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I1E1TMEI1
PUIIS
A
Field
Study
Training
Program
• ENVIRONMENTAL PROTECTION AGENCY *
* OFFICE OF WATER PROGRAMS •
• DIVISON OF MANPOWER AND TRAINING *
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OPERATION OF WASTEWATER
TREATMENT PLANTS
A Field Study Training Program
prepared by
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
William Crooks, Consultant
for the
Environmental Protection Agency
Water Quality Office
Technical Training Grant No. 5TT1-WP-16-03
OD
CO
CO
1970
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PF'EFACE .
The purposes of this home study program are:
a. to develop new qualified treatment plant operators;
b. to expand the abilities of existing operators, permit-
ting better service to both their employers and the
public; and
c. to prepare operators for certification examinations.1
To provide you with information needed to operate a wastewater
treatment plant as efficiently as possible, experienced plant
operators prepared the material on treatment plant processes;
each chapter begins with an introduction and then discusses
start-up, daily operation, interpretation of lab results and
possible approaches to solving operational problems. This
order of topics was determined during the testing program on
the basis of operators' comments indicating the information
they needed most urgently. Additional chapters discuss mainte-
nance, safety, sampling, laboratory procedures, hydraulics,
records, analysis and presentation of data, and report writing.
Plant influents (raw wastewater) and the efficiencies of treat-
ment processes vary from plant to plant and from location to
location. The material contained in this program is presented
to provide you with an understanding of the basic operational
aspects of your plant and with information to help you analyze
and solve operational problems. This information will help you
operate your plant as efficiently as possible.
Wastewater treatment is a rapidly advancing field. To keep pace
with scientific advances, the material in this program must be
periodically revised and updated. This means that you, the
operator, must recognize the need to be aware of new advances
and the need for continuous training beyond this program.
Certification examination. An examination administered by a
state or professional association that operators take to indi-
cate a level of professional competence. In many states the
Chief Operator of a plant must be "certified" (successfully
pass a certification examination), and in other states certi-
fication is voluntary. Current trends indicate that more
states and employers will require operators to be "certified"
in the future.
111
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Originally the concepts for this manual evolved from Mr. Larry
Trumbull, 1967 Chairman of the Operator Training Committee of
the California Water Pollution Control Association. Messrs.
Bill Dendy and Kenneth Kerri, Project Directors, investigated
possible means of financial support to develop and test the
manual and prepared a successful application to the Federal
Water Pollution Control Administration (5TT1-WP-16-03). The
chapters were written, tested by pilot groups of operators and
potential operators, reviewed by consultants and the Federal
Water Quality Administration, and rewritten in accordance with
the suggestions from these sources.
The project directors are indebted to the many operators and
other men who contributed to the manual. Every effort was made
to acknowledge material from the many excellent references in
the wastewater treatment field. Special thanks are due Messrs.
John Brady and William Crooks who both contributed immensely to
the manual. Mr. F. J. Ludzack, Chemist, National Training Center,
Environmental Protection Agency, Water Quality Office, offered
many technical improvements. A note of thanks is also due our
typists, Miss Linda Smith, Mrs. Gloria Uri, Mrs. Daryl Rasmussen,
Mrs. Vicki Sadlem, Mrs. Peggy Courtney, and Mrs. Pris Jernigan.
Illustrations were drawn by Mr. Martin Garrity.
Kenneth D. Kerri
Bill Dendy
1971
IV
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INSTRUCTIONS TO PARTICIPANTS
Procedures for reading the lessons and answering the questions
are contained in this section.
To progress steadily through this program, you should establish a
regular study schedule. For example, many operators in the past
have set aside two hours during two evenings a week for study.
The study material is contained in seventeen chapters. Some are
longer and more difficult than others. For this reason, many of
the chapters are divided into two or more lessons. The time
required to complete a lesson will depend on your background and
experience. It might take some people an hour to complete a
lesson, and some might require three hours, but that is perfectly
all right. The important thing is that you understand the
material in the lesson!
Each lesson is arranged for you to read a short section, write
the answers to the questions at the end of the section, check your
answers against suggested answers; and then you decide if you under-
stand the material
sufficiently to continue
or whether you should
read the section again.
You will find that this
procedure is slower than
reading a normal textbook,
but you will remember much
more when you have finished
the lesson.
At the end of the first
three chapters, you will
find an "objective test."
Mark your answers on the
IBM answer sheet. In the
later chapters you will be
asked to answer questions
before ("pre-test"l you
read the chapter. The pre-
test indicates to you the
important concepts you will find in the lessons. Some discussion
and review questions are provided following eacli lesson in the later
chapters. These questions review the important points you have
covered in the lesson.
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The objective test at the end of each lesson contains true or
false, multiple choice, fill in the blank, or match the answers
types of questions. The purposes of this exam are to review
the chapter and to give experience in taking different types of
exams. Mail to the program director only your answers to pre-
tests and objective tests on IBM answer sheets.
You are your own teacher in this program. You could merely
look up the suggested answers from the answer sheet or copy
them from someone else, but you would not understand the material.
Consequently, you would not be able to apply the material to the
operation of your plant nor recall it during an examination for
certification or a civil service position.
You will get out of this program what you put into it.
VI
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SUMMARY OF PROCEDURE
OPERATOR
1. Marks answers to pre-test on IBM answer sheet (Chapters 4-16)
2. Reads sections in lesson.
3. Writes answers to questions at end of sections in his
notebook. You should write the answers to the questions
just like you would if these were questions on a test.
4. Checks his answers with suggested answers.
5. Decides whether to reread section or to continue with
the next section.
6. Writes answers to discussion and review questions at the
end of lessons in his notebook
7. Marks answers to objective test on IBM answer sheet.
8. Mails material to program director.
Professor Kenneth Kerri
Department of Civil Engineering
Sacramento State College
6000 Jay Street
Sacramento, California 95819
B. PROGRAM DIRECTOR
1. Mails lessons in advance to keep operators studying.
2. Corrects tests, answers any questions, and returns results
to operator.
VII
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C. ORDER OF WORKING LESSONS
To complete this program you will have to work all of the chapters.
You may proceed in numerical order, or you may wish to work some
lessons sooner. Chapter 15, Basic Mathematics and Treatment Plant
Problems, will be mailed to you with Chapter 4 because Chapter 4
requires the use of simple mathematics. If you have trouble with
the math in Chapter 4 or some of the following chapters, you may
find it helpful to refer to the math chapter, or you may decide
to work the math chapter first.
Chapter 14, Laboratory Procedures and Chemistry, will be mailed
to you with Chapter 5 because the operation of sedimentation and
flotation treatment processes requires some laboratory tests.
Again, you may wish to refer to the lab chapter while working on
Chapter 5 and the other chapters, or you may wish to work the
lab chapter first.
Safety is a very important chapter. Everyone working in a treat-
ment plant must always be safety conscious. You must take extreme
care with your personal hygiene to prevent the spread of disease
to yourself and your family. Operators in treatment plants daily
encounter situations and equipment that can cause a serious dis-
abling injury if the operator is not aware of the potential danger
and does not exercise adequate precautions. For these reasons,
if you decide to work on the chapter on Plant Safety and Good
Housekeeping early, please notify the Project Director and he will
be happy to comply with your wish.
Vlll
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COURSE OUTLINE
Chapter Topic
1 INTRODUCTION, by Larry Trumbull and William Crooks
2 WHY TREAT WASTES? by William Crooks
3 WASTEWATER FACILITIES, by John Brady and William Crooks
4 RACKS, SCREENS, COMMINUTERS, AND GRIT REMOVAL, by
Larry Bristow
5 SEDIMENTATION AND FLOTATION, by Elmer Herr
6 TRICKLING FILTERS, by Larry Bristow
7 ACTIVATED SLUDGE, by John Brady
8 SLUDGE DIGESTION AND HANDLING, by John Brady
9 WASTE TREATMENT PONDS, by A. L. Hiatt
10 DISINFECTION AND CHLORINATION, by Leonard Horn
11 MAINTENANCE, by Norman Farnum, Stan Walton, and
Roger Peterson
12 PLANT SAFETY AND GOOD HOUSEKEEPING, by Robert Reed
13 SAMPLING RECEIVING WATERS, by Bill Dendy
14 LABORATORY PROCEDURES AND CHEMISTRY, by James Paterson
15 BASIC MATHEMATICS AND TREATMENT PLANT PROBLEMS, by
William Crooks
16 ANALYSIS AND PRESENTATION OF DATA, by Kenneth Kerri
17 RECORDS AND REPORT WRITING, by George Gribkoff and
John Brady
TECHNICAL CONSULTANTS
William Garber Warren Prentice
Carl Nagel Larry Trumbull
Joe Nagano Ralph Stowell
Frank Phillips
IX
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CHAPTER 1
INTRODUCTION
by
Larry Trumbull
and
William Crooks
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TABLE OF CONTENTS
CHAPTER 1. INTRODUCTION
Page
K0_ What is a Treatment Plant Operator? 1-1
1.01 What does a Treatment Plant Operator do? ... 1-2
1.02 Who does the Treatment Plant Operator
work for? 1-2
1.03 Where does the Treatment Plant Operator
work? 1-3
1.04 What pay can a Treatment Plant Operator
expect? 1-3
1.05 What does it take to be a Treatment Plant
Operator? 1-3
1.1 Your Personal Training Course 1-6
1.2 What Do You Already Know? 1-6
K5 The Water Quality Protector: YOU 1-6
1.4 Your Qualifications 1-9
1.41 Your Job 1-10
1.5 Manpower Needs and Future Job Opportunities 1-14
1.6 Training Yourself to Meet the Needs 1-15
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CHAPTER 1. INTRODUCTION
This portion of Chapter 1 was prepared especially for the new
or the potential wastewater1 treatment plant operator. If you
are an experienced operator, you may find some new viewpoints.
1.0 WHAT IS A TREATMENT PLANT OPERATOR?
Before modern man entered the scene, water was purified in a
natural cycle as shown below:
Fig. 1.1 Natural purification cycle
But modern man and his intensive use of the water resource could
not wait for sun, wind, and time to accomplish the purification
of soiled water; consequently treatment plants were built. Thus,
nature was given an assist by a team consisting of designer,
builders, and treatment plant operators. Designers and builders
occupy the scene only for an interval, but operators go on forever.
They are the final and essential link in maintaining and protecting
the aquatic environment upon which all life depends.
1 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 waste-
water that enters a plant. The term sewage usually refers to
household wastes, but this word is being replaced by the term
wastewater.
1-1
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1.01 What does a Treatment Plant Operator do?
Simply described, he keeps a wastewater (sewage) treatment plant
working. Physically he turns valves, pushes switches, collects
samples, lubricates equipment, reads gauges and records data.
Fig. 1.2 The operator's duties
He may also maintain equipment and plant area by painting, weeding,
gardening, repairing and replacing. Mentally he inspects records,
observes conditions, makes calculations to determine that his plant
is working effectively, and predicts necessary maintenance and
facility needs to assure continued effective operation of his plant.
He also has an obligation to explain to supervisors, councilmen,
civic bodies, and the general public what his plant does, and most
importantly, why its continued and expanded financial support is
vital to the welfare of the community.
1.02 Who does the Treatment Plant Operator work for?
His paycheck usually comes from a city, sanitation district, or
other public agency. He may, however, be employed by one of the
many large industries which operate their own treatment plants.
The operator is responsible to his employer for maintaining an
economic and efficiently operating facility. An even greater
obligation rests with the operator because the great numbers of
people who rely upon downstream water supplies are totally de-
pendent upon the operator's competence and trustworthiness for
their welfare. It is these vitally affected people for whom, in
the final analysis, the operator is really working.
1-2
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1.03 Where does the Treatment Plant Operator work?
Obviously he works in a wastewater treatment plant. But the
different types and locations of treatment plants offer a wide
range of working conditions. From the mountains to the sea,
wherever people congregate into communities, will be found waste-
water treatment plants. From a unit process operator at a complex
municipal facility to a one-man manager of a small town plant,
each man can select his own special place in treatment plant
operation.
1.04 What pay can a Treatment Plant Operator expect?
In dollars? Prestige? Job satisfaction? Community service? In
opportunities for advancement? By whatever scale you use, returns
are what you make them. If you choose a large municipality, the
pay is good and advancement prospects are tops. Choose a small
town and pay may not be as good; but job satisfaction, freedom
from time-clock hours, community service, and prestige may well
add up to outstanding personal achievement. Total reward depends
on you.
1.05 What does it take to be a Treatment Plant Operator?
Desire. First you must choose to enter this profession. You can
do it with a grammar school, a high school, or a college degree.
While some jobs will always exist for manual labor, the real and
expanding need is for trained operators. New techniques, advanced
equipment, and increasing instrumentation require a new breed of
operator, one who is willing to learn today, and gain tomorrow,
for surely his plant will move towards newer and more effective
operating procedures and treatment processes. Indeed, the truely
service-minded operator assists in adding to and improving his
plant performance on a continuing basis.
Fig. 1.3 Tomorrow's forgotten man stopped learning yesterday
1-3
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You can be an operator tomorrow by beginning your learning today;
or you can be a better operator, ready for advancement, by
accelerating your learning today.
This training course, then, is your start towards a better
tomorrow, both for you and for the public who will receive better
water from your efforts.
1-4
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QUESTIONS
Place an X by the correct answer or answers. After you have
answered all the questions, check your answers with those given
at the end of the chapter on page 1-17. Reread any sections you
did not understand and then proceed to the next section. You are
your own teacher in this training program, and you should decide
when you understand the material and are ready to continue with
new material.
EXAMPLE
This is a training course on:
A. Accounting
B. Engineering
X C. Wastewater Treatment Plant Operation
D. Salesmanship
l.OA. Wastewater is the same thing as:
A. Steam
B. Soil
C. Sewage
D. Asphalt
l.OB. What does an operator do?
A. Collect Samples
B. Lubricate Equipment
C. Record Data
l.OC. Who may a Treatment Plant Operator work for?
A. City
B. Sanitation District
C. Industry
Check your answers on Page 1-17.
1-5
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1.1 YOUR PERSONAL TRAINING COURSE
Beginning on this page you are embarking on a training course
which has been carefully prepared to allow you to improve your
knowledge and ability to operate a wastewater treatment plant.
You will be able to proceed at your own pace; you will have an
opportunity to learn a little or a lot about each topic. The
course has been prepared this way to fit the various needs of
operators, depending on what kind of plant you have or how much
you need to learn about it. To study for certification exami-
nations you will have to cover all the material. You will never
know everything about your plant or about the wastewater which
flows through it, but you can begin to answer some very important
questions about how and when certain things happen in the plant.
You can also learn to manipulate your plant so that it operates
at maximum efficiency.
1.2 WHAT DO YOU ALREADY KNOW?
If you already have some experience operating a wastewater
treatment plant, you may use the first three chapters for a
review. If you are relatively new to the wastewater treatment
field, these chapters will provide you with the background
information necessary to understand the later chapters. The
remainder of this introductory chapter describes your role as
a protector of water quality, your qualifications to do your
job, a little about manpower needs in the wastewater treatment
field, and some information on other training opportunities.
1.3 THE WATER QUALITY PROTECTOR: YOU
Historically Americans have shown a great lack of interest in the
protection of their water resources. We have been content to
think that "the solution to pollution is dilution." For years we
were able to dump our wastes with little or no treatment back
into the nearest receiving water.2 As long as there was enough
dilution water to absorb the waste material, nature took care of
our disposal problems for us. As more and more towns and
2 Receiving Water. A stream, river, lake, or ocean into
which treated or untreated wastewater is discharged.
1-6
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Fig. 1.4 Pollution
Courtesy Water Pollution Control Federation
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industry sprang up, waste loads increased until the natural
purification processes could no longer do the job. Many water-
ways were converted into open sewers. Unfortunately, for many
areas this did not signal the beginning of a clean-up campaign.
It merely increased the frequency of the cry: "We don't have
the money for a treatment plant," or the ever-popular, "If we
make industries treat their wastes they will move to another
state". Thus, the pollution of our waters increased (Fig. 1.4).
Within the last few years we have seen many changes in this
depressing picture. We now realize that we must give nature a
hand by treating wastes before they are discharged. Adequate
treatment of wastes will not only protect our health and that
of our downstream neighbors, it can also increase property
values, allow game fishing and various recreational uses to
be enjoyed, and attract water-using industries to the area.
Today we are seeing massive efforts being undertaken to control
water pollution and improve water quality throughout the nation.
This includes the efforts not only of your own community, county
and state, but also the federal government.
Great sums of public and private funds are now being invested
in large, complex municipal and industrial wastewater treatment
facilities to overcome this pollution; and you, the treatment
plant operator, will play a key role in the battle. Without
efficient operation of your plant, much of the research,
planning, and building that has been done and will be done to
accomplish the goals of water quality control in your area will
be wasted. You are the difference between a facility and a
performing unit. You are, in fact, a water quality protector
on the front line of the water pollution battle.
Fig. 1.5 Water quality protector
1-8
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The receiving water quality standards and waste discharge require-
ments that your plant has been built to meet have been formulated
to protect the water users downstream from your plant. These uses
may include domestic water supply, industrial water supply, agri-
cultural water supply, stock and wildlife watering, propagation of
fish and other aquatic and marine life, shellfish culture, swimming
and other water contact sports, boating, esthetic enjoyment,
hydroelectric power, navigation, and others.
Therefore, you have an obligation to the users of the water down-
stream, as well as to the people of your district or municipality.
You are the key water quality protector and must realize that
you are in a responsible position.
QUESTIONS
Write your answers in a notebook and then compare your
answers with those on page 1-17.
1.3A Why must municipal and industrial waste-
waters receive adequate treatment?,
1.3B How did many receiving waters become polluted?
1.4 YOUR QUALIFICATIONS
The skill and ability required for your job depend to a large
degree on the size and type treatment plant where you are employed.
You may work at a large modern treatment plant serving several
hundred thousand persons and employing a hundred or more operators.
In this case you are probably a specialist in one or more phases
of the treatment process.
On the other hand, you may operate a small plant serving only a
thousand people or fewer. You may be the only operator at the
plant or, at best have only one or two additional employees.
If this is the case you must be a "jack-of-all-trades" because
of the diversity of your tasks.
1-9
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1.41 Your Job
To describe the operator's duties, let us start at the beginning.
Let us say that the need for a new or improved wastewater treat-
ment plant has long been recognized by the community. The
community has voted to issue the necessary bonds to finance the
project, and the consulting engineers have submitted plans and
specifications. It is to the best interests of the community
and the consulting engineer that you be in on the ground floor
planning. If it is a new plant you should be present, or at
least available, during the construction period in order to become
completely familiar with the entire plant, including the equipment
and machinery and its operation. This will provide you with the
opportunity to relate your plant drawings to actual facilities.
You and the engineer should discuss how the treatment plant should
best be run and the means of operation he had in mind when he
designed the plant. If it is an old plant being remodeled, you
are in a position to offer excellent advice to the consulting
engineer. Your experience provides valuable technical knowledge
concerning the characteristics of wastewater, its sources, and
the limitations of the present facilities. Together with the
consultant, you are a member of an expert team to advise the
district or city.
Once the plant is operating, you become an administrator. In
a small plant your duties may not include supervision of personnel,
but you are still in charge of records. You are responsible for
operating the plant as efficiently as possible, keeping in mind
that the primary objective is to protect the receiving water
quality by continuous and efficient plant performance. Without
adequate, reliable records of every phase of operation, the
effectiveness of your operation has not been documented (recorded).
You may also be the budget administrator. Most certainly you are
in the best position to give advice on budget requirements, manage-
ment problems, and future planning. You should be aware of the
necessity for additional expenditures, including funds for plant
enlargement, equipment replacement, and laboratory requirements.
You should recognize and define such needs in sufficient time to
inform the proper officials to enable them to accomplish early
planning and budgeting.
You are in the field of public relations and must be able to
explain the purpose and operation of your plant to visitors
(Fig. 1.6), civic organizations, school classes, representatives
of news media, even to city council or directors of your district.
Public interest in water quality is increasing, and you should be
1-10
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T
Fig. 1.6 Visitors
1-11
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prepared to conduct plant tours that will contribute to public
acceptance and support. A well-guided tour for officials of
regulatory agencies or other operators may provide these people
with sufficient understanding of your plant to allow them to
suggest helpful solutions to operational problems.
The appearance of your plant indicates to the visitor the type
of operation you maintain. If the plant is dirty and rundown
with flies and other insects swarming about, you will be
unable to convince your visitors that the plant is doing a
good job. Your records showing a high-quality effluent will mean
nothing to tnese visiting citizens unless your plant appears
clean and well maintained and the effluent looks good.
Fig. 1.7 Special care and safety must be practiced when
visitors are taken through your treatment plant.
An accident could spoil all of your public re-
lation efforts.
Another aspect of your public relations duties is your dealings
with the downstream water user. Unfortunately, the operator is
often considered by the downstream user as a polluter rather than
a water quality protector. Through a good public information
program, backed by facts supported by reliable data, you can
correct the impression held by the downstream user and establish
"good neighbor" relations (Fig. 1.8). This is indeed a challenge.
Again, you must understand that you hold a very responsible
position and be aware that the sole purpose of the operation of
your plant is to protect the downstream user, be that user a
private property owner, another city or district, an industry,
or a fisherman.
You are required to understand certain laboratory procedures in
order to conduct various tests on samples of wastewater and re-
ceiving waters. On the basis of the data obtained from these tests,
you may have to adjust the operation of the treatment plant to meet
stream standards or discharge requirements.
1-12
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Fig. 1.8 Clean Water
Courtesy Water Pollution Control Federation
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As an operator you must have a knowledge of the complicated
mechanical principles involved in many treatment mechanisms.
In order to measure and control the wastewater flowing through
the plant you must have some understanding of hydraulics.
Practical knowledge of electrical motors, circuitry, and
controls is essential also.
All operators must be aware of the safety hazards in and
around treatment plants. You should plan or be a part of an
active safety program. Chief operators frequently have the
responsibility of training new operators and should encourage
all operators to become certified.
Clearly then, the modern day wastewater treatment plant operator
must possess a broad range of qualifications.
QUESTIONS
1. 4A Why is it important that the operator be present
during the construction of a new plant?
1.4B How does the operator become involved in
public relations?
1.5 MANPOWER NEEDS AND FUTURE JOB OPPORTUNITIES
The wastewater treatment field, like so many others, is changing
rapidly. New plants are being constructed, and old plants are
being modified and enlarged to handle the wastewater from our
growing population and to treat the new chemicals being produced
by our space age technology. Operators, maintenance personnel,
foremen, managers, instrument men, and laboratory technicians are
sorely needed.
A look at past records and future predictions indicates that waste-
water treatment is a rapidly growing field. In 1967 it was esti-
mated that over $1 billion was spent in the previous year for
industrial and municipal waste treatment facilities, and $9 billion
in the previous 14 years. Municipalities employed approximately
20,000 operators in 1967, and it was estimated that 30,000 trained
operators will be needed by 1972 to operate existing, expanded, and
planned new plants.
1-14
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Fig. 1.9 Trained operators are needed
Industry employed approximately 3500 operators in 1967 and will
probably need around 12,000 plant operators by 1972. The need
for trained operators is increasing rapidly and is expected to
continue in the future.3
1.6 TRAINING YOURSELF TO MEET THE NEEDS
This training course is not the only one available to help you
improve your abilities. The states have offered various types
of both long- and short-term operator training through their
health departments or water pollution control agencies. Both
local and state water pollution control associations have pro-
vided training classes, conducted by members of the associations,
largely on a volunteer basis. The Water Pollution Control Federation
has developed two visual aid training courses to complement its
Manual of Practice No. 11. State and local colleges have provided
valuable training under their own sponsorship or in partnership
with others. Many state, local and private agencies have conducted
both long- and short-term training as well as interesting and
informative seminars. The California Water Pollution Control
Association has prepared two textbooks, one on laboratory procedures
3 Data contained in this paragraph were obtained from "Manpower
and Training Needs in Water Pollution Control", Report of the
Department of the Interior, Federal Water Pollution Control
Administration to the Congress of the United States, Senate
Document No. 49, 90th Congress, First Session, Washington, D.C.,
1967.
1-15
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and one on mathematics. Excellent textbooks have been written
by many state agencies. Those of the New York State Health
Department and the Texas Water Utilities Association deserve
special attention.
Listed below are several very good references in the field of
wastewater treatment plant operation that are frequently referred
to throughout this course. The name in quotes represents the
term usually used by operators when they mention the reference.
1. "MOP 11". Operation of Wastewater Treatment Plants, WPCF
Manual of Practice No. 11, Water Pollution Control Federation,
3900 Wisconsin Avenue, Washington, D.C. 20016. Price $2.00
to members; $4.00 to others.
2. "New York Manual". Manual of Instruction for Sewage Treatment
Plant Operators, distributed in New York by the New York State
Department of Health, Office of Public Health Education,
Water Pollution Control Board. Distributed outside of New York
State by Health Education Service, P.O. Box 7283, Albany,
New York 12224. Price $1.50.
3. "Texas Manual". Manual of Wastewater Operations, prepared
by Texas Water Utilities Association.Obtainable from Texas
Water Utilities Association, c/o Mrs. Earl H. Goodwin,
2202 Indian Trail, Austin, Texas 78703. Price $10.00.
4. Sewage Treatment Practices, by Don E. Bloodgood, obtainable
from Water and Sewage Works Magazine, Scranton Publishing
Company, Inc., 35 East Wacker Drive, Chicago, Illinois 60601.
Price $1.25.
5. Operator Short Course, by Gerson Chanin, Water and Wastewater
Work Book Series/1, Water and Wastes Engineering, Magazine
Publishing Division, The Reuben H. Donnelley Corporation,
466 Lexington Avenue, New York, New York 10017. Price $3.00.
These publications cover the entire field of treatment plant
operation. At the end of many of the chapters yet to come,
lists of other references will be provided.
1-16
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SUGGESTED ANSWERS
CHAPTER 1. INTRODUCTION
You are not expected to have the exact answer suggested for
questions requiring written answers, but you should have the
correct idea.
l.OA. C
l.OB. A, B, C
l.OC. A, B, C
1.3A. Municipal and industrial wastewaters must receive adequate
treatment to protect receiving water uses.
1.3B. Receiving waters become polluted by a lack of public
concern and by discharging wastewater into a receiving
water beyond its natural purification capacity.
1.4A. The operator should be present during the construction of
a new plant in order to become familiar with the plant
before he begins operating it.
1.4B. The operator becomes involved in public relations by
explaining the purpose and operation of his plant to
visitors, civic organizations, newspaper people, and
his supervisors.
1-17
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DIRECTIONS FOR WORKING OBJECTIVE TEST
CHAPTER 1. INTRODUCTION
1. Complete the answer sheet as shown in the example on the
next page.
Name Doakes, John P.
Date September 28, 1970
City Clearwater^ California
1. Time: 1 hour, 10 minutes (include time working tests)
Instructor Your Program Director
Name of Test Chapter 1, Objective
2. Mark your answers on the answer sheet.
For example, Question 1.1 has two correct answers (2 and 3).
Therefore, you should place a mark under both Columns 2 and 3
on the answer sheet.
Questions 1.3 through 1.6 are true or false questions. If a
question is true, then mark Column 1, and if false mark Column 2,
The correct answer to Question 1.3 is true; therefore, place a
mark in Column 1.
3. Be sure to write the time you worked on the lesson, including
your time working the tests.
4. Mail IBM answer sheet to your program director.
1-18
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-------
OBJECTIVE TEST
CHAPTER 1. INTRODUCTION
Please mark correct answers on IBM answer sheet.
1.1 The used water and solids from a community that flow to a
treatment plant are called ?
1. Effluent 3. Sewage
2. Wastewater 4. Mixed Liquor
1.2 Receiving water uses protected by an operator include:
1. Fishing 3. Drinking Water Supply
2. Boating 4. None of These
TRUE OR FALSE:
1.3 In many treatment plants the operator must be a "jack-of-
all-trades".
1.4 A treatment plant operator is a water quality protector.
1.5 Plant visitors are impressed by records showing efficient
plant operation, and their opinions are never influenced by
the appearance of the plant and grounds.
1.6 After finishing this program, an operator will need to
continue to study if he is to keep pace with changes
occurring in the field.
Please write how long you worked on this chapter on your answer
sheet.
1-21
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CHAPTER 2
WHY TREAT WASTES?
by
William Crooks
-------
TABLE OF CONTENTS
Chapter 2. Why Treat Wastes?
Page
PRONUNCIATION GUIDE 2-i
GLOSSARY , 2-ii
2.0 Prevention of Pollution 2-1
2.1 What is Pure Water? 2-1
2.2 Types of Waste Discharges 2-2
2.5 Effects of Waste Discharges 2-3
2.30 Sludge and Scum 2-4
2.31 Oxygen Depletion 2-4
2.32 Other Effects 2-6
2.33 Human Health 2-7
2^.4 Solids in Wastewater 2-9
2.40 Types of Solids 2-9
2.41 Total Solids 2-9
2.42 Dissolved Solids 2-10
2.43 Suspended Solids 2-10
2.44 Organic and Inorganic Solids .2-12
2.45 Floatable Solids '. . . 2-12
2.5 Additional Reading 2-12
2.6 Review 2-13
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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
of 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 pro-
nunciation 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 differences between the
Key used in this program and the Webster's New World Dictionary Key,
College Edition, 19681 are shown below:
Term Project Key
acid AS-id
coliform COAL-i-form
biological B U Y-o-LODG E-i k-cu II
WebsterKey
'as-ad
'kp-la-f 6 r m
bi-a-l'aj-i-kal
In using this Key, you should accent (say louder) the syllable which
appears in capital letters. The following chart is presented to give
examples of how to pronounce words using the Project Key.
Syllable
Word
acid
coagulant
biological
1st
AS
CO
BUY
2nd
id
AGG
o
3rd
you
LODGE
4th
lent
ik
5th
cull
The first word acid has its first syllable acdented. The second word,
coagulant, has its second syllable accented. The third word, biologi-
cal, has its first and third syllables accented.
We hope you will find the Key useful in unlocking the pronunciation of
any new word.
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
Aerobic Bacteria (AIR-0-bick back-TEAR-e-ah): Bacteria which
will live and reproduce only in an environment containing oxygen
which is available for their respiration (breathing), such as
atmospheric oxygen or oxygen dissolved in water. Oxygen combined
chemically, such as in water molecules, H20, cannot be used for
respiration by aerobic bacteria.
Anaerobic Bacteria (AN-air-0-bick back-TEAR-e-ah): Bacteria that
live and reproduce in an environment containing no "free" or dis-
solved oxygen. Anaerobic bacteria obtain their oxygen supply by
breaking down chemical compounds which contain oxygen, such as
sulfate (S04).
Disinfection (DIS-in-feck-shun): The process by which pathogenic
organisms are killed. There are several ways to disinfect, but
chlorination is the most frequently used method in water and
wastewater treatment.
Imhoff Cone; A clear cone-shaped container marked with
graduations used to measure the volumetric concentration of
settleable solids in wastewater.
Inorganic Waste (IN-or-GAN-nick): Waste material such as sand, |j|
salt, iron, calcium, and other materials which are not converted
in large quanitites by organism action. Inorganic wastes are
chemical substances of mineral origin and may contain carbon
and oxygen, whereas organic wastes are chemical substances of
animal or vegetable origin and contain carbon and hydrogen
along with other elements.
Milligrams per liter, mg/1 (MILL-i-GRAMS per LEET-er): A
measure of the concentration by weight of a substance per unit
volume. For practical purposes, one mg/1 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 parts per million (10 ppm).
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.
2-ii
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Organic Waste (or-GAN-nick): Waste material which comes from
animal or vegetable origin. Organic waste generally can be con-
sumed by bacteria and other small organisms. Inorganic wastes
are chemical substances of mineral origin and may contain carbon
and oxygen, whereas organic wastes contain mainly carbon and
hydrogen along with other elements.
Pathogenic Organisms (path-o-JEN-nick OR-gan-iz-ums) : Bacteria
or viruses 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.
pH: Technically, this is the logarithm of the reciprocal of the
hydrogen-ion concentration, which will be explained in Chapter 14,
Laboratory Procedures and Chemistry. For now, it is sufficient
to understand that pH may range from 0 to 14, where 0 is most acid
and 14 is most alkaline, and 7 is neutral. Most natural waters
have a pH between 6.5 and 8.5.
Pollution: Any interference with beneficial reuse of water or
failure to meet water quality requirements.
Primary Treatment: A wastewater treatment process consisting of
a rectangular or circular tank which allows those substances in
wastewater that readily settle or float to be separated from the
water being treated.
Secondary Treatment: A wastewater treatment process used to convert
dissolved or suspended materials into a form more readily separated
from the water being treated.
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.
2-iii
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CHAPTER 2. WHY TREAT WASTES?
2.0 PREVENTION OF POLLUTION
The operator's main job is to protect the many users of receiving
waters. He must do the best he can to remove any substances
which will unreasonably affect these users.
Many people think any discharge of waste to a body of water is
pollution. However, with our present system of using water to
carry away the waste products of home and industry, it would be
impossible and perhaps unwise to prohibit the discharge of all
wastewater to oceans, streams, and groundwater basins. It is
possible under present day technology to treat wastes in such
a manner that existing or potential receiving water uses are not
unreasonably affected. Definitions of pollution include any
interference with beneficial reuse of water or failure to meet
water quality requirements. Any questions or comments regarding
this definition must be settled by the appropriate enforcement
agency.
2.1 WHAT IS PURE WATER?
Water is a combination of two
parts hydrogen and one part
oxygen, or ^0. This is true,
however, only for "pure" water
such as might be manufactured
in a laboratory. Water as we
know it is not "pure" hydrogen
and oxygen. Even the distilled
water we purchase in the store
has measurable quantities of
various substances in addition
to hydrogen and oxygen. Rain
water, even before it reaches
the earth, contains many sub-
stances. These substances,
since they are not found in
"pure" water, may be consider-
ed "impurities". When rain
falls through the atmosphere,
it gains nitrogen and other
gases. As soon as the rain
flows overland it begins to
Fig. 2.1 Water + Impurities
2-1
-------
dissolve from the earth and rocks such substances as calcium,
magnesium, sodium, chlorides, sulfates, iron, nitrogen,
phosphorus, and many other materials. Organic matter (matter
derived from plants and animals) is also dissolved by water
from contact with decaying leaves, twigs, grass, or small
insects and animals. Thus it should be realized that a fresh
flowing mountain stream may pick up many natural "impurities",
some possibly in harmful amounts, before it ever reaches
civilization or is affected by the waste discharges of man.
Many of these substances, however, are needed in small amounts
to support life and be useful to man. Concentrations of im-
purities must be controlled or regulated to prevent harmful
levels in receiving waters.
QUESTIONS
2.1A What are some of the dissolved substances
in water?
2. IB How does water pick up dissolved substances?
2.2 TYPES OF WASTE DISCHARGES
The waste discharge that first comes to mind in any discussion
of stream pollution is the discharge of domestic wastewater.
Wastewater contains a large amount of organic waste.l Industry
also contributes substantial amounts of organic waste. Some
of these organic industrial wastes come from vegetable and
fruit packing; dairy processing; meat packing; tanning; and
processing of poultry, oil, paper and fiber (wood), and many
more.
1 Organic waste (or-GAN-nick). Waste material which comes from
animal or vegetable origin. Organic waste generally will be
consumed by bacteria and other small organisms. Inorganic
wastes are chemical substances of mineral origin and may con-
tain carbon and oxygen, whereas organic wastes contain mainly
carbon and hydrogen along with other elements.
2-2
-------
Another classification of wastes is inorganic wastes.2 Domestic
wastewater contains inorganic material as well as organic, and many
industries discharge inorganic wastes which add to the mineral
content of receiving waters. For instance, a discharge of salt
brine (sodium chloride) for water softening will increase the
amount of sodium and chloride in the receiving waters. Some
industrial wastes may introduce inorganic substances such as
chromium or copper, which are very toxic to aquatic life. Other
industries (such as gravel washing plants) discharge appreciable
amounts of soil, sand or grit, which also may be classified as
inorganic waste.
There are two other major types of wastes that do not fit either
the organic or inorganic classification. These are heated
(thermal) wastes and radioactive wastes. Waters with temper-
atures exceeding the requirements of the enforcing agency may
come from cooling processes used by industry and from thermal
power stations generating electricity. Radioactive wastes
are usually controlled at their source, but could come from
hospitals, research laboratories, and nuclear power plants.
QUESTIONS
2.2A Several of the following contain significant
quantities of organic material. Which are
they?
a. Domestic Wastewater
b. Cooling Water from Thermal Power Stations
c. Paper Mill Wastes
d. Metal Plating Wastes
e. Tanning Wastes
2.2B List four types of pollution.
2.3 EFFECTS OF WASTE DISCHARGES
Certain substances not removed by wastewater treatment processes
can cause problems in receiving waters. This section reviews
some of these substances and discusses why they should be treated.
2 Inorganic waste (IN-or-GAN-nick). Waste material such as sand,
salt, iron, calcium, and other mineral materials which are not
converted in large quantities by organism action. Inorganic
wastes are chemical substances of mineral origin and may contain
carbon and oxygen, whereas organic wastes are chemical substances
of animal or vegetable origin and contain mainly carbon and
hydrogen along with other elements.
2-3
-------
2.30 Sludge and Scum
If certain wastes (including domestic wastewater) do not
receive adequate treatment, large amounts of solids may
accumulate on the banks of the receiving waters, or they
may settle to the bottom to form sludge deposits or float
to the surface and form rafts of scum. Sludge deposits
and scum are not only unsightly; but if they contain
organic material, they may also cause oxygen depletion and
be a source of odors. Primary treatment3 units in the waste-
water treatment plant are designed and operated to remove
the sludge and scum before they reach the receiving waters.
2.31 Oxygen Depletion
Most living creatures need oxygen to survive, including fish
and other aquatic life. Although most streams and other
surface waters contain less than 0.001% dissolved oxygen
(10 milligrams of oxygen per liter of water, or 10 mg/1),^
most fish can thrive if there are at least 5 mg/1 and other
conditions are favorable. When oxidizable wastes are dis-
charged to a stream, bacteria begin to feed on the waste
and decompose or break down the complex substances in the
waste into simple chemical compounds. These bacteria also
use dissolved oxygen (similar to human respiration or
breathing) from the water and are called aerobic bacteria.5
As more organic waste is added, the bacteria reproduce
3 Primary treatment. A wastewater treatment process consist-
ing of a rectangular or circular tank which allows those
substances in wastewater that readily settle or float to
be separated from the water being treated.
k Milligrams per liter, mg/1 (MILL-i-GRAMS per LEET-er). A
measure of the concentration, by weight of a substance per
unit volume. For practical purposes, one mg/1 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/1) , or 10 parts of oxygen per
million parts of water, or 10 parts per million (10 ppm).
5 Aerobic bacteria (AIR-0-bick back-TEAR-e-ah). Bacteria
which will live and reproduce only in an environment con-
taining oxygen which is available for their respiration,
such as atmospheric oxygen or oxygen dissolved in water.
Oxygen combined chemically, such as in water molecules,
H20, cannot be used for respiration by aerobic bacteria.
2-4
-------
rapidly; and as their population increases, so does their use
of oxygen. Where waste flows are high the population of
bacteria may grow large enough to use the entire supply of
oxygen from the stream faster than it can be replenished by
natural diffusion from the atmosphere. When this happens
fish and most other living things in the stream which require
dissolved oxygen die.
Fig. 2.2 Oxygen depletion
Therefore, one of the principal objectives of wastewater treat-
ment is to prevent as much of this "oxygen-demanding" organic
material as possible from entering the receiving water. The
treatment plant actually removes the organic material the same
way a stream does, but it accomplishes the task much more
efficiently by removing the wastes from the wastewater.
Secondary treatment6 units are designed and operated to use
natural organisms such as bacteria in the plant to stabilize7
and remove organic material. ~
Another effect of oxygen depletion, in addition to the killing
of fish and other aquatic life, is the problem of odors. When
6 Secondary treatment. A wastewater treatment process used to
convert dissolved or suspended materials into a form more
readily separated from the water being treated.
7 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.
2-5
-------
all the dissolved oxygen has been removed, anaerobic bacteria8
begin to use the oxygen which is combined chemically with
other elements in the form of chemical compounds, such as
sulfate (sulfur and oxygen), which are also dissolved in the
water. When anaerobic bacteria remove the oxygen from sulfur
compounds, hydrogen sulfide (H2S) is released which has a
"rotten egg" odor. This gas is not only very odorous, but it
also erodes concrete and can discolor and remove paint from
homes and structures. Hydrogen sulfide also may form explosive
mixtures with air and is capable of paralyzing your respiratory
center. Other products of anaerobic decomposition (putrefaction:
PU-tree-fack-SHUN) also can be objectionable.
2.32 Other Effects
Some wastes adversely affect the clarity and color of the
receiving waters, making them unsightly and unpopular for
recreation.
Many industrial wastes are highly acid or alkaline, and
either condition can interfere with aquatic life, domestic
use, and other uses. An accepted measurement of a waste's
acidity or alkalinity is its pH.9 Before wastes are dis-
charged they should have a pH~s~imilar to that of the receiving
water.
Waste discharges may contain toxic substances, such as heavy
metals or cyanide, which may affect the use of the receiving
water for domestic purposes or for aquatic life.
8 Anaerobic bacteria (AN-air-0-bick back-TEAR-e-ah). 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 (SC^) and nitrate
(N03) .
9 pH. Technically, this is the logarithm of the reciprocal
of the hydrogen-ion concentration, which will be explained
in Chapter 14, Laboratory Procedures and Chemistry. For
now, it is sufficient to understand that pH may range
from 0 to 14, where 0 is most acid and 14 is most alkaline,
and 7 is neutral. Most natural waters have a pH between
6.5 and 8.5.
2-6
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Taste- and odor-producing substances may reach levels in the
receiving water which are readily detectable in drinking water
or in the flesh of fish.
Treated wastewaters contain nutrients10 capable of encourag-
ing excess algae and plant growth in receiving waters. These
growths hamper domestic, industrial, and recreational uses.
Conventional wastewater treatment plants do not remove a
major portion of the nitrogen and phosphorus nutrients.
QUESTIONS
2.3A What causes oxygen depletion when organic
wastes are discharged to the water?
2. 3B What kind of bacteria cause hydrogen sulfide
gas to be released?
2.33 Human Health
Up to now we have discussed the physical or chemical effects
that a waste discharge may have on the uses of water. More
important, however, may be the effect on human health through
the spread of disease-producing bacteria and viruses. Initial
efforts to control human wastes evolved from the need to prevent
the spread of diseases. Although untreated wastewater contains
many billions of bacteria per gallon, most of these are not
harmful to humans, and some are even helpful in wastewater
treatment processes. However, humans who have a disease which
is caused by bacteria or viruses may discharge some of these
harmful organisms in their body wastes. Many serious outbreaks
of communicable diseases have been traced to direct contamination
of drinking water or food supplies by the body wastes from a
human disease carrier.
10 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 con-
ventional treatment processes because they are water soluble
and tend to recycle.
2-7
-------
Some known examples of diseases which may be spread through
wastewater discharges are:
Fig. 2.3 Diseases
Fortunately these organisms that grow in the intestinal tract
of diseased humans are not likely to find the environment in
the wastewater treatment plant or receiving waters favorable
for their growth and reproduction. Although many of these
pathogenic organisms11 are removed by natural die-off during
the normal treatment processes, sufficient numbers can remain
to cause a threat to any downstream use involving human contact
or consumption. If these uses exist downstream, the
treatment plant must also include a disinfection12 process.
The disinfection process historically employed is the addition
of chlorine. Proper chlorination of a well-treated waste will
usually result in essentially a complete kill of these patho-
genic organisms. The operator must realize, however, that
11 Pathogenic organisms (path-o-JEN-nick OR-gan-iz-ums).
Bacteria or viruses which can cause disease. There are
many types of bacteria which do not cause disease and
which are not called pathogenic.
12 Disinfection (DIS-in-feck-shun). The process by which
pathogenic organisms are killed. There are several ways
to disinfect, but chlorination is the most frequently
used method in water and wastewater treatment.
2-8
-------
breakdown or malfunction of equipment could result in the
discharge at any time of an effluent which contains patho-
genic organisms.
QUESTIONS
2.3C Where do the disease-causing organisms
in wastewater come from?
2.3D What is the term which means "disease-
causing"?
2.3E What is the most frequent means of dis-
infecting treated wastewater?
2.4 SOLIDS IN WASTEWATER
One of the primary functions of a treatment plant is the
removal of solids from wastewater.
2.40 Types of Solids
In Section 2.2 you read about the different types of pollution:
organic, inorganic, thermal, and radioactive. For a normal
municipal wastewater which contains domestic wastewater as well
as some industrial and commercial wastes, the concern of the
treatment plant designer and operator usually is to remove the
organic and inorganic suspended solids, to remove the dissolved
organic solids (the treatment plant does little to remove
dissolved inorganic solids), and to kill the pathogenic organisms
by disinfection. Thermal and radioactive wastes require special
treatment. "~
Since the main purpose of the treatment plant is removal of
solids from the wastewater, a detailed discussion of the types
of solids is in order. Figure 2.4 will help you understand the
different terms.
2.41 Total Solids
For discussion purposes assume that you obtain a one-liter
sample of Taw wastewater entering the treatment plant. Heat
this sample enough to evaporate all the water and weigh all
the solid material left (residue); it weighs 1000 milligrams.
Thus, the total solids concentration in the sample is 1000
milligrams per liter (mg/1). This weight includes both
dissolved and suspended solids.
2-9
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2.42 Dissolved Solids
How much is dissolved and how much is suspended? To determine
this you could take an identical sample and filter it through a
very fine-mesh filter such as a membrane filter or fiberglass.
The suspended solids will be caught on the filter, and the
dissolved solids will pass through with the water. You can
now evaporate the water and weigh the residue to determine the
weight of dissolved solids. In Fig. 2.4 the amount is shown
as 800 mg/TiThe remaining 200 mg/1 is suspended solids.
Dissolved solids are also called f i Iterable residue.
\
2.43 Suspended Solids
Suspended solids are composed of two parts: settleable and
nonsettleable. The difference between settleable and nonset-
tleable solids depends on the size, shape, and weight per unit
volume of the solid particles; larger-sized particles tend to
settle more rapidly than smaller particles. It is important
to know the amount of settleable solids in the raw wastewater
for design of settling basins (primary units), sludge pumps,
and sludge handling facilities. Also, measuring the amount
of settleable solids entering and leaving the settling
basin allows you to calculate the efficiency of the basin
for removing the settleable solids. A device called an
Imhoff Cone *3 is used to measure settleable solids in
milliliters per liter, ml/1. (The example in Fig. 2.4 shows
a settleable solids concentration of 130 mg/1. The settled
solids in the Imhoff Cone had to be dried and weighed by proper
procedures to determine their weight.
It is possible to calculate the weight of nonsettieabie solids
by subtracting the weight of dissolved and settleable solids
from the weight of total solids. In Fig. 2.4 the nonsettleable
solids concentration is shown as 70 mg/1. Suspended solids are
also called nonfilterable residue.
13 Imhoff Cone. A clear cone-shaped container marked
with graduations used to measure the volumetric
concentration of settleable solids in wastewater.
2-10
-------
Fig.' 2.4 Composition of solids in raw wastewater
-------
2.44 Organic and Inorganic Solids
For total solids or for any separate type of solids, such as
dissolved, settleable, or nonsettleable, the relative amounts
of organic and inorganic matter can be determined. This
information is important for estimating solids handling
capacities and for designing treatment processes for removing
the organic portion in waste. The organic portion can be
very harmful to receiving waters.
2.45 Floatable Solids
There is no standard method for the measurement and evaluation
of floatable solids. Since treatment units are designed to
remove these solids, it is important for you to be aware of
floatable solids in raw wastewater and treated effluent.
Floatable solids are undesirable in the plant effluent from an
aesthetic viewpoint because the sight of floatables in receiv-
ing waters indicates the presence of inadequately treated
wastewater.
2.5 ADDITIONAL READING
For a detailed discussion of the physical and chemical compo-
sition of wastewater you may wish to refer to:
1. MOP 11, pp 4-7
2. New York Manual, pp 1-10
3. Texas Manual, pp 1-18
QUESTIONS
2.4A An Imhoff Cone is used to measure
solids.
2.4B Why is it necessary to measure settleable solids?
2.4C Total solids are made up of and
solids, both of which contain
organic and inorganic matter.
2-12
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2.6 REVIEW
In this chapter you have read why it is necessary to treat
wastewater, something about the types of waste discharges
and their effects, and a brief description of the different
kinds of solids in wastewater. This is intended to be only
a general discussion of these subjects; you will find more
detail in later chapters.
You are now ready to go on to Chapter 3 which deals with a
description of the basic elements of the wastewater collection
and treatment systems. Chapter 3 actually begins the dis-
cussion of how to treat wastewater. Chapter 2 has told you
why you need to do so.
Fig. 2.5 "GO"
2-13
-------
SUGGESTED ANSWERS
Chapter 2. Why Treat Wastes?
2.1A Some of the dissolved substances in water include oxygen,
calcium, carbon, magnesium, chlorides, sodium, sulfates,
iron, nitrogen, phosphorus, and organic material.
You should have listed at least three of the items in
the answer.
2.IB Water picks up dissolved substances as it falls as rain,
flows over land and is used for domestic, industrial,
agricultural, and recreational purposes.
2.2A a, c, and e.
2.2B Organic, inorganic, thermal, radioactive.
2.3A Organic wastes in a water provide food for the bacteria.
These bacteria require oxygen to survive and consequently
deplete the oxygen in the water in a way similar to people
breathing.
2.3B Hydrogen sulfide gas is released by anaerobic bacteria.
2.3C Disease-causing organisms in wastewater come from the
body wastes of humans who have a disease.
2.3D Pathogenic.
2.3E Chlorination is the most frequent means of disinfecting
treated wastewater.
2.4A Settleable.
2.4B Settleable solids must be measured to determine the
efficiency of settling basins. This amount must also
be known to calculate loads on settling basins, sludge
pumps, and sludge handling facilities for design and
operational purposes. You should have recognized the
need to know the efficiency of settling basins.
2.4C Dissolved and suspended.
2-14
-------
OBJECTIVE TEST
Chapter 2. Why Treat Wastes?
Please write your name, date, city, time, instructor, and name
of test on your answer sheet, then mark correct answers on answer
sheet.
2.1 Wastes are treated to:
1. Prevent Pollution
2. Protect Human Health
3. Remove Harmful Wastes from WastoKa":ci
4. Prevent Receiving U.iter.s .frorii Stinlinv
2.2 Diseases possibly spread by wastewater discharges include:
1. Typhoid 3. Q Fever 5. Hepatitis
2. Cholera 4. Dysentery (Jaundice)
2.3 Pathogenic bacteria are:
1. Inorganic 4, Dissolved Cases
2. Disease Producing 5, None of These
3. Easy to See
2.4 What does an Imhoff Cone measure?
1. Total Solids 4. Organic Solids
2. Dissolved Solids 5. Colloidal Solids
3. Settleable Solids
Match the definitions on the following page by placing the correct
number from the column on the right in the proper space in front
of the definition.
EXAMPLE
_ 2^_ Milligrams per liter. 1. MPL
2. mg/1
3. MPN
Mark Column 2 on your answer sheet:
12345
II I M I II It II
II ill II II II
II 1*1 II It II
continue test on next page
1-15
-------
2.5
2.6
Waste material which comes
from animal or vegetable
sources.
Bacteria which will live
and reproduce only in an
environment containing
dissolved oxygen.
Bacteria which obtain their
oxygen by breaking clown
chemical compounds which
contain oxygen, such as
sulfates
1. 0 r g an i c W as t e
2. Inorganic Waste
3. Radioactive Waste
4. Aerobic Bacteria
5. Anaerobic Bacteri
2,1
2,9
2.10
Bacteria which can cause
disease.
A process which kills
disease-causing bacteria.
Any discharge of waste that
reduces receiving water
quality indicators below
the established water
quality standards.
1. Pollution
2. Disinfection
3. Nutrients
4. pH
5. Pathogenic
Organisms
Please write how long you worked on this chapter on your
answer sheet.
2-16
-------
CHAPTER 3
WASTEWATER FACILITIES
by
John Brady
and
William Crooks
-------
TABLE OF CONTENTS
Chapter 3. Wastewater Facilities
Page
GLOSSARY i
3.0 Collection, Treatment, Disposal 3-1
3.1 Collection of Wastewater 3-1
3.10 Sanitary, Storm, and Combined Sewers 3-2
_3_._2_ Treatment Plants 3-5
3.3 Pretreatment 3-8
3.30 General 3-8
3.31 Screening 3-8
3.32 Shredding 3-9
3.33 Grit Chambers 3-10
3.4 Flow Measuring Devices 3-12
3.5 Primary Treatment 3-15
3.6 Secondary Treatment 3-19
3.60 General .3-19
3.61 Trickling Filter 3-19
3.62 Activated Sludge 3-22
3.63 Secondary Clarifiers 3-24
3^. 7 Solids Handling and Disposal 3-26
3.70 General 3-26
3.71 Digestion and Dewatering 3-26
3.72 Incineration. 3-30
3.8 Waste Treatment Ponds 3-31
3.9 Advanced Methods of Treating Wastewater 3-34
3.10 Disinfection 3-35
3.11 Additional Reading 3-38
-------
GLOSSARY
Chapter 3. Wastewater Facilities
Biochemical Oxygen Demand or BOD (BUY-o-KEM-ik-cull OX-zi-gen
de-MAND): The BOD indicates the rate of oxygen utilized by
wastewater under controlled conditions of temperature and time.
Combined Sewer: A sewer designed to carry both sanitary waste-
waters and storm or surface water runoff.
Comminution (com-min-00-shun): A mechanical treatment process
which cuts large pieces of wastes into smaller pieces so they
won't plug pipes or damage equipment (shredding).
Detention Time: The time required to fill a tank at a given
fTow or the "theoretical time required for a given flow of waste-
water to pass through a tank.
Grit: The heavy mineral material present in wastewater, such
as sand, gravel, cinders, and eggshells.
Infiltration (IN-fill-TRAY-shun): Groundwater that seeps into
pipes through cracks, joints, or breaks.
Media: The material in a trickling filter over which settled
wastewater is sprinkled and then flows over and around during
treatment. Slime organisms grow on the surface of the media
and treat the wastewater.
Photosynthesis (foto-SIN-tha-sis): A process in which chlorophyll
(green plant tissue) converts carbon dioxide and inorganic sub-
stances to oxygen and additional plant material, utilizing sun-
light for energy. Land plants grow by the same process.
Primary Treatment: A wastewater treatment process consisting of
a rectangular or circular tank which allows those substances in
wastewater that readily settle or float to be separated from the
water being treated.
Sanitary Sewer (SAN-eh-tar-ee SUE-er): A sewer intended to
carry wastewater from homes, businesses, and industries. Storm
water runoff is sometimes collected and transported in a separate
system of pipes.
-------
Secondary Treatment; A wastewater treatment process used to
convert dissolved or suspended materials into a form more
readily separated from the water being treated.
Shredding: A mechanical treatment process which cuts large
pieces of wastes into smaller pieces so they won't plug pipes
or damage equipment (comminution).
Sludge (sluj): The settleable solids separated from liquids
during processing or deposits on bottoms of streams or other
bodies of water.
Storm Sewer: A separate sewer that carries runoff from storms,
surface drainage, and street wash, hut that excludes domestic
and industrial wastes.
Weir (weer): A vertical obstruction, such as a wall or plate,
pTaced in an open channel and calibrated in order that a depth
of flow over the weir con easily be converted to a flow rate
in MGD (million gallons per day) .
-------
CHAPTER 3. WASTEWATER FACILITIES
3.0 COLLECTION, TREATMENT, DISPOSAL
Facilities for handling wastewater are usually considered to have
three major components or parts: collection, treatment, and
disposal. For a municipality, these components make up the
"sewerage" system or wastewater facilities; but for an individual
industry which handles its own wastewater, the same three components
are necessary. This training course is directed primarily to plant
operators for municipalities, so the discussion in this and later
chapters will be in terms of municipal wastewater facilities.
3.1 COLLECTION OF WASTEWATER
Collection and transportation of wastewater to the treatment plant
is accomplished through a complex network of pipes and pumps of
many sizes.
Major water using industries which contribute waste to the collec-
tion system may affect the efficiency of a wastewater treatment
plant, especially if there are periods during the day or during
the year when these industrial waste flows are a major load on
the plant. For instance, canneries are highly seasonal in their
operations; therefore, it is possible to predict the time of year
to expect large flows from them. A knowledge of the location of
commercial and industrial dischargers in the collection system
may enable an operator to locate the source of a problem in the
plant influent, such as oil from a refinery or a gas station.
The length of time required for wastes to reach your plant can
also affect treatment plant efficiency. Hydrogen sulfide gas
(rotten egg gas) may be released by anaerobic bacteria feeding
on the wastes if the flow time is quite long and the weather is
hot; this can cause odor problems, damage concrete in your plant,
and make the wastes more difficult to treat. (Solids won't settle
easily, for instance.) Wastes from isolated subdivisions located
far away from the main collection network often have this "aging"
problem.
3-1
-------
3.10 Sanitary, Storm, and Combined Sewers
For most sewerage systems the sewer coming into the treatment
plant carries wastes from households and commercial establish-
ments in the city or district, and possibly some industrial
waste. This type of sewer is called a sanitary sewer.1 All
storm runoff from streets, land, and roofs of buildings is
collected separately in a storm sewer,2 which normally dis-
charges to a water course without treatment. In some areas
only one network of sewers has been laid out beneath the
city to pick up both sanitary wastes and storm water in a
combined sewer.3 Treatment plants that are designed to handle
the sanitary portion of the wastes sometimes must be bypassed
during storms due to inadequate capacity, allowing untreated
wastes to be discharged into receiving waters. Separation of
combined sewers into sanitary and storm sewers is very costly
and difficult to accomplish.
Even in areas where the sanitary and storm sewers are separate,
infiltration1* of groundwater or storm water into sanitary
sewers through breaks or open joints can cause high flow
problems at the treatment plant. Replacement or sealing of
leaky sections of sewer pipe is called for in these cases.
The treatment plant operator is generally the first to know
about infiltration problems because of the unusually high
flows he observes at the plant during periods of storm water
runoff.
1 Sanitary Sewer (SAN-eh-tar-ee sUE-er). A sewer intended
to carry wastewater from homes, businesses, and industries.
2 Storm Sewer. A separate sewer that carries runoff from
storms, surface drainage, and street wash, but that ex-
cludes domestic and industrial wastes.
3 Combined sewer. A sewer designed to carry both sanitary
wastewaters and storm or surface water runoff.
k Infiltration (IN-fill-TRAY-shun). Groundwater that seeps
into pipes through cracks, joints, or breaks.
3-2
-------
Sanitary sewers are normally placed at a slope sufficient to
produce a velocity of approximately two feet per second. This
velocity will usually prevent the deposition of solids that may
clog the pipe or cause odors. Manholes are placed every 300 to
500 feet to allow for
inspection (Fig. 3.1) and
cleaning of the sewer.
When low areas of land must
be sewered or where pipe
depth under the ground
surface becomes excessive,
pump stations (Fig. 3.2)
are normally installed.
These pump stations lift
the wastewater to a higher
point from which it may
again flow by gravity,
or the wastewater may be
pumped under pressure
directly to the treatment
plant. A large pump station
located just ahead of the
treatment plant can create
problems by periodically
sending large volumes of
flow to the plant one minute,
and virtually nothing the
next minute.
Fig. 3.1
Manholes allow
inspection of the
collection system
QUESTIONS
3.1A Why should the operator be familiar with the
w£.stewater collection and transportation network?
3. IB List three types of sewers.
3.1C What problem may occur when it takes a long time
for wastewater to flow through the collection
sewers to the treatment plant?
3.ID Why are combined sewers a problem?
3-3
-------
3.2 TREATMENT PLANTS
Upon reaching a wastewater treatment plant, the wastewater flows
through a series of treatment processes (Fig. 3.3) which remove
the wastes from the water and reduce its threat to the public
health before it is discharged from the plant. The number of
treatment processes and the degree of treatment usually depend
on the uses of the receiving waters. Treated wastewaters dis-
charged into a small stream used for a domestic water supply
and swimming will require considerably more treatment than waste-
water discharged into water used solely for navigation.
To provide you with a general picture of treatment plants, the
remainder of this chapter will follow the paths a drop of waste-
water might travel as it passes through a plant. You will be
introduced to the names of the treatment processes, the kinds
of wastes the processes treat or remove, and the location of the
processes in the flow path. Not all treatment plants are alike;
however, there are certain typical flow patterns that are
similar from one plant to another.
When wastewater enters a treatment plant, it usually flows through
a series of pretreatment processes—screening, shredding, and
grit removal. These processes remove the coarse material from
the wastewater. Flow-measuring devices are usually installed
after pretreatment processes to record the flow rates and
volumes of wastewater treated by the plant.
Next the wastewater will generally receive primary treatment.
During primary treatment some of the solid matter carried by
the wastewater will settle out or float to the water surface
where it can be separated from the wastewater being treated.
Secondary treatment processes usually follow primary treatment
and commonly consist of biological processes. This means that
organisms living in the controlled environment of the process
are used to partially stabilized (oxidize) organic matter not
removed by previous treatment processes and to convert it into
a form which is easier to remove from the wastewater.
Waste material removed by the treatment processes goes to
solids handling facilities and then to ultimate disposal.
Waste treatment ponds may be used after pretreatment, primary
treatment, or secondary treatment. Ponds are frequently con-
structed in rural areas where there is sufficient available
land.
3-4
-------
Ul
WAT-BE.
Fig. 3.2 Collection sewer profile
-------
P12E
PH-OW
AMP
zoors
ANP
BEMOVZ
AHO
O/L
Fig. 3.3 Flow diagram of wastewater treatment plant processes
3-6
-------
BAR SCREEN
Hcnidi fttkttCi
Piath
8or 5cr««n
PIAN
EISVATION
(Courtesy Water Pollution Control Federation)
Fig. 3.4 Bar screens
-------
Advanced methods of waste treatment are being developed for
general cleanup of wastewater or removal of substances not
removed by conventional treatment processes. They may follow
the treatment processes previously described, or they may be
used instead of them. Before treated wastewater is discharg-
ed to the receiving waters, it should be disinfected to
prevent the spread of disease.
In the following sections these treatment processes will be
briefly discussed to provide an overall concept of a treatment
plant. Details will be presented in la.ter chapters to provide
complete information on each of these processes.
3.3 PRETREATMENT
3.30 General
Pretreatment processes commonly consist of screening, shredding,5
and grit removal to separate coarse material from the wastewater
being treated.
3.31 Screening
Wastewater flowing into the
treatment plant will occasionally
contain pieces of wood, roots,
rags, and other debris. To pro-
tect equipment and reduce any
interference with in-plant flow,
debris and trash are usually
removed by a bar screen (Fig.
3.4). Most screens in treatment
plants consist of parallel bars
placed at an angle in a channel
in such a manner that the waste-
water flows through the bars.
Trash collects on the bars and
is periodically raked off by
hand or by mechanical means.
In most plants these screenings
are disposed of by burying or
burning. In some cases they are
automatically ground up and re-
turned to the wastewater flow for
removal by a later process.
Fig. 3.5 Screened
§ ground
5 Shredding. A mechanical treatment process which cuts large
pieces of wastes into smaller pieces so they won't plug pipes
or damage equipment (comminution).
3-8
-------
3.32 Shredding
Devices are also available which cut up or shred material while
it remains in the wastewater stream. The most common of these
are the barminutor (Fig. 3.6) and the comminutor (Fig. 3.7).
One of these devices usually follows a bar screen.
Fig. 3.6 Barminutor
Fig. 3.7 Comminutor
(Courtesy Chi-cago Pump)
3-9
-------
3.33 Grit Chambers
Most sewer pipes are laid at a slope steep enough to maintain a
wastewater flow of two feet per second (fps). If the velocity
is reduced slightly below
that, say to 1.5 fps,
some of the larger,
heavier particles will
settle out. If the
velocity is reduced to
about 1 fps, heavy
inorganic material such
as sand, eggshells, and
cinders will settle; but
the lighter organic
material will remain in
suspension. The settled
inorganic material is
referred to as grit.6
Grit should be removed
early in the treatment
process because it is
abrasive and will rapidly
wear out pumps and other
equipment. Since it is
mostly inorganic, it can-
not be broken down by any
biological treatment pro-
Fig. 3.8 Removal of eggshells
cess and thus should be
removed as soon as possible,
Grit is usually removed in a long, narrow trough called a Grit
Chamber (Pig. 3.9). The chamber is designed to provide a flow-
through velocity of 1 fps. The settled grit may be removed
either by hand or mechanically. Since there is normally some
organic solid material deposited along with the grit, it is
usually buried to avoid nuisance conditions. Some plants are
equipped with "grit washers" that clean some of the organic
material out of the grit so that organic solids can remain in
the main waste flow to be treated.
Many treatment plants have aerated grit chambers in which com-
pressed air is added through diffusers to provide better separation
of grit and other solids. Aeration in this manner also "freshens"
a "stale" or septic wastewater, helping to prevent odors and
assist the biological treatment process.
6 Grit. The heavy mineral material present in wastewater,
such as sand, gravel, cinders, and eggshells.
3-10
-------
Fig. 3.9 Grit chamber
WPCF MOP No. 11,
Operation of Wasteuater Treatment Plants
QUESTIONS
3.3A Why is grit removed early in the treatment
process?
3.3B What is usually done with grit which has been
removed from the wastewater?
3-11
-------
3.4 FLOW MEASURING DEVICES
Although flow measuring devices are not for treating wastes,
it is necessary to know the quantity of wastewater flow so
adjustments can be made on pumping rates, chlorination rates,
aeration rates, and other processes in the plant. Flow rates
must be known, also, for calculation of loadings on treatment
processes and treatment efficiency. Most operators prefer to
have a measuring device at the headworks of their treatment
plant.
The most common measuring device is a Parshall Flume (Fig. 3.10).
Basically it is a narrow place in an open channel which allows
the quantity of flow to be determined by measuring the depth of
flow. It is a widely used method for measuring wastewater because
its smooth constriction does not offer any protruding sharp
edges or areas where wastewater particles may catch or collect
behind the metering device.
Another measuring device used in open channels is a weir7 (Fig.
3.10). A weir is a wall placed across the channel over which
the waste may fall. It is usually made of thin metal and may
have either a rectangular or V-notch opening. Flow over the
weir is determined by the depth of waste going through the
opening. A disadvantage of a weir is the relatively dead
water space that occurs just upstream of the weir. If the
weir is used at the head end of the plant, organic solids
may settle out in this area. When this occurs odors and
unsightliness can result. Also, as the solids accumulate the
flow reading may become incorrect.
A good measuring device for flows of treated or untreated waste-
water is a Venturi meter (Fig, 3.10). It is a special section
of contracting pipe, and it measures flow in much the same way
as a Parshall Flume. It does not offer any sharp obstructions
for particles to catch on. Magnetic flow meters (Fig. 3.10)
also are being used successfully to measure wastewater flows.
7 Weir (weer). A vertical obstruction such as a wall or plate,
placed in an open channel and calibrated in order that a
depth of flow over the weir can easily be converted to a
flow rate in MGD (million gallons per day).
3-12
-------
ViNTURI MfflR
End Photo of Parshall Flume
(Drawings courtesy of Water
Pollution Control Federation)
Fig. 3.10 Flow meters
-------
QUESTIONS
3.4A Why are weirs not frequently used to measure the
influent to a plant?
3.4B Why is a Parshall Flume widely used for measuring
wastewater flow?
3-14
-------
3.5 PRIMARY TREATMENT
We have previously discussed the reduction in velocity of the
incoming waste to approximately one foot per second in order
to settle out heavy inorganic material or grit. The next step
in the treatment process is normally called sedimentation or
primary treatment. In this process the waste is directecT into
arid" through a large tank or basin. Flow velocity in these
tanks is reduced to about 0.03 foot per second, allowing the
settleable solids to fall to the bottom of the tank, thus
making the wastewater much clearer. It has therefore become
common practice to call these sedimentation tanks "clarifiers".
The first clarifier that the wastewater flows into is called a
primary clarifier. We will discuss later the need for another
"clarifier after the biological treatment process. This second
clarifier is called a secondary clarifier.
Clarifiers normally are either rectangular (Fig. 3.11) or
circular fFig. 3.12). Primary clarifiers are usually designed
to provide 1.5 to 2 hours detention time.8 Secondary clarifiers
usually provide slightly more time.
Generally the longer the detention time provided, the more
removal of solids that takes place. In a tank with two hours
detention time, approximately 60 percent of the suspended solids
in the raw wastewater will either settle to the bottom or float
to the surface and be removed. Removal of these solids will
usually reduce the Biochemical Oxygen Demand (BOD)9 of the
waste approximately 30 percent. The exact removal depends on
the amount of BOD contained in the settled material.
All primary clarifiers, no matter what their shape, must have
a means for collecting the settled solids (called sludge10) and
8 Detention Time. The time required to fill a tank at a
given flow or the theoretical time required for a given
flow quantity of wastewater to flow through the tank.
9 Biochemical Oxygen Demand or BOD (BUY-o-KEM-ik-cull
OX-zi-gen de-MAND). The BOD indicated the rate of
oxygen utilized by wastewater under controlled con-
ditions of temperature and time.
10 Sludge (sluj). The settleable solids separated from
liquids during processing or deposits on bottoms of
streams or other bodies of water.
3-15
-------
SLUDGE COLLECTOR
DRIVE UNIT
EFFLUENT WEIRS
SCUM SKIMMER AND TROUGH
EFFLUENT TROUGH
TARGET BAFFLE
SLUDGE COLLECTOR CHAIN
AND FLIGHTS
CROSS COLLECTOR
CHAIN AND FLIGHTS
SLUDGE
WITHDRAWAL
PIPE
Fig. 3.11 Rectangular clarifier
(Courtesy Jeffrey)
3-16
-------
EFFLUENT HEIR
DRIVE UNIT
SUMP
Fig. 3.12 Circular clarifier
3-17
-------
the floating solids (called scum). In rectangular tanks,
sludge and scum collectors are usually wooden beams ("flights")
attached to endless chains. The collector flights travel on
the surface, in the direction of the flow, conveying grease
and floatable solids down to the scum trough to be skimmed
off to the solids (sludge) handling facilities. The flights
then drop below the surface and return to the influent end
along the bottom, moving the settled raw sludge to the sludge
hopper. The sludge is periodically pumped from the hopper to
the sludge handling facilities.
In circular tanks, scrapers or "plows", attached to a rotating
arm, rotate slowly around the bottom of the tank. The plows
push the settled sludge toward the center and into the sludge
hopper. Scum is collected by a rotating blade at the surface.
As in the case of the rectangular tank, both scum and sludge
are usually pumped to the solids or sludge handling facilities.
The clear surface water of the primary tank flows out of the
tank by passing over a weir. The weir must be long enough to
allow the treated water to leave at a low velocity; if it leaves
at a high velocity, particles settling to the bottom or those
already on the bottom may be picked up and carried out of the
tank.
QUESTIONS
3.5A What is the purpose of "flights" or "plows" in
a clarifier?
3.5B What happens to the sludge and scum collected
in a primary clarifier?
3-18
-------
3.6 SECONDARY TREATMENT
3.60 General
In many treatment plants the wastewater flows out of the
primary clarifier into another unit where it receives secondary
or biological treatment. This means that the wastewater is
exposed to living organisms (such as bacteria) which eat the
dissolved and nonsettleable organic material remaining in the
waste. The two processes used almost universally for biological
treatment are the trickling filter and activated sludge. These
are both aerobic 'biological treatment processes, which means
the organisms require dissolved oxygen (Fig. 3.13) in order to
live, eat, and reproduce.
Fig. 3.13 Organisms require dissolved oxygen
3.61 Trickling Filter
The trickling filter is one of the oldest and most dependable
of the biological treatment processes. Most of these plants
are removing 65 to 85% of the BOD and suspended solids present
in the influent.
3-19
-------
The trickling filter is a bed of 1% to 5-inch rock, slag
blocks, or specially manufactured "media"11 over which settled
wastewater from the primary clarifier is distributed (Fig.
3.14). The settled wastewater is usually applied by an
overhead rotating distributor and trickles over and around
the media as it flows downward to the effluent collection
channel. Since the media and the voids in between them are
large (usually 2.5- to 4-inch diameter), and since the applied
wastewater no longer has any large particles (they settled
out in the clarifier), the trickling filter does not remove
solids by a filtering action. It would be more correct to
call the filter a biological contact bed or biological reactor
since this is the function it performs. The filter bed offers
a place for aerobic bacteria and other organisms to attach
themselves and multiply as they feed on the passing waste-
water. This process of feeding on, or decomposing, waste is
exactly the same as the process occurring in the stream when
waste is discharged to it. In the trickling filter, however,
the organisms use the oxygen which enters the waste from the
surrounding air, rather than using up the stream's supply of
dissolved oxygen. Thus the voids between the media must be
large so sufficient oxygen can be supplied by circulating air.
The wastewater being distributed on the filter usually has
passed through a primary clarifier, but it still contains
approximately 70 percent of its original organic matter,
which represents food for organisms. For this reason a
tremendous population of organisms develops on the media.
This population continues to grow as more waste is applied.
Eventually the layer of organisms on the media gets so thick
that some of it breaks off (sloughs off) and is carried into
the filter effluent channel. This material is normally called
humus. Since it is principally organic matter, its presence in
a stream would be undesirable. It is usually removed by
settling in a secondary clarifier.^ Humus sludge from the
secondary clarifier is usually returned to the primary clari-
fier to be resettled and pumped to the sludge handling facili-
ties along with the "raw" sludge which settles out as previously
described.
11 Media. The material in a trickling filter over which
settled wastewater is sprinkled and then flows over and
around during treatment. Slime organisms grow on the
surface of the media and treat the wastewater.
3-20
-------
TRICKLING FILTER
*.mtf» noon
*.
CWAU5
0.MHMA ,':;.:
E-I»IST«8«TOR 5OWORT !NfiW8NT
F. DISTRtauTOR ARM
a, vf NT
(Courtesy Water Pollution Control Federation)
Fig. 3.14 Trickling filter
3-21
-------
3.62 Activated Sludge
Another biological treatment unit that is used in secondary
treatment, following the primary clarifier, is the aeration
tank. When aeration tanks are used with the sedimentation
process, the resulting plant is called an activated sludge
plant. The activated sludge process is widely used by large
cities and communities where land is expensive and where
large volumes must be highly treated, economically, without
creating a nuisance to neighbors. The activated sludge plant
is probably the most popular biological treatment process
being built today for larger installations or small package
plants. These plants are capable of BOD and suspended solids
reduction of up to 90 or 99%. The activated sludge process
is a biological process, and it serves the same function as
a trickling filter. Effluent from a primary clarifier is
piped to a large aeration tank (Fig. 3.15). Air is supplied
to the tank by either introducing compressed air into the
bottom of the tank and letting it bubble through the waste-
water and up to the top, or by churning the surface mechanically
to introduce atmospheric oxygen.
Aerobic bacteria and other organisms thrive as they travel
through the aeration tank. With sufficient food and oxygen
they multiply rapidly, as in a trickling filter. By the time
the waste reaches the end of the tank (usually 4 to 8 hours),
most of the organic matter in the waste has been used by the
bacteria for producing new cells. The effluent from the
tank, usually called "mixed liquor", consists of a suspension
containing a large population of organisms and a liquid with
very little BOD. The activated sludge forms a lacey network.
that captures pollutants.
The organisms are removed in the same manner as they were
in the trickling filter plant. The mixed liquor is piped
to a secondary clarifier, and the organisms settle to the
bottom of the tank while the clear effluent flows over the
top of the effluent weirs. This effluent is usually clearer
than a trickling filter effluent because the suspended
material in the mixed liquor settled to the bottom of the
clarifier more readily than the material in a trickling
filter effluent. The settled organisms are known as
activated sludge. They are extremely valuable to the treatment
3-22
-------
TYPICAL ACTIVATED SLUDGE TANK
Fig. 3.15 Aeration tank
3-23
-------
process. If they are removed quickly from the secondary clari-
fier, they will be in 'good condition and hungry for' more food
(organic wastes) (Fig.
3.16). They are there-
fore pumped back (re-
circulated) to the
influent end of the
aeration tank where
they are mixed with
the incoming waste-
water. Here they
begin all over again
to feed on the organic
material in the waste,
decomposing it and
creating new organisms.
Left uncontrolled, the
number of organisms
would eventually be
too great, and therefore
some must periodically
be removed. This is
accomplished by pumping
a small amount of the
activated sludge to the
primary clarifier. The
organisms settle in the
clarifier along with
the raw sludge and are
removed to the sludge
handling facilities.
There are many variations of the conventional activated sludge
process, but they all involve the same basic principle. These
variations will be discussed in Chapter 7, Activated Sludge.
Fig. 3.16 Hungry organisms
ready for
more food
3.63 Secondary Clarifiers
As previously mentioned, trickling filters and activated sludge
tanks produce effluents that contain large populations of micro-
organisms and associated materials (humus). These microorganisms
must be removed from the flow before it can be discharged to the
receiving waters. This task is usually accomplished by a
secondary clarifier. In this tank the trickling filter humus or
activated sludge separates from the liquid and settles to the
3-24
-------
bottom of the tank. It is removed to the primary clarifier to
be resettled with the primary sludge or returned to the begin-
ning of the secondary process to continue treating the waste-
water. The clear effluent flows over a weir at the top of the
tank.
QUESTIONS
3.6A Would it be a good idea to use trickling filter
media of various sizes so it could pack together
better?
3.6B Why is a secondary clarifier needed after a
trickling filter or aeration tank?
3.6C Activated sludge can be pumped from the secondary
clarifier to
3-25
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3.7 SOLIDS HANDLING AND DISPOSAL
3.70 General
Solids removed from wastewater treatment processes are commonly
broken down by a biological treatment process called sludge
digestion. After digestion and dewatering the remaining
material may be used for fertilizer or soil conditioner.
Some solids, such as scum from a clarifier, may be disposed of
by burning or burial.
3.71 Digestion and Dewatering
Settled sludge from the primary clarifier and occasionally
settled sludge from the secondary clarifier are periodically
pumped to a digestion tank. The tank is usually completely
sealed to exclude any air from getting in (Fig. 3.17). This
type of digester is called an anaerobic digester because of
the anaerobic bacteria that abound in the tank.Anaerobic
bacteria thrive in an environment devoid of dissolved oxygen
by using the oxygen which is chemically combined with their
food supply.
Two major types of bacteria are present in the digester. The
first group starts eating on the organic portion of the sludge
to form organic acids and carbon dioxide gas. These bacteria
are called "acid formers". The second group breaks down the
organic acids to simpler compounds and forms methane and
carbon dioxide gas. These bacteria are called "gas formers".
The gas is usually used to heat the digester or to run engines
in the plant. The production of gas indicates that organic
material is being eaten by the bacteria. A sludge is usually
considered properly digested when 50 percent of the organic
matter has been destroyed and converted to gas. This normally
takes approximately 30 days if the temperature is kept at
about 95°F.
Most digestion tanks are mixed to continuously bring the food
to the organisms,to provide a uniform temperature, and to avoid
the formation of thick scum blankets. When a digester is not
being mixed the solids settle to the bottom, leaving an amber-
colored liquid above the sludge known as supernatant. The
3-26
-------
SLUDGE DIGESTER
Fixed cover
O
dfowoff irt-e
) pips
(Courtesy Water Pollution Control Federation)
Fig. 3.17 Sludge digester
3-27
-------
supernatant is displaced from the tank each time a fresh
charge of raw sludge is pumped from the primary clarifier.
The displaced supernatant usually is returned from the
digester back to the plant headworks and mixed with in-
coming raw wastes. Supernatant return should be slow to
prevent overloading or shock loading of the plant.
Above the supernatant level a scum blanket will usually
develop. Scum blankets consist of grease, soap, rubber
goods, hair, petroleum products, plastics, and filter tips
from cigarettes. These scum blankets may contain most of
the added food or sludge. Digestion organisms are usually
below the supernatant and little digestion will occur if
the organisms and food don't get together. Control of
scum blankets consists of mixing the digester contents
and burning or burying skimmings instead of pumping them
to the digester.
Above the scum blanket or normal water level is the gas
collection area. Digester gas is normally about 70% methane
and 30% carbon dioxide. When mixed with air, digester gas
is extremely explosive (Tig- 3.18).
Fig. 3.18 Don't allow digester gas and air to mix
In most newer plants digesting takes place in two tanks. The
first or primary digester is usually heated and mixed. Rapid
digestion takes place along with most of the gas production.
In the secondary tank, the digested sludge and supernatant are
allowed to separate, thus producing a clearer supernatant and
better digested sludge.
Digested sludge from the bottom of the tank is periodically
removed for dewatering. This is accomplished in sand drying
beds (Fig. 3.19), lagoons, centrifuges, and vacuum filters
(Fig. 3.20). The sludge is then burned, buried, or used as
fertilizer on certain crops (not on crops which are eaten
without cooking). Sludge that has been adequately digested
drains readily and is not offensive.
3-28
-------
Sand »-lx,)
Gravel'. • *-t2*-18*
Fig. 3.19 Sludge drying bed
(Courtesy Water Pollution Control Federation)
VACUUM FILTER
Sludge Mums &
Conditioning Tort
Sludge Pickup 8
Dttffltering by Vacuum
Fig. 3.20 Vacuum filter
(Courtesy Water Pollution Coritrol Federation)
3-29
-------
Some of today's activated sludge treatment plants are equipped
with aerobic digesters. An aerobic digester is ususally an
open tank with compressed air being blown through the sludge.
Destruction of organic matter is accomplished by bacteria
which require dissolved oxygen to survive. One advantage
of this process is that there is no explosive gas being pro-
duced. On the other hand, this is also a disadvantage since
the anaerobic digester gas is used as a fuel for boilers and
engines around the plant. Aerobic sludge from an aerobic
digester doesn't thicken as readily as sludge from an an-
aerobic digester. Aerobic sludge filters about as well as an
equivalent concentration of anaerobic sludge.
3.72 Incineration
Burning of wet sludge by wet oxidation or of dewatered sludge
are possible methods of ultimate disposal; however, the process
must not create an air pollution problem. To prevent skimmings
from clarifiers causing operational problems, incineration or
burial are used.
QUESTIONS
3.7A What two basic types of bacteria are present
in an anaerobic digester?
3.7B Why are digesters mixed?
3.7C List some of the ways to dispose of digested
sludge.
3-30
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3.8 WASTE TREATMENT PONDS
A special method of biological treatment deserving attention
is wastewater treatment ponds (Fig. 3.21). They do not
resemble the concrete and steel structures or the mechanical
devices that have been previously discussed. But these simple
depressions in the ground are capable of producing an effluent
comparable to some of the most modern plants with respect to
BOD and bacteria reduction.
In some treatment plants, wastewater being treated may flow
through a coarse screen and flow meter before it flows through
a series of ponds. In other plants the ponds may be located
after primary treatment, while in some plants they are placed
after trickling filters. The type of treatment processes and
the location of ponds are determined by the design engineer
on the basis of economics and the degree of treatment required
to meet the water quality standards of the receiving waters.
When wastewater is discharged to a pond, the settleable solids
fall to the bottom just as they do in a primary clarifier.
The solids begin to decompose and soon use up all the dissolved
oxygen in the nearby water. A population of anaerobic bacteria
then continues the decomposition, much the same as in an
anaerobic digester. As the organic matter is destroyed, methane
and carbon dioxide are released. When the carbon dioxide rises
to the surface some of it is used by algae, which convert it to
oxygen by the process of photosynthesis. 12 This is the same
process used by living plants. Aerobic bacteria, algae, and
other microorganisms feed on the dissolved solids in the upper
layer of the pond much the same way they do in a trickling
filter or aeration tank. Algae produce oxygen for the other
organisms to use.
Some shallow ponds (3 to 6 feet deep) have dissolved oxygen
throughout their entire depth. These ponds are called aerobic
ponds. They usually have a mechanical apparatus adding oxygen
plus their oxygen supply from algae.
12 Photosynthesis (foto-SIN-tha-sis). A process in which
chlorophyll (green plant tissue) converts carbon dioxide
and inorganic substances to oxygen and additional plant
material utilizing sunlight for energy. Land plants grow
by the same process.
3-31
-------
STABILIZATION POND
(Courtesy Water Pollution Control Federation)
(Courtesy Water and Sewage Works Magazine)
Fig. 3.21 Pond
3-32
-------
Deep (8 to 12 feet), heavily loaded ponds may be devoid of
oxygen throughout their depth. These ponds are called anaerobic
ponds. At times, these ponds can be quite odorous, and they
are used in sparsely populated areas only.
Ponds that contain an aerobic top layer and an anaerobic
bottom layer are called facultative ponds. These are the
ponds normally seen in most areas. If they are properly
designed and operated,they are virtually odor free and produce
a well-oxidized (low BOD) effluent.
Occasionally ponds are used after a primary treatment unit.
In this case, they are usually called oxidation ponds. When
they are used to treat raw wastewater, they are called raw
wastewater lagoons or waste stabilization ponds.
The effluent from ponds is usually moderately low in bacteria.
This is especially true when the effluent runs from one pond
to another or more (series flow). The long detention time,
usually a month or more, is required in order for harmful
bacteria and undesirable solids to be removed from the pond
effluent. If the receiving waters are used for water supply
or body contact sports, chlorination of the effluent may still
be required.
QUESTION
3.8A How are facultative ponds similar to:
1. a clarifier?
2. a digester?
3. an aeration tank?
3-33
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3,9 ADVANCED METHODS OF TREATING WASTEWATER
The treatment processes described so far in this chapter are
considered conventional treatment processes. As our population
grows and industry expands, more effective treatment processes
will be required. Advanced methods of waste treatment may
follow conventional processes, or they may be used instead of
these processes. Sometimes advanced methods of waste treat-
ment are called tertiary (TER-she-AIR-ee) treatment because
they frequently follow secondary treatment. Advanced methods
of waste treatment include coagulation-sedimentation (used in
water treatment plants), adsorption, and electrodialysis.
Other new treatment processes that may be used in the future
include reverse osmosis, chemical oxidation, and the use of
polymers.
Advanced methods of treatment are used to reduce the nutrient
content (nitrates and phosphates) of wastewater to prevent
blooms of algae in lakes, reservoirs, or streams. Carbon
filters are used to reduce the last traces of organic materials.
In some parts of the arid west advanced methods are used to
enable the use of the plant effluent for recreational reser-
voirs.
QUESTION
3.9A If wastewater from a secondary treatment
plant were coagulated with alum or lime
and settled in a clarifier, would this be
considered a method of advanced waste
treatment?
3-34
-------
3.10 DISINFECTION
Although the settling process and biological processes remove
a great number of organisms from the wastewater flow, there
remain many thousands of bacteria in every milliliter of
wastewater leaving the secondary clarifier. If there are
human wastes in the water, it is possible that some of the
bacteria are pathogenic, or harmful to man. Therefore,
if the treated wastewater is discharged to a receiving water
that is used for a drinking water supply or swimming or wading,
the water pollution control agency or health department will
usually require disinfection of the effluent prior to discharge.
Disinfection is usually defined as the killing of pathogenic
organisms. The killing of all organisms is called sterilization.
Sterilization is not accomplished in treatment plants as the
final effluent after disinfection always contains some living
organisms due to the inefficiency of the killing process.
Disinfection can be accomplished by almost any process that
will create a harsh environment for the organisms. Strong
light, heat, oxidizing chemicals, acids, alkalies, poisons,
and many other substances will disinfect. Most disinfection
in wastewater treatment plants is accomplished by chlorine,
which is a strong oxidizing chemical.
Chlorine gas is used in most treatment plants although some
of the smaller plants use a liquid chlorine solution as their
source. The dangers in using chlorine gas, however, have
prompted some of the larger plants to switch to hypochlorite
solution (bleach) even though it is more expensive.
Chlorine gas is withdrawn from pressurized cylinders containing
liquid chlorine and mixed with water or treated wastewater to
make up a strong chlorine solution. Liquid hypochlorite solution
can be used directly. The strong chlorine solution is then mixed
with the effluent from the secondary clarifier. The effluent
is then directed to a chlorine contact basin. The basin can be
any size or shape, but better results are obtained if the tank
is long and narrow. This shape prevents rapid movement or short
circuiting through the tank. Square or rectangular tanks can
be baffled to achieve this effect (fig. 3.22). Tanks are usually
designed to provide approximately 20 to 30 minutes theoretical
contact time, although the trend is to longer times. If the
plant's outfall line is of sufficient length, it may function as
an excellent contact chamber since short circuiting will not occur.
3-35
-------
CHLORINE CONTACT BASIN
Chlorine solution feed hot*
(Courtesy Water Pollution Control Federation)
Fig. 3.22 Chlorine contact basin
3-36
-------
QUESTIONS
3.10A Does disinfection usually kill all
organisms in the plant effluent?
3.10B Which would provide better chlorine
contact, a 10,000-gallon cubical tank
or a length of 10-inch pipe flowing
full and containing the same volume as
the cubical tank?
3-37
-------
3.11 ADDITIONAL READING
Some books you can read to obtain further information on
the treatment plant and the various processes involved are:
a. MOP 11
b. New York Manual
c. Texas Manual
d. Sewage Treatment Practices, by Bloodgood
e. Babbitt, Harold E., and E. Robert Bauman, Sewerage and
Sewage Treatment, John Wiley and Sons, New York, Eighth
Edition, 1958. $10.75.
f. Summary Report, Advanced^ Waste Treatment, July 1964-
July 1967, U. S. Department of Interior, FWPCA, WP-20-
AWTR-19. Available from the Publications Office, Ohio
Basin Region, Environmental Protection Agency, Water
Quality Office, Cincinnati, Ohio 45226.
g. Santee Recreation Proceedings, Santee, California, U.S.
Department of Interior, FWPCA, WP-20-7 (1967). Available
from Publications Office source given in (f) above.
h. A Primer on Waste Water Treatment, prepared by the Office
of Public Information, Federal Water Quality Administration,
CWA-12, October 1969. Available from Superintendent of
Documents, U.S. Government Printing Office, Washington,
D.C. 20402. Price $0.55.
3-38
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SUGGESTED ANSWERS
Chapter 3. Wastewater Facilities
3,1A The operator should know the origin of wastes reaching
his plant, the time it takes, and how the wastes are
transported (flow by gravity or by gravity and pumped).
Such knowledge will help him to spot troubles and take
corrective action.
3.IB Sanitary, storm, combined.
3.1C If the flowtime to reach the plant is very long, hydro-
gen sulfide gas may develop which can cause corrosion
damage to concrete in the transportation system and in
the plant. Undesirable odors develop, and solids are
difficult to settle too.
3.ID Flows are sometimes bypassed during storms because a
plant does not have the capacity to handle the additional
wastewater.
3.3A Grit should be removed early in the treatment process
because it is abrasive and will wear out pumps and
other equipment.
3.3B Grit removed from the wastewater is usually buried to
avoid causing a nuisance.
3.4A Weirs are not frequently used to measure influent flows
because solids may collect behind the weir causing
odors and causing flow measurements to be off.
3.4B Parshall Flumes are widely used for measuring waste-
water flow because they have no obstructions.
3.5A "Flights" in rectangular tanks move scum along the
surface to a scum trough and push sludge along the
bottom to a hopper for removal to the sludge handling
facility. "Plows" scrape sludge along the bottom of
circular tanks to a hopper for removal.
3.5B Sludge and scum are usually pumped to the sludge handling
facilities such as a digester. Scum should be burned
or buried if possible.
3-39
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3.6A No. If the media were packed together, air could
not circulate and the organisms on the media would
not get enough oxygen.
3.6B A secondary clarifier is needed after a trickling
filter or aeration tank to allow organisms in the
treated wastewater to be removed by settling.
3.6C Aeration tank or waste sludge handling facilities.
Waste activated sludge could be pumped to either of
the two places listed.
3.7A (1) a group that eats organic sludge to form organic
acids and carbon dioxide gas (acid formers); and
(2) a group that breaks down the organic acids into
simpler compounds and forms methane and carbon dioxide
gas (gas formers).
3.7B Digesters are mixed to bring food and organisms together
and prevent the formation of a scum blanket.
3.7C Digested sludge may be disposed of by using sand drying
beds, centrifuges, vacuum filters, or lagoons. Ulti-
mately the dried sludge may be used as a soil conditioner
or it may be buried.
3.8A A facultative pond acts like a clarifier by allowing
solids to settle to its bottom, a digester because
solids on the bottom are decomposed by anaerobic
bacteria, and an aeration tank because of the action
of aerobic bacteria in the upper layer of the pond.
3.9A Yes.
3.10A No.
3.10B The pipe would provide better chlorine contact because
water cannot short-circuit (take a short route) through
a pipe, but it might not move evenly through a tank and
thus some of the water would have a shorter contact time.
3-40
-------
OBJECTIVE TEST
Chapter 3. Wastewater Facilities
Please mark correct answers in the proper columns on the IBM
answer sheet, as directed at the end of Chapter 1. Return
your answer sheet to your Project Director.
3.1 Name three different types of sewers.
1. Sanitary, Pipes, Storm
2. Sanitary, Storm, Conventional
3. Sanitary, Storm, Combined
4. Sanitary, Storm, Groundwater
5. Conventional, Surface, Combined
3.2 Combined sewers (1. are) or (2. are not] a problem to
treatment plant operators.
3.3 Tne following are biological treatment processes.
1. Trickling Filters
2. Grit Removal
3. Digesters
4. Ponds
5. Shredders
3.4 The purpose of screening is:
1. Thin the Wastewater
2. Remove Large Objects and Debris
3. Grade the Solids into Different Sizes
4. Protect Public Health
3.5 Flow measurements are important because they are used to:
1. Determine Loading on Units
2. Determine Treatment Efficiency
3. Adjust Pumping Rates
4. Determine Cl^ Rates
5. Determine if a Plant is Handling its Design Capacity
3.6 The solids settled in a clarifier are called:
1. Dissolved Solids
2. Colloidal Solids
3. Emulsions
4. Sludge
5. Scum
3-41
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3.7 The trickling filter (1. does) or (2. does not) remove
solids by a filtering action.
3.8 Why is the digester gas mixed with air dangerous?
1. It will Explode
2. It Stinks
3. It Kills Grass
3.9 (1. Disinfection) or (2. Sterilization) is usually
defined as the killing of pathogenic organisms, and
3.10 the killing of all organisms is called (1. disinfection)
or (2. sterilization).
3.11 Ponds are capable of reducing:
1. Land Area and Cost
2. Mosquitoes and Weeds
3. BOD and Bacteria
4. Odors and Algae
5. None of these
Please write time required to work lesson on your answer sheet.
3-42
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CHAPTER 4
RACKS, SCREENS, COMMINUTORS, AND GRIT REMOVAL
by
Larry Bristow
-------
PRE-TEST
Chapter 4. Racks, Screens, Coiruninutors, and Grit Removal
The objective of the
Pre-Test is to indicate
to you the important
topics in this chapter,
as well as to indicate
how well the material
was presented to you.
It is okay if you don't
know many of the answers.
Please write your name
and mark the correct
answers on the IBM
answer sheet as directed
at the end of Chapter 1.
Return the answer sheet
to your Project Director,
An operator must always wash his hands before eating or
smoking to prevent becoming infected with a water-borne
disease.
1. True
2. False
The following items may be found in a treatment- plant-
influent.
1.
2.
3.
4.
5.
Cans
Clothes
Toys
Rocks
Eggshells
3. Detritus is a common name for skimmings.
1.
2.
True
False
P-l
-------
5, "''hat should be done first if a probler:. develops
in a mechanically cleaned screen?
I, Reach in with your hand and fix the equipment.
2, AttempIt to fix the screen with the proper tools.
3. Look at screen and identify problem.
4. Turn off the electrical power to the screen.
5. Find someone to help in case you get into trouble,
6. The methods used to dispose of screenings include:
1. Dumping into nearby river
28 Incineration
3, Shredding or Grinding
4. Selling for hog food
5. Burial
7. Grit is composed oft
1. Grease
2, Sand
3« Rubber Goods
4C Eggshells
5. Wood
80 A stick travels 30 feet in 20 seconds in a grit
chamber* What is the flow velocity in the grit
chamber?
1. 0.5 ft/sec
2, 0,67 ft/sec
3. 1.0 ft/sec
4. 1.5 ft/sec
5, 2.0 ft/sec
-------
TABLE OF CONTENTS
Chapter 4. Racks, Screens, Comminutors, and Grit Removal
Page
GLOSSARY i
4_.^ Caution 4-1
4.1 Introduction to Pretreatment 4-3
4.2 Screens and Racks 4-6
4.20 Manually Cleaned Bar Screens 4-6
4.21 Mechanically Cleaned Screens 4-8
4.3 Disposal of Screenings 4-9
4.4 Comminution 4-12
£.5_ Grit Removal 4-18
4.6 Grit Chambers 4-18
4V_7_ Quantities of Grit 4-28
4.8 Grit Washing 4-28
4.9 Preaeration 4-30
4.10 Additional reading 4-30
-------
GLOSSARY
Chapter 4. Racks, Screens, Comminutors, and Grit Removal
Aerobic Decomposition (AIR-0-bick): Decomposition and decay of
organic material in the presence of free or dissolved oxygen.
Anaerobic Decomposition (AN-air-0-bick): Decomposition and
decay of" organic material in an environment containing no "free"
or dissolved oxygen.
Clarifier (KLAIR-i-fire) (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.
Comminutor (com-min-00-ter): A device used to reduce the size
of the solid chunks in wastewater by shredding (comminuting).
The shredding action can be visualized if you imagine many
scissors cutting or hammering to shreds all the large influent
solids material.
Decomposition, Decay; Generally aerobic processes that convert
unstable materials into more stable forms by chemical or bio-
logical action. Waste treatment encourages decay in a controlled
situation in order that the material may be disposed of in a
stable form. When organic matter decays under anaerobic conditions
(putrefaction), undesirable odors are produced. In aerobic
processes, the odors are much less objectionable than those
produced by anaerobic decomposition.
Detritus (die-TRY-tus): The heavy, coarse material carried by
wastewater.
Digester (die-JEST-er): A tank in which sludge is placed to allow
sludge digestion to occur. Digestion may occur under anaerobic
(more common) or aerobic conditions.
Dissolved Oxygen: Atmospheric oxygen dissolved in water or
wastewater, usually abbreviated DO.
Effluent (EF-lu-ent) : Wastewater or other liquid—raw, partially
or completely treated—flowing from a basin, treatment process,
or treatment plant.
-------
Grit: The heavy mineral material present in wastewater, such as
sand, gravel, cinders, and eggshells.
Grit Removal: Grit removal is accomplished by providing an
enlarged channel which causes the velocity of the flowing waste-
water to be reduced and allows the heavier grit to settle to
the bottom of the channel where it can be removed.
Head Loss; "Head" is a common term used
in discussing pumps. It is a way of
expressing pressure in terms of the
height of a vertical column of water.
In the sketch, the head loss is the
height to which the water must build up
until there is sufficient pressure to
force that particular amount of water
through the slots in the comminutor drum.
Influent (IN-flu-ent) : Wastewater or other liquid—raw or
partially treated--flowing into a reservoir, basin, treatment
process, or treatment plant.
Inorganic Material: Material such as sand, salt, iron, calcium,
and other mineral materials which are not converted in large
quantities by organism action. Inorganic materials are chemical
substances of mineral origin and may contain carbon and oxygen,
whereas organic materials are chemical substances of animal or
vegetable origin and contain mainly carbon and hydrogen along
with other elements.
Organic Material; Material which comes from animal or vegetable
sources. Organic material generally can be consumed by bacteria
and other small organisms. Inorganic materials are chemical
substances of mineral origin and may contain carbon and oxygen,
whereas organic materials contain mainly carbon and hydrogen
along with other elements.
Preaeration: A preparatory treatment of wastewater consisting
of aeration to freshen the wastewater, remove gases, add oxygen,
promote flotation of grease, and aid coagulation.
Pretreatment: Use of racks, screens, comminutors, and grit
removal devices to remove metal, rocks, sand, eggshells, and
similar materials which may hinder operation of a treatment plant.
Putrefaction (PU-tree-FACK-shun): Biological decomposition of
organic matter with the production of ill-smelling products
associated with anaerobic conditions.
Putrescible (pu-TRES-sib-bull): Putrescible material will de-
compose under anaerobic conditions and produce nuisance odors.
11
-------
Rack: Parallel metal bars or rods evenly spaced and in
the influent channel that remove rags, rocks, and cans.
Raw Wastewater: Plant influent or wastewater before treatment.
Screen: A device with openings generally uniformly sized to
retain or remove suspended or floating objects in wastewater
larger than the openings. A screen may consist of bars, rods,
wires, gratings, wire mesh, or perforated plates.
Septic (SEP-tick): A condition produced by the growth of anaerobic
organisms. If severe, the wastewater turns black, giving off foul
odors and creating a heavy oxygen demand.
Sludge (sluj): The settleable solids separated from liquids,
during processing or deposits on bottoms of streams or other
bodies of water.
Sludge Digestion: A process by which organic matter in sludge is
gasified, liquefied, mineralized, or converted to a more stable
form by anaerobic (more common) or aerobic organisms.
Weir, Proportional (weer): A specially shaped weir in which the
flow through the weir is directly proportional to the head.
111
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CHAPTER 4. RACKS, SCREENS, COMMINUTORS, AND GRIT REMOVAL
4.0 CAUTION
Many wastewater treatment plant operators have been seriously
injured due to unnecessary accidents. According to a survey
by the Water Pollution Control Federation in 1967, the waste-
water treatment and pollution control industry has a higher
accident rate than any other industry reporting to the National
Safety Council. Working in a wastewater treatment plant is
not necessarily more dangerous than working in other industries,
The poor record of the past may have been caused by operators
not being aware of unsafe conditions, not immediately correct-
ing these conditions when they became obvious, and not knowing
safe procedures.
There are many potential safety hazards around a wastewater
treatment plant. Accidents can be reduced by thinking safety.
The operator should protect himself from injury by maintaining
firm footing, keeping walk areas clear, immediately cleaning up
spills, and shutting off the electrical power before working on
equipment.
You must take adequate precautions to prevent becoming infected
with water-borne diseases such as dysentery or typhoid. At any
given moment in time, some people in your community are ill; and
disease organisms and viruses from these people are in the
wastewater reaching your plant. The operator who cleans equip-
ment such as pumps, bar screens, and grit chambers often must
place his hands in raw wastewater. Also, the tools used to
work on equipment frequently become contaminated. Good personal
hygiene must be observed by^ all operators at all times.
Always wash your hands thoroughly before eating or smoking.
4-1
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A good practice is to change work clothing before going home.
Any clothing that has been worn at the wastewater treatment
plant must be laundered separately from the family wash.
QUESTIONS
TRUE OR FALSE:
4.0A The wastewater and pollution control industry
in 1967 had an accident rate higher than any
other industry reporting to the National Safety
Council.
4.OB Electrical power must always be shut off before
working on equipment.
4.0C An operator should always wash his hands
thoroughly before eating or smoking.
4-2
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4.1 INTRODUCTION TO PRETREATMENT
In various ways, a little or a lot of almost everything finds
its way into sewers and ends up at the wastewater treatment
plant. Cans, bottles, pieces of scrap metal, sticks, rocks,
bricks, plastic toys, plastic lids, caps from toothpaste tubes,
towels and other rags, sand--all are found in the plant
influent.l
These materials are troublesome in various ways. Pieces of
metal, rocks, and similar items will cause pipes to plug, may
damage or plug pumps, or jam sludge collector mechanisms in
settling tanks (clarifiers).2 Sand, eggshells, and similar
materials (grit) can plug pipes, cause excessive wear in pumps,
and use up valuable space in the sludge digesters.3
If a buried or otherwise inaccessible pipe is plugged, or a
sludge collector mechanism jams, or a critical pump is put out
of commission, serious consequences can result. Reduced plant
efficiency allows a heavy pollutional load on the receiving
waters, causing health hazards to downstream water users, sludge
deposits in stream or lake (with resultant odors and unsightliness),
and sometimes causing the death of fish and other aquatic life.
Also, a good deal of hard (sometimes rather unpleasant) work is
involved, and usually there are heavy (and unbudgeted) expenses.
With these things in nine!, it is evident that an important part
of a wastewater treatment plant is the equipment used to remove
the rocks and other materials as early as possible. These items
of equipment are screens, racks, comminutors, and grit removal
devices and are called pretreatment facilities. See Fig. 4.1 for
location of these processes in a typical plant.
1 Influent (IN-flu-ent) . Wastewater or other liquid—raw or
partly treated—flowing into a reservoir, basin, treatment
process, or treatment plant.
2 Clarifier (KLAIR-i-fire) (settling tank, sedimentation basin)
A tank or basin in which wastewater is held for a period of
time so that the heavier solids settle to the bottom and the
lighter material will float to the water surface.
3 Digester (die-JEST-er). A tank in which sludge is placed to
allow sludge digestion to occur. Digestion may occur under
anaerobic (more common) or aerobic conditions.
4-3
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FUNCTION
AMP
REMOVE ROC&.KOOTS
ANt?
I
PAV4ICAL
Fig. 4.1 Flow diagram of typical plant
4-4
-------
QUESTIONS
4.1A The following items nay be found in a treatment
plant influent:
a. Cans
b. Toys
c. Rubber Goods
d. Pieces of Wood
e. All of These
4.IB What items of equipment are used to remove rocks,
pieces of wood, metal, and rags from wastewater?
4.1C Why should coarse material (rocks, boards, metal,
etc.) be removed at the plant entrance?
4-5
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4.2 SCREENS AND RACKS
Parallel bars may be placed at an angle in a channel in such
a manner that the wastewater will flow through the bars, but
the large solids will be caught on the bars. These bars are
commonly called racks when the spacing between them is 3" to
4" or more. When the spacing is about 1" to 2", they are
usually called bar screens.
4.20 Manually Cleaned Bar Screens
Manually cleaned bar screens (Fig. 4.2) require frequent
attention. As debris collects on the screen, it blocks the
channel, causing the wastewater to back up into the sewer.
This, in turn, causes organic materials^ to settle out;
the dissolved oxygen5 is depleted; and septic6 conditions
develop",1 producing hydrogen sulfide which causes a rotten egg
odor and is corrosive to concrete, metal, and paint. If
cleaning of the screens is infrequent, the sudden rush (when
they do get cleaned) of septic wastewater creates a sudden
"shock" load on the plant, sometimes resulting in a poor
quality plant effluent.7
4 Organic Material. Material which comes from animal or
vegetable sources. Organic material generally can be
consumed by bacteria and other small organisms. Inorganic
materials are chemical substances of mineral origin and
may contain carbon and oxygen, whereas organic materials
contain mainly carbon and hydrogen along with other elements,
5 Dissolved Oxygen. Atmospheric oxygen dissolved in water
or wastewater, usually abbreviated DO.
6 Septic (SEP-tick). Wastewater devoid of dissolved oxygen.
If severe, the wastewater turns black, giving off foul
odors and creating a large oxygen demand.
7 Effluent (EF-lu-ent). Wastewater or other liquid—raw,
partially or completely treated—flowing from a basin,
treatment process, or treatment plant. ——
4-6
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TROUGH
Fig. 4.2 Manually cleaned bar screen
ELEVATOR MECHANISM
Fig. 4.3 Mechanically cleaned bar screen
4-7
-------
Cleaning of bar screens is accomplished with a rake with tines
(prongs) which will fit between the bars. Extreme caution
should be taken when raking the screen--footing' may' be poor
due to the water and grease underfoot, lack of enough room to stand.
location of the receptacle for the debris, etc. You should look
this area over carefully to spot hazards and take corrective action.
Good housekeeping, a guard rail, a hanger or other storage for
the rake, good footing, etc. will greatly reduce the possibility
of injury.
4.21 Mechanically Cleaned Screens
Mechanically cleaned screens (Fig. 4.3) overcome the problem of
wastewater backing up and greatly reduce the time required to
take care of this part of your plant. There are various types
of mechanisms in use, the more common being traveling rakes
which bring the debris up out of the channel and into hoppers
or other receptacles. You should keep these units well lubricated
and adjusted. Follow the manufacturer's recommendations carefully.
A few minutes spent in proper maintenance procedures can save hours
or days of trouble and help to keep the plant operating efficiently.
Occasionally some debris will be present which the equipment
cannot remove. Periodic checks should be made so that these
materials can be removed by hand. To determine if some material
is stuck in the screen, divert the flow through another channel
or "feel" across the screen with a rake or similar device.
4-8
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Always shut the unit off first. Never reach into the operating range
of machinery while it is running. Slow-moving equipment is especially
hazardous. Because it moves slowly, it does not appear dangerous.
However, most geard-down machinery is so powerful that it can crush
almost-any obstruction. A HUMAN HAND, FOR INSTANCE, OFFERS LITTLE
RESISTANCE TO THIS TYPE OF EQUIPMENT.
Various other mechanical methods are in use, involving actual coarse
screens or perforated sheet metal. These units are automatically
cleaned with scrapers, rotating brushes, water sprays, or air jets.
The screens may be in the form of belts, discs, or drums set in a
channel so that the wastewater flows through the submerged portion,
with the collected debris being removed as it passes the brushes or
sprays.
4.3 DISPOSAL OF SCREENINGS
The material removed from the screens is very offensive and hazardous
It produces obnoxious odors and draws rats and flies. Burial,
incineration, and shredding or grinding are three common methods
of disposal. If the screenings are buried, at least six inches
of earth cover must be provided immediately. The final earth
cover must be deep enough to prevent flies from reaching the
screenings through cracks caused by settling. At small plants with
manually cleaned bar screens, an enterprising operator can make
a "press" from a piece of steel pipe or casing, using a heavy screw,
rack and pinion, or even an automobile jack to provide pressure, to
dewater the screenings before disposal. The practice of using
grinders (shredders, disintegrators, etc.) to cut up screenings and
return them to the effluent can impose a great load on following
treatment processes.
4-9
-------
Depending on plant location and surroundings, you may find
it necessary to plan ahead to find areas required for disposal
of screenings. If burial is used, you should estimate how long
a certain area can be used before you must find additional
space for disposal. The disposal site volume divided by the
daily volume of screenings produced will tell you how many
days the site will last. For example, assume your plant has
a flow of two million gallons per day (MGD) and that over a
two-week period you remove an average of 50 gallons of screen-
ings daily. This figures out to four cubic feet (cu ft) per
day. You bury the screenings each day in a pit which you esti-
mate will hold 15 cubic yards of screenings in addition to
the soil used to cover up the screenings.
(1 cu ft = about 7.5 gallons for practical purposes)
Thus:
Volume, cu ft/day _ Volume, gal/day
or Filling Rate " 7.5 gal/cu ft
50 gal/day
7.5 gal/cu ft
= 4 cu ft/day
You should convert gallons to cubic feet (ft3 or cu ft) or
cubic yards (yd3, cu yd) because earth work is figured on this
basis. With this information, you are now prepared to estimate
how long before the pit will be filled up.
First, convert the 15 cu yd (pit) capacity to cu ft:
Pit Capacity, cu ft = Capacity, cu yd x 27 ~
cu yd
ir J IT CU ft 27
= 15 cu yd x 27
cu yd xl5
135
27
= 405 cu ft 405
4-10
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Second, divide the pit capacity by the daily volume of screen-
ings to find time before pit is full:
Time, days = Pit Capacity, cu ft
Filling Rate, cu ft/day
405 cu ft
4 cu ft/day
About 101 days
Thus you have about 101 days from the time you begin to bury
screenings in the pit until you will have to dig another.
You should keep daily records of the volume of screenings
buried to be sure it stays about the same. If it increases
very much, it could be due to an increase in daily wastewater
flow or perhaps some unnecessary disposal of rags or other
material into the sewer. You may get anywhere from 0.5 to
12 cubic feet of screenings per million gallons of wastewater
flow, but it should stay fairly constant for your plant
unless something unusual is happening.
You can check on the daily flow in MGD, or during any time
period, by reading your flow totalizer. The totalizer records
the total flow through the plant. If you record the totalizer
reading at the start and at the end of any time period,
the difference is the total flow for that time period.
QUESTIONS
4.2A Manually cleaned bar screens should be cleaned frequently
to prevent:
a. the screen from breaking
b. septic conditions from developing upstream
c. a shock load on the plant when eventually cleaned
d. formation of hydrogen sulfide, which causes rotten
egg odors and corrosion of concrete and paints
e. all of these
4.2B What safety precautions should be taken when cleaning a
bar screen?
4.2C What should be done first if a problem develops in a
mechanically cleaned screen?
4.3A How can screenings be disposed of?
4.3B A plant receives a flow of 4.4 million gallons (MG) on
a certain day. The day's screenings are calculated to be
11 cubic feet. How many cubic feet of screenings were
removed per MG of flow?
4-11
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4.4 COMMINUTION (com-min-00-shun)
Comminutors are devices which act as a cutter and a screen.
Their purpose is to shred (comminute) the solids and leave
them in the wastewater. This overcomes problems of screen-
ings disposal. As with screens, they are mounted in a
"channel, and the wastewater flows through them. The rags,
etc., are shredded by cutters (teeth) until they can pass
through the openings. Pieces of wood and plastic are rejected
and must be removed by hand. Most of these units have a
shallow pit in front of them to catch rocks and scrap metal.
The flow to the comminutor should be shut off periodically
and the debris removed from the trap. The frequency of
checking the trap can be determined from experience. However,
it is not wise to allow more than a few days between checks.
A comminutor consists of a rotating drum with slots for the
wastewater to pass through (Fig. 4.4). Cutting teeth are
mounted in rows on the drum. The teeth pass through cutter
bars or "combs" with very small clearances so that a shearing
action is obtained. The wastewater passes into the vertically
mounted drum through the slots in the drum and flows out the
bottom. A rubber seal, held in place by a bolted-down ring,
prevents leakage under the drum. This seal should be checked
whenever the rock and scrap metal trap is checked.
Some comminutors also have a mercury seal (Fig. 4.5) to keep
water out of the bearings. This is because these units are
designed so that, at their rated capacity, the top of the
drum will be under several inches of water. This head loss8
will be specified in the manufacturer's instructions. The
mercury seal should be checked annually or after a particularly
heavy flow. Drain the mercury; weigh it (the amount of mercury
will be specified by weight); and if it is dirty, strain it
through some heavy material (such as denim or chamois) before
putting it back in the comminutor. (You will probably have to
Head Loss. "Head" is a common term used in discussing
pumps. It is a way of expressing pressure in terms of
the height of vertical column of water. In this case,
the head loss is the height to which the water must build
up in front of the drum until there is sufficient pressure
to force that particular amount of water through the slots
(Fig. 4.4).
4-12
-------
MOTOR
ROTATING CUTTING SCREEN
FLOW
HEAD LOSS
Fig. 4.4 Conuninutor
-------
MERCURY FILLER PLUG
MOTOR
AND
REDUCTION GEARS
SUPPORT STRUCTURE
AND BEARINGS
MERCURY SEAL
MERCURY DRAIN PLUG
FLOW
CUTTER AND SHAFT MOVE
TOGETHER AS UNIT
•STATIONARY CUTTER BAR
Fig. 4.5 Mercury seal in comminutor
4-14
-------
squeeze the mercury through the cloth or, if laboratory equipment
is available, use a suction flask.) Add more mercury if needed.
CAUTIO N
CAUTIOM
Mercury is poisonous. Breathing the fumes can be fatal or cause
loss of hair and teeth. Wash up thoroughly after handling it.
Remove gold rings, etc., from your hands first, as they may end up
coated with mercury. If your ring is thus coated, it will have to
be heated to burn off the mercury. If you must handle or work with
mercury, be sure to work over a large tray in order to catch any
spills. Plenty of fresh air ventilation is an absolute mus t.
There are many variations of the comminutor. One of the more common
ones has the trade name of "barminutor" (Fig. 4.6). This unit con-
sists of a bar screen made of U-shaped bars arid a rotating drum with
teeth and "shear bars". The rotating drum travels up and down the
bar screen. Careful attention must be given to maintaining the oil
level in these machines; otherwise, water may get into the bearings.
Consult the manufacturer's instructions for detailed procedures.
4-15
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Fig. 4.6 Barminutor
4-16
-------
QUESTIONS
4.4A What are the advantages of comminuting machines over
screens?
4.4B When should you check the mercury seal in a comminutor?
4,4C Handling mercury is hazardous because:
a. It is poisonous
b. Breathing fumes may be fatal
c. Breathing fumes may cause loss of hair and teeth
4-17
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4.5 GRIT REMOVAL
Grit (sand, eggshells, cinders, etc.) is the heavier mineral
matter in wastewater which will not decompose or "break down".
It causes excessive wear in pumps. A mixture of grit, tar,
grease and other cementing materials can form a solid mass in
pipes and digesters that will not move by ordinary means.
Consequently, grit should be removed as soon as possible after
reaching the plant.
4.6 GRIT CHAMBERS (Fig. 4.7)
The simplest means of removing grit from the wastewater flow
is to pass it through channels or tanks which allow the velocity
of flow to be reduced to a range of 0.7 to 1.4 ft/sec. The
objective is to allow the grit to settle to the bottom, while
keeping the lighter organic solids moving along to the next
treatment unit. Experience has shown that a flow-through
velocity of one foot per second (ft/sec) is best.
Velocity is controlled by several means. With multiple-
channel installations, the operator may vary the number of
channels (chambers) in service at any one time to maintain a
flow velocity of approximately one ft/sec in the grit chambers.
Other methods involve the use of proportional weirs (Fig. 4.8)
at the outlet for automatic regulation.
WATER
SURFACE
Fig. 4.8 Proportional weir
4-18
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GRIT SETTLING AREA
CENTER WALL
SLIDE GATES
WEIRS (WHEN USED)
GRIT SETTLING AREA
STOP GATES
Insert when
cleaning to
prevent backflow
Fig. 4.7 Grit Chamber
-------
The proportional weir in Fig, 4.8 will tend to decrease the
velocity in the grit chambers when the flows increase because
the exit area will decrease, thus increasing the depth of water
flow in the channel. If the operator wishes to increase the
velocity in a grit chamber, he could use a proportional weir
and turn it over so the exit area increased as the flow in-
creased. This would tend to keep the depth of water flow in
the channel low and cause higher velocities. A barrier with
a variable height at the outlet of the grit chamber can be
used instead of a proportional weir to regulate velocities.
Flow velocities also may be regulated by the shape of the grit
chamber instead of placing devices at the outlet. Some grit
chambers have cross-sectional shapes similar to a proportional
weir. The operator may regulate the velocities in a grit
chamber by using boards to change cross-sectional shape, but
he should seriously consider any maintenance or operational
problems that might develop when trying to keep the grit chamber
clean.
A simple method of estimating the velocity is to place a stick
in the channel and time its travel for a measured distance.
Calculate as follows:
.. ., . _. , Distance traveled, ft
Velocity, ft/sec = - • - ^^~~ - • - ' -
J> Time, sec
Example :
A stick travels 25 feet in 20 seconds.
Solution: 1.25
n- £<. 207 25.00
Velocity, ft/sec » D"tance, ft ' 20
Time, sec
25 ft
20 sec
= 1.25 ft/sec
The actual velocity probably will be slightly higher than your
estimate, but it is a very quick way to check the grit chamber
velocity.
A more accurate method of determining the average velocity in
the grit chamber is to find the cross-sectional area of the
wastewater flowing in the grit chamber and the quantity of
flow (from the flow meter) and calculate as shown in the following
example.
4-20
-------
Example:
Assume your grit chamber is two feet wide. The wastewater is
flowing at a depth of one foot, and the flow meter registers
a flow of 1 MGD. The cross-sectional area of the flow is
(depth, ft x width, ft = 1 ft x 2 ft) = 2 sq ft. The flow
must be converted into cubic measure. We learned that one
cubic foot equals 7.5 gallons. Thus, from calculations below,
1 MGD = 1.55 cu ft/sec (cubic feet per second, cfs):
1 MGD =
(7.5
gal
cu ft
(1,000,000
->/. nr
day
gal -,
day
fn mm
60 -r— x
hr
60^)
mm
Using this new conversion factor:
, ,, , ... , Flow Rate, cu ft/sec
Average Velocity, ft/sec = Area, Sq ft
= 1.55 ft3/sec
2 ft2
=0.77 ft/sec
To obtain this answer, we converted the flow from MGD to ft3/sec
and divided the flow (1.55 cu ft/sec) by the cross sectional area
of the wastewater in the channel (2 sq ft).
Since we have checked the velocity, we should now determine if
the length of the channel is appropriate for our flow conditions.
All particles settle at different rates based on their size and
weight. Most grit chambers are designed to remove 0.2 mm (milli-
meter) size sand and all other heavier material. Experiments
have shown this size particle will settle downward at about
0.075 ft/sec. This means that if wastewater is flowing in a
channel at a depth of one foot and a particle of 0.2 mm is
introduced at the surface it will take:
Settling Time, sec =
Depth, ft
Settling Rate, ft/sec
1 ft
0.075 ft/sec
= 13.3 seconds to settle
4-21
-------
PART
FLOW VLOC I TY
c/o
I£ this waste were flowing at one foot per second, it would
travel for 13.3 seconds, or a distance of 13.3 feet, before
the particle reached the channel bottom. If the waste were
flowing at a depth of three feet in the channel, it would take
13.3 seconds/ft x 3 ft = 39.9 seconds or 39.9 feet before the
particle reached the bottom. Therefore, the required length
of any grit chamber can be checked by using the formula:
, ,, _ (depth of chamber, ft) (flow velocity, ft/sec)
Lengtn, tt - (Settling Rate, ft/sec)
= (settling time, sec) (flow velocity, ft/sec)
and for 0.2 mm sand and a flow velocity of 1 ft/sec:
Length ft = (depth, ft) (1.0 ft/sec)
Lengtn, tt (0.075 ft/sec)
1.0 x depth, ft
0.075
= 13.3 x depth, ft
In case of dead spots (where organic materials settle out and
become putrescrible9), a deflector (Fig. 4.9) installed at one
side may cure the trouble. Be sure you don't create a new dead
spot. Also, certain trouble spots could be filled in with
concrete.
9 Putrescible (pu-TRES-sib-bull). Putrescible material will
decompose under anaerobic conditions and produce nuisance
odors.
4-22
-------
DEFLECTORS
Fig. 4.9 Deflectors installed in a grit chamber
-------
Removal of grit ranges from use of a scoop shovel to various
types of collectors and conveyors. For hand-cleaned chambers,
the frequency of cleaning is determined by experience. If
the channel can be removed from service during the cleaning
operation, the job is made easier, and no grit is washed into
the plant.
Since there is always a small amount of organic matter in the
grit chamber, disposal of grit should be treated the same as
screenings. Burial is the most satisfactory disposal method.
Failure to quickly cover grit results in odors and attracts
flies and rats.
Cleaning grit chambers manually can be quite hazardous. Take
precautions against
slipping and back
strain. Beware of
dangerous gases wTTen
working" in covered
grit chambers.
There are many types
of mechanical grit
collector mechanisms.
Common ones are chain-
driven scrapers
(called "flights")
(Fig. 4.10) that are
moved slowly along
the bottom and up
an incline out of
the water to a
hopper, or along
the bottom to an
underwater trough
where a screw con-
veyor lifts the grit to a storage hopper or truck. Some
designs use conveyor belts with buckets attached.
An aerated grit chamber is actually a tank with a sloping
bottom and a hopper or trough in the lower end (Fig. 4.11).
Air is injected along the wall of the tank above the trough.
The rolling action of the water in the tank moves the grit
along the bottom to the grit hopper. Grit is removed from
the hopper by a conveyor system.
Aerated grit chambers are most frequently found at activated
sludge plants where there is a readily available air supply,
and the pre-aeration helps to "freshen" the wastewater. The
older wastewater becomes the more difficult it is to treat. A
freshening process tends to make later processes more effective.
4-24
-------
Fig. 4.10 Chain-driven scrapers (flights)
(Courtesy Jeffrey Mfg. Co,)
A grit chamber with a slower flow velocity than recommended may
allow appreciable organic matter to settle out with the grit.
This mixture of grit and organic matter is called detritus.10
In some plants grit chambers are called detritus tanks.Organic
matter may be separated from the grit by blowing air" through or
washing the detritus to resuspend the organic matter. Centri-
fuges also are used to separate grit from sludge or organic matter
from grit.
1 Detritus (de-TRI-tus).
by wastewater.
The heavy, coarse material carried
4-25
-------
WATER SURFACE
o o o
a
o
O 0/0
I
K)
o\
AIR
0 °
0 ° o
0 0
o
0
OOP
*"•.•.W:/
^ H * * /
r / i ^ . r-1 /
3^-<-
GRIT HOPPER AND COLLECTOR MECHANISM
Fig. 4.11 Aerated grit chamber
-------
: QUESTIONS
4.5A Grit is composed mostly of which of the following substances?
a. Grease
b. Sand
c. Rubber Goods
d. Eggshells
e. Wood
4.5B Why bother to remove grit?
4.6A How can you control the velocity in a grit chamber in order
to maintain velocities within a range of approximately 0.7
to 1.4 fps?
4.6B A stick travels 20 feet in 40 seconds in a grit chamber.
a. What is the velocity in the chamber?
b. What corrective action should be taken, if any?
4.6C What is most hazardous about manually cleaning a grit
chamber?
4.6D Assume you wish to calculate the velocity in the grit
chamber at your plant's peak flow. Examining the flow
charts, you determine that peak flows are usually about
2.75 MGD. The grit chamber is three feet wide, and
the flow depth is 17 inches at peak flow. What is the
velocity in the grit chamber under these conditions?
4-27
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4.7 QUANTITIES OF GRIT
Plants having well-constructed separate wastewater collection
systems can usually expect to average 1 to 4 cu ft of grit
per million gallons. These quantities have been rising in
recent years due to household garbage grinders. They can
also be expected to increase during storm periods.
Plants receiving waste from combined collection systems can
expect to average 4 to 15 cu ft of grit per million gallons
with peaks during storm periods many times higher. Grit
collected during storm periods has been reported at over
500 cu ft per million gallons, probably the result of flow
from broken sewers or open channels.
Records of grit quantities should be kept in the same manner
as for screenings.
QUESTION
4.7A Your plant has an average flow of 2.0 MGD.
An average of 4 cu ft of grit is removed
each day. How many cu ft of grit per MG
of flow are removed?
4.8 GRIT WASHING
In some cases it is necessary or desirable to use grit as
fill material. Since a small amount of organic material
settles out with the sand, etc., it becomes necessary to
"wash" the grit, There are a number of devices built for
this purpose. Most use water to wash the grit as it is
being removed from the grit chamber (Fig. 4.12). In aerated
grit chambers, the grit is ordinarily free enough of organics
that it may be considered "washed". Chapter 5 of the Water
Pollution Control Federation's Manual of Practice No. 11
has additional information and should be read carefully by
the operator.
4-28
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Ji.
I
AUX. WASH WATER
(USUALLY WASTEWATER)
MOTOR ^
GRIT FEhU
SCREW-TYPE
IMPELLER
WATER AND ORGANICS OUTLET
TO HOPPER, TRUCK, ETC.
Fig. 4.12 Grit washer
-------
QUESTION
4.8A Why is it sometimes necessary or desirable
to "wash" grit?
4.9 PREAERATION
Preaeration is a wastewater treatment process used to freshen
wastewater, remove gases, add oxygen, promote flotation of
grease, and aid coagularion. The freshening of wastewater
improves the effectiveness of following treatment processes.
The process is usually located before primary sedimentation
(Fig. 4.1). Other processes used to accomplish freshening
include ozonation and prechlorination.
Preaeration consists of aerating wastewater in a channel or
separate tank for 10 to 30 minutes. Aeration may be accomplished
by either mechanical surface aeration units or diffused air
system.11 Air application rates with a diffused air system
normally range from 0.5 to 1.0 cu ft of air per gallon of waste-
water treated.
4.10 ADDITIONAL READING
a. MOP 11, pages 17-24
b. New York Manual, pages 27-29
c. Texas Manual, pages 160-173
d. Sewage Treatment Practices, by Bloodgood,
pages 19-22 and 26-34
11 See Chapter 7, Activated Sludge, for a discussion of
aeration facilities.
4-30
-------
SUGGESTED ANSWERS
Chapter 4. Racks, Screens, Comminutors, and Grit Removal
4.0A True
4.OB True
4.0C True
4.1A (e) All of these.
4.IB Large pieces of material, such as rocks, boards, metal,
and rags, are removed by racks, screens, and grit removal
devices.
4.1C Coarse material must be removed at the plant entrance
to prevent damage to pumps, plugging of pipes, and
filling of digesters.
4.2A (b), (c), and (d). Usually bar screens are very sturdy
and will not collapse under the load from a blockage or
an uncleaned screen.
4.2B Check to make sure that your footing will be secure by
removing any slippery substances such as water and
grease. Be certain there is adequate space to safely
lift the screenings and a receptacle for the screenings
(debris).
4.2C Identify the problem. Shut the machine off before working
on the equipment. Any moving equipment is hazardous,
regardless of its speed.
4.3A Screenings may be disposed of by covering them with a
minimum of six inches of earth or incineration.
4.3B Quantity Removed, _ Volume Removed, cu ft/day
cu ft/MG ~ Average Flow," MGD
_ 11 cu ft/day , A. Vl.;v5
4.4 MGD "•"' "'•*
o O
TT o
= 2.5 cu ft/MG 220
0
4-31
-------
4.4A Advantages of comminuting machines over screens include
the elimination of screenings disposal, flies, and odor
problems. A disadvantage is that plastic and wood may
be rejected and must be removed by hand.
4.4B The mercury seal in a comminutor should be checked
yearly or after a high water level has been experienced.
If a given high water level has not disrupted the seal,
you know that the unit is safe at least up to that level.
4.4C (a), (b), and (c). Mercury must be handled with caution
at all times.
4.5A (b) and (d). Grit is composed of heavy material
that will settle in the grit chamber at proper flow
velocities.
4.SB Grit must be removed to prevent wear in pumps, plugged
lines, and the occupation of valuable space in digesters.
4.6A (a) Vary the number of channels in service in a
multiple-channel- installation.
(b) Use of proportional weirs.
(c) Lining sides with planks if velocity is too
low. This could occur in a new plant.
You have the right idea if your answer includes possible
adjustments of the cross-sectional area of the flow
channel.
4.6B (a) Velocity = 0.5 ft/sec.
(b) Reduce cross-sectional area.
4.6C Slipping or a back injury. Beware of dangerous gases when
working in a covered grit chamber. Also, there have been
instances of gasoline or similar material leaking into the
sewer and creating a potentially explosive hazard.
4.6D (a) Convert the flow of 2.75 MGD to cu ft/sec.
Flow, 1.55 cu ft/sec
~. , = Flow, MGD x • • • • tir,,v>- • • •
cu ft/sec ' MGD „ _
. *
' * 1.55
= (2.75 MGD)
1.55 cu ft/sec
MGD
lT75~
137 5
275
= 4.3 cu ft/sec 4.2625
4-32
-------
4.6D (b) Convert depth of flow from 17 inches to feet.
17 in
Depth, ft =
12 in/ft
= 1.4 ft
(c) Calculate cross-sectional area of channel.
Area, sq ft = (Depth, ft)(Width, ft)
= (1.4 ft)(3 ft)
= 4.2 sq ft
(d) Calculate velocity.
Average Velocity, _ Flow, cu ft/sec
ft/sec Area, sq ft
4.26 cu ft/sec 4.2/4.2 6
4.2 sq ft —-
0 60
= 1.01, or 1 ft/sec
42
4.7A Grit removals should be recorded as cubic feet of grit
per million gallons of flow.
Answer: 2 cu ft of grit/million gallons
NOTE: Uniform reporting of results is important. Every-
one should use the same units. The operator should obtain
a copy of the Water Pollution Control Federation Manual of
Practice No. 6, "Units of Expression for Wastes and
Waste Treatment", and use the units as recommended. The
Manual can be obtained from the Water Pollution Control
Federation, 3900 Wisconsin Avenue, Washington, D.C, 20016,
for 50<£ for WPCF members and 75
-------
EXPLANATION OF OBJECTIVE AND PRE-TESTS
One of the reasons for the Objective and Pre-Tests is to
evaluate the extent the chapter increased your knowledge of
the subject.
Write your name and answers on the answer sheets and the time
it took you to complete the lesson.
4-34
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 4. Racks, Screens, Comminutors, and Grit Removal
DO NOT USE IBM ANSWER SHEET. Please write your answers in your
notebook.
1. Why should coarse material (rocks, boards, metal, etc.)
be removed at the plant entrance?
2. Why do you think the wastewater treatment and pollution
control industry had a higher accident rate in 1967 than
any other industry reporting to the National Safety Council?
3. What are the advantages of comminutors over screens?
4. What precautions should be taken when cleaning a grit
chamber?
5. How can an operator regulate the velocity in a grit chamber?
6. A stick travels 30 feet in 50 seconds in a grit chamber.
What is the flow velocity in the grit chamber? Please show
your calculations in a neat fashion so someone can help you
if necessary.
7. Calculate the grit removed from a grit chamber in cubic
feet per million gallons if during a 24-hour period the
average flow was 3 MGD and 4.5 cu ft of grit were removed.
4-35
-------
OBJECTIVE TEST
Chapter 4. Racks, Screens, Comminutors, and Grit Removal
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. Return the
answer sheet to your Project Director.
1. An operator must always wash his hands before eating or
smoking to prevent becoming infected with a water-borne
disease.
1. True
2. False
z. The following items may be found in a treatment plant
influent.
1. Cans
2. Clothes
3. Toys
4. Rocks
5. Eggshells
3. Detritus is a common name for skimmings.
1. True
2. False
4. Pretreatment may include a :
1. Bar Screen
2. Grit Chamber
3. Detritus
4. Flow Meter
5. Clarifier
5. What should be done first if a problem develops in a
mechanically cleaned screen?
1. Reach in with your hand and fix the equipment.
2. Attempt to fix the screen with the proper tools.
3. Look at screen and identify problem.
4. Turn off the electrical power to the screen.
5. Find someone to help in case you get into trouble.
4-37
-------
6. The methods used to dispose of screenings include:
1. Dumping into a nearby river
2. Incineration
3. Shredding or Grinding
4. Selling for hog food
5. Burial
7. Grit is composed of:
1. Grease
2. Sand
3. Rubber Goods
4. Eggshells
5. Wood
8. A stick travels 30 feet in 20 seconds in a grit chamber.
What is the flow velocity in the grit chamber?
1. 0.5 ft/sec
2. 0.67 ft/sec
3. 1.0 ft/sec
4. 1.5 ft/sec
5. 2.0 ft/sec
Please write on your IBM answer sheet the total time
required to work this chapter.
4-38
-------
CHAPTER 5
SEDIMENTATION AND FLOTATION
by
Elmer Herr
-------
EXPLANATION OF PRE-TEST
The purpose of the Pre-Test is to indicate to you the items
that are important in this chapter. Do not be disappointed
if you don't know any of the answers.
Please write your name and answers on the IBM answer sheet.
P-i
-------
PRE-TEST
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. There may be
more than one answer to each question.
EXAMPLE
The purpose of detaining water in a sedimentation tank is to:
1. Store for future use
2. Allow solids to settle to the bottom
3. Allow grease to float to the surface
4. Hold until trickling filter is ready
5. Provide chlorine contact time
To answer this question, you should mark on your answer sheet:
EXAMPLE:
' ' 'it '
! ! lift
t i iht
1 ' 'f '
i fe ' ' ' ' '
i fit it f i
tHi it 11
'iff' ' ' ' '
1. Skimmed solids may be disposed of by:
1. Pumping to digester
2. Burying with material from bar screen
3. Incineration
4. Sold for grease and oil content
5. None of these
2. What items should be checked before starting a clarifier?
1. Remove debris from pipes arid tank
2. Lubricate equipment
3. Sample effluent
4. Turn off chlorinator
5. Run a clarity test
3. Generally, pH is significantly affected by a clarifier:
1. True
2. False
P-l
-------
4. An operator can tell if "thin" sludge is being pimped by:
1. The sound of the sludge pump
2. The smell of the sludge
3. The color of the sludge
4. Pressure gauge readings on the suction
and discharge of the pump
5. Visual observation
5. The maintenance program for a properly operating ciarifier
should include:
1. Sample influent
2. Regular inspection
;j. Keep a list of repairs
4. Prompt adjustment or repair when necessary
Lubricate equipment at regular intervals
6. 'Dangerous gases an operator may encounter in and around a
treatment plant include:
1, Hydrogen sulfidc
2. Nitrogen
i. Chlorine
4. Fumes from gasoline
5. Methane
7. U'hat factors influence the settling characteristics of
solids in a ciarifier'.
1. Flow velocity and/or turbulence
2. Temperature
3, Laboratory analyses
4. Short circuiting
5. Detention time
8. If short circuiting occurs in a ciarifier, the operator
should:
1. Check the wiring
2. Identify the cause
3. Change fuses
4. Try installing baffles
5. Restart the pump
9. Plant analysis of samples is a reliable method of measuring
ciarifier efficiency:
1. True
2. False
P-2
-------
10. What are "sloughings"?
1. Troughs
2. Slop
3. Material washed off trickling filter media
4. Waste activated sludge
5. Grit
11. Secondary or final clarifiers are needed to:
1. Increase sludge digestion
2. Allow septic conditions to develop
3. Provide a home for organisms
4. Remove solids from biological processes
5. None of these
12. An Imhoff tank has:
1. Two compartments
2. Sludge scrapers
3. A piping system that allows the flow in the tank
to be reversed from one end to the other end
4. A separate sludge digestion compartment under
the settling area
5. Gas vents
13.
14,
15,
Primary clarifiers are designed to ren.ove colloidal
solids:
1. True
2. False
Estimate the detention time in a 20,000-gallon sedimen-
tation tank if the flow is '0.2 ?'GD. Select the closest
answer.
1.
2.
3.
4.
5.
5 hr
8 hr
0 hr
4 hr
2.8 hr
Estimate the detention time in a sedimentation tank
90 it long, 30 ft wide, and 12 ft deep, if the flow
is 3.0 MGD. Select the closest answer.
1.
2.
3.
4.
5.
1.5 hr
1.8 hr
2.0 hr
2.4 hr
2.8 hr
P-3
-------
TABLE OF CONTENTS
Chapter 5. Sedimentation and Flotation
Page
GLOSSARY i
5.0 Introduction ..... 5-1
5.1 Operation and Maintenance 5-7
5.10 Start-up 5-7
5.11 Daily Operation and Maintenance 5-9
S.2_ Sampling and Laboratory Analysis 5-10
5.20 General 5-10
5.21 Sampling 5-11
5.22 Calculation of Clarifier Efficiency 5-11
5.23 Typical Clarifier Efficiencies 5-12
5.24 Response to Poor Clarifier Performance .... 5-13
5.3 Sludge and Scum Pumping 5-18
5.4 General Maintenance 5-21
5.5 Safety 5-22
5.6 Principles of Operation 5-25
5.60 General 5-25
5.61 Primary Clarifiers 5-25
5.62 Secondary Clarifiers or Final Settling Tanks . 5-37
5;.7 Flotation Processes 5-40
5.8 Tmhoff Tanks 5-43
5^.9 Septic Tanks 5-47
5.10 Additional Reading 5-48
-------
GLOSSARY
Chapter 5. Sedimentation and Flotation
Activated Sludge Process (ACK-ta-VATE-ed sluj): A biological
wastewater treatment pro'cess in which a mixture of wastewater
and activated sludge is aerated and agitated. The activated
sludge is subsequently separated from the treated wastewater
(mixed liquor) by sedimentation, and wasted or returned to the
process as needed.1
Bulking (BULK-ing): Bulking occurs in activated sludge plants
when the sludge becomes too light and will not settle properly.
Coagulants (ko-AGG-you-lents): Chemicals added to destabilize,
aggregate and bind together colloids and emulsions to improve
settleability, filterability, or drainability.
Colloids (KOL-loids): Very small solids (particulate or in-
soluble material) in a finely divided form that remain dispersed
in liquid for a long time due to their small size and electrical
charge.
Density (DEN-sit-tee): The weight per unit volume of any
substance. The density of water (at 4°C) is 1.0 gram per
cubic centimeter (gms/cc) or about 62.4 Ibs per cubic foot.
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.
Emulsion (e-MULL-shun): A liquid mixture of two or more liquid
substances not normally dissolved in one another, but one liquit
held in suspension in the other.
Flights; Scraper boards, made from redwood or other rot-
resistant woods, used to collect and move settled sludge or
floating scum.
See Chapter 7, Activated Sludge.
-------
Flocculated (FLOCK-you-lay-ted): An action resulting in the gathering
of fine particles to form larger particles. .
JL.
Freeboard: The vertical *T
distance from the normal Wall
water surface to the top Height
of the confining wall. I
Freeboard
Water Depth
Launders (LAWN-ders): Sedimentation tank effluent troughs.
Lineal (LIN-e-al): The length in one direction of a'line.
For example, a board 12 ft long has 12 lineal feet in its
length.
Millimicron (MILL-e-MY-cron): One thousandth of a micron
or a millionth of a millimeter.
Molecule (MOLL-ee-kule): The smallest portion of an element
or compound retaining or exhibiting all the properties of the
substance.
Septic Conditions (SEP-tick): A condition produced by anaerobic
organisms. If severe, the wastewater turns black, giving off
foul odors and creating a heavy oxygen demand.
Sloughings (SLUFF-ings): Trickling filter slimes that have
been washed off the filter media. They are generally quite
high in BOD and will degrade effluent quality unless removed.
Sludge Gasification; Sludge gasification will form bubbles
of gas in the sludge and cause large clumps of sludge to rise
and float on the water surface.
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 from 0.5 to 2.5.
Trickling FiIter (TRICK-ling): A treatment process in which
the wastewater trickles over media that provides the opportunity
for the formation of slimes which clarify and oxidize the waste-
water.
11
-------
Weir Diameter (weer): Circular
cTarifiers have a circular weir
within the outside edge of the
clarifier. All the water leaving
the clarifier flows over this
weir. The diameter is the
length of a line from one edge
of a weir to the opposite edge
and passing through the center
ox the circle formed bv the weir.
DIAMETER
CIRCULAR
WEIR
DIAMETER
SECTION
111
-------
CHAPTER 5. SEDIMENTATION AND FLOTATION
(Lesson 1 of 3 Lessons)
5.0 INTRODUCTION
Raw or untreated wastewater contains some materials which will
settle to the bottom or float to the water surface readily when
the wastewater velocity is allowed to become very slow. Sewers
are designed to allow the raw wastewater to flow rapidly to
prevent this from happening. Grit chambers (see Chapter 4) are
designed to allow the wastewater to flow at a slightly slower
rate than in the sewers so that heavy, inorganic grit will
settle to the bottom where it can be removed. Settling tanks
decrease the wastewater velocity far below the velocity in a
collection sewer.
In most municipal wastewater treatment plants, the treatment unit
which immediately follows the grit chamber (see Figs. 5.1 and
5.2 for typical plant layout) is the sedimentation and flotation
unit. This unit is sometimes called a settling tank, sedimentation
tank, or clarifier. The most common name is primary clarifier,
since it helps to clarify or clear up the wastewater.
A typical plant (Figs. 5.1 and 5.2) may have clarifiers located
at two different points. The one which immediately follows the
bar screen or comminutor or grit chamber (some plants don't have
all of these) is called the primary c1ari fier, merely because it
is the first clarifier in the plant. The other, which follows
the biological treatment unit (if there is one), is called the
secondary c1ari fier. The two types of clarifiers operate almost
exactly the same way. The reason for having two types is that
the biological treatment unit converts more solids to the
setteable form, and they have to be removed from the treated
wastewater.
The main difference between the two types of clarifiers is in the
sludge density handled. Primary sludges are usually denser than
secondary sludges. Effluent from a secondary clarifier is normally
clearer than primary effluent.
5-1
-------
PPE A£RATIOM
AMP
^IOL06lCAL
Fig. 5.1 Flow diagram of typical plant
5-2
-------
SCREENING
GRIT
REMOVAL
•
FLOW
MFTFR
> r
PRE-AERATION
(
\^
PRIMARY
CLARIFICATION
PRIMARY
CLARIFICATI
(NO.2)
SUPERNATANT & SECONDARY SLUDGE RETURN
BIOLOGICAL
TREATMENT
SOLIDS
DENATERING
CHLORINE
CONTACT
TO
RECEIVING
WATERS
Fig. 5.2 Plan diagram of a typical primary wastewater treatment plant
-------
Solids which settle to the bottom of a clarifier are scraped
to one end (in rectangular clarifiers) or to the middle
(circular clarifiers) into a sump. From the sump the solids
are pumped to the sludge handling or sludge disposal system.
Systems vary from plant to plant and include sludge digestion,
vacuum filtration, incineration, land disposal, lagoons and
burial. Figures 5.3 and 5.4 show detailed sketches of rec-
tangular and circular clarifiers.
Disposal of skimmed solids varies from plant to plant. They
may be buried with material cleaned off the bar screen, in-
cinerated, pumped to the digester, or they may be even sold
for their grease and oil content. Pumping skimmed solids to
a digester is not considered good practice because skimmings
can cause operational problems in digesters.
This chapter contains information on start-up, daily operation,
and maintenance procedures; sampling and laboratory analyses;
some problems to look out for; safety; and basic principles of
sedimentation and flotation. You may wish to refer to the two
chapters containing details of laboratory analyses and mathe-
matics for further information.
5-4
-------
SCUM BAFFLE-
EFFLUENT WEIRS v/. SCUM SKIMMER AND TROUGH
SLUDGE COLLECTOR
-DRIVE UNIT
EFFLUENT TROUGH
TARGET BAFFLE
SLUDGE COLLECTOR CHAIN
AND FLIGHTS
CROSS COLLECTOR
CHAIN AND FLIGHTS
SLUDGE
WITHDRAWAL
Fig. 5.3 Rectangular sedimentation basin
-------
EFFLUENT WEIR
COUNTER
BALANCE
WEIGHTS-!
SLUDGE
WITHDRAWAL
PIPE
INFLUENT
BLADES AND SCRAPER
SQUEEGEES
AND/OR SUCTION
MECHANISM
SUMP
Fig. 5.4 Circular clarifier
-------
5.1 OPERATION AND MAINTENANCE
5.10 Start-up
Before starting up a new unit or one which has been out of
service for cleaning or repair, inspect the tank carefully
as outlined in this section. Now is a good time to become
familiar with the "internal workings" of the clarifier
because they are usually under water.
A. Circular Clarifiers
Check items:
1. Control gates for operation
2. Clarifier tank for sand and debris
3. Collector drive mechanism for lubri-
cation, drive alignment, and complete
assembly
4. Squeegee blades on the collector
plows for proper distance from the
floor of the tank
5. Tank sumps or hoppers and return
lines for debris and obstructions
If everything checks out properly, turn the mechanism on and
let it make several revolutions, checking that the squeegee
does not travel high and low, missing the bottom or scraping
in some areas. The scraping action should control the entire
area form the outside wall to the sludge hopper. Also be
certain that the mechanism runs smoothly without jerks or jumps.
If the unit is water lubricated, be sure sufficient water is in
the tank to cover the center bearing.
If the unit is equipped with a stall alarm, test it to see if
the mechanism will stop on overload. With the unit running,
time the period for the plows to make one complete revolution
around the tank and record the time for later reference.
Check the amperage that the motor draws and record. Let the
unit operate for several hours; and if no problems develop, it
should be okay.
5-7
-------
B. Rectangular Clarifiers
The tank hoppers, channels, control gates, and weirs should
be checked the same as the circular clarifiers. The sludge
collectors are different in rectangular clarifiers. Wooden
flights2 are laid across the tank and each end of the flight
is attached to an endless chain along both sides of the tank.
The collector chains are driven by connecting shaft and
sprockets dragging the flights along rails imbedded in the
floor of the tank, and along each side just under the surface
of the water.
Each wooden flight is equipped with metal wearing shoes to
ride the rails.
Check to insure that the flights are straight across the
tank, and that the chain on one side is not one or two links
ahead or behind the chain on the opposite side. If this
occurs, the wooden flights will run at an angle across the
tank, piling the sludge higher on the trailing side.
Caution should be exercised before starting the sludge
collectors in an empty clarifier if they have not been
operational for several weeks. The wearing shoes on the
flights may have started rusting where they are sitting
on the rails. A good practice is to lift each individual
flight off the rail to be certain it is free and apply a
light grease or 90 wt. oil to the shoe and rail. If these
Flights. Scraper boards, made from redwood or other rot-
resistant woods, used to collect and move settled sludge
or floating scum.
5-8
-------
precautions are not taken, when the collector is turned on
the flight shoes could stick to the rails, and the whole
collector system could be pulled down to the floor of the
tank. Once the collectors are started in a new tank, each
flight should be checked for a clearance of one to two inches
between the wall and the end of the flight. If a flight is
too long, it may rub the tank wall and break the flight,
jamming other flights and breaking them. Once a broken
flight is detected, it should be replaced or removed from
the chain drives.
5.11 Daily Operation and Maintenance
During normal operations you should schedule the following
daily activities:
1. Inspection. Practice frequent inspections with a stop,
look, listen, and then think routine.
2. Cleanup. Wash off with water under pressure accumulations
of solid particles, grease, slime, and other material from
walkways, handrails, and all other exposed parts of the
structure and equipment.
3. Lubrication. Grease all moving equipment according to
manufacturer's specifications and check oil levels in
motors where appropriate.
4. Preventive Maintenance. Follow manufacturer's specifi-
cations .
5. Flight boards. Examine bolts for looseness and corrosion.
6. Chain and sprocket. Check for wear because 0.005 ft in wear
on each of 400 link pins will cause about 2 ft of extra slack,
7. Record-keeping. Write in your pocket notebook any unusual
observations and transfer these notes to the plant record
sheet (typical sheet is shown in the Appendix).
8. Sampling and Laboratory Analysis. Details are in the next
section (5.2) .
9. Sludge and Scum Pumping. See section 5.3
5-9
-------
5.2 SAMPLING AND LABORATORY ANALYSIS
5.20 General
Proper analysis of representative samples is the only con-
clusive method of measuring the efficiency of clarifiers.
Tests may be conducted in the plant at the site where the
sample is collected or in the laboratory. The particular
tests depend upon whether the effluent from the clarifier
goes to another treatment process or is discharged to
receiving waters.
Detailed procedures for performing control tests in primary
treatment plants and sedimentation processes in other plants
are outlined in Chapter 14, Laboratory Procedures and Chemistry.
The frequency of testing and the expected ranges will vary from
plant to plant. Strength of the wastewater, freshness, charac-
teristics of the water supply, weather, and industrial wastes
will all serve to affect the "common" range of the various test
results.
Tests
1. Dissolved
Oxygen (DC)
2. Settleable
Solids
3. pH
4. Temperature
5, BOD
6. Suspended
Solids
7. Chlorine
Residual
(if needed)
8. Coliform
Group
Bacteria
(if needed)
*Depends on region,
system
Frequency
Daily
Daily
Daily
Daily
Weekly
(Minimum)
Weekly
(Minimum)
Daily
Weekly
Location
Effluent
Influent
Effluent
Influent
Effluent
Influent
Influent
Effluent
Influent
Effluent
Plant
Effluent
Common Range
0-2 mg/1
5 -
0.5 -
6.5 -
6.5 -
50 -
150 -
60 -
150 -
60 -
15 ml
4 ml
8.0*
8.0*
85°*
400 mg/1
160 mg/1
400 mg/1
150 mg/1
0.5 - 3.0 mg/1
Effluent 500,000 - 100,000,000
per 100 ml
water supply and discharges to the collection
5-10
-------
5.21 Sampling
Samples of the influent to the clarifier and the effluent from
it will give you information on the clarifier efficiency for
removal of solids,
bacteria, and BOD. As
with all sampling, the
purpose is to collect
samples which represent
the true nature of the
wastewater or stream
being sampled. The
amount of solids, BOD,
bacteria, and the
clarity and pH will
probably vary through-
out the day, week, and
year. You must determine
these variations in order
to understand how well
your clarifier is doing
its job. Details on
laboratory analysis and
A "^IWd^/**"^ ~~ data recording are con-
v —i^tHtr • tained in Chapter 14,
Laboratory Procedures
and Chemistry,
5.22 Calculation of Clarifier Efficiency
To calculate the efficiency of any wastewater treatment process,
you need to collect a sample of the influent and the effluent
of the process, preferably composite samples for a 24-hour period.
The particular water quality indicators (BOD, suspended solids)
you are interested in are measured and the efficiency is calcu-
lated. You can calculate the efficiency of a clarifier in
removing several different items, such as efficiency in removing
BOD or efficiency in removing suspended solids. Calculations of
treatment efficiency are for process control purposes. Your main
concern must be the quality of the plant effluent, regardless of
percent of wastes removed.
5-11
-------
Example:
The influent BOD to a primary clarifier is 200 mg/1, and the
effluent BOD is 140 mg/1. What is the efficiency of the primary
clarifier in removing BOD?
Formula:
Efficiency, % =
(In - Out)
In
100?
= C200 mg/1 - 140 mg/1) 1QO%
200 mg/1
(60 mg/1)
100?
200 mg/1
= (.30) 100%
= 30% BOD Removal
5.23 Typical Clarifier Efficiencies
Following is a list of some typical percentages for primary
clarifier efficiencies:
Expected
Removal
Efficiency
90% to 95%
40% to 60%
10% to 15%
25% to 35%
25% to 75%
Settleable solids
Suspended solids
Total solids
Biochemical oxygen demand
Bacteria
pH will generally not be affected significantly by a clarifier.
You can expect wastewater to have a pH of about 6.5 to 8.0,
depending on the region, water supply and wastes discharged
into the collection system.
5-12
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Clarifier efficiencies are affected by many factors, including:
1. Types of solids in the wastewater, especially if there
is a significant amount of industrial wastes.
2. Age of wastewater when it reaches the plant. Older
wastewater becomes stale or septic, and solids do
not settle properly because gas bubbles form under
them.
3. Rate of wastewater flow as compared to design flow.
4. Mechanical conditions and cleanliness of clarifier.
5.24 Response to Poor Clarifier Performance
If laboratory analysis or visual inspection indicates that a clari-
fier is not performing properly, then the source of the problem must
be identified and corrective action taken.
Problem Check Items (pages 5-14 to 16)
1. Floating chunks of sludge 1, 2, 3, 4, 5
2. Large amounts of floating scum 2.3*, 2.4*, 2.5*
3. Loss of solids over effluent 1, 2, 3, 4, 5, 2.7*, 2.8*
weirs
4. Low removal efficiencies 5
5. Low pH plus odors 1, 2, 3, 4, 5, 6
*
6. Deep sludge blanket, but 3, 2.1*, 2.2*, 2.3*, 2.6
pumping thin sludge
7. Sludge collector mechanism 6
jerks or jumps
8. Sludge collector mechanism 6
will not operate. Drive motor
thermal overloads, or overload
protective switches keep trip-
ping.
*Check Item 2 is divided into two parts, (a) circular clarifier and
(b) rectangular clarifier. If you have a floating scum problem
[Problem 2 above), check under 2. COLLECTOR MECHANISM (page 5-15)
either section (a) circular or (b) rectangular items 3, 4, and 5,
depending on the type of clarifier in your plant.
5-13
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CHECK ITEMS
1. SLUDGE PUMP
Piston Pumps
1. Ball check seating
2. Shear pin
3. Packing adjustment
4. Drive belts
5. High pressure switch
6. Pumping time
Positive Displacement Scru (screw) Pumps
1. Pump gas bound
2. Rotor plugged
3. Drive belt
4. Packing adjustment
5. Pumping time
Centrifugal Pumps
1. Pump gas bound
2. Packing adjustment
3. Impeller plugged
4. Pumping time
Air Injector
1. Air supply
2. Foot valves
3. Slide valves
4. Electrodes
5. Pumping time
5-14
-------
2. COLLECTOR MECHANISM
a. Circular Clarifier
1. Driv.e motor
2. Overload switch
3. Skimmer dump arm
(a) operation
(b) rubber squeegee
4. Scum trough
5. Scum box
b. Rectangular Clarifier
1. Drive motor
2. Clutch and drive gear
3. Flights
4. Scum trough
5. Skimmer operation
6. Cross collector
7. Inlet line or slot
8. Target baffle
3. PIPES AND SLUDGE SUMP
Sometimes pipes or sumps may be cleaned by back flushing.
4. QUALITY OF SUPERNATANT RETURN FROM DIGESTER
5. INFLUENT
a. Change in Composition or Temperature
b. Change in Flow Rate
An increase in flow rate can cause hydraulic over-
load. This can be determined by calculating the
detention time, weir overflow rate, and surface
5-15
-------
loading rate (Section 5.61). If a tank is
hydraulically under-loaded, a tank should be
removed from service or effluent recirculated
back to the primary clarifier to reduce the
length of detention time.
6. JERKING, JUMPING, OR STALLED COLLECTOR MECHANISM
a. Sludge Blanket Too Deep
Pump out sludge if mechanism is all right
b. Drive Unit May Have Bad Sprocket or Defective Chain Link
c. Broken Flight, or Rock or Stick Jammed Between
Flight or Squeegee Blade and Floor of Tank
If items (b) or (c) occur, or mechanism won't operate
properly, tank must be dewatered. Never attempt to
back up or help pull a collector mechanism because
severe equipment damage will result.
Your corrective action will depend on the source of the problem
and the facilities available in your plant.
5-16
-------
QUESTIONS
5.2A List five basic laboratory measurements used to
determine clarifier efficiency.
5.2B About what percentage of settleable solids should
you expect to be removed by your clarifier?
5.2C At what two points should samples be collected
for measuring clarifier efficiency?
5.2D What is the suspended solids efficiency of a
primary clarifier if the influent concentration
is 300 mg/1 and the effluent is 120 mg/1?
5-17
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5.3 SLUDGE AND SCUM PUMPING
The particles which settle to the floor of the clarifier are
called sludge. The accumulated sludge should be removed fre-
quently, and this is accomplished by mechanical cleaning devices
and pumps in most tanks. (See Fig. 5.3 and 5.4) Mechanically
cleaned tanks need not be shut down for cleaning. Septic
conditions3 may develop rapidly in primary clarifiers if sludge
is not removed at regular intervals. The proper interval is
dependent on many conditions and may vary from thirty minutes
to eight hours, and as much as twenty-four hours in a few
instances. Experience will dictate the proper frequency of
removal. Sludge septicity can be recognized when sludge gas-
ification^ causes large clumps of sludge to float on the" water
surface. Septic sludge is generally very.odorous and acid
(has a low pH).
Excess water should be eliminated from the sludge if possible
because of its effects on the volume of sludge pumped and on
digester operation. A good thick primary sludge will contain
from 4.0 to 8.0 percent dry solids as indicated by the Total
or Suspended Solids Test in the laboratory. Conditions which
may affect sludge concentration are the specific gravity, size
and shape of the particles, and temperature, and turbulence
in the tank.
3Septic conditions (SEP-tick). A condition produced by anaerobic
organisms. If severe, the wastewater turns black, giving off
foul odors and creating a heavy oxygen demand.
^Sludge gasification. A process in which soluble and suspended
organic matter are converted into gas. Sludge gasification
will form bubbles of gas in the sludge and cause large clumps
of sludge to rise and float on the water surface.
5-18
-------
Withdrawal (pumping) rates should be slow in order to prevent
pulling too much water with the sludge. While the sludge is
being pumped, take samples frequently and examine them visually
for excess water. If the samples show a "thin" sludge, it is
time to stop pumping. Practice learning to recognize the
differences between thin or concentrated sludges. There are
several methods for determining "thick" or "thin" sludge with-
out a laboratory analysis:
1. Sound of the sludge pump.
The sludge pump will
usually have a different
sound when the sludge is
thick than when it is
thin.
2. Pressure gauge readings.
Pressure will be higher
on the discharge side of
the pump when sludge is
thick.
3. Sludge density gauge
readings.
4. Visual observation of a
small quantity (gallon
or less) .
5. Watch sludge being pumped
through a site glass in
the sludge line.
When you learn to use the indicators listed above, you should compare
them frequently with lab tests. The laboratory Total Sclids Test is
the only accurate method for determining exact density. However,
this analytical procedure is too slow for controlling a routine
pumping operation. Many operators use the centrifuge test to obtain
quick results.
Floating material (scum) may leave the clarifier at the effluent
unless a method has been provided for holding it back. A baffle
is generally provided in the tank at some location to collect scum.
Primary clarifiers often have a scum collection area where the scum
is skimmed off by some mechanical method, usually a skimming arm or
a paddle wheel. If mechanical methods are not provided, use hand
tools such as skimming dipper attached to a broom handle.
Frequently check the scum trough to be sure it is working properly.
Clean the box with a brush and hot water. Scum may be disposed of
by burning or burial.
See Chapter 11, Maintenance, Section 11.3 for details on how to
unplug pipts and pumps.
5-19
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QUESTIONS
5.3A How often should sludge be removed from a
clarifier?
5.3B How can you tell when to stop pumping sludge?
5.3C How can floating material (scum) be kept from
the clarifier effluent? -
5-20
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5.4 GENERAL MAINTENANCE
Following are some hints to help you keep your clarifiers
operating properly:
1. Maintain a record and file system for future reference.
This should contain sheets to write down a description
and date for all repairs and regular maintenance activities
such as lubrication. Other items to be kept in the file
are operating instruction manuals; brochures; names,
addresses, and telephone numbers of manufacturer's repre-
sentatives.
2. Always lubricate equipment at the intervals recommended
by the manufacturer and use the proper lubricants (follow
manufacturer's recommendations). It is very important
that you do not over-lubricate.
3. Clean all equipment and structures regularly.
4. Inspect and correct (if possible) all peculiar noises,
leaks, pressure and vacuum gauge irregularities, belts,
electrical systems, and safety devices.
5. When a sedimentation tank must be drained for inspection
or repairs, keep wooden flights moist by periodic sprinkling
with a hose to prevent cracking and warping.
5-21
-------
5.5 SAFETY
Gases
Any enclosed area, such as a wet well for a
pump, may have poisonous, asphyxiating, or
explosive gases accumulated in it if venti-
lation is not proper. The most common of
these are :
a.
b.
c.
d.
Hydrogen Sulfide (H2S) . Causes a "rotten
egg" odor. It readily combines with oxygen
to form sulfuric acid which will dissolve
concrete. If you breathe too much H2S it
will paralyze your respiratory center.
Chlorine (Cl2) . Very irritating to eyes,
mouth, and nose. Causes death by suffo-
cation (asphyxiation) and by formation of
acid in the lungs.
Carbon Dioxide (C02) . Odorless, taste-
less. This can cause asphyxiation by
displacing oxygen from an enclosed,
poorly ventilated area.
Carbon Monoxide (CO). Colorless, odorless,
non-irritating, flammable, explosive. Look
out for carbon monoxide around gas engines
or leaky gas systems in poorly ventilated
places .
Gasoline and other petroleum products.
May cause fires or explosions, or dis-
place oxygen and asphyxiate you.
f. Methane (CHiJ . Explosive, odorless, and
may cause asphyxiation.
For a detailed discussion of the hazards and
safety precautions when dangerous gases may be
present, refer to Chapter 12, Plant Safety and
Good Housekeeping. The New York Manual, pages
174 and 175, Table 10, Common Dangerous Gases
Encountered in Sewers and at Sewage Treatment
Plants, contains information on the simplest
and cheapest safe methods of treating for gases,
5-22
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2. Falls
Avoid falls by:
a. Cleaning up oil and grease slicks on walkways promptly.
b. Walking, not running, when near open tanks.
c. Avoiding clutter. Pick up and store hoses, ropes
cables, tools, buckets, lumber, etc.
d. Not sitting on, climbing through, or hanging over
guardrails or handrails.
e. Providing gratings, deck covers, or safety chains
on or around openings to pits below floor level.
Drowning
To prevent drowning:
a. Put handrails and proper walkways by all open tanks.
b. Cover open pits with gratings, deck plates, etc.
c. Have life preservers, life lines, or inner tubes
handy to throw to anyone who may fall in. Appropriate
equipment should be worn when necessary.
Strains and Overexertion
Use proper wrenches or equipment:
a. To move stuck or reluctant valves.
b. To lift heavy objects.
5-23
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DISCUSSION AND REVIEW QUESTIONS
Chapter 5. Sedimentation and Flotation
(End of Lesson 1 of 3 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 are to indicate
to you how well you understand the material in this section.
1. What is the function of a primary clarifier?
2. What items should be checked before starting up
a new clarifier or one which has been out of
service for cleaning or repair?
3. Calculate the efficiency of a clarifier removing
BOD if the influent BOD is 260 mg/1 and the
effluent is 155 mg/1. Show your work.
4. What would you do if the solids and BOD removal
efficiencies of a primary clarifier suddenly
dropped and the effluent appeared to contain more
solids than usual?
5. What precautions should you take to avoid strains
and overexertion when working around a treatment
plant?
6. How often should sludge be pumped from a primary
clarifier?
5-24
-------
CHAPTER 5. SEDIMENTATION AND FLOTATION
(Lesson 2 of 3 Lessons)"
5.6 PRINCIPLES OF OPERATION
5.60 General
Sedimentation and flotation units are designed to remove physically
those solids which will settle easily to the bottom or float easily
to the top. Sedimentation is usually the principal basis of design
in such units and will be discussed in more detail in this section.
Flotation of fats, oils, hair, and other light material also is
very important to protect the esthetics of receiving waters.
The sedimentation and flotation units commonly found are:
1. Primary clarifiers
2. Secondary clarifiers
3. Flotation units
4. Imhoff tanks
This section will describe each unit individually as it relates to
another process or as a process by itself.
5.61 Primary Clarifiers
The most important function of the primary clarifier is to remove
as much settleable and floatable material as possible. Organic
settleable solid removal is very important because it causes a
high demand for oxygen (BOD) in receiving water or subsequent bio-
logical treatment units in the treatment plant.
Many factors influence the design of clarifiers. Settling charac-
teristics of suspended particles in water are probably the most
important considerations. The design engineer must consider the
speed at which particles will settle in order to determine the
correct dimensions for the tank. Rapid movement of water
(velocity) will hold most particles in suspension and carry them
along until the velocity of water is slowed sufficiently for
particle settling. The rate of downward travel (settling) of a
particle is dependent on the weight of the particle in relation
5-25
-------
to the weight of an equal volume of water (specific gravity),5
the particle size and shape, and the temperature of the liquid.
Organic settleable solids are seldom more than 1 to 5 percent heavier
than water; and, therefore, their settling rates are slow.
If the horizontal velocity of water is slowed to a rate of 1.0 to 2.0
feet of travel per minute (grit chamber velocities were around 1 ft/sec)
most particles with a specific gravity of 1.05 (5% more than water) will
settle to the bottom of the container. Specific gravity of water is
1.000 at 4.0 degrees Celsius (formally Centigrade) or 39°F; it weighs
8.34 Ibs per gallon. Wastewater solids with a specific gravity of 1.05
will weigh 8.76 Ibs per gallon (1.05 times 8.34 Ibs equals 8.76 Ibs per
gallon). The relationship of the particle settling rate to liquid
velocity may be explained very simply by use of a sketch (Fig. 5.5).
O-
LLJ
0
2
4
6
n
•s.
** "^x fy/
^X4* J>
x^
m
>«
^•s^^
v •<
VERTICAL
T SETTLING RATE =
1 FT/6 M
10 FT/60
• i
IN OR
MIN
i
LENGTH = 200 FT
HORIZONTAL FLOW OF WATER =
200 FT/100 MIN
^C/f. DIRECTION OF
x»
^x
1 1 ^v«l 1 , 1
10 20 30 40 50 60 70 80 90 100
TIME IN MINUTES
Fig. 5.5 Path of settling particle
Suppose the liquid velocity is horizontal at the rate of 2.0 feet per
minute and the tank is 200 feet long. It will take 100 minutes (200 ft
divided by 2.0 ft/min) to travel through the tank. If the particle,
during its diagonal course of travel, settles vertically toward the
5 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 may have a specific gravity
of from 0.8 to 2.6. If the specific gravity of a particle is less
than one it will tend to float, and if greater than one it will
tend to sink. Most organic sludges have a specific gravity be-
tween 1.01 and 1.05.
5-26
-------
bottom of the tank at a rate of 1.0 foot in 6 minutes, it will rest on
the floor of the tank in 60 minutes if the tank is 10 feet deep. If
the particle settles at the rate of 10 feet in 60 minutes, it should
settle in the first 60 percent portion of the tank because the liquid
surrounding it requires 100 minutes to flow through the tank.
There are many factors which will influence settling characteristics
in a particular clarifier. A few of the more common ones are as
follows:
Temperature. Water expands as temperature increases (above 4°C) and
contracts as temperature decreases (above 4°C). Below 4°C the oppo-
site is true. In general, as. water temperature increases, settling
rate of particles increases; and, as temperature decreases, so does
the settling rate. Molecules6 of water react to temperature changes.
They are closer together when liquid temperature is lower; thus,
density7 increases and water becomes heavier per given volume because
there is more of it in the same space. As water becomes more dense,
the density difference between water and solid particles becomes less;
and therefore the particles settle slower. This is illustrated in
Fig. 5.6.
WATER MOLECULES ARE EXPANDED.
THIS ALLOWS FOR EASY SETTLING.
& o o
oo
WATER MOLECULES ARE CLOSE.
PARTICLE SETTLING DIFFICULT.
WARM WATER
100°C (LESS DENSE)
(7.989 LBS/GAL)
COLD WATER
4°C (MORE DENSE)
(8.335 LBS/GAL)
Fig. 5.6 Influence of temperature on settling
5 Molecules (MOLL-ee-kules). The smallest portion of an element
or compound retaining or exhibiting all the properties of the
substance.
7 Density (DEN-sit-tee). The weight per unit volume of any sub-
stance. The density of water (at 4°C) is 1.0 gram per cubic
centimeter (gms/cc) or about 62.4 Ibs per cubic foot. If one
cubic centimeter of a substance (such as iron) weighs more than
1.0 gram (higher density), it will sink or settle out when put
in water. If it weighs less (lower density, such as oil), it
will rise to the top and float. Sludge density is normally
expressed in gms/cc.
5-27
-------
Short Circuits. As wastewater enters the settling tank, it
should be evenly dispersed across the entire cross section of
the tank and should flow at the same velocity in all areas
toward the discharge end. When the velocity is greater in
some sections than in others, serious "short circuiting" may
occur. The high velocity area may decrease the detention
time in that area, and particles may be held in suspension
and pass through the discharge end of the tank because they
do not have time to settle out. On the other hand, if velocity
is too low, undesirable septic conditions may occur. Short
circuiting may easily begin at the inlet end of the sedimen-
tation tank (Fig 5.7), This is usually prevented by the use
of weir plates, baffles, port openings, and by proper design
of the inlet channel. Short circuiting also may be caused by
turbulence and stratification of density layers due to temperature
or salinity.
5-28
-------
HIGH VELOCITY AREA
POOR SETTLING .
x
x X
x x
X X
X
LOW VELOCITY AREA
SEPTIC CONDITIONS AND ODORS
Top View Looking Down
XX
Side View - Warm Influent
Side View - Cold Influent
Fig. 5.7 Short circuiting
5-29
-------
Detention Time.8 Wastewater should remain in the clarifier
long enough to allow sufficient settling time for solid par-
ticles. If the tank is too small for the quantity of flow
and the settling rate of the particles, too many particles
will be carried out the effluent of the clarifier. The relation-
ship of "detention time" to "settling rate" of the particles
is important. Most engineers design for about 2.0 to 3.0 hours of
detention time. This is, of course, flexible and dependent on
many circumstances.
Detention time can be calculated by use to two known factors:
1. Flow in gallons per day
2. Tank dimensions
Example:
The flow is 3.0 million gallons per day (MGD), or 3,000,000 gal/day.
Tank dimensions are 60 feet long by 30 feet wide by 10 feet deep.
What is the 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.
5-30
-------
Formulas:
Detention _ Tank Volume, cu ft x 7.5 gal/cu ft x 24 hr/day
Time, hrs ~ 'Flow, gal/day
Tank Volume, cu ft = Length, ft x Width, ft x Depth, ft
Calculations:
Tank Volume, cu ft = Length, ft x Width, ft x Depth, ft
= 60 ft x 30 ft x 10 ft
= 18,000 cu ft
Detention _ Tank Volume, cu ft x 7.5 gal/cu ft x 24 hr/day
Time, hrs Flow,gal/day
= 18,000 cu ft x 7.5 gal/cu ft x 24 hr/day
=
3,000,000
3,240,000 gal-hr/day
3,000,000 gal/day
1.08 hours
gal/day
24
x7.5
120
168
180.0
1
1
3
18,000
180
,440,000
800 0
,240,000
Evaluation. If detention time is only 1.08 hours and if labora-
tory" tests indicate poor removal of solids, then additional tank
capacity should be placed into operation (if available) in order
to obtain additional detention time. You must realize that flows
fluctuate considerably during the day and night and any calculated
detention time is for a specific flow.
Discussion. The formula given in this section allows you to
calculate the theoretical detention time. Actual detention time
is less than the detention time calculated using the formula and
can be measured by the use of dyes, tracers, or floats.
5-31
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Weir Overflow Rate. Wastewater leaves the clarifier by flowing over
weirs and into effluent troughs (launders)9 or some type of weir
arrangement. The number of lineal10 feet of weir in relation to the
flow is important to prevent short circuits or high velocity near
the weir or launder which might pull settling solids into the
effluent. The weir overflow rate is the number of gallons of waste-
water that flow over one lineal foot of weir per day. Most designers
recommend about 10,000 to 20,000 gallons per day per lineal foot of
weir. Higher weir overflow rates have been used for materials with
a high settling rate or for intermediate treatment. Secondary clari-
fiers and high effluent quality requirements generally need lower
weir overflow rates than primary clarifiers. The calculation for
weir overflow rate requires two known factors:
1. Flow in gpd
2. Lineal feet of weir
Example;
The flow is 5.0 MGD in a circular tank with a 90-foot weir
diameter. What is the weir overflow rate?
10
Launders (LAWN-ders). Sedimentation tank effluent troughs.
When the flow leaves a sedimentation unit, it usually flows
into a trough after it leaves the tank. The top edge of
the trough over which wastewater flows as it titers the
trough is considered a weir.
Lineal (LIN-e-al). The length in one direction of a line.
For example, a board 12 feet long has 12 lineal feet in its
length.
ll
Weir Diameter (weer). Circular
clarifiers have a circular weir
within the outside edge of the
clarifier. All the water leaving
the clarifier flows over this
weir. To find the length of this
weir, the weir diameter must be
known. The diameter 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.
DIAMETER
CIRCULAR
WEIR
DIAMETER
SECTION
5-32
-------
Formulas:
.. . _ -.. , /r. Flow Rate, gpd
Weir Overflow, gpd/ft = —>—££.
Length of Weir, ft
Length of Circular Weir = 3.14 x Weir Diameter, ft
Calculations:
Length of Cir-
cular Weir, ft
= 3.14 x (Weir Diameter, ft)
= 3.14 x 90 ft
= 283 Lineal Feet of Weir
3.14
90_
282.60
Weir Over-
flow, gpd/ft
Flow Rate, gpd
Length of Weir, ft
5,000,000 gaI/day
283 ft
= 17,668 gpd/ft
17.668
283/5,000,000
2 83
2 170
1 981
189 0
169 8
19 20
16 98
2 220
2 264
5-33
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Surface Settling Rate or Surface Loading Rate. This term is
expressed in terms of gpd/sq ft of tank surface area. Some
designers and operators have indicated that the surface
loading rate has a direct relationship to the settleable solids
removal efficiency in the settling tank. The suggested
loading rate varies from 300 to 1200 gpd/sq ft, depending on
the nature of the solids and the treatment requirements. Low
loading rates are frequently used in small plants in cold
climates. In warm regions, low rates may cause excessive
detention which could lead to septicity. The calculation for
surface loading rate requires two known factors:
1. Flow in gpd
2. Square feet of liquid surface area
Example:
The flow in a secondary plant is 5.0 MGD in a tank 90 feet long
and 35 feet wide. What is the surface loading rate?
Formula;
Surface Loading Rate, gpd/sq ft =
Calculations:
Surface Area, sq ft = Length, ft x Width, ft
= 90 ft x 35 ft
= 3150 sq ft
Surface Loading _ Flow Rate, gpd
Rate, gpd/sq ft ~ Area, sq ft
5,000,000 gpd
3150 sq ft
= 1587 gpd/sq ft
5-34
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Detention Time, Weir Overflow Rate, and Surface Loading Rate are
three mathematical methods of checking the performance o'f exist-
ing facilities against the design values. However, laboratory
analysis of samples is the only reliable method of measuring
clarifier efficiency. If laboratory results indicate a poorly
operating clarifier, the mathematical methods may help you to
identify the problem.
QUESTIONS
5.6A What is "short circuiting" in a clarifier?
5.6B Why is "short circuiting" undesirable?
5.6C How can "short circuiting" be corrected?
5.6D A circular clarifier has a diameter of 80 feet and
an average depth of 10 feet. The flow of waste-
water is 4.0 MGD. Calculate the following:
1. Detention Time, in hours
2. Weir Overflow Rate, in gpd/ft
3. Surface Loading Rate, in gpd/sq ft
5-35
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DISCUSSION AND REVIEW QUESTIONS
Chapter 5. Sedimentation and Flotation
(End of Lesson 2 of 3 Lessons)
Please write the answers to these questions in your notebook
before continuing with Lesson 3. The problem numbering continues
from Lesson 1.
7. Explain how temperature influences clarifier performance,
8. Draw a clarifier and indicate what is meant by short
circuiting.
9. A circular clarifier has a diameter of 60 feet and an
average depth of 8 feet. The flow of wastewater is
2.0 MGD. Calculate the following:
1. Detention Time, in hours
2. Weir Overflow Rate, in gpd/ft
3. Surface Loading Rate, in gpd/ft^
4. Comment on the hydraulic loading on the clarifier.
5-36
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CHAPTER 5. SEDIMENTATION AND FLOTATION
(Lesson 3 of 3 Lessons)
5.62 Secondary Clarifiers or Final Settling Tanks
Secondary clarifiers usually follow a biological process in the
flow pattern of a treatment plant. (See Figs. 5.1 and 5.2.)
The most common biological processes are the Activated Sludge
Process12 and the Trick 1ing FiIter.13
In some plants a chemical process may be used instead of a bio-
logical process, but the latter is far more common for municipal
treatment plants.
The final settling tank is sometimes referred to as a "humus tank"
when used after a trickling filter to settle out slough in gsltf
from the filter media. Filter sloughings are a product of bio-
logical action in the filter; the material is generally quite
high in BOD and will degrade the effluent quality unless it is
removed. The specific description of trickling filters is covered
in Chapter 6.
12 Activated Sludge Process (ACK-ta-VATE-ed sluj). A biological
wastewater treatment process in which a mixture of wastewater
and activated sludge is aerated and agitated. The activated
sludge is subsequently separated from the treated wastewater
(mixed liquor) by sedimentation, and wasted or returned to the
process as needed.
13 Trickling Filter. A treatment process in which the wastewater
trickles over media that provide the opportunity for the form-
ation of slimes which clarify and oxidize the wastewater.
llf Sloughings (SLUFF-ings) . Trickling filter slimes that have
been washed off the filter media. They are generally quite
high in BOD and will degrade effluent quality unless removed.
5-37
-------
Secondary clarifier detention times are about the same as for
primary clarifiers, but the surface loading and weir overflow
rates are generally lower due to the less dense characteristics
of secondary sludges. The following are ranges of loading
rates for secondary clarifiers used after biological filters:
Detention Time - 1.0 to 2.0 hours
Surface Loading Rate - 300 to 1200 gpd/sq ft
Weir Overflow Rate - 5,000 to 15,000 gpd/lineal ft
The amount of solids settling out in a secondary clarifier
following a trickling filter will be very irregular due to a
number of varying conditions in the biological treatment process.
In general, you can expect to pump about 30% to 40% as much
sludge from the secondary clarifier as from the primary; thus,
total sludge pumping will increase by that amount. These figures
indicate how the trickling filter "creates" settleable solids
which were not present in the raw wastewater in settleable form.
The sludge in the secondary settling tank will usually have a
completely different appearance and characteristics than the
sludge collected in a primary settling tank. It will usually
be much darker in color, but should not be grey or black, A
grey sludge usually indicates insufficient biological stabili-
zation (treatment). Sludge will turn black if it is
allowed to stay in the secondary clarifier too long. If this
happens, then the return sludge or waste sludge pumping rate
should be increased or the time of pumping lengthened or made
more frequent. Secondary sludges generally require continuous
or frequent pumping at a rate sufficient to maintain a
reasonably concentrated sludge and a low sludge blanket in the
clarifier.
The particle sizes may be very irregular with generally good
(rapid) settling characteristics. The sludge may appear to
be a fluffy humus type of material and will usually have little
or no odor if sludge removal occurs at regular intervals. The
sludge collected in the final settling tanks is sometimes dis-
posed of by transferring to a primary settling tank to be mixed
with primary sludge, and it is sometimes transferred directly
to the digestion system, depending on the particular plant design
and the characteristics of the sludge.
Final settling tanks which follow the activated sludge process
are designed similarly to those used for the trickling filter,
except that they are more conservative in design because the
sludge tends to be less dense. Their purpose is identical,
except that the particles to be settled are received from the
aeration tank rather than the trickling filter. Most final
sedimentation tanks used with the activated sludge process are
5-38
-------
mechanically cleaned due to the importance of rapidly returning
sludge to the aeration tank. (This is explained in Chapter 7,
Activated Sludge.) The sludge volume in the secondary tank will
be greater from the activated sludge process than from the
trickling filter process.
The standard laboratory tests used to measure solids removal in
primary settling tanks are used also for secondary settling
tanks.
QUESTIONS
5.6E Why are secondary clarifiers needed in secondary
treatment plants?
5.6F What usually is done with the sludge that settles
out in secondary clarifiers?
5-39
-------
5.7 FLOTATION PROCESSES
Wastewater always contains some solids in suspended form that
neither settle nor float to the surface and therefore remain
in the liquid as it passes through the clarifier. Dissolved
solids will, of course, travel through the clarifiers because
they are unaffected by these units. There are two other types
of solids in wastewater known as "Colloids" and "Emulsions"
that are very difficult to remove.
A "colloid" is a particle held in suspension due to its very
small size and its electrical charge. It is usually less that
200 millimicrons15 in size, and generally will not settle
readily.If organic, it exerts a high oxygen demand, so its re-
moval is desirable.
An "emulsion" is a liquid mixture of two or more liquid sub-
stances not normally dissolved in one another, but one liquid
held in suspension in the other. It usually contains suspended
globules of one or more of the substances. The globules
usually consist of grease, oil, fat, or resinous substances.
This material also exerts a high oxygen demand.
One method for removing emulsions and colloids is by a "flotation
process", pumping air into the mixture to cause the suspended
material to float to the surface where it can be skimmed off.
15 Millimicron (MILL-e-MY-cron). One thousandth of a micron
or a millionth of a millimeter.
5-40
-------
The particles can be flocculated16 with air or chemical coagulants17
and forced or carried to the liquid surface by minute air bubbles.
Figure 5.8 shows the chain of events in the flotation process.
SMALL PARTICLES
WILL NOT SETTLE.
SMALL PARTICLES
IN FLOCCULATED
FORM.
FLOCCULATED PAR
TICLES ATTACHED
TO AIR BUBBLES.
BUBBLES CARRY
PARTICLES TO
SURFACE.
ACCUMULATED
SCUM OR FOAM
ON SURFACE.
MOST AIR BUB-
BLES ARE
RELEASED.
Fig. 5.8 Flotation process
Most of the air bubbles are released at the liquid surface. Particles
are removed in the form of scum or foam by skimming.
There are two common flotation processes in practice today:
1. Vacuum Flotation. The wastewater is aerated for a short
time in a tank where it becomes saturated with dissolved
air. The air supply is then cut off and large air bubbles
pass to the surface and into the atmosphere. The waste-
water then flows to a vacuum chamber which pulls out dis-
solved air in the form of tiny air bubbles which float
the solids to the top.
2. Pressure F1o ta t ion. Air is forced into the wastewater
in a pressure chamber where the air becomes dissolved in
the liquid. The pressure is then released from the
wastewater, and the wastewater is returned to atmospheric
pressure where the dissolved air is released from solution
in the form of tiny air bubbles. These air bubbles rise
to the surface and, as they rise, they carry solids to
the surface.
16 Flocculated (FLOCK-you-lay-ted). An action resulting in the
gathering of fine particles to form larger particles.
17 Coagulants (ko-AGG-you-lents). Chemicals added to destabilize,
aggregate, and bind together colloids and emulsions to improve
settieability, filterability, or drainability.
-------
Any flotation process is based upon release of gas bubbles in
the liquid suspension (Fig- 5.8) under conditions in which the
bubbles and solids will associate with each other to form a
combination with a lower specific gravity than the surrounding
liquid. They must stay together long enough for the combin-
ation to rise to the surface and be removed by skimming.
QUESTIONS
5.7A Why is the "flotation process" used in some waste-
water treatment plants?
5.7B Would you place the flotation process before or
after primary sedimentation?
5.7C Give a very brief description of:
1. Colloid
2. Emulsion
5. 7D Give a brief description of the Vacuum Flotation
process.
5-42
-------
5.8 IMHOFF TANKS
Imhoff tanks are rarely constructed today. Your plant may
consist of only an Imhoff tank if it serves a very small com-
munity or if it was constructed many years ago. It is quite
possible that you may never have operating responsibility for
one of these units. They will be discussed for general know-
ledge and for the few operators who will have operating
responsibility for them.
The Imhoff tank combines sedimentation and sludge digestion
in the same unit. There is a top compartment where sedimen-
tation occurs and a bottom compartment for digestion of settled
particles (sludge). The two compartments are separated by a
floor and a slot designed to allow settling particles to pass
through to the digestion compartment (Fig. 5.9).
Wastewater flows slowly through the upper tank as in any other
standard rectangular sedimentation unit. The settling solids
pass through the slot to the bottom sludge digestion tank.
Anaerobic digestion of solids is the same as in a separate
digester. Gas bubbles are formed in the digestion area by
bacteria. As the gas bubbles rise to the surface they carry
solid particles with them. The slot is designed to prevent
solids from passing back into the upper sedimentation area as
a result of gasification where they would pass out of the unit
with the effluent.
The same calculations previously used for clarifiers can be used
to determine loading rates for the settling area of the Imhoff
tank. (Chapter 8, Sludge Digestion, will explain the anaerobic
process in the sludge digestion area of this unit.) Some typical
values for design and operation of Imhoff tanks are:
Settling Area
Wastewater Detention Time - 1.0 to 4.0 hours
Surface Settling Rate - 600 to 1200 gpd/sq ft
Weir Overflow Rate - 10,000 to 20,000 gpd/ft
Suspended Solids Removal - 45% to 65%
BOD Removal - 25% to 35%
Dijges tipn Area
Digestion Capacity - 1.0 to 3.0 cu ft/person
Sludge Storage Time - 3 to 12 months
5-43
-------
GAS VENTS
\
SETTLING COMPARTMENT
SLUDGE DIGESTION
COMPARTMENT
SLUDGE WITHDRAWAL LINE
Fig. 5.9 Imhoff tank
5-44
-------
Here are a few operational suggestions:
1. In general, there is no mechanical sludge scraping device
for removing settled solids from the floor of the settling
area. Solids may accumulate before passing through the slot
to the digestion area. It may be necessary to push the accu-
mulation through the slot with a squeegee or similar device
attached to a long pole. Dragging a chain on the floor and
allowing it to pass through the slot is another method for
removing the sludge accumulation.
2. Scum from the sedimentation area is usually collected by hand
tools in a separate container for disposal. It may also be
transferred to the gas venting area where it will work down
into the digestion compartment. Scum in the gas vents should
be kept soft and broken up by soaking it periodically with
water or by punching holes in it and mixing it with the liquid
portion of the digestion compartment. The addition of 10 pounds
of hydrated lime per 1000 connected population per day may be
helpful for controlling odors from the gas vent area and also
for adjusting the chemical balance of the scum for easier
digestion.
3. Some Imhoff tanks have the piping and valving to reverse the
direction of flow from one end toward the other end. If
possible, the flow should be reversed periodically for the
purpose of maintaining an even sludge depth in the digestion
compartment. The sludge level in the digestion area must be
lower than the slot in the floor of the settling area to
prevent plugging of the slot. A line of gas bubbles directly
over the slot indicates the sludge level in the digestion
chamber is too high.
4. The explanation of sludge digestion in. Chapter 8 will
supply information that can be applied to the digestion
area in the Imhoff tank. Neither sludge mixing nor heating
devices are used in an Imhoff tank. Sludge loading rates,
withdrawal rates, laboratory tests, and visual appearance
of sludges are very similar to what they are in an unheated
digester. If visual appearance is the only method you have
of judging the sludge, it is safe to assume that if sludge
in the digestion area is relatively odorless or has a musty
smell and is black or very dark in color, the process is
working satisfactorily.
5-45
-------
The laboratory testing program for an Imhoff tank should be
complete enough to identify operational problems and to supply
necessary information to regulatory agencies. The following
minimum program is suggested, assuming adequate laboratory
facilities, personnel, and size of the system.
TYPICAL
SUGGESTED ANALYSIS USUAL RANGE REMOVAL %
Settling Area
Settleable Solids 3.0 - 10.0 ml/1 75 - 90
Suspended Solids 200 - 400 mg/1 45 - 65
pH 6.7-7.3
Alkalinity 100 - 300 mg/1
BOD 200 - 500 mg/1 25 - 35
Digestion Area
pH 6.7-7.3
Alkalinity 1000 - 3000 mg/1
Vol. Acids 100 - 500 mg/1
Efficiency of operation can be determined by measuring the settle-
able solids, suspended solids, or BOD of the influent and effluent.
5-46
-------
QUESTIONS
5.8A What are the two components of an Imhoff tank?
5.8B Describe the sludge from "an Imhoff tank which
is operating properly.
5.8C How could you maintain a fairly level sludge
blanket in the digester portion of an Imhoff tank?
5.8D How can you force settled material into the
digestion compartment?
5.9 SEPTIC TANKS
Septic tanks are used mostly for treating the wastewater from
individual homes or from small populations (such as camps)
where sewers have not been provided. They operate very much
like an Imhoff tank except there is not a separate digestion
compartment. Detention time is usually long (12 to 24 hours)
and most settleable solids will remain in the tank. They
must be pumped out and disposed of periodically to prevent
the tank from filling up. Part of the solids in the septic
tank are liquified and discharged with the wastewater into
the soil mantle. Conditions are not favorable for rapid
gasification and most waste stabilization occurs in the soil.
Septic tank effluent is usually disposed of in underground per-
forated pipes called "leach lines", and sampling of effluent may
be impossible. The ability of the soil mantle to leach the
septic tank effluent is the critical factor in subsurface waste
disposal systems.
For additional information on septic tanks, refer to the Manual of
Septic Tank Practice, U.S. Public Health Service, Washington, D.C.
5-47
-------
5.10 ADDITIONAL READING
a. MOP 11, pages 25-38 and 89-97
b. New York Manual, pages 31-45
c. Texas Manual, pages 174-201
d. Sewage Treatment Practices, pages 35-47
DISCUSSION AND REVIEW QUESTIONS
Chapter 5. Sedimentation and Flotation
(End of Lesson 3 of 3 Lessons)
Write the answers to these questions in your- notebook before
continuing. The problem numbering continues from Lesson 2.
10. Why should floatable solids be removed from wastewater?
11. What is the critical factor in subsurface wastewater
disposal systems?
5-48
-------
SUGGESTED ANSWERS
Chapter 5. Sedimentation and Flotation
5.2A Settleable solids, suspended solids, total solids, BOD,
and coliform group bacteria.
5.2B 90% to 95%.
5.2C Influent and effluent.
5.2D Efficiency, % = (In j-0"^ 100%
- (300 mg/1 - 120 mg/1)
- 300 mg/1 10°°
= 60%
5.3A Often enough to prevent septic conditions or sludge gasification.
5.3B Stop pumping sludge when it becomes thin. Thin sludge can
be detected by the sound of the sludge pump, differences in
sludge pump pressure gauge readings, and by visual observa-
tion of the sludge.
5.3C Scum can be kept out of the clarifier effluent by a baffle
placed around the inside edge of the overflow weir.
(END OF ANSWERS TO QUESTIONS IN LESSON 1)
5.6A Short circuiting occurs in a clarifier when the flow is
not uniform throughout the tank.
5.6B Short circuiting is undesirable because where the velocity
is too high, particles will not have time to settle. Where
the velocity is too low, undesirable septic conditions may
develop.
5.6C Short circuiting may be corrected by installing weir plates
or baffles.
5-49
-------
' - x (Diameter, ft)2 x Depth, ft
= 5- x (80 ft)2 x 10 ft
3.14
x 6400 x 10
0.785 x 64,000
50,240 cu ft
.785
64000
3140000
4710
50240.000
Tank Volume,
gal
50,240 cu ft x 7.5 gal/cu ft 50240
7.5
= 376,800 gal
251200
551680
376800.0
1. Detention
Time, hrs
Tank Volume, gal x 24 hr/day
Flow, gal/day
376,800 gal x 24 hr/day
4,000', 000 gal /day
= .376800 x 6
= 2.2608
= 2.3 hrs
2. Weir Overflow
Rate, gpd/ft
Flow Rate, gpd
Length of Weir, ft
4,000,000 gpd
3.14 x 80 ft
4,000,000 gpd
251.2 ft
= 15,923 gpd/ft
15923.
251.2 4000000.0
2512
14880
12560
23200
22608
5920
5024
896 0
753 6
5-50
-------
5.6D (Continued)
3. Surface Loading Rate
Calculate Surface Area, sq ft
Surface Area, sq ft = -r x (Diameter, ft)2
5.14
4
x (80 ft)2
0.785 x 6400
5.024 sq ft
0.785
6400
314000
4710
5024.000
Surface Loading
Rate, gpd/sq ft
Flow Rate, gpd
Surface Area, sq ft
4,000,000 gpd
5,024 sq ft
= 800 gpd/sq ft (close enough)
(END OF ANSWERS TO QUESTIONS IN LESSON 2)
5.6E Secondary clarifiers are needed in secondary treatment
plants to remove solids from the secondary process.
5.6F Sludge settling in the secondary clarifier may be returned
to the primary clarifier to be settled with the primary
sludge, pumped to the beginning of the biological process
for recycling, or pumped directly to the sludge handling
facilities.
5.7A The flotation process is used to remove "colloids" and
"emulsions".
5.7B After.
5-51
-------
5.7C Colloid - A very small solid that remains dispersed in
a liquid for a long time due to its small size and
electrical charge.
Emulsion - A liquid mixture of two or more liquid sub-
stances in a relatively stable suspension which do not
combine chemically.
5.7D The vacuum flotation process consists of aerating the
wastewater and applying a vacuum to pull out the air
which will carry the solids to the water surface.
5.8A (1) Settling area, and (2) Sludge digestion area.
5.8B Digested sludge in an Imhoff tank is relatively odor-
less or has a musty smell, and it is black or very dark
in color.
5.8C A fairly level sludge blanket is maintained by reversing
the flow at regular intervals.
5.8D Settled material may be forced into the digestion com-
partment by pushing it through the connecting slot with
a squeegee.
(END OF ANSWERS TO QUESTIONS IN LESSON 3)
5-52
-------
OBJECTIVE TEST
Chapter 5. Sedimentation and Flotation
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end cf Chapter 1. There may be
more than one answer to each question.
EXAMPLE
The purpose of detaining water in a sedimentation tank is to:
1. Store for future use
2. Allow solids to settle to the bottom
3. Allow grease to float to the surface
4. Hold until trickling filter is ready
5. Provide chlorine contact time
To answer this question, you should mark on your answer sheet:
EXAMPLE:
1234
' ' 'ft' '•' ' '
t t t|Mi tBt i i
i i iHi iWt t r
5
t i
t t
i i
i i
1. Skimmed solids may be disposed cf by:
1. Pumping to digester
2. Burying with material from bar screen
3. Incineration
4. Sold for grease and oil content
5. None cf these
2. What iten.s should be checked before starting a clariiier?
1. Remove debris from pipes and tank
2. Lubricate equipment
3. Sample effluent
4. Turn off chlorinator
5. Run a clarity test
3. Generally, pH is significantly affected by a clariiier:
1. True
2. False
5-53
-------
4. An operator can tell if "thin" sludge is being pumped by:
1. The sound of the sludge pump
2. The smell of the sludge
3. The color of the sludge
4. Pressure gauge readings on the
suction and discharge of the pump
5. Visual observation
5. The maintenance program for a properly operating clari-
fier should include:
1. Sample influent
2. Regular inspection
3. Keep a list of repairs
4. Prompt adjustment or repair when necessary
5. Lubricate equipment at regular intervals
6. Dangerous gases an operator may encounter in and around
a treatment plant include:
1. Hydrogen sulfide
2. Nitrogen
3. Chlorine
4. Fumes from gasoline
5. Methane
7. What factors influence the settling characteristics of
solids in a clarifier?
1. Flow velocity and/or turbulence
2. Temperature
3. Laboratory analyses
4. Short circuiting
5. Detention time
8. If short circuiting occurs in a clarifier, the operator
should:
1. Check the wiring
2. Identify the cause
3. Change fuses
4. Try installing baffles
5. Restart the pump
9. Plant analysis of samples is a reliable method of
measuring clarifier efficiency:
1. True
2. False
5-54
-------
10. What are "sloughings"?
1. Troughs
2. Slop
3. Material washed off trickling filter media
4. Waste activated sludge
5. Grit
11. Secondary or final clarifiers are needed to:
1. Increase sludge digestion
2. Allow septic conditions to develop
3. Provide a home for organisms
4. Remove solids from biological processes
5. None of these
12. An Imhoff tank has:
1. 'IWo compartments
2. Sludge scrapers
3. A piping system that allows the flow in the tank
to be reversed from one end to the other end
4. A separate sludge digestion compartment under
the settling area
5. Gas vents
13. Primary clarifiers are designed to remove colloidal solids:
1. True
2. False
14. Estimate the detention time in a 20,000-gallon sedimentation
tank if the flow is 0.2 MGD. Select the closest answer.
1. 1.5 hr
2. 1.8 hr
3. 2.0 hr
4. 2.4 hr
5. 2.8 hr
15. Estimate the detention time in a sedimentation tank 90 f'c
long, 30 ft wide, and 12 ft deep, if the flow is 3.0 MCD.
Select the closest answer.
1. 1.5 hr
2. 1.8 hr
3. 2.0 hr
4. 2.4 hr
5. 2.8 hr
Please write on your IBM answer sheet the total time required
to work all three lessons and this objective test.
5-55
-------
APPENDIX
Monthly Data Sheet
5-57
-------
MONTHLY RECOR
UJ
t-
Q
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
zr
28
29
30
31
o
M
T
w
T
F
S
S
MAX.
MIN.
AVG.
WEATHER
FAIR
i.
•'
II
a.
"
FAIR
a
C3
S
S
O
u.
1.200
1.051
1.120
0.187
I.008
uot
o.m
.OK,
D 19
RAW WASTEWATER
TEMP.
70
61
6?
70
£9
68
6V
fcl
FLOW METER:
LAST 445237
,., 413741
rnTA, ai.466 MG
X
a.
7.3
7?
7.3
7.1
7.0
7.2
7.3
(
7.1
10
a
o
CO
K
h-
LJ
CO
B
\o
II
9
7
9
a
<=)
Q
O
m
no
205
220
164
232
211
195
SUSP. SOLIDS
208
218
222
201
248
210
215
2IO
to.
o
1
l-
o
1.0
1.0
1.5
1.0
\.o
0.75
0.75
1.0
CLEANWATER, U.S.A.
WATER POLLUTION CONTROL PLANT
EFFLUENT
X
o.
7.2
7.1
7.1
7.0
7-0
7.1
7.1
7.1
o
o
CD
118
128
154
130
140
136
140
135
CO
0
$
CL
CO
a
no
108
III
t'/
112.
100
101
IOG
ELECTRIC METER:
LAST 5021
MIII T BO y 20fl = 16,640 KWH
O
Q
1.0
I.I
0.1
1.2
0.7
0.6
0.1
0.9
RAW
L<
co
UJ
IT
CM
_J
O
2.1
2.4
3.0
i.a
1.1
2.1
2.0
2.0
DIGESTION
UJ
O ^
3 <
_l Q
(K O
4750
4IO&
4302
3810
400?
4 HO
3115
4154
SLUDGE :
^T 6285B&
le, 614SI4
STROKES-
TOTAL '29T
sniM
5
a
CO O
100
no
120
115
12.0
110
*
IOO
CM
0
0
32
32
33
33
34
32
33
3100
Q
CO 10
< K
C9 LL
10400
IO900
IDB60
nzoo
toeoo
nooo
to&oo
10810
74 x 1-0 -I28.7M- GALS
erf
X
1
o
z
X
s
4
_
8
&
8
4
4
5
GAS Ml
LAS!
Is
TOTA
OP
REMARKS
SLUOSB 4-0*16=0 - IC.OOO SAL..
;TER:
- TI6406
363216 \\
L 33S.IIO FT3
FRATOR:
SUMMARY DATA
% REMOVAL
INF.- EFF.
BOD
30
S S
49
SLUDGE DATA
% SOLIDS -AVG.
LBS. DRY SOLIDS /DAY
% VOL. SOLIDS- AVG.
LBS. VOL. SOLIDS /DAY
LBS. VOL. SOL./ 10
30 FT.} DAY
GAL. SLUDGE TO BEDS
CU. YDS. CAKE REMOVED
FT.3 GAS/ LB. VOL
SOLIDS
FT? GAS/ MG. FLOW
CU. YDS. GRIT / MG. FLOW
COST
MAN DAYS 44
4.B
I&6.3
76
IZ64-
253
48000
22
65
10,640
1.0
DATA
PAYROLL
POWER PURCHASED
OTHER UTILITIES
(GAS ETC.)
GASOLINE, OIL, GREASE
CHEMICALS 8 SUPPLIES
MAINTENANCE
VEHICLE COSTS
OTHER
TOTAL
OPERATING COST/MG.
OPERATING COST/ CAPITA /MG
8 I25O ~
250 ~
L 60-
30"
feO~
130
70~
20"
81870-
8 5S.37
* 0.19
-------
CHAPTER 6
TRICKLING FILTERS
by
Larry Bristow
-------
TABLE OF CONTENTS
.Chapter 6. Trickling Filters
Page
6.0 Introduction 6-1
6.00 General Description 6-1
6.01 Principles of Treatment Process 6-2
6.02 Principles of Operation 6-8
6.1 Starting and Operating a Filter 6-13
6.10 Pre-Start Up 6-13
6.11 Placing Filter in Service 6-14
6.12 Daily Operation 6-15
6.2 Sampling and Analysis 6-17
6.20 General 6-17
6.21 Typical Trickling Filter Plant Lab Results . . . 6-17
6.22 Response to Poor Trickling Filter Performance. . 6-18
6.3 Daily Operation Problems 6-25
6.30 Ponding 6-25
6.31 Odors 6-27
6.32 Filter Flies 6-28
6,33 Weather Problems 6-29
6.4 Maintenance 6-31
6.40 Bearings and Seals 6-31
6.41 Distributor Arms 6-31
6.42 Maintenance of Fixed Nozzles 6-32
6.5 Safety 6-34
6.6 Classification of Filters 6-37
6.60 General 6-37
6.61 Standard-Rate Filters 6-37
6.62 High-Rate Filters 6-38
6.63 Roughing Filter 6-38
6.64 Filter Staging 6-39
111
-------
Page
6.7 Loading Parameters 6-41
6.70 Typical Loading Rates 6-41
6.71 Computing Hydraulic Loading 6-41
6.72 Computing Organic (BOD) Loading 6-43
6.8 Additional Reading 6-46
IV
-------
EXPLANATION OF PRE-TEST
Write your name and mark your answers on the IBM sheet. The
objective of the Pre-Test is to indicate to you the important
topics in this chapter, as well as to indicate how well the
material was presented to you.
many of the answers.
It's okay if you don't know
P-i
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PRE-TEST
Chapter 6. Trickling Filters
Name Date
Please write your name and mark the correct answers on the IBM answer
sheet. There may be more than one answer to each question.
1. Loading on a trickling filter may be expressed as
1. Ib H20/day
2. Ib BOD/day/1000 cu ft
3. Ib H20/sq ft/day
4. gal/day/sq ft
5, gal/day/inon cu ft
2. Masking agents:
1. Cover the filter
2. Mask the plant
3. Produce desirable odors
4. Are sprayed into the air
5. Tend to make undesirable odors unnoticeable
3. A shock load is :
1. A heavy blow
2. A big load in a truck
3. An unexpected strong waste
4. An unexpected bump
5. None of these
4. A flow of 1400 gpm is approximately the same as:
1. 1 MGD
2. 2 MGD
3. 0.5 MGD
4. 0.33 MGD
5. 0.75 MGD
5. Physical methods of waste treatment include:
1. Trickling filters
2. Disinfection
3. Sedimentation
4. Screens
5. Activated sludge
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6. Before starting up a new trickling filter plant the opera-
tor should check:
1. Oil reservoirs for proper amount and type of oil
2. Rotation of distributor arm
3. Underdrain system for debris
4. Zoogleal film on filter media
5. To be sure there are no voids in the filter media
7. In operating a trickling filter the operator should:
1. Adjust the process to obtain the
best possible results for the least cost
2. Use the lowest recirculation rates that
will yield good results to conserve power
3. Rotate the distributor as fast as possible to
better spray settled wastewater over the media
4. Maintain aerobic conditions in the filter
5. Bubble oxygen up through the filter
8. Which test best measures the efficiency of a trickling filter?
1. Total solids
2. pH
3. BOD
4, Temperature
5. Sludge age
9. To correct an odor problem in a trickling filter the operator
should:
1. Take corrective action immediately
2. Shut off flow to the filter
3, Try to maintain aerobic conditions
4. Check ventilation in the filter
5. Increase recirculation rate
10. Maintenance of a distributor moved by hydraulic action
includes:
1. Cleaning the filter media
2. Cleaning orifices in the distributor arms
3. Changing the mercury if the distributor arm
does not rotate smoothly
4, Adjusting turnbuckles occasionally on guy rods
to keep rotating arms at proper level
5. Greasing gears that rotate distributor
P-2
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11. The differences between high-rate filters and standard-rate
filters include:
1. Higher flows per day per square foot of surface area
2. Higher pounds of BOD per day per cubic foot of media
3. Higher BOD reductions
4. Greater depth of filter
5. Higher rate of odor production
12. The hydraulic loading on a trickling filter 90 feet in
diameter with a flow of 0.6 MGD is approximately:
1. 100 gpd/sq ft
2. 95 gpd/sq ft
3. 90 gpd/sq ft
4. '85 gpd/sq ft
5 . None of these
13. The organic load applied to a trickling filter in pounds
of BOD per day for a filter with a diameter of 75 feet,
a flow of 0.4 MGD, and a filter influent BOD of 100 mg/1
would be approximately:
1. 350 Ibs/day
2. 335 Ibs/day
3. 325 Ibs/day
4. 300 Ibs/day
5. None of these
14. Successful trickling filter operation depends on:
1. Maintenance of a chlorine residual in the effluent
2. Washing slimes off the filter media
3. Preventing sludge bulking
4. Maintenance of a good growth of organisms on the
filter media
5. Filtering the solids out of the wastewater
15. The basic parts of a trickling filter include:
1. Distribution box
2. Distribution system
3. Pumps
4. Underdrain system
5. Media
16. Problems associated with trickling filters include:
1. Bulking
2. Filter flies
3. Clogging
4. Turbid effluent
5. Snails
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17. Trickling filtration is primary treatment process.
1. True
2. False
If wastewater recirculation rates are too low, then
(18)
18. 1. Aerobic
2. Anaerobic
conditions may develop in the secondary clarifier;
however, if recirculation rates are too high (19)
19. 1. Solids will wash out of the secondary clarifier
2. The effluent will be sparkling clear
P-4
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GLOSSARY
Chapter 6. Trickling Filters
Aerobic Process (AIR-0-bick): The waste treatment process is con-
ducted under aerobic (in the presence of "free" or dissolved oxygen)
conditions.
Anaerobic (AN-air-0-bick): A condition in which "free" or dissolved
oxygen is not present.
Colloids (KOL-loids): Very small solids (particulate or insoluble
material) in a finely divided form that remain dispersed in a liquid
for a long time due to their small size and electrical charge.
Distributor; The rotating mechanism that distributes the wastewater
evenly over the surface of a trickling filter or other process unit.
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, causing a spraying action.
Loading; Quantity of material applied to a device at one time.
Masking Agents: Liquids which are dripped into the wastewater,
sprayed into the air, or evaporated (using heat) with the "fumes"
or odors discharged into the air by blowers to make an undesirable
odor less noticeable.
Microorganisms (micro-ORGAN-is-zums): 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.
Orifice (OR-i-fiss): 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.
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Physical Waste Treatment Processes; Racks, screens, comminutors,
sedimentation, and flotation.Chemical or biological reactions
are not an important part of the process.
Ponding; A condition occurring on trickling filters when the
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.
Protozoa (pro-toe-ZOE-ah): A group of microscopic animals,
principally of one cell, that sometimes cluster into colonies.
Recirculation: The return of part of the effluent from a treat-
ment process to the incoming flow.
Secondary Treatment; A wastewater treatment process used to
convert dissolved or suspended materials into a form more
readily separated from the water being treated.
Shock Load: The arrival at a plant of waste which is toxic to
organisms in sufficient quantity or strength to cause operating
problems, such as odors or sloughing off of the growth or slime
on the trickling filter media. Organic or hydraulic overloads
also can cause a shock load.
Trickling Filter: A treatment process in which the wastewater
trickles over media that provide the opportunity for the formation
of slimes which clarify and oxidize the wastewater.
Trickling Filter Media: Rocks or other durable materials that make
up the body of the filter. Synthetic (manufactured) media have been
used successfully.
Two-Stage Filters: Two filters are used. Effluent from the first
filter goes to the second filter, either directly or with a clarifier
between the two filters.
Zoogleal Film (ZOE-glee-al): 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 description.
G-2
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CHAPTER 6. TRICKLING FILTERS
(Lesson 1 of 3 Lessons)
6.0 INTRODUCTION
6.00 General Description
In the initial chapters of this course, you have learned about
physical methods of wastewater treatment. In general, these
techniques (processes) consist of the screening of large particles,
settling of heavy material, and floating of light material by pre-
liminary and primary treatment units (screen, grit chamber, clarifier)
Although primary treatment is very efficient for removing settleable
solids, it is not capable of removing other, lighter suspended solids
or dissolved solids which may exert a strong oxygen demand on the
receiving waters.
In order to remove the very small suspended solids (colloids) and
dissolved solids, most waste treatment plants now being built include
"secondary treatment".1 This additional process increases overall
plant removal of suspended solids and BOD to 90% or more. The two
most common secondary treatment processes are trick ling fiIters and
activated sludge. This chapter will deal with trickling filters.2
1 Secondary treatment. A wastewater treatment process used to
convert dissolved or suspended materials into a form more
readily separated from the water being treated.
2 Trickling filters are sometimes called biofilters, accelo
filters, or aero-filters, depending on the recirculation pattern.
6-1
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Figures 6.1 and 6.2 show where a trickling filter is usually
located in a plant.
More trickling filters, have been built in this country than
any other type of secondary treatment device. Most trickling
filters are large in diameter, shallow, cylindrical structures
filled with stone and having an overhead distributor. (See
Fig. 6.3.) Many variations of this design have been built.
Square or rectangular filters have been constructed with fixed
sprinklers for wastewater distribution.
6.01 Principles of Treatment Process
Trickling filters, or biological oxidation beds, consist of
three basic parts:
1. The media (and retaining structure)
2. The underdrain system
3. The distribution system
The media provide a large surface area upon which a biological
slime growth develops. This slime growth, sometimes called a
zoogle al fi1m,3 contains the living organisms that break down
the organic material. The media may be, rock, slag, coal, bricks,
redwood blocks, molded plastic (Fig. 6.4), or any other sound,
durable material. The media should be of such sizes and stacked
in such a fashion to provide voids for air to ventilate the filter
and keep conditions aerobic. For rock, the size will usually be
from about two inches to four inches. Although actual size is
not too critical, it is important that the media be uniform in
size to permit adequate ventilation. The depth ranges from about
three to eight feet.
The underdrain system has a sloping bottom, leading to a center
channel, which collects the filter effluent. It also supports
the media and permits air flow. Common methods are the use of
spaced redwood stringers, or any of a number of prefabricated
blocks of concrete, vitrified clay, or other material.
3 Zoogleal Film (ZOE-glee-al). A complex population of organisms
that form a slime growth on the trickling filter media and
break down the organic matter in the wastewater. These slimes
consist of living organisms, silt, and other debris. Slime
growth is a more common definition.
6-2
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FUNCTION
-i BEMOVZ
"REMOVAL
FEE AEEATlON
ANP
, &OOT4
Fig. 6.1 Flow diagram of treatment plant
6-3
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RECIRCULATION LINE
PRIMARY
CLARIFICATION
SECONDARY
TRICKLING
FILTER
PRIMARY
TRICKLING
FILTER
PRETREATMENT
PRIMARY
CLARIFICATION
SECONDARY
CLARIFIER
HUMUS SLUDGE
SUPERNATANT
ANAEROBIC
DIGESTER
ANAEROBIC
DIGESTER
(SECONDARY)
SOLIDS
DENATURING
CHLORINE CONTACT
TO
RECEIVING
WATERS
Fig. 6.2 Plan to typical trickling filter plant
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DISTRIBUTOR ARM
ROTATION
SPEED RETARDER
OUTLET
RAILING EDGE
SPLASH PLATES
RETAINING
WALL
OUTLET
VALVE
VENTILATION
PORT
SUPPORT GRILL &
UNDERDRAINAGE SYSTEM
SLOPED FLOOR
UNDERDRAIN CHANNEL
OUTLET BOX
OUTLET PIPE
INLET PIPE
\
Fig. 6.3 Trickling filter
6-6
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Fig. 6.4 Installation of synthetic media in trickling filter
(Courtesy of The DOT.J Clierrrlaal Company)
6-7
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The distribution system, in the vast majority of cases, is a
rotary-type distributor which consists of two or more horizontal
pipes supported a few inches above the filter media by a central
column. The wastewater is fed from the column through the hori-
zontal pipes and is distributed over the media through orifices
located along one side of each of these pipes (or arms).
Rotation of the arms is due either to the "jet-like" or rotating
water sprinkler reaction from wastewater flowing out the orifices
or by some mechanical means. The distributors are equipped with
a mercury or mechanical type seal at the center column to pre-
vent leakage and protect the bearings, guy rods for seasonal
adjustment of the pipes (arms) to maintain them in a horizontal
position, and quick-opening gates at the end of each arm to
permit easy flushing.
Today the fixed nozzle distribution system is not as common as
the rotary type. Each fixed nozzle consists of a circular orifice
with an inverted cone-shaped deflector mounted above the center
which breaks the flow into a spray. Some types have a steel ball
in the inverted cone. (See Fig. 6.5.) The fixed nozzle system
requires an elaborate piping system to insure relatively even
distribution of the wastewater. Flow is usually intermittent and
is controlled by automatic siphons which regulate the flow from
dosing tanks. (See Fig. 6.5.) The nozzles extend six to twelve
inches above the media and are shaped so that an overlapping spray
pattern exists at the Start of dosing when the head in the dosing
tank is the greatest. The pattern is carefully worked out to pro-
vide a relatively even distribution of the wastewater.
6.02 Principles of Operation
The maintenance of a good growth of organisms on the filter media
is crucial to successful operation.
6-8
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DISCHARGE LEVEL
STEEL BALL
AUTOMATIC SIPHON,
OR DOSING CHAMBER
AIR VENT
BLOW-OFF TRAP
TO FILTER
FIXED-SPRAY NOZZLES
Fig. 6.5 Siphon and nozzle details for fixed spray filters
-------
The term "filter" is rather misleading, indicating that solids
are separated from liquid by a straining action, but this is not
the case. Passage of wastewater through the filter causes the
development of a gelatinous coating of bacteria, protozoa, and
other organisms on the media. This growth of organisms absorbs
and utilizes much of the suspended colloidal and dissolved organic
matter from the wastewater as it passes over the growth in a
rather thin film. Part of this material is utilized as food for
production of new cells, while another portion is oxidized to
carbon dioxide and water. Partially decomposed organic matter
together with excess and dead film is continuously or periodically
washed (sloughed) off and passes from the filter with the effluent.
For the oxidation (decomposition) processes to be carried out,
the biological film requires a continuous supply of dissolved
oxygen, which may be absorbed from the air circulating through
the filter voids (spaces between the rocks or other media).
Adequate ventilation of the filter must be provided; therefore
the voids in the filter media must be kept open. Clogged voids
can create operational problems, including ponding and reduction
in overall filter efficiency.
A method of increasing the efficiency of trickling filters is to
add recirculation. Recirculation is a process in which filter
effluent is recycled and brought into contact with the biological
film more than once. Recycling of filter effluent increases the
contact time with the biological film and helps to seed the lower
portions of the filter with active organisms. Due to the increased
flow rate per unit of area, higher velocities occur which tend to
cause more continuous and uniform sloughing of excess growths,
thus preventing ponding and restriction of ventilation. This
increased hydraulic loading also decreases the opportunity for
snail and filter fly breeding. It has been observed that the
thickness of the biological growth is directly related to the
organic strength of the wastewater (the higher BOD, the thicker
the layers of organisms). By the use of recirculation, the strength
of wastewater applied to the filter can be diluted, thus preventing
excessive build-up.
Recirculation may be constant or intermittent and at a steady or
fluctuating rate. Recycling may be practiced only during periods
of low flow to keep rotary distributors in motion, to prevent
drying of the filter growths, or to prevent freezing. Recirculation
in proportion to flow may be utilized to reduce the strength of the
wastewater applied to the filter while steady recirculation of a
constant amount keeps the distributors in operation and also tends
to even out the highs and lows of organic loading, but involves
higher pumping costs.
6-10
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It is generally agreed that any organic waste which can be
successfully treated by other aerobic biological processes
can be treated on trickling filters. This includes, in
addition to domestic wastewater, such wastewaters as might
come from food processing, textile and fermentation industries,
and certain pharmaceutical processes. Industrial wastewaters
which cannot be treated are those which contain excessive con-
centrations of toxic materials, such as pesticide residues,
heavy metals, and highly acidic or alkaline wastes.
For maximum efficiency, the slime growths on the filter media
should be kept fairly aerobic. This can be accomplished by
proper design of the wastewater collection system and proper
operation of primary clarifiers, or by pretreatment of the
wastewater by aeration or addition of recycled filter effluent.
The air supply to the slimes may be improved by increased air
or wastewater recirculation. The thin slime growth may be
aerobic on the surface, but anaerobic next to the media. A
trickling filter media of rock or slag can accumulate slimes
only on the outside surface, but manufactured media provides
considerably more surface area per unit of dead space.
I/.
The temperature of the
wastewater and of the
climate also affects
filter operation, with
temperature of the waste-
water being the more
important. Of course,
temperature of the
wastewater will vary
with the weather.
Within limits, activity
of the organisms increases
as the temperature rises.
Therefore, higher loadings
and greater efficiency
are possible in warmer
climates if aerobic conditions
can be reasonably maintained
in the filter.
6-11
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QUESTIONS
6.0A Primary treatment is effective in removing (a)
and (b) , but not nearly
as effective in removing (c)
6.OB What is the purpose of "secondary treatment"?
6.0C How does the trickling filter process work?
6.0D What causes the distributor arms or pipes on a trickling
filter to operate?
6.0E How does recirculation increase the efficiency of a trickling
filter?
6-12
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6.1 STARTING AND OPERATING A FILTER4
6.10 Pre-Start Up
A new plant is seldom started up without some unexpected, frus-
trating problems. Some careful checking ahead of time can prevent
many of these situations.
If at all possible, you should arrange to be present when your new
equipment is serviced. You should see that the correct oil is
used in all oil reservoirs. Many contractors will put motor oil
in everything and consider it serviced. For future reference,
record the amount and type of oil each reservoir holds.
Insist on being present when the mercury is installed in the mercury
seal chamber on trickling filter distributors. This is expensive
material, and in case wastewater leaks past the seal, you should
definitely know whether the recommended amount of mercury was in-
stalled.
After the oil and mercury have been installed in a distributor,
check the arms for even adjustment and level. Rotate the unit by
hand and observe for smooth turning. Any vibration or roughness
should be corrected before putting the unit in service.
If the distributor has adjustable orifices, get the erection sheet
and a rule and check out the orifice settings. File the erection
sheet for future reference.
In a trickling filter plant with fixed spray nozzles, each nozzle
should be checked to insure that it is free of foreign objects.
In order to prevent damage to pumps, crawl into the underdrain
system of the filter and remove any debris (rocks, pieces of wood,
etc.). Check painted surfaces for damaged areas. Touch these up
before they get wet to prevent corrosion and further damage. A few
nicks and scratches in a distributor arm can seriously affect the
life of the original protective coatings.
Contracts for treatment plant construction often include
services of the consultant or contractor to assist in start-
up of new facilities. The operator should make full use of
these services when available.
6-13
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Check all valves in the system for smooth operation. On sliding
gate valves, see that the gates seat properly. There are adjust-
able wedges and stops on this type of valve. With the valve ad-
justed, set the lock nut on the stem to prevent jamming the gate
closed too tightly. These small precautions will yield years of
trouble-free valve operation.
In addition to the general items covered in this section, you
should be certain that the correct manufacturer's manual has been
furnished for each piece of equipment. Read each manual carefully
and follow the given recommendations. Obtain the oils and greases
recommended; or, if you buy from one oil company, have their repre-
sentative furnish you a written list of his company's products that
are equivalent to those recommended by the equipment manufacturer.
6.11 Placing Filter in Service
When you have checked out all equipment mechanically, starting up
the trickling filter portion of the plant is very simple. Start
the wastewater flow to the filters, observing the rotating arms
carefully for smooth operation, speed of rotation, and even distri-
bution of the waste over the media. Time the speed of rotation,
record the flow rate, and log them for future reference.
For fixed nozzles, observe the spray pattern. Some debris will
usually show up to plug some of the nozzles, the amount depending
on how thoroughly the plant was checked out previous to start-up.
It is important to keep the nozzles clear so that the wastewater
is distributed over ail of the filter media.
It will take several days for any growth to develop on the filter
media, and up to several weeks for full development. Time of year,
weather conditions, and
strength of the waste are
all factors which will
affect the time needed for
growth development.
During this period of growth
development, an unstable
effluent will be produced.
This effluent will exert a
pollutional load on the
receiving waters. Heavy
chlorination is usually used
during this time to reduce
the pollutional load and the
health hazard to some extent.
6-14
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In some locations, the use of chlorine in this manner may be
restricted, such as where fish are threatened. If an older
plant is being phased out, it may be possible to load the new
facilities lightly or intermittently until a full growth is
established.
Starting up of pumps, clarifiers, and other equipment is covered
in other chapters.
6.12 Daily Operation
Once growth on the media has been established and the plant is in
"normal operation", very little routine operational control is
required. Careful daily observation is important. Items to be
checked daily are:
1. Any indication of ponding
2. Filter flies
3. Odors
4. Plugged orifices
5. Roughness or vibration of the distributor arms
6. Leakage past the mercury seal
Occasionally the underdrains should be checked for accumulation of
debris in order to prevent stoppages.
Refer to the appropriate paragraphs in the following section on
operational problems for procedures to correct these conditions.
Operation of clarifiers is interconnected with trickling filter
operation. If the recirculation pattern permits, it is a good idea
to return filter effluent to the primary clarifier. This is a very
effective odor control measure. In some plants, increasing the
recirculation rate will increase the hydraulic loading on the
clarifier. Be sure the hydraulicloading remains within the
engineering design' limits. I~f the" hydraulic loading is too low,
septic conditions may develop in the clarifier, while excessively
high loadings may wash solids out of the clarifier.
Recirculation during low inflow periods of the day and night may
help to keep the slime growths wet, minimize fly development and
wash off excessive slime growths. It may be necessary to reduce
or stop recirculation during high flow periods to avoid clarifier
problems from hydraulic overloading. Recirculation of final
clarifier effluent dilutes influent wastewater and recirculated
sludge improves slime development on the media.
6-15
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You should, by evaluating your own operating records, adjust the
process to obtain the best possible results for the least cost.
Use the lowest recirculation rates that will yield good results
(but not cause ponding or other problems) to conserve power.
Power costs are a large item in a plant budget. Also, reduced
hydraulic loadings mean better settling in the clarifiers, re-
sulting in less chlorine usage in plants which disinfect the
final effluent, since organic matter exerts a high chlorine demand.
If filter effluent, rather than secondary clarifier effluent, is
recirculated, the hydraulic loading on the secondary clarifier is
not affected.
QUESTIONS
6.1A Prepare a check list of items that should be in-
spected before a trickling filter is placed in
service.
6.IB During start-up of a trickling filter, why
should the plant effluent be heavily chlorinated?
6.1C Prepare a check list of items needing daily
inspection during "normal operation".
6. ID What may happen to a clarifier effluent if the
clarifier is not operated within design hydraulic
loadings?
6-16
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6.2 SAMPLING AND ANALYSIS
6.20 General
The trickling filter is a biological treatment unit and therefore
loadings and efficiencies of the unit are normally determined on
the basis of influent characteristics (inflow and biochemical oxygen
demand (BOD) test) and required quality of effluent or receiving
waters (dissolved oxygen and solids). Detailed procedures for
performing the trickling filter control tests are given in
Chapter 14, Laboratory Procedures and Chemistry. The frequency
of each test and expected ranges will vary from plant to plant.
Strength of the wastewater, freshness, characteristics of the
water supply, weather, and industrial wastes will all serve to
affect the "common" range of the various test results.
6.21 Typical Trickling Filter Plant Lab Results
Test
1. Dissolved
Oxygen
2. Settleable
Solids
3. pH
4. Temperature
5. BOD
6. Suspended
Solids
7. Chlorine
Residual
8. Coliform
Bacteria
9. Clarity
Frequency
Daily
Daily
Daily
Daily
Daily
Weekly
(Minimum)
Daily
Location
Prim. Effl.
Influent
Influent
Final Effl.
Influent
Common Range
1.0 - 2.0 mg/1
5-15 ml/1
6.8 - 8.0
7.0 - 8.5
Weekly
(Minimum)
Influent
Prim. Effl.
Final Effl.
150 -
60 -
15 -
400 mg/1
160 mg/1
40 mg/1
Weekly
(Minimum)
Influent
Prim. Effl.
Final Effl.
150 - 400 mg/1
60 - 150 mg/1
15 - 40 mg/1
Final Effl. 0.5 - 2.0 mg/1
Final Effl.,
Chlorinated
Final Effl.
50 - 700/100 ml
1 - 3 ft
6-17
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NOTES: Results of tests listed on the previous page as "Primary
Effluent" may vary at different plants due to the many
variations in recirculation patterns and activities of
the waste dischargers into the collection system.
Settleable solids tests of the effluent may be required
by some regulatory agencies. If your plant is operating
efficiently, the settleable solids will be so low as to
be unreadable. In this case, record as "Trace".
Dissolved Oxygen and Settleable Solids or Clarity Tests
on trickling filter effluent are sometimes useful in evalu-
ating problems when they occur. The operator should know
what range is "common" for his plant.
An easy test that should be made periodically by the operator is to check
trie distribution of wastewater over the filter. Pans of the same
size are placed level with the rock surface at several points along
the radius of a circular filter. The distributor arm should then
be run long enough to almost fill the p?'.ns. The arm is then stepped
and the amount or depth of water in each pan is measured. The amount
in each pan should not differ from the average by more than 5%. If
the distribution is not uniform, the orifices must be adjusted.
6.22 Response to Poor Trickling Filter Performance
There are several operational procedures an operator can follow to
correct deficiencies in plant performance. The ability to make
corrections will depend on your alertness and ingenuity, as well
as the design of the collection system and treatment plant. In
Section 6.21, the common ranges are listed for a number of lab test
results. If your plant is not operating within or near the common
ranges for your plant, then you may have problems.
Suspended Solids. An effluent that is high in suspended solids may
be expected to affect al'' the other test results listed. Ordinarily
this will be due to three principal factors:
1. Heavy sloughing from the filters,
2. High hydraulic loading or short-circuiting through
the secondary or final clarifier, and
3. Shock loading caused by toxic wastes or hydraulic
or organic overloads.
Heavy sloughing may be due to seasonal weather changes, a period of
heavy organic loading on the filters, or corrective action taken to
overcome ponding, filter flies, or other problems (see Section 6.3).
High hydraulic loading or short-circuiting in the secondary clarifier
6-18
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will carry the light solids from the filters over the weirs. If
a plant is not receiving more flow than it was designed to handle,
you may be able to adjust recirculation rates or the flow pattern
(see Fig. 6.7, Page 6-40) to reduce the clarifier loading. Refer
to Chapter 5, Sedimentation and Flotation, for solutions to problems
created in clarifiers by short-circuiting and sludge withdrawal.
BOD. The effluent BOD will generally go up or down along with the
suspended solids. This is not always the case, however. Anything
you can do to assure that the wastewater arrives at the plant in
an aerobic condition will reduce the organic load (and odors);
consequently, the effluent BOD will be lower. Aeration has been
used in force mains with some degree of success when applied
properly.
The recirculation rate and flow pattern will affect effluent
quality. These can be varied experimentally, keeping in mind that
too low a recirculation rate leads to filter flies and ponding,
while too high a rate may cause excessive sloughing or overload
the clarifiers. Biological systems respond to a change in their
environment and establish a balance with the existing conditions,
but it takes time. If you change your operation, give your plant
a couple of weeks to reach an equilibrium state (level out) before
you decide whether or not you have helped the situation.
The shortcomings of the BOD test must be recognized. It is difficult
to use as a daily operational tool unless the influent BOD remains
fairly constant. If an industry dumped some wastewater with a high
BOD, you could not measure the BOD and base your operational adjust-
ments on the test results because they will not be available for
five days. You will have to adjust your operation on the basis of
your experience and the probable BOD. Use the COD test to estimate
rapid changes in the influent load. For control purposes the COD
test procedure may be altered and a very short heating time may be
acceptable.
S e 111 e able Solids. High settleable solids in the effluent mean that
solids are being carried over the clarifier weir. It also means that
the suspended solids will be high. Refer to the paragraph in this
section on suspended solids for corrective action.
Dissolved Oxygen. One of the principal functions of a trickling
filter plant is to stabilize the oxygen demanding substances in
the wastewater being treated. This is achieved by the addition of
dissolved oxygen to the water. If the suspended solids and BOD
are within range, the DO is almost certain to be in range also.
Increased recirculation will increase the DO. In plants with
very low inflows, excessive detention time in the clarifiers may
cause the problem. If this is the case, remember that any agitation
6-19
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of the effluent will cause it to pick up dissolved oxygen. If
the elevation is available, a staircase type of effluent dis-
charge will help; otherwise it may be necessary to aerate the
effluent, using compressed air or paddle type aerators (see
Chapter 7, Activated Sludge).
Chlorine Demand. Difficulty in maintaining a chlorine residual in
the effluent (assuming normal detention period) will primarily be
due to excessive solids in the effluent. Refer to the paragraph on
Suspended Solids.
C1arity. Clarity of the effluent also is primarily related to the
amount, size, shape, and characteristics of the suspended solids
in the effluent. In some cases, industrial or food processing
wastes may cause discoloration. Trickling filter effluents tend
to be slightly turbid.
pH. The pH of the effluent should move from whatever value is
found in the influent toward neutral (a pH of 7.0). Normally the
influent pH will be somewhat acidic (a pH of less than 7.0) and
will move up to 7.0 or slightly higher. Other than pH changes
caused by industrial waste dumps or other unusual wastes entering
the plant, the pH will remain "normal" as long as the suspended
solids and BOD are within reasonable limits. Corrective action
requires chemical neutralization.
Coliform Count. Where the bacterial count requirement must be met,
excessive solids in the effluent are a serious problem. Even with
high chlorine residuals, some particles are not penetrated com-
pletely by the chlorine, yielding sporadic results. If in-plant
corrections do not solve the solids carry-over problem, some type
of water treatment plant techniques may have to be employed, such
as coagulation and settling, or sand or diatomaceous earth filters.
Good disinfection is achieved if the previous treatment processes
do their job.
6-20
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QUESTIONS
6.2A How would you determine if the distribution of
wastewater over a trickling filter is even?
6.2B List the laboratory tests used to measure the
efficiency of a trickling filter.
6.2C (1) Calculate the efficiency of a trickling
filter plant if the suspended solids of
the plant influent is 200 mg/1 and the
plant effluent suspended solids is 20 mg/1.
(2) What is the efficiency of the trickling
filter only if the effluent suspended
solids from the primary clarifier (waste-
water applied to filter) is 140 mg/1?
END OF LESSON 1 OF 3 LESSONS
on
Trickling Filters
6-21
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 1 of 3 Lessons)
Chapter 6. Trickling Filters
Name Date
Write the answers to these questions in your notebook before
continuing.
1. Draw a sketch of a trickling filter and label the essential
parts.
2. Why is recirculation important in the operation of a trickling
filter?
3. Why should a trickling filter be carefully checked before a
new one is started or an existing one is placed in service
again?
4. Why would the efficiency of waste removal by a new trickling
filter be low during the first few days?
5. What would you do if laboratory results or visual inspection
indicated a sudden drop in efficiency of a trickling filter?
6. Calculate the suspended solids removal efficiency of a trickling
filter plant if the influent suspended solids were 360 mg/1 and
the effluent suspended solids were 40 mg/1.
7. Why do laboratory test results for trickling filter plants vary
from
a. plant to plant?
b. month to month within a plant?
6-23
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CHAPTER 6. TRICKLING FILTERS
(Lesson 2 of 3 Lessons)
6.3 DAILY OPERATION PROBLEMS
In actual operation, the trickling filter is one of the most trouble-
free types of secondary treatment. It requires less operating
attention and control. Where recirculation is used, difficulties
due to shock loads5 are less frequent and recovery is faster.
Suspended solids in the trickling filter effluent tend to make the
effluent somewhat turbid; thus, a poorer quality effluent due to
shock loads may not be visibly evident. Recirculation is used to
maintain a constant load on the filter and thus produce a better
quality of effluent. However, there are some problems which
include ponding; odors; insects; and, in colder climates, freezing.
These problems are all controllable, and in most cases, preventable.
6.30 Ponding
Ponding is normally the result of excessive organic loading without
a corresponding high recirculation rate. Another cause of ponding
can be the use of media which is too small or not sufficiently uniform
in size. In non-uniform media, the smaller pieces fit between the
larger ones and thus make it easier for the slimes to plug the filter.
If this condition exists, replacement of the media is the most satis-
factory solution. Other causes of ponding include a poor or improper
media permitting cementing or break up, accumulation of fibers or
5 Shock Loads. The arrival at a plant of waste which is toxic to
organisms in sufficient quantity or strength to cause operating
problems, such as odors or sloughing off of the growth or slime
on the trickling filter media. Organic or hydraulic overloads
also can cause a shock load.
6-25
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trash in the filter voids, a high organic growth rate followed by
a shock load and rapid uncontrolled sloughing, or an excessive
growth of insect larvae or snails which may accumulate in the voids.
Ponding results from a loss of open area in the filter. If the
voids are filled, flow tends to collect on the surface in ponds.
The cause of ponding must be located since it may increase rapidly
and take over large areas of the filter. Increasing the hydraulic
loading by increasing the recirculation ratio or adjusting the ori-
fices on the distributor assembly so that it distributes flow more
evenly is likely to flush off some of the heavier portions of the
biological film and may slowly cure this condition.
Minor ponding, which may occur from time to time, can be eliminated
by any of several methods, including the following:
1. Jet filter surface with a high pressure water stream.
Sometimes stopping a rotary distributor over the
ponded area will flush the growth from the voids.
One way to do this is to shut off the flow momentarily,
wait for the distributor to stop, move the distributor
to the problem area, and then restart the flow while
keeping the distributor over the ponded area.
2. Hand turn or stir the filter surface with a rake, fork,
or bar. Remove any accumulation of leaves or other
debris.
3. Dose the filter with chlorine at about 5 mg/1 for
several hours. If done during a period of low flow,
the amount of chlorine used is held to a minimum.
4. If it is possible to flood the filter, then keeping
the media submerged for 24 hours will cause the growth
to slough somewhat. Keep the surface of the media
covered, but don't let the water rise high enough to
get in the distributor bearings. Under these conditions
the growths tend to become anaerobic and loosen or
liquify. The resulting liquid is a mess to dump.
5. Shut off flow to the filter for several hours. The
growth will dry, and part of it will be flushed our
when the unit is put back in service.
6-26
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It is important to keep in mind that your primary purpose is to
consistently turn out an effluent of good quality. With this in
mind, the corrective actions on the previous page are listed in
order, starting with procedures that will least affect the
effluent. If at all possible, ponding should be corrected before
it becomes serious. Items 4 and 5 are drastic measures. However,
the job must be done so that full efficiency of the filter is
restored. In cases 4 and 5, where effluent chlorination is used,
it is usually a good idea to increase the amount of chlorine in
the effluent until the filter has been restored to normal operation.
6.31 Odors
Since operation of trickling filters is an aerobic6 process, no
serious odors should exist. The presence of foul odors indicates
that anaerobic7 conditions are predominant. (Anaerobic conditions
are usually present next to the media surface. As long as the
surface of the slime growth zoogleal film is aerobic, odors
should be nimor.) Corrective measures should be taken immediately.
Some things to check:
1. Do everything possible to maintain aerobic conditions
in the sewer collection system and in the primary
treatment units.
2. Check ventilation in the filter. Heavy biological
growths or stoppages in the underdrain system will
cut down ventilation. Examine ventilation facilities
such as the draft tube or other inlets for stoppages.
If necessary, force air into underdrains using mechanical
equipment such as fans or compressors. Natural venti-
lation through a filter will occur if the vents are
open and the difference in air temperature and filter
temperature is greater than 3°F.
3. Increase the recirculation rate to provide more oxygen
to the filter bed and increase sloughing.
4. Keep the wastewater splash from the distributor away
from exposed structures, grass, and other surfaces to
retain the growth on the media. If slime growths appear on
sidewalks and other surfaces, remove the slimes immediately.
6 Aerobic (AIR-0-bick). A condition in which "free" or dissolved
oxygen is present.
7 Anaerobic (AN-air-0-bick). A condition in which "free" or dis-
solved oxygen is not present.
6-27
-------
In some cases during hot weather, odors will be noticeable from
filters in good condition. If these odors are a serious problem
(close neighbors), the situation can sometimes be resolved with
one of the commercially available masking agents.a This should
be a last resort.
6.32 Filter Flies
The tiny, gnat-size filter fly (psychoda) is the primary nuisance
insect connected with
,w ./•;...; . trickling filter opera-
tions. They arc
occasion-
ally found in great numbers
and can be an extremely
difficult problem to plant
operating personnel as well
as nearby neighbors. Pre-
ferring an alternate wet
and dry environment for
development, the flies are
found most frequently in
low-rate filters and are
usually not much of a
problem in high-rate
filters. Control can
usually be accomplished
by the use of one or more
of the following methods:
1. Increase recircu1ation. A continuous hydraulic loading of
200 gpd/sq ft or more will keep filter fly larvae washed out
of the filter.
2. Apply approved insecticides with caution to filter walls and
to other plant structures. If not prohibited by your local
control agencies, the surface of the filter (and the walls of
the retaining structure) may be sprayed with approved doses
of an insecticide.
8 Masking Agents. Liquids which are dripped into the wastewater,
sprayed into the air, or evaporated (using heat) with the "fumes"
or odors discharged into the air by blowers to make an undesirable
odor less noticeable.
6-28
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3. Flood filter for 24 hours at intervals frequent enough
to prevent completion of the life cycle. This cycle
is as short as seven days in hot weather. A poor effluent
will result from this practice and should be accurately
monitored.
4. A low dosage of chlorine applied weekly may do the job.
5. Shrubbery, weeds, and tall grass provide a natural
sanctuary for filter flies. Good grounds maintenance
and cleanup practices will help to minimize fly problems.
6.33 Weather Problems
Cold weather usually does not offer much of a problem to wastewater
flowing in a pipe or through a clarifier. Occasionally, however,
wastewater sprayed from distributor nozzles or exposed in thin
layers on the media may reach the freezing point and cause a build-
up of ice on the filter. Several measures can be taken to reduce
ice problems on the filter:
1. Decrease the amount of recirculation, provided sufficient
flow will remain to keep the filter working properly.
2. Operate two-stage filters9 in parallel rather than in
series.
3. Adjust orifices and splash plates to reduce the spray
effect.
4. Construct wind screens, covers, or canopies to reduce
heat losses.
5. Break up and remove the larger areas of build-up.
6. Partially open end gates to provide a stream rather
than a spray along the retaining wall.
7. Add hot water or steam to the influent if necessary.
9 Two-Stage Filters. Two filters are used. Effluent from the
first filter goes to the second filter, either directly or
with a clarifier in between the two filters. (See Fig. 6.7,
page 6-40.)
6-29
-------
Although the efficiency of the filter unit is reduced during
periods of icing, it is important to keep this unit running.
Taking the unit out of service will not only reduce the quality
of the effluent but may lead to additional maintenance problems,
such as ice forming, with the possibility of structural damage.
Also, moisture may condense in the oil and damage the bearings.
QUESTIONS
6.3A What are some of the causes of ponding?
6.3B How would you correct a ponding problem?
6.3C How would you control odor problems in a trickling
filter?
6.3D Trickling filter flies can be controlled by what
methods?
6.3E Why should a trickling filter not be taken out of
service during icing conditions?
6-30
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6.4 MAINTENANCE
6.40 Bearings and Seals
The mercury seal in the base of the distributor keeps the waste-
water from leaking out of the center column and possibly into the
bearings. (See Fig. 6.6.) The bearings ride in removable races,
immersed in oil. A good grade of turbine oil with oxidation and
corrosion inhibiting agents is recommended. Your manufacturer's
manual will contain oil specifications. Check the oil weekly.
To check, drain out about a pint into a clean container and, if
the oil is clean and free of moisture, return it to the unit.
Droplets of water and oil are easily distinguished. Maintain
the correct oil level. If the oil is dirty, drain the oil, re-
fill with a mixture of approximately 1/4 oil and 3/4 solvent
(such as kerosene), and operate the distributor for a few minutes.
Drain again, and refill with the correct oil.
If water is found in the oil, check the mercury seal. Drain the
mercury from the seal and from the overflow pockets (Fig. 6.6),
and weigh it. If necessary, add mercury to maintain the amount
specified by the manufacturer.
WARNING
6.41 Distributor Arms
Work on distributor orifices only after the arms have stopped moving,
unless you are using a pressure hose for cleaning and stand outside
the filter wall. The distributor arms should be flushed weekly by
opening the end dump gates one at a time. Clean debris out of the
orifices at this time, also. Observe operation of the filter each
day, cleaning the orifices as often as needed. When there is con-
siderable plugging, you should install a coarse hardware cloth or similar
type screen if possible, ahead of the filters. Screens are easier
to clean and good distribution is maintained over the filter media.
Observe the distributor daily for smooth operation. If it becomes
jumpy or seems to vibrate, or slows down with the same amount of waste-
water passing through it, the bearings and races are probably damaged
6-31
-------
and will require replacement. A thorough oil check each week
will probably keep this from happening.
The speed of rotation of the distributor should not be excessive.
On larger distributors, approximately 1 rpm is normal. The
manufacturer's literature will state the maximum allowable speed.
Rotation of the distributor is due to the reaction of the water
flowing through the orifices. This is similar to the reaction
of a fire hose or of some types of lawn sprinklers. To reduce
the speed of rotation, provision is usually made on the front
of each arm for orifices which are easily installed (Fig. 6.3).
The reaction of the water flowing through these orifices cancels
some of the thrust of the regular orifices. If the speed of
rotation is too slow, check for mechanical problems and, if none,
increase flow to distributor.
Since most distributors appear rather large and bulky, most
operators are surprised to find that they are delicately balanced.
As soon as wastewater begins to flow from the orifices, the distri-
butor arm should start to move. The fan-like pattern as the waste-
water leaves the deflecting plates should be uniform. If the plates
have developed a slime growth that is affecting uniform distribution,
the slime should be brushed off.
6.42 Maintenance of Fixed Nozzles
Fixed nozzles should be observed frequently and cleaned often if
plugging is persistent. If frequent plugging is a problem, screens
may be used ahead of the filter to remove debris.
QUESTIONS
6.4A What is the purpose of the mercury seal in a rotary
distributor?
6.4B Why should you drain some of the oil from the dis-
tributor each time it is checked?
6.4G How would you slow down the rotational speed of a
distributor?
6-32
-------
THIS PART ROTATES
_V
\
DISTRIBUTOR BASE
-ADJUSTABLE RINGS
MERCURY
OVERFLOW
POCKET
MERCURY
OVERFLOW DRAIN
-OIL LEVEL INDICATOR AND DRAIN
MERCURY SEAL
PREVENTS LEAKAGE
WASTEWATER FLOW
Fig. 6.6 Distributor base
-------
6.5 SAFETY
Do not carry oil in glass containers,
soles will help your footing.
In order to work around a
trickling filter safely,
several precautions should
be taken. First, shut off
the flow to the f i Iter and
allow the distributor to
stop rotating before
attempting to work oh it.
On all but the very small
units, the force of the
rotating distributor arms
is about the equivalent of
a good-sized truck. A man
just can't reach out and
stop one without endangering
himself. Serious injuries
can result.
The slime growth on a filter
is very slippery. Extreme
care should be taken when
walking on the filter med"ia.
Rubber boots with deeply ridged
QUESTION
6.5A Why should the flow to a trickling filter be shut off
before attempting to work on the filter?
END OF LESSON 2 OF 3 LESSONS
on
Trickling Filters
6-34
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 3 Lessons)
Chapter 6. Trickling Filters
Name Date
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 1.
8. Define the term shock load.
9. How would you correct a ponding problem?
10. Why should a ponding problem be corrected as soon as possible?
11. What action would you take to prevent odor problems from
developing in a trickling filter?
12. Why should wastewater be kept from leaking into the bearings
of the distributor base?
13. Why should the flow to a trickling filter be shut off before
attempting to work on the filter?
6-35
-------
CHAPTER 6. TRICKLING FILTERS
(Lesson 3 of 3 Lessons)
6.6 CLASSIFICATION OF FILTERS
6.60 General
Depending upon the hydraulic and organic loadings applied, filters
are classified as standard-rate, high-rate, or roughing filters.
Further designations, such as single-stage, two-stage, series or
parallel, and others are used to indicate the flow pattern of the
plant. The hydraulic loading applied to a filter is the total volume
of liquid, including recirculation, expressed as gallons per day
per square foot of filter surface area (gpd/sq ft). The organic
loading is expressed
as the pounds of BOD
applied per day per
1000 cubic feet of
filter media
(Ibs BOD/day/1000 cu ft).
Where recirculation is
used, an additional
organic loading will
be placed on the
filter; however, this
added loading is omitted
in most calculations
because it was included
in the influent load.
6.61 Standard-Rate Filters
The standard-rate filter is operated with hydraulic loading range
of 25 to 100 gals/day/sq ft, and an organic BOD loading of 5 to 25
lbs/day/1000 cu ft. The filter media is usually 6 to 8 feet in depth,
with application to the filter by a rotating distributor, although
many are equipped to provide some recirculation during low flow periods,
The filter growth is often heavy and in addition to the bacteria and
protozoa10 many types of worms, snails, and insect larvae can be found.
10 Protozoa (pro-toe-ZOE-ah). A group of microscopic animals,
principally of one cell, that sometimes cluster into colonies,
6-37
-------
The growth usually sloughs off at intervals, noticeably in
spring and fall. The effluent from a standard-rate filter
treating municipal wastewater is usually quite stable with
BODs as low as 20 to 25 mg/1.
6.62 High-Rate Filters
High-rate filters were the result of trying to reduce costs
associated with standard-rate filters or attempting to treat
increased wasteloads with the same facility. Studies indi-
cated that essentially the same BOD reductions could be obtained
at the higher design loadings.
High-rate filters are normally 3 to 5 feet deep with recommended
loadings being 100 to 1000 gal/day/sq ft and 25 to 300 Ibs BOD/
day/1000 cu ft. These filters are designed to receive waste-
water continually, and practically all high-rate installations
utilize recirculation.
Due to the heavy flow of wastewater over the media, more uniform
sloughing of the filter growths occurs. This sloughed material
is somewhat lighter than from a standard-rate unit and therefore
more difficult to settle. Effluent with BODs as low as 20 to 50
mg/1 is sometimes produced by plants treating municipal waste-
water.
6.63 Roughing Filter
A roughing filter is actually a high-rate filter receiving a very
high organic loading. Any filter receiving an organic loading of
over 300 Ibs of BOD/day/1000 cu ft of media is considered to be
in this class. This type of filter is used primarily to reduce
the organic load on subsequent oxidation processes such as a
second-stage filter or activated sludge process. Many times
they are used in plants which receive strong organic industrial
wastes. They are also used where an intermediate (50-70% BOD
removal) degree of treatment is satisfactory.
Operation of the filter is basically the same as for the high-rate
filters with recirculation. Overall BOD reductions are much lower,
but reductions per unit volume of filter media are greater.
6-38
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6.64 Filter Staging
Fig. 6.7 shows various filter and clarifier layouts. The decision
as to the number of filters (or stages) required is one of design
rather than operation. In general, however, at smaller plants
where the flow is fairly low, the strength of the raw wastewater
is average, and effluent quality requirements are not too strict,
a single-stage plant (one filter) is often sufficient and most
economical. In slightly overloaded plants the addition of some
recirculation capability can sometimes improve the effluent quality
enough to meet receiving water standards without the necessity of
adding more stages.
In two-stage filter plants, two filters are operated in a series.
Sometimes a secondary clarifier is installed between the two
filters. Recirculation is almost universally practiced at two-
stage plants with many different arrangements being possible.
Choice of recirculation scheme used is based on consideration of
which arrangement produces the best effluent under the particular
conditions of wastewater strength and other characteristics.
(See Fig. 6.7.)
QUESTIONS
6.6A What are the three general classifications of trick-
ling filters?
6.6B What are the principal differences between standard-
rate and high-rate filters?
6-39
-------
RECIRCULATION LINE
INFLUENT
EFFLUENT
PRIMARY CLARIFIER JRICKUNIGFILTER SECONDARY CLARIFIER
Typical Single-Stage Recirculation Patterns
Typical Two-Stage Recirculation Patterns
Fig. 6.7 Trickling filter recirculation patterns
6-40
-------
6.7 LOADING PARAMETERS
6.70 Typical Loading Rates
STANDARD-RATE FILTER:
Media - 6.to 8 ft depth, growth sloughs
periodically
Hydraulic Loading - 25 to 100 gal/day/sq ft
Organic (BOD) Loading - 5 to 25 Ibs BOD/1000 cu ft
HIGH-RATE FILTER:
Media - 3 to 5 ft depth, growth sloughs
continually
Hydraulic Loading - 100 to 1000 gal/day/sq ft
Organic (BOD) Loading - 25 to 300 Ibs BOD/1000 cu ft
6.71 Computing Hydraulic Loading
In computing hydraulic loadings, several bits of information must
be gathered. To figure the hydraulic loading, we must know:
1. The gallons per day applied to the filter, and
2. The surface area of the filter.
NOTE; Hydraulic loadings are expressed as:
gal/sq ft/day,11 or
gal/day/sq ft = gpd/sq ft.11
Both expressions mean the same. The hydraulic rate indi-
cates the number of gallons of wastewater per day applied
to each square foot of surface area or the gallons of water
applied to each square foot each day.
11 Loadings as well as test results should always be presented
using the same units. Theoretically a rate should have the
time unit last (gal/sq ft/day); however, because flows are
calculated as gal/day, it is easier to understand if loadings
are reported as gal/day/sq ft. The Water Pollution Control
Federation's MOP No. 6, Units of Expression for Wastes and
Waste Treatment, uses both terms.
6-41
-------
Suppose we have a high-rate filter that is fed by a pump rated at
2100 gpm, and the filter diameter is 100 feet.
Hydraulic Loading, _ F^low Rate, gpd
gpd/sq ft Surface Area, sq ft
For our problem, we must obtain the flow rate in gpd and surface
area12 in square feet or ft2.
Flow Rate,
gal
= 2100 x
min
hr
24 hrs
day
= 3,024,000 gal/day
(b) Surface Area,
sq ft
0.785 x (Diameter, ft)2
0.785 x 100 ft x 100 ft
7850 sq ft
(c)
Hydraulic
Loading,
gpd/sq ft
^ Flow Rate, gpd
Surface Area, sq ft
5,024,000 gpd
7850 sq ft
= 385 gpd/sq ft
385
7850 / 3,024,000.
2 355 0
669 00
628 00
41 000
39 250
1 750
12 Area of a
Circle, sq ft
0.785 x Diameter, ft x Diameter, ft, or
0.785 D2
6-42
-------
It is important to note in computing hydraulic loadings that when
filter effluent is recirculated to the filter influent, recirculated
flow must be added to the primary clarifier effluent flow 'irf order
to calculate the total hydraulic loading. When filter effluent is
recirculated to the primary clarifier influent, recirculated flow
must be added to the clarifier influent flow.
6,72 Computing Organic (BOD) Loading
Using the same filter as in the above example of hydraulic loading,
assume that the laboratory test results show that the wastewater
being applied to the filter has a BOD of 100 mg/1. We need to know
the pounds of BOD applied per day and the volume of the media in
cu ft.
NOTE: Organic (BOD) loadings are expressed as:
Ibs BOD/1000 cu ft/day, or
Ibs BOD/day/1000 cu ft.
Both expressions mean the same. The organic loading indi-
cates the pounds of BOD applied per day to the volume of
filter media for treatment.
Organic (BOD) Loading, _ BOD Applied, J-bs/day ^
Ibs BOD/day/1000 cu ft " Volume of Media in 1000 cu ft
To solve this problem we must first calculate the BOD applied in
Ibs/day and volume of media in cu ft.
Volume of Media, , ~
£ = (Surface Area, sq ft) (Depth, ft)
= (7850 sq ft) (3 ft)
= 23,550 cu ft
Volume of Media,
in 1000 cu ft = 23'5
£*.
cu ft
= 23.5 thousand cubic feet
6-43
-------
100 mg
M mg
3<024 J x
day
= 2522 Ibs BOD/day
gal
25.22016
Organic BOD Loading,
Ibs BOD/day/1000 cu ft
BOD Applied, Ibs BOD/day
Volume of Media (in 1000 cu ft)
2522 Ibs BOD/day
23.5 (1000 cu ft) 23-5
107 Ibs BOD/day/1000 cu ft
107.
172 0
164 5
In computing BOD loadings, it is standard practice to ignore the BOD
of the recirculated effluent, where recirculation is used. To attempt
to perform this calculation (using the recirculated load) is compli-
cated and makes it difficult to compare your loadings and resulting
effluent quality with other plants.
13 The units of this formula can be proved by remembering that
one liter equals one million milligrams.
m
mg
L 1,000,000 mg
Therefore,
M mg
BOD xMGDx 8.34^-
L gal
x x 2* = Ib BOD/day.
M mg day gal
6-44
-------
QUESTIONS
6.7A What is hydraulic loading of a trickling filter and how
is it expressed?
6,7B What information must be available to figure the hydraulic
loading on a trickling filter?
6.7C What is the hydraulic loading on a trickling filter 80
feet in diameter that is receiving a flow of 3200 gpm?
6.7D Is the filter in Problem 6.7C within the normal hydraulic
loading range for high-rate filters?
6.7E What information is needed to figure the BOD loading on
a trickling filter?
6.7F Compute the BOD loading on a standard-rate trickling
filter with a diameter of 100 feet, media depth 8 feet,
which is receiving 350 gpm of wastewater with a BOD of
100 mg/1.
6.7G Is the filter in Problem 6.7F loaded within normal limits
for a standard-rate filter?
6-45
-------
5.8 ADDITIONAL READING
a. MOP 11, pages 98-107
o. New York Manual, pages 47-58
c. Texas Manual, pages 202-235
d. Sewage Treatment Practices, pages 47-54
END OF LESSON 3 OF 3 LESSONS
on
Trickling Filters
6-46
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 3 of 3 Lessons)
Chapter 6. Trickling Filters
Name Date
Write the answers to the questions before continuing. The problem
numbering continues from Lesson 2.
A trickling filter is 70 feet in diameter and the depth
of the media is 5 feet. The average daily flow is 2450
gpm and the BOD of the influent to the filter is 100 mg/1.
Show your work and calculate:
14. Flow in gallons per day.
15. Surface area of filter.
16. Hydraulic loading.
17. BOD applied in pounds per day.
18. Volume of filter media.
19. Organic loading.
6-47
-------
SUGGESTED ANSWERS
Chapter 6. Trickling Filters
6.0A (a) and (b) Settleable solids and scum or floatable
solids. (c) BOD or organic or oxygen demanding material.
6.OB The purpose of secondary treatment is to remove soluble
and nonsettleable or nonfloatiiig oxygen demanding substances.
6.0C The trickling filter process works by distributing settled
wastewa'cer over the filter media. Microorganisms grow on
the filter media and convert colloidal and soluble oxygen
demanding substances to forms that will separate from the
wastewater being treated.
6.0D The distributor arms or pipes on a trickling filter rotate
because of the reaction from the force of the water leaving
the arms (as with a lavm sprinkler or fire hosej, or by
mechanical means (a motor and gears).
G.OE Recirculation increases the efficiency of a trickling filter
by increasing the time of contact of the wastewater with the
biological slime growth on the filter media, and by washing
off excess growths (sloughing). Sloughing keeps the bio-
logical film in an aerobic condition and seeds the lower
regions of the filter with active organisms. Sometimes
recirculation is used to prevent intermittent drying of
slimes on the filter media.
6.1A Items that should be checked before placing a filter in
service:
x Check type and amount of oil used in all oil reservoirs.
x Be present when mercury seal in distributor base is filled,
x Record amount of mercury used.
x Check distributor arms for rotation and level.
x Check distributor orifices.
x Remove debris from underdrain system.
x Touch up any damage to painted surfaces.
x Examine valves for seating and smooth operation.
x Remove any trash on or in the media.
6-49
-------
6.IB During start-up heavy chlorination is necessary to reduce the
health hazard and the pollutional load in the receiving waters
because the slime growths have not developed on the filter
media.
6.1C Items requiring daily checking:
x Ponding
x Filter Flies
x Odors
x Plugged Orifices
x Roughness or Vibration of Distributor Arms
x Leakage Past the Mercury Seal
x Splash beyond the Filter Media
x Cleanup of Slimes not on Media
6. ID If a clarifier is operated below design hydraulic loading,
the solids in the clarifier will become septic and cause
a poor effluent. When the hydraulic loading is too high,
some solids may be washed out of the clarifier.
6.2A To determine if the distribution of wastewater over the
trickling filter is even, place pans of the same size in
the media at several points along the radius of the filter.
Run the distributor until the pans are almost full. The
amount of water in each pan should not vary by more than 5%.
6.2B Laboratory tests used to measure the efficiency of a trickling
filter include BOD, suspended solids, and coliform group bacteria.
6.2C (1) Plant Efficiency:
BOD Efficiency, % = ^In. jn°Ut-> x 100%
- (200 mg/1 - 20 mg/1) ,.
200 mg/1 X 100°
= 90%
(2) Trickling Filter Efficiency:
Trickling Filter _ (In - Out) „
Efficiency, % !H x i(KH
- (140 mg/1 - 20 mg/1) ^
140 mg/1x iUU°
= 85.7%
END OF ANSWERS TO LESSON 1 AND START OF ANSWERS TO LESSON 2
6-50
-------
6.3A Causes of ponding include excessive organic loadings
without corresponding high recirculation rate, media too
small or not sufficiently uniform in size, accumulation
of debris in filter voids, or an excessive growth of
insect larvae or snails.
6.3B To correct a ponding problem:
(a) Locate cause.
(b) Increase hydraulic loading by increasing recircu-
lation.
(c) Adjust distributor so it will rotate more slowly
and. flush off some of the slime.
(d) If media is non-uniform, it should be replaced.
(e~) Jet filter surface with a high pressure water
stream or step distributor and allow it to flush
problem area.
(f) Rake or turn ponding area.
(g) Shut off filter for a few hours and allow growth
to dry so part of it may be flushed out.
(h) Flood filter.
(i) Dose filter with chlorine.
There are many possible ways to correct ponding. The
approach for a particular problem should be aimed at the
cause and the quickest and easiest way to correct the
situation. You are not expected to have listed all the
answers, but to know some of them.
6.3C To correct an odor problem in a trickling filter:
(a) Maintain aerobic conditions in collection system
and primary units.
(b) Maintain ventilation in filter.
(c) Increase recirculation rate if odor problems develop.
6-51
-------
6.3D Trickling filter flies can be controlled by:
(a) Increasing recirculation.
(b) Flooding filter weekly.
(c) Carefully applying insecticides.
(d) Cleaning around the filter, including grass
and shrubbery.
6.3E A trickling filter should not be taken out of service
during icing conditions because the quality of the effluent
will be reduced and additional maintenance problems could
develop.
6.4A The purpose of the mercury seal is to prevent wastewater
leakage from the center column before the wastewater is
distributed over the media.
6.4B Some oil should be drained from the distributor each time
it is checked to examine the condition of the oil and to
be sure the oil line is not plugged.
6.4C The rotational speed of a distributor can be reduced by
opening orifices on the front side of the distributor
arms.
6.5A Flow to a trickling filter should be shut off before
attempting to work on a filter because the rotating
arms can cause serious injury.
END OF ANSWERS TO LESSON 2 AND START OF ANSWERS TO LESSON 3
6.6A The three general classifications of trickling filters are
standard-rate, high-rate, and roughing filters.
6.6B The principal differences between standard-rate and high-
rate filters include BOD loadings, hydraulic loadings, and
depth of the media.
6.7A The hydraulic loading on a trickling filter is the amount
of wastewater applied per day over the surface area, ex-
pressed as gallons/day/sq ft, or gpd/sq ft.
6.7B Gallons/day applied to the filter and surface area of the
filter in sq ft. These two items are all that are needed.
However, it is necessary to convert the other data into
the proper form (gpm to gal/day, surface area in sq ft) .
6-52
-------
6.7C Given:
Diameter = 80 ft
Flow = 3200 gpm
Required: Hydraulic Loading
Flow Rate, gpd
Hydraulic Loading,
gpd/sq ft
Surface Area, sq ft
Find flow rate, gpd, and surface area in sq ft.
Flow Rate, 1 ,_ . „. ,
, ' __„„ gal 60 nun 24 hrs
gpd = 3200 —.— x —r x —5
r mm hr day
= 4,608,000 gal/day
Surface Area. „ „„,. ,... ^ /- s 9
f ' = 0.785 x (Diameter, ft)z
= 0.785 x 80 ft x 80 ft
Hydraulic
Loading,
gpd/sq ft
= 5025 sq ft (rounded off)
= Flow Rate, gpd
Surface Area, sq ft
4,608,000 gpd
5025 sq ft
= 917 gpd/sq ft
6.7D Yes. The hydraulic loading range for high-rate filters is
200 to 1000 gpd/sq ft.
6.7E To calculate the BOD loading on a trickling filter, the pounds
of BOD applied per day and the volume of filter media in
thousands of cu ft are needed. Since BOD is reported in mg/1,
the standard formula for converting mg/1 to pounds per day is
needed (mg/1 x MGD x 8.34), and usually gpm will have to be
converted to MGD (700 gpm = 1 MGD). There are many conversion
factors that can be used to obtain the correct answers, and you
should use the ones you are familiar with and understand.
6-53
-------
6.7F Given:
Diameter = 100 ft
Depth = 8 ft
Flow = 350 gpm
BOD = 100 mg/1
Required; Organic (BOD) Loading
Organic (BOD) Loading, _ BOD Applied, Ibs BOD/day
Ibs BOD/day/1000 cu ft ~ Volume of Media, 1000 cu ft
Find surface area, media volume, and BOD applied.
Surface Area, sq ft = 0.785 x (Diameter, ft)2
= 0.785 x 100 ft x 100 ft
= 7,850 sq ft
Volume of Media, cu ft = (Surface Area, sq ft) (Depth, ft)
= (7,850 sq ft) (8 ft)
= 62,800 cu ft
= 62.8 (1000 cu ft)
Flow Rate, MGD = (350 gpm)
700 gpm/MGD
= 0.5 MGD
BOD Applied, Ibs/day = (BOD, mg/1) (Flow, MGD) (8.34 Ig/gal)
= 100
g . _ M gal 0 _„ Ib
.,-2— x 0.5 —j&— x 8.34 —=-
M mg day gal
= 417 Ibs BOD/day
Organic (BOD) Loading, _ BOD Applied, Ibs/day
Ibs/day/1000 cu ft ~ Volume bfMecTia," 1000 cu ft
417 Ibs/day
62.8 (1000 cu ft)
= 6.6 Ibs BOD/day/1000 cu ft
6.7G Yes. The BOD loading range for standard-rate filters is 5
to 25 pounds of BOD per day per 1000 cu ft.
END OF ANSWERS TO LESSON 3.
6-54
-------
OBJECTIVE TEST
Chapter 6. Trickling Filters
Name Date
Please write your name and mark the correct answers on the IBM answer
sheet as directed at the end of Chapter 1. There may be more than one
answer to each question.
1. Loadings on a trickling filter may be expressed as:
1. Ib H20/day
2. Ib BOD/day/1000 cu ft
3. Ib H20/sq ft/day
4. gal/day/sq ft
5. gal/day/1000 cu ft
2. Masking agents:
1. Cover the filter
2. Mask the plant
3. Produce desirable odors
4. Are sprayed into the air
5. Tend to make undesirable odors unnoticeable
3. A shock load is:
1. A heavy blow
2. A big load in a truck
3. An unexpected strong waste
4. An unexpected bump
5. None of these
4. A flow of 1400 gpm is approximately the same as:
1. 1 MGD
2. 2 MGD
3. 0.5 MGD
4. 0.33 MGD
5. 0.75 MGD
5. Physical methods of waste treatment include:
1. Trickling filters
2. Disinfection
3. Sedimentation
4. Screens
5. Activated sludge
6-55
-------
6. Before starting up a new trickling filter plant the opera-
tor should check:
1. Oil reservoirs for proper amount and type of oil
2. Rotation of distributor arm
3. Underdrain system for debris
4. Zoogleal film on filter media
5. To be sure there are no voids in the filter media
7. In operating a trickling filter the operator should:
1. Adjust the process to obtain the best possible
results for the least cost
2. Use the lowest recirculation rates that will
yield good results to conserve power
3. Rotate the distributor as fast as possible to
better spray settled wastewater over the media
4. Maintain aerobic conditions in the filter
5. Bubble oxygen up through the filter
8. Which test best measures the efficiency of a trickling filter?
1. Total solids
2. pH
3. BOD
4. Temperature
5. Sludge age
H. To correct an odor problem in a trickling filter the operator
should:
1. Take corrective action immediately
2. Shut off flow to the filter
3. Try to maintain aerobic conditions
4. Check ventilation in the filter
5. Increase recirculation rate
10. Maintenance of a distributor moved by hydraulic action includes;
1. Cleaning the filter media
2. Cleaning orifices in the distributor arms
3. Changing the mercury if the distributor arm
does not rotate smoothly
4. Adjusting turnbuckles occasionally on guy
rods to keep rotating arms at proper level
5. Greasing gears that rotate distributor
6-56
-------
11. The differences between high-rate filters and standard-rate
filters include:
1. Higher flows per day per square foot of surface area
2. Higher pounds of BOD per day per cubic foot of media
3. Higher BOD reductions
4. Greater depth of filter
5. Higher rate of odor production
12. The hydraulic loading on a trickling filter 90 feet in
diameter with a flow of 0.6 MGD is approximately:
1. 100 gpd/sq ft
2. 95 gpd/sq ft
3. 90 gpd/sq ft
4. 85 gpd/sq ft
5. None of these
13. The organic load applied to a trickling filter in pounds
of BOD per day for a filter with a diameter of 75 feet,
a flow of 0.4 MGD, and a filter influent BOD of 100 mg/1 would
be approximately:
1. 350 Ibs/day
2. 335 Ibs/day
3. 325 Ibs/day
4. 300 Ibs/day
5. None of these
14. Successful trickling filter operation depends on:
1. Maintenance of a chlorine residual in the effluent
2. Washing slimes off the filter media
3. Preventing sludge bulking
4. Maintenance of a good growth of organisms on the
filter media
5. Filtering the solids out of the wastewater
15. The basic parts of a trickling filter include:
1. Distribution box
2. Distribution system
3. Pumps
4. Underdrain system
5. Media
16. Problems associated with trickling filters include:
1. Bulking
2. Filter flies
3. Clogging
4. Turbid effluent
5. Snails
6-57
-------
17. Trickling filtration is a primary treatment process.
1. True
2. False
If wastewater recirculation rates are too low, then (18)
18. 1. Aerobic
2. Anaerobic
conditions may develop in the secondary clarifier; however,
if recirculation rates are too high (19) | ^
19. 1. Solids will wash out of the secondary clarifier
2. The effluent will be sparkling clear
Please write on your IBM answer sheet the total time required to
work all three lessons and this objective test.
6-58
-------
APPENDIX
(Monthly Data Sheet)
-------
MONTHLY RECOR
UJ
<
0
1
2
3
4
b
6
7
8
9
10
1 1
12
13
14
15
16
17
IB
19
20
21
22
23
24
?f>
26
2 f
?R
29
30
31
>-
<
o
M
T
W
T
F
S
S
MAX.
MIN.
AVG.
WEATHER
FAIR
M
ii
II
C.LDY
II
FAIR
o
o
S
z
0
u.
UOO
1.051
I.I ZO
0.187
I.OOS
110?
o."m
.016
D
RAW WASTEWATER
cc
2
UJ
1-
70
6V
6?
70
fe«
ftfl
(,1
69
FLOW METER :
LftST 4*5237
TOTAI : 31.468 MP.
I
Q.
7.3
7.£
7.3
7.1
7.0
7.2
7.3
7.1
CO
8
H
UJ
OT
S
10
II
1
V
9
8
9
ELECTR
LAST
1st
MULT. §0
o
o
m
110
205
220
164
232
211
111
115
en
o
O
en
CL-
OT
o
en
208
a 18
z^^
201
ii-W
2.10
ZIS"
z\o
19
PRIM. EFF.
0
o
m
132
143
153
IZ7
162
147
131
130
1C METER !
51%
4&2I
X 375 _
9
i
a:
in
3
CO
15
101
108
12
120
IrtK
18
100
o
Q
a. 3
i.H
2.0
2.1
2.0
? ?
2.1
2.0
CLEAN WATER, U.S.A.
WATER POLLUTION CONTROL PLANT
OPE
FINAL EFFLUENT
I
o.
7.6
7.4-
7.0
7.2
7.3
71
7.2
7.3
301000_KWH
0
o
CO
21
31
23
26
51
V)
IB
3O
OT
9
8
OJ
in
D
CO
21
£4
ae
32
2.5
^0
29
27
0
d
7.0
6.8
5.1
6.3
B.I
7fi
7.4
6.4
CO
UJ
cc
fVJ
o
2.1
2.4
3.0
1.6
1.1
? 1
2.0
2.0
DIGESTION
RAW SLUDGE
GALS /DAY
5140
5I35
5380
47fi5
50IO
5240
43^5
4S80
<
0
13
0 <
CO O
IOO
110
to
120
II5T
120
no
100
RAW SLUDGE:
STROKES SCUM 3.IOO
TOTAL;IS+.OOO * i.o _ 154,000 GALS
OJ
0
0
s«
32
3Z
33
33
34
^i?
aa
33
GAS
L
1
Q V
0 <
ce Q
°- ^
tn ro
< K
o u.
IO800
11450
11220
11570
10110
i iaoo
leioo
11,000
OT
K
I
(9
Z
X
S
4
—
8
8
a
4
4
4-
REMARKS
SUUOSE TO*! BEO - le.oooaAL.
METER:
fl<:T 724216
,st 363aie
r^T A L- 341.000 rT3
•RATOR:
SUMMARY DATA
% REMOVAL
INF- PRI
INF-EFF
SLUDGE
BOD
30.0
S4.6
SS
5Z.4-
87. Z
DATA
% SOLIDS — AVG.
LBS. DRY SOLIDS /
DAY
% VOL. SOLIDS — AVG.
LBS. VOL. SOLIDS /
DAY
LBS. VOL. SOLIDS/IOOOFT3/DAY
GALS. SLUDGE TO BEDS
CU. YDS. CAKE REMOVED
FT3 GAS/LB. VOL.
SOLIDS
FT3 GAS/MG FLOW
4.4
1,627
76
1,388
27.7
48,000
22
SjO
10,800
COST DATA
MAN navs 4-4 PAYROLL
POWER PURCHASED
OTHER UTILITIES (GAS,H20)
GASOLINE, OIL. GREASE
CHEMICALS AND SUPPLIES
MAINTENANCE
VEHICLE COSTS
OTHER
TOTAL
OPERATING COST/MG TREATED
OPERATING COST /CAPITA/ MO.
8 1,250
450—
60~
SO"
95
140
70
20~
ft 2J05-
| £6.83
| 0.21
-------
CHAPTER 7
ACTIVATED SLUDGE
by
John Brady
-------
TABLE OF CONTENTS
Chapter 7. Activated Sludge
Page
7.0 Introduction 7-1
7.00 General 7-1
7.01 Definitions 7-1
7.02 Process Description 7-3
7.1 Requirements for Control 7-7
7.2 Basic Variables and Record Keeping 7-15
7.20 General 7-15
7.21 Variables in Collection System 7-15
7.210 Combined Sewer Systems 7-15
7.211 Waste Dischargers to the System 7-15
7.212 Maintenance of the Collection System. . . 7-16
7.22 Operational Variables 7-16
7.23 Plant Records 7-18
7.24 Typical Lab Results for an Activated
Sludge Plant 7-21
7.25 Design Variables 7-22
7.250 Aeration Methods 7-22
7.251 Variation of Activated Sludge Process . . 7-25
7.5 Checking Out a New Plant 7-31
7.30 A New Activated Sludge Plant: Description. . . . 7-31
7.31 Aerator 7-33
7.310 Control Gates 7-33
7.311 Mud Valves 7-34
7.312 Weirs 7-35
7.313 Movable Gates 7-35
7.314 Water Sprays 7-35
7.315 Air System 7-36
111
-------
Page
7.315 Air System 7-36
A. Air Filters 7-36
B. Blowers (Compressors) 7-37
C. Air Headers 7-40
D. Diffusers 7-42
E. Blower Testing 7-42
7.32 Secondary Clarifiers 7-43
7.33 Return Sludge and Waste Sludge Pumps 7-43
7.4 Process Start-Up Procedures 7-49
7.40 General 7-49
7.41 First Day 7-49
7.42 Second Day 7-51
7.43 Third through Fifth Days 7-51
7.44 Sixth Day 7-53
7.5 Routine Operational Control 7-59
7.50 General 7-59
7.51 Determination of Sludge Age 7-60
7.52 Wasting Activated Sludge 7-63
7.53 Determination of Waste Sludge Pumping Rate . . . 7-65
7.54 Summary 7-66
7.6 Package Plants (Extended Aeration) 7-69
7.60 Introduction 7-69
7.61 Pre-Start Check-Out 7_6g
7.62 Starting the Plant 7-11
7.63 Operation of Aeration Equipment 7-72
7.64 Wasting Sludge 7-72
7.65 Operation 7-73
7.66 Laboratory Testing 7-74
iv
-------
Page
7.7 Operational Problems 7-79
7-79
7.70 Typical Problems
7.71 Plant Changes 7-81
7.72 Sludge Bulking 7"86
7.73 Septic Sludge 7-88
7.74 Toxic Substances 7-89
7.75 Rising Sludge 7-89
7.76 Frothing 7-89
7.8 Aerator Loading Parameters 7-95
7.80 General 7-95
7.81 Food/Organism Ratio 7-95
7.82 Calculation of Food/Organism Aerator Loading . . 7-96
7.83 Mean Cell Residence Time CMCRT) 7-98
7.84 Calculation of Mean Cell Residence Time 7-99
7.9 Modifications of the Activated Sludge Process 7-101
7.90 Reasons for Other Modes of Operation 7-101
7.91 Contact Stabilization 7-101
7.92 Kraus Process 7-103
7.93 Step-Feed Aeration 7-103
7.94 Complete Mix 7-106
7.95 Modified Aeration 7-108
7.10 Acknowledgment 7-109
7.11 Additional Reading 7-109
-------
GLOSSARY
Chapter 7. Activated Sludge
Absorption (ab-SORP-shun) : Taking in or reception of one substance
into" the body of another by physical or chemical action, and dis-
tributed throughout the absorber.
Activated Sludge (ACK-ta-VATE-ed): 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 teaming with bacteria, fungi, and
protozoa.
Activated Sludge Process; A biological wastewater treatment
process in which a mixture of wastewater and activated sludge is
aerated and agitated. The activated sludge is subsequently sepa-
rated from the treated wastewater (mixed liquor) by sedimentation,
and wasted or returned to the process as needed.
Adsorption (add-SORP-shun): To gather (a gas, liquid, or dissolved
substance) on the surface or interface zone of another substance.
Aercition Tank (air-A-shun) : The same a aerator. The tank where
raw or settled wastewater is mixed with return sludge and aerated.
Aeration Liquor; Mixed liquor. The contents of the aeration tank,
which is composed of living organisms plus material carried into the
tank by the untreated wastewater or primary effluent.
Aerobes: Bacteria that must have molecular (dissolved) oxygen (DO)
to survive.
Agglomeration (a-GLOM-er-A-shun): The growing or coming together of
dispersed suspended matter into larger floes or particles which settle
rapidly.
Aliquot (AL-li-kwot): Portion of a sample.
G-7-1
-------
Bacterial Culture (back-TEAR-e-al): 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 nitri-
fying organisms are obligate aerobes (require oxygen) and may
require from 0.5 to 4.0 mg/T of dissolved oxygen throughout the
whole system to function properly.
Batch Process: A batch process is a treatment process in which
a tank or reactor is filled, the waste is treated, and the tank
contents are released. The tank may then be filled and the
process repeated.
Bulking (BULK-irig) : Bulking occurs in activated sludge plants
when the sludge becomes too light and will not settle properly.
Cathodic Protection (ca-THOD-ick): An electrical system for
prevention of rust, corrosion, and pitting of steel and iron
surfaces in contact with water or wastewater.
Composite (Proportional) Samples (com-POZ-it): Samples collected
at regular intervals in proportion to the existing flow and then
combined to form a sample representative of the entire period of
flow over a given period of time.
Coning (CONE-ing): A condition that may be established in a sludge
hopper during sludge withdrawal when part of the sludge moves toward
the outlet while the remainder tends to stay in place. Development
of a cone or channel of moving liquid surrounded by relatively
stationary sludge.
Pi ffused-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.
Piffuser: A diffuser is a device (porous plate, tube, bag) used
to break the air stream from the blower system into fine bubbles
in the mixed liquor.
Endogenous (en-DODGE-en-us): A diminished level of respiration in
which materials previously stored by the cell are oxidized.
G-7-2
-------
Facultative (FACK-ul-tay-tive): Facultative bacteria can use
either molecular (dissolved) oxygen or oxygen obtained from food
materials. In other words, facultative bacteria can live under
aerobic or anaerobic conditions.
Filamentous Bacteria (FILL-a-men-tuss): Organisms that grow in a
thread or filamentous form.
Flights: Scraper boards, made from redwood or .other rot-resistant
woods, used to collect and move settled sludge or floating scum.
Floe: Groups or "clumps" of bacteria that have come together and
formed a cluster. Found in aeration tanks and secondary clarifiers.
Mechanical Aeration; The surface of the aeration tank is agitated
to cause spray and waves by a paddle wheel, mixers, rotating
brushes, or some other method of splashing water into the air or
air into the water where the oxygen can be absorbed.
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: The mixture of primary effluent or raw wastewater
and return sludge undergoing activated sludge treatment in an
aeration tank.
Nitrification: The biochemical conversion of unoxidized nitrogenous
matter (ammonia and organic nitrogen) to oxidized nitrogen (usually
nitrate). The second-stage BOD is sometimes referred to as the
nitrification stage. First-stage BOD is called the carbonaceous
stage (carbon compounds oxidized to C02)
Protozoa (pro-toe-ZOE-ah): A group of microscopic animals, principally
of one cell, that sometimes cluster into colonies.
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.
Supernatant (sue-per-NAY-tent): 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 the primary
clarifier.
Volute (vol-LOOT): The spiral-shaped casing surrounding a pump
impeller that collects the liquid discharged by the impeller.
G-7-3
-------
Zoogleal Mass (ZOE-glee-al): 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 for the storage of food supplies.
G-7-4
-------
PRE-TEST
Chapter 7. Activated Sludge
PLEASE WORK THIS PRE-TEST BEFORE READING THE CHAPTER. You are not
expected to know many of the answers. Write your name and mark
the correct answers on the IBM answer sheet as directed at the end
of Chapter 1. There may be more than one correct answer to each
question.
Match the word with the correct definition by marking the number
of the definition on the answer sheet opposite the number of the
word.
EXA14PLE
Word
Definition
1. Plant Operator 1.
2.
3.
4.
5.
1 2
1 t )7
' 'i
7 ' 'M
' 'I
i i*
Women ' s Liberation advocate
Hard-working water quality protector
Uneducated individual
Town clown
None of these
345
t i i
1 1 !
1 1 !
1 I I
1 1 1
1.
2.
3.
4.
Word
Aliquot
Coning
Flights
Floe
5. Meniscus
6. Orifice
7. Protozoa
8. Zoogleal Mass
Definition
1. Airline schedule
2. Bacteria that have come together and
formed a cluster
3. Portion of a sample
4. Scraper boards used to remove settled
sludge to collection hoppers
5. Caused by sludge when removed too
quickly
1. A thin plate with a hole in the
middle used to measure flow
2. Membranes in the nose and throat
3. Jelly-like substances of bacteria
4. The curved top of a column of liquid
in a tube
5. A group of microscopic animals found
in treatment processes
P-l
-------
9. The activated sludge process:
1. Requires aeration
2, Requires activated carbon
3. Is a biological process
4, Usually follows primary sedimentation
5. Is an anaerobic process
10. Before starting a new plant, the operator should check:
1. The blower system
2. Control gates and mud valves
3. The aeration equipment
4. For chips and scrapes on painted gates
5. Effluent weirs for level
11. The hoist used to lift the air headers in the aeration tank
must be properly anchored or it:
1. Will float away
2. Could fall into the aerator
3. Won't allow even distribution of the air
4. Could hurt someone
5. Could not lift the aerator.
12. How many pounds of solids are in a 400,000-gallon aeration
tank if the suspended solids concentration is 1200 mg/1?
Select the closest answer.
1. 3600
2. 4000
3. 4400
4. 4800
5. 5200
13. When the return sludge rate is too low, what happens?
1. The tank will not fill.
2. There will be insufficient organisms to meet the waste
load entering the aerator.
3. The activated sludge in the aerator will starve.
4. The activated sludge in the secondary clarifier could
become septic.
5, The sludge blanket in the secondary clarifier could
become too high.
14. When operating an activated sludge plant, which is the most
important suspended solids test for operational control?
1. Primary effluent
2. Aerator mixed liquor
3. Return sludge
4. Final clarifier effluent
5. Plant influent
P-2
-------
15. The main operational pr ocess contro1s available to an
operator include:
1. Air rates
2. Pounds of solids under aeration
3. Maintenance
4. Return sludge rate
5. BOD test
16. What should be the waste sludge pumping rate if a plant
should be wasting 2000 pounds per day and the concentration
of return sludge is 5000 mg/1? Select the closest answer.
1. 30 gpm
2. 33 gpm
3. 35 gpm
4. 36 gpm
5. 40 gpm
17. What items would you check if an activated sludge plant
becomes upset?
1. Influent temperature
2. Daily flow rates
3. BOD loadings
4. Digester operation
5. Chlorinator
18. How long would you allow an activated sludge process to
react and stabilize after a change?
1. 3 hours
2. 12 hours
3. 1 day
4. 2 days
5. 1 week
19. Causes of sludge bulking include:
1. Bulk of sludge too large
2. Air supply too low
3. Loading rate too high
4. Aeration period too short
5. Sludge going septic in secondary clarifier
20. Package plants usually:
1. Operate the aeration device continuously
2. Have an operator at the plant 24 hours a day
3. Waste sludge out the effluent, but shouldn't when operated properly
4. Have an extensive lab testing program
5. None of these
P-3
-------
!1. The effectiveness of the organisms in the aerator depends
on the :
1. Temperature
"> nl-i
t~ • |'J ''
Presence of inhibiting substances
Characteristics of food supply
5. Time of reaction or time available for the reaction
22. What is the food/organism loading ratio in an activated sludge
plant with a flow of 1 MGD? The average BOD to the aerator is
140 mg/1, the aeration tank contains 250,000 gallons, and the
mixed liquor suspended solids concentration is 2000 mg/1.
Select the closest answer.
1. 25 Ibs BOL) per day/100 Ibs MLSS
2. 28 Ibs BOD per day/100 Ibs MLSS
3. 30 Ibs BOU per day/100 Ibs MLSS
4. 32 Ibs BOD per day/100 Ibs MLSS
5. 35 Ibs BOD per day/100 Ibs MLSS
23. Why is the COD test a better operational control test than
the BOD test?
1. It isn't better.
2. The oxygen demand is not caused by biological organisms
3. Liver/one uses it.
4. The results are available sooner.
5. This chapter says so.
24. Why should all of the diffusers in an aeration tank be cleaned
at once?
1. To get the job done in a hurry
2. So the air will flow evenly out all of the diffusers
3. To improve step-feed aeration
4. So the plant won't use too much air
5. None of these
P-4
-------
CHAPTER 7. ACTIVATED SLUDGE
(Lesson 1 of 8 Lessons)
7.0 INTRODUCTION
7.00 General
When wastewater enters an activated sludge plant, the pretreatment
processes (Chapter 4) remove the coarse or heavy solids (grit) and
other debris, such as roots, rags, and boards. Primary clarifiers
(Chapter 5) remove much of the floatable and settleable material.
Normally settled wastewater is treated by the activated sludge
process, but in some plants the raw wastewater flows from the pre-
treatment processes directly to the activated sludge process.
7.01 Definitions
ACTIVATED SLUDGE (Fig. 7.1). Activated sludge consists of sludge
particles produced in raw or settled wastewater (primary effluent)
by the growth of organisms in aeration tanks in the presence of
dissolved oxygen.. The term "activated" comes from the fact that
the particles are teaming with bacteria, fungi, and protozoa.
ACTIVATED SLUDGE PROCESS (Fig. 7.1). The term activated sludge
process refers to a method or process of wastewater treatment.
In this treatment process there is maintained a biological culture
consisting of a large number of organisms. All of them require
food (wastewater or substrate) and oxygen to make the process work.
The bacterial population is maintained at some mass (solids concen-
tration) l to balance the food available from the wastewater for the
microorganisms2 (food/microorganism ratio) with the oxygen input
capability of the plant equipment.
1 Solids Concentration. The solids in the aeration tank
carry bacteria that feed on wastewater.
2 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.
7-1
-------
INFLUENT
WASTE
MIXED LIQUOR
AERATION TANK
SECONDARY CLARIFIER
EFFLUENT
Fig. 7.1 Activated sludge and activated sludge process
7-2
-------
7.02 Process Description
Secondary treatment in the form of the activated sludge process
(Figs. 7.2 and 7.3) is aimed at oxidation and removal of soluble
or finely divided suspended materials that were not removed by
previous treatment. This is accomplished in an aeration tank
by aerobic organisms within a few hours when the water is being
treated while it flows through the tank. Soluble or finely
divided suspended solids are intended to be stabilized3 in the
aeration tank by partial oxidation to form carbon dioxide, water,
sulfates, and nitrates. Remaining solids are intended to be con-
verted to a form where they can be settled and removed as sludge
during clarification.
Afc/?AT! ON
After the aeration period the wastewater is routed to a secondary
settling tank for a liquid-organism (water-solids) separation.
Settled organisms are quickly returned back to the aeration tank.
The resultant clarifier effluent is usually chlorinated and dis-
charged from the plant.
Conversion of dissolved and suspended material to settleable solids
is the main objective of high-rate activated sludge processes,
while low-rate processes stress oxidation. The oxidation may be
by chemical or biological processes. In the activated sludge process,
the biochemical oxidation carried out by living organisms is stressed.
The same organisms also are effective in conversion of substances to
settleable solids if the plant is operated properly.
3 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.
7-3
-------
HiMCfioM
AMP
GEMOVZ BOCK$. J200T4
AHV HELP* K£MOV£: O/L
Fig. 7.2 Flow diagram of a typical plant
7-4
-------
PRETREATMENT
EXCESS
ACTIVATED
SLUDGE
AERATION
TANK
RETURN
ACTIVATED
SLUDGE
ANAEROBIC
DIGESTER
(PRIMARY)
DIGESTER
(SECONDARY
CHLORINE
CONTACT
TO
RECEIVING
'WATERS
CHLORINATION
Fig. 7.3 Plan layout of a typical activated sludge plant
-------
QUESTIONS
7.0A What is the purpose of the activated sludge process in
treating wastewater?
7.OB What is a stabilized waste?
7-6
-------
7.1 REQUIREMENTS FOR CONTROL
Control of the activated sludge process is based on evaluation
of and action upon several interrelated factors to favor effective
treatment of the influent wastewater. These factors include:
1. Effluent quality requirements.
2. Wastewater flow, concentration, and characteristics
of the wastewater received.
3. Amount of activated sludge (containing the working
organisms) to be maintained in the process relative
to inflow.
4. Amount of oxygen required to stabilize wastewater
oxygen demands and to maintain a satisfactory level
of dissolved oxygen to meet organism requirements.
5. Equal division of plant flow and waste load between
duplicate treatment units (two or more clarifiers or
aeration tanks).
6. Transfer of the pollutional material (food) from the
wastewater to the floe mass (solids or workers) and
separation of the solids from the treated wastewater.
7. Effective control and disposal of inplant residues
(solids, scums, and supernatants) to accomplish
ultimate disposal in a nonpollutional manner.
8. Provisions for maintaining a suitable environment for
the work force of living organisms treating the wastes.
Keep them healthy and happy.
Effluent quality requirements may be stated by your regularoty
agency in terms of percentage removal of wastes. Current regu-
lations frequently specify allowable quantities of wastes that
may be discharged. These quantities are based upon flow and
concentrations of significant items such as solids, oxygen demand,
coliform bacteria, nitrogen, and oil as specified by your regulatory
agencies.
The effluent quality requirements largely determine the mode of
activated sludge operation and the degree of control required.
For example, if an effluent containing 50 mg/1 of suspended solids
and BOD (refers to five-day BOD) is satisfactory, a high-rate
activated sludge process is likely to be applicable. If the limit
7-7
-------
is 10 mg/1, the high-rate process would not be suitable.
If a high degree of treatment is required, very close process
control and additional treatment after the activated sludge process
may be needed.
Flow concentrations and characteristics of the influent are subject
to limited control by the operator. Municipal ordinances may
prohibit discharge to the collection system of materials signifi-
cantly damaging to treatment structures or safety. Control over
wastes dumped into the collection system requires inspection to
insure compliance. It may be necessary to require alternate means
of disposal, pretreatment, or controlled discharge of significantly
damaging items to permit dilution to an acceptable level -by the
time the waste arrives at the treatment plant.
The material entering the aeration tanks is mixed with the acti-
vated sludge to form a mixture of sludge, carrier water, and
influent solids. These solids come from roofs or streets in
combined sewer systems and also from the discharges from homes,
factories, and businesses. Included in the return sludge solids
are many different types of helpful living organisms that were
grown during previous contact with wastewater. These organisms
are the workers in the treatment process. They use the incoming
wastes for food and as a source of energy for their life processes
and for the reproduction of more organisms. These organisms will
use more food contained in the wastewater in treating the wastes.
The activated sludge also forms a lacy mass that entraps many
materials not used as food.
Some organisms (workers)
will require a long time
to use the available food
in the wastewater at a
given waste concentration.
Many organisms will compete
with each other in the use
of available food (waste)
to shorten the time factor
and increase the portion of
waste stabilized. The ratio
of food to organisms is a
primary control in the
activated sludge process.
Organisms tend to increase
with waste (food) load and
time spent in the aeration
tank. Under favorable con-
ditions the operator will
remove (sludge wasting) the
excess organisms to maintain
-wr: #y~-
•t'^M*
"' '"'•
7-8
-------
the required number of workers for effective waste treatment.
Therefore, removal of organisms from the treatment process
(sludge wasting) is a very important control technique.
Oxygen, usually supplied from air, is necessary to sustain the
living organisms and for oxidation of wastes to obtain energy
for growth. Insufficient oxygen will inactivate aerobic organ-
isms, make facultative1* organisms work less efficiently, and
favor production of foul-smelling intermediate products of
decomposition and incomplete reactions.
An increase in organisms in an aeration tank will require greater
amounts of oxygen. More food in the influent encourages more
organism activity and more oxidation; consequently, more oxygen
is required in the aeration tank. An excess of oxygen is required
for complete waste stabilization. Therefore, the dissolved oxygen
(DO) content in the aeration tank is an essential control test.
Some minimum level of oxygen must be maintained to favor the desired
type or organism activity to achieve the necessary treatment effi-
ciency.
Flows must be distributed evenly among two or more similar treat-
ment units. If your plant is equipped with a splitter box or a
series of boxes, it will be necessary to periodically check and
estimate whether the flow is being split as intended.
Activated sludge solids concentrations in the aerator and the
secondary clarifier should be determined by the operator for
process control purposes. Solids are in a deteriorating condition
as long as they remain in the secondary clarifier. Depth of sludge
blanket in the secondary clarifier and concentrations of solids in
the aerator are very important for successful wastewater treatment.
Centrifuge tests will give a quick estimate of solids concentrations
and locations in the units. Precise solids tests should be made
periodically for comparison with centrifuge solids tests. Before
any changes are made in the mode of operation, precise solids
measurements should be obtained. Settleability tests show the
degree and volume of solids settling that may be obtained in a
secondary clarifier; however, visual plant checks show what is
actually happening.
Facultative (FACK-ul-tay-tive). Facultative bacteria can use either
molecular (dissolved) oxygen or oxygen obtained from food materials.
7-9
-------
Primary clarifiers remove easily settleable or floatable material.
Activated sludge tends to convert soluble solids to suspended
cell mass material and to gather and agglomerate5 particles too fine
to settle rapidly into readily separated material. If the soluble
solids transfer fails, then the process fails to provide a satis-
factory effluent.
There must be organisms, oxidizing conditions, and suitable time
to cause the conversion of soluble solids and to agglomerate the
fine particles to form a floe mass.
This floe mass consists of millions of organisms (1012 to 1018/100 ml
in a good activated sludge), including bacteria, fungi, yeast,
protozoa, and worms. When a floe mass is returned to the aerator
from the final clarifier, the organisms grow as a result of taking
food from the inflowing wastewater. The surface of the floe mass
is irregular and promotes the transfer of wastewater pollutants
into the solids by means of mechanical entrapment, absorption,
adsorption, or adhesion. Many substances not used as food also
are transferred to the floe mass, thus improving the quality of
the plant effluent.
Material taken into the floe mass is partially oxidized to form
cell mass and oxidation products. Ash or inorganic material (silt
and sand) taken in by the floe mass increases the density of the
mass. Mixing in the aerator promotes collisions and thus produces
larger floe masses. The net effect after the aeration period is
to form a floe mass which will separate from the wastewater and
settle to the bottom of the secondary clarifier. This sludge contains
most of the residual contaminants and organisms.
Growth of organisms and accumulated residues produce solids for
disposal (waste activated sludge). Certain materials are converted
and removed from the wastewater to the atmosphere in the form of
stripped gases (carbon dioxide or other volatile gases), and also
as water and as solids (sludge). To produce a good effluent the
operator must strive to minimize the return of these solids (other
than as return sludge) to the process. They must be removed from
the wastewater being treated and disposed of in the plant by a
manner which prevents any material from returning to the plant flow.
For example, maintain as high a concentration of solids in the return
sludge as possible to reduce the amount of water needed to return
these solids back to the aerator. Don't pump waste activated sludge
5 Agglomerate. To cause the growing or coming together of dispersed
suspended matter into larger floes or particles which settle rapidly.
7-10
-------
directly to an anaerobic digester because it will return to the
aeration tank as supernatant with an added load on the organisms.
The organisms have already attempted to treat the solids once and
won't be too effective next time. If screenings are removed at
the headworks, don't grind them up and return them to the plant
flow. Once material is removed from the wastewater, keep it out,
except as necessary to maintain the process.
To maintain the working organisms in the activated sludge, you
must provide a suitable environment. Intolerable concentrations
of acids, bases, and other toxic substances are undesirable and
may kill the working organisms. Unduly fluctuating loads may cause
overfeeding, starvation, and other factors that are all capable
of upsetting the activated sludge process. Insufficient oxygen
can cause an unfavorable environment which results in decreased
organism activity.
An outstanding example of a toxic substance added by operators is
the uninhibited use of chlorine for odor control (prechlorination).
Chlorination is for disinfection. Chlorine is a toxicant and
should not be allowed to enter the activated sludge process because
it is not selective with respect to type of organisms damaged.
It may kill the organisms that you should be retaining as workers.
Chlorine is effective in disinfecting the plant effluent after
treatment by the activated sludge process.
The successful operation of an activated sludge plant requires the
operator to be aware of the many factors influencing the process
and to check them repeatedly. The actual control of the process
as outlined in this section is relatively simple. Control consists
of maintaining the proper solids (floe mass) concentration in the
aerator for the waste (food) inflow by adjusting the waste sludge
pumping rate and regulating the oxygen supply to maintain a satis-
factory level of dissolved oxygen in the process.
QUESTIONS
7.1A Why is air added to the aeration tank in the
activated sludge process?
7.IB What happens to the air requirement in the aeration tank
when the strength (BOD) of the incoming water increases?
7.1C What factors could cause an unsuitable environment for
the activated sludge process, in an aeration tank?
END OF LESSON 1 OF 8 LESSONS
on
ACTIVATED SLUDGE
7-11
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 7. Activated Sludge
(Lesson 1 of 8 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 con-
tinuing.
1. Sketch the activated sludge process.
2. Define activated sludge.
3. Define facultative bacteria.
4. Some activated sludge plants do not have a primary clarifier.
True or False?
5. Why must the activated sludge retention time not be too long
in the final clarifier?
6. How can the operator control the activated sludge process?
7-13
-------
CHAPTER 7. ACTIVATED SLUDGE
(Lesson 2 of 8 Lessons)
7.2 BASIC VARIABLES AND RECORD KEEPING
7.20 General
Wastewater flows and constituents fluctuate daily. The activated
sludge plant operator attempts to maintain the process at some
balanced state that will be capable of handling the minor variations
in flows or wastewater characteristics and produce the desired
quality of effluent. To accomplish this goal he must establish his
process on known data and knowledge obtained at other plants and
relate them to his plant. After his plant becomes operational, he
then must relate his control procedures to his own experience. The
variations that affect his operation are derived from two sources:
(1) the dischargers to the collection system and (2) inplant
operational variables.
7.21 Variables in Collection System
7.210 Combined Sewer Systems
During storms the treatment plant will receive an increase in flow
which may cause the following problems:
1. Reduced wastewater time in treatment units (hydraulic
overload).
2. Increased amounts of grit and silt which lower the
volatile (food) content of the solids.
3. Increased organic load during initial washout of
accumulated sewer deposits.
4. Rapid changes in wastewater temperature and solids content.
7.211 Waste Dischargers to the System
Various industries and businesses can cause considerable fluctuation
in flows and waste characteristics entering a plant. You should become
7-15
-------
acquainted with the managers
of plants whose discharges
could upset your treatment
processes. Convince these
men in a friendly manner how
vital it is to your plant
processes and the receiving
waters for you to be notified
of any potentially harmful
discharges. Try to obtain
their cooperation and request
them to notify you whenever
an accidental spill, a process
change, or a cleaning operation
occurs which could cause un-
desirable waste discharges.
This requires diplomacy to
obtain cooperation from dis-
chargers to regulate their own
discharges and to reduce the
number of midnight dumps.
7.212 Maintenance of the Collection System
Advance notice of collection system maintenance crew activities
can be very helpful. If a lift station has been out of service
for a period of time, large volumes of septic wastewater could cause
a shock load on your treatment processes. Similar problems could
be created when a blockage in a line is cleared or a new line is
connected to the system. Analysis of inflow quantities and charac-
teristics when these flows reach a treatment plant can indicate
whether or not they will cause a serious problem.
7.22 Operational Variables
Continual review of laboratory test results is essential in determining
whether a treatment plant is discharging effluent of the required
quality in terms of such water quality indicators as COD, suspended
solids, and nitrogen. If the desired quality of the plant effluent
is not achieved, the operator must determine what factor or factors
have changed to upset plant performance and thus reduce efficiency.
Important factors that could have changed include:
1. Higher COD or BOD load applied to the aerator
(influent load).
2. More difficult to treat wastes have adversely
changed influent characteristics.
7-16
-------
3. Unsuitable mixed liquor suspended solids concentra-
tion in the aerator.
4. Lower or higher rate of wasting activated sludge.
5. Unsuitable rate of returning sludge to the aerator
could adversely influence mixed liquor suspended solids.
6. Higher solids concentrations in digester supernatant6
returned to the plant flow, or return too rapid.
7. Dropping of oxygen concentration in the aerator below
desirable levels.
Examination of plant records should reveal the items which have
changed that could have upset the treatment process.
QUESTIONS
7.2A What two major variables affect the way an activated
sludge plant is operated?
7.2B What variables in the collection system can affect the
operation of an activated sludge plant?
7.2C What problems can be caused in an activated sludge plant
when excessive storm water flows through the process?
6 Supernatant (sue-per-NAY-tent). Liquid removed from settled
sludge. 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 the
primary clarifier.
7-17
-------
7.23 Plant Records
Accurate daily plant and laboratory records on the items listed
below can help the operator determine the best operating ranges
for operational controls on the basis of plant performance.
Records also are capable of indicating when problems develop and
identifying the source of the problem. Record the following
data on a daily basis. (Also see Monthly Data Sheet in the
Appendix.)
1. Suspended Solids and Volatile Content
a. Primary effluent
b. Aerator mixed liquor
c. Return sludge
d. Final clarifier effluent
2. BOD, COD, or TOC
a. Plant influent
b. Primary effluent
c. Final clarifier effluent
NOTE: COD is recommended to determine the strength of
influent wastewater because the results are available
within four hours and can be used to control the acti-
vated sludge process. For many years operators attempted
to use the BOD test for operational control, but the test
has the following disadvantages:
(1) Procedural errors can cause a large variation
in results.
(2) Five days of waiting are required before results
are available.
(3) Only a portion of the load on the activated
sludge process is measured by the test.
3. Dissolved Oxygen
a. Aerator
b. Final clarifier (inside the effluent weir)
c. Final effluent
4. Settleable Solids
a. Influent
b. Mixed liquor settleability test
c. Digester supernatant
d. Final effluent
7-18
-------
5. Temperature
a. Influent
b. Aerator
c. Final effluent
6. pH
a. Influent
b. Primary effluent
c. Aerator7
d. Final effluent
7. Clarity or Turbidity (Secchi Disc)8
a. Final clarifier
8. Chlorine Demand
a. Final clarifier effluent
9. Coliform Group Bacteria9
a. Plant effluent
10. Meter Readings and Calculations
a. Daily flow
b. Pounds of solids under aeration
c. Pounds of COD or BOD to aerators
d. Pounds of activated sludge solids to waste
e. Pounds of solids in effluent
f. Return sludge rate
g. Waste sludge rate
h. Air to aerators (diffused air system); hours operated
at various speeds (mechanical aeration)
i. Sludge age
7 Measure aerator pH in the aerator or immediately after sample
is collected, because the pH can change very rapidly once the
sample is out of the aerator. Do not take sample to the lab.
8 Secchi Disc (SECK-key). A flat, white disc lowered into the
water by a nylon rope until it is just distinguishable. At
this point, the depth of the disc from the water surface is
the recorded secchi disc reading.
9 Check with your regulatory agency for test and procedures.
Tests approved by agencies include MPN, membrane filter,
and fecal coliform.
7-19
-------
j. Pounds of solids in sludge to digester
k. Pounds of solids in digester supernatant
1. Power cost
Accurate records will indicate when the proper operational
procedures have been determined that produce the best effluent.
This effluent will be low in COD (or BOD) and suspended solids,
and the effluent clarity will be good. Waste loadings and opera-
tional procedures will vary continuously due to seasonal changes
which require the operator to constantly review his records for
changes and to make appropriate changes to maintain the best possible
effluent quality. Process control consists not only of maintaining
the equipment, but of making a constant daily review of process conditions
to determine when adjustments must be made to compensate for the
many variables that can influence effluent quality. Remember that
the sight, smell, and touch observations often are your first
indications that problems are developing and frequently offer
indications of appropriate corrective action.
QUESTIONS
7.2D Why should the strength or waste load of the influent to
the activated sludge process be measured by the COD test
instead of the BOD test?
7.2E Why should the aerator pH be measured in the aerator?
7.2F Sight and smell observations are often the operator's
first indication that process problems are developing.
True or False?
7-20
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7.24 Typical Lab Results for an Activated Sludge Plant
Typical results of lab tests for an activated sludge plant are
provided to assist in the evaluation of lab results and plant
performance. Remember that every plant is different and is
influenced by different conditions.
Test
COD
BOD
SUSPENDED
SOLIDS
DISSOLVED
OXYGEN
CHLORINE
RESIDUAL
(30 min.)
Location
Influent
Primary Effl.
Final Effl.
(Conv. Act. SI.)
Influent
Primary Effl.
Final Effl.
(Conv. Act. SI.)
Influent
Primary Effl.
Mixed Liquor
Return Sludge
Final Effl.
(Conv. Act. SI.)
Mixed Liquor
Final Effl. (Outfall)
Final Effl.
Common Range
300
200
30
150
100
10
150
60
1000
2000
10
2
2
0.5
- 700
- 400
- 70
- 400
- 280
- 20
- 400
- 160
- 4500
- 10,000
- 20
- 4
- 6
- 2.0
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1*
COLIFORM GROUP
BACTERIA, MPN
CLARITY
(Secchi Disc)
pH
Final Effl.
(Chlorinated)
Final Effl.
Influent
Effluent
23 - 700/100 ml
3 -
6.8 - 8.0
7.0 - 8.5
ft
Regulatory agencies normally specify a chlorine residual
remaining after a certain time period.
7-21
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7.25 Design Variables
Several different types of activated sludge plants have been
built using various flow arrangements, tank configurations, or
oxygen application equipment. However, all of these variations
are essentially modifications of the basic concept of conven-
tional activated sludge.
7.250 Aeration Methods
Two methods are commonly used to supply oxygen from the air to
the bacteria--mechanical aeration and dif f used aeration. Both
methods are mechanical processes with the difference being
whether the mechanisms are at or in the aerator or at a remote
location.
Mechanical aeration devices agitate the water surface in the
aerator to cause spray and waves by paddle wheels (Fig. 7.4),
mixers, rotating brushes, or some other method of splashing
water into the air or air into the water where the oxygen can
be absorbed.
Mechanical aerators in the tank tend to be lower in installation
and maintenance costs. Usually they are more versatile in terms
of mixing, production of surface area of bubbles, and oxygen
transfer per unit of applied power.
Diffused air systems use a device called a diffuser (Fig. 7.5)
which is used to break up the air stream from the blower system
into fine bubbles in the mixed liquor. The smaller the bubble,
the greater the oxygen transfer due to the greater surface area
of rising air bubbles surrounded by water. Unfortunately, fine
bubbles will tend to regroup into larger bubbles while rising
unless broken up by suitable mixing energy and turbulence.
7-22
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Fig. 7.4 Mechanical Aeration Device
(Courtesy INFILCO INC.)
7-23
-------
Fig. 7.5 Air diffuser
(Courtesy Paul Hall-bach, National
Training Center, Water Quality Office/EPA)
7-24
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7.251 Variation of Activated Sludge Process
The activated sludge plant may be operated in any one of three
operational zones on the basis of "sludge age"10 which is an
expression of pounds of organic loading added per day per pound
of organisms maintained in the particular process. Sludge age
is a control guide that is widely used and is an indicator of
the length of time a pound of solids is maintained under aeration
in the system. If the amount of solids under aeration remains
fairly constant, then an increase in the influent solids load
will decrease the sludge age. Use of this measure of sludge
age is recommended for the new activated sludge plant operator
because of the ease in understanding this approach. The experienced
operator may not accept this method of control because it ignores
the soluble COD that is related to the solids production but not
measured by suspended solids tests on the influent.
The following values are typical sludge ages for different types
of municipal activated sludge plants with negligible industrial
wastes. Actual loadings must be related to the type of waste and
local situation.
1. High-Rate. A high-rate activated sludge plant operates at
the highest loading of food to microorganisms; the sludge
age ranges from 0.5 to 2.0 days. Due to this higher loading
the system produces a lower quality of effluent than the
other types of activated sludge plants. This system requires
greater operational surveillance and control and is more
easily upset.
2. Conventional. Conventional activated sludge plants are the
most common type in use today. The loading of food to micro-
organisms is approximately 50% lower than in a high-rate plant,
and the sludge age ranges from 3.5 to 7.0 days. This method
of operation produces a high quality of effluent and is capable
of absorbing some shock loads without effluent quality being
adversely affected.
10
Sludge Age, days =
(Suspended Sol, in Mixed Liq., mg/l)i (Aerator Vol., MG) (8.34 Ibs/gal)
(Suspended Sol. in Primary Effl., mg/T) (Flow, MGD) (8.34 Ibs/gal)
Suspended Solids Under Aeration, Ibs
Suspended Solids Added, "ibs/day
7-25
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3. Extended Aeration. Extended aeration is commonly employed in
smaller package-type plants or so-called complete oxidation
systems. These are the most stable of the three processes
due to the light loading of food to microorganisms, and the
sludge age is commonly greater than ten days. Effluent
suspended solids commonly are higher than found under con-
ventional loadings.
For a summary of the loadings for different types of activated
sludge processes, see Table 7-1.
There are other variations of activated sludge processes such as
contact stabilization, step-feed, Kraus and complete mix which are
discussed in Section 7.9.
QUESTIONS
7.2G List two methods of supplying oxygen from air to bacteria
in the activated sludge process.
7.2H Write the formula for calculating sludge age.
END OF LESSON 2 OF 8 LESSONS
on
ACTIVATED SLUDGE
7-26
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TABLE 7-1
AERATION TANK CAPACITIES AND PERMISSIBLE LOADINGS*
PROCESS
Modified or
"HIGH -RATE"
Conventional
Extended
Aeration
PLANT DESIGN
FLOW, MGD
All
To 0.5
0.5 to 1.5
1.5 up
All
AERATION RETENTION
PERIOD, HOURS
BASED ON DESIGN FLOW
2.5 up
7.5
6.0 to 7.5
6.0
24
PLANT DESIGN
LOAD
Ib BOD/day
2000 up
To 1000
1000 to 3000
3000 up
All
AERATOR LOADING
Ib BOD per day/lb MLSS
1/1 (or less)
1/2 to
1/4
As high as 1/10
to
As low as 1/20
SLUDGE
AGE,
DAYS
0.5 - 2.0
3.5 - 7.0
10
or
Longer
I
r-o
* Recommended Standards for Sewage Works (10 State Standards), Great Lakes-Upper Mississippi
River Board of State Sanitary Engineers, 1968 Edition, published by Health Education Service,
P. 0. Box 7283, Albany, New York 12224. Price, $1.00.
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 7. Activated Sludge
(Lesson 2 of 8 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 1.
Write the numbers for the correct answers to question 7 on
your answer sheet in your notebook.
7. During storms an activated sludge plant will receive an
increased inflow which may cause the following problems:
1. Dilution of wastes which makes them easy to treat
2. Reduced wastewater time in treatment units
3. Increased amounts of grit and silt
4. Increased organic loading
5. Fluctuating wastewater temperatures
8. How can the operator attempt to reduce problems caused by
waste discharges into the collection system?
9. How can maintenance activities in a collection system cause
operational problems in an activated sludge treatment plant?
10. What can the operator determine from laboratory test results
on the plant effluent?
11. What are some of the disadvantages of using the BOD test
for operational control?
12. The operator .of an activated sludge plant must constantly
review his records and make appropriate changes to account
for seasonal changes. True or False?
13. What is the difference between mechanical aeration and
diffused aeration?
7-29
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CHAPTER 7. ACTIVATED SLUDGE
(Lesson 3 of 8 Lessons)
7.3 CHECKING OUT A NEW PLANT
This section outlines the steps you should follow when checking
out a new plant. The descriptions are based on a particular
typical type of plant layout (Fig. 7.3). Your plant may vary
from this plant; but by following this outline and obtaining
assistance during checkout from the design engineer and repre-
sentatives of the equipment manufacturers, many initial operating
problems can be eliminated.
7.30 A New Activated Sludge Plant: Description
Imagine that your primary treatment plant has just been expanded
to a diffused air activated sludge plant. You will continue to
use your old screens, grit chamber, and primary clarifiers.
The new aeration tank is 100 feet long, 45 feet wide, and 16.5
feet deep, and has a "Y" wall dividing it down the center.
Air headers11 are located along the full length of the tank on
each side of the "Y" and spaced approximately 10 feet apart.
Air bubbles come out at the bottom of the tank through the headers
equipped with diffusers (Fig. 7.5). Drawings of the aeration tank
and secondary clarifier are provided in Fig. 7.6.
The new secondary clarifier is circular with an 80-foot inside
diameter and a 12-foot side wall depth sloping from the wall to
the center of the tank. The tank is equipped with a sweep mechanism
fitted with suction devices to collect the sludge after it has
settled.
The resident engineer informs you that the contractor has completed
his work and the new system may be put into service. First item on
the agenda is to completely recheck the equipment and structures.
Normally the contractor and the construction inspector are charged
with this responsibility; but many times important items are over-
looked, due to time schedules, negligence, or oversight.
There is nothing more disappointing than starting a new plant and
having to shut down after two or three days because of some small
11 Air Headers. Pipes carrying air from the main line in the "Y"
wall to the air diffusers near the bottom of the aeration tank.
7-31
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Q
O
O _ Q _ Q _ Q
O O
o
o
1 - 8 CONTROL GATES
S SPRAY LINES
PLAN
WAIbK SUKI-AUL-
_L
1
I
1 nn'
I UU
SIDE
W^
HEADERS
Dl PCIIQCIT?"
1 r rUotno
,7 ^
v-^'
- — Y- WALL
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END
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1
16
WATER SURFACE
SCUM BAFFLE AND
DIRECTIONAL
FLOW CONTROL
FROM AERATOR
EFFLUENT WEIR
EFFLUENT
TROUGH
RETURN SLUDGE OR WASTE SLUDGE
Fig. 7.6 Activated sludge process units
7-32
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item that would have required only an hour or so to correct
on a preliminary checkout. When each item is checked, be sure
that you know what it is supposed to do, how it is done, how to
service it correctly and safely. If possible, have a contractor
or manufacturer's representative present during checkout and start-
up. When each item of equipment is examined, check your manual
of instructions to be sure your equipment is discussed. Start
NOW with an orderly file on each piece of equipment.
7.31 Aerator
7.310 Control Gates
In Fig. 7.6 (Plan) there are eight gates or mud valves indicated
by "X". The gates are marked by rectangles and the mud valves by
circles. Open and close the gates even if it does permit the entry
of some wastewater and check them for ease of operation and access.
They must travel smoothly with no binding or jumping during
opening and closing. Now is the time to check your means of noting
the gate or valve location in the open, closed, or partially opened
position. If you don't have a rising stem or otherwise visible
indicator of valve position, count the valve turns and record.
When you have the gates open, check the aerator influent line or
channel for debris such as rocks, sand, timber, waste concrete,
or other foreign material. Short pieces of 2 x 4 boards and
other form-lumber can suddenly appear during initial flow, and
this material can jam a pump or stall a clarifier mechanism.
After the line or channel is clean, close the gate, making sure
there is no foreign material along the side guides and dogs.12
When the gate closes, be sure it is properly seated.
'C\
12 Dogs. Wedges attached to a slide gate and frame that
force the gate to seal tightly.
7-33
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The gate should have been painted for rust and corrosion pro-
tection, and now is an excellent time to touch up any chips
or scrapes. Remove the housing protecting the threaded stem
and check to be sure there is lubricant on the stem threads,
and see if there is a stop-nut at the top of the stem. If
there is not a stop-nut, insert one, because the gate could
fall into the aeration tank when you or some other operator
opens it just a little bit too far, or the stem could be bent
attempting to close it farther than necessary.
7.311 Mud Valves (Shear Gates)
These valves may be used for tank drainage or for step-feed
aeration.13 Open and close each valve, checking for ease of
operation and proper seating. Give each stem a generous coat
of heavy-duty waterproof grease because the stems are normally
exposed directly to the wastewater.
QUESTIONS
7.3A Why should the operator completely check the equipment
and structures before start-up?
7.3B Why should lines and channels be cleaned before start-
up?
7.3C Why should chips and scrapes on gates be painted before
a tank is filled?
7.3D What is the purpose of stop-nuts on the stems of valves?
13 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.
7-34
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7.312 Weirs
Weirs are used to control flow at the outlet or effluent end
of the aeration tank. Check these with a surveyor's level
to be sure one end is not higher than the other. Recheck
after tank is filled. If they are not level, the effluent
will not be evenly distributed over the weir, which could cause
short circuiting and an uneven distribution of solids in the
effluent. The weirs should have an adequate protective paint
coating, unless they are made of a corrosion-resistant material,
7.313 Movable Gates
Check the guide slots of bulkheads for nicks or rocks and make
sure the gate seats and operates properly.
7.314 Water Sprays for Froth Control
Check to see if there is a nozzle in each water spray head which
will form a fan of water. The fan of water should have an angle
to the tank surface of approximately 45°. Turn the water on for
a few minutes and check to be sure the spray properly covers the
desired area.
The nozzles must be properly installed to cover the
intended area of the aerator or they will be ineffec-
tive, spraying the rails and walks. This creates a
hazardous condition of algae growths in the summer,
or ice conditions in the winter, and also does not
dissipate much foam.
There should be no leakage in the piping system, and the water fans
should overlap one another for effective control. At the dead-end
of each pipeline, check the operation of the valve that allows
flushing the whole line when opened. A "Y" strainer should be in-
stalled at the inlet end of the system to filter out large material,
thus saving time in the future on maintenance.
QUESTIONS
7.3E Why should an effluent weir be level?
7.3F What dangers are created if a foam spray nozzle sprays on
a rail or walk?
7-35
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7.315 Air System
Check the air system by following it through in the direction
of air flow to the aeration tank.
A. Air Filters
Filters remove dust and dirt from the air before it is
compressed and sent to the aeration tank.
First check the access doors or hatches to the filter
chamber. These should be lined around the edges with
rubber or some other material to form a tight seal. If
there is a gap or torn place, repair it. Check the inside
of the filter chamber floors for cleanliness and debris--
remove any sand, dirt, paper, or other debris.
Check the filter bags for proper coating of filter media.
The main check is to be sure that they are securely in-
stalled and that one of the workmen did not leave a tool
or some item that could go directly into one of the blowers.
A manometer is installed to read the difference in pressure
between the inlet side of the filters and the outlet side.
The "U" tube manometer is mounted on the outside of the
filter housing with two small copper lines running to the
intake and outlet side of the filters.
To check the manometer, remove the glass "U" tube from the
manometer housing, taking care not to break it. Blow air
through each line back to the manometer, checking to see
that the lines are clear and not plugged or accidentally
crimped during installation. If the lines are equipped
with fittings, check for tightness and leakage. If the
lines are okay, fill the manometer "U" tube with the re-
quired fluid. This could be a specified oil, or water may
be acceptable. Fill the "U" tube approximately half the
distance from the top of the tubes to the bottom of the
"U"; both columns should be the same height. If water is
permissible to use, a drop or two of red or blue chart ink
added to the tube before the water is added gives a good
color and an easy indicator for reading the manometer.
See Chapter 16, Section 16.2, for instructions on how to
read manometers.
7-36
-------
The difference in pressure recorded by the manometers will
be small when the filters are clean, but as they become
dirtier, the manometer reading will increase and each column
will move farther away from the manometer zero mark. When
this difference reaches approximately two to three inches of
water column more than the initial difference, it is probably
time to clean or change the filters. The manufacturer's
operating manual should be reviewed for the recommended maximum
allowable pressure differential as well as the procedure for
cleaning the screens.
Check the air duct valving from the filters to the inlet side
of the air blowers (compressor) for proper installation. Also
check these ducts or pipes for dirt and debris.
QUESTIONS
7.3G Why and how is air cleaned before being compressed and
sent to the aeration tank?
7.3H How can you determine when the air filters need cleaning?
B. Blowers (Compressors)
The blowers are of the positive displacement type. Read the
manufacturer's manual and thoroughly understand it before the
blowers are ever started. This manual should be provided by
the manufacturer and can be obtained by writing to the company
indicated on the equipment name plate.
Special attention must be
directed towards starting
and stopping procedures.
Prepare a list of items
to' be' checked before the
start button is pushed.
Check switches, indicators,
and pump connectors with
drawings. Check the type
of oil and oil level.
Start the oil circulation
pump and check the circu-
lation system and oil level
before the blowers are
started.
Check inlet and discharge
valves by opening and
closing them and noting ease
of operation. These units
7-37
-------
are to be started under no load (the discharge air is vented
to atmosphere until the unit is running properly), and then
valved in slowly to put the air into the system and load the
unit. When the unit is shut down, the reverse of the starting
procedure is followed. Be absolutely positive of the correct
procedure for starting and stopping the unit, including proce-
dures for starting and stopping one unit while the others are
operating. Improper procedures can shorten the life of the
equipment considerably. Your supervisor will not be happy if
he finds out that equipment has broken or worn out because of
improper procedures.
Next, check the driver (electric motor), the blower base plates,
and the coupling for alignment. Usually the contractor's mill-
wright sets the equipment and aligns the couplings with a dial
indicator. Request the dial readings from him and file them
with the rest of the equipment data. These readings are in-
valuable in case of equipment failure, or for future checks on
proper alignment. These should be no more than 0.005 of an
inch off, and larger equipment calls for even closer tolerances.
Check for base plate bolts or nuts because if one corner is
loose, the whole alignment will be thrown out on start-up.
Do not attempt to tighten base plate nuts or bolts because this
also will cause misalignment. If one nut is loose or there is
a gap between the equipment mount and the base plate, the
coupling must be realigned and the equipment mounts shimmed.
If the blower and driver are securely anchored and all lubri-
cation points are in good condition, coupling alignments are
satisfactory, motor and compressor will turn with a reasonable
pull on the outside pulleys, and all safety guards are installed
and well clear of the moving parts, then you are ready to check
the main air lines or "air mains".
On both the inlet and discharge sides of the blower, air mains
(air lines) are connected through a flexible coupling in order
to keep vibration at a minimum and allow for heat expansion
because, when air is compressed, heat is generated, thus in-
creasing the discharge temperature as much as 100°F or more.
Check to be certain there is sufficient room for movement in
flexible couplings.
The discharge air line from the blower is equipped with an
air relief valve which protects the blower from excessive
back pressure and overload. It is adjusted by weights or
springs to open when air pressure exceeds a point above normal
7-38
-------
operating range, around 7.5 to 10 psi. Check this valve to
insure its free operation by manually lifting the valve off
the seat.
Between the air relief valve and the discharge side of the
blower is a pressure gauge to read discharge pressure. Check
the gauge for proper installation by looking for air leaks
and for easy accessibility to read.
A metering device should be located in a straight section of
the air main on the discharge side of the blower. This device
consists of an orifice plate inserted between two specially
made pipe flanges. The orifice plate is made of stainless
steel with a precision hole cut through the center of it which
will vary in diameter according to the flow rates to be
measured. The plate is made of 1/8-inch thick material and
is slightly larger than the inside diameter of the pipe. A
rectangular shaped handle is attached to the plate. The
plate is installed between the flanges, blocking the pipeline
except for the hole in the center of the plate. One side is
bevelled, leaving a sharp edge on the opposite side. The
handle of the orifice plate will have numbers stamped into it
giving the orifice size. These numbers on the handle are
stamped on the same side as the sharp edge of the orifice
opening. When viewing the plate to read the numbers, the
blower should be behind you. The sharp edge of the plate
and the numbers must be on the side toward the blower for
it to read properly.
On top of each pipe flange holding the orifice plate will be
a hole tapped and connected to tubing leading to the instruments
which indicate the rate of air flow. Check these to see that
there are no air leaks. The instruments themselves should have
been installed and calibrated correctly, but occasionally an
orifice plate is installed backwards or an instrument line is
left disconnected. When the meter is properly connected to a
dial or totalizer, a zero reading should be recorded when the
pump is off.
Check the condensate trap or drain located near the aeration
tank at the lowest point of the air main. Open and close the
drain line and remove any dirt or sand in the air main at this
location.
Inspect the air main from the blowers to the air headers for
leaks, tightness, and expansion allowances.
7-39
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QUESTIONS
7.31 Why is it important to read the blower or compressor
manufacturer's manual before starting the equipment?
7.3J If your plant does not have a manufacturer's manual,
how would you obtain one?
7.3K Why should proper procedures be followed when starting,
operating, and stopping equipment?
7.3L How should the sharp edge of a metering orifice be
placed in a pipe?
C. Air Headers
The air main runs down the center "Y" wall of the aeration
tank, distributing air to the headers along the tank. This
plant is equipped with "swing headers". A swing header is
merely a pipe with movable couplings so the header may be
raised from the tank with a hoist to service the diffusers.
Take the hoist that is to be used to raise and lower the air
headers out to the center "Y" wall and make sure it properly
fits each air header. The hoist is anchored by the air header
opposite the one to be lifted. Sometimes the correct spacing
is missed and the hoist is either too short or too long. In
either case, you would not be able to lift those two headers,
for there is no other safe way to anchor the hoist. If you
attempted to lift a header without the hoist anchored, it could
catapult into the tank, possibly taking the operator with it
and surely damaging the hoist (and probably the diffusers and
headers too).
Each header is equipped with a valve to shut the air off when
removing it from the tank to replace or clean the diffusers.
Consequently, the other headers may be kept in service, thus
not disrupting the air supply to the tank contents. Inspect
each air header valve for proper operation, and determine which
position of the stem indicates open and which position indicates
closed.
The center "Y" wall is a hazardous area and caution
is required when working here. If the aeration tank
is empty, a 16-foot fall could be fatal. When the
tank is in service you could drown if you fell into
it. A good policy is that any work on the center "Y"
wall calls for TWO MEN AND LIFE PRESERVERS
LIFE LINES.
7-40
-------
Other safety precautions that should be observed at all times
when working on center "Y" walls include:
1. Wear shoes with soles that retard slipping. Cere
inserted composition soles provide the best traction
for all-around use.
2. Slippery algal growths should be scrubbed and washed
down whenever they appear.
3. Keep the area clear of spilled oil or grease.
4. Do not leave tools, equipment, and materials where
they could create a safety hazard.
5. Adequate lighting should be permanently installed for
night work.
6. Ice conditions in winter may require spiked shoes and
sanding icy areas if ice cannot be thawed away with
wash water.
7. Remove only sections of removable handrails necessary
for immediate job. Removed sections should be
properly stored out of the way and secured against
falling.
Since the aeration tank is empty or nearly empty, place a ladder in the
tank and continue the check-out.
First, remove any debris, including sand or dirt, from the bottom
of the tank.
Next, check the air headers. This is the continuation of the air
system to the bottom of the tank with the pipes creating an inverted
"T". The horizontal run of pipe forming the cross-bar on the top of
the "T" should be perfectly level. If one end is 1/2-inch higher
than the other end, then more air will escape through the high end,
causing poor air distribution. The contractor should have set them
with a surveyor's level to insure that they are all at the same ele-
vation, but it is advisable to check them again. Be sure diffusers
are secure and header or diffuser plugs are in place; replace damaged
or defective items.
The pipe should have been flushed with water to remove dirt, dust,
and scale.
7-41
-------
QUESTIONS
7.3M Why must the hoist used to lift the air headers be
properly anchored?
7.3N What precautions would you take when working on the
center "Y" wall?
7.30 Why must the horizontal pipes containing the air
diffusers all be at the same elevation (level)?
D. Diffusers
Thread-type diffusers are installed in our example plant.
Before the diffusers were installed,the pipe should have been
flushed clean with water. Inspect the diffusers. A light
application of grease on the threads (taking care that none
of the lubricant touches the opening into the diffuser)
should have been applied for ease in removing the diffusers
when they need cleaning. Do not use a wrench when installing
threaded diffusers; normal "hand tight" is sufficient, and even
this can create a problem when the time arrives to remove them.
E. Blower Testing
After you have inspected the air headers and diffusers in the
aeration tank, check the blower operation.
Start with the blowers discharging air directly to the atmos-
phere. Review the stop and start procedure for the blowers and
turn them on. If at all possible, let them run for three or
four hours to check on any heating problems or vibrations.
Check temperatures, amperage readings from the electric motors,
and air flow rates and differential pressures across the
filter system, and record them.
Repeat these checks after the process tanks are filled. Now
is the time to check the air relief valves for correct settings
by closing several valves out on the headers until the air relief
valves open. Also take another set of amperage readings on the
blower motor to see if it is overloaded under operating conditions,
If everything functions properly for four hours, you can feel
fairly certain that you will not have any immediate problems from
the blowers.
7-42
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QUESTIONS
7.3P While the blowers are running, what items should be
checked, and why?
7.3Q Why should a light application of grease be applied to
the threads of a diffuser?
7.32 Secondary Clarifiers
CIRCULAR CLARIFIERS - check items:
1. Control gates for operation
2. Clarifier tank for sand and debris
3. Collector drive mechanism for lubrication, drive alignment,
and complete assembly
4. Squeegee blades on the collector plows for proper distance
from the floor of the tank
5. Connecting lines or channels between aerator and clarifier
for debris
6. Pump suction line assembly and controls
7. Inlet baffles and discharge weirs for level
8. Scum control mechanism
Once the collectors are started in a new tank, each flight should
be checked for a clearance of one to two inches between the wall
and the end of the flight. If a flight is too long, it may rub
the tank wall and break the flight, jamming other flights and
breaking them. Once a broken flight is detected, it should be
replaced or removed from the support structure.
7.33 Return Sludge and Waste Sludge Pumps
Since these two items are identical except for size, the same
checks may be used.
7-43
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Clean out trash in all sludge hoppers, lines, valves, gates,
sweeps, and drive mechanisms before checking pumps.
To check out pumps, FIRST lock out the pump motor
at the power panel so it cannot be started.
Remove the handhole cover, clean out the pump casing or volute,14
and check the impeller for debris and secure fit to the pump
shaft. Replace the handhole cover. Install or check pressure
gages on the suction and discharge lines of the pump. Check
inlet and outlet valve operation and connecting lines for clearance.
Check pump and motor bearings for lubrication. Inspect coupling
alignment, and base plate anchor bolts. Turn on the seal water
to the pump. Since the pump has not operated, back off the
packing gland nuts and rotate the pump shaft by hand through
several revolutions. Leave the packing nuts loose and adjust
them properly after start-up. If everything checks out satis-
factorily, then run some water into the final clarifier hopper
or return sludge well where the pump suction is located so it
may be operated for a few minutes. While the water is filling
the hopper or wet well, check the suction and discharge valves
and check (flap) valves on the system. Check the other valves
on the return sludge line for proper operation. Open both inlet
and discharge valves before starting the pump so the water may
flow during the pump test.
There should be several hundred gallons of water available in
the final clarifier for the pump test. Prime the pump if necessary
and, if everything has checked out properly, unlock the controls at
the power panel and turn the pump on. First check pump rotation
and the packing gl.and for water, but let it flow freely for now.
Read both pressure gages on suction and discharge and the level
of the water in the clarifier or wet well; record all three measure-
ments in order that the operational characteristics and efficiency
of the pumps may be checked. Take an amperage reading on the motor
and record. If possible, make sure that the meter is functioning,
and record a flow meter reading too. The water available will not
afford a very long run, but it will indicate any major problems.
When the pump is shut off, make sure the check valve closes and seats,
Volute. The spiral-shaped casing surrounding a pump im-
peller that collects the liquid discharged by the impeller.
7-44
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To check the waste sludge pump, the return sludge pump also
must be running. Run the waste sludge pump now to be sure
it will operate properly when you are ready to start wasting
activated sludge.
QUESTION
7.3R List all the information which should be recorded for
future reference when you test the return sludge and
waste sludge pumps.
END OF LESSON 3 OF 8 LESSONS
on
ACTIVATED SLUDGE
7-45
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 7. Activated Sludge
(Lesson 3 of 8 Lessons)
Write the answers to these questions in your notebook before
continuing . The problem numbering continues from Lesson 2.
14. What should the operator look for when checking
out control gates and mud valves?
15. What happens when spray nozzles are not installed
properly and spray falls on rails and walks?
16. Why should proper procedures be followed when
checking equipment?
17. What safety precaution should be exercised before
checking the impeller of a return sludge pump?
18. Why should the equipment manufacturer's manual be
thoroughly read and understood before any equipment
is started?
7-47
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CHAPTER 7. ACTIVATED SLUDGE
(Lesson 4 of 8 Lessons)
7.4 PROCESS START-UP PROCEDURES
7.40 General
Procedures for starting the activated sludge process are outlined
in this lesson. Procedures and example calculations will be for
the plant checked out in the previous lesson. An initial average
daily flow of 4.0 MGD will be assumed, and the plant will be opera-
ted as a conventional activated sludge plant.
Start-up help should be available from the design engineer, vendors,
nearby operators, or other specialists. The equipment manufacturers
or contractor should be under contract for start-up instruction and
assistance. During start-up they should be present to be sure that
any equipment breakdowns are not caused by improper start-up pro-
cedures.
The operator may have several options in the choice of start-up pro-
cedures with regard to number of tanks used and procedures to establish
a suitable working culture in the aeration tanks. The method described
in this lesson is recommended because it provides the longest possible
aeration time, reduces chances of solids washout, and provides the
opportunity to use most of the equipment for a good test of its
acceptability and workability before the end of the warranty.
7.41 First Day
First, start the air blowers and have air passing through the
diffusers before primary effluent is admitted to the aeration tanks.
This prevents diffuser clogging from material in the primary effluent.
Fill both aeration tanks to the normal operating water depth, thus
allowing the aeration equipment to operate at maximum efficiency.
Employing all of the aeration tanks will provide the longest possible
aeration time. You are trying to build up a population with a minimum
amount of seed organisms, and you will need all the aeration capacity
available to give the organisms a chance to reach the settling stage.
When both aeration tanks have been filled, begin filling the two
secondary clarifiers. Use of all the secondary clarifiers will
provide the longest possible detention time to reduce washout of
light solids containing rapidly growing organisms and will help
enhance solids build-up.
7-49
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When the secondary clarifiers are approximately three-fourths
full, start the clarifier collector mechanism and return sludge
pumps. Return sludge pumping rates must be adjusted to rapidly
return the solids (organisms) back to the aeration tanks. The
solids should never remain in the secondary clarifiers longer
than 1.5 hours. Trouble also may develop if the return sludge
pumping rate is too high (greater than 50% of the raw waste-
water flow), because the high flows through the clarifier may
not allow sufficient time for solids to settle to the bottom
of the clarifier. A conventional activated sludge plant usually
operates satisfactorily at return sludge rates of 20 to 30 percent
of raw wastewater flow, but the rate selected should be based
upon returning organisms back to the aerator where they can
treat the incoming wastes. A thin sludge will require a higher
return percentage than a thick one. Addition of a coagulant or
coagulant aid at the end of the aeration tank will hasten solids
build-up and improve effluent during start-up.
When the secondary clarifiers become full and begin to overflow,
start effluent chlorination to disinfect the plant effluent.
Filling the aeration tanks and aerating the wastewater starts
the activated sludge process. The aerobes in the aeration tank
have food and are now being supplied with oxygen; consequently,
this worker population will begin to increase.
After two or three hours of aeration you should check the dissolved
oxygen (DO) of the aeration tanks, to determine if sufficient air
is being supplied. (See Chapter 14, Laboratory Procedures and
Chemistry, for procedure to run DO test.)
Check the DO at each end and at the middle of the aerator. Oxygen
must be available for the aerobes throughout the tank. If the DO
is less than 2.0 mg/1, increase the air supply. If the DO is
greater than 2.0 mg/1 the air supply may be decreased, but not to
the point where the tank would stop mixing. There will probably be
an excess amount of DO at first due to the limited number of organisms
initially present to use it.
After a biological culture of aerobes is established in the aeration
tanks, sufficient oxygen must be supplied to the aeration tank to
overcome the following demands:
1. DO usually is low in both influent wastewater
and return sludge to the aerator.
2. Influent wastewater may be septic, thus
creating an immediate oxygen demand.
3. Organisms in the presence of sufficient food
create a high demand for oxygen.
7-50
-------
The effluent end of the aerator should have a dissolved oxygen
level of 2.0 mg/1. DO in the aerator should be checked every
two hours until a pattern is established. Thereafter, DO
should be checked as frequently as needed to maintain the desired
DO level. Daily flow variations will create different oxygen
demands; and until these patterns are established, it is not
known whether sufficient or excess air is being delivered to
the aeration tanks. Frequently excess air is provided during
early mornings when the infloiv waste load is low. Air supply
may be too low during the afternoon and evening hours because
the waste load tends to increase during the day.
7.42 Second Day
Collect a sample from the aeration tank and run a 60-minute
settleability test using a 1000 ml graduated cylinder. If
possible, use a 2000 ml cylinder with a five-inch diameter15
in order to obtain better results. Observe the sludge settling
in the sample for approximately one hour. It will probably
have the same color as the primary effluent during the first
few days. After a few minutes in the cylinder, very fine parti-
cles will start forming with a light buff color. The particles
remain suspended, not settling, similar to fine particles of dust
in a light beam. After an hour, a small amount of these particles
may have settled to the bottom of the cylinder to a depth of 10 or
20 ml, but most are still in suspension. This indicates that you
are making a start toward establishing a good condition in the
aeration tank, but many more particles are needed for effective
wastewater treatment.
7.43 Third through Fifth Days
During this period of operation the only controls applied to the
system usually consist of maintaining DO concentrations in the system
and maintaining proper sludge return rates. A sampling program
should be started in accordance with Section 7.23, Plant Records,
to develop and record the necessary data required for future plant
control.
Aeration of wastewater to maintain DO will require some time before
settling will produce a clear liquid over the settled solids. Time
15 Mallory Direct Reading Settleometer (a 2 liter graduated cylin-
der approximately 5 inches in diameter and 7 inches high). Obtain
from Scientific Glass Apparatus Co., Inc. , 735 Broad Street,
Bloomfield, New Jersey. Catalog No. JS-1035. Price $16.50 each.
7-51
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is required for organisms to grow to the point where there are
sufficient numbers to perform the work needed--to produce an
activated sludge. Usually within 24 to 72 hours of aeration
you will note that the settleable solids do not fall through
the liquid quite so rapidly, but the liquid remaining above
the solids is clearer.
The active solids (organisms) are light and may wash out of the
clarifier to some extent. Hopefully you can retain most of them,
because a rapid solids build-up will not occur unless they are
retained. A good garden soil will add organisms and solids
particles for start-up. Mix the soil with water and hose in
the lighter slurry, but try to avoid a lot of grit. A truck-
load of activated sludge from a neighboring treatment plant also
will help to start the process. Hopefully you will not have to
treat design flows during plant start-up. More time is needed
both for aeration and clarification until you have collected
enough organisms in your return sludge to enable you to produce
a clear effluent after a short period of mixing with the influent
followed by settling.
QUESTIONS
7.4A Why should chlorination equipment be put in service when
effluent starts leaving the plant?
7.4B How is the return sludge rate selected during initial
start-up?
7.4C Why should the blowers be started before primary effluent
is admitted to the aeration tanks?
7.4D At what locations in the aeration tank would you check the
DO, and why?
7-52
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7.44 Sixth Day
A reasonably clear effluent should be produced by the sixth day.
Solids build-up in the aeration tank should be closely checked using
the 60-minute settleable solids test during the first week. Results
of this test indicate the flocculating, settling, and compacting charac-
teristics of the sludge. Suspended solids build-up is very slow at
first but increases as the waste removal efficiency improves. This
build-up should be carefully measured and evaluated each day.
Microorganisms in the system are so varied and small that it is
impossible to count them. To obtain an indication of the size of
the organism population in the aeration tank, the solids are
measured either in mg/1 or in pounds of dry solids. Suspended
solids determinations for aerator mixed liquor will give the
desired information in mg/1, and the total pounds of solids may
be calculated on the basis of the size of the aerator.
Solids^lbs = SusPended Solids, mg/1 x Aerator Volume, MG x 8.34 Ibs/gal
The suspended solids test (see Chapter 14, Laboratory Procedures and
Chemistry) conducted on activated sludge plant mixed liquor is normally
a grab sample obtained at the effluent end of the aerator. The sample
should be collected at the same time every day, preferably during
peak flows, in order to make day-to-day comparisons of the results.
Collect the mixed liquor sample approximately five feet from the
effluent end of the aeration tank and 1.5 to 2 feet below the water
surface to insure a good sample. A return sludge sample also should
be collected at this time every day to determine its concentration.
With information from the lab tests, estimates of the organism mass
(weight) in the aerator can be calculated.
Information needed:
1. Aeration Tank Dimensions
100 ft long, 45 ft wide, and 16.5 ft deep
2. Results of Laboratory Tests
Mixed Liquor Suspended Solids, 780 mg/1
7-53
-------
Steps to calculate pounds of solids in aeration tank:
1. Determine aeration tank volume.
Aerator
Volume, = Length, ft x Width, ft x Depth, ft
cu ft
= 100 ft x 45 ft x 16.5 ft
= 74,250 cu ft
2. Convert cu ft to gallons.
Aerator
Volume, = 74,250 cu ft x 7.48 gals/cu ft
gals
= 555,390 gals
or = 555,000 gals (approximately)
or = 0.55 MG
3. Calculate pounds of solids under aeration.
Formula:
q ,. , lh Mixed Liquor Suspended Solids, mg/1 x
' = Aerator Volume, MG x 8.34 Ibs/gal
780 mg
1,000,000 mg
780 mg
x 0.55 M Gals x 8.34 Ibs/gal
M mg
= 780 x 4.6* Ibs
= 3588 Ibs
x 0.55 M Gals x .8.34 Ibs/gal
The factor 4.6 Ibs is equivalent to 0.55 x 8.34, a constant for
your plant. You will use this value every day as long as you
use the same aeration tank capacity. Only a change in the
suspended solids concentration will cause a change in the pounds
of solids in the aeration tank.
7-54
-------
Close observation of the suspended solids build-up and results
from the 60-minute settleability test will indicate the solids
growth rate, condition of solids in aerator, and how much sludge
should be returned to insure proper return of the organisms to
the aerator. It will be necessary to return all of the sludge
for 10 to 15 days or longer if the wastewater is weak.
Results from the 60-minute settleability test can be used to
estimate if the return sludge rate is too high or too low. If
the volume of settled sludge in the cylinder is indicative of
amount of sludge settling in the secondary clarifier, the
volume of return sludge should be equal to or slightly greater
than the percentage of settling sludge in the cylinder multiplied
by the sum of the primary effluent and the return sludge flows.
Estimate the return sludge pumping rate.
Information needed:
1. Flow to Aerator from Primary Clarifier, 4.0 MGD
2. Return Sludge Flow, 1.0 MGD
3. Volume of Mixed Liquor Solids Settled in 60 Minutes,
360 ml in 2 liters, or 18%
Example;
Flow to Aerator from Primary Clarifier = 4.0 MGD
Return Sludge Flow to Aerator = 1.0^ MGD
Total Flow through Aerator = 5.0 MGD
= Aerator Flow, MGD x Settleable Solids, %
= 5.0 MGD x 0.18
= 0.9 MGD or 900,000 gals/day
Return Sludge _ 900,000 GPP
Rate, GPM ~ 1440 min/day
= 625 GPM
Therefore, the initially selected 700 GPM return sludge rate is
acceptable at this time. It insures that most solids are being
7-55
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returned to the aeration tank. A return sludge pumping rate
slightly higher than calculated is recommended to return the
organisms as fast as possible to the aerator. Too high a return
sludge rate must be avoided because the resulting high flows
reduce the detention time in the aerator and secondary clarifier.
If the return sludge rate is too low, the following un-
desirable conditions may develop:
1. Insufficient organisms will be in the aerator to
treat the influent waste (food) load. This normally
occurs during the first week or two of start-up.
2. Too long a detention time in the secondary clarifier
could allow the sludge to become septic.
3. Accumulation of sludge in the clarifier creates a deep
sludge blanket which will allow solids to escape in
the effluent.
QUESTIONS
7.4E When and where should solids samples be collected to
provide the operator with a record of solids build-up
in the aeration tank?
7.4F Determine the pounds of solids in an aeration tank with
a volume of 0.25 MG and a Mixed Liquor Suspended Solids
(MLSS) concentration of 640 mg/1.
7.4G Estimate the return sludge pumping rate (GPM) i
plant inflow is 2.0 MGD and the return sludge flow is
0.5 MGD. The results of the 60-minute settleability
test indicate the volume of solids settled to be 340 ml
in 2 liters, or 17%.
END OF LESSON 4 OF 8 LESSONS
on
ACTIVATED SLUDGE
7-56
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 7. Activated Sludge
(Lesson 4 of 8 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 3.
19. When starting a new activated sludge plant, who might
the operator contact for assistance and advice?
20. When starting the activated sludge process, why should
you use all of the aerators and all of the secondary
clarifiers?
21. What are the essential laboratory tests for
starting the activated sludge process, and why?
7-57
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CHAPTER 7. ACTIVATED SLUDGE
(Lesson 5 of 8 Lessons)
7.5 ROUTINE OPERATIONAL CONTROL
7.50 General
Effectiveness of the activated sludge treatment process in
reducing the waste load depends upon the amount of activated
sludge solids in the system and the health of the organisms
which are a part of the solids. To successfully maintain con-
trol of the solids and health of the organisms requires continuous
(seven days a week) observation and checking by the plant operators.
Sludge age16 is one of the methods used by operators to determine
and maintain the desired amount of activated sludge solids in
the aeration tank. Sludge age is recommended for operational
control because suspended solids are relatively easy to measure.
In addition, sludge age considers two factors vital to successful
operation: (1) solids (food) entering the treatment process and
(2) solids (organisms) available to treat the incoming waste (food).
A critical point to recognize is that the solids test is capable
of indicating both the amount of food carried by the inflow to
the process and the number of organisms available to treat the waste.
Operation of a conventional activated sludge plant is illustrated
in this section because the example plant selected to indicate
start-up procedures has an allowable effluent BOD of 20 mg/1.
A sludge age of five days (See Table 7-1, Section 7.25) will serve
as a satisfactory loading target during start-up for this plant.
After the plant is in operation, various sludge ages may be tried
in an effort to improve the quality of the plant effluent.
Always remember that you must maintain the DO in the aerator and
more air will be required when aeration tank solids increase in
concentration and activity.
A - Mixed Liquor Suspended Solids in Aerator, Ibs
Suspended Solids in Primary Effluent, Ibs/day
7-59
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7.51 Determination of Sludge Age
Whether a new plant is being started or the operation of an exist-
ing plant is being checked, the sludge age is used to indicate
when activated sludge should be wasted and, if necessary, the waste
sludge pumping rate.
Information needed to determine sludge age:
1. Mixed Liquor Suspended Solids = 2380 mg/1
2. Primary Effluent Composite Suspended Solids = 72 mg/1
(average of daily values for past week)
3. Average Daily Influent Flow =4.0 MGD
1. Determine pounds of mixed liquor suspended solids in aerator.
Solids in
Aerator, = Mix. Liq. Susp. Sol., mg/1 x Aerator Vol., MG x 8.34 Ibs/gal
Ibs
= 2380 mg/1 x 4.6 (factor from Section 7.44, Page 7-54)
= 10,948 Ibs, or approximately 11,000 Ibs
2. Determine pounds of solids added per day to system by primary
effluent.
Solids
Added by
Effluent = Prim' Ef£1' Susp. Sol., mg/1 x Flow, MGD x 8.34 Ibs/gal
Ibs/day _ g>34 lbs/gal
= 72 x 33.4 Ibs/day
= 2404 Ibs/day, or approximately 2400 Ibs/day
3. Calculate sludge age in days.
. ° _ _ Suspended Solids in Aerator, Ibs _
Suspended Solids in Primary Effluent, Ibs/day
11,000 Ibs
2400 Ibs/day
= 4.5 days
7-60
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If the results of lab tests and calculations indicate a sludge
age of 4.5 days when the target sludge age is five days, no
sludge should be wasted. If a sludge age of 4.5 days was obtained
during the start-up of the example plant, the operator should
continue to allow the solids to increase in the aerator. In an
existing plant, if the sludge age is below the desired level,
any sludge wasting should be stopped.
A simple way to find the desired pounds of aerator solids to be
maintained is to multiply the average daily pounds of primary
effluent solids added per day by the desired sludge age.
Example:
Find the desired pounds of solids to be maintained in the aerator.
Information needed:
Desired Sludge Age, days = 5 days
Solids in Primary Effluent, Ibs/day = 2400 Ibs/day
Calculate pounds of solids desired in aerator.
. _ Suspended Solids in Aerator, Ibs
days Suspended Solids in Primary Effluent, Ibs/day
Rearrange the equation to obtain:
Suspended
. = Sludge Age, days x Susp. Sol. in Prim. Effl., Ibs/day
lbs = 5 days x 2400 Ibs/day
= 12,000 lbs
7-61
-------
O c
Suspended solids in the
mixed liquor in the
aerator should be allowed
to build up until 12,000
pounds of solids are in
the aerator. Sludge
wasting may be started
when the desired level
is exceeded.
To determine when an excess
of activated sludge is in
the aerator and some should
be wasted, many operators
calculate the desired mixed
liquor suspended solids con-
centration in the aerator.
When this concentration is
exceeded, some of the
excess activated sludge is
wasted.
Calculation of the desired mixed liquor suspended solids concentration
in mg/1 can be determined from either of the two formulas listed below
(they are the same).
Desired Mixed
Liquor Suspended
Solids, mg/1
or =
Desired SUSP. Sol, in Aerator, Ibs
Weight of Water in Aerator, million Ibs
Desired Susp. Sol, in Aerator, Ibs
Vol. of Aerator, M gal x 8.34 Ibs/gal
= 12>0°° lbs (factor from Section 7.44, Page 7-54)
4.6 M lbs
= 2608 mg/1
= 2600 mg/1 (target concentration)
Wasting of activated sludge from the example plant should not start
until the mixed liquor suspended solids concentration exceeds 2600 mg/1.
7-62
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7.52 Wasting Activated Sludge
The amount of activated sludge wasted may vary from 1% to 20%
of the total incoming flow. Normally waste activated sludge is
expressed in gallons per day or pounds of solids removed from
the aeration system. It is preferred that wasting be continuous.
The main purpose is to maintain a sludge age that produces the
best effluent.
Wasting (Fig. 7.7) is normally accomplished by diverting a portion
of the return sludge to a primary clarifier, thickener, aerobic
digester, or anaerobic digester. Normal operations in a conven-
tional activated sludge plant will concentrate return sludge and
waste sludge solids three to four times as much as the solids
concentration of the mixed liquor. This may provide return sludge
with a concentration of 2,000 to 10,000 mg/1, or 0.2 to 1.0% in
terms of total solids. If the waste sludge line was discharged
directly to the anaerobic digestion system, it would contain
10 to 20 times as much water as should be entering the anaerobic
system with that amount of solids. Operating an anaerobic digester
would be difficult under this condition. It would be wiser to
waste to the primary clarifiers where combining with primary sludge
minimizes the addition of excess water to the digester.
Wasting activated sludge will occur in the effluent whether or not
it is controlled. In all activated sludge plants, wasting must be
controlled by the operator. Mixed liquor suspended solids which
need to be wasted accumulate from two sources. The first is the
suspended solids in the plant flow from the primary clarifiers or
raw wastewater. The second and main source is the new cell pro-
duction by the microorganisms.
For every pound of BOD or solids removed in the activated sludge
system, a part of that pound will remain in the system as micro-
organisms. The rate of production of excess sludge will depend on
the type of process being operated and the nature of the waste load.
The high-rate activated sludge plant is capable of producing 0.75
pounds of sludge volatile matter for every pound of BOD removed.
The conventional plant runs around 0.55 pounds of excess sludge
per pound of BOD removed in the activated sludge system. The
extended aeration plant drops down to about 0.15 pounds of excess
sludge per pound of BOD removed. Excessive silt or inert material
may increase sludge production beyond that indicated by the BOD test.
7-63
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ANAEROBIC
DIGESTER
WASTE SLUDGE-NOT ADVISABLE
PRIMARY SLUDGE - YES
J
k
w
PRIMARY
CLARIFIER
ASTE SLUDGE
PRIMARY
EFFLUENT _
>
r
k
^
AERATION TANK
>,
1
SECONDARY
CLARIFIER
RETURN SLUDGE
EFFLUENT
>_
Fig. 7.7 Waste sludge flow diagram
7-64
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7.53 Determination of Waste Sludge Pumping Rate
To illustrate the determination of a waste sludge pumping rate,
assume the following plant data:
1. Mixed Liquor Suspended Solids = 2985 mg/1
2. Return Sludge, Suspended Solids = 6200 mg/1
3. Primary Effluent, Suspended Solids = 72 mg/1
4. Average Daily Flow = 4.0 MGD
Using the procedures outlined in this lesson, the following infor-
mation can be calculated:
1. Solids in Aeration Tank = 13,731 pounds
2. Solids Added by Primary Effluent = 2400 Ibs/day
3. Sludge Age =5.7 days
The results of the calculations indicate that the sludge age is too
high (5.7 days instead of 5 days) and the solids in the aeration tank
also are too high (13,731 pounds instead of 12,000 pounds). To
reduce the sludge age and solids in the aerator, some of the activated
sludge removed by the secondary clarifier should be pumped to the inlet
of the primary clarifier.
The formula to calculate the waste return sludge pumping rate is:
Waste Return Sludge Pumping Rate, MGD
Solids to be Wasted, Ibs/day
Return Sludge Cone., mg/1 x 8.34 Ibs/gal
(15,700 Ibs - 12,000 lbs)/day*
6200 mg/1 x 8.34 Ibs/gal
= 1700 Ibs/day = J^TOO =
6200 mg/1 x 8.34 Ibs/gal 51,700
Biological cultures should be subject to slow changes rather than
rapid ones; therefore, the pounds wasted will be removed during a
24-hour period.
7-65
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Usually the waste sludge pumping rate is expressed in gallons
per minute instead of MGD.
Pump Waste _ Pumping Rate, gals/day
Rate, GPM ~ 1440 min/day
52,000 gals/day
1440 min/day
= 22.2 GPM
Set the waste pumping rate at 20 GPM for the next 24-hour period.
It is better to waste a little less activated sludge than the
theoretical calculation.
7.54 Summary
After a plant is started, the sampling and laboratory testing
program must be continued to identify and correct operational
problems whenever they start to develop. See Lesson 7 for possible
approaches to solving operational problems.
QUESTIONS
7.5A Why must some activated sludge be wasted?
7.5B Where is the best place for excess activated sludge to
be wasted?
7.5C Calculate the sludge age for an activated sludge process
if the aerator volume is 0.5 MG and the mixed liquor sus-
pended solids concentration is 2100 mg/1. The influent
flow is 4.0 MGD, and the primary effluent suspended solids
concentration is 70 mg/1.
END OF LESSON 5 OF 8 LESSONS
on
ACTIVATED SLUDGE
7-66
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DISCUSSION AND REVIEW QUESTIONS
Chapter 7. Activated Sludge
(Lesson 5 of 8 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 4.
22. Estimate the pounds of solids under aeration in a
200,000-gallon tank when the suspended solids con-
centration is 1600 mg/1. Show your work.
23. What level of dissolved oxygen should be maintained
in the aeration tank during start-up?
24. What do the letters MLSS stand for?
25. Calculate the desired pounds of mixed liquor suspended
solids in an aeration tank if the primary effluent sus-
pended solids are 1800 pounds per day and the loading
is based on a five-day sludge age. Show your work.
26. Calculate the desired mixed liquor suspended solids con-
centration (mg/1) if 4000 Ibs are desired in a 200,000-
gallon aeration tank. Show your work.
27. If sludge should be wasted at a rate of 0.05 MGD,
what should be the waste pumping rate in GPM?
28. Why must some activated sludge be wasted?
7-67
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CHAPTER 7. ACTIVATED SLUDGE
(Lesson 6 of 8 Lessons)
7.6 PACKAGE PLANTS (Extended Aeration)
7.60 Introduction
You may be assigned to operate a small extended aeration plant
(Fig. 7.8). You may not have laboratory facilities and may not
be supplied materials for simple tests, such as dissolved oxygen
(DO), pH, or settleable solids. Fortunately, this type of plant
is usually under a light load and/or sized for a long retention
of the solids (extended aeration), and the sludge age may be
greater than ten days. The operation of these plants is the
same as the operation of any other activated sludge plant. A
high quality effluent requires attention, understanding, and good
plant operation.
This type of plant comes in many sizes, but basically there are
just two compartments or tanks made from one large tank. The
larger compartment is used for aeration, and the smaller one
for clarification and settling. Usually provisions are not made
for a primary settling compartment. The plant may be mechanically
aerated or a small air compressor may provide air through diffusers,
The settling tank is usually a double hopper tank equipped with a
pump or air lift system for the return of sludge from the hoppers
of the settling tank back to the aeration tank.
7.61 Pre-Start Check-Coat
If the plant is being installed, an excavation is dug to accommo-
date the plant which is usually transported by truck to the site
and placed in the excavation by a crane. The inlet sewer and dis-
charge lines are connected and the plant is ready for service after
power has been connected.
While the tank is empty, check the following:
1. Tank must be level from one end to the other.
2. If the tank is constructed of metal,
is cathodic protection17 required?
17 Cathodic Protection (ca-THOD-ick). An electrical system for
prevention of rust, corrosion, and pitting of steel and iron
surfaces in contact with water or wastewater.
7-69
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Fig. 7.8 Package plant
7-70
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3. Condition of paint on exterior and interior.
4. Removal of all rocks and debris from both compartments.
5. If equipped with comminutor or grinder, check lubrication,
clearance of cutters, and operation.
6. Check aeration device:
a. Lubrication
b. Direction of rotation
c. Mechanical aeration—proper agitator depth
d. Compressor, if diffused air
(1) Air filter and oil bath
(2) Air header and valves
(3) Air lift tubes and valves
(4) Diffusers installed
(5) Swing header lifts easily and free
7. Record and file the following data:
a. Plant model and serial number
b. Two copies of plant manual
c. Name plate data from equipment
(1) Comminutor
(2) Comminutor motor
(3) Aeration motor
(4) Compressor or agitator
(5) Amperage of running equipment
(6) Oils and greases specified for each unit
8. Check influent gate or valve for proper operation.
7.62 Starting the Plant
(See Section 7.4 for detailed instructions.) Once the flow is
admitted to the aeration compartment and it is filled, the aerator
compressor or agitator may be started. If the plant is the diffused
air type and equipped with air lifts for return sludge, the air line
7-71
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valve to the air lifts will have to be closed until the settling
compartment is filled or all the air will attempt to go to the
empty compartment. Once the settling compartment is filled
from the overflow from the aeration tank, the air lift valves
may be opened and adjusted to return a constant stream of water
and solids to the aeration tank. This adjustment is usually
two to three turns open on the air valve to each air lift.
There may be a build-up of foam during the first week or so of
start-up, and a one-inch water hose with a lawn sprinkler may be
used to keep it under control until sufficient mixed liquor solids
are obtained.
7.63 Operation of Aeration Equipment
Aeration equipment should be operated continuously. If a diffused air
system is employed, the operator controls air flow to the diffuser by
the header control valve which forces excess air to the air lifts in
the settling compartment. Good treatment rarely results from inter-
rupted operation and should not be attempted. Performance of the
aeration equipment usually can be determined by the appearance of the
water in the settling compartment and the effluent that goes over the
weir.
If the water is murky or cloudy and the aeration compartment has
a rotten egg odor (I^S), insufficient air is supplied and the air
supplied or aeration rate should be increased. If the water is
clear in the settling compartment, the aeration rate is probably
sufficient.
7.64 Wasting Sludge
Supposedly there is no control over the wasting of sludge in these
plants because the excess sludge is carried out of the system with
the effluent. In many localities the water quality standards are
too strict to allow this practice. The operator then must waste
a portion of the plant solids content out of the system periodically.
For best results, in terms of effluent quality, waste about 5 percent
of the solids each week during summer operation to prevent excessive
solids "burping".
To waste the excess activated sludge, turn off the return pumps or
air lifts for one hour and continue to let the rest of the plant
function. After one hour of not returning sludge, about five percent of
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the waste solids in the settling compartment are pumped out with a
portable pump to a sand or soil drying bed. The amount of solids
pumped is determined by measuring the depth of the sludge blanket
and then lowering it five percent. Record the pumping time and
weekly waste solids for this time period if results are satisfactory.
Annually, check the bottom of the hoppers for rocks, sticks, and
grit deposits. Also check the tail pieces of the air lifts to be
sure that they are clear of rags and rubber goods and in proper
working condition.
Frequency and amount of wasting may be revised after several months
of operation by examining:
1. The amount of carryover of solids in the effluent.
2. The depth to which the solids settle in the settling
compartment when the aeration device is off (should
be greater than one-third of the distance from top to
bottom).
3. The appearance of floe and foam in the aeration com-
partment as to color, settleability, foam make-up, and
excess solids on water surface of the tank.
4. Results of laboratory testing (Section 7.66, Page 7-74)
A white, fluffy foam indicates low solids content in the aerator,
while a brown, leathery foam suggests high solids concentrations.
If excessive effluent solids are noticed periodically during typical
daily flows, the solids loading may be too great for the aerator.
Excessive solids indicate the sludge age is too long and more solids
should be wasted.
7.65 Operation
Preferably this type of plant should be checked every day. Each
visit should include the following:
1. Check appearance of aeration and final
clarification compartment.
2. Check aeration unit for proper operation and lubrication.
3. Check return sludge line for proper operation. If the
air lift is not flowing properly, briefly close the outlet
valve which forces the air to go down and out the tail piece.
This will blow it out and clear any obstructions. Reopen
the discharge valve and adjust to desired return sludge flow.
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4. Check comminuting device for.lubrication and operation.
5. Hose down aeration tank and final compartment.
6. Brush weirs when necessary.
7. Skim off grease and other floating material
such as plastic and rubber goods.
8. Check plant discharge for proper appearances, grease,
or material of wastewater origin that is not desirable.
7.66 Laboratory Testing
Testing for solids condition may be accomplished by the settling
test. Using a quart jar, take a sample from the aeration compart-
ment after the aeration device has been operating for several
minutes (10 - 15) and fill the jar to the top. Let the jar stand
and watch the floe form
and settle to the bottom
of the jar. At the end , -"""
of 30 minutes, the j ar
should be approximately
half full of the settled
solids, or slightly less,
and have a chocolate
brown color with clear
water above it. The
solids should appear
granular. If the solids
do not settle half way
and the water above them
is cloudy or murky in
appearance, a longer
aeration period, more air,
or solids wasting is needed.
If the solids settle to
less than 1/4 of the jar
and the water above the
solids is murky or cloudy, no wasting of solids should be done
and the solids level in the aerator should be allowed to increase.
If the solids settle to the bottom of the jar with a clear liquor
on top and stay down one hour and come up in two hours, this is
an indication of good operation. Solids should never be allowed
to remain in the settling compartment longer than two hours. If
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the solids should rise in one hour, this is an indication
usually of too much air, or too many solids. Make slight adjust-
ment to reduce the air to the aeration compartment or increase
the return sludge rate.
The final clarifier should be equipped with a scum baffle.
A properly operated plant will produce some light, oxidized
floe that will float to the surface of the settling compartment.
A scum baffle will prevent this flow from leaving the compart-
ment in the plant effluent. The better the treatment, the more
likely scum will develop, unless the unit is septic.
If equipment is available for other testing, DO, pH, and suspended
solids tests should be run on the unit occasionally. See Chapter 14,
Laboratory Procedures and Chemistry, for procedure details.
QUESTIONS
7.6A How frequently should a package plant be visited?
7.6B When should sludge be wasted?
7.6C What should you do if you take a sample in a jar
from the aeration compartment and after 30 minutes
a. solids do not settle to the bottom half of the jar?
b. solids settle to the bottom and then float to the top?
END OF LESSON 6 OF 8 LESSONS
on
ACTIVATED SLUDGE
7-75
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 7. Activated Sludge
(Lesson 6 of 8 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 5.
29. How would you control foaming on the aeration
compartment of a package plant?
30. How would you operate the aeration device
in a package plant?
31. How would you waste sludge in a package plant?
7-77
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CHAPTER 7. ACTIVATED SLUDGE
(Lesson 7 of 8 Lessons)
7.7 OPERATIONAL PROBLEMS
7.70 Typical Problems
An activated sludge plant can accept quite a shock load now and
then without adverse effects to the system, but it cannot survive
a continuous series of shock loads.
Many factors may change that the operator cannot anticipate or
control but must compensate for by adjusting his operational
controls. For example, a conventional activated sludge plant
has operated satisfactorily for several weeks. The secondary
clarifier had good clarity of 68 inches with a Secchi disc, and
the effluent BOD and suspended solids were running from 5 to
18 mg/1. The aeration tanks had been maintained at 15,000 pounds
of mixed liquor suspended solids with a volatile content of 78.5%,
and sludge age of five days.
A minimum DO of 2.8 mg/1 had been measured in the last two-
thirds of the aerator. Sludge wasting had been at a rate of
2000 Ibs/day from the system.
This week the situation has changed; the clarity in the secondary
tanks has dropped to 18 inches. The suspended solids in the
secondary clarifier effluent have remained about the same, but
the BOD test started five days ago came out at 38 mg/1. If a
COD test had been run at the time the BOD was started, an
operational correction could have been made at that time.
Overall, the plant effluent has definitely deteriorated from
the previous week.
Only you and your records can determine the cause and what
corrective action should be taken.
Has plant flow increased or decreased? Have air rates been
maintained? Have you received some toxic or untreatable slug
dose in the influent? Are your sludge return pump and lines
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clear? Has the BOD load to the aeration tank changed? Have
mixed liquor solids been the same? These are just a few of the
conditions that may change effluent quality.
The difficult decision after determining the cause or probable
cause is—should a change be made?
This is where the operator who knows his plant is effective.
If he knows the situation is unusual and will only last a
couple of days, appropriate minor changes should be con-
templated to immediately improve the effluent quality. But if the
condition occurred before and lasted several weeks according to
past records, a process change may be necessary to compensate
for it. This is where experience with your plant and records
plays an important role in activated sludge operation.
By keeping accurate records you can find the desirable operating
range in terms of efficiency of waste removal and cost of opera-
tion. Usually each plant will have some mixed liquor suspended
solids concentration where the plant will function best. This
concentration should produce a clear final effluent, with low
suspended solids and BOD of 8 to 20 mg/1. However, depending
on plant design, type of waste, and season of year, the best
mixed liquor suspended solids concentration might be found to be
anywhere from 1000 to 4000 mg/1. When a satisfactory mixed liquor
suspended solids concentration is found for a specific plant
under certain conditions, the operator should attempt to maintain
this level until something changes.
If the mixed liquor suspended solids are allowed to start building
up, the final effluent will begin to deteriorate by becoming
turbid. When the mixed liquor suspended solids are allowed to
increase too high for the conventional activated sludge plant,
other problems can develop. The previous return sludge rate for
the plant flow would not be sufficient. Return rates may have to
be increased considerably. If the return sludge rate was not
increased, the activated sludge in the final clarifiers would
build a higher blanket. The deep blanket in the final tank
could cause solids to be swept over the weirs during peak flow.
Another limiting factor is aeration equipment. The amount of
oxygen supplied to the aerator also limits the microorganism
mass that can be maintained in an aerobic state. A high oxygen
demand in the aerator can be created by a high solids content in
the plant influent.
The other factor "is the organisms themselves. If insufficient
food is available, only a limited number of organisms will develop
energy to multiply. This is where the struggle for survival
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begins. When food supply is low, the microorganisms begin to
feed upon themselves. This is the period of most complete
oxidation, and new sludge production is at a minimum. Extended
aeration plants are designed to operate under these conditions
which tend to increase solids in the plant effluent.
QUESTIONS
7.7A Why are plant records of the activated sludge
operation important?
7.7B What could happen if the mixed liquor suspended
solids were allowed to increase beyond the best
range in an activated sludge process?
7.71 Plant Changes
If the plant becomes upset, the first action before making any
changes is to check the plant data for at least three previous
weeks. The problem probably started last week or earlier. To
look for the cause of the problem, ask yourself the following
questions:
1. Have any changes been made to other plant units
such as the digesters or primary clarifiers?
Was a digester supernatant with excessive amounts
of solids returned to the primary clarifiers?
Return of supernatant should be slow and easy
and at low load periods. Digester supernatant
solids mixed with raw wastewater and waste
activated sludge may create a light sludge that
may be washed out of the primary clarifier.
The solids washed out of the primary clarifier
create undesirable recycle and loading problems.
2. Have plant daily flows and waste concentrations
increased or decreased? Heavy rains following a
dry spell, a new industrial plant, or a different
process discharge from an existing industry can
cause problems.
3. Has temperature of the influent changed a
•significant amount?
4. Has the sampling program been consistent?
Most of the time a plant upset can be found due to some in-plant
problem and not the influent raw wastewater, unless your plant
is frequently overloaded.
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Condition 1:
A high solids content in digester supernatant can throw a curve
to the operator. The solids in digester supernatants are
usually high in inunediate oxygen demand and contain high colloidal
and dissolved solids. If a large quantity of low volatile content
solids escapes from the primary clarifier to the aeration system,
several undesirable events occur. The supernatant solids are
picked up by the activated sludge in the aerator and carried
through the system. This creates extra oxygen demand, and air
output must be increased. Digester solids make a good settling
activated sludge, but the color of the floe will be darker.
Total pounds of solids in the aerator will increase due to the
supernatant solids, and the operator will normally increase waste
sludge rates to hold the established range of solids or sludge
age. Consequently, the effluent from the plant deteriorates.
Why? Lab tests show that the solids in the aerator are at the
desired level, and DO of the mixed liquor has been held at 2.0 mg/1
(probably more air was required).
What has occurred is that by wasting apparently excess activated
sludge, many of the microorganisms have been replaced in the aerator
by digested or inert solids. They are sampled the same as mixed
liquor suspended solids and are included as total pounds of solids
under aeration. This is whv many plants base aerator loadings on
mixed liquor VOLATILE suspended solids and not mixed liquor
suspended solids.They are making the assumption that the volatile
content of the mixed liquor suspended solids is microorganisms.
Most activated sludge mixed liquor suspended solids fall into a
range of 70 to 80% volatile content for municipal waste when the
process is operating properly. This would mean that if you are
striving to maintain a sludge age of five days, you are attempting
to maintain a prescribed number of organisms for every pound of
food applied to the aeration tanks. A five-day sludge age is
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equivalent to 20 pounds of food for every 100 pounds of organisms.
When the supernatant was admitted into the aeration tank, the
pounds of solids in the aerator were increased. When sludge was
wasted to maintain the five-day sludge age, many of the organisms
needed to treat the incoming wastes were replaced by the inert
supernatant solids. This placed a higher food load on the remain-
ing organisms of maybe 30 to 35 pounds per 100 pounds of organisms
and reduced the effective sludge age from five days to possibly
3.5 days.
Storm wash may sweep excessive silt into the plant by infil-
tration into sewers or through combined sewer systems. Solids
increase drastically but the percent of volatile solids may drop
to 50% of the total solids. Wasting apparently excess solids on
a suspended solids basis without consideration of the pounds of
volatile solids in the aerator may produce serious organism losses.
In the example plant, the supernatant solids may not appear to
produce much of a change, but over a period of several days
the system could become severely upset. When the total pounds
of volatile solids in the aerator becomes too low due to ex-
cessive amounts of inert solids from digester supernatant or
storm inflow, the solution to the problem is to stop wasting
sludge for several days. This will provide the time necessary
to rebuild the microorganism population to handle the incoming
waste load.
Try to hold the solids in the digester a little longer and try to
increase solids concentration in the sludge fed to the digester.
It is possible that the poor supernatant was due to overloading the
digester and/or insufficient seed sludge in the digester. In
this case the problem "snowballs"--first the digester is over-
loaded, then supernatant solids overload the aerator which
overloads the clarifier, and the problem keeps getting worse.
Condition 2: (Flow or Waste Changes)
Always be alert for the possibility of toxic dumps, accidental
spills (particularly the midnight variety), storms, or other
up-sewer factors that may change the influent flow or waste
characteristics.
A frequent problem is the increased flows from storm infiltra-
tion or other sources. These flows may create shorter aeration
7-83
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times or loss of activated sludge solids from the final clari-
fiers due to a hydraulic overload. To compensate for this
condition, regulate return and waste sludge rates to hold as
much of the solids as possible in the aerator.
Changes in waste characteristics may be caused by isolated
dumps or spills, or changes may be seasonal. Become acquainted
with plant managers whose activities may cause changes in the
waste loadings on your plant and encourage these people to
notify you whenever a problem discharge occurs. Try to convince
them to release unusual dumps at a low discharge rate rather
than all at once. Certain industries such as canneries create
seasonal problems which the operator should prepare for in advance.
Condition 5: (Temperature Changes)
The activated sludge system is influenced by temperature changes
similar to the response of trickling filters to temperature
changes in spring and fall. During the summer, the activated
sludge plant may operate satisfactorily in a certain loading
range and air rates, but in winter the best loading ranges
and air rates change and the plant requires less air and more
solids under aeration. Usually a temperature change is not
significant unless it raises or lowers the temperature more
than 10°F.
Temperature is an important factor in oxidation relative to
sludge accumulation. A high temperature produces a rapid micro-
organism growth and waste oxidation. Low temperatures cause a
slower growth rate and more waste storage in the organism cell
with less oxidation. Therefore, a larger net sludge production
will result with lower biological activity, and the process will
have a tendency to produce a thinner sludge.
Condition 4; (Changes in Sampling Program)
Data on system performance can be greatly affected by changes
in a sampling program. If improper sampling locations or labora-
tory procedures are used, lab results could vary considerably.
When the lab data varies widely from one day to the next, check
sampling location, time, and lab procedures for errors.
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When a major change is contemplated, first review
the plant data. Next, make only one major change
at a time. If two changes are made, you won't
know whether one or both changes provided the
corrective action. When a change is made, give
the system at least one week before attempting
another change or modification. Don't make too
many changes too fast.
QUESTIONS
7.7C How would you determine the best solids loading for
an aerator?
7.7D What would you do if an activated sludge plant became
upset?
7.7E (a) What can happen if a digester supernatant with a
high solids content is returned to the primary
clarifier?
(b) How can this situation be remedied?
7.7F How would you correct or compensate for an upset created
by high flows from storm water infiltration?
7.7G How would you correct an upset apparently caused by a
temperature difference due to seasonal changes?
7.7H What would you do if a review of the lab data revealed
considerable variation from day to day?
7.71 How long would you allow an activated sludge process to
react and stabilize after a change?
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7.72 Sludge Bulking
Bulking is the term applied to the condition in which the mixed
liquor solids tend to show a very slow settling rate and compact
to a limited extent. The liquid that does separate from the
solids usually produces a crystal clear, high-quality effluent,
but generally there is not enough time for complete removal of
the solids in the secondary clarifier. The sludge blanket in
the clarifier becomes deeper and rises to overflow the weirs and
is discharged with the effluent.
Bulking may be associated with production of a highly jelly-like,
water-logged (hydrated) sludge that has a very low sludge density,
or by filamentous growth that may grow from one floe mass to
another and act as stay rods to prevent compaction of the sludge
particles and produce poor settling results.
Low pH, low DO, and low nitrogen concentrations have been related
to bulking. High food-to-organism loading rates (low sludge ages)
are the major items that will produce bulking consistently.
Organisms that grow rapidly tend to become spread out and will not
clump or form a floe mass until growth rates decrease. It is
difficult to retain enough low-density (light) sludge to decrease
the food-to-organism load ratio (or increase sludge age) without
chemical flocculation or other tricks to increase the sludge
density (weight). A rain may provide enough silt to favor increased
sludge density. Low loads during weekends may help. Addition
of some preaerated digested sludge (Kraus process, Section 7.92)
helps reduce bulking. Some of the polyelectrolyte flocculent
aids are very effective in controlling a bulking activated sludge.
If it is possible, bulking may be reduced by decreasing the load
to the aeration tanks until the sludge becomes sufficiently oxidized
to flocculate. Addition of clay or bentonite has been used to
control bulking.
The main objective of most bulking control procedures is to
increase sludge age or decrease the ratio, of waste (food) load
added per day per unit of mixed liquor volatile solids in the
aerator. Aluminum sulphate (A12 (S04)3 • 14 H20), iron as ferric
chloride (FeCl3) , or ferric sulphate (Fe2 (S04) 3 • 3 H20) added
as a flocculent with alkaline (lime) addition to prevent low pH
are good methods for holding solids under aeration. The proper
polyelectrolyte may cost more than other chemicals, but alkali
addition may not be required to increase the pH.
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Chlorination is not an effective cure because chlorine inacti-
vates the organisms that are needed to treat the wastes.
Effluent turbidity may increase for several days after an
application of chlorine, and bulking is likely to return if
the solids retention problem is not corrected.
When bulking occurs it will generally be associated with the
load ratio or sludge age. Plant records should be reviewed in
an attempt to locate the cause of the problem. Identification
of the cause will not remedy the present bulking condition,
but should be considered a valuable lesson, and measures should
be taken to prevent the same conditions from occurring again.
To prevent sludge bulking from occurring, the following items
should be carefully controlled in an activated sludge plant:
1. Suitable Sludge Age. Carefully review plant records
and maintain a sludge age that produces the best
quality effluent. Watch influent solids loadings,
maintain desired level of solids in the aerator, and
carefully regulate waste sludge rates. Generally,
bulking may be cured by increasing the sludge age.
2. Low DO. Prevent low levels of DO from developing.
Mixed liquor DO determinations are a quick, simple
test; and if a DO probe is used, it gives a con-
tinuous reading. There is no valid excuse for low
DO concentrations during normal conditions if suffi-
cient oxygenation capacity is available, unless a
slug of waste with an excessive oxygen demand is
received.
3. Short Aeration Period. Bulking caused by the aeration
period being too short is usually the result of a
design problem, unless the operator has formed the
habit of returning too high a volume of return sludge.
This can be corrected by reducing the return sludge
rate and thickening the return sludge solids concen-
tration by coagulation (ko-AGG-u-LAY-shun), if
necessary, thereby still returning the same number
of organisms to meet the new food (waste) entering
the aerator, but effectively reducing the total
flow through the aerator and clarifier.
4. Filamentous Growth. Occurrence of filamentous growth
may be caused by incorrect sludge age or nutritional
differences, such as a shortage or abundance of nitrogen,
7-87
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phosphorus, or carbon. If filamentous growths are
allowed to become well established, they create a
difficult problem to overcome. Control may be achieved
by maintaining a higher sludge age, and in special
instances supplementing the nutrient deficiency.
7.73 Septic Sludge
Septic sludge may be produced when any type of sludge remains too
long in such places as hoppers and channels. It is likely to cause
a foul odor, rises slowly, and sometimes rises in clumps. Even
small amounts can upset an aerator.
Septic sludge may occur in poorly designed or constructed hoppers,
wet wells, channels, or pipe systems. This occurs when activated
sludge is allowed to be deposited and anaerobic decomposition starts.
Septic sludge deposits also may develop on the floor of the aerator
due to insufficient air rates that are not keeping the tank com-
pletely mixed. A high solids load also can cause septic problems.
To effectively control septic sludge, aerators must be thoroughly
mixed and sludge must be pumped frequently. In channels and pipe-
lines, a velocity over 1.5 feet per second will prevent the formation
of sludge deposits that could become septic.
Sludge going septic in the secondary clarifier may develop from
four causes:
1. Return sludge rate too low, thus holding the solids in
the final clarifier too long and allowing them to become
septic.
2. Clarifier collection mechanism turned off, thus the
sludge is not being moved to the draw-off hopper.
3. Sludge draw-off lines plugged, obstructed, or used infrequently.
4. Return sludge pump off or a valve closed.
A good operator checks his system several times a day. In most new
activated sludge plants the secondary clarifiers have air lift
samplers or photocells to indicate sludge blanket level in the tank.
Whenever the final clarifier sludge blanket level changes, an
immediate investigation should be undertaken. In any of the cases
above, the correction is quite obvious—restore suitable return
sludge flow as soon as possible.
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7.74 Toxic Substances
Toxicity causes inhibition or death of working organisms to
produce system and effluent upsets. The operator has limited
control over the cause. When this cause is identified, sludge
wasting should be stopped immediately and all available solids
returned to the aerator. Toxic materials such as heavy metals,
acids, insecticides, and pesticides should never be dumped into
a sewer system without proper control.
7.75 Rising Sludge
Rising sludge is not to be confused with bulking. The sludge
settles and compacts satisfactorily on the bottom of the clari-
fier, but after settling it rises to the top of the secondary
tank in patches or small particles the size of a pea. This is
usually accompanied by a fine scum or froth (brown in color)
on the surface of the aeration and secondary tanks.
Rising sludge is caused by denitrification or septicity and
results from too long a detention time in the secondary clarifiers.
The secondary clarifiers should be equipped with scum baffles and
skimmers to prevent these solids from escaping in the plant effluent,
Denitrification is most common when the sludge age is high
(extended aeration). When this type of activated sludge flows
from the aerator to the secondary clarifier or becomes short of
oxygen, the organisms first use the available dissolved oxygen
and the oxygen in the nitrates resulting in the release of
nitrogen gas. Denitrification is an indication of good treat-
ment, providing the sludge in the settleability test stays on
the bottom of the cylinder for at least one hour, but floats to
the surface in two hours. If it floats up too early in the
settleability test, the sludge age should be reduced or the food-
to-organism ratio should be increased. If the sludge stays down
for an hour in the settleability test but problems are still
present in the secondary clarifier, increase the return sludge
rates to move the solids out of the clarifier at a faster rate.
7.76 Frothing
Aerator frothing has been a problem for some plants. There have
been many theories presented on the cause, such as surfactants
(detergents), polysaccharides, and over-aeration. Whatever the
cause, there is a definite relationship between froth build-up
7-89
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on the aerator and the amount of suspended solids in the mixed
liquor and air supply to the aerator.
For control:
1. Maintain higher mixed liquor suspended solids con-
centrations.
2. Reduce air supply during periods of low flow while
still maintaining DO.
3. Return supernatant to the aeration tank during low
flows (be cautious in this method—supernatant should
be returned slowly and steadily because too much
supernatant could cause an excess oxygen demand),
Most plants are equipped with water sprays along the aerator to
dissipate the foam. If mixed liquor solids are allowed to be
reduced, low water sprays will not be sufficient to hold the
foam. When this occurs, two problems develop—maintenance and
safety.
SAFETY FIRST--The froth from an aerator is an
excellent vehicle for minute grease particles
and when deposited on "Y" walls or walks will
leave a grease deposit that is very slippery.
More than one operator has been injured by
slipping on a walk or step previously coated
with foam.
This deposit not only is unsafe, but unsightly, and it must be
cleaned up immediately. The best way to remove this type of
deposit is with water (preferably hot), trisodium phosphate
(TSP), and a stiff bristle deck brush. Wet the area to be
cleaned, lightly sprinkle TSP granules on the area, let the
TSP dissolve for a few minutes, and then brush the area to
spread the TSP and loosen the grease. Let it work for five
minutes, rebrush, and then hose off.
7-90
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QUESTIONS
7.7J How can froth or foam be controlled in an aerator?
7.7K How can grease deposits (from foam) on walks be removed?
7.7L How would you differentiate between bulking and rising
sludge?
7.7M What would you do to correct a rising sludge problem?
END OF LESSON 7 OF 8 LESSONS
on
ACTIVATED SLUDGE
7-91
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DISCUSSION AND REVIEW. QUESTIONS
Chapter 7. Activated Sludge
(Lesson 7 of 8 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 6.
32. When an activated sludge plant becomes upset,
what should the operator do first?
33. Why do many activated sludge plants base aerator
loadings on mixed liquor volatile suspended solids
and not mixed liquor suspended solids?
34. When attempting to correct an upset activated sludge pro-
cess, why should only one major change be made at a time?
35. Is sludge bulking undesirable? Why?
36. What is the purpose of the 60-minute Settleability Test?
37. Can a frothing aerator deposit grease on walks?
7-93
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CHAPTER 7. ACTIVATED SLUDGE
(Lesson 8 of 8 Lessons)
7.8 AERATOR LOADING PARAMETERS
7.80 General
Sludge age has been suggested as the method for controlling the
solids in the activated sludge process. Other operational con-
trols used successfully by operators include the waste load
(food)/sludge volatile solids (organisms) ratio and the mean
cell residence time (MCRT). Mathematically, one can show that
aerator loadings based on sludge age, food/organism ratio, and
MCRT are theoretically similar. In each case the operator
selects a number or value for the parameter to start with on
the basis of experience and data available from other plants.
He then adjusts this value until he finds an operating range
which produces the best quality effluent for his plant.
In each case, the critical factor is the food/organism relation-
ship which cannot be precisely estimated for any specific plant.
The operator attempts to maintain in the aerator tank sufficient
solids (organisms) to use up the incoming waste (food). He
doesn't want too many organisms nor too few organisms in the
aeration tank in relation to the incoming food. Operation of
the activated sludge process requires removing the organisms
(settled activated sludge) from the secondary clarifier as
quickly as possible. The organisms are either returned to the
aerator to use the incoming food, or they are wasted. Therefore,
a critical decision is to determine the amount of solids to be
wasted. This procedure has been discussed and an example pro-
vided in Section 7.52 for the sludge age aerator loading parameter.
Select a method to operate your plant and stick with it. Don't
continually try to switch from one method to another.
7.81 Food/Organism Ratio
The food-to-organism loading ratio is based upon the food provided
each day to the microorganism mass in the aerator. Food (waste)
provided is preferably measured by the COD of the influent to the
aerator. COD is recommended because test results are available
7-95
-------
within four hours and process changes can be made before the
process becomes upset. Many operators load aerators on the
basis of the BOD test, but results five days later are too
late for operational control. The ratio of food load provided
each day to the volatile solids in the aerator is the recip-
rocal of the sludge age (see Table 7-1, Section 7.25). Typical
loading parameters have been established for the three opera-
tional zones of activated sludge and are summarized as follows:
1. High-Rate
COD: 1 Ib COD per day/1 Ib of MLVSS18 under aeration.
BOD: >0.5* Ib BOD per day/1 Ib of MLVSS under aeration.
2. Conventional
COD: 0.5 to 1.0 Ib COD per day/1 Ib of MLVSS under aeration.
BOD: 0.25 to 0.5 Ib BOD per day/1 Ib of MLVSS under aeration.
3. Extended Aeration
COD: <0.2* Ib COD per day/1 Ib MLVSS under aeration.
BOD: 0.05 to 0.10 Ib BOD per day/1 Ib MLVSS under aeration.
* > means greater than. Greater than 0.5 Ib BOD.
< means less than. Less than 0.2 Ib COD.
7.82 Calculation of Food/Organism Aerator Loading
Determine the amount of mixed liquor volatile suspended solids to
be maintained in the aerator of the conventional plant studied in
this chapter. Assume a food/organism ratio of 0.5 Ib COD per day/
1 Ib of mixed liquor volatile suspended solids under aeration.
Frequently this loading is expressed as 50 Ibs COD per day/100 Ibs
of MLVSS.
MLVSS means Mixed Liquor Volatile Suspended Solids.
7-96
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Information needed:
1. Average COD of primary effluent, 150 mg/1
2. Average daily flow, 4.0 MGD
3. Average volatile content of mixed liquor
suspended solids, 80%
Find pounds of COD provided aerator per day.
Aerator
Loading, = Prim. Effl. COD, mg/1 x Daily Flow, MGD x 8.34 Ibs/gal
Ibs COD/day
= 150 mg/1 x 4.0 MGD x 8.34 Ibs/gal
= 5004 or 5000 Ibs COD/day
Find desired pounds of Mixed Liquor Volatile Suspended Solids under
aeration, based upon 0.5 Ib COD per day/1 Ib of MLVSS. ~
MLVSS, _ Primary Effluent COD, Ibs/day
Ibs ~ Loading Factor in Ibs COD/day/T Ib MLVSS
5000 Ibs COD/day
0.5 Ib COD/day/Ib MLVSS
5000
0.5/Ibs MLVSS
= 10,000 Ibs MLVSS under aeration
The MLVSS is a measure of the organisms in the aerator available to
work on the incoming waste (food). When operating your plant on the
basis of MLVSS, you should determine any flucuations that may occur
during the week and make appropriate adjustment.
7-97
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If the COD load applied to the aerator increases or drops to a
significantly different level for two consecutive days, a new
mixed liquor solids value should be calculated and activated
sludge wasting adjusted to achieve the new value of solids desired
under aeration. Calculation of waste sludge rates is outlined in
Sections 7.52 and 7.53.
7.83 Mean Cell Residence Time (MCRT)
Another approach for solids control used by operators is the Mean
Cell Residence Time (MCRT) or Solids Retention Time (SRT). This
is a refinement of the sludge age. Both terms are almost the
same. The equation for MCRT is:
MCRT, _ Pounds of Suspended Solids in Total Secondary System
days Lbs of Susp Sol Wasted/day V Lbs of Susp Sol Lost in EffI/day
The most desirable MCRT for a given plant is determined experimentally
just as with the use of sludge age or the mixed liquor volatile sus-
pended solids concentration. The desired MCRT for conventional plant
operation should fall between 5 and 15 days. (Don't confuse this time
with the recommended range for Sludge Age of 3.5 to 10 days.)
A way of determining MCRT for the example plant in this chapter
would be as follows:
Required Data:
1. Aerator
3.
4,
5,
Final clarifier volume
Total secondary system volume
Wastewater flow to aerator
= 1,000,000 gals
= 500,000 gals
= 1.5 MG
= 4.0 MGD
Waste sludge flow for past 24 hrs = 0.075 MGD
= 2400 mg/1
= 6200 mg/1
Mixed liquor suspended solids
concentration
Waste sludge (or return sludge)
suspended solids concentration
Final effluent suspended solids
concentration = 12 mg/1
7-98
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7.84 Calculation of Mean Cell Residence Time
MCRT,
days
MCRT
Suspended Solids in Total Secondary System, Ibs
Susp Sol Wasted, Ibs/day + Susp Sol Lost in Effl, Ibs/day
Susp Sol in Mixed Liq, mg/1 x (Aerator, MG + Final Clari-
fier Vol, MG) x 8.34 Ibs/gal
(Susp Sol in Waste, mg/1 x Waste' RatV, MGD" x 8.34 Ibs/gal)
+(Susp Sol in Effl, mg/1 x Plant Flow, MGD x 8.34 Ibs/gal)
2400 mg/1 x (1.0 MG + .0.5 MG) x 8.34 Ibs/gal
(6200 mg/1 x 0.075 MGD x8.34 Ibs/gal)
+ (12 mg/1 x 4.0 MGD x 8.34 Ibs/gal)
2400 mg/1 x 1.5 MG x 8.34 Ibs/gal
(6200 mg/1 x 0.075 MGD x 8.34 Ibs/gal)
+ (12 mg/1 x 4.0 MGD x 8.34 Ibs/gal)
30,024 Ibs
3878 Ibs/day + 400 Ibs/day
30,024 Ibs
4278 Ibs/day
= 7.0 days
If you are operating the plant on the basis of MCRT and the plant
operates satisfactorily at the MCRT of 8, 9, 10, 11, or even 15
days, the main method of control is to adjust the waste sludge
rate to maintain the MCRT at the desired number of days.
7-99
-------
Rearranging the equation on the previous page, calculation of the
sludge waste rate from the system merely means plugging in the
chosen MCRT (use 7 days) and solids figures.
Example :
Waste
on j
Sludge,
Ibs/day
Susp Sol in System, Ibs „ „ , . ^,-j, •,, /,
- r ,f — * - - Susp Sol in Effl, Ibs /day
MLK1' days
2400 mg/1 x 1.5 MG x 8.34 Ibs/gal
7 days
12 mg/1 x 4.0 MGD
x 8.34 Ibs/gal
= 4289 Ibs/day - 400 Ibs/day
= 3889 Ibs/day
The waste sludge pumping rate of 3878 Ibs/day appears to be correct
to maintain a Mean Cell Residence Time of 7 days.
QUESTIONS
7.8A Why is it sometimes necessary to waste some activated sludge?
7.8B If you calculate that your plant has 12,000 pounds of mixed
liquor volatile suspended solids under aeration and you need
9,000 pounds under aeration, how many pounds should be wasted?
7.8C What should be the waste sludge pumping rate (GPM) if a plant
should be wasting 3000 pounds per day and the concentration
of return sludge is 6000 mg/1?
7.8D Estimate the waste sludge rate (Ibs/day) from an activated
sludge plant operating at an MCRT of 10 days. The system
contains 40,000 pounds of suspended solids and the effluent
has a suspended solids concentration of 10 mg/1 at a flow
of 5 MGD.
7-100
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7.9 MODIFICATIONS OF THE ACTIVATED SLUDGE PROCESS
7.90 Reasons for Other Modes of Operation
Modification of the conventional activated sludge process has been
developed to improve operational results under certain circumstances.
Some of these conditions may be:
1. Current or actual loadings are in excess of
design loading for conventional operation.
2. Wastewater constituents require added nutrients
to properly treat influent waste load.
3. Flow or strength of waste varies seasonally.
7.91 Contact S t ab i 1i z at i on (Fig. 7.9)
Operation of an activated sludge plant on the basis of contact
stabilization requires two aeration tanks. One tank is for
separate reaeration of the return sludge for a period of at
least four hours before it is permitted to flow into the other
aeration tank to be mixed with the primary effluent requiring
treatment. Loading factors are the same as for conventional
activated sludge, but at times the solids in the aeration tank
may be almost twice as high as normal ranges in conventional
plants.
If the solids content in aeration tank "A" (mixed liquor aerator,
Fig. 7.9) and aeration tank "B" (return sludge aeration only) are
combined, the loading ratio of food/organisms is the same as
conventional operation, but if you only look at aeration tank "A"
where the load is applied, we approach double the load ratio
established for conventional activated sludge.
Contact stabilization attempts to have organisms assimilate and
store large portions of the influent waste load in a short time
(as short as 30 minutes). The activated sludge is separated from
the treated wastewater in the secondary clarifier and returned to
the reaeration tank "B". No new food is added to the reaeration
tank and the organisms must use the waste material they collected
and stored in the first aeration tank. When the stored food is
used up, the organisms begin searching for more food and are
ready to be returned to tank "A".
Process controls for a contact stabilization plant are the same
as those described for a conventional plant in this chapter. When
a plant has exceeded design flows, or is subject to periodic high
7-101
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INFLUEN
o
to
MIXED LIQUOR
AERATOR 8A'
REAERATED
RETURN
SLUDGE
RETURN SLUDGE
REAERATION
AERATOR 'B'
Fig. 7.9 Plan layout of contact stabilization plant
-------
flows or shock waste loads, then contact stabilization is capable
of treating the plant influent because a ready reserve of organisms
is available in the reaeration tank "B".
7.92 Kraus Process (Fig. 7.10)
The Kraus process is a modification of conventional activated
sludge, and the process is patented by its developer. The process
is widely used when the wastewater contains a much greater ratio
of carbonaceous to nitrogenous material than found in normal
domestic wastewater.
This imbalance commonly occurs when wastes from canneries or
dairies are treated. When the organisms use all of a limiting
constituent, they refuse to remove the remaining portions of
the other constituents. Normally this nutrient deficiency is
nitrogenous material which is readily available in anaerobic
digester supernatant and sludges. Feeding anaerobic digester
supernatant or digester sludge to the aeration system will
usually supply the proper nutrients to maintain the balance.
The method of application is very important.
In the Kraus process, the return sludge is sent to the reaeration
aerator ("B") to be mixed with the digested sludge from a completely
mixed digester. In the reaeration tank ("B") , the digested sludge
and the return sludge are mixed, reaerated, and then sent to the
mixed liquor aerator ("A"). The amount of digested sludge introduced
to the system is determined by laboratory evaluation and by carbo-
naceous material removal through the system.
The same controls apply as described for controlling a conventional
activated sludge plant. The main objective is to properly balance
nutrients; however, one added advantage (similar to contact stabili-
zation) is the ability to maintain a large mass of organisms under
aeration in a relatively smaller system.
7.93 Step-Feed Aeration (Fig. 7.11)
Step-feed aeration actually is a step-feed process based on con-
ventional activated sludge loading parameters. The difference
between step-feed and conventional operation is that in conventional
activated sludge the primary effluent and return sludge are intro-
duced at one point only, the entrance to the aeration tanks. In
step-feed aeration the return sludge is introduced separately and
in many cases allowed a short reaeration period by itself at the
entrance to the tank. The primary effluent is admitted to the aeration
tanks at several different locations. These locations distribute
7-103
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INFLUENT
>
AERATION
TANK 'A'
SECONDARY
CLARIFIER
EFFLUENT
AERATION
TANK 8B'
DIGESTER SLUDGE
RETURN
SLUDGE
Fig. 7.10 Kraus process
-------
MODES OF FLOW
MODE 1
100% Primary Effluent
X Conventional Flow Activated Sludge Process
Return Sludge
Flow
Aerator
Effluent
MODE 2
Return Sludge
25°-,
25?
Flow
Step-Feed
25% 25% Primary Effluent
\ \ \ \
Aerator
Effluent
MODE 3
Return Sludge
Step-Feed
33-1/3% 33-1/3% 33-1/3%
\
\
Flow
Aerator
Effluent
MODE '4
Return Sludge
0%
Step-Feed
50% 50%
\
Flow
Aerator
Effluent
or Contact Stabilization
100% Influent
Several possible modes ,of feeding primary effluent to the aeration
tanks. Some tanks may have more or fewer points of discharge into
the tank.
Fig. 7.11 Modes of step aeration
7-105
-------
the waste load over the aeration tank and reduces oxygen sags in
an aerator. If you introduce the influent near the outlet end
of the aeration tank, the process will become similar to contact
stabilization.
Step-feed aeration distributes the oxygen demand from the wastewater
over the entire aerator instead of concentrating it at the inlet end.
Some of its advantages over conventional operation include less
aeration volume to treat the same volumes of wastewater, better con-
trol in handling shock loads, and better control of the solids entering
the secondary clarifiers. When a conventional plant is operating
above design loads and the secondary clarifiers cannot handle
the solids load, switching to step-feed aeration or contact
stabilization allows the operator to maintain the desired amount
of solids under aeration. Successful operation requires good waste
storage transfer into the solids in the short time interval before
the waste reaches the effluent end of the aeration tank.
This mode of operation is controlled by the same procedures
used for the conventional process except that the mixed liquor
suspended solids determinations must be made at each point of
wastewater addition to measure the waste content and dilution
factor provided by the primary effluent to determine the total
pounds of solids in the aeration tank.
7.94 Complete Mix (Fig. 7.12)
The complete mix mode of operation is a design modification of
tank mixing techniques to insure equal distribution of applied
waste load, dissolved oxygen, and return sludge throughout the
aeration tank. The theory of this modification is that all
parts of the aeration tank should be similar in terms of amounts
of food, organisms, and air. This is accomplished by providing
diffuser location and application points of influent and return
sludge to the aerator at several locations. Providing a similar
condition throughout the entire aeration tank allows a food/organism
ratio of 1/1 and still produces effluent qualities comparable to
conventional operation. Generally, smaller aeration tanks are
more completely mixed than larger ones. Usually aeration is more
efficient in a complete mix facility such as illustrated in
Fig. 7.12 because of the locations of the air headers.
7-106
-------
. |
1
V- |
H
1
1
r
^ 1
_ EFFLUENT
FROM AERATOR
PLAN VIEW
AIR HEADERS - NOTE VARIOUS POSITIONS
(HERRING BONE PATTERN)
RAW flASTE AND RETURN
SLUDGE INLET POINTS
Fig. 7.12 Air header locations in complete mix
7-107
-------
7.95 Modified Aeration (.fig. 7.13)
PRIMARY EFFLUENT
OR RAW WASTEWATER
RETURN
SLUDGE
10%
AERATION TANK
2 HOURS DETENTION
EFFLUENT
*-
SLUDGE TO PRIMARY INFLUENT
IF PRIMARY CLARIFIER AVAILABLE
,. ALTERNATE
EXCESS stuDGE
TO THICKENER
Fig. 7.13 Modified aeration
Modified aeration is also known as high-rate activated sludge.
Frequently it is used as intermediate treatment where the dis-
charge requirements demand higher treatment than primary, but
not as high as conventional activated sludge, in terms of BOD
and suspended solids removals.
Either raw wastewater or primary effluent is applied to an aeration
tank with a detention time of two hours and a mixed liquor suspended
solids concentration of less than 1000 mg/1. Air requirements are
lower because of fewer organisms (solids) under aeration. Effluent
quality ranging from primary treatment to conventional activated
sludge treatment can be achieved by the operator by controlling
the air supply, aeration period, and the pounds of solids under
aeration.
7-108
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7.10 ACKNOWLEDGEMENT
Mr. F. J. Ludzack, Chemist, National Training Center, Federal
Water Quality Administration, provided many helpful comments to
the development of this chapter. His contributions are grate-
fully appreciated.
7.11 ADDITIONAL READING
a. MOP 11, pages 108-122.
b. New York Manual, pages 58-69.
c. Texas Manual, pages 236-282.
d. Sewage Treatment Practices, pages 55-62.
e. Jenkins, D., and Garrison, W.E., "Control of Activated Sludge
by Mean Cell Residence Time," JWPCF, Vol. 40, No. 11, p. 1905
(November 1968).
f. McKinney, R.E., and O'Brien, W.J., "Activated Sludge—Basic
Design Concepts," JWPCF, Vol. 40, No. 11, p. 1831 (November
1968).
g. Stewart, M.J., "Activated Sludge Process Variables--The Complete
Spectrum," Water and Sewage Works Magazine, Reference Volume,
p. R-241 (November 30, 1964).
h. Aeration Practice, MOP No. 5, Water Pollution Control Federation,
3900 Wisconsin Avenue, Washington, D.C. 20016. $3.00 to
members, $6.00 to others.
or
Journal Water Pollution Control Federation, Vol. 41, Nos. 11
and 12, and Vol. 42, No. 1.
END OF LESSON 8 OF 8 LESSONS
on
ACTIVATED SLUDGE
7-109
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DISCUSSION AND REVIEW QUESTIONS
Chapter 7. Activated Sludge
(Lesson 8 of 8 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 7.
38. What is the formula for calculating the
Mean Cell Residence Time?
39. Calculate the MCRT for an activated sludge process.
Plant inflow is 4.0 MGD, MLSS is 2700 mg/1, waste
sludge flow 0.05 MGD, total secondary system volume
is 2.0 MG, waste sludge suspended solids concentration
is 6500 mg/1, and final effluent suspended solids
concentration is 15 mg/1.
40. Why might an operator wish to use step-feed aeration?
41. What is the name of the treatment process that is
capable of producing effluents with a quality (BOD
and suspended solids) between primary treatment and
conventional activated sludge?
7-111
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SUGGESTED ANSWERS
Chapter 7. Activated Sludge
7.0A The purpose of the activated sludge process in treating
wastewater is to oxidize and remove soluble or finely
divided suspended materials that were not removed by
previous treatment.
7.OB A stabilized waste is 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.
7.1A Air is added to the aeration tank in the activated sludge
process to provide oxygen to sustain the living organisms
and for oxidation of wastes to obtain energy for growth.
The application of air also encourages mixing in the aerator.
7.IB Air requirements increase when the strength (BOD) of the
incoming wastes increases because more food (wastes)
encourages biological activity (reproduction and respiration).
7.1C Factors that could cause an unsuitable environment for the
activated sludge process in an aeration tank include:
1. Intolerable concentrations of acids, bases, and
other toxic substances.
2. Unduly fluctuating loads that cause overfeeding
or starvation,
3. Insufficient oxygen.
7.2A The two major variables that affect the operation of an
activated sludge plant are (1) the dischargers to the
collection system and (2) in-plant operational variables.
7.2B Variables in the collection system affecting the activated
sludge plant include the (1) wastes discharged, (2) storm
water inflow, and (3) maintenance activities.
7.2C Excessive storm water can upset the activated sludge process
by (1) reducing treatment time of the wastewater, (2) in-
creasing the amount of grit and silt, (3) increasing the
organic loading, and (4) causing fluctuations in wastewater
temperature and solids content.
7-113
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7.2D The COD test is recommended to measure the strength of the
influent wastewater to the activated sludge process because
the results are available within four hours and can be used
to control the process.
7.2E The aerator pH should be measured in the aerator because
the pH of the sample can change very rapidly outside of
the aerator.
7.2F True.
7.2G The two methods used to supply oxygen from air to bacteria
in the activated sludge process are (1) mechanical aeration
and (2) diffused aeration.
7.2H Sludge Age, _ Suspended Solids Under Aeration, Ibs
days Suspended Solids Added, Ibs/day
7.3A The main reasons are to familiarize the operator with plant
equipment and locations of piping. Also to be reasonably
sure that everything will function properly when the plant
is put into service.
7.3B Lines and channels should be cleaned before start-up to
remove any sand, debris, or material that will occupy space
or damage equipment. Cleaning also will familiarize the
operator with the flow routes.
7.3C Chips and scrapes on gates should be painted for the pro-
tection of the equipment. The cost of equipment is expensive,
and it is part of the operator's responsibility to obtain as
long a life as possible for plant equipment.
7.3D If the sluice gate travels down from an overhead stem, it
may be possible to drop the slide gate into the tank. The
main purpose of the stop-nuts on the stems of mud valves is
to set length of travel.
7.3E The effluent weir should be level to prevent short-circuiting
and an uneven flow of solids over the weir.
7.3F The water sprayed on a walk may create a hazard by being
slippery either from ice in the winter or algal growths in
the summer.
7.3G Air passing through porous media diffusers must be free of
dirt or it will clog the inside of the diffuser making it
necessary to remove the diffusers for cleaning. The dirt is
removed by filters.
7-114
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7.3H Some filters clean themselves while in operation and require
only routine maintenance. Fixed filter cleaning is determined
by the differential pressure between the intake and discharge
of the filter.
7.31 Each manufacturer normally supplies a one-year warranty on
their equipment. If the equipment is mistreated due to im-
proper operation, the warranty becomes void, and your community
or district must absorb the cost. Proper operation prolongs
the life of equipment and reduces the cost of repairs and
replacement.
7.3J Usually in the construction specifications the equipment
suppliers are requested to supply three or four copies of
instructions for each piece of equipment. If they are lost,
a new one may be obtained by writing to the manufacturer and
giving the name, size, serial number, and the treatment plant
location and contract number if possible.
7.3K Proper starting, operating, and stopping procedures must be
followed when running equipment to reduce equipment wear
and failure.
7.3L The sharp edge of a metering orifice is usually on the same
side as the orifice information which is stamped on the
orifice plate handle. The sharp edge should be placed so as
to be facing the stream flow with the bevel on the discharge
side. If the orifice is installed backwards, it will give
an incorrect reading.
7.3M If the hoist is not anchored properly and a header is being
raised, the hoist could catapult into the aeration tank and
could cause injury to man and equipment.
7.3N Important safety precautions which should be observed when
working on a center"Y" wall include the wearing of life
preservers, having help standing by, keeping the area clear
and free of slippery materials, providing secure footing, and
requiring adequate lighting.
7.30 If air diffuser headers, or the pipe containing them, are
slanted so that one end of the header cross arm is higher
than the other (by as little as 1/2 inch), the air will be
unevenly released into the aerator. The diffusers on the
high side at low air rates will allow most of the air to
7-115
-------
pass out of them through the path of least resistance
rather than go through the diffusers on the low end of
the header, which have only 1/2 inch more water over
the top of them. This creates an undesirable flow pattern
in the tank.
7.3P Whenever a blower is first put on the line, the bearing
lubrication and temperature should be checked, along with
driven equipment load, air flow rates, and temperature.
7.3Q Grease should be applied to the threads of a diffuser to
serve as a protective coating and to make it easier to
remove the diffuser for cleaning.
7.3R a. Name of pump:
b. Location of pump:
c. Pump suction pressure:
d. Pump discharge pressure:
e. Water level in wet well:
f. Motor amperage:
g. Pump discharge (flow):
h. Date of test:
i. Name of operator:
7.4A Chlorination equipment should be put in service to dis-
infect the plant effluent and to protect the health of
the receiving water users.
7.4B Return sludge rates during start-up are selected to return
the settled activated sludge in the secondary clarifier as
fast as possible and to keep the sludge blanket in the
secondary clarifier as low as possible.
7.4C Blowers should be started and air should be flowing out
the diffusers before wastewater is admitted to the aeration
tanks to prevent diffuser clogging by waste solids. This
is particularly important if porous type diffusers are used.
7.4D DO should be checked at the effluent end of the aerator for
control, and periodically checked at the inlet and midpoint
to see if sufficient air is being supplied.
7-116
-------
7.4E To record the solids build-up in the aeration tank the
operator should collect a grab sample at the same time
every day, preferably during peak flows. The sample of
mixed liquor should be collected approximately 5 feet from
the effluent end of the aeration tank and 1.5 to 2 feet
below the water surface to insure a good sample.
7.4F Calculate pounds of solids under aeration.
Solids, Ibs
= Mixed Liq Susp Sol, mg/1 x Aerator Vol, MG x 8.34 Ibs/gal
= 640 mg/1 x 0.25 MG x 8.34 Ibs/gal
= 1334 Ibs
7.4G Estimate return sludge pumping rate, GPM.
Flow to aerator from primary clarifier = 2.0 MGD
Return sludge flow to aerator = 0.5 MGD
Total flow through aerator = 2.5 MGD
= Aerator Flow» MGD x Settleable Solids, %
= 2.5 MGD x 0.17
= 0.425 MGD
Return Sludge _ 425,000 GPP
Rate, GPM ~ 1440 min/day
= 295 GPM
7.5A Some activated sludge must be wasted to prevent an excessive
solids build-up in the aerator.
7.5B The best place to waste excess activated sludge is to divert
it to the primary clarifier, sludge thickener, or aerobic
digester, but not directly to an anaerobic digester.
7.5C Sludge Age, _ Suspended Solids in Aerator, Ibs
days Suspended Solids in Primary Effluent, Ibs/day
(2100 mg/1)(0.5 MG)(8.34 Ibs/gal)
(70 mg/1)(4.0 MGD)(8.34 Ibs/gal)
(°-5) » 3.75 days
7-117
-------
7.6A A package plant should be visited every day.
7.6B For best results, in terms of effluent quality, waste
about 5% of the solids each week during warm weather
operation.
7.6C a. If the solids do not settle in the jar, the
aeration rate should be increased.
b. If the solids settle and then float to the
surface, the aeration rate should be reduced
a little each day until the solids settle
properly.
7.7A Plant records of the activated sludge operation are
important because they are helpful in identifying the
cause of operational problems or upsets and indicating
what corrective action should be taken.
7.7B If the mixed liquor suspended solids were allowed to
build up too high, the quality of the plant effluent
would deteriorate.
7.7C The best solids loading for an aerator is determined by
experimentation and careful measurement of loading para-
meters and effluent quality.
7.7D Check the plant records to determine the cause and then make
adjustments to process. However, only one change at a time
should be made to the activated sludge system, and one week
should be allowed to observe the response.
7.7E When digester supernatant with a high solids content is
returned to the primary clarifier, this may greatly increase
the suspended solids content of the primary effluent, par-
ticularly if waste activated sludge is also being applied
to the same primary clarifier. The remedy is to draw sludge
from the digester to reduce the supernatant load to the plant.
7.7F During the high flows a solids loss could occur. If possible,
change the plant to step-feed aeration to retain more mixed
liquor solids in the aeration tank. If the solids were
already lost, stop wasting and attempt to build more solids.
7.7G There could be a significant increase in air flow rates to
maintain desired DO level in the mixed liquor if the waste-
water temperature increases. The suspended solids in the
mixed liquor should be increased if the wastewater tempera-
ture increases. Also, bacteria are more active at higher
temperatures.
7-118
-------
7.7H When lab data varies considerably from day to day, check
sampling times, locations, methods, and laboratory proce-
dures for causes of variations.
7.71 Allow one week for a plant to stabilize after a process
change. An experienced operator who knows his plant may
be able to determine if he is on the proper approach after
several days, but some plants require up to two weeks to
stabilize after a change.
7.7J Froth or foam may be controlled by:
1. Maintaining higher mixed liquor suspended solids con-
centrations.
2. Reducing air supply during periods of low flow while
still maintaining DO.
3. Returning supernatant to the aeration tank during low
flows.
7.7K Grease deposits can be removed from walks using trisodium
phosphate and a stiff bristle deck brush and hose.
7.7L Bulking sludge will be indicated by large mats of floating
sludge or a tremendous amount of suspended solids being
carried out of the final clarifier in the effluent. Rising
sludge will be light flocculent particles of floe collecting
mainly on the surface of the final tanks and forming a thin
surface scum. Rising sludge is accompanied by high DO in
the aerator effluent and final clarifier.
7.7M Several adjustments may be attempted to correct a rising
sludge problem, but only one should be undertaken at a time.
1. Increase return sludge rates, but control final clari-
fier sludge level.
2. Increase load to aerator by removing a primary clarifier
from service if more than one is being used.
3. Admit raw wastewater directly to the aerator during
low flows.
4. Check the possibility of going to a tapered aeration
diffuser placement.
7.8A New microorganisms are continually being reproduced, and
some of them must be removed from the system to control
their population in order to balance the food supply.
7-119
-------
7.8B Solids Wasted, Ibs
= Solids in System, Ibs - Desired Solids, Ibs
= 12,000 Ibs - 9,000 Ibs
= 3000 Ibs
7.8C Waste Sludge Rate, MGD
Solids to be Wasted, Ibs/day
Return Sludge Cone., mg/1 x 8.34 Ibs/gal
5000 Ibs/day
6000 mg/1 x 8.34 Ibs/gal
= 3000/day 1 (Remember, one liter = 1 M mg)
6000 8.34/MG ^ ' •
3000/day 3000/day
50,040/MG °r 50,000/MG
= 0.06 MGD
Waste Sludge Rate, GPM
0.06 MGD
1440 min/day
60,000 gals
1440 rains
= 41.8 GPM
7.8D Waste „ „ , . „ ^ ,,
Sludge, = Susp Sol in System, Ibs _ Sol ^ ££f lbg/
Ibs/day MCRT> da/s
- 10 mg/1 x 5.0 MGD x 8.34 Ibs/gal
= 4000 Ibs/day - 417 Ibs/day
= 3583 Ibs/day
7-120
-------
OBJECTIVE TEST
Chapter 7. Activated Sludge
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. There may be
more than one correct answer to each question.
Match the word with the correct definition by marking the number
of the definition on the answer sheet opposite the number of the
word.
1.
1.
2.
3.
4.
5.
6.
7.
8.
Word
Plant Operator
1
; i
t i
7 ' '
-*•• i »
i i
Word
Aliquot
Coning
Flights
Floe
Meniscus
Orifice
Protozoa
Zoogleal Mass
1.
O
& •
3.
4.
5.
2
| . .
1 If] t
T •£ '
t HJj f
•W«
i.
2.
3.
4.
5.
1.
2.
3.
4.
5.
EXAMPLE
Definition
Women 's Liberation advocate
Hard-working water quality protector
Uneducated individual
Town clown
None of these
345
i i
i t
i i
1 !
t 1
Definition
Airline schedule
Bacteria that have come together and
formed a cluster
Portion of a sample
Scraper boards used to remove settled
sludge to collection hoppers
Caused by sludge when removed too
quickly
A thin plate with a hole in the
middle used to measure flow
Membranes in the nose and throat
Jelly-like substances of bacteria
The curved top of a column of liquid
in a tube
A group of microscopic animals found
in treatment processes
7-121
-------
9. The activated sludge process:
1. Requires aeration
2. Requires activated carbon
3. Is a biological process
4. Usually follows primary sedimentation
5. Is an anaerobic process
10. Before starting a new plant, the operator should check:
1. The blower system
2. Control gates and mud valves
3. The aeration equipment
4. For chips and scrapes on painted gates
5. Effluent weirs for level
11. The hoist used to lift the air headers in the aeration tank
must be properly anchored or it:
1. Will float away
2. Could fall into the aerator
3. Won't allow even distribution of the air
4. Could hurt someone
5. Could not lift the aerator
12. How many pounds of solids are in a 400,000-gallon aeration
tank if the suspended solids concentration is 1200 mg/1?
Select the closest answer.
1. 3600
2. 4000
3. 4400
4. 4800
5. 5200
13. When the return sludge rate is too low, what happens?
1. The tank will not fill.
2. There will be insufficient organisms to meet the waste
load entering the aerator.
3. The activated sludge in the aerator will starve.
4. The activated sludge in the secondary clarifier could
become septic.
5. The sludge blanket in the secondary clarifier could
become too high.
14. When operating an activated sludge plant, which is the most
important suspended solids test for operational control?
1. Primary effluent
2. Aerator mixed liquor
3. Return sludge
4. Final clarifier effluent
5. Plant influent
7-122
-------
15. The main operational process controls available to an
operator include:
1. Air rates
2. Pounds of solids under aeration
3. Maintenance
4. Return sludge rate
5. BOD test
16. What should be the waste sludge pumping rate if a plant
should be wasting 2000 pounds per day and the concentration
of return sludge is 5000 mg/1? Select the closest answer.
1. 30 gpm
2. 33 gpm
3. 35 gpm
4. 36 gpm
5. 40 gpm
17. What items would you check if an activated sludge plant
becomes upset?
1. Influent temperature
2. Daily flow rates
3. BOD loadings
4. Digester operation
5. Chlorinator
18. How long would you allow an activated sludge process to
react and stabilize after a change?
1. 3 hours
2. 12 hours
3. 1 day
4. 2 days
5. 1 week
19. Causes of sludge bulking include:
1. Bulk of sludge too large
2. Air supply too low
3. Loading rate too high
4. Aeration period too short
5. Sludge going septic in secondary clarifier
20. Package plants usually:
1. Operate the aeration device continuously
2. Have an operator at the plant 24 hours a day
3. Waste sludge out the effluent, but shouldn't when operated properly
4. Have an extensive lab testing program
5. None of these
7-123
-------
21. The effectiveness of the organisms in the aerator depends
on the:
1. Temperature
2. pH
3. Presence of inhibiting substances
4. Characteristics of food supply
5. Time of reaction or time available for the reaction
22. What is the food/organism loading ratio in an activated sludge
plant with a flow of 1 MGD? The average BOD to the aerator is
140 mg/1, the aeration tank contains 250,000 gallons, and the
mixed liquor suspended solids concentration is 2000 mg/1.
Select the closest answer.
1. 25 Ibs BOD per day/100 Ibs MLSS
2. 28 Ibs BOD per day/100 Ibs MLSS
3. 30 Ibs BOD per day/100 Ibs MLSS
4. 32 Ibs BOD per day/100 Ibs MLSS
5. 35 Ibs BOD per day/100 Ibs MLSS
23. Why is the COD test a better operational control test than
the BOD test?
1. It isn't better.
2. The oxygen demand is not caused by biological organisms.
3. Everyone uses it.
4. The results are available sooner.
5. This chapter says so.
24. Why should all of the diffusers in an aeration tank be cleaned
at once?
1. To get the job done in a hurry
2. So the air will flow evenly out all of the diffusers
3. To improve step-feed aeration
4. So the plant won't use too much air
5. None of these
Please write on your IBM answer sheet the total time required to work
Chapter 7.
7-124
-------
APPENDIX
Monthly Data Sheet
-------
MONTHLY RECORI
UJ
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2
^
4
5
6
7
8
9
10
1
1?
13
14
15
16
17
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19
20
21
22
23
24
25
26
27
28
29
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31
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£.£*
CLEAR
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LEW
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234
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WATIIR iPOLLyTiow CONTROL PLANT
FINAL EFFLUENT
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SLUDGE:
ST 798324
1st 432984
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OPERATOR:
AERATION SYSTEM
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SUSP SOLIDS
2036
2078
2211
2213
2106
2069
1905
2138
2037
1861
2123
1954
1937
1121
2010
2162
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1 534
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2016
22C3
2541
2401
2332
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ETER;
218 IIIO
1265230
-------
CHAPTER 8
SLUDGE DIGESTION AND HANDLING
by
John Brady
CWith a special section by William Garber)
-------
TABLE OF CONTENTS
Chapter 8. Sludge Digestion and Handling
8^.0 Introduction 8-1
8.00 Purpose of Sludge Digestion 8-1
8.01 How Sludge Digestion Works 8-3
8.1 Components in the Anaerobic Sludge Digestion Process . 8-9
8.10 Pipelines and Valves 8-9
8.11 The Digester 8-10
A. Fixed Cover Tanks 8-10
B. Floating Cover 8-10
C. Digester Depth 8-12
D. Raw Sludge Inlet 8-12
E. Supernatant Tubes 8-12
F. Sludge Draw-off Lines 8-14
8.12 Gas System 8-17
A. Gas Dome • • 8-18
B. Pressure Relief and Vacuum Relief Valves . . 8-20
C. Flame Arresters 8-25
D. Thermal Valves 8-25
E. Sediment Traps 8-31
F. Drip Traps--Condensate Traps 8-31
G. Gas Meters 8-31
H. Manometers 8-31
I. Pressure Regulators 8-32
J. Waste Gas Burner 8-32
8.13 Sampling Well (Thief Hole) 8-38
8.14 Digester Heating 8-38
8.15 Digester Mixing 8-41
A. Gas Mixing 8-41
B. Mechanical Mixing 8-43
8.2 Operation of Digesters 8-47
8.20 Raw Sludge and Scum 8-47
8.21 Starting a Digester 8-48
111
-------
Page
8.22 Feeding 8-54
8.23 Neutralizing a Sour Digester 8-56
8.24 Enzymes 8-58
8.25 Foaming 8-58
8.26 Gas Production 8-59
8.27 Supernatant and Solids 8-61
8.28 Rate of Sludge Withdrawal 8-62
8.3 Digester Sludge Handling 8-65
8.30 Sludge Drying Beds 8-65
8.31 Blacktop Drying Beds 8-70
8.32 Sludge Lagoons 8-72
8.33 Withdrawal to Land 8-73
8.34 Mechanical Dewatering 8-74
A. Vacuum Filters 8-74
B. Centrifuge 8-79
8.4 Digester Controls and Test Interpretation 8-83
A. Temperature 8-83
B. Volatile Acid/Alkalinity Relationship. . . . 8-83
C. Digester Gas 8-84
D. pH 8-85
E. Solids Test 8-86
F. Volume of Sludge 8-86
G. Raw Sludge 8-88
H. Recirculated Sludge 8-88
I. Secondary Digested Sludge 8-91
J. Digester Supernatant 8-93
K. Computing Digester Loadings 8-93
L. Computing Gas Production 8-96
M. Solids Balance 8-97
IV
-------
Page
8.5 Operational Checks and Sampling Schedule 8-103
8.50 Daily 8-103
A. Raw Sludge Pump 8-103
B. Recirculated Digester Sludge 8-103
C. Digesters 8-103
8.51 Weekly 8-104
A. Sludge and Gas System Valves 8-104
B. Supernatant Tubes 8-104
C. Supernatant Box 8-104
D. Lubricate Equipment 8-104
8.52 Monthly 8-104
A. Scum Blanket 8-104
B. Digester Structure 8-104
C. Gas Piping System 8-104
8.53 Quarterly 8-105
A. Gas Safety Devices 8-105
8.54 Semiannually 8-105
A. Manometers 8-105
B. Water Seals 8-105
8.55 Three to Eight Years 8-105
A. Clean and Repair Digester 8-105
8.56 Digester Sampling Schedule 8-105
A. Daily . 8-105
B. Twice Per Week 8-105
C. Weekly 8-106
D. Monthly to Quarterly 8-106
8.6 Aerobic Sludge Digestion 8-107
8.60 Introduction 8-107
8.61 Process Description 8-109
8.62 Operation 8-109
-------
Page
8.63 Operational Records 8-111
8.64 Operational Problems 8-112
A. Scum 8-112
B. Odors 8-112
C. Floating Sludge 8-112
8.65 Maintenance Problems 8-112
A. Diffuser Maintenance 8-113
B. Aeration Equipment 8-113
8.7 Additional Reading 8-114
VI
-------
PRE-TEST
Chapter 8. Sludge Digestion and Handling
The purpose of this Pre-Test is to indicate to you the important
points in this chapter. Work this test before reading the chapter.
It's okay if you don't know many of the answers.
Please write your name and mark the correct answers on the IBM
answer sheet. There may be more than one answer to each question.
1. The environment in an anaerobic digester may be controlled
by regulating the:
1. Air supply
2. Food supply
3. Domestic water supply
4. Temperature
5. Mixing
2. Material not readily decomposed in digesters includes:
1. Rubber goods
2. Fruit
3. Plastic
4. Hair
5. Grit
3. Sludge should be pumped from the primary clarifier to the
digester several times a day to:
1. Keep the pump from becoming clogged
2. Prevent temporary overloading of the digester
3. Maintain better conditions in the clarifier
4. Permit thicker sludge pumping
5. Prevent coning
4. Digester gas may be used as a fuel when the methane content
exceeds:
1. 25%
2. 35%
3. 50%
4. 65%
5. 75%
P-l
-------
5. The following precautions must be taken when applying
sludge to a drying bed:
1. Withdraw the sludge slowly from the digester
2. Loosen sand before applying sludge
3. Make sure the bed is covered with sludge
4. Never smoke in the vicinity where the sludge is
being drawn
5. When finished, flush the draw-off line and leave
one end open
6. High volatile acid/alkalinity relationship in a digester
may be caused by:
1. Overloading the tank with organic material
2. Pumping too thin a raw sludge
3. Filling the tank too full
4. Withdrawing supernatant
5. Adding lime
7. Useful digester control tests include:
1. BOD
2. pH
3. Volatile acid/alkalinity relationship
4. DO
5. Temperature
8. Laboratory tests indicate that the volatile content of a
raw sludge was 71% and after digestion the content is 53%,
The percent reduction in volatile matter is:
1. 25%
2. 50%
3. 54%
4. 60%
5.
Calculate the volatile matter destroyed (Ibs/day/cu ft)
in a 20,000 cubic foot digester receiving 2400 gallons per
day of raw sludge. The solids content is 5%, the volatile
content 71%, and the volatile solids are reduced 50% by
digestion:
1. .015
2. .018
3. .020
4. .023
5. .025
P-2
-------
10. A positive displacement pump should never be started against
a closed valve because:
1. It will pump nothing
2. Excessive pressure may damage the line, the pump, or the motor
3. The sludge will spill
4. The valve will swing open
5. The power driver will stall and overheat
11. Digester gas may be used to:
1. Heat digesters
2. Supply oxygen to activated sludge aeration tanks
3. Digest solids
4. Run engines
5. Gas rats around the plant
12. Flame arresters should be installed:
1. Between vacuum and pressure relief valves and the
digester dome
2. After sediment trap on gas line from digester
3. At waste gas burner
4. Before every boiler, furnace, or flame
5. In the vent of the waste gas burner
13. The pilot flame in the waste gas burner should be checked
daily to:
1. Make sure it has not been blown out by the wind
2. Prevent valuable gas from escaping
3. Prevent odorous gas from escaping
4. Prevent explosive conditions from developing
5. Make sure proper temperatures are maintained in
the digester
14. The contents of a primary digester should be mixed to:
1. Distribute food in the tank
2. Allow solids separation
3. Prevent formation of a scum blanket
4. Warm up the sludge
5. Keep the temperature the same throughout the tank
15. Successful digester operation depends on:
1. Understanding what's happening in the digester
2. Keeping all the digested sludge out of the digester
3. .Analysis and application of information from
laboratory tests
4. Cleaning the digester at regular intervals to
maintain capacity
5. Regularly checking the skimmers
P-3
-------
16. Sludge pumped to the digester should be as thick as possible;
1. To reduce heat requirements in the digester
2. So the sludge will settle to the bottom of the digester
3. So large amounts of digested sludge will not be dis-
placed to the secondary digester
4. So a scum blanket won't be formed in the digester
5. None of these
17. The temperature of a digester should not be changed more
than one degree per day to:
1. Avoid excessive heat losses
2. Avoid overloading the heat exchanger
3. Allow the walls of the digester time to expand and
contract
4, Allow the organisms in the digester time to adjust
to the temperature change
5. Allow time for heating gas to be produced in the
digester
18. The function of the water seal on the gas dome of the
digester is to keep:
1. Air from entering the digester
2. Digester gas from escaping the digester
3. Insects and rodents out of the digester
4. Sludge from leaking out of the digester
5. Foam inside the digester
19. Sludge or gas should not be removed too rapidly from
the digester because:
1. The sludge drying beds may become overloaded
2, If a vacuum develops in the tank it may collapse
3. If a vacuum develops in the tank air may be drawn in
and form an explosive mixture
4. The water seal could break
5. The waste gas burner may become overloaded
20. A scum blanket in a digester may be broken up by:
1. Vigorously mixing the digester contents
2, Burning
3. Use of long poles
4. An ax
5. Rolling back the blanket
P-4
-------
21. The purpose of the secondary digester is to allow:
1. For more sludge digestion
2. An opportunity for more mixing
3. Storage for seed sludge
4. The liquids and solids in digested sludge to separate
5. The designer to make more money
22. What could be happening if gas production in a digester
starts decreasing?
1. The volatile acid/alkalinity relationship is increasing
2. The raw sludge volume fed to the digester is decreasing
3. The raw sludge volume fed to the digester is excessive
4. The scum blanket is breaking up
5. The volatile acid/alkalinity relationship is decreasing
23. Sludge should be withdrawn slowly from a digester to prevent;
1. Coning
2. Supernatant from overloading the plant
3. Forming a vacuum in the digester
4. The possibility of an explosive gas
mixture developing in the digester
5. The possibility of the digester cover collapsing
24. What would you do if the volatile acid/alkalinity relation-
ship started to increase in a digester?
1. Increase time of mixing
2. Maintain constant temperature throughout the digester
3. Decrease sludge withdrawal rates
4. Return some digested sludge
5. Reduce volume of raw sludge pumped to digester
25. After sludge has been applied to the drying bed, the sludge
draw-off line should be:
1. Closed at both ends to keep out rodents and insects
2. Open at one end to allow gas to escape
3. Washed out
4. Left full of sludge
5. Filled with plant effluent
P-5
-------
GLOSSARY
Chapter 8. Sludge Digestion and Handling
Anaerobic Digestion (AN-air-0-bick): 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 the complex solids to vola-
tile acids; and (2) Methane fermenters break down the acids to
methane, carbon dioxide, and water.
BTU: British Thermal Unit. The amount of heat required to raise
the temperature of one pound of water one degree Fahrenheit.
Buffer: A measure of the ability or 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 the pH.
Cpning_ (CONE-ing) : A condition that may be established in a sludge
hopper during sludge withdrawal when part of the sludge moves toward
the outlet while the remainder tends to stay in place. Development
of a cone or channel of moving liquid surrounded by relatively
stationary sludge.
Dewaterable: 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.
Elutriation (e-LOO-tree-a-shun): The washing of digested sludge
in plant effluent with a suitable ratio of sludge to effluent.
The objective is to remove (wash out) fine particulates or certain
soluble components in sludge.
Endogenous^ (en-DODGE-en-us): A diminished level of respiration in
which materials previously stored by the cell are oxidized.
Enzymes (EN-zimes): Enzymes are substances produced by living
organisms that speed up chemical changes.
Hydrolysis (hi-DROL-e-sis): The addition of water to the molecule
to break down complex substances into simpler ones.
Inoculate (in-NOCK-you-LATE): To introduce a seed culture into a
system.
Liquefaction (LICK-we-FACK-shun): Liquefaction as applied to sludge
digestion means the transformation of large solid particles of
sludge into either a soluble or a finely dispersed state.
G-8-1
-------
Mesophilic Bacteria (mess-0-FILL-lick) (medium temperature):
A group' of bacteria that thrive in a temperature range between
68°F and 113°F.
Psychrophi1ic Bacteria (sy-kro-FILL-lick) (cold temperature):
A group of bacteria that thrive in temperatures below 68°F.
Saprophytic Organisms (SAP-pro-FIT-tik): Organisms living on
dead or decaying organic matter. They help natural decomposition
of the organic solids in wastewater.
Stasis (STAY-sis) : Stagnation or inactivity of the life processes
within organisms.
Stuck: A stuck digester does not decompose organic matter
properly. It is characterized by low gas production, high
volatile acid/alkalinity relationship, and poor liquid-solids
separation. A digester in a stuck condition is sometimes
called a "sour" digester.
Supernatant (sue-per-NAY-tent): In a sludge digestion tank, the
supernatant is the liquor between the surface scum and the settled
sludge on the bottom of the tank.
Thermoph i1i c Bacte r i a (thermo-FILL-lick) (hot temperature):
A group of bacteria that thrive in temperatures above 113°F.
Wet Oxidation: Any process in which substances are converted to
a higher oxidation state in a water media such as activated sludge,
trickling filters, ponds, or digesters.
G-8-2
-------
CHAPTER 8. SLUDGE DIGESTION AND HANDLING
(Lesson 1 of 5 Lessons)
8.0 INTRODUCTION
Settled solids removed from the bottom and floating scums removed
from the top of clarifiers and sedimentation tanks are a watery,
odorous mixture called raw sludge and scum. Frequently this raw
sludge is pumped to a sludge digester for treatment before disposal,
In the anaerobic sludge digester, the most common kind, bacteria
decompose the organic solids in the absence of dissolved oxygen.
Figure 8.1 shows the location of an anaerobic sludge digester in
a typical plant. Figures 5.2, 6.2, and 7.2 also show plan views
of the location of sludge digestion and handling facilities in
relation to other treatment processes.
8.00 Purpose of Sludge Digestion
Anaerobic digestion1 reduces wastewater solids from a sticky, smelly
mixture to a mixture that is relatively odor free, readily dewaterable,2
and capable of being disposed of without causing a nuisance.
In the process organic solids are liquefied, the solids volume is
reduced, and valuable methane gas is produced in the digester by the
action of two different groups of bacteria living together in the same
environment. One group consists of saprophytic organisms,3 commonly
referred to as "acid formers". The second group, which utilized the
1 Anaerobic Digestion (AN-air-0-bick). 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:
saprophytic bacteria (see.Footnote 3) and methane fermenters
break down the acids to methane, carbon dioxide, and water.
2 Dewaterable. 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.
3 Saprophytic Organisms (SAP-pro-FIT-tik). Organisms living on dead
or decaying organic matter. They help natural decomposition of the
organic solids in wastewater.
8-1
-------
"REMOVAL
PEB AS2AT/ON
BIOLOGICAL CHEMICALS
Fig. 8.1 Flow diagram of typical plant
-------
acid produced by the saprophytes, are the "methane fermenters".
The methane fermenters are not as abundant in raw wastewater as
are the acid formers. The methane fermenters desire a pH range
of 6.5 to 8.0 and will reproduce only in that range.
The object of good digester operation is to maintain suitable
conditions in the digester for a growing (reproducing) population
of both acid formers and methane fermenters. You must do this by
the control of food supply (organic solids) , volatile acid/alka1inity
relationship, mixing, and temperature. Generally, you have done your
job properly if the digester reduces the volatile (organic) solids
content by between 40 and 60% of what they were in the raw sludge.
To obtain the desired degree of organic solids reduction may require
from 5 to 120 days of digestion time. The time required depends on
how good a job you are required to do on digesting the sludge, and on
the adequacy of mixing, the organic loading rate, and the temperature
at which the bacterial culture is maintained.
8.01 How Sludge Digestion Works (by William Garber)
The equations shown in Fig. 8.2 illustrate one way of outlining what
happens in a digester. These equations indicate two general types
of reactions:
1. Acid forming reactions which proceed at a rate
dependent upon temperature, pH, and food conditions.
2. Methane fermentation reactions which proceed at a
rate dependent upon temperature, pH, and food conditions.
You must try to operate an anaerobic sludge digester so that the rate
of acid formation and methane fermentation are approximately equal;
otherwise the reaction will get out of balance. The most common condition
of unbalance that occurs is that the methane fermenters, which are
sensitive anaerobes, fail to keep pace and the digester becomes acid
because the rate at which acids are converted is too low.
The literature has been full of terms such as "Standard-Rate" and
"High-Rate" digestion. These terms refer to digester loading and
not to the rates of bacterial action. In "High-Rate" systems,
mixing is used to obtain the best possible distribution of the
substrate (food) and seed (organism) so that more bacterial reaction
can occur.
5-3
-------
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Fig. 8.2 Reactions in a digester
-------
Mixing is the most important factor in the so-called "High-Rate"
processes, and it is considered to accomplish the following:
1. Utilize as much of the total content of a digester
as possible.
2. Quickly distribute the raw sludge food throughout the
volume of sludge in the tank.
3. Put the microorganisms in contact with the food.
4. Dilute the inhibitory by-products of microbiological
reactions throughout the sludge mass.
5. Achieve good pH control by distributing buffering alka-
linity throughout the digestion tank.
6. Obtain the best possible distribution of heat through
the tank.
7. Minimize the separation of grit and inert solids to the
bottom or floating scum material to the top.
A digester may be operated in one of three temperature zones or
ranges, each of which has its own particular type of bacteria. The
lowest range (in an unheated digester) utilizes psychrophilic (cold
temperature loving) bacteria.4 Temperature of the sludge inside
tends to adjust to the outside temperature. However, below 50°F
little or no bacterial activity occurs and the necessary reduction
in sludge volatiles (organic matter) will not occur. When the
temperature increases above 50°F, bacterial activity increases to
a measurable rate and digestion starts again. The bacteria appear
to be able to survive temperatures well below freezing with little
or no harm. The psychrophilic upper range is around 68°F. Digestion
in this range requires from 50 to 180 days, depending upon the degree
of treatment (solids reduction) required. Few digesters are designed
today to operate in this range, but there are many still in use,
including most Imhoff tanks and similar unheated digesters with no
mixing devices. Generally these digesters are not very effective in
digesting sludge.
Psychrophilic Bacteria, (organisms) (sy-kro-FILL-lick). A group
of bacteria that thrive in temperatures below 68°F.
8-5
-------
The middle range of organisms are called the mesophilic (medium
temperature loving) bacteria5; they thrive between about 68°F
and 113°F. This is the most common operational range, with
temperatures usually being maintained at about 95 °F to 98°F.
Digestion at that temperature may take from 5 to 50 days or more
(normally around 25 to 30 days), depending upon the required
degree of volatile solids reduction and adequacy of mixing. The
so-called "High-Rate" processes are usually operated within the
mesophilic temperature range. These are nothing more than pro-
cedures to obtain good mixing so that the organisms and the food
can be brought together to allow the digestion processes to pro-
ceed as rapidly as possible. With the most favorable conditions
the time may be no more than five days for an intermediate level
of digestion.
The third range of organisms are called thermophilic (hot tempera-
ture loving) bacteria,6 and they thrive above" 113°F. The time
required for digestion in this range falls between 5 and 12 days,
depending upon operational conditions and degree of volatile
solids reduction required. However, the problems of maintaining
temperature, sensitivity of the organisms to temperature change,
and some reported problems of poor solids-liquid separation are
reasons why only a few plants have actually been operated in the
thermophilic range.
You cannot merely raise the temperature of the digesters and have
a successful operation in another range. The bacteria must have
time to adjust to the new temperature zone and to develop a
balanced culture before continuing to work. An excellent rule
for digestion is never change the temperature more than one degree
a day to allow the bacterial culture to become acclimated (adjust
to the temperature changes).
Secondary digestion tanks are sometimes used to allow liquids
(supernatant)7 to separate from the solids, to provide a small
amount of additional digestion, and to act as a "seed" source (the
settled, digested sludge). However, digestion tanks generally have
too small a "surface area to depth" ratio to be good sedimentation
tanks. Separation of solids from liquids is more efficient in
5 Mesophilic Bacteria (mess-0-FILL-lick). A group of bacteria
that thrive in a temperature range between 68°F and 113°F.
6 Thermophilic Bacteria (thermo-FILL-lick). A group of bacteria
that thrive in temperatures above 113°F.
7 Supernatant (sue-per-NAY-tent). In a sludge digestion tank,
the supernatant is the liquor between the surface scum and
the settled sludge on the bottom of the tank.
8-6
-------
lagoons or in tanks designed for separation. If a significant
amount of digestion occurs in the secondary tank, the result
may be poor separation of solids. Secondary digesters should be
used for solids concentration and for a reservoir of alkalinity
and seed sludge which may be returned to the primary digester
when needed.
You have certain other items you can use for control in addition
to mixing and temperature selection. These include:
1. Varying the sludge concentration or water added to
the system.
2. Varying the rate and frequency of feeding, with continuous
feed the most desirable.
3. Closely controlling grit and skimming in order that
capacity of the tank is affected as little as possible
by these materials.
4. Cleaning regularly to maintain capacity.
5. A good maintenance program to maintain the maximum
degree of flexibility.
6. Maintaining records and laboratory control in order
that process condition is known at all times.
Although digestion is a complex process and only a portion of its
theory is understood, enough is known to allow you to exercise
good operational control. For sludge digestion as for any of the
wastewater processes, remember that for the most successful opera-
tion you need to do the following:
1. Understand the theory of the process so you know what
you are basically trying to do.
2. Know your facilities thoroughly so that you can attain
maximum flexibility of operation.
3. Keep careful records and use laboratory analyses to
follow the process continually.
4. Maintain your facilities in the best possible condition
at all times.
8-7
-------
QUESTIONS
8.01A Why must raw sludge be digested?
8.01B What happens during digestion?
8.01C What are some of the important factors in controlling the
rate of reproduction of acid-forming and methane bacteria
in a digester?
8-8
-------
8.1 COMPONENTS IN THE ANAEROBIC SLUDGE DIGESTION PROCESS
To understand and operate an anaerobic sludge digester, the operator
must be familiar with the location and function of the various com-
ponents of the digestion facility.
8.10 Pipelines and Valves
Raw sludge pipelines are usually constructed of cast iron or steel
to withstand pumping pressures. In recent years glass-lined or
epoxy-lined sludge lines have been used to alleviate the problem
of grease deposits. These deposits cut capacity and may cause
stoppages. Some plants use "go-devil" type cleaners and/or hot
chemical solutions such as T.S.P. instead.
The valves used in sludge and scum lines are mostly of the plug
type. They give positive control where a gate or butterfly valve
may become blocked by rags or other material which will not allow
the valve to seat. In some cases a gate or butterfly valve is indi-
cated because a quick closing plug valve could result in water hammer
and damage the pipeline.
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8-9
-------
QUESTIONS
8.10A Why are plug type valves used in sludge lines?
8.10B Why should a positive displacement pump never
be started against a closed valve?
8. IOC Why should a sludge line never be closed at both
ends ?
8.11 The Digester
Digestion tanks may be cylindrical or cubical in shape. Most tanks
constructed today are cylindrical. The floor of the tank is sloped
so that sand, grit, and heavy sludge will tend to be removed from
the tank. Most digesters constructed today have either fixed or
floating covers.
A. Fixed Cover Tanks
A fixed cover tank has a stationary roof, generally slab, conical,
or cone-shaped, and constructed of concrete or steel. Both types
of covers are normally designed to maintain no more than an eight-inch
water column of gas pressure on the tank roof (Fig. 8.3), but some are
designed for pressures of 25 inches or more. The domed cover is
designed to hold a larger volume of gas. Any type of mixing device
may be used with a fixed cover tank, and the tank must be equipped
with pressure and vacuum relief valves.
A fixed cover digester can have an explosive mixture in the tank when
sludge is withdrawn if proper precautions are not taken to prevent air
from being drawn into the tank. Each time a new charge of raw sludge
is added, an equal amount of supernatant is displaced because the tank
is maintained at a fixed level.
B. Floating Cover
A floating cover moves up and down with the tank level and gas pressure,
Normally the vertical travel of the cover is about eight feet, with
stops (corbels) or landing edges for down (lowering) control and
8-10
-------
r<
WATER SEAL
•NORMAL WATER LEVEL
NLET BOX
SLUDGE DRAW OFF LINE
DIGESTER
"^•^SUPERNATANT BOX
•'" AND TUBES
NOTE: USUALLY WATER SEALS ARE LOCATED
IN THE VERTICAL SIOEWALLS OF
FLOATING COVER DIGESTERS, RATHER
THAN AS SHOWN ON ROOF.
VACUUM RELIEF
PRESSURE RELIEF
ARRESTOR
INCHES OF
WATER PRESSURE
DIGESTER GAS PRESSURE
DIGESTER ROOF
FLAME ARRESTOR-
SEDIMENT TRAP ITTTJ
I-'ig. 8.3 Water seal on digester
-------
maximum water level for upward travel. Maxiirum v/ater level is
controlled by an overflow pipe that must be kept clear to prevent
damage to the floating cover by overfilling. Gas pressure is
dependent upon the weight of the cover. The advantages of a
floating cover include less danger of explosive mixtures forming
in the digester, better control of supernatant withdrawal, and
better control of scum blankets. Disadvantages include higher
construction and maintenance costs.
C. Digester Depth
A typical operation depth for digesters is around 20 feet (side
wall water level depth). The bottom slopes downward to the center
of the tank. A gas space of two to three feet is usually provided
above normal liquid sludge level, but some floating covers allow
more room for gas storage.
D. Raw Sludge Inlet
Typically the raw sludge feed is piped to the top of the primary
digester and admitted on the side opposite the supernatant over-
flow pipe (Fig. 8.4) to the secondary digester. .Typically this
line also carries any recirculated digester sludge in the system
so that the raw sludge is immediately seeded with bacteria as it
enters the tank.
E. Supernatant Tubes (Fig. 8.4)
On a fixed cover digester there may be three to five supernatant
tubes set at different levels for supernatant removal. Normally
only one tube is used at a time. The tube used is selected to
return the supernatant liquor with the lowest quantity of solids
back to the primary clarifier, or to sludge drying beds, provided
space is available.
A single adjustable tube is also used at some plants. On the
floating cover digester there is usually only one supernatant
tube. This may be adjusted to pull supernatant liquor from various
levels of the tank by raising or lowering the tube. In smaller
plants the supernatant withdrawal may be done only once or twice
a day, because the floating cover allows the tank to handle volume
changes. An adjustable tube usually allows a supernatant with the
least solids content to be selected. The digester should be visually
checked a minimum of once per day for liquor levels to prevent over-
filling and structural damage to the tank.
8-12
-------
3 FT. SUPERNATANT TUBE IN SERVICE
ADJUSTABLE RINGS-THREE LENGTHS
DIGESTER ROOF
NORMAL DIGESTER WATER LEVEL
Fig. 8.4 Supernatant tubes and box
8-13
-------
F. Sludge Draw-off Lines
The sludge draw-off lines are typically placed on blocks along
the sloping floor of the digester. Sludge is withdrawn from the
center of the tank. Very seldom are they placed under the floor
of the digester because they would not be accessible in case of
blockages. These lines are normally six inches in diameter and
equipped with plug valves. The lines are used to transfer the
digester sludge periodically to a sludge disposal system of
either drying beds or some type of dewatering system. These
lines also transfer seed sludge from the secondary digester to
the primary digester and recirculate bottom sludge to seed and
break up a scum blanket.
QUESTIONS
8.11A Why should you maintain no more than an eight-inch
water column of gas pressure on the roof of a fixed
cover digester?
8.11B Why must a fixed cover digester be equipped with
pressure and vacuum relief valves?
8.11C What are the advantages of a floating cover in
comparison with a fixed cover digester?
8.11D Why is it desirable to mix recirculated digester
sludge with raw sludge?
END OF LESSON 1 OF 5 LESSONS
on
SLUDGE DIGESTION AND HANDLING
8-14
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 8. Sludge Digestion and Handling
At the end of each lesson in this chapter you will find some
discussion and review questions which 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
continuing.
1. Briefly explain what happens when sludge is added to an
anaerobic digester.
2. Why is it important to keep the contents of a digester
well mixed?
3. Why should the floor of a digester be sloped?
4. Why do digesters have supernatant tubes?
8-15
-------
CHAPTER 8. SLUDGE DIGESTION AND HANDLING
(Lesson 2 of 5 Lessons)
8.12 Gas System (Fig. 8.5)8
The anaerobic digestion process produces 7 to 12 cubic feet of gas
for every pound of volatile matter destroyed, depending upon the
characteristics of the sludge. The gas consists mainly of methane
(CHiJ and carbon dioxide (C02). The methane content of the gas in
a properly functioning digester will vary from 65 to 70%, with
carbon dioxide running around 30 to 35% by volume. One or two
percent of the digester gas is composed of various other gases.
Digester gas (due to the methane) possesses a heat value of approxi-
mately 500 to 600 BTU9 per cubic foot, whereas natural gas with a
higher methane content may range from 900 to 1200 BTU per cubic foot.
Digester gas is utilized in plants in various ways: for heating the
digesters, for heating the plant buildings, for running engines, for
air blowers for the activated sludge process, or for electrical power
for the plant.
WARNING
A/UX£P WITH OXV6r£M
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8 Many figures in this section were made available courtesy of
VAREC, Inc., 301 East Alondra Blvd., Gardena, California 90247.
Mention of commercial products or manufacturers is for illustra-
tive purposes and does not imply endorsement by Sacramento State
College, EPA/WQO, or any other state or federal agency.
9 BTU: British Thermal Unit. The amount of heat required to raise
the temperature of one pound of water one degree Fahrenheit.
8-17
-------
The gas system removes the gas from the digester to a point of use,
or to be burned in the waste gas burner as excess. The following
items are components of the gas system.
A. Gas Dome
This is a point in the digester roof where the gas from the tank is
removed. On fixed cover tanks there may also be a water seal
(Fig. 8.3) incorporated to protect the tank structurally from excess
positive pressure,10 or vacuum created by withdrawal of sludge or
gas too rapidly.
If gas pressure is allowed to build up to 11 inches of water column
pressure, it will escape around the water seal to the atmosphere
without lifting the roof. If sludge is drawn or gas used too
rapidly, the vacuum could exceed eight inches and break the water
seal, thus allowing air to enter the tank. Without the water seal,
the vacuum could become great enough to collapse the tank. Air in
the tank creates an explosive condition. In addition, sulphuric
acid corrosion is often found where air is consistently in contact
with the gas. The pipeline between the gas storage tank and the
digester will protect the digester from water seal leaks, if the
line is clear. When liquids are pumped into the digester, gas can
go out the line to the storage tank and when liquids are pumped out
of the digester, gas can return through the line.
QUESTIONS
8.12A What are the two main gaseous components of
digester gas after gas production has become
well established?
8.12B What are some uses of digester gas?
8.12C Why must the digester gas be controlled with
extreme caution?
10 Positive Pressure. A positive pressure is a pressure greater
than atmospheric. It is measured as pounds per square inch
(psi) or as inches of water column. A negative pressure
(vacuum) is less than atmospheric and is sometimes measured
in inches of mercury.
8-18
-------
TYPICAL FLOW AND INSTALLATION DIAGRAM
MULTIPLE DIGESTER GAS SYSTEM
oo
i
vo
DIGESTER
(Fixed or floating roof)
DIGESTER
(Fixed or floating roof)
FULL SIZE 17"X22" PRINTS
OF THIS SCHEMATIC
AVAILABLE ON REQUEST
This schematic is for general guidance purposes
only and is not intended to represent a specific design-
Fig. 8.5 Digester gas system
Courtesy of VAREC
-------
B. Pressure Relief and Vacuum Relief Valves
(Fig. 8.6, VAREC Fig. No. 5800-81)
The pressure relief valve and the vacuum relief valve both are
attached to a common pipe, but each works independently. The
pressure relief valve is equipped with a seat and weighted with
lead washer weights. Each weight is stamped with its equivalent
water column height11 such as 1" H20 or 3" H20. There should be
sufficient weights, combined with the weight of the pallet, to
equal the designed holding pressure of the tank. The gas pressure
is normally established between six inches and eight inches of
water. If the gas pressure in the tank exceeds the pop-off setting,
then the valve will open and vent to the atmosphere for a couple
of minutes, through the pressure relief valve. This should occur
before the water seal blows out. The water seal can be broken
when a tank is overpumped or gas removal is too slow.
The vacuum relief valve operates similarly to the pressure relief
valve except that it relieves negative pressures to prevent the
tank from collapsing. Operating of either one of these valves is
undesirable, because this allows the mixing of digester gas with
air and can create an explosion outside the tank if the pressure
relief valve opens and inside the tank if the vacuum relief opens.
WARNING
|-
A diA4, A4IXTUE?£ I? AT 10
c^A^TO -A1C
AHP UPP&e DM
These two valves should be checked at least every six months for
proper operation.
11 Water Column Height. When pressure builds up in a digester,
the gas pressure would force water up a tube of water connected
to the outside of the digester. The higher the water column
height, the greater the gas pressure.
8-20
-------
FIGURE NO.
5800-81
PRESSURE RELIEF AND
VACUUM BREAKER VALVE
WITH FLAME ARRESTER
for Use on Digesters and Gas Holders
The "Varec" Figure No. 5800-81 unit consists
of a Figure No. 2000-81 Pressure Relief and
Vacuum Breaker Valve and a Figure No. 50-91
Flame Arrester. Maximum protection against ex-
cessive pressure and vacuum is afforded and acci-
dental ignition of sludge gas within the digester
and gas holder from external sources is eliminated.
Valve is light weight and corrosion resistant
construction. Interior parts are readily accessible
for inspection and maintenance purposes. Pallets
are dead weight loaded and include replaceable
synthetic rubber sludge gas resistant seat inserts
to insure gas tight seating and long life service
with minimum maintenance. Seat rings, pallets
and guide posts are anodized for extra corrosion
protection and are removable.
Flame arrester consists of a flame arresting bank
assembly enclosed within a gas-tight housing. The
bank consists of a multiple number of individual
corrugated stamped sheets and is readily remov-
able from the housing for inspection and cleaning
purposes. The arrester is listed by Underwriters
Laboratories and is approved by Associated Fac-
tory Mutual Laboratories.
FIGURE NO. 5800-81
SETTINGS
Valves are furnished with variable pressure
settings from 2" to 10" of water in increments of
1" of water. Vacuum setting is 2" of water unless
otherwise specified.
STANDARD MATERIALS OF CONSTRUCTION
Valve is substantially aluminum (impervious
to the attack of sludge gas) throughout except
for synthetic rubber pallet seat inserts and steel
studs, nuts and screws.
Flame arrester bank is all aluminum and the
housing consists of cast aluminum ends and cast
iron side and cover plates. Gaskets are graphited
asbestos.
3-21
-------
FIG. 50-91
ENTRAI NMENT
SEPARATOR FLAME
ARRESTER.
FIG. N2 5800-81
SIZES, DIMENSIONS AND APPROXIMATE
SHIPPING WEIGHTS-FIG. 5800-81
E)N° BOLTS
'—..
pJDIA. BOLTS
STO 125 LB. FLANGE
FLOW CURVES
SIZE
A
B
C
D
E
F
G
H
J
K
M
SHIP
WT.-LBS.
2"
12%
93/4
4%
6
4
5/8
%
9
5'/8
12%
22%
65
3"
163/8
105/8
6
7%
4
S/8
3/4
11 3/4
63/4
13%
24%
100
4"
20
14
7%
9
8
5/8
%
14%
8%
16S/8
30%
150
6"
25
17
9'/2
11
8
%
1
16%
9 y4
21 '/2
38%
250
LARGER SIZES AVAILABLE.
i
S
THOUSANDS SCFM 0.7 SPOR.GAS
I ,'. I I I A I I I ,'e
THOUSANDS SCFH 1.0 SP OR. AIR
\
s
S
I! 1
\
s
8-22
-------
An Explosive Gas Mixture was Accidentally Ignited,
The Digester Cover Blew Off,
And Landed on Top of a Pickup Truck.
Fig. 8.7 Results of digester explosion
8-23
-------
QUESTIONS
8.12D How would you adjust the pressure relief valve to
prevent pressures within the digester from exceeding
the design pressure?
8.12E How could the water seal be broken in a digester?
8.12F Why is the operation of either the pressure relief
valve or the vacuum relief valve undesirable?
8-24
-------
C. Flame Arresters CFig. 8.8, VAREC Fig. No. 450)
A typical flame arrester is a rectangular box holding approximately
50 to 100 corrugated aluminum plates with punched holes. If a flame
should develop in the gas line, it would be cooled below the ignition
point as it attempted to pass through the baffles, but gas could flow
through with little loss in pressure.
To prevent explosions, flame arresters should be installed:
1. Between vacuum and pressure relief valves and the
digester dome.
2. After sediment trap on gas line from digester.
3. At waste gas burner.
4. Before every boiler, furnace, or flame.
Flame arresters should be serviced every three months by
valving the gas off, pulling one end plate, and sliding
the baffle cartridge out of the housing. A build-up of
scale, salts from condensate, and residue build-up on the
plates restricts gas flow.
The cartridge in the flame arrester is designed to slide open so
the baffles may be separated and washed without complete dismantling.
When the unit is reassembled it should be tested for leaks by swabbing
a soapsuds solution over potential leaky areas and inspecting for
bubbles.
D. Thermal Valves
Another protective device installed near a flame source and near
the gas dome is the thermal valve. This valve is round, with a
weighted seat attached to a stem. The stem sets on a fusible disk
holding the seat up. If enough heat is generated by a flame, the
fusible element melts and drops the stem and valve seat to cut off
gas flow. Most valves are equipped with a wing nut on top of the
valve body. If the wing nut is removed, it uncovers a glass tube
which shows visually if the stem is up. If the stem cannot be seen,
then the valve is closed, and no gas can flow. If this occurs, the
valve is removed and heated in boiling water to remove the melted
8-25
-------
fusible slug. A new slug is installed (slightly larger than an
aspirin tablet), the stem replaced on top of it, and the valve is
ready for service. These valves should be dismantled at least
once a year in order to be positive that the stem is free to fall
and not gummed up with residue or scale from the gas.
Figure 8.9 (VAREC Fig. No. 440) shows a flame arrester connected
to a pressure relief valve.
QUESTIONS
8.12G How would you service a flame arrester?
8.12H Why should you check the thermal valves at least
once a year?
8-26
-------
RGURE
NO. 450
FLAME TRAP ASSEMBLY
FIGURE NO. 450
Assembly consists of "Varec" Flame Trap Fig. No.
53-81 and Thermal Operated Shutoff Valve Fig. No. 430.
It is usually installed in all gas lines to gas utilization
equipment, as close as possible to the points of com-
bustion, and in lines leading from each digester and
gasholder. May be installed in either horizontal or
vertical pipelines.
It is designed to arrest and stop flame propagation
— and to stop explosion waves, thus insuring protection
of major equipment.
FEATURES
Simple and positive flame trap. The fusible element
melts at 260° and stops gas flow within 15 seconds.
Compression type fusible element prevents shutoff valve
closing unless contacted by flame. Three extra fusible
elements shipped with each unit.
Since this unit is manufactured of aluminum, it resists
the attack of any of the corrosive elements common
to sludge gas.
Indicator rod shows when valve is in normal open
position.
The "Varec" Flame Trap Fig. No. 53-81 of this unit
is listed by the Underwriters' Laboratories and approved
by Associated Factory Mutual Laboratories.
Net free area through flame arresting bank is approxi-
mately four times corresponding pipe size. Each passage-
way has a net free area of approximately 0.042 sq. inches.
By actual test these units have more flow capacity with
less pressure drop than any known contemporary device.
Flow capacity curves are shown on the following page
to assist in selecting the correct size of equipment.
Flame Trap element is easy to inspect and clean. It
has good vertical and horizontal drainage. Drip Trap
connection is provided in case Unit is installed at low
point in line.
MATERIALS OF CONSTRUCTION
Flame Trap Housing — aluminum and cast iron
Flame Trap Element — aluminum
Thermal Valve Body & Cover — aluminum
Guide Stem — stainless steel
Sight Glass — pyrex
Cover and cap gaskets — graphited asbestos
Sight glass gasket — synthetic rubber
Spring — stainless steel
8-27
All designs subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prior equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general Information not to be used for construction. Certified drawings are available.
-------
FIGURE NO. 450
.WINGED
INSPECTION CAP
ilGHT GLASS
INDICATOR ROD
SIZES, DIMENSIONS, WEIGHTS
SIZE
2"
3"
4"
6"
A
2
3
4
6
B
4%
6
7%
*>y-i
c
6
7%
9
11
D
X
%
%
1
E
8^
10%
11%
1"%
F
3K2
4!/2
5
5/2
G
14/z
16
20
24%
H
8%
10
11%
15
J
4
4
8
8
K
%
%
y,
%
APPROX. WT. LBS.
NET
55
80
100
155
SHIP
90
125
150
215
NOTE: Available in 8" size upon ipecial order.
6 12 16 20
CAPACITY IN THOUSANDS CUBIC FEET PER HOUR GAS ISP OR.'0.7)
8-28
All designs subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prior equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general information not to be used for construction. Certified drawings are available.
-------
FIGURE NO.
440
PRESSURE RELIEF AND FLAME TRAP ASSEMBLY
FIGURE NO. 440
Assembly consists of "Varec" Figure No. 386 Back Pressure
Regulator, a "Varec" Figure No. 53-81 Flame Trap and a
Thermal Shutoff Control unit.
It is usually installed in the waste gas line, just upstream
of the waste gas burner.
It is designed to maintain a predetermined back pressure
throughout the gas system so that only surplus gas is wasted,
and to stop flame and explosion waves.
FEATURES
Simple, foolproof, sensitive in operation and a positive
flame trap. The fusible element melts at 260°F. and stops
gas flow within 15 seconds. Compression type fusible element
prevents shutoff valve closing unless contacted by flame.
Three extra fusible elements supplied with each unit.
Since the main bodies of the unit are constructed of
aluminum and the stems, needle valve, and other important
moving parts are of 18.8 stainless steel, this unit resists the
attack of any of the corrosive elements common to sludge
gas.
The "Varec" Flame Trap Fig. No. 53-81 of this unit is
listed by the Underwriters' Laboratories and approved by
Associated Factory Mutual Laboratories. The Flame Trap
element is easy to inspect and clean. Drip Trap connection
is provided in case unit is installed at a low point in line.
Net free area through flame arresting bank is approxi-
mately four times corresponding pipe size. Each passageway
has a net free area of approximately 0.042 sq. inches. By
actual test these units have more flow capacity with less pres-
sure drop than any known contemporary device.
Flow capacity curves are shown on the following page to
assist in selecting the correct size of equipment.
The Back Pressure Regulator unit is equipped with setting
indicator so operator can easily adjust setting to requirements.
RANGE OF OPERATION
Range of operation is 2 to 12 inches water. Special springs
available for higher operating pressures. Equipment supplied
by factory set at 6 inches of water if not specified otherwise.
Operator can adjust to his requirements.
MATERIALS OF CONSTRUCTION
Regulator Body — cast aluminum
Diaphragm Case — cast aluminum
Bonnet — cast aluminum
Spring — Cadmium-plated steel
Diaphragm — corded synthethic rubber
Cap — brass
Thermal Shutoff Valve — aluminum, brass & stainless
steel
Flame Trap Housing — heavy cast aluminum ends and
cast iron side and cover plates
Flame Trap Element — aluminum
8-29
All designs subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prior equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general information not to be used for construction. Certified drawings are available.
-------
FIGURE NO. 440
CONN, "A".
CONTROL LINE
CONNECTION
N.PT
CONN.
304 STAINLESS
STEEL DOUBLE
ACTING NEEDLE
VALVE
PACKING GLAND
BY-PASS
FUSIBLE-^
ELEMENT
JTO WASTE
GAS BURNER—
ATMOSPHERE
SECTION A-A
VALVE
SIZES, DIMENSIONS, WEIGHTS
Pipe
Size
Net Wt.
Ibs.
Ship.Wt.
Ibs.
3l/2"
8%'
221/g"
16"
10
2QI/;"
90
125
160
23%"
20"
11V
30
5%'
24%"
20I/;"
15
26'/2"
ISO
200
210
260
NOTE: Available in 8" ii» upon Iptcial order.
19 20 29 30 19
CAPACITY IN THOUSANDS CUBIC FEET PER HOUR OASISP CR • 0.7)
8-30
All designs1 subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prior equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general Information not to be used for construction. Certified drawings are available.
-------
E. Sediment Traps
A sediment trap is a tank 12 to 15 inches in diameter and two
to three feet in length. It is usually located on top of the
digester near the gas dome. The inlet gas line is near the top
of the tank and on the side. The outlet line comes directly from
the top of the sediment tank. The sediment trap is also equipped
with a perforated inner baffle, and a condensate drain near the
bottom. The gas enters the side at the top of the tank, passes
down and through the baffle, then up and out the top. Moisture
is collected from the gas in the trap, and any large pieces of
scale are trapped before entering the gas system. The trap should
be drained of condensate frequently but may have to be drained twice
a day during cold weather, because greater amounts of water will be
condensed.
F. Drip Traps--Condensate Traps
(Fig. 8.10, VAREC Fig. Nos. 245 and 246)
Digester gas is quite wet and in traveling from the heated tank to
a cooler temperature the water condenses. The water must be trapped
at low points in the system and removed, or it will impede gas flow
and cause damage to equipment, such as compressors, and interfere
with gas utilization. Traps are usually constructed to have a storage
space of one to two quarts of water. All drip traps on gas lines
should be located in the open air and be of the manual operation type.
Traps should be drained at least twice a day and possibly more often
in cold weather. Automatic drip traps are not recommended because
many automatic traps are equipped with a float and needle valve
orifice and corrosion, sediment, or scale in the gas system can keep
the needle from seating. The resulting leaks may create gas concen-
trations with a potential hazard to life and equipment.
G. Gas Meters
Gas meters may be of various types, such as bellows, diaphragm,
shunt flow, propeller, and orifice plate or differential pressure.
They are described in detail in the metering section of Chapter 11,
Maintenance.
H. Manometers
Manometers are installed at several locations to indicate gas pressure
within the system in inches of a water column.
8-31
-------
I. Pressure Regulators (Pig. 8.11, VAREC Fig. No. 387)
Pressure regulators are typically installed next to and before the
waste gas burner. Such regulators are usually of the diaphragm
type and control the gas pressure on the whole digester gas system.
They are normally set at eight inches of water column by adjusting
the spring tension on the diaphragm. Whenever an adjustment of a
pressure setting is made, check the gas system pressure with a
manometer for the proper range. If the gas pressure in the system
is below eight inches of water column, no gas flows to the waste
burner. When the gas pressure reaches eight inches of water column,
the regulator opens slightly, allowing gas to flow to the burner.
If the pressure continues to increase, the regulator opens further
to compensate. The only maintenance this unit requires is on the
thermal valve on the discharge side which protects the system from
back flashes. This unit is spring loaded and controlled by a fusible
element that vents one side of the diaphragm, thus stopping the
gas flow when heated. Maintenance includes checking for proper
operation of the regulator and of the fusible element. Gas
regulators are also placed at various points in the system to
regulate the gas pressure to boilers, heaters, and engines. Diaphragm
conditions in the regulators should be checked at periodic intervals.
J. Waste Gas Burner (Fig. 8.12)
Waste gas burners are used to burn the excess gas from the digestion
system. The waste gas burner is equipped with a continuous burning
pilot flame, so that any excess gas will pass through the gas regu-
lator and be burned. The pilot flame should be checked daily to be
sure that it has not been blown out by wind. If the pilot is out,
gas will be vented to the atmosphere creating an odorous and
potentially explosive condition.
QUESTIONS
8.121 How frequently should you drain a sediment trap?
8.12J Why must drip or condensate traps be installed in
gas lines?
8.12K What is a deficiency in automatic drip and conden-
sate traps?
8.12L How would you adjust the gas pressure of the digester
gas system?
8.12M Why should the pilot flame in the waste gas burner
be checked daily?
8-32
-------
faec
FIGURE NOS.
245 & 246
DRIP TRAPS
Automatic
Varec Drip Traps are for collection and safe
removal of condensate from gas lines and equip-
ment. Drip traps should be installed at all low points
in gas pipe systems where condensation will collect.
The Varec Figure No. 245 Automatic Drip
Trap employs a float operated needle valve which
automatically drains off collected condensate. This
feature is particularly desirable where a closed dis-
charge to drain is permissible and where condensate
occurs too frequently for manual operation.
Standard construction is alum, body and cover,
stainless steel ball float and needle valve assembly
and graphited asbestos gasket. Available with 1/2",
", l" NPT connections.
FIG. NO. 245 AUTOMATIC
Rotating Disc Type
The Varec Figure No. 246 Drip Trap is manu-
ally operated. Handle rotates disc from open inlet
position to drain position. Ports and disc are so
arranged that gas cannot escape regardless of disc
position. Both ports and shaft are positively sealed
by synthetic rubber "O" rings. Vent hole is provided
to allow inflow of air to bowl while draining.
Standard construction is cast aluminum bowl
and handle. Aluminum cover plate and disc are
anodized. Other working parts are stainless steel.
Heavy duty construction throughout. Available in
2M> quart capacity with l" NPT connections.
FIG. NO. 246
ROTATING DISC TYPE
8-33
AM designs subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prio.1 equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general information not to be used for construction. Certified drawings are available.
-------
INLET
-OUTLET
FIGURE NO. 245
VENT HOLE OPEN TO
ATMOSPHERE WHEN
OUTLET IS OPEN
FIGURE NO. 246
SIZES, DIMENSIONS AND APPROXIMATE SHIPPING WTS. - FIG. NOS. 245 AND 246
FIGURE NO.
245 AUTOMATIC
246 MANUAL
N. P. T.
CONNECTION
Vi", */*",\"
1"
A
—
8%
B
—
H3/8
APPROX. SHIPPING
WEIGHTS -IBS.
23
15
8-34
AH designs subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prior equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general information not to be used for construction. Certified drawings are available.
-------
FIG. NOS.
386 & 387
BACK PRESSURE
REGULATOR
SINGLE PORT
The Figure No. 386 Regulator Valve is designed to
control upstream pressure in sludge gas lines. Positive
shut-off as well as accurate control is provided. Pointer
type indicator, in weather-proof bonnet, facilitates set-
ting adjustment. No weights or dismantling necessary
to make adjustment.
Valve is the single port type operated by a spring loaded
diaphragm.
Setting range is 2" W.C. to 12" W.C as standard. Higher
settings available (20" W.C. maximum) on special order.
MATERIALS OF CONSTRUCTION:
Heavy cast aluminum valve body, diaphragm housing
and pallet, stainless steel operating shaft, heavy corded
synthetic rubber diaphragm and cadmium plated steel
spring.
FIGURE NO. 386
PRESSURE (REDUCING)
REGULATOR
SINGLE PORT
The Figure No. 387 Regulator Valve is designed to
control downstream pressure in sludge gas lines. Posi-
tive shut-off as well as accurate control is provided.
Pointer type indicator, in weather-proof bonnet, facili-
tates setting adjustment. No weights or dismantling
necessary to make adjustment.
Valve is single port type operated by a spring loaded
diaphragm.
Setting range is 2" W.C. to 12" W.C. as standard. Higher
settings available (20" W.C. maximum) on special order.
MATERIALS OF CONSTRUCTION:
Heavy cast aluminum valve body, diaphragm housing
and pallet, stainless steel operating shaft, heavy corded
synthetic rubber diaphragm and cadmium plated steel
spring.
FIGURE NO. 387
8-35
All designs subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prior equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general information not to be used for construction. Certified drawings are available.
-------
125 POUND
FLANGE DRILLING
SECTIONAL ELEVATION
FIG. NO 386
4"
SECTIONAL ELEVATION
FIG. NO 387
(REGULATOR SIZE)
6"
10
IS 20 25 30 35
THOUSANDS SCFH 0.7 SP. GR. GAS
40
45
50
SIZES, DIMENSIONS, WEIGHTS
SIZES
2"
3"
4"
6"
A
18V,
20
23
26
B
3
3%
4'/2
5'A
C
l4>/2
l4'/2
21
21
D
8%
10
M%
IS
Approx. Wt., Ibt.
Net
75
100
130
160
Ship.
100
140
175
220
NOTE: Availoblo In 8"
-------
GAS PIPING SCHEMATIC
ENCLOSED INSTALLATION
VAREC FIG.70-81 EXPLOSION RELIEF VALVES
oo
i
VAREC
WASTE GAS BURNER
v— FIG. 239
V BUILDING-
VAREC
FLAME CHECK
FIG. 52
-r"
VAREC
3 UNIT MANOMETER
-FIG. 217
VAREC
PRESSURE RELIEF 8
FLAME TRAP ASSEMBLY
-FIG.440
VAREC
REMOTE COVER
POSITION INDICATOR
FIG. 102
VAREC
FLAME CHECK
FIG.52 v
rfr
-TO WASTE GAS BURNER
GAS SUPPLY
TO LABORATORY
VAREC
PRESSURE REDUCING
REGULATOR-FIG.387
-BUILDING
VAREC
CHECK VALVE
FIG. 211-92
GAS SUPPLY TO'
SERVICE EQUIPMENT
VAREC
-FLAME TRAP
ASSEMBLY-FIG.450
PI LOT SUPPLY TO
WASTE GAS BURNER—7
NOTE-INSTALL DRIP TRAPS AT ALL LOW POINTS
VAREC
DRIP TRAP
FIG.245 OR 246
VAREC
DRIP TRAP
FIG.245 OR 246
GAS SUPPLY FROM
DIGESTER
/ VAREC
^-SEDIMENTS DRIP TRAP
ASSEMBLY-FIG.233, 218, 246
FULL SIZE I7"X22" PRINTS
OF THIS SCHEMATIC
AVAILABLE ON REQUEST
This schemotic is for general guidance purposes
only and is not intended to represent a specific design.
Fig. 8.12 Waste gas burner
Courtesy of VAfflC
-------
8.13 Sampling Well (Thief Hole)
(Fig. 8,13, VAREC Fig. Nos. 42-81 and 48-81)
The sampling well consists of a 3- or 4-inch pipe Cwi-tn a hinged
seal cap) that goes into the digestion tank, through the gas zone,
and is always submerged a foot or so into the digester sludge.
This permits the sampling of the digester sludge without loss of
digester gas pressure, or the creation of dangerous conditions
caused by the mixing of air and digester gas. However, caution
must be used not to breathe gas which will always be present in
the sample well and will be released when first opened. A sampling
well is sometimes referred to as a "thief hole".
8.14 Digester Heating
Digesters can be heated in several ways. Newer facilities typically
provide digesters that are heated by recirculating the digester sludge
through an external hot water heat exchanger. Digester gas is used
to fire the boiler, which is best maintained between 140 and 180°F
for proper operation. The hot water is then pumped from the boiler
to the heat exchanger where it passes through one jacket system,
while the recirculating sludge passes through an adjacent jacket,
picking up heat from the hot water. In some units the boiler and
exchanger are combined and the sludge also is passed through the unit.
Circulation of 130°F water through pipes or heating coils attached
to the inside wall of the digester is another method of heating
digesters, although not too common in newer plants. This approach
creates problems of cooking sludge on the pipes and insulating them,
thus reducing the amount of heat transferred. Some facilities use
submerged combustion of the gas with heat exchange between the hot
gaseous products evolved and the liquid sludge.
Other plants inject steam directly into the digesters for heating.
The steam is produced in separate boilers or is recovered in connection
with vapor phase cooling of engines. Careful treatment of the
evaporated water to prevent scaling of the system is necessary so the
practice is generally confined to plants with good laboratory control.
QUESTIONS
8.13A Why should a digester have a special sampling well?
8.14A What causes a reduction in the amount of heat trans-
ferred from coils within the digester?
8-38
-------
FIGURE NOS.
42-81 & 48-81
SAMPLING HATCH or
HANDHOLE COVER
Non-sparking Gas-tight
VAREC Sampling Hatches or Hand-
hole Covers are for use on digester covers
or roofs. Insurance requirements are com-
plied with in that this equipment is
non-sparking, self-closing and gas-tight.
Construction is non-corrosive in sludge
gas service.
Above photo shows simplicity
of operation
Figure No. 42-81 incorporates a standard
125 Ib. A.S.A. flanged base for mounting.
It is of extra heavy construction, basically
of aluminum throughout. Specialty features
are included such as a safety foot pedal for
quick opening, a hand wheel which may be
padlocked closed, and a synthetic rubber
insert in cover to insure a gas-tight seal.
Figure No. 42-81
Flanged Base
Figure No. 48-81 is substantially same as
Figure No. 42-81 in that it includes all the
specialty features and is of same materials
of construction. However, the base is for
Standard Pipe Thread mounting.
Figure No. 48-81
Screwed Base
8-39
AM designs subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prior equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general information not to be used for construction. Certified drawings are available.
-------
F) DIA.aC
G NO. HOLES
OIA. HOLES
THERMOMETER
HOLDER
125 ASA DRILLING
FIGURE NO. 42-81
FOOT
PEDAL
FIGURE NO. 48-81
SIZE
2"
3"
4"
6"
8"
10"
A
2
3
4
6
8
10
B
—
4%
5X
6%
6X
7
C
—
7Y-L
9
11
13^2
16
D
—
J*
y.
%
\
%
E
5%
6%
8Ya
9X
10%
12
STD. 125-LB. DRILLING
F
—
6
7H
9H
11J4
14%
G
—
4
8
8
8
12
H
—
%
%
y.
%
1
j
5
5
6Y,
8
7%
—
K
3
5Ji
6^8
9X2
11X2
—
APPROX. SHIPPING WEIGHTS
42-81
10
12
15
22
31
40
48-81
11
17
25
44
60
84
8-40
Alt designs subject to change without notice. Such change does not imply any obligation on the part of Varec, Inc. with respect to prior equipment shipments.
Installation, mounting arrangement, and dimensions are preliminary general information not to be used for construction. Certified drawings are available.
-------
8.15 Digester Mixing
Mixing is very important in a digester. The ability of the mixing
equipment to keep the tank completely mixed speeds digestion greatly.
Several important objectives
are accomplished in a well-
mixed digester.
. """""" a. Inoculation12 of the raw
sludge immediately with
microorganisms.
b. Prevention of a scum
blanket from forming.
c. Maintenance of homogeneous
contents within the tank,
including even distribution
of food, organisms, alka-
linity, heat, and waste
bacterial products.
d. Utilization of as much of
the total contents of the
digester as possible and
minimization of the build-
up of grit and inert solids
on the bottom.
A. Gas Mixing
This type of mixing is the most generally used in recent years, and
various approaches have been patented by manufacturers. Gas is pulled
from the tank, compressed, and discharged through gas outlets or orifices
within the digester, or at some point several feet below the sludge
surface. The gas rising to the surface through the digesting sludge
carries sludge with it, creating a gas lift with a rolling action of
the tank contents. The gas mixer may be operated on either a start
and stop or a continuous basis, depending upon tank conditions. The
components required for gas mixing include inlet and discharge gas
lines, a positive displacement compressor, and a stainless steel gas
line header in the digester. The gas header is equipped with a cross
arm to hold a specified number of gas outlets, and may be mounted in
a draft tube. The gas compressor is sized for the digester and may
range from 30 to 200 cfm of gas.
12 Inoculation (in-NOCK-you-LAY-shun).
culture into a system.
Introduction of a seed
8-41
-------
Work with "natural gas evolution" mixing at the Los Angeles County
Sanitation District's plants has indicated that loadings of over
0.4 pounds of volatile solids per cubic foot per day were possible,
but that if the loading dropped below 0.3 pounds immediate strati-
fication occurred. In terms of gas recirculation, adequate mixing
has been calculated from this study to be of the order of 500 cfm
(cubic feet per minute) per 100,000 cubic feet of tank capacity
if released at about a 15-foot depth. If released at a 30-foot
depth, about 250 cfm per 100,000 cubic feet of tank capacity should
be satisfactory. If hydraulic processes are used, either by re-
circulation or by draft tubes and propellers, then something like
30 HP per 100,000 cubic feet of tank capacity is required.
Maintenance requires that the condensate be drained from the lines
at least twice a day, that the diffusers be cleaned to prevent high
discharge pressures, and that the compressor unit be properly lubri-
cated and cooled.
QUESTIONS
8.15A Why should a digester be kept completely mixed?
8.15B What maintenance is necessary for the proper
operation of digester mixing by the use of gas?
8-42
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B. Mechanical Mixing
Propeller mixers are found mainly on fixed cover digesters. Normally
two or three of these units are supported from the roof of the tank
with the props submerged 10 to 12 feet in the sludge. An electric
motor drives the propeller stirring the sludge.
Draft tube propeller mixers are either single or multiple unit
installations'. The tubes are of steel and range from 18 to 24
inches in diameter. The top of the draft tube has a rolled lip
and is located approximately 18 inches below the normal water level
of the tank. The bottom of the draft tube may be straight or
equipped with a 90° elbow. The 90° elbow type is placed so that
the discharge is along the outside wall of the tank to create a
vortex (whirlpool) action.
The electric motor driven propeller is located about two feet
below the top of the draft tube. This type unit usually has
reversible motors so the prop may rotate in either direction.
In one direction the contents are pulled from the top of the
digester and forced down the draft tube to be discharged at the
bottom. By operating the motor in the opposite direction, the
digested sludge is pulled from the bottom of the tank and dis-
charged over the top of the draft tube to the surface.
If two units are in the same tank, an effective operation for
breaking up a scum blanket is operating one unit in one direction
and the other unit in the opposite direction, thereby creating a
push-pull effect. The draft tube units are subject to shaft bearing
failure due to the abrasiveness of sludge, and due to corrosion by
hydrogen sulfide (H2S) in the digester gas. Maintenance consists
of lubrication and, if belt-driven, adjustment of belt tension.
A limitation of draft tube type mixers is digester water level. If
the water level is maintained at a constant elevation, a scum blanket
forms on the surface. The scum blanket may be a thick layer and the
draft will only pull liquid sludge from under the blanket, not dis-
turbing it. Lowering the level of the digester to just three or four
inches over the top of the draft tube forces the scum to move over
and down the draft tube. This applies mainly to single direction
mixers.
Pumps are sometimes used to mix digesters. This method is common
in smaller tanks. When external heat exchangers are employed, a
larger centrifugal pump is used to recirculate the sludge and dis-
charge it back into the digester through one or two directional
nozzles at the rate of 200 to 1000 gpm.
8-43
-------
The tank may or may not be equipped with a draft tube such that the
pump suction may be from the top or valved from the bottom of the
digester. Control of scum blankets with this method of mixing is
dependent upon how the operator maintains the sludge level and
where the pump is pulling from and discharging to the digester.
Maintenance of the pump requires normal lubrication and a good pump
shaft sealing water system. The digested sludge is abrasive and
pump packing, shafts, wearing
rings, and impellers are rapidly
worn. Another problem associated
with pump mixing is the clogging
of the pump impeller with rags,
rubber goods, and plastic material.
A pump may run for days not pump-
ing due to clogging because the
* **, llf«6t.*./ **{ 1^ flT^^^~ operator was not checking the
equipment for proper operation.
Pressure gauges should be
installed on the pump suction
and discharge pipes. When a
gauge reading different than
normal occurs, the operator has
an indication that some condition
has changed that requires checking.
QUESTIONS
8.15C How would you break up a scum blanket in a digester
with two or more draft tube propeller mixers?
8.15D Why should pressure gauges be installed on mixing
pump suction and discharge lines?
END OF LESSON 2 OF 5 LESSONS
on
SLUDGE DIGESTION AND HANDLING
8-44
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 8. Sludge Digestion and Handling
Write the answers to these questions before continuing with
Lesson 3. The problem numbering continues from Lesson 1.
5. Why is digester gas considered dangerous?
6. What two purposes are served by the digester gas system?
7. Under what kind of circumstances will the pressure
relief valve and vacuum relief valve operate?
8. Where should flame arresters be installed in the
digester gas system?
9. How would you test for gas leaks around a flame
arrester after it has been serviced?
10. Why must drip and condensate traps be drained regularly?
11. What means are used to mix the contents of digesters?
8-45
-------
CHAPTER 8. SLUDGE DIGESTION AND HANDLING
CLesson 3 of 5 Lessons)
8.2 OPERATION OF DIGESTERS
A digester can be compared with your own body.
Both require food; but if fed too much, both
become upset. Excess acid will upset both.
Both like to be warm, with a body temperature
of 98.6°F near optimum. Both have digestive
processes that are similar. Both discharge
liquid and solid waste. Both utilize food
for cell reproduction and energy. If some-
thing causes upsets, in a digester, just think
how you would react if it happened to you
and recall what would be the proper remedy.
The remedies for curing upset digesters will
be discussed throughout this chapter.
8.20 Raw Sludge and Scum
Raw sludge is normally composed of solids
settled and removed from the primary and
secondary clarifiers. Raw sludge contains
carbohydrates, proteins, and fats, plus
organic and inorganic chemicals that are
added by domestic and industrial uses of water.
Solids are composed of organic (volatile) and inorganic material with the
volatile content running from about 60% to 80% of the total, by weight.
Some plants do not have grit removal equipment; so the bulk of the
inert (inorganic) material such as sand, eggshells, and other debris
will end up on the bottom of the digester occupying active digestion
space. The rate of debris accumulation is predictable so that the
amount is a function of the period of time between digester cleanings.
Where cleaning has been neglected, a substantial portion of the active
volume of the digester becomes filled with inert debris. Scum-forming
products, such as kitchen grease, soaps, oils, cellulose, plastics,
and other floatable debris, are generally all organic in nature but
may create problems if the scum blanket in the digester is not con-
trolled. Control is by providing adequate mixing and heat.
Several products end up in the digester that are not desirable because
the bacteria cannot effectively utilize or digest them, and they cannot
be readily removed by the normal process. These products include:
8-47
-------
1. petroleum products and mineral oils
2. rubber goods
3. plastics (back sheets to diapers)
4. filter tips from cigarettes
5. hair
6. grit (sand and other inorganics)
Consequently, these items tend to accumulate in the digester and,
without adequate mixing, may form a hard, floating mat and a sub-
stantial bottom deposit. On the other hand, a well-mixed tank may
also present operational problems. For example, the material
shredded by a comminuter or barminuter may become balled together
by the mixing action and plug the digester supernatant lines.
Scum from the primary clarifiers is comprised mainly of grease and
other floatable material. It may be collected and held in a scum
box and then pumped to the digester once a day, or it may be added
continuously or at a frequency necessary to maintain the proper
removal of scum from the raw wastewater flow. Many operators prefer
not to pump scum to the digesters, but to dispose of it by burning or
burial. Scum may also refer to the floating and gas buoyed material
found on the surface of poorly mixed digesters. This material may
contain much cellulose, rubber particles, mineral oil, plastic,
and other debris. It may become 5 to 15 feet thick in a digester,
but should not occur in a properly operating digester. A thick
scum layer will reduce the active digestion capacity of a digester.
8.21 Starting a Digester
When wastewater solids are first added to a new digester, naturally
occurring bacteria attack the most easily digestible food available,
such as sugar, starches, and soluble nitrogen. The anaerobic acid
producers change these foods into organic acids, alcohols, and
carbon dioxide, along with some hydrogen sulfide. The pH of the
sludge drops from 7.0 to about 6.0 or lower. An "acid regression
stage"13 then starts and lasts as long as six to eight weeks. During
this time ammonia and bicarbonate compounds are formed, and the pH
gradually increases to around 6.8 again, establishing an environment
for the methane fermentation or alkaline fermentation phase. Organic
acids are available to feed the methane fermenters. Large quantities
of methane gas are produced as well as carbon dioxide, and the pH
increases to 7.0 to 7.2. Once alkaline fermentation is well estab-
lished, strive to keep the digesting sludge in the 7.0 to 7.2 pH range,
13 Acid Regression Stage. A time period when the production of
volatile acids is reduced. During this stage of digestion
ammonia compounds form and cause the pH to increase.
8-48
-------
If too much raw sludge is added to the digester, the acid
fermenters will predominate, driving the pH down and creating an
undesirable condition for the methane fermenters. The digester
will go sour or acid again. When a digester recovers from a sour
or acid condition, the breakdown of the volatile acids and forma-
tion of methane and carbon dioxide is usually very rapid.. The
digester may then foam or froth, forcing sludge solids through
water seals and gas lines and causing a fairly serious operational
problem. A sour digester usually requires 30 to 60 days to recover.
As noted at the beginning of this section, the first group .of
organisms must do its part before food is available to the next
group. Once the balance is upset, so is the food cycle to the
next group. When the tank reaches the methane fermentation phase,
there is sufficient alkaline material to buffer the acid stage and
maintain the process. Operational actions such as poor mixing,
addition of excess food, excess water supplied to dilute the alka-
line buffer, over-drawing digested sludge, or improper temperature
changes can cause souring again.
The simplest way to start a digester is with seed sludge (actively
digesting material) from another digester. The amount of s.eed to
use is dependent upon factors such as mixing processes, digester
sizes, and sludge characteristics, but amounts between 10 and 50%
of the digester capacity have been used.
Example (seed volume based on tank capacity):
Calculate the volume of seed sludge needed for a 40-foot diameter
digester with a normal water depth of 20 feet, if the seed required
is 25% of the tank volume. Most digesters have sloping bottoms,
but assume the normal side wall water depth represents the average
digester depth:
Tank Diameter, D = 40 feet
Depth, H =20 feet
IT
?
8-49
-------
Tank Volume, = £
CU ft r >
40 1600
= 0.785 (40 ft)2 x 20 ft x40 x20
1600 32000
= 25,120 cu ft
0.785
32000
1570000
2355
25120.000
Tank Volume, = (25jl2Q cu ft) (y<5 gal/cu ft) 2512Q
S 7^5
= 188,400 gal 125600
175840
188400.0
Seed required assumed to be 25% or 1/4 of the digester tank volume:
Seed Volume, _ Tank Volume, gal ,17inn
1 — * T-/-LUU
g 4 4 / 188400
188,400 gal ~.
~ 4 28
28.
= 47,100 gal *
Therefore, 47,100 gallons of seed sludge would be needed. If seed
sludge is not available, the tank may be started by filling the
digester with raw wastewater and heating the tank to 85-95°F with
natural gas or other fuel. Allow the bacteria to take the natural
course of decomposition as earlier described. The time required for
a start of this nature ranges from 45 to 180 days.
Rather than estimate the volume of seed sludge on the basis of digester
capacity, a better approach is to determine the volume of seed necessary
to maintain digestion under the expected initial loading. To use this
approach, allow 0.03 to 0.10 pound of new volatile solids to be added
per day per pound of volatile solids under digestion.
8-50
-------
Example (seed volume based on raw sludge to be added):
Initially a new plant expects to pump 500 gallons of raw sludge per
day to the digester. The raw sludge is estimated to contain 6%
solids with a volatile content of 68%. Estimate the pounds of
volatile solids needed by the digester and the gallons of seed
sludge, assuming the seed sludge contains 10% solids with 50% vola-
tile solids and weighs nine pounds per gallon. (Digested sludge con-
taining 10% solids weighs more than water [8.34 Ib/gal] without any
solids.)
Find pounds of volatile matter pumped to digester per day.
(Vol. of Sludge, gpd)(Solids, %)(Volatile, %)(8.34 Ib/gal)
Volatile
Matter
Pumped,
Ibs/day = ^ gal/day)(0.06)(0.68)(8.34 Ib/gal)
= 170 Ibs/day
Select a digester loading between 0.03 and 0.10 pounds of new volatile
solids added per day per pound of volatile solids in digester. Try
0.05 Ib VM per day per pound under digestion.
Find pounds of seed volatile matter needed.
0.05 Ib VM added/day _ 170 Ib VM added/day
1 Ib VM in digester Seed, Ib VM
Seed, Ib VM = (170 Ib VM added/day) m
0.05 Ib VM added/day
= 3400 Ibs VM
Find gallons of seed sludge needed.
Seed Sludge, _ Seed, Ib VM
gal (9 Ib/gal) (Solids, %) (VM, %)
3400 Ib VM
(9 Ib/gal)(0.10)(0.50 VM)
= 7560 gal
8-51
-------
To start a digester, add the necessary seed sludge and fill the
remainder of the tank with raw sludge and wastewater. Some
operators do not fill a digester during start-up but this practice
is not recommended. The reason is that the tank may develop an
explosive mixture of gases if air is allowed into the partially-
filled digester.
During the start-up of a digester, once production of a good,
burnable gas is obtained the raw sludge feed rate can be gradually
increased -until the system is handling the total load.
8-52
-------
QUESTIONS
8.20A What is U) raw sludge? (2) scum?
8.21A What happens if you add too much raw sludge to the
digester?
8. 2 IB What causes a digester to foam and froth?
8.21C Calculate the recommended volume of seed sludge to
start a digester 50 feet in diameter and 25 feet
deep (average) . Assume 700 gallons per day of raw
sludge will be added, containing 6.5% solids and
70% volatile matter. Assume seed sludge contains
10% solids with 50% volatile solids and weighs
nine pounds per gallon. Use a digester loading of
0.05 Ib VM added per day per Ib VM under digestion.
8.21D Why is it dangerous to start a digester when it is
only partially full?
8. 2 IE How could you determine when a new digester is ready
for the raw sludge feed rate to be gradually increased
to the full plant load?
8-53
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8.22 Feeding
Food for the bacteria in the digester is the sludge from the primary
and secondary clarifiers. Make every effort to pump as thick a
sludge to the digester as possible. This may be accomplished by
holding a blanket of sludge as long as possible in the primary clari-
fier, long enough to allow sludge concentration, but not long enough
for sludge to start rising. In some plants concentration is accom-
plished in separate sludge thickening or flotation tanks.
Better operational performance occurs when the digester is fed several
times a day, rather than once a day because you are avoiding temporary
overloads on the digester and you are using your available space more
effectively. If the plant is producing only 500 gallons of 6% sludge
a day, one feeding may be allowable; however, for volumes much greater
than 500 gallons a day, several pumpings a day should be used. This
not only helps the digestion process, but maintains better conditions
in the clarifiers, permits thicker sludge pumping, and prevents coning1*
in the primary clarifier hopper. On fixed cover digesters frequent
feeding spreads the return of digester supernatant over the entire day
instead of a return in one slug with possible upset of the secondary
treatment system. Sludge is usually concentrated by holding a thick
blanket on the bottom of the clarifier; but if sludge sets for a pro-
longed period, lowest layers may stick to the bottom and will no longer
flow with the liquid. When pumping is attempted, liquid flows but
solids remain in the hopper in a cone around the outlet.
It is never desirable to pump thin sludge or water to a digester.
A sludge is considered thin if it contains less than 4% solids
(too much water). Reasons for not pumping a thin sludge include:
1. Excess water requires more heat than may be available.
2. Excess water reduces holding time of the sludge in the digester.
3. Excess water forces seed and alkalinity from the digester,
jeopardizing the system due to insufficient buffer15 for
the acids in the raw sludge.
14 Coning (CONE-ing). A condition that may be established in a sludge
hopper during sludge withdrawal when part of the sludge moves toward
the outlet while the remainder tends to stay in place. Development
of a cone or channel of moving liquid surrounded by relatively
stationary sludge.
15 Buffer. A measure of the ability or 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 the pH.
Buffer capacity is measured by titration with standard alkali and
acid until the pH reaches some reference or end point (a pH of 4.5
or 8.5). The higher the volume (ml) of known reagent requirements,
the higher the buffer capacity.
8-54
-------
Sludge concentrations above about 12% solids will usually not
digest well in conventional digestion tanks since adequate mixing
cannot be obtained. This, in turn, leads to improper distribution
of food, seed, heat, and metabolic products so that the souring
and a stuck16 digester results. However, most plants have diffi-
culty in obtaining a raw sludge of 8% solids. Where a trickling
filter or activated sludge process is used as the secondary system,
sludges may have a solids range from 1 to 3%. A good activated
sludge is likely to be oxidized to the point of negligible action
in an anaerobic digester.
Feeding a digester must be regulated on the basis of laboratory
test results in order to insure that the volatile acid/alkalinity
reltaionship does not start to increase and become too high. See
Section 8.4B.
QUESTIONS
8.22A How would you attempt to pump as thick a
sludge as possible to a digester?
8.22B Why should sludge be pumped occasionally throughout
the day rather than as one slug each day?
8.22C Why should the pumping of thin sludge be avoided?
16 Stuck. A "stuck" digester does not decompose the organic
matter properly. Some operators refer '.o it as constipated.
It is characterized by low gas production, high volatile acid/
alkalinity relationship, and poor liquid-solids separation.
A digester in a stuck condition is sometimes called a "sour"
digester.
8-55
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8.23 Neutralizing a Sour Digester
The recovery of a sour digester can be accelerated by neutralizing
the acids with a caustic material such as soda ash, lime, or
ammonia, or by transferring alkalinity in the form of digested
sludge from the secondary digester. Such neutralization increases
the pH to a level suitable for growth of the methane fermenters
and provides buffering material which will help maintain the required
volatile acids/alkalinity relationship and pH. When ammonia is added
to a digester, an added load is eventually placed on the receiving
waters. The application of lime will increase the solids handling
problems. Soda ash is more expensive than lime, but doesn't add as
much to the solids deposits. Transferring secondary digester sludge
has the advantage of not adding anything extra to the system that
was not there at an earlier time and, if used properly, will reduce
both the effluent load and the solids handling problem.
If digestion capacity and available recovery time are great enough,
it is probably preferable to simply reduce loading while heating
and mixing so that natural recovery occurs. However, there are
often conditions in which such neutralization is necessary.
When neutralizing a digester, the prescribed dose must be carefully
calculated. Too little will be ineffective, and too much is both
toxic and wasteful. In considering dosage with lime, the small
plant without laboratory facilities could use as a rough guide a
dosage of about one pound of lime added for every 1000 gallons of
sludge to be treated. Thus, a 188,000-gallon digester full of
sludge would receive 188 pounds of lime. A more accurate method is
to add sufficient lime to neutralize 100% of the volatile acids in
the digester liquor. (See Volatile Acids Test in Chapter 14, Labora-
tory Procedures and Chemistry.)
Example:
Volatile acids in digester sludge = 2300 mg/1. We should add lime
equivalent to 2300 mg/1.
Lime
Required, = Volatile Acids, mg/1 x Tank Volume, MG x 8.34 Ibs/gal
Ibs
= 2300 mg/1 x 0.188 MG x 8.34 Ibs/gal
= 2300 x 1.57 Ibs
= 3611 Ibs
8-56
-------
The lime must be mixed into a solution before being added to the
digester because dry lime would settle to the bottom in lumps
which are not only ineffective but take up digester capacity and
are difficult to remove when cleaning the digester. Use all of
the mixing energy available while liming and thereafter in
digester mixing. The easiest application point is through the
scum box if one is available. Add small quantities of lime daily
until the pH and volatile acid/alkalinity relationship (Section
8.4B) of the tank are restored to desired levels and gas pro-
duction is normal.
In any case, use lime only if recovery by natural methods cannot
be accomplished within the time available.
QUESTIONS
8.23A What happens when lime is added to a digester?
8.23B How much lime should be added to a 100,000-gallon
digester, using the "rough guide" dosage in the
previous section?
8.23C Why should lime be added in solution to the digester
rather than in dry form?
8.23D For how long a time should you add lime to a digester?
8-57
-------
8.24 Enzymes
17
In recent years several products containing "commercial" enzymes
or other biocatalysts (BUY-o-CAT-a-lists) have been marketed for
starting digesters, controlling scum, or simply to maintain oper-
ation. Such biocatalysts or enzymes have never been shown to be
effective in controlled tests and could, in fact, cause as much
harm as good. A biological system such as found in the digesters
develops a balanced enzyme and biocatalyst system for the conditions
under which it is operating. The quantities of natural enzymes
developed within the digesting sludge are many, many times greater
than any amount you could either add or afford to purchase.
8.25 Foaming
Large amounts of foam may be generated during start-up by the almost
explosive generation of gas during the time of acid recovery. Foam-
ing is the result of active gas production while solids separation
has not progressed far enough (insufficient digestion). It is
encouraged during start-up by overfeeding. Foaming can be prevented
by adequate mixing of the digester contents before foaming starts.
Bacteria can go to work very quickly when they have the proper
environment. Almost overnight they can generate enough gas to
create a terrific mess of black foam and sludge. The foam not only
plugs gas piping systems, but can exert excess pressures on digester
covers, cause odor problems, and ruin paint jobs on tanks and build-
ings.
17 Enzymes (EN-zimes). Enzymes are substances produced by
living organisms that speed up chemical changes.
8-58
-------
To clean up the mess, first drop the level of the digester a
couple of feet by withdrawing some supernatant. Next, cut off
the gas system and flush it with water. Then hose the outside
of the digester off as soon as possible or the paint will be
stained a permanent grey. Drain and refill the water seal to
remove the water fouled by the foaming. Use a strainer type
skimming device to remove any rubber goods and plastic materials
that have entered the water seal.
To control the foaming the best method is to stir the tank gently
to release as much of the trapped gas from the _~oam as possible.
Some operators even stop mechanical mixing equipment and stir
with long, woeden poles. Try not to add too much water from the
cleaning hoses as this reduces the temperature and dilutes the
tank, which could create conditions for more foaming later. Do
not feed the tank heavily, preferable net at all, until the foaming
has subsided.
Foaming may occur when a thick sludge blanket is broken up, tempera-
ture changes radically, or the sludge feeding to the digester is
increased. Avoid any conditions that give the acid formers the
opportunity to produce more food than the methane fermenters can
handle, because when the methane fermenters are ready, they may
work too fast.
If there had been adequate mixing, foaming problems would not have
developed. Start mixing from top to bottom of the tank before foam-
ing starts, not afterwards.
8.26 Gas Production
When a digester is first started, extremely odorous gases are produced,
including a number of nitrogen and sulphur compounds such as skatole,
indole, mercaptans, and hydrogen sulfide. Many of these are also
produced during normal digestion phases, but they are generally so
diluted by carbon dioxide and methane that they are hardly notice-
able. Their presence can be determined by testing if so desired.
During the first phases of digester start-up, most of the gas is
carbon dioxide (CC>2) and hydrogen sulfide (H2S) . This combination
will not burn and therefore is usually vented to the atmosphere.
When methane fermentation starts and the methane content reaches
around 60%, the gas will be capable of burning. Methane
production eventually should predominate, generating a gas
8-59
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with 65% to 70% methane and 30% to 35% C02 by volume. Digester
gas will burn when it contains 56% methane, but is not usable
as a fuel until the methane content approaches 62%. When the
gas produced is burnable, it may be used to heat the digester
as well as for powering engines and for providing building
heating.
QUESTIONS
8.24A What is the function of enzymes in digestion?
8.25A How would you attempt to control a foaming digester?
8.25B What preventive measures would you take to prevent
foaming from recurring?
8.26A Why is the gas initially produced in a digester not
burnable?
8-60
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8.27 Supernatant and Solids
Plants constructed today are typically equipped with two separate
digestion tanks or one tank with two divided sections. One tank
is called the primary digester and is used for heating, mixing,
and breakdown of raw sludge. The second tank, or secondary
digester, is used as a holding tank for separation of the solids
from the liquor. To accomplish such separation, the secondary
tank must be quiescent (qui-ES-sent) (without mixing).
Most of the sludge stabilization work is accomplished in the
primary digester, and 90% of the gas production occurs there.
It is desirable to very thoroughly mix the primary tank, but it
is undesirable to return the digested mixture to the plant as a
supernatant. Therefore, when raw sludge is pumped to the primary
digester, an equal volume is transferred to the secondary digester,
and settled supernatant from the secondary digester is returned
to the plant.
In the primary digester the binding property of the sludge is broken,
allowing the water to be released. In the secondary digester the
digested sludge is allowed to settle and compact, with some digestion
continuing. When the solids settle they leave a light amber colored
liquor zone between the top of the settled sludge and the surface
of the digester. By adjusting or selecting the supernatant tube,
the liquor with the least solids is returned to the plant.
The settled solids in the secondary digester are allowed to compact
so that a minimal amount of water will be handled in the sludge
dewatering system. These solids are excellent seed or buffer
sludge in case the primary digester becomes upset. A reserve of
30 to 100 thousand gallons should always be held in the secondary
digester. This represents a natural enzyme reserve and may save
the system during a shock load. Primary and secondary
sludge digesters should be operated as a complement to each other.
If you need more seed or buffering capacity in the primary digester,
it should be taken from the secondary digester.
The secondary tanks should be mixed frequently, preferably after
sludge has been withdrawn and supernatant will not be returned to
the plant. Usually secondary digesters are provided with mixers or
recirculating pumps, preferably arranged for vertical mixing. This
periodic mixing prevents coning of solids on the bottom of the tank
and the formation of a scum blanket on the top. Mixing also helps
the release of slowly produced gas that may float solids or scum.
If your plant has only one digester, stop mixing for one day before
withdrawing digested sludge to drying beds.
8-61
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8.28 Rate of Sludge Withdrawal
The withdrawal rate of sludge from either digester should be no
faster than a rate at which the gas production from the system is
able to maintain a positive pressure in the digester (at least
two inches of water column). If the draw-off rate is too fast,
the gas pressure drops due to volume expansion.
WARNING: If continued, a negative pressure develops on
the system (vacuum). This may create an explosive hazard
by drawing air into the digester. If the primary digester
has a floating cover, the sludge may be drawn down to
where the cover rests on the corbels without danger of
losing gas pressure.
Some operators prefer to pump raw sludge or wastewater to a digester
during digested sludge drawoff to maintain a positive pressure. If
gas storage lines permit it, return gas to the digester to maintain
pressure in the digester.
QUESTIONS
8.27A What is the purpose of the secondary digester?
8.27B When raw sludge is pumped to the primary digester,
what happens in the secondary digester?
'8.27C How is the level of supernatant withdrawal selected?
8.28A How would you determine the rate of sludge withdrawal?
END OF LESSON 3 OF 5 LESSONS
on
SLUDGE DIGESTION AND HANDLING
8-62
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DISCUSSION AND REVIEW QUESTIONS
Chapter 8. Sludge Digestion and Handling
Write the answers to these questions before continuing with
Lesson 4. The problem numbering continues from Lesson 2.
12. What kinds of material or products frequently end up in
digesters that are not desirable because bacteria cannot
effectively utilize or digest them?
13. Why should seed sludge be added to a new digester?
14. Why should a digester be fed at regular intervals during
the day, rather than once a day?
15. What are enzymes?
16. How can an operator attempt to prevent a digester from
starting to foam?
17. Why should secondary digesters be mixed, if at all?
8-63
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CHAPTER 8. SLUDGE DIGESTION AND HANDLING
(Lesson 4 of 5 Lessons)
8.3 DIGESTER SLUDGE HANDLING
After sludge has passed through a digestion system, it must be
dewatered and disposed of.
Small treatment plants are usually provided with sludge drying beds,
while larger plants utilize mechanical dewatering and drying systems,
Discharge by pipeline or barge to the ocean is sometimes used.
8.30 Sludge Drying Beds (See Fig, 8.14)
The drying process is accomplished through evaporation and percolation
of the water from the sludge after it is spread on a drying bed. The
drying bed is constructed with an underdrain system covered with
coarse crushed rock. Over the rock is a layer of gravel, and then a
layer of pea gravel covered with six to eight inches of sand.
Before sludge is applied, loosen the compacted sand layer by using a
sludge fork with tines eight to twelve inches long. Stick the tines
of the fork into the sand bed and rock it back and forth several times.
This is to loosen the sand only, and care should be taken that the
gravel and sand layer are not mixed. After the whole surface of the
bed is loosened, rake it with a garden rake to break up the sand clods.
Then level the bed by raking or dragging a 4" x 6" or 2" by 12" board
on ropes to smooth the surface.
Sludge is then drawn to the bed from the bottom of the secondary di-
gester. Draw the sludge slowly so as not to create a negative pressure
in the digester and to prevent coning of sludge in the bottom of the
digester. A thick sludge of 8% solids travels slowly, and if the draw-
off rate is too fast, the sludge around the pipe flows out and the
thicker sludge on the bottom moves too slow to fill the void. Conse-
quently, the thinner sludge above the draw-off pipe moves in; and when
it does, the supernatant level is reached, thus allowing almost nothing
but water to go to the drying bed. The thin sludge and supernatant
flowing down to the draw-off pipe washes a hole (shaped like a cone) in
the bottom sludge. When this occurs it sometimes may be remedied by
"bumping". This is accomplished by quickly closing and opening the
draw-off valve on a gravity flow system, which creates a minor shock wave
and sometimes washes the heavier sludge into the cone. If the digested
sludge is pumped to the drying bed, quickly start and stop the pump
using the power switch to create the "bumping" action.
8-65
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CLEAN OUT AT GRADE-
SLUDGE LINE
FROM DIGESTE
BED 1
BED UNDERDRAIN
BED 2
REMOVABLE REDWOOD
PLANKS FOR BED FILLING
1
I i
I !
SLUDGE INLET
TO BEDS
BED 4
WALKWAY ON TOP OF
BED WALL
I >
!
J
BED DRAIN LINE RETURNING TO PLANT HEADWORKS
PLAN SECTION
TJD
CLEAN OUT AT
AT GRADE
rifts
SAND BED SURFACE
SLUDGE INLET
•• o o o a o o<3 o J 1 ° ooo oooo o O
CROSS SECTION
DRAIN LINES
•SAND
•PEA GRAVEL
ROCK
N LINE
Fig. 8.14 Sludge drying bed
8-66
-------
To draw sludge slowly is time consuming and requires frequent
checks to be sure it does not thicken and stop flowing completely
or cone and run too fast.
The sludge being drawn to the bed is sampled at the beginning of
the fill, when the bed is half full, and just before the bed is
filled to the desired level. The samples may be mixed together
or analyzed separately for total and volatile solids.
The depth to which the sludge is applied is normally around 12
inches, but sometimes it is as deep as 18 inches in arid regions.
If it is deeper, the time required for drying is too long. A
bed filled with 20 inches of sludge would require approximately
the same time to dry as a bed loaded with 14 inches, dried and
removed and filled with another load 14 inches deep.
WARNING
NO SMOKIN6 OR OP£N FUAMES
Auowep IN f-ne V\ON\TV
COMIX) M^>
BV
AMP SU££L£^ OM
AMP PlC£"^> CAU^^-D B'V AN
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-------
When the sludge has formed cracks clear to the sand, it may then
be removed by hand with forks. The one major drawback of sand
beds is that heavy equipment, such as a skip loader, cannot be
used because the weight could damage the underdrain system. Also,
the scraping action could mix the sand with the gravel or remove
some of the sand with the dried sludge which will have to be
replaced.
Some operators lay 2" x 12" boards across the sand for wheel-
barrows or light trucks and fork the sludge cake into them to
haul to a disposal site. The dried sludge cake is normally
three to six inches thick and is not heavy unless a large amount
of grit was present in the sludge. The operator calculates the
amount of cake in cubic feet by the depth of the dry sludge cake
and surface area of the bed. The total dry pounds is arrived at from
the total solids in the sludge samples when the sludge was drawn.
Dried sludge makes an excellent soil conditioner and a low-grade
fertilizer. However, in many states air dried digested sludge may
only be used on lawns, shrub beds, and orchards and cannot be used
on root crop vegetables unless heat dried (at 1450°F), or unless
it has been in the ground that the crop is to be planted in for
over one year. It is always best to check with the state or local
health department before dried sludge is used on a food crop.
If a bed of "green" sludge (partially digested) is accidentally
drawn, it will require special attention. The water will not drain
rapidly, odors will be produced, and the water held provides an
excellent breeding ground for nuisance insects. Flies, rat-tail
maggots, psychoda flies, and mosquitoes will breed profusely in this
environment. An application of dry lime spread over the bed by
shovel, and a spraying of a pesticide, is beneficial. The sludge
from such a bed should never be used for fertilizer.
Dry sludge cake will burn at a slow smoldering pace, producing quite
an offensive odor; therefore, don't allow it to catch fire.
WARNING
SLU(?<2£ POWDeeOB PUST IS
AMP KICKec? INTO "PHe AlB IT W! LU
£1M1LA£ TO A PU4-TeXP/-0
-------
QUESTIONS
8.30A How would you prepare a drying bed prior to applying
sludge?
8.30B Why should sludge be drawn slowly from the digester?
8.30C What would you do if thin sludge suddenly started flow-
ing onto the drying bed on a gravity flow system, indicating
that a sludge cone had formed in the bottom of the digester?
8.30D Why should no smoking or open flames be allowed in
the vicinity where sludge is being drawn?
8.30E What should you do to the sludge draw-off line after
sludge is applied to the drying bed?
8.30F Why should heavy equipment such as skip loaders not be
used to remove dried sludge from a sand drying bed?
8.30G What is the volume of dry sludge in a bed 100 feet long
and 25 feet wide if the dried sludge is six inches thick?
How many two cubic yard dump truck loads would be re-
quired to haul away this sludge?
8.30H If green sludge (partially digested) accidentally was
applied to a drying bed, how would you handle this
situation?
8-69
-------
8.31 Blacktop Drying Beds (See Fig. 8.15)
This type of bed has become prevalent in the past few years and
has several advantages if designed properly. It is made of black-
top or asphalt with both sides sloping gradually to the center to
a one-foot wide drain channel. The drain channel runs the full
length of the bed with a three- or four-inch drain line on the
bottom. The drain line is covered with rock, gravel, and sand
as in a sand bed. The drain line usually has a cleanout at the
upper end, and a control valve on the discharge end.
When the bed is to be used, the cleanout on the drain line is
removed and the line is flushed with clear water and the clean-
out cover replaced. It is recommended that the drain line valve
be closed and the drain line and drain channel be filled with
water to the top of the sand, so that the sand is not sealed
with sludge. Sludge is then admitted to the bed. Some plants
have operated successfully without pre-filling the collection
system with water.
The depth the sludge is applied to the bed is between 18 and 24
inches.
The sludge is sampled in the same way as when using a sand bed,
except one additional sample is taken in a glass jar or beaker
and set aside. By watching the jar of sludge, you can observe
at some time during the first 24 to 36 hours that the sludge
will rise to the top, leaving liquor on the bottom. This is
primarily caused by the gas in the sludge. (Later, the sludge
will again settle to the bottom and the liquor will be on the
surface.) The drain valve on the drying bed should be opened
when the sludge separates and rises to the top of the jar. The
liquor collected in the sludge bed drains is normally returned
to the primary clarifiers.
After the sludge has started to crack and has a crust, drying
time may be reduced by driving a vehicle through the bed to mix
the sludge. When the cake is dry a skip loader is used to clean
the bed.
Blacktop beds may be able to handle two to three times as much
sludge as sand beds in a given period of time.
8-70
-------
DRAIN LINE RETURN TO PLANT HEADWORKS f^N
1
•
•
1
i
J
M
L
[
BED 1
f BLACK
1 (
t )
.
1 / °
•™T> L \
f
f
f
f
TOP f
1
1
SLUDGE f
INLET
VALVE
/ Li
•
-
- BED 2
• DRAIN
LINE AND
GRAVEL
JILL
•
1
t
t
1
1
ol^^v 1
< °'u- VA'VF
i
BED 3
f
! * ^ U r. n\
SLUDGE LINE FROM DIGESTERS
ENTRANCE RAMP WITH REDWOOD STOP LOG
PLAN VIEW
PLANT MIX BLACKTOP-
SLUDGE LINE
CROSS SECTION ONE BED
Fig. 8.15 Blacktop drying bed
8-71
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8.32 Sludge Lagoons
Sludge lagoons are deep ponds that hold digested sludge and, in
some instances, supernatant. Digested sludge is drawn to the
lagoon periodically and may require a year or two to fill. When
the lagoon is full, sludge is discharged into another lagoon
while the first one dries. This drying period can require a
year or two before the sludge is removed. Some large cities have
used lagoons for many years, avoiding the use of covered secondary
digestion tanks.
QUESTIONS
8.31A How would you attempt to reduce drying time in
blacktop beds?
8.32A How does a sludge lagoon operate?
8-72
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8.33 Withdrawal to Land
Wet sludge can be spread on land to reclaim the land or on farm
land and ploughed in as a soil conditioner and fertilizer. Used
with lagoons this gives a flexible system. This is an excellent
method of sludge disposal wherever applicable, because it returns
the nutrients to the land and completes the cycle as intended by
nature.
Transporting sludge to the disposal site is accomplished by tank
truck or pipeline. The application of wet sludge to the land
depends upon the topography and the crop to be raised on that
land. When applied to grass or low ground cover crops, appli-
cation may be by spraying from the back of the tank truck while
driving over the land, by the use of irrigation piping, or by
shallow flooding.
The best method, but most costly, is leveling the land, constructing
ridges and furrows, and then pumping the sludge down the furrows
similar to irrigation practices used in arid regions. This method
is not only capable of reclaiming land unsuitable for growing
plants and trees, but may yield crops equal to or greater than
those raised with commercial fertilizers.
Some precautions that must be practiced with this method of sludge
disposal include:
1. Never apply partially digested ("green") sludge or scum.
2. Residential areas must not be located near land disposal
sites.
3. Land disposal sites must not be located on a flood plain
where the sludge may be washed into the receiving waters
during flooding.
4. Domestic water wells must not be located on the land
receiving the sludge.
5. Root crop vegetables must not be grown on the land.
6. Cooperation with the landowner as to application time,
drying, and covering must be guaranteed.
7. Access to the land during wet weather must be provided.
8-73
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8.34 Mechanical Dewatering
In plants where large volumes of sludge are handled and drying
beds are not feasible, mechanical dewatering may be used.
Mechanical dewatering falls into two methods: vacuum filters
and centrifuges. Each is capable of reducing the moisture
content of sludge to 60% to 80%, leaving a wet, pasty cake
containing 20% to 40% solids. This cake may then be disposed
of as land fill, barged to sea, dried in furnaces for fertilizer,
or incinerated to ash in furnaces or wet oxidation units.
A. Vacuum Filters (Figs. 8.16 and 8.17)
For digested sludge to be dewatered by this method usually requires
a conditioning of the sludge by the addition of chemicals.
Elutriation (e-LOO-tree-a-shun) is the washing of the digested
sludge in plant effluent in a suitable ratio of sludge to effluent.
Elutriation may be accomplished in from one to three separate tanks,
similar to small rectangular clarifiers. The sludge is pumped to
the elutriation tank and mixed with plant effluent. Next this
mixture is admitted to the other tanks to establish a counter-
current wash. The sludge is then allowed to settle and is collected
by flights and pumped to the next elutriation tank. After one to
three washings it is then pumped to the conditioning tanks. The
main purpose of the elutriation tanks is to remove the fine sludge
particles which require large amounts of chemicals for coagulation.
It also removes amino acids and salts which may have a small coagu-
lant demand. After elutriation the sludge will react with the
chemicals better and produce better cake. The elutriate (effluent
from elutriation tanks) is returned to the primary clarifiers and
may result in a very heavy recirculating load since it is chiefly
fine solids. Many treatment plants have discontinued the practice
of elutriation. Although the process saves approximately $1 per ton
of dry solids handled on chemical costs, the costs are excessive for
treating the elutriate (wash water) in the biological treatment
processes.
Sludge conditioning is accomplished by the addition of various
coagulants or flocculating agents such as ferric chloride, alum,
lime, and polymers. In the conditioning tank the amount of chemical
solution added is normally established by laboratory testing of sludge
grab samples by adding various chemical concentrations to the grab
samples to obtain a practical filtration rate by vacuum. This test
establishes the operating rate for the chemical feed pumps or
rotameters from the chemical head tanks, which is normally less
than 10% of the dry sludge solids rate to the conditioning tank.
(Both rates could be in pounds per 24 hours.) In this tank the
8-74
-------
00
on
Fig. 8.16 Vacuum filter
Courtesy of Komline-Sanderson Engineering Corporation
-------
chemical is mixed into the sludge by gentle agitation for several
minutes. The conditioned sludge then flows to the filter bath
where it is continuously and gently agitated. After operation
has started, chemical feed is regulated according to cake appear-
ance and behavior.
Filter drums are 10 to 18 feet in diameter, and 12 to 20 feet in
length. They may use cloth blankets of dacron, nylon, or wool,
or use steel coil springs in a double layer, to form the outer
drum covering and filter media. The drum inside is a maze of
pipe work running from a metal screen and wood surface skin, and
connecting to a rotating valve port at each end of the drum.
Cloth blankets are stretched and caulked to the surface of the
filter drums with short sections of 1/4" cotton rope at every
screen section. The sides of the blanket are also stretched and
stapled to the end of the drums. The nap18 of the blanket should
be out. After the blanket is stretched completely around the drum,
it is then wrapped with two strands of 1/8" stainless steel wire,
approximately 2" apart for the full length of the drum.
The installation of a blanket may require several days, and it
lasts from 200 to 20,000 hours. The life of the blanket depends
greatly on the blanket material, conditioning chemical, backwash
frequency, and acid bath frequency. An improper adjustment of the
scraper blade, or accidental tear in the blanket, will usually
require its replacement.
Both cloth blankets and coil spring filters require a high pressure
wash after 12 to 24 hours, of operation, and in some instances, an
acid bath after 1000 to 5000 operating hours.
The filter drum is equipped with a variable speed drive to turn the
drum from 1/8 to 1 rpm. Normally, the lower rpm range is used to
give the filter time to pick up sufficient sludge as it passes through
the conditioned sludge tub under the filter. Normally less than 1/5
of the filter surface is submerged in the tub and pulling sludge to
the blanket or springs by vacuum to form the cake mat. As that area
passes through the conditioned sludge, the vacuum holds a layer 1/8
to 1/2 inch thick of sludge to the media, and continues to pull the
water from the sludge to approximately 210 degrees from the bottom
point of the filter after it leaves the vat. This is the drying
cycle. At this point the vacuum is released and a light air pressure
(3.0 psi) is applied to the inside of the blanket, lifting the sludge
18 Nap. The soft fuzzy surface of the fabric.
8-76
-------
00
I
EXTERNAL PIPING
DRUM
COIL SPRINGS
WASH HEADERS
FILTER
VALVE
DRUM DRIVE
SLUDGE LEVEL
t
AGITATOR
DRIVE
INLET 1 DRAIN
Fig. 8.17 Coilfilter elevation
Courtesy of Komli.ne-Scm.derson Engineering Corporation
-------
so that it falls from the blanket into a hopper or conveyor belt.
The drum then rotates past a scraper blade to remove sludge that
did not fall. The applied air is then phased out as that
section starts into the filter tub, and vacuum is applied in
order to pick up another coating of sludge.
The thickness of the sludge cake and moisture content depend
upon the sludge, chemical feed rate, drum rotation speed, mixing
time, and condition of the blanket or coil springs. A filter may
blank out (lose sludge cake) for any of the above reasons or due
to the loss of vacuum or filtrate pumps. Filtrate is the liquor
separated from the sludge by the filter; it is returned to the
primary clarifiers.
QUESTIONS
8.33A What are some of the advantages of applying sludge
to land?
8.34A How is sludge disposed of in many large plants or
areas where drying beds are not feasible?
8.34B How would you prepare digested sludge for drying by
vacuum filtration?
8.34C How would you determine the chemical feed rate to
condition sludge?
8.34D What factors influence the life of a filter blanket?
8-78
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B. Centrifuge
Centrifuges are gaining in popularity for dewatering raw or primary
sludges for furnaces or incineration units. Their use on digested
sludge is becoming more widespread and is expected to replace vacuum
filters as the prime digested sludge dewatering device. Most
digested sludges are conditioned with polymers before being fed to
a centrifuge.
Centrifuges are various sized cylinders that rotate at high speeds.
The sludge is pumped to the center of the bowl where centrifugal
force established by the rotating unit separates the lighter liquid
from the denser solids. The centrate19 is returned to the primary
clarifiers, and the sludge cake is removed to a hopper or to a con-
veyor for disposal.
The feed rate, pool depth, centrifuge rpm, and other factors
determine the condition of the discharge cake or slurry and the
quality of centrate. The centrate usually contains a high amount
of suspended solids that become difficult to handle in the primary
clarifiers and digesters. A large amount of grit in the sludge greatly
increases the wear rate on the centrifuge. Similar to the wash water
from the elutriation process, centrate from vacuum filters also exerts
a difficult load on biological treatment processes.
QUESTIONS
8.34E Centrifuges are commonly used to dewater
what types of sludges?
8.34F How would you regulate the condition of
the sludge cake from a centrifuge?
END OF LESSON 4 OF 5 LESSONS
on
SLUDGE DIGESTION AND HANDLING
19 Centrate. The liquor leaving the centrifuge after
most of the solids have been removed.
8-79
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 8. Sludge Digestion and Handling
Write the answers to these questions before continuing with
Lesson 5. The problem numbering continues from Lesson 3.
18. What kind of sludge should be placed on a sand drying bed?
19. What precautions should be taken when applying sludge to a
drying bed?
20. What are the advantages of a blacktop drying bed over a
sand drying bed?
21. Why have some plants discontinued elutriation?
22. What are some of the operational problems encountered
in using a centrifuge to dewater sludge?
8-81
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CHAPTER 8. SLUDGE DIGESTION AND HANDLING
(Lesson 5 of 5 Lessons)
8.4 DIGESTER CONTROLS AND TEST INTERPRETATION
NOTE; See Chapter 14, Laboratory Procedures and Chemistry, for
testing procedures.
A. Temperature
A thermometer is usually installed in the recirculated sludge line
from the digester to the heat exchanger. This thermometer will
accurately measure the temperature of the digester contents when
circulation is from bottom to top. The temperature from the di-
gester is recorded and should be maintained between about 95 and
98°F for mesophilic digestion. Never change the temperature more
than 1°F per day. Accurate temperature readings also may be taken
from the flowing supernatant tube or from the heat exchanger sludge
inlet line. The same temperature should be maintained at all levels
of the tank.
B. Volatile Acid/Alkalinity Relationship
The volatile acid/alkalinity relationship is the key to successful
digester operation. As long as the volatile acids remain low and
the alkalinity stays high, anaerobic sludge digestion will occur in
a digester. Each treatment plant will have its own characteristic
ratio for proper sludge digestion (generally less than 0.1). When
the ratio starts to increase, corrective action must be taken imme-
diately. This is the first warning that trouble is starting in a
digester. If corrective action is not taken immediately or is not
effective, eventually the C02 content of the digester gas will in-
crease, the pH of the sludge in the digester will drop, and the
digester will become sour.
A good procedure is to measure the volatile acid/alkalinity relation-
ship at least twice a week, plot the volatile acid/alkalinity
relationship against time, and watch for any adverse trends to develop.
Whenever something unusual happens, such as an increased solids load
from increased waste discharges or a storm, the volatile acids/
alkalinity relationship should be watched closely. Chapter 14,
Laboratory Procedures and Chemistry, contains a procedure for
measuring volatile acids by titration which gives satisfactory
results for operational control.
8-83
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The volatile acid/alkalinity relationship is an indication of
the buffer capacity of the digester contents. A high buffer
capacity is desirable and is achieved by a low ratio which exists
when volatile acids are low and the alkalinity is high (120 rag/1
volatile acids/2400 mg/1 alkalinity). Excessive feeding of raw
sludge to the digester, removal of digested sludge, or a shock
load such as produced by a storm flushing out the collection
system may unbalance the volatile acid/alkalinity relationship.
A definite problem is developing when the volatile acid/alkalinity
relationship starts increasing. Once the relationship reaches the
vicinity of 0.5/1.0 (1000 mg/1 volatile acids/2000 mg/1 alkalinity),
serious decreases in the alkalinity usually occur. At a relation-
ship of 0.5/1.0 the concentration of C02 in digester gas will start
to increase. When the relationship reaches 0.8 or higher, the pH
of the digester contents will begin to drop. When the relation-
ship first starts to increase, ample warning is given for corrective
action to be taken before problems develop and digester control is
lost.
Response to an Increase in Volatile Acid/Alkalinity Ratio;
When the ratio starts to increase, extend mixing time of digester
contents, control heat more evenly, and decrease sludge withdrawal
rates. Mixing should be vertical mixing from the bottom of the tank
to the top of any scum blanket. If possible, some of the concen-
trated sludge in the secondary digester should be pumped back to
help correct the ratio. In addition, the primary digester should
not be operated as a continuous overflow unit when raw sludge is
added, but it should be drawn down to provide room for some sludge
from the secondary digester too. During heavy rains when, extra
solids are flushed into the plant, it may be necessary to add some
digested sludge to the primary digester. Use the volatile acid/
alkalinity ratio as a guide to determine the amount of digested
sludge that should be returned to the primary digester for control
purposes.
C. Digester Gas (C02 and Gas Production)
This is a useful test to record. The change of C02 in the gas is
an indicator of the condition of the digester. Good digester gas
will have a C02 content of 30 to 35%. The volatile acid/alkalinity
relationship will start to increase before the carbon dioxide (C02)
content begins to climb. If the C02 content exceeds 42%, the
digester is considered in poor condition and the gas is close to the
burnable limit (44 to 45% C02).
8-84
-------
Gas production in a properly operating digester should be con-
stant if feed is reasonably constant. If the volume produced
gradually starts falling, trouble of some sort is indicated.
D.
pH is normally run on raw sludge, recirculated sludge, and super-
natant. This information is strictly for the record and not for
plant control. The raw sludge, if stale, will be acid and run in
the range of 5.5 to 6.8. Digester liquors should stay around 7.0
or higher. pH is usually the last indicator to change and gives
little warning of approaching trouble. It is therefore the least
desirable control method.
QUESTIONS
8.4A Where would you obtain the temperature of a digester?
8.4B Why is the volatile acid/alkalinity relationship very
useful in digester control?
8.4C What should be done when the volatile acid/alkalinity
relationship starts to increase?
8.4D Why is pH a poor indicator of approaching trouble in
a digester?
8-85
-------
E. Solids Test
Samples are collected of the raw sludge, recirculated sludge, and
supernatant. Each sample is tested for total solids and volatile
solids.
The information from these tests is used to determine the pounds
of solids handled through the system, the digester loading rates,
and the percent of reduction of the organic matter destroyed by
the digester. All of these tests are necessary for the maintenance
of close digester operation.
F. Volume of Sludge
Volumes of sludge are needed to determine the pounds of solids
handled through the system. In smaller plants which use a positive
displacement pump, the volume of raw sludge is determined by the
volume the pump displaces during each revolution. For instance, a
10-inch piston pump with a 3-inch stroke will discharge one gallon
per revolution. These pumps are equipped with a counter on the end
of the shaft and are seldom operated faster than 50 gpm.
Example
Calculate the volume pumped per stroke (revolution) by a piston pump
with a 10-inch diameter piston and the stroke set at three inches.
Volume of
Cylinder, = Area, sq ft x Depth, ft
cu ft
= 0.785 D2H
10"
= 0.833 or 0.83 ft
12"/ft
3"
= 0.25 ft
12"/ft
= 0.785 x (0.83 ft)2 x 0.25 ft
= 0.785 x 0.69 ft x 0.25 ft
= 0.785 x 0.17 .83 .69
.83 .25
= 0.133 cu ft 249 345
664 158
.6889 .1725 .13345
8-86
-------
Volume of
Cylinder, = 0.133 cu ft x 7.48 gal/cu ft
gal
= 0.995 gals/stroke
= 1.0 gal/stroke
(approximately) 0.9948T4
This is the maximum volume that can be pumped per stroke with this unit.
Slow or incomplete valve closures are likely to reduce this amount.
You may check it by taking the delivery volume and dividing it by the
number of strokes to fill a drying bed or tank.
Units:
The piston travels the depth of the cylinder each stroke. We could
have written our original equation in volume per stroke by indicating
depth as distance per stroke.
Volume, cu ft/stroke = Area, sq ft x Depth, ft/stroke
Therefore, if the pump counter recorded 2800 revolutions, ideally the
pump handled a total of 2800 gallons for that period of time, which
is normally a 24-hour period.
If a centrifugal pump is provided, it would be necessary to
determine the volume pumped within the system. Thus by determining
how long it took to pump one foot of sludge to the digester, the
volume per minute could be determined. The quantity of sludge pumped
per day is an important variable, and the operator should make a real
effort to determine the quantity. The volume of sludge pumped to the
digester should be approximately the same each day.
QUESTIONS
8.4E Why would you run a solids test on digester sludge?
8.4F Calculate the volume of sludge pumped per stroke by
a 12-inch diameter piston pump with the stroke set
at four inches.
8.4G If a piston pump discharges 1.2 gallons per stroke and
the counter indicates 2000 revolutions during a 24-hour
period, estimate how many gallons were pumped during
that day.
8.4H Why would you want to know the volume of sludge pumped
per day?
8-87
-------
G. Raw Sludge
If the 2800 gallons of raw sludge pumped by the piston pump con-
tained 6.5% total solids and had a volatile content of 68%:
1. How many pounds of dry sludge were handled?
2. What part is subject to digestion (volatile solids)?
Example
Sludge Pumped
Solids
Volatile
= 2800 gallons
= 6.5%
= 68%
Dry
Solids,
Ibs
= Gals Pumped x % Solids as decimal x 8.34 Ibs water/gal
= 2800 gals x 0.065 x 8.34 Ibs/gal
= 182 gals x 8.34 Ibs/gal of solids
= 1518 Ibs during pumping period
2800
.065
14000
16800
182.000
182 x 8.34 = 1517.88
Volatile
Solids, =
Ibs
% Volatile as decimal x Total Solids, Ibs
0.68 x 1518 Ibs
1032 Ibs of volatile solids during pumping period
H. Re ci rcu 1 ated S ludge
Laboratory tests indicate that the dry solids in a recirculated
digested sludge sample was 4.5% and contained 54.2% volatile con-
tent. This indicates that the process is reducing the volatile
content of the sludge, but the 4.5% solids content is lower than
that of the raw sludge being pumped to the digester. The reduction
8-88
-------
is a result of the conversion of a substantial portion of the vola-
tile solids in the raw sludge to methane, carbon dioxide, and water.
Therefore, the reduction in solids comes from some of the solids
being converted to gas and some of the solids being washed out in
the supernatant.
The reduction of volatile solids that has occurred in the primary
digester is arrived at mathematically by the following formula:
p = R : ,D x 100% = T Inrr n,^ x 100
R - (R x D) In - (In x Out)
P = Percent Reduction of Volatile Matter
In = R = Percent Volatile Matter in Raw Sludge
Out = D = Percent Volatile Matter in Digested Sludge
Example :
In = 68% Volatile Matter in Raw Sludge
Out = 54.2% Volatile Matter in Digested Sludge
P = In :
In - (In x Out)
n fi_ n . 0.68 0.54 0.68
' - u.3* 1QO% -0.54 0.68 -0.37
0.68- (0.68x0.54)
324
'
n « n M x 100% °'3672
°'68 ' °'37 or 0.37
— x 100% .45
U
-------
What is actually happening in the calculation of the percent
reduction of volatile matter may be visualized by the follow-
ing example. Start with 100,000 pounds of raw sludge solids
consisting of 75% volatile (organic) solids and 25% fixed
(inorganic) solids. After digestion, 50,000 pounds of volatile
matter has been converted to methane, carbon dioxide, and
supernatant water containing recycle solids, nitrogen, and a
COD. The remaining digested sludge consists of 25,000 pounds
volatile matter and 25,000 pounds of fixed solids.
BEFORE DIGESTION
100,000 IBS RAW SLUDGE
AFTER DIGESTION
GH4, C02, H20*
AFTER DIGESTION
75%
VOLATILE
25%
FIXED
75,000 Ibs
I! 25, 000 ibs 1111
VOLATILES CON-
VERTED TO CH4,
C0?, AND H20.
\'
REMAINING
DIGESTED SLUDGE
25,000 Ibs
lIljIEliirB
t
50,000
50%
VOLATI
50%
FIXED
Ibs
LE
* SUPERNATANT WATER CONTAINING
RECYCLE SOLIDS, NITROGEN AND
A COD.
8-90
-------
Check 1:
Percent Reduction _ (Reduction of Vol. Solids, Ibs) x 100%
of Volatile Matter ~ Starting" Amt of Vol. Solids, Ibs
(75,000 Ibs - 25,000 Ibs) x 100%
75,000 Ibs
50,000 x 100%
75,000
= 66.7%
Check 2:
P = In : Out „
In - (In x Out)
°'75 - °'50 x 100%
0.75 - (0.75 x 0.50)
0 25
of?x 100%
= 66.7%
I. Secondary Digested Sludge
Laboratory results indicate that a total digested sludge solids sample
was 9.6% solids and 42.8% volatile content. The raw sludge solids
volatile content was 68%. The overall percent reduction, P, could
then be arrived at by using the formula,
In - x 100%
In - (In x Out)
(0.68 - 0.45) x 100%
0.68 - (0.68) (0.43)
0.25 x 100%
0.68 - 0.29
x 100%
0.25 .. ,„-.
0.68
= 0.64 x 100% = 64%
8-91
-------
If sludge is drawn from the secondary digester, the total
pounds of dry solids may be calculated by using the 9.6% solids
results for that example and the volume of the withdrawn sludge,
Thus,
Volume Secondary Digester Sludge in Gallons
x Solids, % x Weight of Sludge, lb/gal20
= Total Solids, Ibs
Total Solids, Ibs x Volatile Solids, % = Volatile Solids, Ibs
By subtracting from the raw sludge figures, the pounds reduction
of total and volatile solids can be found.
QUESTIONS
8.41 During a 24-hour period, 3000 gallons of 5% total
solids sludge with a volatile content of 70% was
pumped to a digester. Calculate the pounds of:
(1) solids, and (2) volatile material pumped.
8.4J Calculate the reduction in volatile solids if the
percent volatile entering the digester is 70% and
the percent leaving is 45%.
P =
In - Out
In - (In x Out)
x 100"
20 A gallon of water weighs 8.34 pounds. A gallon of digested
sludge will weigh slightly more due to solids. The best way
to find the weight is to weigh a gallon of the sludge.
8-92
-------
J. Digester Supernatant
The total solids test is run on the digester supernatant to deter-
mine the solids load returned to the plant. The total solids in
the digester supernatant should be kept below 1/2 of 1% (0.005 or
5000 mg/1). High solids content in the supernatant usually indicates
that too much seed or digested sludge is being withdrawn from the
digester. This kind of withdrawal could increase the volatile acid/
alkalinity relationship which is also undesirable.
Another simple method for checking supernatant is to draw a sample
into a 1000 ml graduate and let it stand for four or five hours.
The sludge on the bottom of the graduate should be below 50 ml, with
an amber colored liquor above it. If supernatant solids are allowed
to build too high, an excessive solids and BOD load is placed on the
secondary system and primary clarifier. Sludge withdrawn from the
secondary digester or supernatant removal tubes should be changed to
a different level in the digester where the liquor contains the least
amount of solids when the supernatant load becomes too heavy on the
plant.
Plants should be designed to allow all sludge solids and liquids to
go to a lagoon or some such system for final or ultimate disposal,
rather than returning them to the plant.
K. Computing Digester Loadings
Digester loadings are reported as pounds of volatile matter per cubic
foot or 1000 cubic feet of digester volume per day. The loading rate
should be around 0.15 to 0.35 pounds of volatile solids per cubic foot
in a heated and mixed digester. For an unmixed or cold digester, the
loading rate should not exceed 0.05 pounds of volatile matter per
cubic foot, assuming that each cubic foot contains approximately 0.5
pounds of predigested solids.
Going back to the 40-foot diameter and 20-foot water depth digester
described earlier, a raw sludge volume was pumped of 280U gallons,
at 6.5% solids and 68% volatile matter. It was determined that
there were 1032 pounds of volatile solids added to the digester per
day.
Example
.
cu ft/day Volume of Digester, cu ft
8-93
-------
1052 Ibs of Vol. Matter/day
25,120 cu ft
= 0.041 Ibs Vol. Matter/cu ft/day
.041
25120 / 1032.000
1004 80
27 200
25 120
This would be a light loading, but it is not uncommon in small, new
plants.
The pounds of solids that should remain in the digester to maintain
a suitable environment must be determined too. To retain a favor-
able volatile acid/alkalinity relationship of around 0.1, at least
ten pounds of digested sludge should be retained in the digester for
every pound of volatile matter added to the digester.
Digested
Sludge .. .. ... ... , .., ,, 10 Ibs Dig. Sludge in Storage
in Storage, = Vo1' Mat' Added> Ibs/day x 1 lb ^ Mat.ldded per Day
= 1032 Ibs/day x
' '
1 lb Added/Day
= 10,320 Ibs old sludge in storage on a dry solids basis
The actual amount of sludge retained will depend on digester conditions
and the volatile acid/alkalinity ratio.
Sometimes data are reported as pounds of volatile matter destroyed per
cubic -foot or 1000 cubic feet of digester capacity per day. Using the
same data from above and starting from the beginning with 2800 gallons,
at 6.5% solids, and 68% volatile, assume a volatile solids reduction
of 50%.
8-94
-------
Example
Volatile Matter Destroyed, Ibs/day/cu ft
Volume of Sludge Pumped, gal/day x % Solids
x % Volatile x % Reduction x 8.34 Ibs/gal
Volume of Digester, cu ft
Volume of Solids
JL
^2800 gals/day x 0.065\c 0.50 x 8.34 Ibs/gal
25,120 cu ft
• j U
.68
400"
300
2800 gpd x 0.065 x 0.34 x 8.34 Ibs/gal .3400
25>12o cu ft
.065
.34
260
195
2800 x 0.022 x 8.34 .02210
25,120 cu ft
2800 gpd
.022
5600
5600
61.6 x 8.34 61'600
25,120 cu ft
8.34
6JL.6
5004
834
5004
513.7 Ib/day 513.744
25,120 cu ft
.024
25120 / 513.70
= 0.0204 Ibs/day/cu ft
or
= 20.4 lbs/day/1000 cu ft
8-95
-------
L. Computing Gas Production
Digester gas data should be recorded in cubic feet produced per
day by the digestion system, as recorded daily from the gas meter.
The carbon dioxide (C02) content should normally be tested once
or twice a week. (See Chapter 14, Laboratory Procedures and
Chemistry.) Gas production should range between 7 and 12 cubic
feet for each pound of volatile matter destroyed in the digesters.
Assume that the gas meter readings have averaged 6000 cubic feet
of gas per day. Using the data from the calculation of volatile
matter destroyed in pounds per day of 513.7, compute gas produced
per pound of volatile matter destroyed.
Example
Gas Produced, cu ft/lb of vol. matter destroyed
Gas Produced, cu ft/day
Ibs of Volatile Matter Destroyed, Ib/day
6000 cu ft gas/day 11.67
513.7 Ibs Volatile Matter Destroyed/day 513.7 / 60000
5137
= 12 cu ft gas fib vol. matter destroyed 8630
5137
34930
30822
41080
QUESTIONS
8.4K Why would you run a total solids test on the digester
supernatant?
8.4L What would you do if the total solids were too high
in the digester supernatant?
8-96
-------
M. Solids Balance, by F. Ludzack
What comes into a treatment plant must go out. This is the basis
of the solids balance concept. If you measure what comes into
your plant and can account for at least 90 percent of this material
leaving your plant as a solid (sludge), liquid (effluent), or gas
(digester gas), then you have control of your plant and know what's
going on in the treatment processes. This approach provides a good
check on your metering devices, sampling procedures, and analytical
techniques. It is an eye opener when tried for the first time and
advanced operators are urged to calculate the solids balance for
their plant.
Using the data from Section G, Raw Sludge, page 8-88, the following
example will illustrate the solids balance concept on a digester and
drying bed.
INPUT TO DIGESTER
2800 gallons of raw sludge with
solids content, 6.5% and volatile
solids content, 68%
DIGESTER OUTPUT or INPUT TO DRYING BED
Digested solids with
solids content, 4.5% and
volatile solids content, 54%
Calculate the pounds of total solids, water, volatile and inorganic
solids pumped into the digester.
Total solids to digester.
Dry
Solids, = Gals pumped x % Solids as decimal x 8.34 Ibs water/gal
Ibs
= 2800 gals x 0.065 x 8.34 Ibs/gal
= 1518 Ibs solids
Total water and solids to digester.
cv Total Solids, Ibs
Solids, = -g — •„• v-j - -r- - : - =-
,, % Solids as decimal
Ibs
1518 Ibs
0.065
= 23,400 Ibs
8-97
-------
Water to digester.
Water, Ibs = Water § Solids, Ibs - Solids, Ibs
= 23,400 Ibs - 1518 Ibs
= 21,882 Ibs
or
= 21,900 Ibs
Volatile Solids to digester.
Volatile
Solids, = Total Solids, Ibs x % Solids as decimal
Ibs
= 1518 Ibs x 0.68
= 1032 Ibs
Inorganic Solids to digester.
Inorganic
Solids, = Total Solids, Ibs - Volatile Solids, Ibs
Ibs
= 1518 Ibs - 1032 Ibs
= 486 Ibs
Calculate the percent reduction in volatile matter in the
digester to find the pounds of gas produced during digestion,
Percent reduction of volatile matter
P . m - Out
In - fin x Out)
0.68 - 0.54
0.68 - (0.68 x 0.54)
= 45%
Gas out of digester
Gas, Ibs = Volatile Solids, Ibs x % reduction as a decimal
= 1032 Ibs x .45 Ibs
= 465 Ibs
8-98
-------
Determine the pounds of total, volatile, and inorganic solids removed
from the digester to the drying bed as digested sludge.
Volatile Solids to drying bed
Volatile
Solids, = Volatile solids to digester, Ibs - Volatile solids out
Ibs as gas, Ibs
= 1032 Ibs - 465 Ibs
= 567 Ibs
Total solids to drying beds
Volatile Solids, Ibs
Total
Solids, =
Ibs
%Volatile Solids as a decimal
567 Ibs
0.54
1050 Ibs
Inorganic solids to drying beds
Inorganic
Solids, = Total Solids, Ibs - Volatile Solids, Ibs
Ibs
= 1050 Ibs - 567 Ibs
= 483 Ibs
(Note: Almost same as 486 Ibs
to digester)
Total solids and water to drying bed
Water
Solids
Ibs
Total Solids, Ibs
Solids as decimal
1050 Ibs
0.045
23,400 Ibs
(Note:
Same volume as put into
digester because of thinner
sludge going out.)
8-99
-------
Find total pounds of water to drying bed and compare amounts of
water into and out of digester.
Water to drying bed
Water, Ibs = Water £ Solids, Ibs - Solids, Ibs
= 23,400 Ibs - 1050 Ibs
= 22,350 Ibs
or say = 22,400 Ibs
Compare amounts of water in and out of digester.
Water
Change, = Water Out, Ibs - Water In, Ibs
Ibs
= 22,400 Ibs - 21,900 Ibs
= 500 Ibs drawdown in digester
In this case more water was withdrawn in the thin sludge than was
added with the thick sludge. No supernatant was withdrawn from
the digester or recycled. All of the recycle material must come
from the dewatering operation.
DRYING BED OUTPUT
Dried residue removed, 2 Ibs water/1 Ib solids
or 33% solids
Determine the pounds of water removed with the dried solids and
the pounds of drainage water recycled to the plant.
Water in solids
Water in
Solids, = Total Solids, Ibs x 2 Ibs water/lb solids
Ibs
= 1050 Ibs x 2 Ibs water/lb
= 2100 Ibs
8-100
-------
Drainage water recycled to plant
Recycle
Water, = Water to Drying Bed, Ibs - Water in Solids, Ibs
Ibs
= 22,400 Ibs - 2,100 Ibs
= 20,300 Ibs (less evaporation)
Estimate pounds of solids recycled to plant based on constituents
in drainage or recycled water. Assume the recycled water contained
3500 mg COD/1 which is equivalent to 3500 Ibs COD per million pounds
of recycled water. The 20,300 pounds of recycled water amounts to
approximately 0.02 million pounds.
Find the pounds of COD recycled.
COD, Ibs = 3500 Ibs COD/M Ibs water x M Ibs water recycled
= 3500 Ibs COD/M Ibs x 0.02 M Ibs
= 70 Ibs
Convert the recycled COD load to pounds of recycled solids assuming
1.4 pounds of COD in each pound of recycled solids.
COD, Ibs
Solids, = - --- -
COD,lbs/Solids, Ibs
70 Ibs COD
1.4 lb COD/lb Solids
= 50 Ibs
Convert the recycled TKN [Total Kjeldahl Nitrogen) load in the re-
cycled water to pounds of solids assuming a concentration of 600 mg
TKN/1.
Recycle
Solids, = 600 Ibs TKN/M Ibs water x M Ibs water recycled
Ibs
= 600 Ibs/M Ibs x 0.02 M Ibs
= 12 Ibs
8-101
-------
Estimate total recycle solids
Total
Recycle _ Recycle COD solids, Ibs + Recycle TKN Solids, Ibs
oo J.ids j
Ibs
= 50 Ibs + 12 Ibs
= 62 Ibs
SUMMARY
Constituent
Total Solids, Ibs
Volatile Solids, Ibs
Inorganic Solids, Ibs
Water, Ibs
Gas Out, Ibs
To complete the solids balance, the quantity of water actually re-
cycled and its solids content should be compared with the calculated
values. Another helpful solids balance is to compare calculated and
actual digester inputs and outputs on an annual basis.
Input to
Digester
1,518
1,032
486
21,900
Input to
Drying Bed
1,050
567
483
22,400
465
Recycle
to Plant
62
20,300
8-102
-------
8.5 OPERATIONAL CHECKS AND SAMPLING SCHEDULE
Items listed below are provided to help you keep your digester in a
healthy condition.
5.50 Daily
A. Raw Sludge Pump
1. Raw sludge volume pumped in past 24 hours. (Pump counter
reading or meter reading.)
2. Pumps operating properly (check motor, pump, packing,
suction, and discharge pressures while pump is operating).
3. Visual check of raw sludge being pumped.
4. Sludge line valve positions.
5. Pump time clock operation.
B. Recirculated Digester Sludge
(Check in mixing line or heat exchanger.)
1. Temperature of recirculated sludge.
2. Boiler and heat exchanger temperature and pressures.
3. Boiler and heat exchanger operation.
4. Recirculated sludge pump operation (check motor, pump,
packing, suction, and discharge pressures while pump
is operating).
C. Digesters
1. Drain gas line condensate traps and sedimentation trap.
2. Record digester gas pressure and/or floating cover position.
3. Read gas meter.
4. Check supernatant tubes for operation and hose down
supernatant box.
8-103
-------
5. Record level of water seal on fixed cover digester.
6. Check operation of mixing equipment.
7. Examine waste gas burner for proper operation.
8.51 Weekly
A. Sludge and Gas System Valves
Exercise all sludge and gas system valves by opening and closing.
B. Supernatant Tubes
Check all supernatant tubes for operation and sample each for
clearest supernatant to be returned to plant.
C. Supernatant Box
Hose down supernatant box and flush supernatant line to plant.
D. Lubricate Equipment
Lubricate the equipment.
8.52 Monthly
A. Scum Blanket
Check digester for scum blanket build-up.
B. Digester Structure
Examine digester structure for cracks and possible gas leaks.
C. Gas Piping System
Inspect gas piping system for leaks.
8-104
-------
8.53 Quarterly
A, Gas Safety Devices
Clean and check digester gas safety devices.
8.54 Semiannually
A. Manometers
Clean and refill gas manometers.
B. Water Seals
Flush and refill digester dome water seals.
8.55 Three to Eight Years
A. Clean and Repair Digester
Dewater digester and clean out, repair, and paint as required.
8.56 Digester Sampling Schedule
A. Daily
1. Temperature.
2. Carbon dioxide content of digester gas.
B. Twice Per Week (Minimum)
1. Recirculated sludge.
a. Volatile Acids
b. Alkalinity
c. Calculate Volatile Acid/Alkalinity Relationship
8-105
-------
C. Weekly
1. Raw sludge.
a. pH
b. Total Solids
c. Volatile Solids
2. Recirculated sludge.
a. pH
b. Total Solids21
c. Volatile Solids21
3. Supernatant
a. pH
b. Total Solids
c. Volatile Solids
D. Monthly to Quarterly
1. Sound digester by sampling from bottom up at five-foot
intervals and test for:
a. Total Solids
b. Volatile Solids
2. Use sample results from Cl) to determine:
a. Sludge concentrations at various levels in
the digester.
b. Depth of grit accumulation at bottom of digester.
(A gradual build-up of grit will occur, and you
should estimate the date when the digester will
have to be cleaned.)
c. Quantity of sludge available and condition of
sludge to be drawn to drying beds.
d. Presence of scum blanket and its thickness.
e. On mixed tanks as primary digesters the effective-
ness of digester mixing equipment in mixed primary
digesters.
21 Collect raw sludge samples daily at the start, middle, and end of
the pumping cycle. Once a week prepare a composite sample by mix-
ing the daily samples together and run total and volatile solids
tests.
8-106
-------
8.6 AEROBIC SLUDGE DIGESTION
8.60 Introduction
Aerobic digestion of solids occurs, whether intentional or not, in
any of the conventional secondary treatment processes. In the ex-
tended aeration process, the aerobic digestion process is continued
almost to the maximum obtainable limit of volatile matter reduction.
A separate aerobic digester is intended mainly to insure that re-
sidual solids from aerobic biological treatment processes are digested
to the extent that they will not cause objectionable odors during
disposal. The aerobic digester is a separate operation following
other processes to extend
decomposition of solids and
regrowth of organisms to a
point where available energy
in active cells and storage
of waste materials are suf-
ficiently low to permit the
material to be considered
stable enough for discharge
to some ultimate disposal
operation. Neither aerobic
nor anaerobic sludge digestion
completes the oxidation of
volatile materials in the
digester.
Important comparisons between
aerobic and anaerobic sludge
digestion are summarized in
the following sections.
Anaerobic Sludge Digestion
1. Does not use aeration as part of the process.
2. Works best on fresh wastes that have not been treated
by prior stabilization processes.
3. Uses putrefaction as a basic part of the process.
8-107
-------
4. Tends to concentrate sludge and improves drainability.
5. Produces methane gas that provides energy for other
operations.
6. Generates major digestion products consisting of solids,
carbon dioxide, water, methane, and ammonia.
7. Produces liquids that may be difficult to treat when
returned to the plant.
8. Generates sludges that need additional stabilization
before ultimate disposal.
Aerobic Sludge Digestion
1. Has lower equipment costs, but operating costs are higher.
2. Tends to produce less noxious odors.
3. Produces liquids that usually are easier to treat
when returned to the plant.
4. Generates major digestion products consisting of residual
solids, carbon dioxide, water, sulfates, and nitrates.
Most of these products are close to the final stabilization
stage.
5. May achieve nitrogen removal by stopping aeration long
enough to allow the conversion of nitrates to nitrogen
gas. Aeration must be restarted before sulfates are
converted to sulfides (H2S).
6. Tends to work better on partially stabilized solids from
secondary processes that are difficult to treat by the
anaerobic digestion process.
7. Produces a sludge that has a higher water content. Aerobic
sludges are difficult to concentrate higher than 4 percent
solids.
8. Uses oxygenation and mixing provided by aeration process
equipment.
9. Has less hazardous cleaning and repairing tasks.
10. Works by aerobic decay which produces less odors when
operated properly.
8-108
-------
8.61 Process Description
Aerobic digestion tanks may be either round or rectangular, eighteen
to twenty feet deep, with or without covers, depending on geographical
location and climatic conditions. The tanks use aeration equipment
(mechanical or diffused air) to maintain aerobic conditions. Each
tank has a sludge feed line at mid-depth of the tank, a sludge draw-
off line at the bottom of the tank, and a flexible, multilevel super-
natant draw-off line to remove liquor from the upper half of the tank.
Covers are used in colder climates to help maintain the temperature
of the waste being treated. Covers should not be used if they
reduce evaporative cooling too much and the liquid contents become
too warm. When the liquid becomes too warm offensive odors may
develop and the process effluent will have a very poor quality.
Aerobic digestion requires the waste solids to be held at least
twenty days in the digester. Detention time depends on the origin
of the sludge being treated. Twenty days will provide sufficient
digestion time for sludges from an extended aeration process where
the sludges are already well digested. Sludges from a contact
stabilization process require more than twenty days. When temper-
atures are very low the sludge may have to be held until the
weather warms in the spring.
8.62 Operation
Aerobic digesters are operated under the principle of extended
aeration from the activated sludge process, relying on the mode or
region called endogenous22 respiration. Aerobic digestion consists
of continuously aerating the sludge without the addition of new food,
other than the sludge itself, so the sludge is always in the endogenous
region. Aeration continues until the volatile suspended solids are
reduced to a level where the sludge is reasonably stable, does not
create a nuisance or odors, and will readily dewater.
22 Endogenous (en-DODGE-en-us): A diminished level of respiration
in which materials previously stored by the cell are oxidized.
8-109
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To place aerobic digesters (assume this plant has three aerobic
digesters) in series into service, fill the first digester with
primary effluent to within three feet of the normal water level
and start the aeration equipment. Divert to the aerobic digestion
process whenever sludge is pumped. Waste aerobic sludge from the
secondary clarifier will provide the seed to start the process.
Maintain a dissolved oxygen level near 1.0 mg/1 in the aerobic
digester.
Pump raw primary and secondary sludges to the aerobic digester in
the same manner sludge is pumped to an anaerobic digester, except
sludge concentrations in the range of 1.5 to 4 percent are commonly
pumped to the aerobic digester.
When the aerobic digester has filled to normal water level, turn
off the aeration equipment and allow the solids to settle to the
bottom of the tank. This will leave a supernatant above the solids.
Don't leave the aeration equipment off too long because odors will
start to develop.
After the solids have settled, adjust the flexible, multi-level
supernatant line to draw-off a foot or two of water from the upper
portion of the tank. Sufficient water is removed from the digester
in order to accomodate another 24-hour flow of sludges from the
primary and secondary clarifiers. Restart the aeration equipment
when sufficient water has been removed.
Water withdrawn from the aerobic digester may be discharged to a
pond or returned to the primary clarifier. If the water is returned
to the primary clarifier, the clarifier should be capable of handling
the extra flow. Primary effluents frequently have undesirably high
solids levels.
Next day, repeat the process of stopping aeration, allowing settling,
and removing a portion of the supernatant liquor to make room for
another day's pumping of sludge. After a week or two the solids
level will build-up to occupy approximately fifty percent of the tank
volume during the settling period with a suspended solids concen-
tration of 10,000 to 15,000 mg/1.
Place the second aerobic digestion tank in service at this time.
Fill the second aerobic digester with primary or secondary effluent
to within three feet of the normal water level. Transfer a foot or
so of sludge from the bottom of the first digester to the second
one, leaving sufficient room in the first to accept another 24-hour
period of sludge pumping. Start the aeration equipment in both digesters,
8-110
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On the next day supernatant should be removed only from the second
digester to the primary clarifier. Transfer enough supernatant from
the first aerobic digester to allow enough room for one day's sludge
pumping. When the second aerobic digestion tank attains the desirable
solids level, place the third aerobic digester into service.
After all three tanks are in operation, the aeration equipment is
seldom stopped in the first tank. Remove supernatant from the
second and third tanks only. Withdraw solids from the third tank
for disposal to drying beds or mechanical dewatering as required.
The water levels in the tanks should be kept equal when the tanks
are operated in a series.
New sludge is introduced into the first tank. All of the tanks
receive organisms and their stored materials as food. When starting
with new cell mass containing negligible silt, up to about 40 percent
of the volatile material can be digested. By the time the sludge
reaches the third tank most of the food has been used by the organisms,
but they still require energy. Under these conditions they use their
own cell material to the extent that only their empty shells remain.
The greatest oxygen demand is exerted in the first tank, and the
demand decreases as the sludge is moved to the second and third tanks.
Usually sufficient oxygen is being supplied in the third tank if the
sludge is kept mixed and not allowed to settle to the bottom of the
digester. Dissolved oxygen levels in the tanks should be maintained
at or above 1.0 mg/1.
8.63 Operational Records
Successful operation requires the operator to record the following
information:
1. Volume of raw and secondary sludges transferred to
the aerobic digesters.
2. Pounds of solids transferred and volatile content.
3. Volume of supernatant liquor withdrawn from last
digestion tank.
5-111
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Weekly
1. Supernatant solids and volatile solids content in digesters.
When Sludge is Withdrawn
1. Volume of sludge withdrawn for dewatering.
2. Pounds of solids dewatered and volatile content.
3. Pounds of volatile solids destroyed during digestion.
8.64 Operational Problems
A. S cum
The aerobic digesters will have to be skimmed periodically to remove
floating grease and other material that will not digest. This
material should be disposed of by incineration or burial with the
scum collected from the primary clarifier.
B. Odors
Odors should not be a problem in aerobic digestion unless insufficient
oxygen is supplied or a shock load reaches the aerobic digestion tanks.
If an odor problem does occur, a very effective cure is to recycle
sludge from the bottom of the second or third tank back to the first
tank. This is also good practice in activated sludge plants that have
bulking.problems because sludge from the last aerobic digester responds
very quickly when returned to an aerator.
C. Floating Sludge
Floating sludge may become quite thick in the second and third tanks
when aeration is stopped during removal of the supernatant. To avoid
clogging, the supernatant draw-off line should be installed so the
withdrawal point is from two to six feet below the water surface. The
floating sludge is a problem only during supernatant removal. Scum
and solids must be removed from the supernatant to prevent interference
with other treatment processes and degradation of the plant effluent.
8.65 Maintenance Problems
Usually this process requires very little maintenance. Routinely hose
the side walls of open tanks for appearance and fly control.
8-112
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A. Diffuser Maintenance
If diffused air is used for aeration, only open orifice or nozzle
type diffusers should be installed because of the daily stopping
of air flow during supernatant removal.
B. Aeration Equipment
Aeration equipment should be operated continuously except when
settling is needed for supernatant removal. Both settling and
supernatant removal should be accomplished in 0.5 to 1.5 hours.
QUESTIONS
8.6A Why do some plants have aerobic digesters?
8.6B What are some of the advantages of aerobic digestion
in comparison with anaerobic digestion?
8.6C What dissolved oxygen levels should be maintained
in aerobic digesters?
5-113
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8.7 ADDITIONAL READING
a. MOP 11, pages 39-88.
b. New York Manual, pages 85-116.
c. Texas Manual, pages 303-396 and 413-444.
d. Sewage Treatment Practices, pages 63-79.
e. Anaerobic Sludge Digestion, WPCF Manual of Practice No. 16,
Water Pollution Control Federation, 3900 Wisconsin Avenue,
Washington, D.C. 20016. Price $1.50 to members; $3.00 to
others. Indicate your member association when ordering.
f. Dague, Richard R., Digester Con t r o1, J. Water Pollution
Control Federation, Vol. 40, No. 12, p 2021 (December 1968).
g. Sludge Dewatering, WPCF Manual of Practice No. 20, Water
Pollution Control Federation, 3900 Wisconsin Avenue,
Washington, D.C. 20016. Price $3.00 to members; $5.00
to others. Indicate your member association when ordering.
END OF LESSON 5 OF 5 LESSONS
on
SLUDGE DIGESTION AND HANDLING
8-114
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DISCUSSION AND REVIEW QUESTIONS
Chapter 8. Sludge Digestion and Handling
Write the answers to these questions before continuing. The problem
numbering continues from Lesson 4.
23. Why is temperature measured in a digester?
24. Why should the temperature in the digester not
be changed by more than one degree per day?
25. What is the first warning that trouble is
developing in an anaerobic digester?
26. How would you try to stop and reverse an increasing
volatile acid/alkalinity relationship?
27. What is the percent reduction in volatile matter in
a primary digester if the volatile content of the
raw sludge is 69% and the volatile content of the
digested sludge is 51%?
P = I" - Out 0
In - (In x Out)
28. How often should the volatile acid/alkalinity
relationship in a digester be checked?
8-115
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SUGGESTED ANSWERS
Chapter 8. Sludge Digestion and Handling
8.01A Raw sludge must be digested so wastewater solids may be
disposed of without creating a nuisance.
8.01B During digestion the organic solids are broken down to
other stable products, thus reducing the solids volume
and releasing the water from the solids.
8.01C Some of the important factors in controlling sludge
digestion include regulation of food supply (organic
solids), temperature, mixing, and volatile acid/
alkalinity relationship.
8.10A Plug type valves are used in sludge lines because they
are less apt to become fouled up by rags than other
types of valves.
8.10B A positive displacement pump will continue to build
pressure with each revolution until the safety de-
vices shut the pump off, the motor stalls and over-
heats, or either the pump or the pipe breaks.
8.IOC A sludge line should never be sealed at both ends
because sludge in it can produce gas and create
pressures high enough to break the line or valves.
8.11A Normally the digester roof is designed to contain a
maximum operating pressure. If the pressure is exceeded,
the water seal could be broken, allowing air to enter the
tank and form an explosive mixture of gases. High gas
pressures may cause structural damage to the tank in
severe cases.
8.11B Fixed cover digesters must be equipped with pressure
and vacuum relief valves to break a vacuum or bleed
off excessive pressure to protect the digester from
structural damage.
8.11C Floating cover. Advantages: Fluctuates with sludge
level and gas pressure in digester. Less danger of
explosive mixtures than in fixed cover digester.
Better control of supernatant withdrawal and scum
blankets.
3-117
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8.1ID Mixing recirculated digester sludge with raw sludge pro-
vides immediate seeding of the raw sludge with anaerobic
bacteria from the digester.
END OF ANSWERS TO QUESTIONS IN LESSON 1.
8.12A The two main gaseous components of digester gas are methane
and carbon dioxide.
8.12B Digester gas is used to mix digesters; for fuel to heat
digesters and plant buildings; and to run engines on pumps,
blowers, and generators.
8.12C Digester gas must be handled with extreme caution due to
its ability to burn and explode.
8.12D The pressure relief valve is adjusted by placing the correct
amount of lead weights on the pressure relief pallet and
then checking the digester pressure with a water manometer
to insure the proper setting.
8.12E The water seal in a digester could be broken by either
excessive gas pressure or a vacuum in the tank.
8.12F The operation of either the pressure or vacuum relief valves
can create an explosive condition due to digester gas mixed
with air.
8.12G a. Cut off the gas flow in that line.
b. Put out all flames and pilot lights in the area.
c. Remove end housing and slide out cartridge contain-
ing flame arrester baffles.
d. Clean the baffles in solvent and dry.
e. Reinstall cartridge and replace end plate.
f. Return pressure to gas line and soap test for gas leaks.
8.12H Thermal valves should be checked at least once a year to
make sure that the stem and valve seat are clean and the
valve will operate when needed.
8-118
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8.121 A sediment trap should be drained as often as necessary
to prevent water from entering the gas lines, which may
be from one to three times per day.
8.12J Drip or condensate traps should be installed to keep
water out of the gas lines which would restrict gas flows.
8.12K Automatic drip and condensate traps may stick open, venting
gas to atmosphere and creating a hazardous condition.
8.12L The gas pressure of the digester system may be adjusted
by connecting a manometer to the gas system and adjusting
the regulator to hold eight inches water column of gas
pressure on the digester.
8.12M The pilot flame in the waste gas burner should be checked
daily to prevent unburned waste gas from being vented to
the atmosphere and creating a potentially hazardous condition.
8.13A A digester should have a special sampling well in order
that the tank contents may be sampled at various depths
without venting the digester gas to atmosphere.
8.14A If the temperature of the hot water in the heating coils of
this type of heating system is maintained too high, it will
cook the sludge onto the coils, thus acting as insulation
and reducing the heat transferred.
8.ISA Complete mixing greatly speeds the digestion rate by pro-
viding the bacteria with greater access to the organic
material, and retards or prevents formation of scum blankets.
8.15B Maintenance consists of compressor lubrication, condensate
drainage from the gas lines, and prevention of high back
pressure due to plugged diffusers.
8.15C An effective operation for breaking up scum in digesters
with draft tube mixers is to operate one unit (tube) as a
top suction and the other unit as a bottom suction. The
direction of flow in the tubes should be reversed each day.
8.15D Pressure gauges should be installed because if a change in
the pressures is noted, then this is an indication that the
pump is not functioning properly and the desired mixing may
not be taking place in the digester.
END OF ANSWERS TO QUESTIONS IN LESSON 2.
8-119
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8.20A Raw sludge is normally composed of solids settled and
removed from the clarifiers or sedimentation tanks.
Scum is composed mainly of grease and other floatable
material.
8.21A If too much raw sludge is added to the digester, the
acid fermentation predominates, which lowers the pH of
the sludge and slows down the methane fermenters.
8.21B A digester will usually foam and froth when large amounts
of material have been converted by the acid formers as
food for the methane bacteria group, which in turn pro-
duces large volumes of gas causing the digester to foam.
8. 2 1C Find pounds of volatile matter pumped to digester per day.
Volatile
Pulped = CVo1' SludSe» gpd) (Solids, %) (Volatile, %)(8.34 Ib/gal)
Ibs/day _ ^JQQ gal/dayj (0.065) CO. 70) (8.34 Ib/gal)
= 265 Ib/day
Find pounds of seed volatile matter needed.
0.05 Ib VM Added/day = 265 Ib VM Added/day
1 Ib VM in Digester Seed, Ib VM
Seed Ib VM - (265 Ib VM Added/day) Ib VM
' 0.05 Ib VM Added/day
= 5300 Ibs VM
Find gallons of seed sludge needed.
c j o-i j i Seed, Ib VM
Seed Sludge, gal = •*-•• - • - ........ •
K (9 Ib/gal) (Solids, %) (VM, %)
5300 Ib VM
(9 Ib/gal)(0.10)(0.50 VM)
= 11,800 gal
8.21D It is hazardous to start a digester when it is only partially
full due to explosive conditions created by a mixture of air
and methane in partially full digesters.
8-120
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8.2IE A new digester is ready for the raw sludge rate to be
gradually increased to the full plant load when it is
producing a burnable gas.
8.22A As thick a sludge as possible may be pumped to the
digester by operating the sludge pump for several
minutes each hour to clear the sludge hopper, and at
a rate not to exceed 50 gpm.
8.22B a. Better performance of primary clarifier.
b. Raw sludge will be well mixed in digester.
c. Less chance of pumping thin sludge or water to
the digester.
d. Supernatant is returned to the plant throughout
the day, rather than in one large slug.
8.22C The pumping of thin sludge should be avoided because too
much water pumped to the digester increases heating re-
quirements, reduces digester holding time, washes buffer
and seed sludge out of the digester, and imposes a
heavier supernatant load on the plant.
8.23A Lime is added to a digester in an attempt to neutralize
the acids and increase the pH to 7.0.
8.23B Assume a dosage of one pound of lime per 1000 gallons of
digester sludge.
_. ,, Digester Sludge Volume, gal
Lime Dose, Ibs = —s S i_&—
1000 gals/lb lime
100,000 gal
1000 gals/lb lime
= 100 Ibs of lime
8.23C Lime must be mixed into a slurry before being added to
a digester or it will settle to the bottom in lumps which
will harden and be ineffective.
8.23D Lime should be added daily until the volatile acids/
alkalinity relationship, gas production, and pH levels
are restored.
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8.24A Bacteria secrete enzymes that help break down compounds
that the bacteria in the digester may use as food.
8.25A To control a foaming digester, stop feeding, lower the
sludge level by a foot or two for room, start mechanical
mixers, and wash away the foam with a hose.
8.25B To prevent foam from recurring:
a. Maintain temperature in digester.
b. Feed sludge at regular, short intervals.
c. Exercise caution when breaking up scum blankets.
d. Don't overdrain sludge from digester.
e. Keep contents of digester well mixed from top
to bottom at all times.
8.26A The gas initially produced in a digester is not burnable
because it contains mostly C02. Generally digester gas
• will burn when the methane content reaches 50%, but for
use as a fuel the methane content should be at least 60%.
8.27A The purpose of the secondary digester is to allow separa-
tion of the sludge from the water, to store digested sludge,
and to allow more complete digestion. This reserve of di-
gested sludge is needed to act as seed sludge or buffer
sludge to be transferred to the primary digester if it be-
comes upset.
8.27B When raw sludge is pumped to the primary digester, usually
an equal volume of sludge from the primary digester is
transferred to the secondary digester and supernatant is
displaced from the secondary digester back to the plant.
8.27C The level of supernatant withdrawal is selected on a fixed
cover digester by selecting the supernatant tube that
reaches the clearest supernatant zone in the digester. On
floating cover tanks, the supernatant draw-off line is raised
or lowered to the clearest supernatant zone in the digester.
8.28A The rate of sludge withdrawal can be determined by watching
the gas pressure on the digester that the sludge is being
drawn from and not letting the gas pressure drop below two
inches of water column.
END OF ANSWERS TO QUESTIONS IN LESSON 3.
8-122
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8.30A Prior to applying sludge to a drying bed the operator
should loosen the sand, break the clods, and level the
sand bed.
8.30B Sludge should be drawn slowly from the digester to
prevent (1) coning of the sludge and (2) causing a
negative pressure in the digester.
8.30C To eliminate a sludge cone you should open and close
the valve rapidly to "bump" the sludge in the tank.
If the sludge remains thin, stop drawing it.
8.30D Flames and smoking should not be allowed due to the
presence of methane gas which is flammable.
8.30E
8.30F
After sludge has been applied to the drying beds, the
draw-off line should be flushed with water so the solids
won't cement in the line and one valve left open so any
gas produced will not rupture the line.
be drained if freezing is a problem.
The line should
Heavy equipment should not be used to remove dried sludge
from a sand drying bed because the equipment may damage
the underdrain system, mix the sand and gravel in the bed,
or remove sand that will have to be replaced.
,30G Volume, cu ft = Length, ft x Width, ft x Depth, ft
= 100 ft x 25 ft x 0.5 ft
Volume, yards =
No. of Trucks =
1250 cu ft
1250 cu ft
27 cu ft/cu yd
46.3 cubic yards of dry sludge
Volume, yds
Truck Capacity, yds/truck
46.3 yds
2 yds/truck
23.15 trucks
23 or 24 trucks
8-123
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8.30H If green sludge were applied to a drying bed, then the
operator should apply dry lime and if allowable, an
insecticide to control odors and insects. The sludge
should be burned or buried when dried.
8.31A To reduce drying time in a blacktop drying bed, obtain
a separate sample of the sludge applied to the bed. When
the sludge goes to the surface of the sample, open the
drain line and slowly bleed off the lower liquor. When
the sludge begins to dry and crack, mix the bed, thereby
exposing wet sludge.
8.32A A sludge lagoon is filled and then sludge is diverted to
another lagoon. The sludge in the full lagoon is tilled,
dried, and removed.
8.33A Applying sludge to land improves the condition of the
soil and returns nutrients to the soil.
8.34A Mechanical dewatering (vacuum filters and centrifuges) is
used to prepare sludge for disposal in large plants or
areas where drying beds are not feasible.
8.34B Digested sludge can be prepared for vacuum filtration
by washing by elutriation and conditioning with a coagulant.
8.34C The chemical feed rate to condition sludge is determined by
sampling and adding various dosages of flocculant to the
samples and running filterability tests with a Buchner
funne1.
8.34D The life of a filter blanket is influenced by care, mainte-
nance, and the type of material.
8.34E Centrifuges are used to dewater raw or primary sludges and
digested sludges for incinerators or furnaces.
8.34F The condition of the sludge from a centrifuge is regulated
by the sludge feed rate, bowl speed, and if chemical con-
ditioners are used, by dosage rates and pool depth.
END OF ANSWERS TO QUESTIONS IN LESSON 4.
8-124
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8.4A The temperature of a digester may be obtained from the
digester recirculation sludge line which carries sludge
from the digester to the heat exchanger or from the operating
supernatant tube.
8.4B The volatile acid/alkalinity relationship is useful in
digester control because it is the first indicator that
the digestion process is starting to get out of balance
and that corrective action is necessary.
8.4C When the volatile acid/alkalinity relationship starts
increasing, the operator should reduce the raw sludge
feed, maintain heat at the regular level, and thoroughly
mix the tank contents. If the volatile acids continue
to increase, add seed sludge from the secondary digester.
8.4D pH is a poor indicator because it is usually the last
indicator to change, and by the time it changes signifi-
cantly the digester is already in serious trouble.
8.4E Solids tests are run on digester sludge to determine the
pounds of sludge, the pounds of volatile sludge available
,to the bacteria, the pounds of volatile sludge destroyed
or reduced, the digester loading rates, reductions, and the
amount of solids handled through the system.
8.4F Volume, cu ft = Area, sq ft x Depth, ft
= -— x Depth, ft
12" I
2l(/f"tJ
2 4"
X
Volume, gal
12l(ft 12"/ft
= 0.785 x 1 sq ft x 0.33 ft
= 0.259 cu ft
= 0.259 cu ft x 7.48 gals/cu ft
= 1.93732 or 1.9 gals/stroke
8.4G Gallons = 1.2 gals/rev x 2000 rev/day
= 1.2 gals x 2000/day
= 2400 gals/day
8-125
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8.4H 1. Gallons pumped per day.
2. Pounds of dry solids/day to the digester.
3. Estimated gallons of supernatant returned to the plant.
4. Volume of sludge for ultimate disposal.
8'41 Ibs S°lldS> = Gals Pumped x % Solids x 8.34 Ibs/gal
= 3000 gals x 0.05 x 8.34 Ibs/gal
= 1251 pounds
Volatile
Content,
Ibs
= % Volatile x Ibs Dry Solids
= 0.70 x 1251 Ibs Dry Solids
= 875.70 pounds
8.4J Find % reduction, P.
P =
In - Out
x 100%
In - (In x Out)
0.70 - 0.45
0.70 - (0.'70 x 0.45)
x 100%
X 100%
x 100%
0.65 x 100%
65% reduction of volatile matter
,4K Total solids tests are run on the digester supernatant to
estimate the solids load being returned to the plant.
,4L If the total solids reached 0.5 of 1%, sludge should be
drawn or supernatant withdrawal level changed.
8-126
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8.6A Aerobic digestion is commonly used to handle waste
activated sludge because of the operational problems
encountered when a waste aerobic activated sludge
with a low solids content is placed in an anaerobic
digester.
8.6B Advantages of aerobic digestion in comparison with
anaerobic digestion include fewer operational, main-
tenance, and safety problems. Aerobic digesters do
not require mixing, heating, and gas handling
facilities. Potentially explosive methane gas is not
produced and close operational control of the volatile
acids/alkalinity relationship is not necessary.
8.6C Dissolved oxygen levels in aerobic digesters should
be above 1.0 mg/1.
END OF ANSWERS TO QUESTIONS IN LESSON 5.
8-127
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OBJECTIVE TEST
Chapter 8. Sludge Digestion and Handling
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. There may be
more than one answer to each question.
1. The environment in an anaerobic digester may be controlled
by regulating the:
1. Air supply
2. Food supply
3. Domestic water supply
4. Temperature
5. Mixing
2. Material not readily decomposed in digesters includes:
1. Rubber goods
2. Fruit
3.. Plastic
4. Hair
5. Grit
3. Sludge should be pumped from the primary clarifier to the
digester several times a day to:
1. Keep the pump from becoming clogged
2. Prevent temporary overloading of the digester
3. Maintain better conditions in the clarifier
4. Permit thicker sludge pumping
5. Prevent coning
4. Digester gas may be used as a fuel when the methane content
exceeds:
1. 25%
2. 35%
3. 50%
4. 65%
5. 75%
8-120
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5. The following precautions must be taken when applying
sludge to a drying bed:
1. Withdraw the sludge slowly from the digester
2. Loosen sand before applying sludge
3. Make sure the bed is covered with sludge
4. Never smoke in the vicinity where the sludge is
being drawn
5. When finished, flush the draw-off line and leave one
end open
6. High volatile acid/alkalinity relationship in a digester
may be caused by:
1. Overloading the tank with organic material
2. Pumping too thin a raw sludge
3. Filling the tank too full
4. Withdrawing supernatant
5. Adding lime
7. Useful digester control tests include:
1. BOD
2. pH
•3. Volatile acid/alkalinity relationship
4. DO
5. Temperature
8. Laboratory tests indicate that the volatile content of a
raw sludge was 71% and after digestion the content is 53%.
The percent reduction in volatile matter is:
1. 25%
2. 50%
3. 54%
4. 60%
5. 68%
9. Calculate the volatile matter destroyed (Ibs/day/cu ft)
in a 20,000 cubic foot digester receiving 2400 gallons per
day of raw sludge. The solids content is 5%, the volatile
content 71%t and the volatile solids are reduced 50% by
digestion:
1. .015
2. .018
3. .020
4. .023
5. .025
8-130
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10. A positive displacement pump should never be started against
a closed valve because:
1. It will pump nothing
2. Excessive pressure may damage the line, the pump, or the motor
3. The sludge will spill
4. The valve will swing open
5. The power driver will stall and overheat
11. Digester gas may be used to:
1. Heat digesters
2. Supply oxygen to activated sludge aeration tanks
3. Digest solids
4. Run engines
5. Gas rats around the plant
12. Flame arresters should be installed:
1. Between vacuum and pressure relief valves and the
digester dome
2. After sediment trap on gas line from digester
3. At waste gas burner
4. Before every boiler, furnace, or flame
5. In the vent of the waste gas burner
13. The pilot flame in the waste gas burner should be checked
daily to:
1. Make sure it has not been blown out by the wind
2. Prevent valuable gas from escaping
3. Prevent odorous gas from escaping
4. Prevent explosive conditions from developing
5. Make sure proper temperatures are maintained in the digester
14. The contents of a primary digester should be mixed to:
1. Distribute food in the tank
2. Allow solids separation
3. Prevent formation of a scum blanket
4, Warm up the sludge
5. Keep the temperature the same throughout the tank
15. Successful digester operation depends on:
1. Understanding what's happening in the digester
2. Keeping all the digested sludge out of the digester
3. Analysis and application of information from laboratory
tests
4. Cleaning the digester at regular intervals to maintain
capacity
5. Regularly checking the skimmer
8-131
-------
16. Sludge pumped to the digester should be as thick as possible:
1. To reduce heat requirements in the digester
2. So the sludge will settle to the bottom of the digester
3. So large amounts of digested sludge will not be dis-
placed to the secondary digester
4. So a scum blanket won't be formed in the digester
5. None of these
17. The temperature of a digester should not be changed more
than one degree per day to:
1. Avoid excessive heat losses
2. Avoid overloading the heat exchanger
3. Allow the walls of the digester time to expand and
contract
4. Allow the organisms in the digester time to adjust
to the temperature change
5. Allow time for heating gas to be produced in the
digester
18. The function of the water seal on the gas dome of the
digester is to keep:
1. Air from entering the digester
2. Digester gas from escaping the digester
3. Insects and rodents out of the digester
4. Sludge from leaking out of the digester
5. Foam inside the digester
19. Sludge or gas should not be removed too rapidly from
the digester because:
1. The sludge drying beds may become overloaded
2. If a vacuum develops in the tank it may collapse
3. If a vacuum develops in the tank air may be drawn in
and form an explosive mixture
4. The water seal could break
5. The waste gas burner may become overloaded
20. A scum blanket in a digester may be broken up by:
1. Vigorously mixing the digester contents
2. Burning
3. Use of long poles
4. An ax
5. Rolling back the blanket
8-132
-------
21. The purpose of the secondary digester is to allow:
1. For more sludge digestion
2. An opportunity for more mixing
3. Storage for seed sludge
4. The liquids and solids in digested sludge to separate
5. The designer to make more money
22. What could be happening if gas production in a digester
starts decreasing?
1. The volatile acid/alkalinity relationship is increasing
2. The raw sludge volume fed to the digester is decreasing
3. The raw sludge volume fed to the digester is excessive
4. The scum blanket is breaking up
54 The volatile acid/alkalinity relationship is decreasing
23. Sludge should be withdrawn slowly from a digester to prevent:
1. Coning
2. Supernatant from overloading the plant
3. Forming a vacuum in the digester
4. The possibility of an explosive gas mixture develop-
ing in the digester
5. The possibility of the digester cover collapsing
24. What would you do if the volatile acid/alkalinity relation-
ship started to increase in a digester?
1. Increase time of mixing
2. Maintain constant temperature throughout the digester
3. Decrease sludge withdrawal rates
4. Return some digested sludge
5. Reduce volume of raw sludge pumped to digester
25. After sludge has been applied to the drying bed, the sludge
draw-off line should be:
1. Closed at both ends to keep out rodents and insects
2. Open at one end to allow gas to escape
3. Washed out
4. Left full of sludge
5. Filled with plant effluent
Please write on your IBM answer sheet the total time required to work
all five lessons and this objective test.
8-133
-------
APPENDIX
Monthly Data Sheet
-------
CLEANWATER, USA
WATER POLLUTION CONTROL PLANT
MONTHLY RECORD
19
LlJ
<
Q
1
2
3
4
5
6
7
8
9
10
1 1
12
13
14
15
16
17
18
19
20
21
22
26
24
25
26
27
28
29
30
31
<
Q
s
M
T
W
T
F
S
S
M
T
W
T
F
S
S
M
T
W
T
F
S
S
M
T
W
T
F
S
S
M
MAX.
MIN.
AVG.
RAW SLUDGE
GALLONS
PER DAY
I285O
laaeo
11990
12020
11460
II72O
imo
13010
III7O
IIOOO
12000
11410
12000
II7GO
12460
11820
12280
11440
11560
12070
(i960
12510
IEI80
10560
11870
11430
11510
11840
12120
11700
13010
IO560
1 1871
% SOL IDS
2.4
3.1
3.4
3.5
3.8
1.3
1.9
2.9
2.1
4.6
4.6
1.3
afl
% VOLATILE
R07
73.5
73.1
83.4
79.2
81.7
75.3
70.6
73.2
77. 7
83.4
70.6
76.8
I
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£9
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94
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103
137
86
£9
86
120
86
—
120
IZO
92
ALKALINITY
MG/L
I45O
1400
IG90
I7OO
1790
1610
I2SO
—
1670
1400
I5S4
*
I
(9
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s
24
a4
24
24
24
24
24
2.4
2.4
2.4
24
24
24
24
24
24
24
24
24
24
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24
a4
24
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GAS
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3V 170
££800
28900
28320
aSTIO
25580
24310
24550
24550
24550
aSG40
Z5940
28750
31450
34150
32550
28400
27900
31000
32380
34420
37810
37430
375&0
37/30
35320
31150
29520
32860
37820
24310
30529
CD
£s
Li. Li.
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8?
41
39
39
39
! 32
i
33
41
32
36
SLUDGE DISPOSAL
o
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% SOLIDS
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REMARKS
-------
CHAPTER 9
WASTE TREATMENT PONDS
by
A. Hiatt
-------
TABLE OF CONTENTS
Chapter 9. Waste Treatment Ponds
Page
9.1 Introduction 9-1
9.2 History of Ponds in Waste Treatment. 9-1
9.5 Pond Classifications and Uses 9-6
9.4 Explanation of Treatment Process 9-8
9.5 Pond Performance 9-11
9.6 Starting the Pond 9-15
9.7 Daily Operation and Maintenance 9-17
9.70 Scum Control 9-17
9.71 Odor Control 9-17
9.72 Weed Control 9-18
9.73 Insect Control 9-18
9.74 Levee Maintenance 9-19
9.75 Headworks and Screening 9-20
9.76 Some Operating Hints 9-20
9.8 Surface Aerators 9-22
9.9 . Sampling and Analysis 9-22
9.90 General 9-22
9.91 Frequency and Location of Lab Samples .... 9-24
9.92 Expected Treatment Efficiencies 9-26
9.93 Response to Poor Pond Performance 9-27
9.10 Safety 9-28
9.11 Design Criteria 9-31
9.110 Location 9-31
9.111 Chemistry of Waste 9-31
9.112 Headworks and Screening 9-31
9.113 Flow Measuring Devices 9-32
9.114 Inlet and Outlet Structures 9-32
9.115 Levee Slopes 9-35
9.116 Pond Depths 9-35
9.117 Pond Loading 9-37
111
-------
Page
9.12 Acknowledgment 9-44
9.13 Additional Reading 9-44
9.14 Pond Attachment 9-47
IV
-------
GLOSSARY
Chapter 9. Waste Treatment Ponds
Advanced Waste Treatment: Any process of water renovation that up-
grades water quality to meet specific reuse requirements. May
include general cleanup of water or removal of specific parts of
wastes insufficiently removed by conventional treatment processes.
Bipf1oecu1ation (BUY-o-flock-u-LAY-shun): A condition whereby
organic materials tend to be transferred from the dispersed form
in wastewater to settleable material by mechanical entrapment and
assimilation.
Facultative Pond (FACK-ul-tay-tive): 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.
pH: pH is an expression of the intensity of the alkaline or acidic
strength of a water. Mathematically, pH is the logarithm (base 10)
of the reciprocal of the hydrogen ion concentration.
pH =
The pH may range from 0 to 14, where 0 is most acid, 14 is most
alkaline, and 7 is neutral. Natural waters usually have a pH
between 6.5 and 8.5.
Photosynthesis (foto-SIN-the-sis): 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. Land plants grow by
the same process.
Population Equivalent: A means of expressing the strength of
organic material in wastewater. Domestic wastewater consumes,
on an average, approximately 0.2 Ib of oxygen per person per
day, as measured by the standard BOD test.
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.
Tertiary Treatment (TER-she-AIR-ee): See Advanced Waste Treatment.
G-9-1
-------
Toxicity (tocks-IS-it-tee) : A condition that may exist in wastes
that will inhibit or destroy the growth or function of any organism.
G-9-2
-------
PRE-TEST
Chapter 9. Waste Treatment Ponds
The purpose of the Pre-Test is to indicate to you some of the
important material contained in this chapter. It's alright
if you don't know many answers. Please write your name and
mark the correct answers on the IBM answer sheet.
1. Ponds are used to:
1, Store wastewater while it is treated
2. Provide a surface for evaporation
3. Grow mosquitoes
4. Ice skate on
5. Grow tules
2. When starting a pond, wastewater should be added:
1. When the bottom is covered with grass
2. When the pond is empty
3. When the wind is blowing in the right direction
4. When the mayor returns from his vacation
5. When the pond bottom is covered with at least one foot
of water
3. Scum rafts may be broken up by:
1. Agitation with garden rakes
2. Jets of water from pumps
3. The use of outboard motors on boats
4. A thrashing machine
5. Breaking down the bindings
4. Important operation and maintenance aspects of ponds include
control of:
1. Odors
2. Waste gas burner
3. Scum
4. Drying beds
5. Weeds and insects
P-l
-------
5. Pond performance can be indicated by what tests?
1. pH
2. Carbon dioxide
3. Methane
4. Dissolved oxygen
5. Hardness
6. Facultative ponds are:
1. Faulty operating ponds
2, Completely aerobic
3. Aerobic on the top and anaerobic on the bottom
4. Very shallow ponds
5. The most common type in current use
7. Ponds may not operate properly if:
1. The influent organic matter content fluctuates
considerable every few days
2. Temperature stays below freezing for a long time
3. There is no scum blanket
4. The influent contains a powerful fungicide
5. The influent has a high sulfur content
8. The influent to the first pond should be discharged at the:
1. Surface
2. Mid-depth
3. Bottom of the pond
9. The effluent should leave the final pond:
1. At; the surface
2. Just below the surface with a scum baffle around the outlet
3. At the bottom of the pond
10. The pond outfall should be:
1. Free
2. Submerged
11, Minimum pond depth should be:
1. 3 feet
2. 4 feet
3. 5 feet
12. Pond loadings may be expressed in:
1. Acres per day of BOD
2. Acres of people per clay
3. Pounds of BOD per acre per day
4. Persons per acre
5. Pounds BOD/day/acre
P-2
-------
13. Pond performance is a function of:
1. Type and quantity of algae
2. pH
3. Type of soil
4. Short circuiting
5. Surface area
14. Dissolved oxygen in a pond is increased by:
1. Surface aerators
2. Photosynthesis
3. Wind action
4. Algae liberating oxygen from the water molecule
5. Sludge gases from bottom deposits floating to the surface
15. Advantages of ponds for smaller installations include:
1. No maintenance
2. Low cost to build and operate
3. No insect problems
4. Capability to handle fluctuating loads
5. Satisfactory treatment of wastes
16. Estimate the population served if the inflow to a plant is
1.2 MGD.
1. 1200
2. 6000
3. 12,000
4. 120,000
5. None of these
17. Two ponds serve a summer resort and are operated in series.
They cover an area of 150 ft by 250 ft (average width and
length of both ponds combined). The average depth is four
feet, and the average inflow is 25,000 gpd. The detention
time is approximately:
1. 40 days
2. 45 days
3. 50 days
4. 55 days
5. 60 days
18. and when the influent BOD is 200 mg/1, the organic loading
is approximately:
1. 40 Ib BOD/day/ac
2. 42 Ib BOD/day/ac
3. 45 Ib BOD/day/ac
4. 48 Ib BOD/day/ac
5. 50 Ib BOD/day/ac
P-3
-------
19. Ponds are simple to operate. (Select best answer.)
1. Very
2. Deceptively
3. Not
4. Quite
5. Sort of
P-4
-------
CHAPTER 9. WASTE TREATMENT PONDS
USED FOR TREATMENT OF WASTEWATER AND OTHER WASTES
(Lesson 1 of 3 Lessons)
9.1 INTRODUCTION
Shallow ponds (three to five feet deep) are often used to treat
wastewater and other wastes instead of, or in addition to, conven-
tional waste treatment processes. (See Figs. 9.1 and 9.2 for
typical plant layouts.) Wastes which are discharged into ponds
are treated or stabilized1 by several natural processes acting
at the same time. Heavy solids settle to the bottom where they
are decomposed by bacteria. Lighter suspended material is broken
down by bacteria in suspension.
Dissolved nutrient materials, such as nitrogen and phosphorous,
are utilized by green algae which are actually microscopic plants
floating and living in the water. The algae utilize carbon dioxide
(C02) and bicarbonates to build body protoplasm. In so growing
they need nitrogen and phosphorous in their metabolism much as
land plants do. Like land plants, they release oxygen and some
carbon dioxide as waste products.
In recent years, ponds have become more popular as treatment
facilities. Extensive studies of their performance have led to a
better understanding of the natural processes by which ponds treat
wastes. Information is also available which can help operators to
regulate the pond processes for efficient waste treatment.
9.2 HISTORY OF PONDS IN WASTE TREATMENT
The first wastewater collection systems in the ancient Orient and
in ancient Europe were discharged into adjacent bodies of water.
These systems accomplished their intended purpose until overloading,
as in modern systems, made them objectionable.
1 Stabilized Wastes. 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.
9-1
-------
In ancient times, ponds and lakes were purposefully fertilized
with organic wastes to encourage the growth of algae which, in
turn, greatly increased the production of fish due to the food
supply provided by the algae. This practice still persists and
is a recognized art in Germany.
Evidently, the first ponds constructed in the United States were
built for the purpose of excluding waste waters from intrusion into
places where they would be objectionable. Once constructed, these
ponds performed a treatment process that finally became recognized
as such. The tendency over the years has been to equate pond treat-
ment efficiency with the non-emission cf odors. Actually, the
opposite is true as the greatest organic load destroyed per unit
of area (high treatment efficiency) may be accompanied by objection-
able odors.
Armed with the current scientific knowledge of ponding and utilizing
the experience of both successes and failures, engineers have designed
and constructed a great number of ponds performing a variety of
functions since 1958. Ponds that have been designed with adequate
engineering, backed by the research of a qualified biological con-
sultant, and operated in a purposeful manner have produced successful
results.
Ponding of wastewater as a complete process offers the following
advantages for smaller installations, provided land is not costly
and the location is isolated from residential, commercial, and
recreational areas:
1. Does not require expensive equipment.
2. Does not require highly trained operating personnel.
3. Is economical to construct.
9-2
-------
INF.
FLOW
METER
L.
BAR SCREEN
V,
r
mm
t
w
DISINFECTION
EFF.
• >-
Measure,
record
f low
Remove
coarse
mater ia
Biological
Process
Chlorine Contact
(Kill pathogenic
organisms)
I
•l/J
—*- ^\^_ I
INFLUENT ^^>
r
\
1 \ H i
LJJ y-
V — "HI y — ~—
\
CHLORINATION
— ^r. — rr/~+
/ EFFLUENT
Fig. 9.1 Typical plant; ponds only
-------
4. Provides treatment that is equal to or superior to
some conventional processes.
5. Makes a satisfactory short-term method of treating
wastewater on a temporary basis until a permanent
plant can be constructed.
6. Is adaptable to fluctuating loads.
7. Is probably the most trouble-free of any treatment
process when utilized correctly, provided a consistently
high quality effluent is not required.
QUESTIONS
9.2A If a pond is giving off objectionable odors, are the
wastes being effectively treated? Explain your answer.
9.2B Discuss the advantages of ponds.
9-4
-------
INF.
FLOW , PRELIM.
MbltK * ihtAlMtNl
\
Measure, Screening,
record grit
flow removal
(Remove
coarse
material )
PRIMARY
TREATMENT
Seri
tat
imen-
on
SECONDARY $$m$ Dl SIN-
TREATMENT — * * FECTION
Biological
Process
(Remove (Remove sus-
settleable pended and
and
float
materials
^
r
na dissolved
) solids)
DIGESTION
AND
SLUDGE
HANDLING
(Solids
-> Disposa )
— — /
INFLUENT x L-
*9
— I—
|^
v,:|
TJ
• t -
CHLORINATION
1
=^MW^^V- {,/ 1 >
^llllf \ /EFFLUENT
TO DIGESTION
Fig. 9.2 Typical plant; ponds after secondary treatment
-------
9.3 POND CLASSIFICATIONS AND USES
Ponding of raw wastewater, as a complete treatment process, is
used to treat the wastes of single families as well as large
cities up to the size of the city of Melbourne, Australia, which
handles 78 million gallons of wastewater per day. Ponds designed
to receive wastes with no prior treatment are often referred to
as raw wastewater (sewage) lagoons or stabilization ponds. This
requires sizable areas of land.
Ponds are quite commonly used in series (one pond following another)
after a primary wastewater treatment plant to provide additional
clarification, BOD removal, and disinfection. These ponds are
sometimes called oxidation ponds.
Ponds are sometimes used in series after a trickling filter plant,
thus giving a form of "tertiary"2 treatment. These are sometimes
called polishing ponds.
Ponds placed in series with each other can provide a high quality
effluent which is acceptable for discharge into most watercourses,
if stringent disinfection standards are not required.
It is possible to have a great many different variations in ponds
due to depth, operating conditions, loading, etc., and a bold
line of distinction is often impossible. Current literature
generally uses three broad pond classifications: aerobic,
anaerobic, and facultative.
Aerobic ponds are characterized by having dissolved oxygen distri-
buted throughout their contents practically all of the time. They
usually require an additional source of oxygen other than the rather
minimal amount that can be diffused from the atmosphere at the water
surface. The additional source of oxygen may be supplied by algae,
by mechanical agitation of the surface, or by bubbling air through
the pond.
2 Tertiary (TER-she-AIR-ee) . Tertiary refers to the third treat-
ment process or the process following a secondary treatment
process, such as a trickling filter. Some refer to tertiary
treatment as advanced waste treatment, meaning processes that
remove wastes not normally removed by conventional (secondary)
treatment processes.
9-6
-------
Anaerobic ponds, as the name implies, are usually without any dis-
solved oxygen throughout their entire depth. Treatment depends on
fermentation of the sludge at the pond bottom. This process, under
certain conditions, can be quite odorous, but it is highly efficient
in destroying organic wastes. Anaerobic ponds are mainly used for
industrial processing wastes, although some domestic waste ponds
find their way into this category when they become badly overloaded.
Facultative (FACK-ul-tay-tive) ponds are the most common type in
current use. The upper portion (supernatant) of these ponds is
aerobic, while the bottom layer is anaerobic. Algae supply most
of the oxygen to the supernatant. Facultative ponds are most common
because it is almost impossible to maintain completely aerobic or
anaerobic conditions all the time at all depths of the pond.
Pond uses may be classified according to detention time. A pond
with a detention time of less than three days will perform in ways
similar to a sedimentation or settling tank. Some algal growth
will occur in the pond, but it will not have a major effect on the
treatment of the wastewater.
Prolific algal growth will be observed in ponds with detention
periods from three to around 20 days, but large amounts of algae
will be found in the pond effluent. In some effluents, the
stored organic material may be greater than the amount in the
influent. Detention times in this range merely allow the organic
material to change form and delay problems until the algae settle
out in the receiving waters. Effluent BODs may show considerable
reductions from influent BOD concentrations, but this is because
BOD is a rate estimate (oxygen used during a 5-day period). The
rate of oxygen used is temporarily slowed down, but will increase
when anaerobic decomposition of settled dead algal cells starts.
Longer detention periods in ponds provide time for algal sedimen-
tation, hopefully in ponds with anaerobic conditions on the bottom
and aerobic conditions on the surface. Combined aerobic-anaerobic
treatment provided by long detention periods produces definite
stabilization of the influent.
QUESTIONS
9.3A What is the difference between raw wastewater (sewage)
lagoons, oxidation ponds, and polishing ponds?
9.3B What is the difference between the terms aerobic,
anaerobic, and facultative?
9.3C Describe three possible uses of ponds.
9-7
-------
9.4 EXPLANATION OF TREATMENT PROCESS
Waste disposal ponds are classified according to their dissolved
oxygen content. Oxygen in an aerobic pond is distributed through-
out the entire depth practically all the time. An anaerobic pond
is predominantly devoid of oxygen most of the time because oxygen
requirements are much greater than the oxygen supply. In a
facultative pond, the upper portion is aerobic most of the time,
whereas the bottom layer is predominantly anaerobic.
In aerobic ponds, organic matter contained in the wastewater is
first converted to carbon dioxide and ammonia, and finally, in the
presence of sunlight, to algae. Algae are simple one-cell micro-
scopic plants which are essential to the successful operation of
both aerobic and facultative ponds.
By utilizing sunlight through photosynthesis,3 the one-celled
plant uses the oxygen in the water molecule to produce free oxygen,
making it available to the aerobic bacteria that inhabit the pond.
Each pound of algae in a healthy pond is capable of producing 1.6
pounds of oxygen on a normal summer day. Algae subsist on carbon
dioxide and other nutrients in the wastewater. Algae occur in a
pond without seeding and multiplying greatly under favorable conditions,
In anaerobic ponds, the organic matter is first converted by a group
of organisms called the "acid producers" to carbon dioxide, nitrogen,
and organic acids. In an established pond, at the same time, a
group called the"methane fermenters" breaks down the acids and
other products of the first group to form methane gas and alkalinity.
Water is another end product of organic reduction.
In a successful facultative pond, the processes characteristic
of aerobic ponds occur in the surface layers, while those similar
to anaerobic ponds occur in its bottom layers.
During certain periods sludge decomposition in the anaerobic zone
is interrupted and it begins to accumulate. If sludge accumulation
3 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. Land plants grow by the same
process.
9-8
-------
occurs and decomposition does not set in, it is probably due to
lack of suitable bacteriological population, low pH,1* presence
of inhibiting substances, or a low temperature. Under these
circumstances the acid production will continue at a slower rate,
but the rate of gas (methane) production slows down considerably.
Sludge storage in ponds is continuous with small amounts stored
during warm weather and larger amounts when it is cold. During
low temperatures the bacteriological population cannot multiply
fast enough to handle the waste. When warm weather comes, the
"acid producers" start in decomposing the accumulated sludge deposits
built up during the winter. If the organic acid production is too
great, a lowered pH will occur with the possibilities of an upset
pond and resulting hydrogen sulfide odors.
Hydrogen sulfide is ordinarily not a problem in properly designed
and operated ponds because it dissociates (divides) into hydrogen
and hydrosulfide ions at high pH and may form insoluble metallic
sulfides or sulfates. It is because of this high degree of dis-
sociation and the formation of insoluble metallic sulfides that
ponds having a pH above 8.5 do not emit odors, even when hydrogen
sulfide is present in relatively large amounts.
All of the organic matter that finds its way to the bottom of a
stabilization pond through the various processes of sludge
decomposition is subject to methane fermentation, provided that
proper conditions exist or become established'.
In order for methane fermentation to exist, an abundance of organic
matter must be deposited and continually converted to organic acids.
An abundant population of methane bacteria must be present. They
require a pH level within the sludge of from 6.5 to 7.5, alkalinity
of several hundred mg/1 to buffer (neutralize) the organic acids
(volatile acid/alkalinity relationship), and suitable temperatures.
pH. pH is an expression of the intensity of the alkaline or
acid strength of water. Mathematically, pH is the logarithm
(base 10) of the reciprocal of the hydrogen ion concentration.
pH =
The pH may range from 0 to 14, where 0 is the most acid, 14
the most alkaline, and 7 is neutral. Most natural waters
usually have a pH between 6.5 and 8.5.
9-9
-------
Once methane fermentation is established, it accounts for a
considerable amount of the organic load removal.
QUESTIONS
9.4A How is oxygen produced by algae?
9.4B Where does the algae found in a pond come from?
9.4C What happens to unstable organic matter in a pond?
9-10
-------
9.5 POND PERFORMANCE
The treatment efficiencies that can be expected by ponds vary
more than most other treatment devices. Some of the many
variables are:
1. Physical Factors
a. type of soil
b. surface area
c. depth
d. wind action
e. sunlight
f. temperature
g. short circuiting
h. inflow variations
2. Chemical Factors
a. organic material
b. pH
c. solids
d. concentration and nature of waste
3. Biological Factors
a. type of bacteria
b. type and quantity of algae
c. activity of organisms
d. nutrient deficiencies
e, toxic concentrations
The performance expected from a pond depends upon its design.
The design, of course, is determined by the waste discharge
requirements or the water quality standards to be met in the
receiving waters. Overall treatment efficiency may be about
the same as primary treatment (only settling of solids), or
it may be equivalent to the best secondary biological treat-
ment plants. Some ponds, usually those located in hot, arid
areas, have been designed to take advantage of percolation
and high evaporation rates so that there is no discharge.
Depending on design, ponds can be expected to provide BOD re-
movals of from 50 to 90%. Facultative ponds, under normal
design loads with 50 to 60 days detention time, will usually
remove approximately 90 to 95% of the coliform bacteria and
70 to 80% of the BOD load approximately 80% of the time.
9-11
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Physical sedimentation by itself has been found to remove
approximately 90% of the suspended solids in three days, and
about 80% of the dissolved organic solids in ten days. How-
ever, in a pond with a healthy algae and bacteria population,
a phenomenon known as bioflocculation5 can occur which will
remove approximately 85% of both suspended and dissolved solids
within hours. Bioflocculation is accelerated by increased tem-
perature, wave action, and high dissolved oxygen content.
Pond detention times are sometimes specified by regulatory
agencies to assure adequate treatment and removal of bacteria.
Many agencies specify effluent or receiving water quality
standards in terms of median and maximum MPN values that should
not be exceeded. In critical water use areas chlorination or
other means of disinfection can be used to further reduce the
coliform level.
A pond is generally regarded as not fulfilling its function
when it creates a visual or odor nuisance, or leaves a high BOD,
solids, grease, or coliform group bacteria concentration in the
discharge.
QUESTIONS
9.5A What is bioflocculation?
9.5B What biological factors influence the treatment
efficiency of a pond?
9.5C What factors indicate that a pond is not fulfilling
its function (operating properly)?
END OF LESSON 1 OF 3 LESSONS
on
WASTE TREATMENT PONDS
5 Bioflocculation. A condition whereby organic materials tend
to be transferred from the dispersed form in wastewater to
settleable material by mechanical entrainment and assimilation.
9-12
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DISCUSSION AND REVIEW QUESTIONS
Chapter 9. Waste Treatment Ponds
(Lesson 1 of 3 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 this lesson.
Write the answers to these questions in your notebook before
continuing.
1. When wastewater flows through different treatment processes
in a plant, where might ponds be located?
2. Why are most ponds facultative ponds?
3. Where does the oxygen in a pond come from that is produced
by algae?
4. What is photosynthesis?
5. What are the three types of factors that may influence pond
performance?
9-13
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CHAPTER 9. WASTE TREATMENT PONDS
(Lesson 2 of 3 Lessons)
9.6 STARTING THE POND
One of the most critical periods of a pond's life is the time that
it is first placed in operation. If at all possible, at least one
foot of water should be in the pond before wastes are introduced.
The water should be turned into the pond in advance to prevent
odors developing from waste solids exposed to the atmosphere. Thus
a source of water should be available when starting a pond.
It is a good practice to
start ponds during the
warmer part of the year
because a shallow starting
depth allows the contents
of the pond to cool too
rapidly if nights are cold.
Generally speaking, the
warmer the pond contents,
the more efficient the
treatment processes.
Algal blooms will normally
appear from seven to twelve
days after wastes are intro-
duced into a pond, but it
generally takes at least 60
days to establish a thriving
biological community. A
definite green color is
evidence that a flourishing
algae population has been established. After this length of time
has elapsed, bacterial decomposition of bottom solids will usually
become established. This is generally evidenced by bubbles coming
to the surface near the pond inlet where most of the sludge deposits
occur. Although the bottom is anaerobic, travel of the gas through
the aerobic surface layers generally prevents odor release.
9-15
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Wastes should be discharged to the pond intermittently during
the first few weeks with constant monitoring of the pH. The
pH in the pond should be kept above 7.5 if possible. Initially
the pH of the bottom sludge will be below 7 due to the digestion
of the sludge by acid-producing bacteria. If the pH starts to
drop, discharge to the pond should be diverted to another pond
or diluted with make-up water if another pond is not available
until the pH recovers. A high pH is essential to encourage a
balanced anaerobic fermentation (bacterial decomposition) of
bottom sludge. It also is indicative of high algal activity
since removal of the carbonates from the water in algal metabolism
tends to keep the pH high. A continuing low pH indicates acid
production which will cause odors.
QUESTIONS
9.6A Why should at least one foot of fresh water cover
the pond bottom before wastes are introduced?
9.6B Why should ponds be started during the warmer part
of the year if at all possible?
9.6C What does a definite green color in a pond indicate?
9.6D When bubbles are observed coming to the pond surface
near the inlet, what is happening in the pond?
9-16
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9.7 DAILY OPERATION AND MAINTENANCE
Because ponds are deceptively simple, they are probably neglected
more than "any other type of wastewater treatment process. Many
of the complaints that arise from ponds are the result of neglect
or poor housekeeping. Following are listed the day-to-day
operational and maintenance duties that will help to insure peak
treatment efficiency and to present your plant to its neighbors
as a well-run waste treatment facility.
9.70 Scum Control
Scum accumulation is a common characteristic of ponds and is
usually the greatest in the spring of the year when the water
warms and vigorous biological activity resumes. Ordinarily,
wind action will dissipate scum accumulations and cause them
to settle; however, in the absence of wind or in sheltered areas,
other means must be used. If scum is not broken up, it will dry
on top and become crusted. It is not only more difficult to break
up then, but a species of blue-green algae is apt to become
established on the scum which can give rise to disagreeable odors.
If scum is allowed to accumulate, it can reach proportions where
it cuts off a significant amount of sunlight from the pond.
Rafts of scum cause a very unsightly appearance in ponds and
can quite likely become a source of botulism that will have a
devastating effect on waterfowl and shore birds which may be
attracted to the facility.
Many methods of breaking up scum have been used, including agitation
with garden rakes from the shore, jets of water from pumps or tank
trucks, and the use of outboard motors on boats in large ponds.
Scum is broken up most easily if it is attended to promptly.
9.71 Odor Control
It is probably inevitable that, at some time, odors will come from
a wastewater treatment plant no matter what kind of process is used.
Most odors are caused by overloading (see Section 9.117 to determine
pond loading) or poor housekeeping practices and can be remedied
by taking corrective measures. However, there are times, such as
when unexpected shutdowns occur, that plant processes may be upset
and cause odors. For these unexpected occurrences it is strongly
advised that a careful plan for emergency odor control be available.
Odors usually occur during the spring warmup in colder climates
because biological activity is reduced during cold weather.
9-17
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For ponds, recirculation from aerobic units, the use of floating
aerators, and heavy chlorination should be considered as means
to reduce odors. Recirculation from an aerobic pond to the inlet
of an anaerobic pond (1 part recycle flow to 6 parts influent
flow) will reduce or eliminate odors. Usually floating aeration
and chlorination equipment are too expensive to have setting idle
waiting for an odor problem to develop. Odor masking chemicals
also have been promoted for this purpose and have some uses for
concentrated specific odor sources. However, in almost all cases,
process procedures of the type mentioned previously are preferable.
In any event, waiting until the emergency arises before planning
for odor control is poor procedure. Often several days are needed
to receive delivery of materials or chemicals if they are required.
Try to have possible alternate methods of control ready to go if
they are needed.
In some areas, sodium nitrate has been added to ponds as a source
of oxygen to prevent odors. To be effective, sodium nitrate must
be dispersed throughout the water in the pond. Once mixed in the
pond it acts very quickly because many common organisms (faculta-
tive groups) may use the oxygen in nitrates instead of dissolved
oxygen. Liquid sodium hydrochloride or chlorine solution is a
faster acting solution, but not necessarily the best chemical be-
cause it will interfere with biological stabilization of the wastes,
9.72 Weed Control
Weed control is an essential part of good housekeeping and is not
a formidable task with modern herbicides and soil sterilants.
Weeds around the edge are most objectionable because they allow a
sheltered area for mosquito breeding and scum accumulation. In
most average ponds there has been little need for mosquito control
when edges are kept free of weed growth. Aquatic weeds, such as
tules, will grow in depths shallower than three feet, so an operating
pond level of at least this depth is necessary. Tules may emerge
singly or well scattered but should be removed promptly by hand as
they will quickly multiply from the root system. Weeds also can
hinder pond circulation.
9.73 Insect Control
Mosquitoes will breed in sheltered areas of standing water where
there is vegetation or scum to which the egg rafts of the female
mosquito can become attached. These egg rafts are fragile and
will not withstand the action of distrubed water surfaces such as
caused by wind action or normal currents. Keeping the water edge
clear of vegetation and keeping any scum broken up will normally
give adequate control. Shallow, isolated pools left by a receding
pond level should be drained or sprayed with a larvacide.
9-18
-------
Any of several minute shrimp-like animals may infest the pond
from time to time during the warmer months of the year (March-
November) . These predators live on algae and at times will
appear in such numbers as to almost clear the pond of algae.
During the more severe infestations there will be a sharp drop
in the dissolved oxygen of the pond, accompanied by a lowered
pH. This is a temporary condition because the predators will
outrun the algae supply, and there will be a mass die-off of
insects which will be followed by a rapid greening up of the
pond again.
Ordinarily there should be no great concern about these infesta-
tions because they soon balance themselves; however, in the case
of a heavily loaded pond, a sustained low dissolved oxygen con-
tent may give rise to noxious odors. In that event any of several
commercial sprays can be used with excellent control. Dibrom-8
has been used with good results.
Chironomid midges are often produced in wastewater ponds in sufficient
numbers to be serious nuisances to nearby residential areas, farm
workers, recreation sites, and industrial plants. When emerging in
large numbers they may also create traffic hazards. At present
the only satisfactory control is through the use of insecticides
such as parathion, Abate, Sursban, and Fenthion. Control measures
are time consuming and may be difficult, particularly if there is
a discharge to a receiving stream. If possible, lower the level in
the ponds enough to contain a day's inflow before applying an
insecticide. Holding the insecticide for at least one day will
kill more insects and reduce the effect of the insecticide on re-
ceiving waters. For better results, insecticides should be applied
on a calm day and any recirculation pumps should be stopped.
9.74 Levee Maintenance
Levee slope erosion caused by wave action is probably the most
serious maintenance problem. If allowed to continue, it will
result in a narrowing of the levee crown which will make accessi-
bility with maintenance equipment most difficult.
If the levee slope is composed of easily erodable material, the
only long-range solution is the use of bank protection such as
stone riprap or broken concrete rubble.
Levee tops should be crowned so that rain water will drain over the
side in a sheet flow rather than flowing a considerable distance
along the levee crown and gathering enough flow to cause erosion
when it finally spills over the side and down the slope.
If the levees are to be used as roadways during wet weather, they
should be paved or well graveled.
9-19
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9.75 Headworks and Screening
It is important to clean the bar screen as frequently as possible.
The screen should be visited at least once or twice a day with more
frequent visits during storm periods. Screenings should be disposed
of daily in a sanitary manner, such as by burial, to avoid odors
and fly breeding.
Many pond installations have grit chambers at the headworks to
protect raw wastewater lift pumps or prevent plugging of the
influent lines. There are many types of grit removal equipment.
Grit removed by the various types of mechanical equipment or by
manual means will usually contain small amounts of organic matter
and should therefore be disposed of in a sanitary manner. Disposal
by burial is the most common method.
9. 76 Some Operating Hints
Anaerobic ponds should be covered and isolated for odor control
and followed by aerobic ponds. Floating polystyrene planks can
be used to cover anaerobic ponds and can be painted for protection
from the sun. These will help to confine odors and heat and tend
to make the anaerobic ponds more efficient.
Placing ponds in series tends to cause the first pond to become
overloaded and may never allow it to recover; the overload may
be carried to the next pond in series. Feeding ponds in parallel
allows you to distribute the incoming load evenly between units.
Whether ponds are operated in series or in parallel6 should depend
on the loading situation.
When operating ponds in series, the accumulation of solids in the
first pond may become a serious problem after a long period of use.
Periodically the flow should be routed around the first pond. This
pond should then be drained and the solids removed and buried.
PONDS IN SERIES
PARALLEL
9-20
-------
3. It can be helpful to provide for a large amount of recircu-
lation, say 25 to 100%. This allows the algae and other
aerobic organisms to become thoroughly mixed with incoming
raw wastewater. At the same time, good oxygen transfer can
be attained by passing the incoming water over a deck or
other type of aerator. This procedure can cause heat loss,
however.
4. Heavy chlorination at the recirculation point can assist in
odor control, but will probably interefere with treatment.
5. As with any treatment process, it is necessary to measure the
important parameters (DO fluctuations during a 24-hour period
and solids) at frequent, regular intervals and plot them so
that you have some idea of the direction the process is taking
in time to take corrective action when necessary.
6. When solids start floating to the surface of a pond during the
spring or fall overturn, the pond should be taken out of service
and cleaned. Measurement of the sludge depth on the bottom of
a pond also will indicate when a pond should be cleaned.
7. Before applying insecticides or herbicides, be sure to check
with appropriate authorities regarding the long term effects
of the pesticide you plan to use. Do not apply pesticides
that may be toxic to organisms in the receiving waters.
QUESTIONS
9.7A Why should scum not be allowed to accumulate on the
surface of a pond?
9.7B How can scum accumulations be broken up?
9.7C What are the causes of odors from a pond?
9.7D What precaution would you take to be prepared for an
odor problem which might develop?
9.7E Why are weeds objectionable in and around ponds?
9.7F How can weeds be controlled and removed in and around
ponds?
9.7G Why should insects be controlled?
9.7H Why should a pond be lowered before an insecticide is
applied?
9.71 Why are the contents of ponds recirculated?
9-21
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9.8 SURFACE AERATORS (Fig. 9.3)
Surface aerators have been used in two types of applications:
1. To provide additional air for ponds during the night
or during cold weather, or for overloaded ponds.
2. To provide a mechanical aeration device for ponds operated
as an aerated lagoon. Aerated lagoons operate similar to
an activated sludge aeration tank without returning any
settled activated sludge.
In both cases the aerators are operated by time clocks with estab-
lished on-off cycles. Laboratory tests on the dissolved oxygen in
a pond indicate the time period for on and off cycles to maintain
aerobic conditions in the surface layers of the pond. Adjustments
in the on-off cycles are necessary when changes occur in the
quantity and quality of the influent and seasonal weather conditions.
Some experienced operators have correlated their lab test results to
pond appearance and regulate the on-off cycles using the following
rule: If the pond has foam on the surface, reduce the operating
time of the aerator; and if there is no evidence of foam on the pond
surface, increase the operating time of the aerator.
Maintenance of surface aerators should be conducted in accordance
with manufacturer's recommendations.
9.9 SAMPLING AND ANALYSIS
9.90 General
Probably the most important sampling that can be accomplished easily
by any operator is routine pH and dissolved oxygen analysis. It is
very desirable to make pH, temperature, and dissolved oxygen tests
several times a week, and occasionally during the night, throughout
operation of the pond. These values should be recorded because
they will serve as a valuable record of performance. The time of day
should be varied occasionally for the tests so that the operator be-
comes familiar with the pond's characteristics at various times of
the day. Usually the pH and dissolved oxygen will be lowest just at
sunrise. Both will get progressively higher as the day goes on,
reaching their highest point in late afternoon.
9-22
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Fig. 9.3 Surface aerator
Courtesy of EIMCO
9-2Z
-------
It is especially important to remember to avoid getting any
atmospheric oxygen into the sample taken to measure dissolved
oxygen. This is most necessary when samples are taken in the
early morning or if the dissolved oxygen in the pond is low from
overloading. If possible, measure the dissolved oxygen with an
electric probe, being careful not to allow the membrane on the
end of the probe to be exposed to the atmosphere.
Ponds often have clearly developed individuality, each being a
biological community that is unique unto itself. Identical adjacent
ponds receiving the same influent in the same amount often have a
different pH and a different dissolved oxygen content at any given
time. One pond may generate considerable scum while its neighbor
is devoid of scum. For this reason, each pond should be given
routine testing as regards to pH and dissolved oxygen. Such
testing may indicate an unequal loading because of the internal
clogging of influent or distribution lines that might not be
apparent from visual inspection. Tests also may indicate differences
or problems that are being created by a build-up of solids or solids
recycle.
As an operator becomes familiar with operating a pond, he can soon
learn to correlate the results of some of the chemical tests with
visual observations. A deep green sparkling color generally indi-
cates a high pH and a satisfactory dissolved oxygen content. A dull
green color or lack of color generally indicates a declining pH and
a lowered dissolved oxygen content. A grey color indicates the pond
is being overloaded.
9.91 Frequency and Location of Lab Samples
The frequency of testing and expected ranges of test results vary
considerably from pond to pond, but you should establish those
ranges within which your pond functions properly. Test results will
also vary during the hours of the day. Table 9-1 summarizes the
typical tests, locations, and frequency of sampling.
Tests of pH, DO, and temperature are important indicators of the
condition of the pond, whereas BOD, coliform, and solids tests
measure the efficiency of the pond in treating wastes. BOD is
also used to calculate the loading on the pond.
In order to estimate the organic loading on the pond, the operator
must have some knowledge of the biochemical oxygen demand (BOD) of
the waste and the approximate average daily flow. Influent BOD and
solids will vary with time of day, day of week, and season, but a
pond is a good equalizer if not overloaded. Recirculation will help
an overloaded pond.
9-24
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TABLE 9-1
FREQUENCY AND LOCATION OF LAB SAMPLES
Test
Frequency
Location
Common Range
pH*
Dissolved
Oxygen (DO)*
Temperature
BOD
Coliform Group
Bacteria
Chlorine Residual
Suspended Solids
Dissolved Solids
Daily
Daily
Daily
Weekly
Weekly
Daily
Weekly
Weekly
Pond
Pond
Effluent
Pond
Influent
Effluent
Effluent
Effluent
Influent
Effluent
Influent
Effluent
7.5+
0.5-2.0 mg/1
*pH values above 9.0 and DO levels over 15 mg/1 are not uncommon.
BODs should be measured on a weekly basis. Samples should be taken
during the day at low flow, medium flow, and high flow. The average
of these three tests will give a reasonable indication of the organic
load of the wastewater being treated. If it is suspected that the
BOD varies sharply during the day or from day to day, or if unusual
circumstances exist, the sampling frequency should be increased to
obtain a clear definition of the variations. If the pond DO level
is supersaturated (Chapter 14, DO), the sample must be aerated to
remove the excess oxygen before the BOD test is performed. A typical
data sheet for a plant consisting mainly of ponds is provided in the
Appendix at the end of this chapter.
9-25
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9.92 Expected Treatment Efficiencies7
Table 9-2 is provided as a guide to indicate probable removal
efficiencies of typical ponds.
TABLE 9-2
EXPECTED RANGES OF REMOVAL BY PONDS
Item
BOD
BOD (facultative pond) 8
Coliform Bacteria
(facultative pond)
Suspended Solids
Dissolved Solids
Detention Time
50 to 60 days
50 to 60 days
After 3 days
After 10 days
Expected Removal
50 to 90%
70 to 80%9
90 to 95%
90%
80%
7 Waste Removal, % =
In
x 100%
8 Facultative Pond (FACK-ul-tay-tive) . 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.
9 Expected removal approximately 80% of the time with poorer
removals during the remainder of the time.
9-26
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Example ;
The influent BOD to a series of ponds is 300 mg/1, and the
effluent BOD is 60 mg/1. What is the efficiency of BOD removal?
BOD Removal, % = CIn " Out) x 100%
In
- (500 mg/1 - 60 mg/1)
300 mg/1
= 24° x 100%
300 mg/1
= 0.80 x 100%
= 80%
9.93 Response to Poor Pond Performance
See Section 9.7, Daily Operation and Maintenance, especially 9.76,
Some Operating Hints.
QUESTIONS
9.9A If the color of a pond is dull green or colorless,
what is happening in the pond?
9.9B Why should the pH, temperature, and dissolved oxygen
be measured in a pond?
9.9C If the pH and dissolved oxygen are dropping dangerously
low in a pond, how can this situation be corrected?
9.9D Influent BOD to a series of ponds is 200 mg/1. If the
BOD in the effluent of the last pond is 40 mg/1, what
is the BOD removal efficiency?
9-27
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9.10 SAFETY
Because a pond has little mechanical equipment does not mean
that it is devoid of hazards. Catwalks should have guard rails
and non-skid walking surfaces. Headworks and any enclosed
appurtenances should be well ventilated to prevent dangerous
gas accumulations.
WARNING
AM OPERATOR SHOULD
A.
ANW TA/^K T-HAT
POMP
Tetanus and typhoid are ever-present dangers when working around
wastewater. Adequate precautions should be observed.
Fences should surround ponds to keep unauthorized persons and
animals out of the pond area. They should be located in such a
manner that they will not interfere with mechanical or hand
maintenance of levee slopes.
QUESTIONS
9.10A What safety devices should be provided on walkways
over ponds?
9.10B Why should an operator be accompanied by a helper
when performing any dangerous task?
END OF LESSON 2 OF 3 LESSONS
on
WASTE TREATMENT PONDS
9-28
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DISCUSSION AND REVIEW QUESTIONS
Chapter 9. Waste Treatment Ponds
(Lesson 2 of 3 Lessons)
Write the answers to these questions before continuing with
Lesson 3. The problem numbering continues from Lesson 1.
6. Why should water be introduced into a new pond before
any wastewater?
7. Why is good housekeeping an important factor in
operating a properly functioning pond?
8. What precautions should be taken when applying
an insecticide?
9. Why may chlorine compounds or chlorine solution not
be the best method of odor control in a pond?
10. What lab tests measure the condition of a pond?
11. Estimate the BOD removal efficiency of a series of ponds
if the influent BOD is 250 mg/1 and the effluent BOD is
50 mg/1.
12. Why should fences be placed around ponds?
9-29
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CHAPTER 9. WASTE TREATMENT PONDS
(Lesson 3 of 3 Lessons)
9.11 DESIGN CRITERIA
A review of some common design criteria will give an insight to
the theory and operation of a pond.
9.110 Location
The general considerations for the location of other types of
wastewater treatment plants also apply to the location of ponds.
Isolation should be as great as can be economically provided.
Attention to the direction of prevailing winds with due regard
for present and projected downwind residential, commercial, and
recreational development is of utmost importance.
9.111 Chemistry of Waste
Before the design of any pond is undertaken, it should be determined
whether there are any possible toxic effects (interfere with algal or
bacterial growth) from the waste. Some natural water supplies may
have a high sulfur content or other chemicals that limit the possibility
of desired sludge decomposition.
Certain wastes, such as dairy products and wine products, are
difficult to treat because of their low pH. Any processing wai^e
should be carefully investigated before one can be certain that it
can be successfully treated by ponding. Some process wastes contain
powerful fungicides and disinfectants that may have a great inhibitive
effect on the biological activity in a pond.
9.112 Headwprks and Screening
A headworks with a bar screen is desirable to remove rags, bones, and
other large objects that might lodge in pipes or control structures.
A trash shredder is a luxury that may not be warranted. Any
material that gets past an adequate bar screen will in all
probability not harm the influent pump. Any fecal matter will
be pulverized in going through the pump.
9-31
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9.113 Flow Measuring Devices
It is highly desirable that an influent measuring device be installed
to give a direct reading on the daily volume of wastes that are
introduced into the ponds. This information, along with a BOD
measurement of the influent, is required to estimate the organic
loading on the pond. Comparison of influent and effluent flow
rates is necessary for estimating percolation and evaporation
losses.
A measuring device provides basic data for prediction of future
plant expansion needs or for detecting unauthorized or abnormal
flows. Reliable, well-kept records on flow volume help justify
budgets and greatly assist an engineer's design of a plant expansion
or new installation.
9.114 Inlet and Outlet Structures
Inlet structures should be simple and foolproof and should be
standard manufactured articles so that replacement parts are
readily available. Telescoping friction fit tubes (see Fig. 9.4)
for regulating spill or discharge height should be avoided because
a biological growth may become attached and prevent the tubes from
telescoping if they are not cleaned regularly.
A submerged inlet will minimize the occurrence of floating material
and will help conserve the heat of the pond by introducing the
warmer wastewater into the depths of the pond. Warm wastewater
introduced at the bottom of a cold water mass will channel to the
surface and spread unless it is promptly and vigorously mixed with
cold water. Warm wastewater spilled onto the surface of the pond
will spread out in a thin layer on the surface and not contribute
to the warmth of the lower regions of the pond where heat is needed
for bacterial decomposition. Inlet and outlet structures should be
so located in relation to each other to minimize possible short
circuiting.
Valves that have stems extending into the stream flow should be
avoided. Stringy material and rags will collect and form an
obstruction and may render the valve inoperative.
Free overfalls (Fig. 9.5) at the outlet should be avoided to minimize
release of odors, foaming, and gas entrapment which may hamper pipe
flows. Free overfalls should be converted to submerged outfalls if
they are causing nuisances and other problems.
9-32
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THREADED STEM
WHEEL HANDLE
VALVE BOX
V-NOTCH
FRICTION FIT
BETWEEN PIPES
Fig. 9.4 Telescoping friction fit tubes
for regulating discharge
9-33
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POND
G:
FOAM
STREAM
FREE OVERFALL--UNDESIRABLE
SCUM BAFFLE
SUBMERGED OUTLET--NO FOAMING PROBLEMS
Fig. 9.5 Free overflow and submerged outlet
9-34
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If a pond has a surface outlet, floating material can be kept
out of the effluent by building a simple baffle around the out-
let. The baffle can be constructed of wood or other suitable
material. It should be securely supported or anchored.
9.115 Levee Slopes
The selection of the steepness of the levee slope must depend on
several variables. A steep slope erodes quicker from wave wash
unless the levee material is of a rocky nature or else protected
by riprap. However, a steep slope minimizes waterline weed growth.
It is more difficult to operate equipment and to perform routine
maintenance on steep slopes. A gentle slope will erode the least
from wave wash, is easier to operate equipment on, and is easier
to perform routine maintenance on. However, waterline weed growth
will have a much greater opportunity to flourish.
9.116 Pond Depths
The operational depth of ponds deserves considerable attention.
Depending upon conditions, ponds of less than three feet of depth
may be completely aerobic if there are no solids on the bottom
(unlikely) because of the depth of sunlight penetration. This
means that the treatment of wastes is accomplished essentially by
converting the wastes to algae cell material. Ponds of this
shallow depth are apt to be irregular in performance because
algae blooms will increase to such proportions that a mass die-
off will occur with the result of all algae precipitating to the
bottom and thereby adding to the organic load. Such conditions
could lead to the creation of an anaerobic pond. The bottoms of
shallow ponds will become anaerobic when solids collect on the
bottom and after sunset.
Discharges from shallow, aerobic ponds contain large amounts of
algae. To operate efficiently these ponds should have some means
of removing the algae grown in the pond before the effluent is
discharged to the receiving waters. If the algae are not removed
from the effluent, the organic matter in the wastewater is not re-
moved or treated and the problem is merely transferred to some
downstream pool.
An observed phenomenon of lightly loaded, shallow secondary ponds
•and tertiary ponds is that they are apt to become infested with
filamentous algae and mosses that not only limit the penetration
of sunlight into the pond but hamper circulation of the pond's
contents and clog up inlet and outlet structures. When the loading
is increased, this condition improves.
9-35
-------
Pond depths of four feet or more allow a greater conservation
of heat from the incoming wastes to foster biological activity
as the ratio between pond volume and pond area is more favorable.
In facultative ponds, depths over four feet provide a physical
storage for dissolved oxygen accumulated during the day to carry
over through the night when no oxygen is released by the algae,
unless floating algae and poor circulation keep all the oxygen
near the surface. This physical storage of DO is very important
during the colder months when nights are long.
A pond operating depth of at least three feet is recommended to
prevent tule and cattail growth. Ponds less than three feet deep
should be lined to prevent troublesome weed growth. Weeds that
emerge along the shore line can be effectively controlled by
spraying with any of several products available.
QUESTIONS
9.11A Why are some wastes not easily treated by ponds?
9.11B What is the minimum recommended pond operating depth?
9.11C Why should the inlet to a pond be submerged?
9.11D Why should the outlet be submerged?
9. HE How could problems created by a surface outlet be
reduced or corrected?
9.11F Why should free overfalls be avoided?
9.11G Why are shallow ponds apt to be irregular in performance?
9.11H Why should the influent to a pond be metered?
9-36
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9.117 Pond Loading
The waste loading on a pond is generally spoken of in relation
to its area, and may be stated in several different ways:
1. Ibs of BOD per day per acre = Ibs BOD/day/acre
(This is called organic loading.)
2. inches (or feet) of depth added per day
CThis is called hydraulic loading or overflow rate.)
or 3. persons (or population served) per acre
CThis is called population loading.)
Detention time is related directly to pond hydraulic loading,
which is actually the rate of inflow of wastewater. It may be
expressed as million gallons per day (MGD), or as the number of
acre-inches per day or acre-feet per day (one acre-foot covers
one acre to a depth of one foot or twelve inches and is equal to
43,560 cu ft). We must know the pond volume in order to determine
detention time; this is most easily computed on an acre-foot basis.
A. Detention Time
„ . .. ,. , , Pond Volume (ac-ft)
Detention (in days) = - *
Influent Rate (ac-ft/day)
This equation does not take into consideration water which may be
lost through evaporation or percolation. Detention time may vary
from 30 to 120 days, depending on the treatment requirements to
be met.
B. Population Loading
Loading calculated on a population-served basis is expressed simply
as:
XT,:n A Population Served, persons
No. of Persons per Acre = —*• —*•
Area of Pond, ac
The population loading may vary from 50 to 500 persons per acre,
depending on many local factors.
9-37
-------
C. Hydraulic Loading
The hydraulic loading or overflow rate is expressed as:
, . Inflow (ac-in per day)
Inches per day = *• • • • • * «.
Pond Area, ac
The hydraulic loading may vary from half an inch to several inches
per day, depending on the organic load of the influent.
NOTE; If the wastewater inflow rate is known in million
gallons per day (MGD), it can be converted to an
equivalent number of acre-inches per day as follows:
Inflow, acre-inches per day = (Inflow, MGD) x 36.8 10
If the pond detention time is known, the hydraulic loading can
also be calculated, as follows:
T , , Depth of Pond, in
Inches per day = *•—: : *—•
Detention Time, days
D. Organic Loading
The organic loading is expressed as:
= CBOD.mg/1) (Flow, MGD) (8.54 Ibs/gal) H
day per acre) Pond area> ac
Typical organic loadings may range from 10 to 50 Ibs BOD per day
per acre.
1° 1 MGD = i*000'000 Sal x 1 cu ft x 1 ac ^ 12 in = 36 8 ac-in
day 7.48 gal 43,560 sq ft 1 ft ~ ' day
11 Recall Ibs/day = (Cone. mg/M mg)(M gal/day)(8.34 Ibs/gal)
9-38
-------
EXAMPLE CALCULATIONS
NOTE TO OPERATOR; If you have difficulty following the work shown
in Example 1 below, you should refer to the Pond Attachment at the
end of this chapter (Section 9.14) for further details. If you
have no trouble, continue with the lesson.
EXAMPLE NO. 1:
Use of the pond loading formulas can be illustrated by examining a
typical situation. The following data should be obtained so that
all the calculations can be performed:
1. Depth of Pond
2. Width of Pond
Bottom
Water Surface
Average Width
3. Length of Pond
Bottom
Water Surface
Average Length
4. Side Slopes
Essential Data
= 4 feet
412 feet
428 feet
420 feet
667 feet
683 feet
675 feet
Influent
6. BOD
7. Population
SURFACE
(2 ft horizontal
to 1 ft vertical) = 2:1
0.2 million gallons per day
0.2 MGD
200,000 gallons per day
200 mg/1
200 Ibs BOD per million Ibs of wastewater
2000 persons
9-39
-------
To calculate the loading parameters, first determine the pond area
and volume.
I. POND AREA, ACRES
Pond Area ac = .C.Avera8e Width, ft) (Average Length, ft)
' " 43,560 sq ft/ac
(420 ft)(675 ft)
43,560 sq ft/ac
= 6.51 ac
II. POND VOLUME, ACRE-FEET
Volume, ac-ft = (Area, ac)(Depth, ft)
= (6.51 ac)(4 ft)
= 26.04 ac-ft (say 26 ac-ft)
Convert flow rate from gallons per day to ac-ft/day.
Flow Rate, _ 200,000 gal cu ft ac
ac-ft/day ~ day X 7.48 gal X 43,560 sq ft
= 0.61 ac-ft/day
III. LOADING PARAMETERS
NOTE TO OPERATORS; Details for calculations in the remainder of
Example 1 have not been given. If you have trouble, go to the end
of this lesson and study Section 9.14, Pond Attachment, for details,
and try to apply them to this section.
1. Detention Time
Detention Time, _ Pond Volume, ac-ft
~ Flow Rate, ac-ft/day
26 ac-ft
0.61 ac-ft/day
= 42.6 days
9-40
-------
2. Population Loading
Number of
Persons
per acre
Population Served by Sewer System, persons
Pond Area, ac
2000 Persons
6.51 ac
= 307 persons/ac
NOTE: If there is a significant waste flow from industry mixed
in with the domestic waste, an adjustment must be made to take
the industrial waste into consideration. This is usually done
by analyzing the industrial waste and converting it to a "popu-
lation equivalent".12
3. Hydraulic Loading (Overflow Rate)
Inches per day
Depth of Pond, in
Detention Time, days
(Depth, 4 ft) (12 in/ft)
42.6 days
1.13 in/day
4. Organic Loading
Organic Load,
Ib BOD/day/ac
(BOD Cone., mg/1) (Flow, MGD) (8.34 Ib/gal)
Area, ac
200 Ib x 0.2 M gal x 8.34 Ib x 1
M Ib day gal 6.5 ac
= 51 Ibs BOD/day/ac
12 Population Equivalent. A means of expressing the strength of
organic material in wastewater. Domestic wastewater consumes,
on an average, approximately 0.2 Ib of oxygen per person per
day, as measured by the standard BOD test.
9-41
-------
EXAMPLE NO. 2:
NOTE TO OPERATORS: Details for calculations in Example 2 have not
been given. If you have trouble, go back and study the procedures
for Example 1 and try to apply them to Example 2.
Suppose that a small wastewater treatment plant must be completely
shut down for major repairs that will require several months of work.
Enough vacant land is near the plant to enable 16 acres of temporary
ponds to be constructed as raw wastewater (sewage) lagoons. Determine
if this is feasible, given the following data:
Influent Rate
BOD
Pond Area
Average Operating
Depth
1 MGD
150 mg/1
150 Ibs BOD per million Ibs of wastewater
16 acres
42 in
= 42 inches =
12 in/ft
= 3.5 ft
Assume that at least a 60-day detention period (average time the waste-
water must take to flow through the pond for disinfection) is desired
for bacterial die-off.
Assume that the organic loading (BOD) should not exceed 50 Ibs per
day per acre.
Calculate what the waste detention time would be in the pond:
One acre-foot = 325,829 gallons
Pond Volume, ac-ft = Pond Area, ac x Pond Depth, ft
= 16 ac x 3.5 ft
= 56 ac-ft
Influent Flow Rate = 1,000,000 gals per day
1,000,000 gpd
325,829 gal/ac-ft
= 3.07 ac-ft per day
56 ac-ft
Detention Time
3.07 ac-ft per day
18.2 days
9-42
-------
Thus the detention time would not be sufficient to satisfy require-
ments. Increasing the depth to 5 feet would help.
Calculate the organic loading:
at MGD)(8.34 Ibs/gal)
= (150 mg/l)(l MGD)(8.34 Ibs/gal)
= 1250 Ibs BOD per day
The organic loading per acre of pond would be:
Organic Loading, _ Loading, Ibs BOD/day
Ibs BOD/day/ac ~ Area, ac
1250 Ibs BOD per day
16 ac
= 78.1 Ibs BOD/day/ac
Therefore, the organic loading would exceed the desired maximum of
50 Ibs BOD/day/acre.
QUESTION
9.111 Given a pond receiving a flow of 2.0 MGD from 20,000
people. Influent BOD is 180 mg/1. Pond area is 24
acres, and the average operating depth is four feet.
Determine the detention time, organic loading, popu-
lation loading, and hydraulic loading.
9-43
-------
9.12 ACKNOWLEDGMENT
Liberal use has been made of the many papers presented by Professor
W. J. Oswald of the University of California at Berkeley on the sub-
ject of the treatment of wastes by ponding.
9.13 ADDITIONAL READING
a. New York Manual, page 71
b. Texas Manual, pages 283-302
c. Raw Sewage Lagoons in California, by California State Depart-
ment of Public Health, Bureau of Sanitary Engineering, Berkeley,
California, May 1969.
d. Waste Stabilization Lagoons - Design, Construction, and Operation
Practices Among Missouri Basin States, Missouri Basin Engineering
Health Council, 1960. Reproduced by U.S. Public Health Service,
Region VI, Kansas City, Missouri.
END OF LESSON 3 OF 3 LESSONS
on
WASTE TREATMENT PONDS
9-44
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 9. Waste Treatment Ponds
(Lesson 3 of 3 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 2.
13. Why is it desirable for a pond to be isolated?
14. How can scum be controlled from leaving a pond?
15. How can erosion of levee slopes be controlled?
A pond receives an inflow of 0.01 MGD from 100 people. The pond is
150 feet long, 150 feet wide, and 4 feet deep. Influent BOD is
200 mg/1. Determine the following loading parameters.
16. Detention Time in days
17. Population loading in persons per acre
18. Hydraulic loading in inches per day
19. Organic loading in pounds of BOD applied per day per acre
9-45
-------
9.14 POND ATTACHMENT (Details of Example Calculations)
References: New York Manual, pages 215-219
Chapter 15, Basic Mathematics
Solution: Example 1
I. Pond Area, sq ft = (Average Width, ft)(Average Length, ft)
A. Calculate average width.
WIDTH
WATER SURFACED
428 FT
AVERAGE WIDTH
412 FT
Average _ Water Surface Width, ft + Bottom Width, ft
Width, ft 2
428 ft + 412 ft
840 ft
428
412
840
420 ft
420
2 / 840
04
_4
00
9-47
-------
B. Calculate average length.
LENGTH
WATER SURFACE> 683 FT
AVERAGEILENGTH
667 FT
Average ^ Water Surface Length, ft + Bottom Length, ft
Lengtn , - -
ft 2
685 ft + 667 ft
2 683
667
- 155° ft 1350
2
= 675 ft 675
2 / 1350
12_
15
il
10
10_
0
C. Calculate pond area.
,
,;' = (Average Width, ft) (Average Length, ft)
= (420 ft) (675 ft) 675
420
= 283,500 sq ft QOO
1350
2700
283,500
Units: When we multiply ft by ft we obtain square feet or ft2,
9-48
-------
Area, acres = Area' S(l ft
43,560 sq ft/ac
283,500 sq ft 6.508
43,560 sq ft/ac 43560 / 283500.
261360
= 6.5 ac 22140 o
21780 0
360 00
OOP 00
360 000
348 480
11 520
Units: The sq ft on top (numerator) and bottom (denominator)
cancel out, and the /acre on the bottom shifts to the
top (numerator).
Our result is 6.508 acres, but we will round our answer off
to the nearest tenth (0.1), or 6.5. This is sufficient
accuracy.
II. Calculate pond volume.
Pond Volume, ,, , .,„. , ,. .
ac-ft = (Area, ac)(Depth, ft)
= (6.51 ac)(4 ft)
= 26.04 ac-ft
9-49
-------
SUGGESTED ANSWERS
Chapter 9. Waste Treatment Ponds
9.2A Objectionable odors coming from a pond could be caused by
development of anaerobic conditions locally or throughout
most of the pond, such as in an overloaded pond or one not
functioning properly.
9.2B Advantages of ponds include low initial and operating
costs, ease of expansion, and adaptability to fluctuating
loads, provided land is cheap.
9.3A The difference between raw wastewater (sewage) lagoons,
oxidation ponds, and polishing ponds is the amount of
treatment wastewater receives before reaching the pond.
Wastewater receiving no treatment flows directly into a
raw wastewater (sewage) lagoon. A pond located after a
primary clarifier or sedimentation tank is called an
oxidation pond, and a polishing pond is placed after a
trickling filter or activated sludge plant.
9.3B Aerobic ponds have DO distributed throughout the pond;
anaerobic ponds do not contain any DO. Most ponds are
facultative and have aerobic (have DO) conditions on
the surface and are anaerobic (no DO) on the bottom.
9.3C The use of a pond will depend on the detention period.
Ponds with detention times less than three days will act
like sedimentation tanks. In ponds with a detention period
from three to 20 days the organic material in the influent
will be converted to algae, and high concentrations of
algae will be found in the effluent. Ponds with longer
detention periods provide time for algal sedimentation and
a better effluent.
9.4A Algae produce oxygen from the water (H20) molecule.
9.4B Algae simply appear in a pond on their own without seeding.
They are found in soil, water, and air and multiply under
favorable conditions.
9-51
-------
9.4C Organic matter in a pond is converted to carbon dioxide
and ammonia and, finally, in the presence of sunlight,
to algae. The organic matter in anaerobic bottom sections
is first converted by a group of organisms called "acid
producers" to carbon dioxide, nitrogen, and organic acids.
Next, a group called the "methane fermenters" breaks down
the acids and other products of the first group to form
methane gas. Another end product of organic reduction is
water.
9.5A Bioflocculation is a condition whereby organic materials
tend to be transferred from the dispersed form in waste-
water to settleable material by mechanical entrapment and
assimilation.
9.5B Biological factors influencing the treatment efficiency
of a pond include the type of bacteria, type and quantity
of algae, activity of organisms, and nutrient deficiencies.
9.5C A pond is not functioning properly when it creates a visual
or odor nuisance, or leaves a high BOD, solids, grease, or
coliform group bacteria concentration in the effluent un-
less it was designed to be anaerobic in the first stages and
aerobic in later ponds for final treatment.
9.6A At least one foot of water should cover the pond bottom before
wastes are introduced to prevent decomposing solids from being
exposed and causing odor problems.
9.6B Ponds should be started during the warmer months because
higher temperatures are associated with efficient treat-
ment processes.
9.6C A definite green color in a pond indicates a flourishing
algae population and is a good sign.
9.6D When bubbles are observed coming to the pond surface near
the inlet, this indicates that the solids which settled to
the bottom are being decomposed anaerobically by bacterial
action.
9.7A Scum should not be allowed to accumulate on the surface of
a pond because it is unsightly, may prevent sunlight from
reaching the algae, and an odor-producing species of algae
may develop on the scum.
9.7B Scum accumulations may be broken up with rakes, jets of
water, or by use of outboard motors.
9.7C Odors are caused in ponds by overloading or poor house-
keeping.
9-52
-------
9.7D An odor control chemical should be available before an
odor problem develops. Sodium nitrate or a floating
aerator will help control odors and improve treatment of
the wastewater.
9.7E Weeds are objectionable in and around ponds because they
provide a shelter for the breeding of mosquitoes and scum
accumulation and also hinder pond circulation.
9.7F Weeds may be controlled by herbicides and soil sterilants.
9.7G Insects should be controlled because they may, in sufficient
numbers, be a serious nuisance to nearby residential areas,
farm workers, recreation sites, industrial plants, and
drivers on highways .
9.7H A pond should be lowered before the application of an
insecticide to improve the mortality of insects and reduce
the effect of the insecticide on the receiving waters by
holding the wastewater at least one day. Lowering of the
pond also will dry-up weeds and insects.
9.71 The contents of ponds are recirculated to allow algae and
other aerobic organisms to become thoroughly mixed with
incoming raw wastewater.
9.9A When a pond turns dull green, grey, or colorless, generally
the pH and dissolved oxygen have dropped too low. This
condition may be caused by overloading or lack of circulation.
9.9B pH, temperature, and dissolved oxygen should be measured
to provide a record of pond performance and to indicate
the status (health) of the pond and whether corrective
action is or may be necessary. DO may be expected to be
low in the morning and increase with sunlight hours.
9.9C When the pH and dissolved oxygen drop dangerously low,
the loading should be reduced or stopped. Recirculating
water from a healthy pond to the problem pond should help
the situation. Recirculation from outlet to inlet areas
is beneficial for seeding, DO, and mixing.
9.9D BOD Removal, % = (In jn°Ut'> x 100%
- (200 mg/1 - 40 mg/1)
~ - 200 mgVl X
200 mg/1
= 0.80 x 100%
= 80%
9-53
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9.10A Walkways over ponds should have handrails and non-skid
walking surfaces.
9.10B An operator should be accompanied by a helper when per-
forming any dangerous task because immediate aid might
prevent serious injury or loss of life.
9.11A Some wastes are not easily treated by ponds because they
contain substances with interfering concentrations which
hinder algal or bacterial growth.
9.11B The minimum recommended pond operating depth is three
feet. At shallower depths aquatic weeds become a nuisance.
9.11C The inlet to a pond should be submerged to distribute the
heat of the influent as much as possible and to minimize
the occurrence of floating material.
9.11D The outlet of a pond should be submerged to prevent the
discharge of floating material.
9.HE The discharge of floating material over a surface outlet
may be corrected by constructing a baffle around the out-
let.
9.11F Free overfalls should be avoided to minimize odors, foaming,
and gas entrapment which may hamper the flow of water in
pipes. They are generally controlled with pipes at the out-
fall.
9.11G Any pond is apt to be irregular in performance because
the algae grow, die, and settle to the bottom, thus
creating a new organic load. Algae produce and store
organic matter that must be stabilized later. Objectionable
"burps" of unstable material are common in pond effluents.
9.11H The influent to a pond should be metered to justify budgets,
indicate unexpected fluctuations in flows which may cause
upsets, and provide data for future expansion when necessary.
9.111 Given: Flow = 2.0 MGD
Population = 20,000 people
Influent BOD = 180 mg/1
Pond Area = 24 acres
Average Depth = 4 feet
Reqd.: Detention Time
Organic Loading
Population Loading
Hydraulic Loading
9-54
-------
9.111 (contd.)
Determine pond volume in acre-feet.
Volume, ac-ft = '(Area, ac)(Depth, ft)
= (24 ac)(4 ft)
= 96 ac-ft
Convert flow rate from MGD to ac-ft per day.
Flow, ac-ft/day = 2,000,000 gal cu ft x _
day 7.48 gal 43,560 sq ft
= 6.1 ac-ft/day
Determine detention time in days.
Detention Time, _ Pond Volume, ac-ft
days " Flow Rate, ac-ft/day
96 ac-ft 15.7
acre
6.1 ac-ft/day 6.1 / 96.0
6J_
= 15.7 days 350
505
450
427
Calculate organic loading in pounds of BOD per day per acre.
Organic Load, = (BOD, mg/1)(Flow, MGD)(8.54 Ibs/gal)
Ib BOD/day/ac Area, ac
180 Ib 2.0 MG 8.54 Ibs 1
X •--T—«-i J- — x. L -- ~ X
M Ib day gal 24 ac
= 125 Ib BOD/day/ac
9-55
-------
9.111 (contd.)
Estimate the population loading in persons per acre.
Population Loading, _ Population, persons
persons/ac ~ Area, ac
20,000 persons
24 ac
= 833 persons/ac
Calculate the hydraulic loading in inches per day.
Hydraulic Loading, _ Pond Depth, in
in/day Detention Time, days
C4 ft)(12 in/ft)
15.7 days
48 5.057
15.7 15. 7/ 48.0
47.1
= 3.06 in/day 900
785
1150
1099
9-56
-------
OBJECTIVE TEST
Chapter 9. Waste Treatment Ponds
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1.
1. Ponds are used to:
1. Store wastewater while it is treated
2. Provide a surface for evaporation
3. Grow mosquitoes
4. Ice skate on
5. Grow tules
2, When starting a pond, wastewater should be added:
1. When the bottom is covered with grass
2, When the pond is empty
3. When the wind is blowing in the right direction
4, When the mayor returns from his vacation
5. When the pond bottom is covered with at least one foot
of water.
3. Scum rafts may be broken up by:
1. Agitation with garden rakes
2. Jets of water from pumps
3. The use of outboard motors on boats
4. A thrashing machine
5. Breaking down the bindings
4. Important operation and maintenance aspects of ponds include
control of:
1. Odors
2. Waste gas burner
3. Scum
4. Drying beds
5. Weeds and insects
9-57
-------
5. Pond performance can be indicated by what tests?
1. pH
2. Carbon dioxide
3. Methane
4. Dissolved oxygen
5. Hardness
b. Facultative ponds are:
1. Faulty operating ponds
2. Completely aerobic
5. Aerobic on the top and anaerobic on the bottom
4. Very shallow ponds
5. The most common type in current use
7. Ponds may not operate properly if:
1. The influent organic matter content fluctuates
considerably every few days.
2. Temperature stays below freezing for a long time
3. There is no scum blanket
4. The influent contains a powerful fungicide
5. The influent has a high sulfur content
S. The influent to the first pond should be discharged at the:
1. Surface
2. Mid-depth
3. Bottom of the pond
9. The effluent should leave the final pond:
1. At the surface
2. Just below the surface with a scum baffle around the outlet
3. At the bottom of the pond
10. The pond outfall should be:
1. Free
2. Submerged
11. Minimum pond depth should be:
1. 3 feet
2. 4 feet
3. 5 feet
12. Pond loadings may be expressed in:
1. Acres per day of BOD
2. Acres of people per day
3. Pounds of BOD per acre per day
4. Persons per acre
5. Pounds BOD/day/acre
9-58
-------
13.
14.
15,
16.
17.
18.
Pond performance is a function of:
Type and quantity of algae
pH
Type of soil
Short circuiting
Surface area
1.
2.
3.
4.
5.
Dissolved oxygen in a pond is inci-eased by:
1. Surface aerators
2. Photosynthesis
3. Wind action
4. Algae liberating oxygen from the water molecule
5. Sludge gases from bottom deposits floating to the surface
Advantages of ponds for smaller installations include:
1. No maintenance
2. Low cost to build and operate
3. No insect problems
4. Capability to handle fluctuating loads
5. Satisfactory treatment of wastes
Estimate the population served if the inflow to a plant is
1.2 MGD.
1. 1200
2. 6000
3. 12,000
4. 120,000
5. None of these
Two ponds serve a summer resort
They cover an area of 150 ft by
length of both ponds combined).
feet, and the average inflow is
time is approximately:
and are operated in series.
250 ft (average width and
'Hie average depth is four
25,000 gpd. The detention
1.
2.
3.
4.
5.
and
is
1.
2.
3.
4.
5 .
40 days
45 days
50 days
55 days
60 days
when the influent
approximately :
40 Ib BOD/day/ac
42 Ib BOD/day/ac
45 Ib BOD/day/ac
48 Ib BOD/day/ac
50 Ib BCD/day/ac
BOD is 200 i>ig/l, the organic loading
-------
19. Ponds are simple to operate. (Select best answer.)
1. Very
2. Deceptively
3. Not
4. Quite
5. Sort of
Review Question:
20. Estimate the velocity in a grit chamber if a stick travels
30 feet in 40 seconds.
1. 0.50 ft/sec
2. 0.75 ft/sec
3. 1.00 ft/sec
4. 1.25 ft/sec
5. 1.33 ft/sec
Please write on your IBM answer sheet the total time required to
work all three lessons and this objective test.
9-60
-------
APPENDIX
(Monthly Data Sheet)
-------
MONTHLY RECORl
UJ
t-
<
O
1
2
3
4
5
6
7
8
9
10
1 1
12
13
14
15
in
17
IB
19
20
21
??
23
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TOTAL
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-------
CHAPTER 10
DISINFECTION AND CHLORINATION
by
Leonard W. Horn
(With a special section by J. L. Beals)
-------
TABLE OF CONTENTS
Chapter 10. Disinfection and Chlorination
Page
10.0 Principles of Wastewater Disinfection with Chlorine . 10-1
10.00 Introduction 10-1
10.01 Disinfection 10-2
10.02 Reaction of Chlorine in Wastewater ...... 10-6
10.03 Rules of Disinfection 10-10
10.04 Chlorine Requirement 10-12
10.1 Points of Chlorine Application 10-17
10.10 Collection System Chlorination 10-17
10.11 Prechlorination 10-17
10.12 Plant Chlorination 10-17
10.13 Postchlorination 10-18
10.2 Chlorination Process Control 10-19
10.20 Chlorinator Control 10-19
10.200 Manual Control 10-19
10.201 Start-Stop Control 10-19
10.202 Step-Rate Control 10-19
10.203 Timed Program Control 10-19
10.204 Flow Proportional Control 10-19
10.205 Chlorine Residual Control 10-20
10.206 Compound Loop Control 10-20
10.21 Chlorination Control Nomogram 10-22
10.22 Hypochlorinator Feed Rate 10-26
111
-------
Page
10.23 Chlorine Solution Discharge Lines,
Diffusors, and Mixing 10-28
10.230 Solution Discharge Lines 10-28
10.231 Chlorine Solution Diffusors 10-28
10.232 Mixing 10-29
10.24 Measurement of Chlorine Residual 10-30
10.5 Safety and First Aid 10-33
10.30 Chlorine Hazards 10-33
10.31 Why Chlorine Must be Handled with Care. . . . 10-35
10.32 Protect Yourself from Chlorine 10-35
10.33 First Aid Measures 10-37
10.4 Chlorine Handling 10-39
10.40 Chlorine Containers 10-39
10.400 Cylinders 10-39
10.401 Ton Tanks 10-42
10.402 Chlorine Tank Cars 10-46
10.41 Removing Chlorine from Containers 10-47
10.410 Connections 10-47
10.411 Valves 10-47
10.412 Ton Tanks 10-47
10.42 Chlorine Leaks 10-48
10.5 Chlorination Equipment and Maintenance ....... 10-55
10.50 Chlorinators 10-55
10.500 Vacuum-Solution Feed Chlorinators . . 10-55
10.501 Partial Vacuum, Pressure Type,
and Pulsating Type Chlorinators . . . 10-56
10.51 Hypochlorinators 10-56
10.52 Installation, Operation, and Maintenance. . . 10-58
IV
-------
10.53 Installation Requirements 10-60
10.530 Piping, Valves, and Manifolds .... 10-60
10.531 Chlorinator Injector Water Supply . . 10-62
10.6 Other Uses of Chlorine 10-64
10.60 Odor Control 10-64
10.61 Protection of Structures 10-65
10.62 Aid to Treatment 10-66
10.620 Sedimentation 10-66
10.621 Trickling Filters 10-66
10.622 Activated Sludge 10-67
10.623 Reduction of BOD 10-67
10.7 Acknowledgments 10-68
10.8 References 10-68
10.9 Additional Reading 10-69
v
-------
PRE-TEST
Chapter 10. Disinfection and Chlorination
Name Date
Please write your name and mark the correct answers on the IBM answer
sheet as directed at the end of Chapter 1. There may be more than
one correct answer to each question.
1. Disease producing bacteria are called:
1. Saprophytes
2. Facultative
3. Parasitic
4. Pathogenic
5. Coliform
2. Reduction of the number of pathogenic organisms in
wastewater may be accomplished by:
1. Sedimentation
2. Prechlorination
3. Postchlorination
4. Providing chlorine contact time
5. Adding orthotolidine
3. Chlorine may be applied for H^S control in the:
1. Collection lines
2. Plant headworks
3. Trickling filter
4. Aeration tank
5. Plant effluent
4. An operator should never enter a room containing high
concentrations of chlorine gas without:
1. Help standing by
2. Notifying proper authorities
3. A self-contained air or oxygen supply
5. You should never tamper with or apply heat to the
fusible plug of a chlorine container.
1. True
2. False
P-l
-------
6. Chlorine cylinders:
1. Can easily be lifted by one man
2. Can be handled safely
3. Contain a fusible metal safety plug
4. Should be rolled horizontally
5. Should be stored at temperatures above 50°F
and kept away from steam pipes
7. What should be the approximate chlorine feed rate for
a flow of 1.5 MOD and a chlorine dosage of 15 mg/1?
1. 200 lbs/24 hr
2. 100 lbs/24 hr
3. 20 lbs/24 hr
4. 10 lbs/24 hr
5. 2 lbs/24 hr
8. Chlorine should be applied continuously to:
1. Keep the plant equipment from breaking down
2, Keep the plant effluent disinfected
3. Keep the chlorine pipes from developing leaks
4, Keep the chlorine supplier in business
5. Protect the downstream water users
9. Field chlorination studies have shown that:
1. Constant vigilance is required to maintain a consistently
high degree of disinfection at most wastewater treatment plants
2. Thorough mixing of chlorine solution with wastewater is
essential to achieve maximum efficiency of coliform kill
for a given chlorine dosage.
3. Chlorine feed rates required to produce a desired dis-
infection level are constant from day to day.
4. Actual contact time in most chlorine chambers is the
same as the theoretical contact time.
5. Chlorine residuals can be increased without limit and
the coliform densities will always continue to be reduced
with each increase in residual.
10. Chlorinators should be located:
1. Near point of application
2. Outdoors
3. In a separate room
4. In a room that will not allow chlorine to leak into rooms
where operators work or where controls and equipment are
located.
5. In an adequately heated room
11. Postchlorination is generally more effective in a well-
clarified effluent than in a turbid one.
1. True
2. False
P-2
-------
12. Teflon tape makes a good:
1. Joint lubricant
2. Leak stopper
13. Hydrogen sulfide is found in most collection systems.
1. True
2. False
14. To protect the health of downstream water users, treatment
plant effluents must be:
1. Sterilized
2. Disinfected
15. Hydrogen sulfide:
1. Is associated with corrosion
2. Causes odors
3. Smells like chlorine
4. Can paralyze your respiratory system
5. Can form an explosive mixture with air
P-3
-------
GLOSSARY
Chapter 10. Disinfection and Chlorination
Amperometric (am-PURR-o-MET-rick): A method of measurement that
records electric current flowing or generated, rather than record-
ing voltage. Amperometric titration is an electrometric means of
measuring concentrations of substances in water.
Bacteria (back-TEAR-e-ah): 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.
Biodegradation (BUY-o-de-grah-DAY-shun): The breakdown of
organic matter by bacteria to more stable forms which will
not create a nuisance or give off foul odors.
Chioramines (KLOR-a-means): Chloramines are compounds formed
by the reaction of chlorine with ammonia.
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, nature and amount
of the impurities in the water.
Chlorine Requirement: The amount of chlorine which must be added
to produce the desired result under stated conditions. The result
(the purpose of chlorination) may be based on any number of criteria,
such as a stipulated coliform density,.a specified residual chlorine
concentration, the destruction of a chemical constituent, or others.
In each case a definite chlorine dosage will be necessary. This
dosage is the chlorine requirement.
Chlororganic (chlor-or-GAN-nick): Chlororganic compounds are organic
compounds combined with chlorine. These compounds generally originate
from or are associated with living or dead organic materials.
G-10-1
-------
Coliform (COAL-i-form): The coliform group of organisms is a
bacterial indicator of contamination. This group has as one
of its primary habitats the intestinal tract of human beings.
Coliforms also may be found in the intestinal tract of warm-
blooded animals, and in plants, soil, air, and the aquatic
environment.
Colorimetric: A means of measuring unknown concentrations of
water quality in a sample by comparing the sample's color, after
the addition of specific reagents, with the color of known con-
centrations.
Degradation (de-grah-DAY-shun): The conversion of a substance to
simpler compounds.
Disinfection (DIS-in-feck-shun): The process by which pathogenic
(disease) organisms are killed. There are several ways to dis-
infect but chlorination is the most frequently used method in water
and wastewater treatment.
Enteric: Intestinal.
Enzymes (EN-zimes): Enzymes are substances produced by living
organisms that speed up chemical changes.
Hepatitis; Hepatitis is an acute viral infection of the liver
(yellow jaundice).
Hypochlorinators : Hypochlorinators are devices that are used to
feed calcium, sodium or lithium hypochlorite as the disinfecting
agent.
Hypochlprites (hi-po-KLOR-ites): Hypochlorites are compounds
containing chlorine that are used for disinfection. They are
available as liquid or solids (powder, granules, and pellets),
in barrels, drums, and cans.
MPN: MPN is the Most Probable Number of coliform group organisms
per unit volume. Expressed as density of organisms per 100 ml.
Motile (MO-till) : Motile organisms exhibit or are capable of
movement.
Nomogram; A chart or diagram containing three or more scales
used to solve problems with three or more variables instead of
using mathematical formulas.
Orthotolidine (or-tho-TOL-i-dine): Orthotolidine is a clori-
metric indicator of chlorine residual in which a yeHow-colored
compound is produced.
G-10-2
-------
Parasitic Bacteria (PARA-SIT-tick): Parasitic bacteria are those
bacteria which normally live off another living organism, known as
the host.
Pathogenic (path-o-JEN-nick) Organisms: Bacteria or viruses 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 waste-
water treatment processes actively cleaning up organic wastes.
PostChlorination: Chlorination of the plant discharge or effluent
following plant treatment.
Prechlorination: Chlorination at the headworks of a plant;
influent Chlorination prior to plant treatment.
Re 1 ique fact i on (re-LICK-we-FACK-shun): The return of a gas to a
liquid. For example, a condensation of chlorine gas returning to
the liquid form.
Residual Chlorine: Residual chlorine is the amount of chlorine
remaining after a given contact time and under specified conditions.
Saprophytes (SAP-pro-fights): Organisms living on dead or decaying
organic matter; they help natural decomposition of the organic
solids in wastewater.
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.
G-10-3
-------
CHAPTER 10. DISINFECTION AND CHLORINATION
(Lesson 1 of 4 Lessons)
10.0 PRINCIPLES OF WASTEWATER DISINFECTION WITH CHLORINE
10.00 Introduction
Wastewater contains organisms from both the healthy and sick
people discharging their wastes into the collection system.
Disease-producing organisms are potentially present in all
wastewaters, and these organisms must be removed or killed before
treated wastewater can be discharged to the receiving waters.
The purpose of disinfection is to destroy pathogenic organismsl
and thus prevent the spread of water-borne diseases.
tfACTVi 0 <=>& N
The conventional waste treatment processes described in previous
chapters remove pathogens from wastewater in varying degrees.
The destruction and removal of pathogens is brought about in
several ways:
1. Physical removal through sedimentation and filtration
2. Natural die-away of organisms in an unfavorable environ-
ment during storage
3. Destruction by chemicals introduced for treatment purposes
1 Pathogenic (path-o-JEN-nick) Organisms. Bacteria or viruses
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.
10-1
-------
Although the number of microorganisms in polluted waters is
reduced by treatment processes and natural purification, the
term disinfection is used in practice to describe treatment
processes that have as their major objective the killing of
pathogenic organisms (Fig. 10.1). Because chlorine and some
of its compounds disinfect so well, and because they are
available at reasonable cost, they have been used almost to
the exclusion of other disinfecting agents. This chapter on
disinfection will be concerned primarily with the principles
and practice of chlorine disinfection.
10.01 Disinfection
The main use of chlorine in domestic waste treatment is dis-
infection. Strictly defined, disinfection is the destruction
of all pathogenic organisms, while sterilization is the total
destruction or removal of all microorganisms. When wastewater
effluents are discharged to receiving waters which may be used
as a source of public water supply, shellfish growing areas,
or for recreational purposes, treatment for the destruction of
pathogenic organisms is required to minimize the health hazards
of pollution of these receiving waters. Such treatment is known
as disinfection.
Chlorination for disinfection purposes requires killing essentially
all of the pathogens in the domestic waste effluent. Many other
sensitive organisms in contact with chlorine are destroyed too.
No attempt is made to sterilize wastewater, which is both un-
necessary and impractical. In some instances sterilization would
be detrimental where other treatment, dependent upon the activity
of the saprophytes,2 follows chlorination. Chlorine is a non-
selective killer. It affects organisms on the basis of sensitivity,
growth rate, concentration and exposure time.
2 Saprophytes (SAP-pro-fights). Organisms living on dead or
decaying organic matter; they help natural decomposition of
the organic solids in wastewater.
10-2
-------
TREATMENT
n REMOVE KOC&,
REMOVAL
AMP
F&EStiZMZ WA4TEWATE&.
M/P MEIW KEMOVg
Fig. 10.1 Typical flow diagram of wastewater treatment plant
10-3
-------
To accomplish disinfection, sufficient chlorine must be added
to satisfy the chlorine demand3 and leave a residual chlorine1*
that will destroy bacteria.The residual must be maintained
for a sufficient "contact time" to insure killing the pathogens.
For most wastewater, extending chlorine contact time can be
more effective than increasing dosages.
Special laboratory equipment is necessary to measure the effec-
tiveness of chlorination for reducing the number of bacteria.
The tests require several days to complete. Thus bacterial
examinations are not generally practical for the day-to-day
control of the application of chlorine. For many years dis-
infection requirements often specified an orthotolidine5
chlorine residual of 0.5 milligrams per liter after a chlorine
contact time of thirty minutes. Compliance with this require-
ment generally resulted in MPNs6 of about 3000 coliform7
organisms per 100 ml (California, 1966). However, this result-
ing MPN may vary considerably (several orders of magnitude) from
plant to plant. Considering dilution with water having a low coliform
content, this standard appeared suitable when public contact with
the waters was limited. Today people are living more intimately
with wastewater than ever before. Wastewater effluents are
3 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, nature and amount of
impurities in water. Chlorine Demand = Chlorine Applied -
Chlorine Residual.
4 Residual Chlorine. Residual Chlorine is the amount of chlorine
remaining after a given contact time and under specified conditions.
5 Orthotolidine (or-tho-TOL-i-dine). Orthotolidine is a colorimetric
indicator of chlorine residual in which a yellow-colored compound
is produced.
6 MPN. MPN is the Most ^Probable Number of coliform group organisms
per unit volume expressed as density of organisms per 100 ml.
7 Coliform (COAL-i-form). The coliform group of organisms is a
bacterial indicator of contamination. This group has as one
of its primary habitats the intestinal tract of human beings.
Coliforms also may be found in the intestinal tract of warm-
blooded animals, and in plants, soil, air, and the aquatic en-
vironment.
10-4
-------
used for irrigating
lawns, parks, ceme-
teries, freeway
planting, golf
courses, college
campuses, athletic
fields, and other
public areas.
Recreational lakes
used for boating,
swimming, water
skiing, fishing, and
other water sports
are frequently made
up partially and,
in a few cases,
solely of treated
effluents. As public
contact has increased
and diluting waters
have decreased or
become of poor
quality, it has become obvious that more consideration must be given
to disinfection practices.
QUESTIONS
10.OA What is the purpose of disinfection? Why is this important?
10.OB How are pathogenic bacteria destroyed or removed from water?
10.OC Why is chlorination used for disinfection?
10.OD Why are wastes not sterilized?
10-5
-------
10.02 Reaction of Chlorine in Wastewater
In order to determine where in the treatment process and how much
chlorine should be applied to accomplish the purpose desired, it
is necessary to know the action of chlorine when added to waste-
water.
Chlorine is an extremely active chemical that will react with many
compounds to produce may different products. If a small amount of
chlorine is added to wastewater, it will react rapidly with such
substances as hydrogen sulfide, thiosulfates (industiral wastes),
and ferrous iron. Under these conditions, chlorine is converted to
chloride and little or no disinfection will result. If enough
chlorine is added to react with all of these substances, called re-
ducing compounds, a little more chlorine added will react with
ammonia or other nitrogenous compounds present and form chloramines,
which have disinfecting action. Again, if enough chlorine is added
to react with all the reducing compounds and all the nitrogenous
matter, this chlorine will react with organic matter to produce
chlororganic compounds8 or other combined forms of chlorine, which
have slight disinfecting action. Finally, if enough chlorine is
added to react with all of the above compounds, any additional
chlorine will form free available chlorine (HOC1) which has the
highest disinfecting action. (Fig. 10.2, Page 10-9)
The exact mechanism of this disinfection action is not fully known.
In some theories, chlorine is considered to exert a direct action
against the bacterial cell, thus destroying it. A more recent
theory is that the toxic character of chlorine inactivates the
enzymes9 upon which the living microorganisms are dependent for
utilizing their food supply. As a result, the organisms die of
starvation. From the point of view of wastewater treatment, the
mechanism of the action of chlorine is much less important than
its effects as a disinfecting agent.
8 Chlororganic (chlor-or-GAN-nick). Chlororganic compounds are
organic compounds combined with chlorine. These compounds
generally originate from or are associated with living or dead
organic materials
9 Enzymes (EN-zimes). Enzymes are substances produced by living
organisms that speed up chemical changes.
10-6
-------
The quantity of reducing substances, both organic and inorganic,
in wastewater varies, so the amount of chlorine that has to be
added to wastewater for different purposes will vary. The
chlorine used by these organic and inorganic reducing substances
is defined as the chlorine demand. It is equal to the amount
added minus that remaining as combined chlorine after a period
of time, which is generally thirty minutes. Thus,
Chlorine Demand = Chlorine Dose - Chlorine Residual
Although significant kill of sensitive organisms occurs while
the chlorine demand is being satisfied, disinfection is caused
primarily by that amount remaining after the chlorine demand
has been satisfied. This quantity of chlorine in excess of the
chlorine demand is defined as residual chlorine and is expressed
as milligrams per liter (mg/1).
It should be noted that in wastewater treatment chlorination
is not normally to the "break point" (Fig. 10.2) so that a
free residual would exist. The "break point" for good secondary
effluent would be a chlorine dosage of approximately 150 mg/1.
Thus we are talking primarily about a combined residual. However,
with some of the more advanced treatment processes in which a
high degree of nitrification occurs, treatment to free chlorine
residuals beyond the break point is possible at a chlorine dose
of less than 25 mg/1.
Both chlorine addition and contact time are essential for organism
kill.Experimental determination of the best combination of
combined residual and contact time is necessary to insure both
proper chlorination and minimum use of chlorine. Changes in pH
affect the disinfection ability of chlorine and the operator must
reexamine the best combination of chlorine addition and contact
time when the pH fluctuates.
It must be emphasized that wastewaters are not and need not be
carried to a free residual for effective bactericidal action
at the present time in most locations. With increasingly stringent
receiving water standards requiring higher quality effluents in
the future, the need for disinfection to the free chlorine residual
is a distinct possibility. Complete disinfection ("kill" of patho-
genic bacteria and viruses) is assured mainly by chlorination to a
free available chlorine residual.
Calculation of the chlorine dosage and chlorine demand is illustrated
in the following problem.
10-7
-------
EXAMPLE:
A chlorinator is set to feed 50 pounds of chlorine per 24
hours; the wastewater flow is at a rate of 0.85 MGD, and the
chlorine as measured by the OT (orthotolidine) tests after
thirty minutes of contact is 0.5 mg/1. Find the chlorine
dosage and chlorine demand in mg/1.
Chlorine Feed
or Dose, mg/1
Chlorine
Demand, mg/1
59.
0.85 / 50.00
42 5
7 50
7 65
50 Ibs chlorine/day
0.85 MG/day
59 Ibs chlorine per MG
59 Ibs chlorine/MG
8.34 Ibs/gal
7.1 Ibs chlorine/million pounds water
7.1 ppm (p_arts per million parts)
7.1 mg/1
Chlorine Dose, mg/1 - Chlorine Residual, mg/1
7.1 mg/1 - 0.5 mg/1
6.6 mg/1
QUESTIONS
10.OE How does chlorine react with wastewater?
10.OF How much chlorine must be added to waste-
water to produce disinfecting action?
10.OG How is the chlorine demand determined?
10.OH How is the chlorine dosage determined?
10.01 Calculate the chlorine demand of treated
domestic wastewater if:
Flow Rate = 1.2 MGD
Chlorinator = 70 Ibs of chlorine per 24 hours
Residual = 0.4 mg/1 after thirty minutes
10-8
-------
o
I
10
CHLORINE
RESIDUAL,
mg/l
INITIAL
CHLORINE
DEMAND
COMBINED
RESIDUAL
CHLORINE
OXIDATION OF
COMBINED RESI-
DUAL MATERIALS
(CHLORAMINES)
BREAK POINT
FOR SECONDARY
HASTEWATER,
APPROXIMATELY
25 TO 150 MG/L
FREE CHLORINE
RESIDUAL ON A
1 TO 1 BASIS
CHLORINE DOSAGE, mg/l
Fig. 10.2 Break-point chlorination curve
-------
10.03 Rules of Disinfection
The State of California presently (1969) specifies the coliform
MPN in the effluent as a primary standard for effectiveness of
disinfection. It has been established that the bacteria causing
enteric10 diseases are less resistant to the chlorine than the
non-pathogenic intestinal bacteria, designated as the coliform
group. For this reason the destruction of the coliform group
of bacteria generally provides an effective criterion of waste-
water disinfection. However, certain viruses, spores, and
pathogenic bacteria inside solids may be more resistant than
coliform group bacteria to chlorine. When a chlorine residual
criterion is also set, it is considered to be a secondary
standard and is valid only if, and as long as, bacterial kill
meets the MPN standard. One sample is not as meaningful as a
series of samples indicating trends.
Studies have shown great variation in MPNs in chlorinated waste-
water samples even under apparently similar conditions. These
variations occur for numerous reasons, some of which are as
follows:
1. MPN does not directly measure the true number of coli-
form bacteria present, but rather is an expected or
probable number based on analysis of samples from a
large population (all of the wastewater flowing by
the sampling point).
2. Small samples from large amounts of a source are not
representative unless the source is uniform, and cer-
tainly wastewater is far from uniform.
3. Many variables affect the number of coliform bacteria
present in a chlorinated waste: numbers and charac-
teristics of bacteria prior to chlorination, concen-
tration and nature of the specific agent accomplishing
the disinfection, accessibility of the disinfectant
to the microorganisms, and various environmental factors.
4. The test is not always performed under ideal conditions.
For example, culture media dilutions or other factors
may be unfavorable for valid coliform counts.
10 Enteric: Intestinal
10-10
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Several different methods including MPNs, membrane filters, and
fecal coliforms may be specified for defining adequate disinfection,
The format used is geared to fit the specific discharge and the
downstream uses of the receiving waters. Check with your state
regulatory agency for the requirements applicable to your plant.
Because of limited laboratory facilities available at most waste-
water treatment plants, the following statement has been included
in disinfection requirements issued in California:
"Methods other than bacterial testing for the demonstra-
tion of effectiveness of disinfection will be accepted *
after the discharger has provided sufficient labora-
tory data showing that statistically sound correlation11
exists at all times between bacterial results and
measurements produced by the alternate proposed method."
Many of the smaller dischargers in California have asked the
State for assistance in correlating chlorine residual and coli-
form MPN. The State has conducted studies at several plants.
The studies have not been of a research nature, but were con-
ducted for the purpose of determining whether disinfection as
being practiced at the specific plants was adequate to protect
the public health. Following are some of the findings from
these studies:
1. It is difficult to maintain a consistently high
degree of disinfection at most wastewater treat-
ment plants. Chlorination is apparently more
effective in a well-clarified effluent than one
in which significant suspended solids are present.
A lump of solids may consume available chlorine
before the chlorine penetrates the particle.
Organisms imbedded within the particle are thus
protected from the chlorine and are not disin-
fected.
2. Thorough mixing of chlorine solution with the waste-
water is essential to achieve maximum efficiency of
coliform kill for a given chlorine dosage.
3. Higher chlorine residuals (after a given contact time)
are required for primary treated wastes than for
secondary treated wastes to effect a comparable coli-
form quality.
4. Two-stage chlorination (pre- and post-chlorination)
provides more consistent production of low coliform
density than postchlorination alone.
11 Correlation: Relationship
10-11
-------
9.
10,
Generally speaking, a correlation exists between chlorine
residual and coliform density. (Coliform densities de-
crease with increased chlorine residuals.) The individu-
alities of wastewater treatment plants and their effluent
conditions, as well as sampling and analysis techniques,
make it difficult to apply a correlation determined from
one plant to other plants.
Chlorine residuals, and corresponding feed rates, required
to afford a desired disinfection level vary from day to
day and from morning to afternoon at most treatment plants.
Increases in chlorine residuals above a certain point do
not appear to reduce coliform densities significantly.
Increases in detention time above a certain point do not
appear to reduce coliform densities significantly.
The actual contact time in most chlorine contact chambers
is considerably less than the theoretical contact time.
Samples of wastewater chlorinated in a laboratory do not
give results comparable to those obtained in chlorine
contact chambers.
11. The better the treatment the more effective the disinfection
at a given chlorine dosage.
10.04 Chlorine Requirement
The object of disinfection is the destruction of pathogenic bacteria,
and the ultimate measure of the effectiveness is the bacteriological
result. The measurement of residual chlorine does supply a tool for
practical control. If the residual chlorine value commonly effec-
tive in most wastewater treat-
ment plants does not yield
satisfactory bacteriological
kills in a particular plant,
the residual chlorine that
does must be determined and
used as a control in that
plant. In other words, the
0.5 mg/1 residual chlorine,
while generally effective, is
not a rigid standard but a
guide that may be changed to
meet local requirements.
One special case would be the use of chlorine in the effluent from
a plant serving a tuberculosis hospital. Studies have shown that a
residual of at least 2.0 mg/1 should be maintained in the effluent
from this type of institution, and that detention time should be
10-12
-------
at least two hours at the average rate of flow instead of the
thirty minutes which is normally used for basis of design.
Two-stage chlorination may be particularly effective in this
case.
It will generally be found that in a domestic waste the
following dosages of chlorine are a reasonable guideline to
produce chlorine residual adequate for disinfection. Indivi-
dual plants may require higher or lower dosages, depending upon
type and amount of suspended and dissolved organic compounds
in the chlorinated sample.
TYPE OF TREATMENT DOSAGE
(Based on Average Flow)
Primary plant effluent 20 - 25 mg/1
Trickling filter plant effluent 15 mg/1
Activated sludge plant effluent 8 mg/1
Sand filter effluent 6 mg/1
QUESTIONS
10.OJ Which is more resistant to chlorination, bacteria
causing enteric diseases or non-pathogenic intestinal
bacteria, designated as the coliform group?
10.OK Why does one find great variation in MPNs in chlori-
nated wastewater samples even under apparently similar
conditions?
10.OL What are some of the findings of studies attempting to
correlate chlorine residual and coliform MPN?
10.OM How is the effectiveness of the chlorine residual for
a particular plant determined?
END OF LESSON 1 OF 4 LESSONS
on
DISINFECTION AND CHLORINATION
Please answer the discussion and review questions before continuing
with Lesson 2.
10-13
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DISCUSSION AND REVIEW QUESTIONS
Chapter 10. Disinfection and Chlorination
(Lesson 1 of 4 Lessons)
At the end of each lesson in this chapter you will find discussion
and review questions that you should work before continuing. The
purpose of these questions is to indicate to you how well you under-
stand the material in the lesson.
Write the answers to these questions in your notebook before
continuing.
1. Why must wastewaters be disinfected?
2. Why is chlorination used to disinfect wastewater?
3. To improve disinfection, which is more effective--
increasing the chlorine dose, or extending the
chlorine contact time?
4. What constituents in wastewater are mainly responsible
for the chlorine demand?
5. Calculate the chlorinator setting (Ibs per 24 hours) to
treat a waste with a chlorine demand of 12 mg/1, when a
chlorine residual of 2 mg/1 is desired, if the flow is
1 MGD.
6. How do suspended and dissolved organic compounds in an
effluent affect disinfection?
10-15
-------
CHAPTER 10. DISINFECTION AND CHLORINATION
(Lesson 2 of 4 Lessons)
10.1 POINTS OF CHLORINE APPLICATION
10.10 Collection System Chlorination
One of the primary benefits of up-sewer chlorination is to prevent
the deterioration of structures. Other benefits include odor and
septicity control, and possibly BOD reduction to decrease the load
imposed on the wastewater treatment processes. In some instances,
the maximum benefit may result from a single application of chlorine
at a point on the main intercepting sewer before the junction of
all feeder sewer lines. In others, several applications at more
than one point on the main intercepting sewer or at the upper ends
of the feeder lines may prove most effective. Chlorination should
be considered as a temporary or emergency measure in most cases,
with emphasis being placed on proper design. Aeration also is
effective in controlling septic conditions in collection systems.
Although many problems result from improper design or design for
future capacity requirements, the need for hydrogen sulfide pro-
tection exists under the best of conditions.
10.11 Prechlorination
Prechlorination is defined as the addition of chlorine to wastewater
at the entrance to the treatment plant, ahead of settling units and
prior to the addition of other chemicals.
In addition to its application for aiding disinfection and odor
control at this point, prechlorination is applied to reduce plant
BOD load, as an aid to settling, to control foaming in Imhoff
units, and to help remove oil. Current trends are away from pre-
chlorination to up-sewer aeration for control of odors.
10.12 Plant Chlorination
Chlorine is added to wastewater during treatment by other processes,
and the specific point of application is related to the results
desired. The purpose of plant chlorination may be for control and
prevention of odors, corrosion, sludge bulking, digester foaming,
filter ponding, filter flies, and as an aid in sludge thickening.
Here again, chlorination should be an emergency measure.
10-17
-------
10.13 Postchlorin ati on
Postchlorination is defined as the addition of chlorine to municipal
or industrial wastewater following other treatment processes. This
point of application should be before a chlorine contact unit12 and
after the final settling unit in the treatment plant. This is the
most effective place for chlorine application after treatment and
on a well clarified effluent. Postchlorination is employed primarily
for disinfection. As a result of chlorination for disinfection, some
reduction in BOD may be observed; however, chlorination is rarely
practiced solely for the purpose of BOD reduction.
QUESTIONS
10.1A What is the purpose of up-sewer chlorination?
10.IB Where should chlorine be applied in sewers?
10.1C What are the reasons for prechlorination?
10.ID Why might chlorine be added to wastewater during
treatment by other processes?
10.IE What is the objective of postchlorination?
12 Chlorine Contact Unit. A baffled basin that provides
sufficient detention time for disinfection to occur.
10-18
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10.2 CHLORINATION PROCESS CONTROL
10.20 Chlorinator Control
The control of chlorine flow to points of application is accom-
plished by six basic methods and a seventh method which combines
two of the basic six.
10.200 Manual Control
Feed rate adjustment and starting and stopping of equipment is
done by hand.
10.201 Start-Stop Control
Feed rate adjustment by hand, starting and stopping (by inter-
rupting injector water supply) controlled by starting of waste-
water pump, flow switch, level switch, etc.
10.202 Step-Rate Control
Chlorinator feed rate is varied according to the number of waste-
water pumps in service. As each pump starts, a pre-set quantity
of chlorine is added to the flow of chlorine existing at starting
time. This system can be applied conveniently with installations
employing up to eight pumps.
10.203 Timed Program Control
Chlorine feed rate is varied on a timed step-rate basis regulated
to correspond to the times of flow changes or by using a time-
pattern transmitter which employs a revolving cam cut to match a
flow pattern.
10.204 Flow Proportional Control
Chlorinator feed rate is controlled by a system which converts
wastewater flow information into a chlorinator control value.
This can be accomplished by a variety, of flow metering equipment,
including all process control instrumentation presently available
and nearly all metering equipment now in use on wastewater systems,
10-19
-------
10.205 Chlorine Residual Control
Chlorine feed rate is controlled to a desired chlorine residual
(usually combined chlorine) level. After mixing and reaction
time (about five minutes maximum), a wastewater sample is
titrated by an amperometric13 analyzer-recorder (or indicator).
As the residual chlorine level varies above or below the
desired (setpoint) level, the chlorinator is caused to change
its feed rate to bring the chlorine residual back to the
desired level.
10.206 Compound Loop Control
Any "automatic" control system (step-rate, timed program, flow
proportional, or residual) can be employed in two ways:
(1) by positioning the feed rate valve, or (2) by varying the
vacuum differential across the feed rate valve. Compound loop
control employs both controls simultaneously. For instance,
a flow proportional (or step-rate, or timed program) control
system may position the feed rate valve, and a residual control
system may vary the vacuum differential across the feed rate
valve. Thus, changes in flow cause changes in feed rate valve
position, but changes in chlorine demand may occur without any
flow change. When this happens the residual analyzer detects
a change in chlorine residual and by varying the vacuum differ-
ential across the feed rate valve causes the chlorinator to
change rates to meet the desired chlorine residual level.
Various combinations of compound loop control can be employed.
Generally speaking, the part of the system requiring the fastest
response should be applied to valve positioning (since it
responds faster). If flow changes are rapid, flow control
should be by valve position. If flow and demand change rates
are nearly the same, the magnitude of change may dictate
the selection of control.
13 Amperometric (am-PURR-o-MET-rick). A method of measurement
that records electric current flowing or generated, rather
than recording voltage. Amperometric titration is an elec-
trometric means of measuring concentrations of substances
in water.
10-20
-------
The selection of control methods should be based on treatment
costs and treatment results (required or desired). A waste
discharger must normally meet a disinfection standard. A small
treatment plant might do this with a compound loop control
system costing several thousand dollars, but may save less than
one hundred dollars a year in chlorine consumed. In this case
the expense would not be justified. A manual system might be
employed which would meet the maximum requirements and over-
chlorinate at a minimum requirement periods. It is not unheard
of for a plant to have maximum chlorine residual requirements
because of irrigation and/or marine life tolerances. In these
cases the uncontrolled or promiscuous application of chlorine
cannot be considered, no matter how large the added cost.
A chlorine residual level may be required at some point down-
stream from the best residual control sample point. In this
case a residual analyzer should be used to monitor and record
residuals at this point. It may also be employed to change
the control set point of the controlling residual analyzer.
Ultimate control of dosage for disinfection rests on the results
desired, that is, the bacterial level or concentration acceptable
or permissible at the point of discharge. Determination of
chlorine requirements according to the current edition of
Standard Methods for the Examination of Water and Wastewater is
the best method of control. You must remember that the chlorine
requirement or chlorine dose will vary with wastewater flow, time
of contact, temperature, pH, and major waste constituents such as
hydrogen sulfide, ammonia, and amount of dead and living organic
matter.
QUESTIONS
10.2A How can chlorine gas feed be controlled?
10.2B Control of chlorine dosage depends on the bacterial
_______________ desired.
10.2C Define amperometric.
10-21
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10.21 Chlorination Control Nomogram111
Determination of chlorine residual after contact gives confirma-
tory data on previous choice of dosage, and may serve to indicate
need for readjustment of dosage. The contact period must be
specified as longer contact period increases chlorine uptake.
Since feed rate is expressed in pounds per day, the rate setting
of the feeder must be calculated from determination of chlorine
required and the flow. The simplest means of making the calcu-
lation is by a chlorination control nomogram taken from the
WPCF Manual of Practice No. 11, 1968 (Fig. 10.3). To use this
nomogram:
1. Lay a straight edge (ruler) on point on Line A, repre-
senting flow, and on point on Line B, representing
chlorine required,15 and read point on Line C, which
shows setting for chlorine feeder.
2. For any value in excess of maximum indicated on
Scales A, B, or C, introduce proper factor of ten
or multiple thereof. The application of a factor
of ten will be presented later in Example 2.
3. Greatest accuracy will be obtained when the angle of
the straight edge approaches a right angle with Line
B. Multiplier of ten may be applied to aid in ac-
complishing this objective.
4. If straight edge does not cross all three scales, intro-
duce necessary factors of ten and move straight edge to
points where all three scales will be crossed.
Let's try some examples using Fig. 10.3. Assume the given
chlorine dosage was selected on the basis of preliminary
tests as capable of producing the desired results.
14 Nomogram. A chart or diagram containing three or more scales
used to solve problems with three or more variables instead
of using mathematical formulas.
15 Chlorine Requirement. The amount of chlorine which must be
added to produce the desired results under stated conditions.
The result (the purpose of chlorination) may be based on any
number of criteria, such as a stipulated coliform density, a
specified residual chlorine concentration, the destruction of
a chemical constituent, or others. In each case a definite
chlorine dosage will be necessary. This dosage is the chlorine
requirement.
10-22
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O.I
I-100
0.2 —
gO.3-
o.
CO
z
o
-200
0.4-
o
z
o
-300
0.5
o 0.6
= -400
0.7-I
-500
0.8 — :
-600
0.9—-
10.0
-- 9.0
-- 8.0
1.0
•694.4
-- 7.0
--6.0
--S.O
if)
oc
O
X
t
CO
tr
ui
Q.
(O
o
•z.
o
Q.
I
UJ
cr
4.0 o
UJ
UJ
3
5- O
-r2.0
ir 1-0
•s- 0
Fig. 10.3 Chlorination control nomogram
(Source: WPCF MOP No. 11, 1968)
10-23
-------
EXAMPLE 1
Given:
Procedure:
Answer:
Check:
Chlorine
Feed Rate
EXAMPLE 2
Given:
Procedure:
Note:
Maximum Flow Rate = 0.5 MGD
Chlorine Dosage = 1.0 mg/1
Place one end of straight edge (ruler) on 0.5 MGD
(Line A) and draw a line through the point on
Line B representing a chlorine dosage of 1.0 mg/1.
Extend the line to Line C and read the point indi-
cating the chlorine feed rate.
Chlorine Feed Rate = 4.2 Ibs per 24 hours
= (Max. Flow, MGD) (Dosage, mg/1)(8.34 Ibs/gal)
8.34
= 0.5 -x 1.0
day M mg gal
= 4.17, say 4.2 Ibs per day
Maximum Flow Rate = 5.0 MGD
Chlorine Dosage = 1.0 mg/1
5.0 MGD is off our scale on Line A. Reduce flow
by a factor of ten to 0.5 MGD, or 5.0 MGD/10 =
0.5 MGD. The problem is the same as Example 1,
and the chart gives a chlorine feed rate of 4.2
Ibs per 24 hrs. The flow rate is actually ten
times 0.5 MGD (10 x 0.5 MGD = 5 MGD). Therefore
the required chlorine feed rate is 10 x 4.2 Ibs
per 24 hours (10 x 4.2 = 42) or 42 Ibs per 24
hours.
On a cold day, a 150-lb cylinder may not be ade-
quate to provide this feed rate.
16 Recall concentrations in mg/1 are the same as mg/M mg.
10-24
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EXAMPLE 3
Given:
Procedure:
Maximum Flow Rate = 0,4 MGD
Chlorine Dosage = 5.0 mg/1
A line through a flow of 0.4 MGD (Line A) and
5.0 mg/1 (Line B) misses Line C. The chlorine
dosage should be reduced by a factor of ten to be
able to use the nomogram.
Chlorine Dosage = 5>0 mg/1 = 0.5 mg/1
Chlorine
Feed Rate
Actual
Feed Rate
1.7 Ibs per 24 hours
(from chart)
= (10)(1.7 Ibs per 24 hrs)
= 17 Ibs per 24 hrs
The chlorine feed rate must be ten times the rate
from the chart because the chlorine required was
reduced by a factor of ten to use the chart.
The results from the chart should be checked using the mathematical
calculations used in Example 1 to avoid errors. It should be noted
that the chlorine requirement should take into consideration the
chlorine demand so that a desired residual is obtained after a
given contact period. As discussed in Section 10.02, chlorine
requirements vary with the wastewater characteristics, concentra-
tion, flow, and temperature. Adjustment of chlorine feeder rates
to meet all these variations is the ultimate goal of good operation
practice. More frequent adjustments are usually required for
primary effluent than for secondary effluent.
Suggested schedule for adjusting manual feeder rates:
1. In large plants — at least every hour
2. In medium-sized plants—every two to four hours
3. In small plants—every eight hours
Other methods of chlorinator control have been described in Section
10.20.
10-25
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10.22 Hypochlorinator17 Feed Rate
Chlorine for disinfection and other purposes is provided in
some plants by the use of hypochlorites.18 The amount of
chlorine delivered depends on the type of hypochlorite. For
example, HTH (high test hypochlorite) contains 67 percent,
by weight, of chlorine, and chlorinated lime contains 34 per-
cent.
Manufacturers of hypochlorites define available chlorine as the
amount of gaseous chlorine required to make the equivalent hypo-
chlorite chlorine. If you prepare a hypochlorite solution for
disinfection and immediately measure the chlorine residual, you
will find the chlorine residual about half of the expected value
based on the manufacturer's amount of available chlorine. When
hypochlorites are mixed with water, approximately half of the
chlorine forms hydrochloric acid (HC1) and the other half forms
hypochlorite (OC1-), the chlorine residual that you measured.
EXAMPLE:
A wastewater requires a chlorine feed rate of 17 Ibs per day.
How many pounds of chlorinated lime will be required to provide
the needed chlorine?
Chlorinated Lime _ Chlorine Required, Ibs/day
Feed Rate, Ibs/day ~ Portion of Chlorine in Ib of Hypochlorite
17 Ibs/day
0.34
= 50 Ibs/day
17 Hypochlorinator. Hypochlorinators are devices that are used
to feed calcium, sodium, or lithium hypochlorite as the dis-
infecting agent.
18 Hypochlorites. Hypochlorites are compounds containing
chlorine that are used for disinfection. They are
available as liquid or solids (powder, granules, and
pellets), in barrels, drums, and cans.
10-26
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QUESTIONS
10.2D How is the rate of dosage for a chlorinator determined?
10.2E Determine the chlorine feed rate, pounds per 24 hours,
if you are treating:
1. A flow of 0.5 MGD and the chlorine required is 1.0 mg/1.
2. Flow =0.8 MGD and chlorine required =4.0 mg/1.
3. Flow = 6 MGD and chlorine required = 25 mg/1.
10.2F How frequently should feeder rates be adjusted with manual
controls? Why?
10.2G How many pounds of HTH (high test hypochlorite) should be
used per day by a hypochlorinator dosing a flow of 0.55 MGD
at 12 mg/1 of chlorine?
10-27
-------
10.23 Chlorine Solution Discharge Lines, Diffusors, and Mixing
10.230 Solution Discharge Lines
Solution discharge lines are made from a variety of materials
depending upon the requirements of service. Two primary requisites
are that it must be resistant to the corrosive effects of chlorine
solution and of adequate size to carry the required flows. Addi-
tional considerations are pressure conditions, flexibility (if
required), resistance to external corrosion and stresses when
underground or passing through structures, ease and tightness of
connections, and the adaptability to field fabrication or alteration.
Development of plastics in the past several years has contributed
greatly to chemical solution transmission. Polyvinyl chloride (PVC)
pipe and black polyethylene flexible tubing have all but eliminated
the use of rubber hose. Both are generally less expensive and both
outlast rubber in normal service. The use of hose is almost ex-
clusively limited to applications where flexibility is required or
where extremely high back pressures exist.
PVC and polyethylene can be field fabricated and altered. PVC
should be Schedule 80 to limit its tendency to cold flow and
partially collapse under vacuum conditions, or for higher pressure
ratings if required. Schedule 80 PVC may be threaded and assembled
with ordinary pipe tools or may be installed using solvent welded
fittings.
Rubber lined steel pipe has been used for many years where resistance
to external stresses is required. It cannot be field fabricated or
altered and is thus somewhat restricted in application. PVC lining
of steel pipe has not yet become economically competitive, but
other plastics have been developed which can readily compete with
rubber lining and are adaptable to field fabrication and alteration.
Never use neoprene hose to carry chlorine solutions because it will
become hard and brittle in a short time.
10.231 Chlorine Solution Diffusors
These diffusors are normally constructed of the same materials used
for solution lines. Their design is an extremely important part of
a chlorination program. This importance is almost completely related
to the mixing of the chlorine solution with the wastewater being
treated; however, strength, flexibility, etc., also must be given
10-28
-------
consideration. In most circular, filled conduits flowing at
0.25 ft/sec (or greater) a solution injected at the center of
the pipeline will mix with the entire flow in ten pipe diameters,
Mixing in open channels can be accomplished by the use of a
hydraulic jump (Fig. 10.4) or by sizing diffusor orifices so
that a high velocity (about 16 ft/sec) is attained at the
diffusor discharge. This accomplishes two things: (1) intro-
ducing a pressure drop to get equal discharge from each orifice,
and (2) imparting sufficient energy to the surrounding waste-
water to complete the mixing. Generally speaking, a diffusor
should be supplied for each two to three feet of channel depth.
HIGH FLOW XT HYDRAULIC LOW FLOW
VELOCITY .X"*0 JUMP VELOCITY
Fig. 10,4 Hydraulic jump
10.232 Mixing
Mixing is extremely important ahead of a chlorine contact tank
or a residual sampling point. Since a contact tank is usually
designed for low velocity, little mixing occurs after waste-
water enters it. It is therefore necessary to achieve mixing
before the contact tank is entered. The same is true for a
chlorine residual sampling point; otherwise erratic results will
be obtained by the residual analyzing system.
QUESTIONS
10.2H Why does little mixing of the chlorine solution
with wastewater occur in chlorine contact basins?
10.21 Chlorine solution discharge lines may be made of
or
10-29
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10.24 Measurement of Chlorine Residual
Refer to Chapter 14, Laboratory Procedures and Chemistry, for
procedures to measure chlorine residual. Amperometric titra-
tion provides the most convenient, fastest, and most repeatable
results; however, apparatus costs are high (approximately $500).
The orthotolidine test should be run shortly after the chlorine
has been applied. The iodometric method will produce satisfactory
results in samples containing wastewater, such as plant effluents
and receiving waters.
END OF LESSON 2 OF 4 LESSONS
on
DISINFECTION AND CHLORINATION
Please answer the discussion and review questions before
continuing with Lesson 3.
10-30
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 10. Disinfection and Chlorination
(Lesson 2 of 4 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 1.
7. Where might chlorine be applied in the treatment of
wastewater?
8. Where is chlorine usually applied for disinfection pur-
poses?
9. What is the ultimate control of chlorine dosage for
disinfection?
10. Determine the chlorine feed rate for a flow of 0.75
MGD and a chlorine dosage of 18 mg/1.
11. Why must the chlorine solution be well mixed with the
wastewater?
10-31
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CHAPTER 10. DISINFECTION AND CHLORINATION
(Lesson 3 of 4 Lessons)
10.3 SAFETY AND FIRST AID
All persons handling chlorine should be thoroughly aware of its
hazardous properties. Personnel should know the location and use
of the various pieces of protective equipment and be instructed
in safety procedures. For additional information on this topic, see
the Water Pollution Control Federation's Manual of Practice No. 1,
Safety in Wastewater Works, and the Chlorine Institute's Chlorine
Manual, 4th edition.19
10.30 Chlorine Hazards
Chlorine is a gas, heavier than air, extremely toxic and corrosive
in moist atmospheres. Dry chlorine gas can be safely handled in
steel containers and piping, but with moisture must be handled in
corrosion-resisting materials such as silver, glass, teflon, and
certain other plastics. Chlorine gas at container pressure should
never be piped in silver, glass, teflon, or any other plastic material.
The gas is very irritating to the mucous membranes of the nose, to the
throat, and to the lungs; a very small percentage in the air causes
severe coughing. Heavy exposure can be fatal. (See Table 10-1.)
WARNING
A
OP
60 INTTO A ROOM CONTAIN
Pieorecnve: CLOTRJN^S ANP
19 Write to: Water Pollution Control Federation, 3900 Wisconsin
Avenue, Washington, D.C. 20016; price to WPCF members, $0.75;
others, $1.50. The Chlorine Institute, Inc., 342 Madison Avenue,
New York, New York 10017; price $0.75.
10-33
-------
TABLE 10-1
PHYSIOLOGICAL RESPONSE TO CONCENTRATIONS OF CHLORINE GAS20
Parts of Chlorine Gas
Effect Per Million Parts of Air
By Volume, (ppm)
Slight symptoms after several
hours' exposure
Detectable odor
60-minute inhalation without
serious effects
Noxiousness
Throat irritation
Coughing
Effects dangerous to one-half
to one hour
Death after a few deep breaths
1
3
4
5
15
30
40
1000
20 Adapted from data in U.S. Bureau of Mines Technical Paper
248 (1955).
10-34
-------
10.31 Why Chlorine Must Be HandledWith Care
You must always remember that chlorine is a hazardous chemical
and must be handled with respect. Concentrations of chlorine
gas in excess of 1000 ppm may be fatal after a few breaths.
Because the characteristic sharp odor of chlorine is notice-
able even when the amount in the air is small, it is usually
possible to get out of the gas area before serious harm is
suffered. This feature makes chlorine less hazardous than
gases such as carbon monoxide, which is odorless, and hydrogen
sulfide, which impairs your sense of smell in a short time.
Inhaling chlorine causes general restlessness, panic, severe
irritation of the throat, sneezing, and production of much
saliva. These symptoms are followed by coughing, retching
and vomiting, and difficulty in breathing. Chlorine is par-
ticularly irritating to persons suffering from asthma and
certain types of chronic bronchitis. Liquid chlorine causes
severe irritation and blistering on contact with the skin.
10.32 Protect Yourself From Chlorine
Every person working with chlorine should know the proper ways
to handle it, should be trained in the use of self-contained
breathing apparatus, and should know what to do in case of
emergencies.
WARNING
MARKS'
IN
NOT
ANV
OE
Here are some items you should always remember in order to
protect yourself and others from possible injury:
10-35
-------
In an emergency, only authorized persons with adequate
safety equipment should be in the danger area. Have
your fire department examine your chlorine handling
facilities and safety equipment so they will be aware
of what you have and the possible dangers. They are
well trained in the use of breathing apparatus and
may be able to help you in an emergency, especially if
they are familiar with chlorine hazards.
In any chlorine atmosphere, short shallow breathing is
safer than deep breathing. Recovery from exposure depends
on the amount of chlorine inhaled, so it is important to
keep that amount as small as possible.
Clothing contaminated with liquid or gaseous chlorine
continues to give off chlorine gas and irritate the body
even after leaving a contaminated area. Therefore, con-
taminated clothing should be removed immediately and the
exposed parts of the body washed with a large amount of
cool water.
The use of a breathing apparatus is advisable during these
operations. All caution should be taken to prevent any
liquid from coming in contact with clothing not designed
for protection, because the liquid can penetrate the cloth
and cause skin problems.
d. Learn the correct way of using the breathing apparatus,
practice using it regularly, and take safety drills
seriously. What you learn may save your life. The fire
department is well trained in the use of breathing apparatus
and can be very helpful in training.
10-36
-------
e. If you have found a chlorine leak and left the area before
the leak was stopped, you should use an apparatus with a
separate air supply when you return and repair the leak.
Never rely on a cannister type mask for protection in
repairing chlorine leaks. Cannister masks are not recom-
mended because they do not supply oxygen. They only remove
chlorine, if they are effective. Some agencies allow the
use of cannister type masks; however, most operators who
have had experience repairing chlorine leaks do not use
cannister masks because of their short shelf life (ap-
proximately three to four months) and inability to provide
adequate protection against high concentrations of chlorine.
Extensive ventilation is recommended.
f. Cooperate in taking care of all safety equipment, handling
it carefully, and returning it to its proper storage place
after use. Defective equipment, or equipment which you
can't find when you need it, will not protect you.
g. Always be sure that you know the location of first aid
cabinets, breathing apparatus, showers, and other safety
equipment. Review emergency instructions regularly to
be sure you know them.
h. Notify your police department that you need help if it
becomes necessary to stop traffic on roads and to evacuate
persons in the vicinity of a chlorine leak.
10.33 First Aid Measures
a. Be sure you know the location of breathing apparatus, first
aid kits, and other safety equipment at all times.
b. Remove clothing contaminated with liquid chlorine at once.
Carry patient away from gas area—if possible to a room
with a temperature of 70°F. Keep patient warm, with
blankets if necessary. Keep him quiet.
c. Place patient on his back with his head higher than the
rest of his body.
d. Call a doctor and fire department immediately. Immediately
begin appropriate treatment. "
e. Eyes. If even small quantities of chlorine have entered
the eyes, hold the eyelids apart and flush copiously with
lukewarm running water. Continue flushing for about fifteen
minutes. Do not attempt any medication except under specific
instructions from a physician.
10-37
-------
£. Sk in. Get patient under a shower immediately, clothes
and all. Remove clothing while the shower is running.
Wash the skin with large quantities of soap and water.
Do not attempt to neutralize chlorine with chemicals.
Do not apply salves or ointments except as directed by
a physician.
g. Inhalation. If the patient is breathing, place him in a
comfortable position; keep him warm and at rest until a
physician arrives.
If breathing seems to have stopped, begin artificial
respiration immediately. Mouth-to-mouth resuscitation
or any of the approved methods may be used. Oxygen
should be administered if equipment and trained personnel
are available.
Automatic artificial respiration is considered preferable
to manual, but only when administered by an experienced
operator.
Rest is recommended after severe chlorine exposure.
h. Th roat I r r itation. Drinking milk will relieve the dis-
comforts of throat irritation from chlorine exposure.
Chewing gum or drinking spirits of peppermint also will
help reduce throat irritation. Follow emergency rules
given by your physician. In the absence of such rules,
the first aid steps above are suggested.
Taken in part from Chlorine Safe Handling Pamphlet, published by
The Chemical Division of PPG Industries, Inc.
QUESTIONS
10.3A What are the hazards of chlorine gas?
10.3B What type of breathing apparatus is recommended when
repairing a chlorine leak?
10.3C What first aid measures should be taken if a person
comes in contact with chlorine?
10-38
-------
10.4 CHLORINE HANDLING
10.40 Chlorine Containers
10.400 Cylinders
Cylinders containing 100 to 150 pounds of chlorine are convenient
for the average small consumer. These cylinders are usually of
seamless steel construction (Tig* 10.5).
A fusible plug is placed in the valve, below the valve seat
(Fig. 10.6). This plug is a safety device. The fusible metal
softens or melts at 158° to 165°F, to prevent building up of
excessive pressures and the possibility of rupture due to a fire
or high surrounding temperatures.
Cylinders will not explode and can be handled safely.
The following are procedures for handling chlorine cylinders.
1. Move cylinders with a properly balanced hand truck with
clamp supports that fasten at least two-thirds of the
way up the cylinder.
2. 100- and 150-pound cylinders can be rolled in a vertical
position. Lifting of these cylinders should be avoided
except with approved equipment. Never lift with chains,
rope slings, or magnetic hoists.
3. Protective cap should always be replaced when moving a
cylinder.
4. Cylinders should be kept away from direct heat (steam
pipes, radiators, etc.).
5. Cylinders should be stored in an upright position.
10-39
-------
Chlorine Cylinder
Protection
Hood
Valve
Neck Ring
Cylinder
Body
If— Foot Ring
Net
Cylinder
Contents
100 Lbs.
150 Lbs.
Approx.
Tare,
Lbs.*
73
92
Dimensions,
Inches
A
8'/4
10 1/4
B
54 Va
54 Vs
"Stamped tare weight on cylinder shoulder
does not include valve protection hood.
Fig. 10.5 Chlorine cylinder
(Courtesy of PPG Industries3 Inc., Chemical D-Lwis-ion)
10-40
-------
Poured Type Fusible Plug
Screwed Type Fusible Plug
STEM
PACKING GLAND
PACKING NUT
PACKING
^PACKING COLLAR
OUTLET CAP
(Special straight threads)
GASKET
STANDARD CYLINDER VALVE
Fig. 10.6 Standard cylinder valve
Reproduced with permission (1959, 1966)
The Dow Chemical Company
10-41
-------
10.401 Ton Tanks
Ton tanks are of welded construction and have a loaded weight
of as much as 3700 pounds. They are about 80 inches in length
and 30 inches in outside diameter. The ends of the tanks are
crimped inward to provide a substantial grip for lifting clamps
(Fig. 10.7).
The following are some characteristics of and procedures for
handling ton tanks.
Most ton tanks have eight openings for fusible plugs and valves
(Figs. 10.7 and 10.8). Generally, two operating valves are
located on one end near the center and six or eight fusible
metal safety plugs, three or four on each end. These are
designed to melt within the same temperature range as the
safety plug in the cylinder valve.
WARNING
IT \^V£*KY IMPORTANT T-HA.T
^HOULP NOT g£r TAAAPE-R^-P WVT44
ANY
MOT
H- Of- Ti-V£ OALOPIN-E 1M
TAMK VAMU.
Ton tanks are shipped by rail in multi-unit tank cars. Single
units may be transported by truck or semi-trailer.
Ton tanks should be handled with a suitable lift clamp in con-
junction with a hoist or crane of at least two-ton capacity
(Fig. 10.7).
Ton tanks should be stored and used on their sides, above the
floor or ground, on steel or concrete supports. They should
not be stacked more than one high.
10-42
-------
Net Weight of Chlorine . . .2000 Ibs. 2-Ton Minimum 15/16",
Tare Wt. of Tank (average) 1550 Ibs. Capacity Hoist
Gross Weight Full (average) . . ^^ 2%"
3550 Ibs.
I* W 64 'I ^3/>'R
I I ,,,„ 11/Krl ,. J 78 l\
HP—
21/4"
Spacer -
each end
Chlorine Gas Eduction Pipe
Valve
Protection
Hood
Chlorine
Liquid
Detail "A"
Fusible Plugs,
(at least 3 each end)
Fig. 10.7 Ton tank lifting beam
(Courtesy of PPG Industries, Inc., Chemical Division)
10-43
-------
Ton Tank Valve
100 and 150 Ib. Cylinder Valve
-Stem-
-Packing Gland Nut-
—Packing Gland —
— Ring Packing
-Packing Retainer—
-Cap
-Disc
Fusible Plug
Special 3/4" Straight Thread
Body
Standard 3/4" Pipe Thread
Fig. 10.8 Comparison of ton tank valve with cylinder valve
(Courtesy of PPG Industries, Inc., Chemical Division)
10-44
-------
p, EXPANSION CHAMBER (HEATED)
l| (NO VALVE)
LIQUID CHLORINE
TOt PROCESS
THERMOMETER
(PREFERRED METHOD)
CHLORINE GAS TO PROCESS
_L$-CHLORINE GAGE
' IMP
n
BAROMETRIC LEG-*
SAFETY
VALVE
LIQUID
CHLORINE
FLEXIBLE
CONNECTORS
• -SHUT Off VALVES
/-RELIEF VALVE
165 LBS
VALVE
L-WATER SEPARATOR
AIR LINE
TO GAS
VALVE
/-CONDENSATE (NO VALVE)
|lH
JlH-SEAL POT (NO TliAP)
COMPRESSOR ON-OFf CONTROL
125-150 L8S PRESSURE
\L REGENERATIVE TYPE AIR
DRYERS -40° DEW POFNT
Fig. 10.9 Typical chlorine tank car unloading arrangement
Reproduced with permission (1959, 1966) The Dow Chemical Company
-------
Ton tanks should be placed on trunnions which are equipped
with rollers so that the withdrawal valves may be positioned,
one above the other. The upper valve will discharge chlorine
gas, and the lower valve will discharge liquid chlorine (see
Fig. 10.7). Trunnion rollers should not exceed 3-1/2 inches
in diameter so that the containers will not rotate too easily
and be turned out of position. Roller shafts should be equipped
with a zerk type lubrication fitting and slotted for even
lubrication. Roller bearings are not advised because of the
ease with which they rotate. Locking devices are not required
when these rules are observed.
10.402 Chlorine Tank Cars
Chlorine tank cars are of 16-, 30-, 55-, 85-, or 90-ton capacity.
All have four-inch cork board insulation protected by a steel
jacket. The dome of the standard car contains four angle valves
plus a safety valve. The two angle valves located on the axis
line of the tank are equipped for discharging liquid chlorine.
The two angle valves at right angles to the axis of the tank
deliver liquid chlorine (Fig. 10.9).
The following are some procedures for unloading chlorine tank cars.
Unloading of tank cars should be performed by trained personnel
in accordance with Interstate Commerce Commission (ICC) regulations.
In most situations chlorine is withdrawn from tank cars as a
liquid and then passed through chlorine evaporators. Sometimes
dry air is passed into the tank car through one of the gas valves
to assist in liquid withdrawal. This practice is referred to as
"air padding".
QUESTIONS
10.4A How may chlorine be delivered to a plant?
10.4B What is the purpose of the fusible plug?
10-46
-------
10.41 Removing Chlorine From Containers
10.410 Connections
Outlet threads on container valves are not tapered pipe threads.
Use fittings and gaskets for connections furnished by your
chlorine supplier or chlorinator equipment manufacturer. Do
not try to use regular pipe thread fittings. New gaskets should
be used for each new connection where required.
Flexible 3/8-inch 2000-pound Cpsi) annealed copper tubing is
recommended for connections between chlorine containers and
stationary piping. Care should be taken to prevent sharp bends
in the tubing because this will weaken it and eventually the
tubing will start leaking. Many operators recommend use of a
sling to hold the tubing when disconnecting it from an empty
cylinder to prevent the tubing from flopping around and getting
kinked or getting dirt inside it.
A shut-off valve is needed after the container valve or at
beginning of stationary piping, to simplify changing of con-
tainers.
10.411 Valves
Do not use wrenches longer than six inches, pipe wrenches, or
wrenches with an extension on container valves. To unseat,
strike end of wrench with heel of hand to rotate the valve stem
in a counterclockwise direction. Then open slowly.
One complete turn permits maximum discharge. Do not force
valve beyond this point.
If valve is too tight to open, loosen the packing gland nut
slightly to free the stem.
10.412 Ton Tanks
One-ton tanks (Fig- 10.7) must be placed on their side with the
valves in a vertical position. Connect the flexible tubing to
the top valve to remove chlorine gas from the tank. The bottom
valve is used to remove liquid chlorine and is used only with a
chlorine evaporator. The valves are similar to those on the
smaller chlorine cylinders (fusible plugs are not located at
valves on ton containers) and must be handled with the same care.
10-47
-------
10.42 Chlorine Leaks
Chlorine leaks must be taken care of immediately or they will
become worse.
Corrective measures should be undertaken only by trained men
wearing proper safety equipment. All operators should be
trained to safely repair chlorine leaks.
All other persons should leave the danger area until conditions
are safe again.
If the leak is large, all persons in the adjacent areas should
be warned and evacuated. Obtain police help. You must always
consider your neighbors...PEOPLE, animals, and plants.
1. Before any new system is put into service, it should be
cleaned, dried, and tested for leaks. Pipelines may be
cleaned and dried by flushing and steaming from the high
end to allow condensate and foreign materials to drain out.
After the empty line is heated thoroughly, dry air may be
blown through the line until it is dry. After drying,
the system may be tested for tightness with 150 psi dry air.
Leaks may be detected by application of soapy water to the
outside of joints. Small quantities of chlorine gas may
now be introduced into the line, the test pressure built up
with air, and the system tested for leaks. Whenever a new
system is tested for leaks, at least one chlorinator should
be on the line to withdraw chlorine from the system in case
of a leak. The same is true in case of an emergency leak
at any installation. If a chlorinator is not running, at
least one or more should be started. Preferably, all
available chlorinators should be put on the line,
2. To find a chlorine leak, tie a rag on a stick, dip the rag21
in a strong ammonia solution, and swab it over the sus-
pected points. Waving the rag around the room also may
help locate the source of a leak. White fumes will indi-
cate the exact location of the leak. Location of leaks by
this method may not be possible for large leaks which
diffuse the gas over large areas.
21 A one-inch paint brush may be used instead of a rag.
10-48
-------
If the leak is in the equipment in which chlorine is being
used, close the valves on the chlorine container at once.
Repairs should not be attempted while the equipment is in
service. All chlorine piping and equipment that is to be
repaired by welding should be flushed with water or steam.
Before returning equipment to use, it must be cleaned, dried,
and tested as previously described.
If the leak is in a chlorine cylinder or container, use the
emergency repair kit supplied by most chlorine suppliers.
These kits can be used to stop most leaks in a chlorine
cylinder or container and can usually be delivered to a
plant within a few hours if one is not already at the site
of the leak. It is advisable to have emergency repair kits
available at your plant at all times and to train personneT
in their use. Location of such kits should be posted out-
side chlorine storage areas.
If chlorine is escaping as a liquid from a cylinder or a
ton tank, turn the container so that the leaking side is
on top. In this position, the chlorine will escape only
as a gas, and the amount which escapes will be only 1/15
as much as if the liquid chlorine were leaking. Keeping
the chlorinators running also will reduce the amount of
chlorine gas leaking out of a container. Increase the
feed rate to cool the supply tanks as much as possible.
For situations where a prolonged or unstoppable leak is
encountered, emergency disposal of chlorine should be pro-
vided. Chlorine may be absorbed in solutions of caustic
soda, soda ash, or agitated hydrated lime slurries (Table
10-2). Chlorine should be passed into the solution through
an iron pipe or a properly weighted rubber hose to keep it
immersed in the absorption solution. The container should
not be immersed because the leaks will be aggravated due
to the corrosive effect, and the container may float when
partially empty. In some cases it may be advisable to move
the container to an isolated area. Discuss the details of
such precautions with your chlorine supplier.
Never put water on a chlorine leak. A mixture of water and
chlorine will increase the rate of corrosion of the container
and make the leak larger. Besides, water may warm the
chlorine, thus increasing the pressure and forcing the
chlorine to escape faster.
10-49
-------
TABLE 10-2
CHLORINE ABSORPTION SOLUTIONS'
Absorption Solution
Caustic Soda (100%)
Soda Ash
Hydrated Lime**
a
b
c
a
b
c
a
b
c
Alkali
Clb)
125
188
2500
300
450
6000
125
188
2500
Water
(gal)
40
60
800
100
150
2000
125
188
2500
Chlorine Container Size (Ib net):
a = 100, b = 150, c = 2000
* Source: The Chlorine Institute.
** Hydrated lime solution must be continuously and vigor-
ously agitated while chlorine is to be absorbed.
10-50
-------
7. Leaks around valve stems can often be stopped by closing
the valve or tightening the packing gland nut. Tighten
the nut or stem clockwise.
8. Leaks at the valve discharge outlet can often be stopped
by replacing the1""gasket" or adapter connection.
9. Leaks at fusible plugs and cylinder valves usually require
special handling and emergency equipment. Call your
chlorine supplier immediately and obtain an emergency repair
kit for this purpose if you do not have a kit readily avail-
able.
10. Pin hole leaks in the walls of cylinder and ton tanks can
be stopped by using a clamping pressure saddle with a turn-
buckle available in repair kits. This is only a temporary
measure, and the container must be emptied as soon as possible,
If a repair kit is not available, use your ingenuity. One
operator stopped a pin hole leak temporarily until a repair
kit arrived by placing several folded layers of neoprene
packing over a leak, a piece of scrap steel plate over the
packing, wrapping a chain around the cylinder and steel plate,
and applying leverage pressure with a crowbar.
11. A leaking container must not be shipped. If the container
leaks or if the valves do not work properly, keep the con-
tainer until you receive instructions from your chlorine
supplier for returning it. If a chlorine leak develops in
transit, keep the vehicle moving until it reaches an open
area.
12. Do not accept delivery of containers showing evidence of
leaking, stripped threads, or abuse of any kind.
QUESTION
10,4C How would you look for a chlorine leak?
END OF LESSON 3 OF 4 LESSONS
on
DISINFECTION AND CHLORINATION
Please answer the discussion and review questions before continuing
with Lesson 4.
10-51
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 10. Disinfection and Chlorination
(Lesson 3 of 4 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 2.
12. What type of breathing apparatus should be worn when
entering an area in which chlorine gas is present?
13. Why should clothing be removed from a person who has been
in an area contaminated with liquid or gaseous chlorine?
14. How could your police department assist you in the event
of a serious chlorine leak?
15. Why should chlorine containers and cylinders be stored
where they won't be heated?
16. Why are slings used to hold chlorine tubing when changing
chlorine cylinders?
17. Why should water never be poured on a chlorine leak?
18. How would you attempt to repair a pin hole leak in a
chlorine cylinder?
10-53
-------
CHAPTER 10. DISINFECTION AND CHLORINATION
(Lesson 4 of 4 Lessons)
10.5 CHLORINATION EQUIPMENT AND MAINTENANCE (by J. L. Beals)
10.50 Chlorinators
Chlorine may be delivered from a feeder by one of two methods:
1. Solution feed, commonly practiced, in which the chlorine
gas is controlled, metered, introduced into a stream of
injector water, and then conducted as a solution to the
point of application.
2. Direct feed, sometimes called dry feed, in which the gas
is introduced directly through a suitable diffuser at
the point of application. This method is used only when
a source of injector water at adequate pressure, or power
for an injector pump, is not available. Operating diffi-
culties experienced in metering dry chlorine gas directly
to the point of application make this type of equipment
a "last resort".
Following are the common types of feeders used in wastewater treat-
ment plants.
10.500 Vacuum-Solution Feed Chlorinators
This type of equipment (Fig. 10.10) comprises in excess of 90% of
all gas chlorination equipment in service today in water and waste-
water treatment operations. The primary advantage of vacuum
operation is safety. If a failure or breakage occurs in the
vacuum system, the chlorinator either stops the flow of chlorine
into the equipment or allows air to enter the vacuum system rather
than allowing chlorine to escape into the surrounding atmosphere.
In case the chlorine inlet shut-off fails, a vent valve discharges
the incoming gas to the outside of the chlorinator building.
The operating vacuum is provided by a hydraulic injector. The
injector operating water absorbs the chlorine gas, and the resultant
chlorine solution is conveyed to a chlorine diffusor through corro-
sion resistant conduit.
10-55
-------
A vacuum chlorinator also includes a vacuum regulating valve
to dampen fluctuations and give smooth operation. A vacuum
relief prevents excessive vacuum within the equipment.
A typical vacuum control chlorinator is shown in Fig. 10.10.
Chlorine gas flows from a chlorine container to the gas inlet
(located above the circled Y in the middle right of the figure).
After entering the chlorinator the gas passes through a spring
loaded pressure regulating valve which maintains the proper
operating pressure. A rotameter is used to indicate the rate
of gas flow. The rate is controlled by a V-notch variable
orifice. The gas then moves to the injector where it is dis-
solved in water and leaves the chlorinator as a chlorine solution
(HOC1) ready for application.
10.501 Partial Vacuum, Pressure Type, and Pulsating Type
Chlorinators
Aside from the pressure type which has been described previously,
these types of equipment are limited in application and few remain
in service. Pulsating and partial vacuum chlorinators are primarily
designed for extremely low feed rates. Vacuum-solution feed equip-
ment can feed less than 0.25 Ibs/day. The reduced cost of hypo-
chlorination has almost eliminated their use.
10.51 Hyp o ch1orin at ors
Hypochlorinators are devices that are used to feed chlorine in the
form of calcium, sodium, or lithium hypochlorite. Hypochlorites
are available as liquids or various forms of solids (powder, pellets),
and in a variety of containers or in bulk.
QUESTION
10.5A How is chlorine delivered (fed) to the
point of application?
10-56
-------
VENT
-VACUUM REGULATING VALVE
-8" TO SB" WATER VACUUM SIGNAL
VACUUM TRANSMITTER
O
I
on
6'TO 96" WATER VACUUM
V-NOTCH
VARIABLE ORIFICE
PRESSURE GAUGE
20 PSIO MINIMUM
ROTAMETER
TO 2'"WATER
PRESSURE DROP
YTOZ
PRESSURE-VACUUM
RELIEF VALVE
OPENS AT
l" TO 2" WATER PRESSURE
35" TO 4O" WATER WUUM
MANUAL FEED
RATE ADJUSTER
22 TO24"
WATER VACUUM
GAS PRESSURE
REGULATING VALVE
BIAS
ADJUSTMENT
REMOTE FROM
CHLORINATOR
INJECTOR
GAUGE
IO"Hg MINIMUM
CONTROL VACUUM
CHECK VALVE
INJECTOR WATER
SUPPLY
SOLUTION
DISCHARGE
O
O
O
c <
II
3
o
«
o
Fig. 10.10 Vacuum solution feed chlorinator
(Courtesy Wallace & Tieman)
no
o
o
o
o
o
H
i
z
o
31
O
5
o-n
-------
10.52 Installation, Operation, and Maintenance
The following are some features of importance when working with
chlorine facilities.
1. Chlorinators should be located near point of application.
2. If possible, there should be a separate room for chlori-
nators and chlorine container storage Ca°ove ground) to
prevent chlorine gas leaks from damaging equipment and
harming personnel. There should be no access to this
room from a room containing equipment or where personnel
work.
3. Ample working space around the equipment and storage space
for spare parts should be provided.
4. There should be an ample supply of water to operate chlori-
nator at required capacity under maximum pressure conditions
at the chlorinator injector discharge.
5. The building should be adequately heated. The temperature
of chlorine cylinder and chlorinator should be above 50°F.
Line heaters may be used to keep chlorine piping and chlori-
nator at higher temperatures to prevent condensing of gas
into liquid in the pipelines and chlorinator. The maximum
temperature at which a chlorine cylinder is stored should
not exceed 110°F.
6. It is not advisable to draw more than 40 pounds of chlorine
from any one 100- to 150-pound cylinder in a 24-hour period
because of the danger of freezing and slowing up the
chlorine flow. With ton containers, the limit of chlorine
gas is about 450 pounds per day. When evaporators are
provided, these limitations do not apply.
7. There should be adequate light.
8. There should be adequate ventilation. Continuous ventilation
is desirable. Forced ventilation must be provided to remove.
gas if a large leak develops. The outlet of a forced venti-
lation system must be near the floor because chlorine is
2,5 times heavier than air. Use a pressurized fan (keep
room under slight positive pressure). Do not suck air from
the room through the fan, because chlorine gas can damage
the fan motor. Louvers on vents should swing out and always
be open, or open automatically. It should be impossible to
lock the louvers shut.
10-58
-------
9. Adequate measuring and controlling of chlorine dosage is
required. Scales and recorders indicating loss in
weight are desirable as a continuous check and as a
record of the continuity of chlorination. Record
weights daily.
10. There should be continuity of chlorination. When chlori-
nation is practiced for disinfection, it is needed continu-
ously for the protection of downstream water users.
Therefore, arrange that chlorination will function for
1440 minutes per day. To secure continuous chlorination,
the chlorine gas lines from cylinders should feed to a
manifold so that the cylinders can be removed without
interrupting feed of gas. Duplicate units or an emergency
hypochlorinator should be provided.
11. For additional information on chlorinator maintenance, refer
to Chapter 11, Maintenance.
QUESTIONS
10.5B Why should chlorinators be in a separate room?
10.5C Why is room temperature important for proper chlorinator
operation?
10.5D Why should not more than 40 pounds of chlorine per day
be drawn from any one cylinder?
10.5E Why is adequate ventilation important in a chlorinator room?
10.5F How can chlorinator rooms be ventilated?
10.5G How can chlorination rates be checked against the chlori-
nator setting?
10.5H Why should chlorination be continuous?
10.51 How can continuous chlorination be achieved?
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10.53 Installation Requirements
(Section A from Wallace § Tiernan
Catalog Sheet Nos. 5.110 and 5.111)
10.530 Piping, Valves, and Manifolds
After you have determined (a) the availability of various types
of chlorine containers and selected the type most suited to
particular needs, (b) the inventory required and the space needed,
(c) the method of handling the containers, and (d) the type of
weighing scales to be used, the final step in regard to chlorine
supply is to plan the required piping.
CONNECTIONS AT CONTAINERS: It is standard practice to connect an
auxiliary tank valve (either union or yoke type) to the container
valve to facilitate changing containers, to minimize the release
of gas when containers are changed, and to serve as a shut-off
valve in the event the container valve is defective. From this
auxiliary valve a flexible connection is used to connect to the
manifold, or, in the case of small installations, directly to the
chlorinator.
CONNECTIONS AT CHLORINATOR: In general, small chlorinators are
equipped to receive a flexible connection directly from the
chlorine container and no other piping is necessary. Larger
chlorinators may use a flexible connection from a manifold, if
located close to the container, or may employ piping from the
manifold to the chlorinator where the distance is greater.
CONNECTIONS AT EVAPORATOR: Where evaporators are used, the piping
from the manifold to the evaporator carries liquid chlorine, and
the piping from the evaporator to the chlorinator carries chlorine
gas. Evaporators normally are furnished with all necessary immediate
valves and fittings.
PIPING—MATERIALS AND JOINTS: Best practice calls for the use of
extra heavy, black, genuine wrought iron, or seamless carbon steel
(Schedule 80) pipe for conducting chlorine gas or liquid and
fittings that are forged or cast carbon steel, 300 Ib USA flanged.
Except in unusual cases, the size will be 3/4" or 1". In most
installations, it will be found practical to use threaded joints.
These joints should be put together using teflon tape as a joint
lubricant. Unions of the flanged, ammonia type, two-bolt oval
10-60
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are recommended. For pipe sizes larger than one inch in diameter,
a four-bolt oval should be used. From the standpoint of mainte-
nance, line valves should be kept to a minimum. Insulation is
required only in those unusual cases where it is necessary to pre-
vent chlorine gas lines from becoming chilled or liquid lines from
becoming overheated.
PIPING—CHLORINE GAS: It is important to observe the correct
temperature conditions in conducting chlorine gas from the location
of the containers to the point of use. To avoid difficulty with
reliquefaction22 of chlorine, piping and control equipment should
be at a higher temperature than that of the chlorine containers.
In general, a difference of 5 or 10°F is recommended. It is
preferable to run chlorine gas lines overhead through relatively
warm areas rather than along the floor or through basement areas
where lower temperatures may be encountered.
Where it is not possible to secure suitable temperature conditions,
the use of an external chlorine pressure reducing valve near the
containers is recommended.
The use of a chlorine pressure reducing valve is also recommended
in those localities where severe temperature changes are likely
to be encountered during a 24-hour period.
PIPING—LIQUID CHLORINE: In the case of liquid chlorine, it is
important to avoid conditions that will encourage vaporization.
Thus it is important to keep liquid chlorine lines as cool as, or
cooler than, the containers. Avoid running liquid chlorine lines
through overheated areas where gasification is likely to take place.
Valves in liquid chlorine lines should be kept to a minimum, and
it is particularly important to avoid situations where it is easy
to close two valves in a line thus trapping liquid which, upon an
increase in temperature, may develop dangerous pressures.
The use of an expansion chamber is recommended where traps occur
in the line or where it is necessary to run lines a considerable
distance. An expansion chamber is generally a 100-pound or 150-
pound empty chlorine cylinder installed in an inverted position
directly above the liquid line by means of a tee. As the name
implies, the cylinder provides an area of expansion in the event
that valves at both ends of the line are closed.
22 Re liquefaction (re-LICK-we-FACK-shun). The return of a gas to
a liquid. For example, a condensation of chlorine gas returning
to liquid form.
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VALVES AND MANIFOLDS: Chlorine valves consist of the following:
(a) auxiliary tank valves for use at the container, (b) header
valves for use on or in conjunction with manifolds, (c) line
valves for insertion in liquid and gas lines for shut-off purposes,
and (d) pressure reducing valves to reduce the pressure in gas
lines where necessary. Manifolds are assemblies to receive the
flexible connections from the container, generally provide a
shut-off valve, and include the means of connecting to the
chlorinator piping. They are available in types and sizes to
accommodate any required number of containers and may be mounted
in any convenient manner.
10.531 Chlorinator Injector Water Supply
The injector operating water supply serves to produce the vacuum
under which vacuum chlorinators function and to dissolve the
chlorine and discharge it as a solution at the point of appli-
cation. The quantity of water required and the minimum pressure
at which it is supplied depend upon:
1. maximum chlorinator feed rate, and
2. back pressure at injector discharge CPressure at point
of chlorine application, plus friction loss in solution
line, and plus or minus elevation differences between
injector and point of application).
Water quantity and pressure can vary from one to two gpm at
15 psi (for 10 Ibs/day at 0 back pressure) up to 360 gpm at
60 psi (8000 Ibs/day at 20 psi back pressure). In some extremely
high back pressure situations, injector water may be required up
to 300 psi. These conditions do not occur often in wastewater
treatment installations, and back pressures exceeding 20 psi
(except in force main applications) are uncommon.
Plant effluent is used frequently as injector operating water.
When this is the case, a pump is usually required to provide the
required quantity and pressure. If a pump is used exclusively
for injector operation, it should be designed for 25 to 50% over
capacity to allow for wear. Injector water is often supplied
from a service water system also providing water for other purposes.
If a potable water supply is the only source of injector water,
precautions must be taken to insure against direct cross-connections
between wastewater and potable water. (Consult your local public
health authority.)
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Injector water requirements vary so widely depending upon make,
model, capacity, back pressure, etc., that it is advisable to
consult the chlorinator manufacturer if a new system is to be
installed or if an existing system must be altered and any of
these operating conditions are to be changed.
QUESTIONS
10.5J What is the best piping material for conducting chlorine
gas or liquid?
10.5K Plant is used frequently as the chlorinator
injector water supply.
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10.6 OTHER USES OF CHLORINE
10.60 Odor Control
Chlorination of wastewater for odor control is used to inhibit
the growth of odor-producing bacteria and to destroy hydrogen
sulfide (H2S), the most common odor nuisance, which has the
smell of rotten eggs. Hydrogen sulfide, in addition to creating
an odor nuisance, can be an explosion hazard when mixed with air
in certain concentrations. Breathing H2S can impair your ability
to smell, and too much will paralyze your respiratory center,
causing death in severe cases. It also can cause corrosion of
metals and concrete, being particularly damaging to electrical
equipment even in low concentrations.
The presence of hydrogen sulfide may be detected in significant
quantities in any collection and treatment system where sufficient
time is allowed for its development. It may be expected to be
present most often in new systems where flows are extremely low
in comparison with design capacity, and particularly in lift
stations where pump operating cycles may be at a low frequency.
Collection systems which serve large areas often allow time for
H2S development even when operating at design capacity.
The purpose of this section is not to discuss the reasons for
odor production, but rather their elimination or control by
chlorination; however, the correction of an odor problem will
usually require a decision being made between system modification
and treatment. Sometimes both may be required. Choices of this
type often hinge on the costs involved, and it will frequently
be found that modifications to major system components are far
more costly than treatment. When this is the case, chlorination
is usually the most economical solution. Other solutions include
the use of air or ozone.
Sulfides develop whenever given time to do so. The rate of
sulfide production increases with temperature (about 7% on the
average with each 1°C increase in wastewater temperature).
The odors which are controllable with chlorine are specifically
hydrogen sulfide which can be inactivated by chlorination at
levels well below the chlorine demand point. This is commonly
referred to as "sub-residual chlorination". The reason that
this is true is based on the fact that the C12 + H2S reaction
precedes most other chlorine-consuming reactions. Since it is
known that bacterial kills occur at sub-residual levels, it is
logical that odor-producing bacteria can be reduced in numbers
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without satisfying the chlorine demand. This can be accomplished
without significantly interfering with organisms beneficial to
the treatment processes.
The quantities of chlorine required to accomplish control of
odors vary widely from plant to plant and at any given plant
fluctuate over a broad range. Hydrogen sulfide is generally
found in higher concentrations when flows are low. For this
reason it is usually not economical to chlorinate for odor
control in direct proportion to flow. Tests should be run over
periods which include all the various conditions which could
possibly affect odor production in order that a basis for
treatment may be established.
When the requirements are known, the primary concern is to
apply chlorine at the proper location. The best locations are
generally up-sewer ahead of the plant influent structures,
and up-sewer ahead of lift stations. This is done to allow
mixing and reaction time before the waste reaches a point of
agitation.
Sometimes force mains empty into the gravity sections of a
collection system several hours after pumping. If odor problems
result, a treatment point should be placed upstream at a point
where the sewer is still under pressure and flowing full; thus
treatment can be completed before odors are released to the
atmosphere.
Hydrogen sulfide should not be considered merely an odor nuisance.
It must always be kept in mind that it can create an explosion
hazard, it can paralyze your respiratory center, and it should
always be considered a source of corrosion. For these reasons,
odor masking agents should not be used except possibly as addi-
tional treatment for odors not eliminated by chlorination.
Excessive use of masking agents could prevent detection of a
serious problem condition.
10.61 Protection of Structures
The destruction of hydrogen sulfide in wastewater also reduces
the production of sulfuric acid that is highly corrosive to
sewer systems and structures. This is particularly significant
where temperatures are high and time of travel in the sewer
system is unusually long. The treatment is similar to that for
odor control: chlorination sufficient to prevent hydrogen sulfide
10-65
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formation or to destroy hydrogen sulfide that has been produced
(about 2 mg/1 chlorine per mg/1 of hydrogen sulfide). Sulfide
problems also may be corrected by oxygenation in sewers. The
choice between oxygenation and chlorination will usually depend
on the costs involved.
10.62 Aid to Treatment
Among its many uses, chlorine improves treatment efficiency in
the following ways.
10.620 Sedimentation
Prechlorination at the influent of a settling tank improves
clarification by improving settling rate, reducing septicity23
of raw wastewater, and increasing grease removal. Maximum
grease removal is achieved when chlorination is combined with
aeration ("aero-chlorination"). It is an expensive procedure,
and some studies have indicated that benefits are minimal.
Generally grease removal in this manner is considered a bene-
ficial side effect or "bonus" reaction to chlorine which is
essentially applied for other reasons. Excess chlorination
ahead of secondary processes can inhibit the bacterial action
critical to the process and decrease sedimentation efficiency.
10.621 Trickling Filters
Continuous chlorination at the filter influent controls slime
growths and destroys filter fly larvae (Psychoda). Generally
the chlorine is applied to produce a residual of 0.5 mg/1
(continuous) at the orifices or nozzles. Caution should be used
because some filter growth may be severely damaged by excessive
chlorination. Suspended solids will increase in a trickling
filter effluent after chlorination for filter fly control. Also,
it will be difficult to evaluate filter performance on the basis
of BOD removals because chlorine can interfere with the BOD test.
As a general statement, it would be well to look closely at
23 Septicity (sep-TIS-it-tee) is the condition in which organic
matter decomposes to form foul-smelling products associated
with the absence of free oxygen.
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loadings, operation, and general adequacy of the process when
filter fly chlorination is continuously necessary, because
continuous chlorination may be an expensive alternative for
adequate design and operation.
10.622 Activated Sludge
Chlorination of return sludge reduces bulking of activated sludge
that is caused by overloading. The point of application should
be where the return sludge will be in contact with the chlorine
solution for about one minute before the sludge is mixed with
the incoming settled wastewater. Chlorine is also commonly
used to control filamentous organisms. Again, chlorine used in
this manner is an expensive alternative for adequate design and
operation. The main effort should be directed toward process
improvement, considering chlorination mainly as an emergency
solution. Never forget that chlorine is toxic to organisms that
are needed to treat the incoming wastes.
10.623 Reduction of BOD
Chlorination of raw wastewater to produce residual of 0.5 mg/1
after 15 minutes of contact may cause a reduction of 15 to 30%
in the BOD of the wastewater (Baity, 1929). Generally a reduction
of at least 2 mg/1 of BOD is obtained for each mg/1 of chlorine
absorbed up to the point at which the residual is produced.
Snow (1952) has shown that the BOD reduction also depends on the
condition of the wastewater. He reported a 10% reduction in
fresh wastewater and a 25 to 40% reduction in stale wastewater.
Both real and apparent effects of chlorination are evident in the
wastewater and in the test bottle.
QUESTIONS
10.6A How can odors be controlled? Why?
10.6B How can sulfuric acid damage to structures be mini-
mized or eliminated? Why?
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10.7 ACKNOW LE DGMENTS
Portions of the information contained in this chapter were taken
in part from Chapter 17, Disinfection and Chlorination, Water
Pollution Control Federation Manual of Practice No. 11; and
from Chapter 7, Chlorination of Sewage, Manual of Instruction
for Sewage Treatment Plant Operators (New York Manual). Both
publications are excellent references for additional study.
Mr. J. L. Reals provided many helpful comments.
10.8 REFERENCES
Baity, H.G., "Reduction of BOD in Sewage by Chlorination",
Sewage Works J. , 1, 279
California State Department of Public Health, "Laws and Regu-
lations Relating to Ocean Water-Contact Sports Areas" (1958).
California State Department of Public Health, "Statewide Stan-
dards for the Safe Direct Use of Reclaimed Waste Water for
Irrigation and Recreational Impoundments" (1968) .
California State Department of Public Health, "Laws and Regu-
lations Relating to Swimming Pools" (1966).
California State Department of Public Health, "Some Experience
with Disinfection of Waste Water in California", G.E. Browning
and F.R. McLaren (1966).
Chlorine Institute, "Chlorine Manual" (1969).
Dow Chemical, "Dow Chlorine Handbook" (1966).
New York State Department of Health, "Manual of Instruction for
Sewage Plant Operators" (1966).
PPG Industries, Inc., Chemical Division, "Chlorine Safe Handling
Pamphlet".
Snow, W.B., "Biochemical Oxygen Demand of Chlorinated Sewage",
Sewage and Industrial Wastes, 24, 689 (1952).
U.S. Bureau of Mines, Technical Paper 248 (1955).
U.S. Public Health Service, "Drinking Water Standards" (1962).
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Water Pollution Control Federation, Manual of Practice No. 1,
"Safety in Waste Water Works".
Water Pollution Control Federation, Manual of Practice No. 4,
"Chlorination of Sewage and Industrial Wastes" (under revision).
Water Pollution Control Federation, Manual of Practice No. 11,
"Operation of Waste Water Treatment Plants" (1968).
10.9 ADDITIONAL READING
a. MOP 11, pages 127-135.
b. New York Manual, pages 73-83.
c. Texas Manual, pages 397-412,
d. "Chlorine—Safe Handling", PPG Industries, Inc., Chemical
Division, One Gateway Center, Pittsburgh, Pennsylvania 15222.
e. Chlorination Guide, Water and Sewage Works Magazine, Scranton
Publishing Company, 355 East Wacker Drive, Chicago, Illinois 60601.
Price, $1.25.
f. Chlorine Manual (4th edition), The Chlorine Institute, Inc.,
342 Madison Avenue, New York, New York 10017. Price $0.75.
g. Safety in Waste Water Works, MOP No. 1, Water Pollution Control
Federation, 3900 Wisconsin Avenue, Washington, D.C. 20016.
Price to WPCF members, $0.75; others, $1.50.
Films on chlorine safety also are available from the Chlorine Institute
and PPG Industries, Inc.
END OF LESSON 4 OF 4 LESSONS
on
DISINFECTION AND CHLORINATION
Please answer the discussion and review questions before continuing.
10-69
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DISCUSSION AND REVIEW QUESTIONS
Chapter 10. Disinfection and Chlorination
(Lesson 4 of 4 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 3.
19. How is the rate of chlorine gas flow in a chlorinator
controlled?
20. How often should the weights of chlorine cylinders be
recorded?
21. Why must chlorination be continuous?
22. Why should the temperature of chlorine piping and control
equipment be higher than the temperature of the chlorine
containers?
23. Why must direct cross-connections be avoided between a
public water supply and the injector water supply?
24. What is "sub-residual chlorination"?
25. Why should sulfides be controlled?
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SUGGESTED ANSWERS
Chapter 10. Disinfection and Chlorination
10.OA The purpose of disinfection is to destroy pathogenic
organisms. This is important to prevent the spread
of water-borne diseases.
10.OB Pathogenic bacteria are destroyed or removed from water
by (1) physical removal through sedimentation or fil-
tration, (2) natural die-away in an unfavorable environ-
ment by storage and (3) destruction through chemical
treatment.
10.OC Chlorine is used for disinfection because it meets the
general requirements of disinfection so well, and because
it has been found to be the most economically useful and
available chemical for disinfection.
10.OD Sterilization of wastes is impractical and unnecessary
and may be detrimental to other treatment processes
that are dependent on the activity of non-pathogenic
saprophytes.
10.OE Chlorine reacts with reduced substances in wastewater,
organic matter to form chlororganic compounds, and
nitrogenous compounds to form chloramines.
10.OF To produce an effective disinfecting action, sufficient
chlorine must be added after the chlorine demand is
satisfied to produce a chlorine residual likely to
persist through the contact period.
10.OG Chlorine Demand = Chlorine Dose - Chlorine Residual
10.OH Chlorine Dose = Chlorine Demand + Chlorine Residual
10.01 Chlorine
Dose
Chlorine
Demand
= 70 lb/day lb
(1.2 MG/day) (8.34 Ib/G) " M lb
= 7.0 mg/1
Chlorine Dose - Chlorine Residual
7.0 mg/1 - 0.4 mg/1
6.6 mg/1
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10.OJ Non-pathogenic intestinal bacteria designated as the
coliform group are more resistant to chlorination
than bacteria causing enteric diseases.
10.OK MPN is a probable measure based on a sample from a
large population. Small samples from large amounts
of material may not be representative from a non-
uniform substance such as wastewater. Variability
in environmental factors also affects the MPN.
10.OL Generally, MPN coliform densities decrease with increased
chlorine residuals in laboratory and plant studies; but
variability in individual plants, mixing, character of
wastes, detention time, and other environmental factors
make it difficult to apply a correlation determined from
one plant to other plants.
10.OM The ultimate measure of effectiveness is the bacterio-
logical result. The residual chlorine that yields satis-
factory bacteriological results in a particular plant must
be determined and used as a control in that plant.
10.1A The purpose of up-sewer chlorination is to control odors
and septicity, prevent deterioration of structures, and
decrease BOD load.
10.IB Chlorine should be applied in sewers where odor and H2S
control is necessary. These locations may be at several
points in the main interceptor sewer or at the upper ends
of feeder lines.
10.1C Prechlorination provides partial disinfection and odor
control.
10.ID Plant chlorination provides control of odors, corrosion,
sludge bulking, digester foaming, filter ponding, filter
flies, or sludge thickening, but may interfere with bio-
logical treatment processes.
10.IE Postchlorination is employed primarily for disinfection.
10.2A Chlorine gas feed can be controlled by manual, start-
stop, step-rate, timed program, flow proportional, chlorine
residual, and compound loop controls.
10.2B Control of chlorine dosage depends on the bacterial
reduction desired.
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10.2C Amperometric is a method of measurement that records
electric current flowing or generated, rather than record-
ing voltage. Amperometric titration is an electrometric
means of measuring concentrations of substances in water.
10.2D Feed in pounds per day can be calculated from the chlorine
requirement and the rate of flow by the use of chlorination
control nomogram.
10.2E (1) 4.2 Ibs per 24 hrs
(2) 270 Ibs per 24 hrs
(3) 1250 Ibs per 24 hrs
10.2F Large plants: at least every hour
Medium-sized plants: every 2 to 4 hours
Small plants: every 8 hours
In small plants chlorine costs are relatively low in
comparison to labor costs necessary for frequent adjust-
ment.
10.2G Find chlorine dosage in pounds per day.
Chlorine
Dosage, = Chlorine Dose, mg/1 x Flow, MGD x 8.34 Ibs/gal
Ibs/day
= 12 mg/1 x 0.55 MGD x 8.34 Ibs/gal
= 55 Ibs/day
HTH Feed _ , _. , ., .,
D . _ Chlorine Required, Ibs/day
Kate, —
Ibs/day Portion of Chlorine in pound of HTH
55 Ibs/day
0.67
= 82 Ibs/day
10.2H Little mixing of chlorine solution with wastewater occurs
in chlorine contact basins because of the low flow velocities
in a basin.
10.21 Polyvinyl chloride (PVC) or black polyethylene flexible
tubing. Rubber lined steel pipe has been used, but rubber
hose is rarely used today.
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10.3A Chlorine gas is extremely toxic and corrosive in moist
atmospheres.
10.3B Self-contained air or oxygen supply type of breathing
apparatus is recommended when repairing a chlorine leak.
10.3C First aid measures depend on the severity of the contact.
Remove the victim from the gas area and keep him warm and
quiet. Call a doctor and fire department immediately.
Keep the patient breathing.
10.4A Chlorine may be delivered to a plant in 100- or 150-
pound cylinders, ton containers, or tank cars.
10.4B Fusible plugs are provided as a safety device to prevent
the building up of excessive pressures and the possibility
of rupture due to a fire or high surrounding temperatures.
10.4C To look for a chlorine leak, wear a self-contained breathing
apparatus to enter the area if the leak is severe. A rag
or paint brush dipped in a strong solution of ammonia water
and moved around the area will locate the leak if the room
is not full of chlorine gas.
10.5A Chlorine is normally delivered (fed) to the point of appli-
cation as a solution feed (under vacuum); however, in some
cases it is fed as a direct feed (under pressure).
10.5B Chlorinators should be in a separate room because chlorine
gas leaks can damage equipment and are hazardous to personnel.
10.5C Room temperature is important for proper chlorinator operation
to prevent clogging, chlorine ice formation, and condensation
in lines and chlorinator.
10.5D Not more than 40 pounds of chlorine per day should be drawn
from a chlorine cylinder because of the danger of freezing
and slowing up of chlorine flow.
10.5E Adequate ventilation is important in a chlorinator room to
remove any leaking chlorine gas.
10.5F Chlorinator rooms can be ventilated using forced ventilation
with the outlet near the floor because chlorine is heavier
than air.
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10.5G Chlorination rates can be checked by the use of scales
and loss in weight recorders.
10.5H Disinfection must be continuous for the protection of
downstream water users.
10.51 Continuous chlorination can be achieved by the use of a
cylinder feed manifold so cylinders can be removed without
interrupting feed of gas and provide duplicate units or
emergency hypochlorinators.
10.5J The best material for conducting chlorine gas or liquid
is extra heavy, black, genuine wrought iron pipe.
10.5K Plant effluent is used frequently as the chlorinator
injector water supply.
10.6A Odors can be controlled by chlorination by the reaction
with sulfides and the delay of decomposition and stabili-
zation. Sulfides should be controlled because they smell
like rotten eggs, are a source of corrosion, can paralyze
your respiratory tract, and can form explosive mixtures
with air.
10.6B Sulfuric acid damage to structures can be minimized by
chlorination or oxygenation which destroys hydrogen sulfide.
Hydrogen sulfide produces sulfuric acid which damages sewer
systems and structures.
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OBJECTIVE TEST
Chapter 10. Disinfection and Chlorination
Name Date
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. There may be
more than one correct answer to each question.
1. Disease producing bacteria are called:
1. Saprophytes
2. Facultative
3. Parasitic
4. Pathogenic
5. Coliform
2. Reduction in the number of pathogenic organisms
in wastewater may be accomplished by:
1. Sedimentation
2. Prechlorination
3. Postchlorination
4. Providing chlorine contact time
5. Adding orthotolidine
3. Chlorine may be applied for H2S control in the:
1. Collection lines
2. Plant headworks
3. Trickling filter
4. Aeration tank
5. Plant effluent
4. An operator should never enter a room containing
high concentrations of chlorine gas without:
1. Help standing by
2. Notifying proper authorities
3. A self-contained air or oxygen supply
5. You should never tamper with or apply heat to the fusible
plug of a chlorine container.
1. True
2. False
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6. Chlorine cylinders:
1. Can easily be lifted by one man
2. Can be handled safely
3. Contain a fusible metal safety plug
4. Should be rolled horizontally
5. Should be stored at temperatures above 50°F
and kept away from steam pipes
7. What should be the approximate chlorine feed rate for
a flow of 1.5 MGD and a chlorine dosage of 15 mg/1?
1. 200 lbs/24 hr
2. 100 lbs/24 hr
3. 20 lbs/24 hr
4. 10 lbs/24 hr
5. 2 lbs/24 hr
8. Chlorine should be applied continuously to:
1. Keep the plant equipment from breaking down
2. Keep the plant effluent disinfected
3. Keep the chlorine pipes from developing leaks
4. Keep the chlorine supplier in business
5. Protect the downstream water users
9. Field chlorination studies have shown that:
1. Constant vigilance is required to maintain a consistently-
high degree of disinfection at most wastewater treatment plants,
2. Thorough mixing of chlorine solution with wastewater is
essential to achieve maximum efficiency of coliform kill
for a given chlorine dosage.
3. Chlorine feed rates required to produce a desired dis-
infection level are constant from day to day.
4. Actual contact time in most chlorine chambers is the
same as the theoretical contact time.
5. Chlorine residuals can be increased without limit and
the coliform densities will always continue to be reduced
with each increase in residual.
10. Chlorinators should be located:
1. Near point of application
2. Outdoors
3. In a separate room
4. In a room that will not allow chlorine to leak into rooms
where operators work or where controls and equipment are
located.
5. In an adequately heated room
11. Postchlorination is generally more effective in a well-
clarified effluent than in a turbid one.
1. True
2. False
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12. Teflon tape makes a good:
1. Joint lubricant
2. Leak stopper
13. Hydrogen sulfide is found in most collection systems,
1. True
2. False
14. To protect the health of downstream water users, treatment
plant effluents must be:
1. Sterilized
2. Disinfected
15. Hydrogen sulfide:
1. Is associated with corrosion
2. Causes odors
3. Smells like chlorine
4. Can paralyze your respiratory system
5. Can form an explosive mixture with air
Review Questions;
A rectangular sedimentation tank 10 feet deep, 30 feet wide, and
120 feet long handles a flow of 3 MGD.
16. The detention time is:
1. 1.5 hr
2. 2.0 hr
3. 2.15 hr
4. 2.25 hr
5. 2.5 hr
17. The surface loading rate is approximately:
1. 500 gpd/sq ft
2. 600 gpd/sq ft
3. 700 gpd/sq ft
4. 800 gpd/sq ft
5. 900 gpd/sq ft
Please write on your IBM answer sheet the total time required to
work Chapter 10.
10-81
-------
CHAPTER 11
MAINTENANCE
GENERAL PROGRAM
by
Norman Farnum
MECHANICAL MAINTENANCE
by
Stan Walton
FLOW MEASUREMENT
by
Roger Peterson
UNPLUGGING PIPES,
PUMPS AND VALVES
by
John Brady
-------
TABLE OF CONTENTS
Chapter 11. Maintenance
Page
11.0 Treatment Plant Maintenance—General Program .... 11-1
11.00 Preventive Maintenance Records 11-2
11.01 Building Maintenance 11-5
11.02 Plant Tanks and Channels 11-6
11.03 Plant Grounds 11-7
11.04 Chlorinators 11-9
11.040 Maintenance 11-9
11.041 Chlorine Safety 11-12
11.05 Library 11-12
11.1 Mechanical Maintenance 11-15
The format of this section differs slightly from
the others. It was designed specifically to assist
you in planning an effective preventive maintenance
program. The contents are at the beginning of the
section, and the paragraphs are numbered for easy
reference on equipment service record cards.
11.2 Flow Measurements—Meters and Maintenance 11-81
11.20 Flow Measurements, Use and Maintenance. . . . 11-81
11.21 Manufacturers' and Operators' Responsibilities 11-82
11.22 Various Devices for Flow Measurement 11-82
11.23 Meter Location 11-85
11.24 Conversion and Readout Instruments
and Controls 11-86
11.240 Mechanical Meters 11-86
11.241 Transmitters 11-86
11.242 Receivers 11-86
11.243 Controllers 11-86
111
-------
Page
11.25 Sensor Maintenance 11-87
11.26 Conversion and Readout
Instrument Maintenance 11-89
11.3 Unplugging Pipes, Pumps and Valves 11-91
11.30 Plugged Pipeline 11-91
11.31 Scum Lines 11-91
11.32 Sludge Lines 11-92
11.33 Digested Sludge Lines 11-92
11.34 Unplugging Pipelines 11-92
11.340 Pressure Methods 11-93
11.341 Cutting Tools 11-94
11.342 Hydraulic Nozzle Pressure Unit .... 11-95
11.343 Last Resort 11-95
11.35 Plugged Pumps and Valves 11-96
11.4 Summary 11-97
11.5 Additional Reading 11-97
IV
-------
PRE-TEST
Chapter 11. Maintenance
Name Date
The objective of the Pre-Test is to indicate to you what items are
important in this lesson. Please work this Pre-Test before reading
the chapter. You are not expected to know many of the answers, if
any at all.
Write your name, date, and mark your answers on the IBM answer
sheet as directed at the end of Chapter 1. There may be more than
one answer to each question.
1. The duties of a wastewater treatment plant operator may include:
1. Regulation of plant treatment processes
2. Public relations
3. Maintaining equipment and buildings
4. Painting and cleaning plant buildings
5. Keeping maintenance records
2. Equipment service cards and service record cards should:
1. Identify the piece of equipment that the record
card represents
2. Record sick leave
3. Maintain selective service records
4. Indicate the work to be done
5. Indicate the work done
3. What happens if you do not periodically drain and inspect
plant tanks and channels?
1. Serious maintenance problems could develop
2. Costly repairs could result
3. The operator will not know if cracks are
developing in underground tanks and channels
4. An emergency situation may develop and force you to
discharge partially or improperly treated wastes into
receiving waters during critical conditions.
5. The operator will stay out of trouble
4. How can a chlorine leak be detected?
1. By an explosiometer
2. Smell
3. Green or reddish deposits on metal
4. By waving an ammonia soaked rag
5. By checking the leak gage
P-l
-------
5. A reciprocating pump:
1. Has a rotating impeller
2. Has a piston that moves back and forth
3. Has two check valves
4. Is used to pump sludge
5. Makes a regular "thunk-thunk" sound when
working properly
6. Before starting, a pump should:
1. Have its shaft turned by hand to see that it rotates freely
2. Run in the shipping crate so it can be returned if it
doesn't work
3. Be properly lubricated
4. Be allowed to sit outside arid become accustomed to
adverse conditions
5. Be checked to ensure that the shafts of the pump and
motor are aligned
7. Float and electrode switches should be checked at least once
a week to see that:
1. Floatable solids are floating
2. Controls respond to changing water levels in the
wet well as expected
3. Pump motor starts and stops at the proper time
A, The switches change the direction of flow
5. None of these
8. Level control systems in a wet well include:
1. Electrodes
2. Hearts
3, Floats
4. Diaphragms
5. Bubblers
9. If a pump will not start, check for:
1. Tripped circuit breakers
2. Loose terminal connections
3. Water in the wet well
4. Nuts, bolts, scrap iron, wood, or plastic in the wrong places
5. Shaft binding or sticking
10. Preventi.ve maintenance of electric motors includes:
1. Frequently starting and stopping the motor to give it a rest
2. Lubricating bearings
3. Checking temperature of motor
4. Keeping motor free from dust, dirt, and moisture
5. Keeping motor outdoors where it can stay cool
P-2
-------
11. Maintenance of couplings between the driving and driven
elements includes:
1. Keeping proper alignment
2. Keeping proper alignment even with flexible couplings
3. Draining old oil in fast couplings
4. Keeping the electrodes free of scum and corrosion
5. Regular use of a crowbar to line them up
12. Pump maintenance includes:
1. Preventing all water seal leaks around packing glands
2. Operating two or more pumps of the same size alternately
to equalize wear
3. Checking operating temperature of bearings
4. Checking packing gland
5. Lubricating the impeller
13. Approximately how far down should the level in a wet well be
lowered in one minute by a pump with a rated capacity of 200
gpm? The wet well is five feet wide and five feet long.
1. 0.1 ft
2. 0.5 ft
3. 1.0 ft
4. 1.1 ft
5. 2.0 ft
14. Maintenance of gate valves includes:
1. Lubricating with Prussian blue
2. Tightening or replacing the stem stuffing box packing
3. Operating inactive valves to prevent sticking
4. Lubricating bearing
5. Refacing leaky valve seats
15. Flow records provide:
1. Data to control plant processes
2. Nice listening music
3. Information for regulatory agencies
4. Something to keep the operator working
5. For plant input and output determination
16. If a flow meter appears to be operating improperly, the operator
should:
1. Shake it
2. Check connections
3. Look for foreign objects in the system
4. Check need for lubrication
5. Hammer on it
P-3
-------
17. If a flow meter does not read properly, what items should
be checked as potential causes of error?
1. Installation of sensor and readout devices
2. Restrictions in the sensor and transmitter
3. Power supply to instruments
4. Check instruments according to manufacturer's instructions
5. Blow the transmission lines out with high pressure air
18. Reciprocating pumps should be operated when:
1. Suction and discharge line valves are closed
2. Suction line valve open and discharge line valve closed
3. Suction line valve closed and discharge line valve open
4. Suction and discharge line valves are open
19. Modern gate valves can be repacked without removing them
for service.
1. True
2. False
Old gaskets should be salvaged.
1. True
2. False
P-4
-------
CHAPTER 11. MAINTENANCE
(Lesson 1 of 6 Lessons)
11.0 TREATMENT PLANT MAINTENANCE—GENERAL PROGRAM
A treatment plant operator has many duties. Most of them have to
do with the efficient operation of his plant. It is his responsi-
bility to discharge an effluent that will meet all the requirements
established for his plant. By doing this, he will develop a good
working relationship with the regulatory agencies, water sportsmen,
water users, and plant neighbors.
Another duty an operator has is that of a plant maintenance man.
A good maintenance program is a must in order to maintain success-
ful operation of the plant. A good maintenance program will cover
everything from mechanical equipment to the care of the plant
grounds, buildings, and structures.
Mechanical maintenance is of prime importance as the equipment
must be kept in good operating condition in order for the plant
to maintain peak performance. Manufacturers provide information
on the mechanical maintenance of their equipment. You should
thoroughly read their literature on your plant equipment and
understand the procedures. Contact the manufacturer or his local
representative if you have any questions. Follow the instructions
very carefully when performing maintenance on equipment. You also
must recognize tasks that may be beyond your capabilities or repair
facilities, and you should request assistance when needed.
For a successful maintenance program, your supervisors must under-
stand the need for and benefits from equipment that operates con-
tinuously as intended. Disabled or improperly working equipment is
a threat to the quality of the plant effluent, and repair costs for
poorly maintained equipment usually exceed the cost of maintenance.
11-1
-------
11.00 Preventive Maintenance Records
Preventive programs help operating personnel keep equipment in
satisfactory operating condition and aid in detecting and
correcting malfunctions before they develop into major problems.
A frequent occurrence in a preventive maintenance program is the
failure of the operator to record the work he is doing. When
this happens the operator must rely on his memory to know when to
perform each preventive maintenance function. As days pass into
weeks and months, the preventive maintenance program is lost in
the turmoil of everyday operation.
The only way an operator can keep track of his preventive mainte-
nance program is by good record keeping. Whatever record system
he chooses to use, it should be kept up to date on a daily basis
and not left to memory for some other time. Equipment service
record cards (Fig- 11.1) are easy to set up and require little
time to keep up to date.
An equipment service card (master card) should be filled out for
each piece of equipment in the plant. Each card should have the
equipment name on it, such as Sludge Pump No. 1, Primary Clarifier,
etc.
1. List each required maintenance service with an item
number.
2. List maintenance services in order of frequency of
performance. For instance, show daily service as
items 1, 2, and 3 on the card; weekly items as 4
and 5; monthly items as 6, 7, 8, and 9; and so on.
3. Describe each type of service under work to be done.
Make sure all necessary inspections and services are shown. For
reference data, list paragraph or section numbers as shown in
the mechanical maintenance section of this lesson (Section 11.1).
Also list frequency of service as shown in the time schedule
columns of the same section. Under time, enter day or month
service is due. Service card information may be changed to fit
the needs of your plant or particular equipment as recommended
by the equipment manufacturer. Be sure the information on the
cards is complete and correct.
T'ie service record card'should have the date and work done,
listed by item number and signed by the operator who performed
the service. Some operators prefer to keep both cards clipped
together, while others place the service record card near the
equipment.
11-2
-------
EQUIPMENT SERVICE CARD
EQUIPMENT: #1 Raw Wastewater Lift Pump
Item No.
1
2
3
4
5
6
7
8
Work to be Done
Check water seal and packing gland
Operate pump alternately
Inspect pump assembly
Inspect and lube bearings
Check operating temperature of
bearings
Check alignment of pump and motor
Inspect and service pumps
Drain pump before shutdown
Reference
Par. 12
Par. 12
Par. 12
Par. 12
Par. 12
Par. 12
Par. 12
Par. 12
Frequency
Daily
Weekly
Weekly
Quarterly
Quarterly
Semi- Ann.
Semi -Ann.
Time
Monday
Wed.
1-4-7-10*
1-4-7-10
4 § 10
4 $ 10
* 1-4-7-10 represent the months of the year when the equipment, should be
serviced--!, January, 4. April, 7. July, and 10. October.
SERVICE RECORD CARD
EQUIPMENT: #1 Raw Wastewater Lift Pump
Date
1-5-70
1-6-70
1-7-70
Work Done
(Item No.)
1 5 2
1
1-3-4-5
Signed
J.B.
J.B.
R.W.
Date
Work Done
(Item No.)
Signed
Fig. 11.1 Equipment service card and service record card
11-3
-------
When the service record is filled, it should be filed for
future reference and a new card attached to the master card.
The equipment service card tells what should be done and when,
while the service record card is a record of what you did and
when you did it.
QUESTIONS
11.OA Why should you plan a good maintenance program
for your treatment plant?
11.OB What general items would you include in your
maintenance program?
11.OC Why should your maintenance program be accom-
panied by a good record keeping system?
11.OD What is the difference between an equipment
service card and a service record card?
11-4
-------
11.01 Building Maintenance
Building maintenance is another program that should be main-
tained on a regular schedule. Buildings in a treatment plant
are usually built of sturdy materials to last for many years.
It is important that they be kept in good repair. In select-
ing paint for a treatment plant, it is always a good idea to
have a painting expert help the operator select the types of
paint needed to protect the buildings from deterioration. He
also will have some good ideas as to color schemes to help blend
the plant in with the surrounding area. Consideration should
also be given to the quality of paint. A good quality, more
expensive material will usually give better service over a
longer period of time than the economy type products.
Building maintenance programs depend on the age, type, and use
of a building. New buildings require a thorough.check to be
certain essential items are available and working properly,
while older buildings require careful watching and prompt
attention to keep ahead of leaks, breakdowns, replacements
when needed, and changing uses of the building. Attention
must be given to the maintenance requirements of many items
in all plant buildings, such as electrical systems, plumbing,
heating, cooling, ventilating, floors, windows, roofs, and
drainage around the buildings. Regularly scheduled examinations
and necessary maintenance of these items can prevent many costly
and time-consuming problems in the future.
In each plant building, periodically check all stairways,
ladders, catwalks, and platforms for adequate lighting, head
clearance, and sturdy and convenient guardrails. Protective
devices should be around all moving equipment. Whenever any
repairs, alterations, or additions are built, avoid building
man traps such as pipes laid on top of floors or hung from the
ceiling at head height which could create serious safety hazards.
Organized storage areas should be provided and maintained in an
accessible and neat manner.
11-5
-------
Keep all buildings
clean and orderly.
Janitorial work should
be on a regular schedule.
All tools and plant equip-
ment should be kept clean
and in their proper place.
Floors, walls, windows,
etc., should be cleaned
at regular intervals in
order to maintain a neat
appearance. A treatment
plant kept in a clean,
orderly condition makes a
safe place to work and aids
in building good public and
employer relations.
11.02 Plant Tanks and Channels
Plant tanks and channels such as-clarifiers, channels, grit chambers,
and wet wells should be drained at least once a year and inspected.
Be sure the groundwater level is down far enough so the tanks will not
float on the groundwater or rupture when empty.
Schedule inspections of tanks and channels during periods of low inflow.
Route flows through alternate units, if available; otherwise provide
the best possible treatment with remaining units not being inspected
or repaired.
All metal and concrete surfaces that come in contact with wastewater
or fumes should have a good protective coating. The coating should
be reapplied where necessary at each inspection.
Digesters should also be drained and cleaned on a regular basis.
Once every five years (actual times range from three to eight years)
has been accepted as an approximate interval for this operation.
Most digesters have a sludge inlet box on one side and a supernatant
box on the opposite side. A sludge sampler can be lowered in the
pipes in both of these boxes for a check for sand and grit build-up.
To determine the amount of grit build-up, you must know the side wall
depth of the digester. If the sludge sampler will only drop to
within four feet of the bottom, you can assume that you have a
four-foot build-up of sand and grit. By measuring the depth of sand
and grit at periodic intervals, you can determine how fast the build-
up is accumulating. In digesters, all metal and concrete surfaces
are inspected for deterioration.
11-6
-------
On surfaces where the protective coatings are dead and flake off,
it is necessary to sand blast the entire surface before new coat-
ings are applied. Usually two or more coats are needed for proper
protection.
The protective coatings used on these types of tanks and channels are
usually of black asphaltic type paint. These coatings should be
used wherever practical. In areas where fumes and moisture are not
severe, aluminum or a color scheme may be desirable. In these areas,
a rubber base paint or some similar material may be used. Follow
the recommendations of a paint expert.
AMP
FAILURE To FO ^O MAV
IN C
QPERAT/OM4 PUR1M6 TPi£ CR1TICAU
ROW- R16W TEMPER ATLIT2£
AMP FUMP^> WHEN VOU
MINIMIZE TWE P1^£HA^6£ OP
TO
11.03 Plant Grounds
Plant grounds that are well groomed and kept in a neat condition
will greatly add to the appearance of the overall plant area.
This is important to the operator in building good relations
with plant neighbors as well as the general public. It also
aids in the eyes of management as to your ability as an operator.
If the plant grounds have not been landscaped, it is sometimes
the responsibility of the operator to do so. This may consist
of planting shrubs and lawns or, just keeping the grounds neat
and weed free. Some plant grounds may be entirely paved. In
any case they should be kept clean and orderly at all times.
11-7
-------
Control rodents and insects so they won't spread diseases or
cause nuisances.
For the convenience of visitors and new operators, signs directing
people to the plant, indicating the way to different plant facili-
ties, identifying plant buildings and the direction of flow and
contents flowing in a pipe can all be very helpful. Well-lighted
and well-maintained walks and roadways are very important.
Plant grounds should be fenced to prevent unauthorized persons
and animals from entering the area. Keep items occasionally used
and old, discarded equipment neatly stored to avoid the appearance
of a cluttered junk yard. Groom your plant grounds in a fashion
that you will be proud of, and you will be amazed at the favorable
impression your facility will convey to the public and adminis-
trators.
QUESTIONS
11.OE What items should be included in a building
maintenance program?
11.OF When plant tanks and channels are drained, what items
would you inspect?
11.OG Why are neat and well-groomed grounds important?
11-8
-------
11.04 Chlorinators
11.040 Maintenance
Chlorine gas leaks around chlorinators or containers of chlorine
will cause corrosion of equipment. Check every day for leaks.
Large leaks will be detected by odor; small leaks may go un-
noticed until damage results. A green or reddish deposit on
metal indicates a chlorine leak. Any chlorine gas leakage in
the presence of moisture will cause corrosion. Always plug the
ends of any open connection to prevent moisture from entering
the lines. Never pour water on a chlorine leak because this will
only compound the problem by enlarging the leak. (Chlorine gas
reacts with water to form hydrochloric acid.
WARNING
IMPORTANT
e
TOXIC TO
Ammonia water will detect any chlorine leak. A small piece of
cloth, soaked with ammonia water and wrapped around the end of a
short stick, makes a good applicator to detect leaks. If chlorine
gas leakage is occurring, a white cloud of ammonium chloride will
form. It is good practice to make this test at all gas pipe joints,
both inside and outside the chlorinators, at regular intervals.
Bottles of ammonia water should be kept tightly capped to avoid
loss of strength. All pipe fittings must be kept tight to avoid
leaks. New gaskets should be used for each new connection.
11-9
-------
CAUTION
•TO LOCATE A CHt-ORlM^ L^AK, PO
SPgAV O(? 4WAS erQUlPAAerMT"
AMMONIA WAT££/ WAV^ AKJ AMMONUA
AMP VOU £AM DBTECT
-F MAKV LaAvk:^> .4OMe
AV^. A ^>T|C^1 WITH
A CLOTH OM TH^esip i w T^ROMTOF TUHA\
APE- LOOWMC-r ^O^ ^WLOUl MB
Ammonia bottles are not recommended for use in rooms containing
chlorine because after one squeeze, the entire area may be full
of white smoke and you may have trouble locating the leak. An
ammonia bottle may be used to look for chlorine leaks around
connections and cylinders. Use a cloth soaked in ammonia water
in a room.
The exterior casing of chlorinators should be painted as required;
however, most chlorinators manufactured recently have plastic
cases that do not require protective coatings. A clean machine is
a better operating machine. Glass bell jars may be cleaned with
water and a washing compound. Parts of a chlorinator handling
chlorine gas must be kept dry to prevent the chlorine and moisture
from forming hydrochloric acid. Some parts may be cleaned, when
required, first with water to remove water soluble material, then
with wood alcohol, followed by drying. The above chemicals leave
no moisture residue. Another method would be to wash them with
water and dry them over a pan or heater to remove all traces of
moisture.
11-10
-------
Water strainers on chlorinators frequently clog and require
attention. They may be cleaned by flushing with water or,
if badly fouled, they may be cleaned with dilute hydrochloric
acid, followed with a water rinse.
The atmospheric vent lines from chlorinators must be open
and free. These vent lines evacuate the chlorine to the
outside atmosphere when the chlorinator is being shut down.
It is advisable to place a screen over the end of the pipe
to keep insects from building a nest in it and clogging it up.
When chlorinators are removed from service, as much chlorine
gas as possible should be removed from the supply lines and
machines. The chlorine valves at the containers are shut off
and the chlorinator injector is operated for a period to remove
the chlorine gas. With visible bell jar chlorinators, the
absence of the characteristic yellow color of chlorine is an
indication that the chlorine has been expelled. In "V" notch
chlorinators (Chapter 10), the rotameter goes to the bottom
of the manometer tube when the chlorine has been expelled.
All chlorinators will give continuous trouble-free operation
if properly maintained and operated. Each chlorinator manufacturer
provides with each machine a maintenance and operations instruc-
tion booklet with line diagrams showing the operation of the
component parts of the machine. Manufacturer's instructions
should be followed for maintenance and lubrication of your
particular chlorinator. If you do not have an instruction
booklet, you may obtain one by contacting the manufacturer's
representative in your area.
QUESTIONS
11.OH Why should chlorine leaks be detected and repaired?
11.01 How would you search for chlorine leaks?
Taken in part from Operating and Maintaining Chlorinator and
Chlorine Containers, by LeRoy W. VanKleek, reprinted from
Waste Engineering, July 1965. Distributed by Wallace § Tiernan,
Incorporated.
11-11
-------
11.041 Chlorine Safety
For information on chlorine safety, see Chapter 10, Disinfection
and Chlorination, and Chapter 12, Plant Safety and Good House-
keeping. READ these chapters BEFORE_ attempting maintenance on
chlorinators, lines, or cylinders.
11.05 Library
A plant library can contain helpful information to assist in
plant operation. Material in the library should be cataloged
and filed for easy retrieval. Items in the library should
include:
1. Plant plans and specifications.
2. Manufacturers' instructions.
3. Reference books on wastewater treatment.
4. Professional journals and publications.
5. Manuals of Practice and Safety Literature published by
the Water Pollution Control Federation, 3900 Wisconsin
Avenue, Washington, D.C. 20016
6. First-aid book.
7. Reports.
8. A dictionary.
END OF LESSON 1 OF 6 LESSONS
on
MAINTENANCE
Please answer the discussion and review questions before continuing
with Lesson 2.
11-12
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 11. Maintenance
(Lesson 1 of 6 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.
1. Why should the operator thoroughly read and understand
manufacturers' literature before attempting to maintain
plant equipment?
2. Why must administrators or supervisors be made aware of
the need for an adequate maintenance program?
3. What is the purpose of a maintenance record keeping program?
4. What kinds of maintenance checks should be made periodically
of stairways, ladders, and catwalks?
5. When should inspection and maintenance of the underwater
portions of plant structures such as clarifiers and
digesters be scheduled?
6. Why should rodents and insects be controlled?
7. What items should be included in a plant library?
11-13
-------
CHAPTER 11. MAINTENANCE
(Lesson 2 of 6 Lessons)
11.1 MECHANICAL MAINTENANCE
Table of Contents
Paragraph General Maintenance Page
1 Repair Shop 11-17
2 Pumps 11-17
3 Description of Pumps 11-17
4 Pump Lubrication 11-25
5 Starting a Pump 11-25
6 Pump Shutdown 11-28
7 Float and Electrode Switches 11-29
8 Pump Driving Equipment 11-29
9 Electrical Controls 11-30
10 Operating Troubles 11-31
11 Preventive Maintenance 11-37
12 Pumps, General (Incl. Packing) 11-37
13 Reciprocating Pumps, General 11-43
14 Propeller Pumps, General 11-47
15 Electric Motors 11-51
16 Belt Drives 11-54
17 Chain Drives 11-55
18 Variable Speed Belt Drives 11-58
19 Couplings 11-61
20 Shear Pins 11-63
21 Gate Valves 11-67
22 Check Valves 11-71
23 Plug Valves 11-71
24 Sluice Gates 11-74
25 Acknowledgment 11-76
11-15
-------
The format of this section differs from the other chapters.
It was designed specifically to assist you in planning an
effective preventive maintenance program. The table of con-
tents is outlined on the preceding page, and the paragraphs
are numbered for easy reference when you use the Equipment
Service Cards and Service Record Cards mentioned in Section
11.0.
An entire book could be written on the topics covered in this
section. Step-by-step details for maintaining equipment are
not provided because manufacturers are continually improving
their products and these details could soon be out of date.
You are assumed to have some familiarity with the equipment
being discussed. For details concerning a particular piece
of equipment you should contact the manufacturer.This section
indicates to you the kinds of maintenance you should include
in your program and how you could schedule your work. Carefully
read the manufacturer's instructions and be sure you clearly
understand the material before attempting to maintain and
repair equipment. If you have any questions or need any help,
do not hesitate to contact the manufacturer or his local repre-
sentative.
A glossary is not provided in this section because of the large
number of technical words that require familiarization with the
equipment being discussed. The best way to learn the meaning
of these new words is from manufacturers' literature or from
their representatives. Some new words are described in the
lesson where necessary.
11-16
-------
Paragraph 1; Repair Shop
Many large plants have fully equipped machine shops staffed with
competent mechanics. But for smaller plants, adequate machine
shop facilities often can be found in the community. In addition,
most pump manufacturers maintain pump repair departments where
pumps can be fully reconditioned.
The pump repair shop in a large plant commonly includes such things
as welding equipment, lathes, drill press and drills, power hacksaw,
flame-cutting equipment, micrometers, calipers, gauges, portable
electric tools, grinders, a forcing press, metal-spray equipment,
and sand-blasting equipment. You must determine what repair work
you can and should do and when you need to request assistance
from an expert.
Paragraph 2; Pumps
Pumps serve many purposes in wastewater collection systems and
treatment plants. They may be classified by the character of the
material handled: raw wastewater, grit, effluent, activated sludge,
raw sludge, digested sludge, etc. Or, they may relate to the con-
ditions of pumping: high lift, low lift, recirculation, high
capacity, etc. They may be further classified by principle of
operation, such as centrifugal, propeller, reciprocating, and turbine.
The type of material to be handled and the function or required per-
formance of the pump vary so widely that the designing engineer must
use great care in preparing specifications for the pump and its con-
trols. Similarly, the operator must conduct a maintenance and
management program adapted to the peculiar characteristics of the
equipment.
Paragraph 5: Description of Pumps
A. Centrifugal Pumps
A centrifugal pump (Fig5- 11.2 and 11.3) is fundamentally a very
simple device, an impeller rotating in a casing. The impeller is
supported on a shaft which is, in turn, supported by bearings.
Liquid coming in at the center (eye) of the impeller (Fig. 11.4)
is picked up by the vanes and by the rotation of the impeller and
is thrown out by centrifugal force into the discharge.
Centrifugal pumps designed for pumping wastewater usually have smooth
channels and impellers with large-sized openings to prevent clogging.
11-17
-------
FLOW OUT
HEAVY-DUTY
THRUST BEARING
WITH DOUBLE
LOCKNUTS
ALLOY-STEEL SHAFT
GROUND TO SIZE
i
t-1
00
HSAVY-DUTY
RADIAL BEARING
SHIM ADJUSTMENT TO
COMPENSATE FOR WEAR
HEAVY CAST-IRON
FRAME, VERY RIGID
VENT PLUG
MACHINED
CENTERING FIT
FULL-SIZE PASSAGEWAYS
IN IMPELLER & CASING
FLOW IN
IMPELLER
DRAIN
PLUG
Fig. 11.2 Horizontal wastewater pump
(Source: War Department Technical Manual TM5-666)
-------
ALLOY-STEEL SHAFT
• GROUND TO SIZE
SHIM ADJUSTMENT
TO COMPENSATE
FOR WEAR
HEAVY CAST-IRON
FRAME, VERY RIGID
FULL-SIZE
PASSAGEWAYS
IN IMPELLER
AND CASING
MACHINED
CENTERING
FIT
FLOW IN
ELBOW WITH
FULL-SIZE
CLEANOUT
HEAVY-DUTY
THRUST BEARING
WITH DOUBLE
LOCKNUTS
HEAVY-DUTY
RADIAL BEARING
DEEP STUFFING BOX
IMPELLER
FLOW OUT
RIBBED
CAST-IRON
BASE
DRAIN PLUG
Fig. 11.3 Vertical ball-bearing type wastewater pump
(Source: War Department Technical Manual TM5-666)
11-19
-------
Discharge
x v Suction
\
Jmpel/er
eye
- Vanes
Refer to Fig. 11.3 for location of impeller in pump.
Fig. 11.4 Diagram showing details of
centrifugal pump impeller
(Source: Centrifugal Pumps by Karassik
and Carter of Worthington Corporation)
11-20
-------
Closed Radial
(Closed radial impellers are used in wastewater treatment plants.)
Open Radial
Fig. 11.5 Impellers
(Source: Centrifugal Pumps by Karassik
and Carter of Worthington Corporation)
11-21
-------
MOTOR
SHAFT TUBE
LINE SHAFT
DISCHARGE COLUMN
SHAFT BEARING
PROPELLER SHAFT
TOP BOWL
BOTTOM BEARING
FLOW IN
DISCHARGE TUBE
FLOW OUT
(See Fig. 11.7 for
propeller details)
FLOW IN
SUCTION SCREEN
Fig. 11.6 Propeller pump
(Source: Unknown)
11-22
-------
Mixed Flow
Propeller
Fig. 11.7 Impellers (continued)
(Source: Centrifugal Pumps by Karassik
and Carter of Worthington Corporation)
11-23
-------
Impellers may be of the open or closed type (Fig. 11.5), but
most pumps are provided with the two-blade impeller. Single-
blade impellers, however, are used successfully.
B. Propeller Pumps
There are two basic types of propeller pumps (Fig. 11.6), axial
flow and mixed flow impellers. The axial flow propeller pump is
one having a flow solely parallel to the axis * of the impeller
(Fig. 11.7). The mixed flow propeller pump is one having a flow
that is both radial2 and axial3 to the impeller (Fig. 11.7).
C. Reciprocating Pumps
The word reciprocating means moving back and forth, so a recipro-
cating pump is one that moves sludge by a piston that moves back
and forth. A simple reciprocating pump is shown in Fig. 11.8.
If the piston is pulled to the left, Check Valve A will open and
sludge will enter the pump and fill the casing.
When the piston reaches the end of its travel to the left and is
pushed back to the right, Check Valve A will close, Check Valve B
will open, and wastewater will be forced out the exit line.
PISTON
FLOW IN
FLOW OUT
Fig. 11.8 Simple reciprocating pump
(See page 11-44 for pump details)
1 Axis of impeller. In line with the shaft.
2 Radial to impeller. Material being pumped flows around the
impeller or parallel to the shaft.
3 Axial to impeller. Material being pumped flows at right angle
to the impeller or perpendicular to the shaft.
11-24
-------
D, Vertical Wet Well Pumps
A vertical wet well pump is a vertical shaft, diffuser type centri-
fugal pump with the pumping element suspended from the discharge
piping (Fig. 11.9). The needs of a given installation determine
the length of discharge column. The pumping bowl assembly may
connect directly to the discharge head for shallow sumps, or
may be suspended several hundred feet for raising water from
wells. Vertical turbine pumps are used to pump water from deep
wells, and may be of the single-stage or multi-stage type.4
Paragraph 4: Pump Lubrication
Pumps, motors, and drives should be oiled and greased in strict
accordance with the recommendations of the manufacturer. Cheap
lubricants may often be the most expensive in the end. Oil should
not be put in the housing while the pump, shaft is rotating because
the rotary action of the ball bearings will pick up and retain a
considerable amount of oil which will drain down when the unit
comes to rest, resulting in an overflow of oil around the shaft
or out of the oil cup.
Paragraph 5: Starting a Pump
The initial start-up work described in this paragraph should be
done by a competent and trained person, such as a manufacturer's
representative, consulting engineer, or an experienced operator.
The operator can learn considerable about pumps and motors by
accompanying and helping a competent person put new equipment into
operation.
Before starting, a pump should be lubricated according to the
lubrication instructions. The shaft should be turned by hand to
see that it rotates freely, after which a check should be made to
see that the shafts of the pump and motor are aligned and the
flexible coupling adjusted. (Refer to Paragraph 19.) If the unit
is belt driven, sheave (pulley) alignment and belt adjustment should
be checked. (Refer to Paragraph 16.) The electric current charac-
teristics should be checked with the motor characteristics and the
Multi-Stage Pump. Has more than one impeller. Single-stage has
one.
11-25
-------
r\-r
I
Principal parts are
underlined on page 11-27.
o
69
6C'
—.BO;
-661
FLOAT ROD
SEAL ASSEMBLY
Fig. 11.9 Vertical wet well pump
(Courtesy Chicago Pump)
11-26
-------
Part
No. Description
Part
No. Description
1. Motor Adapter
2. Shaft
3. Elastic Stop Nut
4. Grease Fitting
5. Bearing. Ball
6. Bearing. Pedestal
7. Truarc Retaining Ring
8. Packing Gland Stud
9. Grease, Fitting
10. Pipe Reducing Coupling
11. Leather Washer
12. Floor Plate
13. Packing Box
14. Hanger Pine
IS. Grease Line
16. Bronze Sleeve Bearing
17. Hex Head Cap Screw
18. Street Ell
19. Hex Nut
20. Perfect Seal Ring
21. Impeller Lock Screw
22. Impeller Set Screw
23. Impeller (See Part No. 78)
24. Discharge Casing
25. Suction Gasket
26. Hex Head Cap Screw
27. Bearing Adapter
28. Pump Coupling Key
29. Hex Head Cap Screw
30. Bearing Cap
31. Hex Nut
32. Hex Head Cap Screw
33. Gland Clamp
34. Hex Nut
35. Split Packing Gland
36. Hex Head Cap Screw
37. Discharge Ell
38. Packing Gasket
39. Rubber Gasket
40. Pedestal Gasket
41. Intermediate Bearing Plate
42. Discharge Pipe
43. Discharge Casing Bearing
44. Packing Ring Flange
45. Impeller Key
46. Suction Cover
47. Hollow Head Cup Point
Set Screw
48. Cap Plug Protector
49. Packing
50. Hex Nut
51. Set Screw Coupling
52. Pump Coupling Half
53. Coupling Disc
54. Motor Coupling Half
55. Float Rod Button
56. Hollow Head Set Screw
57. Float Rod
58. Mechanical Alternator
(duplex units only)
59. Float Rod Seal Housing
60. Cap, Float Rod Seal
61. Hex Head Cap Screw
62. Reducing Coupling
63. Float Rod Guide Pipe
64. Float
65. Float Lock Nut
66. Float Rod Seals
67. Switch Stand Assembly
68. Lock Washer
69. Round Head Machine Screw
70. Float Switch
71. Upper Shaft
72. Taper Pin
73. Auxiliary Coupling
74. Lower Discharge Pipe
75. Discharge Ell
76. Upper Discharge Pipe
77. Positioning Pins
78. Impeller Wearing Ring
79. Casing Wearing Ring
80. Felt Washer, Float Rod Seal
Fig. 11.9 Vertical wet well pump (contd.)
(Courtesy Chicago Pump)
11-27
-------
wiring should be inspected. Thermal units in the starter should
be checked to be sure that they are set properly. Motor rotation
should be determined by momentary contact to be certain that the
motor will turn the pump in the direction indicated by the rota-
tional arrows on the pump. If separate water seal units or vacuum
primer systems are used, these should be started. Finally, it
must be made certain that all valves in the suction and discharge
lines are open. Sometimes there is an exception (see following
paragraph) in the case of the discharge valve.
A pump should not be run without first having been primed. To
prime a pump, the pump must be completely filled with water or
wastewater. In some cases, automatic primers are provided. If
they are not, it is necessary to vent the casing. Most pumps are
provided with a valve to accomplish this. The trapped air should
be allowed to escape until water or wastewater flows from the vent,
after which the vent cap should be replaced. In the case of
suction-lift applications, the pump must be filled with water
unless a self-primer is provided. In nearly every case, it is
permissible to start a pump with the discharge valve open.
Exceptions to this, however, are where water hammer or velocity
distrubances might result, or where the motor does not have
sufficient margin of safety or power. Sometimes there are no
check valves used in the discharge line. In this case (with the
exception of positive displacement pumps) it is necessary to
start the pump and then open the discharge lines. Where there are
common discharge headers, it is essential to start the pump and
then open the discharge valve. A positive displacement pump (re-
ciprocating, etc.) should never be operated against a closed dis-
charge.
After starting the pump, again check to see that the direction of
rotation is correct. Packing-gland boxes (stuffing boxes) should
be observed for slight leakage as described in Paragraph 12. Check
to see that the bearings do not overheat from over- or under-
lubrication. The flexible coupling should not be noisy; if it is,
the noise may be caused by misalignment or improper clearance or
adjustment. Check to be sure pump anchorage is tight. Compare
delivered pump flows and pressures with pump performance curves.
If pump delivery falls below performance curves, look for obstruc-
tions in the pipelines. Inspect piping for leaks.
Paragraph 6: Pump Shutdown
When shutting down a pump for a prolonged period, the motor dis-
connect switch should be opened, locked out, and tagged with reason
for tag noted; all valves on the suction, discharge, and water-seal
lines should be shut tightly, and the pump should be completely
11-28
-------
drained by removing the vent and drain plugs. Sludge should not
be permitted to remain in pumps or piping for any length of time;
cases are on record where the gas produced has ruptured pipes and
sludge pumps.
It is also a good policy to inspect the pump and bearings thoroughly
so that all necessary servicing may be done during the inactive
period. The bearing housing should be drained and subsequently
replenished with fresh lubricant.
Paragraph 7: Float and Electrode Switches
To ensure the best operation of the pump, a systematic inspection
of the water level controls should be made at least once a week.
Check to see that:
1. Controls respond to a rising water level in the wet
well.
2. The unit starts when the float switch or electrode
system makes contact, and the pump stops at the pre-
scribed level in the wet well.
3. The motor speed comes up quickly and is maintained.
4. A brush-type motor does not spark profusely in start-
ing or running.
5. Grease and trash are not interfering with controls.
Be sure to remove scum from water-level float controls.
6. Any necessary adjustments are properly completed.
Paragraph 8; Pump Driving Equipment
Driving equipment used to operate pumps includes electric motors
and internal combustion engines. In rare instances, pumps are
driven with steam turbines, steam engines, air and hydraulic motors.
In all except the large installations, electric motors are used
almost exclusively, with synchronous and induction types being
the most commonly used. Synchronous motors operate at constant
speeds and are used chiefly in large sizes. Three-phase,
squirrel-cage induction motors are most often used in treatment
plants. These motors require little attention and, under average
11-29
-------
operating conditions, the factory lubrication of the bearing will
last approximately one year. (Check with the manufacturer as to
what he considers average operating hours.) In lubricating motors,
it should be remembered that too much grease may cause bearing
trouble or damage the winding.
Clean and dry all electrical contacts. Check for loose electri-
cal contacts. Make sure that hold-down bolts on motors are secure.
Check voltage while the motor is starting and running. Examine
bearings and couplings.
Paragraph 9: Electrical Controls
A variety of electrical equipment is used to control the operation
of wastewater pumps or to protect electric motors. The simplest
type of control unit consists of a counter-weighted float which
actuates a switch. When the float is raised by the wastewater to
a predetermined level, a switch is tripped which starts the pump;
and when the wastewater level falls to the cutoff level, the float
switch stops the pump. The time required for each cycle and the
length of time between cycles depend on the pumping rate and the
quantity of wastewater flow.
Where starters, disconnect switches, and cutouts are used, they
should be installed in accordance with the local regulations
(city and/or county codes) regarding this equipment. In the case
of larger motors, the power company often requires starters which
do not overload the power lines.
The electrode type, bubbler type, and diaphragm type water level
control systems are all similar in effect to the float-switch
system.
QUESTIONS
11.1A How would you find out how to lubricate a pump?
11.IB What problems can develop if too much grease is
used in lubricating a motor?
11-30
-------
Paragraph 10; Operating Troubles
The following list of operating troubles includes most of the
causes of failure or reduced operating efficiency. The remedy
or cure is either obvious or may be identified from the descrip-
tion of the cause.
SYMPTOM A—Pump Will Not Start
CAUSES:
1. Blown fuses or tripped circuit breakers attributed to:
A. Rating of fuses or circuit breakers not correct
B. Switch (breakers) contacts corroded or shorted
C. Terminal connections loose or broken somewhere in
the circuit
D. Automatic control mechanism not functioning
properly
E. Motor shorted or burned out
F. Wiring hookup or service not correct
G. Switches not set for operation
H. Contacts of the control relays dirty and arcing
I. Fuses or thermal units too warm
J. Wiring short-circuited
K. Shaft binding or sticking by reason of rubbing im-
peller, tight packing glands, or clogging of pump
2. Loose connection, fuse, or thermal unit
11-31
-------
SYMPTOM B--Reduced Rate of Discharge
CAUSES:
1. Pump not primed
2. Mixture of air in the wastewater
3. Speed of motor too low
4. Improper wiring
5. Defective motor
6. Discharge head too high
7. Suction lift higher than anticipated
8. Impeller clogged
9. Discharge line clogged
10. Pump rotating in wrong direction
11. Air leaks in suction line or packing box
12. Inlet to suction line too high, permitting air to enter
13. Valves partially or entirely closed
14. Check valves stuck or clogged
15. Incorrect impeller adjustment
16. Impeller damaged or worn
17. Packing worn or defective
18. Impeller turning on shaft because of broken key
19. Flexible coupling broken
20. Loss of suction during pumping may be caused by leaky suction
line, ineffective water or grease seal
11-32
-------
SYMPTOM C—High Power Requirements
CAUSES:
1. Speed of rotation too high
2. Operating heads lower than rating for which pump was
designed, resulting in excess pumping rates
3. Check valves open, draining long force main back into well
4. Specific gravity or viscosity of liquid pumped too high
5. Clogged pump
6. Sheaves on belt drive misaligned or maladjusted
7. Pump shaft bent
8. Rotating elements binding
9. Packing too tight
10. Wearing rings worn or binding
11. Impeller rubbing
SYMPTOM D--Noisy Pump
CAUSES:
1. Pump not completely primed
2. Inlet clogged
3. Inlet not submerged
4. Pump not lubricated properly
5. Worn impellers
6. Strain on pumps caused by unsupported pining fastened to
the pump
7. Foundation insecure
8. Mechanical defects in pump
9. Misalignment of motor and pump where connected by flexible shaft
11-33
-------
QUESTIONS
11.1C What items would you check if a pump will not start?
11.ID How would you attempt to increase the discharge from
a pump if the flow rate is lower than expected?
END OF LESSON 2 OF 6 LESSONS
on
MAINTENANCE
Please answer the discussion and review questions before continuing
with Lesson 3.
11-34
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 11. Maintenance
(Lesson 2 of 6 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 1.
8. What should you do if you can't understand the
manufacturer's instructions?
PICK THE CORRECT WORD:
9. Cheap lubricants may be the (1) most or (2) least expensive
in the end.
10. Start-up of a new pump should be done by (1) a new operator
or (2) a trained person.
11. How can you determine if a new pump will turn in the direction
intended?
12. When shutting down a pump for a prolonged period, what pre-
cautions should be taken with the motor-disconnect switch?
13. How can you tell if a new pump is delivering design flows
and pressures?
14. What is a maintenance problem with water-level float controls?
11-35
-------
CHAPTER 11. MAINTENANCE
(Lesson 3 of 6 Lessons)
Paragraph 11; Preventive Maintenance
The following paragraphs list some general preventive maintenance
services and indicate frequency of performance. There are many
makes and types of equipment and the wide variation of functions
cannot be included; therefore, you will have to use some judgment
as to whether the services and frequencies will apply to your
equipment. If something goes wrong or breaks in your plant, you
may have to disregard your maintenance schedule and fix the problem
now.
PA1UY;
Q, QUACreCLY; S,4£MIANNUAUV; A, ANMUAUV
Frequency
of
Service
Paragraph 12; Pumps, General
This paragraph lists some general preventive maintenance
services and indicates frequency of performance. Typical
centrifugal pump sections are shown in Figs. 11.2 and
11.3.
1. CHECK WATER-SEAL PACKING GLANDS FOR LEAKAGE. See
that the packing box is protected with a clear-water
supply from an outside source, making sure that
water seal pressure is at least 3 psi greater than
maximum pump discharge pressure. See that there are
no cross-connections.5 Check packing glands for leak-
age during operation. Allow a slight seal leakage when
5 Cross-Connection. A cross-connection is a connection where waste-
water .or water from the seal could enter a water supply.
11-37
-------
Frequency
of
Service
D
W
W
D
W
W
2.
3.
4.
5.
6.
7.
pumps are running to keep packing cool and in good
condition. The proper amount of leakage depends
on equipment and operating conditions. If excessive
leakage is found, hand tighten glands' nuts evenly, but
not too tight. After adjusting packing glands, be
sure shaft turns freely by hand. If serious leakage
continues, renew packing, shaft, or shaft sleeve.
CHECK GREASE-SEALED PACKING GLANDS. When grease is
used as a packing gland seal, maintain constant
grease pressure on packing during operation. When
a spring-loaded grease cup is used, keep it loaded
with grease. Force grease through packing at rate
of about one ounce per day.
OPERATE PUMPS ALTERNATELY. If two or more pumps
of the same size are installed, alternate their
use to equalize wear, keep motor windings dry, and
distribute lubricant in bearings.
INSPECT PUMP ASSEMBLY. Check float controls noting
how they respond to rising water level. See that
unit starts when float switch makes contact and that
pump empties basin at a normal rate. Apply light
oil to moving parts.
Service stand-by pump and run assembly long enough
to obtain normal motor temperature rise.
CHECK MOTOR CONDITION. See Paragraph 15.
CLEAN PUMP. First lock out power. Clean-out handholes
are provided on the pump volute. To clean pump, close
all valves, drain pump, remove handhold cover, and
remove all solids.
CHECK PACKING GLAND ASSEMBLY. Check packing gland,
the unit's most abused and troublesome part. If
stuffing box leaks excessively when gland is pulled
up with mild pressure, remove packing and examine
shaft sleeve carefully. Replace grooved or scored
shaft sleeve because packing cannot be held in
stuffing box with roughened shaft or shaft sleeve.
Replace the packing a strip at a time, tamping each
11-38
-------
Frequency
of
Service
10,
strip thoroughly and staggering joints. (See
Fig. 11.10.) Position lantern ring (water-seal
ring) properly. If grease sealing is used, com-
pletely fill lantern ring with grease before
putting remaining rings of packing in place.
The type of packing used is less important than
the manner in which packing is placed. Never use
a continuous strip of packing. This type packing
wraps around and scores the shaft sleeve or is
thrown out against outer wall of stuffing box,
allowing wastewater to leak through and score
the shaft.
INSPECT AND LUBRICATE BEARINGS. Unless otherwise
specifically directed for a particular pump model,
drain lubricant and wash out oil wells and bearing
with solvent. Check sleeve bearings to see that
oil rings turn freely with the shaft. Repair or
replace if defective. Refill with proper lubricant.
Measure bearings and replace those worn excessively.
Generally, allow clearance of 0.002 inch plus 0.001
inch for each inch or fraction of inch of shaft-
journal diameter.
CHECK OPERATING TEMPERATURE OF BEARINGS. Check bear-
ing temperature with thermometer, not by hand. If
antifriction bearings are running hot, check for over-
lubrication and relieve if necessary. If sleeve
bearings run too hot, check for lack of lubricant.
If proper lubrication does not correct condition, dis-
assemble and inspect bearing. Check alignment of pump
and motor if high temperatures continue.
CHECK ALIGNMENT OF PUMP AND MOTOR. For method of
aligning pump and motor, see Paragraph 19. If mis-
alignment recurs frequently, inspect entire piping
system. Unbolt piping at suction and discharge
nozzles to see if it springs away, indicating strain
on casing. Check all piping supports for soundness
and effective support of load.
11-39
-------
WATER-SEAL SUPPLY
GLAND
SHAFT
Fig. 11.10 Method of packing shaft
(Source: War Department Technical Manual TM5-666)
11-40
-------
Frequency
of
Service
Vertical pumps usually have flexible shafting
which permits slight angular misalignment; however,
if solid shafting is used, align exactly. If
beams carrying intermediate bearings are too light
or are subject to contraction or expansion, re-
place beams and realign intermediate bearings
carefully.
11. INSPECT AND SERVICE PUMPS.
a. Remove rotating element of pump and inspect
thoroughly for wear. Order replacement parts
where necessary.
e.
f.
Remove any deposit or scaling.
water-seal piping.
Clean out
Determine pump capacity by pumping into empty
tank of known size or by timing the draining
of pit or sump.
„ „ .. Volume, gallons
Pump Capacity, epm = * & • • •
^ Time, minutes
Test pump efficiency. Refer to pump manufac-
turer's instructions on how to collect data
and perform calculations. Or see Chapter 15
on Mathematics and Treatment Plant Problems.
Measure total dynamic suction and discharge
lifts to test pump and pipe condition. Record
figures for comparison with later tests.
Inspect foot and check valves, paying particular
attention to check valves, which can cause water
hammer when pump stops. (See Paragraph 22 also.)
Examine wearing rings. Replace seriously worn
wearing rings to improve efficiency. Check
wearing ring clearances which generally should
be no more than 0.003 inch per inch of wearing
diameter.
CAUTION: To protect rings and casing, never allow
pump to run dry through lack of proper priming when
starting or loss of suction when operating.
11-41
-------
Frequency
of
Service
A
12. DRAIN PUMP BEFORE PROTRACTED SHUTDOWN. When
shutting down pump for a long period, open motor-
disconnect switch; shut all valves on suction,
discharge, water-seal, and priming lines; drain
pump completely by removing vent and drain plugs.
This procedure protects pump against corrosion,
sedimentation, and freezing. Inspect pump and
bearings thoroughly and perform all necessary
servicing. Drain bearing housings and replenish
with fresh oil, purge old grease and replace.
When a pump is out of service, run it monthly to
warm it up and to distribute lubrication so the
packing will not "freeze" to the shaft. Resume
periodic checks after pump is put back in service,
QUESTIONS
11.IE What is a cross-connection?
11. IF Is a slight water-seal leakage desirable when a pump
is running? If so, why?
11.1G How would you measure the capacity of a puup?
.11.1H Estimate the capacity of a pump (in GPM) if it lowers
the water in a 10-fcot wide x 15-foot long wet well
1.7 feet in five minutes.
11.11 What should be done to a pump before it is shut down
for a long time, and why?
11-42
-------
Frequency
of
Service
W
Paragraph 15: Reciprocating Pumps, General (See pig. 11.11)
The general procedures in this paragraph apply to all
reciprocating sludge pumps described in this section.
1. CHECK SHEAR PIN ADJUSTMENT. Set eccentric by placing
shear pin through proper hole in eccentric flanges
to give required stroke. Tighten the two 5/8- or
7/8-inch hexagonal nuts on connecting rods just
enough to take spring out of lock washers. (See
Paragraph 20.) When a shear pin fails, eccentric
moves toward neutral position, preventing damage to
the pump. Remove cause of obstruction and insert new
shear pin. Shear pins fail because of one of three
common causes:
(1) Solid object lodged under piston
(2) Clogged discharge line
(3) Stuck or wedged valve
2. CHECK PACKING ADJUSTMENT. Give special attention to
packing adjustment. If packing is too tight, it re-
duces efficiency and scores piston wells. Keep packing
just tight enough to keep sludge from leaking through
gland. Before pump is installed or after it has been
idle for a time, loosen all nuts on packing gland.
Run pump with sludge suction line closed and valve
covers open for a few minutes to break in the packing.
Turn down gland nuts no more than necessary to prevent
sludge from getting past packing. Tighten all pack-
ing nuts uniformly.
When packing gland bolts cannot be taken up farther,
replace packing. Remove old packing and thoroughly
clean cylinder and piston walls. Place new packing
into cylinder, staggering packing-ring joints, and
tamp each ring into place. Break in and adjust pack-
ing as explained above. When chevron type packing
is used, tighten gland nuts only finger tight because
excessive pressure ruins packing and scores plunger.
11-43
-------
Principal parts are
underlined on page 11-45
Fig. 11.11 Reciprocati:
(Courtesy ITT Marlow, a Unit of Inter-
national Telephone and Telegraph Corp.)
[ELBOW FOR AIK
11-44
-------
ITEM
1
2
3
4
5
0
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
23
27
28
29
30
31
32
__33
34
35
36
37
38
39
40
41
42
43
. 44
45
46
47
48
49
50
51
52
53
54.
55
DESCRIPTION
.Countershaft Pulley
Motor Pulley
. "V" Belts
Belt Guard Hood
Belt Guard Bottom Section
Belt Guard Back Plate
Countershaft
Key
Pillow Block Bearings
Key, Pinion
Pinion
Gear
Gear Case
Gear Case Cover
Gasket, Gear Case
_Grease Retainer 1-3/8" I. D.
.Grease Retainer 1-3/4" I. D.
Main Shaft
Pillow Block Bearings
Eccentric
Eccentric Bushing
Driving Flange
Driven Fiance
Pump Body
Suction Elbow
Suction Elbow, Air Chamber
Discharge Valve Chamber
Valve Chamber Cover
Gasket, Cover
Valve Chamber Yoke Right
Valve Chamber Yoke. Left
Yoke Spacer
Valve Chamber Handle
Valve Seat
Gasket, Valve Seat
Ball Valve, 5-1/8" Dia.
Stuffing Box
Gasket, Stuff. BoxtoPuirra
Gland
Packing
Air Chamber
Nipple, 8" long (Discharge)
Nipple, 16" long
1/4" #64T Pet Cock
1/4" Ball Snifter Cock
1" Bronze Gate Valve
Plunger ;
Crosshead
Crosshead Wrist Pin
Connecting Rod
Connecting Rod Bushing
Connecting Rod Shim
Sight Feed Oiler
Drain Rod Assembly
Driving Flange Bushing
Fig. 11.11 Reciprocating pump (contd.)
(Courtesy ITT Marlowt a Unit of Inter-
national Telephone and Telegraph Corp.)
11-45
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Frequency
of
Service
W
CHECK BALL VALVES. When valve balls are so worn
that diameter is 5/8 inch smaller than original
size, they may jam into guides in valve chamber.
Check size of valve balls and replace if badly
worn.
CHECK VALVE-CHAMBER GASKETS. Valve-chamber gaskets
on most pumps serve as a safety device and blow out
under excessive pressure. Check gaskets and re-
place if necessary. Keep additional gaskets on
hand for replacement.
CHECK ECCENTRIC ADJUSTMENT. To take up babbitt
bearing, remove brass shims provided on connecting
rod. After removing shims, operate pump for at
least one hour and check to see that eccentric does
not run hot.
NOTE UNUSUAL NOISES. Check for noticeable water
hammer when pump is operating. This noise is most
pronounced when pumping water or very thin sludge;
it decreases or disappears when pumping heavy sludge.
Eliminate noise by opening the 1/4-inch petcock on
pump body slightly; this draws in a small amount of
air, keeping discharge air chamber full at all times.
CHECK CONTROL VALVE POSITIONS. Because any plunger
pump may be damaged if operated against closed
valves in the pipeline, especially the discharge line,
make all valve setting changes with pump shut down;
otherwise pumps which are installed to pump from two
sources or to deliver to separate tanks at different
times may be broken if all discharge line valves are
closed simultaneously for a few seconds or discharge
valve directly above pump is closed.
GEAR REDUCER. Check oil level by removing plug on
the side of the gear case. Unit should not be in
operation.
CHANGE OIL AND CLEAN MAGNETIC DRAIN PLUG.
11-46
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Frequency
of
Service
W
w
D
M
D
D
W
W
W
W
A
10. CONNECTING RODS. Set oilers to disperse two drops
per minute.
11. PLUNGER CROSSHEAD. Fill plunger as required to half
cover the wrist pin with oil.
12. PLUNGER TROUGH. Keep small quantity of oil in trough
to lubricate the plunger.
13. MAIN SHAFT BEARING. Grease bearings monthly. Pump
should be in operation when lubricating to avoid
excessive pressure on seals.
14. CHECK ELECTRIC MOTOR. See Paragraph 15.
Paragraph 14: Propeller Pumps, General (.Pig. 11.6)
1. CHECK MOTOR CONDITION. See Paragraphs 15-1 and 15-2.
2. CHECK PACKING GLAND ASSEMBLY. See Paragraph 12-7.
3. INSPECT PUMP ASSEMBLY. See Paragraph 12-4.
4. LUBE LINE SHAFT AND DISCHARGE BOWL BEARING. Main-
tain oil in oiler at all times. Adjust feed rate to
approximately four drops per minute.
5. LUBE SUCTION BOWL BEARING. Lube through pressure
fitting. Usually three or four strokes of gun are
enough.
6. OPERATE PUMPS ALTERNATELY. See Paragraph 12-3.
7. LUBE MOTOR BEARINGS. See Paragraph 15.
11-47
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QUESTIONS
11.1J What are some of the common causes of shear pin failure
in reciprocating pumps?
11.IK What may happen when water or a thin sludge is being
pumped by a reciprocating pump?
END OF LESSON 3 OF 6 LESSONS
on
MAINTENANCE
Please answer the discussion and review questions before continuing
with Lesson 4.
11-48
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 11. Maintenance
(Lesson 3 of 6 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 2.
15. What would you do if considerable water was leaking from
the water-seal of a pump?
16. When two or more pumps of the same size are installed,
why should they be operated alternately?
17. What should be checked if pump bearings are running hot?
18. What happens when the packing is too tight on a reciprocating
pump?
19. Why should changes in control valves for reciprocating pumps
be adjusted when the pump is shut down?
11-49
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CHAPTER 11. MAINTENANCE
(Lesson 4 of 6 Lessons)
Frequency
of
Service
W
Paragraph 15; Electric Motors
In order to ensure the proper and continuous function of
electric motors, the items listed in this paragraph must
be performed at the designated intervals. If operational
checks indicate a motor is not functioning properly,
these items will have to be checked to locate the problem.
1. CHECK MOTOR CONDITIONS.
)
a. Keep motors free from dirt, dust and moisture.
b. Keep operating space free from articles which
may obstruct air circulation.
c. Check for excessive grease leakage from bearings.
2. NOTE ALL UNUSUAL CONDITIONS.
a. Unusual noises in operation.
b. Motor failing to start or come to speed normally,
sluggish operation.
c. Motor or bearings which feel or smell hot.
d. Continuous or excessive sparking commutator or
brushes. Blackened commutator.
e. Intermittent sparking at brushes.
f. Fine dust under coupling having rubber buffers
or pins.
g. Smoke, charred insulation, or solder whiskers
extending from armature.
11-51
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Frequency
of
Service
A
h. Excessive humming.
i. Regular clicking.
j. Rapid knocking.
k. Brush chatter.
1. Vibration.
m. Hot commutator.
LUBRICATE BEARINGS.
a. Check grease in ball bearings and replenish
when necessary.
Follow instructions below when preparing bearings
for grease.
b. Wipe pressure gun fitting, bearing housing,
and relief plug to make sure that no dirt
gets into bearing with grease.
c. Before using grease gun always remove relief
plug from bottom of bearing to prevent excessive
pressure in housing which might rupture bearing
seals.
d. Use clean screw driver or similar tool to remove
hardened grease from relief hole and permit
excess grease to run freely from bearing.
e. While motor is running, add grease with hand
operated pressure gun until it flows from relief
hole, purging housing of old grease. If there
is no bottom or relief plug on bearing housing,
insert grease cautiously through upper plug.
Usually four or five strokes of gun are enough.
If bearing is over-lubricated, seal may be
ruptured. If lubricating a running motor is
dangerous, follow above procedure with motor
at a standstill.
11-52
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Frequency
of
Service
A
f. Allow motor to run for five minutes or until
all excess grease has drained from bearing
housing.
g. Stop motor and replace relief plug tightly
with wrench.
USING A STETHOSCOPE,6 CHECK BOTH BEARINGS. Listen
for whines, gratings, or uneven noises. Listen all
around the bearing and as near as possible to the
bearing. Listen while the motor is being started
and shut off. If unusual noises are heard, pin-
point the location.
IF YOU THINK THE MOTOR is running unusually hot,
check with a thermometer. Place thermometer on
the casting near the bearing, holding it there
with putty or clay.
DATEOMETER.7 If there is a dateometer on the motor,
after changing the oil in the motor, loosen the
dateometer screw and set to the corresponding year.
11.1L
QUESTION
What are the major items you would include when checking
an electric motor?
6 Stethoscope. An instrument used to magnify sounds and carry them
to the ear.
7 Dateometer. A small calendar disc.
11-53
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Frequency
of
Service
Paragraph 16; Belt Drives
1. GENERAL. Maintaining a proper tension and align-
ment of belt drives ensures long life of belts and
sheaves. Incorrect alignment causes poor operation
and excessive belt wear. Inadequate tension reduces
the belt grip, causes high belt loads, snapping, and
unusual wear.
a. Cleaning belts. Keep belts and sheaves clean
and free of oil, which causes belts to deterio-
rate. To remove oil, take belts off sheaves
and wipe belts and sheaves with a rag moistened
in a non-oil base solvent. Carbon tetrachloride
is not recommended because exposure to its fumes
has many toxic effects on humans. It also is
absorbed into the skin on contact and is cumulative,
b. Installing belts. Before installing belts, re-
place worn or damaged sheaves, then slack off
on adjustments. Do not try to force belts into
position. Never use a screw driver or similar
lever to get belts onto sheaves. After belts
are installed, adjust tension; recheck tension
after eight hours of operation. (See Table I.)
c. Replacing belts. Replace belts as soon as they
become frayed, worn, or cracked. NEVER REPLACE
ONE V-BELT ON A MULTIPLE DRIVE. Replace the
complete set with a set of matched belts, which
can be obtained from any supplier. All belts in
a matched set are machine-checked to ensure equal
size and tension.
d. Storing spare belts. Store spare belts in a cool
dark place. Tag all belts in storage to identify
them with the equipment on which they can be used.
2. V-BELTS. A properly adjusted V-belt has a slight bow
in the slack side when running; when idle it has an
alive springiness when thumped with the hand. An
improperly tightened belt feels dead when thumped.
11-54
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Frequency
of
Service
If the slack side of the drive is less than 45
from the horizontal, vertical sag at the center
of the span may be adjusted in accordance with
Table I below.
TABLE I. HORIZONTAL BELT TENSION
Span
Cinches)
10
20 50 100 150 200
Vertical From .01 .03 .20 .80 1.80 3.30
Sag
(inches) To .03 .09 .58 2.30 4.90 8.60
M
M
Check tension. If tightening belt to proper
tension does not correct slipping, check for
overload, oil on belts, or other possible
causes. Never use belt dressing to stop belt
slippage. Rubber wearings near the drive are
a sign of improper tension, incorrect align-
ment, or damaged sheaves.
Check sheave (pulley) alignment. Lay a long
straight edge or string across outside faces
of pulley, and allow for differences in
dimensions from center lines of grooves to
outside faces of the pulleys being aligned.
Be especially careful in aligning drives with
more than one V-belt on a sheave, as mis-
alignment can cause unequal tension.
Paragraph 17; Chain Drives
1. GENERAL. Chain drives may be designated for slow,
medium, or high speeds.
a. Slow-speed drives. Because slow-speed drives
are usually enclosed, adequate lubrication is
difficult. Heavy oil applied to the outside
of the chain seldom reaches the working parts;
in addition, the oil catches dirt and grit and
becomes abrasive. For lubricating and cleaning
methods, see 5 and 6 below.
11-55
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Frequency
of
Service
b. Medium- and high-speed drives. Medium-speed
drives should be continuously lubricated with
a device similar to a sightfeed oiler. High-
speed drives should be completely enclosed in
an oiltight case and the oil maintained at
proper level.
CHECK OPERATION. Check general operating condition
during regular tours of duty.
CHECK CHAIN SLACK. The correct amount of slack is
essential to proper operation of chain drives.
Unlike other belts, chain belts should not be tight
around the sprocket; when chains are tight, working
parts carry a much heavier load than necessary.
Too much slack is also harmful; on long centers
particularly, too much slack causes vibrations and
chain whip, reducing life of both chain and sprocket.
A properly installed chain has a slight sag or
looseness on the return run.
CHECK ALIGNMENT. If sprockets are not in line or
if shafts are not parallel, excessive sprocket and
chain wear and early chain failure result. Wear on
inside of chain, side walls, and sides of sprocket
teeth are signs of misalignment. To check alignment,
remove chain and place a straight edge against sides
of sprocket teeth.
CLEAN. On enclosed types, flush chain and enclosure
with solvent. On exposed types, remove chain and
soak and wash it in solvent. Clean sprockets, in-
stall chain, and adjust tension.
NOTE: If chains are too large to soak them con-
veniently, wash them by applying solvent with a
brush.
CHECK LUBRICATION. Soak exposed type chains in oil
to restore lubricating film. Remove excess lubricant
by hanging chains up to drain.
11-56
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Frequency
of
Service
Do not lubricate underwater chains which operate
in contact with considerable grit. If water is
clean, lubricate by applying waterproof grease
with brush while chain is running.
Do not lubricate chains on elevators or on con-
veyors of feeders which handle dirty or gritty
materials. Dust and grit combine with lubricants
to form a cutting compound which reduces chain
life.
7. CHANGE OIL. On enclosed types only, drain oil
and refill case to proper level.
8. INSPECT. Note and correct abnormal conditions
before serious damage results. Do not put a new
chain on worn sprockets. Always replace worn
sprockets when replacing a chain because out-of-
pitch sprockets cause as much chain wear in a
few hours as years of normal operation.
9. TROUBLE SHOOTING. Some common symptoms of improper
chain-drive operation and their remedies follow:
a. Excessive noise. Correct alignment, if mis-
aligned. Adjust centers for proper chain
slack. Lubricate in accordance with afore-
mentioned methods. Be sure all bolts are
tight. If chain or sprockets are worn, re-
verse or renew if necessary.
b. Wear on chain, side walls, and sides of teeth.
Remove chain and correct alignment.
c. Chain climbs sprockets. Check for poorly
fitting sprockets and replace if necessary.
Make sure tightener is installed on drive
chain.
d. Broken pins and rollers. Check for chain speed
which may be too high for the pitch, and substi-
tute chain and sprockets with shorter pitch if
necessary. Breakage also may be caused by
shock loads.
11-57
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Frequency
of
Service
W
M
e. Chain clings to sprockets. Check for incorrect
or worn sprockets or heavy, tacky lubricants.
Replace sprockets or lubricants if necessary.
f. Chain whip. Check for too-long centers or
high pulsating loads and correct cause.
g. Chains get stiff. Check for misalignment,
improper lubrication, or excessive overloads.
Make necessary corrections or adjustments.
Paragraph 18: Variable Speed Belt Drives (See Fig. 11.12)
1. CLEAN DISKS. Remove grease, acid, and water from
disk faces.
2. CHECK SPEED-CHANGE MECHANISM. Shift drive through
entire speed range to make sure shafts and bearings
are lubricated and disks move freely in lateral
direction on shafts.
3. CHECK V-BELT. Make sure it runs level and true. If
one side rides high, a disk is sticking on shaft because
of insufficient lubrication or wrong lubricant. In
this case, stop the drive at once, remove V-belt, and
clean disk hub and shaft thoroughly with solvent until
disk moves freely. Relubricate with soft ball-bearing
grease and replace V-belt in opposite direction from
that in which it formerly ran.
If drive is not operated for 30 days or more, shift
unit to minimum speed position, placing spring on
variable speed shaft at minimum tension and relieving
belt of excessive pressure.
4. LUBRICATE DRIVE. Make sure to apply lubricant at
all the six force-feed lubrication fittings (Fig.
11.12: A, B, D, E, G, and H) and the one cup type
fitting (C).
NOTE: If the drive is used with a reducer, Fitting E
is not provided.
11-58
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A, B, D, E, G, and H are force-feed lubrication fittings.
C is a cup type lubrication fitting.
Fig. 11.12 Reeves varidrive
(Source: War Department Technical Manual TM5-666)
11-59
-------
Frequency
of
Service
W
a. Once every ten days to two weeks, use two or
three strokes of a grease gun through fittings
A and B at ends of shifting screw and variable
speed shaft, respectively, to lubricate bearings
of movable disks. Then, with unit running, shift
drive from one extreme speed position to the
other to ensure thorough distribution of lubri-
cant over disk-hub bearings.
b. Add two or three shots of grease through fittings
D and E to lubricate frame bearing on variable
speed shaft.
c. Every 90 days add two or three cupfuls of grease
to Cup C which lubricates thrust bearing on
constant speed shaft.
d. Every 90 days use two or three strokes of grease
gun through Fitting G and H to lubricate motor-
frame bearings.
CAUTION: Be sure to follow manufacturer's
recommendation on type of grease. After lubri-
cating, wipe excessive grease from sheaves and
belt.
QUESTIONS
11.1M How can you tell if a belt on belt drive equipment has
proper tension and alignment?
11. IN Why should sprockets be replaced when replacing a chain
in a chain drive unit?
11-60
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Frequency
of
Service
Paragraph 19; Couplings
1. GENERAL. Unless couplings between the driving and
driven elements of a pump or any other piece of
equipment are kept in proper alignment, breaking
and excessive wear results in either or both the
driven machinery and the driver. Burned-out
bearings, sprung or broken shaft, and excessively
worn or ruined gears are some of the damages caused
by misalignment. To prevent outages and the expense
of installing replacement parts, check the alignment
of all equipment before damage occurs.
a. Improper original installation of the equipment
may not necessarily be the cause of the trouble.
Settling of foundations, heavy floor loadings,
warping of bases, excessive bearing wear, and
many other factors cause misalignment. A rigid
base is not always security against misalignment.
The base may have been mounted off level, which
could cause it to warp.
b. Flexible couplings permit easy assembly of equip-
ment, but they must be aligned as exactly as
flanged couplings if maintenance and repair are
to be kept to a minimum. Rubber-bushed types
cannot function properly if the bolts cannot
move in their bushings.
2. CHECK COUPLING ALIGNMENT. Excessive bearing and motor
temperatures caused by overload, noticeable vibration,
or unusual noises may all be warnings of misalignment.
Realign when necessary (Fig. 11.13) using a straight
edge and thickness gage or wedge. To ensure satis-
factory operation, level up to within 0.005 inch as
follows:
a. Remove coupling pins.
b. Rigidly tighten driven equipment; slightly tighten
bolts holding drive.
11-61
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STRAIGHT EDGE
PARALLEL MISALIGNMENT
•STRAIGHT EDGE
FEELER GAGE -
ANGULAR MISALIGNMENT
FEELER GAGE
PERFECT ALIGNMENT
Fig. 11.13 Testing alignment, straight edge
(Source: Unknown)
11-62
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Frequency
of
Service
c. To correct horizontal and vertical misalign-
ment, shift or shim drive to bring coupling
halves into position so no light can be seen
under a straight edge laid across them. Place
straight edge in four positions, holding a light
back of straight edge to help ensure accuracy.
d. Check for angular misalignment with a thickness
or feeler gage inserted at four places to make
certain space between coupling halves is equal.
e. If proper alignment has been secured, coupling
pins can be put in place easily using only
finger pressure. Never hammer pins into place.
f. If equipment is still out of alignment repeat
the procedure.
3. CHANGE OIL IN FAST COUPLINGS. Drain out old oil and
add gear oil to proper level. Correct quantity is
given on instruction card supplied with each coupling.
Paragraph 20; Shear Pins
Many wastewater treatment units utilize shear pins as
protective devices to prevent damage in case of sudden
overloads. To serve this purpose these devices must be
in operational condition at all times. Under some operating
conditions shearing surfaces of a shear pin device may
freeze together so solidly that an overload fails to break
them.
Manufacturers' drawings for particular installations
usually specify shear pin material and size. If this
information is not available, obtain the information from
the manufacturer, giving him model, serial number, and
load conditions of unit. When necessary to determine shear
pin size, select the lowest strength which does not break
under the unit's usual loads. When proper size is determined
never use a pin of greater strength, such as a bolt or a nail,
11-63
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Frequency
of
Service
M
Q
If necked pins are used, be sure the necked-down portion
is properly positioned with respect to shearing surfaces.
When a shear pin breaks, determine and remedy the cause
of failure before inserting new pin and starting drive
in operation.
1. GREASE SHEARING SURFACES.
2. REMOVE SHEAR PIN. Operate motor for a short time
to smooth out any corroded spots.
3. CHECK SPARE INVENTORY. Make sure an adequate supply
is on hand, properly identified and with record of
proper pin size, necked diameter, and longitudinal
dimensions.
QUESTIONS
11.10 What factors could cause couplings to become out of
alignment?
11.IP What is the purpose of shear pins?
END OF LESSON 4 OF 6 LESSONS
on
MAINTENANCE
Please answer the discussion and review questions before continuing
with Lesson 5.
11-64
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DISCUSSION AND REVIEW QUESTIONS
Chapter 11. Maintenance
(Lesson 4 of 6 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 3.
20. Why would you use a stethoscope to check an electric motor?
21. How would you determine if a motor is running unusually hot?
22. How would you clean belts on belt drive?
23. Why should you never replace only one belt on a multiple
drive unit?
24. What do rubber wearings near a belt drive indicate?
25. How can you determine if a chain in a chain drive unit
has the proper slack?
26. What happens when couplings are not in proper alignment?
11-65
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CHAPTER 11. MAINTENANCE
(Lesson 5 of 6 Lessons)
Frequency
of
Service
Paragraph 21: Gate Valves (Fig. 11.14)
The most common maintenance required by gate valves
(Fig. 11.14) is oiling, tightening, or replacing the
stem stuffing box packing.
1.
2.
REPLACE PACKING. Modern gate valves can be repacked
without removing them from service. Before repack-
ing, open valve wide. This prevents excessive leakage
when the packing or the entire stuffing box is removed
by drawing stem collar stem tightly against bonnet on
a nonrising stem valve, and tightly against bonnet
bushing on rising stem valve.
a. Stuffing box. Remove all old packing from
stuffing box with a packing hook or a rat-
tail file with bent end. Clean valve stem
of all adhering particles and polish it with
fine emery cloth. After polishing remove
the fine grit with a clean cloth to which a
few drops of oil have been added.
b. Insert packing. Insert new split-ring pack-
ing in stuffing box and tamp it into place
with packing gland. Stagger ring splits.
After stuffing box is filled, place a few
drops of oil on stem, assemble gland, and
tighten it down on packing.
OPERATE VALVE.
sticking.
Operate inactive gate valves to prevent
LUBRICATE GEARING. Lubricate gate valves as recommended
by manufacturer. Lubricate thoroughly any gearing
in large gate valves. Wash open gears with solvent and
lubricate with grease.
LUBRICATE RISING-STEM THREADS. Clean threads on rising-
stem gate valves and lubricate with grease.
11-67
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125-Pound Ferrosteel Wedge Gate Valves
Names of Parts
STEM COLLAR
GASKET '
stuffing box
bushings
disc bushing
bonnet bushing
bonnet
Non-Rising Stem Valve
Bronze Trimmed — Open
Outside Screw and
Yoke Valve
Bronze Trimmed — Closed
These illustrations are representative of sizes 12-inch and smaller only
CHECK VALVES
PIN
PIN
LEATHER DISK
FACING
DISK
Fig. 11.14 Valves
(Source: Crane Co.)
11-68
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Frequency
of
Service
5. LUBRICATE BURIED VALVES. If a buried valve works
hard, lubricate it by pouring oil down through a
pipe which is bent at the end to permit oiling the
packing follower below the valve nut.
6. REFACE LEAKY GATE VALVE SEATS. If gate valve seats
leak, reface them immediately, using the method
discussed below. A solid wedge disk valve is used
for illustration, but the general method also
applies to other types of reparable gate valves.
Proceed as follows:
a. Remove bonnet and clean and examine disk and
body thoroughly. Carefully determine extent
of damage to body rings and disk. If corrosion
has caused excessive pitting or eating away of
metal, as in guide ribs in body, repairs may be
impractical.
b. Check and service all parts of valve completely.
Remove stem from bonnet and examine it for
scoring and pitting where packing makes contact.
Polish lightly with fine emery cloth to put stem
in good condition. Use soft jaws if stem is put
in vise.
c. Remove all old packing and clean out stuffing
box. Clean all dirt, scale, and corrosion from
inside of valve bonnet and other parts.
d. Do not salvage an old gasket. Remove it com-
pletely and replace with one of proper quality
and size.
e. After cleaning and examining all parts, determine
whether valve can be repaired by removing cuts
from disk and body seat faces or by replacement
of body seats. If repair can be made, set disk
in vise with face leveled, wrap•fine emery cloth
around a flat tool, and rub or lap off entire
bearing surface on both sides to a smooth, even
finish. Remove as little metal as possible.
11-69
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Frequency
of
Service
g.
h.
Repair cuts and scratches on body rings, lapping
with an emery block small enough to permit con-
venient rubbing all around rings. Work carefully
to avoid removing so much metal that disk will
seat too low. When seating surfaces of disk
and seat rings are properly lapped in, coat
faces of disk with Prussian blue8 and drop disk
in body to check contact. When good, continuous
contact is obtained, the valve is tight and ready
for assembly. Insert stem in bonnet, install new
packing, assemble other parts, attach disk to
stem, and place assembly in body. Raise disk to
prevent contact with seats so bonnet can be
properly seated on body before tightening the
joint.
Test repaired valve before putting it back in
line to ensure that repairs have been properly
made.
If leaky gate valve seats cannot be refaced,
remove and replace seat rings with a power lathe.
Check up body with rings vertical to arbor and
use a strong steel bar across ring lugs to unscrew
them. They can be removed by hand with a diamond
point chisel if care is taken to avoid damaging
threads. Drive new rings home tightly. Use a
wrench on a steel bar across lugs when putting
in rings by hand. Always coat threads with a
good lubricant before putting them in. Lap in
rings to fit disk perfectly.
Prussian Blue. A paste or liquid used to show a contact area.
11-70
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Frequency
of
Service
M
M
Paragraph 22: Check Valves (Fig. 1.14)
1. INSPECT DISK FACING. Open valves to observe con-
dition of facing on swing check valves equipped
with leather or rubber seats on disk. If metal
seat ring is scarred, dress it with a fine file
and lap with fine emery paper wrapped around a
flat tool.
2. CHECK PIN WEAR. Check pin wear on balanced disk
check valve, since disk must be accurately positioned
in seat to prevent leakage.
Paragraph 25; Plug Valves (Figs. 11.15 and 11.16)
1. ADJUST GLAND. The adjustable gland holds the plug
against its seats in body and acts through com-
pressible packing which functions as a thrust cushion.
Keep gland tight-enough at all times to hold plug
in contact with its seat. If this is not done, the
lubricant system cannot function properly; and solid
particles may enter between the body and plug and
cause damage.
2. LUBRICATE ALL VALVES. Apply lubricant by removing
lubricant screw and inserting stick of plug valve
lubricant for stated temperature conditions. Check
valve fitting within shank prevents line pressure
from blowing out when lubricant screw is removed.
Inject lubricant into valve by turning screw down
to keep valve in proper operating condition. If
lubrication has been neglected, several sticks of
lubricant may be needed before lubricant system
is refilled to operating condition. Be sure to
lubricate valves which are not used often to ensure
that they are always in operating condition. Leave
lubricant chamber nearly full so extra supply is
available by turning screw down. Use lubricant
regularly to increase valve efficiency and service,
promote easy operation, reduce wear and corrosion,
and seal valve against internal leakage.
11-71
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Lubricated Plug Valve
i Lever Sealed Valve
Fig. 11.15 Plug valves
(Source: Homestead Valve Manufacturing Co.)
11-72
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LUBRICANT CHECK VALVE
RESILIENT PACKING
FORGED STEEL COVER
GASKET AND STAINLESS
STEEL SEALING
DIAPHRAGM
LUBRICANT SEALING
GROOVES
LUBRICANT CHAMBER
BODY
LUBRICANT SCREW
WRENCH SQUARE
SHANK
PACKING-GLAND
NUT
BOLTED PACKING
GLAND
CAP SCREW OR
COVER NUT
METAL PACKING RING
PLUG
Fig. 11.16 Plug valves (contd.)
CSource: War Department Technical Manual TM5-666)
11-73
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Frequency
of
Service
M
Paragraph 24; Sluice Gates (Fig. 11.17)
There are two general types of sluice gates: those
which seat with the pressure (Fig. 11.17), and those
which seat against the pressure. Both are maintained
similarly.
1. TEST FOR PROPER OPERATION. Operate inactive sluice
gates. Oil or grease stem screws.
2. CLEAN AND PAINT. Clean sluice gate with wire brush
and paint with proper corrosion-resistant paint.
3. ADJUST FOR PROPER CLEARANCE. For valves seating
against pressure, check and adjust top, bottom, and
side wedges until in closed position each wedge
applies nearly uniform pressure against gate.
(Fig. 11.18)
QUESTIONS
11.1Q What maintenance is required by:
a. gate valves?
b. sluice gates?
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Fig. 11.17 Sluice gate
(Source: ARMCO)
11-75
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Paragraph 25: Acknowledgment
Major portions and basic concepts in this section on mechanical
maintenance are from the War Department Technical Manual, TM5-
666, Inspections and Preventive Maintenance Services, Sewage
Treatment Plants and Sewer Systems at Fixed Installations, War
Department, September 1945.
END OF LESSON 5 OF 6 LESSONS
on
MAINTENANCE
Please answer the discussion and review questions before continuing
with Lesson 6.
11-76
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WEDGE BLOCK
WEDGE
C. I. SLIDE
C. I. FRAME
BRONZE SEATING SURFACES
'MACHINE BOLT
Fig. 11.18 Adjustment of sluice gate wedges
(Source: ARMCO)
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 11. Maintenance
(Lesson 5 of 6 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 4.
27. Why should inactive gate valves be operated periodically?
28. Why should plug valves which are not used very often be
lubricated regularly?
11-79
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CHAPTER 11. MAINTENANCE
(Lesson 6 of 6 Lessons)
11.2 FLOW MEASUREMENTS—METERS AND MAINTENANCE
11.20 Flow Measurements, Use and Maintenance
Flow measurement is the determination of the quantity of a mass'in
movement within a known length of time (Fig. 11.19). Usually the
mass which may be solid, liquid, or gas is contained within physical
boundaries such as tanks, pipelines, and open channels or flumes.
The limits of such physical or mechanical boundaries provide a
measurable dimensional area that the mass is passing through. The
speed at which the mass passes through these boundaries is related
to dimensional distance and units of time; it is referred to as
velocity. Therefore, we have the basic flow formula:
Quantity = Area x Velocity
Q = AV
or
Q, cu ft/sec = (Area, sq ft)(V, ft/sec)
The performance of a treatment facility cannot be evaluated or
compared with other plants without flow measurement. Individual
treatment units or processes in a treatment plant must be observed
in terms of flow to determine their efficiency and loadings. Flow
measurement is important to plant operation as well as to records of
operation. It is essential that the devices used for such measurement
be understood, be used properly, and most important, be maintained so
that information obtained is accurate and dependable.
MASS
AREA
Fig. 11.19 Flow mass
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11.21 Manufacturers' and Operators' Responsibilities
Equipment and instrument manufacturers should be required to
furnish instruction manuals and parts lists. In the parts list
it should be required that the manufacturer designate recommended
spare parts, and such parts should be obtained and be available
for use.
Instrumentation and flow measurement devices should be considered
as fragile mechanisms. Rough handling will damage the units in
as serious a manner as does neglect. Treat the devices with care,
keep them clean, and they will perform their designated functions
with accuracy and dependability.
11.22 Various Devices for Flow Measurement
The selection of a type of flow metering device, and its location,
is made by the designer in the case of new plant construction. It
is also possible that a metering device will have to be added to
an existing facility. In both cases the various types available,
their limitations, and criteria for installation should be known.
Often the criteria for installation must be understood for the
proper use and maintenance of a fluid flow meter. Metering devices
commonly used in treatment facilities include:
Type
Constant
Differential
Head Area
Common Name
Rotameter
Weirs
Rectangular
Cipoletti
V-Notch
Proportional
Application
Liquids and Gases
a. Chlorination
Liquids—partially filled
channels, basins, or clari-
fiers
a. Influent
b. Basin control
c. Effluent
d. Distribution
Velocity
Meter
Flumes
Parshall
Palmer-Bowlus
Nozzles
Propeller
Liquids—partially filled
pipes and channels
a. Influent
b. Basin control
c. Effluent
d. Distribution
Liquids — channel flow ,
clean water piped flow
11-82
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Type
Common Name
Application
Velocity
Meter
Magnetic
Differential
Head
Shuntflo
Venturi Tube
Flow Nozzle
Orifice
Displacement
Piston
Diaphragm
Liquids and sludge in
closed pipe
a. Influent
b. Basin control
c. Sludge recirculation
d. Distribution
Gases—closed pipe
a. Digester gas
Gases and liquids
in closed pipes
a. Influent
b. Basin control
c. Effluent
d. Digester gas
e. Distribution
Gases and liquids in
closed pipes
a. Plant water
b. Digester gas
A description of how each device works is in reality a definition
of the meter type.
Constant Differential--A mechanical device called the "float" is
placed in a tapered tube in the flow line. The difference in pressures
above and below the float causes the float to move with flow variations.
Instantaneous rate of flow is read out directly on a calibrated scale
attached to the tube.
Head Area—A mechanical constriction or barrier is placed in the open
flow line causing an upstream rise in liquid level. The rise or "head"
(H) is a function of velocity of flow and when referenced to empirical
flow formula provides an indication of the flow rate. When first
starting to pump sludge in a long line, the pressure may increase con-
siderably before the sludge starts flowing.
Velocity Meters—The velocity of the liquid flowing past the measure-
ment point through a given area gives a direct relation to flow rate.
The propeller type is turned by fluid flow past propeller vanes which
move gear trains. These gear trains are used to indicate the fluid
velocity or flow rate. The velocity of liquid flow past the probes of
a magnetic meter is related to electrical formula and read out as the
flow rate through secondary instrumentation. (See Section 11.24.) Pitot
tubes are used to measure the velocity head (H) in flowing water to
give the flow velocity (V = /~2gTT). (Fig. 11.20)
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FLOW
T
H where V=V2gfT
Fig. 11.20 Pitot tube
Differential Producers—A mechanical constriction [Fig. 11.21)
in pipe diameter (reduction in pipe diameter) is placed in the
flow line shaped to cause the velocity of flow to increase
through the restriction. When the velocity increases, a pressure
drop is created at the restriction. The difference between line
pressure at the meter inlet and reduced pressure at the throat
section is used to determine the flow rate which is indicated by
a secondary instrument.
DIFFERENTIAL
PRESSURE
FLOW
CONSTRICTION
Fig. 11.21 Differential producer
Displacement Units — Liquids or gas enters, fills a tank or
chamber of known dimensions, activates a mechanical counter,
and empties the tank in readiness for another filling. Mech-
anical gearing activated by chamber fill and evacuation actuates
a counter which is referenced to time and thus flow rate is
determined.
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11.23 Meter Location
The selection of a particular type of meter or measuring device
and its location in a particular flow line or treatment facility
is usually a decision made by the plant designer. Ideally the
flow should be in a straight section before the meter. In open
channels the flow should not be changing directions, nor should
waves be present in the metering section above the measuring
device. Valves, elbows, and other items that chould disrupt the
flow ahead of a meter can upset the accuracy and reliability of
a flow meter. Most flow meters are calibrated (checked for
accuracy) in the factory, but they also should be checked in
their actual field installation. When a properly installed and
field calibrated meter starts to give strange results, check for
obstructions in the flow channel and the flow metering device.
QUESTIONS
11.2A What is flow measurement?
11.2B Write the fundamental flow formula.
11.2C Why should flow be measured?
11.2D List several types of flow measuring devices.
11.2E If a flow meter does not read properly, what items
should be checked as potential causes of error?
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11.24 Conversion and Readout Instruments and Controls
Conversion and readout instrumentation is used to convert the initial
measurement (for example, depth of water) to a more commonly used
number or value (depth of water in a Parshall flume to flow of water
in MGD). The type of device depends upon what the sensor (device)
measures and what kind of results are desired. Often the conversion
device only will transmit the signal (depth of water) to another
meter which will interpret the signal and convert it to a usable
number (flow in MGD). Instruments used with flow measurement equip-
ment are classified as transmitters, receivers, recorders, controllers,
and summators or totalizers. All of the different devices available
are too numerous to list. Most devices used today will fall into the
classifications outlined in the following paragraphs.
11.240 Mechanical Meters
Mechanical meters are those devices which measure the variable
flow indicator and convert this value into a usable number. Con-
version of the flow variable to a scale or meter giving the usable
number may be by gear trains, hydraulic connections, magnetic
sensing, electrical connections, and many other devices.
11.241 Transmitters
Transmitters send the flow variable, as measured by the measuring
device, to another device for conversion to a usable number.
Variables are transmitted mechanically, electrically, and pneu-
matically.
11.242 Receivers
Receivers pick-up the transmitted signal and convert it to a usable
number. Receivers may present the measurement as an instantaneous
flow rate, record the flow on a chart against time, and total or sum
the flow during a time period. Receivers may have one, two, or all
three of these features.
11.243 Controllers
Controllers are similar to receivers except they are capable of
comparing received signals with other values and sending corrective
or adjusting signals when necessary. The compared value may be
manually set or it may be based on another received signal. The
11-86
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correction or adjustment may be proportional to the size of the
deviation of the compared values, may be a gradual adjustment,
or may provide a predetermined correction based on the size of
the deviation and your objectives.
Selection and adjustment of controllers should be done by a
specialist in the field or the manufacturer's representative.
Maintenance must be done according to manufacturer's instructions.
11.25 Sensor Maintenance
Each individual sensing meter will have its own maintenance require-
ments .In any instrument, the sensor is the most common source of
problems. Fortunately, the electronics or drive are easy to check.
The important and common maintenance requirements are tabulated
below in relation to meter types. Not all the maintenance problems
can be listed. It is a proven fact that if preventive maintenance
is regularly applied the uncommon problem is a rare occurrence.
The most important single item to be considered in maintenance is
good housekeeping. This must take many forms since it is applied
to various devices. Good housekeeping, the act of providing pre-
ventive maintenance for each of the various sensors, includes being
sure that foreign bodies are not interfering with the measuring
device. Check for and remove deposits which will accumulate from
normal use. Repair the sensor or measuring device whenever it is
damaged.
Common preventive maintenance suggestions:
Motor Type Suggested Maintenance
Constant Differential Disassemble and clean tube and float
Rotameters when deposits are observed.
Head Area
Weirs: Flow formula is based on square
Rectangular clean edges to the meter shape with
Cipoletti free fall over the weir. Clean and
V-Notch brush off deposits as accumulated.
Proportional Keep clear of foreign bodies and
interference.
11-87
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Motor Type
Head Area
Flumes:
Parshall
Palmer-Rowlus
Nozzles
Velocity Meter
Propeller
Shuntflo
Magnetic
Differential
Producers
Displacement
Suggested Maintenance
Normally used with float wells, keep
sensor line between well and flume
clean; clean off deposits.
Should not be used on anything but
clear water. Grease and check yearly.
Keep dampening chamber fluid level to
line; periodically drain to remove
collected sediment.
Manufacturers are providing various
cleaning mechanisms to clean the
internal parts regularly. If you as
an operator manually operate, be sure
to perform maintenance on schedule;
if automatically, check action fre-
quently. Provide for periodic meter
removal from line and physically
clean meter.
Venturi, nozzle, and orifice hydraulic
connections should be back-flushed
regularly. Installation should be
arranged for internal surface cleaning
on a reasonable schedule.
Periodically drain and flush. Keep
greased as necessary; check frequently
on operation.
External connections between the sensing and conversion and readout
devices should be checked to ensure such connections are clean in
appearance and connections are firm. Be sure no foreign obstruction
will interfere or promote wear. On mechanical connections, grease
as directed; on hydraulic or pneumatic connections, disconnect and
ensure free flow in the internal passage.
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11.26 Conversion and Readout Instrument Maintenance
Both the mechanically actuated unit and the transmitters will have
direct sensor connections. Cleaning and checking on a regular
schedule is essential to avoid problems with the usual accumulation
of foreign material. Maintenance for the internal parts to either
device is minimized when the sensor connections are clean and
operable. Normal wear will occur and is increased when sediments
and deposits are not removed regularly as directed. Lubricate
mechanical components as directed by the equipment manufacturers'
instrument manuals. Do not over-lubricate, because it causes
other difficulties equally
as troublesome as under-
lubrication.
Receiver maintenance is
limited to periodic check-
ing of mechanical parts,
proper lubrication, and
good housekeeping within
the unit. Moisture
should be eliminated by
heat if required. Pneumatic
instruments should be watched
carefully to ensure that
foreign particles which
might be introduced by the
air supply do not cause
clogging in the actuating
elements. Pneumatic systems
are usually protected by air
filters or traps at the
supply source and individual units at the instrument. Filters should
be cleaned and blown down on a regular schedule to ensure their efficient
operation in cleaning the air supply. In the case of clogging of
small orifices and devices of the pneumatic system, do not attempt to
pressurize the system at higher than normal operating pressure for
cleaning. Such action will damage internal" parts. Follow procedures
as outlined by the manufacturer and as shown in the instruction manuals.
Most reputable manufacturers are equipped to provide repair service
in the case of worn parts, or mechanical failure. It is recommended
that major service be left to trained employees of the manufacturer.
It is preferred that manufacturers have field service available for
repair on the plant premises; however, if such service is not avail-
able, the device should be returned to the factory.
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Many manufacturers have a maintenance contract service available
wherein a trained service employee periodically, on a prescribed
schedule, checks the instrument in all ways including accuracy
and wear factors. Such periodic checking allows for replacement
of parts prior to a complete breakdown. Parts which would normally
wear over a time period are replaced by this serviceman who will
anticipate such need from an experience factor.
Do not attempt instrument service, parts replacement, or
repair work unless you have read the instruction manual
thoroughly and you understand what you are doing. Follow
the procedures as set forth in the instruction manual care-
fully.
All instruments are connected to a power supply of some source.
That power supply is potentially dangerous unless handled properly.
Be sure all electrical power is shut off and secured so that
others cannot unintentionally switch the source on. On electrical
and electronic devices the electrical power used and/or generated
within the device is exceptionally dangerous, both to the man
and to the other component equipment. Do not attempt service
unless you are qualified to do so.
Recording charts often seem to accumulate at a rapid rate, and a
decision must be made whether to store or destroy old records.
Inconvenient as it may be, records should be retained. They are
the backbone of reference information needed for future planning
and plant expansion when necessary. Above all, if properly used,
they are an index for efficiency checks unparalleled in value.
Storage space may be minimized by preparing summary records, micro-
film photocopy, or selective sampling and storage of the usual and
unusual.
QUESTIONS
11.2F What is the purpose of transmitting instruments?
11.2G What is the most important item in maintaining flow
meters?
11.2H What should you do with old recording chart records?
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11.3 UNPLUGGING PIPES, PUMPS AND VALVES
11.30 Plugged Pipelines
Plugged pipelines are encountered in lines transporting scum, raw
sludge, digested sludge, or grit. The frequency of a particular
line plugging depends on the type of material passing through the
line, the construction material of the line, the type of pumps or
system used to move the material, and the routine maintenance per-
formed on the line. This section outlines the preventive maintenance
measures to reduce plugging problems in the different lines in a
wastewater treatment plant and the methods of unplugging pipes,
pumps, and valves.
11.31 Scum Lines
Scum will cause more problems in pipelines than any other substance
pumped in a wastewater treatment plant. Problems are more frequent
and more severe in colder weather when grease tends to coagulate faster.
Preventive maintenance includes:
1. Hose down scum troughs, hoppers, and flush lines
to scum box at least every two hours when an
operator is on duty and problems are occurring.
2. Clean lines monthly using:
a. Rods equipped with cutters
b. High pressure hydraulic pipe cleaning units
c. Steam cleaning units
d. Chemicals such as "Sanfax" or "Hot Rod" (strong
hydroxides). This method is least desirable be-
cause of costs and the possibility that the
chemicals could be harmful to biological treat-
ment processes.
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11.32 Sludge Lines
Sludge lines will plug more often when scum and raw sludge are
pumped through the same line, or storm waters carry in grit and
silt that are not effectively removed by the grit removal facilities,
Preventive maintenance includes:
1. Flush lines monthly with plant effluent or wastewater.
2. If possible, recirculate warm digested sludge for an
hour through the line each week if grease tends to
build-up on pipe walls.
3. Rod or high pressure clean lines monthly or quarterly,
depending on severity of problem.
4. If possible, force cleaning tool (pig) through line
using pressures produced by pump. Line must be
equipped with valves and wyes to install and remove
pig. Pumps must be located to allow pig to be forced
through the line. A plastic bag full of ice cubes
makes an excellent cleaning tool or pig. Force the
bag down the line with hot water. If the line plugs,
the ice'will melt to the point where the bag will
continue down the line.
11.33 Digested Sludge Lines
Problems develop in digested sludge lines of small plants from in-
frequent use, ineffective grit removal, and failure to remove sludge
from the line after withdrawing sludge to a drying bed.
Preventive maintenance includes checking:
1. Condition of pipeline for wear or obstructions,
such as sticks and rags.
2. Pump impellers for wear. A worn impeller will
not maintain desired velocity and pressure in
the line.
11.34 Unplugging Pipelines
Selection of a method to unplug a pipe depends on the location of the
blockage and access to the plugged line. Pressure methods and cutting
tools are the most common techniques used to clear stopped lines.
11-92
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11.340 Pressure Methods
Requirements;
1. Must be able to valve off or plug one end of pipe-
line in order to move obstruction or blockage down
the line and out other end to a free discharge.
2. Pressure may be developed using water or air pressure.
Maximum available pressures are usually less than 80
psi.
3. Pipeline must have tap and control valves to control
applied water or air pressure.
Precautions:
1. Never use water connected to a domestic water supply
because you may contaminate the water supply.
2. Do not exceed pipeline design pressures, usually 125 psi.
3. Never attempt to use a positive displacement pump by
over-riding the safety cut-out pressure switches.
This practice may damage the pump.
Procedure:
1. Plug or valve off one end of pipe, but leave other end
open. For example, (1) close valve to digester but
open line to the drying beds, or a raw sludge line, or
(2) close suction valve on raw sludge pump, and open
pipe back to primary clarifier hopper.
2. Connect hose from pressure supply to tap and valve on
pipeline as close as possible to the plugged or valved-
off end.
3. Apply pressure to supply hose and then slowly open control
tap valve and allow pressure to build-up until obstruction
is moved.
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Do Not Exceed Pipeline Working Design Pressure.
11.341 Cutting Tools
Cutting tools are usually available from sewer maintenance crews
and may consist of hand rods, power rods, snakes, or high pressure
(600-1000 psi) hydroflush units.
Requirements:
1. One end of the line must be open and reasonably accessible.
2. Cutting tools should be able to remove material causing
stoppage when line is cleared.
Limitations:
1. Most of these units can not clean lines with sharp bends
or pass through some of the common types of plug valves
used in sludge lines.
2. A 4-inch cutter may have to be used on a 6-inch line due
to 90-degree bends.
3. A part of the line may have to be dismantled to use a
cutting tool.
4. Rods are difficult to hand push over 300 feet. The
operator must have firm footing and room to work.
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Hand Rods:
1. Use sufficient sections to clean full length of line.
2. Insert cutter in the open end of the pipeline and twist
rods as they are pushed up the line.
3. If rods start, to twist up due to torque, pull back and
let rod unwind.
Power Rods:
1. Power drive unit must be located over plugged line.
Don't attempt to run 40 feet across a clarifier and
then into sludge line.
2. Don't run rods into line too fast because you may hit
obstruction or valve and break cutter off of rods which
are very difficult to recover.
11.342 Hydraulic Nozzle Pressure Unit
This unit is very good for removing grease, sludge or grit from
pipelines.
Procedure:
1. Insert nozzle and hose 3 feet into line.
2. Increase pressure in cleaning system to 600 to 1000
psi and let hose off reel slowly into pipeline.
3. Keep track of hose footage in line in order to prevent
nozzle from attempting to go through an open valve. The
nozzle and hose may catch on the valve and require dis-
mantling the valve to free the nozzle.
4. Run water through nozzle while reeling in hose.
11.343 Last Resort
If the methods described in this section fail, the only solution is
to attempt to locate the position of the stoppage, drain the line,
dismantle the plugged section of the pipeline, and remove the ob-
struction.
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11.35 Plugged Pumps and Valves
Isolate plugged pump or valve from the remainder of treatment
plant by valving-off plugged section and locking-out power
supply to pump. Remove pump inspection plate or dismantle
valve and remove material causing blockage. Exercise caution
when removing materials to avoid damaging the pump or valve.
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11.4 SUMMARY
1. Establish and follow a regular maintenance program.
2. Thoroughly read and understand manufacturers' maintenance
instructions. Ask for assistance if you do not understand
them. Follow the manufacturers' instructions in your
maintenance program.
3. Critically evaluate the maintenance and repair capabilities
of yourself and your facilities. Request the help of an
expert when necessary.
11.5 ADDITIONAL READING
a. MOP 11, pages 9-16 and 164-172.
b. New York Manual, pages 157-168.
c. Texas Manual, pages 102-133, 134-159,
and 445-460.
END OF LESSON 6 OF 6 LESSONS
on
MAINTENANCE
Please answer the discussion and review questions before continuing
with the Objective Test.
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DISCUSSION AND REVIEW QUESTIONS
Chapter 11. Maintenance
(Lesson 6 of 6 Lessons)
Write the answers to these questions in your notebook before
continuing. The problem numbering continues from Lesson 5.
29. Calculate the quantity of flow in cubic feet per second
when wastewater flows through an area of 2.5 square feet
at a velocity of 1.5 feet per second.
30. What type of flow meter is used to measure the flow of
chlorine gas?
31. What does a pitot tube measure?
32. Why should a flow meter be calibrated in its field
installation?
33. What is the most common source of problems in flow
meter instruments?
34. Why should major repairs of instrumentation be conducted
by trained employees of the manufacturer?
35. How can scum lines be kept from plugging?
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SUGGESTED ANSWERS
Chapter 11. Maintenance
11.OA A good maintenance program is essential for a wastewater
treatment plant to operate continuously at peak design
efficiency.
11.OB The most important item is maintenance of the mechanical
equipment—pumps, valves, scrapers, and other moving
equipment. Other items include plant buildings and grounds.
11.OC A good record system tells when maintenance is due and
also provides a record of equipment performance. Poor
performance is a good justification for replacement or
new equipment.
11.OD Both cards are vital in a good record keeping system. The
equipment service record card is a permanent or master card
that indicates when or how often certain maintenance work
should be done. The service record card is a record of who
did what work on what date and is helpful in determining
when the future maintenance work is due. It may keep your
warranty in force.
11.OE A building maintenance program will keep the building in
good shape and includes painting when necessary. Attention
also must be given to electrical systems, plumbing, heating,
cooling, ventilating, floors, windows, and roofs. The
building should be kept clean, tools should be stored in
their proper place, and essential storage should be available.
11.OF When plant tanks and channels are drained, the operator should
check surfaces for wear and deterioration from wastewater or
fumes. Protective coatings should be applied where necessary
to prevent further damage.
11.OG Well-groomed and neat grounds are important because many
people judge the ability of the operator and the performance
of his plant on the basis of the appearance of the plant.
11.OH Chlorine is toxic to humans and will cause corrosion damage
to equipment.
11.01 Large chlorine leaks can be detected by smell. Small leaks
are detected by soaking a cloth with ammonia water and hold-
ing the cloth near areas where leaks might develop. A white
cloud will indicate the presence of a leak.
11-101
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11.1A Pumps must be lubricated in accordance with manufacturers'
recommendations. Quality lubricants should be used.
11.IB In lubricating motors, too much grease may cause bearing
trouble or damage the winding.
11.1C If a pump will not start, check for blown fuses or tripped
circuit breakers and the cause, such as a loose connection,
fuse, or thermal unit.
11.ID To increase the rate of discharge from a pump, you should
look for something causing the reduced rate of discharge,
such as pumping air, motor malfunction, plugged lines or
valves, impeller problems, or other factors.
11.IE A cross-connection is a connection between two piping
systems where an undesirable water (water from water seal)
could enter a domestic water supply.
11. IF Yes. A slight leakage is desirable when the pumps are
running to keep the packing cool and in good condition.
11.1G To measure the capacity of a pump, measure the volume
pumped during a specific time period.
Capacity, GPM = Volume, gallons
Time, minutes
11.1H Capacity, GPM = Volume> gallons
Time, minutes
10 ft x 15 ft x 1.7 ft x 7.5 gal/cu ft
5 minutes
= 382.5 GPM
11.11 Before a prolonged shutdown the pump should be drained to
prevent damage from corrosion, sedimentation, and freezing.
Also, the motor-disconnect switch should be opened to dis-
connect motor.
11.1J Shear pins commonly fail in reciprocating pumps because of
(1) a solid object lodged under piston, C2) a clogged dis-
charge line, or (3) a stuck or wedged valve.
11.IK A noise may develop when pumping thin sludge due to water
hammer, but will disappear when heavy sludge is pumped.
11-102
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11.1L When checking an electric motor, the following items
should be checked periodically, as well as when trouble
develops:
1. Motor condition
2. Note all unusual conditions
3. Lubricate bearings
4. Listen to motor
5. Check temperature
11.1M A properly adjusted horizontal belt has a slight bow in
the slack side when running. When idle, it has an alive
springiness when thumped with the hand. Vertical belts
should have a springiness when thumped. To check for proper
alignment, place a straight edge against the pulley face or
faces. If a ruler won't work, use a transit for long runs,
or the belt may be examined for wear.
11.IN Always replace sprockets when replacing a chain because
old, out-of-pitch sprockets cause as much chain wear in
a few hours as years of normal operation.
11.10 Improper original installation of equipment, settling of
foundations, heavy floor loadings, warping of bases, and
excessive bearing wear could cause couplings to become out
of alignment.
11.IP Shear pins are designed to fail if a sudden overload occurs
that could damage expensive equipment.
11.1Q The most common maintenance required by (a) gate valves is
oiling, tightening, or replacing the stem stuffing box
packing. The most common maintenance required by (b) sluice
gates is testing for proper operation, cleaning and painting,
and adjusting for proper clearance.
11.2A Flow measurement is the determination of the rate of flow
past a certain point, such as the inlet to the headworks
structure of a treatment plant. It is measured and recorded
as a quantity (gallons or cubic feet) moving past a point
during a specific time interval (seconds, minutes, hours, or
days). Thus we obtain a flow rate or quantity in cu ft/sec
or MGD.
11.2B Quantity = Area x Velocity, or Q = AV.
11.2C Flow should be measured in order to determine wastewater
treatment plant loadings and efficiency.
11-103
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11.2D Different types of flow measuring devices include constant
differential, head area, velocity meter, differential head,
and displacement.
11.2E Potential causes of flow meter errors include foreign objects
fouling the system or the meter may not be installed in the
intended location. (Liquids should flow smoothly through
the meter and flow should not be changing directions, nor
should waves be present on the liquid surface above the
measuring device.) Check the primary sensor, transmitter,
receiver, and power supply.
11.2F Transmitting instruments can take a reading (depth measurement)
from a flow metering device (Parshall flume) and send it to a
readout instrument which converts the depth measurement to a
flow rate (MGD).
11.2G The most important item in flow meter maintenance is good
housekeeping. Your instruments must be kept clean and in
good working condition.
11.2H Old recording charts should be stored for future reference,
such as checks on plant performance, budget justifications,
and information needed for future planning. Storage space
may be minimized by preparing summary records, microfilm
photocopy, or selective sampling and storage of the usual
and unusual.
11-104
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OBJECTIVE TEST
Chapter 11. Maintenance
Name Date
Please write your name and mark the correct answers on the IBM answer
sheet as directed at the end of Chapter 1. There may be more than
one answer to each question.
1. The duties of a wastewater treatment plant operator may include:
1. Regulation of plant treatment processes
2. Public relations
3. Maintaining equipment and buildings
4. Painting and cleaning plant buildings
5. Keeping maintenance records
2. Equipment service cards and service record cards should:
1. Identify the piece of equipment that the record card
represents
2. Record sick leave
3, Maintain selective service records
4. Indicate the work to be done
5. Indicate the work done
3. What happens if you do not periodically drain and inspect
plant tanks and channels?
1. Serious maintenance problems could develop
2. Costly repairs could result
3. The operator will not know if cracks are developing in
underground tanks and channels
4. An emergency situation may develop and force you to dis-
charge partially or improperly treated wastes into
receiving waters during critical conditions
5. The operator will stay out of trouble
4. How can a chlorine leak be detected?
1. By an explosiometer
2, Smell
3. Green or reddish deposits on metal
4. By waving an ammonia soaked rag
5. By checking the leak gage
11-105
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5. A reciprocating pump:
1. Has a rotating impeller
2. Has a piston that moves back and forth
3. Has two check valves
4. Is used to pump sludge
5. Makes a regular "thunk-thunk" sound when working properly
6, Before starting, a pump should:
1. Have its shaft turned by hand to see that it rotates freely
2. Run in the shipping crate so it can be returned if it
doesn't work
3. Be properly lubricated
4. Be allowed to sit outside and become accustomed to
adverse conditions
5. Be checked to ensure that the shafts of the pump and
motor are aligned
7. Float and electrode switches should be checked at least once
a week to see that:
1. Floatable solids are floating
2. Controls respond to changing water levels in the wet well
as expected
3. Pump motor starts and stops at the proper time
4. The switches change the direction of flow
5. None of these
8. Level control systems in a wet well include:
1, Electrodes
2. Hearts
3. Floats
4. Diaphragms
5. Bubblers
9. If a pump will not start, check for:
1. Tripped circuit breakers
2. Loose terminal connections
3. Water in the wet well
4. Nuts, bolts, scrap iron, wood, or plastic in the wrong places
5. Shaft binding or sticking
10. Preventive maintenance of electric motors includes:
1, Frequently starting and stopping the motor to give it a rest
2. Lubricating bearings
3. Checking temperature of motor
4, Keeping motor free from dust, dirt and moisture
5, Keeping motor outdoors where it can stay cool
11-106
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11. Maintenance of couplings between the driving and driven
elements includes:
1. Keeping proper alignment
2. Keeping proper alignment even with flexible couplings
3. Draining old oil in fast couplings
4. Keeping the electrodes free of scum and corrosion
5. Regular use of a crowbar to line them up
12. Pump maintenance includes:
1. Preventing all water seal leaks around packing glands
2. Operating two or more pumps of the same size alternately
to equalize wear
3. Checking operating temperature of bearings
4. Checking packing gland
5. Lubricating the impeller
13. Approximately how far down should the level in a wet well be
lowered in one minute by a pump with a rated capacity of 200
gpm? The wet well is five feet wide and five feet long.
1. 0.1 ft
2. 0.5 ft
3. 1.0 ft
4. 1.1 ft
5. 2.0 ft
14. Maintenance of gate valves includes:
1. Lubricating with Prussian blue
2. Tightening or replacing the stem stuffing box packing
3. Operating inactive valves to prevent sticking
4. Lubricating bearing
5. Refacing leaky valve seats
15, Flow records provide:
1. Data to control plant processes
2. Nice listening music
3. Information for regulatory agencies
4. Something to keep the operator working
5. For plant input and output determination
16, If a flow meter appears to be operating improperly, the operator
should:
1. Shake it
2. Check connections
3. Look for foreign objects in the system
4. Check need for lubrication
5. Hammer on it
11-107
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17. If a flow meter does not read properly, what items should be
checked as potential causes of error?
1. Installation of sensor and readout devices
2. Restrictions in the sensor and transmitter
3. Power supply to instruments
4. Check instruments according to manufacturer's instructions
5. Blow the transmission lines out with high pressure air
18. Reciprocating pumps should be operated when:
1. Suction and discharge line valves are closed
2. Suction line valve open and discharge line valve closed
3. Suction line valve closed and discharge line valve open
4. Suction and discharge line valves open
19. Modern gate valves can be repacked without removing them
from service.
1. True
2. False
20. Old gaskets should be salvaged.
1. True
2. False
Review Questions:
A trickling filter 95 feet in diameter and four feet deep receives a
flow of 3 MGD with a BOD of 120 mg/1.
21. The hydraulic loading on the trickling filter is approximately:
1. 200 gpd/sq ft
2. 400 gpd/sq ft
3. 600 gpd/sq ft
4. 800 gpd/sq ft
5. 1000 gpd/sq ft
22. The organic loading on the trickling filter is approximately:
1. 25 Ibs BOD/1000 cu ft
2. 50 Ibs BOD/1000 cu ft
3. 100 Ibs BOD/1000 cu ft
4. 200 Ibs BOD/1000 cu ft
5. 300 Ibs BOD/1000 cu ft
Please write on your IBM answer sheet the total time required to
work Chapter 11.
11-108
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CHAPTER 12
PLANT SAFETY AND GOOD HOUSEKEEPING
by
Robert Reed
-------
TABLE OF CONTENTS
Chapter 12. Plant Safety and Good Housekeeping
Page
12.0 Introduction--Why Safety? 12-1
12.1 Kinds of Hazards 12-2
12.10 Physical Injuries 12-2
12.11 Infections and Infectious Diseases 12-3
12.12 Oxygen Deficiency 12-4
12.13 Toxic or Suffocating Gases or Vapors 12-4
12.14 Radiological Hazards 12-4
12.15 Explosive Gas Mixture 12-5
12.16 Fire 12-5
12.17 Electrical Shock 12-5
12.18 Noise 12-5
12.2 Specific Hazards 12-6
12.20 Collection Systems 12-6
12.200 Manholes 12-6
12.201 Excavations 12-9
12.202 Sewer Cleaning 12-9
12.203 Traffic Hazards 12-9
12.21 Treatment Plants and Pumping Stations 12-13
12.210 Headworks 12-13
12.211 Grit Chambers 12-20
12.212 Clarifiers or Sedimentation Basins . . 12-21
12.213 Digesters and Digestion Equipment. . . 12-21
12.214 Trickling Filters 12-26
12.215 Aerators 12-27
12.216 Ponds 12-28
12.217 Chlorine 12-30
12.218 Applying Protective Coatings 12-31
12.219 Housekeeping 12-32
111
-------
Page
12.5 Safety in the Laboratory 12-35
12.30 Collecting Samples 12-35
12.31 Equipment Set-Up and Performance of Tests . . 12-36
12.4 Fire Prevention 12-39
12.40 Ingredients Necessary for a Fire 12-39
12.41 Fire Control Methods 12-39
12.42 Fire Prevention Practices 12-40
12.43 Acknowledgment 12-41
12.5 Water Supplies 12-42
12.6 Safety Equipment and Information 12-43
12.7 "Tailgate" Safety Meetings 12-44
12.8 Summary 12-46
12.9 Additional Reading 12-49
. COMMON &UQe,
A AL-WAV-6 .
T
V vou
PON't
IV
-------
PRE-TEST
Chapter 12, Plant Safety and Good Housekeeping
The objective of the Pre-Test is to indicate to you some of the
important items in the chapter. You are not expected to know
all of the answers.
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. There may be
more than one correct answer to each question.
1. To prevent coming in contact with infections and infectious
diseases, the operator should:
1. Wash his hands before eating
2. Wear protective gloves when in contact with wastewater
and sludges
3. Not wear his work clothes home
4. Never repair equipment that comes in contact with sludge
5. Wash his hands before going to the lavatory
2. An oxygen deficiency, or dangerous concentrations of toxic
or suffocating gases, may be found in:
1. Manholes
2. Wet wells
3. Empty digesters
4. Chlorinator rooms
5. Pump rooms
3. Manholes may be lifted with:
1. Your fingers
2. Your back
3. A manhole hook
4. Traffic may be warned of a job in a street or other traffic
area by:
1. High-level signs and flags far enough ahead of the job
to adequately alert drivers
2. Leaving some manholes open so everyone can see that you
are working
3. Traffic cones arranged to guide traffic around work area
4. Hoping autos headed toward the work area will be warned
by other drivers
5. A flagman directing traffic
P-l
-------
5. When working on any piece of electrical equipment, the
circuit breaker should be (pick only the best answer):
1. Open
2. Closed
3. Tagged
4. Locked out
5. Locked out and tagged
6. Good housekeeping around a treatment plant means:
1. Reading magazines
2. Hosing down all spills immediately
3. Keeping the coffee fresh and warm
4. Providing a proper place for equipment and tools
5. Keeping all walking areas clean and free of slimes,
oils, and greases
7. Why should explosion-proof lights be used when working in
an empty digester?
1. If there is an explosion, the lights won't go out.
2. Explosion-proof lights will not produce a spark which
could cause an explosion.
8. The greatest hazard working in a clarifier is:
1. Explosions
2. Asphyxiation
3. Slipping
9. When working in an empty digester, an operator should:
1. Ventilate the digester
2. Test for H2S
3. Test for explosive gas mixtures
4. Use explosion-proof lights
5. Wear nonsparking shoes
10. Gases may accumulate in sludge pump rooms from:
1. Ch1orinat ors
2. Leakage
3. Blowers
4. Normal pump cleaning
P-2
-------
11. When working around a trickling filter, the operator should:
1. Never walk on the filter media while the rotating
distributor is moving
2. Ride on the distributor to get from one side to the
other
3. Wear rubber gloves when handling mercury from the seal
4. Always provide a firm base when jacking up the distri-
butor for repairs
5. Never try to stop a rotating distributor by standing
in front of it
12. When applying protective coatings in a tank, the operator
should:
1. Check with the manufacturer for safety precautions
2. Provide adequate ventilation
3. Wear protective clothing
4. Apply protective creams to exposed skin areas
5. Avoid breathing fumes from the protective coating
13. When working in the lab. you may:
1. Smoke whenever you wish
2. Use laboratory glassware for a coffee cup
3. Add acid to water
4. Never look into the end of a container during a
reaction or when heating the container
5. Hold a piece of glassware in your bare hands while
heating it
14. The purpose of a safety meeting is to:
1. Provide an awareness of the need for safety at all times
2. Review potential safety hazards and outline the necessary
precautions
3. Get off work
4. Discuss vacation plans
5. Discuss the causes of accidents
P-3
-------
CHAPTER 12. PLANT SAFETY AND GOOD HOUSEKEEPING
(Lesson 1 of 3 Lessons)
12.0 INTRODUCTION--WHY SAFETY?
A cat may have nine lives, but you have only one! Protect it!
Others may try, but only your efforts in thinking and acting
safely can ensure you the opportunity of continuing to live your
single life!
You are working at an occupation that has an accident frequency rate
second only to that of the mining industry! Not a very desirable
record.
Your employer has the responsibility of providing you with a safe
place to work. But you, the operator who has overall responsibility
for your treatment plant, must accept the task of seeing to it that
your plant is maintained in such a manner as to continually provide
a safe place to work. This can only be done by constantly thinking
safety.
You have the responsibility of protecting yourself and other plant
personnel or visitors by establishing safety procedures for your
plant and then by seeing that they are followed. Train yourself to
analyze jobs, work areas, and procedures from a safety standpoint.
Learn to recognize potentially hazardous actions or conditions. When
you do recognize a hazard, take immediate steps to eliminate it by
corrective action. If correction
is not possible, guard against
the hazard by proper use of warn-
ing signs and devices and by the
establishing and maintaining of
safety procedures. As an indi-
vidual, you can be held liable
for injuries or property damage
as a result of an accident caused
by your negligence.
REMF.MBER: "ACCIDENTS DON'T JUST
HAPPEN—THEY ARE CAUSED"!! Hosv
true it is! Behind every accident
there is a chain of events which
lead to an unsafe act, unsafe
condition, or a combination of both,
THINK SAFETY!
12-1
-------
Accidents may be prevented by using good common sens,e, applying
a few basic rules, and particularly by acquiring a good knowledge
of the hazards peculiar to your job as a plant operator.
The Bell system has one of the best safety records of any
industry. A variation of their successful policy statement
is :
"There is no job so important
nor emergency so great
that we cannot take time
to do our work safely."
Although this chapter is intended primarily for the wastewater
treatment plant operator, the operators of many small plants
have the responsibility of sewer maintenance also. Therefore
the safety aspects of both sewer maintenance and plant operation
will be discussed.
12.1 KINDS OF HAZARDS
You are equally exposed to accidents whether working on the
collection system or working in a treatment plant. As a worker,
you may be exposed to:
1. Physical injuries
2. Infections and infectious diseases
3. Oxygen deficiency
4. Toxic or suffocating gases or vapors
5. Radiological hazards
6. Explosive gas mixtures
7. Fire
8. Electrical shock
9. Noise
12.10 Physical Injuries
The most common of physical injuries are cuts, bruises, scrapes,
and broken bones. Injuries can be caused by moving machinery.
Falls from or into tanks, deep wells, catwalks, or conveyors can
be disabling. Most of these can be avoided by the proper use of
ladders, hand tools, and safety equipment, and by following estab-
lished safety procedures.
12-2
-------
12.11 Infections and Infectious Diseases1
Although treatment plants and plant personnel are certainly not
expected to be "pristine pure", personal cleanliness is a great
deterrent to infections and infectious diseases. Immunization
shots for protection against typhoid and tetanus are essential.
Make it a habit to thoroughly wash your hands before eating or
smoking, or going to the lavatory. If you have any cuts or
other broken skin areas on your hands, wear proper protective
gloves when in contact with wastewater or sludge in any form.
Bandages covering wounds should be changed frequently.
Do not wear your work clothes home, because diseases may be
transmitted to your family. Provisions should be made in your
plant for a locker room where each employee has a locker. Work
clothes should be placed
or hung in lockers and not
thrown on the floor. Your
work clothes should be
cleaned at least weekly or
more often if necessary.
If your employer does not
supply you with uniforms and
laundry service and you must
take your work clothes home,
launder them separately from
your regular family wash.
All of these precautions will
reduce the possibility of you
and your family becoming ill
because of your contact with
wastewater.
1 You must attempt to avoid skin infections and infectious
diseases such as typhoid fever, dysentery, hepatitis, and
tetanus.
12-3
-------
12.12 Oxygen Deficiency
Oxygen deficiency may exist in any enclosed, and particularly
below grade (ground level) , unventilated structure where a gas
heavier than air, such as carbon monoxide, has displaced the air.
AN
LI
A MANHOLE
-STRUCT UK£ WITHOUT
FOR OXV^rEM TTBPlO^MCV ANP
Ventilation may be provided by fans or blowers. Equipment is
available to measure oxygen deficiency and must be used whenever
you enter a potentially hazardous area. Try your local fire
department for sources of this type of equipment in your area.
12.13 Toxic or Suffocating Gases or Vapors
Toxic or suffocating gases may come from industrial waste dis-
charges or from the decomposition of domestic wastewater. You
must become familiar with the waste discharges into your system.
On pages 174 and 175 of The New York Manual, Table 10, Common
Dangerous Gases Encountered in Sewers and at Sewage Treatment
Plants, contains information on the simplest and cheapest safe
method of testing for gases.
12.14 Radiological Hazards
The newest of hazards to plant operators is a result of the in-
creasing use of radioactive isotopes in hospitals, research labs,
and various industries. Check your sewer service area for the
possible use of these materials. If you are receiving a discharge
that may contain a radioactive substance, contact the contributor
of the discharge. He will usually cooperate with monitoring this
type of waste.
12-4
-------
12.15 Explosive Gas Mixtures
Explosive gas mixtures may develop in confined areas in treatment
plants from mixtures of air and methane, natural gas, manufactured
fuel gas, or gasoline vapors. Explosive ranges can be detected by
using a combustible gas indicator. Avoid explosions by keeping
open flames away from areas potentially capable of developing ex-
plosive mixtures by providing adequate ventilation with fans or
blowers.
12.16 Fire
Burns from fires can cause very serious injury. Avoid the accumulation
of flammable material and store any material of this type in approved
containers at proper locations. Know the location of fire fighting
equipment and the proper use of the equipment.
12.17 Electrical Shock
Electrical shock frequently causes serious injury. Do not attempt
to repair electrical equipment unless you know what you are doing.
12.18 Noise
Loud noises from gas engines and gas or electric blowers can cause
permanent ear damage. Operators and maintenance men must wear the
proper ear protecting devices whenever working in noisy areas for
any length of time.
QUESTIONS
12.1A How can you prevent the spread of infectious
diseases from your job to you and your family?
12.IB What should you do before entering an unventilated,
enclosed structure?
12.1C What are potential sources of toxic or suffocating
gases or vapors?
12-5
-------
12.2 SPECIFIC HAZARDS
In the remainder of this chapter an attempt will be made to
acquaint you with the specific hazards, by location and/or
types of work, that you may expect to encounter in the field
of wastewater collection and treatment.
12.20 Collection Systems
Good design and the use of safety equipment will not prevent
physical injuries in sewer work unless safety practices are
understood by the entire crew and are enforced.
Never attempt to do a job unless you have sufficient help, the
proper tools, and the necessary safety equipment. There are no
shortcuts to safetyI
12.200 Manholes2
Manhole work usually requires job site protection by barricades
and warning devices. These devices are necessary to warn high-
way traffic and pedestrians for the protection of the public and
the workmen.
Never use your fingers or hands to remove a manhole cover!
Always use a tool such as a pick with the point bent in the
form of a hook, or a special tool specifically designed for
this purpose. You have only ten fingers. Protect them!
When lifting a cover, the use of the rule "Lift with your legs,
not with your back" will help eliminate back strains. (Fig- 12.1)
Once the cover is removed, leave it flat on the ground and far
enough away from the manhole to provide adequate room for a working
area. This is usually at least two to three feet.
If there are ladder rungs or steps installed in the side of the
manhole, be very cautious when using these. Be alert for loose
or corroded steps. Always test each step individually before
placing your weight upon it.
2 Also see "Safe Work Procedure No. 1, Preparation for Manhole
Work", Jour. Water Poll. Control Fed., Vol. 42, No. 2, p 331
CFeb. 1970).
12-6
-------
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-------
If possible, it is much safer to use a ladder as a means of
entering a manhole. Be certain, however, that the bottom feet
are properly placed so that the ladder will not slip or twist
when your weight is placed upon it.
No one should enter a
manhole when by"himselfI
There should always be
at least one person stand-
ing by at the top of the
manhole to observe the man
as he enters, works, and
leaves the manhole. There
should always be at least
one more person within
hailing distance of the
manhole in case it is
necessary to remove the
man from the manhole
because of injury, or a
truck wench or man lift
may be used.
Before entering a manhole,
put on an approved safety
harness equipped with a hand line or life line. Both of these
should be inspected by a fellow worker as well as the wearer. Be
sure to wear a safety hat or cap.
If a man is to be working in wastewater, he should wear a properly
fitted pair of rubber gloves, or an approved substitute that will
provide protection from infection.
Never enter a manhole without first checking for explosive gases
or other gases that may cause an oxygen deficiency. Provide for
adequate ventilation to remove these gases. There are instruments
available that can detect explosive gases or oxygen deficiency.
Your local fire department can usually supply you with information
on this type of equipment.
INFORMATION ON
TO TA&L£r tO,
IN
\"7A- AMP
MANUAL-.
12-8
-------
Tools and equipment should be lowered into a manhole by means
of a bucket or basket. Do not drop them into the manhole for
the man in the hole to catch. Attempting to carry tools in
one hand while climbing down a ladder is an unsafe practice.
12.201 Excavations3
If it becomes necessary for you to excavate a sewer line,
become familiar with the fundamentals of excavating and the
proper, safe approach for shoring a ditch. Check with your
State Safety Office or Industrial Accident Commission. They
can usually provide you with pamphlets on these subjects.
Don't wait until an emergency arises to obtain the information.
12.202 Sewer Cleaning
Never use a cleaning tool or piece of equipment unless you have
been properly trained in its use or operation. Insist that the
vendor provide you with this training. Know the limitations
and capabilities of your tools and equipment. Do not use tools or
equipment improperly because you could be seriously injured.
If you use chemicals of any kind for root or grease control in
your system, be thoroughly familiar with their use, and specifi-
cally, with any hazards involved.
12.203 Traffic Hazards
Before starting any job in a street or other traffic area, even
if you are just going to open a manhole, adequate warning to and
protection from traffic must be provided.
Traffic may be warned by high-level signs and flags far enough
ahead of the job to adequately alert the driver, by traffic cones
(the newer fluorescent red cones do an excellent job) arranged to
guide traffic around your work area, by signs or barricades to
direct traffic, by a flagman to direct and control traffic, or by
any combination of these. The local police department, state
highway police, or road department may be able to provide you with
some basic patterns on the use of cones, barricades, and other
3 Also see "Wastewater Wisdom Talk, Trench Shoring", Jour. Water
Poll. Control Fed., Vol. 42, No. 6, p 1273 (June 1970).
12-9
-------
warning or traffic control devices. Traffic warning devices
must be placed in such a fashion to avoid causing confusion
and congestion.
An added protection, whenever possible, is to place your work
vehicle between you and the oncoming traffic. This will alert
traffic to your presence. The use of flashing or revolving
amber or red warning lights (whichever are permissible in your
area) is an excellent means of alerting traffic to your presence.
QUESTIONS
12.2A Why should someone always be standing at the top of
a manhole when you enter it?
12.2B How would you determine if there is an oxygen deficiency
or toxic gas present in a manhole?
12.2C From whom should you learn the proper use of new sewer
cleaning equipment?
12.2D List three ways to alert traffic that you are working
in a street or traffic area.
END OF LESSON 1 OF 3 LESSONS
on
PLANT SAFETY AND GOOD HOUSEKEEPING
Please answer the discussion and review questions before continuing
with Lesson 2.
12-10
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 12. Plant Safety and Good Housekeeping
(Lesson 1 of 3 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 this lesson.
Write the answers to these questions in your notebook.
1. What is the operator's responsibility with regard to safety?
2. Accidents don't just happen—they are !
3. How can an operator avoid physical injuries?
4. Immunization shots protect against what infection and
infectious disease?
5. What precautions should the operator take to avoid
transmitting disease to his family?
6. What should the operator do when he discovers an area with
an oxygen deficiency?
7. What kind of job site protection is usually required when
you are working in a manhole?
8. Lift with your legs, not your .
9. How should tools and equipment be transported to the
bottom of a manhole?
12-11
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CHAPTER 12. PLANT SAFETY AND GOOD HOUSEKEEPING
(Lesson 2 of 3 Lessons)
12.21 Treatment Plants and Pumping Stations
Because hazards found in pumping stations are identical to those
found in treatment plants, the items discussed hereafter may be
applied to both situations.
12.210 Headworks
Structures and equipment in this category may consist of bar screens,
racks, comminuting or grinding equipment, pump rooms, wet pits, and
chlorination facilities.
1. Bar Screens or Racks. These may be either manually or auto-
matically cleaned.When manually cleaning screens or racks, be
certain that you have a clean, firm surface to stand upon. Re-
move all slimes, rags, greases, or other material that may cause
you to slip. GOOD HOUSEKEEPING IN THESE AREAS IS MANDATORY.
When raking screens, leave plenty of room for the length of your
rake handle so as not to be thrown off balance by striking a
wall, railing, or light fixture. Wear gloves to avoid slivers
from the rake handle or scraping your knuckles on concrete.
Injury may allow an infection to enter your body.
Place all material in a container that may be easily removed
from the structure. Do not allow material to build up on the
working surface.
If your rack area is provided with railings, check to see that
they are properly anchored before you lean against them. If
removable safety chains are provided, never use these to lean
against or as a means of providing extra leverage for removing
large amounts of material.
A hanging or mounting bracket of some type should be used to
hold the rake when not in use. Do not leave it lying on the
deck.
If mechanically raked screens or racks are installed, never
work on the electrical or mechanical part of this equipment
12-13
-------
without first turning the unit off by means of a push-
button lockout for momentary stoppages, and by turning
off, locking out, and tagging the main circuit breaker
if it is necessary to remove or make a major adjustment
or repair to the unit.
AMP
O
. _ PO NOT
MAM
\\
The time and date the unit was turned off should be noted
on the tag, as well as the reason it was turned off. The
tag should be signed by the man who turned the unit off.
No one should then turn on the main breaker and start the
unit until the tag has been removed by the person who placed
it there, or until he has specific instructions from the
person who tagged the breaker. Your local safety equipment
supplier can obtain these tags for you.
2. Comminuting or Grinding Equipment. This equipment may consist
of barminutors, comminutors, grinders, or disintegrators.
NEVER work on the mechanical or electrical parts of the unit
without first locking out the unit at either a push-button
lockout or the main circuit breaker of the control panel.
Be certain the breaker is properly tagged as explained in the
previous section.
Good housekeeping is essential in the area of comminuting
equipment. Keep all walking areas clean and free of slimes,
oils, greases, or other materials. Hose down all spills
immediately. Provide a proper place for equipment and tools
used in this area.
See that proper guards are installed and kept in place around
cables, cutters, hoists, revolving gears, and high-speed
equipment such as grinders. If it is necessary to remove the
guards prior to making adjustments on equipment, be certain
that they are reinstalled before restarting the unit.
12-14
-------
DO NOT
START
THIS EQUIPMENT
BEING
REPAIRED
STATE COMPENSATION
INSURANCE FUND
OF
CALIFORNIA
A-1
Fig, 12.2 Typical warning tag
(Source: State Compensation Fund of California)
12-15
-------
DANGER
MAN
WORKING
ON LINE
DO NOT CLOSE THIS
SWITCH WHILE THIS
TAG IS DISPLAYED
SIGNATURE: 1
This is the ONLY person authorized to remove this tag.
INDUSTRIAL INDEMNITY/INDUSTRIAL UNDERWRITERS/
INSURANCE COMPANIES
;§£• 4E210—R66
Fig. 12.3--Typical Warning Tag (Con't).
Source: Industrial Indemnity/Industrial Underwriters/Insurance Cos.
12-16
-------
3. Pump Rooms. The same basic precautions apply here as they
do to any type of enclosed room or pit where wastewater or
gases may enter and accumulate.
Always provide adequate ventilation to remove gases and supply
oxygen. If the room is below ground level and provided with
only forced air ventilation, be certain the fan is on before
entering the area. Wear a harness with a safety line (as
for manhole work) when entering pits, wet wells, tanks, and
below-ground pump rooms.
The tops of all stairwells or ladders should be protected by
a removable safety chain. Keep this chain in place when the
stairwell or ladder is not being used.
Never remove guards from pumps, motors, or other equipment
without first locking out or turning off equipment at main
breaker and properly tagging. Always replace all guards
before starting units.
Guards should be installed around all rotating shaft couplings,
belt drives, or other moving parts normally accessible.
Maintain good housekeeping in pump room. Remove all oil and
grease, and clean up spills immediately.
If you have a multi-level pump building, never remove and
leave off equipment removal hatches unless you are actually
removing or replacing equipment. Be sure to provide barricades
or ropes around the opening to prevent falls. Be extremely
cautious when working around openings that have raised edges.
These are hazardous because you can stumble over them easily.
Never start a positive displacement pump against a closed valve.
On piston pumps, the yoke over the ball check could break and
endanger personnel in the vicinity.
All emergency lights used in these areas should be explosion
proof. Be sure to keep light shields in place and replace
immediately when broken. Permanent lights should be of an
approved explosion-proof type. Until the area has been checked
for an explosive atmosphere, NO OPEN FLAMES (such as a welding
torch) OR SMOKING SHOULD BE ALLOWED.
12-17
-------
CAUTION
VOL)
OUT
PAMErL^. i^ voa PO NOT
015 AT2& MOT
4. Wet Pits—Sumps. Covered wet pits or sumps are potential
death traps. Never enter one by yourself. Use a safety
harness and have sufficient personnel available to lift
you out. Always use forced air to ventilate the area, and
check for explosive gases and oxygen deficiency before
entering. Also, be particularly alert for hydrogen sulfide
gas. Use your nose initially, but do not continue to depend
upon it as you will become insensitive to the odor. A
small, reasonably priced hydrogen sulfide detection unit
may be purchased. Check with your local safety equipment
supplier.
After you have determined the atmosphere is safe, use extreme
care in climbing up and down access ladders to pit areas. The
application of a nonslip type coating on ladder rungs is
helpful. If available, a truck hoist is safer than a ladder
for entering pit areas.
Watch your footing on the floor of pits and sumps. They are
very slippery.
Never attempt to carry tools or equipment up or down ladders
into pits or sumps. Always use bucket and handline or sling
for this purpose.
Only explosion-proof lights and equipment should be used in
these areas.
A good safety practice is to turn off all chlorination, whether
located upstream or directly in sump, and allow ample time
before entering the area. This, with forced ventilation, will
give time for the area to be cleared of chlorine fumes.
12-18
-------
Chlorination safety is discussed in Chapter 10, Disinfection and
Chlorination.
QUESTIONS
12.2E Why should slimes, rags, or greases be removed from
around bar screens or racks?
12.2F What precautions would you take when working on elec-
trical or mechanical equipment?
12.2G What parts of equipment should have guards installed
around them?
12.2H Why should you not depend on your nose to detect hydrogen
sulfide gas over long periods of time?
12.21 How would you transport tools or equipment into or out
of pits or sumps?
12-19
-------
12.211 Grit Chambers
Grit chambers may be of various designs, sizes, and shapes;
but they all have one thing in common: they get dirty. Good
housekeeping is neededI Keep walking surfaces free of grit,
grease, oil, slimes, or other material that will make a slippery
surface.
Before working on mechanical or electrical equipment, be certain
that it is turned off and properly tagged (Figs. 12.2 and 12.3).
Install and maintain guards on gears, sprockets, chains, or other
moving parts that are normally accessible.
If it becomes necessary to enter the chamber, pit, or tank for
cleaning or other work, do so with extreme caution. If this is
a covered area, provide and maintain adequate ventilation to
remove gases from the area and to supply oxygen to the workers.
Use only explosion-proof lights. Always check for explosive
gases and oxygen deficiency before entering.
Be sure of your footing when working in these structures.
Rubber boots with a nonskid cleat type sole should be worn.
Step slowly and cautiously as there is usually an accumulation
of slippery material or slimes on the bottom. Use hand holds
and railings; if none are available, install them now.
Use ladders, whether vertical or ships ladders, cautiously.
If possible, apply nonslip material or coatings to ladder rungs,
Keep handrails free of grease and other slippery substances.
If it is necessary to take tools or equipment into the bottom
area, lower these in a bucket or sling by handline. Never
attempt to carry items up or down a ladder.
12-20
-------
12,212 Clarifiers or Sedimentation Basins
The greatest hazard involved in working on or in a clarifier
is the danger of slipping. If possible, maintain a good non-
skid surface on all stairs, ladders, and catwalks. This may
be done by using nonskid strips or coating. Be extremely
cautious during freezing weather. A small amount of ice can be
very dangerous.
Your housekeeping program should include the brushing or clean-
ing of effluent weirs and launders (effluent troughs); When
it is necessary to actually climb down into the launder, always
wear a harness with a safety line and have someone with you. A
fall may result in a very serious injury.
Be cautious when working on the bottom of a clarifier. When
hosing down, always hose a clean path to walk upon. Avoid
walking on the remaining sludge whenever possible.
Always turn off and lock out or turn off and tag clarifier
breaker before working on drive unit. If necessary, adjustments
may be made on flights or scrapers while the unit is in operation;
but keep in mind that, although these are moving quite slowly,
there is tremendous power behind their movement. Stay clear of
any situation where your body or the tools you are using may get
caught under one of the flights or scrapers.
Guards should be installed over or around all gears, chains,
sprockets, belts, or other moving parts. Keep these in place
whenever the unit is in operation.
Railing should be installed along the tank side of all normal
walkways. If the unit is elevated above ground, railings should
be installed along the outside of all walkways, also. Check with
your State Safety Office for requirements on railing installation.
12.213 Digesters and Digestion Equipment4
Digesters and their related equipment include many hazardous areas
and potential dangers.
Also see "Safe Work Procedure No. 2, Entering and Working in
Digesters", Jour. Water Poll. Control Fed., Vol. 42, No. 3,
Part 1, p 466 (March 1970).
12-21
-------
No smoking and no open flames should be allowed in the vicinity
of digesters, in digestion control buildings, or in any other
areas or structures used in the sludge digestion system. This
includes pipe galleries, compressor or heat exchanger rooms,
and others. All these areas should be posted with signs in a
conspicuous place which forbid smoking and open flames. Methane
gas produced by anaerobic conditions is explosive when mixed with
the proper proportion of air.
All enclosed rooms or galleries in this system should be well
ventilated with forced air ventilation. Before entering any
enclosed area or pit which is not ventilated, a check should be
made for explosive gases and hydrogen sulfide. Do not depend
upon your nose for hydrogen sulfide (H2S) detection in these
areas. A small amount of H2S in the air will make your sense
of smell immune to the odor in a short period of time. Use an
H2S detector.
When you are working in these areas, forced air ventilation with
a portable blower should be provided. Again, do not go into an
area by yourself where H2S is present. Have someone watch you.
Never enter a partially empty or completely empty digester with-
out first thoroughly ventilating the structure and then checking
for an explosive atmosphere and the presence of hydrogen sulfide
gas. Explosion-proof lights and nonsparking tools5 and shoes
should always be used when working around, on top of, or in a
digester unless it has been completely cleaned and emptied,
continuously ventilated by a blower, and constant checks are
made of the atmosphere in the tank.
A
AllOW
WIT-HIK AM
Be certain that guardrails are installed along the edges of the
digester roof or cover in areas where it is necessary to work
close to the edge. A fall from the top of a digester could be
fatal.
5 Nonsparking tools are especially manufactured for use in areas
where potentially explosive mixtures of gases may be present.
12-22
-------
Explosion blew off top of digester
and landed on top of pickup truck
Fig. 12.4 Blown-up digester
12-23
-------
When working on equipment such as draft tube mixers, compressors,
diffusers, etc., be certain that the unit which operates or
supplies gas to these types of equipment is properly locked out
and appropriately tagged (Figs. 12.2 and 12.3).
If you have a heated digester, read and heed the manufacturer's
instructions before working on the boiler or heat exchanger.
Know that the gas valve is turned off before attempting to
light the pilot. Be certain that the fire box has been venti-
lated according to the manufacturer's instructions before
lighting the pilot.
CAUTION
C5A4 &U&H&&5 A££ NJOt^P top BlDWlM
-------
Sludge pump rooms should be well ventilated to remove any
gases that might accumulate from leakage, spillage, or from
a normal pump cleaning. If you spill digesting sludge, clean
it up immediately to prevent the possible accumulation of gases.
Provide thorough, regularly scheduled inspection and maintenance
of your gas collection system. Inspect drip traps regularly.
The so-called "automatic" drip trap is known to jam open fre-
quently, allowing gas to escape.
Good maintenance of flame arresters will ensure that they will
be able to perform their job of preventing a backflash of the
flame.
QUESTIONS
12.2J How can the danger of slipping be reduced on
slippery surfaces?
12.2K Why should no smoking or open flames be allowed
in the vicinity of digesters?
12.2L What safety precautions would you take before
entering a recently emptied digester?
12.2M What would you do before relighting a waste gas
burner?
12,2N Why should you never start a positive displacement
pump against a closed discharge valve?
12-25
-------
12.214 Trickling Filters
When it becomes necessary to inspect or service a rotating
distributor, stop the flow of wastewater to the unit and allow
it to come to rest.
op WAL^ ON
A£ £orATJM6
IN MOTION,
Provide an approved ladder or stairway for access to the media
surface. Be positive this is free from obstructions such as
hose bibs, valve stems, etc.
Extreme caution should be used when walking on the filter media.
The biological slimes make the media very slippery. Move
cautiously and be certain of your footing.
ALLOW ANVOKJ^ TO Rl I7£r A,
Although a rotating distributor moves fairly slowly, the force
behind it is powerful. An operator who has fallen off and been
dragged by a distributor is fortunate if he can walk away under
his own power.
WARNING
roxie.
Always wear rubber gloves when handling mercury. When cleaning
mercury, follow the manufacturer's recommendations. Do so only
in the open in a well-ventilated room. Be sure to have a tray
under the working area during mercury clean-up. It is extremely
difficult to recover mercury from the floor. Dry mercury vaporizes
slowly, and mercury vapors also are toxic.
12-26
-------
Refrain from smoking and eating when handling mercury. Always
wash your hands thoroughly when finished.
When inspecting underdrains, check to determine that the
channels or conduits are adequately ventilated. Gases are not
normally a problem here, but may be if there is a build-up of
solids which have become septic.
If it becomes necessary to jack up a distributor mechanism
for inspection or repair, always provide a firm base off the
media or drainage system for the jack plate. A firm base may
be provided by wooden planks which will spread the weight over
a large area. However, sometimes the only way to obtain firm
support is to remove the media and use the drainage system as
a firm base. Remember you are lifting a heavy weight. Do not
attempt inspection or repair work until the distributor has been
adequately and properly blocked in its raised position.
12.215 Aerators
Guardrails should be installed on the tank side of usual work
areas or walkways. If the tank is elevated above ground, guard-
rails should also be installed on the ground side of the tank.
An operator should never go into unguarded areas by himself.
When working on Y-walls, or other unguarded areas where work
is done infrequently, at least a two-man team should do the work.
Approved life preservers with permanently attached hancilines
should be accessible at strategic locations around the aerator.
You should wear a safety harness with a life line when servicing
aerator spray nozzles and other items around an aerator.
An experiment in England found that if an operator fell into a
diffused aeration tank, he should be able to survive because air
will collect in the clothing and tend to help keep him afloat.6
Drownings apparently occur when a person is overcome by the
initial shock or there is nothing to grab hold of to keep afloat
or to pull oneself out of the aerator.
When removing or installing diffusers, be aware of the limitations
of your working area. Inspect and properly position hoists and
other equipment used in servicing swing diffusers.
6 Kershaw, M.A., "Buoyancy of Aeration Tank Liquid", Jour.
Water Poll. Control Fed., Vol. 33, No. 11, p 1151 (Nov. 1961).
12-27
-------
When it is necessary to work in an empty aerator, lower your-
self into the aerator with a truck hoist if one is available.
Ladders are awkward and dangerous; but if portable ladders must
be used, properly position them so that they will not slip or
twist. A good practice is to tie the top of the ladder so that
it cannot slip. Be extremely careful when using fixed ladders
as they become very slippery. The floor of the aerator also
is likely to be extremely slippery.
If your plant is in an area subject to freezing weather, be
aware of possible ice conditions around these units and use
caution accordingly.
12.216 Ponds
Ponds of any kind present basically the same hazards. Therefore,
the following safety measures will apply to ponds in general.
If it is necessary to drive a vehicle on top of the pond levees,
maintain the roadway in good driving condition by surfacing it
with gravel of asphalt. Do not allow chuck holes or the formation
of ruts. Be extremely cautious in wet weather. The material
used in the construction of most levees becomes very slippery
when wet. Slippery conditions should be corrected using crushed
rock or other suitable material.
Never go out on the pond for sampling or other purposes when by
yourself. Someone should be standing by on the bank in case you
get into trouble. Always wear an approved life jacket when
working from a boat or raft on the surface of the pond. And,
as in any boating activity, do not stand up in the boat while
performing work.
12-28
-------
QUESTIONS
12.20 What precautions should you take when working with
mercury?
12.2P How would you stop the rotating distributor on a
trickling filter?
12.2Q Why should you never work alone on the center "Y"
wall of an aerator?
12-29
-------
12.217 Chlorine
AMP .
WlT-H CAUTlOM/
The most common causes of accidents involving chlorine gas are
leaking pipe connections and over-chlorinating.
Chlorine bottles or cylinders should be stored in a cool, dry
place, away from direct sunlight or from heating units. Some
heat is needed to cause desired evaporation and to control
moisture condensation on tanks. Chlorine bottles or cylinders
should never be dropped or allowed to strike each other with
any force. Cylinders should be stored in an upright position
and secured with a chain, wire rope, or clamp. They should
be moved only by hand truck and should be well secured during
moving. One-ton tanks should be blocked so that they cannot
roll. They should be lifted only by an approved lifting bar
with hooks over the ends of the containers. Never lift a
bottle or cylinder with an improvised sling.
Connections to cylinders and tanks should be made only with
approved clamp adaptors or unions. Always inspect all surfaces
and threads of the connector before making connection. If you
are in doubt as to their conditions, do not use the connector.
Always use a new approved type gasket when making a connection.
The reuse of gaskets very often will result in a leak.Check
for leaks as soon as the connection is completed. Never wait
until you smell chlorine. If you discover even the slightest
leak, correct it immediately, as leaks tend to get worse rather
than better. Like accidents, chlorine leaks generally are caused
by faulty procedure or carelessness.
Obtain from your chlorine supplier and post in a conspicuous
place^ (outside the chlorination room) the name and telephone
number of the nearest emergency service in case of severe leak.
Cylinder storage and chlorinator rooms should be provided with
means of ventilating the room. As chlorine is approximately two
and a half times heavier than air, vents or an exhaust fan should
be provided at floor level. Ideal installations have a blower
mounted on the roof to blow air into the room and are vented at
the floor level to allow escaped chlorine to be blown out of the
building.
12-30
-------
Always enter enclosed cylinder storage or chlorinator rooms
with caution. If you smell chlorine when opening the door to
the area, immediately close the door, turn on ventilation,
and seek assistance.
Never attempt to enter an atmosphere of chlorine when by
yourself or without an approved air supply and protective
clothing. Aid can usually be obtained from your local fire
department, which will normally have available a self-
contained breathing apparatus which will allow a person to
enter safely into an atmosphere of chlorine.
An excellent booklet may be obtained from PPG Industries, Inc.,
Chlorine—Safe Handling.'7 Safety information on chlorine
handling is also contained in Chapter 10, Disinfection and
Chlorination. Your local chlorine supplier will probably pro-
vide you with all the information you need to handle and use
chlorine safely. It is your responsibility to obtain, read,
and understand safety information and to practice safety.
12.218 Applying Protective Coatings
CAUTION1 When applying protective coatings in a clarifier
or any other tank or pit, whether enclosed or open topped, use
protective equipment to prevent skin burns from vapors from
asphaltic or bitumastic coatings. This may involve the use of
protective clothing as well as protective creams to be applied
to exposed skin areas. An air supply must be used when paint-
ing inside closed vessels or in an open deep tank. Many paint
fumes are heavier than air; therefore, ventilation must be from
the bottom upward.
Check with your paint supplier for any hazards involved in
using his products.
7 PPG Industries, Inc., Chemical Division, One Gateway Center,
Pittsburgh, Pennsylvania 15222.
12-31
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12.219 Housekeeping
Good housekeeping can and has prevented many accidents.
Have a place for your tools and equipment. When they are
not being used, see that they are kept in their proper place.
Clean up all spills of oil, grease, wastewater, sludge, etc.
Keep walkways and work areas clean.
Provide proper containers for wastes, oily rags, papers, etc.
Empty these frequently.
Remove snow and melt ice with salt in areas where persons
may slip and fall.
A clean plant will reduce the possibility of physical injuries
and infections.
QUESTIONS
12.2R How should one-ton chlorine tanks be lifted?
12.2S Why are chlorine vents placed on floor level?
12.2T What should you do if you open a door and smell chlorine?
12.2U What factors are important in keeping a neat and safe
plant?
END OF LESSON 2 OF 3 LESSONS
on
PLANT SAFETY AND GOOD HOUSEKEEPING
Please answer the discussion and review questions before continuing
with Lesson 3.
12-32
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 12. Plant Safety and Good Housekeeping
(Lesson 2 of 3 Lessons)
Write the answers to these questions in your notebook.
The problem numbering continues from Lesson 1.
10. When cleaning racks or screens, on what kind of surface
should the operator stand?
11. Never lean against a removable safety chain. True or False?
12. Why should only qualified electricians work on an electrical
control panel?
13. Why should effluent weirs and launders on clarifiers be
brushed or cleaned?
14. Why should no smoking or open flames be allowed in the
vicinity of the digester or sludge digestion system?
15. Why should a tray be placed under the working area during
mercury clean-up?
16. Why should you never go out on a pond for sampling or
other purposes by yourself?
17. Where should the name and telephone number of the nearest
emergency chlorine leak repair service be posted?
18. What safety precautions should be taken when applying
protective coatings?
12-33
-------
CHAPTER 12. PLANT SAFETY AND GOOD HOUSEKEEPING
(Lesson 3 of 3 Lessons)
12.3 SAFETY IN THE LABORATORY8
In addition to all safety practices and procedures mentioned in
the previous sections of this chapter, the collecting of samples
and the performance of laboratory tests require that you be aware
of the specific hazards involved in this type of work.
Laboratories use many hazardous chemicals. These chemicals should
be kept in limited amounts and used with respect. Your chemical
supplier may be able to supply you with a safety manual.
12.30 Collecting Samples
Whenever possible, rubber gloves should be worn when your hands
may come in direct contact with wastewater or sludge. When you
have finished sampling, always wash the gloves thoroughly before
removing them. After removing the gloves, wash your hands
thoroughly, using a disinfectant type soap.
COLLECT ANY ^ANYPUe^ WITH
YOUR BA12£r HANP^ \f- VOU
Do not climb over or go beyond guardrails or chains when collecting
samples. Use sample poles, ropes, etc., as necessary to collect
samples.
Also see "CRC Handbook of Laboratory Safety", by Norman V.
Steere, Chemical Rubber Publishing Company, 18901 Cranwood
Parkway, Cleveland, Ohio 44128. Price $24.50.
12-35
-------
12.31 Equipment Set-Up and Performance of Tests
Following are some basic procedures to follow when working in
the laboratory:
1. Use proper safety goggles or face shield in all tests where
there is danger to the eyes.
LOQk /NTO -THE: O^^N £:NP OP-
PUTZlM£r AR^AefiOM OK
H &ATI M <3
2. Use care in making rubber-to-glass connections. Lengths of
glass tubing should be supported while they are being inserted
into rubber. The ends of the glass should be flame polished9
to smooth them out, and a lubricant such as water should be
used. Never use grease or oil. Gloves or some other form of
protection for the hands should be used when making such
connections. The tubing should be held as close to the end
being inserted as possible to prevent bending or breaking.
Never try to force rubber tubing or stoppers from glassware.
Cut the rubber as necessary to remove it.
3. Always check labels on bottles to make sure that the proper
chemical is selected. Never permit unlabeled or undated con-
tainers to accumulate around or in the laboratory. Keep
storage areas organized to facilitate chemical selection for
use. Clean out old or excess chemicals. Separate flammable,
explosive, or special hazard items for storage in an approved
manner. See Section 12.9, Additional Reading, Reference 10.
ALL PCM 60/^4
Flame Polished. Sharp or broken edges of glass (such as the end
of a glass tube) are flame polished by placing the edge in a flame
and rotating it. By allowing the edge to melt slightly, it will
become smooth.
12-36
-------
4. Never handle chemicals with the bare hand. Use a spoon or
spatula for this purpose.
5. Be sure that your laboratory is adequately ventilated.
ALWAV4
IN A
\\OOV
Even mild concentrations of fumes or gases can be dangerous.
6. Never use laboratory glassware for a coffee cup or food dish.
This is particularly dangerous when dealing with wastewaters.
7. When handling hot equipment of any kind, always use tongs, as-
bestos gloves, or other suitable tools. Burns can be painful
and can cause more problems (encourage spills, fire, and shock).
8. When working in the lab, avoid smoking and eating except at
prescribed coffee breaks or at the lunch period.
N4 6 OR
Do not pipette chemicals or wastewater samples by mouth.
use a suction bulb on an automatic burette.
10. Handle all chemicals
and reagents with
care. Read and be-
come familiar with
all precautions or
warnings on labels.
Know and have avail-
able the antidote
for all poisonous
chemicals in your
lab.
11. A short section of
rubber tube on each
water outlet is an
excellent water
flusher to wash
away harmful
Always
12-37
-------
chemicals from the eyes and skin. It is easy to reach and
can quickly be directed on the exposed area. Eyes and
skin can be saved if dangerous materials are washed away
quickly.
12. Dispose of all broken or cracked glassware immediately.
Chipped glassware may still be used if it is possible to
fire polish the chip in order to eliminate the sharp edges.
This may be done by slowly heating the chipped area until
it reaches a temperature at which the glass will begin to
melt. At this point remove from flame and allow to cool.
-MOU? AKVV Pl£C£ OP
Always use a suitable glove or tool.
13.
TO
g/JT
14. Wear a protective smock or apron when working in the lab.
This may save you the cost of replacing your work clothes
or uniform. Protective eye shields should be worn too.
QUESTIONS
12.3A What safety precautions would you take when collecting
laboratory samples from a plant influent?
12.3B Why should you always wash your hands before eating?
12.3C Why should chemicals and reagents be handled with care?
12-38
-------
12.4 FIRE PREVENTION
Fires are a serious threat to the health and safety of the opera-
tor and to the buildings and equipment in a treatment plant.
Fires may injure or even cause the death of an operator. Equip-
ment damaged by fire may no longer function properly, and your
treatment plant may have difficulty adequately treating the
influent wastewater.
Good safety practices with respect to fire prevention require a
knowledge of:
1. Ingredients necessary for a fire
2. Fire control methods
3. Fire prevention practices
12.40 Ingredients Necessary for a Fire
The three essential ingredients of all ordinary fires are:
1. FUEL--paper, wood, oil, solvents, and gas.
2. HEAT—the degree necessary to vaporize fuel
according to its nature.
3. OXYGEN—normally at least 15 percent of oxygen
in the air is necessary to sustain a fire. The
greater the concentration, the brighter the
blaze and more rapid the combustion.
12.41 Fire Control Methods
To extinguish a fire, it is necessary to remove only one of the
essentials by:
1. Cooling (temperature and heat control)
2. Smothering (oxygen control)
3. Isolation (fuel control)
4. Interrupting the chemical chain reaction in
certain types of fires
12-39
-------
Fires are classed as A-, B-, C-, or D-type fires, according to
what is burning.
Class A fires (general combustibles such as wood, cloth, paper,
or rubbish) are usually controlled by cooling--as by use of
water to cool the material.
Class B fires (flammable liquids such as gasoline, oil, grease,
or paint) are usually smothered by oxygen control--as by use of
foam, carbon dioxide, or a dry chemical.
Class C fires (electrical equipment) are usually smothered by
oxygen control—use of carbon dioxide or dry-chemical extin-
guishers—nonconductors of electricity.
Class D fires occur in combustible metals, such as magnesium,
lithium, or sodium, and require special extinguishers and
techniques.
You can control and extinguish fires when they occur by knowing where
fire extinguishers and hoses are kept and knowing where yard hydrants
are located, what each is for, and how to use them.
12.42 Fire Prevention Practices
You can prevent fires by:
1. Maintaining a neat and clean work area, preventing accumu-
lation of rubbish.
2. Putting oil- and paint-soaked rags in covered metal containers.
3. Observing all "no smoking" signs.
4. Keeping fire doors, exits, stairs, fire lanes, and fire-
fighting equipment clear of obstructions.
5. Keeping all burnable materials away from furnaces or other
sources of ignition.
6. Reporting any fire hazards you see that are beyond your
control, especially electrical hazards which are the source
of many fires.
12-40
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Finally, here again are the things to remember:
1. Prevent fire by good housekeeping and proper handling of
flammables.
2. Make sure that everyone obeys "no smoking" signs in all
areas near explosive or flammable gases.
3. In case of fire, turn in the alarm immediately and make
sure that the fire department is properly directed to the
place of the fire.
4. Use the available portable fire-fighting equipment to
control the fire until help arrives.
5. Use the proper extinguisher for that fire.
6. Learn how to operate the extinguishers.
If it is necessary to get out of the building, do not stop to
get anything--just get out!
Can you prevent fires? You can if you try, so let's see what we
can do to preserve our well-being and the water pollution control
system.
If you guard against fires, you will be protecting your lives and
your community.
12.43 Acknowledgment
Material in this section on Fire Prevention appeared in the July 1970
issue of the Journal of the Water Pollution Control Federation, on
pages 1426 and 1427, as a Wastewater Wisdom talk. Originally, the
information appeared as a National Safety Council "5 Minute Safety
Talk", published in the Industrial Supervisor.
QUESTIONS
12.4A What are the necessary ingredients of a fire?
12.4B, How should oil- and paint-soaked rags be handled?
12-41
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12.5 WATER SUPPLIES
Inspect your plant to see if there are any cross-connections
between your potable (drinking) water and items such as water
seals on pumps, feed water to boilers, hose bibs below grade
where they may be subject to flooding with wastewater or sludges,
or any other location where wastewater could contaminate a
domestic water supply.
If any of these or other existing or potential cross-connections
are found, be certain that your drinking water supply source is
properly protected by the installation of an approved back-flow
prevention device.
It is a good practice to have your drinking water tested at
least monthly for coliform group organisms. Sometimes the best
of back-flow prevention devices do fail.
You may find in your plant that it will be more economical to
use bottled drinking water. If so, be sure to tack up con-
spicuous signs that your water is not drinkable. This also
applies to all hose bibs in the plant from which you may obtain
water other than a potable source. This is a must in order to
inform visitors or absent-minded or thirsty employees that the
water from each marked location is not for drinking purposes.
QUESTION
12.5A Why do some wastewater treatment plants use bottled
water for drinking purposes?
12-42
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12.6 SAFETY EQUIPMENT AND INFORMATION
Post conspicuously on your bulletin board the location and types
of safety equipment available at your plant (such as first aid
kit, breathing apparatus, explosiometers, etc.)* You, as the
plant operator, should be thoroughly familiar with the operation
and maintenance of each piece of equipment. You should review
these at fixed intervals to be certain that you can safely use
the piece of equipment as well as to be sure that it is in
operating condition.
Contacts should be made with your local fire and police depart-
ments to acquaint them with hazards at your plant as well as to
inform them of the safety equipment that is necessary to cope
with problems that may arise. Quite often it is possible to
arrange a joint training session with these people in the use
of safety equipment and the handling of emergencies. They also
should know access routes to and around the treatment plant.
If you have any specific problems of a safety nature, do not
hesitate to contact officials in your state safety agency. They
can be of great assistance to you. And do not forget your equip-
ment manufacturers; their familiarity with your equipment will
be of great value to you.
Also posted in conspicuous places in your plant should be such
information as the phone numbers of your fire and police depart-
ments, ambulance service, chlorine supplier or repairman, and
the nearest doctor who has agreed to be available on call.
Having these immediately available at telephone sites may save
your or a fellow worker's life. Check and make sure these
numbers are listed at your plant. If they are not listed,
ADD THEM NOW.
QUESTION
12.6A What emergency phone numbers should be listed in a
conspicuous place in your plant?
12-43
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12.7 "TAILGATE" SAFETY MEETINGS10
Safety is crucial. Accidents cost money. No one can afford to
lose time from his job due to injury. Safety meetings provide
the opportunity to explain and discuss safe procedures and safe
conditions.
In some states, by law, you may be required to conduct safety
meetings at fixed intervals with employees. Whether this is
required or not, it certainly is a good practice. Once every
7 to 10 days is a good frequency. These meetings should usually
be confined to one topic, and should be no longer than 10 to 20
minutes. It will be worthwile to review monthly any accidents
during the past month at one of the meetings. Do not use this
meeting to fix blame. Try to dig into the cause and to determine
what can be or has been done to prevent a recurrence of the accident
To help you conduct "tailgate" safety meetings, this chapter was
arranged to discuss the safety aspects of different plant opera-
tions. The material in some sections was deliberately repeated
to cover the topic and to remind you of dangers. Some plants
select topics for their "tailgate" safety meetings from a "safety
goof box". The box is placed in a convenient location. Whenever
anyone sees an unsafe situation or sees someone perform a hazardous
act without proper safety precautions, he places a note in the box
identifying the situation or person and the act. The box is opened
at each safety meeting, and the cause of the "goof" and the steps
that can be taken to correct and prevent it from happening again
are discussed.
Your state safety agency, your insurance company, equipment and
material suppliers, and the Water Pollution Control Federation
are all excellent sources of literature and aids that may help you
in conducting "tailgate" safety meetings. Some of these agencies
may be able to supply you with posters, signs, and slogans that
are very effective safety reminders.11 You may wish to dream up
some reminders of your own.
10 "Tailgate". The term "tailgate" comes from safety meetings
regularly held by the construction industry around the tail-
gate of a truck.
11 Chemical Laboratory Safety Posters have been prepared by the
Manufacturing Chemists Association, 1825 Connecticut Avenue,
N.W., Washington, D.C. 20009. Price $2.50 per set of twelve
posters.
12-44
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QUESTIONS
12.7A What is the purpose of "tailgate" safety meetings?
12.7B How frequently should safety meetings be held for treat-
ment plant operators?
12-45
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12.8 SUMMARY
Following is a summary of the safety precautions that have been
discussed in the previous sections.
1. Good design without proper safety precautions will not
prevent accidents. All personnel must be involved in
a safety program and provided with frequent safety
reminders.
2. Never attempt to do a job unless you have sufficient help,
the proper tools, and necessary safety equipment.
3. Never use fingers to remove a manhole cover or heavy grate.
Use the proper tool.
4. "Lift with your legs, not your back" to prevent back strains.
5. Use ladders of any kind with caution. Be certain that
portable ladders are positioned so they will not slip or
twist. Whenever possible, tie the top of a ladder used
to enter below-grade structures. Do not use metal ladders
near electrical boards or appliances.
6. Never enter a manhole, pit, sump, or below-grade enclosed
area when by yourself.
7. Always test manholes, pits, sumps, and below-grade
enclosed areas for explosive atmosphere, oxygen deficiency,
and hydrogen sulfide. Before entering, thoroughly venti-
late with forced air blower.
8. Wear or use safety devices such as safety harnesses, gas
detectors, and rubber gloves to prevent infections and
injuries.
9. Never use a tool or piece of equipment unless you are
thoroughly familiar with its use or operation and know
its limitations.
12-46
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10. When working in traffic areas,.always provide:
a. Adequate advance warning to traffic by signs, flags,
etc.
b. For channeling the flow of traffic around your work
area by use of traffic cones, barricades, or other
approved items.
c. Protection to workers by placing your vehicle between
traffic and job area, and/or by use of flashing or
revolving lights, or other devices.
d. Flagmen when necessary to direct and control flow
of traffic.
11. Before starting a job, be certain that work area is of
adequate size. If not, make allowances for this. Keep
all working surfaces free of material that may cause
surface to be slippery.
12. See to it that all guardrails and chains are properly
installed and maintained.
13. Provide and maintain guards on all chains, sprockets,
gears, shafts, and other similar moving pieces of equip-
ment that are normally accessible.
14. Before working on mechanical or electrical equipment,
properly turn off and/or tag breakers to prevent the
accidental starting of the equipment while you are working
on it. Wear rubber gloves and boots wherever you may
contact "live" electrical circuits.
15. Never enter a launder, channel, conduit, or other slippery
area when by yourself.
16. Do not allow smoking or open flames in the area of, on
top of, or in any structure in your digestion system.
Post all these areas with warning signs in conspicuous
places.
17. Never enter a chlorine atmosphere by yourself and without
proper protective equipment. Seek the cooperation of your
local fire department in supplying self-contained breathing
apparatus.
12-47
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18. Obtain and post in a conspicuous location the name and
telephone number of the nearest chlorine emergency service.
Acquaint your police and fire department with this service.
19. Inspect all chlorine connectors and lines before using.
Discard any of these that appear defective.
20. Keep all chlorine containers secured to prevent falling
or rolling. Use only approved methods of moving and
lifting containers.
21. Maintain a good housekeeping program. This is a proven
method of preventing many accidents.
22. Conduct an effective safety awareness and training program.
These are the highlights of what has been previously discussed.
Whenever in doubt about the safety of any piece of equipment,
structure, operation, or procedure, contact the equipment manu-
facturer, your city or county safety officer, or your state
safety office. One of these should be able to supply you with
an answer to your questions.
ACC1 PENTS PON't JUST
You can be held personally liable for injuries or damages caused
by an accident as a result of your negligence.
Can you afford the price of one?
Can you afford the loss of one or more men?
Can your family afford to lose you?
12-48
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12.9 ADDITIONAL READING
a. MOP 11, pages 156-163.
b. New York Manual, pages 169-182.
c. Texas Manual, pages 689-706.
d. Chlorine--Safe Handling, PPG Industries, Inc., Chemical
Division,' One Gateway Center, Pittsburgh, Pennsylvania 15222.
e. Safety in Wastewater Works, WPCF Manual of Practice No. 1,
Water Pollution Control Federation, 3900 Wisconsin Avenue,
Washington, D.C. 20016. Price: $0.75 to members, $1.50 to
others. Indicate your member association when ordering.
f. Safety Program Promotional Packet, Water Pollution Control
Federation, 3900 Wisconsin Avenue, Washington, D.C. 20016.
g. Chlorine Manual, The Chlorine Institute, Inc., 342 Madison
Avenue, New York, New York 10017. Price $0.75.
h. Motivating for Safety, Journal of American Water Works
Association, Vol. 61, No. 2, pp 57-59 (February 1969).
i. Test Your Safety Sense, National Safety Council, 425 North
Michigan Avenue, Chicago, Illinois 60611.
j. CRC Handbook of Laboratory Safety, by Norman V. Steere,
Chemical Rubber Publishing Company, 18901 Cranwood Parkway,
Cleveland, Ohio 44128. Price $24.50.
END OF LESSON 3 OF 3 LESSONS
on
PLANT SAFETY AND GOOD HOUSEKEEPING
12-49
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DISCUSSION AND REVIEW QUESTIONS
Chapter 12. Plant Safety and Good Housekeeping
(Lesson 3 of 3 Lessons)
Write the answers to these questions in your notebook. The problem
numbering continues from Lesson 2.
19. How can samples for lab tests be collected if you shouldn't
go beyond guardrails or chains?
20. What should be done with the jagged ends of glass tubes?
21. How should hot lab equipment be handled?
22. How can a fire be extinguished?
23. Fires can be prevented by good housekeeping and proper
handling of flammables. True or False?
24. Why should plant water supplies be checked monthly for
coliform group bacteria?
25. Why should safety equipment be checked periodically?
26. Where would you look for safety posters, signs, and slogans
to aid in "tailgate" safety meetings?
27. Carefully study this illustration. List the safety
hazards and indicate how each one can be corrected.
12-51
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SUGGESTED ANSWERS
Chapter 12. Plant Safety and Good Housekeeping
12.1A The operator can protect himself and his family from
disease by thoroughly washing his hands after being
in contact with wastewater and sludges and by careful
cleaning of his work clothes.
12.IB Before entering an unventilated, enclosed structure
you should check for oxygen deficiency and provide
ventilation.
12.1C Toxic gases and vapors originate from the discharge
of certain industrial wastes into the wastewater
collection system. The decomposition of certain
wastes will produce dangerous gases too.
12.2A Someone should always be standing near a manhole when
you enter it in case you collapse from an oxygen
deficiency or are overcome by a toxic gas. An addi-
tional man should be in the vicinity to help the man
at the top of the manhole recover you by pulling on
the safety harness if you need help.
12.2B Instruments are available to measure the concentra-
tions of oxygen and toxic gases in manholes and other
enclosed areas.
12.2C Insist that the equipment vendor provide you and your
coworkers with the proper instruction regarding the
use of equipment.
12.2D Traffic may be alerted by signs, flags, fluorescent
cones, flagmen, and flashing lights on a truck parked
in front of the manhole.
12.2E Slimes, rags, or greases should be removed from any
area because they may cause people to slip and they
are unsightly.
12.2F When working on a mechanical or electrical part of
equipment, you should fasten a tag to the breaker
handle reading "DANGER, Do Not Start, Man Working
on Equipment", or some other similar notice.
12-53
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12.2G Guards should be placed around moving parts of equip-
ment such as rotating shaft couplings, belt drives,
and other moving parts normally accessible.
12.2H Our noses eventually become insensitive to some odors,
such as hydrogen sulfide gas. This phenomenon is known
as "factory fatigue".
12.21 Tools and equipment should not be carried, but should
be transported in and out of pits and sumps by the use
of buckets and handline or sling.
12.2J Slippery surfaces such as stairs, ladders, and cat-
walks can be made less dangerous if nonskid strips or
coatings are applied at proper locations.
12.2K Smoking and open flames should not be allowed in the
vicinity of digesters because when methane gas is
mixed with the proper portion of air it forms an explo-
sive mixture.
12.2L Before entering a recently emptied digester, you should
ventilate the digester and check for an explosive
atmosphere.
12.2M Before relighting a waste gas burner, the main gas valve
should be turned off and the stack allowed to vent
itself for a few minutes.
12.2N If a positive displacement pump is started against a
closed discharge valve, pressures could build up and
break a pipe or damage the pump.
12.20 When working with mercury you should wear rubber gloves.
Mercury spills should be avoided. When finished, you
must wash your hands thoroughly.
12.2P The rotary distributor may be stopped by turning off
the flow of water or by some other means of slowing
down the distributor. Extreme care must be taken because
of the force developed by the distributor.
12.2Q You should never work alone on the center "Y" wall
of an aerator because you could fall into the aerator
and need help getting out.
12.2R Chlorine containers should only be lifted by an approved
lifting bar with hooks over the ends.
12-54
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12.2S Chlorine gas is heavier than air and is best removed
when leaks occur by blowing the gas out of the room
at floor level.
12.2T If you open a door and smell chlorine, immediately
close the door and seek help.
12.2U Good housekeeping can and has prevented many accidents.
You should keep your plant clean, provide containers
for wastes, and empty them regularly.
12.3A When collecting influent samples, rubber gloves should
be worn to protect the operator's hands if there is any
chance of direct contact with the wastewater. If
possible, sample poles or other similar types of sam-
plers should be used.
12.3B Hands should always be washed before eating to prevent
the spread of disease.
12.3C Chemicals and reagents should be handled with care
to protect your body from serious injuries and possible
poisoning.
12.4A The necessary ingredients of a fire are fuel, heat,
and oxygen.
12.4B Oil- and paint-soaked rags should be placed in covered
metal containers.
12.5A Some treatment plants use bottled drinking water because
it is an economical and reliable source of potable
water. This practice reduces the possibility of the
spread of disease from unknown cross-connections or
defective devices installed to prevent contamination
by back-flows.
12.6A The following phone numbers should be conspicuously
listed in your plant: Fire Department, Police Depart-
ment, Ambulance, Chlorine Supplier or Repairman, and
Physician. Check your list to be sure they are all
listed and the numbers are correct.
12.7A The purpose of safety meetings is to remind operators
of the need for safety, and to review potential hazards
and how to correct or avoid dangerous situations.
12.7B Safety meetings should be held every 7 to 10 days.
12-55
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OBJECTIVE TEST
Chapter 12. Plant Safety and Good Housekeeping
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. There may be
more than one correct answer to each question.
1. To prevent coming in contact with infections and infectious
diseases, the operator should:
1. Wash his hands before eating
2. Wear protective gloves when in contact with wastewater
and sludges
3. Not wear his work clothes home
4. Never repair equipment that comes in contact with sludge
5. Wash his hands before going to the lavatory
2. An oxygen deficiency, or dangerous concentrations of toxic
or suffocating gases, may be found in:
1. Manholes
2. Wet wells
3. Empty digesters
4. Chlorinator rooms
5. Pump rooms
3. Manholes may be lifted with:
1. Your fingers
2. Your back
3. A manhole hook
4. Traffic may be warned of a job in a street or other traffic
area by:
1. High-level signs and flags far enough ahead of the job
to adequately alert drivers
2. Leaving some manholes open so everyone can see that you
are working
3. Traffic cones arranged to guide traffic around work area
4. Hoping autos headed toward the work area will be warned
by other drivers
5. A flagman directing traffic
12-57
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5. When working on any piece of electrical equipment, the
circuit breaker should be (pick only the best answer}:
1. Open
2. Closed
3. Tagged
4. Locked out
5. Locked out and tagged
6. Good housekeeping around a treatment plant means:
1. Reading magazines
2. Hosing down all spills immediately
3. Keeping the coffee fresh and warm
4. Providing a proper place for equipment and tools
5. Keeping all walking areas clean and free of slimes,
oils, and greases
7. Why should explosion-proof lights be used when working in
an empty digester?
1. If there is an explosion, the lights won't go out.
2. Explosion-proof lights will not produce a spark which
could cause an explosion.
8. The greatest hazard working in a clarifier is:
1. Explosions
2. Asphyxiation
3. Slipping
9. When working in an empty digester, an operator should:
1. Ventilate the digester
2, Test for H2S
3. Test for explosive gas mixtures
4. Use explosion-proof lights
5. Wear nonsparking shoes
10. Gases may accumulate in sludge pump rooms from:
1. (Jhlorinators
2. Leakage
3. Blowers
4. Normal pump cleaning
12-58
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11. When working around a trickling filter, the operator should:
1. Never walk on the filter media while the rotating
distributor is moving
2. Ride on the distributor to get from one side to the
other
3. Wear rubber gloves when handling mercury from the seal
4. Always provide a firm base when jacking up the distri-
butor for repairs
5. Never try to stop a rotating distributor by standing
in front of it
12. When applying protective coatings in a tank, the operator
should:
1. Check with the manufacturer for safety precautions
2. Provide adequate ventilation
3. Wear protective clothing
4. Apply protective creams to exposed skin areas
5. Avoid breathing fumes from the protective coating
13. When working in the lab, you may:
1. Smoke whenever you wish
2. Use laboratory glassware for a coffee cup
3. Add acid to water
4. Never look into the end of a container during a
reaction or when heating the container
5. Hold a piece of glassware in your bare hands while
heating it
14. The purpose of a safety meeting is to:
1. Provide an awareness of the need for safety at all times
2. Review potential safety hazards and outline the necessary
precautions
3. Get off work
4. Discuss vacation plans
5. Discuss the causes of accidents
Review Questions:
15. How many pounds of solids are under aeration in an aeration
tank with a capacity of 0.4 MG when the MLSS is 2000 mg/1?
1. 650 pounds
2. 5000 pounds
3. 6500 pounds
4. 6700 pounds
5. 7000 pounds
12-59
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16. What is the food-to-organism ratio in an aeration tank
if 1000 pounds of BOD are added per day and 3500 pounds
of solids are under aeration?
1. 25 Ibs BOD per day per 100 Ibs of aeration solids
2. 28 Ibs BOD per day per 100 Ibs of aeration solids
3. 30 Ibs BOD per day per 100 Ibs of aeration solids
4. 32 Ibs BOD per day per 100 Ibs of aeration solids
5. 35 Ibs BOD per day per 100 Ibs of aeration solids
Please write on your answer sheet the total time required to
work all three lessons and this Objective Test.
12-60
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CHAPTER 13
SAMPLING RECEIVING WATERS
by
Bill B. Dendy
-------
TABLE OF CONTENTS
Chapter 13. Sampling Receiving Waters
Page
13.0 Introduction 13-1
13.1 Sampling (Selection of Samples) 13-2
13.10 General 13-2
13.11 Temperature 13-3
13.12 Dissolved Oxygen 13-10
13.13 Review of Sampling Results 13-13
13.2 Sampling (Collection Techniques) 13-15
13.20 Collection 13-15
13.21 Frequency of Sampling 13-15
13.22 Size of Sample 13-16
13.23 Labeling of Samples 13-16
13.3 Safety 13-16
13^4 Other Types of Receiving Waters 13-17
13.5 What to Measure 13-17
13.6 Additional Reading 13-19
111
-------
PRE-TEST
Chapter 13. Sampling Receiving Waters
WOEK se^oce vou
THIS
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. Don't be dis-
couraged if you don't know the answers. The Pre-Test indicates
to you the important topics in this chapter.
Select the best answer (only one answer).
1. The two types of measurements required in connection with
operating a treatment plant are:
1, Temperature and dissolved oxygen
2. Effluent and downstream
3. Upstream and downstream
4. In-plant and receiving water
5. Temperature and receiving water
2. Receiving water sampling requires proper:
1. Safety and temperature
2. Equipment and "flailing the water"
3. Selection of samples and collection techniques
4. Water quality objectives and night work
5. Snap-on belts and flags
3. To determine the location and amount of lowest dissolved
oxygen downstream from a discharge it is necessary to:
1. "Flail the water"
2. Observe safety precautions
3. Measure the effluent
4. Make an "oxygen profile" of the stream
5. Make yearly measurements
P-l
-------
4. The average annual temperature for a stream can be measured
by sampling in only one month out of the year.
1. True
2. False
5. Results from a sampling program should always be accepted
without question or verification.
1. True
2. False
6. Proper sample collection techniques are specified in:
1. Standard Methods for the Examination of Water and Wastewater
2^ Playboy" Magazine
3. All design manuals for concrete pipe
4. Water quality objectives
5. Safety precautions
7. Some receiving water characteristics which should be measured
immediately after the sample is collected are:
1. Calcium and vitamins
2. Temperature, pH, and dissolved gases
3. Sulfur and molasses
4. Velocity and dissolved solids
5. Profiles and effluents
8. A record must be made of every sample collected.
1. True
2. False
P-2
-------
GLOSSARY
Chapter 13. Sampling Receiving Waters
Estuaries (ES-chew-wer-eez): Bodies of water at the lower end
of a river that are subject to tidal fluctuations.
Fixed: A sample is "fixed" in the field by adding chemicals
that prevent the water quality of the sample from changing
before final measurements are performed later in the lab.
Representative Sample: A portion of material or water identical
in content to that in the larger body of material or water being
sampled.
Respiration: The physical and chemical processes by which an
organism supplies its cells and tissues with oxygen needed for
metabolism and relieves them of carbon dioxide formed in energy-
producing reactions.
G-13-1
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CHAPTER 13. SAMPLING RECEIVING WATERS
13.0 INTRODUCTION
The purposes of treating wastewater are to protect the health of
people who may come in contact with it, to prevent nuisance due
to odors or unsightliness, and to prevent the wastewater from
interfering with the many uses of streams, lakes, estuaries,1
oceans, or underground waters.
In order to find out whether or not a treatment plant is accom-
plishing all of these tasks, it is necessary to measure and record
the effect of the plant discharge (effluent) in the receiving waters.
There are two types of measurements required in connection with
operating a treatment plant. One kind is in-plant measurement
for determining how well the plant operates as compared with what
it is designed to do. For instance, a plant might be designed to
remove 90% of the suspended solids in the raw wastewater. In-plant
wastewater measurements are used to see if it is actually removing
that much, by determining the amount of suspended solids in the
influent (raw wastewater) and effluent and calculating the percent
reduction while the wastewater flows through the plant. Results of
in-plant measurements are used to regulate or control plant processes
for effective waste treatment. In-plant sampling site selection and
procedures are presented in Chapter 14, Section 14.3.
Receiving water measurements are used to determine the effect of
the waste discharge on the receiving waters and on the beneficial
uses of the receiving waters, after it leaves the plant. It is
possible that a plant could be operating according to its design
1 Estuaries (ES-chew-wer-eez). Bodies of water at the lower end
of a river that are subject to tidal fluctuations.
13-1
-------
and be removing 90% of the suspended solids, yet still be causing
a bad effect on the receiving water which receives the effluent.
This could happen because the plant was not designed properly or
there has been a change in the receiving water, such as a reduction
in stream flow, since the plant was built. Also a 90% reduction
on a very concentrated waste may not be good enough.
Receiving water measurements are as important as the in-plant
measurements' because the real purpose of the plant is to pro-
tect the receiving waters. However, plants should always be
operated as efficiently as possible, therefore in-plant measure-
ments must not be slighted. Also, it is absolutely necessary that
the plant effluent be measured so that it can be related to
effects in the receiving waters.
The usual approach in measuring the effect of a discharge on
receiving waters is to take a measurement in an area which
is not affected (upstream) and in an area which is affected
(downstream) and compare the two. This comparison shows how
much effect the discharge has on the receiving waters. It
also shows whether the discharge is causing a violation of the
water quality objectives or standards which have been set by
the water pollution control agency or health department.
13.1 SAMPLING (Selection of Samples)
13.10 General
To plan a water quality survey, you must understand the reasons for
or objectives of the survey. The overall objectives of each survey
greatly influence the location of sampling stations, types of samples,
frequency and time of day of collecting samples, and other factors.
When developing sampling programs, survey planners also must realize
that water quality characteristics vary from one body of water to
another, from place to place in a given body of water, and from time
to time at a fixed location in a given body of water.
A sampling program must be prepared in a manner that will produce ac-
curate and useful results. The collection, handling, and testing of
each sample should be scheduled and conducted in such a manner to
assure that the results will be descriptive of the sources of the
individual samples at .the time and place of collection. Select
locations of sampling stations and collect samples during times of
the day and/or night that will provide the data needed to meet the
objectives of your survey. Collect enough data over a period of time
to adequately describe the condition or quality of the water at each
sampling station.
13-2
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To illustrate these important items, consider a simplified example
of a waste discharge into a flowing river. Assume the river flows
at 500 cubic feet per second (cfs) and the treatment plant dis-
charges at 10 cfs (6.46 MGD). Assume that it is desirable to find
out what is the effect on the river. To determine the effect, the
following questions must be answered.
1. What are the characteristics of the river
upstream from the discharge?
2. What are the river characteristics downstream?
3. If upstream and downstream river characteristics are
different, does the discharge cause the difference?
4. Are the downstream river characteristics in violation
of established standards or objectives?
5. If the river downstream is in violation of standards
or objectives, did the discharge cause it?
Start with Question 1. Assume that you wish to measure:
a. Temperature
b. Dissolved Oxygen
13.11 Temperature
You must develop a temperature measurement program which will
accurately describe the river temperature upstream from the dis-
charge. How can this be done so that the changes from hour to
hour during the day and from month to month during the year are
known? Also, how can the temperature be measured so that the
average for the river cross-section can be found, as well as the
variations from the average in the cross-section? (See Fig. 13.1)
In some rivers which are deep and slow moving, the temperature
may be several degrees cooler on the bottom than on the top.
Thus, if the temperature measurement up-river from the discharge
was taken near the bottom and the one down-river near the top,
it might appear that the discharge had caused the stream to warm
up when it actually had little effect.
The first thing to do is locate the river cross-section (line
across the stream) to be sampled. This may be located at a
bridge or near a boat dock or some other accessible place. Then
measure the temperature at several points across the stream and
at several depths at each point (see Fig. 13.1). Measurements
also should be taken near shorelines, in backwater areas, and near
13-3
-------
SHORELINE
* SAMPLING POINTS
RIVER BOTTOM
NOTE: Sampling points should be located near the shoreline and
approximately one foot below the water surface and one
foot above the bottom. The number of sampling points
between the water surface and the bottom will depend on
the depth of the water, and the number of vertical sam-
pling sections will depend on the width of the stream.
Fig. 13.1 River cross-section showing
typical sampling points
13-4
-------
the stream bottom. These are locations where problems first
develop. If the temperatures are all about the same (within
about 1°C or 2°F),2 you can assume the stream is well mixed with
a uniform temperature.
Next thing to consider is the time of day. Most streams will be
cooler at night than during the day. Usually mid-channel tempera-
ture measurements vary less than those in shallow stretches. The
minimum (lowest) temperature usually occurs about dawn and the
highest in the late afternoon. The best way to measure these vari-
ations is to use a 24-hour recorder. If no recorder is available,
take a measurement each hour for 24 hours (a little night work
never hurt anybody!) to get an average temperature for the day, add
up all the numbers, and divide by 24. Then see what time of day
the average value and the maximum value usually occur. (This may
vary with the season.) It is usually accurate enough for most
streams to measure the temperature at those times and use the values
for an average daily and maximum daily. For example, assume the
following measurements on the next page were recorded:
2 °C means "degrees centigrade" or degrees Celsius", both
of which refer to a particular temperature scale; °F means
"degrees Fahrenheit", a different temperature scale.
13-5
-------
Time Temperature °C
12 NOON 12.4
1PM 12.8
2 PM 13.2
3 PM 13.6
4 PM 14.0
5 PM 13.8
6 PM 13.6
7 PM 13.3
8 PM 13.0
9 PM 12.7
10 PM 12.4
11 PM 12.0
12 MIDNIGHT 11.6
1 AM 11.2
2 AM 10.8
3 AM 10.5
4 AM 10.3
5 AM 10.1
6 AM 10.0
7 AM 10.2
8 AM 10.4
9 AM 10.8
10 AM 11.2
11 AM 11.8
TOTAL = 285.7°C
Average Temperature, °C = Sum of Measurements, °C
6 r ' Number of Measurements
285.7°C
24
13-6
-------
The average temperature of 11.9°C occurs at about 11 AM and
again about 11 PM. If every day is like this, a measurement
taken at 11 AM each day will give a fairly accurate record
of the daily average temperature. Periodic rechecks of the
hourly variation should be made. The same goes for the maximum
value, which occurs at 4 PM.
The next thing to consider is the seasonal variation in tem-
perature. Streams normally warm up in summer and cool off in
winter. Obviously, if a measurement is taken daily (as explained
above) this record will show all variations throughout the year.
But, usually the daily average temperature does not change very
much day to day.
Assume that the daily values for each month have been used to
calculate monthly averages and that the following numbers have
been obtained.
Monthly Average
Month Temperature, °C
January 7.0
February 6.0
March 8.0
April 10.0
May 12.0
June 14.0
July 16.0
August 19.0
September 18.0
October 14.0
November 10.0
December 8.0
TOTAL = 142. 0°C
... , . Or, Sum of Measurements, °C
Yearly Average, °C = — - - ~— - '— —
Number of Measurements
142. 0°C
12
Minimum Monthly 0
Average, °C = b.U C
Maximum Monthly
Average, °C
or ' = 19.0°C
13-7
-------
The month-to-month changes in temperature are not very predictable
because some years are colder than others, or summer lasts longer,
or something else unusual can happen. The minimum and maximum
monthly averages indicate the extent of the monthly changes for the
observed year.
This discussion of temperature measurement does not mean that
temperature is the most important characteristic to measure, although
it is important from the standpoint of protecting fish. It does show
how important it is for you to be careful when selecting a sample for
measuring any characteristic of wastewater or the receiving waters.
It is important to plan ahead so that each sample will indicate or
represent the actual conditions of the river. If this is accomplished,
you have obtained a representative sample.3 Going out blindly taking
measurements (sometimes known as "flailing the water") can yield a
lot of numbers which don't mean very much, but only the person who
takes the measurement knows that. Others who use the numbers may
assume they are meaningful and act accordingly. Always plan ahead
to get maximum benefit from your receiving water sampling program.
Now go back to Question 2. What are the characteristics (in this
case, temperature) down-river from the discharge? The same pro-
cedure for sample selection downstream should be used as previously
explained. There is an additional consideration, however. The
cross-section selected for a sampling station should be far enough
downstream for the waste discharge to have become well mixed.
If the stream is very sluggish and deep, the discharge may not mix
thoroughly for a mile or more; so it will be necessary to sample in
such a way that the unmixed condition can be described properly.
(Fig. 13.2) The higher the stream velocity, shallower the water,
and the sharper the bends in the stream, the greater the turbulence
and thus the quicker the discharge becomes mixed with the receiving
waters.
Before going out in the filed to measure water quality, obtain a
range of expected values for guidance in sampling and interpreting
results. Try various sampling locations to find high and low
values for different times of the day and season.
Look now at. the problem of measuring the temperature (or other
characteristic) of the treatment plant effluent. Wastewater flow
from a municipal discharge normally has a variable flow rate and
variable characteristics. Fortunately, this variation follows
similar patterns from day to day, week to week, year to year, so
a logical sampling program can be set up to keep track of the
characteristics of the plant effluent.
3 Representative Sample. A portion of material or water identical
in content to that in the larger body of material or water being
sampled.
13-8
-------
SECTION A
SAMPLING POINTS WILL
HELP TO SHOW MIXED AND
UNMIXED AREAS
SECTION B
V *
WASTE DISCHARGE
MIXING ZONE
OR PATTERN
Fig. 13.2 Waste mixing in a river
13-9
-------
REMEMBER:
The effluent measurement program
mus t be designed to te11 the
operator how much volume of flow
and what quality of constituents
are entering the receiving waters,
hourly, daily, weekly, monthly,
and yearly.
It is desirable to have a con-
venient access where the effluent
can be sampled easily. A remote
sampling location or one which is
difficult to reach will discourage
regular sampling. Wherever the
sampling station is located, it
must provide meaningful samples.
13.12 Dissolved Oxygen
Another measurable characteristic of the stream is dissolved oxygen.
The principles for collecting samples for measuring dissolved oxygen
are the same as for measuring temperature. In fact, the amount of
dissolved oxygen that can be in water depends on temperature, among
other things.
Cold water will hold more dissolved oxygen than hot water. This does
not mean that cold water always will contain more oxygen. Cold waters
tend to slip under warmer waters because they have a greater density.
In the lower layers of a body of water they are farther from the
sources of oxygen from surface aeration and algal activity. Bottom
waters may be close to deposits of organic materials that use oxygen.
The net result could be lower oxygen concentrations in colder waters
if they remain near the bottom too long.
In measuring the dissolved oxygen downstream from a treatment plant
discharge, it is important to remember that a decrease in dissolved
oxygen may not be noticeable immediately downstream, even if the
effluent is well mixed with the stream. Many hours of flow time may
be required for the oxygen to be reduced due to organic material in
the discharge. So it is necessary to make an "oxygen profile" of the
stream to get a good measure of the effect of the effluent.
Making a profile means merely measuring the dissolved oxygen at
several different cross-sections downstream from the discharge to
find out where the lowest dissolved oxygen level occurs. For this
example, assume the same waste discharge and river used in the previous
example.
13-10
-------
Number the cross-sections to be sampled as follows:
Cross-Section No. Location
1 1 mile above discharge
2 1 mile below discharge
3 3 miles below discharge
4 5 miles below discharge
5 7 miles below discharge
6 9 miles below discharge
7 11 miles below discharge
Identify the location of any additional waste discharges or points
of inflow from tributary streams. Selection of the number and
location of sampling cross-sections depends on stream characteristics,
accessibility, and information desired. Normally locations are
selected to show critical conditions and changes in the receiving
waters.
At each cross-section, be sure representative samples are being
selected. Always remember that a gallon of sample is supposed to
be identical to the millions of gallons of water that flow past
the sampling point.
Now, assume that you have checked and found that only one properly
located sample was required to represent each cross-section and
that the following measurements were obtained:
Cross-Section No. Temperature, °C Dissolved Oxygen, mg/1
1 13.5 10.5
2 13.5 10.0
3 13.5 9.0
4 13.5 7.5
5 13.5 6.0
6 13.5 7.1
7 13.5 8.9
(Note that the temperature is constant for all cross-sections. This
is to simplify the example. If the temperature increased downstream
from the discharge, some of the drop in dissolved oxygen would be due
to the temperature increase and some would be due to the organic
material. You also should be sure to notice any effects due to tribu-
taries or other waste discharges.)
Fig. 13.3 shows a plot or graph of the measurements listed above.
This is a good way to show the dissolved oxygen profile. Profiles
for different days or months can be plotted on the same sheet in
different colors to show how the profile changes from season to
season or from year to year. The location of the low point may
move up or down the stream, depending on the amount of flow in the
13- 11
-------
LOCATION OF DISCHARGE
C3
X
CD
CO
C/O
11
10
9
8
7
6
5
4
3
2
1
0
2345
CROSS-SECTION NUMBER
Fig. 13.3 Dissolved oxygen profile
13-12
-------
stream and other factors. Therefore, several points must be
obtained for each profile to be sure the amount and location
of low point can be determined. Additional discharges will
complicate the profile.
13.13 Review of Sampling Results
To determine if sampling stations are in the proper location and
producing meaningful results, the results from the testing pro-
gram must be carefully reviewed. If the results don't appear
correct, try to determine why they appear strange. Look for
sampling errors, testing errors, and recording errors. Attempt
to verify each step in your sampling program. Remember that you
sample because something unusual can happen. Don't reject strange
results because they are unusual, but investigate and attempt to
identify the reasons for the results. Establish additional
sampling locations when necessary and eliminate or relocate stations
that are not producing meaningful results.
QUESTIONS
13.1A An assistant plant operator collected samples and measured
the temperature at one stream cross-section each hour for
24 hours. Following are the results he reported:
Time
5 PM
6 PM
7 PM
8 PM
9 PM
10 PM
11 PM
12 MIDNIGHT
Temperature
°C
13.5
13.4
14.3
14.7
14.5
13.8
14.0
13.7
13.4
22.7
12.7
12.2
Time
5 AM
6 AM
7 AM
8 AM
9 AM
10 AM
11 AM
12 NOON
Temperature
°C
12.4
11.0
11.0
10.8
10.6
10.5
10.7
11.6
11.4
11.8
12.4
13.0
TOTAL
310.1°C
Average Temperature, °C = gum of Measurements, °C
Number of Measurements
310.1 °C
24
= 12.9°C
You are the supervisor. What would be your response to
these results?
13-13
-------
13.IB Which measurement would you be doubtful about?
a. 12 MIDNIGHT
b. 4 AM
c. 10 PM
d. 6 AM
13.1C Assume that you tell him to collect a new set of measure-
ments two days later. He measures (not copies) all the
same numbers except for the one you questioned earlier,
and the new reading for that hour is 13.0. What are the
new total and average values?
a.
b.
c.
d.
e.
296
316
300
306
298
.3
.9
.4
.1
.9
and
and
and
and
and
13.
12.
12.
12.
13.
2
6
5
7
0
13.ID a. What are the new maximum and minimum values?
b. At what times did they occur?
c. Which sample most nearly represented the average value?
13-14
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13.2 SAMPLING (Collection Techniques)
13.20 Collection
The proper techniques to follow and precautions to observe to
be sure a good sample is obtained are adequately covered in
several publications. (See Section 13.6, Additional Reading.)
In all of these books the emphasis is on having the proper
equipment and supplies (See Chapter 14, Section 14.3) to do
a good job. Remember that behind all the instructions on tech-
niques is the"basic' idea that the sample must be collected and
preserved in such a manner that it does not change significantly
from the time it is first obtained in the field until the final
analysis is completed.
For example, if a gallon of water is selected from a stream for
a dissolved oxygen measurement, be sure that the amount of dis-
solved oxygen in the sample does not change before it is measured.
The same goes for any other characteristic.
Some characteristics change so rapidly that they should be measured
immediately. This is true of temperature, pH, and dissolved oxygen.
Some of the dissolved gases can be "fixed"4 for a while to allow
transporting the sample to the laboratory for measurement. Proce-
dures for "fixing" can be found in "Standard Methods" and other
publications on analysis. It is usually not a good idea to try
to fix a sample containing a significant amount of organic matter,
such as a plant effluent, because it tends to change anyway. Take
a field kit to the sampling location and test at the site.
13.21 Frequency of Sampling
Regular sampling intervals should be developed in cooperation with
the regulatory agency having authority over the plant and the
receiving waters. When the treatment plant effluent is not meeting
discharge requirements or the receiving waters are not meeting
established water quality standards, the frequency of sampling may
be increased.
** Fixed. A sample is "fixed" in the field by adding chemicals
that prevent the water quality indicator from changing before
final measurements are performed later in the lab.
13-15
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13.22 Size of Sample
When samples are tested in the field, the size of sample should be
sufficient to perform the desired tests. If samples are pre-
served and transported to a lab for analysis, the size of sample
should be at least twice the amount needed to perform the desired
tests to allow for back-up or repeat tests.
13.23 Labeling of Samples
A record must be made of every sample collected. Every sample
bottle must be identified and should have attached to it a label
or tag indicating the exact location where the sample was collected,
date, hour, air and water temperature, and name of collector.
Other pertinent data such as water level or river flow and weather
conditions should be recorded. Precipitation, cloud conditions and
prevailing winds during the last few days should be noted when
collecting samples. The weather during the three or four days before
sampling may be entirely different from the weather on the day of
sampling, but may significantly affect the character of the sample.
Sampling points should be identified on maps, including a detailed
description, and identified in the field by easily located markers
or landmarks.
13.3 SAFETY
Take adequate precautions to prevent falling or slipping onto the
water when sampling. Not only can this save your life, it also will
prevent muddying the sample.
Choose sampling cross-sections
or "stations" carefully so that
safe access is possible in
winter and summer. Use snap-on
safety belts when leaning over
bridge railings or stream
banks. When sampling on a
bridge, be sure there is enough
room for the man collecting the
samples and traffic. Wear a life
preserver when sampling from a
boat; and be sure the boat is
well marked with lights, reflec-
tors, and flags to prevent
collisions. At least two people
should man a sampling boat.
When the sampler's attention is
focused on the job he is doing,
he cannot keep an eye out for
other watercraft.
13-16
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13.4 OTHER TYPES OF RECEIVING WATERS
This lesson on sampling receiving waters has been limited to
very simple examples of flowing streams or rivers. Some other
types of receiving waters you may encounter are:
1. Oceans
2. Estuaries
3. Groundwaters
4. Lakes
These receiving waters usually require a more sophisticated
approach to sampling and measurement of characteristics. The
basic rules are the same, however, for sample selection and
collection techniques. The best answer to sampling these types
of receiving waters is to seek advice from a consultant, a
regulatory agency, or other experts on where and how to sample
and on how to evaluate the results.
13.5 WHAT TO MEASURE
There are hundreds, possibly thousands, of characteristics which
could be measured in receiving waters and plant effluents. Many
of them are not important to the operation of a treatment plant;
however, it is possible to list a minimum number of characteris-
tics which should enable the operator to measure the effect of
his plant's effluent and find out if it meets water quality
objectives.
Following is a listing of characteristics which should be observed
or measured in the receiving waters and in the plant effluent:
13-17
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Effluent
Receiving Waters
1.
2.
3.
4.
5.
6.
7.
8.
The
may
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Visual Inspection (color,
floating materials)
Coliform Group Bacteria
and Chlorine Residual
Biochemical Oxygen Demand
Suspended Solids and
Settleable Solids
Temperature
PH
Odor
Grease
Visual Inspection (color,
floating materials)
Coliform Group Bacteria
Dissolved Oxygen
Suspended Solids and
Clarity
Temperature
PH
Odor
Grease
list above is basic. Some additional characteristics which
be important in various situations are:
Effluent
Total Dissolved Solids
Chlorine
Hardness
Viruses
Toxicity
Biostimulants (such as
nitrogen, phosphorus,
etc.)
Iron and Manganese
Chlorinated Hydrocarbons
(pesticides)
Fluoride
ABS
Phenols
Receiving Waters
Total Dissolved Solids
Chlorine
Hardness
Viruses
Health of Aquatic Animals
Algae and other Aquatic Plants
Iron and Manganese
Chlorinated Hydrocarbons
(pesticides)
Fluoride
ABS
Phenols
13-18
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Many of these effluent tests are for the record rather than for
plant control purposes. The operator can do nothing in adjust-
ment of treatment plant processes to affect the characteristics.
However, he will often be asked to measure them because they
are listed in the plant's waste discharge requirements or
receiving water standards. Some of them, such as toxicity, can
be controlled by ordinances which prevent toxic substances from
being put in the wastewater collection system. Others, such as
total dissolved solids, may require the city to find a new water
supply.
QUESTIONS
13.2A What is a "fixed" sample?
13.3A What safety precautions should be taken when sampling?
13.4A What characteristics should be observed or measured
in the effluent and receiving waters of a treatment
plant?
13-19
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13.6 ADDITIONAL READING
a. MOP 11, pages 173-177.
b. New York Manual, pages 127-130.
c. Standard Methods for Examination of Water and Wastewater,
produced by APHA, AWWA, and WPCF, Water Pollution Control
Federation, 3900 Wisconsin Avenue, Washington, D.C. 20016.
Price: $16.50 to members, prepaid only; otherwise $22.50
plus postage. Indicate your member association when order-
ing. (This publication also contains instructions for building
a sampler.)
13-20
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DISCUSSION AND REVIEW QUESTIONS
Chapter 13. Sampling Receiving Waters
Please write the answers to these questions in your notebook.
1. Why should receiving waters be sampled?
2. Can a treatment plant operate as effectively as possible
and still have a bad effect on the receiving waters? Why?
3. Why are receiving waters measured upstream from the point
of discharge?
4. Where should samples be collected in the cross-section of a
stream at a particular sampling location? Assume you are
trying to find the point in the section which will give you
a representative measurement of the entire section.
5. Why should more than one sampling station be established
downstream from the point of wastewater discharge?
6. What does the term "representative sample" mean?
7. What is a major concern regarding sample water quality
after the sample has been collected?
8. How large a sample should be collected?
9. What information should be included on a sample label?
10. What safety precautions should be taken when sampling from
a bridge?
13-21
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SUGGESTED ANSWERS
Chapter 13. Sampling Receiving Waters
13.1A I would contact the assistant plant operator and attempt
to verify the results he recorded. Also I would ask him
if he noticed anything unusual.
13.IB (c) 10 PM
13.1C (c) 300.4 and 12.5
13.ID a. Maximum 14.7°C and Minimum 10.5°C.
b. Time of maximum temperature, 4 PM; minimum temperature, 6 AM.
c. 11 AM.
13.2A A "fixed" sample is a sample which has chemicals added to
prevent a particular water quality indicator from changing
before the sample can be analyzed.
13.3A Adequate safety precautions should be taken when sampling to
prevent falling or slipping into the water. Provisions should
be made to warn other watercraft (flags) . An assistand should
be available to rescue anyone falling into the water and to
warn other watercraft.
13.4A Effluent
1. Visual Inspection (color,
floating materials)
2. Coliform Group Bacteria
and Chlorine Residual
3.
4.
5.
6.
7.
8.
BOD
Suspended Solids and
Settleable Solids
Temperature
FH
Odor
Grease
Receiving Waters
Visual Inspection (color,
floating materials)
Coliform Group Bacteria
DO
Suspended Solids and
Clarity
Temperature
PH
Odor
Grease
13-23
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OBJECTIVE TEST
Chapter 13. Sampling Receiving Waters
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1.
1. The two types of measurements required in connection with
operating a treatment plant are:
1. Temperature and dissolved oxygen
2. Effluent and downstream
3. Upstream and downstream
4. In-plant and receiving water
5. Temperature and receiving water
2. Receiving water sampling requires proper:
1. Safety and temperature
2. Equipment and "flailing the water"
3. Selection of samples and collection techniques
4. Water quality objectives and night work
5. Snap-on belts and flags
3. To determine the location and amount of lowest dissolved
oxygen downstream from a discharge, it is necessary to:
1. "Flail the water"
2. Observe safety precautions
3. Measure the effluent
4. Make an "oxygen profile" of the stream
5. Make yearly measurements
4. The average annual temperature for a stream can be measured
by sampling in only one month out of the year.
1, True
2. False
5. Results from a sampling program should always be accepted
without question or verification.
1. True
2. False
6. Proper sample collection techniques are specified in:
1. Standard Methods for the Examination of Water and Wastewater
2. Playboy Magazine
3. All design manuals for concrete pipe
4. Water quality objectives
5. Safety precautions
13-25
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7. Some receiving water characteristics which should be measured
immediately after the sample is collected are:
1. Calcium and vitamins
2. Temperature, pH, and dissolved gases
3. Sulfur and molasses
4. Velocity and dissolved solids
5. Profiles and effluents
8. A record must be made of every sample collected,
1. True
2. False
Review Questions:
9. What is the volatile acid/alkalinity relationship in a digester
if the alkalinity is 1760 mg/1 and the volatile acids are 140 mg/1?
1. 0.05
2. 0.08
3. 0.10
4. 0.125
5. 0.15
10. A digester contains 1000 pounds of volatile matter under digestion.
If 0.05 pounds of new volatile solids can be added per day per
pound of volatile matter under digestion, how many pounds of
sludge solids can be added per day with a volatile content of 70%?
1. 20 pounds per day
2. 50 pounds per day
3. 70 pounds per day
4. 100 pounds per day
5. 200 pounds per day
Please write on your IBM answer sheet the total time required to
work this chapter.
13-26
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CHAPTER 14
LABORATORY PROCEDURES AND CHEMISTRY
by
James Paterson
(with a special section by Joe Nagano)
-------
TABLE OF CONTENTS
CHAPTER 14 LABORATORY PROCEDURES AND CHEMISTRY
14.0 Introduction 14-1
14.00 Should You Start This Lesson Now? 14-1
14.01 Material in This Lesson 14-2
14.02 References 14-3
14.03 Acknowledgments 14-4
14.1 Glossary of Terms and Equipment 14-4
14.10 Terminology 14-4
14.11 Equipment 14-6
14.2 Safety and Hygiene 14-12
14.20 Laboratory Safety 14-12
14.21 Personal Hygiene for Wastewater
Treatment Plant Personnel 14-17
14.3 Sampling 14-21
14.30 Importance 14-21
14.31 Accuracy of Laboratory Equipment 14-21
14,32 Selection of a Good Sampling Point
to Obtain a Representative Sample 14-22
14.33 Time of Sampling 14-23
14.34 Compositing and Preservation of Samples . . . 14-23
14.35 Sludge Sampling 14-25
14.36 Sampling Devices 14-26
14.37 Summary 14-27
14.4 Laboratory Work Sheet 14-30
14.5 Plant Control Tests 14-39
Test No. Title
1 Total Alkalinity 14-41
2 Biochemical Oxygen Demand or BOD 14-41
3 Carbon Dioxide (C02) in Digester Gas. . . 14-43
4 Chemical Oxygen Demand or COD 14-49
5 Chlorine Residual 14-57
111
-------
Test No. Title Page
6 Clarity 14-67
7 Coliform Group Bacteria 14-71
8 Dissolved Oxygen or DO 14-93
I. In Water 14-93
II. In Aerator 14-101
9 Hydrogen Sulfide (H2S) 14-117
I. In Atmosphere 14-117
II. In Wastewater 14-118
10 pH 14-121
11 Settleability of Activated Sludge Solids. 14-127
I. Settleability 14-127
II. Sludge Volume Index (SVI) 14-130
III. Sludge Density Index (SDI) 14-132
12 Settleable Solids 14-135
13 Sludge Age 14-141
14 Sludge (Digested) Dewatering
Characteristics 14-145
15 Supernatant Graduate Evaluation 14-149
16 Suspended Solids 14-155
I. - Gooch Crucible 14-155
II. Centrifuge 14-171
17 Temperature 14-175
I. Wastewater 14-175
II. Digester Sludge 14-179
18 Total and Volatile Solids (Sludge). . . . 14-183
19 Turbidity (See Clarity)
20 Volatile Acids 14-193
21 Volatile Solids (See Total Solids)
14.6 Recommended General Laboratory Supplies 14-215
14.7 Additional Reading 14-219
IV
-------
*#
The objective of the Pre-Test is to indicate to you the important
topics in this chapter. You are not expected to know the answers
to the questions, and your improvement in the Objective Test is an
indication of how effective your efforts were in learning the
material.
P-i
-------
PRE-TEST
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Please write your name and mark the correct answers on the IBM answer
sheet. There may be more than one correct answer to each question.
TRUE OR FALSE (1-10) :
1. A rubber bulb should be used to pipette wastewater or polluted
water.
1. True
2. False
2. Acid may be added to water, but not the reverse.
1. True
2. False
3. Always wear safety goggles when conducting any experiment in
which there may be danger to the eyes.
1. True
2. False
4. Smoking and eating should be avoided when working with infectious
material such as wastewater and sludge.
1. True
2. False
5. In the washing of hands after working with wastewater, the kind
of soap is less important than the thorough use of soap.
1. True
2. False
6. The pH scale nay range from 0 to 14, with 7 being a neutral
solution.
1. True
2. False
P-l
-------
7. If at all possible, samples for the BOD test should be
collected before chlorination
1. True
2. False
8. The COD test is a measure of the chemical oxygen demand
of wastewater.
1. True
2. False
9. The BOD test is a measure of the organic content of waste-
water.
1. True
2. False
ID. The answers from the total solids and suspended solids tests
are always the same.
1. True
2. False
Possible definitions of the words listed below are given on the
right. If the definition of a word is after the number 2, mark
column 2 on your answer sheet.
Word Definition
1. Surrounding
11. Aliquot 2. Capacity to resist pH change
12. Ambient 3. Portion of a sample
13. Blank 4. Inside
14. Buffer 5. Test run without sample
15. Large errors in laboratory tests may be caused by:
1. Improper sampling
2. Large samples
3. Poor preservation
4. Poor quality effluent
5. Lack of mixing during compositing
P-2
-------
16. The most critical factor in controlling digester operation
is the:
1. C0?
2. Gas production
3. Volatile solids
4. Volatile acids/alkalinity relationship
5. pH
17. The COD test:
1. Measures the biochemical oxygen demand
2. Estimates the first-stage oxygen demand
3. Measures the carbon oxygen demand
4. Estimates the total oxygen consumed
5. Provides results quicker than the BOD test
18. A clarity test on plant effluent:
1. Tells if the effluent is safe to drink
2. Is measured by an amperemeter
3. Should always be measured at the same time
4. Should always be measured under the same light conditions
5. Is measured by a Secchi Disc
19. Coliform group bacteria are:
1. Measured by the membrane filter method
2. Measured by the multiple fermentation technique
3. Measured by the modified Winkler procedure
4. Harmful to humans
5. Indicative of the potential presence of bacteria
originating in the intestines of warm-blooded animals
20. The saturation concentration of dissolved oxygen in water
does not vary with temperature.
1. True
2. False
21. DO probes are commonly used to measure dissolved oxygen in
water in:
1. Aeration tanks
2. Sludge digesters
3. Manholes
4. Streams
5. BOD bottles
P-3
-------
22. Hydrogen sulfide:
1. Reacts with moisture and oxygen to form a
substance corrosive to concrete
2. Is sometimes written as H2S
3. Smells like rotten eggs
4. Is formed under aerobic conditions
5. Should not be controlled in the collection system
23. Results from the settleability test of activated sludge
solids may be used to:
1. Calculate SVI
2. Calculate SDI
3. Calculate sludge age
4. Determine ability of solids to separate from liquid
in final clarifier
5. Calculate mixed liquor suspended solids
24. Results of the settleable solids test run using Imhoff
cones may be used to:
1. Calculate the Imhoff Settling Index
2. Calculate the efficiency of a plant
3. Calculate the pounds of solids pumped to the digester
4. Indicate the quality of the influent
5. Indicate the quality of the effluent
25. Precautions that must be observed in running the suspended
solids-Gooch crucible test include:
1. Collecting and testing a representative sample
2. Proper temperature level in oven at all times
3. Lack of leaks around and through the glass fiber
4. Thoroughly mixing sample before testing
5. Discarding any large chunks of material in sample
26. A chlorine residual should be maintained in a plant effluent;
1. To keep the chlorinator working
2. For disinfection purposes
3. For testing purposes
4. To protect the bacteriological quality of the receiving
waters
5. None of these
P-4
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CHAPTER 14. LABORATORY PROCEDURES AND CHEMISTRY
14.0 INTRODUCTION
14.00 Should You Start This Lesson Now?
Laboratory procedures and results are the means by which we control
the efficiency of our treatment processes and measure the effective-
ness of the processes. To operate your plant as efficiently as
possible, you must understand the laboratory procedures and relate
them to the actual operation of your plant.
This lesson has been given to you at this time mainly for reference
purposes. When you read the lessons on the treatment processes you
should begin to wonder how certain tests are performed that are
essential for proper plant operation. At this time you should refer
to this lesson for a general discussion and a description of the
laboratory procedure.
It might seem logical to you to complete this lesson first in order
to better understand the operational aspects of the treatment process
lessons. Many operators and potential operators who were interested
in this profession have taken this course. Most of them have said
that they wanted to learn about the treatment processes first and
then learn how to apply the lab procedures to plant operation. Many
potential operators experienced difficulty with the terminology when
they tried to work this chapter before completing the lessons on the
treatment processes. If you are an experienced operator and are
anxious-to learn more chemistry and to obtain a better understanding
of lab procedures, you may decide to try this lesson first.
14-1
-------
Past experience has indicated that most operators prefer to use
this section as a reference while studying the lessons on treat-
ment processes. You are the operator who wants to learn more
about treatment plant operation, and you are encouraged to use
this material in any manner that you feel best fits ycur par-
ticular situation and professional goals. Now is the time for
you to decide whether you are going to:
1. Thumb through this lesson, proceed through the chapters
on treatment processes, and then complete this lesson;
2. Complete the lessons on treatment processes, referring
to this lesson when interested, and then complete this
lesson;
3. Complete this lesson and then the lessons on treatment
processes; or
4. Follow your own plan.
14.01 Material in This Lesson
A few of the lab procedures outlined in this chapter are not
"Standard Methods" (4),1 but are used by many operators because
they are simple and easy to perform. Some of these procedures
are not accurate enough for scientific investigations, but are
satisfactory for successful plant control and operation. When
lab data must be submitted to regulatory agencies for monitoring
and enforcement purposes, you should request the agency to
provide you with a list of approved test procedures.
Each test section contains the following information:
1. Discussion of test.
2. What is tested?
3. Apparatus.
4. Reagents.
5. Procedures.
6. Precautions.
7. Examples.
8. Calculations.
Numbers in parentheses refer to references in Section 14.02.
14-2
-------
If you would like to read an introductory discussion on laboratory
equipment and analysis, the Water Pollution Control Federation has
a good publication entitled "Simplified Laboratory Procedures" (3).
Good discussions on the use of the analytical balance may be found
in "Laboratory Procedures" (1) or "Simplified Procedures" (3).
14.02 References
1. "Laboratory Procedures for Operators of Water Pollution Control
Plants" by Joe Nagano. Obtain from Secretary-Treasurer,
California Water Pollution Control Association, P.O. Box 61,
Lemon Grove, California 92045. Price $3.25 to members of CWPCA;
$4.25 to others.
2. "FWPCA Methods for Chemical Analysis of Water and Wastes,"
Environmental Protection Agency, Water Quality Office, Ana-
lytical Quality Control Laboratory, 1014 Broadway, Cincinnati,
Ohio 45202. (November 1969)
3. "Simplified Laboratory Procedures for Wastewater Examination,"
WPCF Publication No. 18, 1968, 60 pages. $2 to WPCF members;
$3 to others.
4. "Standard Methods for Examination of Water and Wastewater,"
13th Edition , 1971, 874 pages. $16.50 to WPCF members;
$22.50 plus postage to others.
Both References 3 and 4 may be obtained by writing:
Water Pollution Control Federation
3900 Wisconsin Avenue
Washington, D.C. 20016
Order forms may be found in the Journal of the Water Pollution Control
Federation.
14-3
-------
14.03 Acknowledgments
Many of the illustrated laboratory procedures were provided by
Mr. Joe Nagano, Laboratory Director, Hyperion Treatment Plant,
City of Los Angeles, California. These procedures originally
appeared in Laboratory Procedures for Operators of Water
Pollution Control Plants, prepared by Mr. Nagano and published
by the California Water Pollution Control Association. The
lists of equipment, reagents, and procedures outlined in this
chapter are similar to those listed in the references in
Section 14.02. Use of information from these references is
gratefully acknowledged.
14.1 GLOSSARY OF TERMS AND EQUIPMENT
14.10 Terminology
> Greater than.
DO > 5 mg/1, would be
read as DO greater than
5 mg/1.
< Less than.
DO < 5 mg/1, would be
read as DO less than
5 mg/1.
Aliquot (AL-li-kwot).
Portion of a sample.
Ambient Temperature (AM-bee-ent). Temperature of the surroundings.
Amperometric (am-PURR-o-MET-rick). A method of measurement that
records electric current flowing or generated, rather than record-
ing voltage. Amperometric titration is an electrometric means of
measuring concentrations of substances in water.
Anaerobic Environment (AN-air-0-bick). A condition in which "free"
or dissolved oxygen is not present.
14-4
-------
Blank. A bottle containing dilution water or distilled water,
but the sample being tested is not added. Identical tests are
frequently run on a sample and a blank and the differences
compared.
Buffer. A measure of the ability or 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 the pK.
Composite (proportional) Samples (com-POZ-it) . Samples collected
at regular intervals in proportion to the existing flow and then
combined to form a sample representative of the entire period of
flow over a given period of time.
Distillate. In the distillation of a sample, a portion is
evaporated; the part that is condensed afterwards is the distillate.
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 precipi-
tate 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.
Flame Polished. Sharp or broken edges of glass (such as the end
of a" glass tube) are flame polished by placing the edge in a flame
and rotating it. By allowing the edge to ir.elt slightly, it will
become smooth.
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 (F^SOjJ is 98. A 1M solution of sulfuric acid would consist
of 98 grams of H^SO^ dissolved in enough distilled water to make
one liter of solution.
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 (f^SC^) in grams is 98.
Atomic Number Molecular
Element Weight of Atoms Weight
H 1 2 2
S 32 1 32
0 16 4 6£
98
14-5
-------
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 of a compound which
contains one gram atom of ionizable hydrogen or its chemical
equivalent. For example, the equivalent weight of sulfuric
acid (t^SOiJ is 49 (98 divided by 2 because there are two re-
placeable hydrogen ions). A IN solution of sulfuric acid
would consist of 49 grams of H2SO(+ dissolved in enough water
to make one liter.
Oxidation (ox-i-DAY-shun). 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.
Percent Saturation. Liquids can contain in solution limited
amounts of compounds and elements. 100% saturation is the
maximum theoretical amount that can be dissolved in the solution.
If more than the maximum theoretical amount is present, the
solution is supersaturated.
o c . .. Amount in Solution 1r._0
% Saturation = -—: =• 7-: -, x 100%
Maximum Theoretical
Amount in Solution
Reagent (re-A-gent). A substance which takes part in a chemical
reaction that is used to measure, detect, or examine other sub-
stances .
Representative Sample. A portion of material or water identical
in content to that in the larger body of material or water being
sampled.
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 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.
14.11 Equipment
Equipment can be better described by a photo or a sketch than
a written description; consequently, this portion of the
glossary will describe equipment in this manner. Photos of
equipment shown were provided by Van Waters § Rogers.
14-6
-------
ILLUSTRATIONS OF LABORATORY APPARATUS
60809-021 Series
Test Tube
^e>
60824-116 Series
Culture Tube
Without Lip
13912-207
Beaker
30209-025
Funnel
29140-023
Flask,
Erlenmeyer
(ER-len-MY-er)
Wide Mouth
29619-642
Flask,
Volumetric
29110-102
Flask,
Boiling
Flat Bottom
23130-049
23131-020
Condenser
29126-022
Flask,
Boiling
Round Bottom
Short Neck
29209-083
Flask,
Distilling
29415-100
Flask,
Filtering
Funnel,
Buchner
With
Perforated Plate
14-7
-------
16269-027
Bottle,
Reagent
v -v
/^N
101
16285-114
Bottle,
BOD
' •«'
•fa_
Bh
24707-265
Cylinder,
Graduated
23810-021
Crucible
Porcelain
23835-000
25310-019 25313-017
Crucible Dish,
Gooch Evaporating
(GOO-ch)
Porcelain
|
^i
-4
i
i
(— >
\
^
La
.
.-=
fc*
I
i
|
\
- •<
^
<-o
l-S»
^ h
I
17685-005 17454
Dish,
Evaporating
Shallow Form
(
S(
*
443
=i
ff
3
JU.
it
™J
TT
17590-044
Support, Buret Buret Buret
§ Buret Clamp (bur-RET) Automatic
14-8
-------
Clamp, Beaker,
Safety Tongs
21750-009
Clamp, Dish,
Safety Tongs
21752-004
Clamp, Flask,
Safety Tongs
21611-046
Clamp, Utility
62765-029 Series
Tripod, Concentric
Ring
21770-028
Clamp, Test Tube
21677-000
Clamp Holder
17951-029
Burner, Bunsen
21633-049
Clamp
62730-024 Series
Triangle
Fused
14-9
-------
66187-004
Cone,
Imhoff
(IM-hoff)
66190-009
Cone Support
25353-248
Dish, Petri
66176-325
Color Comparison
Tubes, Nessler
25026-026
Desiccator
(DES-ick-kay-tor)
52368-022 Series
Oven, Mechanical Convection
53047-024 Series
Pipette
CPIE-pet)
Volumetric
53224-028 Series
Pipet, Serological
61048-033 Series
Thermometer, Dial
33976-009
Hot Plate
30632-003
Muffle Furnace, Electric
14-10
-------
-JA
35960-000
BOD Cabinet
57980-000
Spectrophotometer
Weight = 95.5580 gm.
11274-008 Reading Scale
11274-008
Balance, Analytical
54906-001
Pump, Air Pressure § Vacuum
60776-002
Test Paper, pH 1-11
14-11
-------
CHAPTER 14 LABORATORY PROCEDURES AND CHEMISTRY
(Lesson 1 of 8 Lessons)
14.2 SAFETY AND HYGIENE, by A.E. Greenberg from California Water
Pollution Control Association Operators Laboratory Manual
14.20 Laboratory Safety
Safety is important in the laboratory as well as in the rest
of the treatment plant. Therefore, each employee working in
a laboratory should be thoroughly familiar with this section.
On questions of safety, consult your state's General Industrial
Safety Orders or similar document and Sax's "Dangerous Chemicals".2
Personnel working in a wastewater treatment plant laboratory
must realize that a number of hazardous materials and conditions
exist. PREVENT ACCIDENTS. Be alert and careful. Be aware of
potential dangers at all times. The major threats to you are
listed for your safety.
1. Infectious Materials
Wastewater and sludge contain millions of bacteria, some
of which are infectious and dangerous, and can cause
diseases such as tetanus, typhoid, dysentery, poliomelytis,
and hepatitis. Personnel handling these materials should
thoroughly wash their hands with soap and water, particularly
before handling food. Do not pipette wastewater or polluted
samples by mouth. Use a rubber bulb. Though not mandatory,
inoculations by your County Health Department are recommended
for each employee.
2 See Sax, N.I., Dangerous Properties of Industrial Materials,
Third Edition, Reinhold, New York, 1968, price $35.
14-12
-------
2. Corrosive Chemicals
A. Acids
(1) Examples: Sulfuric, hydrochloric, nitric, glacial
acetic, Pomeroy solutions Nos. 1 and 2, and chromic
acid cleaning solutions.
(2) Acids are extremely corrosive to human tissue, metals,
clothing, wood, cement, stone, and concrete. Use glass-
ware or polyethylene containers.
(3) In case of accidental spills, immediately dilute with
large portions of water and neutralize the acid with
sodium carbonate or bicarbonate
until bubbling and foaming stops.
Clean up neutralized material.
If spills occur on bench tops,
dilute, neutralize, and squeeze
into sink. If spills occur on
person, immediately wash off
with water. If spills occur
on face (spills of concentrated
acid) , immediately flood with
large quantities of cold water.
Notify supervisor. Remember to
add acid to water, but not reverse.
Pour and pipette carefully to
prevent spilling and dropping.
Prevent contact with metals,
particularly equipment.
B. Bases
(1) Examples: Sodium hydroxide, potassium hydroxide,
ammonium hydroxide, alkaline iodide sodium azide
solution.
(2) Handle with extra care and respect. They are extremely
corrosive to skin, clothing, and leather. Use glass-
ware and polyethylene containers.
Ammonium hydroxide is extremely irritating to the
eyes and respiratory system. Pour ammonium hydroxide
under a laboratory hood with fan in operation.
14-13
-------
(3) In case of accident, wash with large quantities
of water and use saturated boric acid solution
to neutralize.
Miscellaneous
(1) Chlorine gas solution avoid inhalation. Handle
in hood. Secure cover to prevent escape of vapors.
(2) Ferric salts, Ferric chloride very corrosive to
metals. Avoid body contact and wash off imme-
diately.
(3) Strong oxidants avoid body contact. Wash off
immediately. Use of perchloric acid by untrained
personnel must be prohibited.
3. Toxic Materials
Avoid ingesting or inhaling.
A. Solids: Cyanides, chromium, cadmium, and other heavy
metal compounds.
B. Liquids: Use in vented hood. Carbon tetrachloride,
ammonium hydroxide, nitric acid, bromine, chlorine
water, aniline dyes, formaldehyde, chloroform, and
carbon disulfide. Carbon tetrachloride is absorbed
into skin on contact; its vapors will damage the lungs;
and it will build up in your body to a dangerous level.
C. Gases: Use in vented hood. Hydrogen sulfide, chlorine,
ammonia, nitric, hydrochloric acid.
D. Most laboratory chemicals have toxicity warnings and
antidotes on their labels. Learn about the materials
you use. Don't breathe, eat, or drink them; and if
they come in contact with your body, quietly apply
large quantities of water to wash the substance away.
14-14
-------
4. Explosive or Inflammable Materials
A. Gases: Acetylene, hydrogen.
B. Liquids: Carbon disulfide, benzene, ethyl ether,
petroleum ether, acetone, gasoline.
Store these materials according to fire regulations to
prevent fire hazards. If large quantities must be stored,
they should be located in a .separate storage building.
Do not use near open flame or exposed heating elements.
Use under a vended laboratory hood. Do not distill to dry-
ness or explosive mixtures may result. Use face mask. Do
not throw flammable liquids into sinks. Cigarette discard
may cause fire. DC not let gas cylinders fall.
5. Broken Equipment
A. Inexpensive Items--Beak3rs and flasks should be dis-
carded, except for minor chips which can be flame
polished3 easily.
B. Expensive Items—Should be set aside for salvage if
possible. Discard if damaged beyond repair.
Flame Polished. Sharp or broken edges of glass (such as the
end of a glass tube) are flame polished by placing the edge
in a flame and rotating it. By allowing the edge to melt
slightly, it will become smooth.
14-15
-------
6. Miscellaneous
A. Use safety goggles or face mask
in any experiment in which there
is danger to the eyes. Never look
into the end of the test Lube during
reaction or heating.
Use care in making rubber-to-glass
connections. Lengths of glass
tubing should be supported while
they are being inserted into rubber.
The ends of the glass should be
flame polished, and either wetted
or covered with a lubricating jelly
for ease in joining connections.
Never use grease or oil. Gloves
or grippers should be worn when
making such connections, and the
tubing should be held as close to
the end being inserted as possible
to prevent bending or breaking.
Never try to force rubber tubing
or stoppers from glassware. Cut
the rubber or material off.
B. Always check labels on bottles to
make sure that the chemical selected
is correct. All chemicals and bottles
should be clearly labeled. Never
handle chemicals with bare hands.
Use spatula, spoon, or tongs.
C. Never work in a poorly ventilated
area. Toxic fumes even in mild
concentrations can kncck you out.
Be sure you have adequate venti-
lation before you start work in the
laboratory.
S-noking and eating should be avoided v;hen working with
infectious materials such as wastewater and sludge. Never
use laboratory glassware for serving the food.
Always use the proper type of equipment for handling hot
containers, such as protective gloves, tongs, clothing,
glasses, etc.
14-16
-------
F. Where cylinders of oxygen or other compressed gases
are used in the laboratory, they should be stored in
separated and ventilated sections. They should be
chained or clamped in an upright position while being
used. The protective caps should never be removed until
the cylinder is set and clamped in place, ready for
attachment of valve gage and connections. Always use
fittings approved for the cylinder being used and care-
fully follow instructions.
G. In working in the plant, be careful around:
(1) Digesters—Do not smoke.
(2] Chlorinators--Be aware of chlorine leaks. Chlorine
may be detected by its odor, or a white mist will
form near a rag soaked in ammonia.
(3) Power and Blower—Wear ear plugs or ear covers if
working over one hour in engine room.
(4) Open Wastewater Tanks—Be careful; don't fall in.
(5) Closed Wastewater Tanks—Avoid running over tank
covers by foot or vehicle.
(6) In Tanks or Near Construction—Wear hard hats.
14.21 Personal Hygiene for Wastewater Treatment Plant Personnel
Although it is highly unlikely that personnel can contract diseases
by working in wastewater treatment plants, such a possibility does
exist with certain diseases.
1. Some diseases are contracted through breaks in the skin, cuts,
or puncture wounds. In such cases the bacteria causing the
disease may be covered over and trapped by flesh, creating a
suitable anaerobic environment4 in which the bacteria may
thrive and spread throughout the body.
Anaerobic Environment (AN-air-0-bick). A condition in which
"free" or dissolved oxygen is not present.
14-17
-------
hor protection against diseases contracted through breaks
in the skin, cuts, or puncture wounds, everyone working in
or around wastewater must receive immunization from tetanus.
Immunization must be received before the infection occurs.
To prevent diseases from entering open wounds, care must be
taken to keep wounds protected either with band aids or, if
necessary, with rubber gloves or waterproof protective
clothing.
2. Diseases that may be contracted through the gastrointestinal
system or through the mouth are typhoid, cholera, dysentery,
amebiases, worms, salmonella, enfectious hepatitis, and
polio virus. These diseases are transmitted by the infected
wastewater materials being ingested or swallowed by careless
persons. The best protection against these diseases is
furnished by thorough cleansing. Hands, face, and body
should be thoroughly washed with soap and water, particularly
the hands, in order to prevent the transfer of any unsanitary
materials or germs to the mouth while eating. A change of
working clothes into street clothes before leaving work is
highly recommended to prevent carrying unsanitary materials
to the employee's home. Personal hygiene, thorough cleansing,
and washing of the hands are effective means of protection.
Immunization is provided for typhoid and polio. Little is
known about infectious hepatitis except that it can be trans-
mitted by wastewater. It is frequently associated with gross
wastewater pollution.
3. Diseases that may be contracted by breathing contaminated
air include (1) tuberculosis, (2) infectious hepatitis, and
(3) San Joaquin fever. There has been no past evidence to
indicate the transmission of tuberculosis through the air
at wastewater treatment plants. However, there was one
case of tuberculosis being contracted by an employee who
fell into wastewater and, while swimming, inhaled waste-
water into his lungs. San Joaquin fever is caused by a
fungus which may be present in wastewater. However, there
is no record of operators contracting the disease while on
the job.
14-18
-------
The best insurance against these diseases is proper personal
hygiene and immunization. Your plant should have an immunization
program against (1) tetanus, (2) typhoid, (3) polio, and (4) small-
pox (although smallpox is not related to wastewater). The
immunizations should be provided to protect you. Check with your
local or state health department for recommendations regarding
immunization.
In the washing of hands, the kind of soap is less important than
the thorough use of the soap. (Special disinfectant soaps are
not essential.)
The use of protective clothing is very important, particularly
gloves and boots. The protection of wounds and cuts is also
important. Report injuries and take care of them.
The responsibility rests upon you.
There is no absolute insurance against contraction of disease
in a wastewater treatment plant. However, the likelihood of
transmission is practically negligible. There appears to be no
special risk in working at treatment plants. In fact, operators
may receive a natural immunization by working in this environment.
14-19
-------
QUESTIONS
14.2A Why should you always use a rubber bulb to
pipette wastewater or polluted water?
14.2B Why are inoculations against disease recommended
for people working around wastewater?
14.2C What would you do if you spilled a concentrated
acid on your hand?
14.2D True or False: You may add acid to water, but
never water to acid.
14.2E If you are working in a wastewater treatment
plant, why should you change your clothes before
going home at night?
14-20
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14.3 SAMPLING, by Joe Nagano, from California Water Pollution
Control Association Operators Laboratory Manual
14.30 Importance
Before any laboratory tests are performed, it is highly important
to obtain a proper, representative sample. Without a representative
sample, a test should not even be attempted because the test result
will be incorrect and meaningless. A laboratory test without a good
sample will most likely lead to erroneous conclusions and confusion.
The largest errors produced in laboratory tests are usually caused
by improper sampling, poor preservation, or lack of enough mixing
during compositing0 and testing.
14.31 Accuracy of Laboratory Equipment
Laboratory equipment, in itself, is generally quite accurate.
Analytical balances weigh to 0.1 milligram. Graduated cylinders,
pipettes, and burettes usually measure to 1% accuracy, so that the
errors introduced by these items should total less than 5%, and
under the worst possible conditions only 10%. Under ideal conditions
let us assume that a test of raw wastewater for suspended solids
should run about 300 mg/1. Because of the previously mentioned
equipment or apparatus variables, the value may actually range
from 270 to 330 mg/1. Results in this range are reasonable for
operation. Other less obvious factors are usually present which
make it quite possible to obtain results which are 25, 50, or even
100% in error, unless certain precautions are taken. Some examples
will illustrate how these errors are produced.
The City of Los Angeles Terminal Island Treatment Plant is a
primary treatment facility with a flow of 8 million gallons per
day. It has an aerated grit chamber, two circular 85-foot clari-
fiers of 750,000 gallon capacity, and two digesters 100 and 75 feet
in diameter.
5 Composite (Proportional) Samples (com-POZ-it). Samples collected
at regular intervals in proportion to the existing flow and then
combined to form a sample representative of the entire period of
flow over a given period of time.
14-21
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Monthly summary calculations based upon the suspended solids test
showed that about 8,000 pounds of suspended solids were being
captured per day during sedimentation assuming 200 mg/1 for the
influent and 100 mg/1 for the effluent. However, it also appeared
that 12,000 pounds per day of raw sludge solids were being pumped
out of the clarifier and to the digester. Obviously, if sampling
and analyses had been perfect, these weights would have balanced.
The capture should equal the removal of solids. A study was made
to determine why the variance in these values was so great. It
would seem logical to expect that the problem could be due to
(1) incorrect testing procedures, (2) poor sampling, (3) incorrect
metering of the wastewater or sludge flow, or (4) any combination
of the three or all of them.
In the first case, the equipment was in excellent condition.
The operator was a conscientious and able employee who was
found to have carried out the laboratory procedures carefully
and who had previously run successful tests on comparative
samples. It was concluded that the equipment and test proce-
dures Were completely satisfactory.
14.32 Selection of a Good Sampling Point to Obtain
a Representative Sample
A survey was then made to determine if sampling stations were in
need of relocation. By using Imhoff cones and running settleable
solids tests along the influent channel and the aerated grit
chamber, one could quickly recognize that the best mixed and
most representative samples were to be taken from the aerated
grit chamber rather than the influent channel.
The settleable solids ran 13 ml/1 in the aerated grit chamber
against 10 ml/1 in the channel. By the simple process of
determining the best sampling station, the suspended solids
value in the influent was corrected from 200 mg/1 to the more
representative 300 mg/1. Calculations, using the correct
figures, changed the solids capture from 8,000 pounds to 12,000
pounds per day and a balance was obtained.
This study clearly illustrates the importance of selecting a
good sampling point in securing a truly representative sample.
It emphasizes the point that even though a test is accurately
performed, the result may be entirely erroneous and meaningless
insofar as use for process control is concerned, unless a good
representative sample is taken. Furthermore, a good sample is
highly dependent upon the sampling station.Whenever possible,
14-22
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select a place where mixing is thorough and the wastewater quality
is uniform. As the solids concentration increases, above about
200 mg/1, mixing becomes even more significant because the waste-
water solids will tend to separate rapidly with the heavier solids
settling toward the bottom, the lighter solids in the middle, and
the floatables rising toward the surface. If, as is usual, a
one-gallon portion is taken as representative of a million-gallon
flow, the job of sample location and sampling must be taken
seriously.
14.33 Time of Sampling
Let us consider next the time and frequency of sampling. In
carrying out a testing program, particularly where personnel
and time are limited due to the press of operational responsi-
bilities, testing may necessarily be restricted to about one
test day per week. If the operator should decide to start his
tests early in the week, by taking samples early on Monday
morning he may wind up with some very odd results.
One such incident will be cited. During a test for ABS (alkyl
benzene sulfonate), samples were taken early on Monday morning
and rushed into the laboratory for testing. Due to the detention
time in the sewers, these wastewater samples actually represented
Sunday flow on the graveyard shift, the weakest wastewater obtain-
able. The ABS content was only 1 mg/1, whereas it would normally
run 8 to 10 mg/1. So the time and day of sampling is quite important,
and the samples should be taken to represent typical weekdays or
even varied from day to day within the week for a good cross-section
of the characteristics of the wastewater.
14.34 Compositing and Preservation of Samples
Since the wastewater quality changes from moment to moment and
hour to hour, the best results would be obtained by using some
sort of continuous sampler-analyzer. However, since operators
are usually the sampler-analyzer, continuous analysis would
leave little time for anything but sampling and testing. Except for
tests which cannot wait due to rapid chemical or biological change
of the sample, such as tests for dissolved oxygen and sulfides, a
fair compromise may be reached by taking samples throughout the
day at hourly or two-hour intervals.
When the samples are taken, they should be immediately refrigerated
to preserve them from continued bacterial decomposition. When all
of the samples have been collected for a 24-hour period, the samples
from a specific location should be combined or composited together
according to flow to form a single 24-hour composite sample.
14-23
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To prepare a composite sample, (1) the rate of wastewater flow
must be metered and (2) each grab sample must then be taken
and measured out in direct proportion to the volume of flow
at that time. For example, Table I illustrates the hourly flow
and sample volume to be measured out for a 12-hour proportional
composite sample.
TABLE I
DATA COLLECTED TO PREPARE PROPORTIONAL COMPOSITE SAMPLE
Flow
Time MGD Factor Sample Vol
Flow
Time MGD Factor Sample Vol
6
7
8
9
10
11
A
AM
AM
AM
AM
AM
AM
0
0
0
1
1
1
sample
.2
,4
.6
.0
.2
.4
100
100
100
100
100
100
composited
20
40
60
100
120
140
in this
12
1
2
3
4
5
N
PM
PM
PM
PM
PM
manner would
1.
1.
1.
1.
1.
0.
5
2
0
0
0
9
total
100
100
100
100
100
100
1140 ml.
150
120
100
100
100
90
1140
Large wastewater solids should be excluded from a sample, particu-
larly those greater than one-quarter inch in diameter.
A very important point should be emphasized. During compositing
and at the exact moment of testing, the samples must be vigorously
remixed so that they will be of the same composition and as well'
mixed as when they were originally sampled. Sometimes such remixing
may become lax, so that all the solids are not uniformly suspended.
Lack of mixing can cause low results in samples of solids that
settle out rapidly, such as those in activated sludge or raw waste-
water. Samples must therefore be mixed thoroughly and poured
quickly before any settling occurs. If this is not done, errors
of 25 to 50% may easily occur. For example, on the same mixed
liquor sample, one person may find 3,000 mg/1 suspended solids
while another person may determine that there are only 2,000 mg/1
due to poor mixing. When such a composite sample is tested, a
reasonably accurate measurement of the quality of the day's flow
can be made.
If a 24-hour sampling program is not possible, perhaps due to
insufficient personnel or the absence of a night shift, single
representative samples should be taken at a time when typical
characteristic qualities are present in the wastewater. The
samples should be taken in accordance with the detention time
14-24
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required for treatment. For example, this period may exist
between 10 AM and 5 PM for the sampling of raw influent. If
a sample is taken at 12 Noon, other samples should be taken
in accordance with the detention periods of the serial processes
of treatment in order to follow this slug of wastewater or plug
flow. In primary settling, if the detention time in the pri-
maries is two hours, the primary effluent should be sampled at
2 PM. If the detention time in the succeeding secondary treat-
ment process required three hours, this sample should be taken
at 5 PM.
14.35 Sludge Sampling
In sampling raw sludge and feeding a digester, a few important
points should be kept in mind as shown in the following illus-
trative table.
For raw sludge from a primary clarifier at Los Angeles' Terminal
Island Plant, the sludge solids varied considerably with pumping
time as shown by samples withdrawn every one-half minute.
TABLE II
DECREASE IN PERCENT TOTAL SOLIDS DURING PUMPING
Pumping Time>
In Minutes
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Total Solids
Percent
7.0
7.1
7.4
7.3
6.7
5.3
4.0
2.3
2.0
1.5
Cumulative
Solids
Average
7.0
7.1
7.2
7.2
7.1
6.8
6.4
5.9
5.5
5.1
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a. Table II shows that the solids were heavy during the first
2.5 minutes, and thereafter rapidly became thinner and
watery. Since sludge solids should be fed to a digester
with solids as heavy as possible and a minimum of water,
the pumping should probably have been stopped at about
3 minutes. After 3 minutes, the water content did become
greater that desirable.
b. In sampling this sludge, the sample should be taken as a
composite by mixing small equal portions taken every 0.5
minutes during pumping. If only a single portion of sludge
is taken for the sample, there is a chance that the sludge
sample may be too thick or too thin, depending upon the
moment the sample is taken. A composite sample will pre-
vent this possibility.
c. It should also be emphasized again that as a sludge sample
stands, the solids and liquid separate due to gasification
and flotation or settling of the solids, and that it is
absolutely necessary to thoroughly remix the sample back
into its original form as a mixture before pouring it for
a test.
d. When individual samples are taken at regular intervals
in this manner, they should be carefully preserved to
prevent sample deterioration by bacterial action. Re-
frigeration is an excellent method of preservation and
is generally preferable to chemicals since chemicals may
interfere with tests such as BOD and COD.
14.36 Sampling Devices
Automatic sampling devices are wonderful timesavers and should be
employed where possible. However, like anything automatic,
problems of which the operator should be aware do arise in their
use. Sample lines to auto-samplers may build up growths which
may periodically slough off and contaminate the sample with a
high solids content. Very regular cleanout of the intake line
is required. Another problem occurred at Los Angeles' Hyperion
Plant when the reservoir for the automatic sampler was attacked
by sulfides. Metal sulfides flaked off and entered the sample
container producing misleading high solids results. The
reservoir was cleaned and coated with coal-tar epoxy and little
further difficulty has been experienced.
14-26
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Manual sampling equipment includes dippers, weighted bottles,
hand-operated pumps, and cross-section samplers. Dippers con-
sist of wide-mouth corrosion resistant containers (such as
cans or jars) on long handles that collect a sample for testing.
A weighted bottle is a collection container which is lowered
to a desired depth. At this location a cord or wire removes
the bottle stopper so the bottle can be filled. Sampling pumps
allow the inlet to the suction hose to be lowered to the sampling
depth. Cross-sectional samplers are used to sample where the
wastewater and sludge may be in layers, such as in a digester or
clarifier. The sampler consists of a tube, open at both ends,
that is lowered at the sampling location. When the tube is at
the proper depth, the ends of the tube are closed and a sample
is obtained from different layers.
Many operators build their own sampler (Fig. 14.1) using the
material described below:
1. Sampling Bucket. A coffee can attached to an eight-foot
length of 1/2-inch electrical conduit or a wooden broom
handle with a 1/4-inch diameter spring in a four-inch loop.
2. Sampling Bottle. Plastic bottle with rubber stopper equipped
with two 3/8-inch glass tubes, one ending near bottom of
bottle to allow sample to enter and the other ending at the
bottom of the stopper to allow the air in the bottle to
escape while the sample is filling the bottle.
For sample containers, wide-mouth plastic bottles are recommended.
Plastic bottles, though somewhat expensive initially, not only
greatly reduce the problem of breakage and metal contamination,
but are much safer to use. The wide-mouth bottles ease the
washing problem. For regular samples, sets of plastic bottles
bearing identification labels should be used.
14.37 Summary
1. Representative samples must be taken before any tests are
made.
2. Select a good sampling location.
3. Collect samples and preserve them by refrigeration.
4. If possible, prepare 24-hour composite samples. Mix samples
thoroughly before compositing and at the time of the test.
14-27
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1/2" Conduit
Length to Suit
,
1/4" Spring to Retain Sample Bottle
Coffee Can
/ \
Quart
Plastic
Bottle
Rubber Stopper
n II
\i i ! ! 7
Glass Tube Vent
Glass Tube - Cut to
fit 1/2" clearance from
bottom of bottle
Fig. 14.1 Sampling bottle
14-28
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QUESTIONS
14.3A What are the largest sources of errors found in
laboratory results?
14.3B Why must a representative sample be collected?
14.3C How would you prepare a proportional composite
sample?
14-29
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14.4 LABORATORY WORK SHEET
All laboratory results should be recorded immediately after a
sample has been measured. There is no standard laboratory form;
however, your plant or the agency that regulates your discharge
may have a preferred form. Figure 14.2 is a typical laboratory
work sheet (sometimes called a bench sheet) and will be referred
to throughout the chapter.
14-30
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PLANT
DATE
SUSPENDED SOLIDS § DISSOLVED SOLIDS
SAMPLE
Crucib le
Ml Sample
Wt Dry $ Dish
Wt Dish
Wt Dry
, _ Wt Dry, gm x 1,000,000
. Ml Sample
Wt Dish § Dry
Wt Dish § Ash
Wt Volatile
o, v , _ Wt Vol „
Wt Dry
BOD
# Blank
SAMPLE
DO Sample
Bottle #
% Sample
Blank or adj blank
DO after incubation
Depletion, 5 days
Dep %
Nitrate N03
Sample
Graph Reading
COD
Sample
Blank Titration
Sample Titration
Depletion
/I Pep x N FAS x 8000
Ml Sample
Sett. Solids
Sample
Direct Ml/1
Fig. 14.2 Typical laboratory work sheet
14-31
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TOTAL SOLIDS
SAMPLE
Dish No.
Wt Dish $
Wt Dish
Wt Wet
Wt Dish +
Wt Dish
Wt Dry
% solids =
Wet
Dry
x 100%
Wt Wet
Wt Dish + Dry
Wt Dish + Ash
Wt Volatile
% Volatile = ^ Vo1 x 100%
Wt Dry
PH
Vol. Acid
Alkalinity as
Grease (Soxlet)
Sample
Ml Sample
Wt Flask + Grease
Wt Flask
Wt Grease
/I = Wt Grease, mg x 1,000
mg Ml Sample
H2S (Gas) (Starch-Iodine)
Blank
S ample
Diff
Diff x .68
mg/1 x 43.6
Ml
Ml
Ml
mg/1
grain/100 cu ft
Fig. 14.2 Typical laboratory work sheet (continued)
14-33
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END OF LESSON 1 OF 8 LESSONS
on
Laboratory Procedures and Chemistry
EXPLANATION OF DISCUSSION AND REVIEW QUESTIONS
Work this portion of the discussion and review questions after you
have completed answering the questions in Lesson 1. At the end of
each lesson in this chapter you will find some discussion and review
questions that you should complete before continuing.
The purpose of these questions is to indicate to you how well you
understand the material in this chapter.
14-35
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DISCUSSION AND REVIEW QUESTIONS
(Lesson 1 of 8 Lessons)
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Write the answers to these questions in your notebook before continuing.
1. What precautions should an operator take to protect himself
from diseases when working in a wastewater treatment plant?
2. Why should work with certain chemicals be conducted under a
ventilated laboratory hood?
3. What is meant by a representative sample?
4. How would you obtain a representative sample?
14-37
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CHAPTER 14. LABORATORY PROCEDURES AND CHEMISTRY
(Lesson 2 of 8 Lessons)
14.5 PLANT CONTROL TESTS
Tests in this section are listed in alphabetical order. Many
of the tests are conducted at primary, secondary, and advanced
wastewater treatment plants. Certain tests are commonly used
to control digester operation and activated sludge plants.
Typical plant and special plant control tests are summarized below.
A. Typical Plant Control Tests
TEST NO. TITLE
2 Biochemical Oxygen Demand or BOD, Procedure with DO
4 Chemical Oxygen Demand or COD
5 Chlorine Residual
6 Clarity
7 Coliform Group Bacteria
8 Dissolved Oxygen or DO
9 Hydrogen Sulfide
10 pH
12 Settleable Solids
16 Suspended Solids (Gooch Crucible)
17 Temperature (Wastewater)
B. Digester Control Tests
TEST NO. TITLE
1 Alkalinity, Procedure with Volatile Acids
3 Carbon Dioxide (C02) in Digester Gas
14 Sludge Dewatering Characteristics
15 Supernatant Graduate Evaluation
17 Temperature (Digester Sludge)
20 Volatile Acids
21 Total and Volatile Solids (Sludge)
14-39
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C. Activated Sludge Control Tests
TEST NO. TITLE
8 Dissolved Oxygen (In Aerator)
11 Settleability
13 Sludge Age
11 Sludge Density Index (SDI)
11 Sludge Volume Index (SVI)
16 Suspended Solids (Centrifuge)
14-40
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(Total Alkalinity)
(BOD)
1, Total Alkalinity
The alkalinity test is located with the volatile acid test be-
cause the volatile acid/alkalinity relationship is critical in
the successful operation of sludge digesters.
2. Biochemical Oxygen Demand or BOD
The BOD test is placed with the dissolved oxygen (DO) test be-
cause to measure the rate of oxygen uptake in the BOD test, the
DO must be measured.
14-41
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3. Carbon Dioxide (C02) in Digester Gas
A. Discussion
Changes in the anaerobic sludge digestion process will be observed
in the gas quality and are usually noted after the volatile acids
or volatile acid/alkalinity relationship starts to increase. The
C02 content of a properly operating digester will range from 30%
to 40% by volume. If the percent is above 44%, the gas will not
burn. The easiest test procedure for determining this change is
with a C02 analyzer.
B. What is Tested?
Sample Preferred
C02 in Digester Gas 30% - 35% by Volume
METHOD A
C, Apparatus
1. One Bunsen burner
2. Plastic tubing
3. 100 ml graduated cylinder
4. 250 ml beaker
D. Reagents
C02 Absorbent (KOH). Add 500 g potassium hydroxide (KOH) per liter
of water.
14-43
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Cco2)
E. Outline of Procedure
1. Clean out sampling line
by allowing gas from
sampling outlet to burn
until line is full of
gas from digester.
Gas
Outlet
Bunsen
Burner
2. Displace air in
graduated
cylinder.
3. Place graduate upside
down in beaker containing
C02 absor-
bent.
4. Insert hose in graduate
and run gas for 60 seconds.
5. Remove hose from
graduate and then
turn off gas.
Wait 10 minutes.
6. Read volume of
gas remaining to
nearest ml.
PRECAUTIONS
1. Avoid any open flames near the digester.
2. Work in a well ventilated area to avoid the formation of ex-
plosive mixtures of methane gas.
3. If your gas sampling outlet is on top of your digester, turn
on outlet and vent the gas to the atmosphere for several
minutes to clear the line of old gas. Start with step 2,
displace air in graduated cylinder. NEVER ALLOW ANY SMOKING
OR FLAMES NEAR THE DIGESTER AT ANY TIME.
14-45
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(C02)
PROCEDURE
1. Measure total volume of a 100 ml graduate by filling it to
the top with water (approximately 125 ml). Record this
volume.
2. Pour approximately 125 ml of C02 absorbent in a 250 ml beaker.
CAUTION: Do not get any of this chemical on your skin
or clothes. Wash immediately with running water until
slippery feeling is gone or severe burns can occur.
3. Collect a representative sample of gas from the gas dome on
the digester, a hot water heater using digester gas to heat
the sludge, or any other gas outlet. Before collecting the
sample for the test, attach one end of a gas hose to the gas
outlet and the other end to a Bunsen burner. Turn on the
gas, ignite the burner, and allow it to burn digester gas
for a sufficient length of time to insure collecting a
representative gas sample.
4. With gas running through hose from gas sampling outlet, place
hose'inside inverted calibrated graduated cylinder and allow
digester gas to displace air in graduate. Turn off gas.
CAUTION: The proper mixture of digester gas and air
is explosive when exposed to a flame.
5. Place graduate full of digester gas upside down in beaker
containing C02 absorbent.
6. Insert gas hose inside upside down graduate.
7. Turn on gas, but do not blow out liquid. Run gas for at
least 60 seconds.
8. Carefully remove hose from graduate with gas still running.
9. Immediately turn off gas.
10. Wait for ten minutes and shake gently. If liquid continues
to rise, wait until it stops.
11. Read gas remaining in graduate to nearest ml. (Fig. 14.3)
14-46
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Cco2]
Fig. 14.3 C02 measurement using in-
verted graduated cylinder
F. Example
Total Volume of Graduate = 126 ml
Gas Remaining in Graduate = 80 ml
G. Calculation
CO
2 —
(Total Volume, ml - Gas Remaining, ml)
• • • • - ......... • ......... " .....
Total Volume, ml
(126 ml - 80 ml]
126 ml
x 100-
126
37%
x 100%
.365
126 / 46.0
37 8
8 20
7 56
640
630
14-47
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(C02)
METHOD B
(ORSAT)
The Orsat gas analyzer can measure the concentrations of carbon
dioxide, oxygen, and methane by volume in digester gas. To
analyze digester gas by the Orsat method, follow equipment manu-
facturer's instructions. This procedure is not recommended for
the inexperienced operator.
QUESTIONS
3.A What are the dangers involved in running the
C02 in digester gas test?
3.B What is the percent C02 in a digester gas if
the total volume of the graduated cylinder is
128 ml and the gas remaining in the cylinder
after the test is 73 ml?
14-48
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4. Chemical Oxygen Demand or COD
A. Discussion
COD is a good estimate of the first-stage oxygen demand for most
municipal wastewaters. An advantage of the COD test over the BOD
test is that you do not have to wait for five days for the results.
The COD test also is used to measure the strength of wastes that
are too toxic for the BOD test. COD is usually higher than the
BOD, but the amount will vary from waste to waste. The method
related here is a quick, effective measure of the strength of a
waste.
B. What is| Tested?
Sample Common Range, mg/1
Influent 200 - 400
Effluent 40 - 80
Industrial Waste 200 - 4000
C. Apparatus
Two 50 mi graduated cylinders
10 ml pipette
50 ml burette
Boiling flask
Reflux condenser
Hot plate
14-49
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(COD)
D. Reagents
1. Standard potassium dichromate (I^SOiJ 0.250 N. Dissolve
12.259 g dried K2Cr207 in distilled water and make up to
1 liter.
2. Surfuric acid-silver sulfate reagent. Add 22 g of silver
sulfate (Ag2SOi+) to a 9-lb bottle of concentrated sulfuric
acid (I-^SOL,) . It takes one to two days to dissolve.
3. Standard ferrous ammonium sulfate solution, 0,25 N. Dissolve
98 g Fe(NHl4)2(SOit)2'6H20 in distilled water, add 20 ml
concentrated F^SOtj, cool and dilute to 1 liter. This solution
is unstable and must be standardized daily.
4. Ferroin Indicator. Dissolve 1.485 g of 1,10 phenanthroline
(C12H8N2-H20) , together with 0.695 g ferrous sulfate crystals
7H20) , in water and make up to 100 ml.
5. Silver sulfate, reagent powder.
6. Mercuric sulfate (HgSO^) analytical grade crystals.
14-50
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(COD)
E. Outline of F'rocedure
5. Add 30 ml
H2SOtt-Ag2SOu
Solution
4. Add 10 ml
0.25 N K2Cr207
3. Add 2 ml
cone. H9S
2. Add
20 ml
Sample
,Cooling Water
Vent
7.
Reflux Two
Hours, Cool
§ Wash Down
3.
Add Ferroin
Indicator
Titrate
to red
end point,
* Reflux condenser, Friedrichs, VWR - 23157-001
** Flask, boiling, flat bottom, VWR - 29113-068
PROCEDURE
1. Place 0.4 g mercuric sulfate into a 250 ml Erlenmeyer flask
with a ground glas? neck.
2. Measure 20.0 ml sample into the flask.
3. Add 2.0 ml concentrated sulfuric acid. Swirl until contents
are well mixed.
4. Pipette 10.0 ml standard potassium dichromate solution into
the flask.
14-51
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(COD)
5. Carefully add 30 ml sulfuric acid-silver sulfate reagent
into the flask while swirling the flask. Use caution.
Make sure contents of the flask are thoroughly mixed before
heat is applied.
6. Add a few glass beads to reduce bumping and connect to con-
denser. The reflux mixture must be thoroughly mixed before
heat is applied. If this is not dene, local hot spots on
bottom of flask may cause mixture to be blown out of flask.
7. Prepare a blank5 by repeating above steps and by substituting
distilled water for the sample.
8. Reflux samples and blank for two hours. (If sample mixture
turns completely green, the sample was too strong. Dilute
sample with distilled water and repeat above steps substi-
tuting diluted sample.)
9. While the samples and blank are refluxing, standardize the
ferrous ammonium sulfate solution:
a. Pipette 10.0 ml standard potassium dichromate solution
into a 250 ml Erlenmeyer flask. Add about 100 ml of
water.
b. Add 30 ml concentrated HpSO^ with mixing. Let cool.
c. Add 2-3 drops ferroin indicator, titrate with ferrous
ammonium sulfate (FAS) solution. Color change of solution
is from orange to greenish to red.
ml FAS
10 ml K2Cr207
Concentration Ratio, R = • •- % =
ml FAS . . .i . ...
10. After refluxing mixture for two hours, wash down condenser.
Let cool. Add distilled water to about 140 ml.
11. Titrate reflux mixtures with standard FAS.
Blank - ml FAS
Sample - ml FAS
5 Blank. A bottle containing dilution water or distilled water,
but the sample being tested is not added. Tests are frequently
run on a sample and a blank ami the differences compared.
14-52
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(COD)
F. Precautions
1. Wastewater sample should be well mixed. If large particles
are present, sample should be homogenized.
2. Flasks and condensers should be clean and free from grease
or other oxidizable materials, otherwise erratic results
would be obtained.
3. The standard ferrous ammonium sulfate solution is unstable
and should be standardized daily or each time the COD test
is performed.
4. Use extreme caution in handling concentrated H2SOtt. Spillage
on skin or clothing should be immediately washed off and
neutralized.
5. The solution must be well mixed before it is heated. If the
acid is not completely mixed in the solution when it is heated,
the mixture could spatter and some of it will pass out the vent,
thus ruining the test.
6. Mercury sulfate is very toxic. Avoid skin contact and
breathing of this chemical.
G. Example
1. Standardization of ferrous ammonium sulfate, FAS.
ml 0.25 N K2Cr207 = 10.0
ml FAS = 11.0
Concentration ml K2Cr207
Rati°' R = ml FAS
10.0
11.0
2. Sample test.
Sample Taken = 20.0 ml
A = ml FAS used for blank = 10.0 ml
B = ml FAS used for sample = 3.0 ml
14-53
-------
(COD)
H. Calculation for COD
Method 1
COD, mg/1 = (A - B) x R x 100
= (10.0 - 3.0) (10/11) (100)
= 635 mg/1
Method 2 (According to Standard Methods)
COD, mg/1 = (A - B) x C x 8000
ml Sample
where
C = Normality of FAS
N = Normality of K2Cr207 Standard
r _ ml K2Cr207
L - - x N
ml FAS
= 0.227
COD mg/1 = (10.0 - 5.0) (0.22 7) (8000)
' 20
= 635 mg/1
14-54
-------
QUESTIONS
4.A What does the COD test measure?
4.B What are some of the advantages of the COD test
over the BOD test?
14-55
-------
5. Chlorine Residual
A. Discussion
A chlorine residual should be maintained in a plant effluent
for disinfection purposes. The amount of residual remaining
in the treated wastewater after passing through a contact
basin or chamber may be related to the numbers of bacteria
allowed in the effluent by regulatory agencies.
Method A (lodometric) is used for samples containing waste-
water, such as plant effluents or receiving waters. Method B
(Orthotolidine - Arsenite) gives best results if sample is
collected and tested shortly (within 20 minutes) after chlorine
has been added; however, all of the chlorine demand may not be
satisfied. Method C (Amperometric7 Titration) gives the best
results, but the titrator is expensive.
B. What is Tested?
Common Range, mg/1
Sample (After 30 Minutes)
Effluent 0.5 - 2.0 mg/1
C. Apparatus
METHOD A (lodometric)
1. One 250 ml graduated cylinder
2. One 10 ml measuring pipette
3. One 500 ml Erlenmeyer flask
4. Two 5 ml measuring pipettes
5. One 50 ml Buret
7 Amperometric (am-PURR-o-MET-rick). A method of measurement
that records electric current flowing or generated, rather
than recording voltage. Amperometric titration is an electro-
metric means of measuring concentrations of substances in water.
14-57
-------
(Chlorine Residual)
METHOD B (Orthotolidine-Arsenite or OTA)
One permanent glass color comparator
Three comparator cells
METHOD C (Amperometric Titratioi_j
See Standard Methods
D. Reagents
METHOD A
1. Standard phenylarsine oxide solution, 0.00564 N. Dissolve
approximately 0.8 g phenylarsine oxide powder in 150 ml
0.3 N NaOH solution. After settling, remove upper 110 ml
of this solution into 800 ml distilled water and mix thoroughly.
Adjust pH up to between 6 and 7 with 6 N HC1 and dilute to
950 ml with distilled water. To standardize this solution
accurately measure 5 to 10 ml of freshly standardized
0.0282 N iodine solution into a flask and add 1 ml KI
solution. Titrate with phenylarsine oxide solution, using
starch solution as an indicator. Adjust to exactly 0.00564 N
and recheck against the standard iodine solution; 1.00 ml =
200 yg available chlorine. CAUTION: Toxic - avoid ingestion.
2. Potassium iodide, crystals.
3. Acetate buffer solution, pH 4.0. Dissolve 146 g anhydrous
NaC2H302, or 243 g NaC2H302 • 3H20, in 400 ml distilled water,
add 480 g concentrated acetic acid, and dilute to 1 liter
with distilled water.
4. Standard iodine titrant, O.Q282 N. Dissolve 25 g KI in a
little distilled water in a 1-liter volumetric flask, add
the proper amount of 0.1 N iodine solution exactly standard-
ized to yield a 0.0282 N solution, and dilute to 1 liter.
Store in amber bottles or in the dark, protecting the solution
from direct sunlight at all times and keeping it from all
contact with rubber.
5. Starch indicator. Make a thin paste of 6 g of potato starch
in a small quantity of distilled water. Pour this paste into
one liter of boiling, distilled water. Allow to boil for a
few minutes, then settle overnight. Remove the clear super-
natant and save; discard the rest. For preservation, add two
drops of toluene (C6H5CH3).
14-58
-------
(Chlorine Residual)
METHOD B
1. Orthotolidine solution for chlorine comparison. Dissolve
1.35 g orthotolidine dihydrochloride (C14H16N2 • 2HC1) in
500 ml of distilled water. Add this solution, with constant
stirring, to a mixture of 350 ml distilled water and 150 ml
concentrated HC1. Store at normal temperatures in amber
bottles or in the dark. Protect from direct sunlight and
use within six months. Avoid contact with rubber.
2. Sodium arsenite solution. Dissolve 5.0 g NaAs02 in distilled
water and dilute to 1 liter. (CAUTION: Toxic; take care to
avoid ingestion.)
METHOD C
See Standard Methods
14-59
-------
(Chlorine Residual)
E. Procedure
METHOD A
1. Place 5.00 ml
phenylarsine
oxide solution
to Erlenmeyer
flask
2. Add excess
KI
(approx 1 g)
3. Add 4 ml
acetate buffer
solution
4.
Add 200 ml
sample
5.
Mix with
stirring
rod
6.
Add 1 ml
starch
solution
7.
ml
Titrate until
blue color
first appears
and remains
after mixing
14-60
-------
(Chlorine Residual)
METHOD A
1. Place 5.00 ml 0.00564 N phenylarsine oxide solution in an
Erlenmeyer flask.
2. Add excess KI (approx. 1 g).
3. Add 4 ml acetate buffer solution, or enough to lower the
pH to between 3.5 and 4.2.
4. Pour in 200 ml of sample.
5. Mix with a stirring rod.
6. Add 1 ml starch solution just before titration.
7. Titrate to the first appearance of blue color, which
remains after complete mixing.
METHOD B
1. Label the three comparator cells "A," "B," and "C." Use
0.5 ml of orthotolidine reagent in 10-ml cells, 0.75 ml in
15-ml cells, and the same ratio for other volumes of sample,
Use the same volume of arsenite solution as orthotolidine.
2. Add orthotolidine reagent to Cell A.
3. Add sample to mark on wall of Cell A. Mix quickly, and
immediately (within 5 seconds) add arsenite solution. Mix
quickly again and compare with color standards as rapidly
as possible.
Free available chlorine and
interfering colors, A = mg/1
4. Add arsenite solution to Cell B.
14-61
-------
(Chlorine Residual)
5. Add sample to mark on wall of Cell B. Mix quickly, and
immediately add orthotolidine reagent. Mix quickly again
and compare with color standards as rapidly as possible.
Interfering colors present _ /1
in immediate reading, EI ~ m
6. Compare with color standards again in exactly 5 minutes.
Interfering colors present _ .
in 5-minute reading, B2 ~ •
7. Add orthotolidine reagent to Cell C.
8. Add sample to mark on wall of Cell C. Mix quickly and compare
with color standards in exactly 5 minutes.
Total amount of residual chlorine _ ,..
and interfering colors present, C ~ m^
F. Examples and Calculations
Method A
Titration of a 200 ml sample required 0.4 ml of 0.0282 N I.
™.i n • j i /i (1 - ml I) 1000
Chlorine Residual, mg/1 = •£ =—r~ =-
' 6 Sample Volume, ml
(1 - 0.4) (1000)
200
= CO.6) (5)
= 3.0 mg/1
NOTE: The larger the ml of I used in the titration, the smaller
the (1 - ml I) term and thus the lower the chlorine residual.
This is why this test is sometimes called the back titration
test for chlorine residual. If 1 ml of I is used in the
titration, you have titrated back to a zero chlorine residual.
14-62
-------
(Chlorine Residual)
Method B
Results from the OTA test on a plant effluent.
A = 0.5 mg/1
B! = 0.2 mg/1
B2 = 0.3 mg/1
C = 1.4 mg/1
Total Available Residual
Chlorine, mg/1
2
= 1.4 mg/1 - 0.3 mg/1
= 1.1 mg/1
Free Available Residual
Chlorine, mg/1
.
l
= 0.5 mg/1 - 0.2 mg/1
= 0.3 mg/1
Combined Available
Residual Chlorine, mg/1
Total Available -
Residual Cl, mg/1
1.1 mg/1 - 0.3 mg/1
0.8 mg/1
Free Available
Residual Cl, mg/1
Total available residual chlorine consists of free available chlorine
(HOC1 and OC1~) and combined available chlorine (chloramines--compounds
formed by the reaction of chlorine with ammonia).
14-63
-------
(Chlorine Residual)
QUESTIONS
5.A Why should plant effluents be chlorinated?
5.B Discuss the important differences between the lodometric
titration, orthotolodine, and amperometric titration
methods of measuring chlorine residual.
END OF LESSON 2 OF 8 LESSONS
on
Laboratory Procedures and Chemistry
Work the next portion of the discussion and review questions
before continuing with Lesson 3.
14-64
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 2 of 8 Lessons)
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Write the answers to these questions in your notebook. The problem
numbering continues from Lesson 1.
5. How can you obtain a representative sample of digester gas?
6. Why is the COD test run?
7. Why should a chlorine residual be maintained in a plant effluent?
14-65
-------
CHAPTER 14. LABORATORY PROCEDURES AND CHEMISTRY
(Lesson 3 of 8 Lessons)
6. Clarity
A. Discussion
All high quality effluents should have a clarity reading taken
at high noon or some other specific time. This test is based
on how far you can see through your plant effluent under similar
conditions at the same time every day. The objective of the test
is to indicate the clearness or clarity of the plant effluent.
The test can be performed either in the lab by looking down
through the effluent in a graduated cylinder, or in the field
by looking down through the effluent in a clarifier or chlorine
contact basin. Sometimes this test is referred to as a tur-
bidity measurement, but you are interested in the clarity of
your effluent.
B. What is Tested?
Common Range
Sample (Field Test)
Secondary Clarifiers: Poor Good
Trickling Filter 1 ft 3 ft
Activated Sludge 3 ft 6 ft
Activated Sludge Blanket
in Secondary Clarifier 1 ft 4 ft
Chlorine Contact Basins 1 ft 5 ft
C. Apparatus
1. One clarity unit (Secchi (SECK-key) Disc) and attached
cord marked in one-foot units.
2. One 1000 ml graduated cylinder
3. Hach Turbidimeter, Model 2100 A
D. Reagents
None
14-67
-------
(Clarity)
E. Procedures
1. Field Test. Tie end of marked nylon rope to handrail where
tests will be run, for example, in final sedimentation unit.
Always take tests at the same time each day for comparable
results. Lower disc slowly until you just lose sight of it.
Stop. Bring up slowly until just visible. Stop. Look at
the marks on the rope to see the depth of water that you can
see the disc through. Bring up disc and store. Record results.
2. Lab Test. Use a clean 1000 ml graduate. Fill with a well-
mixed sample up to the 1000 ml mark. During every test the
same lighting conditions in the lab should be maintained.
Look down through the liquid in the cylinder and read the
last visible number etched on the side of the graduate and
record results.
3. Hach Turbidimeter. Follow manufacturer's instructions.
Whether you use one or each of these tests, you should run
either test at the same time every day and under similar
conditions for comparable results.
14-69
-------
(Clarity)
F. Example and Calculation
1. Each foot of depth is better clarity with Secchi disc.
2. Each 100 ml seen in depth is better clarity.
3. Turbidimeter reading indicates degree of clarity.
QUESTION
6.A What does the clarity test tell you about
the quality of effluent?
6.B What happens when you attempt to measure
clarity under different conditions, such
as lighting and clarifier loadings?
14-70
-------
7. Coliform Group Bacteria
A. Discussion
Coliform bacteria are measured to indicate the presence of
bacteria originating in the intestines of warm-blooded animals.
High coliform counts indicate the usefulness of water may have
been impaired. Coliform bacteria are considered harmless, but
their presence may be indicative of the presence of disease-
producing organisms that may be found with them.
B. What is Tested?
Sample
Effluent:
Primary
Nonchlorinated Secondary
Chlorinated Secondary
Receiving Waters
Usual Range, MPN/100 ml
5,000 to 1,000,000
> 240,000
50 to 500
1,000 to 1,000,000
C. Sampling Bottles
Wide-mouthed bottles with 200 to 400 ml capacity are used to collect
samples. Before sterilization by autoclave, add sodium thiosulfate
(0.1 ml of a 10% solution per 4 ounce bottle) to the bottles to
neutralize any chlorine residual in the samples. When filling bottles
in the field, do not flush out sodium thiosulfate or contaminate
sample or bottle. Fill bottles approximately three-quarters full and
start test in lab within four hours, or sooner.
D. Media Preparation
1. General Discussion
Careful media preparation is necessary to meaningful bacterio-
logical testing. Attention must be given to the quality, mixing,
and sterilization of the ingredients. The purpose of this care
is to assure that if the bacteria being tested for are indeed
present in a sample, every opportunity is presented for their
14-71
-------
(Coliform)
development and ultimate identification. Much bacteriological
identification is done by noting changes in the medium; conse-
quently, the composition of the medium must be standardized.
Much of the tedium of media preparation can be avoided by purchase
of dehydrated media (Difco, BBL, or equivalent). The operator
is advised to make use of these products; and, if only a limited
amount of testing is to be done, consider using tubed, prepared
media.
2. Glassware
All glassware must be thoroughly cleansed using a suitable detergent
and hot water (160°F), rinsed with hot water (180°F) to remove all
traces of residual detergent, and finally rinsed with distilled or
deionized water.
3. Water
Only distilled water or demineralized water which has been tested
and found free from traces of dissolved metals and bactericidal
and inhibitory compounds may be used for preparation of culture
media.
4. Buffered8 Dilution Water
Prepare a stock solution by dissolving 34 grams of KI^PO^ in
500 ml distilled water, adjusting the pH to 7.2 with IN NaOH.
Prepare dilution water by adding 1.25 ml of the stock solution
per liter of distilled water. This solution can be dispersed
into various size dilution blanks or used as a sterile rinse water
for the membrane filter test.
Buffer. A measure of the ability or 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 the pH.
14-72
-------
(Coliform)
5. Coliform Test--FermentationTube Method
a. Lactose Broth or Lauryl Tryptose Broth
For the presumptive coliform test, dissolve the recommended
amount of the dehydrated medium in distilled water. Dispense
solution into fermentation tubes containing an inverted glass
vial. Autoclave the capped tubes at 121°C for 15 minutes.
b. Brilliant Green Bile Lactose Broth
For the confirmed coliform test, dissolve 40 grams of the
dehydrated medium in one liter of distilled water. Dispense
and sterilize as with Lactose Broth.
c. Compensation for Diluting Effect of Samples
Large volumes of samples can dilute the medium in the fermen-
tation tube. Use the concentrations listed below to compensate
for diluting effects when using lauryl tryptose broth.
No. ml Ml of sample Nominal No. grams
medium or dilution concentration dehydrated
in tube before medium per
inoculation liter
10 0.1 to 1.0 Ix 35.6
10 10 2x 71.2
20 10 1.5x 53.4
35 100 4x 137.3
6. Coliform Test-Elevated Temperature for Fecal Coliforms
EC Broth
For the fecal coliform test, dissolve 37 grams of the dehydrated
medium in one liter of distilled water. Dispense and sterilize
as with Lactose Broth.
7. Coliform Test--Membrane Filter Method
M-Endo Broth
Prepare this medium by dissolving 48 grams of the dehydrated
product in one liter of distilled water which contains 20 ml
of ethyl alcohol per liter. Heat solution to boiling only--
DO NOT AUTOCLAVE. Prepared media should be stored in a
refrigerator and used within 96 hours.
14-73
-------
(Coliform)
8. Autoclaving
Steam autoclaves are used for the sterilization of the liquid media
and associated apparatus. They sterilize (killing of all organisms)
at a relatively low temperature of 121°C within 15 minutes by
utilizing moist heat.
Components of the media, particularly sugars such as lactose, may
decompose at higher temperatures or longer heating times. For this
reason adherence to time and temperature schedules is vital.
Autoclaves operate in a manner similar to the familiar kitchen
pressure cooker:
1. Water is heated in a boiler to produce steam.
2. The steam is vented to drive out air.
3. The steam vent is closed when the air is gone.
4. Continued heat raises the pressure to 15 lbs/in2 (at this
pressure, pure steam has a temperature of 121°C).
5. The pressure is maintained for the required time.
6. The steam vent is opened and the steam is slowly vented
until atmospheric pressure is reached. (Fast venting will
cause the liquids to boil.)
7. Sterile material is removed to cool.
i
In autoclaving fermentation tubes, a vacuum is formed in the inner
tubes. As the tubes cool, the inner tubes are filled with sterile
medium. Capture of gas in this inner tube from the culture of
bacteria is the evidence of fermentation.
14-74
-------
CColiform)
E. Test for Coliform Bacteria
1. General Discussion
The test for coliform bacteria is used to measure the suitability
of a water for human use. The test is not only useful in determin-
ing the bacterial quality of a finished water, but it can be used
by the operator in the treatment plant to guide him in achieving
a desired degree of treatment.
2. Multitube Fermentation Technique
Coliform bacteria are detected in water by placing portions of
a sample of the water in lactose broth. Lactose broth is a
standard bacteriological medium containing lactose (milk) sugar
in tryptose broth. The coliform bacteria are those which will
grow in this medium at 35°C temperature and ferment and produce
gas from the sugar within 48 hours. Thus to detect these bac-
teria the operator need only inspect fermentation tubes for gas.
In practice, multiple fermentation tubes are used in a decimal
dilution for each sample.
3. Materials Needed
1. Fifteen sterile tubes of lactose broth are needed
for each sample.
2. Use five tubes for each dilution.
3. Dilution tubes or blanks containing 9 ml or 99 ml
of sterile buffered distilled water.
4. Quantity of one and 10 ml sterile pipettes.
14-75
-------
(Coliform)
4. Technique for Inoculation and/or Dilution of Sample (Fig. 14.4)
All inoculations and dilutions of water specimens must be accurate
and should be made so that no contaminants from the air, equipment,
clothes or fingers reach the specimen, either directly or by way of
the contaminated pipettes.
1. Shake the specimen bottle vigorously 20 times before removing
sample volumes.
2. Into the first row of five lactose tubes pipette 1.0 ml into
each tube. It is important to realize that the sample volume
applied to the first row of tubes will depend upon the type
of water being tested. The sample volume applied to each tube
can vary from 10 ml (or more) for high quality waters to as
low as 10~5 or 0.00001 ml (applied as 1 ml of diluted sample)
for fecal specimens.
3. Make a 1:10 dilution of the sample by adding 1.0 ml of
the water sample to the contents (9ml) of a sterile water
tube or add 11 ml to a 99 ml blank. Mix diluted sample
thoroughly by shaking.
4. Inoculate the next five tubes of lactose broth with 1.0 ml
of the water sample.
5. Make a 1:100 dilution of the sample by adding 1.0 ml of the
water specimen diluted 1:10 to the contents of a sterile
water tube or by adding 11 ml to a 99 ml blank. Mix thor-
oughly by shaking.
6. Inoculate the next five tubes of lactose broth with 1.0 ml
of the 1:100 dilution.
7. After measuring all portions of the sample into their
respective tubes of medium, gently shake the rack of
inoculated tubes to insure good mixing of sample with
the culture medium. Avoid vigorous shaking, because
air bubbles may be shaken into the fermentation tubes
and thereby invalidate the test.
14-76
-------
(Coliform)
Pipette, 1 ml
USE FIVE TUBES
Incubate Gas,
35°C ± 0.5°C
+ Test
(gas)
Sterile Buffered
Distilled Water
Lactose Broth or Lauryl
Tryptose Lactose Broth
Fig. 14.4 Coliform bacteria test
14-77
-------
(Coliform)
5. 24-Hour Lactose Broth Presumptive Test
Place all inoculated lactose broth tubes in 35 °C ± 0.5°C incubator.
After 24 ± 2 hours have elapsed, examine each tube for gas formation
in inverted vial (inner tube). Mark + on report form for all tubes
that show presence of gas. Mark - for all tubes showing no gas
formation. Save all positive tubes for confirmation test. The
negative tubes must be reincubated for an additional 24 hours.
6. 48-Hour Lactose Broth Presumptive Test
Record both positive and negative tubes at the end of 48 ± 3 hours.
Save all positive tubes for confirmation test.
7. 24-Hour Brilliant Green Bile Confirmation Test
Confirm all presumptive tubes that show gas at 24 or 48 hours.
Transfer, with the aid of a sterile 3 mm platinum wire loop,
one loop-full of the broth from the lactose tubes showing gas,
and inoculate a corresponding tube of BGB (Brilliant Green Bile)
broth by mixing the loop of broth in the BGB broth. "Discard"
all positive lactose broth tubes after transferring is completed.
Always sterilize inoculation loops and needles in flame immediately
before transfer of culture; do not lay loop down or touch it to any
nonsterile object before making the transfer. After sterilization
in a flame, allow sufficient time for cooling, in the air, to pre-
vent the heat of the loop from killing the bacterial cells being
transferred. Wooden sterile applicator sticks also are used to
transfer cultures, especially in the field where a flame is not
available for sterilization.
After 24 hours has elapsed, inspect each of the BGB tubes for gas
formation. Those with any amount of gas are considered positive
and are so recorded on the data sheet. Negative BGB tubes are
reincubated for an additional 24 hours.
8. 48-Hour Brilliant Green Bile Confirmation Test
1. Examine tubes for gas at the end of the 48 ± 3 hour period.
Record both positive and negative tubes.
2. Complete reports by decoding MPN index and recording MPN
on work sheets.
14-78
-------
(Coliform)
9. Method of Calculation of the Most J3 rob able. Number
Select the highest dilution with all positive tubes, before a
negative tube occurs, plus the next two dilutions.
Example No. 1 - Select the underlined dilutions
Dilutions 0 -1 -2 -3 -4 -5
Readings 5 5 5 2 0_ 0
Read MPN as 49 per 100 ml from Table III
Report results as 49,000/100 ml
We added three zeros to 49 because we started with the -2 dilution
and Table III starts three dilution columns to the left (-1 or 0.1 ml,
0 or 1 ml, and 1 or 10 ml) .
Example No. 2 - Select the underlined dilutions
Dilutions 0 -1 -2 -3 -4 -5
Readings 555 5 0 0_
Read MPN as 23 per 100 ml from Table III
Report results as 230,000 per 100 ml
If positive tubes extend beyond three chosen dilutions, include
positives beyond chosen dilutions by moving them forward.
Example No. 3
Dilutions
Readings
This becomes
The MPN is 460 per 100 ml
If unreasonable positives occur, such as:
5 1 0 0 (2)
*discard them.
0
5
5
-1
1
1
-2
0
1
-3
1
0
-4
0
0
-5
0
0
14-79
-------
(Coliform)
TABLE III
MPN INDEX FOR VARIOUS COMBINATIONS OF POSITIVE AND NEGATIVE RESULTS
IN A PLANTING SERIES OF FIVE 10-ml, FIVE 1-ral AND
FIVE 0.1-ml PORTIONS OF SAMPLE
Number of tubes giving positive
reaction out of
Five 10-ml
portions
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
Five 1-ml
portions
0
0
0
1
1
1
2
2
3
0
0
0
0
1
1
1
2
2
2
3
3
4
0
0
0
0
1
1
1
2
2
2
Five 0.1 ml
portions
0
1
2
0
1
2
0
1
0
0
1
2
3
0
1
2
0
1
2
0
1
0
1
1
2
3
0
1
2
0
1
2
MPN Index
(organisms
per 100 ml)
<2
2
4
2
4
6
4
6
6
2
4
6
8
4
6
8
6
8
10
8
10
11
5
7
9
12
7
9
12
9
12
14
14-80
-------
(Coliform)
TABLE III (cont'd.)
MPN INDEX FOR VARIOUS COMBINATIONS OF POSITIVE AND NEGATIVE RESULTS
IN A PLANTING SERIES OF FIVE 10-ml, FIVE 1-ml AND
FIVE 0.1-ml PORTIONS OF SAMPLE
Number of tubes giving positive
reaction out of
Five 10-ml
portions
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
4
4
A
4
4
4
4
4
4
4
4
4
4
Five 1-ml
portions
3
3
4
0
0
0
1
1
1
1
2
2
2
3
3
4
4
5
0
0
0
0
1
1
1
2
2
2
3
3
3
Five 0.1 ml
portions
0
1
0
0
1
2
0
1
2
3
0
1
2
0
1
0
1
0
0
1
2
3
0
1
2
0
1
2
0
1
2
MPN Index
(organisms
per 100 ml)
12
14
15
8
11
13
11
14
17
20
14
17
20
17
21
21
24
25
13
17
21
25
17
21
26
22
26
32
27
33
39
14-81
-------
(Coliform)
TABLE III (cont'd.)
MPN INDEX FOR VARIOUS COMBINATIONS OF POSITIVE AND NEGATIVE RESULTS
IN A PLANTING SERIES OF FIVE 10-ml, FIVE 1-ml AND
FIVE 0.1-ml PORTIONS OF SAMPLE
Number of tubes giving positive
reaction out of
Five 10-ml
portions
4
4
4
4
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
Five 1-ml
portions
4
4
5
5
0
0
0
0
0
1
1
1 '
1
2
2
2
2
2
2
3
3
3
3
3
3
4
4
4
4
4
4
5
5
5
5
5
5
Five 0.1 ml
portions
0
1
0
1
0
1
2
3
4
0
1
2
3
0
1
2
3
4
5
0
1
2
3
4
5
0
1
2
3
4
5
0
1
2
3
4
5
MPN Index
(organisms
per 100 ml)
34
40
41
48
23
31
43
58
76
33
46
63
84
49
70
94
120
148
177
79
109
141
175
212
253
130
172
221
278
345
426
240
348
542
920
1600
>2400
14-82
-------
(Coliform)
F. Test for Fecal Coliform Bacteria
1. General Piscussion
Many regulatory agencies are measuring the bacteriological
quality of water using the fecal coliform test because this
test is a more reliable test for indicating the potential
presence of pathogenic organisms than is the coliform group
of organisms. The procedure described is an elevated temper-
ature test for fecal coliform bacteria.
2. Materials Needed
Equipment required for the tests are the same as those required
for the 24-Hour Lactose Broth Presumptive Test, a water bath,
and EC Broth.
3. Procedure
1. Run lactose broth or lauryl tryptose broth presumptive
test.
2. After 24 hours temporarily retain all gas-positive tubes,
3. Label a tube of EC broth to correspond with each
gas-positive tube of broth from presumptive test.
4. Transfer one loop-full of culture from each gas-
positive culture in presumptive test to the
correspondingly labeled tube of EC broth.
5. Incubate EC broth tubes 24 t 2 hours at 44.5°C i
0.2°C in a waterbath with water depth sufficient
to come up at least as high as the top of the culture
medium in the tubes. Place in waterbath as soon as
possible after inoculation and always within 30 minutes
after inoculation.
6. After 24 hours remove the rack of EC cultures from
the waterbath, shake gently, and record gas pro-
duction for each tube. Gas in any quantity is a
positive test.
7. As soon as results are recorded, discard all tubes.
This is a 24-hour test for EC broth inoculations and
not a 48-hour test.
14-83
-------
(Coliform)
8. Transfer any additional 48-hour gas positive tubes
from the presumptive test to correspondingly labeled
tubes of EC broth. Incubate for 24 ± 2 hours at
44.5°C ± 0.2°C and record results on data sheet.
9. Codify results and determine MPN of fecal coliforms
per 100 ml of sample.
G. Membrane Filter Method
1. General Discussion
In addition to the fermentation tube test for coliform bacteria,
another test is used for these same bacteria in water analysis.
This test uses a cellulose ester filter, called a membrane filter,
the pore size of which can be manufactured to close tolerances.
Not only can the pore size be made to selectively trap bacteria
from water filtered through the membrane, but nutrients can be
diffused up through the membrane to grow these bacteria into
colonies. These colonies are recognizable as coliform because
the nutrients include fuchsin dye which peculiarly colors the
colony. Knowing the number of colonies and the volume of water
filtered, the operator can then compare the water tested with
water quality standards.
2. Materials Needed
1. One sterile membrane filter having a 0.45y pore size.
2. One sterile 47 mm Petri dish with lid.
3. One sterile funnel and support stand.
4. Two sterile pads.
5. One receiving flask (side-arm, 1000 ml).
6. Vacuum pump, trap, suction or vacuum gage, connecting sections
of plastic tubing, Glass "T" hose clamp to adjust pressure by-
pass.
7. Tweezers, alcohol, Bunsen Burner, grease pencil.
14-84
-------
(Coliform)
8. Sterile buffered distilled water for rinsing.
9. M-Endo Media.
10. Sterile pipettes--two 5 ml graduated, one 1 ml for aliquot
or one 10 ml for larger aliquot. Quantity of one ml pipettes
if dilution of sample is necessary. Also, quantity of dilution
water blanks if dilution of sample is necessary.
11. One moist incubator at 35°C temperature. Auxiliary incubator
dish with cover.
14-85
-------
(Coliform)
3. Illustration of Inoculation of Membrane Filter
Fig. I
1. Center membrane filter on
filter holder. Handle mem-
brane only on outer 3/16
inch with tweezers sterilized
before use in ethyl or methyl
alcohol and passed lightly
through a flame.
Fig. II
2. Place funnel
onto filter
holder.
Fig. Ill
Fig. IV
Fig. V
3. Pour or pipette sample
aliquot into funnel.
Avoid spattering. After
suction is applied rinse
four times with sterile
buffered distilled water.
4. Remove membrane filter from
filter holder with sterile
tweezers. Place membrane
on pad. Cover with Petri
top.
Incubate in
inverted
position for
22+2 hours.
Count colonies
on membrane.
14-87
-------
(Coliform)
4. Procedure for Inoculation of Membrane Filter
All filtrations and dilutions of water specimens must be accurate
and should be made so that no contaminants from the air, equipment,
clothes or fingers reach the specimen either directly or by way of
the contaminated pipette.
1. Secure tubing from pump and bypass to receiving flask. Place
palm of hand on flask opening and start pump. Adjust
suction to % atmosphere with hose clamp on pressure bypass.
Turn pump switch to OFF.
2. Set sterile filter-support-stand and funnel on receiving flask.
Loosen wrapper. Rotate funnel counter-clockwise to disengage
pin. Recover with wrapper.
3. Place Petri Dish on bench with lid up. Write indentification
on lid with grease pencil.
4. Unwrap sterile pad container. Light Bunsen burner.
5. Unwrap membrane filter container.
6. Sterilize tweezers by dipping in alcohol and passing quickly
through Bunsen burner.
7. Center membrane filter on filter stand with tweezers after
lifting funnel. Membrane filter with printed grid should
show grid uppermost (Fig. I) .
8. Replace funnel and lock against pin (Fig. II).
9. Shake sample or diluted sample. Measure proper aliquot9
with sterile pipette and add to funnel.
10. Add a small amount of the sterile dilution water to funnel.
This will help check for leakage and also aid in dispersing
small volumes (Fig. Ill) .
11. Now start vacuum pump.
9 Aliquot (AL-li-kwot). Portion of sample.
14-88
-------
(Coliform)
12. After filtration of entire sample is finished, add rinse
water from four consecutive dilution water tubes at each
90° of funnel quadrant, pouring just below inner lip of
funnel. Allow each rinse to completely pass through
funnel before proceeding to next rinse.
13. When membrane filter appears barely moist, switch pump to
OFF.
14. Sterilize tweezers as before.
15. Remove membrane filter with tweezers after first removing
funnel as before (Fig. I) .
16. Center membrane filter on pad containing M-Endo medium
with a rolling motion to insure water seal. Inspect
membrane to insure no captured air bubbles are present.
(Fig. IV).
17. Place inverted Petri Dish in incubator for 22 t 2 hours.
5. Procedure for Counting Membrane Filter Colonies
1. Remove Petri Dish from incubator.
2. Remove lid from Petri Dish.
3. Turn so that your back is to window.
4. Tilt membrane filter in base of Petri Dish so that green and
yellow-green colonies are most apparent. Direct sunlight has
too much red to facilitate counting.
5. Count individual colonies utilizing an overhead fluorescent
light. The coliform colony is characterized by a "metallic
sheen" and only those colonies showing ANY amount of this
sheen are considered to be coliforms.
6. Report total number of "coliform colonies" on work sheet.
Use the membranes that show from 20 to 80 colonies and do
not have more than 200 colonies of all types (including non-
sheen or, in other words, non-coliforms).
14-89
-------
Example:
A total of 42 colonies grew after filtering a 10 ml sample.
No. of colonies counted x 100 ml
3acteria/100 ml =
Sample volume filtered, ml x 100 ml
= (42 colonies) (100 ml)
(10 ml) (100 ml)
= (4.2) (100 ml)
100 ml
= 420 per 100 ml
QUESTIONS
7.A Why should sodium thiosulfate crystals be added to
sample bottles for coliform tests before sterilization?
7.B Steam autoclaves effect sterilization (killing of all
organisms) at a relatively low temperature ( °C)
within minutes by utilizing moist heat.
7.C Calculate the Most Probable Number (MPN) of coliform
group bacteria from the following test results:
Dilutions 0 -1 -2 -3 -4 -5
Readings 55512 0
7.D How is the number of coliforms estimated by the membrane
for filter method?
END OF LESSON 3 OF 8 LESSONS
on
Laboratory Procedure? and Chemistry
Work the next portion of the discussion and review questions
before continuing with Lesson 4.
14-90
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 3 of 8 Lessons)
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Write the answers to these questions in your notebook. The
problem numbering continues from Lesson 2.
8. Why must the clarity test always be run under the
same conditions?
9. What is the purpose of the coliform group bacteria
test?
10. What does MPN mean?
14-91
-------
CHAPTER 1.4. LABORATORY PROCEHURES AND CHEMISTRY
(Lesson 4 of 8 Lessons)
3. Dissolved Oxygen or DO and Biochemical Oxygen Demand or BOD
I. IN WATER
A. Discussion
The dissolved oxygen (DO) test is, as the name implies, the testing
procedure to determine the amount of oxygen dissolved in samples of
water or wastewater. There are various types of tests that can be
run to obtain the amount of dissolved oxygen. This procedure is the
Sodium Azide Modification of the Winkler Method and is best suited for
relatively clean waters. Interfering substances include color,
organics, suspended solids, sulfides, chlorine, and ferrous and
ferric ioon. Nitrites will not interefere with the test if fresh
azide is used.
The generalized principle is that iodine will be released in pro-
portion to the amount of dissolved oxygen present in the sample.
By using sodium thiosulfate with starch as the indicator, one can
titrate the sample and determine the amount of dissolved oxygen.
B. What is Tested?
Sample
Influent
Primary Clar. Effluent
Secondary Effluent
Oxidation Ponds
Activated Sludge--
Aeration Tank Outlet
Common Range, mg/1
Usually 0,>1 is very good.
Usually 0, Recirculated from
filters > 2 is good.
50% to 95% Saturation, 3 to
>8 is good.
1 to 25+*
>2 desirable
(> means greater than)
(* supersaturated with oxygen)
14-93
-------
(DO and BOD)
C. Apparatus
METHOD A (Sodium Azide Modification of Winkler Method)
1. Buret, graduated to 0.1 ml.
2. Three 300 ml glass-stoppered BOD bottles
3. Wide-mouth Erlenmeyer flask, 500 ml.
4. One 10 ml measuring pipette.
5. One 1-liter reagent bottle to collect activated sludge.
METHOD B (DO Probe)
Follow manufacturer's instructions. See Section H for Discussion,
Calibration, and Precautions.
D. Reagents
1. Manganous sulfate solution. Dissolve 480 g manganous sulfate
crystals (MnSO(4.4H20) in 400 to 600 ml distilled water. Filter
through filter paper, then add distilled wateof to the filtered
liquid to make a 1-liter volume.
2. Alkaline iodide-sodium azide solution. Dissolve 500 g sodium
hydroxide (NaOH) in 500 to 600 ml distilled water; dissolve
150 g potassium iodide (KI) in 200 to 300 ml distilled water
in a separate container. Exercise caution. Mix chemicals in
pyrex glass bottles using a magnetic stirrer. Add the chemicals
to the distilled water slowly and cautiously. Avoid breathing
the fumes and body contact with the solution. Heat is pro-
duced when the water is added, and the solution is very
caustic. Place an inverted beaker over the top of the mixing
container and allow the container to cool at room temperature.
Mix both solutions when they are cool.
Dissolve 10 g sodium azide (NaN3) in 40 ml of distilled water.
Exercise caution again. This solution is poisonous.
Add the sodium azide solution with constant stirring to the
cooled solution of alkaline iodide; then add distilled water
to the mixture to make a 1-liter volume. Sodium azide will
decompose in time and is no good after three months.
14-94
-------
(DO and BOD)
3. Sulfuric acid. Use concentrated reagent-grade acid
Handle carefully, since this material will burn hands and
clothes. Rinse affected parts with tap water to prevent
injury.
CAUTION: When working with alkaline azide and sulfuric acid,
keep a nearby water faucet running for frequent hand rinsing.
4. 0.0375 N sodium thiosulfate solution. Dissolve exactly
9.308 g sodium thiosulfate crystals (Na2S203'5H20) in
freshly boiled and cooled water and make up to 1 liter.
For preservation, add 0.4 g or 1 pellet of sodium hydroxide
(NaOH). Solutions of "thio" should be used within two weeks
to avoid loss of accuracy due to decomposition of solution.
5. Starch solution. Make a thin paste of 6 g of potato starch
in a small quantity of distilled water. Pour this paste
into one liter of boiling, distilled water, allow to boil
for a few minutes, then settle overnight. Remove the clear
supernatant and save; discard the rest. For preservation,
add two drops toluene (C6H5CH3).
6. Copper sulfate solution. Make a 10 percent solution by dis-
solving 10 grams of copper sulfate in 100 ml of water.
Sodium Azide Modification of the Winkler Method
NOTE: The sodium azide destroys nitrates which will
interfere with this test.
E. Outline of Procedure
1.
Take
300 ml
Sample
White floe
No DO
below
surface
JM
4. Mix by
Inverting
\.
^*
Add
2 ml
KI +
$
p 0
o o
0 0
o*0
0 O
A
0 0 0
0 0
0 o 0
0 3
o 0 0
>_
~
NaOH Brown floe
below DO present
surface
Reddish-
Brown
Iodine
Solution
14-95
-------
(DOjmd BOD)
Titration of Iodine Solution;
1. Pour Bottle
Contents
into Flask.
Reddish-
Brown
•So
Pale
Yellow
Blue
2. Titrate
3. Add Starch
Indicator
14-96
-------
(DO and BOD)
PROCEDURE
The reagents are to be added in the quantities, order, and methods
as follows:
1. Collect a sample to be tested in 300 ml (BOD) bottle taking
special care to avoid aeration of the liquid being collected.
Fill bottle completely and add cap.
2. Remove cap and add 2 ml of manganous sulfate solution below
surface of the liquid.
3. Add 2 ml of alkaline-iodide-sodium azide solution below the
surface of the liquid.
4. Replace the stopper, avoid trapping air bubbles, and shake
well by inverting the bottle several times. Repeat this
shaking after the floe has settled halfway. Allow the floe
to settle halfway a second time.
5. Acidify with 2 ml of concentrated sulfuric acid by allowing
the acid to run down the neck of the bottle above the surface
of the liquid.
6. Restopper and shake well until the precipitate has dissolved.
The solution will then be ready to titrate. Handle the .
bottle carefully to avoid acid burns.
7. Pour contents of bottle into an Erlenmeyer flask.
8. If the solution is brown in color, titrate with 0.0375 N
sodium thiosulfate until the solution is pale yellow color.
Add a small quantity of starch indicator and proceed to
step 10.
9. If the solution has no brown color, or is only slightly
colored, add a small quantity of starch indicator. If
no blue color develops, there is zero Dissolved Oxygen.
If a blue color does develop, proceed to step 10.
10. Titrate to the first disappearance of the blue color. Record
the number of ml o£ sodium thiosulfate used.
11. The amount of oxygen dissolved in the original solution will
be equal to the number of ml of sodium thiosulfate used in
the titration provided significant interfering substances are
not present.
mg/1 DO = ml sodium thiosulfate
14-97
-------
(DO and BOD)
F. Example
The DO titration of a 300 ml sample requires 5.0 ml of 0.0375 N
Sodium Thiosulfate. Therefore, the dissolved oxygen concentra-
tion in the sample is 5 mg/1.
G. Calculation
You will want to find the percent saturation of DO in the
effluent of your secondary plant. The DO is 5.0 mg/1 and the
temperature is 20°C. At 20°C, 100% DO saturation is 9.2 mg/1.
The dissolved oxygen saturation values are given in Table IV.
Note that as the temperature of water increases, the DO satura-
tion value (100% Saturation Column) decreases. Table IV gives
100% DO saturation values for temperatures in °C and °F.
DO Saturation, % - D0 ^Sample, mg/1 x 100%
DO at 100% Saturation, mg/1
5-° '"°// x 100% .54
9.2 mg/1
.54 x 100%
54%
9. 2 / 5 .0, 0
460
H. DO Probe
1. Discussion
Measurement of the dissolved oxygen (DO) concentration with a
probe and electronic readout meter is a satisfactory substitute
for the Sodium Azide Modification of the Winkler Method under
many circumstances. The probe is recommended when samples con-
tain substances which interfere with the modified Winkler procedure,
such as sulfite, thiosulfate, polythionate, mercaptans, free
chlorine or hypochlorite, organic substances readily hydrolyzed
in alkaline solutions, free iodine, intense color or turbidity,
and biological floes. A continuous record of the dissolved
14-98
-------
CDO and BOD)
TABLE IV
EFFECT OF TEMPERATURE ON OXYGEN SATURATION
FOR A CHLORIDE CONCENTRATION OF ZERO Mg/1
°c
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
2£
21
22
23
24
25
°F
32.0
33.8
35.6
37.4
39.2
41.0
42.8
44.6
46.4
48.2
50.0
51.8
53.6
55.4
57.2
60.0
61.8
63.6
65.4
67.2
68.0
69.8
71.6
73.4
75.2
77.0
mg/1 DO at
Saturation
14.6
14.2
13.8
13.5
13.1
12.8
12.5
12.2
11.9
11.6
11.3
11.1
10.8
10.6
10.4
10.2
10.0
9.7
9.5
9.4
9.2
9.0
8.8
8.7
8.5
8.4
14-99
-------
CDO and BOD)
oxygen content of aeration tanks and receiving waters may be
obtained using a probe. In determining the BOD of samples,
a probe may be used to determine the DO initially and after
the five-day incubation period of the blanks and sample dilutions,
2. Procedure
Follow manufacturer's instructions.
3. Calibration
To be assured that the DO probe reading provides the dissolved
oxygen content of the sample, the probe must be calibrated. Take
a sample that does not contain substances that interfere with
either the probe reading or the modified Winkler procedure.
Split the sample. Measure the DO in one portion of the sample
using the modified Winkler procedure and compare this result with
the DO probe reading on the other portion of the sample. Adjust
the probe reading to agree with the results from the modified
Winkler procedure.
When calibrating the probe in an aeration tank of the activated
sludge process, do not attempt to measure the dissolved oxygen
in the aerator and then adjust the probe. The biological floes
in the aerator will interfere with the modified Winkler procedure,
and the copper sulfate-sulfamic acid procedure is not sufficiently
accurate to calibrate the probe. An aeration tank probe may be
calibrated by splitting an effluent sample, measuring the DO by
the modified Winkler procedure, and comparing results with the
probe readings. Always keep the membrane in the tip of the probe
from drying because the probe can lose its accuracy until re-
conditioned.
4. Precautions
1. Periodically check the calibration of the probe.
2. Keep the membrane in the tip of the probe from drying out.
3. Dissolved inorganic salts, such as found in sea water, can
influence the readings from a probe.
4. Reactive compounds, such as reactive gases and sulfur com-
pounds, can interfere with the output of a probe.
5. Don't place the probe directly over a diffuser because you
want to measure the dissolved oxygen in the water being
treated, not the oxygen in the air supply to the aerator.
14-100
-------
(DO and BOD)
8. Dissolved Oxygen
II. IN AERATOR
Copper Sulfate-Sulfamic Acid Flocculation, page 413, 12th Edition,
1965, "Standard Methods".
A. Discussion
This modification is used for biological floes that have high
oxygen utilization rates in the activated sludge process, and
when a DO probe is not available. It is very important that
some oxygen be present in aeration tanks at all times to maintain
aerobic conditions.
This test is similar to the regular DO test except that copper
sulfate is added to kill oxygen-consuming organisms, and sulfamic
acid is added to combat nitrites before the regular DO test is run.
NOTE: If the results indicate a DO of less than 1 mg/1, it is
possible that the DO in the aeration tank is ZERO!
When the DO in the aeration tank is near zero, consider-
able DO from the surrounding atmosphere can mix with the
sample when it is collected, when the inhibitor is added,
while the solids are settling, and when the sample is
transferred to a BOD bottle for the DO test. If you use
this test, use a deep container and avoid stirring. See
article by Hughes and Reynolds JWPCF, Vol. 41, pg. 184,
January 1969, for a discussion of the shortcomings of
this test.
B. What is Tested?
Sample Common DO Range, mg/1
Aerator Mixed Liquor 0.1 - 3.0
C. Apparatus
1. One tall bottle, approximately 1000 ml.
2. Regular DO apparatus.
14-101
-------
(DO and BOD)
D. Reagents
1. Copper sulfate-sulfamic acid inhibitor solution. Dissolve
32 g technical grade sulfamic acid (NH2S02OH) without heat
in 475 ml distilled water. Dissolve 50 g copper sulfate,
CuSOtt-5H20, in 500 ml water. Mix the two solutions together
and add 25 ml concentrated acetic acid.
2. Regular DO reagents.
E. Outline of Procedure
1. Add 10 ml of
inhibitor.
2. Dip into mixed
liquor.
Stopper bottle.
Settle
sample.
4. Siphon over 300 ml
of sample into
BOD bottle.
2,
3.
Add at least 10 ml of inhibitor (5 ml copper sulfate and
5 ml sulfamic acid) to any TALL bottle (1-quart milk bottle)
with an approximate volume of 1000 ml. Place filling tube
near the bottom. An emptying tube is placed approximately
1/4 inch from the top of the bottle cork. Attach bottle to
rod or aluminum conduit and lower into aeration tank.
Allow bottle to fill and then withdraw.
Let stand until clear supernatant liquor can be siphoned into
a 300 ml BOD bottle. Do not aerate in transfer.
4. Then run regular DO.
14-103
-------
(JDO and BOD)
F. and G. Example and Calculations
Same as regular DO test.
QUESTIONS
8.A Calculate the percent dissolved oxygen saturation if
the receiving water DO is 7.9 mg/1 and the temperature
is 10 °C.
8.B How would you calibrate the DO probe in an aeration tank?
8.C What are the limitations of the copper sulfate-sulfamic acid
procedure for measuring DO in an aeration tank when the DO
in the tank is very low?
14-104
-------
(DO and BOD)
Biochemical Oxygen Demand or BOD
A. Discussion
The BOD test gives the amount of oxygen used by microorganisms
to utilize the substrate (food) in wastewater when placed in a
controlled temperature for five days. The DO (dissolved oxygen)
is measured at the beginning and recorded. After the 5-day
incubation period the DO is again determined. The BOD is then
calculated on the basis of the reduction of DO and the size of
sample. This test is an estimate of the availability of food
in the sample (food for organisms that take up oxygen) expressed
in terms of oxygen use. Results of a BOD test indicate the rate
of oxidation and provide an indirect estimate of the availability
to organisms or concentration of the waste.
Samples are incubated for a standard period of five days because
a fraction of the total BOD will be exerted during this period.
The ultimate or total BOD is normally never run for plant control.
A disadvantage of the BOD test is that the results are not avail-
able until five days after the sample was collected.
B. What is Tested?
Sample Common Range, mg/1
Influent 150 - 400
Primary Effluent 60 - 160
Secondary Effluent 10 - 60
Digester Supernatant 1000 - 4000+
Industrial Wastes 100 - 3000+
C. Apparatus
1. 300 ml BOD bottles with ground glass stoppers
2. Incubator, 20°C
3. Pipettes, 10 ml graduated, 1/32 to 1/16-inch diameter tip
4. Burette and stand
5. Erlenmeyer flask, 500 ml
14-105
-------
CDC and BOD)
D. Reagents
See Section D, page 14-94 under DO portion of this procedure for
the preparation of manganous sulfate, alkaline iodide-sodium azide,
sulfuric acid, sodium thiosulfate, and starch solutions.
1. Distilled water. Water used for solutions and for preparation
of the solution water must be of highest quality. It must
contain no copper or decomposable organic matter. Ordinary
distilled water for your car's battery is not good enough.
2. Phosphate buffer solution. Dissolve 8.5 g monobasic potassium
phosphate (Kf^POiJ , 21.75 g dibasic potassium phosphate
(K2HPOLf) , 33.4 g dibasic sodium phosphate crystals
(Na2HPO(+ «7H20), and 1.7 g ammonium chloride (NH^Cl) in
distilled water and make up to 1 liter. The pH of this
buffer should be 7.3 and should be checked with a pH meter.
3. Magnesium sulfate solution. Dissolve 22.5 g magnesium sul-
fate crystals (MgS04 «7H20) in distilled water and make up
to 1 liter.
4. Calcium chloride solution. Dissolve 27.5 g anhydrous calcium
chloride (CaCl2) in distilled water and make up to 1 liter.
5. Ferric chloride solution. Dissolve 0.25 g ferric chloride
(FeCl3« 6H20) in distilled water and make up to 1 liter.
6. Dilution water. Add 1 ml each of phosphate buffer (step 7),
magnesium sulfate (step 3), calcium chloride (step 4), and
ferric chloride solutions (step 5) for each liter of dis-
tilled water. Store at a temperature as close to 20 °C as
possible for at least 24 hours to allow the water to become
stabilized. This water should not show a drop in DO of more
than 0.2 mg/1 on incubation for five days.
Many plants do not prepare reagents. Small plants and plants that
do not run many tests find it quicker and easier to purchase com-
mercially prepared reagents. These reagents may be available in
the desired strength or they may consist of dry pillows which are
added to the sample, rather than the liquid reagent. Check with
your chemical supplier for these reagents.
14-1U6
-------
(DO and BOD)
1. Fill 2 BOD bottles
with BOD dilution
water.
OUTLINE OF PROCEDURE
4.
20°C
A
1
1 Incubate
5 days
&
Test for D.O.
\
3. Fill with
dilution water
I
2. Add
sample
5. Immediately test 2 £ 4 for initial D.O.
6. Add
2 ml
below
surface
7. Add 2 ml
Alkaline KI
below
surface
Test for D.O.
0.375 N
Na2S203
Add 2 ml 9. Transfer 10. Titrate
H2S04
Bottle Con-
tents to
Flask
14-107
-------
(DO and BOD)
E. Outline of Procedure
The test is made by measuring the oxygen used or depleted during
a 5-day period at 20°C by a measured quantity of wastewater sample
seeded into a reservoir of dilution water saturated with oxygen.
This is compared to an unseeded or blank reservoir of dilution
water by subtracting the difference and multiplying by a factor
for dilution. See outline on Page 14-107.
PROCEDURE
1. BOD bottles should be of 300 ml capacity with ground glass
stoppers and numbers. To clean the bottles, carefully rinse
with tap water followed by distilled water.
2. Fill two bottles completely with dilution water and insert
the stopper tightly so that no air is trapped beneath the
stopper. Siphon dilution water from its container when
filling BOD bottles.
3. Set up one or more dilutions of the sample to cover the
estimated range of BOD values. From the estimated BOD,
calculate the volume of raw sample to be added to the BOD
bottle based on the fact that:
The most valid DO depletion is 4 mg/1. Therefore,
ml of sample added _ (4 mg/1) (300 ml)
per 300 ml ~ Estimated BOD, mg/1
1200
Estimated BOD, mg/1
Examples:
a. Estimated BOD = 400 mg/1
ml of sample added _ 1200
to BOD bottle ~ 400
= 3 ml
14-108
-------
(DO and BOD)
b. Estimated BOD = 200 mg/1: use 6 ml •
100 mg/1: use 12 ml
20 mg/1: use 60 ml
When the BOD is unknown, select more than one sample size.
For example, place several samples--! ml, 3 ml, 6 ml, and
12 mi — into four BOD bottles.
For samples with very high BOD values, it may be difficult
to accurately measure small volumes or to get a truly repre-
sentative sample. In such a case, initial dilution should
first be made on the sample. A dilution of 1:10 is convenient.
4. To perform the BOD test, first fill two BOD bottles with
BOD dilution water. Nos. (1) and (2) in illustration,
Page 14-107
5. Next, for each sample to be tested, carefully measure out the
two portions of sample and place them into two new BOD bottles,
Nos. (3) and (4). Add dilution water until the bottles are
completely filled. Insert the stoppers. Avoid entrapping air
bubbles. Be sure that there are water seals on the stoppers.
6. On bottles (2) and (4) immediately determine the initial
dissolved oxygen.
7. Incubate the remaining dilution water blank and diluted sample
at 200C for five days. These are bottles (1) and (3).
8. At the end of exactly five days (± 3 hours), test bottles
(1) and (3) for their dissolved oxygen by using the sodium
azide modification of the Wihkler method or a DO probe.
At the end of five days, the oxygen content should be at
least 1 mg/1. Also, a depletion of 2 mg/1 or more is
desirable. Bottles (1) and (2) are only used to check the
dilution water quality. Their difference should be less
than 0.2 mg/1 if the quality is good and free of impurities.
14-109
-------
(DO and BOD)
F. Precautions
Since this is a bioassay (BUY-o-ass-SAY)t that is, living organisms
are used for the test, environmental conditions must be quite exact.
1. The temperature of the incubator must be at 20°C. Other
temperatures will change the rate of oxygen used.
2. The dilution water should be made according to Standard
Methods for the most favorable growth rate of the bacteria.
This water must be free of copper which is often present
when copper stills are used by commercial dealers. Use all
glass or stainless steel stills.
3. The wastewater must also be free of toxic wastes, such as
hexavalent chromium.
4. Don't use cleaning solutions to wash BOD bottles.
5. Wastewater normally contains an ample supply of seed bacteria;
therefore seeding is usually not necessary.
G. Chlorinated Samples
It is very difficult to obtain reliable and reproducible results
from the BOD test, and a chlorinated sample is even more difficult.
For this reason, samples for BOD tests should be collected before
chlorination.
H. Example
BOD Bottle Volume = 300 ml
Sample Volume = 15 ml
Initial DO of ... ..
Diluted Sample = 8<0 mg/1
DO of Sample and Dilution _ /1
After 5-day Incubation " mg/
14-110
-------
I. Calculations
(DO and BOD)
BOD,
mg/1
Initial DO of
Diluted Sam-
pie,
V.
mg/1
DO of Diluted"^
Sample After
5-Day Incuba-
tion/ mg/1
30D Bottle Vol., ml]
Sample Volume, ml
[8.0 mg/1 - 4.0 mg/1)
(4.0) (300)
15
= SO mg/1
For acceptable results, the percent depletion of oxygen in the BOD
test should range from 30% to 80% depletion.
% Depletion
DO of Diluted Sample, mg/fj
- DO After 5 Days, mg/lj
DO of Diluted Sample, mg/1
x 10Q%
= (8.0 mg/1 - 4.0 mg/1)
8.0 mg/1
= - x 100
- 50%
When a sample requires a large volume in the BOD test and a small
amount of dilution water, or if a sample has a high DO (plant or
pond effluent) , the initial DO of the mixture may be determined
as fellows.
Example:' BOD Bottle Volume
Sample Volume
Sample DO
DO of Dilution Water
DC of Sample and Dilution
After 5-Day Incubation
300 ml
60 ml
2.0 mg/1
8.0 mg/1
4.0 mg/1
14-111
-------
(DO and BOD)
DO of Initial
Mixture of
Dilution Water
and Sample, mg/1
m] of Sample x DO of Sample + ml of
Dilution H20 x DO of Dilution H20
BOD Bottle Volume
BOD, mg/1
60 ml x 2.0 mg/1 + 240 ml x 8.0 mg/1
300 ml
120 + 1920
300
6.-8 mg/1
6.8
300/2040.0
1800
240.0
240.0
NOTES
DO of
Diluted
Sample,
mg/1
N
DO After
5 Days ,
mg/1
j
/• .>
BOD Bottle Vol., ml
Sample Vol. , ml
^ >
= (6.8 mg/1 - 4.0 mg/1)
300 ml
60 ml
= 14.0 mg/1
1. On effluent samples where the DO is run on the sample and the
blue bounces back on the end point titration, this indicates
nitrite interference and can cause the BOD to be higher than
actual by as much as 10% to 15% of the answer. This fact
should be considered in interpreting your results. The end
point also may waver because of decomposition of azide in an
old reagent or resuspension of sample solids. To correct a
wavering end point, try preparing a new alkaline-azide solution
or more of the old solution should be used because it may be
decomposing.
2. Researchers and equipment manufacturers are continually striving
to develop quicker and easier tests to measure BOD. If you find
a test procedure that provides you with an effective operational
control test, use it. Be sure to check with your regulatory
agencies for the procedures they require you to use in your
effluent monitoring program.
14-112
-------
QUESTIONS
8.D How would you determine the amount of organic
material in wastewater?
8.E How would you prepare dilutions to measure the
BOD of cannery waste having an expected BOD of
2000 mg/1?
8.F What is the BOD of a sample of wastewater if
a 2 ml sample in a 300 ml BOD bottle had an
initial DO of 7.5 mg/1 and a final DO of 3.9 mg/1?
8.G Why should samples for the BOD be collected
before chlorination?
8.H Why should opened bottles of "Thio" be used or
restandard!zed within two weeks?
END OF LESSON 4 OF 8 LESSONS
on
Laboratory Procedures and Chemistry
Work the next portion of the discussion and review questions
before continuing with Lesson 5.
14-113
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 4 of 8 Lessons)
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Write the answers to these questions in your notebook. The problem
numbering continues from Lesson 3.
11. What is the formula for calculating the percent
saturation of DO?
12. What precautions should be exercised when using
a DO probe?
13. What is a blank, as referred to in laboratory
procedures?
14. What are some of the disadvantages of the BOD test?
15. What precautions should be taken when running a
BOD test?
16. Calculate the BOD of a 5 ml sample if the initial
DO of the diluted sample was 7.5 mg/1 and the DO
of diluted sample after 5-day incubation was 3.0 mg/1?
14-115
-------
CHAPTER 14. LABORATORY PROCEDURES AND CHEMISTRY
(Lesson 5 of 8 Lessons)
9. Hydrogen Sulfide (H2S)
I. IN ATMOSPHERE
A. Discussion
The rate of concrete corrosion is often directly related to the rate
of H2S production or amount of H2S in the atmosphere. This test deals
with the time it takes a paper tape or unglazed tile to turn black.
It is a qualitative measurement of the H2S present in the sewer atmos-
phere. H2S is recognized by its characteristic odor of rotten eggs.
B. What is Tested?
Sample
Atmosphere in sewers, out-
lets from force mains, wet
pits, pumping stations, and
influent areas to treatment
plants.
Common Range
Not black in
24 hours
Black in less
than 1 hour
= Good, 24+ hr
= Bad, < 1 hr
C. Apparatus
Lead acetate paper or unglazed tile soaked in lead acetate,
D. Reagents
Saturated lead acetate solution.
E. Procedure
1. Obtain pieces of unglazed tile or use lead acetate paper. Cut
tile with hacksaw into ^ inch strips.
2. Soak strips in tile in lead acetate solution.
14-117
-------
(H2S)
3. Dry tile in drying oven or air dry.
4. An open manhole or any point where wastewater is exposed to the
atmosphere is a good test site. Drive a nail between metal crown
ring of manhole, concrete, or other convenient place. Tie paper
or tile with cotton string to nail and then replace it and return
in half an hour or less. If tile is not black or substantially
colored, return periodically until black. If H2S is present as
indicated by a color change, then measure flow, temperature, pH,
and BOD for further evaluation of problem.
II. IN WASTEWATER
A. Discussion
In sewers, when there is no longer any dissolved oxygen, H2S tests
are run to determine the rate of H2S increase as the wastewater
travels to a pumping station or treatment plant. If the wastewater
is exposed to the atmosphere, H2S will be released and a typical
rotten egg odor will be detected. Anaerobic bacteria found in
wastewater can liberate H2S from the solids. When the gas leaves
the wastewater stream and comes in contact with moisture and
oxygen, sulfuric acid is formed which is very corrosive to concrete.
Not all odors in wastewater are from H2S, and there is no correlation
between HaS and other odors. The total H2S procedure is good up to
18 mg/1, and higher concentrations must be diluted before testing.
H2S production can be controlled by up-sewer aeration which reduces
H S formation and also stabilizes the wastewater in the collection
system.
14-118
-------
(H2S)
B. What is Tested?
Sample Wastewater From Possible Results, mg/1
the Following Locations Gob'd ' ' " ' " ' Bad
Sewers . 1 1
Outlets from force mains .1 1
Wet pits, pumping stations .1 .5
Influents to treatment plants Preferably 0 .5
All of the above locations should be sampled, if pertinent, when
using up-stream aeration to control H2S.
C. Apparatus
1. One LaMotte-Pomeroy Sulfide Testing Kit to test:
a. Total Sulfides
b. Dissolved Sulfides
c. Hydrogen Sulfide in solution
Obtain from LaMotte Chemical Products Company. Order by Code
#4630, $27.50, FOB, Chestertown, Maryland 21620.
2. One LaMotte-Pomeroy Accessory Hydrogen Sulfide Kit for testing
H2S in air and gases (not essential). Obtain from LaMotte
Chemical Products Company. Order by Code #4632, $22.00, FOB,
Chestertown, Maryland 21620.
D. Reagents
The instructions are in the kit.
E. Procedure
The instructions are in the kit.
14-119
-------
(H2S)
F. Example
The instructions are in the kit,
G. Calculations
The instructions are in the kit.
QUESTION
9.A Why would you measure the H2S concentration:
1. In wastewater?
2. In the atmosphere?
14-120
-------
10. pH_
A. Discussion
The intensity of the alkaline or acid strength of water is
expressed by its pH.
Mathematically, pH is the logarithm of the reciprocal of the
hydrogen ion concentration, or the negative logarithm of the
hydrogen ion concentration.
PH = log -^ = -log (H+)
For Example
If a wastewater has a pH of 1, then the hydrogen ion concentration
(H+) = 10"1 = 0.1.
If pH = 7, then (H+) = 10~7 = 0.0000001.
pH Scale
0 increasing acidity -- 7 -- increasing alkalinity 14
1 «. 2 «- 3 +- 4 ^ 5 •«- 6 /^ 8 -*• 9 •*• 10 -*• 11 -»• 12 -»• 13
Neutral
6 through 8
In a solution, both hydrogen ions (H+) and the hydroxyl ions (OH~)
are always present. At a pH of 7, the concentration of both hydrogen
and hydroxyl ions equals 10"7 moles per liter. When the pH is less
than 7, the concentration of hydrogen ions is greater than the hydroxyl
ions. The hydroxyl ion concentration is greater than the hydrogen ions
in solutions with a pH greater than 7.
The pH test indicates whether a treatment process may continue to
function properly at the pH measured. Each process in the plant has
its own favorable range of pH which must be checked routinely.
Generally a pH value from 6 to 8 is acceptable for best organism
activity.
14-121
-------
CPH)
The paper tape colorimetric comparison method is explained in
this section. This is not considered a "Standard Method" but
will give a rough indication of the pH. Most wastewater contains
many dissolved solids and buffers which tend to minimize pH changes,
There are many ranges of pH tapes available. Normally a range of
5 to 8 will cover the inplant control testing.
B. What is^ Tested?
Wastewater Common Range
Influent or Raw Wastewater (domestic) 6.8 to 8.0
Raw Sludge (domestic) 5.6 to 7.0
Digester Recirculated Sludge or
Supernatant 6.8 to 7.2
Plant Effluent Depending on
Type of Treatment 6.0 to 8.0
C. Minimum Apparatus List
1. pH Meter.
or 2. Three rolls of paper tapes (range 5 to 8).
or 3. Colorimetric set (range 6.8 to 8.4)--permanent glass which
can be used with chlorine comparator or liquid color tubes
that are less stable.
D. Reagents
(to be used with corresponding apparatus listed under Section C)
1. Buffer tablets of various pH values. Distilled water.
2. None.
3. Brom thyml blue (for pH 6.2 to 7.6).
Phenol red (for 6.4 to 8.0).
14-122
-------
(PH)
E. Procedures
Use the same samples used for the other tests.
METHOD A (pH Meter)
Procedure
1. Due to the differences between the various makes and models
of pll meters commercially available, specific instructions
cannot be provided for the correct operation of all instru-
ments. In each case, follow the manufacturer's instructions
for preparing the electrodes and operating the instrument.
2. Standardize the instrument against a buffer solution with a
pH approaching that of the sample.
3. Rinse electrodes thoroughly with distilled water after re-
moval from buffer solution.
4. Place electrodes in sample and measure pH.
5. Remove electrodes from sample, rinse thoroughly with dis-
tilled water.
6. Immerse electrode ends in beaker of pH 7 buffer solution.
7. Shut off meter.
Precautions
1. To avoid faulty instrument calibration, prepare fresh buffer
solutions as needed, once per week, from commercially avail-
able buffer tablets.
2. pH meter, buffer solution, and samples should all be at the
same temperature (constant) because temperature variations
will give erroneous results.
3. Watch for erratic results arising from electrodes, faulty
connections, or fouling of electrodes with oily or precipitated
matter.
14-123
-------
(PH)
METHOD B (Paper Tape)
Procedure
1. Measure pH directly in tank or immediately after collecting
sample.
2. Tear off tape lh to 2" long. Dip half of tape in tank or
sample and quickly read results.
3. Remove tape and compare color with colors on package, and
record pH on Laboratory Work Sheet in proper column from
which the sample came. For example, if the sample came
from the plant influent and the color of the portion of the
tape wetted by the sample matches a color on the package
indicating a pH of 7.2, then record 7.2 on Laboratory Work
Sheet in the influent column on the pH row. (See Fig. 14.2
second page of work sheet).
This procedure applies to liquids that have solids which separate
(settle or float) easily.
METHOD B (Paper Tape-High Solids Cone, in Sample)
Procedure
The following procedure is for samples containing higher solid
concentrations such as found in the raw sludge, digester recircu-
lated sludge, digester supernatant, and digested sludge samples.
1. Obtain representative samples and identify them.
2. Allow samples to stand until some of the solids have settled
and water is visible above the solids. Sufficient water
should be above the solids to allow the tape to be dipped in
the sample and not discolored by the solids.
3. Bend the tape by making a sharp crease %" from end. Very care-
fully allow tape to touch liquid surface.
End of . 4. Remove tape from liquid surface
bent and compare the color with pH
^f~ I—
tape
color standard on the package.
Record on Laboratory Work Sheet.
14-124
-------
(PH)
METHOD C (Colorimetric Comparitor)
Procedure
1. Fill the three tubes or two rectangular bottles provided with
the comparitor unit to the indicator line with a portion of
the sample being tested.
2. Add the recommended amount of indicator solution.
3. Place the tubes in the comparitor in such a way that the color
standards are opposite the tubes not containing the indicator
solution.
4. Compare the colors by rotating the comparitor disk or changing
the standard color solution vials. Read the pH of the indi-
cator having the color closest to the color of the sample.
Record results on Laboratory Work Sheet.
5. Thoroughly wash and dry sample tubes when test is completed
and before returning tubes to comparitor unit for storage.
F. Precautions
1. Collect fresh samples and test immediately. The pH of a
sample can change rapidly due to loss of C02 and biological
activity. A fresh effluent sample could have a pH of 6.5
and after standing overnight the pH could be 8.0.
2. Always measure aerator pH directly in the aerator.
3. The pH of a composite sample will not accurately describe pH
conditions in your plant. A ten-minute slug of a highly acid
waste can upset plant performance for a day or longer, but
you may not notice it in a composite sample. Measure pH in
place, frequently and quickly, for best description of
environment encountered by organisms in treatment processes.
14-125
-------
QUESTIONS
10.A How would you measure the pH by the paper tape
colorimetric comparison method for:
1. Plant influent?
2. Raw sludge?
10.B What precautions should be exercised when using
a pH meter?
14-126
-------
11. Settleability of Activated Sludge Solids
I. SETTLEABILITY
A. Discussion
This test is run on mixed liquor or return sludge and plotted on
attached graph (Fig. 14.5). All pertinent information is filled
in for process control of aerators.
T3
O
_Q
a
a>
0
60
10 15 20
Time, minutes
Fig. 14.5 Settleability of activated sludge solids
Settleability is important in determining the ability of the solids
to separate from the liquid in the final clarifier. The activated
sludge solids should be returned to the aeration tank, and the
quality of the effluent is dependent upon the absence of solids
flowing over the effluent weir.
The suspended solids should be run on the same sample of mixed
liquor that the Settleability test is run. This will allow.you to
calculate the Sludge Volume Index (SVI) or the Sludge Density Index
(SDI) which are explained in other sections.
14-127
-------
(Settleability)
The 2000 ml graduate that is filled with mixed liquor in the
settleability test is supposed to indicate what will happen to
the mixed liquor in the final clarifier--the rate of sludge
settling, turbidity, color, and volume of sludge at the end of
60 minutes.
B. What is Tested?
Sample
Mixed Liquor or
Return Sludge
Working Range
Depends on desirable mixed
liquor concentration
C. Apparatus
2000 ml graduated cylinder.10
D. Reagents
None.
E. Procedure
1. Mix sample and pour
into 2000 ml graduate.
Sample
2. Record settleable solids, %, at 5-minute intervals,
A
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15
20
30
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10 Mallory Direct Reading Settleometer (a 2 liter graduated cylinder
approximately 5 inches in diameter and 7 inches high). Obtain from
Scientific Glass Apparatus Co., Inc., 735 Broad Street, Bloomfield,
New Jersey. Catalog No. JS-1035. Price $16.50 each.
14-129
-------
(Settleability)
1. Collect a sample of mixed liquor or return sludge.
2. Carefully mix sample and pour into 2000 ml graduate. Vigorous
shaking or mixing tends to break up floe and produces slower
settling or poorer separation.
3. Record settleable solids, %, at regular intervals.
F. Example and Calculation
The percent settling rate can be compared for the various days of
the week and with other measurements—suspended solids, SVI, per-
cent sludge solids returned, aeration rate, and plant inflow. A
very slow settling mixed liquor usually requires air and solids
adjustment to encourage increased stabilization during aeration.
A very rapidly settling mixed liquor usually gives poor effluent
clarification.
II. SLUDGE VOLUME INDEX (SVI)
A. Discussion
The Sludge Volume Index (SVI) is used to indicate the condition
of sludge (aeration solids or suspended solids) for settle-
ability in a secondary or final clarifier. The SVI is the volume
in ml occupied by one gram of mixed liquor suspended solids after
30 minutes of settling. It is a useful test to indicate changes
in sludge characteristics. The proper SVI range for your plant
is determined at the time your final effluent is in the best con-
dition regarding solids and BOD removals and clarity.
B. What is Tested?
Sample Preferable Range, SVI
Aerator Solids or
Suspended Solids °° "
14-130
-------
(Settleability - SVI)
C. Apparatus
See 11. Settleability of Activated Sludge Solids, Part I,
Settleability, and 16. Suspended Solids.
D. Reagents
None,
E. Procedure
See Section 11, I, on Settleability, and 16, Suspended Solids,
F. Example
30-minute settleable solids test = 360 ml or 18%.
Mixed liquor suspended solids = 1500 mg/1.
G. Calculations
Sludge Volume _ % Settleable Solids x 10 ,000
Index, SVI Mixed Liquor Suspended Solids, mg/1
- 18 x 10,000
Tsffi
15
30
= 120
14-131
-------
(Settleability - SDI)
III. SLUDGE DENSITY INDEX (SDI)
A. Discussion
The Sludge Density Index (SDI) is used in a way similar to the SVI
to indicate the settleability of a sludge in a secondary clarifier or
effluent. The calculation of the SDI requires the same information
as the SVI test.
T _ mg/1 of suspended solids in mixed liquor
ml/1 of settled mixed liquor solids x 10
or
SDI = 100/SVI
B. What is Tested?
Sample Preferable Range, SDI
Aerator Solids or n 4 1 n
Suspended Solids
C. through G.
These items are not included because of their similarity to the
SVI test.
QUESTIONS
11.A Why should you run settleability tests on mixed liquor?
11.B What is the Sludge Volume Index (SVI)?
11.C Why is the SVI test run?
11.D What is the relationship between the Sludge Density
Index (SDI) and SVI?
END OF LESSON 5 OF 8 LESSONS
on
Laboratory Procedures and Chemistry
Work the next portion of the discussion and review questions
before continuing with Lesson 6.
14-132
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 5 of 8 Lessons)
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Write the answers to these questions in your notebook. The problem
numbering continues from Lesson 4.
17. Hydrogen sulfide is measured because it causes
18. What factors promote H2S production in sewers?
19. The pH scale runs from to , with 7 being neutral,
20. Calculate the SVI if the mixed liquor suspended solids are
2000 mg/1 and the 30-minute settleable solids test is 500 ml
or 25%.
21. Calculate the SDI if the SVI is 125.
14-133
-------
CHAPTER 14. LABORATORY PROCEDURES AND CHEMISTRY
(Lesson 6 of 8 Lessons)
12. Settleable Solids
A. Discussion
The settleable solids test is the volume of settleable solids in
one liter of sample that will settle to the bottom of an Imhoff
cone during a specific time period. The test is an indication of
the volume of solids removed by sedimentation in sedimentation
tanks, clarifiers, or ponds. The results are read directly in
milliliters from the Imhoff cone.
B. What is Tested?
Sample
Influent
Primary Effluent
Secondary Effluent
Common Ranges Found
12 ml/1 medium wastewater
20 ml/1 strong wastewater
8 ml/1 weak wastewater
0.1 ml/1 - 3 ml/1
Trace --0.5 ml/1
Over .5 ml/1 poor
C. Apparatus
1. Imhoff Cones.
2. Rack for holding Imhoff Cones.
3. Glass stirring rod, or wire.
14-135
-------
D. Outline of Procedure
(Settleable Solids)
Mix well and
pour 1 liter
into Irnhoff
Cone.
Settle
45 Minutes
Gently Stir
Sides
Settle
15 Minutes
1 Liter
Read
Sludge
Volume
1.
2.
3.
4.
5.
PROCEDURE
Thoroughly mix the wastewater sample by shaking and immediately
fill an Imhoff cone to the liter mark.
Record the time of day that the cone was filled. T =
Allow the waste sample to settle for 45 minutes.
Gently spin the cone to facilitate settling of material adhering
to the side of the cone.
After one hour, record the number of milliliters of settleable
solids in the Imhoff cone. Make allowance for voids among the
settled material.
14-137
-------
(Settleable Solids)
6, Record the settleable solids as ml/1 or milliliters per
liter.
Settleable Solids, Influent = ml/1
Settleable Solids, Effluent = ml/1
Settleable Solids, Removal = ml/1
E. Example
Samples were collected from the influent and effluent of a primary
clarifier. After one hour, the following results were recorded:
Settjleable Solids, ml/1
Influent 12.0
Effluent 0.2
F. Calculations
1. Calculate the efficiency or percent removal of the above primary
clarifier in removing settleable solids.
% Removal _ (Infl. Set Sol, ml/1 - Effl. Set Sol, ml/1)
of Set Sol ~ Influent Set Sol, ml/1
12 ml/1 - 0.2 ml/1 Ox 12.0
—• U.— -1 * n ""*""""" " * J\. JL.\J\) 0 n n
12 ml/1 -0.2
11.8
.983
= ii-^2- x 100% 12/ 11.8
12 10 8
1 00
= 98% -**L
40
2. Estimate the gallons per day of sludge pumped to a digester
from the above primary clarifier if the flow is 1 MGD (1 million
gallons per day). In your plant, the Imhoff cone may not
measure or indicate the exact performance of your clarifier
14-138
-------
(Settleable Solids)
or sedimentation tank, but with some experience you should
be able to relate or compare your lab tests with actual
performance.
Sludge Removed by Clarifier, ml/1
= Influent Set Sol, ml/1 - Effluent Set Sol, ml/1
= 12 ml/1 - 0.2 ml/1
= 11.8 ml/1
To estimate the gpd (gallons per day) of sludge pumped to a
digester, use the following formula:
Sludge to Digester, gpd
= Total Set Sol Removed, ml/1 x 1000 x Flow, MGD
- n a ml Y 100Q mg 1 M
— J. J- • O »V~™' '"" A
M mg ml day
= 11,800 gpd
This value may be reduced by 30 to 75% due to compaction of
the sludge in the clarifier.
If you figure sludge removed as a percentage (1.18%), the sludge pumped
to the digester would be calculated as follows:
1.18% Sludge to Digester, gpd
100% = Flow of 1,000,000 gpd
ci A <- n- A 1.18% x 1,000,000 gpd
Sludge to Digester, gpd = ' ' ' 'inn?-
= 11,800 gpd
G. C1in i ca 1 Cent ri fuge
Settleable solids also may be measured by a small clinical centri-
fuge. A mixed sample is placed in 15 ml graduate API tubes and
spun for 15 minutes. The solid deposition in the tip of the tube
is related to plant performance for plant control. A centrifuge
also is used in Section 16, Suspended Solids, II, Centrifuge.
QUESTION
12.A Estimate the volume of solids pumped to a digester
in gallons per day (gpd) if the flow is 1 MGD, the
influent settleable solids is 10 ml/1, and the eff-
luent settleable solids is 0.4 ml/1 for a primary
clarifier.
14-139
-------
13. Sludge Age
A. Discussion
Sludge age is a control guide that is widely used and is a rough
indicator of the length of time a pound of solids is maintained
under aeration in the system. The basis for calculating the sludge
age is weight of suspended solids in the mixed liquor in the aeration
tank divided by weight of suspended solids added per day to the
aerator.
Suspended Solids in Mixed Liquor, mg/1
Sludge Age, _ x Aerator Volume in MG x 8.54 Ibs/gal
days SS in Primary Effluent, mg/1*
x Daily Flow, MGD x 8.34 Ibs/gal
Any significant additional loading placed on the aerator by the
digester supernatant liquor must be added to the above loadings by
considering the additional flow (MGD) and concentration (mg/1).
The selection of the method of determining sludge age is discussed
in Chapter 7, Activated Sludge.
B. What is Tested?
Sample Common Range, mg/1
Suspended solids in aerator Depends on process
and BOD or suspended solids
in primary effluent
Sludge age Conventional process,
2.5-6 days
* NOTE: Sludge age is calculated by three different methods:
1. Suspended solids in primary effluent, mg/1
2. Suspended solids removed from primary effluent, mg/1, or
primary effluent, suspended solids, mg/1 - final effluent,
suspended solids, mg/1
3. BOD or COD in primary effluent, mg/1
14-141
-------
(Sludge Age)
C. Apparatus
See 16, Suspended Solids Test.
D. Reagents
None.
E. Procedure
See 16, Suspended Solids Test.
F. Example
Suspended Solids in Mixed Liquor = 1500 mg/1
Aeration Tank Volume = 0.50 MG
Suspended Solids in Primary Effl. = 100 mg/1
Daily Flow = 2.0 MGD
G. Calculations
Susp. Solids in Mixed Liquor, mg/1
Sludge Age, _ x Aerator Vol., MG x 8.34 Ibs/gal
days ~ susp. Solids in Primary Effl., mg/1
x Flow, MGD x 8.34 Ibs/gal
Mixed Liquor Susp. Solids, Ibs
Primary Effluent SS, Ibs/day
1500 mg/1 x 0.50 MG x 8.34 Ibs/gal
100 mg/1 x 2.0 MGD x 8.34 Ibs/gal
1500 x 0.50
100 x 2.0
7.5
2.0
= 3.75 days
14-142
-------
QUESTION
13.A Determine the sludge age in an activated sludge process
if the volume of the aeration tank is 200,000 gallons
and the suspended solids in the mixed liquor equals
2000 mg/1. The primary effluent SS is 115 mg/1, and
the average daily flow is 1.8 MGD.
14-143
-------
14. SJudge (Digested) Dewatering Qiaracteristics
A. Discussion
The dewatering characteristics of digested sludge are very
important. The better the dewatering characteristics or
drainability of the sludge, the quicker it will dry and the
less area will be required for sludge drying beds.
B. What is Tested?
PREFERRED RANGE
Sample Method A Method B
Digested Sludge Depends on 100-200 ml
appearance
C. Apparatus
METHOD A
1000 ml graduated cylinder.
METHOD B
1. Imhoff cone with tip removed.
2. Sand from drying bed.
3. 500 ml beaker.
D. Reagents
None.
E. Procedure
Two methods are presented in this section. Method A relies on a
visual observation and is quick and simple. The only problem is that
operators on different shifts might record the same sludge draining
characteristics differently. Method B requires 24 hours, but the
results are recorded by measuring the volume of liquid that passed
through the sand. Method B would be indicative of what would happen
if you had sand drying beds.
14-145
-------
(Sludge Dewatering)
METHOD A
1. Add digested sludge
to 1000 ml graduate,
Sample
Container
2. Pour sample from graduate
back into container.
3. Watch solids
adhere to
cylinder walls.
1. Add sample of digested sludge to 1000 ml graduate.
2. Pour sample back into sample container. Set graduated
cylinder down.
3. Watch graduate. If solids adhere to cylinder wall and
water leaves solids in form of rivulets, this is a
good dewatering sludge on a sand drying bed (Fig. 14.6)
Fig. 14.6
Sludge on graduated
cylinder walls for
sludge dewatering
test
14-146
-------
(Sludge Dewatering)
METHOD B
1. Pour digested sludge
on top of sand in
Imhoff cone.
2. Place beaker under
tip and wait 24
hours.
3. Measure liquid
that has passed
through the sand.
Broken Tip
1. Broken glass Imhoff cone that has tip removed and a glass wool
plug in the end to hold the sand in the cone.
2. F-ill halfway with sand from sand drying bed.
3. Fill remainder to 1 liter with digested sludge.
4. Place 500 ml beaker under cone tip and wait 24 hours.
5. Record liquid that has passed through sand in ml. If
less than 100 ml has passed through sand, you have poor
sludge drainability.
QUESTION
14.A What are the differences in the use of (1) a graduated
cylinder and (2) an Imhoff cone, filled with sand, that
has a broken tip, to measure the dewaterJ.ng characteristics
of digested sludge?
14-147
-------
15. Supernat£.nt Graduate Evaluation
A. Discussion
The digester supernatant solids test measures the percent of
settleable solids being returned to the plant headworks. The
settleable solids falling to the bottom of a graduate should
not exceed the bottom 5% of the graduate in most secondary
plants. When this happens, you are imposing a load on the
primary settling tanks that they were not designed to handle.
If the solids exceed 5% you should run a suspended solids
Gooch crucible test (Section 16) on the sample and calculate
the recycle load on the plant that is originating from the
digester.
B. What is Tested?
Sample Common Values
Supernatant % Solids should be <5%
C. Apparatus
100 ml graduated cylinder.
D. Reagents
None.
14-149
-------
(Supernatant)
E. Procedure
1. Fill 100 ml graduate
with supernatant.
2. After 60 minutes,
read ml of solids
at bottom.
Supernatant
Sample
L
10 ml
100 ml Graduate
1. Fill a 100 ml graduated cylinder with supernatant sample.
2. After 60 minutes, read the ml of solids that have settled
to the bottom.
3. Calculate supernatant solids, %.
Supernatant Solids, % = ml of Solids
F. Example
Solids on bottom of cylinder, 10 ml.
G. Calculations
Supernatant Solids, % = ml of Solids
= 10 ml
= 10% Solids (High) by Volume
14-150
-------
QUESTION
15.A Why should the results of the supernatant solids test
be less than 5% solids?
END OF LESSON 6 OF 8 LESSONS
on
Laboratory Procedures and Chemistry
Work the next portion of discussion and review questions before
continuing with Lesson 7.
14-151
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 6 of 8 Lessons)
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Write the answers to these questions in your notebook. The
problem numbering continues from Lesson 5.
22. Calculate the efficiency or percent removal of a
primary clarifier when the influent settleable
solids are 10 ml/1 and the effluent settleable
solids are 0.3 ml/1.
23. Why does the actual volume of sludge pumped from
a clarifier not agree exactly with calculations
based on the settleable solids test?
24. What does sludge age measure?
25. Why should the dewatering characteristics of
digested sludge be measured?
26. What happens to the plant when the supernatant
from the digester is high in solids?
14-153
-------
CHAPTER 14. LABORATORY PROCEDURES AND CHEMISTRY
(Lesson 7 of 8 Lessons)
16. Suspended Solids
I. GOOCH CRUCIBLE
A. Discussion
One of the tests run on wastewater is to determine the amount of
material suspended within the sample. The result obtained from
the suspended solids test does not mean that all of the suspended
solids settle out in the primary clarifier or, for that matter, in
the final clarifier. Some of the particles are of such size and
weight that they will not settle without additional treatment.
Therefore, suspended solids are a combination of settleable solids
and those solids that remain in suspension.
B. What is Tested?
Sample Common RangesA pgA
Influent Weak 150 - 400+ Strong
Primary Effluent Weak 60 - 150+ Strong
Secondary Effluent 10 Good - 60+ Bad
Activated Sludge Tests Depending on Type of Process
Mixed Liquor 1000 - < 5,000
Return or Waste Sludge 2000 - < 12,000
Digester Tests:
Supernatant 3000 - < 10,000
IVhen supernatant suspended solids are greater than 10,000 mg/1,
the total solids test is usually performed.
14-155
-------
(Suspended Solids - Gooch)
C. Apparatus^
1. 2.4 cm glass fiber filter.
2. No. 4 Gooch crucible.
3. Distilled water,
4. Filter flask.
5. Graduated cylinder.
6. Vacuum pump or aspirator.
7. Oven.
8. Analytical balance.
D. Outline of Procedure
The procedure is outlined on Page 14-157.
(Method with Gooch Crucible and Glass Fiber Filter)
14-156
-------
(Suspended Solids - Gooch)
2.
Filtering Flask
Seat filter, by add-
ing distilled water
and applying vacuum.
n n n
6
O
\J \J
Dry crucibles in oven
at 103°C.
4. Cool.
5. Pour
measured
volume of
sample in
Gooch
crucible.
7. Filter out suspended
solids with vacuum.
8. Wash graduate, crucible,
and filter with distilled
water to complete solids
transfer.
5. Weigh crucible.
n n n
a
o
U \ VJ
9. Dry crucibles plus
suspended solids
at 103°C.
11. Weigh crucible
plus suspended
solids.
nnn
10. Cool.
14-157
-------
(Suspended Solids - Gooch)
E. Preparation of Gooch Crucible
1. Put a No. 4 Gooch crucible into filtering apparatus.
2. Insert 2.4 cm glass fiber filter and center it.
3. Apply suction.
4. Wash filter with 100 ml of distilled water to seat well.
5. Dry at 103°C for one hour.
6. If volatile suspended solids are to be determined, ignite
crucible in muffle furnace for one hour at 550°C.
7. Cool in desiccator.
8. Weigh and record tare weight.
F. How to Perform the Test
1. Depending on the suspended solids content, measure out a
25, 50, or 100 ml portion of a well mixed sample into a
graduated cylinder. Use 25 ml if sample filters slowly.
Use larger volumes of sample if samples filter easily,
such as secondary effluent. Try to limit filtration time
to about 15 minutes or less.
2. Wet prepared Gooch crucible with distilled water and apply
suction.
3. Filter sample through the Gooch crucible.
4. Wash out dissolved solids on the filter with about 20 ml
of distilled water. (Use two 10 ml portions.)
5. Dry crucible at 103°C for one hour or other specified time.
Some samples may require up to three hours to dry if the
residue is thick.
6. Cool crucible in desiccator for 20-30 minutes.
7. Weigh and record weight.
8. Total Weight = g
Tare Weight = g
Solids Weight = g
14-158
-------
(Suspended Solids - Gooch)
G. Precautions
1. Check and regulate the oven temperature at 103° - 105°C.
2. Observe crucible and glass fiber for any possible leaks. A
leak will cause solids to pass through and give low results.
The glass fiber filter may become unseated and leaky when the
crucible is placed on the filter flask. The filter should be
reseated by adding distilled water to the filter in the crucible
and applying vacuum before filtering the sample.
3. Mix the sample thoroughly so that it is completely uniform in
suspended solids when measured into a graduated cylinder before
sample can settle out. This is especially true of samples heavy
in suspended solids, such as raw wastewater and mixed liquor in
activated sludge which settle rapidly. The test can be no better
than the mix.
4. It is a good practice to prepare a number of extra Gooch crucibles
for additional tests if the need arises. If a test result appears
faulty or questionable, the test should be repeated. Check filtration
rate and clarity of water passing through the filter.
H. Example and Calculations
This section is provided to show you the detailed calculations. After
some practice, most operators use the lab work sheet as shown at the
end of the calculations.
CALCULATIONS FOR SUSPENDED SOLIDS TEST
(or use lab work sheet at end of calculations)
Example: Assume the following data.
Volume of sample = 50 ml.
Recorded Weights
Crucible weight 21.6329 g
Crucible plus dry solids 21.6531 g
Crucible plus ash11 21.6360 g
11 Obtained by placing the crucible plus dry solids in a muffle
furnace at 550°C for one hour. The crucible plus remaining
ash are cooled and weighed.
14-159
-------
(Suspended Solids - Gooch)
1. Compute total suspended solids.
21.6531 g
- 21.6529 g
Weight of Crucible plus Dry Solids, grams
- Weight of Crucible, grams
= 0.0202 g
or
= 20.2 mg
1000 milligrams (mg)
or
20.2 mg = 0.0202 g
= Weight of Dry Solids, grams
1 gram (g)
Total
Suspended
Solids,
mg/1
Weight^ of Dry Solids, mg x 1000 ml/1
Sample Volume, ml
= 20.2 mg x
= 404 mg/1
1000 ml/1
50 ml
_
50/~20200.
200
200
200
2. Compute volatile or organic suspended solids.
21.6531 g
- 21.6360 g
= 0.0171 g
or
= 17.1 mg
Weight of Crucible plus Dry Solids,
- Weight of Crucible jplus Ash, g
= Weight of Volatile Solids, g
Volatile
Suspended
Solids,
mg/1
Weight of Volatile Solids^, mg x 1000 ml/1
Sample Volume, ml
17.1 mg x 1000 ml/1
50 ml
= 342 mg/1
342
50/ 17100
150
210
200
100
100
14-160
-------
(Suspended Solids - Gooch)
3. Compute the percent volatile solids.
Volatile _ [Weight Volatile, mg) 100%
Solids, % Weight Total Dry Solids, mg
17.1 mg
20.2 mg
x 100%
= 84.7%
.8465
20.2 / 17.10
16 16
940
808
1320
1212
1080
1010
4. Compute fixed or inorganic suspended solids.
21.6360 g
- 21.6329 g
= 0.0031 g
or
= 3.1 mg
Weight of Crucible plus Ash,
- Weight of Crucible, g
= Weight of Fixed Solids, g
Fixed
Suspended
Solids,
mg/1
Weight of Fixed Solids, mg x 1000 ml/1
Sample Volume, ml
3.1 ing x 1000 ml/1
50 ml
= 62 mg/1
To check your work:
Fixed Susp. Solids
Total Susp. Solids, mg/1 - Volatile
Susp. Solids, mg/1
= 404 mg/1 - 342 mg/1
= 62 mg/1 (Check)
404
-342
62
14-161
-------
(Suspended Solids - Gooch)
5. Compute the percent fixed solids.
Fixed Solids, % = (Weight Fixed, mg? x 100%
Weight Total, mg
x 100%
20.2 mg
= 15 . 3%
The above calculations are also performed on a Laboratory Work
Sheet (Fig. 14.7) to illustrate the use of the work sheet.
CALCULATIONS FOR OVERALL PLANT REMOVAL OF
SUSPENDED SOLIDS IN PERCENT
Example : Assume the following data.
Influent suspended solids 202 mg/1
Primary Effluent suspended solids 110 mg/1
Secondary Effluent suspended solids 52 mg/1
Final Effluent suspended solids 12 mg/1
To calculate the percent removal or treatment efficiency for a
particular process or the overall plant, use the following formula:
Removal, % = CIn " x 100
In
Compute percentage removed between influent and primary effluent:
(.I.n .".
Removal, % = ... .". x 100%
In
- (202 mg/1 - 110 mg/1) x %
202 mg/1
= -22. x 100% 202
202 -110
92
= 45.5%
14-162
-------
(Suspended Solids - Gooch)
Compute percentage removed between influent and secondary effluent;
Removal, % = (In - Out) x 100%
In
=
UU2 mg/1 - bZ mg/lj 0,
202 mg/1
150 inr,o. -74
••• * x lull's /
202 202/ 150.00
141.4
8 60
74% s 08
52
202
-52
150
Compute percentage removed between influent and final effluent
(overall plant percentage removed) :
Removal, % = (In - Out) x 1QO%
In
= (202 mg/1 - 12. mg/1) x 1(JO%
202 mg/1
x 100%
202
= 94.1% removal for the plant in suspended solids
CALCULATIONS FOR POUNDS SUSPENDED SOLIDS REMOVED PER DAY
Example: Assume the following data.
Influent suspended solids 200 mg/1
Effluent suspended solids 10 mg/1
Flow in million gallons/day 2 MGD
1 gallon of water weighs 8.34 Ibs
14-163
-------
(Suspended Solids - Gooch)
Compute pounds suspended solids removed:
The general formula for computing pounds removed is
Mfl "I" ^ T* "1 3 1
A (Concentration In, mg/1 - Concentration Out, mg/1)
Removed, —
Ibs/day x Flow, MGD x 8.34 Ib/gal
(200 mg/1 - 10 mg/1) x 2 MGD x 8.34 Ib/gal
= 190 x 2 x 8.34
= 3169 Ibs/day of suspended
solids removed by plant
8.34
380
000
6672
2502
3169.20
DERIVATION
This section is not essential to efficient plant operation, but is
provided to furnish you with a better understanding of the calcu-
lation if you are interested. For practical purposes,
1 mg/1 = 1 ppm or 1 part per million
or =1 mg/million mg, because 1 liter = 1,000,000 mg
Therefore:
Ibs _ mg M gal Ibs
day M mg day gal
= Ibs/day
14-164
-------
(Suspended Solids - Gooch)
PLANT
DATE
CLEAN WATER
SUSPENDED SOLIDS $ DISSOLVED SOLIDS
SAMPLE
Crucible
Ml Sample
Wt Dry S Dish
Wt Dish
Wt Dry
/I = Wt Dry, gm x 1,000,000
Wt Dish
Wt Dish
Ml Sample
Dry
Ash
Wt Volatile
vol = - x 100%
Wt Dry
INFL.
#015
50
21.6531
21.6329
0.0202
404 mg/1
21.6531
21.6360
0.0171
84.
BOD
# Blank
SAMPLE
DO Sample
Bottle #
% Sample
Blank or adj blank
DO after incubation
Depletion, 5 days
Dep %
Nitrate N03
S amp le
Graph Reading
Sett. Solids
Sample
Direct 'Ml/1
COD
Sample
Blank Titration
Sample Titration
Depletion
, _ Pep x N FAS x 8000
Ml Sample
Fig. 14.7 Calculation of solids content
on Laboratory Work Sheet
14-165
-------
(Suspended Solids - Gooch)
TOTAL SOLIDS
AMPLE
Dish No.
Wt Dish 5 Wet
Wt Dish
Wt Wet
Wt Dish + Dry
Wt Dish
Wt Dry
o, * nd_ _ Wt Dry x 100%
Wt Wet
Wt Dish + Dry
Wt Dish + Ash
Wt Volatile
„..,.., Wt Vol x 100%
Wt Dry
pH
Vol. Acid
Alkalinity as CaC03
Grease (Soxlet)
Sample
Ml Sample
Wt Flask + Grease
Wt Flask
Wt Grease
, _ Wt Grease, mg x 1000
mg ~ Ml Sample
H2S (Gas) (Starch-Iodine)
Blank
Sample
Diff
Diff x .68
mg/1 x 43.6
Ml
.Ml
Ml
mg/1
grain/100 cu ft
Fig. 14.7 Calculation of solids content on
Laboratory Work Sheet (continued)
14-167
-------
QUESTIONS
16.A Why does some of the suspended material in wastewater fail
to be removed by settling or flotation within one hour?
16.B Given the following data:
100 ml of sample
Crucible weight 19.3241 g
Crucible plus dry solids 19.3902 g
Crucible plus ash 19.3469 g
Compute:
a. Total suspended solids
b. Volatile suspended solids
c. Percent volatile
d. Fixed suspended solids
e. Percent fixed
16.C Compute the percent removal of suspended solids by the
primary clarifier, secondary process (removal between
primary effluent and secondary effluent), and overall
plant:
Influent suspended solids = 221 mg/1
Primary effluent SS = 159 mg/1
Final effluent SS = 33 mg/1
16.D If the data in problem 16.C is from a 1.5 MGD plant,
calculate the pounds of suspended solids removed:
a. By the primary unit
b. By the secondary unit
c. By the overall plant
14-169
-------
16. Suspended Solids
II. CENTRIFUGE
A. Discussion
This procedure is frequently used in plants as a. quick and easy
method to estimate the suspended solids concentration of the
mixed liquor in the aeration tank instead of the regular suspended
solids test. Many operators control the solids in their aerator
on the basis of centrifuge readings. Others prefer to control
solids using Fig. 14.8. In either case, the operator should
periodically compare centrifuge readings with values obtained
from suspended solids tests. If the solids are in a good settling
condition, a 1% centrifuge solids reading could have a suspended
solids concentration of 1000 mg/1. However, if the sludge is
feathery, a 1% centrifuge solids reading could have a suspended
solids concentration of 600 mg/1.
The centrifuge reading versus mg/1 suspended solids chart (Fig 14.8)
:must be developed for each plant by comparing centrifuge readings
with suspended solids determined by the regular Gooch crucible
method. The points are plotted and a line of best fit is drawn
as shown in Fig. 14.8. This line must be periodically checked by
comparing centrifuge readings with regular suspended solids tests
because of the large number of variables influencing the relation-
ship, such as characteristics of influent waste, mixing in aerator,
and organisms in aerator. If you don't have a centrifuge or if
your solids content is over 1500 mg/1, determine suspended solids
by the re-gular method.
B. What is Tested?
Sample Common Range
Suspended Solids in Mechani- 800 - 1200 mg/1
cal Aeration Tanks
Suspended Solids in Diffused 1000 - 3000 mg/1
Aeration Tanks
C. Apparatus
1. Centrifuge.
2. Graduated centrifuge tubes, 15 ml.
14-171
-------
(Suspended Solids - Centrifuge)
D. Reagents
None.
E. Procedure
1. Collect sample in regular sampling can.
2. Mix sample well and fill each centrifuge tube to the 15 ml
line with sample.
3. Place filled sample tubes in centrifuge holders.
4. Crank centrifuge at fast speed as you count slowly to 60.
Be sure tc count and crjmk at the same speed for all tests.
It is extremely important to perform each step exactly the
same every time.
5. Remove one tube and read the amount of suspended solids con-
centrated in the bottom of the tube. This reading will be
1/10 of ml. Results in other tubes should be compared.
6. Refer to the conversion graph to determine suspended solids
in mg/1.
NOTE: The reason for filling tubes to the 15 ml mark is that the
graph (Fig. 14.8) is computed for samples of this size.
F. Example
Suspended solids concentration on bottom of centrifuge tube is 0.4 ml.
G. Calculations
From Fig. 14.8, find 0.4 ml on centrifuge reading side and follow
line horizontally to line on chart. Drop downward from line on chart
to mg/1 suspended solids and read result of 900 mg/1.
If the suspended solids concentration is above or below the desired
range, then you should make the proper changes in the pumping rate
of the waste and return sludge. For details on controlling the solids
concentration, refer to Chapter 7, Activated Sludge.
14-172
-------
0.4 •
0.3 -
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en
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en
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0.1 *
I
®
.....
xl
;an
ius
)en
xi
ipl
pe
!S/
ide
t7i]fu(j
x
Lir
X
rte;
d
e \
e (
x
ISL
Ol
.III
\n
x
Q
1
re<
ds
dge
es
,x
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Ifc
an
R
:F
X
r
d
iad
t
i
.**
r'
inc
X
x^
x'
_^!
X^
6
X
>.
•*•
x
I
_^
X
X
^
X
-------
(Suspended Solids - Centrifuge)
H. Development of Fig. 14.8
To develop Fig. 14.8 take a sample from the aeration tank and
measure suspended solids and also centrifuge a portion of the
sample to obtain the centrifuge sludge reading in ml of sludge
at the bottom of the tube. Obtain other samples of different
solids concentrations to obtain the points on the graph. Draw
a line of best fit through the points. Periodically the points
should be checked because the influent characteristics and con-
ditions in the aeration tank change.
QUESTION
16.E What is the advantage of the centrifuge test
for determining suspended solids in an aeration
tank in comparison with other methods of measuring
suspended solids?
14-174
-------
17. Temperature
I. WASTEWATER
A. Discussion
This is one of the most frequently taken tests. One of the many
uses is to calculate the percent saturation of dissolved oxygen
in the DO test. (Refer to DO Test for procedure.)
Changes of plus or minus 4°F from the average or expected value
should be investigated and the cause corrected if possible.
For example, an influent temperature drop may indicate large
volumes of cold water from infiltration. An increase in temperature
may indicate hot water discharged by industry is reaching your plant.
A temperature measurement should be taken where samples are
collected for other tests. This test is always immediately
performed on a grab sample because it changes so rapidly.
Always leave the thermometer in the liquid while reading
the temperature. Record temperature on suitable work sheet,
including time, location, and sampler's name.
B. What is Tested?
Sample Common Range
Influent12 65 °F to 85°F13
Effluent12 60 °F to 95°F or
higher from ponds
Receiving Water12 60°F to ambient
temperature14
Digester (Recirculated 60°F to 100°F
Sludge before Heat Ex-
changer- -Supernatant)
12 If dissolved oxygen (DO) measurements are performed on any
samples, the temperature should be measured and recorded.
13 Depends on season, location, and temperature of water supply.
llf Ambient Temperature (AM-bee-ent) . Temperature of the
surroundings.
14-175
-------
(Temperature)
C. Apparatus
1. One NBS (National Bureau of Standards) thermometer for
calibration of the other thermometers.
2. One Fahrenheit mercury-filled, 1° subdivided thermometer.
3. One Celsius (formerly called Centigrade) mercury-filled,
1° subdivided thermometer.
4. One metal case to fit each thermometer.
There are three types of thermometers and two scales.
Scales
1. Fahrenheit, marked °F.
2. Celsius, marked °C (formerly Centigrade).
Thermometers
1. Total immersion. This type of thermometer must be totally
immersed when read. This will change most rapidly when
removed from the liquid to be recorded.
2. Partial immersion. This type thermometer will have a solid
line around the stem below the point where the scale starts.
3. Dial. This type has a dial that can be easily read while
the thermometer is still immersed. Dial thermometer readings
should be checked (calibrated) against the NBS thermometer.
Some dial thermometers can be recalibrated (adjusted) to read
the correct temperature of the NBS thermometer.
D. Reagents
None.
14-176
-------
(Temperature)
E. Procedures
Use a large volume of sample, preferably at least a 2-pound coffee
can or equivalent volume. The temperature will have less chance
to change in a large volume than in a small container. Collect
sample in container and immediately measure and record temperature.
Do not touch the bottom or sides of the sample container with the
thermometer. To avoid breaking or damaging glass thermometer,
store it in a shielded metal case. Check your thermometer accuracy
against the MBS certified thermometer by measuring the temperature
of a sample with both thermometers simultaneously. Some of the
poorer quality thermometers are substantially inaccurate (off as
much as 6°F).
F. Example
To measure influent temperature, obtain sample in large coffee can,
immediately immerse thermometer in can, and record temperature when
reading becomes constant. For example, 72°F.
G. Galculati ons
Normally, we measure and record temperatures using a thermometer
with the proper scale. However, we could measure a temperature in
°F and convert to °C, or we might measure a temperature in °C and
convert to °F. The following formulas are used to convert tempera-
tures from one scale to the other.
1. Measure in °F, want °C:
°C = 5/9 (°F - 32°)
2. Measure in °C, want °F:
°F = 9/5 (°C) + 32°
3. Example Calculation:
The measured influent temperature was 77°F.
What was the temperature in °C?
14-177
-------
(Temperature)
°C = 5/9 (OF - 32°)
77
= 5/9 (77° - 32°) -32_
45
= 5/9 (45°) __5
9 /45
= 25° 5
xl-
25"
QUESTIONS
17.A What could a change in influent temperature indicate?
17.B Why should the thermometer remain immersed in the
liquid while being read?
17.C Why should thermometers be calibrated against an
accurate NBS certified thermometer?
14-178
-------
17. Temperature
II. DIGESTER SLUDGE
A. Discussion
The rate of sludge digestion in a digester is a function of the
digester temperature. The normal temperature range in a digester
is around 95 to 98°F. The temperature of a digester should not
be changed by more than 1°F per day because then the helpful
organisms in the digester are unable to adjust to rapid temperature
changes.
B. Apparatus and Procedure
Refer to I., WASTEWATER.
END OF LESSON 7 OF 8 LESSONS
on
Laboratory Procedures and Chemistry
Work the next portion of the discussion and review questions
before continuing with Lesson 8.
14-179
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 7 of 8 Lessons)
Chapter 14. Laboratory Procedures and Chemistry
Name
Date
Write the answers to these questions in your notebook.
numbering continues from Lesson 6.
The problem
27. Given the following data:
100 ml of sample
Crucible weight
Crucible plus dry solids
Crucible plus ash
Compute:
1. Total suspended solids
2. Volatile suspended solids
3. Percent volatile
28.
29,
30,
31,
19.9850 g
20.0503 g
20.0068 g
Estimate the pounds of solids removed per day by a primary
clarifier if the influent suspended solids is 220 mg/1 and
the effluent suspended solids is 120 mg/1 when the flow is
1.5 MGD.
What is the ambient temperature?
Convert a temperature reading of 50°F to °C.
Why should the temperature of a digester not be changed by
more than 1°F per day?
14-181
-------
CHAPTER 14. LABORATORY PROCEDURES AND CHEMISTRY
(Lesson 8 of 8 Lessons)
18. Total and Volatile Solids (Sludge)
A. Discussion
Total solids measure the combined amount of suspended and dissolved
materials in the sample.
This test is used for wastewater sludges or where the solids can be
expressed in percentages by weight and the weight can be measured
on an inexpensive beam balance to the nearest .01 of a gram. The
total solids are composed of two components, volatile and fixed
solids. Volatile solids are composed of organic compounds which
are of either plant or animal origin. Fixed solids are inorganic
compounds such as sand, gravel, minerals, or salts.
B. What is Tested?
Sample
Raw Sludge
Raw Sludge plus Waste
Activated Sludge
Recirculated Sludge
Supernatant :
Good Quality, has
Suspended Solids
Poor Quality
Digested Sludge
to Air Dry
COMMON RANGE, % BY WEIGHT
Total
6% to 9%
2% to 5%
1.5% to 3%
Volatile
75%
80%
75%
Fixed
25% ± 6%
20% ± 5%
25% ± 5%
< 1%
> 5%
3% too Thin
to < 8%
503
503
50% ± 10°
50% ±
14-183
-------
(Total and Volatile Solids)
C. Apparatus
1. Evaporating dish.
2. Analytical balance.
3. Drying oven, 103° - 105°C.
4. Measuring device—graduated cylinder.
5. Muffle furnace, 550°C.
D. Outline of Procedure
f
1. Ignite empty dish
in muffle furnace
4. Measure out
sludge
2. Cool
3. Weigh
dish
5. Evaporate water at
103-105°C
\
7. Weigh dish
+ residue
6. Cool dish
+ residue
14-184
-------
(Total and Volatile Solids)
PROCEDURE
1. Dry the dish by ignition in a muffle furnace at 550°C for
one hour. Cool dish in desiccator.
2. Tare the evaporating dish to the nearest 10 milligrams, or
0.01 g on the Mettler single pan balance. Record the weight
as Tare Weight = ^ gms.
3. Weigh dish plus 50 to 100 ml of well mixed sludge sample.
Record total weight to nearest 0.01 gram as Gross Weight =
gms.
4. Evaporate the sludge sample to dryness in the 103°C drying
oven.
5. Weigh the dried residue in the evaporating dish to the
nearest 10 milligrams, or 0.01 g. Record the weight as
Dry Sample and Dish = ^ gms.
6. Compute the net weight of the residue by subtracting the
tare weight of the dish from the dry sample and dish.
E. Precautions
1. Be sure that the sample is thoroughly mixed and is representative
of the sludge being pumped. Generally, where sludge pumping is
intermittent, sludge is much heavier at the beginning and is less
dense toward the end of pumping. Take several equal portions of
sludge at regular intervals and mix for a good sample.
2. Take a large enough sample. Measuring a 50 or 100 ml sample
which is closely equal to 50 or 100 grams is recommended.
Since this material is so heterogeneous (non-uniform), it is
difficult to obtain a good representative sample with less
volume. Smaller volumes will show greater variations in answers,
due to the uneven and lumpy nature of the material.
3. Control oven temperature closely at 103° - 105°C. Some solids
are lost at any drying temperature. Close control of oven
temperatures increase the losses of volatile solids in addition
to the evaporated water.
14-185
-------
(Total and Volatile Solids)
Heat dish long enough to insure evaporation of water,
usually about 3-4 hours. If heat drying and weighing
are repeated, stop when the weight change becomes small
per unit of drying time. The oxidation, dehydration,
and degradation of the volatile fraction won't completely
stabilize until it is carbonized or becomes ash.
Since sludge is so non-uniform, weighing on the analytical
balance should probably be made only to the nearest 0.01
grams or 10 milligrams.
Ou11ine of P r o cedure for V o 1atile Solids
(continue from total solids test)
1. Ignite dried solids
at 550°C
2. Cool
3. Weigh fixed solids
1.
2.
3.
4.
PROCEDURE
Determine the total solids as previously described in Section D.
Ignite the dish and residue from total solids test at 550 °C for
one hour or until a white ash remains.
Cool in desiccator for about 30 minutes.
Weigh and record weight of Dish Plus Ash =
gms,
14-186
-------
(Total and Volatile Solids)
G. Example
Weight of Dish (Tare) = 20.31 g
Weight of Dish plus
Wet Solids (Gross) = 70.31 g
Weight of Dish plus
Dry Solids = 22.81 g
Weight of Dish plus Ash = 20.93 g
H. Calculations
See Laboratory Work Sheet (Fig. 14.9) or calculations shown below,
1. Find weight of sample.
Weight of Dish plus Wet Solids (Gross) = 70.31 g
Weight of Dish (Tare) = 20.31 g
Weight of Sample = 50.00 g
2. Find weight of total solids.
Weight of Dish plus Dry Solids = 22.81 g
Weight of Dish (Tare) = 20.31 g
Weight of Total Solids = 2.50 g
3. Find % solids.
% Solids = (Weight of Solids, g) 100%
Weight of Sample, g
(2.50 g) 100%
50.00 g
= 5%
4. Find weight of volatile solids.
Weight of Dish plus Dry Solids = 22.81 g
Weight of Dish plus Ash = 20.93 g
Weight of Volatile Solids = 1.88 g
14-187
-------
(Total and Volatile Solids)
5. Find % volatile solids.
% Volatile Solids = (Weight of Volatile Solids, g) 100%
Weight of Total Solids, g
(1.88 g) 100%
2.50 g
= 76%
QUESTION
18.A What is the origin of the volatile solids found in a
digester?
18.B What is the significance of volatile solids in a
treatment plant?
19. Turbidity
See Clarity.
14-188
-------
(Total and Volatile Solids)
PLANT
DATE
SUSPENDED SOLIDS $ DISSOLVED SOLIDS
SAMPLE
Crucible
Ml Sample
Wt Dry § Dish
Wt Dish
Wt Dry
/;L _ Wt Dry, gm x 1,000,000
Ml Sample
Wt Dish $ Dry
Wt Dish § Ash
Wt Volatile
o, Vol _ Wt Vol „
Wt Dry
BOD
# Blank
SAMPLE
DO Sample
Bottle #
% Sample
Blank or adj blank
DO after incubation
Depletion, 5 days
Dep %
Nitrate N03
Sample
Graph Reading
COD
Sample
Blank Titration
Sample Titration
Depletion
,, Dep x N FAS x 8000
mg/1 = f . .
Ml Sample
Sett. Solids
Sample
Direct Ml/1
Fig. 14.9 Calculation of total solids
on Laboratory Work Sheet
14-189
-------
(Total and Volatile Solids)
TOTAL SOLIDS
SAMPLE
Dish No.
Wt Dish § Wet
Wt Dish
Wt Wet
Wt Dish + Dry
Wt Dish
Wt Dry
«• Solid" - Wt Dry x 100%
Wt Wet
Wt Dish + Dry
Wt Dish + Ash
Wt Volatile
* Volatile - Wt Vo1 x 100%
Wt Dry
pH
Vol. Acid
Alkalinity as CaC03
RAW
7
70.31
20.31
50.00
22.81
20.31
2.50
5.0%
22.81
20.93
1.88
76%
Grease (Soxlet)
Sample
Ml Sample
Wt Flask + Grease
Wt Flask
Wt Grease
mg/1 - Wt Grease>
x 100°
Ml Sample
H2S (Gas) (Starch-Iodine)
Blank
Sample
Diff
Diff x .68
mg/1 x 43.6
Ml
Ml
Ml
mg/1
grain/100 cu ft
Fig. 14.9 Calculation of total solids on
Laboratory Work Sheet (continued)
14-191
-------
20. Volatile Acids and Total Alkalinity
A. Discussion
Volatile acids are determined on sludge samples from the digesters.
Most modern digesters have sampling pipes where you can draw a
sample from various levels of the tank. Be sure to allow the
sludge in the line to run for a few minutes in order to obtain a
representative sample of the digester contents. Samples also may
be collected from supernatant draw-off tubes, or thief holes.15
The concentrations of volatile acids and alkalinity are the first
measurable changes that take place when the process of digestion
is becoming upset. The volatile acid/alkalinity relationship can
vary from 0.1 to about 0.5 without significant changes in digester
performance. When the relationship starts to increase, this is a
warning that undesirable changes will occur unless the increase is
stopped. If the relationship increases above 0.5, the composition
of the gas produced can change very rapidly, followed by changes
in the rate of gas production, and finally pH.
In a healthy and properly functioning digester, the processes or
biological action taking place inside the digester are in equilibrium.
When fresh sludge is pumped into a digester, some of the organisms
in the digester convert this material to volatile (organic) acids.
In a properly operated digester, other organisms feed on the newly
produced volatile acids and eventually convert the acids to methane
(CHiJ gas, which is burnable and carbon dioxide (C02). If too much
raw sludge is pumped to the digester or the digester is not function-
ing properly, an excess of volatile acids are produced. If excessive
amounts of volatile acids are produced, an acid environment unsuitable
for some of the organisms in the digester will develop and the digester
may cease to function properly unless the alkalinity increases too.
Routine volatile acids and alkalinity determinations during the
start-up process for a new digester are a must in bringing the
digester to a state of satisfactory digestion.
Routine volatile acids and alkalinity determinations during digestion
are important in providing the information which will enable the
operator to determine the health of the digester.
15 Thief Hole. A digester sampling well.
14-193
-------
(Volatile Acids and Total Alkalinity)
For digester control purposes, the volatile acid/alkalinity relation-
ship should be determined. When the volatile acid/alkalinity
relationship is from less than 0.1/1.0 to 0.5/1.0, the loading and
seed retention of the digester are under control. When the relation-
ship starts increasing and becomes greater than 0.5/1.0, the digester
is out of control and will become "stuck" unless effective corrective
action is taken.
B. What is Tested?
Sample Desirable Range
Recirculated Sludge 150 - 600 mg/1
(expect trouble if alkalinity less than
two times volatile acids)
METHOD A
(Silic Acid Method)
C. Apparatus
1. Centrifuge or filtering apparatus.
2. Two 50 ml graduated cylinders.
3. Two medicine droppers.
4. Crucibles, Gooch or fritted glass
5. Filter flask
6. Vacuum source
7. One 50 ml beaker
8. Two 5 ml pipettes
9. Buret
14-194
-------
(Volatile Acids and Total Alkalinity)
D. Reagents
1. Silic acid, solids, 100-mesh. Remove fines from solid
portion of acid by slurrying the acid in distilled water
and removing the supernatant after allowing settling for
15 minutes. Repeat the process several times. Dry the
washed acid solids in an oven at 103°C and then store in
a desiccator.
2. Chloroform-butanol reagent. Mix 300 ml chloroform, 100 ml
n-butanol, and 80 ml 0.5 N F^SO^ in separatory funnel and
allow the water and organic layers to separate. Drain off
the lower organic layer through filter paper into a dry
bottle.
3. Thymol blue indicator solution. Dissolve 80 mg thymol
blue in 100 ml absolute methanol.
4. Phenolphthalein indicator solution. Dissolve 80 mg
phenolphthalein in 100 ml absolute methanol.
5. Sulfuric acid, 10 N.
6. Standard sodium hydroxide reagent, 0.02 N. Prepare in
absolute methanol from cone. NaOH stock solution in water.
14-195
-------
fVolatile Acids and Total Alkalinity)
E. Outline of Procedure
3. Add a
few drops
of thymol
blue.
4. Add
10 N
dropwise until
turns thymol
blue.
1. Separate solids by
centrifuging or
filtering sample.
2. Measure 10-15 ml
of sample into
beaker.
6. Add 5 ml
acidified
sample.
7. Add 50 ml
chloroform-butanol
5. Place 10 g silic
acid in crucible
and apply suction,
Apply suction until
all of reagent has
entered solid acid
column.
9. Remove filter flask,
10. Add a few
drops of
phenolphthalein
11. Titrate with
0.02N NaOH.
14-197
-------
[Volatile Acids and Total Alkalinity)
PROCEDURE
1. Centrifuge or filter enough sludge to obtain a sample of
10 to 15 ml. This same sample and filtrate should be
used for both the volatile acids test and the total
alkalinity test.
2. Measure volume (10 to 15 ml) of sample and place in a
beaker.
Volume of sample, B = _ ml.
3. Add a few drops of thymol blue indicator solution.
4. Add 10 N I-^SO^, dropwise, until red color just turns
to thymol blue color.
5. Place 10 grams of silic acid (solid acid) in crucible
and apply suction. This will pack the acid material
and the packed material is sometimes called a column.
6. With a pipette, distribute 5.0 ml acidified sample
(from step 4) as uniformly as possible over the column.
Apply suction briefly to draw the acidified sample into
the silic acid column. Release the vacuum as soon as
the sample enters the column.
7. Quickly add 50 ml chloroform-butanol reagent to the column.
8. Apply suction and stop just before the last of the reagent
enters the column.
9. Remove the filter flask from the crucible.
10. Add a few drops of phenolphthalein indicator solution to
the liquid in the filter flask.
11. Titrate with 0.02 N NaOH titrant in absolute methanol, taking
care to avoid aerating the sample. Nitrogen gas or C02 - free
air delivered through a small glass tube may be used both to
mix the sample and to prevent contact with atmospheric C02
during titration (C02 - free air may be obtained by passing
air through ascarite or equivalent) .
Volume of NaOH used in sample titration, a = _ ml.
12. Repeat the above procedure using a blank of distilled water.
Volume of NaOH used in blank titration, b = _ ml.
14-198
-------
(Volatile Acids and Total Alkalinity)
F. Precautions
1. The sludge sample must be representative of the digester.
The sample line should be allowed to run for a few minutes
before the sample is taken. The sample temperature should
be as warm as the digester itself.
2. The sample for the volatile acids test should not be taken
immediately after charging the digester with raw sludge.
Should this be done, the raw sludge may short-circuit to
the withdrawal point and result in the withdrawal of raw
sludge rather than digested sludge. Therefore, after the
raw sludge has been fed into the tank, the tank should be
well mixed by recirculation or other means before a sample
is taken.
3. If a digester is performing well with low volatile acids
and then if one sample should unexpectedly and suddenly
give a high value, say over 1000 mg/1 of volatile acids,
do not become alarmed. The high result may be caused by
a poor, nonrepresentative sample of raw sludge instead
of digested sludge. Resample and retest. The second
test may give a more typical value. When increasing
volatile acids and decreasing alkalinity are observed,
this is a definite warning of approaching control problems.
Corrective action should be taken immediately, such as
reducing the feed rate, reseeding from another digester,
maintaining optimum temperatures, improving digester mixing,
decreasing sludge withdrawal rate, or cleaning the tank
of grit and scum.
14-199
-------
(Volatile Acids and Total Alkalinity)
G. Example
Equivalent Weight of Acetic Acid, A =60 mg/ral
Volume of Sample, B = 10 ml
Normality of NaOH titrant, N = 0.02 N
Volume of NaOH used in sample titration, a = 2.3 ml
Volume of NaOH used in blank titration, b = 0.5 ml
H. Calculation
Volatile Acids, mg/1 _ A x 1000 ml/1 x N (a - b)
(as acetic acid) B
60 mg/ml x 1000 ml/1 x 0.02 (2.3 ml - 0.5 ml)
10 ml
= 216 mg/1
METHOD B
(Nonstandard Titration Method)
C. Apparatus
1. One pH meter.
2. One adjustable hot plate.
3. Two Burets and stand.
4. One 100 ml beaker.
D. Reagents
1. pH 7.0 buffer solution
2. pH 4.0 buffer solution
3. Standard acid.
4. Standard-base.
14-200
-------
E. Outline of Procedure
(Volatile Acids and Total Alkalinity)
1. Separate solids by
centrifuging or re-
moving water above
settled sample.
r\
m
2.
Measure
50 ml §
place in
beaker.
3. Titrate with
sulfuric acid
to a pH of
4.0.
4. Note acid used
and continue
titrating to
pH 3.5 to 3.3.
5. Lightly boil
sample for
3 minutes.
6. Cool in water bath.
Titrate to pH of 4.0,
with 0.05 N NaOH, note
buret reading, and com-
plete titration to a pH
of 7.0.
14-201
-------
(Volatile Acids and Total Alkalinity)
PROCEDURE
1. Buffer the pH meter at 7.0 and check pH before treatment
of sample to remove the solids. Filtration is not necessary.
Decanting (removing water above settled material) or centri-
fuging sample is satisfactory. Do not add any coagulant aids,
2. Titrate 50 ml of the sample in a 100 ml beaker to pH 4.0
with the appropriate strength sulfuric acid (depends on
alkalinity), note acid used, and continue to pH 3.5 to 3.3.
A magnetic mixer is extremely useful for this titration.
3. Carefully buffer pH meter at 4.00 while lightly boiling the
sample a minimum of three minutes. Cool in cold water bath
to original temperature.
4. Titrate sample with standard 0.050 N sodium hydroxide up to
pH 4.00, and note buret reading. Complete the titration at
pH 7,0. (If this titration consistently takes more than
10 ml of the standard hydroxide, use 0.100 N NaOH.)
5. Calculate volatile acid alkalinity (alkalinity between pH
4.0 and 7.0).
Volatile Acid ml 0.050 N NaOH x 2500
Alkalinity mi Sample
For a 50 ml sample the volatile acid alkalinity equals
50 x ml 0.050 N NaOH, or 100 x ml 0.100 N NaOH.
6. Calculate volatile acids.
Case 1: > 180 mg/1 volatile acid alkalinity.
Volatile Acids = Volatile Acid Alkalinity x 1.50
Case 2: < 180 mg/1 volatile acid alkalinity.
Volatile Acids = Volatile Acid Alkalinity x 1.00
Steps 1 and 2 will give the analyst the pH and total alkalinity,
two control tests normally run on digesters. The difference
between the total and the volatile acid alkalinity is bicarbonate
alkalinity. The time required for Steps 3 and 4 is about ten
minutes.
This is an acceptable method for digester control to determine
the volatile acid/alkalinity relationship, but not of sufficient
accuracy for research work.
14-202
-------
(Volatile Acids and Total Alkalinity)
For details regarding this test see DeLallo, R. , and Albertson,
O.E., Volatile Acids by Direct Titration, Water Pollution Control
Federation, Vol. 33, No. 4, pp 356-365, April 1961. The procedure
is reproduced from the article.
F. Example and Calculation
Titration of pH 4.0 to 7.0 of a 50 ml sample required 8 ml of
0.05 N NaOH.
Step 5 - Calculate volatile acid alkalinity (alkalinity between
pH 4.0 and 7.0).
Volatile Acid _ ml 0.05 N NaOH x 2500
Alkalinity, mg/1 ~ ml Sample
8 ml x 2500
50 ml
= 400 mg/1
Step 6 - Calculate volatile acids.
Case 1: 400 mg/1 > 180 mg/1. Therefore,
. ., ,, = Volatile Acid Alkalinity x 1.50
Acids, mg/1
= 400 mg/1 x 1.50
= 600 mg/1
QUESTION
20.A What is the volatile acid concentration in a
digester if a 50 ml sample required 5 ml of 0.05 N
NaOH for a titration from a pH of 4.0 to 7.0?
14-203
-------
(Volatile Acids and Total Alkalinity)
Total Alkalinity
A. Discussion
Tests for total alkalinity of digesters are normally run on settled
supernatant samples. The alkalinity of the recirculated sludge is
a measure of the buffer capacity in the digester. When organic
matter in a digester is decomposed anaerobically, organic acids
are formed which could lower the pH, if buffering materials
(buffer capacity) were not present. If the pH drops too low, the
organisms in the digester could become inactive or die and the
digester becomes upset (no longer capable of decomposing organic
matter).
For digester control purposes, the volatile acid/alkalinity relation-
ship should be determined. When the volatile acid/alkalinity
relationship is from less than 0.1/1.0 to 0.5/1.0, the loading and
seed retention of the digester are under control. When the relation^
ship starts increasing and becomes greater than 0.5/1.0, the digester
is out of control and will become stuck unless effective corrective
action is taken. The pH will not be out of range as long as the
volatile acid/alkalinity relationship is low. This relationship
gives a warning before trouble starts.
All samples must be settled so that a liquid free of solids is available
for the test. Tests cannot be calculated correctly if solids are in
the sample.
B. What is Tested?
Sample Common Range
Recirculated Sludge 2-10 Times Volatile Acids
14-205
-------
(Volatile Acids and Total Alkalinity^
C. Apparatus
1. Centrifuge and centrifuge tubes, or settling cylinder.
2. Graduated cylinders (25 ml and 100 ml)
3. 50 ml Buret
4. 400 ml Erlenmeyer Flask or 400 ml beaker
5. pH Meter or a methyl orange chemical color
indicator may be used (see Procedure)
D. Reagents
1. Sulfuric Acid, 0.2 N. Cautiously add 30 ml of concentrated
sulfuric acid (H2S(\) to 300 ml of distilled water. Dilute
to 1 liter with boiled distilled water. Standardize against
0.02 N sodium carbonate (Step 2).
2. Sodium Carbonate, 0.02 N. Dry in oven before weighing. Dis-
solve 1.06 g of anhydrous sodium carbonate (Na2C03) in boiled
distilled water and dilute to 1 liter with distilled water.
3. Methyl Orange Chemical Color Indicator. Dissolve 0.5 g
methyl orange in 1 liter of distilled water.
14-206
-------
(Volatile Acids and Total Alkalinity")
E. Procedure
4. Titrate
1.
Centrifuge
or settle
JT\
3. Place electrodes of
pH meter in beaker
Sludge
S amp 1e
2. Add 190 ml of
distilled water
or 3. Add 2 drops of
methyl orange
This procedure is followed to measure the alkalinity of a sample
and also the alkalinity of a distilled water blank.
1. Take a clean 400 ml beaker and add 10 ml or less of clear
supernatant (in case of water or distilled water, use 200 ml
sample). Select a sample volume that will give a useable
titration volume. If the liquid will not separate from the
sludge by standing and a centrifuge is not available, use
the top portion of the sample. This _same sample and filtrate
should be used for both the total alkalinity test and the
volatile acids test.
2. Add 190 ml distilled water (in case of water or distilled
water determination skip this step).
14-207
-------
(Volatile Acids and Total Alkalinity)
3. Place the electrodes of pH meter into the 400 ml beaker
containing the sample.
4. Titrate to a pH of 4.5 with 0.02 N sulfuric acid. (In
case of a lack of pH meter, add 2 drops of methyl orange
indicator. In this case, titrate to the first permanent
change of color to a red-orange color. Care must be
exercised in determining the change of color and your
ability to detect the change will improve with experience.)
5. The alkalinity of the distilled water should be checked
and if significant, subtracted from the calculation.
6. Calculate alkalinity.
Alkalinity of
Distilled = ml of 0.02 N H2S04 x 5*
Water, mg/1
Total Alka- _ ml of 0.02 N H2SOi+ x 100* - mg/1
linity, mg/1 ~ alkalinity of distilled H20
F. Example
Results from alkalinity titrations on
1. Distilled Water 4 ml 0.02 N
2. Recirculated Sludge 19.8 ml 0.02 N H2SO[+
G. Calculations
Alkalinity of - XT
Distilled H20, mg/1 = ™1 °f 0.02 N H2SO, x 5
= 4 ml x 5
= 20 mg/1
"'Use 5 if measuring alkalinity of water or distilled water
(200 ml sample) and 100 if measuring alkalinity of sludge
(10 ml sample).
14-208
-------
(Volatile Acids and Total Alkalinity)
Total Alka-
linity, mg/1,
of recircu-
lated sludge
ml of 0.02 N HaSOtt x 100 - mg/1 alka-
linity of distilled H20
19.8 ml x 100 - 20 mg/1
1980 mg/1 - 20 mg/1
1960 mg/1
QUESTIONS
20.B Why would you run a total alkalinity test on
recirculated sludge?
20.C What is meant by the buffer capacity in a
digester?
20.D If the total alkalinity in a digester is
2000 mg/1 and the volatile acids concen-
tration is 300 mg/1 per liter, what is
the volatile acid/alkalinity relationship?
14-209
-------
21. Volatile Solids
See Total Solids,
END OF LESSON 3 OF 8 LESSONS
on
Laboratory Procedures and Chemistry
14-211
-------
DISCUSSION AND REVIEW QUESTIONS
(Lesson 8 of 8 Lessons)
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Write the answers to these questions in your notebook. The
problem numbering continues from Lesson 7.
32. Why are solids only weighed to the nearest 0.01 gram
when determining the total and volatile solids content
of digesters?
33. What is a thief hole?
34. What relationship is the critical control factor
in digester operation?
14-213
-------
14.6 RECOMMENDED GENERAL LABORATORY SUPPLIES
Supplies needed in addition to apparatus listed for tests. Source:
WPCF Publication No. 18, Simplified, Laboratory Procedures for Waste-
water Examination,
Quantity Description
12 Pinch clamps, medium
200 Corks, assorted
1 Cork borer set, sizes 1 through 6
1 Cork borer sharpener
2 Ib Glass tubing, 8 mm
4 Thermometers, -20° to 100°C
40 ft Rubber tubing, 1/4-in. ID, 3/32-in. wall
2 Ib Rubber stoppers, assorted (sizes 6 through 12)
1 Tripod, concentric ring, 6 in. OD
1 Latest edition, Standard Methods for the Examination of
Water & Wastewater
2 Funnels, 50 mm
2 Funnels, 100 mm
2 pair Balance watch glasses, 3 in.
4 Beakers, Pyrex, 1000 ml
4 Beakers, Pyrex, 600 ml
6 Beakers, Pyrex, 400 ml
4 Beakers, Pyrex, 250 ml
4 Beakers, Pyrex, 100 ml
4 Beakers, Pyrex, 50 ml
2 Bunsen burners
2 Brushes, medium
2 Brush, B
2 Brush, A
2 Brush, Flask
2 Aprons, plastic, 42 in. length
3 Wire gauzes, 4x4 in.
3 Triangles, 2-1/2 in. per side
1 tube Stopcock lubricant
14-215
-------
SUPPLEMENTAL EQUIPMENT FOR THE BOD TEST
Quantity Description
12 Flask, Erlenmeyer, 500 ml
12 Flask, Erlenmeyer, 250 ml
2 Pipettes, volumetric, 25 ml
2 Pipettes, volumetric, 10 ml
2 Pipettes, volumetric, 5 ml
2 Flasks, volumetric, graduated to contain and
deliver 1000 ml
2 Flasks, volumetric, graduated to contain and
deliver 500 ml
2 Flasks, volumetric, graduated to contain and
deliver 100 ml
6 Bottles, 32 oz
6 Bottles, 16 oz
6 Bottles, 8 oz
24 BOD bottles, with funnel opening
2 Burets, 50 ml
1 Buret clamp, double
2 Bottles, dropping, 30 ml
2 Spatulas, 75-mm blade
3 Bottles, storage, 2-1/2 gal
1 Buret support, medium
9 Ib Sulfuric acid, CP
5 Ib Sodium hydroxide pellets, CP
12 Bulb, rubber, pipette, 2 ml
24 Holder, rubber, stopper
4 Flask, volumetric, w/o stopper, 100 ml
2 Ib Potassium iodide, CP
1 Ib Starch, soluble potato
1 Ib Sodium thiosulfate, CP
5 Ib Manganous sulfate, CP
100 g Sodium azide, CP
1 Ib Magnesium sulfate
1/4 Ib Ferric chloride
1 Ib Potassium phosphate, mono-basic
1 Ib Potassium phosphate, dibasic
14-216
-------
Quantity
Description
1 Ib
1/4 Ib
1 oz
1 Ib
10 g
1
1
1 Ib
Sodium phosphate, dibasic heptahydrate
Ammonium chloride
Potassium bi-iodate, primary standard
Potassium dichromate
Sodium diethyldithio carbamate
Incubator, BOD
Refrigerator
Calcium chloride, 20 mesh
SUPPLEMENTAL EQUIPMENT FOR THE CHLORINE RESIDUAL TEST
Quantity Description
1 Comparator, water analysis
1 Disc for comparator, chlorine
6 Ib Hydrochloride acid, CP
25 g Orthotolidine dihydrochloride
Quantity
1
1
1
12
2
2
2
2
4
4
2
1
1
1
12
SUPPLEMENTAL EQUIPMENT FOR SOLIDS ANALYSES
Description
Brush, camel hair, 1-in. wide
Balance with cover
Weights, balance set, 50 g
Crucibles, Gooch, No. 4
Holders, crucible
Cylinder, graduated, 1000 ml
Cylinder, graduated, 500 ml
Cylinder, graduated, 250 ml
Cylinder, graduated, 100 ml
Cylinder, graduated, 50 ml
Cylinder, graduated, 25 ml
Cylinder, graduated, 10 ml
Desiccator, 250 mm
Desiccator plate
Dishes, evaporating, size 0
14-217
-------
Quantity
Description
3 Flask, filtering, 500 ml
2 Pipettes, 25 ml
6 Pipettes, 10 ml
2 Pipettes, 5 ml
1 Hot plate, 660 w
2 Tongs, crucible
1 Tongs, furnace, 18 in.
8 ft Tubing, rubber, (heavy) 1/4-in. ID
2 Filter pumps
1 Clock, interval timer, 2 hr
1 Furnace, muffle
2 boxes Paper, filter, glass fiber, 2.4 cm
1 Water baths, four-hole
1 Balance, platform, triple beam
2 Bottles, washing, polyethylene, 500 ml
6 Pencils, wax, red
2 boxes Filter paper, 12.5 cm, Whatman No. 41
1 bottle Ink, marking, black
1 Ib Rod, glass, 6 mm
1 File, triangular, 4 in.
12 Bulb, rubber, pipet, 2 oz
1 Balance desiccator
1 Oven, drying
24 2.4 cm glass fiber filter
2 Buchner funnel, size 2A
6 Tube "T", connecting, 1/4-in.
5 Ib Drierite
SUPPLEMENTAL EQUIPMENT FOR COLIFORM GROUP
BACTERIA ANALYSES
Quantity Description
1 Sterilizer or autoclave
12 3 mm wire transfer loop
24 Pipets, measuring, 10 ml
48 Pipets, measuring, 1 ml, or quantity of disposable
sterile pipets
14-218
-------
Many equipment suppliers will furnish suggested equipment lists
upon request and indication of size of plant and tests being
performed. Lists may be obtained from:
Central Scientific Company Van Waters £ Rogers
1700 Irving Park Road Post Office Box 2062
Chicago, Illinios Terminal Annex
Los Angeles, California 90054
14.7 ADDITIONAL READING
a. MOP 11
b. New York Manual, pages 127-148
c. Texas Manual, pages 565-587
d. Laboratory Procedures for Operators of Water Pollution Control
Plants, Nagano, Joe. Obtain from Secretary-Treasurer, California
Water Pollution Control Association, P.O. Box 61, Lemon Grove,
California 92045. Price $3.25 to members of the CWPCA; $4.25
to others.
e. Simplified Laboratory Procedures for Wastewater Examination,
WPCF Publication No. 18, Water Pollution Control Federation,
3900 Wisconsin Avenue, Washington, D.C. 20016. Price $2.00
to members; $4.00 to others. Indicate your member association
when ordering.
f. Standard Methods for Examination of Water and Wastewater, pro-
duced by APHA, AlVWA, and WPCF, Water Pollution Control Federation,
3900 Wisconsin Avenue, Washington, D.C. 20016. Price $16.50 to
members prepaid only; otherwise $22.50 plus postage. Indicate
your member association when ordering.
g. Chemistry for Sanitary Engineers, Sawyer, Clair N. and
McCarty, Perry L., McGraw-Hill Book Company, New York, 1967.
Price $13.50.
h. FWPCA Methods for Chemical Analysis of Water and Wastes,
Federal Water Quality Control Administration, Division of
Water Quality Reserach, Analytical Quality Control Laboratory,
1014 Broadway, Cincinnati, Ohio 45202 (November 1969).
14-219
-------
14-220
-------
SUGGESTED ANSWERS
Chapter 14. Laboratory Procedures and Chemistry
14.2A * A bulb should always be used to pipette wastewater
or polluted water to prevent infectious materials
from entering your mouth.
14.2B Inoculations are recommended to reduce the possibility
of contracting diseases.
14.2C Immediately wash area where acid spilled with water and
neutralize the acid with sodium carbonate.or bicarbonate.
14.2D True. You may add acid to water, but never reverse.
14.2E Work clothes should be changed before going home at
night to prevent carrying unsanitary materials and
diseases home which could infect you and your family.
14.3A The largest sources of errors found in laboratory results
are usually caused by improper sampling; poor preservation;
and lack of sufficient mixing, compositing, and testing.
14.3B A representative sample must be collected or the test
results will not have any significant meaning. To
efficiently operate a wastewater treatment plant, the
operator must rely on test results to indicate to him
what is happening.
14.3C A proportional composite sample may be prepared by collect-
ing a sample every hour. The size of this sample is
proportional to the flow when the sample is collected.
All of these proportional samples are mixed together to
produce a proportional composite sample. If an equal
volume of sample was collected each hour and mixed, this
would be simply a composite sample.
3.A The dangers encountered in running the C02 on digester
gas include:
1. Digester gas contains methane, which is
explosive when mixed with air.
2. The C02 gas absorbent is harmful to your skin.
14-221
-------
0 (Total Volume, ml - Gas Remaining, ml) x 100%
.5.B -8 LU2 = Total Volume, ml
(128 ml - 73 ml) x 100% 128
128 ml - 75
55
x 100%
= 43%
4.A The COD test is a measure of the strength of a waste
in terms of its chemical oxygen demand. It is a good
estimate of the first-stage oxygen demand. (Either
answer is acceptable.)
4.B The advantage of the COD test over the BOD test is
that you don't have to wait five days for the results.
5. A Plant effluents should be chlorinated for disinfection
purposes to protect the bacteriological quality of the
receiving waters.
5.B The idometric method gives good results with samples
containing wastewater, such as plant effluent or re-
ceiving waters. Orthotolidine will give satisfactory
results if used within 20 minutes of the application
of chlorine; however, the entire chlorine demand may
not yet have been satisfied. Amperometric titration
gives satisfactory results, but the equipment is ex-
pensive.
6.A The clarity test indicates the relative change of depth
you can see down in the final clarifier or contact basin.
This reflects a visual comparison of color, solids, and
turbidity from one test to the next. CXR Indication of
quality of effluent.
6.B When clarity is measured under different conditions the
results can not be compared. You won't be able to tell
whether your plant performance is improving, staying the
same, or deteriorating.
14-222
-------
7.A Sodium thiosulfate crystals should be added to sample
bottles for coliform bacteria tests before sterilization
to neutralize any chlorine that may be present when the
sample is collected. Care must be taken not to wash the
bottles out when a sample is collected.
7.B 121°C within 15 minutes.
7.C Dilutions -2 -3 -4 -5
Readings 5 1 2_ 0
MPN = 63,000/100 ml
7.D The number of coliforms is estimated by counting the
number of colonies grown on the membrane filter.
o A rvn o ^ <-• o DO of Sample, mg/1 x 100%
8.A DO Saturation, % = ~r-r • • *•• • ••'——^ ^
' DO at Saturation, mg/1
(7.9 mg/1) 100% .699
11.3 mg/1
= 70% 1 1
1 0 17
1 030
1 017
8.B To calibrate the DO probe in an aeration tank, a
sample of effluent can be collected and split. The
DO of the effluent is measured by the modified Winkler
procedure, and the probe DO reading is adjusted to agree
with the Winkler results.
8.C When the DO in the aeration tank is very low, the
copper sulfate-sulfamic acid procedure can give high
results. The results are high because oxygen enters
the sample from the air when the sample is collected,
when the copper sulfate-sulfamic acid inhibitor is
added, while the solids are settling, and when the
sample is transferred to a BOD bottle for the DO test.
8.D BOD test or volatile solids test.
14-223
-------
8.E
8.F
8.G
8.H
9.A
To prepare dilutions for a cannery waste with an expected
BOD of 2000 mg/1, take 10 ml of sample and add 90 ml of
dilution water to obtain a new sample with an estimated
BOD of 200 mg/1 (10 to 1 dilution):
BOD Dilution, ml = •=— = — : - T
' Estimated BOD, mg/1
1200
200
= 6 ml
BOD,
mg/1
Initial DO of
Diluted Sam-
ple, mg/1
DO of Diluted
Sample After
5-Day Incuba-
tion, mg/1
BOD Bottle Vol. , ml
Sample Volume, ml
f-7 r It ? r, /^ [300 ml I
= (7.5 mg/1 - 3.9 mg/1) -—j-
= (3.6 mg/1) (150)
= 540 mg/1
Samples for the BOD test should be collected before chlori-
nation because chlorine interferes with the organisms in
the test. It is difficult to obtain accurate results with
dechlorinated samples.
A solution of sodium thiosulfate at 0.0375 N is very weak
and unstable and will not remain accurate over two weeks.
(1) You would measure the H2S in the wastewater to know
the strength of HZS and an indication of the corrosion
taking place on the concrete.
(2) H2S in the atmosphere produces a rotten egg odor. It
is indicative of anaerobic decomposition of organics
in wastewater which occurs in the absence of oxygen.
10.A (1) To measure plant influent pH with a paper tape,
collect representative sample, mix sample with a
clean stirring rod, and dip tape in sample while
it is still moving. Compare tape color with pack-
age color and record results.
(2) To measure raw sludge pH with a paper tape first
allow raw sludge sample to settle. Dip tape in
liquid at top, compare resulting color, and record
results.
pH of both samples should be measured in place or as soon
as possible.
14-224
-------
10.B Precautions to be exercised when using a pH meter include:
(1) Prepare fresh buffer solution weekly for
calibration purposes.
(2) pH meter, samples, and buffer solutions should
all be at the same temperature.
(3) Watch for erratic results arising from faulty
operation of pH meter or fouling of electrodes
with interfering matter.
11.A Settleability tests should be run on the mixed liquor to
determine the settling characteristics of the sludge floe
at regular intervals for 60 minutes. The results are used
in the SVI and SDI determinations.
11.B The SVI is the volume in ml occupied by one gram of mixed
liquor suspended solids after 30 minutes of settling.
ll.C The SVI test is used to indicate changes in sludge
characteristics.
11.D Sludge Density Index (SDI) = 100/SVI
Sludge
12.A t0 °1- = (Total Set Sol Removed, ml/1) (1000) (Flow, MGD)
*
gpd = (10 ml/1 - 0.4 ml/1) (1000 mg/ml) (1 M Gal/day)
C 1 M Gal ]
day
This value may be reduced by 30 to 75% due to
compaction of the sludge in the clarifier.
13.A The sludge age of a 200,000 gallon aeration tank that has
2000 mg/1 mixed liquor suspended solids, a primary effluent
of 115 mg/1 SS, and an average flow of 1.8 MGD:
Sludge Vol of Aeration Tank „ „ ,., orirvri /,
Age, = .2MG x Sus Solids, 2000 mg/1
days Flow/ MGD," 1.8" x Primary Effl, 115" mg/1
0.2 MG x 2000 mg/1
1.8 MGD x 115 mg/1
= 1.93
14-225
-------
14.A (1) Results from the graduated cylinder are available
immediately, but different operators may interpret
the results differently.
(2) Results are not available until the next day, but
different operators will record the same result.
15,A If the supernatant solids test is greater than 5%,
the supernatant could be placing a heavy solids load on
the plant and the appropriate operational adjustments
should be made.
16.A The specific gravity is very near that of H20 and is not
light enough to float nor heavy enough to settle.
16.B Solids calculations will be shown in detail here to illus-
trate the computational approach and the units involved.
After you understand this approach, use of the laboratory
work sheet on the following pages is more convenient.
a. Total Suspended Solids
Volume of Sample, ml = 100 ml
Weight of Dried Sample § Dish, grams = 19.3902 g
Weight of Dish (Tare Weight), grams = 19.5241 g
Dry Weight = 0.0661 g
or = 66.1 mg
Total
Suspended
Solids,
mg/1
Weight of Solids, mg x 1000, ml/I
Volume of Sample, ml
66.1 mg x 1000 ml/I
100 ml
= 661 mg/1
b. Volatile Suspended Solids
Weight of Dried Sample § Dish, grams = 19.3902 g
Weight of Ash fT Dish, grams = 19.3469 g
Weight Volatile, grams = 0.0433 g
or = 43.3 mg
14-226
-------
Volatile
Suspended _ Weight of Volatile, mg x 1000 ml
Solids, Volume of Sample, ml
mg/1
(45.3 mg) (1000 ml/1)
100 ml
= 433 mg/1
c. Percent Volatile Solids
o „ -, ^-i c- TJ Weight Volatile, mg x 100%
% Volatile Solids = — — s - i — s -
Weight Dry, mg
= . __
661 mg 661 / 433.0
396 6
= 65.5% 36 40
33 05
" 3 350
3 305
d. Fixed Solids
Total Suspended Solids, mg/1 = 661 mg/1
Volatile Suspended Solids, mg/1 = 433 mg/1
Fixed Solids, mg/1 = 228 mg/1
e. Percent Fixed Solids
Total Solids, % = 100.00%
Volatile Solids, % = 65 . 50%
Fixed Solids, % = 34.5 %
01-
% Fixed - Fixed' mg x 100%
Total, mg
661 mg
= 34.5% (Check)
14-227
-------
16. C Calculate Percent Reduction through Primary:
% Removal = (In " ^ x 100% In = Inf luent to
jn plant or unit
Out = What is leaving
plant or unit
= (221 mg/1 - 159 mg/1) %
221 mg/1
= - x 100% 221 62.0
44 2
= 28% reduction through primary
17 68
Calculate Percent Removal by Secondary System:
Rem0val = ^In " Out^ x 100% In = 159 mg/1 SJL in
In primary effluent
Out = 33 mg/1 SS in
final effluent
= (159 mg/1 - 33 mg/1) %
159 mg/1
.79
159/ 126.0
= 79% removal from primary . , , _
effluent to final effluent -
14 70
14 31
Calculate Overall Plant Efficiency:
On , (In - Out) .,.,.„ In = 221 mg/1 SS in
% Removal = A - - - L x 100% plant influent
Out = 33 mg/1 SS in
plant effluent
= (221 mg/1 - 33 mg/1) x
221 mg/1
221
= 85.5% overall plant removal
14-228
-------
16.D Calculate the pounds of solids removed per day by each unit:
Amount
Removed, = Cone. Reduction, mg/1 x Flow, MGD x 8.34 Ib/gal
Ib/day
where MGD = million gallons per day
A. Influent, mg/1 = 221 mg/1
Primary Effluent, mg/1 = 159 mg/1
Primary Removal, mg/1 = 62 mg/1
Amount Removed, ,..„ ... ,, r .„ . fo _. 1U/ ..
IT /j f-n • % = (62 mg/1) (1.5 MGD) (8.34 Ib/gal)
Ib/day (Primary) v &/ ^ v. j \. & j
= 775.6 Ibs/day
removed by primary
B. Primary Effluent, mg/1 = 159 mg/1
Final Effluent, mg/1 = 55 mg/1
Secondary Removal, mg/1 = 126 mg/1
Amount Removed, /•,-,/- /•••, ,--, r *<^r^ /-o -7, n_ / •,-,
lu/j ,c j •> = (126 mg/1) (1.5 MGD) (8.34 Ib/gal)
Ib/day (Secondary) ^ &< j \. j ^ & >
= 1576 Ib/day
removed by secondary
C. Influent, mg/1 = 221 mg/1
Final Effluent, mg/1 = 33 mg/1
Overall Removal, mg/1 = 188 mg/1
Amount
Removed, = (188 mg/1) (1.5 MGD) (8.34 Ib/gal)
mg/1
= 2351 Ibs/day
removed by plant
or = Primary Removal, Ib/day + Secondary, Ib/day
= 775 + 1576
= 2351 (Check)
14-229
-------
16.E The advantages of the centrifuge over the regular
suspended solids test are:
(1) Speed of answer! Not as accurate as
other methods, but results are sufficiently
close.
(2) Answers very acceptable if suspended solids
concentration is below 1000 mg/1.
Pis advantage: Small plants cannot always afford
the $500 or more cost of the centrifuge.
17.A Changes in influent temperature could indicate a new
influent source. A drop in temperature could be caused
by cold water from infiltration, and an increase in
temperature could be caused by an industrial waste dis-
charge.
17.B The thermometer should remain immersed in the liquid
while being read for accurate results. When removed
from the liquid, the reading will change.
17.C All thermometers should be calibrated against an
accurate National Bureau of Standards thermometer
because some thermometers can be purchased that
are substantially inaccurate (off as much as 6°) .
18.A Volatile solids found in a digester are organic compounds
of either plant or animal origin.
18.B Volatile solids in a treatment plant represent the waste
material that may be treated by biological processes.
20.A Volatile Acid ml 0.05 N NaOH x 2500
Alkalinity, mg/1 ml Sample
5 ml x 2500
50 ml
= 250 mg/1
Since 250 mg/1 > 180 mg/1,
Volatile Acids, ,, , ^. 1 . . , .,, ,. . ^ , ,.„
, ' = Volatile Acid.Alkalinity x 1.50
= 250 mg/1 x 1.50
= 375 mg/1
14-230
-------
20.B The alkalinity test is run to determine the buffer capacity
and the volatile acids/alkalinity relationship in a digester.
20.C The buffer capacity in a digester as measured by the total
alkalinity tests indicates the capacity of the digester to
resist changes in pH.
Volatile Acid = 500^ mg/1
Alkalinity 2000 mg/1
= 0.15
14-231
-------
F TEST
Chapter 14. Laboratory Procedures and Chemistry
Name Date
Please write your name and mark the correct answers on the IBM answer
sheet. There may be more than one correct answer to each question.
TRUE OR FALSE (1-10) :
1. A rubber bulb should be used to pipette wastewater or polluted
water.
1. True
2. False
2. Acid may be added to water, but not the reverse.
1. True
2. False
3. Always wear safety goggles when conducting any experiment in which
there may be danger to the eyes,
1. True
2. False
4. Smoking and eating should be avoided when working with infectious
material such as wastewater and sludge.
1. True
2. False
5. In the washing of hands after working with wastewater, the kind
of soap is less important than the thorough use of soap.
1. True
2. False
6. The pH scale may range from 0 to 14, with 7 being a neutral solution,
1. True
2. False
-------
7. If at all possible, samples for the BOD test should
be collected before chlorination.
1. True
2. False
8. The COD test is a measure of the chemical
oxygen demand of wastewater.
1. True
2. False
9. The BOD test is a measure of the organic content
of wastewater.
1. True
2. False
10. The answers from the total solids and suspended
solids tests are always the same.
1. True
2. False
Possible definitions of the words listed below are given on the
right. If the definition of a word is after the number 2, mark
column 2 on your answer sheet.
Word Definition
1. Surrounding
.11. Aliquot 2. Capacity to resist pH change
12. Ambient 3. Portion of a sample
13. Blank 4. Inside
14. Buffer 5. Test run without sample
15. Large errors in laboratory tests may be caused by:
1. Improper sampling
2. Large samples
3. Poor preservation
4. Poor quality effluent
5. Lack of mixing during compositing
14-234
-------
16. The most critical factor in controlling digester
operation is the:
1. CO 2
2, Gas production
3. Volatile solids
4. Volatile acids/alkalinity relationship
5. pH
17. The COD test:
1. Measures the biochemical oxygen demand
2. Estimates the first-stage oxygen demand
3. Measures the carbon oxygen demand.
4. Estimates the total oxygen consumed
5, Provides results quicker than the BOD test
18. A clarity test on plant effluent:
1. Tells if the effluent is safe to drink
2. Is measured by an amperemeter
3, Should always be measured at the same time
4. Should always be measured under the same light conditions
5. Is measured by a Secchi Disc
19. Coliform group bacteria are: •
1. Measured by the membrane filter method
2. Measured by the multiple fermentation technique
3. Measured by the modified Winkler procedure
4. Harmful to humans
5. Indicative of the potential presence of bacteria
originating in the intestines of warm-blooded animals
20. The saturation concentration of dissolved oxygen in
water does not vary with temperature.
1. True
2. False
21 DO probes are commonly used to measure dissolved oxygen
in water in:
1. Aeration tanks
2. Sludge digesters
3. Manholes
4. Streams
5. BOD bottles
14-235
-------
22. Hydrogen sulfide:
1. Reacts with moisture and oxygen to form a substance
corrosive to concrete
2. Is sometimes written as H~S
3. Smells like rotten eggs
4. Is formed under aerobic conditions
5. Should not be controlled in the collection system.
23. Results from the settleability test of activated sludge
solids may be used to:
1. Calculate SVI
2. Calculate SDI
3. Calculate sludge age
4. Determine ability of solids to separate from liquid
in final clarifier
5. Calculate nixed liquor suspended solids.
24. Results of the settleable solids test run using Imhoff
cones may be used to:
1. Calculate the Imhoff Settling Index
2. Calculate the efficiency of a plant
3. Calculate the pounds of solids pumped to the digester
4. Indicate the quality of the influent
5. Indicate the quality of the effluent
25. Precautions that must be observed in running the suspended
solids-Gooch crucible test include:
1. Collecting and testing a representative sample
2. Proper temperature level in oven at all times
3. Lack of leaks around and through the glass fiber
4. Thoroughly mixing sample before testing
5. Discarding any large chunks of material in sample
26. A chlorine residual should be maintained in a plant effluent:
1. To keep the chlorinator working
2. For disinfection purposes
3. For testing purposes
4. To protect the bacteriological quality of the receiving
waters
5. None of these
14-236
-------
PLANT
DATE
SUSPENDED SOLIDS $ DISSOLVED SOLIDS
SAMPLE
Crucible
Ml Sample
Wt Dry § Dish
Wt Dish
Wt Dry
71 _ Wt Dry, gm x 1,000,000
m£/ Ml Sample
Wt Dish § Dry
Wt Dish § Ash
Wt Volatile
o, Vol _ Wt Vol „ „
Wt Dry
Nitrate N03
Sample
Graph Reading
COD
Sample
Blank Titration
Sample Titration
Depletion
,. Dep x N FAS x 8000
mg/1 = —K.
Ml Sample
BOD
# Blank
SAMPLE
DO Sample
Bottle #
% Sample
Blank or adj blank
DO after incubation
Depletion, 5 days
Dep %
Sett. Solids
Sample
Direct Ml/1
Typical Laboratory Work Sheet
14-237
-------
TOTAL SOLIDS
SAMPLE
Dish No.
Wt Dish
Wt Dish
Wt Wet
Wet
Wt Dish + Dry
Wt Dish
Wt Dry
% Solids =
Wt Wet
x 100%
Wt Dish + Dry
Wt Dish + Ash
Wt Volatile
.% Volatile = Wt Vo1 x 100%
Wt Dry
pH
Vol. Acid
Alkalinity as CaC03
Grease (Soxlet)
Sample
Ml Sample
Wt Flask + Grease
Wt Flask
Wt Grease
/I = Wt Grease, m_g_x_ 1000
Ml Sample
H2S (Gas) (Starch-Iodine)
Blank
Sample
Diff ^^
Diff x .68
mg/1 x 43.6
Ml
Ml
Ml
mg/l
grain/100 cu ft
Typical Laboratory Work Sheet (continue-;
14-239
-------
CHAPTER 15
BASIC MATHEMATICS AND
TREATMENT PLANT PROBLEMS
by
William Crooks
-------
TABLE OF CONTENTS
Chapter 15. Basic Mathematics and Treatment Plant Problems
Page
15.0 Introduction 15-1
15.1 Whole Numbers and Decimals 15-2
15.10 Addition 15-2
15.11 Subtraction 15-3
15.12 Multiplication 15-5
15.13 Division 15-9
15.2 Fractions 15-12
15.20 General 15-12
15.21 Improper Fraction 15-12
15.22 Reducing a Fraction to Lowest Terms. . . . 15-13
15.23 Adding and Subtracting 15-14
15.24 Multiplication 15-15
15.25 Division 15-16
15.26 Decimal Fractions 15-16
15.27 Percentage 15-17
15.28 Sample Problems Involving Percent 15-18
15.29 Ratio and Proportion . 15-21
15.3 Squares, Cubes, and Roots 15-25
15.30 Squares and Square Roots 15-25
15.31 Cubes and Cube Roots 15-27
-------
Page
15.4 Averages and Median 15-28
15.5 Areas • 15-30
15.50 General. . .' 15-30
15.51 Rectangle 15-30
15.52 Triangle 15-31
15.53 Circle 15-32
15.54 Cylinder 15-34
15.55 Cone 15-36
15.56 Sphere 15-37
15.6 Volumes 15-38
15.60 Rectangle 15-38
15.61 Prism 15-39
15.62 Cylinder 15-39
15.63 Cone 15-39
15.64 Sphere 15-40
15^.7 Metric System 15-40
15.70 Measures of Length 15-41
15.71 Measures of Capacity 15-42
15.72 Measures of Weight 15-42
15.73 Temperature 15-43
15.74 Milligrams per Liter 15-45
15.75 Example Problems 15-46
15.8 Weight-Volume Relations 15-48
11
-------
F age
15.9 Force, Pressure, and Head 15-49
15.10 Velocity and Rate of Flow 15-54
15.100 Velocity . . . 15-54
15.101 Rate of Flow 15-55
15.11 Pumps. -. 15-57
15.110 General -. 15-57
15.111 Work . . . . 15-58
15.112 Power 15-58
15.113 Horsepower 15-58
15.114 Head 15-60
15.115 Pump Characteristics 15-62
15.116 Evaluation of Pump Performance ...... 15-66
15.117 Pump Speed—Performance Relationships. . . 15-69
15^.12 Steps in Solving Problems 15-71
15.120 Identify Problem 15-71
15.121 Selection of Formula 15-72
15.122 Units and Dimensional Analysis 15-72
15.123 Calculations 15-73
15.124 Significant Figures 15-74
15.125 Check Your Results 15-76
15.13 Typical Treatment Plant Problems 15-77
15.130 Grit Chambers 15-77
15.131 Sedimentation Tanks and Clarifiers .... 15-78
111
-------
Page
15.132 Trickling Filters 15-80
15.133 Activated Sludge 15-82
15.134 Sludge Digestion 15-84
15.135 Ponds 15-87
15.136 Chlorination 15-89
15.137 Laboratory Results 15-90
15.138 Efficiency of Plant or Treatment Process . 15-91
15.139 Blueprint Reading 15-91
15.14 Summary of Formulas 15-93
15.140 Length of Clarifier Weir 15-93
15.141 Area 15-93
15.142 Volume 15-93
15.143 Velocity 15-94
15.144 Sedimentation Tanks and Clarifiers .... 15-94
15.145 Trickling Filters 15-94
15.146 Activated Sludge 15-94
15.147 Sludge Digestion 15-95
15.148 Ponds 15-95
15.149 Other Formulas 15-96
15.1490 Chlorination 15-96
15.1491 Laboratory Results 15-96
15.1492 Efficiency of Plant
or Treatment Process 15-96
15.1493 Pumps 15-96
IV
-------
Page
15.15 Conversion Tables 15-97
15.16 Additional Reading 15-101
-------
EXPLANATION OF PRE-TEST
READ SECTION 15. 0^ INTRODUCTION, BEFORE WORKING PRE-TEST
This Pre-Test is designed to determine those areas of math in
which you may need additional help. It is suggested that you
work all problems in the Pre-Test and compare your answers with
the answers provided. If you do not obtain the answer written
beside the problem, turn to the page number in this chapter
which appears directly beside the answer. On this page you
will find an explanation for solving that particular problem.
If you obtain the correct answer for a problem, you may skip
that section in the chapter. If time is available, however,
it may be worthwhile to at least thumb through that particular
section.
If you cannot obtain the given answer, ask a friend to help you
or notify your Program Director. Tell your Program Director
what you tried and what happened, and he will try to help you.
You are not required to mail your calculations or answers for
the Pre-Test to your Program Director; however, if you would
like him to review any or all of your work, please mail it to
him.
Since the purpose of this chapter is to help you work math
problems, you are not expected to have memorized formulas and
conversion factors (7.5 gal = 1 cu ft). While working the Pre-
Test you may refer to Sections 15.14, Summary of Formulas, and
15.15, Conversion Tables, for helpful information. On many
examinations you are expected to have memorized certain basic
formulas and conversion factors. By working many problems you
will gradually memorize this information.
P-i
-------
PRE-TEST
Chapter 15. Basic Mathematics and Treatment Plant Problems
1.
2 .
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Add 349 and 75.
Subtract 296 from 485.
Multiply 24 x 17.
Divide 1.25 by 0.045.
Change 13/8 to a mixed number.
Reduce 216/324 to its lowest terms.
, , , 1 1
Add J+-.
1 ?
Multiply 2 — by — .
Divide — by — .
6 } 12
5 , - -,
nxpress — as a decimal.
Express — as a percent.
Express 0.4% as a fraction.
What percent is 20 of 25?
Find 90% of 5.
16 is 80% of what amount?
Answer
424
189
408
27.78
~8
2
3
7
12
1
J *""""'
3
0.833
40%
1
250
80%
4.5
20
Page
15-2
15-3
15-5
15-10
15-12
15-13
15-14
15-15
15-16
15-16
15-17
15-17
15-19
15-19
15-20
p-1
-------
Answer Page
16. Certain bolts cost 90<£ a dozen.
How much would three bolts cost? 23
-------
Answer
Page
29. Convert 20° centigrade (Celsius)
to fahrenheit.
30. Convert -13°F to °C.
31. Flew is 3.5 K'GD with a BCD con-
centration of 200 mg/1. Calcu-
late pounds of BOD per day.
32. Change 1000 cu ft of water to
gallons.
33. How many gallons of water weigh
750 Ibs?
34. What is the gauge pressure under
two feet of water?
35. What is the force acting on a
five feet long wall, four feet
deep?
36. Flow in a 2.5 foot wide channel
is 1.4 ft deep and measures 11.2
cfs. What is the average velocity?
37. A flow of 500 gpm is pumped 100 ft
by a pump with an efficiency of
70%. What is the pump horsepower?
68°F 15-44
-25°C 15-44
5838 Ib/day 15-46
7480 gal 15-48
90 gal 15-48
0.866 psi 15-50
2496 Ibs 15-51
3.2 ft/sec 15-56
18.0 HP 15-59
P-3
-------
CHAPTER 15. BASIC MATHEMATICS AND TREATMENT PLANT PROBLEMS
15.0 INTRODUCTION
This chapter has been provided early in your training program to
help you gain the greatest benefit from your efforts. Whether
to start this lesson now or wait until later is your decision.
The lessons on treatment processes were written in a manner
requiring very little background in mathematics. You may wish
to concentrate your efforts on the treatment processes at this
time and refer to this lesson when you need help. Some operators
prefer to complete this lesson now so they will not have to
worry about how to do the mathematical manipulations when they
are studying the treatment process lessons. You are encouraged
to try to work this chapter now, rather than waiting until later.
The intent of this chapter is to provide you with a quick review
of some basic mathematical principles and examples of typical
plant problems. It is not intended to be a math textbook. Some
operators will be able to skip over the review of addition, sub-
traction, multiplication, and division. Others may need more
help in these and other areas. Basic arithmetic textbooks are
available at every local library or bookstore and should be
referred to if needed. Deserving special mention is a manual,
Elementary Mathematics and Basic Calculations, a reprint available
from Water and Sewage Works magazine.
When possible, you may wish to perform multiplication and division
with the aid of a slide rule. Handbooks frequently have tables
containing the square, square root, and other valuable information
which saves computational time. These methods also are good ways
to check your calculations. After you have worked a problem in-
volving plant operations, you should check your calculations,
examine your answer to see if it appears reasonable, and if possible,
have another operator check your work before making any operational
changes.
15-1
-------
15.1 WHOLE NUMBERS AND DECIMALS
15.10 Addition
Not many people will make a mistake when adding 2 plus 2. However,
it is surprising how many cannot correctly add 22.222 and 0.0022.
The reason is they violate one of the main rules of addition or
subtraction, and that is:
1. KEEP ALL DECIMAL POINTS AND NUMBERS IN COLUMNS
When the rule is followed correctly, the above addition
is easily performed.
22.222
+ 0.0022
22.2242
Another common error is made in the following manner:
349
+ 75
414 (Wrong)
In this case another rule is violated.
2. WRITE DOWN ALL CARRYOVER NUMBERS
If this rule is followed, the previous problem becomes;
+ 7S
424
Carryover numbers should be written lightly over the
next column to the left.
Many can remember a teacher saying to them, "You can't add apples
and oranges". This is our third rule of addition.
3. ALL NUMBERS MUST BB IN THE SANE DIMENSIONAL (ft, Ib, sec) UNITS
If we needed a string 2 feet long and one 6 inches long,
we would either say:
15-2
-------
2 ft + 1/2 ft = 2 1/2 ft of string, or
2 ft
1/2 ft
? 1/2 ft"
or we might say:
24 inches + 6 inches = 30 inches of string, or
24 in
6 in
30 in
Two and one-half feet and .30 inches are the same length.
We must use the same dimensional units when we add any
series of numbers"!
15.11 Subtraction
Since subtraction is simply the reverse of addition, the three
rules for addition generally apply to subtraction:
1. KEEP ALL DECIMAL POINTS AND NUMBERS IN COLUMNS
Example: Subtract 0.042 from 3.574.
3.574
-0.042
3.532
Since subtraction is the reverse of addition, carryovers are
not made, but "borrowing" is sometimes necessary.
2. WRITE DOWN ALL BORROWED NUMBERS
Example: Subtract 296 from 485.
As before, the numbers should be grouped in columns.
15-3
-------
COLUMN LABELS
Hun-
dreds Tens Units
485
-2
1
^
+ 10
17
9
8
6'
9
or
1st Step - Borrow one from the eight (leaving seven)
and add ten to the five to get 15--
Subtract six from 15 and write down nine.
2nd Step - Borrow one from the four and add ten to
the seven to get 17--subtract nine from
17 and write down eight.
3rd Step - Subtract two from three and write down one.
The best way to check a subtraction is by addition. Thus,
the preceding problem can be checked by:
+296
485 (Check)
The final rule of subtraction is the same as for addition.
3. ALL NUMBERS MUST BE IN THE SAME DIMENSIONAL UNITS
15-4
-------
15.12 Multip1ication
Multiplication is simply a short-cut method of addition. In
other words, 3 x 4 is simply:
3 + 3 + 3 + 3 = 12
or 4+4+4 =12
Thus a multiplication problem can always be checked by addition.
In the interest of time, however, every operator should memorize
the multiplication table through 10.
Multiplication problems involving larger numbers can be solved by
addition also. For example, 24 x 17 can be solved by adding a
column of seventeen 24's or a column of twenty-four 17's. This
procedure, however, would take considerable time, and therefore
the simple multiplication steps are preferred.
24 1st Step -4x7= 28—write down eight and
x 17_ carry the two to the next column.
8
24 2nd Step - 2 (from 2 in 24) x 7 = 14;
x 17 14+2 (carried 2) = 16—write
168 down 16.
24 3rd Step - Erase all carryovers. 4x1= 4—
x 17 write down four in second row, but
168 one place to left.
4
24 4th Step -2x1= 2—write down two.
x 17
168
24
24 5th Step - Add numbers.
x 17
168
24
408
15-5
-------
Another approach to multiplication is the regrouping concept we
illustrated in the subtraction section by placing the number in
the appropriate hundreds (H), tens (T), and units (U) columns.
The idea behind this approach is that
10 ones or 10 units (U) = 1 ten (T)
and
Problem: Multiply 24 x 17 or 24
x 17
10
10 tens or 10 tens (T) = 1 hundred (H) = 100
H
1st Step 7x4
2nd Step 7x2
3rd Step 1x4
4th Step 1x2
T
2
1 4
U
= 28 units or 2T + 8U
Unit (7) times Ten (2)
makes right digit (4)
go in T column or
1H + 4T
T x U = the Tens column
T x T = the Hundreds
column
5. Add Columns
6. Regroup
3
1
10
Since 10T = 1H
7. Answer
To multiply numbers, you may use any method that you understand.
These methods are presented to show you different approaches used
by many operators which give the same answers.
15-6
-------
The first important rule to remember in multiplication is:
1. THE NUMBER OF DECIMAL PLACES IN THE ANSWER IS EQUAL TO
THE SUM OF DECIMAL PLACES IN THE NUMBERS MULTIPLIED
Example: 14.032 3 decimal places
1.03 + 2 decimal places
42096
00000
14032
14.45296 5 decimal places
Another way to determine the location of the decimal point is
to multiply the numbers without the numbers past the decimal
point. For example 14 x 1 = 14. Therefore, 14.032 x 1.03
must be equal to more than 14.
A basic difference between addition and multiplication is that
the multiplied numbers do not have to have similar dimensional
units.
2. NUMBERS DO NOT HAVE TO HAVE THE SAME DIMENSIONAL UNITS
specify
them thi
For this reason it is important to specify the units
that go with the numbers and carry them through to
the answer.
Example: A 20-pound weight on the end of an
8-foot lever would produce--
20 Ibs x 8 ft = 160 ft-lbs
Example: Three men working five hours each
would put in--
3 men x 5 hours = 15 man-hours of labor
The multiplication operation is indicated by several different
symbols. The most common, of course, is the multiplication
sign (x) or times sign. Multiplication also can be indicated
by parentheses ( ) or by brackets £ ] or simply with a dot • .
Thus, the above example can be written five ways:
15-7
-------
3 men x 5 hours = 15 man-hours
(3 men)(5 hours) = 15 man-hours
[3 men] (j5 hours3 = 15 man-hours
3 men • 5 hours = 15 man-hours
(3 men) x 5 hours = 15 man-hours
When solving a problem with parentheses or brackets, always
complete the indicated operation within the parentheses or
brackets prior to performing the multiplication.
Example: (25 - 4) (8 + 2) (3 • 2) =
C21) (10) (6)
21 x 10 x 6 = 1260
Example: [l5 - (3 + 2) (4 - 2)] \6 + (7 - 3)]
[15 - (5) (2) ] [6 + 4 ] =
[l5 - 10 3 [ 10 ] 50
15-8
-------
15.13 Division
Division offers a means of determining how many times one number
is contained in another. It is a series of subtractions. For
example, if we say divide 48 by 12, we are also saying, how
many times can we take 12 away from 48?
By subtraction:
48-12 =
36-12 =
24-12 =
12-12 =
36 (one)
24 (two)
12 (three)
0 (four)
By division:
4
12/"48~ 1st Step -
_4
12/48
4jB
0
Twelve will not divide into four,
but will divide into 48 at least
four times.
2nd Step - Multiply 4 x 12 and write answer
under 48. Remainder is zero.
Answer is four even.
Division problems can be written in many ways:
2
S/lo"
10 * 5 = 2
10 *_
T "
10/5 = 2
In each case,
5 = divisor
10 = dividend
2 = quotient
It is always easier to divide by a whole number.
* You will encounter this form in Section 15.2 as a fraction.
15-9
-------
1. MOVE THE DECIMAL POINT OF THE DIVISOR ALL THE WAY TO THE
RIGHT AND THE DECIMAL POINT OF THE DIVIDEND THE SAME
NUMBER OF PLACES TO THE RIGHT
Example: Divide 1.25 by 0.045.
0.045./I.250.
2 .
45/1250.0
1st Step - Move decimal point three places
to right in divisor and dividend.
2nd Step - Forty-five will not divide into
one or 12, but will go into 125
about two times.
45/1250.0
90
35
3rd Step - Multiply 45 by 2 and subtract
answer from 125.
45/1250.0
90
350
4th Step - Bring down zero.
27
45/1250.0
90
350
5th Step - Forty-five will go into 350 about
seven times.
45/1250.0
90
350
315
35
6th Step - Multiply 45 by 7 and subtract
answer from 350.
27.7
45/1250.0
90
350
315
35
7th Step - Bring down zero. Once again,
45 will go into 350 about
7 times.
15-10
-------
If this problem is continued, sevens will continue to show
up in the answer. The answer, then, is 21.111> etc. In
most cases 27.78 will be sufficiently accurate. This is
called "rounding off" the numbers. The last number 7 was
increased to 8 because the number after it was 5 or higher.
When solving a division problem, complete the indicated operations
above and below the division line before dividing.
Example:
25 - (2) (3) + 18/2 + (4) (9)
19 - (3) (4) 12
25-6 + 9 + 36_ _
19 - 12 12
4 + 3-5
15-11
-------
15.2
FRACTIONS
15.20 General
A fraction in its most common form is a part of a whole. For
instance, if a pie is divided into two equal parts and one part
is eaten, only one half of the pie remains.
1/2 + 1/2 =
Thus it can be seen that a fraction is division that has not
been completed. As previously explained, in the fraction 1/2,
one is the dividend and two is the divisor. More commonly,
however, one is called the numerator and two is called the
denominator.
If the pie were divided into eight equal pieces and five were
eaten, we would have less than one half a pie. We would have
3/8 of a pie remaining.
5/8 +3/8 = 1
15.21 Improper Fraction
An improper fraction has a larger numerator than denominator
and is therefore greater than one. An improper fraction may be
reduced to a whole or mixed number by dividing the denominator
into the numerator.
Example:
_13_ (numerator)
8 (denominator)
15-12
-------
The reverse of this operation would be changing a whole or mixed
number into a fraction. To accomplish this the whole number is
multiplied by the denominator, the numerator is added, and this
total is written over the denominator.
_ .. n •, /„ 4x2 + 1
Example: 2 1/4 = =-
9_
4
15.22 Reducing a Fraction to Lowest Terms
To change a fraction to its lowest terms, divide the numerator and
denominator by the largest number that will divide evenly into both;
c i 15 15 v 15 1
Example: — = = —
r 45 45 T 15 3
NOTE: At this point it should be remembered that the numerator
and denominator can be divided or multiplied by the same
number without changing the value of the fraction.
Sometimes it will not be possible to reduce the fraction to its
lowest terms with the first trial division. In this case, division
continues until it can no longer be performed by a number larger
than one.
Example:
216 _ 216 * 3 _ 72 = 72 + 9 _8 8*4 = 2_
324 324 v 3 108 108 * 9 12 12 * 4 3
In solving this problem all of these steps could have been eliminated
if we had realized that 108 will divide into the numerator twice and
into the denominator three times. This is usually difficult to see,
however, and smaller numbers must be used as trial divisors.
15-13
-------
Adding and Subtracting
Whenever fractions are added or subtracted it is necessary that
the denominators be the same. In adding or subtracting fractions,
you simply add or subtract numerators.
c i 3 4 7 ' i 2
Example: - + - = - = 1?
73 41
Example: — - — = — = —
8882
If the denominators are not the same, they must be made the same
before addition or subtraction takes place. In changing the form
of a fraction, the numerator and denominator must be multiplied
by the same number.
r, , 35 3(2) 5 65 11 , 1
Example: — + — = *• < + — = — + — = _= i —
r ,-/»>,« 10 10 10 10
Example:
In some cases the denominators cannot be changed to one of the
problem's existing denominators. For instance, in adding 1/3
and 1/4, the 1/3 can't be changed to an even fourth, and the
1/4 can't be changed to an even third. In this case, they must
both be changed to the least common denominator. The least
common denominator is the smallest number that each denominator
will go into one or more times without a remainder.
Example- — + — The lowest number that both 3 and 4
3 4 will both go into is 12. Three will
go into twelve 4 times; four will go
into twelve 3 times.
Therefore, the least common denominator is 12. We obtained 12 by
multiplying 3x4.
12 12 12
15-14
-------
15.24 Multiplication
Multiply all of the numerators together for a new numerator, and
multiply all of the denominators together for a new denominator.
In multiplication, denominators need not be the same.
. 52 10 5
Example: - x - = - - -
Before multiplying mixed numbers, change the mixed nuirbers to
improper fractions:
i -.12 52 10 .
Example: 2?x? = 7x? = -=l
In some cases a problem can be simplified by dividing (or canceling)
prior to beginning the multiplication. This operation also speeds
up the process of reducing the answer to its simplest form. To
reduce numbers by cancellation, look for a number in the numerator
and denominator that can be divided by the same number.
Example: 'f x \ x 1 = -L <2 S°es into 4"2 times^
Z( A2 5 10 (3 goes into 3—1 time)
Example - the same problem without cancellation:
2_ 3_ j_ = _6_ _ J_
3 X 4 X 5 60 " 10
Another example of calculation:
"V_j(J[__3__5_=_15_ (3 goes into 9 and 24)
1$* I* ' 4 X 8 ~ 32 (7 goes into 28 and 35)
15-15
-------
15.25 Division
To divide two fractions, invert the divisor and multiply.
. 1.1 13 3 . 1
Example: — * — = — x — = — = 1 —
y 23212 2
,
Example:
53 5 \1 10 , 1
-*=x = =3
15.26 Decimal Fractions
Decimal fractions are fractions which have 10, 100, 1000, etc.,
for denominators. They are usually called decimals.
— = 0.5 = five-tenths
10
= 0.15 = fifteen-hundredths
100
375 25 = 375.025 = three hundred seventy-five
1000 and twenty-five thousandths
or = three hundred seventy-five
point zero two five
To change any fraction to a decimal, divide the numerator by the
denominator.
Example:
= 3*4 = 43.000
0.833 .... Cnot even)
Example:
- = 5*6 = 6/5.000
4 8_
20
1_8
20
ii
2
15-16
-------
To change a decimal to a fraction, multiply the decimal by
10/10, 100/100, 1000/1000, etc. It should be noted that multi-
plying by these factors is multiplying by one (100/100 = 1) and
does not change the value of the answer.
Example: 0.25 x
Exa^e: 0.375 x
15.27 Percentage
Expressing a number in percentage is just another, and sometimes
simpler, way of writing a fraction or a decimal. It can be
thought of as parts per 100 parts, since the percentage is the
numerator of a fraction whose denominator is always 100, Twenty-
five parts per 100 parts is more easily recognized as 25/100 or
0.25. However, it is also 25%. In this case, the symbol % takes
the place of the 100 in the fraction and the decimal point in the
decimal fraction.
For the above example it can be seen that changing from a fraction
or a decimal to percent is not a difficult procedure.
1. To change a fraction to percent, multiply by 100%.
Example: - x 100% = 222. = 40%
v 5 5
c c;nn3;
Example: -x 100% = 2^il = 125%
^4 4
2. To change percent to a fraction, divide by 100%.
Example: 15% * 100% = 15% x —— = — = —
100% 100 20
Example: 0.4% * 100% = 0.4% x —^— = ^— = —— = -2—
100% 100 1000 250
In these examples note that the two percent signs cancel each
other.
15-17
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Following is a table comparing common fractions, decimal
fractions, and percent to indicate their relationship to
each other:
Common Fraction Decimal Fraction Percent
285
100
100
100
20
100
1
100
1
1000
2.85
1.0
0.20
0.01
0.001
0.000001
285%
100%
20%
1%
0.1%
0.0001%
1,000,000
15.28 Sample Problems Involving Percent
Problems involving percent are usually not complicated since
their solution consists of only one or two steps. The principal
error made is usually a misplaced decimal point. The most
common type percentage problem is finding:
1. WHAT PERCENT ONE NUMBER IS OF ANOTHER
In this case, the problem is simply one of reading care-
fully to determine the correct fraction and then converting
to a percentage.
15-18
-------
Example: What percent is 20 of 25?
20 4
= 0.8
25 5
0.8 x 100% = 80%
Example: Four is what percent of 14?
— = 0.2857
14
0.2857 x 100% = 28.57%
Example: Influent BOD to a clarifier is 200 mg/1. Effluent
BOD is 140 mg/1. What is the percent removal in
the clarifier? (NOTE: 200-140 = the part removed
in the clarifier.)
200 - 140 60 .. _n „ ,, . . , , , . ,
?on = ?77ff = ^.30 or the original load is removed
0.30 x 100% = 30% removal
Therefore % removal = (In - Out) x 100%
In
Another type of percentage problem is finding:
2. PERCENT OF A GIVEN NUMBER
In this case the percent is expressed as a decimal, and the
two numbers are multiplied together.
Example: Find 7% of 32.
0.07 x 32 = 2.24
Example: Find 90% of 5.
.90 x 5 = 4.5
15-19
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Example: What is the weight of dry solids in a ton
(2000 Ibs) of wastewater sludge containing
5% solids and 95% water?
NOTE: 5% solids means there are 5 Ibs of dry
solids for every 100 Ibs of wet sludge.
Therefore
2000 Ibs x 0.05 = 100 Ibs of solids
A variation of the preceding problem is:
3. FINDING A NUMBER WHEN A GIVEN PERCENT OF IT IS KNOWN
Since this problem is similar to the previous problem,
the solution is to convert to a decimal and divide by the
decimal.
Example: If 5% of a number is 52, what is the number?
_^_ = 1040
0.05
A check calculation may now be performed—
what is 5% of 1040?
0,05 x 1040 = 52 (Check)
Example: 16 is 80% of what amount?
J£- - 20
0.80
Example: Percent removal of BOD in a clarifier is 35%.
If 70 mg/1 are removed, what is the influent BOD?
Influent BOD = —^- = 200 mg/1
0.35 5
15-20
-------
Check:
Original load x % removal = load removed
200 mg/1 x 0.35 = 70 mg/1
15.29 Ratio and Proportion
Ratio is the comparison of two numbers of the same denomination.
For example, 1 inch compared to 3 inches, or 3 boxes compared to
7 boxes. Ratios are written either as fractions, 1/3, or as
1:3 (which is read "the ratio of one to three").
Proportion is the equating of ratios. For example, 3/6 is equal
to 1/2. A proportion is usually written in the form a/b = c/d,
or a:b = c:d (which is read as a is to b as o is to d) .
To solve the proportion a/b = c/d, we multiply diagonally across
Therefore, a x d = b x c. This procedure is sometimes called
cross multiplication.
This can be proved by substituting the previous example:
3x2 = 6x1
6 = 6
15-21
-------
When one complete ratio is known and one term of the second
ratio is known, the proportion relationship indicates what
the unknown number should be.
For instance, if one number from the previous example were
missing, the number could be found by cross multiplying.
£ = I
6 2
a x 2 = 6x1
a x 2 _ 6 x 1 Divide both sides
2 2 of equation by 2.
6x1
2
6_
2
= 3
A few example problems should indicate how to deal with ratios
and proportions.
Example: Certain bolts cost 90 cents a dozen. How much would
three bolts cost?
In setting up this proportion, we would say: 12 bolts
cost 90 cents; 3 bolts cost x cents. Therefore, the
proportion is written either as 12/3 = 90/x or
12/90 = 3/ar.
12. = 1
90 x
12 x x = 90 x 3
~ - 90 x 3'
"
4
= 22 1/2 or 23$ (to the nearest penny)
15-22
-------
Example: If 3 Ibs of salt are added to 10 gallons of water
to make a solution of a given strength, how many
pounds would be added to 129 gallons to make a
solution of the same concentration?
3 Ibs x
10 gal 129 gal
x (10 gal) = 3 Ibs C129 gal)
= 3 Ibs Q129
. 10
587 Ibs
10
= 38.7 Ibs
NOTE: Gallons in the numerator and gallons in the denominator
can be canceled without changing the value of the
solution.
Although proportions are usually not difficult to solve, some
care must be taken when using them. Some varying quantities
are inversely proportional to each other. Their products,
rather than their ratios, are constant. This can be easily
explained by an example.
Example: If three men can do a certain job in 10 hours,
how long would it take five men tc do the same
job?
This problem is inversely proportional. If this
fact were not noticed, many would solve it by
direct proportion.
3 men
10 hours
x 10 hrs
3
50 hrs
3
= 16 2/3 hrs (Wrong)
15-23
-------
The solution is wrong since increasing the manpower
should decrease the time required to do the job.
The problem is therefore inversely proportional and
the products of the varying quantities should be
equated.
3 men x 10 hours = 5 men (x hrs)
3 rtgty x 10 hrs
= 6 hrs
It is important for the operator to remember that gas pressure-
volume problems are also inversely proportional. The higher the
pressure, the smaller the volume of gas.
Example: A vessel contains 100 cubic feet of gas at 5 Ibs
per square inch pressure. What is the pressure
if the volume is reduced to 40 cubic feet?
100 cu ft x 5 psi = 40 cu ft (x psi)
100 jzty f t x 5 psi
3J = n . .
40 £0 ft
500 psi
40
= 12.5 psi
NOTE: In this problem the temperature was assumed to remain constant.
15-24
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15.3 SQUARES, CUBES, AND ROOTS
15.30 Squares and Square Roots
Squaring a number simply means multiplying a number by itself.
For instance, in squaring two we obtain four (2x2=4).
In squaring three, the answer is nine. A short way of
writing 2 x 2 is by using the superscript 2 in the following
manner, 22. Thus, if we were trying to indicate the squaring
of numbers we would write:
I2 = 1
22 = 4
32 = 9
42 = 16
:2 -_
= 25, and so on
A reverse of this process is to take a number that has been
squared and find the number which was multiplied by itself to
form the square. This process is called finding the square root.
The sign \Tindicates square root. The square root of 4 is
written, / 4 , and the answer is 2. The reverse of the previous
column would then be:
/T = i
25 = 5, and so on
A difficulty arises when the square root of a number does not
result in a whole number. Such is the case for / 20 . Since
the / 16 is 4, and the / 25 is 5, the answer is between 4
and 5. Two solutions are available to the operator who does
not possess a calculating machine, slide rule, table of square
roots, or a logarithm table. One method is an exact method
15-25
-------
which is similar to a long division problem. For this method,
the operator must refer to a mathematical textbook. Quite
frankly, this method is cumbersome and difficult to remember
if you do not work with it frequently.
The other method is a trial and error method. This method is
shown here because it is a method which will enable the solution
of square root problems using only the knowledge of multiplication.
Example: Find the square root of 20.
As previously discussed, the answer is between
4 and 5. Therefore, simply guess a number and
square it.
Assume 4.3:
4.3 x 4.3 = 18.49
Next assume 4.4:
4.4 x 4.4 = 19.36
Since (4.4)2 is close to 20, next try 4.44
numbers are picked because they are quickly multi-
plied) .
4.44 x 4.44 = 19.7136
Next assume 4.46:
4.46 x 4.46 = 19.8916
Next assume 4.47:
4.47 x 4.47 = 19.9809
For most purposes, 4.47 would be sufficiently close
to use as the answer.
For most numbers the trial and error solution takes more time
than the exact solution. Its advantage is that it requires no
memorized steps for solution, except multiplication.
15-26
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15.31 Cubes and Cube Roots
Multiplying a number by itself twice results in the cube
of the number. For example, the cube of2is2x2x2=23,
or 8. The cube of a number is indicated by a superscript 3.
13 = 1
23 = 8
33 = 27
43 = 64
53 = 125, and so on
The reverse of this process is to take the cube root of a
number.
3
The sign / indicates cube root.
Cube roots can be found by methods similar to those discussed for
square roots. The operator does not usually come in contact with
many problems involving cubes or cube roots.
A rather simple solution for square roots and cube roots is by use
of logarithms. The only mathematical step involved is division by
2 or 3. The only disadvantage is that you must have a logarithm
table handy. Since logarithms also offer a quick means of multiplying
large numbers, it is suggested that the operator become familiar
with them and keep a "log" table handy at his desk. Directions for
using logarithms are found in math textbooks and in Chapter 16,
Section 16.6.
If at all possible you should obtain a handbook containing logarithms
and tables of squares, square roots, cubes, cube roots, tank capacities
and other valuable information. Manufacturers' literature sometimes
contains this type of information.
15-27
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15.4 AVERAGES AND MEDIAN
Computing an average from a set of data offers a way of simpli-
fying the data or comparing one set of data with another. If
an average value is computed by adding a series of items and
then dividing the total by the number of items, the result is
called an arithmetic mean.
Example: Influent BOD's at a treatment plant are determined
every day. The following composite values were
obtained during one week: 210, 180, 175, 215, 195,
155, and 200. What is the arithmetic mean for the
week?
. Sum of items or values 210
Average =
Number of items or values
210+180+175+215+195+155+200
7
= 190 mg/1
Weekly average or mean BOD = 190 mg/1
Another arithmetic tool to analyze a set of data is the median.
The median in a set of data is the middle value. There are just
as many values above a median as there are below.
To determine the median, the data should be written in ascending
or descending order and the middle value identified.
Example: What is the median BOD in the preceding problem?
215
210
200
195 - Median Weekly median BOD = 195 mg/1
180
175
155
15-28
-------
Median coliform numbers are sometimes used as a standard by
regulatory agencies to avoid allowing too much weight to
large coliform values.
Example: Five days of sampling resulted in most probable
number (MPN) of coliform group bacteria per
100 ml of 23, 5, 2, 2300, and 16. Find the mean
and median coliform content.
Mean =
Mean MPN/100 ml =
Sum of values
Number of values
23+5+2+2300+16
Mean MPN/100 ml = 469 coliform
Median MPN/100 ml = 16 coliform
The above example indicates that the median value completely
eliminates the effect of the one large sample, while the mean
value is affected a great deal. Most agencies feel that the
minimum and maximum values of a group of data should always
be stated along with a mean or median. The difference between
the maximum and minimum values is called the range.
15-29
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15.5 AREAS
15.50 General
Areas are measured in two dimensions or in square units. In
the English system of measurement the most common units are
square inches, square feet, square yards, and square miles.
In the metric system the units are square millimeters, square
centimeters, square meters, and square kilometers.
15.51 Rectangle
The area of a rectangle is equal to its length (L) multiplied
by its width (W).
L< T *J
*
W
_*_
A = L x W
Example: Find the area of a rectangle if the length is 5 feet
and the width is 3.5 feet.
Area, sq ft = Length, ft x Width, ft
= 5 ft x 3.5 ft
= 17.5 ft2
= 17.5 sq ft
Example: The surface area of a settling basin is 330 square feet.
One side measures 15 feet. How long is the other side?
A = L x W
330 sq ft = L ft x 15 ft
L ft x 15 ft _ 330 ft2 Divide both sides of
15 ft 15 ft equation by 15 ft.
330 ft2
L ft =
15 ft
= 22 ft
15-30
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15.52 Triangle
The area of a triangle is equal to one half the base multi-
plied by the height. This is true for any triangle.
A
2
B
x
H
NOTE: The area of any triangle is equal to 1/2 the
area of the rectangle that can be drawn around
it. The area of the rectangle is B x H. The
area of the triangle is 1/2 B x H.
Example: Find the area of triangle ABC:
A te.
48 in
B
5 ft
The first step in the solution is to make all the
units the same. In this case, it is easier to
change inches to feet.
48 in = 48
iif
12 r
= 4 ft
NOTE:
All conversions should be calculated in the above manner,
Since 1 ft/12 in is equal to unity, or one, multiplying
by this factor changes the form of the answer but not
its value.
Area, sq ft =
NOTE:
1/2 (Base, ft)(Height, ft)
= 1/2 x 5 ft x 4 ft
— ft2
2
= 10 sq ft
Triangle ABC is one half the area of rectangle ABCD.
The triangle is a special form called a Right Triangle
since it contains a 90° angle at point B.
15-31
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15.53 Circle
A square with sides of 2R can be drawn around a circle with a
radius of R.
2R
2R
The area of the square is: A = 2R x 2R = 4R2.
It has been found that the area of any circle inscribed within
a square is slightly more than 3/4 of the area of the square.
More precisely, the area of the preceding circle is:
A circle = 3 - R2 = 3.14 R2
7
The formula for the area of a circle is usually written:
A =
7TR2
The Greek letter TT (pronounced pie) merely substitutes for the
value 3.1416.
Since the diameter of any circle is equal to twice the radius,
the formula for the area of a circle can be rewritten as follows
A r>2 n n D D TrD2
A = TrR^1 = TTXRxR=TTX — X — =
224
3.14
D2 =
0.
785
D2
The type of problem and the magnitude of the numbers in a problem
will determine which of the two formulas will provide a simpler
solution. All of these formulas will give the same results if
you use the same number of digits to the right of the decimal
point.
15-32
-------
Example: What is the area of a circle with a diameter of
20 centimeters?
In this case, the formula using a radius is more con-
venient since it takes advantage of multiplying by 10.
Area, sq cm = IT (R, cm)2
= 3.14 x 10 cm x 10 cm
= 314 sq cm
Example: What is the area of a trickling filter with a 50-foot
radius?
In this case, the formula using diameter is more con-
venient.
Area, sq ft = 0.785 (Diameter, ft)2
= 0.785 x 100 ft x 100 ft
= 7850 sq ft
Occasionally the operator may be confronted with a problem giving
the area and requesting the radius or diameter. This presents the
special problem of finding the square root of the number.
Example: The surface area of a circular clarifier is approximately
5000 square feet. What is the diameter?
A = 0.785 D2, or
Area, sq ft = 0.785 (Diameter, ft)2
5000 sq ft = 0.785 D2
0.785 D2 _ 5000 sq ft
0.785 0.785
— To solve, substitute
given values in equation.
Divide both sides by
0.785 to find D2.
D2 =
5000 sq ft
0.785
= 6369 sq ft. Therefore,
= square root of 6369 sq ft, or
Diameter, ft = / 6369 sq ft
15-33
-------
As previously mentioned, it is sometimes easier to
use a trial and error method of finding square roots.
Since 80 x 80 = 6400, we know the answer is close to
80 feet.
Try 79 x 79 = 6241
Try 79.5 x 79.5 = 6320.25
Try 79.8 x 79.8 = 6368.04
The diameter is 79.8 ft, or approximately 80 feet.
15.54 Cylinder
With the formulas presented thus far, it would be a simple matter
to find the number of square feet in a room that was to be painted.
The length of each wall would be added together and then multiplied
by the height of the wall. This would give the surface area of the
walls (minus any area for doors and windows). The ceiling area
would be found by multiplying length times width and the result
added to the wall area gives the total area.
The surface area of a circular cylinder, however, has not been dis-
cussed. If we wanted to know how many square feet of surface area
are in a tank with a diameter of 60 feet and a height of 20 feet,
we could start with the top and bottom.
60 ft
20 ft
The area of the top and bottom ends are both ir x R2
Area, sq ft = 2 ends (TT) (Radius, ft)2
= 2 x TT x (30 ft)2
= 5652 sq ft
15-34
-------
The surface area of the wall must now be calculated. If we
made a vertical cut in the wall and unrolled it, the straightened
wall would be the same length as the circumference of the floor
and ceiling.
20 ft
\
t
I
I
:•:•:•:
I
. . .
^-
\
Circumference = IT x D
This length has been found to always be IT x D. In the case of
the tank, the length of the wall would be:
Length, ft
Area would be:
A , sq ft
w n
= (IT) (Diameter, ft)
= 3.14 x 60 ft
= 188.4 ft
= Length, ft x Height, ft
= 188.4 ft x 20 ft
= 3768 sq ft
Outside Surface Area
to Paint, sq ft =
Area of top and bottom, sq ft +
Area of wall, sq ft
5652 sq ft + 3768 sq ft
9420 sq ft
A container has inside and outside surfaces and you may need
to paint both of them.
15-35
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15.55 Cone
The lateral area of a cone is equal to 1/2 of the slant height
(S) multiplied by the circumference of the base.
= l/2SxirxD = irxSxR
In the case the slant height is not given, it may be calculated
by:
S = / R2 + H2
Example: Find the entire outside area of a cone with a diameter
of 30 inches and a height of 20 inches.
Slant Height, in = / (Radius, in)2 + (Height, in)2
= / (15 in)2 + (20 in)2
= / 225 in2 + 400 in2
Area of
Cone, sq in
= / 625 in2
= 25 in
= IT (Slant Height, in) (Radius, in)
= 3.14 x 25 in x 15 in
= 1177.5 sq in
Since the entire area was asked for, the area of the
base must be added.
15-36
-------
Area, sq in
Total Area,
sq in
0.785 (Diameter, in)2
0.785 x 30 in x 30 in
706.5 sq in
Area of Cone, sq in +
Area of Bottom, sq in
1177.5 sq in + 706.5 sq in
1884 sq in
15.56 Sphere
The surface area of a sphere or
ball is equal to TT multiplied by
the diameter squared.
= TTD2
If the radius is used, the formula
becomes:
A = TiD2 = IT x 2R x 2R = 4-rrR2
O
Example: What is the surface area of a sphere shaped methane gas
container 20 feet in diameter?
Area, sq ft = TT (Diameter, ft)2
= 3.14 x 20 ft x 20 ft
= 1256 sq ft
15-37
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15.6 VOLUMES
15.60 Rectangle
Volumes are measured in three dimensions or in cubic units.
To calculate the volume of a rectangle, the area of the base
is calculated in square units and then multiplied by the
height. The formula then becomes:
V =
L
X
W
X
H
Example: The length of a box is two feet, the width is 15
inches, and the height is 18 inches. Find its volume.
Volume, cu ft = Length, ft x Width, ft x Height, ft
= 2 ft x 1 - ft x 1 - ft
4 2
= 1 ft x - ft x - ft
4 Z
15
cu ft
= 3 - cu f t
4
15-38
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15.61 Prism
The same general rule that applies to a rectangle also applies
to a prism.
Volume = Area of Base x Height
Example: Find the volume of a prism with a base area of 10 square
feet and a height of 5 feet.
Volume, cu ft = Area of Base, sq ft x Height, ft
= 10 sq ft x 5 ft
= 50 cu ft
15.62 Cylinder
The volume of a cylinder is equal to the area of the base multi-
plied by the height. ^^^
T
H
V = TrR2 x H = 0.785 D2 x H
Example:
* U r
A primary clarifier has a diameter of 100 feet and a
depth of 12 feet. Find the volume.
Volume, cu ft = 0.785 x (Diameter, ft)2 x Height, ft
= 0.785 x 100 ft x 100 ft x 12 ft
= 94,200 cu ft
15.63 Cone_
The volume of a cone is equal to 1/3 the volume of circular
cylinder of the same height and diameter.
V
3
R2
x H
15-39
-------
Example: Calculate the additional volume in the cone portion of
the clarifier in Section 15.62 if the depth at the
center of the clarifier is 16 ft. H = 16 ft - 12 ft.
Volume, cu ft = -=- x (Radius)2 x Height, ft
= j x 50 ft x 50 ft x 4 ft
= 10,500 cu ft
15.64 Sphere
The volume of a sphere is equal to Tr/6 times the diameter cubed.
Example: How much gas can be stored in a sphere with a diameter
of 12 feet? (Assume atmospheric pressure.)
Volume, cu ft = — x (Diameter, ft)3
6
= ^ x U ft x 12 ft x 12 ft
= 904.32 cubic feet
15.7 METRIC SYSTEM
The two most common systems of weights and measures are the
English system and the Metric system. Of these two, the Metric
system is more popular with most of the nations of the world.
The reason for this is that the metric system is based on a
system of tens and is therefore easier to remember and easier
to use than the English system. Even though the basic system
in this country is the English system, the scientific community
uses the Metric system almost exclusively. Although many organi-
zations have urged, for good reason, that the United States switch
to the Metric system, the English system still is the standard
system of measurement in the United States.
In order to study the Metric system, one must know the meanings
of the terminology used. Following is a list of Greek and Latin
prefixes used in the Metric system.
15-40
-------
PREFIXES USED IN THE METRIC SYSTEM
Prefixes
Milli
Centi
Deci
Unit
Deka
Hecto
Kilo
Meaning
1/1000 or 0.001
1/100 or 0.01
1/10 or 0.1
1
10
100
1000
15.70 Measures of Length
The basic measure of length is the meter.
1 kilometer (km) = 1000 meters (m)
1 meter (X) = 100 centimeters (cm)
1 centimeter (cm) = 10 millimeters (mm)
Kilometers are usually used in place of miles, meters are used in
place of feet and yards, centimeters are used in place of inches,
and millimeters are used for fractions of an inch.
1 kilometer
1 meter
1 meter
1 centimeter
1 millimeter
LENGTH EQUIVALENTS
0.621 mile 1 mile
3.28 feet 1 foot
39.37 inches 1 inch
0.3937 inch 1 inch
0.0394 inch 1 inch
1.64 kilometers
0.305 meter
0.0254 meter
2.54 centimeters
25.4 millimeters
NOTE: The above equivalents are reciprocals. If one equivalent
is given, the reverse can be obtained by division. For
instance, if one meter equals 3.28 feet, one foot equals
1/3.28 meter, or 0.305 meter.
15-41
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15.71 Measures of Capacity or Volume
The basic measure of capacity in the Metric system is the liter.
For measurement of large quantities the cubic meter is sometimes
used.
1 kiloliter (kl) = 1000 liters (1) = 1 cu meter (m3)
1 liter (1) = 1000 milliliters (nil)
Kiloliters, or cubic meters, are used to measure capacity of large
storage tanks or reservoirs in place of cubic feet or gallons.
Liters are used in place of gallons or quarts. Milliliters are
used in place of quarts, pints, or ounces.
CAPACITY EQUIVALENTS
1 kiloliter
1 liter
1 liter
1 milliliter
264.2 gallons
1.057 quarts
0.2642 gallon
0.0338 ounce
1 gallon
1 quart
1 gallon
1 ounce
0.003785 kiloliter
0.946 liter
3.785 liters
29.57 milliliters
15.72 Measures of Weight
The basic unit of weight in the Metric system is the gram. One
cubic centimeter of water at maximum density weighs one gram,
and thus there is a direct, simple relation between volume of
water and weight in the Metric system.
1 kilogram (kg) = 1000 grams (gm)
1 gram (gm) = 1000 milligrams (mg)
1 milligram (mg) = 1000 micrograms (yg)
Grams are usually used in place of ounces, and kilograms are used
in place of pounds.
WEIGHT EQUIVALENTS
1 kilogram = 2.205 pounds 1 pound
1 gram = 0.0022 pound 1 pound
1 gram = 0.0353 ounce 1 ounce
1 gram = 15.43 grains 1 grain
0.4536 kilogram
453.6 grams
28.35 grams
0.0648 gram
15-42
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15.73 Temperature
Just as the operator should become familiar with the Metric
system, he should also become familiar with the centigrade
(Celsius) scale for measuring temperature. There is nothing
magical about the centigrade scale—it is simply a different
size than the Fahrenheit scale. The two scales compare as
follows:
Fahrenheit
Centigrade
212°F
Water Boils
100 °C
32°F
0°F
Water Freezes
0°C
-17.8°C
o
The two scales are related in the following manner;
Fahrenheit = (°C x 9/5) +32°
Centigrade = (°F - 32°) x 5/9
15-43
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Example: Convert 20° Centigrade to Fahrenheit,
F = (°C x 9/5) + 32°
F = (20° x 9/5) + 32°
F = + 320
5
= 36° + 32°
= 68°F
Example: Convert -10°C to °F.
F = (-10° x 9/5) + 32°
F = -90°/5 + 32°
= -18° + 32°
= 14°F
Example: Convert -13°F to °C.
C = (°F - 32°) x
C = (-13° - 32°) x -
C = -45° x -
9
C = -5° x 5
C = -25°C
15-44
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15.74 Milligrams per Liter
Milligrams per liter (mg/1) is a unit of expression used in
laboratory and scientific work to indicate very small concen-
trations or dilutions. Since wastewater contains small con-
centrations of dissolved substances and solids, and since small
amounts of chemical compounds are sometimes used in wastewater
treatment processes, the term milligrams per liter is also
common in treatment plants. It is a weight/volume relationship,
As previously discussed:
1000 liters = 1 cubic meter = 1,000,000 cubic centimeters
Therefore
1 liter = 1000 cubic centimeters
Since one cubic centimeter of water weighs one gram,
1 liter of water = 1000 grams or 1,000,000 milligrams
milligram
liter
1 milligram
1,000,000 milligrams
1 part
million parts
1 part per
million (ppm)
Milligrams per liter and parts per million (parts) may be used
interchangeably as long as the liquid density is 1.0 gm/cu cm
or 62.43 Ib/cu ft. A concentration of 1 milligram/liter (mg/1)
or 1 ppm means that there is 1 part of substance by weight for
every 1 million parts of water. A concentration of 10 mg/1
would mean 10 parts of substance per million parts of water.
To get an idea of how small 1 mg/1 is, divide the numerator
and denominator of the fraction by 10,000. This, of course,
does not change its value since 10,000 * 10,000 is equal to one,
1 J2S. = 1 mg _ 1/10,000 mg _ 0.0001 mg =
1 1,000,000 mg'l,000,000/10,000 mg ~ 100 mg
Therefore, 1 mg/1 is equal to one ten-thousandth of a percent,
or
1% is equal to 10,000 mg/1
15-45
-------
To convert rag/1 to %, move the decimal point four places or
numbers to the left.
Working problems using milligrams per liter or parts per
million is a part of everyday operation in most wastewater
treatment plants.
15.75 Example Problems
Example: A plant effluent flowing at a rate of five million
pounds per day contains 15 mg/1 of solids. How
many pounds of solids will be discharged per day?
ir /, 15 Ibs solids
15 mg/1 =
million Ibs water
Solids
Discharged, = Concentration, Ibs/M Ibs x Flow, Ibs/day
Ibs/day
15 Ibs 5
x —
day
= 75 Ibs/day
There is one thing that is unusual about the above problem and
that is the flow is reported in pounds per day. In most treatment
plants flow is reported in terms of gallons per minute or gallons
per day. To convert these flow figures to weight, an additional
conversion factor is needed. It has been found that one gallon of
water (and wastewater, since it is almost all water) weighs 8.34
pounds. Using this factor, it is possible to convert flow in
gallons per day to flow in pounds per day.
Example: A plant influent of 3.5 million gallons per day (MGD)
contains 200 mg/1 BOD. How many pounds of BOD enter
the plant per day?
Flow, Ibs/day = Flow, M gal x 8.34 —
day gal
3.5 million jjl x 8.34 Ibs
day
= 29.19 million Ibs/day
15-46
-------
Ibs/day "^ = Concentration» rag/1 * Flow, M Ib/day
BOD - 200^* 29^9.
day
= 5838 Ibs/day
In solving the above problem a relation was used that is most
important to understand and commit to memory.
Lbs/day = Cone., mg/1 x Flow, MGD x 8.34 Ib/gal
Example: A chlorinator is set to feed 50 pounds of chlorine
per day to a flow of 0.8 MGD. What is the chlorine
dose in ppm?
Cone, or Dose, _ Ibs/day
PPm ~ MGD x 8.34 Ib/gal
50 Ib/day
0.80 MG/day x 8.34 Ib/gal
50 Ib
6.672 M Ib
= 7.5 ppm, or 7.5 mg/1
Example: Treated effluent is pumped to a spray disposal field
by a pump that delivers 500 gallons per minute.
Suspended solids in the effluent average 10 mg/1.
What is the total weight of suspended solids deposited
on the spray field during a 24-hour day of continuous
pumping?
Flow, MGD = Flow, gpm x 60 min/hr x 24 hr/day
M ft
day
= 720,000 gal/day
= 0.72 MGD
500 gal 60 izift* 24
= &— X T-~- X
* Remember that 1 mg 1 Ib They are identical ratios.
M mg M Ib '
15-47
-------
Weight of
Solids,
Ibs/day
= Cone., mg/1 x Flow, MGD x 8.34 Ib/gal
10 M ^ 0.72 M til 8.54 Ib
day
= 60.248 Ibs/day or about 60 Ibs/day
15.8 WEIGHT-VOLUME RELATIONS
Another factor for the operator to remember, in addition to the
weight of a gallon of water, is the weight of a cubic foot of
water. One cubic foot of water weighs 62.4 Ibs. If these two
weights are divided, it is possible to determine the number of
gallons in a cubic foot.
62.4
ft
o „„
8.34
_ . .
= 7-48
_ .
ft
Thus we have another very important relation to commit to memory,
8.34 Ib/gal x 7.48 gal/cu ft = 62.4 Ib/cu ft
It is only necessary to remember two of the above items since the
third may be found by calculation. For most problems, 8 1/3 Ibs/gal
and 7 1/2 gal/cu ft will provide sufficient accuracy.
Example: Change 1000 cu ft of water to gallons.
1000 cu ft x 7.48 gal/cu ft = 7480 gallons
Example: What is the weight of three cubic feet of water?
62.4 Ib/cu ft x 3 cu ft = 187.2 Ibs
Example: The net weight of a tank of water is 750 Ibs. How many
gallons does it contain?
750
8 1/3
750 gal =
25/3
gal _3- = 90 gals
*
15-48
-------
15.9 FORCE, PRESSURE, AND HEAD
In order to study the forces and pressures involved in fluid
flow, it is first necessary to define the terras used.
Force; The push exerted by water on any surface being
used to confine it. Force is usually expressed
in pounds, tons, grams, or kilograms.
Pressure: The force per unit area. Pressure can be expressed
in many ways, but the most common term is pounds
per square inch (psi).
Head; Vertical distance from the water surface to a
reference point below the surface. Usually ex-
pressed in feet or meters.
An example should serve to illustrate these terms.
If water were poured into a one-foot cubical container,
the force acting on the bottom of the container would be
62.4 pounds.
I
1 ft
JL
1 ft-
i ft
The pressure acting on the bottom would be 62.4 pounds per
square foot. The area of the bottom is also 12 in x 12 in
144 in2. Therefore, the pressure may also be expressed as:
Pressure, psi =
62.4 Ib
62.4 Ib/sq ft
144 sq in/sq ft
sq ft
= 0.433 Ib/sq in
= 0.433 psi
Since the height of the container is one foot, the head
would be one foot.
15-49
-------
The pressure in any vessel at one foot of depth or one foot of
head is 0.443 psi acting in any direction.
If the depth of water in the previous example were increased to
two feet, the pressure would be:
P =
2 (62.4 Ib) _ 124.8 Ib
144 sq in
144 sq in
= 0.866 psi
Therefore we can see that for every foot of head the pressure
increases by 0.433 psi. Thus, the general formula for pressure
becomes:
p>
psi =
0
.433
(H,
ft)
H = feet of head
p = pounds per square
inch of pressure
P,
Ib/sq
ft
= 62
.4
CH,
ft)
H = feet of head
P = pounds per square
foot of pressure
We can now draw a diagram of the pressure acting on the side of
a tank. Assume a four-foot deep tank. The pressures shown on
the tank are gage pressures. These pressures do not include the
atmospheric pressure acting on the surface of the water.
15-50
-------
x.X7 ^ w ^ ^^
/
/
Po
Pi
P2
P3
Pk
The
=" /
/
0.433 1^1
x/ 0.866 psi v
X124.8 psf
1.299 psi ^
/ 187.2 psf
1.732 psi w
249.6 psf
t '
1 ft
^
>
k t
ft
3
t
>
i, i
ft
4
V
i
ft
/
= 0.433 x 0 = 0.0 psi P0 = 62.4 x 0 = 0.0 Ib/sq ft
= 0.433 x 1 = 0.433 psi Px = 62 .4 x 1 = 62 .4 Ib/sq ft
= 0.433 x 2 = 0.866 psi P2 = 62.4 x 2 = 124.8
= 0.433 x 3 = 1.299 psi P3 = 62.4 x 3 = 187.2
= 0.433 x 4 = 1.732 psi P^ = 62.4 x 4 = 249.6
Ib/sq ft
Ib/sq ft
Ib/sq ft
average pressure acting on the tank wall is 1.732 psi/2 =
0.866 psi, or 249.6 psf/2 = 124.8 psf.
If the wall were five feet long, the pressure would be acting
over the entire 20 square foot (5 ft x 4 ft) area of the wall.
The total force acting to push the wall would be:
Force, Ib = (Pressure, Ib/sq ft)(Area, sq ft)
= 124.8 Ib/sq ft x 20 sq ft
= 2496 Ibs
15-51
-------
If the pressure in psi were used, the problem would be similar:
Force, Ib = (Pressure, Ib/sq in) (Area, sq in)
= 0.866 psi x 48 in x 60 in
= 2494 Ib*
The general formula, then, for finding the total force acting
on a side wall of a tank is:
F = force in pounds
H = head in feet
F = 31.2 x H2 x L
L = length of wall in feet
31.2 = constant with units of
Ibs/cu ft and considers the
fact that the force is exerted
at H/2 or half the depth of the
water.
Example: Find the force acting on a five-foot long wall in
a four-foot deep tank.
Force, Ib = 31.2 (Head, ft)2 (Length, ft)
= 31.2 Ib/cu ft x (4 ft)2 x 5 ft
= 2496 Ibs
Occasionally an operator is warned: Never empty a tank during
periods of high groundwater. Why? The pressure on the bottom
of the tank caused by the water surrounding the tank will tend
to float the tank like a cork if the upward force of the water
is greater than the weight of the tank.
F = upward force in pounds
H = head of water on tank
bottom, in feet
F = 62.4 x H x A
A = area of bottom of tank
in square feet
62.4 = a constant with units of
Ibs/cu ft
* Difference in answer due to rounding off of decimal points,
15-52
-------
This formula is approximately true if the tank doesn't crack,
leak, or start to float.
Example: Find the upward force on the bottom of an empty
tank caused by a groundwater depth of 8 feet above
the tank bottom. The tank is 20 ft wide and 40 ft
long.
Force, Ib = 62.4 (Head, ft)(Area, sq ft)
= 62.4 Ib/cu ft x 8 ft x 20 ft x 40 ft
= 399,400 Ib
15-53
-------
15.10 VELOCITY AND RATE OF FLOW
15.100 Velocity
The velocity of a particle or substance is the speed at which
it is moving. It is expressed by indicating the length of
travel and how long it takes to cover the distance. Velocity
can be expressed in almost any distance and time units. For
instance, a car may be traveling at a rate of 280 miles per
five hours. However, it is normal to express the distance
traveled per unit time. The above example would then become:
,r n . ,, 280 miles
Velocity, mi/hr =
5 hours
= 56 miles/hour
The velocity of water in a channel, pipe, or other conduit
can be expressed in the same way. If the particle of water
travels 600 feet in five minutes, the velocity is:
.. T .. _. , . distance, ft
Velocity, ft/mm =
time, minutes
600 ft
5 min
= 120 ft/min
If it is desired to express the velocity in feet per second,
multiply by 1 min/60 seconds.
NOTE: is like — and does not change the relative
60 seconds 1
value of the answer. It only changes the form of the answer.
Velocity, ft/sec = (Velocity, ft/min)(1 hr/60 sec)
120 ft 1
- x
60 sec
120 ft
60 sec
= 2 ft/sec
15-54
-------
15.101 Rate of Flow
If water in a one-foot wide channel is one foot deep, then the
cross sectional area of the channel is 1 ft x 1 ft = 1 sq ft.
1 ft
If the velocity in this channel is 1 ft per second, then each
second a body of water 1 sq ft in area and 1 ft long will pass
a given point. The volume of this body of water would be 1
cubic foot. Since one cubic foot of water would pass by every
second, the rate of flow would be equal to 1 cubic foot per
second, or 1 cfs.
To obtain the rate of flow in the above example the velocity
was multiplied by the cross sectional area. This is another
important general formula.
Q = rate of flow, cfs or
cu ft/sec
V = velocity in ft/sec
A = area, in sq ft
Q =
V x A
15-55
-------
Example: Flow in a 2.5 foot wide channel is 1.4 ft deep and
measures 11.2 cfs. What is the average velocity?
In this problem we want to find the velocity.
Therefore, we must rearrange the general formula
to solve for velocity.
= Q
.. n .. ,.. , Flow Rate, cu ft/sec
Velocity, ft/sec = -
Area, sq ft
11.2 cu ft/sec
2.5 ft x 1.4 ft
11.2 ft/sec
3.5
= 3.2 ft/sec
Example: Flow in an 8-inch pipe is 500 GPM. What is the
average velocity?
Area, sq ft = 0.785 (Diameter, ft)2
= 0.785 (8/12 ft)2
= 0.785 (2/3 ft)2
= 0.785 (2/3 ft)(2/3 ft)
= 0.785 (4/9 ft2)
= 0.35 sq ft
r,, ,- „, . , . cu ft 1 min
How, cfs = Flow, gal/min x x
7.48 gal 60 sec
500 jj.1 cu ft 1
X
7.48 HI 60 sec
500 cu ft
448.8 sec
= 1.114 cfs
15-56
-------
Velocity, ft/sec =
Flow, cu ft/sec
Area, sq ft
1.114 ft3/sec
0.35 ft2
= 3.18 ft/sec
15.11 PUMPS
15.110 General
Atmospheric pressure at sea level is approximately 14.7 psi.
This pressure acts in all directions and on all objects. If
a tube is placed upside down in a basin of water and a 1 psi
partial vacuum is drawn on the tube, the water in the tube
will rise 2.31 feet.
13.7 psi absolute pressure
(-1 psi gage pressure)
14.7 psi absolute pressure
(0 psi gage pressure)
NOTE: 1 ft of water = U.433 psi; therefore,
1
The action of the partial vacuum is what gets water out of a
sump or well and up to a pump. It is not sucked up, but it is
pushed up by atmospheric pressure on the water surface in the
sump. If a complete vacuum could be drawn, the water would rise
2.31 x 14.7 = 33.9 feet; but this is impossible to achieve. The
practical limit of the suction lift of a positive displacement
pump is about 22 feet, and that of a centrifugal pump is 15 feet.
15-57
-------
15.111 Work
Work can be expressed as lifting a weight a certain vertical
distance. It is usually defined in terms of foot-pounds.
Example: A 165-pound man runs up a flight of stairs 20 feet
high. How much work did he do?
Work, ft-lb = Weight, Ib x Height, ft
= 165 Ib x 20 ft
= 3300 ft-lb
15.112 Power
Power is a rate of doing work and is usually expressed in foot-
pounds per minute.
Example: If the man in the above example runs up the stairs
in three seconds, how much power has he exerted?
n *-* iu / Work, ft-lb
Power, ±t-lbs/sec =
Time, sec
3300 ft-lbs 60
3 Hi minute
= 66,000 ft-lb/min
15.113 Horsepower
Horsepower is also a unit of power.. One horsepower is defined as
33,000 ft-lbs per minute or 746 watts.
Example: How much horsepower has the man in the previous
example exerted as he climbs the stairs?
Horsepower, ,„ _ , . . ^ f HP )
Iir) = (Power, ft-lb/min) -
HP \. • i ) [33,000 ft-lb/min)
= 66,000 ft-lb/miu x Horsepower -
33,000 ft-lb/min
= 2 HP
15-58
-------
Work is also done by lifting water. If the flow from a pump
is converted to a weight of water and multiplied by the vertical
distance it is lifted, the amount of work or power can be
obtained.
Horse-
;. = Flow, gal x L.ft> ft x 8.34 Ib
HP min 8al
Horsepower
33,000 ft-lb/min
Solving the above relation, the amount of horsepower necessary
to lift the water is obtained. This is called water horsepower.
Water, HP = (Flow, gpm) (H, ft)
3960*
However, since pumps are not 100% efficient (they cannot trans-
mit all the power put into them), the horsepower supplied to a
pump is greater than the water horsepower. Horsepower supplied
to the pump is called brake horsepower.
Brake, HP = Flow, gpm x H, ft
3960 x E
P
= Efficiency of Pump
(Usual range 50-85°
depending on type
and size of pump)
Motors are also not 100% efficient; therefore, the power supplied
to the motor is greater than the motor transmits.
Motor, HP =
Flow,
3960
gpm x H, ft
x E x E
p m
E = Efficiency of motor
m (Usual range 80-95%,
depending on type
and size of motor)
The above formulas have been developed for the pumping of water
and wastewater which have a specific gravity of 1.0. If other
liquids are to be pumped, the formulas must be multiplied by
the specific gravity of the liquid.
Example: A flow of 500 gpm of water is to be pumped against
a total head of 100 feet by a pump with an efficiency
of 70%. What is the pump horsepower?
* 8.34 Ib
gal
HP
33,000 ft-lb/min
15-59
-------
Brake, HP =
Flow, gpm x H. ft
3960 x E
P
500 x 100
3960 x 0.70
= 18 HP
Example: Find the horsepower required to pump gasoline
(specific gravity = 0.75) in the above problem.
Brake, HP =
500 x 100 x 0.75
3960 x 0.70
= 13.5 HP (gasoline is lighter and
requires less horsepower)
15.114 Head
Basically, the head that a pump must work against is determined
by measuring the vertical distance between the two water surfaces,
or the distance the water must be lifted. This is called the
static head. Two typical conditions for lifting water are shown
below.
If a pump were designed in the above examples to pump only against
head H, the water would never reach the intended point. The reason
for this is that the water encounters friction in the pipelines.
Friction depends on the roughness and length of pipe, the pipe
diameter, and the flow velocity. The turbulence caused at the
pipe entrance (point A); the pump (point B); the pipe exit
(point C); and at each elbow, bend, or transition also adds to
these friction losses. Tables and charts are available for
15-60
-------
calculation of these friction losses so they may be added to
the measured or static head to obtain the total head. For
short runs of pipe which do not have high velocities the
friction losses are generally less than 10% of the static
head.
Example: A pump is to be located eight feet above a wet
well and must lift 1.8 MGD another 50 feet to a
storage reservoir. If the pump has an efficiency
of 75% and the motor an efficiency of 90%, what
is the cost of the power consumed if one kilowatt
hour costs 1 cent?
Since we are not given the length or size of pipe
and the number of elbows or bends, we will assume
friction to be 10% of static head.
Static Head, ft = Suction Lift, ft +
Discharge Head, ft
= 8 ft + 50 ft
= 58 ft
Friction
Losses, ft
= 0.1 (Static Head, ft)
= 0.1 CS8 ft)
= 5.8 ft
Total Head, ft
= Static Head, ft +
Friction Losses, ft
= 58 ft + 5.8 ft
= 63.8 ft
Flow, gpm
1,800,000 gal
24
60 min
= 1250 gpm (assuming pump runs
24 hours per day)
15-61
-------
Motor, HP
= Flow, gpm x H. ft
3960 x E x E
p m
1250 x 65.8
3960 x 0.75 x 0.9
30 HP
Kilowatt- hrs =
30 H? x 24 hrs/day x 0.746
537 kilowatt-hrs/day
Cost
KWH x $0.01/KWH
537 x 0.01
$5.37/day
15.115 Pump Characteristics
The discharge of a centrifugal pump, unlike a positive displace-
ment pump, can be made to vary from zero to a maximum capacity
which depends on the speed, head, power, and specific impeller
design. The interrelation of capacity, efficiency, head, and
power is known as the characteristics of the pump.
The first relation normally looked at when searching for a pump
is the head vs. capacity. The head of a centrifugal pump normally
rises as the capacity is reduced. If the values are plotted on
a graph they appear as follows:
Capacity
15-62
-------
Another important characteristic is the pump efficiency. It
begins from zero at no discharge, increases to a maximum, and
then drops as the capacity is increased. Following is a graph of
efficiency vs. capacity:
Capacity
The last important characteristic is the brake horsepower or
the power input to the pump. The brake horsepower usually
increases with increasing capacity until it reaches a maximum,
then it normally reduces slightly.
0
Capacity
These pump characteristic curves are quite important. Pump
sizes are normally picked from these curves rather than calcu-
lations. For ease o£ reading, the three characteristic curves
are normally plotted together. A typical graph of pump charac-
teristics is shown as follows:
15-63
-------
8 10 12 14 16
Capacity in 100 gpm
18 20
22
24
The curves show that the maximum efficiency for the particular
pump in question occurs at approximately 1475 gpm, a head of
132 feet, and a brake horsepower of 58. Operating at this
point the pump has an efficiency of approximately 85%. This can
be verified by calculation:
BHP - Flow>
ft
3960 x E
As previously explained, a number can be written over one without
changing its value :
BHP _ gpm x H
1 " 3960 x E
15-64
-------
Since the formula is now in ratio form, it can be cross multi-
plied.
BHP x 3960 x E = gpm x H x 1
Solving for E,
gpm x H
E =
3960 x BHP
E = 1475 gpm x 132 ft
3960 x 58 HP
= 0.85 or 85% (Check)
The preceding is only a brief description of pumps to familiarize
the operator with their characteristics. The operator does not
normally specify the type and size of pump needed at his plant.
If a pump is needed, the operator should be able to supply the
information necessary for a pump supplier to provide the best
possible pump for the lowest cost. Some cf the information needed
includes:
1. Flow range desired
2. Head conditions
a. Suction head or lift
b. Pipe and fitting friction head
c. Discharge head
3. Type of fluid pumped and temperature
4. Pump location
15-65
-------
15.116 Evaluation of Pump Performance
1. Capacity
Sometimes it is necessary to determine the capacity of a pump.
This can be accomplished by determining the time it takes a
pump to fill a portion of a wet well.
Example:
a. Measure the size of the wet well.
Length = 10 ft (We will measure the time it takes
...,., ..- ,.. to fill the well only to a depth
Width = 10 ft _ -. - . ., ' .c 4.
of five feet, or the time for water
Depth = 5 ft in the well to rise five feet.)
Volume, cu ft = L, ft x W, ft x D, ft
= 10 ft x 10 ft x 5 ft
= 500 cu ft
b. Record time for water to rise five feet in wet well.
Time = 10 minutes 30 seconds
= 10.5 minutes
c. Calculate pumping rate or capacity.
n . n . Volume, gallons
Pumping Rate, gpm = ~2
Time, minutes
(500 cu ft)(7.5 gal/cu ft)
10.5 min
5750
10.5
= 357 gpm
15-66
-------
2. Efficiency
To estimate the efficiency of the pump in the previous example,
the total head must be known. This head may be estimated by
measuring the suction and discharge pressures. Assume these
were measured as follows:
2 in. mercury
vacuum
20 psi
Suction
side
Discharge
side
flow
No additional information is necessary if we assume the pressure
gages are at the same height and the pipe diameters are the same.
Both pressure readings must be converted to feet.
Suction Head, ft = 2 in Mercury x
= 2.27 ft
1.155 ft water'
1 in Mercury
Discharge Head, ft = 20 psi x 2.31 ft/psi*
= 46.20 ft
Total Head, ft
= Suction Head, ft + Discharge Head, ft
= 2.27 ft + 46.20 ft
= 48.47 ft
See Conversion Tables—Section 15.15, Pressure.
15-67
-------
Calculate the power output of the pump or water horsepower:
Water Horsepower, _ (F1ow, gpm)(He ad, ft)
HP " 3960
(357 gpm)(48.47 ft)
3960
= 4.4 HP
To estimate the efficiency of the pump, measure the kilowatts
drawn by the pump motor. Assume the meter indicates 8000 watts
or 8 kilowatts. The manufacturer claims the electric motor is
80% efficient.
Brake Horsepower,
HP
= (Power to elec. motor)(motor eff.)
(8 kw)(0.80)
0.746 kw/HP
= 8.6 HP
Pump
Efficiency, %
Water Horsepower, HP x
Brake Horsepower, HP
4.4 HP x 100%
8.6 HP
= 51%
The following diagram may clarify the above problem:
Power Input
to Motor or
Motor HP
>*
Q 1
o KW or
10.7 HP
MOTOR
1
Motor Loss
1.6 kw or
2.1 HP
Power Input
to Pump or
Brake HP ^
^ PUMP
r i i
8.6 HP >
Power Transmitted
to Water
nr Uat-pT
Horsepower ^
\ 4.4 HP
Pump Loss
3.1 kw
4.2 HP
or
15-68
-------
15.117 Pump Speed—Performance Relationships
Changing the velocity of a centrifugal pump will change its
operating characteristics. If the speed of a pump is changed,
the flow, head developed, and power requirements will change.
The operating characteristics of the pump will change with
speed approximately as follows:
Flow, Q
-n
Head, H
n
n
N
r = rated
n = now
N = pump speed
Power, P =
n
Nr
Actually, pump efficiency does vary with speed; therefore, these
formulas are not quite correct. If speeds do not vary by more
than a factor of two (if the speeds are not doubled or cut in
half), the results are close enough. Other factors contributing
to changes in pump characteristic curves include impeller wear
and roughness in pipes.
Example: To illustrate these relationships, assume a pump
has a rated capacity of 600 gpm, develops 100 ft
of head, and has a power requirement of 15 HP when
operating at 1500 rpm. If the efficiency remains
constant, what will be the operating characteristics
if the speed drops to 1200 rpm?
15-69
-------
Calculate new flow rate or capacity:
Flow, Q
'N
n
N
(1200 rpm} ...
*— 600 gpm
[1500 rpmj
-I 600 gpm
J
= (4) (120 gpm)
= 480 gpm
Calculate new head:
Head, H.
n
N
n
N~
r
2
H
r
(1200 rpm
[1500 rpm
100 ft
5
100 ft
16
(25.
= 16 (4 ft)
= 64 ft
(100 ft)
Calculate new power requirement:
Power, P
n
n
1200 rPm]3 15 HP
1500 rpmj
15-70
-------
4|3
15HP
64
(15 HP)
,125,
f \
= |£i (3 HP)
(^DJ
= 7.7 KP
15.12 STEPS IN SOLVING PROBLEMS
15.120 Identify Problem
To solve any problem, you have to identify the problem, determine
what kind of answer is needed, and collect the information needed
to solve the problem. A good approach to this type of problem is
to examine the problem and make a list of known and unknown infor-
mation.
Example: Find the theoretical detention time in a rectangular
sedimentation tank 8 feet deep, 30 feet wide, and
60 feet long when the flow is 1.4 MGD.
Unknown
Detention Time, hours
Known
Depth
Width
Length
Flow
=
=
=
s
8 ft
30 ft
60 ft
1.4 MGD
Sometimes a drawing or sketch will help to illustrate a problem
and indicate the knowns, unknowns, and possibly additional infor-
mation needed.
15-71
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15.121 Selection of Formula
Most problems involving mathematics in wastewater treatment
plant operation can be solved by selecting the proper formula,
inserting the known information, and calculating the unknown.
In our example, we could look in Chapter 5, Sedimentation and
Flotation, or in Section 15.14 of this chapter, Summary of
Formulas, to find a formula for calculating detention time.
From Section 15.14:
Detention _ (Tank Volume, cu ft) (7^5 gal/cu ft) (24 hr/day)
Time, hrs ~ Flow, gal/day
To convert the known information to fit the terms in a formula
sometimes requires extra calculations. The next step is to find
the values of any terms in the formula that are not in the list
of known values.
Flow, gal/day = 1.4 MGD
= 1,400,000 gal/day
From Section 15.140:
Tank Volume, = (Length, ft) (Width, ft) (Height, ft)
cu ft
= 60 ft x 30 ft x 8 ft
= 14,400 cu ft
Solution of Problem:
Detention _ (Tank Volume, cu ft) (7.5 gal/cu ft) (24 hr/day)
Time, hrs ~ Flow'," gal/day "
(14,400 cu ft) (7.5 gal/cu ft) (24 hr/day)
l', 400', 000 ga 1 /day
= 1.9 hr
The remainder of this section discusses the details that must
be considered in solving this problem.
15-72
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15.122 Units and Dimensional Analysis
Each term in a formula or mathematical calculation must be of the
correct units. The area of a rectangular clarifier (Area, sq ft =
Length, ft x Width, ft) can't be calculated in square feet if the
width is given as 246 inches or 20 feet 6 inches. The width must
be converted to 20.5 feet. In the example problem, if the tank
volume were given in gallons, then the 7.5 gal/cu ft would not be
needed. The units in a formula must always be checked before any
calculations are performed to avoid time-consuming mistakes.
Detention _ (Tank Volume, cu ft) (7.5 gal/cu ft) (24 hr/day)
Time, hrs Flow, gal/day
= hr (all other units cancel)
NOTE: We have hours = hr. One should note that the hour unit
on both sides of the equation can be cancelled out, and
nothing would remain. This is one more check that we
have the correct units. By rearranging the detention
time formula, other unknowns could be determined.
If the design detention time and design flow were known, the
required capacity of the tank could be calculated.
Tank Volume, _ (Detention Time, hr) (Flow, gal/day)
cu ft ~ (7.5 gal/cu ft) (24 hr/day)
If the tank volume and design detention time were known, the
design flow could be calculated.
Flow, _ (Tank Volume, cu ft) (7.5 gal/cu ft) (24 hr/day)
gal/day Detention Time, hr
Rearrangement of the detention time formula to find other unknowns
illustrates the need to always use the correct units.
15-73
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15.123 Calculations
Sections 15.12, Multiplication, and 15.13, Division, outline the
steps to follow in mathematical calculations. In general, do the
calculations inside parentheses ( ) first and brackets C 3 next.
Calculations should be done above and below the division line
before dividing.
Detention _ (Tank Volume, cu ft) (7.5 gal/cu ft) (24 hr/day)
Time, hrs Flow, gal day
(14,400 cu ft) (7.5 gal/cu ft) [24 hr/day)
1,400,000 gal/day
14400
180
1152000
14400
2,592,000
2,592,000 gal-hr/day
1,400,000 gal/day
1.85
1400/ 2592
1400
11920
11200
7200
7000
1.85, or
1.9 hr
15-74
-------
15.124 Significant Figures
In calculating the detention time in the previous section the
answer is given as 1.9 hr. The answer could have been calculated:
Detention _ 2,592,000 gal-hr/day
Time, hrs "T,400"000 gal/day
= 1.850428571428571428 hours
How does one know when to stop dividing? Common sense and significant
figures both help.
First, consider the meaning of detention time and the measure-
ments that were taken to determine the knowns in the formula.
Detention time in a tank is a theoretical value and assumes
that all particles of water throughout the tank move through
the tank at the same velocity. This assumption is not correct;
therefore, detention time can only be a representative time for
some of the water particles.
Will the flow of 1.4 MGD be constant throughout the 1.9 hours,
and is the flow exactly 1.4 MGD, or could it be 1.35 MGD or
1.428 MGD? A carefully calibrated flow meter may give a reading
within 2% of the actual flow rate. Flows into a tank fluctuate
and flow meters do not measure flows extremely accurately; so
the detention time again appears to be a representative or typical
detention time.
Tank dimensions are probably satisfactory within 0.1 ft. A flow
meter reading of 1.4 MGD is less precise and it could be 1.3 or 1.5
MGD. A 0.1 MGD flow meter error when the flow is 1.4 MGD is
(0.1/1.4) x 100% = 7% error. A detention time of 1.9 hours, based
on a flow meter reading error of plus or minus 7%, also could have
the same error or more, even if the flow was constant. Therefore,
the detention time error could be 1.9 hours x 0.07 = ±0.13 hours.
In most of the calculations in the operation of wastewater treat-
ment plants, the operator uses measurements determined in the lab
or read from charts, scales, or meters. The accuracy of every
measurement depends on the sample being measured, the equipment
doing the measuring, and the operator reading or measuring the
results. Your estimate is no better than the least precise
measurement. Do not retain more than one doubtful number.
To determine how many figures or numbers mean anything in an
answer, the approach called "significant figures" is used. In
the example the flow was given in two significant figures (1.4 MGD),
and the tank dimensions could be considered accurate to the
nearest tenth of a foot (depth = 9.0 ft) or two signifi-
cant figures. Since all measurements and the constants contained
15-75
-------
two significant figures, the results should be reported as two
significant figures or 1.9 hours. The calculations are normally
carried out to three significant figures (1.85 hours) and
rounded off to two significant figures (1.9 hours).
Decimal points require special attention when determining the
number of significant figures in a measurement.
Measurement Significant Figures
0.00325 3
11.078 5
21,000. 2
Example: The distance between two points was divided into
three sections, and each section was measured by
a different group. What is the distance between
the two points if each group reported the distance
it measured as follows:
Distance, ft Significant Figures
11,300. 3
2,438.9 5
87.62 4
Distance 13,826.52
Group A reported the length of the section it
measured to three significant figures; therefore,
the distance between the two points should be re-
ported as 13,800 feet (3 significant figures).
When adding, subtracting, multiplying, or dividing, the number
of significant figures in the answer should not be more than the
term in the calculations with the least number of significant
figures.
15.125 Check Your Results
After having completed your calculations, you should carefully
examine your calculations and answer. Does the answer seem
reasonable0 If possible, have another operator check your
calculations before making any operational changes.
15-76
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15.13 TYPICAL TREATMENT PLANT PROBLEMS
15.130 Grit Chambers
1. Grit Chamber Velocity
Example: Estimate the velocity of wastewater flowing through
a grit chamber if a stick travels 32 feet in 36
seconds.
Known Unknown
Distance = 32 ft Velocity, ft/sec
Time = 36 sec
.. , .. ,.. . Distance Traveled, ft
Velocity, ft/sec = '-
Time, sec
32 ft
36 sec
= 0.89 ft/sec
2. Volume of Grit Removed
Example: A grit chamber removed 3.2 cu ft of grit during a
period when the total flow was 0.8 MG. How many
cu ft of grit are removed per MG?
Known Unknown
Vol. of Grit = 3.2 cu ft Grit Removed,
Vol. of Flow = 0.8 MG CU £t/MG
Grit Removed, _ Volume of Grit, cu ft
cu ft/MG ~ Volume of Flow, MG
5.2 cu ft
0.8 MG
= 4.0 cu ft/MG
15-77
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15.131 Sedimentation Tanks and Clarifiers
Example: A circular clarifier handles a flow of 0.9 MGD.
The clarifier is 50 feet in diameter and 8 feet
deep. Find the detention time, surface loading
rate, and weir overflow rate.
Unknown
0.9 MGD Detention Time, hours
50 ft Surface Loading, gpd/sq ft
8 ft Weir Overflow, gpd/ft
Detention Time
Detention _ (Tank Volume, cu ft) (.7.5 gal/cu ft) (24 hr/day)
Time, hrs ~ Flow, gal/day
Tank
Volume,
cu ft
= (Area, sq ft)(Depth, ft)
Clarifier
Area, = 0.785 (Diameter, ft)2
sq ft
Clarifier Area, sq ft = 0.785 (Diameter, ft)2
= 0.785 (50 ft)2
= 1962.5 sq ft, or
= 1960 sq ft
Tank Volume, cu ft
= (Area, sq ft)(Depth, ft)
= (1960 sq ft)(8 ft)
= 15,680 cu ft
15-78
-------
Detention _ (_T_ank Volume, cu ft) (7.5 gal/cu ft) (24 hr/day)
Time, hrs Flow, gal/day
(15,680 cu ftp(7.5 gal/cu ft) (24 hr/day)
900,000 gal/day
2,820,000
900,000
= 3.1 hr
Surface Loading Rate
Surface Loading, gpd/sq ft =
Weir Overflow Rate
Flow, gpd
Area, sq ft
900,000 gpd
1960 sq ft
= 459 gpd/sq ft
Weir Overflow, gpd/ft
Flow, gpd
Length of Weir, ft
Length of Weir, ft
3.14 (Diameter, ft)
3.14 (50 ft)
157 ft
Weir Overflow, gpd/ft
Flow, gpd
Length of Weir, ft
900,000 gpd
157 ft
= 5730 gpd/ft
15-79
-------
15.132 Trickling Filters
Example: A flow of 1.1 MGD is applied to a 50-ft diameter
trickling filter which is 4 feet deep. The BOD
of the wastewater is 120 mg/1. Calculate the
hydraulic and organic loadings on the filter.
Known
Flow
Diameter
Depth
BOD
1.1 MGD
50 ft .
4 ft
120 mg/1
Unknown
Hydraulic Loading, gpd/sq ft
Organic Loading,
Ibs BOD/day
1000 cu ft
Hydraulic Loading
Hydraulic Loading, gpd/sq ft =
Flow, gpd
Surface Area, sq ft
Surface Area, sq ft
= 0.785 (Diameter, ft)2
= 0.785 C50 ft)2
= 1960 sq ft
Hydraulic Loading, gpd/sq ft =
Flow, gpd
Surface Area, sq ft
1,100,000 gpd
1960 sq ft
= 561 gpd/sq ft
15-80
-------
Organic Loading
n .... Ibs BOD/day BCD Applied, Ibs/day
Organic Loading, • — = *•*• •
1000 cu ft Volume of Media, 1000 cu ft
wf MGD)(8.34 Ib/gal)
Volume of Media, ,„ _ .... r _
(Surface Area, sq ft) (Depth, ft)
1000 cu f t
= CBOD> mg/DCFlow, MGD) (8.34 Ib/gal)
= (120 mg/l)(l.l MGD) (8.34 Ib/gal)
= 1100 Ibs BOD/day
Volume of Media, , . _ ^- , _ .
1000 cu ft (Surface Area, sq ft)(Depth, ft)
= (1960 sq ft)(4 ft)
= 7840 cu ft
= 7.84 - 1000 cu ft
Organic Loading, lbs BOD/day - BOD Applied, Ibs/day
1000 cu ft Volume of Media, 1000 cu ft
1100 lbs BOD/day
7.84 (1000 cu ft)
= 140 lbs BOD/day/1000 cu ft
15-81
-------
15.133 Activated Sludge
Example: Lab results and flow rate for an activated sludge
plant are listed below under the known column.
Information helpful to the operator in controlling
the process is listed in the unknown column. The
aerator or aeration tank volume is 0.50 MG.
Known
Mixed Liquor Suspended Solids (MLSS) = igOO mg/1
Mixed Liquor Volatile Content = 76%
Thirty-Minute Settleable Solids Test* = 360 ml, or 17%
Primary Effluent BOD' = 140 mg/1
Primary Effluent Suspended Solids = 110 mg/1
Flow Rate =2.0 MGD
Unknown
Pounds of Solids in the Aerator
Sludge Volume Index, SVI
Pounds of BOD Applied to Aerator
Sludge Age
Pounds of Solids in Aerator
Aerator Solids, Ibs = (MLSS, mg/1)(Tank Vol., MG)(8.34 Ibs/gal)
= (1800 mg/1)(0.50 MG)(8.34 Ibs/gal)
= 7500 Ibs
Sludge Volume Index, SVI
(Settleable Solids, %)(10,000)
MLSS, mg/1
(17)(10,OOP)
1800
= 94
* Thirty-minute results obtained from 60-minute settleable solids
test using 2 liter cylinder.
15-82
-------
Pounds of BOD Applied to Aerator
Aerator
Loading, = (Primary Effluent BOD, mg/1)(Flow, MGD)(8.34 Ibs/gal)
Ibs BOD/day
= (140 rag/1) (2.0 MGD)(8.34 Ibs/gal)
= 2335 Ibs BOD/day Applied to Aerator
Sludge Age
Chapter 7, Activated Sludge, and Chapter 14, Laboratory Procedures
and Chemistry, discuss the different methods of calculating sludge
age and the meaning of the results.
_ (MLSS, mg/1)(Tank Volume, MG)(8.34 Ib/gal)
days " CSS in Primary Effl., mg/1)(Flow, MGD)(8.34 Ib/gal)
Mixed Liquor Solids, Ibs (or Aerator Solids, Ibs)
Primary Effluent Solids, Ibs/day
7500 Ibs
(110 mg/1)(2.0 MGD)(8.34 Ib/gal)
7500 Ibs
1834 Ibs/day
= 4.1 days
15-83
-------
15.134 Sludge Digestion
1. C02 in Digester Gas
Example: The total volume of a 100 ml graduate used in the C02
test is 127 ml. The volume of gas remaining in the
graduate after the C02 test was 82 ml. Find the per-
cent C02 in the digester gas.
Known Unknown
Total Volume = 127 ml Percent C02
Gas Remaining = 82 ml
(Total Volume, ml - Gas Remaining, ml) 0
o — i . . . 1UU-6
Total Volume, ml
= (127 ml - 82 ml) 1QQ%
127 ml
45 ml
127 ml
= 35%
100%
2. Volatile Acid/Alkalinity Relationship
Example: The volatile acids in a digester are 250 mg/1, and the
alkalinity is 1750 mg/1. Find the volatile acid/alkalinity
relationship.
Known Unknown
Volatile Acids = 250 mg/1 Volatile Acid/Alkalinity
Alkalinity = 1750 mg/1
Volatile Acid/ _ Volatile Acid, mg/1
Alkalinity ~ Alkalinity, mg/1
250 mg/1
1750 mg/1
= .14
15-84
-------
3. Voluire Per Stroke cf a Piston Pump
Example: Calculate the volume (in gallons) pumped per stroke
(revolution) by a piston pump with a bore of 2 5/12
inches and a stroke of 3 inches.
Known
Dia. of Piston = 2 5/12 in
Length of Stroke = 3 in
Unknown
Volume, gallons
Cylinder Volume, = (Area, sq in) (Length, in)
cu in
= (0.785) (2.417 in)2 (3in)
= 13.75 cu in
Cylinder Volume, _ 13.75 cu in
gal 231 cu in/gal
= 0.06 gal, or volume pumped per
stroke is 0.06 gal.
The actual volume pumped per stroke will be slightly below
0.06 gallon because the system is not 100% efficient.
4. Percent Reduction of Volatile Matter
Example: Find the percent reduction of volatile matter in a
digester if the percent volatile matter in the raw
sludge was 71 percent and the digested sludge was
composed of 53 percent volatile matter.
Known
In, % VM in Raw Sludge =71%
Out, % VM in Dig. Sludge = 53%
(In - Out)
In - (In x Out)
.>
p (.71 - .53) 1
I .71 - (.71 x .53) I
10° °
Unknown
P, % Reduction of VM
15-85
-------
— x 100%
.33
= .55 x 100%
= 55%
5. Digester Loading
Example: A digester with a volume of 25,000 cu ft receives 2000
pounds of raw sludge per day with a volatile content
of 70%.
Known Unknown
Digester Volume = 25,000 cu ft Digester Loading,
Raw Sludge = 2000 pounds lb VM/day/cu £t
Volatile Content = 70%
Volatile Matter f „. , ., . , ... 0.
Added, Ib/day = (Raw Slud§e> Ibs/day)(Volatile, %)
= (2000 Ibs/day)(0.70)
= 1400 Ibs/day
Digester Loading, _ Volatile Matter Added, Ib/day
lb VM/day/cu ft ~ - Digester Volume, cu ft
1400 Ibs/day
25,000 cu ft
= 0.056 Ibs VM/day/cu ft
15-86
-------
15.135 Ponds
Example: To calculate the different loadings on a pond, the
information listed under known must be available.
Known
Ave. Depth
Ave. Width
Ave. Length
Flow
BOD
Population
Unknown
4 ft
400 ft
600 ft
0.5 MGD
150 mg/1
5000 persons
Detention Time, days
Population Loading, persons/acre
Hydraulic Load, in/day
Organic Load, Ibs BOD/day/acre
Detention Time
Detention Time, days =
Pond Volume, ac-ft
Flow Rate, ac-ft/day
Pond Area, acres
(Average Width, ft)(Average Length, ft)
43,560 sq ft/acre
(400 ft) (600 ft)
43,560 sq ft/acre
= 5.51 acres
Pond Volume, ac-ft
= (Area, ac) (Depth, ft)
= (5.51 acres)(4 ft)
= 22.0 ac-ft
15-87
-------
Flow Rate, ac-ft/day =
(500,000 gal/day)
(7.48 gal/cu ft)(43,560 sq ft/ac)
1.53 ac-ft/day
Detention Time, days =
Pond Volume, ac-ft
Flow Rate, ac-ft/day
22.0 ac-ft
1.53 ac-ft/day
14.3 days
Population Loading
Population Loading,
persons/ac
Hydraulic Loading
Hydraulic Loading,
in/day
Population Served, persons
Pond Area, acres
5000 Persons
5.51 Acres
= 907 persons/acre
Depth of Pond, inches
Detention Time, days
(4 ft)(12 in/ft)
14.3 days
3.36 in/day
Organic Loading
Organic Loading,
Ib BOD/day/ac
(BOD, mg/l)(Flow, MGD)(8.54 Ib/gal)
Area, ac
(150 mg/l)C0.5 MGDK8.54 Ib/gal)
5.51 ac
625.5 Ib BOD/day
5.51 ac
= 114 Ib BOD/day/ac
15-88
-------
15.136 Chlorination
1. Chlorine Demand
Example: Determine the chlorine demand*of an effluent if the
chlorine dose is 10.0 mg/1 and the chlorine residual
is 1.1 mg/1.
Known Unknown
Chlorine Dose = 10,0 mg/1 Chlorine Demand, mg/1
Chlorine Residual = 1.1 mg/1
Chlorine
Demand, = Chlor. Dose, mg/1 - Chlor. Residual, mg/1
mg/1 = 10.0 mg/1 - 1.1 mg/1
= 8.9 mg/1
2. Chlorine Feed Rate
Example: To maintain a satisfactory chlorine residual in a
plant effluent, the chlorine dose must be 10 mg/1
when the flow is 0.37 MGD. Determine the chlori-
nator setting (feed rate) in pounds per day.
Known Unknown
Dose = 10 mg/1 Chlorinator Setting, Ibs/day
Flow =0.37 MGD
Chlorine Feed ,_ ..... ..„, *,^^ fc> -,» 11 / T>
Rate, Ibs/day = (Dose> mg/1)(Flow, MGD)(8.34 Ib/gal)
= (10 mg/1) (0.37 MGD) (8.34 Ib/gal)
= 30.9, or
= 31 Ibs/day
*"Standard Methods" uses the term chlorine demand when referring
to stabilized water such as a domestic water supply and the
term chlorination requirement when referring to wastewater.
15-89
-------
15.137 Laboratory Results
1. Dissolved Oxygen (DO) Saturation, Percent
Example: The dissolved oxygen in a receiving water was 10.3 mg/1
when the temperature was 50°F (Saturation DO = 11.3 mg/1).
Determine the percent DO saturation.
Known
Unknown
DO of Sample = 10.3 mg/1 DO Saturation, %
DO at 100% Sat. = 11.3 mg/1
DO Satu- _ DO of Sample, mg/1
ration, % DO at 100% Saturation, mg/1
= 1Q'3 "g/1 x 100%
11.3 mg/1
= 91.2%
2. Biochemical Oxygen Demand (BOD)
Example: Laboratory results are listed under known.
x 100!
Known
BOD Bottle Volume
Sample Volume
Initial DO of
Diluted Sample
= 300 ml
= 12 ml
= 8.0 mg/1
Unknown
BOD, mg/1
DO of Sample and
Dilution After 5-Day
Incubation Period = 4.0 mg/1
BOD,
mg/1
Initial DO of
DO of Diluted
„.,.,„ , Sample After
Diluted Sample, - __ * _ , o
mg/1
(8.0 mg/1 - 4.0 mg/1)
100 mg/1
5-Day Incuba-
tion, mg/1
BOD Btl. Vol., ml
Sample Vol., ml
300 ml
12 ml
15-90
-------
15.138 Efficiency of Plant or Treatment Process
Example: The influent BOD to a treatment plant is 200 mg/1,
and the effluent BOD is 20 mg/1. What is the BOD
removal efficiency of the plant?
Known Unknown
Influent BOD = 200 mg/1 Plant Efficiency, %
Effluent BOD = 20 mg/1
Efficiency, % = .(In " ^ 100%
In
= (200 mg/1 - 20 mg/1) ,
200 mg/1
100%
200 mg/1
= 90%
15.139 Blueprint Reading
Example: A set of blueprints for a treatment plant has a scale
of 1/4 inch = 1 foot. On the prints, the laboratory
dimensions were measured and found to be 6 inches wide
and 9 inches long. What is the floor area of the
laboratory?
Known Unknown
Scale: 1/4 in = 1 ft Area, sq ft
Length = 9 in
Width = 6 in
Area, sq ft = (Length, ft) (Width, ft)
Find actual length and width in feet.
15-91
-------
1/4 in
1 ft
Length, ft
1/4 in
1 ft
Width, ft
Area, sq ft =
9 in
Length, ft
1 ft
= (9 in)
= (9) (4)
= 36 ft
6 in
1/4 in
Width, ft
(6 in)(l ft)
(1/4 in)
C6) (4)
24 ft
(Length, ft)(Width, ft)
(36 ft)(24 ft)
864 sq ft
15-92
-------
15.14 SUMMARY OF FORMULAS
15.140 Length
LENGTH OF CLARIFIER WEIR or circumference of a circle;
Length, ft = 3.14 (Diameter, ft)
15.141 Area
RECTANGLE:
Area, sq ft = (Length, ft)(Width, ft)
TRIANGLE:
Area, sq ft = (1/2)(Base, ft)(Height, ft)
CIRCLE:
Area, sq ft = 0.785 (Diameter, ft)2
CYLINDER (wall) :
Area, sq ft = 3.14 (Diameter, ft)(Height, ft)
SPHERE:
Area, sq ft = 3.14 (Diameter, ft)2
15.142 Volume
RECTANGLE:
Volume, cu ft = (Length, ft)(Width, ft)(Height, ft)
CYLINDER:
Volume, cu ft = 0.785 (Diameter, ft)2 (Height, ft)
SPHERE:
Volume, cu ft = 0.524 (Diameter, ft)3
15-93
-------
15.143 Velocity
w , .. f. I Distance Traveled, ft
Velocity, ft/sec =
Time, sec
or
.. , .. c. , Flow Rate, cu ft/sec
Velocity, ft/sec = — —*-. ~- —
Cross-Sectional Area, sq it
15.144 Sedimentation Tanks and Clarifiers
Detention _ (Tank Volume, cu_ft)(7.5 gal/cu ft) C24 hr/day)
Time, hrs Flow, gal/day
Surface
Loading _ Flow, gal/day
Rate, ~ Area, sq ft
gpd/sq ft
Weir
Overflow _ Flow, gal/day
Rate, ~ Length of Weir, ft
gpd/ft
15.145 Trickling Filters
„ , i- r j- j/ £* Flow, gal/day
Hydraulic Loading, gpd/sq ft = Surface'^a> ^ ft
Organic Loading, lbs BOD/daX = BOD Applied, Ibs/day
1000 cu ft Volume of Media, 1000 cu ft
15.146 Activated Sludge
Aeratorf lbs = (MLSS' mg/1) (Tailk Vol*» MG)C8.34 Ib/gal)
where MLSS = Mixed Liquor Suspended Solids
Aerator
Loading, = (Primary Effl. BOD, mg/1)(Flow, MGD)(8.34 Ib/gal)
lbs BCD/day
15-94
-------
0, , w , T , ,OWT^ (30-Minute Settleable Solids. %) (10.000)
Sludge Volume Index (SVI) = •-• , ...... . . .-. .. , .» .^—i—i L.
MLSS, mg/1
30-Minute Settleable Solids, grams
°r = 100 ml
Sludge Density Index (SDI) =
ludge _ (MLSS, mg/1) (Tank Vol., MG) (8.54 Ib/gal)
= (SS in Primary Effl., mg/1) (Flow, MGD) (8.34 Ib/gal)
Mixed Liquor Solids^ Ibs, or Solids in Aerator, Ibs
Primary Effluent Solids, Ibs/day
NOTE: See Chapter 7, Activated Sludge, or Chapter 14, Laboratory
Procedures and Chemistry, for other terms used instead of
primary effluent solids.
Digester = (Total Volume, ml - Gas Remaining, ml) %
^ T1 ^\^ol Wrxll IVTV^N **» T
1005
15.147 Sludge Digestion
C02 in
Digests - rp—i—i- W--T =r-
Gas, % Total Volume> ml
Reduction of Volatile Matter, % = [ In ~ Out 1
[_In - In x Out |
Digester Loading, _ Volatile Matter Added, Ib/day
Ib VM/day/cu ft ~ Digester Volume, cu ft
15.148 Ponds
Detention _ Pond Volume, ac-ft
Time, days ~ Flow Rate, ac-ft/day
= p°Pulation Served, persons
~ Pond Area, acres
Depth of Pond, inches
Loading, = Detention Time, days
in/day ' J
.
persons /ac
15-95
-------
Lading, = (BOD, mg/1)(Flow, MGD) (8.34 Ib/gal)
Ib BOD/day/ac Area, acre
15.149 Other Formulas
15.1490 Chlorination
Chlorine Demand, mg/1 = Chlorine Dose, mg/1 - Chlorine Residual, mg/1
Chlorine Feed Rate, Ibs/day = (Dose, mg/1)(Flow, MGD)(8.34 Ib/gal)
15.1491 Laboratory Results
™ 0 ^ _. o DO of Sample, mg/1 x 100%
DO Saturation, % = *•—'——
DO at 100% Saturation, mg/1
BOD,
mg/1
!*,-<-• i nn
Initial DO
D0 of Diluted
_ . . _.
„.,.,„ , Sample After
Diluted Sample, -
mg/1 tion, mg/1
BOD Bottle Vol., ml
Sample Vol., ml
15.1492 Efficiency of Plant or Treatment Process
Efficiency, % = d" - Out) 100%
In
15.1493 Pumps
Water, HP = (Flow, gpm) (H, ft)
3960
Brake, HP = (Flow, gpm) (H, ft)
(3960) (Ep)
Motor HP = CFlow, gpm) (H, ft)
M0t°r' (3960) (Ep) (EJ
15-96
-------
15.15 CONVERSION TABLES
Tables in this section were taken from Water and .Wastewater
Engineering, Volume 1, Water Supply and Wastewater Removal,
by G. M. Fair, J. C. Geyer, and D. A. Okun, John Wiley § Sons,
Inc., New York, 1966. Price $15.95. The tables are also
found in Volume 2, Water Purification and Wastewater Treatment
and Disposal, 1968. Price $17.00.
The American and English weights and measures referred to in
this book are alike except for the gallon. The United States
gallon is employed. The United States billion, which equals
1000 million, is also employed.
Miles
Yards
LENGTH
Feet
Inches
Centimeters
1
—
--
—
1
Square
Miles
1
—
--
--
1760 5280
1 3 36
1 12
1
m = 100 cm = 5.281 ft =
AREA
Square Square
Acres Feet Inches
640
1 43,560
1 144
1
1 sq m = 10.76 sq ft
—
91.44
30.48
2.540
59.37 in
Square
Centimeters
—
—
929.0
6.452
15-97
-------
Cubic
Feet
1
—
—
—
_ _
VOLUME
Imperial U.S.
Gallons Gallons
6.23 7.481
1 1.2
1
—
_ mm mm —
Cubic
Inches
1728
277.4
231
57.75
61. 02
Liters
28.32
4.536
3.785
0.946
1
1 cu m = 35.31 cu ft = 264.2 gal
1 Imperial (UK) gal weighs 10 Ib 1 US gal weighs 8.34 Ib
1 cu ft of water weighs 62.43 Ib 1 cu m weighs 2283 Ib
1 cu m = 103 1 and weighs 1000 kg
VELOCITY
Miles per Feet per Inches per Centimeters Kilometers
Hour Second Minute per Second per Hour
1 1.467 1056 — 1.609
1 720 30.48
1 0.423
TIME
Days Hours Minutes Seconds
1 24 1440 86,400
1 60 3,600
1 60
15-98
-------
WEIGHT
Tons Pounds Grams Grains Metric Tons
1 . 2000 — — 0.9078
1 454 7000
1 15.43
1 long ton = 2240 Ib
1 ppm = 1 mg/1 = 8.34 Ib per MG
Cubic Feet per
Second
DISCHARGE
Million Gallons
Daily
Gallons per
Minute
1 0.6463 448.8
1.547 1 694.4
1 in per hour per acre = 1.008 cfs
1 cu m/sec = 22.83 MGD = 35.32 cfs
Pounds per
Square Inch
1
0.4335
0.4912
PRESSURE
Feet of Water
2.307
1
1.133
Inches
2
0
1
of Mercury
.036
.8825
1 atm = 14.70 psia = 29.92 in. Hg =
33.93 ft water = 76.0 cm Hg
15-99
-------
POWER
Kilowatts Horsepower
Foot-Pounds
per Second
Kilogram-
Meters per
Second
0.7457
1.341
1
737.6
550
102.0
76.04
Kilowatt-Hours
WORK AND ENERGY
Horsepower-
Hours
British Thermal
Units
1
0.7457
1.341
1
3412
2544
TEMPERATURE
9
Degree Fahrenheit = 32 + — x Degrees Centigrade
J
0 5 10 15 20 25 30 35 40 45 50 55 60 C
32 41 50 59 68 77 86 95 104 113 122 131 140 F
DENSITY OF WATER
1 gram/cm3 = 62.43 Ib/cu ft
15-100
-------
15.13 ADDITIONAL READING
a. MOP 11.
b. New York Manual, pages 183-190 and 215-219.
c. Texas Manual, pages 588-608.
d. Elementary Mathematics and Basic Calculations, Scranton
Publishing Company, 35 East Wacker DriveV Chicago,
Illinois 60601. Price $1.25.
e. Mathematics for Operators of Water Pollution Control Plants.
Obtain from Secretary-Treasurer', California Water Pollution
Control Association, P.O. Box 61, Lemon Grove, California
92045. Price $2.35 to members of CWPCA; $3.00 to others.
f. Mathematics Made Simple, A. Sperling and M. Stuart, Doubleday
and Company, Inc., Garden City, New York, 1962. Price $1.95.
15-101
-------
OBJECTIVE TEST PROCEDURE
1. Work the problems in your notebook. Be neat and orderly
so that your work may be followed and checked.
2. Mark your answers on the IBM answer sheet.
3. Mail the IBM answer sheet to your Program Director.
You may refer to the chapter for formulas and conversion factors.
15-102
-------
OBJECTIVE TEST
Chapter 15. Basic Mathematics and Treatment Plant Problems
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1. There will be
only one answer to each question. If necessary, select the closest
answer.
A rectangular sedimentation tank is 35 feet wide, 70 feet long,
and 9 feet deep. The flow is 1.6 MGD.
1. The detention time is:
1. 0.5 hr
2. 1.0 hr
3. 2.0 hr
4. 2.5 hr
5. 3.5 hr
2. The surface loading rate is:
1. 500 gpd/sq ft
2. 600 gpd/sq ft
3. 650 gpd/sq ft
4. 750 gpd/sq ft
5. 1000 gpd/sq ft
A 65-ft diameter trickling filter receives a flow of 2.5 MGD with
a BOD of 125 mg/1. The filter is 4 feet deep.
3. The hydraulic loading is:
1. 500 gpd/sq ft
2. 600 gpd/sq ft
3. 750 gpd/sq ft
4. 800 gpd/sq ft
5. 1000 gpd/sq ft
4. The organic loading is:
1. 25 Ib BCD/day/1000 cu ft
2. 100 Ib BCD/day/1000 cu ft
3. 150 Ib BCD/day/1000 cu ft
4. 200 Ib BCD/day/1000 cu ft
5. 300 Ib BCD/day/1000 cu ft
15-103
-------
Information for an activated sludge plant is summarized below.
Mixed Liquor Suspended Solids (MLSS1 = 2100 rag/1
Mixed Liquor Volatile Content = 73%
Thirty-Minute Settleahle Solids Test = 420 ml* or 21%
Primary Effluent BOD = 145 mg/1
Primary Effluent Suspended Solids = 115 mg/1
Flow Rate = 2.2 MGD
Aeration Tank Volume = 70,000 cu ft
*2 liter cylinder
5. The pounds of solids in the aeration tank are:
1. 1,000 Ibs
2. 2,000 Ibs
3. 5,000 Ibs
4. 9,000 Ibs
5. 10,000 Ibs
6. The aeration tank loading is:
1. 1,000 Ibs BOD/day
2. 2,500 Ibs BOD/day
3. 5,000 Ibs BOD/day
4. 7,500 Ibs BOD/day
5. 10,000 Ibs BOD/day
7. Raw sludge pumped to a digester was 75 percent volatile
matter, and the digested sludge was 55 percent volatile
matter. Calculate the percent reduction of volatile matter.
1. 50%
2. 55%
3. 59%
4. 60%
5. 61%
A waste treatment pond is 225 ft wide, 310 ft long, and 4.5 ft
deep. The inflow is 0.108 MGD, has a BOD of 170 mg/1, and serves
a population of 975 people.
8. The detention time of the pond is:
1. 20 days
2. 25 days
3. An day
-------
9. The population loading on the pond is:
1. 500 persons/acre
2. 600 persons/acre
3. 700 persons/acre
4. 800 persons/acre
5. 900 persons/acre
10. Hydraulic loading is:
1. 2.00 in/day
2. 2.25 in/day
3. 2.50 in/day
4. 2.75 in/day
5. 3.00 in/day
11. Organic loading is:
1. 80 Ib BOD/day/ac
2. 85 Ib BOD/day/ac
3. 90 Ib BOD/day/ac
4. 95 Ib BOD/day/ac
5. 100 Ib BOD/day/ac
12. Determine the chlorine feed rate for a chlorinator when
the dose is 12 mg/1 and the flow is 0.28 MGD.
1. 25 Ibs/day
2. 28 Ibs/day
3. 30 Ibs/day
4. 32 Ibs/day
5. 35 Ibs/day
13. Calculate the BOD of a 3 ml sample in a 300 ml BOD bottle
if the initial DO of diluted sample was 8.3 mg/1 and the
DC of sample and dilution was 3.4 mg/1 after the 5-day
incubation period.
1. 100 mg/1
2. 200 mg/1
3. 300 mg/1
4. 400 mg/1
5. 500 mg/1
14. The influent suspended solids to an activated sludge plant
is 245 mg/1, and the effluent suspended solids is 17 mg/1.
The suspended solids removal efficiency for the plant is:
1. 85%
2. 90%
3. 93%
4. 95%
5. 98%
15-105
-------
15. A pump is capable of delivering 4 horsepower to water
being pumped against a 33-ft head. Estimate the flow cf
water being pumped.
1. 50 gpra
2. 100 gpm
3. 150 gpra
4. 300 gpm
5. 500 gpm
16. The discharge pressure gage on a pump reads 15 psi.
This is equivalent to how many feet of water or feet
of head?
1. 5 ft
2. 10 ft
3. 25 ft
4. 35 ft
5. 50 ft
17. 100 mg/1 is the same as:
1. 100%
2. 10%
3. 1%
4. 0.1%
5. 0.01%
Please write on your IBM answer sheet the total time required to
work this chapter.
15-106
-------
CHAPTER 16
ANALYSIS AND PRESENTATION OF DATA
Kenneth Kerri
-------
TABLE OF CONTENTS
Chapter 16. Analysis and Presentation of Data
Page
16.0 Introduction 16-1
16.1 Causes of Variations in Results 16-1
16.10 Water or Material Being Examined 16-2
16.11 Sampling 16-2
16.12 Testing 16-3
16.2 Manometer and Gage Reading 16-4
16.5 Chart Reading 16-7
16.4 Average Value 16-8
16^. 5_ Range of Values 16-10
16.6 Median, Mode, and Gedmetric Mean 16-13
16.7 Graphs 16-23
16.70 Bar Graphs 16-23
16.71 Trends 16-27
16.72 Summary 16-28
16. 8 Variance and Standard Deviation 16-29
16.9 Summary 16-35
16.10 Additional Reading 16-36
111
-------
PRE-TEST
Chapter 16. Analysis and Presentation of Data
Complete this test before you read Chapter 16. Do not be dis-
couraged if you dcniTt know any of the answers because a lot of
the information in this chapter is new to most operators.
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1.
1. Data should be collected and (select best answer):
1. Filed
2. Forgotten
3. Analyzed
4. Lost
5. Values placed in all columns on report sheet
2. Laboratory results of influent BOD at a particular plant vary
due to:
1. Nothing—the results should not be different
2. Differences in the composition of the influent
3. Operators titrating to different end points
4. Operators not following the exact same testing procedure
every time
5. Collecting samples in a different manner
3. The characteristics of a sample may change between collection
and analysis due to:
1. Nothing—the characteristics don't change
2. Temperature changes during transportation to the lab
3. Chemical changes in the sample
4. Biological changes in the sample
5. Changes in the variance
4. A representative sample:
1. Describes the overall situation
2. Represents the equipment manufacturers
3. Represents the people
P-l
-------
5. At the beginning of a week a totalizer on the plant inflow
read 1,823,471 gallons. Seven days later, the totalizer
reads 2,619,582 gallons. The average daily flow during the
week was approximately:
1. 0.01 MGD
2. 0.11 MGD
3. 1.11 MGD
4. 0.10 MGD
5. 0.13 MGD
6. Bar graphs can be used to show:
1. Growth
2. Characteristics of data
3. Dispersion of data
4. Your supervisor results of lab tests
5. How neat you can draw
7. Plotting data on graph paper to show trends may be helpful to;
1. Justify budget increases
2. Describe the variance
3. Predict when expansion will be necessary
4. Illustrate the need to look for the cause of trend
5. Illustrate patterns of effluent quality
At 1:30 p.m. every day of the week the dissolved oxygen in the
Number 1 pond of a wastewater treatment facility is measured and
the results are summarized below in mg/1:
WEEK DAY
8.
The
1.
2.
3.
4.
5.
The
1.
2.
3.
4.
1
2
M T W T F
9.8 9.5 9.6 9.2 8.9
8.1 8.4 8.0 7.6 7.5
average DO in the pond over the two-week period was
8.1
8.4
8.5
8.7
8.9
mg/1
mg/1
mg/1
mg/1
mg/1
range of DO was :
7.5
9.8
1.3
2.3
to 9.8 mg/1
to 7.5 mg/1
mg/1
mg/1
P-2
-------
10. The median DO was:
1. 8.0 mg/1
2. 8.1 mg/1
3. 8.4 mg/1
4. 8.6 mg/1
5. 8.9 mg/1
11. Is there a trend in the DO concentration in the pond?
1. Yes
2. No
12. The variance, S2, in the DO level in (mg/1)2 is:
1. 0.65
2. 0. 70
3. 0.72
4. 0.75
5. 0.78
13. The standard deviation, S, in the DO level in mg/1 is;
1. 0.70
2. 0 . 75
3. 0.80
4. 0.85
5. 0.90
P-3
-------
CHAPTER 16. ANALYSIS AND PRESENTATION OF DATA
(Lesson 1 of 2 Lessons)
16.0 INTRODUCTION
Collection of data without analysis, interpretation, and use of
results is a waste of time and money. This chapter will attempt
to provide you with simple, easy methods to analyze data. To
show you how to make the results of your testing meaningful and
easily interpreted, a section on Data Presentation also is included.
Many times your supervisor can understand what is happening in
your plant or why you need a budget increase if you can show him
charts indicating trends or changes in plant operation or treat-
ment process efficiencies.
Whether samples are collected, analyzed, interpreted, and used by
the same person or a different person performs each task, every
job is equally important if the application of results is to be
effective. When running lab tests the samples must be representative.1
Persons reviewing and interpreting lab results assume the tests were
performed in a careful, prescribed manner and the results are accu-
rate. Operators applying the interpretation of lab results to
operational controls rely on proper interpretation to insure
effective adjustments in the treatment processes.
All samples collected and analyzed must be needed by someone.
Numbers from test results provide an accurate description or indi-
cation of the quantity of work completed or to be completed.
Mathematical analysis of data is a means to estimate how well your
test results can be repeated on a given sample (quality control) or
how much a group of samples vary (another form of quality control).
Presentation of data in tables, graphs, or charts makes the infor-
mation more usable by illustrating trends, variations, and signifi-
cant changes.
16.1 CAUSES OF VARIATIONS IN RESULTS
When you collect samples of wastewater or receiving water and
measure their characteristics (for instance, temperature, pH, BOD),
your results will be affected by several factors. Three principal
factors which must be taken into account, no matter where the sample
1 Representative Sample. A portion of material or water identical
in content to that in the larger body of material or water being
sampled.
16-1
-------
is taken—influent raw wastewater, treatment process influent or
effluent, receiving waters—are:
1. Actual variations in the characteristics
of the water or material being examined
2. Sampling procedures
3. Testing or analytical procedures
16.10 Water or Material Being Examined
The properties or characteristics of the wastewater or receiving
water are what you are attempting to measure, such as temperature,
pH, or BOD. These and many other water quality indicators vary
continuously depending on what is being discharged into a waste-
water collection system (sewerage system), the effectiveness of
treatment processes, and the response of the receiving waters
and their changing characteristics. Your objective is to describe
the characteristics of the wastewater or receiving water being
sampled in terms of average values and also to give an indication
of variation or spread of results from the average values.
16.11 Sampling
Characteristics of a sample can vary if you do not always sample
at the same location or during the same time of day. If you ob-
serve the flow in a
wastewater line or influent,
y°u can see tne Differences
in characteristics at various
depths, differences between
flow in the middle and edge
of a pipe or channel, and
also differences above or
below a bend.
After a sample has been
collected in a sampling
jar or bottle, heavy
material may settle to the
bottom, and the jar must be
mixed before the sample is
tested. Also, if the sample
is not analyzed immediately,
its characteristics can
undergo chemical or
16-2
-------
biological changes if the sample is not treated and stored
properly following collection.
16.12 Testing
The results from two identical samples can differ depending on
the analyzing apparatus and the operator conducting the measure-
ment. Fluctuations in voltage can cause changes in instrument
readings, and different individuals may titrate to slightly
different end points. Using reagents from different bottles,
filter paper from different packages, or different pieces of
equipment that were not calibrated identically or were not warmed
up during the same time period can cause differences in test
results. Variations in test results may be caused by omitting
a step in the lab procedure, and interfering substances can cause
testing errors.
Your objective is to reduce or eliminate sampling and testing
errors as much as possible so you can obtain an accurate descrip-
tion of the water being sampled.
QUESTIONS
16.1A What three major factors can cause variations in
lab test results?
16.IB Why should most samples be tested immediately by
the lab?
16-3
-------
16.2 MANOMETER AND GAGE READING
Manometers and gages are installed in wastewater treatment plants
to measure pressures and pressure differences. Both types of
instruments should be calibrated and zeroed before using. Cali-
bration and zeroing of any instrument means periodic checking of
the instrument against a known standard to be sure the installed
instrument reads properly. Manometers and gages can be zeroed in
by making sure the instruments read zero when no pressure is being
applied to the manometer or gage. If the reading is not zero, then
the scales should be adjusted according to manufacturer's recommen-
dations .
To read a manometer, note the scale reading opposite the menicus.2
This reading may have to be converted from inches of mercury to
head in feet of water, pressure in psi, or flow in GPM, depending
on the use of the manometer.
2 Menicus. The curved upper surface of a column of liquid (water,
oil, mercury) in a small tube. Water will form a valley when
the liquid wets the walls of the tube, while mercury will form
a hill and the walls of the tube are not wetted.
Water
(Read Bottom)
MENICUS
Mercury
(Read Top)
16-4
-------
EXAMPLE MANOMETER READINGS
Manometer A
reads 3 inches
of water
Manometer B
reads 3 inches
of mercury
MANOMETER A
Water
-
' *.
**~&*
— 4
o
— 2
MANOMETER B
Mercury
...^^^•^
• — *«—j
O
<. i
X \ _
-4
-5
-
— 2
Gage readings are read directly from a scale behind a gage pointer
and the units must be recorded. Sometimes a gage will have two
scales and care must be taken to be sure the proper scale reading
and units are recorded. Gage readings may have to be converted to
more convenient numbers.
EXAMPLE GAGE READINGS
16-5
-------
QUESTIONS
16.2A Why must instruments be periodically calibrated and
zeroed?
16.2B If the gage shown in this section under EXAMPLE GAGE
READINGS indicated a pressure of 2 psi, what would be
the pressure head in feet of water?
16-6
-------
16.3 CHART READING
Before data can be analyzed and presented, frequently it must
be reduced to or tabulated in a usable form. Today, more and
more, data are being recorded on a continuous basis on strip
charts and circular charts.
For instance, sometimes flow data are recorded in depths of
flow in inches or feet through a Parshall flume, and sometimes
the recorder will convert the depth to a flow rate, such as
MGD. To compile or tabulate data from such continuous charts,
select an appropriate time interval, such as a few hours
(Fig. 16.1). Prepare a table with a column for (1) the time
and (2) the value you read from the chart. A third column (3)
may be necessary if you have to convert a depth of flow to a
flow rate (MGD). Conversion charts from depth of flow to
flow rate in MGD are provided by the manufacturer of a flow
meter.
When reading manometers, gages, and charts, care must be taken
to be sure the correct number is read and properly recorded.
6 a.m. 8 a.m. 10 a.m. Noon
TIME, HR.
Fig. 16.1 Strip chart flow depth
16-7
-------
TABLE 16-1
TABULATION OF DEPTHS AND FLOWS
FROM THE STRIP CHART (FIG. 16.1)
CD
Time
6 AM
8 AM
10 AM
12 NOON
(2)
Depth
(in.)
12
12 1/2
13 1/2
14 1/2
(3)
Flow3
(MGD)
0.61
0.65
0.74
0.84
16.4 AVERAGE VALUE
When you collect representative samples from a plant influent
and measure a particular water quality indicator, such as BOD,
the results are not always the same. For example, you might
measure the BOD of a trickling filter influent to determine
the organic loading and find the BOD varying considerably
during a 6-day period. To calculate an expected daily organic
loading, the average daily BOD must be calculated.
EXAMPLE 1;
The results of six BOD tests on a trickling filter influent
from composite (proportional) samples collected at daily inter-
vals during a 6-day period indicated the BOD to be 150 mg/1,
200 mg/1, 250 mg/1, 200 mg/1, 100 mg/1, and 120 mg/1. What is
the average daily BOD?
Procedure:
Add the six measurements and divide by six, the number of
measurements.
3 These figures would be obtained from the manufacturer's
"conversion chart" for the particular flume or flow meter.
16-8
-------
Sum of All DAY BOD
Average BOD, _ Measurements, mg/1
mg/1 Number of
Measurements
1020 ..
= —•.— mg/1
6
= 170 mg/1 Sum = 1020
You have calculated the average BOD by adding all BOD measure-
ments and dividing by the number of measurements. '
The average value of any other characteristic is calculated the
same way. For example, if you wanted to calculate a month's
average daily flow into a plant, you would add up the daily flows
for the month and divide by the number of days in the month.
Hint:
Frequently plant flows are recorded on an integrator or
totalizer4 and the flow during a particular time period
can be determined by obtaining the difference between
the totalizer readings at the beginning and end of the
time period.
EXAMPLE 2;
At the beginning of a month a plant totalizer reads 103,628,457
gallons, and 30 days later you record the totalizer value as
114,789,321 gallons. Calculate the average daily flow for the
month.
Step 1:
Find the total monthly flow.
Reading at end of time period = 114,789,321 gals
Reading at start of time period = 105,628,457 gals
Total flow during month = 11,160,864 gals
Totalizer. A totalizer continuously sums or adds up the
flow into a plant in gallons or million gallons or some
other unit of measurement.
16-9
-------
Step 2:
Calculate the average daily flow, gal/day:
Average Daily
Flow, gal/day
Sum of Flows, gal
Number of Days
(measurements)
11.160,864 gals
30 Days
= 372,029 gals/day
or
372,029 gals/day
1,000,000 gals/MG
= 0.372 MGD
Note:
The average daily flow for the month also could be calcu-
lated by adding the 30 daily flows during the month and
dividing by 30. This approach can be used to check the
results obtained using the difference in the totalizer
readings as shown above.
16.5 RANGE OF VALUES
You have seen how to evaluate lab results in terms of average
values. This does not give any indication as to whether all of
the data were close to the average value or if there was a con-
siderable spread or dispersion of data. A useful method of
indicating the spread in results is the range. The range is
obtained by subtracting the smallest measurement from the
largest one.
Range = Largest Value - Smallest Value
Procedure:
Step 1: Rank data by arranging observations in ascending
(increasing) or descending (decreasing) order,
using the data from EXAMPLE 1: 250, 200, 200,
150, 120, 100.
16-10
-------
Step 2; Subtract the smallest (100) from the largest (250).
Largest 250 mg/1
Smallest -100 mg/1
Answer: Range of BOD/mg/1 = 150 mg/1
Try another example to review the calculations for the average
value and range, then you will be ready to study other ways of
describing the dispersion of data and the idea of graphical
presentation using this problem.
EXAMPLE 5;
The average daily BOD for two weeks is given below. Calculate
the average 2-week BOD and the range for these measurements.
Data; 160, 155, 160, 160, 180, 165, 155, 170, 160, 165, 155,
150, 145, 160.
Average BOD, _ Sum of All Measurements, mg/1 160 mg/1
mg/1 Number of Measurements 155
160
160
= 2240 mg/1 180
14 165
155
170
160
165
155
150
145
160
= 160 mg/1 for two weeks 2240 mg/1
BOD^mg/l = LarSest BOD» mg/1 - Smallest BOD, mg/1
= 180 mg/1 - 145 mg/1 180
-145
= 35 mg/1 for two weeks 35
16-11
-------
QUESTIONS
Mixed liquor samples were collected at the beginning, middle, and
end of an aeration tank and the solids concentrations were 2138
mg/1, 1863 mg/1, and 1921 mg/1.
16.4A Calculate the average mixed liquor concentration.
16.5A What is the range of these measurements?
16-12
-------
16.6 MEDIAN, MODE, AND GEOMETRIC MEAN
Sometimes the average value and range calculations are not the
best way to describe or analyze data. For example, frequently
when running multiple tube coliform bacteria tests you will
obtain some extremely high MPNs (most probable number of coli-
form group bacteria), especially after a rain, equipment fail-
ure, or chlorine dosage mishap.
EXAMPLE 4:
Data; MPN/100 ml = 240, 220, 240, 230, 240, 7200, 260, 250,
270, 300, 250. Calculate average MPN.
Procedure:
Determine sum of measurements.
240
Average _ Sum of Measurements, MPN/100 ml 220
MPN/100 ml ~ Number of Measurements 240
= 882
Sum = 9700
Average MPN = 882 Coliform Bacteria/100 ml. Note that this value
is greater than all of our measurements except the largest one.
For this reason, multiple tube coliform results are sometimes
reported as a MEDIAN VALUE.
The median is defined as the middle measurement when the measure-
ments are ranked in order of magnitude (size).
Procedure:
Rank data in ascending or descending order.
Measurement: 220 230 240 240 240 250 250 260 270 300 7200
Rank: 123456789 10 11
I
Median
16-13
-------
Measurement 6 is our middle measurement. Therefore, the
MEDIAN MPN/100 ml = 250, which better describes the usual
value of the measurements.
If you had only ten measurements (eliminate #11 of 7200), the
MEDIAN would fall between measurements 5 and 6 (240 and 250)
and would be 245.
Another useful value is the MODE. The mode is the measurement
that occurs most frequently. In our example, the measurement
240 occurs three times, which is more than any other. There-
fore: MODE MPN/100 ml = 240.
An examination of the data in EXAMPLE 4 indicates that the median
and mode do a better job of describing or predicting the MPN value
we would expect than the average calculation. For this reason
these terms are sometimes used to report data.
QUESTION
16.6A The results of the SVI (Sludge Volume Index) test for an
activated sludge plant for one week were as follows: 120,
115, 120, 120, 125, 110, 115. What are the median and mode
values for the SVI data?
Geometric Mean:
There are other ways of reporting the results of coliform tests in
addition to those mentioned above. The geometric mean is sometimes
used because all measurements are used in the calculations, but an
extreme value has a lesser influence on the result. The easiest
way to find the geometric mean is to plot the results on log proba-
bility paper and read the geometric mean on the paper.
To plot data on probability paper, the probability or plotting point
of each measurement must be determined. The plotting point is
calculated from the following formula:
P = —-— x 100%
n + 1
where:
P is the probability (%) the measurement will not
be exceeded,
n is the number or sum of measurements, and
m is the rank when the measurements are arranged
in ascending or increasing order.
16-14
-------
For our example:
Rank
m
1
2
3
4
5
6
7
8
9
10
11
Measurement
MPN/100 ml
220
230
240
240
240
250
250
260
270
300
7200
Probability
%
8.3
16.7
25.0
33.3
41.7
50.0
58.3
66.7
75.0
83.3
91.7
Plot the data as shown on Fig. 16.2.
To estimate the geometric mean from the data plotted on Fig. 16.2:
1. Draw a line of best fit through the data.
2. Draw a vertical line down the 50 percent line to where it
intersects with the line of best fit.
3. From the intersection of the 50 percent line and the line of
best fit, draw a horizontal line to the scale representing the
measurements.
4. Read the Geometric Mean MPN = 265/100 ml.
A problem with plotting data is that different operators will draw
different lines of best fit through the data, thus giving different
geometric means. This problem can be overcome by calculating the
geometric mean. To calculate the geometric mean, all of the measure-
ments must be converted to logarithms, the average of the logs is
found, and then this average is converted to the geometric mean.
16-15
-------
15 20
30
40 50 60
PERCENTAGE
70
80 85 90
95
Fig. 16.2 Determination of geometric mean
from log probability paper
16-16
-------
To find logarithms, the characteristic and the mantissa of a
measurement must be determined. The characteris tic of a
measurement is one less than the number of figures to the
left of the decimal point. The mantissa of a number is found
by looking in log tables in math books or handbooks and is the
same regardless of the location of the decimal point. Looking
up the mantissa of 245 in the log table shown below gives 3892.
TABLE OF COMMON LOGARITHMS OF NUMBERS
N
22
23
24
25
0
3424
3617
3802
3979
12345
3444
3636
3820 3838 3856 3874 |5892|
6789
3909 3927 3945 3962
The logarithm of a number is the characteristic plus the mantissa.
EXAMPLES;
Number
24,500
2,450
245
24.5
2.45
.245
.0245
.00245
.00245
Ch ara cte r i s t i c
4
3
2
1
0
-1
-2
-3
-3
Mantissa
.3892
.3892
.3892
.3892
.3892
.3892
.3892
.3892
.3892
Logarithm
4.3892
3.3892
2.3892
1.3892
£.3892
1.3892
21.3892
3.3892
or 7.3892-10
Note that if the characteristic is negative, the logarithm is
written with the minus (-) sign over the characteristic (3".3892)
or the characteristic is subtracted from 10 and a -10 is placed
after the mantissa (7.3892-10).
16-17
-------
EXAMPLE 5:
Calculate the geometric mean of the data used in the previous
problem.
Measurement
MPN/100 ml
220
230
240
240
240
250
250
260
270
300
7200
Average of Logarithms =
Characteristic
Mantissa
2
2
2
2
2
2
2
2
2
2
3
.3424
.3617
.3802
.3802
.3802
.3979
.3979
.4150
.4314
.4771
.8573
Sum of Logarithms
Logarithm
2.3424
2.3617
2.3802
2.3802
2.3802
2.3979
2.3979
2.4150
2.4314
2.4771
3.8573
= 27.8213
Sum of Logarithms
Number of Measurements
27.8215
11
2.5292
To find the geometric mean, convert the average of the logarithms
(2.5292) back to a number. The characteristic is 2 and the mantissa
is 5292. First find a mantissa of 5292 in a Table of Common Logarithms
of Numbers and determine the closest number as shown below.
N
0
TABLE OF COMMON LOGARITHMS OF NUMBERS
1 2.3 4 5 6 7
8
32
33
34
5051
5185 5198 5211 5224 5237 5250 5263 5276 5289 5302
5315 5328
16-18
-------
A mantissa of 5292 falls between 5289 and 5302, but closer to
5289. Therefore the number is 338. Since 338 has a charac-
teristic of 2, the
GEOMETRIC MEAN MPN = 338/100 ml
The geometric mean for this example is greater than all of the
other measurements except one. In many calculations of the
geometric mean, the results will be closer to the median.
END OF LESSON 1 OF 2 LESSONS
on
ANALYSIS AND PRESENTATION OF DATA
Please answer the discussion and review questions before
continuing with Lesson 2.
16-19
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 16. Analysis and Presentation of Data
(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.
1. Collection of data without ,
and of results is a waste of time and money.
2. Whether samples are collected, analyzed, interpreted, and used
by the same person or a different person performs each task,
every job is equally important if the application of results
is to be effective. True or False?
3. What are the three principal factors that can cause variations
in test results?
4. How could errors occur when reading charts and gages?
The solids concentrations of sludge withdrawn from a primary clari-
fier during the past seven days are given below:
Day: 1234567
Solids, %: 6.0 6.5 6.0 5.0 6.5 7.5 8.0
5. What is the average solids concentration?
6. What is the range of solids concentration?
7. What is the median solids concentration?
8. What is the mode solids concentration?
16-21
-------
CHAPTER 16. ANALYSIS AND PRESENTATION OF DATA
(Lesson 2 of 2 Lessons)
16.7 GRAPHS
16.70 Bar Graphs
Sometimes results can be illustrated by graphs to show the charac-
teristics (average value and dispersion) of data. Many people,
especially supervisors, can easily interpret data presented
graphically and appreciate this approach.
PROCEDURE:
Step 1. Group the data from EXAMPLE 3 into class intervals of equal
width (say 5 mg/1) and range of interval (for instance, 177.5 -
182.5 mg/1). See (a) below. The length or size of class width (5,
10, or 20) is usually constant. Width of class interval depends on
spread of data (wide range, wide interval) and is selected in order
that all or most of the data can be placed in 5 to 10 intervals.
(There are eight intervals in this example.)
Step 2. Determine class midpoints —180 mg/1, 175, 170, etc. See
(b) below. Class midpoints are always numbers that are easy to
plot or work with (for instance: 2, 4, 6, 8, 10; or 5, 10, 15, 20,
25; or 10, 20, 30, 40, 50; or 25, 50, 75, 100, 125).
Step 3. Determine frequency. Count the number of measurements (in
this case, from EXAMPLE 3) that were recorded in each class interval.
This is usually accomplished by systematically going through your
list of measurements, placing a check or 1 (column c below) opposite
the appropriate class midpoint or class interval, and then adding up
the checks or 1's to obtain the frequency (d).
Step 4. Plot results.
Number of
Class Interval Class Midpoint Measurements Frequency
(a) (b) (c) (d)
182.5 - 177.5 180 1 1
177.5 - 172.5 175 0
172.5 - 167.5 170 1 1
167.5 - 162.5 165 11 2
162.5 - 157.5 160 "1M4. 5
157.5 - 152.5 155 111 3
152.5 - 147.5 150 1 1
147.5 - 142.5 145 1 1
16-23
-------
BAR GRAPH SHOWING DISTRIBUTION OF BOD
AVERAGE BOD 160 mg/l
J
4
3
t
;
i i i i ,
i i i i , i
140 145 150 155 160 165 170 175 180
BOD, mg/l
Sometimes the plotting points on a bar graph are connected to
form a smooth curve. The resulting curve describes either a
normal or a skewed distribution of the data, depending on the
shape of the curve. If the distribution is normal, the
average, median, and mode values will be approximately the
same. In skewed distributions the average, median, and mode
are different (Fig. 16.3).
16-24
-------
C3
LU
QC
140
150
160
AVERAGE
ALL EQUAL 160 mg/l
NORMAL DISTRIBUTION OF DATA
170 180 BOD mg/l
MEDIAN AND MODE BOD VALUES
180 BOD mg/l
MODE MEDIAN AVERAGE
146 151 157 mg/l
SKEWED DISTRIBUTION OF DATA
Fig. 16.3 Normal and skewed distribution of data
16-25
-------
QUESTION
16.7A The results of the SVI (Sludge Volume Index) test for
an activated sludge plant for one week were as follows:
120, 115, 120, 120, 125, 110, 115.
a. Calculate the average SVI.
b. What is the range?
c. Draw a bar graph showing the distribution
- (spread) of SVI.
16-26
-------
16.71 Trends
Plotting data on graphs5 is very helpful to illustrate trends
in the operation of your plant. Occasionally plotting data will
reveal unexpected trends. This approach could be used to indi-
cate to supervisors or the public the increase in plant inflow
or decrease in the quality of plant effluent to justify increases
in budgets or plant expansion. To look for or show a trend,
plot the value you are interested in (for instance, flow, MGD,
or effluent BOD, mg/1) against time (.day, week, month, year).
EXAMPLE 6:
Analysis of flow data (totalizer readings) provides the following
annual information:
Year: 1965
Average Daily Flow, MGD: 1.25
Plot the data:
1966
1.38
1967
1.42
1968
1.58
1969
1.65
1970
1.81
FLOW,
MGD
2.0 i
1.9
1.8
1.7
.6
.5
.3
.2
1.1
1.0
YEAR.... 1
^
: s''\
*-xxX^ PROJECTED
. FUTURE
./ FLOW
^^*
-
—
965 1966 1967 1968 1969 1970 1971 1972
5 Graph paper may be obtained at most stationery stores.
graph paper at end of this chapter.
See
16-27
-------
Interpretation of Data:
The graph shows a continuously increasing average daily flow.
If your plant has a capacity of 2 MGD, the graph would clearly
show the need for expansion in the near future if past trends
in population growth or any industrial expansion continue.
You could extend the trend (dashed line) to project future
flows and predict when you expect to reach plant capacity
(1971-1972).
Applications:
Plotting data and looking for trends may be helpful to indicate
broken pipes and illegal connections or discharges. You should
always attempt to identify the cause of a trend. An industry
may clean up on Friday afternoon and dump a slug of waste into
the collection system that may reach your plant Friday night.
If you plot your data and note a reduction in the quality of
your effluent every Friday night or Saturday, you might start
looking for the cause of the problem.
Some operators record flows continuously on daily circular charts.
Every year they change the color of the ink, but use the same
chart on the same day for several years. This is a good way to
identify trends, too.
16.72 Summary
Two methods have been given in this section to present data:
1. Bar Graphs
2. Line Graphs
How does the operator determine which method to use? Bar graphs
are used to summarize data and indicate number of times or fre-
quency a given value was measured. Line graphs illustrate trends
by showing how a particular measurement changes with time.
QUESTION
16.7B Weekly alkalinity tests on digester sludge are given below:
Week 123456789 10
Alka-
linity, 1730 1670 1690 1680 1630 1620 1590 1530 1480 1420
mg/1
a. Is a trend apparent?
b. Should any action be taken by the operator?
16-28
-------
16.8 VARIANCE AND STANDARD DEVIATION
Variance and standard deviation are terms frequently used in
professional journals that report the results of research
findings. Knowledge of this material is important in the
field of quality control because these terms describe the
spread of measurements or results.
In previous discussions, results have been described in terms
of an average value and a range. The bar graphs below show
the results of three different tests, but they all have the
same average value and range.
5
^co 4
CD z 3
DC S
QJ LU 2
CD DC
= CO 1
Z5 o
•
•
-
.
•
i
—
,
i
1
1
1
1
I I
140 150 160
BOD, rag/1
I
140 150 160
BOD, mg/l
n
140 150 160
BOD, mg/l
III
For all three cases, the average value is 150 mg/l and the range
is 20 mg/l (160-140), using the midpoints for our calculations.
Another term (parameter) to describe the above results is the
variance, S2 , a measure of the dispersion or spread of the results,
The variance is calculated by taking the difference between each
measurement, X, and the average value of all the measurements, X,
squaring it, summing up the squared differences, and dividing by
the total number of differences, n, minus one, as shown in the
following formula.
16-29
-------
Variance, S'
-Yl 2
Z CX-X)
n-1
= Each Measurement
Average Value, X =
Z X
n
n
= Number of Measurements
Z = Summation of All Values
In the denominator, one is subtracted from n, because X in the
numerator is calculated from n measurements. X is influenced by
all of our measurements. By dividing by n-1 we obtain a more con-
servative description of the actual dispersion. The larger n be-
comes, the more insignificant becomes the "minus one" term. When
analyzing plant data, the number of measurements is usually small;
therefore, the "minus one" term is important.
Step 1. Calculate the variance for the results shown in Bar Graph I.
Measurement
X, mg/1 X-X
140
145
150
155
160
140-150
145-150
150-150
155-150
160-150
= -10
= - 5
0
= . 5
= 10
CX-X):
C-io) c-io)
C- 5)(- 5)
C o) c o)
C 5)( 5)
C 10) c 10)
TOTAL
I
= 100
= 25
0
= 25
= 100
n
Freq.
2
3
5
3
2
= 15
CX-X) 2 Freq.
C100K2)
C 25) (3)
C 0)C5)
C 25) C3)
C100)C2)
z cx-x)2
= 200**
= 75
0
= 75
= 200
= 550
Crag/1)
s2 =
E CX-X)2
n-1
550
14
= 39.3 Cmg/1)2
39.28
14 /550
42_
130
126
4 0
2 8
1 20
1 12
* Units should be Cmg/l)2« The term is meaningless, but is included
to_maintain the proper units. For the first row, X is 140 mg/1;
X-X is 140 mg/1-150 mg/1 = -10 mg/1; CX-X)2 is C~10 mg/1)C-10 mg/1)
= 100 Cmg/1)2; and CX-X)2 Freq. is C100 Qng/l]2)C2) = 200 (mg/l)*.
** Instead of writing 140 twice, subtracting 140-150 twice, and squaring
C-10)C-10) twice, we performed our calculations once on one line and
then multiplied by the frequency, 2. We did the same for the other
measurements, X.
16-30
-------
Step 2.
Calculate the variance for the results shown in Bar Graph II.
Measurement, X X-Y (X-Y)2 Freq. (X-T)2 Freq.
140
145
150
155
160
-10
- 5
0
5
10
100
25
0
25
100
3
3
3
3
3
300
75
0
75
300
TOTAL n = 15 £ (X-X)2 = 750
S2 = E CX-Y)2 53.57
n-1 14/ 750
750 70
isTT 50
ii> 1 42_
= 53.6 Cmg/1)2 8 0
1 00
98
Step 3.
Calculate the variance for the results shown in Bar Graph III.
Measurement, X X-X CX-X)2 Freq. (X-Y)2 Freq.
140
145
150
155
160
-10
- 5
0
5
10
100
25
0
25
100
••^•^•^••^H*
4
3
1
3
4
400
75
0
75
400
S2 =
TOTAL n = 15 E (X-X)2 = 950
67.85
n-1
950
15-1
= 67.9 (mg/1)2
16-31
-------
In comparing the variance of the three bar graphs, note that as
more and more measurements shift away from the average value,
the value of the variance increases, thus indicating an increase
in the dispersion of our results.
The dispersion is frequently described in terms of S, the
standard deviation, which has the same units as the average
value, mg/1. The standard deviation, S, is the square root
of the variance, S2. The square root of a number is one of
two equal numbers that when multiplied together give that number.
EXAMPLES;
The square root of 9 = 3 or
16 = 4 or
25 = 5 or
4=2 or
1=1 or
S2 = S or
1.44 = 1.2 or
(mg/1)2 = mg/1 or / (mg/1)2 = mg/1
To obtain the square root of a number there are several potential
methods listed below in order of ease of use.
1. Look up the values in a table in a math book or handbook.
2. Use a. slide rule.
3. Attempt a trial and error approach by multiplying a number by
itself.
4. By direct calculation.
EXAMPLE 7:
Find the standard deviation, S, of the variance S2 = 39.3 (mg/1)2.
Use of a math book or handbook, or a slide rule are the quickest
and easiest ways to find the square root of a number. If these
sources are not available, the square root may be calculated.
Trial and Error:
First try Step 3, multiplying a number by itself.
9
~T6~
~^S
T~
1~
"s2"
1.44
= 3 and
= 4 and
= 5
= 2
= 1
= S
= 1.2
(3) (3)
(4) (4)
etc.
= 9
= 16
16-32
-------
Trial:
II
III
IV
6.0
6.0
36.00
Less
than
39.3,
too
small
6.5
6.5
325
390
42.25
Greater
than
39.3,
too
large
6.3
6.3
189
378
39.69
Greater
than
39.3,
too
large
6.2
6.2
124
372
38.44
Less
than
39.3,
too
small
Trial III is closest to 39.3. Therefore S = 6.3 mg/1.
Direct Calculation:
To calculate the square root directly, the following steps are used.
1. Begin at the decimal point and separate the number in groups
of two, to the left, or right, or in both directions, depend-
ing on the number, as shown below.
/ 39.30 00
Other Examples6 ;
/ 0.66 20
/ 0.04 31
2. Select the largest number which, when squared, is equal to or
less than the number contained in the first number or pair of
numbers on the left.
6.
/ 39.30
Other Examples:
1
/ 128.
. 8
/ 0.66 20
/ 0.04 31
6 These other examples are provided to indicate how to determine
the square root of other numbers.
16-33
-------
3. Square this number, subtract it from the first number or
pair of numbers, and bring down the next pair of numbers.
Double the 6, obtain 12, and estimate how many twelves will
go into 33. The answer is 2. Place 2 over 30 and to the
right of 12, obtaining 122. Multiply 122 by 2 to get 244.
Subtract 330-244 = 86 and bring down the next pair of numbers
(00).
6. 2
/39.30 00
36.
122 / 3.30
2.44
86 00
5. Double 62, obtain 124, and estimate how many times 124 goes
into 860. Try 7. Place 7 over 00 and to the right of 124
to obtain 1247. Multiply 1247 by 7 to get 8729. This is
larger than 8600. Reduce 7 to 6. Multiply 1246 by 6 to
get 7476. Subtract, 8600-7476 = 1124, and bring down the
next pair of numbers.
6. 2 6
/ 39.30 00
36
122 / 3 20
2 44
Therefore, S = 6.26
or S = 6.3 mg/1
1246 / 86 00
74 76
Checks
QUESTION
16. 8A
Calculate the variance and standard deviation of the SVI
data given in Question 16. 7A. SVI = 120, 115, 120, 120,
125, 110, 115.
n-1
16-34
-------
16.9 SUMMARY
1. Average or Mean Value
Sum of All Measurements E X
X =
Number of Measurements n
where X is each measurement or test result, and n is the number
of measurements or observations.
2. Range
Range = Largest X - Smallest X
3. Median
Median = Middle measurement when measurements are ranked
in order of magnitude (may fall between two
measurements)
Mode = Measurement that occurs most frequently (may be
more than one mode)
5. Variance and Standard Deviation
4. Mode
Variance, S2 =
Standard
Deviation, =
S
n-1
16-35
-------
16.10 ADDITIONAL READING
a. "Graphical Approach to Statistics", Water and Sewage Works
Magazine, Scranton Publishing Company, Inc., 35 East Wacker
Drive, Chicago, Illinois 60601. $1.25.
b. "Basic Statistical Methods for Engineers and Scientists",
by A.M. Neville and J.B. Kennedy, International Textbook
Company, Scranton, Pennsylvania 18515. $8.50.
END OF LESSON 2 OF 2 LESSONS
on
ANALYSIS AND PRESENTATION OF DATA
16-36
-------
DISCUSSION AND REVIEW QUESTIONS
Chapter 16. Analysis and Presentation of Data
(Lesson 2 of 2 Lessons)
Work these questions before continuing. Write your answers in
your notebook. The problem numbering continues from Lesson 1.
The solids concentrations of sludge withdrawn from a primary clari-
fier during the past seven days are given below:
Day: 12345 67
Solids, %: 6.0 6.5 6.0 5.0 6.5 7.5 8.0
9. Draw a bar graph showing the distribution of data.
10. Draw a line graph to illustrate if any trend is developing.
11. Is a trend apparent?
12. Calculate the variance, S2, for the solids data.
13. Determine the standard deviation, S, for the solids data
using any method you prefer.
16-37
-------
SUGGESTED ANSWERS
Chapter 16. Analysis and Presentation of Data
16.1A Variations in test results may be caused by:
1. Water or material Csludge) being examined
2. Sampling
3. Testing Canalyst, procedure, reagents, equipment)
Many factors in each of these three categories also can
cause changes. For example, in sampling, variations
could be caused by changing the location where the sample
was obtained and when the sample was obtained.
16.IB Samples should be tested immediately by the lab because
sometimes the items (BOD, DO) we wish to measure will
change with time due to biological or chemical reactions
taking place in the sample container.
16.2A Instruments must be periodically calibrated and zeroed
before using to insure accurate results.
16.2B A gage reading of 2 psi also would give a reading of
4.6 feet of water.
16.4A Calculate the average mixed liquor concentration in mg/1.
Average Concen- Sum of All Measurements, mg/1 2138
tration, mg/1 ~ Number of Measurements 1863
1921
5922 mg/1 5922
3
= 1974 mg/1
16.5A Range of measurements.
Range, mg/1 = Largest Value - Smallest Value
= 2138 mg/1 - 1863 mg/1 2138
-1863
= 275 mg/1 275
16-39
-------
16.6A Rank SVI
1 125
2 120
3 120
4 120
5 115
6 115
7 110
Free
1
Median SVI = 120 Half of the values
are larger and half
are smaller.
Mode SVI = 120
Value that occurs
most frequently
(three times).
16.7A SVI
125
120
115
110
SUMS
^req.
1
3
2
SVI x Freq.
125
360
230
110
825
or
Sum of SVI
125
120
120
120
115
115
110
825
a. Average
SVI
Sum of SVI
Number of SVI
825
7
= 118
117.8
7 f 825
7_
12
_7
55
49
60
56
b. Range of SVI = Largest SVI - Smallest SVI
= 125 - 110
= 15
16-40
-------
16.7A c. Bar Graph.
Freq.
110
115 120
SVI
125
16. 7B
1800
1700
1600
1500
1400
1300
1200
1100
1000
•
. *\^_.*
~"~ * — .
^*^*
*
.
.
1 2 3 4 5 6 7 8 9 10
WEEK
a. Yes, a trend is apparent.
b. Corrective action should be taken to prevent the
continued drop of alkalinity. See Chapter 8 on
Sludge Digestion and Handling.
16-41
-------
STEP
X
125
120
115
110
SUM
1.
: Cl) (2)
Freq. X Freq. X-X"
1 125 125-118 =
3 360 120-118 =
2 230 115-118 =
!_ 110 110-118 =
7 825
Calculate average SVI, X.
Y _ Sum Measurements
Sum Freq.
825
7
= 118
(3) (4)
(X-X)2 (X-X)2 p.
7 49 49
24 12
-3 9 18
-8 64 64
143
117.8
7 / 825
7_
12
7
55
49_
60
56
2. Determine X-X = X - 118 = 125 - 118 =
3. Determine (X-T)2 = (7)2 = 49
4. Determine (X-X)2 (Freq.) = 49 x 1 = 49
5. Calculate variance, S2.
2 = Z CX-XJ2 23.8
6 / 143
12
- 24 5°
^ 48
16-42
-------
16. 8A
6. Calculate standard deviation, S.
S =
= / 24
= 4.9
4.9
/ 24.
16
89 I 8 00
8 01
Close enough.
16-43
-------
OBJECTIVE TEST
Chapter 16. Analysis and Presentation of Data
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1.
1. Data should be collected and (select best answer):
1. Filed
2. Forgotten
3. Analyzed
4. Los t
5. Values placed in all columns on report sheet
2. Laboratory results of influent BOD at a particular plant vary
due to:
1. Nothing—the results should not be different
2. Differences in the composition of the influent
3. Operators titrating to different end points
4. Operators not following the exact same testing procedure
every time
5. Collecting samples in a different manner
3. The characteristics of a sample may change between collection
and analysis due to:
1. Nothing—the characteristics don't change
2. Temperature changes during transportation to the lab
3. Chemical changes in the sample
4. Biological changes in the sample
5. Changes in the variance
4. A representative sample:
1. Describes the overall situation
2. Represents the equipment manufacturers
3. Represents the people
5. At the beginning of a week a totalizer on the plant inflow
read 1,823,471 gallons. Seven days later, the totalizer
reads 2,619,582 gallons. The average daily flow during the
week was approximately:
1. 0.01 MGD
2. 0.11 MGD
3. 1.11 MGD
4. 0,10 MGD
5. 0.13 MGD
16-45
-------
6. Bar graphs can be used to show:
1. Growth
2. Characteristics of data
3. Dispersion of data
4. Your supervisor results of lab tests
5. How neat you can draw
7. Plotting data on graph paper to show trends may be helpful to:
1. Justify budget increases
2. Describe the variance
3. Predict when expansion will be necessary
4. Illustrate the need to look for the cause of trend
5. Illustrate patterns of effluent quality
At 1:30 PM every day of the week the dissolved oxygen in the
Number 1 pond of a wastewater treatment facility is measured and
the results are summarized below in mg/1:
WEEK DAY
1
2
M
9.8
8.1
T
9.5
8.4
W
9.6
8.0
T
9.2
7.6
F
8.9
7.5
8. The average DO in the pond over the two-week period was
1, 8.1 mg/1
2. 8.4 mg/1
3. 8.5 mg/1
4. 8.7 mg/1
5. 8.9 mg/1
9. The range of DO was:
1. 7.5 to 9.8 mg/1
2. 9.8 to 7.5 mg/1
3, 1.3 mg/1
4. 2.3 mg/1
5. 0.8 mg/1
10. The median DO was:
1. 8.0 mg/1
2. 8.1 mg/1
3. 8.4 mg/1
4. 8.6 mg/1
5. 8.9 mg/1
16-46
-------
11. Is there a trend in the DO concentration in the pond?
1. Yes
2. No
12. The variance, S2, in the DO level in (mg/1)2 is:
1. 0.65
2. 0. 70
3. 0.72
4. 0.75
5. 0.78
13. The standard deviation, S, in the DO level in mg/1 is:
1.
2.
3.
4.
5.
0.70
0.75
0.80
0.85
0.90
Review Questions:
Ponds receiving 0.2 MGD have overall dimensions of 400 ft by 500 ft
with an average influent BOD of 160 mg/1. The average water depth
is 4.5 ft. Select the closest answer.
14. The theoretical detention time in the ponds is:
1.
2.
3.
4.
5.
25 days
35 days
50 days
65 days
75 days
15.
The organic loading is
1. 20 Ib BOD/day/ac
2, 30 Ib BOD/day/ac
3. 40 Ib BOD/day/ac
4. 50 Ib BOD/day/ac
5. 60 Ib BOD/day/ac
Please write on your IBM answer sheet the total time required to
work both lessons and this Objective Test.
16-47
-------
GRAPH PAPER
See Next Sheet
16-49
-------
-------
CHAPTER 17
RECORDS AND REPORT WRITING
by
George Gribkoff
(with a supplement by John Brady)
-------
TABLE OF CONTENTS
Chapter 17. Records and Report Writing
Page
17.0 Introduction 17-1
17.1 Records 17-1
17.10 Importance of and Need for Records 17-1
17.11 Type of Records 17-2
17.110 Operation Records 17-3
17.111 Physical Plant and Stock Inventory. . 17-4
17.112 Maintenance Records 17-4
17.113 Financial or Cost Records 17-4
17.114 Personnel 17-4
17.12 Frequency of Records 17-5
17.120 Daily Records 17-5
17.121 Monthly Records 17-8
17.13 Keeping and Maintaining Monthly Records . . . 17-8
17.14 Evaluation of Records 17-9
17.2 Report Writing 17-11
17.20 Importance of Reports 17-11
17.21 Major Principles of Report Writing 17-12
17.22 Organization of the Report 17-12
17.23 Mechanics of Writing a Report 17-14
17.24 Effective Writing 17-15
17.25 Types of Reports .' 17-16
17.250 Monthly Reports 17-17
17.251 Annual Reports 17-20
17.26 Obtain Reports by Other Operators 17-21
17.3 Typical Monthly Report 17-22
17.4 Additional Reading 17-25
111
-------
NO PRE-TEST
for
Chapter 17. Records and Report Writing
-------
CHAPTER 17. RECORDS AND REPORT WRITING
17.0 INTRODUCTION
Most books on plant operation discuss record keeping adequately
but are very sketchy on their treatment of report writing.
However, report writing is the main means by which those who
have information communicate with those who need it. Operators
must communicate effectively with management and the general
public on the operation of their plant and on requests for
additional funds for improvements and personnel.
Any business transaction or operation requires records for efficient
management; this is also true for operation of waste treatment
facilities.
17.1 RECORDS
The administrator, superintendent, and operators of a wastewater
treatment facility should know the cost and efficiency of their
plant. Well-kept records will make the task of writing treatment
plant cost and efficiency reports much easier.
17.10 Importance of and Need for Records
Records are needed for the following reasons:
A. Plant Operation. Review of operating records can indicate
the efficiency of the plant and its treatment units and
past and future problems.
B. Records are needed to show type and frequency of maintenance
of operating units and evaluation of effectiveness of mainte-
nance programs. (See Chapter 11, Maintenance.)
17-1
-------
C. Records can provide data upon which to base recommendations
for modifying plant operation and facilities.
D. Records of past performance and operational procedures
are invaluable tools for the engineer in the evaluation
of present performance and serve as a basis for the design
of future treatment units.
E. Records are used to support budget requests for personnel,
additional facilities, or equipment.
F. Records may be needed in damage suits brought against your
district or municipality. They can be especially helpful
to the operator if an accident occurs. As soon as possible
after an accident someone should record the chain of events
leading to the accident, exactly what happened, and any
preventive or corrective action.
G. Records for water pollution and public health aspects may
be required by regulatory agencies.
H. Records provide the actual data for the preparation of weekly,
monthly, or annual reports to administrative officials, the
public, and regulatory agencies.
Records must be permanent, complete, and accurate. Write entries
on data sheets in ink or with an indelible pencil. A lead pencil
should never be used because notations can smudge and be altered
or erased. False and misleading records may actually do more
harm than lack of records.
Record keeping costs time and money, and only useful records should
be kept. Periodically records no longer useful should be discarded.
Lab analyses of receiving water quality should be kept indefinitely.
Some compromise is necessary between collecting useless records and
avoiding the frustrations of not finding needed information. Keep
your records neat and organized. A record misfiled is a record
lost, and a lost record is worthless.
17.11 Type of Records
The type of records to be kept will depend on the size and type
of plant. A small primary plant may not require the number or
the variety of records required of large secondary or advanced
wastewater treatment plants.
17-2
-------
The specific records required will be determined by the size and
type of treatment processes in the plant and are discussed more
fully under respective chapters dealing with plant processes.
Typical data sheets are included at the ends of chapters on
Sedimentation and Flotation (Primary Plant), Trickling Filters,
Activated Sludge, Sludge Digestion and Handling, and Ponds.
Records are generally separated into five classifications:
1. Operation and performance records
2. Descriptive and inventory records
of the physical plant and stock
3. Maintenance records
4. Financial or cost records
5. Personnel
17.110 Operation Records
The minimum amount of record keeping that may be required is as
follows:
1. Daily records of flows into the plant.
2. Chemical, physical, and bacteriological characteristics of
influent and effluent.
3. Amount of electrical power consumed.
4. Amount of chlorine used.
5. Unusual happenings such as bypasses, floods, storms, complaints,
and other significant events. Any other unusual event should
be recorded if there is any possibility that a record of these
events may be needed in the future, either for legal or adminis-
trative purposes. The main idea to keep in mind is to record
only that data which may eventually be used.
17-3
-------
17.111 Physical Plant and Stock Inventory
As a minimum, the following records are essential for proper
evaluation of plant facilities and for making future recom-
mended modifications or additions.
1. Contract and "as built" plans and specifications of waste
treatment facility. This includes detailed piping and
wiring of plant.
2. Plans and operating instructions for plant equipment.
3. Costs of major equipment and unit items.
4. A complete record and identification card for all major
equipment." The card should include name of manufacturer
and identifying code number.
5. Lists of tools, materials, chemicals, lab reagents and
supplies, and office supplies.
6. A record card for each industrial waste discharger con-
taining information on type, quantity, characteristics,
and times of expected waste discharges.
17.112 Maintenance Records
See Chapter 11, Maintenance.
17.113 Financial or Cost Records
Keep lists of purchases and expenses to date during fiscal year.
Comparisons should be made with budget allocation to avoid excess
purchases.
17.114 Personnel
Employee personnel records, including annual performance ratings,
should be maintained for each of the plant employees.
17-4
-------
17.12 Frequency of Records
Records at most waste treatment facilities are kept daily and
on a monthly basis.
17.120 Daily Records
Data to be recorded will depend upon the type and size of the
plant. Specific record forms are contained at the end of
chapters pertaining to a particular type of treatment plant.
One of the most important daily records is a day-by-day diary
or log of events and operations during the day. A daily diary
or log should be maintained in every plant, and in large plants
at each section (such as lab, maintenance). The log may be a
spiral notebook or a standard daily diary made for that purpose.
The information entered in the plant log should be pertinent only
to plant functions. Log entries should include at the top of
the page the day of the week, the date, and the year. The names
of the operators working at the plant, and their arrival and
departure times, should also be included. Log entries should be
made during the day of various activities and problems as they
develop. Do not wait until the end of the day to write up the
log as some items may be overlooked. If the operator will take
a few minutes to make log entries in the morning and afternoon,
he will develop a good log. Logs are beneficial to the operator
and to people who replace the operator during vacations, illnesses,
or leaves of absence. A well-kept log may prove very helpful to.
the operating agency as legal evidence in certain court cases.
An example of one day's log entries in a small trickling filter
plant is outlined below:
Tuesday, June 10, 1969
J. Doakes, Operator. A. Smith, Assistant Operator.
G. Doe, Maintenance Helper.
8:20 AM Made plant checkout, changed flow charts,
No. 2 supernatant tube plugged on No. 2
digester, cleared tube.
9 AM Started drawing sludge from bottom of No. 2
digester to No. 1 sand bed.
9:15 AM Smith and Doe completed daily lubrication
and maintenance, put No. 2 filter recircu-
lation pump on, took No. 1 pump off.
17-5
-------
10 AM Received three tons of chlorine, containers
Nos. 1583, 1296, 495; returned two empty
containers Nos. 1891 and 1344. Replaced bad
flex connector on No. 2 chlorine manifold
header valve, and connected container No. 495
on standby.
10:50 AM Collected and analyzed daily lab samples.
1:15 PM Pumped scum pit, 628 gallons to No. 1
digester.
1:30 PM Restored sludge pump No. 2 by removing
plastic bottle cap from discharge ball
check; pump back in operation.
2:45 PM Smith and Doe hosed down filter distributor
arms and cleaned orifices. Doe smashed
finger when closing one of the end gates on
filter arm. Sent Doe to Dr. Jones, filled
out accident report, and notified Mr. Sharp
of accident.
3:10 PM Stopped drawing sludge to No. 1 bed. Drew
18,000 gallons of sludge; sample in refriger-
ator to be analyzed Wednesday.
3:20 PM Electrician from Delta Voltage Company in
with repaired motor for No. 2 effluent pump,
Invoice No. A-1824, motor installed and pump
OK.
4:10 PM Doe back from doctor, stated he will lose
fingernail, and required three stitches and
tetanus shot. Must go back next Thursday.
4:30 PM Plant checkout for tonight, put No. 2 chlorine
container on line, in case No. 1 should run
empty during the night.
17-6
-------
Helpful Tip;
Many operators carry a
pencil and pocket notebook
with them at all times on
the job. During the day
they record all events and
items of importance and
write the information in
the plant diary at the end
of the day.
As an example, the minimum daily records kept at a fairly large size
treatment plant with digester tanks may include the following items:
1. Precipitation and weather temperature
2. Raw wastewater flow (MGD from totalizer)
3. Influent and effluent temperatures
4. pH of influent and effluent
5. Grit (cu ft/mil gal)
6. Chlorine use (Ibs)
7. Influent and effluent (5-day BOD, mg/1)
8. Influent and effluent (suspended solids, mg/1)
9. Influent and effluent (settleable solids, mg/1)
10. Raw sludge (gal)
PH
Total solids, %
Volatile solids, %
17-7
-------
11. Digested bottom sludge
Total solids, %
Volatile solids, %
pH
Volatile acids and alkalinity, mg/1
Temperature
12. Gas produced (cu ft)
13. Effluent chlorine residual Cmg/l) ai*d coliform count, MPN
14. Any unusual influent characteristics such as appearance or
odors
17.121 Monthly Records
Monthly records should reflect the totals and averages of the
values recorded daily or at some other frequency and in some cases
should give maximum and minimum daily results, such as maximum and
minimum daily flows.
17.13 Keeping and Maintaining Monthly Records
Daily recorded data are usually written on monthly data sheets.
The monthly data sheet is designed to meet the reporting needs of
a particular plant and should have all important data recorded
that may be used later for preparation of monthly or annual reports.
MONTHLY DATA SHEET (See Appendix)
The monthly data sheet may be a single 8-1/2 x 11" sheet for a small
primary plant, or it may be a number of sheets pertinent to various
treatment units in a secondary or advanced waste treatment plant.
Normally every plant operator makes up a monthly data sheet for his
plant to record daily information. These sheets are numbered down
the left hand side to 31 to cover 31 days in a month. Then from
left to right across the sheet are marked off different columns to
record daily information. These columns should contain the day of
the week, weather conditions, plant flow, influent and effluent
temperature, pH, settleable solids, BOD, raw sludge pumped,
digester sludge drawn, gas production, DO, and other pertinent
information. A space for remarks is helpful to record and explain
unusual events.
17-8
-------
Sometimes the operator may use two or three different sheets
to collect pertinent data. Since each plant is different,
the operator prepares his plant data sheet to record the data
he needs for proper plant operation and for the requirements
of his agency and the regulatory agencies.
In addition to routine daily operation, maintenance and waste-
water characteristics, the monthly data sheet should contain
any unusual happenings that may affect interpretation of results
and preparation of a monthly report such as unusual weather,
floods, bypasses, breakdowns, or changes in operations or mainte-
nance procedures.
A typical monthly data sheet (Appendix) and monthly report
(Section 17.3) for an activated sludge plant are at the end of
this chapter.
17.14 Evaluation of Records
Records are not useful unless they are evaluated and used as
indicators of plant operation and maintenance. Records are
also useful as sources for reports to management or the public.
The recorded data should enable the operator to determine
operation and maintenance of his plant. The information shown
by the records should also indicate to him and his supervisor
the efficiency of each unit in the plant. Records kept on the
quality of the effluent and the receiving waters should be
analyzed for the discharge's effect on the receiving waters.
The importance of looking at and analyzing records frequently
cannot be overemphasized.
Records should not only be analyzed as a single piece of data,
but any one variation should be looked upon for its relation to
another source of data. For example, a sudden drop in temperature
of the influent might be accompanied by greatly increased flows.
This could indicate storm water inflows or infiltration of
sewer lines. Infiltration by storm waters also could influence
the BOD and suspended solids concentrations in the plant influent.
Or one might observe a sudden increase in 5-day BOD concentrations
in the plant effluent. This may indicate a seasonal increase due
to beginning of cannery operations, or it may indicate a break-
down of industrial treatment facilities discharging untreated
wastes into the wastewater collection system.
Before any meaningful interpretation can be made of any sudden
variation in data, an expected range of values has to be
determined for the particular treatment unit under consideration
based upon expected or past performance.
17-9
-------
For example, if average daily flows during weekdays were around
two million gallons per day and suddenly a flow of 1.5 million
gallons per day was recorded, this may indicate malfunctioning
of metering equipment or a break in sewer lines or a bypass
ahead of the plant. Conversely, unusually high flows may
indicate storm water infiltration, surface water runoff flowing
into the system through manholes, or an unusual dump of waste-
water.
An excellent way to facilitate review of daily records and detect
sudden changes or trends is a prepared chart showing values
plotted against days. Unless results are plotted, slight
changes and trends can go undetected. The deviation from the
expected values may have been caused by unusual circumstances
or an error in observation or analysis. Procedures for plotting
and interpreting data are provided in Chapter 16, Analysis and
Presentation of Data.
QUESTIONS
17.1A Why is it important to keep records of plant operation?
17.IB Why should unusual happenings be recorded and described?
17.1C Why do many operators carry a pencil and pocket notebook
on the job?
17.ID Why should records frequently be reviewed and analyzed?
17-10
-------
17.2 REPORT WRITING
This section will cover the major principles and mechanics of
report writing, the type of report usually required of a plant
operator, and a discussion and example of effective writing.
To many, the thought of writing a report represents a task that
is to be approached with fear and with a sense of inadequacy.
This need not be the case. Anyone who can read and is willing
to put forth the effort can prepare an adequate report. The
typical treatment plant operator may regard the writing of
reports as an unwelcome chore and thus may approach the subject
with a natural resistance.
You should approach the task of report writing as if your next
pay raise depended on a neat, organized, and brief report.
One operator's annual report was so well written that a local
newspaper used the report to develop a six-article series on
his treatment plant. The newspaper stories explained the opera-
tion of the plant and its effectiveness in protecting the fish
life, water supplies, and recreational uses of the receiving
waters. Shortly after the articles appeared in the newspaper
the operator received a substantial increase in salary.
17.20 Importance of Reports
A report serves many purposes. It can serve as the basis of a
request for additional budget and personnel, plant additions,
or changes in plant operation. A report also is a means by which
your ability, actions, and knowledge are communicated to manage-
ment and your supervisor. It should be visualized as an oppor-
tunity to tell your story to your supervisor, management, or the
general public. Your ability to prepare and submit effective
reports is one factor considered for advancement in your pro-
fession.
Furthermore, you and your plant operation are partially judged
by the information contained in your report, its style, and its
appearance. A poorly prepared report may result in an impression
that the plant is not operating efficiently; or, still worse, it
can result in little action on or rejection of recommendations or
requests.
It is not enough that you operate a plant efficiently; you must
demonstrate this to your supervisors, administrators, and regu-
latory agencies in a clearly understandable and well-prepared
report.
17-11
-------
The narrative type of report writing will be discussed first
because it is the non-routine part of a typical monthly,
quarterly, or annual report.
17.21 Major Principles of Report Writing
Whatever the report or its size, there are some basic principles
common to good report writing:
1. Know the purpose and objective of your report.
2. Tailor your report to the person or persons to
whom it is directed.
3. Know your subject.
4. Organize the report to present order of ideas in
a logical manner.
5. Use language in the report that will be under-
stood by the reader.
6. Use facts and figures.
7. Be as exact and brief as possible.
8. Write effectively.
In starting to prepare a narrative report, the most important ques-
tions are what is the purpose of this report and for whom is it
written? The next important step is the organization of the ideas
and subject matter in a logical .order.
17.22 Organization of the Report
There is no single way to organize a formal report. It is important
to remember that a written report does not necessarily organize and
present the material in the same order in which the information was
gathered. Organization means simply that the topics in the report
are set forth in logical sequence to tell the story effectively.
Some reports may follow a general format such as:
17-12
-------
A. Brief statement of problem
B. Summary
C. Conclusions and recommendations
D. Body of report
1. Technical and administrative background
2. Investigation details
3. Any necessary supporting material to back up
conclusions and recommendations
4. Appendix (if necessary) including detailed data
and tables to support body of report
The conclusion and recommendation section of a report should
receive the most attention and review. It is important that
these be stated clearly and briefly and in language that will
be understood by your readers. It also is important to make
certain that your conclusions and recommendations are supported
in the body of the report.
A memorandum to a supervisor or a narrative portion in a report
should be checked for organization and content as follows:
1. Is the material presented in an organized way?
2. Is there duplication?
3. Is there omission of an important item?
4. Is the material presented really necessary to make your
point and support your conclusions or recommendations?
Unnecessary material in a communication or report only serves to
weaken your case by clouding the main issues.
The above list applies to almost any written communication and can
be summarized by the four Cs of good report writing:
Conciseness
Clearness
Completeness
Candor
17-13
-------
17.23 Mechanics of Writing a Report
In the previous section examples were given on organizational
plans for formal reports; but what are the mechanics of writing
a memorandum, a short report, or a section in a larger report?
Following are some guidelines for preparing a report:
A. List ideas and topics you plan to cover in a report.
B. Arrange ideas in logical sequence.
C. Gather supporting material needed to support the ideas
to be presented in the report.
D. BEGIN WRITING—this is most important! Prepare a rough
draft of the report based on listed ideas and their
organization. At this stage of preparation, writing
without undue concern about sentence structure or grammar
is suggested. It is more important at this stage to record
your ideas. It is much easier in a later rewriting of
the preliminary draft to eliminate unnecessary material
than it is to add to the report.
E. Prepare conclusions and recommendations, if any, after
writing the main body of the report.
F. Review preliminary draft for content, logical presentation
and organization, and eliminate any unnecessary information.
It is at this stage that you can reorganize your order of
presentation for a more effective report and check for
simplicity and understandability.
G. Review report for sentence sense, spelling, grammar, and
briefness.
H. Make another draft (if necessary).
I. Have a colleague or supervisor review the draft if possible.
J. Finally, check your report for overall effectiveness:
1. Will your initial statements create interest in
the contents of the report?
2. Will the reader understand it?
3. Is the presentation of ideas in logical order?
4. Are major points emphasized?
17-14
-------
5. Has all irrelevant material been eliminated?
6. Are the sentences direct and effective?
7. Is the report neat and attractive?
8. Does the report support your conclusions and recom-
mendations?
A report does not have
to be a literary master-
piece. The more factual
and brief it is, the more
likely it is to be
favorably considered.
17.24 Effective Writing
While the organization
of a report and presen-
tation of ideas in a
logical manner are the
chief components of a
good report, effective
writing is also necessary.
Effective writing is simply
the putting together of
words in a gramatically correct and brief manner, eliminating
needless words, expressions, and repetitions. A good technical
report impresses no one favorably if it is full of flowery and
confusing language.
Fortunately, there is an excellent self-tutor publication avail-
able entitled, "Effective Writing" (A Tutor Text), by Kellog Smith
and Jane Stapleford, published by Doubleday and Company, Inc.
The "Tutor Text" teaches and reviews, by means of multiple choice
questions and answers, the basic grammar necessary for effective
writing. Anyone who can read can improve his writing by
utilizing this book and answering the multiple choice questions
in the text.
The book covers such important subjects on effective writing as:
subject-verb agreement, reference pronouns, placement of modifiers,
parallel sentence structure, subordination and presentation of
ideas, and most important, concise writing.
17-15
-------
The next few paragraphs are provided to show you examples of
different styles of writing. More details may be found in the
reference by Smith and Stapleford, "Effective Writing" (A
Tutor Text).
Following are some examples of direct versus indirect writing
and use of active voice as contrasted to the passive voice:
Indirect; This report which you requested in your
letter of December 15, 1968, on the efficiency of
the trickling filter units is submitted for your
approval. It is concerned with removal of organic
material and future operation using different size
of filter media.
Direct: As requested in your letter of December 15,
1968, the report on trickling filter efficiency for
removal of organic material and possible filter media
size changes is submitted for your approval.
Besides being more direct, we have used eleven words less, or
cut the sentence by 25%. Whenever possible, use active sentence
construction rather than passive.
Passive; It is recommended that the monitoring of
the effluent be started immediately.
Active; Monitoring of the effluent should start
immediately.
Paralle.l sentence construction will make your sentence clearer,
Non-Parallel; The supervisor pointed out how Brown
opposed progress, how he encouraged the men to slow
down, that he never showed initiative, and that he
could not maintain the machines.
Parallel; The supervisor pointed out that Brown
opposed progress, that he encouraged the men to slow
down, that he never showed initiative, and that he
could not maintain the machines.
17.25 Types of Reports
There are many types of reports ranging all the way from a memo-
randum to an annual report to management.
17-16
-------
Specifically, it may be (1) a monthly plant operation report,
(2) a report to a regulatory agency, such as a health department,
or (3) a quarterly or annual report to management or the public.
17.250 Monthly Reports (See Section 17.3)
The monthly reports are used in the preparation of the annual
report. Preparation of the monthly•report consists of the
following preliminary activities:
1. Gathering daily records
2. Reviewing daily log sheets for any significant or
unusual events during the month
3. Jotting down ideas that one wishes to include in the
narrative section of the report
In small plants, a monthly report may consist mainly of data
sheets giving the pertinent facts on:
1. Laboratory analyses and effectiveness of plant
treatment and its various units
2. Cost data on labor, chemicals, and maintenance
3. Maintenance records
4. Remarks stating unusual significant events during the
month
5. Effect on receiving waters
6. Conclusions and recommendations
In some larger plants a monthly report may be required in addition
to the monthly data sheets.
The monthly report is a brief summary of combined information from
the monthly data sheets and daily logs. The report is put together
in outline form with a dozen or so subheadings required for a
secondary plant. The reports are useful to the operator and his
supervisor to keep them informed of plant functions and problem
areas.
The subheadings may be labeled as to flow pattern through the plant
and generally describe in narrative form the physical characteris-
tics, maintenance and operation problems, and unusual events during
the month.
17-17
-------
MONTHLY REPORT
A. Flow
1. Total amount of flow passed through the plant for month
2. Maximum daily flow
3. Minimum daily flow
4. Average daily flow
5. Flow meter problems
B. Headworks
1. Screening: shredding device, operation and maintenance
problems
2. Screen material removed, cu ft/MG
3. Grit removed, cu ft/MG
4. Unusual material in the wastewater, such as oil, silt, odors
C. Primary clarifiers
1. Operation or maintenance problems
2. Scum removal, note plugged scum lines
3. Sludge pumped, solids concentration
4. Effluent characteristics
D. Secondary treatment system
1. Trickling filter
a. Loading rates, average
b. Recirculation rates, average
c. Maintenance problems
2. Activated sludge
a. Loading rates, average
b. Mixed liquor concentration, average
c. Mixed liquor DO level
E. Secondary clarifiers
1. Operation or maintenance
2. Sludge pumped, solids concentration
F. Chlorination
1. Pounds of chlorine used/month
2. Pounds of chlorine used/day, average
3. Chlorine residuals
4. Chlorinator problems
17-18
-------
G. Outfall
1. Effluent characteristics
2. General appearance and condition around plant discharge
3. Condition of receiving system
H. Raw sludge pumps
1. Problems and maintenance
I. Digesters
1. Gallons of raw sludge pumped to digesters
2. Gas production
3. Temperature, pH, volatile acids, alkalinity
4. Operation problems and maintenance performed
J. Sludge drying beds
1. Gallons of sludge drawn
2. Yards of dry cake removed
3. Moisture content of cake or pounds of dry solids
4. Maintenance or cleaning problems
K. Gas system and boilers
1. Operation and maintenance
L. General
1. Power failures
2. Accidents
3. Visitors
4. Grounds and building maintenance
5. Plant cost
a. Man-hours worked
b. Equipment parts
c. Power and fuel
d. Chemicals
e. Miscellaneous
17-19
-------
17.251 Annual Reports
The annual report receives wider distribution and is the report
more likely to be reviewed by the public, management, and other
governmental agencies.
The annual report is, in part, a compilation of data obtained
in the monthly reports. It summarizes the plant's yearly
efficiency, cost data, and analysis of plant operation costs,
and contains recommendations for next year's operations.
In addition, an annual report should contain a short introduction
to provide a background to the reader, giving a brief history and
reason for the report.
The body of the report should contain schematic drawings,
pictures, and other attractive graphs whenever possible, and
should include at least the following items:
a. A letter of transmittal
b. Conclusions and recommendations
c. A brief description and schematic diagram of the system
d. An organization chart showing the various functional divisions
and their chiefs
e. A statistical summary of general plant data such as:
(1) Population served
(2) Wastewater flows (maximum, average, minimum)
C3) Plant unit data, percent removal and efficiency of
various units
f. Body of report which includes a brief description and support-
ing tables, graphs, or charts needed to back up final recom-
mended actions or requests on such topics as:
(1) Wastewater quality
C2) Chlorination
(3) Screening
(4) Pumping
(5) Sludge digestion
(6) Receiving water quality (maps—summary data)
(7) Maintenance and repair
(8) Financial data such as assets, liabilities, revenue
17-20
-------
g. Appendix which includes summary data by month for the annual
report year, giving minimum, maximum, and average values for:
(1) General plant data
(2) Treatment unit data
(3) Loadings and efficiency of treatment
(4) Chemical, physical, and bacteriological data on
influent and effluent
(5) Chemical, physical, and bacteriological data on
receiving waters
Report writing, especially for an operator not experienced in
report writing, can seem like a formidable task. But with pro-
vided guidelines, a review of effective writing, and some real
effort, anyone who can read can produce an effective report.
17.26 Obtain Reports by Other Operators
A very helpful guide to writing a report is to obtain a report
written by another operator. Usually a report may be obtained by
writing a nearby city or operator and asking for a copy. If you
explain that you are an operator and would appreciate a copy of
their report, your request will probably be granted. A representative
of a regulatory agency should be able to recommend to you examples
of we11-written reports.
QUESTIONS
17.2A What is the purpose of writing monthly and annual reports?
17.2B How could you obtain a copy from another plant?
17-21
-------
17.3 TYPICAL MONTHLY REPORT
CLEANWATER TREATMENT PLANT
MONTHLY REPORT FOR JUNE 1969
by John Brady
Flow: Cleanwater treated a total raw wastewater flow of 68.497
million gallons this month, with a daily average of 2.283 MG.
There were no unusual flow conditions during the month.
Grit Chamber; The grit chamber was cleaned on 6/23, with 1.5
cubic yards of grit removed, consisting mainly of eggshells and
sand.
Screening: The top bearing of barminutor No. 1 travel motor was
replaced on 6/4 and a spring on the micro switch was also replaced.
A broken comb was replaced on the No. 2 barminutor on 6/15 and
all combs on that unit were reset to 0.006 inch clearance.
Raw Wastewater Pumps; No problems with No. 1 and No. 3 pumps.
No. 2 pump was repacked on 6/9.
Primary Clarifiers; On 6/21 the No. 2 primary clarifier was de-
watered for annual inspection. The mechanism was in good condition
and only required resetting the clearance of the brass plow
squeegees to their original 1/8 inch. The tank weirs and scum
baffle were wire brushed and repainted with 395-A. The tank was
returned to service on 6/26. While the No. 2 primary was out of
service, the No. 1 primary carried the full plant load without any
detrimental effect on the efficiency of the plant.
Aerator; No problems. The aerator loading was maintained at 25
pounds of BOD per 100 pounds of mixed liquor suspended solids, and
a constant return sludge rate of 30%.
Final Clarifier and Return Sludge Pumps: No operational problems
with the final clarifier. The No. 2 return sludge pump was returned
from J § M Machine Shop on 6/1 and re-installed. J § M replaced
the shaft sleeve and both shaft bearings at a cost of $182.36
(Invoice No. 34475). However, the pump was not ready for service
until 6/2 as J § M had packed the pump bearings with an all-purpose
medium industrial lubricant rather than the P.M. oil film low
temperature grease of -65° to 100°F, as specified.
17-22
-------
Chlorination: No problems. Used 9950 pounds of chlorine at an
average rate of 335 pounds per day. One hundred twenty-five
pounds per day were used for post-chlorination maintaining an
average chlorine residual of 4.4 mg/1. Two hundred ten pounds
per day were used for pre-chlorination for odor control.
Outfall: Other than the foam build-up around the outfall and
the foam drift downstream for approximately 500 yards, the
receiving stream was in good condition. The stream sampling
below the outfall remained at 8.9 mg/1 DO, 2.0 mg/1 BOD, and
average temperature of 58°F.
Raw Sludge Pump: On 6/9 and 6/30, the raw sludge pump was
plugged with a piece of plastic and a wooden stick under the
discharge ball check. In each case the pump was restored to
service during the 8 AM shift.
Digesters: Digester No. 1 was operated as the primary and No. 2
as the secondary. The temperature in the No. 1 tank was raised
from 91°F to 94°F. During the month the tank was continuously
mixed. The recirculated sludge contained an average volatile
acids content of 150 mg/1, with the alkalinity at 2550 mg/1
(volatile acid/alkalinity relationship of 0.06).
Sludge Drying; Supernatant from the No. 2 digester became heavy
on 6/12 with the settleable solids ranging from 9 to 15% by volume.
On 6/17, 28,000 gallons of digested sludge was drawn from the
No. 2 digester to the No. 3 drying bed to reduce supernatant load.
The drawn sludge contained 8.3% solids with a volatile content of
52.6%.
The No. 1 and No. 4 drying beds were cleaned, yielding a total of
63 cubic yards of dry sludge.
Gas System and Boiler: On 6/7 it was found that low gas production
was recorded for 6/6. The No. 2 digester pressure relief was found
to be venting at various times. The entire gas system piping units
were cleaned and inspected with the problem location found on 6/13
in the gas meter itself. The condensate and residue had gummed up
the gear train from the bellows slide arms. The unit was cleaned
with kerosene, relubricated with molly cote, and returned to service
with no further problems.
Power Supply; There were two power outages this month, on 6/24 and
6/27, with the plant being out of service 40 to 45 minutes each
time. The cause of the outages was due to a service fuse dropping
17-23
-------
on one phase at the utility pole by the main gate, leaving only
the two phases from which to operate.
Each time the main power board was shut down to protect plant
equipment.
General;
6/3 Replaced broken hinge on main gate.
6/6 Mosquito abatement personnel moved their oil storage tank
from the plant grounds.
6/15 Left main gate barricade chopped down by vandals.
6/17 Replaced left main gate barricade.
6/19 State Water Pollution Control engineer visited plant and
collected effluent samples.
6/24 Received 400 return sludge meter charts (Invoice No. 111323)
6/25 Flame-Out Fire Equipment Supply Company representative in
and made yearly check on plant fire extinguishers.
Submitted: /s/ John J- Smith
Chief Operator
17-24
-------
17.4 ADDITIONAL READING
1. MOP 11, pages 147-153.
2. New York Manual, pages 119-156.
3. Olman, J.N., Jr., "Technical Reporting", Henry Holt and Company,
New York U952), 289 p. illus. 25 cm. Price $8.50.
4. Smith, K., and Stapleford, J., "Effective Writing", Doubleday
and Company, Inc., Garden City, New York. 481 p. (.A. Tutor
Text). Price $6.50.
5. Souther, J.W., "Technical Report Writing", John Wiley $ Sons,
Inc., New York (1957), 70 p. Price $3.95.
17-25
-------
SUGGESTED ANSWERS
Chapter 17. Records and Report Writing
17.1A Records are important to:
a. Document plant performance, efficiency, and problems
b. Justify budget requests
c. Provide design criteria for remodeling, expansion,
and new processes
d. Verify observations of plant operation
e. Help if legal action is threatened
f. Document quality of receiving waters
g. Report preparation for supervisors and regulatory
agencies
h. Identify significant departures from normal values
and take corrective action
i. Show type and frequency of maintenance of operating
units
If you recognized the importance of keeping records to
document plant performance and justify budgets, you have
identified the important concepts. See Section 17.10,
Importance of and Need for Records.
17.IB Unusual happenings should be recorded and described because
they have an important influence on the interpretation of
laboratory analyses describing the operation and efficiency
of your plant and the condition of the receiving water.
Also they could prove very helpful to the operator in case
of an accident. See Section 17.11, Type of Records.
17.1C Many operators carry a pencil and pocket notebook on the
job to record all important events as they occur during
the day. See Section 17.12, Frequency of Records.
17.ID Records should frequently be evaluated to determine if your
plant is operating properly and to identify any developing
difficulties before they can become serious problems. See
Section 17.14, Evaluation of Records.
17-27
-------
17.2A The purpose of monthly and annual reports is to provide
a brief description of the operation of your plant for
the benefit of management and regulatory agencies. See
Section 17.20, Importance of Records.
17.2B Write a letter to another operator or city and ask for
a copy of one of their reports. See Section 17.26,
Obtain Reports by Other Operators.
17-28
-------
OBJECTIVE TEST
(No Discussion and Review Questions)
Chapter 17. Records and Report Writing
Please write your name and mark the correct answers on the IBM
answer sheet as directed at the end of Chapter 1.
1. Well-written plant reports are important because they:
1. Look nice
2. Communicate to management the accomplishments of you
and your plant
3. Can serve to justify a plant budget
4, Keep the operator from maintaining his equipment
5. Explain to the public the operation and function of
your plant
2. Plant records are important because they:
1. Provide essential information when a plant is modified
or expanded
2. Show type and frequency of maintenance of operating units
3. Make pleasant music
4. Fill up storage space so the public won't think there is
any wasted space around the plant
5. Provide data required by regulatory agencies
3. What types of records should be kept by an operator?
1. Operation
2. Inventory
3. Complaints
4. Music
5. Maintenance
4. Which of the following entries should be made in the plant log?
1. Jones won the football pool.
2. Smith cleaned clarifier weirs today.
3. Switched chlorine feed from No. 2 cylinder to No. 1.
4. Heavy thunderstorm hit north end of town around 3 PM and
lasted for approximately 15 minutes.
5. Mayor Charles visited plant and discussed some recent odor
complaints by plant neighbors.
17-29
-------
5. Records are not useful unless they are:
1. Evaluated
2. Used to fill bookcases
3. Used to prop up slide projectors
4. Used as indicators of plant operation and maintenance
5, Burned for heat
6. A poorly prepared report may:
1. Prevent the operator from getting a pay raise
2. Indicate to management that the operator doesn't
know what he is doing
3. Indicate to the regulatory agency that the plant is
not operating efficiently
4. Convince the public that they shouldn't spend any
more money on the plant
5. Indicate that the operator doesn't care about his job
7. Some of the basic principles of good report writing include:
1. A college degree
2. Knowledge of the subject
3. A good typewriter
4. Organizing the report to present ideas in a logical fashion
5. Using facts and figures
8. Effective writing means:
1. Use of correct grammar
2. Elimination of needless words
3. Putting words together in a brief manner
4. Determining the effectiveness of your plant
5. Avoiding repetitive statements
9. Reports written by other operators are very helpful in
preparing a report. These reports may be obtained:
1. By asking another operator for a copy of one of
his reports
2. By buying one
3. By asking your plant consulting engineer to help
you find a report
4. By requesting a representative from a regulatory
agency to assist in finding a report
5. From an effective writing textbook
10. Books on report writing may be:
1. Obtained from a library
2. Found in most treatment plants
3. Obtained by writing the publisher
4. Found in most homes
5. Of no use to an operator
17-30
-------
11. Well-kept records will make the task of writing reports
much easier.
1. True
2. False
12. Entries on data sheets should be written in ink, because
lead pencil entries may smudge and can be altered or erased.
1. True
2. False
Review Questions:
13. Estimate the pounds of solids in a 350,000-gallon aeration
tank if the suspended solids concentration is 1400 mg/1.
1. 3500
2. 3900
3. 4000
4. 4100
5. 4500
14. Calculate the percent reduction in volatile matter.during
digestion if the raw sludge was 72% volatile matter and the
digested sludge is 51%.
1. 50%
2. 55%
3. 60%
4. 65%
5. 70%
15. Determine the organic loading on a pond in pounds of BOD per
acre per day if the inflow is 1.5 MGD with a BOD of 145 mg/1
and the pond area is 30 acres,
1. 50 Ibs BOD/ac/day
2. 55 Ibs BOD/ac/day
3. 60 Ibs BOD/ac/day
4. 65 Ibs BOD/ac/day
5. 70 Ibs BOD/ac/day
16. Lab tests indicate a chlorine dose of 10 mg/1 is necessary for
adequate disinfection of the plant effluent for a flow of 1.2
MGD. What should be the feed setting on the chlorinator?
1. 10 lbs/24 hr
2. 50 lbs/24 hr
3. 100 lbs/24 hr
4. 200 lbs/24 hr
5. 500 lbs/24 hr
17-31
-------
Please write on your IBM answer sheet the total time required
to work this chapter.
CONGRATULATIONS
You've worked hard and completed a very difficult program.
17-32
-------
APPENDIX
(Monthly Data Sheet)
17-33
-------
MONTHLY RECOR
UJ
5
o
1
13
14
15
16
17
IB
19
20
21
??
23
24
25
26
2/
28
29
50
31
<
O
S
M
T
W
1
F
S
S
M
T
W
T
F
S
S
M
T
W
T
F
S
R
M
T
W
T
F
S
S
M
MAX
MIN
AVG
FLOW (
LAST
1st
TOTAl
WEATHER
(XttRR
CLEAR
CLEAR
CL6AO
CLEAR
CLEAR
ClGAB
CLBAR
CLUR
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEW
CLEAR
4.M.
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEAR
CLEW
Q
O
S
1
I
U.
1.762
ii.34
? IBS
2.012
2.48
2.38
2.13
1.867
?fi34
2307
2.IH8
??0?
?!7fl
2.008
1.942
1.4U
M?l
IfeTT
2.457
2.418
2.2I3
87fl
2.90 1
?34I
2.42I
2.562
2.428
2.I4S
.862
.V4t
.90)
.782
2.283
METER :
22204-6
153549
r> IQ
RAW WASTEWATER
01
S
LU
75
74
74
74
74
74
75
7&
75
76
Y6
76
77
78
76
7fi
78
76
78
79
7G
7fi
77
78
76
71
I'M
78
VH
7.3
7.2
7.2
7.3
7.4
7S
7.3
A3
7.1
7.3
7.3
7.2
7?
7.1
7.3
7.3
7.5
7.1
7,3
7.3
7.3
7.3
7.3
A3
7.3
7.3
v.a
7.4
7.1
7.3
CO
o
5
CO
14
13
8
IZ
13
13
13
12
14
16
IB
II
II
12
12
II
8
15
12
II
12
1?
12
13
13
12
10
12
7
13
18
7
12
ELECT
LAST
1st
TOTA
MULT ±
d
d
m
ilur
IbH
174
192
lbt>
168
193
187
212
176
2ie
155
186
g
3
CO
81
3
TbO1
I'iB
134
142
156
144
118
142
170
102
no
102
139
PRIM. EFF.
d
0
to
118
ib6
109
135
i^r
II?
81
84
117
120
III
•w
81
105
113
I?R
110
105
B7
105
104
ni
133
114
81
143
I2B
84
II V
I01/
156
84
112
SUSP SOLIDS
84
84
66
74
m
n
n
14
te
H
IR
14
1
II
8
S
II
15
IZ
H
in
10
ii
m
18
10
14
13
14
12
10
Ib
16
14
b
11
8
IZ
RAW
LA
ST
TOT/i
I
18
Ib
1
14
II
e,
7
15
II
8
10
H
18
8
H
in
II
7
7
12
H
10
13
10
8
6
10
5
tt
b
18
5
10
d
d
0.9
1.0
1 ?
0.8
I.V
?fi
1.2
0.8
1 C
1.5
I.I
?.o
3.5
3.1
1.3
l.fl
1.1
ze
?.1
3. 1
1. 2
o,s
O.3
?.2
2.8
1. 7
O.H
0.6
0.5
l.ti
3.5
0.5
1. 6
CO
LU
CK
(M
-I
U
2.7
2.8
8R
4.4
b.ii
fiO
4.4
4.2
1^
6.6
fo.fc.
^R
4.0
3.8
4.4
^0
6.6
^4i4
fi.2
4.4
4.2
4?
2.5
42
4.0
4.3
3.8
3.5
3.1
3.b
0.8
2.5
4.4
SLUDGE;
ST 798324
ut 432984
OPERATOR:
AERATION SYSTEM
J
5 «
> Q
CO _J
m o
-1 CO
6746
6859
7224
73O5
70/4
6754
6216
7057
G767
GUI
7035
6352
G3I3
6335
6873
7082
G2I5
G227
4844
5846
G892
7518
6388
79£2
7G88
G697
G923
7161
7852
7C88
8388
4S44
6868
SUSP SOLIDS
2036
2078
2211
2213
2106
2069
1905
2138
2037
1861
2123
1954
IS37
1121
2O90
2IG2
1137
l'
co'
T3,
72
76
81
bu
77
78
84
7fl
9.1
H4
17
87
82
8£
1?
98
48
110
104
9b
114
iai
W
18
102
44
91
qs
^T
121
72
91
o"
d
P.5
1.4
?.l
2.0
ii.b
^ S
2.6
0.9
?.S
2.8
I.V
^0
4.8
4.3
2.2
?S
25
3.3
4,5
4.1
2.6
1 8
I.S
3.G
4.1
2.6
I.Vt
1.7
1.0
2.H
4.8
0.9
2.6
ETER;
2I8IIIO
1265230
1 915^80
g
RETURN
SUSR SOLI
51£l
4GB3
6625
G64I
6018
58£2
5564
G758
G022
GI35
GI83
G027
5542
4856
5753
6852
6654
5767
4762
5123
5928
3814
831fi
8824
7382
C8G7
7436
8412
7117
T/3b
8824
4G83
G328
_FT3
RETURN-MOD
0.702
0.711
0708
0.712
uva;
0700
0.70S
0.703
n.712
0705
O.VOO
o.vm
0.689
Q703
0.711
n,7?l
0.618
0.717
0.721
0.719
0.706
OTO
0.741
0.700
0.713
0.698
uvta
0.7DS
0.7DO
O.VI3
0.741
0.698
0.708
RETU
LAS
1
TO!
8
o
UJ sc
t- n
CO _l
< «I
^ 0
70
72
71
70
78
80
8O
'/£
70
G4
VO
70
72
70
73
7A
74
83
25
0
35
35
70
71
72
70
64
68
&G
70
83
O
65
^
UJ O
t- X
2«
13
3480
Z8I2
3122
3877
3166
31.11
3712
4058
3515
3274
3601
3518
3327
2834
3502
4343
4106
3992
9.1.2
0
1730
1136
4101
5225
4432
4008
3169
4770
31 IV
4515
5225
0
3511
SUMMARY DATA
% REMOVAL
INF-PRI
INF- EFF
SLUDGE
B.O.D.
31.7
S3.5
S. S.
41.6
92.8
DATA
% SOLIDS - AVG.
LBS. DRY
SOLIDS/ DAY
% VOL. SOLIDS —
LBS. VOL
LBS. VOL.
AVG.
SOLIDS / DAY
SOL./1OOO FT3/DAY
GALS. SLUDGE TO BEDS
CU. YDS. CAKE REMOVED
FT3 GAS/LB. VOL. SOLIDS
FT3 GAS/LB. MG
COST
FLOW
5.G
5579
79.8
4452
£7.5
28,000
G3
G.8
14,286
DATA
MAW DAYS 63 P&YRni "
POWER PURCHASED
OTHER UTILITIES (GAS.HgO)
GASOLINE, OIL, GREASE
CHEMICALS AND SUPPLIES
MAINTENANCE
VEHICLE
COSTS
OTHER
TOTAL
OPER. COST/MG TREATED
OPER. COST/ CAPITA /MO.
KN SLUDGE:
$J 676350*8
«st 67613800
rAI 21.248
_MG
WASTE
LAST
1st
TOTAL
SLUDGE:
134251
132560
2,325.78
520.32
NONE
108.56
547.25
238.48
NOME
NONE
$ 3,740.39
$ 54.C2
$ 0.158
1961 X IOOO Mft
-------
GLOSSARY
A Summary of All the Words Defined
in
OPERATION OF WASTEWATER TREATMENT PLANTS
-------
Project Pronunciation Key
by Warren L. Prentice
The Project Pronunciation Key is designed to aid you in the pro-
nunciation 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, College Edition, 19681 are shown below:
Ter m
acid
col if o r m
biological
Project Key
AS-id
COAL-i-form
BU Y-o-LODGE-ik-cull
Webster Key
'as-ad
ko-la-f 6 r m
bi-a-laj-i-kal
In using this key, you should accent (say louder) the syllable which
appears in capital letters. The following chart is presented to give
examples of how to pronounce words using the Project Key.
SYLLABLE
WORD
acid
coagulant
Biological
1st
AS
CO
BUY
2nd
id
AGG
o
3rd
you
LODGE
4th
lent
ik
5th
cull
The first word, acid, has its first syllable accented. The second
word, coa.guj.ant, has its second syllable accented. The third word,
biological, has its first and third syllables accented.
We hope you will find the key useful in unlocking the pronunciation
of any new word.
1 The Webster's New World Dictionary, College Edition, 1968, was
chosen rather than an unabridged dictionary because of its avail-
ability to the operator.
G-iii
-------
GLOSSARY
Absorption (ab-SORP-shun) : Taking in or reception of one substance
into the body of another by molecular or chemical action, and dis-
tributed throughout the absorber.
Activated Sludge (ACK-ta-VA-ted sluj): 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 teaming with bacteria, fungi, and
protozoa.
Activated Sludge Process (ACK-ta-VATE-ed sluj): A biological
wastewater treatment process in which a mixture of wastewater and
activated sludge is aerated and agitated. The activated sludge is
subsequently separated from the treated wastewater (mixed liquor)
by sedimentation, and wasted or returned to the process as needed.
Adsorption (add-SORP-shun): To gather (a gas, liquid, or dissolved
substance) on the surface or interface zone of another substance.
Advanced Waste Treatment; Any process of water renovation that
upgrades water quality to meet specific reuse requirements. May include
general cleanup of water or removal of specific parts of wastes in-
sufficiently removed by conventional treatment processes.
Aeration Bay (air-A-shun): The same as aeration tank or aerator.
The tank where raw or settled wastewater is mixed with return sludge
and aerated.
Aeration Liquor; Mixed liquor. The contents of the aeration tank,
which is composed of living organisms plus material carried into the
tank by the untreated wastewater or primary effluent.
Aerobic (AIR-0-bick): A condition in which "free" or dissolved oxygen
is present in the aquatic environment.
Aerobic Bacteria (AIR-0-bick back-TEAR-e-ah): Bacteria which live
and reproduce only in an environment containing oxygen which is avail-
able for their respiration (breathing), such as 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-0-bick): Decomposition and decay of organic
material in the presence of "free" or dissolved oxygen.
G-l
-------
Aerobic Process (AIR-0-bick) : A waste treatment process conducted
under aerobic (in the presence of "free" or dissolved oxygen) con-
ditions.
Agglomeration (a-GLOM-er-A-shun) : The growing or coming together
of dispersed suspended matter into larger floes or particles which
settle rapidly.
Aliquot (AL-li-kwot) : Portion of a sample.
Ambient Temperature (AM-bee-ent) : Temperature of the surroundings.
Amperometric (am-PURR-o-MET-rick) : A method of measurement that
records electric current flowing or generated, rather than re-
cording voltage. Amperometric titration is an electrometric means
of measuring concentrations of substances in water.
Anaerobic (AN-air-0-bick) : A condition in which "free" or dissolved
oxygen is not present in the aquatic environment.
Anaerobic Bacteria (AN-air-0-bick back-TEAR-e-ah) : Bacteria that
live and reproduce in an environment containing no "free" or dis-
solved oxygen. Anaerobic bacteria obtain their oxygen supply by
breaking down chemical compounds which contain oxygen, such as
.sulfates
Anaerobic Decomposition (AN-air-0-bick) : Decomposition and decay of
organic material in an environment containing no "free" or dissolved
oxygen.
Anaerobic Digestion (AN-air-O-bick) : 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) Sapro-
phytic bacteria break down complex solids to volatile acids, and
(2) Methane Fermenters break down the acids to methane, carbon
dioxide, and water.
BOD (BEE-OH-DEE) : See Biochemical Oxygen Demand.
BTU (BEE-TEA- YOU) : 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 are living organisms, micro-
scopic 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.
G-2
-------
Bacterial Culture (back-TEAR-e-al): 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 com-
pounds) 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 0.8 mg/1
of dissolved oxygen throughout the whole system to function properly.
Batch Process: A batch process is a treatment process in which a
tank or reactor is filled, the water is treated, and the tank con-
tents are released. The tank may then be filled and the process
repeated.
Biochemical Oxygen Demand or BOD: The BOD indicates the rate of
oxygen utilized by wastewater under controlled conditions of temperature
and time.
Bioassay (BUY-o-ass-SAY) : (1) an assay method using a change in
biological activity as a qualitative or quantitative means of
analyzing a material's response to biological treatment, or (2) A
method of determining toxic effects of industrial wastes or other
wastes by using live organisms such as fish for test organisms.
B i ode grada tion (BUY-o-de-grah-DAY-shun): 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): A condition whereby organic
materials tend to be transferred from the dispersed form in wastewater
to settleable material by mechanical entrapment and assimilation.
B1ank: A bottle containing 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.
Buffer; A measure of the ability or 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 the pH.
Bulking (BULK-ing): Bulking occurs in activated sludge plants when
the sludge becomes too light and will not settle properly.
Cathodic Protection (ca-THOD-ick): An electrical system for pre-
vention of rust, corrosion, and pitting of steel and iron surfaces
in contact with water and wastewater.
Chloramines (KLOR-a-means): Chloramines are compounds formed by
the reaction of chlorine with ammonia.
G-3
-------
Ch1orine 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, nature, and amount of the impurities in
the water.
Chlorine Requirement: The amount of chlorine which must be added to
produce the desired result under stated conditions. The result (the
purpose of chlorination) may be based on any number of criteria, such
as a stipulated coliform density, a specified residual chlorine con-
centration, the destruction of a chemical constituent, or others. In
each case a definite chlorine dosage will be necessary. This dosage
is the chlorine requirement.
Chlororganic (chlor-or-GAN-nick): Chlororganic compounds are organic
compounds combined with chlorine. These compounds generally originate
from or are associated with living or dead organic materials.
Clarifier (KLAIR-i-fire): Settling Tank, Sedimentation Basin. A
"tank" or b as in 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.
Coagulants (co-AGG-you-lents): Chemicals added to destabilize, aggregate
and bind together colloids and emulsions to improve settleability,
filterability, or drainability.
Coliform (COAL-i-form) : The coliform group of organisms is a
bacterial indicator of contamination. This group has as one of
its primary habitats the intestinal tract of human beings. Coliforms
also may be found in the intestinal tract of warm-blooded animals,
and in plants, soil, air, and the aquatic environment.
Colloids (KOL-loids): Very small solids (particulate or insoluble
material) in a finely divided form that remain dispersed in a liquid
for a long time due to their small size and electrical charge.
Colorimetric; A means of measuring unknown concentrations of water
quality indicators in a sample by comparing the sample's color,
after the addition of specific reagents, with the color of known con-
centrations.
Combined Sewer: A sewer designed to carry both sanitary wastewaters
and storm or surface water runoff.
Comminution (com-min-00-shun): A mechanical treatment process which
cuts large pieces of wastes into smaller pieces so they won't plug
pipes or damage equipment (shredding).
G-4
-------
Comminutor (com-min-00-ter): A device used to reduce the size of the
solid chunks in wastewater by shredding (comminuting). The shredding
action can be visualized if you imagine many scissors cutting or
hammering to shreds all the large influent solids material.
Composite (Proportional) Samples (com-POZ-it): Samples collected
at regular intervals in proportion to the existing flow and then
combined to form a sample representative of the entire period of
flow over a given period of time.
Coning (CONE-ing): A condition that may be established in a sludge
hopper during sludge withdrawal when part of the sludge moves toward
the outlet while the remainder tends to stay in place. Development
of a cone or channel of moving liquid surrounded by relatively
stationary sludge.
Conventional Treatment; The pretreatment, sedimentation, flotation,
trickling filter and activated sludge wastewater treatment processes.
Cross-Connection: A connection where wastewater or water from a
pump seal could enter a drinking water supply.
D£ (DEE-OH): Abbreviation of Dissolved Oxygen. DO is the atmospheric
oxygen dissolved in water or wastewater.
Dateometer (date-0-meter): A small calendar disc attached to motors
and equipment to indicate the year in which the last maintenance
service was performed.
Decomposition, Decay; Generally aerobic processes that convert unstable
materials into more stable forms by chemical or biological action.
Waste treatment encourages decay in a controlled situation in order
that the material may be disposed of in a stable form. When organic
matter decays under anaerobic conditions (putrefaction), undesirable
odors are produced. In aerobic processes, the odors are much less
objectionable than those produced by anaerobic decomposition.
Degradation (de-grah-DAY-shun): The conversion of a substance to
simpler compounds.
Density (DEN-sit-tee): The weight per unit volume of any substance.
The density of water (at 4°C) is 1.0 gram per cubic centimeter
(gms/cc) or about 62.4 Ibs per cubic foot.
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.
G-5
-------
Detritus (de-TRI-tus): The heavy, coarse material carried by
wastewater.
Dewaterable: 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.
Diffused Air Aeration: A diffused air activated sludge plant takes
air, compresses it, and then discharges the air below the water sur-
face of the aerator through some type of air diffusion device.
Piffuser: A diffuser is a device (Porous plate, tube, bag) used
to break the air stream from the blower system into fine bubbles
in the mixed liquor.
Digester (die-JEST-er): A tank in which sludge is placed to allow
sludge digestion to occur. Digestion may occur under anaerobic
(more common) or aerobic conditions.
Disinfection (DIS-in-feck-shun): The process by which pathogenic
(disease) organisms are killed. There are several ways to disinfect,
but chlorination is the most frequently used method in water and
wastewater treatment.
Dissolved Oxygen: Atmospheric oxygen dissolved in water or waste-
water, usually abbreviated DO.
DistiHate; In the distillation of a sample, a portion is evaporated;
the part that is condensed afterwards is the distillate.
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.
Effluent (EF-lu-ent): Wastewater or other liquid—raw, partially or
completely treated--flowing from a basin, treatment process, or
treatment plant.
Elutriation (e-LOO-tree-a-shun): The washing of digested sludge in
plant effluent with a suitable ratio of sludge to effluent. The
objective is to remove (wash out) fine particulates or certain
soluble components in sludge.
Emulsion (e-MULL-shun): A liquid mixture of two or more liquid
substances not normally dissolved in one another, but one
liquid held in suspension in the other.
G-6
-------
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.
Endogenous (en-DODGE-en-us): A diminished level of respiration
in which materials previously stored by the cell are oxidized.
Enteric: Intestinal.
Enzymes (EN-zimes): Enzymes are substances produced by living organisms
that speed up chemical changes.
Estuaries (ES-chew-wer-eez): Bodies of water at the lower end of a
river that are subject to tidal fluctuations.
Facultative (FACK-ul-tay-tive): Facultative bacteria can use either
molecular (dissolved) oxygen or oxygen obtained from food materials.
In other words, facultative bacteria can live under aerobic or
anaerobic conditions.
Facultative Pond (FACK-ul-tay-tive): 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.
Filamentpus Bacteria (FILL-a-men-tuss): Organisms that grow in a
thread or filamentous form.
Fixed: A sample is "fixed" in the field by adding chemicals that
prevent the water quality of the sample from changing before final
measurements are performed later in the lab.
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, causing a spray-
ing action. Also see Distributor.
G-7
-------
Flame Polished; Sharp or broken edges of glass (such as the
end of a glass tube) are flame polished by placing the edge in
a flame and rotating it. By allowing the edge to melt slightly,
it will become smooth.
Flights: Scraper boards, made from redwood or other rot-resistant
woods, used to collect and move settled sludge or floating scum.
Floe: Groups or "clumps" of bacteria that have come together and
formed a cluster. Found in aeration tanks and secondary clarifiers.
Flocculated (FLOCK-you-lay-ted): An action resulting in the gathering
of fine particles to form larger particles. ,
A. r,
Freeboard: The vertical distance WALL
from the normal water surface to HEIGHT
the top of the confining wall.
Grit: The heavy mineral material present in wastewater such as
sand, eggshells, gravel, and cinders.
Grit Removal: Grit removal is accomplished by providing an enlarged
channel 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.
..
\7
1
FREEBOARD
WATER DEPTH
Head Loss: "Head" is a common term used in
discussing pumps. It is a way of express-
ing pressure in terms of the height of a
vertical column of water. In the sketch, .—
the head loss is the height to which
the water must build up until there is
sufficient pressure to force that
particular amount of water through the
slots in the comminutor drum.
in
J
I
r = :
HEAD
-f^-J
LOSS
/
— —
Hepa.t3.tis: Hepatitis is an acute viral infection of the liver
(yelYovT ~j aundice).
G-8
-------
Hydrolysis (hi-DROL-e-sis): The addition of water to the molecule
to break down complex substances into simpler ones.
Hyp o ch1orin at ors (hi-po-KLOR-i-NAY-tors): Hypochlorinators are
devices that are used to feed calcium, sodium, or lithium hypo-
chlorite as the disinfecting agent.
Hypochlorites (hi-po-KLOR-ites): Hypochlorites are compounds con-
taining chlorine that are used for disinfection. They are avail-
able as liquids or solids (powder, granules, and pellets) in
barrels, drums, and cans.
Imhoff Cone: A clear, cone-shaped container marked with
graduations used to measure the volumetric concentration
of settleable solids in wastewater.
Infiltration (IN-fill-TRAY-shun): Groundwater that seeps into pipes
through cracks, joints, or breaks.
Influent (IN-flu-ent) : Wastewater or other liquid—raw or partially
t re at e'd- - f 1 ow in g into a reservoir, basin, treatment process, or
treatment plant.
Inoculate (in-NOCK-you-LATE): To introduce a seed culture into a
system.
Inorganici Waste; Waste material such as sand, salt, iron, calcium,
and other mineral materials which are not converted in large
quantities by organism action. Inorganic wastes are chemical sub-
stances of mineral origin and may contain carbon and oxygen, whereas
organic wastes are chemical substances of animal or vegetable origin
and contain mainly carbon and hydrogen along with other elements.
Launders (LAWN-ders): Sedimentation tank effluent troughs.
Lineal (LIN-e-al): 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 as applied to sludge
digestion means the transformation of large solid particles of
sludge into either a soluble or a finely dispersed state.
Loading: Quantity of material applied to a device at one time.
G-9
-------
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 sul-
furic acid (H2SOtt) is 98. AIM solution of sulfuric acid would
consist of 98 grams of H2SOi+ dissolved in enough distilled water
to make one liter of solution.
MPN (EM-PEA-EN): MPN is the Most Probable Number of coliform
group organisms per unit volume expressed as a density of
organisms per 100 ml.
Manometer (man-NOM-meet-her): 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.
Masking Agents; Liquids which are dripped into the wastewater,
sprayed into the air, or evaporated (using heat) with the "fumes"
or odors discharged into the air by blowers to make an undesirable
odor less noticeable.
Mechanical Aeration: The surface of the aeration tank is agitated
to cause spray and waves by a paddle wheel, mixers, rotating brushes,
pumps discharging water into the air like a fountain or discharging
the water down a series of steps creating falls or some other method
of splashing water into the air or air into the water where the
oxygen can be absorbed.
Media; The material in a trickling filter over which settled waste-
water is sprinkled and then flows over and around during treatment.
Slime organisms grow on the surface of the media and treat the
wastewater.
Meniscus; The curved top of a column of liquid (water, oil,
mercury) in a small tube. Water will form a valley when the
liquid wets the walls of the tube, while mercury will form a hill
and the walls of the tube are not wetted.
WATER MERCURY
(READ
BOTTOM) -
(READ
TOP)
m
G-10
-------
Mesophilic Bacteria (mess-0-FILL-lick) : Medium temperature: A
group of bacteria that thrive in a temperature range between 68 °F
and 113°F.
Microorganisms (micro-ORGAN-is-zums) : 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.
Milligrams Per Liter, mg/1 (MILL-i-GRAMS per LEET-er) : A measure
of the concentration by weight of a substance per unit volume.
For practical purposes, one mg/1 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/1), or 10 parts of
oxygen per million parts of water, or 10 parts per million (10 ppm) .
Millimicron (MILL-e-MY-cron) : One thousandth of a micron or a
millionth of a millimeter.
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. When the mixed liquor flows from the aeration
tank it goes into the secondary clarifiers or final sedimentation
tank. Mixed liquor also may refer to the contents of mixed aerobic
or anaerobic digesters.
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 (F^SOiJ in grams is 98.
ATOMIC NUMBER MOLECULAR
ELEMENT WEIGHT OF ATOMS WEIGHT
H 1 2 2
S 32 1 32
0 16 4 64
98
Molecule (MOLL-ee-kule) : The smallest portion of an element or
compound retaining or exhibiting all the properties of the substance.
Motile (MO-till) : Motile organisms exhibit or are capable of movement.
Muffle Furnace : A small oven capable of temperatures up to 600 °C
and used in laboratories for burning or incinerating samples to
determine their loss on ignition (volatile) or fixed solids (ash)
content.
G-ll
-------
Multi-Stage Pump; A pump that has more than one impeller. A
single-stage pump has one impeller.
N or Normal: A normal solution contains one gram equivalent weight
or a reactant (compound) per liter of solution. The equivalent
weight of an acid is that weight of which contains one gram atom of
ionizable hydrogen or its chemical equivalent. For example, the
equaivalent weight of sulfuric acid (I^SOiJ 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 h^SO^ dissolved in
enough water to make one liter of solution.
Nitrification; The biochemical conversion of unoxidized nitrogenous
matter (ammonia and organic nitrogen) to oxidized nitrogen (usually
nitrate). The second-stage BOD is sometimes referred to as the
nitrification stage (first-stage BOD is called the carbonaceous
stage—carbon compounds oxidized to C02) .
Nomogram; A chart or diagram containing three or more scales used
to solve problems with three or more variables instead of using
mathematical formulas.
Nonsparking Tools; These tools will not produce a spark during use.
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.
Obligate Aerobes: Bacteria that must have molecular (dissolved)
oxygen (DO) to survive.
Organic Waste; Waste material which comes 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 and may contain carbon and oxygen, whereas organic
wastes contain mainly carbon and hydrogen along with other elements.
Orifice (OR-i-fiss): 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 is a colorimetric
indicator of chlorine residual in which a yellow-colored compound is
produced.
G-12
-------
Oxidation Cox-i-DAY-shun): 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.
Parasitic Bacteria (PARA-SIT-tick): Parasitic bacteria are those
bacteria which normally live off another living organism, known
as the host.
Pathogenic Organisms (path-o-JEN-nick OR-gan-iz-ums): Bacteria
or viruses 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.
Percent Saturation: Liquids can contain in solution limited amounts
of compounds and elements. 100% saturation is the maximum theoretical
amount that can be dissolved in the solution. If more than the maxi-
mum theoretical amount is present, the solution is supersaturated.
Percent Saturation = Amount in Solution
Maximum Theoretical
Amount in Solution
p_H_ (PEA-A-ch) : pH is an expression of the intensity of the alkaline
or acidic strength of a water. Mathematically, pH is the logarithm
(base 10) of the reciprocal of the hydrogen ion concentration.
pH =
The pH may range from 0 to 14, where 0 is most acid, 14 most
alkaline, and 7 neutral. Natural waters usually have a pH
between 6.5 and 8.5
Photosynthesis (foto-SIN-the-sis): 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. Land plants grow by the same process.
Physical Waste Treatment Processes: Racks, screens, comminutors,
sedimentation, and flotation. Chemical or biological reactions are
not an important part of the process.
Pollution; Any interference with beneficial reuse of water or
failure to meet quality requirements.
G-13
-------
Ponding; A condition occurring on trickling filters when the 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: A means of expressing the strength of organic
material in wastewater. Domestic wastewater consumes, on an average,
approximately 0.2 Ib of oxygen per person per day, as measured by the
standard BOD test.
Postchlorination; Chlorination of the plant discharge or effluent
following plant treatment.
Preaeration: A preparatory treatment of wastewater consisting of
aeration to freshen the wastewater, remove gases, a.dd oxygen, promote
flotation of grease, and aid coagulation.
Prechlorination: Chlorination at the headworks of the plant;
influent chYorination prior to plant treatment.
Pretreatment: Use of racks, screens, comminutors, and grit removal
devices to remove metal, rocks, sand, eggshells, and similar
materials which may hinder operation of a treatment plant.
Primary Treatment; A wastewater treatment process consisting of
a rectangular or circular tank which allows those substances in
wastewater that readily settle or float to be separated from the
water being treated.
Protozoa (pro-toe-ZOE-ah): A group of microscopic animals,
principally of one cell, that sometimes cluster into colonies.
Prussian Blue; A paste or liquid used to show a contact area.
'Psychrophilic Bacteria (sy-kro-FILL-ik): Cold Temperature: A group
of bacteria that thrive in temperatures below 68°F.
Putrefaction (PU-tree-FACK-shun): Biological decomposition of organic
matter with the production of ill-smelling products associated with
anaerobic conditions.
Putrescible (pu-TRES-sib-bull): Putrescible material will decompose
under anaerobic conditions and produce nuisance odors.
Rack: Parallel metal bars or rods evenly spaced and placed at an
angle in the influent channel that remove rags, rocks, and cans
from wastewater.
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Raw Wastewater: Plant influent or wastewater before any treatment.
Reagent (re-A-gent): A substance which takes part in a chemical
reaction that is used to measure, detect, or examine other substances.
Receiving Water: A stream, river, lake, or ocean into which treated
or untreated wastewater is discharged.
Recirculation: The return of part of the effluent from a treatment
process to the incoming flow.
Re1iqui fact ion (re-LICK-we-FACK-shun): The return of a gas to a
liquid. For example, a condensation of chlorine gas returning to
the liquid form.
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 is the amount of chlorine
remaining after a given contact time and under specified conditions.
Respiration; The physical and chemical processes by which an organism
supplies its cells and tissues with oxygen needed for metabolism and
relieves them of carbon dioxide formed in energy-producing reactions.
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.
Sanitary Sewer (SAN-eh-tare-ee SUE-er): A sewer intended to carry
wastewater from homes, business, and industries. Storm water runoff
sometimes is collected and transported in a separate system of pipes.
S ap rophyt i c Organis ms (SAP-pro-FIT-tik): Organisms living on dead
or decaying organic matter. They help natural decomposition of the
organic solids in wastewater.
Sereen: A device with openings generally uniformly sized to retain
or remove suspended or floating objects in wastewater larger than
the openings. A screen may consist of bars, rods, wires, gratings,
wire mesh, or perforated plates.
Secondary Treatment: A wastewater treatment process used to convert
dissolved" or suspended materials into a form more readily separated
from the water being treated.
Septic (SEP-tick): A condition produced by the growth of anaerobic
organisms. If severe, the wastewater turns black, giving off foul
odors and creating a heavy oxygen demand.
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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,
Sewage; The used water and solids from homes that flow to a
treatment plant. The preferred term is wastewater.
Shock Load; The arrival at a plant of a waste which is toxic to
organisms in sufficient quantity or strength to cause operating
problems, such as odors or sloughing off of the growth or slime on
the trickling filter media. Organic or hydraulic overloads also can
cause a shock load.
Shredding: A mechanical treatment process which cuts large pieces
of wastes into smaller pieces so they won't plug pipes or damage
equipment (comminution).
Sloughings (SLUFF-ings): Trickling filter slimes that have been
washed off the filter media. They are generally quite high in BOD
and will degrade effluent quality unless removed.
Sludge (sluj): The settleable solids separated from liquids during
processing or deposits on bottoms of streams or other bodies of water.
Sludge Digestion: A process by which organic matter in sludge is
gasified, liquefied, mineralized, or converted to a more stable form
by anaerobic (more common) or aerobic organisms.
Sludge Gasification: A process in which soluble and suspended organic
matter are converted into gas. Sludge gasification will form bubbles
of gas in the sludge and cause large clumps of sludge to rise and
float on the water surface.
Spe ci fi c Grayity: 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
0.8 to 2.6.
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 wil]
not give off obnoxious odors.
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.
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Stasis (STAY-sis): Stagnation or inactivity of the life processes
within organisms.
Stethoscope: An instrument used to magnify sounds and convey them
to the ear.
Storm Sewer: A separate sewer that carries runoff from storms,
surface drainage, and street wash, but excludes domestic and
industrial wastes.
Stuck: A stuck digester does not decompose organic matter properly.
It 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" digester.
Supernatant (sue-per-NAY-tent): 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 the primary
clarifier.
Tertiary Treatment (TER-she-AIR-ee): See Advanced Waste Treatment.
Thermophi1ic Bacteria (thermo-FILL-lik): Hot temperature: A group
of bacteria that thrive in temperatures above 113°F.
Thief Hole: A digester sampling well.
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.
Totalizer: A totalizer continuously sums or adds up the flow into
a plant in gallons or million gallons or some other unit of measure-
ment.
Toxicity (tocks-IS-it-tee) : A condition that may exist in wastes
that will inhibit or destroy the growth or function of any organism.
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Trickling Filter: A treatment process in which the wastewater
trickles over media that provide the opportunity for the formation
of slimes which clarify and oxidize the wastewater.
Trickling Filter Media: Rocks or other durable materials that make
up the body of the filter. Synthetic (manufactured) media have
been used successfully.
Two-Stage Filters; Two filters are used. Effluent from the first
filter goes to the second filter, either directly or with a clarifier
between the two filters.
Volute (vol-LOOT) : The spiral-shaped casing surrounding a pump
impeller that collects the liquid discharged by the impeller.
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.
Weir (weer): A vertical obstruction, such as a wall, or plate,
placed in an open channel and calibrated in order that a depth of
flow over the weir can easily be converted to a flow rate in MGD
(million gallons per day).
Weir Diameter (weer) : Circular clarifiers have a circular weir
within the outside edge of the clarifier, and all of the water
leaving the clarifier flows over this weir. This diameter 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.
DIAMETER
CIRCULAR WEIR
DIAMETER
N H
SECTION
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Weir, Proportional (weer): A specially shaped weir in which the
flow through the weir is directly proportional to the head.
Wet Oxidation: Any process in which substances are converted to a
higher o xi d ation state in a water media, such as activated sludge,
trickling filters, ponds, or digesters.
Zoogleal Film (ZOE-glee-al): 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): 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.
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