposal and/or utilization of sludge following stabilization
without additional treatment to reduce water content is to be
avoided for the following reasons:
1. Water content (97 to 98 percent) of stabilized sludge is too
high to permit landfill or composting operations.
2. Sludge application and surface runoff problems in the wet
season are difficult to handle.
3. Land requirements necessary to evaporate the excessive
moisture are unreasonable.
22.61 Regulatory Constraints
Wherever various methods of sludge disposal are evalu-
ated, consideration must be given to the requirements of vari-
ous regulatory and planning authorities of the local, state, and
federal agenices. Unfortunately, many of the requirements are
still in a formative stage. Important restraints include allowable
emissions to the atmosphere from furnaces, groundwater and
surface water limitations, and the health aspects of sludge
applied to land involved in the food chain.
22.610 Regulation of Sludge Disposal
Sludge may be disposed of in a sanitary landfill at the treat-
ment plant site. Under these conditions, surface runoff must be
prevented. Also, percolation of leachate to groundwater must
be carefully controlled or eliminated.
At dedicated land disposal (DLD) sites, stabilized sludge is
applied to the land and then ploughed under. At sites of this
type, sludge must be covered the same day it is applied. Public
access must be avoided because pathogens or parasites may
not have been removed.
22.611 Regulation of Sludge Reuse In Agriculture
If sludge is to be reused for agricultural purposes, the treat-
ment plant owners should also own nearby land to assure
necessary monitoring and controls. Use of sludge on agricul-
tural land requires close monitoring of cadmium levels and any
other heavy metals, as well as toxic substances and patho-
gens applied to the land. Because of the potential problems
from toxic substances, viruses and pathogens, the application
of sludges on food crops should only be attempted at this time
when careful monitoring is involved.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 276.
22.61 A What are two important restraints regarding the dis-
posal of sludge?
22.61 B Why should sludges not be applied to food crops?
-------
Wastewater Solids
Stabilization
and Volume
Reduction
Processes
Land
Disposal/Utilization
Dewater
Thicken
Thicken
Dewater
Dewater
Dewater
Dewater
Scum
Grit
Incinerate
Screenings
Stabilization
Liquid
Storage
Compost
Mech Dry
Primary-Secondary-Tertiary Sludge
On-Site
DLD
Landfill
On-Site
DLD
Landfill
Landfill
Rendering
Reclamation
Agricultural
Reclamation
On-Site
DLD
Landfill
Agricultural
Reclamation
Permanent
Lagoons
On-Site
High-Rate
DLD
Non-agri-
cultural Use
Agricultural
Use
Bagged for
Home Use
(/)
o
E
en
»
TJ
O
(0
Q>
IO
W
Fig. 22.39 Alternatives for land disposal and lor utilization w
-------
236 Treatment Plants
TRACTOR SPREADER
TANK TRUCK SPREADING
LIQUID SPRAYER
SOIL INJECTION
LIQUID SPRAYER
FLOTATION TRACTOR MOUNTED
CENTER PIVOT IRRIGATION
TRAVELING IRRIGATION STATIONARY IRRIGATION
I. Adapted from "Sludge Processing and Disposal - LA/OMA Project"
Fig. 22.40 Typical liquid sludge application systems on land
-------
Solids Disposal 237
4HS0URCE of sludge
(FROM STORAGE LAGOON OR
ANAEROBIC DIGESTER)
fr" UMBILICAL -v
HOSE \
UMBILICAL CORD TRACTOR — SURFACE SPREADING
it
UMBILICAL HOSE
UMBILICAL CORD TRACTOR — SOIL INJECTION
Fig. 22.40 Typical liquid sludge application systems on land
(continued)
-------
238 Treatment Plants
TRENCHING
w.
LANDFILL
MANURE
SPREADER
SURFACE SPREADING
Fig. 22.41 Typical dewatered sludge application systems on
land
-------
Solids Disposal 239
22.62 Disposal Options
22.620 Stabilized Sludge — Dewatered
STORAGE. Storage often must be provided in the sludge
treatment system to accommodate differences between dis-
posal rates and production rates. Sludge storage is effective
when part of a liquid treatment system, such as anaerobic or
aerobic digesters. Mechanically dewatered sludge is very dif-
ficult to store for any length of time. If lime and/or ferric chloride
have been used to condition sludge for mechanical dewater-
ing, the sludge may be stored for a longer period than if poly-
mers were used. Three to five days are usually the limit for
successful storage of mechanically dewatered sludge. Dewa-
tered sludge from drying beds or drying sludge lagoons often
can be stored for long periods of time in open stockpiles.
TRANSPORTATION. The number of trucks required to haul
the dewatered stabilized sludge cake to the disposal site must
be determined. Route possibilities should have been evaluated
in the Environmental Impact Report for the project. Round-trip
travel, loading, and unloading time need to be estimated
(about 2-Vi hours per 50 mile round-trip). Operating hours for
truck transport also must be considered. If the transportation
hours of operation are less than the hours of operation of the
dewatering facility, storage will have to be provided at the de-
watering facility. Usually it is not desirable to deposit sludge
cake at a landfill on Saturdays, Sundays, or holidays. How-
ever, if the dedicated land disposal (DLD) site is located at the
treatment plant site, sludge cake may be deposited at any
time. On-site dedicated land disposal sometimes uses
pneumatic ejection pipelines for transporting material to the
disposal site. Agricultural reuse is often seasonal and trucking
must always be at the pleasure of the farmer, not the operator
of the treatment plant.
22.6200 Sanitary Landfill Disposal. Sludge cake (20 to 30
percent solids) discharged from the dewatering machines
(centrifuges, vacuum filters, or filter presses) or (50 to 60 per-
cent solids) removed from drying beds or drying lagoons (see
Chapter 12, Section 12.7, "Digested Sludge Handling") can be
transported to a sanitary landfill for disposal with the municipal
refuse. The impact on the capacity of the landfill needs is de-
termined as shown by the following calculation:
Given: Rate of Municipal Refuse Deposit, D tons/day
Rate of Sludge Cake Production, P cu yd/day
Assume: A Compacted Density of 560 Ibs/cu yd
Find: The percent of increased usage of landfill, U.
Usage, % = 560 Ibs/cu yd x P, Sludge Cake, in yd/day x 100%
2000 lbs/ton x D, Refuse Deposit, tons/day
The additional water associated with the stabilized sludge
will provide better compaction in the landfill which will slightly
reduce the percentage of increased usage. The landfill
operator must be able to and willing to accept the sludge cake.
A higher rate may be charged for sludge cake if special han-
dling is needed.
LANDFILL MOISTURE ABSORPTION CAPACITY. The
water balance of a landfill is important in minimizing leachate
formation. The absorption capacity of the landfill should be
investigated when adding materials with large amounts of
water such as sludges. A GENERAL GUIDEUNE IS THAT NO
MORE THAN 25 TO 40 GALLONS OF WATER PER CUBIC
YARD (125 TO 200 LITERSICU M) OF REFUSE BE AL-
LOWED.
PLACEMENT OF SLUDGE IN A LANDFILL. Direct dumping
or tailgating of sludge cake on the working face of the landfill is
the method used most often. However, the following factors
need to be considered for large-scale operations:
1. Operators must work in the immediate area.
2. Compaction must be achieved.
3. The general public discharging trash at the landfill must be
protected.
DURING DRY WEATHER, either open-air drying or mixing
with soil cover material prior to placement in the landfill would
improve the operation.
DURING WET WEATHER, direct disposal in trenches or pits
would probably be necessary to avoid surface runoff contami-
nation and extremely unpleasant working conditions.
22.6201 On-Site Dedicated Land Disposal (DLD). Sludge
cake (20 to 30 percent solids) discharged from the dewatering
machines (centrifuges, vacuum filters, or filter presses) and
cake (50 to 60 percent solids) from drying beds and drying
lagoons can be moved to an area (DLD) on the treatment plant
site that has been dedicated to the disposal of sludge cake,
incinerator ash, and dewatered grit and screenings. To avoid
the potential problems of having future development im-
mediately adjacent to the sludge disposal areas, buffer land
adjacent to these areas should be acquired by the treatment
plant.
Surface runoff control facilities must be provided.
1. Flood Protection. The disposal site should be protected
from flooding by a continuous dike.
2. Existing Drainage. The existing drainage into the disposal
site should be intercepted and directed outside the flood-
protection dike.
3. Contaminated Runoff. Runoff from the disposal site should
be collected in a detention basin and allowed to evaporate
during the summer or recycled to the treatment plant head-
works.
PLACEMENT OF SLUDGE CAKE IN A DEDICATED LAND
DISPOSAL SITE. Several methods of placement of sludge
cake in a DLD site can be used and are described in the
following paragraphs.
TRENCHING. This method has been used in some areas for
many years.
1. Shallow trenches. Construct a trench about 4 feet (1.2 m)
deep. Add sludge to a depth of about 2 feet (0.6 m). Backfill
the trench to its original grade. Substantial amounts of land
are required. Small treatment plants can use pits instead of
trenches.
2. Deep trenches. Construct a trench about 20 feet (6 m)
deep. Add sludge cake in 2-foot (0.6 m) lifts with a 1 foot
(0.3 m) soil cover over each lift. When the trench is full,
place a 5-foot (1.5 m) soil cover on top and sow grass on
this cover. An average annual cake production of 50 tons/
day (dry) will require about 20 acres/year for disposal.
Trenching of sludge cake prevents rapid decomposition of
organic material and rapid removal of water, both of which
would reduce the sludge disposal volume. Also, the DLD site is
unsuitable for many purposes when trenching operations are
complete because the surface may not support much weight.
Depending on the area available, a DLD site may not be suita-
ble for retrenching at the end of 20 years. Additional land would
then be required. Also, at the end of 20 years the ground
surface elevation may have been raised about 5 to 7 feet (1.5
to 2.1 m).
-------
240 Treatment Plants
Long-term effects of trenching on groundwater are unknown
and depend on soil conditions and level of groundwater table.
Water addition to the trench areas will be about 100 gal/cu yd
(500 liters/cu m). This is 2Vi times the 40 gal/cu yd (200 liters/
cu m) criteria for sanitary landfills. Specific site evaluation is
required to satisfy the regulatory agencies and trench liners or
leachate control facilities may be necessary.
Trenching operations are most difficult and sometimes im-
possible during extreme wet periods. No matter how the
sludge cake is moved to the DLD site, by truck or by pneumatic
ejection pipelines, it must be mixed with soil and/or buried daily
to avoid odor production. Bulldozers, roadgraders, or bucket
loaders have been successfully used to mix the materials be-
fore placement. To operate in wet weather, either paved areas
or a well prepared gravel base is needed. Also, rainwater that
collects in the trenches or other working areas will have to be
transported to a detention basin and allowed to evaporate dur-
ing the summer or be recycled to the treatment plant head-
works.
LANDFILLING. Landfilling of sludge cake is an above-
ground operation of mixing or interlaying sludge with soil. Usu-
ally several feet is excavated beneath the existing ground sur-
face to obtain sufficient soil for final cover material. The exca-
vated site is used as a cell where the sludge is mixed with the
soil on a 1:1 ratio to aid in the placement of the material.
The problems and disadvantages of landfilling are similar to
those listed for trenching.
a. Continued use of land 20 ac/yr (8 hectares/yr) for a 50
ton/day (45,000 kg/day) cake production.
b. Large quantities of water are added to the DLD site cre-
ating potential leaching.
c. Large excavation operations could damage existing natu-
ral (clay soils) groundwater protection.
d. Operations will raise the ground surface several feet.
e. Wet weather may prevent operations.
The advantages of landfilling sludge cake only are also simi-
lar to those for trenching.
a. Odor problems are minimized if sludge is covered each
day.
b. Operations eliminate off-site transport.
c. Operations are fully controlled by the treatment plant.
d. Operations will also provide for on-site disposal of in-
cinerator ash, dewatered grit, and screenings.
INCORPORATION INTO SURFACE SOILS. Mixing sludge
cake with surface soils is a method that minimizes the prob-
lems of trenching and landfilling while retaining the advantages
of on-site disposal. However, it is only recommended for use in
dry weather because of the inability to move equipment and
the odor-generation potential in wet weather. Extensive stor-
age facilities are required to successfully practice this method
of sludge cake disposal.
About 200 dry tons/acre (450,000 dry kg/hectare) could be
applied in a 6-month dry season. Sludge could be re-
incorporated every few weeks after the soil/sludge mixture has
dried. The DLD site may have a life of at least 40 years.
Equipment required for this operation consists of dump
trucks or manure-type spreading equipment to haul dewatered
sludge from the dewatering facility to the DLD. Since travel
time should be minimal to an on-site DLD, only relatively small
trucks are needed. Tractor, plow, and disking equipment also
are necessary.
22.6202 Agricultural Reclamation. The main reasons for
using wastewater solids for agriculture are to supply the nutri-
tional requirements of crops and improve the tilth of the soil by
adding humus without adversely affecting the crop produced,
the soil, or the groundwater. Determining safe loadings within
the above limitations requires a complete chemical and biolog-
ical analysis of the wastewater solids coupled with an evalua-
tion of soil types, crops, and irrigation practices.
APPLICATION RATE. The controlling factor for the sludge
application rate may be the nitrogen requirement of the crop.
Proposed long-term annual cadmium application criteria (0.5
kg/ha/yr proposed by EPA in 40 CFR 257.3-5) would allow an
annual application of about 12.5 tons/acre (dry) (28,000 kg/ha)
if the cadmium concentration was 18 mg Cd/kg dry solids. The
following assumptions concerning nitrogen requirements and
losses result in a 3.3 ton/acre/yr (dry) (7,400 kg/ha) sludge
application rate.
1. Nitrogen content of 6 percent (dry weight basis of dewa-
tered sludge).
2. One application per season before or between plantings
(this procedure will require sludge storage facilities).
3. Rate of nitrogen mineralization is assumed to be an annual
percentage of the remaining unmineralized portion. This
results in 67 percent of the nitrogen being mineralized in 20
years. Nitrogen must be mineralized by the crop.
4. Loss of 25 percent of mineralized nitrogen to the atmos-
phere via volatization (ammonia release) and denitrification
(nitrogen gas release). This loss is appropriate when sludge
is disked into soil after application.
5. Crop demand is 200 pounds nitrogen/acre/yr (255 kg
N/ha/yr) which is appropriate for many crops, including field
corn.
Average = Annual Crop Nitrogen Demand, lbs/acre
Annua! ^ Qontent o/0 x n Mineral, % x N Remain, % x 2000 lbs/ton
Sludge
Applica- , 200 |bs/acre
tion
Rate, dry 6%/100% x 67%/100% x 75%/100% x 2000 lbs/ton
tons/acre
200 lbs/acre
0.06 x 0.67 x 0.75 x 2000 lbs/ton
= 3.3 dry tons sludge/acre
This analysis results in a low application rate that optimizes
the reuse of the sludge nitrogen. If maximum nitrogen reuse
was not an objective, higher sludge application rates (7.5
tons/acre or 16,800 kg/ha) could be made without injuring most
crops. Nitrogen not used by the crop is denitrified during the
winter when the soil becomes saturated with water. In this
manner, nitrogen does not move downward in the soil to pol-
lute groundwater.
Double-cropping in some areas may permit additional
sludge application.
A zinc-to-cadmium (Zn/Cd) ratio lower than the EPA's
guideline of 1000:1 may not have an adverse effect on crops,
but monitoring of cadmium additions should be done on a regu-
lar basis.
METHOD OF APPLICATION. For low rates of sludge appli-
cation (3.3 tons/acre/yr or 7,400 kg/ha/yr), good control over
-------
Solids Disposal 241
spreading methods is necessary. Manure spreaders or similar
equipment are recommended for applying the sludge cake. A
plowing and/or disking operation should follow closely to incor-.
porate the sludge into the soil and cover it. Application of
sludge to land controlled by the treatment plant affords
maximum matching of disposal rates to plant production rates.
Treatment plant agreements with individual land owners to
spread sludge at certain times is less desirable because it
reduces flexibility and reliability of operation. Monitoring of
spreading sites will also be more difficult.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 276.
22.62A What methods are available for the disposal of me-
chanically dewatered digested sludge?
22.62B What kinds of surface runoff control facilities must be
provided at an on-site dedicated land disposal opera-
tion?
22.621 Stabilized Sludge — Liquid Process
Stabilized sludge can be disposed of in a liquid form (less
than 10 percent solids) by: (1) high-rate incorporation into the
surface soils of a site dedicated to land disposal (DLD); (2)
low-rate application to agricultural sites; or (3) confinement in
permanent lagoons.
STORAGE. Long-term storage (about 5 years) of sludge in
facultative ponds immediately after digestion is recommended
in order to:
1. Separate the daily production of sludge by the wastewater
treatment process from the final disposal operation which
may be seasonal, sporadic, highly variable in quantity, or
subject to changing regulatory requirements;
2. Achieve substantial additional destruction of remaining vol-
atile solids;
3. Maximize reduction of total volume by evaporation; and
4. Consolidate sludge to about 6 to 12 percent solids.
TRANSPORTATION. Liquid transportation of stabilized
sludge is usually best accomplished by pipelines. This is espe-
cially true when high-rate on-site dedicated land disposal is
used. Sludge concentrations much above four to six percent
can be difficult to pump if the pipeline designer did not realize
that the friction head loss increases when the sludge concen-
tration increases.
For agricultural reuse of liquid stabilized sludges, trucks are
usually the best means of transportation. The main advantage
here is the flexibility of application sites. Sludge is dredged at 8
or 10 percent solids concentration and placed in large, spe-
cially designed tanker trucks on the order of 10,000 gallons (38
cu m) each or another type of truck. The material' is flooded
onto the field and disked in. If 10 percent solids concentrations
are achieved, smaller open trucks with manure-type spreading
devices fitted onto them may be used. This allows a less
sophisticated operation and makes it easier for farmers to use
existing equipment.
22.6210 High-Rate Dedicated Land Disposal. This process
uses facultative sludge lagoons (FSLS) for storage and further
stabilization prior to disposal.
Sludge is dredged from the facultative sludge lagoons and
transported by pipeline to a dedicated land disposal (DLD) site
which should be located adjacent to the facultative sludge la-
goons. The DLD site should be loaded at a rate of about 100
dry tons/acre/yr (224,000 kg/ha/yr) and should be expected to
operate for at least 40 years. Several sludge-spreading tech-
niques have been tested for DLD operations, but shallow injec-
tion beneath the surface of the soil appears to be the most
cost-effective and environmentally acceptable operation at this
time.
RATE OF APPLICATION. The disposal system should oper-
ate over the months with the greatest potential net evapora-
tion. Experiments indicate that an application of 100 dry tons/
acre (224,000 kg/ha) of sludge at six percent solids concentra-
tion would be feasible over a four to six-month period in some
areas.
The application rate results in a water loading rate of 1,570
tons/acre (3,520,000 kg/ha) for an average of 14 inches (36
cm) of water which must be evaporated. Despite the fact that
evaporation from wet soil will be less than lake evaporation,
there is no problem in meeting these evaporation needs in
most arid areas.
DISPOSAL TECHNIQUES. Techniques for spreading
sludge at six percent solids concentration dredged from the
bottom of the facultative sludge lagoons include:
1. RIDGE AND FURROW. This technique could be very
cost-effective if sludge could be made to flow down lurrows,
then after being applied, be covered by splitting the ridges
and throwing the dirt over the top of the sludge in the fur-
rows. The system seems to be unmanageable due to:
a. Difficulty in maintaining the required relationship be-
tween the sludge viscosity (percent solids) and slope of
the furrows.
b. Clogging of sludge debris in the individual furrow gates
of the distribution pipe.
c. Cloddy, puddled soil that does not cover the sludge
adequately. This may be due to soil characteristics.
(However, this type of soil is usually needed for protec-
tion of the groundwater.)
2. FLOODING. This method consists of spreading the sludge
as evenly as possible over the surface of the disposal area
and then incorporating it with the soil. Flooding needs to be
controlled with low (6 to 8 inch or 15 to 20 cm) borders or
dikes running the length of the field in the direction of flow.
The borders control the lateral movement of sludge, thus
giving more uniform coverage. After spreading to an aver-
age depth of 11/2 to 2 inches (3.8 to 5.1 cm), the sludge is
turned into the soil with a large disk. At this application rate,
the result is a well aerated soil/sludge mixture. At heavier
applications, which may occur in some areas due to uneven
flooding, the mixture approaches saturation and results in
anaerobic conditions and some odors.
A comparison of flooding with other methods produces
the following disadvantages:
a. Occasional odor problems from areas receiving exces-
sive sludge application.
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242 Treatment Plants
b. Difficulty of maintaining proper relationship between
slope of the land and sludge viscosity makes even or
uniform sludge application practically impossible.
However, the advantages of flooding over subsurface injec-
tion are:
a. Lower labor requirement and total cost. Cost compari-
son of the two systems in early 1978 showed that flood-
ing would cost about $20/ton (2.24/kg), while subsur-
face injection would cost about $25.50/ton (2.8'/kg).
b. Lower energy requirements since sludge would not be
pumped through a small diameter hose and an injection
system (both have high head losses).
3. SUBSURFACE INJECTION. Subsurface injection is pres-
ently the preferred disposal technique because of its ability
to ensure consistent sludge application rates and to avoid
odorous conditions. This system uses an umbilical cord (4
inch hose) tractor-mounted subsurface injector (Fig.
22.42) to distribute sludge at about 6 to 8 inches (14 to 20
cm) beneath the surface of the soil. The sweep on the
injector unit opens a small cavity in the soil into which the
sludge flows. After the sweep passes, the soil falls back into
place leaving the sludge completely covered.
Sludge is transported from the dredge, operating in the facul-
tative sludge lagoons, through pipes to the OLD site. Booster
pumps may be needed at appropriate locations to move sludge
the required distance. A pipeline extends into the DLD site,
underground, and risers are appropriately located for hookup
with the injection system. A 4-inch (10 cm) diameter flexible
hose is attached to the riser and the tractor-mounted injection
unit." Sludge application is directly beneath the surface of the
ground and there is no visible evidence of the sludge after the
injection unit moves on.
Problems may include:
a. Insufficient durability of the flexible supply hose.
b. Coordination of dredging and injection. When the tractor-
injector is being turned at the end of a row, the flow must
be stopped or relieved through a booster pump bypass
system. This requires good communication between the
injector, booster pump and the dredge operators.
The cleanliness and odor-free operation of subsurface injec-
tion make it a desirable disposal technique despite its slightly
higher cost.
SITE LAYOUTS
1. Each dedicated land disposal site layout should have a
gross area which includes area for drainage, road access,
and injector turning.
2. Each site should be approximately 1,300 feet (400 m) wide.
This dimension is determined by the 660-foot (220 m)
length of the subsurface injector feed hose and the turn-
around space required at each side of the field.
3. Each site should be approximately 800 feet (240 m) in
length. This dimension is determined by the area required
to allow one injector to operate continuously (six hours/day,
five days/week during peak dry months. Consideration also
must be given to the net evaporation during the dry month.
Peak dry-month operation assumes one pass is made over
the DLD site each week. During other harvesting months, it
is assumed maximum operation will be limited to one injec-
tor making one pass every four weeks.
4. Each DLD site should be graded so that runoff drains
(flows) from the center of the DLD to ditches on both sides.
Runoff from these ditches should collect in a runoff deten-
tion basin at the end of the field. To prevent erosion, the
maximum field slope should be held to 0.5 percent and the
drainage ditches on the sides of each dedicated land dis-
posal site should be designed so that the runoff water veloc-
ity does not exceed five feet per second. These field ditches
should be "V" ditches with minimum side slopes of 4:1.
These flat side slopes will permit vehicle access across the
ditches during the dry weather for each dedicated land dis-
posal site control. The collected runoff must be returned to
some point in the liquid treatment process.
5. Each dedicated land disposal site should be surrounded by
an isolation berm designed to keep uncontaminated sur-
face runoff out and contaminated DLD site runoff in. The
berm should be 15 feet (4.5 m) wide at the top and should
be provided with 3:1 side slopes. The top of the berm
should be finished with an all-weather gravel road.
6. Each dedicated land disposal site should be provided with
an all-weather gravel access road to assure light truck ac-
cess at all times to its isolation berm system.
7. Capability to purge sludge from the dedicated land disposal
piping without discharging excessive purge water on the
dedicated land disposal site must be provided.
SYSTEM OPERATIONAL CRITERIA
1. Dedicated land disposal sites should be loaded at a
minimum of 100 tons (dry weight) per acre (224,000 kg/ha)
of harvested sludge per year.
2. Dedicated land disposal sites should be disked as required
to assure all sludge is covered daily. Intermittent disking is
helpful in drying the fields quickly.
3. Harvested sludge piping should be flushed and purged at
the end of each day's run. Sludge purged from piping
should be injected into the disposal site. When starting
each day's operation, liquid within harvested sludge piping
should be purged, as much as possible, back to the faculta-
tive sludge laggons.
EQUIPMENT NEEDS. The operation of the dredge is very
important to the efficient application of sludge to the DLD site.
This operation should be able to average 6 percent solids con-
centration, although even with a 4Vz percent average solids
content, the operation would still be quite effective. The greater
the solids content, the more efficient the operation becomes
since the system is limited by the amount of water which must
be evaporated. Problems may be encountered trying to main-
tain a constant solids content in the dredged material since the
sludge mass in the facultative sludge lagoons shifts from time
to time.
22.6211 Agricultural Reclamation. This process uses facul-
tative sludge lagoons, as described previously for sludge stor-
age, and further stabilization prior to its use on nearby crop-
land. The purpose of this process is to maximize reuse of the
nutrient components of the sludge. Some degree of control
must be exercised over the land to be used for sludge spread-
ing in order to ensure that full sludge utilization is guaranteed
each year. Short of such a guarantee, a backup disposal sys-
tem may be necessary.
-------
Solids Disposal 243
TRACTOR AND INJECTION UNIT
INJECTION UNIT
Fig. 22.42 Sludge tractor and injector unit
(From Sewage Sludge Management Program. Wastewater Solids Processing and Disposal. Draft EIR, Sacramento Area Consultants, October. 1978)
-------
244 Treatment Plants
APPLICATION RATE. The controlling factor in the rate of
sludge application is the nitrogen requirement of the crop. The
same assumptions apply to agricultural reclamation as to liquid
sludge application rates. The slightly lower nitrogen content
(5.9 percent) allows a slightly higher application rate of 3.4 ton
(dry weight)/acre/yr (7,600 kg/ha/yr).
METHOD OF APPLICATION. For these rather low rates of
sludge application, good control over spreading methods is
necessary. Several techniques are discussed briefly in the fol-
lowing paragraphs.
1. SUBSURFACE INJECTION. The concentration of solids in
the sludge pumped from the storage ponds should be three
or four percent to allow pumping of sludge the required
distances for umbilical cord injection systems. This also
keeps trucking costs down when subsurface injection tank-
ers are used. This would increase costs of operating an
injection system. Overall, costs of subsurface injection
would be rather high but it would provide a safe, non-
odorous application system with excellent control over ap-
plication rate.
2. RIDGE AND FURROW OR CONTROLLED FLOODING.
Portable irrigation pipe is often used to take sludge from
fixed sludge feeder mains to the actual spreading areas. A
3.4 ton/acre (7,600 kg/ha) sludge application at 3 percent
solids concentration would be about 1 inch (2.5 cm) of
liquid/sludge mixture. Each spreading area is leveled or
managed along contours. Spreading can be done directly
from the back of tanker trucks. Sludge is disked into the soil
after spreading to minimize odors. Timing and scheduling of
sludge application and crop planting must be properly man-
aged.
3. SLUDGE MIXED WITH IRRIGATION WATER. This system
requires a tie-in between a crop irrigation system and the
sludge dredging system. The advantage is that a separate
sludge distribution system is unnecessary although there
are costs associated with the interties. Sludge application is
spread over several irrigation applications depending on
the crop type and other factors. This helps to minimize the
problem of scheduling sludge applications and crop plant-
ing. Disadvantages include the fact that the sludge is not
diked into the soil immediately but dries as a layer of sludge
cake in the furrows. This may produce additional odors.
22.6212 Permanent Lagoons. This process uses faculta-
tive sludge lagoons as described previously for further stabili-
zation and volume reduction prior to transfer to permanent
lagoons for disposal. The land used for lagoons is permanently
dedicated to the disposal of sludge. Many agencies operate
permanent sludge lagoons, sending anaerobically digested
sludge directly to them without the intermediate step of long-
term storage and stabilization in a facultative pond. These
types of lagoons typically have odor problems. To minimize
that problem, the facultative pond is sometimes used as a
highly controlled intermediate environment to achieve substan-
tial additional volatile solids destruction. An obvious secondary
advantage of facultative ponds is their storage capacity which
allows transferring sludge to lagoons at the most advantage-
ous times.
Permanent lagoons should be approximately 20 feet (6 m)
deep with a 15-foot (4.5 m) working depth. Sludge is perma-
nently stored at an average solids concentration of 12.5 per-
cent and an assumed solids loading of 2,900 tons (dry
weight)/acre/yr (6,500,000 kg/ha/yr). Their construction is simi-
lar to facultative ponds without the mechanical and piping
equipment and electrical connections. Such lagoons have to
be located on land dedicated in perpetuity (forever) for that
purpose and always maintained with a top cap layer of aerobic
liquid to minimize nuisance odors and VECTOR40 problems.
Liquid levels are maintained with plant effluent and rainfall.
Barriers surrounding the lagoons aid in odor dispersion. Load-
ing is intermittent from facultative ponds.
Permanent lagoons provide additional odor-generation po-
tential. If odors become a problem with the lagoons, surface
aeration equipment could be added; however, the increased
costs, both capital and operational, are substantial.
22.622 Disposal of Reduced Volume Sludge
22.6220 Composting Process. (Also see Section 22.51.)
Most stabilized, dewatered sludge is composted by either of
two methods: (a) windrows (Fig. 22.43) or (b) static pile (Fig.
22.44). Both processes require the mixing of freshly dewatered
sludge or a bulking material like wood chips or rice hulls to
achieve 35 to 40 percent solids content at the start of compost-
ing. This solids content is required to allow sufficient voids and
air passages for the aerobic composting process to be sus-
tained. Material will be at about 60 percent solids when com-
posting is complete.
Two problems are associated with WINDROW COMPOST-
ING: (1) odors released when windrow is turned and mixed,
and (2) improved sludge dewatering resulting in finer solids
that make it more difficult to maintain aerobic conditions in the
windrow with the same proportion of bulking material. These
problems are causing more windrow operators to shift to static
pile composting. Temperatures of 60°C are achieved in com-
posting which is considered adequate for removal of patho-
gens. Temperatures within static piles are usually better con-
trolled than in windrowing.
In a STATIC PILE operation, a pug-mill might best be used to
achieve a uniform 35 percent solids mixture of dewatered sta-
bilized sludge and bulking material. This mixture is placed in a
pile containing 150 to 200 cu yd (115 to 150 cu m). A forced-air
system draws air through the pile to a perforated pipe network
beneath the pile. Warm, moist air is drawn off and blown
through a small pile of previously composted material to re-
duce odors. The static pile is also covered with a layer of
composted material to contain odors. The process takes about
3 weeks to complete. The compost material is then typically
stored a month for curing. Open storage may have a slight
musty odor. After curing, the material is ready for bulk use or it
can be dried further, pulverized and then bagged for sale.
22.6221 Mechanical Drying. Mechanical drying systems
usually consist of a cylindrical steel shell that revolves at five to
eight rpm. One end of the dryer is slightly higher than the other
end. Mechanically dewatered sludge is fed into the higher end.
Flights projecting from the inside wall of the shell continually
raise the sludge and shower it through the dryer gas, moving
the sludge toward the outlet. Dry gas enters the dryer at
1,200°F (650°C) and usually flows in the same direction as the
sludge being dried. After the sludge has been rotated in the
dryer for 20 to 60 minutes, the dried sludge is discharged at a
temperature of 180 to 200°F (82 to 93°C). Exhaust gases are
conveyed to a cyclone where entrained solids are separated
from the gases. The dried sludge either goes on to further
processing or to disposal.
22.6222 Incinerator Ash. On-site landfilling of incinerator
ash is accomplished similar to a sanitary landfill and provides
good control over disposal of this material. Ash also is dis-
posed of on a dedicated land disposal site as long as it is
turned under the soil quickly and not subject to wind action.
40 Vector. An insect or other organism capable of transmitting germs or other agents of disease.
-------
APPROXIMATE WINDROW SPACING
SEWAGE SLUDGE COMPOSTING
USING COBEY ROTOSHREDDER
SLUDGE VOLUME PER ACRE = 3900 YD3/ACRE
Fig. 22.43 Approximate windrow spacing
-------
246 Treatment Plants
3.0 M
i
%&?&^STATIC--S^
/&&tW&9MPOST^tfsg&!\
WATER
REMOVAL
-12 TO 15 M-
DEODORIZED
EXHAUST
AIR
SCREENED
COMPOST
(4 MJ)
GENERAL LAYOUT
SCREENED COMPOST
BULKING AGENT AND
SLUDGE MIXTURE
UNSCREENED COMPOST.
OR BULKING AGENT
PERFORATED
PIPE
SUBSEQUENT PILES
FOR EXTENDED PILE
METHOD
5.5 TO 7.5 M
CROSS SECTION
Fig.. 22.44 Typical static compost pile for 40 cubic meters of dewatered sludge
(from EPA Capaul* Report, EPA 825/2-77-014)
-------
Solids Disposal 247
22.6223 Utilization Options. There are basically three op-
tions for use of the composted and mechanically dried materi-
als.
1. Provide a bagged commercial product for sale to the public
as a soil amendment.
2. Provide compost for agricultural land use. This would pro-
vide more of a marketing problem due to concern over
some materials used for bulking: for example, wood chips
have nitrogen demand and some tree leaves have toxic
effects. Coarse bulking agents, such as wood chips, are
usually screened out and reused.
3. Provide compost for nonagricultural land uses. This would
include use in parks, golf courses or other recreational
areas. There may be only a limited demand for this material
due to the established use of high-nitrogen fertilizer on golf
courses and turf farms, and the trend to more natural vege-
tation parks.
22.623 Screenings, Grit and Scum
Screenings, grit and scum are usually the most difficult sol-
ids to handle and dispose of because of odor and vector prob-
lems.
22.6230 Dewatered Screenings and Grit. Dewatered grit
and screenings can be placed in an on-site landfill as long as
they are buried the same day as produced to avoid odors.
22.6231 Dewatered Scum. Dewatered scum should be
disposed of in a sanitary landfill. Another possibility is the sale
of the scum for recovery of grease and other potentially useful
byproducts.
22.6232 Dewatered Raw Sludge. Process incinerated ash
from dewatered raw sludge the same as incinerated ash from
grit, scum and screenings.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 276.
22.62C How can liquid digested sludge be disposed of?
22.62D How can liquid sludge be spread over land?
22.62E How can composted material be disposed of?
22.62F Why must the surface layer of liquid on permanent
lagoons be aerobic?
22.63 Environmental Controls (Monitoring)
The size and nature of the disposal facilities requires that
major attention be directed to proper operation and control.
Under such conditions, a monitoring program is essential and
its elements are described here. An annual report should be
issued describing each year's operation and monitoring re-
sults. This report is important in communicating with regulatory
agencies and local citizens to ensure that problems which
develop are being resolved, and in documenting operating re-
sults for future enlargements of the system.
The recommended monitoring program for sludge disposal
systems is basically a data collection and analysis function
aimed at determining if permit conditions, operational and reg-
ulatory constraints, and design objectives are being met.
Listed below is a typical recommended monitoring schedule
for sludges and other constituents of a liquid dedicated land
disposal system with facultative sludge lagoons. Most of this
schedule is similar to monitoring that is routinely conducted by
treatment plant staff.
Sampling
Sample Type Frequency Constituents
Raw and thickened sludge Daily Flow, TS. VS
(to digesters)
Digested sludge
(from digesters)
Facultative sludge
lagoon stored sludge
Facultative sludge
lagoon supernatant
layer (each pond)
Recycled supernatant
(total of all ponds)
22.630 Odors
The following monitoring is recommended to prevent occur-
rences of odors and to assess and correct odor problems.
1. Meteorological monitoring for wind machine and general
operational control includes the following. It is expected that
this information will be continuously recorded.
Air temperature measurement at 25 feet (7.5 m) and 5
feet (1.5 m) above the ground. This provides data to calcu-
late AT which indicates the strength of low-level inversion
conditions.
Wind direction. This is used primarily to calculate the rate
of change of wind direction.
Wind speed measurement.
These measurements are also necessary to provide a
historical record. If and when an odor complaint is recorded
at the treatment plant, the meteorology occurring at the time
of the problem is available to assist in assessing the prob-
lem and correcting it.
2. The best overall odor monitoring program is the number of
complaints received from nearby residents. It may be dif-
ficult to determine from complaints received which facility
was the problem. For this reason, a response team should
be available to immediately check on all odor complaints,
track them back to the source if possible, and provide a
written record. In this manner, problem areas can be iden-
tified and solutions undertaken.
However, in order to avoid problems and determine if the
system is operating as intended, odor readings (using an
olfactometer as described in Chapter 20, "Odor Control")
from the surface of the ponds should be taken periodically,
perhaps for three consecutive days during each quarter.
Also, odor testing at the ponds should involve qualitative
operator judgements recorded daily.
22.631 Sludge/Dedicated Land Disposal Soils
Recommended monitoring of sludge removed from the
facultative sludge lagoons is intended mainly for operational
purposes, but also to determine if sludge chemical content is
compatible with future reuse options. Removed sludge should
be monitored for the following:
Sampling Frequency
Daily each dredge
Two composites from each
pond dredged/season
Daily Flow, TS, VS
Quarterly TS, VS
Profiles
Every two pH, temp, H2S, DO
days
Daily when TKN, NHa-N, P04-P,
operating COD, BOD, SS, pH
Constituents
TS, Flow
Alkalinity, CI, NHs-N, Soluble
S04, TP, TN, Ca, Mg, K, Na,
As, Be, Cd, Cr, Cu, Pb, Hg. Mn,
Ni, Se, Ag, Zn, PCB 1242, PCB
1254, Technical Chlordane,
DDE, TS, VS, pH, EC
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248 Treatment Plants
Daily records should be made of the location and quantity of
sludge spread on the DLD sites. Each DLD site should be
sampled in two locations at the end of each spreading season.
Soils should be sampled for pH, nitrogen, and heavy metals.
22.632 Groundwater
Potential degrading of groundwater is associated with
sludge disposal due to the substantial amount of water (80 to
98 percent) that would be buried with the sludge. This water
may travel laterally (side ways) as well as vertically.
Groundwater monitoring wells should be provided around all
the disposal facilities. There should be at least four test wells
for a DLD site. Two of these should not extend below the
confining soil layer and two should extend below this level. The
following sampling program should be used for groundwater
monitoring wells.
Sampling
Type Frequency Constituents
Ponds Quarterly Alkalinity (phenolphthalein and
methyl orange), CI, TPO4, hard-
ness (Ca and Mg), pH, TKN,
NH3-N, NOj-N, organic-N, COD,
pH, EC
DLD/Landfill Annually Same as above
22.633 Surface Water Monitoring
Surface water runoff which needs to be monitored includes
the DLD landfill contaminated runoff, which is designed to be
recycled to the plant, as well as any intermittent and continu-
ously flowing surface streams which pass through the plant
site. Following the first storm with substantial runoff, a sample
of DLD and landfill runoff water should be taken. At two or
three other times during the rainy season, additional samples
should be taken and analyzed. Runoff constituents sampled
should include the complete list of items analyzed for the plant
influent.
Any surface streams which pass through the site require
monitoring. These samples should be taken periodically
throughout the year. Constituents sampled should include the
complete list of items analyzed for plant effluent.
22.634 Public Health Vectors
A variety of disease-causing organisms can be found in un-
treated wastewater and wastewater solids. These include:
1. Bacteria such as SALMONELLA, SHIGELLA, STREP-
TOCOCCUS, and MYCOBACTERIUM which are responsi-
ble for typhoid and paratyphoid fever, shigellosis, scarlet
fever, and tuberculosis.
2. Protozoans and their cysts such as ENTAMOEBA HIS-
TOLYTICA which induces amoebic dysentery.
3. Helminths and their ova which include both parasitic and
free-living roundworms, flukes, and tapeworms which can
infect humans and animals.
4. Viral agents which can infect humans and animals.
5. Viral agents of human and animal origin which can cause
infectious hepatitis, polio, meningitis, and a variety of other
diseases.
One of the basic goals of wastewater treatment processes is
to destroy pathogenic microorganisms. Sludge treatment pro-
cesses such as anaerobic digestion, incineration, composting
and disinfection have variable effectiveness in reducing
pathogenic microorganism concentrations.
Stabilization destroys most of the pathogenic organisms.
Further destruction is accomplished with composting and
further anaerobic digestion in facultative sludge lagoons.
When appropriate precautions are taken, plant operators are
exposed to an undefinably low level of risk; public exposure
and risk are even less.
The potential for the propagation or attraction of birds, ro-
dents, and flies is discussed below briefly.
1. BIRDS. Salmonella bacteria are known to be excreted by
birds which have fed on food material found in polluted
waters. Gull feces have been found to contain S. TYPHORA
and S. TYPNI even after they have been isolated from ac-
cess to polluted waters. Gulls have been implicated in
SALMONELLA contamination of a community surface
water supply in Alaska after feeding near a wastewater out-
fall.
Several species of birds have been observed feeding on
floatable materials on facultative sludge lagoons. This is a
common occurrence in most wastewater treatment plants
which have open basins in which edible organic materials
are concentrated. No cases of disease transmission by
birds in wastewater treatment plants have been reported.
None of the operations discussed pose any public health
problems due to birds. The potential aircraft hazard as-
sociated with attracting birds to the facultative sludge la-
goons is probably minimal. If you find a dead bird, pick it up
with a shovel and bury it. You could become infected with
lice if you pick up dead birds with your hands.
2. RODENTS. Rats, domestic mice, and other rodents which
can multiply in response to human activities that create a
favorable environment for their survival can serve as vec-
tors for a number of human diseases including lepto-
spirosis, plague, and the dwarf tapeworm HYMENOLEPIS
NANA. To date (1980), no conditions associated with the
five years of operation of facultative sludge lagoons have
been observed which contribute to the propagation of ro-
dents. Sludge storage and disposal procedures can be
conducted so as to prevent the propagation of rodents.
3. FLIES. Flies are a known nuisance and vector of disease
which can propagate as a result of certain treatment plant
operations or disposal practices. Facultative sludge la-
goons have not contributed to fly breeding.
If sanitary landfilling, agricultural reclamation, lagooning, or
composting are the disposal or reuse methods, proper man-
agement of the processes will minimize fly propagation or at-
traction. There is no evidence to indicate that anaerobically
digested sludge will support fly breeding.
22.64 Acknowledgment
This section was reviewed by Warren Uhte who provided
many helpful comments and suggestions.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 276.
22.63A What items should be measured in an odor-
monitoring program?
-------
Solids Disposal 249
22.63B How many and where should the groundwater
monitoring wells be located for a dedicated land dis-
posal (OLD) site?
22.7 REVIEW OF PLANS AND SPECIFICATIONS
On occasion, operators will be asked to review and com-
ment on design drawings and specifications. Engineering
drawings generally contain much detail and can be rather
complicated to understand. When you are asked to review
design drawings, you should be concerned with those features
that will directly affect day-to-day operation, routine mainte-
nance and periodic repairs.
Day-to-day operation, maintenance and repairs are affected
by effort(s) required to open and close valves; read meters;
lubricate equipment; repair pumps and drive motors; replace
equipment such as chains, sprockets, and bearings; unclog
and clean pipes and float control mechanisms, and wash down
the area.
Regardless of the equipment or process being installed, the
operator should be sure that the following provisions are incor-
porated into the design:
1. All valves are easily accessible and enough area is pro-
vided to facilitate turning of the valves;
2. All meters and gages are easily readable and located
where process adjustments can be made if so indicated by
the meters and gages;
3. Sufficient area is provided around pumps and drives to
facilitate routine maintenance and repairs; and
4. Sufficient area, wash water capacity and drains are pro-
vided around major pieces of equipment such as thickeners
and centrifuges to facilitate repairs and clean up operations.
In general, the operator needs to sit back and reflect on
those items or situations from past experience that caused
trouble with daily operating and routine maintenance tasks.
The operator has to contend with the system(s) or unit pro-
cesses being installed and if given the opportunity to provide
input into the final design, you should take full advantage of
ensuring that equipment is accessible and enough working
area is provided.
When reviewing plans and specifications, you must consider
what you will do if each particular treatment process breaks
down. Vou have to decide where to store the sludge and how
long you might have to store it. For example, if you have cen-
trifuges to thicken the sludge and then burn the sludge in an
incinerator, what will you do if the incinerator is out of service?
Can the sludge be hauled to a sanitary landfill? How many
truck loads would have to be hauled per day? Where would the
sludge be stored while the truck is traveling to and from the
dump? These are the types of questions the operator must
answer, because they are the problems you will have to solve
when equipment fails. Simple alterations in the design before
facilities are built can make problems caused by equipment
failures easier to solve.
Specific areas of concern for the unit processes described in
this chapter are summarized in Table 22.26.
QUESTION
Write your answer in a notebook and then compare your
answer with the one on page 276.
22.7A List the important items you would consider when re-
viewing plans and specifications.
Of L&&OIO h Of 9 LBttOMv \
OKi
TABLE 22.26 SPECIFIC 0 & M ITEMS CONSIDERED
WHEN REVIEWING PLANS AND SPECIFICATIONS
UNIT PROCESS
RECOMMENDED PROVISIONS
Gravity
Thickening
Dissolved
Air
Flotation
1. Sludge collectors and surface scrapers
are equipped with variable-speed
motors.
2. Sludge withdrawal line is at LEAST 4
INCHES (10 cm) in diameter and valves
are provided on the suction side and dis-
charge side of the sludge withdrawal
pump.
3. A Tee with a valve is provided between
the suction valve described in Item 2 and
the sludge outlet to facilitate back-
flushing in the event of clogging.
4. A valve is provided on the suction side
and discharge side of the influent sludge
pump.
5. Sample taps and valves are provided on
the influent, effluent and sludge with-
drawal lines to facilitate sample collec-
tion.
1. Surface and bottom sludge collectors are
equipped with variable-speed motors.
2. Same as Item 2, Gravity Thickening.
3. Same as Item 3, Gravity Thickening.
4. Same as Item 4, Gravity Thickening.
5. Same as Item 5, Gravity Thickening.
6. A sight glass is provided on the retention
tank.
7. Level indicators in the retention tank are
accessible for cleaning or repairs.
Centrifugation 1. Sludge hoppers are provided with move-
and Filtration able catch troughs to collect and divert
wash water to a common drain.
2. A wash water supply and drains are pro-
vided in the area of sludge conveyors to
facilitate cleaning operations.
3. A permanent wash water line and valve
are provided on the influent to the unit.
4. Same as Item 4, Gravity Thickening.
5. Same as Item 5, Gravity Thickening.
-------
250 Treatment Plants
Chemical 1. Dry chemical feeders are equipped with
Conditioning Infra-red heating lamps to prevent the
absorption of moisture.
2. An eductor-type dry chemical feeder is
provided to serve as standby for automat-
ic feeders.
3. A bulk storage tank is provided for liquid
chemicals.
4. Chemical feed pumps are equipped with
variable-speed motors.
5. The walking areas around chemical sys-
tems are coated with a non-skid type
paint.
Thermal 1. A water softener is provided where ap-
Conditioning propriate to remove hardness from the
boiler make-up water. Also provisions to
de-aerate the water.
2. An acid resistent flushing system should
be incorporated for acid washing of reac-
tors and heat exchangers.
3. Sample taps and valves should be pro-
vided on the influent, high-rate, and de-
cant overflow and underflow lines.
4. The decant tank should be totally en-
closed and equipped with a vent fan.
5. Gas scrubbers and/or carbon absorbers
be provided to clean the vent gases.
6. Same as Item 2, Gravity Thickening.
7. Same as Item 3, Gravity Thickening.
8. Same as Item 4, Gravity Thickening.
DISCUSSION AND REVIEW QUESTIONS
Chapter 22. SLUDGE HANDLING AND DISPOSAL
{Lesson 5 of 5 Lessons)
Write the answers to these questions in your notebook be-
fore continuing. The problem numbering continues from Les-
son 4.
25. Why are chemically stabilized and wet oxidized sludges
generally not suited for compost operations?
26. How would you determine the frequency of turning com-
post stacks?
27. How does incineration reduce the volume of sludge?
28. Where should air be added to the furnace for proper com-
bustion?
29. How can you tell by looking at the flames in the burning
zone how much air is present?
30. What happens if the incinerator shaft speed is too high or
too slow?
31. Why should the disposal or utilization of sludge from di-
gesters without additional treatment be avoided?
32. What are the main reasons for using wastewater solids for
agricultural purposes?
33. What are the advantages of using trucks to spread di-
gested sludge in an agricultural reclamation project?
PLEASE WORK THE OBJECTIVE TEST NEXT.
22.8 METRIC CALCULATIONS
This section contains the solutions to all problems in this
chapter using metric calculations.
22.80 Conversion Factors
ft X 0.3048 =
m
mx 3.281 =
ft
lb x 0.454 =
: kg
kg x 2.205 =
= lb
gal x 3.785 =
liters
liter x 0.264 =
gal
MGDX3785 =
cu m/day
cu m/day x 0.000264 =
= MGD
GPMx0.063 =
L/sec
Usee x 15.85 =
= GPM
1000 L
1 cu m
M
1 kg
22.81 Problem Solutions
The problem numbering in this section is the same as the
numbering of the example problems throughout the chapter.
The numbers are rounded off in the metric system.
EXAMPLE 1. PRIMARY SLUDGE PRODUCTION
Known Unknown
Flow, cu m/day = 6000 cu m/day 1. Dry SS entering plant,
kg/day
Infl. SS, mg//. = 350 mgIL 2. Dry SS leaving primary
clarifier, kg/day
Effl. SS, mgIL =150 mg/L 3. Dry sludge solids pro-
duced, kg/day
-------
Solids Disposal 251
1. Calculate the amount of dry influent suspended solids, kg/
day.
Infl. Susp. = Flow, cu m/day x Susp. Sol, mg/L x
Sol, kg/day
1 kg
1000 L
1,000,000 mg 1 cu m
1 kg
1000 L
= 6000 cu m 350 mg x
day L 1,000,000 mg 1 cu m
= 21,000 kg/day
2. Calculate the amount of dry suspended solids leaving the
primary clarifier, kg/day.
1 kg
1000 L
Prim. Clar. = Flow, cu m SS, mg x
Effl. Susp day L 1,000,000 mg 1 cu m
Sol, kg/day _ 6000 cu m x 150 mg
1 kg
day
= 900 kg/day
1000 L
1,000,000 mg 1 cu m
3. Calculate the amount of dry primary sludge produced, kg/
day.
Primary = Infl Susp Sol, kg/day - Effl Susp Sol, kg/day
kg/day' = 2100 k9/day ~ 900 kg/day
= 1200 kg/day
Flow, cu m x (In SS, mgIL - Effl SS, mg/L) x
1 kg 1000L
OR
Primary
Sludge,
kg/day
day
1,000,000 mg 1 cum
= 6000 cum x / 350 mg - 150 mg \ x
(350 mg - 150 mg \
T T)
1 kg
1000 L
1,000,000 mg 1 cum
= 1200 kg/day
NOTE: All answers are in terms of kilograms of dry solids per
day
EXAMPLE 2. SECONDARY SLUDGE PRODUCTION
Known
Flow, cu m/day
Infl BOD, mgIL
Effl BOD, mg IL
Y, kg SI Sol Prod
Unknown
= 6000 cu m/day 1. BOD Entering, kg/day
= 200 mg/L 2. BOD Leaving, kg/day
= 30 mg/L 3. BOD Removed, kg/day
_ 0.50 kg SI Sol 4. Sludge Prod, kg/day
kg BOD Removed kg BOD
1. Determine the 5-day BOD entering the secondary system,
kg BOD/day.
Entering BOD, = Flow, cum x BOD, mg x 1 kg x 1000 L
kg BOD/day day L 1,000,000 mg 1 cu m
= 6000 cum x 200 mg x 1 kg 1000 L
day L 1,000,000 mg 1 cu m
= 1200 kg BOD/day
2. Determine the 5-day BOD leaving the secondary system,
kg BOD/day.
Leaving BOD, = Flow, cum x
kg BOD/day ^
1 kg
BOD, m£ x
L 1,000,000 mg
_ 6000 cu m x 30 mg x 1 kg x
day
= 180 kg BOD/day
x 1000L
1 cu m
1000 L
1,000,000 mg 1 cum
3. Determine the 5-day BOD removed from the secondary
system, kg BOD/day.
BOD Removed, = Entering BOD, kg BOD/day
kg BOD/day - Leaving BOD, kg BOD/day
= 1200 kg BOD/day - 180 kg BOD/day
= 1020 kg BOD/day
OR
BOD Removed, = Flow, cu m (In BOD, mg/L-Ef BOD, mg/L)
kg BOD/day
day
1 kg
x 1000L
1,000,000 mg 1 cu m
6000 cu m x (200 mg/L - 30 mg/L) x
day
1 kg
1000 L
1,000,000 mg 1 cu m
= 1020 kg BOD/day
4. Determine the secondary sludge produced in terms of kilo-
grams of dry sludge solids per day.
Sludge = BOD Removed, x Y, kg Sl So' Prod/day
Produced, kg BOD/day kg BOD Rem/day
kg dry
solids/day
= 1020 kg BOD/day x 0 50 kg Sl Sol/day
1 kg BOD/day
= 510 kg dry sludge solids/day
Known Unknown
Primary Sludge = 1200 kg/day Primary Sludge Volume,
Quantity, kg/day liters/day
Sludge Solids, % = 5%
Determine the daily primary sludge volume in liters per day.
Primary = Sludge Quantity, kg dry solids/day x 1 liter/kg
Sludge Sludge Solids, %/100%
Volume,
liters/day _ 1200 kg/day x 1 L
5%/100% 1 kg
= 1200
0.05
= 24,000 liters/day x 1 cu m/1000 L
= 24 cu m/day
Known Unknown
Secondary Sludge =510 kg/day Secondary Sludge Volume,
Quantity, kg/day liters/day
Sludge Solids, % = 1.0%
Determine the daily secondary sludge volume in liters per
day.
Secondary Sludge = Sludge Quantity, kg dry solids/day x 1 liter/kg
Volume, Sludge Solids, %/100%
liters/day = 510 kg/day x 1 liter/kg
1.0%/100%
= 51,000 liters/day x 1 cu m/1000 L
= 51 cu m/day
-------
252 Treatment Plants
EXAMPLE 3.
Known
Sludge Solids, % = 3.0%
Sludge Vol,
liters/day
= 8000 liters
day
Unknown
1. Amount of Dry Sludge,
kg/day
2. Thickened Sludge Volume,
liters/day
1. Determine the amount of primary dry sludge withdrawn in
kilograms per day.
Dry Sludge = Sludge Vol, llters x 1 k9 x Sl So1' %
Solids,
kg/day
day 1 liter
8000 liters * 1 k9 x 3 °%
100%
day
= 240 kg/day
1 liter 100%
2. Calculate the new thickened sludge volume in liters per
day.
Sludge Volume,
liters/day
_ Dry Sludge Solids, kg/day x 1 liter
SI Sol, %/100% x 1 kg
= 240 kg/day x 1 liter
5.0%/100% x 1 kg
= 4800 liters/day x 1 cu m/1000 L
= 4.8 cu m/day
EXAMPLE 4.
Known
ThiGkener Diameter, m
Sludge Flow,liters/sec
Blend Flow, liters/sec
Total Flow, liters/sec
6 m
1.25 liters/sec
: 5.00 liters/sec
: 6.25 liters/sec
Unknown
Hydraulic Surface
Loading, cu m per
day/sq m
Determine the flow in cubic meters per day and the water
surface area in square meters. Calculate the hydraulic surface
loading in cubic meters per day per square meter.
Hydraulic _ Total Flow, liters/sec x 86,400 sec/day x i cum
Surface
Loading,
cu m per 4
day/ sq m _ 6.25 liters/sec x 86,400 sec/day x 1 cum
— x (Diameter, m)2 x 1000 L
Z x (6 m)2 x 1000 L
Calculate the solids loading.
Solids
Loading,
kg/day/sq m
Solids Applied, kg/day
Surface Area, sq m
18,900 kg/day
- (14 m)2
4
123 kg/day/sq m
EXAMPLE 6.
Known
Gravity Thickener
Flow, liters/sec
(Primary Sludge)
Infl SS, %
Infl SS, mg/L
Effl SS, %
Effl SS, mg/L
Unknown
Thickener Efficiency, %
= 1.25 liters/sec
= 3.0%
= 30,000 mg/L
= 0.15%
= 1,500 mg/L
Determine the thickener efficiency in removing sludge sol-
ids.
Efficiency, % = (Infl SS, mg/L - Effl SS, mg/L) x 1QQ%
Infl SS, mg/L
= (30,000 mg/L - 1,500 mg/L) x 100%
30,000 mg/L
= 95%
EXAMPLE 7.
Known Unknown
Primary Sludge Cone., % = 3.0% Concentration Factor
Thickened Sludge = 7.0%
Cone., %
Concentration _ Thickened Sludge Concentration, %
Factor
Influent Sludge Concentration, %
_ 7.0% Sludge Solids
3.0% Sludge Solids
= 2.33
_ 540 cu m/day
28.27 sq m
= 19 cu m per day/sq m
EXAMPLE 5.
Known
Thickener Diameter, m =14 meters
liters
6.25 liters
Unknown
Solids Loading,
kg/day/sq m
Sludge Flow,
sec sec
Sludge Solids, % = 3.5%
Determine the solids applied to the thickener in kilograms
per day.
Solids = F, liters x 86 40oi^x Solids- % x 1 k9
Applied,
kg/day
sec
liters
= 6.25
sec
= 18,900 kg/day
day
x 86,400 sec x
100% 1 liter
3.5% x 1 kg
day 100% 1 liter
EXAMPLE 8.
Known
Gravity Thickener
Diameter, m
Side Water Depth, m
Flow In, liters/sec
(Primary Sludge)
= 12 m
= 3 m
Unknown
1. Sludge - Volume Ratio,
days
2. Will sludge blanket
increase or decrease?
Sludge Out, liters/sec = 2.5 LIs
Primary Sludge Con., % = 3.5%
Sludge Out Cone., % = 7.0%
: 6.25 L/s 3. What changes would
increase underflow sludge
concentration?
Thickener Effluent
Susp Sol, mg/L
%
Sludge blanket, m
= 700 mg/L
= 0.07%
= 1 m
4. What changes would stop
gasification? How would
these changes affect
thickened sludge concen-
trations?
-------
Solids Disposal 253
1. Calculate the Sludge - Volume Ratio (SVR) in days,
a. Determine the sludge blanket volume in cubic meters.
Sludge
Blanket
Volume,
cu m
-x (Diameter, m)2 x Blanket, m
-x (12 m)s x 1 m
= 113 cu m
Determine the sludge pumped in cubic meters per day.
Sludge = Sludge Out, x eoHOLx 1440^;
1 cu m
Pumped,
cu m/day
2.5 lilers x 60
sec
sec
min
min
x 1440-
sec min day
= 216 cu m/day
day 1000L
1 cum
1000/.
c. Calculate the Sludge - Volume Ratio (SVR) in days.
SVR days = Slud9e Blanket Volume, cu m
Sludge Pumped, cu m/day
113 cum
216 cu m/day
= 0.5 days
2. Will the sludge blanket increase or decrease? If the quan-
tity of solids entering the thickener is greater than the
quantity exiting the thickener, then the blanket depth will
increase. If the quantity of solids entering the thickener is
less than the quantity exiting the thickener, the blanket
thickness will decrease. The solution to this problem is
based on mass balance calculations, as shown below:
a. Determine the kilograms of sludge solids entering the
thickener daily.
Sludge = Flow In,
liters
sec
: 86,400_??5_ x 1 k9 x Sl ln' %
Solids sec day 1 L 100%
Entering,
k9/daV = fi ^liters x Rfi 4nn sec y 1 kg v 3.5%
sec day 1L 100%
= 18,900 kg/day
b. Determine the kilograms of sludge solids withdrawn in
the thickener underflow daily.
Sludge = Sludge Out,lilers x Bfi,4nn sec x 1 **9 x SI Out %
Solids sec day 1 L 100%
Withdrawn,
kg/day = 2.5 litefS x 86,400-£££. x 1 x 7 0%
sec day 1 L 100%
= 15,120 kg/day
c. Determine the kilograms of solids lost in the thickener
effluent daily.
Solids = Flow. I*!™ X 86,400^ x U
-------
254 Treatment Plants
1, Calculate the sludge solids entering in kilograms per min-
ute.
Solids
Entering,
kg/min
= Infl Flow, x 60
sec
sec x 1 kg y SI Sol In, %
x _L_^ x
min 1 L
100%
= 10 L x 60 sec x
1 kg x 3.0%
sec
= 18 kg/min
min
1 L
100%
2. Calculate the sludge solids leaving the thickener in kilo-
grams per minute.
Solids = Underflow, ^xeoi^xl^x Unfl Sl- %
Withdrawn, sec mjn 1L 100o/o
kg/min
= 1 L x 60 sec x 1 x 6-0%
sec min 1 L 100%
= 3.6 kg/min
The number of kilograms exiting with the effluent can be
neglected if effluent is clear and no solids carryover is ob-
served.
Based on the visual estimations of sludge concentration and
the above calculations, sludge is being stored at the rate of
14.4 kg/min (kg enter - kg exit). The sludge blanket thickness
is 0.5 meter but let us assume typical operation for this thick-
ener indicates that a blanket thickness of 1.5 meters can be
maintained. The operator should therefore determine the time
required to fill the thickener with 1.0 additional meters of sludge
at the present conditions. The calculations are shown below:
Storage
Time, min
Storage
Volume, cu m
1000 kg Unfl SI %
1 cu m
100%
Sludge Storage Rate, kg/min
(12 mf
x 1 m x 1000 kg x 6.0%
1 cu m
100%
14.4 kg/min
Storage
Time, hrs
= 470 min
_ 470 min
60 min/hr
= 7.8 hours
If the unit is left as is, the blanket will reach a thickness of 1.5
meters in approximately 8 hours. When the storage volume is
full, that is, 1.5 meters sludge thickness, problems may arise if
the withdrawal rate is not increased at that time because
sludge will continue being stored. To avoid drastic changes in
the withdrawal rates, the operator should make a slight ad-
justment at this time. The adjustment should be made based
on the ratio of volume stored to total storage volume as shown
below.
Sludge _ (Stored Sludge Height, m) x Solids Entering,
Storage -j-ota| storage Height, m) kg/min
H3t0,
kg/min _ 0.5 m x 18 kg/min
1.5 m
= 6 kg/min
We, therefore, want to store solids at a rate of 6 kg/min
instead of the current 14.4 kg/min. To obtain this storage rate,
the desired sludge withdrawal rate must be determined in
kilograms per minute.
Sludge = Solids Entering, - Sludge Storage
Withdrawal kg/min Rate, kg/min
R
-------
Solids Disposal 255
NOTE: The conversion factor of 1.20 kilograms of air per cubic
meter of air will change with temperature and elevation
or pressure.
The ratio of air supplied to quantity of solids applied to the
flotation unit is then the air-to-solids (A/S) ratio. The following
example illustrates the determination of air/solids (A/S) ratio.
Unknown
Air-to-Solids (A/S)
Ratio
EXAMPLE 12.
Known
Solids Flow, L/sec = 6.25 L/sec
SI Cone, mg/L = 9000 mg/L
= 0.9% Solids
Air, cu m/min = 0.15cum/min
Calculate the air-to-solids (A/S) ratio.
Air, kg Air, cu m/min x 1.20 kg/cu m
Solids, kg Solids, L_ x 1 kg x SI Cone, % x 60 sec
sec L 100% min
0.15 cu m/min x 1.20 kg/cu m
6.25 L 1 kg 0.9% v 60 sec
min
Unknown
Percentage of recycle.
x
sec L 100%
_ 0.18 kg air
3.375 kg solids
= 0.05 kg air/kg solids
EXAMPLE 13.
Known
Waste Flow, L/sec = 3.0 LI sec
Recycle Flow, = 4.5 L/sec
LI sec
Calculate the percentage of recycle.
Recycle, % = jeeyele Flow, L/sec x 1Q0%
Waste Flow, L/sec
= 4-5 L/sec x 1 oo%
3.0 L/sec
= 150%
EXAMPLE 14.
Known Unknown
Dissolved Air Flotation Unit Solids Removal Efficiency, %
EnfJ Solids, mg/L = 7500 mgIL
Effl Solids, mg/L = 50 mg/L
Determine the solids removal efficiency, %.
Solids Removal = (|nfl Solids, mg/L - Effl Solids, mg/%) x iqq%
Efficiency, % Infl Solids, mg/L
_ (7500 mg/L - 50 mg/L) 100%
7500 mg/L
= 99.3%
EXAMPLE 15.
Known
Scroll Centrifuge
Flow, cu m/day = 480 cu m/day
Sludge Solids,
mg/L
%
8,000 mg/L
0.80%
Unknown
1. Hydraulic Load,
cu m/hr
2. Solids Load,
kg SI Sol/hr
Determine the hydraulic load in cubic meters per hour.
Hydraulic _ Flow, cu m/day
Load' cu m/hr 24 hr/day
_ 480 cu m/day
24 hr/day
= 20 cu m/hr
Calculate the solids load in kilograms of sludge solids per
hour.
Solids Load, = F|ow cu m/hf x 1000 kg x SI Sol, %
kg/hr
cu m
_ 2q cu m x 1000 kg x 0.80%
100%
hr
160 kg/hr
cu m
100%
EXAMPLE 16.
Known
Basket Centrifuge
Flow, L/sec
Sludge Solids, %
Run time, min
Skimming Time, min
= 3 L/sec
= 0.8%
= 20 min
= 1.5 min
Unknown
1. Hydraulic Load, liters/hr
2. Solids Load, kg/hr
1. Determine the hydraulic load in liters per hour.
Hydraulic _ liters
Load, ~ 1
liters/hr SBC
Run "Hme, min
_ X 3600 _
Run Time, min + Skm Time, Min hr
= 3
liters
sec
x 3600 _
(20 min + 1.5 min) hr
- 10,047 liters/hr x 1 cu m/1000 liters
= 10 cu m/hr
If the unit were fed continuously at a rate of 3 liters per
second, the hydraulic loading rate would be 10,800 liters/hr (3
liters/sec x 3600 sec/hr).
2. Calculate the solids load in kilograms of sludge solids per
hour.
Solids Load, _ Plnu. cum 1000 kg SI Sol, %
kg/hr ' F,0W'1T
_ 1Qcu m x 1000 kg x 0.8%
hr cu m 100%
= 80 kg/hr
EXAMPLE 17.
Known
Unknown
1.2 meter diameter basket centrifuge 1. Time required to fill
storage volume, min
Flow, L/sec = 3 L/sec
Infl Solids, % = 0.75%
Basket Solids, % = 7.0%
Solids Storage, = 0.5 cu m
Volume, cu m
1. Calculate the amount of stored solids in kilograms.
Solids, kg = Storage Vol, cu m x 1000 ^9 * Bkt Sol. %
cu m 100%
= 0.5 cu m x 1000 k9 x 7 0%
cu m 100%
= 35 kg
Therefore, under these conditions the centrifuge could
store 35 kilograms of dry solids.
-------
256 Treatment Plants
2. Determine the time required to fill the storage volume or the
feed time in minutes.
Feed time, min =
Stored Solids, kg
Flow, liters x I kg x 60 sec x Infl Sol, %
sec L min
35 kg
100%
I kg x 60 sec x 0.75%
L m
100%
3 liters x
sec
35 kg
1.35 kg/min
= 26 minutes
For the conditions given in the above example, feed times
less than 26 minutes will result in wetter discharge solids and
feed times greater than 26 minutes will result in poor effluent
quality.
EXAMPLE 18.
Known Unknown
0.6-meter diameter by 1.5-meter long Sludge Solids Removal
scroll centrifuge Efficiency, %
Flow, liters/sec = 80 Usee
Infl SS, % = 0.80%
mgIL = 8,000 mg/Z.
Effl SS, % = 0.20%
mg IL = 2,000 mg IL
Determine the sludge solids removal efficiency as a percent.
Efficiency, % = (|nfl SS, % - Effl SS, %) x 1QQ%
Infl SS, %
= (0.80% - 0.20%) x 1QQ%
0.80%
= 0.60 x 1QQ%
0.8
= 75%
EXAMPLE 19.
Known Unknown
1.2-meter diameter basket centrifuge Average Total Thickened
Sludge Solids Re-
moved, %
Storage Volume, = 0.5 cu m
cu m
Infl SI Sol, % = 0.80%
mgIL = 8,000 mg//.
Skimmed Vol, cu m= 0.4 cu m
Skimmed SI, % = 4.0%
Knife Vol, cu ft = 0.1 cu m
Knife Solids, % = 7.5%
Calcuate the average thickened sludge solids as a percent.
Thickened = Sk Vo1, cu m x sk Sl- % + Kn Vol> cu m x Kn Sol, %
Sludge, % Sk Vol, cu m + Kn Vol, cu m
0.4 cu m x 4.0% + 0.1 cu m x 7.5%
0.4 cu m + 0.1 cu m
1.6 + 0.75
0.5
4.7%
You must realize that this mathematical calculation assumes
perfect mixing of the skimmed and knifed solids. In actual prac-
tice perfect mixing is very difficult to achieve.
Unknown
Digestion Time, days
Effect of Increasing Sludge
Solids to 3.5%
EXAMPLE 20.
Known
Aerobic Digester
Diameter, ft = 12 m
Depth (SWD), ft = 3 m
Flow, cu m/day = 40 cu m/day
Thickened Sludge,
% = 2.5% Sludge Solids
mg IL = 25,000 mgIL
1. Calculate the digestion time in days.
a. Calculate the digester volume.
Volume, = JL* (Diameter, m>2 x SWD, m
cu m 4
= —X (12 m)2 x 3 m
4
= 339 cu m
b. Determine the digestion time in days.
Digestion = Digestion Volume, cu m
Time, days Flow, cu m/day
_ 339 cu m
40 cu m/day
= 8.5 days
2. Determine the effect of increasing the sludge solids from
2.5 percent to 3.5 percent sludge solids. The total sludge
volume pumped to the aerobic digester will be decreased
and the digestion time will be increased. Calculate the new
digestion time in days.
a. Determine the new flow to the aerobic digester in cubic
meters per day.
Flow GPD = ^'ow at 2-5% SS, cu m/day x SS, %
SS, %
= 40 cu m/day x 2.5%
3.5%
= 28.6 cu m/day
b. Calculate the new digestion time.
Digestion = Digester Volume, cu m
Time, days
Flow, cu m/day
339 cu m
28.6 cu m/day
= 11.9 days
The overall impact of thickening the sludge to 3.5 percent
sludge solids is an increase in digestion time and a potential
increase in digester efficiency.
EXAMPLE 21.
Known
Aerobic Digester
Diameter, m = 12 m
Depth (SWD), m = 3 m
Flow, cu m/day = 28.6 cu m/day
Sludge Solids, % = 3.5%
Volatile Matter, % = 75%
Unknown
Volatile Sludge Solids
Loading, kg VSS/day/
cu m
-------
Solids Disposal 257
Volume,
cu m
Calculate the volatile sludge solids (VSS) loading in kilo-
grams of VSS per day per cubic meter of aerobic digester.
a. Determine the digester volume in cubic meters,
jr x (Diameter, m)2 x Depth, m
4
_ tt x (12 m)2 x 3 m
4
= 339 cu m
b. Calculate the volatile sludge solids (VSS) loading in kilo-
grams of VSS per day per cubic meter.
VSS Loading, _ VSS Added, kg/day
kg VSS/day/cu m 0jgester volume, cum
Flow, cu m x 1000 kg x SS, % x VM, %
day cu m 100% 100%
Digester Volume, cu m
28.6 cu m x 1000 kg x 3.5% x 75%
day cum 100% 100%
339 cu m
= 750 kg VSS/day
339 cu ft
= 2.2 kg VSS/day/cu m
EXAMPLE 22.
Known
Aerobic Digester
Air Required,
cu m per min/cu m
Length, m
Width, m
SWD, m
Unknown
Air Rate, cu m/min
_ 0.040 cu m/min
cu m digester
= 30 m
= 8 m
= 3 m
Determine the rate of air that must be delivered to the
aerobic digester in cubic meters of air per minute.
a. Calculate the digester volume in cubic meters.
Digester = Length, m x Width, m x SWO, m
Vol, cu m
= 30mx8mx3m
= 720 cu m
b. Determine the rate of air that must be supplied in cu
m/min.
Air Rate, _ Air Required, cu m/min air x Dig. Vol, cu m
cu m/m cu m digester
= 0.040 cu m air/min x 720 cu m
cu m digester
= 28.8 cu m air/min
EXAMPLE 23.
Given: An operator measures the dissolved oxygen (DO) con-
centration with time on an air-saturated sample taken
from an aerobic digester. The following measurements
were recorded:
Time
0 Min
1 Min
2 Min
3 Min
4 Min
5 Min
D.O. (mg/i.)
7.1
6.0
5.2
4.5
3.9
3.2
Find: The oxygen uptake in mg/L/hr.
Solution:
Unknown
Oxygen Uptake, mg/L/hr
Known
Aerobic Digester
DO Measurements with Time
for an Air Saturated Sample
Calculate the oxygen uptake for the air-saturated sample
from an aerobic digester in mg/L/hr. Generally the 2-minute
DO reading is used in order to allow the DO probe and the
sample time to stabilize. The 5-minute DO reading also is used
in the calculation.
Oxygen Uptake,
mgJL/hr
_ (DO,, mg/L - D02, mg/L) x 60 min
(Time2, min - Time,, min) hr
_ (5.2 mg/L - 3.2 mg/L) x 60min
(5 min - 2 min) hr
_ 2.0 mg/L x 60min
3 min hr
= 40 mg/L/hr
EXAMPLE 24
Known
Aerobic Digester
Flow, cu m/day
Sludge Sol In, %
Vol Sol In, %
Sludge Sol Out, %
Vol Sol Out, %
: 34 cu rn/day
^ 3.6%
74%
2.6%
64%
Unknown
1. Sludge Solids In, kg/day
Volatile Solids In, kg/day
2. Sludge Solids Out, kg/day
Volatile Solids Out, kg/day
3. Sludge Solids Removal Eft, %
4. Volatile Solids Removal Eff, %
1. Determine the sludge solids and volatile solids entering the
aerobic digester in kilograms per day.
Sludge Solids
Entering,
kg/day
Flow cu m x 1000 k9 x ss ln- %
day
cu m
100%
Volatile
Solids
Entering,
kg/day
= 34 cu m x 1000 k9 v 3-6%
day cu m 100%
= 1,224 kg SS/day
= Sludge Solids, M. x VSS' %
day 100%
= 1.934 k9 ss x 74%
day 100%
= 906 kg VSS/day
2. Calculate the sludge solids and volatile solids exiting the
aerobic digester in kilograms per day.
Sludge Solids = n™, cumx 1000kgy SS Out. %
Exiting,
kg/day
day
cu m
100%
Volatile
Solids
Exiting,
kg/day
= ™ cu m * 1000 k9 y 2.6%
day cu m 100%
= 884 kg SS/day
= Sludge Solids, x vss- %
day 100%
= 884
kg SS v 64%
day 100%
= 556 kg VSS/day
-------
258 Treatment Plants
3. Calculate the efficiency of the sludge solids destruction as a
percent.
SS Destruction =
-------
Solids Disposal 259
This example illustrates the need to equate polymers on a
cost per kg of solids ($/kg) basis rather than on a gram of
product per kg of solids (gm/kg) basis. Even though more
grams of Product B were required, it yielded a lower cost than
Product A.
Unknown
Dry Polymer Added, kg
EXAMPLE 28.
Known
Volume of Solution, = 100 liters
liters
Polymer Solution, % = 0.1%
Determine the kilograms of dry polymer to be added by set-
ting up the problems as a proportion.
Polymer Solution, % _ Dry Polymer, kilograms
100%
Vol of Sol, liters x 1 kg/liter
Dry Polymer, kg
100 liters x 1 kg/liter
Rearrange the terms in the above equation and solve for the
kilograms of dry polymer.
Dry Polymer, kg = 100 liters x 1 ki x
liter 100%
= 0.10 kg of Dry Polymer
In the above example, if 0.10 kilograms of dry Polymer are
mixed with 100 liters of water, the solution strength would be
0.10 percent.
EXAMPLE 29.
Known
Unknown
Volume of Solution, L = 2000 liters Strength of Polymer
Solution, %
Dry Polymer Added, kg = 3 kg
Calculate the strength of the polymer solution as a percent.
Polymer Solution, % = Dry Poiymer Added, kg x 100%
Vol of Sol, liters x 1 kg/liter
= 3 kg polymer x 1£)0%
2000 liters x 1 kg/liter
= 0.15%
EXAMPLE 30.
Known
Lime Solution
Lime Dose, kg = 100 kg
Water Volume, = 400 liters
liters
Unknown
Strength of Lime Solution, %
Calculate the strength of the lime solution as a percent.
Lime Solution, % = Dry Lime Dose, kg x 1QQ%
Volume of Water, liters x 1 kgIL
= 100 kg lime 1Q0%
400 liters water x 1 kg/L
= 25%
EXAMPLE 31.
Known
Liquid Polymer, liters = 20 liters
Volume Water, liters = 1500 liters
Unknown
Strength of Polymer
Solution, %
Calculate the strength of the polymer solution as a percent.
Poiymer = Liquid Polymer, liters y 100o/o
Solution, % Total Volume, liters
_ 20 liters
-x 100%
1500 liters
= 1.33%
EXAMPLE 32.
Known Unknown
Quantity and Cost of Polymer
A and Polymer B
Sludge Solids, % = 2%
mgIL = 20,000 mgIL
Polymer A Is a dry powder
0.05 to 0.25 percent solution.
Calculate the dry polymer dose in grams.
Dry Polymer, grams = Volume,/, x 1000 9m x Solution, %
L 100%
Jar Tests Run on Polymers
A and B
= 1 L x 1000 9m x °-10%
L 100%
= 1.00 grams
Therefore, 1.00 grams of dry polymer mixed with 1 titer of
water will produce 0.10 percent polymer solution.
Calculate the liquid polymer dose in milliliters.
Liquid Polymer, ml = Volume, L x 1000 ml x Solution, /o
100%
= If. X1000 ml X 25%
100%
= 25 ml
Determine the amount of water to be mixed with the liquid
polymer.
Volume Water, ml = Total Volume, ml - Liquid Polymer, ml
= 1000 ml - 25 ml
= 975 ml
Therefore, 25 ml of liquid polymer mixed with 975 ml of water
will produce a 2.5 percent solution.
POLYMER A (DRY)
Determine the dosage of Polymer A in grams of polymer per
kilogram of sludge solids treated.
Dosage, 9H = So1' % x p°'y™r-ml x U™
kg 100% (Added) m|
SI Vol, L x JJ
-------
260 Treatment Plants
POLYMER B (LIQUID)
Dosage 9m = So1' % x Po|ymer Added, ml
1. Calculate the reactor detention time in minutes.
kg
SI Vol, L x SI Sol, %
2.5 x 50
1.0 x 2.0
= 62.5 gm liquid Polymer/kg sludge solids
Calculate the cost per kg to use Polymer A if the dry Polymer
costs $1.00 per kilogram.
Cost,
$1.00
$ _ 2.5 gm Polymer x
kg kg sludge solids kg Polymer
= $0.0025/kg sludge solids
1 kg
1000 gm
Calculate the cost per kg to use Polymer B if the liquid
Polymer costs $0.11 per kilogram.
Cost,
$0.11
$ _ 62.5 gm Polymer x
kg kg sludge solids kg Polymer
- $0.0069/kg sludge solids
1 kg
1000 gm
EXAMPLE 33.
Known
Waste Activated Sludge
Sludge Flow, liters/sec
SI Sol, %
. mg/L
Polymer Flow, liters/sec
Polymer Solution, %
= 18 LI sec
= 0.90%
= 9,000 mg/L
= 1.2 L/sec
= 0.05%
Unknown
1. Kilograms of dry
polymer to be mixed
with 20 cubic meters of
water to produce a 0.05
percent polymer solu-
tion.
2. Dosage in grams
polymer per kilogram of
sludge solids.
1. Determine the kilograms of dry polymer to be mixed with 20
cubic meters of water to produce a 0.05 percent polymer
solution.
Dry Polymer = Polymer Sol, % x Vol, cu m x 1000 kg/cu m
Required, kg 100%
_ 0.05% x 20 cu m x 1000 k9
100% cu m
= 10 kg
2. Calculate the dosage in grams of polymer per kilograms of
sludge solids.
Dosage = ®0'' % x P°'ymer Added, LIsec x 1000 gm
kg
SI Flow, L/sec x SI Sol, %
_ 0.05% x 1.2 L/sec x 1000 gm
18 L/sec x 0.9% kg
= -a 7 gm polymer
kg sludge solids
kg
EXAMPLE 34.
Known
Thermal Conditioning System
Treat Waste Activated Sludge
WAS Flow, L/sec = 12 L/sec
Reactor Vol, cu m = 30 cu m
Sludge Solids, % = 3.5%
Unknown
Reactor Detention Time
Reactor Detention Time if
Solids at 2.5%
Detention
Time, min
= Reactor Volume, cumx 1000 L 1 min
Flow Usee cu m 60 sec
= 30cumx 1000/. x 1 min
12 LI sec cu m SO sec
= 42 min
2. Calculate the reactor detention time if the sludge solids
concentration drops from 3.5% to 2.5%. A reduction in sol-
ids concentration causes an increase in WAS flow.
New Flow,
L/sec
Detention
Time, min
= Old Flow, L/sec x Qld Sl So1' %
New SI Sol, %
= 12 L/sec
2.5%
= 16.8 L/sec
_ Reactor Volume, cu m
Flow, L/sec cu m
x 1000 L x 1 min
60 sec
_ 30 cu m
16.8 L/sec
= 30 min
x 1000 L x 1 min
cu m 60 sec
EXAMPLE 35.
Known
Plate Area, sq m
SI Sol, %
Filtration Time,
hrs
Sludge Volume, L
Discharge and
Restart, min
= 10 sq m
= 3.0%
= 2 hrs
= 2500 liters
= 20 min
Unknown
1. Solids Loading, kg/hr/sq m
2. New Filter Yield, kg/hr/sq m
3. If solids drop to 2% SI Sol,
what problems might
devetopl
Calculate the solids loading in kilograms per hour per
square meter.
Solids
Loading,
kg/hr/sq m
SI Vol, liters x 1 k9 x Sl So1- %
liter
100%
Filt Time, hr x Area, sq m
2500 liters * 1 kg * 3 0%
liter 100%
2 hr x 10 sq m
3.75 kg/hr/sq m
2. Calculate net filter yield in kilograms per hour per square
meter.
Net Filter
Yield,
kg/hr/sq m
Loading, k9^f x Filt Time, min
sq m
Filt Time, min + Down Time, min
_ 3.75 kg/hr/sq m x 120 min
120 min + 20 min
= 3.21 kg/hr/sq m
3. What would happen if the feed concentration decreased to
2 percent sludge solids?
If the feed solids concentration decreases to 2 percent
sludge solids, the cake MAY be wetter upon discharge if the
filtration time is not increased. The operator should check the
filtrate flow and adjust the filtration time so that the filtrate flow
is near zero when the feed pump is turned off.
-------
Solids Disposal 261
Unknown
Hydraulic Loading,
liters per sec/m
EXAMPLE 36
Known
Belt Filter Press
Belt Width, m = 2 m
Flow, liters/sec = 6 liters/sec
SI Sol, % = 5%
Determine the hydraulic loading in liters per second per me-
ter.
Hydraulic _ Flow, liters/sec
Loading,
Llslm
Belt Width, m
_ 6 liters/sec
Unknown
1. Filter Loading,
kg/hr/sq m
2. Filter Yield,
kg/hr/sq m
2 m
= 3 liters per sec/m
EXAMPLE 37.
Known
Vacuum Filter
Diameter, m = 2 m
Length, m = 4 m
Surface Area, sq m = 25 sq m
SI Sol Loading, = 2000 kg/day
kg/day
Filter Operation, = 7 hrs/day
hrs/day
Drum Cycle Time, = 3 min
min
Dewatered Sludge = 25%
Sol, %
Solids Recovery, % = 95%
Calculate the filter loading in kilograms per hour per square
meter.
Filter
Loading,
kg/hr/sq m
SI Sol Loading, kg/day
Fil Operation, hrs/day x Area, sq m
= 2000 kg/day
7 hrs/day x 25 sq m
= 11.4 kg/hr/sq m
Calculate the filter yield in kilograms per hour per square
meter.
SI Sol Loading, J^x "ecov, %
Filter Yield, = ^ 1Q0%
kg/hr/sq m Fil Op, hr/day x Area, sq m
ponn k9 x 95%
= day 100%
7 hr/day x 25 sq m
= 10.9 kg/hr/sq m
EXAMPLE 38.
Known
Information given in Example 37.
If drum cycle time reduced to 2 min,
Dewatered SI Sol, % = 30%
Solids Recovery, % = 35%
Filter Yield, = 5.5 kg/hr/sq m
kg/hr/sq m
Unknown
Time filter must be op-
erated in hours.
Calculate the time the filter must be operated to process
2000 kilograms per day of primary sludge solids.
SI Sol Loading, _k9 x Recov' °/o
Filter Yield, = daY 100%
kg/hr/sq m Fil Op, hr/day x Area, sq m
Rearrange the terms.
SI Sol Loading, k9 x Recov, %
Filter Opera- = day
100%
tion, hr/day
Fil Yield, kg/hr x Area, sq m
2000
kg
sq m
95%
day 100%
5.5 kg/hr x 25 sq m
sq m
= 13.8 hours/day
Therefore, the filter must be operated for 13.8 hours per day
to produce a dewatered sludge cake of 30 percent solids when
using a 2-minute cycle time.
EXAMPLE 39
Known
Two Sand Beds
Length, m
Width, m
SI Depth, cm
SI Depth, cm
Drying Time
Bed A, days
Bed B, days
Sludge Removal,
days
Sludge Solids, %
60 m
8 m
8 cm (Bed A)
24 cm (Bed B)
6 days
21 days
1 day
Unknown
1. Sludge Applied, cu
m/application and
kilograms/application
for both Beds A and B.
2. Loading Rates, kg/yr/
sq m for both Beds A
and B.
3. Which application
depth should be used?
= 3%
1. Determine the sludge applied in cubic meters per applica-
tion and kilograms per application for both Beds A and B.
BED A
Sludge Applied,
cu m/appli.
_ L, m x w, m x D, cm/apl
100 cm/m
60mx8mx8 cm/apl
100 cm/m
= 38.4 cu m/application
Sludge Applied, = SI Appl, x 1000 *9 x Sl So'- %
kg/appli. apl cu m 100%
_ ± cu m x 1000 kg y 3.0%
apl cu m 100%
= 1,152 kg/application
BED B
Sludge Applied, = L- m * W. m x D, cm/apl
cum / 100 cm/m
application ^ 60 m x 8 m x 24 cm/apl
100 cm/m
= 115.2 cu m/application
-------
262 Treatment Plants
Sludge Applied, = SI Appl, cu m x
1000 kg SI Sol, %
kg/appli.
apl
cu m
100%
115.2
cum x 1000 kg x 3.0%
100%
apl cu m
= 3,456 kg/application
2. Determine the loading rates for the sludge applied in kilo-
grams per year per square meter for both Beds A and B.
BED A
Loading Rate, =
kg/yr/sq m
SI Appl, kg/apl x 365 days/yr
L, m x W, m x Cycle, days/apl
1152 kg/apl x 365 days/yr
60 m x 8 m x (6 days + 1 day)/apl
= 125 kg/yr/sq m
BED B
Loading Rate, = SI Appl, kg/apl x 365 days/yr
kg/yr/sq m L, m x W, m x Cycle, days/apl
_ 3456 kg/apl x 365 days/yr
60 m x 8 m x (21 days + 1 day) apl
= 119 kg/yr/sq m
3. Which application depth should be used?
Based on the data given and the above analysis, there is no
substantial difference in the amount of solids that can be
applied per year for application depths of 8 centimeters and 24
centimeters.
The operator should choose the 24-centimeter application
because it will result in less operator time. An 8-centimeter
application would require the operator to refill and possibly
remove solids every 7 days while a 24-centimeter application
will require operator attention every 22 days.
EXAMPLE 40.
Known
Flow, cu m/day
Sludge, kg/day
(dewatered
digested
sludge)
Dewatered SI Sol, %
Final Compost, %
Unknown
= 20,000 cu m/day Kilograms of compost
= 2,000 kg/day
= 30% solids
= 30% moisture
(70% solids)
blended daily with
dewatered sludge
to produce a mix-
ture with 50% mois-
ture content.
Determine the moisture content of the dewatered sludge.
Sludge = 100% - Dewatered SI Sol, %
Moisture, % = 100% _ 30%
= 70%
Calculate the kilograms of compost that must be blended
daily with the dewatered sludge to produce a mixture with 50
percent moisture content.
Sludge, kg/day * SI Moist, % + Comp, kg/day x C Moist, %
Mixture
Moisture. %
Rearranging terms.
Compost,
kg/day
Sludge, kg/day x SI M, % - Sludge, kg/day x Mix M, %
Mix M, % - Comp. M. %
2000 kg/day x 70% - 2000 kg/day x 50%
50% - 30%
2000 kg/day (70% - 50%)
50% - 30%
= 2000 kg/day
EXAMPLE 41.
Known Unknown
Flow, cu m/day = 20,000 cu m/day Kilograms per day of com'
Sludge, kg/day = 1200 kg/day
post to produce an ini-
tial mixture of 50%.
(dewatered digested
secondary sludge)
Dewatered = 17% solids
Sludge, %
Final Compost, % = 30% moisture
Calculate the kilograms per day of compost that must be
recycled to produce an initial mixture of 50 percent.
Sludge
Mixture, %
Compost,
kg/day
100% - Dewatered SI Sol, %
17%
100%
83%
Sludge, kg/day :
SI M, % - Sludge, kg/day x Mix M,«
1200-!51 x 83%
day
Mix M, % - Comp. M,e
^9 v crv»/_
1200-
day
= 1200 kg/day.
50% - 30%
(83% - 50%)
= 1980 kg/day
From Section 22.6202, Agricultural Reclamation.
Known
Crop Nitrogen
Demand, kg/ha
N Content, %
N Mineralization
N Loss
or N Remain
= 448,000 kg/ha
= 6%
= 67%
= 25%
= 75%
Unknown
Sludge Application Rate,
dry kg/ha/yr
Calculate the sludge application rate in kilograms of dry
sludge solids per hectares per year.
Sludge
Application
Rate, dry
kg/ha/yr
Annual Crop Nitrogen Demand, kg/ha
N Content, % x N Mineral, % x N Remain, %
448,000 kg/ha/yr
x 67% x 75%
Sludge, kg/day + Compost, kg/day
6%
100% 100% 100%
_ 448,000 kg/ha/yr
0.06 x 0.67 x 0.75
= 14,860,000 dry kg sludge/ha/yr
-------
Solids Disposal 263
SUGGESTED ANSWERS
Chapter 22. Sludge Handling and Disposal
Answers to questions on pages 134 and 135.
22.0A The two types of sludges produced at a wastewater
treatment facility are primary sludge and secondary
sludge. Primary sludge includes all the solids which
settle to the bottom of the primary sedimentation basin
and are removed from the waste stream. Primary
sludges are usually fairly coarse and fibrous, have
specific gravities greater than water and are com-
posed of 70 to 80 percent volatile matter. Secondary
sludge is generated as a by-product of biological de-
gradation of organic wastes. Secondary sludges are
finer than primary sludge solids, less fibrous, have
specific gravities closer to that of water, and consist of
75 to 80 percent volatile matter.
22.OB Volumes of primary sludge depend on inflow, influent
suspended solids, and efficiency of the primary
sedimentation basin.
22.0C Known
Flow, MGD
Influent SS, mgIL
Effluent SS, mg/L
= 2.0 MGD
= 200 mgIL
= 120 mg/L
Unknown
Sludge, lbs/day
Determine the quantity of primary sludge in pounds
per day.
Primary = Flow, MGD x (Infl SS, mg/L - Effl. SS mgIL) x 8.34 lbs/gal
" 20 MGD * <200 m9"- "" 120 "WW * 8 34 lbSj'9al
= 2.0 MGD x 60 mgIL x 8 34 lbs/gal
= 1,335 lbs/day
22.0D Variables that influence the production of secondary
sludges include the flow to the biological system, the
BOD loading to the biological system, the efficiency of
the biological system in removing BOD, and the
growth rate of the bacteria in the system.
22.0E Known
Flow, MGD
Sec. Infl BOD, mg/L
Sec. Effl BOD, mgIL
Growth Rate, Y,
Unknown
Sec. Sludge, lbs/day
= 2.0 MGD
= 180 mg/L
= 30 mg/L
lbs SI _ 0.5 lbs sludge
1 lb BOD removed
lb BOD rem
Estimate quantity of secondary sludge in pounds per
day.
Sec. Sludge,
lbs/day
Flow, MGD x (Infl BOD, mgIL - Effl Bod, mg/i.) x
8.34 lbs/gal x
0.S lbs sludge
1 lb BOD removed
2.0 MGD x (180 mgIL - 30 mg/L) x 8.34 lbs/gal x 0.5
1,251 lbs/day
22.OF Known Unknown
Conditions in Problem 22.0E Sludge, gal/day
Sludge, lbs/day = 1335 lbs/day
Susp Solids, % = 4.0%
Estimate the primary sludge volume in gallons per
day.
Sludge, = Sludge, lbs/day
gal/day 8.34 lbs/gal x (Solids, %/100%)
1335 lbs/day
8.34 lbs/gal x (4.0%/100%)
= 4,002 gallons/day
Answers to questions on page 135.
22.1 OA The primary function of sludge thickening is to re-
duce the sludge volume to be handled in subsequent
processes.
22.10B Known Unknown
Sec. Sludge, gal/day = 12,000 gal Dry Sludge, lbs/day
Solids Cone., % = 1.0%
Determine the amount of dry sludge in pounds per
day.
Dry = Sludge, gal/day x 8.34 lbs/gal x Solids Cone., /«
Sludge, 100%
lbs/day 1%
= 12,000 gal/day x 8.34 lbs/gal x
100%
= 12,000 gal/day x 8.34 lbs/gal xo.01
= 1,000 lbs/day
22.10C Known Unknown
Sec. Sludge, lbs/day = 1000 lbs/day Sludge Volume,
Solids Cone., % = 1.5% gal/day
Determine sludge volume in gallons per day.
Sludge Vol,= Sec. Sludge, lbs/day
gal/day 8.34 lbs/gal x Solids Cone., %
100%
1000 lbs/day
8.34 lbs/gal x 1.5%
100%
= 8,000 gal/day
-------
264 Treatment Plants
Answers to questions on page 140.
22.11 A Main components of gravity thickeners include:
1. Inlet and distribution assembly,
2. Sludge rake,
3. Vertical steel members or "pickets" mounted on
the sludge rake,
4. Effluent or overflow weir, and
5. Scum removal equipment.
2.11B 1. The inlet baffle causes the influent to flow down-
ward towards the bottom of the tank where the
solids settle. The inlet baffle provides for an even
distribution of sludge throughout the tank and re-
duces the possibility of short-circuiting to the
effluent end of the thickener.
2. Sludge rakes cause the settled sludge to move
towards the center of the tank to be removed by a
sludge pump.
3. The vertical pickets provide for gentle stirring of
the settled sludge as the rake rotates. This gentle
stirring action opens up channels for the vertical
release of entrapped gases and free moisture
which promotes or enhances the concentration of
the settled sludge.
22.11C The age of the sludge to be thickened is very impor-
tant. Fresh primary sludge usually can be concen-
trated to the highest degree. If gasification occurs
due to anaerobic conditions, sludges are difficult to
thicken. Secondary sludges are not as well suited for
gravity thickening as primary sludge. Secondary
sludges contain large quantities of "bound" water
which renders the sludge less dense than primary
sludge solids.
22.11D As the temperature of the sludge (primary or sec-
ondary) increases, the rate of biological activity in-
creases and the sludge tends to gasify and rise at a
higher rate. During summer time operation, the set-
tled sludge has to be removed at a faster rate from
the thickener than during winter time operation when
the sludge temperature is lower and biological activ-
ity and subsequent gas production proceeds at a
slower rate.
22.11E Known Unknown
Diameter, ft = 30 ft Hydraulic Surface Loading,
gpd/sq ft
Sludge Solids, % = 3% Solids Loading, lbs/day/
sq ft.
Flow, GPM = 60 GPM
Determine the water surface area.
Surface Area, = —(Diameter, ft)2
sq ft 4
= 0.785 (30 ft)2
= 707 sq ft
Calculate the hydraulic surface loading.
Hydraulic
Surface
Loading
Flow, gpd
Surface Area, sq ft
gpd/sq "ft _ 60 gal/min x 1440 min/day
707 sq ft
= 122 gpd/sq ft
Determine the solids applied to the thickener, lbs/
day.
Solids = Flow, gpd x 8.34 lbs/day x Solids, ao
Applied, 100%
lbs/day
= 60 gal/min x 1440 min/day x 8.34 lbs/gal x 3%
100%
= 21,617 lbs/day
Calculate the solids loading.
Solids = Solids Applied, lbs/day
Loading, Surface Area, sq ft
Ibs/day/sq ft
= 21^617 lbs/day
707 sq ft
= 31 Ibs/day/sq ft
22.11F Known Unknown
Flow, GPM = 40 GPM Suspended Solids
Removal Eff., %
WAS Cone., % = 0.9%
, mg/L = 9,000 mgIL Concentration Factor
Underflow Sludge, % = 3%
Eff. Susp. Sol., mg/L = 1,800 mg//.
Calculate the suspended solids removal efficiency, %.
Efficiency, % = mg/L - Effl., mg/L) x 100%
Inf., mg/L
_ (9,000 mg/L - 1,800 mg/L) x 100%
9,000 mg/L
80%
Determine the concentration factor.
Concentration = Thickened Sludge Concentration, %
Factor Influent Sludge Concentration, %
= 30%
0.9%
= 3.33
Answers to questions on page 144.
22.11G Routine visual checks on gravity thickeners as well
as other equipment help the operator identify equip-
ment malfunctions and/or decreases in process effi-
ciency.
22.11H The term "hole" or coning refers to a cone-shaped
hole that can develop in the sludge blanket which
allows liquid from above the sludge blanket (rather
than sludge from the sludge blanket) to be pumped
from the thickener. A hole in the sludge blanket can
best be corrected by lowering the flow to the thick-
ener, increasing the speed of the collectors to keep
the sludge at the point of withdrawal and decreasing
the rate of underflow sludge pumping.
22.111 Possible causes of solids rising to the surface:
1. Gasification,
2. Septic feed,
3. Blanket disturbances,
4. Chemical inefficiencies, and
5. Excessive loadings.
-------
Solids Disposal 265
Procedures to correct the problem(s):
1. Increase sludge withdrawal rate,
2. Increase sludge pumping from clarifier,
3. Lower collector speed,
4. Increase chemical feed rate, and
5. Lower flow if possible.
Answers to questions on page 149.
22.12A The main components of dissolved air flotation
(DAF) units are: (1) air injection equipment, (2) agi-
tated or unagitated pressurized retention tank, (3)
recycle pump, (4) inlet or distribution assembly, (5)
sludge scrapers, and (6) an effluent baffle.
22.12B 1. The function of the distribution box is to allow the
air to come out of solution in the form of minute air
bubbles which attach to the solids and cause
them to rise to the surface.
2. The retention tank provides a location to dissolve
air into the liquid.
3. The effluent baffle is provided to keep the floated
solids from contaminating the effluent.
22.12C A sight glass should be provided to periodically
check the level of the air-liquid interface because on
occasion the float mechanisms may fall and the re-
tention tank will either fill completely with liquid or fill
completely with air.
22.12G Known
Same as problem 22.12 F
Unknown
Solids Loading,
Ibs/day/sq ft
Influent Sludge, % = 0.75
, mg/i.
Influent Sludge
Flow, elm
Air, cfm
Recycle Ratio, % = 100%
Determine solids applied, lbs/day.
Solids Applied, _ Flow, cu ft x 1440 min x 62.4 lbs x SS, %
lbs/day
= 7,500 mgIL A/S Ratio, lb air/lb solids
Recycle Flow Rate, GPM
= 2.5 cu ft/min
= 0.75 cu ft/min
min
cu ft >
_ 2.5
min
= 1,685 lbs/day
day
1440 min
day
cu ft 100%
62.4 lbs x 0.75%
cu ft
100%
Calculate solids loading, Ibs/day/sq ft.
Solids Loading, _ Solids Applied, lbs/day
IWdayteqlt surface Area, sq
= 1,685 lbs/day
78.5 sq ft
21.5 Ibs/day/sq fl
Determine the air supply in pounds per hour.
Air Supply, _ Air Flow, cu ft x 60 min x 0.075 lbs air
lbs/hr "rnirT "hT cuft
_ 0.75 cu ft x 60 min x 0.075 lbs
min fir cu ft
= 3.375 lbs/hr
22.12D The performance of DAF thickeners depends on (1)
type and age of the feed sludge, (2) solids and hy-
draulic loading, (3) air to solids (A/S) ratio, (4) recycle
rate, and (5) sludge blanket depth.
22.12E The age of the sludge usually does not affect flota-
tion performance as drasticially as it affects gravity
concentrators. A relatively old sludge has a natural
tendency to float due to gasification and this natural
buoyancy will have little or no adverse effects on the
operation of flotation thickeners.
22.12F Known Unknown
Diameter, ft = 20 ft Hydraulic Surface Loading,
gpd/sq ft
Flow, GPM =100 GPM
Determine the liquid surface area, sq ft.
Surface Area, = x (Djameteri ft)*
= 0.785 x (20 ft)*
= 314 sq ft
Calculate the hydraulic surface loading, gpd/sq ft.
Surface = Flow, gpd
Loading,
gpd/sq ft
Surface Area, sq fl
_ 100 gal/min x 1440 min/day
314 sq ft
= 458 gpd/sq ft
Determine the solids applied in pounds per hour.
Solids Applied, _ Solids Applied, lbs/day
lbs"1r 24 hr/day
_ 1685 lbs/day (from 22.20D)
24 hr/day
= 70.2 lbs/hr
Calculate the pounds of air to pounds of solids
(A/S) ratio.
Air, lbs _ Air Supply, lbs/hr
Solids, lbs Solids Applied, lbs/hr
_ 3.375 lbs air/hr
70.2 lbs solids/hr
= 0.05 lbs air/lb solids
Determine the recycle flow, GPM.
Remote Flow, = ,nf|ow GpM x Recycle Ratio, %
QPM 100%
= 2.5 cu ft x 7.5 ga[ x 100%
100%
or
min cu ft
= 18.8 GPM
= 19 GPM for pumping rate
-------
266 Treatment Plants
22.12H Known
OAF Unit
Unknown
SS Removal Eff., %
Infl. Sludge, % = 1.0% Concentration Factor
, mg/L = 10,000 mg/L
Eff I. Sludge, % = 3.8%
(Thickened Sludge)
Eff I. Liquid SS, = 50 mg IL
mg IL
Determine the suspended solids removal effi-
ciency.
SS Efficiency, %
(SS inf., mg/L-SS Eff.,_mg/L) x 100%
SS Inf., mg//.
(10,000 mg//. - 50 mg/L) x 100%
100,000 mg//.
= 99.5%
Determine the concentration factor for the thick-
ened sludge.
Concentration = Thickened Sludge Concentration, %
Factor, (cf) Influent Sludge Concentration, %
= 3.8%
1.0%
= 3.8
Answers to question on page 150.
22.121 PROBLEM. Poor effluent quality (high suspended
solids) and thinner than normal sludge.
Possible Causes Possible Solutions
a. A/S low.
a. Increase air input.
Repair and/or turn on com-
pressor.
b. Pressure too low or b. Repair and/or turn on com-
too high. pressor.
c. Recycle pump inop- c. Turn on recycle pump,
perative.
d. Re-aeration pump in- d. Turn on re-aeration pump,
operative.
e. Chemical addition in- e. Increase dosage,
adequate.
f. Loading excessive. f. Lower flow rate.
Answers to questions on page 160.
22.13A Three centrifuge designs commercially available
today are (1) basket centrifuges, (2) scroll cen-
trifuges, and (3) disc-nozzle type centrifuges. Basket
centrifuges operate in a batch mode, while scroll and
disc-nozzle type operate continuously.
22.13B Centrifugal thickening is affected by (1) type and age
of the feed sludge, (2) solids and hydraulic loading,
(3) bowl speed and resulting gravitational ("g")
forces, (4) pool depth and differential scroll speed for
scroll centrifuges, and (5) size and number of noz-
zles for disc centrifuges.
22.13C Centrifuges are not commonly used to thicken pri-
mary sludges because they have inlet assemblies
that are highly subject to clogging.
2213D Known Unknown
20 in X 60 in scroll centrifuge Hydraulic Loading, gal/hr
Feed Rate, GPM = 30 GPM Solids Loading, Ibs/hr
Infl. Solids, % -- 1.1%
, mg/L - 11,000 mg IL
Calculate the hydraulic loading in gallons per hour.
Hydraulic Load, - Flow, GPM x 60 min/hr
- 30 gal/min x 60 min/hr
= 1,800 gal/hr
Calculate the solids loading in pounds of solids
per hour.
Solids Load, = Flow, gal/hr x 8.34 lbs/gal x ®.®;. %
Ibs/hr 100%
1800 gal/hr x 8.34 lbs/gal x
165 lbs solids/hr
1.1%
100%
22.13E Known Unknown
48-inch diameter basket centrifuge Hydraulic Loading,
Feed Rate, GPM = 30 GPM
gal/hr
Solids Loading,
Ibs/hr
Infl. Solids, % = 1,1%
, mg//_ = 11,000 mg/L
Feed Time, Min = 25 min
Down Time, Min = 3 min
Calculate the hydraulic loading in gallons per hour.
Hydraulic
Load,
gal/hr
Flow, GPM x
60 min
hr
Run Time, min
30
gal
60'
(Run, min i Down, min)
25 min
hr (25 min + 3 min)
30 x 60 x
25
28
= 1,607 gal/hr
Calculate the solids loading in pounds of solids per
hour.
Solids Load, = Hyd. Load, 8.34^ xSA^
,bs/hr hr gal 100%
= 1,607 x 8.34 !^_ x 1-1%
hr gal 100%
= 147 lbs solids/hr
22.13F As the differential scroll speed is increased, the sol-
ids that are compacted on the bowl wall are con-
veyed out of the centrifuge at a faster rate, resulting
in a decrease in the concentration of these solids.
Lower concentrations result because as the solids
are moved out at a faster rate they are subjected to
centrifugal forces for shorter periods of time.
22.13G Known Unknown
20-inch diameter disc centrifuge Efficiency, %
Flow, GPM = 25 GPM Concentration
Factor, (cf)
Infl. SS, % = 0.65%
, mg/L = 6,500 mg/L
Effl, SS, % = 0.03%
, mg/L = 300 mg/L
Thick. SI, % = 4.9%
, mg/L = 49,000 mg/L
-------
Solids Disposal 267
Calculate the efficiency of the disc centrifuge.
Efficiency, % =
-------
268 Treatment Plants
Unknown
Digestion Time, days
VSS Loading, Ibs/day/cu ft
22.221 Known
Aerobic Digester
Dimensions, ft
L = 120 ft
W = 25 ft
SWD = 11 ft
Flow, gpd = 24,000 gpd
Sludge Solids, % = 3.1%
Volatile Matter, % = 73%
Calculate the aerobic digester volume in cubic feet
and gallons.
Volume, cu ft = length, ft x Width, ft x SWD, ft
= 120 ft x 25 ft x 11 ft
= 33,000 cu ft
Volume, gal = 33,000 cu ft x 7.48 gal/cu ft
= 246,840 gallons
Determine the digestion time in days.
Digestion Time, = Di9ester Volume' 9al
22.22M
days
Flow, gpd
246,840 gallons
24,000 gpd
= 10.3 days
Calculate the VSS applied in pounds of volatile
matter per day.
VSS Applied, = Flow, gpd x 8'^4 lt3S x
SS, % x VM, %
lbs/day
gal
100%
= 24,000 gpd x 8 34 lbs x 3-1% x
100%
73%
100% 100%
gal
= 4,530 lbs VSS/day
Determine the VSS loading in pounds per-day per
cubic foot.
VSS Applied, lbs/day
VSS Loading,
Ibs/day/cu ft
Digester Volume, cu ft
4530 lbs VSS/day
33,000 cu ft
0.14 lbs VSS/day/cu ft
22.22J DO in aerobic digesters should be maintained at
concentrations greater than 1.0 mgIL to avoid the
growth of filamentous organisms which can lead to
sludge bulking and/or foaming.
22.22K DO is measured in aerobic digesters by lowering a
DO probe into the digester, gently raising and lower-
ing the probe 6 to 12 inches and recording the
readout measurement after the readout has stabil-
ized.
22.22L Known Unknown
02 Uptake Data 02 Uptake Rate, mg/L/hr
Calculate the Os uptake rate in mg/L/hr.
02 Uptake,
mg/L/hr
(DO, - D02) x 60 min
(Time, - Time2) hr
(4.2 mg/L - 1.8 mg/L) y 60 min
5 min - 2 min hr
= 48 mg/L/hr
Known
Digester
Volume, Gal
Inflow, gpd
Infl. Sludge
SS, %
VM, %
Effl. Sludge
SS, %
VM, %
Unknown
: 1,000,000 gal Digestion Time, days
= 91,000 gpd vss Loading,
Ibs/day/cu ft
= 5.1% VSS Destruction, %
= 76%
= 3.7%
= 67%
Calculate the digestion time in days.
Digestion Time, = Digester Volume, gal
days
Inflow, gpd
= 1,000,000 gal
91,000 gpd
= 11.0 days
Calculate the digester volume in cubic feet.
Volume, cu ft = Jfo1"™. 9aL
7.48 gal/cu ft
= 1,000,000 gal
7.48 ga!/cu ft
= 133,700 cu ft
Determine the volatile suspended solids applied
(entering) in lbs/day.
VSS Applied, = Inflow, gpd x8-34 lbs x SS. % x VM, %
lbs/day gal 100% 100%
= 91,000 gpd x 8 34 lbs x 51 % x 76%
gal
100% 100%
29,400 lbs/day
Calculate the VSS loading in pounds per day per
cubic foot.
VSS Loading,
Ibs/day/cu ft
VSS Applied, lbs/day
Digester Volume, cu ft
= 29,400 lbs/day
133,700 cu ft
= 0.22 lbs VSS/day/cu ft
Determine the volatile suspended solids exiting in
lbs/day.
VSS Exiting, = Inflow, gpd x 6 34 lbs x SS' % x VM- %
lbs/day gal 100% 100%
= 91,000 gpd x 8 34 lbs x 3-7% x 67%
gal 100% 100%
= 18,800 lbs/day
Calculate the VSS destruction as a percent.
VSS Destruction, = (VSS Apphod, Ids, day - VSS Exiting, lbs/day) x 100%
% VSS Applied, lbs/day
= (29,400 lbs/day - 10.800 lbs/day) x 100%
29,400 lbs/day ~ "
= 36.0%
Answers to questions on page 170.
22.22N Process inefficiencies can be detected by careful ob-
servation of the physical sludge and routine monitor-
ing of the DO and Oz uptake rates. Laboratory
analyses of influent and effluent suspended solids (%
solids) and volatile matter content (% volatile matter)
also will reveal process inefficiencies.
-------
Solids Disposal 269
22.220 Normally digester DO is 1.5 mg/L A DO residual of
4.0 mg/L is measured. The operator should verify the
DO and check the 02 uptake rates. If the 02 uptake
rate is normal, the air rate should be lowered. If the
02 uptake rate is low, the cause should be identified
and corrected. Possible causes include low digester
temperature, low digester pH, too high or too low a
VSS loading, and digestion time too high or too low.
22.22P Foaming problems.
Potential Causes Corrective Measures
Strength of
Solution, %
1. Filamentous growth.
2. Excessive
turbulance.
Increase air rate.
Add defoamant.
Lower air rate.
Add defoamant.
Answers to questions on page 171.
22.23A Two chemicals used to stabilize sludges are lime and
chlorine.
22.23B Major limitations of using chemicals to stabilize
sludge include (1) costs, and (2) the volume of
sludge is not reduced.
22.23C Chemicals are used as a temporary stabilization pro-
cess at overloaded plants or at plants experiencing
stabilization facility upsets.
ewP OFAN«w£(Z$s
f0 QUBfSTlOM,
IMU 6Wi
Answers to questions on page 177.
22.30A Solid particles present in sludge usually require con-
ditioning in order to separate from wastewater be-
cause they are fine in particle size, hydrated (com-
bined with water) and may carry an electrostatic
charge.
22.30B Different types of sludge conditioning methods in-
clude: (1) chemical treatment, (2) thermal treatment,
and (3) elutriation. These are the most common.
Other types include: freezing, electrical treatment
and ultrasonic treatment.
22.31 A The addition of chemicals to sludge reduces the nat-
ural repelling forces and allows the solids to come
together (coagulate) and gather (flocculate) into a
heavier solid mass.
22.31 B Chemical types and dosage requirements vary from
plant to plant because sludge types and characteris-
tics vary from plant to plant.
22.31 C Chemical requirements are determined for a particu-
lar sludge by the use of laboratory-scale "jar tests."
Various amounts of a chemical are added to different
jars containing the sludge. The chemical require-
ments are based on the volume of chemical solution
required for floe formation.
22.31 D Known Unknown
Polymer Added, lbs = 3 lbs
Total Volume, gal = 360 gallons
Determine the strength of the polymer solution in
percent.
Solution % = Polymer Added, lbs x iqq%
Total Volume, gallons x 8.34 lbs/gal
3 lbs x 100%
360 gallons x 8.34 lbs/gal
= 0.10%
22.31 E Known Unknown
Lime Added, lbs =10 lbs
Total Volume, gal = 100 gallons
Determine the strength of the lime solution in per-
cent.
Chemical Added, lbs x 100%
Strength of
Solution, %
Solution, % =
Total Volume, gallons x 8.34 lbs/gal
10 lbs x 100%
100 gallons x 8.34 lbs/gal
= 1.20% lime
22.31 F Known Unknown
Liquid Polymer, gal =10 gal Strength of Solution, %
Volume Water, gal = 790 gal
Determine the strength of the polymer solution in
percent.
Solution, % = Polymer Added, gal x 100%
Total Volume, gallons
_ 10 gal x 100%
(790 gal + 10 gal)
= 1.25%
22.31 G Known Unknown
Ferric Chloride, gal = 5 gal Strength of Solution, %
Volume Water, gal = 50 gal
Determine the strength of the ferric chloride solu-
tion in percent.
Solution. % = Ferric chloride, gal x 100%
Total Volume, gallons
= 5 gal x 100%
(50 gal + 5 gal)
= 9.1%
22.31 H Known Unknown
Sludge Cone., Polymer dose, lbs/ton
% = 3.0% Polymer cost, $/ton
mg/L = 30,000 mglL
Polymer,
Volume, ml = 60 ml
Strength, % = 0.15%
Cost, $/lb = $1,50/lb
Sludge Volume = 1 liter
= 0.265 gal
Determine the dosage in pounds of polymer per
ton of sludge.
Dosage = Po|ymef Solution, % x Polymer Added, ml x 2
lb/ton Sludge Volume, L x Sludge Cone., %
= 015 x 60 x 2
1 x 3.0
= 6 lbs dry polymer/ton o1 sludge
-------
270 Treatment Plants
Determine the cost in dollars of polymer per ton of
sludge.
Cost, $/ton = Dosage, lb/ton x Polymer Cost, $/lb
6 lbs Polymer x $1.50
ton of sludge lb Polymer
= $9.00/ton of sludge
22.311 Known Unknown
Polymer Solution, % = 2.5% Dosage, lbs/ton
Polymer Flow Rate, GPM = 3 GPM Cost, $/ton
Sludge Flow, GPM = 30 GPM
Sludge Cone., % = 4%
Polymer Cost, $/lb = $0.20/lb
Determine the dosage of polymer in pounds of
polymer per ton of sludge.
Dosage, lbs/ton = Poly So1' % * Poly F|0IW' GPM x 2000 lbs/ton
Sludge Flow, GPM x Sludge Cone., %
= 2.5% X 3.0 GPM x 2000 lbs/ton
30 GPM x 4%
= 125 lbs/ton
Determine the cost in dollars of polymer per ton of
sludge.
Cost, $/ton = Dosage, lb/ton x Polymer Cost, $/lb
= 125 lbs/ton x $0.20/lb
= $25/ton of sludge
Answers to questions on page 179.
22.31 J Dry chemicals should be kept in a dry place to avoid
chemical handling and transferring problems. If al-
lowed to get wet, the dry chemicals will not move
freely.
22.31 K The purpose of wetting dry polymers is to produce a
properly mixed solution that will not have balls of
undissolved polymer.
22.31 L Procedures to prepare a batch solution of dry chemi-
cals.
1. Calculate amount of dry chemical needed.
2. Weigh out dry chemical.
3. Partially fill mix tank until impellers are sub-
merged.
4. Turn on mixer.
5. Add product to mix tank.
6. Fill tank to desired level.
7. Allow to mix before use to sufficiently cure solu-
tion.
8. Turn off the mixer.
Procedures to prepare a batch solution of liquid
chemicals.
1. Calculate the volume of liquid chemical needed.
2. Measure the volume of liquid chemical.
3. Follow steps 3 through 8.
22.31 M Curing time is important to allow the chemical to fully
dissolve and be as effective as possible.
22.31 N Chemical tanks should be covered to prevent foreign
material from entering and possibly clogging equip-
ment. Polymers must be covered to protect polymers
from ultraviolet sun rays.
22.310 Polymers should not be added to the suction side of
sludge feed pumps because the shearing forces
through such pumps tend to shear any floe forma-
tion.
22.31 P If sludge thickening or dewatering inefficiencies can-
not be traced back to equipment failures, check the
chemical mixing (preparation) and addition equip-
ment. With automatic feeding systems, the operator
should check (1) the level of dry product in the stor-
age hopper and replenish if necessary, (2) the screw
conveyor and unplug if necessary, (3) the quality of
the solution, and (4) the chemical addition pump.
Answers to questions on page 181.
22.32A When sludge particles are exposed to extreme heat
at elevated pressures, the surrounding sheath hydro-
lyzes (decomposes) and ruptures the cell wall allow-
ing bound water to escape.
22.32B The performance and efficiency of thermal condition-
ing systems are affected by: (1) the concentration
and consistency of the influent sludge, (2) reactor
detention times, and (3) reactor temperature and
pressure.
22.32C Known Unknown
Reactor Volume, gal =1,000 gal Detention Time, min
Sludge Flow, GPM =33 GPM
Sludge Cone., % =4.0%
Calculate detention time in minutes.
Detention Time, _ Reactor Volume, gal
min Flow, GPM
= 1,000 gal
33 gal/min
= 30 min
22.32D Known Unknown
Information from 22.32C Reactor Detention Time, min
Sludge Concentration
Decreases to 2.5%
Estimate the reactor detention time in minutes.
Old Detention Time, min x Old Cone., %
New Sludge Cone., %
4.0%
Detention Time,
min
= 30 min x
2.5%
= 48 min
22.32E Operating controls available to optimize thermal
conditioning facilities include: (1) inlet sludge flow,
(2) reactor temperature and detention time, and (3)
sludge withdrawal from the decant tank.
22.32F Gasification usually is not a problem in gravity
thickeners with thermally treated sludge because of
the lack of biological activity.
Answers to questions on page 182.
22.32G Continuous operation is desirable because energy is
not wasted in allowing the heat exchanger and reac-
tor contents to cool down and be heated back to the
desired temperature each day when operated as a
batch process.
22.32H Start-up procedures:
1. Fill reactor and heat exchangers with water if
necessary.
2. Turn on boiler make-up water pump or open valve
to the steam boiler.
3. Open required steam valves.
4. After desired temperature is reached, open inlet
sludge and outlet valves.
-------
Solids Disposal 271
5. Turn on sludge grinder and stirring mechanisms.
6. Turn on vent fan and activate odor control equip-
ment.
7. Turn on sludge feed pump.
Reverse procedure for shutdown.
22.321 A log of the pressure drop across the heat exchang-
ers must be kept so the operator can determine when
the pressure drop is excessive. When the pressure
drop becomes excessive, the system should be acid
flushed to remove scale deposits and to unplug the
heat exchangers.
22.32J Loss of sludge dewaterability.
Possible Causes Corrective Measures
Low
Temperature
2. Low or Short
Detention Time
3. Poor Operation
of Decant
1. Increase Temperature. Check
fuel supply and system,
instrumentation and make-up
water supply.
2. Thicken feed sludge.
3. Thicken underflow sludge.
Answers to questions on page 184.
22.33A The major difference between LPO, IPO, and HPO is
the pressures (low, 400 psig; intermediate, 500 to
600 psig; high, 1,000 to 1,500 psig) in the reactor. As
the pressures increase, the amount of air reacted
with the feed sludge and temperatures also increase.
22.33B The performance and efficiency of wet oxidation
units are dependent on: (1) the concentration and
consistency of the feed sludge, (2) reactor detention
times, (3) reactor temperature and pressure, and (4)
the quantity of air supplied.
22.33C Air pollution control equipment is required on thermal
treatment units due to the production of noxious
odors.
Answer to question on page 185.
22.34A Elutriation improves the dewaterability of sludge by
washing out the fine, difficult to dewater solids. Prob-
lems associated with the elutriation process result
from solids lost to the plant effluent with the elutria-
tion effluent (elutriate). The loss of these fine solids
into the plant effluent will deteriorate the effluent qual-
ity while recycling to the plant headworks generally
results in operational problems due to buildup of fine
solids throughout the system.
Answers to questions on page 189.
22.40A The primary objective of sludge dewatering is to re-
duce sludge moisture and consequently sludge vol-
ume to a degree that will allow for economical dis-
posal.
22.40B Unit processes most often used for sludge dewater-
ing are: (1) pressure filtration, (2) vacuum filtration,
(3) centrifugation, and (4) sand drying beds.
22.41 A Flow through plate and frame filter presses de-
creases with filtration time because as the cake
builds up between the plates, the resistance to flow
increases as the water passes through thicker and
thicker layers of compacted solids.
22.41 B Pressure filtration performance is affected by (1)
sludge type, (2) conditioning, (3) filter pressure, (4)
filtration time, (5) solids loadings, (6) filter cloth type,
and (7) precoat.
22.41 C Increasing the operating pressure might result in
wetter cakes when dewatering secondary sludges.
As the pressure is increased, the sludge retained on
the filtering media may compress to a higher degree
and reduce the porosity (openings) of the sludge
cake that is formed. If the openings are reduced, fine
low-density solids may be captured which result in
wetter cakes because these solids have large sur-
face areas and relatively large quantities of water
associated with them.
22.41 D The time of filtration depends on the physical size of
the filter and applied solids loading rate. The
operator controls filtration time on the basis of the
actual filtrate flow rate. When the cavities between
the plates are filled with solids and the filtrate flow is
almost zero, the filtering sequence is complete.
22.41 E The purpose of precoating is to reduce the fre-
quency of media washing and to facilitate cake dis-
charge.
22.41F Normal operating procedures for a filter press are as
follows:
1. Slurry precoat mix.
2. Transfer slurry to tank containing sludge and
gently stir. Add ferric chloride if used.
3. Apply the precoat material to the filter.
4. Introduce the conditioned sludge to the filter.
5. When the filtrate flow decreases to near zero,
turn off the feed pump.
6. Disengage and open the press for cake dis-
charge.
7. Close the press and repeat the above proce-
dures.
22.41 G Secondary sludges do not dewater as readily as
primary sludges because secondary sludges contain
fine, low-density solids that have large surface areas
and relatively large quantities of water associated
with them.
Hill
evo ofAMivezz
?0 QU&bTlOM
Answers to questions on page 190.
22.41 H If discharge cakes from a filter press are wet
throughout, try to identify the cause and correct the
problem. Causes of wet cakes include: (1) low filtra-
tion time, (2) low pressure, and (3) chemical inef-
ficiencies.
22.411 Solids may cling to filtering media when the cakes
are discharged due to precoat inefficiencies.
-------
272 Treatment Plants
Answers to questions on page 193.
22.41 J The purpose of the drainage zone (portion of the
belt) is to allow for most of the free water to drain
through the filter and to be collected in a trough on
the underside of the belt.
22.41 K Mix chambers can be used to ensure adequate
polymer and sludge contact.
22.41 L Some belt filter presses use a reaction chamber in-
stead of the horizontal drainage zone to allow most
of the free water to drain out.
22.41 M In the "press" or "dewatering zone" the entrapped
solids are subjected to shear forces created as the
two belts travel over rollers which bring them closer
and closer together. Water is forced from between
the belts and collected in filtrate trays while the re-
tained solids are scraped from the two belts when
they separate at the discharge end of the press.
22.41 N The ability of belt filter presses to dewater sludge
and to remove suspended solids is dependent on:
(1) sludge type, (2) conditioning, (3) belt tension or
pressure, (4) belt speed, (5) hydraulic loading, and
(6) belt type.
22.410 When using a belt press to dewater secondary
sludges, the sludges may tend to slip towards the
belt sides and eventually squeeze out from between
the belts. The net effects are that these solids con-
taminate the effluent by falling into the filtrate trays
and continued housekeeping is required.
22.41 P As the belt tension is increased, more water is gen-
erally squeezed from the belt which results in drier
cakes.
22.41 Q Low belt speed affects belt press performance be-
cause as the belt speed decreases, cake dryness
increases because the sludge is subjected to pres-
sure and shearing forces for longer periods of time.
22.41 R Washing out means that large quantities of free
water unable to be released in the drainage zone will
travel to the dewatering zone and flow out from be-
tween the belts and drastically reduce effluent qual-
ity.
22.41 S The ideal operating belt speed is the slowest the
operator can maintain without "washing out" the
belt.
22.41 T Porosity of a belt depends on the belt type. As the
porosity increases, the resistance to flow decreases
and larger volumes of water are able to be drained. If
the porosity is too low, the belt may blind or plug
which will produce frequent "washouts."
Answers to questions on page 193.
22.41 U If "washing out" of the belt develops, check: (1)
polymer dosage, (2) hydraulic loading, (3) belt
speed, and (4) washing equipment.
22.41V Blinding can be corrected by reducing the polymer
dosage.
Answers to questions on page 199.
22.41 W The purpose of the agitator in the trough is to keep the
chemically conditioned sludge well mixed and to pre-
vent the sludge from settling in the trough.
22.41 X In the "mat formation' or "sludge pick-up zone," the
vacuum is applied to the compartments of the drum
submerged in the trough. This vacuum causes the
sludge to be picked up on the filter media and a
sludge mat is formed.
In the "drying zone" of the cycle, the drum rotates
out of the trough. When this occurs, the vacuum is
decreased slightly and water is sucked from the
sludge mat, through the filter media and discharged
through internal pipes to a drainage system.
22.41 Y The filter media passes through a washing zone to
remove fine particles and to reduce the possibility of
media blinding.
22.41 Z Factors affecting vacuum filtration performance in-
clude: (1) sludge type, (2) conditioning, (3) applied
vacuum, (4) drum speed or cycle time, (5) depth of
submergence, and (6) media type and condition.
22.41 AA The operator should maintain a vacuum of 15 to 30
inches (38 to 75 cm) of mercury.
22.41 AB The lower the cycle time the higher the degree of
dewatering. Cycle time controls the rate of sludge
pick-up and the thickness of the sludge mat in the
"formation zone." Also cycle time controls the length
of time the sludge remains in the "drying zone."
22.41 AC Known Unknown
Vacuum Filter Filter Yield, Ibs/hr/sq ft
Surface Area, sq ft = 300 sq ft
Sludge Flow, GPM = 75 GPM
Suspended Solids, % = 4.7%
Filter Recovery, % = 95%
Calculate the filter yield in pounds per hour
applied per square foot of filter surface area.
Filter Yield, _ Flow, GPM x 8.34 lbs/gal x 60 min/hr
Ibs/hr/sq ft Surface Area, sq ft
x Solids, % x Recovery %
x~100% x 100%
= 75 gal/min x 8.34 lbs/gal x 60 min/hr
300 sq ft
x 4.7% x 93%
x 100% x 100%
= 1640 Ibs/hr
300 sq ft
= 5.5 Ibs/hr/sq ft
22.41 AD As the porosity (openings) of the media increases,
the ability to capture suspended solids decreases
because fine, low density solids can pass directly
through the media. If the porosity of the media de-
creases too much, the media can blind with fine sol-
ids or chemical coatings, sludge will not be picked up
in the formation zone and the vacuum filter will be
rendered inoperative.
Answers to questions on page 200.
22.41 AE A loss of vacuum can be caused by: (1) filter media
misaligned, (2) tear in filter media. (3) trough empty
and (4) vacuum pumps inoperative. A loss of vac-
uum will result in deteriorations of effluent quality
and wet cakes that are difficult to discharge from the
belt.
-------
Solids Disposal 273
22.41 AF If sludge is not picked up in the formation zone, a
poor effluent quality will result. To look for the cause
of poor effluent quality, look for (1) a loss of vacuum,
or (2) insufficient chemical conditioning.
22.41AG To increase cake dryness, the operator could: (1)
increase vacuum, (2) reduce drum speed, and (3
improve chemical conditioning.
Answers to questions on pages 200 and 201.
22.42A Higher scroll speeds are usually required to dewater
sludges as compared to sludge thickening because
the concentration of feed sludge is somewhat higher
for dewatering than for thickening.
22.42B Known Unknown
Sludge Flow, GPM = 60 GPM Hydraulic Loading, gal/hr
Sludge Solids, % = 3.0% Solids Loading, lbs
solids/hr
Polymer Solution, % = 2.5% Polymer Dose, lb
polymer/ton sludge
Polymer Flow, GPM = 2 GPM
Determine the hydraulic loading in gallons per
hour.
Hydraulic = Flow, GPM x 60 min/hr
Loading,
gallons/hr = 60 gal/min x 60 min/hr
= 3,600 gal/hr
Calculate the solids loading in pounds per hour.
Solids Loading, = Flow, GPM x 8 34 lbs/gal * 60 min/hr x Solids, %
pounds/hr
100%
= 60 gal/min x 8.34 lbs/gal x 60 min/hr x 3.0%
100%
= 900 pounds solids/hr
Determine the polymer flow in pounds per hour.
Polymer Flow, = Flow, GPM x 8.34 lbs/gal x 60 min/hr x Polymer, %
ibs,hr ioo%
= 2 gal/min x 8.34 lbs/gal x 60 min/hr x 2.5%
100%
= 25 pounds polymer/hr
Calculate the polymer dose in pounds of polymer
applied per ton of sludge treated.
Polymer Dose, _ Polymer Flow, Ibs/hr x 2000 lbs/ton
lbs/polymer Solids Loading, Ibs/hr
ton sludge
_ 25 lbs polymer/hr x 2000 lbs/ton
900 pounds solids/hr
- 55.6 pounds polymer per ton sludge
22.42C Known Unknown
48-in. diam. basket centrifuge Is feed time ok?
Sludge Flow, GPM = 50 GPM
Sludge Feed, % = 2.7% Solids
Solids Recovery, % = 95%
Stored Solids, % = 23%
Feed Time, min =17 min
Basket Capacity, cu ft = 16 cu ft
Determine the volume available to store solids in
pounds.
Solids Stored, = Volume, cu ft x 7 48 6al x 8 34 lbs y Solids, %
,ba cu tt gal 100%
= 16 CU ft x 7ASVa x S3""'8 y 23%
cu tt gal 100%
= 230 lbs solids
Determine solids retained in pounds per minute.
Solids Retained, = Flow, GPM x 8.34 lbs/gal x So^dS' % x Recovery. %
Ibs/min 100% 100%
= 50 gal y 6.34 lbs y 2.7% v 95%
min
gal
10.7 lbs solids/min
100% 100%
Calculate feed time in minutes.
Feed Time, _ Solids Stored, lbs
min
Solids Retained, Ibs/min
230 lbs solids
10.7 lbs solids/min
21.5 min
The feed time should be increased from 17 to 21
minutes.
22.42D It the centrate quality is poor, but discharge solids
are dry:
Possible Causes Possible Solutions
1. Lower feed time.
2. Lower flow rate.
3. Increase chemical dosage.
1. Feed time too long.
2. Flow rate too high.
3. Chemical Inefficient.
Answers to questions on page 203.
22.43A Sludge drying beds are usually not used for sludges
that have been stabilized via wet oxidation because
of the odorous nature of thermally heated sludge.
22.43B Factors affecting sand drying bed performance in-
clude: (1) sludge type, (2) conditioning, (3) climatic
conditions, (4) sludge application rates and depths,
and (5) dewatered sludge removal techniques.
22.43C Care must be taken to prevent chemical overdosing
for two reasons: (t) media blinding with unattached
polymer may develop, and (2) large floe particles that
settle too rapidly may also blind the media.
22.43D Primary sludge from the bottom of a digester may
require prescreening because greases, hair-like and
stringy material can clog the sand bed.
22.43E Drying beds are usually covered in wet or cold cli-
mates to protect the drying sludge from rain and to
reduce the drying period during cold weather.
Covered drying beds should be well ventilated to
promote evaporation and the cover serves to control
odors and insects.
22.43F Known Unknown
Sand Drying Bed Application Depth, in
Length, ft = 150 ft
Width, ft = 30 ft
Loading, Ibs/yr/sq ft = 15 Ibs/yr/sq ft
Applications, no./mo. = 1 per month
Sludge solids, % = 3.0%
Determine the total pounds of sludge that can be
applied during the year.
Sludge Applied,= Loading, Ibs/yr/sq ft x Length, ft x Width ft
tbs/vr
= 15 Ibs/yr/sq ft x 150 ft x 30 ft
= 67,500 Ibs/yr
-------
274 Treatment Plants
NOTE: Standby area riot included in this calculation.
Calculate the total volume of sludge applied in gal-
lons per year.
Sludge Applied, = SludgeAppliedJbs/^
gallons/yr 8.34 lbs/gal x Sludge Solids, %/100%
67,500 Ibs/yr
8.34 lbs/gal x 3.0%/100%
= 269,784 gal/yr
Calculate the depth of sludge in inches per appli-
cation.
Sludge Depth, = Sludge Applied, gal/yr x 12 in/ft
in/applic. 7.48 gal/cu ft x Length, ft x Width, ft x Appl/yr
269,784 gal/yr x 12 in/ft
7.48 gal/cu ft x 150 ft x 30 ft x 12 appl/yr
= 8 in/application
22.43G To determine the optimum depth of sludge to be
applied to sand beds, the operator should apply dif-
ferent depths of sludge to different sand beds, allow
the sludge to dry and be removed, and then calculate
the loading rate in pounds of sludge per year per
square foot of drying bed area. The highest loading
rate indicates the optimum depth of sludge.
22.43H Sand bed compaction should be avoided to prevent
reduced drainage rates, longer drying times, and an
increased potential for plugging.
22.431 The sand bed surface should be raked after sludge is
removed to break up any scum or mat formations.
22.43J The final concentration to which the sludge can be
dried is dependent on the climatic conditions and
time the sludge remains in the bed after the majority
o1 water has drained through the sand.
22.43K The only problem that appears to develop at most
sludge drying bed installations is plugging of the
media surface.
Answers to questions on page 206.
22.44A One limitation of using sand drying beds is that the
dried sludge must be removed manually with forks or
shovels.
22.44B To fill a surfaced drying bed that has gravel only in
the drainage trench, start by adding water until the
gravel is flooded. Digested sludge may be applied to
the drying bed after the gravel is flooded.
22.44C When water-sludge separation is observed in a
beaker containing digested sludge, partially open the
drying bed drain line valve to drain off the water from
the drying bed.
Answer to question on page 207.
22.45A A successful sludge dewatering program requires
that: (1) the operator be very familiar with the opera-
tion of the particular dewatering device(s) used, (2)
sludge conditioning be optimum, and (3) the influent
sludge be as thick and consistent as possible.
6MP OfMObMfaTO QUe^TlOM;
M 1&&OU4'
Answers to questions on page 212.
22.50A The distinction between drying and incineration is
that DRYING removes water from sludge WITHOUT
the COMBUSTION of solid material while INCINER-
ATION results in COMBUSTION OR BURNING of
solid material. Composting is a drying process which
removes moisture without the combustion of solid
material.
22.51 A A suitable environment must be established in com-
post piles for the thermophilic facultative aerobic mi-
croorganisms.
22.51 B Chemically stabilized or wet-oxidized sludges are
generally not suited for compost operations. Chemi-
cal stabilization produces environments that are un-
suitable for microorganism survival and will not sup-
port life of composting bacteria unless the sludges
are neutralized and favorable conditions exist.
Sludge that has been stabilized by wet oxidation can
be composted, but noxious thermal odors are likely
to occur in and around the compost operation.
22.51 C Criteria necessary to create a suitable compost envi-
ronment include:
1. Sludges must be blended with previously com-
posted material or bulking agents such as saw-
dust, straw, wood shavings, rice hulls, or leaves.
2. Aeration must be sufficient to maintain aerobic
conditions in the composting material.
3. Proper moisture content and temperatures must
be maintained.
22.51 D Factors affecting composting include: (1) sludge
type, (2) initial moisture content and homogeneity of
the mixture, (3) frequency of aeration or windrow
turning, (4) climatic conditions, and (5) desired mois-
ture content of the final product.
22.51 E Secondary sludges are not as easy to compost as
primary sludges because of the plastic nature of de-
watered secondary sludge and its higher moisture
content. Dewatered secondary sludges tend to
clump together and form "balls" when they are
blended with compost material. The "balls" that are
formed within the windrows readily dry on the outer
surface but remain moist on the inside. The net effect
of this "balling" phenomenon is the occasional cre-
ation of anaerobic conditions with odor production
and a reduction in composting temperature.
22.51 F Known Unknown
Dewatered Primary Compost, lbs/day
Sludge Solids, % = 27% (need to produce
Dewatered Primary 60% moisture
Sludge Solids, content of mixture)
lbs/day = 4700 lbs/day
Dewatered Secondary
Sludge Solids, %
Dewatered Secondary
Sludge Solids,
lbs/day
Combined Sludge
Moisture, %
Compost Moisture
Product, % = 30%
Determine the moisture content of the dewatered
primary and secondary sludges in percent.
Primary Sludge = 100% - Primary Sludge Solids %
Moisture, % =100%-27%
= 73%
15%
= 3300 lbs/day
60%
-------
Solids Disposal 275
Secondary Sludge
Moisture, %
100% - Secondary Sludge Solids, %
100% - 15%
= 85%
Determine the moisture content of the dewatered
primary and secondary sludges in percent.
Primary Sludge = 100% - Primary Sludge Solids, %
= 100% - 27%
= 73%
Moisture, %
Secondary Sludge = 100% - Secondary Sludge Solids, %
Moisture, % _ 100<>/o . 15o/o
= 85%
Determine the pounds per day of compost prod-
ucts that must be recycled and blended.
Mixture = Primary' lbs/clay * Pri- Moist, % + Sec, lbs/day x
Moisture, % Primary, lbs/day +
Sec. Moist. % + Compost, lbs/day, x Mix Moist, %
Sec, lbs/day + Compost, lbs/day
60% = 4700 lbs/day * 73% + 3300 lbS,day *
4700 lbs/day + 3300 lbs/day +
85% + Compost, lbs/day x 30%
Compost, lbs/day
Divide both sides by 100%:
q g0 _ 3431 + 2805 + 0.30 Compost, lbs/day
8000 + Compost, lbs/day
+Compost = 3431 + 2805 + °'30 ComP°sl' lbs'day
lbs/day)
4800 + 0.60
Compost,
lbs/day
= 6216 + 0.30 Compost, lbs/day
Subtract 0.30 Compost, lbs/day and 4800 from
both sides of equation.
0.30 =1416
Compost,
lbs/day
Compost,
lbs/day
4720 lbs/day
22.51 G Operational procedures for windrow composting.
1. Dewater sludge to highest degree practical.
2. Blend dewatered sludge with recycled compost or
bulking agents to a consistency that will stack.
3. Form the windrow piles and turn (aerate) once or
twice daily for the first 4 to 5 days after windrow
formation.
4. Turn the piles approximately once every two days
to once a week until the process is complete.
5. Load the compost onto trucks for disposal and
recycle purposes.
22.51 H The higher ratio of blend material and the longer
compost times for secondary sludge develop be-
cause dewatered secondary sludges are wetter than
dewatered primary sludges and it is more difficult to
produce a homogeneous blend when secondary
sludges are composted.
Answers to questions on page 214.
22.52A Indirect dryers use indirect contact of sludge with
preheated gases by circulating steam through a
jacketed hollow in an outer shell of a rotating cylindri-
cal compartment. Direct driers use the direct contact
of sludge with preheated gases.
22.52B The multiple-hearth furnace (MHF) is a direct drier
because the hot gases come in contact with the
sludge on the hearths.
22.52C Flights on rotary driers elevate and mix the sludge
being dried to provide frequent contact of all wetted
particles with hot gas streams or heated surfaces for
direct or indirect drying, respectively.
22.52D Blending of the sludge with the dried product is gen-
erally practiced to improve the conveying charac-
teristics of the sludge and to reduce the potential for
balling and bridging.
22.52E Sludge should be dewatered to the highest degree
practical to reduce the volume of water delivered to
the drier and to facilitate the drying process.
22.52F As the drum speed increases, the drying time de-
creases because the sludge is picked up and tum-
bled towards the outlet at a faster rate. To increase
the drying time the operator should lower the drum
speed and/or reduce the quantity of sludge applied, if
possible.
Answers to questions on page 221.
22.53A Sludge incineration is the conversion of dewatered
sludge cake by combustion to ash, carbon dioxide,
and water vapor.
22.53B The refractory is a term for bricks resistant to high
temperatures.
22.53C On the center shaft there are arms to which plows
are attached. These arms are called rabble arms and
the plows are called rabble teeth.
22.53D The purpose of the lute cap is to prevent air and
sludge from passing through the shaft opening,
rather than the drop holes.
22.53E The purpose of the sand seal is to prevent the es-
cape of heat and gases from the furnace and the
entrance of air.
Answers to questions on page 227.
22.53F Furnace off-gas system.
Part
1. Emergency
by-pass
damper
2. Cyclone
separator
3. Precooler
4. Venturi
scrubber
5. Impingement
scrubber
6. Induced draft
fan
Purpose
Vent gases to the atmosphere dur-
ing emergency conditions. This
device protects equipment and
operating personnel.
Cause fly ash and heavy particles
to settle out into the cyclone bin.
Cool the furnace exhaust gases to
saturation temperature and to wet
the small particles of light ash.
Clean the particulate matter from
the cooled furnace gases.
Trap remaining particles in flowing
water.
Pull gases through the off-gas sys-
tem and vent gases.
Regulate suction or draft within the
MHF.
Remove ash for ultimate disposal.
7. Induced draft
damper
8. Ash handling
system
22.53G Burners are provided to supply the necessary heat to
ignite the sludge.
22.53H The three ingredients necessary for combustion to
occur are fuel, air, and temperature.
-------
276 Treatment Plants
Answers to questions on page 232.
22.531 The three distinct zones in a furnace are the drying,
combustion, and cooling zones.
22.53J The factors that influence the amount of fuel required
include:
1. Conditions in the furnace,
2. Moisture content of the sludge,
3. Volatile content of the solids, and
4. Feed rate of the cake.
22.53K Combustion is a chemical reaction which requires
oxygen, fuel, and heat. In the furnace, air provides
oxygen, the primary fuel is sludge, and heat comes
from the burning sludge.
22.53L Shaft speed adjustment may be required for changes
in cake feed rate, moisture content of sludge cake,
heating value of dry solids, increase or decrease of
temperatures by burners, the number of burners
operating and the amount of excess air allowed into
the furnace.
22.53M A burnout occurs when the sludge feed has been
stopped and the fire continues to burn.
Answers to questions on page 234.
22.53N To bring a cold furnace up to temperature:
1. Slowly increase the temperature until the temper-
ature is up to 200°F (93°C) throughout the fur-
nace.
2. Hold the temperature at 200°F (93°C) until the
refractory is dry and warm.
3. Increase the temperature at a rate of 50°F/hr
(28°C/hr) until the temperature on a given hearth
reaches 1000T (540°C).
4. Once the temperature of a hearth reaches 1000°F
(540°C), the temperature of the hearth may be
increased at a rate of 100°F/hr (56°C/hr) until the
burning zone of the furnace reaches 1600°F
(870°C). At this point the feed to the furnace may
be started.
22.530 An autogenous burn occurs when the volatile content
of the sludge cake is high enough that the cake will
burn without the additional heat input from the burn-
ers.
22.53P MHFs should be operated on a continuous basis to
extend refractory life. If operation is not continuous,
the refractory expands and contracts, ash gets into
the joints and when the MHF is reheated the bricks
expand and the bricks can break.
22.53Q Smoke is caused by too low an oxygen content in the
furnace. The solution to this problem is to add air at
or below the fire.
22.53R When in the furnace area, wear protective clothing
including heavy leather gloves, face shield, hard hat,
long sleeve shirt, and long pants.
Answer to question on page 234.
22.54A Three purposes of facultative sludge storage lagoons
are to:
1. Reduce volume of sludge,
2. Store sludge, and
3. Stabilize sludge.
Answers to questions on page 234.
22.61 A Two important restraints on the ultimate disposal of
sludge include allowable emissions to the atmo-
sphere from furnaces and the health aspects of
sludge applied to land involved in the food chain.
22.61 B Sludge should not be applied on food crops because
of the potential problems from toxic substances, vi-
ruses and pathogens.
Answers to questions on page 241.
22.62A Mechanically dewatered sludge may be disposed of
by:
1. Sanitary landfill disposal,
2. On-site dedicated land disposal,
3. Agricultural reclamation, and
4. Composting and utilization.
22.62B The following types of surface runoff control facilities
must be provided at an on-site dedicated land dis-
posal operation:
1. Flood protection. The disposal site should be pro-
tected from flooding by a continuous dike.
2. Existing drainage. The existing drainage into the
disposal site should be intercepted and directed
outside the flood-protection dike,
3. Contaminated runoff. Runoff from the disposal
site should be collected in a detention basin and
allowed to evaporate during the summer or recy-
cled to the treatment plant neadworks.
Answers to questions on page 247.
22.62C Liquid digested sludge can be disposed of by:
1. High-rate incorporation into the surface soils of a
site dedicated to land disposal (DLD),
2. Low-rate application to agricultural sites, and
3. Confinement in permanent lagoons.
22.62D Liquid sludge can be spread over land by:
1. Ridge and furrow,
2. Flooding, and
3. Subsurface injection.
22.62E Composted material can be disposed of by:
1. Providing a bagged commercial product for sale
to the public as a soil amendment,
2. Providing compost for agricultural land use, and
3. Providing compost for nonagricultural land uses.
22.62F The surface layer of liquid on permanent lagoons
must be aerobic to minimize nuisance odors and vec-
tor problems.
Answers to questions on pages 248 and 249.
22.63A An odor-monitoring program should monitor:
1. Meteorological conditions (air temperature at 5
and 25 feet above the ground, wind direction, and
wind speed), and
2. Number of complaints.
22.63B There should be at least four test wells for a DLD site.
Two of these should not extend below the confining
soil layer and two should extend below this level.
Answer to question on page 249.
22.7A Important items to consider when reviewing plans and
specifications include:
1. Space for operation and maintenance of valves
and pumps,
2. Meters and gages easily readable and located for
ease in process adjustment if necessary,
3. Sufficient area, wash water capacity and drains to
maintain, repair, and clean up equipment and
areas, and
4. Provision for handling sludge when equipment
fails.
ewp orMbweehTo oueZTioM iul&aou $
-------
Solids Disposal 277
OBJECTIVE TEST
Chapter 22. SLUDGE HANDLING AND DISPOSAL
Please mark correct answers on the answer sheet as di-
rected at the end of Chapter 1. Return the answer sheet to your
Program Director.
1. The flow to the primary and secondary treatment systems
is the same as the plant influent flow.
1. True
2. False
2. Primary and secondary sludges are produced the same
way.
1. True
2. False
3. The size of sludge handling equipment depends on the
amount of water in the sludge mass.
1. True
2. False
4. The operator has no control over the depth of the sludge
blanket in gravity thickeners.
1. True
2. False
5. Primary sludges are generally easier to treat than excess
biological sludges in dissolved air flotation thickeners.
1. True
2. False
6. Dissolved air flotation thickeners that treat primary
sludges should be equipped with bottom sludge scrapers
and sludge removal equipment.
1. True
2. False
7. Centrifuges are commonly used to thicken primary
sludges because the sludge inlet assemblies do not have
problems with clogging.
1. True
2. False
8. Stabilized organic material usually gives off obnoxious
odors.
1. True
2. False
9. The aerobic digestion process developed from the
anaerobic digestion process.
1. True
2. False
10. Lime stabilization results in a greater volume or mass of
sludge.
1. True
2. False
11. Chlorine stabilization can create a corrosive condition.
1. True
2. False
12. Jar tests should be followed by on-site tests for more ac-
curate results.
1. True
2. False
13. Solution strengths of liquid polymers are based on the
ratio of polymer weight to the weight of water.
1. True
2. False
14. Dry chemicals are usually mixed with water before appli-
cation as a sludge conditioner. Drums or bulk storage
tanks of dry chemicals should not be allowed to absorb
moisture.
1. True
2. False
15. Polymers may be added to the suction side of sludge feed
pumps without worrying about forces shearing any floe
formation.
1. True
2. False
16. The high temperatures maintained in thermal reactors will
sterilize the sludge and biological activity leading to gas
production (gasification) is not likely to occur in the decant
tanks.
1. True
2. False
17. Operation of the decant tank in a thermal conditioning
system should follow the same procedures as for gravity
thickeners.
1. True
2. False
18. The major difference between thermal conditioning and
wet oxidation is that air is introduced for wet oxidation.
1. True
2. False
-------
278 Treatment Plants
19. Secondary sludges dewater more readily and require less
chemical conditioners than primary sludges when dewa-
tered by filter presses.
1. True
2. False
20. A firm and dry cake indicates good filter press operation
and no adjustments are necessary.
1. True
2. False
21. When operating a vacuum filter, attempt to maintain as
high a vacuum as possible to obtain high degrees of dewa-
tering.
1. True
2. False
22. Volume reduction processes should result in a complete
destruction of pathogenic organisms in the sludges due to
the low temperatures.
1. True
2. False
23. The plastic nature of dewatered secondary sludge and
increased moisture content make secondary sludges
easier to compost than primary sludges.
1. True
2. False
24. For complete combustion to occur in a multiple-hearth fur-
nace, there must be a specific ratio between the amount of
fuel and the amount of air.
1. True
2. False
25. The higher the volatile content of the solids in the sludge
feed, the higher the fuel requirements.
1. True
2. False
26. In the multiple-hearth furnace, an excess amount of air
must be available at all times.
1. True
2. False
27. If the burning zone in an MHF is too high, maintain the
steady cake feed rate but INCREASE the speed of the
central shaft (if possible).
1. True
2. False
28. Disposal of sludge cake by trenching operations in a dedi-
cated land disposal site is not difficult during extreme wet
periods.
1. True
2. False
29. Incinerated ash from grit, scum and screenings can be
disposed of on a DLD site as long as it is turned under the
soil quickly and not subject to wind action.
1. True
2. False
30. Successful operation of gravity thickeners depends on
1. Control of sludge organisms.
2. Proper application of the forces of gravity.
3. Sludge blanket depth.
4. Solids and hydraulic detention times.
5. Solids and hydraulic loadings.
31. Possible causes of gasification in a gravity sludge thick-
ener include
1. Air dissolving in the sludge.
2. Gases sinking into the sludge blanket.
3. Sludge held too long in the clarifiers.
4. Sludge scrapers operating at too low a speed.
5. Too long a detention time in the thickeners.
32. A gravity thickener has a clear effluent, but the thickened
(underflow) sludge is thin (dilute). How can the thickened
sludge concentration be increased?
1. Decrease depth of sludge blanket.
2. Decrease sludge pumping from the clarifier.
3. Decrease sludge withdrawal rate.
4. Decrease solids loading.
5. Increase sludge withdrawal rate.
33. In dissolved air flotation thickeners, floated solids are kept
out of the effluent by the use of ?
1. Effluent baffles
2. Hardware cloth screens
3. Macroscreens
4. Scum scrapers
5. Water sprays
34. High suspended solids in the effluent of a dissolved air
flotation thickener unit may be caused by improper
1. A/S ratio.
2. Chemical conditioning.
3. Recycle rate.
4. Sludge blanket thickness.
5. Hydraulic loading.
35. Which is the most important laboratory analysis of aerobic
digester contents?
1. Alkalinity
2. pH
3. Oxygen uptake rates
4. Residual dissolved oxygen
5. Temperature
36. What problems are created by excessive air rates in an
aerobic digester?
1. Filamentous organisms will grow
2. Turbulence will be created which affects sludge
settleability
3. Odor problems will develop
4. Foaming problems may develop
5. Energy is wasted
-------
Solids Disposal 279
37. Problems than can develop during the storage of dry
polymers include
1. Activated polymer microorganisms biodegrading the
polymer molecule.
2. Foreign material entering the storage tank and clog-
ging equipment.
3. Temperatures above 130°F (54°C) breaking down the
polymer molecule.
4. Temperatures below 0°F (-18°C) freezing the polymer
into lumps.
5. Ultraviolet sun rays deteriorating the polymer
molecules.
38. Key operating guidelines that the operator can control on a
day-to-day basis for a thermal conditioning system include
1. Detention time.
2. Inlet sludge flow.
3. Reactor recirculation rates.
4. Reactor temperature.
5. Sludge withdrawal from decant tank.
39. The performance and efficiency of wet oxidation units are
dependent on the
1. Concentration and consistency of the feed sludge.
2. Quantity of air supplied.
3. Reactor detention time.
4. Reactor pressure.
5. Reactor temperature.
40. Unit processes most often used for sludge dewatering are
1. Centrifugation.
2. Pressure filtration.
3. Sand drying beds.
4. Vacuum filtration.
5. Wet oxidation.
41. A belt filter press is processing secondary sludges. Some
of the sludge is squeezing out from between the belts and
contaminating the effluent by falling into the filtrate trays.
How would you correct this problem?
1. Blend primary sludge with the secondary sludge
2. Build baffles around the belts
3. Chlorinate the effluent
4. Filter the effluent
5. Move the filtrate trays
42. What could be the possible cause of "washing out" of the
belt on a belt filter press?
1. Belt blinding
2. Belt speed too low
3. Belt tension needs adjustment
4. Hydraulic load too high
5. Polymer dosage insufficient
43. In wet or cold climates, sand drying beds are usually
covered with greenhouse-type enclosures to
1. Control odors.
2. Grow vegetables and flowers.
3. Promote evaporation.
4. Reduce the drying period.
5. Treat "green" sludge.
44. Compaction of the sand in a sand drying bed will result in
1. Increased potential for plugging.
2. Longer drying times.
3. Need for more sand to maintain the specified depth of
sand.
4. Reduced drainage rates.
5. Use of front-end loaders to remove dried sludge.
45. Windrow composting may have which of the following op-
erational problems?
1. Aerobic conditions
2. Anaerobic conditions
3. Balling
4. Bulking
5. Low compost temperatures
46. Incineration designs include
1. Composting.
2. Fluidized-bed reactor.
3. Multiple-hearth furnace.
4. Rotary kiln.
5. Wet oxidation.
47. Sludge cake is moved through a multiple-hearth furnace
by a process called
1. Blowing.
2. Dozing.
3. Pushing.
4. Rabbling.
5. Turning.
48. The measurement of the negative pressure or vacuum
created by convection flow in an MHF is called the
1. Draft
2. Head
3. Lift
4. Piezometer
5. Rabble
49. In order to minimize leachate formation in a landfill, gener-
ally no more than gallons of water per cubic yard of
refuse should be allowed.
1. Oto 10
2. 10 to 25
3. 25 to 40
4. 40 to 65
5. 65 to 95
50. Contaminated runoff from an on-site dedicated land dis-
posal operation may be disposed of by
1. Discharge to a nearby stream.
2. Discharge to groundwater.
3. Evaporation during the dry season.
4. Irrigation.
5. Recycle to plant headworks.
-------
280 Treatment Plants
51. Freshly dewatered sludge must be mixed with either pre-
viously composted sludge or a bulking material to achieve
35 to 40 percent solids content at the start of composting
to allow sufficient voids and air passages
1. For the aerobic composting process to be sustained.
2. For winds to prevent the compost from exceeding
combustion temperatures.
3. To prevent odors from causing nuisances.
4. To prevent the windrows from flowing or settling.
5. To provide for continued anaerobic decomposition of
the sludge.
52 and 53
To prevent erosion, the maximum field slope should be held
to (52) percent and the drainage ditches on the sides of
each DLD site should be designed so that the runoff velocity
does not exceed (53) feet per second.
1. 0.1
53. 1.
1
2. 0.2
2.
2
3. 0.3
3.
3
4. 0.4
4.
4
5. 0.5
5.
5
54. Five thousand gallons of sludge with a sludge solids con-
centration of 2 percent is thickened to a sludge solids
concentration of 5 percent. What is the reduction in vol-
ume of sludge? HINT: How many gallons of water were
removed by the thickening process?
1. 834 gallons
2. 1000 gallons
3. 2000 gallons
4. 3000 gallons
5. 4000 gallons
55. An air rotameter and compressor provide for 12 cubic feet
per minute (SCFM) of air to be injected into a pressurized
retention tank. How many pounds of air applied to the unit
per hour?
1. 54 Ibs/hr
2. 90 Ibs/hr
3. 100 Ibs/hr
4. 720 Ibs/hr
5. 6000 Ibs/hr
56. An aerobic digester has a volume of 100,000 gallons and
treats a flow of 10,000 GPD of thickened secondary
sludge. How long is the digestion time?
1. 0.1 day or 2.4 hours
2. 0.13 day or 3.2 hours
3. 1 day
4. 7.48 days
5. 10 days
57. An aerobic digester with a volume of 100,000 gallons re-
ceives 10,000 GPD of thickened secondary sludge. The
sludge is 3.0 percent sludge solids and 70 percent volatile
matter. What is the volatile sludge solids loading?
1. 0.10 lbs VSS/day/cu ft
2. 0.13 lbs VSS/day/cu ft
3. 0.18 lbs VSS/day/cu ft
4. 0.20 lbs VSS/day/cu ft
5. 1.0 lbs VSS/day/cu ft
The following information is provided to answer questions 58
and 59.
A waste activated sludge is pumped at 50 GPM with a
sludge solids concentration of 2.0 percent sludge solids. Jar
tests indicate that 48 pounds per day of dry polymer are nec-
essary for successful gravity thickening. The dry polymer costs
$2.50 per dry pound.
58. What is the polymer dosage in pounds of polymer per ton
of dry sludge solids?
1. 2
2. 4
3. 5.5
4. 8
5. 10
59. What is the unit cost in dollars of polymer per ton of dry
sludge solids?
1. 5
2. 10
3. 13.75
4. 20
5. 25
60. A vacuum filter treats 5,000 pounds of sludge per day. The
surface area of the filter is 200 square feet, the filter oper-
ates 8 hours per day with 95 percent solids recovery. What
is the filter yield?
1. 2.88 Ibs/hr/sq ft
2. 3.00 Ibs/hr/sq ft
3. 3.12 Ibs/hr/sq ft
4. 3.25 Ibs/hr/sq ft
5. 3.38 Ibs/hr/sq ft
END OF OBJECTIVE TEST
-------
CHAPTER 23
SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
by
James L. Johnson
and
Ross Gudgel
-------
282 Treatment Plants
TABLE OF CONTENTS
Chapter 23. Solids Removal From Secondary Effluents
Page
OBJECTIVES 286
GLOSSARY 287
LESSON 1
23.0 Need to Remove Solids from Secondary Effluents 289
23.1 Solids Removal from Secondary Effluents Using Chemicals 289
23.10 Chemicals Added to Improve Settling 292
23.100 Aluminum Sulfate (dry) 292
23.101 Aluminum Sulfate (liquid) 292
23.102 Ferric Chloride 293
23.103 Lime 293
23.104 Polymeric Flocculants 293
23.11 Chemical Mixing Equipment 294
23.12 Chemical Feed Equipment 294
23.120 Types of Chemical Metering Equipment 294
23.121 Selecting a Chemical Feeder 294
23.122 Reviewing Chemical Feed System Designs 302
23.123 Chemical Feeder Start-Up 302
23.124 Chemical Feeder Operation 302
23.125 Shutting Down Chemical Systems 302
23.13 Determining Chemical Dosage 305
23.130 Jar Test 305
23.131 Procedure for Plants Without Laboratory Facilities 305
23.132 Phosphate Monitoring 305
23.14 Good Housekeeping 305
23.15 Safe Working Habits 307
23.16 Operation 307
23.160 Operational Strategy 307
23.161 Abnormal Operation 307
23.162 Troubleshooting 308
23.17 Maintenance 308
-------
Solids Removal from Effluents 283
LESSON 2
23.2 Solids Removal from Secondary Effluents Using Microscreens 309
23.20 Components of a Typical Microscreen 312
23.200 Drum 312
23.201 Microfabric 312
23.202 Water Spray System 312
23.203 Solids Waste Hopper 312
23.204 Support Bearings 312
23.205 Drum Drive Unit 312
23.206 Ultraviolet Light 312
23.207 Structure 312
23.208 Bypass Weir 312
23.21 Operation of Microscreens 313
23.210 Pre-Start Checklist 313
23.211 Normal Operation 313
23.212 Abnormal Operation 313
23.213 Operational Strategy 314
23.214 Shutdown of Microscreen 314
23.215 Troubleshooting 314
23.22 Maintenance of Microscreen 315
23.23 Safety 315
LESSON 3
23.3 Solids Removal from Secondary Effluents Using Gravity Filters 316
23.30 Gravity Filters 316
23.300 Use of Filters 316
23.301 Description of Filters 316
23.302 Filtering Process 316
23.303 Backwashing Process 316
23.31 Methods of Filtration 317
23.310 Filter Types 317
23.311 Surface Straining 317
23.312 Depth Filtration 317
23.32 Location of Filters in a Treatment System 317
23.33 Major Parts of a Filtering System 317
23.330 Inlet 317
23.331 Filter Media 317
23.332 Filter Underdrains 317
23.333 Filter Media Scouring 317
-------
284 Treatment Plants
23.334 Washwater Troughs 324
23.335 Backwash Water Drain 324
23.336 Backwash Water Supply 324
23.337 Backwash Water Rate Control 324
23.338 Used Backwash Water Holding Tank 324
23.339 Effluent Rate-Control Valve 324
23.34 Filter System Instrumentation 324
23.340 Head Loss 324
23.341 Filter Flow-Rate and Totalizer 326
23.342 Applied Turbidity 326
23.343 Effluent Turbidity 326
23.344 Indicator Lights 326
23.345 Alarms 326
23.35 Operation of Gravity Filters 326
23.350 Pre-Start Checklist 326
23.351 Normal Operation 326
Filtering 326
Backwashing 327
23.352 Abnormal Operations 328
23.353 Operational Strategy 329
23.354 Shutdown of a Gravity Filter 331
23.36 Troubleshooting 331
23.37 Safety 331
23.38 Review of Plans and Specifications 333
LESSON 4
23.4 Solids Removal from Secondary Effluents Using Inert-Media Pressure Filters 334
by Ross Gudgel
23.40 Use of Inert-Media Pressure Filters 334
23.41 Pressure Filter Facilities 334
23.410 Holding Tank (Wet WeH) 334
23.411 Filter Feed Pumps 336
23.412 Chemical Feed Systems 336
23.413 Filters 338
23.414 Backwash System 340
23.415 Decant Tank (Backwash Recovery) 342
23.42 Operation 343
23.420 Operational Strategy 343
23.421 Abnormal Operation 343
-------
Solids Removal from Effluents 285
23.43 Maintenance 343
23.44 Safety 345
23.45 Review of Plans and Specifications 345
23.46 Acknowledgments 346
23.5 Additional Reading 346
-------
286 Treatment Plants
OBJECTIVES
Chapter 23. SOLIDS REMOVAL FROM SECONDARY
EFFLUENTS
After completion of Chapter 23, you should be able to do the
following:
CHEMICALS
1. Describe the proper procedures for using chemicals to re-
move solids from your treatment plant's secondary effluent.
2. Operate and maintain chemical feed equipment.
3. Safely store and handle chemicals.
4. Review plans and specifications of chemical feed systems.
5. Start up and shut down a chemical feed system.
6. Select the most cost-effective chemicals and determine
proper dosage.
7. Troubleshoot a chemical feed system.
8. Develop an operational strategy for a chemical feed sys-
tem.
MICROSCREENS
1. Identify and describe the components of a microscreen unit.
2. Safely operate and maintain a microscreen.
3. Start up and shut down a microscreen unit.
4. Troubleshoot a microscreen treatment process.
5. Develop an operational strategy for a microscreen treat-
ment process.
6. Review plans and specifications for microscreens.
FILTRATION
1. Identify and describe the components of gravity and pres-
sure filters.
2. Safely operate and maintain filters.
3. Start up and shut down filters.
4. Troubleshoot a filtration system.
5. Develop operational strategies for gravity and pressure fil-
tration systems.
6. Review plans and specifications for filter systems.
-------
Solids Removal from Effluents 287
GLOSSARY
Chapter 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
AGE TANK AGE TANK
A tank used to store a known concentration of chemical solution for feed to a chemical feeder. Also called a "day tank."
AIR BINDING AIR BINDING
The clogging of a filter, pipe or pump due to the presence of air released from water.
ANHYDROUS (an-HI-drous) ANHYDROUS
Very dry. No water or dampness is present.
BATCH PROCESS BATCH PROCESS
A treatment process in which a tank or reacter is filled, the water is treated, and the tank is emptied. The tank may then be filled and
the process repeated.
COAGULATION (co-AGG-you-LAY-shun) COAGULATION
The use of chemicals that cause very fine particles to clump together into larger particles. This makes it easier to separate the solids
from the liquids by settling, skimming, draining or filtering.
CONTINUOUS PROCESS CONTINUOUS PROCESS
A treatment process in which water is treated continuously in a tank or reactor. The water being treated continuously flows into the
tank at one end, is treated as it flows through the tank, and flows out the opposite end as treated water.
DAY TANK DAY TANK
A tank used to store a known concentration of chemical solution for feed to a chemical feeder. Also called an "age tank."
ELECTROLYTE (ELECT-tro-LIGHT) ELECTROLYTE
A substance which dissociates (separates) into two or more ions when it is dissolved in water.
FILTER AID FILTER AID
A chemical (usually a polymer) added to water to help remove fine colloidal suspended solids.
FLOCCULATION (FLOCK-you-LAY-shun) FLOCCULATION
The gathering together of fine particles to form larger particles.
FLOW-EQUALIZATION SYSTEM FLOW-EQUALIZATION SYSTEM
A device or tank designed to hold back or store a portion of peak flows for release during low-flow periods.
JAR TEST JAR TEST
A laboratory procedure that simulates coagulation/flocculation with differing chemical doses. The purpose of the procedure is to
ESTIMATE the minimum coagulant dose required to achieve certain water quality goals. Samples of water to be treated are placed
in six jars. Various amounts of chemicals are added to each jar, stirred and the settling of the solids is observed. The lowest dose of
chemicals that provides satisfactory settling is the dose used to treat the water.
POLYELECTROLYTE (POLY-electro-light) POLYELECTROLYTE
A high-molecular-weight substance that is formed by either a natural or a synthetic process. Natural polyelectrolytes may be of
biological origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polyelectrolytes consist of simple
substances that have been made into complex, high-molecular-weight substances. Often called a "polymer."
-------
288 Treatment Plants
POLYMER (POLY-mer) POLYMER
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polymers may be of biological
origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polymers consist of simple substances that
have been made into complex, high-molecular-weight substances. Often called a "polyelectrolyte."
SLAKE SUKE
To become mixed with water so that a true chemical reaction takes place, such as in the slaking of lime.
TURBIDITY UNITS TURBIDITY UNITS
Turbidity units, if measured by a nephelometric (reflected light) procedure, are expressed in nephelometric turbidity units (NTU).
Those turbidity units obtained by other instrumental methods or visual methods are expressed in Jackson Turbidity Units (JTU) and
sometimes as Formazin Turbidity Units (FTU). The FTU nomenclature comes from the Formazin polymer used to prepare the
turbidity standards for instrument calibration. Turbidity units are a measure of the cloudiness of water.
WATER HAMMER WATER HAMMER
The sound like someone hammering on a pipe that occurs when a valve is opened or closed very rapidly. When a valve position is
changed quickly, the water pressure in a pipe will increase and decrease back and forth very quickly. This rise and fall in pressures
can do serious damage to the system.
-------
Solids Removal from Effluents 289
CHAPTER 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
(Lesson 1 of 4 Lessons)
23.0 NEED TO REMOVE SOLIDS FROM SECONDARY
EFFLUENTS
As increasing demands are placed upon our nation's receiv-
ing waters, it has become necessary to set wastewater treat-
ment plant discharge standards at a level that cannot be con-
sistently met by conventional secondary wastewater treatment
plants.
At some locations, National Pollutant Discharge Elimination
System (NPDES) discharge requirements as stringent as
those listed in Table 23.1 are being imposed. To comply with
these requirements, the effluent from a standard secondary
treatment plant or pond system must receive additional or ter-
tiary treatment. Improving solids removal from the effluent of
secondary wastewater treatment plants may be accomplished
by chemical addition or by several filtration processes. In addi-
tion to removing solids, these treatment processes also re-
move particulates, BOD and coliforms. This chapter will review
methods presently in use for upgrading solids removal from the
effluent of secondary treatment plants. These tertiary treat-
ment methods include the addition of chemicals, mi-
croscreens, and gravity and pressure filters. Figure 23.1 shows
the location of these tertiary treatment processes in relation to
other conventional processes.
TABLE 23.1 EXAMPLE OF STRICT NPDES
REQUIREMENTS
Water Quality Indicator
7-day
Average
30-day
Average
No Sample
to Exceed
Biochemical Oxygen
Demand (BOD5), mgIL
5
5
7.5
Suspended Solids, mgIL
5
5
7.5
Total Coliform, MPN/100 ml
MEDIAN, not average
2.2
2.2
240
Chlorine Residual, mg/L
AFTER dechlorination
0
0
0
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 347.
23.0A What do the initials NPDES stand for?
23 .OB Why do some locations have stringent discharge re-
quirements?
23.0C How can solids be removed from secondary effluents?
23.1 SOLIDS REMOVAL FROM SECONDARY
EFFLUENTS USING CHEMICALS
Chemical treatment is a three-step process consisting of 1)
COAGULATION\ 2) FLOCCULATION2, and 3) liquid/solids
separation. The three steps must occur in the proper se-
quence. During the coagulation phase the chemical(s) are
added to the wastewater and rapidly mixed with the process
flow. At this time certain chemical reactions occur quickly, re-
sulting in the formation of very small particles usually called
"pin point floe."
Flocculation follows coagulation and consists of gentle mix-
ing of the wastewater. The purpose of the gentle or slow mixing
is to produce larger, denser floe particles that will settle rapidly.
The liquid/solids separation step follows flocculation and is al-
most always conventional gravity settling, although other pro-
cesses such as dissolved air flotation are used occasionally.
A chemical treatment process can be added on to an exist-
ing primary or secondary treatment plant as a tertiary treat-
ment process. Chemical treatment performed in this manner
requires the construction of additional basins or tanks, which
may significantly increase the capital cost of the treatment
plant. However, chemical treatment can be practiced by ad-
ding chemicals at specific locations in existing primary or sec-
ondary treatment plants. This approach is often called chemi-
cal addition, and it eliminates the need for constructing addi-
tional clarifiers.
Regardless of the form of the chemical treatment process
(tertiary or chemical addition), the most important process con-
trol guidelines are:
1. Providing enough energy to completely mix the chemicals
with the wastewater,
2. Controlling the intensity of mixing during flocculation, and
3. Controlling the chemical(s) dose.
Chemical treatment can easily be added to existing second-
ary treatment processes as chemical addition, and it may be
added on a permanent basis to remove solids from the sec-
ondary effluent (Fig. 23.2). Filters (Sections 23.3 and 23.4)
often are installed after chemical treatment to produce a highly
polished effluent. Also, chemicals may be added to reduce
emergency problems such as those created by sludge bulking
in the secondary clarifier, upstream equipment failure, acciden-
tal spills entering the plant, and seasonal overloads. Chemi-
cals can effectively be used as a "band-aid" during problem
situations with relatively minor capital expense.
1 Coagulation (co-AGG-you-LAY-shun). The use of chemicals that cause very fine particles to clump together into larger particles This makes
it easier to separate the solids from the liquids By settling, skimming, draining or filtering.
2 Flocculation (FLOCK-you-LAY-shun). The gathering together of fine particles to form larger particles
-------
290 Treatment Plants
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PRIMARY
CLARIFICATION
EXCESS
ACTIVATED
SLUDGE
RETURN
ACTIVATED
SLUOGE
SECONDARY
CLARIFIER
SUPERNATANT
r ANAEROBIC^
DIGESTER
[SECONDARY);
ANAEROBIC
DIGESTER
(PRIMARY)
SOLIDS TO
DISPOSAL
DECHLORINATION
REMOVED SOLIDS
TO
RECEIVING
WATERS
CHLORINATION
CHLORINE
CONTACT
PRETREATMENT
SECONDARY
EFFLUENT
POLISHING
SOLIDS
DEWATERING
AERATION
TANK
Fig. 23,2 Plan layout of a typical activated sludge plant with secondary effluent polishing process
W
o
a
<0
3
-------
292 Treatment Plants
Keep in mind that the addition of chemicals is usually meant
to capture some additional solids; therefore, more sludge must
be handled. Care must be taken in controlling dosage into the
secondary system because large chemical additions may be
toxic to the organisms. This will reduce the activity or even kill
the organisms treating the wastes in the system.
Whenever applying chemicals it is important to always know,
understand, and carefully control the dosage. You must under-
stand each chemical's characteristics so the chemical will be
properly stored and safely handled. MANY OF THE CHEMI-
CALS USED ARE HARMFUL, ESPECIALLY TO THE EYES.
SAFETY IS OF THE UTMOST IMPORTANCE WHEN CHEMI-
CALS ARE STORED OR APPLIED.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 347.
23.1A Why might chemicals be used in a wastewater treat-
ment plant in addition to removing solids from second-
ary effluents?
23.1B What precaution must be exercised when adding
chemicals upstream from a biological treatment pro-
cess?
23.10 Chemicals Added to Improve Settling
Secondary effluent quality may be improved by adding
coagulant aids ahead of the secondary settling tanks. Chemi-
cals usually added are alum, ferric chloride, lime or polyelectro-
lytes. Other useful chemicals may include sodium aluminate,
ferric sulfate, ferrous chloride and ferrous sulfate. These chem-
icals may be used alone or in combinations as determined by
laboratory testing (Section 23.12, "Determining Chemical
Dosage") and the results obtained in actual plant operation.
23.100 Aluminum Sulfate (Dry) (Alt (SO J, 14 Hfi)
Alum may be purchased in varying grades identified as
lump, ground, rice, and powdered. Lump alum consists of
lumps varying in size from 0.8 inches to 8 inches (2 to 20 cm) in
diameter and is rarely used due to its irregularity in size and the
difficulties of applying and achieving a satisfactory dose.
Ground (granulated) alum is a mixture of rice-size material and
some fines (very small particles). This form of alum is used by
the majority of the water and wastewater plants. Ground alum
feeds easily and doesn't bulk (stick together) in the hoppers if
kept free of moisture or water. Also, ground alum doesn't re-
quire special protection of the hopper interiors from corrosion
and wear.
Commercial filter alum (ground alum) is shipped in 100-
pound (45 kg) bags or in bulk trucks and railroad hopper cars.
Special care should be taken to prevent alum from getting
damp or it will cake into a solid lump. All mechanical equip-
ment, such as conveyors, should be run until well-cleaned of
all alum before shutting down because the alum can harden
and jam the equipment. Keep alum dry by storing it inside a
well-ventilated location. Storage bins should have a 60-degree
slope to the bottom to insure complete emptying. Be sure the
alum will not get wet when hosing down equipment or washing
floors.
Both dry dust and liquid forms of alum are irritating to the
skin and mucous membranes and can cause serious eye in-
jury. Wear protective clothing to protect yourself from dust,
splashes, or sprays. Proper clothing consists of a face shield,
rubber gloves, rubber shoes and rubber clothing when working
around alum dust.
23.101 Aluminum Sulfate (Liquid)
Alum is also available as a liquid. One gallon weighs about
11 pounds and contains the equivalent of 5.4 pounds of dry
aluminum sulfate. Obtain a chemical analysis from the supplier
for each delivery to determine the exact content. Liquid alum is
preferred by operators because of its ease of handling; how-
ever, you must pay shipping costs for transporting the water
portion.
Liquid alum is shipped in 2,000- to 4,000-gallon tank trucks
or 55- to 110-ton railroad tank cars.
Alum becomes very corrosive when mixed with water; there-
fore, dissolving tanks, pumps and piping must be protected.
Liquid storage tanks must be constructed of corrosion resistant
material such as rubber-lined steel or fiberglass. Bulk liquid
alum storage tanks must be protected from extreme cold be-
cause normal commercial concentrations will crystallize at
temperatures below 32°F (0°C) and freeze at about 18T
(-8°C).
Alum will support a bacterial growth and/or cause sludge
deposits in feed lines if wastewater is used to transport the
alum to the point of application. These growths and deposits
can completely plug the chemical feed line. This problem can
be reduced by maintaining a high velocity to scour the line
continuously. Also, a concentrated alum solution will not sup-
port the bacterial growth so reducing the amount of carrier
water helps.
Alum reduces the alkalinity in the water being treated during
the coagulation process. Hydrated lime, soda ash, or caustic
soda may be required if there isn't enough natural alkalinity
present to satisfy the alum dosage.
Overdosing of alum may depress the pH to a point that it will
reduce the biological activity in the secondary system. Also,
this lowered pH may allow the chlorine added as a disinfectant
to further depress the pH and affect the aquatic life in the
receiving waters. This, along with chemical costs, emphasizes
the need to maintain proper chemical dosages and close
monitoring of effluent quality.
Regularly analyze the bulk chemicals to determine if the
concentration has changed. If the concentration has changed,
the operator must adjust the chemical feed rate. Also test the
effluent quality to determine if sufficient solids are being re-
moved or if an adjustment in the chemical feed rate might be
helpful.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 347.
23.1C What are the four most common chemicals added to
improve settling of solids?
23.1 D Why should alum be kept dry?
23.1 E Why should all mechanical equipment, such as con-
veyors, be run until well-cleaned of all alum before
shutting down?
-------
Solids Removal from Effluents 293
23.102 Ferric Chloride
Ferric chloride is available in three forms — ANHYDROUS3,
crystal hydrated and liquid. The dry forms will absorb enough
moisture from the air to quickly form highly corrosive solutions.
Anhydrous ferric chloride is shipped in 150- and 350-pound
drums. Once these drums are opened, they should be com-
pletely emptied to prevent the formation of corrosive solutions.
Care must be taken when making up solutions because the
temperature of the solution will rise as the chemical dissolves.
Crystal ferric chloride is shipped in 100-, 400-, or 450-pound
drums. Store the crystals in a cool, dry place and always com-
pletely empty any opened containers. The heat rise in dissolv-
ing crystal ferric chloride is much lower than that of anhydrous
ferric chloride and is not a problem.
Liquid ferric chloride is shipped in rubber-linked tank cars or
trucks and must be stored in corrosion-resistant tanks.
Positive displacement metering pumps should be used for
accurate measurements. Both the feeder and the lines must be
corrosion-resistant.
All forms of ferric chloride will cause bad stains. This staining
will occur on almost every material including walls, floors,
equipment and even operators.
Safety precautions required for handling ferric chloride in
concentrated forms should be the same as those for acids.
Wear protective clothing, face shields and gloves. Flush off all
splashes on clothing and skin immediately.
23.103 Lime
Hydrated lime (calcium hydroxide or Ca(OH)2) is used to
coagulate solids or adjust the pH to improve the coagulation
process of other chemicals. Lime may be purchased in 50- or
100-pound bags or in bulk truck or railroad car loads. Lime
should be stored in a dry place to avoid absorbing moisture.
Lime also may be purchased as anhydrous or quicklime, but
must be SLAKED4 before using. Quicklime is more difficult to
store because it will easily absorb moisture and cake.
Quicklime is less expensive to purchase than lime; however,
the added equipment for slaking and the requirement for in-
creased operational safety must be considered.
Heat is generated when, water is added to quicklime. If the
controlled water supply fails and the water is shut off while the
lime feed continues, boiling temperatures can be reached
quickly. If a boiling reaction results, hot lime may cause the
slaker to erupt and spew out hot lime. If high temperature
controls are properly installed, they should activate an alarm
and/or shut down the unit. Mixers and pumps should be in-
spected frequently (daily) for wear because the lime slurry will
rapidly erode or wear moving parts.
When transporting concentrated lime slurries in pipelines, a
scale will build up on the inside of the pipe and eventually plug
the line. A 2- to 3-inch (50 to 60 mm) diameter pipe may need
replacing every year or two due to this scale. Rubber or flexible
piping with easy access and short runs will permit cleaning by
squeezing the walls and washing out the broken scale.
Standby lines should be provided for use during the cleaning
operation.
Lime is irritating to the skin, the eyes, the mucous mem-
branes and the lungs. Protect your eyes and lungs with safety
equipment and wear protective clothing when working around
lime.
23.104 Polymeric Flocculants
Polymeric flocculants are high-molecular-weight organic
compounds with the characteristics of both polymers and
ELECTROLYTES5. They are commonly called POLYELEC-
TROLYTES . These flocculants may be of natural or synthetic
origin. Polyelectrolytes are classified on the basis of the type of
charge on the polymer chain. Negative-charged polymers are
called "anionic" and positive-charged polymers are called
"cationic." Polymers carrying no electrical charge are called
"nonionic polyelectrolytes."
A great assortment of polyelectrolytes is available to the
wastewater plant operator. They may be applied alone or in
combination with other chemicals to aid coagulation. With this
large selection of polymers available, it is possible to find a
beneficial combination for almost all conditions. Because of
this selection, extensive laboratory testing should be con-
ducted before treating the entire plant effluent. Most polyelec-
trolyte suppliers have field representatives who will assist with
the testing of their products at the treatment plant.
Polyelectrolytes are commonly used in very small doses,
usually less than 1 mg/L. The effective dosage range is limited.
An overdose can be worse than no polymer addition at all.
Polyelectrolytes are available as a dry powder or as a liquid.
Care must be taken when storing powders because they may
quickly absorb moisture and become ineffective.
Solutions for treating wastewater are made up from powders
in a batch tank and fed from a separate tank. When mix-
ing a batch, care is required to add the powder slowly while
continuously mixing. If care is not taken, useless lumps will
form that can clog feed pumps and lines.
Polyelectrolytes are considered non-hazardous to handle;
however, good housekeeping must be practiced because
polyelectrolytes will create an extremely slippery surface when
wet. Clean up spills immediately! Chlorine will break down a
polyelectrolyte. To clean up a spill, neutralize the polyelectro-
lyte with either salt (NaCI), liquid bleach or HTH powder. This
procedure may be used with any type of polyelectrolyte. Some
polyelectrolytes have a low pH and can be corrosive to the
make-up day or age tank (tank used to store solution).
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 347 and 348.
23.1F What safety precautions are required for handling fer-
ric chloride in concentrated solutions?
23.1G How can the scale of lime that builds up on the inside
of pipe be cleared?
23.1 H What problems can be created when a polyelectrolyte
is spilled?
23.11 How would you clean up a polyelectrolyte spill?
3 Anhydrous (an-HI-drous). Very dry. No water or dampness is present.
4 Slake. To become mixed with water so that a true chemical reaction takes place, such as in the slaking of lime.
5 Electrolyte (ELECT-tro-LIGHT). A substance which dissociates (separates) into two or more ions when it is dissolved in water.
« Polyelectrolyte (POLY-electro-light). A hlgh-molecular-weight substance that is formed by either a natural or synthetic process. Natural
polyelectrolytes may be of biological origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polyelectrolytes
consist of simple substances that have been made into complex, high-molecular-weight substances. Often called a "polymer."
-------
294 Treatment Plants
23.11 Chemical Mixing Equipment
Chemical mixing equipment (Figure 23.3) is needed to pre-
pare a solution of known concentration that can be metered
(measured) into the water being treated. Polyelectrolytes can
be difficult to dissolve. Also polyelectrolytes may need a period
of aging prior to application. A dissolving tank with a mechan-
ical mixer is used to prepare the solution for feeding. The re-
sulting solution is stored in a day tank (holding tank) from
which it is metered out at the proper dosage into the water
being treated.
23.12 Chemical Feed Equipment
Chemical feeders (metering equipment) are required to ac-
curately control the desired dosage. The chemical to be used
and the form in which it will be purchased must be determined
first because chemicals used for solids removal in wastewater
treatment usually can be purchased in either solid or liquid
form.
After metering, solid chemicals are generally converted into
a solution or a slurry prior to applying to the wastewater
stream. Both slurries and liquids often have flushing water
used to rapidly carry the chemical to the point of application.
23.120 Types of Chemical Metering Equipment
To maintain accurate feed rates there cannot be any slip-
page in the metering equipment; therefore, most liquid feeders
are of the positive displacement type. The quality of the water
used for both mixing and flushing the polymer system is impor-
tant. Poor quality plant effluent may cause clumps ("fish eyes")
to form which will plug feeders, small orifices and even piping.
POSITIVE DISPLACEMENT PUMPS
A piston pump (Figure 23.4) is used for metering chemicals
due to the accuracy of the positive displacement stroke and the
ease of adjusting the piston stroke to regulate the chemical
feed rate. With each stroke a fixed amount or volume of chemi-
cal or solution is discharged. By knowing the amount dis-
charged per stroke and the number of strokes per minute, it is
easy to calculate the chemical output.
Other positive displacement pumps besides the piston pump
include the gear pump (Fig. 23.4) and the diaphragm pump
(Figs. 23.5 and 23.6). Each of these pumps will produce a
constant chemical flow rate for a specific setting.
The feed rate for dry chemicals must also be chemically
controlled. Typical dry chemical feeders include the screw
feeder, vibrating trough, rotating feeder, and belt-type
gravimetric feeder.
SCREW FEEDER
A screw feeder unit maintains a desired output by varying
the speed and/or the amount of time the screw rotates as it
moves chemicals out the discharge port. Care must be taken
that the chemical doesn't cake up in the hopper and stop feed-
ing the screw. Also, the screw must be kept clean or the
amount discharged per revolution will change (Fig. 23.7).
VIBRATING TROUGH FEEDER
The vibrating trough maintains a constant depth of chemical
discharged and controls its chemical output by the magnitude
and the length of time of the vibrations.
Care must be taken that the chemical doesn't cake in the
hopper and stop feeding into the trough. Also, caking on the
trough will prevent an even flow of chemical which could
change the output volume.
ROTARY FEEDER
Rotary feeders are similar to the positive displacement gear
pump because a fixed amount of chemical is discharged from
between each tooth (Fig. 23.8). The output can be controlled
by the speed and/or running time of the rotor. Care must be
taken to maintain the rotor lobes clean and free of buildup that
will change the chemical output volume.
BELT-TYPE GRAVIMETRIC FEEDER
A gravimetric belt feeder (Fig. 23.9) maintains a constant
chemical weight on a revolving belt. This is accomplished
using a vibrating trough and a balance system. The chemical
output is controlled by the amount of chemical on the belt and
the speed and time the belt travels. The amount of chemical is
varied by the opening or closing of a feed gate or as a weighing
deck moves up or down.
Care must be taken with this unit to assure that chemicals
don't buildup on the balance because this will change the
chemical output. By catching and weighing the chemical dis-
charged at a constant speed over a measured amount of time,
the feeder output can be calculated.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 348.
23.1 J How are chemical solutions prepared for feeding?
23.1 K List the most common types of chemical feeders or
metering equipment.
23.121 Selecting a Chemical Feeder
When you must decide which chemical feeder to purchase
for your situation, include the following considerations:
1. TOTAL OPERATING RANGE
Will the unit run at today's lowest expected chemical output
as well as the future required output?
2. ACCURACY
Will the unit maintain the same feed rate after it has been
installed, calibrated and operated?
3. REPEATABILITY
Can you return to previous settings and obtain the same
feed rates as before?
4. RESISTANCE TO CORROSION
Will the equipment, including electrical components, with-
stand the corrosive environment to which they may be ex-
posed?
5. DUST CONTROL
Is a means provided to control dust if needed?
6. AVAILABILITY OF PARTS.
Are replacement parts readily available?
7. SAFETY
Is the system designed with safety of both operation and
maintenance in mind?
8. ECONOMICS
Costs of purchase, installation, operation, maintenance, re-
placement and energy requirements.
-------
Solids Removal from Effluents 295
OPTIONAL
MIXING J"
FUNNEL I
ADD A MEASURED AMOUNT OF CHEMICAL
WATER METER
MECHANICAL MIXER
MEASURED
AMOUNT OF
WATER
DISSOLVING TANK
(BATCH MIXED)
DAY TANK OR
STORAGE TANK
KNOWN
CONCENTRATION
OF SOLUTION
CHEMICAL
FEEDER
(FLOW-
PACED)
TO WATER
BEING
TREATED
Fig. 23.3 Dry chemical dissolver, day tank and feeder.
-------
296 Treatment Plants
Liquid cylinder
£
Discharge manifold
¦>//////y//7////zz,
Suction manifold
PISTON PUMP
Suction
Discharge
GEAR PUMP
Fig. 23.4 Piston and gear pump
(CourtMy of Chemical Engineering. 76 8, 45 (April 1989))
-------
Solids Removal from Effluents 297
DISCHARGE
VALVE
DRIVING
DIAPHRAGM
SILICONE OIL
TFE DIAPHRAGM
SUCTION VALVE
STROKE ADJUSTER
ADJUSTING WEDGE
RETURN SPRING
PUSH ROD
BALL BEARING
ECCENTRIC
BALL BEARING
SILICONE
OIL
DIAPHnAGM
INPUT SHAFT
ft WORM
OIL PUMP
ECCENTRIC
nr:i"r
RETURN SPRING
PUSH ROD
BALL BEARING
DISCHARGE
VALVE
DIAPHRAGM
UJ.1
SUCTION
VALVE
J
BALL BEARING
INPUT SHAFT
ft WORM
OIL PUMP
Fig. 23.5 Positive displacement diaphragm pumps
(Permission of Wallace ft Tiernan Division, Pennwatt Corporation)
-------
298 Treatment Plants
Eccentric Drive
Open —
(5) Intake
Hydraulic Fluid
Reservoir —
Closed —
(6) Pumping
Chamber "
(2) Capacity
Control Port
Outlet
Open
(3) Capacity
Setting Slide
(7)'Plunger
Check Valve
(4) Prestressed Assembly—
Diaphragm
(Retracted) Closed
(4) Prestressed Diaphragm
(Entended)
Eccentric Drive
SUCTION STROKE
DISCHARGE STROKE
Fig. 23.6 Positive displacement diaphragm metering
(Permission ot BIF, a Unit ot General Signal)
-------
Solids Removal from Effluents 299
OPTIONAL
HOPPER
AGITATOR
ECCENTRIC
DRIVE .
FEEDER
PULLEY
CONTROL BOX
HOPPER AGITATING PLATE
ROTATING FEED SCREW
MOTOR
OPTIONAL
FEEDER
DOWN-SPOUT
AND TANK
GEAR REDUCER
AGITATOR
I
Fig. 23.7 Volumetric screw feeder
(PimWon of WaNaca & Tlaman DivMon, Pannwatt Corporation)
-------
Dry Chemical
Liquid
Chemical
Supply
(Option)
Positiv*
Ventillation
L*v«l—
Probes
Mixing Ibnk
^)to Plant Chemical
' Feed Pump
Dump VWva
Fig. 23.8 Rotary feeder
(Permission of Neptune Microffoc)
-------
Solids Removal from Effluents 301
-VERTICAL
GATE
FLEXURES
OECKS
STATIONARY
DECK
IDLER
COUNTER
WEIGHTS
Fig. 23.9 Gravimetric belt feeders
(Permission of Wallace & Tiernan Division, Pennwalt Corporation)
-------
302 Treatment Plants
23.122 Reviewing Chemical Feed System Designs
When reviewing chemical feeding system designs and spec-
ifications, the operator should check the following items:
1. Review the results of pre-design tests to determine the
chemical feed rate for both the present and future. The
chemical feeders should be sized to handle the full range
of chemical doses or provisions should be made for future
expansion.
2. Determine if sampling points are provided to measure
chemical feeder output.
3. Be sure provisions are made for standby equipment in
order to maintain uninterrupted dosages during equipment
maintenance.
4. Look for ADEQUATE VALVING to allow bypassing or re-
moving equipment for maintenance without interrupting
the chemical dosage.
5. Examine plans for valving to allow flushing the system with
water before removing from service.
6. Be sure corrosion resistant drains are provided to prevent
chemical leaks from reaching the floor; for example, drips
from pump packing.
7. Check for corrosion-resistant pumps, piping, valves, and
fittings as needed.
8. Determine amount of maintenance required. The system
should require a minimum of maintenance. Equipment
should be standard, with replacement parts readily avail-
able.
9. Consider the effect of changing head conditions, both suc-
tion and discharge, on the chemical feeder output. Chang-
ing head conditions should not affect the output if the
proper chemical feeder has been specified.
10. Determine whether locations for monitoring readouts and
dosage controls are convenient to the operation center
and easy to read and record.
23.123 Chemical Feeder Start-Up
After the chemical feed system has been purchased and
installed, the operator must carefully check it out before start-
ing it up. Even if the contractor that installed the system is
responsible for insuring that the equipment operates as de-
signed, the operation by plant personnel, the functioning of the
equipment, and the results from the process are the responsi-
bility of the chief operator. Therefore, before start-up, check
the following items:
1. Inspect the electrical system for proper voltage, for prop-
erly sized overload protection, for proper operation of con-
trol lights on the control panel, for proper safety lock-out
switches and operation and for proper equipment rotation.
2. Confirm that the manufacturer's lubrication and start-up
procedures are being followed. Equipment may be dam-
aged in minutes if it is run without lubrication.
3. Examine all fittings, inspection plates and drains to assure
that they will not leak when placed into service.
4. Determine the proper positions for all valves. A positive
displacement pump will damage itself or rupture lines in
seconds if allowed to run against a closed valve or system.
5. Be sure that the chemical to be fed is available. A progres-
sive cavity pump will be damaged in minutes if it is allowed
to run dry.
6. Inspect all equipment for binding or rubbing.
7. Confirm that safety guards are in place.
8. Examine the operation of all auxiliary equipment including
the dust collectors, fans, cooling water, mixing water, and
safety equipment.
9. Check the operation of alarms and safety shutoffs. If it is
possible, operate these devices by manually tripping each
one. Examples of these devices are alarms and shutoffs
for high water, low water, high temperature, high pressure,
and low chemical levels.
10. Be sure that safety equipment, such as eyewash, drench
showers, gas masks, face shields, gloves and vent fans, is
in place and functional.
11. Record all important nameplate data and place it in the
plant files for future reference.
23.124 Chemical Feeder Operation
Once the chemical feed equipment is in operation and the
major "bugs" are worked out, the feeder will need to be "fine
tuned." To aid in fine tuning and build confidence in the entire
chemical feed system, the operator must maintain accurate
records (Figures 23.10 and 23.11). These records will include
the flows and characteristics of the waste before treatment, the
dosage and conditions of the chemical treatment, and the re-
sults obtained after treatment. A comment section should be
used to note abnormal conditions, such as a feeder plugged for
a short time, a sudden change in the characteristics of the
influent waste, and related equipment that malfunctions. Daily
logs should be summarized into a form that operators can use
as a future reference.
23.125 Shutting Down Chemical Systems
If the equipment is going to be shut down for an extended
length of time, it should be cleaned out to prevent corrosion
and/or the solidifying of the chemical. Lines and equipment
could be damaged when restarted if chemicals left In them
solidify. Operators could be seriously injured if they open a
chemical line that has not been properly flushed out.
The following items should be included in your checklist for
shutting down the chemical system:
1. Shut off the chemical supply,
2. Run dry chemicals completely out of the equipment and
clean equipment,
3. Flush out all the solution lines,
4. Shut off the electrical power,
5. Shut off the water supply and PROTECT FROM FREEZ-
ING, and
6. Drain and clean the mix and feed tanks.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 348.
23.1L List the items that should be considered when select-
ing a chemical feeder.
23.1M What information should be recorded for a chemical
feeder operation?
-------
Solids Removal from Effluents 303
SODIUM HYDROXIDE LOG
TANK
#1
GAL.
TANK
#2
GAL.
TANK
#3
GAL.
GAL. #3
BEFORE
TRANS.
GAL. #3
AFTER
TRANS.
H20
TO
NAOH
DILUTE
GAL.
USED
TOTAL
GAL
REC.
REMARKS
1
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<200
2
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3
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4
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5
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l&o
6
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7
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8
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too
9
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10
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11
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12
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&5o
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13
14
15
16
17
18
19
20
21
22
23
24
25
26
Fig. 23.10 Typical record of chemical feeder operation
-------
CHEMICAL FEED RECORD
CHEMICAL /^LUiAA /C? gALLQ/Q< &/1 LOCATION ^£
lS<7,S7k
mw
I7.q
£•£,
ep-r
f&er-fv/z-
6-5/ofco
\tA"
I hi"
1Z"
W.Qpfo
\abioO
A
20.^
a
b-Z/l^OD
I oi"
\ei"
3*
m. w
i £V,
%,bl&
A
Zl.0
TO.
TOTAL
MAX.
MIN.
AVG.
/
CHEMICAL
COST
$/MG
Fig. 23.11 Typical form for chemical feeder operation
-------
Solids Removal from Effluents 305
23.13 Determining Chemical Dosage
The proper chemical dosage is very important. A slight
amount over or under the optimum is often worse than not
adding chemicals at all. A combination of two or more chemi-
cals will often result in improved treatment and reduced overall
costs.
The wastewater entering the system may change composi-
tion from weekdays to weekends, from season to season, or
from year to year. Because of these variations, the operator
must carefully observe the efficiency of the chemical treat-
ment.
When chemicals are added to reduce the effluent sus-
pended solids, the operator should daily:
1. Run suspended solids tests on influent and effluent,
2. Calculate suspended solid removal efficiency,
3. Calculate chemical dosage,
4. Run turbidity tests on effluent,
5. Observe visual appearance of effluent, and
6. Maintain complete records.
23.130 Jar Test (Figure 23.12)
The most common method used to determine coagulation
dosages is the jar test. The jar test is an attempt to duplicate
plant conditions by using laboratory equipment. Jar tests can
be misleading unless they reflect actual plant suspended sol-
ids conditions. Be sure to run jar tests on samples of the water
to be treated. For example, a plant is adding metal salts for
phosphorus removal (Chapter 24) and a polymer for sus-
pended solids control to the effluent from an activated sludge
aeration tank. Before the type of polymer and dose can be
determined, you will have to build up the metal hydroxy phos-
phate precipitate in the activated sludge system to "steady-
state" or "equilibrium" conditions.
Equal amounts of influent samples (usually 500 to 1,000 ml)
to be treated are set up in a gang stirrer (Figure 23.12) for the
jar test. Chemicals are added in varying doses and all portions
of the sample are rapidly mixed. After rapid mixing, the sam-
ples are slowly mixed to approximate the conditions in the
plant. Mixing is then stopped and the floe formed is allowed to
settle. The appearance, the time to form a floe, and the settling
conditions are recorded. The supernatant (liquid above the
settled sludge) is analyzed for turbidity, suspended solids and
pH. With this information the operator selects the best dosage
to feed on the basis of clarity of effluent and minimum cost of
chemicals.
23.131 Procedure for Plants Without Laboratory Facilities
Source: PROCEDURE FOR DETERMINING THE ALUM
DOSAGE Permission of Industrial Chemicals Divi-
sion, Allied Chemical Corporation, Solvay, New York
In case a laboratory is unavailable, it is possible to maintain
reasonable control by conducting coagulation tests by means
of a simple hand-stirring method.
Clear glass fruit jars, one- to two-quart capacity, are a good
substitute for beakers and are easily obtainable. If necessary,
the local druggist or high school chemistry teacher will usually
assist in preparing alum solutions and lime suspensions. If a
pipet is unavailable, a common medicine dropper will deliver
approximately 20 drops to a ml. A calibrated dropper (1.0 ml)
may be obtained from the drug store.
Procedure:
1. Dissolve 9.46 grams of alum and dilute to 1 liter (8.95
grams of alum to one quart). One ml of this solution will
provide a treatment of 10 mg/L of alum when added to one
quart (946 ml) of the water sample.
2. With the pipet or medicine dropper, add 1 ml of the alum
solution to one quart of the sample and stir rapidly for ap-
proximately two minutes. Actual rapid mixing time should
be similar to the actual detention time of the water being
treated in the flash mixer. This actual detention time may
vary from 50 seconds to six minutes depending on design
and flows. Then stir gently for at least fifteen minutes to
permit floe particles to grow. Again, this actual gentle mixing
time should be similar to the actual process flocculation
time. The speed of gentle mixing paddles in the jar test
should be similar to the actual floccuiator paddles. When
running the jar test, try adjusting the paddle speed to pro-
duce the best floe particle growth and then operate the
floccuiator paddles at this speed. Under some conditions
the best floe can be produced by stopping the flocculators.
Avoid violent agitation during this floe conditioning stage to
prevent the breakup of the fioc particle.
3. Observe the quality of the floe, the rate of settling, and the
clarity of the settled water.
4. Repeat the above using a higher alum dose until the de-
sired floe and clarity are achieved.
Helpful Factors:
1 liter
1 quart
1 grain/gal =
1 grain/gal =
1 mg/L
1000 ml
946 ml
17.1 mg/L
143 lbs/million gallons
8.34 lbs/million gallons
23.132 Phosphate Monitoring
When the coagulant is being used to precipitate phosphate
as well as to remove solids, coagulant dosage control may be
obtained by automaticaffy analyzing the incoming wastewater
for soluble orthophosphate. The coagulant feeder is set to
maintain a selected ratio of coagulant-to-phosphate either au-
tomatically or manually. Equipment is available that will au-
tomatically do this type of coagulant feeding.
Coagulant dosages that produce good phosphate removal
will generally produce good solids removal if polymers are
used to aid in flocculating the fine, precipitated matter. Usually
the polymer feed should be flow-paced; however, the polymer
feeder may function with manual adjustments.
23.14 Good Housekeeping
Good housekeeping is a part of the total plant operation.
Good housekeeping around the chemical feed systems is very
important to good operations and safety. A dry chemical feeder
that weighs its output will change its feed rate if chemicals are
allowed to build up on the scales. Good housekeeping will
reduce the hazard of slipping around chemica/ handling areas
and will keep the dust down in work areas. Good housekeep-
ing is a daily duty and must not be neglected.
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306 Treatment Plants
Fig. 23.12 Jar test units with mechanical (top) and magnetic
(bottom) stirrers
(Source: EPA Process Design Manual for Suspended Solids Removal)
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Solids Removal from Effluents 307
23.15 Sale Working Habits
Chemical feed equipment and chemical handling areas have
safety hazards that each operator should become aware of for
each plant. In addition to the usual electrical and mechanical
hazards associated with automatic equipment, chemical feed-
ing hazards include:
1. Strong acids,
2. Strong caustics,
3. High pressures,
4. High temperatures,
5. Dust in the air, and
6. Slippery walk areas.
Develop safe working habits by always wearing proper
safety equipment and protective clothing.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 348.
23.1N What factors can cause a change in chemical dose
requirements?
23.10 How are coagulation dosages determined?
23.1 P What is the jar test?
23.16 Operation
23.180 Operational Strategy
The development of an operational strategy for a chemical
treatment process will prepare you to deal with sudden
changes in the water being treated, to train new operators and
to plan for the future. Items that should be considered in your
strategy include:
1. The jar test is the most important control test for chemical
treatment. Set up your laboratory so jar tests can be run
quickly and easily. Accurate jar tests can result in significant
chemical and cost savings. For example, if the dosage of a
polyelectrolyte costing $2.00 per pound could be reduced
by 0.5 mg/L in a 10 MGD plant, the cost savings would be
$83.40 per day.
2. Monitor chemical feeders closely to assure proper output.
New equipment should have actual feed rates measured
and compared with feed settings at least weekly.
3. Adjust chemical dosages whenever the flow rate changes.
Long detention times during low flows may not require as
high a chemical dosage as shorter detention times during
high flows.
4. Monitor water conditions and quality at least daily for alka-
linity, pH, temperature, turbidity, and suspended solids be-
cause these water quality indicators may signal a need for a
chemical dosage change. If you are removing phosphor-
ous, measure soluble phosphorous also.
5. Consider in-plant conditions when collecting samples for jar
tests and adjusting chemical dosages. For example, if
one-half of the primary clarifiers in a plant are out of sen/ice
or if a digester is upset, these situations can affect required
chemical doses.
23.161 Abnormal Operation
This section contains a list of abnormal conditions that could
occur at any time during the operation of a wastewater treat-
ment plant. Included are recommendations that should help
you adjust the chemical treatment system in order to maintain
a high quality effluent.
1. High solids concentrations in effluent leaving the secondary
clarifiers due to bulking sludge, rising sludge or solids
washout.
a. Inspect chemical feeders for proper output.
b. Run jar tests to determine if dosage requirements have
changed.
c. Examine overall plant operations to locate cause of
high solids.
d. Increase sludge removal rates from clarifiers.
2. Low suspended solids in effluent leaving the secondary
clarifiers.
a. Inspect chemical feeders for proper output.
b. Run jar tests to determine if dosage requirements have
changed.
c. Record in log book conditions and dosage that pro-
duced low solids in the effluent. You need to know how
you produced a good quality effluent.
3. High flows passing through the treatment plant.
a. Prepare to feed a greater quantity of chemicals.
b. Run jar tests to determine dosage that will produce
rapid settling rates because detention times are re-
duced.
c. Be sure jar test flash mixing and flocculation times are
similar to actual detention times through these units
during the high flows.
4. Low flows passing through the treatment plant.
a. Run jar tests to determine optimum dosage because
longer detention times may allow a reduction in chemi-
cal dosage which will reduce chemical costs.
b. Watch for chemical overdoses that could produce toxic
conditions in biological treatment processes or in the
receiving waters.
5. A change in the pH of the water being treated by one or
more units.
a. Inspect chemical feeders to determine if the chemicals
being added are causing the pH change.
b. Run jar tests to determine if chemical feed rates need
adjusting.
c. Extreme pH changes may affect biological activity and
effectiveness of disinfection. Try to control chemical
feeders to minimize chemical changes.
d. If existing chemical dosages will not cause coagulation,
new chemicals may be required. For example, you may
have to switch from one type of polyelectrolyte to
another type.
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308 Treatment Plants
6. A change in water temperature resulting from seasonal
weather conditions, groundwater infiltration and/or wet
weather inflows.
a. Run a jar test to determine if new chemical feed rates
are required. Coagulation and settling rates change
when the temperature changes.
23.162 Troubleshooting
PROBLEM: NO COAGULATION.
Inspect the following items:
1. Chemical feed pump operation,
2. Chemical supply and valve positions,
3. Solution carrier water flow and valve positions,
4. Applied water for a significant change,
5. Actual feeder output by catching a timed sample, and
6. Feed chemical strength.
Run a jar test to determine the proper dosage. Be sure the
jar test chemicals are the proper strength.
PROBLEM: FOAMING.
Foam can develop in rapid-mix tanks and flocculators. Con-
trol foam by the use of water spray from hoses or surface spray
nozzles.
23.17 Maintenance
All equipment maintenance must be performed in accord-
ance with manufacturers' instructions. Good housekeeping is
very important whenever working with chemicals. Chemical
feed pumps and bottom sludge pumps must be periodically
disassembled and cleaned. Weir plates, baffles and drains
must be kept clean to maintain proper basin hydraulics. Weir
crests must always be kept clean. Motors, drive systems and
paddles will require servicing and repair. Frequency and type
of maintenance and repair will depend on housekeeping,
chemicals and equipment.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 348.
23.1Q What water quality indicators should be monitored
when operating a chemical treatment process?
23.1R What abnormal conditions could be encountered in
the water being treated when operating a chemical
treatment process?
23.1 S List two problems that could occur when operating a
chemical treatment process.
END OF LESSON 1 OF 4 LESSONS
ON
SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
-------
Solids Removal from Effluents 309
DISCUSSION AND REVIEW QUESTIONS
(Lesson 1 of 4 Lessons)
Chapter 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
At the end of each lesson in this chapter you will find some
discussion and review questions that you should answer be-
fore continuing. The purpose of these questions is to indicate
to you how well you understand the material in this lesson.
Write the answers to these questions in your notebook before
continuing.
1. Why do some NPDES permits impose stringent discharge
requirements on some treatment plants?
2. What precautions should be taken when using alum to im-
prove the settling of solids?
3. Why should extensive laboratory testing be conducted be-
fore treating a secondary effluent with a polyelectrolyte to
remove solids?
4. Why are piston pumps used for metering chemicals?
5. What economic factors should be considered when select-
ing a chemical feeder?
6. Why should chemical feed equipment be cleaned before
being shut down for an extended length of time?
7. Explain how to run the jar test.
8. Why should you develop an operational strategy for a
chemical treatment process?
CHAPTER 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
(Lesson 2 of 4 Lessons)
23.2 SOLIDS REMOVAL FROM SECONDARY
EFFLUENTS USING MICROSCREENS (Also see
Chapter 28, Section 28.2, Screening and
Microscreening Applied to Industrial Wastes)
Microstraining is a form of filtering used to clarify water by
filtering out very small suspended solids. The process involves
passing water through a very finely woven fabric called mi-
crofabric (Figure 23.13). Microfabric is usually made of stain-
less steel wire, plastic, polyester or nylon cloth. The polyester
or nylon microfabric can be manufactured with openings as
small as 1.0 microns (0.00004 inch) in size.
The filtered solids quickly build up a mat on the screen,
thereby removing particles smaller than the actual openings of
the fabric as the water passes through the mat.
The microfabric is attached to the outside of a drum. The
applied water flows into the drum through one end and out
through the wall (Figures 23.14 and 23.15). The solids remain
inside the drum because they cannot pass through the mi-
crofabric. To prevent clogging of the microfabric, the drum is
rotated and the mat of solids is washed off by a water spray
system. The cleaned fabric rotates back into the process
stream again in a continuous operation.
The solids are washed into a hopper inside the drum and
carried back into the system for retreatment. These solids may
be returned to the primary clarifier or they can be disposed of
by thickening and pressing (Chapter 22) before ultimate dis-
posal to landfill, incineration or byproduct recovery depending
on the type of solids.
The process of microstraining is capable of:
1. Reducing the organic loading on the receiving waters,
2. Removing particles from the effluent,
3. Reducing the coliform group organisms in the water being
treated,
4. Improving the effectiveness of the disinfectant,
5. Lowering the turbidity level, and
6. Improving the overall appearance of the effluent.
Fig. 23.13 Isometric drawing of microfabric with
typical diatom shown against the fabric
(Permission of Crane Co.)
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310 Treatment Plants
Important features of these units include:
1. They can be installed where space is limited,
2. They operate under open, gravity-flow conditions in con-
crete tanks or packaged steel tank units, and
3. They will operate with a minimal amount of manpower.
Microscreens added to existing treatment plants will affect
other plant systems. The operator must be prepared to make
the necessary adjustments to compensate for this problem.
The solids leaving the plant in the effluent will be less; there-
fore the solids handling equipment will have an increased load-
ing. This results in more sludge to pump, dewater, digest, and
dispose of as a solid.
The water sprays cleaning the microfabric will add a flow
load of from one- to five-percent of the influent flow to the
treatment system.
VARIABLE DRIVE WASHWATER
DRIVE PINION HOPPER
RAW WATER
INLET
BACKWASH
SPRAY NOZZLE
HEADERS
WASTE
OUTLET
STRAINING
OCCURS OVER
ENTIRE
SUBMERGED
SECTION OF
MICROFABRIC
PERIPHERAL
SEAL
PERIPHERAL
RACK ON DRUM
WATER-LEVEL
IN TANK
Fig. 23.14 Microscreen
(Permission of Crane Co.)
-------
SPRAY SYSTEM
BACKWASH HOPPER
MESH SYSTEM
EFFLUENT
DRUM LIFT
EFFLUENT
(/>
O
E
o>
3D
O
3
o
<
a>
o
3
5
c
-------
312 Treatment Plants
Plant staff may have to be increased to meet the need for
additional labor to properly maintain and service microscreen
units.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 348.
23.2A What is microstraining?
23.2B What materials are generally used to manufacture mi-
crofabric?
23.20 Components of a Typical Microscreen
23.200 Drum
The drum is the main physical structure of the microscreen
unit. This drum provides the frame around which the mi-
crofabric is attached. Drum diameters range from 5 to 10 feet
(1.5 to 3.0 meters) in diameter and 1 to 10 feet (0.3 to 3.0
meters) in length. The drum operates with about 70 percent of
its surface area submerged. This keeps a large area of the
microfabric in the process flow.
23.201 Microfabric
The microfabric physically separates the solids from the
water leaving the unit. The microfabric openings are extremely
small. They are in the range of 1 to 60 microns. To get an idea
of the size of an opening, a 60-micron fabric has about 60,000
openings per square inch and a 23-micron fabric has about
165,000 openings per square inch.
Microfabric is usually made of woven stainless steel or plas-
tic. The plastic is used for the smaller openings and is less
subject to chemical attack by chlorine or acid cleaning solu-
tions. The stainless steel can better withstand steam cleaning
used to remove grease and oil. Manufacturers will design and
provide microfabric for each special application.
Microfabric is supplied either in small sections (8 in x 12 in
or 20 cm x 30 cm) or in larger (18 in x 24 in or 45 cm x 60 cm)
panels. The small sections are supported by and fastened di-
rectly to the drum frame white the panels have a supporting
mesh of stainless steel bonded to the fabric.
Standard design calls for a 1 foot (30 cm) head loss at aver-
age flows and 2 feet (60 cm) head loss for normally expected
maximum flows. Occasional peak head losses of 4 feet (120
cm) can be tolerated. One manufacturer indicates that stain-
less steel microfabric operated with a head loss of 3 inches
(7.5 cm) under average conditions would have a life of 10
years; while the same fabric operated continuously at 24-inch
(60 cm) head loss might last only 6 months.
Any flexing or movement of the fabric as it passes in and out
of the process water will shorten its life. Chlorine in the process
water and strong cleaning acid will also shorten the life of the
microfabric.
23.202 Water Spray System
Water spraying on the outside of the drum as it reaches the
highest point provides continuous backwashing of the mi-
crofabric. Water pressures ranging from 15 to 60 psi (1 to 4
kg/sq cm) are used with generally better results obtained using
the higher pressures. Water consumption for backwashing var-
ies from 1 to 5 percent of the flow through the filter.
23.203 Solids Waste Hopper
The hopper is located inside the revolving drum and catches
the solids washed from the microfabric. Removed solids are
returned to the primary treatment system and reprocessed or
they may be disposed of by thickening and pressing before
ultimate disposal to landfill, incineration or byproduct recovery.
23.204 Support Bearings
Support bearings may be water-lubricated axial or grease-
lubricated bearings located on the upper inside surface of the
rotating drum. Both types of bearings will allow the operating
water level to be above the drum center line. These bearings
require careful maintenance in accordance with the manufac-
turer's recommendations to prevent early failure.
23.205 Drum Drive Unit
The drum rotational speed may be adjusted manually or
automatically in relation to the flow or head loss in the unit.
Optimum speed will be determined with experience and usu-
ally does not require frequent adjustment.
23.206 Ultraviolet Ughts
Ultraviolet (UV) lights are used to reduce biological growths
on the microfabric. These growths can survive the water spray
cleaning and will eventually clog the fabric. Ultraviolet lights
reduce the manhours required to clean the microfabric with
special washes. Ultraviolet light is EXTREMELY dangerous to
the eyes. All plant staff must be aware of the dangers and
protect their eyes.
23.207 Structure
The structure in which the microscreen unit is installed may
be concrete or steel. Both need a good drain to permit easy
dewatering and cleaning. A sloped bottom and a sump will aid
in cleaning.
23.208 Bypass Weir
A bypass weir is needed to permit flows in excess of unit
capacity to be bypassed. The manufacturer's recommended
maximum head loss through the drum should never be ex-
ceeded to prevent damage to the microfabric.
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Solids Removal from Effluents 313
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 348.
23.2C List the major components of a typical microscreen.
23.2D What is the purpose of ultraviolet lights used with a
microscreening process?
23.21 Operation of Microscreens
23.210 Pre-Start Checklist
Before starting up any major piece of equipment, a thorough
check of the system must be made to prevent damage to the
equipment and injury to personnel. The following items should
be included in your checklist for microscreens.
1. Be sure all debris from construction has been removed from
the unit. Wood scraps and concrete chips can easily dam-
age equipment, especially the microfabric.
2. Inspect the electrical installation for completeness. Be sure
controls are properly covered, fuses properly sized, and
proper safety lockouts have been installed.
3. Check motor and drives for proper alignment, for proper
safety guards installed in place, and for free rotation of
motor and drives.
4. Examine motors, drive units, bearings, and chain for proper
lubrication.
5. Check motor for proper rotation.
6. Examine motor and drive unit for excessive vibration.
7. Study the operation of water sprays, ultraviolet lights and
other auxiliary equipment for proper operation.
8. Inspect the entire unit for any safety hazards.
23.211 Normal Operation
Normal operation requires the operator to carefully follow the
procedures outlined below.
1. Have the drum rotating when the process water first enters
the microscreen or the fabric may plug and be damaged.
2. Open the inlet gates and start the drive motor, water sprays,
lights and related equipment.
3. Maintain a log of the operation of the unit. Include the follow-
ing items:
a. Hours of operation,
b. Volume of water processed, gallons or cubic meters,
c. Rate of application, gpd or cu m/day,
d. Applied suspended solids and BOD, lbs or kg/day,
e. Effluent suspended solids and BOD, lbs or kg/day,
f. Percent removal of suspended solids and BOD, %,
g. Chemicals added, pounds or kilograms,
h. Head loss through the screen, inches or centimeters,
i. Maintenance performed on the unit, and
j. Remarks of special observations.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 348.
23.2E Before starting a microscreen unit, what items would
you inspect in the electrical installation?
23.2F What items should be included in the log of the opera-
tion of a microscreen?
23.212 Abnormal Operation
When operating a microscreen, be prepared to solve prob-
lems created by the abnormal conditions listed in this section.
PROBLEM: HIGH FLOWS
Problems caused by high flows include:
1. Excessive head loss (above 12 inches or 30 centimeters)
through the microscreen (be sure to check manufacturer's
recommendations),
2. Excessive solids in the microscreen effluent,
3. Plugging of the microfabric with solids and/or grease, and
4. Untreated water overflowing the microscreen bypass weir.
SUGGESTED CORRECTIVE ACTION
1. Increase the drum rotation speed.
2. Increase the water spray pressure.
3. Place additional units in service.
4. Hand clean the microfabric with a bactericide, hot water or
steam.
5. Reduce the flow by using a FLOW-EQUALIZATION SYS-
TEM7 or by storing the excess flow in the influent line until
the flows drop.
6. Add chemicals to upstream processes to reduce the sus-
pended solids loading by improving settling.
PROBLEM: LOW APPLIED WATER FLOWS
Problems caused by low applied flows include:
1. Lower suspended solids loadings, and
2. Thinner mat buildup on microfabric. This thinner mat may
reduce filtering effectiveness.
SUGGESTED CORRECTIVE ACTION
1. Reduce the drum rotation speed.
2. Reduce the water level within the microscreen.
3. Remove some of the microscreen units from operation (if
you have more than one on line) to maintain design flows to
units in service.
7 Flow-equalization system. A device or tank designed to hold back or store a portion of peak flows for release during low-flow periods.
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314 Treatment Plants
PROBLEM: HIGH SOUDS LOADING
Problems caused by high solids loadings include:
1. Excessive head loss (above 12 inches or 30 centimeters)
through the microscreen (be sure to check manufacturer's
recommendations),
2. Excessive solids in the microscreen effluent,
3. Plugging of the microfabric with solids, and
4. Untreated water overflowing the microscreen bypass weir.
SUGGESTED CORRECTIVE ACTION
Use same action as suggested to solve problems created by
high flows.
PROBLEM: HIGH OR LOW pH LEVELS
Problems caused by high or low pH levels include:
1. A high pH may result in the buildup of mineral deposits that
will plug the holes on the microfabric.
2. A rapid change in pH may upset upstream treatment pro-
cesses, thus increasing the suspended solids loadings
applied to the microscreen.
3. A low pH may result in the corrosion of metal, especially the
microfabric.
SUGGESTED CORRECTIVE ACTION
1. If rapid pH changes are occurring, monitor the plant influent
and chemically adjust the pH as necessary to maintain the
pH within desired levels. Attempt to correct the cause of the
pH changes at the source.
2. Adjust the pH chemically to a balanced relationship with the
alkalinity and temperature to prevent corrosion or scaling
(use of Langelier Saturation Index)8.
3. Divert abnormal pH flows into a flow-equalization system
and return these flows slowly by intermixing them with the
normal flows.
4. Remove mineral scaling from the microfabric with a mild
acid wash.
PROBLEM: HIGH CONCENTRATIONS OF OIL AND
GREASE
Problems caused by high concentrations of oil and grease
include:
1. Plugging of the microfabric;
2. When the microfabric is plugged, there will be a high head
loss through the unit, reduced flow through, and ineffective
cleaning of the fabric by the water sprays.
3. Untreated water may overflow the microscreen bypass
weir.
SUGGESTED CORRECTIVE ACTION
1. Reduce oil and grease loadings at the source.
2. Improve effectiveness of oil and grease removal equip-
ment.
3. Add chemicals to improve oil and grease removals.
4. Increase the drum rotation speed.
5. Increase the water spray pressure.
6. Place additional microscreens in service.
7. Clean the microfabric with hot water, steam or chemicals.
23.213 Operational Strategy
The development of an operational strategy for a mi-
croscreening process treating wastewater will aid in dealing
with situations such as sudden changes in applied water, train-
ing new operators or planning for the future. This section lists
items for you to consider when developing your own opera-
tional strategy.
1. Maintain the filtering rates within the design limits.
2. Adjust the drum rotational speed as needed to compensate
for extreme flow or suspended solids loadings.
3. Monitor and log head loss and flow rates daily because of
an increasing head loss may indicate incomplete cleaning
of the microfabric by the water spray system.
4. If the applied suspended solids load is increasing greatly
due to poor settling in an upstream process, add chemicals
to improve settling.
5. Be prepared to clean the microfabric manually if plugging
occurs.
6. To increase the life of the microfabric, do not apply chlorine
to the wastewater being treated at a location upstream from
the microscreen.
23.214 Shutdown of Microscreen
The microscreen should not be left standing in dirty water. If
the unit is to be left out of service for a week or longer, the tank
should be drained and the microfabric cleaned. This will pre-
vent clogging from solids drying on the fabric and also prevent
slimes from growing in the portion underwater.
When a unit is shut down, complete these steps:
1. Shut off the applied water flow.
2. Allow the water to filter out of the drum.
3. Drain the microscreen structure.
4. Clean the fabric with water sprays.
5. Hose down the sump.
6. Hose down the trough.
7. Shut off the water sprays.
8. Shut off the drive unit.
9. Shut off the ultraviolet lights.
When treating wastewaters of typical strength and pH, cor-
rosion usually is not a serious problem. If chlorine has been
applied to the wastewater, corrosion can be a problem.
23.2f5 Troubleshooting
PROBLEM: POOR SUSPENDED SOUDS REMOVAL
1. Check the hydraulic load. Performance is better at lower
hydraulic loads. How does the flow compare with design
flow?
2. Inspect the upstream units. Increased suspended solids
loading to the microscreen will result in increased effluent
suspended solids.
• If you wish to use this method, consult a textbook on sanitary engineering or water treatment.
-------
Solids Removal from Effluents 315
3. Determine the drum speed. At lower drum speeds a thicker
mat of solids can build up and provide better straining.
4. Look for excessive turbulence upstream. Breaking up of the
flocculated particles at the microscreen influent will result in
poorer suspended solids removal.
5. Check for pin floe carry-over from the upstream secondary
clarifiers. Pin floe will result in a poor quality effluent even if
the microscreen is operating properly because of the diffi-
culty of removing pin floe.
PROBLEM: HIGH HEAD LOSS THROUGH MICROSCREEN
1. Determine the drum rotation speed. If drum is rotating too
slowly, the mat will become too thick and produce a high
head loss.
2. Inspect the upstream units. Increased suspended solids
loadings will result in a rapid buildup of the solids mat.
3. Examine the water spray system for clogging of nozzles.
4. Determine the pressure in the water spray system. A higher
pressure may be needed.
5. Look for a buildup of iron, manganese or grease on the
microfabric. The fabric may need a special cleaning with
acid, steam or hot water.
PROBLEM: POOR SOLIDS REMOVAL AND LACK OF HEAD
LOSS
1. Look for damaged or torn microfabric.
2. Inspect for improperly installed microfabric panel.
3. Check for damaged end seal on the drum.
4. Look for plugged or inoperative head toss indicator.
23.22 Maintenance of Microscreen
As with all equipment, the operator must read the manufac-
turer's recommendations and follow them as they pertain to
each installation. The following maintenance points should be
considered:
1. Lubricate bearings, chains, and drive units as recom-
mended.
2. Wash down daily and maintain good housekeeping prac-
tices.
3. Dewater sump monthly (or as needed) and remove solids
and debris.
4. Inspect microfabric condition monthly.
5. Clean algae and slime growth with chlorox or bactericidal
soap.
6. Clean grease and oil from microfabric with hot water or
steam. CAUTION. Do not clean PLASTIC microfabric with
steam. Use only hot water (120°F or 49°C) to remove
grease. Steam may damage plastic microfabric.
23.23 Safety
Always think safety when working around mechanical
equipment. Lock out and tag the drive units before working on
the motor, the drive units, the drum or any electrical system.
When cleaning with an acid wash or a chlorine solution,
wear protective clothing. This includes rubber aprons, rubber
gloves and boots, and face shield and eye goggles if splashing
of the chemical may occur.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 348.
23.2G What kinds of abnormal conditions could you en-
counter when operating a microscreen?
23.2H What problems are caused by high or low pH levels
when operating a microscreen?
ENO OF LESSON 2 OF 4 LESSONS
ON
SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
-------
316 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 4 Lessons)
Chapter 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 1.
9. How do microscreens remove particles smaller than the
actual openings of the fabric?
10. What is the impact of microscreens on the solids handling
facilities of a treatment plant?
11. Why is a pre-start inspection important before starting any
major piece of equipment?
12. What operational action would you consider taking if a
microscreen had to handle higher-tharvdesign flows and
solids loading?
CHAPTER 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
{Lesson 3 of 4 Lessons)
23.3 SOLIDS REMOVAL FROM SECONDARY
EFFLUENTS USING GRAVITY FILTERS
23.30 Gravity Filters
23.300 Use of Filters
Gravity filtration is second only to gravity sedimentation for
the separation of wastewater solids. This same process, using
deep-bed filtration and granular media, has long been used in
municipal and industrial water supplies. However, these sys-
tems are more frequently used for domestic water supplies that
have much lower suspended solids concentrations than found
in the effluent from secondary wastewater treatment plants.
23.301 Description of Filters
Water generally flows through filters from top to bottom. An
inlet pipe conveys water to an inlet sump that directs the water
to the filter. Filters consist of a top layer of sand. Underneath
the sand is a layer of gravel which supports the sand. Under-
draws are located under the gravel to collect the filtered water.
23.302 Filtering Process
Water to be treated enters at the top of the filter bed through
an inlet valve and is distributed over the entire filter surface.
The water passes evenly down through the media (sand) and
leaves the solids behind. Filtered water then travels out the
bottom of the filter and into the underdrain collection system
which is designed to uniformly collect the flow. Once inside the
underdrain collection system, the water passes through a flow
meter and rate-control valve. The rate-control valve maintains
the desired flow through the filter and prevents backwash
water from entering the filtered water during backwashing.
Most filters operate on a batch basis whereby the filter oper-
ates continuously until its capacity to remove solids is reached.
At this time it is completely removed from service and clewed.
Other designs are available that filter continuously with a por-
tion of the media always undergoing cleaning. The cleaning of
the media may take place either externally or in place.
23.303 Backwashing Process
As suspended solids are removed from water, the filter
media becomes clogged. This is indicated by a head loss read-
ing. Through operating experience, the maximum head toss
before backwashing will be determined. The filter should be
backwashed after the solids capacity of the media has been
met, but before solids break through into the effluent.
Backwashing consists of closing valves to stop influent How
and to protect the filtered water. Backwash water either flows
by gravity or is pumped to the filter. This water flows through
the underdrain system and back through the media. As the
water flows through the media, the sand particles are lifted and
are cleaned by rubbing against each other. The solids retained
by the media are washed away with the backwash water and
the media has been cleaned.
If the media is cleaned externally, the media is removed from
the filter bed, cleaned in a separate system and recycled back
into the bed. In-place cleaning involves washing a small sec-
lion of the filter bed with a traveling backwash water or air-
pulsing system while the remainder of the bed remains in serv-
ice.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 349.
23.3A When should a gravity filter be cleaned?
23.3B Do most filters operate on a batch or on a continuous
basis?
-------
Solids Removal from Effluents 317
23.31 Methods of Filtration
23.310 Filter Types
Most filters used in wastewater treatment are "rapid sand"
filters (Figure 23.16). They also may be called "downflow" (wa-
ter flows down through the bed) or "static bed" (bed does not
move or expand when filtering). These filters operate continu-
ously until they must be shut down for backwashing. Other
designs, such as the upflow and the biflow, are on the market.
Both of these designs are attempts to use more of the filter
media, thereby removing and holding more solids per filter run.
In the upflow filter (Figure 23.17), water enters the bottom
and is removed from the top. The biflow system has water
applied at both the top and bottom and water is withdrawn from
the interior of the bed. Filters are always backwashed in an
upflow direction regardless of the operating flow direction.
23.311 Surface Straining
Downflow filters are designed to remove suspended solids
by either the surface-straining method or the depth-filtration
method. In surface straining the filter is designed to remove the
solids at the very top of the media. The fine grade-sized media
is uniform throughout the bed. Because of this conformity,
surface-straining systems will have a rapid head loss buildup,
short filter runs, and they must be backwashed frequently.
There are, however, no problems with breakthrough of solids.
The solids compress into a mat at the surface which aids in
removing solids; however, the mat is difficult to remove during
backwashing. Backwashing, although needed more fre-
quently, requires less water per wash than does a depth-
filtration system.
23.312 Depth Filtration
Depth filtration is designed to permit the solids to penetrate
deep into the media, thereby capturing the solids within as welt
as on the surface of the media. Depth filtration will have a
slower buildup of head loss, but solids will break through more
readily than with surface straining.
To reduce breakthrough, yet retain depth filtering, the
multi-media design is used. This combines a fine, denser
media (sand) on the bottom with a coarse, lighter media (an-
thracite coal) on the top (Figure 23.18). The coarse media
remove farge solids that would quickly clog finer media. The
fine media will surface-strain solids that penetrate the full depth
of the coarse media bed thereby preventing a breakthrough of
solids. The filter is designed to prevent the fine media from
escaping unless the head loss becomes too great.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 349.
23.3C What is meant by the following terms that are used to
describe "rapid sand" filters?
1. Downflow
2. Static bed
23.3D From what part of the filter are solids removed by
1. Surface straining?
2. Depth filtration?
23.32 Location of Filters in a Treatment System
In wastewater treatment, the filters may be used in the fol-
lowing modes (Figure 23.19):
1. To polish secondary effluent without the addition of chemi-
cals as filter aids just ahead of the filters,
2. To polish secondary effluent with the addition of chemicals
as filter aids just ahead of the filters,
3. To polish secondary effluent that has been chemically pre-
treated and settled, and
4. To polish raw wastewater that has undergone coagulation,
flocculation and sedimentation in a physical-chemical
treatment system.
23.33 Major Parts of a Filtering System (Figure 23.20)
This section describes the major parts of a filtering system
and also how each part works or functions during the filtration
process.
23.330 Inlet
The filter inlet gate allows the applied water to enter the top
of the filter media. When closed it will permit emptying the filter
for backwashing or maintenance.
23.331 Filter Media
The filter media selection is one of the most important de-
sign considerations. Filter beds are made up of silica sand,
anthracite coal, garnet or ilmenite. Garnet and ilmenite are
commonly used in multi-media beds.
Because of rapid plugging, the conventional single-media
filter bed commonly used in portable water systems is gener-
ally unsatisfactory in removing solids from wastewater.
To lengthen filler runs and use the full bed depth, the dual-
and multi-media filters are used. A layer of coarse media
(anthracite) is placed over finer, dense material (sand or gar-
net). The coarse layer allows deep penetration of the solids
into the bed causing a minimum of head loss. The fine mate-
rial prevents breakthrough of solids into the effluent.
23.332 Filter Underdralns (Figure 23.21)
The filter underdrain system is designed to contain the filter
media within the bed to maintain uniform water flows through
the entire bed during both filtering and backwashing.
23.333 Filter Media Scouring
If the filter media is not cleaned thoroughly at each
backwashing, a buildup of solids will occur. The end result of
incomplete cleaning is the formation of mud balls within the
bed. These mud balls settle to the filter bottom and in time
require rebuilding the entire bed. "Surface wash" and "air
scour" are two systems used to improve cleaning of the media.
The surface wash system consists of either fixed or rotating
nozzles installed just above the media. During a backwash, the
bed expansion places the nozzles within the media where
high-pressure water jetting out of the nozzles will agitate and
clean the surface. Because these wash systems are designed
primarily to break up the surface mat, deep filtering beds need
nozzles placed deeper within the media.
-------
318 Treatment Plants
INFLUENT
DIFFERENTIAL
PRESSURE OR
HEAD LOSS WHEN
WATER IS FLOW-
ING THROUGH
FILTER
WATER SURFACE
ABOVE SAND
F,NE MED,A
SILICA SAND
UNDERDRAIN CHAMBER
EFFLUENT
TYPICAL
DIFFERENTIAL
PRESSURE
SENSOR
Fig. 23.16 Differential pressure through a sand filter
-------
Solids Removal from Effluents 319
COVER OPTIONAL
(FOR CLOSED SYSTEM)
"GRID"
DEEP SAND LAYER
GRAVEL LAYERS
WASH WATER
INLET RAW WATER
FILTRATE OUTLET
SAND "ARCHES"
SPECIAL VENT
AIR FOR
SANDFLUSH CLEANING
Fig. 23.17 Cross section of upflow filter
(Source: EPA Process Design Manual lor Suspended Solids Removal)
-------
Treatment Plants
MEDIA
DEPTH
30 "-40"
INFLUENT
>»:* {••LVr/yv*
•J FIN
K^SAND'V&j
^coarse'-4
UNDERDRAIN-
CHAMBER
EFFLUENT
EFFLUENT.
OVERFLOW TROUGH
6-10
in n, n n
V*'V; FINE
i ,«¦, ; •
,r j«
S "
SAND. .V
"t?
O c?
£ COARSE
¦GRID TO
RETAIN
SAND
FEED
CHAMBER
INFLUENT
(a) CONVENTIONAL DOWNFLOW (b) UPFLOW FILTER
FILTER
30"-40"
* COAL
SILICA J*.
Jqu SAND fh«
COAL
SILICA
,.f SAND .CP
Q - a "VVJ
GARNET
SAND
UNDERDRAIN
~ CHAMBER
28 - 48
(C) DUAL-MEDIA DOWNFLOW FILTER
(d) MULTI-MEDIA DOWNFLOW FILTER
Fig. 23.18 Filter configurations
(Source: EPA Process Design Manual for Suspended Solids Removal)
-------
PRETREATMENT
il
DE-
CHLORINATION
DE-
CHLORINATION
DE-
CHLORINATION
PRIMARY
CLARIFICATION
AERATION
»
TANK
I
CHLORINATION
CHLORINE
CONTACT
CHLORINE
CONTACT
CHLORINE
CONTACT
FILTRATION
SECONDARY
CLARIFICATION
Fig. 23.19 Four possible modes of using filters to remove solids
FILTRATION
SECONDARY - /
CLARIFICATION / ^
MODE NO. 1
CHEMICAL ADDITION V J
r
4
FILTRATION
SECONDARY A.
CLARIFICATION \
MODE NO. 2
^ )
MODE NO. 3
CHEMICAL ADDITION
DE-
CHLORINATION
CHLORINE
FROM
PRETREATMENT
PRIMARY ^
CLARIFICATION /
CONTACT
FILTRATION
CO
O
5!
(0
3D
-------
322 Treatment Plants
Rate of flow and loss
Operating,
table
Operating
floor
Pipe gallery
floor
Filter drain
Filter to waste
Filter bed wash-
water troughs
Influent to filters
Perforated
laterals
Wash line
wash troughs
P
Filter sand
Graded grave
Concrete filter
tank
Pressure lines to
hydraulic valves from
operating tables
Effluent to
clear well
Cast-iron,
manifold
Fig. 23.20 Typical rapid sand filter
(From WATER SUPPLY AND TREATMENT by C.P. Hoover, permission of National Lime Association)
-------
Solids Removal from Effluents 323
SAND
UNDERDRAIN
BLOCKS
A. HEADER LATERALS
(COURTESY OF THE AWWA)
HEADER
LATERALS
8/32" DIA DISPERSION ORIFICES
APPROX 49 PER SO FT. -
mm
MM YtfZZZSZZ
OIA CONTROL ORIFICES
APPROX. t PER •«. PT.
COMPENSATMM LATERAL
(SECONDARY)26*5 SOINt
PEED LATERAL (PRIMARY)
101 SO IN.
B. LEOPOLD BLOCK SYSTEM
(Courtoay f. B- Leopold Co )
0
.turn i/r-'*ioi««M
1/£-J2Sc?2S™5 TO
1 L*ER\ft- U< /
i" later Vf-\tt f
T 1
«urr FILTER SIZE
FILTER ARE
UO PT)
FuJMC AREA
(SO IN)
RECOMMENCED
IS^ MAXIMUM
Fig. 23.21 Underdrains
(Source: EPA PROCESS DESIGN MANUAL FOR SUSPENDED SOUDS REMOVAL)
-------
324 Treatment Plants
The air scour system injects air into the bottom of the bed.
This agitates the entire bed, yet requires no additional wash-
water. Care must be taken to prevent air and water flowing at
the same time, or the media will be washed out and lost.
23.334 Washwater Troughs
During backwashirig, the accumulated solids strained out by
the filter media are carried out of the filter bed via the
backwash water troughs. The troughs must be level to uni-
formly collect and withdraw the backwash water, This will help
prevent dead spots (short-circuiting) during the backwash op-
eration.
A smooth trough surface, such as fiberglass, will reduce
routine cleaning; however, fiberglass troughs may be dam-
aged more easily by the weight of the backwash water than
steel or concrete troughs. Filter troughs, particularly fiberglass,
must be well anchored to assure that they will not warp or
attempt to float during backwashing. They also must be de-
signed to withstand the weight of water if filled when there is no
water over the bed.
23.335 Backwash Water Drain
In a wastewater treatment plant, the filter drain allows the
backwash water to leave the filter and return to the plant
headworks for reprocessing. This drain must be opened before
the backwash water flow begins, but not before the water is
filtered down below the level of the backwash trough. If the
drain opens while the filter is still full of applied water, the water
above the troughs will needlessly be recycled back through the
plant.
The drain should be closed completely before the inlet valve
is opened or applied water again wilt be wasted.
23.336 Backwash Water Supply
The backwash water is usually water that has gone through
the comptete treatment process and is of the best quality avail-
able. If non-filtered water is supplied to the backwash system,
clogging of the underdrain system may occur.
Filter backwashes require large volumes of water over a
short period of time; therefore, small- to medium-size plants
need a washwater storage reservoir. Water from the chlorine
contact tank commonly is used.
Large filters are often split in half to reduce the size of pumps
and piping required for backwashing. This also can reduce the
water storage requirements because a pause between wash-
ing the two halves will provide time to refill the storage reser-
voir.
Sectional filters (Figure 23.22), designed to backwash one
small section at a time, do not require a large backwash water
storage supply. These filters use pumped water as it is being
filtered through other sections.
23.337 Backwash Water ftate Control
The backwash water may be supplied through pumps or by
gravity from a storage tank. Both methods require careful con-
trof of the flow rate.
Backwash water supplied through pumps will maintain a
more constant flow over the entire wash cycle than washwater
from gravity storage. Water supplied from storage tanks may
require adjustment of the rate-control valve to maintain con-
stant flows as the storage tank level drops, due to a decrease
in the available pressure head on the backwash water.
23.338 Used Backwash Water Holding Tank
The filter backwash water contains solids concentrated from
many gallons of applied water. Because of the high solids
concentration, this water must be retreated in the treatment
process. Since the backwash flow rates are very high, they
must be dampened through a holding tank to avoid hydraulic
overloads on the treatment plant. When these high flows are
returned to the plant headworks, a plant can become upset in
all except very large treatment plants or those using sectional
filters. To prevent such overloads, backwash water holding
tanks are used. The holding tank is filled during a backwash
operation and slowly emptied back to the plant headworks
between washings.
Holding tanks will become a source of foul odors if good
housekeeping is not practiced; therefore, the tank should have
a sloped bottom and a water spray system for cleaning.
23.339 Effluent Bate-Control Valve
A valve automatically controls the filtered water flow leaving
the bed. This valve is designed to maintain a constant water
level in the fitter. When operating a clean filter, this valve will be
closed down restricting the flow. As the head loss through the
media increases, this valve must open more to maintain a
constant flow. This valve must be closed during filter backwash
to prevent backwash water from mixing with previously filtered
water.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 349.
23.3E What kind of material is used for filter media?
23.3F What can happen if the filter media is not thoroughly
cleaned during each backwashing?
23.3G Why should the backwash water be of the best quality
available?
23.3H What is the purpose of a used backwash water hold-
ing tank?
23.34 Filter System Instrumentation
Instrumentation is essential for all but the small package
plant installations. Instrumentation associated with filtering is
used to monitor the plant performance, to operate the plant in
the absence of the operator and to trigger an alarm if abnormal
conditions develop. The system may be simple or very com-
plex and, depending on the facilities, each has its place.
instrumentation, just as all equipment, is only as useful as
allowed by the quality of maintenance. Stated another way, if
there are intermittent errors in a flow-meter signal and they are
not corrected, then the operator cannot trust any of the
readings and must disregard all of them. The usefulness of the
instrument is then very limited.
Comments regarding instrumentation in the following sec-
tions are applicable to plants of all sizes.
23.340 Head Loss
Head loss is one of the most important control guidelines in
the operation of the rapid-sand filter. Each filter or filter half
requires a head loss indicator, preferably one with a read-out
chart. This will indicate the present condition of the bed, its
ability to remove solids, and the effectiveness of the backwash
operation.
-------
A.
Influent lin*.
f.
Effluent and backwash ports.
K.
Washwoter hood.
P
Mechanism drive motor.
B
influent ports.
G.
Effluent channel.
1.
Washwater pump assembly.
O.
Backwash support retaining springs.
C.
Influent channel.
M.
Effluent d
-------
326 Treatment Plants
Head loss is determined by measuring the water pressure
above and below the filter media (see Figure 23.16, page 318).
With the filter out of service, the pressure will be the same
(zero difference).
When water flows through the bed, the pressure below the
media will be less than the pressure above the media (when
the pressure levels are measured or read at the same eleva-
tion). Measured in feet (or meters) of water, the difference
becomes the head loss.
As the media bed becomes filled with solids, the head loss
becomes greater. There is a point at which little or no water
can pass through the filter. The operator wants the head loss to
always be less than at that point; therefore, the filter backwash
control point must be less than the maximum design head loss.
A typical set point to start backwash is at 7.0 feet (2.0 m) of
head loss. If a filter is operating with a 6,0-foot (1.8 m) head
loss, the operator knows the filter will need washing soon. If
after washing the head loss is 4.0 feet (1.2 m), this indicates a
very poor washing or it may indicate a malfunctioning instru-
ment. After a proper washing, the head loss should be less
than 0.5 feet (0.15 m) at start-up. The head loss will then slowly
increase to the point where backwashing is required again.
23.341 Filter Flow-Rate and Totalizer
Each filter or filter half requires a flow indicator and totalizer
on the filtered water line. This is needed to determine proper
filtering rates (gal/min/sq ft or liters/sec/sq meter). Also, with
the total volume filtered and the volume of backwash water
used, the percent of production (filtered) water used for
backwashing can be calculated. This is important because ex-
cessive wash water usage is costly and must be controlled.
The backwash water should average 5 to 10 percent of total
water production.
23.342 Applied Turbidity
A continuous-reading turbidimeter with read-out chart on the
applied water is useful in monitoring the performance of the
secondary settling tanks. This read-out will alert the operator to
pending problems if the turbidity suddenly increases. With ex-
perience, chemical dosages can be adjusted as turbidity
changes.
23.343 Effluent Turbidity
A continuous reading of turbidity with a chart on the filter
effluent will monitor the filter performance. A sudden increase
may indicate a filter breakthrough (cracked bed) and may be
used or instrumented to set off alarms if specified limits are
exceeded. One unit, with proper valving, may be used to
monitor more than one filter.
23.344 Indicator Lights
Indicator lights are beneficial to operators in keeping track of
the filter system. Lights can easily indicate which filter is in
service, out of service, or backwashing. They can indicate if
filter pumps, wash water pumps or air blowers are running, out
of service or on standby and ready to run. Indicator lights can
be used with the alarm system to show abnormal conditions.
23.345 Alarms
Alarms needed to alert the operator should include high
applied water level, high turbidity and pump malfunctions.
Backwash water supply and holding tanks both need high
water level alarms.
All alarms should be tested for proper functioning at least every
60 days.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 349.
23.31 How is the head loss through the filter media deter-
mined?
23.3J How often should filter system alarms be tested for
proper operation?
23.35 Operation of Gravity Filters
23.350 Pre-Start Checklist
Before starting up any major system, such as gravity filters,
a thorough check of each component must be made to prevent
damage to the equipment and/or injury to personnel. The fol-
lowing items should be included in your checklist for starting
filtering systems.
1. Be sure all construction debris has been removed. Wood
scraps, concrete chips, nails and other trash can damage
equipment such as pumps and valve seats. Trash
dropped into the filter media will work its way to the bot-
tom, thus reducing the effective area of the filter.
2. Inspect the electrical installation for completeness. Check
safety lockouts, safety covers and equipment overload
protections.
3. Check motors and drives for proper alignment, for proper
safety guards, and for free rotation.
4. Examine motors, drive units and bearings for proper lubri-
cation.
5. Check motors for proper rotation. (A three-phase motor
may run in either direction.)
6. Inspect pumps and motors for excessive vibration.
7. Fill tanks and piping and look for leaks.
8. Open and close valves manually and run each valve
through a complete cycle to check limit setting.
9. Put the automatic controls through a "dry run."
10. Inspect the total system for safety hazards.
11. Backwash the media several times. Skim the fines from
the surface between each washing prior to placing filter
into service.
23.351 Normal Operation
Since most wastewater gravity filters are deep-bed,
downflow, rapid-sand type filters, this section will present in-
formation based on them. Nevertheless, most of the informa-
tion can be applied to other filter designs with some possible
modifications.
FILTERING
The applied water enters at the top of the filter bed through
an inlet valve and is distributed over the entire filter surface.
The water passes evenly down through the media and leaves
the solids behind. Filtered water then travels out the bottom of
the filter and into the underdrain collection system which is
designed to uniformly collect the flow. Once inside the under-
drain collection system, the water passes through a flow meter
and rate-control valve. The rate-control valve maintains the
desired flow through the filter and prevents backwash water
from entering the filtered water during backwashing. Success-
ful filter operation depends on effective backwashing of the
filter media.
-------
Solids Removal from Effluents 327
BACKWASHiNG
As suspended solids are removed from water, the filter
media becomes clogged. This is indicated by the head loss
reading (Figure 23.16, page 318). Through operating experi-
ence, the maximum head loss before backwashing will be de-
termined. The filter should be backwashed after the solids ca-
pacity of the media has been met, but before solids break
through into the effluent.
By maintaining complete records, the operator can monitor
the filter efficiency and determine if the backwashings are
adequate.
Backwashing a filter manually, although sometimes neces-
sary, is very time-consuming; moreover, manual backwash-
ings are inconsistent. Automatic backwashing, on the other
hand, can be a simple procedure which requires a minimum of
operator time.
To maintain smooth operations, the automatic backwash
cycle should be initiated by the operator. This mode of opera-
tion permits the operator to backwash at a convenient time
thereby allowing time for keeping records current and complet-
ing the necessary maintenance duties. Automatically starting
backwashes, although workable in a large system, can be very
inconvenient to the operation of a small system.
At the start of the backwash cycle, the rate-control valve
must be opened slowly to a low-rate of backwash. This pre-
vents damaging the underdrain system or disturbing the rock
and gravel layers of the bed. This damage can occur when an
empty bed has high backwash water flows suddenly injected
into it or if trapped air in the piping and underdrain system is
violently forced into the bed. After the air has been purged and
the water level is up to the washwater troughs, the bed can no
longer be damaged by high backwash rates.
Some plants use an air scouring system to clean the filter
media. The air scour system injects air into the bottom of the
media bed. This agitates the entire bed, yet requires no addi-
tional washwater. Care must be taken to prevent air and water
flowing at the same time, or the media will be washed out and
lost.
To prevent the loss of filter media into the backwash troughs:
1. Draw the water-level in the filter down to within a few inches
over the top of the filter media,
2. Pause a moment after air washing before starting the water
wash,
3. Wash with a low water-flow rate until the trapped air has
escaped the filter media, and
4. Never backwash a filter with water containing air.
The media becomes intermixed during the high agitation of
air scrubbing or high-rate backwashing. With proper control,
however, the media will automatically regrade due to the dif-
ference in specific gravities of the particles.
By design, the filter media is prevented from escaping into
the underdrain system; nevertheless, operational care must be
taken to prevent damaging the underdrains while backwashing
or the filter media will be lost into the collection system.
Uniform water flow through the filter bed is important to pre-
vent the breakthrough of solids due to high velocities. Also,
high velocities will cause the media to be disturbed and relo-
cated if the backwash flow is not uniform.
The following situations indicate a disturbed or damaged
filter underdrain:
1. Consistently poor quality effluent (high suspended solids
levels) while there is little buildup of the filter head loss.
2. Boiling areas and very quiet ("dead") areas of the filter
media during backwashing. This is most noticeable during
high wash rates in a nearly clean filter.
3. Filter media in the effluent.
Improper control of the system during backwashing is gen-
erally the cause of damaged filter bottoms, providing they were
properly installed. Damage to the filter bottom could result if:
1. The maximum backwash rate is allowed to enter into an
empty filter, or
2. A large volume of air preceded the maximum backwash
rate causing a WATER HAMMER.9
The only way to correct a damaged filter bottom is to remove
the media and rebuild the bed. A bed with the media displaced
to a minor extent may be corrected by extended and properly
controlled backwashing. This will regrade the media.
After backwashing, the filter normally has water up to the
sides of the troughs. To fill the remaining portion of the filter,
open the inlet valve. If the filter has been drained for mainte-
nance, fill the filter, as if you were starting to backwash, up to
the top of the sides of the troughs. Now you can fill the filter
using the inlet valve. Be sure to waste some of the filtered
water at the start until completely filtered and clear water is
leaving the filter. An empty filter should not be filled through the
inlet valve because the water falling onto the media will disturb
the bed and result in uneven filtering. Also, filling the backwash
troughs with water in an empty filter will place an unnecessary
load (weight of water) on the troughs.
After the filter media is clean, the backwash water flow is
slowly reduced. This permits the media to regrade itself
through gravity settling. The heavier particles (gravel, garnet,
sand) will settle to the bottom first and as the uplift velocities
reduce, the lighter particles (anthracite coal) will settle, thereby
regrading the filter bed back to its original placement. This
regrading must occur at the end of each backwash cycle.
When the used backwash water holding tank is empty, the
tank should be inspected. A check observation of the solids
settled on the bottom of the empty holding tank will alert the
operator to any loss of filter media due to improper backwash
procedures, such as excessively high flow rate or short-
circuiting.
By analyzing the records and observing the complete wash
cycle, the operator can determine if the backwashing se-
quence is adequate. If the backwashings are not complete,
experiment with one or all of the following:
1. Adjust the media scouring time,
2. Adjust the low wash rate,
3. Adjust the high wash rate,
4. Adjust the time of regrading the media, and/or
5. Backwash more frequently by beginning to wash at a lower
head loss.
» Water Hammer. The sound like someone hammering on a pipe that occurs when a valve is opened or closed very rapidly When a valve
position Is changed quickly, the water pressure in a pipe will increase and decrease back and forth very quickly This rise and fall in
pressures can do serious damage to the system.
-------
328 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 349.
23.3K Why should a pre-start check be conducted before
starting filtering systems?
23.3L What is the purpose of the rate-control valve?
23.3M When should a filter be backwashed?
23.352 Abnormal Operations
Following is a list of conditions that are not normally found in
the day-to-day operation of filtration systems; however, these
conditions could occur at almost any time. Recommendations
are added to aid you in adjusting to the situation.
1. High solids in the applied water due to bulking sludge,
rising sludge, or solids washout in the secondary clarifier.
a. Run JAR TESTS10 and adjust chemical dosage as
needed.
b. Place more filters in sen/ice to prevent breakthrough.
c. Prepare to backwash more frequently.
2. Low suspended solids in applied water; however, solids
pass through filter.
a. Run jar tests and adjust chemical dosage as needed.
Test a combination of chemicals and polyelectrolytes.
b. Place more filters in service to reduce velocity through
the media.
c. Backwash filter and pre-coat clean filter with FILTER
AID"
3. Loss of filter aid chemical feed.
a. Place more filters in service to reduce velocity through
media.
b. Backwash more frequently.
c. Pre-coat clean filters by hand when placed into serv-
ice.
4. High wet weather peak flows.
a. Place more filters in service.
b. Run jar tests and adjust chemical dosage as needed.
c. Prepare for peak daily flows by backwashing early.
5. Low applied water flows.
a. Reduce number of filters in service. Run one-half of a
filter at a time.
b. Prepare to take one filter out of service and backwash
when flow or head loss increases, thereby preventing
breakthrough.
6. High color loading.
a. Run jar tests and adjust chemical dosage as needed.
b. Add chlorine to applied water.
c. Usually color cannot be removed with filtration; con-
sequently the problem must be corrected at the
source.
7. High temperature.
a. Run jar tests and adjust chemical dosage as needed.
b. Prepare for AIR BINDING12 of filters because water
will release gases more readily at higher tempera-
tures.
c. Place more filters in service to reduce head loss
through the media.
d. Increase backwash water flow rates to obtain the
same bed expansion used when backwashing with
colder water.
8. Low water temperature.
a. Run jar tests and adjust chemical dosage as needed.
b. Prepare for air binding of filters as cold water will carry
more gases to the filters. Backwash more frequently if
air binding occurs.
c. Place more filters in service to reduce head loss
through filter media.
d. Reduce backwash water flow rates to obtain the same
bed expansion used when backwashing with warmer
water.
9. Air binding.
a. Backwash at a lower head loss.
b. Place more filters on line to reduce head loss through
media.
c. Take filter out of service and allow air to escape to the
atmosphere. This will reduce head loss; however, if
placed back into service without backwashing, solids
will likely be drawn through the media and into the
effluent.
10. Negative pressure in filter.
a. Reduce flow through the filter by adding additional
units.
b. Backwash at a lower head loss.
c. Skim surface of media (about one-half inch or 1.3 cm)
to remove fines.
d. Prevent filter from running at a low filtration rate. This
builds a mat on the surface and then sharply in-
creases to a high rate of water through the filter.
e. A negative pressure within the filter will cause a false
reading from the differential pressure sensor.
10 Jar Tests. A laboratory procedure that simulates coagulation Iflocculation with differing chemical doses. The purpose of the procedure Is to
ESTIMATE the minimum coagulant dose required to achieve certain water quality goals. Samples of water to be treated are placed in six
jars. Various amounts of chemicals are added to each jar, stirred and the settling of the solids is observed. The lowest dose of chemicals that
provides satisfactory settling is the dose used to treat the water.
11 Filter Aid. A chemical (usually a polymer) added to water to help remove fine colloidal suspended solids.
12 Air Binding. The clogging of a filter, pipe or pump due to the presence of air released from water.
-------
11. High BOD and COD.
a. Handle same as high suspended solids.
b. Chlorinate applied water.
12. High coliform group bacteria levels.
a. Chlorinate applied water to increase contact time.
Solids Removal from Effluents 329
4. Run jar tests to maintain optimum chemical dosages. As
the applied water quality changes (solids, alkalinity, tem-
perature), the filter aid requirements will change. The
operator must be aware of the changes and the effective-
ness of the chemicals applied.
5. With complete backwashing, a high quality effluent can be
maintained without wasting any filtered water before plac-
ing the filter back into service.
b. Place additional units in service to increase contact
time.
c. Run jar tests and adjust chemical dosage as needed
to reduce suspended solids.
13. Chlorine in applied water.
a. Discontinue adding polyelectrolytes as chlorine will
interfere with them.
b. Run jar tests and adjust chemical dosage as needed.
14. pH change in applied water.
a. Run jar tests and adjust chemical dosage as needed.
b. Change type of filter aid if necessary.
15. High grease and oil in applied water.
a. If in solution, they will pass through media.
b. If not in solution, they will be trapped in the bed, thus
requiring extra hosedown during each backwash.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 349.
23.3N List at least five of the various types of abnormal
operating conditions that cculd occur while operating
a filtration system.
23.30 How would you adjust to a situation in which you were
treating a high solids content in the water applied to a
filter?
23353 Operational Strategy
The development of an operational strategy for the filtration
of wastewater will aid in dealing with situations such as sudden
changes in applied water, in training new operators or in plan-
ning for the future. Following are points to consider when
developing or reviewing your plans.
1. Maintain the filtering rates within the design limits. Add
units or remove them from service as needed. Very low
filtering rates will produce matting on the surface. This
matting will cause breakthroughs if the flows are increased
sharply. Excessively high rates will pull the solids through
the filter and into the effluent.
2. Each backwash must be a complete cleaning of the media
or solids will build up and form rnudballs, or cause the
media to crack.
3. To remove mudballs, first backwash thoroughly. Then
super chlorinate manually and draw the chlorinated water
into the filter media. Allow this chlorinated water to stand
for 24 or 48 hours to soak the mudballs and finally
backwash thoroughly again.
6. If the effluent turbidity reaches 3 to 4 TURBIDITY UNITS,'13
a change should be made to correct the problem. Either
adjust chemical dosage, adjust flow rate or backwash the
filter.
7. Filter walls that are constructed with a smooth surface
{sacked) or painted with a good sealant are easy to keep
clean. A rough surface provides an excellent area for
algae and slimes to grow.
8. Controls and instrumentation must be protected from the
elements. Cabinets that must be opened to adjust instru-
ments must be out of the rain, dust and extreme heat.
9. Air used to operate instruments or transmit signals must
be CLEANED AND DRIED to prevent damaging the
equipment.
10. Every three or four months, measure and record the
freeboard to the filter media surface (Figure 23.23). A
small amount of media loss is normal, but an excessive
amount (2 to 3 inches or 5 to 7 centimeters) indicates
operational problems.
11. After the filters have been in service for some time, obtain
a profile of the media to determine if it is being displaced.
A plug sample will show if the media are being regraded
after each backwash.
12. When landscaping around uncovered filters, keep trees
and shrubs that will drop leaves into the bed away from the
filter because leaves are very difficult to backwash out of
the media.
13. Never throw trash such as cigarette butts into the filter
media, because this trash may not backwash out and in-
stead may work its way into the media.
14. Occasionally chlorinate ahead of the filters to control algae
and slime growths on the walls and within the media
There will be a short period of discolored effluent after the
initial application, but the waiter will turn clear in a short
while.
15. Calculate the unit cost to treat wastewater. Apply this cost
to the volume of water used per backwash. Inform all
operators of this because it may easily cost in excess of
$100 per filter wash.
16. Always fill an empty filter bed through the backwash sys-
tem to prevent disturbing the media surface. If an empty
filter is filled through the influent valve, water will flow into
the washwater troughs, over the top edges and onto the
top of the media. The force of this falling water will disturb
the media.
17. Allow dry filter media to soak several hours before
backwashing. Dry media will tend to float out with the
backwash water.
,3 Turbidity units, if measured by a nephelometric (reflected light) instrumental procedure, are expressed In nephelometric turbidity units
(NTU). Those turbidity units obtained by other instrumental methods or visual methods are expressed in Jackson Turbidity Units (JTU) and
sometimes as Formazln Turbidity Units (FTU). The FTU nomenclature comes from the Formazin polymer used to prepare the turbidity
standards for Instrument calibration. Turbidity units are a measure of the cloudiness of water.
-------
330 Treatment Plants
TOP OF WALL
SECTION OF FILTER
FREE BOARD
PROBE
ANTHRACITE
SAND .
GRAVELV £.?, O.o ^V>S^.
% ¦ y o -o»u i
I
,~1
',',v
PLUG SAMPLE
ANTHRACITE
SAND
* 1-1/2 IN. PIPE
Fig. 23.23 Section of filter and plug sample
-------
Solids Removal from Effluents 331
18. Maintain a log (Figure 23.24) of the filtering operation
which includes the following:
a. Time filter was placed into service and total hours run
between washings,
b. Volume of water processed between washings,
c. Applied water rate at start and end of filter run,
d. Head loss at start and end of filter run,
e. Applied suspended solids and BOD,
f. Effluent suspended solids and BOD,
g. Percent removal of suspended solids and BOD,
h. Chemicals added as filter aids, mgIL,
i. Chlorine added to applied water, mg/L,
j. Remarks of special observations and maintenance,
k. Backwash water flow rates and duration,
I. Surface wash flow rate and duration, and
m. Influent and effluent turbidity.
23.354 Shutdown of a Gravity Filter
If the filter is to be out of service more than a week, it should
be dewatered and air dried. This will help control slime and
algae growth on the walls, troughs and within the media. Dried
algae can be hosed from the walls prior to backwashing and
returning to service.
To remove a filter from service, switch controls to the manual
mode of operation and then:
1. Close the influent valve,
2. Filter all the water possible through the rate-control valve,
and
3. Open the drain valve.
Hose down and backwash the filter before returning it to
service.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 349.
23.3P How would you determine if media are being lost from
a filter?
23.30 Why should trees and shrubs be kept away from un-
covered filters?
23.36 Troubleshooting
PROBLEM: HIGH TURBIDITY AND SUSPENDED SOUDS IN
THE EFFLUENT.
1. Check for excessive head loss. Breakthrough will occur at a
high head loss.
2. Look for fluctuating flows. Widely varying flows will cause
breakthrough.
3. Determine filter aid dosages.
4. Examine backwash cycle for complete wash.
5. Inspect for damaged bed due to backwashing.
PROBLEM: RAPID BUILDUP OF HEAD LOSS.
1. Check applied water suspended solids.
2. Check filter aid dosage.
3. Determine applied water flow rate.
4. Check backwash cycle for complete wash.
5. Inspect head loss differential pressure sensor for air in one
side. This will give a false reading.
PROBLEM: INSIGNIFICANT BUILDUP OF HEAD LOSS.
1. Check applied water suspended solids.
2. Check applied water flow rate.
3. Determine filter aid dosages.
4. Check head loss differential pressure sensor for air in one
side. This will give a false reading.
5. Examine filter effluent for suspended solids going out (filter
breakthrough).
6. Inspect for damaged bed due to backwashing.
7. Backwash and check for complete cycle.
PROBLEM: RAPID LOSS OF FILTER MEDIA.
1. Look for washout during backwash cycle.
2. Examine for media in effluent indicating a damaged filter
underdrain.
3. Check for excessive scouring during backwash cycle time.
Excessive scouring will grind the media into fines.
PROBLEM: HIGH HEAD LOSS THROUGH CLEANED
FILTER.
1. Inspect differential pressure sensor for air in one side.
2. Check for incomplete backwash cycle.
3. Look for mudballs in filter media. Take a plug sample. (Fig.
23.23, page 330.)
PROBLEM: FLOW INDICATED WHEN EFFLUENT VALVE
IS CLOSED.
1. Inspect differential pressure sensor for air in one side.
2. Check instrumentation loop for calibration.
3. Examine valve for proper position.
PROBLEM: BACKWASH STOPS BEFORE COMPLETING
CYCLE.
1. Look for sticking valve.
2. Inspect for electrical relay hang-up.
3. Check for timer out of sequence.
4. Examine backwash water supply.
5. Inspect electrical control (pump lock-out).
23.37 Safety
Always think safety when working around moving equipment
and motors with automatic controls. Filtration systems have
electrical, chemical and mechanical safety hazards. Operators
are usually well protected from electrical hazards; however,
there are times when opening a panel to look for trouble or to
adjust a timer may expose you to electrical hazards. Always
-------
MONTH ¦ IAN 7K
FILTER LOG
FILTER NUMBER i
START FILTER
STOP FILTER
FILTER WASH
DATE
TIME
FILTER
RATE
MGO
HEAD
LOSS
FEET
DATE
TIME
FILTER
RATE
MGO
HEAD
LOSS
FEET
HRS.
FTU
DATE
TIME
REMARKS
OPER.
A
B
A
B
A
B
A
B
t'ini
o/oo
-
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—
-
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—
> -AUfoMAf"?
A.&
hA-lt
ftoo
/.$
16
-
-
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1000
If
/¦r
7
7
t-b
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MANUAL &AC^^A6H
g/fyt'/
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to
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£>S
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IS
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Fig. 23.24 Log of filter operation
-------
Solids Removal from Effluents 333
use safety equipment (rubber electrical gloves, voltage test
meters, fuse pullers, and lock-out switches) and approved
safety procedures when working with electricity.
Chemical hazards include chemical burns and skin irritation
from direct contact with chemicals. Also, there is the hazard of
slipping and falling caused by chemical spills. Good house-
keeping will reduce the safety hazards caused by chemicals.
Mechanical hazards associated with filters are similar to
those found throughout the treatment plant. Safety guards
must be in place, equipment operated automatically must be
identified by warning signs, and work areas should be well
lighted.
23.38 Review of Plans and Specifications
While reviewing the plans and specifications of a gravity
filtration system, you should consider the items listed in this
section.
1. Filters require regular servicing; therefore, provisions must
be made to handle the normal flows during periods of
servicing. Regular maintenance includes servicing of
valves, instruments and filter media.
2. The quality of the water applied to the filters must be con-
sidered when a filtering media is specified. A high sus-
pended solids content in the applied water will quickly plug
a fine-media filter, thereby requiring frequent backwash-
ing.
3. Install sufficient instrumentation to adequately monitor the
process and to determine operating efficiencies. Include
instrumentation to measure and record applied flows,
backwash flows, head loss, and water quality before and
after filtration.
4. Be sure that each step in the automatic system is com-
plete before the following or next step can begin.
5. Provide a means to reset the automatic system if the
backwash cycle is interrupted.
6. Keep the automatic backwashing system uncomplicated,
especially in small plants. The operator should be on hand
at the start of a filter backwash cycle. Housekeeping
chores can be performed while keeping an eye on the filter
washing process.
7. Install instruments out of the weather and well protected
from the weather. Even weather-proof cabinets must be
opened during the maintenance and servicing of instru-
ments and equipment.
8. Install the instruments' read-out meters, charts and gages
in a convenient and centralized location.
9. Separate and shield instrumentation signals from all high
voltage (110 volts and higher) and from other equipment
noise that may be picked up by the instruments as a false
signal.
10. Provide adequate storage for chemicals. A minimum sup-
ply of chemicals must be on hand even while waiting for a
full shipment.
11. Provide adequate storage for both the backwash water
supply and the used backwash water.
12. When reviewing designs for the future, keep today's flows
in mind. Equipment operating below 10 percent capacity
may be useless for years.
13. Visit similarly designed plants that are currently in opera-
tion and talk to the operators regarding possible design
improvements.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 349.
23.3R What are the three main types of safety hazards
around filtration systems?
23.3S When reviewing plans and specifications for a filtration
system, instrumentation should be available to mea-
sure and record what items?
23.3T Where should the instruments' read-out meters,
charts and gages be installed?
bk
END OF LESSON 3 OF 4 LESSONS
ON
SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
-------
334 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
(Lesson 3 of 4 Lessons)
Chapter 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 2.
13. Why are multi-media filters used?
14. How can a filter bottom be damaged?
15. What is the purpose of instrumentation used with a filter
system?
16. How does a rapid-sand filter work?
17. Why should you attempt to maintain filtering rates within
the design limits?
18. How would you remove a gravity filter from service?
CHAPTER 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
By Ross Gudgel
(Lesson 4 of 4 Lessons)
23.4 SOLIDS REMOVAL FROM SECONDARY
EFFLUENTS USING INERT-MEDIA PRESSURE
FILTERS
23.40 Use of Inert-Media Pressure Filters
Inert-media pressure filters remove suspended solids and
turbidity from the secondary effluent after the addition of chem-
ical coagulants such as a polymer and/or alum. The filtration
process is used to meet waste discharge requirements for final
effluent suspended solids and turbidity limits established by an
NPDES permit when these limits cannot be met by secondary
treatment processes. Filtration also will have a direct bearing
on the disinfection of the final effluent by the removal of more
solids from the water to be disinfected. Fewer solids will reduce
the amount of chlorine necessary to meet the NPDES permit
coliform requirements.
The filter system usually consists of:
1. A holding tank or wet well for secondary effluent storage,
2. Filter feed pumps which pump the secondary effluent from
the holding tank to the filters,
3. A chemical coagulant feed pump system which injects the
necessary coagulants into the influent line to the filters,
4. Single, dual, or multi-media filters that trap the suspended
solids and remove the turbidity,
5. A filter backwash wet well for clean backwash water stor-
age,
6. Filter backwash pumps which pump clean water back
through the filter to remove the trapped suspended solids,
and
7. A decant tank that provides for holding the spent backwash
water to allow the suspended solids to settle while the
clarified water is either directly recycled to the filtlers or is
returned to the headworks.
Figure 23.25 shows a schematic view of the items outlined
above and further discussed in the following sections.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 350.
23.4A What is the purpose of the inert-media pressure filter?
23.4B What chemicals are commonly used with the filtration
process and why?
23.4C List the major components of a pressure filter system.
23.41 Pressure Filter Facilities
The following sections describe facilities which are typical for
a filter plant with a capacity of 5 MGD. Facilities at larger or
smaller plants would be quite similar but might differ signif-
icantly in the numbers and sizes of the various components.
23.410 Holding Tank (Wet Well)
Secondary effluent from the treatment plant's secondary
sedimentation tanks is conducted through a channel or pipe to
a holding tank. The purpose of this tank is to store water and to
allow additional settling to the suspended solids before the
water is applied to the filters. Most tanks of this type are very
similar to secondary clarifiers. They have flights or scrapers to
move the settled solids towards a sludge hopper for return to
the solids handling facility.
A bypass structure should be provided to permit secondary
effluent to bypass the pressure filters during emergency condi-
tions, such as equipment failures or clogged filters. Bypassed
flows should go into emergency holding basins or into the
chlorine contact tank for final treatment before discharge. An
alternate emergency storage procedure would be to divert
secondary effluent into the decant tank.
-------
UMIUCt Uln MFLUfNT
Fig. 23.25 Schematic view of pressure filter system
-------
336 Treatment Plants
Spent backwash water may also be returned to the decant
tank. Both flows receive some settling and the clarified effluent
then overflows into the holding tank through weir slots between
the two tanks for recycle to the filters. In either method of
operation, the floatable materials in the holding tank are col-
lected and discharged to the solids handling section of the
plant for disposal. For additional information on clarifier opera-
tion and maintenance, see Chapter 5, "Sedimentation and Flo-
tation."
23.411 Filter Feed Pumps (Figure 23 26)
Filter feed pumps lift the secondary effluent from the holding
tank and pump it through the filters. Generally they are of the
vertical-turbine wet-pit type pump with either a closed or
semi-open impeller. The pumps are driven by either fixed-
speed, multi-speed (two speed), or variable-speed motors or a
combination of these. Each pump should be equipped with a
manually adjusted bypass valve to avoid the possibility of the
system operating at the shutoff pressure of the pumps. If this
happens, the pumps could be damaged because no water
would flow through the pumps. Each valve should be adjusted
to allow a given bypass flow as recommended by the manufac-
turer.
The water level in the holding tank may be sensed by a level
transmitter. The transmitter provides a signal used for starting
and stopping of the pumps and for a set point signal for the
controller which controls filter flow.
Starting and stopping of the pumps is controlled by a
HAND-OFF-AUTO (HOA) switch for each pump. Another
switch is used to select the sequence of automatic starting
(lead or lag). Normal automatic start-stop control of the pumps
may be by means of current trips using the signal representing
the water level in the holding tank. A low-water probe in the
holding tank will stop all pumps it the water level drops below a
pre-set elevation. For additional information on the operation
and maintenance of pumps, see Chapter 15, "Maintenance."
23.412 Chemical Feed Systems
Various types of chemicals may be added to the filter influent
flow to insure coagulation and flocculation of the suspended
material. This coagulation and flocculation aids the filtering
process by joining many of the finely divided and colloidal sus-
pended solids into a floe mass which is easily trapped on or in
the filter media, thus allowing clear water to pass through the
filter. Alum and polymers are the most common chemicals
used.
A discussion of the reasons for using chemicals and the
method of feed is contained in this section.
ALUM {ALUMINUM SULFATE) (Figure 23.27)
Alum is a coagulant which produces a hydrous oxide floe.
This floe causes suspended material to stick together by elec-
trostatic or interionic force when contact of the chemical and a
solid particle is made in the filter influent flow.
The alum may be pumped by a mechanical diaphragm, posi-
tive displacement pump. The dosage is manually adjusted by
adjustment of the pump stroke length. Motor speed may be
controlled by a silicon controlled rectifier (SCR) drive unit that
uses a filter-flow signal to pace the pump in the automatic
mode. The SCR drive is also equipped with a manual poten-
tiometer for manual speed control and a meter indicating per-
centage of total or full motor speed.
The pump discharge check valve has a built-in back pres-
sure device to prevent nonlinear delivery due to low discharge
pressure and to prevent siphoning. All wetted parts of the
pump are selected for their chemical resistance.
POLYMERS (POLYELECTROLYTES)
Polymers are flocculation aids which are classified on the
basis of the type of electrical charge on the polymer chain.
Polymers possessing negative charges are called "anionic,"
positive charged polymers are called "cationic," and polymers
that carry no electrical charge are called "nonionic." Polymers
cause the suspended material to stick together by chemical
bridging or chemical enmeshment when contact is made in the
filter influent flow.
Generally only the "anionic" polymers are used in conjunc-
tion with alum.
Polymer usually is injected into the influent line of the filters
downstream from the point of alum injection.
The polymer may be prepared for use (dilution and aging) by
a polyelectrolyte mixer unit. This unit consists of a dry polymer
feeder with storage hopper, a solution-water flow meter with
regulating valve, pressure regulating valve, pressure gage,
solenoid valves, dilution water flow meter with regulating valve,
polymer wetting cones, a mixing/aging tank, slow-speed mixer,
transfer pump, metering/storage tank, and a metering pump
with SCR drive.
The dry feeder is a screw-type feeder capable of metering
dry polymer of densities ranging from 14 to 42 Ibs/cu ft (225 to
675 kg/cu m) at an adjustable rate to the wetting cones in order
to prepare various solution concentrations.
The mixing/aging tank and the metering/storage tank are
sized based on the projected use of polymer. The tanks usually
are made of steel and are provided with a fiberglass liner. The
mixer, a low-shear type (to avoid breaking up floe), is fitted with
a stainless steel shaft and impellers.
The slow speed, positive displacement, "progressing cavity"
type transfer pump conveys the mixed polymer solution from
the mixing/aging tank to the metering/storage tank with mini-
mal polymer shear. The metering pump is capable of delivering
various amounts of polymers at various percent solutions.
Flow pacing, adjustment of the dosage rate, and operation of
the polymer metering pump are the same as for the alum feed
pump.
EXAMPLE 1
Known Unknown
Polymer = 72 lbs polymer/day Polymer Dose,
Delivered, lbs/day mg/L
Flow Through = 6000 gpm
Filter, gpm
Determine pounds of polymer per million pounds of water
which is the same as mg per million mg or mg/L.
Polymer Polymer delivered, lbs polymer/day
Dose, mg/L flow through filter, M lbs water/day
72 lbs polymer/day
6000 gal/mln x 6.34 lbs/gal * 60 min/hr * 24 hr/day
_ 72 Iba polymer/day
72,057,600 lbs water/day
72 Iba polymer/day
72 M Iba water/day
» 1 mg polymer/liter water
- 1 mg/i
-------
Solids Removal from Effluents 337
*
Fig. 23.26 Filter feed pumps
Fig. 23.27 Alum storage tank and feed pump
Fig. 23.29 Filter vessels
-------
338 Treatment Plants
A variable-area flow meter (rotameter) is provided to indicate
flow of dilution water to the metered polymer (Figure 23.30).
The polymer is mixed automatically by the polyelectrolyte
mixer. The dry feeder is calibrated to dispense a metered
quantity of dry polymer to obtain a desired solution concentra-
tion. The dry polymer drops to the wetting cones from the
feeder hopper, where it is spread on a high velocity water
surface and the individual grains of polymer are wetted to form
a polymer solution. This solution then flows to the aging tank
where it is mixed and aged. On completion of the aging cycle,
the polymer solution is pumped to the metering/storage tank by
the transfer pump. When the aging tank empties, the polymer
preparation and mixing cycle begins again. The metering
pump, calibrated to deliver a desired dosage, draws the
polymer solution from the metering/storage tank and delivers it
to the influent line of the filters.
Steps to calculate polymer and alum dosage are outlined in
the following examples, Information concerning the concentra-
tion of chemical (lbs/gal) delivered to your plant may be ob-
tained from the chemical manufacturer or supplier.
EXAMPLE 2.
Determine polymer dosage, mg/L. Polymer is supplied to
your plant at a concentration of 0.5 pounds polymer per gallon
(60 gm/L or 60 kg/cu m). The polymer feed pump delivers a
flow of 0.10 gpm (0.0063 L/sec) and the flow to the filter is
3,000 gpm (190 L/sec). Calculate the concentration or dose of
polymer in the water applied to the filter.
Unknown
Known
Polymer Cone., Ib/gal = 0.5 lbs/gal
Polymer Pump, gpm = 0.1 gpm
Flow to Filter, gpm = 3000 gpm
ENGLISH
Calculate polymer dose, mg/L
Dose, mg/L = F|0W- gal/min x Conc'. lbs polymer/gal
Flow, gal/min x 8.34 lbs water/gal
_ 0.1 gal/min x 0.5 lbs polymer/gal
3000 gal/min x 8.34 lbs water/gal
= 0.05 lbs polymer x 1,000,000*
25,020 lbs water
_ 2.0 lbs polymer
1 M lbs water
2.0 mg polymer
Polymer Dose,
mg/L
1 M
1 M mg water*
= 2.0 mg/L
* We multiplied the top and the bottom by the same number,
1,000,000 or 1 M. This is similar to multiplying the top and bottom
by 1, you do not change the equation.
" 1 M mg water = 1 liter.
METRIC
„ Flow, L/sec x Cone., gm polymer/L x 1000 mg/gm
Dose, mg/L
Flow, L/sec
_ 0.0063 L/sec x 60 gm polymer/L x 1000 mg/gm
190 L/sec
= 380 mg polymer/sec
190 L water/sec
= 2 mg/L
EXAMPLE 3. Determine alum dosage, mg/L
Liquid alum usually is supplied at a concentration of 5.4
pounds alum per gallon (650 gmIL or 650 kg/cu m). In this
example, the alum feed pump delivers 88 ml per minute and
the flow to the filter is 3,000 gpm (190 L/sec). Calculate the
concentration or dose of alum in the water applied to the filter.
Known
Alum Cone., Ib/gal = 5.4 lbs/gat
Alum Pump, ml/min = 88 ml/min
Flow to Filter, gpm = 3000 gpm
ENGLISH
Calculate alum dose, mg/L
Flow, mJ/min x Cone., lbs ak/m/gal * 0.00026 gal/ml'
Unknown
Alum dose,
mg/L
Dose, mg/L
Flow, gal/min * 8.34 lbs wat&r/gal
86 ml/min * 5.4 lbs alum/gal * 0.00026 gal/ml
3.000 gal/min x 0.34 lbs water/gal
0.125 lbs alum 1,000,000
25,020 lbs water
5 lbs alum
1 M lbs water
= 5mgIL
1 M
* Conversion factor. 1 ml = 0.00028 gallons
METRIC
Dose mg/L = Flow, ml/min x Conc.,gm polymer/l x 1000 mg/gm
Flow, L/sec x 60 sec/min x 1000 ml/L
_ 88 ml/min x 650 gm polymer/L x 1000 mg/gm
180 L/sec x 60 sec/min x 1000 ml/L
= 950 mg/sec
190 L/sec
= 5 mg IL
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 350.
23.4D What is the purpose of the holding tank?
23.4E Cross out the incorrect words within the following pa-
rentheses in order to make the statement correct.
Alum is used for (COAGULATION OR FLOCCULA-
TION) while polymers are used for (COAGULATION
OR FLOCCULATION).
23.4F Polymer is supplied at a concentration of 0.6 pounds
polymer per gallon (72 gmIL or 72 kg/cu m). The
polymer feed pump delivers a flow of 0.15 gpm
(0.0095 L/sec) and the flow to the filters is 5,000 gpm
(135 L/sec). Calculate the concentration or dose of
polymer in the water applied to the filter.
23.413 Filters (See Figure 23.25, page 335)
This section discusses the purpose of the parts of the filters.
VESSELS (Figure 23.28 and 23.29, page 337)
In our example, each pressure vessel containing filter media
consists of a cylindrical shell closed at both ends. Manways
are provided to allow entry to the vessel for media installation
and maintenance work. Pressure gages are attached to the
manway covers to facilitate monitoring of the vessel pressure.
-------
Solids Removal from Effluents 339
POLYMER
STORAGE
FEEDER
HOPPER
OPTIONAL
MIXING
FUNNEL
ADD A MEASURED AMOUNT OF CHEMICAL
MECHANICAL MIXER
WATER METER
MEASURED
AMOUNT OF
WATER
DISSOLVING TANK
(BATCH MIXED)
DAY TANK OR
STORAGE TANK
KNOWN
CONCENTRATION
OF SOLUTION
CHEMICAL
FEEDER
(FLOW
PACED)
TO WATER
BEING
TREATED
Fig. 23.30 Polymer dissolver, day tank and feeder
-------
340 Treatment Plants
A direct spring-loaded pressure relief valve is installed on top
of the filter and is set to release at a preset pressure. The relief
valve is provided to prevent vessel rupture in case effluent flow
is restricted or stopped while influent flow continues.
A combination-type air-release valve with a large orifice is
also installed on top of the filter to permit air to exhaust when
the filter vessel is charged with water and to allow air to reenter
when the filter vessel is drained. A small orifice is also provided
to exhaust small pockets of air which may collect during opera-
tion of the filter.
INTERIOR PIPING (Figure 23.25, page 335)
Interior vessel surfaces, influent and effluent headers, and
supports are painted with a protective coating to inhibit corro-
sion. The influent header is suspended and supported from the
upper side of the vessel by lugs. Each filter is equipped with
rotary surface wash arms that are installed and supported just
beneath the influent header. These are self-propelling, revolv-
ing "straight line" wash arms.
The surface wash piping consists of an influent water line,
solenoid valve, a central bearing of all-bronze construction, a
bronze tee having a nozzle affixed to emit a water stream
directly below and from the center of the tee, and arms extend-
ing laterally from the tee. The lateral arms are fitted with
numerous brass nozzles located at double-angle positions to
most effectively cover the area of the filter bed to be cleaned.
Each nozzle is fitted with a synthetic rubber cap slitted to act as
a check valve to keep filter media away from the nozzle.
Water to the wash arms is supplied from an external source,
usually from the treatment plant wash water system. Water
from the surface wash arms quickly breaks up the mat of sus-
pended material that has accumulated in and on the top layer
of filter media. This occurs during the first portion of the
backwash cycle.
The effluent header is encased in concrete fill in the lower
section of the filter. PVC underdrain laterals are attached to the
effluent header. Each lateral has numerous small diameter
holes facing toward the bottom of the filter. The ends of the
laterals are capped. The filtered water is collected by the un-
derdrain laterals which passes the water to the effluent header
for discharge from the filter.
UNDERDRAIN GRAVEL (Support Media)
The inert filtering media is supported by underdrain gravel
consisting of specifically sized, hard, durable, rounded stones
with an average specific gravity of not less than 2.5. The gravel
is placed in the filter in many specific layers starting with the
larger stones (2-inch or 5-cm diameter) on the bottom and
progressing to the smallest stones (1/4-inch or 0.7-cm diameter)
on top. The depth of each layer, specific stone sizes, and
overall gravel depth will depend on the application, type, and
quantity of inert media that will be used in a filter.
INERT MEDIA
Granular filter media commonly used in wastewater filtration
include anthracite coal, silica sand, and garnet sand. These
filter media range in size from 0.20 mm to 1.20 mm and spe-
cific gravities range from 1.35 to 4.5. The largest size media,
anthracite coal, has the lowest specific gravity. Conversely, the
smallest media, garnet sand, has the highest specific gravity.
Inert-media filter configurations vary according to the spe-
cific characteristics of the water to be filtered. The common
applications use either silica sand or garnet sand as a single-
media; anthracite coal and silica sand or garnet sand as a
dual-media; and anthracite coal, silica sand, and garnet sand
as a multi-media or mixed media filter.
In most filter applications, any of the various media used are
placed in the filter with 60 percent of the larger size, lower
specific gravity media on top, 30 percent of the medium size
and specific gravity in the middle, and 10 percent of the smaller
size, higher specific gravity media on the bottom. Thus, the
smaller size filter media is placed on the support media first,
followed by the medium size filter media and then the larger
size filter media. Total filter media depth varies with the appli-
cation.
Due to the size and density ratio of the media and its place-
ment in the filter, the larger size and lower specific gravity
media stay at the top and the smaller size higher specific grav-
ity media remain at the bottom. Most dual-media filters are
designed to keep the media separated after backwashing.
FLOW CONTROL METHOD (Figure 23.31)
In filter operation, the rate of flow through a filter is ex-
pressed in gallons per minute per square foot:
Rate of flow, Driving force __ Total available head
gpm/sq ft puter resistance Total head loss
Therefore, as the total head loss increases, the ratio of flow
decreases. The driving force refers to the pressure drop across
the filter which is available to force the water through the filter.
At the start of the filter run, the filter is clean and the driving
force need only overcome the resistance of the clean filter
media. As filtration continues, the suspended solids removed
by the filter collect on the media surface or in the filter media, or
both, and the driving force must overcome the combined re-
sistance of the filter media and the solids removed by the filter.
The filter resistance (head loss) refers to the resistance of
the filter media to the passage of water. The head loss in-
creases during a filter run because of the accumulation of the
solids removed by the filter. The head loss increases rapidly as
the pressure drop across the suspended solids mat increases,
because the suspended solids already removed compress and
become more resistant to flow. As the head loss increases, the
driving force across the filter must increase proportionally to
maintain a constant rate of flow.
The constant-rate method of filtration is commonly used for
pressure filters. In this method, a constant pressure is supplied
to the filter and the filtration rate is then held constant by the
action of a manually or automatically operated filter rate-of-flow
controller. At the beginning of the filter run, the filter is clean
and has little resistance. If the maximum available water pres-
sure was applied to the filter, and the effluent flow was not
restricted, the flow rate would be very high. To maintain a
constant flow rate, some of the available pressure is dissipated
by the rate of flow controller (RFC). At the start of the filter run,
the RFC is nearly closed to provide the additional head loss
needed to maintain the desired flow rate. As filtration con-
tinues, the filter gradually becomes clogged with suspended
solids and the RFC opens proportionally. When the valve is
fully opened, any further increase in the head loss will not be
balanced by a corresponding decrease in the head loss of the
RFC. Thus, the ratio of pressure to filter resistance will de-
crease, and the flow rate will decrease. This action is also
known as filter differential pressure. When the flow rate de-
creases, filter differential pressure increases and this is an
indication that the filter run must be terminated and a filter
backwash should be initiated.
23.414 Backwash System
As the suspended material accumulates on the filter media
surface, or in the filter media bed, or both, the differential pres-
sure across the filter increases, flow through the filter de-
creases, and filter effluent quality deteriorates. The filter
-------
Solids Removal from Effluents 341
AlAKMS
IE SY5TEM
Fig. 23.32 Backwash pumps
Fig. 23.31 Filter controls
Fig. 23.33 Decant tank drain line automatic valves
Fig. 23.34 Backwash recovery tank and feed pumps
-------
342 Treatment Plants
backwash cycle removes the suspended solids accumulation
from the filter, thus restoring the filter efficiency.
WET WELL
The backwash wet well is used to store a large volume of
filtered and/or chlorinated wastewater to backwash the filters.
The water, usually from the chlorine contact tank, flows to the
wet well until it is filled up and then it flows to further final
treatment processes. This flow method insures a continuous
water supply to the wet well.
PUMPS (Figure 23.32, page 341)
The filter backwash pumps lift the filtered and/or chlorinated
wastewater from the backwash wet well and pump it through
the filters to remove the trapped suspended material. The
pumps are generally of the vertical-turbine wet-pit type with
either a closed or semi-open impeller. The pumps may be
driven by fixed-speed motors.
The pump system is equipped with a solenoid-operated
bypass valve installed on the common discharge line to pre-
vent the possibility of the system operating at the shut-off pres-
sure of the pumps. A pressure switch with an adjustable
operating range (psi) will cause the valve to open upon rising
pressure. The bypass flow is returned to the backwash wet
well. The common discharge line is also equipped with an air
relief valve that purges air from the system to prevent air slugs
from disturbing the filter media bed.
Normal start-stop of the pumps may be controlled by means
of current switches in the backwash program unit. Lead-lag
position selector switches provide the means of selecting the
sequence of starting for the pumps. A low water probe in the
backwash wet well will stop the pumps in the event that the
water level drops below a pre-set elevation.
The backwash pump common discharge line is provided
with an orifice plate and flow-control valve. Flow control is
accomplished by means of a cascade control system using a
cam programmer to provide a setpoint signal. A cam is cut so
as to gradually introduce the backwash flow to the filters,
thereby avoiding sudden disturbance or uneven expansion of
the filter media bed.
BACKWASH CYCLE
Whenever possible, the filters should be backwashed during
the plant's low flow hours when the full capacity of the filters is
not needed. The backwash cycle may be activated either
manually, automatically by a pre-set filter differential-pressure
level, or automatically by a program timer. In the manual mode,
only a desired fitter may be backwashed. In the automatic
modes all filters in the system that are "ON LINE" may be
washed when the differential pressure reaches the pre-set
level. Upon completion of backwash of one filter, the next filter
in an "ON LINE" status will begin to backwash.
The total backwash duration per filter usually is adjustable.
The total backwash flow and duration should be adequate to
fluidize and expand the media bed. The largest media size and
the warmest expected water temperature will dictate the filter
backwash rates required.
When the backwash cycle is manually or automatically acti-
vated, the following sequence occurs:
1. Filter influent valve (V-1) and effluent valve (V-2) close to
terminate filter feed flow. (See Figure 23.25, page 335, for
locations of valves.)
2. Backwash influent valve (V-3) and effluent valve (V-4) open
to allow backwash flow into and out of the filter.
3. The surface wash arms' influent water line solenoid valve
(V-5) opens allowing the wash arms to function in initially
breaking up the mat of suspended material that has ac-
cumulated on the top layer of filter media.
4. The backwash pumps start pumping against a closed
backwash control valve. The backwash flow rate is brought
up to full rate in one to two minutes as determined by the
cam programmer transmitting a gradual "open" signal to
the backwash flow-control valve operator.
As the surface wash continues to operate, the backwash
flow gradually enters the filter from the bottom. As the flow
increases, the bed fluidizes and expands upward (about 20
percent of the total media depth) allowing a uniform rolling
action of the filter media bed which results in cleaning of the
media due to the hydrodynamic shear (water causes grains
to clean each other) that occurs. The media bed expands
upward and into the rotating surface wash arms. The arms
now aid in breaking up the suspended material and mud
balls that have accumulated in the top section of the media.
5. After two to five minutes of surface wash, the surface wash
influent water line solenoid valve closes. Surface wash is
discontinued two to ten minutes before the backwash ends
so that the surface of the filter media will be smooth and
level at the beginning of the cleaned filter run cycle.
6. After seven to twenty minutes of backwash, the backwash
flow-control valve gradually begins to close. Shortly after
the backwash flow-control valve is fully closed, the
backwash pumps stop.
7. Backwash influent valve (V-3) and effluent valve (V-4)
close.
8. Filter influent valve (V-1) and effluent valve (V-2) open.
NOTE: When the backwash cycle is activated, the filter flow-
control valve fully closes. Upon completion of the cycle
the valve opens slightly.
The valve sequence indicated in items 1, 2, 8 and 9 occurs
simultaneously to insure that the filter does not become "air
bound" (clogged by air released from water). Air binding will
reduce or block filter influent flow and/or create media bed
disturbance when filter backwash begins.
23.415 Decant Tank (Backwash Recovery) (Figures 23.33
and 23.34, page 341)
Most decant tanks are very similar to secondary clarifiers
because they have flights or scrapers to collect settled material
toward a sludge hopper.
Filter backwash effluent leaves the filter and may be dis-
charged to the decant tank. The suspended material in the
backwash water is allowed to settle and the clarifier effluent
overflows to the holding tank through weir slots between the
two tanks for recycle to the filters. The settled material is col-
lected toward a hopper in the tank for periodic discharge to the
solids handling facility.
If poor settling occurs in the decant tank, all spent backwash
flow may be returned to the head end of the plant through the
tank drain line. The drain line may be equipped with a propeller
meter and a motor-operated butterfly valve. The common
opening limit of the valve should be set to discharge tank flow
at a rate which will not hydraulically overload the plant.
The tank may be equipped with high water level probes
which will open the motor-operated valve fully to allow a pre-
determined volume of water to leave the tank rapidly. This may
be necessary if the tank becomes surcharged (overloaded)
due to frequent filter backwashes.
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Solids Removal from Effluents 343
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 350.
23.4G List the major components of pressure filters.
23.4H How is the mat of suspended material on the media
surface initially broken up during a backwash?
23.41 What is the source of water used to backwash the
filter?
23.4J What is the purpose of the decant tank?
23.42 Operation
23.420 Operational Strategy
This lesson has covered some of the basic concepts of
inert-media pressure filters used to remove suspended solids
and turbidity from secondary effluents before chlorination.
If the filters become overloaded due to high suspended sol-
ids concentration, excessive plant flows, high chemical con-
centrations, or exposure to very cold temperatures, be pre-
pared for the problems discussed in this section.
1. High suspended solids concentrations will cause a filter to
plug up fast, thus requring very frequent filter backwashes.
This will result in high recycle flow rates through the plant
and eventually the filters. This problem may be eliminated
or reduced by having adequate spent backwash storage
capacity or by having a "closed" filter system that will allow
for clarification and reuse of spent backwash water for sub-
sequent backwashes.
2. If no backwash storage or "closed" system is provided,
hydraulic surcharge (overload) on the upstream side of the
filters will result. Provisions must be made for filter bypass
and/or storage. If bypass is the only alternative, you should
anticipate increased chlorine demands at the chlorine injec-
tion point as a result of the increase in unfiltered suspended
material. Adjust the chlorine dosage to compensate for the
greater demands.
3. By allowing suspended material to bypass the filters and
enter the chlorine contact tanks, more frequent cleaning of
these tanks will be required.
4. If higher than normal plant flows can be anticipated (rain), it
would be a good idea to operate the filter holding tank/wet
well at a lower water level to provide for additional water
storage. This action will reduce the surcharge possibility on
the upstream side of the filters. This preventive action
should also be used if a filter must be taken out of service
for repairs or inspection.
5. If liquid alum is used and it is exposed to cold temperatures,
the liquid alum will start to crystallize and the delivery of
alum to the filter influent flow will be seriously impaired. If
climatic conditions of this type are common in your area,
consider storing the alum in an enclosed, warm space.
6. If chemical feed pump check valves or anti-siphon devices
fail, large quantities of chemical will be drawn into the filters.
This will result in short filter-run times due to increased
differential pressure across the filter when a polymer is the
chemical involved. When excessive alum concentrations
are involved, the alum will pass through the filter media and
filter effluent turbidity and suspended solids values will in-
crease due to the alum breakthrough.
7. Filter flow and differential pressure valves may be sensed
by differential pressure cells. These cells are water-
activated and are fed through small-diameter piping. During
periods of extremely cold weather these cells could freeze
and prevent proper functioning of the filter and control in-
struments. Heavy insulation and/or heat tape will prevent
the water in the cell piping from freezing.
23.421 Abnormal Operation
Efficient filter operation is essential if your final effluent qual-
ity is to comply with the waste discharge requirements estab-
lished for your plant. Table 23.2 lists a few of the more com-
mon filter operational problems and suggestions on how to
correct them.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 350.
23.4K What happens when large quantities of alum or
polymer accidentally reach the filter?
23.4L What precautions should be taken in regions where
freezing temperatures occur?
23.4M What could cause high operating filter differential
pressures?
23.43 Maintenance
A comprehensive preventive maintenance program is an
essential part of plant operations. Good maintenance will in-
sure longer and better equipment performance. The following
may be used as a guideline in performing the required mainte-
nance on the pressure filter system.
A filtration system performance test should be done monthly.
This test will enable you to evaluate and determine if the
pumps, valves, filters, and control instruments are functioning
properly. If they are not, the proper corrective action must be
taken. A sample performance test form for three filters is
shown in Figure 23.35.
Filter media and interior vessel surfaces should be inspected
quarterly. The filter should be backwashed just prior to the
inspection. Some of the items to look for are:
1. Is the media surface fairly flat and level? If not, the surface
wash time should be reduced.
2. Are there mudball formations on or in the media? If so, an
increased surface wash time in conjunction with a lower
backwash rate should bring the media back to a clean con-
dition.
3. Are very small quantities of mid-filter media particles visible
on the top layer media surface? This condition is normal
(refer to Section 23.413, Filters, page 338).
4. Do the surface wash arms rotate freely and in the proper
direction? If not, the trouble could be a defective central
bearing and tee. Are any nozzles plugged? If so, they must
be cleaned.
CAUTION: Wear goggles when observing the operation of
the surface wash arms. The velocity of water
produced from the wash arms is great and will
kick up surface media.
-------
344 Treatment Plants
TABLE 23.2 ABNORMAL FILTER OPERATION
ABNORMAL CONDITION
POSSIBLE CAUSE
OPERATOR RESPONSE
PUMPS
Do not meet pumping requirements.
Insufficient motor speed.
Install higher rpm motors.
Pump impeller improperly set in bowl of
pump.
Set impeller as per manufacturer's instruc-
tions.
Excessive filter-system head losses.
Air in filter system. Analyze problem and
take corrective action such as install higher
rpm motors, redesign pump station, rede-
sign force main, redesign orifice plates.
Broken pump shaft.
Replace.
FILTERS (GENERAL)
High operating filter differential pressure.
Filled with suspended material.
Backwash filters at least once every 24
hours.
Excessive chemical feed "binding" media.
Evaluate and reduce dosage. Backwash fil-
ter.
Water discharges from pressure-relief
valve.
Effluent valve(s) blocked or closed.
Investigate and correct valve problem
Foreign object lodged between valve and
seat.
Secure filter and clean valve seat.
Water discharges from air-relief valve.
Air pocket in underdrain system (most
common after a backwash).
Secure filter for 2 to 3 minutes to allow ves-
sel water level to stabilize, return filter to
service. Adjust filter feed and backwash
valves to open and close simultaneously to
keep vessel full of water.
MEDIA
Support media upset.
Air slug forced out by the backwash flow.
Install air relief valve on backwash influent
line.
Backwash flow pumped too suddenly.
Install flow-control valve for regulated flow
rates.
Backwash flow rate too high.
Install valve stops or limiting orifices.
Mud ball formation. Media surface cracks.
Inadequate surface wash time.
Increase surface wash time. Check to in-
sure arms are operating.
Backwash water dirty at end of wash cycle.
Insufficient backwash time.
Increase time until clean water appears.
Media surface uneven after backwash.
Surface wash too long.
Decrease surface wash time.
5. Is there a small amount of foreign matter on the media
surface (plastic, cigarette butts)? This condition is fairly
normal and is most prevalent at the extreme effluent end of
the backwash effluent header. The foreign matter is carried
away by the backwash water during the next backwash
cycle. If a large accumulation of foreign matter develops,
the matter will have to be removed by manual means.
6. Inspect all interior metal surfaces to insure that the
corrosion-inhibitive protective coating is in good condition.
If not, prepare the affected surface and reapply the proper
coating. An epoxy tar is frequently used for this purpose.
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Solids Removal from Effluents 345
At least once monthly, the backwash rate should be ob-
served to insure that the flow rate is correct as specified by the
manufacturer's backwash rate-flow curve and that the
backwash flow is allowed to enter the filter at a regulated rate.
Observe the backwash effluent flow. The water should be clear
at the end of the wash cycle. If it is not, an increase in the wash
time is indicated.
The flow rates for the chemical feed pumps should be
checked at least every two weeks. Corrective adjustments
should be made to maintain the proper flow rates.
23.44 Safety
Safety precautions for sedimentation tanks and pumps set
forth in Chapters 5, 14, and 15 should be observed when
operating and maintaining this equipment in the pressure filter
system.
In addition, the following safety precautions should be ob-
served:
1. Wear safety goggles and gloves when working with alum or
polymers. Flush away any alum or polymer that comes in
contact with your skin with cool water for a few minutes.
2. Be very careful when walking in an area where polymer
mixing takes place. When a polymer is wet, it is very slip-
pery.
3. When inspecting the interior of a filter vessel:
a. Insure that all flow-control instruments are in the "OFF"
position and that all valves are in the "MANUAL" or
"OFF" position. Position all valves to prevent flow from
entering the filter.
b. Always ventilate vessel. Open two manway covers. In-
stall and start an exhaust blower in one manway to
provide fresh air circulation before entering the filter.
c. Check vessel atmosphere for toxic gases (hydrogen
sulfide), explosive conditions (Lower Explosive Limit),
and sufficient oxygen.
d. Entering a filter vessel is a three person operation. Two
must be outside the vessel whenever one person is
inside.
e. Wear a hardhat when working inside a filter or around
the filter vessel piping to protect your head from injury.
23.45 Review of Plans and Specifications
As an operator you can be very helpful to design engineers
in pointing out some design features that would make your job
easier. This section attempts to point out some of the items
that you should look for when reviewing plans and speci-
fications for expansion of existing facilities or construction of
new pressure filter systems.
1. The variable hydraulic and suspended solids load in sec-
ondary effluents must be considered in the design to avoid
short filter runs and excessive backwash-water require-
ments.
2. A filter that allows penetration of suspended solids (a
coarse-to-fine filtration system) is essential to obtain rea-
sonable filter run lengths. The filter media on the influent
side should be at least 1 to 1.2 mm in diameter.
3. Auxiliary agitation of the media is essential to proper
backwashing. Surface washers should be installed.
DATE: 7-21-78 BY: REDNER
&
VALENCIA WRP FILTER AND FILTER FEED PERFORMANCE TESTS KETTLE
Test
i
PUMPS RUNNING
Filters on
Discharge Through
Filters, GPM
Holding
Tank
Level
Pressure
at Pump
Discharge
Filter
Differential
Pressure
FILTER EFFLUENT
FLOW CONTROL
VALVE, % OPEN
#
1
2
3
1
2
3
1
2
3
TOTAL
FEET
PSI
1
2
3
1
2
3
1
on
off
off
on
off
off
1400
1400
7.8
1.5
6.5
100
0
0
2
off
on
off
on
off
off
1100
1100
8.3
3.0
8.3
100
0
0
3
off
off
on
on
off
off
970
970
8.5
3.5
9.5
100
0
0
4
on
on
off
on
on
off
850
1400
2250
8.5
—
9.0
5.0
100
100
0
5
on
on
off
on
on
on
725
1224
1000
2950
8.5
5.0
8.5
5.0
5.0
100
100
100
6
on
off
on
on
on
on
700
1200
1000
2900
8.5
5.2
8.5
5.0
5.0
100
100
100
7
off
off
on
on
on
on
625
1075
925
2625
8.5
3.0
8.5
5.5
5.5
100
100
100
8
on
on
on
on
on
on
900
1275
1150
3325
7.7
8.0
9.5
6.0
6.0
100
100
100
9
on
off
off
off
off
on
1150
1150
7.7
3.0
7.0
0
0
100
10
on
off
off
off
on
off
1300
1300
7.9
3.0
6.5
0
100
0
11
on
off
off
on
off
off
975
975
8.0
3.2
10.0
100
0
0
NOTE: The filter effluent flow control valve should be 100% open during the monthly test.
REMARKS:
Fig. 23.35
Filtration system performance test chart
-------
346 Treatment Plants
4. The effect of recycling used backwash water through the
plant on the filtration rate and filter operation must be con-
sidered in predicting peak loads on the filters and resulting
run lengths.
5. The filtration rate and head loss should be selected to
achieve a minimum filter run length of 6 to 8 hours during
peak-load conditions. This requirement will mean an aver-
age filter run length of 24 hours. Estimates of head loss
development and filtrate quality should be based on pilot-
scale observations of the proposed facility conducted at the
treatment plant before the full-scale facility is designed.
6. Manways should be sized large enough to allow operators
and equipment ease of entering and leaving the filter.
7. A media core sample port(s) should be provided to allow
evaluation of the entire media depth.
8. Ladders and walkways should be provided to allow easy
access to vessels, pipes, and valves.
9. Filter-flow charts should be provided to aid in monitoring
filter performance.
23.46 Acknowledgments
1. County Sanitation Districts of Los Angeles, Valencia Water
Reclamation Plant.
2. Mr. Jerry Schmitz, Draftsman, County Sanitation Districts of
Los Angeles.
23.5 ADDITIONAL READING
1. WASTEWATER FILTRATION DESIGN CONSIDER-
ATIONS, EPA Technology Transfer Seminar Publication,
July 1974, U.S. Environmental Protection Agency, Center
for Environmental Research Information (CERI), 26 West
St. Clair Street, Cincinnati, Ohio 45268.
2. PROCESS DESIGN MANUAL FOR SUSPENDED SOLIDS
REMOVAL, Technology Transfer, U.S. Environmental Pro-
tection Agency, Center for Environmental Research Infor-
mation (CERI), 26 West St. Clair Street, Cincinnati, Ohio
45268.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 350.
23.4N What safety precautions should be taken when work-
ing with alum or polymers?
23.40 How frequently should a filter system performance test
be conducted?
23.4P What caution should be exercised when observing the
operation of the surface wash arms?
a
END OF LESSON 4 OF 4 LESSONS
ON
SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
-------
Solids Removal from Effluents 347
DISCUSSION AND REVIEW QUESTIONS
(Lesson 4 of 4 Lessons)
Chapter 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 3.
19. How are floatable and settleable solids removed from a 21. During what time of the day should the filters be
holding tank? backwashed?
20. How would you attempt to control corrosion of the interior 22. What is the impact on downstream treatment processes if
surfaces of a pressure-filter vessel? suspended solids get past the filtration system?
PLEASE WORK THE OBJECTIVE TEST NEXT.
SUGGESTED ANSWERS
Chapter 23. SOLIDS REMOVAL FROM SECONDARY EFFLUENTS
Answers to questions on page 289.
23.0A NPDES stands for National Pollutant Discharge Elimi-
nation System.
23.0B Some locations have stringent discharge require-
ments because more and more wastes are being dis-
charged into the receiving waters and increasing de-
mands are being placed on the waters by water users.
23.0C Solids can be removed from secondary effluents by
the addition of chemicals to cause coagulation and
sedimentation, microscreens and gravity and pressure
filters.
Answers to questions on page 292.
23.1 A Chemicals may be added to reduce emergency prob-
lems such as those created by sludge bulking in the
secondary clarifier, upstream equipment failure, acci-
dental spills entering the plant, and seasonal over-
loads. Chlorine is the most common chemical used for
disinfection.
23.1B When adding chemicals upstream from a biological
treatment process, be sure that the chemical or its
concentration is not toxic to the organisms treating the
wastewater in the biological process.
Answers to questions on page 292.
23.1C The four most common chemicals added to improve
settling are alum, ferric chloride, lime and polyelectro-
lytes (polymers).
23.1 D Alum should be kept dry to prevent it from caking into
a solid lump.
23.1 E All mechanical equipment, such as conveyors, should
be run until well-cleaned of all alum before shutting
down because the alum can harden and jam the
equipment.
Answers to questions on page 293.
23.1F Safety precautions required for handling ferric chloride
in concentrated forms should be the same as those for
acids. Wear protective clothing, face shields and
gloves. Flush off all splashes on clothing and skin im-
mediately.
23.1 G Rubber or flexible piping with easy access and short
runs will permit cleaning by squeezing the walls and
washing out the broken scale. Solid piping that is
plugged by scale usually requires replacement.
-------
348 Treatment Plants
23.1 H Clean up polyelectrolyte spills immediately. Polyelec-
trolytes will create an extremely slippery surface when
wet.
23.11 Polyelectrolyte spills can be cleaned up by using
chlorine. To clean up a spill, neutralize the polyelectro-
lyte with either salt (NaCI), liquid bleach or HTH pow-
der.
Answers to questions on page 294.
23.1 J Chemical solutions are prepared for feeding by mixing
known amounts of chemicals and water together using
a mechanical mixer. The resulting solution is stored in
a day tank (holding tank) from which it is metered out
at the proper dosage into the water being treated.
23.1K Common types of chemical feeders or metering
equipment include:
1. Positive displacement pumps such as the piston
pump, diaphragm pump, gear pump and progres-
sive cavity pump;
2. Screw feeder;
3. Vibrating trough;
4. Rotary feeder; and
5. Belt-type gravimetric feeder.
Answers to questions on page 302.
23.1 L Items that should be considered when selecting a
chemical feeder include:
1. Total operating range.
2. Accuracy.
3. Repeatability.
4. Resistance to corrosion.
5. Dust control.
6. Availability of parts.
7. Safety.
23.1 M The following information regarding a chemical feeder
operation should be recorded:
1. Flows;
2. Characteristics of wastewater before and after
treatment; and
3. Dosage and conditions of chemical treatment.
Answers to questions on page 307.
23.1N Factors that can cause a change in chemical dose
requirements include:
1. Day of the week (weekdays or weekends);
2. Season of year (temperature and seasonal load-
ings); and
3. Year to year (changes resulting from industrial and
population growth).
23.10 The most common method used to determine coagu-
lation dosages is by running the jar test.
23.1P The jar test is an attempt to duplicate or simulate plant
conditions by using laboratory equipment.
Answers to questions on page 308.
23.1Q Water quality indicators that should be monitored
when operating a chemical treatment process include
alkalinity, pH, temperature, turbidity and suspended
solids.
23.1 R Abnormal conditions that could be encountered in the
water being treated when operating a chemical treat-
ment process include high solids, high or low flows,
and change in pH and temperature.
23.1S Problems that could occur when operating a chemical
treatment process include no coagulation (solids not
settling out) and foaming.
END OF ANSWERS TO QUESTIONS IN LESSON 1
Answers to questions on page 312.
23.2A Microstraining is a form of filtering used to clarify water
by filtering out microscopic or very small suspended
solids.
23.2B Microfabric is usually made of stainless steel wire,
polyester, nylon cloth or plastic.
Answers to questions on page 313.
23.2C Major components of a typical microscreen include
drum, microfabric, water spray system, solids waste
hopper, drum drive units, ultraviolet lights, structure
and bypass weir.
23.2D Ultraviolet lights are used to reduce biological growths
on the microfabric. These growths can survive the
water spray cleaning and will eventually clog the fab-
ric.
Answers to questions on page 313.
23.2E Before starting a microscreen unit, inspect the electri-
cal installation to be sure the controls are properly
covered, fuses properly sized, and proper safety lock
outs have been installed.
23.2F Items that should be included in the log of the opera-
tion of a microscreen include:
1. Hours of operation,
2. Volume of water processed, gallons or cubic me-
ters,
3. Rate of application, gpd or cu m/day,
4. Applied suspended solids and BOD, lbs or kg/
day,
5. Effluent suspended solids and BOD, lbs or kg/
day,
6. Percent removal of suspended solids and BOD,
%,
7. Chemicals added, pounds or kilograms,
8. Head loss through screen, inches or centimeters,
9. Maintenance performed on the unit, and
10. Remarks of special observations.
Answers to questions on page 315.
23.2G Abnormal conditions that could be encountered when
operating a microscreen include:
1. High or low flows;
2. High solids loadings;
3. High or low pH values; and
4. High concentrations of oil and grease.
23.2H Problems caused by high or low pH levels include:
1. A high pH may result in the buildup of mineral de-
posits that will plug the fabric holes.
2. A rapid pH change may upset upstream treatment
processes, thus increasing solids loadings.
3. A low pH may result in the corrosion of metal, es-
pecially the microfabric.
END OF ANSWERS TO QUESTIONS IN LESSON 2
-------
Solids Removal from Effluents 349
Answers to questions on page 316.
23.3A A gravity filter should be cleaned when (1) the pres-
sure drop (head loss) across the bed becomes so
great that the flow is reduced, or (2) increased solids
are observed in the effluent.
23.3B Most filters operate on a batch basis whereby the filter
operates continuously until its capacity to remove sol-
ids is reached. At this time it is completely removed
from service and cleaned.
Answers to questions on page 317.
23.3C Meanings of the following terms are:
1. Downflow. Water flows down through the bed.
2. Static bed. Bed does not move or expand while
water is being filtered.
23.3D 1. In surface straining, the filter is designed to remove
the solids at the very top of the media.
2. Depth filtration is designed to pull the solids deep
into the media, thereby capturing the solids within
as well as on the surface of the media.
Answers to questions on page 324.
23.3E Materials used for filter media include silica sand, an-
tracite coal, garnet or ilmenite. Garnet and ilmenite are
commonly used in multi-media beds.
23.3F If the filter media is not thoroughly cleaned during
each backwashing, a buildup of solids will occur. The
end result of incomplete cleaning is the formation of
mudballs within the bed.
23.3G If nonfiltered water is supplied to the backwash sys-
tem, clogging of the underdrain system may occur.
23.3H Used backwash water holding tanks are needed to
prevent hydraulically overloading the treatment plant
when backwash waters are returned to the head-
works.
Answers to questions on page 326.
23.31 The head loss through the filter media is determined
by measuring the water pressure above and below the
filter media. When water flows through the media the
pressure below the media will be less than the pres-
sure above the media (when the pressure levels are
measured or read at the same elevation).
23.3J Filter system alarms should be tested for proper func-
tioning at least every 60 days.
Answers to questions on page 328.
23.3K A pre-start check should be conducted before starting
filtering systems to prevent damage to the equipment
and/or injury to personnel.
Answers to questions on page 329.
23.3N Abnormal operating conditions include:
1. High solids in applied water due to bulking sludge,
rising sludge, or solids washout in the secondary
clarifier.
2. Low suspended solids in applied water; however,
solids pass through filter.
3. Loss of filter aid chemical feed.
4. High wet weather peak flows.
5. Low applied water flows.
6. High color loading.
7. High water temperature.
8. Low water temperature.
9. Air binding.
10. Negative pressure in filter.
11. High BOD and COD.
12. High coliform group bacteria levels.
13. Chlorine in applied water.
14. pH change in applied water.
15. High grease and oil in applied water.
23.30 To treat a high solids content in the water applied to a
filter:
1. Run jar tests and adjust chemical dosage as
needed;
2. Place more filters in service to prevent break-
through; and
3. Prepare to backwash more frequently.
Answers to questions on page 331.
23.3P To determine if media are being lost, every three or
four months measure and record the freeboard to the
filter media surface. A small amount of media loss is
norma I, but an excessive amount (2 to 3 inches or 5 to
7 centimeters) indicates operational problems.
23.3Q Trees and shrubs should be kept away from un-
covered filters because leaves will drop into the filter
and they are very difficult to backwash out of the
media.
Answers to questions on page 333.
23.3R The three main types of safety hazards around filtra-
tion systems are electrical, chemical and mechanical.
23.3S Filtration instrumentation should measure and record
applied flows, backwash flows, head loss, and water
quality before and after filtration.
23.3T Install all read-out meters, charts and gages of instru-
ments in a convenient and centralized location.
Hi
23.3L The purpose of the rate-control valve is to maintain the
desired flow through the filter and prevent the
backwash water from entering the filtered water during
backwashing.
23.3M A filter should be backwashed after the capacity of the
media to hold solids is well used up, but before solids
break through into the effluent.
-------
350 Treatment Plants
Answers to questions on page 334.
23.4A The purpose of the inert-media pressure filter is to
remove suspended solids and turbidity from sec-
ondary effluents to meet waste discharge require-
ments established by NPDES permits.
23.4B Chemicals commonly used with the filtration process
are polymers and/or alum. The chemicals are used as
coagulants for the solids and turbidity to aid in their
removal by filtration.
23.4C Major components of a pressure filtration system in-
clude:
1. A holding tank or wet well;
2. Filter feed pumps;
3. Chemical coagulant feed pump system;
4. Filters;
5. Filter backwash wet well;
6. Filter backwash pumps; and
7. Decant tank.
Answers to questions on page 338.
23.4D The purpose of the holding tank is to store water and
to allow additional settling of the suspended solids be-
fore the water is applied to the filter.
23.4E Alum is used for COAGULATION while polymers are
used for FLOCCULATION.
23.4F Known
Polymer Cone., Ib/gal = 0.6 lbs/gal
Polymer Pump, gpm = 0.15 gpm
Flow to Filter, gpm = 5,000 gpm
ENGLISH
Calculate polymer dose, mg/L.
Unknown
Polymer Dose,
mg/L
Dose, mg/L
Flow, gal/min x Cone., lbs polymer/gal
Flow, gal/min x 8.34 lbs water/gal
0.15 gal/min x 0.6 lbs polymer/gal
5,000 gal/min x 8.34 lbs/gal
0.09 lbs polymer 1,000,000
41,700 lbs water
2.2 mg/L
1 M
METRIC
Dose, =
mg/L
Flow, L/sec x Cone., gm polymer/L x 1,000 mg/gm
Flow, L/sec
0.0095 L/sec x 72 gm polymer/L x 1,000 mg/gm
315 L water/sec
= 2.2 mg/L
Answers to questions on page 350.
23.4G Major components of pressure filters include:
1. Vessels;
2. Interior piping;
3. Underdrain gravel (supporting media);
4. Inert media; and
5. Flow controls.
23.4H Water from the surface arms initially breaks up the mat
of suspended material on the media surface.
23.41 The water used to backwash the filter comes from the
chlorine contact tank (filtered and chlorinated) to the
backwash wet well before it is used for backwashing.
23.4J The decant tank receives the backwash water from
the filters. The backwash water is allowed to settle and
the clarified effluent is recycled to the filters. The set-
tled material is collected and discharged to the solids
handling facility.
Answers to questions on page 343.
23.4K When a large quantity of polymer reaches a filter,
short filter-run times will result due to increased differ-
ential pressure across the filter. When excessive alum
concentrations are involved, the alum will pass
through the filter media and filter effluent turbidity and
suspended solids will increase due to alum break-
through.
23.4L In areas where freezing temperatures occur, heavy
insulation and/or heat tape will prevent the water in the
cell piping from freezing. Also liquid alum should be
stored in an enclosed, warm space.
23.4M High operating differential pressures could occur if
either (1) the media is filled with suspended material;
and/or (2) excessive chemical feed is "binding" the
media.
Answers to questions on page 346.
23.4N Safety precautions that should be taken when working
with alum or polymers include:
1. Wear safety goggles and gloves when working with
alum or polymers. Flush away any alum or polymer
that comes in contact with your skin with cool water
for a few minutes.
2. Be very careful when walking in an area where
polymer mixing takes place. When a polymer is
wet, it is very slippery.
23.40 Filter system performance tests should be conducted
quarterly.
23.4P Wear goggles when observing the operation of the
surface wash arms.
euo
of
<0
QU&rfoM
IM
-------
Solids Removal from Effluents 351
OBJECTIVE TEST
Chapter 23. SOLIDS REMOVAL FROM SECONDARY
EFFLUENTS
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one correct answer to each question.
1. Ferric chloride is corrosive.
1. True
2. False
2. Safety precautions required for handling ferric chloride in
concentrated forms should be the same as those for acids.
1. True
2. False
3. An overdose of a polyelectrolyte to a secondary effluent
containing solids can be worse than no polyelectrolyte ad-
dition at all.
1. True
2. False
4. A progressive cavity pump may operate without feed ma-
terial and not be damaged.
1. True
2. False
5. A coagulant may be used to precipitate phosphate as well
as to remove solids from the water being treated.
1. True
2. False
6. Good housekeeping around chemical feeding systems is
very important to good operations, but not important to
safety.
1. True
2. False
7. If the microscreen drum is not rotating when the process
water first enters the microscreen, the fabric may plug and
be damaged.
1. True
2. False
8. Apply chlorine to control biological growths on the mi-
crofabric.
1. True
2. False
9. Rapid-sand filters may use either an upflow or a downflow
backwashing process.
1. True
2. False
10. Downflow filters are designed to remove suspended solids
by either the surface-straining method or the depth-
filtration method.
1. True
2. False
11. The conventional single-media filter bed commonly used
in potable water systems is generally unsatisfactory in re-
moving solids found in wastewater because of plugging.
1. True
2. False
12. The finer, dense sand is placed over the coarse media
(anthracite) in a dual-media filter.
1. True
2. False
13. Chlorine will not interfere with polyelectrolytes.
1. True
2. False
14. Dry filter media can be backwashed without any problems.
1. True
2. False
15. Alum is injected into the influent line of the filters
downstream of the point of polymer injection.
1. True
2. False
16. Solids can be removed from secondary effluents by
1. Activated sludge process.
2. Addition of chemicals.
3. Chlorination.
4. Filtration.
5. Microscreens.
17. Chemicals used to improve the settling of solids include
1. ABS.
2. Alum.
3. Cations.
4. Lime.
5. Soda water.
18. Which of the following items should be inspected or
checked before starting a chemical feeder?
1. Direction of rotation of moving parts in motors
2. Operation of control lights on control panel
3. Operation of safety lock-out switches
4. Proper voltage
5. Size of overload protection
19. A jar test can be used to determine
1. The most economical coagulation dosages.
2. The number of jars of chemicals.
3. The pH of a sample.
4. The plant conditions by using laboratory equipment.
5. What the clarity will probably be in the plant effluent.
-------
352 Treatment Plants
20. Microstraining is capable of
1. Disinfecting the effluent.
2. Improving the effectiveness of the disinfectant.
3. Removing soluble BOD.
4. Reducing the coliform group organisms in the water
being treated.
5. Reducing the organic loading on the receiving waters.
21. Possible corrective actions to solve microscreen problems
when treating high concentrations of oil and grease in-
clude
1. Adding chemicals to improve oil and grease removals.
2. Decreasing the drum rotation speed.
3. Decreasing the water spray pressure.
4. Placing fewer microscreens in service.
5. Reducing oil and grease loadings at source.
22. Why should an empty filter not be filled through the inlet
valve?
1. Filling the backwash troughs in an empty filter places
an unnecessary loading on the troughs.
2. Question wrong. An empty filter should be filled
through the inlet valve.
3. This is a waste of production water.
4. Untreated water will be discharged from the filter.
5. Water falling onto the media will disturb the bed.
23. Indications of a disturbed or damaged filter underdrain
include
1. Boiling areas and quiet areas of the filter media during
backwashing.
2. Filter media in the effluent.
3. Poor quality effluent suspended solids.
4. Reduced effluent chlorine requirements.
5. Reduction in effluent MPN.
24. Information that can be obtained from the head loss indi-
cator on a rapid-sand filter includes
1. Depth of filter media.
2. Effectiveness of the backwash operation.
3. Efficiency of BOD removal.
4. Present condition of sand filter.
5. Turbidity in the effluent.
25. Which of the following items should be included in your
checklist for starting filtering systems?
1. Backwash frequently to reduce head loss.
2. Check motors for proper rotation.
3. Fill tanks and piping and look for leaks.
4. Inspect pumps and motors for excessive vibration.
5. Inspect the total system for safety hazards.
26. Which of the following items would you check if laboratory
tests indicated high turbidity and suspended solids in the
effluent of a filter?
1. Check for excessive head loss.
2. Determine filter aid dosages.
3. Examine backwash cycle for complete wash.
4. Inspect for damaged bed due to backwashing.
5. Look for fluctuating flows that could cause break-
through.
27. What conditions determine the backwash rate for a pres-
sure filter?
1. Largest media sire
2. Quality of the backwash water
3. Settleability of solids in the secondary clarifier
4. Suspended solids concentrations in the water applied
to the filter.
5. Warmest expected water temperature
28. Which of the following conditions can cause operational
problems with a pressure filter?
1. Excessive plant inflows
2. High chemical concentrations
3. High coliform MPNs
4. High suspended solids concentrations
5. Very cold temperatures
29. Factors that could upset the support media of a pressure
filter include
1. Air slug forced out by backwash flow.
2. Backwash flow rate too high.
3. High suspended solids concentrations in the water
applied to the filter.
4. Pumping backwash flow too suddenly.
5. Surface wash too long.
30. Factors that should be considered when reviewing plans
and specifications for new pressure filters include
1. Filter media that allows penetration of suspended sol-
ids in order to obtain reasonable filter run lengths.
2. Hoists to allow for inspection and maintenance of air
headers.
3. Ladders and walkways to allow easy access to ves-
sels, pipes and valves.
4. Manways sized large enough to allow operators and
equipment ease of entering and leaving filters.
5. Media core sample ports to evaluate entire depth of
media.
END OF OBJECTIVE TEST
-------
CHAPTER 24
PHOSPHORUS REMOVAL
John G. M. Gonzales
-------
354 Treatment Plants
TABLE OF CONTENTS
Chapter 24. Phosphorus Removal
Page
OBJECTIVES 356
GLOSSARY 357
LESSON 1
24.0 Why is Phosphorus Removed from Wastewaters? 358
24.00 Phosphorus as a Nutrient 358
24.01 Need for Phosphorus Removal 358
24.1 Types of Phosphorus Removal Systems 358
24.10 Lime Precipitation 358
24.11 Luxury Uptake 358
24.12 Aluminum Sulfate Flocculation and Precipitation (Sedimentation) 358
24.2 Lime Precipitation 359
24.20 How the Lime Precipitation Process Removes Phosphorus 359
24.21 Equipment Necessary for Lime Precipitation 359
24.22 Operation 359
24.220 Pre-Start-Up. Importance of Checking Chemical Strength 359
24.221 Equipment Operating Procedures 361
24.222 Placing Lime Precipitation for Phosphorus Removal into Operation 361
24.223 Daily Operation 361
24.224 Shutdown of Lime Clarification Operation 362
24.225 Sampling and Analysis 362
24.226 Operational Strategy 362
24.2260 Daily Operating Procedures 362
24.2261 Abnormal and Emergency Conditions 362
24.2262 Troubleshooting 366
24.23 Maintenance 366
24.24 Safety 366
24.25 Loading Guidelines 367
24.26 Review of Plans and Specifications 367
24.27 Additional Reading on Lime Precipitation for Phosphorus Removal 388
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Phosphorus Removal 355
LESSON 2
24.3 Luxury Uptake of Phosphorus 369
24.30 How the Luxury Uptake Process Works 369
24.300 Process Description 369
24.301 Wastewater Treatment Units Used 369
24.302 Basic Principles of Operation 369
24.31 Phosphorus Stripping Tank 369
24.32 Lime Clarification Process 369
24.33 Start-Up, Operation, and Shutdown of Luxury Uptake Phosphorus Stripping Process 369
24.330 Pre-Start-Up 369
24.331 Placing Phostrip Equipment into Operation 369
24.332 Daily Operation 372
24.333 Shutdown of Phosphorus Stripping Process 372
24.334 Return of Activated Sludge Process to Normal Operation 372
24.335 Sampling and Analysis 372
24.336 Operational Strategy 372
24.34 Maintenance 372
24.340 Piping 372
24.341 Pumps and Equipment 37^
24.342 Lime Feed 373
24.343 Lime Slurry and Mixing Operation 373
24.344 Sludge Withdrawal and Disposal Pumps 373
24.35 Safety 373
24.36 Loading Guidelines 373
24.37 Review of Plans and Specifications 373
24.38 Additional Reading on Phosphorus Removal by Luxury Uptake Using an
Anaerobic Phosphorus Stripping Tank 373
24.4 Phosphorus Removal by Alum Flocculation 373
24.40 Variation in the Alum Flocculation Process 373
24.400 Alum Flocculation as Used in a Clarification Process 373
24.401 Alum Flocculation as Used in Conjunction with Filtering of Suspended Solids 375
24.41 Maintenance of Alum Feeding Pumps and Associated Equipment 375
24.42 Operation of Alum Flocculation for Phosphorus and Suspended Solids Removal 375
24.420 Daily Operating Procedures 375
24.421 Abnormal Conditions 375
24.43 Safety 377
24.44 Loading Guidelines 377
24.45 Review of Plans and Specifications 377
24.46 Additional Reading for Phosphorus Removal by Alum Flocculation 377
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356 Treatment Plants
OBJECTIVES
Chapter 24. PHOSPHORUS REMOVAL
Following completion of Chapter 24, you should be able to
do the following:
1. Explain the need for phosphorus removal and describe
some of the different systems used for this purpose at vari-
ous treatment plants,
2. Place a phosphorous removal system into service,
3. Schedule and safely conduct operation and maintenance
duties,
4. Sample influent and effluent, interpret lab results and make
appropriate adjustments in the treatment process,
5. Recognize abnormal operating conditions, understand the
cause, and take corrective action to ensure proper phos-
phorus removal,
6. Inspect a newly installed phosphorus removal facility to de-
termine if installation has been proper, and
7. Review plans and specifications for a phosphorus removal
system.
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Phosphorus Removal 357
GLOSSARY
Chapter 24. PHOSPHORUS REMOVAL
AGGLOMERATION (a-GLOM-er-A-shun) AGGLOMERATION
The growing or coming together of small scattered particles into larger floes or particles which settle rapidly. Also see FLOC.
CENTRATE CENTRATE
The water leaving a centrifuge after most of the solids have been removed.
COAGULATION (co-AGG-you-U\Y-shun) COAGULATION
The use of chemicals that cause very fine particles to clump together into larger particles. This makes it easier to separate the solids
from the liquids by settling, skimming, and draining or filtering.
ELECTRO-MAGNETIC FORCES ELECTRO-MAGNETIC FORCES
Forces resulting from electrical charges that either attract or repel particles. Particles with opposite charges are attracted to each
other. For example, a particle with positive charges is attracted to a particle with negative charges. Particles with similar charges
repel each other. A particle with positive charges is repelled by a particle with positive charges while a particle with negative charges
is repelled by another particle with negative charges.
ENDOGENOUS (en-DODGE-en-us) ENDOGENOUS
A reduced level of respiration (breathing) in which organisms break down compounds within their own cells to produce the oxygen
they need.
FLOCCULATION (FLOCK-you-LAY-shun) FLOCCULATION
The gathering together of fine particles to form larger particles.
FLOC FLOC
Groups or clumps of bacteria and particles that have come together and formed a cluster.
POLYELECTROLYTE (POLY-electro-light) POLYELECTROLYTE
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polyelectrolytes may be of
biological origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polyelectrolytes consist of simple
substances that have been made into complex, high-molecular-weight substances. Often called a "polymer."
POLYMER (POLY-mer) POLYMER
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polymers may be of biological
origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polymers consist of simple substances that
have been made into complex, high-molecular-weight substances. Often called a "polyelectrolyte."
PRECIPITATE (pre-SIP-i-tate) PRECIPITATE
To separate (a substance) out in solid form from a solution, as by the use of a reagent. The substance precipitated.
RECALCINE (re-CAL-seen) RECALCINE
A lime-recovery process in which the calcium carbonate in sludge is converted to lime by heating at 1800°F (980°C).
RECARBONATION (re-CAR-bun-NAY-shun) RECARBONATION
A process in which carbon dioxide is bubbled through the water being treated to lower the pH.
RESPIRATION RESPIRATION
The process in which an organism uses oxygen for its life processes and gives off carbon dioxide.
SLAKE SLAKE
To become mixed with water so that a true chemical reaction takes place, such as in the slaking of lime.
SLURRY (SLUR-e) SLURRY
A thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry).
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358 Treatment Plants
CHAPTER 24. PHOSPHORUS REMOVAL
(Lesson 1 of 2 Lessons)
24.0 WHY IS PHOSPHORUS REMOVED FROM
WASTEWATER?
24.00 Phosphorus as a Nutrient
Phosphorus provides a nutrient or food source for algae.
Phosphorus combined with inorganic nitrogen poses serious
pollution threats to receiving waters because of high algae
growths which result from the presence of the two nutrients in
water. Algae in water are considered unsightly and can cause
tastes and odors in drinking water supplies. Dead and decay-
ing algae can cause serious oxygen depletion problems in
receiving streams which in turn can kill fish and other aquatic
wildlife.
By removing phosphorus in the effluent of a wastewater
treatment plant, the lake or river that the treatment plant dis-
charges into will have one less nutrient that is essential for
algae growth. This reduction in an essential nutrient reduces
the growth of the algae.
24.01 Need for Phosphorus Removal
The U.S. Environmental Protection Agency and other water
quality regulating agencies recognize the need to protect rivers
and lakes from excessive growths of algae. Because of this,
the agencies are requiring that wastewater treatment plants
remove phosphorus in the effluent in order to protect the river
or stream by eliminating a nutrient that can cause algae
growth.
24.1 TYPES OF PHOSPHORUS REMOVAL SYSTEMS
Lime precipitation, luxury uptake, and filtration following
aluminum sulfate flocculation are the most common types of
phosphorus removal systems.
24.10 Lime Precipitation
When lime (calcium hydroxide (Ca(OH)2) is mixed with
effluent from a wastewater treatment plant in sufficient concen-
tration to bring about high pH in the water, a chemical com-
pound is formed which consists of phosphorus, calcium and
the hydroxyl (OH ) ion. This compound can be FLOCCU-
LATED1 or combined in such a way as to form heavier solids
which can settle in a clarifier for phosphorus removal. A sub-
stantial amount of the lime reacts with the alkalinity of the
wastewater to form a calcium carbonate PRECIPITATE2 which
also settles out with the phosphorus sludge. This calcium car-
bonate precipitate can be separated out of the sludge and
RECALCINED3 in a furnace to convert the calcium back to lime
for reuse.
24.11 Luxury Uptake
Bacteria found in a normal activated sludge process use
phosphorus within the make-up of the cell structure that forms
the bacteria. When the bacteria are in a state of ENDOGEN-
OUS4 RESPIRATION5 or are very hungry and need food and
oxygen, they tend to absorb phosphorus quite freely. This pro-
cess is called "luxury uptake" in which the bacteria take ex-
cess phosphorus into their bodies due to the stimulation of
being placed in a proper environment containing food and oxy-
gen. When these same bacteria are placed in an environment
where there is no oxygen (anaerobic), the first element that is
released by the bacteria as they almost begin to die is phos-
phorus. As the phosphorus is released, it can be drawn off and
removed from the wastewater stream.
24.12 Aluminum Sulfate Flocculation and Precipitation
(Sedimentation)
Aluminum sulfate (alum) in combination with wastewater
also can flocculate phosphorus in much the same way as lime
precipitation. The flocculation that happens with aluminum sul-
fate addition is the formation of aluminum phosphate particles
that attach themselves to one another and become heavy and
settle to the bottom of a clarifier. The aluminum sulfate and
phosphorus mixture can then be withdrawn, thereby removing
the phosphate or phosphorus from the wastewater flow. This
alum FLOCe is difficult to settle out in a clarifier. Therefore, a
sand or mixed-media filter is usually placed after the clarifier to
remove the remaining floe.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 378.
24.OA Why is phosphorus removed from wastewater?
24.1A List the three major types of systems used to remove
phosphorus from wastewater.
1 Flocculation (FLOCK-you-LA Y-shun). The gathering together of fine particles to form larger particles.
2 Precipitate (pre-SIP-i-tate). To separate (a substance) out in solid form from a solution, as by the use of a reagent The substan^
precipitated. ance
s Recajcine (re-CAL-seen). A lime-recovery process in which the calcium carbonate in sludge is converted to lime by heating at 1800"F
(980°C).
4 Endogenous (en-DODGE-en-us). A reduced level of respiration (breathing) in which organisms break down compounds within their n
cells to produce the oxygen they need. n
s Respiration. The process in which an organism uses oxygen for its life processes and gives off carbon dioxide.
6 Floe. Groups or clumps of bacteria and particles that have come together and formed a cluster.
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Phosphorus Removal 359
24.2 LIME PRECIPITATION
24.20 How the Lime Precipitation Process Removes
Phosphorus
There are three general physical or chemical reactions
which take place during lime precipitation for phosphorus re-
moval (Fig. 24.1).
1. COAGULATION.7 When chemicals are added to wastewa-
ter, the result may be a reduction in the ELECTRO-
MAGNETIC FORCES8 which tend to keep suspended par-
ticles apart. After chemical addition, the electrical charge on
the particles is altered so that the suspended particles con-
taining phosphorus, tend to come together rather than re-
main apart.
2. Flocculation. Flocculation occurs after coagulation and
consists of the collection or agglomeration of the sus-
pended material into larger particles. Gravity causes these
larger particles to settle.
3. Sedimentation. As discussed in previous chapters on pri-
mary and secondary clarification methods, sedimentation is
simply the settling of heavy suspended solid material in the
wastewater due to gravity. The suspended solids which set-
tle to the bottom of clarifiers can then be removed by pump-
ing and other collection mechanisms.
24.21 Equipment Necessary for Lime Precipitation
Lime precipitation for phosphorus removal requires lime
feeding systems, mixing and flocculation areas, chemical
clarifiers for sedimentation and the proper pumps and piping
for removal of lime phosphorus sludge. Other equipment in-
cludes facilities for pH adjustment of the effluent, recovery of
the lime, and disposal of the phosphorus sludge. More specif-
ically, the equipment needed for precipitation includes the fol-
lowing:
1. Lime Feed Equipment. Lime usually comes in a dry form
(calcuim oxide (CaO)) and must be mixed with water to
form a SLURRY9 (calcium hydroxide (Ca(OH)2)) in order to
be fed to a wastewater treatment process to produce the
required results.
Calcium Oxide + Water -> Calcium Hydroxide
CaO + H20 -> Ca(OH)2
2. Mixing Chamber. A basin in which the lime slurry is blended
with the wastewater as rapidly as possible with the use of a
high-speed mixer called a "flash mixer." After this instant
mixing of the lime slurry and wastewater, a slower mixing
process called coagulation and flocculation follows to allow
the formation of floe. This floe consists of suspended and
colloidal matter, including the phosphorus precipitate.
3. Clarification Process. Clarification is used to allow the floe
to settle out of the wastewater being treated. In order to
settle lime phosphorus sludges, the velocity of the flowing
wastewater must be slowed down sufficiently to allow for
sedimentation. Because of the coagulation and flocculation
process which produces heavier particles, a clarifier similar
to a secondary sedimentation clarifier may be used in the
process to settle lime phosphorus sludges.
4. Pumps and Piping for Lime Phosphorus Removal Process.
After the lime phosphorus mixture has been settled on the
bottom of the chemical clarifier, pipes and pumps must be
used to transport the sludge to a thickening process for
further dewatering and disposal.
24.22 Operation
24.220 Pre-Start-Up. Importance of Checking Chemical
Strength.
1. Lime (calcium hydroxide) is the most important ingredient in
the phosphorus removal system. The calcium hydroxide
strength must be checked in order to be sure that a high
concentration of lime is available to form the chemical reac-
tion necessary to precipitate phosphorus. Chemical
strength is tested by determining the percentage of avail-
able calcium oxide in the dry lime that is being fed into the
system. A concentration of at least 90 percent calcium
oxide is needed to insure a highly reactive slurry for proper
lime precipitation of phosphorus. See Chapter 16, "Labora-
tory Procedures and Chemistry," Section 16.47, "Lime
Analysis," for the testing procedures.
2. Lime Feeding Equipment. A routine check of lime feeding
equipment is necessary several times during each work
shift. Lime feeding is usually handled by slakers or equip-
ment that mixes dry powdered lime with water to obtain a
slurry. This slurry is then fed to the mixing basin for coagula-
tion and flocculation of phosphorus. Since most dry lime
has a certain amount of grit, rocks and sand in the mixture,
a grit removal system associated with the SLAKER10 or lime
mixing feed system is important to prevent plugging and
equipment wear. A rock-hard lime precipitate called calcium
carbonate will form when lime combines with carbon
dioxide. This rock-hard substance will attach itself to almost
anything. Slaking mechanisms, piping and equipment must
be kept free from a serious buildup of this calcium carbon-
ate (limestone).
3. Pumps, Valves and Piping. The most serious problem
faced in a lime system is the formation of limestone (cal-
cium carbonate). All pumps, valves and piping must be
regularly checked and cleaned to prevent a buildup of
limestone scale which can cause plugging and malfunction.
This applies to both the lime feed system which carries lime
to the mixing chamber and to the chemical clarification unit.
Similar maintenance procedures also apply to the lime
slurry return system which takes settled lime and phos-
phorus sludge from the bottom of the clarifier and conveys
the sludge to further dewatering and disposal processes.
4. Clarifier Mechanism. Lime clarifier mechanisms function
the same way as secondary clarifiers. The clarifier sweeper
arm should be able to move at a slow rate to collect the
settled lime-phosphorus sludge at the bottom of the tank.
7 Coagulation (co-AGG-you-LAY-shun). The use of chemicals that cause very fine particles to clump together into larger particles. This
makes it easier to separate the solids from the liquids by settling, skimming, draining or filtering.
8 Electro-Magnetic Forces. Forces resulting from electrical charges that either attract or repel particles. Particles with opposite charges are
attracted to each other. For example, a particle with positive charges is attracted to a particle with negative charges. Particles with similar
charges repel each other. A particle with positive charges is repelled by a particle with positive charges while a particle with negative
charges is repelled by another particle with negative charges.
• Slurry (SLUR-e). A thin watery mud or any substance resembling It (such as a grit slurry or a lime slurry).
Slake. To become mixed with water so that a true chemical reaction takes place, such as the slaking of lime.
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CHEMICAL TREATMENT
& PHOSPHATE REMOVAL
LIME
RAPID
MIX
CHEMICAL
CLARIFIER
SECONDARY
EFFLUENT
FLOCCULATION
PHOSPHOROUS
RICH
SETTLED
LIME SLUDGE
LIME SLUDGE PUMPS
LIME SLUDGE
THICKENER
LIME
RECALCINING
FURNACE
OPTIONAL
CENTRIFUGE
LIME SLUDGE PUMPS
RECALCINED LIME
TO RE-USE
Fig. 24.1 Lime precipitation process
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Phosphorus Removal 361
24.221 Equipment Operating Procedures
1. Lime Feed for pH Control. pH adjustment for phosphorus
removal means raising the pH to a very highly alkaline state
(pH of 11 or higher) so that phosphorus and calcium hy-
droxide bond together forming a heavier substance that will
settle out in a clarification process. Adding lime (calcium
hydroxide) to the wastewater being treated will produce a
high enough pH to allow the formation of this lime-
phosphorus precipitate. The pH must be maintained above
11.0 in order to achieve the highest possible phosphorus
removal using the lime clarification process.
The lime-slurry-feeding system must be periodically
checked for proper operation. Most lime-feed systems have
automatic pH controllers that make this adjustment for you.
The lime-feed system must be cleaned and maintained so it
accurately measures out the quantity of lime necessary to
adjust the pH to the proper level.
2. Clarification and Settling Process. After mixing, flocculation
and coagulation, the lime-phosphorus precipitate is ready
for settling in a clarification tank. The hydraulic loading rates
must be adjusted to prevent short-circuiting or hydraulic
washout of the floe prior to its complete settling to the bot-
tom of the clarifier. A well operated chemical clarifier will be
very clear and you should be able to see down into the
clarifier at least 10 feet (3 m).
3. Pumping and Disposal of Lime Precipitate. Once the lime
precipitate containing phosphorus is removed from the
wastewater stream, it is important not to allow the same
phosphorus to be recycled back through the treatment
plant. Two methods of disposal are commonly used. In the
first method, centrifugation of the lime mud removes the
phosphorus from it. The remaining lime sludge can be
further processed to recover the lime. In the second
method, the phosphorus-lime sludge is simply pumped to
an appropriate disposal site.
When pumping lime precipitate from the clarifiers, the
operator must adjust pumping rates so that all of the lime
sludge is removed. Without proper pump regulation and
adequate pumping times, heavy accumulations of lime
could build up within the ciarifier. Poor pump regulation
could also lead to the pumping of only a very thin slurry
composed mainly of water and little lime sludge to the dis-
posal facilities.
24.222 Placing Ume Precipitation for Phosphorus
Removal Into Operation
1. Flow Rate into Chemical Clarifier. The operator should
check the design criteria for the chemical clarifier to be
certain that the overflow rates (weir loading rates and hy-
draulic loading rates) are not exceeded when starting up
the chemical clarifier. The clarifier operates best at or below
the overflow rate that was designed into the facility.
2. pH Adjustment in Flash-mix Basin. Check the pH adjust-
ment in the rapid mix basin to be certain that the pH of the
combined wastewater and lime slurry is 11 or above. If pH
falls below 11, phosphorus removal efficiencies could be
reduced. Measuring the pH on a regular and routine basis
will provide a double check for the operator on the automat-
ic pH adjustment and recording mechanism installed in the
rapid mix basin area.
3. Turbidity and Phosphate Measurement of Clarifier Effluent.
Along with phosphorus removal, a chemical clarifier is ca-
pable of removing turbidity from the secondary effluent at a
wastewater treatment plant. The operator should check the
removal efficiency of turbidity through the chemical clarifier
as well as checking for efficiency levels for phosphorus
removal. This is done along with calculations in the labora-
tory to determine the total phosphorus remaining in the
effluent of the chemical clarifier compared to phosphorus
levels in the effluent of the secondary portion of the treat-
ment plant.
4. Pumping of Precipitated Lime Sludge for Disposal and for
Lime Phosphate Separation. Some treatment plants use
sludge drying beds to dry the lime sludge prior to final dis-
posal by landfilling or other means. Other treatment plants
recover as much of the lime as possible for reuse. These
treatment plants must use two centrifuges. By operating the
first centrifuge at a low removal efficiency, most of the
phosphorus sludge is discharged with the CENTRATE"
while most of the calcium carbonate is removed from the
centrifuge as a cake ready for the lime recovery process in
a multiple hearth furnace. The centrate containing most of
the phosphorus sludge is passed through the second cen-
trifuge for separation of the phosphorus compounds as a
cake. The centrate is usually returned to the primary
sedimentation system and the dewatered phosphorus
sludge (cake) goes to a landfill for ultimate disposal.
The operator must be certain that pumping equipment is
operating efficiently. If the lime sludge is to be dewatered,
the operator must see that the percent concentration of
solids remaining after the dewatering process will provide
the most efficient lime recovery operation.
The solids handling portion (Chapter 22) of this manual
discusses thickening and centrifugation processes in more
depth. This chapter is very closely related to solids handling
and you will need to understand the solids handling chapter
thoroughly before you can reach a thorough working
knowledge of the phosphorus removal system using lime
precipitation.
24.223 Dally Operation
1. Routine pH Monitoring to Check Automatic Feed. As previ-
ously indicated, pH must be maintained about 11 in order to
efficiently operate the phosphorus removal system. Routine
checking with a pH meter will assure the operator of correct
pH levels in the chemical clarification process. Measure-
ment will also serve to check the automatic feed system to
be certain that the pH control is properly functioning in the
automatic mode.
2. Routine Phosphate Test for Removal Efficiencies. The pur-
pose of chemical clarification and lime precipitation of
phosphorus is to remove phosphate compounds from sec-
ondary clarified wastewater treatment plant effluent. Daily
tests for removal of phosphate compounds through the
chemical clarification system are necessary to determine
the precise pH setting that works best for the treatment
plant and conditions of operation at the facility. The phos-
phate test results are also required by State regulatory
agencies that monitor phosphate levels in the final effluent
from the wastewater treatment facility.
3. Calcium Oxide Content of Lime Feed. Phosphorus removal
from wastewater requires substantial amounts of calcium
oxide to raise the pH level of the wastewater so that chemi-
cal bonding occurs. Calcium oxide purchased for this pur-
pose should contain at least 90 percent available calcium
11 Centrate. The water leaving a centrifuge after most of the solids have been removed.
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362 Treatment Plants
oxide. Consult Chapter 16 on laboratory testing procedures
for methods used in calculating and testing for calcium
oxide content (Section 16.47, "Lime Analysis").
4. Daily Maintenance of Pumps, Piping and Other Equipment
to Prevent Lime Scale Plugging. Lime (calcium hydroxide)
and carbon dioxide form what is known as limestone or
calcium carbonate. Calcium carbonate is a very stubborn
substance that sticks to all types of surfaces. This scaling
ability of the calcium carbonate causes pumps, piping and
other equipment to scale very readily and they must be
cleaned to prevent plugging problems. Daily maintenance
will ensure that pumps operate properly and that pipes do
not become completely plugged. Hot water or steam is very
effective in dislodging limestone buildup within pipes or
pumps. The hot water makes the calcium carbonate scale
(limestone) soft and readily available for chipping away or
scouring to remove the scale.
24.224 Shutdown of Lime Clarification Operation
If the lime clarification system for phosphorus precipitation
must be shut down, take the following steps in the order listed:
1. Shut off valve to clarifier basin stopping the secondary
effluent flow into the chemical clarifier.
2. Shut down lime feed equipment.
3. Bypass chemical clarifier by opening proper valves beyond
secondary clarifier.
4. Pump settled lime sludge from clarifier basin.
5. If necessary, pump liquid from chemical clarifier basin into
RECARBONATION12 basin to inspect empty clarifier and
perform any repairs that are necessary.
6. Flush equipment and chemical lines with water.
24.225 Sampling and Analysis
1. Phosphorus Removal Efficiencies. The purpose of lime
precipitation of phosphorus is to reduce the phosphorus
level in the effluent of the wastewater treatment plant and
as a nutrient source for the receiving waters. Daily phos-
phorus tests should be run on composite samples of chem-
ical clarifier effluent and also secondary clarifier effluent to
see a comparison of results for determining two factors:
a. Does the treatment plant meet effluent discharge re-
quirements for phosphorus?
b. Is the chemical clarification lime precipitation process
adequately performing at the efficiencies desired?
Consult the chemical analysis portion of Chapter 16 of
this training manual to understand the laboratory testing
process used for phosphorus analysis and interpretation of
results.
2. Calcium Oxide Content of Lime Feed. A calcium oxide con-
tent of at least 90 percent available calcium oxide is needed
in dry lime (quick lime) to bring the pH of the secondary
treated water up to at least 11.0. The operator should check
the concentration of any lime purchased. Consult the labo-
ratory analysis section (Section 16.47) of Chapter 16 in this
training manual to determine how to run a calcium oxide
test and interpret the results. These test results will insure
the use of high-grade lime as well as inform the operator
about the reliability of the supplier.
Calcium oxide content is also very important for treat-
ment plants who recalcine their own lime. If the calcium
oxide content drops in the recalcined lime, it is most likely
due to higher concentrations of phosphorus within the lime
sludge. When higher concentrations of phosphorus are re-
turned to the system, lime clarification of phosphorus pre-
cipitation becomes less efficient. If calcium oxide levels
drop too low in recalcined lime (less than 70 percent oxide),
the recalcined lime should be wasted or disposed of rather
than reused within the system.
3. Jar Tests to Determine Flocculation Efficiency. An effi-
ciently operated chemical clarification unit will allow for
proper settling of as large and as heavy a floe as possible.
JAR TESTS13 enable the operator to determine what pH
levels form the largest floe possible and allow the fastest
settling of the floe formation. POLYELECTROLYTES14 have
been used with lime precipitation of phosphorus removal
and are added after the fast-mix reaction. The jar tests
are very good indicators of the concentration of
POLYMERS15 that produces optimum floe formation and
sedimentation of the calcium hydroxide phosphate combi-
nation floe particles.
24.226 Operational Strategy
24.2260 Daily Operating Procedures. There are three main
areas to check in the daily operation of a phosphorus-lime
precipitation chemical-clarification unit:
1. Lime Feed System. The lime-feed system must be oper-
ated very efficiently. Be certain to check the automatic dry
lime feed system, the mixing process of dry lime and water,
the slurry transfer to the rapid-mix basin and the grit re-
moval system to remove sand from the lime slurry.
2. Flash Mixing, Coagulation and Flocculation. After the lime
has been fed into the secondary effluent flow stream, it is
very important that the mixing time and chemical feed ratio
(polymer and lime) be correct so that pH can be maintained
above 11.0 and to promote formation and rapid settling of
the largest possible floe.
3. Lime Clarification, Sedimentation and Sludge Removal.
After the lime sludge removal process has entered the
chemical clarification state, it is important for the operators
to make sure that lime does not build up too heavily and
that lime phosphorus sludges are pumped on a regular
basis from the bottom of the clarifier. The lime sludge
should be properly pumped and piped to the disposal area
or the thickener process for further dewatering.
24.2261 Abnormal and Emergency Conditions
1. Changing Flow Conditions. During low flow conditions,
check the automatic lime-feed system to be sure it has
adjusted to the reduced flows. Excessive lime-feed rates
12 Recarbonation (re-CAR-bun-NAY-shun). A process in which carbon dioxide is bubbled through the water being treated to lower the pH.
,3 See Chapter 23, Section 23.130, "Jar Test," for details on how to run a jar test.
14 Polyelectrolyte (POLY-electro-light). A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural
polyelectrolytes may be of biological origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polyelectrolytes
consist of simple substances that have been made into complex, high-molecular-weight substances. Often called a "polymer."
15 Polymer (POLY-mer). A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polymers may be
of biological origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polymers consist of simple substances
that have been made into complex, high-molecular-weight substances. Often called a polyelectrolyte.
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Phosphorus Removal 363
into the clarifier waste the chemicals and increase the
costs. If the automatic lime-feed system cannot be throttled
down far enough, manual feed control is necessary.
High flows can pose a more serious problem to lime
clarification processes. First, high flows may cause a lower-
ing of pH if the lime-feed system is not properly pacing the
flow by adding excess lime when the high flow conditions
occur. Secondly, high flow can mean hydraulic overloading
of chemical clarification units thereby causing a decrease in
the efficiency of phosphorus removal in the clarification
unit.
2. Factors Affecting Phosphorus Removal Efficiency
a. Short-circuiting. Short-circuiting can be caused by too
high a flow within the chemical clarification unit. A high
flow will not allow adequate detention time. When
short-circuiting occurs, the flocculated particles do not
settle properly and are washed over the effluent weirs.
b. Changes in pH. Fluctuating pH levels may have the
effect of causing cloudy conditions in certain portions of
the clarification tank. The most efficient manner in
which to operate a chemical clarification unit is to main-
tain a constant pH above 11.0. When the pH drops
below 11.0 for even a short period of time, floe for that
flow may not be as large and a cloud of suspended
particles may appear within the clarification unit.
c. Solids Loading. Since most chemical clarification units
for phosphorus precipitation follow a secondary
clarifier, it is important that the secondary clarifier run
as efficiently as possible. If solids are not settled prop-
erly within the secondary clarification unit causing high
solids to appear in the chemical clarifier phosphorus
precipitation units, then removal efficiencies for phos-
phorus will decrease. Under these conditions it will be
more difficult to maintain a high pH in the clarifier and
clarity will be impaired substantially.
d. Small Straggler Floe. Usually a small floe will occur
because of improper pH or because the polyelectrolyte
being used is either at too high a dose or too low a dose
for proper control of the flocculation process. The
straggler floe will not settle as readily as the large floe
and, therefore, efficiency in the phosphorus removal
process may be drastically reduced.
e. Storm Water. If substantial high flows result because of
high storm water runoff into the sewer system, phos-
phorus removal efficiencies will be substantially re-
duced because of the short-circuiting due to lack of
detention time within the clarification basin. Be sure to
cut down valving if you suspect a high flow condition
that has resulted from a storm condition. High flows
through the chemical clarifier will cause settled floe to
rise and will prevent sedimentation of the particles.
f. Industrial Dischargers. Industrial dischargers who ig-
nore discharge restrictions can cause serious problems
for the chemical clarification unit. Discharge of toxic
wastes can destroy secondary biological systems,
thereby reducing the secondary clarification efficiency
ahead of the phosphorus removal system.
g. Plugged Pumps or Piping. Lime-phosphorus sludge
must be pumped from the bottom of a chemical clarifier
as it accumulates. If plugging problems occur because
of a calcium carbonate buildup, they should be cor-
rected immediately. If piping or pump problems are al-
lowed to continue, they could result in an excess build-
up of solids within the chemical clarifier and seriously
reduce phosphorus removal efficiency.
h. Lime Feed Equipment to Maintain Adequate Lime Sup-
ply. The most important phase of the chemical clarifica-
tion process that requires close control is the lime-feed
process. If there is a breakdown in the lime feed opera-
tion, phosphorus removal cannot take place. Lime feed-
ing must be continuous and have an adequate feed
supply program. The lime slakers or mixers should be
regularly inspected. All piping should be examined and
deposited scale chipped off the pipes. The lime feed
should also be using a high concentration of calcium
oxide.
i. Operational Problems with Upstream or Downstream
Treatment Processes. The most serious effect from an
upstream treatment process on chemical clarification
and phosphorus removal is an upset condition in the
secondary treatment process of the treatment plant. The
upset condition can cause a lowering of the pH, too
many suspended solids in the chemical clarifier and a
substantial problem for removal efficiencies for not only
phosphorus but turbidity and suspended solids. The sol-
ids carryover from a secondary clarifier also interferes
with any recalcining operation that may be used at the
treatment plant if lime is reclaimed.
Downstream treatment processes will usually include
a recarbonation basin to bring the pH back to a neutral
point. Carbon dioxide from the recalcining process is
commonly used in the recarbonation basin. If the carbon
dioxide feed is not adequate, a high pH will result in the
remainder of the treatment plant. This condition may be
in violation of the discharge permit for the treatment
facility. Most states require a pH in the relatively neutral
range before discharge to any body of water or even for
land disposal. The operator should be sure that the re-
carbonation process is working properly and that an
adequate supply of carbon dioxide is being fed to bring
the pH back down to a range within the plant's effluent
discharge permit requirements.
j. Recarbonation for pH Control and Calcium Carbonate
Recapture. Effluent from a high pH chemical clarifier
used for phosphorus reduction will usually have a pH of
at least 11. Use of carbon dioxide (COs) is the most
common method of neutralizing the pH (bring the pH of
the water down to almost 7). A by-product of the lowered
pH is the formation of settleable calcium carbonate that
can be recalcined for reuse in the lime treatment proce-
dure. The process can be accomplished by either using
a single or a two-stage recarbonation and settling pro-
cess.
Single-stage recarbonation as shown in Fig. 24.2
uses a process of adding carbon dioxide (C02) gas to
the effluent from a chemical clarifier. The gas is bubbled
into the effluent stream to allow calcium carbonate to
form. As a by-product of the calcium carbonate forma-
tion, pH is reduced.
The calcium carbonate precipitate formed is captured
on filters which usually follow a chemical clarification
process. The calcium carbonate captured on the filter
media must be settled following a filter backwashing
procedure.
Two-stage recarbonation and settling as shown in Fig. 24.3
is a more effective method to reduce wastewater pH and re-
capture calcium carbonate. Carbon dioxide gas is bubbled into
a basin just after the chemical clarification process. However,
unlike single-stage recarbonation, the calcium carbonate pre-
cipitate formed is allowed to settle in a basin or tank. The
settled calcium carbonate is collected and pumped to dewater-
-------
WASTE
WASHWATER
FILTER
AID
MAKEUP
LIME
SLAKER
RECYCLED LIME
CARBON
DIOXIDE
THICKENER
CENTRIFUGE
CALCINER
SLUDGE
LIME
DISPOSAL
SLUDGE
SUPERNATANT
t >
1
WASTEWATER
RAPID
FLOCCULATOR
CHEMICAL
RECARBON-
'
FILTER
TREATED
FEED
MIX
CLARIFIER
ATOR
WATER
i.
CARBON
DIOXIDE
<•>
o>
3
<0
WASHWATER
Fig. 24.2 Single-stage lime recarbonation process
(Source: Process Design Manual for Phosphorus Removal, EPA 625/1-76-001A)
-------
WASTE
WASHWATER
FILTER
AID
TREATED
WASTEWATER
WATER
FEED
CARBON
DIOXIDE
CARBON
DIOXIDE
SLUDGE
SLUDGE
WASHWATER
SLUDGE TO RECALCINATOR
OR DISPOSAL
SLAKER
RAPID
MIX
RECARBON
ATOR
RECARBON
ATOR
FLOCCULATOR
FILTER
CALCIUM
CARBONATE
SETTLING
TANK
CHEMICAL
CLARIFIER
LIME
¦o
7
O
M
Fig. 24.3 Single-stage lime recarbonation process "O
(Source: Proem Dwign Manual lor Phoiphanw Ramoval, EPA 625/1-78-001 A) o
C
<0
3D
-------
366 Treatment Plants
ing and recalcination or hauled to a landfill. Carbon dioxide gas
is again bubbled into the wastewater stream to further reduce
the pH.
Usually pH is reduced to around 8.0 to 8.5 in first-stage
recarbonation and further reduced to 7.0 in second-stage re-
carbonation. After second-stage recarbonation, the wastewa-
ter is treated by filtration. An additional advantage of two-stage
recarbonation over single-stage recarbonation is the lower
quantities of calcium carbonate that can plug filters that follow
the recarbonation process.
The stack gases from the recalcination furnace usually are
used as a source of carbon dioxide gas. Additional carbon
dioxide may be required to be produced by an auxiliary burner
or from commercially tanked carbon dioxide.
24.2262 Troubleshooting
The following are some of the important points to look for
when operating a lime clarification system for removal of phos-
phorus. These points and guidelines are some of the many that
operators should consider when operating the equipment for
the phosphorus removal system.
1. Remove any debris from the bottom of the chemical clarifi-
cation basins.
2. Make sure the sludge scraper mechanisms for chemical
clarification units are operating in good condition before
allowing any flow to enter the sedimentation basin.
3. A high torque level on the rotation of the clarifier drive
mechanism provides a warning that the rotating collection
arms of the chemical clarifier have a problem or that the unit
is binding.
4. Pumps which operate at slower-than-normal feed rates or
which will not pump are a strong indication that the pump or
the sludge lines are plugged. Observation of pump pres-
sure gages will indicate if a pump is not working properly.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 378.
24.2A What equipment is necessary for the removal of phos-
phorus by the lime precipitation process?
24.2B Why must the slaker or lime mix feed system have a
grit removal system?
24.2C Daily operation of a lime precipitation process to re-
move phosphorus consists of what tasks?
24.2D Why are low flow conditions of concern for the lime
precipitation process?
24.2E What factors affect phosphorus removal efficiency in
the lime precipitation process?
24.23 Maintenance
1. Pumps and Seals. As indicated in previous sections, pumps
are a very important and major part of any wastewater
treatment facility. Pumps and seals must be kept properly
maintained in order that the pumps can work and function at
their peak efficiency without needing major repair over the
period of use. Seals and packing must be kept in good
condition so that the pump can run cool and efficient at all
times. Lime is both caustic and abrasive and therefore can
wear equipment at a rapid rate. Special attention must be
paid to any pumps that handle lime sludges in order to be
certain that plugging and excessive wear are not major
problems in the pump operation.
2. Piping. Because of the tendency of lime to form scale, pip-
ing must be kept clean at all times. Lime builds up on the
interior walls of pipes and can plug the pipes at a rapid rate.
Flushing and scouring pipes are periodically necessary in
order to ensure that the lime sludge is being moved to other
parts of the treatment plant as expected.
3. Clarifier Mechanism. Since the clarifier rotating arm moves
continuously, it is very important that the proper oil and
grease be provided for lubrication. Be certain that the bear-
ings are lubricated and that no obstructions cause jamming
or excessive wear on the equipment. Be sure to check the
manufacturer's recommendations for the operation of the
clarifier mechanism. Ali internal parts must be sealed and
preventive maintenance should ensure that lime and
weather elements do not affect the operation of the working
gears within the mechanism drive.
4. Lime Slaking Mechanism. The lime slaking mechanism
must be kept in good operating order in order to provide the
correct amount of lime slurry for the lime feed station. Grit
must be removed from the slaker mechanism and the mix-
ing arms must be kept free of excessive buildups of lime.
Be sure to check the manufacturer's recommendation on
slake temperature. Frequently inspect the water sprays
used for condensing the steam and for dust control. The
lime slaking mechanism should be cleaned frequently to
prevent lime build-up.
5. Flash-mix Basin. Lime has a tendency to build up on the
surface of the mixing paddles in a rapid-mixing chamber.
Be sure that no excessive amounts of lime are allowed to
gather on any mixing paddles. This could cause heavily
weighted sides that set the mechanism off balance. The
mixing paddles should be cleaned frequently to prevent
lime buildup.
6. Automatic pH Control. The pH probe that helps the lime
feed system work in automatic mode must be cleaned on a
daily basis to ensure that a lime scale buildup does not
cause false readings. The automatic recording station to
control the pH must be calibrated periodically to ensure that
the mechanism is functioning properly.
7. Ratio of New Lime to Recalcined or Reclaimed Lime. If the
treatment plant has a recalcining furnace in which lime is
reclaimed, be sure that the ratio of new lime to recalcined
lime is adjusted so that the quality of lime fed to the mixing
chamber is high enough to provide adequate pH control
and phosphorus removal. This ratio is computed by using
the known factors of calcium oxide content in both the re-
calcined or reclaimed lime and the new lime.
24.24 Safety
1. Lime is a Powerful Caustic Solution. Because lime has an
extremely high pH, it is a very caustic solution and can
cause eye irritation and skin irritation when it comes in con-
tact with operators. Be very careful when using lime. Wear
goggles and face masks to prevent the lime from entering
eyes or lungs. If you are exposed to lime in either your eyes
or parts of your body, be sure to rinse with water thoroughly
and, in the case of severe burns, be certain to see a physi-
cian immediately. A mild solution of boric acid may be kept
on hand to help flush eyes in case of a severe lime burn or
exposure of the eyes to dry lime.
2. Polymers Can Cause Slick Surfaces. Many times a lime
process uses polymers to help form colloidal particles of
-------
Phosphorus Removal 367
lime and phosphorus to provide faster sedimentation in a
lime clarification unit. These polymers, when wet, are ex-
tremely slippery. Be very careful when walking near sur-
faces that have been exposed to any kind of polyelectrolyte
or polymer. Be sure to wash down any surfaces where
polymers have been spilled and use guard railings on stairs
or near concrete areas that may have polyelectrolytes on
the surface.
24.25 Loading Guidelines
1. Typical Loading Rates. The typical loading rate for a chemi-
cal clarification unit is normally 800 gallons per day per
square foot (32 cu m per day/sq m) of surface area to 1500
gallons per day per square foot (60 cu m per day/sq m) of
surface area.
2. Hydraulic Loading Computation. In order to calculate the
hydraulic loading rate for a lime clarification unit, the
operator must know two things: (1) the flow into the lime
clarification unit, and (2) the surface area of the clarifier. To
calculate the hydraulic loading rate, divide the average gal-
lons per day (cubic meters per day) of flow to the clarifier by
the square feet (square meters) of surface area. This will
give the overflow rate or hydraulic loading of the lime clarifi-
cation unit.
Hydraulic Loading, gpd/sq ft = Flow, gpd
Hydraulic Loading,
cu m/day/sq m
Surface Area, sq ft
_ Flow, cu m/day
Surface Area, sq m
3. Phosphate Loading Computation. Phosphate loading is
normally designed as pounds per day (kilograms per day)
of phosphorus to be treated. This hading can either be a
total loading rate of phosphate into the lime clarification unit
or it can be the phosphorus removed from the lime clarifica-
tion unit. To calculate the phosphate loading, the operator
needs to know: (1) the gallons per day (cubic meters per
day) of flow entering the lime clarification system, (2) the
milligrams per liter of phosphate in the secondary effluent,
and (3) the milligrams per liter of phosphate in the chemical
clarification effluent. In order to compute the PHOS-
PHATE16 loading, use the following equations:
Phosphate
Loading, kg/day
= Flow, MGD x Phosphate, mg/L x 8.34 lbs/gal
Phosphate
Loading.
kg/day
Flow, cu m x Phosphate,-!??, x 1 kfl
day L 1,000,000 mg
1000 L
To determine the efficiency of the phosphate removal pro-
cess by lime clarification, use the following equations:
(Influent - Effluent )
Phosphate Removal
Efficiency. %
Phosphate Removal
Efficiency, %
Phosphate Removal
Efficiency, %
Phosphate, lbs/day Phosphate, lbs/day
Influent Phosphate, lbs/day
x 100%
(Influent - Effluent 'xt00%
Phosphate, kg/day Phosphate, kg/day
Influent Phosphate, kg/day
(Infl. Phos., mgIL - Effl. Phos., mg/L) x 100%
Infl. Phos.. mg/L
24.26 Review of Plans and Specifications
In many instances, it is very beneficial to the design en-
gineer, to the operator and to the facility for the operator to
review the plans and specifications of an expanded treatment
plant or new treatment facility prior to the completion of the
plans and specifications. The design review helps the design
engineer to know what details to look for to make operations
easier and to anticipate problems that might otherwise require
design modifications after construction is completed. Without
the operator's assistance, modification might later be neces-
sary because someone forgot or did not have the knowledge to
recommend specific details for better operational control of the
phosphorus removal process.
The following are some of the items that can be reviewed by
the operators to aid the design engineer during the facility's
design for phosphorus removal:
1. Abrasive nature of quick lime or powdered calcium hy-
droxide. Because of the abrasive nature of lime, it is impor-
tant that large sweeping curves be used in any air transfer
of dry lime. The large sweeping curves will not let the cen-
trifugal force and velocity of the particles of lime eat through
the interior of the pipe wall on the curves while transferring
lime from the hauling vehicle to the storage bins.
2. Lime-water mixture causing steam. Because of the quick
chemical reaction of lime with water, a great deal of heat is
formed causing a certain amount of steam. This steam can
cause the lime to clump up into large particles reducing the
effectiveness of a lime storage bin and its feed mechanism.
Because of the steam, clumping can cause bridging, and
lime feeding into chemical slakers may be a severe prob-
lem. Provisions should be made for water sprays to control
dust and to condense vapors so they will not rise into the
storage bin.
3. Accessibility to piping for lime feed. Because of the ability of
lime to build up on the surfaces of metal and other materi-
als, it is important to be able to clean lime feed pipes. If a
long distance exists between the lime mixing and slaking
area and the rapid-mix basin, several manholes should be
located within the pipe route to ensure easy access for
cleaning.
4. Flexible piping arrangement. Because pumps and pipes
plug up frequently in a lime sludge pump station, it is impor-
tant that alternate piping and valving be provided so that
lime sludge removal can continue while cleaning and re-
pairs are made on the affected equipment.
5. Handling of dry lime from the unloading dock. The trucks
hauling dry lime to storage bins at the treatment plant must
have enough room to maneuver and park in the unloading
area. Usually, the trucks have their own pneumatic exhaust
system to transfer the lime from the truck to the storage
bins. If the bins are taller than the truck, it is critical that the
feed line first go straight up from the unloading vehicle. This
will prevent lime from depositing on the bottom of the pipe
with the air flowing over the top. This arrangement will allow
much faster unloading time for the vehicles.
18 Phosphate In these equations usually refers to total phosphate and includes orthophosphates, polyphosphates, and organic phosphorus
Both poly and organic forms of phosphorus must be converted to orthophosphate for measurement.
-------
368 Treatment Plants
6. Dust control. Because lime is extremely hazardous to
human health, it is important that proper dust control be
provided. Exhaust fans and lime filter bags must be pro-
vided to keep lime dust from spreading throughout the lime
feeding building or into the operational area causing
operators breathing problems and other unpleasant condi-
tions.
7. Safety of lime bins. Because pneumatic feeding
mechanisms are the most common devices for transferring
lime to the storage bins, it is important that these bins be
properly vented and that dust collectors be provided at
each vent.
24.27 Additional Reading on Lime Precipitation for
Phosphorus Removal
1. HANDBOOK OF ADVANCED WASTEWATER TREAT-
MENT, Second Edition, Culp. R. G., Wesner, M., Culp, G.
G., Van Nostrand Reinhold, New York City, N. Y„ 1977.
Obtain from Litton Educational Publishing, Inc., 7625 Em-
pire Drive, Florence, Kentucky 41042. Price: $32.50.
2. PROCESS DESIGN MANUAL FOR PHOSPHORUS RE-
MOVAL, EPA 625/1-76-001 a, U. S. Environmental Protec-
tion Agency, Center for Environmental Research Informa-
tion (CERI), 26 West St. Clair Street, Cincinnati, Ohio
45268, April 1976.
3. WASTEWATER SYSTEMS ENGINEERING, Parker, Homer,
Prentice-Hall, 301 Sylvan Avenue, Englewood Cliffs, New
Jersey 07632, 1975. Price: $24.95.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 378.
24.2F What is the purpose of the lime slaking mechanism?
24.2G What is recalcined lime?
24.2H Why might a lime process also use a polymer?
24.21 What forms of phosphorus are included in the total
phosphate measurement?
24.2J What provisions can be made when a facility is de-
signed to reduce problems that will arise when pumps
or pipes become plugged with lime?
END OF LESSON 1 OF 2 LESSONS
ON
PHOSPHORUS REMOVAL
Please work the discussion and review questions before
continuing with Lesson 2.
DISCUSSION AND REVIEW QUESTIONS
Chapter 24. PHOSPHORUS REMOVAL
(Lesson ,1 of 2 Lessons)
At the end of each lesson in this chapter you will find some
discussion and review questions that you should work before
continuing. The purpose of these questions is to indicate to you
how well you understand the material in the lesson. Write the
answers to these questions in your notebook before continu-
ing.
1. How is phosphorus removed from wastewaters by "luxury
uptake?"
2. What is the most serious problem in a lime system and how
can this problem be avoided or corrected?
3. Why would you perform a jar test when removing phos-
phorus by the lime precipitation process?
4. Why must lime be kept from gathering on the mixing pad-
dles in the flash-mix basin?
5. List the safety hazards you might encounter when working
with lime.
-------
Phosphorus Removal 369
CHAPTER 24. PHOSPHORUS REMOVAL
(Lesson 2 of 2 Lessons)
24.3 LUXURY UPTAKE OF PHOSPHORUS
24.30 How the Luxury Uptake Process Works
24.300 Process Description (Fig. 24.4 and 24.5)
Luxury uptake of phosphorus is a biological treatment pro-
cess whereby the bacteria usually found in the activated
sludge treatment portion of the secondary wastewater treat-
ment plant are withdrawn to an environment without oxygen
(anaerobic). When the bacteria are faced with the situation of
apparent death, the bacteria release phosphorus from their cell
structure in large quantities. Phosphorus can then be removed
and disposed of by using lime for settling similar to the previ-
ously discussed lime clarification process. After the bacteria
have released their phosphorus, they are placed back into an
ideal environment with oxygen and food. In this environment,
since the bacteria are lacking in phosphorus in their cell struc-
ture, the first thing they take in is phosphorus. This phosphorus
take-up is known as luxury uptake and is used in the process
for biological removal of the phosphorus within the wastewater
treatment facilities.
24.301 Wastewater Treatment Units Used
Luxury uptake of phosphorus is found at activated sludge
treatment plants. The units used include the standard ones for
an activated sludge plant plus a relatively deep detention basin
where anaerobic conditions exist (see anaerobic phosphorus
release tank in Figs. 24.4 and 24.5). Another unit commonly
found in the luxury uptake and removal system is a lime clarifi-
cation tank (clarifier) which is usually capable of treating 10
percent of the wastewater flow stream through the treatment
facility. Return pumps and piping continue to move the acti-
vated sludge through an anaerobic state to a phosphorus re-
lease point and back to aeration for the luxury uptake process
to begin all over.
24.302 Basic Principles of Operation
Because luxury uptake can only take place in a very con-
trolled environment, the bacteria cannot be exposed to any
condition which would prevent them from either taking up
phosphorus into their cell structure or releasing the phos-
phorus at the proper time. The basic operation requires the
operators to remove the activated sludge from the secondary
clarifier and provide the proper detention time in an anaerobic
tank for the release of the phosphorus trapped within the cell
structure of the bacteria. The operator must closely regulate
the time of the anaerobic condition. The bacteria should not be
allowed to die. However, the length of time should be sufficient
to remove as much of the phosphorus as possible. Return the
activated sludge to an area of the aeration tank where suffi-
cient oxygen and primary effluent exist so that the bacteria can
be revived and can take up the maximum amount of phos-
phorus within their cell structure.
24.31 Phosphorus Stripping Tank
1. Control to maintain anaerobic conditions. The most impor-
tant part of the phosphorus removal system using luxury
uptake is the control of the anaerobic tank which causes the
bacteria to release phosphorus from their cell structure.
This tank must be kept in strict anaerobic conditions and the
rate of sludge application into the facility must be at the
prescribed design flow. The proper detention time must be
maintained within the anaerobic tank in order that the bac-
teria have enough time to release the phosphorus from the
cell structure.
2. Sludge Recycle. The sludge will separate from the liquid
within the anaerobic phosphorus stripping tank. The sludge
recycle is extremely important. Once the bacteria have re-
leased the phosphorus from their cell structure, the acti-
vated sludge which is now basically anaerobic, must quickly
be returned to the aeration facility in order to revive the
bacteria. A great deal of care must be taken to ensure that
the sludge return is not too fast nor too slow. Operators
should be very careful of this system to ensure proper com-
patibility with the activated sludge portion of the plant and to
maintain the highest efficiency of phosphorus removal
using the luxury uptake principle.
3. Effluent from the Phosphate Stripper. The liquid from the
anaerobic phosphate stripping tank flows into a chemical
clarification unit where lime is used to coagulate and settle
the phosphorus which has been released from the bodies of
the bacteria. The lime used will be substantially less than
the previously-described lime clarification system for
phosphorus removal. The luxury uptake and phosphorus
stripping process require that lime will be applied to only
approximately 10 percent of the entire flow stream. Once
the phosphorus has been stripped from the effluent, it is
allowed to blend with the secondary effluent prior to tertiary
treatment or final disposal.
24.32 Lime Clarification Process
1. Lime Feeding System. The lime feed system for the phos-
phorus stripping system used in luxury uptake is identical to
the system described in the lime clarification section of this
chapter. Please refer to Section 24.21 of this chapter for the
lime feeding system to understand the basic guidelines
used and operational duties.
2. Lime Mixing Tank. The lime slaker and lime mixing tank are
identical to the mixing system and feed system described in
Section 24.21 of this chapter.
3. Lime Clarification. Lime clarification will be identical to the
lime clarification for removal of phosphorus as described in
Section 24.21. The only difference will be the smaller flow
that will be required using the luxury uptake principle.
24.33 Start-Up, Operation, and Shutdown of Luxury
Uptake Phosphorus Stripping Process
24.330 Pre-Start-Up
1. Check lime feed system. The lime feed system should be
checked out in very much the same way as that described
in Section 24.22 of this chapter.
2. Check sludge recycle and return system. The sludge pump-
ing and piping system functions identically to the system
described in Section 24.22. All of the points described in
that section should be applied to the operation of the luxury
uptake phosphorus removal system described in this sec-
tion.
24.331 Placing Phostrlp Equipment Into Operation
1. pH Control. pH control for the lime clarification unit is impor-
tant and the operator should ensure that pH is above 11.0.
-------
LUXURY UPTAKE
(PHOSTRIP)
VENT
CLARIFIER
STRIPPER
(ANAEROBIC f
>HOSPHOROUS
RELEASE I
TANK)
SECONDARY
CLARIFIER
LIME
MIX
AERATION
| LIME |
SLURRY
DRAIN
ELUTRIATION (INFLUENT)
COMPRESSED
AIR
© STRIPPER FEED
® STRIPPER SLUDGE RETURN
© SECONDARY SLUDGE RETURN
@ SLUDGE RECYCLE
Fig. 24.4 Luxury uptake of phosphorus (elevation flow
diagram)
-------
LUXURY UPTAKE
(PHOSTRIP)
/ANAEROBIC\
PHOSPHOROUS
\ RELEASE /
\ TANK /
© AEROBIC RECYCLE
RECIRCULATION
ANOXIC RECYCLE
AERATION TANK
/ LIME >
CLARIFICATION
i TANK i
SECONDARY
CLARIFIER
SUPERNATANT © PRIMARY EFFLUENT
SECONDARY EFFLUENT
PHOSPHOROUS
SLUDGE TO
DEWATERING
O SAMPLING POINTS
AND DISPOSAL
FACILITIES
Fig. 24.5 Luxury uptake of phosphorus (plan flow diagram)
-------
372 Treatment Plants
2. Sludge feed. Sludge feeding into or out of the phosphorus
stripping tank must be at proper rates in order to maintain
peak efficiencies of phosphorus removal. Refer to the de-
sign feed rate in the operation and maintenance manual
provided by the design engineer. This feed rate should be
complied with as closely as possible in order to prevent
excess phosphorus from leaving the stripping tank or to
prevent the activated sludge from dying during the
anaerobic conditions.
3. Phosphorus separation process. When an anaerobic condi-
tion is achieved within the phosphorus stripping tank, the
bacteria will release phosphorus as soon as their extinction
is threatened. The phosphorus must be removed im-
mediately and it is done so in the liquid stream of the strip-
ping tank. This liquid stream proceeds to the lime clarifica-
tion tank. The sludge at the bottom of the phosphorus strip-
ping tank is removed and pumped directly to the head of the
aeration tank for further luxury uptake of phosphorus and a
revival of the bacteria.
24.332 Dally Operation
1. pH Control. Because the liquid stream from the phosphorus
stripping tank will be sent to lime treatment for final clarifica-
tion of the phosphorus, control of the pH above 11 is ex-
tremely important. Control of pH, whether it be automatic or
manual, must be done properly. Please refer to Section
24.22 on lime clarification in this chapter for details.
2. Phosphorus Stripping Controls. In order to determine the
efficiency of the phosphorus stripping tank, the operator
should check the laboratory results to determine if more or
less time is needed within the stripping tank for the efficient
removal of as much phosphorus as possible. Be sure that
the activated sludge contained in the phosphorus stripping
tank is not totally dead and will be revived within the aera-
tion tank when pumped back to the head of that unit.
24.333 Shutdown of Phosphorus Stripping Process
If the phosphorus stripping process must be shutdown, the
treatment facility will operate as a standard activated sludge
plant. Instead of a portion of the activated sludge going to an
anaerobic phosphorus stripping tank, all of the return sludge
will return directly to the aeration tank.
24.334 Return of Activated Sludge Process to Normal
Operation
To return the activated sludge part of the treatment facility to
normal operation is a quick and easy job. However, there may
be certain operational problems that could occur, such as
straggler floe and some decrease of the dissolved oxygen up-
take rate. These must be checked very closely and the
operator should refer to Chapters 8, 11 and 21 on activated
sludge in order to ensure that the treatment facility is operating
in a proper mode.
24.335 Sampling and Analysis
1. pH Control. If the lime clarification process for the phos-
phorus removal is automatically controlled, a pH test should
be manually run on the lime clarification tank each 8 hours
to ensure that the automatic controls are functioning prop-
erly.
2. Anaerobic Phosphorus Stripping Conditions. A dissolved
oxygen probe should be lowered into the anaerobic phos-
phorus stripping tank to ensure that no dissolved oxygen
exists within the tank. If dissolved oxygen exists, it may be a
sign that sludge is being fed too fast or withdrawn too fast
from the stripping unit.
3. Sludge Return and Re-aeration. Returning the sludge at the
proper time is very important. Be sure to check at the site
where the sludge is returned to the aeration tank to ensure
that adequate dissolved oxygen exists within the aeration
system. If dissolved oxygen drops substantially, it may be
necessary to increase the air supply to that section of the
aeration tank where the activated sludge is returned from
the anaerobic phosphorus stripping unit.
24.336 Operational Strategy
1. Sludge Flow Quantities. The operator should make certain
that sludge flow in and out of the phosphorus stripping tank
is at exactly the correct setting. Make sure that flow does
not enter too fast; otherwise, anaerobic conditions may be
upset and the phosphorus stripping process will be incom-
plete. Make sure that sludge is withdrawn at a fast enough
rate to ensure that the activated sludge does not die and is
returned to the aeration tank within the proper time limit.
2. Lime Feed and Clarification. The lime feed and clarification
unit must be operated properly. For details on operation,
please see Section 24.22 on lime clarification for phos-
phorus removal.
3. Control of Sludge Withdrawal and Effluent from Lime
Clarification Unit. Proper controls must be placed on the
pumping of the phosphorus sludge from the clarification
unit. These controls are discussed in detail in Section 24.22
on lime clarification for phosphorus removal.
4. Abnormal Operating Conditions. An abnormal condition
which may prevail and inhibit the operator's ability to pro-
vide sufficient control for phosphorus removal is dissolved
oxygen in the phosphorus stripping tank. This phosphorus
stripping tank must be maintained at anaerobic or no-
oxygen conditions at all times for the release of the phos-
phorus from the cell structure of the bacteria. Other abnor-
mal conditions can occur in the lime clarification process.
Check the abnormal conditions that are found in Section
24.22 on lime clarification for phosphorus removal.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 379.
24.3A What is luxury uptake of phosphorus?
24.3B Where and under what conditions do bacteria release
phosphorus from their cell structure in the luxury up-
take process?
24.3C List the units (pieces of equipment) used in the lime
clarification process of the luxury uptake process.
24.3D How often should the pH be run manually on the lime
clarification tank to ensure that the automatic controls
are functioning properly?
24.34 Maintenance
24.340 Piping
The piping of a phosphorus stripping process using luxury
uptake will be similar to an activated sludge plant except that
two additional tanks are provided. Those tanks are the
anaerobic stripping tank and the chemical clarification unit.
The piping that will need the most care and attention is the lime
clarification process piping. Be certain to check the mainte-
nance section on lime clarification for phosphorus removal in
Section 24.23 of this chapter.
-------
Phosphorus Removal 373
24.341 Pumps and Equipment
The pumps that pump the activated sludge into and out of
the anaerobic phosphorus stripping tank must be operated
properly. They must be equipped with variable-speed controls
in order that the operator can adjust the feed rate into and out
of the anaerobic phosphorus stripping unit. The pumps and
equipment must be maintained so that the activated sludge is
properly pumped into and out of the phosphorus stripping unit.
The bacteria found in the activated sludge must not release
phosphorus until they have reached the anaerobic stripping
tank. Also, the activated sludge that has undergone anaerobic
conditions must be returned to the aeration system as quickly
as possible.
24.342 L/me Feed
The lime feed equipment is similar to that described in the
previous section. Be sure to check the maintenance portion of
Section 24.23 on lime feed for phosphorus removal because it
is applicable for luxury uptake processes using lime clarifica-
tion.
24.343 Lime Slurry and Mixing Operation
The lime slurry and mixing operation must be kept clean at
all times. Be sure to read Section 24.23 on maintenance in the
previous portion of this chapter describing lime clarification for
phosphorus removal.
24.344 Sludge Withdrawal and Disposal Pumps.
The lime sludge pumps must be kept clean at all times be-
cause of the ability of lime to stick to all surfaces. The operator
should read Section 24.23 on how to maintain pumps and
other equipment when using a lime precipitation method for
phosphorus removal.
24.35 Safety
1. Lime. Lime is a very strong base and can cause serious
burns and other injuries to portions of the human body. Be
sure to read the precautions described in Section 24.24 of
this chapter.
2. Gases Off the Anaerobic Phosphate Stripping Tank. As
with any unit of wastewater treatment, whenever anaerobic
conditions prevail, certain gases are released from the tank.
Just as it is important not to smoke around an anaerobic
digester, it is also important not to smoke around an
anaerobic phosphorus stripping tank. The gases given off
could include methane which could cause explosions or a
fire. Operators must understand and be very cautious
around any tank where anaerobic conditions exist and from
which explosive gases may be emitted.
24.36 Loading Guidelines
1. Typical Loading Rates. Because the use of luxury uptake
and phosphorus stripping in anaerobic conditions is rela-
tively new, loading rates for various units will depend on the
design and the operation of that specific treatment facility.
2. Hydraulic Loading for Phosphate Stripper. The hydraulic
loading for a phosphate stripper depends on the dissolved
oxygen of the activated sludge when it enters the anaerobic
stripper and it also depends on the ability of the anaerobic
phosphate stripper to remain anaerobic at all times during
the expulsion of phosphorus from the cell structure of the
bacteria.
3. Hydraulic Loading Rate for Lime Clarifier. The hydraulic
loading rate for lime clarification units is described in Sec-
tion 24.25 on lime clarification for phosphorus removal.
Please check Section 24.25 for average loading rates for
the chemical clarification units.
24.37 Review of Plans and Specifications
1. Lime Storage and Unloading Facilities at the Treatment
Plant. If lime is used to coagulate and settle phosphorus
from the waste stream of the phosphorus stripping tank, it is
very useful if the operator can provide information to the
design engineer and have the opportunity to review the
plans and make comments. Some of the items to look for in
the design of the lime storage area are included in Section
24.26 on lime clarification for phosphorus removal.
2. Maintaining Proper Dissolved Oxygen. The operator may
want to insist on automatic dissolved oxygen probes which
can help to determine if the proper anaerobic conditions
exist in the phosphorus stripping unit to ensure that phos-
phorus is released from the cell structure of the bacteria.
Warning signals and devices can be included to ensure that
the operator is notified if oxygen is recorded in the stripping
tank. Automatic dissolved oxygen meters and controls can
be very useful in maintaining adequate dissolved oxygen
within the aeration system after the anaerobically treated
sludge has been returned to the aeration tanks.
24.38 Additional Reading on Phosphorus Removal by
Luxury Uptake Using an Anaerobic Phosphorus
Stripping Tank
1. BIOLOGICAL-CHEMICAL PROCESS FOR REMOVING
PHOSPHORUS by Union Carbide Corporation under a
grant by the U. S. Environmental Protection Agency, Cin-
cinnati, Ohio.
2. THE PHOSTRIP PROCESS by Union Carbide Corporation,
Tanawanda, New York.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 379.
24.3E How can lime be harmful to your body?
24.3F Why should you not smoke around a phosphorus
stripping tank?
24.3G Why might an operator insist on automatic dissolved
oxygen probes in the phosphorus stripping unit?
24.4 PHOSPHORUS REMOVAL BY ALUM
FLOCCULATION
24.40 Variations In the Alum Flocculation Process
24.400 Alum Flocculation as Used In a Clarification
Process (Fig. 24.6)
Aluminum sulfate (alum) can be used in the same manner as
lime for precipitation of phosphorus in a clarifier. Jhe same
principles of coagulation, flocculation and sedimentation apply
when using alum for the removal of phosphorus in effluent from
a secondary treatment facility. However, because of the differ-
ence in cost between aluminum sulfate and lime, lime is more
commonly used for the precipitation of phosphorus.
-------
w
-J
CHEMICAL TREATMENT
& PHOSPHATE REMOVAL
(D
0)
3
(D
3
D>
3
W
ALUM
RAPID
MIX
'V
'"W . /
CHEMICAL
CLARIFIER
FILTER
EFFLUENT
i /
FLOCCULATION
ALUM
& PHOSPHORUS
t
SLUDGES
TO DISPOSAL
Fig. 24.6 Alum flocculation as used in a clarification process
-------
Phosphorus Removal 375
When alum is used for phosphorus removal, two general
reactions occur. In the first reaction, alum reacts with the alka-
linity of the wastewater to form an aluminum hydroxide floe.
Alum + Alkalinity -> u *lumLnu™. + Sulfate + £arb°n
Hydroxide Floe Dioxide
AI2(S04)3 + 6 HCOj — 2 AI(OH)3i + 3S04~~ + COa
The alum also reacts with the phosphate present.
Alum + Phosphate -» nlumi?.L"71 + Sulfate
Phosphate
AI2(S04)3 + 2PO„~ — 2AIPO,i + 3 SO„~
Phosphorus removal is by the formation of an insoluble
complex precipitate and by adsorption on the aluminum hy-
droxide floe. Depending on the alkalinity of the wastewater,
dosages of 200 to 400 mg/L of alum are commonly required to
reduce phosphorus in the effluent down to 0 to 0.5 mg/L. Op-
timum phosphorus removal is usually achieved around a pH of
6.0. Alum feed is frequently controlled by automatic pH equip-
ment which doses according to the pH set point (the more
alum, the lower the pH). Jar tests can be used to determine the
optimum pH set point and alum dosage rate.
If it is necessary to achieve low effluent phosphorus residu-
als (less than 1.0 mg/L) in the effluent, the chemical clarifier is
usually followed by either a pressure filter or a multi-media
gravity filter. Phosphorus sludge from the clarifier goes to de-
watering and disposal facilities. At present, there are no eco-
nomical methods available for alum recovery.
24.401 Alum Flocculatlon as Used in Conjunction with
Filtering of Suspended Solids (Fig. 24.7)
1. Aluminum Sulfate (Alum) as a Coagulant. Because of the
proven ability of alum to coagulate and flocculate sus-
pended particles from water and wastewater, the use of
alum as a filtering aid has been common for many years.
When alum is added to the wastewater entering a filtration
unit, electromagnetic forces are established on the filter
media which allow the trapping of suspended solids and
substantially improve the quality of effluent.
Treatment plants which have used aluminum sulfate as a
filtering aid have also experienced a reduction in the phos-
phorus as the wastewater flows through the filtration units.
Although filtration is not usually considered an efficient
method to remove phosphorus, the filtering with alum addi-
tion has provided a reduction of phosphorus at the same
time that BOD and suspended solids are being reduced
from the wastewater.
2. Expected Efficiencies of Phosphorus Removal Using Alum
in Conjunction with Filtration. Most advanced wastewater
treatment facilities which use a phosphorus removal system
followed by filtration can expect that low levels of phos-
phorus would enter the filter unit. Experiences at various
wastewater treatment facilities have indicated that total
phosphorus removal through filters using alum as a filtering
aid achieved 70 to 95 percent phosphorus removal efficien-
cies. Influent data indicated a total phosphorus, however, of
less than one milligram per liter. Dissolved phosphorus can
be reduced 65 to 90 percent assuming that the incoming
phosphorus loading would be less than 0.5 mg/L. Particu-
late phosphorus can be removed up to 100 percent be-
cause this phosphorus is usually attached to suspended
solids which are almost totally removed from the wastewa-
ter as it passes through a properly operated filter using
aluminum sulfate for coagulation.
24.41 Maintenance of Alum Feeding Pumps and
Associated Equipment
1. Pump Plugging Problems. Aluminum sulfate usually is de-
livered in a dry powder form or as a liquid; however, it is
used as a liquid. The operators of a treatment facility must
mix the dry alum with water to obtain a solution for feed to
the water before entrance to the filtration units. Because of
the chemical nature of aluminum sulfate, it sticks to sur-
faces very easily. This has caused pump plugging problems
for many treatment plants. Most of the pumps that feed
aluminum sulfate are small, metered, chemical feed pumps.
Alum has a tendencyy to plug these pumps very rapidly and
therefore, the pumps require a considerable amount of care
and maintenance to ensure that the proper dosage of alum
is being fed to the filtration units. If plugging problems oc-
cur, the accuracy of the feed amount is questionable.
2. Pipe Plugging and Deterioration. Most pipes used for the
transport of aluminum sulfate are either plastic or small
glass tubing. Alum can stick to most surfaces and can de-
teriorate metal due to the chemical reaction formed when
the aluminum sulfate and ferrous metal react with one
another. Once liquid aluminum sulfate dries, plugging is a
certain result. Pipes may become permanently plugged
with aluminum sulfate and require replacement. The
operators should keep pumps and pipes clean and should
remember to run clear water periodically through an alum
feedline to be sure that any potential plugging problems are
alleviated.
24.42 Operation of Alum Flocculatlon for
Phosphorus and Suspended Solids Removal
24.420 Dally Operating Procedures
When used as a filtration aid, aluminum sulfate dosages
must be precise. Even slight over or under doses may cause
reduced efficiency. The operator must rely on jar testing and
sampling of influent and effluent from a filter bed to be certain
that the feed rate or dosage of alum in milligrams per liter is
correct for the optimum phosphorus and suspended solids re-
moval efficiency. The operator should perform the following
steps to be certain that aluminum sulfate feed is at the correct
ratio:
1. Check the results of jar tests to be certain the dosage of
alum will form a good floe.
2. Check laboratory results to be certain that the alum is not
overdosed or underdosed so that phosphorus also is re-
moved as efficiently as possible through the filtration unit.
3. Check chemical feed pumps and alum feed piping system
to be certain that the setting on the pump actually corre-
sponds to the desired feed rate for efficient operation.
24.421 Abnormal Conditions
1. Pump or Piping Plugging Problems. As mentioned previ-
ously, the most important maintenance item for any alum
feeding system is keeping the aluminum sulfate from plug-
ging either piping or the chemical feed pump used for the
feed of the alum (aluminum sulfate).
2. Operational Problems with Upstream or Downstream
Treatment Processes. Tertiary filtration depends to a great
extent on the upstream treatment units functioning prop-
erly. The operator should be certain of the quality of the
wastewater entering the filtration unit. This quality can
change daily depending on the upstream processes and
the efficiency of their performance. The operator must
-------
FILTRATION
CO
o>
FILTER
FILTER
EFFLUENT
ALUMINUM—/' X
SULPHATE
TERTIARY
PUMPS
TO
DRAIN
BACKWASH
WATER
DECANTING
TANK
-------
Phosphorus Removal 377
check the various guidelines including suspended solids
loading to calculate and to adjust the dosage of chemicals
needed in the filtration unit. Filters also require backwash-
ing to keep them clean and in proper operation. If upstream
treatment units are not functioning properly, backwashing
cycles may be needed more frequently than normal.
3. Alum Overdoses. One of the most common problems with
using chemicals as filtering aids is the possibility of overdos-
ing the filters with the chemical. Aluminum sulfate will react
in a very negative way when it is overdosed into a wastewa-
ter system. The result is a lowering of the pH; this will hinder
the ability of alum to coagulate the suspended solids. The
low pH causes a cloudy condition which is visible to the
operator in the form of substantial turbidity and suspended
solids. If you observe a cloudy appearance in the effluent
from the filtration unit, first check to make sure that the alum
feed is not in an overdose condition. Underfeeding alum
sulfate is better than overdosing with the chemical.
4. Suspended Solids Interference. If treatment units upstream
are not operating properly, a substantial amount of sus-
pended solids will load up the filter units and interfere with
their ability to remove both suspended solids and phos-
phorus. From the standpoint of efficient operation, overload-
ing of suspended solids onto the filtration units must not
occur. If this occurs, frequent backwashing will be required
and an increased quantity of aluminum sulfate and/or
polymer may have to be added to overcome the additional
load placed on the filter units.
24.43 Safety
1. Aluminum Sulfate Mixed with Water. When aluminum sul-
fate mixes with water, a very slippery combination occurs.
Operators should be very cautious around any floor that is
wet with a spill of aluminum sulfate. Any surface continually
exposed to slippery aluminum sulfate should be roughed up
to prevent slipping and to avoid injury. Safety railings
should be provided near any containers or working areas in
which aluminum sulfate can be found.
2. Materials Handling Precautions. Aluminum sulfate usually
is delivered in a dry powder form. The operator should be
very careful when mixing the powder with water that the
powder does not get into the operator's respiratory system
or eyes. Protective goggles and masks should be worn to
protect your eyes and respiratory system. Use fans and
filters to provide a safe air for breathing in the work area.
The operator should also be careful not to allow powdered
aluminum sulfate to fall on a wet surface, thereby creating a
slippery condition.
24.44 Loading Guidelines
1. Alum Feed Rates for Effective Suspended Solids Removal.
Aluminum sulfate is usually added as a filtering aid to re-
move suspended solids. The dosage rates at various
treatment facilities range from 1 to 20 milligrams per liter
depending on the incoming suspended solids and wastewa-
ter quality. Some phosphorus also will be removed with the
suspended solids, but this procedure and dosage do not
produce substantial phosphorus removal. See Section
24.400 for information on how to remove phosphorus by the
use of alum. To determine the best operating dosage for
aluminum sulfate at your facility, you should rely on jar tests
and other laboratory results to determine the best dosage
rate for your treatment facility and type of wastewater. The
feed rates of aluminum sulfate are usually low; therefore, be
certain that the chemical feed pump is operating properly to
provide an accurate chemical-flow ratio.
2. Hydraulic Loading on Filtration Process Using Aluminum
Sulfate as a Filtering Aid. The standard design rate for a
pressure filtration unit is 5 gallons per minute per square
foot (3.4 liters per second per square meter). Loading rates
can vary depending on the type of filter system used. The
most commonly used is the pressure filter. The operator
should calculate the hydraulic loading based on the flow of
wastewater distributed over the surface area of the filtration
unit. If a gravity filter unit is used, the operator should obtain
information from the manufacturer or design engineer on
the proper application rate of wastewater onto the unit.
24.45 Review of Plans and Specifications
1. Storage of Aluminum Sulfate. Because aluminum sulfate
comes in a powdered form, it is important to store the prod-
uct in a dry environment, preferably inside a building. Usu-
ally operators make up a large batch of aluminum sulfate
liquid at one time in order to have enough on hand to last
several days. The tanks holding the liquid aluminum sulfate
should be fiberglass, non-ferreous material or be rubber-
lined to protect the metal from the corrosive effects of the
aluminum sulfate.
2. Piping and Pump Diagrams. Because aluminum sulfate has
the capability of sticking to many surfaces, it is important for
the design of a treatment facility using alum to have flexible
piping so that if a feedline becomes plugged or a pump is
out of service for maintenance, the alum feed can continue
without interruption. A pipe chase will enable operators to
get to the alum piping in order to make repairs or replace
the pipe if needed. A system of flushing the pumps and
piping is necessary to help prevent any plugging problems
which can plague the operation of a facility.
24.46 Additional Reading for Phosphorus Removal by
Alum Flocculation
1. HANDBOOK OF ADVANCED WASTEWATER TREAT-
MENT, Second Edition, Culp, Russell L., George M.
Wesner, and Gordon L. Culp, Van Nostrand Reinhold Co.,
New York City, New York, 1977. Obtain from Litton Educa-
tional Publishing, Inc., 7625 Empire Drive, Florence, Ken-
tucky 41042. Price: $32.50.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 379.
24.4A What is a major difference between the use of lime
and alum for precipitation of phosphorus-rich parti-
cles?
24.4B How would you determine the optimum alum dosage?
24.4C If upstream treatment units are not functioning prop-
erly, what happens to filter backwashing cycles?
24.4D What would you do if you observed a cloudy appear-
ance in the effluent from a filtration unit?
24.4E What should be done to a floor that is continually ex-
posed to slippery alum?
END OF LESSON 2 OF 2 LESSONS
ON
PHOSPHORUS REMOVAL
Please answer the discussion and review questions before
continuing.
-------
378 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
Chapter 24. PHOSPHORUS REMOVAL
(Lesson 2 of 2 Lessons)
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 1.
6. What happens to the effluent from the phosphate stripper?
7. In the luxury uptake process, what happens if the sludge
feed rate is (a) too high or (b) too low into or out of the
phosphorus stripping tank?
8. How would you adjust the feed into and out of an
anaerobic phosphorus stripping tank?
9. Alum has proved to be an effective coagulant for removing
what pollutants from wastewater?
10. Why do pumps moving alum solutions clog?
11. How would you keep alum feed lines from plugging?
PLEASE WORK THE OBJECTIVE TEST NEXT.
SUGGESTED ANSWERS
Chapter 24. PHOSPHORUS REMOVAL
Answers to questions on page 358.
24.0A Phosphorus is removed from wastewater because it
provides a nutrient or food source for algae. Dead
algae can cause serious oxygen depletion problems in
receiving streams which in turn can kill fish and other
aquatic life. Also, algae can cause taste and odor
problems in drinking water supplies.
24.1 A The three major types of systems used to remove
phosphorus from wastewater are:
1. Lime precipitation;
2. Luxury uptake; and
3. Aluminum sulfate flocculation and precipitation.
Answers to questions on page 366.
24.2A Equipment necessary for the lime precipitation pro-
cess include:
1. Lime feed equipment;
2. Mixing equipment and mixing chamber;
3. Clarifiers; and
4. Pumps and piping.
24.2B The slaker or lime mix feed system must have a grit
removal system because most dry lime has a certain
amount of grit, rocks and sand in the mixture. This
material must be removed to prevent plugging and
equipment wear.
24.2C Daily operation of a lime precipitation process to re-
move phosphorus consists of :
1. Routine pH monitoring to check automatic feed;
2. Routine phosphate test for removal efficiencies;
3. Calcium oxide content of lime feed; and
4. Daily maintenance of pumps, piping, and other
equipment to prevent plugging by lime scale.
24.2D Low flow conditions are of concern to avoid the possi-
bility of feeding excess lime and thereby wasting lime
and money.
24.2E Phosphorus removal efficiency may be affected by:
1. Short-circuiting;
2. Changes in pH;
3. Solids loading;
4. Small straggler floe;
5. Storm water;
6. Industrial dischargers;
7. Plugged pumps or piping;
8. Inadequate lime supply; and
9. Operational problems with upstream or
downstream treatment processes.
Answers to questions on page 368.
24.2F The purpose of the lime slaking mechanism is to con-
vert calcium oxide to calcium hydroxide in a slurry
form.
24.2G Recalcined lime is lime from a lime-recovery process
in which the calcium carbonate in sludge is converted
to lime by heating at 1800°F (980°C).
24.2H Many times a lime process uses polymers to help form
colloidal particles of lime and phosphorus to provide
faster sedimentation in a lime clarification unit.
24.21 The forms of phosphorus in the total phosphate
measurement include the forms of orthophosphate,
polyphosphate and organic phosphorus.
24.2J To reduce problems that will arise when pumps or
pipes become plugged with lime, alternate piping and
valving should be provided so that while repairing or
cleaning one pipe train or pump, continued operation
can be provided.
END OF ANSWERS
TO
QUESTIONS IN LESSON 1
-------
Phosphorus Removal 379
Answers to questions on page 372.
24.3A Luxury uptake of phosphorus is a biological process
whereby the bacteria normally found in the activated
sludge treatment portion of the secondary wastewater
treatment plant are withdrawn to an environment with-
out oxygen (anaerobic) for release of phosphorus.
When these bacteria are returned to an ideal environ-
ment, the first thing they take in is phosphorus. This
phosphorus take-up is known as luxury uptake.
24.3B In the luxury uptake process, bacteria release phos-
phorus from their cell structure in the phosphorus re-
lease tank under anaerobic conditions.
24.3C The units used in the lime clarification process of the
luxury uptake process include:
1. Lime slaking equipment,
2. Lime feeding system, and
3. Lime clarification unit.
24.3D The pH should be run manually on the lime clarifica-
tion tank each 8 hours to ensure that the automatic
controls are functioning properly.
Answers to questions on page 373.
24.3E Lime is a very strong base and can cause serious
burns and other injuries to your body.
24.3F You should not smoke around a phosphorus stripping
tank because the methane gas produced by the
anaerobic conditions can create explosive conditions
just like in an anaerobic digester.
24.3G An operator may insist on automatic dissolved oxygen
probes to determine that continuous anaerobic condi-
tions exist in the phosphorus stripping unit to ensure
that phosphorus is released from the cell structure of
the bacteria.
Answers to questions on page 377.
24.4A A major difference between lime and alum for precipi-
tation of phosphorus rich-particles is that alum is more
expensive than lime.
24.4B The optimum alum dosage can be determined by the
jar test. Add varying amounts of alum to each jar con-
taining the water being treated. The jar that produces
the best clarification with the minimum amount of alum
indicates the optimum alum dosage.
24.4C If upstream treatment units are not functioning prop-
erly, filter backwashing cycles may be more frequent
than normal.
24.4D If you observe a cloudy appearance in the effluent
from a filtration unit, first check to make sure that the
alum feed is not in an overdose condition.
24.4E Any floor that is continually exposed to slippery alum
should be roughed up to prevent slipping and to avoid
injury.
END OF ANSWERS
TO
QUESTIONS IN LESSON 2
-------
380 Treatment Plants
OBJECTIVE TEST
Chapter 24. PHOSPHORUS REMOVAL
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one correct answer to each question.
1. Recalcine is a lime-recovery process in which the calcium
carbonate in sludge is converted to lime by heating at
1800T (980°C).
1. True
2. False
2. In the lime phosphorus removal process, the lime phos-
phorus sludge is pumped from the chemical clarifier to an
anaerobic digester.
1. True
2. False
3. Calcium carbonate and carbon dioxide combine to form
calcium hydroxide.
1. True
2. False
4. Pumps handling lime sludges are not subject to wear be-
cause the lime forms a protective coating over the moving
parts.
1. True
2. False
5. The use of alum and filtration can remove BOTH dissolved
and particulate phosphorus from wastewater.
1. True
2. False
6. Chemicals used to remove phosphorus from wastewater
include
1. Aluminum sulfate.
2. Calcium hydroxide.
3. Chlorine.
4. Copper sulfate.
5. Lime.
7. Lime feeding equipment should be routinely checked
1. Every hour.
2. Several times during each shift.
3. Once each shift.
4. Three times a week.
5. Once a week.
8. The plugging of pipes by limestone scale in a lime system
can be prevented by
1. Backwashing.
2. Forward flushing.
3. Regular cleaning with hot water or steam.
4. Regular recarbonation.
5. Washing with hydrochloric acid.
9. In a properly operated chemical clarifier you can see down
below the water surface at least
1. 1 foot.
2. 2 feet.
3. 4 feet.
4. 7 feet.
5. 10 feet.
10. In the lime precipitation process for phosphorus removal,
the pH of the combined wastewater and lime slurry should
be or above.
1. 5
2. 7
3. 8
4. 9
5. 11
11. The pH probe or sensing mechanism that helps the lime
feed system work in automatic mode must be cleaned on
basis to ensure that a scale buildup does not inter-
fere with the function of the pH control readout probe.
1. An hourly
2. A two-hour
3. A daily
4. An every other day
5. A weekly
12. In the luxury uptake process, the pH in the lime clarifica-
tion unit should be above (choose the most accurate an-
swer)
1. 3.0.
2. 5.0.
3. 7.0.
4. 9.0.
5. 11.0.
13. The hydraulic loading for a phosphate stripper depends on
the
1. Ability of the anaerobic phosphate stripper to remain
anaerobic.
2. Ability of the aerobic phosphate stripper to remain
aerobic.
3. BOD loading of the unit.
4. Dissolved oxygen of the activated sludge.
5. pH of the wastewater being treated.
14. Most pipes used for the transport of aluminum sulfate are
made of which of the following materials?
1. Asbestos cement
2. Cast iron
3. Copper
4. Glass
5. Plastic
END OF OBJECTIVE TEST
-------
CHAPTER 25
Daniel J. Hinrichs
-------
382 Treatment Plants
TABLE OF CONTENTS
Chapter 25. Wastewater Reclamation
Page
OBJECTIVES 384
GLOSSARY 385
LESSON 1
DIRECT REUSE OF EFFLUENT
25.0 Uses of Reclaimed Wastewater 386
25.00 Direct Reuse of Effluent 386
25.01 Equipment Requirements 388
25.02 Limitations of Direct Reuse 388
25.03 Case Histories 388
25.030 South Lake Tahoe Public Utility District, California 388
25.031 Muskegon County, Michigan 390
25.032 Windhoek, South Africa 390
25.033 Nuclear Generating Station, Phoenix, Arizona 390
25.034 Specialty Steel Mill, Syracuse, New York 395
25.1 Operating Procedures 397
25.10 Pre-start Inspection 397
25.11 Start-up 397
25.12 Normal Operation 397
25.13 Shutdown 398
25.14 Operational Strategy 398
25.15 Emergency Operating Procedures 398
25.16 Troubleshooting Guide 398
25.2 Monitoring Program 398
25.20 Monitoring Schedule 398
25.21 Interpretation of Test Results and Follow-up Actions 398
25.3 Safety 400
25.4 Maintenance 400
25.5 Review of Plans and Specifications 400
-------
Wastewater Reclamation 383
LESSON 2
EFFLUENT DISPOSAL ON LAND
25.6 Land Treatment System 401
25.60 Description of Treatment Systems 401
25.61 Equipment Requirements 401
25.62 Sidestreams and Their Treatment 401
25.63 Limitations of Land Treatment 406
25.7 Operating Procedures 406
25.70 Pre-Start Checklist 406
25.71 Start-Up 406
25.72 Normal Operation 408
25.73 Shutdown 411
25.74 Operational Strategy 411
25.75 Emergency Operating Procedures 413
25.76 Troubleshooting Guide 413
25.8 Monitoring Program 415
25.80 Monitoring Schedule 415
25.81 Interpretation of Test Results and Follow-up Actions 415
25.9 Safety 415
25.10 Maintenance 416
25.11 Review of Plans and Specifications 416
25.12 References and Additional Reading 416
25.120 References 4"l(>
25.121 Additional Reading 416
-------
384 Treatment Plants
OBJECTIVES
Chapter 25. WASTEWATER RECLAMATION
Following completion of Chapter 25, you should be able to
do the following:
1. Safely operate and maintain a wastewater reclamation facil-
ity,
2. Describe the various methods of wastewater reclamation,
3. Develop operational strategies for wastewater reclamation
facilities,
4. Monitor a wastewater reclamation program and make ap-
propriate adjustments in treatment processes, and
5. Review the plans and specifications for a wastewater re-
clamation facility.
-------
Wastewater Reclamation 385
GLOSSARY
Chapter 25. WASTEWATER RECLAMATION
CATION EXCHANGE CAPACITY CATION EXCHANGE CAPACITY
The ability of a soil or other solid to exchange cations (positive ions such as calcium, Ca+2) with a liquid.
DRAINAGE WELLS DRAINAGE WELLS
Wells that can be pumped to lower the ground water table and prevent ponding.
DRAIN TILE SYSTEMS DRAIN TILE SYSTEMS
A system of tile pipes buried under the crops that collect percolated waters and keep the groundwater table below the ground
surface to prevent ponding.
EVAPOTRANSPIRATION (e-VAP-o-tran-spi-RAY-shun) EVAPOTRANSPI RATION
The total water removed from an area by transpiration (plants) and by evaporation from soil, snow and water surfaces.
HYDROLOGIC CYCLE (Hl-dro-loj-ic) HYDROLOGIC CYCLE
The process of evaporation of water into the air and its return to earth by precipitation (rain or snow). This process also includes
transpiration from plants, groundwater movement and runoff into rivers, streams and the ocean.
RECHARGE RATE RECHARGE RATE
Rate at which water is added beneath the surface of the ground to replenish or recharge groundwater.
RECLAMATION RECLAMATION
The operation or process of changing the condition or characteristics of water so that improved uses can be achieved.
RECYCLE RECYCLE
The use of water or wastewater within (internally) a facility before it is discharged to a treatment system. Also see REUSE.
REUSE REUSE
The use of water or wastewater after it has been discharged and th^n withdrawn by another user. Also see RECYCLE.
SIDESTREAM SIDESTREAM
Wastewater flows that develop from other storage or treatment facilities. This wastewater may or may not need additional treatment.
SODIUM ADSORPTION RATIO (SAR) SODIUM ADSORPTION RATIO
This ratio expresses the relative activity of sodium ions in the exchange reactions with soil. The ratio is defined as follows:
Na
SAR =.
[%(Ca + Mg)f
where Na, Ca, and Mg are concentrations of the respective ions in milliequivalents per liter of water.
Na, meqIL = Na- m9/L Ca, meqIL = Ca- m9"-
23.0 mg/meq 20.0 mg/meq
Mg, meqIL = _ Mg, mgIL
12.15 mg/meq
-------
386 Treatment Plants
CHAPTER 25. WASTEWATER RECLAMATION
(Lesson 1 of 2 Lessons)
DIRECT REUSE OF EFFLUENT
25.0 USES OF RECLAIMED WASTEWATER
25.00 Direct Reuse of Effluent
Why might the effluent from your wastewater treatment plant
be reused directly by someone? The main reason is that
someone needs water and the effluent from your wastewater
treatment plant is of an acceptable quality to meet their needs.
Effluent reuse is considered when (1) the volume of municipal
water needed is not available, (2) the cost of purchasing avail-
able treated water is too expensive, (3) surface waters are not
available or the cost of treatment is excessive, and (4)
groundwaters are either not available or the costs of pumping
and any treatment is prohibitive. In the future as discharge
requirements become more and more stringent, the quality of
plant effluents will become more and more attractive as the
best available source of water. For these reasons, you must be
able to produce an effluent that can be used either directly or
reclaimed for beneficial uses. Effluent from wastewater may be
reclaimed for the uses listed in Table 25.1. Table 25.2 lists the
treatment levels necessary for various beneficial uses.
Irrigation is covered in Lesson 2, "Effluent Disposal on
Land." Indirect reuse is the same as disposal by dilution.
Groundwater recharge by spreading basins is included with
the section on irrigation. This section includes direct reuse by
industry, deep well injection, and recreation (Figures 25.1,25.2
and 25.3). Generally, the operation of these systems is similar.
If water or wastewater is used again within (internally) a
facility before it is discharged to a treatment system, this water
is considered RECYCLED. If this water is discharged and then
withdrawn by another user, the water is REUSED. RECLAMA-
TION is the operation or process of changing the condition or
characteristics of water so that improved uses can be
achieved.
TABLE 25.1 TREATMENT LEVELS REQUIRED FOR
VARIOUS BENEFICIAL USES*
Beneficial Use Treatment Levels6
Agricultural Irrigation — Forage Crops 1
Agricultural Irrigation — Truck Crops 1
Urban Irrigation — Landscape 4
Livestock and Wildlife Watering 1
Power Plant and Industrial Cooling
Once-through 1
Recirculation 1
Industrial Boiler Make-up
Low pressure 6
Intermediate pressure 10
Industrial Water Supply
Petroleum and Coal Products 3a or 4
Primary Metals 1
Paper and Allied Products 5c or 8
Chemicals and Allied Products 7 to 11
Food Products 7 to 11
Fisheries
Warm Water 6
Cold Water 6
Recreation
Secondary Contact 4
Primary Contact 5 or 6
Public Water Supply
Groundwater, spreading 13b
Groundwater, injection 11
Surface Water 9, 10, or 12
Direct Potable 11
• WATER REUSE AND RECYCLING, Volume 2, EVALUATION OF
TREATMENT TECHNOLOGY, by Culp/Wesner/Culp for De-
partment of Interior, Office of Water Research and Technology,
OWRT/RU-7911, Washington, D.C. 1979.
b See Table 25.2 for an explanation of processes that produce the
desired treatment levels.
TABLE 25.2 TREATMENT LEVELS'
Treatment Level Treatment System
1a Activated sludge
1b Trickling filter
1c Rotating biological contactors
2a 2-Stage nitrification
2b Rotating biological contactors
2c Extended aeration
3a Nitrification-Denitrification
3b Selective ion exchange
4 Filtration of secondary effluent
5a Alum added to aeration basin
5b Ferric chloride added to primary
5c Tertiary lime treatment
6a Tertiary lime, nitrified effluent
6b Tertiary lime plus ion exchange
7 Carbon adsorption, filtered
secondary effluent
8 Carbon, tertiary lime effluent
9 Carbon, tertiary lime,
nitrified effluent
10 Carbon, tertiary lime, ion
exchange
11 Reverse osmosis of AWT effluent
12a Physical-Chemical system, lime
12b Physical-Chemical system, ferric chloride
13a Irrigation
13b Infiltration-Percolation
13c Overland flow
• WATER REUSE AND RECYCLING, Volume 2, EVALUATION OF
TREATMENT TECHNOLOGY, by Culp/Wesner/Culp for Depart-
ment of Interior, Office of Water Research and Technology,
OWRT/RU-7911, Washington, D.C. 1979.
-------
Wastewater Reclamation 387
EFFLUENT
STORAGE
»-TO INDUSTRY
Fig. 25.1 Industrial reuse
EFFLUENT-
STORAGE
OR
BLENDING
WELLS
Fig. 25.2 Deep well injection
RESERVOIR
EFFLUENT
DIFFUSERS
Fig. 25.3 Recreation use
-------
388 Treatment Plants
25.01 Equipment Requirements
Equipment used in wastewater reclamation plants is very
similar to equipment used in most conventional wastewater
treatment plants. Equipment requirements consist of a trans-
mission system of pipes, ditches, or canals to transport water
to the user's location. Metering and control systems are nec-
essary for monitoring flows and water quality delivered to us-
ers.
Deep well injection systems include pipelines, pumps, and
wells along with the meters and control equipment. Often,
treated effluent (the reclaimed wastewater) is mixed with fresh
water prior to injection to dilute the treated effluent. In these
instances a blending tank is required. Effluent and fresh water
are pumped to the blending tank and the mixture is pumped to
the injection wells. Most injection systems are used in coastal
areas to serve as barriers for preventing contamination of
groundwater by salt water. There may be other uses for injec-
tion wells such as injection into oil wells to aid oil pumping
operations. Oil that was not removed by previous pumping
efforts will float on top of water and be easier to pump from
underground areas.
The equipment requirements for disposal to a recreation
lake are basically the same as disposal by dilution (Chapter
13).
There are several variations possible with these systems,
but each must provide a means for delivering water to the point
of use. In some instances storage or blending with fresh water
may be desired, so Figures 25.1 and 25.2 show provisions for
storage.
25.02 Limitations of Direct Reuse
Industrial reuse of wastewater will increase in the future.
Water quality requirements for industrial use vary consid-
erably. For example, cooling and washing waters do not re-
quire as high or as consistent a quality as water used in food
processing or manufacturing processes. For these reasons
large industries often have their own water treatment plants on
the site to provide the degree of treatment required for produc-
tion processes. Under these conditions reclaimed effluent may
be used directly for washing purposes or serve as influent to a
specialized water treatment plant. In either case, industries
desire as consistent a quality as possible from your wastewa-
ter reclamation plant.
Regardless of the use of treated effluent or reclaimed
wastewater, the user of the water will expect the water to be
supplied to meet specific water quality criteria. These criteria
are just as important as NPDES permit requirements. If water
quality criteria are not met, operators must have a plan to notify
users, or to store or to dispose of the inadequately treated
wastewater.
Industrial reuse requires a fairly uniform quality of water. If
any water quality indicator fluctuates, notify the industrial user.
Water quality indicators of concern include but are not limited
to temperature, pH, color, and hardness or scale-forming min-
erals such as calcium, magnesium and iron.
Deep well injection must follow procedures developed to
maintain the RECHARGE RATES.' Important considerations
include type of pumps, pump discharge pressures and mainte-
nance of any venting systems. Slime growths caused by or-
ganisms in the presence of proper temperature, food and nu-
trients can reduce recharge rates. Care must be taken to avoid
contamination of groundwaters used as a drinking water sup-
ply. Groundwaters can be contaminated by the discharge of
excessive amounts of trace organics, minerals, nutrients or
toxic materials.
Water reclaimed for recreation use must consider protection
of public health and aesthetics. As a minimum standard, public
health considerations require the absence of pathogens as
measured by the coliform group bacteria test. Aesthetics are
evaluated by the lack of floatables and scums. The clearer a
body of water, the more pleasing the appearance. Nutrients
can contribute to algal growths which reduce the aesthetic
value of water used for recreation. Inadequate removal of BOD
can result in the depletion of oxygen in the receiving waters
which may cause fish kills.
Table 25.1 lists the various beneficial uses of water that are
quite likely to use reclaimed water now and in the future. These
different uses require different treatment processes and de-
grees of treatment (treatment levels) to produce a reclaimed
effluent suitable for direct reuse by industry or other type of
water user. These treatment levels are described in terms of
treatment processes or treatment systems in Table 25.2. To
determine the effluent quality you should expect from a waste-
water reclamation plant, Table 25.3 lists the expected effluent
quality from various combinations of treatment processes used
to reclaim wastewater. This table also could be used to deter-
mine whether the effluent could be used by certain beneficial
uses.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 417.
25.0A List the possible uses of reclaimed wastewater.
25.0B How can deep well injection aid oil pumping opera-
tions?
25.03 Case Histories
The following case histories were developed at actual
operating wastewater reclamation facilities. The data shown
for the first three case histories were taken from HEALTH AS-
PECTS OF WASTEWATER RECHARGE. This publication was
prepared by a consulting panel for the California State Water
Resources Control Board, Department of Water Resources
and Department of Health.
25.030 South Lake Tahoe Public Utility District, California
(Fig. 25.4)
This system was developed to treat wastewater for reuse in
a recreation lake and for crop irrigation. The unit processes
include primary sedimentation, activated sludge, lime addition
and chemical clarification, ammonia stripping, filtration, acti-
vated carbon adsorption, and chlorination. The major function
of the primary sedimentation process is to remove suspended
solids. The activated sludge process removes suspended sol-
ids and BOD. Lime addition and chemical clarification remove
phosphorus. Ammonia removal is accomplished by ammonia
stripping towers. Filters are provided for suspended solids and
turbidity removal. The activated carbon adsorption process
removes COD, BOD, and methylene blue active substances
(MBAS, a surface active agent). The chlorination process is
provided for pathogen reduction and during cold weather is
used for nitrogen removal by breakpoint chlorination.
1 Recharge Rate. Rate at which water is added beneath the surface of the ground to replenish or recharge groundwater.
-------
Wastewater Reclamation 389
TABLE 25.3 ANTICIPATED PERFORMANCE OF VARIOUS UNIT PROCESS COMBINATIONS*
AWT Pretreatment
AWT Process
ESTIMATED AWT PROCESS EFFLUENT QUALITY
BOD COD Turb. PO, SS Color NH,-N
(mg/L) (mg IL) (JU) (mg/L) (mg IL) (units) (mg IL)
Preliminary0
c.s
50-100
80-180
5-20
2-4
10-30
30-60
20-30
C.S.F
30-70
50-150
1-2
0.5-2
2-4
30-60
20-30
C,S.F.AC
5-10
25-45
1-2
0.5-2
2-4
5-20
20-30
C,S,NS,F,AC
5-10
25-45
1-2
0.5-2
2-4
5-20
1-10
Primary
c,s
50-100
80-180
5-15
2-4
10-25
30-60
20-30
C,S,F
30-70
50-150
1-2
0.5-2
2-4
30-60
20-30
C, S.F.AC
5-10
25-45
1-2
0.5-2
2-4
5-20
20-30
C,S,NS,F,AC
5-10
25-45
1-2
0.5-2
2-4
5-20
1-10
High-rate
F
10-20
35-60
6-15
20-30
10-20
30-45
20-30
Trickling
c,s
10-15
35-55
2-9
1-3
4-12
25-40
20-30
Filter
C,S,F
7-12
30-50
0.1-1
0.1-1
0-1
25-40
20-30
C,S.F.AC
1-2
10-25
0.1-1
0.1-1
0-1
0-15
20-30
C,S,NS,F,AC
1-2
10-25
0.1-1
0.1-1
0-1
0-15
1-10
Conventional
F
3-7
30-50
2-8
20-30
3-12
25-50
20-30
Activated
C,S
3-7
30-50
2-7
1-3
3-10
20-40
20-30
Sludge
C,S,F
1-2
25-45
0.1-1
0.1-1
0-1
20-40
20-30
C,S.F.AC
0-1
5-15
0.1-1
0.1-1
0-1
0-15
20-30
C,S,NS,F,AC
0-1
5-15
0.1-1
0.1-1
0-1
0-15
1-10
Culp. Copyright 1978 by Litton Educational Publishing, Inc. Reprinted by permission of Van Nostrand Reinhold.
b C,S - Coagulation and sedimentation; F - mixed-media filtration; AC - activated carbon adsorption; NS - ammonia stripping. Lower effluent
NH, value at l8°C.d
c Preliminary treatment - grit removal, screen chamber, Parshall flume, overflow.
d For details on C, S and F, see Chapter 23; AC, Chapter 28; and NS, Chapter 21 for ammonia removal by nitnfication.
ACTIVATED
SLUDGE
CHEMICAL
AMMONIA
tECARBONATION
AND
EFFLUENT
CLARIFICATION
STRIPPING
SETTLING
TO
RECREATION
RESERVOIR
(FISHING &
BOATING)
CHLORINATION
CARBON
ADSORPTION
FILTRATION
SOUTH LAKE TAHOE, CALIFORNIA
Fig. 25.4 Wastewater reclamation processes used at South
Lake Tahoe, California
-------
390 Treatment Plants
These processes remove BOD, COD, suspended solids,
turbidity, nitrogen, phosphorus, and pathogens from the water
being treated. These constituents are removed to make the
recreation lake safe for human contact (pathogen removal),
prevent unsightly algae growth (nitrogen and phosphorus re-
moval), and provide a pleasant appearance (suspended solids
and turbidity removal). Table 25.4 shows water quality follow-
ing each of these unit processes.
25.031 Muskegon County, Michigan (Fig. 25.5)
This system reclaims wastewater for crop irrigation. Irriga-
tion water leaches through the soil and then enters two
streams through the subsurface drainage system. The treat-
ment process consists of aerated ponds and during cold
weather, storage lagoons. These processes reduce BOD,
suspended solids, and pathogens. The purpose of this treat-
ment system is primarily to prevent nuisance conditions from
developing in the fields. The soil provides additional treatment
to water passing through the soils to the drain tiles. Table 25.5
shows water quality indicators at various stages in the process.
25.032 Windhoek, South Africa (Fig. 25.6)
Wastewater is treated in ponds and then reclaimed and
blended with other water for a drinking water supply. The pro-
cesses consist of recarbonation of pond effluent followed by
algae flotation, chemical clarification, breakpoint chlorination,
filtration, and carbon adsorption. Recarbonation lowers the pH.
Algae flotation removes algae to prevent taste and odor prob-
lems. Chemical clarification removes phosphorus and turbidity.
Breakpoint chlorination destroys pathogens and reduces am-
monia levels. Suspended solids and COD are removed by
filtration and carbon adsorption. Treatment results are shown
on Table 25.6.
25.033 Nuclear Generating Station, Phoenix, Arizona
(Fig. 25.7)
Secondary effluent from the City of Phoenix's Wastewater
Treatment Plant is pumped 40 miles (64 km) through a pipeline
to the Arizona Public Service's Palo Verde Nuclear Generating
Station in the desert. Advanced waste treatment processes
produce a highly treated water that is used for make-up water
in the cooling towers. There are no liquid discharges from the
process and the reclamation plant meets the requirement of
"no discharge."
The function of the Water Reclamation Facility is to supply
suitable feedwaters for all of the Palo Verde Nuclear Generat-
TABLE 25.5 MUSKEGON TREATMENT RESULTS
Water
Quality
Indicator
Plant
Influent
Aerated
Ponds
Lagoon
Drain
Tiles
Creeks
BOD, mg/L
220
85
12.5
2.2
2
DO, mg/L
0
1.5
6
2.9
1.6
Suspended
Solids,
325
250
15
0
20
mg/L
Ammonia,
9
5
1.4
0.4
0.5
mg/L
Nitrate,
0
08
1.6
2.8
1.6
mg/L
Phosphate,
6.5
5
2.9
.05
.08
mg/L
ing Station site uses. The largest water use by far will be the
circulating water cooling tower makeup of up to 60,000 GPM
(327,000 cu m/day) for all three units. This flow rate is based
on 15 cycles of concentration in the cooling towers. Since
some of the constituents in this water will cause problems of
corrosion or deposition, the water is chemically treated before
use (Table 25.7). Ammonia causes corrosion of copper and
contributes to biological growths in the storage reservoir. Alka-
linity contributes to scale formation. Biochemical oxygen de-
mand (BOD) is a measure of the organic materials in the water
and contributes to organic materials that cause fouling in con-
denser tubes. Calcium and magnesium contribute to scale
formation as do silica and sulfate. Phosphorus also acceler-
ates biological growth in the storage reservoir. Suspended sol-
ids cause sludge formation or deposits.
Upon arrival at the nuclear power site the first treatment
process is biological nitrification (Fig. 25.7) by the use of trick-
ling filters with plastic media. Nitrification is used to convert the
ammonia to nitrate. An additional advantage of this process is
a reduction in alkalinity with a subsequent 50 percent reduction
in lime demand and sludge handling. Fifty percent of the water
going through the nitrification process is recycled to stabilize
the results.
Lime (Ca(OH)2) is added to the effluent from the trickling
filters to increase the pH to 11.3. Lime addition is used to
precipitate solids and also to reduce the magnesium (90%)
and silica (75%) content in order to control scaling problems.
Lime reduces the phosphate content by 95 percent. Sodium
carbonate (NajCOj) is added to precipitate calcium and soften
the water. After lime and sodium carbonate are added and
mixed with the water, solids-contact clarifiers (Fig. 25.8) are
used to allow the solids and precipitates to settle out.
TABLE 25.4 LEVELS OF WATER QUALITY INDICATORS AFTER EACH UNIT PROCESS
UNIT PROCESSES
Water
Quality
Indicator
Raw
Waste-
water
Primary
Secondary
Chemical
Clarifi-
cation
Ammonia
Stripping
Filtra-
tion
Carbon
Adaorption
Chlorination
BOD (mg/L)
140
100
30
30
30
3
1
0.7
COD (mg/L)
280
220
70
70
70
25
10
10
SS (mg/L)
230
100
26
10
10
0
0
0
Turbidity
250
150
15
10
10
0.3
0.3
0.3
(JTU)
MBAS (mgIL)
7
6
2
2
2
0.5
0.1
0.1
Ammonia
20
20
15
15
1
1
1
1
(mg/U
Phosphorus
12
9
6
0.7
0.7
0.1
0.1
0.1
mg/L)
Coliform
50
15
25
50
50
50
50
<2.2
MPN/100 ml
-------
OPTIONAL
RAW
WASTEWATER
AERATED
LAGOONS
STORAGE
RESERVOIRS
SPRAY
IRRIGATION
CHLORINATION,
NITROGEN
ADDITION,
PUMPING
HOLDING
POND
SEEPAGE RECYCLED DRAIN TILES
OR TO BLACK CREEK TO TWO CREEKS
MUSKEGON COUNTY, MICHIGAN
Fig. 25.5 Wastewater reclamation processes used at Muskegon County, Michigan
-------
3
-------
SECONDARY
SODIUM
CARBONATE
LIME
CLARIFICATION
RECYCLE
MIXING
TRICKLING
FILTERS
(PLASTIC
MEDIA)
BIOLOGICAL
NITRIFICATION
PRECIPITATE
SOLIDS,
MAGNESIUM
AND SILICA
AND UP
pH TO 11.3
PRECIPITATE
CALCIUM
AND SOFTEN
WATER
MIX LIME
AND SODIUM
CARBONATE
SOLIDS AND
PRECIPITATES
SETTLE OUT
COOLING TOWERS
SULFURIC
ACID
COOL WATER
USED TO REMOVE pH TO
HEAT FROM 7.0
NUCLEAR REACTOR
STORAGE
RESERVOIR
LOWER
HOLD WATER
UNTIL NEEDED
MIXED-MEDIA
FILTER
POLYMER CHLORINE
ANTHRACITE
SAND
REMOVE
SOLIDS
COAGULATION
OF FINE
SUSPENDED
PARTICLES
PREVENT
SLIME
GROWTHS
SULFURIC
ACID
LOWER
pH TO
9.0
RECARBON-
ADD CO2
TODROP
pH TO
10.2 TO 10.4
Fig. 25.7 Wastewater reclamation processes used for cooling towers at a nuclear generating station
-------
394 Treatment Plants
NEUTRALIZATION
FLOCCULATION
AID
CHEMICAL
ADDITION
,, /- TURBINE l
i EFFLUENT
CLARIFICATION
ZONE
INFLUENT t
THICKENING
ZONE
REACTION ZONE
TO SLUDGE DISPOSAL
DRAFT
TUBE
Fig. 25.8 Typical solids-contact clarifier
-------
Wastewater Reclamation 395
TABLE 25.6 TREATMENT RESULTS
Water Chemical
Quality Clarification and Activated
Indicator
Effluent
Flotation
Chlorlnatlon
Filtration
Carbon
Total N, mg/L
35
32
15
14
13
Organic N,
3.2
1.3
0.9
0.7
—
mg/L
Ammonia N,
14.9
14
0.2
0.3
0.1
mg/L
Nitrate,
17
17
14
13
13
mg/L
Phosphate,
10
—
—
—
—
mg/L
ABS,® mg/L
8
7
4
4
0.7
BOD, mg/L
30
4
1
1
0.3
pH
8.5
7.1
8.0
8.0
8.0
8 Alkyl Benzene Sulfonate. A type of surfactant, or surface active agent, present in synthetic detergents in the United States before 1965. ABS
was especially troublesome because it caused foaming and resisted breakdown by biological treatment processes. ABS has been replaced in
detergents by Linear Alkyl Sulfonate (LAS) which is biodegradable.
TABLE 25.7 POTENTIAL PROBLEM CONSTITUENTS IN
RECLAIMED WASTEWATER, mg/L
Effluent From City
Target for
Constituent
Treatment Plant
Reclaimed Water
Ammonia8
24-40
5
Alkalinity"
216-283
100
BOD
6 - 42
10
Calciumb
110 - 195
70
Magnesiumb
60-116
8
Phosphorus0
14 - 41
0.5
Silicad
25-34
10
Sulfate
73-90
200
Suspended Solids
20 - 60
10
• mg/L as N
b mg/L as CaC03
0 mg/L as P
d mg/L as Si02
After clarification carbon dioxide is used to lower the pH to
between 10.2 and 10.4. Sulfuric acid is used to drop the pH to
9 and to stop the formation of any more calcium carbonate
(CaC03). Chlorine is added to prevent slime growth in the
filters, and polymer is used to facilitate coagulation of fine sus-
pended particles. The water then passes through mixed-media
gravity filters containing anthracite and sand to remove any
fine or light solids remaining in suspension in the water. The
filters are backwashed with water from the storage reservoir
and the backwash water is recycled to the headworks of the
trickling filters.
Effluent from the gravity filters is held in a reservoir until
needed for cooling tower make-up water. When the water is
pumped to the cooling towers the pH is lowered by the use of
sulfuric acid to 7.0 to control scaling problems in the cooling
towers.
Polymers are added to the solids from the clarifiers before
treatment by a classification centrifuge to separate the calcium
carbonate. Centrate (water from centrifuge) is recycled back to
the trickling filter headworks. The calcium carbonate is passed
through a multiple-hearth furnace to recover the lime for reuse.
All residues not recycled from the centrifuge and ash from the
furnace are disposed of in a landfill.
25.034 Specialty Steel Mill, Syracuse, New York (Fig. 25.9)
Wastewater reclamation and recycling at steel mills requires
the identification of sources of wastewater and a determination
of the best means of collecting, treating, and recycling or dis-
posing of the wastewater. Table 25.8 summarizes sources of
wastewater and treatment methods for a specialty steel mill.
TABLE 25.8 STEEL MILL WASTEWATER SOURCES AND
TREATMENT
Source Treatment
1. Cooling tower Discharge into municipal collection system,
blowdown
2. Rolling mill Collect, provide chemical treatment and re-
wastewaters cycle within mill.
3. Pickling rinse Collect, provide chemical treatment and re-
waters cycle within mill.
4. Spent pickling Haul to approved disposal site,
and plating
baths
5. Sanitary waste- Collect and discharge into municipal collec-
waters
tion system.
Process wastewaters that receive chemical treatment are
collected from the various sources in the mill and ultimately
reach the aeration tank at the treatment plant (Fig. 25.9).
Wastewater is aerated to convert soluble iron to an insoluble
iron precipitate by oxidation and also to cool the water.
Chemicals are added in Tank A (similar to Fig. 25.8) to the
effluent from the aeration tank. An anionic polymer and ferric
chloride provide for chemical coagulation and flocculated sol-
ids are recycled within the clarifier (Tank A) in order to provide
a prolonged contact between the entering wastewater and
previously formed solids. This recycling process increases ab-
sorption of the pollutants into the floe particles. Clarified
effluent flows over V-notch weirs and is reused in mill opera-
tions. The weirs are baffled to hold back floating materials.
Water not recycled flows to Tank B (similar to Fig. 25.8) for
additional treatment prior to discharge. Tables 25.9 and 25.10
show the removal efficiencies for Tanks (clarifiers) A and B.
-------
MAKE-UP WATER
FROM CITY
PROCESS
WASTEWATERS
10% Q
STEEL MILL
RECYCLE 90% Q
1
ANIONIC
POLYMER
FERRIC
CHLORIDE
SOLIDS
RECYCLE
RECYCLE PUMP STATION
TREATED WATER
RECYCLED TO MILL
RECYCLE WET WELL
STORAGE OF TREATED WATER
POLYMER NaOH
4.
AERATION
TANK
CONVERT SOLUBLE
IRON TO AN
INSOLUBLE
PRECIPITATE
COAGULATION
AND
FLOCCULATION
EFFLUENT
TO DISCHARGE
CHEMICAL MIXING
& LIQUID-SOLIDS
SEPARATION
LIQUID-SOLIDS
SEPARATION
& pH ADJUSTMENT
SOLIDS TO THICKENER
TO BELT FILTER
TO LANDFILL
Fig. 25.9 Wastewater reclamation processes for a specialty steel mill
-------
Wastewater Reclamation 397
Material contained in this section was obtained from a paper,
"Optimization of Wastewater Treatment and Reuse at a Spe-
cialty Steel Mill," presented by Robert H. Wills, Jr., and Richard
W. Klippel at the 52nd Annual Conference of the Water Pollu-
tion Control Federation in Houston, Texas, October 7-12,
1979. Mr. Wills is Chief Operator of the Crucible Incorporated
Wastewater Treatment and Reuse Facility, Syracuse, New
York, and Mr. Klippel is Industrial Waste Manager for
Calocerinos & Spina Consulting Engineers, Liverpool, New
York. See Chapter 28, "Industrial Waste Treatment," Section
28.6, for details on how this wastewater reclamation facility is
operated.
TABLE 25.9 REMOVAL EFFICIENCIES FOR TANK A,
AVERAGE DAILY VALUES
Water Quality Influent, Effluent,
Indicator mgIL mgIL Removal, %
TSS
87.0
21.8
75
TOC
17.0
13.3
21
Cyanides-Total
0.06
0.49
18.4
Cyanides-Oxid.
.027
0.03
0
Nitrate
21.1
22.5
0
Sulfate
609.0
633.0
0
Chloride
106.0
113.0
0
Cadmium-Total
LT 0.01
LT 0.01
ND
Cadmium-Soluble
LT 0.01
LT 0.01
ND
Chromium-Hex.
0.15
0.02
86.7
Chromium-Total
3.80
0.75
80
Chromium-Soluble
0.83
0.14
83
Copper-Total
0.48
0.41
14.6
Copper-Soluble
0.10
0.35
0
Iron-Total
27.5
9.0
67.3
Iron-Soluble
4.2
1.95
53.5
Zinc-Total
0.64
0.56
12.5
Zinc-Soluble
0.32
0.51
0
Fluoride
13.9
16.8
0
LT means Less Than
ND means Not Determined
25.1 OPERATING PROCEDURES
Operating procedures are generally the same for each type
of wastewater reclamation system with variations depending
on the processes used. The procedures listed in this section
apply mainly to the uses shown in Figures 25.1,25.2 and 25.3
25.10 Pre-start Inspection
1. Examine most recent lab test results.
2. Read preceding day's log for special instructions.
25.11 Start-up
1. Determine quantity of water required.
2. Read meter totalizer and log.
3. Open valves.
4. Open valves to blending tank from freshwater supply (if
blending tank is used).
5. Start the pumps.
25.12 Normal Operation
1. Make one inspection per shift of each pump, check oil
levels and packing, and clean area. Listen for any unusual
sounds.
2. Lubricate equipment where necessary.
3. Record flow near the end of the shift.
4. Visually inspect product water every two hours. Look for
unusual amounts of solids, floatables or colors, and try to
detect any odors.
5. Collect samples and/or analyze samples immediately in ac-
cordance with Section 25.2, "Monitoring Program."
TABLE 25.10 REMOVAL EFFICIENCIES FOR TANK B, AVERAGE DAILY VALUES
Water Quality mg/L Concentration Kilograms Per 4-Hour Period
Indicator
Influent
Effluent
% Removal
Influent
Effluent
% Removal
TSS
21.8
9.0
58.6
4.45
1.99
55.3
TOC
13.3
9.8
26.3
2.72
1.95
28.3
Cyanides-Total
0.049
.062
0
0.016
0.02
0
Cyanides-Oxid.
0.03
.032
0
0.011
0.0059
46.3
Nitrate
22.5
21.8
3.2
4.54
5.9
0
Sulfate
633
654
0
129.3
127
1.8
Chloride
113
114
0
23
2.22
3.0
Cadmium-Total
ND
ND
0
ND
ND
0
Cadmium-Soluble
ND
ND
0
ND
ND
0
Chromium-Hex.
0.2
.022
0
0.0041
0.0045
70
Chromium-Total
0.75
.245
67.3
0.15
0.045
70
Chromium-Soluble
0.14
.03
79.6
0.03
0.006
80.0
Copper-Total
0.41
.063
84.6
0.08
0.012
85.0
Copper-Soluble
0.35
.017
95.1
0.07
0.002
97.1
Iron-Total
9.0
2.30
74.5
3.5
0.45
87.1
Iron-Soluble
1.95
.028
98.6
0.41
0.008
98.0
Zinc-Total
0.56
.13
76.8
0.113
0.027
76.0
Zinc-Soluble
0.51
.06
88.2
0.1
0.01
90
Fluoride
16.8
14.8
120
3.58
3.0
16.2
ND means Not Determined
-------
398 Treatment Plants
25.13 Shutdown
1. Turn off pumps.
2. Close all valves.
3. Record meter totalizer reading.
4. Make entry in log.
25.14 Operational Strategy
System flows are controlled by pump run times and valve
adjustments. If blending is used, then desired water quality
constituent values are reached by adding fresh water. For
example, if the plant effluent ammonia concentration is 20
mg/L, the desired concentration is 10 mgIL, and the fresh
water ammonia concentration is zero, the delivered water
should be slightly less than 50 percent plant effluent and
slightly more than 50 percent fresh water.
The process control consists of techniques to blend flows or
provide further treatment. Blending procedures are described
in the previous paragraph. Further treatment can be accom-
plished by adding chemicals such as chlorine to kill coliform
and pathogenic bacteria or aeration to increase dissolved oxy-
gen. Unacceptable effluent could be returned to the treatment
processes for further treatment.
Important observations include detection of odors and col-
ors. Greases and oils also can be seen. Observations of any of
these pollutants in the plant effluent means the treatment pro-
cess is probably upset.
25.15 Emergency Operating Procedures
If one of the treatment processes fails and effluent quality
standards cannot be met, immediately stop flow to the water
users and send flow to emergency holding pond or tank, if one
is available. Otherwise reroute the flow in accordance with
established procedures to an acceptable means of disposal.
If the power is off, the flow must be contained in the
emergency holding area.
25.16 Troubleshooting Guide (Table 25.11)
If your plant is not meeting the water quality requirements of
the waters users, try to identify the cause of the problem and to
select the proper corrective action. Solutions to the problems
listed in this section have been covered in more detail in previ-
ous chapters.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 417.
25.1A How can coliform and pathogenic bacteria be killed in
reclaimed wastewater?
25.1B Why is a "blend" water sometimes mixed with plant
effluent?
25.1C What could be the probable causes of a wastewater
reclamation plant being unable to maintain a chlorine
residual?
25.2 MONITORING PROGRAM
25.20 Monitoring Schedule
The monitoring system may vary depending on the type of
wastewater reuse and local conditions. The requirements for
individual reclamation systems must be provided by the user.
Table 25.12 shows a typical monitoring schedule that could be
used for any of the three reclamation systems shown in Fig-
ures 25.1, 25.2 and 25.3. Samples for these tests should be
taken from valves in the effluent pipeline before the effluent
leaves the plant. Temperature, dissolved oxygen, pH, conduc-
tivity and turbidity all may be monitored continuously with the
results plotted by recorders.
In addition to monitoring effluent water quality, flow rates
also must be recorded. Hydraulic loading rates on wells in
terms of gallons per day per well are very important. Any loss
of loading capacity by any well must be investigated im-
mediately. If a recharge well is losing its recharge ability, try to
identify the cause of the problem and select appropriate cor-
rective action.
TABLE 25.12 WATER QUALITY MONITORING
SCHEDULE
Grab Sample,
Dally
24-hour Composite
Sample, Weekly
Grab Sample,
Weekly
24-hour Compoalte
Sample, Monthly
Alkalinity
Bicarbonate
COD
Calcium
Chloride
Dissolved
Oxygen
Electrical
Conductivity
Magnesium
Ammonia Nitrogen
Bicarbonate
Boron
COD
Cadmium
Calcium
Chloride
Chromium
Cyanide
Fluoride
Iron
MBAS
Magnesium
Manganese
Nitrate Nitrogen
Organic Nitrogen
Phenol
Phosphorus
Selenium
Sodium
Sulfate
Conforms
Color
Odor
Arsenic
Barium
Copper
Lead
Mercury
Silver
Clogging of the well may be caused by slimes and can be
corrected by applying chlorine (10 to 15 mg/L in the well) to kill
the slimes or by allowing the well to rest, which can dry out or
starve some slimes. If activated carbon is used in a treatment
process, clogging may be caused by carbon fines (very tiny
pieces of carbon). These fines may be removed by passing the
water through a sand/anthracite filter.
25.21 Interpretation of Test Results and Follow-up
Actions
If pH, dissolved oxygen, chemical oxygen demand, nitrogen
compounds, phosphorus, coliforms, or odor standards are not
met, then adjustments are needed in the treatment processes.
If the concentrations of other water quality indicators exceed
standards and cannot be removed by treatment, industrial dis-
charge sites should be tested to see if there is someone dis-
charging excessive quantities into the wastewater collection
systems. Whenever one of the standards is not met, NOTIFY
THE USER IMMEDIATELY. If a blending tank is available, add
more fresh water to dilute the effluent.
-------
Wastewater Reclamation 399
TABLE 25.11 TROUBLESHOOTING GUIDE
Indicators/Observations
Probable Cause
Check or Monitor
Solutions
PONDS
1. Floatables in effluent
1 a. Outlet baffle not in proper
location
1 b. Excessive floatables and
scum on pond surface
1 a. Visually inspect outlet baffle
1 b. Visually inspect pond
surface
REVIEW CHAPTER 9
1 a. Adjust outlet baffle
1b. Remove floatables from
pond surface using hand
rakes or skimmers. Scum
can be broken up using jets
of water or a motor boat.
Broken scum often sinks.
2. Excessive algae in effluent
2. Temperature or weather
conditions may favor a
particular species of algae.
2. Visually observe effluent or
run suspended solids test
2. Operate ponds in series.
Draw off effluent from below
pond surface by use of a good
baffle arrangement.
3. Excessive BOD in effluent
3. Detention time too short,
hydraulic or organic overload,
poor inlet and/or outlet
arrangements and possible
toxic discharges
3a. Influent flows
3b. Calculate organic loading
3c. Observe flow thru inlet and
outlet structures
3d. Dead algae in effluent
3a. Inspect collection systems
for infiltration and correct at
source.
3b. Use pumps to recirculate
pond contents.
3c. Rearrange inlets and outlets
or install additional ones.
3d. Prevent toxic discharges.
SECONDARY CLARIFIERS FOR
TRICKLING FILTERS,
ROTATING BIOLOGICAL
CONTACTORS
OR
ACTIVATED SLUDGE
1. Floatables in effluent
1a. Clarifiers hydraulically
overloaded
1b. Skimmers not operating
properly
1a. Visually observe effluent or
calculate hydraulic loadings
1b. Observe skimmer movement
at beaching plate
REVIEW CHAPTER 6
REVIEW CHAPTER 7
OR
REVIEW CHAPTERS 8, 11 AND
21
1a. Install hardware cloth or
similar screening device in
effluent channels.
Review Chapter 5.
1b. Lower skimmer arm or
replace neoprene.
2. Excessive suspended solids
in effluent
2a. Clarifiers hydraulically
overloaded
2b. Biological treatment process
organically overloaded
2a. See 1a above
2b. Calculate BOD or organic
loading
2a. See 1a above and review
operation of biological
treatment process.
2b. Review operation of
biological treatment process.
3. High BOD in effluent
3a. See 2b above
3a. See 2b above
3a. See 2b above
DISINFECTION
1. Unable to maintain chlorine
residual
1a. Chlorinator not working
properly
1b. Increase in chlorine demand
1 a. Inspect chlorinator
1b. Run chlorine demand tests
REVIEW CHAPTER 10
1a. Repair chlorinator.
1b. Increase chlorine dose
and/or identify and correct
cause of increase in
demand.
2. Unable to meet coliform
requirements
2a. Chlorine residual too low
2b. Chlorine contact time too
short
2c. Solids in effluent
2d. Sludge in contact basin
2e. Diffuser not properly
discharging chlorine
2f. Mixing inadequate
2a. See 1 above
2b. Measure time for dye to pass
thru contact basin
2c. Observe solids or run
suspended solids test
2d. Look for sludge deposits in
contact basin
2e. Lower tank water level and
inspect
2f. Add dye at diffuser
2a. See 1 above.
2b. Improve baffling
arrangement.
2c. Install hardware cloth or
similar screening device in
effluent channels. Review
operation of biological
treatment process.
2d. Drain and clean contact
basin.
2e. Clean diffuser.
2f. Add mechanical mixer or
move diffuser.
-------
400 Treatment Plants
25.3 SAFETY
Always work with another operator when collecting samples
or working around storage reservoirs or blending tanks. Take
necessary precautions to avoid slipping or falling into the water
and drowning. Pump station safety has been discussed in
Chapter 14, "Plant Safety and Good Housekeeping."
A major safety consideration is the health of persons coming
in contact with reclaimed water. Be sure the effluent from your
wastewater reclamation facility is adequately disinfected at all
times. If the effluent ever presents a potential threat to the
public's health, NOTIFY THE USERS IMMEDIATELY.
25.4 MAINTENANCE
There are very few maintenance considerations except for
pumps which are covered in Chapter 15, "Maintenance." Me-
tering system maintenance consists mainly of cleaning and
visual inspections. Otherwise maintenance means good
housekeeping.
25.5 REVIEW OF PLANS AND SPECIFICATIONS
Plans and specifications should be reviewed to insure a pip-
ing system with alternate flow paths. If problems develop, there
must be a way to pipe the effluent to temporary storage or back
to treatment. In other words, there must be an alternate route
for the flow.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 417.
25.2A List possible causes of clogging in a recharge well and
possible cures for each cause.
25.2B What would you do if reclaimed effluent was being
used by industry and one of the water quality stan-
dards was not being met?
25.3A Why should you always work with another operator
when working around storage reservoirs or blending
tanks?
&MP OF l&b'bON1 OP 2 LB640N4
ObJ
WA5T6WAT&£ (ZBCCAMATfON
DISCUSSION AND REVIEW QUESTIONS
(Lesson 1 of 2 Lessons)
Chapter 25. WASTEWATER RECLAMATION
At the end of each lesson in this chapter you will find some
discussion and review questions that you should answer be-
fore continuing. The purpose of these questioqs is to indicate
to you how well you understand the material in this lesson.
Write the answers to these questions in your notebook before
continuing.
1. What are some of the limitations of or precautions for direct
use of reclaimed wastewater?
2. What would you do if one of your treatment processes failed
and you were unable to meet effluent quality standards?
3. What is the purpose of a monitoring program?
4. Why should you be concerned about protecting the public
health when operating a wastewater reclamation facility?
5. Why should you look for alternate flow paths when review-
ing the plans and specifications for a wastewater reclama-
tion facility?
-------
Wastewater Reclamation 401
CHAPTER 25. WASTEWATER RECLAMATION
(Lesson 2 of 2 Lessons)
EFFLUENT DISPOSAL ON LAND
25.6 LAND TREATMENT SYSTEMS
25.60 Description of Treatment Systems
When a high quality effluent or no discharge is required, land
treatment offers a means of wastewater reclamation or ulti-
mate disposal. Land treatment systems use soil, plants and
bacteria to treat and reclaim wastewaters. They can be de-
signed and operated for the sole purpose of wastewater dis-
posal, for crop production, or for both purposes (Fig. 25.10). In
land treatment, effluent is pretreated and applied to land by
conventional irrigation methods. When systems are designed
for crop production, the wastewater and its nutrients (nitrogen
and phosphorus) are used as a resource. This system is then
comparable to the reuse systems described in Lesson 1. With
either approach, treatment is provided by natural processes
(physical, chemical and biological) as the effluent flows
through the soil and plants. Part of the wastewater is lost by
EVAPOTRANSPIRATION2 and the rest goes back to the
HYDROLOGIC CYCLE3 through surface runoff and/or percola-
tion to the groundwater system. Land disposal of wastewater
may be done by one of the following methods shown in Figure
25.11.
1. Irrigation,
2. Overland flow, and
3. Infiltration-percolation.
The method of irrigation depends on the type of crop being
grown. Irrigation methods include traveling sprinklers, fixed
sprinklers, furrow and flooding. Infiltration-percolation systems
are not suited for crop growth. Overland flow systems are simi-
lar to other treatment processes and have runoff which must
either be discharged or recycled in the system. The other sys-
tems usually do not have a significant surface runoff. Typical
loading rates for these systems are shown in Table 25.13.
Land application systems include the following parts:
1. Treatment before application,
2. Transmission to the land treatment site,
3. Storage,
4. Distribution over site,
5. Runoff recovery system (if needed), and
6. Crop systems.
25.61 Equipment Requirements
Irrigation systems apply water by sprinkling or by surface
spreading (Figure 25.12). Sprinkler systems may be fixed or
movable. Fixed systems are permanently installed on the
ground or buried with sprinklers set on risers that are spaced
along pipelines. These systems have been used in all types of
terrain. Movable systems include center pivot, side wheel roll,
and traveling gun sprinklers.
Surface irrigation systems include flooding, border-check,
and ridge and furrow systems. Flooding systems are very simi-
lar to overland flow systems except the slopes are nearly level.
Border-check systems are simply a controlled flooding system.
Ridge and furrow systems are used for row crops such as corn
where the water flows through furrows between the rows and
seeps into the root zone of the crop.
An overland flow system consists of effluent being sprayed
or diverted over sloping terraces where it flows down the hill
and through the vegetation. The vegetation provides a filtering
action, thus removing suspended solids and insoluble BOD.
This system can be operated as a treatment system or, with a
recycle system included, can be operated as a disposal sys-
tem. When operated as a disposal system, the overland flow
process is nearly the same as flood irrigation so it will be in-
cluded with the flood systems in the following paragraphs.
25.62 Sidestreams4 and Their Treatment
There are two possible sidestreams with land disposal sys-
tems. Unlined storage reservoirs will result in wastewater per-
colating down to groundwater. If the water stored in reservoirs
is the final effluent from a treatment plant, percolation down to
the groundwater probably is acceptable. However, if the water
is untreated or partially treated (primary effluent), the reservoir
should be lined or an underground collection system should be
installed to collect any percolation or seepage from the reser-
voir. In some areas percolation may cause a rise in the area's
groundwater level. To prevent groundwater problems, a seep-
age ditch may be built around the outside of the reservoir. This
ditch should be located somewhat lower than the bottom of the
reservoir. Wastewater that percolates through the reservoir
bottom is collected in the ditches. This water can be pumped
back into the reservoir. The groundwater table also could be
lowered by a series of shallow wells with water being pumped
out as necessary. Lowering of the groundwater could result in
increased percolation rates.
The other major sidestream is surface runoff. Runoff quan-
tities vary depending on the type of irrigation system used. In
all systems provisions should be made for collecting runoff and
returning this flow to be reapplied. In some locations runoff
water can be discharged to surface water. Discharge is the
preferred approach due to saving costs and minimizing opera-
tional problems.
1 Evapotranspiration (e- VAP-o-tran-spi-RA Y-shun). The total water removed from an area by transpiration (plants) and by evaporation from
soil, snow and water surfaces.
3 Hydroiogic Cycle (Hl-dro-loj-lc). The process of evaporation of water into the air and its return to earth by precipitation (rain or snow). This
process also includes transpiration from plants, groundwater movement and runoff into rivers, streams and the ocean.
4 Sidestream. Wastewater flows that develop from other storage or treatment facilities. This wastewater may or may not need additional
treatment.
-------
402 Treatment Plants
EVAPO TRANSPIRATION
TREATED
PLANT
LAND
SURFACE
EFFLUENT
STORAGE
DISPOSAL
RUNOFF
RESERVOIR
SITE
<
'
PERCOLATION
Fig. 25.10 Land disposal system schematic
-------
Wastewater Reclamation 403
EVAPORATION
SPRAY OR
SURFACE
APPLICATION
SLOPE
VARIABLE
l "-'i
(a) IR RI GAT I ON
EVAPORATION
SPRAY OR
SURFACE APPLICATION
PERCOLATION THROUGH
UNSATURATED ZONE
INFILTRATION
ZONE OF AERATION
AND TREATMENT
ORIGINAL WATER
(b) INFILTRATION-PERCOLATION table
EVAPORATION
SPRAY APPLICATION
8RASS AND VE6ETATIVE LITTER
SHEET FLOW
SLOPE 2-4#
RUNOFF
COLLECTION
100-300 FT
(c) OVERLAND FLOW
Fig. 25.11 Methods of land application
(From COSTS OF WASTEWATER TREATMENT BY LAND APPLICATION by Pound, C.E., el al, U.S. Environment*! Protection Agency,
Washington, D C, 20400, EPA-43W9-75-003, June 1975.)
-------
404 Treatment Plants
TABLE 25.13 TYPICAL LOADINGS FOR IRRIGATION, INFILTRATION-
PERCOLATION, AND OVERLAND FLOW SYSTEMS*
Factor
Irrigation
Low-rate High rate
Infiltration-Percolation
Overland flow
Liquid loading rate,
in/wk
Annual application,
ft/yrc
Land required for
1-MGD flow rate,
acres 8
Application
techniques
Vegetation required
Crop production
Soils
Climatic
constraints
Wastewater lost to:
Expected treatment
performance
BOD and SS removal
Nitrogen removal
Phosphorus removal
0.5 to 1.5
2 to 4
280 to 560
1.5 to 4.0
4 to 18
62 to 280
Spray or surface
Yes Yes
Excellent Good/fair
Moderately permeable soils
with good productivity
when irrigated
Storage often needed
Evaporation and
percolation
98 + %
85 + %d
80 to 99%
4 to 120
18 to 500
6 to 62
Usually surface
No
Poor/none
Rapidly permeable soils,
such as sands, loamy
sands, and sandy loams
Reduce loadings in
freezing weather
Percolation
85 to 99%
0 to 50%
60 to 95%
2 to 9
8 to 40
28 to 140
Usually surface
Yes
Fair/poor
Slowly permeable soils
such as clay loams and
clays
Storage often needed
Surface runoff and
evaporation with some
percolation
92 + %
70 to 90%
40 to 80%
* COSTS OF WASTEWATER TREATMENT BY LAND APPLICATION by Pound, C.E. et al, U.S. Environmental Protection Agency, Washington,
D.C., 20460, EPA-430/9-75-003, June 1975.
in/wk x 2.54 = cm/wk
c ft/yr x 0.3 = m/yr
"Dependent on crop uptake
"acres x 0.00107 = hectares for 1 cu m/day
or
acres x 9.24 = hectares for 1 cu m/sec
-------
Wastewater Reclamation 405
RAIN DROP ACT ION-
M ,, , /
^ ?'/CSX/yy/s
t 11 m 11111111 i r
//,
s:=^m^
(a) SPRINKLER
COMPLETELY FLOODED
C 'y ¦¦'¦ /; ¦' '- r>* ¦•• %
V .-•' ,..j^ —/ / i •—-¦_+ A <\ %
/nTTTTTTTTTTTlx /rT
(b) FLOODING
(c) RIDGE AND FURROW
Fig. 25.12 Irrigation technic/lies
(From EVALUATION OF LAND APPUCATION SYSTEMS by Pound, C.6., <* *, U.S. Envlronnwntal
Protection Agancy, WMhlngton, D.C. 20440. EPA 43W-74-015. S*ptamt»r 1974.)
-------
406 Treatment Plants
25.63 Limitations of Land Treatment
Problems encountered using land treatment systems usually
involve soil problems and weather conditions. If proper care is
not taken, the soils can lose their ability to percolate applied
water. During the cold winter season, plants and crops will not
grow. Under these conditions no water will be treated by tran-
spiration processes. Also, precipitation can soak the soil so no
wastewater can be treated. Provisions must be made to store
wastewater during cold and wet weather.
One of the most common land treatment problems is the
sealing (water won't percolate) of the soil by suspended solids
in the final effluent. These solids are deposited on the surface
of the soil and form a mat which prevents the percolation of
water down through the soil. There are three possible solutions
to this problem:
1. Remove the suspended solids from the effluent,
2. Apply water intermittently and allow a long enough drying
period for the solids mat to dry and crack, or
3. Disc or plow the field to break the mat of solids.
Another serious problem is the buildup of salts in the soil. If
the effluent has a high chloride content, there can be enough
salts in the soil within one year to create a toxic condition to
most grasses and plants. To overcome salinity problems:
1. Leach out the salts by applying fresh water (not effluent), or
2. Rip up the field and turn it over to a depth of 4 to 5 feet (1.2
to 1.5 meters).
The severity of both soil sealing due to suspended solids
and salinity problems due to dissolved solids depends on the
type of soil in the disposal area. These problems are more
difficult in clay soils than in sandy soils.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 418.
25.6A Define the terms evapotranspiration and hydrologic
cycle.
25.6B List the three methods by which land disposal of
wastewater is accomplished.
25.6C What are the major parts of a land application system?
25.6D A plot of land 2000 feet long by 1000 feet wide is used
for a land disposal system. If 1 million gallons is
applied to the land during a 24-hour period, calculate
the hydraulic loading in:
1. MGD per acre, and
2. Inches per day.
25.7 OPERATING PROCEDURES
The operating procedures described below apply to a spray
irrigation system. This system is for an area where crops are to
be grown. The operating procedures for this type of system are
more complex than the other systems. The procedures are
explained first and then an example is presented to show how
to use the procedures.
25.70 Pre-start Checklist
Table 25.14 consists of a list of items that should be checked
before starting a land disposal system.
25.71 Start-up
1. Determine need to irrigate. The amount of water that can be
applied depends on the type of crop. Some crops require a
lot of water while other crops will not tolerate any excess
water. The procedures in this section are prepared to help
you determine when you should irrigate and how much
water should be applied. THESE PROCEDURES ARE
BASED ON SOIL CONDITIONS AND MAY REQUIRE AD-
JUSTMENT BASED ON THE TYPE OF CROP BEING IR-
RIGATED. The chart shown on Table 25.15 will aid in de-
termining if you need to irrigate based on soil conditions. To
use this table you must first determine the type of soil you
are irrigating. Walk around the field and try to identify the
different types if more than one type of soil is present. Pick
up a handful of soil and examine the grains or particles.
Small, hard, tiny particles indicate a sandy soil. Very fine,
soft, smooth particles signify a clay soil. Once you've iden-
tified the type of soil, the moisture content can be estimated
by squeezing the soil together in your hand. The wetter the
soil, the more likely the soil will stick or cling together. By
the way the soil sticks together and the type of soil, you can
estimate when the available moisture content drops to 50
percent or less. Irrigate when the moisture content is 50
percent or less.
Soils vary throughout an area of land and some areas
need irrigating before others. Many farmers have specific
areas in their fields which they call "hot spots." Due to soil
characteristics or other reasons, these areas dry out faster
than the rest of the field. Whenever the soil will not form a
ball when squeezed together or crops start to show signs of
stress due to lack of water, this is the time to irrigate.
2. Determine amount of moisture to apply using Table 25.16.
To use this table, determine the soil type by examining a
handful of soil as described in Step 1. The root zone depth
is determined by the type of crop. If necessary, dig down to
determine how far down the roots are growing. By the use
of Table 25.15, you can estimate the percent of available
moisture remaining in the soil before irrigation. Knowing the
percent available moisture in the soil before irrigation, you
can determine the net inches of water to apply this time
when you are irrigating from Table 25.16.
3. Determine the time required to apply one inch (2.5 cm) o
water from Figures 25.13 or 25.14. Figure 25.13 is used for
small areas (up to 60 acres) and Figure 25.14 is used for
larger areas (over 60 acres). To use the tables determine
(1) the area of land you wish to irrigate and (2) the capacity
of your irrigation system in gallons per minute. By starting at
the bottom of the figure with the known area, draw a line
vertically upward. Next draw a line from the system capacity
on the left, horizontally to the right. Where these two lines
intersect is the time required to apply one inch of water to
the area being irrigated.
4. Multiply time required to apply one inch (2.5 cm) of water by
the inches of moisture to apply to determine the total run
time for the irrigation system. After you have determined the
net inches of water you wish to apply from Table 25.16
(Step 2), multiply the net inches times the time required
(Figures 25.13 and 25.14) to determine the total irrigation
time.
If you need help determining soil types, irrigation re-
quirements, soil moisture content, types of crops to plant,
salt tolerance of plants, depth of root zone and any fertilizer
needs, contact your local farm adviser. In many areas an
expert adviser is available free of charge through some
agency of the federal, state or local government.
-------
Wastewater Reclamation 407
TABLE 25.14 PRE-START CHECKLIST*
Check Check
Every At The
Time Beginning
Pump ll Of TIM
Started Season
Electric Motors
Replace winter lubricant.
Oil bath bearings. Drain oil and replace with
proper weight of clean oil.
Grease lube bearings. If grease gun is used,
be sure old grease is purged through outlet
hole.
Before turning on switch, have power com-
pany check voltage.
Check for proper rotation of motor and pump.
Check fuses to make sure they are still good.
Check electrical contact points for excessive
corrosion.
Physically inspect for rodent and insect inva-
sion.
Pumps
Replace oil or grease with proper weight
bearing lubricant.
Tighten packing gland to proper setting.
Check discharge head, discharge check
valve, and suction screen thoroughly for
foreign matter.
Pump shaft should turn freely without notice-
able dragging.
Aluminum Pipe
If you didn't properly handle and store alumi-
num pipe or tubing last fall, make a mental
note to do that at the end of this growing sea-
son. Always carefully drain aluminum tubing
or pipe when you are finished using it. Alumi-
num pipe bends very easily.
If you pick up a length of pipe that is half full
of water and has one end plugged, you will
bend the pipe. Rush out the pipe to clean it,
drain the pipe, place the pipe on a long-bed
trailer for transport, and then store the pipe
on racks until you are ready to use the pipe
next season.
Inspect pipe ends to make certain that no
damage has occurred. Ends should be round
for best operation. A slightly tapered wooden
plug of the proper diameter can be used to
round out the ends. The diameter of alumi-
num pipe varies from 2 to 12 inches (50 to
300 mm).
TABLE 25.14 PRE-START CHECKLIST*(Continued)
Check
Every
Time
Pump It
Started
Check
At The
Beginning
Of The
Season
Check pipe for pit corrosion of tubing. If
"spots" are in evidence, contact the alumi-
num pipe supplier for advice.
Inspect pipe gaskets, couplers (irrigation
pipe couplings), and gates to find those in
need of replacement.
_ Check pipeline to see that all couplers are
still fastened, pipe supports haven't fallen
over, and gates and valves are still open.
_ Pipe makes an excellent nesting area for
small animals. Flush out the pipeline before
installing the end plug. Make sure you are
away from power lines when you raise the
pipe to drain water from the pipe.
Sprinkler Systems
Sprinkler bearing washers should be re-
placed if there is indication of wear.
_ Visually check all moving parts, seals, bear-
ings and flexible hose for replacement or re-
pair.
_ Check to see that hose is laid out straight or
on a long radius for turns. Be sure there are
no kinks in the hose. There should be suffi-
cient hose at the end of the sprinkler to act as
a brake or to hold back the sprinkler system
initially as it drags the hose through the field.
Also check earth anchors.
_ If possible, operate the system to check
speed adjustment, alignment, and safety
switch mechanisms.
Check sprinkler oscillating arm for proper ad-
justment. If damage has occurred to the
sprinkler oscillating arm, the arm should be
replaced or bent back to the correct angle.
Your dealer can help in correcting a dam-
aged arm. The angle of water-contact sur-
face, if not correct, will change the turning
characteristics of the sprinkler. Excessive
wear of sprinkler nozzles can be checked
with proper size drill bit.
REMEMBER, inspection and corrective maintenance now
may save considerable time and money later.
• WATER RESOURCES MANUAL, Noram, Edward (editor), permis-
sion of The Irrigation Association, Silver Spring, Maryland 20906.
-------
408 Treatment Plants
TABLE 25.15 FEEL AND APPEARANCE GUIDE FOR DETERMINING SOIL MOISTURE"
The chart below is very useful in knowing how much available moisture is in your soil. Although the plant's daily moisture use may range from 0.1
inches to 0.4 inches per day (0.25 to 1.0 cm), it will average about 0.20 inches (0.5 cm) per day, and 0.25 inches (0.6 cm) per day during hot
days.
Moisture
Condition
Percent of available
moisture remaining
in soil, %
SOIL TEXTURE
Sands-Sandy Loams
Loams-Silt Loams
Clay Loams-Clay
Dry
Wilting point
Dry loose, flows through fin-
gers.
Powdery, sometimes slightly
crusted but easily broken down
into powdery condition.
Hard, baked, cracked; difficult
to break down into powdery
condition.
Low
50% or less
Will form a weak ball when
squeezed but won't stick to
tools.
Pliable, but not slick, will ball
under pressure — sticks to
tools.
TIME TO IRRIGATE WHEN AVAILABLE MOISTURE IS 50 PERCENT OR LESS
Fair
50 to 75%
Tends to ball under pressure
but seldom will hold together
when bounced in the hand.
Forms a ball somewhat plastic,
will stick slightly with pressure.
Doesn't stick to tools.
Forms a ball, will ribbon out be-
tween thumb and forefinger,
has a slick feeling.
Good
75 to 100%
Forms a weak ball, breaks eas-
ily when bounced in the hand,
can feel moistness in soil.
Forms a ball, very pliable, slicks
readily, clings slightly to tools.
Easily ribbons out between
thumb and forefinger, has a
slick feeling, very sticky.
Ideal
Field Capacity
100%
Soil mass will cling together.
Upon squeezing, outline of ball
is left on hand.
Wet outline of ball is left on
hand when soil is squeezed.
Sticks to tools.
Wet outline of ball is left on
hand when soil is squeezed.
Sticky enough to cling to fin-
gers.
a WATER RESOURCES MANUAL, Norum, Edward (editor), permission of Sprinkler Irrigation Association, Silver Spring, Maryland 20906.
5. Check pump discharge check valve and suction screen for
foreign matter.
6. Check pipeline to see that all couplings are still fastened,
blocks or pipe supports haven't fallen over, and gates and
valves are open.
7. Start pump.
8. Inspect the irrigation system to be sure everything is work-
ing properly.
25.72 Normal Operation
1. Run the pump or pumps the time determined by Step 4 of
the start-up procedure and as shown in the example.
2. Turn the pump off earlier if water begins to pond on the
fields.
EXAMPLE
Using the procedures outlined in this section, this example
shows how to determine the total time to irrigate.
1. Determine need to irrigate. A loamy soil formed a weak ball
when squeezed. Table 25.15 indicates the moisture condi-
tion is low (50% or less) and that it is time to irrigate.
2. The loamy (light sandy) soil has a crop with a root-zone
depth of 3 feet (0.9 m) and 50 percent of the available
moisture is retained in the soil at irrigation. Table 25.16
indicates that 1.5 inches (3.8 cm) of water should be
applied to the soil.
3. The land to be irrigated is a 40-acre plot and the pump has
a capacity of 1000 GPM. From Figure 25.13, find 40 acres
across the bottom and draw a line vertically upward to the
top. Find the system capacity of 1000 GPM along the left
side and draw a line horizontally to the right. These lines
intersect between the diagonal lines labeled 15 hours and
20 hours at approximately 18 hours. Therefore we should
irrigate for 18 hours to apply one inch of water.
4. Determine the total time to irrigate.
Time, hours = Time, (hr) to irrigate one inch x Amount to apply, in
= 18 hours/inch x 1.5 inches
= 27 hours
TABLE 25.16 AMOUNT OF MOISTURE TO APPLY TO
VARIOUS SOILS UNDER DIFFERENT MOISTURE
RETENTION CONDITIONS"
Available
Root Moisture Not InchM to Apply Per Irrigation With
Soli Zona Plant* Various Percent* Available Moisture
Typa Depth Will Use Retained In the Soil before Irrigation
Percent Available Moisture
before Irrigation
Feet
Inehes
67%
50%
33%
Light
1
1.00
0.33
0.50
0.67
Sandy
Vh
1.50
0.50
0.75
1.00
2
2.00
0.56
1.00
1.33
ZVt
2.50
0.63
1.25
1.67
3
3.00
0.99
1.50
2.00
Medium
1
1.69
0.57
0.85
1.13
1Vi
2.53
0.84
1.26
1.70
2
3.38
1.11
1.69
2.26
2%
4.21
1.39
2.11
2.82
3
5.06
1.67
2.53
3.38
Heavy
1
2.39
0.79
1.20
1.59
1V4
3.58
1.18
1.79
2.38
2
4.78
1.58
2.39
3.25
2 Vi
5.97
1.97
2.98
3.97
3
7.17
2.36
3.58
4.77
* WATER RESOURCES MANUAL, Norum, Edward (editor), permission of
Sprinkler Irrigation Association, Sliver Spring, Maryland 20906.
-------
Wastewater Reclamation 409
1700 --
1600"~
1500" -
1400--
1300 --
siioo--
1000--
< 900--
S 800--
w 700--
600--
500--
400--
300--
200--
ACRES
Fig, 25.13 Time required to apply one inch (2.5 cm) of water on small acreages
(From WATER RESOURCES MANUAL, Norum, Edward (editor), permission
ol Sprinklar Irrigation Association, Silver Spring, Maryland.)
-------
410 Treatment Plants
1500
1000
hours
ACRES
300
Fig. 25.14 Time required to apply one inch (2.5 cm)
of water on large acreages
(From WATER RESOURCES MANUAL, Norum, Edward (editor), permission
of Sprinkler irrigation Association, Silver Spring, Maryland.)
-------
Wastewater Reclamation 411
25.73 Shutdown
This shutdown procedure applies to the end of season shut-
down.
1. Drain all lines.
2. Plug open ends of pipelines.
3. Lubricate motors and pumps for winter.
4. Store small movable materials and equipment.
5. Store aluminum tubing or piping.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 418.
25.7A List the major items of equipment that should be in-
spected before starting a spray irrigation system.
25.7B Determine the time required to irrigate 30 acres of a
medium-type soil where the root-zone depth is 2 feet
and 50 percent of the available moisture is retained in
the soil at irrigation. Use the figures and tables in this
lesson to answer this question.
25.74 Operational Strategy
Physical Control. The main objective of a land disposal
system is to dispose of effluent without harming surface waters
or creating nuisance conditions. An irrigation system can be
designed and operated to produce a crop. The sale of this crop
then helps reduce treatment costs. Physical control is then
used to dispose of effluent at the highest rate possible without
damaging the crop. For all types of land disposal systems,
physical controls consist of valves and/or gates which are used
to direct treated effluent to different disposal areas.
Process Control. There are three areas of process control;
storage reservoirs, runoff and seepage water recycle systems,
and systems where crops are grown. The first is tne storage
reservoir. The reservoir usually will have been provided with
aeration or mixing devices. These devices may be operated
full time or for a limited time each day by using timers. The
correct time to operate is determined by measuring the dis-
solved oxygen (DO) content at several points in the reservoir.
A minimum of 4 points should be sampled. An example show-
ing six sampling locations is illustrated in Figure 25.15.
Each sample should have at least 0.4 mg/L of DO and the
average of all samples should be at least 0.8 mg/L. Two sam-
ple sets of test results are shown below:
Set 1 —
Sample No.
1
2
3
4
5
6
Set 2 —
Sample No.
1
2
3
4
5
6
Average
Average
mg/L DO
1.2
1.8
2.0
1.6
0.2
0.4
72.
6
mg/L DO
1.0
0.4
0.8
1.4
0.6
1.2
5^4
6
1.2 mg/L
= 0.90 mg/L
Fig. 25.15 Possible reservoir sampling locations
Set 1 does not meet the requirements. The average DO is
1.2 mg/L which is good, but one sample (#5) is 0.2 mg/L which
does not meet the minimum requirement. This result indicates
that there is adequate aeration but either a portion of the sys-
tem is not operating properly or the reservoir is not being
adequately mixed.
Even though Set 2 has a lower average DO than Set 1, the
average is greater than 0.8 and all samples are 0.4 mg/L or
greater. Therefore, Set 2 is acceptable.
The second area of process control is the runoff and seep-
age water recycle systems. These recycle systems may not be
necessary, depending on the particular application. For exam-
ple, the storage reservoir may be lined so there would be no
seepage water to recycle. Sprinkler systems that are carefully
controlled will have no significant runoff. Your goal is to dis-
pose of as much water as possible without causing runoff and
seepage from the disposal area. This is done to reduce recycle
pumping costs. The reduction in seepage and runoff is accom-
plished by taking more care in applying effluent and turning off
sprinklers or closing gates when water begins to stand in the
field.
The third area of process control applies to those systems
where crops are grown. In dry climates such as found in the
southwestern states and western mountain states, farmers
who irrigate are concerned with saline and alkali soils. Some
minerals found in the effluent may cause a decrease in crop
production in soils of this type. Analyses and irrigation prac-
tices for these areas are described in detail in the U.S. De-
partment of Agriculture Handbook No. 60, SALINE AND AL-
KALI SOILS5 A diagram for the classification of irrigation wat-
ers (taken from Handbook No. 60) is shown on Figure 25.16.
A simplified version of this table with other critical con-
stituents (substances) is shown on Table 25.17.
s DIAGNOSIS AND IMPROVEMENT OF SALINE AND ALKALINE SOILS, Richards, LA. (editor), Agricultural Handbook No. 60, U.S. Depart-
ment of Agriculture, Washington, D.C.
-------
412 Treatment Plants
100 2 3 4 5 6 7 8 1000 2 3 4 5000
30
CI-S4
26
26
C2-S4
24
C3-S4
22
C4-S4
CI-S3
20
o
AC
<
N
<
X
C2-S3
<
-j
<
z
3
i
CO
C3-S3
CI-S2
C4-S3
C3-S2
C4-S2
Cl-Sl
C2-SI
C3-SI
100
250 750 22 50
CONDUCTIVITY — MICROMHOS/CM. (ECxlO6) AT 25* C.
MEOIUM
LOW
HIGH
VERY HIGH
SALINITY HAZARD
Fig. 25.16. Diagram for the classification of irrigation waters
(From DIAGNOSIS AND IMPROVEMENT OF SAUNE AND ALKAUNE SOILS. Richards, L.A. (editor), Agricultural Handbook No. 60. U.S. Department of Agriculture, Washington, D.C.)
-------
Wastewater Reclamation 413
TABLE 25.17 CLASSIFICATION OF IRRIGATION
WATERS'
Class I
Class II
Class III
Excellent
to Good
Good to
Injurious
Injurious to
Unsatisfactory
Chemical Properties
"Suitable
under most
conditions"
"Suitability
dependent on
soil crop,
climate and
other factors"
"Unsuitable
under most
conditions"
Total dissolved
solids (mg/L)
Less than 700
700-2,000
More than 2,000
Chloride (mg/i)
Less than 175
175-350
More than 350
Sodium (percent of
base constituents)
Less than 60
60-75
More than 75
Boron (mg/L)
Less than 0.5
0.5-2.0
More than 2.0
DIAGNOSIS AND IMPROVEMENT OF SALINE AND ALKALINE SOILS, Richards, L A.
(editor). Agricultural Handbook No. 60, U.S. Department of Agriculture, Washington, D.C.
Your local U.S. Department of Agriculture, Soil Conservation
Service office, can provide a list of crops that can be irrigated
with Class II and Class III water.
There is nothing that can be done that is economically feasi-
ble to control the concentration of these constituents. If one of
the constituents exceeds the Class I limit, the crop should be
changed to one that is more tolerant. Special agricultural prac-
tices can be used to minimize the effects of these constituents.
These practices vary from one local area to another. The local
soil conservation service office and farm adviser can assist by
providing information appropriate to the area.
Important observations and interpretations were discussed
earlier for determining when to irrigate. The most important
observations in a system where crops are grown and surface
runoff is not allowed are observing ponding or runoff. When
this occurs, either the application amount was excessive or the
rate of application was greater than the soil infiltration rate.
Visual appearance of the crop being grown is extremely im-
portant. Discoloration in plant leaves can indicate excess water
(poor drainage) or a nutrient or mineral deficiency. Your local
farm adviser can assist in diagnosing the problems.
Observations are critical in storage reservoirs. Odors can
result if effluent treatment was inadequate and/or if insufficient
aeration is provided to the reservoir.
25.75 Emergency Operating Procedures
Loss of power will disrupt the sprinkler systems the most
since pumping is required (assuming electrical motors for
pumps). If power is lost, the effluent is retained in the storage
reservoir. Gravity-flow flood irrigation systems won't be af-
fected during power outages.
Loss of other treatment units is generally not a problem for a
few days. Longer downtimes may result in an overloaded and
an odorous storage reservoir and possible odors at the dis-
posal area.
25.76 Troubleshooting Guide (Table 25.18)
TABLE 25.18 TROUBLESHOOTING GUIDE
Indicators/Observations
Probable Cause
Check or Monitor
Solutions
1. Water ponding in irrigated
area where ponding normally
has not been observed.
la. Application rate is exces-
sive.
lb. If application rate is normal,
drainage may be in-
adequate.
1c. Broken pipe in distribu-
tion system.
1a. Application rate.
1b(l) Seasonal variation in
groundwater level.
1b(2) Operability of any drain-
age wells.
1b(3) Condition of drain tiles.
1c. Leaks in system.
1a. Reduce rate to normal
value.
1b(1) Irrigate portions of the
site where groundwater
is not a problem or store
wastewater until level
has dropped.
1b(2) Repair drainage wells or
increase pumping rate.
1b(3) Repair drain tiles
1c. Repair pipe.
2. Lateral aluminum distribution
piping deteriorating.
2a. Effluent permitted to remain
in aluminum pipe too long
causing electrochemical
corrosion.
2b. Dissimilar metals (steel
valves and aluminum pipe).
2a. Operating techniques.
2b. Pipe and valve specifi-
cations.
2a. Drain aluminum lateral lines
except when in use.
2b. Coat steel valves or install
cathodic or anodic pro-
tection.
3. No flow from some sprinkler
nozzles.
Nozzle clogged with particles
from wastewater due to lack
of screening at inlet side of
irrigation pumps.
3. Screen may have developed
hole due to partial plugging
of screen.
3. Repair or replace screen.
4. Wastewater is running off of
irrigated area.
4a. Sodium adsorption ratio of
wastewater is too high and
has caused clay soil to be-
come impermeable.
4b. Soil surface sealed by sol-
ids.
4c. Application rate exceeds in-
filtration rate of soil.
4a. Sodium adsorption ratio
(SAR) should be less than
9.
4b. Soil surface.
4c. Application rate.
4a. Feed calcium and mag-
nesium to adjust SAR.
4b. Strip crop area.
4c. Reduce application rate
until compatible with infiltra-
tion rate.
4d. Break in distribution piping. 4d. Leaks in distribution piping. 4d. Repair breaks.
-------
414 Treatment Plants
TABLE 25.18 TROUBLESHOOTING GUIDE (Continued)
Indicators/Observations Probable Cause Check or Monitor
5. Irrigated crop is dead.
7. Irrigation pumping station
shows normal pressure
but above normal flow.
8. Irrigation pumping station
shows above average pres-
sure but below average flow.
9. Irrigation pumping station
shows below normal flow
and pressure.
10. Excessive erosion occuring.
11. Odor complaints.
12. Center pivot irrigation rigs
stuck in mud.
13. Nitrate concentration of
groundwater in vicinity of ir-
rigation site is increasing.
4e. Soil permeability has de-
creased due to continuous
application of wastewater.
4f. Rain has saturated soil.
5a. Too much (or not enough)
water has been applied.
5b. Wastewater contains ex-
cessive amount of toxic
elements.
5c. Too much insecticide or
weed killer applied.
5d. Inadequate drainage has
flooded root zone of crop.
7a. Broken main, lateral, riser,
or gasket.
7b. Missing sprinkler head or
end plug.
7c. Too many laterals on at one
time.
8. Blockage in distribution sys-
tem due to plugging
sprinklers, valves, screens,
or frozen water.
10a. Excessive application
rates.
10b. Inadequate crop cover.
11a. Wastewater turning sep-
tic during transmission to ir-
rigated site and odors
being released as it is dis-
charged to pretreatment.
11b. Odors from storage re-
servoirs.
12a. Excessive application
rates.
12b. Improper tires or rigs.
12c. Poor drainage.
13a. Application of nitrogen is
not in balance with crop
needs.
13b. Nitrogen being applied dur-
ing periods when crops are
dormant.
13c. Crop is not being harvested
and removed.
4e. Duration of continuous op-
eration on the given area.
4f. Rainfall records.
5a. Water needs of specific
crop versus application
rate.
5b. Analyze wastewater and
consult with county agricul-
tural agent.
5c. Application of insecticide or
weed killer.
5d. Water ponding.
6a. N and P quantities applied
— check with county ag-
ricultural agent.
6b. Consult with county agricul-
tural agent.
7a. Inspect distribution system
for leaks.
7b. Inspect distribution system
for leaks.
7c. Number of laterals in serv-
ice.
10a. Application rate.
10b. Condition of crop cover.
11a. Sample wastewater as it
leaves transmission sys-
tem.
11b. DO in storage reservoirs.
13a. Check Ibs/acre/yr of ni-
trogen being applied with
needs of crops.
13b. Application schedules.
13c. Farming management.
Solutions
4e. Each area should be al-
lowed to rest (2-3 days) be-
tween applications of
wastewater to allow soil to
drain.
4f. Store wastewater until soil
has drained.
5a. Reduce (or increase) appli-
cation rate.
5b. Eliminate industrial dis-
charges of toxic materials.
5c. Proper control of applica-
tion of insecticide or weed
killer.
5d. (See Item 1)
6a. If increased wastewater
application rates are not
practical, supplement
wastewater N or P with
commercial fertilizer.
6b. Adjust application schedule
to meet crop needs.
7a. Repair leak.
7b. Repair leak.
7c. Make appropriate valving
changes.
8. Locate blockage and elimi-
nate.
9a. Replace impeller (See Sec-
tion 25.11, "Review of
Plans and Specifications,"
No. 5.)
9b. Clean screen.
10a. Reduce application rate.
10b. (See Items 5 and 6)
11a. Contain and treat off-gases
from discharge point of
transmission system by
covering inlet with building
and passing off-gases
through deodorizing sys-
tem.
11b. Improve pretreatment or
aerate reservoirs.
12a. Reduce application rates.
12b. Install tires with higher flota-
tion capabilities.
12c. Improve drainage (See Item
1b).
13a. Change crop to one with
higher nitrogen needs.
13b. Apply wastewater only dur-
ing periods of active crop
growth.
13c. Harvest and remove crop.
6. Growth of irrigated crop is
poor.
6a. Too little nitrogen
(N) or phosphorus
(P) applied.
6b. Timing of nutrient applica-
tion not consistent with crop
need. (Also, see 5a — 5c)
9a. Pump impeller is worn. 9a. Pump impeller.
9b. Partially clogged inlet 9b. Screen,
screen.
-------
Wastewater Reclamation 415
QUESTIONS
TABLE 25.20 WELL MONITORING PROGRAM
Write your answers in a notebook and then compare your
answers with those on page 418.
25.7C What is the main objective of a land disposal system?
25.7D List the three main areas of process control in a land
disposal system.
25.7E How many points in a storage reservoir should be
sampled for DO?
25.7F What are the minimum recommended DO require-
ments for a storage reservoir?
25.7G What are the probable causes of water ponding in an
irrigated area where ponding normally has not been
observed?
25.8 MONITORING
25.80 Monitoring Schedule
The four monitoring areas for an irrigation system where
crops are grown are: effluent, vegetation, soils, and groundwa-
ter (or collected seepage). This is reduced to the two areas of
effluent and groundwater for systems where crops are not
grown. Wells should be monitored to identify any adverse ef-
fects on groundwaters. Testing requirements and frequencies
are shown on Table 25.19.
Wells should be monitored to identify any harmful effects on
groundwaters. Sampling wells should be located within the
irrigation site as well as near the site and on all sides to identify
any changes or trends in water quality. Typical tests and fre-
quencies are listed in Table 25.20.
TABLE 25.19 TESTING REQUIREMENTS
Area
Wells
Area
Test
Effluent and
groundwater
or seepage
BOD
Fecal coliform
Total coliform
Flow
Nitrogen
Phosphorus
Suspended
solids
pH
Total dissolved
solids (TDS)
Boron
Chloride
Frequency
two times per week
weekly
weekly
continuous
weekly
weekly
two times per week
daily
monthly
monthly
monthly
Vegetation
Soils
variable depending on crop —
Conductivity
pH
Cation exchange
capacity6
two times per month
two times per month
two times per month
Test
Frequency
Salinity
Conductivity
Monthly
Chloride
Quarterly
TDS
Quarterly
Chemical Buildup
Nitrate
Monthly
Calcium
Semi-annually
Magnesium
Semi-annually
Toxicity (Heavy Metals)
Cadmium
Monthly
Lead
Annually
Zinc
Annually
Mercury
Annually
Molybdenum
Annually
Selenium
Annually
Organics
Trihalomethanes
Quarterly
Pesticides
Quarterly
(depends on local
25.81
application)
Interpretation of Test Results and Follow-up
Actions
Excessive levels and concentrations greater than desired for
effluent BOD, fecal and total conforms, nitrogen, phosphorus,
and suspended solids are not a concern for crop-growing op-
erations. The total dissolved solids (TDS), boron, chloride, and
pH are important during long periods of land treatment, but not
for times less than 2 to 3 weeks. Excessive nitrogen is a poten-
tial problem in spreading basins since nitrate in water supplies
can be harmful to infants. If TDS, boron, or chloride levels
increase and do not return to previous levels, a change in
farming practices may be necessary.
Increased levels in any of the constituents in the groundwa-
ter are unacceptable. Most likely the only constituent that will
increase is nitrate-nitrogen. If this occurs, then a nitrogen re-
moval system (partial or complete) should be added to the
treatment plant.
25.9 SAFETY
Safe operating procedures should be practiced in all under-
takings. The operation of a sprinkler irrigation system has
caused fatalities among operation personnel. Many of the
fatalities have resulted from contact with electricity used either
to power the pumping plant or to transmit electricity associated
with the area being irrigated.
Moving of portable sprinkler lateral pipelines has been the
worst offender. Raising a pipeline into the air to dislodge a
small animal or debris and contacting overhead electrical
transmission lines has resulted in severe electrical shock or
death to the person holding the pipe.
A sprinkler throwing a stream of water into a power line has
shorted the power to ground through the sprinkler system and
• Cation Exchange Capacity. The ability of a soil or other solid to exchange cations (positive ions such as calcium, Ca+2) with a liquid.
-------
416 Treatment Plants
resulted in severe electrical injuries to anyone touching the
sprinkler system parts.
Always have the electric motor well bonded to a good
ground with suitable-size conductors. Injuries have occurred
from touching an ungrounded motor or pump frame having
shorted electrical windings in electrically powered pumping
plants.
Electrical shocks have occurred from faulty starting equip-
ment and from working on energized circuits. Always pull the
line disconnect switch; lock out and tag it when making repairs
or checks on electrical equipment of any kind.
Look over each sprinkler system and mark the potential
safety hazards, then avoid the hazards.
Surface spreading systems can be hazardous due to wet
surfaces and muddy areas.
25.10 MAINTENANCE
Maintenance of land treatment systems requires keeping the
wastewater distribution piping, valves and sprinklers in good
working condition. Pump and valve maintenance is discussed
in Chapter 15, "Maintenance." Storage reservoir maintenance
is similar to pond maintenance outlined in Chapter 9.
25.11 REVIEW OF PLANS AND SPECIFICATIONS
Many operational and maintenance problems can be
avoided by a careful review of the plans and specifications for
a land treatment system. Be sure to look for the items listed in
this section.
1. Ponding
Ponding problems can be avoided if the proper site is
selected and provided with proper drainage. Soils at the site
must be suitable for percolation and for planned crops.
Adequate drainage (no ponding) can be provided by level-
ing or sloping of the land surface so the water will flow
evenly over all of the land. DRAINAGE WELLS7 or DRAIN
TILE SYSTEMS8 may be necessary to remove excess
water and prevent ponding.
2. Plastic pipe laterals
Plastic pipe laterals installed above ground may break
because of cold weather or deteriorate due to sunlight. In-
stall plastic pipe laterals below ground.
3. Screens
Install screens on the inlet side of irrigation pumps to
prevent spray nozzles from becoming plugged.
4. Buffer area
Be sure sufficient buffer area is provided around spray
areas to prevent mist from drifting onto nearby homes and
yards. If necessary, do not schedule spraying during days
when the wind is blowing toward neighbors.
5. Odor
If odors may be a problem, consider furrow or flood irriga-
tion rather than spraying. Spraying can cause odor prob-
lems by releasing odors to the atmosphere.
6. Protection of pumps
Excessive wear on pumps can result from sand in the
water being pumped. If sand is a problem, improve pre-
treatment or install a sand trap ahead of the pumps. Re-
member to drain out of sen/ice pumps before freezing
weather occurs in the fall or winter.
7. Alternate place to pump effluent
An alternate location to pump or dispose of effluent is
very important in case of system failure.
25.12 REFERENCES AND ADDITIONAL READING
25.120 References
1. Pound, C.E., et al., COSTS OF WASTEWATER TREAT-
MENT BY LAND APPLICATION, Environmental Protection
Agency, EPA-430/9-75-003, June 1975, available through
the Superintendent of Documents, U.S. Government Print-
ing Office, Stock Number 055-001-01031-1, Washington,
D.C. 20402. Price $2.35.
2. Pound, C.E., et al., EVALUATION OF LAND APPLICATION
SYSTEMS, Environmental Protection Agency, EPA 430/9-
74-015, September 1974, no longer available through the
Superintendent of Documents, U.S. Government Printing
Office, Washington, D.C. Consult your library.
3. Norum, Edward (editor), WASTEWATER RESOURCES
MANUAL, available through The Irrigation Association,
13975 Connecticut Avenue, Silver Spring, Maryland 20906.
Price $50.00.
4. Richard, L.A. (editor), DIAGNOSIS AND IMPROVEMENT
OF SALINE AND ALKALINE SOILS, Agricultural Handbook
No. 60, U.S. Department of Agriculture, August 1969, avail-
able through the Superintendent of Documents, U.S. Gov-
ernment Printing Office, Stock Number 001-000-00763-7,
Washington, D.C. 20402. Price $3.00.
25.121 Additional Reading
1. MANUAL OF WASTEWATER OPERATIONS, Chapters 3
and 22, prepared by the Texas Water Utilities Association.
Obtainable from Texas Water Utilities Association, 6521
Burnet Lane, Austin, Texas 78757. Price $15.00.
2. Culp, G.L. and Folks-Heim, N„ FIELD MANUAL FOR PER-
FORMANCE EVALUATION AND TROUBLESHOOTING
AT MUNICIPAL WASTEWATER TREATMENT FACILITIES,
Environmental Protection Agency, EPA 430/9-78-001, Jan-
uary 1978, U.S. Government Printing Office, Stock Number
055-001-01078-8, Washington, D.C. 20402. Price $5.50.
3. California Fertilizer Association, WESTERN FERTILIZER
HANDBOOK, available through Customer Service, The In-
terstate Printers and Publishers, Inc., 19-27 North Jackson
Street, Danville, Illinois, 61832. Price $4.56.
4. McKee, J.E. and Wolf, H.W., WATER QUALITY CRITERIA,
Second Edition, report to California State Water Quality
Control Board, SWPCB Publication 3A, Sacramento,
California, 1963. Price $7.60.
5. QUALITY CRITERIA FOR WATER, U.S. Environmental
Protection Agency, Washington, D.C. 20460, July 1976.
7 Drainage wells. Wells that can be pumped to lower the groundwater table and prevent ponding.
8 Drain tile systems. A system of tile pipes buried under the crops that collect percolated waters and keep the groundwater table below the
ground surface to prevent ponding.
-------
Wastewater Reclamation 417
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 418.
25.8A What are the four monitoring areas for an irrigation
system where crops are grown?
25.9A What is the major cause of accidents to operators
while working with sprinkler irrigation systems?
25.1 OA What equipment needs to be maintained in a land
treatment system?
25.11A List the items that should be examined when review-
ing plans and specifications for a land disposal sys-
tem.
&NP Of L&bGOU 2 OP 2 LE640
WA<*T6WA"T68 tZ&CLAMATlON
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 2 Lessons)
Chapter 25. WASTEWATER RECLAMATION
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 1.
6. How does land treatment work?
7. What should be done with wastewater that seeps out of
storage reservoirs and runs off from a land treatment sys-
tem?
9. How long should the pumps be run while irrigating a plot of
land?
10. What water quality indicators should be monitored to in-
sure that a land disposal system does not adversely affect
a groundwater supply?
11. How can safety hazards be avoided while operating a
sprinkler irrigation system?
WORK THE OBJECTIVE TEST NEXT
SUGGESTED ANSWERS
Chapter 25. WASTEWATER RECLAMATION
Answers to questions on page 388.
25.0A Uses of reclaimed wastewater include:
1. Irrigation for crop or plant growth,
2. Indirect reuse by downstream users,
3. Direct reuse by industry,
4. Use as a fresh water barrier to prevent salt water
intrusion by deep well injection,
5. Groundwater recharge by spreading basins, and
6. Reservoirs for recreation.
25.0B Oil that was not removed by previous pumping efforts
will float on top of water supplied by deep well injec-
tion. The oil is then easier to pump to the surface from
underground areas.
Answers to questions on page 398.
25.1 A Coliforms and pathogenic bacteria can be killed by
chlorination.
25.1B "Blend" water is sometimes mixed with plant effluent
because this may be the best (most economical)
means of achieving the water quality desired by the
water users.
25.1C Probable causes of wastewater reclamation plant
being unable to maintain a chlorine residual include:
1. Chlorinator not working properly, and
2. An increase in the chlorine demand.
Answers to questions on page 400.
25.2A Possible causes
of clogging
1. Slimes
Possible cures
for cause
2. Carbon fines
1. Chlorination or allow well to
rest.
2. Remove fines by passing
the water through a sand/
anthracite filter.
25.2B If reclaimed effluent was being used by industry and
one of the water quality standards was not being met,
NOTIFY THE INDUSTRY IMMEDIATELY.
25.3A Always work with another operator when working
around storage reservoirs or blending tanks so help
will be available and prevent you from drowning if you
fall into the water.
END OF ANSWERS TO QUESTIONS IN LESSON 1
-------
418 Treatment Plants
Answers to questions on page 406.
25.6A EVAPOTRANSPIRATION. The total water removed
from an area by transpiration and by evaporation from
soil, snow and water surfaces. HYDROLOGIC CY-
CLE. The processes involved in the transfer of mois-
ture from the sea to the land and back to the sea
again.
25.6B Land disposal of wastewater is accomplished by:
1. Irrigation,
2. Overland flow, and
3. Infiltration-percolation.
25.6C The major parts of land application systems include:
1. Preapplication treatment,
2. Transmission to the land site,
3. Storage,
4. Distribution over site,
5. Runoff recovery system (if needed), and
6. Crop systems.
25.6D Known Unknown
Length, ft = 2000 ft Hydraulic Loading,
Width, ft = 1000 ft 1. MGD/acre
Flow, MGD= 1 MGD 2. Inches/day
1. Determine surface area in acres.
Length, ft x Width, ft
Area, acres
43,560 sq ft/acre
_ 2000 ft x 1000 ft
43,560 sq ft/acre
= 45.9 acres
2. Determine hydraulic loading, MGD/acre.
Loading, MGD/ac = Flow' MGD
Area, acre
_ 1 MGD
45.9 acres
= 0.02 MGD/ac
3. Determine hydraulic loading, inches/day
Loading, in/day
_ Flow, MGD x 1,000,000/M x 12 in/ft
Length, ft x Width, ft x 7.48 gal/cu ft
= 1 M Gal/day x 1,000,00Q/M x 12 in/ft
2000 ft x 1000 ft x 7.48 gal/cu ft
= 0.8 in/day
Answers to questions on page 411.
25.7A The major items of equipment that should be in-
spected before starting a spray irrigation system in-
clude:
1. Electric motors,
2. Pumps,
3. Aluminum tubing, and
4. Sprinkler systems.
25.7B Known
Area, ac = 30 acres
Soil type = Medium
Root
zone, ft = 2 ft deep
Moisture = 50% retention
Unknown
Time to irrigate, hr
1. Determine inches of water to be applied.
From Table 25.16
Application, in = 1.69 inches
2. Determine time to irrigate 30 acres to apply one
inch with a 1200 GPM pumping system capacity.
From Table 25.18
Time to irrigate 1 inch = 11 hours
3. Determine total time to irrigate in hours.
Time, hrs = Time (hr) to irrigate x Amount to apply, in
= 11 hour/inch x 1.69 inches
= 18.6 hours
Answers to questions on page 415.
25.7C The main objective of a land disposal system is to
dispose of effluent without harming surface waters or
creating nuisance conditions.
25.7D The three main areas of process control in a land
disposal system are:
1. Storage reservoir,
2. Runoff and seepage water recycle systems, and
3. Impact of minerals in effluent on crop production in
saline and alkali soils.
25.7E A minimum of four points in a storage reservoir should
be sampled for DO.
25.7F The minimum DO requirements for a storage reservoir
are a minimum DO of 0.4 mgIL for ail samples and the
average of all samples should be at least 0.8 mg IL.
25.7G Probable causes of ponding include:
1. Application rate is excessive;
2. If application rate is normal, drainage may be in-
adequate; and
3. A broken pipe in the distribution system.
Answers to questions on page 417.
25.8A The four monitoring areas for an irrigation system
where crops are grown are:
1. Effluent,
2. Vegetation,
3. Soils, and
4. Groundwater.
25.9A The major cause of accidents to operators while
working with sprinkler irrigation systems is contact
with electricity used either to power the pumping
plant or to transmit electricity associated with the
area being irrigated.
25.10A Equipment requiring maintenance in a land treatment
system includes distribution piping, pumps, valves
and sprinklers.
25.11A Items to be examined when reviewing the plans and
specifications for a land disposal system include:
1. Ponding,
2. Plastic pipe laterals,
3. Screens,
4. Buffer area, and
5. Protection of pumps.
END OF ANSWERS TO QUESTIONS IN LESSON 2
-------
Wastewater Reclamation 419
OBJECTIVE TEST
Chapter 25. WASTEWATER RECLAMATION
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one correct answer to each question.
1. Industrial cooling waters must be of a higher quality than
water used for food processing.
1. True
2. False
2. One purpose of the aeration tank in a wastewater reclama-
tion plant for a steel mill is for biological oxidation.
1. True
2. False
3. There are no safety hazards associated with the handling
of portable sprinkler pipelines.
1. True
2. False
4. An industry may use reclaimed effluent directly for wash-
ing purposes or as influent to a specialized water treat-
ment plant.
1. True
2. False
5. The method of irrigation depends on the type of crop being
grown.
1. True
2. False
6. Which of the following constituents in reclaimed water
could cause problems for the water user in a nuclear
generating station?
1. Ammonia
2. Alkalinity
3. Calcium
4. Silica
5. Sulfate
7. Reclaimed wastewater may be used for
1. A freshwater barrier to prevent salt water intrusion.
2. Cooling water by industry.
3. Distilled water in a car battery.
4. Irrigation of crops.
5. Recreation lakes.
8. Problems that may develop during the injection of re-
claimed wastewaters into deep wells include
1. Groundwater contamination.
2. Increased lowering of groundwater table.
3. Salt water intrusion.
4. Slime growths.
5. Well clogging and loss of recharge capacity.
9. Safety hazards around a wastewater reclamation facility
include
1. Drowning.
2. Electrical shock.
3. Pathogenic bacteria.
4. Slippery surfaces.
5. Toxic gases.
10. Water quality criteria for wastewater reclaimed for recre-
ational uses include
1. Alkalinity.
2. Coliform group bacteria.
3. Floatable solids.
4. Hardness.
5. Nutrients.
11. What would you do if the effluent from a wastewater rec-
lamation facility did not meet the water quality standards of
the water users?
1. Divert the flows to emergency storage if available
2. Install better monitoring equipment
3. Locate the cause of the problem and attempt to correct
the problem
4. Notify the user immediately
5. Try to have the standards adjusted to more reasonable
values
12. Land disposal of wastewater may be done by which of the
following methods?
1. Dilution
2. Discharge to a river
3. Infiltration-percolation
4. Irrigation
5. Overland flow
13. Which of the following methods of wastewater disposal
are best suited for crop production?
1. Deep-well injection
2. Groundwater recharge
3. Infiltration-percolation
4. Irrigation
5. Overland flow
14. Which of the following chemical properties are used in the
classification of irrigation waters?
1. BOD
2. Boron
3. Chloride
4. pH
5. Total dissolved solids
-------
420 Treatment Plants
15. How can an operator determine if too much water is being
applied to a land disposal irrigation system?
1. By observing growth of multiple crops
2. By observing ponding
3. By observing runoff
4. By observing that the storage reservoir is empty
5. By observing weeds
16. Probable causes of ponding in a land disposal system
include
1. Broken pipe in distribution system.
2. Bulking sludges.
3. Clogged sprinkler nozzles.
4. Excessive application rates.
5. Inadequate drainage.
17. What could be possible causes of a dead irrigated crop?
1. Inadequate drainage has flooded root zone of crop
2. Not enough water has been applied
3. Too much insecticide or weed killer applied
4. Too much water has been applied
5. Wastewater contains an excessive amount of toxic
elements
18. Safety hazards when operating a sprinkler irrigation sys-
tem include
1. A sprinkler throwing a stream of water into a power line.
2. Drowning.
3. Faulty electrical pump motor starting equipment.
4. Portable sprinkler pipelines coming in contact with
overhead electrical transmission lines.
5. Ungrounded motor or pump frames.
19. Possible solutions to deterioration of lateral aluminum dis-
tribution piping include
1. Adding corrosion inhibiting chemicals to water.
2. Adjusting the pH of the water.
3. Burying the pipe.
4. Draining lines except when in use.
5. Installing cathodic or anodic protection.
20. Why might the effluent from your wastewater treatment
plant be reused directly by someone?
1. Cost of obtaining groundwater is prohibitive.
2. Cost of purchasing treated water is too high
3. Sufficient municipal water is not available
4. Surface waters are not available
5. To discourage community growth
21. Which of the following tests are performed on the soils in
an effluent disposal on land program?
1. BOD
2. Cation exchange capacity
3. Conductivity
4. DO
5. pH
22. Which one(s) of the following items are limitations of land
treatment systems?
1. Energy requirements for land treatment systems are
high
2. Maintenance requirements for land treatment systems
are both complex and costly
3. Rain can soak the soil so no wastewater can be treated
4. Salts can build up in the soil to levels toxic to plants
5. Suspended solids can form a mat that will seal the land
surface
23. Problems caused by the buildup of salts in soils can be
corrected by
1. Adding an acid to the soil, such as nitric acid.
2. Adding a base to the soil, such as sodium hydroxide.
3. Leaching out the salts by applying fresh water.
4. Removing the salts from the effluent by a distillation
process.
5. Ripping up the field and turning it over to a depth of 4 or
5 feet.
24. The most important observations in a land treatment sys-
tem where crops are grown and surface runoff is not al-
lowed are observing
1. Exfiltration.
2. Percolation.
3. Ponding.
4. Salt buildup.
5. Surface runoff.
euPOFO
-------
CHAPTER 26
INSTRUMENTATION
George Ohara
-------
422 Treatment Plants
TABLE OF CONTENTS
Chapter 26. Instrumentation
Page
OBJECTIVES 424
GLOSSARY 425
LESSON 1
26.0 Need for Instrumentation and Controls 426
26.00 What Are Instruments and Controls? 426
26.01 Why Use Instruments and Controls? 430
26.010 Accuracy 430
26.011 Repeatability 430
26.012 Sensitivity 434
26.013 Permanence 434
26.1 What Do Instruments Measure? 434
26.10 Temperature 434
26.11 Pressure 434
26.12 Flow 438
26.13 Level 438
26.14 Density 438
26.15 Velocity 438
26.16 Analytical Measurements 438
26.2 Units of Measure 438
LESSON 2
26.3 How Do Instruments (Sensors) Measure? 444
26.4 Indicators 454
26.5 Controllers 454
26.50 What Are Controllers? 454
26.51 How Do Controllers Work? 456
26.6 Recorders 457
26.60 What Are Recorders? 457
-------
Instrumentation 423
26.61 Types of Recorders 459
26.610 Circular Chart 459
26.611 Strip Chart 459
26.612 Recording Media 459
26.613 Mechanisms 459
26.7 Integrators or Totalizers 459
LESSON 3
26.8 Operation 461
26.80 How Instruments and Controls Affect Plant Operation 461
26.81 Preliminary Treatment 461
26.82 Primary Treatment 463
LESSON 4
26.83 Activated Sludge Process 466
26.84 Anaerobic Sludge Digestion 468
26.9 Routine Maintenance and Troubleshooting 471
26.10 Additional Reading 474
26.11 Acknowledgment 474
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424 Treatment Plants
OBJECTIVES
Chapter 26. INSTRUMENTATION
After completion of Chapter 26 you should be able to do the
following:
1. Describe the need for instrumentation and controls,
2. Indicate the variables or values measured by instruments
and how they are measured,
3. Identify a controller and describe its purpose,
4. Identify recorders — indicators and describe their purpose,
5. Read instruments and controls and make proper adjust-
ments in operation of treatment plant,
6. Determine location and cause of instrument and control
failures and take corrective action, and
7. Maintain instruments and controls.
ALWAYS REMEMBER: If you don't know what you are do-
ing, HANDS OFF!
-------
Instrumentation 425
GLOSSARY
Chapter 26. INSTRUMENTATION
HYDROSTATIC SYSTEM HYDROSTATIC SYSTEM
In a hydrostatic sludge removal system, the surface of the water in the clarifier is higher than the surface of the water in the sludge
well or hopper. This difference in pressure head forces sludge from the bottom of the clarifier to flow through pipes to the sludge well
or hopper.
OFFSET (or DROOP) OFFSET
The difference between the actual value and the desired value (or set point) characteristic of proportional controllers that do not
incorporate reset action.
PROCESS VARIABLE PROCESS VARIABLE
A physical or chemical quantity which is usually measured and controlled.
SET POINT SET POINT
The position at which the control or controller is set. This is the same as the desired value of the process variable.
SOFTWARE PROGRAMS SOFTWARE PROGRAMS
Computer programs designed and written to monitor and control wastewater treatment processes or other processes.
TIME LAG TIME LAG
The time required for processes and control systems to respond to a signal or to reach a desired level.
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426 Treatment Plants
CHAPTER 26. INSTRUMENTATION
(Lesson 1 of 4 Lessons)
26.0 NEED FOR INSTRUMENTATION AND CONTROLS
With today's tougher discharge and monitoring require-
ments, more and more wastewater treatment plants are being
designed and constructed with sophisticated instrumentation
and control systems to help operators do their job. Con-
sequently, this chapter on instrumentation and controls is ded-
icated to familiarizing the operator with the role instruments
and controls play in the operation of a wastewater treatment
plant. We will define instruments and controls, what they do,
how they do their job, how they are related to plant operations,
and the care they should receive. This chapter will not attempt
to cover the theory of instruments and controls, their design,
construction, and repair. These matters are best left to qual-
ified instrument personnel that have the necessary training,
experience, and equipment to do the job. So let's get started!
26.00 What are Instruments and Controls?
Simply stated AN INSTRUMENT IS NOTHING MORE THAN
A MEASURING DEVICE. Let's look at a few samples.
One of the simplest and most common examples of a
measuring device is the rule or tape measure. Rulers are used
to measure linear (lengthwise) distances. The distances may
be measured in the terms of inches, feet, fractions, decimals or
in metric units. Depending upon the job we have to do, we may
choose to use a 6-inch pocket scale or a 100-foot tape meas-
ure as a measuring device (Fig. 26.1).
Another common and familiar instrument is the clock or wrist
watch which we use to measure time. We may measure time in
units of seconds, minutes, hours or days, depending upon our
needs. The clock may be mounted on a building for all to see or
it may be a wrist watch for personal use (Fig. 26.2).
Another common instrument is the bathroom scale that we
use to measure our weight. Scales may measure in terms of
pounds and ounces, pounds and decimals of a pound, or in
grams in the metric system. There are many different types of
scales used to measure weight. A postage scale (Fig. 26.3)
used to weigh letters cannot be used to weigh groceries nor
can the scale used to weigh chlorine containers be used to
weigh the small amounts of solid residues measured in the lab.
An instrument is selected on the basis of a particular job it
has to do.
In review of what has been discussed, we may simply state
that instruments are measuring devices. They may directly or
indirectly measure many quantities whose values or changes
in values are both necessary and useful information for operat-
ing a treatment plant.
Next, let us describe controls and their uses. Simply stated
CONTROLS ARE DEVICES OR A SERIES OF DEVICES THAT
EFFECT SOME CHANGE DUE TO SOME OTHER CHANGE
IN CONDITIONS.
One of the most sophisticated and common control systems
is the human body. An example of this concept is a person
opening a door. We can designate the eyes as a sensing in-
strument to determine (measure) whether the door is closed or
open and the nervous system as a transmission system (mes-
sage sending-receiving device). The brain is the control logic
and the arms-hands are the control output. We can simulate a
control system as follows:
1. The eyes measure the door as closed.
2. The eyes transmit a signal to the brain whose logic has
been established for "door open."
3. The brain, receiving the signal coded as "closed door,"
institutes an action to open the door.
4. The brain transmits a coded signal to the arm and hand
calling for turning of the door knob and opening the door.
5. The eyes then measure the door as opened and transmit a
signal coded as "satisfactory" to the brain ending this par-
ticular control sequence.
An example of a simple household control system is the
thermostatically controlled heating system in your house. In
this case the thermostat (Fig. 26.4), which is a temperature
measuring and sensing device, sends an electrical signal to
the heater causing it to fire up whenever the room temperature
drops below a pre-determined level. After the rooms have
warmed up to the pre-determined level, the thermostat stops
sending an electrical message to the heater (Fig. 26.5) and the
heater will shut down automatically. The control process may
be analyzed as follows:
1. The thermostat senses the temperature has dropped below
70°F (21 °C) and trips an electrical relay.
2. The relay transmits an electrical message to the heater's
fuel regulation system where another device (solenoid)
turns the fuel source to the "ON" position; this causes the
heater to "light up" and produce heat.
3. After a period of heating, the room warms up to 70°F (21 °C)
or slightly more and causes the thermostat to cease send-
ing an electrical signal to the heater's fuel regulation sys-
tem. This, in turn, causes the heater to go "OFF" and pre-
vents overheating of the room.
4. The whole sequence will repeat itself when the room tem-
perature again falls below 70°F (21 °C).
So far we have discussed a sophisticated biological control
system, the human body, and a simple electrical control sys-
tem. Next let us examine a simple hydro-mechanical control
system that is familiar to all of us.
The toilet bowl flush tank uses a simple hydraulic and me-
chanical control system. When the bowl is flushed and the tank
is empty, the tank starts to fill up automatically. Also, the tank
-------
Instrumentation 427
Fig. 26.1 Rulers and tape measures are common devices
used to measure length.
Fig. 26.2 Clocks are instruments that measure time.
-------
428 Treatment Plants
Fig. 26.3 A postage scale measures weight.
-------
Instrumentation 429
Fig. 26.5 A gas burner heater system is controlled by a
thermostat.
-------
430 Treatment Plants
shuts off automatically when it is full. This control system may
be analyzed as follows:
1. The bowl is flushed and the water level drops in the flush
tank.
2. This causes the float to drop (Fig. 26.6). The dropping of the
float mechanically opens a hydraulic valve which releases
water into the flush tank.
3. As water begins to rise in the tank, the float also rises. This
in turn controls the amount of water entering the flush tank.
Thus, the higher the float level, the lower the rate of water
coming into the tank.
4. Finally, when the water level in the flush tank reaches its
pre-set level, the float will also have risen to its maximum
height. When the float reaches its maximum height (Fig.
26.7), it will automatically shut off the valve feeding water
into the flush tank. This is accomplsihed through a set of
mechanical levers.
5. The sequence will repeat itself whenever the toilet is
flushed again.
The example above illustrates a hydro-mechanical control
system using a simple float as the water-level measuring de-
vice and control system to either turn the water "ON" or "OFF"
into the flush tank.
Therefore, an instrument may be defined as a measuring
device; a control system is a device or series of devices that
cause changes to occur. In the next section, we will examine
why we need instruments and controls to operate a treatment
plant.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 475.
26.OA Why are treatment plants being designed and con-
structed with sophisticated instrument-control sys-
tems?
26.OB What is an instrument?
26.0C What is a control?
26.01 Why Use Instruments and Controls?
So far we have discussed simple instrument and control
systems; now let us examine why they are necessary and
useful in operating a treatment plant. Since instruments basi-
cally measure values, let us examine why we need to use
instruments in place of or to assist the opeator's sense of sight,
hearing, touch, and smell. When we talk about measuring, we
are taking into consideration the following related factors:
1. Accuracy of the measurement,
2. Repeatability of the measurement,
3. Sensitivity of the measurement, and
4. Permanence of the measurement.
26.010 Accuracy
Let us first examine the need for accuracy of measurement.
In some instances it may be adequate to "eyeball" a linear
measurement. An example of this would be roughly pacing off
the width of a sand sludge drying bed. No great degree of
accuracy is required or implied by this method. However, in
another situation where we were installing expensive piping
between pieces of machinery, we would want to increase the
degree of accuracy by using a tape measure instead of pacing
off the distance. Another situation requiring still greater accu-
racy would be measuring the diameter of a replacement pump
shaft. Here a micrometer would be used for measuring the
diameter of the shaft to the nearest thousandth of an inch (Fig.
26.8). In the last two examples, an operator's eyeball calibra-
tion is inadequate for the accuracy needed and specific in-
struments must be used.
In another example, an operator would be able to tell the
passing of a day's time, let's say from sunset to sunset, and
that would be accurate enough to mark the days off a calendar.
However, if the operator wanted to operate the primary sludge
pumps ten minutes each hour, a watch would be needed since
the degree of accuracy required is greater than the ability to
"guesstimate" the passing of time (Figs. 26.9 and 26.10).
So, we may conclude that depending upon the degree of
measurement accuracy required, different types of instruments
are needed to assist the operator perform different tasks. The
accuracy of an instrument depends on the preciseness or
exactness of the measurements.
26.011 Repeatability
For our use, repeatability may be defined as the ability to
measure something again and obtain the same answer that
resulted previously.
In our very first accuracy measurement example of pacing
off the width of a sludge drying bed, our repeatability would
probably not be too consistent. However, since the information
would not be sought day after day and would not change, it
would not be too important. However, in the situation where we
were using a micrometer to measure the diameter of a pump
shaft, repeatability would be very critical. We could not tolerate
even a small discrepancy in repeatability.
Therefore, we may summarize that the repeatability of in-
struments is unquestionably superior to that of human sense
measurements and that in many treatment plant operations
using flow, temperature, pressure and other process variables,
repeatability is absolutely essential for good operations.
-------
Instrumentation 431
Fig. 26.6 Toilet bowl float in down position. Water will flow
into toilet.
Fig. 26.7 Toilet bowl float in up position. Water will be shut
off from flowing into toilet.
-------
432 Treatment Plants
Fig. 26.8 A micrometer is used for close tolerance
measurements.
-------
Instrumentation 433
1978
JANUARY
12 3 4 5 6 7
6 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31
FEBRUARY
12 3 4
5 6 7 8 9 lO 11
12 13 14 15 16 17 18
19 20 21 22 23 24 2S
26 27 28
MARCH
12 3 4
5 6 7 8 9 lO 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31
APRIL
1
2 3 4 5 6 7 8
9 10 1 1 12 13 14 15
18 17 18 19 20 21 22
23 24 25 26 27 28 29
30
MAY
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 28 30 31
JUNE
1 2 3
4 5 6 7 8 9 lO
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30
JULY
1
2 3 4 S 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25 26 27 28 29
30 31
AUGUST
1 2 3 4 9
6 7 8 9 10 1112
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30 31
SEPTEMBER
1 2
3-4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
OCTOBER
1 2 3 4 5 6 7
8 9 10 1 1 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31
NOVEMBER
12 3 4
5 e 7 a 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30
DECEMBER
1 2
3 4 5 6 7 8 9
lO 1 1 12 13 14 IS 10
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31
1979 fid
JANUARY
12 3 4 5 6
7 8 O 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
FEBRUARY
1 2 3
4 5 6 7 8 9 lO
11 12 13 14 15 16 17
18 19 20 21 22 29 24
MARCH
1 2 3
4 B 6 7 8 9 10
APRIL
12 3 4 5 9 7
8 9 10 1 1 12 13 14
15 16 17 18 19 20 21
Fig. 26.9 A calendar is used to measure long lengths of time.
Fig. 26.10 A sundial is used to measure the approximate
time of day. Sundials cannot measure time precisely.
-------
434 Treatment Plants
26.012 Sensitivity
Sensitivity, for our use, may be defined as the ability to
measure the smallest or largest value necessary.
As an example, the tape measurement would not be sensi-
tive enough to measure to the nearest one thousandth of an
inch. In another example, if we wanted to measure the gas
pressure in an anaerobic sludge digester, we would want a
pressure gage calibrated in inches or centimeters of water
because 9 inches of water in only 0.32 psi. Therefore, a pres-
sure gage calibrated in five-pounds-per-square-inch (5 psi or
0.4 kg/sq cm) increments would be too insensitive for our
needs. In yet another example, a laboratory scale or balance
(Fig. 26.11), calibrated in hundredths of a gram would be more
sensitive than necessary and would not have the capacity to
measure the weight of a chlorine cylinder in pounds. There-
fore, the operator needs instruments that are properly sensitive
to measure the smallest or largest unit (length, weight, time)
increments necessary.
26.013 Permanence
For the purposes of our use, permanence will be defined as
maintaining accuracy, sensitivity, and repeatability over a long
period of time. That is to say, a ruler or tape measure con-
structed out of paper would have little permanence. Con-
versely, a ruler constructed out of Invar metal would have very
high permanence since it would be dimensionally stable.
In summary, we might say that good instruments exhibit a
high degree of permanence, which is necessary for precise
process control.
To this point we have discussed the ability of instruments to
behave in an accurate, sensitive, repeatable and permanent
manner in measuring numerous PROCESS VARIABLES1
necessary for plant operations.
Instruments also measure variables which cannot be directly
measured otherwise, for instance electricity. Human senses,
for all practical purposes are incapable of measuring voltage
and amperage (Fig. 26.12). Instruments also measure vari-
ables that would be unsafe to measure otherwise, such as
extreme heat. Instruments that record also remove much of the
drudgery associated with constant and repeated data taking.
With the proper instruments, operators can measure chemical
variables such as dissolved oxygen levels, pH (Fig. 26.13),
chlorine residuals, and certain specific ions which could not
otherwise be easily and/or quickly determined. Also, valuable
time is saved by not having operators do jobs that could be
done by instruments.
Therefore, we need and use instruments to accurately and
quickly measure physical and chemical process variables that
influence and/or control treatment plant processes. Human
senses and "gut feelings" are no longer adequate to control a
modern treatment plant.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 475.
26.0D Why do we need to use instruments in place of or to
assist the operator's sense of sight, hearing, touch,
and smell?
26.0E What is meant by the sensitivity of a measurement?
26.0F What is the difference between an instrument's accu-
racy and repeatability?
26.1 WHAT DO INSTRUMENTS MEASURE?
Thus far we have learned that instruments are some sort of
measuring device. Also, that they are needed and used be-
cause they provide a more accurate, consistent, sensitive, and
permanent means of monitoring (measuring) treatment pro-
cesses than we can achieve by seeing, hearing, touching, or
smelling.
Next we will discuss which values or variables are measured
by instruments commonly used in wastewater treatment
plants. We will define the meaning of the following meas-
urements:
1. Temperature,
2. Pressure,
3. Flow,
4. Level,
5. Density,
6. Velocity, and
7. Analytical measurements (physical, chemical, or biologi-
cal).
26.10 Temperature
Temperature may be defined as the degree of "hotness" or
"coldness" of a substance from a given reference temperature.
High temperatures are associated with a high level of molecu-
lar activity in a substance, and conversely, cold temperatures
are associated with a low level of molecular activity. A good
example of this would be water which, if heated enough, would
turn into steam; if cooled enough, it would turn into ice.
Therefore, a thermometer (Fig. 26.14) or some other
temeprature-measuring device is used to measure the degree
of hotness or coldness. With this information, we are able to
control heat-sensitive processes within their optimum ranges
(anaerobic sludge digestion) or be warned if safe temperature
levels are exceeded (steam boiler).
26.11 Pressure
Pressure may be defined as a stress (push) uniformly
exerted in all directions. For example, gas inside of a balloon
exerts pressure uniformly to all parts of the balloon. A man-
ometer (Fig. 26.15) or some other pressure-measuring instru-
1 Process Variable. A physical or chemical quantity which is usually measured and controlled.
-------
Instrumentation 435
Fig. 26.11 A laboratory scale or balance is used to
accurately measure small amounts of weights. Heavy
quantities cannot be measured by lab scales.
-------
436 Treatment
Fig. 26.12 A wattmeter is used to measure electrical energy.
Human senses cannot measure electrical quantities.
Plants
ELECTRIC
TYPE I-55-S ,37-
SINGLE STATOR <3®
W • CAT HO •
FM 2S
WATTHOUR METER
630XS8
TURN OFF AFTER EACH USE
Fig. 26.13 A laboratory pH meter is used to measure a
chemical quality of a liquid.
-------
Instrumentation 437
TlUiUU
fWhMMi [ B
Fig. 26.14 A liquid-filled thermometer is used to measure
temperature.
Fig. 26.15 An inclined manometer is used to measure
relatively low pressures.
-------
438 Treatment Plants
ment is commonly used to measure the amount of pressure.
Therefore, we are able to measure air pressure in order to limit
the air pressure inside an air tank so that safe limits are not
exceeded. Also, the suction and discharge pressures of a
pump allow us to determine the total dynamic head (TDH) on a
pump.
26.12 Flow
Flow may be defined in two ways, rate of flow and total flow
or volume. Rate of flow may be defined as the volume of mate-
rial passing a given point at any given INSTANT OR TIME
PERIOD. Total flow may be defined as the amount or volume
of flow passing a given point WITHIN A SPECIFIC TIME
PERIOD.
For example, the return activated sludge (RAS) "flow rate"
may be 200 GPM and the "total flow volume" would be 0.288
million gallons during one day.
Flow volume, _ p|QW ra(e ga|/nnjn x 7(me (jay x 1440 min/day x 1 Million
MQ 1,000,000
= 200 gal/min x 1 day x 1440 min/day x 1 Million
1,000,000
= 0.288 MGal
26.13 Level
Level may be defined as a height measurement. Liquid sur-
face levels can be measured directly by a floating ball or a
measuring (dip) stick. For example, the amount of diesel fuel in
a tank can be determined from the level of fuel. Sight tubes are
used to measure liquid levels directly in a tank (Fig. 26.16).
Levels also can be measured by indirect means such as elec-
trical probes or by ultrasonic sound waves which bounce back
like radar and induce a signal. Hydrostatic pressure in psi can
be converted to a level or head by using the conversion factor
2.31 feet = 1 psi.
26.14 Density
Density may be defined as the weight of a material per unit
volume. For example, the density of water is 62.4 Ibs/cu ft.
Liquid density may be measured by a hydrometer such as the
type used to measure the amount of anti-freeze in a radiator.
Primary sludge density may be measured by radioactive sens-
ing cells.
26.15 Velocity (Speed)
Velocity may be defined as the length of travel in a given unit
of time or: velocity = distance/time. An automobile speedome-
ter (Fig. 26.17) measures velocity in terms of miles per hour.
Another velocity or speed measurement is the RPM (revolu-
tions per minute) made by an engine or pump (Fig. 26.18).
26.16 Analytical Measurements
Instruments also may be used to make analytical meas-
urements. Chemical analytical or laboratory measurements
are made for pH, dissolved oxygen, electrical conductivity,
chlorine concentrations, and others. Physical measurements
include turbidity and temperature while examples of a biologi-
cal measurement are the tests to indicate the concentrations of
coliform group bacteria or algae. Many laboratory meas-
urements involve instruments using some sort of specialized
probe and meter.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 475.
26.1 A Why are instruments used instead of our human
senses of seeing, hearing, touching, and smelling?
26.1B What do instruments measure?
26.1C How can flow be defined?
26.2 UNITS OF MEASUREMENT
Now that we understand what variables instruments meas-
ure, let us examine the common units of expression for these
measurements.
1. TEMPERATURE
A unit of expression for temperature is the
Fahrenheit scale, where the freezing of
water is set at 32°F, and boiling of water is
set at 212°F, covering a range of 180°F be-
tween the two points.
Another common unit of temperature ex-
pression is the Celsius or Centigrade scale,
which is commonly used in laboratory
measurements and the metric system. The
freezing of water is set at 0°C and boiling of
water is set at 100°C, covering a range of
100°C between the two points.
There are two other less commonly used
temperature scales which incorporate the
value of "Absolute Zero" where, theoreti-
cally, no molecular motion exists. The Kelvin
scale sets the freezing point of water at
+273°K and the boiling point at +373°K, giv-
ing a spread of 100° just like the Celsius
scale. The Rankine scale sets the freezing
point of water at +491,7°R and the boiling
point at +671.7°R, giving a 180° spread be-
tween the points just like the Fahrenheit
scale.
The most common expression for pressure
is pounds per square inch (psi). This means
that each square inch of surface area is sub-
jected to that many pounds of force. 1 psi =
0.070 kg/sq cm
Pounds per Another pressure expression is given in
Square Foot: pounds per square foot (psf). This means
each square foot of surface area is sub-
jected to that many pounds of force. 1 psf =
4.882 kg/sq m
Fahrenheit:
(English)
Celsius or
Centigrade:
(Metric)
Kelvin
(Metric) &
Rankine
(English):
PRESSURE
Pounds per
Square Inch:
-------
Instrumentation 439
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Fig. 26.16 Sight tubes are used to measure liquid levels
directly in a tank.
-------
440 Treatment Plants
Fig. 26.17 A speedometer is used to measure linear velocity.
REVOLl
Fig. 26.18 A tachometer is used to measure rotational
velocity.
-------
Instrumentation 441
Inches or Pressure may also be expressed in terms of
Feet of inches of water, feet of water, or inches of
Head: mercury (Hg). Each of these expressions is
related to the pressure that would be re-
quired to support a column of given liquid
sometimes called "Head." Mathematically
stated, since one cubic foot of fresh water
weighs 62.4 pounds and there are 144
square inches per square foot, a one square
inch column of water one foot or 12 inches
high exerts a pressure of 0.433 Ibs/sq in. For
example, when the manometer connected
to the dome of an anaerobic sludge digester
reads 9 inches (23 cm) of water (H2O), what
the manometer is telling us is that the gas
pressure inside the digester is exerting a
force equivalent to that required to support a
column of water (head) 9 inches (23 cm)
high.
Pressure, Ibs/sq in
Density, Ibs/cu ft x Head, ft
Pressure, Ibs/sq in =
Gage and
Absolute
Pressure:
Vacuum
Pressure:
Weight, lbs
Area, sq in
_ Volume, cu ft x Density, Ibs/cu ft
Area, sq in
_ Area, sq in x Height, in x Density, Ibs/cu ft
Area, sq in x 1728 cu in/cu ft
_ 1 sq in x 12 in x 62.4 Ibs/cu ft
1 sq in x 1728 cu in/cu ft
= 0.433 lbs
1 sq in
= 0.433 Ibs/sq in
Therefore, 0.433 psi = 1 ft head = 0.3 m
or 1 psi = 2.31 ft head = 0.7 m
Pressure also is expressed as gage pres-
sure or absolute pressure (Fig. 26.19). Gage
pressure does not take into consideration
the weight of the atmosphere above the
earth; one atmosphere = 14.7 psi or 29.97
inches of mercury at sea level. Therefore, in
converting to absolute pressure from gage
pressure you must add barometric pressure
(14.7 psi) to the gage pressure reading.
Gage Pressure,
psi
- Barometric Pressure, - Absolute Pressure,
psi psi
For practical purposes, operators commonly
use gage pressure because they want to
know the DIFFERENCES in water pressure.
Usually atmospheric (barometric) pressure
does not influence work done by operators.
Absolute pressure is used when working
with gases and calculating changes result-
ing from changes in the pressure, tempera-
ture, and/or volume of a gas.
So far we have been discussing positive
pressures. Whenever a pressure falls below
atmospheric pressure, a negative pressure
is exerted which is called a vacuum. Con-
sequently, when an open-tube manometer
on a vacuum filter or vacuum receiver reads
20 inches (51 cm) of mercury (Hg), this is
equivalent to a negative or minus gage
pressure of 9,76 Ibs/sq in (0.69 kg/sq cm).
Mercury has a density 13.55 times heavier
than water.
144 sq in/sq ft
13.55 x 62.4 Ibs/cu ft x 20 in
144 sq in/sq ft x 12 in/ft
9.79 Ibs/sq in (0.69 kg/sq cm)
Atmos. Press., psi + Gage Press., psi
14.7 psi + (-9.8 psi)*
= 4.9 psi
* — means a vacuum or negative pressure.
Note that the units of pressure are the same for liquids arid gases.
Absolute Pressure
psi
3. FLOW RATE
Liquids:
Gases:
Solids:
4. LEVEL
5. DENSITY
Percent
Solids:
Specific
Gravity:
6. VELOCITY
Flow rates for liquids are usually expressed
as volume per unit time. The most common
units are gallons per minute, gpm (gal/min),
cubic feet per second (cfs or cu ft/sec) and
million gallons per day (MGD). In each of the
above cases, a given volume of liquid
moves past a given point during a unit of
time.
Flow rates for gases are usually expressed
as cubic feet per minute (cfm or cu ft/min),
cubic feet per hour (cfh or cu ft/hr), and cubic
feet per day (cfd or cu ft/day). Many instru-
ments are calibrated in SCFM where the S
refers to Standard conditions of tempera-
ture, pressure and humidity. The same flow
rate definitions apply to gases as for liquids.
Flow rates for solids are commonly ex-
pressed as pounds per hour (pph or Ibs/hr),
pounds per day (ppd or lbs/day) or tons per
hour. They also may be expressed in vol-
umetric terms such as cubic feet per day
(cfd or cu ft/day) or cubic yards per day (cyd
or cu yd/day). Therefore, we may conclude
that flow may be measured in terms of vol-
ume or weight.
The units for expression for level are usually
expressed in terms of inches or feet (cm or
m). However, in the laboratory, the metric
units of measurement are used such as mil-
limeter (mm), centimeter (cm), or meter (m).
Although we have defined density as weight
per unit volume, instrumentation in a treat-
ment plant can be calibrated to read in per-
cent solids for sludges.
The density of liquids is measured by a hy-
drometer expressing units of specific gravity
(which is the ratio of specific gravity of a
liquid to the specific gravity of water, which
is one).
Velocity measurements in a treatment plant are usually ex-
pressed in terms of feet per second (fps or ft/sec); feet per
minute (fpm or ft/min); or for rotational velocities, in revolu-
tions per minute (rpm or rev/min).
-------
4
PUMP DISCHARGE PRESSURE
PRESSURE
SCALE
GAGE PRESSURE
PSIG
ATMOSPHERIC
PRESSURE
to
-VACUUM IN INCHES
OF MERCURY
\
PUMP SUCTION LIFT
BAROMETRIC
PRESSURE
ABSOLUTE ZERO
(PERFECT VACUUM)'
4o
ABSOLUTE
PRESSURE
PSIA
io
fo —ZERO POINT
FOR START OF
MEASUREMENT
Fig. 26.19 Measurement of pressures
-------
Instrumentation 443
7. ANALYTICAL MEASUREMENTS
Analytical measuring instruments are very specific in what
and how they measure. Some of the units of expression for
the more common analytical instruments found in a treat-
ment plant laboratory are discussed in the next paragraphs.
pH meters read in units of pH; dissolved oxygen meters
read in milligrams per liter (mg/L); and electrical conductiv-
ity meters usually read in mhos which are equal to 1/ohm.
There are also other more sophisticated laboratory in-
struments such as Total Organic Carbon Analysers, Gas
Chromatographs, Infrared Spectrophotometers, Atomic
Absorption Units, and others which are way beyond the
capability of this section, and therefore will not be discussed
further. Table 26.1 summarizes the common units of meas-
urement.
QUESTION
Write your answer in a notebook and then compare your
answer with the one on page 475.
26.2A Complete the following table by writing both the Eng-
lish and Metric units for the following variables meas-
ured by instruments or sensors.
Measurement
1. Temperature
2. Pressure
3. Flow
4. Level
5. Density
6. Velocity
English
Metric
euo 09 UV&Gti 1 Of-4
Please answer the discussion and review questions before
continuing with Lesson 2.
TABLE 26.1 UNITS OF MEASUREMENTS AND
ABBREVIATIONS
Measurement Common Unit* of Measurement
snd Abbreviations
1. Temperature
2. Pressure
3. Flow
4. Level
5. Density
6. Velocity
7. Analytical
8. Energy or
Work
9. Power
ENGUSH
a) Fahrenheit:
Freezing Point of Water = +32T
Boiling Point of Water = +212°F
b) Rankine:
Freezing Point of Water = +491.7°R
Boiling Point of Water = +671.7°R
METRIC
c) Celsius or Centigrade:
Freezing Point of Water = 0°C
Boiling Point of Water = +100°C
d) Kelvin:
Freezing Point of Water = +273°K
Boiling Point of Water = +373°K
ENGUSH
a) Pounds per square Inch = psi or lb/in2
b) Pounds per square foot = psf or lb/ft2
c) Inches of water = inches H20
d) Feet of water = feet H20
e| Inches of Mercury = inches Hg
f) Absolute pressure = psia
g) Gage pressure » psig
a) Liquids (volume)
gallons per minute
gpm or gal/min
gallons per hour = gph or gal/hr
cubic feet per second - cfs or ft'/sec
million gallons per day = MOD
b) Gases (volume)
cubic feet per minute = cfm or fp/sec
cubic feet per hour = cfh or ff/hr
cubic feet per day - cfd or ff/day
c) Solids or Liquids (weight)
pound per minute - ppmin or Ibs/min
pound per hour = pphr or Ibs/hr
pound per day » ppd or lbs/day
d) Solids (volume)
Cubic feet per day - cfd or fP/day
Cubic yard per day « cyd or yd'/day
a) inches « In
b) feet - ft
a) Percent solids =¦ %
b) Specific Gravity - Sp.Gr.
c) Parts per Million « ppm
a) Linear.
feet per second » fps or ft/sec
feet per minute - fpm or ft/mln
b) Rotational:
Revolutions per minute -= RPM
a) Hydrogen Ion Concentration - pH
b) Dissolved Oxygen - ppm or mg/L
c) Electrical Conductivity - mhos
foot - pounds
foot - pounds/sec or horsepower
METRIC
kg/sq cm
kg/sq m
mm H,0
m HO
mm Hg
kg/sq cm
kg/sq cm
L/sec or
cu m/sec
L/sec
cu m/sec
cu m/day
L/sec or
cu m/sec
L/sec
Usec
gm/sec
gm/secor
kg/hr
kg/day
cu m/day
cu m/day
mm
m
m/sec
m/min or
mm/sec
RPM
pH
mg/L
mhos
joule
joule/sec
or watt
-------
444 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
(Lesson 1 of 4 Lessons)
Chapter 26. INSTRUMENTATION
At the end of each lesson in this chapter you will find some
discussion and review questions that you should work before
continuing. The purpose of these questions is to indicate to you
how well you understand the material in the lesson.
Write the answers to these questions in your notebook.
1. Why do treatment plants have instruments and controls?
2. Why are some instruments more accurate, consistent and
sensitive than human senses?
3. How would you measure the depth of water in a wet well?
CHAPTER 26. INSTRUMENTATION
(Lesson 2 of 4 Lessons)
26.3 HOW DO INSTRUMENTS (SENSORS) MEASURE?
Now that we are familiar with the units of measurements
expressed by instruments, let's examine in a simple manner
how treatment plant instruments function. The operator must
be reasonably familiar with what makes instruments "tick" in
order to determine if an instrument or control is operating
properly or if a problem exists.
Due to a wide and ever-expanding variety of instrumentation
and control systems, only the most common types that an
operator might work with will be discussed in this section.
1. TEMPERATURE
Temperature measurements involve the transfer of heat
or cold between the material whose temperature is being
measured and the temperature sensing instrument. Let's
examine the workings of several of the more common
temperature-sensing instruments.
A. LIQUID-FILLED THERMOMETER
Everyone is familiar with this device, a sealed, hollow
glass tube filled with liquid. Let us examine how a mer-
cury filled thermometer works. Mercury expands when
heated. Consequently, when heat is applied to or re-
moved from a mercury thermometer, the volume of
mercury expands or contracts at a much greater rate
than the glass tube containing the mercury. This forces
the mercury to move up or down a precise amount for
each degree change in temperature. The amount of
mercury movement and sensitivity of the thermometer
depends on the size (diameter) of the bore of the glass
tube. The outside of the glass tube is equally sub-
divided to correspond to the change in mercury volume
as a function of the change in temperature.
All liquid-filled thermometers work on the stated
basic principle that the liquid inside the thermometer
expands at a greater rate than the glass tube surround-
ing it and the distance of movement in the tube is cali-
brated in degrees. A variation of this principle uses a
bulb containing the temperature sensitive liquid which
is connected to a capillary tube in which the expanding
liquid travels up or down in the tube (Fig. 26.20). The
capillary tube is connected to a specially shaped hollow
tube which bends as the liquid from the capillary tube
enters or leaves it. The free end of the hollow tube is
connected to a mechanical linkage which is calibrated
to indicate the change in temperature.
Still another variation of the above principle uses a
gas as the expanding media in the bulb instead of the
liquid; otherwise, they are quite similar in operation and
principle.
SPIRAL
POINTER
INDICATING
SCALE
Fig. 26.20 An expanding or contracting fluid may be used to
measure temperature.
-------
Instrumentation 445
B. BIMETALLIC THERMOMETER
In a bimetallic-type of temperature measuring de-
vice, two metals with different rates of thermal expan-
sion are fused together. When heat is applied to the
bimetallic element which has one end fixed, the metal
with the greater coefficient of thermal expansion ex-
pands a greater amount and causes the bimetallic
element to bend or flex. The amount of bending is
called "flexivity." The bending end of the bimetallic
element is mechanically connected to a pointer which
indicates the temperature change in degrees.
C. THERMOCOUPLE
Simply stated, a thermocouple is a device consisting
of two different types of metallic wires joined together,
which when heated produce an electrical voltage (elec-
tromotive force or EMF). The voltage produced is pro-
portional to the amount of heat applied at the junction
of the two different metals and can be read by a mil-
livoltmeter which is calibrated so as to convert the
change in voltage to the corresponding change in tem-
perature (see Fig. 26.21).
T2
REFERENCE
JUNCTION
MEASURING
JUNCTION
THERMOCOUPLE
INSTRUMENT
MEASURING
JUNCTION
REFERENCE
JUNCTION
Fig. 26.21 A thermocouple is used to measure temperature.
So far we have examined several ways of sensing tempera-
ture. Each method has its most suitable application based on
such factors as temperature range, accuracy, sensitivity,
costs, durability, and corrosion resistance.
2. PRESSURE
We defined pressure as the amount of force applied to a
unit area. For our purpose, we will be primarily concerned
with gage pressure which is the amount of pressure shown
on the pressure-measuring instrument. Let us examine how
several common pressure-sensing (measuring) instru-
ments function.
A. MANOMETER
A manometer is a liquid-filled glass tube device (Fig.
26.22). The liquid is raised or lowered by the pressure
exerted by the fluid (liquid or gas) being measured.
Different ranges of pressure may be measured by
changing the liquid in the manometer to one of a lower
or higher specific gravity; water and mercury are the
most common liquids used. The sensitivity of a man-
ometer also may be increased by inclining (sloping) the
measuring leg of the manometer rather than using a
vertical measuring leg.
The applied pressure on one tube of a U-tube man-
ometer (the other tube is open to atmospheric pres-
sure) is equal to the total vertical height of the liquid
column times the density of the liquid.
Pressure, Ibs/sq ft = Height, ft x Density, Ibs/cu ft
or Pressure, Ibs/sq in = Height, in x Density, Ibs/cu in
When pressure is applied to both tubes of a U-tube man-
ometer, the differential pressure may be read directly without
regard to the actual pressures involved. Again, in this case, the
differential pressure is equal to the height of the liquid column
times the density of the manometer liquid (Fig. 26.23).
Differential Pressure, psi = Pt, Ibs/sq in - P,, Ibs/sq in
= Height, in x Density, Ibs/cu in
When reading the U-tube manometer, the value of h is the
difference in height between the top of the liquid of the left and
right legs of the U-tube. To eliminate this step, a well manome-
ter can be used. In this type of manometer, the area of the well
is large enough in comparison to the bore of the manometer so
that the applied pressure may be read directly (Fig. 26.24).
Also, the scale of the manometer may be made (calibrated) to
compensate for the drawdown of the fluid in the large well.
Pressure, psi = Height, in x Density, Ibs/cu in
B. PRESSURE GAGES
The most common types of pressure-measuring in-
struments use some type of element that undergoes
elastic deformation (bends or flexes and then returns to
its original shape or location). Both low and high pres-
sures may be measured with gages employing this
principle.
BOURDON TUBE (Fig. 26.25)
The Bourdon Tube is one of the most common pres-
sure element devices employing the elastic deforma-
tion principle. The element consists of a thin metal
tube, elliptical in cross section, formed into a "C"
shape; one end of the "C" is rigidly attached to a socket
where the pressure to be measured is applied, the
other free end is mechanically linked to a gage move-
ment which is calibrated to indicate the desired pres-
sure units. When pressure is applied to the "C" shaped
tube, it begins to straighten (unwind) out Oust like a
New Year's Eve party blower). The amount of move-
ment caused by the straightening out process is not
linear; it moves more per unit pressure at first and then
decreases in the amount of movement as the pressure
increases. Therefore, only a small part of the possible
movement is used to measure pressure. A 0 to 60 psi
(4.22 kg/sq cm) element will move only 0.25 of an inch
(0.64 cm).
In elastic deformation elements, pressures in excess
of that designed for a particular unit will deform the
element and it will not return to zero (or original shape),
thus ruining the gage. Lower pressure elements are
usually made of copper alloys; some of the higher
pressure elements are made of carbon steels.
DIAPHRAGM OR BELLOWS ELEMENTS
Another type of elastic deformation pressure ele-
ment is the diaphragm or the bellows (Fig. 26.26). In
both of these systems, the applied pressure deforms
(moves) the diaphragm or the bellows a small amount.
The amount of movement is mechanically linked to a
gage movement for expression of the applied pressure.
Diaphragm- and bellows-type pressure elements are
commonly used for low pressures such as 0 to 10
inches (25.4 cm) of water. Although the bellows are
-------
446 Treatment Plants
}
1
atmospheric pressure
density of the
manometer fluid
• «
P =» h x d
Fig. 26.22 A simple U-tube manometer used to measure
pressure.
-------
Instrumentation 447
P2 P1
density of the
manometer fluid
«•
"h
d
P
P
Fig. 26.23 A U-tube manometer used to measure a
differential pressure.
-------
448 Treatment Plants
Large
Reservoir
Zero Line
small
distance
4.»
. * •" "• • •
• » * i » . .
h ~ h,
d =¦ density of the
manometer fluid
h x d
Fig. 26.24 A wet-well manometer used to measure pressure
-------
Instrumentation 449
SCALE
100
POINTER
TIP
(CLOSED END)
UNK
BOURDON
TUBE
GEARED
SECTOR
AND PINION
SOCKET
PRESSURE
Fig. 26.25 A Bourdon tube is used to measure pressure.
PIVOT
SOLDER
PRESSURE INLET
Fig. 26.26 A metal diaphragm is used to measure pressure.
-------
450 Treatment Plants
usually constructed from metals, the diaphragms can
be made from different materials depending upon the
application, such as the need for a corrosion-resistant
material.
3. FLOW
There are several different types of instruments used to
measure flow in either pipes or open channels. All of these
instruments attempt to measure the flow velocity and area.
Flow or Quantity = Area x Velocity
= AV
or Q, cu ft/sec = Area, sq ft x Velocity, ft/sec
Many flow meters estimate the velocity by measuring the
difference in pressure as the fluid flows through a restriction
such as an orifice or a Venturi. Because flow meas-
urements are so important to the operation of a wastewater
treatment plant, this topic was covered in Chapter 15,
"Maintenance," Section 15.4, "Flow Measurements." Flow
measurements are used by operators to determine what
and how many units of treatment plant facilities must be
on-line at any one time. Daily flows are used to calculate
plant loadings and plant efficiencies.
4. LEVEL
The simplest and most direct means of measuring levels
for clean liquids is the sight tube. However, it may not be
practical to install a sight tube in many applications, there-
fore, other level-measuring devices are employed.
A. FLOAT SYSTEM
A float tied to a cable or rod is one of the most com-
monly used level-measuring devices. The float rests on
the surface of the liquid being measured and rises or
falls with the liquid surface. In another system, the float
is connected to a mechanical linkage and the bouyancy
of the float is used to signal the liquid level (Fig. 26.27).
B. ELECTRIC PROBE
Electric probes are commonly used to measure a
single level, such as a high- or low-level alarm. In the
case of the high-level alarms, the rising liquid allows an
electrical current to flow between two contacts in the
probe. When the current flows, a relay is tripped which
energizes a secondary signal. In the low-level situation,
the reverse is true. When the liquid drops below the
probe, the electrical current stops flowing and causes
another relay to activate another secondary signal.
C. CAPACITANCE PROBE
Similar to electric probes, capacitance probes are
also used. In this system, the capacitance (an electrical
term used to measure the capability of holding an elec-
trical charge) changes when the liquid is in or out of
contact with the probe, which in turn actuates a relay,
which can trip a secondary device or send a signal.
D. ULTRASONIC SOUND
Another type of probe is the ultrasonic probe. This
device uses a miniature transmitter and receiver at the
end of the probe. The signal sent by the transmitter to
the receiver changes when the probe is in or out of the
liquid, which in turn activates a relay system to perform
the necessary function.
The ultrasonic system also may be used to con-
stantly monitor the process level. In this system the
transmitter and receiver are mounted on top of the tank
and the time interval it takes for a transmitted ultrasonic
sound signal to be reflected off the liquid surface or
solid being measured and bounced back to the re-
ceiver is electronically translated into a level meas-
urement (Fig. 26.28).
E. DIAPHRAGM BOX
The diaphragm-box level indicator uses a sealed box
containing a flexible diaphragm exposed to the liquid
being measured. The hydrostatic pressure exerted
upon the submerged diaphragm causes the volume of
the sealed box to fluctuate with the changes in liquid
level; this change in air volume (pressure) is transmit-
ted through a tube to a pressure gage calibrated to
read in inches or feet (centimeters or meters).
F. BUBBLER TUBE
The bubbler tube uses air pressure to measure liquid
levels. This system is based on the required air pres-
sure necessary to overcome the hydrostatic pressure
at the bottom of a container. In practice, a tube is verti-
cally lowered into a container and the air pressure in-
creased to the point where water is blown out of the
tube and air bubbles begin to flow out. The PRESSURE
REQUIRED to force air out of the tube VARIES WITH
THE LIQUID LEVEL and this relationship is converted
to level measurement. This particular system is appli-
cable only to liquid surfaces open to the atmosphere
and cannot be used for sealed containers (Fig. 26.29).
5. DENSITY
Process density measurements in a treatment plant are
usually made for primary sludge or return activated sludge
concentrations in a pipeline. Almost all of the measuring
instruments use the principle of sending a signal across the
sludge flow path and relating the density of the sludge to the
strength of the signal received. This is based on the fact
that the greater the density of the sludge, the greater the
attentution (reduction) in signal strength. The signal source
may be a radioactive cell, an ultrasonic sound wave, or a
light beam. The reduction in signal strength is usually cali-
brated against flows with known solids concentrations and
the instruments are adjusted to read accordingly.
6. VELOCITY
Usually the only velocity measurement made in a treat-
ment plant is rotational velocity or RPM. This is commonly
accomplished by some type of tachometer.
An electro-mechanical tachometer uses a flexible cable
or some other device to pick up the rotating movement. The
tachometer may use a gear box to increase or decrease the
rotating motion. This rotating movement is used to drive a
small electrical generator whose electrical output is cali-
brated in RPM (revolutions per minute). The faster the RPM
the higher the electrical output and visa versa.
Another tachometer system uses a strobe light. The fre-
quency of the strobe light is adjusted until the motion of the
equipment whose rotation is being measured appears to
stop or stand still. This frequency is then converted into the
equivalent RPM.
An electrical tachometer consists of a transducer which
converts rotational speed into an electrical signal coupled to
an indicator or recorder. One type of transducer is a mag-
netic pickup head which produces electric pulses each time
a tooth of a rotating gear passes. The pulses can be digit-
ally counted and displayed in terms of revolutions per min-
ute.
-------
Instrumentation
LEVEL OF
LIQUID
RECORDER
COUNTERWEIGHT
FLOAT
STILLING WELL
Fig. 26.27 A float is used to measure liquid level.
-------
Treatment Plants
Receiver
Transmitter
Reflecte
S icrnal
level beinq Measured
Fig. 26.28 Ultrasonic sound is used to measure liquid levels.
-------
Instrumentation 453
LEVEL (PRESSURE)
RECORDER
REGULATOR
5
NEEDLE
VALVE
FLOW
INDICATOR
BUBBLE
TUBE
CLEARANCE
-AIR
Fig. 26.29 A bubbler tube is used to measure liquid level
-------
454 Treatment Plants
7. ANALYTICAL MEASUREMENT
Most analytical instruments are more fragile, sophisti-
cated, and expensive and also require a greater degree of
attention than do most of the routine treatment plant pro-
cess instruments. These analytical instruments are used
mainly in the laboratory. Consequently, their theory of op-
eration is beyond the scope of this section which has been
devoted to familiarizing the operator with the basic instru-
ments used in process control.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 475.
26.3A List three different types of temperature-measuring in-
struments or sensors.
26.3B What are the most common liquids used in manomet-
ers to measure pressures?
26.3C Determine the pressure in psi if a manometer reads:
1. 8 inches of water; and
2. 8 inches of mercury.
Assume water has a density of 62.4 lbs per cubic
foot and that mercury has a specific gravity of 13.55.
26.4 INDICATORS
We have examined some measuring tools such as rulers
which give a direct measurement. Other instruments require a
secondary device to make the measurement. For example, a
thermocouple needs an electrical meter to indicate and trans-
late voltage (electrical pressure) into temperature readings.
The indicators may be as simple as a notch on an oil level dip
stick or as complex as a digital readout on a Cathode Ray
Tube (CRT) connected to a computer. Indicators also are
known as the measuring element and are a part of most in-
strumentation systems (Fig. 26.30). The indicator may be vis-
ual or audio (sound sensed).
Visual indicators usually consist of two major parts, the fixed
or moveable scale (unit of measurement) and a movable indi-
cator. In some cases, the fixed scale may be as simple as color
coding, such as green for "OK" and red for an unacceptable
situation. Most of the indicators in a treatment plant use either
a fixed scale and movable indicator (pointer) such as a pres-
sure gage or a movable scale and movable indicator like those
used on a circular-flow recording chart.
The scales on an indicator may be straight, curved, or circu-
lar in shape. The scale divisions (units of measurement) also
may be uniformly divided or unequally divided. For example, a
liquid-filled theromometer has equal uniform divisions, but an
ohm meter (measure of electrical resistance) has unequally
divided scale divisions.
In most cases the units of measurement are direct reading,
such as a pressure gage indicating the pressure in psi. How-
ever, in some cases it may be necessary to convert the gage
reading into some other unit of measurement. An example of
this would be a mercury filled U-tube manometer reading 10
inches (24.4 cm) of mercury. We would have to divide the 10
inches of mercury by 2.04 inches of mercury per psi to get a
pressure of 4.9 psi.
Pressure, psi = Height, inches of mercury
2.04 inches of mercury/psi
= 10 in. Hg
2.04 in. Hg/psi
= 4.9 psi
The same type of situation could exist for temperature
readings from thermocouples which produce a signal in mil-
livolts which would be converted to degrees by multiplication or
division by a conversion factor (K).
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 475.
26.4A What is the purpose of transmitting instruments?
26.4B What are the different types of receivers?
26.5 CONTROLLERS
26.50 What are Controllers?
One of the basic objectives of an instrumentation system is
the automatic control of measurable process variables (flow,
pressure, level, or temperature). Therefore, by the use of pri-
mary measurement elements and controllers we automatically
measure the process variable, compare it with the desired
value (SET POINT2) and institute some corrective action
(change the energy level) if the measured process variable is
different from the desired range of values. The process vari-
able also may be simultaneously recorded or monitored as
needed.
We will examine some simple process control functions
used in treatment plants. Remember that there are many ways
to accomplish process control and each system should be tai-
lored to meet the needs of your treatment plant. Usually there
are five parts to a control system.
1. PRIMARY ELEMENT OR SENSOR
The primary element or sensor is the instrument that
measures (senses) a physical condition or variable of inter-
est. A float or a thermocouple would be an example of a
primary element. We have just examined many of these
types of devices.
2 Set Point. The position at which the control or controller Is set. This is the same as the desired value ol the process variable.
-------
Instrumentation 455
WET
WELL
RECEIVER
(INDICATOR)
MOTOR ON
WET WELL
PUMP
TRANSMITTER
CONTROLLER
MEASURING
MEASURING
INSTRUMENT
(SENSOR OR PROBE)
Fig. 26.30 Instrumentation system.
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456 Treatment Plants
2. TRANSMITTER
A mechanical, hydraulic, pneumatic, or electrical system
that transmits a signal from the primary element to the re-
ceiving element, and/or control device.
3. RECEIVING ELEMENT OR RECEIVER
The receiving element receives the signal or output of the
primary element.
The millivolt meter connected to the thermocouple is an
example. Another example would be the pressure gage that
expresses the level in a diaphragm-box level system.
4. CONTROLLING ELEMENT OR CONTROLLER
The controlling element or controller is the device that
reacts to the changes in the measured variable. The device
may react pneumatically, electrically, mechanically, or hy-
draulically depending upon the application. An example of
this would be an electrical relay connected to the pressure
gage from a diaphragm box. Whenever the level reached a
previously determined set point, it would cause the pres-
sure gage mechanism to physically move. This movement
would trigger a relay to perform some secondary action,
such as turning off (switching off) the pump to the tank.
5. FINAL ELEMENT
The final element is the device that controls the energy
supplied to the process being controlled. The final element
could be the pump being turned-off (as in the previous
example) or it could be a more sophisticated system where
several valve openings would be modulated (changed).
In the previous pressure diaphragm box example, the
liquid in the tank is the controlled medium, the controlled
variable would be the liquid level in inches or feet (centime-
ters or meters), and the manipulated variable is the pump
being turned on or off. The set point would be a predeter-
mined maximum level the operator selects for the tank. The
set point also may be called the control point.
The control system may or may not include facilities to
visually or audibly monitor or record the process. Systems
which automatically control without indicating the control
process are called "blind" systems.
In summary, a control system is a series of devices which
measures, compares, controls an energy source, and finally
causes some action to be taken automatically to maintain a
previously established or desired control variable. The control-
ler may perform this function with or without visual indications
or verifications.
26.51 How Do Controllers Work?
The human body is an excellent example of a controller. Let
us examine how it works. In the very beginning of this chapter,
we used the example of a person opening a door. However, for
this example let us have a person desiring warm water for a
shower. In this example, the eyes and skin would be the pri-
mary sensing elements. The nerves would be the transmitter.
The brain would be the receiver and also measuring and con-
trolling elements and the hands would be the final element.
When a person first enters a shower, the eyes sense that the
shower water is off. The brain measures this message and
compares it with the set point of warm water. The brain then
activates the hand to turn on both the hot and cold shower
faucet handles. If the desired warm water comes out, no other
action is initiated since the skin signals (feedback) to the brain
that all is "OK." However, if the water is too warm or too cold,
the skin signals the brain which again measures the signal
from the sensing element (skin) and compares it to the desired
set point (warm water) and then signals the right or left hand to
adjust either the hot or cold water faucet. This feedback pro-
cess automatically continues until the desired set point is
reached.
Although we have defined what controllers (control ele-
ments) are and discussed how a system would operate, we
need to better define some of the terminology (name of) and
specific control methods.
OPEN AND CLOSED LOOPS
Control systems are divided into two general categories, (1)
open loop, and (2) closed loop systems. In an open loop sys-
tem, there is no information fed back to the controller to change
the control function. An example of this would be an automatic
lawn sprinkler system operated by a clock-timer. The sprinkler
system will operate at the set time every day and for the set
watering duration, regardless of whether it is raining or not. In
an automatic closed loop system, a moisture sensing device
would be added to the sprinkler control system which would tell
the controller not to water during a rain or when a moist ground
condition exists. In other words, a closed loop system incorpo-
rates some sort of feedback mechanism to modify the behavior
of the controller.
MANUAL CONTROL
The simplest control system is the manual control system in
which the operator senses, measures, and initiates any neces-
sary action. Assuming the operator is alert, it is the most flexi-
ble and sophisticated system available since it uses the mas-
sive resources and adaptability of the human brain. Our brain
probably will never be completely surpassed. However, one of
the weaknesses associated with manual control is the lack of
consistency or uniformity, since no two people think or act
alike, and the human senses are not adequate to monitor ail
process situations.
ON-OFF CONTROL
The thermostat control for heating is a good example of
on-off control. If the set point is set at 68°F (20°C), the control-
ler will turn the heater on at about 67°F (19°C) and shut it off at
about 69°F (21 °C). Another way to look at it is that the final
control element has only two positions (heater on or heater
off).
PROPORTIONAL CONTROL
The next more complex level in control systems is the pro-
portional control mode. This system has the capability to give
the final control element varying intermediate positions be-
sides on and off. The amount of control exercised is dependent
upon how much deviation (difference) exists between the set
point and the measured variable (OFFSET3). An example of
3 Offset (or Droop). The difference between the actual value and the desired value (or set point) characteristic of proportional controllers that
do not Incorporate reset action.
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Instrumentation 457
this would be three pumps connected to fill a tank. The propor-
tional control system would turn one pump on if the level
dropped to % depth; turn two pumps on if that level dropped to
Vfe depth; and turn on all three pumps if the level dropped to V«
depth. In other words, the degree of control exercised would be
proportional to the need, but the degree of control exercised
will not change until the measured variable changes. In this
example, three pumps would remain on as long as the level did
not exceed Vi depth.
PROPORTIONAL CONTROL WITH RESET
Proportional control with reset is a proportional control sys-
tem with the addition of reset control. Reset control may be
thought of as a correction device that cannot function by itself.
What reset control does is provide a correction signal to
minimize the amount and time the measured variable deviates
from the desired set point. As an example, if the control system
for a gas water heater had proportional control only, it would
regulate the amount of gas sent to the burners based on the
amount of water temperature deviation from the set point.
However, if we also had proportional control with reset, the
reset poriton would also fire an additional burner to reduce the
amount of time for the measured variable (temperature of wa-
ter) to reach the set point (water temperature).
PROPORTIONAL CONTROL WITH RESET AND DERIVATIVE
The next more complex control system adds a derivative
function to proportional control with reset.
The derivative function controls the rate at which the correc-
tive action takes place based upon the rate at which the meas-
ured variable is changing. Therefore, if the control system
senses (measures) a slow or small amount of deviation occur-
ring, the proportional control system would most likely handle
the situation. However, if a large or rapidly occuring deviation
was measured, the derivative control would attempt to in-
crease the action taken by the final element to minimize the
amount and time period that the measured variable was under
or over the set point.
Let's again use the person desiring warm water for a shower
as an example. The measuring elements are the eyes and
skin; the measured variables are the water temperature and
volume; the control element is the brain, and the final elements
are the hands. With on and off control only, the hot and cold
water would turn on or off. If we add proportional control, we
would turn the faucet on or off proportional to the amount of hot
or cold water we desired based on the temperature of the
shower water. If we add reset, we would control or turn the hot
or cold faucet in anticipation of the water temperature changing
due to the TIME LAG4 between the faucet and shower head.
Finally, if we add derivative control, we would control the rate
at which we turned the faucet handle. That is to say if we were
close to the desired water temperature we would turn the
faucet handle a small amount very slowly. However, if we were
being scalded with very hot water, we would most rapidly turn
the hot water off and the cold water on.
RATIO CONTROL
Ratio control is a closed loop system where two or more
variables are mixed or metered at a predetermined ratio. An
example of ratio control is the blending of two liquids such as
adding polymer to wastewater (Fig. 26.31). In this case, the
main line flow (wastewater) signal goes to the controller. The
controller sends a signal to the secondary flow-control valve
(polymer) to control the amount of polymer added. The flow of
polymer is also measured and a signal is sent back to the
controller to determine if the required amount is being added
(closed loop control).
So in summary, we have discussed in simple terms the dif-
ferent classes of controllers and how they are supposed to
perform. The actual working components of controllers are
complex and sophisticated and some of the features of control-
lers such as Bandwidth, Reset Rate, and others have been left
out for the sake of clarity. In addition, program controllers
which control on the basis of time and Cascade controllers
which use two controllers for a wider range of controls may
also be found in a treatment plant, but have not been included
in this discussion in an attempt to keep explanations as simple
and straight forward as possible.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 475.
26.5A List the five common parts to a control system.
26.5B What are the common types of control methods?
26.6 RECORDERS
26.60 What Are Recorders?
We have discussed "Indicators" (measuring elements)
which usually give some visual indication of process status.
However, in many cases it is necessary to keep a continuous
and permanent record of process variables. To obtain a con-
tinuous and permanent record, we normally use some sort of
recording device, commonly called a "Recorder".
A recorder is a device that records information onto a sheet
of paper that is moving at a specified speed. In this manner,
the value of the process variable at any given point in time may
be retrieved. Although this information could be taken manu-
ally by an operator reading a visual indicator and noting the
time, it would be a very burdensome procedure especially if
many process variables were to be continuously monitored.
Also, in some instances the frequency or location of monitoring
required may make it impractical to use operators. Recorders
are more practical than having operators take readings every
second or take readings in the middle of the night at remote
locations where there are no operators.
4 Time Lag. The time required for processes and control systems to respond to a signal or to reach a desired level.
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458 Treatment Plants
FLOW
TRANSMITTER
RATIO
CONTROLLER
FLOW TRANSMITTER
Fig. 26.31 Ratio control system.
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Instrumentation 459
26.61 Types of Recorders
There are two basic types of recorders found in a treatment
plant. One type uses a circular chart and the other type uses a
long strip of paper (Fig. 26.32). In both cases, the papers have
lines indicating the various levels of process variables and
time.
26.210 Circular Chart
In the circular chart, the process variable coordinates are
concentric circles radiating outwards and the time frame is
shown as arcs crossing the concentric circles. Circular flow
charts are sometimes referred to as polar or polar graphic
charts.
The chart is mechanically rotated at speeds between 15
minutes and 28 days per revolution, thus covering a wide
range of time periods. The size of the chart may vary between
3 and 12 inches (7.5 and 30 cm) in diameter. Circular charts
may use up to four recording pens. Each pen records a differ-
ent variable or measurement.
26.611 Strip Chart
The other commonly used type of recorder is called a "Strip
Chart Recorder." Strip charts use a long continuous piece of
paper to record data. The chart may move horizontally or verti-
cally with the time frame axis printed horizontally for horizontal
recorders and vertically for vertical recorders. The strip may be
up to 12 inches (30 cm) in width and available in various
lengths. The speed of the strip chart may be moved rapidly for
special recordings. The strip may be rolled up or "Z" folded
after being marked. Strip charts also have the capability of
operating twelve or more marking pens simultaneously.
26.612 Recording Media
Most circular or strip chart recorders use some sort of pen to
record the information. Numerous means of inking the pen
have been devised to prevent skipping or smearing of ink. In
some units ball point, felt tip, electrical stylus, or some other
marking device may be used.
26.613 Mechanisms
Recorder mechanisms will vary depending upon what is
being recorded. Some circular chart pressure recorders use a
modified Bourdon Tube mechanism and a spring-wound clock
motor to move the chart. This design does not require any
external power source and is suitable for field use. Other re-
corders require some source of power supply for the chart
drive and recording pen mechanisms.
26.7 INTEGRATORS OR TOTALIZERS
Integrators or totalizers are devices that add and/or multiply.
They are calculating devices which may operate continuously
or intermittently. Some of the devices are mechanically oper-
ated and others are electrically powered. They may tally up the
amount of digester gas produced or count the number of times
a booster pump is switched on. Integrators are sometimes
called summators or totalizers. A common example of an in-
tegrator would be the odometer on your car's speedometer.
Their basic use in a treatment plant is to sum up the amount
of liquid or gaseous flow. This is commonly done by updating a
digital counter. The operator usually subtracts the numbers
recorded from the previous time period to determine the quan-
tity that was produced or used.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 476.
26.6A What is the purpose of recorders?
26.6B List the two basic types of recorders found in treat-
ment plants?
26.7A What is the basic use of integrators or totalizers in
treatment plants?
Of 2 Of A \,e&bOH4>
I CUA^WfAriOM
Please answer the discussion and review questions before
continuing with Lesson 3.
-------
Ordering Instruction*
•U
o>
o
¦
tt
I
<5
TJ
0)
3
0)
Fig. 26.32 Circular and strip charts
fPanrtwon of BIF. a Unit ot G«n»rH Signal)
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Instrumentation 461
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 4 Lessons)
Chapter 26. INSTRUMENTATION
Please write the answers to these questions in your
notebook before continuing with Lesson 3. The problem num-
bering continues from Lesson 1.
4. How can the depth of water in a wet well be measured or
sensed? List as many different types of devices as you
can recall.
5. Why are recorders used instead of operators?
6. What is the purpose of a controller or a control system?
7. Why does an operator need to know the rate of inflow to a
treatment plant?
8. How does a thermocouple work?
9. Give an example of each of the following types of indi-
cators:
1. Fixed scale and movable indicator, and
2. Movable scale and movable indicator.
10. What is the difference between an open and closed loop
control system?
11. What is the basic use of an integrator in a treatment plant?
CHAPTER 26. INSTRUMENTATION
(Lesson 3 of 4 Lessons)
26.8 OPERATION
26.80 How Instruments and Controls Affect Plant
Operation
So far we have discussed what instruments and controls are
supposed to do. Now we will discuss how instruments and
controls are used in basic treatment plant operations.
Instrumentation and controls are necessary and often opera-
tions are performed automatically because:
1. Time is saved by not having an operator do the job,
2. An operator couldn't do the job.
3. Hiring an operator to do the job would be impractical or too
costly,
4. The job can be done better and faster automatically, and
5. An operator would not want to do the job.
The instrumentation and controls in a treatment plant per-
form a number of small jobs, each simple and repetitious,
which would be a nuisance, an annoyance, an inconvenience,
a source of errors, or a safety hazard lor an operator to perform
manually. You must be able to recognize when instruments
and controls are not doing their job properly and be able to take
command of the situation and do whatever is necessary to
make the instrumentation and control systems operate prop-
erly. Instruments and controls do not replace operators, but
serve as helpers working for the operator.
26.81 Preliminary Treatment
Depending upon the particular design of the treatment plant,
the preliminary treatment section could contain instrumenta-
tion monitoring and/or controlling the following functions:
1. Influent level (high-low levels),
2. Influent flow (rate),
3. Explosive gas detection (hydrocarbon, LEL),
4. Bar screen operation (On-Off),
5. Grit removal (On-Off),
6. Ventilation system (On-Off),
7. Valves and gates (closed, percent open),
8. Sump pump (On-Off),
9. High water alarm, and
10. pH.
In addition to the above list of instruments and controls,
some plants may have influent pump controls, specific ion
probes, dissolved solids concentration instruments, or special
application instruments or controls such as computers. How-
ever, they are beyond the scope of this introductory discussion
into the interface of treatment plant operations and instruments
and controls. More information may be obtained from the ma-
terial listed in Section 26.10, "Additional Reading."
1. INFLUENT LEVEL
Most treatment plants have some type of level detection
system in the influent sewer or channel leading to the bar
screens. The level detection system may be a simple high
or low water alarm system or the level detection system
may actually measure the depth of flow. Operators need to
know the depth of flow (or rate of flow) into the plant so that
the operator can determine how many bar screens or grit
channels to put on-line. Abnormally low flows could indicate
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462 Treatment Plants
an obstruction in the influent sewer line or worse yet, failure
in the sewer system. A high water alarm could indicate
blockage at the bar screens or perhaps only a partially
opened valve or gate hindering the downstream flow. In
small plants, an increase in level could mean that some
large industrial discharger was on-line and that treatment
processes would have to be adjusted accordingly.
High or low water level detection may be done with elec-
trical probes connected to visual or audible annunciators
(alarms). The alarm level is usually mechanically adjusted
up or down as needed.
The water level detection system may be a bubbler tube
system translating air pressure requirements into water
level or an ultrasonic proximity device sensing water level
by reflected sound waves. A simple stilling well containing a
float attached to a cable and indicator also may be used.
2. INFLUENT FLOW
One of the most important and necessary pieces of in-
formation provided by instruments is the rate of flow and
total flow in 24 hours.
The rate of flow (GPM or MGD) determines what and how
many units of treatment planf facilities must be on-line at
any one time. For example, if each of 3 grit channels is
designed to handle 30 MGD (113,550 cu m/day) and the
flow rate into the plant is 60 MGD (227,100 cu m/day), two
grit channels should be in service. If low flows at night
amount to 20 MGD (75,700 cu m/day) only one grit channel
should be in service. Finally, if during wet weather the flows
reach 80 MGD (302,800 cu m/day), all three grit channels
should be on-line.
The daily flow is used to calculate the amount (pounds or
kilograms) of suspended solids and organics coming into
the plant, and in and out of the various unit processes (as-
suming additional flow metering is not used). For example,
in determining the pounds of suspended solids loading on a
plant or treatment process we use the formula:
Susp. Solids
Loading, = Flow, MGD x SS Cone., mgIL x 8.34 lbs/gal
lbs/day
The pounds (kilograms) per day of solids coming into the
plant or the pounds (kilograms) per day leaving the plant
both require a knowledge of the flow rate:
S°lids Enta** = Ro MQD x ss in mg/i_ x 834 |bs/ga|
Plant, lbs/day
Solids, Leaving = F) MGD x ss 0uti mg/L x 8.34 ibs/gai
Plant, lbs/day
The same basic calculation is required to determine the
BOD (organic) load and removal efficiencies.
Without accurate flow rate information it would be very
difficult, if not impossible, to operate a modern treatment
plant efficiently. Accurate flow measurements and records
usually are required by regulatory agencies and most plants
continuously monitor the flow rate on a circular or strip
chart. Therefore, it cannot be stressed too strongly that
accurate and reliable flow measurements are necessary in
order to properly operate a treatment plant.
3. EXPLOSIVE GAS DETECTION
Some of the treatment plants that are subject to receiving
wastewater which contains spills of gasoline or other petro-
leum products have installed an explosive or combustible
gas detection instrument. This type of instrument is de-
signed to sense the Lower Explosive Limit (LEL) for hydro-
carbons mixed in air.
This type of instrument may be portable or permanently
installed. Usually it has some type of sampling pump that
passes the air sample across a combustible gas detection
cell, which activates an alarm when the LEL is approached.
In some permanent installations it may actually shut off
electric motors or other ignition sources before the LEL is
reached.
The major emphasis given to this type of instrumentation
is for safety. This instrument may or may not be useful in
detecting hydrocarbon concentrations which affect treat-
ment, but it is unquestionably necessary for safety reasons
if the treatment plant is subject to explosive gases or va-
pors.
4. BAR SCREEN OPERATION
Instrumentation or control for a bar screen may consist of
a simple in or out of service indicator with manual start and
stop switches. This is usually accomplished by connecting
a panel light to the bar screen rake or conveyor motor so
that the light is on when the motor is running and is off when
the motor is off or trips-out on overload. A light indicating
availability of power also may be provided. An alarm (usu-
ally audible) may be sounded if the bar screen motor trips-
out. Another indication of bar screen difficulties would be
the rising water level ahead of any plugged bar screen, and
subsequently a high water level alarm will sound.
The bar screens are one of the most important pieces of
equipment in a treatment plant since all of the plant flow
usually must pass through the bar screen. Any plugging or
obstruction of the screen usually will result in a lowered
water level downstream and an increased water level up-
stream. If the problem is not immediately resolved, flooding
may occur. Although it is possible to bypass the bar screens
in many plants, this usually leads to other problems later
since rags, trash, and other debris usually caught by the bar
screen hang up someplace later in the treatment process.
In most cases the number of bar screens on-line is con-
trolled by the plant influent flow. However, in special cases
of heavy rag loads or debris loads, additional bar screens
may be put on-line. The bar screenings hopper also may
have a level alarm detection device for high levels.
5. GRIT REMOVAL
The gravity design grit channels are very simple and reli-
able in operation. The instruments and controls associated
with this system may be an indicator showing whether the
grit collection drive system and pumps were on or off. Usu-
ally some alarm function also is available for motors tripping
out on overload.
The grit hoppers also may contain a grit level detection
device or a high grit level alarm. The grit level device usu-
ally works on the ultrasonic sound wave principle and is
similar to the influent water level sensing instruments. The
high level alarms may be electric probes, optical sensors or
ultrasonic sound wave instruments.
Usually, aerated grit removal systems would also feature
instrumentation to indicate and to control the amount of air
being used, and an alarm to indicate high air pressure or
loss of air. High air pressure would usually indicate plugging
of the grit aerators and loss of air or low pressure would
indicate leakage or low water level in the grit tank.
-------
Instrumentation 463
In most plants the number of grit tanks in service is a
function of flow and is manually controlled by the operator.
6. VENTILATION SYSTEM
Most preliminary treatment ventilation systems consist of
single-stage fans or blowers evacuating foul air to the acti-
vated sludge process, an odor removal system or direct to
the atmosphere. In most cases an indicator light shows
which fans are on-off and if power is available to the fans.
Alarms indicating motor trip out also may be provided.
A manometer or other low pressure gage also may be
used to show the air pressure in the air duct. This is one
means of determining whether the proper amount of foul air
is actually being removed. As an example, the fan motor
may be running but failure of the vee belts to the fan would
result in no air transport.
The ventilation system must be kept operating both for
the operator's safety and for minimizing the accumulation of
concentrations of moist or otherwise corrosive and toxic
gases.
7. VALVES AND GATES
Motor-operated gates and valves are usually monitored
to indicate whether they are opened, closed, or percent
open and if power (air or electrical) is available to the motor
operator. The valves and gates also may be remotely
opened or closed in many cases, as well as being con-
trolled locally.
Gates and valves control the flow of wastewater in a
treatment plant and their proper operation is absolutely es-
sential to efficient treatment plant operations. Motor-
controlled gates may be used ahead of bar screens and grit
tanks. They also usually feature limit switches that cut the
power off to the motor operators when a gate reaches the
top or bottom of its travel. Without this provision, the gates
or valves are likely to jam themselves open or closed or,
worse yet, some structural failure of the system could re-
sult. Large butterfly valves can be modulated (partially
opened or closed) to keep a constant flow rate to one bat-
tery (portion of a treatment process such as one clarifier) of
the plant and the remaining flow would be diverted to
another battery.
8. SUMP PUMP
Usually a sump pump has indicators showing power
availability and whether it is on or off. However, in some
cases a level sensing and control system will turn on a
second set of pumps if the flow is greater than that which
can be handled by one pump.
A common system could incorporate the use of a float
connected to a switch. When water enters the sump, it
raises the float which trips a switch starting the sump pump
motor. After the pump dewaters the sump, the float drops
tripping the switch and turning the pump off.
9. HIGH WATER ALARM
In basements or pipe galleries, high water alarm probes
are usually installed to alarm any possible flooding condi-
tions that may occur. The devices are usually electrical
probes that short out when touched by water and ring an
audible alarm.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 476.
26.8A List as many functions in the preliminary treatment
section as you can recall that could contain instrumen-
tation.
26.8B Why does an operator need to know the influent level
to a plant?
26.8C How can gasoline or other petroleum products be de-
tected in a wet well?
26.8D Why should wet well ventilation systems be kept
operating continuously?
26.82 Primary Treatment
Primary treatment usually consists of gravity sedimentation
tanks with facilities (flights) to scrape the settled organic solids
into a sludge hopper or sump; facilities to move floatable mate-
rials into grease or scum troughs or boxes; and weirs to control
the flow of the clarified effluent.
Usually an operator would be concerned with the following
instrumented activities in primary treatment:
1. Collector drive motor, ON-OFF — Power Available,
2. Flights, running — stopped,
3. Grease skimmers, ON-OFF — Power Available,
4. Primary sludge blanket depth, feet or inches (meters or
centimeters),
5. Primary sludge pumps, ON-OFF — Power Available,
6. Primary sludge draw-off valve, OPEN-CLOSED — %
Open,
7. Primary sludge flow (gpm or Usec),
8. High water alarm, Audible — Visible, and
9. Water level control valve, Closed — % Open.
Some treatment plants may have additional facilities which
are instrumented, such as primary influent or effluent channel
aeration, secondary treatment flow diversion or control sys-
tems, temperature probes, and others depending upon the
specific situation.
1. COLLECTOR DRIVE MOTOR
Depending upon the location of the power control panel
and the operations control room, the drive motors usually
have colored lights indicating that power is available, and
whether the motor is "ON" or "OFF". The motors usually
have "local" (on-site) on and off switches, circuit breaker
switches at the electrical power panel, and in addition may
have control switches in the central control room.
2. FUGHTS
A flight movement-detection system is used to ensure
that sludge is being continuously moved. In some instances
the collector chain may fail and scraping of the primary
(raw) sludge to the discharge point would cease even
though the collector drive motor would still be operating.
Unless flight movement failure is promptly detected and
the primary tank is taken out of service, dewatered and
washed down, serious odor problems could result as well
as transfer of septic wastes to the secondary treatment
system, which would negatively affect the process. The ac-
tual flight movement detection system may be as simple as
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464 Treatment Plants
a pivoted stick which moves everytime a flight strikes it. A
more sophisticated flight detection system uses a proximity
device which sends out an ultrasonic signal which is re-
flected everytime the flight passes by. An alarm signal
would be generated if a signal is not reflected back after a
specified time delay.
3. GREASE SKIMMERS
Grease skimmers are usually rotating blades driven by
an electric motor. Their function is to scrape and push float-
ables (grease-oils) into a trough for transport to further
treatment. In most cases the grease skimming operation is
relatively simple and reliable. Complexity of the skimming
operation depends on the amount of floatables being re-
moved in the primary tank. The skimmers may be operated
continuously or only once a shift depending upon the load
of scum and floatables.
The controls for the grease skimmer drive motors are
similar to those used for flight collector drive motors. There
are usually colored indicator lights showing power available
and whether the units are on or off. The drives may be
turned on and off locally, or remotely in the central control
room. In some installations, a timer may be incorporated
into the skimmer drive control to regulate the amount of
time the skimmers operate each period.
4. PRIMARY SLUDGE BLANKET DEPTH
One of the important measurements in the operation of
primary sedimentation tanks is the primary sludge blanket
level. Unless the proper level is maintained by controlling
the removal of sludge from the tanks, two situations could
occur. One problem develops when high blankets and poor
suspended solids and BOD removal efficiencies occur in
the primary tanks. The other is the removal of dilute sludge
or, in the worst case, primary wastewater instead of sludge
from the sludge hopper.
Sludge blanket depths may be manually measured by
using a hose and an aspirator. This is done by lowering the
hose into the tank until sludge comes out of the aspirator
and then measuring the length of hose used.
Another method of measuring blanket depths uses two
ultrasonic transmitters and receivers (probes), one for low
level and one for high level. The height of the low and high
level probes are mechanically set at the desired minimum
and maximum blanket levels. Whenever the sludge blanket
level drops below the desired minimum, a signal is gener-
ated which may turn on an indicator light, alarm or turn off
the sludge pump. Conversely, when the sludge blanket
level exceeds the maximum desired level, another indicator
light or alarm may come on or the sludge pump may be
turned on depending upon the specific design.
The probes operate on the principle that the denser
sludge mixture attenuates (decreases) the signal level be-
tween the ultrasonic transmitter and receiver more than that
which would occur due to wastewater alone. The changes
in signal level correspond to the sludge blanket density.
Under these circumstances, the lower probe should always
indicate an attenuated (decreased or diminished) signal
and the upper probe should indicate an unattenuated (un-
diminished) signal.
5. PRIMARY SLUDGE PUMPS
One of the most important and critical operations in the
primary treatment system is the proper operation of the
primary sludge pumps. Under-pumping can result in high
sludge blankets and poor removal efficiencies in the pri-
mary tanks. When this happens the suspended solids and
BOD capture efficiencies could be adversely affected.
Under the worst circumstances, when a pump does not
work, a situation similar to that of inoperative flights caused
by a broken collector chain would result. These circum-
stances could produce odors and septic wastes.
Over-pumping, on the other hand, can send very dilute
primary sludge to the anaerobic digesters and cause prob-
lems in digester operation by reducing the hydraulic deten-
tion time and temperature and also by wasting energy by
unnecessary pumping.
Again the basic controls for the pump motors would con-
sist of colored lights to indicate power availability, and
whether the motor was on or off. The control switches are
usually located next to the pumps and also may be dupli-
cated in the central control room.
The amount of pumping can be regulated by manually
turning the pumps on and off, by using a timer control to
turn the pumps on and off for a given number of minutes
each hour in sequence or by using a signal from a sludge
density meter control to turn the pumps off after the pumps
have been turned on manually or by timer sequence.
6. PRIMARY SLUDGE DRAW-OFF VALVES
In some treatment plants, primary sludge is removed
from the tanks by a HYDROSTATIC SYSTEM5 (gravity) in-
stead of using pumps. In these installations the controls
usually operate a motorized valve. Indicator lights usually
show whether a valve is open or closed. In addition, there
may be an indicator (meter) located in the control showing
what percent the valve is open with a switch to power the
valve open or closed. A mechanical indicator is usually at-
tached to the valve itself to indicate the valve position.
A timer system also may be incorporated to open each
valve a predetermined amount for a set number of minutes
each hour.
A sludge density meter also may be used to control the
closing of each draw-off valve. In this case when the pri-
mary sludge density drops below a pre-set limit, for exam-
ple four percent, a signal is generated closing that particular
valve and opening the valve in the next tank. This process
is continuously repeated.
7. PRIMARY SLUDGE FLOW AND PRESSURE
Most treatment plants carefully meter the amount of pri-
mary sludge that is withdrawn and sent to the anaerobic
digestion system. The amount of flow per day is used to
compute the volatile solids quantity and distribution to the
digesters. Improper metering could result in shock over-
loads to the digester which could upset the process. The
percent solids of the primary sludge and its volatile solids
content are usually analyzed in the laboratory. However, a
sludge density meter may be used to determine the percent
solids concentration and a historically valid number for the
percent volatile solids may be used in the calculations:
s Hydrostatic System. In a hydrostatic sludge removal system, the surface of the water in the clarifier is higher than the surface of the water in
the sludge well or hopper. This difference in pressure head forces sludge from the bottom of the clarifier to flow through pipes to the sludge
well or hopper.
-------
Instrumentation 465
Digester
Loading,
lbs VS/day
Prim SI 9al x 8 34 lbs x Tot So1, % x Vo1 So1, %
day gal 100% 100%
or
Digester = prjm si liters x 1 k9 x Tot Sol. % x Vol Sol, %
Loading, 'day 1 /_ 100% 100%
kg VS/day
The primary sludge flow is usually metered by a Venturi
meter, or a magnetic flow meter, although other closed-
conduit metering devices may be used. The signal from the
flowmeter is usually transmitted to a read out device (meter)
and flow recorder (circular or strip chart). An integrator is
usually included to determine the total sludge flow per day.
The flow readings may be indicated locally or in the central
control room.
Besides knowing the flow rate and total flow, the operator
also is interested in the primary sludge line pressure.
Higher than normal pressure readings usually indicate a
possible obstruction in the line or that the line is due for
routine cleaning. In most cases, a pressure gage is
mounted directly on the line; however, a pressure trans-
ducer may be used to transmit a signal to a remote indicator
in the central control room.
8. HIGH WATER ALARM
A high water alarm system is usually incorporated into
the primary treatment system to indicate potential or possi-
ble flooding. The alarm systems are usually identical
throughout the plant and they are discussed in the prelimi-
nary treatment section.
9. WATER LEVEL CONTROL VALVE
Modulating (regulating or adjusting) butterfly valves are
used in some plants to control the flow into each primary
tank in an attempt to equalize the flow and water level in
each tank. This will promote the most efficient use of the
tanks in service. When some tanks get more flow, their
suspended solids and BOD capture efficiencies usually
drop and cause an overall decrease in treatment efficiency.
The actual operation of a level control system usually
incorporates some type of level detection device (probes or
proximity device) which transmits a signal to a motorized
valve. The water level signal and percent opening of the
valve are calibrated together to obtain the desired water
level in each tank. If the water level is dropping, the valve
would open more and if the water level is rising, the valve
would close. The percent open of each valve is usually read
at the motorized valve operator and in most cases should
change with the change in flow.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 476.
26.8E List the instrumented activities that could concern an
operator in primary treatment.
26.8F How can movement of flights be detected?
26.8G How can sludge pumps be controlled or regulated?
26.8H Why are butterfly valves used in some plants to con-
trol the flow to each primary tank?
Of- L&&90U 3 0*A
I NftTGUMfeMfAtlOfO
Please answer the discussion and review questions before
continuing with Lesson 4.
-------
466 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
(Lesson 3 of 4 Lessons)
Chapter 26. INSTRUMENTATION
Please write the answers to these questions in your
notebook before continuing with Lesson 4. The problem num-
bering continues from Lesson 2.
12. Why are operations performed automatically by in-
strumentation and controls?
13. Why are accurate flow measurements and records impor-
tant?
14. How would you determine if a wet well ventilation system
was working?
15. What problems can develop if an improper sludge blanket
depth is maintained in a primary clarifier?
CHAPTER 26. INSTRUMENTATION
(Lesson 4 of 4 Lessons)
26.83 Activated Sludge Process
After primary treatment, wastewater can be further purified
by secondary treatment. One of the common forms of biologi-
cal secondary treatment is the activated sludge process. In this
process, dissolved and colloidal organic wastes not removed
by primary treatment are broken down and stabilized by bac-
teria in the presence of air.
In the activated sludge process, primary effluent is gently
mixed into a biological culture (mixed liquor suspended solids
or MLSS) by air diffusion in the aeration tank. After a period of
time, the mixture (MLSS) is sent to the secondary clarifiers
where the biological floe settles out. Part of the settled biologi-
cal floe (return activated sludge or RAS) is returned to the
aeration tank and the excess biological floe (waste activated
sludge or WAS) is sent to the head of the primary sedimenta-
tion tanks or to some other alternative sludge treatment pro-
cess. In order for the process to function properly and effi-
ciently, the operator must carefully control (balance) the
amounts of organic waste, biological floe, and air in the aera-
tion tanks. Since the operator usually has little or no control
over the amount of organic waste coming into the aeration
tank, the operator can only control (balance) the amount of
biological mass (MLSS) and air used.
Usually, an operator would be concerned with the following
instrumented activities in the aeration part of the process:
1. Primary effluent flow (MGD or cu m/day);
2. Aeration air rate (cfm or cu m/sec);
3. Aeration air pressure (psi or kg/sq cm);
4. Air compressor — ON-OFF, Power Available, Temperature
(°F or °C) of Air and Oil, Speed (rpm), % Vane Opening, Oil
Level, Oil Pressure and Blower Vibration;
5. Mixed liquor suspended solids (mg/L);
6. Dissolved oxygen concentration in the mixed liquor sus-
pended solids (MLSS) (mg/L); and
7. Final sedimentation tanks (Influent Flow, Return Activated
Sludge Flow (RAS), and Waste Activated Sludge Flow
(WAS).
Other laboratory information is also necessary to operate the
activated sludge process, for example, BOD and COD, sus-
pended solids, percent volatile solids, sludge settleability, and
sludge volume index (SVI).
1. PRIMARY EFFLUENT FLOW
In many cases the primary effluent inflow is the same as
the plant flow, except in cases where only part of the flow
receives secondary treatment, where there are process re-
cycle flows, or there are sidestreams such as cooling water
flows. Flow rate and 24-hour total flow are usually meas-
ured in terms of million gallons per day (cu m/day). Accu-
rate flow measurements and laboratory data are necessary
to determine the organic loading in the aeration system and
for information such as the air rate per gallon (cu m) of
wastewater treated.
Flow rates are usually recorded on a circular or strip chart
and the total flow is obtained from an integrator or totalizer.
The flow sensing, indicating and recording devices have
been previously discussed as part of preliminary treatment
instrumentation.
2. AERATION AIR RATE
The aeration air flow rate is usually measured in terms of
cubic feet per minute (cfm) or cubic meters per second (cu
m/sec). The air flow rate may be measured at each air
compressor or be read as a total from the main air header,
usually by a differential pressure metering device such as
an orifice plate.
-------
Instrumentation 467
Accurate air flow measurements are very important be-
cause oxygen (air) is one of the basic components in the
activated sludge process. Insufficient or under-aeration
process air will usually result in under-treatment and poor
effluent quality; while excess or over-aeration will waste
energy and unnecessarily stress and wear the air compres-
sion system.
In most conventional activated sludge treatment plants,
air is supplied at the rate of 1 to 2 cubic feet of air per gallon
(0.13 to 0.26 cu m of air per cu m) of wastewater being
treated. For example, in a 5 MGD plant the air rate may be
6,000 cfm (2.8 cu m/sec). To determine the air rate per
gallon of wastewater treated, perform the following calcula-
tion:
Air Supplied,
cu ft/gal
Total Cubic Feet of Air per Day
Total Gallons of Wastewater Treated per Day
6000 cu ft air/min x 1440 min/day
5,000,000 gallons wastewater/day
1.728 cu ft air/gallon treated
Total Cubic Meters of Air per Day
or
Air Supplied,
cu m air
cu m water Total Cubic Meters of Wastewater Treated per Day
_ 2.8 cu m/sec x 60 sec/min x 1440 min/day
19,000 cu m/day
= 12.7 cu m air/cu m water
= GtP p av
\ lOHt, Of w
it Atfi/m
tz{7A
3. AERATION AIR PRESSURE
Besides the air flow rate, another important measure-
ment is air pressure. Abnormally high or low air pressures
usually indicate clogged air diffusion devices or air leaks.
Pressure gages are usually placed at the air compres-
sors and also downstream at main aeration lines. A differ-
ence in pressure between the two points would indicate
head losses (pressure losses) due to partially closed valves
or other restrictions, such as before and after air filters.
Most aeration systems operate at about 7 psig (0.5 kg/sq
cm) to overcome the static head on submerged diffusers.
Bourdon tube pressure gages are commonly used to
measure pressure directly. The read-out of pressure is
usually transmitted and also displayed in the control room
by use of pressure transducers. Unlike air flow, air pressure
is usually fairly constant and usually is not automatically
recorded.
4. AIR COMPRESSOR: ON-OFF, POWER AVAILABLE,
TEMPERATURE (AIR AND COMPRESSOR OIL), SPEED,
% VANE OPEN, VIBRATION, RUNNING HOURS, OIL
LEVEL, AND OIL PRESSURE
Besides the air flow, pressure and temperature, it is nec-
essary to know other facts about the air generation system.
In multi-air compressor systems, a read-out (from either
TV screen (CRT, page 454) or computer print-out) is pro-
vided to show what compressors are operating and if power
is available (for electricity driven compressors) or the status
of other fuel supply systems (for example, how much diesel
fuel is in the storage tanks). Available fuel volumes may be
measured by a float or other sensing devices which will
indicate the amount of fuel remaining. Also, air compressor
failure or power failure alarms are usually incorporated into
the system. As discussed previously for electrically oper-
ated equipment, the ON-OFF indicator lights are wired into
the power supply. Liquid fuel volume indicators usually
have float or similar types of level indicators that are cali-
brated to read in terms of gallons (cubic meters) or fractions
of tank capacity.
Another important measurement in air compression op-
eration is the temperature of both air and lubrication oil.
Excessive compressed air temperatures may indicate an
open bypass valve or other possible mechanical malfunc-
tions. Excessive lubrication oil temperatures may indicate
motor overload, low oil levels or inoperative oil coolers.
High oil temperatures usually trigger alarm circuits and also
may automatically shut the compressor off in some in-
stallations.
Ambient (surrounding or room level) air and compressed
air temperatures may be measured directly by the use of
bimetallic thermometers or capillary bulb thermometers in
the air stream. However, remote reading thermometers will
commonly use some sort of a thermocouple for gas or oil
temperature sensing.
Compressor speed in terms of RPM is used by the
operator to determine if the proper amount of air flow and
pressure is resulting from a given RPM for engine-driven
compressors. Most air compressors operate efficiently
within given RPM ranges; however, low ranges are very
inefficient while high speeds may damage the equipment or
cause the motor to overheat.
The RPM is usually measured by a mechanical drive
tachometer, electrical generator tachometer, electrical im-
pulse tachometer, or photo electric tachometer. All except
the mechanical drive tachometer allows for remote signal
transmission and read-out of RPM.
Constant RPM electrically driven air compressors mod-
ulate the inlet air vanes to control air discharge output. This
information is usually read as percent opening of the inlet
vanes.
Some compressors, usually electrically driven, are
equipped with vibration sensing devices. These devices are
designed to sense displacement, velocity, or acceleration.
They are basically a safety device to shut down the com-
pressor and initiate an alarm if the compressor or motor
starts to vibrate excessively due to any unbalanced forces
or loose floor connections.
Both internal combustion and electrically driven air com-
pressors usually have some sort of Hour-Meter to deter-
mine how many hours each unit has operated since the last
repair or overhaul. To equalize wear, compressors are usu-
ally rotated after so many hours of operation. Also the
Hour-Meter can be used to schedule preventive mainte-
nance functions such as oil changes.
Most Hour-Meters are a form of electric clock that regis-
ters the number of hours on a totalizer. The hours of run-
ning time may be indicated at the compressor control panel
and/or remotely indicated in a central control room.
Electrically driven compressors also usually have an
ammeter read-out for indicating power consumption. The
-------
468 Treatment Plants
ammeter also may be set to signal an alarm and/or shut off
the compressor when it is overloaded.
Another important measurement is that of oil level. The
measurement may be manually performed by a dip stick,
read from a sight glass, or by use of other level sensing
devices (electronic or ultrasonic systems) which may ini-
tiate alarms if the oil level is too high or too low.
5. TEMPERATURE OF MIXED LIQUOR SUSPENDED
SOUDS (MLSSj
Temperature changes greatly influence all biological pro-
cesses. You must carefully monitor the temperature of the
mixed liquor in the activated sludge process. The biological
metabolism rate (activity) increases with temperature in-
creases and decreases with decreasing temperature. Con-
sequently, more biological mass is required during cooler
temperatures to obtain the same degree of treatment.
Therefore, you must increase the MLSS concentration dur-
ing the cooler months and decrease it during the warmer
months in accordance with the particular conditions at the
plant.
7. The instrumentation and control of the final secondary
sedimentation tanks are very similar to the primary
sedimentation tanks. For all practical purposes, the follow-
ing operations are identical:
The temperature readings may be taken and recorded
manually or they may be continously monitored and re-
corded on a chart. The temperature may be sensed by any
of the previously described temperature sensing devices.
6. DISSOLVED OXYGEN CONCENTRATION
In some activated sludge plants, dissolved oxygen (DO)
meters are provided to monitor the level of dissolved oxy-
gen in the aeration mixed liquor suspended solids.
The oxygen level in mg/L is monitored to ensure that
adequate oxygen (air) is being provided in the aeration
tanks. A dissolved oxygen level of 1 to 4 mg/L is usually
maintained in the aerators, depending upon the particular
requirements of the given activated sludge process.
The oxygen level is measured by a probe and meter. The
probe may be portable or permanently installed in the
aerator. Single or multi-probes may be installed in one or
more aerators. At the present state of development, most
00 meters are basically lab instruments and should be
treated with care. The probes require frequent cleaning and
the meters should be calibrated routinely to ensure their
accuracy.
In some plants the output from the DO meters controls
the aeration blowers (compressors) thereby theoretically
optimizing the air flow rate to the biological culture in the
aeration tanks. Remote oxygen level read-outs are usually
indicated and recorded along with the corresponding air
rates.
$
-Cm' -
a. Collector drive motor,
b. Sludge blanket depth,
c. Sludge pumps,
d. Sludge draw-off valves, and
e. High water alarm.
The operation of the sludge pumps for return activated
sludge (RAS) and metering may vary slightly from primary
sludge pumping and metering since usually only part of the
flow (25 percent up to 100 percent) is returned to the aera-
tion tank; the remaining waste activated sludge (WAS) is
usually routed back to the head of the primary tanks or to
some other sludge handling process.
Consequently, the total RAS flow and WAS flow may be
metered or the RAS flow to the aeration tanks and the WAS
flow may be monitored. In either case, it is important to
have accurate measurements of RAS and WAS flows to
calculate the return rate, and the Mean Cell Residence
Time (MCRT).
A turbidimeter is used in some plants to monitor the
effluent quality from the secondary sedimentation tanks. In
on-line turbidimeters, a pump directs a small stream of final
effluent across a light beam. The scattering or attenuation
of the light beam due to particles in the effluent is measured
and indicated in turbidity units. The turbidity may be con-
tinuously monitored or measured from grab samples
analyzed in the lab. The process used is commonly dictated
by the legal monitoring requirements specified in the
NPDES permit for the plant.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 476.
26.81 How is air flow measured?
26.8J Where are air pressure gages usually placed in the
aeration system of the activated sludge process?
26.8K How are oil levels in air compressors measured?
26.84 Anaerobic Sludge Digestion
The settled organic solids from the primary sedimentation
tanks and the waste activated sludge from secondary treat-
ment require further processing. One common method of pro-
cessing and treating the sludge is "anaerobic sludge diges-
tion." Under ideal environmental conditions, anaerobic bac-
teria stabilize and convert most of the organic matter into
methane gas, carbon dioxide gas and water. In this airless
process, you must carefully control the amount and rate of
-------
Instrumentation 469
sludge feeding to the digester, the operating temperature of
the digester, and the rate of change of temperature. Excessive
organic loadings or temperature changes adversely affect the
anaerobic bacteria and can cause an upset of the biological
treatment process.
The following activities are usually instrumented or con-
trolled:
1. Raw sludge feed controller,
2. Digester tank level and alarms,
3. Digester sludge flow,
4. Digester gas flow,
5. Digester gas pressure,
6. Digester sludge temperature,
7. Digester heating system (steam, hot water),
8. Digester transfer and recirculation pumps,
9. Digester gas quality,
10. Combustible gas alarm, and
11. Digester gas mixing compressor.
1. RAW SLUDGE FEED CONTROL
Feeding the digester(s) with primary sludge may be a
relatively simple operation in small primary treatment
plants with only one or two digesters. In these situations
the primary sludge is intermittently fed to the digester
whenever the sludge pumps are activated. The sludge
9olids and volatile solids concentrations are analyzed in
the laboratory. The flow may be metered or estimated
from the pump curves and time of pump operation. Load-
ings are calculated on the basis of solids concentrations
and flows. In all systems the pumping is either controlled
by the sludge blanket depth or sludge concentration.
However, in larger plants with many primary tanks and
digesters, more sophisticated controls are necessary
since large volumes of primary sludge must be continu-
ously distributed to many digesters. In addition, not all
digesters are loaded at the same rate since individual di-
gesters may have varying operating capacities. For
example, a modern, clean, heated, and gas-mixed diges-
ter may be loaded between 0.1 and 0.2 pounds of volatile
solids per day per cubic foot (1 and 2 kg VS/day/cu m) of
digester capacity. Uncleaned, unmixed digesters may be
able to handle only 0.05 lbs VS/day/cu ft (0.5 kg VS/day/cu
m). Consequently, a well operating and closely controlled
primary sludge feed system is essential.
As an example, a primary sludge feed system would
pump all of the primary sludge to one battery (row) of
digesters for a set period of time or for a set volume such
as so many gallons (cubic meters). In either case, the
calculations would be based on the pounds (kilograms) of
volatile solids pumped during that time period to that bat-
tery. Next, each digester in that battery would be fed the
desired amount of sludge (pounds or kilograms of volatile
solids) controlled by the amount of time a valve to that
digester was open, the percentage opening of the valve,
or the gallons (cubic meters or liters) of sludge metered
into that particular digester. The gallons (cubic meters or
liters) of sludge metered in the last case may be monitored
by a flow meter or by the change in digester tank level.
Therefore, in its most basic form, much of the control is
done manually by the operator. In the most automated
form, the control is performed by SOFTWARE PRO-
GRAMMING6 from a computer. In most cases, each bat-
tery of digesters is loaded in sequence or by level priority
continually around the clock.
Ideally, the control system would permit continuous
loading of all digesters in proportion to the pounds of vol-
atile solids being sent to the digestion system. Such a
system would proportion a part of the total primary sludge
flow to each digester by having a flow meter and automatic
control valve at each digester. In addition, the digested
sludge flow withdrawal rate would also be automatically
controlled to maintain a set or desired level in the digester.
In order to obtain this level of control, a process control
computer would be necessary and discussion of such a
system is beyond the scope of this chapter.
2. DIGESTER TANK LEVEL AND ALARMS
Almost all digester tanks have some means of deter-
mining their liquid level. Some of the older digesters use
simple overflow pipes. An example is the opening of an
overflow pipe at the desired digester level and pumping
primary sludge into the digester until digested sludge over-
flows from the pipe. Other systems use a variable-level
swing overflow pipe in which the discharge level of the
pipe is raised or lowered to the desired level and primary
sludge coming into the digester automatically displaces or
forces digested sludge out of the overflow.
These examples obviously require the operator to be at
the digester to determine or change the level. Other level
control systems may use a pressure transducer calibrated
to translate liquid hydrostatic pressure into feet (meters) of
sludge in the digester. The tank level may be indicated
and recorded in the control room from where it would also
be possible to raise or lower the level by operating pow-
ered remote control valves.
In addition to digester tank levels, most systems use
some type of high or low level alarm. The alarms may be
triggered by any of the previously discussed level sensing
instruments or software sensing devices which detect
when levels are too low or too high. A low level alarm
could indicate that a digested sludge valve was accidently
left open, a possible control system malfunction, or a pos-
sible leak or break somewhere in the system. A high level
alarm could indicate plugging of the overflow, a control
system malfunction, or an inoperative digested sludge
withdrawal system.
3. DIGESTED SLUDGE FLOW
The digested sludge is not metered in some plants be-
cause the operators assume that digested sludge flow
equals the primary sludge flow. For small plants with one
or two digesters, this assumption is probably acceptable.
However, in large plants with large capacities it is impor-
tant to know the digested sludge flow pattern. This permits
monitoring of the rate and frequency of withdrawal and
provides a verification of the primary sludge flow. Flows
may be monitored from each tank, battery of digesters, or
total digested flow.
Venturi meters or magnetic flow meters are commonly
used to measure the digested sludge flows. Flow data are
usually recorded, especially in situations where the di-
8 Software Programs. Computer programs designed and written to monitor and control wastewater treatment processes or other processes.
-------
470 Treatment Plants
gested sludge receives additional treatment, such as de-
watering or chemical conditioning. The flow rate and total
flow are usually recorded at the control room.
4. DIGESTER GAS FLOW
Gas production from each digester is monitored daily.
This information is used to analyze the volume of gas
production per pound (gram or kilogram) of volatile solids
added and destroyed. Gas production is also a strong
indicator of digester performance with low gas production
usually indicating some type of problem.
Since digester gas pressure is relatively low, about 8 to
12 inches (20 to 30 cm) of water, metering systems with
very low head losses must be used. Also, the meters must
operate over a fairly wide range of gas flows. Positive
displacement meters and turbine meters are commonly
used to measure gas flows. The total gas production may
be manually determined from daily mechanical integrator
readings of the gas production rate, or it can be automati-
cally monitored continuously and recorded in the control
room.
5. DIGESTER GAS PRESSURE
Digester gas pressure must be monitored to ensure that
the safety valves are operating properly (fixed cover diges-
ters). Although the gas pressure is relatively low, usually 8
to 12 inches (20 to 30 cm) of water, higher pressures may
seriously over pressure the digesters and a low pressure
may indicate gas leakage from the system.
The gas pressures in many digesters are monitored by
the use of water-filled manometers. Since the gas pres-
sure is relatively constant, it is usually not automatically
monitored and recorded, but visually checked by an
operator during every shift.
6. DIGESTER SLUDGE TEMPERATURE
One of the most important operating controls is digester
temperature. To achieve efficient digestion, the tempera-
ture should be maintained near 95°F or 35°C (mesophilic
operations). Therefore, nearly every digester has some
type of built-in temperature sensing device. Ther-
mocouples are commonly used with remote readings in
the control room. Temperatures are usually continuously
recorded on a circular chart. Manual temperature readings
may be made by placing a thermometer in sludge running
into the sample sink.
7. DIGESTER HEATING SYSTEM
Assuming that the digesters are heated either by direct
steam injection, steam eductors, or by steam-heated ex-
changers, some means of indicating the rate of steam flow
and the total pounds of steam used per day is necessary.
Usually, steam pressure is also monitored. Steam to each
digester is usually controlled by remotely controlled steam
valves. The percent opening and length of time each valve
is opened is determined by the temperature in the diges-
ter. A fully automated digester heating system would use a
process controller to sense the difference between the
existing digester temperature and the set point tempera-
ture and route steam (heat) according to the needs of
each digester. This process controller would also control
the steam production of the steam boiler to match the
digester heating needs.
8. DIGESTER TRANSFER AND RECIRCULATION PUMPS
Transfer and recirculation pumps are an important part
of anaerobic sludge digestion operation. The pumps are
used to mix the digester contents, transfer sludge between
digesters, pump out digested sludge and pump supernat-
ant out of digesters. Several pumps are usually intercon-
nected to maximize flexibility of operations.
The instrumentation and control of the transfer or recir-
culation pumps are very similar to primary sludge and re-
turn activated sludge pumping operations.
9. DIGESTER GAS QUALITY
In some plants, automatic means of analyzing digester
gas quality is provided. Either the carbon dioxide (COz) or
methane (CH4) gas content is analyzed and the read-out
is usually given in percent carbon dioxide or methane.
The percent of carbon dioxide or methane in digester
gas is usually a good indicator of the status of the biologi-
cal process. Digestion gas usually contains 60 to 70 per-
cent methane and the remainder is considered to be car-
bon dioxide gas. Upset digesters tend to have a much
lower percentage of methane gas and a higher percent-
age of carbon dioxide gas, for example, 40 to 50 percent
CH4 and 50 to 60 percent C02.
The digester gas quality can be measured at the diges-
ter itself or a small side stream of digester gas may be
pumped to the analyzer from the digester or the main gas
line. In most cases, digester gas tends to be saturated with
moisture and some type of moisture trap or drier is neces-
sary to protect the analyzer. Also, some digester gases
tend to have significant amounts of corrosive hydrogen
sulfide (H2S) gas and a means of absorbing the H2S also
may be necessary.
A gas chromatograph may be used to perform the gas
analysis. Instruments like the gas chromatograph and
spectrophotometers are basically laboratory instruments
and require significant skill and knowledge to operate and
maintain them.
10. COMBUSTIBLE GAS ALARM
In plants where there are tunnels or other confined
spaces, a combustible gas alarm may be provided. This
instrument is essentially identical to the explosive gas de-
tection instrument described in the preliminary treatment
section. This device is calibrated to activate an alarm at a
set Lower Explosive Limit (LEL). If the tunnels or other
spaces being monitored do not have a good ventilation
pattern in which to place the detector, a sample pump may
be built in to pass air over or through the detection device.
The purpose of the instrument is to detect any explosive
gas leaks or to detect the generation of explosive gases in
confined spaces for the safety of the plant and operators.
11. DIGESTER GAS MIXING COMPRESSOR
In most modern treatment plants, some form of digester
gas mixing is usually provided. Gas mixing is one of the
more popular means of mixing the digester. Digester gas
compression is similar to aeration air compression with the
following differences: (1) the volume is much less, (2) the
pressure is usually higher, (3) digester gas tends to be
saturated with moisture and contain particulate impurities,
and (4) for higher pressure, reciprocating compressors
may be used instead of centrifugal or rotary vane types.
-------
Instrumentation 471
As a rule, the gas mixing volume and pressure remain
constant and consequently the load on the compressor
and its driver also remain constant. Depending upon the
design, individual compressors may be provided for each
digester, or several manifolded together. In either case
ON-OFF, power availability, flow, pressure, and alarm
functions are usually provided.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 476.
26.8L List the activities that are usually instrumented or con-
trolled in the anaerobic sludge digestion process.
26.8M Under what circumstances would digested sludge flow
be recorded?
26.8N How are temperatures measured in an anaerobic
sludge digester?
26.80 What is the purpose of digester transfer and recircula-
tion pumps?
26.9 ROUTINE MAINTENANCE AND
TROUBLESHOOTING
So far we have discussed how instruments and controls
work and how they are used in treatment plant process control.
Next we will discuss what the operator's role is in maintaining
and troubleshooting the instruments and controls. As we have
already pointed out, though, unless the operator is qualified,
the repair of most types of instruments should be assigned to a
specialist in the field. There are many practical and important
things an operator can and must do to keep the system oper-
ating efficiently.
First, it is important for the operator to recognize that like
other equipment in a treatment plant, instruments and controls
need attention such as cleaning, adjusting, calibrating, repair-
ing and/or replacement from time to time. In most cases, in-
struments and controls are more fragile than other pieces of
treatment plant equipment and must be given appropriate care
whenever handled.
Before we begin routine maintenance or troubleshooting the
instruments and controls, it is essential that the operator be
familiar with the process and the instrumentation and/or con-
trols used to control the process. If you don't know what you're
doing, leave it alone and request assistance!
A routine maintenance program will minimize instrument and
control failures. The routine maintenance program should be a
written, prescribed procedure defining what the operator is re-
sponsible for and what the instrument specialist is responsible
for and who will do what and when. Each plant with its different
processes, instruments, controls and people will have a unique
routine maintenance program. The maintenance program
should provide for a file on each instrument and control sys-
tem. Date of purchase, date of installation, installer, make, and
model-serial numbers should all be recorded, along with any
maintenance manual, or technical specifications supplied with
the equipment. Provisions for on-the-job and off-the-job train-
ing should be sought whenever possible.
Based on the manufacturers' recommendations and plant
experience, spare parts, plus any special tools should be pur-
chased ahead of time and properly stored. Whenever possible,
appropriate areas for instrument maintenance and storage
should be dedicated for this purpose; areas with high humidity
and corrosive gases are to be avoided.
Before troubleshooting for instrument and control failures,
the operator must make certain that the difficulty is truely due
to defective instrumentation or control and not due to some
quirk in operations. There have been cases where so-called
instrument failures have been traced back to simple things like
unplugged power supplies, the pneumatic air receiver left out
of service after being drained of water and similar types of
minor problems.
Before starting work on the system, safety precautions must
be observed, such as unplugging electrically connected in-
struments and controls. Even though they may be low voltage,
there is always the possibility of shock to the operator and/or
damage to the equipment. Also, care must be exercised when
handling toxic materials such as mercury or flammable mate-
rial such as alcohol which could be encountered when working
with manometers. Care also must be exercised with certain
types of density meters that use a radioactive cell which by law
can only be handled by an appropriately licensed technician.
Such devices are required to be identified and labeled accord-
ingly.
Additional precautions must be observed whenever you in-
tend to work on or remove instruments and controls directly
attached to live or operating processes. For example, before
you remove a pressure gage from an air or water line, be sure
that the service has been turned off. Before you turn the serv-
ice off, be sure it will not adversely affect the system or some-
one else.
In other words, be sure that others are advised of your in-
tended scope of work. They must be notified or warned of what
you are going to do, when you are going to do it, how long it will
take, and what will be affected. Therefore, just like any other
piece of plant equipment, instruments and controls being
worked on should be "tagged-out". This will advise others that
the instruments and controls are out of service and must not be
used.
The "tagged-out1' instruments and controls (Fig. 26.33) must
also be "logged" in the shift or daily operations log book. You
must note alarm functions that are out of service, so that other
means may be used to detect out-of-limit conditions. The use
of "Good Communications" and "Common Sense" will avoid a
lot of unnecessary "Headaches."
Table 26.2 contains some guidelines on what maintenance
and trouble-shooting duties an operator can generally perform.
-------
472 Treatment Plants
Fig. 26.33 "Tagged-out" controls
-------
Instrumentation 473
TABLE 26.2 MAINTENANCE AND TROUBLESHOOTING DUTIES
Instrument - Device Maintenance - Service by the Operator
1. THERMOMETERS
Liquid or 1. Check for leakage or breakage
Capillary 2. Clean off surface
3. Replace with spare
Bimetallic 1. Clean sensing surface
2. Replace with spare
Thermocouples 1. Check for loose connections, corrosion, or
damaged insulation, and repair as neces-
sary
2. PRESSURE GAGES
Manometer 1. Clean and/or add fluid
2. Check and tighten connections
Bourdon Tube, 1. Check for sticking or damage
Diaphragm or 2. Replace with spare
Bellows
3. LEVEL INDICATORS
7. METERS (Also see Chapter 15, Section 15.4, "Flow Mea-
surements - Meters and Maintenance")
Venturi
Orifice Plate
Magnetic
Weirs
1. Check purge water
2. Check flow zero
3. Clean taps with bayonet, if appropriate
1. Check flow zero
2. Clean taps with bayonet, if appropriate
1. Check flow zero
2. Check power supply
1. Clean weir face
2. Check level Indicator
Float
Probes
Electric
Capacitance
Ultrasonic
Bubbler Tube
1. Clean float
2. Check and clean cable and pulley; lubricate
as necessary
8. ALARM FUNCTIONS -
HIGH TEMPERATURE,
PRESSURE & LEVEL
Lights 1. Test bulb, change as necessary
Audible Signal 1. Test for sound
9. CONTROLLERS
Check and clean connections
Pneumatic
1. Check for air supply availability
Clean probe if possible
Check power supply (fuse)
Electronic
1. Check for power availability
Timers
1. Check to see that they are working
Check air supply
Check air tube and clean
Auto Manual
1. Switch from one mode to the other, to see
that they work
Diaphragm Box 1. Clean
or Sight Tubes
4. DENSITY METERS
Optical 1. Clean (flush) sensors with water
Ultrasonic 2. Check "zeroing" with water
Radioactive 3. Check power supply (fuse)
5. RPM INDICATOR
TACHOMETER
10. INTEGRATORS
Mechanical or 1. Check power supply
Electrical
11. OTHER INSTRUMENTS
LEL Probe
1. Check zero setting
2. Check alarm function
3. Test with gas, if appropriate
Cable Drive
1.
Check cable, clean, lube, tighten
DO Probe
1.
Clean probe
D C. Generator
1.
Check terminal connections
2.
Check for loose connections
2.
Check drive coupling
pH Probe
1.
Clean probe
Strobe
1.
2.
Check battery or power supply
Check for burned out bulb
Turbidimeter
2.
1.
Check electrolyte
Check meter zero
Pulse Detector
1.
Check terminal connections
2.
Check pulse sensor clearance
CH4 or C02
1.
Check for gas supply
Analyzer
2.
Check for power supply
VISUAL READ-OUTS
Circular or
Strip Chart
1.
2.
Change charts
Check for irregular movements
OTHER CONTROLS -
INDICATORS
3.
Check power supply
On-Off Lights
1.
Test bulbs
Pens
1. Clean pen
2. Refill or replace ink cartridge
Percent Open- 1. Manually check indicator against valve
Closed opening
-------
474 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 476.
26.9A What kind of attention do instruments and controls re-
quire?
26.9B What information should you provide other operators
before you start to work on an instrument or control?
2. INSTRUMENTATION FOR WASTEWATER TREATMENT
SYSTEMS, by J.S. Samkoff, Technical Reprint IW-113,
Ecodyne Industrial Waste Treatment Division, 2720, U.S.
Highway 22, Union, New Jersey 07083.
3. OPERATORS MANUAL FOR AUTOMATION AND IN-
STRUMENTATION, M-2, American Water Works Associa-
tion, 6666 West Quincy Avenue, Denver, Colorado 80235.
Price $7.00 to members; $14.00 to others.
26.10 ADDITIONAL READING
1. INSTRUMENTATION IN WASTEWATER TREATMENT
PLANTS, MOP 21, Water Pollution Control Federation,
2626 Pennsylvania Avenue, N.W., Washington, D.C.
20037, 1978. Price $6.00 to members; $12.00 to others.
26.11 ACKNOWLEDGMENT
Material in this chapter was reviewed by Norman Ole
Thompson.
6MP Qt L&&OHA 09-A
Please answer the discussion and review questions before
working the objective test.
DISCUSSION AND REVIEW QUESTIONS
(Lesson 4 of 4 Lessons)
Chapter 26. INSTRUMENTATION
Please write the answers to these questions in your
notebook before continuing with the objective test. The prob-
lem numbering continues from Lesson 3.
16. Why are accurate air flow measurements very important in
the activated sludge process?
17. How is the air compressor speed in RPM measured?
18. What precautions should be taken to ensure accurate dis-
solved oxygen readings in aeration tanks?
19. A low level alarm in a sludge digester could indicate what
types of problems?
20. Why must the digester gas pressure be monitored in fixed
cover digesters?
21. Where should combustible gas alarms be installed?
22. What special safety hazards may be encountered when
maintaining and troubleshooting instruments and con-
trols?
PLEASE WORK THE OBJECTIVE TEST NEXT.
-------
Instrumentation 475
SUGGESTED ANSWERS
Chapter 26. INSTRUMENTATION
Answers to questions on page 430.
26.0A Plants are being designed and constructed with
sophisticated instrument and control systems be-
cause of tougher discharge and monitoring require-
ments and also to help operators do their job.
26.0B An instrument is a measuring device.
26.0C A control is a device or series of devices that effect
some change due to some other change in conditions.
Answers to questions on page 434.
26.0D Instruments are used in place of or to assist the
operator's sense of sight, smell, touch and hearing
because of the need for:
1. Accuracy of the measurement,
2. Repeatability of the measurement,
3. Sensitivity of the measurement, and
4. Permanence of the measurement.
26.0E The sensitivity of a measurement is the ability to
measure the smallest or largest value necessary.
26.0F An instrument's accuracy depends on the preciseness
or exactness of the measurements. Repeatability is
the ability of an instrument to measure something
again and obtain the same answer that resulted previ-
ously.
Answers to questions on page 438.
26.1A Instruments are used instead of our human senses
because they provide a more accurate, consistent,
sensitive and permanent means of monitoring
(measuring) treatment processes.
26.1 B Instruments measure temperature, pressure, flow,
level, density, velocity and analytical measurements
(physical, chemical and biological).
26.1C Flow can be defined as a "flow rate" (volume passing
a point at any given instant or time period) or as a
"total flow or volume" (total volume passing a point
within a specified time period).
Answer to question on page 443.
26.2A Typical units of measurement for the listed parameters
in both English and metric units.
Parameter
English
Metric
1. Temperature
°F or °R
°C or K
2. Pressure
psi or psf
in. H,0 or Hg
kg/sq cm
or kg/sq m
cm H,0 or Hg
3. Flow
Liquids (volume)
Gases (volume)
Solids or Liquids
(weight)
Solids (volume)
cfs, GPM or MOD
elm
Ib/hr
cu ft/day
or cu yd/day
L/s or cu m/s
cu m/s
g/s
cu m/day
4. Level
In. or ft
cm or m
5. Density
Ibs/cu It
kg/cu m
6. Velocity
Linear
Rotational
ft/sec or ft/hr
RPM
m/sec or m/hr
RPM
0MP OFAMGW&80 TO C&X&iTIOW3
IN l&tAObi t
Answers to questions on page 454.
26.3A Three different types of temperature measuring in-
struments or sensors are:
1. Liquid filled thermometer,
2. Bimetallic thermometer, and
3. Thermocouple.
26.3B The most common liquids used in manometers to
measure pressures are water and mercury.
26.3C Known Unknown
Density of = 62.4 Ibs/cu ft Pressure, psi, if
Water manometer reads:
1. 8 inches of water
Specific 2. 8 inches of mercury
Gravity of = 13.55
Mercury
1. Determine pressure in psi if manometer reads 8
inches of water.
Pressure, psi = Density, Ibs/cu in x Height, in
= 62.4 Ibs/cu ft x 8 in
1728 cu in/cu ft
= 0.29 psi
2. Determine pressure in psi if manometer reads 8
inches of mercury.
Pressure, psi = Density, Ibs/cu in x Height, in
_ 13.55 x 62.4 Ibs/cu ft x 8 in
1728 cu in/cu ft
= 3.91 psi
Answers to questions on page 454.
26.4A The purpose of transmitting instruments is to send the
variable, as measured by the measuring device (sen-
sor), to another device for conversion to a usable
number.
26.4B The different types of receivers include indicators,
recorders, totalizers (integrators) and multipurpose.
Answers to questions on page 457.
26.5A The five common parts to a control system are:
1. Primary element or sensor,
2. Transmitter,
3. Measuring element or receiver,
4. Controlling element, and
5. Final element.
26.5B The common types of control methods include:
1. Open and closed 5. Proportional control with
loops, reset, and
2. Manual control, 6. Proportional control with
3. On-off control, reset derivative.
4. Proportional con-
trol,
-------
476 Treatment Plants
Answers to questions on page 459.
26.6A The purpose ot recorders is keeping continuous and
permanent records of process variables.
26.6B The two basic types of recorders found in treatment
plants are circular charts and strip charts.
26.7A Integrators or totalizers are used in treatment plants to
sum up the amount of liquid or gaseous flow.
£j0(7 OP TO QUe&rtOWS
IN L&440S)Z
Answers to questions on page 463.
26.8A The preliminary treatment section could contain in-
strumentation monitoring and/or controlling the follow-
ing functions:
1. Influent Level (high-low levels)
2. Influent Flow (rate)
3. Explosive Gas Detection (hydrocarbon, LEL)
4. Bar Screen Operation (On-Off)
5. Grit Removal (On-Off)
6. Ventilation System (On-Off)
7. Valves and Gates (Closed, percent Open)
8. Sump Pump (On-Off)
9. High Water Alarm
26.8B The influent level is an important indicator of the rate
of inflow. The number of bar screens or grit channels
on-line depends on the inflow rate. Abnormally low
flows could indicate an obstruction in the influent
sewer line or, worse yet, failure of the sewer pipe. A
high water alarm could indicate a blockage at the bar
screens or perhaps only a partially opened valve or
gate hindering the flow downstream.
26.80 Gasoline or other petroleum products can be detected
in a wet well by using an explosive or combustible gas
detection instrument. This instrument may or may not
be useful in detecting hydrocarbon concentrations
which affect treatment, but it is necessary for safety
reasons with regard to explosive gases and vapors.
26.8D Wet well ventilation systems must be kept operating
continuously both for the operator's safety and for
minimizing the accumulation of concentrations of
moist or otherwise corrosive and toxic gases.
Answers to questions on page 465.
26.8E Instrumented activities that could concern an operator
in primary treatment include:
1. Collector drive 5. Sludge pumps,
motor, 6. Sludge draw-off valve,
2. Flights, 7. Sludge flow,
3. Grease skimmers, 8. High water alarm, and
4. Sludge blanket 9. Water level control valve,
depth,
26.8F Flight movement can be detected by:
1. A pivoted stick moving every time a flight strikes it,
or
2. An ultrasonic signal which is reflected by a passing
flight.
26.8G Sludge pumps can be controlled or regulated by:
1. Turning the pumps on and off,
2. Using a timer control, and
3. Using a sludge density meter control.
26.8H Butterfly valves are used to control the flow to each
primary tank to equalize the flow and promote the
most efficient use of tanks in service.
Of AN^W&(2^ TO QUe&TlOMe
IN U044ON 5
Answers to questions on page 468.
26.81 Air flow is usually measured by a differential pressure
metering device such as an orifice plate.
26.8J Air pressure gages are usually placed at the air com-
pressors and also downstream at main aeration lines.
26.8K Oil levels in air compressors may be measured manu-
ally by a dip stick, read from a sight glass or by the use
of electronic or ultrasonic systems.
Answers to questions on page 471.
26.8L Activities that are usually instrumented or controlled in
the anaerobic sludge digestion process include:
1. Raw sludge feed controller,
2. Digester tank level and alarms,
3. Digester sludge flow,
4. Digester gas flow,
5. Digester gas pressure,
6. Digester sludge temperature,
7. Digester heating system (steam, hot water),
8. Digester transfer and recirculation pumps,
9. Digester gas quality,
10. Combustible gas alarm, and
11. Digester gas mixing compressor.
26.8M Digested sludge flow would be recorded if the sludge
receives additional treatment, such as dewatering or
chemical conditioning.
26.8N Temperatures in an anaerobic sludge digester may be
measured by:
1. A built-in temperature-sensing device such as a
thermocouple,
2. Manually placing a thermometer in sludge running
into the sample sink.
26.80 Digester transfer and recirculation pumps are used to
mix the digester contents, transfer sludge between di-
gesters, pump out digested sludge and pump super-
natant or plant effluent in or out of digesters.
Answers to questions on page 474.
26.9A Instruments and controls need attention such as
cleaning, adjusting, calibrating, repairing and/or re-
placement from time to time.
26.9B Before starting to work on an instrument or control,
notify other operators what you are going to do, when
you are going to do it, how long it will take, and what
will be affected.
Of AMtNfifM XO QLi&STtOHG
-------
Instrumentation 477
OBJECTIVE TEST
Chapter 26. INSTRUMENTATION
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one answer to each question.
1. One of the most sophisticated and common control sys-
tems is the human body.
1. True
2. False
2. A control system is a measuring device.
1. True
2. False
3. Repeatability means measuring something over and over
again until you get the same answer twice.
1. True
2. False
4. Gage pressure does not take into consideration the weight
of the atmosphere above the earth.
1. True
2. False
5. A manometer with a vertical leg is more sensitive than a
manometer with an inclining or sloping measuring leg.
1. True
2. False
6. In a control system, the final element is the device that
controls the energy supplied to the process being con-
trolled.
1. True
2. False
7. A recorder is a device that records information onto a
sheet of paper that is moving at a specific speed.
1. True
2. False
8. In large treatment plants, all digesters are loaded at the
same rate to evenly balance the digester loadings.
1. True
2. False
9. If you don't know how to maintain or troubleshoot instru-
ments and controls, leave them alone and request assist-
ance.
1. True
2. False
10. Special areas should be designated for instrument main-
tenance and storage and areas with high humidity and
corrosive gases should be avoided.
1. True
2. False
11. Which of the following are measuring devices?
1. Bathroom scale
2. Computer
3. Heater
4. Ruler
5. Thermometer
Questions 12, 13, and 14. In the human body the eyes are
the (12) the nervous system is (13)
and the brain is the (14)
Answers to questions 12, 13, and 14.
1. Control logic
2. Indicator
3. Probe
4. Sensing instrument
5. Transmission system
15. The operation of a toilet bowl flush tank is an example of
what type of control system?
1. Biological and cybernetic
2. Cybernetic and electrical
3. Electrical and hydraulic
4. Hydraulic and mechanical
5. Mechanical and pneumatic
16. What method or device should you use to measure the
diameter of a replacement pump shaft?
1. Engineer's scale
2. Metallic tape
3. Micrometer
4. Ruler
5. Surveyor's chain
17. Temperature can be measured on which of the following
scales?
1. Celsius
2. Fahrenheit
3. Joule
4. Kelvin
5. Pascal
18. Common types of pressure gages include
1. Bellows.
2. Bourdon.
3. Diaphragm.
4. Parshall.
5. Venturi.
19. Liquid levels may be measured by
1. Bubbler tubes.
2. Floats.
3. Probes.
4. Sight tubes.
5. Ultrasonic sounds.
-------
478 Treatment Plants
20. A tachometer measures
1. Density.
2. Distance.
3. Rotational velocity.
4. Temperature.
5. Time.
21. The primary element in a control system is also called a
1. Controller.
2. Receiver.
3. Recorder.
4. Sensor.
5. Transmitter.
22. The set point is the position at which the is
set.
1. Controller
2. Receiver
3. Recorder
4. Sensor
5. Transmitter
23. Different types of control systems include
1. Manual.
2. On-Off.
3. Project.
4. Proportional.
5. Ratio.
24. Abnormally low flows into a treatment plant could indicate
1. A broken sewer pipe.
2. A downstream blockage.
3. A failure in the sewer system.
4. An industrial waste discharge.
5. An obstruction in the sewer.
25. What types of alarm systems are usually installed in grit
channels?
1. Collection drive system on or off
2. Explosive gas detection
3. High water level
4. Motors tripped-out on overload
5. Oxygen deficiency
26. Sludge blanket depths may be measured by use of
1. Bubbler tubes.
2. Floats connected to cables and pulleys.
3. A hose and an aspirator.
4. Pressure gages.
5. Ultrasonic transmitters and receivers.
27. Primary sludge flow is usually metered by
1. A magnetic flow meter.
2. An orifice.
3. A Parshall flume.
4. A Venturi meter.
5. A weir.
28. Excessive air compressor lubrication oil temperatures
may indicate
1. Heater malfunction.
2. High oil levels.
3. Inoperative oil coolers.
4. Low oil levels.
5. Motor overload.
29. Which of the following factors are usually measured by air
compressor vibration sensing devices?
1. Acceleration
2. Displacement
3. Flow
4. Time
5. Velocity
30. A high level alarm in a sludge digester could indicate
1. A control system malfunction.
2. A digested sludge valve left open.
3. An inoperative digested sludge withdrawal system.
4. A plugging of the overflow.
5. A possible leak or break somewhere in the system.
31. Digester gas flows are commonly measured by the use of
1. Orifice plates.
2. Positive displacement meters.
3. Rotameters.
4. Turbine meters.
5. Venturi meters.
32. Which of the following maintenance services can be per-
formed by operators on Venturi meters?
1. Check flow zero
2. Check level indicator
3. Check power supply
4. Check purge water
5. Clean taps
33. Which of the following maintenance services can be per-
formed by operators on LEL meters?
1. Check alarm function
2. Check electrolyte
3. Check zero setting
4. Check probe
5. Test with gas
• env of- o&jecTNZ re«r •
-------
CHAPTER 27
INDUSTRIAL WASTE MONITORING
by
Larry Bristow
-------
480 Treatment Plants
TABLE OF CONTENTS
Chapter 27. Industrial Waste Monitoring
Page
OBJECTIVES 482
GLOSSARY 483
LESSON 1
27.0 Need for Industrial Waste Monitoring 484
27.00 Objectives of Industrial Waste Monitoring 484
27.01 Importance of a Monitoring Program 484
27.02 Objectionable Characteristics of Industrial Waste 484
27.1 Administration of a Monitoring Program 485
27.10 Organization 485
27.11 The Data Base 485
27.12 Enforcement 485
27.13 Dealing with Industry 486
27.2 How to Monitor Discharges 486
27.20 Monitoring Programs 486
27.200 Self-Monitoring 486
27.201 Continuous Monitoring 486
27.21 Monitoring Provisions 486
27.22 Need for Representative Samples 486
27.23 Sampling Points 486
27.24 Types of Samples 487
27.240 Grab Samples 487
27.241 Composite Samples 487
27.25 Portable Equipment 487
27.26 Handling Portable Samplers 491
27.27 Care of Equipment 491
27.28 Maintenance 491
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Industrial Monitoring 481
LESSON 2
27.3 Locating Sources of Discharges 495
27.30 "Prospecting" in the Sewers 495
27.31 Identifying Waste Materials 495
27.4 Sample Preservation and Security 495
27.40 Storage Time 495
27.41 Storage Temperature 498
27.42 Chemical Preservation 498
27.43 Security 498
27.5 Flow Metering 498
27.50 Need for Accurate Measurements 498
27.51 Water Meters 498
27.6 Safety 498
27.60 Traffic Safety 498
27.61 Confined Spaces 502
27.62 Equipment Storage 502
27.63 Battery Charging 502
27.7 Monitoring Strategies 502
27.70 Development of Strategies 502
27.71 Regulation of High Flows 503
27.72 Decisions on Industrial Discharges 503
27.73 Reaction to Industrial Discharges 503
27.74 Warning Systems 506
27.8 Additional Reading 506
APPENDIX 511
ci -i
A Industrial Sewer-Use Permit Application J
520
B Sample Sewer-Use Ordinance
coy
C Standard Form A - Municipal
D Safety Orders for Battery Charging 529
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482 Treatment Plants
OBJECTIVES
Chapter 27. INDUSTRIAL WASTE MONITORING
Following completion of Chapter 27, you should be able to
do the following:
1. Develop an industrial waste monitoring program,
2. Justify an industrial waste monitoring program,
3. Administer and manage the program,
4. Locate sources of industrial waste discharges,
5. Collect and preserve representative samples,
6. Document the "chain of possession" of your sampling pro-
gram,
7. Develop a monitoring strategy, and
8. Conduct your duties in a safe manner.
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Industrial Monitoring 483
GLOSSARY
Chapter 27. INDUSTRIAL WASTE MONITORING
COMPOSITE (PROPORTIONAL) SAMPLE COMPOSITE (PROPORTIONAL) SAMPLE
(com-POZ-it)
A composite sample is a collection of individual samples obtained at regular intervals, usually every one or two hours during a
24-hour time span. Each individual sample is combined with the others in proportion to the flow when the sample was collected. The
resulting mixture (composite sample) forms a representative sample and is analyzed to determine the average conditions during the
sampling period.
GRAB SAMPLE GRAB SAMPLE
A single sample of wastewater taken at neither a set time nor flow.
PERISTALTIC PUMP (peri-STALL-tick) PERISTALTIC PUMP
A type of positive displacement pump.
REFRACTORY MATERIALS (re-FRACK-tory) REFRACTORY MATERIALS
Materials difficult to remove entirely from wastewater such as nutrients, color, taste- and odor-producing substances and some toxic
materials.
REPRESENTATIVE SAMPLE REPRESENTATIVE SAMPLE
A portion of material or water identical in content to that in the larger body of material or water being sampled.
SLUGS SLUGS
Intermittent releases or discharges of industrial wastes.
TRUNK SEWER TRUNK SEWER
A sewer that receives wastewater from many tributary branches or sewers and serves a large territory and contributing population.
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484 Treatment Plants
CHAPTER 27. INDUSTRIAL WASTE MONITORING
(Lesson 1 of 2 Lessons)
27.0 NEED FOR INDUSTRIAL WASTE MONITORING
The rapid advance of industrial technology has added new
concerns for the wastewater treatment field. Chemical com-
pounds of increased complexity and quantities are being dis-
charged into the sewers. The impact of these waste dis-
charges on treatment processes is harmful in some cases and
unknown in others. This, coupled with increased knowledge of
the effects of these chemicals on health and the environment,
creates new or additional problems for many treatment plant
operators. This chapter will discuss the problems associated
with, and methods of regulating, industrial waste discharges.
For information on actually treating industrial wastes, see
Chapter 21, "Activated Sludge," and Chapter 28, "Industrial
Waste Treatment."
27.00 Objectives of Industrial Waste Monitoring
Several chapters in this course discuss shock loads and how
to minimize their effects. Industrial wastes often cause that
shock load. A program for monitoring and regulating industrial
discharges is essential to:
1. Prevent serious shock loads and thus assure that no disrup-
tions of plant processes occur,
2. Provide physical protection of personnel and facilities,
3. Prevent discharge of pollutants from treatment plants, and
4. Provide a data base for fair and reasonable sewer-use
charges and for engineering data.
27.01 Importance of a Monitoring Program
A discharge of industrial wastes may affect a treatment plant
to the extent that it fails to meet the discharge requirements set
by the NPDES permit, the regulating agency, or other author-
ity. One cause for the failure may be a process upset occuring
due to toxic materials that destroy or affect the metabolism of
microorganisms that are part of the treatment process. Another
cause may be toxic materials that pass through the treatment
process and are present in the plant effluent. Hydraulic over-
loads can upset treatment processes by "washing out" the
microorganisms in the treatment process. Solids carry-over to
the effluent will result from a process upset, as will odors result-
ing from upset biological treatment processes.
Industrial discharges may cause problems in both the collec-
tion system and treatment plant including excessive solids that
may cause stoppages, corrosive substances that may damage
the pipes, and flammable materials that may cause fires or
explosions. Dangerous gases may result from some dis-
charges. In some cases, the gases will cause an oxygen defi-
ciency. In others, toxic gases such as hydrogen sulfide or
cyanide may be present. Additionally, some gases may create
flammable or explosive conditions.
27.02 Objectionable Characteristics of Industrial Wastes
Some undesirable properties and effects of various indus-
trial waste discharges are presented in this section.
Possible Collection System Problems:
1. Acid and Alkali Wastes - cause corrosion of pipes.
2. Thermal Wastes - hot discharges raise the temperature of
the wastewater, speeding up decomposition and thus caus-
ing septic conditions. Septic conditions can produce odor
and corrosion problems as well a toxic, flammable, explo-
sive and oxygen-deficient atmospheres.
3. Solids - excessive solids may settle and cause stoppages
and septic conditions.
4. Oils and Greases - build up on pipe walls, reducing capacity
and causing stoppages and septic condtions.
5. Odors - the discharge itself may be odorous, or the odors
may result from the conditions caused by the discharge.
6. Toxic Substances - may include infectious wastes, poisons
(such as pesticides) or gases (such as cyanide or hydrogen
sulfide).
7. Flammable and Explosive Materials - includes fuels, paint
thinners, and hydrogen sulfide.
NOTE: Hydrogen sulfide results from septic conditions. Hydro-
gen sulfide will cause odors, corrosion, and can be ex-
plosive and toxic to your respiratory system.
Possible Treatment Plant Problems:
1. Organic Overloads - more suspended and dissolved solids
than the plant can handle.
2. Toxic Substances - (see previous section on collection sys-
tems).
3. Oils and Greases - may flow through plant and form surface
scums on receiving waters (see previous section on collec-
tion systems).
4. Acids and Alkalies - cause corrosion of pipes and can be
toxic to organisms in treatment processes.
5. Hydraulic Overloads - reduce detention or treatment times
and cause incomplete treatment of wastes.
6. Refractory Materials - materials that are not removed by
plant processes, such as nutrients, color, taste and odor
producing substances, and some toxic materials.
7. Hazardous Wastes - solvents, fuels, corrosives, poisonous
substances, infectious wastes, radioactive wastes, gases
(explosive, toxic or oxygen-displacement).
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Industrial Monitoring 485
Thus, it is possible for a seemingly harmless food-
processing plant waste, for example, to discharge excessive
solids and organic materials and cause intolerable conditions
in the collection system and a wastewater treatment plant.
QUESTIONS
Write your answers in a notebook and then compare youi
answers with those on page 507.
27.OA What are the objectives of an industrial waste monitor-
ing program?
27.OB List the adverse characteristics of industrial wastes
that could seriously impact on (1) collection systems
and (2) treatment plants.
27.1 ADMINISTRATION OF A MONITORING PROGRAM
27.10 Organization
The U.S. Environmental Protection Agency (EPA) requires
monitoring programs that control problems at their sources.
State agencies also have monitoring requirements. In some
cases, these may be more stringent than the basic EPA regula-
tions. In order to abide by these regulations and achieve the
objectives listed in Section 27.00, certain actions will be nec-
essary. Essential actions include the building and maintenance
of a data base and the establishment and enforcement of ef-
fective local ordinances regulating industrial discharges.
27.11 The Data Base
A file should be established and maintained on each dis-
charging industry. The technical data contained in the file is
essential for making decisions in areas such as operation and
maintenance of treatment plant processes, program monitor-
ing, and engineering design of facilities. The following informa-
tion should be included in each discharger's file.
1. Industry Identification. Name of firm, products or services
provided, raw materials or chemicals used, and a brief de-
scription of manufacturing and treatment processes used
(e.g., batch, continuous, seasonal).1
2. Flow Data. Characteristics of the wastewater discharge in-
cluding flow patterns (peaks and lows), total volume, and
BOD, suspended solids, pH, and other critical characteris-
tics.
3. Laboratory Results. Dates, times, and results of laboratory
tests on discharges.
4. Billing Information. Calculations used to establish billing
rates.
5. Treatment Information. Pretreatment measures used by the
industry and any special measures that must be taken by
the treatment plant.
6. Reports of Unusual Circumstances or Incidents. Data on
spills, product or process changes, or changes in pretreat-
ment efforts by the industry.
7. Industrial Facilities. Layout of the industrial site showing
location of sewer lines and connectors, chemical storage
areas, spill protection measures provided, monitoring
facilities, and location of person to contact upon arrival for
inspection visit.
8. Emergency Information. Names and phone numbers of at
least two persons with the industry who have authority to
take appropriate action in case of accidents or spills.
27.12 Enforcement
A good sewer-use ordinance is the proper tool to provide the
necessary authority to control industrial wastes. The objectives
of the ordinance are to provide for the control of industrial
discharges to the degree that (1) no harm is done to personnel
or wastewater collection and treatment facilities, and (2) that
these discharges do not cause the wastewater treatment plant
to violate its discharge requirements. Also, it should provide for
equitable sewer service charges.
There are several specific powers that should be authorized
in a sewer-use ordinance.
1. Inspecting and monitoring.
2. Requiring pretreatment and/or flow adjustment.
3. Curtailing or ceasing of discharge.
4. Requiring spill protection measures.
5. Issuing permits to dischargers.
Regulatory agencies usually will require the local agency
to use a permit system. This is a good mechanism for in-
spections and gathering base information. A sample copy
of an Industrual Sewer-Use Permit Application is located in
Appendix A.
6. Billing for sewer service charges.
a. Normal sewer-use charges.
b. Special charges and/or fines for damages caused by
spills.
Billing rates should be fair and equitable for everyone.
Charges to industry for treating flows, including BOD and
suspended solids, should be similar to the charges to busi-
nesses and homeowners. Sufficient funds should be col-
lected from all dischargers to cover all of the operating and
maintenance costs of the wastewater collection and treat-
ment facilities. Fines and extra charges for accidental spills,
dumps or additional loadings should be greater than the
extra costs associated with resulting problems and a poor
1 EPA's Standard Form A (see Appendix C) may be used lor this purpose. This form includes a space for the standard industrial classification
code number of the industry involved. The code numbers are published by the Superintendent of Documents, U.S. Government Printing
Office, Washington, D.C. 20402. The stock number of the book is 041-001-00066-6, price is $10.25 and the title is "Standard Industrial
Classification (SIC) Manual." Use of these code numbers is often mandatory. (NOTE: Many industries will fit into two or more classifications.
The EPA Form A (Appendix C) provides only for the "major" product or service. This is not adequate for monitoring purposes. In these cases,
more than one Form A per industry, or special forms will be needed.)
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486 Treatment Plants
plant effluent in order to discourage future problems result-
ing from negligence.
A sample ordinance, prepared by the Environmental Pro-
tection Agency (EPA), is included in Appendix B.
27.13 Dealing with Industry
Your personal contact with industry representatives can be
crucial. You have the authority to seriously affect their opera-
tions. However, you must obtain their cooperation. Good
communications are a must. If you are going to require an
action or response to a problem on the part of an industry, first
be sure that you can show the need for the action. Most people
will cooperate fully if they are convinced that a real need exists.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 507.
27.1 A Why is a good data base on industrial waste dis-
charges important?
27.1B What information should be collected to develop a
data base?
27.1C A sewer-use ordinance provides authority for what en-
forcement activities?
27.2 HOW TO MONITOR DISCHARGES.
Monitoring is the key to industrial waste control. There must
be a program of surveillance to assure compliance with pre-
scribed limits. In the larger cities with heavy industrial areas,
self-monitoring by the Industries, with spot-checks by the local
agency, is usually practiced. Smaller communities may do their
own monitoring, or at least a part of it.
27.20 Monitoring Programs
27.200 Self-Monitoring
Self-monitoring by industry is common in large industrial
areas. The burden of monitoring a large number of industries
otherwise would be overwhelming to a local agency. Self-
monitoring may be used where the industry has laboratory
facilites or access to a commercial laboratory. The laboratories
used should be certified by the appropriate health department
or regulatory agency.
Routine inspections should be made, as well as examination
of regular reports received from the industry. In addition, ran-
dom sampling (with the samples analyzed at a different labora-
tory) should be done to confirm the results of the self-
monitoring program. When this is done, the sample should be
split so both laboratories might analyze it. This will bring to light
any variations in procedure between the laboratories. When
making inspections, be sure to abide by all of the security and
safety procedures of the firms or companies being inspected.
27.201 Continuous Monitoring
Special sensors are available for continuously monitoring a
number of water quality indicators. The most commonly used
ones are for temperature, pH, and specific conductance. In
some cases, frequent cleaning and calibration of the special
sensors will be necessary.
There is considerable research being done in the field of
continuous monitoring. A broader range of water quality indi-
cators and increased reliability may be expected in the future.
27.21 Monitoring Provisions
Suitable provisions must be provided for monitoring indus-
trial wastes. In most cases, this is done by industry. For
monitoring purposes, a flow meter frequently must be installed.
While water meter data can be used to determine total flow in
some cases, this does not provide peak flow data. A good
sampling location is required, with possible locations ranging
from a special manhole to complete monitoring structures.
27.22 Need for Representative Samples2
As is true in sampling for treatment plant process control,
good sampling of industrial wastes is both difficult and of the
utmost importance. The sample should be representative; that
is, it should be an accurate representation of the entire waste-
water discharge. This is essential if you are to know the actual
characteristics of the discharge. No matter how highly trained
the laboratory technicians or how sophisticated their equip-
ment, their work can be no better than the samples that have
been collected for analysis. Very often a great deal of empha-
sis is placed on the accuracy of the laboratory analyses, with
only casual attention given to obtaining the samples. The col-
lection of samples must be carefully thought out and performed
by responsible, trustworthy individuals. Representative sam-
ples of slug discharges of chemicals or wastes from industrial
plants are difficult to obtain even when you know the time of
discharge.
27.23 Sampling Points
A good sampling point is one that is easily accessible and
may be located anywhere that a representative sample of the
industrial wastewater discharge may be obtained. Remember
that you are sampling only the flow from one industrial waste
discharger and not the total flow in a municipal collection sys-
tem. This usually involves a special manhole or monitoring
structure.
The special manhole may simply be an ordinary manhole
that is easily accessible. The manhole may have a measuring
weir or flume. Where continuous monitoring of certian water
quality indicators (such as pH) is needed, a special monitoring
station may be necessary. The station would house the
monitoring equipment, which would typically be a flow meter,
sampler, refrigerator, and pH or other special monitoring
equipment. Sometimes the monitoring station is equipped with
an alarm system and provisions to stop or divert the discharge
to a holding tank or pond. For example, a pH probe is installed
to monitor the discharge from an industry. An accidental spill in
the plant produces a discharge with a pH of 4.7. If the minimum
pH was 6.0, an alarm would sound. Downstream from the
probe a flow diversion device would divert the discharge to a
holding basin or to a pretreatment facility to neutralize the dis-
charge. Other facilities in a sampling station may include a sink
and a small workbench.
The sampling point needs to be located where the wastewa-
ter flow from the industrial plant is well mixed and before the
flow is discharged into the public sewer. Flat, sluggish areas
are poor sampling locations because solids will tend to settle to
the bottom. Under these circumstances, the sample may con-
tain too many or too few solids, depending on the manner in
2 Representative Sample. A portion of material or water identical in content to that in the larger body of material or water being sampled.
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Industrial Monitoring 487
which the sample was collected. Solids also may settle out
upstream from weirs. Bubbling air through the wastewater
stream has been used for mixing in channels and above weirs.
The solids-settling problem is reduced when flumes are used
as primary measuring devices.
Where oil or other similar material is floating, representtive
sampling is very difficult. If it is possible to divert the entire
waste stream to a large container for a short time period, the
approximate quantity of floatables or oil may be determined by
measuring the material that rises to the top of the container.
If the industry has two or more outlets that discharge pro-
cess waste into the sewer, the monitoring problem is com-
pounded. If possible, the outlets should be combined into one
discharge. Otherwise, separate facilities will be required on
each discharge.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 507.
27.2A Why are self-monitoring programs commonly used in
large industrial areas?
27.2B What type of maintenance may be needed for the
sensors used in continuous monitoring programs?
27.2C Define the term "representative sample."
27.2D Where or under what conditions would you attempt to
collect a representative sample?
27.24 Types of Samples
27.240 Grab Samples3
The simplest and least expensive sampling method is the
grab sample. However, grab samples are not useful for dis-
charges that vary in makeup (constituents) or quantity. This is
particularly true when the samples are being taken for billing
purposes. Grab samples can be useful for qualitative analyses
to determine if particular materials (e.g., heavy metals that
must be preserved so they won't precipitate out) are present.
The grab sample should be obtained from the center of the
wastewater flow.
To determine the peak concentration and time of occurrence
of a toxic waste discharge, collect grab samples hourly or use
a composite sampler that collects samples at regular time
intervals and does not mix the samples. Analyze the individual
samples — do not mix them.
27.241 Composite Samples4
Composite samples will provide the most accurate repre-
sentation of a wastewater stream that can be obtained at a
reasonable cost. The simplest method is by taking grab sam-
ples at predetermined times, either by hand or through a
clock-controlled sampler. The principal objection to timed grab
samples is that the sample quantities are the same for high
and low flow periods. This can be overcome if the samples are
stored in individual bottles, and then proportionally combined
based on ratios from a flow meter chart. Another limitation of
composite samples is that an isolated or peak discharge of a
concentrated toxic waste could be diluted by the other samples
taken during the sampling period.
Automatic flow-proportional sampling is the standard
method for obtaining representative samples. In this method,
the sampler is activated by a flow meter. A sample is collected
for each pre-selected quantity of flow (e.g., one sample for
each 10,000 gallons).
This results in more frequent samples during periods of high
flow. Other flow-proportional sampling systems use uniform
timing and vary the quantity of sample according to the flow.
Various methods are used to obtain the samples. Scoops,
conveyors with small "buckets" attached, vacuum chambers,
and small pumps are the most common. Some samplers ob-
tain the sample directly from the wastewater flow. In others a
pump supplies a constant stream of the wastewater to the
samplers, with an overflow line carrying the excess back to the
sewer. Figure 27.1 shows a sampling device, a peristaltic (a
type of positive displacement pump) pump sampler.
Flow proportional samplers usually are installed in perma-
nent monitoring facilities. Most of these samplers combine the
various samples in a refrigerated compartment. This prevents
deterioration and change of the samples.
27.25 Portable Equipment
Samplers, flow meters and some instruments, such as pH
meters and conductivity meters, are available for field work.
Portable in flow meters use a weir or Palmer-Bowlus flume for
easy installation in a sewer line. The meters themselves use
floats, air or nitrogen bubbling, built-in electronic sensing,
motor-operated sensing probes, or sonar for sensing the water
level behind the weir or in the measuring flume. Recording
charts and totalizers usually are part of the equipment so that a
record of the flow is obtained. (Portable flow meters and re-
corders are shown in Figure 27.2.)
Most portable samplers use peristaltic pumps or vacuum
chambers to pick up the samples (Figures 27.1 and 27.3).
Power is supplied by rechargeable batteries or, when possible,
from a 110-volt AC line using a "power-pack" which fits the
same space usually occupied by the battery.
The pumping rate must be considered when a sample is
collected. A velocity of 2 to 5 feet per second (0.6 to 1.5 m/sec)
in the sampler suction tubing produces repeatable results.
Lower velocities tend to leave solids behind in the tubing, while
higher velocities may pull in large chunks of material, yielding
erratic results in the data.
3 Grab Samples. Single samples of wastewater taken at neither a set time nor flow.
4 Composite (Proportional) Samples (com-POZ-it). A composite sample is a collection of individual samples obtained at regular intervals,
usually every one or two hours during a 24-hour time span. Each Individual sample is combined with the others in proportion to the flow when
the sample was collected. The resulting mixture (composite sample) forms a representative sample and is analyzed to determine the average
conditions during the sampling period.
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488 Treatment Plants
PUMP COVER
r— PUMP TUBE (MEDICAL GRADE RUBBER)
SUCTION TUBING
CLAMP
PUMP DISCHARGE
PUMPROLLER
Fig. 27.1 Peristaltic pump sampler
-------
FLOW MOTOR WITH RECORDER
TOTALIZER AND BATTERY
PALMER-BOWLUS FLUME WITH
BUILT-IN LEVEL SENSOR
PALMER-BOWLUS FLUME WITH LEVELING DEVICE.
•u
Fig. 27.2 Portable flow meters and recorders S
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490 Treatment Plants
SAMPLE SIZE ADJUSTMENT TUBE
SUCTION
TUBING
AIR-VACUUM CONTROL
MEASURING CHAMBER
SOLENOID VALVES
Fig. 27.3 Vacuum chamber sampler
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Industrial Monitoring 491
Most portable samplers use individual bottles for each sam-
pling period. The bottles are on a rotating table or plate on a
timer that positions a different bottle under the sampler dis-
charge during each sampling time. This permits a sample from
a particular sampling time to be individually inspected. The
separate samples are combined to make a composite sample.
The usefulness of a portable sampler will depend on the
flexibility of its controls. Desirable features include automatic
purging before and after the sample is taken, and timing flexi-
bility to allow a range of sample times from every few minutes
to a couple of hours between samples. At times you may want
to take more than one sample per bottle, or to fill several bot-
tles during each sampling cycle. All of these features, plus
other refinements, are provided by several manufacturers in
their portable samplers.
Chilling the sample for preservation may be important (see
Section 27.4 on sample preservation). An ice compartment is
generally provided for this purpose. If the sampler is to be used
in one location for some time, it may be practical to use chilled
water. A small refrigerated-water chilling unit, a small water-
circulating pump, and some plastic tubing will do the job. The
tubing can enter the sampler by notching the cover, or short
lengths of 1/8-inch (3 mm) pipe can be installed through the
bottom by using lock nuts, washers, and a good sealant (Fig-
ure 27.4).
27.26 Handling Portable Samplers
Most portable samplers are designed to fit into a manhole
and are equipped with harnesses to permit hanging them
within the manhole. Usually missing is something to hook the
harness to. Also missing is a way to keep the suction hose
approximately in the middle of the wastewater flow. This is
especially noticeable if you are sampling a TRUNK SEWER5.
The following method has served well to overcome these prob-
lems. Many other ideas also will work with the individual situa-
tion and your ingenuity usually determining your approach.
Figure 27.5 shows a sampler and the gear for supporting it.
1. A special "manhole ring" (Figure 27.6) is suspended inside
the manhole from the inside of the manhole frame. The
manhole cover sits on top of the "manhole ring." The
"manhole ring" can be made up by a sheet metal shop from
16-gage galvanized sheet metal. The ring cylinder should
be slightly smaller than the inside diameter of the top of the
manhole.
2. A harness for the sampler is made of nylon or other syn-
thetic rope and attached to the "manhole ring" with harness
snaps. Several harnesses of various lengths should be
made for manholes of various depths. The harness snaps
should be inspected frequently for possible replacement
because they may corrode rapidly under conditions found in
manholes.
3. A knotted rope is attached from the "manhole ring" to the
sampler to raise and lower the sampler.
4. A piece of pipe with a bail on it is suspended from the
sampler. This serves as a "hanging wet well." The suction
line is taped to the bail to hold it in place, and a piece of
nylon cord suspends it to the desired depth.
In a sewer, debris such as rags may hang up on this device,
but it will swing downstream and the debris will slide off. In
practice, this method has yielded good results with very few
missed samples.
27.27 Care of Equipment
Cleanliness is a very important part of getting accurate tests.
Contamination of sample containers, tubing, and internal parts
of samplers will affect the sample, and thereby lead to inaccu-
rate laboratory results.
Another potential problem that can lead to inaccurate test
results is interference due to the type of material from which
the tubing and containers are made. Depending on the materi-
als, some elements in the wastewater may adsorb on the walls
of the tubing or container. Also, some wastewater constituents
may react with tube or container materials causing impurities
that may dissolve into the sample. This is a greater problem
with the containers because the contact time of the sample
with the tubing is very limited. While this type of interference
normally is not a problem, it is important when testing for very
low levels of heavy metals and other toxins (i.e., in parts per
billion or micrograms per liter). If you are faced with this situa-
tion, it is a good idea to obtain sample containers made from
Teflon or linear polyethylene. These materials are excellent in
that they don't adsorb materials from the sample or contain
impurities that can dissolve into the sample.
27.28 Maintenance
The reliability of samplers varies considerably. A unit that is
considered poor by one operator may perform well for another.
The most reliable equipment will be that used where regular
maintenance is performed in accordance with the manufactur-
er's instructions. Replacement items must also be as specified.
For example, if a specific tubing is designated for a peristaltic
pump, substitutes may cause malfunctions. Where samplers
are equipped with desiccant (drying) cartridges, it is important
to keep them changed as instructed. To service sampling
equipment, both mechanical and electronic skills are required.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 508.
27.2E What are the differences between grab and composite
samples from the standpoint of industrial waste
monitoring? What are the problems with each type?
27.2F How is power provided for portable sampling equip-
ment in the field?
27.2G Why is the flow velocity in the sampler suction tube
important?
27.2H What kind of care and maintenance should be pro-
vided monitoring equipment?
OF-
IthhOH 1
OP 2 /
WfclW/AU
u WA*T6
MONITOR
Work the discussion and review questions before continuing
with Lesson 2.
5 Trunk Sewer,
population.
A sewer that receives wastewater from many tributary branches or sewers and serves a large territory and contributing
-------
INTERNAL WATER LEVEL
SAMPLER
WATER
CHILLING
UNIT
PUMP
FLOW
DETAIL OF SAMPLER MODIFICATION
1/8 IN. PIPE - ALL THREAD
NUT
.WASHER
SEALANT
Fig. 27.4 Sketch of arrangement for chilling sampled waters
-------
MANHOLE RING
Sampler harness suspended
from manhole ring. Note
suction tube of sampler
at bottom.
Entire sampler in rack
may be raised or lowered
by harness.
Fig. 27.5 Hanging Sampler
SUCTION TUBING
Protective tube around
sampler suction tube.
3
a
c
0)
o
3
3
CO
A
to
CO
-------
Treatment Plants
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Industrial Monitoring 495
DISCUSSION AND REVIEW QUESTIONS
CHAPTER 27. INDUSTRIAL WASTE MONITORING
(Lesson 1 of 2 Lessons)
At the end of each lesson in this chapter you will find some
discussion and review questions that you should answer be-
fore continuing. The purpose of these questions is to indicate
to you how well you understand the material in this lesson.
Write the answers to these questions in your notebook before
continuing.
1. What adverse impacts can occur if an improperly pretreated
industrial waste reaches a wastewater treatment plant?
2. How would you effectively deal with an industrial waste
discharger?
3. Why must representative samples be collected?
4. How would you collect a representative sample when the
wastewater has oil or other floating materials on the sur-
face?
5. How would you attempt to determine the peak concentra-
tion and time of occurrence of a toxic waste discharge?
CHAPTER 27.
INDUSTRIAL WASTE MONITORING
(Lesson 2 of 2 Lessons)
27.3 LOCATING SOURCES OF DISCHARGES
27.30 "Prospecting" in the Sewers
Often, the problem facing the wastewater treatment plant
operator is that of an industrial waste from an unknown source.
The magnitude of the problem is, of course, directly propor-
tional to the problems caused by the unknown discharge.
When trying to locate the source, established procedures must
be followed to obtain accurate results. Some of the equipment
used and techniques of locating the sources of discharges are
discussed in Section 27.2, "How to Monitor Discharges."
To trace an industrial discharge causing problems, begin at
the treatment plant or at a point in the collection system where
the discharge has been discovered. If the discharge is visible
through color or solids and continuous, simply inspect the
sewer at each sewer line intersection and follow it up to its
source. If a visual check isn't sufficient, use portable samplers
in the same way. If several samplers are available, the process
can be speeded up greatly.
If the discharge is intermittent, the task can be very difficult
and time consuming. SLUGS6 can pass by the sampler be-
tween sampling periods. If short sampling time intervals are
used, the samplers must be inspected every few hours.
Solvents float on the surface and will not be picked up by
ordinary sampling equipment. If you are looking for petroleum
solvents or similar floatable materials, you can fasten the suc-
tion tubing to a block of styrofoam or similar material and thus
hold the suction end of the sampling tube very close to the
surface.
Techniques other than sampling will be appropriate at times.
For instance, a solvent discharge problem might be solved by
inspecting ail the shops, stores, service stations, and laundries
connected to that part of the collection system. A survey of the
area may prove to be helpful. Use the permit application forms
provided in the Appendix (A and C) either directly, or use them
as a guide for preparation of your own survey forms.
27.31 Identifying Waste Materials
Once a sample has been collected and analyzed by the
laboratory, the next problem is to interpret the results. A list of
the common types of discharges from some businesses or
industries is contained in Table 27.1. Once the type of dis-
charge is determined, one helpful source of information is the
telephone directory. The "yellow page" listings can usually
produce a list of firms or industries to inspect. Personal visits or
inspections can then help to get the problem solved.
27.4 SAMPLE PRESERVATION AND SECURITY
27.40 Storage Time
Laboratory tests are most accurate if a sample is analyzed
immediately after it is collected. Prompt testing prevents physi-
cal, chemical and/or biological changes in the sample. While
immediate testing usually isn't possible, in most cases refrig-
eration adequately preserves the quality of the sample (see the
sample preservation list in Table 27.2). A related problem
arises when samples must be tested within a specified time
after collection. For example, practically all BOD samples are
from 24-hour composite samples plus additional storage time.
As indicated on the list, the storage time for BOD is 48 hours.
Even though you won't be able to get perfectly accurate test
results under these circumstances, you can minimize the
amount of error if you maintain a consistent storage time for
each sample tested. This will maintain a constant degree of
error on all samples, and thereby reduce errors in interpreta-
tion of results.
8 Slugs. Intermittent releases or discharges of industrial wastes.
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496 Treatment Plants
TABLE 27.1 TYPES OF POLLUTANTS FROM SOME COMMON INDUSTRIES
TYPES OF POLLUTANTS
Type of Industry
Canneries
X
X
X
X
Chemical Mfg.
X
X
X
X
X
X
X
Dairy Products
X
X
X
X
X
X
Detergent Mfg.
X
X
X
X
X
X
X
Electroplating
X
X
X
X
X
X
Glass, Asbestos
X
X
X
X
X
X
X
X
X
X
Grain Mills
X
X
X
X
X
X
Leather Tanning
X
X
X
X
X
X
X
Meat Products
X
X
X
X
X
Rubber Products
X
X
X
X
X
Sugar Processing
X
X
X
X
X
X
Paper Mills
X
X
X
X
X
X
X
Plastics
X
X
X
X
X
Wood Products
X
X
X
X
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Industrial Monitoring 497
TABLE 27.2 RECOMMENDED STORAGE PROCEDURES AND SAMPLE PRESERVATION TECHNIQUES
RECOMMENDED STORAGE PROCEDURE
Analysis
Total Solids
Suspended Solids
Volatile Suspended Solids
COD
BOD
Sample Storage
Refrigeration @ 4°C
OK
Up To Several Days
Up To Several Days
Up To Several Days
48 Hours For Grab Samples
or
Up To 48 Hours In Composite
Sampling Systems
Frozen
OK
NO
NO
OK
Lag Develops,
Must Use
Fresh Wastewater
Seed
Analysis
Phosphorous, Total
Solids
Specific Conductance
Sulfate
Sulfide
Threshold Odor
Turbidity
SAMPLE PRESERVATION
Preservative
H2S04 to pH <2 at 4°C
Refrigeration at 4°C
Refrigeration at 4°C
Refrigeration at 4°C
2 ml Zn acetate per liter at 4°C
Refrigeration at 4°C
Refrigeration at 4°C
Maximum
Holding Period
Acidity-Alkalinity
Refrigeration at 4°C
14 days
Biochemical Oxygen Demand
Refrigeration at 4°C
6 hours
Calcium
None required
7 days
Chemical Oxygen Demand
2 mg H,S04 per liter
28 days
Chloride
None required
28 days
Color
Refrigeration at 4°C
48 hours
Cyanide
NaOH topH 12
14 days
Dissolved Oxygen
Determine on site
1 hour
Fluoride
None required
28 days
Hardness
HNO, to pH <2
6 months
Metals, Total
5 ml HN03 per liter
6 months
Metals, Dissolved
Filtrate: 3 ml 1:1 HNO, per liter
6 months
Nitrogen, Ammonia
H2S04 to pH <2 at 4°C
28 days
Nitrogen, Kjedahl
H2SO, to pH <2 at 4°C
28 days
Nitrogen, Nitrate-Nitrite
H.SO„ to pH <2 at 4°C
28 days
Oil and Grease
H2S04 to pH <2 at 4°C
28 days
Organic Carbon
H2S04 to pH <2
28 days
pH
Determine on-site
No holding
Phenolics
HjSO, to pH <2 at 4°C
28 days
28 days
28 days
28 days
28 days
28 days
7 days
48 hours
Sources: U.S. Environmental Protection Agency,
HANDBOOK FOR MONITORING INDUSTRIAL WASTEWATER and U.S. Environmental Protection Agency, FEDERAL
REGISTER, VOL. 44, NO. 244, Tuesday, December 18, 1979, pages 75028-75052
-------
498 Treatment Plants
27.41 Storage Temperature
The recommended temperature for sample storage is 4°C.
At this temperature, the rate of chemical reactions and biologi-
cal activity is significantly reduced. Set the control on the re-
frigeration unit in permanent installations or chilling water unit
for a modified portable sampler. When using portable samplers
in the field, put ice on the compartment and hope for the best. If
you are working where the wastewater stream is warm, you
can use dry ice. Experiment to find out how much to use (too
much may freeze the samples). Samples must be kept chilled
while they are being transported to the laboratory.
27.42 Chemical Preservation
In some cases, it is appropriate to add chemicals to preserve
the samples (See Table 27.2 for detailed recommendations.)
For portable samplers, the chemical can be measured into
each sample bottle in advance.
27.43 Security
Once a sample has been obtained and is ready for labora-
tory analysis, it is extremely important to insure that each sam-
ple is carefully labeled. Test results are useless if there is any
doubt that they are for the correct sample. A good starting point
is to firmly affix a label or tag to the sample container (Figure
27.7). Another reason for careful labeling is so the "chain of
possession" is traceable. If legal action results, you must be
able to prove that the sample was in the possession of respon-
sible people at all times and also that no one tampered with the
sample.
A logging or "sign-in" system should be used at the labora-
tory. This system should include the name of the person deliv-
ering the sample as well as the date and time received. The
laboratory should then assign a number which identifies the
sample and appears on the laboratory report.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 508.
27.3A How would you attempt to trace or locate an industrial
waste discharge?
27.3B How can the intake for an automatic sampler be ad-
justed to sample solvents or other floatables?
27.4A Why should a sample be analyzed as soon as possi-
ble?
27.4B Why are samples stored at 4°C?
27.5 FLOW METERING
27.50 Need for Accurate Measurements
Measuring the flow from an industry is equally as important
as obtaining good samples. The quantity of pollutants cannot
be calculated without accurate flow data. Knowledge of the
quantities of pollutants from the various industries is essential
to reaching decisions regarding pretreatment requirements to
be set, and also to prepare accurate and equitable billing calcu-
lations. Flow and pollutant data on industries also may be an
important part of the design work for future expansions or new
facilities. Flows indicate the hydraulic loading on both the col-
lection system and the wastewater treatment facilities.
27.51 Water Meters
In many cases, the flow to the sewer can be calculated
based on data from water meters placed on public water
supplies or private wells. When water-meter data is used, al-
lowances may have to be made for evaporation, irrigation, or
water used in the product (e.g., soft drinks). Water meters on
boiler feed lines, product lines, or irrigation water will serve to
verify this type of usage.
For the larger industries, open-channel flow meters such as
Parshall flumes generally are used. For these ("fixed") in-
stallations, the same type of equipment is used as for treat-
ment plants. Refer to the section on metering in Chapter 15,
"Maintenance," for detailed information.
For the smaller enterprises, portable metering equipment
often is installed in existing collection systems. There are many
types of portable meters available. The standard approach is
to use a compact flume, such as a Palmer-Bowlus flume, as
the primary flow-measuring device. Some compact flumes
have provisions for several types of primary devices (flumes,
V-notch and rectangular weirs) for measuring the flows. The
level in the primary device is sensed by a float, bubbler, electri-
cal probe, sonar (ultrasonic), or built-in capacitance sensor in
the flume. The meters generally are equipped with a totalizer
and small strip-chart recorder, although at least one manufac-
turer uses a circular chart. Also, there is usually a connection
for controlling a sampler so that flow-proportional sampling can
be done in the field.
If you are purchasing a flow meter and the recorder is an
optional feature, you are strongly advised to include the re-
corder. Knowing the flow pattern can be very helpful in evaluat-
ing the discharges by an industry, and perhaps in helping them
to correct problems.
27.6 SAFETY
27.60 Traffic Safety
Obtaining a sample from a manhole in the street without
getting run over requires some advance preparation and effort.
Table 27.3 shows a good example of a traffic safety instruction
sheet. Follow these instructions very carefully as they apply to
your situation every time you must collect a sample from a
manhole in a street. Figure 27.8 shows how cones may be
used in a typical layout for blocking one lane of the street when
you must work in the street. Proper and improper barricades
for directing traffic are shown in Figure 27.9.
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Industrial Monitoring 499
COLLECTED BY
DATE
TIME
RECEIVED BY
DATE
TIME
TEST
SITE
BOD
COD
~ etc.
O&G
etc.
NOTE: Co. A is the Johnson Brewing Co.
Fig. 27.7 Label or identification tag for sample container
-------
500 Treatment Plants
ROAO
work.;;."
AHEAD
CLOSING RIGHT LANE
WORK
ARErA
/
A
/I
CLOSER./
/
/
/
I6HT LAN
CLOSED $
ROM)
WORK.
: AHEAD
Fig. 27.8 Typical layout for blocking one lane of traffic
(Source: Work Area Traffic Control by San Diego County Chapter, American Public Works Association.)
-------
Industrial Monitoring 501
use these:
Reflectors
Rubber or
Plastic
Traffic Cone -
Reflectors
-A
G
O
•"2..
Raised Pavement Markers
NOT THESE
Used Oil Drum
Metal
Pipe —) C
Sandbags
Concrete or Metal Base
Rock or
Chunk of Concrete
Fig. 27.9 Proper and improper barricades for directing traffic
(Source: Work Area Traffic Control by San Diego County Chapter, American Public Works Association.)
-------
502 Treatment Plants
TABLE 27.3 TRAFFIC SAFETY INSTRUCTIONS
Safe working conditions must be maintained at all times.
This is especially important when taking samples from
manholes located within normal traffic lanes.
The important considerations are: (1) to be visible to on-
coming traffic, and (2) to guide this traffic safely around you.
The following basic procedure is for your general guidance.
(For unusual situations, look at the situation carefully and
use common sense. If you consider a particular location too
hazardous, skip that location and contact your supervisor
for advice.)
1. Wear red safety vest, hard hat, and safety glasses.
2. Slow down in advance of work area. Use hand signals
and turn on beacon (the rotating yellow light on the vehi-
cle roof). Do not stop suddenly.
3. Park vehicle between you and the prevailing traffic,
about 10 feet (3 m) away from work area.
4. Turn wheels away from you and oncoming traffic, set
hand brake firmly, and place in parking gear.
5. Leave vehicle carefully — set out traffic cones as quickly
and as safetly as possible. Figure 27,8 shows how
cones may be used for blocking one lane of a street.
Proper and improper barricades for directing traffic are
shown in Figure 27.9.
6. Be alert to the traffic at all time.
7. Finish all work and be ready to go before retrieving traffic
cones.
27.61 Confined Spaces
Use a manhole hook or manhole lift to open manhole covers.
Do NOT use a bar because if you jab with it, you may cause a
spark which could be disastrous if an explosive atmosphere
existed in the manhole. When a manhole cover is off, guard the
area around the open manhole with traffic cones or a portable
guardrail. Remove items from shirt pockets before working
over the open manhole. When replacing the cover remove any
dirt or other debris from the base, so that the cover will seat
properly.
OSHA7 regulations (and common sense) dictate several
precautionary measures which must be taken before entering
manholes or other areas that may be confined spaces. Before
entering an area that may be a confined space, the atmos-
phere in the area must be tested for oxygen deficiency, toxic
gases (e.g., hydrogen sulfide), and explosive conditions
(Lower Explosive Limit). If you discover explosive conditions,
you must not enter. NOTIFY THE PROPER AUTHORITIES
IMMEDIATELY. If there is an oxygen deficiency, you may use
a self-contained breathing apparatus only for emergency entry.
Correct any situation in which an oxygen deficiency exists or
toxic gases are encountered by providing adequate ventilation.
Do not work in a confined space until all detection devices
indicate that the area is safe for entry. The important fact to
remember is that you seldom get a second chance. BE SURE
it's safe before entering confined spaces.
If there is no oxygen deficiency, no toxic gases and no ex-
plosive conditions, the area or space is considered NOT CON-
FINED. Before entering the area, you must be wearing a safety
harness. Two people must be standing by topside to help the
person out of the hole or area in an emergency. The atmos-
phere in the area must be continuously monitored (oxygen,
toxic gases, explosive conditions) whenever anyone is working
in the hole. If the monitor alarm goes off, the person in the hole
must be removed immediately.
NEVER enter a confined space even with a self-contained
breathing apparatus and sufficient people standing by unless
you absolutely must enter the space. If at all possible eliminate
the hazardous condition creating the confined space before
entering and working in the area.
For details on safe traffic regulation and manhole entry, see
Chapter 4, "Safety, Inspecting and Testing Collection Sys-
tems," in OPERATION AND MAINTENANCE OF WASTEWA-
TER COLLECTION SYSTEMS by John Brady and Kenneth D.
Kerri.
27.62 Equipment Storage
Orderliness is the key to avoiding accidents and equipment
damage in the storage area. Common hazards include items
protruding from shelves, items falling from shelves, and items
placed in normal traffic patterns on the floor. Containers should
be cleaned before storage and protected so they will stay
clean. Chemicals should be stored separately from other
items, with a separate room being preferable. All reagent bot-
tles must be marked with the date opened or the date the
reagents were prepared.
27.63 Battery Charging
There are some hazards to consider when using samplers
which operate from lead-acid batteries. When a lead-acid bat-
tery is being charged, hydrogen is given off. Therefore, good
ventilation is essential. New batteries must be shipped dry;
therefore, you must add the electrolyte (diluted sulfuric acid)
yourself. Protective clothing (goggles, gloves, aprons) must be
worn. Eyewash facilities must be provided. Some excerpts
from safety orders for battery charging are given in Appendix
D.
27.7 MONITORING STRATEGIES
27.70 Development of Strategies
The following discussion is based on the assumption that an
industrial discharge is the cause of the particular problem
under consideration. This will, of course, be obvious in many
cases. However, the "state of the art," particularly regarding
activated sludge, is not sufficiently advanced that the operator
can always be certain about the effects of a particular industrial
7 OSHA. The Williams-Steiger Occupational Safety and Health Act of 1970.
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Industrial Monitoring 503
discharge. A process that is not completely healthy may be
seriously upset by a discharge that would otherwise have little
effect. Extremely small quantities of certain exotic chemical
compounds (such as pesticides) may upset the process, and
not be detected at all by most monitoring programs. These
items are very important when preparing a plan of action on
how to operate wastewater treatment plants that must handle
industrial wastes.
27.71 Regulation of High Flows
Hydraulic loading is an important factor in plant perform-
ance. The flow from an industry may greatly affect a treatment
plant, particularly where a sizeable industry has located in a
smaller community. Regulation of the industrial flow to coincide
with low domestic flow periods may be required. Seasonal
industries, such as canneries, or vacation shutdown periods
may have a significant impact on treatment plant operation.
27.72 Decisions on Industrial Discharges
When a new industry is locating in your area, decisions will
have to be made regarding pretreatment, controlled timing or
rate of discharge and installation of monitoring equipment.
Several basic items need to be covered. Will there be any toxic
or hazardous materials in the discharge? Will there be dis-
charges that can cause problems in the sewers (e.g., oxygen
consuming wastes, explosive hazards, or solids settling)? Cal-
culate what the BOD loading will be and compare it to the
design capacity (less present loading) of the treatment plant.
Consider whether there might be clarifier hydraulic overloading
or excessive floatable or settleable solids. High solids loading
could lead to overloading the solids treatment capacity of the
digesters.
If a color is to be discharged, will it be from dyes or food
colors? Food coloring usually is no problem, because the col-
ors disappear within the plant processes. Other sources of
color will require some testing. Some wastes can be treated by
acclimatizing organisms to the specific toxic materials present
in the wastes. This is usually best handled by a pretreatment
process at the industry.
In general, you would not want to allow one new firm or
industry to use up all of the remaining hydraulic, BOD, or solids
capacity in your treatment plant. A new industry often will at-
tract more businesses, provide more jobs and cause an in-
crease in home construction. Some plant capacity should be
reserved for these other or secondary activities resulting from
a new industry.
Tables 27.1 (page 496), 27.4 and 27.5 summarize helpful
information indicating what to expect when evaluating the po-
tential impact of a new industry. These tables indicate the
types of wastes that can be expected, whether they might
interfere with treatment processes and whether the pollutants
might pass through a treatment plant untreated.
27.73 Reaction to Industrial Discharges
Table 27.6 lists some common industrial discharge situa-
tions and possible problems that may result, and suggested
actions to take. The table is useful primarily as an "idea file." A
listing of all the types of discharges that might occur is impos-
sible as is providing a specific corrective action for each possi-
ble case or problem. The operator should review the situations
listed plus any others that might be peculiar to the community,
and prepare for these possibilities. Pre-planning will allow you
to implement preventive maintenance measures such as the
purchase of neutralizing chemicals or construction of a holding
basin.
TABLE 27.4 POLLUTANTS THAT MIGHT INTERFERE
WITH WASTEWATER TREATMENT PLANTS
Inorganic Substances
Organic Substance#
Other Substances
Acidity, alkalinity
Alcohols
Corrosive materials
and pH
Agricultural
Explosives and
Ammonia
chemicals
flammable materials
Alkali and alkaline
Carbon tetrachloride
High temperature
earth metals
Chlorinated hydrocarbon
wastes
Arsenic
Materials that cause
Borate (and other
Chloroform
blockages
boron species)
Methylene chloride
Bromine
Miscellaneous organic
Cadmium
chemicals
Chloride
Oils and grease
Chlorine
Organic nitrogen
compounds
Chromium
Phenols
Copper
Surfactants
Cyanide
Iron
Lead
Manganese
Mercury
Nickel
Silver
Sulfate
Sulfide
Zinc
Source: JOINT TREATMENT OF INDUSTRIAL AND MUNICIPAL
WASTEWATERS, Water Pollution Control Federation,
Washington, D.C.
TABLE 27.5 POLLUTANTS THAT MIGHT PASS
THROUGH WASTEWATER TREATMENT PLANTS
Cadmium
Chloride
Chromium
Copper
Cyanide
Iron
Lead
Manganese
Mercury
Nickel
Nitrogen
Organic carbon
Phenolics
Phosphorus
Radioactive wastes
Suspended solids
Zinc
Source: JOINT TREATMENT OF INDUSTRIAL AND MUNICIPAL
WASTEWATERS, Water Pollution Control Federation,
Washington, D.C.
-------
504 Treatment Plants
TABLE 27.6 REACTIONS TO INDUSTRIAL DISCHARGES
SITUATION
1. Gasoline, solvent; other hydrocarbons
PROBLEM
a. Explosive or flammable conditions in wet
wells and headworks
b. Possible damage to secondary processes a.
ACTIONS
Hold gasoline or solvent on top of primary
clarifiers and allow wind to disperse fumes.
Inspect wet well headworks ventilation and
provide extra ventilation with blowers only
(no suction of vapors into fans).
Divert to holding basin.
Keep personnel clear of area.
Pure oxygen plants. Vent and purge reac-
tors with air. Shut down oxygen feed until
L.E.L. out of alarm range and normal
readings are obtained.
Watch DO levels, waste and return sludge
rates.
2. Excessive solids
a. Cause stoppages in sewers
b. Overload treatment processes
a. Flush sewers.
a. Increase pumping from clarifiers.
b. Balance feed to digesters.
c. Watch for septic conditions in primary
clarifiers.
d. Watch for low DO in aeration systems.
3. Acid or caustic wastes a.
4. Color and turbidity a.
5. High temperature waste a.
b.
c.
Toxic to organisms in biomass
Color and turbidity in effluent
Septic conditions in sewers
Upset biological treatment processes
Trickling filter ponding
Increased oxygen demand
a. Neutralize.
b. If too late and the biomass is damaged,
adjust air rates, wasting rates, and foam
control devices. Increase chlorine dosage
for adequate disinfection.
a. Food colors assimilated in secondary pro-
cesses.
b. Trace discharge back to source.
c. Wastes from different industries may com-
bine to form permanent colors. Control
colors at source.
a. Try prechlorination to correct.
a. Stop high temperature discharges at
source.
a. Increase recirculation rates.
a. More air is required in activated sludge
process.
6. High organic load (suspended and dis- a. Septic conditions in sewers
solved solids)
b. Upset biological treatment processes
7. Oil and grease
a. Grease build-up in sewers
b. Scum blankets in digesters
c. Excessive grease in clarifier scum box. Dif-
ficulty in pumping.
d. Secondary processes
(1) May carry oil and grease over weirs
(2) Trickling filters. Plugged orifices and
ponding.
(3) Activated sludge. Oil coats biomass
and foam problems develop.
a. Try prechlorination to correct.
a. Activated sludge.
(1) More air required.
(2) Fast solids build-up. Try increasing
wasting.
(3) Foam. Try using sprays and/or de-
foamers.
b. Trickling filters. Increase recirculation
rates.
a. Clean more frequently.
a. Increase mixing.
a. Try removing grease more frequently.
a. Increase maintenance.
(1) Increase skimming at clarifier sur-
face.
(2) Increase frequency of cleaning and
hosing.
(3) Skim floating sludge and scum from
surface of secondary clarifiers.
-------
Industrial Monitoring 505
SITUATION
TABLE 27.6 REACTIONS TO INDUSTRIAL DISCHARGES (Continued)
PROBLEM ACTIONS
8. Toxic substances (heavy metals and
pesticides)
10. Taste and odor problems
11. Pathogenic wastes
Radioactive wastes
12. Hydaulic shock load
Usually not detected in plant effluent
Plant processes deteriorate
Trickling filter sloughing can occur
Extensive lab work to identify material
9. Nutrients (nitrogen and phosphorus) a.
b.
Poor removals of nutrients by conventional
plant processes and may cause aquatic
growths in receiving waters.
Conversion of ammonia nitrogen to nitrite
nitrogen will cause high chlorine demands
and possibly reduce coliform kills.
Undesirable tastes and odors in drinking
waters
Hydrogen sulfide from:
(1) Septic conditions in sewers
(2) Tannery and other wastes
Harmful to humans and usually not detect-
able at treatment plant
a. Overload treatment processes
a. Prevent from entering collection system.
b. Try to build up biomass by stopping all
sludge wasting and return sludge rates. If
necessary, obtain seed sludge from
another plant.
c. If wasting is continued, do not waste toxic
substances to another biological process
(aerobic or anaerobic digester). Try to
minimize wasting of helpful organisms.
d. Usually less air is required because of re-
duced biological activity. Excess air rates
may strip out some toxic substances.
e. Increase foam control if necessary.
f. Find out what is being discharged and trace
to source.
a. Source control of nutrients.
b. Tertiary treatment to remove nutrients.
a. Change process to avoid converting am-
monia to nitrite by lowering DO levels and
MCRT.
a. Phenolic compounds good example. They
pass through the plant and cause water
supply problems. Control at source.
b. Carefully control chlorine so tastes and
odors won't get worse.
a. Control hydrogen sulfide.
(1) Try prechlorination.
(2) Control at source.
a. Control at source, such as hospitals and
clinics.
a. Reduce if possible by:
(1) Diverting to storage basin; and/or
(2) Restricting influent flow.
b. Increase chlorination rate.
b. Activated sludge process may lose solids a. Stop wasting.
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506 Treatment Plants
27.74 Warning Systems
Continuous monitoring and alarm systems for treatment
plant influents are becoming common. Conductivity, pH, ex-
plosive atmosphere (L.E.L.), and oxygen deficiency detectors
are suitable for continuous monitoring. Special sensors are
available for many wastewater constituents; however, few are
suitable at present for continuous use. High water level or flow
alarms are available to warn of surges or hydraulic overloads.
The operator should keep abreast of progress in this field.
Reading the technical journals and attending seminars and
conferences will help to keep you current.
27.8 ADDITIONAL READING
1. MOP 11, Chapter 29,* "Effects of Industrial Wastes on
Wastewater Treatment."
2. NEW YORK MANUAL, Chapter 10, "Industrial Wastes."
3. TEXAS MANUAL, Chapter 26, "Industrial Wastes."
4. HANDBOOK FOR MONITORING INDUSTRIAL WASTE-
WATER, U.S. Environmental Protection Agency, Technol-
ogy Transfer, Cincinnati, Ohio 45268.
5. OPERATION AND MAINTENANCE OF WASTEWATER
COLLECTION SYSTEMS, Kenneth D. Kerri and John
Brady, California State University, Sacramento, 6000 Jay
Street, Sacramento, California 95819. Price $30.00.
6. STANDARD INDUSTRIAL CLASSIFICATION MANUAL,
Stock Number 041-001-00066-6, Superintendent of Docu-
ments, U.S. Government Printing Office, Washington, D C
20402. Price $10.25.
7. JOINT TREATMENT OF INDUSTRIAL AND MUNICIPAL
WASTEWATERS, Water Pollution Control Federation, 2626
Pennsylvania Avenue, NW, Washington, D.C. 20037.
Order No. M0021. Price: $2.00 to members; $4.00 to
others.
* Depends on edition.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 508.
27.5A Why should the flow from an industry be measured?
27.6A List the major areas of potential safety hazards while
monitoring industrial wastes.
27.7A How would you regulate or handle a large, fluctuating
industrial flow that hydraulically overloads a treatment
plant during the day?
27.7B What types of potentially harmful industrial waste dis-
charges can be continuously monitored and con-
nected to alarm systems?
OP i&Aom
Work the next portion of the discussion and review questions
before continuing with the objective test.
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Industrial Monitoring 507
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 2 Lessons)
Chapter 27. INDUSTRIAL WASTE MONITORING
How would you attempt to locate an industrial waste dis-
charge that is causing problems?
Why is the "chain of possession" of a sample important?
How would you measure the flow from an industry?
How could you check or verify the accuracy of an industrial
laboratory analyzing samples from its own self-monitoring
program?
10. What are the potential hazards that could be encountered
when entering a manhole?
11. What basic items would you consider when reviewing the
application or permit of an industrial waste discharger?
12. What would you do if a gasoline or solvent was discovered
on the surface of the wet well in the headworks of your
treatment plant?
PLEASE WORK THE OBJECTIVE TEST NEXT.
SUGGESTED ANSWERS
Chapter 27. INDUSTRIAL WASTE MONITORING
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 1.
6.
7.
8.
9.
Answers to questions on page 485.
27.0A Objectives of an industrial waste monitoring program
include:
1. Prevention of shock loads on treatment processes;
2. Provision of physical protection for personnel and
facilities;
3. Prevention of discharge of pollutants from treat-
ment plants; and
4. Provision of a data base for equitable sewer-use
charges and for engineering design.
27.06 Adverse characteristics of industrial wastes that could
have serious impacts are:
1. Collection systems — acid wastes, thermal wastes,
solids, oil and grease, odors, toxic substances,
flammable and explosive material; and
2. Treatment plants — organic overload, toxic sub-
stances, oil and grease, acids and alkalies, hydrau-
lic overload, materials not removed by plant pro-
cesses and other hazardous wastes.
Answers to questions on page 486.
27.1 A A good data base on industrial waste discharges is
important in making decisions regarding treatment of
plant process control, billing or use charges, documen-
tation of incidents, and engineering design work.
27.1B Information collected to develop a data base includes
industry identification, flow data, laboratory results, bil-
ling information, treatment information, reports of un-
usual circumstances or incidents, industrial facilities
and emergency information.
27.1C A sewer-use ordinance should provide authority for
the following enforcement activities:
1. Inspecting and monitoring,
2. Requiring pretreatment and/or flow adjustment,
3. Curtailing or ceasing of discharge,
4. Requiring spill protection measures,
5. Issuing permits to dischargers, and
6. Collecting money by billing for treatment provided.
Answers to questions on page 487.
27.2A Self-monitoring programs are commonly used in large
industrial areas because the burden of monitoring a
large number of industries would be overwhelming to
a local agency.
27.2B Sensors used in continuous monitoring programs may
require frequent cleaning and calibration to maintain
their accuracy.
27,2C Representative sample. A portion of material or water
identical in content to that of the larger body of mate-
rial or water being sampled.
27.2D Attempt to collect representative samples at sampling
points where the wastewater flow is well mixed.
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508 Treatment Plants
Answers to questions on page 491.
27.2E The differences between grab and composite samples
include:
1. Grab samples are simpler and less expensive.
While they can indicate the contents of the waste
stream at the time of sampling, they are not useful
for variable discharges.
2. Composite samples provide a more accurate rep-
resentation of a wastewater stream. A problem
with composite samples is that peak concentra-
tions of toxic substances may be missed.
27.2F Portable sampling equipment obtains power in the
field from rechargable batteries or, when possible,
from a 110-volt AC line using a "power pack."
27.2G The flow velocity in the sampler suction tube is impor-
tant in obtaining repeatable results. If velocities are
too low, solids will be left behind in the tubing. If vel-
ocities are too high, large chunks of material may be
pulled into the sample and yield erratic results.
27.2H Monitoring equipment should be kept clean at all times
to avoid contaminating samples. Regular mainte-
nance should be performed in accordance with the
manufacturer's instructions.
END OF ANSWERS TO QUESTIONS IN LESSON 1.
Answers to questions on page 498.
27.3A An industrial waste discharge may be traced or lo-
cated by looking for signs or evidence of the waste.
Begin at the treatment plant or collection point where
the waste has been discovered, then follow signs of
the waste back to the source. Look for indicative color
or solids. If the discharge is not visible, use portable
samplers to follow the waste to its source.
27.3B The intake to an automatic sampler can be adjusted to
sample solvents or other floatables by fastening the
suction tubing to a block of styrofoam or other similar
material to hold the suction very close to the surface.
27.4A A sample should be analyzed as soon as possible to
prevent physical, chemical or biological changes in the
sample.
27.4B Samples are stored at 4°C to reduce the rate of chemi-
cal reactions and biological activity.
Answers to questions on page 506.
27.5A The flow from an industry should be measured to de-
termine the hydraulic loading on the collection system
and the treatment facilities and also to determine the
quantities of pollutants or wastes discharged.
27.6A Major areas of potential safety hazards while monitor-
ing industrial wastes include:
1. Traffic safety.
2. Confined spaces.
3. Equipment storage areas.
4. Battery charging.
27.7A If an industry hydraulically overloads a treatment plant
during the day, try requiring the industry to store a
portion of its discharges during peak flow periods for
release during low flow periods such as the graveyard
shift.
27.7B Potentially harmful industrial waste discharges that
can be continuously monitored and connected to
alarm systems include conductivity, pH, explosive at-
mosphere, and oxygen deficiency conditions.
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Industrial Monitoring 509
OBJECTIVE TEST
Chapter 27. INDUSTRIAL WASTE MONITORING
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one correct answer to each question.
1. industrial wastes can have undesirable impacts on both
collection systems and treatment plants.
1. True
2. False
2. When dealing with an industrial waste discharger, be sure
that you can show the need for any necessary action.
1. True
2. False
3. A good sampling point is easily accessible and located
anywhere that a representative sample can be obtained.
1. True
2. False
4. Composite samples always reveal peak concentrations of
toxic waste discharges.
1. True
2. False
9. Extremely small quantities of certain exotic chemical com-
pounds (such as pesticides) may upset the activated
sludge process, and not be detected at all by most
monitoring programs.
1. True
2. False
10. If a new industry wants to use all of the remaining hydrau-
lic and BOD capacity in your treatment plant, this request
should be granted.
1. True
2. False
11. Why should industrial wastes discharged into a collection
system be monitored?
1. To impose fines on industries
2. To prevent shock loads from upsetting wastewater
treatment processes
3. To protect operators of wastewater collection systems
and treatment plants from hazardous and toxic sub-
stances
4. To protect the public by preventing toxic industrial
wastes from reaching drinking water supplies
5. To protect wastewater collection and treatment
facilities from corrosive and other harmful substances
12. Information on file for each industrial waste discharger
should include
1. Calculations used to determine billings.
2. Flow data and lab analyses of discharges.
3. Names and phone numbers of at least two representa-
tives of the industry with authority to act in an
emergency.
4. Profits earned by industry last year.
5. Total number of employees.
SIC stands for
1. Selected Incidents of Catastrophes caused by indus-
trial wastes dischargers.
2. Selected Industrial Cases of solutions to industrial
problems.
3. Sicknesses caused by industrial wastes.
4. Standard Industrial Classification of industries.
5. Standard Industrial Code of industrial wastes.
Before visiting an industry with an industrial monitoring
program, the file should be reviewed. The file should con-
tain a layout of the industry showing location of
1. Chemical storage areas.
2. Person to contact upon arrival for inspection visits.
3. Personnel office.
4. Sewer lines and connections.
5. Spill protection measures.
Desirable features of available portable samplers include
1. A rinse cycle for washing sample bottles.
2. Automatic purging of lines before and after collecting a
sample.
3. Direct analysis of total suspended solids.
4. Flexibility to collect samples at various time intervals.
5. Sensor to find location of representative samples in
sewer.
16. Samples are stored at 4°C in order to
1. Freeze the sample.
2. Melt the ice in the sample.
3. Reduce biological activity in the sample.
4. Reduce the pH of the sample.
5. Reduce the rate of chemical reactions in the sample.
5. A block of styrofoam or other similar material can be used
to hold the suction end of a sampling tube very close to the
surface when sampling for petroleum solvents or similar
floatable materials.
1. True
2. False
6. Chemicals may be added to preserve samples in some
cases.
1. True
2. False
7. Cleanliness is not important to sampling accuracy.
1. True
2. False
8. A knowledge of traffic safety is very important for persons
involved in industrial waste monitoring.
1. True
2. False
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510 Treatment Plants
17. Flows should be measured from an industry in order to
1. Calculate the quantities of pollutants discharged.
2. Check compliance with pretreatment requirements.
3. Determine which flow meter works best.
4. Measure toxic gases released.
5. Prepare accurate and equitable billing calculations.
18. Industrial wastewater quality indicators that may be con-
tinuously monitored include
1. Floatable solids.
2. pH.
3. Settleable solids.
4. Specific conductance.
5. Temperature.
19. Hazards that may be found in equipment storage areas
include
1. Chemicals stored in the same room as the equipment.
2. Hydrogen gas produced by the charging of a lead-acid
battery.
3. Improperly marked reagent bottles.
4. Items on the floor in normal traffic patterns.
5. Items protruding from shelves.
20. What types of continuous monitoring and alarm systems
are commonly available?
1. BOD
2. Explosive atmosphere (L.E.L.)
3. High water level or flow
4. Oxygen deficiency
5. pH
21. Which of the following actions would you consider taking if
a solvent was discovered in the wet well of your treatment
plant?
1. Divert solvent to holding basin if available
2. Increase feed to digesters
3. Keep personnel clear of area until safe to enter
4. Provide extra ventilation to wet well
5. Remove solvent by incineration in wet well
22. Which of the following actions would you consider taking if
your treatment plant received a high temperature waste?
1. If a trickling filter plant, try increasing recirculation rates
2. If an activated sludge plant, try increasing aeration
rates or oxygen supply
3. Try cooling the waste at the headworks
4. Try prechlorinating in collection system to reduce sep-
tic conditions
5. Try stopping high temperature discharges at source
¦ „
o0j#rrNe
-iw
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Industrial Monitoring
APPENDIX A
INDUSTRIAL SEWER-USE PERMIT APPLICATION
Source: Water Quality Division,
Department of Public Works,
Sacramento County,
Sacramento, California
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512 Treatment Plants
INDUSTRIAL SEWER USE PERMIT APPLICATION
SANITATION DISTRICT
1. NAME OF BUSINESS
2. ADDRESS OF PREMISES.
3. OWNER OF BUSINESS
4. OWNER'S ADDRESS (Street).
(City) .
(Zip).
5. OWNER OF PROPERTY (IF DIFFERENT).
6. PROPERTY OWNER'S ADDRESS (Street) _
(City) _
PAGE I
GENERAL
(Instructions on reverse)
DISTRICT USE
SUP #
AP # _
CP # _
SIC #
(Zip).
7. SEND SEWER BILLS TO: ~ BUSINESS (1&2); ~ BUSINESS OWNER (3&4); ~ PROPERTY OWNER (5&6)
8. PERSON TO CONTACT ABOUT THIS APPLICATION Phone
9. DESCRIPTION OF BUSINESS
10. RATE BASIS:
UNIT QUANTITY
11. WASTEWATER GENERATING OPERATIONS:
12. SEASONAL VARIATIONS
13. ARE ANY OF THE FOLLOWING MATERIALS USED OR STORED ON THE PREMISES?
1. Flammable or explosive materials. 2. Acid, alkaline, or corrosive material. 3. Pesticides or
toxic material such as Aldrin, Dieldrin, Benzidine, Cadmium, Cyanide, DDD, DDE, DDT,
Endrin, Mercury, PCB's, Toxaphene, Etc. 4. Oil, grease or solvents. 5. Metal solutions.
6. Phenols. 7. Large amounts of soaps or detergents. 8. Radioactive material. 9. Dyes.
I I NO d YES (if yes, please give description, and the approximate quantities used and/or stored.)
14. PERSON TO CONTACT IN AN EMERGENCY
TITLE Phone Emergency No.
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Industrial Monitoring 513
INSTRUCTIONS FOR COMPLETING PAGE 1
1. ENTER NAME OR TITLE OF BUSINESS.
2. ENTER FULL STREET ADDRESS OF BUILDING OR PREMISES PRODUCING THE WASTEWATER.
3. ENTER NAME OF INDIVIDUAL OR FIRM THAT IS THE OWNER OF THE BUSINESS.
4. ENTER MAILING ADDRESS OF OWNER OF BUSINESS.
5. ENTER NAME OF LEGAL OWNER OF PROPERTY UPON WHICH THE BUSINESS IS LOCATED, IF IT IS DIFFERENT
THAN THE OWNER OF THE BUSINESS.
6. ENTER MAILING ADDRESS OF PROPERTY OWNER.
7. INDICATE WHERE SEWER BILLS SHOULD BE SENT. (UNLESS OTHERWISE INDICATED, THE BILLS WILL BE
SENT TO THE PROPERTY OWNER).
8. IDENTIFY PERSON WHO IS THOROUGHLY FAMILIAR WITH THE FACTS REPORTED ON THESE FORMS AND
MAY BE CONTACTED BY THE DISTRICT.
9 DESCRIBE THE PRINCIPAL ACTIVITY ON THE PREMISES, SUCH AS FOOD CANNING, BANK, ETC.
10. DETERMINE FROM TABLE BELOW WHICH UNIT WOULD BE APPLICABLE FOR THIS TYPE OF BUSINESS AND
THE NUMBER OF UNITS. IF, FOR EXAMPLE, THE BUSINESS IS A MARKET, ENTER "AREA" FOR UNIT. THEN
ENTER THE NUMBER OF SQUARE FEET IN THE STORE FOR QUANTITY
BUSINESS
UNIT
BUSINESS
UNIT
Auto dealerships
Area (s.f.)
Market
Area (s.f.)
Bakeries
Area (s.f.)
Medical, Dental
Area (s.f.)
Banks and financial
Area (s.f.)
Mortuaries
Slumber rooms
Barber/beauty shops
Chairs
Offices
Area (s.f.)
Bars
Area (s.f.)
Places of Worship
Area (s.f.)
Bowling alleys
Lanes
Public agencies
Area (s.f.)
Car wash (full service)
Flow*
Rest/convalescent homes
Beds
Car wash (self service)
Stalls
Restaurants
Area (s.f.)
Dry cleaners
Area (s.f.)
Retail stores
Area (s.f.)
Garages
Bays
Schools
Attendance
Halls, Lodges
Area (s.f.)
Service stations
Pumps
Health studio, Gym
Area (s.f.)
Theaters
Seats
Hotel, Motel
Sleeping Rooms
Used car lots
Fixture units
Laundry (self service)
Machines
Warehouses
Area (s.f.)
Laundry (commercial)
Flgw*
Others
Flow
'estimate number of gallons of wastewater discharged each month
11. DESCRIBE WASTEWATER GENERATING PROCESS OCCURING ON THE PREMISES, INCLUDING PLANT
OPERATIONS, RAW MATERIALS USED, CHEMICALS USED, AND ANY VARIATIONS IN DISCHARGE
VOLUMES.
12. INDICATE WHETHER THE BUSINESS ACTIVITY IS CONTINUOUS THROUGHOUT THE YEAR OR IF IT IS
SEASONAL. DESCRIBE THE SEASONAL VARIATION, LISTING MONTHS OF SEASONAL ACTIVITY.
13. LIST SIGNIFICANT RAW MATERIALS USED OR STORED ON PREMISES AND INDICATE DURATION OF
STORAGE. INCLUDE ALL HAZARDOUS, POISONOUS, OR TOXIC MATERIALS EVEN IF THEY ARE KEPT
ON PREMISES ONLY OCCASIONALLY. NEGLECT MATERIALS USED IN LABORATORY OR QUALITY
CONTROL OPERATIONS. IF QUANTITIES IN INVENTORY VARY, SELECT AN AVERAGE AMOUNT OR
GIVE RANGES. USE ADDITIONAL SHEETS IF NECESSARY.
14. GIVE NAME, TITLE, AND TELEPHONE NUMBER(S) OF A RESPONSIBLE PERSON WHO CAN BE CONTACT-
ED IN CASE OF AN EMERGENCY (e.g. SPILLING OF A TOXIC MATERIAL)
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514 Treatment Plants
INDUSTRIAL SEWER USE PERMIT APPLICATION
PAGE 2
LAYOUT
SANITATION DISTRICT
(Instructions on reverse)
SITE PLAN OF PREMISES
-------
INSTRUCTIONS FOR COMPLETING PAGE 2
Industrial Monitoring 515
DRAW A SITE PLAN SHOWING LOCATION OF ALL PERTINENT BUILDINGS, SHEDS,
WAREHOUSES, LOADING AND UNLOADING FACILITIES, FENCES, PROPERTY LINES,
STREETS AND ROADS. INDICATE ALL SEWERS, STORM DRAINS, DRAINAGE DITCHES,
MANHOLES, SAMPLING AND MONITORING LOCATIONS, WATER LINES AND METERS,
AND SHOW THE SIZES OF THESE ITEMS. SHOW ALL POINTS OF CONNECTION TO THE
PUBLIC SEWER AND DRAIN LINES. INDICATE SCALE AND NORTH ARROW. USE
ADDITIONAL SHEETS IF NECESSARY. (BUILDING AND/OR SITE PLANS ACCEPTABLE
TO THE DISTRICT MAY BE SUBSTITUTED FOR THIS FORM.)
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516 Treatment Plants
INDUSTRIAL SEWER USE PERMIT APPLICATION
SANITATION DISTRICT
PAGE 3
WASTEWATER DATA
(Instructions on reverse)
1. WATER
D PRIVATE WELL
2. WASTEWATER FLOW RATE TO SEWER:
SOURCE
~ PUBLIC (METERED)
PEAK
MAX.
AVERAGE
~ PUBLIC (UNMETERED)
HOURLY
DAILY
DAILY
~ OTHER
(g«l/hour)
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Industrial Monitoring 517
INSTRUCTIONS FOR COMPLETING PAGE 3
1. INDICATE WHERE WATER USED ON THE PREMISES IS OBTAINED.
2. LIST TOTAL DISCHARGES FROM PREMISES TO EACH SEPARATE SEWER.
PEAK HOURLY - Indicate expected maximum flow in a one-hour period at any time in the year. Do not include
batch discharges.
MAXIMUM DAILY - Indicate expected maximum flow during a 24 hour period.
AVERAGE DAILY - Estimate the flow during an average 24 hour period.
3. THESE ITEMS ARE REGULATED AND MAY BE DISCHARGED ONLY WITH THE SPECIFIC PERMISSION OF THE
DISTRICT. INDICATE WHETHER YOU ANTICIPATE DISCHARGING THESE. IF SO, GIVE DETAILS IN "REMARKS"
(#5).
4. DESCRIBE, ON A SEPARATE SHEET, AMY PRETRE ATMENT GIVEN THE WASTEWATER BEFORE IT IS DISCHARGED
INTO THE SEWER. THE TREATMENT FACILITY SHOULD BE DESCRIBED IN SUFFICIENT DETAIL TO ENABLE AN
ESTIMATION OF ITS EFFECTIVENESS.
5. GIVE ANY DETAILS REQUIRED BY #3. ALSO PROVIDE ANY INFORMATION ABOUT YOUR OPERATION THAT
YOU FEEL MIGHT HAVE AN EFFECT ON THE SEWERAGE SYSTEM.
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518 Treatment Plants
INDUSTRIAL SEWER USE PERMIT APPLICATION
PAGE 4
SANITATION DISTRICT CERTIFICATION
(Instructions on reverse)
WARNING - DISCHARGE OF SUBSTANCES INTO THE PUBLIC SEWER IS REGULATED BY LAW AND IS SUBJECT
TO CIVIL AND CRIMINAL PENALTIES. IF YOU ANTICIPATE DISCHARGING ANYTHING OTHER
THAN NORMAL DOMESTIC SEWAGE, YOU ARE ADVISED TO READ THE "SEWER USE ORDINANCE"
ADOPTED BY THE BOARD OF DIRECTORS OF THE DISTRICT.
The Sewer Use Ordinance prohibits any discharge which would cause a hazard or interfere with the operation of
the District's facilities, or would result in contamination, nuisance, or pollution of public waterways (refer to the
ordinance for wording). In addition, the ordinance specifically prohibits the discharge to public sewers of the
following:
PROHIBITED DISCHARGES - (BRIEF DESCRIPTION, see Sect. 6.4, Regional Sewer
Use Ordinance)for full description):
1. Unpolluted storm or other waters.
2. Wastewater having pH lower than 5.0, or other corrosive properties.
3. Certain pesticides and other toxic pollutants.
4. Solid or viscous substances capable of causing an obstruction to the flow in sewers, or other interference
with the proper operation or maintenance of the sewerage system.
5. Wastes which cannot be treated by the District's processes.
6. Materials prohibited by the EPA.
NOTE - A SEWER USE PERMIT PERTAINS ONLY TO THE DISCHARGE OF WASTEWATER INTO THE PUBLIC
SEWERAGE SYSTEM . CONNECTION TO THE PUBLIC SEWER, AND THE INSTALLATION OR
MODIFICATION OF ON-SITE PLUMBING, REQUIRES SEPARATE PERMITS.
CERTIFICATION: 1 certify that the information contained herein is true and correct to the best of my
knowledge.
Signature Date
Name (type or print) Title .
SEWER USE PERMIT
The above named applicant is hereby authorized to use the public sewerage system subject to the
following conditions:
1. Compliance with applicable sewer use ordinances
2. Payment of all applicable fees and charges
3.
The applicant shall report to the Water Quality Division any changes (permanent or temporary) to
the premises or operations that could significantly change the quality or volume of the discharge, or
deviate from the conditions under which this permit is granted. This permit is not transferable.
LOCAL APPROVAL
Signed
Date
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Industrial Monitoring 519
INSTRUCTIONS FOR COMPLETING PAGE 4
CERTIFICATION:
The application must be signed and dated by an officer, employee, or other agent
of the business who has legal authority to bind the applicant business. Also type
or print the name and title of the person signing the application.
RETURN THE APPLICATION TO:
Industrial Waste Section
Water Quality Division
*************************************************
Do not complete the portion below the line. The Water Quality Division will determine what
conditions will be applied to the permit, then will sign and return the permit to the applicant.
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Treatment Plants
APPENDIX B
SAMPLE SEWER-USE ORDINANCE
Source: U.S. Environmental Protection Agency
-------
Industrial Monitoring 521
ORDINANCE NO
AN ORDINANCE establishing rules and regulations for the
discharge of wastewaters into the wastewater treatment sys-
tem of the City of ; and
WHEREAS, the Federal Water Pollution Control Act
Amendments of 1972, P.L. 92-500 (hereinafter referred to as
the "Act") have resulted in an unprecedented program of
cleaning up our Nation's waters; and
WHEREAS, this City has already made and will continue to
make a substantial financial investment in its wastewater
treatment system to achieve the goals of the Act; and
WHEREAS, this City seeks to provide for the use of its
wastewater treatment system by industries served by it without
damage to the physical facilities, without impairment of their
normal function of collecting, treating and discharging domes-
tic wastewater, and without the discharge by this City's waste-
water treatment system of pollutants which would violate the
discharge allowed under its National Pollutant Discharge
Elimination System (NPDES) permit and the applicable rules
of all governmental authorities with jurisdiction over such dis-
charges;
NOW, THEREFORE, BE IT ORDAINED AND ENACTED by
the City Council of the City of ,
County of , State of
, as follows:
SECTION 1: DEFINITIONS
Unless the context specifically indicates otherwise, the fol-
lowing terms as used in this Ordinance, shall have the mean-
ings hereinafter designated:
(a) "BIOCHEMICAL OXYGEN DEMAND" (BOD) means
the quantity of oxygen utilized in the biochemical oxidation of
organic matter under standard laboratory procedure in five (5)
days at 20°C, expressed in terms of weight and concentration
(milligrams per liter).
(b) "COOLING WATER" means the water discharged from
any use such as air conditioning, cooling or refrigeration, dur-
ing which the only pollutant added to the water is heat.
(c) "COMPATIBLE POLLUTANT' means BOD, sus-
pended solids, pH and fecal conform bacteria, and such addi-
tional pollutants as are now or may be in the future specified
and controlled in this City's NPDES permit for its wastewater
treatment works where said works have been designated and
used to reduce or remove such pollutants.
(d) "DIRECTOR/("SUPERINTENDENT") means the
(director/superintendent of wastewater treatment system/of
water pollution control/or public works) of this City or the duly
appointed deputy, agent or representative.
(e) "DOMESTIC WASTES" means liquid wastes (i) from
the non-commercial preparation, cooking and handling of food
or (ii) containing human excrement and similar matter from the
sanitary conveniences of dwellings, commercial buildings, in-
dustrial facilities, and institutions.
(f) "GARBAGE" means solid wastes from the domestic
and commercial preparation, cooking and dispensing of food,
and from the handling, storage and sale of food.
(g) "INCOMPATIBLE POLLUTANT" means any pollutant
which is not a "compatible pollutant" as defined in this section.
(h) "INDUSTRIAL WASTEWATER" means the liquid
wastes resulting from the processes employed in industrial,
manufacturing, trade or business establishments, as distinct
from domestic wastes.
(i) "NATIONAL POLLUTANT DISCHARGE ELIMINATION
SYSTEM" (NPDES) means the program for issuing, condition-
ing and denying permits for the discharge of pollutants from
point sources into the navigable waters, the contiguous zone
and the oceans pursuant to Section 402 of the Act.
(j "PERSON" means any individual, firm, company,
partnership, corporation, association, group or society, and in-
cludes the State of , and agen-
cies, districts, commissions and political subdivisions created
by or pursuant to State law.
(k) "pH" means the logarithm of the reciprocal of the con-
centration of hydrogen ions in grams per liter of solution.
(I) "PRETREATMENT" means application of physical,
chemical and biological processes to reduce the amount of
pollutants in or alter the nature of the pollutant properties in a
wastewater prior to discharging such wastewater into the pub-
licly owned wastewater treatment system.
(m) "PRETREATMENT STANDARDS" means all appli-
cable Federal rules and regulations implementing Section 307
of the Act, as well as any nonconflicting State or local stan-
dards. In cases of conflicting standards or regulations, the
more stringent thereof shall be applied.
(n) "SIGNIFICANT INDUSTRIAL USER" means any indus-
trial user of the City's wastewater treatment system whose flow
exceeds (1) (50,000) gallons per day, or (ii) (five (5)) percent of
the daily capacity of the treatment system.
(o) "STORM WATER" means any flow occurring during or
immediately following any form of natural precipitation and re-
sulting therefrom.
(p) "SUSPENDED SOLIDS" means the total suspended
matter that floats on the surface of, or is suspended in, water,
wastewater or other liquids, and which is removable by labora-
tory filtering.
(q) "UNPOLLUTED WATER" is water not containing any
pollutants limited or prohibited by the effluent standards in ef-
fect, or water whose discharge will not cause any violation of
receiving water quality standards.
(r) "USER" means any person who discharges, causes or
permits the discharge of wastewater into the City's wastewater
treatment system.
(s) "USER CLASSIFICATION" means a classification of
user based on the 1972 (or subsequent) edition of the Stan-
dard Industrial Classification (SIC) Manual prepared by the
Office of Management and Budget.
(t) "WASTEWATER" means the liquid and water-carried
industrial or domestic wastes from dwellings, commercial build-
ings, industrial facilities, and institutions, together with any
groundwater, surface water, and storm water that may be pre-
sent, whether treated or untreated, which is discharged into or
permitted to enter the City's treatment works.
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522 Treatment Plants
(u) "WASTEWATER TREATMENT SYSTEM" (system)
means any devices, facilities, structures, equipment or works
owned or used by the City for the purpose of the transmission,
storage, treatment, recycling, and reclamation of industrial and
domestic wastes, or necessary to recycle or reuse water at the
most economical cost over the estimated life of the system,
including intercepting sewers, outfall sewers, sewage collec-
tion systems, pumping, power, and other equipment, and their
appurtenances; extensions, improvements, remodeling, addi-
tions, and alterations thereof; elements essential to provide a
reliable recycled supply such as standby treatment units and
clear well facilities; and any works, including site acquisition of
the land that will be an integral part of the treatment process or
is used for ultimate disposal of residues resulting from such
treatment.
(v) Terms not otherwise defined herein shall be as adopted
in the latest edition of STANDARD METHODS FOR THE
EXAMINATION OF WATER & WASTEWATER, published by
the American Public Health Association, the American Water
Works Association, and the Water Pollution Control Federa-
tion.
SECTION 2: PROHIBITIONS AND LIMITATIONS OF
WASTEWATER DISCHARGES
(a) PROHIBITIONS ON WASTEWATER DISCHARGES.
No person shall discharge or deposit or cause or allow to be
discharged or deposited into the wastewater treatment system
any wastewater which contains the following;
(1) OILS AND GREASE. (A) Oil and grease concentrations
or amounts from industrial facilities violating Federal pretreat-
ment standards. (B) Wastewater from industrial facilities con-
taining floatable fats, wax, grease or oils (Optional: (C) Wax,
grease or oil concentrations of mineral origin of more than
( ) mg/L whether emulsified or not, or containing sub-
stances which may solidify or become viscous at temperatures
between 32° and 150°F (0° and 65°C) at the point of discharge
into the system.) (Optional: (D) Total fat, wax, grease or oil
concentrations of more than ( ) mg/L, whether emulsified
or not, or containing substances which may solidify or become
viscous at temperatures between 32° and 150°F (0° and 65°C)
at the point of discharge into the system.)
(2) EXPLOSIVE MIXTURES. Liquids, solids or gases which
by reason of their nature or quantity are, or may be, sufficient
either alone or by interaction with other substances to cause
fire or explosion or be injurious in any other way to the sewer-
age facilities or to the operation of the system. At no time shall
two successive readings on an explosion hazard meter, at the
point of discharge into the sewer system, be more than five
percent (5%) nor any single reading over ten percent (10%) of
the Lower Explosive Limit (L.E.L.) of the meter. Prohibited ma-
terials include, but are not limited to, gasoline, kerosene,
naphtha, benzene, toluene, zylene, ethers, alcohols, ketones,
aldehydes, peroxides, chlorates, perchlorates, bromates, car-
bides, hydrides and sulfides.
(3) NOXIOUS MATERIAL. Noxious or malodorous solids,
liquids or gases, which, either singly or by interaction with other
wastes, are capable of creating a public nuisance or hazard to
life, or are or may be sufficient to prevent entry into a sewer for
its maintenance and repair.
(4) IMPROPERLY SHREDDED GARBAGE. Garbage that
has not been ground or comminuted to such a degree that all
particles will be carried freely in suspension under flow condi-
tions normally prevailing in the public sewers, with no particle
greater than one-half (V2) inch in any dimension.
(5) RADIOACTIVE WASTES. Radioactive wastes or
isotopes of such half-life or concentration that they do not
comply with regulations or orders issued by the appropriate
authority having control over their use and which will or may
cause damage or hazards to the sewerage facilities or person-
nel operating the system.
(6) SOLID OR VISCOUS WASTES. Solid or viscous
wastes which will or may cause obstruction to the flow in a
sewer, or otherwise interfere with the proper operation of the
wastewater treatment system. Prohibited materials include,
but are not limited to, grease, uncomminuted garbage, animal
guts or tissues, paunch manure, bones, hair, hides or flesh-
ings, entrails, whole blood, feathers, ashes, cinders, sand,
spent lime, stone or marble dust, metal, glass, straw, shavings,
grass clippings, rags, spent grains, spent hops, waste paper,
wood, plastic, tar, asphalt residues, residues from refining or
processing of fuel or lubricating oil, and similar substances.
(7) EXCESSIVE DISCHARGE RATE. Wastewaters at a flow
rate or containing such concentrations or quantities of pollut-
ants that exceeds for any time period longer than fifteen (15)
minutes more than five (5) times the average twenty-four (24)
hour concentration, quantities or flow during normal operation
and that would cause a treatment process upset and sub-
sequent loss of treatment efficiency.
(8) TOXIC SUBSTANCES. Any toxic substances in
amounts exceeding standards promulgated by the Adminis-
trator of the United States Environmental Protection Agency
pursuant to Section 307(a) of the Act, and chemical elements
or compounds, phenols or other taste or odor-producing sub-
stances, or any other substances which are not susceptible to
treatment or which may interfere with the biological processes
or efficiency of the treatment system, or that will pass through
the system.
(9) UNPOLLUTED WATERS. Any unpolluted water includ-
ing, but not limited to, water from cooling systems or of storm-
water origin, which will increase the hydraulic load on the
treatment system.
(10) DISCOLORED MATERIAL. Wastes with objection-
able color not removable by the treatment process.
(11) CORROSIVE WASTES. Any waste which will cause
corrosion or deterioration of the treatment system. AH wastes
discharged to the public sewer system must have a pH value in
the range of (6) to (9) standard unit. Prohibited materials in-
clude, but are not limited to, acids, sulfides, concentrated
chloride and fluoride compounds and substances which will
react with water to form acidic products.
(b) LIMITATIONS ON WASTEWATER DISCHARGES.
(Use either Option A or Option B.)
(Option A — General Limitations)
No person shall discharge or convey, or permit or allow to be
discharged or conveyed, to a public sewer any wastewater
containing pollutants of such character or quantity that will:
(1) Not be susceptible to treatment or interfere with the pro-
cess or efficiency of the treatment system.
(2) Constitute a hazard to human or animal life, or to the
stream or water course receiving the treatment plant effluent.
(3) Violate pretreatment standards.
(4) Cause the treatment plant to violate its NPDES permit or
applicable receiving water standards.
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Industrial Monitoring 523
(Option B — Specific Limitations)
The following are the maximum concentrations of pollutants
allowable in wastewater discharges to the wastewater treat-
ment system. Dilution of any wastewater discharge for the pur-
pose of satisfying these requirements shall be considered a
violation of this Ordinance.
Concentration (mg/L) or
Mass Limitation (kg/kg)
(Options: See, e.g.,
Federal Guidelines;
State and Local Pre-
treatment Programs,
Volume I, Section C)
Pollutant
Arsenic
Barium
Boron
Cadmium
Chromium (Total)
Chromium (Trivalent)
Chromium (Hexavalent)
Chlorinated Hydrocarbons
Copper
Cyanide
Iron
Lead
Manganese
Mercury
Nickel
Phenolic Compounds
Phosphorus
Selenium
Silver
Surfactants
Zinc
PH
Temperature Not over 150°F (except where
higher temperatures are per-
mitted by law).
(c) SPECIAL AGREEMENTS. Nothing in this Section shall
be construed as preventing any special agreement or ar-
rangement between the City and any user of the wastewater
treatment system whereby wastewater of unusual strength or
character is accepted into the system and specially treated
subject to any payments or user charges as may be applicable.
SECTION 3: CONTROL OF PROHIBITED WASTES
(a) REGULATORY ACTIONS. If wastewaters containing
any substance described in Section 2 of this Ordinance are
discharged or proposed to be discharged into the sewer sys-
tem of the City or to any sewer system tributary thereto, the
Director and (Corporation Counsel/City Attorney) may take any
action necessary to:
(1) Prohibit the discharge of such wastewater.
(2) Require a discharger to demonstrate that in-plant modifi-
cations will reduce or eliminate the discharge of such sub-
stances in conformity with this Ordinance.
(3) Require pretreatment, including storage facilities, or flow
equalization necessary to reduce or eliminate the objection-
able characteristics or substances so that the discharge will
not violate these rules and regulations.
(4) Require the person making, causing or allowing the dis-
charge to pay any additional cost or expense incurred by the
City for handling and treating excess loads imposed on the
treatment system.
(5) Take such other remedial action as may be deemed to be
desirable or necessary to achieve the purpose of this Ordi-
nance.
(b) SUBMISSION OF PLANS. Where pretreatment or
equalization of wastewater flows prior to discharge into any
part of the wastewater treatment system is required, plans,
specifications and other pertinent data or information relating
to such pretreatment or flow-control facilities shall first be sub-
mitted to the Director for review and approval. Such approval
shall not exempt the discharge or such facilities from com-
pliance with any applicable code, ordinance, rule, regulation or
order of any governmental authority. Any subsequent altera-
tions or additions to such pretreatment or flow-control facilities
shall not be made without due notice to and prior approval of
the Director.
(c) PRETREATMENT FACILITIES OPERATIONS. If pre-
treatment or control of waste flows is required, such facilities
shall be maintained in good working order and operated as
efficiently as possible by the owner or operator at his own cost
and expense, subject to the requirements of these rules and
regulations and all other applicable codes, ordinances, and
laws.
(d) ADMISSION TO PROPERTY. Whenever it shall be
necessary for the purposes of these rules and regulations, the
Director, upon the presentation of credentials, may enter upon
any property or premises at reasonable times for the purpose
of (1) copying any records required to be kept under the provi-
sions of this Ordinance, (2) inspecting any monitoring equip-
ment or method, and (3) sampling any discharge of wastewa-
ter to the treatment works. The Director may enter upon the
property at any hour under emergency circumstances.
(e) PROTECTION FROM ACCIDENTAL DISCHARGE.
Each industrial user shall provide protection from accidental
discharge of prohibited materials or other wastes regulated by
this Ordinance. Facilities to prevent accidental discharge of
prohibited materials shall be provided and maintained at the
owner or operator's own cost and expense. Detailed plans
showing facilities and operating procedures to provide this pro-
tection shall be submitted to the Director for review, and shall
be approved by him before construction of the facility. Review
and approval of such plans and operating procedures shall not
relieve the industrial user from the responsibility to modify the
facility as necessary to meet the requirements of this Ordi-
nance.
(f) REPORTING OF ACCIDENTAL DISCHARGE. If, for
any reason, a facility does not comply with or will be unable to
comply with any prohibition or limitations in this Ordinance, the
facility responsible for such discharge shall immediately notify
the Director so that corrective action may be taken to protect
the treatment system. In addition, a written report addressed to
the Director detailing the date, time and cause of the accidental
discharge, the quantity and characteristics of the discharge
and corrective action taken to prevent future discharges, shall
be filed by the responsible industrial facility within five (5) days
of the occurrence of the noncomplying discharge.
SECTION 4: INDUSTRIAL WASTEWATER MONITORING
AND REPORTING
(a) DISCHARGE REPORTS.
(1) Every significant industrial user shall file a periodic Dis-
charge Report at such intervals as are designated by the Direc-
tor. The Director may require any other industrial users dis-
charging or proposing to discharge into the treatment system
to file such periodic reports.
(2) The discharge report shall include, but, in the discretion
of the Director, shall not be limited to, nature of process, vol-
ume, rates of flow, mass emission rate, production quantities,
hours of operation, concentrations of controlled pollutants or
other information which relates to the generation of waste.
Such reports may also include the chemical constituents and
quantity of liquid materials stored on site even though they are
not normally discharged. In addition to discharge reports, the
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524 Treatment Plants
Director may required information in the form of (Industrial Dis-
charge Permit Applications and (optional)) self-monitoring re-
ports.
(b) RECORDS AND MONITORING
(1) All industrial users who discharge or propose to dis-
charge wastewaters to the wastewater treatment system shall
maintain such records of production and related factors,
effluent flows, and pollutant amounts or concentrations as are
necessary to demonstrate compliance with the requirements of
this Ordinance and any applicable State or Federal pretreat-
ment standards or requirements.
(2) Such records shall be made available upon request by
the Director. All such records relating to compliance with pre-
treatment standards shall be made available to officials of the
U. S. Environmental Protection Agency upon demand. A
summary of such data indicating the industrial user's com-
pliance with this Ordinance shall be prepared (quarterly) (op-
tional) and submitted to the Director.
(3) The owner or operator of any premises or facility dis-
charging industrial wastes into the system shall install at his
own cost and expense suitable monitoring equipment to facili-
tate the accurate observation, sampling, and measurement of
wastes. Such equipment shall be maintained in proper working
order and kept safe and accessible at all times.
(4) The monitoring equipment shall be located and main-
tained on the industrial user's premises outside of the building.
When such a location would be impractical or cause undue
hardship on the user, the Director may allow such facility to be
constructed in the public street or sidewalk area, with the ap-
proval of the public agency having jurisdiction over such street
or sidewalk, and located so that it will not be obstructed by
public utilities, landscaping or parked vehicles.
(5) When more than one user can discharge into a com-
mon sewer, the Director may require installation of separate
monitoring equipment for each user. When there is a signifi-
cant difference in wastewater constituents and characteristics
produced by different operations of a single user, the Director
may require that separate monitoring facilities be installed for
each separate discharge.
(6) Whether constructed on public or private property, the
monitoring facilities shall be constructed in accordance with
the Director's requirements and all applicable construction
standards and specifications.
(c) INSPECTION, SAMPLING AND ANALYSIS.
(1) COMPLIANCE DETERMINATION. Compliance deter-
minations with respect to SECTION 2 prohibitions and limita-
tions may be made on the basis of either instantaneous grab
samples or composite samples of wastewater. Composite
samples may be taken over a 24-hour period, or over a longer
or shorter time span, as determined necessary by the Director
to meet the needs of specific circumstances.
(2) ANALYSIS OF INDUSTRIAL WASTEWATERS. Labora-
tory anafysis of industrial wastewater samples shall be per-
formed in accordance with the current edition of "Standard
Methods," "Methods for Chemical Analysis of Water and
Waste" published by the U. S. Environmental Protection
Agency or the "Annual Book of Standards, Part 23, Water,
Atmospheric Analysis" published by the American Society for
Testing and Materials. Analysis of those pollutants not covered
by these publications shall be performed in accordance with
procedures established by the (State Department of Environ-
mental Health).
(3) SAMPLING FREQUENCY (Optional). Sampling of in-
dustrial wastewater for the purpose of compliance determina-
tion with respect to SECTION 2 prohibitions and limitations will
be done at such intervals as the Director may designate. How-
ever, it is the intention of the Director to conduct compliance
sampling or to cause such sampling to be conducted for all
major contributing industries at least once in every (1 year)
(optional) period.
SECTION 5: INDUSTRIAL DISCHARGE PERMIT SYSTEM
(OPTIONAL)
(a) WASTEWATER DISCHARGE PERMITS REQUIRED.
All significant industrial users proposing to connect to or dis-
charge into any part of the wastewater treatment system must
first obtain a discharge permit therefore. All existing significant
industrial users connected to or discharging to any part of the
City system must obtain a wastewater discharge permit within
ninety (90) (optional) days from and after the effective date of
this Ordinance.
(b) PERMIT APPLICATION. Users seeking a wastewater
discharge permit shall complete and file with the Director an
application on the form prescribed by the Director, and accom-
panied by the application fee. In support of this application, the
user shall submit the following information:
(1) Name, address, and SIC number of applicant.
(2) Volume of wastewater to be discharged.
(3) Wastewater constituents and characteristics including,
but not limited to, those set forth in SECTION 2 of this Ordi-
nance as determined by a reliable analytical laboratory.
(4) Time and duration of discharge.
(5) Average and (30) (optional) minute peak wastewater
flow rates, including daily, monthly and seasonal variations, if
any.
(6) Site plans, floor plans, mechanical and plumbing plans
and details to show all sewers and appurtenances by size,
location and elevation.
(7) Description of activities, facilities and plant processes
on the premises including all materials and types of materials
which are, or could be, discharged.
(8) Each product produced by type, amount, and rate of
production.
(9) Number and type of employees, and hours of work.
(10) Any other information as may be deemed by the direc-
tor to be necessary to evaluate the permit application.
The Director will evaluate the data furnished by the user and
may require additional information. After evaluation and accep-
tance of the data furnished, the Director may issue a wastewa-
ter discharge permit subject to terms and conditions provided
herein.
(c) PERMIT CONDITIONS. Wastewater discharge permits
shall be expressly subject to all provisions of this Ordinance
and all other regulations, user charges and fees established by
the City. The conditions of wastewater discharge permits shall
be uniformly enforced in accordance with this Ordinance, and
applicable State and Federal regulations. Permit conditions will
include the following:
(1) The unit charge or schedule of user charges and fees for
the wastewater to be discharged to the system.
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Industrial Monitoring 525
(2) The average and maximum wastewater constituents and
characteristics.
(3) Limits on rate and time of discharge or requirements for
flow regulations and equalization.
(4) Requirements for installation of inspection and sampling
facilities, and specifications for monitoring programs.
(5) Requirements for maintaining and submitting technical
reports and plant records relating to wastewater discharges.
(6) Daily average and daily maximum discharge rates, or
other appropriate conditions when pollutants subject to limita-
tions and prohibitions are proposed or present in the user's
wastewater discharge.
(7) Compliance schedules.
(8) Other conditions to ensure compliance with this Ordi-
nance.
(d) DURATION OF PERMITS. Permits shall be issued for a
specific time period, not to exceed (five) (optional) years. A
permit may be issued for a period of less than (one) (optional)
year, or may be stated to expire on a specific date. If the user is
not notified by the Director (30) (optional) days prior to the
expiration of the permit, the permit shall automatically be ex-
tended for (x) months. The terms and conditions of the permit
may be subject to modification and change by the (responsible
official) during the life of the permit, as limitations or requir-
ments as identified in Section 2 are modified and changed. The
user shall be informed of any proposed changes in the permit
at least (30) (optional) days prior to the effective date of
change. Any changes or new conditions in the permit shall
include a reasonable time schedule for compliance.
(e) TRANSFER OF A PERMIT. Wastewater discharge per-
mits are issued to a specific user for a specific operation. A
wastewater discharge permit shall not be reassigned or trans-
ferred or sold to a new owner, new user, different premises, or
a new or changed operation.
(f) REVOCATION OF PERMIT. Any user who violated the
following conditions of the permit or of this Ordinance, or of
applicable State and Federal regulations, is subject to having
the permit revoked. Violations subjecting a user to possible
revocation of the permit include, but are not limited to, the
following:
(1) Failure of a user to accurately report the wastewater
constituents and characteristics of the discharge;
(2) Failure of the user to report significant changes in opera-
tions, or wastewater constituents and characteristics;
(3) Refusal of reasonable access to the user's premises for
the purpose of inspection or monitoring; or
(4) Violation of conditions of the permit.
SECTION 6: ENFORCEMENT PROCEDURES
(a) NOTIFICATION OF VIOLATION. Whenever the Director
finds that any person has violated or is violating the Ordinance,
or any prohibition, limitation or requirement contained herein,
the Director may serve upon such person a written notice stat-
ing the nature of the violation and providing a reasonable time,
not to exceed thirty (30) days, for the satisfactory correction
thereof.
(b) SHOW CAUSE HEARING.
(1) If the violation is not corrected by timely compliance, the
Director may order any person who causes or allows an unau-
thorized discharge to show cause before the (hearing author-
ity) why service should not be terminated. A notice shall be
served on the offending party, specifying the time and place of
a hearing to be held by the (hearing authority) regarding the
violation, and directing the offending party to show cause be-
fore (said authority) why an order should not be made directing
the termination of service. The notice of the hearing shall be
served personally or by registered or certified mail (return re-
ceipt requested) at least (ten) days before the hearing. Service
may be made on any agent or officer of a corporation.
(2) The (hearing authority) may itself conduct the hearing
and take the evidence, or may designate any of its members or
any officer or employee of the (assigned department) to:
(A) Issue in the name of the (hearing authority) notices of
hearings requesting the attendance and testimony of witnes-
ses and the production of evidence relevant to any matter
involved in any such hearings.
(B) Take the evidence.
(C) Transmit a report of the evidence and hearing, including
transcripts and other evidence, together with recom-
mendations to the (hearing authority) for action thereon.
(3) At any public hearing, testimony taken before the hearing
authority or any person designated by it, must be under oath
and recorded stenographically. The transcript, so recorded,
will be made available to any member of the public or any part
to the hearing upon payment of the usual charges therefor.
(4) After the (hearing authority) has reviewed the evidence, it
may issue an order to the party responsible for the discharge
directing that, following a specified time period, the sewer serv-
ice be discontinued unless adequate treatment facilities, de-
vices or other related appurtenances shall have been installed
or existing treatment facilities, devices or other related ap-
purtenances are properly operated, and such further orders
and directives as are necessary and appropriate.
(c) LEGAL ACTION. Any discharge in violation of the sub-
stantive provisions of this Ordinance or an Order of the (hear-
ing authority) shall be considered a public nuisance. If any
person discharges sewage, industrial wastes or other wastes
into the City treatment system contrary to the substantive pro-
visions of this Ordinance or any Order of the (hearing author-
ity), the (Corporation Counsel/City Attorney) shall commence
an action for appropriate legal and/or equitable relief in the
(Circuit) Court of this County.
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526 Treatment Plants
SECTION 7: PENALTY; COSTS
Any person who is found to have violated an Order of the
(hearing authority) or who willfully or negligently failed to com-
ply with any provisions of this Ordinance, and the orders, rules
and regulations issued hereunder, shall be fined not less than
(One Hundred Dollars) (optional) nor more than (One
Thousand Dollars) (optional) for each offense. Each day on
which a violation shall occur or continue shall be deemed a
separate and distinct offense. In addition to the penalties pro-
vided herein, the City may recover reasonable attorneys' fees,
court costs, court reporters' fees and other expenses of litiga-
tion by appropriate suit at law against the person found to have
violated this Ordinance or the orders, rules and regulations
issued hereunder.
SECTION 8: SAVINGS CLAUSE
If any provision, paragraph, word, section or article of this
Ordinance is invalidated by any court of competent jurisdiction,
the remaining provisions, paragraphs, words, sections, and
articles shall not be affected and shall continue in full force and
effect.
SECTION 10: EFFECTIVE DATE
This Ordinance shall be in full force and effect (Option A)
from and after its passage, approval and publication, as pro-
vided by law. (Option B)
on the day of , 19
INTRODUCED the day of 19
FIRST READING: 19
SECOND READING: 19
PASSED THIS day of , 19
AYES:
NAYS:
ABSENT:
NOT VOTING:
APPROVED by me this day of , 19
MAYOR
ATTEST: (Seal) City Clerk
Published the day of , 19
SECTION 9: CONFLICT
All ordinances and parts of ordinances inconsistent or con-
flicting with any part of this Ordinance are hereby repealed to
the extent of such inconsistency or conflict.
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Industrial Monitoring 527
APPENDIX C
STANDARD FORM A — MUNICIPAL
Section IV. Industrial Waste Contribution to Municipal System
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528 Treatment Plants
FORM APPROVED
OMB No. 15S-ROIOO
STANDARD FORM A-MUNICIPAL
FOR AGENCY USE
1
1
1
|
SECTION nr. INDUSTRIAL WASTE CONTRIBUTION TO MUNICIPAL SYSTEM
Submit a description of each major industrial facility discharging to the municipal system, using a separate Section IV for each facility descrip-
tion. Indicate the 4 digit Standard Industrial Classification (SIC) Code for the industry, the major product or raw material, the flow (in thou-
sand gallons per day), and the characteristics of the wastewater discharged from the industrial facility into the municipal system. Consult Table
111 for standard measures of products or raw materials, (see instructions)
1* Major Contributing Facility
(see instructions)
Name
Number& Street
City
County
State
Zip Code
2. Primary Standard Industrial
Classification Code ($e«
instructions)
3. Principal Product or Raw
Material (see Instructions)
Product
Raw Material
4. Flow Indicate the volume of water
discharged into the municipal sys-
tem in thousand gallons per day
and whether this discharge Is Inter-
mittent or continuous.
5, Pretreatment Provided Indicate If
pretreatment is provided prior to
entering the municipal system
401b
401c
40 Id
401e
401f
402
403b
404a
404b
405
Quantity
Units (See
Table 111}
403©
403d
403f
..thousand gallons per day
~ Intermittent (int) Q Continuous (con)
Q Yes
~ No
6. Characteristics of Wastewater
(see instruction)
Parameter
Name
Parameter
Number
Value
EPA Form 7550-22 (7-73)
G P 0 865.7 06
This section contain* 1 pa£e.
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Industrial Monitoring 529
APPENDIX D
SAFETY ORDERS FOR BATTERY CHARGING
Source: California Administrative Code (Safety Orders)
SAFE PROCEDURES FOR BATTERY CHARGING
Changing and Charging Storage Batteries. Battery charging
installations shall be located in areas designated for that pur-
pose. Employees assigned to work with storage batteries shall
be instructed in emergency procedures such as dealing with
accidental acid spills.
The area shall be adequately ventilated to prevent concen-
trations of flammable gases exceeding 20 percent of the lower
explosive limit, and to prevent harmful concentration of mist
from the electrolyte.
While batteries are being charged, smoking and open flame
shall be prohibited in battery charging area and signs stating
that prohibition shall be posted in the area.
Electrolyte (acid or base, and distilled water) for battery cells
shall be mixed in a well ventilated room. Acid or base shall be
poured gradually into the water while stirring. Water shall never
be poured into concentrated (greater than 75 percent) acid
solutions.
When charging batteries, the vent caps should be kept in
place but loosened to avoid electrolyte spray. Care shall be
taken to assure that vent caps are functioning.
Fire extinguishing equipment adequate to cope with the
hazards which may be encountered shall be provided and
maintained close at hand.
Eye protection devices which provide side as well as frontal
eye protection for employees shall be provided when measur-
ing storage battery specific gravity or handling electrolyte, and
the employer shall ensure that such devices are used by the
employees. The employer shall also ensure that acid resistant
gloves and aprons shall be worn for protection against spatter-
ing.
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CHAPTER 28
INDUSTRIAL WASTE TREATMENT
by
Mark Acerra
Paul Amodeo
Dan Campbell
Tony Diaper
John Gonzales
Jim Palmer
Robert Wills, Jr.
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532 Treatment Plants
TABLE OF CONTENTS
Chapter 28. Industrial Waste Treatment
Page
OBJECTIVES 539
GLOSSARY 540
LESSON 1
28.0 Need to Treat Industrial Wastes 545
by Dan Campbell
28.00 Uses of Water by Industry 545
28.01 Reasons for Treatment of Industrial Wastes 545
28.010 Dissolved and Suspended Wastes 545
28.011 Drinking Water 545
28.012 Cooking Water 547
28.013 Water-contact Recreation 547
28.014 Water for Fish, Wildlife and Aquatic Vegetation 548
28.015 Non-body Contact Water Recreation 548
28.016 Agricultural Use 548
28.017 Industrial Use 548
28.02 Types of Industrial Wastewater 548
28.020 Dairy Wastes 548
28.021 Tannery Wastes 549
28.022 Pulp and Paper Wastes 549
28.023 Meat Packing Wastes 549
28.024 Fermentation Wastes 550
28.025 Fruit and Vegetable Processing Wastes 550
28.026 Textile Wastes 551
28.027 Petroleum Wastes 552
28.028 Metal Finishing Wastes 552
28.029 Coke Wastes 552
28.03 Solutions to Treating Industrial Wastes 553
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Industrial Waste Treatment 533
LESSON 2
28.1 Flotation 554
by Jim Palmer
28.10 Process Analyst 554
28.100 Process Description 554
28.101 Purpose of the Flotation Process 554
28.102 Part Identification 554
28.103 Part Description 559
28.104 Safety 559
28.11 Systems Operation 560
28.110 System Start-up Procedures 560
28.111 System Shutdown Procedures 560
28.112 Start-up and Shutdown Procedure Evaluation 560
28.113 Wastestream Evaluation 561
28.114 Reaction to Abnormal Indicators 561
28.115 Recording of Data 562
28.116 Sampling 562
28.117 Routine Calculations 562
28.118 Effect of Operator Actions and Reactions 563
28.119 Frequency of System Monitoring 564
28.12 Preventive Maintenance 564
28.120 Pertinent Procedures 564
28.121 Procedures and Their Frequencies 565
28.122 Required Actions by the Operator 565
28.123 Importance of Preventive Maintenance 565
28.124 Determination of Preventive Maintenance 566
28.13 Corrective Maintenance 566
28.130 Evaluation for Corrective Maintenance 566
28.131 Causes of Component or Part Malfunction 566
28.132 Equipment Required to Perform Corrective Maintenance 5(5(3
28.133 Corrective Maintenance Procedures
28.134 Importance of Efficient and Quick Corrective Maintenance 567
LESSON 3
28.2 Screening and Microscreening Applied to Industrial Waste Treatment 568
by Tony Diaper
28.20 Need for Screening and Microscreening 568
28.21 Description of Screens 569
28.210 Stationary Screens 569
28.211 Moving Screens 569
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534 Treatment Plants
28.212 Microscreens 572
28.213 Mechanical Equipment 578
28.22 Safety Procedures 578
28.23 Operating Procedures 579
28.230 Start-up Procedures 579
28.231 Normal Operation 579
28.232 Abnormal Operation 579
28.233 Operational Strategy 580
28.234 Shutdown Procedures 580
28.235 Troubleshooting 580
28.24 Maintenance 583
28.240 Preventive Maintenance 583
28.241 Maintenance Schedule 584
28.242 Corrective Maintenance 584
28.25 Review of Plans and Specifications 585
28.250 Concrete Channels and Chambers 585
28.251 Design of Coarse Screens 585
28.252 Design of Microscreens 586
28.253 Facilities Checklist 586
28.26 Additional Reading 587
LESSON 4
28.3 Neutralization 588
by Mark Acerra
28.30 Need for Neutralization 588
28.31 Basic Principles 589
28.32 Chemistry 590
28.33 Processes Requiring pH Adjustment and Neutralization 596
28.330 Precipitation of Metal Salts 596
28.331 Coagulation and Flocculation 597
28.332 Other Processes 598
28.333 Sludge Conditioning and Disposal 598
28.334 Summary 605
28.34 Process Mechanics 605
28.35 Safety 608
28.36 Construction Activities 609
28.360 Sidewalk Superintendent 609
28.361 Preparation for Start-up 609
28.362 Unit Check-out and Start-up 609
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Industrial Waste Treatment 535
28.37 Operation and Maintenance 609
28.38 Instrumentation 611
LESSON 5
28.4 Coagulation and Precipitation 612
by Paul Amodeo
28.40 Need for Coagulation and Precipitation 612
28.400 Purpose of Coagulation and Precipitation 612
28.401 Description of Process 612
28.41 Principles of Coagulation 612
28.410 Physical Activities 612
28.411 Destabilizaton Mechanisms 613
28.412 Properties of Some Common Coagulants 614
28.413 Testing Coagulants for Dosage Selection 614
28.42 Description of Equipment 616
28.420 Storage and Delivery of Coagulants 616
28.421 Mixing Units 622
28.422 Flocculators 622
28.423 Clarifiers 622
28.43 The Precipitation Process 628
28.430 Factors in Design Consideration 628
28.431 Clarifier Efficiency 631
28.44 Safety 631
28.440 Safety in Handling Coagulant Chemicals 631
28.441 Safety around Machinery 631
28.442 Other Hazards 631
28.45 Operation, Start-up and Maintenance 631
28.450 Start-up Maintenance Inspection 631
28.451 Actual Start-up 632
28.452 Operational Strategy Checklist 632
28.453 Abnormal Operating Procedures and Troubleshooting 633
LESSON 6
28.5 Adsorption (Activated Carbon) 635
by John Gonzales
28.50 Principles of Activated Carbon Adsorption 635
28.500 Purpose of Carbon Adsorption 635
28.501 How Does Carbon Adsorption Work? 635
28.502 The Manufacture of Activated Carbon 635
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536 Treatment Plants
28.51 The Carbon Adsorption Process 635
28.510 General Physical Principles 635
28.511 Equipment Necessary for Carbon Adsorption 635
28.512 Pre-Start-Up 641
28.513 General Operating Procedures 641
28.514 Placing Carbon Adsorption Units into Operation 641
28.515 Operational Procedures 646
28.52 Activated Carbon Regeneration 649
28.520 Purpose for Regeneration of Activated Carbon 649
28.521 General Procedure for Reactivation 649
28.522 Specifics in Reactivation Process 649
28.53 Sampling and Analysis 654
28.530 Sampling 654
28.531 Analysis 654
28.54 Operational Strategy 654
28.540 Daily Operating Procedures 654
28.541 Abnormal and Emergency Conditions 656
28.542 Sampling Ports 657
28.543 Abnormal Conditions Regarding the Carbon Regeneration Furnace 657
28.55 Safety 657
28.550 Carbon Adsorbs Oxygen 657
28.551 Carbon Dust 657
28.552 Excessive Pressures within Carbon Contactor Tanks 657
28.56 Loading Guidelines 658
28.560 Typical Loading Rates 658
28.561 Hydraulic Loading Rates 658
28.562 Chemical Oxygen Demand Loading Rates 658
28.57 Review of Plans and Specifications 658
28.570 Loading Station for Truck or Train Delivery of Fresh Activated Carbon 658
28.571 Valving Placed at Easy-to-Reach Locations 658
28.572 Dust Control for Unloading Fresh Carbon 658
28.573 Proper Ventilation in Carbon Regeneration Furnace Room 658
28.574 Scaffolding and Catwalks 658
28.575 Warning Alarms and Signs 658
28.576 Upstream Processes 658
28.58 Additional Reading on Activated Carbon Adsorption 658
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Industrial Waste Treatment 537
28.6 How to Operate an Industrial Wastewater Treatment Plant 660
by Robert Wills, Jr.
28.60 Routine Operational Control of a Specialty Steel Wastewater Treatment and Recycle Facility 660
28.600 Description of Treatment Facilities 660
28.601 Operational Strategy 660
28.61 Daily Inspections 664
28.62 Process Adjustments 666
28.63 Day-to-Day Mechanical Operations 666
28.630 Clarifiers 666
28.631 Sludge Thickener 673
28.632 Aeration Tank 673
28.633 Recycle Pump 673
28.634 Vacuum Filters 673
28.635 Chemical Feed Systems 674
28.636 Instrumentation 674
28.64 Aeration Tank Operation 674
28.640 Objectives 674
28.641 Operation 674
28.642 Initial Starting 675
28.643 Restarting Aerator 675
28.644 Aerator Draining Procedures 675
28.645 Safety 676
28.646 Troubleshooting 676
28.65 Tank A (SCTA) 677
28.650 Objectives 677
28.651 Operation 677
28.652 Starting the Drive Units 677
28.653 Interpreting What You See 677
28.66 Tank B (SCTB) 678
28.660 Objectives 678
28.661 Operation 678
28.67 Sludge Thickener 678
28.670 Objectives 678
28.671 Operation 678
28.68 Operation of Processes 678
28.680 Normal Operation 678
28.681 Troubleshooting 678
28.682 Interpreting What You See 679
28.683 Sludge Quality 679
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538 Treatment Plants
28.684 Upset Conditions 679
28.685 Safety 679
APPENDIX LABORATORY PROCEDURES 680
I. Influent and Effluent 680
A. Chemical Oxygen Demand (COD) 680
B. Turbidity 680
II. Status of Activated Carbon 680
A. Abrasion Number (Ro-Tap) 681
B. Abrasion Number (NBS) 681
C. Apparent Density 682
D. Decolorizing Index 682
E. Effective Size and Uniformity Coefficient 686
F. Hardness Number 686
G. Iodine Number 686
H. Methylene Blue Number 690
I. Moisture 694
J. Molasses Number 694
K. Sieve Analysis (Dry) 695
L. Total Ash of Regenerated Carbon 695
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Industrial Waste Treatment 539
OBJECTIVE
Chapter 28. INDUSTRIAL WASTE TREATMENT
Industrial waste pretreatment and treatment processes
covered in Chapter 28 include:
1. Flotation,
2. Screening and microscreening,
3. Neutralization,
4. Coagulation and precipitation, and
5. Adsorption (activated carbon).
Biological treatment of industrial wastes is covered in Chap-
ter 21, Section 21.5, "Industrial Waste Treatment."
Following completion of Chapter 28, you should be able to
do the following:
1. Identify various types of processes,
2. Safely operate and maintain the processes,
3. Start-up, operate and shut down the processes,
4. Develop an operational strategy for the processes,
5. Understand and interpret laboratory data and make appro-
priate adjustments in the treatment processes,
6. Understand and recognize abnormal conditions and be-
come aware of troubleshooting necessary under normal
operation,
7. Prepare a maintenance program and schedule for the pro-
cesses, and
8. Review the plans and specifications for the processes.
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540 Treatment Plants
GLOSSARY
Chapter 28. INDUSTRIAL WASTE TREATMENT
ABSORPTION (ab-SORP-shun) ABSORPTION
Taking in or soaking up of one substance into the body of another by molecular or chemical action (as tree roots absorb dissolved
nutrients in the soil).
ACID ACID
(1) A substance that tends to lose a proton. (2) A substance that dissolves in water with the formation of hydrogen ions. (3) A
substance containing hydrogen which may be replaced by metals to form salts.
ACIDITY ACIDITY
The capacity of water or wastewater to neutralize bases. Acidity is expressed in milligrams per liter of equivalent calcium carbonate.
Acidity is not the same as pH because water does not have to be strongly acidic (low pH) to have a high acidity. Acidity is a measure
of how much base can be added to a liquid without causing a great change in pH.
ADSORPTION (add-SORP-shun) ADSORPTION
The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another substance.
AGGLOMERATION (a-GLOM-er-A-shun) AGGLOMERATION
The growing or coming together of small scattered particles into larger floes or particles which settle rapidly. Also see FLOC.
ALKALI ALKALI
Any of certain soluble salts, principally of sodium, potassium, magnesium, and calcium, that have the property of combining with
acids to form neutral salts and may be used in chemical processes such as water or wastewater treatment.
ALKALINITY (AI-ka-LIN-ity) ALKALINITY
The capacity of water or wastewater to neutralize acids. This capacity is caused by the water's content of carbonate, bicarbonate,
hydroxide, and occasionally borate, silicate and phosphate. Alkalinity is expressed in milligrams per liter of equivalent calcium
carbonate. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have a high alkalinity.
Alkalinity is a measure of how much acid can be added to a liquid without causing a great change in pH.
ANION ANION
A negatively charged ion in an electrolyte solution, attracted to the anode under the influence of electric potential.
BAFFLE BAFFLE
A flat board or plate, deflector, guide or similar device constructed or placed in flowing water, wastewater or slurry systems to cause
more uniform flow velocities, to absorb energy, and to divert, guide or agitate liquids.
BASE BASE
A compound which dissociates (separates) in aqueous solution to yield hydroxyl ions.
BATCH PROCESS BATCH PROCESS
A treatment process in which a tank or reactor is filled, the water is treated, and the tank is emptied. The tank may then be filled and
the process repeated.
BLINDING BLINDING
The clogging of the filtering medium of a microscreen or a vacuum filter when the holes or spaces in the media become sealed off
due to grease or the material being filtered.
BUFFER BUFFER
A solution or liquid whose chemical makeup neutralizes acids or bases without a great change in pH.
BUFFER ACTION BUFFER ACTION
The action of certain ions in solution in opposing a change in hydrogen-ion concentration.
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Industrial Waste Treatment 541
BUFFER CAPACITY BUFFER CAPACITY
A measure of the capacity of a solution or liquid to neutralize acids or bases. This is a measure of the capacity of water or
wastewater for offering a resistance to changes in pH.
BUFFER SOLUTION BUFFER SOLUTION
A solution containing two or more substances which, in combination, resist any marked change in pH following addition of moderate
amounts of either strong acid or base.
CHEMICAL EQUIVALENT CHEMICAL EQUIVALENT
The weight in grams of a substance that combines with or displaces one gram of hydrogen. Chemical equivalents usually are found
by dividing the formula weight by its valence.
CHEMICAL PRECIPITATION CHEMICAL PRECIPITATION
(1) Precipitation induced by addition of chemicals. (2) The process of softeninq water by the addition of lime or lime and soda ash as
the precipitants.
CLARIFICATION (KLAIR-i-fi-KAY-shun) CLARIFICATION
Any process or combination of processes the main purpose of which is to reduce the concentration of suspended matter in a liquid.
CLARIFIER (KLAIR-i-fire) CLARIFIER
Settling Tank, Sedimentation Basin. A tank or basin in which wastewater is held for a period of time, during which the heavier solids
settle to the bottom and the lighter materials will float to the water surface.
COAGULANT (co-AGG-you-lent) COAGULANT
A chemical that causes very fine particles to clump together into larger particles. This makes it easier to separate the solids from the
liquids by settling, skimming, draining or filtering.
COAGULANT AID COAGULANT AID
Any chemical or substance used to assist or modify coagulation.
COAGULATION (co-AGG-you-LAY-shun) COAGULATION
The use of chemicals that cause very fine particles to clump together into larger particles. This makes it easier to separate the solids
from the liquids by settling, skimming, draining or filtering.
CONTINUOUS PROCESS CONTINUOUS PROCESS
A treatment process in which water is treated continuously in a tank or reactor. The water being treated continuously flows into the
tank at one end, is treated as it flows through the tank, and flows out the opposite end as treated water.
DEFINING DEFINING
A process that arranges the activated carbon particles according to size. This process is also used to remove small particles from
granular contactors to prevent excessive head loss.
DETENTION TIME DETENTION TIME
The time required to fill a tank at a given flow or the theoretical time required for a given flow of wastewater to pass through a tank.
DIAPHRAGM PUMP DIAPHRAGM PUMP
A pump in which a flexible diaphragm, generally of rubber or equally flexible material, is the operating part. It is fastened at the edges
in a vertical cylinder. When the diaphragm is raised suction is exerted, and when it is depressed, the liquid is forced through a
discharge valve.
DOCTOR BLADE DOCTOR BLADE
A blade used to remove any excess solids that may cling to the outside of a rotating screen.
EFFLORESCENCE (EF-low-RESS-ense) EFFLORESCENCE
The powder or crust formed on a substance when moisture is given off upon exposure to the atmosphere.
EFFLUENT (EF-lu-ent) EFFLUENT
Wastewater or other liquid — raw, partially or completely treated — flowing FROM a basin, treatment process, or treatment plant.
ELECTROLYTE (ELECT-tro-LIGHT) ELECTROLYTE
A substance which dissociates (separates) into two or more ions when it is dissolved in water.
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542 Treatment Plants
END POINT END POINT
Samples are titrated to the end point. This means that a chemical is added, drop by drop, to a sample until a certain color change
(blue to clear, for example) occurs which is called the END POINT of the titration. In addition to a color change, an end point may be
reached by the formation of a precipitate or the reaching of a specified pH. An end point may be detected by the use of an electronic
device such as a pH meter. The completion of a desired chemical reaction.
EQUALIZING BASIN EQUALIZING BASIN
A holding basin in which variations in flow and composition of a liquid are averaged. Such basins are used to provide a flow of
reasonably uniform volume and composition to a treatment unit. Also called a balancing reservoir.
FLOC FLOc
Groups or clumps of bacteria and particles or coagulants and impurities that have come together and formed a cluster. Found in
aeration tanks, secondary clarifiers and chemical precipitation processes.
FLOCCULATION (FLOCK-you-LAY-shun) FLOCCULATION
The gathering together of fine particles to form larger particles.
GATE GATE
A movable watertight barrier for the control of a liquid in a waterway.
HYDROGEN-ION CONCENTRATION (H+) HYDROGEN-ION CONCENTRATION (H+)
The weight of hydrogen ion in moles per liter of solution. Commonly expressed as the pH value, which is the logarithm of the
reciprocal of the hydrogen-ion concentration.
pH = log 1
(H7)
HYDROLYSIS (hi-DROL-e-sis) HYDROLYSIS
The addition of water to the molecule to break down complex substances into simpler ones.
HYGROSCOPIC (HI-grow-SKOP-ic) HYGROSCOPIC
A substance that absorbs or attracts moisture from the air.
IMPELLER IMPELLER
A rotating set of vanes designed to impart rotation of a mass of fluid.
IMPELLER PUMP IMPELLER PUMP
Any pump wherein the water is moved by the continuous application of power from some rotating mechanical source.
INFLUENT (IN-flu-ent) INFLUENT
Wastewater or other liquid — raw or partially treated — flowing INTO a reservoir, basin, treatment process, or treatment plant.
IONIC CONCENTRATION IONIC CONCENTRATION
The concentration of any ion in solution, generally expressed in moles per liter.
IONIZATION IONIZATION
The process of adding electrons to, or removing electrons from, atoms or molecules, thereby creating ions. High temperatures,
electrical discharges, and nuclear radiation can cause ionization.
LIQUEFACTION (LICK-we-FACK-shun) LIQUEFACTION
The conversion of large solid particles of sludge into very fine particles which either dissolve or remain suspended in wastewater.
MICRON (MY-kron) MICRON
A unit of length. One millionth of a meter or one thousandth of a millimeter. One micron equals 0.00004 of an inch.
MICROSCREEN MICROSCREEN
A device with a fabric straining media with openings usually between 2 and 60 microns. The fabric is wrapped around the outside of
a rotating drum. Wastewater enters the open end of the drum and flows out through the rotating screen cloth. At the highest point of
the drum, the collected solids are backwashed by high-pressure water jets into a trough located within the drum.
NEUTRALIZATION (new-trall-i-ZAY-shun) NEUTRALIZATION
Addition of an acid or alkali (base) to a liquid to cause the pH of the liquid to move towards a neutral pH of 7.0.
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Industrial Waste Treatment 543
NONCORRODIBLE NONCORRODIBLE
A material that resists corrosion and will not be eaten away by wastewater or chemicals in wastewater.
OVERFLOW RATE OVERFLOW RATE
One of the guidelines for the design of settling tanks and clarifiers in treatment plants.
Overflow Rate, _ Flow, gallons/day
gpd/sq ft Surface Area, sq ft
pH (PEA-A-ch) pH
pH is an expression of the intensity of the alkaline or acid condition of a liquid. Mathematically pH is the logarithm (base 10) of the
reciprocal of the hydrogen-ion concentration.
pH = Log 1
(H+)
The pH may range from 0 to 14, where 0 is most acid, 14 most alkaline, and 7 is neutral. Natural waters usually have a pH between
6.5 and 8.5.
PHENOLPHTHALEIN ALKALINITY PHENOLPHTHALEIN ALKALINITY
A measure of the hydroxide ions plus one half of the normal carbonate ions in aqueous suspension. Measured by the amount of
sulfuric acid required to bring the water to a pH value of 8.3, as indicated by a change in color of phenolphthalein. It is expressed in
milligrams per liter of calcium carbonate.
ROTARY PUMP ROTARY PUMP
A type of displacement pump consisting essentially of elements rotating in a pump case which they closely fit. The rotation of these
elements alternately draws in and discharges the water being pumped. Such pumps act with neither suction or discharge valves,
operate at almost any speed, and do not depend on centrifugal forces to lift the water.
SCREEN SCREEN
A device used to retain or remove suspended or floating objects in wastewater. The screen has openings that are generally uniform
in size. It retains or removes objects larger than the openings. A screen may consist of bars, rods, wires, gratings, wire mesh, or
perforated plates.
SEPTIC (SEP-tick) SEPTIC
This condition is produced by anaerobic bacteria. If severe, the wastewater turns black, gives off foul odors, contains little or no
dissolved oxygen and creates a heavy oxygen demand.
SOLUTE SOLUTE
The substance dissolved in a solution. A solution is made up of the solvent and the solute.
SUSPENDED SOLIDS SUSPENDED SOLIDS
(1) Solids that either float on the surface or are suspended in, water, wastewater, or other liquids, and which are largely removable
by laboratory filtering. (2) The quantity of material removed from wastewater in a laboratory test, as prescribed in "Standard
Methods for the Examination of Water and Wastewater" and referred to as nonfilterable residue.
TITRATE (TIE-trate) TITRATE
To TITRATE a sample, a chemical solution of known strength is added on a drop-by-drop basis until a color change, precipitate, or
pH change in the sample is observed (end point). Titration is the process of adding the chemical solution to completion of the
reaction as signaled by the end point.
TURBID TURBID
Having a cloudy or muddy appearance.
TURBIDITY UNITS TURBIDITY UNITS
Turbidity units, if measured by nephelometric (reflected light) instrumental procedure, are expressed in Nephelometric Turbidity
Units (NTU). Those turbidity units obtained by other instrumental methods are expressed in Jackson Turbidity Units (JTU) and
sometimes as Formazin Turbidity Units (FTU). The FTU nomenclature comes from the Formazin polymer used to prepare the
turbidity standards for instrument calibration. Turbidity units are a measurement of the cloudiness of water.
ULTRAFILTRATION ULTRAFILTRATION
A membrane filtration process used for the removal of organic compounds in an aqueous (watery) solution.
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544 Treatment Plants
WEIR WEIR
(1) A wall or plate placed in an open channel and used to measure the flow. The depth of the flow over the weir can be used to
calculate the flow rate, or a chart or conversion table may be used. (2) A wall or obstruction used to control flow (from clarifiers) to
assure uniform flow and avoid short-circuiting.
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Industrial Waste Treatment 545
CHAPTER 28. INDUSTRIAL WASTE TREATMENT
(Lesson 1 of 6 Lessons)
28.0 NEED TO TREAT INDUSTRIAL WASTE
by Dan Campbell
28.00 Uses of Water by Industry
Most industrial processes either require water or are made
more efficient by the use of water for one purpose or another.
As the water is being used, some of the other materials used in
the industrial process may become mixed in with the water.
That part of the water which is not re-used by the industry is
discharged as industrial wastewater.
Figure 28.1 shows some of the major potential uses of water
by industry. At "A" the water is taken from its source. This
could be taken directly from a surface water source such as a
river or lake, directly from a groundwater source including vari-
ous types of wells, or from a community water supply. Note
that whatever the source, water used by industry may need to
be treated by the industry before it is suitable for use.
The water may then be used by industries in a number of
ways, as shown at "B." In many cases, water is necessary to
the process itself. An obvious example is laundry, but other
examples include the pulp and paper industry, dairies, brew-
eries, distilleries and others. In many cases, water is used to
make processing of other materials easier or more efficient. In
any of these cases, this is referred to as "process water."
Another use of water by industry is for the transport of materi-
als to, through, and from the industrial process, such as in
vegetable processing. As shown in Figure 28.1, water also is
used for cooling, as for example in refineries and steel mills.
Many industries use washwater for both products (fruit and
vegetable processing, some metal finishing operations) and
facilities (canneries, dairies).
After being put to one or more of the above uses, the water
may be recycled for repeated use if its characteristics have not
been changed so much it becomes unsuitable "C." This may
be done directly or the water may be treated to make re-use
possible. When the water is treated, materials are removed.
These materials may then be a disposal problem "E." Also,
these materials may have value to the industry or other indus-
tries either in the same or a different process. An example of
this is the use of wastes from steel pickling by municipal
wastewater treatment plants "D." When it is uneconomical for
the industry to recycle this water, it becomes industrial waste-
water "F."
In almost all cases, industrial wastewater is not suitable for
direct discharge to a receiving water, but must first be treated
to remove pollutants. Figure 28.1 shows three possible alterna-
tives for treatment industrial wastewater:
(G) Discharge to a Publicly Owned Treatment Works
(POTW) to be combined with municipal wastes and pos-
sibly wastes from other industries, treated, and returned
to the environment;
(H) Pre-treatment by industry, followed by discharge to a
POTW, as above; and
(I) Treatment by industry to the extent required before dis-
charge to a receiving water.
Whatever scheme is used, the ultimate objective is the pro-
tection of the receiving water for protection of the public health
and for the various uses of the receiving waters.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 696.
28.0A List four general uses of water by industries.
28.0B What are the three alternative arrangements possible
for treating industrial wastewater?
28.01 Reasons for Treatment of Industrial Wastes
28.010 Dissolved and Suspended Wastes
During any of the four general uses of water by industry, the
water may acquire waste materials. These may be in the form
of "dissolved" matter, usually defined for wastewater purposes
as those which will pass through a fine filter, or in the form of
"suspended" matter, that is, particles which may settle to the
bottom or float to the surface if given enough time. More fre-
quently they are combinations of dissolved and suspended
matter. Depending on the specific nature of the matter which is
added, the characteristics of the water may be changed, thus
affecting its potential for use.
An important basic concept is that water in the environment
belongs to all of us, not to any individual or group. Individuals
or groups are allowed to use water, but they must use it in such
a way as not to interfere with its use by others with rights to use
the water. Let's briefly examine some of the uses of water and
some ways in which wastes can interfere with the use of water.
28.011 Drinking Water
Use of water for drinking and other domestic purposes is the
most basic use of water and generally has priority over any
competing use. There are many ways in which water can be
rendered unsafe or unfit for drinking. These different types of
contamination are discussed in the following paragraphs.
1. BIOLOGICAL CONTAMINATION. This problem usually
stems from prior use of water to carry human wastes. Sani-
tary wastewater, domestic wastes, or simply sewage or
wastewater are terms used to designate this category of
wastes. Bacteria, viruses and other microorganisms are
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546 Treatment Plants
MANAGEMENT/DISPOSAL OF
WASTE RESIDUAL MATERIAL
RECOVERY OF
MATERIALS FOR
USE IN OR OUT
OF PROCESS
RECYCLING/RE-USE
MANUFACTURING
PROCESSES
TREATMENT BY
INDUSTRY
TRANSPORT OF
MATERIALS
COOLNG
WASHWATER
MANAGEMENT/DISPOSAL OF
WASTE RESIDUE MATERIAL
TREATMENT AT
PUBLICLY OWNED
TREATMENT WORKS
REGULATED BY
NATIONAL/STATE
PERMIT .
WATER SOURCE —
• SURFACE WATER
• GROUNDWATER
• COMMUNITY WATER SUPPLY
TREATED, IF
NECESSARY. FOR
INDUSTRIAL USE
REGULATED BY NATIONAL,
STATE AND LOCAL
PRE-TREATMENT
REGULATIONS AND SEWER-USE
ORDINANCES
Fig. 28.1 Use of water by industry
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Industrial Waste Treatment 547
excreted from the human body and other warm-blooded
animals. Some of these organisms may cause disease if
they are successful in completing or short-circuiting a cycle
through wastewater treatment, discharge to the environ-
ment, and treatment for water supply, and are ingested by a
human. In addition to sanitary wastewater, such mircoor-
ganisms may reach environmental waters through storm-
water as it washes the land of animal wastes and through
certain industries, most notably slaughterhouses and tan-
neries.
Protection of human populations from this biological con-
tamination has been the historical foundation for public
wastewater treatment and water treatment, with disinfec-
tion being the particular process most involved. Where
wastewater and water treatment are routine practices, dis-
eases which might otherwise be transmitted through drink-
ing water, such as typhoid, cholera and dysentery, are rare.
Industries which may potentially discharge pathogenic or-
ganisms must be sure that their wastes are adequately
disinfected.
2. CHEMICAL CONTAMINATION. This is potentially a whole
host of problems, rather than a single, neat category. De-
pending on their nature and concentration, foreign chemi-
cals in drinking water may produce sudden illness, or may
produce long-term "chronic" illness which is not diagnosed
for years, but which may have severe effects. This is not to
say that all chemicals in water, even drinking water, are
bad. Chlorine, for example, has been used for generations
as a disinfectant, and its use has undoubtedly saved untold
number of lives. We are now learning, however, that when
combined with certain other chemicals, chlorine may cause
long-term disease. This serves to emphasize that we are
not free to use water to "wash away" compounds we are
not sure what else to do with when we want to get rid of
them. The problem is made even more complex because
many of the compounds considered toxic are dnagerous at
even extremely low concentrations, measured as mi-
crograms per liter or parts ber billion. Imagine trying to find
six black pingpong balls in a room filled with them and
999,999,994 white ones. This is equivalent to six parts per
billion and roughly equivalent to 6 micrograms per liter.
Some of the categories of chemical contamination are listed
below:
a. TOXIC CHEMICALS — A great variety of chemicals
have toxic effects in drinking water. These range from
simple chemical elements such as mercury, chromium,
and other metals to compounds consisting of numbers
of elements such as pesticides. From an industrial
wastewater standpoint, the most likely source of this
type of contamination is from the manufacturing pro-
cesses in which these chemicals are either used or
made and from in-plant spills and accidents.
A number of recent episodes with toxic and poten-
tially toxic chemicals points out that many of the dan-
gers of toxic compounds are not even suspected at the
time we begin using them.
b. CHEMICALS NOT NORMALLY TOXIC — Many chem-
icals are not considered toxic in concentrations nor-
mally encountered, but may present other problems if
present in drinking water. Oils and greases present in
water supplies may pass through water treatment pro-
cesses in concentrations high enough to cause tastes
and odors. Inorganic salts in low concentrations are
considered beneficial to water supplies. In higher con-
centrations, however, they present problems. Sulfate in
high concentrations produces a laxative effect. Waters
high in inorganic salts cause crusting or deposits on the
insides of pipes, thus decreasing the capacity of the
pipes.
3. RADIOACTIVE CONTAMINATION. Long-term health dam-
age and even death could be caused by the presence of
radioactive contaminants in drinking water.
4. OTHER TYPES OF CONTAMINATION. Other factors such
as temperature, color, and turbidity, may be problems in
water supplies. These factors may not cause health prob-
lems of themselves, but may cause people to use a differ-
ent source of water which may be unsafe because the safe
source is made unattractive.
28.012 Cooking Water
Water used for food preparation may be ingested, and of
course the food is ingested. Consequently, the potential prob-
lems are very much like those listed above for drinking water.
28.013 Water-contact Recreation
Activities such as swimming and water skiing, in which the
body has direct contact with the water, are referred to as
water-contact reaction. Although the health risks from water-
contact recreation are not as great as from drinking water, they
are real. The most obvious forms of pollution interfering with
water-contact recreation are those which make the water un-
appealing.
1. BIOLOGICAL CONTAMINATION. The most likely risk from
biological contamination is that of eye, ear, and skin infec-
tion, although accidental ingestion of contaminated water is
also a risk.
2. CHEMICAL CONTAMINATION. Ingestion is considered
less of a problem due to the small volume which might be
accidentally ingested. Acids and other chemicals, if present
in water may cause irritation of the eyes and other sensitive
parts of the body. There are many chemicals, such as some
pesticides, that have toxic effects which are severe upon
contact with the skin.
3. OXYGEN-CONSUMING WASTES. These wastes actually
are a form of chemical pollution. However, this problem is
so severe that it is considered a problem in its own right.
Many organic or oxygen-consuming wastes may be dis-
charged from dairies, breweries, distilleries, pharmaceutical
manufacturing, fruit and vegetable processing, textile man-
ufacturing, paper manufacturing, coke and gas industries
and municipalities.
These types of wastes are actually treated in a stream or
river by the action of the same microorganisms found in a
treatment plant. In this treatment process, the organisms
"breathe" the oxygen which is present in the water. If all the
oxygen is gone, other microorganisms which can get their
oxygen from compounds in the water continue the treat-
ment process. The by-products of this latter type of treat-
ment (anaerobic decomposition) produce unpleasant
odors, colors and sludges that discourage water-contact
recreation.
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548 Treatment Plants
4. INORGANIC ELEMENTS. This also is a form of chemical
pollution, but some types of inorganic elements such as
phosphorus and nitrogen are nutrients that promote the
growth of algae. Algae are microorganisms which, under
proper conditions, can multiply to such an extent in water
that they interfere with water-contact recreation and other
uses of the water. In sunlight, algae add oxygen to water,
but in the absence of light and as they decay, dissolved
oxygen is removed from the water. Algae reduce the clarity
of water and give it a green color. Both of these items are
considered undesirable from an esthetic standpoint. Phos-
phorus and nitrogen also promote the growth of larger veg-
etation such as aquatic weeds.
5. SOUDS AND VISIBLE POLLUTION. Visible pollution obvi-
ously interferes with water-contact and other forms of water
recreation. Floating solids, oil, and foam are potential con-
taminants from industry which would be in this category.
Other types of solids may settle to the bottom of the water
and form sludge beds. Organic material in the sludge beds
decomposes, presenting the problems identified under
"Oxygen-consuming Wastes."
6. OTHER CONTAMINANTS. Increased temperature in water
decreases the amount of oxygen available and at the same
time leads to an increasing rate of microorganism uptake of
the oxygen which is present. This compounds the problems
of oxygen-demanding wastes described above. Radiation
poses a health hazard from contact in which the radioactive
material may remain on the skin.
28.014 Water for Fish, Wildlife and Aquatic Vegetation
Water is necessary for all forms of life. The types of con-
tamination described above, particularly with respect to drink-
ing water, can interfere with the use of the water to support
forms of life other than human. Many fish and other organisms
are even more susceptible to damage from toxic materials than
humans. Many states limit the amount of chlorine which can be
added to wastewater effluent because of the sensitivity of
aquatic life to chlorine. An additional problem is that some
lower forms of life can accumulate some toxic materials. As
fish and higher forms of life consume these smaller organisms,
toxicity levels rise in the higher forms. This bioaccumulation
magnifies the hazard both to the fish and other creatures
higher in the food chain, including humans.
Fish also depend on the dissolved oxygen present in water
for life. For this reason, many of the standards set for levels of
dissolved oxygen in water are based on the needs of fish.
28.015 Non-body Contact Water Recreation
Boating and similar non-contact recreation activities are in-
terfered with primarily by visible types of pollution. Fishing, of
course, would depend on the suitability of water to support fish.
28.016 Agricultural Use
Water for irrigation should be reasonably free from biological
contamination. Many chemicals, including some metals and
inorganic salts will retard or prevent crop growth at certain
concentrations and would be harmful for livestock.
28.017 Industrial Use
The suitability of water for industrial use depends largely on
the industry in question. Water which is safe for drinking some-
times must receive additional treatment for certain industrial
uses.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 696.
28.0C Name three ways in which water can be biologically
contaminated.
28.OD What is the name of the process by which water that
may be biologically contaminated is made safe?
28.OE What are the major potential sources of contamination
of water by toxic materials?
28.0F Describe how oxygen-consuming wastes interfere
with water use.
28.OG What are the potential uses of water with which toxicity
may interfere?
28.02 Types of Industrial Wastewater
Wastewaters produced by industries can be significantly dif-
ferent, even among industries making the same product, de-
pending upon the process used. In this section, we'll describe
some of the major water-using industries and the types of
wastewater which they may produce. We'll also take a look at
some of the major treatment processes which are commonly
used for each type of wastewater, although these are dis-
cussed in detail in other chapters. If your plant uses a type of
treatment process mentioned, you should take particular note
of the chapter in which that treatment process is discussed.
28.020 Dairy Wastes
This is a classification given to wastes from a variety of
milk-product installations, including receiving stations, bottling
plants, cheese factories, and ice cream plants. Dairy process-
ing plants typically produce a waste very high in BOD and
solids. BOD values of dairy wastewater effluent are about
1,000 mg/liter but values up to 10,000 mg/liter are not uncom-
mon. Sources of the waste are from the milk residue washed
away in cleansing and from accidental spills. In addition to the
high organic content of the waste, the wastes frequently arrive
in large volumes over short periods of time (shock loads).
Normal treatment processes for dairy wastes include flow
equalization (that is, storing what would be a shock load in a
large tank and discharging it more uniformly to the treatment
process), pre-treatment by chemical precipitation, and some
form of biological treatment (activated sludge, trickling filter,
rotating biological contactor). Nutrients may have to be added
for microorganisms treating dairy wastes to produce the best
results. See Chapter 21, Section 21.573, "Treatment of Dairy
Wastes," for additional details.
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Industrial Waste Treatment 549
28.021 Tannery Wastes
Tanning is the process of manufacturing leather from animal
hides. A number of separate operations are involved in the
tanning process. Each process has differing characteristics.
The wastes are generally mixed in a controlled manner, al-
lowed to chemically react and settle. The composite of these
wastes is high in salt, BOD, and suspended solids. Flow is
variable because tanning is accomplished in a batch process.
This makes flow equalization helpful for effective treatment.
Combined tannery wastes can be expected to average up to
8,000 mg/liter of suspended solids and up to 1,000 mg/liter of
BOD. Most of the BOD loading in tannery wastes can be ex-
pected from the de-hairing and soaking of the hides. The
wastewater should be screened to remove as much of the
coarse material as possible before subsequent treatment.
After screening, the wastes can be treated biologically with
trickling filters, rotating biological contactors, and/or activated
sludge.
Particular problems with tannery wastes may stem from
some of the process chemicals. The lime, used in the de-
hairing process, can build up and clog sewer lines as well as
possibly clog trickling filter media. Chromic sulfate from the
tanning process can interfere with digestion of sludge from
wastewater treatment.
28.022 Pulp and Paper Wastes
Pulping is the process of recovering fiber from wood or other
vegetable matter for subsequent processing into paper. In the
process, between 10 and 50 percent of the raw material may
be rejected. This, together with the high volume of water used
in the process, the relatively high organic loading, and the
natural resistence of the type of organic material in the wastes
to biological oxidation, make treatment difficult. One of the
most effective means of treatment is the recovery of materials.
BOD ranges from 200 to 1,000 milligrams per liter are com-
mon. The suspended solids consist primarily of cellulose mate-
rials, bark, silt, dregs and grits from the pulping process and
fillers, coatings and similar materials. The solids will usually
settle readily. BOD reduction may be accomplished through
this settling process to some extent and further through biolog-
ical treatment, often in waste stabilization ponds. Other
methods of treatment include chemical precipitation, activated
sludge and lagooning. In the case of biological treatment, it
may be necessary to add nutrients to the wastes for effective
biological oxidation. In the manufacture of paper and paper
products the pulp, either alone or in combination with recycled
paper, is processed with various chemicals. The organic
strength of the wastewater from paper manufacturing depends
largely on the specific type of paper being produced. Average
BOD and suspended solids concentrations could be expected
to be similar to municipal wastewater, although some will be
considerably more concentrated. Treatment through biological
oxidation, such as activated sludge, should be effective for this
type of wastewater, however, it may be necessary to practice
control of the pH level of the wastes as well as the nutrient
level. Refer to Chapter 21, "Activated Sludge," Section 21.55,
"Pulp and Paper Mill Wastes," for additional details.
28.023 Meat Packing Wastes
Wastes from the meat packing industry actually stem from a
number of operations within the industry. The principal opera-
tions are those related to stockyards, slaughter houses, and
packing houses. Stockyard wastes consist principally of ma-
nure, hay, straw, and dirt. These wastes are high in organic
materials and high in nutrients. Stockyard wastes are suitable
for land disposal and should be segregated and hauled or
piped away for that purpose. Slaughter house wastes can be
categorized as those resulting from the killing of the animal and
the preparation of the carcass. Principal wastes are the blood,
grease, manure, body fluids, hair, flesh and fat particles. These
wastes, in undiluted form, are extremely high in organic con-
tent. For example, blood has the highest BOD of any liquid
meat processing material, that is, 400,000 mg/L. Paunch ma-
nure has a BOD of 100,000 mg/L. Therefore, unrecovered
losses to the waste stream should be kept to a minimum.
Packing house wastes are those resulting from preparation
of the carcass into a saleable product. Processes involved are
smoking, cooking, curing, pickling, and sausage making.
Wastes are principally grease, blood, and flesh and fat parti-
cles. Waste streams from slaughter houses and packing
houses tend to be high in BOD, averaging 1,000 to 2,000 mgIL
and high in suspended solids, averaging 500 to 1,500 mg/L.
They will also contain high amounts of nitrogen and grease
that will tend to have a neutral pH. Average water use in
slaughter houses and packing houses is from 1,000 to 5,000
gallons (3,800 to 19,000 liters) of water per 1,000 pounds (455
kg) of live weight killed. Water conservation should be prac-
ticed because of the high pollutant characteristics of meat
packing wastes. Recovery of much of the waste material for
use as by-products often is economical. Such by-products in-
clude glue, soap, animal feed, and fertilizer.
Pre-treatment of wastes in the meat packing industry often
proves economical from the dual standpoints of recovery of the
by-products and of reduced sewer-use charges. Pre-treatment
processes include flow equalization. This is usually econom-
ically advantageous because it permits smaller subsequent
treatment units and averages the flow into the sewer which
often minimizes user charges. Screening is another common
pre-treatment process because a great deal of the pollutional
material in meat packing waters is in solid form. Screens
should be checked frequently and cleaned as needed. Cen-
trifuging is used to a lesser extent to remove residual grease
and fine solids from waste streams. Another common type of
pre-treatment process is the practice of grease and suspended
solids separation, either by gravity and/or dissolved air flota-
tion. Gravity grease recovery systems can remove up to 30
percent of the BOD, 50 pecent of the suspended solids and 60
percent of the grease from the waste stream. Gravity systems
must be checked to be sure that baffles, weirs, and scum
removal mechanisms are kept clean. From a safety considera-
tion, regularly hose down all spills as there will be considerable
grease which will become slippery if not removed. Dissolved
air flotation systems will remove up to 35 percent of the BOD,
60 percent of the suspended solids and up to 90 percent of the
grease from waste streams.
Following these pre-treatment processes, a wide range or a
combination of treatment systems is common. Meat packing
wastes are suitable for treatment by anaerobic processes be-
cause of their characteristics. The temperature of the wastes is
often from 85 to 95°F (29 to 35°C), it is high in BOD and
suspended solids, contains a high content of fats and proteins,
as well as nutrients. These are all characteristics required for
successful anaerobic treatment. The most common types of
anaerobic treatment used for the meat packing industry are
anaerobic lagoons, which are deeper than aerobic or faculta-
tive lagoons. Anaerobic lagoons are commonly from 12 to 18
feet (3.6 to 5.4 m) deep. Effluents from anaerobic lagoons
usually contain up to 100 mg/L of ammonia nitrogen. This con-
centration of ammonia nitrogen is toxic to most aquatic life.
Anaerobic lagoons, therefore, need to be followed by an
aerobic treatment system.
The second type of anaerobic treatment used in the meat
packing industry is the anaerobic contact unit which is an
anaerobic digester with mixing equipment and related settling
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550 Treatment Plants
tanks. About 12 hours of detention time is provided within the
anaerobic digester.
Aerobic types of treatment which are used with success in-
clude lagoons (either aerated lagoons or oxidation ponds), ac-
tivated sludge units, trickling filters or rotating biological con-
tactors. Spray irrigation and overland runoff of treated wastes
are also being used in the meat packing industry.
28.024 Fermentation Wastes
Fermentation is the name given to the breaking down of
sugars and starches into simpler compounds by yeasts. The
manufacture of bread, beer, wine, alcohol and penicillin are
some of the processes using fermentation. The wastes result-
ing from the fermentation process include the unfermented
portions of raw materials, waste liquor from the wet grain and
yeast recovery and washwater from various parts of the pro-
cess. Unfermented portions of raw materials are primarily in-
soluble solids which should be recovered and not discharged
into sewers. Recovered solids are used as animal feed and in
the manufacture of certain chemical products. Water use in the
brewery industry is high, averaging up to 10 to 15 gallons of
water for every gallon of beer produced. Cleaning of vats and
process equipment produces most of the waste volume which
will range from 500 to 1,500 mgIL of BOD. Wastes from the
production of antibiotics are high in BOD. Some may be as
high as 20,000 mg IL. Fermentation wastes are suitable for
bio-oxidation if the pH level is controlled. The wastes will be
acidic. Nutrient addition is usually necessary because the
wastes are deficient in nitrogen and phosphorus. The most
effective bio-oxidation processes for fermentation wastes are
trickling filters and anaerobic digestion.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 696.
28.0H Dairy processing plants typically produce a waste very
high in and
28.01 Why are flows of tannery wastes highly variable?
28.0J Why is the treatment of pulp and paper wastes con-
sidered difficult?
28.0K List three economical by-products from packing house
wastes.
28.0L What is fermentation?
28.025 Fruit and Vegetable Processing Wastes
This is a highly diversified and widespread industry. Waste-
water characteristics and treatment problems are also highly
variable, depending upon the specific product and type of pro-
cessing to which it is subjected. In general, the most significant
problems encountered in the treatment of fruit and vegetable
processing wastes are the seasonal nature of the processing
and the nutrient deficiency commonly existing in the wastewa-
ter.
The specific processes commonly used within the industry
include preliminary cleaning and preparation, blanching, can-
ning (including pasteurization and cooling), and juicing. Pre-
liminary cleaning and preparation includes conveyance of the
fruit or vegetable. This may be accomplished either mechan-
ically or hydraulically. Mechanical means of conveying include
screw conveyors, belt conveyors and vibrating tables. Hydrau-
lic means of conveyance include flow-through pipes and flunk-
ing, that is, flow in open channels. Hydraulic conveyance con-
tributes to waste strength by the leaching of sugars, acids and
starches as well as the washing of foreign matter from the
surface.
There are actually a number of washes typical in the pro-
cessing of any given fruit or vegetable. The initial washing
removes soil, pesticides and other contaminants from the sur-
face of the fruit or vegetable. Other washings in subsequent
phases of the process remove additional process materials.
The third preliminary preparation process is that of peeling.
Use of hot lye peeling is common, followed by high pressure
water spray. Since this process produces a high percentage of
the cannery's pollution load, this first rinse should be segre-
gated and treated separately. Blanching is the process of heat-
ing the product in water or steam for a short time. Other types
of blanching are now being used, including hot air blanching
and microwave blanching. Wet blanching leaches out nutrients
while dry blanching preserves more of the vitamin value of the
product and reduces wastewater volumes as much as 99 per-
cent.
Canning as a process characteristically includes filling of the
container with the product, pasteurization within the container
and cooling of the container. Prior to the canning process, the
product may be pumped, strained, and/or heated and may
have additional materials such as spices, flavorings and pre-
servatives added to it. The process of filling the container in-
evitably will result in spillage, whether the filling is done me-
chanically or by hand. Washing of the container adds to the
wastewater stream. The filled container is then pasteurized
and cooled, normally using large quantities of cooling water.
This cooling water is normally clear and is suitable for reuse for
additional cooling, washing, or fluming. The cooling water
should not be allowed to mix with the wastewater because it is
relatively unpolluted and the additional volume of water would
then need to be subjected to treatment.
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Industrial Waste Treatment 551
Many products are used to produce juice. Sources of wastes
from the juicing process include dry, pressed pulp which
should be treated as an organic solid waste, spent filter cake
from clarification of juices which should also be treated as an
organic solid waste, and water evaporated from the juice to
concentrate it. This water is characteristically high in organic
content.
The soundest approach to wastewater management in the
fruit and vegetable industry, as in most industries, is that of
waste prevention and reduction. A key element of this is the
practice of good housekeeping and operational procedures.
Each step of the process should be thoroughly examined for
the purpose of reducing wastes and assuring that the minimum
amount of water possible is used in each step. Spillage and
breakage, in addition to reducing the amount of product which
can be sold, adds to the wastewater treatment problem.
Screens should be placed over all drains in a plant to prevent
the unnecessary washing of solids into the wastewater stream.
Whenever possible, high pressure — low volume sprays
should be used for cleaning.
Flow meters should be installed so that unnecessarily high
rates of use can be monitored and prevented. Automatic
shut-offs, such as trigger nozzles, should be used. Plant staff
should be educated to the proper use of water valves. They
should be opened only as far as necessary, rather than being
left totally open. Soak and wash tank overflows should be elim-
inated to the extent possible. Another aspect of waste preven-
tion and reduction is the segregation of high concentration
wastes for separate handling. Cooling waters can often be
directly discharged or reused within the plant. If directly dis-
charged, care must be taken that excess heat is not dis-
charged to a stream.
Counter-flow washing as a process technique is often effec-
tively used. In counter-flow washing, the flow of washwater is
opposite to that of the product. In this way the cleanest water is
washing the cleanest product. As the water moves along the
product line, it picks up impurities as it moves toward the least
clean end of the product line.
Another aspect of waste prevention and reduction is the
actual change of process used. Although more drastic than
any of the measures cited above, such a change will often be
of economic benefit to the plant. Examples of process changes
which have been applied are the substitution of dry, caustic,
mechanical or abrasive drum peeling for hot lye peeling and air
cooling instead of water cooling.
Treatment of fruit and vegetable processing wastes can be
accomplished in a variety of ways. Screening, either with sta-
tionary, revolving or vibrating screens, can achieve high settle-
able solids and floating solids removal and sometimes up to 70
percent suspended solids removal. Screens should be in-
stalled as close as possible to the process generating the sol-
ids. Stationary screens will tend to remove only the coarser
particles, whereas revolving and vibrating screens may reduce
the waste load in terms of solids up to 50 percent. Screening
will usually produce no significant effect on BOD, other than
the BOD removed as suspended solids.
One form of pre-treatment which is frequently necessary,
particularly for root crops, is that of grit removal. Soil may make
up a significant percentage of the weight of a root crop.
Another treatment process frequently used is dissolved air flo-
tation which may reduce the suspended solids load of the
wastewater by as much as 80 percent. The organic solids
removed in screening and dissolved air flotation can have a
number of potential by-product uses. They may be further pro-
cessed to make purees, vinegar or alcohol. They may be used
for animal feed. Solids not used in such a fashion may be
composted, landfilled, or otherwise disposed of in a suitable,
sanitary manner.
As with many industrial processes, it is frequently necessary
to equalize the wastewater flow in fruit and vegetable process-
ing wastes because of the flow variation. Sedimentation is ef-
fective for treatment of some types of fruit and vegetable pro-
cessing wastes and ineffective for others. Effectiveness de-
pends upon the amount of settleable solids in the waste
stream. Plain sedimentation is typically effective for treatment
of wastewater from processing potatoes, tomatoes and carrots
and ineffective for products such as apples, peas, peaches,
and pears. Biological treatment of fruit and vegetable process-
ing wastewater is technically feasible and frequently proves to
be practical as typically 85 percent of the BOD in fruit and
vegetable processing wastewater consists of dissolved or-
ganic matter. However, due to the seasonality of production
and the characteristic nutrient deficiency in fruit and vegetable
processing wastewater, biological treatment may not always
be feasible. When feasible, biological treatment can be effec-
tive with trickling filters, activated sludge units, pure oxygen
activated sludge units, and anaerobic filters. Typically it is nec-
essary to add nutrients for effective biological treatment of fruit
and vegetable processing wastewater. This may be done by
mixing with domestic wastewater, or in extreme cases with
anhydrous ammonia or ammonium sulfate. Sludge from the
activated sludge process that has been applied to fruit and
vegetable processing wastewater is difficult to dewater. One
advantage of anaerobic filters as applied to the processing of
fruit and vegetable wastewater is that they can be used effec-
tively on an intermittent basis.
28.026 Textile Wastes
Textile manufacturing is the making of woven fabrics from
either natural or synthetic fibers. Natural fibers are those such
as wool, cotton and silk. Synthetic fibers are those such as
rayon, acrylics or polyester. A primary source of wastes from
natural fibers is the foreign matter present in the fibers such as
dirt, grease and waxes. These are removed by boiling or scour-
ing which generate considerable wastes. The main wastes
from synthetics are the chemicals used in the processing of the
synthetics. The scouring of wool produces the greatest waste
load of any single process in the textile industry. Typically,
1,000 pounds of wool as sheared from the lamb will produce
600 pounds of natural impurities and 400 pounds of finished
wool.
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552 Treatment Plants
Cotton undergoes a process called sizing which is the
strengthening of the thread to make it ready for weaving. The
thread is then rinsed or desized to remove the waste starch of
polyvinyl alcohol, which is the sizing medium. The cotton is
then scoured with caustic to remove natural waxes and other
impurities. These two processes yield approximately 80 per-
cent of the waste load from a typical cotton mill. Textile mills
dealing with synthetics generally have lower water usage and
waste generation than those dealing with natural fibers. For
example, nylon mills typically use 15,000 gallons of water per
1,000 pounds of cloth with a BOD loading of 40 to 50 pounds of
BOD per 1,000 pounds of cloth produced. Cotton, on the other
hand, typically requires well over 20,000 gallons of water per
1,000 pounds of cloth with the BOD loading of 50 to 200
pounds per 1,000 pounds of cloth. The BOD loading for wool is
over 400 pounds per 1,000 pounds of cloth.
Typical treatment problems in the textile industry include
those from lint, fibers and strings which clog pipes and equip-
ment and collect on the sides of tanks and channels. The
natural greases found on the fibers and the soaps used in
processing them produce a scum which is capable of produc-
ing stains and odors as it flows through the treatment process.
Foam may be caused by the soaps and detergents used in
processing the textiles. Textile wastes differ widely in pH. Al-
kaline wastes are generally less of a problem because they are
easier to treat using biological processes. Acidic wastes can
be neutralized by the addition of lime, caustic soda ash or
ammonia. Wastes with a pH below 5.5 should never be al-
lowed to enter a wastewater system because they will cause
the corrosion of concrete and other structures in the treatment
process. Another potential problem with textile wastes is that of
variations in hydraulic flow. Unless the flow is equalized,
periods of high flow will produce reduced treatment times and
increased treatment costs. Periods of low flow may cause
odors and other treatment problems. Some processes in the
manufacture of textiles involve metals which may be toxic to
treatment processes.
Effective treatment of textile wastes, as with most types of
industrial wastes, begins in the manufacturing process itself. A
variety of considerations in the manufacturing process will im-
prove the capability for wastewater treatment. Such tech-
niques include flow reduction, water reuse, waste segregation,
process or material substitution, and good housekeeping. To
treat textile wastes by screening, use either stationary, rotary
or vibrating screens to remove lint and prevent clogging of
pipes and equipment. The lint may also collect on the sides of
tanks and channels yielding odor and other problems.
Equalization is frequently practiced in the treatment of textile
wastes, usually to produce steady levels of BOD. Segregated
wastes are usually equalized, that is, segregated into those
which produced the greatest BOD loading. In cotton this is the
desizing and scouring wastes; in wool, the scouring and wash
after fulling wastes; and in polyester, the knitting oil scour
wastes. Neutralization of the wastewater is also a common
treatment technique. Neutralization is frequently accomplished
by mixing of wastes of acidic and alkaline pHs. Other pre-
treatment techniques may include BOD reduction, particularly
of segregated wastes, and chemical treatment for specific pur-
poses, such as removal of metals or coagulation for removal of
detergents. Subsequent treatment processes which have been
used effectively in the textile industry include trickling filters,
activated sludge, rotating biological contactors and chemical
coagulation.
28.027 Petroleum Wastes
Wastes from the petroleum industry can be categorized as
those resulting from oil production or oil refining. Brine is the
principal waste from oil production. Brine may be disposed of
by injection but caution must be exercised not to pollute
groundwater. Brine may be disposed of into surface waters but
this method will frequently necessitate compensation of
downstream users of the surface water. Brine may also be
treated by solar evaporation, dilution or chemical coagulation.
Refinery wastes include acids, alkalies, sulfur compounds,
phenols, and oil itself. Most of the water used in the refining
industry is used for cooling, but even this may be contaminated
by leakage. For this reason, effective wastewater control re-
quires the reduction of leakage within the plant as well as other
good housekeeping measures.
Treatment of petroleum wastes consists of separation of the
oil, chemical coagulation and sedimentation, and biological
treatment. See Chapter 21, Section 21.58, "Petroleum Refin-
ery Wastes," for additional details.
28.028 Metal Finishing Wastes
Finishing refers to the improvement of the surface of the
metal. This is usually accomplished by one or more of a variety
of processes including cleaning, hardening, softening, rough-
ing, smoothing, coating or plating. Finishing is done to improve
corrosion resistance, durability, appearance, conductivity, or
other physical characteristics of the metal. The most common
finishing processes are steel, iron and copper pickling and
electroplating. The metals most commonly plated are copper,
cadmium, nickel, zinc, and chromium. From an industrial waste
standpoint, precious metal electroplating is of secondary im-
portance. Liquid wastes from the metal finishing industry are
not normally high in volume but are potentially dangerous.
Toxic materials included in metal finishing wastes are acids,
chromium, zinc, copper, nickel, tin and cyanide. Other contam-
inants are alkaline cleaners, grease and oil. Specific sources of
wastes from the metal finishing industry are waste process
solutions (such as cleaners), acid solvents and plating solu-
tions from accidental discharges of process solutions, and
rinse water effluents.
Management of the metal finishing wastewater problem be-
gins with consideration of in-plant process improvements.
Considerable work has been done in this respect. One prob-
lem which has received much attention is that of drag-out. As
the product being finished is moved out of a processing tank,
some of the solution in the tank is carried or dragged out with it!
Among the techniques for minimizing drag-out are proper posi-
tioning of the article being finsihed, drip pans, and shaking and
standing rinses with reuse of the rinse water. Metal finishing
wastes are usually treated chemically because the contami-
nants are generally not only resistant to biological treatment
but are frequently highly toxic to biological organisms. Some of
the specific waste treatment processes include chlorination for
alkaline wastes; reduction and precipitation for cyanide; neu-
tralization for chromium wastes; and ion exhcange and evap-
oration for recovery of valuable metals.
28.029 Coke Wastes
The manufacture of coke is accomplished by heating coal in
the absence of air. Two thousand pounds of coal will yield
about 1,400 pounds of coke with the remainder going into
by-products such as gases, tar and other materials. Wastes
from coke manufacturing tend to be high in BOD and phenol
content as well as containing ammonia creosols, sulfide and
cyanide residuals. These wastes are usually pre-treated to re-
cover ammonia and either convert phenols to less objection-
able materials or recover phenols. Treatment processes used
are biological treatment, such as activated sludge or trickling
filtration or physical treatment, such as steam stripping.
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Industrial Waste Treatment 553
28.03 Solutions to Treating Industrial Wastes
This section has identified the problems associated with the
treatment of various types of industrial wastes. If you have an
industrial waste treatment problem, refer to the previous sec-
tion for the treatment problems caused by the particular indus-
try. Once you've identified the problem and the industry, refer
to the appropriate sections in this chapter or chapters in this
manual to solve the waste treatment problem. For example, if
you are treating dairy wastes with an activated sludge plant
and the problems are being caused by a nutrient deficiency,
refer to Chapter 21, "Activated Sludge," Section 21.5, "Indus-
trial Waste Treatment," to determine how much of which nut-
rients should be added. The procedures for solving a nutrient
deficiency in an activated sludge plant could be applied to
other biological treatment processes.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 696.
28.0M What are the two most significant problems encoun-
tered in the treatment of fruit and vegetable process-
ing wastes?
28.0N What is one major advantage of anaerobic filters as
applied to the processing of fruit and vegetable
wastewater?
28.00 List five typical treatment problems in the textile indus-
try.
28.0P What is the principal problem of wastes from the petro-
leum industry?
28.OQ List five toxic substances found in metal finishing
wastes.
&M 0 OftftMOH 10P6L666OW4
INPUftTBlAl.'WAfiTg TWgACTMtfAtf
Please answer the discussion and review questions before
continuing with Lesson 2.
DISCUSSION AND REVIEW QUESTIONS
(Lesson 1 of 6 Lessons)
Write the answers to these questions in your notebook be-
fore continuing.
1. Identify one advantage and one limitation of the use of
chlorine with wastewaters.
2. What problems could oils and greases cause in receiving
waters used as a source for a drinking water supply?
3. If algae add oxygen to water in the presence of sunlight,
then why are algae considered undesirable?
4. What treatment processes are commonly used to treat
dairy wastes?
5. Why is pre-treatment of wastes often practiced in the meat
packing industry?
6. How could canning cooling waters be reused in a cannery?
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554 Treatment Plants
CHAPTER 28.
INDUSTRIAL WASTE TREATMENT
(Lesson 2 of 6 Lessons)
28.1 FLOTATION by Jim Palmer
28.10 Process Analysis
28.100 Process Description
The dissolved air flotation system is based on the principle
that the solubility of gases in a solution increases as the pres-
sure on the solution increases. For an example, when 100
gallons (378 liters) of water is saturated with air at atmospheric
pressure and at 67 degrees F (19.4°C), this volume contains
approximately 0.25 cubic feet (7 liters) of air; when saturated at
30 PS/G1 (2.1 kg/sq cm), this volume contains 0.75 cubic feet
(21 liters) of air; when saturated at 50 psig (3.5 kg/sq cm), this
volume contains 1.1 cubic feet (31 liters) of air; and so on. But
when this pressurized volume is returned to atmospheric pres-
sure, the dissolved air will return to its original 0.25 cubic feet
(7 liters) of air per 100 gallons (378 liters). Therefore, if water
saturated with air at 50 psig (3.5 kg/sq cm) is released to
atmospheric pressure, it will release from solution 0.85 cubic
feet (24 liters) of air per 100 gallons (378 liters) (1.1 cubic feet
- 0.25 cubic feet or 31 liters - 7 liters). The released air forms
microscopic bubbles which have the characteristic of rising to
the surface of the water. The microscopic air bubbles form on
and attach themselves to the suspended solids in the volume
being treated as a CONTINUOUS PROCESS.2 Since the spe-
cific gravity of the suspended solids is reduced by the attached
air bubbles, the solids/bubble combination will float to the sur-
face of the water. Coagulants may be added to this volume.
The coagulant causes a larger floe of solids, trapping the bub-
ble inside. This can improve or increase the effectiveness of
each single air bubble. After the solids within the volume form
floes, these floes rise to the surface. The volume under this
sludge mat is clear treated water, which is either re-used in
manufacturing or passed on to another stage of water treat-
ment. The recovered solids on the surface of this volume are
removed, and also re-used in manufacturing or passed on to
another system for sludge handling and dewatering.
28.101 Purpose of the Flotation Process
The flotation process may be used for three basic reasons:
1. Solids Recovery. In some manufacturing processes, valu-
able solids are discharged from various sources. By install-
ing a flotation unit, these valuable solids can be recovered
and re-used in the manufacturing process at a fairly low
cost. This is a typical procedure in the pulp and paper indus-
try, the textile industry, the mining industry, and some
chemical industries.
2. Water Recovery. Since all indications in industry point to
future minimum use and discharge of water in manufactur-
ing locations, the re-use of water is very critical. One way to
re-use industrial wastewater with suspended solids as pol-
lutants is to first pass this volume through a flotation unit.
Current industry figures reveal that over 94 percent of the
suspended solids are removed by many of these units. Be-
cause of this high removal efficiency, the clarified water can
be re-used in locations throughout the plant where the re-
maining six percent of the suspended solids will not pro-
duce plugging or other problems.
3. Wastewater Treatment. The flotation unit is used exten-
sively in primary industrial wastewater treatment. This is
due mainly to the unit's high performance levels, simplicity
of operation, and low operating costs.
In all three uses of the flotation process, continuous high
levels of performance are necessary to maintain system
balance, related systems' balance, and/or compliance of
NPDES discharge permit limits.
28.102 Part Identification
Along with understanding the impact of the flotation system
as a whole on system balance, permit requirements, and solids
recovery, it is just as important to understand the effects of
each major part on the flotation system.
Referring to Figures 28.2, 28.3,28.4, and 28.5, the following
parts are of critical importance to the successful operations of
the flotation unit:
1. Unit Feed Pump
2. Check Valves
3. Float Valves
4. Air Induction System
5. Chemical Induction System
6. Retention Tank
7. Inlet Header
8. Flight Scrapers
9. Lamell Panels
10. Weirs
11. Motors/Pumps
12. Flow-Measuring Equipment
13. Sampling Equipment
14. Control Valve
15. Flotation Compartment
1 psig. Pounds per Square Inch Gage. Gage pressure means the pressure above atmospheric pressure. Absolute pressure is the gage
pressure plus the atmospheric pressure. ^ _
Absolute Pressure, psia = Gage Pressure, psig + Atmospheric Pressure, psi
2 Continuous Process. A treatment process in which water is treated continuously in a tank or reactor. The water being treated continuously
flows into the tank at one end, is treated as it flows through the tank, and flows out the opposite end as treated water.
-------
DILUTION WATER
CHEMICAL
CHEMICAL PUMP
CHECK VALVE
• WEIR PLATE
(FLOW MEASURING POINT)
SLUDGE RAMP
CONTROL VALVE
BAFFLE
PLATES
RETENTION TANK
CHECK VALVE
-INLET
HEADER
FLOW METER
LAMELL PANELS
- SLUDGE COMP.
• CLARIFIED
- FINAL DISCHARGE
(WATER SAMPLING POINT)
AIR
SOURCE
CHEMICAL
HEADER
CONTROL VALVE
FLOOR PLAN
FLIGHT SCRAPER
VARI— DRIVE UNIT
RETENTION
tank
FLIGHT SCRAPERS
CHECK VALVE
RECYCLEO
CLARIFIED
PROCESS
V
DISCHARGED
CLARIFIED
WATER
RECOVEREO
SOLIOS
FEED TANK •
WATER
ELEVATION
3F'
CONTROL VALVE
FLOAT VALVES
FEED
PUMP
a
c
CO
#•*
ST
i
I
a>
%
3
®
Fig. 28.2 Flotation unit parts
(NOTE: Circular tanks are commonly used also)
in
in
in
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556 Treatment Plants
Recovered solids being removed The final discharge weir/clarifier
from the surface of the water water compartment.
and discharged into the recovered
solids compartment by the flight
scrapers.
The control valve between the unit Sprocket/hand rails/nip guard areas of unit,
and its retention tank. This also
shows the manhole in the retention
tank.
Fig. 28.3 Photos of flotation unit parts
-------
Chemical pumping system.
Industrial Waste Treatment 557
Flight scraper assembly which
removes solids.
Retention tank. Also shows hand Scraper drive unit and
rail, mid rail, and toe boards associated guards,
on catwalk structure.
Fig. 28.4 Photos of flotation unit parts
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558 Treatment Plants
Lamell panels in flotation Chemical and stock inlet
compartment. headers with baffles located
in flotation compartment.
i *
System imbalance — too much air.
Sludge ramp, oiler and
sprockets.
Fig. 28.5
Photos of flotation unit parts
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Industrial Waste Treatment 559
The failure or misuse of any of these parts can cause a
decrease in performance of the system or total system shut-
down, neither of which should happen in a well operated plant.
28.103 Part Description
As stated before, the operator must be able to identify each
part of the flotation system in order to operate the systems
correctly and to pinpoint possible malfunctions. Along with
identifying each part, their importance and function must also
be known.
Referring to Figure 28.2, the following paragraphs describe
the functions and importance of each part.
1. Unit Feed Pump. This is the pump that feeds the flotation
system with the solution that is to be treated. Improper
operation, worn impellers, blockages, or improper sizing
will affect delivered volume which is very critical in the
operation of the system.
2. In-Line Check Valves. There are three check valves in the
systems. One is in the line between the feed pump and the
retention tank. This prevents siphoning back of the solu-
tion and possible pump damage on system shutdown.
Another check valve is located on the air system line be-
fore it enters the retention tank. This prevents the solution
in the retention tank from backing up in the air line. The
third check valve is on the chemical line before the intro-
duction of the dilution water. This prevents the dilution
water from traveling back into the chemical pump.
3. Float Valve. There are two float valves located above the
feed tank. One is for the addition of fresh water if neces-
sary. The second float valve regulates the recycle flow
from the clarified compartment of the unit to the feed tank.
This flow is necessary to maintain the required flow
through the feed pump and pressurized air unit during
variations in the supply flow to the feed tank.
4. Air Induction System. This consists of a needle valve,
flow-meter, and strainer/cleaner. This is the supply system
for the air that is necessary for the unit's operation, as
explained in Section 28.100.
5. Chemical Induction System. This consists of a chemical
pump, check valves, dilution water, and some sort of dis-
tribution system within the flotation unit. Without this sys-
tem, the performance of the flotation system will decrease
to about 10 to 20 percent solids removal.
6. Retention Tank. This is a pressurized vessel where the
mixing of the treated solution and air takes place. Without
this tank, the flotation system would not operate.
7. Inlet Header. This is a device that distributes the flow from
the retention tank evenly across the floor of the flotation
unit. Partial plugging of this unit causes uneven flow/solids
distribution within the flotation unit.
8. Flight Scrapers. These scrapers remove all of the sus-
pended solids that have surfaced from the solution be-
cause of the air/chemical/solids reactions. Failure of these
units causes buildup of solids from the surface down to the
flow of the unit, plugging off all paths for clarified water and
rising solids in the solution.
9. Lamell Panels. These panels increase the effective area
of flow within the flotation compartment allowing more ac-
tion in a smaller area and causing a smooth transition of
the solids from the bottom of the compartment to the sur-
face.
10. Weirs. There are two weirs on this system. The main weir
controls the level of liquid in the unit. The second weir is
the flow measuring point for discharge readings from the
unit.
11. Motors. The motors in this system operate the feed pump,
the chemical pump, and the flight scrapers.
12. Flow Measuring Equipment. This is usually a flowmeter/
recorder device matched to the final weir that records the
rate of flow and total gallons discharged.
13. Sampling Equipment. This is usually an automatic type
composite sampler with refrigeration to meet all specifi-
cations of the discharge permit.
14. Control Valve. This valve is located between the flotation
unit and the retention tank. The valve controls the pres-
sure drop across the tank and inlet, thus achieving the
necessary mixing of the air with the solution.
15. Flotation Compartment. A tank similar to a clarifier where
the floes are allowed to float to the surface and be re-
moved by skimmers.
28.104 Safety
Industrial safety is an important segment of any process or
operation. Failure to conform with the simple rules and regula-
tions can be hazardous to your health or to your job. More and
more importance is being placed on safety by the federal gov-
ernment, by the state government, and also by the insurance
carriers for separate industries.
There are many areas of potential safety hazards within the
flotation system. The following paragraphs identify the critical
points and the equipment necessary to bring a plant into com-
pliance with safety regulations.
1. Couplings. All couplings on the feed pump, the chemical
pump, and the scraper drive assembly have to be guarded.
2. Rotating Shafts. All rotating shafts that extend over one-half
of their diameter must be guarded.
3. Sprockets. All gears and sprockets on the chain system that
carries the flight scrapers must be enclosed with a guard.
4. Nip Points. All nip points on the chain drive must be
guarded.
5. V-Belts and Pulleys. The pulley system on the belt drive for
the chemical pump has to be guarded.
6. Electrical. All electrical systems must be installed, marked,
and operated according to the National Electric Code.
7. Unit Access. Proper catwalks, stairs, rails, midrails,
toeboards, and head clearances must be installed where
necessary.
8. Wet Floors and Platforms. Since this is a wet process, due
caution, markings, and housekeeping are necessary for a
safe floor and platform working environment.
9. Chemical Handling. Where stated by the manufacturer, the
proper protective equipment must be worn by any person
who handles the chemical.
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560 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 696 and 697.
28.1 A What is the purpose of the coagulants in the dissolved
air flotation process?
28.1 B Why must an operator be able to properly identify the
critical parts of a flotation unit and their functions?
28.1 C What factors could adversely affect the performance
of a flotation unit feed pump?
28.1D What is the purpose of the retention tank in the dis-
solved air flotation system?
28.1E What is the purpose of the flotation tank in the flotation
system?
28.11 Systems Operation
28.110 System Start-up Procedures
Systematic start-up procedures are necessary for the effi-
cient operation of the flotation system and will prevent unnec-
essary wear on system components. Using the correct proce-
dure each time will also point out possible component malfunc-
tions within the system.
The correct sequence for the start-up of this system is listed
below:
1. Close all drain lines from all tanks, compartments, and
dump valves within the system.
2. Fill the flotation unit with fresh water. This will prevent the
feed pump from operating dry which causes unnecessary
wear and damage.
3. Open the chemical feed system and dilution water and
turn on the chemical pump. This will start the reaction with
suspended solids immediately, reducing the volume of
discharged suspended solids on initial start-up.
4. Open the control valve to the 50 percent position. This is
the logical starting point during start-up before actual ad-
justment takes place.
5. Crack open the air induction system. This will also cause
immediate reactions to take place to remove solids on
initial start-up. Opening the system just a little bit does not
put the retention tank in imbalance, but supplies minimum
air to do the job until final adjustments are made.
6. Open the feed valve 50 percent. This also is the ideal
starting position of the valve until all flows balance out and
final adjustments can be made.
7. Start the feed pump.
8. Go back and adjust the air to the retention tank to the
desired level.
9. Adjust the feed valve to the position where all flows are
balanced.
10. Start the flight scraper drive. Failure to do so now will
cause the buildup of sludge to depths within the flotation
compartment where shutdown and wash-up procedures
will be necessary to clean out the unit.
11. Adjust the flight scraper speed to the desired speed. Too
slow a speed will cause heavy buildup of sludge with the
possibility of overloading the drive unit and plugging the
flotation compartment. Too fast movement of the scrapers
causes too much disturbance in the flotation compartment
and dilutes the sludge. The ideal setting is where the
scrapers keep up with the sludge without disturbing the
compartment and deliver the sludge consistency that you
are looking for.
28.111 System Shutdown Procedures
As important as proper start-up procedures are on system
performance and protecting equipment, the correct procedures
must also be followed in shutdown actions on the flotation
system.
The proper sequence is as follows:
1. Turn off the air supply.
2. Turn off the chemical supply.
3. Flush out the retention tank by opening and closing the
drain valve quickly. This removes all rust particles, dirt and
other foreign matter that has settled on the bottom of the
retention tank.
4. Turn off the feed pump.
5. Turn off the flight scraper drive.
6. Drain all of the unit's compartments.
7. Pump fresh water through the system by using the fresh
water inlet to the feed tank and by starting up the feed
pump after all compartments have been drained. This
flushes out all of the lines which cannot be cleaned except
by complete disassembly. Shut the pump off when inlet
flow clears up to the flotation unit.
8. Wash down all the walls, floors, panels, scrapers, and
weirs with fresh water from a hose. This will knock off all of
the accumulated slime and solids which normally build up
during extended use. Failure to wash the inside of the unit
will make the performance level after start-up drop below
accepted levels.
9. Close all drain valves and dump valves after all surfaces
are cleaned.
10. Return all control valves to their normal operation posi-
tions when ready for start up.
28.112 Start-up and Shutdown Procedure Evaluation
After the completion of either the start-up procedure or the
shutdown procedure, an evaluation must be made to be sure
that the proper steps were taken and no steps were omitted.
The proper procedures have been outlined in the two previ-
ous sections. Remember, equipment may be damaged by
using improper procedures. Failure to fill the unit with fresh
water before starting the feed pump can damage the pump.
Not closing the drain valves before filling the units would cause
a waste of water and time. By not turning on the air, the effluent
quality will suffer.
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Industrial Waste Treatment 561
The shutdown procedure is also critical. Leaving the chemi-
cal feed on until after all jobs are completed would be a waste
of chemicals and money. Opening and closing the drain valve
on the retention tank after the feed pump is shut off would be a
waste of energy, and so on.
Incorrect procedures or steps taken out of sequence are
usually very noticeable either by sound, indicator lights,
effluent quality, visual appearances of the unit, or by mechan-
ical malfunctions.
28.113 Wastestream Evaluation
Wastewater evaluation plays an important role in the opera-
tion of a flotation system. The evaluations are just not lab
findings alone. All the senses play a part in the system evalua-
tion. These evaluations are necessary to maintain the system
in balance and to run the system at the lowest cost.
Wastestream evaluations consider the following items:
1. Increase in floating solids. On the clarified water side of the
flotation unit, a small amount of floating solids is normal.
When a sludge mat starts forming on the surface from too
many solids, the system is out of balance.
2. Increase in suspended solids. Lab tests or visual compari-
sons of clarity of the discharged water will reveal an in-
crease in suspended solids.
3. Variations in the flow to the unit. These will be noticed by
variations of the liquid level in the unit or large fluctuations
in the volume of discharge flow.
4. Variations in odor. This can be noticed very rapidly when
entering the area.
5. Variations in pH. Tests for pH levels must be done either in
the field or in the lab.
6. Variation in color or turbidity. Tests can be done in the lab or
the operator may observe changes in the discharge flow.
7. Variation in the floe of floating and suspended solids.
Changes can be detected by observing the unit's sludge
mat or by taking samples and observing floe arrangement.
Wastestream evaluation is very critical to the solving of prob-
lems, for the prevention of problems, and as an aid in
troubleshooting the flotation system.
28.114 React/on to Abnormal Indicators
To keep a system in balance, the operator must first recog-
nize the indicators of an abnormal condition and then take
appropriate corrective action. There are basically two types of
indicators in the flotation process. One type is the non-serious
indicator. Going back to the previous section, an increase in
floating solids, an increase in suspended solids, variations in
pH, variations in color or turbidity, and variations in floe can be
considered non-serious. These variations can be minimized or
totally corrected by the operator without shutting down the sys-
tem.
1. Increase in floating solids can be corrected by one or a
combination of the following, depending on the condition:
a. Adjusting scraper speed,
b. Adjusting air to retention tank,
c. Adjusting chemical to flotation unit, and
d. Adjusting control valve to change tank pressure.
2. An increase in suspended solids can be corrected as in an
increase of floating solids.
3. Variations in pH can result from uneven flows of fresh wa-
ter, varying chemical supply from the chemical pump, or
from changes in the manufacturing process upstream from
the flotation units. The chemical supply can be corrected at
the pump. The other two require an investigation to identify
the source of the problem and to determine corrective ac-
tion.
4. Variations in color or turbidity usually can be corrected by
adjusting the rate of chemical addition and by adjusting the
air supply to the system.
5. Variations in floe can almost always be corrected by finding
the ideal chemical addition rate to the system.
The second group of indicators are the serious ones. These
are the indicators that mandate the shutdown of the total sys-
tem to correct the problem. Again referring to the previous
section, the variation of flow to the unit and the variation of odor
are two indicators of serious imbalances in the system.
1. Variation of flow to the unit could be caused by (a) blockage
in the feed pump; or (b) a worn out pump creating surges in
flow. In both cases, the pump has to be shut down for
inspection and corrective maintenance.
2. Variations in odor usually mean that the normal system
wash-up schedule has not been followed. The corrective
action needed here is to shut down the system and clean it
thoroughly (boiling it out if necessary) to remove the septic/
rotten substances from all the surfaces.
All of the abnormal indicators and any corrective actions
taken should be recorded in the system's log. Serious indi-
cators and the corrective actions taken should be reported to a
supervisor as soon as possible. This is the first step towards
reporting to the agencies involved whenever the quality of the
discharge stream is affected by a slug or spill of insufficiently
treated water.
Whatever the abnormal indicators are or whenever they take
place, immediate corrective action is required to minimize ad-
verse effects on effluent quality,
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562 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 697.
28.1 F What can go wrong if the flight scraper drive is not
started at the proper time?
28.1G What happens when the flight scrapers travel too
slowly?
28.1H What happens when the flight scrapers travel too fast?
28.11 Why is the retention tank and flotation unit flushed out
and washed down during the shutdown procedures?
28.1J List the possible improper start-up and shut-down pro-
cedures and a possible result or consequence of each
improper step.
28.1 K Why is wastestream evaluation important?
28.1 L List two serious indicators that mandate the shutdown
of the flotation unit and give the possible cause of
each indicator.
28.115 Recording of Data
Accurate recording of system data is very important for sys-
tem evaluation and, in some cases, is required under the firm's
or plant's discharge permit. General trends can be noticed
from these reports. For example, performance can be com-
pared to separate stream characteristics such as gradual sys-
tem slime buildup leading to wash-up operations; seasonal
variations may be noticed; or results of overloadings or slugs
on the system can be seen. This overview is needed to operate
the system, to plan other new systems, and to provide for
discharge permit modifications. Also, the data can pinpoint
another possible trouble area: an operator needing additional
training.
The basic items that should be included in this "operation log
book" are as follows:
1. Date
2. Time
3. Operator's name
4. Upstream conditions within the plant
5. Flow to unit
6. Flow from unit
7. Chemical consumption
8. Total suspended solids (TSS) to unit
9. TSS from unit
10. Percent TSS removal
11. Other information required by the company or industry and
state and federal agencies
12. General operating data
a. Breakdowns
b. Spare parts used
c. Abnormal indicators noticed
d. Corrective actions
13. Airflow
14. Air pressure
If accurate records are maintained on a daily basis, the per-
formance of the units, the cost of operation, and the quality of
the discharged flow will improve and remain constant.
28.116 Sampling
There are two types of routine sampling. One type is the
routine sampling schedule set up in your discharge permit for
compliance. The second type of sampling is for your operation
log book. Both are important for the reasons explained in the
two previous sections.
There are two sample points in the flotation system. The first
is before the system, and the second is after. The difference
between the two is the performance level. The first sample
point can also give the system operator data on variations in
loading upstream from the unit.
Samples can be taken either as grab or composite. Grab
samples will give you results of slug loadings, dumps, or acci-
dental spills by themselves instead of mixed with normal varia-
tions. The composite sample is the average loadings over a
specified period of time. This type of sampling of solids, BOD,
and COD levels is required by all discharge permits. Grab
samples for temperature, slugs, spills, and dumps are usually
accepted.
If economic conditions at your firm or plant permit, the
easiest and best method of sampling is to use an automatic
sampler with refrigerator. This device can be set up to sample
at various time periods and volumes. The refrigeration will pre-
serve normal samples until the next day for analysis. pH, tem-
perature, and flow can also be monitored by continuous record-
ing equipment, or can be done manually, whichever is required
by your permit.
In summary, routine sampling and analysis are required
when operating a flotation system for permit compliance and
for operating the units properly.
28.117 Routine Calculations
To operate a flotation system economically and within dis-
charge permit limits, the operator must be prepared to perform
several routine calculations when gathering and using data
about the system.
The majority of flotation units have standard contracted rec-
tangular weirs in the final position where flow is measured. The
influent and effluent flows of the unit can be calculated from
this weir.
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Industrial Waste Treatment 563
The influent flow is the flow over the discharge weir at 0
percent recycle back to the feed tank. The discharge flow is the
flow over the discharge weir at anytime with from 0 percent
recycle to 100 percent recycle. In some installations there is no
recycle flow.
The formula for calculating the flow over this weir is as fol-
lows (Francis Formula):
q^s.sslh*2 (1)
where
Q = the discharge or flow in cubic feet per second (cfs), (the
approach velocity is neglected)
L = the length of the weir in feet, and
H = the head on the weir in feet.
The flow can also be calculated by the formula:
Q'= 3.3L (H + h)3/2 - h3/2, (2)
where
Q' = the discharge or flow in cubic feet per second (cfs),
(the approach velocity is considered)
L = the length of the weir in feet,
H = the head on the weir in feet, and
h = the head in feet due to the approach velocity
(h = V2/2g and g = 32.2 ft/sec2)
If the cross-sectional area of the channel or flume just up-
stream from the weir is less than five times the area of flow
over the weir, the approach velocity will increase the discharge
a noticeable amount. In this situation, use equation (2) to con-
sider the approach velocity (h = V2/2g).
EXAMPLE
Calculate the flow in cubic feet per second (cfs) over a stan-
dard contracted rectangular weir if the weir length is 30 inches
and the head on the weir is 6 inches.
Known
Contracted Rectangular Weir
30 in
Unknown
Flow, cfs
L, ft =
H, ft =
12 in/ft
= 2.5 ft
6 in
12 in/ft
0.5 ft
.3/2
Calculate the flow in cfs over the weir.
Flow, cfs = 3.33 x {L, ft) x (H, ft)3'2
= 3.33 x 2.5 ft x (0.5 ft) "
= 3.33 x 2.5 x 0.35
= 2.94 cfs
The suspended solids loading on the flotation unit can be
calculated as follows:
Suspended Solids = Flow, MGD x TSS, mg/L x 8.34 lbs/gal (3)
Loading, lbs
day
The BOD loading on the flotation unit can be calculated as
follows:
BOD Loading = Flow, MGD x BOD, mg/L x 8.34 lbs/gal (4)
lbs/day
Unknown
1. SS Loading, lbs/day
2. BOD Loading, lbs/day
3. SS Removal, %
To calculate the percent removal of either suspended solids
or BOD, use the following formula:
Removal, % = (Influent, lbs/day - Effluent, lbs/day) y 1Q0% (5)
Influent, lbs/day
EXAMPLE
Determine the suspended solids and BOD loadings on a
flotation unit if the flow is 2 MGD and the influent suspended
solids are 1,500 mg/L with a BOD of 75 mg/L. What is the
percent removal of suspended solids if the effluent flow is 2
MGD and the suspended solids are 100 mg/L?
Known
Flow, MGD = 2 MGD
Infl. SS, mg/L = 1,500 mgIL
Effl. SS, mg/L = 100 mg/L
Infl. BOD, mg/L = 75 mg/L
1. Calculate the influent suspended solids loading in pounds
per day.
SS Loading, = Flow, MGD x Infl. SS, mg/L x 8.34 lbs/gal
lbs/day = 2 MGD x 1500 mg/L x 8 34 |5s/gal
= 25,000 lbs suspended solids/day
2. Calculate the influent BOD loading in pounds per day.
BOD Loading, = Flow, MGD x BOD, mg/L x 8.34 lbs/gal
lbs/day = 2 MGD x 75 mg/L x 8 34 |bs/ga|
= 1,250 lbs BOD/day
3. Determine the percent suspended solids removal.
a. Calculate the effluent suspended solids in pounds per
day.
Effl. SS, = Flow, MGD x Effl. SS, mg/L x 8.34 lbs/gal
lbs/day = 2 MQD x 10Q mg//_ x 8 34 )bs/ga|
= 1,668 lbs SS/day
b. Calculate the percent suspended solids removal.
SS Removal, _ (Infl, lbs SS/day - Effl, lbs SS/day) x t00%
% Infl, lbs SS/day
= (25,000 lbs/day - 1,668 lbs/day) x 100%
25,000 lbs/day
= 93.3%
To calculate the loadings in the metric system, use the fol-
lowing formula:
Loading, = Flow, ^ x SS.™S x 1 k9 x 1-OOOL
day day L 1,000,000 mg 1 cu m
28.118 Effect of Operator Actions and Reactions
As pointed out in previous sections, one problem might have
a number of different solutions. What has to be done by the
operator is to correct the problem systematically, not by just
random adjustments on a number of different components or
parts.
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564 Treatment Plants
There are some basic rules to follow when correcting prob-
lems. They are as listed below:
1. Assess the problem;
2. List possible corrective actions;
3. Proceed to correct the problem by doing one corrective
action (or change one variable) at a time;
4. Record all actions;
5. Evaluate system response to each action; and
6. After problem is corrected, try to prevent it from developing
again.
The operator must not change more than one variable at a
time. Because of the fact that there are numerous solutions to
one problem, a systematic approach has to be taken. This will
decrease the time period of system imbalance and increase
the knowledge of the operator about how to correct various
problems, especially if records are kept.
Also, give each change a chance to affect the unit. If you
change variables without waiting to see the reaction, it is the
same as changing numerous variables at the same time.
Along with systematically changing variables and waiting for
the reactions, the amount of change is also important. Drastic
changes in component or part settings creates other problems
in system operation. Some results of over reactions are:
1. Rapid change in retention tank pressures. This causes var-
iations in the solution/air relationship and can cause system
flow problems.
2. Rapid change in flight scraper speed. Too slow a speed
tends to increase the consistency of the sludge mat. This
will cause the mat to increase in size downward, thus plug-
ging the flotation compartment. This could also cause fail-
ure of the flight scraper assembly because of increased
weight due to the consistency change. Too fast a speed will
disturb the floating action of the solids, causing the per-
formance of the unit to drop. These two changes in sludge
consistency also affect the point of reuse of the recovered
solids.
3. Variations in the chemical flow. This could change the per-
formance of the unit and adversely affect the discharge flow
quality. Over-supplying chemicals will cause a buildup of
chemical in the system which could affect the manufactur-
ing process wherever the clarified water or sludge is used.
In addition, over-use of chemicals is very costly.
4. Extreme changes in total flow into the unit. This generally
upsets the loading balance to the unit, thus decreasing the
efficiency of the system to the point of non-compliance with
set standards or permit requirements.
5. Extreme changes in air flow to retention tank. This has the
same end effect as changes in total flow, almost complete
failure of the system to treat the waste flow.
The operator must know the proper corrective actions and
perform these actions on a systematic basis. Each change has
to be monitored until reactions take place before the operator
makes further adjustments. Each change has to be a gradual
change, not one of large magnitude that will upset the system.
Also, if the operator maintains an operation log book, a repeat
of a similar problem in the future could be assessed on past
experiences, thus cutting down the time of system imbalance.
28.119 Frequency of System Monitoring
The frequency of system monitoring can mean the differ-
ence between compliance and non-compliance with discharge
limits, or the loss of water and solids recovery which is the
purpose of the system.
Reporting schedules to the required government agencies
vary with each location or state. The best system of monitoring
requires personnel on each shift to monitor themselves. Under
this monitoring program, continuous system operational levels
are monitored, pointing out problem areas and abnormal indi-
cators as soon as they develop. Checking the system this
frequently will also keep any or all chemical costs at the
minimum. The information gathered by this testing can be used
for system evaluation, discharge permit calculations, or
operator evaluation.
The frequency of monitoring will increase when abnormal
indicators are present. Continuous monitoring is required
under this condition until system evaluations point out that all
problems have been corrected.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 697.
28.1M Why is a daily operation log necessary?
28.1N What information can be obtained from analysis of
the accumulated log data?
28.10 Results from sampling are recorded for what two pur-
poses?
28.1 P List the basic rules to follow when correcting a prob-
lem.
28.1Q How long should you wait between changes when
attempting to correct a problem?
28.1R When is continuous monitoring required?
28.12 Preventive Maintenance
28.120 Pertinent Procedures
The operator of a flotation unit must know appropriate pro-
cedures in preventive maintenance to maintain the system in
the proper mechanical operating condition. Preventive mainte-
nance, that maintenance which is performed on equipment to
keep it from malfunctioning, is very important to effective sys-
tem operation.
The pertinent procedures in preventive maintenance are as
follows:
1. Facilities Painting. All metal surfaces should be painted
where necessary to prevent deterioration from rust and/or
chemical reactions.
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Industrial Waste Treatment 565
2. System Cleaning. Flowmeters, check valves, control
valves, and inlet headers should be cleaned on a sched-
uled basis to minimize plugging or failure which affects per-
formance of the unit.
3. Adjustment of Chains and Scraper Alignment. This will in-
crease the life of all parts of the flight scraper system.
4. Belt Wear. All V and flat belts should be checked for wear
so as to prevent failure of a part because of a broken or
slipping belt.
5. Grease and Oil. All components which need grease and oil
should be maintained in accordance with the manufactur-
er's specifications.
Preventive maintenance is extremely important to maintain
the flotation system in proper working order and to minimize
system down-time and serious equipment problems.
28.121 Procedures and Their Frequencies
The frequency of preventive maintenance is very important.
Procedures done too often are a waste of time and energy, and
could possibly damage a part. If procedures are done at irregu-
lar time intervals or not at all, part failure or other problems
could develop. Based on the procedures listed in the previous
section, the recommended frequency of preventive mainte-
nance is as follows:
1. Painting. All painting should be done when necessary to
maintain appearance and to prevent surface deterioration.
2. Cleaning of the Unit and Parts. Broken down into separate
units:
a. Outside Unit. Clean once per month.
b. Inside Unit. Clean twice per month.
c. Stock Header. Clean twice per month.
d. Chemical System. Clean once per month.
e. Retention Tank. Clean twice per month.
f. Check Valves. Clean once per month.
g. Control Valves. Clean once per month.
h. Feed Tank. Clean once per month.
i. Room. Clean when necessary.
3. Adjustment of Chains and Scrapers.
a. Chain. Adjust once per month.
b. Scrapers. Adjust once per month.
4. Belt Wear. Check once per month.
5. Grease and Oil. Check and refill as necessary once per
month or as per manufacturer's specifications.
6. Feed Pump. Check wear on internal parts four times per
year.
7. Valves. Check operation twice per month.
If the above schedule of preventive maintenance is followed,
system down-time, mechanical failures, and performance
drops because of separate part failures can be minimized.
28.122 Required Actions by the Operator
The operator of the flotation unit has to know how as well as
when to perform preventive maintenance. A fixed sequence of
maintenance procedures will help the operator.
Complete the job correctly and as quickly and safely as pos-
sible with minimal system interference. If maintenance must
interrupt the system's operation, the use of proper procedures
is even more essential.
Under normal conditions the following steps are necessary
to perform preventive maintenance correctly:
1. Identify the necessary maintenance step. Time is wasted
and possible harmful effects on system balance occur if the
wrong job is done on the equipment.
2. Pick out the proper tools and equipment. This will save time
during the procedure by revealing any missing equipment
that is necessary to perform the maintenance. Collect the
tools you'll need before starting the job, not while you are
trying to do the job.
3. Review the effects of the maintenance on the immediate
operation of the system. If the required preventive mainte-
nance does not affect the immediate operation of the unit,
proceed with the job. If the procedure does affect the opera-
tion, go to the next step.
4. Contact your supervisor if a procedure will affect the opera-
tion of the system. Do this before actual maintenance. Fol-
low your supervisor's orders. The supervisor must know in
advance when maintenance procedures will affect water,
solids, or discharge qualities so appropriate steps can be
taken to compensate for any upset.
5. Perform the work. The work should be done as quickly and
safety as possible so no harm comes to the employees or to
the equipment.
6. Replace all guards and reset parts. These two items are of
critical importance. The correct settings are critical so that
the operator knows where the system is operating. The
replacement of guards is required so nobody will take for
granted that the guards are in place, when they are not, and
possibly get seriously injured.
7. Clean up. This is necessary for general good housekeep-
ing. While cleaning up, try to locate or account for any tools
you have used. Replacement of lost tools increases main-
tenance costs.
28.123 Importance of Preventive Maintenance
As stated in previous lessons, preventive maintenance is
very important for the proper operation of the flotation system.
To be more specific, maintenance affects four areas of opera-
tion:
1. Effect on system operation. The preventive maintenance
schedule will reduce system down-time compared to just
corrective maintenance. Bearings, motors, pumps and
chains have to be oiled or greased in order to prolong part
life. Belts have to be checked for the same reason. If the
preventive maintenance schedule is not followed, separate
part failures will occur at an abnormally high rate. Smooth
and proper system operation cannot be maintained without
preventive maintenance.
2. Effect on system performance. All preventive maintenance
points affect system performance. For example, if the unit is
dirty, performance goes down; if the chemical system is
partially plugged, the solids will not floe to desired levels; if
the air system check valve is plugged, air will not get into
the retention tank to perform its necessary duties; and so
on.
3. Effect on department budget. All unnecessary unit down-
time because of lack of preventive maintenance is costly.
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566 Treatment Plants
Parts are expensive. Part failures due to poor maintenance
create extra labor and repair costs that could have been
avoided. The whole idea of preventive maintenance is to
ensure smooth system performance at the lowest cost.
4. Effect on waste stream. Depending on the purpose of the
flotation system, the final product will be affected. With
proper preventive maintenance procedures, the system will
operate mechanically at the desired levels, maintain re-
quired levels of treatment, and give end results of com-
pliance with the system's requirements.
28.124 Determination of Preventive Maintenance
In addition to your regularly scheduled maintenance tasks,
be alert for the following conditions which also require prompt
attention:
1. Signs of wear. Worn belts on pulleys and worn sprockets on
the flight scraper require adjustment of the pulleys and
chains to reduce wear. Low inlet pressure may indicate a
worn pump in need of repair.
2. Lack of oil. This will be very noticeable by visual inspection
of the dip stick or sight gage.
3. Abnormal noises. After the operator has had experience
operating the system, the operator will be able to pick up
abnormal sounds and possibly identify which part is in need
of maintenance. This is just as important as visual inspec-
tion and the time schedule for preventive maintenance.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 697.
28.1S What is preventive maintenance?
28.1T What are the results of too frequent or irregularly
spaced preventive maintenance procedures?
28.1U Why should all guards be replaced and part settings
be returned to the original settings after maintenance
is performed?
28.1V List the four major areas of plant operation that are
influenced by preventive maintenance.
28.13 Corrective Maintenance
28.130 Evaluation for Corrective Maintenance
Corrective maintenance is also important for the proper op-
eration of a flotation system. However, the operator must eval-
uate the seriousness of each problem to justify corrective
maintenance since total shutdown of the system is usually
required to repair or replace malfunctioning parts.
All of the previous sections in this lesson explain normal and
abnormal conditions of the system including noise, odor, part
failure and visual appearances. Before the system is shut
down for corrective actions, make sure that the problem cannot
be solved by part adjustments. Consider the possibility that
variations upstream of the system have changed causing the
appearance of part malfunctions. A change such as heavy
solids loadings may decrease unit performance and look like
chemical or air system failure if not checked out. Review all
possible causes of the problem before concluding that correc-
tive maintenance is necessary. You could cause even more
serious problems by correcting something that doesn't need to
be corrected.
28.131 Causes of Component or Part Malfunction
The evaluation and correction of equipment malfunctions by
the use of corrective maintenance is necessary. What is just as
important as correcting the problem is understanding why the
part failed so that repeated part failure is eliminated as much
as possible.
There are six general areas of component or part failure that
must be evaluated after every malfunction.
1. Lack of proper preventive maintenance. This will be notice-
able from the lack of oil or grease, continuous uneven part
wear, or lack of cleaning.
2. Improper installation. This will be noticeable by force marks
on metal surfaces, possible lack of small parts, or parts that
are installed backwards.
3. Product defects. Poor quality bearings, valves that do not
close or seat correctly, or check valves that do not work
freely are defective products that should not be installed.
4. Improper operation. At times, there is a temptation to apply
force to certain parts to make them operate. Wrench marks
on surfaces, bent linkages, or removal of certain compo-
nent parts in order to over-ride component operation are
indications that force has been applied.
5. Old age. Parts that simply wear out by use are responsible
for the majority of problems requiring corrective mainte-
nance. With time and normal use, belts dry out and crack
and bearings and linkages wear down. Timely replacement
of worn parts contributes to efficient operation.
6. Overloading. This could be seen in the failure of flight
scraper panels due to overloading of solids to the unit, or in
repeated electrical kick-outs caused by trying to pump more
volume than the system can handle (excessive amps).
Each incident requiring corrective maintenance must be re-
searched to determine the cause of failure in order to operate
the system effectively and reduce unnecessary costs. Re-
peated down-time for the same corrective maintenance job is
not acceptable. Corrective maintenance means resolving the
existing problem as well as preventing its recurrence.
28.132 Required Equipment to Perform Corrective
Maintenance
The operator has to have the proper tools, testing equipment
and spare parts inventory to operate the flotation process as
smoothly as possible.
The tools that are required to perform corrective mainte-
nance are basically those found in a well-equipped mainte-
nance shop — from screwdrivers to chain hoists. Experience
will dictate the proper tools for a specific installation. Electrical
testing equipment is necessary to monitor and troubleshoot
system problems.
Other than tools, the most important maintenance resource
is a spare parts inventory. Without the inventory, unnecessary
down-time of the system will be adding up and will drastically
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Industrial Waste Treatment 567
affect the discharge stream or solids and water recovery.
There is no excuse for this type of down-time.
28.133 Corrective Maintenance Procedures
As in preventive maintenance, the proper steps have to be
taken in corrective maintenance so the job can be done as
quickly and safely as possible to avoid harming the waste
stream or plant personnel.
The steps are as follows:
1. Identify the problem. Review the six general causes of part
failure listed in the previous section. Normal checks may
reveal hot bearings or a system that is not clean, for
example.
2. Line up the necessary tools and parts. This will save time
and will identify a lack of tools or parts necessary to per-
form the maintenance.
3. Evaluate the problem to see if your personnel can correct
the malfunction or if the part has to be shipped out or help
from the outside has to be sent in. This is necessary be-
fore actual tear-down begins. Time and money will be
saved by avoiding unnecessary tear-downs when outside
help could fix it on the spot.
4. Again, notify the supervisor of all conditions before total
shutdown or directly after if emergency conditions cause
automatic shutdown.
5. Put into effect all company emergency plans if the unit is to
be inoperable for an extended period of time or if dis-
charge stream quality is to be affected above discharge
limits.
6. Perform the work as quickly and safely as possible.
7. Replace all guards and component settings for the same
reasons as listed for preventive maintenance procedures.
8. Clean up after the job is completed.
9. Record all information in the operation log book for future
references. This will minimize the recurrence of separate
problems and make other maintenance jobs run more
quickly and smoothly.
10. Reorder all parts used. This is necessary to maintain the
proper spare parts inventory.
28.134 Importance of Efficient and Quick Corrective
Maintenance
In summary of this section, the corrective maintenance pro-
gram has to take place as quickly and safely as possible with-
out affecting the quality of the job.
By missing steps required in corrective maintenance, or by
not maintaining adequate tools, spare parts, or the proper rec-
ords, unnecessary system down-time will prevail. This will, in
its worst form, seriously affect the quality of the discharge flow
from the system. If the discharge flow goes directly from these
units to the receiving stream, noncompliance of permit limits
and its consequences will take place. If the discharge goes to
other stages of treatment, the ineffectiveness due to improper
maintenance will jeopardize the operations of all systems
downstream.
Systematic corrective maintenance is a requirement of
proper system operation. Getting the job done as quickly as
possible can prevent the development of adverse conditions
resulting from prolonged system shutdown.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 697 and 698.
28.1W What does corrective maintenance require?
28.1X List several causes of part malfunctions.
28.1Y Why is a spare parts inventory necessary?
28.1Z Why is quick and efficient corrective maintenance re-
quired?
t>UQ Of tf&bOH t OP6t0»SOW<3
INPUftTClAL WA6T6 TBSAfMeiOT
Please answer the discussion and review questions before
continuing with Lesson 3.
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568 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 6 Lessons)
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 1.
7. How does the dissolved air flotation process work?
8. Why are both solids recovery and water recovery impor-
tant in the flotation process?
9. Why must proper start-up procedures be followed when
starting a flotation unit?
10. Why is it important to make one change in component or
part settings at a time when trying to correct operational
problems?
11. Why is preventive maintenance important?
12. Why and under what conditions should you inform your
supervisor of future preventive maintenance?
13. In evaluating the need for corrective maintenance, what
steps should be taken before shutting down the system?
CHAPTER 28. INDUSTRIAL WASTE TREATMENT
(Lesson 3 of 6 Lessons)
28.2 SCREENING AND MICROSCREENING APPLIED TO
INDUSTRIAL WASTE TREATMENT by Tony Diaper
28.20 Need for Screening and Microscreening
SCREENS3 and MICROSCREENS4 are used in industrial
waste treatment to intercept and remove suspended solids
from the flowing wastewater. There are three grades of
screens which can be used. Coarse screens are used for pri-
mary treatment, microscreens (fine screens) are used for final
polishing and there is an intermediate grade of medium screen-
ing, a relatively recent development, which can be used in
conjunction with, or in place of, a primary clarifier.
Removal of suspended solids by these screens before other
treatment processes allows the downstream processes to
function more effectively. Screening also provides a conven-
ient way of collecting and disposing of particulate matter be-
cause the solids are often removed from the screens in a
semi-dry condition.
Screens take up less space than clarifiers and are not so
much affected in performance by changes in flow rate or tem-
perature. However, if it is more convenient to deal with the
solids removed from the wastewater in the form of a sludge,
then pumping sludge from a clarifier for subsequent treatment
or dewatering may be preferred over a screen. In many cases,
3 Screen. A device used to retain or remove suspended or floating objects in wastewater. The screen has openings that are generally uniform
in size. It retains or removes objects larger than the openings. A screen may consist of bars, rods, wires, gratings, wire mesh, or perforated
plates.
4 Microscreen. A device with a fabric straining media with openings usually between 2 and 60 microns. The fabric is wrapped around the
outside of a rotating drum. Wastewater enters the open end of the drum and flows out through the rotating screen cloth. At the highest point of
the drum, the collected solids are backwashed by high-pressure water jets into a trough located within the drum.
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Industrial Waste Treatment 569
the method of wastewater solids separation (screens or
clarifiers) depends on the method of sludge handling and dis-
posal at a particular plant.
Microscreens are used for final treatment or "polishing" to
prevent the carryover of floating solids and suspended parti-
cles in the effluent following other purification processes. They
safeguard against deterioration in performance of the up-
stream processes, although there is a limit to the deterioration
which can be treated by the microscreen before overloading
and bypassing occurs.
Coarse screens are often placed downstream of grit removal
processes in order to protect the screening equipment. On the
other hand, coarse screens are used upstream of grit removal
in some plants to eliminate floating material before the grit
chamber or channel. However, in industrial waste treatment,
grit usually is not a problem and special provisions for grit
removal are unusual.
Medium screens are used in conjunction with, or in place of,
primary sedimentation tanks. They reduce the organic load on
aeration processes or trickling filters by removing most of the
large particles in suspension. This allows the biological pro-
cess to function more efficiently. Solids dewatering is assisted
by screening because the solids are often removed in a semi-
dry condition.
In some cases, medium screens are used as part of the
solids dewatering process. For example, the underflow from a
clarifier would be pumped as a slurry to the screening process
to assist in removing some of the water in the sludge.
Since microscreens are used for final polishing, the only
in-plant process directly affected is disinfection, if disinfection
is being used. Chlorine is commonly used for disinfection.The
use of microscreens will allow smaller doses of chlorine and
also could give more complete disinfection due to the removal
of floatable and suspended solids.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 698.
28.2A What is the purpose of screens and microscreens in
industrial waste treatment?
28.2B How could microscreens be an aid to disinfection?
28.21 Description of Screens
28.210 Stationary Screens
Bar screens (Fig. 28.6) consist of vertical or inclined steel
bars spaced at intervals across the channel through which the
wastewater flows. They are used ahead of other treatment
processes to eliminate coarse objects which could cause
damage or defects in operation. Bar screens usually have rela-
tively large openings, between one and four inches (2.5 to 10
cm), and their principal function is to prevent heavy floating
objects from entering the treatment plant. They may be
cleaned manually or by mechanical rakes. Mechanical clean-
ing devices consist of rakes that periodically sweep the
screens and remove the solids for disposal (Fig. 28.6). Most
bar screens use endless chains or cables to move the rake
teeth through the screen openings. The screens may be front
or back cleaned.
The following types of controls can be used alone or in com-
bination to clean screens:
1. Manual start/stop,
2. Automatic start/stop by time control,
3. High level switch, and
4. Differential head switch.
Mechanically cleaned bar screen mechanisms will discharge
on the upstream or downstream side of the bars. Front dis-
charge of screenings may be preferable to back discharge as
any screenings lost in handling are upstream of the screen and
therefore will again be subject to the chance of removal.
The Hydroscreen (Fig. 28.7) and Hydrasieve represent a
modern development of the bar screen in which the bars are
arranged horizontally instead of vertically and have much
closer spacing (0.02 inches to 0.06 inches (or 0.05 to 0.15
cm)). In both cases, the bars are made of stainless steel
wedge wire supported in a framework. Incoming water is deliv-
ered to the top of an inclined screen. As the wastewater runs
downward over the outer inclined screening surface, water
drops through the screen to the back and is collected in a
trough while intercepted solids fall to the bottom of the incline
for disposal.
The only cleaning mechanism is the force of the effluent
water which sweeps the intercepted material off the face of the
screen. Manual cleaning by brushing or hosing is required at
intervals, the frequency depending on the nature of the waste.
28.211 Moving Screens (Fig. 28.8).
The Rotostrainer incorporates screening media made of
stainless steel wedge wire similar to that used on the Hydro-
screen. In this case, the screening media is mounted on a
horizontal cylinder which rotates continuously. The cylinder is
carried in a supporting structure with external bearings. The
supporting structure also forms the feed box for the influent to
run outwards over the top of the horizontal rotating cylinder.
The strained water falls through the screening media into the
inside of the cylinder and out through the bottom of the screen
into a collecting trough. The force of the falling water is suffi-
cient to clean off the screen. A wiper or DOCTOR BLADE5 is
fitted to skim off intercepted solids and drop the debris into a
collecting trough for disposal.
Figure 28.8 shows various types of Rotostrainer in-
stallations. If required, the Rotostrainer can be fitted with an
optional internal backwash system which delivers either steam
or hot water under relatively high pressure to the interior of the
cylinder. The steam or hot water removes any material that
may not have been removed by the natural backwashing ac-
tion.
Screenings from the Rotostrainer are usually collected and
discharged to a disposal point by a trough or conveyor system.
From here they may be pressed before disposal to landfill
incineration or byproduct recovery depending on the type of
screenings.
Another type of drum or cylindrical screen (Figure 28.9) uses
woven wire mesh with apertures (holes) between Ve inch and
V2 inch (0.3 and 1.3 cm), mounted on the periphery. In this unit,
the effluent flows into the inside of the drum and gravitates
through the screening media to the outside. The rotation of the
drum is used to bring the intercepted solids up underneath a
row of backwash jets spaced across the top outside of the
drum. These jets spray downwards continuously and flush the
s Doctor Blade. A blade used to remove any excess solids that may cling to the outside of a rotating screen.
-------
Thru-clean screen viewed from
upstream side. Head shaft housing
has been removed to show cycle of
rake movement.
DRIVE
HOUSING
RAKE
WIPER
DOORS
SOLIDS
STRUCTURAL
FRAME
OPERATING
FLOOR
SCREENING CAN
OR CONVEYOR
CHAIN
RAKES
BAR RACK
CLEARANCE
CHANNEL
DEPTH
FLOW
RAKES
<¦*- CLEARANCE
CHANNEL FLOOR
/
INCLINED THRU-CLEAN SCREEN
ELEVATION THRU CHANNEL
Fig. 28.6 Bar screen
(Permission of FMC Corporation, Environmental Equipment Division)
-------
Industrial Waste Treatment 571
Screen Flexibility
The three individual screen panels
are designed for easy removability
allowing for:
• quick changeover to accommodate
any variation in solids concentra-
tions or for instantaneous cleaning.
• a progressive screen space
opening profile can be achieved by
varying the screen space opening
at any one of the three locations.
Screen Construction
Corrosive resistance and
durability is built into the all
stainless steel Hydroscreen.
Three distinct screen angles
allow the solids to travel
uniformly down the screen
face, becoming progressively
drier until they are discharged
from the lower edge.
Screen Installations
The three overlapping screens
fit snugly into the chassis pre-
venting any bypass of solids
to the effluent.
Screen Bar Spacing
Units are available with wire
space openings from 0.010"/
0.25mm to 0.100"/2 50mm
Optional Features
• Top influent feed
• 304 stainless steel
• Flanged inlets and outlets
• Side cleanout panel
• Fiberglass construction in
selected models
Headbox
The headbox is specially designed to receive
and moderate high inflow velocities The
influent flows evenly over a weir onto the
screen surface
Rugged Construction
Available in all 316 stainless steel
continuous weld construction
models.
Leveling Pads
Heavy duty level pads provide
quick and permanent leveling
adjustment.
Fig. 28.7 Hydroscreen
(Parmlttion of Hycor Corporation)
-------
572 Treatment Plants
Above Ground
Influent
Effluent
Screenings
Below Ground
Influent
Effluent
Screenings
Above and Below Ground
Influent
Screenings
Piped Discharge
Piped Discharge
Fig. 28.8 Rotostrainer type of moving screen
(Permission of Hycor Corporation)
Effluent
Open Channel Discharge
debris into a collecting hop per which runs parallel to and along
the axial length of the drum. From here the solids flow by
gravity to disposal. A screw conveyor is sometimes used in the
hopper to assist in removing solids.
These screens are best suited to installations where a fixed
water level can be maintained. The screen is supported by two
bearings and driven from one end. The open end is sealed
against the stationary frame by means of a rubber seal to
prevent bypassing of the liquid.
The main parts of the drum screen are identified on Figure
28.9. The drum screen is operated under open gravity flow
conditions using inlet and outlet channels to bring the water
into the drum and take it away on the downstream side.
Backwash water is usually pumped from the downstream side,
or from a clean water (low or without suspended solids)
source. Arrangements must be made for conveying away
screenings and wash water discharge.
The drum screen is sometimes fitted with a splash cover or
hood containing an inspection door. In other cases the drum is
installed in a superstructure to protect the equipment and pro-
vide the best operating conditions.
A disc strainer (Figures 28.10 and 28.11) is similar to the
drum strainer described above except that a disc is used in
place of a drum. The disc carries the coarse screening media,
usually woven wire cloth, and rotates through the flowing liquid
which gravitates (drops) through the screen. Spray jets are
arranged radially above the water level to wash off the
screenings into a hopper and continuously clean the mesh.
Figure 28.10 is a drawing of a typical disc screen and iden-
tifies the main parts of the design.
As in the case of the drum screen, a rubber lip seal is re-
quired to prevent bypassing of the water around the screen.
The screen is supported on a rotating shaft mounted in two
bearings above the fixed water level. Flow capacity of the
screen depends upon the size of mesh fitted and may be calcu-
lated using a head loss not exceeding one inch (2.5 cm) of
water.
The band screen or traveling screen (Figure 28.12) is
another type of moving screen which uses panels of coarse
wire mesh or perforated plates fixed to a chain which is carried
over top and bottom rollers in the form of an endless belt. The
bottom of this screen is immersed in the flowing water and the
top moves through a hood in which are mounted jets that spray
through the screen and force solids into a backwash collecting
hopper. The movement of the screens is used to lift debris from
the flowing water and to clean the screening media.
Traveling screens are used where water levels are variable
as in the case of river water intakes. Their use is not so com-
mon in wastewater treatment.
Figure 28.12 identifies the main parts of the traveling screen.
Note that it is installed in a concrete channel through which
water flows under gravity. A seal must be provided between
the moving screen and the side of the channel to prevent leak-
age. The fineness of the screen material is limited in practice
by the need to have openings between the screen panels in
order to allow deflection of the panels as they move over the
rollers. A channel must be provided to convey away the waste
material washed from the screen.
All moving screens may run continuously at constant speed
or variable speeds which can be controlled automatically by
the upstream channel level, flow level, or head differential
through the screen.
28.212 Mlcroscreens (Figure 28.13)
Microscreens are similar to the coarse drum screen de-
scribed above except that the straining media is much more
finely woven with apertures (holes) between 2 and 60 MI-
CRONS.6 The fabric (Figure 28.14) can be made of stainless
steel or polyester threads and is mounted on the periphery of a
continuously rotating drum. The rotating drum is carried on
submerged bearings and supports the straining media. The
purpose of drum rotation is to present a clean surface of the
media to the water to allow flow to continue. The rotating drum
brings the dirty fabric under the backwash system at regular
intervals. Sometimes a supplementary cleaning system is
used, such as ultraviolet irradiation, to inhibit the growth of
biological slimes.
The rotation of the drum also lifts intercepted solids from the
wastewater and deposits these solids in a hopper supported
inside the drum. Intercepted solids are washed away by
backwash water that runs from the hopper by gravity into the
disposal system.
The drive unit with variable speed is used to rotate the drum.
The speed control can be manually or automatically operated.
In the case of automatic control, head loss across the screen is
normally used for regulating drum speed.
Figure 28.13 identifies the main parts of the microscreen
which is usually installed in open gravity flow channels to allow
water to percolate through the drum form inside to outside. The
top of the wash water hoppers are in air above the water sur-
face to receive the intercepted solids as they are washed off
the inside of the mesh. Backwash from a clean source is
brought to the header pipe which runs above the top of the
drum in an axial direction. A peripheral seal is provided to
prevent bypass of the water being strained.
6 Micron (MY-kron). A unit of length. One millionth of a meter or one thousandth of a millimeter. One micron equals 0.00004 of an inch.
-------
Industrial Waste Treatment 573
Industrial installation of a drum screen utilizing a dewatering screw conveyor.
Cutaway view of revolving drum screen available
with stainless steel cloth ol 2 to 60 mesh or finer
and up to 10' in diameter.
Encased revolving drum screen separates debris from
river intake water at a woolen mill. Driven by Vi
horsepower motorized worm gear drive, a maximum
flow of 2700 gallons per minute Is screened.
o r%n/\r»T SPRAY WATER PI PES
SUPPORT wlTH NOZZLES SOLIDS
SHAFT | i /
V\ SCREENINGS
' n DISCHARGE TROUGH
HOUSING
ROTATING SCREEN FRAME
COVERED WITH WIRE MESH
DRIVE
ROTATIO
Li * ° " itir
SEAL EFFLUENT
FLOW
I LOW
NFL UENl
DRUM SCREEN
ELEVATION THRU CHANNEL
Fig. 28.9 Revolving drum screen
(Permission of FMC Corporation, Environmental Equipment Division)
-------
cn
Revolving Disc screen installed at a municipal wastewater treatment plant.
O
0)
3
i
Y / '•
¦mf*
3
(/>
REFUSE CONVEYOR
OR TROUGH
SPLASH
GUARD -»
SPRAY WATER PIPES
WITH NOZZLES
SUPPORT BEAMS
DRIVE
DRIVE CHAIN
SOLIDS
FREEBOARD
TO SUIT
WATER
.EvEL
-INFLUENT
WEIR
FFLUENT
ROTATING
— SCREEN
FRAME
SCREEN
WIRE MESH
J-
— 6'-0" MINIMUM
CHANNEL
FLOOR
DISC SCREEN
ELEVATION THRU CHANNEL
Fig. 28.10 Revolving disc screen
(Permission of FMC Corporation, Environmental Equipment Division)
-------
Industrial Waste Treatment 575
Operation and Construction Details
S DUDS
C SCHARGE
FLEXIBLE
EFFLUENT
SEDIMENTATION ZONE
O DISC DRIVE
SYSTEM
Q EFFLUENT
MESH
DISC RIM
SEAL
INFLUENT
PRECOAT
FORMATION
EFFLUENT
TOP VIEW ©DISCS 0D,SC SHAFT
OSUSPENDED
SOLIDS
O influent
Q PRECOAT
O SCREEN MESH ® FLEXIBLE DISC SEAL
SUPPORT STRUCTURE
Flow Description
The process or waste water enters the energy absorbing
inlet chamber before being channeled between the sets of
rotating discs The mesh covered discs capture the sus-
pended solids while allowing the water to flow out to dis-
charge The solids remaining behind form a precoat material
which aids the filtration effect As the solids level between
the discs builds up, a portion is wasted through the solids
discharge opening in the front of the Discostrainer
The continuous rotating mass of solids carried on the revol-
ving discs falls back from the discs as they reach the highest
point of travel This creates a self-cleaning scouring action,
adding greatly to the non-blinding characteristics of the disc
straining process
Component Parts
I Influent
inlet headbox has a specially designed energy dissipating
baffle which feeds the wastewater between each pair of discs
Discs
The discs are arranged in pairs. The smallest unit has one
pair of discs, the largest 10 pairs The discs vary in size from
39" dia to 71" dia
Q Disc Shaft
Discs are mounted on a horizontal stainless steel shaft which
is supported at each end by pillow block bearings
Q Disc Drive System
A shaft mounted variable speed direct drive system rotates
the discs at 5 to 15 rpm.
Q Effluent
Screened liquid flows radially out from between the discs
into an effluent chamber which channels it to a common
discharge pipe
Q Suspended Solids
As the suspended solids agglomerate, a waste portion is
discharged through the front opening of the Discostrainer.
^ Disc Seals
The discs rotate in a specially contoured chamber A mech-
anical seal prevents any leakage of liquid solid between
the outside rim of the disc and the contoured chamber Thus
the total influent must pass through the disc screening mesh.
Screen Mesh Support Structure
The fine screen mesh is supported on each disc by a rugged,
stainless steel radial structure and heavy duty woven mesh
backing which prevents the screen from bowing or bulging
Available from 45 to 425 microns
Q Precoat
The precoat filtration aid media is formed by the solids
captured between the discs This insures a better removal
efficiency of fewer suspended solids
© Spray System
An integral spray system can be provided as an optional
extra It consists of a centrifugal pump and backwash spray
header arrangement The solids washed off the discs are
removed with the excess solids discharged from the Disco-
strainer
VIEW
FRONT
SIDE VIEW
DISC ROTATION
SCREEN
MESH SUPPORT STRUCTURE
SPRAY SYSTEM
DISCS
Fig. 28.11 Disc strainer
(Permission of Hycor Corporation)
-------
576 Treatment Plants
(sprocket
. " '' '
fc Screen
T frame
Chain
and
trays
sprocket
Torque tube
head shaft |
Head terminal
\
Electrofluid
Motogear
Spray pipes
and nozzles
Headi
Fig. 28.12 Thru-flow type traveling screen
(Permission of FMC Corporation, Material Handling Systems Division)
-------
Industrial Waste Treatment 577
VARIABLE
DRIVE
n«v» f*Mltd
INLET
WASTE
OUTLET
PERIPHERAL
SEAL
PERIPHERAL
RACK ON DRUM
STRAINING
OCCURS OVER
ENTIRE
SUBMERGED
SECTION OF
MICROFABRIC
WATER-LEVEL
IN TANK
DRIVE WASHWATER
PINION HOPPER
BACKWASH
SPRAY-NOZZLE
HEADERS
Fig. 28.13 Microscreen
(Permission of Crane-Cochrane)
-------
578 Treatment Plants
Fig. 28.14 Isometric drawing of microfabric with typical
diatom (Cymbella) shown against the fabric
(Permission of Crane-Cochrane)
28.213 Mechanical Equipment
In all cases, the screening media must be of sufficient
strength to withstand the hydraulic pressure created by head
loss as solids are intercepted on the screens. In the case of
wire mesh screens, a support system is sometimes used. The
material should also be NONCORRODIBLE7 and preferably of
the type which assists cleaning such as wedge wire. The bars
in coarse screens are often made wedge-shaped for this pur-
pose.
The structure used to support the straining media varies
depending upon whether a screen is stationary or moving. In
the case of bar screens it consists of structural steel sections
embedded in the concrete sides of the channel. In the case of
the Hydrasieve, the structure incorporates the feed box and is
self-supporting.
In the case of moving coarse screens, bearings will be in-
volved either carrying top and bottom rollers in the case of
band screens or supporting the disc or drum in the case of
rotary strainers. Some difficulty in design is presented by sub-
merged bearings. Ideally, the bearings are lubricated and
should be placed above the water surface. This may not be
possible with the bottom roller on a band screen so water-
lubricated bearings are installed.
For moving screens, some sort of seal is needed between
the moving and stationary sections to prevent the passage of
solids in suspension. All screens require some sort of cleaning
mechanism. In its simplest form, this is a manually operated
rake. Bar screens are often inclined to assist in removing the
intercepted solids. A walkway is provided across the top of the
channel to receive the solids so they can be removed to one
side for disposal.
The automatically operated cleaning mechanism fitted on
some bar screens consists of heavy metal teeth which project
through the bars from front or back and are operated by a
toggle (a projecting knob or arm) which brings them into con-
tact with the intercepted solids allowing them to sweep the bars
clean and lift the solids into a hopper for disposal.
The drive mechanism for the cleaning rake is usually an
electric motor with reduction gear and chain drive. The starter
for the electric motor may be controlled by a time switch or the
differential pressure across the screen. This type of cleaning
mechanism can be applied to vertical or inclined bar screens.
The cleaning system of moving screens usually incorporates
nonclog design backwash jets. These are supplied with clean
water (low or without suspended solids) under 30 to 60 psi (2.1
to 4.2 kg/sq cm) pressure. They create a fan tail which spreads
across the entire width of the screen. Sometimes two rows of
jets are employed and may be assisted by brushes or doctor
blades (wipers).
When jets are used to clean the screen, a hopper must be
placed behind the screen opposite the jet system. This will
collect the solids which are washed off the coarse mesh. The
solids may then travel by gravity into a pipe for disposal or be
removed by a screw conveyor.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 698.
28.2C List the different types of screens?
28.2D What types of controls can be used to clean screens?
28.2E Clean water used to backwash screens and filter
media must be low
28.2F How can the speed of a variable-speed moving screen
be controlled?
28.22 Safety Procedures
High risk activities include manual cleaning of the screens or
microscreens and maintenance of associated machinery. If the
screens are installed indoors, adequate ventilation must be
provided to prevent maintenance personnel from being over-
come by fumes. Problems can develop from toxic gases such
as hydrogen sulfide, explosive conditions or a lack of oxygen.
Use a gas mask (hose type or oxygen breathing apparatus)
or provide adequate ventilation and monitor the atmosphere
when entering enclosed areas because of the possibility of
noxious fumes. Other sources of danger include falling into
channels, slipping on slimy walkways, getting caught in moving
machinery or coming into contact with exposed electrical
wiring. Whenever you discover exposed electrical wiring, have
an electrician correct this hazard immediately.
7 Noncorrodible. A material that resists corrosion and will not be eaten away by wastewater or chemicals in wastewater.
-------
Industrial Waste Treatment 579
Channels adjacent to the screens should be roofed over and
appropriate manholes must be provided with corrosion-
resistant rungs or steps.
Work in basements or tanks should not be undertaken with-
out checking to be sure isolating valves are properly closed,
drainage valves are open, adequate personnel are present,
proper lighting is provided and equipment such as spark-proof
tools, rubber boots, safety belts and rubberized gloves are
available.
Work should never be undertaken in an area normally open
to traffic without an adequate number of barriers and signs.
Also, vehicles should have a rotating beacon on top of the cab.
All workers should wear hard hats and a red vest.
Before draining down a sump, wet well, channel or tank to
enter and service moving machinery, be sure to stop the ma-
chinery and remove the contact breaker from electrical star-
ters. Switchboards and areas of operation must be kept well
lighted at all times. Walkways, stairs and ladders should be
kept clean, free from grease, oil and ice and adequately
lighted. Guards should be used over rotating machinery. Non-
slip surface should be provided on the edges of channels.
Adequate space for servicing should be provided around ma-
chinery and control panels.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 698.
28.2G If an oxygen detector indicates insufficient oxygen,
how can this problem be corrected?
28.2H What kinds of precautions should be taken before
working in an area open to traffic?
28.23 Operating Procedures
28.230 Start-Up Procedures
Before starting any screening equipment, go through these
start-up procedures and check all items listed that apply to
your facility plus any other items that are unique to your facility.
1. Be sure that all components are in place and any tempo-
rary packing has been removed.
2. Examine oil levels and grease points.
3. Check for personnel in area, observe safety precautions.
4. While chambers are dry, try movement of machinery.
5. If equipment can be operated dry, allow it to run for a short
period.
6. Inspect equipment alignments and make adjustments to
gaskets, sprockets, drive chains, rakes and belts.
7. Operate through several cycles. Inspect alignment and
listen for excessive noise. Watch for erratic motion.
8. Check automatic controls, if fitted.
9. While machinery is in slow speed, open chamber inlet
valve gradually to admit water at a slow rate.
10. Watch for any excessive debris being washed in, in which
case speed up screen movement and cleaning mech-
anism.
a Blinding. The dogging of the filtering medium of a microscreen or a
due to grease or the material being filtered.
11. Determine head loss across screen. Guard against surges
of flow. Continue to regulate inlet valve until desired head
loss is achieved.
12. If fitted, operate backwash system as soon as possible
and check operation of jets.
13. Check to see if debris and solids are being flushed off the
screen and are running to disposal.
14. In the case of rakes, check to see that the rake is scraping
the bar screen clean of debris.
15. Check gaskets, water seals, and also look for leaks,
bypassing and irregular motion. Make adjustments as
necessary.
16. If fitted, check automatic controls in functioning mode.
17. Equipment should now be operating normally. Continue to
observe and regulate equipment as necessary for several
hours.
If the correct start-up procedures have been used, the
coarse screen or microscreen will function correctly by treating
the required rate of flow without an excessive head loss.
28.231 Normal Operation
The main parts to be checked regularly include the screen-
ing media which should be examined for cleanliness and struc-
tural soundness, the cleaning system which may consist of
backwash spray jets or a mechanical rake, the drive unit if
fitted, and other moving machinery. The effectiveness of seals
and gaskets as well as the strength and stability of supporting
framework should be inspected regularly. Inspect the screen-
ing media for BUNDING8 or blocked grids. Operational data
should be recorded on a printed form and returned in writing to
the supervisor. A sample form is shown in Figure 28.15.
Sampling of the effluent should be carried out before and
after the screening media. Grab samples are usually used,
although continuous monitoring is preferable. Flow rates
should be observed and recorded. Head loss, rate of rotation
or speed of the screen should be noted every day. Your sam-
pling program must be designed to meet the monitoring and
reporting requirements specified in your sewer-use ordinance
and NPDES permit.
Try to relate the flow rate to the head loss observed using
the proper hydraulic formula in either Section 28.251, "Design
of Coarse Screens," or Section 28.252, "Design of Mi-
croscreens." This will indicate the degree of plugging of the
screening media. In the case of microscreens, a more compli-
cated procedure based on the concentration of solids in sus-
pension is necessary.
28.232 Abnormal Operation
Abnormal conditions of the screening media are shown by
heavy plugging which will lead to an increase of head loss and
reduction of flow rate. The cleaning system may be examined
visually. Backwash jets should present a smooth fantail ex-
tending across the straining surface operating continuously at
adequate pressure. Seals and gaskets should be inspected.
Abnormal conditions of moving machinery are often identified
by erratic movements or unusual noises. Wear on bearings
should be checked when the equipment is drained down.
Overloading of the upstream processes can cause difficul-
ties with operation of microscreens. There are limits to the
vm filter when the holes or spaces In the media become sealed off
-------
580 Treatment Plants
OPERATOR
Name
Date
Shift
Time
FLOW
Weather
Rate .
Temp.
Depth -
Drum Speed
Screen Submergence
Head Loss
Other
BACKWASH
(or rake)
Press
Flow
Other (Supplemental cleaning)
ELEC. POWER
INPUTS
Auto
EFFICIENCY
Drive
Backwash
S.S.
B.O.D.
Other (oil, grease)
Before
Manual
After
Figure 28.15 Sample operational report sheet
amount of suspended solids which can be handled at the de-
sign flow rate. Figures 28.16 and 28.17 illustrate the relation-
ship between suspended solids and the flow rate.
28.233 Operational Strategy
If more than one screen is available, place the number of
screens on line needed to handle the flows and solids to be
treated. Operate each screen within its design hydraulic, solids
loading, and differential head range. When solids loadings
change, adjust procedures or equipment for cleaning the
screens accordingly. Another approach is to keep all screens
operating in order to keep fabric clean and ready for use. The
procedure you develop for your screens will depend on influent
conditions, costs of operation, and effluent requirements.
28.234 Shutdown Procedures
1. Close chamber inlet valve.
2. Open chamber drains.
3. Allow water level to drop slowly while regulating speed of
machinery to prevent excessive differential head. Keep
backwash turned on until level reaches within 1 foot (30 cm)
of pump suction. Then close down backwash system and
shut off backwash pump.
4. Allow water level to continue falling while maintaining dif-
ferential head within safe limits.
5. When chamber is empty, hose off all screen material with
clean water (low or without solids).
6. When all solids are washed out of the chamber and the
media is clean, adjust drive unit to minimum speed setting
and turn off power supply.
NOTE: Screening media should be left in a clean condition,
otherwise it will dry out dirty and be difficult to clean before
putting screen into service next time.
If shutdown is only for a brief period, it may not be neces-
sary to drain chamber completely, as long as machinery is
kept in motion. This will prevent the screening media from
becoming plugged.
Evaluation of whether correct shutdown procedures have
been used will be shown by the screen or microscreen being in
a clean condition when the chambers are dry and empty. An
examination of the mesh/screening material should be made to
insure that it is perfectly clean and does not dry out in a dirty
condition.
A similar restriction applies to coarse screens, but the limits
are not so critical (Section 28.251 and 28.252). Abnormal con-
ditions in the waste stream are shown by excessive flow rate
and concentrations of solids, large trash or floating objects.
This can damage screens either by impingement or by creating
excessive differential head which will rupture the screening
material. The cause of abnormal conditions is often increased
'low rate from rain storms. Sometimes accidental spills or dis-
charges can create upsets and malfunction of upstream pro-
?sses.
Wastewater conditions can be checked visually and flow
. icators will give warning of increased flow rate. A differential
'; ad alarm on the screen will also measure and warn of ex-
: e ss flows or solids. If these conditions occur, attempts should
-a made to improve upstream operating conditions. At the
same time, cleaning of the screens should be increased. In the
case of coarse screens, this means cleaning continuously if
manually operated, or speeding up the device if automatically
operated. In the case of microscreens, the speed of rotation
and the backwash pressure should be increased.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 698.
28.21 During start-up, what kind of a check is made on the
solids and debris?
28.2J List the major items that should be inspected during
the normal operation of a microscreen.
28.2K Heavy plugging of a screen could be caused by what
factors?
28.2L How would you determine if correct shutdown proce-
dures had been used for a screen or microscreen?
28.235 Troubleshooting
Table 28. t lists the problems most frequently encountered
when operating screens and microscreens. Once the trouble
and cause have been identified, the correct solution can be
selected.
-------
Industrial Waste Treatment 581
REPRESENTATIVE FLOW vs. SS
FOR
MICROSTRAINER
CONDITIONS:
A — ACTIVATED SLUDGE SECONDARY
B - MAXIMUM DRUM SPEED — 100 fpm
C - MAXIMUM HEAD LOSS - 6 INCHES
D - FABRIC • MARK '0'
* — 5 FT. DIAMETER BY 3 FT. LONG
5X3*
5 X 1
—»—
1.75
—I—
0.25
0.50
0.75
—l—
1.00
—!—
1.25
—i—
1.50
FLOW - MGD
Fig. 28.16 Recommended flow rate for various suspended solids loadings
(Permission of Cochrane Division-Crane Co.)
-------
582 Treatment Plants
REPRESENTATIVE FLOW vs. SS
FOR
MICROSTRAINER
CONDITIONS:
A - ACTIVATED SLUDGE SECONDARY
B — MAXIMUM DRUM SPEED — 100 fpm
C — MAXIMUM HEAD LOSS - 6 INCHES
D - FABRIC - MARK *0-
* — 10 FT. DIAMETER BY 15 FT. LONG
10 X 15
10 X 10
7'/j X 5
T 1 1 1 1 1 1 1 —r
12 3456789
FLOW - MGD
Fig. 28.17 Recommended flow rate for various suspended solids loadings
(Permission of Cochrane Division-Crane Co.)
-------
Industrial Waste Treatment 583
28.24 Maintenance
28.240 Preventive Maintenance
Stationary screens should be examined visually each day to
check the condition of the screening media and to note
whether there are any obstructions to the flow. Also look for
objects lodged in the screens which should be removed or
rocks at the bottom that could jam or restrict rake travel. Also
the structural condition of the media should be checked and
any defects should be repaired.
If there is a mechanical cleaning device, it should be acti-
vated each day to make sure it operates freely without jam-
ming.
Greasing points should be lubricated according to manufac-
turer's recommendations and any unusual noises or actions
examined for defects. Manufacturers' literature should be used
in carrying out examination and repair to moving machinery.
In the case of moving screens, band, disc or drum-type
screens, the above points should be checked and, in addition,
the movement of the screens must be checked using manufac-
turers' manuals to lubricate and repair as necessary.
If a spray system is fitted, this should be operated manually
at high pressure for a short period to free any potential block-
ages and assist in cleaning the screen.
If the speed of the band, disc or dum screen is manually
adjustable, it should be operated at various speeds for a short
period while the high pressure wash is turned on. At longer
intervals, the structural soundness of the screening media
should be examined after draining down and isolating each
chamber in turn. This can be done using a flashlight to closely
inspect the media and repair any holes, tighten up securing
screws and check for corrosion.
Wear on moving parts should be inspected, including
brushes, bearings, and sealing gaskets. Manufacturers' in-
structions should be used for this purpose. At longer intervals it
will be necessary to clean, scrape and paint the supporting
structure of the screen.
TABLE 28.1 SCREENING AND MICROSCREENING TROUBLESHOOTING CHECKLIST
PROBLEM
1. No wastewater flowing
through screen
Noisy movement of
screen
Suspended solids
passing through
screen
4. High head loss
across screens
5. Screening mechanisms
stop
moving
CAUSE
Inadequate cleaning
Overload conditions, too
many solids
No wastewater flowing to
screen
Inadequate depth of water
Bearing troubles
Inadequate grease
Insufficient oil
Drive mechanism faulty
Ruptured seal
Ruptured screen
Overflow and bypassing of
wastewater
Corrosion of screen
Aperture size too large for
duty
Screen plugged
Too high a concentration
of solids in wastewater
Too high a rate of flow
Inadequate cleaning
Electrical power failure
Drive failure
Bearing failure
SOLUTION
Clean dirty screen using chemicals if necessary.
Improve performance of upstream processes.
Check if upstream channel is blocked.
Increase depth by suitable adjustment of flow.
Remove and repair or replace bearings.
Insure adequate grease is reaching all points.
Check depth of oil in gear boxes.
Check condition of chains and gears.
Repair or replace seal.
Repair or replace screen.
Reduce overflow conditions by improved upstream operation.
Check if corrosive chemicals in water or backwash.
Change screen material.
Clean screen, using chemicals if required.
Improve upstream operation to reduce suspended solids concentration and/or flow
rate.
Step up rate of cleaning and/or speed of drum.
Increase backwash pressure.
If electrical overload has occurred, replace fuse or reset relay.
May have interference in movement, if so, remove obstruction.
Check if chain drive and/or gears are moving freely. Drum bearings should have
adequate lubrication.
-------
584 Treatment Plants
28.241 Maintenance Schedule
DAILY
1. General inspection pertinent to all machinery includes pay-
ing particular attention to any abnormal noise. Check lubri-
cation if noise is apparent.
2. If backwash system fitted, give high pressure wash for short
period.
3. Check head loss, drum or rake speed, backwash pressure
in relation to water quality. Make any necessary adjust-
ments.
4. Check wash water jet nozzles for blockage.
5. In the case of microscreens, check fabric condition as seen
from wash water run down externally. If fabric is blinded
(plugged), wash water will run down on both sides of the
jets. If the fabric is clean, after its passage under the jets,
run down will normally be only on the upcoming side.
6. In the case of coarse screens, check operation of cleaning
mechanism or, if manual cleaning, rake screen as neces-
sary.
7. Visual inspection of condition of screening media. Also look
for objects lodged in screens and objects that could
obstruct flow or movement of screens or cleaning
mechanisms.
WEEKLY
1. Operate equipment through a complete cycle in manual
and automatic modes.
2. Operate cleaning mechanism (backwash jets) at various
settings.
3. Lubricate machinery.
4. If ultraviolet equipment is fitted (supplementary cleaning
equipment), wipe reflector clean. Ultraviolet equipment is
fitted on microscreens with stainless steel mesh to continu-
ously condition the fabric and keep it free from slimes.
Chlorine could be used to control the slimes, but also could
be corrosive.
5. Check functioning of any other supplemental cleaning ap-
paratus.
MONTHLY
1. Inspect all safety features of equipment including access
walkways, guard rails, and manhole covers.
2. Check oil levels in drive units and fill as necessary.
3. Examine screening media for permanent blockage or me-
chanical defects. Repair or clean as necessary.
3 MONTHS
1. Check gasket materials including sealing bands and rubber
wipers, if fitted. Repair or replace as necessary.
2. Check for wear on rubber brushes, if fitted, on drive units
and replace where necessary.
3. Check tightness of all fasteners.
6 MONTHS
1. Check all suspension parts.
2. Check drive sprockets and chains for alignment and wear.
3. Drain oil from drive unit, flush and refill with proper lubrica-
tion.
4. Inspect main bearings and, if necessary,
grease.
12 MONTH MAINTENANCE
with specified
Clean all surfaces, paint as necessary, replace any worn or
corroded parts. (Follow inspection check points included in
manufacturer's instruction manual.)
Operator actions required. Wash dirty media with an acid or
caustic solution depending on the media material and type of
waste. If the media shows signs of wear or damage, it should
be repaired or replaced. For this purpose it will be necessary to
drain down machinery and proceed as described in the section
(28.242) on corrective maintenance. The backwash system
can usually be adjusted without draining down. Oil levels also
can be checked and filled up as necessary while the equip-
ment is in operation. Reports to the supervisor should be made
regularly on the condition and performance of the equipment.
These reports should preferably be in writing on printed forms
which detail the complete maintenance schedule.
Repair or replace the screening media wherever holes
develop; otherwise solids will pass into the downstream pro-
cesses. Also, the condition of the screen will steadily deterior-
ate. Make sure the backwash system is functioning effectively;
otherwise the screen will remain dirty and become progres-
sively blocked, thus hindering flow. Unless the machinery is
lubricated, it will eventually fail.
28.242 Corrective Maintenance
The straining or screening media usually needs the most
attention, particularly if this is made of woven wire cloth since it
can be broken by impingement of floating objects or by stress
due to overloading from differential head and fatigue. Plates or
bars are not so easily damaged.
To carry out a repair on the screen, the machinery should be
stopped, isolated and drained down. Observe the usual safety
procedures (Section 28.22, "Safety Procedure"). Wire mesh
can be repaired in place by soldering or lapping in a new
section. Sometimes a panel must be removed and replaced. If
bars or plates do become damaged, removal and repair or
replacement is usually required.
When there is a defect in the screening media, it is obvious
by the passage of material that would normally be intercepted.
A defect in the machinery is usually shown by erratic uneven
motion or unusual noise. The source of the trouble must be
located by visual inspection and repair carried out as recom-
mended in the manufacturer's manual. In most cleaning sys-
tems, sprays are self-cleaning or designed to avoid plugging
from solids in the backwash water. Occasionally a jet will be-
come jammed or obstructed and this is shown by the section of
the screen beneath the faulty jet remaining dirty. The jet should
be cleaned in place, if this is possible, or removed and
cleaned, repaired or replaced.
-------
Industrial Waste Treatment 585
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 698.
28.2M List items that should be visually inspected every day
that a screen is in operation.
28.2N How can a woven wire screening media be broken?
28.25 Review of Plans and Specifications
Points to watch for in reviewing plans and specifications are
discussed in this section.
28.250 Concrete Channels and Chambers
Concrete channels and chambers should be designed to
allow positive drainage. There should be isolating valves or
sluice gates to allow individual chambers to be dewatered. The
floor of the chamber should be made with a slope running
towards the drain valve. Each separate chamber should have
its own drainage valve. Remember that drains must run by
gravity to the point of disposal. There should be no upward
slope in these drain lines nor should there be any tendency for
back pressure. If gravity disposal is not possible, a drainage
sump may be provided with a dewatering pump. This pump
should be of the "non-clog" design.
When reviewing the chamber work, try to be sure dirty water
is prevented from bypassing the screen and finding its way to
the suction of the backwash pump. This can interfere with
operation of the pump. It can also lead to clogging of the spray
jets if these are fitted on the screen or strainer. Since the
screen or strainer will be of metallic construction, it is best to
keep chlorine away from the unit or backwash pump to elimi-
nate possible corrosion. In the case of microscreens, weirs are
used inside the chambers to maintain the proper drum sub-
mergence and prevent excessive head differences.
Dimensions of the chambers should be checked before in-
stalling the screen. The positions of main parts such as the
drive unit and control equipment should be identified. Make
sure there is adequate working space around these parts. Also
be sure guard rails are provided to prevent anyone falling into
the chamber. Access walkways may be needed above the
machinery if sen/icing of the equipment is required.
28.251 Design of Coarse Screens
The chief design features to consider when selecting
screens are the area of the screen and size of mesh to deal
with required flow and loading conditions. Manufacturers' liter-
ature gives capacity figures for their units, based on the mesh
opening and application. These figures range from 60 to 200
gallons per minute per square foot (40 to 135 liters per sec per
sq m) of submerged or effective area depending upon mesh
size and loading expected.
A rule of thumb which provides a check on capacity is as
follows:
1. Calculate the total effective submerged area which is the
area of coarse screen exposed to flow of effluent. Then
assume that the screen is half blocked with intercepted
debris.
2. Calculate the available open area as total area x percent
open area (mesh) x 50 percent (half blocked).
3. Take an arbitrary figure of one foot per second (0.3 m/sec)
flow velocity. This will give available flow capacity in worst
conditions of loading.
EXAMPLE
Known
DRUM SCREEN
Diameter, ft
Length, ft
Depth Submerged, ft
Portion blanked off
by support structure
7 ft 6 in
5 ft
6ft
0.10 of
submerged area
Unknown
Flow velocity through
screen, fps
Square mesh screen = 10 wires/inch
in each direction
Percentage open
area, %
Flow, GPM
Portion of screen
Plugged
= 58%
= 8,400 GPM
= 0.50
1. Calculate the total submerged area of the screen. If the
screen is 7 feet - 6 inches in diameter and is submerged to
a depth of 6 feet, approximately 70.5 percent of the screen
is submerged.
Submerged = n x Diameter, ft x Length, ft x Portion Submerged
Area,
sq ft = 3.1416 x 7.5 ft x 5 ft x 0.705
= 83.3 sq ft
2. Assume the supporting structure blanks off 10 percent of
the total submerged area. Calculate the net effective sub-
merged area.
Submerged Area, - Supporting Structure Area,
sq ft sq ft
83.3 sq ft - 0.10 (83.3 sq ft)
Net sub-
merged
area,
sq ft
75 sq ft
3. If the drum is fitted with square mesh having 10 wires per
inch each direction, a wire mesh handbook will reveal that
58 percent of the screen area is open area. Calculate the
net effective submerged area available for flow through the
screen.
Net effective = Net submerged area, x Portion open area
submerged sq ft
area, sq ft = 75 sq ft x 0.58
= 43.5 sq ft
4. Calculate the flow of 8,400 gallons per minute to cubic feet
per second.
CUf1 = Flnw
gal x
1 cu ft x
1 min
sec
min
7.48 gal
60 sec
= 8400
gal x
1 cuft x
1 min
min
7.48 gal
60 sec
= 18.7 cu ft/sec
5. Assume half of the net effective submerged area is plugged
and the other half is not plugged. Determine the actual area
for the wastewater being treated to flow through the screen.
Area for = Net effective submerged x Portion not plugged
flow, sq ft area, sq ft
= 43.5 sq ft x 0.50
= 21.75 sq ft
-------
586 Treatment Plants
6. Calculate the velocity of the water flowing through the
screen.
Velocity,
ft _ Flow, cubic feet/sec
sec Area, square feet
_ 18.7 cu ft/sec
21.75 sq ft
= 0.86 ft/sec
Actual velocity should be at or below 1 ft/sec to prevent
excessive head losses.
28.252 Design of Microscreens
Because the fabric used on microscreens is much finer than
other types of screening units, blockage is more critical. There-
fore a special formula has been developed as follows:
H
MQCf e NQ l/S
Where H = head loss, inches
M = constant of 0.0267
Q = flow rate, GPM
A = submerged area
e = exponential constant, 2.718
N = constant of 0.1337
I = filterability index
S = drum speed, sq ft/min
Cf = mesh resistance to flow
= 1.7 for 23/u mesh
= 1.0 for 35fj. mesh
= 0.8 for 60^ mesh
Using a head loss of three inches (7.5 cm), the capacity of a
microscreen may be calculated from the above formula.
Characteristics of the mesh and the effluent must be known to
use the formula (see manufacturer's literature).
Flow capacity figures for microscreens are in the range 10 to
30 GPM per sq ft (6 to 20 liters per sec per sq m) of effective
submerged area.
EXAMPLE
Known
MICROSCREEN
Flow, GPM
Diameter, ft
Length, ft
Mesh Res., Cf
= 700 GPM
= 7 ft 6 in
= 5 ft
= 1.0
Unknown
Head Loss through Screen
in inches
Submerged Area, = 75 sq ft
sqft
Filterability = 3.0
Index, I
Drum Speed of =100 ft/min
Rotation, ft/min
1. Determine filterability index, I, by running a sample of the
water to be treated through the fabric on the screen. Typical
values for wastewater range from 1 to 10 with higher values
for waters with higher suspended solids.
2. Calculate S, the square feet of fabric entering the water
each minute.
Area S, sq ft/min = Speed of Rotation, x Drum Length, ft
ft/min
= 100 ft/min x 5 ft
= 500 sq ft/min
3. Calculate the head loss through the screen in inches.
0.1337 X Q, GPM x 3.0
i* 0.0267 X Q, GPM x Cf v ~
n, in — x ©
A, sq ft
0.267 x 700 GPM x 1.0 „
75 sq ft
S, sq ft/min
0.1337 x 700 GPM x 3.0
500 sq ft/min
2.492 eK
,0.56
e = 2.718
0.56
= 2.492 (2.718)
= 2.492 x 1.753
= 4.4 in
Actual head loss should be at or below 3 inches for good
design. To reduce the head loss on an existing screen, reduce
the flow. If designing a facility to handle this flow, a larger
screen area (A, sq ft) is needed.
28.253 Facilities Checklist
1. Check dimensions against manufacturers drawings of an-
chor bolts, structural, and hydraulic parts.
2. Check for access to all parts for servicing.
3. Check freedom of walk areas.
4. Check space around controls, safety features (rubber
mats).
5. Check doors and other openings for possible removal of
parts.
6. Check handrails and access walkways.
7. Check lifting facilities for heavy items.
8. Check servicing area alongside channels, non-slip sur-
faces or curbing.
9. Check that operating conditions will be suitable during bad
weather conditions.
10. Check that there is adequate lighting, ventilation, and
heating.
11. Examine possibility of danger from other adjacent pro-
cesses including chlorine or other gaseous fumes. Con-
sider possibility of flooding and noise levels from adjacent
machinery.
12. Review design of equipment as to strength of parts, over-
all size, shape of channel admitting water to the screen,
velocity in flowing channel, any recesses or hidden areas,
inlet and outlet piping, gravity or pumped flow.
13. Briefly review overall design of equipment including
adequate lubrication, bearings, gaskets and seals and ac-
cessibility for removal and servicing.
14. Check materials of construction for durability and strength
and suitability for proposed duty, size of screen openings
and strength of supports.
-------
Industrial Waste Treatment 587
15. Check media design, size and strength.
16. Check for adequate cleaning facilities. Also determine
how screenings will be disposed of.
17. Check source of backwash water which should be clean
water (low or without solids) available for hose down;
check chemicals or steam available for supplementary
cleaning. Electric outlets should be located near points of
need and should be of the proper voltage.
18. Check adequate drainage of floors, including basement
and operating levels. These locations should be sloped to
drain valves. Individual drain valves should be provided for
each chamber.
19. Check to see if access ladders or foot rungs are available
for manholes.
20. Check access to electrical wiring for removal purposes,
circuit breakers, fuses, and control panels. Sufficient con-
trol features to enable equipment to be operated in manual
automatic modes should be provided.
21. Check for adequate lighting of controls.
22. Check to see if equipment is near enough to controls to
observe operation during start-up and shutdown.
23. There should be a safety switch on all electrical panels.
24. Check to see if isolating valves are provided to allow indi-
vidual chambers to be drained down. Determine whether
duplicate equipment or standby facilities and emergency
bypasses are provided.
25. Check to see that all levers, valves and handles can be
reached without difficulty from walkways and ladders.
26. Check to be sure that the machinery has adequate greas-
ing and lubrication points.
27. Check whether safety equipment is available in the build-
ing, including protective clothing, gas mask, and life belts.
28. Check flow capacity of screens to insure adequate size for
peak flow conditions and peak loading conditions.
29. Make sure there are no reverse slopes on piping. All pip-
ing must be self-draining with adequate valves, bends,
and tees, and be properly supported and braced.
30. Floor stands should be provided for submerged valve op-
eration.
31. Backwash pumps should have drowned or sumberged
suctions.
32. Chemical feeders should be provided if necessary.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 698.
28.20 When reviewing plans and specifications, what items
should be checked regarding concrete channels and
chambers?
28.2P When reviewing plans and specifications, what items
should be checked regarding electrical outlets?
28.26 Additional Reading
1. MOP 11, Chapter 6, "Screening."*
2. TEXAS MANUAL, Chapter 9, Screens.
3. PROCESS DESIGN MANUAL FOR SUSPENDED SOUDS
REMOVAL, Chapter 8, "Physical Straining Processes,"
Center for Environmental Research Information, U.S. En-
vironmental Protection Agency, 26 West St. Clair Street,
Cincinnati, Ohio 45268.
4. PROCESS DESIGN MANUAL FOR UPGRADING EXIST-
ING WASTEWATER TREATMENT PLANTS, Chapter 7,
"Effluent Polishing Techniques," Center for Environmental
Research Information, U. S. Environmental Protection
Agency, 26 West St. Clair Street, Cincinnati, Ohio 45268.
5. WASTEWATER ENGINEERING, Second Edition, Metcalf &
Eddy, Inc., Chapter 14, "Advanced Wastewater Treat-
ment," McGraw-Hill Book Company, New York, New York.
Price $24.50.
6. Manufacturers' literature and operating manuals.
* Depends on edition.
IN0UGTGlAl/lM6T0
Please answer the discussion and review questions before
continuing with Lesson 4.
-------
588 Treatment Plants
DISCUSSION AND REVIEW QUESTIONS
(Lesson 3 of 6 Lessons)
Chapter 28. INDUSTRIAL WASTE TREATMENT
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 2.
14. Compare the differences between screens and clarifiers in
the removal of solids from wastewaters.
15. How are screenings disposed of from moving screens and
microscreens?
16. Describe how a microscreen removes floatable solids and
suspended particles from wastewater.
17. Identify high-risk activities or safety hazards that you might
CHAPTER 28.
28.3 NEUTRALIZATION9 by Mark Acerra
28.30 Need for Neutralization
Industrial wastes usually contain acidic or alkaline (caustic)
materials which required neutralization before biological treat-
ment or discharge to receiving waters. The neutralization of
water is measured in terms of pH. pH is measured on a scale
from 0 to 14 with 7 being neutral. Levels below 7 are acidic and
above 7 are caustic. In practice, industrial wastewaters are
rarely truly "neutralized" to a pH of 7. They are adjusted to
within an acceptable pH range. The range is determined by
either the water quality criteria of the receiving stream, the
waste treatment process being used, or the physical integrity
of the wastewater collection system.
Water quality criteria are determined by the needs of the
receiving body of water and are usually determined by the
responsible state and federal regulatory agencies. Receiving
water quality criteria are written into NPDES discharge permits
under which the process discharges and are independent of
the process being used to treat the wastewater. pH is an impor-
tant factor in the chemical and biological systems of natural
waters. For example, cyanide toxicity to fish increases as the
pH is lowered. Ammonia has been shown to be 10 times as
toxic at pH 8.0 than as at pH 7.0. The solubility of metal com-
pounds contained in bottom sediments or as suspended mate-
rial is affected by pH. The following pH ranges from "Quality
Criteria of Water" have been adopted (July 1976) by the U.S.
Environmental Protection Agency.
encounter when operating and maintaining screens or mi-
croscreens.
18. How would you determine if correct start-up procedures
were used to start a microscreen?
19. What items should be considered when inspecting the
screening media during normal operation?
20. What abnormal conditions might have to be handled when
operating a screening process?
21. What information should be reported to your supervisor
regarding a screening process?
Range Beneficial Water Uses
5-9 Domestic water supplies (welfare)
6.5-9.0 Freshwater aquatic life
6.5-8.5 Marine aquatic life
NPDES permits for discharges into receiving waters with
these beneficial water uses require effluent pH values within
these ranges. In addition to meeting the water quality criteria of
the receiving stream, industrial wastewaters usually require
treatment for specific pollutants such as oil, grease, metals,
suspended solids, organic materials and other polluting com-
pounds. The various waste treatment processes commonly
used are pH dependent. These processes work or work best
within a specific pH range. Some wastewater streams require
several pH adjustments to accommodate process steps as
well as final discharge to the receiving stream. When pH
makes the difference in whether or not a process will work, pH
control is critically important and must be continuously moni-
tored. When pH determines the relative efficiency of a process,
pH control is not critical if the use of excess treatment chemi-
cals or longer mixing times are available. However, this will
result in higher operating costs and decreased ability to handle
process upsets.
Neutralization can also be important in corrosion control.
Unpainted pieces of steel rusting in the presence of drinking
water indicate a need for corrosion control. The rate of rusting
or corrosion increases in rainwater and increases even more in
saltwater. Concrete can be cleaned or washed with a muriatic
INDUSTRIAL WASTE TREATMENT
(Lesson 4 of 6 Lessons)
9 Neutralization (new-trall-i-ZA Y-shun). Addition of an acid or alkali (base) to a liquid to cause the pH of the liquid to move towards a neutral
pH of 7.0.
-------
Industrial Waste Treatment 589
acid (HCI) solution. Plastic or PVC pipes corrode when ex-
posed to many solvents. Therefore the equipment and pipe in
a treatment plant must be designed to handle the wastes being
processed. The equipment and piping must be used as de-
signed to prevent corrosion as a result of improper use. Also,
ventilation must be adequate to keep the fumes from the pro-
cesses from attacking the motors, switches, lights and other
fixtures in buildings. If the pH of a solution is allowed to drift
outside of the designed range, corrosion can start. Conversely,
some processes require pH adjustment so that they can be
discharged through an existing wastewater collection system.
28.31 Basic Principles
When solutions of an acid and a metallic hydroxide or base
are mixed in equivalent quantities, each exactly cancels the
properties of the other. The process is called NEUTRALIZA-
TION. The products are a salt and water. Evaporation of the
water will reveal the salt in crystalline form. An acid neutralizes
a hydroxide and a hydroxide neutralizes an acid.
pH is an indication of the strength or intensity of acidity or
alkalinity. The pH is an index of hydrogen ion activity and is
used as an indication of acidity and alkalinity while not a meas-
ure of either.
A material which ionizes to form positively charged hydrogen
ions is an acid:
Pure water which ionized to a certain extent produces both
hydrogen and hydroxyl ions in equal concentrations:
H20
H+ + OH"
The degree to which ionization proceeds in pure water is the
basis for the pH scale and is expressed as the ion product
constant of water. From the law of chemical mass action it has
been determined that the product of the hydrogen ion concen-
tration and the hydroxyl ion concentration in water is equal to
1/100,000,000,000,000 or 10~14 with 10~7 hydrogen ions and
10 7 hydroxyl ions. pH is expressed as the negative common
logarithm of the hydrogen ion concentration or
pH = log.
{h+}
The pH index ranges between 0 and 14 as shown in Table
28.2. pH values less than 7 are acidic and greater than 7 are
basic.
The addition of a certain quantity of acid or alkali to some
solutions will not only fail to produce an expected pH change,
but in some cases will result in almost no pH change. Such a
solution is said to be BUFFERED.™ All mixtures of weak acids
and their salts or weak bases and their salts are buffer mix-
tures. The total acidity or alkalinity often are used to estimate
the buffer capacity of a solution.
H2S04
sulfuric
acid
2H
hydrogen
ions
S04=
sulfate
ion
A material which ionizes to form negatively charged hydroxyl
ions is an alkali or base:
NaOH - Na+ + OH"
sodium sodium hydroxyl
hydroxide ion ion
Hydrogen Ion
Concentration
Mols/Llter
TABLE 28.2 VALUES OF pH FOR VARIOUS SUBSTANCES"
pH
Hydroxyl Ion Common
Concentration Household
Mols/Liter
Items
pH of
Various
Industrial
Chemicals0
0
1
0.00000000000001
-0-
«- Sulfuric Acid 4.9% (1.0 N)
1
0.1
0.0000000000001
-1—
¦•-Hydrochloric Acid 0.37% (0.1 N)
Sulfuric Acid 0.49% (0.1 N)
2
0.01
0.000000000001
Lemon juice -»
-2—
«- Acetic Acid 0.6% (0.1 N)
3
0.001
0.00000000001
Orange juice -»
—3—
Acidic
4
0.0001
0.0000000001
Beer -»
—4—
5
0.00001
0.000000001
Cheese -»
—5—
~-Hydrocyanic Acid 0.27% (0.1 N)
6
0.000001
0.00000001
Milk —
-6-
Neutral
-~ 7
0.0000001
0.0000001
Pure Water
-7-
Egg White -»
8
0.00000001
0.000001
-8-
*- Sodium Bicarbonate 0.84% (0.1 N)
9
0.000000001
0.00001
Borax -»
-9-
Milk of
*- Potassium Acetate 0.98% (0.1 N)
10
0.0000000001
0.0001
Magnesia -»
-10-
— Ammonia 0.017% (0.01 N)
Ammonia 1.7% (1.0 N)
Basic
11
0.00000000001
0.001
-11-
12
0.000000000001
0.01
-12-
~-Caustic Soda 0.04% (0.01 N)
«- Lime (Saturated Solution)
13
0.0000000000001
0.1
-13-
~-Caustic Soda 0.4% (0.1 N)
14
0.00000000000001
1
-14-
~-Caustic Soda 4% (1.0 N)
a Source: THE INDUSTRIAL pH HANDBOOK by Beckman Industries, Inc., 1963.
b Representative pH Values. pH of many food products may vary over considerable range.
c pH Values at 25°C. Values rounded off to nearest tenth.
.10 Buffer. A solution or liquid whose chemical makeup neutralizes acids or bases without a great change in pH.
-------
590 Treatment Plants
Neutralization dynamics involve the changes caused in a
solution when an acid mixes with a base. This neutralization
involves the rate of change of pH, the equivalence point and
the end points. In industrial wastewater, the flow being treated
usually varies in strength and makeup. However,the chemistry
involved is well known. Therefore, it is important that the
operator understand the basic concepts involved and uses
them as they apply to treating waste streams and treatment
processes.
28.32 Chemistry
ALKALINITY11 is the sum total of components in the water
that tend to elevate the pH of the water above a value of about
4.5. Alkalinity is measured by titration with a standardized acid
to a pH value of about 4.5 and it is expressed as mg/L CaC03
(calcium carbonate). Alkalinity is a measure of the buffering
capacity of the water and may be defined as its capacity for
neutralizing acid. The basic determination procedure is to take
B ml of sample, add two drops of methyl orange indicator
solution and titrate with standard sulfuric acid solution (.02 N)
until the color changes from pink to orange.
mg1L alkalinity as CaC03 = A x 1000
B
A = ml standard acid used in titration
B = ml sample
ACIDITY12 is also a capacity factor and may be defined as
the capacity for neutralizing a base. Acidity is normally as-
sociated with the presence of carbon dioxide, mineral and or-
ganic acids, and salts of strong acids and weak bases. The
basic determination procedure is to take B ml of sample, add
two drops of methyl orange indicator and titrate with standard
sodium hydroxide solution until color changes to faint orange.
mg/L acidity as CaCOj = A x 1000
B
A = ml standard sodium hydroxide used in titration
B = ml of sample
Freshwater suitable for aquatic life usually has an alkalinity
of more than 20 mg/L and an acidity of zero.
Process water pH adjustment is achieved by adding avail-
able acid or alkaline substances. Alkaline substances com-
monly used are:
1. CaO (calcium oxide or lime), MgO (magnesium oxide),
Ca(OH)2 (calcium hydroxide, a hydrated form of lime) or
Mg(OH>2 (magnesium hydroxide), are the most commonly
used chemicals because of availability, low cost and high
capacity. Sludge bulk (volume) is a major problem, but re-
covery is possible. Lime is either high calcium or dolomitic
and comes either as quicklime or hydrated. It comes in dry
form and is usually mixed with water before use. A solubility
versus pH curve is shown in Figure 28.18 and the plotting
data are in Table 28.3.
2. Sodium hydroxide (caustic soda). Sodium hydroxide
(NaOH) is a convenient, controllable and commonly avail-
able chemical, but expensive. It is generally used for small
or occasional applications or where limitation of sludge de-
posits is sought. Caustic soda is available in liquid form in
two concentrations, 50 percent NaOH which begins to crys-
tallize at 54°F (12°C) and 73 percent NaOH which begins to
crystallize at 145°F (63°C). Therefore they must be properly
stored and or diluted prior to use. Caustic soda is also
available in an anhydrous or dry state (solid, flake, ground
or powdered) at 100 percent concentration. In the dilution
process, considerable heat is generated. Therefore the rate
of dilution and method of cooling must be carefully con-
trolled so that there is no boiling or splattering.
TABLE 28.3 pH OF CALCIUM HYDROXIDE SOLUTIONS
AT 25°C
CaO
gms per L
PH
0.064
11.27
0.065
11.28
0.122
11.54
0.164
11.66
0.271
11.89
0.462
12.10
0.680
12.29
0.710
12.31
0.975
12.44
1.027
12.47
1.160
12.53
Since solubility of lime decreases as the temperature decreases, the
pH of lime solutions is correspondingly lower at lower temperatures.
Data from F. M. Lea and G. E. Bessey, Journal of the Chemical
Society, p. 1612-1615 (1937).
The Alkali Conversion Table (Table 28.4) and Alkali Neu-
tralization Graph (Figure 28.19) show the equivalent amounts
of sodium hydroxide and the various forms of lime available
that must be used to accomplish the same degree of neu-
tralization. The Alkali Neutralization Graph shows the weights
of alkalis required to neutralize a given weight of any of the
acids indicated.
Acid substances commonly used are:
1. Sulfuric acid (H2SO4) is the cheapest and most readily
available. It is strongly corrosive, dense, oily, and colored
clear or dark brown (depending on purity). Sulfuric acid
should be of the USP (United States Pharmaceutical) grade
free of heavy metals and is available in a number of grades
containing 60 to 94 percent H2SO4. In the 93 percent grade,
it is noncorrosive to steel drums, however, upon dilution it is
highly corrosive.
Alkalinity (AL-ka-LIN-ity). The capacity of water or wastewater to neutralize acids. This capacity is caused by the waters content
carbonate, bicarbonate, hydroxide, and occasionally borate, silicate and phosphate. Alkalinity is expressed in milliards nerif,21 .
equivalent calcium carbonate. Alkalinity is not the same as pH because water does not have to be strongly basic (hiah oHI to h«L i L °l
alkalinity. Alkalinity is a measure of how much acid can be added to a liquid without causing a great change in pH
<2Acidity. The capacity of water or wastewater to neutralize bases. Acidity is expressed in miligrams per liter of eauivalent mini,,
carbonate. Acidity is not the same as pH because water does not have to be strongly acidic (low pH) to have a high aciditv Ar.iri tJ
measure of how much base can be added to a liquid without causing a great change in pH. Is a
-------
Industrial Waste Treatment 591
o
0
LA
CM
f—
<
/
z 1
o
«
1-
D
1
_J
o
N
I
o
<3
unnrn »nu«*iNi] pn v,uhvc
OF CALCIUM HYDROXIDE
SOLUTIONS AT 25°C
u.
O
>-
t-
~
m
3
—I
O
2
'J
2
X
2
0 .2 .4 .6 .8 1.0 1.2 1.4
GRAMS CaO PER LITER
Fig. 28.18 Calcium hydroxide pH curve
(From CHEMICAL UME FACTS, permission of National Lime Association, Washington, D.C., 1951)
-------
592 Treatment Plants
TABLE 28.4 ALKALI CONVERSION TABLES"
NaOH
CaO
Ca(OH),
Ca - MgO
Na.CO,
Na.CO,
CaO
Ca(OH),
CaO - MgO
NaOH
1
.70
.93
.60
1.32
1
.53
.70
.45
.75
2
1.40
1.85
1.20
2.65
2
1.06
1.40
.91
1.51
3
2.10
2.78
1.81
3.97
3
1.59
2.10
1.36
2.26
4
2.80
3.70
2.41
5.30
4
2.12
2.80
1.82
3.02
5
3.50
4.63
3.01
6.62
5
2.65
3.49
2.27
3.77
6
4.21
5.56
3.61
7.95
6
3.17
4.19
2.73
4.53
7
4.91
6.48
4.22
9.27
7
3.70
4.89
3.18
5.28
8
5.61
7.41
4.82
10.60
8
4.23
5.59
3.64
6.04
9
6.31
8.33
5.42
11.92
9
4.76
6.29
4.09
6.79
10
7.01
9.26
6.02
13.25
10
5.29
6.99
4.55
7.55
15
10.51
13.89
9.04
19.87
15
7.94
10.48
6.82
11.32
20
14.02
18.52
12.05
26.50
20
10.58
13.98
9.09
15.10
25
17.52
23.15
15.06
33.12
25
13.23
17.47
11.37
18.87
30
21.03
27.78
18.07
39.75
30
15.87
20.97
13.64
22.64
35
24.53
32.41
21.08
46.37
35
18.52
24.46
15.91
26.42
40
28.04
37.04
24.10
53.00
40
21.16
27.96
18.19
30.19
45
31.54
41.67
27.11
59.62
45
23.81
31.45
20.46
33.97
50
35.05
46.30
30.12
66.24
50
26.45
34.95
22.73
37.74
55
38.55
50.93
33.13
72.87
55
29.10
38.44
25.01
41.51
60
42.05
55.57
36.15
79.49
60
31.74
41.94
27.28
45.29
65
44.56
60.20
39.16
86.12
65
34.39
45.43
29.56
49.06
70
49.06
64.83
42.17
92.74
70
37.03
48.93
31.83
52.83
75
52.57
69.46
45.18
99.37
75
39.68
52.42
34.10
56.61
80
56.07
74.09
48.19
105.99
80
42.32
55.92
36.38
60.38
85
59.58
78.72
51.21
112.62
85
44.97
59.41
38.65
64.16
90
63.08
83.35
54.22
119.24
90
47.61
62.91
40.92
67.93
95
66.59
87.98
57.23
125.86
95
50.26
66.40
43.20
71.70
100
70.09
92.61
60.24
132.49
100
52.90
69.90
45.47
75.48
a From CHEMICAL LIME FACTS, permission of National Lime Association, Washington, D.C., 1951.
2. Hydrochloric acid (HCI) or muriatric acid is a clear or slightly
yellow, fuming, pungent liquid. It is poisonous and may con-
tain iron or arsenic. Hydrochloric acid should be obtained in
the purified form (U.S.P.) and is shipped in glass bottles,
carboys, and rubber-lined steel drums, tank cars or trucks.
It contains approximately 35 percent available hydrogen
chloride. Fuming can be reduced by dilution to 20 percent
HCI.
3. Where available C02 or S02 may be applied in gaseous
form. Flue gases are accessible and economical for neu-
tralization of alkaline waters in certain industries.
When mixed with water, acids and bases produce solutions
made up wholly or partially of ions. Solutes that exist almost
completely as ions in solution are termed strong ELECTRO-
LYTES ,13 Those that react incompletely with the water so that
both neutral molecules and ions formed from them are present
are called weak electrolytes. The degree of ionization may be
determined by measuring the electrical conductivity.
Chemical equilibrium exists when the reactants are forming
as rapidly as the products, so that the composition of the mix-
ture remains constant and does not change with time. At any
one temperature, the equilibrium constant K has a fixed numer-
ical value characteristic of the particular chemical equation.
However, in industrial wastewater treatment, the stream being
treated is made up of water plus many contaminants which
provide competing equilibria. Furthermore, reaction rate, tem-
perature and mixing conditions vary as does the waste loading.
Therefore, the pure chemistry involved is not directly used by
the operator in day-to-day activities.
As the graphic representation of pH versus added titrant, the
titration curve provides a means to characterize the substance
to be pH adjusted or neutralized and the amount of adjusting
agent required. Titration curves for process optimization com-
monly are based on chemicals likely to be used in the process
in a manner designed to indicate process variables such as
contact time, temperature, nature and amount of solids, and
handling characteristics in relation to the system pH.
The following titration curves illustrate terminology, charac-
teristics, and changes with respect to a few commonly encoun-
tered adjustments. Figure 28.20 illustrates titration of a strong
base (NaOH) with a strong acid (H2S04). Initial additions of the
titrant have a minor effect upon pH because NaOH plus prod-
uct Na2S04 has little buffer capacity. The curve is almost flat
for each addition of titrant prior to the inflection. The inflection
indicates an approach to the equivalence point. The equiva-
lence point is graphically located half way along the straight
line on the graph between the upper and lower inflections.
Strong acid and base equivalence points commonly occur near
pH 7.0. The product of volume and concentration of added
titrant at the equivalence point is an estimate of sample ba-
sicity.
Figure 28.21 shows the effect of adding 4 percent or 1 N
NaOH to a sample of industrial wastewater made up primarily
of contact cooling water, machining rinse waters and miscel-
laneous combined process discharges. From the curve, the
operator can readily determine the amount of caustic needed
to adjust the pH to whatever value best suits the process used.
Figure 28.21 also shows the effect of adding 2.8 percent or 1
N H2S04 to the same sample of industrial wastewater. The
curves in Figures 28.20 and 28.21 differ significantly but pro-
vide the same basic information. Five gallons of 4 percent
NaOH in 1,000 gallons of wastewater will result in a pH of
11.65, and 5 gallons of 2.8 percent H2S04 in the same 1,000
gallons of wastewater will result in a pH of 3.0.
13 Electrolyte (ELECT-tro-LIGHT). A substance which dissociates (separates) into two or more ions when it is dissolved in water.
-------
Industrial Waste Treatment 593
ALKALI NEUTRALIZATION GRAPH
175
150
125
<
*
.j
<
100
c±
o
o
u.
O
75
s
250
225
200
100
125
SULPHURIC ACID
150
175
175
25
5 100
HYDROCHLORIC ACID
125
150
50
175
275
300
75
200
225
250
25
125
150
NITRIC ACID
100
100
50
HYDROFLOURIC ACID
125
100
75
25
50
HYDROCYANIC ACID
WEIGHT OF 100% ACID
Fig. 28.19 Alkali neutralization graph
(From CHEMICAL UMB FACTS, permission of National Lime Association, Washington, D.C. 1951)
-------
594 Treatment Plants
12
INFLECTION
TITRATION CURVE
OF STRONG BASE
WITH STRONG ACID
NaOH + HC1
10
8
EQUIVALENCE POINT
6
4
0
10
20
40
70
ml OF ADDED REAGENT
Fig. 28.20 Titration curve
(From PHYSICAL CHEMICAL TREATMENT TECHNOLOGY, U.S. Environmental Protection Agency, Washington, D.C., 1972)
-------
?
cc
U1
I-
5 ©
> CO
U. U-
O O
(0 X
Z a
O o
d |
< H
O (C
o
O CO
§ <
O
X
a
13.0 -t
12.0 -
11.0 -
10.0-
4% or 1N NaOK
STARTING pH
2.8% or1N H2S04
13 20
3
a
£
CO
(D
1000 GALLONS OF 4% NaOH OR 4.9% HglSO^
1,000,000 GALLONS OF WASTE WATER
3
o
3
Fig. 28.21 Example titration of an industrial wastewater
(!)
(O
U1
-------
596 Treatment Plants
Similar curves can and should be developed by the operator
as a means of understanding any waste that must be neu-
tralized. They are of further use in monitoring processes and
calibrating automatic instrumentation. The steepness of the
curves near the equivalence points is a good indication of the
difficulty of pH control, especially when mixing times are short,
tankage is too small, titrant concentrations are too high and
feed equipment including pumps as well as instrumentation
are marginally sized.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 698 and 699.
28.3A How does pH affect the rate of corrosion?
28.3B What is pH?
28.3C What is alkalinity?
28.3D To treat the same water, which would produce the
most sludge, lime or caustic soda?
28.3E When diluting caustic soda, what items should be
considered?
28.3F What is a titration curve?
100
28.33 Processes Requiring pH Adjustment and
Neutralization
Almost every wastewater treatment process used to treat
industrial wastewaters involves pH adjustment and the final
effluent usually requires neutralization. The need for an op-
timum pH may be determined by a chemical reaction being
used (such as cyanide destruction), the manufacturer's speci-
fications with respect to a piece of equipment (such as to pro-
tect a reverse osmosis membrane), or by a physical process
(such as coagulation of wastewater and sludge). An industrial
wastewater treatment facility may receive streams separated
as acid and alkaline or separated by pollutant. Process
dynamics and economics often dictate preliminary treatment of
each stream, including pH adjustment. The streams are then
combined for additional treatment including pH adjustment and
neutralization. A few of the more commonly encountered pro-
cesses requiring pH control will be discussed in this section.
28.330 Precipitation of Metal Salts
Metal finishing such as iron pickling and copper plating in-
volves the use of acids, caustics and chemicals. The waste-
waters contain acids, alkaline cleaners, grease and oil, and
heavy metals such as chromium, zinc, copper, iron, nickel, tin
<
tc
o
z
o
o
«
h-
UJ
5
pH UNITS
Fig. 28.22 Precipitation of metal salts versus pH
(From METAL FINISHING WASTES. EPA Technology Transfer, U. S. Environment*! Protection Agency, Washington, 0. C.)
-------
Industrial Waste Treatment 597
200
150
=>
o
<
o
o
100
50
<
i
\ A
-
, 1
/ 1
/ 1
/ #
/ #
m
^ \
. #
1 1
P 1
/ t
/ /
/ /
/
)rQr *T~ l
10
PH
Fig. 28.23 Coagulation of 50 mg/L kaolin with aluminum sulfate and ferric sulfate. Comparison of pH zones of coagulation of day
turbidity by aluminum sulfate, curve A, and ferric sulfate, curve B. Points on the curves represent the coagulant dosage required to
reduce clay turbidity to one-half its original value.
(Adapted from R. F. Pack ham, Proc. Soc. Water Treat. Exam., 12:15 (1963).)
and cyanide. The waste streams come from one or more rinse
tanks as well as the area sump. Metal salts tend to become
insoluble in the neutral pH range, but not all metals will precipi-
tate on neutralization. Metals also precipitate to different de-
grees at different pH values.
Figure 28.22 shows the solubility versus pH curves of vari-
ous metals commonly encountered in metal finishing wastes.
With mixed waste streams, the best pH for the most complete
separation will be that which limits the content of the most toxic
of the metal salts and for which the regulatory limits are most
stringent. With single salt streams, the optimum pH can be
selected. As a rule for mixed streams, a pH from 8.0 to 8.5 is
better (although not truly neutral) than is a pH closer to 7.0. If a
pH outside of the 6.5 to 8.5 range is used, the final effluent will
usually require neutralization prior to discharge.
Neutralization of metal pickling and plating wastes appears
to be a rather unsophisticated chemical process. In practice,
operating experience has shown that what is a relatively sim-
ple bench scale process in a beaker is a complicated and
sophisticated control problem when applied to a continuously
flowing stream which varies in flow rate, free acid or caustic
content and various metal salt concentrations.
28.331 Coagulation14 and Flocculation15
pH is considered to be the single most important variable in
the coagulation process. Jar testing as well as full-scale opera-
tion have clearly shown that there is at least one pH range for
any given water or wastewater within which good coagulation
and flocculation occurs in the shortest time with a given
coagulant dose. The pH range is affected by the chemical
composition of the wastewater and types of coagulant and
coagulant aids used as well as by the concentrations. Alum or
aluminum sulfate - AI2(SO„)3 • 18 H20, ferric chloride - FeCI3
and ferric sulfate - Fe2(S04)3 are the most commonly used
coagulants. Although alum is cheaper, more readily available
and easier to handle, iron salts have the advantage of offering
good coagulation over a broader pH range. This is most impor-
tant where wastewater streams vary significantly in pH and pH
control does not exist. Figure 28.23 shows the coagulation of
50 mg/liter of kaolin (a fine white clay used in the manufacture
of porcelain with aluminum sulfate and ferric sulfate). Points on
the curve represent the coagulant dosage required to reduce
clay turbidity to one half its original value.
14 Coagulation (co-AGG-you-LAY-shunj. The use of chemicals that cause very fine particles to clump together into larger particles. This
makes it easier to separate the solids irom the liquids by settling, skimming, draining or filtering.
'5 Flocculation (FLOCK-you-LAY-shun). The gathering together of fine particles to form larger particles.
-------
598 Treatment Plants
Figure 28.24 shows phosphorous removal relative to alum
dosage with almost zero phosphorous remaining at an alum
dosage of 400 mg/L. However, the addition of alum also lowers
the wastewater pH from above 7 to below 4. Before discharge
to a receiving body of water, neutralization will be required.
This shows that a chemical process sometimes will affect the
wastewater pH even though pH adjustment was not needed.
The amount of pH change is dependent on the buffering capac-
ity of the waste stream.
Figures 28.26 and 28.27 show the dependence of rejection
characteristics on pH and effect of pH on the optical density of
the aqueous solutions. These curves are taken from a study
done on the treatment of TNT manufacturing waste. The
chemistry of the organic compounds at a high pH is suitable for
membrane use. At a neutral or low pH, membrane technology
is inappropriate. This type of technology is expensive but effi-
cient and appropriate where other methods do not exist, water
reuse is desired, or solute or concentrated waste disposal is of
concern.
28.332 Other Processes
Commonly used methods of wastewater treatment such as
biological, reverse osmosis, ozonization, carbon adsorption,
and ultrafiltration are either pH dependent or have a net affect
on wastewater pH. Ultrafiltration is a membrane process used
for the removal of organic compounds in an aqueous (watery)
solution. The process usually operates at relatively low pres-
sures of 100 to 1,000 kilonewtons per square meter (1 to 10
kg/sq cm or 14.5 to 145 psi). Efficiency can be measured in
terms of the amount of dissolved solids or organic materials
rejected by the membrane as well as by the clarity of the SOL-
UTE16 when turbidity is an indicator (Figure 28.25).
28.333 Sludge Conditioning and Disposal
Sludge treatment and dewatering is part of the industrial
wastewater treatment process. Sludges are often classified by
their basic chemical composition, pH, specific resistance and
cake solids.
Specific resistance is an index of sludge fliterability. Poly-
mers are often used in the dewatering of sludge. Figures
28.28, 28.29, and 28.30 show the relationships between spe-
cific resistance (r), pH, polymer dosage (mg/L) and pH for
nonionic, anionic and cationic polymers for a particular sludge.
Figure 28.31 shows optimal polymer dosages versus pH for a
particular sludge.
M
K
E
V)
D
cc
O
z
a.
CO
O
z
b.
PHOSPHORUS
z
Q.
0 100 200 300 400
ALUM DOSAGE, mg/1 a» A12 (S04>3 = 18 HzO
Fig. 28.24 Alum coagulation of wastewater
(From HANDBOOK OF ADVANCED WASTEWATER TREATMENT, 2nd Edition by Russell L. Culp, Geofge M. Wssner and Gordon C. Culp, (C) 1978 by Litton Educational Publishing, Inc.
Reprinted by permission of Van Nostrand ReinhoW)
Solute. The substance dissolved in a solution. A solution is made up of the solvent end the solute.
-------
Industrial Waste Treatment 599
(AQUEOUS SOLUTION) WASTE
STREAM
(SOLUTE) REJECTED
ORGANIC
TREATED OR CLEAN WATER
(SOLVENT)
MEMBRANE
Fig. 28.25 Ultrafiltration process
2.0
WAVE LENGTH = 340 mm
1.8
1.6
1.4
PINK WATER
1.2
1.0
.8
.6
.4
.2
>-2.4 - DNT
0
8
12
6
7
9
5
11
4
10
Fig. 28.26 Effect of pH on the optical density of actual pink water and of 2, 4-DNT solution
(From "Membrane Ultrafiltration (or Treatment and Water Reuse of TNT — Manufacturing Wastes," by Bhattacharyya, Garrison, and Grieves. JWPCF, May 1977,803, permission of Water
Pollution Control Federation)
-------
600 Treatment Plants
1.0
WASTE PINK WATER FROM TNT MANUFACTURE
9
C1 = 55 mg/1 ORGANIC CARBON
P = 2.8 X 103N/m2
U = 154 cm/sec
.8
7
6
PSAL (MILLIPORE)
5
.4
3
2
¦UM-05 (AMICON)
1
F-601 (GULF)
PM 10 (AMICON)-*^
0
4.0
5.0
6.0
7.0
9.0
8.0
10.0
12.0
pH
Fig. 28.27 Dependence of rejection characteristics of ultrafiltration membranes of pH
(From "Membrane Ultrafiltration for Treatment and Water Reuse ot TNT — Manufacturing Wastes," Dy Bhattacharyya, Garrison, and Grieves. JWPCF, May 1977, 803, permission of
Pollution Control Federation)
-------
Industrial Waste Treatment 601
400
300
NONIONIC
200
100
6
Fig. 28.28 Relationship among sludge specific resistance, pH, and dose with 15 x 106 mot wt nonionic polymer
"Effects of pH and Mixing on Polymer Conditioning ol Chemical Sludge," by O'Brien and Novak. Reprinted from the Journal American Water Works Association, 69, by permission of the
(From Association Copyighted 1977 by the American Water Works Association, 666 West Quincy Avenue, Denver, Colorado 80235.)
-------
602 Treatment Plants
o>
300
200
ANIONIC -15 PERCENT
100 -
Fig. 28.29 Relationship among sludge specific resistance, pH, and dose with 15 x 106mol wt,
15 percent hydrolysis anionic polymer
(From "Effects of pH and Mixing on Polymer Conditioning of Chemical Sludge," by O'Brien and Novak. Reprinted from the Journal American Water Works Association, 69, by permission of the
Association. Copyrighted 1977 by the American Water Works Association, 6666 West Quincy Avenue, Denver, Colorado 60235.)
-------
Industrial Waste Treatment 603
Ol
J*
o
T—
X
400
300 —
200 —
100
ANIONIC-40 PERCENT
Fig. 28.30 Relationship among sludge specific resistance, pH, and dose with 15 x 106 mol wt,
40 percent hydrolysis anionic polymer
(From "Effects of pH and Mixing on Polymer Conditioning of Chemical Sludge," by O'Brien and Novak. Reprinted from the Journal American Water Works Association, 69, by permission of the
Association. Copyrighted 1977 by the American Water Works Association, 6666 West Quincy Avenue, Denver, Colorado 60235.)
-------
604 Treatment Plants
A. ANIONIC -50 PERCENT
ANIONIC 40 PERCENT
• ANIONIC 15 PERCENT
~ ANIONIC- 5 PERCENT
O NOIMIONIC
Fig. 28.31 Optimal polymer dose on sludge as a function of pH
(From "Effects of pH and Mixing on Polymer Conditioning of Chemical Sludge," by O'Brien and Novak. Reprinted from the Journal American Water Works Association, 69, by permission of the
Association. Copyrighted 1977 by the American Water Works Association, 6666 West Quincy Avenue, Denver, Colorado 80235.)
-------
Industrial Waste Treatment 605
28.334 Summary
pH is an important consideration either as a control tech-
nique or as an after-effect in almost every wastewater treat-
ment process, regardless of whether the source is industrial or
sanitary or both. The expected effects for each process are
known, but the actual effect must be determined by jar testing
and pilot work before process system design. During start-up
and operation the process used, including pH adjustment and
neutralization, will require fine tuning. pH control is dependent
upon temperature, mixing, control systems, and chemicals
used, as well as the chemistry of neutralization.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 699.
28.3G List the treatment processes that may require pH ad-
justment and neutralization.
28.3H List the most commonly used coagulants.
28.31 What is ultrafiltration?
28.3J How are sludges classified?
28.34 Process Mechanics
Industrial wastewater flows and strength of contaminants
vary considerably by the day of the week, shift of day and time
within each shift. Flows and strengths are production oriented
as well as product dependent. In an old, large manufacturing
facility, the waste is likely to be diluted with other process flows
including cooling water and possibly sanitary waste. In a small
or new manufacturing facility, the waste is likely to be an iso-
lated highly contaminated stream, but with relatively little vol-
ume. All these factors have a direct bearing on the process
mechanics. Treatment is either:
1. Batch or continuous,
2. Automatic or manually controlled,
3. Single or multiple stage,
4. Feed forward or feed back, and
5. Acid and alkali or just acid or just alkali.
Batch means that the waste is collected in a tank, pH ad-
justed and then allowed to reenter the wastewater stream.
Each batch can be checked at the end of adjustment and so
either manual or automatic control, or both, is applicable.
Continuous means that the flow never stops; therefore, the
pH adjustment must be made during the amount of time a slug
of waste is in the tank. Manual control is not practical, espe-
cially if flow and pH of wastewater vary significantly.
Automatic controlling uses automatic instrumentation to con-
trol chemical addition, control valving and to signal process
upset.
Manual controlling uses laboratory instruments and tests to
determine the state of the process. The operator uses nomo-
graphs and judgment to control chemical addition to determine
when proper pH adjustment has been achieved.
Single stage has one point of adjustment. This is adequate
for adjustment to within a range, where mixing is more than
sufficient and where the waste stream is constant in direction
and amount of chemical needed.
Multiple stage has two or more points of adjustment and is
necessary where adjustment to one or more pH points is re-
quired, where mixing and tank size are small or multiple and
where the waste stream requires varying amounts of acid and
alkali.
Feed forward systems sense the pH and add the necessary
chemicals downstream from the point of sensing. Due to time
lag, the slug of wastewater being sensed is not the same as
the slug being adjusted.
Feed back systems sense the pH and add the necessary
chemical upstream from the point of sensing. Here the treated
wastewater is re-sensed. Both feed systems require good mix-
ing, especially in tanks as opposed to in pipelines. Quality of
instrument(s) and placement of sensor(s) is critical.
Acid/alkali processes can make the necessary pH adjust-
ment from a pH either below or above the desired pH. There-
fore both acid and base can be chemically fed.
Acid or alkali means that the pH adjustment is made from
only one direction. Two process loop diagrams shown in Fig-
ures 28.32 and 28.33 illustrate two of the many combinations
available. These graphically indicate the important role played
by the instrumentation. The operator should become thor-
oughly familiar with the operation and maintenance proce-
dures contained in the manufacturer's literature. The operator
also must be capable of manually determining pH by using
electrometric measurement (a lab meter) and special indicator
paper (litmus or pHydrion paper). Typical test procedures for
acidity, alkalinity and pH are outlined in Chapter 16, "Labora-
tory Procedures and Chemistry."
-------
606 Treatment Plants
SET POINT
I
I I LEVEL
CHEMICAL
FEED
0
HIGH LEVEL
'--4
HIGH LEVEL
S-
IN
20 psig
FAS = FILTERED
AIR SUPPLY
-LOW LEVEL
1. Bubble-Type Indicating Level Controller. 2. Relay. 3. Water Inlet Valve. 4. pH Sensor. 5. pH Amplifier. 6. pH Recorder/Controller.
7. Manual-Off-Automatic Switch. 8. Chemical Feed Pump or Feed System. 9. Timer. 10. Drain Valve. 11. Agitator Drive.
Fig. 28.32 Simple batch-type pH control. High level of water initiates batch treatment.
(Permission of Honeywell, Inc.)
Figure 28.32 illustrates the simplest pH control system applicable to many industrial plants having either acid or alkaline streams
that require pH adjustment and/or control.
DESCRIPTION OF OPERATION
Treatment tank fills with water to be treated. Level controller (1) senses when predetermined level (high) is reached. Relay (2)
action in level control signal line closes water inlet valve (3), opens similar inlet valve on alternate treatment tank, energizes pH
control system and starts the agitator. The pH sensor (4) senses pH of the water in the tank. The signal is amplified (5) and recorded
by the pH recorder-controller (6). Chemical pump (8) introduces a neutralizing chemical until the desired set point is reached, when
a backset or frontset switch on the recorder-controller shuts off chemical feed and energizes the timer (9). After the predetermined
holding time has elapsed, the timer times out and relay (2) action opens the drain valve (10) to drain tank contents to service. When
low water level is reached, relay action (2) stops the agitator, closes the drain valve and opens the inlet valve to start the next cycle.
Manual-off-automatic switches (7) provide for remote manual pump operation, and inlet and drain valve actuation.
NOTE: Level control can be of the bubbler type (as illustrated), float type, electric conductance type, or any device that can provide a
115-volt signal when the tank is filled.
This system is suitable for adjusting pH of waters with or without suspended solids content.
-------
Industrial Waste Treatment 607
Low pH Cuto
High pH Cutoff
J
FAS— -
OOP
Acid
Alkali
Water
Water
Out
FAS = Regulated
FiItered
Air Supply
1. Flow Tube. 2. Differential Pressure-to-Current (AP/I) Transmitter. 3. Square Root Extractor. 4. Flow Recorder/Controller. 5. Acid
Pump with Pneumatic Stroke Adjustment. 6. Alkali Pump with Pneumatic Stroke Adjustment. 7,8. Silicon Controlled Rectifier/(SCR)
Controller. 9. pH Sensor. 10. pH Amplifier. 11. pH Recorder/Controller with Auto/Manual Switch. 12 and 13. Relays.
Fig. 28.33 Continuous neutralization of water proportional to pH and flow. Variable flow and high and lor low pH of water. Flow
signal controls speed of acid and alkali pumps; pH of treated water controls the stroke on acid and alkali pumps.
(Permission of Honeywell, Inc.)
Many industrial process waters will fluctuate in terms of flow and many alternate between high and low pH values. The system
described (see Figure 28.33) is capable of feeding either acid or alkali for neutralization proportional to pH and flow.
DESCRIPTION OF OPERATION
Flow is measured by a primary metering element (1) and differential pressure is sensed by a AP/I transmitter (2). The square root
is extracted (3) and flow is recorded by the recorder-controller (4). A transmitting slidewire in the recorder is positioned proportional
to flow and varies the speed of two chemical feed pumps (5 and 6) through individual SCR (silicon controlled rectifiers) controllers (7
and 8).
The pH of the water in the treatment tank is sensed (9) and the signal amplified (10), then recorded by a recorder-controller with
automatic-manual switch (11). If pH is above the set point, i.e., alkaline, the pneumatic signal from the pH controller increases the
stroke of the acid pump (5) equipped with pneumatic spring-to-decrease positioner. If the pH measurement is below set point, i.e.,
acidic, the pneumatic signal increases the stroke of the alkali pump (6) equipped with air-to-decrease, spring-to-increase pump
stroke positioner.
Most chemical pumps will still deliver a minute quantity of chemical solution at zero stroke. For the sake of economy, therefore, it
may be desirable to equip the recorder with backset switches and to provide relays (12, 13) to inhibit acid feed when pH is below a
predetermined value and inhibit alkali feed when pH is above a set level.
-------
608 Treatment Plants
28.35 Safety
Engineering control of hazards is the first step in the safety
considerations at a treatment plant. The ability to contain and
control spills can be designed into an existing or new facility.
Equipment designed to handle the chemicals being used as
well as in the environment created by the chemicals will need
less maintenance and result in fewer injuries. Ventilation
should be adequate to minimize chemical exposure to person-
nel. There should be no reason for skin, eye, nose or throat
irritation. Electrical equipment should be designed to prevent
deterioration or electrical shorting which can result from ac-
cumulations of chemicals on wiring and on terminals. Protec-
tive enclosures or splash walls should be used in critical expo-
sure areas. Access to probes requiring periodic cleaning, cali-
bration and replacement should be properly provided for.
The operator should:
1. Take part in drills regarding locations, purpose and use of
emergency shutdown valves and switches.
2. Be knowledgeable (not just familiar) with the locations, pur-
pose and use of personal protective equipment.
3. Be aware of the locations of and trained in the use of
emergency shower and eye wash stations and other
sources of water for use in emergencies.
4. Be keenly aware of all incompatible chemicals within or
likely to be brought into the treatment plant site. If incompat-
ible chemicals come in contact with each other, hazardous
conditions could result, such as fires, explosions or toxic or
corrosive atmospheres. A partial list is shown in Table 28.5.
5. Have sufficient and proper instructions on how to secure
outside help during an emergency. This includes alerting
fire, police and hospital officials as well as supervisory per-
sonnel.
6. Be provided with proper safety gear such as face shields,
safety shoes, and breathing apparatus.
7. Be able to isolate and purge chemical lines prior to inspec-
tion and maintenance.
8. Be able to lock out and tag equipment during inspection and
maintenance.
9. Have available and use formal procedures to start-up or
take out of service systems, subsystems or units.
TABLE 28.5
Chemical
Acetic acid
Acetylene
Alkaline metals
(such as powdered
aluminum or mag-
nesium, sodium,
and potassium)
Ammonia, anhy-
drous
PARTIAL LIST OF INCOMPATIBLE
CHEMICALS*
Prevent Contact With
chromic acid, nitric acid, hydroxyl com-
pounds, ethylene glycol, perchloric acid,
peroxides, and permanganates
chlorine, bromine, fluorine, copper, silver,
and mercury
carbon tetrachloride or other chlorinated hy-
drocarbons, carbon dioxide, and halogens
mercury (such as in manometers), chlorine,
calcium hypochlorite, iodine, bromine, and
hydrofluoric acid anhydrous.
a Adapted Irom the DANGEROUS CHEMICALS CODE, Bureau of Fire Prevention, Los
Angeles, California (1951).
Chemical
Ammonium nitrate
Aniline
Bromine
Carbon, activated
Chlorate
Chlorine
Chlorine dioxide
Chromic acid
Copper
Cumene hydro-
peroxide
Flammable liquids
Fluorine
Hydrocarbons
(such as butane,
propane, benzene,
gasoline, and tur-
pentine)
Hydrocyanic acid
Hydrofluoric acid,
anhydrous
Hydrogen peroxide
Hydrogen sulfide
Iodine
Mercury
Nitric acid, concen-
trated
Oxalic acid
Perchloric acid
Potassium
Potassium chlorate
Prevent Contact With
acids, metal powders, flammable liquids,
chlorinate, nitrite, sulfur, and finely divided
organic or combustible materials
nitric acid and hydrogen peroxide
ammonia, acetylene, butadiene, butane,
methane, propane (or other petroleum
gases), hydrogen, sodium carbide, turpen-
tine, benzene, and finely divided metals
calcium hypochlorite and all oxidizing agents
ammonium salts, acids, metal powders, sul-
fur, and finely divided organic or combustible
materials
ammonia, acetylene, butadiene, butane,
methane, propane (or other petroleum
gases), hydrogen, sodium carbide, turpen-
tine, benzene, and finely divided metals
ammonia, methane, phosphine, and hydro-
gen sulfide
acetic acid, naphthalene, camphor, glyc-
erine, turpentine, alcohol, and flammable liq-
uids in general
acetylene and hydrogen peroxide
organic or inorganic acids
ammonium nitrate, chromic acid, hydrogen
peroxide, nitric acid, sodium peroxide, and
halogens
everything except special containers
fluorine, chlorine, bromine, chromic acid, and
sodium peroxide
nitric acid and alkalies
ammonia, aqueous or anhydrous
copper, chromium, iron, most other metals
and their salts, alcohols, acetone, organic
materials, aniline, nitromethane, flammable
liquids, and combustible materials
fuming nitric acid and oxidizing gases
acetylene, hydrogen, and ammonia (aque-
ous or anhydrous)
acetylene, fulminic acid, and ammonia
acetic acid, aniline, chromic acid, hyd-
rocyanic acid, hydrogen sulfide, and flamma-
ble liquids and gases
silver and mercury
acetic anhydride, bismuth and its alloys, al-
cohol, paper, and wood
carbon tetrachloride, carbon dioxide, and
water
sulfuric and other acids (see also chlorate)
-------
Industrial Waste Treatment 609
Chemical
Prevent Contact With
Potassium perchlo- sulfuric and other acids (see also chlorate)
rate
Potassium perman-
ganate
Silver
Sodium
Sodium peroxide
Sulfuric acid
glycerine, ethylene glycol, benzaldehyde,
and sulfuric acid
acetylene, oxalic acid, tartaric acid, fulminic
acid, and ammonium compounds
carbon tetrachloride, carbon dioxide, and
water
ethyl or methyl alcohol, glacial acetic acid,
acetic anhydride, benzaldehyde, carbon di-
sulfide, glycerine, ethylene glycol, ethyl ace-
tate, methyl acetate, and furfural
potassium chlorate, potassium perchlorate,
and potassium permanganate (or similar
compounds of such other light metals as
sodium and lithium)
//A
28.36 Construction Activities
Unfortunately, very few industries assign trained operators
before or at the start of construction. An operator on the job
costs industry money, especially with duration of construction
often lasting longer than one year. But more significantly,
trained industrial operators rarely exist. Whereas most munici-
pal wastewater treatment plants are similar, industrial treat-
ment plants vary dramatically from plant to plant. Therefore the
operators receive on-the-job training, usually by the design
engineers. The supervisor and some operators should be on
the construction site during the period when major pieces of
equipment are installed, piped up and wired. This period as
well as start-up are critical periods for the operating staff. They
can have a role as sidewalk superintendents, must prepare for
start-up, and can (and should) perform unit checkout functions.
28.360 Sidewalk Superintendent
During construction, the drawings and specifications are part
of the contract between the company and the contractor.
Operators cannot tell a worker to make a walkway safer or to
provide better access to a pH probe. But the operator can,
through management, indicate unsafe areas, poor quality work
and point out potential operating problems. An alert operator
will walk into a room and ask questions such as:
1. Can I service and maintain the equipment safely?
2. Are switches and controls adequate and properly located?
3. Is lighting sufficient?
4. Is ventilation sufficient?
5. Is proper entrance to and exit from the room provided?
6. Are emergency alarms provided?
The operator can review plans and specs to see if the work
being done is correct. If the answer to one of the above ques-
tions is no or if the work is wrong, the operator should make a
constructive suggestion. The operator should also use this
period to learn what the equipment looks tike stripped down
and bare, especially piping that will become buried, tanks that
will be filled with water and gears and drives that will be en-
closed.
28.361 Preparation for Start-Up
Months before unit check-out and start-up, the operators
should be receiving classroom training in the processes to be
used. They should be acting as sidewalk superintendents.
Safety gear should be provided, explained and used including
drills where applicable. An inventory of equipment, manuals
and tools needed for start-up should be put together. Regular
meetings should be held to discuss the status of the above and
also to provide a forum for discussion. Design engineers
should be available to answer questions. The operators should
use this period to review start-up and operating manuals as
they are being prepared. Key vendor representatives should
be required to give training sessions.
28.362 Unit Check-Out and Start-Up
This phase refers to the "dry" checking of each piece of
equipment and then the start-up of the system and placing it
into normal operation. This is a period when the operators can
develop step-by-step procedures. Examples for a simplified
acid storage and feed system are shown in Tables 28.6, 28.7,
28.8, and 28.9. When operating experience is gained, these
procedures can be modified and incorporated in an operation
and maintenance manual. Formal procedures define areas of
responsibility and significantly reduce the chances of errors
and accidents.
26.37 Operation and Maintenance
Neutralization or pH adjustment systems consist of parts
found in other locations of the treatment plant as well as the
industrial site being served. Pumps are pumps and recorders
are recorders. For the process to work, they must all function
together as a system. The breakdown of one part will either
shut the process down or necessitate manual operation. If cer-
tain parts are allowed to drift or to go out of calibration due to
poor maintenance, process control will suffer. Because a
chemical reaction is taking place and is usually being con-
trolled by sensitive instrumentation, neutralization systems are
trouble-prone and maintenance "hogs" (time consumers). An
ounce of preventive maintenance is often worth a pound of
breakdown maintenance. Points of particular concern are:
1. Primary sensors such as level probes and pH probes,
2. Chemical feed pump bearings and seals,
3. Chemical feed pump stroke controllers or positioners,
4. Automatic valves and limit switches,
5. Screw feeders or vibrators for dry chemicals, and
6. Mixers.
-------
610 Treatment Plants
TABLE 28.6 TYPICAL CHECK-OUT PROCEDURE AND
VERIFICATION
Item — Sulfuric Acid Storage Tanks (3)
Equipment
Check-Out By
DESCRIPTION - Three horizontal fiberglass
liquid sulfuric acid storage tanks of 9,000
gallons each. Each tank has a liquid level
gage and tank number 3 has a high and low
level alarm with an annunciator (noise
alarm) on the main control panel.
CHECK-OUT
1. Tanks set in place and anchored with con-
crete placed in saddles.
2. All piping and valves in place and properly
supported. Refer to drawing M21 and ven-
dor drawing X-16. Four inch vent and over-
flow, 3 inch fill, six inch pump suction, 2 inch
drain. Verify that feed line with outdoor gate
valve and 3 inch quick connect and cap are
installed.
3. Level alarm (hi and low) installed on tanks
#1 and #3 wired to annunciator of main
control panel (level alarm high and level
alarm low).
a. Verify that level switch 15 is at 4/s full
point. Refer to vendor sketch X-18.
b. Verify that level switch 16 is at Vb full
point.
c. Verify that 115-volt power supply is
connected to switches.
d. Verify that angular rotation of floats ini-
tiates main control panel annunciator.
7. Rotameter FEI-10 installed. Four inch,
0-300 GPM. Verify that orifice plate for
rotameter is installed in line.
8. Verify that calibration of rotameter is ac-
cording to manufacturer's instructions.
9. Verify that feed rate positioner operates
over entire range. Feed rate is a function
of 4-20 ma from main control panel. Simu-
late signal and verify calibration stroke po-
sition.
10. Verify that back pressure valves are set at
50 psi, function at that setting, and verify
inlet and outlet direction.
11. Verify that back pressure valve relief port
is piped to appropriate drain.
TABLE 28.8 TYPICAL CHECK-OUT PROCEDURE AND
VERIFICATION
Item — Sulfuric Acid Control Panel
(Refer to Smith & Doe drawing X-20 sheet 3)
Equipment
Check-Out By
1. Verify that 4-20 ma signal from ratio station —
FY7 in main control panel to sulfuric acid
control is connected at terminals 10 and 13.
2. Verify that Smith and Doe system check-out
is complete and that 4-20 ma signal from
FY7 is proportional to flow rates from 500 to
4,500 gallons per day. Refer to item 9 of
metering pump section.
3. Verify pump running time meter control
sequencing properly. Refer to Smith and
Doe drawing X-20 sheet 4.
TABLE 28.7 TYPICAL CHECK-OUT PROCEDURE AND
VERIFICATION
Item — Sulfuric Acid Transfer Pumps
Equipment
Check-Out By
DESCRIPTION - Three Smith & Doe model
44-15 Vi HP pumps to transfer liquid sul-
furic acid from storage tanks to dilution
tee for feed to influent area of neutraliza-
tion tanks.
1. Six-inch suction header in place with
valves, pipe and calibration chamber,
properly supported, expansion must be
possible.
2. Verify that automatic valves function cor-
rectly (AV1, 2, 3).
a. Check that 120-volt power is to valve
motor.
b. Verify that limit switches (open and
closed) are wired properly and power
supply is 120 volts.
3. Pump installed correctly, frame base
bolted to slab and pump charged with lu-
bricant.
4. Motor wired correctly 3 , 460 volts, fed
through control panel from MCC #1,
space G2 and power panel H1.
5. Sulfuric acid control panel installed and
wired correctly from Panel H1. Refer to
vendor drawing X-18 sheet 4.
6. Acid piping and dilution tee and piping to
neutralization tank all in place and prop-
erly supported.
TABLE 28.9 TYPICAL CHECK-OUT PROCEDURE AND
VERIFICATION
Equipment
Check-Out By
1. Verify "as-built" drawings complete. ~
2. Verify all manufacturing drawings.
3. Verify maintenance and operating instruc-
tions complete.
4. Verify all spare parts "on hand" and correct.
Maintenance procedures should be set up and be as formal
and detailed as practical. Most industrial sites are staffed to set
up such programs. The operators should work with these
people to see that a usable program is implemented. The
treatment plant should maintain a complete set of drawings
(up-dated) and equipment manuals. Operating logs showing
all aspects of process, system and equipment operation
should be maintained.
Troubleshooting is another important part of O&M. What do
you do when the process is balky or does not work at all? For
instance, a pH recorder indicates 10.0 when a pH of 8.0 is
desired. Adding acid makes no difference. The operator must
divide and conquer the system by the process of elimination. A
typical procedure is as follows:
Check process stream with portable pH meter.
I. Agrees with recorder
Therefore, suspect acid feed system — check acid feed
pump
1. Pump running normally — check acid supply
-------
Industrial Waste Treatment 611
a. Acid supply adequate and changing — check for
leak
b. Acid supply empty
c. Acid supply adequate and not changing — check
valving
2. Pump running abnormally — check bearings
— check motor and power
supply
— check pistons or impeller
II. Shows actual pH is less than 10.0
Therefore suspect instrumentation — check transmitter
1. Transmitter okay — check primary sensor
a. Sensor okay — check recorder
b. Sensor bad — fix
c. Sensor okay — check signal lines
2. Transmitter bad — fix
III. Neither of the above routes work
Therefore look at interface between equipment and in-
strumentation controls:
1. Signal being generated and received — suspect
equipment
2. Signal not being generated or received — suspect in-
struments
3. Signal being generated and not received — suspect
interface.
This was one of many cause and effect procedures that can
be followed. Regular instrument calibration, if practiced, could
have spotted a faulty sensor/indicator. Then the operator
would have had a prime suspect. Routine equipment inspec-
tion could have uncovered an unusually noisy pump. Then the
operator would have had a different prime suspect.
Troubleshooting requires common sense as well as a good
working knowledge of the process and its parts.
28.28 Instrumentation
Chapter 26, "Instrumentation," does an excellent job of
showing the variety of industrial wastewater systems in terms
of size and degree of sophistication. The chapter ties together
some of the design considerations that must be adapted to the
operating needs as well as the realities of the process.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 699.
28.3K What is a batch process?
28.3L How can an operator manually determine pH?
28.3M Why should ventilation be provided in chemical feed
facilities?
28.3N What kinds of questions should an alert operator con-
sider when walking into a room under construction?
28.40 Why should formal procedures be developed for
start-up, operation and shutdown of equipment and
processes?
6MP Of
IN0UGTClAt/wA#r6 TSBACTMtfHff
Please work the discussion and review questions before
continuing.
DISCUSSION AND REVIEW QUESTIONS
(Lesson 4 of 6 Lessons)
Chapter 28. INDUSTRIAL WASTE TREATMENT
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 3.
22. Why is ventilation important in chemical storage areas?
23. What is a buffered solution?
24. What is the influence of alum on pH?
25. pH control is dependent upon what factors?
26. What is the difference between automatic and manual
controlling?
27. Why should the operator be aware of incompatible chemi-
cals?
-------
612 Treatment Plants
CHAPTER 28. INDUSTRIAL WASTE TREATMENT
(Lesson 5 of 6 Lessons)
28.4 COAGULATION AND PRECIPITATION
by Paul Amodeo
28.40 Need for Coagulation and Precipitation
28.400 Purpose of Coagulation and Precipitation
Sedimentation can be defined in a broad sense as those
operations performed in which a suspension of particles is
separated into a clarified liquid and a more concentrated sus-
pension. Sedimentation can be physically located downstream
of any process in which such a suspension is generated (such
as a biological treatment process) of it may be autonomous (by
itself), representing the bulk of the treatment process of a
plant. The latter is most common in the industrial waste treat-
ment facilities in which metals and large quantities of sus-
pended matter exist prior to any treatment. Most frequently,
sufficient removal of suspensions is not economically accom-
plished by allowing the solids to settle at their own pace. Con-
sequently, chemical coagulation is generally used to enhance
the settling quality of the suspension, thereby decreasing the
detention time required to achieve the desired liquid clarifica-
tion. For the purpose of this section, chemical coagulation to
enhance sedimentation will be primary concern.
28.401 Description of Process
Chemical coagulation involves the following operations:
1. Rapid Mix. In this operation, the suspension to be clarified
is blended rapidly with the chemical coagulant to insure
complete mixing.
2. Flocculation. The above liquid is agitated slowly to insure
contact of coagulating chemicals with particles in suspen-
sion. Floe growth is accelerated by controlled particle colli-
sions. Suspended particles gather together and form larger
particles with higher settling velocities.
3. Clarification. The coagulated particles are allowed to settle
quiescently (in still water) from the clarified liquid.
Care should be taken in interchangeably using the words
flocculation and coagulation. Flocculation, as noted above, is
the act of mixing and stirring the particles so as to insure
adequate contact between suspended particles and the
coagulating chemical. It is, therefore, the operation promoting
coagulation. Coagulation is the actual gathering together of
smaller suspended particles into floes, thus forming a more
readily settleable mass.
There are several different types of coagulating chemicals in
use. Briefly, these may be classified into three broad
categories dependent upon their mode of operation.
1. Electrostatic charge reducers.
2. Interparticle bridgers, and
3. Physical enmeshers.
Coagulating chemicals may be purchased in both solid and
liquid form. Although typically, they have been mainly inorganic
compounds, organic polymer technology is now advancing to
the point where more economical and easier handling organic
polymer substances are being used.
28.41 Principles of Coagulation
28.410 Physiciai Activites
Three separate operations are involved in the coagulation-
precipitation process:
1. Rapid mix,
2. Flocculation, and
3. Precipitation (clarification or liquid-solids separation).
The initial process of rapid mix is important in two regards.
First, it insures that there is a homogeneous mixture (complete
mix) of suspended particles and coagulating chemicals. Sec-
ondly, it provides the initial incentive for particle contact.
Characteristically, the rapid mix operation is of a short duration
in relation to the operations following. Duration should be only
that time necessary to provide a homogeneous mixture be-
cause too long a rapid mix may have an adverse effect upon
coagulating due to the breaking up and separation of the form-
ing floe. Therefore, the speed of the paddles becomes very
important. Too rapid a speed may mechanically break up floe.
Likewise, too slow a speed may not provide the needed mixing
and may promote dead spots within the tank where mixing
does not occur. Residence under these conditions may be
increased for some particles and the settling of floe may occur
before it can be effectively handled by removal equipment in
the downstream processes.
Water with suspended matter is passed from the rapid mix to
the flocculation tank. Paddle configuration (layout) and speed
are such that the water and floe are encouraged to move
slowly through the tank. Stirring during flocculation is for the
purpose of promoting maximum contact between suspended
particles. In doing so, particles gather together or coagulate to
form a larger mass called floe. These aggregates or floes of
particles now have a greater overall density and can be more
readily separated from the liquid portion.
As in the case of the rapid mix, two dangers must be avoided
during flocculation. Paddle speed must be sufficient to main-
-------
tain floe in suspension while at the same time it must not be so
great as to shear and break up the floe formed.
Following flocculation, clarification occurs. During this opera-
tion, floe particles are allowed to settle out from the liquid por-
tion, thereby accomplishing an effective separation. As such,
precipitation is allowed to take place under somewhat quies-
cent (still water) conditions. The efficiency of the sedimentation
process will be a function of the retention time, surface loading,
the weir overflow rate and the solids loading. To some extent,
also, in the initial portion of the operation, the process will be
enhanced by the continuation of floe formation. As the large
floe particles begin to settle, other particles still in suspension
are attracted to the mass and settle out with it.
28.411 Destabilization Mechanisms
Suspended particles of interest for the coagulating operation
fall within the size range of 1 to 2 microns. At this size, they
possess natural stabilizing forces which prevent them from
aggregating or gathering together. These forces include elec-
trostatic repulsion which exists where the line polar charges on
the particles will make them repell one another and physical
separation from the surrounding media which may be effected
by the formation of an adsorbed water layer on the particle. To
bring about coagulation, not only must one disperse the parti-
cles to encourage contact, but one must also bring about a
destabilizing mechanism. This is accomplished in one of three
ways:
Industrial Waste Treatment 613
1. Electrostatic charge reduction,
2. Interparticle bridging, and
3. Physical enmeshment.
Electrostatic charge reduction takes advantage of the fact
that many of the finely dispersed suspended particles in water
possess a negative charge. By the addition of cationic metal
salts (these have a positive charge), the negative charges be-
come neutralized by absorption of the positive ion to the parti-
cle surface. With this mode of treatment, overdose of coagu-
lant chemical should be avoided because this may include the
reverse phenomenon in which there exists an excess of posi-
tive charges. In such a case, an anionic (negative charged)
substance must be added to reestablish destabilization.
Polymers exist which have the capacity to adsorb to sites on
suspended particles and act as a bridge between them (Fig.
28.34). In this way, effective aggregation can be enhanced.
Overdose must again be avoided because the polymer may
adsorb to all of the sites on a colloid without bridging, thereby
bringing about restabilization. This mechanism is in effect
when using non-ionic polymers or polymers with the same
charge as the treated particles.
Physical enmeshment is accomplished by the hydrolysis
products of iron, aluminum or at high pH, magnesium. Those
cations will combine with hydroxyl ions (OH-) found in water
from its natural dissociation as shown below.
H2 - H+ + OH~
WATER
WATER
+
_ + NEGATIVE
y (yv-7 + C0LL0IDAL
PARTICLE
*4® + v+(^_
-0-0
+ 0
-------
614 Treatment Plants
This comes about either as a result of the alkalinity of the
water or as a result of increasing the pH by the use of lime or
soda ash. The metal ions will combine with the hydroxide to
form gelatinous products which will enmesh suspended parti-
cles within them.
(Metal lon)+ + OH" ^ Gelatinous Complex
28.412 Properties of Some Common Coagulants
Several coagulants are now available on the market. With
the advent of polymers, many of the inorganics are being re-
placed with organics (polymers). However, for economic con-
siderations, many of the tried and tested inorganics are still
used widely and should be considered. Among them, the most
common are compounds of aluminum, iron and lime.
Aluminum compounds are generally categorized as alum
and may be purchased in both liquid and dry forms. Dry alum
AI2(S04)3 • 14 H20) is partially hydrated, therefore slightly
HYGROSCOPIC17 and should be stored in an area of con-
trolled humidity. Dry alum is not corrosive unless it absorbs
moisture. Dry alum is sold as approximately 17 percent as
AIz03. When added to water, it is acidic and a 1 percent solu-
tion will have a pH of 3.5. In general, the reaction of alum,
although complex, depending upon the type of sludge, can be
simplified by considering its reaction with hydroxyl ion. Alumi-
num ion goes into solution by the following dissociation.
AI2(S04)3 ^ 2AI+3 + 3(S04)"2
With hydroxyl ions from the water,
H20 ^ H+ + OH"
the following occurs:
2 Al+3 + 6 OH" ^ 2 AI(OH)3.
The hydrated precipitate is the mechanism by which coagu-
lation is enhanced. Aluminum ion may also combine with other
negative ions in a similar manner to give the similar net result.
Iron compounds are also effective coagulants, especially in
the formation of hydrated complexes. The most commonly
used are ferric chloride (FeCI3), ferrous chloride (FeCI2) and
ferrous sulfate (FeSO„). All such compounds are corrosive,
difficult to dissolve in water and may, if added in excess, create
an excess of iron in the effluent.
Ferric chloride is often shipped as a dark brown, oily liquid
and is very corrosive to many common materials. Ferric
chloride will characteristically stain anything with which it
comes into contact and, therefore, precautions should be
taken. Ferrous chloride is slightly less corrosive. Ferric sulfate
(also called copperas) is available in a dry powder, granule,
crystal or lump and must be handled with care. If dry at tem-
peratures less than 68°F (20°C), it is efflorescent (will form a
powder or cust on the surface), however, if moisture is present,
it will hydrate rapidly. If it comes into contact with quicklime, a
high degree of heat is created and an explosive hazard results.
Lime is sold in the forms of quicklime (CaO) and hydrated
lime (Ca(OH),). The density is approximately 55 to 75 pounds
per cubic foot and it is highly alkaline. The reaction is some-
what different from the other coagulating chemicals in that it is
indirect. Addition of lime to water creates a condition in which
calcium carbonate (CaC03) is precipitated. As the pH is ele-
vated above 10.5, magnesium hydroxide (Mg(OH)2) is formed
from the natural magnesium present. This hydroxide pos-
sesses the coagulating properties.
Other inorganics commonly in use are soda ash (Na2C03),
caustic soda (NaOH) and carbon dioxide (C02). Each is used
in conjunction with other organic coagulants as control
mechanisms for pH. This is especially true when using lime
since the high pH maintenance is so important. Both soda ash
and caustic soda are alkaline while carbon dioxide is acidic in
solution with the formation of carbonic acid.
Numerous organic polymers are available which possess
equivalent or superior coagulating properties to the inorganics
without many of the handling problems. These generally func-
tion by means of interparticle bridging or by charge neutraliza-
tion. Sometimes a polymer is used in conjunction with an inor-
ganic coagulant to enhance the coagulating process even
more. In this case, the polymer is considered to be a coagulant
aid.
Polymers are purchased in both powdered and liquid forms.
However, the liquid is more convenient in that it may be used
directly, thus eliminating the need to make up working solu-
tions. Because many polymers tend to cake upon small addi-
tions of water, direct use of powders may cause line plugging
at the point of discharge into a wastewater stream. Caution
must be observed in either case to prevent spillage. Polymers
possess a lubricating property which presents a safety hazard
if left unattended on walkways. A chlorine solution can be used
to clean up a spilled polymer.
28.413 Testing Coagulants for Dosage Selection
The most accepted testing procedure for both coagulant
dose and the determination of optimum coagulating conditions
is the jar test. The jar test is especially versatile in that it is able
to simulate, on a batch basis, the conditions expected to take
place in the coagulating operation. In essence, it is a bench-
scale model of the actual plant process in which a sample of
the water to be treated is given the same sequence of opera-
tions that it would have on a full scale. A special jar test ap-
paratus (Fig. 28.35) is used consisting of a lighted platform
over which are suspended several paddles (usually six) on a
single drive mechanism. The speed of the paddles can be
altered so as to simulate both the rapid mix and the flocculation
operations. Clarification is simulated by turning the paddles off.
The jar test uses up to six separate samples of the raw
wastewater set on the apparatus. The motor is turned on and
the paddles are set rotating at a speed corresponding to that of
the rapid mix of the plant being modeled. Rapid mix continues
for a duration which approximates the normal residence time of
a plug of water passing through the rapid mix tanks. The pro-
posed concentrations of the coagulant to be used are added to
separate vessels at a point similar to the actual rapid mix,
usually at the start of the test.
17 Hygroscopic (HI-grow-SKOP-ic). A substance that absorbs or attracts moisture from the air.
-------
t* Industrial Waste Treatment 615
Jar Test Apparatus
Top View
dr A- A.
©
^ t 1
J Z
1
r
i i,
B
n
1
I'" J
y
L_
Fig. 28.35 Jar test experiment
-------
616 Treatment Plants
Upon completion of the rapid mix simulation, the paddles are
slowed to imitate the speed of the flocculation paddles. Once
again, duration is that which is estimated as the time neces-
sary for a plug of water to pass through the flocculators. Upon
completion of this stage, the paddles are shut off, and the
mixture is allowed to settle quiescently for approximately 10 to
30 minutes or for whatever time is necessary for the bulk of the
particles to precipitate. Visual inspection is made of the settling
characteristics of each dose. Supernatant may be decanted
and tested for turbidity, color or some other measure of effec-
tive removal of suspended matter. From such observations,
the optimum coagulant dose can be selected.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 699.
28.4A List the operations involved in chemical coagulation.
28.4B What is coagulation?
28.4C What is flocculation?
28.4D What can happen if the rapid mix is too long?
28.4E Why are polymers considered more convenient in the
liquid form?
28.42 Description of Equipment
28.420 Storage and Delivery of Coagulant
Coagulants can be divided physically into two categories,
liquid and solid. The physical category will necessarily dictate
the type of equipment necessary to accommodate it.
Solids may be dissolved before actual use and thereby may
use some equipment similar to that for liquid coagulants. Stor-
age of all inorganic solids should be in dry tanks or bins be-
cause almost all inorganic solids exhibit caustic or corrosive
properties if they become moist. Bins for powdered solids gen-
erally will be provided with a dust collector to keep the material
ventilated as well as contained as a precaution against flash
combustion. Exit to the feed system is often assisted by a
shaker or vibrator to prevent caking of the material. In the case
of some limes, a slaker is often found at this point.
Solid feed systems are of three types — volumetric, belt
gravimetric or loss-in-weight gravimetric. Volumetric feeders
are generally screw type (Fig. 28.36). These may be variable
pitch, in which the screw is tapered from the point of accepting
material to the point of discharge, or they may be a constant
pitch, reciprocating feed systems. The latter has two screws
rotating in opposite directions and has two discharge points
while the former has one discharge.
Belt gravimetric feeders consist of a feed belt and a weight
control system. The rate of feed may be changed either by
varying the ratio of weight accepted per foot of belt or by in-
creasing the belt speed. In the case of volumetric, the quantity
of feed is fixed by the size of the screw and the feed rate may
be varied by adjusting the speed of the screw.
OPTIONAL
HOPPER
AGITATOR
ECCENTRIC
DRIVE ,
FEEDER
PULLEY
CONTROL BOX
HOPPER AGITATING PLATE
ROTATING FEED SCREW
MOTOR
OPTIONAL
FEEDER
DOWN-SPOUT
AND TANK
GEAR REDUCER
AGITATOR
Fig. 28.36 Volumetric screw feeder
(Permission ol Wallace & Tiernan Division, Pennwalt Corporation)
-------
The most accurate solid feed system is the loss-in-weight
(gravimetric) in which both the material hopper and feeding
mechanisms are located on enclosed scales. The feed rate
controller reacts to the scale poise weight, thereby delivering
the chemical at the desired rate.
Liquid coagulants may be delivered by any one of a number
of systems including plunger pumps, positive displacement
diaphragm pumps (Fig. 28.37), centrifugal pumps and rotodip
pumps. Positive displacement pumps (rotary) (Fig. 28.38)
must have a recirculation line back to the storage tank to pre-
Industrial Waste Treatment 617
vent excess flow causing rupture due to back pressure.
As previously noted, many solids are converted to liquid
form before entry into the system. This is especially true with
lime (Fig. 28.39), caustic (Fig. 28.40), alum and organic
polymers, (Figs. 28.41 and 28.42). In such cases, measured
amounts of the dry chemical are passed to a make-up or slurry
tank in which a desired fluid dilution is made. Dry chemicals
may also be added directly under the assistance of water jets
spraying at the points of entry. The latter method is an accept-
able means of delivering dry polymer.
DIAPHRAGM
OIL PUMP
RETURN SPRING
PUSH ROD
BALL BEARING
ECCENTRIC
BALL BEARING
INPUT SHAFT
a WORM
DISCHARGE
VALVE
SUCTION
VALVE
SILICONE
OIL
BALL
DISCHARGE
VALVE
DRIVING
DIAPHRAGM
SILICONE Oil
TFE DIAPHRAGM
SUCTION VALVE
STROKE ADJUSTER
ADJUSTING WEDGE
RETURN SPRING
PUSH ROD
BEARING
ECCENTRIC
BALL BEARING
INPUT SHAFT
& WORM
Fig. 28.37 Positive displacement diaphragm pumps
(Permission of Wallace & Tiernan Division, Pennwalt Corporation)
-------
o>
—L
00
(D
tt
B
3
01
3
(0
FROM
Watt
Supply
Liquid
Chemical
Supply
(Option)
Vibrator
Positive
V*nt illation
Chamcal
Pump
Spr»y
Mixing Tank
Dump \Wv»
I
TO Plant Chemical
Feed Pump
Fig. 28.38
Positive displacement rotary solid feeder
(Permission of Neptune Microfloc)
-------
Industrial Waste Treatment 619
OUST COLLECTOR
FILL PIPE (PNEUMATIC)
BULK STORAGE
BIN
NOTE: VAPOR REMOVER
NOT SHOWN FOR CLARITY
BIN GATE
FLEX IBLE
CONNECTION
FLOW RECORDER
WITH PACING
TRANSMITTER,
FEEDER
pH RECORDER
CONTROLLER
SCALE
OR SAMPLE CHUTE
SOLENOID
VALVEv
ROTAMETERS
| LIME
ISLAKER
SLAKING WATER
DILUTION WATER
ROTOD IP-TYPE
FEEDER.
I XER
RELIEF
VALVE
PRESSURE
FEED
LEVEL
PROBES
GRAVITY FEED
TRANSFER
PUMP —
RECIRCULATION
METERING
PUhP-"
HOLDING
TAN K
PRESSURE
VALVE
Fig. 28.39 Typical lime feed system
-------
620 Treatment Plants
-TRUCK FILL LINE
SODIUM HYDROXIDE
STORAGE TANK
-TRANSFER
PUMP
VENT, OVERFLOW
AND DRAIN
DILUTION
WATER
MIXER
DAY TANK
SAMPLE TAP
SODIUM HYDROXIDE
FEEDER
-VENT, OVERFLOW
AND DRAIN
POINT OF
APPLICATION
Fig. 28.40 Typical caustic soda feed system
-------
industrial Waste Treatment 621
-DRY
FEEDER
DISPERSER
WATER SUPPLY-
MIXER
DISSOLVING-AGING
TANK
HOLDING TANK
-SOLUTION FEEDER
POINT OF
APPLICATION
Fig. 28.41 Typical schematic of a dry polymer feed system
-------
622 Treatment Plants
HOT
WATER
SOLENOID
I VALVE
-SCALE
DISPERSER
DRY
FEEDER
SPERSER
MIXER
PRESSURE
REGULATOR
FEEDER
LEVEL
PROBE
MIXER
LEVEL PROBE
CONTROL
METER
VALVE
MIXING-AGING
TANK
MIXING-AGING
TANK
WATER
BLENDER
NOTE: CONTROL & INSTRUMENTATION
WIRING IS NOT SHOWN
TRANSFER PUMP
SOLUTION
FEEDERS.
POINT OF APPLICATION -*r-
HOLDING TANK
LEVEL PROBE
Fig. 28.42 Typical automatic dry polymer feed system
28.421 Mixing Units
Rapid mixing may be accomplished in one of three modes:
(1) high-speed mixers (impeller or turbine), (2) in-line blenders
and pumps, and (3) baffled compartments or pipes (static mix-
ers). The use of high-speed mechanical mixers is most com-
mon. They are often seen in parallel to increase residence
time. Static mixers make use of fluid passing through baffled
chambers at high velocities to bring about turbulence and mix-
ing. In-line blenders and pumps accomplish the same by virtue
of a high velocity.
28.422 Flocculators
Mechanical flocculating units (Fig. 28.43) may be rotary,
horizontal shaft-reel type, rotary-shaft turbine or rotary recip-
rocating. All three rotary systems possess vertical shafts.
Standard rotary and rotary reciprocating units use paddle im-
pellers, the latter consisting of more than one shaft rotating in
opposite directions.
In all flow-through flocculators, tapered flocculation is found
to be most beneficial. By this method, a small dense floe is
formed initially followed by aggregation to form a more dense,
dispersed floe. This is accomplished on single shafts by varia-
tion of the paddle sizes. On multiple-shaft units, variation of the
speed of the individual units and/or the number of paddles per
shaft is effective.
28.423 Clarlflers (Also see Chapter 5, "Sedimentation and
Flotation.")
Clarifiers can take on two basic configurations (Fig. 28.44)
based upon the flow character, that is, vertical or horizontal
flow. Horizontal flow is the most common, taking on both rec-
tangular and circular configurations.
-------
Industrial Waste Treatment 623
CONTROL w| lvE
Mechanical Flocculation Basin
Horizontal Shaft-Reel Type
MOTORIZED SPEED REDUCER
FLEXIBLE COUPLINO
FLOCCULATION
BASIN ,
MULTI-STAGE
V PADDLES
MIXING
BASIN
GUIDE BEARING
WATER- PRESSURE LUBRICATEO
Mechanical Rocculator
Vertical Shaft — Paddle Type
(Courtesy of Ecodyn* Corp.)
Fig. 28.43 Mechanical flocculators
-------
624 Treatment Plants
EFFLUENT
SLUDGE
N FLU EN T
(a)CIRCULAR CENTER-FEED CLARI F I ER WITH
A SCRAPER SLUDGE REMOVAL SYSTEM
INFLUENT
EFFLUENT
lv i-*. SLUDCE
(b)CIRCULAR RIM-FEED, CENTER TAKE-OFF CLARIFIER WITH A
HYDRAULIC SUCTION SLUDGE REMOVAL SYSTEM
INFLUENT
* EFFLUENT
SLUDGE
fc) CIRCULAR RIM-FEED RIM TAKE-OFF CLARIFIER
Fig. 28.44 Typical clarifier configurations
Rectangular clarifiers (Fig. 28.45) with horizontal flow have
the influent entering at one end. Flow generally hits a baffle
and moves by gravity to the opposite end where the effluent
overflows the outlet weirs. A surface skimmer made up of
flights pushes oil and floating debris to a spiral collector located
at one end. Settled sludge is moved by flights along the bottom
to a sludge hop per where it is collected and pumped to a
dewatering facility.
Circular clarifiers with horizontal flow take on one of three
configurations.
1. Center influent with radial effluent,
2. Radial influent with center effluent, and
3. Radial influent and effluent.
In each case, sludge is collected at the center of the conical
base. Oil and scum are skimmed by a radial arm at the surface
of the water which deposits the material into a sump.
Vertical flow units (Fig. 28.46) have the general distinction of
the influent flowing along the bottom and rising toward the top
to be discharged over the effluent weir. One advantage of
vertical flow clarifiers is that flow can be forced up through the
sludge blanket, thus aiding in solids retention and improving
flow control. Both rectangular and circular configurations exist.
-------
Industrial Waste Treatment 625
DRIVE SPROCKET
INFLUENT
ESS FOR
/ DRIVE CHAIN
KE UP
WATER LEVEL
••*s_
FLOW
SKIMMING
T
AVERAGE
WATER
DEPTH
CHAIN S FLIGHT
CROSS COLLECTOR
SLUDGE HOPPER
I m'I .11
v.\
i
ADJUSTABLE WEIRS
T~
2 *6 FLIGHTS
:i?'
PIVOTING FUGHT-
'ughtJ
EFFLUENT
E2
A. WITH CHAIN AND FLIGHT COLLECTOR
TRAVELING
BRIDGE
BRIDGE
TRAVEL
SCUM
TROUGH
COLLECTING
SKIMMING
INFLUENT
WATER LEVEL
SKIMMING POSITION
3LUD0E COLLECTION POSITION
EFFLUENT
SCREW CROSS
COLLECTOR
i'1 '
SLUDGE
HOPPER
B. WITH TRAVELING BRIDGE COLLECTOR
Fig. 28.45 Rectangular sedimentation tanks
(Courtesy of FMC Corp.)
-------
a>
ro
CT>
TREATED WATER
EFFLUENT
CLEAR WATER
SEPARATION *
RAPID MIXING AND RECIRCULATION
SLOW MIXING AND FLOC FORMATION
CHEMICAL INTRODUCTION
> ' *:#if
•••
:.v>.
'••v-
W' . -A:
: i
. Y
si
^'•v^Y
sM
CLARIFIED
WATER
. RAW WATER
INFLUENT
SLUDGE RECIRCULATION
SEDIMENTATION
(0
0)
1
re
3
0)
5
CO
SLUDGE REMOVAL
Fig. 28.46 Solids contact clarifier without sludge blanket
infiltration
(Courtesy of Econodyne Corp.)
-------
EFFLUENT COLLECTOR FLUME
AGITATOR
CHEMICAL FEED INLETS
INFLUENT
SKIMMING
SLOT
FFLUENT
SLUDGE
BLOW-OFF
LINE
SAMPLE CONNS.-
SWING SAMPLE
INDICATOR -
MIXING
ZONE
AGITATOR
ARM
BAFFLES
NSLUDGE
CONCENTRATOR
PRECIPITATOR DRAIN
Fig. 28.47 Solids contact clarifier with sludge blanket filtration
(Courtesy o! the Permutit Co.)
-------
628 Treatment Plants
Circular configurations have solids contact units in which all
three activities leading up to and including coagulation and
precipitation take place (Fig. 28.47). Influent becomes rapidly
mixed with the coagulant at the influent discharge and flows
down through a center baffle. Flocculation occurs in this zone.
Flow proceeds radially upward through the sludge blanket and
clarification occurs. Effluent discharge is radial.
Rectangular configurations may have tube and lamella
separators in which settling becomes compartmentalized.
Tube settlers (Figs. 28.48, 28.49, and 28.50) consist of a col-
lection of closely packed small-diameter tubes placed at an
angle. Flow proceeds upward as sludge settles downward.
The use of parallel plates rather than tubes is the distinction of
a lamella separator. Flow in this case is concurrent. Both con-
figurations depend upon the assumption that the paths of all
discrete particles with the same settling velocities will be
straight parallel lines. In the above two configurations, the sur-
face area of the clarifier is effectively increased without in-
creasing the actual size.
28.43 The Precipitation Process
28.430 Factors In Design Consideration
The operator should consider at least four factors in the
design of a clarifier. These are detention time, weir overflow
rate, surface loading rate, and solids loading. Each of these
factors is readily calculated and will give the operator an indica-
tion of clarifier efficiency.
DIRECTION OF
FLOW
TO SLUDGE
COLLECTION
Fig. 28.48 Tube settlers - flow pattern
Detention time is the length of time it would take a plug of
water to enter a clarifier and to exit in the effluent. This is
related to clarifier efficiency in that particles should be allowed
ample time to settle out. If the detention time is less than the
settling rate, then there will be a carryover of particles into the
effluent. Detention time is calculated knowing the flow and tank
dimensions as follows:
Tank Volume, = Length, ft x Width, ft x Depth, ft
cu ft
or
Tank Volume, = Length, m x Width, m x Depth, m
cu m
and
Tank Vol, cu ft x 7 48 9al x
Detention = cu ft daV
Time, hr Flow, gal/day
or
Detention = Tank Vol, cu m x 24 hr/day
Time, hr Flow, cu m/day
If the detention time proves to be less than the settling rate
(as shown by results of laboratory tests), then it may be neces-
sary to increase the clarifier capacity by placing other basins
into operation.
The weir overflow rate expresses the quantity of water which
passes out of the clarifier in relation to the lineal feet of weir
available. Weir overflow rate is expressed as follows:
Weir Overflow Rate, = Flow, gal/day
gpd/ft Length of Weir, lineal feet
or
Weir Overflow Rate, = Flow, cu m/day
cu m/day/m Length of Weir, m
Surface loading rate expresses the quantity of water being
treated in relation to the available clarifier surface. As previ-
ously stated, sedimentation efficiency increases with in-
creased surface area. Surface loading rate may be expressed
as follows:
Surface Loading Rate, = Flow, gal/day
gpd/sq ft Clarifier Surface Area, sq ft
or
Surface Loading Rate, = Flow, cu m/day
cu m/day/sq m Clarifier Surface Area, sq m
Another very important loading guideline for clarifiers is the
solids loading. Solids loadings are especially important for in-
dustrial waste treatment because the solids carried by indus-
trial wastewater may be significantly different from solids in
municipal wastewaters.
Solids Loading, = Solids-lbs/hr
lbs/hr/sq ft Clarifier Surface Area, sq ft
or
Solids Loading, = Solids' W"
kg/hr/sq m Clarifier Surface Area, sq m
The above characteristics are useful when compared with
the original design considerations and specifications in at-
tempting to diagnose the possible causes for clarifier ineffi-
ciency. These, coupled with the results of laboratory tests,
such as dye tracer studies, will aid the operator in troubleshoot-
ing clarifier performance problems.
Other physical characteristics will also affect clarifier effi-
ciency. One important feature is the settling characteristics of
the particles. Settling rate may be affected by many factors
including particle size, shape, temperature of the surrounding
water and particle weight in relationship to that of the surround-
ing water. Particles of greater weight and density will settle
faster than those of lesser density. The horizontal velocity and
the tank depth will also come into play in determining how long
it takes a particle to settle.
-------
Industrial Waste Treatment 629
Fig. 28.49 Module of steeply inclined tubes
(Courtesy Neptune Microfloc, Inc.)
A particle settling quiescently (in still water) will tend to settle
in a path perpendicular to the settling surface. With flow
through a clarifier, force is applied to a particle causing it to
settle in a plane diagonal to the settling surface. Since it now
has a longer path to travel, the particle will take slightly longer
to settle.
The ultimate settling velocity of the particle will be affected
by the flow, the viscosity of the water and the settling charac-
teristics of the particle. Temperature may play a vital role in the
settling characteristics of the particle. With decreasing temper-
ature, water becomes more dense and more viscous. Con-
sequently, the space between the water molecules becomes
more restricting on the particle's ability to settle. Increased
temperature has the opposite effect. Settling rate is therefore
greater at a warmer temperature than it is at a lower tempera-
ture.
SHORT-CIRCUITING18 of flow can adversely affect clarifier
efficiency. This occurs when the flow is not homogenous
(completely uniform) throughout the tank. That is to say, there
exist zones or layers where the flow is either faster or slower
than the surrounding areas. If velocity is too high in an area,
suspended material may pass out of the clarifier without set-
tling. Too slow a velocity will cause dead spaces with the
danger of an induced septic condition (assuming the presence
of organic or other biologically degradable material).
Short-circuiting may be caused by differences in water den-
sity due to different temperatures existing at the surface and
the bottom of the clarifier. This is especially true in temperate
climates during the winter and summer seasons. Density dif-
ferences may also be induced by a high suspended solids
content in the influent. Short-circuiting may be made worse by
high inlet velocities, high outlet weir rates, and strong winds
blowing along the tank surface. In all cases, the most effective
solution is the use of weir plates, baffles and port openings to
produce a flow velocity throughout the clarifier that is as even
as possible.
18 Short-circuiting. A condition that occurs in tanks or ponds when some of the water or wastewater travels faster than the rest of the flowing
water.
-------
630 Treatment Plants
'V/y'/V, '/ V.
'///// './/.-y. v.-?//.
r
ty.'/s/ssvs.'/;///, W/7VZ"'
TUBE SETTLERS IN EXISTING CLARIFIER
SUPPORT MODULE
TUBE SETTLER
MODULES
Fig. 28.50 Plan view of modified clarifier
-------
28.431 Clarifier Efficiency
Clarifier efficiency may be defined as the percent of a pollu-
tant removed by the clarifier. Efficiency should be based upon
the analysis of both inlet and outlet samples composited over a
24-hour period. Calculation is as follows:
Efficiency, %= — ~ 0ut x 100%
In
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 699.
28.4F List the three common modes of rapid mixing of
coagulant chemicals.
28.4G What is tapered flocculation?
28.4H What is an advantage of vertical-flow clarifier units?
28.41 List the four factors that are considered in the design
of clarifiers.
28.4J What happens if the detention time in a clarifier is too
short?
28.4K List the possible causes of short-circuiting.
Safety
28.440 Safety In Handling Coagulant Chemicals
1. Avoid getting inorganic coagulants on the skin or in the
eyes. These chemicals are either corrosive or caustic and
cause irritation and possibly permanent damage. Areas
contacted should be flushed immediately with water. In the
case of dry chemicals, attempt to mechanically wipe or
brush off as much as possible before flushing.
2. POLYMERS MIXED WITH WATER ARE EXTREMELY
SLIPPERY and can cause a fall hazard if left unattended on
walkways. Spills should be cleaned immediately with
generous portions of water.
3. Gases under pressure should be stored in a cool location
and secured tightly to a vertical support. Areas should be
properly labeled to designate hazard of flammability, corro-
siveness or other applicable type of hazard.
Industrial Waste Treatment 631
24.441 Safety Around Machinery
1. Avoid placing extremities (parts of your body) into any mov-
ing part of machinery.
2. Be aware of areas where piping may be subject to high
pressure.
3. Be sure all power is turned off and appropriately tagged
before working on a piece of machinery for either mechan-
ical or electrical malfunction.
28.442 Other Hazards
1. Be aware of causes for falls. Avoid clutter. Clean grease
and oil and polymer spills immediately.
2. Always be aware of a drowning hazard around open basins.
Make use of handrails in all work locations. Approach ba-
sins through areas which have appropriate walkways. In-
sure the availability of life preservers in work areas.
28.45 Operation, Start-up and Maintenance
28.450 Start-up Maintenance Inspections
The following represents a general start-up inspection
checklist; however, it will also be found meaningful in an over-
all maintenance format. Because of the diverse nature of in-
dustrial wastewater treatment plants and the broad differences
from one manufacturer's equipment to another, it is suggested
that the manufacturer's specifications be consulted for more
in-depth maintenance procedures. For simplicity and to avoid
duplication, some items have been grouped under equipment
type rather than process stage.
A, General
1. Determine that all tanks, basins and piping are clean
and free of debris.
2. Insure that all drawings, equipment manufacturer's
specifications and operating manuals are complete,
up-to-date and available.
3. Verfiy that the correct spare parts are on hand.
4. Insure the proper operation of all Start-Emergency-
Stop controls both on site and at the control panel.
Check all electrical connections and power supplies.
5. Insure that all piping and valves are properly installed
and adequately braced.
B. Motors and Drives
1. Insure that all motors and drives are securely fastened.
Check bearing supports, shaft alignments to drive
motors and belts (for both condition and tightness).
2. Insure proper lubrication of motors, drives, shafts,
chains and bearings according to the manufacturer's
specifications.
3. Verify that motors run at the speeds prescribed and
that all voltage requirements are satisfied.
4. Insure that chains move freely without binding.
5. Insure that all chain guards are in place.
6. Insure that motor rotation is correct.
C. Pumps
1. Piston Pumps. Check ball seatings, packing, shear pin,
drive belts and/or hydraulic fluid.
-------
632 Treatment Plants
2. Centrifugal Pumps. Check impeller for wear or plug-
ging. Check for prime. Check packing.
3. Positive Displacement Pumps. Check screw and rotor
for wear or plugging. Check prime and packing.
4. Diaphragm pumps. Be sure that diaphragm is intact
and working properly.
D. Chemical Feed Systems
1. Insure that all level alarms in tanks are functioning
properly.
2. Insure proper calibration of all flow and metering sys-
tems.
3. Insure that water blenders operate properly and check
dilution mixers for proper placement and installation.
4. Insure proper temperature and pressure for dilution
water.
5. Insure in-line mixers are in place, properly braced with
accommodation for proper bypass.
E. Gates for Control of Flow
1. Insure all gates properly aligned in angles and for travel
clearance.
2. Insure proper lubrication of wheels and rising stems.
3. Insure proper operation in both automatic and manual
modes.
F. Rapid Mix
1. Inspect impeller condition. Insure that impellers are
free from obstruction.
2. Check motors and drives as per above (B).
G. Flocculators
1. Check motors and drives as per above (B).
2. Insure baffles are correctly set and securely anchored.
3. Insure that drive stuffing box is properly placed and
grouted.
4. Insure that drive bearing and sprocket are complete.
5. Insure that mixers rotate freely before coupling to the
gear drive.
6. Insure that sump pumps are in place and operational.
H. Clarifiers
1. Check motors and drives as per above (B).
2. Insure that all sprockets and shafts are in alignment
and free for the rotation of the sludge collectors.
3. Lube all rails. Run collectors in empty tank (dry) for two
hours before allowing the water into the flocculation
tank.
4. Insure all flights are connected to the chain and that all
shoes are attached.
5. Check that all drive sprockets are operational. Insure
that shear pins are installed in all sprockets,
6. Check the operation of limit switches to insure that they
stop the motor.
7. Check cross-collector travel.
I. Scum Collectors
1. Insure that the collectors and trough are properly se-
cured and aligned.
2. Insure that the wiper blade on the spiral collectors has
proper uniform contact with the breaching plate.
28.541 Actual Start-up
The following constitutes a general pattern to be followed
when placing the entire system on-line. Sections may be
applied to the start-up of an individual part.
A. Chemical Feed System
1. Insure proper temperature for dilution waters, if appli-
cable.
2. Check that proper chemical strengths are set on au-
tomatic feeds.
3. Open all manual valves, as appropriate.
4. Set proper flow rate.
B. Mixing Tank
1. Open effluent gates.
2. Allow tanks to fill.
3. Start mixers and adjust speed.
C. Flocculation Tanks
1. Open influent gates.
2. Turn on and adjust paddle drives.
D. Clarifiers
1. Turn on cross-collectors and longitudinal collectors.
2. Start scum collectors.
3. Allow basins to fill.
28.452 Operational Strategy Checklist
A general procedure for the normal operation of a chemical
coagulation-precipitation system is discussed in the following
paragraphs.
A. Chemical Feed System
1. Perform a jar test to determine the proper chemical
dosage.
2. Insure proper chemical dilution.
3. Set controls for the proper feed rate.
4. Report in the operating log the amount of chemical
used per unit time.
B. Rapid Mixing Tanks
1. Insure proper mixing speed by observing the floe
formed.
2. Check for scum formation. If scum accumulates in the
influent, open the scum gates. If scum is floating in the
tanks, adjust the mixer speed. Should the condition
persist, open the slide gates and allow it to pass
through the effluent.
3. Only operate mixers when the tank is filled to capacity.
4. Do not allow mixers to be off for an extended period
while material is still in the tank.
-------
Industrial Waste Treatment 633
Flocculation Tanks
1.
2.
Adjust agitation so that particles receive just enough so
as not to settle.
Check to see that chemical is being added if no floe
forms (see Section 28.453 on Troubleshooting).
3. Adjust all paddles to the same speed unless:
a. Sludge formation occurs at one point. Increase the
paddle speed for this area.
b. Coagulant is added at the floe tanks. Increase the
tip speed of the mixers immediately preceeding the
point of discharge.
c. Coagulant added in the influent channel. Increase
the tip speed of the first mixer.
28.453 Abnormal Operating Procedures and
Troubleshooting
D. Clarifiers
1. If possible, all tanks should be kept in operation since
the best sedimentation occurs with the greatest
amount of the surface area.
2. Sludge control. Level should be kept at a minimum.
3. Never store sludge in the clarifiers. Move it to the thick-
eners for storage.
4. Scum Removal. Check periodically.
Skimmer. Clean daily.
Scum pit. Clean after each pumping.
5. Clean weirs, scum baffles and launders daily.
The following represents a guide to the types of problems an operator should look for with possible causes and solutions.
Problem
Excess scum buildup
Too small floe
Too large floe, settles too soon
Floating sludge
Loss of solids over effluent weir
Thin sludge with deep sludge blanket
Sludge collector, jerkey operation or inop-
erable
Cause
Scum collection device
Improper chemical dosage
Low chemical metering
Chemical feed pump adjusted too low
Paddle speed in flocculators or rapid mix
too fast
Short-circuiting
Change in pH
Improper chemical dosage
Metering setting
Chemical makeup too strong
Too little dilution water
Paddle speed in rapid mix orflocculator too
slow
Coagulant aid added at wrong point
Sludge collectors not functioning properly
Sludge pumping system malfunction
Change in influent character or flow rate
Excess coagulant aid
See too small floe problem above
Improper or misaligned baffling
Cross collectors not functioning
Broken sprocket, chain link, flight or shear
pin
Sludge blanket too deep
Solution
Inspect scum trough, spiral screw and
scum pumps.
Check dosage with jar test.
Adjust metering.
Adjust feed pumps.
Decrease paddle speed.
Baffling changes, adjust weir plates or port
openings.
Neutralize pH.
Check dosage with jar test.
Check and adjust metering.
Check makeup and adjust feed.
Check and adjust metering of dilution wa-
ter.
Increase paddle speed
Optimize point of coagulant aid addition (in
rapid mix, before flocculator, in flocculator).
Check motors, chains, drives and belts for
smooth operation.
Check sludge pumps for operation, pipes
for debris. Switch to standby pump.
Check dosage with jar test and adjust.
Check dosage with jar test and adjust.
Adjust baffling at inlet and outlet.
Check motors, drives and chains for cross
collectors.
Inspect and repair.
Pump out sludge. May have to drain basin
and remove manually.
-------
634 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 699 and 700.
28.4L How should gases under pressure be stored?
28.4M What are some of the causes of falls?
28.4N List the items you would check during the start-up in-
spection of a chemical feed system.
28.40 List the procedures you would follow for the normal
operation of a chemical coagulation-precipitation sys-
tem.
&
&UP Of
IN0U6T(2ial1Iua6T6 iKgAfMgjOT
Please work the discussion and review questions before
continuing. The question numbering continues from Lesson 4.
DISCUSSION AND REVIEW QUESTIONS
(Lesson 5 of 6 Lessons)
Chapter 28. INDUSTRIAL WASTE TREATMENT
Write the answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 4.
28. What is the purpose of chemical coagulation?
29. Why is paddle speed important during flocculation?
30. What happens to inorganic solids used as coagulants if
they become moist?
31. Why is the solids loading especially important in the de-
sign of clarifiers treating industrial wastes?
32. Why should operators have an understanding of the origi-
nal design considerations for clarifiers?
33. What is the most effective cure for short-circuiting?
34. What would you do if a dry coagulant chemical came in
contact with your skin?
-------
Industrial Waste Treatment 635
CHAPTER 28. INDUSTRIAL WASTE TREATMENT
(Lesson 6 of 6 Lessons)
28.5 ADSORPTION19 (ACTIVATED CARBON) by John
Gonzales
28.50 Principles of Activated Carbon Adsorption
28.500 Purpose of Carbon Adsorption
The purpose of activated carbon adsorption in wastewater
treatment plants is to remove organic pollutants from the
effluent of the treatment plant (Figures 28.51 and 28.52). Re-
moval of the organic pollutants frees effluent from color, taste-
and odor-causing pollutants which may remain after preceding
wastewater treatment processes. Uses of activated carbon for
foul-air scrubbing is discussed in Chapter 20, "Odor Control."
In areas across the country where fragile environmental sys-
tems exist which require substantial tertiary treatment of a
plant's effluent, the activated carbon process is considered as
an effluent polishing process. The removal of trace amounts of
organic material can be accomplished using carbon adsorp-
tion. The result is a crystal clear water with no odor and a
biochemical oxygen demand in the effluent of almost zero.
28.501 How Does Carbon Adsorption Work?
Activated carbon can remove trace amounts of organic ma-
terial from effluent by the attraction and accumulation of the
particles to the surface of the carbon. This is the definition of
adsorption. Particles adhere to the surface of the activated
carbon very much like a magnet attracts particles of iron. As
wastewater passes through a field of activated carbon, any
pollutants or contaminants that can be adsorbed onto the car-
bon surface will be attracted. Once the molecules of organic
material have been attracted to the surface, the activated car-
bon will continue to accumulate the organic material until it can
no longer adsorb any more.
28.502 The Manufacture of Activated Carbon
Activated carbon can be produced from wood, coal, nut-
shells, bone, petroleum residues or even sawdust. The mate-
rial utilized to make activated carbon must be a carbonaceous
material in order for the material to go through a process of
carbonization.
Carbon is activated by drying the raw material and slowly
heating it in the absence of air. The result is an activated
carbon that can still burn. However, the lower the heating tem-
perature, the better are the volatile substances driven off but
extreme heat is required to burn the remaining residue to pro-
duce the activated carbon.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 700.
28.5A Why is the activated carbon adsorption process used
to treat wastewater?
28.5B What materials may be used to make activated car-
bon?
28.5C How is activated carbon made?
28.51 The Carbon Adsorption Process
28.510 General Physical Principles
During production of activated carbon, the carbon particles
are put into contact with a water vapor or steam and water
while the carbon particles are still very hot. The result is a
fracturing of the carbon to produce small cracks or fissures
within each of the small particles. These fissures are used in
the attraction and adsorption process.
Molecules of organic materials which pass by the carbon
particles are attracted and held to the surface of the carbon.
Some smaller molecules may find their way into the pores or
the fissures which were produced during the quenching or
cooling cycle of the carbon manufacturing process. Other par-
ticles may be trapped on the surface or wedge themselves into
the larger part of the fissure opening at the surface of the
carbon particle.
28.511 Equipment Necessary for Carbon Adsorption
The most commonly used equipment for carbon adsorption
is a pressure tank (Figure 28.53) filled with activated carbon.
The standard method of operation is to use an upflow carbon
adsorption pressure vessel (Figure 28.54). The reason for an
upflow pressure vessel is to allow adequate detention time
within the chamber for adsorption of the organic material in the
effluent waters. A pressurized upflow carbon contact chamber
(Figure 28.55) will help eliminate short-circuiting that is com-
mon in downflow pressure vessels. Also, flow is easily regu-
lated in upflow and it is possible to fill the carbon contactors
with new granular carbon even while flow is continuing to the
vessel. Although pressurized contact chambers are the most
common, both upflow and downflow gravity activated carbon
contactors are used to treat industrial wastewaters.
'• Adsorption (add-SORP-shun). The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another sub-
stance.
-------
636 Treatment Plants
CHEMICAL
COAGULATION AND
$CO!MCWTA7fON
(OPTIONAL!
MAKEUP
CARBON
CARSON
REGENERATION
FILTRATION
CARBON
ADSORPTION
DISINFECTION
PRELHMNARV
TREATMENT
¦IOLOOICAL
TREATMENT
MAKEUP
CARSON
CARSON
REOCNERATION
CARftO*
AOSORPTION
DISINFECTION
StTTLINO
•IOLOOICAL
TREATMENT
(b)
CARiON
ION
EXPANOIO
UPPLOW
CARiON
AMOftPTIO*
DISINFECTION
PflBLIMMANV
TRIAT1HNT
-------
Industrial Waste Treatment 637
COAGULANT
MAKEUP
CARBON'
CARBON
REGENERATION
DISINFECTION
PRELIMINARY
TREATMENT
CARBON
ADSORPTION
CHEMICAL
CLARIFICATION
FILTRATION
<•>
COAGULANT
PRELIMINARY
TREATMENT
MAKEUP
CARBON
CARBON
REGENERATION
DISINFECTION
CHEMICAL
CLARIFICATION
FILTRATION
EXPANDED
UPFLOW
CARBON
ADSORPTION
lb)
.COAGULANT
PRELIMINARY
TREATMENT
CARBON
ADSORPTION
DISINFECTION
CARBON
REGENERATION
CHEMICAL
CLARIFICATION
10
Fig. 28.52 Typical physical-chemical treatment schemes
(Source: Process Design Manuel lor Carbon Adsorption, Technology Transfer, U.S. Environmental Protection Agency.)
-------
638 Treatment Plants
Fig. 28.53 Carbon columns
-------
Industrial Waste Treatment 639
CARBON
FILLING
HYDRAULIC
GRADIENT
EFFLUENT
MANIFOLD
I" W.S.
EFFLUENT
34" WJ.
EFFLUENT
HEADER.
TRANSFER
JET HCAOER
INFLUENT
MANIFOLD
It" W.»
EFFLUENT
HEADER
»" WJI.
DRAIN
8" FLOW
REVERSAL
LINE
8" W.S.
EFFLUENT
EFFLUENT
MANIFOLD
8" FLOW
REVERSAL
LINE
1 r-O*" DIAM.
DALL
COLUMN
DALL
FLOW
TUBE
10" BYPASS
El:
HEADER
INFL.
r* G.S. SPENT
ARBON LINE
r aw
0" WAFER
STOCK VALVE
8" W.S. DRAIN
24" W.S.
EFFLUENT
10" BYPASS
INFLUENT
FRONT VIEW
SIDE VIEW
Fig. 28.54 Upflow countercurrent carbon column
Orange County, California
-------
640 Treatment Plants
CARBON IN
TOP WAFER VALVE
SURFACE
OF CARBON
OUTLET SCREENS (8)
PRESSURE VESSEL
12 FT DIAMETER
CM
-------
Industrial Waste Treatment 641
28.512 Pre-Start-Up
1. Proper Quantities of Activated Carbon. To determine the
proper quantity of activated carbon, you can assume that
the desired detention time in the carbon containers is 30
minutes. The amount of carbon provided in each carbon
column should be such that flow through the carbon would
take 30 minutes to complete. Check the levels of carbon by
measuring from the top of the carbon column to the surface
of the granular carbon within the pressure vessel. The vol-
ume of the carbon up to the measurement should be calcu-
lated. This volume should be increased if the detention time
through the calculated volume at the desired flow rate is
less than 30 minutes.
2. Activated Carbon Loading Equipment. Proper piping and
measuring equipment are necessary in order to fill carbon
columns to the proper level within the pressure container.
Equipment for loading activated carbon includes dust con-
trol equipment which will be discussed later in this chapter
and defining equipment for washing the carbon before it
enters the carbon column reactors.
3. Valves and Piping. The standard schematic diagram illus-
trating piping is shown in Figure 28.56. Valving and piping
in and around a carbon container must be flexible. Three-
way valves are usually installed in order to provide both the
upflow conditions necessary for the activated carbon treat-
ment, and also to allow for backwashing of filter screens.
Before placing the carbon reactors on line, the valving
should be checked to ensure that the flow direction is cor-
rect for the operation desired. The operator should know
where each pipe leads and the direction of flow through the
pipe that is desired.
4. Carbon Column Reactors. The carbon column reactors
are also known as the pressure containers which contain
the carbon for the adsorption process. The tank is normally
8 to 15 feet (2.4 to 4.5 m) in diameter and can be 15 to 28
feet (4.5 to 8.4 m) tall. Inside the containers are screens
that prevent carbon from flowing in either direction with the
water. The screens keep the carbon within the pressure
vessel.
The carbon column reactors are lined with an epoxy or resin
to prevent corrosion from the contact of the carbon with the
surface of the vessel. Wet carbon can be very corrosive and
the lining protects the steel used in the manufacturing process
of the pressure container.
28.513 General Operating Procedures
1. Counter-Current Flow Principle. The most common form
of operation of a carbon reactor is an upflow condition.
Effluent enters the bottom of the reactor and flows out
through the top. The counter-current principle is the pro-
cess where flow enters the bottom of the carbon column
and new or regenerated carbon is added to the top of the
container. This allows the oldest carbon to contact the
wastewater first and the newest or more virgin carbon will
make contact with the effluent last. In this manner, the
wastewater is polished as it flows up through the carbon
column.
The counter-current flow principle allows the spent or the
most used carbon to be pulled off from the bottom of the
pressure vessel for regeneration. In this way, a regenera-
tion cycle of burning off the adsorped particles is not wasted
on fresh carbon.
2. The Adsorption Mechanism. Adsorption of organic mate-
rial in wastewater takes place in three steps. The first step
is contact of the liquid to the exterior surface of the carbon.
The second step is disbursement of the liquid within the
pore space of the activated carbon. The third step is the
actual capture of the organic molecules within the pore and
capillary structures of the fissures formed in the manufactur-
ing process.
3. Influent and Effluent Piping (Figures 28.57, 28.58 and
28.59). The influent piping around a carbon column reactor
is at the bottom of the pressure vessel. Valves are usually
located at the bottom of the vessel to allow the normal
upflow conditions through the carbon reactor. The valve
allows flow to enter at an equal basis into ports which open
up and are protected by screens within the container itself.
In this manner, a uniform flow is usually achieved through
the carbon for proper adsorption.
The effluent piping of a carbon column reactor is usually
located at the top of the container. As with the influent
piping, screens are located on the ends of several ports
which discharge effluent from the top of the container. Uni-
form flow is achieved throughout the vessel so that short-
circuiting is prevented by having the number of ports in the
bottom as well as the top or effluent side of the carbon
column.
The piping is versatile in that flow can be up or down
through the carbon column (Fig. 28.60). In this manner, the
screens which hold the carbon within the vessel can be
backwashed to prevent clogging with carbon fines or the
small particles of carbon that adhere to the surface of the
screens.
28.514 Placing Carbon Adsorption Units into Operation
1. Flow into Bottom of Carbon Column Reactor. The first
step in placing a carbon column into operation is to adjust
the valving at the bottom of the column so that effluent from
either filtration units or other treatment units which precede
the carbon columns will enter the bottom of the reactor.
Three-way valves must be aligned so that wastewater will
flow through the bottom of the carbon container and out the
top of the final effluent receiving station.
2. Adjusting Flow Rate Through Adsorption Reactors. A
single valve is usually found on most carbon column reac-
tors. This control valve allows the operator to set the de-
sired gallons-per-minute flow rate through the carbon so
that proper adsorption can take place. After the operator
has opened the bottom valves to allow flow into the bottom
of the carbon column, the flow control valve should be ad-
justed until the exact flow rate desired is flowing through the
carbon and out to the final effluent station.
3. Head Loss Measurements. There is a head loss or loss of
pressure between the bottom of a carbon column and the
top or effluent side of the container. This head loss is ex-
pected since the wastewater must pass through carbon and
thereby create a pressure drop or head loss. When head
losses are too high (operator must check operations man-
ual supplied by consulting engineer to determine the op-
timum head loss), backflushing of screens must take place
in order to cut down the pressure drop. Gages are located
both at the top and bottom of carbon columns, as well as in
the control room. The gages are used to help the operator
determine the head loss readings so as to know when a
backwash cycle must take place. Carbon column screens
are backwashed at least once every eight-hour shift.
4. Sampling Effluent to Determine Amount of Carbon Fines.
To determine whether the screens in the carbon column
reactors are doing an efficient job, sample a portion of the
effluent from the top of a carbon column reactor. The
-------
642 Treatment Plants
EFFLUENT
MANIFOLD.
FLOW
METER
EFFLUENT
RATE-OF-FLOW
CONTROL VALVE
OPEN-
CARBON
'COLUMN
BYPASS
VALVE
CLOSED
FINAL
EFFLUENT
CARBON COLUMN
(TYPICAL)
INFLUENT
INFLUENT
MANIFOLD
3-WAY
VALVE
CLOSED
3-WAY VALVE
CARBON
'COLUMN
INFLUENT
HEADER
VALVE
OPEN
INFLUENT
HEADERx
^WASTE AND
DRAIN LINE
Fig. 28.56 Upflow carbon column schematic, normal operation
Orange County, California
-------
Industrial Waste Treatment 643
CARBON
FILLING
CHAMBER
COMBINATION
AIR VACUUM
RELEASE VALVE
WAFER
STOCK
VALVE
UPPER
(OUTLET)
MANIFOLD
REMOVABLE
UNDERDRAIN
SCREENS
CARBON
LEVEL
(BOTTOM
SIMILAR)
Fig. 28.57 Section through top underdrain
Orange County, California
-------
GALVANIZED
IRON DRAIN
COMBINATION PRESSURE
AIR AND AIR-VACUUM
RELIEF VALVE
PIPE FLANGE ON
PIPE SECTION
FLANGED W.S.
PIPE WELD TO
TANK
UJ
to
TEE
GLOBE VALVE
S.S.
PIPE FLANGE
CARBON
COLUMN
TANK —
THREAD WELL POINT
INTO COMPANION
FLANGE
FLANGED PIPE,
WELD TO TANK
CARBON
COLUMN
TANK
10
REMOVABLE WELL
SCREEN, 304 SS,
W 0.020" OPENINGS.
WELL POINT SCREEN, STAINLESS
STEEL, NO. 20 (0.020")
SLOT OPENING, REMOVABLE.
(FOR 8x30 MESH CARBON)
CLOSED BAIL
BOTTOM. 304 SS
Fig. 28.58 Top and bottom underdrains Fig. 28.59 Air-vacuum relief valve detail
Orange County, California
-------
Industrial Waste Treatment 645
EFFLUENT
MANIFOLD
FLOW
METER
EFFLUENT
RATE-OF-FLOW
CONTROL VALVE
CLOSED
CARBON
'COLUMN
BYPASS
VALVE
CLOSED
\ f
FINAL
EFFLUENT
CARBON COLUMN
(TYPICAL)
INFLUENT
INFLUENT
MANIFOLD
3-WAY VALVE
CARBON
COLUMN
INFLUENT
HEADER
VALVE
OPEN
INFLUENT
HEADER^
WASTE AND
DRAIN LINE
Fig. 28.60 Upflow carbon column schematic, upflow to waste
(Used after adding carbon to columns to flush out fines)
Orange County, California
-------
646 Treatment Plants
effluent should be clear with relatively few specks of carbon
in the sample. If excessive carbon fines are found, the
operator can assume that perhaps the carbon is rubbing too
drastically against the screens causing fine particles to
break off and flow out in the effluent or that a hole exists in
one of the screens allowing substantial amounts of carbon
to flow out in the effluent. A daily check on the relative
amount of carbon fines found in the effluent from the carbon
column reactors is necessary. The carbon fines in many
treatment plants are considered as suspended solids and a
reduction in the amount of carbon fines will hfelp reduce the
suspended solids that must be reported to regulatory agen-
cies.
28.515 Operational Procedures
1. Routine Backflushing of Fine-mesh Screens to Reduce
Head Losses through Carbon Reactors (Figures 28.61).
The screens on each carbon column reactor should be
backflushed at least once during each eight-hour shift. This
will help reduce the amount of carbon fines found in the
effluent as well as reduce head losses through the acti-
vated carbon treatment.
If a carbon reactor requires an abnormally high number of
backflushings during a shift, the operator should check the
instruments and prepare the reactor for an inspection to
determine if any damage has taken place inside the vessel.
Backflushing and downflow will help eliminate air pockets
within the carbon column reactors to prevent short-
circuiting and a loss of efficiency in removal of organics.
2. Daily Check for COD Removal Efficiencies. Daily sampling
and analysis are important to determine the efficiency of the
carbon adsorption process. Chemical oxygen demand
(COD) tests are standard and must be performed daily to
determine the effectiveness of the carbon adsorption on the
removal of organics.
With properly regenerated activiated carbon and appro-
priate flow rates and loading conditions, the carbon process
will efficiently remove a substantial percentage of the chem-
ical oxygen demand from the effluent. If the removal ef-
ficiencies for any carbon column are lower than normal,
regeneration or addition of new carbon may be required in
order to bring the COD removal efficiencies back to proper
levels. The COD removal also depends on flow rates and
detention times within the carbon column reactors.
In order to best understand the operation of each carbon
column reactor, a chemical oxygen demand test should be
performed daily on effluent from each carbon column reac-
tor. The COD test will help determine if any problems are
developing in any of the carbon columns. The problems, if
detected early enough, can be corrected before effluent
quality is below effluent standards.
3. Turbidity Measurements. Although effluent from a carbon
column reactor will usually be very clear and free from
color, a daily turbidity measurement is important as a check
on the operating efficiency. A turbidimeter should be used
to determine whether excess carbon fines are causing high
turbidity in the effluent. The turbidimeter can also be used to
indicate whether color is efficiently being removed by the
activated carbon process.
4. Checks on Various Carbon Column Reactors to Determine
Level of Carbon Remaining in Reactor. The operator should
check at least weekly to determine whether an adequate
amount of carbon remains in each of the carbon column
reactors. If additional carbon is needed, make-up or virgin
carbon should be added to achieve the proper detention
time and ratio of pounds of carbon to chemical oxygen de-
mand removed. The operator should check the operations
and maintenance manual provided by the consulting en-
gineer to assess the exact carbon level desired for each of
the reactors. The weekly check on the level of carbon will
make sure that enough activated carbon is in contact with
the wastewater to do an adequate job in removing organics.
5. Troubleshooting. Each day the operator should
troubleshoot to determine if any abnormal or unusual condi-
tions may exist that could cause trouble in the activated
carbon treatment process. The troubleshooting includes a)
checking head losses for abnormally high head losses
through the reactors; b) checking for excessive carbon
fines in the effluent from the carbon treatment process; c)
backflushing the carbon reactors each shift; d) checking
turbidity of effluent from the carbon adsorption process; e)
checking valving configuration to assure flow direction is
correct and the right valves are open or closed; f) checking
flow rate through carbon column for proper detention time
and adequacy of activated carbon adsorption.
1) Shut off flow at base of carbon column reactor. If it
becomes necessary to shut down the carbon adsorption
operation, the operator must shut off the flow into the car-
bon column reactor by closing the valve at the bottom of the
pressure vessel. If all processes except the activated car-
bon adsorption process are to continue operation, the
operator must be certain to turn the three-way valves prop-
erly so as to redirect the flow from various preceding pro-
cesses to other areas besides the carbon adsorption pro-
cess.
2) By-pass carbon adsorption units. The valving ar-
rangement is flexible so that if desired, the operator can
direct flow to other units besides the carbon column reac-
tors (Figure 28.62). The operator can shut off the carbon
column without losing the pressure in the vessel. This can
be accomplished by shutting off the bottom valves as well
as the effluent flow regulating valve to maintain the liquid
within the carbon column vessel. Keep the carbon columns
pressurized if the shutdown is for only a brief period. How-
ever, if the shutdown of the carbon adsorption process is for
a prolonged period of time, the operator should turn the
bottom three-way valve so that the carbon column will
drain, allowing the activated carbon to dry.
3) Notification of regulatory agency. If carbon adsorption
processes must be shut down, the operator must notify
supervisors and/or the regulatory agency. If standards are
strict on effluent from the treatment plant, so that activated
carbon is required in order to meet standards, any deviation
from the standard flow through the carbon column reactors
will result in a violation of the discharge limitations. The
regulatory agency must be notified so that emergency pro-
cedures can be implemented if necessary.
Some treatment plants have a storage reservoir available
that can be used if final treatment processes must be shut
down. Water stored in these reservoirs should be brought
back through the processes for final treatment prior to dis-
charge to any lake or stream which requires the strict stan-
dards.
-------
Industrial Waste Treatment 647
EFFLUENT
MANIFOLD,
FLOW
METER
EFFLUENT
RATE-OF-FLOW
CONTROL VALVE
CLOSED
CARBON
'COLUMN
BYPASS
VALVE
CLOSED
\ /
FINAL
EFFLUENT
CARBON COLUMN
(TYPICAL!
INFLUENT
INFLUENT
MANIFOLD
3-WAY
VALVE
3-WAY VALVE
CARBON
'column
INFLUENT
HEADER
VALVE
OPEN
INFLUENT
HEADER^
WASTE AND
DRAIN LINE
Fig. 28.61 Upflow carbon column schematic - reverse flow
(Used to flush top screens)
Orange County, California
-------
648 Treatment Plants
EFFLUENT
MANIFOLD,
FLOW
METER
EFFLUENT
RATE-OF-FLOW
CONTROL VALVE
CLOSED
FINAL
EFFLUENT
CARBON COLUMN
(TYPICAL)
INFLUENT
MANIFOLD
3 WAY
VALVE
CLOSED
3-WAY VALVE
CLOSED
INFLUENT
HEADER
CARBON
/ COLUMN
h. /BYPASS
JL> VALVE
X OPEN
INFLUENT
,CARBON
COLUMN
INFLUENT
HEADER
VALVE
CLOSED
^WASTE AND
DRAIN LINE
Fig. 28.62 (Jpflow carbon column schematic, by-passing
carbon column, Orange County, California
-------
Industrial Waste Treatment 649
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 700.
28.5D What is the desired detention time in an activated car-
bon pressure vessel?
28.5E Why are three-way valves used in activated carbon
piping?
28.5F How is activated carbon kept in the pressure vessel?
28.5G What is the counter-current flow principle?
28.52 Activated Carbon Regeneration
28.520 Purpose for Regeneration of Activated Carbon
As described previously in this chapter, activated carbon is
produced by heating carbonaceous material to a high tempera-
ture and using water to help form the pore structure necessary
for the adsorption process. Regeneration of activated carbon is
a process whereby the pores and the surface of the carbon are
cleansed of the molecular organic material which has been
adsorbed on the surface.
Activated carbon must be regenerated after the carbon has
adsorbed all of the molecular organic material that can be
adsorbed on the surface and within the pore structure. The
purpose of the regeneration process is to drive off the molecu-
lar organic material and to allow a clean surface to be readied
for additional adsorption of organic material. The most com-
mon method for regeneration of activated carbon is through
heat treatment in a multiple hearth furnace or a rotary kiln. The
carbon undergoes high heat up to 1750 degrees Fahrenheit
(950°C) and steam is added for cleansing the carbon of the
adsorbed material.
28.521 General Procedure for Reactivation
The general procedure for reactivation of activated carbon is
to pull spent carbon from the bottom of carbon column reactors
into dewatering bins (Figure 28.63). The carbon is allowed to
sit for a period of time until it is dry enough to enter a furnace.
The carbon enters the top of a multiple hearth furnace where it
is heated at high temperatures to help drive off the molecules
that have adsorped on the surface of the carbon. Steam is
used in a portion of the furnace to help cleanse the structure of
the carbon. The final step in the regeneration process is a cold
water quench tank which helps open the fissures or pore struc-
ture in the carbon to allow additional area for adsorption.
28.522 Specifics in Reactivation Process
1. Transfer of Spent Activated Carbon to Dewatering or Drain
Bin. Spent activated carbon is carbon which has been effec-
tively used so that it can no longer adsorb organic material.
Spent carbon is conveyed under pressure to a dewatering
bin by the use of a water slurry. Because the carbon tanks
are under pressure, a pressurization of carbon in the form
of a slurry can take place which pushes the carbon through
the bottom of the pressure vessel and out into a piping
system. The piping system will carry the carbon water slurry
to a large bin for the dewatering process.
The dewatering bin (also called a decanting bin) is a large
open container which usually holds two cubic yards (1.5 cu
m) of carbon (Figure 28.64). At the bottom of the dewater-
ing bin is a screen port which allows water to flow from the
carbon slurry. In this manner, the carbon can dry to some
extent by sitting in the bin for a period of time and allowing
the water to flow to the bottom of the bin and out for further
treatment.
2. Adjusting Rate of Feed into Regeneration Furnace. The
carbon regeneration furnace is usually a small multiple-
hearth furnace (Figures 28.65 and 28.66). The furnace is
designed to handle an optimum rate of activated carbon
within the furnace for proper detention time for the regener-
ation of the carbon. The feed rate allows the proper number
of pounds per hour to enter the furnace in the top hearth.
The operator must be careful to adjust the feed rate accord-
ing to the apparent density tests (procedures for performing
apparent density tests are in the Appendix at the end of this
chapter). If the apparent density is too high, the feed rate is
too high and the carbon is not having a long enough deten-
tion time within the furnace to be regenerated properly. If
the apparent density is too low and white ash is apparent on
the edges of the carbon as it comes out of the furnace, the
operator should speed up the feed rate because the carbon
is being burned within the furnace.
3. Setting Automatic Controls for Temperature in Furnace.
Most of the multiple hearth furnaces used for carbon regen-
eration have automatic controls to control the temperature
within the furnace. The automatic controls adjust the air and
gas ratio so that proper temperatures can be obtained at
each successive level in the furnace. Each of the levels is
considered a hearth and the normal regeneration furnace
will have six hearths.
The top hearth of a furnace is considered the drying
hearth. The second hearth through the fifth hearth are con-
sidered the regeneration hearths. Usually, hearths num-
bered 3, 4 and 5 have the highest temperatures. Steam is
usually added to hearths number 3 and number 4 to help
cleanse the carbon of the organic material.
In order to prevent air pollution, afterburners and/or
scrubbers are usually found on the stacks to collect the
gases which are emitted from a multiple-hearth carbon re-
generation furnace. The scrubbers will pull out the organic
material which comes off in the vapor. This scrubbed or-
ganic material is then returned to the treatment plant for
further processing and additional treatment. In this manner,
air pollution can be prevented.
4. Setting Controls for Steam to Portions of Regeneration
Furnace. As indicated above, the normal hearth where
steam is added for additional cleansing of the activated
carbon of organic material are hearths number 3 and
number 4. The operator should check the operations man-
ual for the furnace to determine the desired steam valve
settings for optimum steam levels. The valves should be set
so that the proper amount of steam is injected relative to the
feed rate into the furnace and the temperatures at the
hearth setting.
5. Preventing Buildup of Carbon in Quench Tank. A cold water
quench tank is usually found at the bottom of a multiple
hearth carbon regneration furnace. Carbon is usually
pumped from the quench tank to other tanks for purposes of
DEFINING.20 The operator should check the quench tank
each hour to determine if the pumps are keeping up with the
amount of carbon being produced from the bottom of the
multiple hearth furnace. If carbon is allowed to build up in
the quench tank, an overflow condition may occur and seri-
ous damage could result to the furnace if the carbon is
backed up into the bottom hearth.
20 Defining. A process that arranges the activated carbon particles according to size. This process is also used to remove small particles
from granular contactors to prevent excessive head loss.
-------
650 Treatment Plants
MAKEUP
CARBON
WATER BACK
TO PROCESS
C
• SPENT CARBON
DRAIN AND
FEED TANKS
£
SCREW
CONVEYORS
JZ
Jj—oo
CARBON/l__ --Thxi.
SLURRY/ 1—
CARBON
SLURRY
PUMPS
CARBON FINES
BACK TO
PROCESS-
.SPENT CARBON
FROM CARBON
COLUMNS
SCRUBBER
AND AIR
POLLUTION
•CONTROL
EQUIPMENT
CARBON
REGENERATION
FURNACE
CARBON
SLURRY //—
PUMPS. —
i-txJ
REGENERATED CARBON
DEFINING AND STORAGE
TANKS
.STEAM
SUPPLY
QUENCH
TANK
REGENERATED
•CARBON TO CARBON
COLUMNS
Fig. 28.63 Carbon regeneration system schematic
-------
Industrial Waste Treatment
SPENT
CARBON IN
STEEL DRAIN BIN
COAL TAR EPOXY
LINED
tVARI ABLE-SPEED
SCREW CONVEYOR
DRIVE
SCREENED
DRAIN
INSPECTION
PLATE ^
.EMPTY
TELLTALE
DRAIN
LINE
HIGH-PITCH
CONVEYING
SCREW
SCREENED
DRAIN
SECTION
LOW PITCH
METERING
SCREW
TOP OF
CARBON FURNACE
DRAIN
LINE —
SCREW CONVEYOR AND HOUSING
ARE FABRICATED FROM 316
STAINLESS STEEL
Fig. 28.64 Spent carbon drain bin and furnace feed
arrangement
-------
CARBON IN
TOP WAFER VALVE
SURFACE
OF CARBON
OUTLET SCREENS (8)
IL
PRESSURE VESSEL
12 FT DIAMETER
INLET SCREENS (8)
otd
^ WATER TO
TRANSFER
HEADER
TANK
SUPPORT
LEG
© ©
BOTTOM WAFER VALVE
CARBON OUT
oJ
Fig. 28.65 Carbon regeneration furnace
-------
Industrial Waste Treatment 653
CARBON GAS
IN OUT
HEARTH
RABBLE ARM
uuuu
RABBLE TEETH
IARBON OUT
Fig. 28.66 Cross-sectional view of multiple-hearth furnace
-------
654 Treatment Plants
6. Pumping Reactivated and Quenched Carbon to Defining
Tanks. Because of the corrosive nature and the granular
form of activated carbon, centrifugal pumps and other
vaned pumps will not be adequate for pumping an activated
carbon slurry. The most common pump used for pumping a
carbon slurry is a diaphragm pump. The operator should
check to be certain that the diaphragm pumps are pumping
the quantity of carbon necessary in order to keep up with
the regeneration process.
7. Defining the Regenerated Carbon. Because of the move-
ment of the carbon through the regeneration furnace and
because of the quenching operation, small particles of
granular activated carbon may break off into the carbon
slurry as it is pumped from the quench tank. The fine parti-
cles of regenerated carbon must be defined in order to
prevent clogging of screens in the carbon column reactors
and to prevent suspended solids from being discharged in
the effluent from the treatment plant.
A defining tank or wash tank (Figure 28.67) for the re-
generated carbon consists of a pressure vessel with
screens. Water flows through and around the carbon, float-
ing the smaller, lighter pieces of carbon fines back into
treatment processes where the carbon fines can be further
removed.
The operator should use the defining tanks to be certain
that the carbon has been washed as thoroughly as possible
to prevent the small particles of carbon from causing further
problems within the adsorption process. An adequate
amount of time must be given to the defining process to be
certain that as many of the fine particles are removed as
possible.
8. Pumping Carbon to the Top of Carbon Column Reactors.
After the regeneration process, activated carbon in a slurry
form can be either pumped or pushed under pressure
through a piping system to the tops of the carbon column
reactors. Because the defining tanks are usually pres-
surized, it is normal to use the pressure from those vessels
to force the carbon slurry back to the carbon reactors
through the piping system.
The operator must make sure that the slurry contains
enough water to prevent any clogging within the piping or
valving system as the carbon is returned to the carbon col-
umn reactors.
9. Troubleshooting of Regeneration Process. One of the
common problems that occurs in the activated carbon re-
generation process is the plugging of piping as the carbon
is pushed from one place to another in a slurry. Black iron
pipe is commonly used to transport carbon slurry. The black
iron does not degrade as readily as other steel pipe due to
the corrosiveness of the activated carbon. The black iron is
put together with flanged joints so that the joints can be
removed and elbows taken off to clean a plugged line if
necssary.
Other troubleshooting areas that must be watched
closely by the operator include a) the feed rate to the re-
generation furnace, b) the buildup of carbon in the quench
tank, c) the pumping capacities of the carbon slurry d) the
temperature levels in the carbon regeneration furnace and
e) excessive burning of the activated carbon in the regen-
eration process.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 700.
28.5H What is regeneration of activated carbon?
28.51 What happens if the feed rate is too high to the carbon
regeneration furnace?
28.5J What happens if the feed rate is too low to the carbon
regeneration furnace?
28.5K How is the temperature controlled in a carbon regen-
eration furnace?
28.5L What is the purpose of the defining tank for the regen-
erated carbon?
28.53 Sampling and Analysis
28.530 Sampling
Sampling is very important in the operation of the activated
carbon process. The operator should sample both influent and
effluent to help determine removal efficiencies of organics and
to determine the quantities of carbon fines remaining in the
effluent from the process.
28.531 Analysis
Determination of removal efficiencies of organics is accom-
plished by running chemical oxygen demand tests and turbidity
measurements. Other tests are run to help determine the
status of the carbon in the carbon column contactors. Samples
should be taken at least once a day on each carbon column to
include both influent and effluent. The types of lab analyses
that must be performed in order to achieve the highest effi-
ciency of operation with the activated carbon regeneration pro-
cess include apparent density of regenerated carbon, total ash
of regenerated carbon, iodine number, molasses number,
hardness number, abrasion number and sieve analysis. De-
tails on how to perform these tests are contained in the Appen-
dix at the end of this chapter.
MUAAfr&tz AMAlV4^
28.54 Operational Strategy
28.540 Dally Operating Procedures
Once each shift, the operator in charge of the carbon ad-
sorption process should check to be certain that:
1. The rate of flow is set properly for each carbon adsorption
tank;
2. Head losses measured through each carbon adsorption
unit are within normal operating ranges;
3. Backflushing of carbon columns takes place when head
losses build up or at least once per day;
-------
Industrial Waste Treatment 655
CARBON SLURRY
INLET FUNNEL —
WAFER
'STOCK
VALVE
100 PSI STEEL
TANK EPOXY-
COATED INSIDE
FLEXIBLE
COUPLING
WELD TO TANK
WALL FOR SUPPORT
SCREEN DRAIN
ANO BACKFLUSH
CONNECTION
WELL SCREEN,
SLOTS. 316 SS, 0.020'
CLOSED END
DRAIN FOR
SCREEN BACK-
FLUSH
STANDARD 12"
BY 16" MANHOLE
PRESSURE
WATER INLET.
BAFELE CONE, HOLE
IN BOTTOM, SUPPORT
WITH BARS WELDED
TO TANK
WASHED CARBON
OUTLET AND WASH
WATER INLET
WAFER
STOCK
VALVE
Fig. 28.67 Regenerated carbon wash tank
(For 8x30 math carbon)
-------
656 Treatment Plants
4. Daily samples are taken from each carbon reactor for both
influent and effluent;
5. All valving is correctly set for normal operation;
6. If carbon is being regenerated, the furnace and feed rates
are proper for a complete regeneration of the granular acti-
vated carbon; and
7. A daily log is kept of any problems that occur such as plug-
ged screens, excessive head losses, problems with the re-
generation furnace, plugged lines or any other abnormal
conditions.
28.541 Abnormal and Emergency Conditions
1. Low COD Removal Efficiencies. If low chemical oxygen
demand removal efficiencies are recorded for the activated
carbon process, the operator must prepare for regenera-
tion. The common reason for low removal efficiencies of,
organic matter is plugging of the fissures within the granular
activated carbon so that adsorption efficiencies are im-
paired.
By sampling and analyzing COD removal efficiencies for
each carbon contact reactor, you will know when the re-
generation process should begin. As soon as low removal
efficiencies of organic matter are reported by the laboratory,
begin preparation for the regeneration cycle. Take carbon
columns off line, remove carbon from the bottom and pre-
pare for regeneration in the multiple hearth carbon furnace.
Prepare the furnace, bringing it up to the proper tempera-
ture and adjusting both carbon feed rate and the steam
quantities for the regeneration process.
During the process of adsorption, there are certain losses
in the carbon mass. These losses will lower the quantities of
available activated carbon in the adsorption process. To
counteract the low quantities, be prepared to add fresh
make-up carbon to any carbon column whose total quantity
of granular activated carbon is low. COD removal efficien-
cies should improve after fresh carbon is added to the sys-
tem.
2. High Head Losses. During the operation of the activated
carbon adsorption processes, the head loss will increase.
However, should head losses continue to remain high even
after backflushing, be prepared to inspect the carbon col-
umns.
Inspection of the carbon columns is necessary to deter-
mine if a screen is completely plugged or collapsed. High
head losses may also indicate that the amount of carbon in
the adsorption reactor is too high and therefore causes
plugging of the screens.
3. Fouling of Activated Carbon Granules with Suspended Sol-
ids. The carbon adsorption process usually follows other
wastewater treatment units. Occasionally, the other treat-
ment units may fail and organic matter and suspended mat-
ter in large concentrations may enter the carbon reactors.
This can cause a fouling of the activated carbon granules
and therefore impair the adsorption capabilities.
When you suspect a fouling of the carbon granules with
suspended solids, immediately backflush the carbon con-
tactor in attempts to dislodge and flush out as much of the
suspended solids as possible. Because most of the sus-
pended solids will be trapped at the lower portion of the
carbon reactor due to the upflow operation, an extra regen-
eration cycle may be required in order to burn off the excess
suspended solids.
4. Plugged Screens. Because of the upflow configuration for
normal operation of an activated carbon column, the bottom
screens on the tank will seldom plug with debris and sus-
pended solids. The screens that do tend to plug with carbon
fines and suspended solids are the top screens located at
the highest point or effluent end of the carbon reactor.
When screens are plugged, the head losses will increase
substantially through the carbon reactor. Backflush the
screens in order to dislodge the plugged portions. Occa-
sionally, backflushing will not be adequate to dislodge ma-
terial trapped in the screens. When this happens, enter the
carbon column and wire brush the screens in order to al-
leviate the plugging problem.
5. Collapsed Screens. Do not attempt to force more flow
through the carbon column reactor than the design specifi-
cations allow. Extreme pressures can build up within the
carbon column and cause severe damage to the carbon
tank or to the screens within the vessel.
The screens located within the vessel may collapse if
excess pressure from within builds up due to negligence on
the part of the operator. The high pressure from within
forces against the zero or negative pressure on the other
side of the screens or effluent side. This pressure can
cause the screen to collapse and it will have to be replaced.
6. Air Pockets. Air pockets can develop when the carbon col-
umn reactor is filled too fast. Whenever the carbon column
is empty, fill it slowly to allow air to escape through the
automatic air escape valves at the top of the vessel. By
filling the tank slowly, air is pushed ahead of the water as it
enters the bottom of the tank and will escape without form-
ing air pockets within the body of the granular carbon. Air
pockets must be eliminated from the carbon column reac-
tors to prevent short-circuiting. If air pockets develop inspite
of slow filling rates, backflushing will sometimes eliminate
them.
7. Degradation of Tank and Piping Interior Coatings. Because
of the corrosive nature of activated carbon in its granular
form, interior pipe and tank coating is supplied prior to the
placement of the carbon columns into service. At least once
every six months, the operator should check the inside of
the activated carbon tank to be certain that the coating has
not scaled or chipped away from the interior metal surface.
If you find a chipped spot, contact the supervisor and have
the spot repaired using a coal tar epoxy to seal the interior
lining.
8. Failure of Upstream Processes. Because the carbon ad-
sorption process is usually the last process in the wastewa-
ter treatment plant, the efficiency is highly dependent on the
proper operation of any processes that precede the carbon
-------
Industrial Waste Treatment 657
units. When upstream processes fail, a serious reduction in
efficiency of the carbon process may result. If the treatment
plant is equipped with an emergency holding pond, it may
be in the best interest of the operation of the treatment plant
to temporarily store inadequately treated wastewater rather
than pumping it through the activated carbon columns. The
better the quality of water which enters the carbon column
reactors, the more efficient the adsorption process be-
comes. If wastewater is fouled with suspended solids and
other matter, the adsorption process will be impaired and
the operation will become more expensive due to unneeded
regeneration of the activated carbon.
28.542 Sampling Ports
A small pipe can usually be found at the top of the carbon
reactors from which you can sample effluent from the carbon
columns. Likewise, the effluent from the process which pre-
cedes the carbon adsorption process can be sampled. In this
way, the operator can obtain analyses of the influent and
effluent of the adsorption process. This will be important in
determining the efficiency of the organics removal through ad-
sorption.
28.543 Abnormal Conditions Regarding the Carbon
Regeneration Furnace
1. Refractory Brick in Interior of Furnace. Because of the high
temperatures within a multiple hearth carbon regeneration
furnace, certain elements may deteriorate. Check for dete-
rioration of any of the refractory brick on the interior of the
furnace. The brick should be in good shape in order to
prevent the high heat from reaching the metal exterior of the
furnace. If the high heat is not adsorped or insulated by
good refractory brick, the furnace metal may warp and seri-
ous damage could result.
2. Air and Gas Mixture for Proper Temperature. Although
most carbon regeneration furnaces automatically regulate
the air and gas ratio for temperature control, you should
inspect this ratio to make sure that it is correct. Should the
air/gas mixture ratio become incompatible with proper tem-
perature operation, adjust either the air or the gas in order
to provide proper firing of the furance and adequate tem-
peratures for the regeneration process.
3. Furnace Rabble Arms. The high-heat interior to the acti-
vated carbon regeneration furnace can seriously warp the
rabble arms which move the carbon within the furnace. Be
very careful that rabble arms are not stopped where burn-
ers can force direct heat upon the metal. When this occurs,
the rabble arms tend to melt and sag causing serious dam-
age to the furance.
Also, check the teeth on the rabble arms to be certain that
they have not worn out and can function properly. The teeth
should be able to move the carbon within the furnace and
the bottom of the teeth should be approximately one quarter
inch (60 mm) off the refractory brick of each hearth. Rabble
teeth should be replaced if they are worn. Worn rabble teeth
allow carbon to pile up in one spot which could seriously
damage the furnace structure.
4. Regenerated Carbon Slurry Pumps. Because activated
carbon cannot be pumped through the standard centrifugal
pumps, diaphragm pumps are commonly used for pumping
carbon slurry. Periodically inspect the ball checks and
diaphragms on the slurry pumps to be certain that no ex-
cessive wear is apparent. The capabilities of the pumps
may be seriously impaired if carbon is allowed to interfere
with the ball check or diaphragm. You can visually check
the amount of slurry pumped by each slurry pump. When
the quantity of slurry appears to be substantially reduced,
proceed with maintenance steps for clearing any plugging
problems or diaphragm malfunction.
5. Defining Tank Maintenance. The carbon column defining
tank is similar to the activated carbon adsorption vessels.
•This is a pressure tank which has screens for defining the
carbon after it has been regenerated or while the carbon is
fresh and available as a make-up carbon.
Be certain that any screens in the make-up carbon or
regenerated carbon defining tank are clear and free from
blockage. Also, make certain that any air scrubbing devices
or carbon dust collector mechanisms are functioning prop-
erly. Be very careful not to breathe carbon dust as it can be
harmful to your health.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 700.
28.5M List the possible causes of high head losses through
an activated carbon process.
28.5N Why should the activated carbon column reactor be
filled slowly?
28.50 What would you do if a wastewater treatment process
upstream from a carbon adsorption process failed?
28.5P List the problems an operator could encounter when
operating a carbon regeneration furnace.
28.55 Safety
28.550 Carbon Adsorbs Oxygen
One feature of the activated carbon adsorption process is
that it adsorbs oxygen molecules from the atmosphere.
Operators or maintenance personnel should be very careful
when entering a carbon column tank or any enclosed room
where carbon is in contact with the atmosphere. Prior to enter-
ing a carbon column reactor vessel, the operator or mainte-
nance personnel should be wearing a self-contained breathing
apparatus to provide oxygen and also a safety harness. The
operators should be certain that two operators are standing by
whenever a person enters a carbon column tank. This serves
as a safety precaution so that if the person within the tank is
overcome due to lack of oxygen, the other operators or main-
tenance personnel can pull the affected individual out of the
carbon vessel.
28.551 Carbon Dust
Fresh or dry carbon tends to shed a certain amount of dust
particles when moved or handled. Be very careful when han-
dling dry activated carbon to avoid inhaling the dust. Wear a
face mask to prevent the carbon dust from entering your lungs.
liiil
28.552 Excessive Pressures Within Carbon Contactor
Tanks
Make every effort to prevent excessive pressure buildup
within the carbon contactor vessels. Excessive pressure may
-------
658 Treatment Plants
be caused by too high a flow entering the vessel or by col-
lapsed or plugged screens. If pressures are too high within the
carbon vessel, the vessel itself could explode or rupture.
28.56 Loading Guidelines
28.560 Typical Loading Rates
Two types of loading rates are used for activated carbon
adsorption processes: 1) hydraulic loading rates, and 2) chem-
ical oxygen demand or organic loading rates.
28.561 Hydraulic Loading Rates
The typical hydraulic loading rates entering a carbon adsorp-
tion column range from 2 to 10 gallons per minute per square
foot (1.3 to 6.8 liters per second per square meter). The aver-
age hydraulic loading rate (or surface loading rate) is 5 gallons
per minute per square foot (3.4 liters per second per square
meter).
28.562 Chemical Oxygen Demand Loading Rates
Chemical oxygen demand loading rates average at one-half
pounds of COD applied per day for each pound of carbon (0.5
kg COD/day/kg of carbon) in the contact vessel.
28.57 Review of Plans and Specifications
28.570 Loading Station for Truck or Train Delivery of
Fresh Activated Carbon
Because it is important to add make-up or fresh activated
carbon periodically, an unloading station is needed to receive
the fresh carbon for the adsorption process. The unloading
station should have a proper turnaround if it is a truck station.
The station should be close enough to the rail center for easy
unloading if it is delivered by rail.
Bagged carbon can sometimes be unloaded rapidly by ma-
chine if the proper suction equipment is available to pull carbon
from the bags. Otherwise, operators must empty each bag into
the fresh carbon handling station on an individual basis.
If bulk carbon is to be unloaded at the treatment plant, it is
best to have a suction device to unload the carbon from the
bulk container so that manpower can be cut to a minimum. By
providing a suction device, dust and other hazards can be
reduced or eliminated.
28.571 Valvlng Placed at Easy-to-Reach Locations
Check the design of the activated carbon adsorption process
station to be sure that all valves indicated on the plans are
easy to reach. The valves, if overhead, should be no higher
than six feet (1.8 m). Valves that are at the top of carbon
columns should be easy to reach from a catwalk or other
hand railed-protected operation viewing facility.
28.572 Dust Control for Unloading Fresh Carbon
When unloading fresh carbon, be certain that exhaust fans
are operating and that all staff are wearing face masks to pre-
vent inhaling the carbon dust. The operator should check the
plans to be certain that dust control is adequate to protect all
personnel.
28.573 Proper Ventilation in Carbon Regeneration
Furnace Room
Because of the heat and dust that can be emitted from a
carbon regeneration furnace, check the plans to be certain that
adequate ventilation is provided within the furnace room.
Proper ventilation and air circulation is mandatory in order to
protect the personnel from excessive heat and exposure to fine
particles of carbon, smoke and other hazardous material.
28.574 Scaffolding and Catwalks
Check plans to be certain that all catwalks and scaffoldings
are protected with handrails to comply not only with OSHA
standards but to ensure safety, particularly when the catwalks
are located at the top of the carbon column reactors. Entrance
and exit from access ports into carbon column reactors should
be protected so that the chances of the operator falling are at a
minimum.
28.575 Warning Alarms and Signs
Check the plans to be certain that alarms are adequate to
notify personnel of excessive temperatures or lack of oxygen
within a building. Be certain that the plans call for signs and
warning systems posted at various locations so that all per-
sonnel are aware of the dangers associated with working
around activated carbon.
28.576 Upstream Processes
Filtration is usually an upstream process prior to carbon ad-
sorption. A holding tank or reservoir is desirable upstream from
the carbon adsorption process in order to provide temporary
storage in case of failure of other systems. Check plans to be
certain that such a reservoir is provided for temporary or
emergency storage. Failure of upstream processes would
mean excessive organic or suspended solids loading on the
activated carbon process, thereby reducing its effectiveness.
28.58. Additional Reading on Activated Carbon
Adsorption
1. HANDBOOK OF ADVANCED WASTEWATER TREAT-
MENT, Gordon L. Culp, Russell L. Culp, George "Mac"
Wessner, Van Nostrum Reinholdt Company, 1978.
2. OPERATION AND MAINTENANCE MANUAL FOR
WASTEWATER RECLAMATION FACILITY, South Tahoe
Public Utility District, So. Lake Tahoe, CA 1974.
3. PROCESS DESIGN MANUAL FOR CARBON ADSORP-
TION, U.S. Environmental Protection Agency, Center for
Environmental Research Information (CERI), 26 West St.
Clair Street, Cincinnati, Ohio 45268.
-------
Industrial Waste Treatment 659
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 700.
28.5Q How could activated carbon cause an oxygen defi-
ciency in a carbon column reactor vessel?
28.5R List the items you would consider when reviewing the
plans and specifications for an activated carbon ad-
sorption process.
28.5S What kinds of warning signs and alarms should be
provided with an activated carbon adsorption pro-
cess?
6NP Of MWOto60?6U&£>Oto<->
DISCUSSION AND REVIEW QUESTIONS
(Lesson 6 of 6 Lessons)
Chapter 28. INDUSTRIAL WASTE TREATMENT
Write the answers to these questions in your notebook be-
fore continuing. The problem numbering continues from Les-
son 5.
35. How does activated carbon remove organic material from
wastewater?
36. Why are pressurized upflow carbon contact chambers pre-
ferred over downflow pressure vessels?
37. Why must activated carbon be regenerated?
38. What tests should be run on the effluent of the activated
carbon process and why?
39. What would you do if the results of lab tests showed low
COD removal efficiencies from a carbon adsorption unit?
40. How can too high a pressure build up in carbon contactor
vessels? —
-------
660 Treatment Plants
CHAPTER 28. INDUSTRIAL WASTE TREATMENT
INDUSTRIAL OPERATING PROCEDURES
8.6 HOW TO OPERATE AN INDUSTRIAL WASTEWA-
TER TREATMENT PLANT by Robert Wills, Jr.
The purpose of this section is to provide you with an outline
of the procedures used to operate a wastewater reclamation
and recycle facility at a specialty steel mill. The processes
used are physical and chemical treatment processes, rather
than the conventional biological treatment processes used to
treat domestic wastes. By using this section as a guide, you
should be able to develop similar procedures for the operation
of industrial waste treatment facilities.
28.60 Routine Operational Control of a Specialty Steel
Wastewater Reclamation and Recycle Facility
28.600 Description of Treatment Facilities
Wastewater treated at a steel mill facility comes from several
different sources (Fig. 28.68). These sources include rolling
mill wastewater, cooling tower waters, pickling rinse waters,
boiler blowdown and mill furnace cooling tower waters.
Wastewaters are collected at six different pump stations lo-
cated throughout the mill production facilities. The collected
wastewater is pumped through three force mains to the
wastewater reclamation and recycle facility.
The first treatment process is the aeration tank. THE AERA-
TION TANK IS NOT FOR BIOLOGICAL TREATMENT. Wastes
are blended in the aeration tank. Soluble iron is converted to
insoluble iron that can be precipitated and settled out by the
addition of ferric chloride (Fe Cl3). During aeration some of the
heat picked up by the water in the mill operation is liberated
from the water.
Solids Control Tank A (SCTA or recycle water treatment
tank A) is equipped with a turbine mixer to mix the chemicals
(ferric chloride (FeCI3) and polymer) with the water from the
aeration tank. After mixing, the water enters the settling portion
of the tank for clarification. Ninety percent of the effluent leav-
ing tank A is returned to the steel mill for use as process water
in the steel making operation. Necessary make-up water
comes from the local municipal water supply. The remaining
ten percent of the effluent from Tank A goes to effluent treat-
ment tank B (SCTB or Solids Control Tank B).
In Tank B the pH is adjusted by the addition of lime or some
other caustic to precipitate metals such as chromium and cop-
per. This procedure for pH control also improves the settling of
small floe and enhances effluent quality before discharge.
Solids precipitated and removed from tanks A and B are
pumped to a gravity thickener where they are mixed together
and resettled. Since the sludge from the thickener consists
mainly of inorganic materials (metal floes, rust, dirt) and floc-
culating agents, the sludge compacts to a high solids content
and is very dense. Domestic wastewater sludges are high in
organic material and will not compact to a high degree.
Thickened sludge is dewatered by a vacuum filter. A very dry
cake is produced that is disposed of in a landfill.
Treated wastewater is pumped from the recycle wet well
back to the mill based on the mill's demand for water.
The remainder of this section is in outline form to show you
the procedures that must be developed to successfully operate
industrial wastewater reclamation and recycle facilities.
28.601 Operational Strategy
A. Quality effluents (recycle and discharge) can be achieved
by careful monitoring of the influent waste stream and the
operation of the chemical feed systems in the treatment
facilities (Figures 28.69 and 28.70).
1. Influent waste stream must be monitored due to the
large variability in flows. The main water quality indi-
cators that must be monitored are:
a. Low pH. This indicates an acid dump which means
you probably have high concentrations of soluble
metal coming in. In addition, low pH may cause the
following problems:
1. Foaming due to cleaning additives in pickling
solutions.
2. Previously precipitated metals may resolublize
due to the depressed pH causing higher metal
concentrations in the "clarified" water than in
the effluent.
3. Reduced treatment efficiencies due to the
treatment chemical effectiveness at low pH
levels.
4. Increased corrosion rates in the collection,
transmission, treatment, and recycle systems.
b. High pH. This indicates an alkaline dump which
may or may not affect the plant. High pH may
cause the following problems:
1. Foaming caused by alkaline cleaning solutions.
2. Iron floe carryover. Large tannish-orange floe
which is extremely difficult to settle may be pre-
sent in the entire system. This may cause plug-
ging of filter and strainers in the recycle lines,
coating on heat exchanger surfaces, and viola-
tion of your NPDES permit due to visible solids
carryover and high metal concentrations.
3. Reduced treatment efficiency due to increased
solubility of some metals at higher pH values.
4. Reduced efficiencies for treatment chemicals
used in process.
5. Scale build up in recycle system, especially at
heat transfer areas.
c. High solids concentration.
1. Indicates a large dump of pollutants which may
overload treatment plant, dramatically reduce
its efficiency and increase pollutant recycle/
discharge.
2. You must monitor and determine the plant's av-
erage influent solids concentration and then de-
termine the maximum loading the plant can
take under normal operating conditions.
-------
SCHEMATIC OF EXISTING SYSTEM
CITY WATER
(0.4 MGD)
RECYCLE WATER (4.1 MGD)
CHIP PICKLING
9" ROLLING MILL
12" ROLLING MILL
-H 14" ROLLING MILL*
BOILER HOUSE
SALT FURNACE
26" ROLLING MILL
—Vj 26" MILL FURNACE
' STRAIGHT LINE PICKLE
->c NEEDLE WIRE PICKLE
*[
COPPER PLATING
ROD & BAR MILL
STATION
PS #1
RECYCLE
WET
WELL
RECYCLE
WATER
TREATMEN
TANK A
PS #2
ERATIO
EFFLUENT
REATMEN
TANK B
PS #3
EFFLUENT
DISCHARGE
3
a
c
&
3
St
%
3
&
3
-------
662 Treatment Plants
CONCENTRATION REDUCTION
DURING TREATMENT
2 -
1 -
4.2
1.95
A
B \
0.4 -
0.3 -
0.2 ~
0.1-
SOLUBLE IRON
0.5
0.4 H
0.3
HEX CHROMIUM
.5 -i
.4
\ '3
\ .2
/ A
B \
.10
\ "1
\ .02
1 -
TANK A
TANK B
SOLUBLE COPPER
SD ZINC
.03-
—
.02-
.01-
TANK A
TANK B
NOTES:
1. Scale on left is concen-
tration in mgIL.
2. Start at left with Tank A
influent concentration and
finish on right with Tank
B effluent concentration.
OXID CYANIDE
Fig. 28.69 Effectiveness of waste removal during treatment
-------
100-
90'
80'
70
60
50
40
30
20
10
0 •
Industrial Waste
AVERAGE DAILY % REMOVALS
93.4
86.9
B
14.1
79.7
B
12.6
89.7
il°/o
TOTAL TOTAL TOTAL TOTAL TOTAL
IRON CHROMIUM COPPER ZINC CYANIDE
TSS
Fig. 28.70 Percent removals from Tanks A and B
-------
664 Treatment Plants
d. Flow variations.
1. High flows can cause problems by hydraulically
overloading clarifier portions of Tanks A and B,
thus decreasing effective treatment chemical
dosages (on non-automatic flow paced con-
trolled feed systems), accentuating short-cir-
cuiting (or other clarifier problems), or thermal
shock (induced by excessive city water addi-
tions) (Fig. 28.71).
2. Low flows can cause treatment chemical over-
dose (on non-automatic flow paced controlled
feed systems) which can affect color, turbidity
and cause some chemicals to act as disper-
sants.
e. Other indicators that may cause plant operation
problems include:
1. Oil and grease can indicate large dumps which
can:
a. Exceed oil and grease discharge limita-
tions, even on units with skimmers.
b. Affect chemical treatment.
1. Suspended floe.
2. Cause sludge floe to float instead of set-
tle.
c. Cause new or increase biological growths.
d. Affect sludge compaction and dewatering
abilities.
e. Cause potential fire and safety hazards.
f. Be aesthetically displeasing.
2. Color.
a. White or yellow green — may indicate
emulsifiable oil and its related problem or
lime slurry.
b. Purple — potassium permanganate.
c. Green — caustic solution.
3. Odor.
a. Acrid — check for acid.
b. Petroleum — check for oils or solvents.
2. To improve treatment and effluent quality:
a. Level out flows.
b. Level out pH.
c. Reduce contaminant fluctuations.
d. Optimize chemical usage.
28.61 Daily Inspections
1. Review the wastewater treatment plant (W.W.T.P.) log
book
2. Check all 24-hour chart recorders for unusual readouts or
spikes.
a. pH variations typically indicate problems at pickling
lines or at ion exchange units being regenerated.
b. Excessive effluent discharge typically indicates excess
city water additions, check areas that have emergency
cut in valves.
c. Little or no effluent discharge.
1. Not enough make-up water.
2. Pump station is not returning recycled water to the
W.W.T.P. This creates an unbalanced system be-
cause the pump station will flood and the W.W.T.P.
will run out of recycled water.
3. Recycled water is hot being returned to the
W.W.T.P.
d. Recycled water pressure too high.
1. Pressure relief valve inoperative.
2. Recycle pump malfunction.
3. Instruments controlling recycle pumps malfunction-
ing.
e. Recycled water pressure too low.
1. Pressure relief valve malfunction (stuck open).
2. Instruments controlling recycle pumps malfunction-
ing.
3. Recycle pump malfunction.
f. Recycled water flow too high.
1. If discharge pressure is low and wet well is falling,
there is a break or leak in a recycled water line.
2. If discharge pressure is high, pressure relief valve
and/or instruments controlling the recycle pumps
are malfunctioning.
g. Wet well level too low or dropping.
1. Valve controller on effluent discharge malfunction-
ing.
2. Pump station is not returning recycle water to
W.W.T.P.
3. Recycle water not returning to W.W.T.P. due to
water line break or leak.
4. Needs more make-up water.
3. Review security log book for operational or maintenance
problems.
4. Check effluent discharge quality and recycled water quality.
a. If water is clear, free of suspended solids, floating sol-
ids, foam and oil and grease, go to item 5.
b. If water contains:
1. Suspended or floating solids or pinpoint floe:
a. Check pH of influent and effluent.
1. Too low or too high pH can redissolve some
metals.
2. Rapid pH change can upset treatment.
b. Check chemical feed pumps.
c. Check for excessive flow rate which could hy-
draulically overload the clarifier.
-------
COMPARISON OF TREATMENT
OIL & GREASE
SULFATE
CYANIDE OXIDIZABLE
CHROMIUM TOTAL
COPPER SOLUBLE
IRON TOTAL
TIME
NOTES:
1. The spike of
TSS aligns
with a spike
of Chromium
Total and
Iron Total.
2. The spikes of
Cyanide
Oxidizable and
Copper Soluble
indicate a
problem at a
copper coating
line.
3
a
c
M
£
0>
w
o>
en
-------
666 Treatment Plants
d. Check operation of rake and turbine drive units.
e. Check mill operations for recent dump of oil or
other material which may act as a dispersant.
f. Check for sudden changes of water tempera-
ture.
2. Foam.
a. Check for dump of pickling (acid or alkaline) so-
lution containing detergents.
b. Check for detergents from cleaning operations.
3. Oil and Grease.
a. Check for large dump of oil and grease from mill
operation.
b. Check oil skimmer operation.
c. Check effluent pH (pH fluctuations can break oil
free from the water).
5. Walk around the entire plant, including recycle pump sta-
tion, aeration tank and sludge thickener. Report any ab-
normalities.
28.62 Process Adjustment
1. pH is the most important water quality indicator to control
since it can dramatically effect coagulation, effectiveness of
treatment chemicals, solubility of metals in the wastewater
and the sludge, and corrosion/scaling tendency of the recy-
cled water.
a. pH at the aeration tank should be controlled to meet the
most effective pH range for the treatment chemicals
(6.5 - 7.5).
b. pH of the recycled water should minimize scaling/
corrosion in the plant. This value should be determined
by considering other factors of the system. For exam-
ple, hardness, alkalinity, free mineral acidity, TDS and
to what types of processes the water is being applied.
c. pH of the effluent discharge must be within the NPDES
permit limitations while at the same time maximizing
metal removals.
1. You may not be able to run at a pH value to
minimize a specific metal solubility due to permit
limitations.
2. Adjust pH to the minimum solubility of the metal
most restricted on your permit. See Figures 28.72,
28.73 and 28.74.
2. Frequent jar tests are required at each stage of treatment to
insure the best results for chemical additions to the waste-
water.
a. Be sure to get a representative sample of the wastewa-
ter for jar test and retest before altering feed rates.
b. File results of jar tests for future reference.
3. Know the mill production processes and potential problem
areas.
a. If the W.W.T.P. is subject to large shock loads, try to
reduce shock loads before they get to the W.W.T.P.
1. The variability is a measure of a system's ability to
handle fluctuations.
2. Variability ratio = highest value
lowest value
3. Typical variability ratios for a specialty steel mill are
shown in Figures 28.75 and 28.76.
4. By reducing the variability ratio, the waste can be
treated more efficiently thus achieving better con-
taminant reductions.
4. Minimize flow variations (Fig. 28.77)
a. Dampening or leveling out flow variations to and
through the W.W.T.P. results in optimization of chemi-
cal usage and increased levels of treatment efficiency.
b. Methods for minimizing flow variations include:
1. Limit pump station cycling by matching pumping
rates to inflow to pump the same amount of water
over a longer period of time instead of pumping high
volume quickly, shutting down pumps and waiting
for wet well to fill up.
2. Determine the minimum pressure of recycled water
that can adequately service the mill and adjust con-
trols so that extra recycle pump won't come on until
that pressure is not met.
3. Set automatic valve operators to operate valve at
the slowest possible speeds.
4. Try to get mill start-ups staggered or manually start
additional recycle pump and slowly open discharge
valve as the demand increases.
c. Mill processes in which to expect excess city water
additions:
1. Processes which have emergency cut in valves to
protect the process if the recycled water system
goes down.
2. Processes which have city water addition points or
city water for backup.
3. On days of poor recycle water quality or high recy-
cled water and/or ambient temperature, check pro-
cesses which have complained about similar prob-
lems in the past.
28.63 Day-to-Day Mechanical Operation
28.630 Clarlfiers
a. Rake drive speed should be adjusted to maintain:
1. Proper sludge level.
2. Proper sludge density.
3. Proper torque reading.
4. Proper solids recirculation to the reaction well.
5. Proper oil skimming (if there are skimming devices
on the rake arms).
b. Turbine mixer drive speed should be adjusted to main-
tain:
1. Proper mixing of influent and chemicals.
2. Proper mixing with previously formed floe.
-------
Industrial Waste Treatment 667
1
RATE
pH >-
1. NOBLE METALS
If
RATE
3. ACID SOLUBLE METAL
RATE
pH >"
2. METALS WITH
AMPEROMETRIC OXIDES
1
RATE
4. IRON
Fig. 28.72 Effects of pH on corrosion rates
-------
668 7V„
M"nen, Plams
100 r~
PH
f/9- 2a.
?3
£ffects
of PH
°n meta/
Concentratjon
-------
Industrial Waste Treatment 669
10
1.0
0.1
o>
E
CD
3
-I
O
CO
0.01
0.001
ZINC
CHROMIUM
NICKEL
COPPER
12
SOLUTION, pH
Fig. 28.74 Effects of pH on metal solubility
-------
670 Treatment Plants
CHANGES IN VARIABILITY RATIO
THROUGH TREATMENT
1000 - -
100 - -
10
I-
Z
Ui
3
<
X
Z
<
I-
Z
Hi
3
CD
X
Z
<
ffl
li.
Z
<
*
z
<
GO
z
<
t-
h-
Z
Ui
3
IS
*
z
I-
z
ill
D
-I
u.
z
ffi
*
z
<
H
SOL
IRON
HEX
CHROMIUM
SOL
ZINC
OXID
CYANIDE
SOL
COPPER
Fig. 28.75 Changes in chemical variability ratios during
treatment
-------
Industrial Waste Treatment 671
3735
1000 - -
o
I-
<
oc
>¦
I-
CQ
<
CC
<
>
100- ¦
10- -
0-
VARIABILITY RATIOS
4-HOUR MASS LOADING
1370
215
113
93
66
42 37
24
53
T ' S
IRON
| T HEX
CHROMIUM
T ' S
COPPER
T S
ZINC
T oxid|
CYANIDE
24
TSS
PH
Fig. 28.76 Mass loading variability ratios
-------
WEEK
WEEK
WEEK
WEDNESDAY
THURSDAY
FRIDAY
SATURDAY
FLOW VARIATIONS AT
TREATMENT PLANT
Fig. 28.77 Variations in flows at treatment plant
-------
Industrial Waste Treatment 673
c. Sludge withdrawal rates should be adjusted to main-
tain:
1. Proper sludge level in the solids conditioning tank.
2. Proper sludge density of the sludge being removed.
3. Proper torque reading of the rake drive.
d. Miscellaneous.
1. Sludge withdrawal lines must be flushed after each
use and possibly more often.
2. Check oil levels on main drive gears at least once a
week (sample and analyze oil at least once a year).
3. Drain condensate and/or water from main drive
gears at least once a week.
4. Check drive belts and chains at least once a month.
5. Check scum boxes at least once a week for plug-
ging.
6. Check associated safety equipment (guards, floata-
tion rings, etc.) daily.
28.631 Sludge Thickener
a. Rake drive speed should be adjusted to maintain:
1. Proper sludge level.
2. Proper sludge density.
3. Proper torque reading.
4. Proper sludge mixing.
b. Automatic lifting device should be adjusted to maintain:
1. Proper sludge level, density and mixing.
2. Proper torque readings without setting off alarms or
stalling the unit.
c. Miscellaneous.
1. Sludge entry and withdrawal lines must be flushed
after each use and possibly more often.
2. Check oil levels on main drive gears at least once a
week (sample and analyze oil at least once a year).
3. Drain condensate and/or water from main drive
gears at least once a week.
4. Check drive belts and chains at least one a month.
5. Check associated safety equipment (guards, floata-
tion rings) daily.
28.632 Aeration Tank
a. Check operation and electrical current draw of floating
aerator motor daily.
b. Check performance levels as required (temperature,
DO levels, conversion of iron from soluble to insoluble,
mixing).
c. Miscellaneous.
1. Stop and JOG21 reverse unit when:
a. You see motor current fluctuations.
b. You see rags or stringy material in the influent
which may tangle in the impeller.
2. Pull unit every 6 months:
a. Lubricate motor.
b. Be sure all nuts, bolts and impeller are secure.
3. Lift aerator by the motor, not the float (to prevent
cracking and eventual sinking of the float).
4. Make harness for the aerator and float and attach to
mooring lines.
a. This will prevent cracking and sinking of the
float if aeration tank goes dry or to a low level.
b. Harness can be as simple as nylon straps under
float and through mooring brackets to evenly
distribute the weight.
5. Check associated safety equipment (guards, floata-
tion rings) daily.
28.633 Recycle Pump
a. Seal water lines should be checked at least daily.
b. Bearing temperature should be checked daily (by hand)
and monthly by gage.
c. Gage readouts should be checked and verified as re-
quired.
d. Check air compressor reading and operation.
e. Miscellaneous.
1. Exercise pneumatic valves at least monthly.
2. Check filters and operation of pressure relief valve
at least monthly.
3. Change pump sequence at least monthly.
4. Calibrate instruments at least monthly.
5. Check wet well alarm levels quarterly.
6. Check back-up water supply system:
a. Lake pumps — check quarterly.
b. City water cut-in valves — check operation at
least monthly.
7. Inspect and/or rebuild recycle pump yearly.
8. Check associated safety equipment (guards,
alarms) daily.
28.634 Vacuum Filters
a. Operate units as required, be sure units are recycled at
least once a week.
b. Monitor vacuum reading, percent dry solids in and of
filter cake and physical characteristics of the sludge
and cake.
c. Lubricate, drain condensate, check belts and chains of
all associated drive units as required.
d. Miscellaneous.
1. Clean or repair spray nozzles as required.
2. Clean, repair or replace filter cloth as required.
21 Jog. Stop-start unit to clear impeller or check loading or torque on unit.
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674 Treatment Plants
3. Check associated safety equipment prior to use of
the equipment.
28.635 Chemical Feed Systems
a. Acid/coagulant/polymer feed pumps
1. Must be able to monitor feed rates.
a. Gage on storage tank.
b. Acid proof flow meter or calibration tap.
c. Visible discharge point.
2. Miscellaneous.
a. If chemical feed is not automated, must be regu-
lated to influent flow and solids concentration
determined by jar test.
b. Check belt at least once a month.
c. Check oil at least monthly.
d. Clean pump head and check valves at least
once per year, more often if recycled water is
used as batch make-up water.
3. Check associated safety equipment (face shields,
rubber gloves, eyewash) daily.
b. Polymer mixing unit.
1. Dry polymers.
a. Fill hopper daily and record usage.
b. Check for proper cycling of mixing unit weekly.
c. Flush level sensing units weekly.
d. Calibrate feed rate weekly.
e. Clean up spilled product immediately.
f. Check associated safety equipment daily.
2. Liquid polymers.
a. Check liquid polymer level, replenish as neces-
sary, and record usage.
b. Check for proper cycling of mixing unit weekly.
c. Flush level sensing units weekly.
d. Calibrate feed rate weekly.
e. Clean up spilled product immediately.
f. Check associated safety equipment daily.
3. Lime mixing units.
a. Fill hopper daily and record usage.
b. Check for proper operating and mixing daily.
c. Flush feed lines and clean ejectors daily or as
needed.
d. Calibrate feed rate weekly.
e. Clean entire unit and adjust feed mechanism
quarterly.
f. Maintain good housekeeping.
g. Check associated safety equipment (filters,
vents, showers) daily.
4. Caustic feed units.
a. Check reserve supply and record usage.
b. Check for proper operation daily.
c. Calibrate feed rate weekly.
d. Check associated safety equipment (rubber
gloves, showers, eyewash) daily.
28.636 Instrumentation
a. pH meters/recorders/controllers.
1. Clean and calibrate units at least monthly.
2. Spot check units with litmus paper on a regular
basis and to confirm unusual readings.
3. Have spare units ready to be installed, as needed.
b. Flow meters.
1. Clean and calibrate units at least monthly.
2. Have back up system for monitoring flows, as re-
quired.
3. Verify unusual flow reading if possible.
c. Conductivity
1. Clean and calibrate units at least monthly.
2. Spot check units with portable units or with standard
solutions on a regular basis and to confirm unusual
reading.
d. Other instrumentation.
1. Clean and calibrate units as required.
2. Have back up systems available. For example, tap
for pressure gage by sensor for discharge pressure.
3. Spot check unit as required.
e. Other items.
1. Keep all charts, strips and calibration records as
required by your discharge permit.
2. Have factory service personnel clean and calibrate
all instruments yearly.
28.64 Aeration Tank
28.640 Objectives
a. To oxidize the soluble iron content.
b. To cool the water.
c. To keep the tank's contents mixed.
28.641 Operation
a. Wastewater at this plant is pumped from the pump sta-
tions to the aeration tank via three force mains.
b. A mechanical floating aerator mixes and adds oxygen
to the wastewater.
c. After 20 minutes the aerated water leaves the tank by
an overflow and proceeds to tank A by gravity.
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Industrial Waste Treatment 675
28.642 Initial Starting
a. Turn power on (at motor control center #2 at Recycle
Pump Station).
b. Turn upper current limit up all the way and turn lower
current limit down all the way.
c. Go to aeration tank to be sure aerator is in water and
that it is secured by the mooring cables.
d. Check for floating debris in or around aerator. Remove
any debris.
e. Jog reverse aerator then press start button, be sure
aerator starts.
f. Go back to motor control center #2 and check amme-
ter.
1. If drawing 26-27 Amps reset upper limit to 35A.
2. If drawing more than 27A:
a. Return to tank and stop aerator.
b. Jog reverse aerator several times to clean
aerator propeller.
c. Restart aerator.
d. Recheck ammeter.
1. If reading is still high, repeat procedure.
2. If reading is normal, reset upper current limit
to 35 Amps.
3. If drawing less than 20 Amps:
a. Be sure propeller hasn't spun off the aerator.
b. Be sure aerator is floating in water and is not
suspended in the air.
c. Lower current limit is not connected, leave it at 0
Amps.
28.643 Restarting Aerator
a. Visually inspect unit.
1. Be sure unit is in water and impeller or propeller is at
proper submergence level.
2. Fish out any floating solids.
b. Go to motor control center #2, be sure power is on.
c. Turn upper current limit up all the way and turn lower
limit down all the way.
d. Return to aerator tank and jog reverse aerator several
times to clean propeller.
e. Press start button, be sure aerator starts.
f. Go back to motor control center #2 and check amme-
ter.
1. If drawing 26-27 Amps, reset upper limit to 35A.
2. If drawing more than 27 Amps:
a. Return to tank and stop aerator.
b. Jog reverse aerator several times to clean
aerator propeller.
c. Restart aerator.
d. Recheck ammeter.
1. If reading is still high, repeat procedure.
2. If reading is normal, reset upper current limit
to 35 Amps.
3. If drawing less than 20 Amps:
a. Be sure aerator is floating in water.
b. Be sure propeller hasn't spun off.
c. Lower current limit is not connected, leave it at 0
Amps.
28.644 Aerator Draining Procedures
a. Turn unit off, disconnect power, lock it out.
b. Disconnect mooring cables from tank wall (attach ropes
to cables for easier installation).
c. If not removing aerator from tank:
1. Control flow from pump stations (lock out
whenever possible).
a. If done during plant shutdown, can turn off all
pump stations as long as all water sources are
off.
b. If you can't turn off all pump stations indefi-
nitely, station operators at pump stations #1,
#2, and #3. At specified time have all three
operators shut down pump stations (after they
have pumped them down) for approximately
15 minutes.
2. Open drain if allowed or pump into SCTA (Tank A).
3. Be sure electrical cable does not become entang-
led as water level decreases.
4. Have operators hold ropes which are attached to
mooring cables, so you can guide aerator as water
level decreases.
5. Remove inspection manhole when water level is
below it.
6. Enter aeration tank at inspection manhole (wear
hip boots).
7. If pump stations can be left off for indefinite
periods, you can use small pump to reduce water
level farther; however, do not take it so low that
aerator is hitting bottom.
8. Remove any large particles of debris through
manhole, smaller particles can be flushed through
the drain.
9. Make note of type of debris so that source can be
located.
10. If you have to activate pump station, remove
operator from tank, pump down from pump station,
turn off pump station, then re-enter tank.
11. When complete, be sure area around and includ-
ing drain are free from obstructions.
12. Visually inspect aerator, clean prop and shaft if
necessary, be sure unit is locked out.
13. Get operator out of tank, close drain, or pull pumps,
then put inspection cover back on.
14. Start pump stations, let tank refill.
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Treatment Plants
15. Guide aerator by using ropes attached to mooring
cables.
16. When tank is full, reopen drain to flush out drain
line.
17. When water starts overflowing to SCTA, re-attach
mooring cables.
18. After visual check, turn on power and start aerator.
d. If removing aerator from tank, lock unit out.
1. Pull aerator to platform using mooring cables.
2. Attach choker to two eyebolts on aerator motor (do
not lift by eyebolts on platform).
3. Remove aerator, being sure that electrical cable
does not become entangled.
4. Inspect and clean aerator (keep aerator suspended,
do not place it on ground).
a. Check impeller, to be sure it is tight.
b. Check tightness of all nuts.
c. Have electrician lubricate motor.
d. Check for cracks in the float.
e. Install the power cable.
5. Clean out tank as described in #3, if necessary.
6. When aerator tank is clean and full, replace aerator
being sure not to entangle or damage electrical ca-
ble.
7. When water starts overflowing, re-attach mooring
cables.
8. After visual check, turn on power and start aerator.
9. If aerator hops when started, reverse the rotation of
the motor.
e. Plan on desludging aerator once a year, minimum.
1. Follow instruction under Section 28.644, "Aerator
Draining Procedures."
2. If possible obtain sludge sample prior to desludging
to determine where to put sludge.
3. Clean and inspect valves in force mains at aeration
tank.
.645 Safety
a. While on tank platform:
1. Be sure chain is up and secure.
2. Watch out for burp (water bubbling up onto plat-
form).
3. Check pH at aeration tank; if extremely high or low,
postpone work (if possible) until pH approaches 7.
4. Watch your step when on tank or obtaining samples.
5. Use caution when obtaining samples and always
wash hands afterward.
6. If you must go into an area that may be or is a
confined space, be sure to follow the Confined
Space Entry Procedures.
7. If you feel light headed, nauseous or smell unknown
fumes, leave area and get into fresh air.
8. When using sampling equipment, beware of electri-
cal shock.
9. Hold onto your safety helmet, equipment and rail-
ings during windy periods.
b. If you have to work near or above water:
1. Have at least one person as a "backup."
2. Have a flotation device handy.
3. Use a lifeline, if necessary.
4. Use a boat, if necessary.
5. Be able to swim.
6. Do not have heavy tools in pockets or in belt.
7. Be sure of footing.
8. Be sure all necessary equipment is locked out,
tagged and tried before working on a unit.
9. Never start unit when pieces of material or the im-
peller could be thrown out by centrifugal force.
10. Don't stand on aerator float while it is in the water.
28.646 Troubleshooting
a. Aerator won't restart.
1. Check upper and lower current limits and put at their
extremes.
2. Check ammeter to be sure indicator isn't stuck on
current limit indicator.
b. Running light is on but it looks like it is not operating.
1. If there is a small current drain, the impeller has
probably fallen off.
2. Remove aerator, check for impeller in shroud, put
impeller back on (use locklite) and reset aerator.
c. Unit keeps tripping out.
1. You are probably getting rags or plastic on impeller.
a. Jog reverse unit to clear impeller.
b. Locate source of material and stop it from enter-
ing collection system.
2. Current limit is set too close to operating current.
a. Move upper limit to 35A.
b. Keep lower limit on zero.
c. Or can keep upper limit on 50A.
3. Other electrical problems.
d. Water level goes below overflow line during plant shut-
down.
1. Pump station check valve leaking.
a. Turn off manual valves at tank to determine
which pump station it is.
b. Listen for check valve clatter at that pump sta-
tion.
2. Drain is leaking or not closed.
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Industrial Waste Treatment 677
28.65 Tank A (SCTA)
28.650 Objectives
a. To allow contact and mixing of wastewater and
coagulating chemicals.
b. To allow sufficient time for the waste material to settle
out.
c. To provide clarified water for reuse in the plant.
28.651 Operation
a. The turbine mixer unit constantly spins counter
clockwise to mix the wastewater and chemicals.
b. The clarifier rake arms run continuously (clockwise) to
"rake" the sludge to the center of the tank, to be
pumped out.
28.652 Starting the Drive Units
a. Starting the rake.
1. Be sure the power is on at motor control center #1
(main disconnect on, control switch (start-stop) on
start, and speed indicator on 25%).
2. Go to SCTA and press start button (be sure the stop
lock is off).
3. Be sure rake travels in a clockwise direction (if not,
shut unit down immediately and reverse motor).
4. If possible, start unit at high speed and turn down to
approximately 20 percent as torque builds up on
mechanism indicator.
5. Watch the torque meter and note the highest read-
ing.
a. If torque goes to 50, then SCTA rake drive over-
loading alarm sounds.
b. If torque goes to 90, then the electrical circuit is
opened and stops the rake mechanism.
6. If the torque meter electrically shuts the unit down:
a. Wait until the torque settles down to a lower
number and try to restart. (See — starting pro-
cedure for rake drive torque-out.)
b. Manually and physically reverse rotate the
motor or pulley until the torque is reached. (Be
sure the unit is locked and tagged out and be-
ware of rotation induced by torque already pre-
sent on the rake arms.)
c. By repeating item #2, you may create a "run-
way" for the arms allowing them to come up to
speed and break through the sludge.
d. To keep torque as low as possible, have the
motor at the lowest speed possible.
e. Can try an air or WATER LANCE22 in front of
the rake arms or extended flushing of the sludge
line.
f. Can try increasing the turbine speed.
g. If all else fails, you must dewater the tank and
physically remove the sludge. Getting the rake
operating again is of prime importance; depend-
ing on sludge level and condition you may have
from 2 to 12 hours to repair the rake before the
sludge "hardens" to prevent the rake from mov-
ing.
WARNING: Never physically retain the torque meter or reverse
the rotation of the rake arm. This will cause dam-
age to the rake arms and the drive assembly and
will cause a complete shutdown of the facility to
repair the damage.
7. The rake drive should be running 24 hours a day. If
the oil skimmer (attached to the rake arm) is not
moving, notify the proper personnel at once. The
less time the unit is down, the greater the chance of
restarting it.
b. Starting the turbine mixer.
1. Be sure the power is on and the stop locks are off.
2. Reduce the vari-drive speed to the minimum (if it's
not already there) as soon as the motor is started
(note the original speed settings).
3. Go to SCTA and press the start button.
4. Slowly increase speed to the original setting over a
five-minute period.
c. Stopping the turbine mixer.
1. Reduce the speed to the minimum over a five min-
ute period (note the original speed).
2. Press the stop button.
28.653 Interpreting What You See
a. SCTA reaction well, what to look for:
1. See turbine mixer rotating and stirring the water.
2. See floe forming in the water from the chemical addi-
tion
a. Want to see good sized solid floe (black lines
seem to divide mixing zones in the tank).
b. Don't want to see:
1. Pinpoint floe. Causes:
a. No or inadequate polymer feed.
b. No or inadequate dose of iron salt.
c. High or low pH movement or changes.
d. Inadequate mixing (turbine).
e. Inadequate sludge compaction and removal
(rake).
f. "Clean" influent (no solids or chemicals to react
with to form large floe).
2. Large bulky fluffy floe.
a. High or low pH level.
b. Dispersant dumped into system.
c. Too much polymer (large overdose).
d. Inadequate mixing.
22 Water Lance. A pipe on the end of a water hose that is used to hydraulicaliy jet out solids.
-------
678 Treatment Plants
3. Oil on reaction well surface.
a. Indicates large quantity was dumped into sys-
tem.
b. Find source and eliminate.
c. Oil may cause either item #1 or #2.
28.66 Tank B (SCTB)
28.660 Objectives
a. To further improve water quality prior to discharge.
b. To remove chromium, copper and other metals by pH
control.
28.661 Operation
a. Same as for SCTA except chemical upstream is lime or
caustic.
b. Refer to SCTA Operation.
28.67 Sludge Thickener
28.670 Objectives
a. To mix sludges from Tank A and Tank B.
b. To thicken the sludge before it is pumped to vacuum
filters.
28.671 Operation
a. This tank contains two drive units.
1. Rake drive unit.
a. To mix and help thicken sludge.
b. To draw sludge to the center where it can be
pumped out.
2. Rake lifting unit.
a. To raise and lower the rake arms.
b. To maintain constant sludge thickness.
b. Starting the drive units.
1. Turn on the power at motor control center #1 for
both rake and rake lift units.
2. Go to tank and put rake lift unit switch into down
(automatic) position.
3. Be sure that stop locks are off, then start rake drive.
4. Rake drive should start immediately and lifting de-
vice will operate automatically as neeeded.
5. If the torque goes above 60, the sludge thickener
rake overload alarm will sound.
6. If the torque goes above 90, the rake drive unit will
shut down.
7. If unit stops because of too much torque:
a. Wait until torque reduces to lower number and
try to restart.
b. Manually put lift unit switch into up position to
raise rake arms above the sludge.
c. NEVER restrict or force the torque arm.
d. Can recirculate sludge in tank using vacuum fil-
ter feed pumps. This will "soften" the sludge.
e. Can open flush lines to break up the sludge.
f. Pump all the sludge you can to vacuum filter to
reduce level in the tank.
8. Lift unit operates automatically by torque readings.
a. If torque is below 15, the rake arms are lowered
into the sludge.
b. If torque is above 40, the rake arms are raised.
c. Normal operating range is 20 to 40.
28.68 Operation of Processes
28.680 Normal Operations
a. Try to monitor sludge blanket. It should be approxi-
mately 6 feet at the center of the reaction well.
b. Monitor torque; try not to let it get above 30 at any time
during normal operation.
c. Use ammeter on rake motor as a backup indicator of
load on the rake arms.
d. Pump out sludge as required to maintain sludge blan-
ket and torque.
e. Sample faucets on the side of the tanks can be used to
determine sludge levels.
f. Keep scum box free of debris or it may plug or it may
catch and stall the rake arm.
1. Turn scum box oil line off each night to prevent oil pit
overflow.
2. Open valve each morning.
3. Start oil pit pump each morning, if it's not in automat-
ic operation.
g. SCTB Valve is used to control the amount of water
discharged into Tributary 5A and in effect the level of
the wet well.
1. The valve should be in auto at all times.
2. The valve should control the wet well level at ap-
proximately 10.25 feet with steady and smooth
effluent discharge.
3. The valve will not close completely in auto (to pre-
vent freeze up to the valve).
4. The valve will close upon the loss of the wet well
signal.
28.681 Troubleshooting
a. Rake drive is down.
1. Determine the problem (no power, broken belt, etc.).
2. Repair the problem or put on spare unit as soon as
possible.
3. Getting the rake operating again is of prime impor-
tance; depending on the sludge level and condition
you may have from 2 to 12 hours to repair the rake
before the sludge "hardens" to prevent the rake
from moving.
4. See rake starting procedures.
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Industrial Waste Treatment 679
28.682 Interpreting What You See
a. See Section 28.653, "Interpreting What You See," for
SCTA reaction well, what to look for.
b. SCTA sedimentation zone.
1. Floe blooms (floe masses rising to the surface of the
water.)
a. Caused by:
1. Rake speed too high.
2. pH fluctuations. Locate problem, neutralize.
3. Thermal currents. Locate problem and elimi-
nate.
4. Air entrapment. Air bubbles from aerator,
DO, or other sources lifting sludge.
5. Short circuiting in tank. Flow problems due to
design, flow rate or structural problems.
6. Low sludge bed. No "filtering" of floe through
previously formed sludge. Problem should
be confined to perimeter of reaction well.
7. Dispersants. Floe should be equally distrib-
uted throughout tank.
2. Oil sheen on surface.
a. Sign of large oil spill or dump. Trace it down and
clean up.
b. Sign of pH fluctuations, breaking oil free.
28.683 Sludge Quality
a. Should be of a muddy consistency.
b. Should be 10-15 percent dry solids (SCTA) or 5-10
percent dry solids (SCTB) during normal operating
conditions.
c. SCTA sludge is normally brown, smooth and not gritty.
d. SCTB sludge is normally light brown, smooth, not gritty,
thinner and fluffier.
e. Sludge thickener sludge should be brown, heavy,
thicker and approximately 20 percent and up dry solids.
f. All sludge lines and pumps MUST BE FLUSHED.
g. SCTA sludge line MUST BE FLUSHED 20 minutes
daily.
28.684 Upset Conditions
a. Check existing conditions.
1. pH. Look for fluctuation or oddity which may have
triggered problem.
a. Locate source and type of material.
1. Get sample of material.
2. Get sample of recycled or discharged water.
3. Usual problem areas:
a. South Wire Mill Pickle Lines.
b. North Conditioning Pickle Line.
c. Boiler House — acid regeneration of
water softeners.
d. For extremely low fluctuations check
concentrated acid storage tanks.
b. Check chemical feeders.
1. Check power supply.
2. If it's in automatic sequence, be sure it is cycling
properly.
3. Be sure hoppers/tanks are full.
4. Check strength of chemicals.
a. Specific gravity of FeCI3.
b. Percent polymer in holding tank.
5. Check pump discharges for actual flow.
6. Be sure all valves on pump discharge are open.
c. Check for abnormal conditions.
1. Excessive city water inputs.
2. Large acid or caustic dumps.
3. Oil spills into system.
4. Spill or dump of chemical into the system.
5. Check for production problems (breakdowns,
planned maintenance, abnormal operations).
d. Resolving the upset.
1. Jar test to determine optimum chemical dosages.
2. Adjust chemical feeders.
3. Set-up samplers at W.W.T.P. or at pump stations as
required.
a. Determine abnormal constituents or concentra-
tions.
b. Use discrete samplers to have visual indication
of progress.
4. Obtain help from consultants and chemical repre-
sentatives.
5. When problem is solved, try to pinpoint cause and
duplicate it in jar tests. Develop measures to prevent
reoccurrence and be sure they are implemented.
28.685 Safety. See Section 28.645, Safety.
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Treatment Plants
CHAPTER 28. INDUSTRIAL WASTE TREATMENT
APPENDIX: LABORATORY PROCEDURES
Influent and Effluent Tests
A. Chemical Oxygen Demand (COD)
A measure of the oxygen-consuming capacity of
inorganic and organic matter present in wastewater.
COD is expressed as the amount of oxygen con-
sumed from a chemical oxidant in mg/L during a spe-
cific test. Results are not necessarily related to the
biochemical oxygen demand (BOD) because the
chemical oxidant may react with substances that bac-
teria do not stabilize. See Chapter 16, "Laboratory
Procedures and Chemistry," for test procedures.
B. Turbidity
Turbidity units, if measured by a nephelometric (re-
flected light) instrumental procedure, are expressed in
nephelometric turbidity units (NTU). Those turbidity
units obtained by other instrumental methods or visual
methods are expressed in Jackson turbidity units
(JTU) and sometimes as Formazin turbidity units
(FTU). The FTU nomenclature comes from the For-
mazin polymer used to prepare the turbidity standards
for instrument calibration. Turbidity units are a meas-
ure of the cloudiness of water.
Status of Activated Carbon
A. Abrasion Number (Ro-Tap)
The abrasion number of granular carbon is a
measure of the resistance of the particles to degrad-
ing on being mechanically abraded. This number is
measured by contacting a carbon sample with steel
balls in a pan on a Ro-Tap machine. The abrasion
number is the ratio of the final average (mean) particle
diameter to the original average (mean) particle di-
ameter (determined by screen analysis) times 100.
B. Abrasion Number (NBS)
Similar to A above except different equipment is
used.
C. Apparent Density
The weight per unit volume of a homogenous acti-
vated carbon. To assure uniform packing of a granu-
lar carbon during measurement, a vibrating trough is
used to fill the measuring device.
D. Decolorizing Index
Molasses solution is treated with different weights
of a standard carbon of known Decolorizing Index.
The optical densities of the filtrate are measured and
plotted with the known Decolorizing Index values to
obtain a standard curve. A molasses solution is then
treated with pulverized activated carbon of unknown
decolorizing capacity. The optical density of the fil-
trate is measured and the Decolorizing Index is de-
termined from the standard curve.
E. Effective Size and Uniformity Coefficient
Effective size is the size of the particle that is
coarser than 10 percent, by weight, of the material.
That is, it is the size sieve which will permit 10 percent
of the carbon sample to pass but will retain the re-
maining 90 percent. Effective size is usually deter-
mined by the interpolation of a cumulative particle
size distribution.
Uniformity coefficient is obtained by dividing the
sieve opening in millimeters which will pass 60 per-
cent of a sample by the sieve opening in millimeters
which will pass 10 percent of the sample. These
values are usually obtained by interpolation on a
cumulative particle size distribution.
F. Hardness Number
The hardness number is a measure of the resist-
ance of a granular carbon to the degradation action of
steel balls in a pan in a Ro-Tap machine. This number
is calculated by using the weight of granular carbon
retained on a particular sieve after the carbon has
been in contact with steel balls. This is the Chemical
Warfare Service (CWS) test.
G. Iodine Number
The iodine number is the milligrams of iodine ad-
sorbed by one grain of carbon at an equilibrium filtrate
concentration of 0.02N iodine. The number is meas-
ured by contacting a single sample of carbon with an
iodine solution and extrapolating to 0.02N by an as-
sumed isotherm slope. Iodine number can be corre-
lated with ability to adsorb low molecular weight sub-
stances.
H. Methylene Blue Number
The methylene blue number is the milligrams of
methylene blue adsorbed by one gram of carbon in
equilibrium with a solution of methylene blue having a
concentration of 1.0 mg/L.
I. Moisture
Moisture is the percent by weight of water adsorbed
on activated carbon.
J. Molasses Number
The molasses number is calculated from the ratio of
the optical densities of the filtrate of a molasses solu-
tion treated with a standard activated carbon and the
activated carbon in question. This is a test method of
a Pittsburgh Activated Carbon Company.
K. Sieve Analysis (Dry)
The distribution of particle sizes in a given sample
is obtained by mechanically shaking a weighed
amount of material through a series of test sieves,
and determining the quantity retained by or passing
given sieves.
L. Total Ash of Regenerated Carbon
The total ash of a carbon is a measure of the
amount of the inorganic matter present. This test is
accomplished by a combustion process in which or-
ganic matter is converted to carbon dioxide and water
at a controlled temperature to prevent decomposition
-------
and volatilization of inorganic substances as much as
is consistent with complete oxidation of organic mat-
ter.
TESTS FOR MEASURING THE STATUS OF ACTIVATED
CARBON
Test procedures outlined in this appendix were taken from
PROCESS DESIGN MANUAL FOR CARBON ADSORPTION,
Appendix B, Technology Transfer, U.S. Environmental Protec-
tion Agency, October 1973.
A. Abrasion Number (Ro-Tap)
The Abrasion Number of carbon defines the resistance of
the particles to degradation by the action of steel balls in a
Ro-Tap machine, and is calculated as the percentage change
in mean particle diameter.
1. Equipment
Ro-Tap — Sieve Shaker, Fisher Scientific Catalog No.
4-906.
Sieves — U.S. Standard A.S.T.M. Sieves, 8-inch diame-
ter, full height.
Hardness Testing Pan Assembly — See Section F,
Hardness Testing, Figures A-4 and A-5.
Steel Balls — Ten (10) one-half-inch diameter and ten
(10) three-quarter-inch diameter smooth steel balls.
2. Procedure
Make a dry sieve analysis of 100 grams of the material to be
tested and save the screen fractions. The sieve analysis is to
be done exactly as specified in the Westvaco Dry Sieve
Analysis procedure except that the shaking time in the Ro-Tap
is increased to ten (10) minutes. Sieves should be selected
according to the nominal particle size of the carbon as set forth
in attached Table A-1. Calculate the mean particle diameter of
the sample from the sieve analysis (see Table A-2).
Recombine the fractions from the sieve analysis and place in
the special hardness pan with 20 steel balls (see Figures A-4
and A-5 of hardness pan and equipment list). Shake the pan
assembly on the Ro-Tap machine for 20 minutes with the tap-
per in operation.
At the end of the 20 minutes, remove the steel balls, make
another sieve analysis and calculate the mean particle diame-
ter.
3. Calculations
Abrasion Number = Final mean particle diameter x 1Q0
Original mean particle diameter
The mean particle diameter of the whole sample is corn-
Industrial Waste Treatment 681
(Abrasion Number)
TABLE A-2 FACTORS FOR CALCULATING MEAN
PARTICLE DIAMETERS*
U.S.S. Sieve
Mean Opening
U.S.S. Sieve
Mean Opening
' Number
mm
Number
mm
+4
5.74
4x6
4.06
6x8
2.87
4x8
3.57
8 x 10
2.19
10 x 12
1.84
8 x 12
2.03
12 x 14
1.55
14 x 16
1.30
12 x 16
1.44
16 x 18
1.10
16 x 20
1.02
18 x 20
0.92
20 x 25
0.78
20 x 30
0.72
25 x 30
0.65
30 x 35
0.55
30 x 40
0.51
35 x 40
0.46
40 x 45
0.39
40 x 50
0.36
45 x 50
0.33
50 x 60
0.27
50 x 70
0.25
60 x 70
0.23
70 x 80
0.19
70 x 100
0.18
80 x 100
0.16
" The mean particle diameter of each fraction is assumed to be mid-
way between the sieve opening in millimeters through which the
material has passed and the sieve opening in millimeters on which
the material was retained.
puted by multiplying the weight of the fraction by the respective
mean sieve openings, summing these weighted values and
dividing by total weight of material caught on the sieves and
pan. The following example for a 12 x 30 mesh sample illus-
trates the method of calculation.
Weight
Mean
Retained
Opening,
Weighted
Sieve No.
On Sieve, g
mm
Average
On 12
1.5
2.03a
3.0
16
25.1
1.44
36.1
20
50.2
1.02
51.2
30
22.5
0.72
16.2
Pan
1.1
0.00b
0
100.4
106 5
Mean Particle Diameter = 106 5 = 1.061 mm
100.4
8 Assuming this material would pass the No. 8 sieve (or generally the
next larger sieve in the square root of two series).
b Material caught on the pan is not considered in calculating the
Mean Particle Diameter.
B. Abrasion Number (NBS)
The apparatus consists essentially of an inverted T-shaped
stirrer turning rapidly in a cylindrical vessel containing the acti-
vated carbon. The clearance at the ends of the stirrer and
bottom are the only critical dimensions. The speed of the shaft
is 855 ± 15 rpm. (Obtained with a 2:1 reduction by V belt from
a 1,750 rpm motor 1/10 horsepower or larger.) A simple frame
for holding the drive motor and bearing container assembly is
also required,
TABLE A-1 SUGGESTED SIEVES TO BE USED FOR
SCREEN ANALYSIS
Nominal Sieve Size
U.S.S. (N.B.S.) Sieve Numbers
12 x 40
12, 16, 20, 30, 40, Pan
14 x 40
14, 16, 20, 30, 40, Pan
4 x 30
8,12,16,20,30 Pan
10 x 30
10,12,16,20,30 Pan
12 x 30
12,16,20,30 Pan
-------
682 Treatment Plants
(Apparent Density)
Procedure
1. Prepare a sample of activated carbon by the recommended
sampling procedures having a volume of 250 to 300 ml.
2. Obtain a sieve analysis by the recommended sieving pro-
cedure. Discard the fractions through No. 70 sieve and re-
combine all sieve fractions coarser than No. 70 and place in
hardness tester.
3. Operate the tester for 1 hour ± 1 minute.
4. Repeat the sieve analysis for the stirred mixture.
5. Calculate the percentage through No. 70 and record as the
percent dust formation.
6. Calculate the average particle size, D, before and after stir-
ring from the sieve analysis by means of the following rela-
tionship:
0 = swa
1\N\
where W is the weight of a sieve fraction, and the particle
diameter, D, is obtained as the arithmetic average of open-
ing of sieves above and below the fraction.
7. The percentage reduction in particle size is the decrease in
average particle size calculated as a percentage of the orig-
inal particle size.
8. Since this test abrades particles in proportion to their size,
divide both percentage reduction in particle size and per-
centage dust formation by particle size (mm) before stirring
in order to reduce both results to a standard 1 mm particle
size.
C. Apparent Density
The apparent density is defined as the weight of carbon per
unit volume expressed in grams per cubic centimeter or
pounds per cubic foot.
1. Equipment
Vibrator Feeders — See Figure A-1.
Cylinder— 100 ml A.S.T.M. Graduated Cylinder
2. Procedure
Dry an adequate sample of the carbon to be tested at 140
degrees C for one (1) hour or 110 degrees C for three (3)
hours. Place a representative sample of the dried carbon into
the reservoir funnel of the apparent density apparatus. Material
which flows prematurely into the graduated cylinder is returned
to the reservoir funnel.
Fill the tared graduated cylinder to the 100 ml mark at a
uniform rate so that filling time is not less than 100 seconds nor
more than 133 seconds. The rate can be adjusted by changing
the slope of the metal vibrator and/or raising or lowering the
reservoir funnel. A powerstat can be used to regulate the
speed of the vibrator, thus regulating the rate of filling of the
cylinder. Determine the weight of the carbon in the graduated
cylinder to the nearest tenth of a gram (0.1 gram).
3. Calculations
Apparent Density, gm/cc
4. Dimensions of Funnels and Vibrator
Weight of Activated Carbon
100
Metal Vibrator
Reservoir Funnel
Feed Funnel
1-%-inches wide
3-VHnches long
%-inch deep
Top Diameter 3-inches
Bottom Diameter 1-%-inches
Overall Height 4-inches
Height to flared top 3-1/4-inches
Top Diameter 3-V2-inches
Bottom Diameter 15/i 6-inch
Overall Height 4-inches
Height to flared top 1-VHnches
D. Decolorizing Index
Molasses solution is treated with different weights of a stan-
dard carbon of known Decolorizing Index. The optical densities
of the filtrate are measured and plotted with the known Decol-
orizing Index values to obtain a standard curve. A molasses
solution is then treated with pulverized activated carbon of
unknown decolorizing capacity. The optical density of the fil-
trate is measured and the Decolorizing Index is determined
from the standard curve.
1. Reagents and Equipment
Blackstrap Molasses — This molasses is available only
through the Chemical Division, Westvaco Corporation, as
selection is required to obtain molasses which provides re-
producible data from year to year.
Anhydrous Disodium Phosphate
Phosphoric Acid
Supercel Filter Aid
Standard D. I. Carbon — Small quantities of primary
standard carbon are available from the Chemical Division,
Westvaco Corporation.
Filter Cloth — A chain cloth, 32-inches wide, made by T.
Shriver and Company, Harrison, New Jersey.
Electric Hot Plate — The hot plate is a Type H, 120 volts,
550 watts, made by Precision Scientific Company. This hot
plate is used without the refractory top.
Klett-Summerson Colorimeter — A No. 54 green filter
and a 10 ml Klett-Summerson absorption tube (12.5 mm
-------
Industrial Waste Treatment 683
(Apparent Density)
RESERVOIR FUNNEL
CLAMPED TO RING
STAND
METAL VIBRATOR
DOOR BELL BUZZER
•FEED
FUNNEL
CLAMPED
TO RING
STAND
¦100 ml ASTM
GRADUATED
CYLINDER
SWITCH
TRANSFORMER
NO SCALE
Fig. A-1 Apparent density test apparatus
-------
684 Treatment Plants
(Decolorizing Index)
light path) are used for reading the samples. The instrument
is zeroed using distilled water.
The instrument should give approximately the following
reading when using a 0.5 normal potassium dichromate
(K2Cr207) solution:
0.5 Normal Klett-Summerson
Potassium Dichromate Reading
20 Percent Dilution
60 Percent Dilution
100 Percent Dilution
155
280
350
Return instrument pointer to near zero after each reading.
Analytical Balance — Sensitivity to 0.5 milligram.
Spex-Mixer Mill — No. 800 Spex-Mixer Mill and No. 8001
Grinding Vials, Spex Industries, Inc., 3880 Park Avenue,
Metuchen, New Jersey.
Filter Paper — Whatman No. 5, 15 cm.
2. Preparation of Solutions
Buffer Solution — (8X) — 104 grams anhydrous disodium
phosphate (Na2HP04) or equivalent weight of crystalline
phosphate, are dissolved in about 500 millimeters of warm
distilled water. When the phosphate is completely dissolved,
make up to one liter with distilled water. Acidify with concen-
trated reagent-grade phosphoric acid to pH 6.5 ± 0.1. For
preparation of larger quantities, multiples of these weights and
volumes may be used.
Molasses Solution — Dilute 40 grams of the blackstrap
molasses in about 50 ml (or amount necessary) of distilled
water (approximately 25 degrees C) Add 125 ml of buffer
solution, dilute to one liter with chilled distilled water (approxi-
mately 4 degrees C) and mix thoroughly. (Solution will be
about 13 degrees C.) However, if the molasses solution is to
be used immediately the distilled water does not need to be
chilled before using.
For preparations of larger quantities, multiples of these
weights and volumes can be used.
A Buchner funnel fitted with a filter cloth, is precoated by
slurrying Supercel filter aid with a portion of the blackstrap
molasses solution and filtering. Use sufficient Supercel filter
aid to provide a cake approximately one-half inch thick. After
precoating, change funnel to a clean filter flask. Pour the solu-
tion, to which a small amount of Supercel has been added. The
entire solution is then filtered through the filter aid cake. (If
necessary, this solution should be refiltered until it is clear.) If
this solution is not to be used immediately, it must be refriger-
ated (at about 4 degrees C).
3. Preparation of Standard Curve
1. Weigh accurately (± 0.001 gram) the following weights
of the ground* Standard D. I. carbon (dried at 140 de-
grees C for one (1) hour or 110 degrees C for three (3)
hours) into 150 ml beakers: 0.200, 0.300, 0.400, 0.500,
0.600, 0.700, 0.800, 0.900 and 1.00 gram.
2. Measure 50 ml of the molasses solution, using a
graduated cylinder, and reading the bottom of the
meniscus.
3. Add 10 to 20 ml of the molasses solution to the weighed
carbon. Swirl the contents of the breaker gently until the
carbon is completely wetted. Use the remaining portion
of the molasses solution to wash down the sides of the
beaker.
4. Place the beaker on the hot plate and bring the sample
to a boil (the solution should be brought to boiling in less
than 200 seconds). Boil for 30 seconds and then remove
sample from hot plate.
5. Filter immediately by gravity using a Whatman No. 5,15
cm filter paper (or equivalent). Allow all of the samples to
filter.
6. Allow filtrate to cool to room temperature (approximately
25 degrees C).
7. Read the color of the samples, using the Klett-
Summerson Colorimeter.
8. To prepare the Standard Curve, plot the Klett-
Summerson readings of the samples (from Step 1) ver-
sus the assigned Decolorizing Index Numbers (listed in
the following table) on semilogarithmic, 1 cycle x 70
divisions graph paper.
Weight of Standard
D. I. Carbon
0.200
0.300
0.400
0.500
0.600
0.700
0.800
0.900
1.00
Assigned Decolorizing
Index Number
6.5
8.6
11.2
14.0
16.9
19.9
23.0
27.0
30.8
Draw a straight curve line through these points. (See Figure
A-2). A new standard curve will need to be prepared for a
molasses solution which has been stored at 4 degrees C for
longer than 16 hours.
4. Preparation of Samples to be Tested
1. Weigh 0.460 ± 0.001 gram of the dried ground carbon
sample to be tested, and transfer to a 150 ml beaker.
2. Follow Steps 2 through 7 under Preparation of Standard
Curve.
3. The D. I. of the carbon is determined from the Standard
Curve.
* A ground sample is obtained by placing a 5.5±0.5 gram sample of
dried carbon in a Spex-Mixer Mill containing 64 one-fourth inch
diameter smooth steel balls until 90±5 percent will pass a 325
mesh screen (by wet screen analysis).
-------
KLETT-SUMMERSUN
READING
J
&
o
c
3
-------
686 Treatment Plants
(Effective Size arid Uniformity Coefficient)
E. Effective Size and Uniformity Coefficient
The Effective Size is defined as the size of the particle that is
coarser than 10 percent, by weight, of the material. This size is
usually determined by the interpolation of a cumulative particle
size distribution.
The Uniformity Coefficient is obtained by dividing the sieve
opening in millimeters which will pass 60 percent of a sample
by the sieve opening in millimeters which will pass 10 percent
of the sample. These values are usually obtained by interpola-
tion on a cumulative particle size distribution.
1. Procedure
1. Run a standard sieve analysis as outlined in the sieve
analysis (dry) test procedure.
2. From the percentage retained on each sieve, the
cumulative percent passing each sieve can be obtained
(see Table A-3).
3. On probability x logarithmic paper, plot the sieve open-
ing in millimeters on the ordinate, or vertical scale, ver-
sus the cumulative percent passing each sieve on the
abcissa, or horizontal scale (see Figure A-3).
4. The Effective Size is determined as the millimeter open-
ing at which 10 percent passes on the cumulative per-
cent passing scale.
5. The Uniformity Coefficient is determined by dividing the
millimeter opening at which 60 percent passes by the
millimeter opening at which 10 percent passes.
TABLE A-3 EXAMPLE EFFECTIVE SIZE AND
UNIFORMITY COEFFICIENT DETERMINATION
Sieve
Sieve Opening,
Wt. Retained on
Cumulative
No.
Millimeters
Sieve, gram*
% Retained
% Passing
12
1.680
0.3
0.3
99.7
16
1.190
20.7
20.9
78.8
20
0.840
49.4
49.6
29.0
30
0.590
22.0
22.2
6.8
40
0.420
6.5
6 6
0.2
Pan
0.2
0.2
99.1
100.0
Effective Size: 0.66
Uniformity Coefficient:1 04 =1.575
0.66
F. Hardness Number (CWS)
A sample of carbon of a pre-selected mesh size is sub-
jected to the action of steel balls on a Ro-Tap machine.
The resistance of the carbon to degradation by this action
is termed the Hardness Number.
1. Equipment
Ro-Tap — Sieve Shaker, Fisher Scientific Catalog
No. 4-906.
Sieves — U.S. Standard Sieve Series, 8-inch diame-
ter, full height sieves.
Hardness Testing Pan Assembly — See Figures A-4
and A-5.
2. Procedure
1. Weigh 50.0 grams of prepared size material (see Note
1) and place in a special hardness testing pan (see Fig-
ure A-4).
2. Place 15 one-half-inch diameter and 15 three-eighth-
inch diameter smooth steel balls in the hardness testina
pan.
3. Nest the hardness testing pan with a bottom receiving
pan below, a half-height blank pan and iron sieve cover
above, and place assembly on the Ro-Tap machine for
30 minutes with the tapper in operation.
4. At the end of the 30-minute period, remove the steel
balls on a No. 4 sieve and transfer the sample to a sieve
nested on a bottom receiving pan (see Note 1).
5. Place the sieve assembly on the Ro-Tap machine for 3
minutes with the tapper in operation.
3. Notes on Method
1. Selection of Special Sieve Sizes for Various Grades of
Carbon
a. For 4 x 8, 4 x 10, 6 x 8, 6 x 12 and 6x16 mesh
carbons, prepare 50.0 grams of 6 x 8 mesh material
by shaking approximately 100 grams of original
sample for 3 minutes on a Ro-Tap machine, using
the Nos. 6 and 8 sieves. Repeat, if necessary, until
50.0 grams are obtained. Use a No. 12 sieve for the
final screening step.
b. For 8 x 20, 8 x 30, 10 x 30, 12 x 30 and 12 x 40
mesh carbons, prepare 50.0 grams of 12 x 16 mesh
material and use a No. 20 sieve for the final screen-
ing step.
c. For 4x6 mesh carbon, prepare 50.0 grams of 4 x
6 mesh material and use a No. 8 sieve for the final
screening step.
d. For 8 x 14 mesh carbon, prepare 50.0 grams of 8 x
12 material and use a No. 16 sieve for the final
screening step.
G. Iodine Number
The Iodine Number is defined as the milligrams of iodine
adsorbed by one gram of carbon when the iodine concentra-
tion of the residual filtrate is 0.02 normal.
1. Reagents and Equipment
Hydrochloric Acid, 5 percent weight — To 550 ml of distilled
water add 70 ml of reagent-grade concentrated hydrochloric
acid (HCI).
Sodium Thiosulfate, 0.1 normal — Dissolve 25 grams of
reagent-grade sodium thiosulfate (Na2S203-5H20) in one (1)
liter of freshly boiled distilled water. Add a few drops of
chloroform to minimize bacterial decomposition of the thiosul-
fate solution. Standardize the thiosulfate solution against 0.100
normal potassium biniodate (KH (I03)2). Prepare the 0.1000
normal KH (I03)2 using primary standard quality KH (I03)2
-------
Industrial Waste Treatment 687
(Effective Size and Uniformity Coefficient)
CUMULATIVE % PASSING
Fig. A-3. Cumulative particle size distribution curve
(For determination of Effective Size and Uniformity Coefficient)
-------
688 Treatment Plants
(Hardness Number (CWS))
14 GA. SHEET
BRASS BROWN
& SHARP STD.
SOLDER
CN
SCALE: 1:2
Fig. A-4. Testing pan for determining hardness and abrasion
-------
Industrial Waste Treatment 689
(Hardness Number (CWS))
CORK
LID
HALF-HEIGHT BLANK PAN
RECEIVING PAN
SPECIAL HARDNESS PAN
ELEVATION
NO SCALE
Fig. A-5. Arrangement of Ro-Tap pans for hardness and abrasion test
-------
690 Treatment Plants
(Iodine Number)
which has been dried overnight at 105 degrees C and cooled in
a desiccator. Weigh 3.249 grams KH (I03)2 and make-up to
exactly one liter in a volumetric flask with distilled water. Store
in a glass-stoppered bottle.
To 80 ml of distilled water add, with constant stirring, one ml
of concentrated sulfuric acid (H2S04), 10 ml of 0.1000 KH
(I03)2 solution and approximately one gram of potassium
iodide (Kl). Titrate the mixture immediately with the thiosulfate
solution adding 2-3 drops of starch solution when the iodine
fades to a light yellow color. Continue the titration by adding
the thiosulfate dropwise until a drop produces a colorless solu-
tion. Record the volume of titrate used.
Normality of sodium thiosulfate = 1???
ml of Na2S203 consumed
Iodine Solution — Dissolve 12.7 grams of reagent-grade
iodine (I2) and 19.1 grams of potassium iodide in a small quan-
tity, approximately 20 ml, of distilled water. (If excess water is
used, materials will not go into solution.) Dilute to one (1) liter in
a volumetric flask with distilled water. Store in a glass-
stoppered bottle in a dark place or use in a dark bottle. To
standardize the iodine solution, pipet 25.0 ml into a 250 ml
Erlenmeyer flask and immediately titrate with the 0.1 normal
thiosulfate solution. Add 2-3 drops of starch solution near the
endpoint and continue titrating until solution is colorless. Rec-
ord the volume of titrant used.
ml of Na2S203 used x normality Na2S203
Normality of iodine solution =
25
Starch Solution — To 2.5 grams of starch (potato, arrowroot,
or soluble), add a little cold water and grind in a mortar to a thin
paste. Pour into one (1) liter of boiled distilled water, stir, and
allow to settle. Use the clear supernatant. Preserve with 1.25
grams of salicylic acid per one (1) liter of starch solution.
Filter Paper — Whatman Folded No. 2V, 10.5 cm.
Spex-Mixer Mill — No. 8000 Spex-Mixer Mill and No. 8001
Grinding Vials, Spex Industries, Inc., 3800 Park Avenue,
Metuchen, New Jersey.
2. Procedure
Grind a representative sample of carbon in a Spex-Mixer Mill
(usually 70 seconds) until 90 ± 5 percent will pass a 325 mesh
sieve (by wet seive analysis). Load the Spex-Mixer Mill with a
5.5 ± 0.5 gram sample and use 64 one-fourth inch diameter
smooth steel balls. An adequate sample of the pulverized car-
bon should then be dried at 140 degrees C for one (1) hour, or
110 degrees C for three (3) hours. A moisture balance can also
be used.
Weigh 1.000 gram of the dried pulverized carbon (see Note
1) and transfer the weighed sample into a dry, glass-
stoppered, 250 ml Erlenmeyer flask. To the flask add 10 ml of 5
percent by weight HCI acid and swirl until the carbon is wetted.
Place the flask on a hot plate, bring contents to boil and allow
to boil for only 30 seconds.
After allowing the flask and contents to cool to room temper-
ature, add 100 ml of standardized 0.1 normal iodine solution to
the flask. Immediately stopper flask and shake contents vigor-
ously for 30 seconds. Filter by gravity immediately after the
30-second shaking period through Whatman No. 2V filter pa-
per. Discard the first 20 or 30 ml of filtrate and collect the
remainder in a clean beaker. Do not wash the residue on the
filter paper.
Mix the filtrate in the beaker with a stirring rod and pipet 50
ml of the filtrate into a 250 ml Erlenmeyer flask. Titrate the 50
ml sample with standardized 0.1 normal sodium thiosulfate
until the yellow color has almost disappeared. Add about 1 ml
of starch solution and continue titration until the blue indicator
color just disappears. Record the volume of sodium thiosulfate
solution used.
Notes on Procedure
1. The capacity of a carbon for any adsorbate is dependent on
the concentration of the adsorbate in the medium contact-
ing the carbon. Thus, the concentration of the residual fil-
trate must be specified, or known, so that appropriate fac-
tors may be applied to correct the concentration to agree
with the definition. The amount of sample to be used in the
determination is governed by the activity of the carbon. If
the residual filtrate normality (C) is not within the range
0.008/V to 0.035W given in the Iodine Correction Table A-4,
the procedure should be repeated using a different weight
of sample.
2. The potassium iodide to iodine weight ratio must be 1.5 to 1
in the standard iodine solution.
Calculation
y
Iodine Number = _ D
m
X = A - (2.2B x ml of thiosulfate solution used)
m Weight of sample, grams
Q - N2 x ml thiosulfate solution used
50
X/m = mg iodine adsorbed per gram of carbon
N, = Normality of iodine solution
N2 = Normality of sodium thiosulfate solution
A = N, x 12693.0
B = N2 x 126.93
C = Residual filtrate normality
D = Correction factor (obtained from Table A-4)
H. Methylene Blue Number
The Methylene Blue Number is defined as the milligrams of
methylene blue adsorbed by one gram of carbon in equilibrium
with a solution of methylene blue having a concentration of 1 0
mg per liter.
I. Reagents and Equipment
Methylene Blue — Zinc-free, American Cyanamid Com-
pany. Dry the methylene blue to constant weight. Prepare solu-
tions of 20.00 and 1.00 gIL concentrations.
Colorimeter — An instrument such as the Klett-Summerson
Industrial Model (for colorimetric analysis).
Variable-Speed Shaker — Will Scientific Catalog No. 23690
with Box Carrier Catalog No. 23696.
Filter Paper — Whatman No. 3, Qualitative.
Spex-Mixer Mill — No. 8000 Spex-Mixer Mill and No. 8001
Grinding Vials, Spex Industries, Inc., 3880 Park Avenue
Metuchen, New Jersey.
-------
Industrial Waste Treatment 691
(Iodine Number)
TABLE A-4 IODINE CORRECTION FACTOR (D)
Residual
Filtrate
Normality
(C)
.000
.0001
.0002
.0003
.0004
.0005
.0006
.0007
.0008
.0009
.0080
1.1625
1.1613
1.1600
1.1575
1.1550
1.1538
1.1513
1.1500
1.1475
1.1463
.0090
1.1438
1.1425
1.1400
1.1375
1.1363
1.1350
1.1325
1.1300
1.1288
1.1275
.0100
1.1250
1.1238
1.1225
1.1213
1.1200
1.1175
1.1163
1.1150
1.1138
1.1113
.0110
1.1100
1.1088
1.1075
1.1063
1.1038
1.1025
1.1000
1.0988
1.0975
1.0963
.0120
1.0950
1.0938
1.0925
1.0900
1.0888
1.0875
1.0863
1.0850
1.0838
1.0825
.0130
1.0800
1.0788
1.0755
1.0763
1.0750
1.0738
1.0725
1.0713
1.0700
1.0688
.0140
1.0675
1.0663
1.0650
1.0625
1.0613
1.0600
1.0588
1.0575
1.0563
1.0550
.0150
1.0538
1.0525
1.0513
1.0500
1.0488
1.0475
1.0463
1.0450
1.0438
1.0425
.0160
1.0413
1.0400
1.0388
1.0375
1.0375
1.0363
1.0350
1.0333
1.0325
1.0313
.0170
1.0300
1.0288
1.0275
1.0263
1.0250
1.0245
1.0238
1.0225
1.0280
1.0200
0.180
1.0200
1.0188
1.0175
1.0163
1.0150
1.0144
1.0138
1.0125
1.0125
1.0113
.0190
1.0100
1.0088
1.0075
1.0075
1.0063
1.0050
1.0050
1.0038
1.0025
1.0025
.0200
1.0013
1.0000
1.0000
0.9988
0.9975
0.9975
0.9963
0.9950
0.9950
0.9938
.0210
0.9938
0.9925
0.9925
0.9913
0.9900
0.9900
0.9888
0.9875
0.9875
0.9863
.0220
0.9863
0.9850
0.9850
0.9838
0.9825
0.9825
0.9813
0.9813
0.9800
0.9788
.0230
0.9788
0.9775
0.9775
0.9763
0.9763
0.9750
0.9750
0.9738
0.9738
0.9725
.0240
0.9725
0.9708
0.9700
0.9700
0.9688
0.9688
0.9675
0.9675
0.9663
0.9663
.0250
0.9650
0.9650
0.9638
0.9638
0.9625
0.9625
0.9613
0.9613
0.9606
0.9600
.0260
0.9600
0.9588
0.9588
0.9575
0.9575
0.9563
0.9563
0.9550
0.9550
0.9538
.0270
0.9538
0.9525
0.9525
0.9519
0.9513
0.9513
0.9506
0.9500
0.9500
0.9488
.0280
0.9488
0.9475
0.9475
0.9463
0.9463
0.9463
0.9450
0.9450
0.9438
0.9438
.0290
0.9425
0.9425
0.9425
0.9413
0.9413
0.9400
0.9400
0.9394
0.9388
0.9388
.0300
0.9375
0.9375
0.9375
0.9363
0.9363
0.9363
0.9363
0.9350
0.9350
0.9346
.0310
0.9333
0.9333
0.9325
0.9325
0.9325
0.9319
0.9313
0.9313
0.9300
0.9300
.0320
0.9300
0.9294
0.9288
0.9288
0.9280
0.9275
0.9275
0.9275
0.9270
0.9270
.0330
0.9263
0.9263
0.9257
0.9250
0.9250
-------
692 Treatment Plants
(Methylene Blue Number)
2. Procedure
Grind a representative sample of carbon in a Spex-Mixer Mill
until 90 ± 5 percent will pass a 325 mesh screen (by wet
screen analysis). Load the Spex-Mixer Mill with a 5.5 ± 0.5
gram sample and use 64 one-fourth inch diameter steel balls.
An adequate sample of the carbon should then be dried at 140
degrees C for one (1) hour or 100 degrees C for three (3)
hours.
Add 5.00 grams of pulverized carbon to a 250 ml Erlenmeyer
flask (see Note 1). Add 80 ml of methylene blue solution (20
grams per liter) to the beaker. Shake at about 150 oscillations
per minute for 20 minutes using a mechanical stirrer. Im-
mediately after the stirring period, filter, through a Buchner
funnel under vacuum, using Whatman No. 3 filter paper (see
Note 2). Discard the first 10 to 15 ml of the sample filtrate and
collect the remainder.
3. Colorimetric Analysis
Transfer the filtrate to a solution cell having a 40 mm effec-
tive depth and record the reading using a colorimeter with a
green (540 m/u.) color filter (see Note 4). Prepare a standard
curve using methylene blue concentrations of 0.4,1.0,3.0, and
5.0 mg/L (see Note 3). Determine the concentration of
methylene blue by reference to the standard curve (Table A-5).
The methylene blue number is found by referring to Table A-6.
4. Notes on Procedure
1. The weight of sample taken is determined by the activity
of the carbon. The 5.00 gram sample size is correct for
carbons having methylene blue numbers ranging from
264 to 330. For carbons of higher activity, it will be nec-
essary to use only a 4 gram sample while other carbons
of lower activity will require from 6 to 8 grams to reduce
the concentration of methylene blue in the filtrate rea-
sonably close to that of the standards.
2. Prepare the filter beforehand by placing the filter paper
in the funnel, wetting it thoroughly and removing excess
water with the vacuum. Discard the water from the flask
to prevent dilution of the test filtrate.
3. To prepare standards having methylene blue concentra-
tions of 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0 and 5.0 mg per
liter, dilute 5.0 ml of the 1.0 gram per liter methylene blue
solution to one liter with distilled water. Then transfer 4,
6, 8, 11, 15, 20, 30 and 50 ml of the resulting solution to
separate 50 ml volumetric flasks and dilute to 50 ml with
distilled water.
4. If the filtrate color is deeper than a reading correspond-
ing to 5 mg/L on the standard curve, pipet 0.5,1, 5, or 10
ml into a 50 ml volumetric flask and dilute to the 50 ml
mark with distilled water. Determine the methylene blue
concentration for the diluted sample and use the follow-
ing formula to determine filtrate concentrations:
Filtrate concentration, mg/L = Di'uted concentration x 50
ml sample pipetted into
volumetric flask
TABLE A-5 DILUTION CHART FOR METHYLENE BLUE DETERMINATION
Methylene Blue Concentration, mg/L
Color Standard
50 ml
10 ml
No. of ml of Filtrate Taken
5 ml
1 ml
0.5 ml
3
0.4
2.0
4.0
20.0
40.0
3-Va
0.5
2.5
5.0
25.0
50.0
4
0.6
3.0
6.0
30.0
60.0
4-i/2
0.7
3.5
7.0
35.0
70.0
5
0.8
4.0
8.0
40.0
80.0
5-Vi
0.9
4.5
9.0
45.0
90.0
6
1.0
5.0
10.0
50.0
100.0
6-Vi
1.25
6.25
12.5
62.5
125.0
7
1.50
7.5
15.0
75.0
150.0
7-1/2
1.75
8.75
17.5
87.5
175.0
8
2.00
10.0
20.0
100.0
200.0
8-1/2
2.50
12.5
25.0
125.0
250.0
9
3.00
15.0
30.0
150.0
300.0
9-1/2
4.00
20.0
40.0
200.0
400.0
10
5.00
25.0
50.0
250.0
500.0
-------
Industrial Waste Treatment 693
(Methylene Blue Number)
TABLE A-6 METHYLENE BLUE CORRECTION CHART
(mg Methylene Blue adsorbed per gram of carbon at a filtrate concentration of 1.0 mg/L)
Methylene Blue Number
Hiltrate Concentration
mg Methylene Blue/L
4 gm
5 gm
Sample Size
6 gm
7 gm
8 gm
0.4
416
333
277
238
208
0.5
414
331
276
236
207
0.6
410
328
273
235
205
0.7
408
327
272
234
204
0.8
407
326
271
233
203
0.9
406
325
270
232
203
1.0
405
324
270
232
202
1.2
402
322
268
230
201
1.5
399
319
266
228
200
1.75
398
318
265
227
199
2.0
396
317
264
226
198
2.5
394
315
262
225
197
3.0
391
313
261
224
195
3.5
388
311
259
223
194
4.0
387
310
258
222
193
4.5
386
309
257
221
193
5.0
385
308
256
220
192
6.0
384
307
256
220
192
6.25
382
306
255
219
191
7.0
381
305
254
218
191
7.5
380
304
253
217
190
8.0
380
304
253
217
190
8.75
378
303
252
216
189
9.0
377
302
251
216
189
10.0
376
301
250
215
188
12.5
374
299
250
213
187
15.0
371
297
248
212
185
17.5
370
296
247
212
185
20.0
368
295
246
211
184
25.0
365
292
243
209
184
30.0
363
291
242
208
182
35.0
361
289
241
207
181
40.0
360
288
240
206
180
45.0
358
287
239
205
179
50.0
357
286
238
204
179
60.0
355
284
237
204
178
62.0
353
283
236
203
177
70.0
352
282
235
202
176
75.0
351
281
234
201
175
80.0
351
281
234
201
175
87.5
350
280
233
200
175
90.0
350
280
233
200
175
100.0
348
279
232
199
174
125.0
346
277
231
198
173
150.0
344
275
229
197
172
175.0
342
274
228
196
171
200.0
341
273
227
195
170
250.0
338
271
226
194
169
300.0
336
269
224
192
168
400.0
332
266
222
190
166
500.0
330
264
220
188
165
-------
694 Treatment Plants
(Molasses Number)
I. Moisture
Moisture is the percent, by weight, of water adsorbed on
activated carbon.
1. Procedure
1. Dry an aluminum moisture dish (2-inches in diameter by
%-inch deep) and lid in an electric oven for thirty (30)
minutes at 110 degrees C. Cool in a desiccator and
weigh.
2. Weigh approximately 2 grams of carbon into the tared
dish, recording the exact weight.
3. Place the dish containing the carbon (lid opened to allow
the moisture to escape) in the oven and allow to dry
either three (3) hours at 110 degrees C, or two (2) hours
at 140 degrees C. Close lid tightly, remove from the
oven, cool the dish in a desiccator and weigh.
An alternate method is to use a moisture balance.
2. Calculation
Percent moisture = Loss in weight during drying, g v inn0/.
Initial weight of sample, g
For example:
Weight of dish plus sample = 15.5543
Weight of dish = 13.5478
Weight of sample = 2.0065
Weight of dish plus dried
sample = 15.4635
Loss of weight = .0908
Percent Moisture = x 100%
2.0065 g
= 4.5%
Values reported to the nearest 0.1 percent are satisfactory,
i.e., in the above case, 4.5 percent.
J. Molasses Number
Molasses solutions are treated with pulverized activated
carbon of unknown decolorizing capacity and with a standard
carbon of known Molasses Number. The optical densities of
the filtrates are measured and the Molasses Number of the
unknown is calculated from the ratio of the optical densities
and the standard value.
1. Reagents and Equipment
Standard Carbon — Small quantities of standard carbon are
available from the Chemical Division, Westvaco Corporation.
Molasses Solution — Prepare by diluting 146 grams of
blackstrap molasses with one (1) liter of distilled water. The
weight of molasses to be used varies with the particular lot of
molasses and is adjusted, if necessary, so that the standard
carbon produces a filtrate with an optical density (percent
transmission) of 0.38 to 0.42.
Any grade of commercial molasses which may be pur-
chased will vary considerably in depth of color. The dilution of
the initial solution to give the same final filtrate color with the
standard carbon compensates for such variations. Once such
an adjustment has been made on a given lot of molasses, the
proper dilution may be made routinely. The molasses solution
is stored in a refrigerator and any unused portion discarded
after 24 hours.
A suitable grade of blackstrap molasses can be purchased
from Refined Syrups, Yonkers, New York.
Spex-Mixer Mill — No. 8000 Spex-Mixer Mill and No. 8001
Grinding Vials, Spex-lndustries, Inc., 3880 Park Avenue,
Metchun, New Jersey.
Filter Paper Suspension — Prepare by mascerating 16 cir-
cles of Whatman No. 3, 7-cm filter paper in one (1) liter of
distilled water.
Absorption Cell — Klett-Summerson, No. 902, 10-mm.
Immersion Plate — Klett-Summerson, No. 903, 7.5 mm.
2. Procedure
Grind a representative sample to carbon in a Spex-Mixer Mill
until 90 ± 5 percent will pass a 325-mesh sieve (by wet sieve
analysis). Load the Spex-Mixer Mill with a 5.5 ± 0.5 gram
sample and use 64 one-fourth inch diameter smooth steel
balls. An adequate supply of the carbon should then be dried at
140 degrees C for one (1) hour or 110 degrees C for three (3)
hours. Weigh 0.46 gram portions of pulverized standard car-
bon of known decolorizing capacity and unknown carbon and
transfer to separate 400 ml beakers. Add 50.0 ml of molasses
solution to each beaker and stir until the carbon is thoroughly
wetted.
Place the beakers on hotplate and allow to boil for 30 sec-
onds from time boiling commences.
Immediately after boiling, filter the samples by vacuum
through a Buchner funnel, using Whatman No. 3 filter paper
which has been previously coated by filtering 50 ml of the filter
paper suspension (see Note 1). Discard the first 10 to 15 ml of
the sample filtrate and collect the remainder.
Using a 2.5 mm effective light path and a 425 m/x (blue)
filter, compare the optical densities of the samples against
distilled water in a Fisher Electrophotometer or other suitable
instrument (see Note 2).
Notes on Procedure
1. The Buchner funnels and precoated filter paper should be
prepared beforehand so that no delay is encountered in
filtering the samples. Discard the filtrate from the filter paper
suspension before filtering the samples.
2. Since the Fisher Electrophotometer is not equipped with 2.5
mm cells, the cell holder was modified to accommodate the
10-mm, Klett-Summerson cell. A 2.5 mm effective light path
is obtained by placing the cell with a 7.5 mm glass immer-
sion plate.
Calculations
Molasses Number = K x B
A
K = Molasses Value of Standard Carbon
A = Optical Density of Filtrate from Test Carbon
B = Optical Density of Filtrate from Standard Carbon
-------
Industrial Waste Treatment 695
K. Sieve Analysis (Dry)
The distribution of particle sizes in a given sample is ob-
tained by mechanically shaking a weighed amount of material
through a series of test sieves, and determining the quantity
retained by or passing given sieves.
1. Equipment
Riffle, Jones Sample — Will Scientific Catalog No. L-23621
Ro-Tap — Sieve Shaker, Fisher Scientific Catalog, No.
4-906
Brush — For metal surfaces, brass wire bristle, Will Scien-
tific Catalog No. 6916
Sieves — U.S. Standard A.S.T.M. Sieves, 8-inch diameter,
full height
Balance having a sensitivity of 0.1 gram
2. Procedure
Reduce the sample to be tested to 100 grams by means of a
riffle (see Note 1). Assemble the nest of desired sieves in order
of decreasing size of opening, the sieve having the largest
openings mounted on top. Place the 100.0 gram sample in the
top sieve, install iron cover on top of the assembly and shake
on the Ro-Tap machine for three (3) minutes with the tapper in
operation (see Note 2). Weigh and report the percent of mate-
rial retained on each sieve (see Notes 3 and 4).
Notes on Procedure
1. The sample is carefuly reduced by repeated passes
through the riffle until the amount collected on one of the
riffle pans is close to 100 grams. The entire contents of that
pan are then emptied onto a balance accurate to 0.1 gram
and weighed. No more than 5 grams should be added to, or
taken from, the balance without additional riffling. For
example, if the entire contents from the riffle pan weighed
only 90 grams, the additional 10 grams should be obtained
by riffling another sample down to an approximate 10 gram
portion, after which the entire contents of that riffle pan are
emptied onto the balance. Removing large quantities from
the balance or adding large quantities from the sample
stock without riffling will lead to erroneous results.
2. With sieving samples which are finer than 100 mesh, the
shaking time must be increased. Use 10 minute intervals
until less than 2 grams are collected in the receiving pan in
a 10 minute interval.
3. The sieve should be lightly brushed with a brass wire bristle
brush to free particles held in the screen.
(Sieve Analysis (Dry))
4. The analysis should be rejected if the sum of the individual
fractions is less than 98.0 grams or more than 102.0 grams.
5. Sample Calculations
Wt. Retained on
Sieve No.
Sieve, gms
% Retained
8
6.4
6.4
12
17.5
17.6
16
23.5
23.7
20
48.0
48.3
Pan
3.9
3.9
Total
= 99.3
% Retained = Weight Retained on Each Sieve y 100o/o
Total Wt. Retained on all Sieves
L. Total Ash of Regenerated Carbon
The total ash of a carbon is a measure of the amount of the
inorganic matter present. This test is accomplished by a com-
bustion process in which organic matter is converted to carbon
dioxide and water at a controlled temperature to prevent de-
composition and volatilization of inorganic substances as
much as is consistent with complete oxidation or organic mat-
ter.
1. Apparatus
Electric Furnace — Any types which can be controlled at 600
± 25 degrees C.
Evaporating Dish — Shallow form, 80 mm diameter, 20 mm
height.
Analytical Balance having a sensitivity of 0.1 mg.
Desiccator.
Oven, forced air circulation capable of temperature regula-
tion between 100 and 150 degrees C.
2. Procedure
Heat an evaporating dish in an electrically heated furnace for
thirty (30) minutes at 600 ± 25 degrees C, cool in a desiccator,
and weigh. Weigh five (5) grams of the sample (dry weight
basis) — dry at 110 degrees C for three (3) hours or 140
degrees C for one (1) hour into the tared dish, recording the
exact weight of the dish and sample.
Ash the sample in the furnace at 600 ± 25 degrees C. The
time required for complete ashing varies with the material
being tested. Heating to constant weight assures complete
ashing (leaving the sample in the furnace overnight will assure
complete ashing). During ashing, the furnace door should be
left slightly open to obtain an exchange of oxygen and gases.
After ashing, cool the dish and sample in a desiccator and
weigh.
3. Calculations
Total Ash, % = (Wt. dish and ash, 9) - (Wt, dish, g) x 10Q%
Dry weight of sample, g
-------
696 Treatment Plants
SUGGESTED ANSWERS
Chapter 28. INDUSTRIAL WASTE TREATMENT
Answers to questions on page 545.
28.OA Four of the general ways water is used by industries
are:
1. As process water for industrial uses,
2. To make processing of other materials easier or
more efficient,
3. To transport materials to, through, and from the
industrial process, and
4. For cooling.
28.OB The three alternative arrangements possible for treat-
ing industrial wastewater are:
1. Discharge to a Publicly Owned Treatment Works
(POTW) to be combined with municipal wastes
and possibly wastes from other industries, treated,
and returned to the environment.
2. Pre-treatment by industry, followed by discharge to
a POTW, as above, and
3. Treatment by industry to the extent required before
discharge to a receiving water.
Answers to questions on page 548.
28.OC Water can be biologically contaminated by bacteria,
viruses and other microorganisms excreted from the
human body and other warm-blooded animals. These
excretions may reach the environment through (1)
sanitary wastewater, (2) storm waters washing the
land of animal wastes and (3) through certain indus-
tries, most notably slaughterhouses and tanneries.
28.0D Biologically contaminated water may be made safe by
the DISINFECTION process.
28.OE The major potential sources of contamination of water
by toxic materials is from the manufacturing pro-
cesses in which these chemicals are either used or
made and from in-plant spills and accidents.
28.OF Oxygen-consuming wastes provide food for aquatic
microorganisms that remove dissolved oxygen from
the water as they "breathe." Once all of the dissolved
oxygen in the water is gone, the wastes are treated by
anaerobic decomposition which produces unpleasant
odors, colors and sludges that discourage water-
contact recreation.
28.0G Toxicity may interfere with the following potential uses
of water:
1. Drinking,
2. Cooking,
3. Water-contact recreation,
4. Fish, wildlife and aquatic vegetation,
5. Agricultural use, and
6. Industrial.
Answers to questions on page 550.
28.0H Dairy processing plants typically produce a waste very
high in BOD and SOLIDS.
28.01 Flows from tannery wastes are highly variable be-
cause tanning is accomplished in a batch process.
28.0J Treatment of pulp and paper wastes is considered
difficult because a lot of the raw material is rejected, a
high volume of water is used in the process, organic
loadings are relatively high and there is a natural re-
sistance of the type of organic material in the wastes
to biological oxidation. Treatment through biological
oxidation, such as activated sludge, should be effec-
tive for this type of wastewater, however, it may be
necessary to practice control of the pH level of the
wastes as well as the nutrient level.
28.0K Economical by-products from packing house wastes
include:
1. Glue,
2. Soap,
3. Animal feed, and
4. Fertilizer.
28.0L Fermentation is the breaking down of sugars and
starches into simpler compounds by yeasts.
Answers to questions on page 553.
28.0M The two most significant problems encountered in the
treatment of fruit and vegetable processing wastes are
(1) the seasonal nature of the processing and (2) the
nutrient deficiency commonly existing in the wastewa-
ter.
28.0N One advantage of anaerobic filters as applied to the
processing of fruit and vegetable wastewater is that
they can be used effectively on an intermittent basis.
28.00 Typical treatment problems in the textile industry in-
clude:
1. Lint, fibers and strings,
2. Natural greases,
3. Foam,
4. Highly alkaline and acidic wastes,
5. Fluctuations in flow, and
6. Toxic metals.
28.OP The principal problem of wastes from the petroleum
industry is the brine.
28.OQ Five toxic substances found in metal finishing wastes
include:
1. Acids,
2. Chromium,
3. Zinc,
4. Copper,
5. Nickel,
6. Tin, and
7. Cyanide.
END OF ANSWERS TO QUESTIONS IN LESSON 1
Answers to questions on page 560.
28.1 A Coagulants are used in the dissolved air flotation pro-
cess to cause the formation of a large floe of solids,
trapping the air bubbles inside. This can improve or
increase the effectiveness of each single air bubble.
-------
Industrial Waste Treatment 697
28.1 B An operator must be able to identify the critical parts
and their function because any incorrect identification
or misuse could cause a decrease in performance of
the system or total system shutdown.
28.1C The performance of a flotation unit feed pump could
be adversely affected by improper operation, worn im-
pellers, blockages or improper sizing.
28.1 D The retention tank is a pressurized vessel where the
mixing of the treated wastewater solution and air takes
place. Without this tank, the flotation system would not
operate.
28.1 E The purpose of the flotation tank is to provide a loca-
tion where the floes are allowed to float to the surface
and be removed by skimmers.
Answers to questions on page 562.
28.1 F Failure to start the flight scraper drive immediately
after the feed valve has been adjusted will allow the
buildup of sludge to depths within the flotation com-
partment where shutdown and wash-up procedures
will be necessary to clean out the unit.
28.1G If the flight scrapers travel too slowly, a heavy buildup
of sludge will develop with the possibility of overload-
ing the drive unit and plugging the flotation compart-
ment.
28.1H If the flight scrapers travel too fast, too much distur-
bance will be created in the flotation compartment and
the sludge will become diluted.
28.11 If the retention tank and flotation unit were not flushed
out and washed down during the shutdown proce-
dures, the performance level of the unit after start-up
would be below accepted levels.
28.1 J Improper Procedure
START-UP
1. Not filling unit with fresh
water before starting
feed pump.
2. Not closing drain valve
before filling unit.
3. Not turning on air.
Consequence
Damage to feed pump.
Waste of water and
time.
Effluent quality will suf-
fer.
Waste of chemicals
and money.
Waste of energy.
SHUTDOWN
1. Leaving chemicals on
until after job's com-
pleted.
2. Opening and closing
drain valve on the reten-
tion tank after the feed
pump was shut off.
28.1 K Waste stream evaluation is very critical to the solving
of problems, for the prevention of problems, and as an
aid in troubleshooting the flotation system.
28.1L Serious Indicator Cause
1. Variation of flow.
2. Variation in odors.
Blockage in the feed-
pump or the pump has
been worn out.
Normal system wash-
up schedule has not
been followed.
Answers to questions on page 564.
28.1 M A daily operation log is necessary for accurate record-
ing of system data, system evaluation, and meeting
discharge permit requirements.
28.1 N Information that can be obtained from analysis of the
accumulated log data includes:
1. General trends such as gradual system slime
buildups,
2. Seasonal variations,
3. Results of overbadings or slugs,
4. Information to operate the system,
5. Information to operate new systems,
6. Base data for discharge permit modifications, and
7. Indications of operators needing additional training.
28.10 The two types of sampling are for:
1. Discharge permit compliance, and
2. Operation log book.
Grab and composite are also two types of sam-
pling.
28.1P Basic rules to follow when correcting a problem in-
clude:
1. Assess the problem,
2. List possible corrective actions,
3. Proceed to correct the problem by doing one cor-
rective action (or change one variable) at a time,
4. Record all actions,
5. Evaluate system response to each action, and
6. After problem is corrected, try to prevent it from
developing again.
28.1Q Wait long enough between changes for each change
to take effect and to observe the effectiveness of the
change in correcting the problem.
28.1R Continuous monitoring is required when abnormal in-
dicators are present.
Answers to questions on page 566.
28.1S Preventive maintenance is that maintenance which is
performed on equipment to keep it from malfunction-
ing.
28.1T Preventive maintenance procedures done too often
are a waste of time and energy, and could possibly
lead to component or part damage. If procedures are
done at irregular time intervals or not at all, part failure
or other problems could develop.
28.1 U All part settings should be returned to original settings
so the operator knows where the system is operating.
The replacement of guards is required so nobody will
take for granted that the guards are in place, when
they are not, and possibly get seriously injured.
28.1V The four major areas of plant operation that are influ-
enced by preventive maintenance are:
1. Overall system operation,
2. System performance levels,
3. Budget, and
4. Receiving water quality.
Answers to questions on page 567.
28.1W Corrective maintenance is the repair or replacement of
malfunctioning components. This type of maintenance
usually requires the total shutdown of the system.
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698 Treatment Plants
28.1 X The causes of part malfunction include:
1. Lack of proper preventive maintenance,
2. Improper installation,
3. Product defects,
4. Improper operation,
5. Old age, and
6. Overloading.
28.1Y A spare parts inventory is a necessity. Without the
inventory unnecessary down-time of the system will
be adding up and will drastically affect the discharge
stream or solids and water recovery.
28.1Z Quick and efficient corrective maintenance is required
to get the job done as quickly as possible before ad-
verse conditions arise because of system down-time.
END OF QUESTIONS IN LESSON 2
Answers to questions on page 569.
28.2A The purpose of screens and microscreens is to inter-
cept and remove suspended solids from the flowing
wastewater.
28.2B Microscreens could be an aid to disinfection by remov-
ing floatable and suspended solids prior to the disin-
fection process.
Answers to questions on page 578.
28.2C Different types of screens may be listed as
1. Coarse screens OR 2. Stationary screens
Intermediate grade Moving screens
of medium
screening
Microscreens Microscreens
28.2D The following types of controls can be used alone or in
combination to clean screens:
1. Manual start/stop,
2. Automatic start/stop by time control,
3. High level switch, and
4. Differential head switch.
28.2E Clean water used to backwash screens and filter
media must be low OR WITHOUT SUSPENDED SOL-
IDS.
28.2F The speed of a variable-speed moving screen can be
controlled on the basis of the upstream channel level,
flow level, or head differential through the screen.
Answers to questions on page 579.
28.2G An insufficient oxygen problem can be corrected by
ventilation using fans and/or blowers.
28.2H Before working in an area open to traffic:
1. Put up barriers and signs,
2. Turn on rotating beacon on trucks, and
3. Wear a hard hat and a red vest.
Answers to questions on page 580.
28.21 During start-up check to see if debris and solids are
being flushed off the screen and are running to dis-
posal.
28.2J Major items that should be checked during the normal
operation of a microscreen include:
1. Screening media,
2. Cleaning system,
3. Drive unit and other moving machinery,
4. Effectiveness of seals and gaskets,
5. Strength and stability of supporting framework,
6. Drum speed,
7. Screen submergence, and
8. Head loss.
28.2K Heavy plugging of a screen could be caused by
1. High solids loads, and/or
2. A defective cleaning system.
28.2L Correct shutdown procedures have been used if the
screen or microscreen is in a clean condition when the
chambers are dry and empty.
Answers to questions on page 585.
28.2M Items that should be visually inspected every day a
screen is in operation include:
1. Condition of screening media,
2. Objects lodged in screen or obstructing flow or
equipment movement,
3. Vibrating or erratically moving equipment,
4. Wash water jet nozzles for blockage, and
5. Head loss.
28.2N A woven wire cloth can be broken by impingement of
floating objects or by stress due to overloading from
differential head and fatigue.
Answers to questions on page 587.
28.20 When reviewing plans and specifications regarding
concrete channels and chambers, check
1. Provisions for drainage of facilities,
2. To be sure dirty water is prevented from bypassing
the screen,
3. That chlorine is prevented from reaching the unit or
backwash pump,
4. That adequate working space is provided for oper-
ation and maintenance, and
5. Provisions for guard rails and other safety require-
ments.
28.2P When reviewing plans and specifications regarding
electrical outlets, check for
1. Location near points of need, and
2. Proper voltage.
END OF ANSWERS TO QUESTIONS IN LESSON 3
Answers to questions on page 596.
28.3A The lower the pH, the greater the rate of corrosion. If
the pH of a solution is allowed to drift outside of the
design range, corrosion can start.
28.3B pH is an index of hydrogen ion activity and is used as
an indication of acidity and alkalinity while not a meas-
ure of either.
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Industrial Waste Treatment 699
28.3C Alkalinity is the capacity of water or wastewater to
neutralize acids. It is the sum total of components in
the water that tend to elevate the pH of the water
above a value of about 4.5. Alkalinity is a measure of
the buffering capacity of the water and may be defined
as its capacity for neutralizing acid.
28.3D To treat the same water, lime will produce more
sludge than caustic soda.
28.3E When diluting caustic soda, consideration must be
given to heat generated. The rate of dilution and
method of cooling must be carefully controlled so that
there is no boiling or splattering.
28.3F A titration curve is a plot of pH versus titrant added to a
solution. The curve provides a means of characteriz-
ing the substance to be pH adjusted or neutralized and
the amount of adjusting agent required.
Answers to questions on page 605.
28.3G Treatment processes that may require pH adjustment
and neutralization include:
1. Precipitation of metal salts,
2. Coagulation and flocculation,
3. Biological processes,
4. Reverse osmosis,
5. Ozonization,
6. Carbon adsorption,
7. Ultrafiltration,
8. Sludge conditioning and disposal,
9. Phosphorus removal, and
10. Effluent disposal.
28.3H The most commonly used coagulants are:
1. Alum or aluminum sulfate — AI2(S04)3,
2. Ferric chloride — FeCI3, and
3. Ferric sulfate — Fe2(S04)3.
28.31 Ultrafiltration is a membrane filtration process used for
the removal of organic compounds in an aqueous
(watery) solution.
28.3J Sludges are often classified by their basic chemical
composition, pH, specific resistance and cake solids.
Answers to questions on page 611.
28.3K In a batch process the waste is collected in a tank, pH
is adjusted and then the waste is allowed to re-enter
the wastewater stream.
28.3L pH can be determined manually by using electrometric
measurement (a lab pH meter) and special indicator
paper (litmus or pHydrion paper).
28.3M Ventilation should be provided in chemical feed
facilities to minimize chemical exposure to personnel,
controls and equipment.
28.3N An alert operator should be able to walk into a room
under construction and consider the following ques-
tions:
1. Can I service and maintain the equipment safely?
2. Are switches and controls adequate and properly
located?
3. Is lighting sufficient?
4. Is ventilation sufficient?
5. Is proper entrance and exit from the room pro-
vided?
6. Are emergency alarms provided?
28.30 Formal procedures should be developed for start-up,
operation and shutdown of equipment and processes
to define areas of responsibility and to significantly
reduce the changes of errors and accidents.
'END OF ANSWERS TO QUESTIONS IN LESSON 4
Answers to questions on page 616.
28.4A Chemical coagulation involves the operations of rapid
mix, flocculation and clarification.
28.4B Coagulation is the actual gathering together of smaller
suspended particles into floes, thus forming a more
readily settleable mass.
28.4C Flocculation is the act of mixing and stirring the parti-
cles so as to insure adequate contact between sus-
pended particles and the coagulating chemical.
28.4D If the rapid mix is too long, the forming floe may be
broken up and become separated.
28.4E Polymers are considered more convenient in the liquid
form because they may be used directly, thus eliminat-
ing the need to make up working solutions.
Answers to questions on page 631.
28.4F Rapid mixing of coagulant chemicals may be accom-
plished in one of three modes: (1) high-speed mixers
(impeller or turbine), (2) in-line blenders and pumps,
and (3) baffled compartments or pipes (static mixers).
28.4G In tapered flocculation, a small dense floe is formed
initially followed by aggregation to form a more dense
dispersed floe.
28.4H An advantage of vertical-flow clarifier units is that flow
is forced up through a sludge blanket, thus aiding in
solids retention and improving flow control.
28.41 Four factors that are considered in the design of
clarifiers include:
1. Detention time, OR 1. Flows,
2. Weir overflow rate, 2. Suspended solids,
3. Surface loading rate, 3. Settleable solids, and
• and
4. Solids loading. 4. Floatable solids.
28.4J If the detention time in a clarifier is too short, there will
be a carryover of particles into the effluent.
28.4K Short-circuiting may be caused by:
1. Differences in water density due to different tem-
peratures existing at the surface and bottom of the
clarifier;
2. Density differences due to suspended solids;
3. High inlet and outlet velocities; and
4. Strong winds blowing along the surface of the tank.
Answers to questions on page 634.
28.4L Gases under pressure should be stored in a cool loca-
tion and secured tightly to a vertical support. Areas
should be properly labeled to designate hazard of
flammability, corrosiveness or other applicable type of
hazard.
28.4M Some of the causes of falls include clutter and grease,
oil and polymer spills.
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700 Treatment Plants
28.4N Items to be checked during the start-up inspection of a
chemical feed system include:
1. Level alarms in tanks,
2. Calibration of flow and metering systems,
3. Water blenders and dilution mixers,
4. Temperature and pressure of dilution water, and
5. In-line mixers.
28.40 Procedures for the normal operation of a chemical
coagulation-precipitation system include:
1. Perform a jar test to determine the proper chemical
dosage,
2. Insure proper chemical dilution,
3. Set controls for proper feed rate, and
4. Report in the operating log the amount of chemi-
cals used per unit time.
END OF ANSWERS TO QUESTIONS IN LESSON 5
Answers to questions on page 635.
28.5A The activated carbon adsorption process is used to
treat wastewater to remove organic pollutants from the
plant's effluent. Color-, taste- and odor-causing pollu-
tants are removed by the activated carbon adsorption
process.
28.5B Activated carbon may be made from wood, coal, nut-
shells, bone, petroleum residues or sawdust.
28.5C Carbon is made by drying the raw material and slowly
heating the material in the absence of air.
Answers to questions on page 649.
28.5D The desired detention time in an activated carbon
pressure vessel is 30 minutes.
28.5E Three-way valves are used in activated carbon piping
to provide both the upflow conditions necessary for the
activated carbon treatment, and also to allow for
backwashing of filter screens.
28.5F Activated carbon is kept in the pressure vessel by
screens located at both the top and bottom of the ves-
sel.
28.5G The counter-current flow principle is the process
where flow enters the bottom of the carbon column
and new or regenerated carbon is added to the top of
the container. This principle allows for the oldest car-
bon to contact the wastewater first and the newest or
more virgin carbon to make contact with the effluent
last. In this manner, the wastewater is polished as it
flows up through the carbon column.
Answers to questions on page 654.
28.5H Regeneration of activated carbon is a process
whereby the pores and the surface of the carbon are
cleansed of the molecular organic material which has
been adsorbed on the surface.
28.51 If the feed rate is too high to the carbon regeneration
furnace, the carbon does not have a long enough de-
tention time within the furnace to be regenerated
properly.
28.5J If the feed rate is too low to the carbon regeneration
furnace, the carbon will be burned in the furnace and
lose its effectiveness.
28.5K The temperature in a carbon regeneration furnace is
controlled by adjusting the air and gas ratio.
28.5L The purpose of the defining tank for the activated car-
bon is to wash the carbon as thoroughly as possible to
prevent the small particles of carbon from causing
further problems within the adsorption process. An
adequate amount of time must be given to the defining
process to be certain that as many of the fine particles
are removed as possible.
Answers to questions on page 657.
28.5M Possible causes of high head losses through an acti-
vated carbon process include:
1. Need for backflushing,
2. Fouling of activated carbon granules with sus-
pended solids,
3. Screen plugged or collapsed, and
4. Amount of carbon in the adsorption reactor is too
high.
28.5N The activated carbon column reactor should be filled
slowly to prevent air pockets from forming in the reac-
tor and causing short-circuiting.
28.50 If a wastewater treatment process upstream from a
carbon adsorption process failed, try to prevent sus-
pended solids from reaching the carbon adsorption
process. If an emergency holding pond is available,
temporarily store the inadequately treated wastewater
until the upstream process is working again.
28.5P Problems that could be encountered when operating a
carbon regeneration furnace include:
1. Deterioration of refractory brick,
2. Improper air and gas mixture,
3. Worn out furnace rabble arms,
4. Excessively worn regenerated carbon slurry
pumps, and
5. Plugged screens in the make-up carbon or regen-
erated carbon defining tank.
Answers to questions on page 659.
28.5Q Activated carbon could cause an oxygen deficiency in
a carbon column reactor vessel because activated
carbon adsorbs oxygen molecules.
28.5R Items that should be considered when reviewing plans
and specifications for an activated carbon adsorption
process include:
1. Loading station for delivery of fresh activated car-
bon,
2. Location of valves within easy reach,
3. Dust control for unloading fresh carbon,
4. Proper ventilation in carbon regeneration furnace
room,
5. Scaffolding and catwalks,
6. Warning alarms and signs, and
7. Upstream processes.
28.5S Alarms should be provided to notify personnel of ex-
cessive temperatures or lack of oxygen within a build-
ing. Signs should warn personnel of dangers as-
sociated with working around activated carbon.
-------
Industrial Waste Treatment 701
OBJECTIVE TEST
Chapter 28. INDUSTRIAL WASTE TREATMENT
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one answer to each question.
1. Regardless of the source, water used by industry may
require additional treatment before it is suitable for use.
1. True
2. False
2. The health risks from water-contact recreation are greater
than from drinking water.
1. True
2. False
3. Air cooling is an effective alternative to water cooling in the
fruit and vegetable processing industry.
1. True
2. False
4. The frequency of monitoring should increase when ab-
normal indicators are present.
1. True
2. False
5. Corrective maintenance frequently requires total shut-
down of the system to perform the necessary procedures.
1. True
2. False
6. Some bar screens have horizontal bars instead of vertical
bars.
1. True
2. False
7. The only cleaning mechanism for some bar screens is the
force of the water which sweeps the intercepted material
off the face of the screen. Manual cleaning by brushing or
hosing is required periodically.
1. True
2. False
8. pH is an important factor in the chemical and biological
systems of natural waters.
1. True
2. False
9. pH is considered to be the single most important variable
in the coagulation process.
1. True
2. False
10. At tow pH values, ultrafiltration membrane technology is
most appropriate.
1. True
2. False
11. Industrial wastewater flows and strength of contaminants
are usually constant during each shift.
1. True
2. False
12. Dry alum is corrosive unless it absorbs moisture.
1. True
2. False
13. The settling rate of particles is greater at a warmer tem-
perature than it is at a lower temperature.
1. True
2. False
14. The carbon adsorption process uses an upflow pressure
vessel in order to allow adequate detention time within the
vessel for adsorption of the organic material in the effluent
waters.
1. True
2. False
15. Activated carbon column reactors are lined with an epoxy
or resin because wet carbon can be very corrosive.
1. True
2. False
16. Carbon dust should not be inhaled.
1. True
2. False
17-21. The following is a list of common household items. If
the item is ACIDIC, mark 1 for the correct answer and mark
2 if the answer is BASIC.
1. ACIDIC 2. BASIC
17. Beer
18. Borax
19. Milk
20. Orange juice
21. Milk of magnesia
22. Which of the following uses of water has the highest prior-
ity of use?
1. Agricultural
2. Drinking
3. Fish
4. Industrial
5. Water-contact recreation
23. Water-contact recreation includes
1. Fishing.
2. Picnicking.
3. Sailing.
4. Swimming.
5. Water skiing.
-------
702 Treatment Plants
24. Tannery wastes are usually high in
1. BOD.
2. Coliforms,
3. Suspended solids.
4. Salt.
5. Temperature.
25. The basic purposes of the flotation process are
1. Biological treatment.
2. Grit removal.
3. Solids removal.
4. Water recovery.
5. Wastewater treatment.
26. Potential safety hazards within a flotation system include
1. Chemical handling.
2. Couplings.
3. Electrical systems.
4. Sprockets.
5. Wet floors.
27. Incorrect flotation start-up procedures or steps taken out
of sequence can be detected by
1. High solids content of solids recovery.
2. No chlorine residual in effluent.
3. Observing indicator lights.
4. Poor effluent quality.
5. Visual appearance of unit.
28. Frequency of normal system monitoring should be
1. As often as possible.
2. Each shift monitors itself.
3. Every hour.
4. Once a day.
5. Once a week.
29. Pertinent procedures in flotation system preventive main-
tenance include
1. Adjusting scraper alignment.
2. Cleaning system.
3. Installing new unit feed pump.
4. Painting facilities.
5. Replacing broken belt.
30. Lack of proper preventive maintenance can be revealed
by
1. Continuous uneven part wear.
2. Dirty equipment.
3. Insufficient oil or grease.
4. Old age of components.
5. Overloading.
31. Microscreens are used mainly for final treatment to (select
best answer)
1. Filter out phosphorous in the effluent.
2. Prevent nutrients in the effluent from reaching the re-
ceiving waters.
3. Prevent the carryover of floating solids and suspended
particles remaining in effluent.
4. Remove microorganisms remaining in effluent.
5. Remove pathogenic organisms remaining in effluent.
32. The fabric of a microscreen may be made of
1. Cloth.
2. Nylon.
3. Polyester.
4. Stainless steel.
5. Teflon.
33. Hazardous fumes, gases or conditions that might be en-
countered in a confined space include
1. Gasoline vapors.
2. Hydrogen sulfide.
3. Lack of oxygen.
4. Solvent fumes.
5. Toxic gases.
34. Safety equipment or tools include
1. Atmospheric or gas measuring instruments.
2. Gas mask (hose type or oxygen breathing apparatus).
3. Rubber gloves.
4. Safety belt and harness.
5. Spark-proof tools.
35. Sampling of wastewater being treated by a screening pro-
cess should
1. Be either by grab samples or continuous monitoring.
2. Have all samples chlorinated.
3. Have samples collected before and after the screening
media.
4. Have the samples analyzed at the point of collection.
5. Require all collected samples to be filtered before
analysis.
36. Problems operating a screen properly could be caused by
1. Erratic movement of equipment parts.
2. High grease solids.
3. High solids loads.
4. Openings in the screen being too large.
5. Overloading of upstream treatment processes.
37. Acids commonly used in lowering the pH of a solution
include
1. Acetic acid.
2. Hydrochloric acid.
3. Nitric acid.
4. Phosphoric acid.
5. Sulfuric acid.
38. Efficiency of the ultrafiltration membrane filtration process
can be measured in terms of
1. Cake filterability.
2. Clarity of the solute.
3. Dissolved solids rejected.
4. Horsepower in and out.
5. Organic matter rejected.
39. Different types of coagulating chemicals include
1. Anionic precipitators.
2. Electrostatic charge reducing.
3. Flocculating.
4. Interparticle bridgers.
5. Physical-enmeshers.
-------
Industrial Waste Treatment 703
40. Iron compounds used as coagulants are
1. A potential source of iron in the effluent.
2. Capable of increasing the BOD in the effluent.
3. Corrosive.
4. Difficult to dissolve in water.
5. Potentially dangerous if they (ferric sulfate or cop-
peras) come in contact with quicklime.
41. What could be the possible causes of the floe being too
small in a chemical coagulation and flocculation system?
1. Change in pH
2. Chemical feed pump adjusted too low
3. Improper chemical dosage
4. Paddle speed in flocculators too fast
5. Short-circuiting
42. What could be the cause of excessive carbon fines in the
effluent from activated carbon column reactors?
1. Carbon is being produced in the reactor due to poor
combustion
2. Carbon is flowing out in the effluent due to a hole in one
of the screens
3. Carbon is rubbing too drastically against the screens
4. Microscreens are breaking up the carbon floe upstream
from the reactor
5. Pin floe containing carbon is escaping from the sec-
ondary clarifier
43. Daily operational procedures for an activated carbon pro-
cess include
1. Backflushing of fine-mesh screens.
2. Measuring BOD removal efficiencies.
3. Measuring COD removal efficiencies.
4. Measuring effluent turbidity.
5. Measuring level of carbon remaining in reactor.
44. When operating an activated carbon adsorption process,
which of the following items should be checked once each
shift?
1. Dissolved oxygen level in each carbon adsorption unit
2. Head loss through each carbon adsorption unit
3. Position of all valves to and from each carbon adsorp-
tion unit
4. Rate of flow to each carbon adsorption unit
5. Sample influent and effluent of each carbon adsorption
.unit
45. Loading rates for activated carbon adsorption processes
include
1. Chemical oxygen demand.
2. Hydraulic.
3. Organic.
4. Overflow.
5. Surface.
-------
CHAPTER 29
SUPPORT SYSTEMS
by
Roger Ham
-------
706 Treatment Plants
TABLE OF CONTENTS
Chapter 29. Support Systems
Page
OBJECTIVES 710
GLOSSARY 711
LESSON 1
29.0 Importance of Support Systems 713
29.1 Portable Pumps 713
29.10 Pump Types 717
29.100 Centrifugal Trash Pumps 717
29.101 Positive Displacement Diaphragm Pumps 719
29.102 Positive Displacement Diaphragm (Pneumatic) Pumps 719
29.103 Submersible Pumps 720
29.11 Pump Engines (Refer to Section 29.4) 722
29.12 Seals 722
29.2 Pipes, Valves, and Fittings 722
29.20 Need for Pipes, Valves and Fittings 722
29.21 Pipes 722
29.210 Galvanized Pipe 722
29.211 Cast Ductile Iron/Soil Pipe 725
29.212 PVC (Polyvinyl Chloride) Pipe 725
29.213 Concrete Pipe 725
29.214 Asbestos-Cement Pipe 726
29.215 Welded Steel Pipe 726
29.22 Valves 726
29.220 Use of Valves 726
29.221 Gate Valves 726
29.222 Globe Valves 728
29.223 Eccentric Valves 728
29.224 Butterfly Valves 728
29.225 Check Valves 728
29.23 Fittings for Steel, Ductile and Cast Iron Pipe 729
29.230 Victaulic Couplings 729
-------
Support Systems 707
29.231 Sleeve Coupling 729
29.232 Compression Coupling 729
29.233 Mechanical Flanges 729
29.234 Band Seals 735
LESSON 2
29.3 Auxiliary Electrical Equipment 736
29.30 Safety First 736
29.31 Standby Power Generation 736
29.32 Emergency Lighting 736
29.320 Types of Equipment 736
29.321 Batteries 737
29.33 High Voltage 738
29.330 Transmission 738
29.331 Switch Gear 738
29.332 Power Distribution Transformers 740
29.4 Gasoline Engines 740
29.40 Need to Maintain Gasoline Engines 740
29.41 Four-cycle Engines (Air Cooled) 740
29.410 Strokes in the Cycle 740
29.411 Piston Displacement 740
29.412 Compression Ratio 743
29.413 Valves and Timing 743
29.414 Carburetion 744
29.415 Ignition 744
29.416 Governing 744
29.417 Maintenance 744
29.418 Starting Problems 744
29.419 Running Problems 744
29.42 Large Four-Cycle Engines (Water Cooled) 748
29.420 Differences Between Small and Large Engines 748
29.421 Multi Cylinders 748
29.422 Water Cooled 748
29.423 Engine Lubrication 750
29.424 Ignition Systems — Battery and Magneto 750
29.425 Valves 750
29.426 Maintenance and Troubleshooting 754
29.43 Small Two-cycle Engines (Air Cooled) 754
29.430 How Two-cycle Engines Work 754
-------
708 Treatment Plants
29.431 Maintenance and Troubleshooting 754
29.44 How to Start a Gasoline Engine 754
29.440 Small Engines 754
29.441 Large Engines 756
LESSON 3
29.5 Diesel Engines 757
29.50 How Diesel Engines Work 757
29.51 Operation 757
29.52 Fuel System 757
29.53 Water-Cooled Diesel Engines 760
29.54 Air-Cooled Diesel Engines 760
29.55 How to Start Diesel Engines 761
29.56 Maintenance and Troubleshooting 761
29.6 Heating, Ventilating and Air Conditioning 776
29.60 Operation and Maintenance of Digester Gas- or Natural Gas-Fired Boilers 776
29.600 Gas System 776
29.601 Water System 776
29.602 Control Switches 776
29.603 Boiler Maintenance 776
29.61 Operation and Maintenance of Building Blowers and Exhaust Fans 777
29.610 Need for Blowers and Fans 777
29.611 Terminology 777
29.612 Fan Laws 777
29.613 Types of Fans and Blowers 777
29.614 Maintenance 779
29.62 Operation and Maintenance of Air Conditioning Units 779
29.7 Compressors 781
29.70 Need for Compressors 781
29.71 Rotary Compressors 781
29.72 Reciprocating Compressors 782
29.73 Air Systems 783
LESSON 4
29.8 Water Systems 785
29.80 Avoid Cross Connections 785
29.81 Fresh Water Systems 785
29.82 Types of Hydro-pneumatic Systems 785
129.820 Standard Air-cushion 785
-------
Support Systems 709
29.821 Add-air System 785
29.822 Vent-air System 787
29.83 Backflow Prevention 787
29.830 Need for Backflow Prevention 787
29.831 Devices 789
29.84 Reclaimed Water 789
.9 Grounds Upkeep and Maintenance 789
29.90 Need for Good Appearances 789
29.91 Yard Lighting 789
29.92 Enclosures 790
29.93 Roadways and Walkways 790
29.94 Landscape 791
29.940 Purpose of Landscaping 791
29.941 Irrigating 791
29.942 Controlling Weeds 791
29.943 Fertilizing 791
29.944 Mowing and Pruning 792
29.95 Surface Water Drainage 792
-------
710 Treatment Plants
OBJECTIVES
Chapter 29. SUPPORT SYSTEMS
Following completion of Chapter 29 you should be able to do
the following:
1. Select, operate and maintain portable pumps, pipes,
valves, and fittings used for maintenance and repair jobs;
2. Safely operate and maintain auxiliary electrical equipment,
including during standby and emergency situations;
3. Start up, operate, maintain and shut down gasoline en-
gines, diesel engines, heating, ventilating and air condition-
ing systems;
4. Operate and maintain the plant air and water systems; and
5. Maintain the treatment plant grounds, including drainage
water system, yard lighting, paving, walkways and land-
scaping.
-------
Support Systems 711
GLOSSARY
Chapter 29. SUPPORT SYSTEMS
AIR GAP AIR GAP
An open vertical drop, or vertical empty space, between a drinking (potable) water supply and the point of use in a wastewater
treatment plant. This gap prevents back siphonage because there is no way wastewater can reach the drinking water.
CATHODIC PROTECTION (ca-THOD-ick) CATHODIC PROTECTION
An electrical system for prevention of rust, corrosion, and pitting of steel and iron surfaces in contact with water, wastewater or soil.
CAVITATION (CAV-i-TAY-shun) CAVITATION
The formation and collapse of a gas pocket or bubble on the blade of an impeller. The collapse of this gas pocket or bubble drives
water into the impeller with a terrific force that can cause pitting on the impeller surface.
CROSS CONNECTION CROSS CONNECTION
A connection between drinking (potable) water and an unsafe water supply. For example, if you have a pump moving nonpotable
water and hook into the drinking water system to supply water for the pump seal, a cross connection or mixing between the two
water systems can occur. This mixing may lead to contamination of the drinking water.
DISCHARGE HEAD DISCHARGE HEAD
The pressure (in feet (meters) or pounds per square inch (kilograms per square centimeter)) on the discharge side of a pump. The
pressure can be measured from the center line of the pump to the hydraulic grade line of the water in the discharge pipe.
DYNAMIC HEAD DYNAMIC HEAD
When a pump is operating, the vertical distance (in feet or meters) from a point to the energy grade lines. Also see TOTAL
DYNAMIC HEAD and STATIC HEAD.
ELECTRO-CHEMICAL CORROSION ELECTRO-CHEMICAL CORROSION
The decomposition of a material by: (1) stray current electrolysis, (2) galvanic corrosion caused by dissimilar metals, and (3)
galvanic corrosion caused by differential electrolysis.
ELECTRO-CHEMICAL PROCESS ELECTRO-CHEMICAL PROCESS
A process that causes the deposition or formation of a seal or coating of a chemical element or compound by the use of electricity.
ELECTROLYSIS (ELECT-TROLLY-sis) ELECTROYLSIS
The decomposition of material by an electrical current.
ELECTROLYTE (ELECT-tro-LIGHT) ELECTROLYTE
A substance which dissociates (separates) into two or more ions when it is dissolved in water.
ENERGY GRADE LINE (EGL) ENERGY GRADE LINE (EGL)
A line that represents the elevation of energy head (in feet) of water flowing in a pipe, conduit or channel. The line is drawn above the
hydraulic grade line a distance equal to the velocity head of the water flowing at each section or point along the pipe or channel.
FRICTION LOSS FRICTION LOSS
The head lost by water flowing in a stream or conduit as the result of the disturbances set up by the contact between the moving
water and its containing conduit and by intermolecular friction.
HEAD HEAD
A term used to describe the height or energy of water above a point. A head of water may be measured in either height (feet or
meters) or pressure (pounds per square inch or kilograms per square centimeter). Also see DISCHARGE HEAD, DYNAMIC HEAD
STATIC HEAD, SUCTION HEAD, SUCTION LIFT, and VELOCITY HEAD.
-------
712 Treatment Plants
HYDRAULIC GRADE LINE (HGL) HYDRAULIC GRADE LINE (HGL)
The surface or profile of water flowing in an open channel or a pipe flowing partially full. If a pipe is under pressure, the hydraulic
grade line is at the level water would rise to in a small tube connected to the pipe. To reduce the release of odors from wastewater,
the water surface should be kept as smooth as possible.
OXIDATION (ox-i-DAY-shun) OXIDATION
Oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. The opposite of
REDUCTION.
REDUCTION (re-DUCK-shun) REDUCTION
Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. The opposite of
OXIDATION.
SEIZE UP SEIZE UP
Seize up occurs when an engine overheats and a component expands to the point where the engine will not run. Also called
"freezing."
STATIC HEAD STATIC HEAD
When water is not moving, the vertical distance (in feet or meters) from a point to the water surface.
SUCTION HEAD SUCTION HEAD
The POSITIVE pressure (in feet (meters) or pounds per square inch (kilograms per square centimeter)) on the suction side of a
pump. The pressure can be measured from the center line of the pump UP TO the elevation of the hydraulic grade line on the
suction side of the pump.
SUCTION LIFT SUCTION LIFT
The NEGATIVE pressure (in feet (meters) or inches (centimeters) of mercury vacuum)) on the suction side of the pump. The
pressure can be measured from the center line of the pump DOWN TO the elevation of the hydraulic grade line on the suction side of
the pump.
TOTAL DYNAMIC HEAD (TDH) TOTAL DYNAMIC HEAD (TDH)
When a pump is lifting or pumping water, the vertical distance (in feet or meters) from the elevation of the energy grade line on the
suction side of the pump to the elevation of the energy grade line on the discharge side of the pump.
VELOCITY HEAD VELOCITY HEAD
A vertical height (in feet or meters) equal to the square of the velocity of flowing water divided by twice the acceleration due to gravity
(V2/2g).
WATER HAMMER WATER HAMMER
The sound like someone hammering on a pipe that occurs when a valve is opened or closed very rapidly. When a valve position is
changed quickly, the water pressure in a pipe will increase and decrease back and forth very quickly. This rise and fall in pressures
can do serious damage to the system.
-------
Support Systems 713
CHAPTER 29. SUPPORT SYSTEMS
(Lesson 1 of 4 Lessons)
29.0 IMPORTANCE OF SUPPORT SYSTEMS
Support systems help treatment plants perform their in-
tended purpose of treating wastewater. If the support systems
at your treatment plant are properly operated and maintained,
you can concentrate your efforts on the actual treatment of
wastewater and the quality of your plant's effluent.
Support systems include portable pumps, pipes, valves and
fittings that are used to help you operate and maintain your
treatment plant. Other support system facilities include auxil-
iary electrical equipment, gasoline engines, diesel engines,
heating, ventilating and air conditioning. Two very important
support systems are the plant air and water systems. The air
system includes instrument air, chemical air padding, cleaning,
and shop blowdown. Plant water systems must be carefully
installed and inspected to protect potable (drinking) water from
nonpotable water used for foam control, wash down and irriga-
tion. Many people determine how effectively you are doing
your job by the appearance of your plant. For this reason you
should be able to control drainage runoff, maintain a well-
lighted plant, keep walkways and roadways clear and free of
holes and bumps and present a nice appearing and land-
scaped treatment plant. All of these factors must be the con-
cern of treatment plant operators. When support systems per-
form properly, operator morale is improved as well as plant
performance.
29.1 PORTABLE PUMPS
The use of portable pumps is widespread in the wastewater
treatment field. Pumps vary in design to meet the particular
needs of the user or the job to be done. Within this field you
may be required to move water containing grit, other solids,
groundwater, and wastewater to name a few different types of
water and solids that must be pumped. Before selecting a
pump, thought must be given to the following factors:
1. Type of liquid and solids,
2. Distance liquid is to be pumped,
3. Pressure liquid is to be delivered,
4. Pumping rate in gallons per minute, and
5. Type of power needed (gasoline or diesel engine, electric
motor, or pneumatic).
If you are contemplating the purchase of a new pump, list all
the operating factors and the type of power best suited for your
situation. Don't forget that price is also an important factor.
There is no need to buy an expensive pump if one of lesser
quality and price will fulfill your needs. Also be sure to consider
energy, operating and maintenance costs. Because of the
substantial investment involved, consider if each pump studied
will do the job, do it economically, have few operational prob-
lems, require spare parts that are readily available, and also if
the company selling the pump is service oriented.
In order to select the proper pump, you must be familiar with
the terms in the following paragraphs that are associated with
pumps. Figures 29.1 and 29.2 illustrate these terms.
DISCHARGE HEAD
The pressure (in feet (meters) or pounds per square inch
(kilograms per square centimeter)) on the discharge side of a
pump. The pressure can be measured from the center line of
the pump to the hydraulic grade line of the water in the dis-
charge pipe.
DYNAMIC HEAD
When a pump is operating, the vertical distance (in feet or
meters) from a point to the energy grade lines. Also see
TOTAL DYNAMIC HEAD and STATIC HEAD.
ENERGY GRADE LINE (EGL)
An imaginary line that represents the elevation of energy
head (in feet) of water flowing in a pipe, conduit or channel.
The line is drawn above the hydraulic grade line, a distance
equal to the velocity head of the water flowing at each section
or point along the pipe or channel. This line represents the total
energy of water flowing in a pipe or channel.
FRICTION LOSS
The head lost by water flowing in a stream or conduit as the
result of the disturbances set up by the contact between the
moving water and its containing conduit and by intermolecular
friction.
HEAD
A term used to describe the height or energy of water above
a point. A head of water may be measured in either height (feet
or meters) or pressure (pounds per square inch or kilograms
per square centimeter). Also see DISCHARGE HEAD,
DYNAMIC HEAD, STATIC HEAD, SUCTION HEAD, SUC-
TION LIFT, and VELOCITY HEAD.
HYDRAUUC GRADE LINE (HGL)
The surface or profile of water flowing in an open channel or
a pipe flowing partially full. If a pipe is under pressure, the
hydraulic grade line is at the level water would rise to in a small
tube connected to the pipe. To reduce the release of odors
from wastewater, the water surface should be kept as smooth
as possible.
STATIC HEAD
When water is not moving, the vertical distance (in feet or
meters) from a point to the water surface.
SUCTION HEAD
The POSITIVE pressure (in feet (meters) or pounds per
square inch (kilograms per square centimeter)) on the suction
-------
MOTE: This figure illustrates a pump with a suction lift. Pumps should have a positive suction
head which means the wet well water level should be higher than the pump impeller.
This pump will have difficulty starting unless it is a self-priming pump because
the water level in the wet well is below the pump. Also, if air gets into the
suction line, the only way it can get out is through the pump.
Static
Discharge
Head
Total
Static
Head
Wet Well
Water Level
Static
Negative
Suction Head
or
Suction Lift
Center Line
Purnp Impeller
Fig. 29.1 Static heads (pump is not operating)
(from Operation and Maintenance of Wastewater Collection Systems)
-------
NOTE: This figure illustrates a pump with a suction lift. Pumps should have a positive suction
head which means the wet well water level should be higher than the pump impeller.
This pump will have difficulty starting unless it is a self-priming pump because
the water level in the wet well is below the pump. Also, if air gets into the
suction line, the only way it can get out is through the pump.
Friction Losses
Static
Discharge
Total Dynamic Head
(from Suction E6L
to Discharge EGL)
Center Line of
Pump Impeller
Static
Suction
Friction
Losses
\\
Fig. 29.2 Dynamic heads (pump is operating)
(from Operation and Maintenance of Wastewater Collection Systems)
EGL- Energy Grade Line
HGi_- Hydraulic Grade Line
- Velocity Head
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716 Treatment Plants
A IMPROPER PUMP INSTALLATION
SUCTION LINE SLOPES
DOWN TO PUMP
CAUSING AIR POCKET
TOO MANY ELBOWS AND
FITTINGS IN SUCTION
ANO DISCHARGE LINES
WEIGHT OF PIPE
AND L1QUI0 NOT
SUPPORTED
SUCTION LINE
TOO LONG
PUMP NOT LEVEL
OR SECURE
NON-ECCENTRIC
REDUCER USED
IN SUCTION LINE
THROTTUE AND
CHECK VALVES
INSTALLED IN
SUCTION LINE
NO STRAINER ON
SUCTION LINE
B PROPER PUMP INSTALLATION
THROTTLE AND CHECK
VALVES INSTALLED IN
DISCHARGE LINE
(WHEN REQUIRED)
ECCENTRIC-TYPE
REDUCER USED
WHEN REQUIRED
IN SUCTION LINE
WEIGHT OF PIPE
AND LIQUID
ADEQUATELY
SUPPORTED
PUMP LEVEL AND
SECURaY SUPPORTED
SUCTION LINE
SLOPES UP TO
PUMP PREVENTING
AIR POCKETS
LONG RAOIUS
ELBOWS USED
EFFECTIVELY
SUCTION LINE
SHORT ANO
DIRECT
STRAINER USED ON
SUCTION LINE
Fig. 29.3 Examples of proper and improper portable pump installations
(Permission of the Gorman-Rupp Company, Mansfield, Ohio)
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Support Systems 717
side of a pump. The pressure can be measured from the center
line of the pump UP TO the elevation of the hydraulic grade line
on the suction side of the pump.
SUCTION LIFT
The NEGATIVE pressure (in feet (meters) or inches (centi-
meters) of mercury vacuum) on the suction side of the pump.
The pressure can be measured from the center line of the
pump DOWN TO the elevation of the hydraulic grade line on
the suction side of the pump.
TOTAL DYNAMIC HEAD (TDH)
When a pump is lifting or pumping water, the vertical dis-
tance (in feet or meters) from the elevation of the energy grade
line on the suction side of the pump to the elevation of the
energy grade line on the discharge side of the pump.
VELOCITY HEAD
A vertical height (in feet or meters) equal to the square of the
velocity of flowing water divided by twice the acceleration due
to gravity (V2/2g).
Figure 29.3 shows examples of proper and improper porta-
ble pump installations. When using portable pumps to dewater
tanks or ditches for repairs or maintenance, the items noted in
this figure must be considered. Figure 29.4 shows proper and
improper suction lifts for portable pumps. Always try to have
the suction lift as low as possible and the suction line as short
as possible. High suction lifts and long suction lines increase
the chances of CAVITATION1 and often reduce the pump flow
rate.
PROPER
25 FOOT
SUCTION
urr
1
V, 5 FOOT
A SUCTION
\\ LIFT
A\ t
—J!
IMPROPER
29.10 Pump Types
Pump types are varied to meet different needs. Portable
pumps are usually of the centrifugal or positive displacement
type. This section discusses the four most common portable
pumps used by treatment plant operators:
1. Centrifugal trash pump with gas driven motor,
2. Positive displacement diaphragm pump with gas driven
motor,
3. Positive displacement diaphragm pump with pneumatic (air)
driven system, and
4. Centrifugal submersible pump with electric driven motor.
29.100 Centrifugal Trash Pumps
Centrifugal pumps designed for use as portable pumps are
often referred to as trash pumps because the water being
pumped is not clean and may have solids of various sizes
suspended in the water. When setting up your pump, always
prime the pump with clean water. If the priming water contains
soaps or detergents, problems can develop if a high suction lift
exists.
Always locate the pump as near as possible to the surface of
the water being pumped. A high suction lift will dramatically
reduce pump discharge volume (Figure 29.4). A centrifugal
pump in good condition can perform satisfactorily with a suc-
tion lift or vacuum up to 18 inches (45 cm) of mercury. This
corresponds to a possible suction lift of 20 feet (6.0 m). Con-
siderable effort is required to start portable centrifugal pumps
with excessive suction lift; however, these pumps can operate
with considerable suction lift at decreasing flow rates as the
water level drops.
When setting up a portable pump, lay out the suction and
discharge hoses as straight as possible to reduce friction
losses through kinks and bends in the hoses. The suction hose
has a strainer (Figure 29.5) attached to the entrance to prevent
pulling rocks and debris into the pump to avoid damaging the
pump or plugging the hoses or pipes. Placing the end of the
suction hose in a coarse rock sump or bucket will prevent
material building up on the strainer.
PUT THE SUCTION STRAINER ONTO THE
END OF THE SUCTION HOSE AND NEVER
PUMP WITHOUT IT.
WAYS TO
KEEP
STRAINER
OUT OF
RIVER SILT
TIE INSIDE OLD
PAIL OR BASKET
PLACE ON
BED OF STONES
Fig. 29.4 Proper and improper suction lifts
(Permission of Homelite Textron, Charlotte, North Carolina}
Fig. 29.5 Proper use of suction strainer
(permission ot Homelite Textron, Charlotte, North Carolina)
The most frequent pumping problem is an air leak in the
suction hose or a connection on the suction side of the pump.
To test that the problem is not in the pump, prime the pump,
1 Cavitation (CAV-i-TAY-shun). The formation and collapse of a gas pocket or bubble on the blade of an impeller. The collapse of this gas pocket
or bubble drives water into the impeller with a terrific force that can cause pitting on the impeller surface.
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718 Treatment Plants
TABLE 29.1 PORTABLE PUMP TROUBLESHOOTING GUIDE
PROBLEM
1. Pump engine won't start
2. Pump won't prime
POSSIBLE CAUSE
INSIDE PUMP
a. Pump needs water
b. Water inside pump contaminated
c. Worn pump
OPERATOR RESPONSE
Follow instructions in manufacturer's en-
gine manual.
Test pump suction to determine if problem
is inside or outside pump.
Fill with clean water.
Drain pump and fill with clean water. Even
though pump can pump dirty water, clean
water may be needed for priming.
If possible, reduce the suction lift distance.
If pump cannot prime at low lift, it should be
disassembled and overhauled.
3. Flow is scanty
d. Diaphragm pump valves inoperative, or
pump diaphragm leaking
OUTSIDE PUMP
a. Leaking hose or connections on suc-
tion side of pump
b. Strainer clogged
c. System clogged
Pump OK, but too small for job
Total head including friction is too great
Clean valves or replace leaking diaphragm.
Make couplings tighter.
Clean strainer. Try another method of keep-
ing strainer from clogging.
Clean hoses. If necessary disassemble and
clean out pump.
Install larger pump fitted with larger diame-
ter hoses. If a little faster flow would be ac-
ceptable, try larger hoses with the same
pump.
Do everything possible to decrease the
head. Try to eliminate unneeded elbows,
adapters, and reducers. If possible, move
pump closer to the water and shorten
hoses.
4. Volume decreases during pumping
Pump leaking or worn
Roots and other debris keeping diaphragm
pump valves stuck open
Overhaul pump. Have worn seals, gaskets,
impeller, or housing parts replaced as nec-
essary; or shim to reduce clearance be-
tween impeller and the wear plate or the
housing.
Elevate discharge hose so water rises to
help seal valves. Keep pumping until oppor-
tunity arises to stop and clean pump.
Thaw out by gradually warming pump.
Disassemble pump and remove blockage.
Remove discharge valve and clean cavity.
5. Pump is "frozen" and won't move
6. Diaphragm pump suddenly stops; en-
gine either quits or keeps running and
pump rod slips on shaft
Ice inside pump
Hard object jammed between impeller and
housing
Solid object preventing pump rod from
completing stroke
Accumulation of grit in housing
start the engine or motor, and place your hand over the suction
inlet. The vacuum created by the pump should draw on your
palm with a strong force if there are no leaks. You can also cap
the suction inlet and install a vacuum gage on the suction side
of the pump to indicate pump operation.
Portable pumps must be protected from being damaged.
Whenever a hose must be laid across a roadway, lay a plank
on either side of the hose. A vehicle running over the discharge
hose while the pump is running may damage the hose and
could also cause the pump casing to crack.
If you are operating the pump in weather that is subject to
freezing, always drain the pump to prevent the freezing water
from cracking the casing or binding up the pump. Before start-
Remove grit.
ing the pump, turn the shaft by hand to be sure that it turns
freely. If the impeller is frozen fast, warm the pump slowly until
the ice melts.
When water containing salt or other corrosives has been
pumped, drain the pump bowl and flush with clear water. Also,
rinse off the exterior of the pump. By using a slightly oiled cloth
or shop towel to wipe off the exterior, you will prevent rusting of
the metal. A number of small pumps have cast aluminum cas-
ings and are not as restant to corrosion as pumps having cast
iron casings.
Table 29.1 is a portable pump troubleshooting guide which
indicates some problems and recommended solutions.
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Support Systems 719
Lubrication should be done in accordance with the pump
manufacturer's O&M manual.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 793.
29.0A Support systems include what facilities or equipment?
29.1 A Why are portable centrifugal pumps often referred to
as trash pumps?
29.1 B Why should the suction hose of a portable pump have
a strainer on the end?
29.1 C What precautions would you take when operating a
portable pump in weather that is subject to freezing?
29.101 Positive Displacement Diaphragm Pumps
The diaphragm-type pump is a positive displacement pump.
A flexible membrane (diaphragm) is used in the vertical cylin-
der, instead of a piston, and flap valves are used for check
valves instead of the common ball checks that are used in the
piston type of raw sludge pumps. The concentric movement of
the rod alternates the pump from suction to pressure.
Some of the advantages of the diaphragm pump are as
follows:
1. Self-priming if the suction lift is small (10 to 15 feet or 3 to
4.5 meters),
2. When primed with water, it will pump with a suction lift up to
25 feet (7.5 meters),
3. Large particles will readily pass through the pump (you may
have heard of them referred to as 'mud hogs' for that rea-
son), and
4. They are less likely to become clogged than centrifugal
pumps.
The flow rate is considerably lower with a positive displace-
ment type of pump than with a centrifugal pump. Keeping the
pump close to the surface of the water being pumped will
ensure maximum output.
To ensure that the pump works satisfactorily, the flap valves
must seat properly. Inspect the diaphragm for leaks. If the
pump will not prime, inspect the suction hose connections, flap
valves, and prime water. Also look for a small hole in the dia-
phragm that may be causing the problem.
Taking care of the diaphragm pump is similar to the proce-
dures outlined in Section 29.110, "Centrifugal Pumps." How-
ever, since some materials used for the membrane tend to
deteriorate when exposed to long periods of sunlight, the pump
should be stored in a shaded dry area.
To diagnose problems, refer to Table 29.1, Portable Pump
Troubleshooting Guide.
29.102 Positive Displacement Diaphragm (Pneumatic)
Pumps (Figs. 29.6 and 29.7)
Pneumatically operated diaphragm pumps can be of either
the submersible or nonsubmersible type. The theory of opera-
tion in either case is quite similar.
Some of the advantages of air-powered diaphragm pumps
are as follows:
1. They are resistant to wear,
2. Pumping rate may be adjusted by regulating inlet air,
3. Pump is able to run dry without damage,
4. Discharge line can be closed while pump is operating with-
out damage,
5. Pump performance is more consistent due to less wear,
6. They are self-priming up to approximately 15 feet (4.5 m) of
suction lift,
7. Some models can be submerged which results in no elec-
trical power near the water, and
8. If you have compressed air in the plant, there is no need to
purchase an additional power source.
OPERATION
There are two flexible membranes connected to a common
shaft that moves simultaneously in a parallel path. The dia-
phragm movement is powered by compressed air directed be-
' hind one diaphragm while air is exhausted from behind the
other diaphragm. When the shaft reaches its length of travel,
an air valve transfers the air flow to the diaphragm in the other
chamber. Air in the first chamber is then exhausted. This recip-
rocating action alternately creates suction and discharge of
water in each chamber.
The suction and discharge valves (flap or ball type) control
the flow of water in their respective cycle of operation. This
form of piston-type action is similar to the piston-type positive
displacement pump and the diaphragm pump.
MAINTENANCE
The pump should be flushed thoroughly after use to prevent
dried sediment from obstructing valve operation. If the water
pumped had large particles in it, it may be necessary to dis-
mantle the pump to remove any remaining particles.
TROUBLESHOOTING
If pump will not cycle, check for:
1. Adequate air pressure,
2. Blocked discharge line,
3. Sliding air distribution valve rod hanging up,
4. Excessive air leak,
5. Plugged exhaust port,
6. Ruptured diaphragm, and
7. Open inlet valve.
If pump cycles but will not pump, check to see if:
1. Suction side of pump is pulling in air,
2. Suction line is plugged,
-------
720 Treatment Plants
OUTLET
INLET
NotK Mt« si
pumps wi
check valve off vefve seat A4-4-3/16," M-8'1/4," M-15'3/8"
Patented, one moving piece air valve
directs air supply pressure to
back side of diaphragm
Slurry is pushed out of liquid
chamber, thru pump outlet
At the same time opposite diaphragm
is pulled in by rod connected
to pressurized diaphragm
Suction created draws slurry into
liquid chamber thru pump inlet
When pressurized diaphragm reaches
limit of stroke, air valve shifts air supply
pressure to back side of diaphragm which
was pulled in. Slurry is pushed out of
liquid chamber thru pump outlet.
On discharge stroke, pressure on both sides
of diaphragm is equal & discharge pressure
is equal to air supply pressure.
Fig. 29.6 Diaphragm (pneumatic) pump
(permission of Wilden Pump & Engineering Co., Colton, California)
3. Check valves (ball or flap) are not seating, and
4. Suction lift is too high.
If output flow rate is low, determine if:
1. Air pressure to pump is low,
2. Suction is restricted and accompanied by fast cycling of
pump,
3. Discharge is restricted with slow cycling of pump, and
4. Valve seating is improper.
29.103 Submersible Pumps
Probably the most common type of submersible pump used
in wastewater treatment plants is the 120-volt fractional horse-
power motor driven centrifugal pump (Figures 29.8 and 29.9).
The motor is enclosed in a waterproof enclosure sealed with
'0' rings and a mechanical seal on the output shaft. Some
pumps also have a water-tight float switch attached. Floats can
be adjusted to control desired liquid level.
Most pump units of this type require little maintenance. The
motor bearings are sealed and will generally last the lifetime of
the unit. Mechanical seals are designed with the same life
expectancy. Do not run these pumps dry. This will cause wear
or burning of the seal. Unless the faces match perfectly, water
can enter the motor from the output shaft end and ruin the Fig. 29.7 Diaphragm (pneumatic) pump
motor. (permission o( Warren Rupp Company, Mansfield. Ohio)
VALVE
TOP SUCTION
INLET
BOTTOM
DIAPHRAGM DISCHARGE DIAPHRAGM
CONNECTING
SHAFT
TOUGH RUPPLON '
FLAP TYPE
CHECK VALVES
STAINLESS STEEL
SEATS
PILOT OPERATED
AIR DISTRIBUTION
VALVE
-------
Support Systems 721
A. Volute bolts
B. Oil housing
C. Volute
D. Seal cartridge
E. Oil housing bolts
F. Upper seal cartridge
G. Lower bearing housing bolts
H. Lower bearing housing
I. Lower bearing cover bolts
J. Upper bearing O-ring
K. Upper bearing cover
L. Locking plate bolts
M. Stator lock screw
N. Stator
0. Stator housing
P. Junction box
Q. Housing shoulder
f
N
Fig. 29.8 Submersible centrifugal pump
(permission of Flygt Corp., Norwalk, Conn.)
-------
722 Treatment Plants
Fig. 29.9 Submersible dewatering pump
(permission of Peabody Barnes, Inc., Mansfield, Ohio)
If a submersible pump is used in a sump, periodic cleaning
of the sump will insure that the pump suction will not become
clogged. Larger pumps are used as portable submersibles to
handle greater volumes of water. The open impeller centrifugal
pump can handle wastewater containing large particles.
The closed impeller multi-stage pump is most commonly
used when dewatering clear water from great depths (Figure
29.10). If you were required to remove groundwater from a
construction site, a well point would be driven or set and this
type of pump installed. Since conditions of head and flow vary
in each instance, proper selection of the pump is very impor-
tant.
29.11 Pump Engines (Refer to Section 29.4)
29.12 Seals
Most portable pumps use a mechanical-type seal between
the pump housing and shaft (Figures 29.11 and 29.12). A sta-
tionary element (quite often made of a ceramic material) is "0"
ring- or rubber-mounted in the pump housing. This ensures a
watertight seal. The spring-loaded rotary element is fastened
to the shaft with a rubber/neoprene bellows to form a watertight
seal on the shaft and rides against the face of the stationary
element. In many cases, the rotary element is made of carbon
and is lapped to a micron finish. The rotating (and stationary)
faces of mechanical seals are finished to helium light band
flatness. As the pump rotates, the spring allows the rotary
element to flex with shaft end play and still maintain the pres-
sure necessary to ensure that the rotary face is in contact with
the stationary element.
Mechanical seals vary in design and in the type of material
used in the seal elements. These elements may be made of
stainless steel, tungston carbide, ceramic, carbon, or brass to
name a few materials. Each material has its advantages and
limitations. Two of the quickest ways to damage a mechanical
seal are to:
1. Run it dry without water present at the seal face to dissipate
heat generated by the two surfaces rubbing together. Be-
fore starting a portable centrifugal pump, always make sure
that it is primed.
2. Allow dirt, grease, or dust particles to get on the faces dur-
ing installation.
A number of the small seals are self-aligning. A great
amount of care must be exercised in installation to insure that
the seal surfaces do not become scratched or contaminated
with dirt or sand. A small amount of silicone grease applied on
the "O" ring will allow for ease of installation of the stationary
element. The same grease when applied to the shaft will en-
sure a good seal with the bellows and allow the rotary element
to move on the shaft initially. After the seal is in place, the
bellows allows the rotary element to align itself to the stationary
element.
Before you attempt to replace a seal, refer to the pump
manufacturer's maintenance manual and follow the instruc-
tions. There are many differences or variables and the seals
and shafts can be easily damaged if directions are not followed
exactly.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 793.
29.1D List the advantages of a positive displacement dia-
phragm pump.
29.1 E What would you do if a diaphragm pump suddenly
stops pumping and the engine either quits or keeps
running and the pump rod slips on the shaft?
29.1F What maintenance should be performed on a
pneumatically operated diaphragm pump after use?
29.2 PIPES, VALVES AND FITTINGS
29.20 Need for Pipes, Valves and Fittings
During the process of wastewater treatment, the water is
conveyed by pipes and controlled in part by valves. There are
various reasons for selecting a particular type of pipe or valve.
This section will discuss the common types of pipes and valves
and some of their advantages and some of the limitations.
20.21 Pipes
Why specify one type (material) of pipe over another? The
type installed must be selected to meet your particular needs:
initial cost, durability, ease of installation, availability, compati-
bility with wastewater and solids being processed, and mainte-
nance.
Pipe sizes vary and are usually specified by the inner diame-
ter. The pipe wall thickness is designated by its strength, usu-
ally designated as pipe schedules. The schedule number is the
ratio of internal pressue in PSI divided by the allowable fiber
stress multiplied by 1,000. Typical schedules of iron and steel
pipe are schedules 40, 80, and 160. Other forms of piping are
divided to various classes with specific specification.
29.210 Galvanized Pipe
Galvanized pipe is steel pipe that has been coated with zinc
by an ELECTRO-CHEMICAL PROCESS.2 This zinc is a corro-
sion inhibitor. Most piping installations that must withstand high
2 Electro-chemical process. A process that causes the deposition or formation of a seal or coating of a chemical element or compound by the
use of electricity.
-------
Support Systems 723
pump
Patented
Barform
New check valve with a non-deforming
valve poppet closes against a smooth,
tapered seat for positive, quiet action.
Barthane top bearing has shown to be
40 times more abrasion resistant than
ordinary metal components.
Stainless steel
housing and cable guard
Spira-Seal system
The Spira-Seal system (a Peabody
Barnes exclusive) virtually sandproves
a submersible. The Barthane U-cup
runs on a spiral stainless steel band
around the impeller eye to form a per-
fect seal, eliminate recirculation, and
clear sand and grit out. Tests show th
seal will outlast any other now made.
Superior stage design. The
series cases are especially designed to
deliver efficient, dependable per-
formance. The precision molded Bar-
form has the greatest possible resist-
ance to abrasive action.
Stainless steel hex shaft is extra
strong for a positive drive and rustproof
for maximum durability.
Barform impeller is highly abrasion re-
sistant so it will last longer and keep its
surfaces and water passages smooth
and efficient.
Barthane U-cup has great abrasion re-
sistance, and it's self-compensating for
all operating pressures. It remains flexi-
ble even after years of wear. (A part of
the exclusive SpiraSeal system.)
Stainless steel inlet screen
Stainless steel coupling
NEMA-standard
PSC oil-filled motor
Stainless steel motor
shell
Fig. 29.10 Closed impeller multi-stage submersible pump
(permission of Peabody Barnes, Inc., Mansfield, Ohio)
-------
724 Treatment Plants
s
(GORMAN-RUPP)
GREASE-LUBRICATED (JOHN CRANE)
MECHANICAL SHAFT SELF-LUBRICATED SOLID PACKED PACKING & LANTERN
SEAL MECHANICAL SEAL STUFFING BOX RING STUFFING BOX
Fig. 29.11 Mechanical seals
(permission of The Gorman-Rupp Co., Mansfield, Ohio)
PUMP FASTENERS (4)
END
PLATE
.HPELLER "ST
/
SEALING
WASHER
CERAMIC SEAL
PUMP
FASTENERS (4)
FAN HOUSING
OR FRAME
IMPELLER
END
PLATE
Fig. 29.12 Mechanical seals
(permission of Homelite Textron, Charlotte, North Carolina)
-------
Support Systems 725
pressures are fabricated from galvanized pipe.
Schedule 40 steel pipe has a working pressure up to 175
pounds per square inch (12.3 kg/sq cm) for water, oil, or gas
when used in a non-shock application not exceeding 150 de-
grees F (65°C). Schedule 80 can be used up to 400 psi (28.1
kg/sq cm) of water, gas, or oil at 150 degrees F (65°C).
Galvanized pipe generally uses screwed-type fittings. There-
fore, installation requires cutting and threading the pipe to cor-
rect sizes. The standard length of pipe is 21 feet (6 m)
threaded on both ends with a coupler on one end and a thread
protective cap on the other.
The taper of pipe threads may be designated N.P.T. (Na-
tional Pipe Thread) or A.P.T. (American Pipe Thread). N.P.T.
threading is by far the most commonly used threading in our
industry. A.P.T. threading is generally used in special applica-
tions. One way to remember the difference between the two
types of threading is to think of "normal pipe thread" when you
see N.T.P.
When galvanized pipe is to be buried in soil, it is usually
wrapped with a protective coating of vinyl or a tar-based prod-
uct is used. This gives the pipe added corrosion protection.
Many installations use a form of CATHODIC PROTECTION3 to
prevent ELECTROLYSIS.4 Plates are imbedded in the ground
and a small current is passed between the plates, thereby
reducing ELECTRO-CHEMICAL CORROSION5 or elec-
trolysis.
The pipe is not affected greatly by sunlight or moderate heat
or cold. The expansion and contraction is considerably less
than in PVC pipe. Galvanized pipe does not fare too well in an
atmosphere containing hydrogen sulfide or chloride com-
pounds (salts or chlorine). However, painting over the gal-
vanized surface will prolong its life.
29.211 Cast Ductile Iron/Soil Pipe
In recent years, most manufacturers have been producing
ductile iron pipe instead of the true cast iron type. Ductile pipe
has a greater amount of steel and better load and functional
characteristics than cast iron. This pipe is of high strength and
can carry high external and internal pressures (150 to 350 psi
(10.5 to 24.6 kg/sq cm) working pressure). When laid in a
stable soil, there are few problems with corrosion. In salt
marshes, highly alkaline soil, waste dumps, or cinder fills, extra
protection is provided by using plastic sheathing. Ductile iron is
approximately 35 percent more resistant to corrosion than
standard gray iron pipe.
When selecting ductile pipe, two items are to be considered:
1. Internal pressure of water or sludge being carried, and
2. The type and loading from the trench.
Ductile pipe is made in seven thickness classes and ranges
in diameter from 4 to 48 inches (100 to 1200 mm) nominal pipe
size.
Why choose ductile pipe?
1. Trench backfill (material placed and compacted over pipe in
trench) is not as critical as with other types of pipes (no
need for expensive import backfill material).
2. Trench loading (weight on pipe in trench) is not as critical.
3. There is less infiltration/exfiltration.
4. The pipe is available in 20 foot (6 m) lengths (few joints).
5. The pipe is durable.
6. The pipe is very effective for use in unstable and rocky soil.
7. Pipe joints are easily made.
Perhaps the largest drawback is initial price. You have to
weigh its benefits for your particular application.
SOIL PIPE
Soil pipe is a thin wall or light weight cast iron pipe. This pipe
has been used extensively in drainage lines. Soil pipe also has
corrosion resistance similar to the large cast pipes. One of its
drawbacks is that it breaks easily. It has a low load-bearing
weight and is commonly used in a gravity-flow situation. Under
normal conditions, it will fare quite well.
29.212 PVC (Polyvinyl Chloride) Pipe
The cost of maintenance, repair, and replacement of under-
ground piping caused by corrosion is very important. PVC pipe
is immune to nearly all types of corrosion, be it biological,
chemical, or electro-chemical. Since PVC is a non-conductor,
galvanic effects are non-existent and provisions for cathodic
protection as required with steel and cast iron systems are
unnecessary for PVC systems.
In wastewater collection lines, internal corrosion caused by
sulfuric acid (a result of the hydrogen sulfide cycle) takes its toll
on asbestos cement, concrete, and metal pipes. PVC is not
affected by sulfuric acid in concentrations found in sanitary
sewers. PVC is resistant to biological attack and will not decay.
Metal pipes are slowly destroyed by oxidation. Bacteria and
other microorganisms will not cause deterioration of PVC pipe.
The wear characteristics of PVC are exceptional and it is resis-
tant to abrasion. Since the interior of the pipe is smooth, there
is less friction loss than with other types of pipes.
There are, however, some drawbacks to PVC pipe that
should be considered also. PVC will deteriorate when exposed
to ultra-violet radiation. Painting the pipe will help deter the
effect. PVC pipe will flex, expand, and contract with heat. This
may be a problem in certain applications.
The smaller sizes of PVC pipe are not expensive when com-
pared to galvanized or steel pipe; however, this is not so as the
size increases. PVC is very easy to install and no special tools
nor highly skilled workers are necessary. Consult with your
pipe vendor to insure that the proper class or schedule of PVC
is being used for a particular application.
29.213 Concrete Pipe
To move large volumes of wastewater in gravity sewer sys-
tems, we must be able to install pipe of large sizes that is
structurally strong, reasonably corrosion resistant, and avail-
able at an acceptable price. Concrete pipe meets these qualifi-
cations. Most large concrete pipes are reinforced with rein-
forcement bar. This adds to the load strength that the pipe can
bear. When a line is 15 to 20 feet (4.5 to 6.0 m) below the
surface, it has to withstand great external pressures. Concrete
pipe is not adversely affected by most soil chemicals. How-
ever, it must be laid in an engineering trench and backfilled
under specified conditions.
Internal pipe corrosion in a domestic wastewater system is
one of concrete pipe's limitations. As hydrogen sulfide gas
escapes from the wastewater, it combines with bacteria in the
3 Cathodic Protection (ca-THOD-ick). An electrical system for prevention of rust, corrosion, and pitting of steel and iron surfaces in contact
with water, wastewater or soil.
4 Electrolysis (ELECT-TROLLY-sis). The decomposition of material by an electric current.
5 Electro-chemical Corrosion. The decomposition of a material by (1) stray current electrolysis, (2) galvanic corrosion caused by
dissimilar metals, and (3) galvanic corrosion caused by differential electrolysis.
-------
726 Treatment Plants
slime that coats the pipe interior. The bacteria convert the gas
into sulfuric acid. If the pipe is of a corrodible material, such as
concrete, the sulfuric acid slowly decomposes the concrete.
When the pipe is full and moving at an acceptable rate, deterio-
ration from sulfuric acid is kept at a minimum. Deterioration of
concrete pipe can be slowed if the pipe is made of calcereous
cement which is high in lime that will help to neutralize the
sulfuric acid.
With concrete pipe, there is a greater chance of infiltration/
exfiltration than with other types of pipes; however, this is usu-
ally not a problem.
29.214 Asbestos — Cement Pipe
Asbestos-cement pipe is made of asbestos, sand, and Port-
land cement. When combined with cement, the long asbestos
fibers yield a pipe of considerable strength. This pipe will ac-
cept high external loads as well as being able to operate with a
pressured fluid. Asbestos-cement pipe is very corrosion resis-
tant. There are no electrolysis effects, either chemical or
electro-chemical, and it fares well in salt or alkaline soil.
The interior of the pipe is smooth and has less friction loss
than standard concrete pipe. Since the standard length of pipe
is 13 feet (4 m), there are fewer joints. Asbestos cement pipe
weighs less than comparable sizes of concrete or tile pipe and
is cheaper to transport. However, the initial cost of asbestos-
cement pipe is greater than the price of concrete pipe. As with
concrete pipe, trenching and backfill must be engineered.
Generally, asbestos-cement pipe is not used in rocky areas
without proper pipe bedding.
29.215 Welded Steel Pipe
Welded steel pipe is available in sizes ranging from Vz inch
to 42 inches (12.5 to 1,050 mm). In sizes Vi inch through 12
inches (12.5 to 300 mm) of standard pipe, the inside diameter
is of the nominal pipe size. However, in sizes 14 to 42 inches
(350 to 1,050 mm), the dimension refers to the outside diame-
ter of the pipe.
Sizes from 1 to 12 inches (25 to 300 mm) are available in
four different wall thicknesses (ST, XS, 160, and XX). In sizes
14 to 42 inches (350 to 1,050 mm), it is available in ST and XS
thicknesses only. To see how the pipe schedule is directly
related to wall thickness, the specifications for one-inch (25
mm) pipe are listed below:
Wall Thickness, in/mm
Outside
Pipe Size Diameter
1 inch 1.315
25 mm 33.40
ST
Schedule
40
0.133
3.38
XS
Schedule Schedule XX
80 160 Strong
0.179
4.55
0.250
6.35
0.358
9.09
Welded steel pipe is very versatile because it can be cut and
welded to follow varied contours. This is veiy helpful when
aligning pumps and other pumping-related equipment. Welded
steel pipe allows closer nesting of pipes when space is at a
premium. Less space is required for welded fittings than
flanges and bolts; however, space must be available when
welding the joints.
This pipe provides permanent leak-proof connections via
welding. An advantage of welded steel over threaded pipe is
the fact that none of the pipe wall has been reduced by the
cutting in of threads (the threaded joint is susceptible to corro-
sion and loosening by vibration) and uniform wall thickness is
maintained. In comparison to most other metallic pipes,
welded pipe systems are easier to install and do not require the
heavy and costly tools needed to install other conventional
systems.
Welded steel pipe is not very resistant to corrosion. There-
fore, it is necessary to coat the pipe with a bituminus product.
The interior of the pipe is often coated to prevent corrosion
caused by the materials being transported.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 793.
29.2A Galvanized pipe is subject to corrosion in what types
of atmospheres?
29.2B How can galvanized pipe be protected from corro-
sion?
29.2C What types of locations might cause ductile iron pipe
to corrode?
29.2D What is a major limitation of concrete pipe?
29.22 Valves
29.220 Use of Valves
Valves are the controlling devices placed in piping systems
to stop, regulate, check, divert, or otherwise modify the flow of
liquids or gases. There are specific valves that are more suita-
ble for certain jobs than others. The five most common valves
that you will find in a wastewater treatment facility are dis-
cussed in this section.
29.221 Gate Valves (Figures 29.13 and 29.14)
The basic parts of a gate valve are: the operator (handle),
the shaft packing assembly, the bonnet, the valve body with
seats, the stem, and the disc. Gate valves come in a large
number of sizes, but the principle of operation is quite similar.
One could associate the action of a gate valve to that of a
guillotine having a screw shaft instead of the rope. The valve
disc is raised or lowered by a threaded shaft and is guided on
each side to ensure that it will not hang up in the operation. The
disc is screwed down until it wedges itself between two ma-
chined valve seats. This makes a leakproof seat on both sides
of the disc. The discs are replaceable. Some gate valves have
discs with wedges inside. As more force is applied to the
screwed stem, the wedges force the discs into tighter contact
with the valve seats. The flow should go in the direction of the
arrow on the gate valve.
Gate valves are either of the rising (Figure 29.13) or non-
rising stem (Figure 29.14) type. The rising stem has compan-
ion threads in the valve bonnet. As the valve is opened, the
stem is threaded out, lifting the wedged disc. In the non-rising
type, the stem is held in place in the bonnet by a collar. The
stem is threaded with companion threads in the wedged disc.
As the valve opens,the disc rises on the stem. Consequently,
the hand wheel stays on the same plane.
Gate valves are not commonly used to control flows. With
the valve partially open, the water velocity is increased through
the valve. Minute particles transported in the water can cause
undue seat wear. The vee-ported gate valve can be used in
controlling flows. As the valve is opened, the vee is widened to
allow more flow. Because of the valve design, little damage is
done to the valve seats in the vee-ported type of gate valve.
Suggested operation and maintenance procedures are
listed below:
1. Open valve fully. When at stop, reverse and close valve
one-half turn.
2. Operate all large valves at least yearly to insure proper
operation.
-------
Support Systems 727
packing
Fig. 29.13 Rising Stem Gate Valve
(permission o( Stockham Valves & Fittings, Copyright, 1976)
CXSC RING
Fig. 29.14 Nonrising Stem Gate Valve
(permission ol Stockham Valves & Fittings, Copyright, 1976)
HAND WHEEL
PACKING GLANO
STUfflNG SOX
SONNET
DISCx
•OCT
SEAT RING
STEM
PACKING GLANO
fLANGE
REPACKING
SEAT BUSHING
WHEEL
HAND WHEEL LOCK-NUT
YOKE
HAND
YOKE BUSHING
STEM PIN
DISC RING
-DISC HALVES
WEDGE RING
-*-BODY
PACKING GLANO
BUSHING
PACKING
GLANO
PACKING
SONNET
REPACKING
SEAT BUSHING
UPPER
SPREADER
SEAT
WEARING
PLATE -
LOWER
-------
728 Treatment Plants
3. Inspect valve stem packing for leaks. Tighten as needed.
4. If the valve has a rising stem, keep stem threads clean and
lubricated.
5. Close valves slowly in pressure lines to prevent WATER
HAMMER.6
6. If a valve will not close by using the normal operator, check
for the cause. Using a 'cheater' (bar-pipe wrench) will only
aggravate your problem.
29.222 Globe Valves (Fig. 29.15)
The globe valve seating configuration is quite different from
the gate valve. Globe valves use a circular disc to make a flat
surface contact with a ground-fitted valve seat. This is similar
to placing your thumb over the end of a tube. The parts of the
valve are similar in name and function to the gate valve. They
can be of the rising or non-rising stem type.
What is unique about the globe valve is its internal design
(Fig. 29.15). This design enables the valve to be used in a
controlling mode. The valve seats are not subject to excessive
wear when partially opened like the gate valve. After extended
use, the valve may not have a positive shut off but it will still be
effective in throttling flows. Procedures for operating and main-
taining globe valves are similar to the procedures outlined for
gate valves in Section 29.221.
29.223 Eccentric Valves (Figures 29.16 and 29.17)
The eccentric valve has many desirable features. These fea-
tures include allowance for high flow capacity, quarter turn
operation, no lubrication, excellent resistance to wear, and
good throttling characteristics. The eccentric valve uses a
cam-shaped plug to match an eccentric valve seat. As the
valve is closed, the plug throttles the flow yet maintains a
smooth flow rate. The plug does not come into contact with the
valve seat until it is in the closed position.
Because the plug has a resilient coating, it insures a leak-
tight seal at the valve seats. The Buna-N, neoprene, or viton
plug coating is very wear resistant and can function well under
a wide temperature range. This valve is excellent for control-
ling the flows of slurries and sludges found in wastewater
treatment facilities.
29.224 Butterfly Valves (Fig. 29.18)
The butterfly valve is used primarily as a control valve. The
flow characteristics allow the water to move in straight lines
with little turbulence in the area of the valve disc (butterfly).
Complete flow shutoff can be accomplished but the PSI rating
is relatively low in comparison to eccentric or gate valves.
The butterfly valve uses a machined disc that can be open to
90 degrees to allow full flow through the valve. Quarter turn
operation moves the valve from the 'closed' to 'open' position.
The disc is mounted on a shaft eccentric that allows the disc to
come into its seat with minimum seating torque and scuffing of
the rubber seat. There is no contact between the disc and the
seat until the last few degrees of valve closure.
A resilient rubber is used as the seat and is of a continuous
form that is not interrupted by a shaft connection. Wear resist-
ance characteristics are good when used in slurry and sludge
applications.
When the valve is closed, the disc is forced against the
rubber seat. Wedges with jacking screws compress the rubber
seat via a jack ring. The rubber seat then conforms to the entire
disc circumference. The rubber can be readily replaced when
necessary without complete valve dismantling. Large valves
do not need to be removed from the line for seat replacement.
29.225 Check Valves (Fig. 29.19)
The term 'check valve' describes its function. A check valve
allows water to flow in one direction only. If the water attempts
to flow in the opposite direction, an internal mechanism closes
the valve and "checks" the flow. Three types of check
mechanisms may be used — the swing check, the wafer
check, or the lift check. In the swing check, a moveable disc
rests at a right angle to the flow and seats against a ground
seat. The moveable disc is called the clapper. The clapper can
be one of three types: gravity operated, lever and weight oper-
ated, or lever and spring operated. In many installations the
water being pumped must be delivered at a desired flow rate
and pressure. A clapper with an external means of adjusting
the opening in the check valve may be necessary to produce
desired flows and pressures. By positioning the weight on the
lever or adjusting the spring tension, a check valve can be
made to operate either partially or fully open at various pres-
sures and flows. The spring or counter weight also ensures
that the check valve closes at "no flow." This is very helpful if
the valve is not in a position that will enable gravity alone to
operate the clapper. The gravity-operated clapper does not
have an external adjustment and relies on the weight of the
clapper to close the valve at "no flow" conditions.
Most swing check valves provide for full opening, that is, the
clapper can move up into the bonnet and thus be completely
out of the flow. Head loss in swing check valves may be rela-
tively high and this factor must be considered in selecting the
device for a particular application. This type of check valve is
quite common in pump installations and often has a dampen-
ing feature to cushion the closing of the clapper.
The wafer check has a circular disc that hinges in the center
(diameter) of the disc. Water passing through collapses the
disc and the stoppage of flow allows the disc to return to its
circular form. Because the valve has a tendency to be fouled
up by stringy material, it is not commonly used in handling
domestic wastewater. Wafer check valves are very effective
when used with clean water.
The lift check uses a vertical lift disc or ball. When there is
flow, the disc or ball is lifted from its ground seat and fluid
passes through the valve. As flow stops, the check realigns
itself with its seat and checks or prevents water backflow. The
moveable portion can be a spring or gravity return.
The foot valves used in pump suctions are nearly always of
the vertical lift disc design. A check valve of this type is usually
applied to handle clean water.
Backflow prevention by check valves is essential in many
applications to:
1. Prevent pumps from reversing when power is removed,
2. Protect water systems from being cross-connected,
3. Aid in pump operation as a dampener, and
4. Insure "full pipe" operation (pipe is full of water).
6 Water Hammer. The sound like someone hammering on a pipe that occurs when a valve is opened or closed very rapidly. When a valve
position is changed quickly, the water pressure in a pipe will increase and decrease back and forth very quickly. This rise and fall in
pressures can do serious damage to the system.
-------
Support Systems 729
>rrocx>];Ui
£>jse
Fig. 29.15 Globe Valve
(permission of Stockham Valves and Fittings, Copyright, 1976)
29.23 Fittings for Steel, Ductile and Cast Iron Pipes
This section describes fittings that are used in piping sys-
tems that handle special needs.
29.230 Victaullc Couplings (Figs. 29.20a and 29.20b)
The victaulic coupling is a two-piece bolted unit with a seal-
ing gasket. The victaulic coupling is used in an area where
future disassembly is anticipated. Quite often you will find them
on the suction and discharge sides of pumps. Two bolt cou-
plings are much easier to remove than a bolted flange. Two
grooves are machined into the two pieces of pipe being
coupled. The cast coupling collar locks into the grooves. A
one-piece rubber neoprene gasket makes a seal between the
outside of the two pieces of pipe being secured in place by the
collar.
The victaulic coupling will allow for a small amount of mis-
alignment between pipes. Its primary use is for a quick, easy
coupling of two pipes and to serve as an expansion joint and a
vibration depressor.
29.231 Sleeve Coupling
The sleeve coupling consists of a steel tube with a slight
flare on the inside of both ends. This is to accommodate the
wedged resilient gasket. The sleeve coupling is compressed
against the pipe by pulling two flanges together with bolts and
nuts. Two pieces of pipe generally of the same size are joined
together. This type of coupling also will allow for some mis-
alignment as well as expansion. A sleeve coupling is ideal to
use when joining two unflanged pipes in an area where space
is at a premium. This coupling is fast, sure, and easy to install.
There are a number of variations in sleeve couplings:
1. A transition coupling enables you to connect two sizes (%-
inch or 19 mm variance) or two dissimilar pipes (cast to
steel-cast to PVC);
2. A reducing coupling allows two sizes of pipe to be coupled;
and
3. A 'cut-in' repair coupling enables you to remove a small
damaged area of a pipe and couple the new piece to the old
pipe.
29.232 Compression Coupling
The compression coupling consists of a tube threaded on
each end for the compression nuts and two tapered sealing
grommets. As the nuts at either end are tightened, the sealing
grommet is compressed until a watertight seal is accom-
plished. This type of coupling is used to allow for misalignment
of the two pipes being connected. When faced with joining two
pipe ends that are close together but cannot be coupled by a
standard union, the compression coupling fills the need. This
coupling is a reliable threadless connector.
When installing, make sure that pipe wrench jaw marks are
smoothed down with a file so grommets have a smooth sealing
surface.
29.233 Mechanical Flanges
Mechanical flanges are used to connect unflanged pipes to
flanged fittings (tees, 90-degree bends, valves). One side of
the flange is secured to the pipe by a resilient gasket that is
compressed by a bolt-tightened compression flange (by me-
chanical means). The other end of the flange has a bolt hole
pattern that matches the flange being coupled to. A mechan-
ical flange simplifies the installation of complex piping systems
eoor/
IDENTIFICATION PLATE
HAND WHEEL
Giano
STEM
PACKING NUT
PACKING
UNION BONNET
DISC HOLDER
DISC LOCK NUT
-------
ECCENTRIC ACTION
The DeZurik design matches a single-faced
eccentric or cam-shaped plug with an ec-
centric raised body seat. With rotary
motion only, the plug advances against
the seat as it closes. Here's how it works:
OPEN—The plug is out of the flow path.
There is no bonnet or other cavity to fill
with slurry material. Flow is straight-
through with minimum pressure drop.
CLOSING—At any position between open
and closed, the eccentric plug still has not
touched the seat. There is no friction to
cause wear or binding. Flow is still smooth
and straight. Throttling action is excellent
on all types of services from slurries to gas.
CLOSED—The eccentric plug makes con-
tact with the eccentric seat only in the
fully closed position. Action is easy, with-
out binding or scraping. There is no con-
tinual seat wear. The plug is moved firmly
into the seat to provide a positive, drip-
tight, long-lasting seal.
Fig. 29.16 How eccentric valves work
(permission of DeZuric Corporation, Sartetl, Minnesota)
-------
Support Systems 731
Fig. 29.17 Eccentric valve
(permission o( DeZuric Corporation. Sartell, Minnesota)
-------
732 Treatment Plants
Fig. 29.18 Butterfly valve
(permission of American-Darting Valve, Birmingham, Alabama)
-------
Support Systems 733
Bronze or alloy disc ring
is securely peened into
machined dove-tailed
Tight closing assured
since clapper arm shaft
is set slightly back of
vertical seat face.
Bronze clapper arm shaft
can be extended through
body when lever with
weight or spring is re-
quired.
Fully revolving disc
seats in different posi-
tion on seat ring face
and distributes wear uni-
formly over the entire
seating face.
Bronze seat ring is
screwed in body and
made with lugs and can
be replaced with body
in line. It can be furn-
ished with a resilient in-
sert for bottle-tight ser-
vice on gas or air.
Bronze bushed ductile
iron clapper arm for
added strength and im-
pact resistance.
Body design permits re-
moval > of clapper arm
assembly through bon-
net opening.
machined
groove.
Vertical seating surfaces
provide sensitive seating
action.
Fig. 29.19 Check valve
(permission of American-Darling Valve, Birmingham, Alabama)
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734 Treatment Plants
FOR GROOVED END PIPE
Standard Coupling: Sizes V*"-24'
15
Style 77
General purpose. Best suited to the average conditions under which steel, spiral
and other IPS pipe is installed.
Rigid Couplings: Sizes 2"-12"
Style HP-70
Uniquely designed (or varied rigid services. Tongue-and-recess design assures
proper mating of housing and provides protection from gasket extrusion.
Endseal Coupling: Sizes 2"-12"
For high pressure service. The ENDSEAL gasket is molded of a specially formu-
Style HP-70ES lated and compounded oil-resistant Buna-N, with high modulus for resistance
to extrusion.
Lightweight Coupling: Sizes 2"-8"
Style 75
For light duty applications where relatively low pressures, low external stresses
and lightweight materials are controlling factors.
Snap-Joint Couplings: Sizes 1"-8"
Designed for pipe lines where quick "Make and Break" of pipe joints is important.
Style 78
Fig. 29.20a Victaulic couplings (for grooved end pipe)
(Permission of Victaulic Company of America)
FOR PLAIN END PIPE
Plainlock Coupling: Sizes 1"-6"
S* -
-------
Support Systems 735
since there is no need to thread large pieces of pipe and
flange-bolt holes are easy to align.
29.234 Band Seals
The 'band seal' is a rubber coupling that is used to join clay,
soil pipe, or asbestos-cement pipe. A flexible rubber coupling
is secured to the two pieces by stainless steel screw clamps (it
looks like a large radiator hose clamp that compresses the
rubber and ensures a leak proof-seal). This type of connection
is widely used in gravity flow sewer piping systems. Band seals
allow for maximum deflection of the two adjoining pipes. They
are easy and economical to use.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 793 and 794.
29.2E What is the purpose of valves?
29.2F List the five most common types of valves found in
wastewater treatment facilities.
29.2G What is the purpose of a check valve?
29.2H Why is backflow prevention by check valves essential
in many applications?
29.21 Where are victaulic couplings used?
29.2J Under what conditions are band seals installed?
i&wLcfif c^4
tbtxWoox c&oreM*
Please answer the discussion and review questions before
continuing with Lesson 2.
DISCUSSION AND REVIEW QUESTIONS
(Lesson 1 of 4 Lessons)
Chapter 29. SUPPORT SYSTEMS
Write the answers to these questions in your notebook be-
fore continuing.
1. Why should operators know how to operate and maintain
support systems?
2. Why should you locate a portable pump as near as possible
to the surface of the water being pumped?
3. How would you determine if there is an air leak in the suc-
tion hose of a portable pump?
4. What can happen if a submersible pump with a mechanical
seal is allowed to run dry?
5. What factors would you consider when selecting the type
(material) of pipe to do a particular job?
6. What factors can cause wear on gate valve seats?
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736 Treatment Plants
CHAPTER 29. SUPPORT SYSTEMS
(Lesson 2 of 4 Lessons)
29.3 AUXILIARY ELECTRICAL EQUIPMENT
29.30 Safety First
This section covers some aspects of electrical equipment
that have not been covered in previous chapters. Bear in mind
that a QUALIFIED ELECTRICIAN should perform most of the
necessary maintenance and repair of electrical equipment. If
you don't know the how, why, and when of the job, don't do it.
You could endanger your life as well as your fellow operators.
Never attempt work that you are not qualified to do or are not
authorized to perform.
29.31 Standby Power Generation
Because the treatment of wastewater is considered a critical
service, it is imperative to have that function continue even with
loss of commercial power. A power outage of a short duration
probably will not have adverse effects on plant operation. The
question you must ask yourself is, "Can your plant meet the
needs of the public if a 'brown out' or an earthquake occurs
that eliminates commercial power for an extended length of
time?" If the answer is 'no,' then perhaps a form of standby
power generation should be considered.
Where do you begin? You have to consider whether you
would like to have all of your facility operating or whether just
the vital or key equipment would be sufficient. Since the
characteristics and operating conditions of every plant are dif-
ferent, it is extremely difficult to make specific suggestions.
For the sake of illustration, let us pose a hypothetical situa-
tion. Consider a 10 MGD (38,000 cu m/day) capacity plant with
an average flow rate of 6 MGD (23,000 cu m/day) and a trick-
ling filter for secondary treatment. If you wanted to ensure
minimal operation, prepare a list of needs that must be met:
1. Comminution,
2. Wastewater pumping,
3. Clarification,
4. Trickling filter circulation,
5. Sludge handling,
6. Chlorination/dechlorination, and
7. Minimal lighting.
Calculate the maximum horsepower or total kilowatts nec-
essary to maintain the limited operation:
1. Comminutor — 3 horsepower
2. Wastewater Pump — 75 horsepower
3. Clarification — 2-1.5 horsepower
4. T.F. Circulation — 40 horsepower
5. Sludge Handling — 30 horsepower
6. Chlorination — 15 horsepower
7. Lighting
2.24 KW
56. KW
2.24 KW
30. KW
22.40 KW
11.20 KW
5. KW
129.08 KW
The minimum power required is 129.08 KW. When sizing a
generator for emergency power, you have to make sure that
the generator will be able to start the needed motors. Since the
locked rotor current of the 75 horsepower induction motor on
the wastewater pump is approximately four times running cur-
rent, then the generator must be able to handle 224 KW at that
instant. Size the generator not only by total load, but also for
the highest horsepower motor being started. Consider the se-
quence in which motors will be started. The starting of all the
motors simultaneously (without sequence starting) would be
nearly impossible. Consult experts in power generation for an-
swers to your specific questions regarding your plant because
each plant has different needs. If you are considering standby
power, shop around and get ideas from the equipment manu-
facturers.
After you have determined the size of generator needed,
you must be able to connect it to your power distribution sys-
tem. This may require some sophisticated switch gear. Be-
sides the mechanical functions necessary in connecting the
emergency power with your normal system, it is important that
the two systems cannot be electrically coupled. (Two electrical
systems must be 'in phase' with each other before parallel
coupling.) For this reason mechanical interlocks are used to
insure that one circuit is always open. A "kirk-key" system,
where one key is used for two locks, locking one switch open
before the other can be closed, is sometimes used.
Looking back at the plant described, a generator of 150 KW
with intermittent overload capabilities should handle the load.
(Note: This is an assumption. Actual calculation may indicate a
different size.) An engine-generation system of this size could
handle your minimal power needs. If your wastewater collec-
tion system has ample capacity, it may be possible to throttle
your influent gate, backing up flow and allowing it to enter the
plant at a flow rate you can handle. Be careful not to flood any
homes, businesses, or streets. With a variable-speed influent
wastewater pump capable of pumping 5,500 GPM (30,000 cu
m/day), you would be able to catch up with the flow during the
off peak flow periods.
If you do not have standby power generation at your facility,
talk to others in the treatment field that do and obtain ideas and
information. After due consideration, take the necessary steps
to ensure yourself against interrupted power.
29.32 Emergency Lighting
29.320 Types of Equipment
The most practical form of emergency lighting in most in-
stances is that provided by battery-powered lighting units. Be-
cause they are used primarily for exit lighting, they are more
economical than engine-driven power sources. If you have a
momentary power outage, the system responds without an
engine-generator start-up. All emergency lighting unit equip-
ment is basically the same and consists of a rechargeable
battery, a battery charger, low voltage flood lights, and test
monitoring and control accessories. Proper selection of a unit
for a particular location requires careful consideration of the
following items:
1. Initial cost,
2. Types of batteries,
3. Maintenance requirements, and
4. Lighting requirements.
The three types of batteries most commonly used are: lead
acid, lead calcium, and nickel cadmium. Because poor battery
-------
Support Systems 737
maintenance is quite common in emergency lighting systems,
"maintenance free" batteries are becoming increasingly popu-
lar. These batteries can have a gelatin or acid (wet) ELEC-
TROLYTE.7 The gelatin type is completely spillproof and can
be handled safely without the dangers of acid spills. These
batteries have a shorter life span than the wet type. Since all
batteries undergo evaporation, the gelatin electrolyte will be
exhausted before that of a battery containing liquid. Wet-type
maintenance free batteries require no refilling and, when han-
dled porperly, acid spillage is minimal.
In terms of cost, the maintenance-free battery is more ex-
pensive; but when you consider the human factor, they may be
more reliable and cheaper in the long run. Most systems use a
battery charger that monitors the battery voltage. When re-
quired, the charger then charges the batteries. In earlier de-
signed units, a trickle charger was used. This constant charg-
ing resulted in inoperative batteries in a short time because of
overcharging.
The lamps used are normally 6 to 12 volt sealed-beam 25-
watt lamps. The light pattern provided is most effective when
illuminating a work area. A rule of thumb is that one lamp will
be sufficient for about 1,000 square feet, providing that the full
light pattern can be used. Consult emergency light level codes
(Table 29.2) for your particular application.
When selecting an emergency lighting system, check it very
thoroughly to insure that it will give you the protection needed.
If it fails to work when the chips are down and the main power
is out, you've wasted your money.
29.321 Batteries
This section will discuss wet storage batteries since they are
the most prevalent. Automotive and equipment batteries are
usually of the lead-acid type. This indicates that the dissimilar
plates are made of two types of lead and the electrolyte is
sulfuric acid. Wet-type batteries can also be nickel cadmium or
nickel iron.
Most batteries are a series of cells enclosed in a common
case. Each of these cells develops a potential (voltage) of 2.3
volts per cell when fully charged. Hence, a six-volt battery
contains three cells and a 12-volt battery has six cells. The
voltage output of a 12-volt battery is 13.8 volts when fully
charged. Once a lead-acid battery has been placed in service,
the addition of sulfuric acid is not necessary. The water portion
of the electrolyte solution evaporates as the battery is charged
and discharged. Lost water must be replaced. Deionized or
distilled water should be used. Tap water contains impurities
that shorten the life span of a battery if used to replace lost
water. These minute particles become attached to the lead
plates and do not allow the battery to rejuvenate itself fully
when charged.
When batteries are placed on charge, remove the cell
covers to allow the gas (hydrogen) caused by charging to es-
cape and not to build excessive pressure in the battery. A
battery on charge is as lethal as a small bomb if you ignite the
gas. Do not smoke or cause electrical arcing near the battery.
Do not breathe the gas and make sure that the area where a
battery is being charged is well ventilated.
TABLE 29.2 IES RECOMMENDED EMERGENCY LIGHT LEVELS"
High
HIGH
Elevators
Escalators
Computer rooms
Drafting rooms
Offices
Stairways
Transformer vaults
Engine rooms
Electrical, mechanical,
plumbing rooms
Footcandles 0.5 1.0 2.0 5.0
Dekalux 0.54 1.1 2.2 2.2
Minimum illumination for safety of personnel, absolute minimum at any time and at any location on any plane where safety is related to seeing
conditions.
* Special conditions may require different levels of illumination. In some cases higher levels may be required as for example where security is a
factor. In some other cases greatly reduced levels of illumination, including total darkness, may be necessary, specifically in situations
involving manufacturing, handling, use, or processing of light-sensitive materials (notably in connection with photographic products). In
these situations alternate methods of insuring safe operation must be relied upon.
EMERGENCY LIGHT LEVEL codes and standards vary widely throughout the country. Recommended minimum lighting levels of the Illuminat-
ing Engineering Soceity are being considered as a possible standard by ANSI and the Life Safety Code. These are minimum lighting levels
recommended for safety of personnel.
a Reprinted from December, 1978 issue Electrical Construction and Maintenance, Copyright 1978 McGraw-Hill, Inc. All rights reserved.
Hazard requiring visual
detection
NORMAL
ACTIVITY
LEVEL*
Areas
LOW
Conference rooms
Reception rooms
Exterior floodlighting
Closets
Slight
HIGH
Lobbies
Corridors
Concourse
Restrooms, washrooms
Telephone switchboard
rooms
Exterior entrance
Exterior floodlighting
LOW
Elevators (freight)
File rooms
Mail rooms
Offices
Stairways
Stockrooms
Exterior entrance with
stairs
7 Electrolyte (ELECT-tro-LIGHT). A substance which dissociates (separates) into two or more ions when it is dissolved in water.
-------
738 Treatment Plants
The keys to prolonged life of a battery are to keep the elec-
trolyte level above the cell plates, to keep the battery fully
charged, and above all, to keep the terminals and top clean.
When dirt and residue accumulate on the top of a battery, it
forms a path for current to flow between the negative and
positive posts. Take a multimeter, connect one lead to the
proper post (it will cause up-scale deflection) and slowly slide
the other lead across the top of the battery toward the other
post. If the top is dirty, the meter will deflect more as you
proceed across the top.
To clean the battery, use a stiff-bristled brush (not a wire
brush) and remove the heavy material. Then wash with a solu-
tion of baking soda and water (four teaspoons of baking soda
to one quart of water). This will remove the acid film from the
top and neutralize corrosion on the battery terminals. Rinse
with fresh water and dry the top with a dry, lintless cloth. Re-
move cell caps and wipe between them, then replace. At this
time check to be sure that the battery terminals are clean and
tight. If a battery is charged, but the terminals are loose, proper
voltage and current cannot be delivered.
At one time or other you may have given a battery a boost or
may have seen it done. There is a correct procedure to follow
to eliminate damage to electrical components and to prevent a
battery explosion (Fig. 29.21).
To boost the battery of a disabled vehicle from that of
another vehicle, follow this procedure. (Booster cables are
available at auto-parts stores.)
First, park the auto with the 'live' battery close enough so the
cables will reach between the batteries of the two autos. The
cars can be parked close, but do not allow them to touch. If
they touch, this can create a ground connection and create a
dangerous situation. Now set each car's parking brake. Be
sure that an automatic transmission is set in park, put a
manual-shift transmission in neutral. Make sure your head-
lights, heater, and all other electrical accessories are off (you
don't want to sap electricity away from your dead battery while
you are trying to start your car). If the two batteries have vent
caps, remove them. Then lay a cloth over the open holes. This
will reduce the risk of explosion (relieves pressure within the
battery).
Attach one end of the jumper cable to the positive terminal of
the booster battery (A) (that's the good battery in the other car)
and the other end to the positive terminal of your battery (D).
The positive terminal is identified by a + sign, a red color, or a
'P' on the battery in your car. Each of the two booster cables
has an alligator clip at each end. To attach, you simply
squeeze the clip, place it over the terminal, then let it shut. Now
attach one end of the remaining booster cable to the negative
terminal of the booster battery (B). The negative terminal is
marked with a - sign, a black color, or the letter 'N.' Attach the
other end of the cable to a metal part on the engine of your car
(C). Many mechanics simply attach it to the negative post of
the battery. This is not recommended because a resulting arc
could ignite hydrogen gas present at the battery surface and
cause an explosion. Be sure the cables do not interfere with
the fan blades or belts. The engine in the other car should be
running, although it is not an absolute necessity.
Get in the disabled car and start the engine in a normal
manner. After it starts, remove the booster cables. Removal is
the exact reverse of installation. Remove the black cable at-
tached to your engine, then remove it from the negative termi-
nal of the booster battery. Then remove the remaining cable
from the positive terminal of the 'dead' battery and then from
the positive terminal of the booster battery. Remove the cloths
from the fill-holes. Replace the vent caps and you are done.
Have the battery and/or charging system of the car checked by
a mechanic to correct any problems.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 794.
29.3A Why should a qualified electrician perform most of the
necessary maintenance and repair of electrical
equipment?
29.3B What is the purpose of a "kirk-key" system?
29.3C Why are battery-powered lighting units considered
better than engine-driven power sources?
29.3D Why should the water lost from a lead-acid battery be
replaced with deionized or distilled water?
29.33 High Voltage
29.330 Transmission
In general terms, high voltage is the voltage transmitted to
the plant site by the utility company. The voltage level can vary,
but 12,000 volts is quite common. After the power reaches the
plant, it is transformed down to a useable voltage (460 to 480
volts) either through utility-owned or customer-owned trans-
formers. The NEC (National Electrical Code) denotes high
voltages as those over 600 volts.
Why have high voltage? Since current (amperes) varies in-
versely with voltage, a load of 500 amps on the low voltage
side of the transformer would create a 20 amp load on the high
voltage side of a 12,000 volts/480 volt transformer. Transmis-
sion lines would have to be enormous in order to carry the load
if a lower voltage were used. Where high voltage cables termi-
nate at a transformer or switch gear, certain conditions must be
adhered to. If outdoor transformers are used that have high
voltage wires exposed, an eight-foot (2.4 m) high fence is re-
quired to prevent accessibility by unqualified or unauthorized
persons. Signs attached to the fence must indicate "High Volt-
age." Specifications for clearances, grounding, access, and
enclosures vary with installations. Any modification or repair
work must be completed by qualified people only.
29.331 Switch Gear
When we see the term 'switch gear,' it is usually associated
with the equipment used in the interruption, transfer, or dis-
connecting of voltages over 600 volts. The enclosure is de-
signed and manufactured to safely control high-voltage switch-
ing. Most distribution systems have a load-interrupting switch
-------
Support Systems 739
PROPER BOOSTER CABLE HOOKUP
BOOSTER
BATTERY
VEHICLE
BODY
GROUND
DISCHARGED
BATTERY
Fig. 29.21 Proper booster cable hookup
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740 Treatment Plants
that is capable of disconnecting high voltage lines that are
under load. Because of the arc that is caused in breaking the
circuit, special arc shoes' (arc-suppressant devices) are used
to ensure that the contact points are not pitted. A keyed lock
system is used to prevent opening of the enclosure in the
energized state.
Probably the best preventive maintenance that a treatment
plant operator can provide for switch gear is to keep the ex-
terior and its surroundings clean. If you encounter difficulties in
the course of operating the switches, please obtain qualified
help to do the inspection or repairs needed. Check with your
particular manufacturer to determine what is needed and when
this has to be done to keep your system functioning as de-
signed. If your equipment is in a corrosive atmosphere, it may
be necessary to remove it from service and epoxy paint the
internal buses. All pivoting points should be lubricated with a
lubricant specified by the manufacturer.
29.332 Power Distribution Transformers
If the high voltage transformers are owned by the utility, the
inspection and maintenance is carried out by the utility. Any
peculiar changes, smells, or noises should be reported to the
utility. Where transformers are customer owned, a regular in-
spection program should be established.
Most transformers use an oil to insulate as well as to cool the
windings. As heat is generated in the windings, it is transferred
to the oil. The oil is then cooled by air passing the 'cooling fins'
of the transformer. The primary requirements of the oil are:
1. High dielectric strength;
2. Freedom from inorganic acid, alkali, and sulfur to prevent
injury to insulation and conductors;
3. Low viscosity to provide good heat transfer; and
4. Freedom from sludging under normal operation conditions.
The principal causes of deterioration of insulating oil are
water and oxidation. The oil may be exposed to moisture
through condensation of moist air due to 'breathing' of the
transformer, especially when the transformer is not continu-
ously in service. The moist air condenses on the surface of the
oil and on the inside of the tank. Oxidation causes sludging.
The amount of sludge formed in a given oil depends upon the
temperature and the time of exposure of the oil to the air.
Excessive operating temperatures may cause sludging of any
transformer oil. Check with the manufacturer to determine how
often the oil should be tested. Oil can be revitalized by a clean-
ing procedure that is accomplished at the transformer site.
Any symptoms such as unusual noises, high or low oil
levels, oil leaks, or high operating temperatures should be in-
vestigated at once. If your transformer has a thermometer, it is
of the alcohol type and should be replaced with that type only.
A mercury-type thermometer could cause insulation failures by
reason of proximity of a metallic substance, regardless of
whether it is intact or broken.
The tank of every power transformer should be grounded to
eliminate the possibility of obtaining static shocks frorn it or
from being injured by accidental grounding of the winding to
the case.
If repairs are indicated, use the expertise of a qualified per-
son to ensure that the repairs are made safely as well as
correctly. Your life and the lives of others may depend on the
use of qualified people.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 794.
29.3E Why is electricity transmitted at high voltage?
29.3F What precautions must be taken if outdoor transform-
ers have exposed high voltage wires?
29.3G What kind of maintenance should a treatment plant
operator perform on switch gear?
29.3H What are the symptoms that a power distribution
transformer may be in need of maintenance or repair?
29.4 GASOLINE ENGINES
29.40 Need to Maintain Gasoline Engines
In the wastewater treatment departments of all cities there is
occasion to use gasoline-powered engines that drive pumps,
generators, tractors, and vehicles. Although we all drive au-
tomobiles that are powered by internal combustion engines,
are you aware of the fundamentals?
Very few operators actually do the repair of gasoline-
powered engines. Although you may not be able to perform the
duties of an engine mechanic, there are a number of steps you
can take to ensure that your particular engine is well main-
tained.
At the end of this section you will have an adequate knowl-
edge of how a gasoline engine operates in order to maintain it
so as to provide many hours at optimum performance.
29.41 Four-cycle Engines (Air-Cooled)
29.410 Strokes in the Cycle
For the sake of simplification, this section will be confined to
the air-cooled, single-cylinder engines. The four-cycle princi-
ples apply to liquid-cooled multi-cycled engines as well.
Air cooled engines' operating temperatures vary with load,
air temperature and speed. Some of the advantages of an
air-cooled engine are: (1) no complicated cooling system, (2)
an engine of lighter weight than its liquid-cooled counterpart,
and (3) comparatively easy repairs.
When we talk about compression stroke' and 'power stroke,'
what are they? In a four-stroke-cycle engine, the crankshaft
makes two complete revolutions to each power stroke of the
piston as shown in Fig. 29.22.
First is the intake stroke (A), where the exhaust valve is
closed and the intake valve open. The piston moves downward
and draws a fuel-air mixture into the cylinder. Secondly, the
intake valve closes and the piston moves upward on the com-
pression stroke (B), compressing the fuel-air mixture between
the top of the piston and the cylinder head. The spark occurs,
igniting the mixture and the force of the expanded gases
pushes the piston downward (power stroke C). The exhaust
valve opens and, as the piston moves upward on the exhaust
stroke (D), it forces the burnt gases out of the cylinder. Then
the exhaust valve closes and the engine is ready for another
cycle. Four strokes are required to complete the cycle.
29.411 Piston Displacement (Fig. 29.23)
What is it? Piston displacement is the space displaced by
the piston in its up and down movement stroke. To compute
-------
Support Systems 741
SPARK
PLUG
Is*
INTAKE STROKE
COMPRESSION STROKE
POWER STROKE
°Q
EXHAUST STROKE
Fig. 29.22 Four-stroke-cycle engine
(permission of Briggs and Stratton Corporation, Milwaukee, Wisconsin)
-------
742 Treatment Plants
AREA
PISTON
Fig. 29.23 Piston displacement
(permission of Briggs and Slratton Corporation, Milwaukee, Wisconsin)
PISTON
—o—
Fig. 29.24 Compression ratio 1 to 6
(permission of Briggs and Stratton Corporation, Milwaukee. Wisconsin)
-------
displacement, the following formula is used.
Piston = _TT_ y (Bore jn)z x strok0 Trave! in
Displacement, 4
cubic inches
Calculate the piston displacement in cubic inches for an en-
gine with a piston bore of two inches and a stroke travel of two
inches.
Piston = 3.1416 x (2 |nches)2 x 2 jnches
Displacement, 4 v '
cubic inches
= 6.28 cubic inches
The horsepower of an engine is directly proportional to the
volume of the piston displacement.
29.412 Compression Ratio (Fig. 29.24)
If an engine has a six to one compression ratio, it means that
the volume remaining in the cylinder when the piston is at the
top of the stroke is one-sixth as great as when it was at the
bottom of the stroke.
Usually, the higher the compression ratio, the greater the
efficiency. However, the compression ratio does not indicate
the horsepower rating of an engine.
Support Systems 743
29.413 Valves and Timing
Valves (Fig. 29.25) play an important function in the opera-
tion of gasoline engines. Valves must open and close at the
desired time. This is achieved by a "camshaft" that is geared to
the "crankshaft". The gears are matched up so that the "timing
marks" are directly in line. As the crankshaft revolves, so will
the camshaft that actuates the valves in the desired manner.
The valves are exposed to varied conditions. When the
fuel-air mixture ignites, the temperature in the cylinder can be
in excess of 1,200 degrees F (650°C). The pressure exerted on
the piston and also the valves may be as high as 500 psi (35
kg/sq cm). Valves and their seats are very important. Improper
seating or operation will greatly affect the operation of the en-
gine.
Two terms that you may have heard indicate valve prob-
lems: burnt valve and valve sticking. Valve and valve seat
burning is usually caused by a buildup of carbon or fuel lead on
the valve face or stem. These deposits hold the valve open
allowing the hot flames of combustion to burn the valve face
and seat. Valve sticking is caused by fuel lead, gum, or varnish
that builds up on the valve stem and in the valve guide. When
the exhaust valve does not close properly, the hot gases of
combustion heat up the valve and valve guide. This causes the
oil that lubricates the valve stem to oxidize into a varnish that
causes the valve not to move freely. A sticky intake valve can
be caused by using a fuel with high gum content.
HEAD
MARGIN
VALVE 4,
GUIDES
STEM
Fig. 29.25 Names of valve parts
(permission of Brlggs and Stratton Corporation, Milwaukee, Wisconsin)
-------
744 Treatment Plants
29.414 Carburetion (Fig. 29.26)
The purpose of a carburetor is to produce a mixture of fuel
and air on which an engine will operate. Small-engine car-
buretors use atmospheric pressure, the principles of a venturi
and the air foil (Fig. 29.26). They can be fed by a gravity fuel
system, a vacuum, or a fuel pump. A venturi can be explained
as a narrow space, similar to that of two buildings close to-
gether. The air current through this space is usually of high
velocity. The venturi is placed in the carburetor to produce a
volume of air flow in a specific manner.
As the piston in the cylinder moves downward with the intake
valve open, it creates a low pressure area in the carburetor and
venturi. The air pressure above the fuel in the bowl pushes the
fuel down in the bowl and up through the nozzle discharge
holes. At the same time, air rushes in through the venturi at a
high velocity. The fuel that is forced through the nozzle mixes
with the high volume of air coming through the venturi. This
mixture of fuel and air is sucked into the cylinder and becomes
the combustible mixture for firing the cylinder. The ideal com-
bustion mixture is approximately 15 pounds of air to one pound
of gasoline and is adjusted by the needle valve.
29.415 Ignition (Fig. 29.27)
In small four-cycle engines, a magneto is used to provide the
electricity necessary to fire (spark) the plug in the cylinder head
(Fig. 29.27). The ignition coil is mounted on a laminated steel
yoke. The coil has a primary and secondary winding, like a
transformer. As the fly wheel, which has a permanent magnet
embedded in it, passes the yoke, a voltage is induced in the
primary and secondary windings of the coil.
When the breaker points open, the collapsing primary circuit
produces a peak voltage of 170 volts. This voltage is induced
into the secondary winding producing a stepped-up voltage of
10,000 volts, which is more than ample to fire across the spark
plug electrodes. The high secondary voltage dissipates
rapidly; long enough to develop the necessary spark, but short
enough to insure long electrode life.
The condenser, which is placed in parallel to the contact
points, acts as a buffer. The condenser prevents the electricity
from jumping the contact points causing arcing. When the
points open, the condenser is charged by the low primary volt-
age, allowing the points to open without arc.
When discussing timing, the point of combustion comes
when both the intake and exhaust valves are in the closed
position. Therefore the timing of the valves, the position of the
piston, and the instance of spark at the plug must be in se-
quence. If one or more are not, combustion does not take
place.
29.416 Governing (Fig. 29.28)
The purpose of the governor is to provide a constant engine
speed regardless of load. If the throttle is in a fixed position, the
engine speed would go up or down as the load is decreased or
increased. There are two common types of governors — air
vane and counterweight.
The air vane governor (bottom of Fig. 29.28) is operated by
the force of air provided by the fly wheel fins. The governor is
connected to the carburetor throttle by means of a link. The
force of air tends to close the throttle and slow the engine.
Opposing this movement is the governor spring, which tries to
open the throttle. The governor spring is connected to an ad-
justable control so that the tension can be adjusted by the
operator. Increased tension causes greater engine speed; de-
creased tension lowers engine speed. The point where the
spring pull equals the force of the air vane is called the "gov-
erned speed."
The governor that uses counterweights works similar to the
air vane (top of Fig. 29.28). Instead of using air to oppose the
governor spring, the centrifugal force of the counterweights is
used. The assembly is geared to the engine camshaft or
crankshaft. As engine speed decreases with load, the cen-
trifugal force on the counterweights is lessened. This allows
the governor spring to open the throttle increasing engine
speed. Conversely, if the engine load lessens and the engine
starts to speed up, there will be greater centrifugal force. This
increased force will work against the throttle spring and reduce
engine speed. A properly operating governor will maintain
governed engine speed within fairly close limits.
29.417 Maintenance
In order to have an engine that will provide you with many
hours of trouble-free operation, it must be well cared for
PLEASE REFER TO THE OWNER/OPERATOR MANUAL
FOR YOUR PARTICULAR ENGINE. Typical maintenance pro-
cedures are as follows:
1. Change engine oil regularly every 25 hours;
2. Clean carburetor air filter every 25 hours;
3. Blow dust and chaff from louvered engine vanes regularly;
4. Clean carburetor fuel filter/screen every 100 hours;
5. Lubricate generator and/or starter motor as recommended,
every 100 hours;
6. Lubricate throttle linkage every 100 hours;
7. Clean, gap, or replace spark plug every 100 hours; and
8. Remove carbon deposits from top of piston and valves
every 100 to 300 hours.
29.418 Starting Problems
Listed below are some items to check if you have problems
starting a gasoline engine:
1. No fuel in tank, valve closed;
2. Carburetor not choked;
3. Water or dirt in fuel lines of carburetor;
4. Carburetor flooded;
5. Low compression;
6. Loose spark plug; and
7. No spark at plug.
a. Dirty and improper/gapped plug,
b. Broken or wet ignition cables,
c. Breaker points not opening or closing, and
d. Magneto grounded.
29.419 Running Problems
Check the following items if a gasoline engine does not run
properly.
-------
Support Systems 745
VENTURI
HIGH
FUEL
JAMMED
NEEDLE
LEVEL
VEhT
VENTuDI
NEEDLE
VALVE MOZZU
AIR HORN
FLOAT
VENT
IDLE SPEED
ADJUSTING SCBEW
Fig. 29.26 Carburetion
(permission ot Briggs and Stratton Corporation, Milwaukee, Wisconsin)
-------
746 Treatment Plants
SPARK PLUG
ARMATURE
SUPPORT
BREAKER
POINT
PLUNGE
SPRING
4
CONDENSER
FLAT ON
CRANKSHA
SPARK PLUG FIRING
ARMATURE
AIR GAP
1
Tesnvt
BACK POLE
CERAMIC MAGNET
SECONDARY
BREAKER
POINTS
OPEN
~
¦"•h 00 r
HcondenserH
PRIMARY
CENTER
POLE
Fig. 29.27 Ignition
(permission of Briggs and Stratton Corporation, Milwaukee, Wisconsin)
-------
Support Systems 747
TO
INCREASE
SPEED
©
©
THROTTLE
CLOSING
THROTTLE
OPEN
&
\
COUNTERWEIGHTS^
CLOSED
COUNTERWEIGHTS OPENING
THROTTLE
CLOSING
THROTTLE
OPEN _
ENGINE NOT RUNNING ENGINE RUNNING
Fig. 29.28 Governing
(permission of Briggs and Stratton Corporation, Milwaukee. Wisconsin)
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748 Treatment Plants
1. Engine misses
a.
Faulty spark plug/gapping
b.
Weak ignition spark
c.
Loose ignition cable
d.
Worn breaker points
e.
Water in fuel
f.
Poor compressions
2. Engine surges
a. Carburetor flooding
b. Governor spring connected improperly
3. Engine stops
a. Fuel tank empty
b. Vapor lock
c. Tank air vent plugged
4. Engine overheats
a. Low crankcase oil
b. Ignition timing wrong
c. Engine overloaded
d. Restricted air circulation/high ambient temperature
e. Poor grade of gasoline
5. Engine knocks
a. Poor grades of gasoline
b. Engine under heavy load at low speed
c. Carbon deposits in cylinder head
d. Spark advanced too far
e. Loose connecting rod bearing
f. Worn or loose piston pin
6. Engine backfires through carburetor
a. Water or dirt in fuel
b. Cold engine
c. Poor grade of gasoline
d. Sticking inlet valves
e. Spark plug heat range too hot
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 794.
29.4A List the four strokes in a four-stroke-cycle engine.
29.4B Calculate the piston displacement in cubic inches for
an engine with a piston bore of three inches and a
stroke travel of four inches.
29.4C List two types of valve problems.
29.4D What is the purpose of a carburetor?
29.4E What is the purpose of a governor?
29.42 Large Four-cycle Engines (Water Cooled)
29.420 Differences Between Small and Large Engines
The previous section discussed the fundamentals of small,
four-cycle engines. Those same fundamentals apply to the
large, four-cycle engines, however, there are some differ-
ences:
1. Multi cylinders,
2. Water cooled engine block,
3. Engine lubrication,
4. Ignition systems, and
5. Valves (Inhead/lnblock).
29.421 Multi Cylinders
In an engine with more than one cylinder, it is important to
sequence the detonation of combustion so as to give a smooth
running (balanced operating) engine. Geared to the
crankshaft, the camshaft must operate the inlet and exhaust
valves of each cylinder. Combustion can be taking place in one
or more cylinders, compression stroke in others, and exhaust
and intake strokes in the remaining. Timing of valve operation
relative to the position of the piston is therefore quite similar.
29.422 Water Cooled (Fig. 29.29)
In the air-cooled engine, the heat generated by combustion
was dissipated by the air circulating past the louvered cylinder
block. With the water-cooled system, the same effect is
achieved by using water. Each cylinder is surrounded with a
water jacket through which coolant circulates. This is accom-
plished by a water pump that is belt-driven from the crankshaft.
The heat transfers from the cylinder wall to the water which in
turn is pumped back to the radiator where the heat is dissi-
pated. A fan is mounted on the same shaft as the water pump
and ensures that a large volume of air is blown across the
radiator coils to facilitate rapid disbursement of heat. The
cooled water is then pumped back into the engine.
Internal combustion engines operate more efficiently when
their temperature is maintained within narrow limits. This ob-
jective is achieved with the insertion of a thermostat in the
cooling system which is called a "temperature actuated valve."
When the engine is cold, the thermostat remains closed not
allowing the water to circulate back to the radiator. As the
engine temperature increases to normal operating tempera-
ture, the thermostat opens.
The radiator cap provides a function other than preventing
coolant from splashing out the filler opening. The cap is de-
signed to seal the cooling system so that it operates under
pressure. This improves cooling efficiency and prevents evap-
oration of coolant. The boiling point of water is 212 degrees F
(100°C). However, for every pound of pressure applied to the
system, the boiling point rises 3.25 degrees F (1.8°C). If your
cooling system has a 15 psi (1 kg/sq cm) radiator cap and used
water for coolant, it would have a boiling point near 260 de-
grees F (127°C).
The use of coolant/anti-freeze provides protection against
the radiator coolant freezing and rupturing the system and also
provides better heat transfer and heat dissipation characteris-
tics than water. Most of the name-brand coolants have rust
inhibitors. Rust buildup in the cooling system does not allow
-------
Support Systems 749
WATER JACKET
AIR FLOW TO
REMOVE HEAT
TROM WATER
PUMP
COOLED WATER
•CARING iCHCW
^7-
II
:
BEARINu
IN I
COV[»
P1ATC
0«
CltAMNCl
Shaft ball bearings are sealed a« each end 10 keep lubricant in
and water out of bearings. A spring-loaded seal (in color) is used to
avoid water leakage around pump shaft. Note clearance between im-
peller and cover plate.
Engine temperatures are regulated by transferring excess
heat to surrounding air.
RADIATOR PRESSURE
THERMOSTAT
WATER
PUMP ,
RADIATOR
DRAIN TAP
PUMP BYPASS
PASSAGE
TEMPERATURE COMPENSATING
HOLES IN GASKET
SLOCK DRAIN TAP
\/J
Witfi wafer jockat* entifly around each cylinder and »a/ve, fhere 0 gr«of omoufl, 0f areo exposed to
rhm circulating coolant
Fig. 29.29 Water cooling system
{Source Automotive Encyclopedia, permission of the Goodhearl-Willco* Co., Inc.)
-------
750 Treatment Plants
good heat transfer and the sloughing of rust scale can block
narrow passages.
29.423 Engine Lubrication (Fig. 29.30)
A properly lubricated engine will ensure minimal wear of the
moveable internal parts. The large four-cycle engines usually
have a pressurized lubricating oil system. This system consists
of an oil pump, a gear driven from the camshaft, an oil filter,
and a number of ports and tubes within the engine that direct
the lubricant to the proper places.
The oil pump generally is of two types, rotary or gear type.
The pump suction is at the oil sump, oil is drawn through a
screen and then pumped to the oil filter and through the en-
gine. Fig. 29.30 will give you an insight on how the oil pump
works. An oil filter serves to remove particles from the oil that
may be abrasive or clog the lubricating ports of the engine.
The oil and filter must be changed as specified by the manufac-
turer.
Engine oil is available in different viscosities (flow charac-
teristics) and service ratings. The number designated on the
container indicates its viscosity, as assigned by the Society of
Automotive Engineers (SAE). An SAE 10 oil may be recom-
mended for cold weather operation and an SAE 30 for warm
weather. The designation "W" as 10 W indicates that the oil
will stay fluid over a wider range of temperatures. Thus a 10 W
oil can be used under more severe conditions than SAE 10 oil.
The service ratings are as follows:
MS, MM, and ML for gasoline engines;
DG and DS for diesel engines;
MS severe duty — heavy load-high speed;
MM medium service — moderate load and speed;
ML light service — light load, moderate speed, and short
operating time for engine;
DS severe conditions — high and low temperatures, chang-
ing engine load and where diesel fuel is of high sulfur con-
tent; and
DG moderate service — typical for most farm tractors and
trucking conditions.
When you change engine oil, check the specifications or
owner's manual to ensure the proper lubricant is used.
29.424 Ignition Systems — Battery and Magneto
BATTERY SYSTEM (Fig. 29.31)
The ignition system consists of the battery, ignition coil, dis-
tributor, condenser, ignition switch, spark plugs, and related
high and low tension wiring.
The purpose of the ignition coil is the same as that men-
tioned in Section 29.415, "Ignition." The coil steps up the six or
twelve volts from the battery to a high tension voltage near
20,000 volts that is required to jump the spark plug gap and
initiate combustion. The condenser reduces arcing at the
breaker points and insures long contact life.
One of the major differences between single- and multi-
cylindered engines is the distribution of high tension electrical
current to the respective cylinders. This must be accomplished
when a given cylinder is near the top of the compression
stroke. The ignition distributor (Fig. 29.32) with its contact
points is designed to make and break the primary ignition cir-
cuit and distribute high tension current to the proper spark
plug. This distributor is usually driven by the camshaft that
actuates the valves at one-half crankshaft speed for four-cycle
engines, since the engine fires on every other revolution.
The breaker points sit under the rotor that selectively feeds
high tension voltage through the cap to the plug wires and
covers the spark advance mechanism. The breaker points are
actuated by a cam. Usually there is one lobe on the cam for
each cylinder of the engine. As the cam rotates, it passes the
breaker lever rubbing block causing the points to open and
close. When the breaker points open, the collapsing primary
circuit of the ignition coil induces a voltage into the secondary.
The rotor connects the high tension voltage through the cap to
the appropriate cylinder.
In order to achieve efficient operation of an internal combus-
tion engine throughout its operating range, it is essential that
spark occurs at the correct instant. That instant will vary with
engine speed and load. The method used to advance or retard
the spark is a "centrifugal" and "engine vacuum" advance
mechanism.
When the engine is idling, ignition takes place just before the
piston reaches the top of the compression stroke. At high en-
gine speeds, the time interval for the fuel mixture to ignite and
expand is shorter. In order to obtain maximum power at high
speeds, the ignition must take place slightly earlier in the en-
gine cycle. This is accomplished by the centrifugal advance
mechanism.
Vacuum spark advance is also used to assist the centrifugal
mechanism. A lever connected to the advance unit is actuated
by a spring-loaded diaphragm that is sensitive to vacuum
changes in the carburetor. As the speed of an engine in-
creases, a greater vacuum is produced in the carburetor. The
increased vacuum pulls on the diaphragm causing the spark
advance mechanism to rotate. The cylinder then fires slightly
earlier in the cycle. When the engine speed is lowered, less
vacuum is produced and the mechanism retards the time of
ignition.
MAGNETO SYSTEM (Fig. 29.33)
A magneto is a self-contained device that generates and
distributes electricity needed to ignite the fuel mixture in the
combustion chamber. The magneto develops a low voltage,
steps it up to a high tension voltage, and distributes it at the
proper time. All of this is accomplished without the use of a
battery or ignition coil. (Because no battery is needed and the
voltage generated by the magneto increases with engine
speed, it is a desirable alternative to the battery-powered igni-
tion system.)
The magneto distributes electricity in a manner similar to the
distributor. The magneto has a cap, rotor, breaker points, and
condenser. (See magneto fundamentals in Section 29.415,
"Ignition.")
In general, magnetos are used on engines that operate in a
relatively small range of speed. This is because spark advance
is controlled by centrifugal counterweights that shift the degree
of angle at which the points open and close. Since the range of
control is limited (not so in distributors with vacuum advance),
the engine speed range must also be limited.
29.425 Valves
The valves of large four-cycle engines are either in the block
or cylinder head. By far, a greater number of engines are of the
overhead valve type. Some of the advantages to overhead
valves are:
1. Easier to work on because head is removable,
2. Quieter valve operation,
-------
Support Systems 751
ifthaft Sprocket
Hex Heac
To 0« P»
LAftrnbutor Dfi
Os! rump
Crankvhaft Sprocket
PUMP
FROM OIL
OIL FILTER
OIL RELIEF VALVE
Oil passages drilled in crankshaft conduct oil from main
bearings to connecting rods.
In this engine application, oil goes through a filter placed
between oil pump and oil gallery.
Fig. 29.30 Engine lubrication
(Source Automotive Encyclopedia, permission of the Goodheart-Willcox Co.. Inc.)
-------
752 Treatment Plants
IGNITION
RESISTOR
SWITCH
SOLENOID
SECONDARY
PRIMARY
IGNITION
COIL
BATTERY
CRANKING MOTOR
y CENTER TOWER
-• ROTOR
VACUUM ADVANCE
UNIT
* CONDENSER
TO COIL
PRIMARY
TO SPARK PLUG
DISTRIBUTOR CAP
TERMINAL
REVOLVING CAM
POINT CONTACTS
CENTRIFUGAL
ADVANCE
WEIGHT
Fig. 29.31 Battery ignition system and distributor
(Source Automotive Encyclopedia, permission of the Goodheart-Willcox Co., Inc.)
-------
Support Systems 753
III!! W!
PIPE PLUG
BUSHING
HOUSING
SHAFT
SPRING
ROTOK
CAP SPRING
GROUND UAD-
CAM-
WEIGHT SPRING
TERMINAL
WEIGHT BASE
BREAKER LEVER
CONTACT SUPPORT
CONDENSER
LINKAGE
COUPLING
VACUUM UNIT
Fig. 29.32 Ignition distributor
(Source Automotive Encyclopedia, permission of the Goodheart-Willcox Co., Inc.)
IMPULSE
COUPLING
HIGH TENSION
LEAD ROD
DISTRIBUTOR
GEAR
DISTRIBUTOR
ROTOR
SPARK
PLUGS
MAGNETIC
ROTOR
ROTOR
PINION
BREAKER ARM
FRAME
LAMINATIONS
BREAKER
POINTS
CONDENSER
Fig. 29.33 Rotating magnet magneto
(Source Automotive Encyclopedia, permission ot the Goodheart-Willcox Co., Inc.)
-------
754 Treatment Plants
3. Better valve response, and
4. Ease of valve adjustment.
29.426 Maintenance and Troubleshooting
Regularly scheduled maintenance is a must. Refer to your
owner's manual for specific recommendations.
1. Change engine oil
2. Clean air filter/replace
3. Change oil filter
4. Lubricate starter motor and generator
5. Inspect battery water, terminals
6. Replace fuel filter or clean
7. Inspect drive belts and belt tension
8. Inspect radiator hoses
9. Blow dust and debris from ratiator core
10. Backflush coolant system and add new
coolant
The items listed are in addition to those listed in the preced-
ing sections.
STARTING PROBLEMS
1. Poor battery connection/engine will not crank
2. Distributor cap damp
3. Break in ignition wiring
4. Engine valves out of time/spark advance
ENGINE STOPS
1. Plugged fuel filter/screen
2. No ignition voltage
ENGINE OVERHEATS
1. Low radiator coolant
2. Radiator core partially blocked
3. Faulty water pump
4. Sticking thermostat
29.43 Small Two-cycle Engines (Air Cooled) (Fig. 29.34)
29.430 How Two-cycle Engines Work
The two-cycle engine provides power with each revolution of
the crankshaft. In order to do this, the piston takes over some
of the valve functions along with "ports" in the cylinders. The
key thing to remember about most small two-cycle engines is
that the fuel mixture (oil and gasoline) provides lubrication for
the moveable parts in the crankcase as well as an air-fuel
mixture for combustion.
The fuel-air mixture from the carburetor enters the engine
crankcase through a leaf- or reed-type check valve. At the
bottom of the stroke, the fuel mixture is drawn up the cylinder
port to the top of the combustion chamber. The upward move-
ment of the piston creates a vacuum and draws the fuel from
the carburetor into the crankcase. As the cylinder fires and is
driven to the bottom of the stroke, the crankcase becomes
pressurized. This forces the fuel-air mixture up the cylinder
port and expels exhaust gases through the exhaust port. In the
process, the cylinder is recharged for the compression stroke.
Timing, carburetion, and ignition are all similar to four-cycle
engines.
Probably the most important item in regard to the two-cycle
engine is the proper fuel mixture — usually 50 parts gasoline to
one part oil. Most manufacturers recommend using an SAE 30
oil designed for two-cycle engines. If the fuel mixture contains
too much oil, you'll have poor carburetion, poor engine per-
formance, excessive smoke out the exhaust, and incomplete
burning of the mixture. On the other hand, if the mixture has
too little oil, poor lubrication of crankshaft, connecting rod bear-
ings, and piston cylinder wall takes place. This can cause pre-
mature bearing failure and scored cylinder walls. The engine
will run hot and may SEIZE UP.8 THAT'S HOW IMPORTANT
THE FUEL MIXTURE IS.
A few advantages of the small two-cycle engine are:
1. Cheaper to manufacture,
2. Fewer moving parts,
3. No engine oil changes (decreased maintenance), and
4. Proper engine lubrication is not relative to the position of the
engine. (This feature is sometimes desirable in small pump
and blower use. A four-cycle engine must be kept some-
what level to ensure proper internal engine lubrication.)
29.431 Maintenance and Troubleshooting
The maintenance schedule of a two-cycle engine is similar
to that of the four-cycle engine, with the exception that the
crankcase does not use an "oil bath." Therefore, proper fuel
mixture is a must. Problems associated with starting and
operating are similar for both two- and four-cycle engines.
Please make special note of the information in regard to fuel
mixture contained in Section 29.430.
29.44 How to Start a Gasoline Engine
Because of the wide variety of uses for gasoline-powered
engines, no one starting sequence will apply to all engines. In
general, gasoline engines can be divided into two groups. In
the first group are small engines with magneto ignition and
recoil start. Larger engines with battery-powered ignition and
electric start are in the second group.
29.440 Small Engines
The procedure for starting small engines is as follows:
1. Check fuel tank for adequate fuel;
2. Ensure fuel shut-off valve from the tank to the carburetor is
open;
3. Disengage ignition ground ("kill" switch or mechanism that
grounds the spark plug);
4. Check crankcase lubricating oil;
5. Set throttle to start position or % full throttle;
6. Set choke lever or pull out choke on carburetor;
7. Pull recoil starter twice;
8. If engine has started, push choke to "off"; and
9. If engine does not start after two pulls, disengage the choke
and try three or four more times.
If repeated efforts at starting have been unsuccessful, re-
move the high tension voltage wire from the spark. Hold the
100/150 hours
100/150 hours
100/150 hours
100/150 hours
100/150 hours
500 hours
500 hours
500 hours
500 hours
2 years
Seize up. Seize up occurs when an engine overheats and a component expands to the point where the engine will not run. Also called
"freezing"
-------
Support Systems 755
FLYWHEEL
VALVE
OPEN
•I* J
¦¦•v '.-v
L)> I
//ff^ FLYWHEEL
VALVE
OPEN
FLYWHEEL
VALVE
CLOSED
n
LEAF
VALVE
CLOSED a
FLYWHEEL
TWO CYCLE ENGINE
Provides power impulse for each two
strokes of piston; each revolution of crank-
shaft.
E. Mixture of fuel and air from carburetor
enters engine crankcase through check-
valve. When piston is at bottom of cyl-
inder, port is uncovered. As preceding
movement of piston has compressed gas
in crankcase, mixture flows into cylin-
der. Further compression in cylinder
starts as soon as piston reverses and
covers ports.
F. At the same time compression is occur-
ring in cylinder, movement of piston has
created vacuum in crankcase which
draws fresh charge of mixture from car-
buretor into crankcase. Charge is fired
at limit of piston movement.
G. As expansion of burning charge forces
piston downward, check-valve in crank-
case closes and mixture in crankcase
is compressed.
H. As piston uncovers ports at bottom of
stroke, compressed mixture from crank-
case enters cylinder and is deflected by
baffle on piston head into outer end of
cylinder. Incoming fresh mixture assists
in pushing spent gas out of cylinder.
EffSSSSI FUEL AND AIR MIXTURE
BURNING FUEL MIXTURE
EXHAUST OF SPENT FUEL
Sequence of operation of two cycle engine.
GM's two cycle diesel: A-With piston at bottom of stroke, intake ports are uncovered and blower forces air into cylinder. B-Upward
movement of piston closes intake ports and compresses air, thereby raising its temperature. C—At top of piston stroke, fuel is injected and
ignited by high temperature of compressed air. D—Expanding gases force piston down on power stroke. Exhaust valve is opened and burned
gases are forced out by compressed air.
FUEL
EXHAUST
Fig. 29.34 Two-cycle engine
(Source Automotive Encyclopedia, permission of the GoodhearVWillcox Co., Inc.)
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756 Treatment Plants
end of the wire (grasp the insulated portion, NOT the connec-
tor) Vq inch (3 mm) from the spark plug. Pull the recoil starter.
You should see a small blue spark. This will indicate that the
points are opening and closing and providing ignition voltage.
The next step is to remove the spark plug from the cylinder
head (use a 13/ie inch (20.6 mm) deep socket). Check for a
carbon buildup on the electrode. A piece of carbon may have
lodged between the center electrode and the side electrode.
Also check to see if the plug is wet with fuel or oil. This could
indicate that you have flooded the cylinder with fuel by having
the choke on too long. If there is oil residue, it could indicate
worn piston rings.
Replace the spark plug with a new one if in doubt. If you
must use the one you have, clean it by buffing with a wire
brush. Check the "gap" between the center electrode and side
electrode; it should be approximately .030 inch (30 thousands
of an inch or 0.76 mm).
Try starting the engine as previously described. If the engine
does not sputter or pop, close the fuel shut-off valve, remove
fuel sedimentation bowl and clean. Open fuel valve. Catch a
small amount of fuel in the palm of your hand and examine the
fuel for grit or water. If everything looks okay, replace sediment
bowl and open fuel valve.
Try to start the engine. If you still cannot achieve ignition,
you may have other problems that will require further checking
by a small-engine mechanic. Do not feel disgruntled, you have
checked for the most common problems.
29.441 Large Engines
The procedure for starting large engines is as follows:
1. Check fuel tank for fuel;
2. Check crankcase for oil;
3. Check radiator for coolant (if water cooled);
4. Set throttle to V2 full position;
5. Pull out choke;
6. Turn on ignition switch and press start button;
7. After four or five engine revolutions, push in the choke; and
8. Engine should start.
After repeated tries, further investigation by a mechanic may
be needed.
NOTE: Do not crank engine with the starter motor for more
than one minute initially. Wait two minutes and try again
for 45 seconds. Wait two minutes and try again for 30
seconds. After three trys, let starter motor cool for 5
minutes before trying again. This will avoid starter
motor damage.
Preliminary checks for a large engine that won't start are
similar to procedures for small engines.
Remove spark plug wires. Test each one by holding it Vb inch
(3 mm) from the spark plug or ground, and turn engine over
with the starter. You should see a small blue spark. If you have
no spark, the points are not opening or high tension voltage is
not present from the ignition coil. Check further as needed.
If spark is present, inspect spark plugs. Clean or replace if
needed.
After checking the ignition system, make sure fuel is present
at the carburetor. Remove the fuel line at the carburetor and
direct it away from you and the engine. Engage starter motor
for two revolutions. Fuel should spurt from the line if the fuel
pump is working satisfactorily. Replace fuel line and wipe away
any fuel that may be present on the engine.
With fuel and ignition voltage present, it should start. Repeat
start procedure. If you still cannot start the engine, call on your
mechanic to look for the problem.
NOTE: Some engines have a low oil pressure switch that must
be manually held in until sufficient oil pressure is pre-
sent.
Do not use a starting fluid on gasoline engines unless it is a
LAST RESORT effort to get a critical piece of equipment run-
ning. Hard-starting engines should be inspected and repaired
by a reliable mechanic.
After an engine has been started, give it an opportunity to
warm up before applying the load. Follow manufacturer's rec-
ommendations for the starting procedure since there is some
variation between different makes of engines.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 794.
29.4F How is heat removed from the cylinders in a water-
cooled engine?
29.4G What is a magneto?
29.4H How are the moveable parts in the crankcase of a
small air-cooled two-cycle engine lubricated?
29.41 What happens if the fuel mixture contains (1) too
much oil or (2) too little oil?
nd cf It&ooA 1 of 4 \Mfoo
mpcoqx cwzmf*
Please answer the discussion and review questions before
continuing with Lesson 3.
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Support Systems 757
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 4 Lessons)
Chapter 29. SUPPORT SYSTEMS
Write your answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 1.
7. Why should a wastewater treatment plant have standby
power?
8. How would you determine the capacity of standby genera-
tion equipment?
9. Why should you not smoke or allow electrical arcing near
a battery being recharged?
10. What causes (1) valve and valve seat burning, and (2)
valve sticking?
11. What factors could cause gasoline engine starting prob-
lems?
12. Why is rust a problem in water-cooled systems?
CHAPTER 29. SUPPORT SYSTEMS
(Lesson 3 of 4 Lessons)
29.5 DIESEL ENGINES
29.50 How Diesel Engines Work (Fig. 29.35)
Diesel engines are similar to gasoline engines and are either
two or four cycle. They can be air or water cooled. In general
the diesel engine is of heavier construction to withstand the
higher pressures resulting from higher compression ratios.
The diesel does not use spark plugs, but instead relies on
heat generated by air compressed in the cylinder (1,000 de-
grees F or 540°C) to ignite the fuel mixture. The fuel is a
petroleum product that is heavier than gasoline and with a
higher flash point. Gasoline cannot be used in a diesel be-
cause it would start to burn from the heat generated by com-
pression before the piston reached the top of the stroke.
A diesel has no carburetor. The fuel is sprayed (injected) into
the cylinder while the cylinder is compressing air. The heat of
compression ignites the fuel-air mixture and burns, producing
power similar to a gasoline engine. The introduction of fuel into
the cylinder must be "timed" in the same manner as spark to
the plug in a gasoline engine. Fuel is pumped by a pumping
device that is geared to the crankshaft.
Diesel fuel, unlike gasoline, does not vaporize readily. The
fuel must be broken up in fine particles and sprayed into the
cylinder. The atomization of fuel is accomplished by forcing the
fuel through a nozzle at the top of the combustion chamber. As
the fuel combines with the air in the cylinder, it becomes a
combustible mixture. Since the diesel engine depends upon
the heat of compressed air to ignite the fuel-air mixture, com-
pression pressure must be maintained. Leaking valves or pis-
ton rings (causing "blow by") cannot be tolerated.
The fuel is also important. The automotive-type diesel is
designed to run on a specific type or grade of fuel. Trouble can
be expected if an attempt is made to use other than the proper
type.
29.51 Operation
In the two-cycle engine, intake and exhaust takes place dur-
ing part of the compression and power strokes; whereas, the
four-cycle engine requires four strokes to complete the operat-
ing cycle. During one-half of the cycle, the four-stroke acts as
an air pump. The two-stroke must have a blower (air pump) to
provide the necessary air to expel the exhaust gases and re-
charge the cylinder with fresh air.
In the two-cycle, a series of ports surround the cylinder at a
point higher than the lowest position of the piston. These are
the intake ports that allow air into the cylinder. The four-cycle
engine uses intake valves. The incoming air forces the ex-
pended gases out the exhaust valve, leaving the cylinder full of
clean air.
As the piston starts its upward stroke, the exhaust valve
closes, the intake ports are sealed off by the piston, and the air
in the cylinder is compressed. Shortly before the piston
reaches the top of the stroke, the required amount of fuel is
sprayed into the combustion chamber by the fuel injector. The
intense heat of compression ignites the fuel-air mixture with
the resulting combustion driving the piston down on its power
stroke.
As the piston nears the bottom of the stroke, the exhaust
valve opens and the spent gases are released; assisted by the
incoming fresh air. The cycle is complete.
29.52 Fuel System (Fig. 29.36)
The basic parts of the fuel system are:
1. Primary fuel filter,
2. Secondary fuel filter,
3. Fuel injection pump, and
4. Fuel injector.
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758 Treatment Plants
AIR ENTERING COMBUSTION CHAMBER
THROUGH CYLINDER LINER PORTS
AIR
V
AIR BEING COMPRESSED WITH
THE EXHAUST VALVE CLOSED
T-J083
Scavenging and Compression
AIR
if
CHARGE OF FUEL BEING INJECTED
INTO COMBUSTION CHAMBER
l(
&
EXHAUST TAKING PLACE AND CYLINDER ABOUT
TO BE SWEPT WITH CLEAN SCAVENGING AIR
T-5014
Power and Exhaust
Fig. 29.35 How diesel engines work
(Source GMC Truck Overhaul Manual Series 53, permission of General Motors Corp.)
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Support Systems 759
SECONDARY
FILTER
EXCESS FUEl
STARTING DEVICE
DI.'.'Py
VALVE
FUEl INJECTION
NOZZLE HOLDER
ASSEMBLY
Z\
GOVERNOR
SLEEVE
OVERFLOW
VALVE
FUEL SUPPLY
PUMP
FUEl TANK
PRIMARY
FILTER
HIGH PRESSURE (INJECTION) FUEL
LOW PRESSURE (SUPPLY) FUEL
~ LUBRICATING OIL
1 Nozzle Valve and Body
2 Nozzle Valve Spring
3 Leak-off Lines
4 Hydraulic Head Assembly
5 Fuel Metering Sleeve
6 Pump Plunger
7 Face Gear
8 Tappet and Roller
9 Cam
10 Governor Gears
11 Governor Weights
12 Governor Stop Plate
13 Fulcrum Lever
14 Stop Lever
15 Shut-off (when used)
16 Fuel Return Line
TJ347
Fig. 29.36 Diesel engine fuel system
(Source Maintenance Manual, permission of General Motors Corp.)
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760 Treatment Plants
EXCESS FUEL
STARTING DEVICE
FUEL DELIVERY f
VALVE ,
HYDRAULIC HEAD
ASSEMBLY
GOVERNOR COVER
DROOP SCREW
FUEL SUPPLY
PUMP
GOVERNOR
SPRINGS
GOVERNOR
HOUSING
FULCRUM
LEVER GOVERNOR
SLEEVE GOVERNOR
WEIGHTS
OVER FLOW
VALVE
CONTROL UNIT
COVER
CONTROL
ROD
FACE GFAR
I
PUMP HOUSING
TIMING
ADVANCE
MECHANISM
T-JI7*
Fig. 29.37 Cut-away view of fuel injection pump for 6-cylinder engine
(Source Maintenance Manual, permission of General Motors Corp.)
The primary filter removes all course particles from the fuel
and the secondary filter removes any minute particles that re-
main. This ensures a clean fuel that will not clog the injector
pump or fuel injectors. The heart of the fuel system is the
injection pump (Fig. 29.37). This pump is a gear-type
positive-displacement pump that can deliver fuel to the injector
at a very high pressure. Incorporated in the pump is a timing
advance mechanism to advance or retard the instant when fuel
is injected into the cylinder. At high engine speed, injection
would take place sooner in the cycle. The reverse happens for
lower speeds.
A governor which uses centrifugal weights and is driven by
the pump shaft, activates a fuel control unit. When engine
speed increases, the weights are thrown toward their outer
limit. Geared to the assembly, the fuel control valve is opened
wider allowing more fuel to flow to the injector.
We now have higher engine speed, advanced "timing" of
injection, and the necessary fuel to sustain the faster opera-
tion. When the engine is slowed, the reverse takes place.
Fuel under pressure is fed from the injection pump to the
appropriate fuel nozzles. When the pressure reaches approx-
imately 3,000 psi (90 kg/sq cm), the valve in the injector opens
allowing fuel to be injected into the combustion chambers. As
line pressure drops, the return spring closes the nozzle valve.
Fuel left in the line is fed back to the pump through "leak off"
lines.
29.53 Water-cooled Diesel Engines
Usually the larger diesel engines are of the water-cooled
type, similar to gasoline engines. In order to deliver a sustained
amount of high horsepower, an effective cooling system is
necessary to dissipate the extreme heat of combustion. Be-
cause of this fact, a water-cooled engine of comparative
horsepower to the air-cooled will cost more to manufacture,
and subsequently to maintain.
29.54 Air-cooled Diesel Engines
When a lighter weight, lower horsepower, and more com-
pact engine is desired, the air-cooled engine will serve your
needs. You get the benefits of a diesel engine in a smaller
package (see Air-cooled Engines, Section 29.41).
There are some definite advantages to the diesel engine
over the gasoline engine. The initial cost is greater for the
diesel; however, the diesel:
1. Requires less maintenance because there are:
a. No plugs,
b. No contact points to pit,
c. No ignition coils or high tension wires, and
d. Fewer tune-ups.
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Support Systems 761
2. Is cheaper to operate because:
a. Diesel fuel may be cheaper, and
b. Better fuel efficiency.
Perhaps the biggest drawbacks against diesel engines are:
1. Initial investment costs, and
2. Repair costs.
The pros and cons must be weighed to provide you with an
engine that will fill your particular needs. Whichever engine you
select, remember that a well-cared-for engine will be there to
serve you when it is needed and will provide trouble-free oper-
ation that is essential to most users.
29.55 How to Start Diesel Engines
Diesel engines vary in size and use and have varied starting
procedures. Follow manufacturer's suggested procedures for
your particular engine. As with the gasoline engine, check fuel,
oil, and coolant.
To start a diesel engine, the procedures are as follows:
1. Push in "stop" control,
2. Set throttle to 1/3 full,
3. Turn on switch and engage starter, and
4. Engine should start.
Some engines have glow plugs that are energized when the
switch is placed in the start position. They preheat the air-fuel
mixture in the cylinder to aid in starting. After the engine is
started, maintain the lower RPM's on the engine tachometer
and allow the engine to warm up. The warm-up period is vital to
the diesel engine for efficient engine performance. When
operating the engine, maintain adequate engine RPM's as
recommended by the manufacturer.
When a diesel engine will not start after repeated tries, a
small amount of starting fluid sprayed into the air intake may be
needed to start the engine. If you use starting fluid, do not get
carried away with its use; a little goes a long way. Use it only as
a last resort or as specified by the manufacturer. If your efforts
have failed to start the engine, have a mechanic that is familiar
with diesel engines determine the cause of the problem.
29.56 Maintenance and Troubleshooting
The following pages are from DETROIT DIESEL ENGINES,
SERIES 92 SERVICE MANUAL The material is reproduced
with the permission of the Detroit Diesel Allison Division, Gen-
eral Motors Corporation. For detailed maintenance procedures
for your diesel engines, see your diesel manufacturer's service
manual.
troubleshooting
Certain abnormal conditions which sometimes interfere with
satisfactory engine operation, together with methods of deter-
mining the cause of such conditions, are covered on the follow-
ing pages.
Satisfactory engine operation depends primarily on:
1. An adequate supply of air compressed to a sufficiently high
compression pressure.
2. The injection of the proper amount of fuel at the right time.
Lack of power, uneven running, excessive vibration, stalling
at idle speed and hard starting may be caused by either low
compression, faulty injection in one or more cylinders, or lack
of sufficient air.
Since proper compression, fuel injection and the proper
amount of air are important to good engine performance, de-
tailed procedures for their investigation are given as follows:
LOCATING A MISFIRING CYLINDER
1. Start the engine and run it at part load until it reaches nor-
mal operating temperature.
2. Stop the engine and remove the valve rocker covers.
3. Check the valve clearance.
4. Start the engine. Then hold an injector follower down with a
screw driver to prevent operation of the injector. If the cylin-
der has been misfiring, there will be no noticeable differ-
ence in the sound and operation of the engine. If the cylin-
der has been firing properly, there will be a noticeable dif-
ference in the sound and operation when the injector fol-
lower is held down. This is similar to short-circuiting a spark
plug in a gasoline engine.
5. If the cylinder is firing properly, repeat the procedure on the
other cylinders until the faulty one has been located.
6. If the cylinder is misfiring, check the following:
a. Check the injector timing
b. Check the compression pressure.
c. Install a new injector.
Mininum Compression
Pressure at 600 rpm
Altitude
above
Sea Level
t Air
Density
Turbocharged
Engines
NonTurbocharged
Engines
psi
kPa
psi
kPo
feet
meters
450
3101
500
3445
500
152
.0715
415
2859
465
3204
2.500
762
.0663
385
2653
430
2963
5.000
1,524
.0613
355
2446
395
2722
7,500
2,286
.0567
330
2274
365
2515
10.000
3.048
0525
1 Air density at 500 Jeet altitude based on 85° F (29.4° C)
and 29.38 in. Hg (99.49 kPa) wet barometer.
Table 1
. d. If the cylinder still misfires, remove the cam follower
and check for a worn cam roller, camshaft lobe, bent
push rod or worn rocker arm bushings.
CHECKING COMPRESSION PRESSURE
Compression pressure is affected by altitude as shown in
Table 1.
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762 Treatment Plants
Check the compression pressure as follows:
1. Start the engine and run it at approximately one-half rated
load until normal operating temperature is reached.
Cylinder
Gage Reading
Psi
kPa
1L
470
3239
]R
465
3204
2L
430
2963
2R
460
3170
31
465
3204
3R
460
3170
Table 2
2. Stop the engine and remove the fuel pipes from the injector
and fuel connectors of the No. 1 cylinder.
3. Remove the injector and install an adaptor and pressure
gage (Fig. 1) from Diagnosis Kit J 9531-01.
4. Use a spare fuel pipe to fabricate a jumper connection be-
tween the fuel inlet and return manifold connectors. This will
permit fuel from the inlet manifold to flow directly to the
return manifold.
5. Start the engine and run it at 600 rpm. Observe and record
the compression pressure indicated on the gage.
DO NOT CRANK THE ENGINE WITH THE STARTING
MOTOR TO OBTAIN THE COMPRESSION PRESSURE.
6. Perform Steps 2 through 5 on each cylinder. The compres-
sion pressure in any one cylinder at a given altitude above
sea level should not be less than the minimum shown in
Table 1. In addition, the variation in compression pressures
between cylinders must not exceed 25 psi (172 k Pa or 1.75
kg/sq cm) at 600 rpm.
VALVE
Fig. 1 Checking Compression Pressure
EXAMPLE: If the compression pressure readings were as
shown in Table 2, it would be evident that No. 2L cylinder
should be examined and the cause of the low compression
pressure be determined and corrected.
The pressures in Table 2 are for a turbocharged engine
operating at an altitude near sea level.
Note that all of the cylinder pressures are above the low limit
for satisfactory engine operation. Nevertheless, the No. 2L cyl-
inder compression pressure indicates that something unusual
has occurred and that a localized pressure leak has devel-
oped.
Low compression pressure may result from any one of sev-
eral causes:
A. Piston rings may be stuck or broken. To determine the
condition of the rings, remove the air box cover and in-
spect them by pressing on the rings with a blunt tool (Fig.
2). A broken or stuck ring will not have a "spring-like"
action.
B. Compression pressure may be leaking past the cylinder
head gasket, the valves seats, the injector tube or a hole in
the piston.
Kf. v • v /
Fig. 2 Inspecting Piston Rings
ENGINE OUT OF FUEL
The problem in restarting the engine after it has run out of
fuel stems from the fact that after the fuel is exhausted from the
fuel tank, fuel is then pumped from the primary fuel strainer
and sometimes partially removed from the secondary fuel filter
before the fuel supply becomes insufficient to sustain engine
firing. Consequently, these components must be refilled with
fuel and the fuel pipes rid of air in order for the system to
provide adequate fuel for the injectors.
When an engine has run out of fuel, there is a definite proce-
dure to follow for restarting it:
1. Fill the fuel tank with the recommended grade of fuel oil. If
only partial filling of the tank is possible, add a minimum of
ten gallons (thirty-eight liters) of fuel.
2. Remove the fuel strainer shell and element from the
strainer cover and fill the shell with fuel oil. Install the shell
and element.
3. Remove and fill the fuel filter shell and element with fuel oil
as in Step 2.
4. Start the engine. Check the filter and strainer for leaks.
NOTE: In some instances, it may be necessary to remove a
valve rocker cover and loosen a fuel pipe nut to bleed
trapped air from the fuel system. Be sure the fuel pipe
is retightened securely before replacing the rocker
cover.
Primer J 5956 may be used to prime the entire fuel system.
Remove the filler plug in the fuel filter cover and install the
primer. Prime the system. Remove the primer and install the
filler plug.
FUEL FLOW TEST
The proper flow of fuel is required for satisfactory engine
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Support Systems 763
operation. Check the condition of the fuel pump, fuel strainer
and fuel filter when conducting a fuel flow test.
CRANKCASE PRESSURE
The crankcase pressure indicates the amount of air passing
between the oil control rings and the cylinder liners into the
crankcase, most of which is clean air from the air box. A slight
pressure in the crankcase is desirable to prevent the entrance
of dust. A loss of engine lubricating oil through the breather
tube, crankcase ventilator or dipstick hole in the cylinder block
is indicative of excessive crankcase pressure.
The causes of high crankcase pressure may be traced to
excessive blow-by due to worn piston rings, a hole or crack in a
piston crown, loose piston pin retainers, worn blower oil seals,
defective blower, cylinder gaskets, or excessive exhaust back
pressure. Also, the breather tube or crankcase ventilator
should be checked for obstructions.
The crankcase pressure may be checked with a manometer.
The manometer should be connected to the oil level dipstick
opening in the cylinder block.
Check the readings obtained at various engine speeds with
the ENGINE OPERATING CONDITIONS.
NOTE: The dipstick adaptor must not be below the level of the
oil when checking the crankcase pressure.
EXHAUST BACK PRESSURE
A slight pressure in the exhaust system is normal. However,
excessive exhaust back pressure seriously affects engine op-
eration. It may cause an increase in the air box pressure with a
resultant loss of efficiency of the blower. This means less air
for scavenging which results in poor combustion and higher
temperatures.
Causes of high exhaust back pressure are usually a result of
an inadequate or improper type of muffler, an exhaust pipe
which is too long or too small in diameter, an excessive
number of sharp bends in the exhaust system, or obstructions
such as excessive carbon formation or foreign matter in the
exhaust system.
The exhaust back pressure, measured in inches of mercury,
may be checked with a manometer in the engine diagnosis test
kit J 9531-01. Connect the manometer to an exhaust manifold
(except on turbocharged engines) by removing the 1/s" pipe
plug which is provided for that purpose. If there is no opening
provided, drill an 11/32" hole in the exhaust manifold compan-
ion flange and tap the hole to accommodate a 1/b" pipe plug.
On turbocharged engines, check the exhaust back pressure
in the exhaust piping 6" to 12" from the rear face of the turbine.
The tapped hole must be in a comparatively straight pipe area
for an accurate measurement.
Check the readings obtained at various speeds (at no-load)
with the specifications.
AIR BOX PRESSURE
Proper air box pressure is required to maintain sufficient air
for combustion and scavenging of the burned gases. Low air
box pressure is caused by a high air inlet restriction, damaged
blower rotors, an air leak from the air box (such as leaking end
plate gaskets) or a clogged blower air inlet screen. Lack of
power or black or grey exhaust smoke are indications of low air
box pressure.
High air box pressure can be caused by partially plugged
cylinder liner ports.
To check the air box pressure, connect a manometer to an
air box drain tube.
Check the readings obtained at various speeds with the
ENGINE OPERATING CONDITIONS in Section 13.2.
AIR INLET RESTRICTION
-Excessive restriction of the air inlet will affect the flow of air
to the cylinders and result in poor combustion and lack of
power. Consequently the restriction must be kept as low as
possible considering the size and capacity of the air cleaner.
An obstruction in the air inlet system or dirty or damaged air
cleaners will result in a high blower inlet restriction.
Check the air inlet restriction with a water manometer con-
nected to a fitting in the air intake ducting located 2" above the
air inlet housing (non-turbocharged engines) or compressor
inlet (turbocharged engines). When practicability prevents the
insertion of a fitting at this point, on naturally aspirated engines,
the manometer may be connected to the engine air inlet hous-
ing. The restriction at this point should be checked at a specific
engine speed. Then the air cleaner and ducting should be
removed from the air inlet housing and the engine again oper-
ated at the same speed while noting the manometer reading.
The difference between the two readings, with and without
the air cleaner and ducting, is the actual restriction caused by
the air cleaner and ducting.
Check the normal air inlet vacuum at various speeds (at
no-load) and compare the results with the ENGINE OPERAT-
ING CONDITIONS.
PROPER USE OF MANOMETER
HEIGHT
COIUMN
Hg
h2o
TOP SURFACE OP RUIOS
1171#
CONVEX FCW MiRCURY CONCAVI FO« WATER
Fig. 3 Comparison of Column Height for Mercury and Water
Manometers
The U-tube manometer is a primary measuring device indi-
cating pressure or vacuum by the difference in the height of
two columns of fluid.
PRESSURE CONVERSION CHART
1" water -
- .0735" mercury
1" water :
.0361 psi
1" mercury =
.4919 psi
1" mercury :
13.6000" water
1 psi =
: 27.7000" water
1 psi =
2.0360" mercury
TABLE 3
Connect the manometer to the source of pressure, vacuum
or differential pressure. When the pressure is imposed, add the
number of inches one column of fluid travels up to the amount
the other column travels down to obtain the pressure (or vac-
uum) reading.
The height of a column of mercury is read differently than
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764 Treatment Plants
that of a column of water. Mercury does riot wet the inside
surface; therefore, the top of the column has a convex menis-
cus (shape). Water wets the surface and therefore has a con-
cave meniscus. A mercury column is read by sighting horizon-
tally between the top of the convex mercury surface (Fig. 3)
and the scale. A water manometer is read by sighting horizon-
tally between the bottom of the concave water surface and the
scale.
Should one column of fluid travel further than the other col-
umn, due to minor variations in the inside diameter of the tube
or to the pressure imposed, the accuracy of the reading ob-
tained is not impaired.
Refer to Table 3 to convert the manometer reading into other
units of measurement.
Chart 1
WHITE SMOKE
Check For
Check For
Chock For
Probable Causes
5. MISFIRING CYLINDERS
. INCOMPLETELY BURNED FUEL
3 IMPROPER GRADE OF FUEL
BLACK OR GREY SMOKE
BLUE SMOKE
2. EXCESSIVE FUEL OR IRREGULAR
FUEL DISTRIBUTION
EXHAUST SMOKE ANALYSIS
MAKE CHECKS WITH MINIMUM WATER OUTLET TEMPERATURE OF 160°F
4. LUBRICATING OIL NOT BURNED
IN CYLINDER (BLOWN
THROUGH CYLINDER DURING
SCAVENGING PERIOD)
SUGGESTED REMEDY
1. High exhaust back pressure or a restricted air inlet causes
insufficient air for combustion and will result in incompletely
burned fuel.
High exhaust back pressure is caused by faulty exhaust
piping or muffler obstruction and is measured at the
exhaust manifold outlet with a manometer. Replace faulty
parts.
Restricted air inlet to the engine cylinders is caused by
clogged cylinder liner ports, air cleaner, blower air inlet
screen or aftercooler. These items should be cleaned.
Check the emergency stop to make sure that it is com-
pletely open and readjust it if necessary.
2. Check for improperly timed injectors and improperly posi-
tioned injector rack control levers. Time the fuel injectors as
outlined in FUEL INJECTOR TIMING and perform the ap-
propriate governor tune-up to correct this condition.
Replace faulty injectors if this condition still persists after
timing the injects and performing the engine tune-up.
Avoid lugging the engine below 1200 rpm as this will
cause incomplete combustion.
3. Check for the use of an improper grade of fuel. Consult the
FUEL OIL SPECIFICATIONS for the correct fuel to use.
4. Check for internal lubricating oil leaks and refer to the HIGH
LUBRICATING OIL CONSUMPTION chart.
5. Check for faulty injectors and replace as necessary.
Check for low compression and consult the HARD
STARTING chart.
The use of low octane fuel will cause this condition and
can be corrected by consulting and following the FUEL OIL
SPECIFICATIONS.
-------
Support Systems 765
Chart 2
Check For
5. LOW BATTERY OUTPUT
j Check Fcr
Check For
Check For
Check For
Probable Causes
13. BLOWER NOT FUNCTIONING
2. DEFECTIVE STARTING MOTOR SWITCH
3. INTERNAL SEIZURE
HARD STARTING
LOW COMPRESSION
ENGINE WILL NOT ROTATE
12. IMPROPER VALVE
CLEARANCE ADJUSTMENT
LOW CRANKING SPEED
11. CYLINDER HEAD
GASKET LEAKING
10. COMPRESSION RINGS WORN
OR BROKEN
9. EXHAUST VALVES STICKING
OR BURNED
14. IMPROPER OPERATION OF
FLUID STARTING AID
INOPERATIVE STARTING AID
AT LOW AMBIENT TEMP.
4. IMPROPER LUBRICATING OIL
VISCOSITY
6 LOOSE STARTER CONNECTIONS
OR F AULTY STARTER
NO FUEL
8. INJECTOR RACKS NOT IN FULL-FUEL
POSITION WHEN STARTING AID SCREW
IS NOT USED
I. LOW BATTERY VOLTAGE,
LOOSE STARTER CONNECTIONS
OR FAULTY STARTER
7. AIR LEAKS. FLOW OBSTRUCTION.
FAULTY l-UEL PUMP.
FAULTY INSTALLATION
-------
766 Treatment Plants
Chart 2
HARD STARTING
SUGGESTED REMEDY
1. Refer to Items 2, 3 and 5 and perform the operations
listed.
2. Replace the starting motor switch,
3. Hand crank the engine at least one complete revolution. If
the engine cannot be rotated a complete revolution, inter-
nal damage is indicated and the engine must be disas-
sembled to ascertain the extent of damage and the cause.
4. Use the proper viscosity lubricating oil grade as recom-
mended in the LUBRICATING OIL SPECIFICATIONS.
5. Recharge the battery if a light load test indicates low or no
voltage. Replace the battery if it is damaged or will not
hold a charge.
Connect the leads properly after replacing the terminals
that are damaged or corroded.
At low ambient temperatures, use of a starting aid will
facilitate keeping the battery fully charged by reducing the
cranking time.
6. Tighten the starter connections. Inspect the starter com-
mutator and brushes for wear. Replace the brushes if
badly worn and overhaul the starting motor if the com-
mutator is damaged.
7. To check for air leaks, flow obstruction, faulty fuel pump or
faulty installation, consult the NO FUEL OR INSUFFI-
CIENT FUEL chart.
8. Inspect for governor-to-injector linkage binding that will
prevent the governor from positioning the injector racks
into the full-fuel position. Remove any bind found and
readjust the governor and injector controls if necessary.
9. The cylinder head must be removed and overhauled to
correct this condition.
10. Remove the air box covers and inspect the compression
rings through the ports in the cylinder liners. Overhaul the
cylinder assemblies if the rings are badly worn or broken.
11. To check for compression gasket leakage, remove the
coolant filler cap and operate the engine. A steady flow of
gases from the coolant filler indicates either a cylinder
head compression gasket may be damaged, a seal ring
damaged or dislodged or the cylinder head is cracked.
Remove the cylinder head and replace the compression
gaskets and seal rings.
12. Check the exhaust valve clearance and adjust to the cor-
rect clearance.
13. Remove the blower drive shaft. Inspect the blower drive
shaft and drive coupling. Replace damaged parts. Bar the
engine over. If the engine does not rotate, remove the air
inlet adaptor and visually inspect the blower rotors and
end plates. If damaged, remove and overhaul the blower.
14. Operate the starting aid according to the instructions
under COLD WEATHER STARTING AIDS.
-------
Support Systems 767
Chart 3
ABNORMAL ENGINE OPERATION
Probable Causes j
Chec
Check For
| Check For
13. OIL PICKED UP BY AIR STREAM
15. FAULTY INJF.CTORS
9. ENGINE APPLICATION
14. LOW COOLANT TEMPERATURE
10. HIGH RETURN FUEL TEMPERATURE
2. INSUFFICIENT FUEL
4. LOW COMPRESSION PRESSURES
I. LOW COOLANT TEMPERATURE
II. HIGH AMBIENT AIR TEMPERATURE
8. INSUFFICIENT AIR
7. INSUFFICIENT FUEL
3. FAULTY INJECTORS
12. HIGH ALTITUDE OPERATION
DETONATION
LACK OF POWER
5. GOVERNOR INSTABILITY
(HUNTING)
6. IMPROPER ENGINE ADJUSTMENTS
(TUNE-UP) AND GEAR TRAIN TIMING
UNEVEN RUNNING OR
FREQUENT STALLING
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768 Treatment Plants
Chart 3
ABNORMAL ENGINE OPERATION (Cont'd.)
SUGGESTED REMEDY
1. Watch the engine coolant temperature gage and if the
temperature does not reach 160-185T (71-85°C), while
the engine is operating, consult the ABNORMAL ENGINE
COOLANT TEMPERATURE chart.
2. Check engine fuel spill back and if the return is less than
specified, consult the NO FUEL OR INSUFFICIENT FUEL
chart.
3. Check the injector timing and the position of the injector
racks. If the engine was not tuned correctly, perform an
engine tune-up. Erratic engine operation may also be
caused by leaking injector spray tips. Replace the faulty
injectors.
4. Check the compression pressures within the cylinders and
consult the HARD STARTING chart if compression pres-
sures are low.
5. Erratic engine operation may be caused by governor-to-
injector operating linkage binding or by faulty engine
tune-up. Perform the appropriate engine tune-up proce-
dure as outlined for the particular governor used.
6. Perform an engine tune-up if performance is not satisfac-
tory.
Check the engine gear train timing. An improperly timed
gear train will result in a loss of power due to the valves
and injectors being actuated at the wrong time in the en-
gine's operating cycle.
7. Perform a FUEL FLOW TEST and, if less than the
specified fuel is returning to the fuel tank, consult the NO
FUEL OR INSUFFICIENT FUEL chart.
8. Check for damages or dirty air cleaners and clean, repair
or replace damaged parts.
Remove the air box covers and inspect the cylinder liner
ports. If the ports are over 50% plugged, clean them.
Check for blower air intake obstruction, high exhaust
back pressure or plugged aftercooler (if used). Clean, re-
pair or replace faulty parts.
Check the compression pressures (consult the HARD
STARTING chart).
9. Incorrect operation of the engine may result in excessive
loads on the engine. Operate the engine according to the
approved procedures.
10. Refer to Item 13 on Chart 4.
11. Check the ambient air temperature. A power decrease of
.15 to .5 horsepower per cylinder, depending upon injector
size, for each 10°F (~12.2°C) temperature rise above
90°F (32°C) will occur. Relocate the engine air intake to
provide a cooler source of air.
12. Engines lose horsepower with increases in altitude. The
percentage of power loss is governed by the altitude at
which the engine is operating.
13. Fill oil bath air cleaners to the proper level with the same
grade and viscosity lubricating oil that is used in the en-
gine.
Clean the air box drain tubes and check valve (if used)
to prevent accumulation that may be picked up by the air
stream and enter the engine cylinders. Inspect the check
valve as follows:
1. Disconnect the drain tube between the check valve and
the air box drain tube nut at the air box cover.
2. Run the engine and note the air flow through the valve
at idle engine speed.
3. If the check valve is operating properly, there will be no
air flow at engine speeds above idle.
Inspect the blower oil seals by removing the air inlet
housing and watching through the blower inlet for oil
radiating away from the blower rotor shaft oil seals while
the engine is running. If oil is passing through the seals,
overhaul the blower.
Check for a defective blower-to-cylinder block gasket.
Replace the gasket if necessary. If the blower has been
removed, install a new gasket.
14. Refer to Item 1 of this chart.
15. Check injector timing and the position of each injector.
Perform an engine tune-up, if necessary. If the engine is
correctly tuned, the erratic operation may be caused by an
injector check valve leaking, spray tip holes enlarged or a
broken spray tip. Replace faulty injectors.
-------
Support Systems 769
Chart 4
j Probable Cause* |
Check For~[
ll. LOW FUEL SUPPLY
| Check for
Check For
7. RELIEF VALVE NOT SEATING
9. FUEL PUMP NOT ROTATING
8. WORN GEARS OR PUMP BODY
5. FUEL STRAINER OR LINES RESTRICTED
4. FAULTY INJECTOR TIP ASSEMBLY
FAULTY FUEL PUMP
FAULTY INS
ION
AIR LEAKS
FLOW OBSTRUCTION
10. DIAMETER OF FUEL SUCTION
LINES TOO SMALL
11. RESTRICTED FITTING
MISSING FROM RETURN LINE
13. HIGH FUEL RETURN
TEMPERATURE
12. INOPERATIVE FUEL INTAKE
LINE CHECK VALVE
3. DAMAGED FUEL OIL STRAINER
GASKET
6. TEMPERATURE LESS THAN 10 °F.
ABOVE POUR POINT OF FUEL
NO FUEL OR INSUFFICIENT FUEL
2. LOOSE CONNECTIONS OR CRACKED
LINES BETWEEN FUEL PUMP AND
TANK OR SUCTION LINE IN TANK
-------
770 Treatment Plants
Chart 4
NO FUEL OR INSUFFICIENT FUEL
SUGGESTED REMEDY
1. The fuel tank should be filled above the level of the fuel
suction tube.
2. Perform a FUEL FLOW TEST and, if air is present, tighten
loose connections and replace cracked lines.
3. Perform a FUEL FLOW TEST and, if air is present, replace
the fuel strainer gasket when changing the strainer ele-
ment.
4. Perform a FUEL FLOW TEST and, if air is present with all
fuel lines and connections assembled correctly, check for
and replace faulty injectors.
5. Perform a FUEL FLOW TEST and replace the fuel strainer
and filter elements and the fuel line, if necessary,
6. Consult the FUEL OIL SPECIFICATIONS and use the fuel
oil recommended.
7. Perform a FUEL FLOW TEST and, if inadequate, clean
and inspect the valve and seat in the fuel pump body.
8. Replace the gear and shaft assembly or the fuel pump
body.
9. Check the condition of the fuel pump drive and blower
drive and replace the defective parts.
10. Replace with larger tank-to-engine fuel lines.
11. Install a restricted fitting in the return line.
12. Make sure that the check valve is installed in the line
correctly; the arrow should be on top of the valve assem-
bly or pointing upward. Reposition the valve if necessary.
If the valve is inoperative, replace it with a new valve as-
sembly.
13. Check the engine fuel spill-back temperature. The return
fuel temperature must be less than 150°F (66°C) or a loss
in horsepower will occur. This condition may be corrected
by installing larger fuel lines or relocating the fuel tank to a
cooler position.
-------
Support Systems 771
Chart 5
HIGH LUBRICATING OIL CONSUMPTION
Check For
Check For
Check For
Probable Causes
I. OIL LINKS OR CONNECTIONS LF.AKING
5 BLOWER OILSF.AL LEAKING
.V HIGH CRANKCASF. PRESSURE
II. PISTON AND ROD ALIGNMENT
h. OIL COOLER CORE LF.AKING
4. EXCESSIVE OIL IN AIR BOX
13. EXCESSIVE OIL IN CRANKCASF.
12. EXCESSIVE INSTALLATION ANGLE
2. GASKET OR OIL SEAL LEAKS
9. PISTON PIN RETAINER LOOSE
INTERNAL LEAKS
OIL CONTROL AT CYLINDER
EXTERNAL LEAKS
8. OIL CONTROL RINGS WORN. BROKEN
OR IMPROPERLY INSTALLED
7 EXCESSIVE OIL BUILDUP IN
CYLINDER HEAD
10. SCORED LINERS. PISTONS OR
OIL RINGS
SUGGESTED
1. Tighten or replace the defective parts.
2. Replace defective gaskets or oil seals.
3. Refer to the EXCESSIVE CRANKCASE PRESSURE chart.
4. Refer to the ABNORMAL ENGINE OPERATION chart.
5. Remove the air inlet housing and inspect the blower end
plates while the engine is operating. If oil is seen on the
end plate radiating away from the oil seal, overhaul the
blower.
6. Inspect the engine coolant for lubricating oil contamina-
tion; if contaminated, replace the oil cooler core. Then use
a good grade of cooling system cleaner to remove the oil
REMEDY
from the cooling system.
7. Check for plugged or improper breather.
8. Replace the oil control rings on the piston.
9. Replace the piston pin retainer and defective parts.
10. Remove and replace the defective parts.
11. Check the crankshaft thrust washers for wear. Replace all
worn and defective parts.
12. Decrease the installation angle.
13. Fill the crankcase to the proper level only.
-------
772 Treatment Plants
Chart 6
| Check For
Check For
Check For
Check For
Probable Causes
8. FAULTY F.XHAUST PIPING
BREATHER RESTRICTION
CYLINDER BLOW-BY
3. PISTON RINGS
WORN OR BROKKN
CYLINDER HEAD
G ASK FT LEAKING
2. PISTON OR
LINER DAMAGED
4. OBSTRUCTION OR
DAMAGE TO BREATHER
5. DAMAGED BLOW! R-
TO-BLOCK GASKET
6. CYLINDER BLOCK END
PLATE GASKET LEAKING
7. EXCESSIVE MUFFLER
RESISTANCE
AIR FROM BLOWER
OR AIR BOX
EXCESSIVE EXHAUST
BACK PRESSURE
EXCESSIVE CRANKCASE PRESSURE
SUGGESTED REMEDY
1. Check the compression pressure and, if only one cylinder
has low compression, remove the cylinder head and re-
place the head gaskets.
2. Inspect the piston and liner and replace damaged parts.
3. Install new piston rings.
4. Clean and repair or replace the breather assembly.
5. Replace the blower-to-block gasket.
6. Replace the end plate gasket.
7. Check the exhaust back pressure and repair or replace
the muffler if an obstruction is found.
8. Check the exhaust back pressure and install larger piping
if it is determined that the piping is too small, too long or
has too many bends.
-------
Support Systems 773
Chart 7
MAKE CHECKS WITH MINIMUM WATER OUTLET TEMPERATURE OF 160 F
Probable Causes
Check For
Check For
Check For
Check For
2. LUBRICATING OIL VISCOSITY
3. COOLER CLOGGED
1. SUCTION LOSS
14. AIR LEAK IN PUMP SUCTION
8. FAULTY GAGE
15. PUMP WORN OR DAMAGED
10. GAGE ORIFICE PLUGGED
16. FLANGE LEAK (PRESSURE SIDE)
9. GAGE LINE OBSTRUCTED
3. RELIEF VALVE FAULTY
LUBRICATING OIL
POOR CIRCULATION
OIL PUMP
PRESSURE GAGE
LOW OIL PRESSURE
7. GALLERY, CRANKSHAFT OR
CAMSHAFT PLUGS MISSING
4. COOLER BY-PASS VALVE NOT
FUNCTIONING PROPERLY
6. EXCESSIVE WEAR ON
CRANKSHAFT BEARINGS
II ELECTRICAL INSTRUMENT
PANEL SENDING UNITS FAULTY
2 INTAKE SCREEN PARTIALLY
CLOGGED
5. PRESSURE REGULATOR
VALVF. NOT
FUNCTIONING PROPERLY
-------
774
Treatment Plants
Chart 7
LOW OIL PRESSURE
-SUGGESTED REMEDY-
1. Check the oil and bring it to the proper level on the dipstick
or correct the installation angle.
2. Wrong viscosity of lubricating oil being used; consult the
LUBRICATING OIL SPECIFICATIONS.
Check for fuel leaks at the injector nut seal ring and fuel
pipe connections. Leaks at these points will cause fuel oil
dilution.
3. A plugged oil cooler is indicated by excessively high lubri-
cating oil temperature. Remove and clean the oil cooler
core.
4. Remove the oil cooler by-pass valve and clean the valve
and valve seat and inspect the valve spring. Replace de-
fective parts.
5. Remove the pressure regulator valve and clean the valve
and valve seat and inspect the valve spring. Replace de-
fective parts.
6. Change the bearings. Consult the LUBRICATING OIL
SPECIFICATIONS for the proper grade of oil to use and
change the oil filters.
7. Replace missing plug(s).
8. Check the oil pressure with a reliable gage and replace the
gage if found faulty.
9. Remove and clean the gage line; replace it if necessary.
10. Remove and clean the gage orifice.
11. Repair or replace defective electrical equipment.
12. Remove and clean the oil pan and oil intake screen; con-
sult the LUBRICATING OIL SPECIFICATIONS for the
proper grade of oil to use and change the oil filters.
13. Remove and inspect the valve, valve bore and spring;
replace faulty parts.
14. Disassemble the piping and install new gaskets.
15. Remove the pump, clean and replace defective parts.
16. Remove the flange and replace the gasket.
-------
Support Systems 775
Chart
ABNORMAL ENGINE COOLANT
OPERATING TEMPERATURE
I Probable Causes
Check For |
Check For
3. IMPROPER CIRCULATION
2. POOR CIRCULATION
BELOW NORMAL
ABOVE NORMAL
4. EXCESSIVE LEAKAGE
AT THERMOSTAT SEAL
I. INSUFFICIENT HEAT
TRANSFER
SUGGESTED
1. The cooling system should be cleaned with a good cooling
system cleaner and thoroughly flushed to remove scale
deposits.
The exterior of the radiator core should be cleaned to
open plugged passages permitting normal air flow.
Loose fan belts should be adjusted to the proper tension
to prevent slippage.
Check for an improper size radiator or inadequate
shrouding.
Repair or replace inoperative temperature-controlled
fan or inoperative shutters.
2. Check the coolant level and fill to the filler neck if the
coolant level is low.
Inspect for collapsed or disintegrated hoses. Replace all
faulty hoses.
Thermostat may be inoperative. Remove, inspect and
test the thermostat; replace if found faulty.
REMEDY
Check the water pump for a loose or damaged impeller.
Check the flow of coolant through the radiator. A clog-
ged radiator will cause an Inadequate supply of coolant on
the suction side of the pump. Clean the radiator core.
Remove the coolant filler cap and operate the engine,
checking for combustion gases in the cooling system. The
cylinder head must be removed and inspected for cracks
and the head gaskets replaced if combustion gases are
entering the cooling system.
Check for an air leak on the suction side of the water
pump. Replace defective parts.
3. The thermostat may not be closing. Remove, inspect and
test the termostat. Install a new thermostat if necessary.
Check for an improperly installed heater.
4. Excessive leakage of coolant past the thermostat seal(s)
is a cause of continued low coolant operating temperature,
when this occurs, replace the thermostat seal(s).
-------
776 Treatment Plants
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 794.
29.5A Why is gasoline not used as a fuel in diesel engines?
29.5B List the four basic parts of a diesel fuel system.
29.5C What is the purpose of the fuel injection pump?
29.6 HEATING, VENTILATING, AND AIR CONDITIONING
This section covers the most common forms of heating
(specifically digesters), ventilating, and air conditioning found
in wastewater treatment facilities.
29.60 Operation and Maintenance of Digester Gas
or Natural Gas-Fired Boilers
A large number of parts are similar for almost all gas-fired
hot-water boilers. They will be discussed in this section.
29.600 Gas System
1. GAS PRESSURE REGULATOR. The gas pressure reg-
ulator is a device on the incoming gas line that regulates the
pressure of the gas coming to the boiler. In a natural gas
boiler, the manifold pressure should be 3.5 inches (8.9 cm)
of water pressure. Methane-fired boilers would have a
pressure of 2.5 to 3 inches (6.3 to 7.6 cm) of water pres-
sure.
2. AUTOMATIC GAS VALVE. The gas valve opens and closes
allowing the gas to flow to the burner. The valve is con-
trolled by the operating thermostat. If the pilot valve is not
operating, the circuit for gas valve closure is incomplete;
therefore, the valve cannot be opened without a pilot to
ignite the gas.
3. PILOT SWITCH/VALVE. The pilot can be of the electronic
type that has no pilot flame unless the boiler falls below
operating temperature. After the pilot flame has ignited, the
automatic gas valve opens. When a pilot flame is called for,
an ignition transformer causes an arc across its electrodes
and ignites the pilot. Once a pilot is sensed by a photo-
electric eye, the transformer circuit opens. The other type of
pilot valve requires a "standing" pilot that heats a ther-
mocouple and allows the pilot to remain lighted. If the pilot
is extinguished, the thermocouple cools and the pilot valve
closes. The automatic gas valve will not operate if the pilot
is out since the electrical contacts incorporated in it are
open.
4 CONTROL TRANSFORMER. The most common voltage
used in boiler control is 24 volts, or 120 volts A.C. This
supplies the voltage necessary to operate the solenoid
valves.
5. BURNERS. The burners distribute the gas and con-
sequently, the flame across the combustion or fire box sur-
face. Each burner has a draft shuttle to regulate air to the
burner. As the gas enters the burner, it goes through a
metering orifice. When purchasing a boiler that will be fired
by methane gas, make sure that you obtain the correct
orifices. Natural gas orifices are too small to allow an
adequate volume of methane gas to the burners.
6. DRAFT BLOWERS. These are installed to ensure that an
adequate amount of air is available for good gas combus-
tion. They also allow for good air circulation through the
boiler core.
29.601 Water System
1. LOW WATER CUTOFF VALVE. This valve ensures that suf-
ficient water is available in the boiler at all times for safe
operation. If the water falls below the safe point, a set of
contacts in the valve open and de-energize the circuit to the
automatic gas valve. You cannot restore gas to the burner
until the water level is re-established.
2. MAKEUP WATER VALVE. Some boilers use a float-
actuated valve that monitors the water level in the boiler
and adds water as needed. These boilers may have a set of
contacts that open the electrical circuit, causing the burner
to die when water is added.
3. EXPANSION TANK. This allows for the expansion of water
in the boiler system. Most tanks have a sight glass so the
operator can make a visual observation of the amount of
water available.
4. HIGH PRESSURE RELIEF VALVE. If the water pressure
within the vessel exceeds the maximum allowable pressure
in the boiler, the valve will open and vent excess pressure.
5. HOT WATER CIRCULATION PUMP. Some systems use a
pump to circulate the hot water from the boiler through the
heat exchanger and back. If the pump should fail and the
heat generated in the boiler cannot be dissipated, a high
temperature cut-off shuts down the boiler.
29.602 Control Switches
1. OPERATING SWITCH. This switch is adjustable and an
optimum operating temperature can be set. The boiler
operating cycle is set by this switch.
2. OVER TEMPERATURE CUT-OUT. If the vessel tempera-
ture exceeds the normal operating level, the over tempera-
ture cut-out shuts down the boiler before damage results.
This switch usually will have a manual reset. The boiler
system will have to be examined to determine the cause of
shutdown such as a low water level or a faulty operating
switch.
3. FLUE DRAFT SWITCH. The draft switch must be closed
before the burner will fire. In this way your are assured that
adequate air is available before ignition takes place.
29.603 Boiler Maintenance
1. Drain boiler system sufficiently to remove sludge from bot-
tom of boiler — yearly.
2. Test boiler switches and safety devices to insure proper
operation — yearly.
3. Clean boiler if insufficient draft is suspected. The impurities
of digester gas will build up in the boiler core causing the
flame to flare out at the burner. Do cleaning as needed or
yearly.
4. Inspect chimney for blockages and clean out soot yearly. A
dirty chimney can cause restricted air flow and/or a com-
bustible environment.
5. Blow down the level-control valve to eliminate scale and
sludge buildup in the float cavity — at least twice yearly.
6. Test boiler feed water for hardness. In some cases "sof-
tened" water will have to be used. Hard water causes scale
to build up inside the boiler. Scale will reduce heat transfer
and thus the efficiency of the boiler.
7. Check boiler water level daily.
8. When boiler is cleaned, ensure that none of the orifices on
the burner face are blocked.
-------
Support Systems 777
Regular maintenance should be performed as outlined in the
manufacturer's operation and maintenance manual.
NOTE: Never add cold water to a boiler that has been shut
down because of an over temperature. This could
cause a cast iron vessel to fracture. However, if the
boiler water level is low, water can be added SLOWLY
to the system.
See Table 29.3 for a troubleshooting guide and for service
hints.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 794.
29.6A List the common items that are similar for almost all
gas-fired hot-water boilers.
29.6B How is the automatic gas valve controlled?
29.6C Why should boilers be drained on an annual basis?
29.6D Why does boiler feed water have to be tested for
hardness?
29.61 Operation and Maintenance of
Building Blowers and Exhaust Fans
29.610 Need for Blowers and Fans
Because of the confined spaces found in wastewater treat-
ment plants, it is necessary to provide adequate ventilation.
Where natural ventilation is not possible or adequate, it is nec-
essary to use blowers and fans to ensure the proper rate of air
change in the area.
29.611 Terminology
These are a few terms you should be familiar with:
CFM (cubic feet per minute) — A measure of the volume
flow rate, or air-moving capacity of a fan or blower per minute.
FREE AIR DELIVERY - The conditions existing when there
are no restrictions to air flow at the inlet or outlet of an air-
moving device.
PLENUM CHAMBER - An air chamber maintained under
pressure to serve one or more air distribution ducts.
SP (Static Pressure) — The measurement of the resistance
to the movement of air forced through a system caused by duct
work, inlets and louvers. Static pressure is measured in inches
or centimeters of water, the height in inches to which the pres-
sure will lift a column of water. For a given system, static pres-
sure varies as the square of the flow rate. If the flow rate is
doubled, the static pressure of the system increases four
times.
VENTURI - A panel surrounding the blades of a propeller fan
which increases fan performance.
29.612 Fan Laws
CFM, RPM, and HP (Horsepower) are all related to one
another. When one changes, the others change in a known
manner. These characteristics are known as Fan Laws. CFM
is the most commonly changed variable in an air system.
To change the CFM of a known or existing system the follow-
ing applies:
1. Calculate the ratio between new and existing CFM.
Ratio equals CFM New
CFM Existing
2. To determine RPM, multiply the ratio of step one, times the
existing RPM.
New RPM equals —CFM New times RPM Existing
CFM Existing
3. The new SP determined by multiplying the ratio of step one,
times itself, times existing SP (static pressure).
SP New Equals —(CFM New) |jmes gp Existing
(CFM Existing)2
4. The new HP required is as follows: Multiply ratio of step
one, times itself twice, and then times the existing HP
(horsepower).
HP New equals _1CFM New)3 times HP Existing
(CFM Existing)3
EXAMPLE
KNOWN
Existing Conditions
Flow, CFM ______
Speed, RPM = 1,000 RPM 2. Static Pressure, in
Static Pressure, in = 0.5 inches 3. Motor Power, HP
Motor Power, HP = 0.5 HP
New Condition
Flow, CFM = 5,000 CFM
Determine CFM Ratio
_ New CFM
UNKNOWN
New Conditions
: 4,000 CFM 1. Speed, RPM
CFM Ratio
Existing CFM
_ 5,000 CFM
4,000 CFM
= 1.25
1. Calculate the new speed, RPM.
Speed, RPM = (CFM Ratio)(Existing RPM)
= 1.25 x 1,000 RPM
= 1,250 RPM
2. Calculate the new static pressure, inches.
Static Pressure, = (CFM Ratio)z(Existing SP, in)
in = (1.25)2 x 0.5 in
= 0.78 in
3. Calculate the new motor power, HP.
Motor Power, HP = (CFM Ratio)3 (Existing, HP)
= (1.25)3 x 0.5
= 0.98 HP
New Conditions Are: 5,000 CFM (up 25%), 1,250 RPM (up
25%), 0.78 SP (up 36%), 0.98 HP (up
95%).
29.673 Types of Fans and Blowers
There are different types of fans and blowers. Each meets
different needs of ventilation.
Propeller (Axial) Fan. The air flow is parallel or axial to the
shaft on which the propeller is mounted. These fans have good
efficiency, near free air delivery, and are used in low static
pressure, and high volume application. Usually they are
mounted in a venturi. Use — Simple construction and low cost.
-------
778 Treatment Plants
TABLE 29.3
TROUBLESHOOTING GUIDE AND SERVICE HINTS"
TROUBLE
POSSIBLE CAUSE
REMEDY
1. Pilot Outage
a.
Defective Thermocouple (100% S.O.)
a.
Replace
b.
Heavy Draft Blowing Across Pilot
b.
Redirect Air Movement or
Eliminate
c.
Plugged Pilot Orifice
c.
Replace Orifice
d.
No Gas
d.
Check Manual Pilot Valve
Check Manual Gas Train Valve
Check Manual Meter Valve
Consult Gas Company
e.
Defective Pilotstat or Pilot Switch
e.
Replace
2. Main Gas Valve Will Not Open
a.
No Power
a.
Check Power Source With
(Standard System)
Meter. Also Check Fuses
b.
Defective Gas Valve
b.
Replace
c.
Defective Thermocouple
c.
Replace
d.
Low Water in Boiler or System Causing Low
d.
Check for Leaks
Water Cut-Off to Function
Check Feeder if Supplied
e.
Defective Pilotstat (100% S.O.)
e.
Replace
f.
Defective Pilot Switch
f.
Replace
g-
If Provided — Hi-Pressure Gas Switch Open
9
Check Switch Setting
Check Manifold Gas Pressure
h.
If Provided — Lo-Pressure Gas Switch Open
h.
Check Switch Setting
Check Inlet Gas Pressure
3. Main Gas Valve Will Not Open
a.
No Power
a.
Check Source With Meter
(Electronic System)
Also Check Fuses
b.
Defective Valve
b.
Replace
c.
Relay on Safety
c.
Check for Pilot Outage
d.
Pilot Out
d.
Relight Pilot
May have Defective Pilot
Valve or Ignition Transformer
e.
Defective Relay
e.
Replace
f.
Low Water in Boiler or System —
f.
Check for Leaks
Lo-Water Cut-Off Functioning
Check Water Feeder if
Supplied
g-
Defective Pilotstat (100% S.O.)
g-
Replace
h.
Defective Pilot Switch
h.
Replace
i.
Defective Thermocouple(s)
i.
Replace
j.
If Provided — Hi-Pressure Gas Switch Open
i.
Check Switch Setting
Check Manifold Gas Pressure
k.
If Provided — Lo-Pressure Gas Switch Open
k.
Check Switch Setting
Check Inlet Gas Pressure
4. Burner(s) Burning With Yellow Flame
a.
Air Shutter(s) Closed Too Far
a.
Adjust Air Shutters as
Prescribed
b.
Low Gas Pressure in Manifold
b.
Adjust Pressure Regulator or
(Insufficient Air Injection)
Check Line Pressure
c.
Burner Ports Partially Closed
c.
Replace Burners or Clean
(Rust, etc.)
Parts
d.
Insufficient Air for Combustion
d.
Check Size of Air Openings
Provided Into Room For
Combustion Air.
If Not In Accordance With
Recommended Practice —
Correct.
e.
Incorrect Burner Orifice — (Too Large)
e.
Install Correct Orifice
f.
Gas Pressure Too High In Manifold
f.
Readjust Pressure
(Over-Gased)
5 Gas Spillage From Draft Hood
a.
Insufficient Chimney Draft
a.
1. Increase Height or
Relief Opening
1. Chimney Too Low
Install Induced Draft Fan
2. Chimney Too Small
3. Blockage in Chimney
4. Downdraft Caused by Chimney Location
With Respect to Other Buildings,
Roofs, Etc.
2. Install Induced Draft Fan
3. Remove Blockage
4. Install Chimney Cap
b.
Exhaust Fan in Boiler Room or Connecting
Area
b.
Remove Exhaust Fan or
Isolate Fan From Boiler Room
c.
Insufficient Area Provided for Combustion
Air
c.
Provide Proper Area in
Accordance With Recom-
mended Practice
6. Main Gas Valve Opens
No Gas Flows
a.
b.
Manual Valve Closed at Gas Train
Manual Valve Closed at Meter
a.
b.
Open Valve
Open Valve
c.
If Provided — Test Firing Valve Closed
c.
Open Valve
¦ Permission of the Pearless Heater Company, Boxertown, Pennsylvania
-------
Support Systems 779
DUCT FAN (TUBE-AXIAL). The air flow in this fan is parallel
or axial to the shaft of the propeller. The propeller is housed in
a cylinderical tube or duct. This design enables duct fans to
operate at higher static pressures then propeller fans. Use —
Paint spray booths and other ducted exhaust systems.
Centrifugal blowers have an air flow that is perpendicular to
the shaft on which the wheel is mounted. The wheel is
mounted in a scroll-type housing which is needed to develop
rated pressures. There are four classes of centrifugal blowers
and the classes are determined by the wheel blade position
with respect to the direction of rotation.
FORWARD CURVE. The tips of the blades are inclined in
the direction of rotation (most common type of centrifugal
blower). Use — Residential heating and air conditioning sys-
tems, light-duty exhaust system.
BACKWARD INCLINED. The tips of the blades are inclined
away from the direction of rotation. Use — Commercial,
heavy-duty heating and cooling systems, non-overloading
characteristics.
RADIAL BLADE. Has straight blades. Use — Since the
blades are self-cleaning, it is suitable for moving heavily laden
air (large particles or grease-laden) in restaurants and cafes.
IN-LINE (TUBULAR CENTRIFUGAL FAN). The air flow is
developed in the same manner as a centrifugal blower, but
after the air leaves the impeller it is contained in a tubular
housing. By means of turning vanes, it is discharged in an axial
direction. Use — Can be mounted vertically or horizontally,
thus providing for a simpler installation by minimizing duct
turns and transitions.
29.614 Maintenance
Maintenance of ventilation fans and blowers varies with the
conditions under which they operate. All ventilating equipment
should be inspected and serviced AT LEAST on a yearly basis.
Check fan/blower housing and blades for an accumulation of
dirt. Scrape off excess with a putty knife and brush off the
remaining with a stiff bristle brush. Be careful that the blades
are not bent or damaged during cleaning. Inspect blades for
lose rivets or cracks. Check the condition of belts (belt-driven
units) for cracks, adequate tension, glazing, and condition of
belt sheaves. Motor and cross-shaft bearings should be lubri-
cated. Remove grease relief plug and add grease until all old
grease has been dissipated with new grease. Most greases
designed for ball bearings should be adequate. When fan/
blower is operating, listen for unnatural metallic sounds that
could indicate fan rubbing or bearing failure. Your particular
system may require inspection and maintenance at closer
intervals so check the manufacturer's recommendations.
29.62 Operation and Maintenance of Air Conditioning
Units
A brief explanation of how a refrigeration system works will
help you understand how air conditioning units work. Refriger-
ation has been defined as the process of transferring heat from
one place to another. When a hot object is placed near or
touches a cold object, heat flows from hot to cold. In refrigera-
tion, take the viewpoint that a cold object removes heat from a
hot object. The term "refrigerant" refers to the fluid used in the
system to produce cold by removing heat. One of the early
refrigerants was ammonia. When ammonia is placed in an
open container, it evaporates so rapidly that it appears to be
boiling. When pure ammonia boils, it cools to 28 degrees
below zero F (~33°C). The area from which the boiling am-
monia removes heat is cooled or refrigerated.
The refrigerant gas in enclosed systems is reclaimed (not
allowed to boil off) through the process of absorption and
evaporation. See Fig. 29.38 showing a refrigerator using am-
monia as a refrigerant. The basic operating cycle shows that
the system picks up heat in the evaporator and carries it out-
side the insulated referigerator box to the condenser. Here,
heat is removed by air passing over the condenser fins. The
cooling effect is produced in the evaporator by boiling the refri-
gerant. The boiling refrigerant (-28 degree F or -33°C) ab-
sorbs heat from the interior of the box. Hydrogen is circulated
over the liquid ammonia to speed up the boiling process and to
carry away the heat at a faster rate.
The refrigerant is changed back to a liquid by removing heat
in the condenser. At that point the refrigerant "gives up" heat.
Because the heat is moving from a low temperature to a higher
one, it is necessary to add energy to the system. Usually the
energy is supplied in the form of heat energy. In modern refrig-
eration systems, the heat is produced by compressing the re-
frigerant vapors. Freon 12 fills the requirement as a refrigerant
and is used extensively in current systems.
The air conditioner works very much like the refrigerator. Air
is passed over the evaporator and the heat is removed, The
cool air is then distributed through the building via "cold" air
ducts. In the old axiom, "What goes in must come out," the
warm air in the building is returned through "return air" ducts
and passes over the condenser. The air passing over the con-
denser helps dissipate the heat in the refrigerant, converting it
back to a liquid.
Most air conditioning units require little mechanical mainte-
nance. The compressor is sealed and requires no external
lubrication. Most fan motors have sealed bearings. Check
yours to be sure. There are some things that need to be done
however. The filters in the cold and return air ducts should be
replaced yearly. If an undue amount of dust is present, they
may require earlier cleaning or replacement. The condenser
should be cleared of obstructions. Blow out with a low pressure
air. Examine fan blades for fractures and excessive dirt build-
up. With the power off, spin the fan to determine if bearing
failure is imminent. Make sure that the condensation drip line is
not plugged.
An air conditioner compressor can freeze up (completely
covered with ice). This usually occurs when the air in the build-
ing becomes extremely cool or the compressor is not allowed
to cycle (non-cooling). The compressor will not cycle if the
thermostat is set too low or is in a manual mode. If your air
conditioner unit runs but fails to cool, it is quite possible that
some of the refrigerant charge may have been lost. This may
be caused by a small hole in the tubing. At that point, call upon
a reliable air conditioning service to correct the problem.
Because of the emphasis on energy conservation, the ther-
mostat should be set to maintain a moderate room tempera-
ture; 74 degrees to 78 degrees F (23 to 26°C). If air condition-
ers in your building are usually left on during non-working
hours, time-clock-actuated thermostats that turn off the unit
during off hours and back on again prior to the work day may
be to your advantage.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 794 and 795.
29.6E What is a plenum chamber?
29.6F List the four classes of centrifugal blowers.
29.6G What is refrigeration?
29.6H What might be wrong if an air conditioner runs, but
fails to cool?
-------
780 Treatment Plants
(B)CONDENSER (OUTSIDE
REFRIGERATOR BOX)
AMMONIA
VAPOR
(A)EVAPORATOR
FREEZER
COMPARTMENT
HYDROGEN
V
auuuii
miiriniii
VAPOR
SEPARATOR
• . WATER
OISSOLVED
AMMONIA
ABSORBER
(C)GENERATOR
(D) HEAT ENERGY
SCHEMATIC DIAGRAM OF
BASIC ABSORPTION CYCLE
Fig. 29.38 Refrigeration system
(Source Principles ol Refrigeration by Marsfi and Olivo, permission of Oelmar Publishers Inc , Albany, New York)
-------
Support Systems 781
29.7 COMPRESSORS (See Vol. II, pgs 24 and 25)
29.70 Need for Compressors
With pneumatic tools and instrumentation filling a vital part of
our needs, it is important to look at and understand the heart of
any air system — the compressor. Basically there are two
types of air compressors, rotary and reciprocating. You will find
that there are some variations in design but the principles of
operation are similar for comparable machines.
29.71 Rotary Compressors
Rotary compressors usually fall into one of two categories,
single stage or two stage. In either case, they have sliding
vanes and use oil to cool the compressor as well as lubricate
and assist in sealing.
The rotor chamber (cylinder) is mounted on a base which
supports the compressor. The cylinder has air inlet and dis-
charge ports and oil injection holes. The cylinder bore is offset
from the rotor shaft causing the cylinder bore to be eccentric
with the rotor.
The rotor is slotted to receive sliding vanes which are sealed
by a large volume of lubricating oil that is fed to the bearings
and bore. The vanes are held against the cylinder wall by
centrifugal force when operating. (Low RPM compressors use
a spring-loaded vane to insure a vane-to-bore seal.)
As the rotor turns, air is pulled into the compressor through
the intake port. Since the bore is eccentric with the rotor, dis-
placement is decreased as the rotor turns. The air entrapped
between the vanes is compressed. Lubricating oil assists to
form a seal between the vane and the cylinder wall. Compres-
sed air is expelled through the discharge port and the cycle
renews itself.
Since the oil plays a major role in a rotary compressor, let's
follow it through the system.
Relatively cool lubricating oil, supplied by an oil pump, is
induced under pressure to the rotor bearings and also injected
in measured amounts into the rotor chamber. The oil passes
through the bearings at each end of the rotor, then enters the
close clearances at the vane ends and then passes into the
rotor chamber. All of the oil introduced mixes with the air being
compressed and passes on with it. This removes the heat of
compression to some degree and allows a low final air dis-
charge temperature. Discharged air passes on to the
receiver-separator. There the oil is removed from the air and
collects in the storage reservoir. The oil is then forced on to an
oil cooler. Air pressure causes the oil to flow through the
cooler, oil filter, and back to the oil pump sump.
The two-stage compressor develops a low air pressure in
the first stage (30 psi or 2.1 kg/sq cm). Oil-saturated air is then
passed on to the second stage where the air is compressed
even further. The remaining air/oil cycle is similar to the single
stage. Some compressors incorporate a thermostatically con-
trolled bypass valve that allows some of the oil to bypass the oil
cooler. This arrangement helps to maintain a high compressor
oil temperature, thereby reducing the possibility of water vapor
condensation in the oil system. At a temperature near 185
degrees F (85°C), all oil is circulated through the cooler.
A nonadjustable oil pump relief valve prevents over-
pressure in the oil system. Many units have a high temperature
and high pressure cut-off switch to insure adequate compres-
spr protection.
When a rotary compressor is driven by an engine, a speed;
pressure regulator motor monitors the air pressure versus en-
gine speed. If air pressure declines, engine speed is increased
to produce the needed air. Conversely, engine speed reduces
to an idle when maximum pressure is attained. (Compressors
driven by electric motors are usually operated at a set speed
for a specific volume of air.)
Most engine-powered compressors have an automatic
blowdown unloader valve. When the compressor stops and air
pressure in the compressor and system equalize, the valve
opens and blows down the system to atmospheric pressure.
Be aware of the control valves and switches used in your par-
ticular system. If any malfunction is indicated, discontinue the
use of the compressor until repairs are made.
Since oil plays a large part in compressor operation, it is very
important that the proper oil be used. In high volume and pres-
sure units, the recommended oil is a non-detergent straight
mineral oil (turbine or hydraulic type) which is solvent refined
and contains rust and oxidation inhibitors and anti-foam addi-
tives. Viscosity is in the 150-200 Saybolt universal seconds
range at 100 degrees F (38°C). Check your owner's manual for
further specifications.
Follow owner's manual recommendations with respect to oil
changes, air filter changes, condensate draining, and examina-
tion of internal parts (vanes, rotor, and cylinder). See Table
29.4 for a compressor troubleshooting guide.
When purchasing a rotary compressor, check the specifica-
tions for the following items:
1. Rated capacity in CFM,
2. Rated operating pressure,
3. Duty cycle — intermittent or continuous,
4. Horsepower requirements, and
5. Stages.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 795.
29.7A What are the two most common types of air compres-
sors in use today?
29.7B What type of oil is used in high volume and pressure
compressor units?
29.7C List the items that are important considerations when
purchasing a rotary compressor.
-------
782 Treatment Plants
MALFUNCTION
TABLE 29.4 COMPRESSOR TROUBLESHOOTING GUIDE'
PROBABLE CAUSE
PROBABLE REMEDY
Compressor fails to operate or to provide
rated capacity.
1. Clogged Air Cleaner, cap and/or screen.
1. Clean
2. Pressure Regulator improperly adjusted.
2. Adjust Regulator
3. Engine fails to develop proper R.P.M.'s.
3. See Engine Manual.
4. Broken, sticking, or excessively worn
rotor vanes. j
4. Replace with a complete new set.
5. Broken drive coupling.
5. Replace drive coupling.
6. Faulty Dump Valve.
6. Replace.
Oil Gage fails to indicate pressure.
1. Defective Gage.
1. Replace.
2. Clogged line or fitting.
2. Clean.
Excessive Compressor oil consumption.
1. Clogged Separator return line.
1. Clean.
2. External oil leaks
2. Tighten or replace fittings, etc.
3. Saturated Oil Separator elements.
3. Replace Separator Filter element.
Air Receiver Safety Valve activates.
1. Air Intake Valve malfunctioning.
1. Repair or replace.
2. Speed Control malfunctioning.
2. Repair or replace.
3. Air leaks, broken or cracked tubing.
3. Repair.
Air Receiver Safety Valve blows due to mal-
functioning Air Intake Valve.
1. Incorrect control pressure from Pressure
Regulator.
1. Adjust or replace Pressure Regulator.
2. Ruptured Air Intake Valve bellofram.
2. Replace bellofram.
3. Valve binding on Air Intake Valve shaft.
3. Repair or replace.
Air Receiver Safety Valve blows due to mal-
functioning Speed Control
1. Ruptured Speed Control bellofram.
1. Replace bellofram.
2. Incorrect control pressure from Pressure
Regulator.
2. Adjust or replace Pressure Regulator
Leaks General:
-Oil
— Air
1. Cracked or broken tubing.
1. Replace.
j
2. Loose and/or broken flares or connec-
tions.
2. Tighten and/or replace.
3. Faulty oil seal.
3. Replace.
4. Loose retainers.
4. Tighten.
a permission of Le Rol Division, DRESSER INDUSTRIES, INC., Sidney, Ohio.
29.72 Reciprocating Compressors
The operation of a reciprocating compressor is similar to that
of an internal combustion engine. However, a reciprocating
compressor requires an external power source to provide
compression and force the air into the receiver.
Compressors can have more than one cylinder, just like en-
gines. For the sake of clarity, however, a single-cylinder
single-stage unit will be described. The compressor consists of
an oil-filled crankcase which houses the crankshaft, a connect-
ing rod and piston, a cylinder that has external cooling louvers,
and a head with intake and discharge valves. The receiver (air
tank) is the vessel for compressed air containment.
When the crankshaft rotates to its low position, air is drawn
into the cylinder through the intake valve. As the piston begins
its upward thrust, a positive pressure in the cylinder closes the
intake valve. The exhaust valve is opened and the air being
compressed is forced into the receiver. As the piston starts its
downward stroke, new air is pulled in and the cycle is repeated.
Just as an engine has rings on the piston to aid in compres-
sion, so does the compressor. The cylinder is lubricated by the
oil in the crankcase and the rings, assisted by the oil, make a
seal against the cylinder wall.
The intake and discharge valves on the cylinder head, while
accomplishing the same result as an internal combustion en-
gine, are quite different. In an engine, the valves are timed to
the crankshaft operation and open and close accordingly. The
compressor relies on the compression and decompression of
air in the cylinder to actuate the valves.
-------
Support Systems 783
Sticky intake valves will either prohibit or reduce air intake
and sticky discharge valves will reduce or prevent compres-
sion. If the intake is stuck open, air will be forced back to the
atmosphere. On the other hand, a stuck exhaust allows air to
move into the receiver on half of the stroke and draws it back
into the cylinder on the other half.
If the compressor fails to build up pressure, place your hand
over the intake. It should draw your palm down. Check the
discharge in the same manner to see if air is expelled. The
problem could be in the unloader, however.
Many units have air unloading intake valves and hydraulic or
centrifugal unloaders. In a compressor that runs continually,
the intake valves are unloaded when the high pressure point is
reached. A small copper line connects the valve to the un-
loader and then to the air receiver. The unloader may be either
electrically or mechanically actuated. The unloader operates at
high pressures and allows the pressure of the receiver to com-
press a diaphragm in the intake valve and hold it open. With
the valve in an open condition, air is pulled in and expelled
through the air intake. After the compressor cycles to a non-
compressing mode, the sound is similar to a dog panting.
When pressure in the receiver diminishes, the valve is allowed
to close and compressing resumes.
The hydraulic and centrifugal unloader are used in compres-
sors that stop and start frequently. When in a static condition,
the air valve of the unloader allows receiver air pressure to
hold the intake valves open. As the compressor starts, the oil
pump in the crankcase starts to pump. After pressure in-
creases sufficiently, the loader is activated allowing the intake
valve to close. So with the centrifugal, the unloading valve
closes as compressor speed picks up. A faulty unloader will
not let the intake valves remain open and the compressor will
have to overcome the air pressure of the receiver when start-
ing. Most compressor prime movers cannot develop the start-
ing torque needed to overcome the pressure.
When selecting a location for the air compressor, locate it as
near as possible to the point where compressed air is being
used. The compressor must have an ample supply of cool, dry,
and well circulated air. Compressors with fly wheels that assist
in air circulation over the cooling fins of the compressor should
be installed no closer than twelve inches (30 cm) from a wall.
This will allow for ample air circulation. Make sure pulleys and
drive belts are enclosed in an OSHA-approved belt guard as-
sembly.
Air intake to the compressor should be clean, cool, and dry
to provide satisfactory operation. An air filter is installed on the
compressor intake. (Service in accordance with manufactur-
er's recommendations.) The air filter will usually be of the dry
type but if the compressor is in a location where considerable
dust and other contaminants are prevalent, an oil bath filter
may be used. If it is necessary to pipe to the intake air from a
cool air source, the intake pipe should be one pipe size larger
for each eight feet (2.4 m) beyond the intake port of the com-
pressor. When the intake air is drawn from the outside, a hood
should be installed to prevent rain from entering the intake of
the compressor. Discharge piping should be of sufficient size
that the pressure drop between the receiver and the point of
use is less than 10 percent. Use pipe fittings that offer the least
resistance to air flow (long radius elbows and gate valves).
Discharge piping should be sloped away from the receiver and
a drop leg installed at its lowest point. This allows condensa-
tion to drain away from the receiver so it can be drained off at
the top leg valve.
Compressors are designed to operate at certain minimum
and maximum speeds. When making changes, consult your
owner's manual or factory representative for the operating
guidelines for your machine.
Crankcase oil should be of a given SAE viscosity depending
upon ambient temperature. The type of oil used may vary with
operating conditions (check your owner's manual). Change oil
as specified by the manufacturer. Oil-less compressors do not
use oil as a sealant to piston rings. In some cases, a carbon
ring is used, having a low friction resistance.- Another method is
teflon rings. The main purpose is to provide air that is free of oil
vapor that may gum pneumatic contols. Oil in the receiver can
cause a hazardous situation (possibility of combustion). There-
fore, expel any water and oil from the receiver on a regular
basis.
29.73 Air Systems
When we think of air systems, we usually divide them into
two basic groups:
1. Control — used for pneumatic instruments; and
2. Power System — operating high-volume pneumatic tools.
There are a number of components associated with air sys-
tems whose purpose we should understand.
FILTER. A device connected into the air line to trap solid or
liquid particles that can contaminate and damage equipment.
The selection of the filter requires consideration of need, de-
pending on elements to be removed from the air. Other con-
siderations include:
1. CFM of air to be filtered;
2. Working pressure;
3. Pressure drop across the filter; and
4. Filtration size. The element is usually measured in
thousandths of an inch or microns (0.001 inch equals 25
micrometers (microns)).
PRESSURE REGULATOR. An adjustable valve used to re-
duce air pressure from the receiver level to that required by the
air-using equipment and to maintain it automatically. The reg-
ulator may be installed near the tank or at the point of connec-
tion for the equipment.
LUBRICATOR. A device used to provide constant feeding of
oil mist into the air stream for the lubrication of air-powered
equipment or tools.
Air taken from the atmosphere by the compressor contains
many impurities including water vapor, dust, oil, and smoke.
These contaminants can cause rapid wear, clogging, and erra-
tic operation of air tools, instruments, cylinders, and valves.
There are various types of air-cleaning equipment that can
help insure efficient operation of air-powered equipment.
AFTER COOLERS. Used to remove water vapor from the
compressed air by lowering the temperature of the air and
causing the water vapor to condense into droplets for easy
removal. After coolers are of the following types:
1. Water-cooled types use an external heat exchanger and an
external water supply to cool the compressed air; and
2. Air-cooled types use ambient air to cool the compressed
air. Air circulates over and between the cooling louvers of
the heat exchanger.
REFRIGERATED AIR DRYERS. These dryers are used to
reduce the compressed air temperature to as low as 35 de-
grees F (1.7°C) to remove greater amounts of water than the
after cooler. Piping dryers close to the work allow for cooling
-------
784 Treatment Plants
only that portion of air needed for a specific function. Installing
an after cooler before the dryer may add to its effectiveness.
A separator/drain trap allows for easy removal of condensed
waters and contaminants. Some systems use an automatic-
draining condensate trap. When the condensed water volume
is sufficient, it activates a float-operated valve. Condensate is
ejected from the system by the compressed air. Automatic
traps should be inspected frequently to ensure proper opera-
tion.
Where further moisture removal is needed (as for control
instruments), compressed air, after passing through the after
cooler and dryer is passed through a filter of absorbent mate-
rial. Compressed air used for control instruments must be of
the highest possible quality. This air must be free of water, oil,
water or oil vapors, and all particulate matter. A typical system
includes after cooler, refrigerated dryer, and absorbent filter
(no lubricants are used). Silica-gel is a common filter element.
When the element reaches its saturation point, a moisture-
sensitive tab changes color indicating that replacement is
needed.
The pipe size used in air distribution systems should be
large enough to keep the pressure drop between the tank and
the point of use at a minimum. The main air line should be no
smaller than the compressor outlet. All outlets should be taken
from the top of the main line (tees facing up) to keep moisture
out. Check all piping and fittings regularly to avoid leaks in the
system. Filters, regulators, and other accessories should also
be properly maintained.
All hose bibs for high-pressure air should be marked in ac-
cordance with current regulations. In shops and buildings
where air may be used for other than power applications, it
should be regulated to 30 psi (2.1 kg/sq cm). This pressure is
safe and adequate for use to clean equipment and other shop
uses.
Never direct a high-pressure air hose on yourself or a fellow
employee. Minute particles in the air can be forced into the
skin. Any opening to the body, including cuts, should be
safeguarded against pressurized air. Air entering the blood
system can cause serious medical problems and may lead to
death.
Compressed air is a versatile form of power, use it wisely
and safely. When air is used to blow dust and dirt from em-
ployees' clothing, the air pressure must not exceed 10 psi (0.7
kg/sq cm).
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 795.
29.7D What problems can be caused by sticky valves in a
reciprocating compressor?
29.7E What type or kind of air should be fed to a compres-
sor?
29.7F How is a compressor protected if the intake air con-
tains considerable dust or other contaminants?
29.7G List the major components for power air systems.
29.7H Where should outlets from the main line of an air sys-
tem be taken?
29.71 What is the main difference in components in air sys-
tems used for power tools as compared with air sys-
tems used for pneumatic control?
JncLof \J0bov\ % tfiiMfiovgL
Please answer the discussion and review questions before
continuing with Lesson 4.
DISCUSSION AND REVIEW QUESTIONS
(Lesson 3 of 4 Lessons)
Chapter 29. SUPPORT SYSTEMS
Write your answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 2.
13. What is the purpose of the filters in the diesel fuel system?
14. What are the advantages of air-cooled diesel engines as
compared with water cooled types?
15. What is the major difference between the burner orifices
for methane gas and those for natural gas?
16. Why is adequate ventilation necessary in wastewater
treatment plants?
17. What could be the causes of a compressor oil gage failing
to indicate pressure and how could each cause be cor-
rected?
18. Why should you never direct a high pressure air hose on
yourself or a fellow employee?
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CHAPTER 29. SUPPORT SYSTEMS
(Lesson 4 of 4 Lessons)
Support Systems 785
29.8 WATER SYSTEMS
29.80 Avoid Cross Connections9
The water systems in a wastewater treatment plant are dis-
tinctly divided into two separate systems. Number 1 is the fresh
or potable water supply for the building plumbing needs.
Number 2 is the reclaimed water used for washdown, irriga-
tion, and cooling water for pump seals and packing. You must
safeguard against cross connections between the two sys-
tems. Both systems can, however, be used as a joint water
supply and limit the amount of fresh water used.
29.81 Fresh Water Systems
Sometimes the quality of fresh water delivered to various
parts of the treatment plant may be questionable, especially if
the source of water is a well at the plant site. If your laboratory
tests indicate a high coliform count and the water is to be used
for drinking water, disinfection may be required. A high count
can result from contaminated water lines either through cross
connections of water systems or from old piping systems.
Fresh water should be tested periodically to determine that it is
satisfactory. A monthly testing program should be adequate for
most plants. If a high coliform count is detected, closer inter-
vals of testing should be conducted.
One method of water disinfection is accomplished by pass-
ing water through a two-layered quartz tube. Inside the tube is
a high intensity ultra-violet lamp. As water passes through the
tube at a pre-determined flow rate, the ultra-violet light kills any
pathogenic organisms present. This system is of relatively low
cost and can be easily installed. Chlorination may also meet
your needs to provide a safe water supply. Consult with
chlorinator manufacturers to match equipment with your
needs.
Another method of providing safe drinking water is to pur-
chase bottled water. This is the safest method of providing a
source of drinking water in treatment plants.
29.82 Types of Hydro-pneumatic Systems
There are three basic types of hydro-pneumatic water sys-
tems. Standard air-cushion, add-air, and vent-air. The water
system consists of a turbine pump and water tank with the
necessary pressure switches, probes, or floats that control the
tank pressure and water heights.
29.820 Standard Air-Cushion
In this system, the on/off operation of the pump is controlled
by pressure alone. When the empty tank is filled, the air en-
trapped in the tank is compressed. The pump continues to
pump until the air is compressed to a specific pressure. (At this
point let us use 60 psi or 4.2 kg/sq cm.) A pressure switch that
controls electric power to the motor control relay opens when
the specified maximum pressure is reached.
As water is used from the tank, the water level and air-
cushion pressure decrease to a pre-determined point (20 psi or
1.4 kg/sq cm). The pressure switch closes at this minimum
point and starts the pump to complete the cycle. The type of
switch used in this case is a differential-pressure switch. The
on and off points can be adjusted to provide maximum/
minimum pressures. Sometimes two independent switches are
used.
As long as there is an adequate air cushion, the system
works quite well. Over a period of time, the air that forms the
cushion is gradually absorbed by the water in the tank. Without
an adequate cushion, the pump cycles on and off at short
intervals. The tank has more water and less air. To correct this
problem it is necessary to empty the tank completely, thereby
replenishing the air in the tank.
29.821 Add-air System
One form of add-air system uses an air charger to maintain
proper pressure and level in hydro-pneumatic tanks. The air
charger is connected at approximately one-half the tank
height, with a tube leading to the pump suction. The air charger
works in conjunction with the pump to maintain an air cushion.
When the pump starts, a low pressure area is created at the
pump suction. The pressure in the tank is greater than that at
the pump suction and water flows through the charger venturi.
It
9 Cross Connection. A connection between drinking (potable) water and an unsafe water supply. For example, if you have a pump moving
nonpotable water and hook into the drinking water system to supply water for the pump seal, a cross connection or mixing between the two
water systems can occur. This mixing may lead to contamination of the drinking water.
-------
786 Treatment Plants
To Source of
Compressed Air
Solenoid
Velve
Probe
Pressure
Sensors
At water ii withdrawn,
pressure falls. Whan
pressure raaehaa
preset low veiu*,
pump starts.
Pump
w
Check Valve
Distribution
AUTOCON
0U0TR0L
To Source of
Compressed Air
Solenoid
Valve
Probe
Pressure
Sensors
Whan watar reaches
rafaranca level. pumf
steps.
. Watar absorbs air. heaping
pressure down.
Pump
Distribution
Check Valve
AUTOCON
DUOTROL
To Source of
Compressed Air
Solenoid \ (j
-------
Support Systems 787
A partial vacuum results and air is drawn through the air inlet
valve into the charger body. A deflector causes the water to
flow down the walls of the charger and the water and air are
separated. As air accumulates in the charger, the water level
decreases until a float valve closes. This stops the water flow
from the tank to the pump suction. If the valve failed to close,
the pump would draw air and become air-bound.
With the valve closed, the air in the charger is compressed to
the same pressure as in the tank and remains so until the
pump stops. When the pump stops, the pressure at the pump
suction becomes equal to the tank pressure. The float in the
charger opens and water flows from the tank into the pump. Air
that was accumulated in the charger is forced out and into the
pressure tank. Each time the pump goes through its on/off
cycle the charging action is repeated. This is repeated until the
water level in the tank is below the charger tank inlet. When the
water level rises above the inlet, it automatically begins to
replenish the air cushion.
Another method to add air to a water tank is from a com-
pressor (Fig. 29.39). The compressor can be an integral part of
the system or air can be supplied through a solenoid and con-
nected to the "plant air" system. The controlling device for
water tank level is a probe in conjunction with a pressure
switch. When the pressure in the tank reaches its low level
point, the pressure switch closes and starts the pump. The
pump continues to operate until the water level reaches the
high level probe. A time delay insures that the level is well up
on the probe. A circuit is completed to the "off/pump" relay and
"add-air" relay. If the pressure in the tank is not at its proper
level, the air solenoid opens and adds air as needed.
As long as the add-air relay is closed, air will be added to
compensate for decreasing pressure caused by water with-
drawal. After the water level recedes from the probe, the
"add-air" relay opens and will not allow external air to be ad-
ded. The water level and tank pressure decrease until the low
pressure setting is reached and the pump cycle starts again.
29.822 Vent-air System
The vent-air system is used to prevent air binding when a
large amount of air is trapped in the water being pumped into
the pressure tank. This is quite common when a deep well
pump is used. One type of pump control (Fig. 29.40) is accom-
plished with a probe and pressure switch similar to the "add-
air" system. When the tank pressure reaches its low level, the
pressure switch closes and the pump starts. The pump con-
tinues to run until the water level reaches the "pump/off"
probe. Any excessive air that has built up in the tank is vented
through a pressure relief valve at the top of the tank. The relief
valve can be adjusted to obtain optimum operating pressure.
The cycle is completed when the level reaches the low pres-
sure "pump/on" point.
A second type of control is illustrated in Figure 29.40. The
control system functions as described by notations in the
cross-sectional drawings of the hydro-pneumatic tank.
The three previously mentioned systems should provide
nearly trouble-free operation for many years. Regular mainte-
nance is required on the turbine pump and motor, however.
The motor bearings should be lubricated on an annual basis if
the motors are subject to intermittent operation. Pump packing
should be checked monthly and adjusted as needed to prevent
leakage around the pump shaft. The standard air-cushion sys-
tem will require periodic emptying of the tank to replace the
air-cushion. Problems are infrequent in the air-charging add-air
system. However, the float may stick and cause the pump to
become air-bound. If this is a recurring problem, replacement
of the air charger is usually necessary.
In the system where a probe is used, it often becomes cor-
roded and becomes a poor conductor of electricity. This allows
the tank to fill to increasingly high levels. Remove the probe
and clean with steel wool. New teflon-coated probes can al-
leviate this problem also.
Autocon
Duotrol.
(a)
(b)
(c)
LCVEi DROPS IN TANK
REDUCING WATtft PRCSSUftf
Plf-SCT LOW
Excess Air
Blow Off
AIR ENTERING FROM
WELL CASINO
(continued on next page)
Fig. 29.40 Vent-air system
(Permission of Autocon Industries, Inc., Plymouth. Minnesota)
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 795.
29.8A What are the two separate water systems in a waste-
water treatment plant?
29.8B List the possible sources of fresh or potable water for a
wastewater treatment plant.
29.8C What is a hydro-pneumatic water system?
29.83 Backflow Prevention
29.830 Need for Backflow Prevention
The reason for backflow prevention is to prevent potentially
contaminated water from contaminating the potable water sys-
tem. Where fresh water is used for pump packing or seal cool-
ing, there is a possibility of the pump developing a higher water
pressure than that supplied by the water system. Therefore, it
is essential to have some type of device to check the backflow
of coolant liquid.
-------
788 Treatment Plants
Vent
Solenoid
Valve ff
Probe
Pressure
Sensors
As watar is withdrawn,
praisura falls. Whan
pressurereaches
prasat low vaiua,
pump starts.
Pump
Distribution
Check Valve
AUTOCON
DUOTROL
Vent
Solenoid
Probe
Pressure
Sensors
Air it pumpad in
from casing along
with watar. .
Whan watar reaches
I. pump stops.
Pump
Distribution
Check Valve
AUTOCON
DUOTROL
Vent
Solenoid
Valve
Probe
Pressure
Sensors
Whanavar prassura in tank
aicaads pra sat high value,
air it blown off.
Pump
Distribution
Check Valve
AUTOCON
DUOTROL
Fig. 29.40 Vent-air system (continued)
(Permission of Autocon Industries. Inc., Plymouth, Minnesota)
-------
Support Systems 789
29.831 Devices
AIR GAP.10 Where there is a possibility of connecting a
municipal water system to a contaminating source, an air gap
between the two systems is required. The air gap between the
tank water level and the discharge of the control valve should
be at least six inches (15 cm). This eliminates any possible
chance of contact between the systems.
CHECK VALVE (refer to Section 29.225, "Check Valves").
The check valve prevents backflow by a mechanical means.
As long as the flow is in the direction of the check and at a
pressure greater than the opposing pressure, water will flow. If
at some point those characteristics change, the checking de-
vice (clapper, ball, disc) will close and seat; thus preventing a
reversal of flow. Most regulatory agencies require greater pro-
tection than what is provided by a simple check valve that
could become stuck in the open position. Consult your local
health codes before making any potential cross connections.
Checking devices must be inspected regularly to determine
that they are functioning properly. Where the valve is used in a
cooling system for a pump, it should be inspected at least
semi-annually. Usually a pressure regulator, with strainer, is
used ahead of the check. If heavy sedimentation is apparent,
the time interval for inspecting the check valve should be more
frequent.
ANTI-SIPHON VALVE. This valve is most commonly found
in irrigation systems. In the event that a lawn becomes flooded,
it will not allow the water to siphon back into the fresh water
system. Municipal water departments have a requirement that
anti-siphon valves be installed in irrigation systems.
When using water other than fresh No. 1 water (potable or
drinking water), an anti-siphon valve will prevent flow reversal
which may cause pumps to run backwards or flooding of the
pump water supply.
29.84 Reclaimed Water
Due to the emphasis on water conservation and knowing
that water is a depletable resource, there has been continued
research in the use of reclaimed wastewater treatment plant
effluent. Most of us in this field have been reclaiming a small
portion of our effluent to be used for in-plant purposes for
years. Because of the possibility of contamination or the
spread of diseases, it is important that the reclaimed water be
chlorinated. Some localities have approved the use of No. 2
water (reclaimed water that is not suitable or approved for
drinking) for irrigation and many treatment plants use it for the
irrigation of plant grounds. Since the use of reclaimed water
outside the plant has not been accepted totally, this section will
concentrate on in-plant uses.
Reclaimed plant effluent can be used effectively to cool
pump shaft packing and mechanical seals. Possibly the
biggest drawback in this area is obtaining water that is rela-
tively free of sediment and suspended materials. Strainers
must be cleaned more often and the supply piping tends to
narrow and plug, especially when small (1/4-inch or 7 mm)
pipes are used. A spray of reclaimed water can control foaming
on aeration tanks. Once again, the spray nozzles become
plugged frequently.
The quality of the effluent and the form of filtration or screen-
ing used both affect the potential uses of reclaimed effluent. Do
not use hoses on a reclaim water system and then on a fresh
water system. One way to keep them separate is to use two
different hose sizes and hose bibs. Test reclaimed water and
ensure a low coliform count. If the count is high, increase
chlorine dosage. Post signs at reclaimed water hose stations
(DO NOT DRINK — CONTAMINATED WATER). Although it is
good for area washdown, make sure that fellow employees
wash exposed body parts thoroughly after coming into contact
with reclaimed water.
Do not use this water for boiler make up water. The contam-
inants in the water will adversely affect the boiler system. Prob-
lems include plugged valves, corroded water jackets, and ex-
cessive sludge buildup.
One important application of reclaimed water is conveying
water with a high concentration of chlorine to the dosage point
for effluent chlorination. Reclaimed water may be used as a
dilution or washing means in sludge dewatering systems. Use
reclaimed water when it will work for a particular application,
but remember its limitations. Do not inter-connect reclaimed
and fresh water systems (cross connection).
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 795.
29.8D List three backflow prevention devices.
29.8E What is an "air gap"?
29.8F List five in-plant uses of reclaimed wastewater.
29.9 GROUNDS UPKEEP AND MAINTENANCE
29.90 Need for Good Appearance
One area of need that probably has not been given
adequate attention in the past is general plant grounds main-
tenance and appearance. Since this topic covers a number of
areas, this section will highlight a few of these points. Many
people judge your performance on the basis of the appearance
of your plant. A pleasant-appearing plant is as valuable as a
good neighbor and an important part of an effective public
relations and education program.
29.91 Yard Lighting
There are a couple of objectives to be met when yard or area
lighting is concerned:
1. Provide adequate illumination for work being performed;
2. Provide energy-efficient lighting (greatest illumination per
watt of power expanded); and
3. Install fixtures that require minimal maintenance.
A number of changes have been made over the years to
meet our changing lighting needs. With power costs escalating
at a rapid rate, it is important that we efficiently use all power
consumed. The standard incandescent light bulb, while being
cheap to produce, does not convert energy to light econom-
ically. An incandescent bulb will provide approximately 18 lu-
mens per watt. (Lumen. The unit of luminous flux. The lumi-
nous flux emitted from one international candle.) The common
fluorescent will provide almost 80 lumens per watt.
Most of the new yard lighting systems use either mercury
vapor or high pressure sodium (HPS) lights. The main reason
10 Air Gap. An open vertical drop, or vertical empty space, between a drinking (potable) water supply and the point of use in a wastewater
treatment plant. This gap prevents back siphonage because there is no way wastewater can reach the drinking water.
-------
790 Treatment Plants
is a greater amount of illumination per watt expended. The
"off-yellow" lights that you see being used along streets are
HPS. In this area the monochromatic light developed is not
objectionable. The advantage to HPS is that it will develop 80
percent more lumens than mercury vapor (MV) (95 lumens per
watt). HPS lights can cut illumination costs by one-half. If the
light produced by HPS does not fit your needs, mercury vapor
lights are very effective. Average lumens per watt output is 42.
If your plant is thinking of expanding, or if your yard lighting
power costs are higher than you would like, perhaps some of
the new innovations in lighting would be the answer.
In terms of maintenance, yard lighting is minimal. When it is
necessary to replace fixture lamps, use a lighting scaffold or a
boom truck with bucket. Make sure the power is off and locked
out before starting. Inspect for a loose or broken socket, dam-
aged reflectors, loose electrical connections, corroded con-
duits and fittings, and clean the lighting diffusers. If the fixture
uses a photoelectric cell, turn on the power and place a shop
towel over it. This should initiate power to the lamp ballast. If
the fixture doesn't light, replace the photo cell. With a new lamp
and cell, it should light. Do not attempt additional troubleshoot-
ing or repair unless you are qualified to do so. Usually this
maintenance is carried out by an electrician. Electricians know
how to protect themselves and others as they solve electrical
and lighting problems.
29.92 Enclosures
With respect to enclosures, it is necessary that we use them
as a first line of defense against intrusion. A six-foot {1.8 m)
high cyclone, chain-link fence with barbed wire strands along
its top looks formidable to a casual eye. We must control the
access to our facilities. We can ill afford to have the public
wander through our plants. We must protect the public from
possible injury as well as protect our investment in buildings
and equipment from theft and vandalism.
There are security systems that can add to the effectiveness
of the fence. Some fences are wired to alarms that are sensi-
tive to vibration that could represent an intruder. Gates can use
magnetic switches that activate if the gate is opened without
first turning off the alarm switch. An infra-red light beam, hav-
ing a transmitter and receiver, can be focused along the
perimeter or outside of the property. An interruption of the
beam will activate an alarm. Since gateways are the natural
entrance to the plant, they may be the main point of entrance.
There are a number of electronic gate activators to control
access. Some use a plastic card, similar to a credit card, or a
digital number sequence that can be changed at random, or a
radio signal to operate the gate.
Regardless of what we do, we can only keep the honest
person honest. Anyone intent on obtaining access, will. What
we can do is keep the enclosure in good repair, lock all gates
that are not in use, and control the keys that lock them. In
terms of maintenance, the gate causes the most problems.
Gate hinges should be kept well oiled and the cross connection
bolts should be adjusted as needed to prevent the gate from
dragging.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 795.
29.9A List three objectives of an effective yard lighting sys-
tem,
29.9B What items would you consider when maintaining a
yard lighting system?
29.9C What is the purpose of enclosures?
29.9D How would you maintain a treatment plant gate?
29.93 Roadways and Walkways
Asphalt paving makes up the majority of plant roadways.
There are a few things you can do to make asphalt paving last
a long time. The extent of time that asphalt paving will serve
you was determined greatly by the contractor who installed it. If
you can answer "yes" to the following questions, then you
have a good paving installation to maintain.
1. Was the soil stabilized and adequate subgrade material
used?
2. Was the asphalt mix designed for its application?
3. Was the temperature of the mix within specifications when
laid (a minimum of 235 degrees F (113°C) for asphaltic
mixtures)? and
4. Was the asphalt properly rolled and compacted?
If the subgrade material was not adequate and the asphalt
mix not designed for your use, it will break up. You can, how-
ever, control the routing of heavy trucks and equipment to
specific areas. When asphaltic paving is laid, it must be hotter
than 235 degrees F (113°C) to insure proper laying. If the mix
did not contain the proper proportions of aggregate, oil, and
asphalt, it will not adhere or stick together properly. Even if the
asphalt is of designed thickness, improper compaction can
greatly reduce its effective life span. The most signficiant
shortcoming is low cohesion of the materials used. This
causes an open porous texture that is susceptible to the en-
trance of water and air. Water will enter the pores of the mix
and, as tires pass over it, the water will be forced under pres-
sure through the voids of the asphalt. This can result in loss of
bond and the paving will ravel. Air can enter poorly compacted
asphalt paving and cause rapid oxidation. This will increase
the brittleness of the paving.
Asphalt paving loses a certain amount of oils that must be
replaced. Resealing should be done when this is first noticed.
A thin layer of asphalt oil is evenly spread over the paving. A
small amount of sand is usually added to prevent tracking of
the oil. If you have low spots in the paving where water can
accumulate, have the spots repaired. Standing water invites
unwanted problems. That is why yard drainage must be
adequate.
Concrete walkways are also controlled to some extent by the
contractor who installed them. Here are a few ways we can
maintain walkways. Keep the sidewalk free from algae. A solu-
tion of soap and chlorine (clorox) will remove algae with a small
amount of scrubbing and prevent immediate algae regrowth. A
slippery walk can be etched with muriatic acid and water. One
part acid to ten parts water will do the job. Do not try this
procedure unless you have had experience doing it. A smooth
concrete finish can be lightly sand blasted to roughen it up to
reduce slipperiness. There are also non-skid coatings that can
be applied to the concrete. In most instances, this will be the
preferred solution since they can be easily applied by plant
personnel.
Do not allow weeds or grass to grow in the cracks of the
concrete. Just as a tree root can split a large rock, weed roots
can cause the same effect. Be on the lookout for concrete
sections that have risen, dropped, or tilted. Eliminate this trip-
ping hazard by replacing that section of walkway.
All sidewalks should be kept clear. If you must set an object
down, set if off to the side. Water hoses are a potential tripping
hazard when left lying about. Keep them rolled and on their
racks. Since water is our process product, be aware of it
Water and water spray on concrete is a link in the chain of
events that lead to one of our industry's most common acci-
dents — slips and resultant falls.
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Support Systems 791
29.94 Landscape
29.940 Purpose of Landscaping
Landscaping enhances the appearance of any plant site.
Because our treatment facilities have a certain stigma, it is
important that we enhance the surrounding grounds. When
visitors enter a wastewater treatment plant, many may have
preconceived thoughts. A well manicured lawn, trimmed
shrubs, along with a variety of ground cover will provide a
positive "first impression." Take pride in your treatment plant
and it will be apparent to all who enter your gates.
When a plant is designed and built, landscaping is a very
important part of the construction. Usually landscaping is well
done by professionals. Our responsibility is to maintain that
investment and appearance.
The following paragraphs will shed light on how to best
achieve adequate landscape appearance and yard mainte-
nance.
29.941 Irrigating
If your plant is one of many that enjoy a beautiful green lawn,
you know the importance of proper watering and water cover-
age. If your sprinkler system was installed by a competent
private contractor, chances are it was engineered to provide
adequate lawn coverage. A good indication that coverage is
inadequate is a non-uniform appearance of the lawn. The
sprinkler drops the greatest amount of water near the head and
very little at its outer limits. The small amount of water doesn't
penetrate very deep and the grass roots are very shallow. The
weak grass allows for weeds such as dandelion, sorrel, and
plantain, that can take less water than typical lawn grasses. On
the other hand, spots that are subject to too much water invite
sedge, crabgrass, chickweed, and annual blue grass. The best
answer to unequal water distribution is to alternate the
sprinklers and wetting pattern.
When and how often do you water? Grass shows its need for
water first by loss of resilience. When you walk on grass need-
ing water, there is no spring back. Next, the color changes from
a fresh green to a dull gray-green. The grass tops turn brown
and die in the next stage. Ideally you should water before the
no-spring back sign begins. After living with a lawn for a while
you can sense that timing. Deep watering once a week is
recommended. This causes plants to root deeper. As water is
drawn from the soil by the grass roots, more air enters the
ground and a better growth environment is created. Long slow
watering will allow for good penetration. A three-hour applica-
tion is quite common. Depending upon the type of soil you
have, water penetration will be approximately one inch during
the proper watering period.
Some of the reasons for not using light, frequent waterings
are:
1. Greater water use,
2. Shallow rooting of grass,
3. Encouragement of shallow-rooted weeds,
4. Greater soil compaction, and
5. Rapid buildup of salinity due to lack of leaching.
29.942 Controlling Weeds
If we always grew only what we sowed originally in a lawn,
the task of keeping a lawn would be easier. The trouble is that
soils are generally full of dormant weed seeds waiting for the
right conditions to germinate. Weed seed is also present in
lawn seed mixtures to a small degree. Wind and birds help
bring in new seeds. We will always have weeds. The question
is how to get rid of them. There is a wide variety of chemical
weed killers (herbicides) available. Most herbicides are selec-
tive and control a specific type of weed. They fall into two
classes, broadleaf and grassy.
The term "broadleaf" is used to describe non-grassy weeds.
A few of the familiar ones are: dandelion, curly dock,
chickweed, bur clover, oxalis, knotweed, and English daisy.
The hormone-type weed killers such as 2,4D and 2,4,5-TP are
the best known of the herbicides. They kill broadleaf plants by
speeding growth so the plants literally grow themselves to
death. Depending on the species, weeds may require one to
four treatments to obtain a good kill. This type of chemical is
absorbed by the leaves and carried through the system to the
roots. Both tops and roots are killed. Weeds treated with chem-
icals show curled and twisted stems in the first stage. Finally,
the roots are expanded and ruptured and the entire plant dies.
Select a weed killer that kills the entire plant. Burning the leaf
may indicate a kill, but a vigorous root system could survive
and cause regrowth.
The grassy weeds are also all too familiar: Burmuda grass,
quackgrass, nutgrass, velvet grass, and orchard grass. One
thing to remember if you are applying a chemical to control
grassy weeds: it can also kill the lawn grasses. Therefore, it is
best to do controlled spot killing in the affected areas. Spot
application of dalapon or amitrol will generally take care of
local grasses. Be sure to follow label directions closely. If your
lawn is overcome by grassy weeds, it may be necessary to use
a soil fumigant. The fumigant chemically kills almost everything
in the soil and leaves it sterile. Three commonly used fumi-
gants are Vapam, Mylone, and calcium cyanamid. If applying
the chemical yourself, follow directions closely.
If you are faced with a large weed-control problem, hire a
professional. There are commercial companies who are
knowledgeable and capable of handling your problem. When
faced with weeds that grow along chain link fences or dirt
around buildings, a light application of diesel fuel will do the
trick. All you need is a handheld pressure sprayer to insure
adequate coverage. Do your spraying on calm days without
wind. The objective is to kill only the selected weeds and gras-
ses. When the wind kicks up, discontinue application until the
wind dies down again.
29.943 Fertilizing
Grass has a continual need for nitrogen. Nature does a poor
job of supplying that nutrient in quantities necessary to keep
plants growing thick, green, and dense. If a lawn turns yellow
or pale green or if grass becomes thin and weeds come in, it is
-------
792 Treatment Plants
probably an indication that nitrogen is needed. If you apply a
fertilizer containing nitrogen and the lawn does not respond,
then suspect other trouble such as disease, lack of air, or
grubs and other larvae. The use of reclaimed water for lawn
irrigation substantially reduces the need for fertilizers.
When you purchase a fertilizer, the three-number formula
such as 6-4-2 indicates first the percentage of nitrogen, second
the percentage of phosphorus, and third the percentage of
potassium. Consider the phosphorus and potassium as a
bonus to lawn feeding. The ever-important nitrogen comes in
several forms. Some types are slow acting and may take a
number of weeks or months for the nitrogen to be fully used by
the lawn. Other forms are fast acting and immediate results
can be seen in just a few days. When reading labels, re-
member not all organics are slow acting and not all inorganics
are fast acting. The rate of availability grades down from im-
mediate to gradual over a period of months.
Here are the meanings of the words on the fertilizer label
that refer to nitrogen:
NITRATE. The form of nitrogen that is available to the plant
as is, regardless of temperatures.
AMMONICAL OR AMMONIC. Available to plants when
converted by bacteria to nitrate. Speed of conversion depends
upon soil temperatures.
ORGANIC. Describes sludge, cottonseed meal, and any
other materials that must first be broken down by bacteria.
UREA. A synthetic organic that water and the enzyme
urease change immediately to inorganic ammonia. The am-
monia is then converted to nitrate.
UREA FORM OF UREA FORMALDEHYDE. A nitrogen fer-
tilizer that has been specially compounded for slow release.
How often do you feed a lawn? The color of the grass can
show nitrogen need. An easy method used to determine need
is the number of times per week or month that the lawn needs
cutting. At the start, if cuttings were done every five to eight
days and then extended to eight to fourteen days, more fer-
tilizer is needed. Depending on the fertility of the lawn soil,
grass will show a loss of color in four to eight weeks after
fertilization. Thus, the feed-when-it-needs-it method could re-
quire fertilizer from three to twelve times a year. If fertilizing is a
problem, then feed the lawn adequately in the spring and fall.
This procedure may not be quite as effective as desirable, but
the lawn should do quite well.
How much do I feed the lawn? A rule of thumb is one pound
actual nitrogen for every 1,000 square feet of lawn per month
(this applies only to the growing months). To figure actual ni-
trogen needs, take the percentage stated on the label times
the weight of the fertilizer. For example a 20-pound bag (it
could be liquid) containing 15 percent nitrogen will yield ap-
proximately 3 pounds of nitrogen or enough to feed 3,000
square feet for a month (20 pounds times 0.15 equals 3.0
pounds nitrogen).
Application of fertilizer should be distributed as evenly as
possible. The most effective applicator is a hopper spreader.
Four common mistakes when using the spreader are:
1. You cannot turn an open hopper inside a previous turn. The
square corner will allow for excessive fertilizer application at
that point.
2. You cannot stop and start with the hopper open. Walking at
an unsteady pace will do the same thing.
3. Do not overlap with fertilizer.
4. Do not make 180-degree turns. Since one wheel is still
driving the sifter, dispersal on the turn is very erratic.
After applying fertilizer, water the lawn heavily. Most fertiliz-
ers require a soaking to get the action started. This also pre-
vents burning the grass blades.
29.944 Mowing and Pruning
Mowing and pruning are very important. Lawns must be
mowed and edged at regular intervals to maintain their ap-
pearance. Trees and shrubs should be kept pruned so they
won't interfere with the operation and maintenance of the plant,
as well as to appear neat.
29.95 Surface Water Drainage
Depending on the location of your plant, drainage of storm
water runoff and other surface water runoff can be very impor-
tant. No one wants unwanted water running into buildings or
flooding roadways and walkways. Provisions to handle this
water should have been made when the plant was designed.
Maintenance of these facilities requires keeping all curb drains
and drop inlets free of leaves and other debris. Also, the storm
drain lines must be clear and ready to handle any runoff. Sump
pumps in the drainage system should be included in a regular
preventive maintenance program, depending on the type, size,
and frequency of use of the pumps.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on pages 795 and 796.
29.9E What factors are essential to have a good paving in-
stallation?
29.9F What items would you consider in a walkway mainte-
nance program?
29.9G How do weed seeds get in a lawn?
29.9H How could you tell if a lawn needs nitrogen?
not- of litioon 4 d4 \M5ori&
Please answer the discussion and review questions before
working the objective test.
-------
Support Systems 793
DISCUSSION AND REVIEW QUESTIONS
(Lesson 4 of 4 Lessons)
Chapter 29. SUPPORT SYSTEMS
Write your answers to these questions in your notebook be-
fore continuing. The question numbering continues from Les-
son 3.
19. How can water from a well at a treatment plant be disin-
fected?
20. What is the purpose of backflow prevention devices?
21. Why must reclaimed wastewater be chlorinated?
22. How important is the appearance of your treatment plant?
23. What safety precautions should be taken when maintain-
ing yard lighting fixture lamps?
24. How would you maintain the landscape around your
treatment plant?
SUGGESTED ANSWERS
Chapter 29. SUPPORT SYSTEMS
Answers to questions on page 719.
29.0A Support systems equipment includes portable pumps,
pipes, valves and fittings. Facilities include auxiliary
electrical equipment, gasoline engines, diesel en-
gines, heating, ventilating, air conditioning and plant
air and water systems. Plant appearance also is im-
portant and includes control of drainage runoff, light-
ing, walkways, roadways, and landscaping.
29.1A Portable centrifugal pumps are often referred to as
trash pumps because the water being pumped is not
clean and many have solids of various sizes sus-
pended in the water.
29.1 B The suction hose has a strainer on the end to prevent
pulling rocks and debris into the pump to avoid damag-
ing the pump or plugging the hoses or pipes.
29.1C When operating a portable pump in weather that is
subject to freezing, always drain the pump to prevent
the freezing water from cracking the casing or binding
up the pump. Before starting the pump, turn the shaft
by hand to be sure it turns freely. If the impeller is
frozen fast, warm the pump slowly until the ice melts.
Answers to questions on page 722.
29.1 D Some of the advantages of the positive displacement
diaphragm pump are as follows:
1. Self-priming if the suction lift is small;
2. When primed with water, it will pump with a suction
lift up to 25 feet (7.5 meters);
3. Large particles will readily pass through the pumps;
and
4. Less likely to become clogged than centrifugal
pumps.
29.1E If a diaphragm pump suddenly stops pumping, remove
discharge valve and clean out pump cavity.
29.1 F After use, pneumatically operated diaphragm pumps
should be flushed thoroughly to prevent dried sedi-
ment from obstructing valve operation. If the water
pumped had large particles in it, it may be necessary
to dismantle the pump to remove any remaining parti-
cles.
Answers to questions on page 726.
29.2A Galvanized pipe is subject to corrosion in an atmos-
phere containing hydrogen sulfide or chloride com-
pounds (salts or chlorine).
29.2B Galvanized pipe can be protected from corrosion by
(1) a protective coating of vinyl or a tar-based product,
and (2) some form of cathodic protection.
29.2C Ductile iron pipe might corrode if installed in salt
marshes, highly alkaline soil, waste dumps, or cinder
fills.
29.2D A major limitation of concrete pipe is the ease with
which the inside of the pipe corrodes in the presence
of hydrogen sulfide gas.
Answers to questions on page 735.
29.2E Valves are the controlling devices placed in piping sys-
tems to stop, regulate, check, divert, or otherwise
modify the flow of liquids or gases.
29.2F The five most common types of valves found in
wastewater treatment facilities are gate valves, globe
valves, eccentric valves, butterfly valves, and check
valves.
29.2G The purpose of a check valve is to allow water to flow
in one direction only.
29.2H Backflow prevention by check valves is essential in
many applications to:
1. Prevent pumps from reversing when power is re-
moved,
2. Protect water systems from being cross connected,
3. Aid in pump operation as a dampener, and
4. Insure "full pipe" operation.
-------
794 Treatment Plants
29.21 Victaulic couplings are used in an area where future
disassembly is anticipated. Quite often you will find
them on the suction and discharge sides of pumps.
29.2J Band seals are used to join clay, soil pipe, or asbes-
tos-cement pipe.
END OF ANSWERS TO QUESTIONS IN LESSON 1
Answers to questions on page 738.
29.3A A qualified electrician should perform most of the nec-
essary maintenance and repair of electrical equipment
to avoid endangering lives and to avoid damage to
equipment.
29.3B The purpose of a "kirk-key" system (one key is used
for two locks) is to insure proper connection of standby
power into your power distribution system. The com-
mercial power system must be locked out by the use
of switch gear before the standby power is connected
to your power distribution system.
29.3C Battery-powered lighting units are considered better
than engine-driven power sources because they are
more economical. If you have a momentary power
outage, the system responds without an engine-
generator start-up.
29.3D If water lost from a lead-acid battery is replaced with
tap water, the impurities in the water will become at-
tached to the lead plates and shorten the life of the
battery.
Answers to questions on page 740.
29.3E Electricity is transmitted at high voltage to reduce the
size of transmission lines.
29.3F If outdoor transformers have exposed high voltage
wires, the following precautions must be taken:
1. An eight-foot (2.4 m) high fence is required to pre-
vent accessibility by unqualified or unauthorized
persons; and
2. Signs attached to the fence must indicate "High
Voltage."
29.3G The treatment plant operator must keep the exterior
and surroundings of the switch gear clean.
29.3H Symptoms that a power distribution transformer may
be in need of maintenance or repair include unusual
noises, high or low oil levels, oil leaks or high operat-
ing temperatures.
Answers to questions on page 748.
29.4A The four strokes in a four-stroke-cycle engine are the
(1) intake stroke, (2) compression stroke, (3) power
stroke, and (4) exhaust stroke.
29 4B Known Unknown
Piston bore, in = 3 in Piston Displacement,
Stroke travel, in = 4 in cubic inches
Calculate the piston displacement in cubic inches.
Piston = - x (Bore, in)2 x Stroke Travel, in
Displacement, 4
cubic inches q miR ,2
= 3.141b x (3 in) x 4 in
4
= 28.27 cu in
29.4C Two major types of valve problems are burnt valves
and valve sticking.
29.4D The purpose of a carburetor is to produce a mixture of
fuel and air on which an engine will operate.
29.4E The purpose of a governor is to provide a constant
engine speed regardless of load.
Answers to questions on page 756.
29.4F Heat is removed from the cylinders by a water cooling
system. Each cylinder is surrounded with a water
jacket through which the coolant (water) circulates and
pulls heat from the cylinder. This is accomplished by a
water pump that is belt-driven from the crankshaft.
29.4G A magneto is a self-contained device that generates
and distributes electricity needed to ignite the fuel mix-
ture in the combustion chamber.
29.4H The fuel mixture (oil and gasoline) provides lubrication
for the moveable parts in the crankcase.
29.41 (1) If the fuel mixture contains too much oil, you'll
have poor carburetion, poor engine performance,
excessive smoke out the exhaust, and incomplete
burning of the mixture.
(2) If the fuel mixture has too little oil, you'll have poor
lubrication of the crankshaft, connecting rod bear-
ings, and piston cyclinder wall. This can cause
premature bearing failure and scored cylinder
walls. The engine will run hot and seize up.
END OF ANSWERS TO QUESTIONS IN LESSON 2
Answers to questions on page 776.
29.5A Gasoline is not used as a fuel in diesel engines be-
cause it would start to burn from the heat generated by
compression before the piston reaches the top of the
stroke.
29.5B The four basic parts of a diesel fuel system are:
1. Primary fuel filter,
2. Secondary fuel filter,
3. Fuel injection pump, and
4. Fuel injector.
29.5C The purpose of the fuel injection pump is to deliver fuel
to the injector at a very high pressure.
Answers to questions on page 777.
29.6A Common items that are similar for almost all gas-fired
hot water boilers include:
1. Gas system,
2. Water system,
3. Control switches, and
4. Boiler maintenance.
29.6B The automatic gas valve is controlled by the operating
thermostat.
29.6C Boilers should be drained on an annual basis to re-
move sludge from the bottom of the boiler.
29.6D Boiler feed water must be tested for hardness be-
cause hard water causes scale to build up inside the
boiler.
Answers to questions on page 779.
29.6E A plenum chamber is an air chamber maintained
under pressure to serve one or more air distribution
ducts.
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Support Systems 795
29.6F The four classes of centrifugal blowers include:
1. Forward curve,
2. Backward inclined,
3. Radial blade, and
4. In-line (tubular centrifugal fan).
29.6G Refrigeration is the process of transferring heat from
one place to another.
29.6H If an air conditioner runs but fails to cool, some of the
refrigerant charge may have been lost.
Answers to questions on page 781.
29.7A The two most common types of air compressors in use
today are the rotary and reciprocating types.
29.7B The type oil recommended for high volume and pres-
sure units is a non-detergent straight mineral oil (tur-
bine or hydraulic type), which is solvent refined and
contains rust and oxidation inhibitors and anti-foam
additives. Viscosity is in the 150-200 Saybolt universal
seconds range at 100°F (38°C).
29.7C The following items are important considerations
when purchasing a rotary compressor:
1. Rated capacity in CFM,
2. Rated operating pressure,
3. Duty cycle — intermittent or continuous,
4. Horsepower requirements, and
5. Stages.
Answers to questions on page 784.
29.7D Sticky intake valves in a reciprocating compressor will
either prohibit or reduce air intake and sticky dis-
charge valves will reduce or prevent compression.
29.7E Air fed to a compressor should be clean, cool, and dry
to provide satisfactory operation.
29.7F An oil-bath type of air filter is used if the intake air
contains considerable dust and other contaminants.
29.7G The major components for power air systems include:
1. Filter,
2. Pressure regulator,
3. Lubricator (not used with instrument control sys-
tems).
29.7H Outlets should be taken from the top of the main line
(tees facing up) to keep moisture out.
27.71 Air system components for power tool use include a
lubricator while in pneumatic control systems there is
no lubricator, but an absorbent-type filter is added.
END OF ANSWERS TO QUESTIONS IN LESSON 3
Answers to questions on page 787.
29.8A The two separate water systems in a wastewater
treatment plant are the fresh or potable water supply
and the reclaimed water.
29.8B Possible sources of fresh or potable water for a
wastewater treatment plant include:
1. Public domestic water supply,
2. Wells, and
3. Bottled water.
29.8C A hydro-pneumatic water system consists of a turbine
pump and water tank with the necessary pressure
switches, probes, or floats that control the tank pres-
sure and water height. The air pressure over the water
in the tank forces water out the taps when valves are
opened.
Answers to questions on page 789.
29.8D Backflow prevention devices include:
1. Air gap,
2. Check valve, and
3. Anti-siphon valve.
29.8E An air gap is an open vertical drop, or vertical empty
space, between a drinking (potable) water supply and
the point of use in a wastewater treatment plant. This
gap prevents back-siphonage because there is no
way wastewater can reach the potable water.
29.8F In-plant uses of reclaimed wastewater include:
1. Irrigating treatment plant grounds,
2. Cooling of pump shaft packing and mechanical
seals,
3. Spraying on aeration tanks to control foaming,
4. Washing down areas,
5. Diluting or washing in sludge dewatering systems,
and
6. Conveying water with a high concentration of
chlorine to the dosage point for effluent chlorina-
tion.
Answers to questions on page 790.
29.9A Three objectives of an effective yard or area lighting
include:
1. Provide adequate illumination for work being per-
formed;
2. Provide energy-efficient lighting (greatest illumina-
tion per watt of power expended); and
3. Install fixtures that require minimal maintenance.
29.9B Items that should be considered when maintaining a
yard lighting system include inspecting for:
1. Loose or broken electrical connections,
2. Corroded conduits and fittings,
3. Damaged reflectors,
4. Dirty lighting diffusers (clean if necessary), and
5. Proper operation of photoelectric cell (if used).
29.9C The purpose of enclosures is to prevent the public
from wandering through our plants. We must protect
the public from possible injury as well as protect our
investment in buildings and equipment from theft and
vandalism.
29.9D Maintenance of a treatment plant gate consists of
keeping (1) the hinges well oiled, and (2) the cross-tie
bolts properly adjusted to keep the gate from drag-
ging.
Answers to questions on page 792.
29.9E To have a good paving installation you must have:
1. Soil properly stabilized and adequate subgrade
material used;
2. Asphalt mix designed for its application;
3. Temperature of mix within specifications when laid;
and
4. Asphalt properly rolled and compacted.
29.9F Items that should be considered in a walkway mainte-
nance program include:
1. Keeping walkway free from algae and other slip-
pery materials;
2. Removing weeds and grass from cracks;
3. Correcting concrete sections that have risen,
dropped or tilted; and
4. Keeping walkways clear.
-------
796 Treatment Plants
29.9G Weed seeds get into a lawn from the soil, lawn seeds, 29.9H A lawn needs nitrogen if it turns yellow or pale green or
birds, and the wind. 'f the grass becomes thin and weeds start growing.
END OF ANSWERS TO QUESTIONS IN LESSON 4.
OBJECTIVE TEST
Chapter 29. SUPPORT SYSTEMS
Please write your name and mark the correct answers on the
answer sheet as directed at the end of Chapter 1. There may
be more than one answer to each question.
1. Dynamic heads are measured when a pump is not operat-
ing.
1. True
2. False
2. A suction lift occurs when the surface of the water to be
pumped is below the center line of the pump impeller.
1. True
2. False
3. Centrifugal pumps cannot operate with considerable suc-
tion lift at decreasing flow rates as the water level drops in
the wet well.
1. True
2. False
10. The most practical form of emergency lighting is that pro-
vided by standby power generators.
1. True
2. False
11. The horsepower of a gasoline engine is inversely propor-
tional to the volume of the piston displacement.
1. True
2. False
12. Diesel engines are similar to gasoline engines and may be
either two- or four-cycle.
1. True
2. False
13. Diesel engines use spark plugs.
1. True
2. False
4. An advantage of mechanical seals is that they are not 14.
damaged when run dry.
1. True
2. False
All organic fertilizers are slow acting and all inorganic fer-
tilizers are fast acting.
1. True
2. False
5. Galvanized pipe is steel pipe that has been coated with
zinc by an electro-chemical process.
1. True
2. False
15. A qualified electrician should perform most of the neces-
sary maintenance and repair of electrical equipment.
1. True
2. False
6. PVC pipe is immune to nearly all types of corrosion, be it
biological, chemical or electro-chemical.
1. True
2. False
7. An advantage of PVC pipe is that it will not deteriorate
when exposed to sunlight.
1. True
2. False
8. Standard concrete pipe is smoother and has lower friction
losses than asbestos-cement pipe.
1. True
2. False
9. Gate valves are commonly used to control flow.
1. True
2. False
jw ^ 4W
m #1 ('
W,
16. Which of the following factors must be considered before
selecting a pump?
1. Desired pumping rate in gallons per minute
2. Distance liquid is to be pumped
3. Liquid and any solids to be pumped
4. Location of pump nameplate
5. Type of power needed
-------
Support Systems 797
17. Suction lift is the pressure measured from the center line
of the pump
1. Down to the energy grade line.
2. Down to the hydraulic grade line.
3. Down to the inlet of the suction pipe.
4. Up to the energy grade line.
5. Up to the hydraulic grade line.
18. Proper installation of portable pumps to dewater ditches
requires
1. Long suction line to keep pump away from trench.
2. Pump level and securely supported.
3. Suction line sloping down to pump for priming pur-
poses.
4. Throttle and check valves installed in suction line.
5. Use of elbows and fittings to keep pipe supported by
ground.
19. Advantages of concrete pipe include the pipe's ability to
1. Be installed and backfilled under any conditions.
2. Be manufactured and installed in large sizes.
3. Withstand external corrosion.
4. Withstand external pressures.
5. Withstand internal corrosion.
20. Proper selection of an emergency lighting unit for a par-
ticular location requires careful consideration of which of
the following items?
1. Costs
2. Lighting requirements
3. Nearness of vendor to repair failures
4. Necessary switch gear
5. Types of batteries
21. The keys to prolonged life of a battery are to keep the
1. Battery fully charged.
2. Battery operating continuously.
3. Booster terminals connected to the battery.
4. Electrolyte level above the cell plates.
5. Terminals and top clean.
22. Names of engine valve parts include
1. Bore.
2. Face.
3. Head.
4. Seat.
5. Stroke.
23. The ignition system for a gasoline engine consists of the
1. Battery,
2. Coil.
3. Distributor.
4. Filter.
• 5. Thermostat.
24. Scale is an important consideration in the operation and
maintenance of boilers because scale reduces
1. Cleaning requirements.
2. Corrosion.
3. Efficiency.
4. Heat transfer.
5. Operating costs.
25. Mechanical maintenance for air conditioners includes
1. Clearing compressor of obstructions.
2. Clearing or replacing filters.
3. Lubricating bearings.
4. Lubricating compressor.
5. Making sure condensation drip line is not plugged.
26. If a compressor fails to operate or provide rated capacity,
what could be the cause of the problem?
1. Air cleaner, cap and/or screen clogged
2. Air receiver safety valve malfunctioning
3. Engine fails to develop proper RPMs
4. Pressure regulator improperly adjusted
5. Oil seal faulty
27. Which of the following items are used as checking devices
in a check valve?
1. Ball
2. Check
3. Clapper
4. Disc
5. Slapper
28. Which of the following sources of light produce the most
lumens per watt?
1. Common fluorescent light
2. High pressure sodium light
3. Mercury vapor light
4. Modern light bulb
5. Standard incandescent light bulb
END OF OBJECTIVE TEST
-------
Treatment Plants
CONGRATULATIONS
You've worked hard and completed a very difficult program.
-------
FINAL EXAMINATION
AND
SUGGESTED ANSWERS
FOR
VOLUME III
-------
800 Final Examination
FINAL EXAMINATION
VOLUME III
This final examination was prepared TO HELP YOU review
the material in Volume III. The questions are divided into four
types:
1. True-false,
2. Multiple choice,
3. Problems, and
4. Short answer.
To work this examination:
1. Write the answer to each question in your notebook,
2. After you have worked a group of questions (you decide
how many), check your answers with the suggested an-
swers at the end of this exam, and
3. If you missed a question and don't understand why, reread
the material in the manual.
You may wish to use this examination for review purposes
when preparing for civil service and certification examinations.
Since you have already completed this course, you do not
have to send your answers to California State University, Sac-
ramento.
True-False
1. Microorganisms breakdown nitrate compounds before sul-
fate compounds to obtain oxygen.
1. True
2. False
2. Hydrogen sulfide gas is a more serious problem at lower
temperatures than at higher temperatures.
1. True
2. False
3. Chemicals are the only method available for operators to
control odors.
1. True
2. False
4. The grey appearance of out-of-service activated carbon
that has been in service for along time indicates that the
activated carbon is worn out.
1. True
2. False
5. Pure oxygen systems may be used to supply oxygen to
any of the activated sludge process modes — conven-
tional, step-feed, complete mix or contact stabilization.
1. True
2. False
6. Cold liquid oxygen (LOX) can cause skin burns.
1. True
2. False
7. Changes in activated sludge quality cause changes in the
settling characteristics of the sludge.
1. True
2. False
8. The activated sludge process is controlled by attempting
to achieve preconceived levels of individual variables such
as MLSS, MCRT and F/M ratio.
1. True
2. False
9. Primary sludges have specific gravities closer to that of
water than secondary sludges.
1. True
2. False
10. If gasification problems develop in a gravity thickener as a
result of excessive sludge retention times, the rate of
sludge withdrawal should be increased so as to lower the
sludge blanket depth with a subsequent lowering of the
sludge retention time.
1. True
2. False
11. Sludge should be thickened as much as possible in order
to minimize digestion time in aerobic digesters.
1. True
2. False
12. Chemical stabilization of sludges finds application at over-
loaded plants and at plants experiencing stabilization facil-
ity upsets.
1. True
2. False
13. In the wet oxidation process, an increase in oxidation is
due primarily to reacting the sludge with greater quantities
of oxygen at elevated temperatures and pressures.
1. True
2. False
14. Primary sludges dewater more readily and require more
chemical conditioners than secondary sludges.
1. True
2. False
-------
Industrial Waste Treatment 801
15. The ideal operating belt speed for a belt filter press is the
fastest the operator can maintain without "washing out"
the belt.
1. True
2. False
16. A burnout occurs in a multiple hearth furnace when the
sludge feed has been stopped and the fire burns out.
1. True
2. False
17. Storage often must be provided in sludge treatment and
disposal systems to accommodate differences between
sludge disposal rates and sludge production rates.
1. True
2. False
18. Addition of alum will increase the alkalinity in the water
being treated during the coagulation process.
1. True
2. False
19. The formation of limestone (calcium carbonate) is not a
serious problem in lime systems used for phosphorus re-
moval.
1. True
2. False
20. In the luxury uptake phosphorus removal process, bac-
teria release phosphorus in an aerobic release tank.
1. True
2. False
21. The method of irrigation depends on the type of crop being
grown.
1. True
2. False
22. An instrument is a device that causes changes to occur.
1. True
2. False
23. The scales on an indicator may be straight, curved, or
circular in shape.
1. True
2. False
24. The headworks ventilation system must be kept operating
both for the operator's safety and for minimizing the ac-
cumulation of concentrations of moist or otherwise corro-
sive and toxic gases.
1. True
2. False
25. A good sewer-use ordinance is the proper tool to provide
the necessary authority to control industrial wastes.
1. True
2. False
26. A good sampling point is one that is easily accessible and
may be located anywhere that a representative sample
may be obtained.
1. True
2. False
27. Prompt testing of samples prevents physical, chemical
and/or biological changes in the sample.
1. True
2. False
28. Measuring the flow from an industry is not as important as
obtaining good samples.
1. True
2. False
29. Depending on their nature and concentration, certain
foreign chemicals in drinking water may produce sudden
illness, or may produce long-term "chronic" illness which
is not diagnosed for years, but which may have severe
effects.
1. True
2. False
30. One of the most effective means of treating pulp and
paper wastes is the recovery of materials.
1. True
2. False
31. Due to the seasonality of production and the characteristic
nutrient deficiency in fruit and vegetable processing water,
biological treatment is highly effective.
1. True
2. False
32. The dissolved air flotation system is based on the principle
that the solubility of gases in a solution decreases as the
pressure on the solution increases.
1. True
2. False
33. When attempting to correct a dissolved air flotation thick-
ener process problem, the operator must not change more
than one variable at a time.
1. True
2. False
34. Screens take up less space than clarifiers and are not so
much affected in performance by changes in flow rate or
temperature.
1. True
2. False
35. One operational strategy for operating screens is to place
the number of screens on line needed to handle the flows
and solids to be treated.
1. True
2. False
36. The rate of rusting or corrosion increases in rainwater and
increases even more in saltwater.
1. True
2. False
37. Short-circuiting is not caused by differences in water den-
sity due to different temperatures existing at the surface
and the bottom of the clarifier.
1. True
2. False
-------
802 Final Examination
38. The purpose of activated carbon adsorption in wastewater
treatment is to remove suspended solids from the effluent
of the treatment plant.
1. True
2. False
39. Suction lift is the positive pressure on the suction side of
the pump.
1. True
2. False
40. If the priming water for a pump contains soaps or deter-
gents, problems can develop if a high suction lift exists.
1. True
2. False
Multiple Choice
1 Inorganic gases found around treatment plants include
1. Ammonia.
2. Hydrogen sulfide.
3. Mercaptans.
4. Methane.
5. Skatole.
2. Cryogenic oxygen plants are usually shut down
— for maintenance.
1. Once every six months
2. Once every year
3. Once every two years
4. Once every five years
5. Once every ten years
3. Return activated sludge (RAS) flow rate may be adjusted
or controlled by which of the following techniques?
1. Food/Microorganisms Ratio
2. Mean Cell Residence Time (MCRT)
3. Monitoring the depth of the sludge blanket
4. SVI approach
5. Settleability approach
4. Which of the following items could indicate that a high
organic waste load has reached an activated sludge pro-
cess?
1. Decrease in DO residual in aeration tank
2. Decrease in nutrients in effluent from secondary
clarifier
3. Decrease in turbidity in effluent from secondary clarifier
4. Increase in DO residual in aeration tank
5. Increase in turbidity in effluent from secondary clarifier
5. Major factors affecting biological nutrification include
1. Dissolved oxygen.
2. Nitrogenous food.
3. pH.
4. Toxic materials.
5. Wastewater temperature.
6. Which of the following items are possible causes of sludge
rising and solids carry-over in a gravity thickener with a
clear liquid fuel?
1 Blanket disturbances
2. Chemical inefficiencies
3. Excessive loadings
4. Gasification
5. Septic feed
7. In dissolved air flotation thickeners, floated solids are kept
out of the effluent by use of
1. Effluent baffles.
2. Hardware cloth screens,
3. Macroscreens.
4. Scum scrapers.
5. Water sprays.
8. A belt filter press is processing secondary sludges. Some
of the sludge is squeezing out from between the belts and
contaminating the effluent by falling into the filtrate trays.
How could this problem be corrected?
1. Blend primary sludge with the secondary sludge
2. Build baffles around the belts
3. Chlorinate the effluent
4. Filter the effluent
5. Move the filtrate trays
9, If no coagulation occurs in a chemical treatment process,
which of the following items should be inspected?
1. Actual feeder output by catching a timed sample
2. Applied water for a significant change
3. Feed chemical strength
4. Skimmer arms
5. Tank drain valve
10. Abnormal operating conditions for microscreens include
1. High flows.
2. High pH levels.
3. Low applied water flows.
4. Low pH flows.
5. Toxic wastes.
11. Which of the following items should be inspected or
checked before starting a chemical feeder?
1. Direction and rotation of moving parts in motors
2. Operation of control lights on control panel
3. Operation of safety lock-out switches
4. Proper voltage
5. Size of overload protection
12. Which of the following items would you check if laboratory
tests indicated high turbidity and suspended solids in the
effluent of a gravity filter?
1. Check for excessive head loss
2. Determine filter aid dosages
3. Examine backwash cycle for complete wash
4. Inspect for damaged bed due to backwashing
5. Look for fluctuating flows that could cause break-
through
13. Phosphorus removal efficiencies by the lime precipitation
process are affected by
1. Changes in pH.
2. Performance of lime feed equipment.
3. Plugged pumps or piping.
4. Recarbonation system.
5. Small straggler floe.
-------
14. The hydraulic loading for a phosphate stripper depends on
the
1. Ability of the aerobic phosphate stripper to remain
aerobic.
2. Ability of the anaerobic phosphate stripper to remain
anaerobic.
3. BOD loading of the unit.
4. Dissolved oxygen of the activated sludge.
5. pH of the wastewater being treated.
15. Which of the following chemical properties are used in the
classification of irrigation waters?
1. BOD
2. Boron
3. Chloride
4. pH
5. Total dissolved solids
16. Which of the following tests are performed on the soils in
an effluent disposal on land program?
1. BOD
2. Cation exchange capacity
3. Conductivity
4. DO
5. pH
17. Which method or device should you use to measure the
diameter of a replacement pump shaft?
1. Engineer's scale
2. Metallic tape
3. Micrometer
4. Ruler
5. Surveyor's chain
18. The primary element in a control system is also called a
1. Controller.
2. Receiver.
3. Recorder.
4. Sensor.
5. Transmitter.
19. Sludge blanket depths may be measured by the use of
1. Bubbler tubes.
2. Floats connected to cables and pulleys.
3. A hose and an aspirator.
4. Pressure gages.
5. Ultrasonic transmitters and receivers.
20. Which of the following factors are usually measured by air
compressor vibration sensing devices?
1. Acceleration
2. Displacement
3. Flow
4. Time
5. Velocity
21. Why should industrial wastes discharged into a collection
system be monitored?
1. To impose fines on industries
2. To prevent shock loads from upsetting wastewater
treatment processes
3. To protect operators of wastewater collection systems
and treatment plants from hazardous and toxic sub-
stances
4. To protect the public by preventing toxic industrial
wastes from reaching drinking water supplies
5. To protect wastewater collection and treatment
facilities from corrosive and other harmful substances
Industrial Waste Treatment 803
22. Flows should be measured from an industry in order to
1. Calculate the quantities of pollutants discharged.
2. Check compliance with pretreatment requirements.
3. Determine which flow meter works best.
4. Measure toxic gases released.
5. Prepare accurate and equitable billing calculations.
23. The dissolved air flotation process may be used for
1. Coagulation.
2. Flocculation.
3. Solids recovery.
4. Wastewater treatment.
5. Water recovery.
24. What could be the cause of wastewater not flowing
through a microscreen?
1. Aperture size too large
2. Inadequate cleaning
3. Inadequate depth of water
4. No wastewater flowing to screen
5. Overload conditions, too many solids
25. Hazardous fumes, gases or conditions that might be en-
countered in a confined space include
1. Gasoline vapors.
2. Hydrogen sulfide.
3. Lack of oxygen.
4. Solvent fumes.
5. Toxic gases.
26. Iron compounds used as coagulants are
1. A potential source of iron in the effluent.
2. Capable of increasing the BOD in the effluent.
3. Corrosive.
4. Difficult to dissolve in water.
5. Potentially dangerous if they (ferric sulfate or cop-
peras) come in contact with quicklime.
27. Daily operational procedures for an activated carbon pro-
cess include
1. Backflushing of fine-mesh screens.
2. Measuring BOD removal efficiencies.
3. Measuring COD removal efficiencies.
4. Measuring effluent turbidity.
5. Measuring level of carbon remaining in reactor.
28. Which of the following items are possible causes of a por-
table pump not priming?
1. Dirty water inside pump
2. Leaking connections on suction side of pump
3. No water in pump
4. Pump worn
5. Strainer clogged
29. Possible causes of a gasoline engine not starting include
1. Break in ignition wiring.
2. Distributor cap damp.
3. Engine valves out of time/spark advance.
4. Poor battery connection/engine will not crank.
5. Radiator empty.
30. The keys to prolonged life of a battery are to keep the
1. Battery fully charged.
2. Battery operating continuously.
3. Booster terminals connected to the battery.
4. Electrolyte level above the cell plates.
5. Terminals and top clean.
-------
804 Final Examination
Short Answer
1. Define the following terms:
a. Absorption
b. Oxidation
c. Stripped odors
2. Define the following items:
a. Batch process
b. Bulking
c. Coagulation
d. Filamentous bacteria
e. RAS
3. Why are pure oxygen reactors in the activated sludge pro-
cess staged?
4. How can variations or fluctuations in influent organic load-
ings be smoothed out before the aeration basin?
5. Define the following items:
a. Elutriation
b. Vector
6. List three process alternatives for each of the following
types of sludge processing alternatives:
1. Thickening,
2. Conditioning, and
3. Volume reduction.
7. List the factors that affect the performance of dissolved air
flotation (DAF) thickeners.
8. How can an operator control the digestion time in an
aerobic digester?
9. What is the purpose of wetting dry polymers?
10. How can the cake dryness from a vacuum filter be in-
creased?
11. What safety precautions are required for handling ferric
chloride in concentrated solutions?
12. Why should the backwash water for a gravity filter be of
the best quality available?
13. Why are chemicals commonly used with a filtration pro-
cess?
14. Define the following terms:
a. Recalcine
b. Slake
15. What is luxury uptake of phosphorus?
16. Define the following terms:
a. Reclamation
b. Recycle
17. List possible causes of clogging in a recharge well and
possible cures for each cause.
18. Define the following terms:
a. Offset
b. Set point
19. Why are treatment plants being designed and constructed
with sophisticated instrument-control systems?
20. Why are instruments used instead of our human senses of
seeing, hearing, touching, and smelling?
21. What does a thermocouple measure?
22. What does a Bourdon Tube measure?
23. What is the purpose of transmitting instruments?
24. Why are detection devices for explosive gases installed in
the headworks of treatment plants?
25. How is air flow measured in the activated sludge process?
26. List the adverse characteristics of industrial wastes that
could seriously impact on collection systems,
27. How would you collect a representative sample when the
wastewater has oil or other floating materials on the sur-
face?
28. What would you do if a gasoline, solvent or other type of
hydrocarbon entered your treatment plant?
29. Define the following terms:
a. Adsorption
b. Acidity
c. Defining
d. Micron
e. Ultrafiltration
30. Name three ways in which water can become biologically
contaminated.
31. Heavy plugging of a screen could be caused by what fac-
tors?
32. How does pH affect the rate of corrosion?
33. Why should ventilation be provided in chemical feed
facilities?
34. What is the counter-current flow principle in the activated
carbon treatment process?
35. How could activated carbon cause an oxygen deficiency in
a carbon column reactor vessel?
36. Define the following terms:
a. Air Gap
b. Cavitation
c. Electro-chemical process
37. Why should the suction hose of a portable pump have a
strainer on the end?
38. What would you do if a diaphragm pump suddenly stops
pumping and the engine either quits or keeps running and
the pump rod slips on the shaft?
39. What is the purpose of a carburetor on a gasoline engine?
40. What might be wrong if an air conditioner runs, but fails to
cool?
-------
Industrial Waste Treatment 805
Problems
1. Determine the desired waste activated sludge (WAS) flow
rate using the F/M control technique. The influent flow is 4.0
MGD, total aeration tank volume is 0.8 MG, COD to aera-
tion tank is 110 mg/L, the mixed liquor suspended solids
(MLSS) are 3100 mg/L and 69 percent volatile matter, the
RAS suspended solids are 6,400 mg/L and the desired food
to microorganism (F/M) ratio is 0.28 lbs COD/day/lb
MLVSS. Current WAS flow rate is 0.35 MGD.
2. Estimate the total volume (sum of primary and secondary)
of sludge produced in gallons per day from a 2 MGD acti-
vated sludge plant. Primary clarifier influent suspended sol-
ids are 300 mg/L and 120 mg/L in the effluent. Primary
effluent BOD is 175 mg/L and secondary effluent BOD is 25
mg/L. The bacterial growth rate, Y, is 0.50 lbs SS per lb
BOD. Primary sludge solids are 5 percent solids and sec-
ondary solids are 1.5 percent solids.
3. Jar tests indicate that a waste activated sludge flow of
35,000 GPD with a solids concentration of 1.4 percent
sludge solids will require 20 pounds per day of Polymer A or
180 pounds per day of Polymer B for successful gravity
thickening. Polymer A is a dry product and costs $2.20 per
dry pound. Polymer B is a liquid product and costs $0.22
per liquid pound. Find the cost of using both Polymer A and
B in dollars per ton of sludge.
4. Polymer is supplied at a concentration of 0.5 pounds
polymer per gallon of water being treated. The polymer
feed pump delivers a flow of 0.18 GPM and the flow to the
pressure filters is 6,000 GPM. Calculate the concentration
or dose (mg/L) of polymer in the water applied to the filter.
5. Determine the suspended solids and BOD loadings on a
dissolved air flotation unit if the flow is 0.8 MGD and the
influent suspended solids are 1,800 mg/L with a BOD of
150 mg/L. What is the percent removal of suspended solids
if the effluent suspended solids are 100 mg/L?
SUGGESTED ANSWERS FOR FINAL EXAMINATION
VOLUME III
True-False
1. True
Microorganisms breakdown nitrate compounds
before sulfate compounds to obtain oxygen.
2. False Hydrogen sulfide gas is a more serious problem at
higher temperatures than at lower temperatures.
3. False Good housekeeping and biological odor reduction
towers are methods used to control odors in addi-
tion to chemicals.
4. False The grey appearance of out-of-service activated
carbon is caused by salts. The activated carbon
may not be worn out.
5. True Pure oxygen systems may be used to supply oxy-
gen to any of the activated sludge process modes
— conventional, step-feed, complete mix or con-
tact stabilization.
6. True Cold liquid oxygen can cause skin burns.
7. True Changes in activated sludge quality cause
changes in the settling characteristics of the
sludge.
8. False The activated sludge process is NOT controlled by
attempting to achieve preconceived levels of indi-
vidual variables such as MLSS, MCRT and F/M
ratio.
9. False Secondary sludges have specific gravities
CLOSER to that of water than primary sludges.
10. True If gasification problems develop in a gravity thick-
ener as a result of excessive sludge retention
times, the rate of sludge withdrawal should be in-
creased so as to lower the sludge blanket depth
with a subsequent lowering of the sludge retention
time.
11. False Sludge should be thickened as much as possible
in order to MAXIMIZE digestion time in aerobic
digesters.
12. True Chemical stabilization of sludge finds application
at overloaded plants and at plants experiencing
stabilization facility upsets.
13. True In the wet oxidation process, an increase in oxida-
tion is due primarily to reacting the sludge with
greater quantities of oxygen at elevated tempera-
tures and pressures.
14. False Primary sludges dewater more readily and require
LESS chemical conditioners than secondary
sludges.
15. False The ideal operating belt speed for a belt filter press
is the SLOWEST the operator can maintain without
"washing out" the belt.
16. False A burnout occurs in a multiple hearth furnace
when the sludge feed has been stopped and the
lire continues to burn.
17. True Storage often must be provided in sludge treat-
ment and disposal systems to accommodate dif-
ferences between sludge disposal rates and
sludge production rates.
-------
806 Final Examination
18. False Alum REDUCES the alkalinity in the water being
treated during the coagulation process.
19. False Formation of limestone (calcium carbonate) is a
serious problem in lime systems used for phos-
phorus removal.
20. False In the luxury uptake phosphorus removal process,
bacteria release phosphorus in an ANAEROBIC
release tank.
21. True The method of irrigation depends on the type of
crop being grown.
22. False An instrument is a measuring device.
23. True The scales on an indicator may be straight,
curved, or circular in shape.
24. True The headworks ventilation system must be kept
operating both for the operator's safety and for
minimizing the accumulation of concentrations of
moist or otherwise corrosive and toxic gases.
25. True A good sewer-use ordinance is the proper tool to
provide the necessary authority to control indus-
trial wastes.
26. True A good sampling point is one that is easily acces-
sible and may be located anywhere that a repre-
sentative sample may be obtained.
27. True Prompt testing of samples prevents physical,
chemical and/or biological changes in the sample.
28. False Measuring the flow from an industry is equally as
important as obtaining good samples.
29. True Depending on their nature and concentration, cer-
tain foreign chemicals in drinking water may pro-
duce sudden illness, or may produce long-term
"chronic" illness which is not diagnosed for years,
but which may have severe effects.
30. True One of the most effective means of treating pulp
and paper wastes is the recovery of materials.
31. False Due to the seasonality of production and charac-
teristic nutrient deficiency in fruit and vegetable
processing water, biological treatment MAY NOT
ALWAYS BE FEASIBLE.
32. False The dissolved air flotation system is based on the
principle that the solubility of gases in a solution
INCREASES as the pressure on the solution in-
creases.
33. True When attempting to correct a dissolved air flotation
thickener process problem, the operator must not
change more than one variable at a time.
34. True Screens take up less space than clarifiers and are
not so much affected in performance by changes
in flow rate or temperature.
35. True One operational strategy for operating screens is
to place the number of screens on line needed to
handle the flows and solids to be treated.
36. True The rate of rusting or corrosion increases in rain-
water and increases even more in saltwater.
37. False Short-circuiting may be caused by differences in
water density due to different temperatures exist-
ing at the surface and the bottom of the clarifier.
38. False The purpose of activated carbon adsorption in
wastewater treatment plants is to remove OR-
GANIC POLLUTANTS from the effluent of the
treatment plant.
39. False Suction lift is the NEGATIVE pressure on the suc-
tion side of the pump.
40. True
If the priming water for a pump contains soaps or
detergents, problems can develop if a high suction
lift exists.
Multiple Choice
1. 1,2, 4
2. 2
3. 3, 4, 5
Ammonia, hydrogen sulfide and methane
are inorganic gases found around treatment
plants.
Cryogenic oxygen plants are usually shut
down once every year for maintenance.
RAS flow rate may be adjusted by
1. Monitoring the depth of the sludge blan-
ket,
2. SVI approach, and
3. Settleability approach.
4. 1,2,5 When a high organic waste load reaches an
activated sludge process, the DO residual
will drop due to organism activity, effluent
nutrients will drop due to a lack of nutrients
in most industrial wastes, and effluent turbid-
ity will increase due to a reduction in the
level of treatment.
5. 1,2, 3, 4, 5 All items listed are major factors affecting
biological nitrification — DO, nitrogenous
food, pH, toxic materials, and wastewater
temperature.
6. 1,2,3,4,5 Blanket disturbances, chemical inefficien-
cies, excessive loadings, gasification and
septic feed are all possible causes of sludge
rising and solids carry-over in a gravity
thickener with a clear liquid level.
7. 1
8. 1
9. 1,2,3
Effluent baffles are used to keep floated sol-
ids out of the effluent of dissolved air flota-
tion thickeners.
Blend primary sludge with secondary sludge
to stop secondary sludges from squeezing
out from between belts and contaminating
the effluent by falling into the filtrate trays.
If no coagulation occurs in a chemical treat-
ment process, inspect applied water for a
significant change, actual feeder output by
catching a timed sample, and feed chemical
strength. Also inspect the chemical feed
pump operation, chemical supply and valve
positions and solution carrier water flow and
valve positions.
-------
Industrial Waste Treatment 807
10. 1,2,3,4 Abnormal operating conditions for mi-
croscreens include high flows, high pH
levels, low applied water flows and low pH
levels.
11. 1,2,3,4,5 Before starting a chemical feeder, inspect or
check for direction of rotation of moving
parts in motors, operation of control lights on
control panel, operation of safety lock-out
switches, proper voltage, and size of over-
load protection.
12. 1,2,3,4,5 If laboratory tests indicate high turbidity and
suspended solids in the effluent of a gravity
filter, check for excessive head loss, deter-
mine filter aid dosages, examine backwash
cycle for complete wash, inspect for dam-
aged bed due to backwashing, and look for
fluctuating flows that could cause break-
through.
13. 1, 2, 3, 4, 5 Phosphorus removal efficiencies by the lime
precipitation process are affected by
changes in pH, performance of the lime feed
equipment, plugged pumps or piping, recar-
bonation system and small straggler floe.
14. 2, 4 The hydraulic loading for a phosphate strip-
per depends on the ability of the anaerobic
phosphate stripper to remain anaerobic and
the dissolved oxygen of the activated
sludge.
15. 2, 3, 5 Chemical properties used in the classifica-
tion of irrigation waters include boron,
chloride and total dissolved solids.
16. 2, 3, 5 Tests performed on the soils in an effluent
disposal on land program include cation ex-
change capacity, conductivity and pH.
17. 3 A micrometer should be used to measure
the diameter of a replacement pump shaft.
18. 4 The primary element in a control system is
also called a sensor.
19. 3,5 Sludge blanket depths may be measured by
use of a hose and an aspirator or ultrasonic
transmitters and receivers.
20. 1, 2, 5 Air compressor vibration sensing devices
usually measure acceleration, displacement
and velocity.
21. 2, 3, 4, 5 Industrial wastes discharged into a collec-
tion system should be monitored to prevent
shock loads from upsetting treatment pro-
cesses and to protect operators, the public
and facilities from harmful substances.
22. 1,2,5 Flows should be measured from an industry
in order to calculate the quantities of pollu-
tants discharged, check compliance with
pretreatment requirements, and prepare ac-
curate and equitable billing calculations.
23. 3, 4, 5 The dissolved air flotation process may be
used for solids recovery, wastewater treat-
ment and water recovery.
24. 2, 3, 4, 5 Possible causes of wastewater not flowing
through a microscreen include inadequate
cleaning, indadequate depth of water,
wastewater not flowing to screen and over-
load conditions, too many solids.
25. 1, 2, 3, 4, 5 Hazardous fumes, gases or conditions that
might be encountered in a confined space
include gasoline vapors, hydrogen sulfide,
lack of oxygen, solvent fumes and toxic
gases.
26. 1, 3, 4, 5 Iron compounds used as coagulants are a
potential source of iron in the effluent, corro-
sive, difficult to dissolve in water, and poten-
tially dangerous if they (ferric sulfate or cop-
peras) come in contact with quicklime.
27. 1,3,4 Daily operational procedures for an acti-
vated carbon process include backflushing
of fine-mesh screens, measuring COD re-
moval efficiencies, and measuring effluent
turbidity.
28. 1, 2, 3, 4, 5 Possible causes of a portable pump not
priming include dirty water inside pump
(clean water primes better), leaking connec-
tions on suction side of pump, no water in
pump, pump worn and strainer clogged.
29. 1, 2, 3, 4 Possible causes of a gasoline engine not
starting include a break in the ignition wiring,
distributor cap damp, engine valves out of
time/spark advance, and poor battery con-
nection/engine will not crank.
30. 1, 4, 5
Short Answer
The keys prolonged life of a battery are to
keep the battery fully charged, electrolyte
level above the cell plates, and terminals
and top clean.
1. Define the following terms:
a. Absorption. Taking in or soaking up of one sub-
stance into the body of another by molecular or chem-
ical action (as tree roots absorb dissolved nutrients in
the soil).
b. Oxidation. Oxidation is the addition of oxygen, re-
moval of hydrogen, or the removal of electrons from
an element or compound. In wastewater treatement,
organic matter is oxidized to more stable substances.
c. Stripped odors. Odors that are released from a liquid
by bubbling air through the liquid or by allowing the
liquid to be sprayed and/or tumbled over media.
2. Define the following terms.
a. Batch process. A treatment process in which a tank
or reactor is filled, the water is treated, and the tank is
emptied. The tank may then be filled and the process
repeated.
b. Bulking. Clouds of billowing sludge that occur
throughout secondary clarifiers and sludge thickeners
when the sludge becomes too light and will not settle
properly.
c. Coagulation. The use of chemicals that cause very
fine particles to clump together into larger particles.
This makes it easier to separate the solids from the
liquids by settling, skimming, and draining or filtering.
d. Filamentous bacteria. Organisms that grow in a
thread or filamentous form. Common types are thio-
thrix and actinomyces.
e. RAS. Return Activated Sludge, mg/L Settled acti-
vated sludge that is collected in the secondary clarifier
and returned to the aeration basin to mix with incom-
ing raw or primary settled wastewater.
-------
808 Final Examination
3. Pure oxygen reactors are staged to increase the efficiency
of the use of oxygen.
4. Organic loadings can be smoothed out by the use of an
equalizing tank and also by keeping the contents of the
equalizing tank well mixed.
5. Define the following terms:
a. Elutriation. The washing of digested sludge in plant
effluent. The objective is to remove (wash out) fine
particulates and/or the alkalinity in the sludge. This
process reduces the demand for conditioning chemi-
cals and improves settling or filtering characteristics of
the solids.
b. Vector. An insect or other organism capable of
transmitting germs or other agents of disease.
6. Types of Sludge Processing Alternatives
Thickening Conditioning
Volume
Reduction
1. Gravity 1. Chemical 1. Drying
2. Flotation 2. Thermal 2. Incineration
3. Centrifugation 3. Elutriation 3. Composting
4. Wet Oxidation
7. The performance of DAF thickeners depends on (1) type
and age of the feed sludge, (2) solids and hydraulic load-
ing, (3) air to solids (A/S) ratio, (4) recycle rate, and (5)
sludge blanket depth.
8. The operator can control digestion time by controlling the
degree of sludge thickening prior to digestion. The thicker
the sludge, the longer the digestion time.
9. The purpose of wetting dry polymers is to produce a prop-
erly mixed solution that will not have balls of undissolved
polymer.
10. Cake dryness from a vacuum filter can be increased by (1)
increasing vacuum, (2) reducing drum speed, and (3) im-
proving chemical conditioning.
11. Safety precautions required for handling ferric chloride in
concentrated forms should be the same as those for acids.
Wear protective clothing, face shields and gloves. Flush
off all splashes on clothing and skin immediately.
12. If nonfiltered water is supplied to the backwash system,
clogging of the underdrain system may occur.
13. Chemicals are commonly used with a filtration process as
coagulants for the solids and turbidity to aid in their re-
moval by filtration.
14. Define the following terms:
a. Recalcine. A lime-recovery process in which the
calcium carbonate in sludge is converted to lime by
heating at 1800°F (980°C).
b. Slake. To become mixed with water so that a true
chemical reaction takes place, such as in the slaking
of lime.
15. Luxury uptake of phosphorus is a biological process
whereby the bacteria normally found in the activated
sludge treatment portion of the secondary wastewater
treatment plant are withdrawn to an environment without
oxygen (anaerobic) for release of phosphorus. When the
bacteria are returned to an ideal environment, the first
thing they take in is phosphorus. This phosphorus take-up
is known as luxury uptake.
16. Define the following terms:
a. Reclamation. The operation or process of changing
the condition or characteristics of water so that im-
proved uses can be achieved.
b. Recycle. The use of water or wastewater within (in-
ternally) a facility before it is discharged to a treatment
system.
17. Possible Causes
of Clogging
1. Slimes
2. Carbon fines
Possible Cures
for Cause
1. Chlorination or
allow well to rest.
2. Remove fines by
passing the water
through a sand/
anthracite filter.
18. Define the following terms:
a. Offset. The difference between the actual value and
the desired value (or set point) characteristic of pro-
portional controllers that do not incorporate reset ac-
tion.
b. Set point. The position at which the control or con-
troller is set. This is the same as the desired value of
the process variable.
19. Plants are being designed and constructed with sophisti-
cated instrument and control systems because of tougher
discharge and monitoring requirements and also to help
operators do their job.
20. Instruments are used instead of our human senses be-
cause they provide a more accurate, consistent, sensitive
and permanent means of monitoring (measuring) treat-
ment processes.
21. A thermocouple measures temperature.
22. A Bourdon Tube measures pressure.
23. The purpose of transmitting instruments is to send the
variable, as measured by the measuring device (sensor),
to another device for conversion to a usable number.
Detection devices for explosive gases are installed in the
headworks of treatment plants for safety reasons if explo-
sive gases or vapors may reach and accumulate in the
headworks.
Air flow in the activated sludge process is usually meas-
ured by a differential pressure metering device such as an
orifice plate.
24
25.
-------
Industrial Waste Treatment 809
26. Adverse characteristics of industrial wastes that could
have serious impacts on collection systems include acid
wastes, thermal wastes, solids, oil and grease, odors,
toxic substances, flammable and explosive material.
27. One method of collecting a representative sample when
wastewater has oil or other floating materials on the sur-
face is to divert the entire waste stream to a large con-
tainer for a short time period. The approximate quantity of
floatables or oil may be determined by measuring the ma-
terial that rises to the top of the container.
28. If a gasoline, solvent or other type of hydrocarbon enters
the treatment plant, take the following actions:
1. Hold gasoline or solvent on top of primary clarifiers and
allow wind to disperse fumes,
2. Inspect wet well headworks ventilation and provide
extra ventilation with blowers only (no suction of vapors
into fans),
3. Divert to holding basin,
4. Keep personnel clear of area,
5. In pure oxygen plants, vent and purge reactors with air,
and
6. Locate source and prevent event from happening
again.
29. Define the following terms:
a. Adsorption. The gathering of a gas, liquid, or dis-
solved substance on the surface or interface zone of
another substance.
b. Acidity. The capacity of water or wastewater to neu-
tralize bases. Acidity is a measure of how much base
can be added to a liquid without causing a great
change in pH.
c. Defining. A process that arranges the activated car-
bon particles according to size. This process is also
used to remove small particles from granular contac-
tors to prevent excessive head loss.
d. Micron. A unit of length. One millionth of a meter or
one thousandth of a millimeter. One micron equals
0.00004 of an inch.
e. Ultrafiltration. A membrane filtration process used
for the removal of organic compounds in an aqueous
(watery) solution.
30. Water can become biologically contaminated by bacteria,
viruses and other microorganisms excreted from the
human body and other warm-blooded animals. These
excretions may reach the environment through (1) sani-
tary wastewater, (2) storm waters washing the land of
animal wastes and (3) through certain industries, most
notably slaughterhouses and tanneries.
31. Heavy plugging of a screen could be caused by
1. High solids loads, and/or
2. A defective cleaning system.
32. The lower the pH, the greater the rate of corrosion. If the
pH of a solution is allowed to drift outside of the design
range, corrosion can start.
33. Ventilation should be provided in chemical feed facilities to
minimize chemical exposure to personnel, controls and
equipment.
34. The counter-current flow principle is the process where
flow enters the bottom of the carbon column and new or
regenerated carbon is added to the top of the container.
This principle allows for the oldest carbon to contact the
wastewater first and the newest or more virgin carbon to
make contact with the effluent last. In this manner, the
wastewater is polished as it flows up through the carbon
column.
35. Activated carbon could cause an oxygen deficiency in a
carbon column reactor vessel because activated carbon
adsorbs oxygen molecules.
36. Define the following terms:
a. Air Gap. An open vertical drop, or vertical empty
space, between a drinking (potable) water supply and
the point of use in a wastewater treatment plant. This
gap prevents back siphonage because there is no
way wastewater can reach the drinking water.
b. Cavitation. The formation and collapse of a gas
pocket or bubble on the blade of an impeller. The
collapse of this gas pocket or bubble drives water into
the impeller with a terrific force that can cause pitting
on the impeller surface.
c. Electro-chemical Process. A process that causes
the deposition or formation of a seal or coating of a
chemical element or compound by the use of electric-
ity.
37. The suction hose has a strainer on the end to prevent
pulling rocks and debris into the pump to avoid damaging
the pump or plugging the hoses or pipes.
38. If a diaphragm pump suddenly stops pumping, remove
discharge valve and clean out pump cavity.
39. The purpose of a carburetor on a gasoline engine is to
produce a mixture of fuel and air on which the engine will
operate.
40. If an air conditioner runs but fails to cool, some of the
refrigerant charge may have been lost.
Problems
1. Known Unknown
Intl. Flow, MGD = 4.0 MGD WAS Flow.MGD
Tank Vol., MG = 0.8 MG
COD, mg/L = 110 mg/L
MLSS, mg/L = 3,100 mg/L
MLSS VM, % = 69%
RAS SS, mg/L = 6,400 mg/L
Desired F/M
lbs COD/day = 0 28 lbs _COD/day
lb MLVSS lb MLVSS
Current WAS, MGD = 0.35 MGD
a. Determine COD applied in pounds per day.
COD, lbs/day = Flow, MGD x COD, mg/L x 8.34 lbs/gal
= 4 MGD x 110 mg/L x 8.34 lbs/gal
= 3,670 lbs/day
-------
810 Final Examination
b. Determine the desired pounds of MLVSS.
COD applied, lbs/day
Desired MLVSS,
lbs
F/M, lbs COD/day/lb MLVSS
3,760 lbs COD/day
0.28 lbs COD/day/lb MLVSS
= 13,107 lbs
Use 13,100 lbs*
' From a practical standpoint, you can't measure MLSS or MLVSS
any closer than to the nearest 100 pounds.
c. Determine the desired pounds MLSS.
Desired MLSS. lbs - De^ed MLVSS, lbs
MLSS VM portion
= 13,107 lbs
0.69
= 18,996 lbs
Use 19,000 lbs
d. Determine actual MLSS pounds under aeration.
Actual MLSS, lbs = Tank Vol, MQ x MLSS, mg/L x 8.34 lbs/gal
= 0.8 MG x 3,100 mg/L x 8.34 lbs/gal
= 20,683 lbs
Use 20,700 lbs
e. Calculate the additional WAS, MGD, to maintain the
desired food to microorganism (F/M) ratio.
Additional WAS _ Actual MLSS, lbs - Desired MLSS. lbs
Flow, MGD ras SS. mg/L x 8.34 lbs/gal
= 20.700 lbs - 19,000 lbs
6,400 mg/L x 8.34 lbs/gal
- 0.032 MGD x 694 GPM/MGD
= 22 GPM
f. Calculate the total WAS flow in MGD and GPM.
Total WAS = Current WAS Additional WAS
Flow, MGD Flow, MGD Flow, MGD
= 0.35 MGD + 0.032 MGD
= 0.35 MGD X 694 GPM/MGD
«= 243 GPM
2. Known
Row, MGD = 2 MGD
Prim Effl SS, mg/L = 120 mg/L
Prim Infl SS, mg/L = 300 mg/L
Prim Effl BOD, mg/L =175 mg/L
Sec Effl BOD, mg/L = 25 mg/L
Y, lbs SS/lb BOD = 0.5 lbs SS/lb BOD
Prim Sludge Solids, % = 5%
Sec Sludge Solids, % = 1.5%
Unknown
Volume of Sludge,
gal/day
a. Calculate the amount of dry primary sludge produced in
pounds per day.
Primary Sludge, = Flow, MGD (In SS, mg/L - Et SS, mg/L) 8.34 lbs/gal
lbs/day
= 2 MGD (300 mg/L = 120 mg/L) 8 34 lbs/gal
= 3000 lbs/day (dry solids)
b. Calculate the amount of BOD removed by the second-
ary system in lbs BOD per day.
BOD Removed. = Flow. MGD (BOD In, mg/L - BOD Out, mg/L) 8.34 lbs/gal
lbs/day
= 2 MGD (175 mg/L - 25 mg/L) 8.34 lbs/gal
- 2500 lbs BOD/day
c. Determine the secondary sludge produced in terms of
dry sludge solids per day.
Sludge Produced _ BOD Removed,
lbs dry solids/day lbs BOD/day
x Y.
lbs SI Sol Prod/day
lbs BOD Removed/day
2500 lbs BOD/day x 0 5 lbs Sl Sol/day
1 lb BOD/day
t250 lbs dry sludge solids/day
d. Estimate the total volume of sludge produced in gallons
per day.
Sludge Volume,
gal/day
Primary Sludge Secondary Sludge
Volume, gal/day Volume, gal/day
Prim Sludge, lbs dry solids/day
Prim Sludge Solids, %/100% x 8.34 lbs/gal
+ Sec Sludge, lbs/dry solids/day
Sec Sludge Solids, %/100% x 8.34 lbs/gal
3000 lbs/day 1250 lbs/day
Known
5%/100% X 8.34 lbs/gal 1.5%/100% x 8.34 lbs/gal
= 7200 gal/day + 10,000 gal/day
= 17,200 gal/day
Unknown
Jar Tests on Waste Activated Sludge Costs of Polymers A
Flow, GPD = 35,000 GPD and B, $/ton of sludge
SI Sol, % = 1.4%
Polymer A, lbs/day = 20 lbs/day
Polymer B, lbs/day = 180 lbs/day
Polymer A, $/lb = $2.20/dry lb
Polymer B, $/lb = $0.22/liquid lb
a. Determine the polymer dosage in pounds of polymer
per ton of sludge for both Polymer A and B.
1. Calculate the tons of dry sludge solids per day
treated by the polymers.
Sludge, _ Flow, GPD x 8.34 lbs/gal x SI Sol, %/100%
tons/day - 2000 lbs/ton
_ 35,000 gal/day x 8.34 lbs/gal x 1.5%/100%
2000 lbs/ton
= 2.19 tons/day
2. Calculate the dosage of Polymer A in dry pounds of
polymer per ton of sludge solids.
Polymer A Dose,
lbs polymer
ton sludge
= Amount of Polymer A, lbs/day
Sludge, tons/day
_ 20 lbs Polymer A/day
2.19 tons/day
= 9-1 lbs dry Polymer A/ton sludge
-------
Industrial Waste Treatment 811
3. Calculate the dosage for Polymer B in liquid pounds
of polymer per ton of sludge solids.
Polymer B Dose,
lbs polymer _ Amount of Polymer B, lbs/day
ton sludge Sludge, tons/day
_ 180 lbs Polymer B/day
2.19 tons/day
= 82.2 lbs liquid Polymer B/ton sludge
b. Calculate cost for Polymer A in dollars of polymer per
ton of sludge solids treated.
Cost, $/ton = Dose, 'bsjpolymer x Po|ymer Cost $/(b
ton sludge
= g lbs polymer x $2.20/lb polymer
ton sludge
= $20.02/ton of sludge
c. Calculate the cost for Polymer B in dollars of polymer
per ton of sludge solids treated.
Cost, $/ton = Dose, lba polymer x p0|ymer Cost $/|b
ton sludge
= 82 2 lbs polymer x $0 22/lb polymer
ton sludge
= $18.04/ton of sludge
Known Unknown
Polymer Cone., Ib/gal = 0.5 lbs/gal Polymer Dose,
Polymer Pump, GPM = 0.18 GPM mg/L
Flow to Filter, GPM = 6,000 GPM
Calculate the polymer dose in mg/L.
Dose, mg/L
5. Known
Flow, gal/min x Cone., lbs polymer/gal
Flow, gal/min x 8.34 lbs/gal
_ 0.18 gal/min x 0.5 lbs/gal
6,000 gal/min x 8.34 lbs/gal
_ 0.09 lbs polymer x 1,000,000
50,040 lbs water 1 M
= 1.8 mg/L
Unknown
Flow, MGD = 0.8 MGD 1. SS Loading, lbs/day
Infl SS, mg/L = 1,800 mg/L 2. BOD Loading, lbs/day
Effl SS, mg/L =100 mg/L 3. SS Removal, %
Infl BOD, mg/L = 150 mg/L
a. Calculate the influent suspended solids loading in
pounds per day.
S|bs/day m9' = Flow' MGD X lnfl SS> mg/L * 8,34 lbs/gal
= 0.8 MGD x 1800 mg/L x 8.34 lbs/gal
= 12,000 lbs suspended solids/day
b. Calculate the influent BOD loading in pounds BOD per
day.
B|bs/dayad'n9' = Flow' MGD * BOD' mg/L x 8 34 lbs/gal
= 0.8 MGD =x 150 mg/L x 8.34 lbs/gal
= 1,000 lbs BOD/day
c. Determine the percent suspended solids removal.
SS Removal, % = ^ln>l SS' ~ SS'm^)
Infl SS, mg/L
= (1800 mg/L - 100 mg/L) 10()o/o
1800 mg/L
= 94.4%
-------
GLOSSARY
A Summary of the Words Defined
in
OPERATION OF WASTEWATER TREATMENT PLANTS
-------
814 Treatment Plants
Project Pronunciation Key
by Warren L. Prentice
The Project Pronunciation Key is designed to aid you in the
pronunciation of new words. While this key is based primarily
on familiar sounds, it does not attempt to follow any particular
pronunciation guide. This key is designed solely to aid
operators in this program.
You may find it helpful to refer to other available sources for
pronunciation help. Each current standard dictionary contains
a guide to its own pronunciation key. Each key will be different
from each other and from this key. Examples of the difference
between the key used in this program and the Webster's NEW
WORLD DICTIONARY "Key"1 are shown below:
In using this key, you should accent (say louder) the syllable
which appears in capital letters. The following chart is pre-
sented to give examples of how to pronounce words using the
Project Key,
SYLLABLE
WORD
1st
2nd
3rd
4th
5th
acid
AS
id
coagulant
CO
AGG
you
lent
biological
BUY
0
LODGE
ik
cull
The first word, ACID, has its first syllable accented. The
second word, COAGULANT, has its second syllable ac-
cented. The third word, BIOLOGICAL, has its first and third
syllables accented.
We hope you will find the key useful in unlocking the pro-
nunciation of any new word.
Term
ac id
co I i f o r m
biological
Proje c t Key
A S-i d
COA L-i -f o r m
BU Y-o-LO DG E-i [
Webster Key
as ad
k o -la-f o r m
bi-a-la j-i-ka I
1 The Webster's NEW WORLD DICTIONARY, College Edition, 1968, was chosen rather than an unabridged dictionary because of Its
availability to the operator.
-------
Glossary 815
GLOSSARY
ABS ABS
Alkyl Benzene Sulfonate. A type of surfactant, or surface active agent, present in synthetic detergents in the United States before
1965. ABS was especially troublesome because it caused foaming and resisted breakdown by biological treatment processes. ABS
has been replaced in detergents by linear alkyl sulfonate (LAS) which is biodegradable.
ABSORPTION (ab-SORP-shun) ABSORPTION
Taking in or soaking up of one substance into the body of another by molecular or chemical action (as tree roots absorb dissolved
nutrients in the soil).
ACID ACID
(1) A substance that tends to lose a proton. (2) A substance that dissolves in water with the formation of hydrogen ions. (3) A
substance containing hydrogen which may be replaced by metals to form salts.
ACIDITY ACIDITY
The capacity of water or wastewater to neutralize bases. Acidity is expressed in milligrams per liter of equivalent calcium carbonate.
Acidity is not the same as pH because water does not have to be strongly acidic (low pH) to have a high acidity. Acidity is a measure
of how much base can be added to a liquid without causing a great change in pH.
ACTIVATED SLUDGE (ACK-ta-VATE-ed sluj) ACTIVATED SLUDGE
Sludge particles produced in raw or settled wastewater (primary effluent) by the growth of organisms (including zoogleal bacteria) in
aeration tanks in the presence of dissolved oxygen. The term "activated" comes from the fact that the particles are teeming with
bacteria, fungi, and protozoa. Activated sludge is different from primary sludge in that the sludge particles contain many living
organisms which can feed on the incoming wastewater.
ACTIVATED SLUDGE PROCESS (ACK-ta-VATE-ed sluj) ACTIVATED SLUDGE PROCESS
A biological wastewater treatment process which speeds up the decomposition of wastes in the wastewater being treated. Activated
sludge is added to wastewater and the mixture (mixed liquor) is aerated and agitated. After some time in the aeration tank, the
activated sludge is allowed to settle out by sedimentation and is disposed of (wasted) or reused (returned to the aeration tank) as
needed. The remaining wastewater then undergoes more treatment.
ADSORPTION (add-SORP-shun) ADSORPTION
The gathering of a gas, liquid, or dissolved substance on the surface or interface zone of another substance.
ADVANCED WASTE TREATMENT ADVANCED WASTE TREATMENT
Any process of water renovation that upgrades treated wastewater to meet specific reuse requirements. May include general
cleanup of water or removal of specific parts of wastes insufficiently removed by conventional treatment processes. Typical
processes include chemical treatment and pressure filtration. Also called TERTIARY TREATMENT.
AERATION (air-A-shun) AERATION
The process of adding air. In wastewater treatment, air is added to freshen wastewater and to keep solids in suspension. With
mixtures of wastewater and activated sludge, adding air provides mixing and oxygen for the microorganisms treating the wastewa-
ter.
AERATION LIQUOR (air-A-shun) AERATION LIQUOR
Mixed liquor. The contents of the aeration tank including living organisms and material carried into the tank by either untreated
wastewater or primary effluent.
-------
816 Treatment Plants
AERATION TANK (air-A-shun) AERATION TANK
The tank where raw or settled wastewater is mixed with return sludge and aerated. The same as aeration bay, aerator, or reactor.
AEROBES AEROBES
Bacteria that must have molecular (dissolved) oxygen (DO) to survive.
AEROBIC (AIR-O-bick) AEROBIC
A condition in which "free" or dissolved oxygen is present in the aquatic environment.
AEROBIC BACTERIA (AIR-O-bick back-TEAR-e-ah) AEROBIC BACTERIA
Bacteria which will live and reproduce only in an environment containing oxygen which is available for their respiration (breathing),
namely atmospheric oxygen or oxygen dissolved in water. Oxygen combined chemically, such as in water molecules (H20), cannot
be used for respiration by aerobic bacteria.
AEROBIC DECOMPOSITION (AIR-O-bick) AEROBIC DECOMPOSITION
The decay or breaking down of organic material in the presence of "free" or dissolved oxygen.
AEROBIC DIGESTION (AIR-O-bick) AEROBIC DIGESTION
The breakdown of wastes by microorganisms in the presence of dissolved oxygen. Waste sludge is placed in a large aerated tank
where aerobic microorganisms decompose the organic matter in the sludge. This is an extension of the activated sludge process.
AEROBIC PROCESS (AIR-O-bick) AEROBIC PROCESS
A waste treatment process conducted under aerobic (in the presence of "free" or dissolved oxygen) conditions.
AGE TANK AGE TANK
A tank used to store a known concentration of chemical solution for feed to a chemical feeder. Also called a "day tank."
AGGLOMERATION (a-GLOM-er-A-shun) AGGLOMERATION
The growing or coming together of small scattered particles into larger floes or particles which settle rapidly. Also see FLOC.
AIR BINDING AIR BINDING
The clogging of a filter, pipe or pump due to the presence of air released from water.
AIR GAP air gap AIR GAP
An open vertical drop, or vertical empty space, between a drinking (potable) water
supply and the point of use in a wastewater treatment plant. This gap prevents 1
back siphonage because there is no way wastewater can reach the drinking water.
Pt ANT
AIR UFT AIR LIFT
A special type of pump. This device consists of a vertical riser pipe submerged in the wastewater or sludge to be pumped
Compressed air is injected into a tail piece at the bottom of the pipe. Fine air bubbles mix with the wastewater or sludge to form a
mixture lighter than the surrounding water which causes the mixture to rise in the discharge pipe to the outlet. An air-lift pump works
similar to the center stand in a percolator coffee pot. K H urKS
AIR PADDING AIR PADDING
Pumping dry air into a container to assist with the withdrawal of a liquid or to force a liquid gas such as chlorine or sulfur dioxide out
of a container.
ALGAE (AL-gee) ALGAE
Microscopic plants which contain chlorophyll and float or are suspended and live in water. They also may be attached to structures
rocks, or other similar substances.
ALIQUOT (AL-li-kwot) ALIQUOT
Portion of a sample.
ALKALl ALKALI
Any of certain soluble salts, principally of sodium, potassium, magnesium, and calcium, that have the property of combining with
acids to form neutral salts and may be used in chemical processes such as water or wastewater treatment.
-------
Glossary 817
ALKALINITY (AL-ka-LIN-ity) ALKALINITY
The capacity of water or wastewater to neutralize acids. This capacity is caused by the water's content of carbonate, bicarbonate,
hydroxide, and occasionally borate, silicate, and phosphate. Alkalinity is expressed in milligrams per liter of equivalent calcium
carbonate. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have a high alkalinity.
Alkalinity is a measure of how much acid can be added to a liquid without causing a great change in pH.
AMBIENT TEMPERATURE (AM-bee-ent) AMBIENT TEMPERATURE
Temperature of the surroundings.
AMPEROMETRIC (am-PURR-o-MET-rick) AMPEROMETRIC
A method of measurement that records electric current flowing or generated, rather than recording voltage. Amperometric titration is
a means of measuring concentrations of certain substances in water.
ANAEROBES ANAEROBES
Bacteria that do not need molecular (dissolved) oxygen (DO) to survive.
ANAEROBIC (AN-air-O-bick) ANAEROBIC
A condition in which "free" or dissolved oxygen is NOT present in the aquatic environment.
ANAEROBIC BACTERIA (AN-air-O-bick back-TEAR-e-ah) ANAEROBIC BACTERIA
Bacteria that live and reproduce in an environment containing no "free" or dissolved oxygen. Anaerobic bacteria obtain their oxygen
supply by breaking down chemical compounds which contain oxygen, such as sulfate (S04).
ANAEROBIC DECOMPOSITION (AN-air-O-bick) ANAEROBIC DECOMPOSITION
The decay or breaking down of organic material in an environment containing no "free" or dissolved oxygen.
ANAEROBIC DIGESTION (AN-air-O-bick) ANAEROBIC DIGESTION
Wastewater solids and water (about 5% solids, 95% water) are placed in a large tank where bacteria decompose the solids in the
absence of dissolved oxygen. At least two general groups of bacteria act in balance: (1) SAPROPHYTIC bacteria break down
complex solids to volatile acids, and (2) METHANE FERMENTERS break down the acids to methane, carbon dioxide, and water.
ANHYDROUS (an-HI-drous) ANHYDROUS
Very dry. No water or dampness is present.
ANION ANION
A negatively charged ion in an electrolyte solution, attracted to the anode under the influence of electric potential.
ASEPTIC (a-SEP-tick) ASEPTIC
Free from the living germs of disease, fermentation or putrefaction. Sterile.
ASPIRATE (ASS-per-RATE) ASPIRATE
Use of a hydraulic device (aspirator or eductor) to create a negative pressure (suction) by forcing a liquid through a restriction, such
as a Venturi. An aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump; sometimes used instead
of a sump pump.
BOD (BEE-OH-DEE) BOD
Biochemical Oxygen Demand. The rate at which microorganisms use the oxygen in water or wastewater while stabilizing decom-
posable organic matter under aerobic conditions. In decomposition, organic matter serves as food for the bacteria and energy
results from its oxidation.
BTU (BEE-TEA-YOU) BTU
British Thermal Unit. The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.
BACTERIA (back-TEAR-e-ah) BACTERIA
Bacteria are living organisms, microscopic in size, which consist of a single cell. Most bacteria utilize organic matter for their food
and produce waste products as the result of their life processes.
BACTERIAL CULTURE (back-TEAR-e-al) BACTERIAL CULTURE
In the case of activated sludge, the bacterial culture refers to the group of bacteria classed as AEROBES, and facultative organisms,
which covers a wide range of organisms. Most treatment processes in the United States grow facultative organisms which utilize the
carbonaceous (carbon compounds) BOD. Facultative organisms can live when oxygen resources are low. When "nitrification" is
required, the nitrifying organisms are OBLIGATE AEROBES (require oxygen) and must have at least 0.5 mgIL of dissolved oxygen
throughout the whole system to function properly.
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818 Treatment Plants
BAFFLE BAFFLE
A flat board or plate, deflector, guide or similar device constructed or placed in flowing water, wastewater, or slurry systems to cause
more uniform flow velocities, to absorb energy, and to divert, guide, or agitate liquids.
BASE BASE
A compound which dissociates (separates) in aqueous solution to yield hydroxyl ions.
BATCH PROCESS BATCH PROCESS
A treatment process in which a tank or reactor is filled, the water is treated, and the tank is emptied. The tank may then be filled and
the process repeated.
BENCH SCALE ANALYSIS BENCH SCALE ANALYSIS
A method of studying different ways of treating wastewater and solids on a small scale in a laboratory.
BENZENE BENZENE
An aromatic hydrocarbon (C6H6) which is a colorless, volatile, flammable liquid. Benzene is obtained chiefly from coal tar and is
used as a solvent for resins and fats in the manufacture of dyes.
BIOASSAY (BUY-o-ass-SAY) BIOASSAY
(1) A way of showing or measuring the effect of biological treatment on a particular substance or waste, or (2) a method of
determining toxic effects of industrial wastes or other wastes by using live organisms such as fish for test organisms.
BIOCHEMICAL OXYGEN DEMAND (BOD) BIOCHEMICAL OXYGEN DEMAND (BOD)
The rate at which microorganisms use the oxygen in water or wastewater while stabilizing decomposable organic matter under
aerobic conditions. In decomposition, organic matter serves as food for the bacteria and energy results from its oxidation.
BIOCHEMICAL OXYGEN DEMAND (BOD) TEST BIOCHEMICAL OXYGEN DEMAND (BOD) TEST
A procedure that measures the rate of oxygen use under controlled conditions of time and temperature. Standard test conditions
include dark incubation at 20°C for a specified time (usually five days).
BIODEGRADABLE (BUY-o-dee-GRADE-able) BIODEGRADABLE
Organic matter that can be broken down by bacteria to more stable forms which will not create a nuisance or give off foul odors.
BIODEGRADATION (BUY-o-de-grah-DAY-shun) BIODEGRADATION
The breakdown of organic matter by bacteria to more stable forms which will not create a nuisance or give off foul odors.
BIOFLOCCULATION (BUY-o-flock-u-LAY-shun) BIOFLOCCULATION
The clumping together of fine, dispersed organic particles by the action of certain bacteria and algae. This results in faster and more
complete settling of the organic solids in wastewater.
BIOMASS (BUY-o-MASS) BIOMASS
A mass or clump of living organisms feeding on the wastes in wastewater, dead organisms and other debris. This mass may be
formed for, or function as, the protection against predators and storage of food supplies. Also see ZOOGLEAL MASS.
BLANK BLANK
A bottle containing only dilution water or distilled water, but the sample being tested is not added. Tests are frequently run on a
SAMPLE and a BLANK and the differences compared.
BLINDING BLINDING
The clogging of the filtering medium of a microscreen or a vacuum filter when the holes or spaces in the media become sealed off
due to a buildup of grease or the material being filtered.
BOUND WATER BOUND WATER
Water contained within the cell mass of sludges or strongly held on the surface of colloidal particles.
BREAKOUT OF CHLORINE BREAKOUT OF CHLORINE
A point at which chlorine leaves solution as a gas because the chlorine feed rate is too high. The solution is saturated and cannot
dissolve any more chlorine.
BREAKPOINT CHLORINATION BREAKPOINT CHLORINATION
Addition of chlorine to water or wastewater until the chlorine demand has been satisfied and further additions of chlorine result in a
residual that is directly proportional to the amount added beyond the breakpoint.
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Glossary 819
BUFFER BUFFER
A solution or liquid whose chemical makeup neutralizes acids or bases without a great change in pH.
BUFFER ACTION BUFFER ACTION
The action of certain ions in solution in opposing a change in hydrogen-ion concentration.
BUFFER CAPACITY BUFFER CAPACITY
A measure of the capacity of a solution or liquid to neutralize acids or bases. This is a measure of the capacity of water or
wastewater for offering a resistance to changes in pH.
BUFFER SOLUTION BUFFER SOLUTION
A solution containing two or more substances which, in combination, resist any marked change in pH following addition of moderate
amounts of either strong acid or base.
BULKING (BULK-ing) BULKING
Clouds of billowing sludge that occur throughout secondary clarifiers and sludge thickeners when the sludge becomes too light and
will not settle properly.
CALORIE (KAL-o-ree) CALORIE
The amount of heat required to raise the temperature of one gram of water one degree Celsius.
CARBONACEOUS STAGE (car-bun-NAY-shus) CARBONACEOUS
A stage of decomposition that occurs in biological treatment processes when aerobic bacteria, using dissolved oxygen, change
carbon compounds to carbon dioxide. Sometimes referred to as "first-stage BOD" because the microorganisms attack organic or
carbon compounds first and nitrogen compounds later. Also see NITRIFICATION STAGE.
CATHODIC PROTECTION (ca-THOD-ick) CATHODIC PROTECTION
An electrical system for prevention of rust, corrosion, and pitting of steel and iron surfaces in contact with water, wastewater or soil.
CATION EXCHANGE CAPACITY CATION EXCHANGE CAPACITY
The ability of a soil or other solid to exchange cations (positive ions such as calcium, Ca+2) with a liquid.
CAVITATION (CAV-i-TAY-shun) CAVITATION
The formation and collapse of a gas pocket or bubble on the blade of an impeller. The collapse of this gas pocket or bubble drives
water into the impeller with a terrific force that can cause pitting on the impeller surface.
CENTRATE CENTRATE
The water leaving a centrifuge after most of the solids have been removed.
CENTRIFUGE CENTRIFUGE
A mechanical device that uses centrifugal or rotational forces to separate solids from liquids.
CHEMICAL EQUIVALENT CHEMICAL EQUIVALENT
The weight in grams of a substance that combines with or displaces one gram of hydrogen. Chemical equivalents usually are found
by dividing the formula weight by its valence.
CHEMICAL OXYGEN DEMAND or COD CHEMICAL OXYGEN DEMAND or COD
A measure of the oxygen-consuming capacity of inorganic and organic matter present in wastewater. COD is expressed as the
amount of oxygen consumed from a chemical oxidant in mgIL during a specific test. Results are not necessarily related to the
biochemical oxygen demand because the chemical oxidant may react with substances that bacteria do not stabilize.
CHEMICAL PRECIPITATION CHEMICAL PRECIPITATION
(1) Precipitation induced by addition of chemicals. (2) The process of softening water by the addition of lime or lime and soda ash as
the precipitants.
CHLORAMINES (KLOR-a-means) CHLORAMINES
Chloramines are compounds formed by the reaction of chlorine with ammonia.
CHLORINATION (KLOR-i-NAY-shun) CHLORINATION
The application of chlorine to water or wastewater, generally for the purpose of disinfection, but frequently for accomplishing other
biological or chemical results.
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820 Treatment Plants
CHLORINE DEMAND CHLORINE DEMAND
Chlorine demand is the difference between the amount of chlorine added to wastewater and the amount of residual chlorine
remaining after a given contact time. Chlorine demand may change with dosage, time, temperature, pH, and nature and amount of
the impurities in the water.
Chlorine Demand, mgIL = Chlorine Applied, mg/L - Chlorine Residual, mgIL
CHLORINE REQUIREMENT CHLORINE REQUIREMENT
The amount of chlorine which is needed for a particular purpose. Some reasons for adding chlorine are reducing the number of
coliform bacteria (Most Probable Number), obtaining a particular chlorine residual, or destroying some chemical in the water. In
each case a definite dosage of chlorine will be necessary. This dosage is the chlorine requirement.
CHLORORGANIC (chloro-or-GAN-nick) CHLORORGANIC
Chlororganic compounds are organic compounds combined with chlorine. These compounds generally originate from, or are
associated with, living or dead organic materials.
CILIATES (SILLY-ates) CILIATES
A class of protozoans distinguished by short hairs on all or part of their bodies.
CLARIFICATION (KLAIR-i-fi-KAY-shun) CLARIFICATION
Any process or combination of processes the main purpose of which is to reduce the concentration of suspended matter in a liquid.
CLARIFIER (KLAIR-i-fire) CLARIFIER
Settling Tank, Sedimentation Basin. A tank or basin in which wastewater is held for a period of time, during which the heavier solids
settle to the bottom and the lighter material will float to the water surface.
COAGULANT AID COAGULANT AID
Any chemical or substance used to assist or modify coagulation.
COAGULANTS (co-AGG-you-lents) COAGULANTS
Chemicals that cause very fine particles to clump together into larger particles. This makes it easier to separate the solids from the
liquids by settling, skimming, draining or filtering.
COAGULATION (co-AGG-you-LAY-shun) COAGULATION
The use of chemicals that cause very fine particles to clump together into larger particles. This makes it easier to separate the solids
from the liquids by settling, skimming, draining or filtering.
COLIFORM (COAL-i-form) COLIFORM
One type of bacteria. The presence of coliform-group bacteria is an indication of possible pathogenic bacterial contamination. The
human intestinal tract is one of the main habitats of coliform bacteria. They may also be found in the intestinal tracts of warm-
blooded animals, and in plants, soil, air, and the aquatic environment. Fecal coliforms are those coliforms found in the feces of
various warm-blooded animals; whereas the term "coliform" also includes other environmental sources.
COLLOIDS (KOL-loids) COLLOIDS
Very small, finely divided solids (particles that do not dissolve) that remain dispersed in a liquid for a long time due to their small size
and electrical charge.
COLORIMETRIC MEASUREMENT COLORIMETRIC MEASUREMENT
A means of measuring unknown concentrations of water quality indicators in a sample by measuring the sample's color intensity.
The color of the sample after the addition of specific chemicals (reagents) is compared with colors of known concentrations.
COMBINED AVAILABLE CHLORINE COMBINED AVAILABLE CHLORINE
The concentration of chlorine which is combined with ammonia (NH3) as chloramine or as other chloro derivatives, yet is still
available to oxidize organic matter.
COMBINED AVAILABLE RESIDUAL CHLORINE COMBINED AVAILABLE RESIDUAL CHLORINE
That portion of the total residual chlorine which remains in water or wastewater at the end of a specified contact period and reacts
chemically and biologically as chloramines or organic chloramines.
COMBINED RESIDUAL CHLORINATION COMBINED RESIDUAL CHLORINATION
The application of chlorine to water or wastewater to produce a combined chlorine residual. The residual may consist of chlorine
compounds formed by the reaction of chlorine with natural or added ammonia (NH3) or with certain organic nitrogen compounds.
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Glossary 821
COMBINED SEWER COMBINED SEWER
A sewer designed to carry both sanitary wastewaters and storm- or surface-water runoff.
COMMINUTION (com-mi-NEW-shun) COMMINUTION
Shredding. A mechanical treatment process which cuts large pieces of wastes into smaller pieces so they won't plug pipes or
damage equipment. COMMINUTION and SHREDDING usually mean the same thing.
COMMINUTOR (com-mi-NEW-ter) COMMINUTOR
A device to reduce the size of the solid chunks in wastewater by shredding (comminuting). The shredding action is like many
scissors cutting or chopping to shreds all the large influent solids material.
COMPOSITE (PROPORTIONAL) SAMPLE (com-POZ-it) COMPOSITE (PROPORTIONAL) SAMPLE
A composite sample is a collection of individual samples obtained at regular intervals, usually every one or two hours during a
24-hour time span. Each individual sample is combined with the others in proportion to the flow when the sample was collected. The
resulting mixture (composite sample) forms a representative sample and is analyzed to determine the average conditions during the
sampling period.
COMPOUND COMPOUND
A pure substance composed of two or more elements whose composition is constant. For example, table salt (sodium chloride - Na
CI) is a compound.
CONING (CONE-ing) CONING
Development of a cone-shaped flow of liquid, like a whirlpool, through sludge. This can occur in a sludge hopper during sludge
withdrawal when the sludge becomes too thick. Part of the sludge remains in place while liquid rather than sludge flows out of the
hopper. Also called "coring."
CONTACT STABILIZATION CONTACT STABILIZATION
Contact stabilization is a modification of the conventional activated sludge process. In contact stabilization, two aeration tanks are
used. One tank is for separate re-aeration of the return sludge for at least four hours before it is permitted to flow into the other
aeration tank to be mixed with the primary effluent requiring treatment.
CONTINUOUS PROCESS CONTINUOUS PROCESS
A treatment process in which water is treated continuously in a tank or reactor. The water being treated continuously flows into the
tank at one end, is treated as it flows through the tank, and flows out the opposite end as treated water.
CONVENTIONAL TREATMENT CONVENTIONAL TREATMENT
The pretreatment, sedimentation, flotation, trickling filter, activated sludge and chlorination wastewater treatment processes.
CROSS CONNECTION CROSS CONNECTION
A connection between drinking (potable) water and an unsafe water supply. For example, if you have a pump moving nonpotable
water and hook into the drinking water system to supply water for the pump seal, a cross connection or mixing between the two
water systems can occur. This mixing may lead to contamination of the drinking water.
CRYOGENIC (cry-o-JEN-nick) CRYOGENIC
Low temperature.
DO (DEE-OH) DO
Abbreviation of Dissolved Oxygen. DO is the atmospheric oxygen dissolved in water or wastewater.
DATEOMETER (day-TOM-uh-ter) DATEOMETER
A small calendar disc attached to motors and equipment to indicate the year in which the last maintenance service was performed.
DAY TANK DAY TANK
A tank used to store a known concentration of chemical solution for feed to a chemical feeder. Also called an "age tank."
DECHLORINATION (dee-KLOR-i-NAY-shun) DECHLORINATION
The removal of chlorine from the effluent of a treatment plant.
DECIBEL DECIBEL
A unit for expressing the relative intensity of sounds on a scale from zero for the average least perceptible sound to about 130 for the
average pain level.
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822 Treatment Plants
DECOMPOSITION, DECAY DECOMPOSITION, DECAY
Processes that convert unstable materials into more stable forms by chemical or biological action. Waste treatment encourages
decay in a controlled situation so that material may be disposed of in a stable form. When organic matter decays under anaerobic
conditions (putrefaction), undesirable odors are produced. The aerobic processes in common use for wastewater treatment produce
much less objectional odors.
DEFINING DEFINING
A process that arranges the activated carbon particles according to size. This process is also used to remove small particles from
granular contactors to prevent excessive head loss.
DEGRADATION (de-grah-DAY-shun) DEGRADATION
The conversion of a substance to simpler compounds.
DENITRIFICATION DENITRIFICATION
A condition that occurs when nitrite or nitrate ions are reduced to nitrogen gas and bubbles are formed as a result of this process.
The bubbles attach to the biological floes and float the floes to the surface of the secondary clarifiers. This condition is often the
cause of rising sludge observed in secondary clarifiers or gravity thickeners.
DENSITY (DEN-sit-tee) DENSITY
A measure of how heavy a substance (solid, liquid or gas) is for its size. Density is expressed in terms of weight per unit volume, that
is, grams per cubic centimeter or pounds per cubic foot. The density of water (at 4°C or 39°F) is 1.0 gram per cubic centimeter or
about 62.4 pounds per cubic foot.
DESICCATOR (DESS-i-KAY-tor) DESICCATOR
A closed container into which heated weighing or drying dishes are placed to cool in a dry environment. The dishes may be empty or
they may contain a sample. Desiccators contain a substance, such as anhydrous calcium chloride, which absorbs moisture and
keeps the relative humidity near zero so that the dish or sample will not gain weight from absorbed moisture.
DETENTION TIME DETENTION TIME
The time required to fill a tank at a given flow or the theoretical time required for a given flow of wastewater to pass through a tank.
DETRITUS (dee-TRI-tus) DETRITUS
The heavy, coarse mixture of grit and organic material carried by wastewater.
DEW POINT DEW POINT
The temperature to which air with a given quantity of water vapor must be cooled to cause condensation of the vapor in the air.
DEWATER DEWATER
To remove or separate a portion of the water present in a sludge or slurry.
DEWATERABLE DEWATERABLE
This is a property of a sludge related to the ability to separate the liquid portion from the solid, with or without chemical conditioning.
A material is considered dewaterable if water will readily drain from it.
DIAPHRAGM PUMP DIAPHRAGM PUMP
The pump in which a flexible diaphragm, generally of rubber or equally flexible material, is the operating part. It is fastened at the
edges in a vertical cylinder. When the diaphragm is raised suction is exerted, and when it is depressed, the liquid is forced through a
discharge valve.
DIATOM DIATOM
A group of microscopic, unicellular, marine or fresh-water algae having siliceous (consisting of silica) cell walls.
DIATOMACEOUS EARTH DIATOMACEOUS EARTH
A fine, siliceous earth consisting mainly of the skeletal remains of diatoms.
DIFFUSED-AIR AERATION DIFFUSED-AIR AERATION
A diffused air activated sludge plant takes air, compresses it, and then discharges the air below the water surface of the aerator
through some type of air diffusion device.
DIFFUSER DIFFUSER
A device (porous plate, tube, bag) used to break the air stream from the blower system into fine bubbles in an aeration tank or
reactor.
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Glossary 823
DIGESTER (die-JEST-er) DIGESTER
A tank in which sludge is placed to allow decomposition by microorganisms. Digestion may occur under anaerobic (more common)
or aerobic conditions.
DISCHARGE HEAD DISCHARGE HEAD
The pressure (in feet (meters) or pounds per square inch (kilograms per square centimeter)) on the discharge side of a pump. The
pressure can be measured from the center line of the pump to the hydraulic grade line of the water in the discharge pipe.
DISINFECTION (dis-in-FECT-shun) DISINFECTION
The process designed to kill most microorganisms in wastewater, including essentially all pathogenic (disease-causing) bacteria.
There are several ways to disinfect, with chlorine being most frequently used in water and wastewater treatment plants. Compare
with STERILIZATION.
DISSOLVED OXYGEN DISSOLVED OXYGEN
Molecular oxygen dissolved in water or wastewater, usually abbreviated DO.
DISTILLATE (DIS-tuh-late) DISTILLATE
In the distillation of a sample, a portion is evaporated; the part that is condensed afterwards is the distillate.
DISTRIBUTOR DISTRIBUTOR
The rotating mechanism that distributes the wastewater evenly over the surface of a trickling filter or other process unit. Also see
FIXED SPRAY NOZZLE.
DOCTOR BLADE DOCTOR BLADE
A blade used to remove any excess solids that may cling to the outside of a rotating screen.
DRAIN TILE SYSTEMS DRAIN TILE SYSTEMS
A system of tile pipes buried under the crops that collect percolated waters and keep the groundwater table below the ground
surface to prevent ponding.
DRAINAGE WELLS DRAINAGE WELLS
Wells that can be pumped to lower the groundwater table and prevent ponding.
DROOP DROOP
The difference between the actual value and the desired value (or set point) characteristics of proportional controllers that do not
incorporate reset action. Also called OFFSET.
DYNAMIC HEAD DYNAMIC HEAD
When a pump is operating, the vertical distance (in feet or meters) from a point to the energy grade lines. Also see TOTAL
DYNAMIC HEAD and STATIC HEAD.
EDUCTOR (e-DUCK-tor) EDUCTOR
A hydraulic device used to create a negative pressure (suction) by forcing a liquid through a restriction, such as a Venturi. An
eductor or aspirator (the hydraulic device) may be used in the laboratory in place of a vacuum pump; sometimes used instead of a
suction pump.
EFFLORESCENCE (EF-low-RESS-ense) EFFLORESCENCE
The powder or crust formed on a substance when moisture is given off upon exposure to the atmosphere.
EFFLUENT (EF-lu-ent) EFFLUENT
Wastewater or other liquid — raw, partially or completely treated — flowing FROM a basin, treatment process, or treatment plant.
ELECTRO-CHEMICAL CORROSION ELECTRO-CHEMICAL CORROSION
The decomposition of a material by: (1) stray current electrolysis, (2) galvanic corrosion caused by dissimilar metals, and (3)
galvanic corrosion caused by differential electrolysis.
ELECTRO-CHEMICAL PROCESS ELECTRO-CHEMICAL PROCESS
A process that causes the deposition or formation of a seal or coating of a chemical element or compound by the use of electricity.
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824 Treatment Plants
ELECTRO-MAGNETIC FORCES ELECTRO-MAGNETIC FORCES
Forces resulting from electrical charges that either attract or repel particles. Particles with opposite charges are attracted to each
other. For example, a panicle with positive charges is attracted to a particle with negative charges. Particles with similar charges
repel each other. A particle with positive charges is repelled by a particle with positive charges and a particle with negative charges
is repelled by another particle with negative charges.
ELECTROLYSIS (ELECT-TROLLEY-sis) ELECTROLYSIS
The decomposition of material by an electric current.
ELECTROLYTE (ELECT-tro-LIGHT) ELECTROLYTE
A substance which dissociates (separates) into two or more ions when it is dissolved in water.
ELECTROLYTIC PROCESS (ELECT-tro-LIT-ick) ELECTROLYTIC PROCESS
A process that causes the decomposition of a chemical compound by the use of electricity.
ELECTRON ELECTRON
An extremely small (microscopic), negatively charged particle. An electron is much too small to be seen with a microscope.
ELEMENT ELEMENT
A substance which cannot be separated into substances of other kinds by ordinary chemical means. For example, sodium (Na) is an
element.
ELUTRIATION (e-LOO-tree-A-shun) ELUTRIATION
The washing of digested sludge in plant effluent. The objective is to remove (wash out) fine particulates and/or alkalinity in sludge.
This process reduces the demand for conditioning chemicals and improves settling or filtering characteristics of the solids.
EMULSION (e-MULL-shun) EMULSION
A liquid mixture of two or more liquid substances not normally dissolved in one another, but one liquid held in suspension in the
other.
END POINT END POINT
Samples are titrated to the end point. This means that a chemical is added, drop by drop, to a sample until a certain color change
(blue to clear, for example) occurs which is called the END POINT of the titration. In addition to a color change, an end point may be
reached by the formation of a precipitate or the reaching of a specified pH. An end point may be detected by the use of an electronic
device such as a pH meter. The completion of a desired chemical reaction.
ENDOGENOUS (en-DODGE-en-us) ENDOGENOUS
A reduced level of respiration (breathing) in which organisms break down compounds within their own cells to produce the oxygen
they need.
ENERGY GRADE LINE (EGL) ENERGY GRADE LINE (EGL)
A line that represents the elevation of energy head (in feet) of water flowing in a pipe, conduit or channel. The line is drawn above the
hydraulic grade line a distance equal to the velocity head of the water flowing at each section or point along the pipe or channel.
ENTERIC ENTERIC
Intestinal.
ENZYMES (EN-zimes) ENZYMES
Enzymes are organic substances which are produced by living organisms and speed up chemical changes.
EQUALIZING BASIN EQUALIZING BASIN
A holding basin in which variations in flow and composition of liquid are averaged. Such basins are used to provide a flow of
reasonably uniform volume and composition to a treatment unit. Also called a balancing reservoir.
ESTUARIES (ES-chew-wear-eez) ESTUARIES
Bodies of water which are located at the lower end of a river and are subject to tidal fluctuations.
EVAPOTRANSPIRATION (e-VAP-o-trans-spi-RAY-shun) EVAPOTRANSPIRATION
The total water removed from an area by transpiration (plants) and by evaporation from soil, snow and water surfaces.
EXPLOSIMETER EXPLOSIMETER
An instrument used to detect explosive atmospheres. When the Lower Explosive Limit (L.E.L.) of an atmosphere is exceeded, an
alarm signal on the instrument is activated.
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Glossary 825
F/M RATIO F/M RATIO
Food to microorganism ratio. A measure of food provided to bacteria in an aeration tank.
Food BOD, lbs/day
Microorganisms MLVSS, lbs
_ Flow, MGD x BOD, mgIL x 8.34 lbs/gal
or
Volume, MG x MLVSS, mgIL x 8.34 lbs/gal
BOD, kg/day
MLVSS, kg
FACULTATIVE (FACK-ul-TAY-tive) FACULTATIVE
Facultative bacteria can use either molecular (dissolved) oxygen or oxygen obtained from food materials such as sulfate or nitrate
ions. In other words, facultative bacteria can live under aerobic or anaerobic conditions.
FACULTATIVE POND (FACK-ul-TAY-tive) FACULTATIVE POND
The most common type of pond in current use. The upper portion (supernatant) is aerobic, while the bottom layer is anaerobic.
Algae supply most of the oxygen to the supernatant.
FILAMENTOUS BACTERIA (FILL-a-MEN-tuss) FILAMENTOUS BACTERIA
Organisms that grow in a thread or filamentous form. Common types are thiothrix and actinomyces.
FILTER AID FILTER AID
A chemical (usually a polymer) added to water to help remove fine colloidal suspended solids.
FIXED FIXED
A sample is "fixed" in the field by adding chemicals that prevent the water quality indicators of interest in the sample from changing
before final measurements are performed later in the lab.
FIXED SPRAY NOZZLE FIXED SPRAY NOZZLE
Cone-shaped spray nozzle used to distribute wastewater over the filter media, similar to a lawn sprinkling system. A deflector or
steel ball is mounted within the cone to spread the flow of wastewater through the cone, thus causing a spraying action. Also see
DISTRIBUTOR.
FLAME POLISHED FLAME POLISHED
Melted by a flame to smooth out irregularities. Sharp or broken edges of glass (such as the end of a glass tube) are rotated in a
flame until the edge melts slightly and becomes smooth.
FLIGHTS FLIGHTS
Scraper boards, made from redwood or other rot-resistant woods or plastic, used to collect and move settled sludge or floating
scum.
FLOC FLOC
Groups or clumps of bacteria and particles or coagulants and impurities that have come together and formed a cluster. Found in
aeration tanks, secondary clarifiers and chemical precipitation processes.
FLOCCULATION (FLOCK-you-LAY-shun) FLOCCULATION
The gathering together of fine particles to form larger particles.
FLOW-EQUALIZATION SYSTEM FLOW-EQUALIZATION SYSTEM
A device or tank designed to hold back or store a portion of peak flows for release during low-flow periods.
FOOD/MICROORGANISM RATIO FOOD/MICROORGANISM RATIO
Food to microorganism ratio. A measure of food provided to bacteria in an aeration tank.
Food BOD, lbs/day
Microorganisms MLVSS, lbs
= Flow, MGD X BOD, mgIL x 8.34 lbs/gal
Volume, MG x MLVSS, mgIL x 8.34 lbs/gal
or = BOP, kg/day
MLVSS, kg
Commonly abbreviated F/M Ratio.
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826 Treatment Plants
FORCE MAIN FORCE MAIN
A pipe that conveys wastewater under pressure from the discharge side of a pump to a point of gravity flow.
FREE AVAILABLE CHLORINE FREE AVAILABLE CHLORINE
The amount of chlorine available in water. This chlorine may be in the form of dissolved gas (Cl2), hypochlorous acid (HOCI), or
hypochlorite ion (OCI~), but does not include chlorine combined with an amine (ammonia or nitrogen) or other organic compound.
FREE AVAILABLE RESIDUAL CHLORINE FREE AVAILABLE RESIDUAL CHLORINE
That portion of the total residual chlorine remaining in water or wastewater at the end of a specified contact period. Residual chlorine
will react chemically and biologically as hypochlorous acid (HOCI) or hypochlorite ion (OCI~).
FREE CHLORINE FREE CHLORINE
Free chlorine is chlorine (Cl2) in a liquid or gaseous form. Free chlorine combines with water to form hypochlorous (HOCI) and
hydrochloric (HCI) acids. In wastewater free chlorine usually combines with an amine (ammonia or nitrogen) or other organic
compounds to form combined chlorine compounds.
FREE OXYGEN FREE OXYGEN
Molecular oxygen available for respiration by organisms. Molecular oxygen is the oxygen molecule, 02, that is not combined with
another element to form a compound.
FREE RESIDUAL CHLORINATION FREE RESIDUAL CHLORINATION
The application of chlorine or chlorine compounds to water or wastewater to produce a free available chlorine residual directly or
through the destruction of ammonia (NH3) or certain organic nitrogenous compounds.
FREEBOARD ^ FREEBOARD
The vertical distance from the normal water surface to the top of the confining wall. "J
FREEBOARD
1
* ^
" i
wateFdepth
FRICTION LOSS FRICTION LOSS
The head lost by water flowing in a stream or conduit as the result of the disturbances set up by the contact between the moving
water and its containing conduit and by intermolecular friction.
GASIFICATION (GAS-i-fi-KAY-shun) GASIFICATION
The conversion of soluble and suspended organic materials into gas during anaerobic decomposition. In clarifiers the resulting gas
bubbles can become attached to the settled sludge and cause large clumps of sludge to rise and float on the water surface. In
anaerobic sludge digesters, this gas is collected for fuel or disposed of using the waste gas burner.
GATE GATE
A movable watertight barrier for the control of a liquid in a waterway.
GRAB SAMPLE GRAB SAMPLE
A single sample of wastewater taken at neither a set time nor flow.
GRAVIMETRIC GRAVIMETRIC
A means of measuring unknown concentrations of water quality indicators in a sample by WEIGHING a precipitate or residue of the
sample.
GRIT GRIT
The heavy mineral material present in wastewater, such as sand, eggshells, gravel, and cinders.
GRIT REMOVAL GRIT REMOVAL
Grit removal is accomplished by providing an enlarged channel or chamber which causes the flow velocity to be reduced and allows
the heavier grit to settle to the bottom of the channel where it can be removed.
GROWTH RATE GROWTH RATE
An experimentally determined constant to estimate the unit growth rate of bacteria while degrading organic wastes.
HEAD HEAD
A term used to describe the height or energy of water above a point. A head of water may be measured in either height (feet or
meters) or pressure (pounds per square inch or kilograms per square centimeter). Also see DISCHARGE HEAD, DYNAMIC HEAD,
STATIC HEAD, SUCTION HEAD, SUCTION LIFT and VELOCITY HEAD.
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Glossary 827
HEAD LOSS
An indirect measure of loss of energy or pressure. Flowing water will lose some of
its energy when it passes through a pipe, bar screen, comminutor, filter or other
obstruction. The amount of energy or pressure lost is called "head loss." Head loss
is measured as the difference in elevation between the upstream water surface
and the downstream water surface and may be expressed in feet or meters.
HEAD LOSS
HEAD LOSS
HEADER HEADER
A large pipe to which the ends of a series of smaller pipes are connected. Also called a "manifold."
HEADWORKS HEADWORKS
The facilities where wastewater enters a wastewater treatment plant. The headworks may consist of bar screens, comminutors, a
wet well and pumps.
HEPATITIS HEPATITIS
Hepatitis is an acute viral infection of the liver. Yellow jaundice is one symptom of hepatitis.
HUMUS SLUDGE HUMUS SLUDGE
The sloughed particles of biomass from trickling filter media that are removed from the water being treated in secondary clarifiers.
HYDRAULIC GRADE LINE (HGL) HYDRAULIC GRADE LINE (HGL)
The surface or profile of water flowing in an open channel or a pipe flowing partially full. If a pipe is under pressure, the hydraulic
grade line is at the level water would rise to in a small tube connected to the pipe. To reduce the release of odors from wastewater,
the water surface should be kept as smooth as possible.
HYDRAULIC LOADING HYDRAULIC LOADING
Hydraulic loading refers to the flows (MGD or cu m/day) to a treatment plant or treatment process. Detention times, surface loadings
and weir overflow rates are directly influenced by flows.
HYDROGEN ION CONCENTRATION (H+) HYDROGEN ION CONCENTRATION (H+)
The weight of hydrogen ion in moles per liter of solution. Commonly expressed as the pH value, which is the logarithm of the
reciprocal of the hydrogen-ion concentration.
pH = log 1
(H+)
HYDROGEN SULFIDE (H2S) HYDROGEN SULFIDE (H2S)
Hydrogen sulfide is a gas with a rotten egg odor. This gas is produced under anaerobic conditions. Hydrogen sulfide is particularly
dangerous because it dulls your sense of smell so that you don't notice it after you have been around it for a while and because the
odor is not noticeable in high concentrations. The gas is very poisonous to your respiratory system, explosive, flammable and
colorless.
HYDROLOGIC CYCLE (Hl-dro-loj-ic) HYDROLOGIC CYCLE
The process of evaporation of water into the air and its return to earth by precipitation (rain or snow). This process also includes
transpiration from plants, groundwater movement and runoff into rivers, streams and the ocean.
HYDROLYSIS (hi-DROL-e-sis) HYDROLYSIS
The addition of water to the molecule to break down complex substances into simpler ones.
HYDROSTATIC SYSTEM HYDROSTATIC SYSTEM
In a hydrostatic sludge removal system, the surface of the water in the clarifier is higher than the surface of the water in the sludge
well or hopper. This difference in pressure head forces sludge from the bottom of the clarifier to flow through pipes to the sludge well
or hopper.
HYGROSCOPIC (HI-grow-SKOP-ic) HYGROSCOPIC
A substance that absorbs or attracts moisture from the air.
HYPOCHLORINATION (hi-po-KLOR-i-NAY-shun) HYPOCHLORINATION
The application of hypochlorite compounds to water or wastewater for the purpose of disinfection.
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828 Treatment Plants
HYPOCHLORINATORS (hi-poe-KLOR-i-NAY-tors) HYPOCHLORINATORS
Chlorine pumps or devices used to feed chlorine solutions made from hypochlorites such as bleach (sodium hypochlorite) or
calcium hypochlorite.
HYPOCHLORITE (hi-po-KLOR-ite) HYPOCHLORITE
Hypochlorite compounds contain chlorine and are used for disinfection. They are available as liquids or solids (powder, granules,
and pellets) in barrels, drums, and cans.
IMHOFF CONE f IMHOFF CONE
A clear, cone-shaped container marked with graduations. The cone is used to
measure the volume of settleable solids in a specific volume of wastewater.
IMPELLER * IMPELLER
A rotating set of vanes designed to impart rotation of a mass of fluid.
IMPELLER PUMP IMPELLER PUMP
Any pump in which the water is moved by the continuous application of power from some rotating mechanical source.
INCINERATION INCINERATION
The conversion of dewatered sludge cake by combustion (burning) to ash, carbon dioxide and water vapor.
INDICATOR (CHEMICAL) INDICATOR (CHEMICAL)
A substance that gives a visible change, usually of color, at a desired point in a chemical reaction, generally at a specified end point.
INDOLE (IN-dole) INDOLE
An organic compound (C8H7N) containing nitrogen which has an ammonia odor.
INFILTRATION (IN-fill-TRAY-shun) INFILTRATION
The seepage of groundwater into a sewer system, including service connections. Seepage frequently occurs through defective or
cracked pipes, pipe joints, connections or manhole walls.
INFLOW INFLOW
Water discharged into the sewer system from sources other than regular connections. This includes flow from yard drains,
foundation drains and around manhole covers. Inflow differs from infiltration in that it is a direct discharge into the sewer rather than
a leak in the sewer itself.
INFLUENT (IN-flu-ent) INFLUENT
Wastewater or other liquid — raw or partially treated — flowing INTO a reservoir, basin, treatment process, or treatment plant.
INHIBITORY SUBSTANCES INHIBITORY SUBSTANCES
Materials that kill or restrict the ability of organisms to treat wastes.
INOCULATE (in-NOCK-you-late) INOCULATE
To introduce a seed culture into a system.
INORGANIC WASTE INORGANIC WASTE
Waste material such as sand, salt, iron, calcium, and other mineral materials which are only slightly affected by the action of
organisms. Inorganic wastes are chemical substances of mineral origin; whereas organic wastes are chemical substances usually
of animal or vegetable origin. Also see NONVOLATILE MATTER.
INTERFACE INTERFACE
The common boundary layer between two fluids such as a gas (air) and a liquid (water) or a liquid (water) and another liquid (oil).
IONIC CONCENTRATION IONIC CONCENTRATION
The concentration of any ion in solution, generally expressed in moles per liter.
IONIZATION IONIZATION
The process of adding electrons to, or removing electrons from, atoms or molecules, thereby creating ions. High temperatures,
electrical discharges, and nuclear radiation can cause ionization.
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Glossary 829
JAR TEST JAR TEST
A laboratory procedure that simulates coagulation/flocculation with differing chemical doses. The purpose of the procedure is to
ESTIMATE the minimum coagulant dose required to achieve certain water quality goals. Samples of water to be treated are placed
in six jars. Various amounts of chemicals are added to each jar, stirred and the settling of solids is observed. The lowest dose of
chemicals that provides satisfactory settling is the dose used to treat the water.
JOULE (jewel) JOULE
A measure of energy, work or quantity of heat. One joule is the work done when the point of application of a force of one newton is
displaced a distance of one meter in the direction of the force.
KJELDAHL NITROGEN (KELL-doll) KJELDAHL NITROGEN
Organic and ammonia nitrogen.
LAUNDERS (LAWN-ders) LAUNDERS
Sedimentation tank effluent troughs.
LIMIT SWITCH LIMIT SWITCH
A device that regulates or controls the travel distance of a chain or cable.
LINEAL (LIN-e-al) LINEAL
The length in one direction of a line. For example, a board 12 feet long has 12 lineal feet in its length.
LIQUEFACTION (LICK-we-FACK-shun) LIQUEFACTION
The conversion of large solid particles of sludge into very fine particles which either dissolve or remain suspended in wastewater.
LOADING LOADING
Quantity of material applied to a device at one time.
M or MOLAR M or MOLAR
A molar solution consists of one gram molecular weight of a compound dissolved in enough water to make one liter of solution. A
gram molecular weight is the molecular weight of a compound in grams. For example, the molecular weight of sulfuric acid (H?S04)
is 98. A 1/W solution of sulfuric acid would consist of 98 grams of H2S04 dissolved in enough distilled water to make one liter of
solution.
MBAS MBAS
Methylene Blue Active Substance. Another name for surfactants, or surface active agents, is methylene blue active substances.
The determination of surfactants is accomplished by measuring the color change in a standard solution of methylene blue dye.
MCRT MCRT
Mean Cell Residence Time, days. An expression of the average time that a microorganism will spend in the activated sludge
process.
MCRT days = Solids in Activated Sludge Process, lbs
Solids Removed from Process, lbs/day
MLSS MLSS
Mixed Liquor Suspended Solids, mg/L. Suspended solids in the mixed liquor of an aeration tank.
MLVSS MLVSS
Mixed Liquor Volatile Suspended Solids, mg/L. The organic or volatile suspended solids in the mixed liquor of an aeration tank. This
volatile portion is used as a measure or indication of the microorganisms present.
MPN (EM-PEA-EN) MPN
MPN is the Most Probable Number of coliform-group organisms per unit volume. Expressed as a density or population of organisms
per 100 ml.
MANIFOLD MANIFOLD
A large pipe to which the ends of a series of smaller pipes are connected. Also called a "header."
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830 Treatment Plants
MANOMETER (man-NAH-met-ter) MANOMETER
An instrument for measuring pressure. Usually a glass tube filled with a liquid and used to measure the difference in pressure across
a flow-measuring device such as an orifice or Venturi meter. The instrument used to measure blood pressure is a type of
manometer.
VENTURI METER
£
MANOMETER
MASKING AGENTS MASKING AGENTS
Substances used to cover up or disguise unpleasant odors. Liquid masking agents are dripped into the wastewater, sprayed into the
air, or evaporated (using heat) with the unpleasant fumes or odors and then discharged into the air by blowers to make an
undesirable odor less noticeable.
MEAN CELL RESIDENCE TIME (MCRT) MEAN CELL RESIDENCE TIME (MCRT)
An expression of the average time that a microorganism will spend in the activated sludge process.
MCRT days = Solids in Activated Sludge Process, lbs
Solids Removed from Process, lbs/day
MECHANICAL AERATION MECHANICAL AERATION
The use of machinery to mix air and water so that oxygen can be absorbed into the water. Some examples are: paddle wheels,
mixers, or rotating brushes to agitate the surface of an aeration tank; pumps to create fountains; and pumps to discharge water
down a series of steps forming falls or cascades.
MEDIA MEDIA
The material in a trickling filter on which slime organisms grow. As settled wastewater trickles over the media, slime organisms
remove certain types of wastes thereby partially treating the wastewater. Also the material in a rotating biological contactor or in a
gravity or pressure filter.
MEDIAN MEDIAN
The middle measurement or value. When several measurements are ranked by magnitude (largest to smallest), half of the
measurements will be larger and half will be smaller.
MENISCUS (meh-NIS-cuss) MENISCUS
The curved top of a column of liquid (water, oil, mercury) in a small tube. When the liquid wets the sides of the container (as with
water), the curve forms a valley. When the confining sides are not wetted (as with mercury), the curve forms a hill or upward bulge.
WATER
(READ
BOTTOM) p-
0
MERCURY
(READ
TOP)
MERCAPTANS (mer-CAP-tans) MERCAPTANS
Compounds containing sulfur which have an extremely offensive skunk odor.
MESOPHILIC BACTERIA (mess-O-FILL-lick) MESOPHILIC BACTERIA
Medium temperature bacteria. A group of bacteria that grow and thrive in a moderate temperature'range between 68°F (20°C) and
113°F (45°C). The optimum temperature range for these bacteria in anaerobic digestion is 85 F (30 C) to 100 F (38 C).
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Glossary 831
MICRON (MY-kron) MICRON
A unit of length. One millionth of a meter or one thousandth of a millimeter. One micron equals 0.00004 of an inch.
MICROORGANISMS (micro-ORGAN-is-sums) MICROORGANISMS
Very small organisms that can be seen only through a microscope. Some microorganisms use the wastes in wastewater for food
and thus remove or alter much of the undesirable matter.
MICROSCREEN MICROSCREEN
A device with a fabric straining media with openings usually between 2 and 60 microns. The fabric is wrapped around the outside of
a rotating drum. Wastewater enters the open end of the drum and flows out through the rotating screen cloth. At the highest point of
the drum, the collected solids are backwashed by high-pressure water jets into a trough located within the drum.
MILLIGRAMS PER LITER, mgIL (MILL-i-GRAMS per LEET-er) MILLIGRAMS PER LITER, mg/L
A measure of the concentration by weight of a substance per unit volume. For practical purposes, one mg/L is equal to one part per
million parts (ppm). Thus a liter of water with a specific gravity of 1.0 weighs one million milligrams; and if it contains 10 milligrams of
dissolved oxygen, the concentration is 10 milligrams per million milligrams, or 10 milligrams per liter (10 mg/L), or 10 parts of oxygen
per million parts of water, or 10 parts per million (10 ppm).
MILLIMICRON (MILL-e-MY-cron) MILLIMICRON
One thousandth of a micron or a millionth of a millimeter.
MIXED LIQUOR MIXED LIQUOR
When the activated sludge in an aeration tank is mixed with primary effluent or the raw wastewater and return sludge, this mixture is
then referred to as mixed liquor as long as it is in the aeration tank. Mixed liquor also may refer to the contents of mixed aerobic or
anaerobic digesters.
MIXED LIQUOR SUSPENDED SOLIDS (MLSS) MIXED LIQUOR SUSPENDED SOLIDS(MLSS)
Suspended solids in the mixed liquor of an aeration tank.
MIXED LIQUOR VOLATILE SUSPENDED MIXED LIQUOR VOLATILE SUSPENDED
SOLIDS (MLVSS) SOLIDS (MLVSS)
The organic or volatile suspended solids in the mixed liquor of an aeration tank.
MOLECULAR OXYGEN MOLECULAR OXYGEN
The oxygen molecule, 02, that is not combined with another element to form a compound.
MOLECULAR WEIGHT MOLECULAR WEIGHT
The molecular weight of a compound in grams is the sum of the atomic weights of the elements in the compound. The molecular
weight of sulfuric acid (H2S04) in grams is 98.
Atomic Number Molecular
Element Weight of Atoms Weight
H 1 2 2
S32 1 32
O 16 4 64
98
MOLECULE (MOLL-uh-kule) MOLECULE
A molecule is the smallest portion of an element or compound that still retains or exhibits all the properties of the substance.
MOTILE (MO-till) MOTILE
Motile organisms exhibit or are capable of movement.
MOVING AVERAGE MOVING AVERAGE
To calculate the moving average for the last 7 days, add up the values for the last 7 days and divide by 7. Each day add the most
recent day to the sum of values and subtract the oldest value. By using the 7-day moving average, each day of the week is always
represented in the calculations.
MUFFLE FURNACE MUFFLE FURNACE
A small oven capable of reaching temperatures up to 600°C. Muffle furnaces are used in laboratories for burning or incinerating
samples to determine the amounts of volatile solids and/or fixed solids in samples of wastewater.
MULTI-STAGE PUMP MULTI-STAGE PUMP
A pump that has more than one impeller. A single-stage pump has one impeller.
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832 Treatment Plants
N or NORMAL N or NORMAL
A normal solution contains one gram equivalent weight of a reactant (compound) per liter of solution. The equivalent weight of an
acid is that weight which contains one gram atom of ionizable hydrogen or its chemical equivalent. For example, the equivalent
weight of sulfuric acid (H2S04) is 49 (98 divided by 2 because there are two replaceable hydrogen ions). A 1 N solution of sulfuric
acid would consist of 49 grams of H2S04 dissolved in enough water to make one liter of solution.
NPDES PERMIT NPDES PERMIT
National Pollutant Discharge Elimination System permit is the regulatory agency document designed to control all discharges of
pollutants from point sources into U.S. waterways. NPDES permits regulate discharges into navigable waters from all point sources
of pollution, including industries, municipal treatment plants, large agricultural feed lots and return irrigation flows.
NEUTRALIZATION (new-trall-i-ZAY-shun) NEUTRALIZATION
Addition of an acid or alkali (base) to a liquid to cause the pH of the liquid to move towards a neutral pH of 7.0.
NITRIFICATION (NYE-tri-fi-KAY-shun) NITRIFICATION
A process in which bacteria change the ammonia and organic nitrogen in wastewater into oxidized nitrogen (usually nitrate). The
second-stage BOD is sometimes referred to as the "nitrification stage" (first-stage BOD is called the "carbonaceous stage").
NITRIFYING BACTERIA NITRIFYING BACTERIA
Bacteria that change the ammonia and organic nitrogen in wastewater into oxidized nitrogen (usually nitrate).
NITROGENOUS (nye-TROG-en-ous) NITROGENOUS
Nitrogenous compounds contain nitrogen.
NOMOGRAM NOMOGRAM
A chart or diagram containing three or more scales used to solve problems with three or more variables instead of using mathemati-
cal formulas.
NONCORRODIBLE NONCORRODIBLE
A material that resists corrosion and will not be eaten away by wastewater or chemicals in wastewater.
NONSPARKING TOOLS NONSPARKING TOOLS
These tools will not produce a spark during use.
NONVOLATILE MATTER NONVOLATILE MATTER
Material such as sand, salt, iron, calcium, and other mineral materials which are only slightly affected by the action of organisms.
Volatile materials are chemical substances usually of animal or vegetable origin. Also see INORGANIC WASTE.
NUTRIENT CYCLE NUTRIENT CYCLE
The transformation or change of a nutrient from one form to another until the nutrient has returned to the original form, thus
completing the cycle. The cycle may take place under either aerobic or anaerobic conditions.
NUTRIENTS NUTRIENTS
Substances which are required to support living plants and organisms. Major nutrients are carbon, hydrogen, oxygen, sulfur,
nitrogen and phosphorus. Nitrogen and phosphorus are difficult to remove from wastewater by conventional treatment processes
because they are water soluble and tend to recycle. Also see NUTRIENT CYCLE.
O & M MANUAL (Operation and Maintenance Manual) O & M MANUAL
A manual which outlines procedures for operators to follow to operate and maintain a specific wastewater treatment plant and the
equipment in the plant.
OSHA OSHA
The Williams-Steiger Occupational Safety and Health Act of 1980 (OSHA) is a law designed to protect the health and safety of
industrial workers and treatment plant operators. It regulates the design, construction, operation and maintenance of industrial
plants and wastewater treatment plants. The Act does not apply directly to municipalities at present (1980), EXCEPT in those states
that have approved plans and have asserted jurisdiction under Section 18 of the OSHA Act. However, wastewater treatment plants
have come under stricter regulation in all phases of activity as a result of OSHA standards.
OBLIGATE AEROBES OBLIGATE AEROBES
Bacteria that must have molecular (dissolved) oxygen (DO) to reproduce.
ODOR PANEL 0°0R PANEL
A group of people used to measure odors.
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Glossary 833
OFFSET OFFSET
The difference between the actual value and the desired value (or set point) characteristic of proportional controllers that do not
incorporate reset action. Also called DROOP.
OLFACTOMETER (ol-FACT-tom-meter) OLFACTOMETER
A device used to measure odors in the field by diluting odors with odor-free air.
ORGANIC WASTE ORGANIC WASTE
Waste material which comes mainly from animal or vegetable sources. Organic waste generally can be consumed by bacteria and
other small organisms. Inorganic wastes are chemical substances of mineral origin.
ORGANISM ORGANISM
Any form of animal or plant life. Also see BACTERIA.
ORIFICE (OR-uh-fiss) ORIFICE
An opening in a plate, wall or partition. In a trickling filter distributor, the wastewater passes through an orifice to the surface of the
filter media. An orifice flange set in a pipe consists of a slot or hole smaller than the pipe diameter. The difference in pressure in the
pipe above and below the orifice may be related to flow in the pipe.
ORTHOTOLIDINE (or-tho-TOL-i-dine) ORTHOTOLIDINE
Orthotolidine is a colorimetric indicator of chlorine residual. If chlorine is present, a yellow-colored compound is produced. This
method is no longer approved for tests of effluent chlorine residual.
OVERFLOW RATE OVERFLOW RATE
One of the guidelines for the design of settling tanks and clarifiers in treatment plants.
Overflow Rate, gpd/sq ft = ^low' gallons/day
Surface Area, sq ft
OXIDATION (ox-i-DAY-shun) OXIDATION
Oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. In wastewater
treatment, organic matter is oxidized to more stable substances. The opposite of REDUCTION.
OXIDATION-REDUCTION POTENTIAL OXIDATION-REDUCTION POTENTIAL
The electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element
(the reductant) and used as a qualitative measure of the state of oxidation in wastewater treatment systems.
OXIDIZED ORGANICS OXIDIZED ORGANICS
Organic materials that have been broken down in a biological process. Examples of these materials are carbohydrates and proteins
that are broken down to simple sugars.
OXIDIZING AGENT OXIDIZING AGENT
An oxidizing agent is any substance, such as oxygen (02) and chlorine (Cl2), that can add (take on) electrons. When oxygen or
chlorine is added to wastewater, organic substances are oxidized. These oxidized organic substances are more stable and less
likely to give off odors or to contain disease bacteria. The opposite of REDUCING AGENT.
OZONIZATION (O-zoe-nie-ZAY-shun) OZONIZATION
The application of ozone to water, wastewater, or air, generally for the purposes of disinfection or odor control.
PACKAGE TREATMENT PLANT PACKAGE TREATMENT PLANT
A small wastewater treatment plant often fabricated at the manufacturer's factory, hauled to the site, and installed as one facility.
The package may be either a small primary or a secondary wastewater treatment plant.
PARALLEL OPERATION PARALLEL OPERATION
When wastewater being treated is split and a portion flows to one treatment unit while the remainder flows to another similar
treatment unit. Also see SERIES OPERATION.
PARASITIC BACTERIA (PAIR-a-SIT-tick) PARASITIC BACTERIA
Parasitic bacteria are those bacteria which normally live off another living organism, known as the "host."
PATHOGENIC BACTERIA (path-o-JEN-nick) PATHOGENIC BACTERIA
Bacteria, viruses or cysts which can cause disease (typhoid, cholera, dysentery). There are many types of bacteria which do NOT
cause disease and which are NOT called pathogenic. Many beneficial bacteria are found in wastewater treatment processes
actively cleaning up organic wastes.
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834 Treatment Plants
PERCENT SATURATION PERCENT SATURATION
The amount of a substance that is dissolved in a solution compared with the amount that could be dissolved in the solution,
expressed as a percent.
Amount of Sub. that is Dissolved x 100%
Percent Saturation, %
Amount that Could be Dissolved in Solution
PERCOLATION (PURR-ko-LAY-shun) PERCOLATION
The movement or flow of water through soil or rocks.
PERISTALTIC PUMP (peri-STALL-tick) PERISTALTIC PUMP
A type of positive displacement pump.
pH (PEA-A-ch) pH
pH is an expression of the intensity of the alkaline or acid condition of a liquid. Mathematically, pH is the logarithm (base 10) of the
reciprocal of the hydrogen ion concentration.
pH = Log —
(H+)
The pH may range from 0 to 14, where 0 is most acid, 14 most alkaline, and 7 is neutral. Natural waters usually have a pH between
6.5 and 8.5.
PHENOL (FEE-noll) PHENOL
An organic compound that is a derivative of benzene.
PHENOLPHTHALEIN ALKALINITY PHENOLPHTHALEIN ALKALINITY
A measure of the hydroxide ions plus one half of the normal carbonate ions in aqueous suspension. Measured by the amount of
sulfuric acid required to bring the water to a pH value of 8.3, as indicated by a change in color of phenolphthalein. It is expressed in
milligrams per liter of calcium carbonate.
PHOTOSYNTHESIS (foto-SIN-the-sis) PHOTOSYNTHESIS
A process in which organisms with the aid of chlorophyll (green plant enzyme) convert carbon dioxide and inorganic substances to
oxygen and additional plant material, utilizing sunlight for energy. All green plants grow by this process.
PHYSICAL WASTE TREATMENT PROCESS PHYSICAL WASTE TREATMENT PROCESS
Physical waste treatment processes include use of racks, screens, comminutors, and clarifiers (sedimentation and flotation).
Chemical or biological reactions are not an important part of a physical treatment process.
PLUG FLOW PLUG FLOW
A type of flow that occurs in tanks, basins or reactors when a slug of wastewater moves through a tank without ever dispersing or
mixing with the rest of the wastewater flowing through the tank.
DIRECTION
OF FLOW
PLUG FLOW
POLLUTION POLLUTION
Any change in the natural state of water which interferes with its beneficial reuse or causes failure to meet water-quality require-
ments.
POLYELECTROLYTE (POLY-electro-light) POLYELECTROLYTE
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural poly electrolytes may be of
biological origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polyelectrolytes consist of simple
substances that have been made into complex, high-molecular-weight substances. Often called a "polymer."
POLYMER (POLY-mer) POLYMER
A high-molecular-weight substance that is formed by either a natural or synthetic process. Natural polymers may be of biological
origin or derived from starch products, cellulose derivatives, and alignates. Synthetic polymers consist of simple substances that
have been made into complex, high-molecular-weight substances. Often called a polyelectrolyte.
POLYSACCHARIDE (polly-SAC-a-ride) POLYSACCHARIDE
A carbohydrate such as starch, insulin or cellulose.
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Glossary 835
PONDING PONDING
A condition occurring on trickling filters when the hollow spaces (voids) become plugged to the extent that water passage through
the filter is inadequate. Ponding may be the result of excessive slime growths, trash, or media breakdown.
POPULATION EQUIVALENT POPULATION EQUIVALENT
A means of expressing the strength of organic material in wastewater. In a domestic wastewater system, microorganisms use up
about 0.2 pounds of oxygen per day for each person using the system (as measured by the standard BOD test).
Pop Equiv = Flow, MGD x BOD, mg/L x 8.34 lbs/gal
persons 0.2 lbs BOD/day/person
POSTCHLORINATION POSTCHLORINATION
The addition of chlorine to the plant discharge or effluent, FOLLOWING plant treatment, for disinfection purposes.
POTABLE WATER (POE-ta-bl) POTABLE WATER
Water that does not contain objectionable pollution, contamination, minerals, or infective agents and is considered safe for domestic
consumption.
PRE-AERATION PRE-AERATION
The addition of air at the initial stages of treatment to freshen the wastewater, remove gases, add oxygen, promote flotation of
grease, and aid coagulation.
PRECHLORINATION PRECHLORINATION
The addition of chlorine at the headworks of the plant PRIOR TO other treatment processes mainly for odor and corrosion control.
Also applied to aid disinfection, to reduce plant BOD load, to aid in settling, to control foaming in Imhoff units and to help remove oil.
PRECIPITATE (pre-SIP-i-TATE) PRECIPITATE
To separate (a substance) out in solid form from a solution, as by the use of a reagent. The substance precipitated.
PRECOAT PRECOAT
Application of a free-draining, non-cohesive material such as diatomaceous earth to a filtering media. Precoating reduces the
frequency of media washing and facilitates cake discharge.
PRETREATMENT PRETREATMENT
The removal of metal, rocks, rags, sand, eggshells, and similar materials which may hinder the operation of a treatment plant.
Pretreatment is accomplished by using equipment such as racks, bar screens, comminutors, and grit removal systems.
PRIMARY TREATMENT PRIMARY TREATMENT
A wastewater treatment process that takes place in a rectangular or circular tank and allows those substances in wastewater that
readily settle or float to be separated from the water being treated.
PROCESS VARIABLE PROCESS VARIABLE
A physical or chemical quantity which is usually measured and controlled.
PROTEINACEOUS (PRO-ten-NAY-shus) PROTEINACEOUS
Materials containing proteins which are organic compounds containing nitrogen.
PROTOZOA (pro-toe-ZOE-ah) PROTOZOA
A group of microscopic animals (usually single-celled) that sometimes cluster into colonies.
PRUSSIAN BLUE PRUSSIAN BLUE
A paste or liquid used to show a contact area. Used to determine if gate valve seats fit properly.
PSYCHROPHILIC BACTERIA (sy-kro-FILL-lick) PSYCHROPHILIC BACTERIA
Cold temperature bacteria. A group of bacteria that grow and thrive in temperatures below 68°F (20°C).
PUG MILL PUG MILL
A mechanical device with rotating paddles or blades that is used to mix and blend different materials together.
PURGE PURGE
To remove a gas or vapor from a vessel, reactor or confined space.
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836 Treatment Plants
PUTREFACTION (PEW-tree-FACK-shun) PUTREFACTION
Biological decomposition of organic matter with the production of ill-smelling products associated with anaerobic conditions.
PUTRESCIBLE (pew-TRES-uh-bull) PUTRESC1BLE
Material that will decompose under anaerobic conditions and produce nuisance odors.
PYROMETER (pie-ROM-uh-ter) PYROMETER
An apparatus used to measure high temperatures.
RAS RAS
Return Activated Sludge, mg/L. Settled activated sludge that is collected in the secondary clarifier and returned to the aeration basin
to mix with incoming raw or primary settled wastewater.
RABBLING RABBLING
The process of moving or plowing the material inside a furnace by using the center shaft and rabble arms.
RACK RACK
Evenly spaced parallel metal bars or rods located in the influent channel to remove rags, rocks, and cans from wastewater.
RAW WASTEWATER RAW WASTEWATER
Plant influent or wastewater before any treatment.
REAGENT (re-A-gent) REAGENT
A substance which takes part in a chemical reaction and is used to measure, detect, or examine other substances.
RECALCINE (re-CAL-seen) RECALCINE
A lime-recovery process in which the calcium carbonate in sludge is converted to lime by heating at 1800°F (980°C).
RECARBONATION (re-CAR-bun-NAY-shun) RECARBONATION
A process in which carbon dioxide is bubbled through the water being treated to lower the pH.
RECEIVING WATER RECEIVING WATER
A stream, river, lake or ocean into which treated or untreated wastewater is discharged.
RECHARGE RATE RECHARGE RATE
Rate at which water is added beneath the ground surface to replenish or recharge groundwater.
RECIRCULATION RECIRCULATION
The return of part of the effluent from a treatment process to the incoming flow.
RECLAMATION RECLAMATION
The operation or process of changing the condition or characteristics of water so that improved uses can be achieved.
RECYCLE RECYCLE
The use of water or wastewater within (internally) a facility before it is discharged to a treatment system. Also see REUSE.
REDUCING AGENT REDUCING AGENT
A reducing agent is any substance, such as the chloride ion (CI-) and sulfide ion (S"2), that can give up electrons. The opposite of
OXIDIZING AGENT.
REDUCTION (re-DUCK-shun) REDUCTION
Reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic
conditions in wastewater, sulfate compounds or elemental sulfur are reduced to odor-producing hydrogen sulfide (H2S) or the
sulfide ion (S"2). The opposite of OXIDATION.
RELIQUEFACTION (re-LICK-we-FACK-shun) RELIQUE FACTION
The return of a gas to a liquid. For example, a condensation of chlorine gas returning to the liquid form.
REFRACTORY MATERIALS (re-FRACK-tory) REFRACTORY MATERIALS
Material difficult to remove entirely from wastewater such as nutrients, color, taste- and odor-producing substances and some toxic
materials.
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Glossary 837
REPRESENTATIVE SAMPLE REPRESENTATIVE SAMPLE
A portion of material or water identical in content to that in the larger body of material or water being sampled.
RESIDUAL CHLORINE RESIDUAL CHLORINE
Residual chlorine is the amount of chlorine remaining after a given contact time and under specific conditions.
RESPIRATION RESPIRATION
The process in which an organism uses oxygen for its life processes and gives off carbon dioxide.
RETENTION TIME RETENTION TIME
The time water, sludge or solids are retained or held in a clarifier or sedimentation tank. See DETENTION TIME.
RETURN ACTIVATED SLUDGE (RAS) RETURN ACTIVATED SLUDGE (RAS)
Settled activated sludge that is collected in the secondary clarifier and returned to the aeration basin to mix with incoming raw or
primary settled wastewater.
REUSE REUSE
The use of water or wastewater after it has been discharged and then withdrawn by another user. Also see RECYCLE.
RIPRAP RIPRAP
Broken stones, boulders, or other materials placed compactly or irregularly on levees or dikes for the protection of earth surfaces
against the erosive action of waves.
RISING SLUDGE RISING SLUDGE
Rising sludge occurs in the secondary clarifiers of activated sludge plants when the sludge settles to the bottom of the clarifier, is
compacted, and then starts to rise to the surface, usually as a result of denitrification.
ROTAMETER ROTAMETER
A device used to measure the flow rate of gases and liquids. The gas or liquid being measured flows vertically up a calibrated tube.
Inside the tube is a small ball or a bullet-shaped float (it may rotate) that rises or falls depending on the flow rate. The flow rate may
be read on a scale behind the middle of the ball or the top of the float.
ROTARY PUMP ROTARY PUMP
A type of displacement pump consisting essentially of elements rotating in a pump case which they closely fit. The rotation of these
elements alternately draws in and discharges the water being pumped. Such pumps act with neither suction nor discharge valves,
operate at almost any speed, and do not depend on centrifugal forces to lift the water.
ROTIFERS (ROE-ti-fers) ROTIFERS
Microscopic animals characterized by short hairs on their front end.
ROTOR ROTOR
The rotating part of a machine. The rotor is surrounded by the stationary (non-moving) parts of the machine (stator).
SAR (Sodium Adsorption Ratio) SAR
This ratio expresses the relative activity of sodium ions in the exchange reactions with soil. The ratio is defined as follows:
SAR = Na
[1/2 (Ca + Mg) ]<*
where Na, Ca, and Mg are concentrations of the respective ions in milliequivaients per liter of water.
Na, meq/L = Ca, meq!L = Ca' m9/L
23.0 mg/meq 20.0 mg/meq
Mg, meq/L = —9'
12.15 mg/meq
SCFM SCFM
Cubic Feet of air per Minute at Standard conditions of temperature, pressure and humidity.
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838 Treatment Plants
SVI (Sludge Volume Index) SVI
This is a test used to indicate the settling ability of activated sludge (aerated solids) in the secondary clarifier. The test is a measure
of the volume of sludge compared with its weight. Allow the sludge sample from the aeration tank to settle for 30 minutes. Then
calculate SVI by dividing the volume (ml) of wet settled sludge by the weight (mg) of that sludge after it has been dried. Sludge with
an SVI of one hundred or greater will not settle as readily as desirable because it is as light as or lighter than water.
SVI = Wet Settled Sludge, ml x 1000
Dried Sludge Solids, mg
SANITARY SEWER (SAN-eh-tare-ee SUE-er) SANITARY SEWER
A sewer intended to carry wastewater from homes, businesses, and industries. Storm water runoff should be collected and
transported in a separate system of pipes.
SAPROPHYTIC ORGANISMS (SAP-pro-FIT-tik) SAPROPHYTIC ORGANISMS
Organisms living on dead or decaying organic matter. They help natural decomposition of the organic solids in wastewater.
SCREEN SCREEN
A device used to retain or remove suspended or floating objects in wastewater. The screen has openings that are generally uniform
in size. It retains or removes objects larger than the openings. A screen may consist of bars, rods, wires, gratings, wire mesh, or
perforated plates.
SEALING WATER SEALING WATER
Water used to prevent wastewater or dirt from reaching moving parts. Sealing water is at a higher pressure than the wastewater it is
keeping out of a mechanical device.
SECCHI DISC (SECK-key) SECCHI DISC
A flat, white disc lowered into the water by a rope until it is just barely visible. At this point, the depth of the disc from the water
surface is the recorded secchi disc reading.
SECONDARY TREATMENT SECONDARY TREATMENT
A wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the
water being treated. Usually the process follows primary treatment by sedimentation. The process commonly is a type of biological
treatment process followed by secondary clarifiers that allow the solids to settle out from the water being treated.
SEED SLUDGE SEED SLUDGE
In wastewater treatment, seed, seed culture or seed sludge refers to a mass of sludge which contains very concentrated populations
of microorganisms. When a seed sludge is mixed with the wastewater or sludge being treated, the process of biological decomposi-
tion takes place more rapidly.
SEIZING SEIZING
Seizing occurs when an engine overheats and a component expands to the point where the engine will not run. Also called
"freezing."
SEPTIC (SEP-tick) SEPTIC
This condition is produced by anaerobic bacteria. If severe, the wastewater turns black, gives off foul odors, contains little or no
dissolved oxygen and creates a heavy oxygen demand.
SEPTICITY (sep-TIS-it-tee) SEPTICITY
Septicity is the condition in which organic matter decomposes to form foul-smelling products associated with the absence of free
oxygen. If severe, the wastewater turns black, gives off foul odors, contains little or no dissolved oxygen and creates a heavy oxygen
demand.
SERIES OPERATION SERIES OPERATION
When wastewater being treated flows through one treatment unit and then flows through another similar treatment unit. Also see
PARALLEL OPERATION.
SET POINT SET POINT
The position at which the control or controller is set. This is the same as the desired value of the process variable.
SEWAGE SEWAGE
The used water and solids from homes that flow to a treatment plant. The preferred term is wastewater.
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Glossary 839
SHEAR PIN SHEAR PIN
A straight pin with a groove around the middle that will weaken the pin and cause it to fail when a certain load or stress is exceeded.
The purpose of the pin is to protect equipment from damage due to excessive loads or stresses.
SHOCK LOAD SHOCK LOAD
The arrival at a plant of a waste which is toxic to organisms in sufficient quantity or strength to cause operating problems. Possible
problems include odors and sloughing off of the growth or slime on the trickling-filter media. Organic or hydraulic overloads also can
cause a shock load.
SHORT-CIRCUITING SHORT-CIRCUITING
A condition that occurs in tanks or ponds when some of the water or wastewater travels faster than the rest of the flowing water.
SHREDDING SHREDDING
Comminution. A mechanical treatment process which cuts large pieces of wastes into smaller pieces so they won't plug pipes or
damage equipment. SHREDDING and COMMINUTION usually mean the same thing.
SIDESTREAM SIDESTREAM
Wastewater flows that develop from other storage or treatment facilities. This wastewater may or may not need additional treatment.
SIGNIFICANT FIGURE SIGNIFICANT FIGURE
The number of accurate numbers in a measurement. If the distance between two points is measured to the nearest hundredth and
recorded as 238.41 feet, the measurement has five significant figures.
SINGLE-STAGE PUMP SINGLE-STAGE PUMP
A pump that has only one impeller. A multi-stage pump has more than one impeller.
SKATOLE (SKATE-tole) SKATOLE
An organic compound (C9H9N) containing nitrogen which has a fecal odor.
SLAKE SLAKE
To become mixed with water so that a true chemical reaction takes place, such as in the slaking of lime.
SLOUGHINGS (SLUFF-ings) SLOUGHINGS
Trickling-filter slimes that have been washed off the filter media. They are generally quite high in BOD and will lower effluent quality
unless removed.
SLUDGE (sluj) SLUDGE
The settleable solids separated from liquids during processing or the deposits of foreign materials on the bottoms of streams or
other bodies of water.
SLUDGE AGE SLUDGE AGE
A measure of the length of time a particle of suspended solids has been undergoing aeration in the activated sludge process.
Sludge Age days = SusPended Solids Under Aeration, lbs or kg
Suspended Solids Added, lbs/day or kg/day
SLUDGE DENSITY INDEX (SDI) SLUDGE DENSITY INDEX (SDI)
This test is used in a way similar to the Sludge Volume Index (SVI) to indicate the settleability of a sludge in a secondary claritier or
effluent. SDI = 100/SVI. Also see SLUDGE VOLUME INDEX (SVI).
SLUDGE DIGESTION SLUDGE DIGESTION
The process of changing organic matter in sludge into a gas or a liquid or a more stable solid form. These changes take place as
microorganisms feed on sludge in anaerobic (more common) or aerobic digesters.
SLUDGE GASIFICATION SLUDGE GASIFICATION
A process in which soluble and suspended organic matter are converted into gas by anaerobic decomposition. The resulting gas
bubbles can become attached to the settled sludge and cause large clumps of sludge to rise and float on the water surface.
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840 Treatment Plants
SLUDGE VOLUME INDEX (SVI) SLUDGE VOLUME INDEX (SVI)
This is a test used to indicate the settling ability of activated sludge (aerated solids) in the secondary clarifier. The test is a measure
of the volume of sludge compared with its weight. Allow the sludge sample from the aeration tank to settle for 30 minutes. Then
calculate SVI by dividing the volume (ml) of wet settled sludge by the weight (mg) of that sludge after it has been dried. Sludge with
an SVI of one hundred or greater will not settle as readily as desirable because it is as light as or lighter than water.
SVI = Wet Settled Sludge, ml x 1000
Dried Sludge Solids, mg
SLUDGE-VOLUME RATIO (SVR) SLUDGE-VOLUME RATIO (SVR)
The volume of sludge blanket divided by the daily volume of sludge pumped from the thickener.
SLUGS SLUGS
Intermittent releases or discharges of industrial wastes.
SLURRY (SLUR-e) SLURRY
A thin watery mud or any substance resembling it (such as a grit slurry or a lime slurry).
SODIUM ADSORPTION RATIO (SAR) SODIUM ABSORPTION RATIO (SAR)
This ratio expresses the relative activity of sodium ions in the exchange reactions with soil. The ratio is defined as follows:
SAR = y?
V/2 (Ca + Mg)p
where Na, Ca, and Mg are concentrations of the respective ions in milliequivalents per liter of water.
Na, meq/L = Na,mg/L Ca meq/L = Ca, mg/L
23.0 mg/meq 20.0 mg/meq
Mg, meq/L = Mg, mgIL
12.15 mg/meq
SOFTWARE PROGRAMS SOFTWARE PROGRAMS
Computer programs designed and written to monitor and control wastewater treatment processes or other processes.
SOLUBLE BOD SOLUBLE BOD
Soluble BOD is the BOD of water that has been filtered in the standard suspended solids tesl.
SOLUTE SOLUTE
The substance dissolved in a solution. A solution is made up of the solvent and the solute.
SOLUTION SOLUTION
A liquid mixture of dissolved substances. In a solution it is impossible to see all the separate parts.
SPECIFIC GRAVITY SPECIFIC GRAVITY
Weight of a particle or substance in relation to the weight of water. Water has a specific gravity of 1.000 at 4°C (or 39°F). Wastewater
particles usually have a specific gravity of 0.5 to 2.5.
SPLASH PAD SPLASH PAD
A structure made of concrete or other durable material to protect bare soil from erosion by splashing or falling water.
STABILIZE STABILIZE
To convert to a form that resists change. Organic material is stabilized by bacteria which convert the material to gases and other
relatively inert substances. Stabilized organic material generally will not give off obnoxious odors.
STABILIZED WASTE STABILIZED WASTE
A waste that has been treated or decomposed to the extent that, if discharged or released, its rale and state of decomposition would
be such that the waste would not cause a nuisance or odors.
STANDARD SOLUTION STANDARD SOLUTION
A solution in which the exact concentration of a chemical or compound is known.
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Glossary 841
STANDARDIZE STANDARDIZE
(1) To compare with a standard. In wet chemistry, to find out the exact strength of a solution by comparing with a standard of known
strength. This information is used to adjust the strength by adding more water or more of the substance dissolved. (2) To compare
an instrument or device with a standard. This helps you to adjust the instrument so that it reads accurately or to prepare a scale,
graph or chart that is accurate.
STASIS (STAY-sis) STASIS
Stagnation or inactivity of the life processes within organisms.
STATIC HEAD STATIC HEAD
When water is not moving, the distance (in feet or meters) from a point to the water surface.
STATOR STATOR
That portion of a machine which contains the stationary (non-moving) parts that surround the moving parts.
STEP-FEED AERATION STEP-FEED AERATION
Step-feed aeration is a modification of the conventional activated sludge process. In step aeration, primary effluent enters the
aeration tank at several points along the length of the tank, rather than all of the primary effluent entering at the beginning or head of
the tank and flowing through the entire tank.
STERILIZATION (star-uh-luh-ZAY-shun) STERILIZATION
The removal or destruction of all living microorganisms, including pathogenic and saprophytic bacteria, vegetative forms and
spores. Compare with DISINFECTION.
STETHOSCOPE STETHOSCOPE
An instrument used to magnify sounds and convey them to the ear.
STOP LOG STOP LOG
A log or board in an outlet box or device used to control the water level in ponds.
STORM SEWER STORM SEWER
A separate sewer that carries runoff from storms, surface drainage, and street wash, but does not include domestic and industrial
wastes.
STRIPPED GASES STRIPPED GASES
Gases that are released from a liquid by bubbling air through the liquid or by allowing the liquid to be sprayed or tumbled over media.
STRIPPED ODORS STRIPPED ODORS
Odors that are released from a liquid by bubbling air through the liquid or by allowing the liquid to be sprayed and/or tumbled over
media.
STUCK STUCK
Not working. A stuck digester does not decompose organic matter properly. The digester is characterized by low gas production,
high volatile acid to alkalinity relationship, and poor liquid-solids separation. A digester in a stuck condition is sometimes called a
"sour" or "upset" digester.
SUCTION HEAD SUCTION HEAD
The POSITIVE pressure (in feet (meters) or pounds per square inch (kilograms per square centimeter)) on the suction side of a
pump. The pressure can be measured from the center line of the pump UP TO the elevation of the hydraulic grade line on the
suction side of the pump.
SUCTION LIFT SUCTION LIFT
The NEGATIVE pressure (in feet (meters) or inches (centimeters) of mercury vacuum) on the suction side of the pump. The pressure
can be measured from the center line of the pump DOWN to the elevation of the hydraulic grade line on the suction side of the pump.
SUPERNATANT (sue-per-NAY-tent) SUPERNATANT
Liquid removed from settled sludge. Supernatant commonly refers to the liquid between the sludge on the bottom and the scum on
the surface of an anaerobic digester. This liquid is usually returned to the influent wet well or to the primary clarifier.
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842 Treatment Plants
SURFACE LOADING SURFACE LOADING
Surface loading is calculated by dividing the flow into a sedimentation tank or a clarifier by the surface area of the unit.
Surface Loading, gpd/sq ft = Flow, gpd
Surface Area, sq ft
SURFACTANT SURFACTANT
Abbreviation for surface-active agent. The active agent in detergents that possesses a high cleaning ability.
SUSPENDED SOLIDS SUSPENDED SOLIDS
(1) Solids that either float on the surface or are suspended in water, wastewater, or other liquids, and which are largely removable by
laboratory filtering. (2) The quantity of material removed from wastewater in a laboratory test, as prescribed in STANDARD
METHODS FOR THE EXAMINATION OF WATER AND WASTEWATER and referred to as nonfilterable residue.
TOC TOC
Total Organic Carbon. TOC measures the amount of organic carbon in water.
TARE WEIGHT TARE WEIGHT
The weight of an empty weighing dish or container.
TERTIARY TREATMENT (TER-she-AIR-ee) TERTIARY TREATMENT
Any process of water renovation that upgrades treated wastewater to meet specific reuse requirements. May include general
cleanup of water or removal of specific parts of wastes insufficiently removed by conventional treatment processes. Typical
processes include chemical treatment and pressure filtration. Also called ADVANCED WASTE TREATMENT.
THERMOPHILIC BACTERIA (thermo-FILL-lick) THERMOPHILIC BACTERIA
Hot temperature bacteria. A group of bacteria that grow and thrive in temperatures above 113°F (45°C). The optimum temperature
range for these bacteria in anaerobic decomposition is 120°F (49°C) to 135°F (57°C).
THIEF HOLE THIEF HOLE
A digester sampling well.
THRESHOLD ODOR THRESHOLD ODOR
The minimum odor of a sample (gas or water) that can just be detected after successive odorless (gas or water) dilutions.
TIME LAG TIME LAG
The time required for processes and control systems to respond to a signal or to reach a desired level.
TITRATE (TIE-trate) TITRATE
To TITRATE a sample, a chemical solution of known strength is added on a drop-by-drop basis until a color change, precipitate, or
pH change in the sample is observed (end point). Titration is the process of adding the chemical solution to completion of the
reaction as signaled by the end point.
TOTAL DYNAMIC HEAD (TDH) TOTAL DYNAMIC HEAD (TDH)
When a pump is lifting or pumping water, the vertical distance (in feet or meters) from the elevation of the energy grade line on the
suction side of the pump to the elevation of the energy grade line on the discharge side of the pump.
TOTAL RESIDUAL CHLORINE TOTAL RESIDUAL CHLORINE
The amount of chlorine remaining after a given contact time. The sum of the combined available residual chlorine and the free
available residual chlorine. Also see RESIDUAL CHLORINE.
TOTALIZER TOTALIZER
A device that continuously sums or adds the flow into a plant in gallons or million gallons or some other unit of measurement.
TOXIC (TOX-ick) TOXIC
Poisonous.
TOXICITY (tox-IS-it-tee) TOXICITY
A condition which may exist in wastes and will inhibit or destroy the growth or function of certain organisms.
TRANSPIRATION (TRAN-spear-RAY-shun) TRANSPIRATION
The process by which water vapor is lost to the atmosphere from living plants.
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Glossary 843
TRICKLING FILTER TRICKLING FILTER
A treatment process in which the wastewater trickles over media that provide the opportunity for the formation of slimes or biomass
which contain organisms that feed upon and remove wastes from the water treated.
TRICKLING-FILTER MEDIA TRICKLING-FILTER MEDIA
Rocks or other durable materials that make up the body of the filter. Synthetic (manufactured) media have been used successfully.
TRUNK SEWER TRUNK SEWER
A sewer that receives wastewater from many tributary branches or sewers and serves a large territory and contributing population.
TURBID TURBID
Having a cloudy or muddy appearance.
TURBIDITY METER TURBIDITY METER
An instrument for measuring the amount of particles suspended in water. Precise measurements are made by measuring how light
is scattered by the suspended particles. The normal measuring range is 0 to 100 and is expressed as Nephelometric Turbidity Units
(NTU's).
TURBIDITY UNITS TURBIDITY UNITS
Turbidity units, if measured by a nephelometric (reflected light) instrumental procedure, are expressed in nephelometric turbidity
units (NTU). Those turbidity units obtained by other instrumental methods or visual methods are expressed in Jackson Turbidity
Units (JTU) and sometimes as Formazin Turbidity Units (FTU). The FTU nomenclature comes from the Formazin polymer used to
prepare the turbidity standards for instrument calibration. Turbidity units are a measure of the cloudiness of water.
TWO-STAGE FILTERS TWO-STAGE FILTERS
Two filters are used. Effluent from the first filter goes to the second filter, either directly or after passing through a clarifier.
ULTRAFILTRATION ULTRAFILTRATION
A membrane filter process used for the removal of organic compounds in an aqueous (watery) solution.
UPSET UPSET
An upset digester does not decompose organic matter properly. The digester is characterized by low gas production, high volatile
acid/alkalinity relationship, and poor liquid-solids separation. A digester in an upset condition is sometimes called a "sour" or "stuck"
digester.
VECTOR VECTOR
An insect or other organism capable of transmitting germs or other agents of disease.
VELOCITY HEAD VELOCITY HEAD
A vertical height (in feet or meters) equal to the square of the velocity of flowing water divided by twice the acceleration due to gravity
(V2/2g).
VOLATILE (VOL-a-til) VOLATILE
A volatile substance is one that is capable of being evaporated or changed to a vapor at relatively low temperatures.
VOLATILE ACIDS VOLATILE ACIDS
Acids produced during digestion. Fatty acids which are soluble in water and can be steam-distilled at atmospheric pressure. Also
called "organic acids." Volatile acids are commonly reported as equivalent to acetic acid.
VOLATILE LIQUIDS VOLATILE LIQUIDS
Liquids which easily vaporize or evaporate at room temperature.
VOLATILE SOLIDS VOLATILE SOLIDS
Those solids in water, wastewater, or other liquids that are lost on ignition of the dry solids at 550°C.
VOLUMETRIC VOLUMETRIC
A means of measuring unknown concentrations of water quality indicators in a sample BY DETERMINING THE VOLUME of titrant or
liquid reagent needed to complete particular reactions.
VOLUTE (vol-LOOT) VOLUTE
The spiral-shaped casing which surrounds a pump, blower, or turbine impeller and collects the liquid or gas discharged by the
impeller.
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844 Treatment Plants
WAS WAS
Waste Activated Sludge, mgIL. The excess growth of microorganisms which must be removed from the process to keep the
biological system in balance.
WASTE ACTIVATED SLUDGE (WAS) WASTE ACTIVATED SLUDGE (WAS)
The excess growth of microorganisms which must be removed from the process to keep the biological system in balance.
WASTEWATER
WASTEWATER
The used water and solids from a community that flow to a treatment plant. Storm water, surface water, and groundwater infiltration
also may be included in the wastewater that enters a plant. The term "sewage" usually refers to household wastes, but this word is
being replaced by the term "wastewater."
WATER HAMMER WATER HAMMER
The sound like someone hammering on a pipe that occurs when a valve is opened or closed very rapidly. When a valve position is
changed quickly, the water pressure in a pipe will increase and decrease back and forth very quickly. This rise and fall in pressures
can do serious damage to the system.
WEIR (weer)
WEIR
CROSS SbCTION
WEIR, PROPORTIONAL
(1) A wall or plate placed in an open channel and used to measure the flow. The depth of the flow over the weir can be used to
calculate the flow rate, or a chart or conversion table may be used. (2) A wall or obstruction used to control flow (from clarifiers) to
assure uniform flow and avoid short-circuiting.
WEIR DIAMETER (weer) WEIR DIAMETER
Many circular clarifiers have a circular weir within the outside edge of
the clarifier. All the water leaving the clarifier flows over this weir. The
diameter of the weir is the length of a line from one edge of a weir to
the opposite edge and passing through the center of the circle formed
by the weir.
WEIR, PROPORTIONAL (weer)
A specially shaped weir in which the flow through the weir is directly proportional to the head.
WET OXIDATION WET OXIDATION
A method of treating or conditioning sludge before the water is removed. Compressed air is blown into the liquid sludge. The air and
sludge mixture is fed into a pressure vessel where the organic material is stabilized. The stabilized organic material and inert
(inorganic) solids are then separated from the pressure vessel effluent by dewatering in lagoons or by mechanical means.
WET WELL WET WELL
A compartment or room in which wastewater is collected. The suction pipe of a pump may be connected to the wet well or a
submersible pump may be located in the wet well.
Y, GROWTH RATE Y, GROWTH RATE
An experimentally determined constant to estimate the unit growth rate of bacteria while degrading organic wastes.
ZOOGLEAL FILM (ZOE-glee-al) ZOOGLEAL FILM
A complex population of organisms that form a "slime growth" on the trickling-filter media and break down the organic matter in
wastewater. These slimes consist of living organisms feeding on the wastes in wastewater, dead organisms, silt, and other debris.
"Slime growth" is a more common word.
ZOOGLEAL MASS (ZOE-glee-al)
ZOOGLEAL MASS
Jelly-like masses of bacteria found in both the trickling filter and activated sludge processes. These masses may be formed for or
function as the protection against predators and for storage of food supplies. Also see BIOMASS.
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Index 845
SUBJECT INDEX
VOLUME III
A
ABS, 395
Abnormal operation
activated carbon, 656, 657
alum flocculation, 375
chemical feed systems, 307
coagulation, 633
flotation, 561
gravity filters, 328
lime precipitation, phosphorus, 362
luxury uptake of phosphorus, 372
microscreens, 313, 579
precipitation, 633
pressure filters, 343
screening, 579
Abrasion number, 681
Absolute pressure, 441, 442
Absorption, odor control, 17, 22
Accidental discharge, 523
Acclimation of microorganisms, 74
Accuracy, instruments, 430
Acid storage tank, 610
Acidity, 590
Acids, 70, 504
Activated carbon
abnormal operation, 656, 657
abrasion number, 681
adsorption, 635
air pockets, 656
analysis, 654
apparent density, 682
backflushing, 646, 656
COD loading rates, 658
COD removal efficiencies, 646, 656
carbon columns, 638, 639, 640
carbon dust, 657
carbon fines, 641, 646
counter-current flow, 641
decolorizing index, 682
defining, 649, 657
description, 635
dust control, 658
effluent tests, 680
emergency conditions, 656
equipment, 635
guidelines, loadings, 658
hardness number, 686
head loss, 641, 646, 656
hydraulic loadings, 658
industrial waste treatment, 635
influent tests, 680
loadings, 658
manufacture of activated carbon, 635
methylene blue number, 690
molasses number, 694
odor control, 23
operation, 641, 646, 654
operational strategy, 654
piping, 641-645
plans and specifications, 658
principles, 635
process description, 635
purpose, 635
regeneration, 649-653, 657
review of plans and specifications, 658
safety, 657
sampling, 654, 657
sieve analysis, 695
start up, 641
status, 680
storage reservoir, 646
total ash of regenerated carbon, 695
troubleshooting, 646, 654
turbidity measurements, 646, 680
uniformity coefficient, 686
ventilation, 658
Activated sludge
also see Chapter 8 and Chapter 11
acclimation of microorganisms, 74
Al West, 66
ammonia treatment, 63, 101
amoeboids, 66
artichoke wastes, 95
BOD, 73
biological nitrification, 102
brewery wastewaters, 85
bulking, 64, 78, 85, 89
COD, 73
characteristics, wastes, 72
ciliates, 66, 67, 78
clarification, 78
complete mix, 50, 56
constant percentage RAS flow, 53
constant RAS flow, 53
contact stabilization, 50, 53, 56, 71, 97
control of RAS, 53
control of WAS, 60
controls, 466
conventional, 50, 53, 56, 60, 62
cryogenic air separation, 47, 49
dairy wastes, 97
denitrification, 105
dissolved oxygen, 78, 89, 97, 99, 102
effects of industrial wastes, 70, 71
extended aeration, 53, 60, 62, 97, 99
F/M, 60, 61, 92, 97
filamentous organisms, 65, 78, 85, 89, 93, 97
flagellates, 66, 67
flow, industrial wastes, 72, 73
flow diagram, 45
-------
846 Treatment Plants
Food/Microorganism, 60, 61, 92, 97
food processing wastes, 95
high rate, 60, 62
industrial wastes, 70
instrumentation, 106, 466
laboratory testing, 95, 99
layout, 43, 46
luxury uptake of phosphorus, 372
MCRT, 60, 63, 66, 67, 92, 97, 99
MLVSS, 60, 65
maintenance, 50, 52, 106
mean cell residence time, 60, 63, 66, 67, 92, 97
methods of wasting, 59
microorganisms, 63, 65, 66, 67, 84
microscopic examination, 65, 84
modes, 50, 53
monitoring, 69, 99
neutralization, 77
nitrification, 53, 63, 99, 101
nutrients, 73, 76, 77, 85, 88, 97
observations, 71, 78, 99
odors, 25
operation, activated sludge process, 53, 59
operation, industrial wastes, 77, 89, 97, 99
operation, RAS and WAS, 53, 59
operational strategy, industrial wastes, 71, 77, 85
organic wastes, 71
oxygen generation, 47, 106
PSA, 47, 48
periodic feeding for start-up, 82
petroleum refinery wastes, 99
pH, 73, 78, 97, 99, 101
phenols, 101
pilot plant, 95
pin floe, 66, 67
plan view, 44
pressure swing absorption, 47, 48
pretreatment, 70, 72, 74, 86, 95
protozoa, 65, 66, 84
pulp and paper mill wastes, 79
pure oxygen, 43
record keeping, 79, 95
restart, 76
return activated sludge, 53, 78
review of plans and specs, 105
rising sludge, 105
rotifers, 65, 66, 67, 78
SVI approach for RAS, 57
safety, 51, 83, 106
screening, 74
seed activated sludge, 76
separate sludge re-aeration, 57
settleability approach for RAS, 55
shock loadings, 99
shutdown, 81
silica gel trap, 50
sludge age, 60, 92
sludge blanket depth, 55
sphaerotilus natans, 93
start-up, 50, 76, 81, 82
steady state, 59, 81
step feed, 50, 53, 97
straggler floe, 66, 67
sulfide shock load, 99
surface aerators, 43, 46
suspended solids, 73
temperature effect, 63, 85
toxic wastes, 71, 73, 78
troubleshooting, 56, 58, 60, 83
turbulent mixers, 43
volatile solids inventory, 64
WAS, 59, 78, 92
waste activated sludge, 59, 78, 92
Administration of a monitoring program
data base, 485
dealing with industry, 486
enforcement, 485
organization, 485
Adsorption
see activated carbon
Advanced waste treatment effluent quality, 389
Aerobic digestion
air requirements, 166, 167
batch operation, 164
bulking, 166
continuous operation, 164
description, 163
digestion time, 164, 165, 167, 169
dissolved oxygen, 166, 167, 168, 169, 170
efficiency, 164, 167
factors affecting performance, 164
filamentous organisms, 166, 169, 170
foam, 166, 167, 169, 170
guidelines, operation, 164, 167
hydraulic loading, 169
laboratory analysis, 166
loadings, 165, 169
nitrification, 169
observations, 169
odors, 167
operation, 164, 166
overflow, 163
oxygen uptake, 167, 168, 169, 170
performance, 164, 167
pH,169, 170
sampling, 166
sludge type, 164, 167
solids loading, 169
temperature, 165, 169
time of digestion, 164
toxicity, 170
troubleshooting, 168, 169, 170
underflow, 163
variables, 164
visual inspection, 169
volatile solids loading, 165, 167, 169, 170
Aerobic microorganisms, 8
Age tank, 293
Air binding, 328, 342
Air conditioning systems, 779
Air gap, 789
Air pockets, activated carbon, 656
Air pollution
cyclonic separator, 221
impingement scrubber, 226
scrubbers, 221, 225
Venturi scrubber, 221, 226
Al West, 66
Alarms, level, 450, 463, 465, 469, 473
Alarms, process control, 326, 473
Algae, 348, 548
Alkalies, 70
Alkalinity, 590
Alkalinity test
see Chapter 16
Alkyl Benzene Sulfonate, 395
Alum, 292, 373, 375, 377, 614
Alum flocculation, phosphorus removal
abnormal operation, 375
-------
alum, 373, 375, 377
clarification, 373
equipment, 375
filtration, 375, 377
guidelines, operation, 377
hydraulic loading, 377
jar tests, 375, 377
layout, 374, 376
loadings, 377
maintenance, 375
operation, 375
overdose, alum, 377
pH,377
plans and specifications, 377
plugging of pipes and pumps, 375
pumps, 375, 377
review of plans and specifications, 377
safety, 377
storage of alum, 377
suspended solids removal, 375
variations in process, 373
Aluminum sulfate, 292, 614
Ambient temperature, 50
Ammonia, 7, 11, 12
Ammonia-stripping, 101
Ammonia, treatment, 101
Amoeboids, 66
Anaerobic, 137
Anaerobic digester
see Chapter 12
controls, 468
instrumentation, 468
odors, 26
sludge handling, 131, 239
Anaerobic digestion, 163
also see Chapter 12
Anaerobic filters, 551
Anerobic lagoons, 549
Anaerobic microorganisms, 8
Analytical measurements, 438, 454
Anhydrous, 293
Anti-siphon valve, 789
Apparent density, 682
Artichoke wastes, 95
Asphalt paving, 790
Aspirate, 144
Autogenous burn, 233
Automatic monitoring units, 70
Automatic samplers, 487
Auxiliary electrical equipment
batteries, 737, 739
distribution transformers, 740
emergency lighting, 736
equipment, 736
generator, size, 736
high voltage, 738
kirk-key, 736
lighting, emergency, 736
safety, 736
standby power generation, 736
switch gear, 738
transformers, 740
transmission, 738
B
BOD, industrial wastes, 73
Backflow prevention, 787
Backwashing filters, 316, 327, 340
Baffle, 137
Band screen, 572, 576
Index 847
Band seals, 735
Bar screen, 569, 570
Bar screen instrumentation, 462
Basins
see Lagoons
Basket centrifuge, 161
Batteries, 737
Battery charging, 502, 529
Beds, sludge, 203
Bellows, pressure measurement, 445, 449, 473
Belt filter press
belt speed, 192, 193, 194
belt tension, 192, 193, 194
belt type, 192
blinding, 193, 194
cake, 192, 193, 194
cleaning of belt, 192
conditioning, 190, 193
description, 190
factors affecting performance, 190
guidelines, operating, 190, 193
hydraulic loading, 192, 193, 194
operation, 190, 192
performance, 193
plans and specifications, 249
polymer dosage, 190, 193, 194
pressure, 192
sludge type, 190
solids recovery, 193
troubleshooting, 193
variables, 190
washing out, 193, 194
Belt-type gravimetric feeder, 294, 301, 616
Bench scale analysis, 105, 614
Beneficial uses of water, 386, 588
Benzene, 17
Bioaccumulation, 548
Biochemical oxygen demand, industrial wastes, 73
Biological control system, 426
Biological filter
odor reduction tower, 14
odors, 25
rotating biological reactor
see Chapter 7
trickling filter
see Chapter 6
Biological generation of odors, 7
Biological nitrification, 102
Biological odor reduction towers, 14
Biological treatment, odors, 14, 25
Birds, 248
Blanket depth, gravity thickeners, 138, 139, 141
Blending tank, 387, 388
Blind, filtering medium, 188, 193, 199, 201, 579
Boron, 413, 415
Bound water, 137, 179
Bourdon tube, pressure, 445, 449, 473
Breakpoint chlorination, 102
Brewery wastewater
activated sludge treatment, 86
ammonia addition, 88
BOD, 86
bulking, 89
characteristics of wastewater, 86
chlorination, 89
dechlorination, 89
dissolved oxygen, 89
equalization tank, 86
F/M ratio, 92
filamentous organisms, 89, 93
-------
848 Treatment Plants
flow diagram, 87, 90
foam, 93
grit channel, 86
laboratory testing, 95
layout, 87
MCRT, 92
mixed liquor suspended solids, 89
nutrients, 88
oil and grease, 88
operation, 89
operational strategy, 85
pH, 86
pretreatment, 86
primary clarifier, 88
record keeping, 95
return activated sludge, 89, 92
sludge age, 92
sludge blanket, 92
sludge wasting, 92
sphaerotilus natans, 93
sources of wastewater, 86
temperature, 89
toxic substances, 92
wasting sludge, 92
Brine solution absorption, 17
Bubble tube, 450, 453, 473
Buffer, 589
Bulking
activated sludge, 64, 78, 85
aerobic digesters, 166
brewery wastes, 89, 93
centrifuge thickeners, 155
chemical treatment, 289, 307
filamentous growth, 78, 85, 89, 93
pulp and paper mill wastes, 85
C
COD, industrial wastes, 73
Cadmium, 240
Capacitance probe, level, 450, 473
Carbon adsorption
see activated carbon
Carbon columns, equipment description, 638, 639, 640
Carbon dust, 657
Carbon measurement, 681
Carbon regeneration, physical chemical treatment, 649-653,
657
Case histories, 388, 660
Cathod ray tube (CRT), 454
Cathodic protection, 725
Cation exchange capacity, 415
Caustic soda, 590
Caustic soda feed system, 620
Caustic wastes, 504
Cavitation, 144, 717
Centrate, 150
Centrifuge thickeners and dewatering
also see Dewatering
age of sludge, 155
basket centrifuge, 150, 156, 159, 161, 162
bowl speed, 156, 161
bulking, sludge, 155
cake, 161, 201
centrate, 150, 161
centrifugal forces, 155, 156, 161
depth of pool, 156, 161
detention time, 156
dewatering, 200
differential scroll speed, 156
disc-nozzle centrifuge, 150, 156, 161, 162
factors affecting performance, 150
feed solids, 157
feed time, 156, 161
guidelines, operation, 155, 157, 201
hydraulic loading, 155, 161
nozzle size, 156
number of nozzles, 156
observations, 161
odors, 27
operation, 155, 157
performance, 150, 157, 200
plans and specifications, 249
polymers, 157, 158, 159, 161, 201
pool depth, 156
rising sludge, 155
scroll centrifuge, 150, 156, 159, 161, 162
scroll speed, 156, 161
shutdown, 157
solids loading, 155, 161, 201
solids recovery, 157, 201
start up, 157
thickened sludge, 157, 160
troubleshooting, 161, 162
variables, 150
vibrations, 161, 162
visual inspection, 161
Chain of possession, 498
Characteristics of industrial wastes, 72, 484
Characteristics of odors, 11
Charging batteries, 502, 529
Charts, 459
Chemical addition, 289
Chemical conditioning of sludges
addition of chemicals, 178
alum, 173
automatic feeding systems, 178, 179
centrifuges, 178
chemical requirements, 173, 179
dissolved air flotation thickeners, 178
dosages, chemicals, 179
equipment, 178, 179
ferric chloride, 173, 179
gravity thickening, 178
jar tests, 174, 175
lime, 173, 179
mixing equipment, 178, 179
plans and specifications, 250
polymers, 173, 179
pressure filters, 178
seasonal chemical requirements, 173
solution preparation, 176, 178
troubleshooting, 179
typical chemical requirements, 178
vacuum filtration, 178
Chemical equilibrium, 592
Chemical feed systems, operation, 302, 307, 326, 616 617
632, 674
Chemical oxygen demand
industrial wastes, 73
test
see Chapter 16
Chemical scrubbers, 17
Chemical solution preparation, 178
Chemical stabilization of sludges
chlorine stabilization, 171
lime stabilization, 170
operation, chlorine stabilization, 171
operation, lime stabilization, 171
pH, chlorine stabilization, 170
pH, lime stabilization, 170
-------
Index 849
slurry, lime, 171
troubleshooting, lime stabilization, 171
Chemical treatment, odors, 12
Chemical treatment, secondary effluent solids, 289
Chemical treatment, solids in effluents
abnormal operation, 307
age tank, 293
aluminum sulfate, 292, 336
belt-type gravimetric feeder, 294, 301
chemical addition, 289
chemicals, 292
coagulant aids, 292
coagulation, 289, 308
day tank, 293, 295
dosage, 305
feed equipment, chemicals, 294
feed systems, chemical, 302, 336
ferric chloride, 293
"fish eyes," 294
flocculation, 289
foaming, 308
housekeeping, 305, 308
jar test, 305
lime, 293
liquid/solids separation, 289
maintenance, 308
metering equipment, 294
mixing equipment, 294
monitoring, 305
operation, chemical systems, 302, 307
operational strategy, 307
phosphate monitoring, 305
piston pumps, 294, 296
plans and specifications, 302
polymeric flocculants, 293, 336
positive displacement pumps, 294, 296, 297, 298
protective clothing, 292
record keeping, 302, 303, 304
review of plans and specifications, 302
rotary feeder, 294, 300
safety, 292, 293, 307
screw feeder, 294, 299
selecting chemical feeders, 294
shutdown, chemical systems, 302
start up, chemical systems, 302
toxicity, 292
troubleshooting, 308
vibrating trough feeder, 294
Chemicals, 292
Chemisorption, 23
Chemistry, 590
also see Chapter 16
Chloramines, 12
Chlorination, 89
Chlorination, breakpoint, 102
Chlorination, odor control, 12
Chlorine
disinfection
see Chapter 10
odor control, 12
Chlorine dioxide, 17
Chlorine stabilization of sludges, 171
Chromate, odor control, 14
Ciliates, 66, 67, 78
Circular charts, 459, 473
Clarification, 71, 78
Clarifiers, 622-633
Classes of irrigation waters, 412, 413
Classification of odors, 11
Cleaning equipment, 565
Coagulation, 173, 289, 308, 359, 597, 612
Coagulation and precipitation
abnormal operation, 633
alum, 614
belt gravimetric chemical feeders, 614
bench-scale tests, 614
caustic soda feed system, 620
chemical feeders, 616, 617, 632
chemicals, 612
clarification, 612, 613
clarifiers, 622-633
coagulants, 614, 616, 631
description, 612, 616
destabilization, 613
detention time, 628
dosage, 614
electrostatic charge reducing chemicals, 612, 613
equipment, 616, 631
ferric chloride, 614
flocculation, 612
flocculators, 622, 623, 632, 633
gravimetric feeders, 616
guidelines, operations, 628
hygroscopic, 614
interparticle bridging chemicals, 612, 613
iron coagulants, 614
jar test, 614, 615
lamella separator, 628
lime, 614
lime feed system, 619
mixing, 622
need, 612
operation, 631, 632
operational strategy, 632
overflow rate, 628
physical enmesber chemicals, 612, 613
polymer feed system, 621, 622
polymers, 612, 613, 614
precipitation, 628
principles, 612
purpose, 612
rapid mix, 612
rotary chemical feeder, 618
safety, 631
screw feeder, 616
short-circuiting, 629
solid chemical feed systems, 616
solids loading, 628
start up, 631
storage of coagulants, 616
surface loading, 628
temperature effect, 629
troubleshooting, 633
tube settlers, 628, 629, 630
volumetric feeders, 294, 296-297
weir overflow rate, 628
Coarse screens
see Chapter 4
Coke wastes, 552
Collection systems, 7, 8, 70, 79
Collection systems, odor control, 7
Color, wastewater characteristics, 504
Combustible gas alarm, 470
Combustion, odor control, 17
Comminutors, 71
Complaints, odors, 11
Completely mixed system, activated sludge, 50, 56
Composting
anaerobic conditions, 212, 213
balling, 208, 212, 213
-------
850 Treatment Plants
blending, 208, 211, 212
bulking material, 208
climatic conditions, 211
description, 207, 208
dimensions of stacks, 208
factors affecting performance, 208
frequency of turning stacks, 211, 212
mechanical, 208
moisture content, 208, 211, 212
odors, 208, 212, 244
operation, 208, 211
performance, 212
polymers, 208
pug mill, 213, 244
reduced volume sludge, 244
sludge type, 208, 212
static pile, 244, 246
temperature, 208, 212, 213, 244
time for composting, 212
troubleshooting, 212, 213
turning stacks, 211
variables, 208
windrow, 208, 209, 210, 244, 245
Compressors
also see Chapter 11, Blowers
after coolers, 783
air systems, 783
control, 783
filter, 783
location, 783
lubricating oil, 781
lubricator, 783
need, 781
power system, 783
pressure regulator, 783
reciprocating, 782
refrigerated air dryers, 783
rotary, 781
troubleshooting, 782
Computer systems, controls, 469
Concentration factor, sludge, 140, 149
Concentrators, gravity, sludge, 135, 138
Conditioning of sludges
chemical conditioning, 173
coagulation, 173
elutriation, 173, 184
flocculation, 173
purpose, 173
thermal conditioning, 179
wet oxidation, 182
Confined spaces, 8, 27, 502
Coning, 141
Constant percentage RAS flow, 53
Constant RAS flow, 53
Contact stabilization, activated sludge, 50, 53, 56, 71, 97
Continuous monitoring, 486
Continuous process, 554
Control logic, 426
Control methods, activated sludge, 53, 60
Control methods, instrumentation, 456, 473
Control system, 430
Controllers, 454, 455, 456, 473
Controls
see Instrumentation
Conventional activated sludge, 50, 53, 56, 60, 62
Cooling towers, 76
Corrosion, industrial wastes, 70
Corrosion, pipes, 413
Corrosion, wastewater, 7, 8, 27, 70
Counter-flow washing, 551
Counteraction, odor control, 17
Crop production, 401, 402
Cross connections, 785
Cryogenic air separation, 47, 49
Cyanides, 70
Cycle, sulfur, 10
Cylindrical screen, 569, 572, 573
D
DO probe, 473
Dairy wastes, 97, 548
Data base, 485
Data collection
see Record keeping
Day tank, 293, 295
Decant tank, pressure filters, 342
Dechlorination, 89
Decolorizing index, 682
Deep well injection, 386, 387
Defining, 649, 657
Dehydrogenation, 7
Denitrification, 105, 137
Density, 131
Density measurement, 438, 450
Destabilization, 613
Detention time
aerobic digester, 164
anaerobic digester
see Chapter 12
clarifiers, 628
coagulation and precipitation, 628
primary sedimentation
see Chapter 5
Dewatering sludge
belt filter press, 190
centrifuge, 200
plate and frame filter press, 186
pressure filtration, 186
purpose, 186
sand drying beds, 201
summary, 207
surfaced sludge drying beds, 203
vacuum filtration, 193
Diaphragm box, level measurement, 450, 473
Diaphragm pumps
chemical feeders, 297, 298
trash, 719
Diaphragm sensor, pressure measurement, 445, 449, 473
Diesel engines
abnormal engine operation, 767, 768
air box pressure, 763
air-cooled engines, 760
air inlet restriction, 763
compression pressure, 761
crankcase pressure, 763
crankcase pressure excessive, 772
cylinder, misfiring, 761
description, 757
exhaust back pressure, 763
exhaust smoke analysis, 764
fuel flow, 762
fuel, none or insufficient, 769, 770
fuel system, 757
hard starting engine, 765, 766
lubricating oil consumption high, 771
maintenance, 761
misfiring cylinder, 761
oil pressure low, 773, 774
operation, 757
starting, 761
-------
Index 851
temperatures of engine coolant abnormal, 775
troubleshooting, 761 -
water-cooled engines, 760
Digestion
aerobic, 163
anaerobic, 163
Digital receivers, 455, 456
Digital transmitters, 426, 455, 456
Direct reuse of effluent
advance waste treatment effluent quality, 389
blending tank, 387, 388
case histories, 388
direct reuse, 386
emergency operating procedures, 398
equipment requirements, 388
groundwater, 388
limitations, 399
maintenance, 400
monitoring, 398
Muskegon County, Michigan, 390
nuclear generating station, Phoenix, Arizona, 390
operation, 397, 398
operational strategy, 398
Phoenix, Arizona, nuclear generating station, 390
plans and specifications, 400
review of plans and specifications, 400
safety, 400
shutdown, 398
South Lake Tahoe, California, 388
start up, 397
steel mill, 395
treatment levels for reuse, 386
troubleshooting, 398
uses, 386
water quality criteria, 388
Windhoek, South Africa, 390
Disc-nozzle centrifuge, 161
Disc strainer, 572, 574, 575
Discharge head, 713
Disinfection
see Chapter 10
Disposal of sludges
agricultural reclamation, 240, 242
dedicated land disposal, 239, 241
environmental controls, 247
lagoons, 244
land disposal, 234
monitoring, 247
need, 131
on-site dedicated land disposal, 239, 241
sanitary landfill, 239
utilization, 247
Dissolved air flotation thickeners
age of sludge, 144, 146
air to solids (A/S) ratio, 146, 149, 150
biological flotation, 144
biological sludges, 146
blanket thickness, 147, 149, 150
chemical conditioning, 149, 150
concentration factor, 149
dispersed air flotation, 144
efficiency, 148, 149
effluent, 149, 150
factors affecting performance, 144
float characteristics, 149
guidelines, operation, 146
hydraulic loading, 146, 148, 149
observations, 149
operating guidelines, 146, 148
operation, 146, 147
performance, 148
plans and specifications, 249
polymers, 148
pressure flotation, 144
primary sludge thickening, 146
recycle rate, 147, 149
retention tank, 144, 146
rising sludge, 146
secondary sludge thickening, 146
shutdown, 148
sludge blanket, 147, 149, 150
solids loading, 146, 148, 149
solids recovery, 148
start up, 148
thickened sludge characteristics, 149
troubleshooting, 149, 150
vacuum flotation, 144
variables, 144
visual inspection, 149
withdrawal of sludge, 146
Dissolved oxygen
instrumentation, 468, 473
probe, 468, 473
test
see Chapter 16
Doctor blade, 569
Dosage, chemicals, 305
Downflow filters, 317
Drag-out, 552
Drain tile systems, 416
Drainage, surface water, 792
Drainage wells, 416
Drinking water, 545
Droop, controller, 456
Drum screen, 569, 572, 573
Drying beds, sludge, 203
Drying beds, sludge odors, 26
Dust, carbon, 657
Dynamic head, 713
E
Eductor, 178
Effective size, 686
Effects of industrial wastes, 70
Efficiency, 131
Effluent disposal
see Chapter 13
Effluent, secondary, solids removal
chemicals, 289
filters, gravity, 316
filters, pressure, 334
gravity filters, 316
inert-media pressure filters, 334
microscreens, 289
need, 289
pressure filters, 334
Electric probe, level, 450
Electric receivers, 455, 456
Electric transmitters, 426, 455, 456
Electrical control system, 426
Electricai equipment
see Auxiliary electrical equipment
Electrical safety, 736
Electro-chemical corrosion, 725
Electro-chemical process, 722
Electrolysis, 725
Electrolyte, 20, 293, 592, 737
Electrolytic process, 17
Electro-magnetic forces, 359
Electrostatic charge reducing chemicals, 612, 613
-------
852 Treatment Plants
Elutriation, sludge
definition, 173
guidelines, operation, 184
operation, 184
process description, 184
Emergency lighting, 736
Emergency operation
direct reuse, 398
land disposal, 413
lime precipitation, 362
Emergency storage tanks, 74, 76, 79, 334, 398, 657
Enclosed spaces, 8, 27
Endogenous, 164, 358
Energy grade line, 713
Enforcement, 485
Engines
see Gasoline engines
Equalization flows
filters, 334
industrial wastewater, 74, 76, 86, 548
Equilibrium, chemical, 592
Equilibrium, hydrogen sulfide-sulfide, 8, 9
Equipment
cleaning, 565
disc screen, 572, 574
dissolved air flotation thickener, 559
drum screen, 572, 573
microscreen, 572, 577
painting, 565
Equipment records
see Record keeping
Equipment storage, 502
Evapotranspiration, 401
Explosive gas detection instruments, 462
Explosive gases, 8
Extended aeration, activated sludge, 53, 60, 62, 97, 99
F
F/M, 60, 61, 82, 84, 92, 97, 104
Facultative microorganisms, 8
Fan laws, 777
Fecal odors, 11
Feed systems, chemicals, 294, 302
Fermentation wastes, 550
Ferric chloride, 614
Filamentous organisms, 65, 78, 85, 89, 93, 97, 137, 166, 169,
170
Filter, air, 328
Filter press
belt, 190
odors, 27
plate and frame, 186
sludge dewatering, 186
types, 186
Filters
gravity, sand, 316
inert-media, 334
pressure, 334
trickling
see Chapter 6
Fire triangle, 226
"Fish eyes" (chemicals), 294
Fish kill, 358
Fittings
band seals, 735
compression coupling, 729
couplings, 729
flanges, 729
mechanical flanges, 729
seals, 735
sleeve coupling, 729
victaulic couplings, 729, 734
Flagellates, 66, 67
Flammable oils, 70
Flies, 248
Float mechanism, level measurement, 450, 451, 473
Flocculation, 173, 289, 358, 597
Flocculators, 622, 623, 632, 633
Flotation
abnormal operation, 561
calculations, 562
description, 554
Lamell panels, 558, 559
maintenance, 564, 566
monitoring, 562, 564
operation, 560
parts, 554
purpose, 554
record keeping, 562
safety, 559
sampling, 562, 564
shutdown, 560
start up, 560
Flow equalization
industrial wastes, 74, 548
microscreens, 313
Flow instruments, 438
Flow measurement, 438, 498
Flow regulation, 74, 503
Flow segregation, 74
Fluidized-bed reactors, 214, 216, 217
Foam control
aerobic digestion, 166, 169, 170
brewery wastes, 93
pulp mill wastes, 80
Foaming
aerobic digestion, 166, 169, 170
chemical treatment, 308
Food/Microorganism, 60, 61, 82, 84, 92, 97, 104
Food processing wastes
activated sludge treatment, 95
artichoke wastes, 95
BOD, 95, 97
contact stabilization, 97
dairy wastes, 97
dissolved oxygen, 97, 99
extended aeration, 97
F/M, 97
filamentous organisms, 97
MCRT, 97
mixed liquor suspended solids, 97, 99
moving average, 97
nutrients, 97
odor control, 99
operation, 97, 99
pH, 95, 97
pilot plants, 95
pretreatment, 95
return activated sludge, 99
step-feed aeration, 97
Friction loss, 713
Fruit and vegetable processing wastes, 550
Fuel mixture, gasoline engines, 754
G
Gage pressure, 441, 442
Gas, digester
flow, 470
pressure, 470
quality, 470
-------
Gas chromatograph, 470
Gas-phase hydrocarbon analyzer, 70
Gases
explosive, 8
organic and inorganic, 7
toxic, 8
Gasification, 137
Gasoline, 504
Gasoline engines
air-cooled engines, 740, 754
battery, 750
carburetion, 744, 745
compression ratio, 743
displacement, piston, 740
four-cycle engines, 740, 748
fuel mixture, 754
governing, 744, 747
ignition, 744, 746, 750, 752
lubrication, 750, 751
magneto, 750, 753
maintenance, 744, 754
piston displacement, 740, 742
problems, 744
running problems, 744
seize up, 754
starting, 754
starting problems, 744
strokes in the cycle, 740, 741
thermostat, 748
timing, 743
troubleshooting, 744, 754
valves, 743, 750
water-cooled engines, 748, 749
Generation of odors, 7, 8
Generator, size, 736
Glossary of terms, 813
Good housekeeping, 24, 305
Grab samples, 487
Gravimetric chemical feeders, 294, 301, 616
Gravity filters
abnormal operation, 328
air scour, 324
alarms, 326
algae control, 329, 331
backwashing, 316, 327, 333
depth filtration, 317
description, 316
differential pressure, 318
downflow filters, 317, 320
drain, 324, 326
filter aid, 328
filtering, 316, 326
head loss, 318, 324
inlet, 317
instrumentation, 324, 333
landscaping, 329
location in treatment system, 317
maintenance, 333
media, 317, 331
methods of filtration, 317
mud balls, 317
multi-media, 317, 320
operation, 326
operational strategy, 329
parts, 317
plans and specifications, 333
rapid sand filters, 317, 322
rate control, 324
record keeping, 331, 332
review of plans and specifications, 333
Index 853
safety, 331
scouring media, 317
sectional filters, 324, 325
shutdown, 331
slime control, 329, 331
start up, 326
static bed filters, 317
surface straining, 317
surface wash, 317
totalizer, 326
troubleshooting, 331
troughs, 324
turbidity, 326
types of filters, 317
underdrains, 317, 323
upflow filters, 317, 319, 320
use, 316, 321
water rate control, 324
water supply, 324
Gravity sludge thickening
age of sludge, 137
anaerobic, 137
baffle, 137
blanket depth, sludge, 138, 139, 141
bound water, 137
concentration factor, sludge, 140
concentrators, gravity, 135, 138
coning, 141
denitrification, 137
detention time, 138
effluent, 140
factors affecting performance, 137
filamentous organisms, 137
gasification, 137, 142
guidelines, operation, 138
hydraulic loadings, 138
liquid surface, 140
nitrifying bacteria, 137
observations, 140
operation, 138, 139
overflow rate, 138
performance, 139
plans and specifications, 249
rising sludge, 137
sampling, 139
septicity, 141
short-circuiting, 137
shutdown, 139
sludge-volume ratio (SVR), 138, 141
solids loadings, 138, 139
start up, 139
surface loading, 138, 139
temperature, 138
troubleshooting, 140
variables, 137
withdrawal rates, 139, 142
Grease, industrial wastes, 74, 504
Grit
channels, 71, 86
industrial wastes, 74, 86
Grit channel instrumentation, 462
Grounds upkeep
asphalt paving, 790
drainage, 792
enclosures, 790
fertilizing, 791
gates, 790
good appearance, 789
high pressure sodium lights, 789
irrigating, 791
-------
854 Treatment Plants
landscape, 791
lawn, 791
lighting, 789
lumen, 789
maintenance, yard lighting, 790
mercury vapor lights, 789
mowing, 792
need, 789
paving, 790
pruning, 792
roadways, 790
safety, 790
surface water drainage, 792
walkways, 790
weed control, 791
yard lighting, 789
Groundwater contamination, effluent disposal, 388, 415
Groundwater contamination, lagoons, 234, 240, 248
Groundwater recharge, wastewater, 401, 403
Growth rate, V, sludge, 133
H
Handling of sludges
see Sludge handling and disposal
Hardness number, 686
Hazardous wastes, 484
Hazards
see Safety hazards
Head, 713
Headworks, odors, 25
Heated discharges, 76
Heating systems
blowers, draft, 776
boilers, 776
burners, 776, 778
control switches, 776
control transformer, 776
draft blowers, 776
expansion tank, water, 776
flue draft, 776
gas-fired boilers, 776
gas pressure regulator, 776
gas system, 776
gas valve, 776
maintenance, 776
makeup water, 776
operation, 776
pilot outage, 778
pilot switch/valve, 776
troubleshooting, 778
valves, water system, 776
water system, 776
water valves, 776
Heavy metals, in industrial wastewaters, 70, 505
High pressure sodium lights, 789
High-rate activated sludge, 60, 62
High temperature wastes, 504
High voltage, 738
Holding tanks, 74
Housekeeping
chemical systems, 305
odor control, 24
Hydrasieve, 569
Hydraulic grade line, 713
Hydraulic loading gravity thickeners, 138
Hydraulic shock load, 505
Hydro-mechanical control system, 426
Hydrocarbon gases, measurement, 70, 462
Hydrocarbons, 504
Hydrochloric acid, 592
Hydrogen peroxide
filamentous organism control, 93
odor control, 12, 99
oxygen, source, 76
phenol control, 101
Hydrogen sulfide
equilibrium, 9
industrial wastes, 484
odors, 7, 8
removal from air, 17
tests
see Chapter 16
Hydrogen transfer, 7
Hydrologic cycle, 401
Hydrometer, 438, 441
Hydropneumatic systems, 785
Hydroscreen, 569, 571
Hydrostatic system, 464
Hygroscopic, 614
Hypochlorination, odor control, 12
I
Identification of odors, 8
Incineration (multiple hearth furnace)
activated carbon regeneration, 649, 653
air flow, 229, 230, 231
alarm systems, 230
ash handling system, 226, 244
autogenous burn, 233
auxiliary fuel, 227
bearings, 221
burner, 226
burnout, 230, 232
cake feed rate, 229
clinkering, 233
combustion, 230
combustion zone, 227, 228
conditions in furnace, 227
controls, 227
cooling zone, 227
description, 214, 221, 226
draft, 229
drying zone, 227
fire triangle, 226
flame, 229
fluidized-bed reactors, 214, 216, 217
fuel, 227
furnace zones, 227
hearths, 214, 219, 220
instrumentation, 227
lute cap, 221, 222
moisture content, 229
multiple hearth furnace, 214, 215, 649, 653
off-gas system, 221, 225
operation, 227, 230, 232
oxygen analyzer, 229
oxygen demand, 230
protective clothing, 233
rabbling, 221,222
refractory, 214
rotary kilns, 213, 214, 218
safety, 233
sand seals, 221, 223
shaft, 221
shutdown, 232
smoke, 229, 233
start-up, 232
temperature, 230, 232, 233
troubleshooting, 233
volatile content, 229
-------
Index 855
Incompatible chemicals, 608
Indicators, instruments, 454, 455
Indirect reuse of wastewater, 386
Indole, 7, 11
Industrial and municipal waste treatment
effects on treatment processes, 70
industrial wastes, common, 70
monitoring, 69
operation, 85
operational strategy, 71
organic wastes, 71
toxic wastes, 71
Industrial waste monitoring
also see Monitoring industrial wastes
accidental discharge, 523
administration, 484
battery charging, 502, 529
care of monitoring equipment, 491
chain of possession, 498
characteristics of industrial wastes, 484
charging batteries, 502, 529
composite samples, 487
confined spaces, 502
continuous monitoring 486
data base, 485
dealing with industry, 486
enforcement, 485
equipment storage, 502
flow metering, 498
flows, regulation, 503
grab samples, 487
hazardous wastes, 484
hydrogen sulfide, 484
identifying waste materials, 495
importance, 484
labeling samples, 498
locating sources of discharges, 495
maintenance, 491
monitoring, 486, 502
need, 484
objectives, 484
odors, 484
ordinance, sewer-use, 520
Palmer-Bowlus flumes, 487, 498
Parshall flume, 498
permit, sewer-use, 511
portable sampling equipment, 487
preservation of samples, 495, 498
records, 524
refractory materials, 484
regulation of high flows, 503
representative samples, 486
safety, 498, 529
sample preservation and security, 495, 498
sampling points, 486
security of samples, 495, 498
self-monitoring, 486
sewer service charges, 485
sewer-use ordinance, 70, 72, 485, 520
sewer-use permit, 511
shock loads, 484
slug discharge, 495, 516
standard industrial classification, 485
storage of equipment, 502
storage time and temperature of samples, 495, 498
strategy for monitoring, 502
thermal wastes, 484
toxic wastes, 484
traffic safety, 498
warning systems, 586
water meters, 498
Industrial waste treatment
also see Industrial waste treatment, activated sludge
and Chapters 21 and 27
activated carbon, 635
adsorption, 635
case history, 660
coagulation and precipitation, 612
coke wastes, 552
dairy wastes, 548
fermentation wastes, 550
flotation, 554
fruit and vegetable processing wastes, 550
meat packing wastes, 549
metal finishing wastes, 552
microscreening, 568
need for treatment, 545
neutralization, 588
operation, 660
POTW, 545
petroleum wastes, 552
precipitation, 612
pretreatment, 545
pulp and paper wastes, 549
screening, 568
solutions, 553
steel mill, 660
tannery wastes, 549
textile wastes, 551
types of industrial wastewaters, 548
uses of water, 545
vegetable processing wastes, 550
water quality criteria, 545
Industrial waste treatment, activated sludge
also see Chapters 27 and 28 and Industrial waste treatment
acclimation of microorganisms, 74
ammonia treatment, 101
artichoke wastes, 95
BOD, 73
brewery wastewaters, 85
bulking sludge, 78, 85, 89
COD, 73
characterisitics, 72
clarification, 78
common industrial wastes, 70
contact stabilization, 71, 97
cooling towers, 76
dairy wastes, 97
dissolved oxygen, 78, 89, 97, 99
effects of industrial wastes, 70
emergency storage tanks, 75, 76, 79
equalizing basins, 75, 76, 79
extended aeration, 97, 99
F/M, 92, 97
filamentous organisms, 78, 85, 89, 93, 97
flow, 72, 73
flow regulation, 74
flow segregation, 74
food processing wastes, 95
grease, 74
grit, 74
heated discharges, 76
holding tanks, 74, 76
industrial wastes, 70
influent, 72
laboratory testing, 95, 99
MCRT, 92, 97, 99
microscopic examination, 65, 84
monitoring, 69, 79, 99
need for treatment, 72
-------
856 Treatment Plants
neutralization, 73, 77, 80, 97
nutrients, 72, 73, 76, 77, 80, 85, 88
observations, 78, 99
odors, 78
oil, 74, 99
operation, 77, 89, 97, 99
operational strategy, 71, 77, 85
periodic feeding for start-up, 82
petroleum refinery wastes, 99
pH, 73, 78, 97, 99, 101
phenols, 101
pilot plant, 95
pretreatment, 70, 72, 74, 75, 76, 86, 95
pulp and paper mill wastes, 79
record keeping, 70, 79, 95
restart, 76
return activated sludge (RAS), 78
sampling, 70, 99
screening, 74
seed activated sludge, 76
shock loads, 99
shutdown, 81
sludge age, 92
start-up, 76, 81, 82
step feed, 97
sulfide shock load, 99
suspended solids, 73
toxicity, 73, 78
troubleshooting, 76
waste activated sludge, 78, 92
Industrial wastewater
acid, 504
caustic, 504
color, 504
gasoline, 504
grease, 504
heavy metals, 505
high temperature, 504
hydraulic shock load, 505
hydrocarbons, 504
metals, 505
nitrogen, 505
nutrients, 505
odors, 505
oil, 504
organic solids, 504
pathogens, 505
pesticides, 505
phosphorus, 505
radioactive wastes, 505
solids, 504
solvent, 504
tastes, 505
thermal waste, 504
toxic substances, 505
turbidity, 504
Inert-media pressure filters, 334
also see Pressure filters
Infiltration-percolation, 401, 403
influent instrumentation, 461, 462
Influent odors, 25
Inorganic gases, 7
Inorganic matter, 131
Instrumentation, gravity filters, 324
Instrumentation, pure oxygen, 106
Instrumentation system, 454, 455
Instruments and controls
absolute pressure, 441, 442
accuracy, 430
activated sludge process, 466
aeration air rate, 466
alarms, level, 450, 463, 465, 469, 473
anaerobic sludge digestion, 468
analytical measurements, 438, 454
bar screen operation, 462
bellows, pressure, 445, 449, 473
biological control system, 426
Bourdon tube, 445, 449
bubbler tube, level, 450, 453
capacitance probe, level, 450, 473
cathode ray tube (CRT), 454
charts, 459, 473
circular charts, 459, 473
combustable gas alarm, 470
computers, 469
confined spaces, 470
control logic, 426
control methods, 456
control system, 430
controllers, 454, 455, 456, 473
density, 438, 450
description, 426
diaphragm box, level, 450
diaphragm, pressure, 445, 449, 473
digester controls, 468, 469, 470
dissolved oxygen probe, 468, 473
droop, 456
electric probe, level, 450, 462, 473
electrical control system, 426, 456
explosive gas detection, 462
float system, level, 450, 451, 473
flow, 438
gage pressure, 441, 442
gas chromatograph, 470
grit removal, 462
hydro-mechanical control system, 426, 456
hydrocarbon detection, 462
hydrometer, 438, 441
indicators, 454, 455
influent flow, 462
influent level, 461
integrators, 459, 473
level, 438, 450, 461, 469, 473
lower explosive limit, 462, 470, 473
magnetic meter, 473
maintenance, 471, 473
manometer, 434, 437, 445, 446, 447, 448, 473
manual control, 456
measurements, 434
mechanisms for recorders, 459
micrometer, 430, 432
motor-controlled gates, 463
need, 426
neutralization, 605, 606, 607, 611
offset, 456
on-off control, 456
open and closed loops, 456
operation, plant, 461
orifice plate, 466, 473
permanence, 434
pH probe, 473
pneumatic system, 456
preliminary treatment, 461
pressure, 434, 473
primary element, 454
primary treatment, 461
probe, 455, 473
process variables, 434
proportional control, 456
ratio control, 457, 458
-------
Index 857
receiver, instrument, 455, 456
record keeping, 471
recorders, 457
recording media, 459
repeatability, 430
safety, 471
secondary device, instrument, 454
sensitivity, 434
sensors, 444, 454, 455
set point, 454
sight tube, 438, 439, 450
sludge blanket depth, 464
sludge density meter, 464
software programs, 469
spectrophotometer, 470
speed, measurement, 439
strip charts, 459, 473
strobe light, 450, 473
sump pump, 463
tachometer, 440, 450, 473
temperature, 434, 444, 470
thermocouple, 445, 470, 473
totalizers, 459, 473
transmission system, 426, 455, 456
troubleshooting, 471, 473
turbidimeter, 468, 473
ultrasonic sound, level, 450, 452, 473
units of measure, 438
use, 430
vacuum pressure, 441, 442
valves and gates, 463
velocity, 438, 450
ventilation system, 463
Venturi, 473
weirs, 473
Integrators, instruments, 459, 473
Interface, 43
Interparticle bridging chemicals, 612, 613
Ion exchange, 101
Iron coagulants, 614
Irrigation
sludge, 240, 242
wastewater, 401, 403, 405, 412
J
Jar test, 174, 305, 328, 375, 377, 614, 666, 679
K
Kiln dryer, 213, 214, 218
Kirk-key, 736
L
Labeling samples, 498
Laboratory
procedures
see Chapter 16
safety
see Chapter 16
testing, 95, 99
Lagoons
facultative sludge storage, 234, 242, 244, 247, 248
groundwater contamination, 234, 240, 248
odors, 27, 244
permanent, 244
sludge storage, 234
Lake Tahoe, California, 388
Lamell panels, 558, 559
Lamella separators, 628
Land application
solids, 234
solids management, 234
Land disposal, effluent
boron, 413, 415
cation exchange capacity, 415
classes of irrigation waters, 412, 413
corrosion, pipes, 413
crop production, 401, 402
description, 401
drain tile systems, 416
drainage wells, 416
emergency operating procedures, 413
equipment requirements, 401
evapotranspiration, 401
groundwater, 415
guidelines, loadings, 404
hydrologic cycle, 401
infiltration-percolation, 401, 403
irrigation, 401, 403, 405, 412
layout, 402
limitations, 406
loadings, 404
maintenance, 416
monitoring, 415
observations, 413
odors, 413, 414, 416
operation, 406, 408
operational strategy, 411
overland flow, 401, 403
plans and specifications, 416
ponding, 416
review of plans and specifications, 416
safety, 415
salinity, soil, 406, 411
shutdown, 411
sidestreams, 401
sodium adsorption ratio, 413
soil moisture determination, 408
soil sealing, solids, 406
start up, 406, 407
troubleshooting, 413
wells, monitoring, 415
Land disposal, solids
agricultural reclamation, 234, 240, 242
alternatives, 234, 235, 236, 237, 238
birds, 248
cadmium, 240
dedicated land disposal, 234, 239, 241, 248
disposal options, 239
environmental controls, 247
flies, 248
flooding, 241
groundwater, 234, 240, 248
high-rate dedicated land disposal, 241
lagoons, facultative sludge, 242, 244, 247, 248
landfilling, 240, 244, 247
monitoring , 247, 248
need, 234
nitrogen requirements, 240, 244
odors, 244, 247
on-site dedicated land disposal, 239
operation, 242
options, 238
public health, 248
regulatory constraints, 234
ridge and furrow, 241, 244
rodents, 248
sanitary landfill, 234, 239, 240, 247
sludge type, 247
stabilized sludge, dewatered, 239
stabilized sludge, liquid process, 241
-------
858 Treatment Plants
storage of sludge, 239, 241
subsurface injection, 242, 244
surface runoff, 234, 248
toxic substances, 234
transportation of sludge, 239, 241
trenching, 239
utilization options, 234, 247
vectors, 248
Landscape, 791
Langelier Saturation Index, 314
Lead-acetate strips, 8
Level measurement, instruments, 438, 450, 469
Lighting
emergency, 736
safety, 737
yard, 789
Lime, 80, 170, 293, 359, 369, 373, 590, 614
Lime analysis
see Chapter 16
Lime feed, 373, 619
Lime precipitation, phosphorus removal
abnormal operation, 362
clarification process, 359, 361, 362, 363, 366
description of process, 359, 360
dust control, 368
emergency operation, 362
equipment, 359, 361
guidelines, operation, 367
hydraulic loading, 361, 363, 367
industrial discharges, 363
jar test, 362
layout of process, 360
lime analysis
see Chapter 16
lime feed equipment, 359, 362, 363, 366, 367, 619
lime strength, 359
loadings, 367
maintenance, 366
mixing chamber, 359, 362
operation, 359, 361, 362
operational strategy, 362
pH, 361, 363, 366
plans and specifications, 367
pumps, 361, 362, 363, 366
recalcine, 358, 366
recarbonation, 362, 363, 364, 365, 366
review of plans and specifications, 367
safety, 366, 368
sampling, 361, 362
scale, lime, 362
shutdown, 362
slake, 359
sludge disposal, 361
slurry, 359
start up, 359, 360, 361
storm water, 363
troubleshooting, 366
Lime slurry, 373
Lime stabilization of sludges, 170
Liquid chemical feeders, 617
Locating sources of discharges, 495
Lower Explosive Limit (L.E.L.) instruments, 462, 470, 473
Lumen, 789
Luxury uptake of phosphorus
abnormal operation, 372
activated sludge process, 372
anaerobic conditions, 369, 372, 373
clarification, 369
description, 369
equipment, 369, 373
guidelines, operation, 373
hydraulic loadings, 373
layout, 370, 371
lime clarification, 369
lime feed, 369, 372, 373
lime slurry, 373
loadings, 373
maintenance, 372
mixing tank, 369
operation, 369, 372, 373
operational strategy, 372
pH, 369, 372
piping, 372
plans and specifications, 373
principles of operation, 369, 372
pumps, 373
review of plans and specifications, 373
safety, 373
sampling, 372
shutdown, 372
sludge feed, 372
sludge recycle, 369
sludge withdrawal, 372, 373
start up, 369
straggler floe, 372
stripping tank, 369, 372
M
MCRT, 60, 63, 66, 67, 82, 92, 97 99, 104
MEA (monoethanolamine), 101
MLVSS, 60, 65
Magnetic meters, 473
Maintenance
activated sludge, 50, 52, 106
air conditioning, 779
alum flocculation, 375
blowers, 779
boilers, 776
chemical feed systems, 308
chemical scrubbers, 22
cleaning, 565
controls, 471
diaphragm pumps, 719
diesel engines, 761
direct reuse of effluent, 400
exhaust fans, 779
flotation, 564, 566
gasoline engines, 744, 754
gates, 790
gravity filters, 33
grounds and landscape, 789
instruments, 471,473
land disposal, 416
lighting, yard, 790
lime precipitation, phosphorus, 366
luxury uptake, phosphorus, 372
microscreens, 315, 583
neutralization, 609
painting, 565
pressure filters, 343
pure oxygen systems, 50, 52, 106
sampling equipment, 491
screening, 583
scrubbers, 22
walkways, 790
yard lighting, 790
Manometer, 434, 437, 445, 446, 447, 448, 473, 763
Masking odors, 17
Mean cell residence time, 60, 63, 66, 67, 82, 92, 97, 99, 104
Measurement of odors, 8
-------
Measurements, instruments, 434
Meat packing wastes, 549
Mechanical drying
description, 213, 244
operation, 214
performance, 214
reduced volume sludge, 244
sludge type, 214
types of driers, 213
variables, 213
Mechanisms for recorders, 459
Media
gravity filters, 317
vacuum filters, 199, 200
Mercaptans, 7, 11, 17
Mercury vapor lights, 789
Metal finishing wastes, 552, 597
Metal salts, 596
Metallic ions, odor control, 14
Metals, 70, 505
Metering chemicals, 294
Methylene blue number, 690
Metric conversion factors
activated sludge, 107
sludge handling and disposal, 250
Metric problem solutions
activated sludge, 107
aerobic digestion, 256, 257, 258
agricultural reclamation, 262
centrifuges, 255
chemical doses, 258, 259, 260
composting, 262
dissolved air flotation, 254, 255
drying beds, sludge, 261
filter presses, 260
gravity thickeners, 252
jar tests, 258
industrial waste treatment, 110
land disposal, 262
nitrification, 111
nutrient addition, 110
polymers, 258, 259, 260
primary sludge production, 250
sand drying beds, 261
secondary sludge production, 251
sludge handling and disposal, 25
thickening, 252
ultimate disposal, 262
vacuum filter, 261
Micrometer, 430, 432
Microorganisms, activated sludge, 63, 65, 66, 67
Microscopic examination, 65
Microscreens
also see Screening and microscreening
advantages, 310
backwashing, 312
bearings, 312
bypass weir, 312
corrosion, 314
drive unit, drum, 312
drum, 312
flow-equalization system, 313
flows, 313
head loss, 312, 315
high flows, 313
high solids, 314
low flows, 313
maintenance, 315
microfabric, 309, 312
microstraining, 309
Index 859
oil and grease, 314
operation, 313
operational strategy, 314
parts, 312
pH, 314
protective clothing, 315
safety, 315
scaling, 314
shutdown, 314
solids disposal, 309, 312
solids loading, 314
solids waste hopper, 312
start up, 313
structure, 312
support bearings, 312
troubleshooting, 314
ultraviolet light, 312
use, 309
water spray system, 312
weir, 312
Mixing, chemicals, 294
Molasses number, 694
Monitoring chemical treatment, 305
Monitoring, industrial wastes
also see Industrial waste monitoring
accidental discharge, 523
acids, 70, 484
alkalies, 70, 484
automatic monitoring units, 70
collection system, 70, 484
corrosion, 70, 484
cyanides, 70, 484
flammable oils, 70, 484
flotation processes, 562, 564
greases, 70
hazardous wastes, 484
heavy metals, 70
hydrocarbon analyzers, 70
hydrogen sulfide, 484
labeling samples, 498
metals, 70
monitoring systems, 69, 79, 99
oils, 70
organic toxicants, 70
Palmer-Bowlus flume, 487, 498
Parshall flume, 498
pesticide, 70
pollutant strength, 73
records, 524
refractory materials, 484
safety, 70
sampling units, 70
settleable solids, 70
sewer service charges, 485
sewer-use ordinance, 70, 72, 485, 520
slug discharge, 495, 516
standard industrial classification, 485
strength of pollutant, 73
thermal wastes, 484
toxic gases, 70
water supply, 70
Monitoring, sludge disposal, 247
Monitoring, wastewater reclamation, 398, 415
Monoethanolamine (MEA), 101
Moving average, 62, 97
Multi-media filters, 317
Multiple hearth incinceration
see Incineration
Municipal and industrial waste treatment
also see Monitoring industrial wastes
-------
860 Treatment Plants
activated sludge, 71
clarifiers, 71
comminutors, 71
contact stabilization, 71
effects on treatment processes, 70
grit channels, 71
industrial wastes, common, 70
monitoring, 69
nutrients, 72
observations, 71, 78
operation, 85
operational strategy, 71
organic wastes, 71
recorders, 70
sampling, 70
screens, 71
sludge digesters, 71
toxic wastes, 71
Muriatic acid, 592
Muskegon County, Michigan, 390
N
National pollutant discharge elimination system (NPDES), 69,
289
Neutralization
acid storage tanks, 610
activated sludge, 73, 77, 80
batch-type, pH control, 606
caustic soda, 590
chemistry, 590
coagulation, 597
construction, 609
continuous neutralization, 607
equilibrium, chemical, 592
flocculation, 597
hydrochloric acid, 592
incompatible chemicals, 608
industrial waste treatment, 73, 77, 80
instrumentation, 605, 606, 607, 611
lime, 590
maintenance, 609
mechanics of process, 605
metal pickling and plating wastes, 597
metal salts, 596
muriatic acid, 592
need, 588
operation, 609
pH, 596
precipitation, 596
principles, 589
safety, 608
sludge conditioning and disposal, 598
sodium hydroxide, 590
solute, 598
start up, 609
sulfuric acid, 590
troubleshooting, 610
Nip points, 559
Nitrate compounds, odor control, 14
Nitrification
activated sludge nitrification, 101
aerobic digestion, 169
alkalinity, 104
ammonia-stripping, 101
bacteria, 102, 104, 137
biological nitrification, 102
breakpoint chlorination, 102
ctilorination, breakpoint, 102
denitrification, 105, 137
detention time, 104
dissolved oxygen, 102
F/M, 104
guidelines, 102
industrial wastes, 99
influent nitrogen, 101
ion exchange, 101
MCRT, 63, 104
methods of nitrification, 101
microorganisms, 102, 104 137
nitrogen concentrations, 101
nitrogen cycle, 103
nutrients, 104
operating guidelines, 102
petroleum refinery wastes, 99, 101
pH,104
phosphorus addition, 104
pretreatment, 104
RAS flow rate, 53
rising sludge, 105
sludge age, 104
superchlorination, 102
temperature effects, 63, 104
toxic materials, 104
Nitrifying bacteria, 137
Nitrogen cycle, 103
Nitrogen, industrial wastes, 505
Noncorrodible, 578
Nonvolatile matter, 131
Nuclear generating station, reuse, 390
Nutrient removal, 358
Nutrients, 72, 73, 76, 77, 85, 88, 97, 358, 505
O
OSHA, 502
Observations
activated sludge, 71, 78
centrifuge thickeners, 161
dissolved air flotation thickeners, 149
gravity thickeners, 140
land disposal, 413
Odor control
absorption, 17
activated carbon, 23
ammonia, 7
biological generation, 7
biological odor reduction towers, 14
chemical scrubbers, 17
chemical treatment, 12
chlorination, 12
chromate, 14
combustion, 17
complaints, 11
counteraction, 17
generation of odors, 7
good housekeeping, 24
hydrogen peroxide, 12, 101
hydrogen sulfide, 7, 8
hydrogen transfer, 7
identification, 8
land disposal, 413, 414, 416
masking, modification and counteraction, 17
measurement, 9
metallic ions, 14
need, 7
nitrate compounds, 14
olfactometer, 8, 247
oxygen, 14
ozone, 14, 24
packed tower, 17
pH control, 14
-------
Index 861
phenols, 101
scrubbers, 17
solutions to problems, 12, 25
sources of odors, 7, 8
spray chamber, 17
treatment of odors, 17
troubleshooting, 12, 25
Odor panel, 8
Odors
also see Odor control
ammonia, 7, 11
biological generation, 7
biological odor reduction towers, 14
causes, 7
characteristics, 11
classification, 11
collection systems, 7, 8
complaints, 11
dehydrogenation, 7
detection, 8
fecal, 11
gases, 7
generation of odors, 7, 9
good housekeeping, 24
hydrogen sulfide, 7, 8, 11
hydrogen transfer, 7
identification 8
indole, 7, 11
industrial wastes, 78, 484, 504
land disposal, 247, 413, 414, 416
masking, 17
measurement, 8
mercaptans, 7
monitoring, 247
need for control, 7
nitrogen compounds, 7
pulp and paper mill wastes, 81
rotten egg, 7, 8, 11
skatole, 7, 11
skunk, 11
solutions to problem, 12
sources of odors, 7, 18, 12, 78
sulfur compounds, 7, 8, 11
temperature effect, 8
treatment of odors, 17
troubleshooting, 12, 25
Offset, controller, 456
Oil, industrial wastes, 70, 74, 99
Oil refinery wastes
see Petroleum refinery wastes
Olfactometer, 8, 247
Operation
absorption odor units, 24
activated carbon, 641, 646, 654
activated sludge, industrial wastes, 77, 89, 97, 99
activated sludge process, 53, 59
activated sludge, RAS and WAS, 53, 59
aerobic digestion, 164, 166
air conditioning, 779
alum flocculation, phosphorus, 375
artichoke wastes, 97
belt filter press, 190, 192
blowers, 777
boilers, 776
centrifuges, 155, 157
chemical conditioning, 178
chemical feed systems, 302, 307
chemical scrubbers, 22
chlorine stabilization, 171
coagulation, 631, 632
composting, 211
controls, 461
dairy wastes, 97
diaphragm pumps, 719
direct reuse of effluent, 397, 398
dissolved air flotation thickeners, 146, 147
elutriation, 184
fans, 777
flotation, 560
food processing wastes, 97, 99
gravity filters, 326, 329
gravity sludge thickeners, 138, 139
incineration, 227, 230, 232
industrial waste treatment, 660
instruments, 461
land disposal, 406, 4D8
lime precipitation, phosphorus, 359, 361, 362
lime stabilization, 171
luxury uptake, phosphorus, 369, 372, 373
mechanical drying, 214
microscreens, 313, 579
multiple hearth furnace, 227, 230, 232
neutralization, 609
petroleum refinery wastes, 99
plate and frame filter press, 188, 189
pressure filters, 343
precipitation, 631, 632
pulp and paper mill wastes, 85
pure oxygen, 50
sand drying beds, 201, 202
screens, 479
scrubbers, 22
sludge thickeners, 138, 139, 146, 147
steel mill, 660
surfaced sludge drying beds, 206
thermal conditioning, 180, 181
vacuum filtration, 198, 199
wet oxidation, 184
Operating guidelines
activated carbon, 658
activated sludge, 53, 56, 58, 60, 63, 67
aerobic digestion, 164, 167
alum flocculation, phosphorus, 377
belt filter press, 190, 193
centrifuge, dewatering, 201
centrifuge thickeners, 155, 157
coagulation and precipitation, 628
dissolved air flotation thickeners, 146, 148
elutriation, 184
gravity sludge thickeners, 138
land disposal, effluent, 404
lime precipitation, phosphorus, 367
luxury uptake, phosphorus, 373
nitrification, 102
plate and frame filter press, 186, 189
pulp and paper mill wastes, 85
sand drying beds, 201
thermal conditioning, 180,181
vacuum filtration, 198, 199
wet oxidation, 184
Operational strategy
activated carbon, 654
activated sludge, industrial wastes, 71, 77, 85
activated sludge, RAS and WAS, 53, 59
brewery wastewaters, 85
chemical feed systems, 307
coagulation, 632
direct reuse of effluent, 398
gravity filters, 329
industrial waste monitoring, 502
-------
862 Treatment Plants
industrial wastes, activated sludge, 71
land disposal, 411
lime precipitation, phosphorus, 362
luxury uptake, phosphorus, 372
microscreens, 314, 580
monitoring programs, 502
precipitation, 632
pressure filters, 343
screening, 580
steel mill, 660
Ordinance, sewer-use, 520
Organic
gases, 7
matter, 131
toxicants, 70
wastes, 71, 504
Orifice plates, 466, 473
Overflow rate
coagulation and precipitation, 628
gravity thickeners, 138
Overland flow, 401, 403
Oxidation-reduction potential, 14
Oxidized organics, 7
Oxygen
aerobic digestion, 166-170
odor control, 14
Oxygen activated sludge
see Activated sludge and also Pure oxygen
Oxygen generation equipment, 106
Oxygen production, pure oxygen activated sludge, 47
Ozone, odor control, 14, 24
Ozonization, 17, 24
P
POTW, 545
PSA, pure oxygen, 47, 48
Package plant, aerobic digestion
see Chapter 8
Packed tower, 17
Painting, equipment, 565
Palmer-Bowlus flume, 487, 498
Parshall flume, 498
Pathogens, 505
Paving, 790
Periodic feeding for start-up, 82
Permanence, instruments, 434
Permit, sewer-use, 511
Pesticides, 70, 505
Petroleum refinery wastes
activated sludge treatment, 99
ammonia treatment, 101
characteristics, 99, 552
dissolved oxygen, 99
extended aeration, 99
hydraulic loading, 99
hydrogen peroxide, 101
laboratory testing, 99
MCRT, 99
monoethanolamine (MEA), 101
nitrification, 99, 101
observations, 99
odors, 101
operation, 99
pH, 99, 101
phenols, 101
sampling, 99
shock loading, 99, 101
sulfide shock load, 99
thiocyanate, 101
toxicity, 101
treating ammonia, 101
waste characteristics, 99
pH
industrial waste treatment, 73
neutralization, 596
odor control, 14
test
see Chapter 16
pH measurement
see Chapter 16
pH probe, 473
Phenol, 12, 101
Phoenix, Arizona, reuse, 390
Phosphorus
industrial wastewaters, 505
test in wastewater
see Chapter 16
Phosphorus removal
alum flocculation, 373
lime precipitation, 359
luxury uptake, 369
purpose, 358
types of systems, 358
Physical enmesher chemicals, 612, 613
Pilot plant, activated sludge, 95
Pin floe, 66, 67
Pipe schedules, 722
Pipe threads, 725
Pipes
asbestos cement, 726
cast ductile iron, 725
cathodic protection, 725
concrete, 725
electro-chemical corrosion, 725
electrolysis, 725
galvanized, 722
need, 722
PVC, 725
polyvinyl chloride, 725
schedules, 722
soil pipe, 725
threads, 725
welded steel, 726
Piston pumps, chemical feeders, 294, 296
Plans and specifications
activated carbon, 658
activated sludge, 105
alum flocculation, phosphorus, 377
centrifuges, 249
chemical conditioning, 250
chemical feed systems, 302
direct reuse of effluent, 400
dissolved air flotation, 249
filter presses, 249
gravity filters, 333
gravity thickening, 249
land disposal, 416
lime precipitation, phosphorus, 367
luxury uptake, phosphorus, 373
microscreens, 585
odor control, 27
pressure filters, 345
pure oxygen systems, 105
screening, 585
sludge handling and disposal, 249
thermal conditioning, 250
Plate and frame filter presses
cake, 189, 190
cleaning media, 188
conditioning of sludge, 186,189, 190
-------
description, 186
factors affecting performance, 186
filter cloth, 186, 189
filter yield, 186, 189
guidelines, operation, 186, 189
operation, 186, 188, 189
performance, 189
plans and specifications, 249
precoat, 188, 189, 190
pressure, 186, 189, 190
solids loading, 188
solids recovery, 189
time of filtration, 188, 189, 190
troubleshooting, 189, 190
variables, 186
yield, 186, 189
Pneumatic transmitters, 426, 455, 456
Pollutant strength, 73
Polyelectrolyte, 173, 293, 362
Polymer feed, operation, 302, 621, 622
Polymer usage, 161, 293, 362, 612, 613, 614
Polysaccharide, 179
Ponding, land disposal, 416
Ponds, odors, 27
Portable pumps
centrifugal trash pumps, 717
diaphragm pumps, 719
engines, 740
maintenance, 719
positive displacement pumps, 719
seals, 722
submersible pumps, 720
trash pumps, 717
troubleshooting, 718, 719
types, 717
Portable samplers, 487
Positive displacement pumps, chemicals, 294, 296, 297, 298
Precipitate, 358
Precipitation
see Coagulation and precipitation
Precoat, 186
Preliminary treatment, instruments, 461
Preserving samples, 495, 498
Pressure filters
abnormal operation, 343
air binding, 342
backwash cycle, 342
backwash system, 340
bypass, 334, 343
chemical feed systems, 336
decant tank, 334, 336, 342
emergency storage, 334
equalization of flows, 334
facilities, 334
feed pumps, 336
filters, 338, 344
flow control, 340
holding tank, 334
inert media, 340
layout, 335
maintenance, 343
media, 340, 344
mud balls, 344
operation, 343
operational strategy, 343
performance test, 343
plans and specifications, 345
pumps, 336, 342, 344, 345
review of plans and specifications, 345
safety, 345
Index 863
underdrain gravel, 340
use, 334
vessels, 337, 338
wet well, 334, 342
Pressure measurement, instruments, 434, 473
Pressure swing absorption, pure oxygen, 47, 48
Pretreatment
industrial wastes, 70, 72, 74, 86, 95, 521, 545
nitrification, 104
Primary clarifier, 88
Primary element, instrument, 454
Primary sedimentation
instrumentation, 463
odors, 25
Primary sludge production, 131
Primary treatment, instruments, 463
Probe, instrument, 455
Process variables, 434
Production of sludges, 131
Proteinaceous, 179
Protozoa, 65, 66, 84
Public relations, odors, 11
Pug mill, 213, 244
Pulp and paper mill wastes
activated sludge treatment, 79
bulking sludge, 85
cellulose, 80
color, 81
description, 549
dissolved oxygen, 85
emergency storage tanks, 79
emergency systems, 81
fiber, 80
filamentous growths, 85
flows, 81
foam control, 80
food/microorganism, 82, 84
MCRT, 82
microscopic examination, 84
mixed liquor suspended solids, 85
monitoring, 79
neutralization, 80
nutrients, 80, 85
odor, 81
operating guidelines, 85
operation, 85
periodic feeding for start-up, 82
pH control, 80
protozoa, 84
record keeping, 79
return activated sludge, 85
recycle, 80
safety, 83
shutdown, 81
sources of wastes, 79
start-up, 81, 82
steady state conditions, 81
temperature effects, 85
treatment variables, 80
troubleshooting, 83
turbidity, 81
Pumps
maintenance
see Chapter 15
portable, 713
seals, 722
submersible, 720
trash, 717
Pure oxygen
cryogenic air separation, 47, 49
-------
864 Treatment Plants
description of systems, 43
dissolved oxygen, 50
explosive conditions, 51
gas space pressure, 50
instrumentation, 106
layout, 44, 46
liquid oxygen, 50, 51
maintenance, 50, 52, 106
modes, 50
noise, 106
oxygen, 50
oxygen generation equipment, 106
PSA, 47, 48
plan view, 44
plans and specifications, 105
pressure swing absorption, 47
preventive maintenance, 106
process control, 50
purge, 47, 51
review of plans and specifications, 105
safety, 51, 106
silica gel trap, 50
spill, liquid oxygen, 51
start-up, 50
surface aerators, 43, 46
system control, 50
turbulent mixers, 43
vent, 47, 50
Pure gas, 47, 51
Q
Quantities of sludges, 131
Quicklime, 293
R
RAS
see Return activated sludge
Rabbling, 221
Radioactive wastes, 505, 547
Rapid sand filters, 317
Recalcine, 358
Recarbonation, 362
Receiver mechanisms, 455, 456
Recharge rate, 388
Reclaimed wastewater, 386, 789
Record keeping
brewery wastewaters, 95
chemical treatment, 302. 303, 304
flotation, 562
gravity filters, 331
industrial waste monitoring, 70
industrial waste treatment, 79, 95, 524
instruments, 471
odor complaints, 12, 13
pulp and paper mill wastes, 79
Recorders, 70, 79, 457
Recording media, 459
Recycled wastewater, 386
Refractory furnace, 214, 657
Refractory materials, 484
Regeneration, activated carbon, 649
Regulation of high flows, 503
Repeatability, instruments, 430
Representative samples, 486
Respiration, 358
Respiratory system hazards, 8
Restart, industrial waste treatment, 76
Return activated sludge
adjustment of process, 56, 58
brewery wastes, 89, 92
comparison of RAS control approaches, 53
constant percentage RAS flow, 53
constant RAS flow, 53
control, 53
dairy wastes, 99
flow diagram, 54
industrial waste treatment, 78
measurement of sludge blanket depth, 55
methods of RAS flow control, 53
nitrification, 53
pulp and paper mill wastes, 85
purpose, 53
SVI approach, 57
separate sludge re-aeration, 57
settleability approach, 55
sludge blanket depth, 55
troubleshooting, 56, 58
Reused wastewater, 386
Review of plans and specifications
activated carbon, 658
activated sludge, 105
alum flocculation, phosphorus, 377
centrifuges, 249
chemical conditioning, 250
chemical feed systems, 302
direct reuse of effluent, 400
dissolved air flotation, 249
filter presses, 249
gravity filters, 333
gravity thickening, 249
land disposal, 416
lime precipitation, phosphorus, 367
luxury uptake, phosphorus, 373
microscreens, 585
odor control, 27
pressure filters, 345
pure oxygen, 105
screening, 585
sludge handling and disposal, 249
thermal conditioning, 250
Rising sludge, 105, 137, 146, 155, 307
Roadways, 790
Rodents, 248
Rotary chemical feeder, 294, 300, 618
Rotary kiln dryers
activated carbon regeneration, 649
sludge, 213, 214, 218
Rotating biological contactors
see Chapter 7
Rotifers, 65, 66, 67, 78
Rotostrainer, 569, 572
Rotten egg odors, 7, 8, 11
S
SAR, 413
SVI approach for RAS, 57
Safety hazards
activated carbon, 657
activated sludge, 51, 106
alum flocculation, phosphorus, 377
chemical feed systems, 292, 293, 307
coagulation, 631
direct reuse of effluent, 400
electrical equipment, 736
explosive gases, 8
flotation, 559
gravity filters, 331
hydrogen sulfide, 8
incineration, 233
industrial wastes, 70
-------
industrial waste sampling, 498
instrumentation, 471
land disposal, 415
lime precipitation, phosphorus, 366, 368
luxury uptake, phosphorus, 373
microscreens, 315, 578
monitoring, 498
neutralization, 608
noise, 106
precipitation, 631
pressure filters, 345
pulp and paper mill wastes, 83
pure oxygen, 51, 106
respiratory system, 8
sampling, 498
sand drying beds, 206
screening, 578
steel mill, 676, 679
toxic gases, 8
walkways, 790
Salinity, soil, 406, 411
Samplers, 487
Sampling
activated carbon, 654, 657
chain of possession, 498
chemical preservation of samples, 498
composite samples, 487
continuous sampling, 486
devices, 70
equipment, 70, 487, 491
flotation processes, 562, 564
grab samples, 487
gravity thickeners, 139
industrial wastes, 70, 99, 484, 486
labeling samples, 498
location of sampling points, 486
maintenance of equipment, 491
portable equipment, 487, 491
preservation of samples, 498
representative samples, 486
sampling points, 486
security of samples, 498
storage of samples, 495, 498
temperature of stored samples, 498
time of sample storage, 495
units, 70
Sampling location, 486
Sampling units, 70
Sand drying beds
application of sludge, 202, 203
blinding, 201
cake, 203
chemical requirements, 201
climatic conditions, 201
conditioning, 201
covered, 201
description, 201
factors affecting performance, 201
guidelines, operation, 201
loading rates, 201, 202, 203
operation, 201, 202
performance, 203
plugged media, 203
removal of dried sludge, 202
solids recovery, 203
troubleshooting, 203
type of sludge, 203
variables, 201
Screening and microscreening
also see Microscreens
abnormal operation, 579
band screen, 572, 576
cleaning, 578
cylindrical screen, 569, 572, 573
description, 569
disc strainer, 572, 575, 575
drum screen, 569, 572, 573
hydrasieve, 569
hydroscreen, 569, 571
maintenance, 583
microscreens, 572
moving screens, 569
need, 568
operation, 579
operational strategy, 580
plans and specifications, 585
review of plans and specifications, 585
rotostrainer, 569, 572
safety, 578
shutdown, 480
start up, 579
stationary screens, 569
traveling screen, 572, 576
troubleshooting, 580
ultraviolet irradiation, 572
Screens
industrial waste treatment, 71, 74, 568
pre-treatment, 74
rotating drum, 569, 572, 573
Screw chemical feeders, 294, 299, 616
Screw lift pumps
see Chapter 15
Scroll centrifuge, 156, 161
Seals, pumps, 722
Secondary device, instrument, 454
Secondary effluents, solids removal
chemicals, 289
filters, gravity, 316
filters, pressure, 334
gravity filters, 316
inert-media pressure filters, 334
microscreens, 289
need, 289
pressure filters, 334
Secondary sedimentation, odors, 26
Secondary sludge protection, 133
Secondary treatment, 131
Security of samples, 495, 498
Sedimentation, odors, 25, 26
Seed activated sludge, 76
Seize up, 754
Self-monitoring, 486
Sensitivity, instruments, 434
Sensors, 444, 454, 455
Septic wastewater, 7
Septicity, 141
Set point, 454
Settleability approach for RAS, 55
Settleable solids, 70
Sewer service charges, 485
Sewer-use ordinance, 70, 72, 485, 520
Sewer-use permit, 511
Shock loads, 99, 484
Short-circuiting
coagulation and precipitation, 629
gravity thickeners, 137
Shutdown
absorption, 23
centrifuge thickeners, 157
chemical feed systems, 302
-------
866 Treatment Plants
chemical scrubbers, 22
direct reuse of effluent, 398
dissolved air flotation thickeners, 148
flotation, 560
gravity filters, 331
gravity thickeners, 139
incineration, 232
industrial waste processes, 81
land disposal, 411
lime precipitation, phosphorus, 362
luxury uptake, phosphorus, 372
microscreens, 314, 580
multiple hearth furnace, 232
pulp and paper mill, 81
screening, 580
scrubbers, 22
thermal conditioning, 181
vacuum filtration, 199
Sidestream treatment, 401
Sieve analysis, 695
Sight tube, 438, 439, 450, 473
Silica gel trap, 50
Skatole, 7, 11
Skunk odors, 11
Slake, 293, 359
Sludge
aerobic digestion, 163
anaerobic digestion, 163
belt filter press, 190
centrifuges, 150, 200
characteristics, 131
chemical conditioning, 173
chemical stabilization, 170
composting, 207
conditioning, 173, 598
dewatering, 186
drying beds
see Sand drying beds and Surfaced drying beds
elutriation, 184
growth rate, Y, sludge, 133
handling alternatives, 134
incineration, 214
lagoons, 234
mechanical drying, 213
plate and frame filter press, 186
pressure filtration, 186
primary sludge production, 131
production of sludges, 131
quantities, 131
sand drying beds, 201
secondary sludge production, 133
stabilization, 163
surfaced sludge drying beds, 203
thermal conditioning, 179
thickening, 135
types of sludges, 131
vacuum filtration, 193
volume reduction, 207
volumes of sludges, 134
wet oxidation, 182
Y, growth rate, sludge, 133
Sludge age
activated sludge, 60, 92
nitrification, 104
Sludge beds, 548
Sludge blanket
depth measurement, 55, 464
gravity thickeners, 138
return activated sludge approach, 55
time of measurement, 55
Sludge density meter, 464
Sludge dewatering
see Dewatering, sludge
Sludge digestion, effects of industrial wastes, 71
Sludge disposal
agricultural reclamation, 240, 242
dedicated land disposal, 239, 241
environmental controls, 247
lagoons, 244
land disposal, 234
monitoring, 247
need, 131
on-site dedicated land disposal, 239, 241
sanitary landfill, 239
utilization, 247
Sludge handling and disposal
aerobic digestion, 163
agricultural reclamation, 240, 242
anaerobic digestion, 163
belt filter press, 190
centrifuges, 150, 200
characteristics, 131
chemical conditioning, 173
chemical stabilization, 170
composting, 207
conditioning, 173
dedicated land disposal, 239, 241
dewatering, 186
dissolved air flotation thickeners, 144
elutriation, 184
environmental controls, 247
gravity thickening, 135
growth rate, Y, sludge, 133
handling alternatives, 134
incineration, 214
lagoons, 234, 244
land disposal, 234
mechanical drying, 213
multiple hearth furnace, 214
need, 131
on-site dedicated land disposal, 239
plate and frame filter press, 186
pressure filtration, 186
primary sludge production, 131
production of sludges, 131
quantities, 131
sand drying beds, 201
sanitary landfill, 239
secondary sludge production, 133
stabilization, 163
surfaced sludge drying beds, 203
thermal conditioning, 179
thickening, 135
types of sludges, 131
vacuum filtration, 234
volume reduction, 207
volumes of sludges, 134
utilization, 247
wet oxidation, 182
Y, growth rate, sludge, 133
Sludge retention basins, odors, 27
Sludge volume index
activated sludge
see Chapter 11
test
see Chapter 16
Sludge-volume ratio (SVR), 138, 141
Slug discharge, 495, 516
Slurry, 171, 359
Sodium adsorption ratio, 413
-------
Index 867
Sodium hydroxide, 14, 17, 80, 590
Sodium hypochlorite, 12, 17
Software programs, 469
Soil moisture determination, 408
Soil sealing, solids, 406
Solid chemical feeders, 616
Solids
industrial wastes, 504
land application, 234
Solids loadings
coagulation and precipitation, 628
gravity thickeners, 138, 139
Solids removal from secondary effluents
chemicals, 289
filters, gravity, 316
filters, pressure, 334
gravity filters, 316
inert-media pressure filters, 334
microscreens, 289
need, 289
pressure filters, 334
Solute, 598
Solution preparation, chemical, 178
Solvents, 504
Sources of odors, 7, 8, 11
Specific gravity, 131
Spectrophotometer, 470
Speed measurement, 438
Sphaerotilus natans, 93
Spill, liquid oxygen, 51
Spray chamber, 17
Stabilization of sludges
aerobic digestion, 163
anaerobic digestion, 163
also see Chapter 12
chemical stabilization, 170
purpose, 163
sludge, 163
stabilization, 163
Standard industrial classification, 485, 506
Standby power generation, 736
Start up
absorption, 23
activated carbon, 641
activated sludge, industrial wastes, 76, 81, 82
biological odor reduction towers, 16
centrifuge thickeners, 157
chemical feed systems, 302
chemical scrubbers, 20
coagulation, 631
diesel engines, 761
direct reuse of effluent, 397
dissolved air flotation thickeners, 148
flotation, 560
gasoline engines, 754
gravity filters, 326
gravity thickeners, 139
incineration, 232
industrial waste treatment, 76, 81, 82
land disposal, 406
lime precipitation, phosphorus, 359, 360, 361
luxury uptake, phosphorus, 369
microscreens, 313, 579
multiple hearth furnace, 232
precipitation, 631
pulp and paper mill, 81, 82
pure oxygen, 50
restart, 76
screening, 579
scrubbers, 20
steel mill, 675, 677
thermal conditioning, 181
vacuum filtration, 199
Static bed filters, 317
Static head, 713
Static pile composting, 244
Stationary screens, 569
Steady state, activated sludge, 59, 81
Steel mill, reuse, 395
Steel mill wastewater reclamation and recycling
adjustment of processes, 666
aeration tank, 673, 674
chemical feed systems, 674
clarifiers, 666
description, 660
inspections, 664
instrumentation, 674
jar tests, 666, 679
laboratory procedures, 680
operation, 660, 666, 674, 677, 678, 679
operational strategy, 660
pH, 666
regenerated carbon, 695
safety, 676, 679
sludge blanket, 678
sludge thickeners, 673, 678
solids control tanks, 677, 678
start up, 675, 677
torque meter, 677
troubleshooting, 676, 678
vacuum filters, 673
variability ratio, 666, 670, 671
visual inspection, 677, 679
Step-feed, activated sludge, 50, 53, 97
Storage
acids, 610
coagulants, 616
equipment, 502
reservoir, 646
samples, 495, 498
Storm waters, 363
Straggler floe, 66, 67, 372
Strategy for monitoring, 502
Strategy for operation
see Operational strategy
Strength of pollutant, 73
Strip charts, 459, 473
Stripped gases, 47
Stripped odors, 14
Stripping tank, phosphorus, 369
Strobe light, 450, 473
Submersible pumps, 720
Suction head, 713
Suction lift, 717
Sulfide equilibrium, 9
Sulfide forms 8, 9
Sulfide shock load, 99
Sulfur cycle, 8, 10
Sulfuric acid, 590
Sump pump instrumentation, 463
Super chlorination, 102
Support systems
air conditioning, 779
auxiliary electrical equipment, 736
backflow prevention, 787
batteries, 737
compressors, 781
cross connections, 785
diaphragm pumps, 719
diesel engines, 757
-------
868 Treatment Plants
drainage, 792
electrical equipment, 736
emergency lighting, 736
fittings, 729
gasoline engines, 740
grounds upkeep, 789
heating, 776
high voltage, 738
hydro-pneumatic systems, 785
importance, 713
landscape, 791
lighting, emergency, 736
lighting, yard, 789
pipes, 722
portable pumps, 713
pumps, 713
reclaimed water, 789
roadways, 790
seals, pumps, 722
standby power generation, 736
submersible pumps, 720
surface water drainage, 792
trash pumps, 717
valves, 726
ventilating, 777
walkways, 790
water supply systems, 785
yard lighting, 789
Surface aerators, 43
Surface loading
coagulation and precipitation, 628
gravity thickeners, 138
Surfaced sludge drying beds
application of sludge, 206
cleaning, 206
description, 203, 204, 205, 206
layout, 203, 204, 205
need, 203
operation, 206
removal of sludge, 206
safety, 206
sampling, 206
water-sludge separation, 206
Surveillance, sludge disposal, 247
Suspended solids, industrial wastes, 73
T
Tachometer, 440, 450. 473
Tannery wastes, 549
Tastes in water, 505
Temperature
measurement, instruments, 434, 444, 470
odor, 8
Temperature effect
activated sludge, 63, 85, 89
aerobic digestion, 165
anaerobic digester
see Chapter 12
gravity sludge thickening, 138
nitrification, 104
settling, 629
Terminology, wastewater treatment, 813
Tertiary treatment, 289
Textile wastes, 551
Thermal conditioning, sludge
acid flushing, 181
decant tank, 180, 181, 182
detention time, 179, 180, 181, 182
dewaterability, 182
factors affecting performance, 180
fuel supply, 181
gasification, 181
guidelines, operation, 180, 181
heat exchanger, 182
heating requirements, 180
hydraulic loadings, 180
influent sludge, 180
odor control, 181
operation, 180, 181
performance, 181
plans and specifications, 250
pressure, 180, 181
pressure drop, 181, 182
reactor, 181
shutdown, 181
sludge dewaterability, 182
solids loadings, 180
start up, 181
temperature, 179, 180, 181, 182
troubleshooting, 181, 182
variables, 180
withdrawal of sludge, 180, 182
Thermal wastes, 484, 504
Thermocouple, 445, 470, 473
Thermophilic, 208
Thickening, sludges
centrifuges, 150
dissolved air flotation thickeners, 144
gravity thickening, 135
purpose, 135
Thiocyanate, 101
Threads, pipe, 725
Threshold odor, 11
Tools, 566
Torque meter, 677
Total ash of regenerated carbon, 695
Total dynamic head, 717
Totalizer, 326, 459, 473
Toxic chemicals, 547
Toxic compounds, 14, 71, 92, 505
Toxic gases, 70
Toxic wastes
activated sludge, 71, 73
ammonia, 101
fish, 101
industrial, 484
Traffic safety, 498
Transmission system, instruments, 426, 455, 456
Trash pumps, 717
Traveling screen, 572, 576
Treatment levels for reuse, 386
Treatment plants, odor control, 7, 8
Trickling filters, odors, 25
Transmitters, 526, 455, 456
Troubleshooting
activated carbon, 646, 654
activated sludge, 56, 58, 60
aerobic digestion, 168
belt filter press, 193
centrifuge thickeners, 161
chemical conditioning, sludge, 179
chemical feed systems, 308
coagulation, 633
composting, 212
compressors, 782
controls, 471
diaphragm pumps, 719
diesel engines, 761
direct reuse of effluent, 398
dissolved air flotation thickeners, 149
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gasoline engines, 744, 754
gravity filters, 331
gravity sludge thickeners, 140
heating systems, boilers, 778
incineration, 233
instruments, 471, 473
land disposal, 413
lime precipitation, phosphorus, 366
lime stabilization, 171
microscreens, 314, 580
neutralization, 610
odor problems, 12, 25
plate and frame filter press, 189
portable pumps, 718
precipitation, 633
pretreatment facilities, 76
pulp and paper mill wastes, 83
sand drying beds, 203
screening, 580
steel mill, 676, 678
thermal conditioning, 181
vacuum filtration, 199
wet oxidation, 184
Trunk sewer, 491
Tube settlers, 628
Turbidimeter, 468, 473
Turbidity, 326, 504
Turbidity units, 329
Turbulent mixers, 43
U
Ultimate disposal
effluent, 401
solids, 239
Ultrafiltration, 598, 599
Ultrasonic sound, level measurement, 450, 452, 473
Ultraviolet light, microscreens, 312, 572
Underdrains, gravity filters, 317
Uniformity coefficient, 686
Units of measure, 438
Upflow filters, 317, 319
Upgrading effluents, 289
Urea, 85
V
Vacuum filtration
blinding, 199, 200
cake, 199, 200
conditioning sludge, 198, 199, 200
cycle time, 198, 199, 200
depth of submergence, 199
description, 193
dewatering, 198
drum speed, 198
factors affecting performance, 194
filter loading, 198
filter yield, 198
guidelines, operation, 198, 199
loading, 198
media, 199, 200
odors, 27
operation, 198, 199
performance, 199
plans and specifications, 249
shutdown, 199
solids recovery, 199
sludge type, 194, 199
start up, 199
troubleshooting, 199
vacuum applied, 198,199, 200
Index 869
variables, 194
yield, 198, 199
Vacuum pressure, 441, 442
Valves
butterfly, 728, 732
check, 728, 733
eccentric, 728, 730, 731
gate, 726
globe, 728, 729
need, 722
use, 726
water hammer, 728
Valves, instrumentation, 463
Variability ratio, 666, 670, 671
Vector, 244
Vegetable processing wastes, 550
Velocity head, 717
Velocity, instruments, 438, 450
Ventilating systems
axial fan, 777
blowers, 777
centrifugal blowers, 779
duct fan, 779
exhaust fans, 777
fan laws, 777
fans, 777
free air delivery, 777
maintenance, 779
need, 777
plenum chamber, 777
propeller fan, 777
terminology, 777
types, 777
Venturi, 777
Ventilation
activated carbon, 658
safety, 27
Venturi meters, 473
Vibrating trough chemical feeder, 294
Vibrations, centrifuges, 161, 162
Visual inspection
activated sludge, 71, 78
aerobic digestion, 169
centrifuge thickeners, 161
dissolved air flotation thickeners, 149, 156
gravity thickeners, 140
steel mill, 677, 679
Visual pollution, 548
Volatile matter, 131
Volatile solids inventory, 64
Volume reduction, sludge
composting, 207
incineration, 214
mechanical drying, 213, 244
multiple hearth furnace, 214
purpose, 207
Volumetric chemical feeders, 294, 616
Volumes of sludges, 134
W
WAS
see Waste activated sludge
Walkways, 790
Waste activated sludge
adjustment of process, 60
Al West method, 66
control of wasting, 60
conventional, 60, 62
extended aeration, 60, 62
F/M control, 60, 61
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870 Treatment Plants
filamentous bacteria, 65
flow diagram, 54
high rate, 60, 62
industrial waste treatment, 78, 92
MCRT control, 60, 63
MLVSS control, 60, 65
methods of wasting, 60
microscopic examination, 65
mixed liquor, 60
nitrification, 63
purpose of wasting, 59
sludge age control, 60
steady state, 59
summary of methods, 68
troubleshooting, 60
volatile solids inventory, 64
Wastewater, septic, 7
Wastewater collection systems, 7, 8
Wastewater reclamation
also see Direct reuse of effluent and Land disposal, effluent
case histories, 388
direct reuse, 386
equipment requirements, 388, 401
land disposal, 401
land treatment, 401
limitations, 388, 406
maintenance, 400, 416
monitoring, 398, 415
Muskegon County, Michigan, 390
nuclear generating station, Phoenix, Arizona, 390
operation, 397, 406
Phoenix, Arizona, nuclear generating station, 390
plans and specifications, 400, 416
review of plans and specifications, 400, 416
safety, 400, 415
South Lake Tahoe, California, 388
steel mill, 395
treatment levels for reuse, 386
uses, 386
Windhoek, South Africa, 390
Wastewater treatment plants, 7, 8
Wasting activated sludge, 59
Water, drinking, 545
Water hammer, 327, 728
Water lance, 677
Water meters, 498
Water quality criteria, 388, 545, 588
Water supply, 70
Water supply systems
add-air system, 785
air-cushion systems, 785
air gap, 789
anti-siphon valve, 789
backflow prevention, 787
bottled water, 785
check valve, 789
cross connections, 785
disinfection, 785
fresh water systems, 785
hydro-pneumatic systems, 785
reclaimed water, 789
ultra-violet lamp, 785
vent-air system, 787
Weed control, 791
Weirs, 473, 628
Well point, 722
Wells, monitoring, 415
West, Al, 66
Wet oxidation
air, 182, 184
detention time, 184
factors affecting performance, 184
feed sludge, 184
guidelines, operation, 184
odor control, 182, 184
operation, 184
performance, 184
pressures, 184
temperatures, 184
troubleshooting, 184
variables, 184
Windrow composting, 244
Windhoek, South Africa, 390
Y
V, growth rate, sludge, 133
Yard lighting, 789
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NOTES
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