SERA
United States
Environmental Protection
Agency
Office of Water
Program Operations (WH-547)
Washington DC 20460
EPA III-A 524 77
March! 977
Water
Aerobic
Biological
Wastewater
Treatment
Facilities
Process
Control
Manual
CLEAN
. A A A 4
WATER
MD-14
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To order single copies of this publication, MO-14, "Process Control Manual
for Aerobic Biological Wastewater Treatment Facilities; write to:
General Services Administration (8BRC)
Centralized Mailing Lists Services
Building 41, Denver Federal Center
Denver, Colorado 80225
Please indicate the MO number and title of publication. Multiple copies
may be purchased from:
National Technical Information Service
Springfield, Virginia 22151
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PROCESS CONTROL MANUAL FOR
AEROBIC
BIOLOGICAL
WASTEWATER
TREATMENT
FACILITIES
AWBE-RC LiBKARY U.S.
ENVIRONMENTAL PROTECTION AGENCY
MUNICIPAL OPERATIONS BRANCH
OFFICE OF WATER PROGRAM OPERATIONS
WASHINGTON, D C 20460
March 1977
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_c
ACTIVATED SLUDGE PROCESS
PROCESS CONTROL MANUAL
FOR AEROBIC BOILOGICAL WASTEWATER
TREATMENT FACILITIES
SECTION 1.01
Introduction
SECTION 1.02
Guides
— SECTION 2.01
Introduction
— SECTIOH 2.02
Guides
— SECTION 2.03
— SECTION 2. 04
PrOCBBB
Control
— SECTION 2.05
Operation*!
Problus
-
-
*~
SECTION 3.01
Introduction
SECTION 3. ti2
Description
SECTION 3.03
TRICKLING FILTER PROCESS
SECTION 1.01
Introduction
SECTION 1.02
Troubleshooting
Guide*
I
- SECTION 2.01
Introduction
- SECTION 2.02
Operational
Guides
- SECTION 2.03
Performance
— SECTION 2.04
Process
Control
— SECTION 2.05
Loading
— SECTIOH 2.06
Op« rational
Problem*
- SECTION 3.01
Introduction
- SECTION 3.02
Process
Description
1— SECTION 3.03
TF Classification
1
APPENDIX A
OPERATIONAL
RECORDS
1
APPENDIX B
PLANT
VISITS
1
APPENDIX C
LABORATORY
EQUIPMENT
1
APPENDIX D
GLOSSARY
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ACKNOWLEDGMENTS
This manual was prepared for the Municipal Operations Branch of the Office of Water
Program Operations of the United States Environmental Protection Agency. Develop-
ment and preparation of the manual was carried out by the firm of James M. Mont-
gomery, Consulting Engineers, Inc., Walnut Creek, California under the direction of
Ronald A. Tsugita, Dennis C.W. DeCoite, and Larry L. Russell. Special appreciation
is also due R. Rhodes Trussell, Mark L Cardoza, and Donovan F. Werner for their
assistance in coauthoring the manual. The understanding and encouragement of
Lehn J. Potter, Project Officer, Water Program Operations of the EPA is greatly
appreciated.
Recognition is also due to the many operators for their time and assistance in pro-
viding operations information during the plant visits, and to the following individuals
for their review and comments.
Mr. Edward Becker San Jose, California
Mr. Fred Delvecchio Clemson University
Mr. Larry Freitas OroLoma Sanitary District, California
Dr. David Jenkins University of California, Berkeley
Mr. William Loftin Livermore, California
Mr. Jack L. Muir Tolleson, Arizona
NOTICE
The mention of trade names of commercial products in this publication is for illustra-
tion purposes and does not constitute endorsement and recommendation for use by
the U.S. Environment Protection Agency.
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INTRODUCTION
A. PURPOSE AND INTENT
The purpose of this manual is to provide an on-the-job reference for operators
of activated sludge and trickling filter wastewater treatment plants. It is intended
to assist operators in establishing process control techniques and in optimizing
the performance of these two aerobic biological treatment systems. Other aerobic
biological systems such as aerated lagoons, rotating biodiscs and oxidation
ponds are not included in this manual.
Aerobic biological treatment facilities and the conditions under which they
operate can vary considerably. Although treatment plants may be designed alike,
they may not necessarily perform alike. In the past, many control strategies have
been the result of trial and error tests performed by operators and engineers.
Development of this manual consisted of visiting several operators at their treat-
ment plants throughout the United States. Their practical experiences and
knowledge in plant operations and process control have been incorporated in the
manual. In addition, extensive use was made of the literature contributed over
the years by those individuals, agencies, and institutes seeking to advance and
explain the state-of-the-art of operating aerobic biological wastewater treatment
facilities.
The overall objective of this manual is to aid the operator in determining what
process control and operational measures may be most effective in optimizing
the performance of his particular treatment plant. The manual should also serve
as a basis from which the operator may develop new ideas for process control
and better understand the various measures by relating his own experiences to
the material presented. For this reason, theoretical material has been limited to
that required for basic understanding of aerobic biological treatment.
B. MANUAL ORGANIZATION
The manual is presented in three major divisions:
• The Activated Sludge Process
• The Trickling Filter Process
• Appendices
The Activated Sludge and Trickling Filter Process divisions are each divided into
the following sections:
Section I Troubleshooting
Section II- Process Control
Section III- Fundamentals
Section IV - Laboratory Control
These sections emphasize the fundamentals of operating and controlling aerobic
biological treatment processes. Each of the sections are presented in sufficient
detail to allow the reader to use them independently. References have been
appended to each section for those who wish to gain further insight to the topics
covered in the manual. These references were selected because of their clarity
and value to an operator as an information source.
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Inside front
cover.
Key words.
Inside back
cover.
Abbreviations.
Included on the inside front cover is a quick reference Index to the major topics
in each division section of the manual. After finding the section you desire, go to
the Table of Contents for the subsection of interest. Once you are in the appropri-
ate subsection, thumb down the left hand margin of the text until you find the
key words which best fit your interest. Key words are presented in the manner
shown to the left of this paragraph.
The inside back cover presents a Metric Reference for those unit expressions
which are commonly used for process control parameters. This reference may be
used for converting English and Metric unit expressions.
Abbreviations have been kept to a minimum in the manual. Only those which are
commonly used are included in the text.
Are you
familiar with
aerobic
treatment?
SECTION I
SECTION It
SECTION
SECTION IV
C. USE OF THE MANUAL
This manual assumes that the reader is familiar with the activated sludge and
trickling filter processes as well as their various modes of operation. For those
who are not quite familiar enough, you are encouraged to study Section III,
"FUNDAMENTALS", in each process division.
As stated earlier, each process division is broken down into four sections. These
sections may be used independently or systematically.
TROUBLESHOOTING — If you have a problem, go to the troubleshooting guide
which best describes your situation. Follow the guidance as outlined. If you still
have problems or desire more information on the guidance provided, use the
reference indicated in the last column on the troubleshooting guide. This refer-
ence will lead you into the text of the manual to provide you with more insight, as
well as additional references to get more information. Your next best alternative
would be to seek outside help.
PROCESS CONTROL — This section presents the various strategies commonly
used for controlling the activated sludge and trickling filter processes. Routine
operational procedures as well as process loadings, evaluations, and common
problems are presented here. Step-by-step examples of calculating, interpreting
and applying control tests to process control parameters are also presented.
FUNDAMENTALS — This section is where it all begins. Without a sound back-
ground in understanding the concepts of aerobic biological treatment, a suc-
cessful process control and operational program is difficult to achieve. As a
result, the quality of plant effluent suffers the consequences. Therefore, be
familiar with the fundamentals and the references that show you where to get
more information.
LABORATORY CONTROL — This section is a must. If you want to know why,
read it and follow its guidance because it will help you establish and implement
a successful sampling, testing, and monitoring program for your aerobic treat-
ment facility.
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Fourappendices are provided to supplement the manual.
APPENDIX A
APPENDIX B
APPENDIX C
APPENDIX D
Operators'
responsibility
to achieve best
process control
and operation.
— Includes work sheets which may be removed and duplicated for actual use. It
also provides information to develop an operational records system.
— Presents flow diagrams, operational data, and summary descriptions of those
treatment plants which were visited during development of the manual. Check
them over to see how you compare.
— Is a suggested list of laboratory equipment, supplies and chemicals needed to
perform process control tests discussed in the manual.
— Is a glossary which defines the important terminology commonly used in
discussing aerobic biological treatment.
During the plant visits, four characteristics were observed of those treatment
plants producing a good-quality secondary effluent.
1. Practice of day-to-day process control and operational control procedures.
2. Special effort is made for training and upgrading of plant personnel.
3. Industrial waste discharge ordinances are actively enforced.
4. Process control and operational data is used in direct application to plant
operations.
HOW DO YOU COMPARE?
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ACTIVATED SLUDGE PROCESS
TABLE OF CONTENTS
Topic Page
SECTION I-TROUBLESHOOTING
1.01 INTRODUCTION 1-1
1.02 TROUBLESHOOTING GUIDES 1-1
No. 1 Aeration System Problems I-4
No. 2-Foaming Problems I-6
No. 3 - Solids Washout/Billowing Solids 1-10
No. 4-Bulking Sludge 1-13
No. 5-SludgeClumping 1-16
No. 6-Cloudy Secondary Effluent 1-17
No. 7 - Ashing, Pinpoint/Straggler Floe 1-19
SECTION II - PROCESS CONTROL
2.01 INTRODUCTION 11-1
2.02 OPERATIONAL GUIDES II-2
No. 1-Aeration System II-4
No. 2-Secondary Clarifier II-7
No. 3-Pumping Equipment and Piping in RAS and WAS Systems II-8
2.03 PERFORMANCE EVALUATION II-2
Review of In-Plant Recycled Flows II-9
Aeration Performance II-9
Solids Inventory 11-11
Calculating the Solids Inventory 11-12
COD/BOD and Suspended Matter Removal 11-15
Process Kinetics 11-16
Kinetic Relationships 11-16
Nitrification II-20
Secondary Clarifiers II-22
Surface Overflow Rate II-23
Solids Loading Rate II-23
2.04 PROCESS CONTROL H-24
Aeration and D.O. Control M-24
Return Activated Sludge Control II-25
Constant RAS Flow Rate Control II-27
Constant Percentage RAS Flow Rate Control II-27
Comparison of both RAS Control Approaches II-27
Methods of RAS Flow Rate Control H-29
Sludge Blanket Depth H-29
Mass Balance Approach H-30
Settleability Approach 11-31
SVI Approach H-34
Return Rates with Separate Sludge Reaeration II-35
Waste Activated Sludge Control II-35
Methods of Sludge Wasting M-36
Constant MLVSS Control H-39
Constant Gould Sludge Age Control 11-41
Constant F/M Control H-42
Constant MCRT Control II-49
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ACTIVATED SLUDGE PROCESS
TABLE OF CONTENTS (continued)
Topic Page
Sludge Quality Control 11-54
Mass Balance by Centrifuge 11-54
Settleometer 11-64
Visual Observations 11-70
Turbidity 11-70
Depth of Blanket 11-70
Microscopic Examination 11-71
2.05 OPERATIONAL PROBLEMS N-72
Aeration System Problems II-72
Foaming Problems II-75
Stiff White Foam H-75
Excessive Brown Foam II-76
Solids Washout II-77
Equipment Malfunction II-77
Hydraulic Overload II-78
Solids Overload 11-80
Temperature Currents 11-81
Bulking Sludge II-82
Filamentous Microorganisms Present II-83
No Filamentous Microorganisms Present II-90
Clumping/Rising Sludge II-90
Cloudy Secondary Effluent il-93
Protozoa Are Present II-93
Protozoa Are Not Present II-93
Ashing il-95
Pinpoint Floe II-97
Stragglers/Billowing Solids II-97
SECTION III-FUNDAMENTALS
3.01 INTRODUCTION III-1
Definitions |||-1
3,02 PROCESS DESCRIPTION |||-3
Aeration System 111-4
Diffused Air System HI-4
Fine Bubble Diffusers IH-4
Coarse Bubble Diffusers IH-5
Mechanical Aeration Systems IH-6
Surface Aerators |||.g
Turbine Aerators \\\.j
Sedimentation System \\\.j
3.03 ACTIVATED SLUDGE PROCESS VARIATIONS III-8
Process Loading Ranges III-9
High Rate III-9
Conventional Rate III-9
Extended Aeration Rate 111-11
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ACTIVATED SLUDGE PROCESS
TABLE OF CONTENTS (Continued)
Topic Page
Physical Arrangements of the Process 111-12
Complete Mix Activated Sludge 111-12
Plug-Flow Activated Sludge 111-14
Activated Sludge with Sludge Reaeration 111-15
SECTION IV-LABORATORY CONTROL
4.01 INTRODUCTION IV-1
4.02 LABORATORY SAMPLING AND TESTING PROGRAM IV-1
Grab Samples IV-1
Composite Samples IV-3
MLSS Sampling IV-3
Laboratory Control Program IV-5
4.03 LABORATORY CONTROL TESTS IV-5
Biochemical Oxygen Demand IV-7
Chemical Oxygen Demand IV-8
Soluble COD and BOD IV-9
Settleable Matter IV-9
Total Suspended Matter IV-10
Volatile Suspended Matter IV-10
Nitrite Nitrogen IV-11
Nitrate Ni'rogen IV-12
Total KjelJahl Nitrogen IV-12
Ammonia Nitrogen IV-13
30-Minute Settling Test IV-14
Observations During Test IV-14
Total Phosphorus IV-15
Dissolved Oxygen IV-16
Hydrogen Ion Concentrations - pH IV-17
Temperature IV-18
Microscopic Examination IV-18
Amoeboids IV-19
Flagellates IV-20
Ciliates IV-20
Free Swimming Ciliates IV-21
Stalked Ciliates IV-21
Evaluation of Microscopic Examination IV-22
Selection of a Microscope IV-23
Use of the Microscope IV-23
Procedures for Examination IV-25
Flow IV-25
Sludge Blanket Measurement IV-27
Centrifuge Test IV-29
Suspended Matter Correlation IV-30
Turbidity IV-30
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ACTIVATED SLUDGE PROCESS
LIST OF FIGURES
Figure No. Description Page
1-1 pictorial Reference of Settling Test Observations 1-3
11-1 Five-Day Moving Average Trend Plots for the ll-3
Activated Sludge Process
II-2 Wastewater Nitrogen Cycle 11-21
II-3 Aeration Tank Mass Balance I'-30
II-4 Estimating Return (RAS) from Settleability Test H-33
II-5 Graphical Approach to F/M Calculations for Wastewater Flows H-45
of 0 to 5 mgd
II-6 Graphical Approach to F/M Calculations for Wastewater Flows li-46
of 0 to 10 mgd
II-7 Graphical Approach to F/M Calculations for Wastewater Flows II-47
of 0 to 50 mgd
II-8 Graphical Approach to WAS Calculations not Including Secondary 11-51
Effluent Suspended Solids
N-9 Graphical Approach to WAS Calculation Including Secondary II-52
Effluent Suspended Solids
11-10 Daily Data Sheet for an Activated Sludge Plant II-65
11-11 Plotting Sludge Settling Characteristics II-67
11-12 Plotting Process Variable Trends II-69
11-13 Violent Aeration Tank Surface Turbulance II-73
11-14 Foaming in Aeration Tank II-74
11-15 Solids Washout in Clarifier II-78
11-16 Settling Test Observations for Case 1 and 2 II-79
H-17 Sludge Bulking in Clarifier H-82
11-18 Microscopic Observations II-S4
11-19 Clumping in Clarifier II-92
li-20 Settling Test Observations for Case 3 and 4 11-91
11-21 Ashing in Clarifier II-95
II-22 Settling Test Observations for Case 5 and 6 II-96
111-1 Typical Activated Sludge Process llt-1
\\\-2 Sketches of a Nylon Sock and a Saran Wrapped Tube Diffuser IH-5
lli-3 Sketches of a Sparger and a Disc Type Coarse Bubble Diffuser IH-5
III-4 Typical Floating and Platform Surface Aerator IH-6
IH-5 Typical Turbine Aerator IH-7
III-6 Sludge Collector with Suction Draw Tubes III-8
III-7 Sludge Settleability vs. Organic Loading 111-10
III-8 Complete Mix Activated Sludge Process 111-14
III-9 Plug-Flow Activated Sludge Process 111-15
111-10 Contact Stabilization Activated Sludge Process 111-16
111-11 Step Feed Activated Sludge Process 111-17
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ACTIVATED SLUDGE PROCESS
LIST OF FIGURES (continued)
Figure No. Description Page
IV-1 Wastewater Sampling Guidelines IV-2
IV-2 Typical Sampling and Testing Program IV-6
IV-3 Amoeboids IV-19
IV-4 Flagellates IV-20
IV-5 Free Swimming Ciliate IV-21
IV-6 Stalked Ciliate IV-22
IV-7 Relative Number of Microorganisms vs. Sludge Quality IV-24
IV-8 Worksheet for Microscopic Examination of Activated Sludge IV-26
IV-9 Sludge Blanket Indicators IV-28
IV-10 Correlation of Centrifuge and Suspended Solids Concentration IV-31
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ACTIVATED SLUDGE PROCESS
LIST OF TABLES
Table No. Page
11-1 Guide to Successful Process Control H-1
II-2 Typical Air Requirement Parameters 11-10
II-3 Approximate Relationship of the COD F/M to the MCRT 11-19
II-4 Approximate Relationship of the BOD F/M to the MCRT 11-19
II-5 Typical Design Parameters for Secondary Clarifiers II-22
II-6 Sandard Operating Procedures for Aeration and D.O. Control II-26
II-7 A Guide to Typical RAS Flow Rates II-25
II-8 Standard Operating Procedures for RAS Control II-28
II-9 Standard Operating Procedures for WAS Control II-37
11-10 Typical Ranges for F/M Loadings II-43
11-11 MCRT Needed to Produce a Nitrified Effluent as Related to the M-49
Temperature
11-12 Allowable Concentrations of Heavy Metals II-94
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ACTIVATED SLUDGE PROCESS
SECTION I-TROUBLESHOOTING
Select the
measure with
least adverse
effect.
Know the
process.
1.01 INTRODUCTION
This section of the manual presents troubleshooting procedures for solving
common operating problems experienced in the activated sludge process.
With each problem, or observation, a list is included for the probable causes,
checks to determine the cause, and the suggested corrective measures. You,
the operator, must determine and select one or more of the corrective meas-
ures that will restore the process to full efficiency with the least adverse
effect on the-final effluent quality. In order to evaluate the problem and select
the best corrective measure, you must be thoroughly familiar with your
activated sludge process and how it fits into the overall treatment plant
operation. In addition, you must be familiar with the influent wastewater
characteristics, plant flow rates and patterns, design and actual loading
parameters, performance of the overall plant and individual processes, and
current maintenance procedures. For those operators who are not familiar
with the activated sludge process, refer to Section III, "FUNDAMENTALS"
before attempting to use the troubleshooting guides.
Common
problems with
activated
sludge
processes.
1.02 TROUBLESHOOTING GUIDES
There are seven problems presented that frequently occur in operating the
activated sludge process. These problems are listed below and are referenced
to the troubleshooting guides which begin on the following pages.
Note that the problems are categorized between the aeration tank and secon-
dary clarifier tank. The troubleshooting guides presented for the secondary
clarifier tank are associated with the activated sludge characteristics and
quality, as can be observed when performing the sludge settleability test.
The operator must realize that all observations made during the settleability
test are not necessarily indicative of conditions occurring in the secondary
clarifier tank. In all of the guides presented, the probable causes given for the
observation should be looked at concurrently because many times one problem
may be the result of several causes.
1-1
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ACTIVATED SLUDGE PROCESS
SECTION I-TROUBLESHOOTING
Troubleshooting
Guide No.
Aeration Tank
1
2
Secondary
Clarifier
3
4
5
6
7
INDEX TO TROUBLESHOOTING GUIDES
Problem Indicator
Aeration System Problems
Foaming Problems
Solids Washout/Billowing Solids
Bulking Sludge
Sludge Clumping
Cloudy Secondary Effluent
Ashing, Pinpoint/Straggler Floe
Figure 1-1 presents a pictorial index of typical settleability test results. This
index may be used in comparing actual test results for quick reference
to the troubleshooting guides.
I-2
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ACTIVATED SLUDGE PROCESS
SECTION I-TROUBLESHOOTING
30 MIN.
TROUBLESHOOTING GUIDE- NO. 3
GOOD SETTLING
30 MIN.
TROUBLESHOOTING GUIDE NO. 4
POOR SETTLING
30 MIN.
ONE TO TWO HOURS
30 MIN.
TROUBLESHOOTING GUIDE NO. 5
DENITRIFICATION
TROUBLESHOOTING GUIDE NO. 6
CLOUDY
30 MIN.
TROUBLESHOOTING GUIDE NO.7
ASH ON SURFACE
30 MIN.
OR
TROUBLESHOOTING GUIDE NO.7
PIN POINT FLOC & STRAGGLERS
SETTLING TEST OBSERVATIONS
FIGURE 1-1
1-3
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ACTIVATED SLUDGE PROCESS
AERATION TANK
TROUBLE SHOOTING GUIDE NO. 1 - AERATION SYSTEM PROBLEMS
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
Boiling action, violent
turblance throughout
aeration tank surface.
Large air bubbles, 1/2" or
greater, apparent.
A. Overaeration resulting in
high D.O. and/or floe
shearing.
1. Generally, D.O. should be
in range of 1.0 to 3.0 mg/l
throughout tanks.
1) Reduce air SCFM rate to
maintain D.O. in proper
range.
pgll-24&ll-72
2. Uneven surface aeration
pattern. Dead spots or
inadequate mixing in some
areas of tank.
A. Plugged diffusers.
Underaeration resulting in
low D.O. and/or septic
odors.
1. Check maintenance
records for last cleaning of
diffusers.
2. Spot check diffusers in
tank for plugging.
Check D.O., should be in
range of 1.0 to 3.0 mg/l
throughout tank.
2.
Check for adequate mixing
in aeration tank.
3.
Check RAS rates and
sludge blanket depth in
clarifier.
1) If diffusers have not been
cleaned in the last 12
months, do so.
2) If several are plugged,
clean all diffusers in tank.
1) Increase air SCFM rate to
maintain D.O. in proper
range.
2) Calculate SCFM of air per
linear foot of diffuser
header pipe. Minimum
requirement is 3 SCFM/
linear ft. Adjust air SCFM
rate as necessary to
maintain adequate D.O.
and mixing.
3) Adjust RAS rate to maintain
sludge blanket depth of 1
to 3 feet in clarifier.
PQ M-72
pg II-72
pg II-24
pgll-9
pg H-29
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ACTIVATED SLUDGE PROCESS
AERATION TANK
TROUBLE SHOOTING GUIDE NO. 1 — AERATION SYSTEM PROBLEMS (continued)
OBSERVATION
3. Excessive air rates being
used with no apparent
change in organic or
hydraulic loading. Difficult
to maintain adequate D.O.
level.
PROBABLE CAUSE
A. Leaks in aeration system
piping.
B. Plugged diffusers. Air
discharging from diffuser
header blow-off pipes
causing local boiling to
occur on surface near
diffuser header pipe.
C. Insufficient or inadequate
oxygen transfer.
D. High organic loadings
(BOD, COD, Suspended
matter) from in-plant side
stream flows.
NECESSARY CHECK
1. Check air pipe and joint
connection; listen for air
leakage or soap test flanges
and watch for bubbling
caused by air leaking.
1 . Check maintenance record
for last cleaning of
diffusers.
2. Spot check diffusers in
tank for plugging.
1. Check aeration system
performance.
a. Diffused aeration system
should provide between
800 to 1500 cu. ft. air per
pound BOD removed.
b. Mechanical aeration
system should provide
between 1 to 1.2 pounds
oxygen per pound BOD
removed.
1. Check to see if organic
loading from side stream
flows contributes signifi-
cantly to overall process
loading.
REMEDIES
1) Tighten flange bolts and/or
replace flange gaskets.
1) If diffusers have not been
cleaned in last 12 months,
do so.
2) If several are plugged, clean
all diffusers in tank.
1) Replace with more effec-
tive diffusers or mechanical
aerators.
2) Add more diffusers or
mechanical aerators.
1) If loadings are greater
than 25%, optimize opera-
tional performance or
upgrading of other inplant
processes will be required.
REFERENCES
pg n-72
pgii-72
pg II-9& IH-4
pg II-9& IH-4
pgii-9
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ACTIVATED SLUDGE PROCESS
AERATION TANK
TROUBLESHOOTING GUIDE NO. 2 — FOAMING PROBLEMS
OBSERVATION
1. White, thick, billowing or
sudsy foam on aeration
tank surface.
PROBABLE CAUSE
A. Overloaded aeration tank
(low MLSS) due to process
start-up. Do not be alarmed,
this problem usually occurs
during process start-up.
B. Excessive sludge wasting
from process causing
overloaded aeration tank
(Low MLSS).
NECESSARY CHECK
1. Check aeration tank BOD
loading (1bs/day) and Ibs
MLVSS in aeration tank.
Calculate F/M ratio to
determine Ibs/day MLVSS
inventory for current BOD
loading.
2. Check secondary clarifier
effluent for solids carryover.
Effluent will look cloudy.
3. Check D.O. levels in
aeration tank.
1. Check and monitor for
trend changes which occur
in the following:
a. Decrease in MLVSS mg/l.
b. Decrease in MCRT,
Gould Sludge Age.
c. Increase in F/M ratio.
d. D.O. levels maintained
with less air rates.
e. Increase in WAS rates.
REMEDIES
1) After calculating the F/M
and Ibs MLVSS needed,
you will find that the F/M
ratio is high and the Ibs
MLVSS inventory is low.
Therefore, do not waste
sludge from the process or
maintain the minimum
WAS rate possible if
wasting has already started.
2) Maintain sufficient RAS
rates to minimize solids
carryover especially during
peak flow periods.
3) Try to maintain D.O. levels
between 1.0 to 3.0 mg/l.
Also be sure that adequate
mixing is being provided in
the aeration tank while
attempting to maintain
D.O. levels.
1) Reduce WAS rate by not
more than 10% per day
until process approaches
normal control parameters.
2) Increase RAS rate to mini-
mize effluent solids carry-
over from secondary
clarifier. Maintain sludge
blanket depth of 1 to 3 feet
from clarifier floor.
REFERENCES
pg II-75, 11-12 &II-42
pg n-29
pgll-24
pgll-36
pg n-29
o>
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ACTIVATED SLUDGE PROCESS
AERATION TANK
TROUBLESHOOTING GUIDE NO. 2 — FOAMING PROBLEMS (continued)
OBSERVATION
PROBABLE CAUSE
C. Highly toxic waste, such
as metals or bacteriocide,
or colder wastewater
temperatures, or severe
temperature variations
resulting in reduction of
MLSS.
D. Hydraulic washout of
solids from secondary
clarifier.
E. Improper influent waste-
water and/or RAS flow
distribution causing
foaming in one or more
aeration tanks.
NECESSARY CHECK
1. Take MLSS sample and test
for metals and bacteriocide,
and temperature.
2. Monitor plant influent for
significant variations in
temperature.
1. Check hydraulic detention
time in aeration tank and
surface overflow rate in
secondary clarifier.
1. Check and monitor for
significant differences in
MLSS concentrations
between multiple aeration
tanks.
2. Check and monitor primary
effluent and /or RAS flow
rates to each to aeration
basin.
REMEDIES
1) Reestablish new culture of
activated sludge. If pos-
sible, waste sludge from
process without returning
to other in-plant systems.
Obtain seed sludge from
other plant, if possible.
2) Actively enforce Industrial
Waste Ordinances.
1) Refer to Troubleshooting
Guide No. 3, Observation 1.
1) MLSS and RAS concentra-
tions, and D.O.'s between
multiple tanks should be
reasonably consistent.
2) Modify distribution facili-
ties as necessary to main-
tain equal influent
wastewater and/or RAS
flow rates to aeration
basins.
REFERENCES
pgll-93&ll-94
pgll-94
pgll-23&ll-78
pgll-78&IV-3
pgll-78
-------
ACTIVATED SLUDGE PROCESS
AERATION TANK
TROUBLESHOOTING GUIDE NO. 2 — FOAMING PROBLEMS (continued)
OBSERVATION
2. Shiny, dark-tan foam on
aeration tank surface.
3. Thick, scummy dark-tan
foam on aeration tank
surface.
PROBABLE CAUSE
A. Aeration tank approaching
underloaded (high MLSS)
condition due to insuffic-
ient sludge wasting from
the process.
A. Aeration tank is critically
underloaded (MLSS too
high) due to improper WAS
control program.
NECESSARY CHECK
1. Check and monitor for trend
changes which occur in
the following:
a. Increase in MLVSS mg/
b. Increase in MCRT,
Gould Sludge Age.
c. Decrease in F/M ratio.
d. D.O. levels maintained
with increasing air rates.
e. Decrease in WAS rates.
1. Check and monitor for
trend changes which occur
in the following:
a. Increase in MLVSS mg/l.
b. Increase in MCRT,
Gould Sludge Age.
c. Decrease in F/M ratio.
REMEDIES
1) Increase WAS rate by not
more than 10% per day
until process approaches
normal control parameters
and a modest amount of
light-tan foam is observed
on aeration tank surface.
2) For additional checks and
remedies refer to Trouble-
shooting Guide No. 5 and 6.
3) For multiple tank operation
refer to Observation No. 1,
Probable Cause "E".
1) Increase WAS rate by not
more than 10% per day
until process approaches
normal control parameters
and a modest amount of
light-tan foam is observed
on aeration surface.
REFERENCES
pg II-76&II-36
pgll-76&ll-36
00
-------
ACTIVATED SLUDGE PROCESS
AERATION TANK
TROUBLESHOOTING GUIDE NO. 2 — FOAMING PROBLEMS (continued)
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
CO
d. D.O. levels maintained
with increasing air rates.
e. Decrease in WAS rates.
f. Secondary effluent nitrate
level above 1.0mg/l.
g. Increase in secondary
effluent chlorine
demand.
h. Decrease in aeration
tank effluent pH.
2) For additional checks and
remedies refer to Trouble-
shooting Guide No. 5 and 7.
3) For multiple tank operation
refer to Observation No. 1
Probable Cause "E" of this
guide.
Dark-brown, almost
blackish sudsy foam on
aeration tank surface.
Mixed liquor color is very
dark-brown to almost black.
Detection of septic or sour
odor from aeration tank.
A. Anaerobic conditions
occurring in aeration tank.
1. Refer to Troubleshooting
Guide No. 1, Observation
No. 2 and 3.
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 3 — SOLIDS WASHOUT/BILLOWING SOLIDS
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
Localized clouds of hom-
ogenous sludge solids
rising in certain areas of
the clarifier. Mixed liquor
in settleability test settles
fairly well with a clear
supernatant.
A, Equipment malfunction.
1. Refer to Troubleshooting
Guide No. 1, Observations
1-A.2-A, and2-B.
2. Check the following
equipment for abnormal
operation.
a. Calibration of flow
meters.
b. Plugged or partially
plugged RAS or WAS
pumps and transfer lines.
c.Sludge collection
mechanisms, such as
broken or worn out
flights, chains, sprock-
ets, squeegees, plugged
sludge withdrawal tubes.
3. Check sludge removal rate
and sludge blanket depth
in clarifier.
2)
Repair or replace abnormal
operating equipment.
pg II-77
3)
Adjust RAS rates and
sludge collector mechan-
ism speed to maintain
sludge blanket depth at 1
to 3 feet from clarifier floor.
pg n-29
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 3 — SOLIDS WASHOUT/BILLOWING SOLIDS (continued)
OBSERVATION
PROBABLE CAUSE
B. Air or gas entrapment in
sludge floe or denitrifi-
cation occurring.
C. Temperature currents.
D. Solids washout due to
hydraulic overloading.
NECESSARY CHECK
1 . Perform sludge settleability
test and gently stir sludge
when settling to see if
bubbles are released.
2. If bubbles are released,
check nitrate mg/l in
secondary effluent to see if
the process is nitrifying.
1. Perform temperature and
D.O. profiles in clarifier.
2. Check inlet and outlet
baffling for proper solids
distribution in clarifier.
1. Check hydraulic detention
time in aeration tank and
clarifier, and surface over-
flow rate in clarifier.
REMEDIES
1) If the process is not nitri-
fying, refer to Probable
Cause A above, and
Troubleshooting Guide No.
7, Observation 2.
2) If the process is nitrifying,
refer to Troubleshooting
Guide No. 5, Probable
Cause A.
1) If temperatures exceed 1
to 2 degrees between top
and bottom of ciarifier, use
an additional aeration tank
and clarifier if possible.
2) Modify or install additional
baffling in clarifiers.
3) Refer to Probable Cause
A-1 , and A-2 above.
1) If hydraulic loadings exceed
design capability, use
additional aeration tanks
and clarifiers if possible.
2) Reduce RAS rate to main-
tain high sludge blanket
depth in clarifier.
3) If possible, change process
operation to sludge reaera-
tion or contact stabilization
mode.
4) Refer to Probable Causes
B-1, B-2, and C-2 above.
REFERENCES
pgil-90
pgll-81
pg 11-81
pg II-78
pg 1 1-29
pg 111-15
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 3 — SOLIDS WASHOUT/BILLOWING SOLIDS (continued)
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
2. Localized clouds of fluffy
homogenous sludge rising
in certain areas of the
clarifier. Mixed liquor in
settleability test settles
slowly, leaving stragglers
in supernatant.
A. Overloaded aeration tank
(low MLSS) resulting in a
young, low density sludge.
10
1. Check and monitor trend
changes which occur in
the following:
a Decrease in MLVSS, mg/l.
b. Decrease in MCRT,
Gould Sludge Age.
c. Increase in F/M ratio.
d. Lower air SCFM rate to
maintain D.O. level.
1) Decrease WAS rates by not
more than 10% per day to
bring process back to
optimum parameters.
pg II-97 & II-36
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 4 — BULKING SLUDGE
OBSERVATION
1. Clouds of billowing hom-
ogenous sludge rising
and extending throughout
the clarifier tank. Mixed
liquor settles slowly and
compacts poorly in settle-
ability test, but supernatant
is fairly clear.
PROBABLE CAUSE
A. Improper organic loading
or D.O. level.
B. Filamentous organisms.
NECESSARY CHECK
1. Check and monitor trend
changes which occur in
the following:
a. Decrease in MLVSS mg/l.
b. Decrease in MCRT,
Gould Sludge Age.
c. Increase in F/M ratio.
d. Change in D.O. levels.
e. Sudden SVI increase
from normal, or decrease
inSDI.
1. Perform microscopic
examination of mixed
liquor and return sludge.
If possible, try to identify
type of filamentous organ-
isms, either fungal or
bacterial.
2. If fungal is identified,
check industries for wastes
which may cause problems.
REMEDIES
1 ) Decrease WAS rates by not
more than 10% per day
until process approaches
normal operating para-
meters.
2) Temporarily increase RAS
rates to minimize solids
carryover from clarifier
tank. Continue until normal
control parameters are
approached.
3) D.O. level throughout aera-
tion tank greater than 0.5
mg/l, preferably 1 to 3 mg/l.
1 ) If no filamentous organisms
are observed, refer to
Probable Cause "A" above.
2) Enforce Industrial Waste
Ordinance to eliminate
wastes. Also see Remedy
4 below.
REFERENCES
pgll-82&ll-36
pgll-29
pg II-24
pgll-83
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 4 — BULKING SLUDGE (continued)
OBSERVATION
PROBABLE CAUSE
C. Wastewater nutrient de-
ficiencies.
NECESSARY CHECK
3. If bacterial are identified,
check influent wastewater
and in-plant side stream
flows returning to process
for massive filamentous
organisms.
1. Check nutrient levels in
influent wastewater. The
BOD to nutrient ratios
should be 100 parts BOD
to 5 parts total nitrogen to
1 part phosphorus to 0.5
iron.
2. Perform hourly ML Settle-
ability tests.
REMEDIES
3) Chlorinate influent waste-
water at 5 to 10 mg/l
dosages.
If higher dosages are re-
quired, use extreme cau-
tion. Increase dosage at 1
to 2 mg/l increments.
4) Chlorinate RAS at 2 to 3
lbs/day/1000lbsMLVSS.
5) Optimized operational
performance or upgrading
of other in-plant unit pro-
cesses will be required if
filamentous organisms are
found in side stream flows.
1) If nutrient levels are less
than average ratio, field
tests should be performed
on the influent wastewater
for addition of nitrogen in
the form a anhydrous
ammonia, phosphorus in
the form of trisodium
phosphate and/or iron in
the form of ferric chloride.
2) Observe tests for improve-
ment in sludge settling
characteristics with the
addition of nutrients.
REFERENCES
pgll-89
pgll-9
pgll-83, IV-12. &IV-15
pglV-14
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 4 — BULKING SLUDGE (continued)
OBSERVATION
PROBABLE CAUSE
D. Low D.O. in aeration tank.
E. pH in aeration tank is less
than 6.5
NECESSARY CHECK
1. Check D.O. at various
locations throughout the
tank.
1. Monitor plant influent pH.
2. Check if process is nitrify-
ing due to warm wastewater
temperature or low F/M
loading.
REMEDIES
1) If average D.O. is less than
0.5 mg/l, increase air SCFM
rate until the D.O. level in-
creases to between 1 and 3
mg/l throughout the tank.
2) If D.O. levels are nearly
zero in some parts of the
tank, but 1 mg/l or more in
other locations, balance
the air distribution system
or clean diffusers. Refer to
Troubleshooting Guide No.
1, Observation 2.
1) If pH is less than 6.5, con-
duct industrial survey to
identify source. If possible,
stop or neutralize dis-
charge at source.
2) If the above is not possible,
raise pH by adding an alka-
line agent such as caustic
soda or lime to the aeration
influent.
1) If nitrification is not re-
quired, increase WAS rate
by not more than 10% per
day to stop nitrification.
2) If nitrification is required,
raise pH by adding an alka-
line agent such as caustic
soda or lime to the aeration
influent.
REFERENCES
pgll-83
pgll-86
pglf-20, II-36&IV-12
pgll-86
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 5 — SLUDGE CLUMPING
OBSERVATION
1. Sludge clumps (from size
of a golf ball to as large as
a basketball) rising to and
dispersing on clarifier
surface. Bubbles noticed
on clarifier surface. Mixed
liquor in settleability test
settles fairly well, however
a portion of and /or all of
the settled sludge rises to
the surface within four
hours after test is started.
PROBABLE CAUSE
A. Denitrification in clarifier.
B. Septicity occurring in
clarifier.
NECESSARY CHECK
1. Check for increase in
secondary effluent nitrate
level.
2. Check loading parameters.
3. Check D.O. and tempera-
ture levels in the aeration
tank.
4. Check RAS rates and
sludge blanket depth in
clarifier.
1. Refer to Troubleshooting
Guide No. 1 Observation
No. 2.
2. See 3 and 4 above.
REMEDIES
1) Increase WAS rate by not
more than 10% per day to
reduce or eliminate level of
nitrification. If nitrification
is required, reduce to al-
lowable minimum.
2) Maintain WAS rates to keep
process within proper
MCRT, Gould Sludge Age,
and F/M ratio.
3) Maintain D.O. at minimum
level (1.0 mg/l). Be sure
adequate mixing is pro-
vided in the aeration tank.
4) Adjust RAS rate to maintain
sludge blanket depth of 1
to 3 feet in clarifier.
REFERENCES
pg II-90& II-36
pgll-36
pgll-24
PQll-29
o>
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 6 — CLOUDY SECONDARY EFFLUENT
OBSERVATION
1. Secondary effluent from
clarifier is cloudy and
contains suspended matter.
Mixed liquor in settleability
test settles poorly, leaving
a cloudy supernatant.
PROBABLE CAUSE
A. MLSS in aeration tank low
due to process start-up.
B. Increase in organic loading.
C. Toxic shock loading.
NECESSARY CHECK
1. Refer to Troubleshooting
Guide No. 2, Observation
No. 1.
1. Perform microscopic
examination on mixed
liquor and return sludge.
Check for presence of
protozoa.
2. Check organic loading on
process.
3. Check D.O. level in aeration
tank.
1. Perform microscopic
examination on mixed
liquor and return sludge.
Check for presence of in-
active protozoa.
REMEDIES
1) If no protozoa are present,
possible shock organic
loading has occurred.
2) Reduce WAS rate by not
more than 10% per day to
bring process back to
proper loading parameters
and increase RAS rates to
maintain 1 to 3 foot sludge
blanket in clarifier.
3) Adjust air SCFM rate to
maintain D.O. level within
1.0to3.0mg/l.
1) If protozoa are inactive,
possibility of recent toxic
load on process.
2) Refer to Troubleshooting
Guide No. 2, Observation
No. 1-C.
REFERENCES
pgll-93&IV-18
pgll-42&ll-36
pgll-24
pgll-93
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 6 — CLOUDY SECONDARY EFFLUENT (continued)
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
D. Overaeration causing
mixed liquor floe to shear.
E. Improper D.O. levels
maintained in aeration tank.
1. Perform microscopic
examination on mixed
liquor. Check for dispersed
or fragmented floe and
presence of active
protozoa.
1. Refer to Troubleshooting
Guide No. 1, Observation
No. 2.
1) Refer to Troubleshooting
Guide No. 1, Observation
No. 1-A.
pg IV-18
CO
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLAR1FIER
TROUBLESHOOTING GUIDE NO. 7 — ASHING AND PINPOINT/STRAGGLER FLOG
OBSERVATION
1. Fine dispersed floe (about
the size of a pinhead)
extending throughout the
clarifier with little islands
of sludge accumulated on
the surface and discharging
over the weirs. Mixed liquor
in settleability test, settles
fairly well. Sludge is dense
at bottom with fine particles
ot floe suspended in fairly
clear supernatant.
PROBABLE CAUSE
A. Aeration tank approaching
underloaded conditions
(High MLSS) because of
old sludge in system.
NECESSARY CHECK
1. Check and monitor trend
changes which occur in
the following:
a. Increase in MLVSS mg/l.
b. Increase in MCRT,
Gould Sludge Age.
c. Decrease in F/M ratio.
d. D.O. levels maintained
with increasing aeration
rates.
e. Decrease in WAS rates.
f. Decrease in organic
loading (BOD/COD in
primary effluent).
2. Check for foaming in
aeration tank.
REMEDIES
1) Increase WAS rates by not
more than 10% per day to
bring process back to
optimum control para-
meters for average organic
loading.
2) Refer to Troubleshooting
Guide No, 2 for any foam-
ing which may be occurring
in aeration tank.
3) Adjust RAS rates to main-
tain sludge blanket depth
of 1 to 3 feet in clarifier.
4) Refer to Troubleshooting
Guide No. 1 for additional
observations.
REFERENCES
pgll-97&II-36
pg H-29
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIFIER
TROUBLESHOOTING GUIDE NO. 7 — ASHING AND PINPOINT/STRAGGLER FLOC (continued)
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
2. Small particles of ash-like
material floating on clarifier
surface.
A. Beginning of denitrifi-
cation.
1. Stir floating floe on surface
of 30-minute settling test.
B. Excessive amounts of
grease in mixed liquor.
1. Perform a grease analysis
on MLSS, and check scum
baffles in primary tank.
2. Check grease content in
raw wastewater.
1) If floating floe releases
bubbles and settles, see
Troubleshooting Guide No.
5, Probable Cause A.
2) If it does not settle, refer
to Probable Cause B, below.
1) If the grease content ex-
ceeds 15 percent by weight
of the MLSS, repair or re-
place scum baffles as
needed.
2) If grease content is ex-
cessive, implement an
industrial waste monitoring
and enforcement program.
pgll-95&ll-93
pgll-95
pg II-95
-------
ACTIVATED SLUDGE PROCESS
SECONDARY CLARIF1ER
TROUBLESHOOTING GUIDE NO. 7 — ASHING AND PINPOINT/STRAGGLER FLOC (continued)
OBSERVATION
3. Particles of straggler floe
about 1/4" or larger,
extending throughout the
clarifier and discharging
over the weirs. Mixed liquor
in settleability test, settles
fairly well. Sludge does not
compact well at the bottom
with chunks of floe
suspended in fairly clear
supernatant.
PROBABLE CAUSE
A. Aeration tank slightly
underloaded (Low MLSS)
due to organic load
change.
NECESSARY CHECK
1. Check and monitor trend
changes which occur in
the following:
a. Decrease in MLVSS mg/l.
b. Decrease in MCRT,
Gould Sludge Age.
c. Increase in F/M ratio.
d. Less aeration rate used
to maintain D.O.
e. Increase in WAS rates.
f. Increase or decrease in
organic loading
(BOD/COD in primary
effluent).
2. Check for foaming in
aeration tanks.
REMEDIES
1 ) Decrease WAS rates by not
more than 10% per day to
bring process back to
optimum control par-
ameters for average organic
loading.
2) Refer to Troubleshooting
Guide No. 2 for any foam-
ing which may be occurring
in aeration tank.
3) Adjust RAS rates to main-
tain sludge blanket depth
of 1 to 3 feet in clarifier.
4) Decrease aeration SCFM
rates to maintain minimum
D.O. of only 1.0 mg/l in
aeration tank. Refer to
Troubleshooting Guide No.
1 for additional
observations.
REFERENCES
pgll-97&ll-36
pgll-29
pgil-24
-------
ACTIVATED SLUDGE PROCESS
SECTION I-TROUBLESHOOTING
REFERENCES
Eckenfelder, W.W., Biological Waste Treatment, Pergamon Press, New York, 1961.
Hawkes, H.A., The Ecology of Waste Water Treatment, Pergamon Press, Oxford, 1963.
Kerri, Kenneth D., et al., (A Field Study Training Program), Operation of Wastewater
Treatment Plants, (Chapter 7), Sacramento State College Department of Civil
Engineering.
McKinney, Ross E., Microbiology for Sanitary Engineers, McGraw-Hill Book Company
Inc., New York, 1962.
Stevens, Thompson, Runyan, Inc., Operator's Pocket Guide to Activated Sludge,
Parts I and II. Published by the Authors, 5505 S.E. Milwaukie Avenue, Portland,
Oregon 97202,1975.
Water Pollution Control Federation, Operation of Wastewater Treatment Plants,
Manual of Practice No. 11,1976.
West, Alfred W., Operational Control Procedures for the Activated Sludge Process,
Parts I, II, IMA, and NIB, U.S. EPA, National Training and Operational Technology
Center, Cincinnati, Ohio, 1975.
I-22
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
2.01
INTRODUCTION
Importance of a
properly
controlled
operation.
Acceptable
ranges are
given herein.
The activated sludge process is reliable and has the ability to handle shock
loads. It requires much more monitoring and control than the trickling filter
process. Therefore, proper operation and control is essential to achieve
optimum performance and to avoid operational problems. Table 11-1 presents
guidelines to achieving successful process control.
The operating parameters given in this section are intended as acceptable
ranges to guide the operator in achieving operational control at his plant.
Operation and control of a particular activated sludge process should be based
on its response and performance as related to the control techniques applied.
The success or failure in achieving the best possible performance from the
treatment plant is dependent on the operator. There are five process control
techniques presented under Waste Activated Sludge Control in this section
of the manual. The operator should study each of these technqiues and apply
the waste control program which he feels will provide the best effluent quality.
TABLE 11-1
GUIDE TO SUCCESSFUL PROCESS CONTROL
REQUIREMENT
REFERENCE
1. Sound operational and preventive
maintenance measures.
Section 2.02,
OPERATIONAL GUIDES
2. Laboratory monitoring
Section 4.02,
LABORATORY SAMPLING AND
TESTING PROGRAM
3. Accurate, up-to-date records.
Appendix A,
OPERATIONAL RECORDS
4.' Evaluation of operational and laboratory
data.
Section 4.03,
LABORATORY CONTROL TESTS
5. Application of data to adjustment of the
process.
Section 2.04,
PROCESS CONTROL
6. Troubleshooting problems before they
become serious.
Section 1.02,
TROUBLESHOOTING GUIDES
1-1
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Competent
preventive
maintenance
program is
essential.
2.02 OPERATIONAL GUIDES
Operational guides are provided on the following pages to aid the operator in
establishing routine operational procedures for his activated sludge process.
Performance of the routine operational procedures is by no means complete
without a competent preventive maintenance program. Every item of operating
equipment requires frequent attention, with particular emphasis on lubrica-
tion and other preventive maintenance requirements essential to a trouble-
free operation and minimum maintenance costs. A good preventive maintenance
program helps to improve process performance through a longer more
dependable equipment life.
Competent
process
control
includes
evaluation of
process
performance.
Many factors
affect process
performance.
Importance of
complete and
accurate
records.
2.03 PERFORMANCE EVALUATION
Evaluation of process performance is an essential part of compentent process
control and operation. The evaluation is helpful in determining process
response to various modes of operation, developing performance trends, and
identifying the causes of operational problems. For the activated sludge
process, performance evaluation consists of reviewing the BOD, COD, sus-
pended matter, and nitrogen removal efficiencies to the mode of operation,
F/M parameters, and RAS and WAS rates in relationship to control parameters
such as MCRT, Gould Sludge Age, and sludge quality. The review and applica-
tion of lab testing results is further discussed in Section IV - "LABORATORY
CONTROL" and "APPENDIX A".
Performance of the activated sludge process is affected by many factors
such as: hydraulic and organic loadings, method of wastewater distribution
to multiple tanks, characteristics of applied wastewater (temperature, pH,
toxicants, etc.), and performance of other treatment units in the plant. An
effective means of reviewing your plant performance is to maintain daily
charts or graphs reflecting such data against time. The charts presented in
Figure 11-1 serve as visual aids in identifying the optimum control parameters
and make any trends or changes immediately evident. The preparation and
use of these trend charts are discussed further in "APPENDIX A".
Conclusions reached during the process evaluation are then applied to the
adjustment of the process (basically adjustment of RAS, WAS and aeration
rates) for an efficient and economical operation. Whenever possible, only one
process adjustment should be made at a time to allow sufficient time between
each change for the process to respond and stabilize. This is especially true
when decisions are made to adjust F/M, MCRT and Gould Sludge Age, since
these parameters are directly related to changes in WAS rate. Complete and
accurate records of all phases of plant operations and maintenance are
essential for accurate performance evaluation and process control. The
preparation of operational records is discussed further in "APPENDIX A".
I-2
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
6
O
t-H
H
W
O
2
w
«
§
u
O
H
<
rt
8
M
to
a
8
h
h
M
Z.OOO
1,500
1,000
500
0.6
0.5
0.4
0.3
600
400
200
0
150
100
50
10
15
DAY
20
ACTIVATED SLUDGE PROCESS
(Five-day moving average trend plots)
FIGURE II-l
25
30
11-3
-------
ACTIVATED SLUDGE PROCESS
OPERATIONAL GUIDE NO. 1 — AERATION SYSTEM
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
A. Aeration tank.
1. Inspect for proper operation.
2. Check D.O. level.
3, Perform routine washdown.
4. Check control gates and gate operators
for proper operation.
5. Check froth spray system, if provided.
6. Inspect baffles and effluent weirs.
1a. Mechanical equipment.
1b. Presence of foaming on surface.
1c. Boiling or uneven surface aeration
pattern.
2a. D.O. In range of 1.0 to 3.0 mg/l.
3a. Hose down inlet channels, tank walls—
especially at the water line, effluent
baffles, weirs and channels, and other
appurtenant equipment at water line.
4a. Operate gates and operators to full
open and close position. Adjust gates
to proper position to equalize flow
distribution.
4b. Lubricate as recommended by man-
ufacturer.
5a. Unplug spray nozzles as necessary and
check for proper spray angle.
6a. Maintain baffles in good condition.
Maintain effluent weirs at equal
evaluation.
Twice/shift
Every 2 hrs.
Daily to
weekly
Twice/month
to monthly
Twice/shift
Monthly
TG No. 2
TG No. 1
pgll-26
pg I (-78
-------
ACTIVATED SLUDGE PROCESS
OPERATIONAL GUIDE NO. 1 — AERATION SYSTEM (continued)
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
B, Aeration Piping,
C, Air Compressors
(Centrifugal and positive
placement)
1. Inspect piping for leaks.
2. Inspect diffuser header assemblies.
3. Check aeration pipe valves and diffuser
header assembly control valves for
proper operation.
4. Check air flow meters, gauges and
condensate traps.
1. Check air filters.
2. Check operation of compressors and
motors.
la. Visually observe and listen for leaks at
pipe and joint connections.
2a. Remove header assemblies from tank.
Check diffusers and connections for
damage and plugging.
3a. Operate valves to full open and close
position. Adjust vaives to proper
positons.
4a. Cfieck and calibrate meters and gauges
as recommended by manufacturer.
4b. Drain condensate traps.
1a. Clean or replace filters as recommended
by manufacturer.
2a. Check for excessive vibrations, unusual
noises, lubricant leakage, bearing
overheating.
2b. Check oil levels, if so equipped, main-
tain proper levels.
2c. Check packing, mechanical seals-
adjust and maintain as recommended
by manufacturer.
2d. Check compressor intake and discharge
valves for proper position.
Daily
Twice/year
Monthly
Daily
Generally
dictated by
climatic
conditions
Twice/shift
TQ No. 1
Observation
No. 3
pglll-4
TGNo. 1,
Observation
No. 2
-------
ACTIVATED SLUDGE PROCESS
OPERATIONAL GUIDE NO. 1 — AERATION SYSTEM (continued)
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
D. Mechanical aerators.
o>
3. Check compressor air discharge back
pressure.
4. Perform regualr maintenance as recom-
mended by manufacturer.
5. Alternate compressors in service.
1. Check units for proper operation.
2. Maintain units properly.
3a. Record back pressure. Increasing pres-
sure is indicative of diffuser plugging.
1a. Check for excessive vibration, unusual
noises, motor and gear box overheating.
1b. Check for proper oil level in gear box
and proper motor lubrication.
1c. Check condition of baffles—if so
equipped, and repair or replace as
required.
2a. Follow manufacturer's instructions.
Daily
TGNo. 1,
Observation
No. 3
Daily io
weekly
Twice/shift
-------
ACTIVATED SLUDGE PROCESS
OPERATIONAL GUIDE 2 — SECONDARY CLARIFIER
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
A. Clarifier
1. Inspect for proper operation.
2. Perform daily washdown.
3. Maintain sludge collection equipment
and drive units.
4. Inspect baffles and effluent weirs.
5. Check sludge blanket depth
6. Check D.O. level in clarifier before
discharging over effluent weirs.
7. Check gates and operators for proper
operation.
1a. Mechanical equipment.
1b. Presence of suspended sludge.
2a. Hose down the influent channels, tank
walls—especially at the water line,
effluent weir and launders, effluent
channel and center feed baffles.
3a. Follow manufacturer's instructions.
4a. Maintain baffles in sound condition.
4b. Maintain effluent weirs at an equal
elevation.
5a. Sludge should be removed to maintain
a blanket depth of 1 to 3 feet. Adjust
RAS rates as necessary.
6a. D.O. level should be maintained at
minimum of 0.5 mg/l. Adjust aeration air
as necessary.
7a. Operate gates and operators to full
open and close position. Adjust gates
to proper position to equalize flow
distribution.
Twice/shift
Daily to
weekly
Monthly
Twice/shift
or more
frequently
Twice/shift
Twice/month
to monthly
Pgll-77
TG No. 3,
4, 5,6, 7
pg II-78
pgll-78
pgii-29
pgll-24
-------
ACTIVATED SLUDGE PROCESS
OPERATIONAL GUIDE 3 — PUMPING EQUIPMENT AND PIPING IN RAS AND WAS SYSTEMS
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
A. Pumps
00
1. Check operation of the pumps and
motors.
2. Aternate pumps in service.
3. Maintain pumping units.
4. Fully open and close all valves.
5. Check operation of air vacuum and air
relief valves.
6. Check operation of any pump controls
and instrumentation, such as flow
meters, density meters, control signal
loop.
1a. Check for excessive vibration, unusual
noises, lubricant leakage, and
overheating.
1b. Check oil reservoir level—if so equipped.
1c. Check oil feed rate—if so equipped.
1d. Check packing or mechanical seals-
make adjustment per manufacturer's
instructions.
1e. Check position of suction and discharge
valves.
1f. Check pump suction and discharge
pressure—if so equipped.
3a. Follow manufacturer's instructions.
4a. Make necessary adjustments or repairs.
4b. Maintain valves and operators according
to manufacturer's instructions.
5a. Maintain according to manufacturer's
instructions.
6a. Maintain according to manufacturer's
instructions.
Twice/shift
Daily to
weekly
Monthly
Weekly
Daily
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Review of In-Plant Recycled Flows
Recycled flows
may cause
overloading.
In evaluating the performance of the process or in trying to solve problems,
careful consideration should be given to all in-plant recycled flows. Often,
in-plant recycled flows are the cause of organic or hydraulic overloading. The
sludge processing operations may return decants from digesters, thickeners,
centrifuges, or vacuum filters. The waste backwash water from effluent sand
filtration processes may also cause hydraulic overloading or other process
control problems. The recycled flow from improperly operated sludge pro-
cessing units may account for as much as 25 percent of the total plant organic
loading. Usually, the majority-of recycled flows are passed back to primary
sedimentation units where it is hoped organic solids will settle out. In most
cases this practice is the major cause of overloading biological processes
due to poor removal of solids in the recycled flows sent to the primary sedi-
mentation units.
Minimize the
effect of
recycled flows.
The additional loading will then result in a greater sludge production, and
subsequently an increased loading upon the sludge processing operation.
In the activated sludge process, excessive BOD or COD loadings will even-
tually reduce effluent quality and possibly cause anaerobic conditions to
occur in the process.
Some guidelines that will reduce the effects of recycled flows on the activated
sludge process include the following:
1. Add flow continuously or during low night flows to avoid shock loads.
2. Improve efficiency of sludge handling process.
3. Utilize a lagoon or drying bed for poor quality decants from sludge
processing operations.
4. Avoid pumping excess waterto sludge handling processes.
5. Aerate or pretreat recycled flows to reduce oxygen demands.
Aeration Performance
Aeration Is
Important to
microorganisms.
Two basic
paramenters
to use.
A great deal can be learned about the operation of an activated sludge process
by reviewing aeration requirements and performance. Basically, the mixed
liquor is a suspension of microorganisms that consume the organic matter in
the wastewater while utilizing dissolved oxygen and releasing carbon dioxide
to produce new cell growth.
The air requirement is dependent upon the oxygen transfer rate to the mixed
liquor and the utilization of the dissolved oxygen by the microorganisms. The
oxygen transfer rate is chiefly dependent on the design of the aeration sys-
tem. The rate of dissolved oxygen utilization is dependent upon the micro-
organism activity as it relates to organic loading, pH, temperature, aeration
period and availability of dissolved oxygen. The air requirements may be based
on more than one parameter. The most frequently used parameters by oper-
ators include the amount of air applied per pound COD or BOD removed (CF
air/lb removed) in the process and the amount of air applied per gallon of
wastewater treated (CF air/gal). Typical aeration rates for these parameters
are presented in Table II-2.
II-9
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
TABLE 11-2
TYPICAL AIR REQUIREMENT PARAMETERS
Diffused Aeration
System
CFAir/lb Removed
COD
1000-2000
BOD
800-1500
OF Air/Gal
0.5-3.0
Mechanical Aeration System
System
Ibs 02 Ibs Removed
COD
1.5-1.8
BOD
1.0-1.2
Aeration
requirements
change when
process is
nitrifying.
How to
calculate CF
Air/lb removed.
How to
calculate CF
Air/gal
When evaluating aeration requirements, remember that the 5-day BOD, and
the COD only reflect the carbonaceous portion of the organic loading and not
the nitrogenous portion of the organic loading. The aeration requirements
will be affected by the degree of nitrification as it relates to the nitrogenous
strength of the organic loading as well as by the wastewater temperature
and pH.
The aeration performance parameters can be determined as follows:
Example Calculation
A. Data Required
1. COD or BOD removed, Ibs/day = 22,000 BOD
2. Total Air applied, CF/day = 31,900,000
B. Determine CF air/lb COD or BOD removed.
CF Air/lb removed = Total air applied
BOD, Ibs/day
_ 31,900,000
22,000
= 1450
Example Calculation
A. Data Required:
1. Total air applied, CF/day = 31,900,000
2. Total influent flow/day to aeration tank, gpd = 13,000,000
(exclude RAS flow rate)
B. Determine CF air/gal wastewater treated
CF air/gal =J°talalrapp"gd-
Total flow, gpd
_ 31,900,000
13,000,000
= 2.4
11-10
-------
How to
calculate Ibs
Og/lb removed
using
mechanical
aerators.
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Example Calculation
A. Data Required
1. COD or BOD removed, Ibs/day = 7200 BOD
2. n = Number of aerators in service = 3
3. hp = horsepower per aerator = 100
4. FTR = Field transfer rate, each aerator, Ibs O2/hp/hr = 2
(supplied by aerator manufacturer)
5. T = Time aerators in service, days = 0.83*
"This is determined by dividing the time each aerator is in service by
24 hours/day; M°"rs in service = days
24 hours/day
B. Determine Ibs O2/ib COD or BOD removed
h x FTR >
Ibs 02/lb removed =
COD or BOD removed, Ibs/day
_ (3 x 100 x 2 x 0.83 x 24)
7200
15,936
7200
= 1.6
Microorganisms
relationship
to MLVSS.
Solids Inventory
The amount of suspended matter (SS) that makes up the mixed liquor consists
of living and nonliving organic matter. The living organic matter is referred to
as being "active." The "active" portion of the SS is of major importance be-
cause included in this portion are the microorganisms responsible for treating
the wastewater. The more accurately the concentration of active micro-
organisms is known, the more consistently the activated sludge process can
be controlled.
Typically
70-80% of the
MLSS is volatile.
Many attempts have been made to accurately measure the "active" concen-
tration of the SS. The most common means of estimating the microorganism
concentration is the measurement of volatile suspended matter (VSS). All the
organic material in the SS burns to carbon dioxide and water in the VSS
determination. Typically, 70-80 percent of the MLSS will be VSS. The VSS
determination provides a crude approximation of the concentration of living
biological solids because the VSS also includes a nonliving fraction. Even so,
the VSS has been found to be an acceptable representation of "active" living
microorganisms in activated sludge.
1-11
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
A key to
successful
process control
Is representative
MLSS sampling.
Samples of MLSS must be taken at several locations in the aeration tank to
ensure that a representative sample of the microorganism concentration is
collected. In general, each compartment of an aeration tank must be sampled.
Similarly, aeration tanks that are long and narrow must be sampled at both
ends and at a midpoint to ensure that a representative sample of the mixed
liquor is collected. Sampling techniques to obtain representative MLSS
samples are discussed in Section IV - "LABORATORY CONTROL".
Good sampling procedures are essential for making a meaningful estimate of
the microorganism concentration, and samples for MLSS must be taken
using a consistent technique. There are two acceptable approaches for
obtaining a mixed liquor sample:
1. Composite samples may be taken at consistent intervals throughout
the day from the same locations in the aeration tank.
2. Grap samples taken at the same time each day at the same locations
in the aeration tank.
Accurate
MLVSS samples
very important
Either of these approaches will produce suitable samples. The first method
requires a refrigerated automatic sampler while the second method has the
advantages of not depending on a sophisticated sampler and of developing
a routine for sampling and observation of the aeration tank. Other methods of
sampling, such as grab samples taken at various times will produce less
satisfactory estimates of the MLSS.
The importance of the MLSS samples cannot be over emphasized. It is im-
portant to remember that accurate and representative samples are the key to
controlling the activated sludge process.
MLSS samples
used to
calculate the
Volatile Solids
Inventory
Solids Inventory
varies directly
with MCRT
Should solids in
the clarif ier be
measured in
solids
inventory?
Calculating the Solids Inventory
The purpose of collecting samples of MLSS is to develop an estimate of
the amount of microorganisms in the treatment system by determining
the VSS content in the MLSS. The amount of microorganisms (VSS) in the
treatment system is the solids inventory. The solids inventory must be
known in order to properly control the activated sludge process.
The solids inventory is used to determine F/M, MCRT and the amount of
activated sludge that should be wasted. The solids inventory varies directly
with the MCRT, that is as the MCRT increases the solids inventory in-
creases. It also varies inversely with the F/M, that is, as the F/M increases
the solids inventory decreases.
A recurring discussion in the technical literature involves the question of
whether the solids in the clarifier should be considered as part of the
solids inventory. At present, there is no one answer to the question;
however, all calculations involving F/M or MCRT must be made using the
same solids inventory.
11-12
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Arguments
against.
Argument for.
In general, no
need to
measure these
solids.
There are three basic arguments for not including the solids in the clarifier.
First, the microorganisms in the system cannot grow due to food and
oxygen limitations when they are in the clarifier. Second, loading para-
meters for the activated sludge process were first developed on the basis
of pounds of BOD applied per 1,000 cubic feet of aeration tank, which
ignores the solids in the clarifier. Third, the amount of solids in the clarifier
is not a very significant (less than 10 percent of the total) fraction of the
total solids in the process.
The argument in favor of including the clarifier solids in the solids inven-
tory is simply that these solids are significant and they cannot be ignored.
Additionally, if all of the solids are included in the calculations there is
less likelihood of making an error in the total solids inventory that exists
in the process. Finally, errors in the inventory amount would most likely
be significant at times when operational problems are experienced i.e.
when the sludge is not settling well in the clarifier.
The consequences of ignoring the solids in the clarifier will not affect
process control adjustments in most cases; and it is suggested that
operators use this approach when determining the solids inventory. If
ignoring the solids in the clarifier makes process control inconsistent as
observed by variations in effluent quality, then the operator should con-
sider including the clarifier solids when he determines the solids inventory.
Solids inventory for a typical activated sludge process may be calculated
as follows:
How to
calculate solids
inventory in the
aeration tank.
Example Calculation
A. Data Required:
Aeration tank volume, mg = 1.2
Number of tanks in service = 2
MLSS concentration, mg/1 = 2200
Percent VSS in MLSS,J%_= .72
B.
1.
2.
3.
4.
100
Determine total pounds VSS in aeration tank.
IbsVSS
inventory = (Aer. Tank Vol.) (No. of tanks) (MLSS) (% VSS) (8.34 Ibs/gal.)
Aer. tank
= (1.2) (2) (2200) (.72) (8.34)
= 31,705
How to
calculate the
secondary
clarifier solids
inventory.
If the clarifier is included in determining the solids inventory, the volume
of sludge in the clarifier must be determined by measuring the sludge
blanket in the clarifier and obtaining an average depth. The depth meas-
urement from the water surface to the top of the sludge blanket is sub-
tracted from the average clarifier depth to determine the average sludge
depth in the clarifier. The average sludge depth is then multiplied by the
surface area of the clarifier to obtain the volume expressed as cubic feet
which must be multiplied by 7.48 gal/cu ft and divided by one million to
convert the volume to million gallons (mg) of sludge.
11-13
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
The average VSS concentration of the sludge in the clarifier is roughly
estimated by assuming the top of the sludge blanket is equal to the
MLVSS concentration and the bottom of the sludge blanket is equal to the
VSSRAS concentration. These two concentrations are then averaged to
estimate the concentration of the clarifier sludge.
The pounds of solids inventory (VSS) in the clarifier may be determined
and added to the aeration tank inventory as follows:
Example Calculation
1. MLVSS concentration, mg/l = 1584
2. VSSRAS concentration, mg/l = 3330
3. Clarifier depth, ft. = 10
4. Depth from water surface to sludge blanket (DOB), ft. = 8
5. Clarifier surface area, sq. ft. = 4415
B. Determine the volume of sludge in the clarifier.
Sludge VOl mg - (Clarifier depth, ft. - DOB, ft.) (Surface area, sq. ft.) (7.48 gal/cu. ft.)
1,000,000
_ (10-8) (4415) (7.48)
1,000,000
= 0.066
C. Determine the average VSS concentration of the clarifier sludge.
avg VSS mg/l = MLVSS, mg/l + VSSRAS, mg/l
2
1584 + 3330
2
= 2457
D. Determine total pounds of VSS in the clarifier.
VSS, Ibs, = (avg cone., mg/l) (sludge vol., mg) (8.34 Ibs/gal)
in clarifier
= (2457) (0.066) (8.34)
= 1,352
11-14
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
E. Determine the total VSS inventory by adding the clarifier VSS
inventory to the aeration tank VSS inventory.
Total VSS, Ibs = MLVSS, Ibs + Clarifier VSS, Ibs
= 31,705 + 1,352
= 33,057
What are the
reliable
Indicators of
process
performance?
Suspended
matter Is
related to BOD.
COD/BOD and Suspended Matter Removal
The activated sludge process is designed to remove a high percentage of the
COD/BOD and suspended matter when operated within the proper loading
range. The removal efficiency of these constituents are very reliable indicators
of process performance, (f the efficiency drops below the expected design
performance, action should be taken to locate the reason for the decreased
efficiency. Operational records, process control parameters, lab analysis, and
wastewater characteristics should be reviewed and analyzed when trying to
locate the problem. The information gained from the evaluation should be
implemented into the operation of the unit process. The best practice when
making operational changes is to make one change at a time and then allow
sufficient time (usually two to four weeks) between changes for stabilization
of the biological process.
The activated sludge process is also designed to produce an effluent having a
suspended matter content of 20 mg/l or less when operated within the proper
loading range. Much of the secondary effluent BOD will be directly related to
the amount of suspended matter that has escaped with the clarifier effluent
flow. Careless operational procedures will result in an increased secondary
effluent BOD. Hence, the evaluation of the unit process performance in regard
to the suspended matter removal is valuable in improving both the suspended
matter and COD/BOD removals. An increase of the secondary effluent sus-
pended matter is an indication that the process is not performing as it should.
The process control parameters, operational records, and wastewater char-
acteristics should be reviewed and analyzed to determine what action should
be taken to restore the desired process performance. For guidance in the
troubleshooting of high effluent suspended solids, refer to Section I, "TROU-
BLESHOOTING".
COD/BOD
removal
expressed as %.
The COD/BOD and suspended matter removals are normally expressed as
percentages. These parameters should be recorded daily. The COD/BOD and
suspended matter removals are all calculated by using the same formula. The
example calculation given below shows how to determine the suspended
matter removal efficiency.
11-15
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Example Calculation
A. Data Required
1. Primary effluent suspended matter, mg/l = 160 (COD or BOD)
2. Secondary effluent suspended matter; mg/l = 14 (COD
or BOD)
B. Determine percent removal of suspended matter.
Removal efficiency, % = Influent SS-effluent SS x 10Q
InfuentSS
= 16°-14 x 100
160
= 91
Kinetics are
math short
hand for
controlling
the process.
F/M
MCRT
F/M, MCRT,
KD,Y
Process Kinetics
A great deal of effort and a large number of publications have been put forth
to describe the activated sludge process. The major accomplishment of these
efforts has been the development of an approach to activated sludge design
and operation that is based on the kinetics of microorganism growth. The
term kinetics normally refers to the rate at which chemical or biological
reactions occur; however, microorganism growth kinetics are nothing more
than expressions that relate organic loading to the production of new micro-
organisms.
The concepts of activated sludge kinetics enables engineers to design waste-
water treatment plants on a logical and systematic basis.
There are two basic concepts, the food to microorganism ratio (F/M) and the
mean cell residence time (MCRT), that are expressed in the form shown below:
Food to microorganism ratio = F/M = Ibs COD applied per day
Ibs VSS inventory
Mean cell residence time = MCRT = Ibs solids inventory
Ibs VSS produced per day
Kinetic Relationships
The F/M and the MCRT are related by two constants that are called the
Yield coefficient, Y and the Endogenous Decay coefficient, KD. The Yield
coefficient expresses the ratio of the amount of microorganisms produced
to the amount of food (BOD or COD) consumed. The Yield coefficient is
measured by operating the activated sludge process at several values of
MCRT. Typical values of Y based on COD, for domestic wastewater range
from 0.3 to 0.4 Ibs VSS produced/lb COD removed. The Endogenous Decay
coefficient expresses the decrease in active mass of microorganisms due
to endogenous metabolism. This coefficient is typically about 0.05 Ibs
VSS decayed per day/lb solids inventory.
11-16
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
MCRT related
to the F/M.
The MCRT is related to the F/M as shown below:
1
MCRT, days =
(Y) (F/M) (Removal efficiency) - KD
where,
y = Ibs. VSS produced per Ib. COD removed per day
F/M - jbs- COD applied per day
Ibs, VSS inventory
Removal efficiency = lnfluent COD.mg/1 - Effluent COD*, mg/l x 100
Influent COD, mg/l
KD = Ibs. VSS decay per day per Ib. VSS inventory
•Soluble COD, see Section IV, "LABORATORY CONTROL".
The following example calculations show the interrelationship of MCRT,
microorganism growth, and F/M,
How to
calculate MCRT.
Example Calculation
A. Data Required
1. F/M = 0.55 Ibs COD applied/day/lb MLVSS
2. Y = 0.35 Ibs VSS produced per Ib COD removed
3. KD = 0.05 Ibs decay perday/lb MLVSS
4. Eff. x COD removal efficiency x 90% (0.90)
5. MCRT = 8.1 days
6. Ynet = Net sludge yield = 0.249 Ibs VSS per Ib COD
removed/day
B. Determine the MCRT using kinetics.
1
MCRT, days =
(Y) (F/M) (eff) - KD
(0.35) (0.55) (0.90)-0.05
1 1
0.173-0.05
0.123
Q •*
= O. I
This indicates that an amount of VSS equal to the solids inventory must
be wasted from the process in a 8.1 day period to maintain a constant
MCRT.
11-17
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
How to
calculate Y as
a ratio.
How to
calculate Y as
%/day.
C. Determine the net sludge yield (net growth rate) expressed as a
ratio of Ibs VSS/!b COD removed/day.
Ynet, ratio =
1
(MCRT)(F/M)(Eff.)
1
(8.1) (0.55) (0.90)
= 0.249 Ibs VSS/lb COD removed/day
D. Determine the net sludge yield (net growth rate) expressed as
percent of the solids inventory (SI).
Ynet, %/day = (Ynet, ratio) (F/M)(Eff) (100%)
= (0,249) (0.55) (0.90) (100%)
= 12.3 % of solids inventory
OR
Ynet, %/day = [(Y) (F/M) (Eff)- KD] 100%
= [(0,35) (0.55) (0.90) - 0.05] 100%
= [0.173-0.05] 100%
= 12.3% of solids inventory
This indicates that about 12.3 percent of the solids inventory would have
to be wasted per day to maintain a constant MLVSS or F/M assuming that
other conditions are not changing significantly.
How to
calculate F/M
when MCRT, Y
and %
efficiency is
known.
Solids inventory
must always be
calculated
same way.
E. Determine the F/M when the MCRT, net sludge yield, and removal
efficiency are known.
F/M =
1
(MCRT) (Ynet) (Eff.)
1
(8.1) (0.249) (0.90)
= 0.55 Ibs COD applied/lb solids inventory
All the kinetic calculations must be based on the same solids in-
ventory—either the MLVSS under aeration or the total VSS in the*
activated sludge process.
11-18
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Approximate
relationship of
theMCRTtothe
F/M.
Table 11-3 presents the relationship of MCRT to F/M for two values of the Yield
coefficient.
TABLE 11-3
APPROXIMATE RELATIONSHIP OF THE
F/M TO THE MCRT
= 0.05 per day)
*F/M Range (COD)
MCRT
20
15
10
7.5
5
2.5
Y = 0.3
0.33
0.39
0.50
0.61
0.83
1.50
Y = 0.4
0.25
0.29
0.38
0.46
0.63
1.13
A similar table can be developed for the relationship of MCRT and F/M when
BOD is used instead of COD. A typical range of values for the Yield coefficient
for domestic wastewater on a BOD basis is 0.5 to 0.6 Ibs MLVSS produced per
Ib of BOD removed. The value of KD remains at 0.05 per day. Table II-4 presents
the relationship of the MCRT to the F/M for two values of the Yield coefficient:
TABLE II-4
APPROXIMATE RELATIONSHIP OF THE
F/M TO THE MCRT
= 0.05 per day)
* F/M Range (BOD)
MCRT
20
15
10
7.5
0.50
3
Y = 0.5
0.20
0.23
0.30
0.37
0.42
0.77
Y = 0.6
0.17
0.19
0.25
0.30
0.64
*F/M expressed as Ibs removed/day/lb VSS inventory. To express the F/M as
Ibs applied/day/lb VSS inventory, divide the F/M presented in the Table by
the removal efficiency (as %) of the treatment process.
11-19
-------
Some plants are
designed to
nitrify.
What
establishes
nitrification?
How does
nitrification
occur?
What achieves
nitrification?
What affects
nitrification?
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Nitrification
Many activated sludge processes are designed to attain a high degree of
nitrification. This section is devoted to evaluation of the process performance
based on nitrification.
The degree of nitrification that must be attained in the activated sludge
process is dictated by the maximum allowable limit of ammonia nitrogen
discharged with the final effluent. This limit is usually governed by the NPDES
permit issued by State or Federal regulatory agencies.
In fresh wastewater the nitrogen present predominates as organic nitrogen.
As the organic matter in the wastewater decomposes, a portion of the organic
nitrogen is converted to ammonia nitrogen. When the wastewater is suffi-
cienty aerated, nitrifying bacteria will convert the ammonia nitrogen to nitrite
nitrogen and subsequently to nitrate nitrogen. Nitrate represents the final
form of nitrogen resulting from the oxidation of nitrogenous compounds in
the wastewater. The nitrogen cycle is illustrated in Figure 11-2.
To achieve the desired degree of nitrification, the Mean Cell Residence Time
must be long enough (usually 10 days plus) to allow the nitrifying bacteria
sufficient time to convert nitrogenous compounds to nitrate nitrogen. Since
the nitrifying bacteria grow much slower than the bacteria utilizing the car-
bonaceous compounds, it is possible to waste the nitrifying bacteria from the
system at a higher rate than their growth rate.
The factors affecting the growth rate of the nitrifying bacteria are primarily,
DO, pH, temperature, and the availability of nitrogenous food.
The DO in the aeration tank must usually be 1.0 mg/l or greater when operating
the process to nitrify. Nitrification exerts a substantial oxygen requirement.
The oxygen requirement may be calculated as follows:
, oxidation = IbsNHa x 4.6 = 02 Ibs/day
The optimum pH range is 7.9 to 8.9; however, the range of 7.6 to 7.8 is recom-
mended in order to allow escape of the carbon dioxide to the atmosphere.
Theoretically, 7.1 Ibs of CaCOs alkalinity are destroyed per pound of ammonia
nitrogen oxidized, thus resulting in a decreasing pH within the aeration tank.
The optimum temperature range is 15° to 35° C. The growth rate of nitrifying
bacteria increases as the wastewater temperature increases and conversely
it decreases as the wastewater temperature decreases. Since there is no
control over the wastewater temperature, compensation for slower winter
growth rates by increasing the MCRT and maintaining the pH within the
recommended range must be made.
The growth rate of nitrifying bacteria is affected very little by the organic
load applied. However, the population of the nitrifying bacteria will be limited
by the amount of nitrogenous food available in the wastewater.
II-20
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
ORGANIC
NITROGEN,-NH3
AMMONIA
NITROGEN,NH4
X
il
Z
ui
C5
O
I
ATMOSPHERIC
NITROGEN, N2
T
<
o
Ul
NITRATE
NITROGEN,
GO
O
DC
UJ
NITRITE
NITROGEN, NO2
SOLID LINES SHOW IMPORTANT PATHWAYS IN THE BIOLOGICAL
TREATMENT O-F WASTEWATER. THE BROKEN LINE FOR
NITROGEN FIXATION IS ONLY ADDED TO COMPLETE THE CYCLE.
APPROXIMATELY 60 TO 80% OF THE NITROGEN IN RAW DOMESTIC
WASTEWATER IS IN THE FORM OF AMMONIA NITROGEN. THE
REST IS PRIMARILY IN THE FORM OF ORGANIC NITROGEN.
WASTEWATER NITROGEN CYCLE
FIGURE 11-2
11-21
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Considerations
for
nitrification.
When reviewing the performance of the activated sludge process for the
selection of an optimum F/M ratio; MCRT or Gould Sludge Age must be
considered along with nitrification requirements. These parameters should
be selected to provide the degree of nitrification required by the discharge
permit. IF the ammonia nitrogen limit is being exceeded, the MCRT or Gould
Sludge Age should be increased. Increasing these parameters will increase
the MLVSS and consequently decrease the F/M ratio. With the other condi-
tions constant, a definite relationship will exist between the weight ratio of
the ammonia nitrogen oxidized per day to the MLVSS under aeration.
The growth of cell mass from the oxidation of ammonia is about 0.05 Ibs per
Ib of ammonia nitrogen oxidized. As a result the degree of nitrification will
have little effect on the next sludge yield and WAS rates.
Clariflers serve
a dual
purpose.
How to
calculate
surface
overflow rate.
Secondary Clarifiers
Clarifiers in the activated sludge process serve a dual purpose. They must
provide a clarified effluent and a concentrated source of return sludge for
maintaining process control. Adequate area and depth is essential to allow
the aeration tank effluent (MLSS) to settle and compact without carry over of
solids in the clarified effluent. To prevent solids carry over, secondary Clari-
fiers are designed to be operated within given parameters. These parameters
include the surface overflow rate (gpd/sq. ft.) and solids loading rate (Ibs
solids/day/sq. ft.). Typical ranges for these parameters are presented in Table
11-5.
TABLE 11-5*
TYPICAL DESIGN PARAMETERS FOR SECONDARY CLARIFIERS
Process
Variation
High rate
Conventional and
Sludge Reaeration
Extended Aeration
Surface Overflow
Rate
gpd/sq ft
Average
400-800
200-400
Peak
1,000-1,200
800
Solids
Loading 1
Ib solids/day/sq ft
Average
20-30
20-30
Peak
50
50
Depth
ft
12-15
12-15
"•Allowable solids loadings are generally governed by sludge settling characteristics
associated with cold weather operations.
* Source: "Design Manual for Upgrading Existing Wastewater Treatment Facilities",
EPA Technology Transfer, 1974.
I-22
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Importance of
hydraulic
loading on
sedimentation
units.
Surface Overflow Rate
The surface overflow rate is the parameter commonly used to measure
the hydraulic loading on the secondary clarifier. The surface overflow rate
is expressed as gallons waste flow per day per square foot of surface area
(gpd/sq. ft.). The surface overflow rate is directly related to the clarifier's
ability to effectively allow solids to settle. Normally, if the surface over-
flow rate is within the design range, it can be assumed that the detention
time and weir overflow rates are also within the design range. However,
consideration should be given to flow distribution which can cause short
circuiting of flow through the unit.
The surface overflow rate is determined as shown below:
Example Calculation
A. Data Required
1. Q, Peak hour wastewater flow, gpd = 4,300,000
2. Surface area of clarifier, sq.ft. = 4415
B. Determine the surface overflow rate.
n
Surface overflow Rate, gpd/sq. ft. =
Surface Area, sq.ft.
_ 4,300,000
4415
= 974
Excessive
solids
loadings may
contribute to
wash out
problems.
Solids Loading Rate
Secondary clarifiers in the activated sludge process must be designed and
operated not only for the surface overflow rates but also for solids loading
rates. This is due mainly for settling and compaction of the MLSS which
enters the clarifier. When excessive MLSS concentrations are maintained
in the process, the ability of the clarifier to compact the solids becomes
the governing factor. Therefore solids loading rates on the clarifier be-
come more critical, especially during sudden changes in flow rates which
result in clarifier solids wash out. For this reason, the operator should
periodically check the solids loading rate on the clarifier.
II-23
-------
DO above
1.0
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
The solids loading rate is determined as shown below;
Example Calculation
A. Data Required
1. Q, Peak hour wastewater flow, mgd = 4.3
2. QRAS, RAS flow rate, mgd = 1.3
3. M LSS concentration, mg/l = 2900
4. Surface area of clarifier, sq. ft. = 4415
B. Determine solids loading rate.
Ibssolids/day/sq.ft. = jJLLQRAS)(MLSS)(8j4lb8/ga.)
Surface Area, sq. ft.
_ (4.3 + 1.3) (2900) (8.34)
4415
4415
= 23.5
Select
operating
parameters for
best
performance
with least cost.
2.04 PROCESS CONTROL
Control of the activated sludge process consist of reviewing operating data
and lab test results to select the proper operational parameters (such as F/M,
MCRT, Gould Sludge Age, MLSS concentrations, and sludge quality in relation
to RAS and WAS control rates) that provide the best performance at the least
cost. The plant operator must be both cost-conscious and concerned with the
conservation of power as well as the production of an effluent that will meet
discharge requirements. For example, to conserve power and minimize oper-
ational costs, the operator should select and utilize the control parameters
which will provide the required performance so as not to reduce the quality of
activated sludge and subsequently the quality of secondary effluent.
Proper D.O.
levels.
Frequency of
D.O. monitoring.
Aeration and D.O. Control
The D.O. concentration in the aeration tank should normally be maintained
between 1.0 and 3.0 mg/l. It is believed that a D.O. concentration greater than
1.0 mg/l should be maintained in the aeration tank at all times to get adequate
mixing and microorganism activity. If nitrification is required and the D.O.
concentration is allowed to drop below 1.0 mg/l, nitrifying microorganisms
will become less active and may possible die off. Conversely, overaeration
may result in the breakup of the MLSS floe particles which will appear on the
secondary clarifier surface.
It is very important that the operator monitor the aeration tank D.O. levels and
air flow rates periodically (every 2 hours is suggested) to make appropriate air
rate adjustments as required. If D.O. monitoring instrumentation is provided,
it is imperative that it be properly maintained and calibrated to provide values
that are valid and reliable.
11-24
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Effect of
excessive air
rates.
Since the power costs for operating the activated sludge process are high,
excessive air rates are not only wasteful but also expensive and may result in
poor sludge settling characteristics in the secondary clarifiers.
The concentration of D.O. in the mixed liquor must be sufficient to ensure
that oxygen is available for the microorganisms. When oxygen limits the
growth of the microorganisms, the settleability and quality of the activated
sludge may be poor. Poor sludge settling has been associated with D.O. con-
centrations below 0.5 mg/l in the aeration basin. Procedures for monitoring
and maintaining aeration and D.O. control are presented in Table 11-6 The
operator may develop detailed standard operating procedures (SOP) for his
plant by utilizing this table.
Need well
settling MLSS
to return to the
mixed liquor.
Return Activated Sludge Control
To properly operate the activated sludge process, a good settling mixed liquor
must be achieved and maintained. The MLSS are settled in a clarifier, and
then returned to the aeration tank as the Return Activated Sludge (RAS). The
RAS makes it possible for the microorganisms to be in the treatment system
longer than the flowing wastewater. For conventional activated sludge oper-
ations, the RAS flow is generally about 20 to 40 percent of the incoming
wastewater flow. Changes in the activated sludge quality will require different
RAS flow rates due to settling characteristics of the sludge. Table 11-7 shows
typical ranges of RAS flow rates for some activated sludge process variations.
TABLE 11-7
A GUIDE TO TYPICAL RAS FLOW RATE PERCENTAGES
(Ref: Recommended Standards for Sewage Works, p. 82)
RAS flow rate as % of incoming wastewater
flow to aeration tank
Type of Activated
Sludge Process
Conventional
Modified or "high rate"
Step feed
Contact stabilization
Extended aeration
Average Lower Limit Upper Limit
30
20
50
100
100
15
10
20
50
50
75
50
75
150
200
Basic concepts
for RAS control.
There are two basic approaches that can be used to control the RAS flow rate.
These approaches are based on the following:
1) Controlling the RAS flow rate independently from the influent flow.
2) Controlling the RAS flow rate as a constant percentage of the influent
flow.
II-25
-------
TABLE 11-6
STANDARD OPERATING PROCEDURES
AERATION AND D,0, CONTROL
PROCEDURE
CHECK D.O.
LEVEL
CHECK UNIFORMITY
OF AERATION
PATTERN IN
AERATION
TANK
CHECK AIR
REQUIREMENT
(DIFFUSED
AERATION)
CHECK AIR REQUIRE-
MENT (MECHANICAL
AERATION)
FREQUENCY
EVERY
2 HOURS
DAILY
DAILY
MONTHLY
METHOD
D.O. METER
IODOMETRIC
METHOD*
VISUAL
OBSERVATIONS
CALCULATION
SCF/LB COD OR
LB BOD REMOVED
CALCULATION
LBS 02/LB
COD OR LB BOD
REMOVED
RANGE
NORMALLY
1 TO 3 mg/1
UNIFORM MIXING &
ROLL PATTERN, &
AIR BUBBLE
DISBURSEMENT
SEE TABLE II-2
SEE TABLE II-2
CONDITION
HIGH
SATISFACTORY
LOW
DEAD SPOTS
UNEVEN ROLL
PATTERN
LOCALIZED BOILING
HIGH
SATISFACTORY
LOW
HIGH
SATISFACTORY
LOW
PROBABLE CAUSE
TOO MUCH AERATION
TOO LITTLE AERATION
IMPROPER DISTRIBUTION
OF AIR
IMPROPER DISTRIBUTION
OF AIR
DIFFUSER MALFUNCTION
POOR 02 TRANSFER
OR NITRIFICATION
INACCURATE D.O., COD,
OR BOD MEASUREMENT
LOW LOADING
HIGH LOADING,
INSUFFICIENT AERATION
CAPACITY
RESPONSE
DECREASE AERATION
CONTINUE MONITORING
INCREASE AERATION
PERFORM D.O. PROFILES
AND BALANCE AIR
DISTRIBUTION WITH
HEADER VALVES
PULL AND CHECK FOR
PLUGGED DIFFUSERS
CHECK UNIFORMITY OF AERATION
CHECK FOR NITRIFICATION
CONTINUE MONITORING
RECALIBRATE D.O. METER
CHECK LAB ANALYSIS
REDUCE NUMBER OF UNITS
IN OPERATION— CHECK FOR
ADEQUATE MIXING.
IMPROVE PRIMARY TREATMENT
INCREASE NUMBER OF UNITS
IN OPERATION
COPPER SULFATE-SULFAMIC ACID FLOCCULATION MODIFICATION
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Constant RAS Flow Rate Control
Effect of
constant RAS
on MLSS.
Effect of
constant RAS
on sludge
blanket depth.
Setting the RAS at a constant flow rate that is independent of the aeration
tank influent wastewater flow rate results in a continuously varying MLSS
concentration will be at a minimum during peak influent flows and a
maximum during minimum influent flows. This occurs because the MLSS
are flowing into the clarifier at a higher rate during peak flow when they
are being removed at a constant rate. Similarly, at minimum influent flow
rates, the MLSS are being returned to the aeration tank at a higher rate
than trfey are flowing into the clarifier. The aeration tank and the sec-
ondary clarifier must be looked at as a system where the MLSS are stored
in the aeration tank during minimum wastewater flow and then trans-
ferred to the clarifier as the wastewater flows initially increase. In essence,
the clarifier acts as a storage reservoir for the M LSS, and the clarifier has
a constantly changing depth of sludge blanket as the MLSS moves from
the aeration tank to the clarifier and vice versa. The advantage of using
this approach is simplicity, because it minimizes the amount of effort for
control. It is also especially advantageous for small plants because of
limited flexibility.
Constant %
more complex.
Effect of flow
proportional
RAS control
on MLSS.
Constant RAS
advantages.
Constant
percentage
RAS
advantages.
Disadvantage.
Constant Percentage RAS Flow Rate Control
The second approach to controlling RAS flow rate requires a programmed
method for maintaining a constant percentage of the aeration tank influent
wastewater flow rate. The program may consist of an automatic flow
measurement device, a programmed system, or frequent manual adjust-
ments. The programmed method is designed to keep the MLSS more
constant through high and low flow periods.
Comparison of Both RAS Control Approaches
The advantages of the constant RAS flow approach are the following:
1) Simplicity.
2) Maximum solids loading on the clarifier occurs at the initial start
of peak flow periods.
3) Requires less operational time.
The advantages of the constant percentage RAS flow are the following:
1) Variations in the MLSS concentration are reduced and the F/M
varies less.
2) The MLSS will remain in the clarifier for shorter time periods,
which may reduce the possibility of denitrification in the clarifier.
A disadvantage of using the constant flow approach is that the F/M is
constantly changing. The range of F/M fluctuation due to the effect of
short term variation in the MLSS (because of hydraulic loading) is generally
small enough that no significant problems arise due to using the constant
flow approach.
Disadvantage
of flow
proportional
RAS control.
The most significant disadvantage of the second approach is that the
clarifier is subjected to maximum solids loading when the clarifier con-
tains the maximum amount of sludge. This may result in solids washout
with the effluent.
II-27
-------
ro
oo
TABLE 11-8
STANDARD OPERATING PROCEDURES
RAS CONTROL
PROCESS
COMPLETE
MIX OR
PLUG FLOW
REAERATION
t
CONTROL
METHOD
CONSTANT FLOW
CONSTANT %
OF INFLUENT
FLOW
CONSTANT %
OF INFLUENT
FLOW
CONTROL BY
SLUDGE
BLANKET
LEVEL
CONSTANT %
OF FLOW
MODE OF
OPERATION
MANUAL
MANUAL
AUTOMATIC
AUTOMATIC
AUTOMATIC
WHAT TO
CHECK
SLUDGE BLANKET
% OF INFLUENT
FLOW
SLUDGE BLANKET
SLUDGE BLANKET
SLUDGE BLANKET
RATIO OF
MLSS/RASSS
(CENTRIFUGE
TEST)
FREQUENCY OF
ADJUSTMENT
DAILY
2 HRS
DAILY
DAILY
DAILY
EVERY 2 HRS
WHEN TO
CHECK
EVERY 8 HOURS
EVERY 2 HRS
EVERY 8 HRS
EVERY 8 HRS
EVERY 8 HRS
EVERY 2 HRS
CONDITION
HIGH
SATISFACTORY
LOW
HIGH
SATISFACTORY
LOW
HIGH
SATISFACTORY
LOW
HIGH
SATISFACTORY
LOW
HIGH OR LOW
SATISFACTORY
HIGH RATIO
SATISFACTORY
LOW RATIO
PROBABLE
CAUSE
LOW RAS RATE
HIGH RAS RATE
VARIATIONS
IN DAILY
INFLUENT
FLOW
% OF FLOW
TOO LOW
* OF FLOW
TOO HIGH
% OF FLOW
TOO LOW
% OF FLOW
TOO HIGH
CONTROLLER
MALFUNCTION
RETURN TOO
HIGH
RETURN TOO
LOW
RESPONSE
INCREASE RETURN
CONTINUE MONITORING
DECREASE RETURN
ADJUST TO DESIRED
% OF INFLUENT FLOW
INCREASE % OF FLOW
CONTINUE MONITORING
DECREASE % OF FLOW
INCREASE % OF FLOW
CONTINUE MONITORING
DECREASE % OF FLOW
FIX CONTROLLER OR
MANUALLY ADJUST
ACCORDINGLY
CONTINUE MONITORING
DECREASE RETURN
CONTINUE MONITORING
INCREASE RETURN
o
= o
TJ V>
33 Ł
O 3)
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Smaller plants
benefit from
constant RAS.
How to develop
standard
operating
procedures.
In general, it appears that most activated sludge operations perform well
and require less attention when the constant RAS flow rate approach is
used. Activated sludge plants with flows of 10 mgd or less are often
subject to large hydraulic surges, and performance of these plants will
benefit the most from the use of this approach.
Procedures for monitoring and maintaining RAS flow rates are presented
in Table II-8. The operator may develop detailed standard operating
procedures (SOP) for his plant by utilizing this table.
Methods of RAS Flow Rate Control
Common
approaches for
RAS control.
For either RAS flow rate control approaches discussed above, there are a
number of techniques which may be used to set the rate of sludge return
flow. The most commonly used techniques are listed below:
1) Monitoring the depth of the sludge blanket.
2) Mass balance approach.
3) Settleability approach.
4) SVI approach.
The best
method-measure
blanket depth
in clarifler.
Increasing
blanket-solution
on Short Term is
to Increase RAS
but Long Term
Is to decrease
solids Inventory
by wasting.
Measurements
same time each
day-during
maximum flow.
Sludge Blanket Depth
Monitoring the depth of the sludge blanket in the clarifier is the most
direct method available for determining the RAS flow rate. The sludge
blanket depth and uniformity may be checked routinely by the methods
described in Section IV, "LABORATORY CONTROL." The blanket depth
should be kept to less than one-fourth of the clarifier sidewall water depth.
The operator must check the blanket depth on a routine basis, making
adjustments in the RAS to control the blanket depth.
If it is observed that the depth of the sludge blanket is increasing, how-
ever, an increase in the RAS flow can only solve the problem on a short
term basis. Increases in sludge blanket depth may^tesult from having too
much activated sludge in the treatment system, and/or because of a
poorly settling sludge. Long-term corrections must be made that will
improve the settling characteristics of the sludge or remove the excess
solids from the treatment system. If the^sludge is settling poorly, in-
creasing the RAS flow may even cause more problems by further increasing
the flow through the clarifier. If the sludge is settling poorly due to bulking,
the environmental conditions for the microorganisms must be improved.
If there is too much activated sludge in the treatment system, the excess
sludge must be wasted.
Measurements of the sludge blanket depth in the clarifier should be made
at the same time each day. The best time to make these measurements is
during the period of maximum daily flow, because the clarifier is operating
under the highest solids loading rate. The sludge blanket should be
measured daily, and adjustments to the RAS rate can be made as neces-
sary. Adjustments in the RAS flow rate should only be needed occasionally
if the activated sludge process is operating properly.
II-29
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Blanket depth
points out
sludge
collection
system
malfunctions.
An additional advantage of monitoring the sludge blanket depth is that
problems, such as improperly operating sludge collection equipment, will
be observed due to irregularities in the blanket depth, A plugged pickup
on a clarifier sludge collection system would cause sludge depth to
increase in the area of the pickup, and decrease in the areas where the
properly operating pickups are located. These irregularities in sludge
blanket depth are easily monitored by measuring profiles of blanket depth
across the clarifier with the methods and equipment discussed in Section
IV, "LABORATORY CONTROL"
Constant
blanket level.
Can estimate
HAS flow from
MLVSS/RAS
ratio.
Basis of a
mass balance.
Mass Balance Approach
The mass balance approach is a useful tool for calculating the RAS flow
rate; however, it does assume that the level of the sludge blanket in the
clarifier is constant.
A side benefit of the mass balance approach to RAS flow rate control is
that in plants without functioning RAS flow meters, the RAS flow can be
estimated from the measured MLSS to RASss concentration relationships.
The calculations used in this approach are based on a mass balance
performed on the suspended matter in the activated sludge process. A
mass balance is performed by accounting for all of the suspended matter
that enter and leave the process. A typical mass balance around an aera-
tion tank is shown in Figure 11-3.
CLARIFIER
Q
AERATION TANK
MLSS
RETURN SLUDGE FLOW, R
RAS
JSS
AERATION TANK MASS BALANCE
FIGURE II-3
11-30
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Example Calculation
A. Data Required
1. Q, influent wastewater flow, mgd = 7.5
2. MLSS concentration, mg/l = 2000
3. RASss Return Sludge concentration, mg/l = 7500
B. Determine RAS flow rate based on MLSS to RAS ratio.
QRAS, mgd = Q x MLSS
RASss-MLSS
7.5 x 2000
7500 - 2000
_ 15,000
5500
= 2.7 or
= —— x 100 = 32% of influent flow rate
7.5
Settleability Approach
what is sludge Another method of calculating the RAS flow rate is based on the result
settieabinty? of tne 30.minute settling test. Settleability is defined as the percentage of
volume occupied by the sludge after settling for 30 minutes.
Howl8|t If after 30 minutes of settling, the final sludge volume were 275 ml in a one
determined? liter graduate, the RAS flow rate would be calculated as follows:
Example Calculation
A. Data Required
1. Q, influent wastewater flow, mgd = 7.5
2. SV, sludge settling volume in 30 minutes, ml/I = 275
11-31
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
B. Determine RAS flow rate based on 30-minute sludge settleability
test.
QRAS,mgd= ^ x 100
1000-SV
275 x 100
1000-275
275
725
x 100
= 37.9 or 38% of influent flow rate
Thus,
QRAS, mgd = -38 x 7-5
= 2.8
Figure II—4 can be used to calculate the RAS flow as a percentage of the
influent flow. All the operator does is determine the SV ml/l at 30-minutes
and then read the R/Q off of the vertical axis. To calculate the QRAS.
multiply the R/Q term by Q.
The settleability method is somewhat less accurate than the solids
balance approach, as it suffers from the assumption that measurements
Limited value. made wjtn a |aboratory settling cylinder will model the settling in a clarif ier.
This assumption will seldom (if ever) be true because of the effects of the
cylinder walls and the quiescent nature of the liquid in the cylinder.
Some operators have found that gently stirring (1-2 rpm) the sludge during
the settling test reduces these problems.
II-32
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
100
80
R. = SV x 100%
Q 1000 - SV .
60
40
20
-------
ACTIVATED SLUDGE PROCESS
SECTION li-PROCESS CONTROL
SVI Approach
To determine the RAS flow rate using the Sludge Volume Index (SVI), it is
necessary to combine the mass balance and settleability approach. This
method is subject to the same limitations as the settleability method.
This method is based on using the SVI to estimate the suspended solids
concentration in the RAS. This value for RASss js then used in a mass
balance to determine the RAS flow rate. The RAS flow rate may be deter-
mined as follows:
Example Calculation
A. Data Required
1. SVI = 120
2. Q, Influent Wastewater flow, mgd = 7.5
3. MLSS concentration, mg/l = 2000
B. Determine RASss concentration based on SVI.
RASss. mg/l =1-000.°QO
SVi
_ 1,000,000
120
= 8333
C. Determine RAS flow rate based on SVI
Q x MLSS
QRAS, mgd =
RASss-MLSS
_ 7.5 x 2000
8333 - 2000
_ 15,000
6333
= 2.4 or
Value of SVI
is a process
stability
Indicator — Not
for RAS
calculations.
7.5
x 100 = 32% of influent flow rate
NOTE: The SVI value was chosen to make the calculated RAS flows
similar to those calculated in the previous examples.
The real value in the SVI is not in calculating the RAS flow, but in its
use as a process stability indicator. Changes in the SVI at constant -
MLSS are more important than the SVI value. Never be concerned
about comparing the SVI of different treatment plants, because the
SVI value that indicates good operation in one plant may not neces-
sarily apply to good operation in other plants.
II-34
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
HAS rates are
more significant
with separate
sludge
reaeration.
Return Rates with Separate Sludge Reaeration
In the sludge reaeration variation of the activated sludge process, the return
sludge rate is much more significant. This is true because the rate of return
directly affects the ratio of sludge concentration between the contact portion
of the process and the stabilization or reaeration portion. Refer to Activated
Sludge with Sludge Reaeration in Section III, "FUNDAMENTALS", for more
information. Consideration of the ratio of sludge concentration between
these two portions must be coordinated with the mass balance control
method of setting the return rates. Generally, a higher rate of return will shift
solids from the stabilization portion of the process to the contact portion of
the process. Adequate theory for making rational adjustments of the contact/
stabilization ratio are just becoming available, and, at this point, the operator
must depend on crude rules of thumb or on his own operating experience to
determine which levels are appropriate. These rules of thumb include the
following:
• The SS concentration in the reaeration portion will eventually equal
the RASss- Therefore, the RAS flow rate should be controlled on the
basis of maintaining the desired SS concentration in the reaeration
portion of the process.
• The contact portion SS concentration may be determined by the fol-
lowing formula:
Contact MLSS,mg/l = (QRAS)(RASSS, mg/l)
Q + QRAS
• QRAS may be determined by the following formula:
(Q)(MLSS, mg/l)
QRAS =
RASss, mg/l - MLSS, mg/l
If the SVI remains constant or begins to drop, it indicates that the
solids inventory in the process may be to high and wasting should be
increased. If the SVI increases in conjunction with a rising sludge
blanket in the clarifier, sludge bulking may occur. Sludge wasting
should be increased.
Waste Activated Sludge Control
Activated
sludge is
controlled by
WAS.
The activated sludge process is basically controlled by the amount of activated
sludge that is wasted. The amount of waste activated sludge (WAS) removed
from the process effects all the following:
• Effluent quality
• The growth rate of the microorganism
• Oxygen consumption
• Mixed liquor settleability
• Nutrient quantities needed
• The occurrence of foaming/frothing
• The possibility of nitrifying
11-35
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
WAS Is used
to maintain
a desired
growth rate.
Attempt to
maintain
steady-state.
The objective of wasting activated sludge Is to maintain a balance between
the microorganisms and the amount of food such as COD and BOD. It is known
that when the microorganisms remove BOD from wastewater, the amount
of activated sludge increases (microorganisms grow and multiply). The rate at
which these microorganisms grow is called the growth rate and is defined as
the increase in the amount of activated sludge that takes place in one day.
The objective of sludge wasting is to remove just that amount of micro-
organisms that grow. When this is done the amount of activated sludge formed
by the microorganism growth is just balanced by that which Is removed from
the process. This therefore allows the total amount of activated sludge In the
process to remain somewhat constant. This condition Is called "steady-state"
which is a desirable condition for operation. However, "steady-state" can
only be approximated because of the variations in the nature and quantity of
the food supply (BOD) and of the microorganism population. It is the objective
of process control to approach a particular "steady-state" by controlling any
one or a combination of the following control parameters:
» MCRT
• F/M
* Gould Sludge Age
• Volatile solids Inventory
• MLVSS concentration
• Sludge Quality Control
The best mode of process control will produce a high quality effluent with
consistent treatment at a minimal cost.
Wasting of the activated sludge is normally done by removing a portion of the
WAS is normally RAS flow. The waste activated sludge is either pumped to thickening facilities
a portion of RAS. ancj ^en {O a digester, or to the primary clariflers where it Is pumped to a
digester with the raw sludge. Procedures for making WAS adjustments are
presented In Table II-9 which the operator may use to develop an SOP
An alternate method for wasting sludge is from the mixed liquor in the aeration
tank. There is much higher concentration of suspended matter in the PAS
than there is in the mixed liquor. Therefore, when wasting is practiced from
Alternate tor the mixed liquor larger sludge handling facilities are required. Wasting from
wasting sludge, the RAS takes advantage of the gravity settling and thickening of the sludge
that occurs in the secondary clarifier. However, wasting from the mixed liquor
has the advantage of not wasting excessive amounts of sludge because of
the large quantity of sludge Involved. The extra security of wasting from the
mixed liquor should not be underestimated. Unfortunately, many plants do
not have the flexibility to waste from the mixed liquor nor are there sufficient
sludge handling facilities to handle the more dilute sludge.
Wasting on
intermittent or
continuous
basis.
Methods of Sludge Wasting
Wasting of the activated sludge can be done on an intermittent or con-,
tinous basis. The intermittent wasting of sludge means that wasting is
conducted on a batch basis from day to day.
11-36
-------
TABLE 11-9
STANDARD OPERATING PROCEDURES FOR WAS CONTROL
METHOD OF
CONTROL
CONSTANT
F/M
CONSTANT
MLVSS
CONSTANT
MCRT
CONSTANT
GOULD
SLUDGE
AGE
PROCESS
OPERATION
HIGH RATE
CONVENTIONAL
RATE
EXTENDED
AERATION
HIGH RATE
CONVENTIONAL
RATE
EXTENDED
AERATION
HIGH RATE
CONVENTIONAL
RATE
EXTENDED
AERATION
HIGH RATE
CONVENTIONAL
RATE
EXTENDED
AERATION
WHAT TO
CHECK
MLVSS &
INFLUENT
COD
MLVSS &
INFLUENT
COD OR
BOD
MLSS,
WASSS,
%IAS ,»
EFFLSS
INFLUENT
SS,J MLSS
WHEN TO
CHECK
DAILY
DAILY
DAILY
DAILY
CALCULATIONS
F/M BASED ON-
5 DAY AVG. COD
5 DAY AVG. MLVSS
VOLATILE
SOLIDS
INVENTORY
5 DAY AVG
SOLIDS INVENTORY
5 DAY AVERAGE OF
SOLIDS IN WAS
5 DAY AVERAGE OF
SOLIDS IN EFFLUENT
5 DAY AVG OF
SS INVENTORY &
SS IN INFLUENT
FREQUENCY OF
ADJUSTMENT
DAILY
DAILY
DAILY
DAILY
CONDITIONS
ACTUAL F/M:
HIGH
SATISFACTORY
LOW
ACTUAL
MLVSS:
HIGH
SATISFACTORY
LOW
ACTUAL MCRT:
HIGH
SATISFACTORY
LOW
ACTUAL GSA:
HIGH
SATISFACTORY
LOW
PROBABLE
CAUSE
EXCESSIVE
WASTING
INSUFFICIENT
WASTING
INSUFFICIENT
WASTING
EXCESSIVE
WASTING
INSUFFICIENT
WASTING
EXCESSIVE
HASTING
INSUFFICIENT
WASTING
EXCESSIVE
WASTING
RESPONSE*
REDUCE WAS
INCREASE
WAS
INCREASE
WAS
REDUCE WAS
INCREASE
WAS
REDUCE WAS
INCREASE
WAS
REDUCE WAS
Response - Calculations should be made to determine the WAS rate. However, when increasing or
decreasing daily WAS rates, any changes should not exceed 10 to 15 percent of the previous day's
WAS rate. This is necessary to allow the process to stabilize.
w
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qq
P<
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I-
-------
How to
calculate daily
QWAS
adjustments.
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
If wasting is done from the RAS, the operator must measure the volatile
suspended matter in the HAS to obtain average concentrations. If the
volatile content in the RAS concentration is decreasing, the WAS flow rate
must be increased proportionally to waste the proper amount of VSS.
Similarly, if there is an increase in the RAS volatile content, the WAS flow
rate must be decreased proportionally.
When continuous wasting is practiced, the operator should check the
RASvsS at least once every shift and make the appropriate QwAS adjust-
ment.
Example Calculation
A. Data Required
1. QwAS> Current waste sludge flow rate, mgd = 0.05
2. RASVSS1 Concentration first day, mg/l = 6000
3. RASVSS2 Concentration second day, mg/l = 7500
B. Determine the adjusted WAS flow rate based on RASvsS increase
from 6000 to 7500 mg/l.
QWAS, mgd adjusted = RASvSS1 x QwAS
RASVSS2
How to
calculate QWAS
for intermittent
wasting.
6000
X 0.05
7500
= 0.80 x 0.05
= 0.04
When intermittent wasting is practiced the operator must check the
RASvsS t° calculate the necessary QwAS- ln addition this calculation
must be readjusted for the reduced time of wasting.
Example Calculation
A. Data Required
1. QwAS, adJusted from above, mgd = 0.04
2. P, Selected wasting period, hrs/day = 4
B. Determine the WAS flow rate for the four hour wasting period.
QWAS, mgd @ 4 hours = 24hrs/day.x QWASj adjusted
Pi hrs/day
24
x 0.04
= 6 x 0.04
= 0.24
1-38
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Less variation in
the SS during
the wasting
period with
Intermittent
wasting.
Must allow lor
SS In the
effluent.
Especially
important if
high effluent SS.
Five techniques
of control.
The operator would repeat the QwAS calculation for each wasting period
to take into account the RASyss variations.
Intermittent wasting of sludge has the advantage that less variation in the
suspended matter concentration will occur during the wasting period,
and the amount of sludge wasted will be more accurately known. The
disadvantages of intermitttent wasting are that the sludge handling facili-
ties in the treated plant may be loaded at a higher hydraulic loading rate
and that the activated sludge process is out of balance for a period of time
until the microorganisms regrow to replace those wasted over the shorter
period of time.
In using either of these methods for wasting, the operator does not have
complete control of the amount of activated sludge wasted due to the
solids lost in the effluent. This "wasting" of activated sludge in the effluent
must be accounted for with any method of process control or the system
will always be slightly out of balance. The loss of activated sludge in the
effluent generally accounts for less than five percent of the total solids
that need to be wasted; however, it is necessary to be aware of this loss
and to be able to take it into account by the methods shown in the con-
stant MCRT control section. The need for taking into account the solids
lost in the effluent is especially important if one encounters situations
where large concentrations of SS are washed out in the secondary effluent.
Proper control of the WAS will produce a high quality effluent with mini-
mum operational difficulties. There are five techniques that are commonly
used for controlling the WAS. These techniques are listed below in the
order of their frequency of use in this country.
Frequency of Use*
1. Constant MLVSS Control
2. Constant Gould Sludge Age Control
3. Constant F/M Control
4. Constant MCRT Control
5. Sludge Quality Control
*Developed on the basis of those treatment plants which were visited
during development of the manual.
Constant MLVSS Control
This technique for process control is used by many operators because it
is simple to understand and involves a minimum amount of laboratory
control. The MLVSS control technique usually produces good quality
effluent as long as the incoming wastewater characteristics are fairly
constant with minimal variations in influent flow rates.
With this technique, the operator tries to maintain a constant MLVSS
concentration in the aeration tank to treat the incoming wastewater
organic load. To put it in simple terms, if it is found that a MLVSS concen-
tration of 2000 mg/l produces a good quality effluent, the operator must
II-39
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
waste sludge from the process to maintain that concentration. If the
MLVSS level increases above the desired concentration, more sludge is
wasted until the desired level is reached again.
The laboratory control tests and operational data involved in using this
technique include the following:
• MLVSS concentration
• RASVSS concentration
• Influent wastewater flow rate
• Volume of aeration tank
Whether a new plant is being started or the operation of an existing plant
is being checked, this control technique is used to indicate when activated
sludge should be wasted. In most cases it is not the most reliable tech-
nique because it ignores process variables such as F/M and microorganism
growth rate necessary for maintaining optimum system balance. When
operational problems occur the operator is unable to make rational pro-
cess adjustments due to the lack of process control data.
The control technique is implemented by choosing an MLVSS concentra-
tion which produces the highest quality effluent while maintaining a
stable and economical operation. WAS flow rates are determined as follows:
Example Calculation
A. Data Required
*1. Sl-|, Desired solids inventory in aeration tank, Ibs = 20,016
*2. Sl2, Current solids inventory in aeration tank, Ibs = 21,716
3. RAS concentration, mg/l = 6200
B. Determine sludge to be wasted per day from RAS system.
Sl2-SI-|
QWAS, mgd =
RAS x 8.34 Ibs/gal
_ 21,716-20,016
6200 x 8.34
1700
51,708
= .032
* Refer to Section 2.03 for solids inventory calculations in aeration tank.
II-40
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Constant Gould Sludge Age Control
The concept of sludge age is based on the ratio of the Ibs/day of influent
wastewater suspended matter to the solids inventory in the aeration tank.
Gould first developed the sludge age for use in the Tallmans Island Treat-
ment Plant in New York City. Thus, sludge age is also known as the
Gould Sludge Age (GSA) and it should not be confused with the MCRT.
The GSA is based on the assumption that the ratio between the BOD and
suspended matter is fairly constant in the wastewater. Difficulties are
commonly experienced using the GSA control technique when the BOD
to solids ratio in the wastewater changes. The GSA ranges from 3 to 8
days in most activated sludge plants. The control technique is accomplished
by wasting sludge to maintain a constant GSA which produces the best
effluent quality. It is determined as follows:
Example Calculation
A. Data Required
1. Influent wastewater or primary effluent suspended matter
concentration, mg/l = 100
2. Q, Influent or primary effluent flow rate, mgd = 7.5
*3. SI, solids inventory in aeration tank, Ibs = 20,016
B. Determine Gould Sludge Age in days.
SI
GSA, days =
(pri. effl. mg/l) (Q mg/l) (8.34 Ibs/gal)
20,016
(100) (7.5) (8.34)
_ 20,016
6255
= 3.2
11-41
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
WAS flow rate using the GSA control technique is determined as follows;
Example Calculation
A. Date Required
1. Desired GSA, day = 5
2. Influent or primary effluent suspended matter, Ibs per day
(from above calculation) = 6255
*3. SI, Solids inventory in aeration tank, Ibs = 33,075
4. RASsS concentration, mg/I = 6300
B. Determine desired pounds of MLSS to be maintained in aeration
tank at a 5 day GSA.
MLSS, Ibs desired = GAS x Pri. eff I., Ibs/day
= 5 x 6255
= 31,275
C, Determine WAS flow rate to maintain desired GSA.
SL-MLSS desired
QWAS, mgd =
RAS x 8.34 Ibs/gal
_ 33,075-31.275
6300 X 8.34
1800
52,542
= .034
*Refer to Section 2.03.
Constant F/M Control
Constant F/M control is used to ensure that the activated sludge process
is beina loaded at a rate that the microorganisms in the MLSS are able to
utilize most of the food supply in the wastewater being treated. If too
much or too little food is applied for the amount of microorganisms,
operating problems may occur and the effluent quality may degrade.
Food measured
by COD or BOD. There are four things that should be remembered about the F/M.
1. The food concentration is estimated with the COD (or BOD) tests.
The oxygen demand tests provide crude but reliable approxima-
tions of the actual amount of COD removed by the microorganisms.
appied- 2. The amount of food applied is important to calculate the F/M.
II-42
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
F/M based on
MLVSS and not
MLSS.
Use five day
moving
averages to
calculate F/M.
F/M loading
ranges in
Table 11-10.
3. The quantity of microorganisms can be represented by the quantity
of MLVSS. Ideally, the living or active microorganisms would
simply be counted, but this is not feasible, and studies have
shown that the MLVSS is a good approximation of the micro-
organisms concentrations in the MLSS.
4. The data obtained to calculate the F/M should be based on a five
day moving average.
The range of organic loading of activated sludge plants is described by
the F/M. The three ranges of organic loading are conventional, extended
aeration, and high rate. These ranges have been shown to produce acti-
vated sludge that settles well.
Table 11-10 presents the ranges of F/M that have been used successfully
with the three loading conditions. The F/M values shown are expressed in
terms of BOD, COD and Total Organic Carbon, (TOG). The TOG is an
additional means of estimating organic loading. The values indicated are
guidelines for process control, and they should not be thought of as
minimums or maximums.
TABLE 11-10
TYPICAL RANGES FOR F/M LOADINGS
Conventional
AS Range
F/M
Extended
Aeration
F/M
High Rate
Range
F/M
0.5 to 2.5
0.3 to 1.5
1.5 to 6.0
BOD 0.1 to 0.5 0.05 to 0.1
COD(1) 0.06 to 0.3 0.03 to 0.06
TOC(2) 0.25 to 1.5 0.1 to 0.25
(1) Assumes BOD/COD for settled wastewaters = 0.6
(2) Assumes BOD/TOC for settled wastewaters = 2.5
The F/M is calculated from the amount of COD or BOD applied each day
and from the solids inventory in the aeration tank. Refer to Section 2.03
for solids inventory calculations.
II-43
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
How to
calculate F/M.
Graphical
solution for
F/M calculation.
Step-by-step,
Example Calculation
A. Data Required
1. COD or BOD concentration in wastewater applied to the aera-
tion tank, mg/l = 100
2. Q, Influent or primary effluent flow rate, mgd = 7.5
3. SI, Solid inventory in aeration tank, Ibs = 21,017
B. Determine the F/M ratio expressed as pounds COD or BOD applied
per pound MLVSS.
F/M = (BOD' mg/l) (Q' mgd) (8'34
SI
(100) (7.5) (8.34)
21,017
6255
21,017
= 0.297
Figures II-5, II-6, II-7 can also be used to calculate the F/M as determined
in the above example problem. These figures are for plants having average
influent flows of up to 5, 10, and 50 mgd. The following illustration will
show how to determine the F/M ratio with these figures. Data from Figure
II-6 is used:
1. Use the figure with a maximum flow range near the flow in your
plant. In this case use Figure II-6, which has a maximum flow of
10 mgd, which is the most accurate curve for the flow of 7.5 mgd.
2. Referring to Figure II-6
• Find the flow. 7.5 mgd
• Draw a line vertically to the BOD or COD applied 100 mg/l
• Draw a line parallel to the bottom axis to
intersect the MLVSS line 2,000 mg/l
• Draw a line vertically downward to the Factor 0.37
* Divide the factor by the aeration tank volume 1.26 mil gal
• The F/M is equal to:
029- Ibs BOD Applied/day
Ibs. MLVSS
The F/M is essentially equal to the F/M calculated previously. The differ-
ence between 0.29 and 0.297 is not significant.
The use of Figures II-5, II-6, II-7 is strongly recommended. The figures can
be made to read F/M directly for an individual plant by multiplying the
factor by the aeration tank volume and writing a new values in place of the
factor. The use of a clear plastic sheet to cover the figure and a crayon like*
marker will extend the life of a particular sheet. Additional sheets can
also be printed from the original.
II-44
-------
cn
S 4.5 4 3-S 3 2-5 2
0.40 O.45 O.SO
F/M CALCULATIONS
FIGURE II-5
-------
-b.
CT>
BOD APPLIED=100 mg/l
^•••••f ••••••• •••••«••••
0 0-1 02 0-3 0-4 0-5 0-6 0-7 0-8 0-9 1-0
10 9
V>
= o
^ w
F/M CALCULATIONS
FIGURE II-6
-------
GIVEN:
O =375 mgd
MLVSS = 2,000mfl/l
AERATION TANK
VOLUME = 6.3 mil gal
BOD APPLIEDOOO mg/l
READ
FACTO :=1.85
5 10 15 2-0 25 30 35 4-0 45 50
5O 45 4O 35 30 25 20 15 10
F/M CALCULATIONS
FIGURE II-7
en
T rn
-o^
3) en
O r-
O c
m o
w tn
en m
O -o
O 3)
2 O
-J O
D m
O en
r- cn
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
The determination of WAS flow rates using the constant F/M control
technique Is calculated in the same manner as for the constant MLVSS
and Gould Sludge Age techniques. However, the solids inventory for the
aeration tank can be more logically determined based on the COD or BOD
concentration of the wastewater to be treated when using the F/M for
process control. This is determined as follows:
How to
calculate the
MLSS, rng/1
needed for the
desired F/M.
Example Calculation
A. Date Required
1. Desired F/M = 0.29
2. COD or BOD concentration, mg/l = 100
3. Q, Influent or primary effluent flow rate, mgd = 7.5
4. QA, Aeration tank volume mg = 1.26
5. Percent M LVSS = 70
B. Determine pounds of MLVSS for desired F/M.
MLVSS, Ibs - (BOD, mg/l) (Q, mgd) (8.34 Ibs/gal)
F/M desired
_ (100) (7.5) (8.34)
0.29
= 6255
0.29
= 21,569 (equal to approx. 2000 mg/l of MLVSS)
C. Determine MLSS mg/l required in the aeration tank if
the MLVSS is 70%.
MLSSmg/| =
MLVSS, Ibs
(QA) (% MLVSS)(8.34 ibs/gal)
21569
(1.26) (.7) (8.34)
_ 21,569
7.35
F/M control best
used with MCRT
control.
= 2931
The F/M control technique for sludge wasting is best used in conjunction
with the constant MCRT control technique. Control to a constant MCRT is
achieved by wasting an amount of the aeration tank solids inventory
which in turn fixes or provides a constant F/M ratio.
II-48
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
MCRT is used
to calculate
amount of
sludge to be
wasted.
Constant MCRT Control
Current technology considers MCRT to be the best process control tech-
nique available to the plant operator. By using the MCRT, the operator can
control the organic loading (F/M). In addition, he can calculate the amount
of activated sludge that should be wasted in a logical manner. It is recom-
mended that operators become familiar with the use of constant MCRT
control.
Expresses
Residence Time
of solids.
MCRT controls
type of
microorganisms
in process.
Basically, the MCRT expresses the average time that a microorganism
will spend in the activated sludge process. The MCRT value should be
selected to provide the best effluent quality. This value should correspond
to the F/M loading for which the process is designed. For example, a
process designed to operate at conventional F/M loading rates may not
produce a high quality effluent if it is operated at a low MCRT because the
F/M may be too high for its design. Therefore the operator must find the
best MCRT for his process by relating it to the F/M as well as the effluent
COD, BOD and suspended matter concentrations.
The MCRT also determines the type of microorganisms that predominate in
the activated sludge, because it has a direct influence on the degree of
nitrification which may occur in the process. A plant operated at a longer
MCRT of 15-20 days will generally produce a nitrified effluent. A plant
operating with an MCRT of 5-10 days may not produce a nitrified effluent
unless wastewater temperatures are unusually high. Table 11-11 presents
the typical range of MCRT values that will enable nitrification at various
wastewater temperatures. The values shown have been used successfully
to produce nitrified effluents at numerous plants.
TABLE 11-11
MCRT NEEDED TO PRODUCE A NITRIFIED
EFFLUENT AS RELATED TO THE TEMPERATURE
Temperature, °C
10
15
20
25
30
MCRT, Days
30
20
15
10
7
II-49
-------
ACTIVATED SLUDGE PROCESS
SECTION I! - PROCESS CONTROL
MCRT&
temperature
can indicate
nitrification.
How to
calculate MCRT
and the WAS
based on MCRT.
As stated earlier, MCRT expresses the average time that a microorganism
spends in the activated sludge process. The MCRT and the WAS flow rate
for maintaining a constant MCRT is determined as follows:
Example Calculation
A. Data Required
1. SI, Solids inventory in aeration tank, Ibs = 21,017
2. RASyss concentration, mg/l = 7500
3. QWAS> assumed WAS is from RAS system, mgd = 0.030
4. Efflyss, Effluent volatile suspended matter concentration,
mg/1 = 12
5. Q, Plant flow, mgd = 7.5
6. Desired MCRT, days = 7.5
B. Determine MCRT in days.
MCRT, days
SI
[(RASysS x QWAS) + (efflVSS x Q)]8.34 Ibs/gal
21,017
[(7500 x 0.03) + (12 x 7.5)] 8.34
21,017
[225 + 90] 8.34
_ 21,017
315 x 8.34
_ 21,017
2627
= 8.0
C. Determine WAS flow rate to maintain MCRT of 7.5 days.
SI
QWAS, mgd =
(MCRT desired) (RASysS) (8.34 Ibs/gal)
21,017
(7.5) (7500) (8.34)
21,017
469,125
= 0.045
II-50
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
500 1,000 1,500 2,000
3.0OO 2,500 2,000 1,500 1,000 5
MLVSS, mg/l
GIVEN:
MLVSS : 2,000 mg/l
MCRT : 7-5 DAYS
VSSWAS=7, 500 mg/l
AERATION VOLUME = 1-26 mil gal
FROM
WASTE FLOW FACTOR : 0 035
= WASTE FLOW FACTOR x VOL
QWAS : 0 035 x 1-26
' 0-044 mgd
WASTE ACTIVATED
SLUDGE CALCULATIONS
FIGURE II-8
0-13
11-51
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
3,000 2,500 2,000 1,500 1,000 SCO
MLVSS, mg/1
GIVEN:
=7.5 mgd
MLVSS s 2,000 mg/l
MCRT = 7-S DAYS
= 7,500 mg/l
AERATION VOLUME = 1-26 mil gaj
QxVSSEFFx8.34lb/9al 0-05
EFFLUENT FACTOR
1.26
FROM
WASTE FLOW FACTOR s 0-028
= WASTE FLOW FACTOR x VOL-
°WAS : 0-028 x 1-26
QWAS =""•>»= mgd
WASTE ACTIVATED
SLUDGE CLACULATIONS •
FIGURE I 1-9
11-52
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
a This means that for the next 8 days approximately 45,000 gallons per day
calculations should be wasted from the RAS system. However, the WAS flow rate
mean? should be determined and adjusted daily to maintain the desired MCRT.
Figures 11-8 and 11-9 present a graphical technique for making WAS flow
Graphical rate ca|cu|atjons for maintaining a constant MCRT. These figures are
so^iMon or identical except the Figure 11-8 excludes the volatile suspended matter
calculations. contained in the effluent. This is done because some operators feel a very
low amount of soilds in the effluent does not significantly effect the
MCRT while others do. Figure 11-9 includes the correction for effluent
solids.
The following illustration will show how to determine the WAS flow rate
with these figures.
1. Refer to Figure II-8.
step-by-step. • Locate the MLVSS concentration for your plant
intheMLVSSaxis. 2000 mg/l
• Draw a line that is parallel to the bold vertical
axis. Stop at the sloping bold line.
• Proceed parallel to the MLVSS axis to the MCRT
being used for operation. 7. 5 days
• Note that the MCRT values range from 2.5 to
20 days, in 1 day increments up to 15 days and 2.5
day increments up to 20 days.
• Draw a line parallel to the bold vertical axis and
intersect the VSSwAS for your plant. Note that
the concentrations are shown in increments of
500 mg/l with a range of 500 to 10,000 mg/l.
Thus these figures can be used for calculations
involving wasting from the RAS or the mixed
liquor. In Figure II-9 when you get to the effluent
factor axis, deduct the Ibs/day solids in the
effluent then proceed to the VSSwASf°ry°ur
plant. 7500 mg/l
• At the intersection with the VSSwAS line> draw
a line parallel to the MLVSS axis. Read the value
indicated on the axis labeled waste flow factor - 0.035
• Now multiply the factor by the aeration tank
volume of your plant to determine the WAS flow
rate 0.044 mgd
This value of QwAS is verV close to the value calculated in the example
problem. The use of these figures is a convenient and accurate method
for calculating the WAS flow rate.
II-53
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Sludge Quality Control
The sludge quality control method for process control may be used inde-
pendently or in conjunction with other control methods presented in this
section of the manual.
The control program includes the following laboratory tests and observations:
• 30-minute sludge settleability test
• Measurement of sludge blanket depth
• MLSS concentration by centrifuge test
• RAS concentration by centrifuge test
• Secondary effluent turbidity
• D.O.
• Microscopic examination of MLSS
• Aeration tank observations
• Secondary clarifier observations
The data obtained from the control and monitoring tests are plotted on graphs
against time. These data trend plots are based on 5-day moving averages and
are utilized for making control adjustments to optimize process performance.
The overall objective of this control method is based on maintaining an
activated sludge quality which produces the best effluent.
The control tests (depth of blanket, settleometer and centrifuge, etc.), nomen-
clature and many process relationship calculations are those proposed by
E.B. Mallory in the 1940's. The following procedures to determine the required
interrelated process control adjustments were evolved by West:
West claims that best process performance depends upon satisfying all
interrelated process requirements simultaneously; not by exclusive
dependence upon any single or preconceived factor.
A series of EPA pamphlets, entitled "Operational Control Procedures for the
Activated Sludge Process," describing these procedures have been developed
by the Operational Technology Branch (formerly NFIC-C) of the Municipal
Operations and Training Division, Cincinnati, Ohio. Simplification of these
procedures were prepared by Owen K. Boe of the EPA Region VIM Office,
Denver, Colorado, in a paper entitled "Activated Sludge Control with a Settle-
meter and Centrifuge." The following procedures are derived from the above
publications.
Mass Balance by Centrifuge
The centrifuge test is used to measure sludge concentration because it
saves time over the regular suspended solids test. When sludge separates
in the centrifuge, the amount is measured as a percent of the total volume.
The centrifuge tube is calibrated from 0 to 100 percent.
A sludge unit system has been developed to express the results of the
centrifuge test in a simple and meaningful manner. In order to know how
this system works, we need to know how many microorganisms are in the
aeration tank. A representative sample is taken from the tank and placed
-54
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
into the centrifuge. A 15 minute spin reveals that the level of separated
sludge is 1.0 percent of the volume in the centrifuge tube. However, before
the microorganisms measured can be compared to the microorganisms
in the aeration tank, we must have a system to calculate this quantity.
Looking at our aeration tank system we see that the centrifuge reads 1.0
percent and the tank volume is 1.0 MG (million gallons). Therefore, this
quantity of microorganisms is defined as 1.0 sludge unit, or as shown in
the formula:
1.0% x 1.0 MG = 1.0 Sludge Unit
NOTE: It should be noted by the reader that the centrifuge results are
recorded in percent; however, the decimal percent expression is disre-
garded in order to simplify the calculations.
To understand how this system works, let's look at a couple more examples:
1. Suppose the same aeration tank had twice as many microorganisms
present. Now, when we run the sample on the centrifuge we find
that the separated sludge reads 2.0%. Now, the sludge units are
calculated to be:
2.0% x 1 MG = 2 Sludge Units
which shows twice as many microorganisms as before.
2. Let's also consider what would happen if we had two aeration
tanks instead of one. If both aeration tanks had a reading of 1
percent sludge, then the sludge units would calculate to:
1sttank-1% x 1 MG = LOSIudgeUnit
2nd tank-1% x 1 MG = 1.0 Sludge Unit
Total Sludge Units = 2.0
We now have a system which can be used to measure the quantity of
microorganisms in the plant which only involves two numbers. The first
number is the percent reading taken from the centrifuge and the second
number is the volume of the aeration tank (in million gallons). Since the
volume of the tank usually stays the same, all that is needed to determine
the quantity of microorganisms is a reading from the centrifuge, and this
reading only takes a few minutes to determine.
If we wanted to, we could convert the sludge units to pounds of sludge.
All that is needed for this is to run a suspended solids (SS) test and a spin
test on the same sample. For the previous example, which had a spin of
1%, the SS were found to be 1000 mg/l. This gives a spin ratio of 1000
mg/l/1 %. To calculate pounds, use the following formula:
Ibs = % spin x spin ratio x 8.34 x Vol (million gallons)
So, as in the previous example where the tank volume was 1 MG and the
spin ratio was 1000 mg/l/1 %, we have:
Ibs = -0%) (1000 mg/D x (8.34 Ibs) (1 mg)
1% gal
Therefore:
Ibs = 8340Ibs
-55
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
The sludge unit system may sound a little different at first and may sound
like more work, but it actually provides the plant operator with a tool that
can be used over and over and in many different ways with relatively little
time involved. Also, as will be shown later, the use of these units and data
obtained from the settleometer provides the operator with very useful
data for controlling return sludge rates.
Some good examples of how the centrifuge and the sludge unit system
may be used for process control and evaluation are described below.
1. Aeration Sludge Units — ASU
This is a measurement of the amount of sludge found in the aeration
tanks. ASU's are calculated by multiplying the aeration tank volume in
millions of gallons (AVG) by the daily average aeration tank concentra-
tion (ATC). The Aeration Sludge Units are determined as follows:
Example Calculation
A. Data Required
1. AVG = Aeration volume, million gallons = 1.0
2. ATC = Aeration tank Cone., % = 3.0
B. Now determine the Aeration sludge Units.
ASU = (AVG) (ATC)
= (1.0) (3.0)
= 3 units
2. Clarifier Sludge Units-CSU
This is a measurement of the amount of sludge found in the clarifier.
CSU's are calculated by multiplying the volume of sludge in the
clarifier in millions of gallons (CVG) by the average concentration of
the sludge in the clarifier. The volume of sludge in the clarifier is
found by finding the fraction of the total clarifier volume that is filled
with sludge.
The volume of sludge is determined by the following formula and defining
CVG as volume of clarifier and DOB as the measured distance from the
water surface to the top of the sludge blanket. Therefore:
Sludge Volume =|Average depth of Clarifier- DOB
I Average depth of Clarifier- DOB"|
I Average depth of Clarifier J
The average sludge blanket concentration is found by assuming the con-
centration at the top of the blanket is equal to the aeration tank concen-
tration (ATC) and the concentration at the bottom of the blanket is equal
to the return sludge concentration (RSC). These assumptions are made
since we know the sludge is compacting at the bottom of the clarifier, but
we can't really measure the average concentration. The average concen-
tration is then assumed to be:
I-56
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Average Sludge Concentration = ATC + RSC
2
Now in order to find the total clarifier sludge units, multiply the percent
sludge by the average sludge concentration. Clarifier sludge units are
then determined as follows:
Example Calculation
A. Data Required
1." CVG = Clarifiervolume, million gallons = 0.70
2. ATC = Aeration tank concentration, % = 3
3. RSC = Return sludge concentration, % = 12
4. DOB = Depth of sludge blanket, ft. = 8
5. ACD = Average clarifier depth, ft. = 10
B. Determine the volume of sludge in the clarifier.
Sludge Volume = (ACD-DOB)'CVG
ACD
_ (10-8)0.70
10
= (0.2) (0.70)
= 0.14
C. Determine the average sludge blanket concentration.
ATC + RSC
Average Sludge Concentration =
2
3+12
2
= 7.5
D. Now determine the Clarifier Sludge Units.
CSU = (Sludge Volume) (Average Sludge Cone.)
= (0.14) (7.5)
= 1.05 units
"Perform the calculations within parenthesis first.
3. Total Sludge Units-TSU
This is the measurement of the total amount of activated sludge in the
system. The varying amounts of sludge in the clarifier are included in
this measurement.
II-57
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Total sludge units are determined as follows:
Example Calculation
A. Data Required
1. ASU = Aeration sludge unit = 3.0
2. CSU = Clarifiersludgeunit = 1.05
B. Now determine the total sludge units.
TSU = ASU + CSU
= 3.0 + 1.05
= 4.05 units
4. Return Sludge Units —RSU
This is the measurement of the daily average of sludge units returned
from the clarifier to the aeration tank.
The return sludge units are determined as follows:
Example Calculation
A. Data Required
1. RSC = Average return sludge concentration, % = 12
2. RSF = Average return sludge flow, mgd = 2
B. Now determine the return sludge units.
RSU = (RSC) (RSF)
= (12) (2)
= 24 units/day
5. ClarifierSludge Flow Demand —CSFD
Assuming that the sludge settling concentrations* (SSCt) determined
in the settleometer test relate to the return sludge concentration (if
the sludge had stayed in the clarifier for the same length of time), the
required return sludge flow rate can be determined as follows:
I-58
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Example Calculation
A. Date Required
1. Q = Plant flow rate, mgd = 4
2. RSF = Return sludge flow, mgd = 2
3. RSC = Return sludge concentration, % = 12
4. ATC = Aeration tank concentration, % = 3.0
5. SSCeo = 60 minute sludge settling concentration, % = 10
.ssc _ (Aeration tank cone., %) (1000 ml/I)
Sludge settling volumet, ml/l
t = time
B. Now determine the clarifier sludge flow demand.
CSFD = (RSF) (RSC-ATC)
SSCt -ATC
= (2) (12-3)
10-3
= (2) (9)
7
= 2.6 mgd
Therefore, the return sludge flow rate should be increased from 2 to about
2.6 mgd. The sludge blanket depth measurement in the final clarifier
should be taken into consideration before making any changes in the
return sludge flow rate.
Some trial and error adjustments may be required using the sludge blanket
depth measurement as the final guide.
In general, the following rules of thumb can be applied when comparing
the return sludge concentration (RSC) to the 60 minute and 30 minute
sludge settling concentration (SSC):
• If the RSC is greater than the SSCeo, increase the return sludge
rates.
• If the RSC is less than the SSC3Q, decrease the return sludge rates.
Like all rules of thumb, other plant conditions have to be considered,
such as flexibility in the return sludge system, clarifier sludge blanket
depth measurements, aeration detention times, etc.
II-59
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
6. Waste Sludge Units-WSU
This is the measurement of the total quantity of sludge wasted from
the system each day. Sludge wasting can occur intentionally by pump-
ing sludge to a digester or it can occur unintentionally by being carried
over the clarifier weirs. Usually the amount of sludge lost over the
clarifier weirs is small in comparison to that which is intentionally
wasted. However, to check this out or to measure the quantity of the
sludge unit system, we can make use of the spin ratio.
Effluent sludge units (ESU) are calculated by measuring the total sus-
pended solids in the effluent, dividing by the spin ratio, and multiplying
by the plant daily average flow. Therefore:
ESU = (TSS)(Flow)
Spin Ratio
Intentional sludge wasting (XSU) is calculated by taking the daily average
concentration of sludge wasted (WSC) and multiplying the volume (in
million gallons) of sludge wasted (WSF). Therefore:
XSU = WSC x WSF
The total sludge wasted (WSU) is then determined by adding the effluent
sludge units to the intentional sludge units. The total sludge wasted units
are determined as follows:
Example Calculation
A. Data Required
1. TSS = Total suspended solids in clarifier effluent, mg/l = 30
2. Flow = Plant daily average flow, mgd = 4
3. Spin Ratio = Suspended solids cone., mg/l/centrifuge sludge
cone., % = 1000/1
4. WSC = Average waste sludge concentration, % = 15
5. WSF = Average waste sludge flow, mgd = 0.05
B. Determine the effluent sludge units.
- (TSS) (Flow)
Spin Ratio
1000/1 1000
= 0.120 units/day
C. Determine the units of sludge intentionally wasted.
XSU = (WSC) (WSF)
= (15) (0.05)
= 0.75 units/day
II-60
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
D. Now determine the total sludge wasted.
WSU = ESU + XSU
= 0.12 + 0.75
= 0.87 units/day
Sludge wasting is regulated on the basis of maintaining a "normal set-
tling", good quality sludge as measured by the settleometer and on the
basis of visual observations of the aeration tank and clarifier surfaces.
The following is a summary of Sludge Waste Control.
Sludge wasting should normally be started, or increased, if and when:
a. Mixed liquor settles too rapidly in the settleometer and SSCeo*
rises significantly above 20.
b. "Ash" or "clumps" start rising to the final clarifier surface.
c. A dark-brown, scummy foam appears on the aeration tank surface.
d. A sludge blanket, composed of good quality normally settling
sludge, rises too close to the clarifier water surface.
Sludge wasting should be reduced, if and when:
a. Mixed liquor settles too slowly in the settleometer and SSCeo
values fall to 10 or less. (This will normally be accompanied by a
rising clarifier sludge blanket.)
b. Large billows of white foam start forming on the aeration tank
surface.
*SSCfiO = (Aeration tank cone., %) (1000 ml/I)
Sludge settling volumeeo. m|/l
Changes in the wasting rate should be made a little each day (10 to 15
percent per day). Since sludge quality responds slowly to process control
changes (usually about three days after the adjustments are made),
process control changes should not be made rapidly or irregularly.
About a week is usually required following the control adjustments before
the trend in the process response can be positively confirmed. And finally,
two to four weeks before the biological process stabilizes.
7. Sludge Age-Age
Sludge Age or mean cell residence time (MCRT) has been used by
many authors as an operational tool. The purpose is to define an
average time that activated sludge stays in the plant. To find sludge
age we need only to divide the total sludge units by the total sludge
wasted per day.
11-61
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
This may be calculated as follows:
Example Calculation
A. Data Required
1. TSU = Total sludge units in system = 4.05
2. WSU = Total sludge wasted, units/day = 0.87
B. Now determine the sludge age.
TSU
Age =
WSU
4.05
0.87
= 4.7 days
In the Sludge Quality method of process control, conventional parameters
such as F/M and MCRT are calculated for monitoring and comparative
purposes; but are not used as control parameters.
8. Sludge Detention Time in the Clarifier- SDTc
This is a measurement of the average time that the activated sludge
actually spends in the clarifier at any given time. SDTc is found by
dividing the clarifier sludge units by the average daily return sludge
units and multiplying by 24 hrs/day to obtain the time in hours.
Example Calculation
A. Data Required
1. CSU = Clarifier sludge units/day = 1.05
2. RSU = Return sludge units/day = 24
B. Now determine the sludge detention time in the clarifier.
SDTc _ (CSU) (24 hrs/day)
RSU
_ (1.05) (24)
24
= 1.05 hours
Sludge detention time in the clarifier should be greater than 30 minutes to
provide time for compaction. Any time less than 30 minutes will usually
require a high return rate which will reduce the sludge detention time In
the aerators. (See discussion of SDTa, No. 9 below.) The sludge detention
time in the clarifier should be less than 60 minutes to preserve an "active
biomass".
I-62
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
9. Sludge Detention Time in the Aerator - SDTa
This is the measurement of the average time that the activated sludge
actually spends in the aerator mixing with wastewater. The sludge
detention time affects the efficiency of the organisms to absorb and
make use of the BOD by changing the contact time with the BOD. A
comparison of sludge detention times in the aeration tank to the
clarifier also provides important information for controlling sludge
quality. The operator can control or change his sludge detention times
by changing return rates.
A rule of thumb has been developed which relates the sludge detention
time in the aeration tank to'the detention time in the final clarifier:
a = value must be greater than 1
SDTc
This rule of thumb is based on observations of sludge quality in various
plants where it has been noticed that as SDTa becomes closer to SDTc,
that sludge quality is much more difficult to control.
Tank design, especially in some complete mix plants, may limit the ability
of the operator to control this ratio above one, but this still should be a
goal of plant operations.
SDTa is found by dividing the aeration sludge units by the sludge units
being sent to the clarifier per day, and multiplying by 24 hrs/day. The
sludge flow to the clarifier is found by adding the plant flow (Q) to the
return flow (RSF) and multiplying by the aeration tank concentration (ATC).
The sludge detention time in the aeration tank is determined as follows:
Example Calculation
A. Data Required
1. ASU = Aeration Sludge Units = 3.0
2. Q = Plant flow rate, mgd = 4
3. RSF = Return sludge flow, mgd = 2
4. ATC = Aeration tank concentration, % = 3.0
B. Now determine the sludge detention time in the aeration tank.
SDTa = (ASU) (24 hrs/day)
(Q + RSF) (ATC)
= (3.0) (24)
(4 + 2) (3.0)
= 4 hours
II-63
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Settleometer
The settleometer (also called the sludge settleability test) is the key
indicator for observing sludge quality. Diligent use of the settleometer
can provide an experienced operator with days advance warning of an
impending disruption or change in process control. This advance warning
provides the operator with valuable time to make appropriate process
changes. The settleometer information can also be instrumental when
recovering from an unavoidable operational upset.
In this case the advanced indicators can guide the operator through a
series of process adjustments without wasting excess time waiting for
results from process changes or without trying to make a major adjust-
ment in too short a time.
The two things an operator should look at when running the settleometer
test are the floe formation and the blanket formation. Through experience,
an operator will soon learn that within a few minutes he can detect certain
characteristics which will describe the sludge quality. Is the floe granular,
compact, fluffy or feathery? Does the floe settle individually or does it
first form a blanket? Is the blanket ragged and lumpy, or uniform on the
surface?
After the operator has looked at these characteristics he then should
observe settling rates and compaction characteristics. Is the blanket
settling uniformly, or are segments settling faster than others? Is the
blanket entrapping the majority of the material or are straggler floe escap-
ing? Is the sludge compacting and squeezing out water, or is it maintaining
a constant density throughout?
Observations such as these are important to the operator. They are not
easily translated to numbers, so he should make appropriate notes on his
data sheet for future reference. There are, however, numerical observa-
tions which can be made. Figure 11-10 presents a typical data sheet which
can be used to record appropriate sludge settling parameters. Observa-
tions and recordings are made every 5 minutes for the first half hour, and
then every 10 minutes for the second half hour. More observations are
made in the first half hour to ensure that the operator is taking the time
to observe the floe formation and blanket characteristics.
If the operator also measures the concentration from the original aeration
tank sample with the centrifuge (ATC) he can make some informative
calculations from the data.
The calculation of interest is the conversion of the sludge settling volume
(SSV) to sludge settling concentrations (SSC) which is determined for any
given time (t) of settling as follows:
II-64
-------
ACTIVATED SLUDGE PROCESS
SECTION II- PROCESS CONTROL
Facility Cluar Creek
p,f Saturday
Dlt, 6/12/73
SETTLEOMETER TEST INFORMATION
time ol
teit
T''m<
0
5
10
IS
20
25
30
40
50
60
cc/l
1000
950
890
830
770
720
680
620
570
520
Time
Wasting
Began
700a
ssc*
T
V
3.4 0
3
.58 5
3.32 10
4
4
4
5
b
5
6
.10
15
.42 20
.73 23
.00 JO
.48 40
.97 50
.54 SO
SSY S^C'
cc/l %
1000 2.8
T-. ssv ssc •
m, cc/l
0 1000
9.10 3.08 5 |
820 3.42 10
740 3.79
670 4.18
620 4.52
570 4.92
490 5.72
430 6.52
15 1
20
25
30
JO <
50
i 380 7.381 60 I
SIC RSC DOB tUR3 i FLO INFORMATION
TIME
900a
ATC-
3.
100p| 2.
500JJ
1.000f
ub-Tot
T
> 1
o/
- /o
RSC-
4| I 8 . 6
8
0
f9.0
if
- /o
a.i
q n
Total
Aver.
3.
1
n.n
WASTING INFORMATION
Time
Wasting
Ended
200p
Totjl
TiTi5
Wasted
(mm)
300'
flow
ICP.M)
90
1
Gallons WSC ] ',VSC
V,'a 5 1 f. d Began Ended
(CALI (°/o) (°/o)
27,000 9.2 10.0
WSC
(°.'o)
9.6
Total
'A.i's'fi-d
(CALX o-o )
.26
DOB — Ft
6.C
3.C
3.3
4_rj
'1.2
Turb — ITU
IT
3
3
^
. 2
.7
INF
FLO
1.5
1
. 5 i
.ol
3
.3
1
'!'. 5
RSF INFORMATION
Be'n
800 a
Time
Ended
800a
Total
T ime (mir
1440
RSF
CCAL.'ni.-O
1000
Total
1.4
Totjl ^ 4MP
BODS
Parameter
Eottlett
% D
lullon
Initial D.O.
Final D.O.
D.O. Ocpltt.
Factor
n'C/l
BOD
5
TEST
INFORMATION
BLK
MISC. INFORMATION
TSSiVSS
Parameter
Tirnc
Tare :f
Tare Ł
Solirls WT.
Tare WT.
Dry Solids
WT
Ash WT.
Vo .il.lc WT.
Vol. ol S jmnl
TSS m;/l
VSS m;/
°o VSS
"ssc : s'sv" "
TEST INFORMATION
NOlc: .'
orni.il Dat
."ic dJtt
a period IS rorn 0^00 on
sho^n and continues or 24 hrl.
ACTIVATED SLUDGE PLANT
DAILY DATA SHEET
FIGURE 11-10
11-65
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Example Calculation
A. Data Required
1. ATC = Aeration tank concentration, % = 3.4
2. SSV(t) = Sludge settling volume at any time, ml/I = 680 (at
30m in.)
3. (t) = Length of time of settling, minutes = 30
G<
B. Now determine the sludge settling concentration.
SSC(t) = (ATC) (1000 ml/l)
V ' SSV(t)
SSC3Q = ) (1000 ml/I)
SSV30
_ (3.4) (1000)
680
= 5%
This means that after 30 minutes the sludge has settled to a concentra-
tion of only 5%.
The sludge settling concentrations can be calculated for various times
and plotted (as shown in Figure 11-11) corresponding to the time and day
they were observed. When several days,of data have been plotted, a trend
will have been developed which graphically relates to the settling char-
acteristics observed in the settleometer. Often, it is found that the 5
minute, 30 minute, and 60 minute SSC's adequately represent the settling
characteristics.
The 5 minute sludge settling concentration is an indicator of the critical
floe and blanket formation stage. Here the operator's observations and
notes are very important for future reference.
The majority of the settling occurs before the 30 minute reading, therefore
the distance settled reflects the settling rate of the sludge. For example,
a 30 minute sludge settling volume of 200 would indicate a fast settling
sludge, while a settling volume of 600 would represent a very slow settling
sludge.
The 60 minute sludge settling concentration is indicative of the level of
compaction that can be expected from the sludge. Therefore, there is a
relationship between this concentration and the concentration of the
return sludge that is actually observed in the plant. These numbers will
seldom be the same due to flow characteristica and other physical dif-
ferences found in the clarifiers. The important criteria, however, is that
the settleometer characteristics are reproducible for similar sludge quality
characteristics. This then enables the operator to make some decisions
on return sludge flows form settleometer data.
II-66
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
1000
10 20 30 40 50 60
Time, minutes
10 20 30 40 50 60
Time, minutes
PLOTTING SLUDGE SETTLING CHARACTERISTICS
FIGURE 11-11
11-67
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
A "normal settling" good quality sludge will concentrate to a SSCeo range
of about 12 to 18 in one hour and won't settle any more after two hours.
A "rapidly settling" sludge is an overoxidized sludge that will concentrate
to a SSCeo range greater than 20 in one hour and won't settle any more
after an hour. Rapidly settling sludge is often accopanied by such clarifier
problems as ashing or clumping. The corrective actions for these problems
are described in Section I, "TROUBLESHOOTING".
A "slow settling" sludge that only concentrates to a SSCeo of 10 or less
and takes 3 or 4 hours to reach final settling and compaction is usually a
young sludge. A very young sludge may not settle at all during the first
5 to 10 minutes, and may only concentrate to between 700 and 900 ml/I
during the first hour. Young sludge is often accompanied by a high sludge
blanket in the final clarifier with an imminent danger of sludge bulking
and/or solids washout. The sludge wasting should be reduced to increase
the sludge settleability towards the "normal" range. The return sludge
flow rate may need increasing to lower the blanket level. Corrective
measures for this problem are presented in Section I, "TROUBLESHOOTING".
Sludge settling rates can be used by the operator to numerically relate
one set of sludge characteristics to another. These settling rates can be
used by the operator to describe a rate of settling for which the plant
provides a good quality effluent. Generally this rate will fall between 400
and 1200. This corresponds to a 30 minute reading on the settleometer of
400 to 800 milliliters. As mentioned before, this information should always
be accompanied by notes which relate to the more important, but not
quantitative, data of floe and blanket formation. The sludge settling rate
(SSR) is the increase in sludge concentration per hour and is determined
as follows:
Example Calculation
A. Data Required
1. SSV3Q = 30 minute sludge settling volume, ml/I = 680
B. Perform the following calculation to determine the sludge settling
rate.
SSR_(1000-SSV30)
0.5 hr.
_ (1000-680)
0.5
= 640 ml/l/hr.
The turbidity of the clarifier effluent, the depth of the sludge blanket,
sludge settling rates, and sludge characterisitcs (floe and blanket forma-
tion) should be plotted on trend charts as shown on Figure 11-12 to help
the operator in maintaining control of his facility.
I-68
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
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PROCESS VARIABLE TRENDS
FIGURE 11-12
25
30
1-69
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Visual Observations
A modest accumulation of light colored, crisp-appearing foam on the
aeration tanks is usually indicative of good operation.
During good operation the final clarifier effluent will be relatively clear
with the sludge blanket in the lower half of the clarifier (generally 1 to 3
feet).
For those observations that are indicative of operational problems, see
Section I, "TROUBLESHOOTING".
Turbidity
Turbidity is a quick and convenient indication of the activated sludge
process performance. A well performing activated sludge plant should be
producing an effluent with a settled turbidity of less than 3 JTU's and
sometimes down to 1 JTU. Turbidity measurements can also be used to
measure the degree of severity of pin floe or other solids. Short term varia-
tions due to these type problems may be attributable to hydraulic problems
In the clarifier rather than deterioration of the sludge quality.
Depth of Blanket
Within the final clarifier, a separation of the liquid and solids takes place.
The solids settle to the bottom of the clarifier while the clear liquid is
displaced over the clarifier effluent weirs. If the settled solids are not
removed from the tank at a rate equal to or greater than solids Input by
the aeration effluent flow, a blanket of sludge will accumulate until
eventually the solids are washed out In the clarifier effluent flow.
The location of the sludge blanket in relation to the clarifier depth may be
determined by various types of devices—some are commercially available,
while others must be improvished by the operator.
Determining the sludge blanket depth in the final clarifier in conjunction
with other measurements, such as the plant flow, aeration tank concen-
tration (ATC), sludge settling concentration (SSC), and the return sludge
flow (RSF) and concentration (RSC) provides valuable information that
can be used to control the return sludge flow rates. Additionally, these
measurements can be used to evaluate the operation of multiple units, for
instance the sludge blanket depth In two clarifiers operating in parallel
(both receiving flow from same aeration basin) having equal return sludge
flow rates should be comparable. If the sludge blanket in one clarifier was
rising while the blanket In the other clarifier was falling, It could be con-
cluded that the aeration tank effluent flow was being unevenly distributed
to the clarifiers. Depth of blanket measurements are Important for an
operator so he can have early warning to clarifier malfunctions and to
problems associated with long storage times In the clarifier. An average
value for each clarifier Is usually sufficient for process control, but
11-70
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
measurements should be periodically made at various locations in the
clarifier to detect any localized problems. Coning or plugging of suction
ports can lead to areas in the clarifier where the sludge blanket will build.
A rising blanket may indicate an inadequate sludge return rate, unbalanced
distribution of aeration tank effluent flow, inadequate sludge wasting
rates, or a poorly settling sludge.
The presence of a poorly settling sludge could be verified with the SSC
value. To correct a rising blanket, the operator first determines the reasons
by a review of the lab test results, operational logs, and process control
parameters. After determining the possible reason for the increased
blanket depth, the operator should then take the appropriate corrective
measures.
The procedures for making the sludge blanket measurement are given in
Section IV, "LABORATORY CONTROL".
Microscopic Examination
Microscopic examination of the MLSS can be a significant aid in the
evaluation of the activated sludge process. The presence of various
microorganisms within the sludge floe can rapidly indicate good or poor
treatment. The most important of these microorganisms are the hetero-
tropic and autotrophic bacteria which are responsible for purifying the
wastewater.
In addition, protozoa play an important role in clarifying the wastewater
and act as indicators of the degree of treatment. The presence of rotifers
is also an indicator of effluent stability. A predominance of protozoa
(ciliates) and rotifers in the MLSS is a sign of good sludge quality.
Inversely, a predominance of filamentous organisms and a limited number
of ciliates is characteristic of a poor quality activated sludge. This condi-
tion is commonly associated with a sludge that settles poorly.
There are many other organisms such as nematodes (worms) and water-
borne insect larvae which may be found; however, these do not signif-
icantly affect the quality of treatment.
The microorganisms which are important to the operator are the protozoa
and rotifers. The protozoa eat the bacteria and help to provide a clear
effluent. Basically, the operator should be concerned with three groups of
protozoa, each of which have significance in the treatment of wastewater.
A discussion of these groups and the procedures for performing a micro-
scopic examination are presented in Section IV, "LABORATORY CONTROL".
11-71
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Common
operational
problems.
Corrections
can be made by
a logical
approach.
The 30-minute
settling test
provides data
for problem
solving.
2.05 OPERATIONAL PROBLEMS
This section of the manual discusses operational problems commonly ex-
perienced in the activated sludge process. In general, these problems can be
classified by conditions which the operator can see in the aeration tank and
secondary clarifier.
• Aeration Tank:
1) Aeration Tank:
2) Foaming Problems
• Secondary Clarifier
3) Solids Washout
4) Bulking Sludge
5) Clumping/Rising Sludge
6) Clouding Secondary Effluent
7) Ashing
8) Pinpoint Floe
9) Stragglers/Billowing Solids
Correction of these problems can be approached in a logical manner, by
using sound operational control practices and by maintaining proper equip-
ment operation. Troubleshooting procedures covering these problems are
provided in an easy-top-follow format in Section I, "TROUBLESHOOTING."
The problems occurring in the clarifier can often be associated with observa-
tions made during the 30-minute settleability test. This test is used to indicate
the settling characteristics of the mixed liquor under controlled conditions.
Figures 11-16 , II-20, and II-22 present pictorial guides for interpretation and
application of the various settling test observations. The procedures for
performing the settleability test can be found in Section IV, "LABORATORY
CONTROL."
Aeration System Problems (Refer to Figure 11-13)
Why is aeration
important?
Uniform
aeration &
mixing is
essential.
Perform D.O.
profile.
Aeration and mixing of the MLSS is essential to maintain the environment
for the microorganisms to remain active and healthy. In addition, mixing of
the aeration tank contents is necessary in order to bring these microorganisms
in contact with all the organic matter in the wastewater being treated.
Mixing in the aeration tank can generally be checked by observing the tur-
bulence on the aeration tank surface. The surface turbulence should be
reasonably uniform throughout the tank. Dead spots and nonuniform mixing
patterns will generally indicate a clogged diffuser or that the diffuser header
valves need adjustment to balance the air distribution in the tank. An illustra-
tion of violent turbulence in an aeration tank is shown in Figure 11-13.
Periodically, (generally monthly to every 6 months) a D.O. profile should be
performed in aeration tanks which are equipped with the diffused-type of
aeration system. The air distribution should be adjusted to maintain a D.O. of
no less than 0.5 mg/l, preferably 1 to 3 mg/l, throughout the aeration tank.
II-72
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Some causes
lor aeration
problems.
Corrective
action for
aeration
problems.
Some probable causes of nonuniform aeration include the following:
1. Air rates too high or low for proper operation of the diffuser.
2. Valves need adjustment to balance the air distribution.
3. Diffusers (or mechanical aerators) need repair and/or cleaning. Masses
of air rising over the location of the diffuser blowoff legs (if so equipped)
generally indicates that the diffusers need cleaning. Figure 11-13 is an
indication of this problem.
4. Mechanical equipment limitations.
The following applicable measures should be implemented to correct aeration
problems:
• Adjust air SCFM rate to maintain the D.O. in the proper range (1 to 3
mg/l). The SCFM of air per linear foot of diffuser header pipe should be
greater than 3 SCFM/linear ft. to ensure adequate aeration and mixing
of tank contents.
• Adjust diffuser header valves to balance air distribution and to eliminate
dead spots.
• Clean and check the diffusers. Diffusers should be cleaned on a routine
basis to maintain good aeration performance. Generally every six
months to one year.
• If fine bubble diffusers are extremely troublesome, consider replacing
them with a coarse bubble type of diffuser. Coarse bubble diffusers
require a greater air SCFM rate because of the reduced oxygen transfer
efficiency; therefore, it must be determined that an adequate air
supply is available before making this modification. Outside help
should be obtained.
• Relocate and/or increase the number of diffusers (or mechanical
aerators) to properly mix and aerate the tank contents.
'•(•iiirill^
.
Figure 11-13
11-73
-------
STIFF WHITE FOAMING
GREASY BROWN FOAMING
CARRYOVER OF BROWN FOAM IN CLARIFIER
FOAMING PROBLEMS
FIGURE 11-14
O) >
51
53
= o
to m
w -o
O 3
io
is
w
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Foaming Problems (Refer to Figure 11-14)
Minor foaming
is normal in
aeration tanks.
Two types of
foaming
conditions can
occur.
Foaming can
create unsafe
working
conditions.
The presence of foam on the aeration tank is normal for the activated sludge
process. Frequently, 10 to 25 percent of the aeration tank surface is covered
with film or light froth or foam.
Under certain operating conditions the foam (or froth) can become excessive
and can affect operations. Two types of problem foam are normally seen.
These are a thick brown greasy foam and a stiff white foam.
If the foam is allowed to build-up excessively, it can be blown by the wind
onto walkways and plant structures, causing hazardous working conditions.
In addition, it can create an unsightly appearance as well as cause possible
odors. If the foam is carried over with the flow to the secondary clarifiers, it
will tend to build-up behind the influent baffles and create additional cleaning
problems.
Causes for
white foam.
Stiff White Foam
The stiff white, billowing foam is indicative of an overloaded plant. This
means that the MLSS concentration is too low and the F/M is consequently
too high. The foam may consist of detergents or proteins which cannot be
converted to food by the young and simple bacteria that grow in the MLSS
at a high F/M.
Some probable causes of stiff white, billowing foam include the following:
1. Low MLSS due to process start-up.
2. Excessive wasting of activated sludge causing the MLSS concentra-
tion to drop too low for current organic loading.
3. The presence of unfavorable conditions such as toxic or inhibiting
materials, abnormally low or high Ph's (pH below 6.5 or above 9.0),
insufficient dissolved oxygen, nutrient deficiencies, or seasonal
(summer to winter) wastewater temperature change resulting in
reduced microorganism activity and growth.
4. Unintentional wasting of activated sludge in the effluent of the
secondary clarifier. This condition could be caused by the following:
• Excessive or shock plant loads.
• Biological upset.
• High sludge blanket in sludge clarifier.
• Mechanical deficiencies in the clarifier.
• Denitrification in the clarifier.
• Improper distribution of flows or solids loadings to multiple clarifies.
5. Improper distribution of the wastewater and/or the RAS flows to
multiple aeration tanks.
II-75
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
What are the
corrective
measures for
white foaming.
If flow meters
are not
provided, try
these corrective
measures.
The following applicable measures should be implemented to correct the
foaming problem:
• Reduce the wasting of activated sludge to increase the MLSS concen-
tration. Changes in the wasting rate should be made slowly and
gradually (see Section 2.04 for waste activated sludge control methods
and procedures).
• Maintain sufficient RAS rates to keep the sludge blanket in the lower
half of theclarifier.
• Control the air SCFM rates to maintain D.O. levels of 1 to 3 mg/l in the
aeration tank.
• Industrial waste ordinances must be actively enforced to avoid process
upset and deterioration of the plant effluent.
• Modify the piping or structures as necessary to maintain the proper
distribution (proportional to tank volumes) of flows to multiple aeration
tanks and secondary clarifiers. The construction of some type of flow
distribution structure may be required.
If flow meters are not provided, compare the following measurements:
• The sludge blanket levels in each clarifier.
• The suspended matter concentration of each clarifier's RAS flow.
• The MLSS concentration in each aeration tank.
The corresponding measurements should be nearly equal if the wastewater,
aeration effluent, and RAS flows are being properly distributed.
• If the aeration tanks are equipped with water sprays for froth control,
operate the water sprays when there is danger of the foam being blown
onto the walkways and/or other plant structures.
Causes for
brown foam.
Excessive Brown Foam
This type of foam is associated with plants operating between the con-
ventional and extended aeration loading ranges. Nitrification and fila-
mentous organisms such as Nocardia are often associated with this type
of foam. The thick brown greasy foam is normal at any plant that practices
sludge reaeration. The appearance of this type of foam can result in
additional problems in the clarifier by building up behind the influent
baffles and creating a scum disposal problem as shown in Figure 11-14.
Scum containing filamentous organisms should not be returned to the
aeration tanks. Some probable causes of the foaming problem are as
follows:
1. Aeration tank is being operated at a low F/M ratio because nitrifi-
cation is required by regulatory agency.
2. Build-up of a high MLSS concentration due to insufficient sludge
wasting. This condition could untentionally occur when the
seasonal (winter to summer) wastewater temperature change
results in greater activity of the microorganism and consequently
greater sludge production.
3. Operating in the sludge reaeration mode. A thick brown foam is
normal in the sludge reaeration tank.
4. Improper WAS control program. See Section 2.04, "PROCESS
CONTROL"
II-76
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
What are the
corrective
measures for
brown foaming.
The following applicable measures should be implemented to correct the
foaming problem:
• If nitrification is not required, gradually increase the wasting rate
to increase the F/M ratio (see Section 2.04, "PROCESS CONTROL").
If the scum is not returned to the aeration tanks, include the volatile
solids removed in the scum in the waste sludge calculations.
During normal operation, the amount of volatile solids removed
with the scum is too small to matter. However, during heavy foam-
ing, as much as 10 percent of the waste activated sludge solids
may be removed with the scum.
• When filaments appear in a nitrifying sludge, they may be killed by
the addition of chlorine to the RAS. Recent experiences suggests
that the does of chlorine required will be from 2 to 3 Ib CI2/1000
Ibsof MLVSS/day.
CAUTION: Excessive chlorination can harm the desirable micro-
organisms.
• Implement a better program for controlling the waste of activated
sludge. Read Section 2.04 "PROCESS CONTROL" for more
guidance on waste activated sludge control techniques.
Settleability
test helps to
Identify solids
washout
problem.
What are
causes for
solids washout?
Solids Washout (See Case 1 on Figure 11-16)
This condition can sometimes be quickly detected when good settling is
observed in the 30-minute settling test but billowing homogenous sludge
solids are rising in the secondary clarifier (Figure 11-15) even though the
sludge blanket is in the lower half of the clarifier.
Some probable causes of solids washout are as follows:
1. Equipment malfunction
2. Hydraulic overload
3. Solids overload
4. Temperature currents
The following applicable measures should be implemented to correct the
solids washout problem:
Is the
clarifier working
properly?
Equipment Malfunction
The operator should inspect all equipment in the clarifier to ensure that it
is operating properly. Specifically check the following:
• Sludge Collection Equipment—
Look for broken drives or support members.
Look for uneven blanket depth at several locations in the
clarifier. An uneven blanket may indicate a plugged
suction collector or broken plough.
I-77
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ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Baffles and Skirts —
Look for broken welds, bolts, or supports.
Look for holes in the baffle.
Weir Levels —
Look for unbalanced flow over the weirs. Are the weirs on one
side of the tank more deeply covered than those on the
other side?The weirs should be adjusted to an equal
elevation.
Figure 11-15
Hydraulic Overload
Are the flows
balanced
between
multiple units?
Check the
clarltler
surface
overflow rate.
The operator should check the hydraulic loading on each clarifier by
either measuring the flow to each clarifier or by estimating the flow
balance between multiple units as indicated by the depth of flow over the
weirs in each of the clarifiers. Overloading can result from excessive flow
or unevenly distributed flow between multiple units. Approach and solve
the problem as follows:
• Determine if the flows are being distributed equally to the aeration
basins and clarifier units. The weirs at the effluent end of the aera-
tion tanks must be adjusted to an equal elevation to provide an
equal distribution of loading to each tank. The weirs or gates at the
RAS distribution structures must be adjusted to an equal elevation
to provide proper distribution of RAS flows. The weirs at the
secondary clarifier distribution structures must be adjusted to an
equal elevation to provide a uniform hydraulic loading. In addition,
the effluent weirs must be ajusted to an equal elevation to provide
optimum clarifier performance.
• After checking and correcting the weir elevations where needed,
determine the clarifier surface overflow rate as follows:
I-78
-------
30 MINUTE SETTLING
OBSERVATION
GOOD SETTLING IN TEST
BILLOWING IN CLARIFIER
-J
CD
OBSERVATION
ACTION
30 MINUTE SETTLING
POOR SETTLING IN PERFORM
TEST, SUPERNATANT - MICROSCOPIC
VERY CLEAR EXAMINATION
ACTION
CHECK FOR EQUIPMENT MALFUNCTIONS
REMEDY
REPAIR EQUIPMENT
CHECK HYDRAULIC LOADING
MEASURE TEMPERATURE PROFILES
IMPROVE INLET/OUTLET BAFFLING-REDUCE RAS
. USE ADDITIONAL AERATION TANKS
AND/OR INSTALL BAFFLES
FILAMENTS
CHECK D.O.
REMEDY
IFD.O.IS LOW-INCREASE AIR TO ACHIEVE DO OF I TO 2 MG/L
IFD.O.LEVELS UNEVEN-ADJUST AIR DISTRIBUTION AND/OR
CLEAN DIFFUSERS
y-BOD/N > 100/5 -TRY ADDING N
CHECK N, P, AND FE /- BOD/P > 100/1 — TRY ADDING P
. 5 — TRY ADDING FE
NO FILAMENTS
DISPERSED FLOC
CHECK pH- IFpH<6.5-TRY RAISING pH
CHLORINATE RAS AT 2—3 LBS/ IOOO LBS MLVSS /DAY
CHECK F/M RATIO - IF HIGHER THAN USUAL.DECREASE WASTING
CHECK D.O. - IF ABOVE 3.0 MG/I.REDUCE AERATION
CASE 1 AND CASE 2
FIGURE 11-16
0>
2 O
33 C/3
O r-
o c
m D
w O
o m
O -o
O n
z O
-H O
3 m
O w
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
How to
calculate
clarifier
overflow rate.
Example Calculation
A. Data Required
1. Surface area, each clarifier = 7,850 sq. ft.
2. Two clarifiers, total area = 15,700 sq. ft.
3. Plant flow (peak hour) = 7.5 mgd or 7,500,000 gpd
B. Determine the clarifier surface overflow rate.
_ , ,. . .,,. o Plant flow, gpd
Surface overflow rate, gpd/ftx = ——— '-^L-
Clarifier surface area, sq. ft.
_ 7,500,000 gpd
15,700 sq.ft.
C.
= 478gpd/sq.ft.
Compare the calculated surface overflow rate with the design
rate. If the current rate exceeds the design rate (see Section 2.03,
"SECONDARY CLARIFIERS"), the clarifiers are hydraulically
overloaded, and additional clarifier units are required in operation.
If all clarifiers are operating, plant expansion or flow equalization
is required.
Check the
clarifier solids
loading.
Solids Overload
A special case of overloading of the clarifier is known as solids over-
loading. Solids overloading is related to the Q, RAS flow, and MLSS
concentration. Reducing the MLSS concentration or the RAS flow may
eliminate the poor settling in the clarifier. Determine the solids loading
rate as follows:
How to
calculate
clarifier solids
loading rate.
Example Calculation
A. Data Required
1. Surface area, each clarifier = 7,850 sq. ft.
2. Two clarifiers, total = 15,700 sq.ft.
3. Plant flow, Q (peak hour) = 7.5 mgd
4- QRAS> RAS flow rate (peak hour) = 3.8 mgd
5. Aeration effluent MLSS, peak hour = 2,500 mg/l
B. Calculate the solids loading rate.
Ib/ft2/hr = (Q + QRAS, mgd) (MLSS, mg/l)(8.34 Ibs/gal)
(24 hrs/day) (Clarifier surface area, sq. ft.)
(7.5 + 3.8) (2,500) (.8.34)
(24) (15,700)
= 0.63lbMLSS/sq.ft./hr
11-80
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Are all available
tanks In
operation?
Allow solids to
build in
clarlfler during
peak flow
period.
Decrease the
solids inventory.
C. A solids loading rate value of 1.25 Ib/sq. ft./hr is a practical upper
limit for clarifier operation. If the calculated value for a particular
plant exceeds this value the following approaches should be
tried.
• Utilize any available aeration tank or clarifiers.
• Reduce the RAS flow.
• Reduce the MLSS concentration.
The use of all available aeration tanks makes it possible to reduce the
MLSS concentration without changing the F/M. The extra volume of
additional aeration tank makes it possible to have the same volatile
solids inventory with a lower MLSS concentration, which effectively
reduces the solids loading rate.
If no additional aeration tanks are available, the second approach should
be used. The RAS flow should be reduced by 10 to 20 percent. The depth
of the sludge blanket in the clarifiers should be measured periodically
to ensure the sludge blanket does not build to an excessive depth. Observe
the clarifier to see if the poor settling characteristics are improved. If the
settling does not improve after reducing the RAS flow, the MLSS should
be decreased by slightly increasing the wasting rate. Be aware that the
F/M is increasing during this procedure because the solids inventory will
decrease. A practical limit for MLSS reduction would be a 10 percent
gradual change in one week. If no improvement occurs during these
adjustments, the high effluent suspended solids concentrations are most
likely not due to solids overloading.
How to conduct
a temperature
profile.
Temperature Currents
A temperature profile of the clarifier will identify the presence of any
temperature currents. The temperature probe on a dissolved oxygen meter
is an excellent tool for this procedure. To make the profile, the tempera-
ture is measured and recorded at the head, one quarter, one half, three
quarters and tail end of a rectangular or square clarifier, or at the quarter
points across a circular clarifier. At each point, the temperature is measured
at the surface and the quarter points down to the bottom of the tank. Be
careful that the temperature probe and wires do not get entangled in the
sludge collection equipment.
Install baffles.
If the deeper temperatures are consistently cooler by 1 to 2° C or more,
temperature currents are present. The settling may be improved if baffles
are installed to break up the currents and stop the turbulence.
11-81
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ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Poor settling
and
compaction,
with a clear
supernatant.
Bulking Sludge (See Case 2 on Figure 11-16)
The presence of a clear supernatant above a poor settling sludge indicates
that the settling is being hindered by either the presence of filamentous
microorganisms or dispersed floe. The presence of filamentous microorganisms
is corrected by improving the treatment environment with the addition of
nutrients, such as nitrogen and phosphorous, and/or by correcting the dis-
solved oxygen concentration in the aeration tank. The presence of dispersed
floe indicates either organic overloading or overaeration. Classic sludge
bulking in the clarifier is illustrated in Figure 11-17.
Some probable causes of the bulky sludge problem are as follows:
1.
2.
Filamentous microorganisms present
Low D.O. in aeration tank
Insufficient nutrients
Low pH
Warm wastewater temperature
Industrial wastes
No filamentous microorganisms present
Organic overloading (high F/M)
Overaeration
Figure 11-17
II-82
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Determine if
filamentous
organisms are
present.
What to check
when
filamentous
organisms are
present.
The first step in analyzing this condition is to perform a microscopic examina-
tion of the MLSS. Microscopic analysis of the MLSS is described in Section
IV, "LABORATORY CONTROL" Approach and solve the problem as follows:
Filamentous Microorganisms Present (Figure 11-18)
If filamentous microorganisms are present, the following steps should be
followed:
• Measure the D.O. level at various locations throughout the aeration
tank.
If the average D.O. is less than 0.5 mg/l there is insufficient dis-
solved oxygen in the aeration tank. Solution Increase the air
SCFM rate until the D.O. levels increase to 1 to 3 mg/l throughout
the tank.
If the D.O. levels are nearly zero in some parts of the basin, but are
higher in other locations, the air distribution system is out of
balance or the diffusers in an area of the basin may need to be
cleaned. Solution - Balance air system and/or clean diffusers.
• Calculate the ratios of BOD to nitrogen (use TKN expressed as N),
BOD to phosphorus (expressed as P), and BOD to iron (expressed
as Fe). In general, anhydrous ammonia is used to add N, trisodium
phosphate is used to add P, and ferric chloride is used to add Fe.
How to
calculate
amount of
nutrients to use.
Example Calculation
A. Data Required
1. Influent BOD = 170 mg/l
2. Influent TKN = 4.5 mg/l
3. Suggested ratio, BOD/N = 100/5 = 20
4. Suggested ratio, BOD/P = 100/1 = 100
5. Suggested ratio, BOD/Fe = 100/0.5 = 200
6. Plant Q, average daily = 7.5 mgd
7. Ammonia/nitrogen atomic weight ratio, NHs/N = 17/14 = 1.2
8. Trisodium phosphate/phosphorus atomic weight ratio, Na3
PO4/P = 164/31 = 5.3
9. Phosphroic acid/phosphorus atomic weight ratio, H^PO^IP =
98/31 = 3.16
10. Ferric chloride/iron atomic weight ratio, FeCl3/fe = 162.5/56
= 2.9
B. Calculate the amount of N,P, and Fe needed per day to achieve
the suggested ratios.
BOD, mg/l
Nutrient needed =
Respective suggested ratio from
3,4 or 5 above
II-83
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
GOOD SETTLING SLUDGE
'
FILAMENTOUS ORGANISMS IN BULKING SLUDGE
MICROSCOPIC OBSERVATIONS
FIGURE 11-18
1-84
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Example Calculation
N needed = BOD, mg/l
Suggested ratio, BOD/N
170
20
= 8.5 mg/l
C. Calculate the difference between the nutrient available and the
nutrient needed.
Nutrient shortage = N needed - Nutrient available
Example Calculation
N shortage = N needed -TKN available
= 8.5-4.5
= 4.0 mg/l*
'Nutrient addition is not needed when answer is zero.
D. Calculate the pounds of nutrients that need to be added per day.
Nutrient, Ibs/day - (N shortage, mg/l)(Q, mgd)(8.34 Ibs/gal)
Example Calculation
Nitrogen, Ibs/day = (N shortage, mg/l) (Q, mgd) (8.34 Ibs/gal)
= (4 mg/l) (7.5 mgd) (8.34 Ibs/gal)
= 250lbsof N/day
11-85
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
E. Calculate the pounds of the respective commercial chemical to be
added per day,
Ch . I _ (Nutrient Ibs/day) (Respective atomic wt. ratio)
Ibs/day ' Concentration of chemical, %
Example Calculation
.... .
Anhydrous ammonia =
(assume using a
commercial grade
with a 80% cone.)
(N, Ibs/day) (1 .2
*— - - —
[Concentration, %
(250 Ibs/day) (1.2 NHa/N)
80%
300
0.8
= 375 Ibs of anhydrous ammonia needed/day
Addition of
nutrients.
Nutrients
should be
applied with
Is the aeration
tank pH 6.5.
Prevent
problem at
source.
Effect of
nitrification.
Nutrients should be added at the influent end of the aeration tank. The
settleability of the sludge should be carefully observed to see if it is
improving. If the settleability improves, the dose of nutrient can be reduced
by five percent per week until the settleability begins to decrease. Then
increase the dose by five percent and observe the settleability.
Nutrients are expensive and they should be applied with care. Nutrient
dosage may be increased with increased BOD concentrations which
takes into account the effects of the additional microorganism growth
that will occur. If the settleability does not improve readily, the nutrient
dosing should be continued until the actual problem is identified and
solved, because the problems that are causing the poor settleability may
be interrelated.
If the pH in the aeration tank is less than about 6.5, the settleability of the
sludge may be affected due to inhibition of the bacteria that settle readily.
If the pH of the raw wastewater is less than 6.5, the low pH problem is
probably due to industrial wastes and a survey should be conducted to
identify the industry that is in violation of its discharge permit. The best
procedure, if possible, is to prevent the problem by control at the source.
A good industrial waste monitoring and enforcement program will avoid
many difficulties in this area.
Nitrification destroys alkalinity and reduces the aeration pH level. If this
is the cause of the problem, raise the MLSS pH by adding caustic soda
or lime at the influent end of the aeration tank. If nitrification is required, it
is suggested that the MLSS .pH be maintained in the range of 7.2 to*7.8
to encourage an acceptable rate of nitrification. Care must be exercised
to ensure that the treatment system is not shocked by high pH levels or
overdosed to pH levels above 9.
11-86
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
The best method for determining the amount of caustic required to raise
Determining ^6 P^ involves a batch titration technique. A solution containing a known
amountof concentration of caustic is added dropwise to a sample of MLSS. The
caustic sample volume must be known and the sample must be stirred during this
required. determination. The dropwise addition of caustic is continued until the pH
is approximately 7.2. The amount of caustic added is proportional to the
amount required to raise the pH in the treatment system. The pounds of
caustic soda (NaOH) required is determined as follows:
Example Calculation
A. Data Required
1. Plant Q average daily = 7.5 mgd
ca)culate 2. Normality of NaOH used in titration = 0.02N
caustic needed. 3. Volume of NaOH used to titrate sample = 6.5 ml
4. Equivalent weight of 1.0 N NaOH (one liter) = 40,000 mg/l
5. Concentration of commercial caustic soda solution used =
25%
6. Volume of sample titrated = 1 liter
B. Determine the mg/l of pure NaOH needed to raise the sample pH
to about 7.2.
NaOH needed, =
mg/l
(pure NaOH)
(ml of NaOH used, liter sample volume) (Normality of NaOH) (Equivalent wt)
1000 ml/I
_ (6.5 ml) (0.02 N) (40,000 mg/l)
1000m I/I
= 5.2
C. Determine the Ibs/day of pure NaOH needed to adjust the pH of
the activated sludge.
NaOH needed, Ibs/day = (NaOH needed, mg/l) (Q, mgd) (8.34 Ibs/gal)
(pure NaOH)
= (5.2 mg/l) (7.5 mgd) {8.34 Ibs/gal)
= 325.26
•87
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
D. Determine the Ibs/day of commercial caustic soda solution
needed. Caustic soda is frequently used as a 25 percent by
weight solution.
25% NaOH solution, Ibs/day = Jibs of pure chemical needed/day) (100%)
Solution concentration %
_ (325.2 Ibs/day) (100%)
25%
= 1301
Determining the
amount of lime
required.
When determining the amount of lime needed for pH adjustment, obtain
and weigh a small amount (about 1 or 2 grams) of the actual lime to be
used in the treatment process. While a measured sample is stirring, add
small increments of the weighed lime (or suspension) until the pH is about
7.2. Then, weigh (or measure) that portion of the lime (or suspension) not
used to determine the amount of lime used in the titration. The pounds
of lime required is determined as follows;
How to
calculate lime
needed.
Example Calculation
A. Data Required
1. Plant Q, average daily = 7.5 mgd
2. Weight of lime before titration = 1.0100 grams
3. Weight of lime after titration = 1.0056 grams
4. Weight of lime used in titration = 0,0044 grams
5. Volume of sample titrated = 1000ml
B. Determine the mg/l of lime needed to raise the sample pH to
about 7.2.
Lime needed, mg/l = (Sample vol. ml) (lime used, g) (1000 mg/g)
1000 ml/l
_ (1000 ml) (0.0044g) (1000 mg/g)
1000 ml/l
= 4.4
C. Determine the Ibs/day of lime needed to adjust the pH.
Lime needed, Ibs/day = (Lime needed, mg/l) (Q, mgd) (8.34 Ibs/gal)
= (4.4 mg/l) (7.5 mgd) (8.34 Ibs/gal)
= 275
II-88
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Is the chemical
addition
effective?
Addition of
oxidizing
agents.
Treats the
symptoms—
not the cause.
Determining the
amount of Cl2
required.
The addition of lime or caustic to raise the pH is an expensive operation.
The settleabillty of the sludge should be closely monitored to observe
changes to ensure that benefit is being gained from the addition of caustic
or lime. If no improvement in settleability occurs within a 2 to 4 week
period, then the addition of caustic or lime should be halted.
The chlorination of the RAS is a dependable and effective control of
filamentous microorganisms. The filamentous microorganisms are more
readily affected by the addition of oxidizing agents such as chlorine
because they have a greater surface area to volume ratio. The addition of
other oxidizing agents such as hydrogen peroxide in dosages of 100 to
200 mg/l has also been reported to effectively control the presence of
filamentous microorganisms.
The use of oxidizing agents does not treat the cause of the problem but
only treats the symptoms. The most cost-effective solutions to the prob-
lems relating to filamentous microorganisms will involve treating the
cause of the problem, such as adding nutrients or increasing aeration,
and not the symptoms.
A dose of 2-3 Ibs of C\2 per 1000 Ibs of MLVSS per day has been reported
to effectively control filamentous microorganisms. The chlorine dosage
is expressed in the form of a ratio, which is a logical and useful approach
to chemical dosing in activated sludge systems. The proper chlorine feed
rate is determined as follows:
How to
calculateCl2
feed rate.
Example Calculation
A. Data Required
1. Aeration MLVSS = 2000 mg/l
2. Aeration volume = 1.26 mil gal
3. Desired C\2 dosage lbs/1000 Ibs MLVSS/day = 2.5 Ibs
B. Calculate the volatile solids inventory under aeration.
MLVSS, Ibs = (MLVSS, mg/l) (Aer. vol., mg) (8.34 Ibs/gat)
= (2000 mg/l) (1.26 mg) (8.34 Ibs/gal)
= 21,017 Ibs of MLVSS
C. Calculate the chlorine feed rate.
Cl2, Ibs/day = (C'2 dosage) (MLVSS, Ibs)
1000
_ (2.5 Ibs Cl2(21,017 Ibs of MLVSS)
1000 Ibs MLVSS
= 52.5 Ibs Cl2/day
11-89
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Outside help
may be needed.
If filamentous bulking is occurring quite often, it is recommended that
the operator have an experienced microbiologist identify the type of
filamentous organism causing the problem. After identifying the type of
organism, the microbiologist can provide data on the type and/or source
of the waste contribution to the growth of this organism. For instance, if
the filamentous organisms were identified as Toxothrix, a condition
promoting the production of sulfides (H2S) such as septicity in the col-
lection system or treatment plant is the probable cause. With this type of
insight into the problem, the operator can implement the appropriate
measures to reduce the number of future problems. In addition, the
operator will be better informed on how to handle the problem the next
time it occurs.
IstheF/M
normal?
D.O.
concentration is
important.
No Filamentous Microorganisms Present
Check the F/M to determine if the system is operating at a higher F/M
value than is normally used. The presence of small dispersed floes is
characteristic of an increased F/M. If the F/M is higher than normal by
10 percent or more the wasting rate should be decreased. The decrease in
the F/M should be reflected by the disappearance of the dispersed floes
over a period of a week.
The amount of turbulance and D.O. in the aeration tank is also important.
D.O. concentrations above 3.0 mg/l indicate that excess air is being used,
and the aeration rate should be reduced to lower the D.O. concentrations
to the range of 1 to 3 mg/l. Excessive turbulance (overaeration) in the
aeration tank will hinder MLSS floe formation and may result in the carry-
over of pinpoint floe with the clarifier effluent.
Clumping/Rising Sludge (See Case 3 on Figure II-20)
Result of
dentrification.
When the sludge initially settles during the 30-minute settling test and then
floats to the surface after one to two hours, the problem is generally that
denitrification is occurring in the clarifier, as illustrated in Figure 11-19. Nitrate
ions are reduced to nitrogen gas and bubbles are formed in the MLSS floe as
a result of this process. The bubbles attach to the biological floes and float
the floes to the surface of the clarifier where they eventually flow over the weir.
Causes of
clumping and
rising.
Some probable causes of sludge clumping:
1. The activated sludge process is being operated at a low F/M ratio and
consequently the process has "slipped" slightly or completely into
the nitrification zone.
2. The sludge is being held too long in the clarifier and consequently all
the available dissolved oxygen has been used by the microorganisms.
The return sludge should have a D.O. content of not less than 0.2 mg/l.
II-90
-------
30 MINUTE SETTLING
ONE TO TWO HOURS SETTLING
OBSERVATION
STIR SLUDGE
AND LET
SETTLE AGAIN
ACTION
REMEDY
GIVES OFF BUBBLES _DENITHIFICATION _INCREASE RAS RAIT
AND SETTLES IN CLAMPERS INCREASE WAS RATE
CD
30 MINUTE SETTLING OBSERVATION
POOR
SETTLING PERFORM
CLOUDY MICROSCOPIC
SUPERNA- EXAMINATION
TANT
ACTION REMEDY
-INACTIVE PROTOZOA - HIGH CHANCE OF RECENT TOXIC LOAD — CUT BACK WASTING,MAINTAIN AIR,KEEP CLOSE WATCH
F/M TOO HIGH,
"ORGANIC OVERLOAD
-NO PROTOZOA (
- REDUCE WASTING AND INCREASE RETURN
-LOW D.O.,— INCREASE OXYGEN
-LOW TO NORMAL F/M '
_ADEQUATE D.O.
TOXIC WASTE
IF POSSIBLE GET SEED SLUDGE
STOP WASTING UNTIL SOLIDS BUILD UP
DISPERSED FLOC
"HEALTHY PROTOZOA
TOO MUCH
MIXING
- REDUCE AERATION
CASE 3 AND CASE 4
FIGURE 11-20
tn
T tn
TjO
2 w
O r-
O c
m o
co O
w m
O -o
O 33
Z O
H O
31 m
O co
r- cn
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
3.
Higher than normal wastewater temperature resulting in a higher rate
of microorganism activity which causes the process to nitrify at a
higher F/M ratio. A higher rate of microorganism activity will also
result in a faster depletion of the dissolved oxygen in the clarifier
sludge and consequently a greater potential for septicity and deni-
trification.
Corrective
measures for
sludge
clumping.
Figure 11-19
Clumping In Clarifier
The following applicable measures should be implemented to correct the
sludge clumping problem:
• Increase the return activated sludge flow rate to reduce the detention
time of the sludge in the clarifiers. A periodic measurement of the
clarifier sludge blanket depth will help to determine the proper return
rate.
• Where possible, increasing the speed of the sludge collector may
lessen the problem.
• When the suction type of sludge collector is employed, check that all
suction tubes are flowing freely with a fairly consistent suspended
solids concentration. Some of the suction tubes may be improperly
adjusted or plugged resulting in coning in some areas and a sludge
blanket build-up in other areas.
• If nitrification is not required, gradually increase the sludge wasting
rate to stop nitrification. Initially, the solids inventory should be de-
creased by 10 percent over one week, and then the process operation
must be observed over the following two weeks to see if treatment has
improved.
I-92
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Perform the
30-minute
settling test.
Cloudy Secondary Effluent (See Case 4 on Figure 11-20)
During the periods of high effluent suspended solids concentration, the
settleability (or settling) test should be run immediately and followed up with
additional tests several times a day until the problem is identified and cor-
rected. When the mixed liquor in the settleability test settles poorly leaving
a cloudy supernatant, the next step is to perform a microscopic examination
of the mixed liquor. One of the important purposes of this examination is to
determine if protozoa are present and the status of their health. The use of a
microscope for process control and troubleshooting is further described in
Section IV, "LABORATORY CONTROL."
Protozoa appear
Inactive.
Protozoa are
active.
Protozoa Are Present
If protozoa are present, their actions and appearance should be observed.
When the protozoa appear to be inactive it frequently indicates that a slug
of toxic material has recently entered the treatment system. The operator
should reduce the sludge wasting rate and maintain normal operation
until the material passes through the treatment system. Refer to Table
11-12.
If the protozoa appear normal and active, but the cloudy condition per-
sists, the activated sludge floe may be dispersed due to excessive turbul-
ence (overaeration) in the aeration tank. Generally, overaeration is
characterized by D.O. concentrations above 3 mg/l in the aeration tank.
Proper control of the aeration system is further described in Section 2.04,
"AERATION AND D.O. CONTROL."
No protozoa
present.
What to check.
Protozoa Are Not Present
If no protozoa are present, there are two possibilities. First, the F/M is too
high and the system is operating in an overloaded manner. Approach and
solve the problem as follows:
• Calculate the F/M. Refer to Section 2.04, Constant F/M Control.
• Compare calculated F/M with F/M's for the periods of satisfactory
operation.
• If the F/M is greater than these values, the wasting rate should be
reduced to raise the solids inventory.
• Increase the RAS flow to lower the sludge blanket level in the
clarifier to the minimum. The increased RAS flow will increase the
solids inventory by transferring the MLSS stored in the clarifier
into the aeration tank.
Second, the F/M may be lower than or within the normal range. This
condition is frequently associated with one of the following:
• Low D.O. concentration in the aeration tank. If the average D.O.
measured at several locations in the aeration tank is less than 0.5
mg/l, aeration should be increased until the D.O. is between 1 and
3 mg/l.
II-93
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
A toxic waste entered the treatment system. Toxic waste adversely
affects the health of the activated sludge. A short term solution to
this problem involves the addition of large quantities of healthy
seed sludge to build-up the volatile solids inventory. The long term
solution requires an industrial waste survey to identify the source
of the toxic material and the enforcement of strict industrial waste
discharge ordinances. Table 11-12 shows the levels of heavy metals
that can usually be tolerated by activated sludge microorganisms
on both a long-term and short-term basis.
Ash-like solids
floating on
clarifier
surface.
TABLE 11-12
ALLOWABLE CONCENTRATIONS OF HEAVY METALS
CONSTITUENT
CADMIUM
CHROMIUM
COPPER
IRON
LEAD
MANGANESE
MERCURY
NICKEL
SILVER
ZINC
COBALT
CYANIDE
ARSENIC
CONCENTRATION AT WHICH DAMAGE TO
ACTIVATED SLUDGE MIGHT OCCUR
CONTINUOUS LOADING
1 mg/1
2 mg/1
1 mg/1
35 mg/1
1 mg/1
1 mg/1
0.002 mg/1
1 mg/1
0.03 mg/1
1 to 5 mg/1
>1 mg/1
1 mg/1
0.7 mg/1
SLUG LOADING
10 mg/1
2 mg/1
1.5 mg/1
100 mg/1
0.5 mg/1
5 mg/1
0.25 mg/1
25 mg/1
1 to 10 mg/1
11-94
-------
ACTIVATED SLUDGE PROCESS
SECTION II - PROCESS CONTROL
Ashing (See Case 5 on Figure 11-22)
The appearance of small ash-like sludge particles floating on the surface of
the secondary carifier (Figure 11-21) is commonly referred to as "ashing."
Causes of
•shlng.
Corrective
measures for
•thing.
Figure 11-21
Ashing In Clarlfler
Some probable causes of the ashing problem are as follows:
1. The beginning of denitrification is occurring in the clarifier.
2. The mixed liquor has an unusually high grease content.
The ashing problem should be approached and solved as follows:
First, stir the sludge which floats In the 30-minute settling test.
• If it Settles • This indicates that denitrification has begun—See "Sludge
Clumping" for solution.
• If It does not settle, there may be excessive amounts of grease In the
sludge. Perform a grease analysis. If the grease content exceeds 15
percent by weight of the MLSS, the problem may be one of the following:
• The primary tank scum baffles are malfunctioning due to hydraulic
overloading or mechanical failure. Specific attention should be given
to scum baffles and the scum collection system in the plant.
• Too much grease Is being dumped In the sewer by an industrial or
commercial discharger. If too much grease is In the raw wastewater,
an Industrial waste survey must be conducted to Identify the discharger,
and have the problem corrected.
I-95
-------
30 MINUTE SETTLING
OBSERVATION
ASH ON SURFACE - STIR FLOATING FLOC
ACTION
REMEDY
INCREASE RETURN
- RELEASES BUBBLES AND SETTLES — BEGINNING OF DENITRIFICAT1ON — OR
INCREASE WASTING
PROBABLY EXCESSIVE GREASE
• DOES NOT RELEASE BUBBLES CHECK IF GREASE ABOVE 15 S OF
NOR SETTLE MLVSS BY WEIGHT
TRY TO IMPROVE GREASE
CAPTURE UPSTREAM
GREASE TRAP CLEANING
Cfl >
TJ OT
33 I
to m
to -o
O =0
So
z o
_i m
3 w
g w
30 MINUTE SETTLING
OBSERVATION
PINPOINT FLOC
OR STRAGGLERS
OBSERVED IN
SUPERNATANT
ACTION
DENSE, COMPACT FLOC
REMEDY
EXTENDED AERATION ZONE-INCREASE WASTING
TO MUCH SHEAR-REDUCE AERATION IF POSSIBLE
L.GHT, FLUFFY FLOC -
TOO H lf~H
OVERLOAD
~ REDUCE WAS™G
CASE 5 AND CASE 6
FIGURE 11-22
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Pinpoint Floe (See Case 6 on Figure 11-22)
Old sludge,
poor floe.
The appearance of small dense, pinpoint floe particles suspended in the
secondary clarifier is a common problem often seen in treatment plants
operating near or in the extended aeration range. This problem is generally
related to an old sludge that settles rapidly but lacks good flocculation
characteristics.
Causes of
pinpoint floe.
Corrective
measures for
pinpoint floe.
Some probable causes of the pinpoint floe problem are as follows:
1. The process is being operated at a F/M near or in the extended aera-
tion range resulting in an old sludge with poor floe formation char-
acteristics.
2. Excessive turbulence (overaeration) in the aeration tank shearing the
floe formations.
The following applicable measures should be implemented to correct the
problem:
• If the sludge settling characteristics observed during the 30-minute
settling test indicate a "too rapidly settling" sludge with poor floe
formation, the clarifier effluent quality can be improved by gradually
increasing the wasting rate. If nitrification is required, caution must be
exercised not to decrease nitrification by wasting too much sludge.
• If good settling with a clear supernatant above the settled sludge is
observed in the settling test, check for proper aeration and mixing in
the aeration tank. If the average D.O. concentration in the aeration
tank is more than 3 mg/l, the SCFM air rate should be reduced until the
aeration D.O. is between 1 and 3 mg/l.
Stragglers/Billowing Solids (See Case 6 on Figure II-22)
MLSS too low -
young sludge.
Causes of
stragglers.
The appearance of small, light, fluffy sludge particles rising (sometimes
billowing) to the clarifier surface and discharging over the effluent weirs is a
problem often seen when the MLSS concentration is too low. This problem is
generally related to a young sludge (high F/M) which settles poorly. The
problem of light floe particals is generally worse in shallow clarifiers, partic-
ularly at high HAS flow rates. At some plants, the floes are particularly notice-
able during the early morning hours.
Some probable causes of this problem are as follows:
1. The aeration tank is being operated at a MLSS concentration that is
too low. This would normally occur during process start-up until the
proper MLSS concentration is established. A sludge wasting rate that
is too high will result in low MLSS and a high F/M.
2. Sludge is being wasted on a batch basis during the early morning
hours resulting in a shortage of microorganisms to handle the day-
time organic loading.
3. The return sludge flow rate is high.
II-97
-------
ACTIVATED SLUDGE PROCESS
SECTION II-PROCESS CONTROL
Corrective
measures for
stragglers.
The following applicable measures should be implemented to correct the
problem:
• Decrease the sludge wasting rate to raise the MLSS concentration and
increase the sludge age.
• If possible, avoid high sludge return rates.
• If wasting sludge on a batch (or intermittent) basis, avoid wasting
during the early morning hours. All the organisms are needed at this
time to handle the daily increase in organic loading.
REFERENCES
Boe, Owen, K., "Activated Sludge Control With a Settleometer and Centrifuge," U.S.
Environmental Protection Agency, Region VIII.
Eckenfelder, W.W., Biological Waste Treatment, Pergamon Press, New York, 1961.
Environmental Protection Agency, Process Design Manual for Upgrading Existing
Wastewater Treatment Plants, 1974.
Hammer, Mark, J., Water and Waste-Water Technology, John Wiley & Sons, Inc.,
New York, 1975.
Hawkes, H.A., The Ecology of Waste Water Treatment, Pergamon Press, Oxford, 1963.
Kerri, Kenneth D., et al., "A Field Study Training Program", Operation of Wastewater
Treatment Plants, (Chapter 7), Sacramento State College Department of Civil
Engineering.
McKinney, Ross E., Microbiology for Sanitary Engineers, McGraw-Hill Book Company
Inc., New York, 1962.
Metcalf & Eddy, Inc., Wastewater Engineering, McGraw-Hill, New York, 1972.
Stevens, Thompson, Runyan, Inc., Operator's Pocket Guide to Activated Sludge,
Parts I and II. Published by the Authors, 5505 S.E. Milwaukie Avenue, Portland,
Oregon 97202,1975.
Stewart, M.J., Activates Sludge Process Variations - The Complete Spectrum, Parts
I, II, III. Water and Sewage Works, April, May, June, 1964.
Water Pollution Control Federation: "Sewage Treatment Plant Design," Manual of
Practice No. 8, Washington, D.C., 1967.
Water Pollution Control Federation, "Operation of Wastewater Treatment Plants,
Manual of Practice, No. 11,1976.
West, Alfred W., Operational Control Procedures for the Activated Sludge Process,
Parts I, II, IIIA, and IIIB, U.S. EPA, National Training and Operational Technology
Center, Cincinnati, Ohio, 1975.
II-98
-------
ACTIVATED SLUDGE PROCESS
SECTION III - FUNDAMENTALS
3.01
INTRODUCTION
Where does
activated
sludge come
from?
The term "activated sludge" is derived from wastewater being mixed with air
or oxygen for a length of time to develop a brown floe which consists of
billions of microorganisms and other material. These microorganisms use
most of the suspended and dissolved material found in the wastewater as
their food (BOD) source. The microorganisms are aerobic and therefore re-
quire an air or oxygen supply to function. Their need for food and air or oxygen
is similar to the needs of humans and other animals.
The process
provides an
environment to
control
microorganisms.
The activated sludge process provides the environment to keep these micro-
organisms under controlled conditions so that they can remove most of the
solids from the wastewater as it passes through the process. The environment
is provided by four basic systems which make up the activated sludge process.
These systems include aeration, sedimentation, return activated sludge
(RAS) and waste activated sludge (WAS) as illustrated in Figure 111-1.
SECONDARY
CLARIFIER
(SEDIMENTATION)
SETTLED
WASTEWATER
AERATION TANK
EFFLUENT
AIR OR OXYGEN ADDED
RETURN ACTIVATED SLUDGE
WASTE
ACTIVATED
SLUDGE
TYPICAL ACTIVATED SLUDGE PROCESS
FIGURE III-l
Process
provides
treatment to
reduce
pollution of
receiving
waters.
Be familiar
with the terms
used in
operating the
process.
The purpose of the activated sludge process is to remove as much of the
organic matter in the wastewater as possible by biological means. In doing
this, the process produces an effluent quality high enough that beneficial
uses of receiving waters will not be hindered; thus, a high level of treatment
must be achieved.
Definitions
In order for the operator to understand the concepts involved in operating
the activated sludge process, he must first understand the terms associated
with it.
1-1
-------
ACTIVATED SLUDGE PROCESS
SECTION III - FUNDAMENTALS
ACTIVATED SLUDGE is the floe of microorganisms that form when
wastewater is aerated.
MIXED LIQUOR is the mixture of activated sludge and wastewater
in the aeration tank.
MIXED LIQUOR VOLATILE SUSPENDED MATTER (MLVSS) have
been found to be proportional to the microorganisms concentration in
the aeration tank.
KINETICS is the approach used to mathematically simulate biological
treatment processes by relating the growth rate of the microorganisms
to the food and microorganism concentration.
NET GROWTH RATE is the microorganism rate of growth minus the
microorganism decay rate. Also referred to as the net sludge yield.
MEAN CELL RESIDENCE TIME (MCRT) is the inverse of the net
growth rate and is equal to the average time a microorganism spends
in the treatment process. The MCRT is an important kinetic parameter
that is very useful in process control.
FOOD TO MICROORGANISM RATIO (F/M) is the ratio of the amount
of food expressed as pounds of COD ( or BOD) applied per day, to the
amount of microorganisms, expressed as the solids inventory in
pounds of volatile suspended matter. The F/M is mathematically re-
lated to the MCRT, and is also an important process control tool.
GOULD SLUDGE AGE (GSA) is the ratio of the pounds per day of
influent wastewater suspended matter to the solids inventory in the
aeration tank. Thus, GSA or Sludge Age should not be confused with
the term MCRT.
RETURN ACTIVATED SLUDGE (RAS) is the settled mixed liquor that
is collected in the clarifier underflow and returned to the aeration basin.
WASTE ACTIVATED SLUDGE (WAS) is the excess growth of micro-
organisms which must be removed to keep the biological system in
balance. Various control techniques have been developed to estimate
the amount of WAS that must be removed from the process.
COMPLETE MIX ACTIVATED SLUDGE describes an ideal mixing
situation where the contents of the aeration tank are at a uniform con-
centration. In other words, everything in the tank is dispersed by a
back mixing action.
PLUG FLOW ACTIVATED SLUDGE describes an ideal situation
where the contents of the aeration tank flows along the length of the
tank.
BACK MIXING refers to mixing the contents of a tank in the longi-
tudinal or flow oriented direction.
TRANSVERSE MIXING, also known as cross roll, refers to mixing in a
direction across the direction of flow.
SLUDGE REAERATION refers to the practice of aerating the RAS
before it is added to the mixed liquor.
PROCESS LOADING refers to the organic loading range as measured
by the F/M.
CONVENTIONAL LOADING refers to a process loading of 0.2 to 0.5
Ibs BOD applied/lb MLVSS/day.
HIGH RATE LOADING refers to a process loading of two to three
times the conventional loading rate.
1-2
-------
ACTIVATED SLUDGE PROCESS
SECTION III - FUNDAMENTALS
EXTENDED AERATION LOADING refers to low rate loading that is
one half to one tenth of the conventional loading rate.
SETTLEABILITY is the measure of the volume occupied by the mixed
liquor after settling in a graduated cylinder for 30 minutes. Settleability
is generally expressed as a percentage based on the ratio of the sludge
volume to the supernatant volume.
SOLIDS INVENTORY is the amount of volatile suspended solids in the
treatment system. The Solids Inventory is also known as the Volatile
Solids Inventory.
3.02 PROCESS DESCRIPTION
Influent
Wastewater
combined with
RAS to form
Mixed Liquor.
Waste Activated
Sludge.
Process
Balance
based on food
limited growth
Well settling
mixed liquor is
the key to
activated
sludge
treatment.
The activated sludge process involves growing microorganisms on the
organic material in wastewaters. Return Activated Sludge (RAS) from the
clarifier underflow is combined with the influent wastewater in the aeration
tank to form the mixed liquor. The mixed liquor is usually aerated for a period
of several hours in the aeration tank. During this time some of the organic
material in the wastewater is converted into new microorganisms and some
in converted (oxidized) to various other products including carbon dioxide.
The mixed liquor flows through the aeration tank and into the clarifier where it
settles to form the RAS. The clear liquid remaining above the settled mixed
liquor is called the secondary effluent which is discharged from the process.
A portion of the activated sludge is purposely removed by wasting it from the
process. The wasting of sludge is necessary to maintain the desired quantity
of microorganisms in the process. Wasting is necessary because the micro-
organisms grow and multiply as they eat the food supply in the wastewater.
The basic idea behind successful operation of an activated sludge system is
to keep a balance of microorganisms to the amount of food in the wastewater.
Proper operation will provide the microorganisms with a balanced diet of
food, nutrients, and oxygen. If nutrients or oxygen limit the growth of the
microorganisms, they will not settle satisfactorily in the clarifier. Proper
operation makes food the only part of microorganisms diet that limits their
growth. As long as food is the only limit to their growth, the process can be
controlled and maintained so that they settle well in the clarifier.
If the organic material conversion process is limited by oxygen or nutrients,
the microorganisms in the mixed liquor will not settle well in the secondary
clarifier. The activated sludge process depends on settling the mixed liquor
so that it can be returned to the aeration tank to keep in balance with the
organic material in the incoming wastewater. This balance is generally related
to process loading as expressed by the F/M ratio. Inability to settle the
mixed liquor can result in a high concentration of suspended solids in the
clarifier effluent. Proper control of the activated sludge process will produce
a mixed liquor with good settleability. If the conditions in the aeration system
deteriorate, the formation of undesirable microorganisms can result. Typical
undesirable microorganisms include the filamentous organisms. Filamentous
microorganisms grow as long, thread-like organisms having an increased
surface area. This increased surface area makes it possible for the filamentous
organisms to grow in conditions of low dissolved oxygen or low nutrient
1-3
-------
ACTIVATED SLUDGE PROCESS
SECTION III - FUNDAMENTALS
Filaments make
poor settling
sludge.
concentrations. Unfortunately, filamentous organisms hinder settling by
causing excessive bridging and matting of the floes, resulting in a mixed
liquor which does not settle well. Poor settleability associated with the pre-
sence of too many filamentous organisms is known as bulking sludge.
Cure bulking by
making
environment
less suitable for
their growth.
The consequences of bulking sludge are that poorly settling mixed liquor
cannot be returned to the aeration tank and that the clarifier effluent sus-
pended solids will be high. Operation in a bulking sludge condition will
eventually result in the loss of the mixed liquor over the weirs into the effluent.
Typical approaches to curing bulking include treating the return activated
sludge with oxidizing agents, such as chlorine or hydrogen perioxide, and
improving treatment conditions so that the environment is less favorable to
the growth of filamentous organisms.
Aeration System
Aeration
provides DO
and mixing.
Aeration serves the dual purpose of providing dissolved oxygen and mixing
of the mixed liquor and wastewater in the aeration tank. Aeration is usually
provided by either diffused air or mechanical aeration systems. Diffused air
systems consists of a blower and a pipe distribution system that is used to
bubble air into the mixed liquor. Mechanical aeration systems consist of a
pumping mechanism that disperses water droplets through the atmosphere.
Most common.
Fine and coarse
bubbles.
Diffused Air System
Diffused air systems are the most common types of aeration systems
used in activated sludge plants. The distribution system consists of
numerous diffusers generally located near the bottom of the aeration
tank. The diffusers are located in this position to maximize the contact
time of the air bubbles with the mixed liquor.
Diffusers are designed to either produce fine or coarse bubbles. Fine
bubble diffusers were used frequently in the treatment plants designed in
the period from 1950 to 1970, because it was felt that the increased oxygen
transfer efficiency* of the fine bubble diffusers was important. Unfortu-
nately, the fine bubble diffusers are easily clogged by biological growths
and by dirty air, resulting in high maintenance costs.
Tend to clog.
Fine Bubble Diffusers
The most common type of fine bubble diffusers are nylon or dacron
socks and saran wrapped tubes. These diffusers have oxygen transfer
efficiencies of around eight percent. Sketches of these types of fine
bubble diffusers are shown below In Figure III-2.
The major limitation of fine bubble diffusers Is that they are easily
clogged. Diffusers are self-sealing If dirty air Is pumped Into them.
The diffusers are also subject to clogging because of biological
growths. The air supply for all fine bubble diffusers should be filtered.
Refer to Section I, "TROUBLESHOOTING", for observations which
Indicate dlffuser clogging.
-------
ACTIVATED SLUDGE PROCESS
SECTION III - FUNDAMENTALS
Lower oxygen
transfer
efficiencies,
lower costs and
maintenance
requirements.
Substantially
1*88
maintenance
needs.
SKETCHES OF A NYLON SOCK,
AND A SARAN WRAPPED TUBE
FIGURE III-2
'Oxygen transfer efficiency is defined as the amount of oxygen transferred to
the water divided by the amount of oxygen supplied.
Coarse Bubble Diffusers
Coarse bubble diffusers are usually made by drilling holes in pipes or
by loosely attaching plates or discs to a supporting piece of pipe.
Coarse bubble diffusers have lower oxygen transfer efficiencies than
the fine bubble diffusers. A typical oxygen transfer efficiency would
be about 5 percent. Coarse bubble diffusers are becoming increasingly
popular because of their lower costs and maintenance requirements.
Many of the treatment plants surveyed during the on-site visits had
changed over to the coarse bubble diffusers, and these plants reported
that the coarse bubble diffusers were working quite well. The main-
tenance needs were reported to be substantially less than those of
the fine bubble diffusers. Figure 111-3 presents sketches of two types
of coarse bubble diffusers.
SKETCHES OF A SPARGER AND
DISC TYPE COARSE BUBBLE DIFFUSER
FISURE IJ1-3
111-5
-------
ACTIVATED SLUDGE PROCESS
SECTION III - FUNDAMENTALS
Surface and
Turbine.
Floating or
platform
mounted.
Oxygen transfer
2lb
Mechanical Aeration Systems
There are two types of aerators in common use today. These Include the
surface and turbine aerators. Surface aerators use a rotating propeller
that pumps the mixed liquor through the atmosphere above the aeration
tank. Oxygen transfer is achieved by the aerator propeller spraying the
mixed liquor through the atmosphere. Turbine aerators increase oxygen
transfer efficiency by creating turbulence in the area of the rising bubbles.
Surface Aerators
Surface aerators either float or are mounted on supports in the aeration
tank. Materials, such as epoxy coated steel are used in the construc-
tion of surface aerators to reduce corrosion.
The oxygen transfer efficiency of a surface aerator increases as the
submergence of the propeller is increased. However, power costs also
increase because more water is sprayed.
Oxygen transfer efficiencies for surface aerators are stated in terms
of pounds of oxygen transferred per horsepower per hour (Ib O2/hp/hr),
Typical oxygen transfer efficiencies are about 2 Ib O2/hp-hr. Surface
aerators are sometimes equipped with draft tubes to improve their
mixing characteristics.
Another type of surface aerator used in oxidation ditches is the brush
aerator, which is a horizontally mounted brush located just below the
water surface. The brush is rotated rapidly in the water to supply mix-
ing and aeration.
Figure 111-4 shows a floating and a platform surface aerator.
WATER SURFACE
TYPICAL FLOATING AND PLATFORM SURFACE AERATORS
FIGURE III-4
-------
ACTIVATED SLUDGE PROCESS
SECTION III - FUNDAMENTALS
Improved
oxygen
transfer—Use in
complete mix
process.
Turbine Aerators
Turbine aerators are used because of improved oxygen transfer effici-
ency and lower horsepower requirements. Turbine aerators are most
frequently used in complete mix activated sludge processes. Figure
111-5 shows a typical turbine aerator without the draft tube.
WATER SURFACE
AIR OR O2
DIFFUSER
TYPICAL TURBINE AERATOR
FIGURE III-5
Sedimentation System
Function of
secondary
clarifier.
Description.
As the mixed liquor flows out of the aeration tank, it is transferred to a sedi-
mentation unit which is commonly called a secondary clarifier. The secondary
clarifier provides a reduction in flow velocity needed to allow the mixed
liquor to separate from the treated wastewater and settle by gravity to the
bottom. Effective settling depends on maintaining the best balance between
the microorganisms in the mixed liquor and the organic material contained in
the wastewater to be treated. A good quality activated sludge is essential to
achieve good settling characteristics. A process control parameter which
relates to this balance is called the F/M ratio.
The design and construction of secondary clarifiers for activated sludge
treatment incorporates several methods for the removal of settled sludge.
These generally include the conventional sludge collection equipment found
in rectangular and circular primary sedimentation units which collects to a
central hopper and, in recent years, suction-type collectors as shown in Figure
111-6. Determination and review of clarifier operational parameters are dis-
cussed in Section 2.03, "PERFORMANCE EVALUATION."
1-7
-------
ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
Figure 111-6
Sludge Collector with Suction Draw Tubes
Most technical
articles have
been written for
the engineer
and not the
operator.
Only two basic
ways of
evaluation
process
variations
1) Loading
2) Physical
arrangement.
3.03 ACTIVATED SLUDGE PROCESS VARIATIONS
In the past many technical articles have been written, describing a number of
different variations of the activated sludge process. Generally the processes
included are conventional, tapered aeration, complete mix, extended aeration,
step aeration, contact stabilization, and the Kraus process. Unfortunately,
these discussions have been rather simplified and they have not kept pace
with our increasing understanding of the principles behind all the activated
sludge processes. The articles have been written with the design engineer
rather than the operator in mind. A related,problem is the fact that most
articles discussing the application of process theory to operation do not de-
scribe the operation of these individual process variations, but, rather, describe
principles that are supposed to apply to the process in general, or to the
complete mix or conventional process modes. Another problem is that some
of the "process variations" are very difficult, such as the conventional and
contact stabilization processes, and others are very minor variations or more
basic processes, such as tapered aeration.
If one studies the problem, it becomes obvious that there are only two basic
ways of looking at the question of activated sludge process variations: from
the standpoint of the various ranges of process loading, and from the stand-
point of the various physical arrangements of the process. The various levels
of process loading are described by the F/M ratio and MCRT. The term, "physical
arrangements" is used to refer to the structural arrangement of the aeration
tank as well as the various arrangements of the process streams that are used
to provide flexibility.
I-8
-------
ACTIVATED SLUDGE PROCESS
SECTION III - FUNDAMENTALS
Process Loading Ranges
Three basic
loading ranges.
The loading
range is often
fixed by design.
Over the years a number of studies have been conducted describing the in-
fluence of process loading on the behavior of the activated sludge process,
and most of these have identified three basic ranges of process loading where
the aeration solids can be successfully settled making process operation
feasible. The three basic ranges of process loading are shown in Figure 111-7 for
a plant operating on a typical domestic wastewater at a temperature of about 20
degrees centigrade. For the purpose of this discussion, these loading ranges
will be referred to as the high rate, coventional rate, and extended aeration.
Generally the range of process loading in which a plant is to be operated is
not a matter for the operator to decide. In fact operators who try to operate a
plant in a loading range other than that for which it was designed are usually
disappointed, and this practice is not recommended. Most plants of 1 mgd or
more are designed to operate in the conventional range, although many are
designed to operate in the lower portions of that range to ensure that effective
nitrification occurs.
Not commonly
used.
High Rate
The high rate loading range takes advantage of the settleability of sludge
when the treatment system is loaded at a fairly high rate. Generally, the
level of treatment which results is somewhat comparable to a typical
high-rate trickling filter plant. Although the process can be applied effec-
tively in certain situations, large-scale use of this modification of the
process at their 300 rngd Hyperion plant, choosing to treat only about one
better than it is at slightly lower loadings, is apparently not good enough
and this, combined with the higher level of soluble BOD, greatly reduces
the treatment efficiency. The City of Los Angeles has abandoned this
process at their 300 mdg Hyperion plant, choosing to treat only about one
third of their flow at conventional loading levels. Apparently the quality of
the combined effluents consisting of 100 mgd treated by conventional
activated sludge and 200 mgd treated with primary sedimentation only is
as good or better than the quality when the entire flow was treated by the
high rate process.
Typical
operation for
medium and
large sized
plants.
Nitrification
at lower end of
loading range.
Conventional Rate
For a typical domestic wastewater at about 20 degrees centigrade the con-
ventional process operates between MCRT values of 5 to 15 days and F/M
ratios of 0.2 to 0.5 Ibs BOD applied/lb MLVSS/day. Most large municipal
treatment plants operate in the conventional activated sludge zone. Plants
operating in the middle of this range produce an excellent effluent quality
and do not nitrify. At the lower end of this loading range, an even better
effluent is sometimes produced although problems sometimes occur
when the plant slips slightly or goes completely into nitrification, which
often results in operational problems such as rising sludge in the clarifiers,
the appearance of filaments in the sludge, and the formation of a brown,
greasy-appearing foam.
III-9
-------
400
1/1
i
x
LU
o
as
i
o
ID
WASTEWATER TEMPERATURE IS APPROXIMATELY 20°C
300 ••
200 -•
100 --
s
E D
' 05
HIGH RATE ACTIVATED SLUDGE
EXTENDED
AERATION
CONVENTIONAL
ACTIVATED SLUDGE
-t-
4-
0,20 0.40 0.60 0.80 1.00
F/M RATIO (LB BOD APPLIED/LB SOLIDS INVENTORY/DAY)
1.20
SLUDGE SETTLEABILITY VS. ORGANIC LOADING
FIGURE III-7
-------
ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
Poor sludge
settleabilityat
upper end of
loading range.
Filamenteous growths and poor sludge settleability have been associated
with the conventional process at the upper end of this loading range. Dis-
persed growth and a cloudy effluent are also quite common. Usually the
operator can see this sort of condition coming by plotting a trend of the
organic loading in his treatment process (either the F/M ratio or the actual
MCRT). Other signs of a more physical nature may also be used by the
operator to evaluate an "overloaded" condition. For example, once high
loading levels are reached, a stiff, white detergent-type foam is often
observed on the aeration tanks.
Extended Aeration Rate
Frequently used
with smaller
plants—Less
WAS than
conventional
plant.
Occasional
wasting is
essential.
Pin floe Is
frequent
problem.
Denitrlficatlon
Is also a
problem
The lowest range of process loading where successful operation may be
accomplished is the extended aeration range. Generally plants operating
in this range are small in size and do not receive 24 hour supervision. Such
plants are very conservative in design and generally operate with an
MCRT of 20-40 days and F/M ratio of 0.05 to 0.15 Ibs BOD applied/lb
MLVSS/day, based on typical domestic wastewater at a temperature of 20° C.
The extended aeration process is sometimes referred to as the "total
oxidation process" This name is derived from the fact that these plants
are designed with such low loadings that the simple kinetics theory used
to describe processes of higher loading would predict that all of the in-
fluent BOD will be converted to CO2- This is why some manufacturers
claim that no wasting is necessary for their extended aeration designs. In
actual fact, there is no such thing as the "Total Oxidation Process" and
even after extremely long periods of aeration, suspended matter remain in
the effluent. Although sludge wasting need not be conducted on a daily
basis in plants operating in the extended aeration range, occasional wast-
ing is an absolute necessity.
Often the effluent of the extended aeration processes contains small pin-
point floe which may be observed passing over the weirs of the secondary
clarifier. When the loading in an extended aeration plant is in the higher
portion of the loading range, a number of operating problems may occur.
Because the entire extended aeration range is in the nitrification zone,
denitrification and rising sludge problems may result. Also the same
brown, greasy foam, filaments, and poor settleability mentioned in dis-
cussion of the conventional process at low loading may occur under these
circumstances. If possible, these problems may be improved by using
additional aeration capacity or decreasing the level of MLSS.
Wasting is
necessary.
Other problems associated with the extended aeration process have to do
with the fact that some sludge must be wasted and that many operators
have been told that wasting is not necessary, indeed, many small extended
aeration plants have no facilities installed to make wasting possible.
Under these circumstances, it is not uncommon for sludge to creep over
the clarifier weirs whenever fluctuations in flow occur. Unfortunately, this
results in a significant reduction in removal efficiency.
1-11
-------
ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
Control sludge
wasting.
Need to have
wasting
facilities.
Extended
aeration plants
subject to
problems due to
flow variation.
If the operator of an extended aertion plant frequently experiences losses
of solids over the effluent weirs, there are two remedies which can be
used; regular sludge wasting, and flow equalization. Of the two, sludge
wasting is by far the most important. A conscientious operator should
keep track of the solids he intentionally wastes, and the solids that go
over the effluent weirs. In this manner, the plant can be operated to achieve
a specific value of MCRT.
If plant design provisions have not been made for sludge wasting, the
operator should attempt to improvise some sort of temporary or perma-
nent method. Depending on the specific design of the plant and the
geography and environmental conditions around it, the operator may be
able to arrange for constructing sludge beds or lagoons for wasting
facilities. The sludge from plants of this sort is generally already "aero-
bically" digested: and therefore, if it is placed directly on a sand bed for
drying, or in a lagoon, it will generally not have a foul odor.
Even when regular wasting is carried out, a high degree of flow variation
in extended aeration plants will often cause solids losses. This is probably
due to the particular characteristics of the floe produced in the low loading
range as well as to the flow variations themselves. In some cases, if the
aeration tank is large enough, the operator can design a makeshift system
which will allow the use of the aeration tank as a flow equalization device.
Minor modifications of this sort will go a long way to improve suspended
solids removal in plants where losses are primarily due to hydraulic
fluctuations.
Physical Arrangements of the Process
Physical layout
of process.
As mentioned previously, the term "physical arrangements" is used in this
discussion to describe the structural arrangement of the aeration tank as well
as to the various arrangements of process streams that are used to provide
process flexibility. Using this sort of description there are only three physical
arrangements which are presently used to any great degree in modern acti-
vated sludge plants in the United States. These are complete-mix activated
sludge, plug-flow activated sludge, and activated sludge with reaeration.
Contents of
tank uniformly
mixed.
Measure DO or
SS to check
uniformity of
mixing.
Dye itudlea tool
Complete Mix Activated Sludge
In an ideal complete-mix activated sludge plant, the contents of the tank
are completely homogeneous. In order to ensure that this is achieved,
special arrangements are often employed to uniformly distribute the
Influent and withdraw the effluent from the aeration tank. Attention to the
tank shape and to intensive mixing is important. There are a number of
means which the operator may use to evaluate the degree to which his
particular process operates in the complete mix mode. First and foremost
the entire contents of the tank should be completely uniform. This can
be confirmed by measurements of dissolved oxygen and suspended solids.
If the tank Is thoroughly mixed, these measurements should be nearly
uniform. Dye studies may also be used and will provide even more accurate
Information; however, conducting these studies Is usually beyond the
capability of a typical treatment plant.
1-12
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ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
Typical
laboratory
model
Best
understood.
Very stable
because shock
loads are
diluted.
The complete mix process is important because it operates well, but also
because most laboratory and pilot scale studies use this process arrange-
ment.
For this reason, the complete-mix process is probably the best understood
of the three basic process arrangements that will be discussed here. In
fact most of the information developed by the research community can
be applied to the complete-mix process with much less reservation than
it can to other processes.
As a general rule, the complete-mix process is a very stable process
which is resistant to upsets from shock loads of all kinds. This is a direct
result of the fact the shock is almost uniformly spread throughout the
entire aeration chamber. Some of the stability of this process may also be
due to the fact that the same environment prevails throughout the entire
tank. As a result, a relatively uniform population of microorganisms are
developed in an environment which is nearly the same throughout.
No unique
operating
problems.
Evidence to date does not show any special operating problems which
are unique to the complete-mix process, however, there are a few
comments that can be made about the process in general. Some people
express concern about the fact that some of the wastewater may be
immediately transported from the influent to the effluent end of the
aeration tank without receiving much treatment. A strict application of
the principles of chemical engineering to such a physical arrangement
would indeed suggest that it may be less efficient than others. However,
the data available at present on the relative performance of the complete-
mix process show that it is just as efficient as other process arrange-
ments. It would appear that the application of a rather simplified chemical
engineering view of the complete-mix theory overlooks other facts which
are of overriding importance.
The other major area of comment with regard to the complete-mix process
has to do with sludge settleability. There is considerable evidence accum-
ulating to the effect that the complete-mix process may operate with a
higher typical level of SVI or lower settleability than do competitive
process arrangements. Insufficient evidence is available at the present
time to prove or discount this contention, however, it should be recognized
that the settleability of complete-mix sludges is generally well within the
range of normal operation and the competitive process arrangements
which develop floe having lower SVI's during operating conditions also
have more inconsistent operation.
111-13
-------
ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
A schematic of a typical complete-mix activated sludge process is pre-
sented on Figure 111-8.
SETTLED
WASTEWATER
* *
MECHANICAL AERATORS
ALTERNATE
WAS
SECONDARY
CLARIF1ER
RETURN ACTIVATED SLUDGE
WASTE
ACTIVATED
SLUDGE
COMPLETE MIX ACTIVATED SLUDGE
FIGURE III-8
Wastewater and
RAS flow
through the
plant as a slug
or plug.
Adding
lightweight
partitions is a
possible
modification
to improve
performance.
Process is more
susceptible to
shock loads.
Plug-Flow Activated Sludge
In an ideal plug-flow plant, both the untreated wastewater and the return
sludge are introduced at the head end of the aeration tank and the mixed
liquor is withdrawn at the opposite end. A pulse of dye added at one end
the tank would emerge at the other end exactly as it had entered after a
delay equal to the hydraulic detention time. Ideally the flow passes through
the aeration tank as a "plug" without much longitudinal mixing (mixing in
the direction of flow). Because the tank must be aerated, however, longi-
tudinal mixing cannot be avoided. Generally, long serpentine patterns of
flow and aeration in a spiral pattern are used to encourage plug-flow char-
acteristics. The best means for approaching plug-flow characteristics in
an aeration tank, however, is to compartmentalize the chamber into a
series of completely mixed reactors. A series of 3 or more compartments
will do as good a job as some of the best "plug-flow" designs of the
traditional sort, and a greater degree of compartmentalization will provide
flow characteristics even closer yet to the plug flow ideal. Many plants of
conventional design can be modified to improve their plug-flow character-
istics by the use of iighweight partitions to compartmentalize the aeration
tanks.
The plug flow process is more susceptible to adverse effects from shock
loads than the other processes. This is because the shocks are applied io
the microorganisms at the head end of the tank at maximum concentration.
Adequate dissolved oxygen levels are difficult to maintain at the head end
of the process because such a large oxygen demand is exerted in one
location. The tapered aeration process is an effort to deal with this problem.
111-14
-------
ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
Tapered
Aeration.
Plug Flow is
very popular
andean
produce high
quality effluent.
Tapered aeration is designed to solve this problem by adding greater
amounts of air at the head end of the tank where most of the demand is ex-
erted. In one form or another, tapered aeration is used in most modern plug-
flow activated sludge plants and it should not be considered as a completely
independent process option.
Despite the shortcomings resulting from shock loads and difficulties
encountered in maintaining adequate dissolved oxygen, the plug-flow
process remains very popular and some of these plants are consistently
producing some of the best effluent. Studies have shown that the varied
conditions which the sludge is exposed to as it passes through the
aeration tank produces a healthy and good settling sludge. Plug-flow
activated sludge plants are very effective where the wastewater is mostly
domestic and good industrial waste control is practiced.
A schematic of a typical plug flow activated sludge process is presented
on Figure 111-9.
SETTLED
WASTEWATER
AERATION TANK
RETURN ACTIVATED SLUDGE
SECONDARY
CLARIFIER
EFFLUENT
WASTE
ACTIVATED
SLUDGE
PLUG FLOW ACTIVATED SLUDGE
FIGURE III-9
Reaeration is a
variation of
arrangement of
the process
streams.
Contact
Stabilization
Step Aeration.
Activated Sludge with Sludge Reaeration
Whereas plug-flow and complete-mix are essentially variations in aeration
tank design and mixing, the sludge reaeration processes are variations in
the arrangement of the process streams. All sludge reaeration processes
involve stabilization by aeration of the return sludge prior to its contact
with the untreated wastewater. Most examples require different ratios be-
tween the amount of return sludge under aeration and the amount of
sludge in the contact section of the process. Contact stabilization (Figure
111-10) and step aeration (step feed) (Figure 111-11) are two of the most
popular variations of sludge reaertion. In their typical arrangement, these
two processes represent the extremes of the contact/stabilization ratio,
however, both of them have established a successful record of perform-
ance. In fact, successful process installations with contact/stabilization
ratios over the whole range between contact stabilization and step feed
1-15
-------
ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
can be found in great numbers. Most of these processes have definitely
been shown to greatly increase the capacity of the activated sludge
process to handle high organic loadings in smaller aeration tank volumes
and some have argued that they are also more resistant to shock loading.
SETTLED
WASTEWATER
STABLIZATION
BASIN
SECONDARY i EFFLUENT
CLARIFIER
RETURN ACTIVATED SLUDGE
WASTE
ACTIVATED
SLUDGE
CONTACT STABILIZATION ACTIVATED SLUDGE
FIGURE III-1Q
Sludge
Reaeration is
less well
understood
than other
variations.
Includes solids
in the Contact
and
Stabilization
basins in the
F/M calculations.
COD removal
not significantly
affected by the
volume ratio of
Contact to
Stabilization
basin.
The various arrangements of sludge reaeration have been studied much
less on a laboratory and pilot scale basis than have the other basic process
arrangements, complete-mix and plug-flow. Of the three basic process
arrangements discussed here, the sludge reaeration processes are the
least well understood. On the other hand, they are processes which have
demonstrated great potential.
However, a certain amount of information is available on the behavior of
the sludge reaeration processes based on field and pilot scale data. This
data will be used to describe the processes and their behavior to the
extent possible.
First of all, although volumetric loadings for the sludge reaeration pro-
cesses may be considerably higher than for the two processes described
previously, the overall F/M ratios or MCRT values which may be used for
operation are in about the same range, i.e., in the range which has been
described as conventional activated sludge (F/M values of 0.2 to 0.5 and
MCRT values of 5 to 15 days). In doing these calculations all the solids in
the process should be included in the solids inventory and F/M calculations.
Although it has been adequately demonstrated that the ratio of solids in
the contact section and in the reaeration section has a significant impact
on the degree of removal of certain compounds such as ammonia, the
removal of organic material (COD or BOD) from domestic effluents does
not seem to be significantly affected over a very broad range of contact/
stabilization ratios. For this reason, the effluent quality seems to be about
1-16
-------
ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
SETTLED
WASTEWATER
SECONDARY
CLARIFIER
WASTE
ACTIVATED
SLUDGE
RETURN ACTIVATED SLUDGE
STEP FEED ACTIVATED SLUDGE
FIGURE III-ll
Important point
to be
considered.
the same in processes ranging from step aeration, where the reaeration
section is usually quite small to the contact section. All organic wastes
are not of exactly the same nature. If removals of organic materials are
not as high as expected, the operator should consider taking measures to
increase the fraction of the sludge inventory which resides in the contact
section. The most simple means of accomplishing this is to increase the
recycle ratio. If this measure has been used to the limit of its value, other
options are frequently available. Among the most important of these are
the distribution of raw wastewater feed in a step aeration design and the
addition of another tank to the contact section in others.
Most of the benefits of sludge reaeration are achieved if the organic load
present is mainly in the colloidal state. Generally, the greater the fraction
of soluble BOD, the greater the required contact time. As a result, the
required total aeration volume of this process approaches that of the
conventioanl process as the relative amount of soluble BOD in the waste-
water increases.
Control of
sludge return
more Important
than In other
variations
The control of sludge return assumes much greater importance in the
sludge reaeration processes than it does in the other activated sludge
variations. For example, the rate of return (or the recycle ratio) affects not
only the solids balance between the contact and stabilization sections,
but it is also very important for controlling the overall solids inventory
and the concentration of solids in the contact section.
Do not control
RAS with lust
the blanket level
intheclarlfler.
If the rate of return is controlled in reaeration processes in the same
manner as was suggested for complete-mix and plug-flow some problems
would result. For example, if the return were operated according to the
level of the sludge blanket in the secondary clarifier, the reaeration bays
would always be full of sludge which would be at the maximum concen-
tration that could be achieved in the clarifier. Chances are this concen-
tration does not correspond to the proper F/M ratio for operation. If the
recycle ratio is increased beyond this level, some water will be mixed in
1-17
-------
ACTIVATED SLUDGE PROCESS
SECTION III-FUNDAMENTALS
RAS is used to
control solids
ratio in the
Contact and
Stabilization
basins.
WAS must be
carefully
controlled.
Inexpensive
conversion to
Contact
Stabilization.
with the solids and the concentration in the reaeration bays would be
reduced. Thus, it is possible to adjust the ratio of the solids in the contact
and reaeration bays through the use of the rate-of-return.
This same phenomenon is also important in controlling solids wasting in
a sludge reaeration plant. For example, if the return rate is set up so that
the maximum concentration of return is always provided when wasting is
attempted, the result will always be to reduce the concentration of sludge
in the contact section without substantially influencing the concentration
in the reaeration section.
In general, the sludge reaeration processes are a very good means of im-
proving the capacity of a given set of aeration tanks to handle a higher
BOD load. Operators having overloaded plug-flow or complete-mix plants,
should consider alterations to accommodate some sludge reaeration if
possible. Many times this conversion can be accomplished with only a
small investment in additional piping. One of the big advantages of the
reaeration processes is they reduce the solids loading on the final clarifiers.
REFERENCES
Eckenfelder, W.W., Biological Waste Treatment, Pergamon Press, New York, 1961.
Environmental Protection Agency, Process Design Manual for Upgrading Existing
Wastewater Treatment Plants, 1974.
Hammer, Mark J., Water and Waste-Water Technology, John Wiley & Sons, Inc.,
New York, 1975.
Hawkes, H.A., The Ecology of Waste Water Treatment, Pergamon Press, Oxford, 1963.
Kerri, Kenneth, D., et al., A Field Study Training Program, Operation of Wastewater
Treatment Plants, (Chapter 7), Sacramento State College Department of Civil
Engineering.
McKinney, Ross E., Microbiology for Sanitary Engineers, McGraw-Hill Book Company
Inc., New York, 1962.
Metcalf & Eddy, Inc., Wastewater Engineering, McGraw-Hill, New York, 1972.
Stevens, Thompson, Runyan, Inc., Operator's Pocket Guide to Activated Sludge,
Parts I and II. Published by the Authors, 5505 S.E. Milwaukie Avenue, Portland,
Oregon 97202,1975.
Stewark, M.J., "Activated Sludge Process Variations - The Complete Spectrum,"
Parts I, II, III, Water and Sewage Works, April, May, June, 1964.
»
Water Pollution Control Federation: "Sewage Treatment Plant Design," Manual of
Practice No. 8, Washington, D.C., 1967.
1-18
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
4.01 INTRODUCTION
Laboratory
control is an
essential tool.
An essential tool for proper process control is frequent and accurate sampling
an laboratory control tests. By relating the lab test results to operation, the
operator can select the most effective operational parameters, determine the
efficiency of his treatment processes, and identify developing problems
before they seriously affect effluent quality. Therefore, laboratory facilities
play an important role in the control of an aerobic biological treatment facility.
Good sampling
technique is
essential.
Two types of
samples.
24-hour
composite
sampling is
preferred.
If only grab
samples are
collected, the
operator must
sample during
peak flow
conditions.
4.02 LABORATORY SAMPLING AND TESTING PROGRAM
Good sampling procedures are the key to meaningful laboratory analyses.
A typical sample represents only a small fraction of the total flow, and great
care must be exercised to ensure that the sample is representative. If this is
not accomplished, the subsequent analytical data is worthless for process
control. Therefore, the importance of good and accurate sampling techniques
cannot be overstressed.
The exact location of sampling points within a given treatment plant cannot
be specified because of the varying conditions and the plant design. How-
ever, it is possible to present certain general guidelines which are presented
on Figure IV-1.
Two types of samples may be collected, depending upon the purpose of
sampling. The first is a dip or "grab" sampling which consists of a single
portion collected at a given time. The second type of sample is a "composite"
sample that consists of portions taken at known times and then combined
in volumes that are proportional to the flow at the time of sampling. These
combined portions produce a sample which is representative of the waste-
water characteristics overthe entire sampling period.
The preferred sampling procedure, except for certain lab tests which must be
run immediately (Dissolved Oxygen, Temperature, pH), is to collect hourly
samples for 24 hours with the volume of sample in proportion to the waste-
water flow rate. When available and where possible, automatic sampling
devices should be employed. The sample containers and sample lines should
be frequently cleaned to prevent sample contamination. The hourly grab
samples should be composited into a labeled plastic gallon bottle and kept
refrigerated at 3 or 4° C. to prevent bacterial decomposition. For some tests
(such as the nitrogen tests), other methods of preservation may be needed,
refer to Standard Methods for recommended preservation procedures. A final
composited sample volume of 2 to 3 liters is usually sufficient for conducting
routine tests. Where collection of an hourly sample is not feasible, a 2 or 3
hourly sampling procedure is the next best alternative. The sampling method
and time of sampling should be noted upon the lab record (log) sheet as
reference for later data review and interpretation.
Grab Samples
Grab samples are representative of the instantaneous characteristics of the
wastewater. If it is only possible to collect grab samples, they should be
collected when the treatment plant is operating at peak flow conditions.
IV-1
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Sampling point should be readily
accessible and adequate safety
precautions should.be observed.
MLSS samples should be collected
at a convenient distance from the
sides of the aeration basin.
AERATION I
BASIN
No deposits or materials should be
collected from the side walls or
the water surface.
Sample must be taken where the
wastewater 1s mixed and of
uniform composition.
MIXED
Large or unusual particles should
not be collected with routine
samples.
^ ••'.";' :••••
•'
Sample should be delivered and
analyzed as soon as possible.
Stored samples must be
refrigerated at 3 to 4° C.
s«c.4«c
WASTEWATER SAMPLING GUIDELINES,
FIGURE IV-1
IV-2
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Sample collection should be conducted systematically at various sampling
locations during the flow sequence through the plant. Grab sampling times
may be systematically staggered to account for the respective hydraulic
detention time of each unit process. In this manner, a slug of water may be
theoretically followed through the treatment plant. For example, if the hy-
draulic detention period through a particular unit process unit is two hours,
then the grab sample of the effluent from this unit should be collected two
hours after the influent sample. In this manner, the samples can be assumed
to be representative of the wastewater before and after treatment.
Composite Samples
24-Hour
composites are
the best for
determining
organic loading
and
performance.
Composite samples generally represent the wastewater characteristics over
a specified period of time. The ideal procedure incorporates the use of 24-
hour composite samples consisting of hourly grab samples proportioned to
the flow at the time of sampling. This procedure is only feasible in treatment
facilities with 24-hour attendance or where automatic samples are warranted.
Adequate results, however, can generally be obtained from analysis of com-
posite samples collected over a shorter period. In those facilities where
automatic samplers are not available, collection of composite samples during
the number of shifts worked would be sufficient as long as peak flow periods
are included. A total composited sample volume of approximately three liters
is generally sufficient to perform the routine process control tests.
Take MLSS
samples at
same time and
location each
day.
How to make up
a MLSS
sample when
multiple tanks
are In operation.
MLSS Sampling
MLSS samples taken to develop an estimate of the amount of solids in
the aeration tank should always be taken at the same time of the day
and should always be taken from several places along the tank section.
Ordinarily only one solids analysis need be conducted on a composite
made up of samples taken from every quadrant of every tank. Analysis of
individual samples should also be conducted occasionally to develop addi-
tional information about the condition of the process. Composites from
aeration tanks of different size can be prepared by first combining equal
volume samples from each tank quadrant, and then combining the tank
composites.
When samples of the mixed liquor are taken, a composite should be
prepared from samples withdrawn from all the tanks under aeration. If any
of the aeration tanks are of different size, the sample should be taken in
proportion to tank size. Occasionally, the MLSS concentration in each
tank should be measured. For example, suppose an operator is to collect
a MLSS sample which is to be representative of a complete mix plant
having 3 aeration tanks with a volume of 0.4 mil. gal. and 3 new aeration
tanks having a volume of 0.6 mil. gal. One liter of MLSS has already been
collected from each tank. How much should be taken from each of the six
one liter samples to prepare a 1 liter composite that is representative of
all the aeration tanks?
IV-3
-------
ACTIVATED SLUDGE PROCESS
SECTION IV - LABORATORY CONTROL
. . (Tank Vol., mg) (Composite Vol., liters)
Sample volume per = - '-——
tank liters Total Vol. of all tanks, mg
For the 0.4 mil gal tanks, volume =
(0.4) (1.0 liter)
(3 X 0.4) + (3 X 0.6)
= 0.13 liter (130 ml)
How to
composite
MLSS samples
to be
proprotional
with flow.
For the 0.6 mil gal tanks, volume = —^ (1-°"ter) = 0.2 liters (200 ml)
(3 x 0.4) + (3 x 0.6)
Total Volume = (3 x 0.13) + (3 x 0.2) = 0.99 liters (990 ml)
Composite sampling for processes operating in the step feed and sludge
reaeration modes should be conducted in the same manner described
above and shown in Figure IV-2.
Once the composite sample is made to represent all of the tanks it should
be proportioned to the aeration influent flow rate (either raw wastewater
or primary effluent flow rate). As stated above, composite samples repre-
sent wastewater characteristics over a specified period of time. Generally
a total composited sample of 3 liters is adequate to perform routine
process control tests. Therefore, the total amount of sample required, the
number of samples required, the rate of flow at the time of sampling, and
the estimated average daily flow rate, can be used to calculate the amount
of representative aeration tank sample to be composited during each
sampling period to represent the daily flow. This may be calculated using
the following equation.
Amount of sample to collect, ml =
(Rate of flow, mgd @ time of sampling) (Total sample required, ml)
(Number of samples collected) (Average daily flow, mgd)
Example Calculation
A. Data Required
1. Rate of flow at time of sample collection = 1.5 mgd
2. Total sample volume required, Note ml = (liters) (1000) = 3
liters or 3000 ml
3. Number of samples to be collected = 8
4. Average daily flow = 0.9 mgd
IV-4
-------
ACTIVATED SLUDGE PROCESS
SECTION IV - LABORATORY CONTROL
B. Determine the amount of sample to be collected for the present
flow rate in milliliters.
Calculation for
composite
sampling.
Amount of sample
to collect ml = (Rate of flow, mgd) (Total sample required, ml)
(Number of samples) (Ave. daily flow, mgd)
_ (1.5 mgd) (3000 ml)
(8) (0.9 mgd)
= 625 ml
This equation may also be used to composite other samples taken
from the plant.
Laboratory Control Program
Lab control
requires
adequate
facilities and
technical skills.
The specific laboratory tests and frequency which they are performed for
process control and performance evaluation will vary from plant to plant de-
pending on the variation of the activated sludge process, its size, laboratory
facilities provided, process control method used, available manpower, and
technical skills. A typical sampling and testing program for an activated
sludge process is presented on Figure IV-2.
Laboratory
analyses are the
tools of process
control.
Sampling and
analyses must
be increased
when the
process is upset
Typical
worksheets
provided.
4.03 LABORATORY CONTROL TESTS
This section of the manual is provided to increase understanding and to
develop an appreciation of laboratory control tests.
The tests discussed are those necessary for routine process control when the
biological system is operating properly. Additional analyses and increased
frequency of analysis for the routine analysis may be required for abnormal
conditions. Specific suggestions are made for abnormal operation in Section
I, "TROUBLESHOOTING." However, the operator must rely upon his own
judgement to determine which analyses he needs to conduct to supply the
information that he desires.
Typical worksheets have been provided in Appendix A to assist the operator
in developing systematic data collection, calculation, and recording. Pre-
cautionary procedures are presented for each of the tests presented in this
section to make the operator aware of the common pitfalls. Except where a
specific note is made, all analyses are referenced to the fourteenth edition of
"Standard Methods for the Examination of Water and Wastewater".
IV-5
-------
ACTIVATED SLUDGE PROCESS
SECTION IV - LABORATORY CONTROL
ALTERNATE
SETTLED
WASTEWATER
* » 2
AERATION TANK
QBAS
RETURN ACTIVATED SLUDGE
SECONDARY
CLARIFIER
WASTE
ACTIVATED
SLUDGE
TYPICAL ACTIVATED SLUDGE PLANT
DESCRIPTION
FLOW
BOD
COD
SUSPENDED SOLIDS TOTAL *
SUSPENDED SOLIDS VOLATILE*
NITROGEN -KJELDAHL
AMMONIA
NITRITE
NITRATE
PHOSPHORUS
30 MIN. SETTLING
DO
pH
TEMPERATURE
AIR INPUT-SCFM
SLUDGE BLANKET
MICROSCOPIC EXAMINATION
LOCATION OF SAMPLE
SETTLED SEWAGE
OR
RAW SEWAGE
CR
p><~r
Ł><^
5>"<,?
CR
R-,' -i'-l;!
(D»
SECONDARY
CLARIHER
EFFLUENT
CR
i2**^
^>
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Biochemical Oxygen Demand (BOD)
The 5-day BOD.
The biochemical oxygen demand is determined by incubating a sample of
known volume in the presence of microorganisms, excess nutrients, and
dissolved oxygen. A properly conducted BOD analysis will have organic
matter as the growth limiting substance. If oxygen is limiting, the analysis is
not meaningful.
The BOD is an index of the amount of oxygen that will be consumed by the
decomposition of the organic matter in a wastewater. The analysis consists
of measuring the initial dissolved oxygen concentration, incubation for five
days at 20° C, and measuring the final dissolved oxygen. The difference in dis-
solved oxygen concentration corrected for the initial dilution and sample volume
is called the BOD. The BOD test is related to both the organic loading upon the
biological process as well as the removal efficiency of the process. The
difference between the BOD applied and the BOD leaving the process is equal
to the BOD removed by the process. This difference is part of the data required
to determine the loading upon the process. For example, the organic loading
upon the activated sludge process is expressed as the pounds BOD applied
per day pound of mixed liquor volatile suspended solids (Ibs BOD/day/lb
MLVSS). The efficiency of the process is determined by the following formula:
BOD applied, Ib/day - BOD leaving, Ib/day x 100 = the remQva| eff|c|ency| %
BOD applied, Ib/day
In this determination, the aeration tank and clarifier are considered, as one
system.
Minimum of two
dilutions, at
least2mg/ID.O.
used—must be
at least 2 mgfl
left after S-days.
Mix samples
well.
Avoid aeration
during bottle
filling.
Note 5-Days
mean 120 Hours.
Precautionary Procedures
When performing BOD analyses the following procedures should be
followed in conjunction with the procedures outlined in Standard Methods.
1) A minimum of two dilutions per sample should be used. Only
analyses with oxygen depeltions of greater than 2 mg/l but with
no less than a residual of 2.0 mg/l after five days of incubation at
20° C should be used to calculate the BOD. Generally, the highest
value calculated should be used to represent the BOD.
2. Samples should be well mixed before the dilutions are made. A
wide tip pipette should be used for making the dilutions. The wide
tip does not clog with suspended solids.
3 .Samples and the dilution water must be carefully added to the
BOD bottle to avoid aeration and the possibility of entraining
bubbles in the solution.
4) The BOD incubator must be maintained at 20° ± 1° C for the
entire 5 day (Note: 120 hours) period. Record the temperature of
the incubator from a NBS certified thermometer placed in a beaker
of water in the incubator.
IV-7
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Toxic slide.
Primary
standard made
from glucose.
Use allythiourea
to inhibit
nitrifiers.
5) If the BOD value of the more dilute sample is always greater, this
may indicate that there is some toxic material in the wastewater,
which is inhibiting the bacteria. A series of dilutions should be set
up and run. If the BOD is increasing with higher dilution, this may
indicate a condition known as a toxic slide. Further analyses
should be conducted to determine the nature of the toxic material,
and if it appears that the concentration of the toxicant is significant,
efforts should be initiated to identify the source and reduce the
concentration of the toxicant in the wastewater.
6) Use of a primary standard is strongly recommended. The standard
should be made of glucose—glutamic acid mixture—and it should
be made up at a BOD near those levels in the treatment plant
influent. The primary standard should be made up and analyzed
weekly. Any significant variation (more than ± 20%) should cause
the operator to be suspicious. Efforts should be undertaken to re-
view the laboratory procedure, and find out what is causing the
problem. Each operator should analyze the standard and the results
should be within ± 10%. Operators not falling within this range
should review their laboratory techniques, and make the appropriate
adjustments.
7) Wastewaters that have been partially nitrified may produce high
BOD results. The increased oxygen demand results from the
oxidation of ammonia to nitrate. The use of allylthiourea in the
dilution water will inhibit the nitrifiers and alleviate this problem.
Chemical Oxygen Demand (COD)
COO is fast and
reproducible.
The COO is
better for
process control.
The COD is an estimate of the total oxygen demand that results from the de-
gradable organic matter. The analysis consists of oxidizing the organic
matter with potassium dichromate in a heated strongly acidic solution.
While the BOD analysis is an index of the biodegradable organic matter, it is
not very useful for process control because of the five day lag in time. The COD
test is rapid (3-4 hours); it is not subject to interferences from toxic materials;
and it is not affected by ammonia oxidation.
The COD removal of a biological process is directly relatable to the amount of
biological growth that can result from this removal. The COD analysis suffers
from the disadvantage that it does not measure the rate of or biodegrability
of matter removal, and therefore it is difficult to predict the effects of effluents
on the oxygen resources of receiving waters and the treatability of a particular
wastewater.
The analyst
must establish
his variability.
Precautionary Procedures
When performing the COD test, the following procedures should be
followed in conjunction with those outlined in Standard Methods. *
1) Initially, the.analyst should run triplicate samples to establish the
variability of his analyses. Once this variability is established,
samples can be analyzed without replication.
IV-8
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
2) Use a wide tip pipette to ensure that a representative sample is
taken.
3) Glassware used for the COD analyses must be washed with hy-
drochloric acid, hot washed, and rinsed three times with distilled
water.
4) Extreme caution and safety precautions should be practiced when
handling the chemical reagents for the test. Goggles, a rubberized
apron and asbestos gloves are essential equipment.
5) If a sample mixture turns green during or immediately following
the heating period, the analysis is not valid and should be re-
examined in a more dilute sample. If the problem reoccurs, then
the laboratory technique should be reevaluated and the sample
should be checked for likely interferences, such as high chloride
concentration or the presence of a strong base.
6) A primary standard consisting of potassium acid phtalate should
be analyzed on a weekly basis to ensure that the analyses are con-
sistent. The COD concentration of the standard should be near
the level of the COD of the wastewater. (See Standard Methods.)
Soluble COD
and BOD.
Soluble COD and BOD
The discussions on BOD and COD have been limited to the measurement of
the total COD and BOD. The soluble BOD and COD are more meaningful for
measuring performance (conversion of food to cell growth). The soluble BOD
or COD is determined in exactly the manner described above, except that the
sample is filtered through a membrane filter prior to the analysis. The use of
this filtering apparatus is discussed underthe suspended matter analysis.
Settleable Matter
Symptoms
highlighted by
settleablllty
test.
The settleable matter test (also known as the Imhoff Cone Test) is a measure
of the volume of solid matter that settles to the bottom of an Imhoff cone in
one hour. The volume of settled solids is read as milliliters per liter (ml/1)
directly from the graduations at the bottom of the Imhoff cone.
This test is of value in providing a quick and efficient check of a sedimentation
unit. Additionally, a rough estimate of the volume of solids removed by the
sedimentation unit can be made. Only a trace of settleable solids should re-
main in the secondary effluent. Poor settleable matter removal may indicate
the following related problems which may occur in sedimentation basins:
Primary and Secondary
1) Hydraulic overload.
2) Irregular flow distributions to multiple units.
3) Excessively high velocity currents.
4) Effluent weirs of uneven height—short circuiting.
5) Impropersampling technique.
6) Improper raw sludge removal rates.
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ACTIVATED SLUDGE PROCESS
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Secondary only
1) Biological upset.
2) Improper RAS pumping rate.
Measure of the
filterable solids.
Use of this test.
A measure of
the organic
matter-
proportional to
the
microorganism
concentration
In the mixed
liquor.
Precautionary Procedures
When performing the settleable matter test, the following procedures
should be followed in conjunction with those outlined in Standard Methods.
1) Take a sample volume greater than one liter.
2) Use grab samples for this analysis.
3) Fill the Imhoff cone exactly to the one liter mark in one rapid pour-
ing without stopping.
4) After the sample has settled for 45 minutes, either gently tap the
sides of the cone or gently spin the cone between the palms of
your hands to settle those solids adhering to the sides of the cone
above the compacted settled layer at the bottom of the cone.
5) Read and record the volume of settled matter (ml/l) at the end of
one hour. Read the graduation at the average solids depth and not
at a peak or void area on the surface of the settled solids.
Total Suspended Matter
The suspended matter test refers to the solids in suspension that can be re-
moved by standard filtering laboratory procedures. The suspended matter is
determined by filtering a known volume of sample through a weighed glass-
fiber or membrane filter disc in an appropriate filtering apparatus. The filter
with the entrapped solids is oven-dried at 103° 105° C and then cooled in a
desiccator and subsequently weighed. The increase in filter weight represents
the suspended matter.
The significance of the suspended matter test is generally dependent on the
type of treatment process and the location of measurement within the process
application. Results of the test have the following uses in process control:
1) Evaluating the organic strength of the wastewater.
2) Evaluating clarifier solids loading.
3) Determine the sludge recycle rate by calculation.
4) Calculating clarifier solids capture.
5) Estimating the solids inventory.
Volatile Suspended Matter
The volatile suspended soilds test is performed by volatilizing the non-filterable
residue from the total suspended solids test. This volatilization is done by
burning in a furnace at about 550° C. The results of this test indicate the
amount of volatile and nonvolatile solids contained in the sample.
This test is an index of the quantity of microorganisms in the activated sludge.
The test has the same significance as the total suspended matter test with
two additional applications which are the determination of F/M ratios and the
MLSS levels to be maintained in the aeration basin of an activated sludge
plant.
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ACTIVATED SLUDGE PROCESS
SECTION IV - LABORATORY CONTROL
Use wide tipped
pipette.
Temperature
between 103-
105'C.
Precautionary Procedures
When performing the suspended matter test, the following procedures
should be followed in conjunction with the procedures outlined in Stand-
ard Methods.
1) The sample must be thoroughly mixed prior to taking a sample
aliquot.
2) Do not use a small-tipped pipette to measure the sample aiquot. A
wide-tipped pipette should be utilized to permit passage of the
larger solids and to facilitate rinsing. An alternate method of
obtaining a sample aliquot would be to pour it into a graduated
cylinder.
3) Rinse all adhering solids from graduate (or pipette) with distilled
water. Pour rinse water through the filter.
4) Test results that appear faulty or questionable should be dis-
regarded.
5) It is important to always maintain a temperature of between 103 -
105° C in the drying oven. The temperature must be monitored
and recorded in a record book.
6) Be sure that the filter is properly seated in the filtration apparatus
before pouring the sample. This is easily accomplished by wetting
the filter with distilled water, then applying vacuum to the filtra-
tion apparatus.
7) Samples containing high solids levels may require more than one
hour to completely dry. This is especially true of return sludge
samples.
8) Be consistent in the length of time the filter apparatus and paper
are allowed to cool in the dessicator both before and after filtering.
9) Use Whatman GF/C filters and a millipore filter apparatus with
sintered glass seat for this analysis.
Nitrite Nitrogen
NO2 partially
oxidized form
of nitrogen
High NO2
concentrations
Imply
Incomplete
nitrification
Nitrite (NO2) is an intermediate oxidation state of nitrogen between ammonia
nitrogen and nitrate nitrogen. Nitrite is transatory and readily amendable to
both bacterial oxidation to nitrate or reduction to nitrogen gas depending
upon environmental factors such as dissolved oxygen and microbial conditions.
The nitrite concentration can be used to monitor how well nitrification is
progressing in a treatment process. High nitrite concentrations Indicate incom-
plete nitrification, and could lead to problems, such as high chlorine and
oxygen demands.
Precautionary Procedures
When performing the nitrite nitrogen test, the following procedures should
be followed in conjunction with the procedures outlined in Standard
Methods.
1) Use extreme caution in handling the chemical reagents to avoid
injury or damaged clothing.
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ACTIVATED SLUDGE PROCESS
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Analyze as soon
as possible.
Sample must be
cool.
2) Due to the instability of nitrite (NO2), the composite samples used
for the nitrite analysis should be preserved by one of the following
methods: (a) freezing, or (b) addition of 5 ml of chloroform/1 of
sample. In general it is advisable to analyze only fresh grab samples
for nitrite.
3) The samples must be cool when the analysis is performed or
erroneous results will be measured.
4) Deviation from standard procedure may yield erroneous results. Be
consistent in your laboratory technique.
Nitrate Nitrogen
Nitrate is seldom found in raw wastewater or primary effluent, because
facultative microorganisms can readily use nitrate as an oxygen source. In
the biological treatment process, the ammonia nitrogen can be microbio-
logically oxidized to nitrite and then to nitrate depending on the microorgansims
present and the environmental factors such as pH, temperature, and dis-
solved oxygen.
Secondary effluent may contain from 0 to 50 mg/l nitrate nitrogen depending
on the total nitrogen content in the raw wastewater and conditions of treatment.
Activated sludge systems that have a long MCRT (usually 10 days or more)
and adequate oxygen can also produce a nitrified effluent.
Use the
Brucine
Method.
Precautionary Procedures
When performing the nitrate nitrogen test, the following procedures
should be followed in conjunction with the procedures outlined in Stand-
ard Methods.
1) Use the Brucine method for routine analysis.
2) Analyze the sample as soon as possible to avoid bacterial re-
duction of the nitrate.
3) Preserve samples that cannot be analyzed immediately by either
freezing or by the addition of 5 ml of chloroform/l of sample.
Total Kjeldahl Nitrogen (TKN)
TKN measures
organic and
ammonia
nitrogen.
Most nitrogen in
raw
wastewaters in
this form.
This test measures the ammonia and organic nitrogen but not the nitrite or
nitrate nitrogen. The sample is digested with acid and catalysts that convert
the organic nitrogen to ammonia nitrogen. The ammonia is then distilled off
into a boric acid solution and measured by either a colorimetric analysis called
nesslerization or by titration.
In raw wastewater, nitrogen is primarily found as organic and ammonia nitro-
gen depending on the degree of decomposition. As decomposition increases,
the organic nitrogen is biologically decomposed (ammonified) to ammonia
nitrogen.
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ACTIVATED SLUDGE PROCESS
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The results of this test are valuable because it can be used to:
1) Evaluate the performance of a treatment process designed to nitrify.
2) Evaluate nutrient (nitrogen) deficiency.
3) Evaluate oxygen requirements for activated sludge.
Do not breathe
the fumes.
Precautionary Procedures
When performing the Total Kjeldahl Nitrogen test, the following proced-
ures should be followed in conjunction with the procedures outlined in
Standard Methods:
1) Use extreme caution in handling the reagents to avoid injury.
2) Perform the digestion step under a ventilated hood. Do not breathe
in the fumes given off during digestion.
3) The TKN test may be performed on the same composite samples
as for the BOD and Suspended matter tests. The samples should
be preserved by refrigeration at 3 to 4° C for not more than 24 hours.
4) Deviation from standard procedures may yield erroneous results.
Be consistent in lab technique.
A measure of
the form of
nitrogen that
causes high
chlorine
demands and
fish toxicity.
Ammonia Nitrogen
This test measures the nitrogen present in the wastewater as ammonia.
Ammonia nitrogen in domestic wastewater is generally between 10 and 40
mg/l. Primary treatment may increase the ammonia nitrogen content slightly
due to decomposition of some protein compounds during treatment. In
secondary treatment process, ammonia can be oxidized to nitrite then to
nitrate in varying degrees depending on factors, such as the residence time
of the microorganisms, wastewater temperature, and oxygen reliability.
The significance of this test is associated with the oxygen demand required
to oxidize ammonia in the biological treatment process or receiving stream.
Theoretically, the oxidation of one pound of ammonia nitrogen requires 4.6
pounds of oxygen. This test is also valuable in evaluating the performance of
a treatment process designed to nitrify. Other significant problems relating
to ammonia are high chlorine demands, fish toxicity, and high oxygen demand
in receiving waters.
Precautionary Procedures
When performing the Ammonia Nitrogen test, the following procedures
should be followed in conjunction with the procedures outlined in Stand-
ard Methods.
1) Use extreme caution in handling the chemical reagents to avoid
injury or damaged clothing.
2) Deviation from standard procedures may yield erroneous results.
Consistency in laboratory techniques is essential.
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ACTIVATED SLUDGE PROCESS
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An important
measure of
mixed liquor
settling.
Observe at 5
min intervals
for first 30 min,
10 min
thereafter.
Stirring can
improve results.
Related to the
SVI.
Important to
observe results
with time—Do
not read only at
30 minutes.
30-Minute Settling Test
The 30-minute settling test of MLSS provides an index of the activated sludge
settling and compaction characteristics in the secondary clarifier. The test, in
itself, is simple to perform and requires only a graduated glass cylinder and a
clock. It is performed by transferring a thoroughly mixed one-liter sample of
mixed liquor to a one liter graduated cylinder and then recording the milli-
liters of sludge settled in the one-liter graduated cylinder at five minute intervals
for the first 30 minutes and then at ten minute intervals up to one hour. This
test can also be conducted with stirring, and the operator should try both
methods to see which most closely models his sedimentation results in the
clarifier.
This test indicates how well the activated sludge mixed liquor concentrates
and compacts. The usual index of sludge settleability and compaction is the
Sludge Volume Index (SVI) or its reciprocal the Sludge Density Index (SDI)
which are based on the sludge level at the end of the 30-minute period. Some
results, however emphasize that an SVI of 100 (SDI of 1.0) is indicative of a
well functioning activated sludge plant. This may not necessarily be true be-
cause these indices represent only the 30-minute settling and do not neces-
sarily account for the clarity of the liquid above the sludge. Observations
should be made during the 30-minute test to determine whether the sludge
particles are agglomerating well, settling uniformly, and leaving a clear liquid
or whether sludge particles are settling rapidly and leaving a cloudy liquid
above. The latter behavior is indicative of several operational problems which
are discussed in Section 2.05. During the 30-minute test, a well settling sludge
will normally settle to approximately half of its original volume in the first 5 to
10 minutes.
Precautionary Procedures
When performing the 30-minute settling test, the following procedures
should be followed in conjunction with procedures outlined in Standard
Methods.
1) A morning and afternoon grab sample (or two samples per shift)
should be tested for settleability.
2) Grab samples should be taken during peak as well as average flow
periods.
3) Each sample should be collected consistently and at the same
location.
3) Vigorous mixing and pouring of sample should be avoided.
5) Be certain to fill the settling cylinder exactly to the one-liter mark.
6) Record time test is set up and temperatures of sample.
7) Record settling level every five minutes for the first 30 minutes
and every 10 minutes for the second 30-minute period.
Observations During Test
*
An important factor in running the 30-minute settling test is to observe
the settling and compaction characteristics of the MLSS. Often operators
walk off after setting up the test and come back to read and record the
settling level at the end of 30 minutes. In doing this, they may miss impor-
tant information by not observing how the sludge settles. Use of the 30-
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ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
minute test only to calculate the SVI or SDI does not provide the maximum
benefit for process control. The operator should attempt to record the
following observations during the test so that correlations to other labor-
atory control tests used for process control can be made:
A. First Five to Ten Minutes
*1) Do sludge particles agglomerate while forming blanket?
*2) Does sludge compact slowly and uniformly, leaving a clear liquid?
or
3) Do sludge particles fall through a cloudy liquid?
4) How much and what type of straggler floe, if any, remains in the
liquid?
B. End of 30 Minutes
*1) Has the sludge floe compacted to the appearance of looking
crisp with sharp edges and somewhat like a sponge? or,
2) Does the floe look feather-edged fluffy and somehwat homog-
enous?
C. End of 60 Minutes
1) Has any settled sludge floated to the surface of the cylinder?
*2) Did it take two to four hours for the sludge to split or float to the
surface?
3) These observations provide a check on the final clarifier sludge
blanket charcteristics and removal rates in relation to sludge
detention time in the clarifier.
*A well settling sludge will have the characteristics of Items A-1 and A-2,
B-1,andC-2.
Total Phosphorus
Phosphorus is one of the nutrients essential to biological growth in secondary
treatment processes. Most wastewaters have more phosphorus available
then is required for biological growth and assimilation of the carbonaceous
BOD. A deficiency of phosphorus may result from high waste loading from
industries, such as canneries which generally have wastes that are high in
carbohydrates and low in nutrients. Such a phosphorus deficiency may limit
biological growth and lead to poor BOD removals.
Typical raw domestic wastewater contains approximately 10 mg/l of phosph-
orus of which 20 to 30 percent may be removed by the growth of microorgan-
isms which are wasted from the process. Greater removals may be obtained
by various processes involving addition of a metal ion such as iron or aluminum
to chemically precipitate iron or aluminum phosphate. Other removal pro-
cesses involve pH adjustment by addition of lime or other means and chemi-
cal precipitation of a calcium phosphate.
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ACTIVATED SLUDGE PROCESS
SECTION IV • LABORATORY CONTROL
Precautionary Procedures
When performing the total phosphorus test, the following procedures
should be followed in conjunction with the procedures outlined In Stand-
ard Methods.
1) Use extreme caution in handling the chemical reagents to avoid
injury or damaged clothing.
2) Record specific procedures used for pretreatment of sample and
measurement of phosphorus concentration with test results. Also,
clearly indicate the expression of the test results, P or PO4. (Note:
1.00 mg/l P equals 3.06 mg/l PO4.)
3) Deviation from standard procedure may yield erroneous results.
Be consistent in your laboratory technique.
An Important
parameter.
DO
measurements
can be used
to control
aeration.
Dissolved Oxygen
Dissolved oxygen (DO) is that oxygen dissolved in liquid and is usually
expressed as milligrams per liter (mg/l). There are various types of tests to
determine the DO content of water. Generally, the iodometic methods and the
membrane electrode (DO probe) are best suited for the domestic wastewater
application. The azide modification of the iodometric method (also known as
Winkler Method) is recommended for most wastewater and stream samples.
When determining the DO in activated sludge mixtures {MLSS and RAS), and
other biological floes which have a high oxygen utilization rate, the copper
sulfate-sulfamic acid flocculation modification should precede the azide
modification to retard biological activity and to flocculate suspended solids.
The membrane electrode method is becoming increasingly more popular
because of its speed, ease of operation, and adaptability to process control
instrumentation. Often, the membrane electrodes are used for continuous
monitoring and control of DO in activated sludge units. The membrane elec-
trodes must be properly maintained and calibrated on a daily basis to ensure
that their measurements are accurate and usable for process control.
The significance of the DO test in process control is in its measurement of
the dissolved oxygen available for and essential to aerobic decomposition of
the organic matter; otherwise, anaerobic decomposition may occur with the
possible development of nuisance conditions. In the activated sludge process,
the DO test is used to monitor the aeration process as a basis for control of
the air supply rates, in order to maintain a desired DO residual, while avoiding
overaeration and power wastage. The DO test is also used in the determination
of BOD as discussed previously. Fish and most aquatic life require dissolved
oxygen to sustain their existence and the DO test is an important measure-
ment in plant effluents and receiving water quality.
Precautionary Procedures
When performing the DO test, the following procedures should be followed
in conjunction with the procedures outlined in Standard Methods.
1) Use extreme caution in handling the chemical reagents to avoid
injury or damaged clothing.
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ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Use special care
in sampling.
Perform
immediately
after sampling.
2) The use of special DO sampling equipment is preferable for col-
lecting samples. The samples should be taken with the sample
container completely immersed and without aeration of the sample
or entrapment of any air bubbles.
3) Perform DO test immediately following collection of sample.
4) The following substances will interfere in the azide modification
of the iodometric DO analysis: iron salts, organic matter, excessive
suspended matter, sulfide, sulfur dioxide, residual chlorine,
chromium, and cynaide.
Hydrogen Ion Concentration (pH)
An important
measure for the
microorganism.
The intensity of acidity or alkalinity of a solution is numerically expressed
by its pH. A pH value of 7.0 is neutral, while values 7 to 14 are alkaline and
values 0 to 7 are acid. pH can be measured colorimetrically or electrome-
tically. The electrometric method (pH meter) is preferred in all applications
because it is not as subject to interference by color, tubidity, colloidal
matter, various oxidants and reductants as is the less expensive colori-
metric method.
The pH measurements are valuable in process control because pH is one of
the environmental factors that affect the activity and health of microorganisms.
Sudden changes or abnormal pH values may be indicative of an adverse in-
dustrial discharge of a strongly acid or alkaline waste. Such discharge are
detrimental to biological processes as well as to the collection system and treat-
ment equipment, and should be either stopped or neutralized prior to discharge.
Generally, the pH of the secondary effluent will be close to 7. A pH drop may
be noticeable in a biological process achieving nitrification because alkalinity
is destroyed and carbon dioxide is produced during the nitrification process.
Use grab
samples-
analyze
Immediately.
Calibrate the
pH meter daily.
Exercise
extreme care
with electrodes.
Precautionary Procedures
When performing the pH test, the following procedures should be followed
in conjunction with the procedures outlined in Standard Methods.
1) Grab samples should be used for the pH measurement. The pH
test should be performed on the samples immediately following
collection before the temperature or dissolved gas content can
change significantly. Do not heat or stir the pH sample as a change
in temperature or dissolved gas content will affect the pH value.
2) Do not contaminate the buffer by pouring the used buffer solution
back into the buffer container.
3) Calibrate the pH meter daily with a buffer solution of approximately
the same temperature and pH as the sample to be tested. Adjust
the pH meter's temperature compensator for each pH measurement.
4) Avoid fouling the electrodes with oil or grease.
5) Erratic results or drifting should prompt an investigation of the
electrodes.
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ACTIVATED SLUDGE CONTROL
SECTION IV - LABORATORY CONTROL
Temperature
affects growth
of
microorganisms.
Temperature
In process control, accurate temperature measurements are helpful in eval-
uating process performance because temperature is one of the most important
factors affecting microbial growth. Generally stated, the rate of microbial
growth doubles for every 10° C increase in temperature within the specific
temperature range of the microbe. Temperature measurements can be helfpul
in detecting infiltration/inflow problems and illegal industrial discharges.
Thermometers are calibrated for either total immersion or partial immersion.
A thermometer calibrated for total immersion must be completely immersed
in the wastewater sample to give a correct reading, while a partial-immersion
thermometer must be immersed in the sample to the depth of the etched circle
around the stem fora correct reading.
If a Fahrenheit thermometer is used, its reading may be converted to Centi-
grade by following formula:
C =
Measure
immediately.
F-32C
Precautionary Procedures
When obtaining the temperature of a sample, the following procedures
should be followed in conjunction with the procedures outlined in Stand-
ard Methods.
1) To attain truly representative temperature measurement, it is
necessary either to take the temperature reading at the point of
sampling or immediately following sample collection. A large
sample volume should be used to avoid a temperature change
during the measurement.
2) The accuracy of the thermometer used should be occasionally
verified against a precision thermometer certified by the National
Bureau of Standards (NBS).
3) The thermometer should be left in the sample while it is read.
Microscopic Examination
A useful tool.
The important
protlsts.
Microscopic examination of the MLSS can be a significant aid in the evaluation
of the activated sludge process. The presence of various microorganisms
within the sludge floe can rapidly indicate good or poor treatment. The most
important of these microorganisms are the heterotropic and autotrophic
bacteria which are responsible for purifying the wastewater. In addition,
protozoa play an important role in clarifying the wastewater and act as indica-
tors of the degree of treatment. The presence of rotifiers is also an indicator
of effluent stability.
A predominance of protozoa (ciliates) and rotifiers in the MLSS is a sign of
good sludge quality. The treatment under these conditions, with proper RAS,
WAS and aeration rates, can be expected to produce effluent BOD concentra-
tions of less then 10 mg/l.
IV-18
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ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Inversely, a predominance of filamentous organisms and a limited number of
ciliates is characteristic of a poor quality activated sludge. This condition is
commonly associated with a sludge that settles poorly. The sludge floe is
usually light and fluffy because it has a low density. There are many other
organisms such as nematodes (worms) and waterborne insect larvae which
may be found; however, these do not significantly affect the quality of
treatment.
The microorganisms which are important to the operator are the protozoa and
rotifers. As discussed previously, the protozoa eat the bacteria and help to
provide a clear effluent. Basically, the operator should be concerned with three
groups of protozoa, each of which have significance in the treatment of
wastewater. These groups include the following:
1) Amoeboids
2) Flagellates
3) Ciliates
Amoeboids (Figure IV-3)
The cell membranes of Amoeboids are extremely flexible; and the
mobility of these organisms is created by the movement of protoplasm
within the cell. Food matter is ingested by absorption through the cell
membrane. Amoeboids may predominate in the MLSS floe during
start-up periods of the activated sludge process or when the process
is recovering from an upset condition.
AMOEBOIDS
FIGURE IV-3
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ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Flagellates (Figure IV-4)
These organisms are characterized by the tail (Flagella) which extends
from their round or elliptical cell configuration. Their mobility is
created by a whipping motion of the tail, which allows them to move
with somewhat of a corkscrew motion. Flagellate predominance may
be associated with a light-dispersed MLSS floe, a low population of
bacteria, and a high organic load (BOD). As a more dense sludge floe
develops,, the flagellate predominance will decrease with an increase
of bacteria. When the flagellates no longer are able to successfully
compete for the available food supply, their population decreases to
the point of insignificance".
FLAGELLATES
FIGURE IV-4
dilates
These organisms are characterized by the rotating hair-like membrane
(cilia) which cover all or part of their cell membrane. Their mobility is
created by the movement of the cilia, and the cilia around the gullet
are utilized for the intake of food. Ciliates may predominate during
the period of fair to good settling of the activated sludge.
They are considerably larger than flagellates and for the purposes of
microscopic examination may be classified into two basic groups,
which are the free swimming and the stalked ciliates.
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ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Free Swimming Ciliates (Figure IV-5)
Free swimming ciliates are usually apparent when there is a large
number of bacteria in the activated sludge. These organisms feed or
graze on the bacteria and clarify the effluent. Therefore, their presence
is generally indicative of a treatment process that is approaching an
optimum degree of treatment. A relative predominance of flagellates
indicates decreased treatment efficiency and the MCRT of the system
should be increased to maintain a relative predominance of free
swimmers, stalked ciliates and higher forms of organisms such as
rotifers.
FREE SWIMMING CILIATES
FIGURE IV-5
Stalked Ciliates (Figure IV-6)
These organisms are frequently present when the free swimmers are
unable to compete for the available food. A relative predominance
of these organisms along with rotifers will indicate a stable and
efficiently operating process.
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ACTIVATED SLUDGE PROCESS
SECTION IV - LABORATORY CONTROL
STALKED CILIATES
FIGURE IV-6
Changes in
MCRT are
reflected in the
appearance of
the mixed liquor.
Relative
predominance
of rotifers and
ciliates
indicates
process
stability.
Use an
inexpensive
camera to
record the
mixed liquor
appearance.
Evaluation of Microscopic Examination
Observation of microorganism activity and predominance in the activated
sludge can provide guidance in making process control adjustments.
Study of Figure IV-7 can be used to assist the operator with the decision
of increasing or decreasing the MCRT based on the relative predominance
of ciliates and rotifers in the MLSS. The decline of ciliates and rotifers
is frequently indicative of a poorly settling sludge. These observations
make it possible to detect a change in organic or chemical loading before
an upset occurs. These changes can be correlated with observations of
the settling characteristics of the MLSS in the 30-minute settling test, and
by calculation of the F/M. If the other tests confirm these observations,
adjustments to the MLSS should be made to alleviate the problem.
In summary, relative predominance of ciliates and rotifers are an indication
of process stability. This predominance is associated with the efficiency
of treatment under various loading conditions. An increase or decrease in
the predominance of these organisms may be indicative of process upset
before there is a major effect on process performance.
A great deal of information can be provided if photographic records of
sludge conditions are kept in a systematic and well documented manner.
Inexpensive (approximately $100) Polaroid cameras are available for this
purpose, and it is strongly recommended that a camera of this type be
obtained along with the microscope. These photographic records can be
used to anticipate seasonal variation or conditions of unusual operation.
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ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Selection of a Microscope*
Features which should be considered when selecting a microscope
include the following:
1) Built-in illumination or an external system which allows variations
of light intensity.
2) A condenser system.
3) A movable stage. Stage should be controlled by coaxial handle
rather than a manual push-pull.
4) 10X and 40X objectives.
5) 10X eyepiece.
Auxiliary equipment should include:
6) Light blue filter (daylight type)
7) Slides
8) Coverslips
9) Several small dropping pipettes
10) Storage box
11) Dust cover.
Relatively low The cost of a microscope can vary between $150.00 and $2,500.00, de-
micros e is pending upon the individual's requirements in the way of illumination,
8Uitabie. lenses and auxiliary equipment. A relatively inexpensive instrument is all
that is required for the examination of activated sludge.
'Adapted from "Activated Sludge Process Analyses and Interpretation
Workshop Manual," Ministry of the Environment, Toronto, Ontario.
(Additional information is also included.)
Use of the Microscope
Procedures for preparing slides and using the microscope should include
the following:
1) Clean cover slip and slide.
2) Use pipette to pick up sludge. Put finger on top of pipette until
the immersed end of a widetip pipette reaches the bottom of
sludge sample. Release your finger to allow sludge into the pipette.
Replace your finger on top of pipette and remove the pipette
from the sampler beaker. A long tipped eye dropper may also be
used.
3) Allow one drop of sludge from the pipette to drop in the middle
of the clear area of the glass slide by lifting your finger from top
of pipette momentarily, and then replacing your finger.
4) Pick up cover slip by two corners. Do not touch the cleaned area.
5) Pull cover slip along glass slide towards drop of sludge.
6) As soon as cover slip touches drop of sludge, allow cover slip to
fall onto glass slide.
7) Pick up glass slide. Place on microscope stage.
8) Move stage up to within approximately 1/8 inch of objective.
Look at glass slide through the eyepiece of the microscope.
IV-23
-------
<
ro
4
J
5
<;
S
N
t
IH
I]
>
H
H
5
4
C
j
r
STRAG
FREE SWIM.
CLLIATES
-^-^jjjj-)
FLAGELLATES
&
/>tAo
AMOEBOIDS
GLERS
ROTIFERS
STALKED
CILIATES
vjrkrfogy
-^
FREE
SWIMMING
CILIATES
•-~_-^^G^v
^^
FLAGELLATES
AMOEBOIDS
^
^
vjvjvJJJ aJi. 1 1 J-iiJNvj
ROTIFERS
^^
^^
STALKED
CILIATES
&
-fiffi
Ł Kil.it.
SWIMMING
CILIATES
eK=?x
^)
FLAGELLATES
AMOEBOIDS
^
P
NEMATODES
<^K
ROTIFERS
Ł$$
'^r^oCa— --
STALKED
CILIATES
7^
FREE
SWIMMING
CILIATES
FLAGELLATES
AMOEBOIDS
PIN I
'LOG
JN.E..MA IvJJJiljO
A
^^
ROTIFERS
OTA T Pfirr)
CILIATES
FREE SWIM.
CILIATES
FLAGELLATES
AMOEBOIDS
w >
m o
o >
-3
si
O G)
31 m
38
RELATIVE NUMBER OF MICROORGANISMS VS. SLUDGE QUALITY
FIGURE IV-7
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
9) Use the coarse adjustment on the microscope to bring the sludge
into the field of focus.
10) Use fine adjustment to refine focus to suit your eyes.
11) Identify organisms in the sludge.
Procedures for Examination
When performing a microscopic examination of activated sludge, a sheet
of paper should be kept handy to sketch the types observed. In the event
that unknown varieties of microorganisms are made, the operator may
identify these later. The objective of the examination is to determine
relative predominance of microorganisms. This may be accomplished by
the procedures outlined below and utilizing a worksheet as illustrated in
Figure IV-8.
Examination Procedures:
1) Record the date, time, temperature, and location of the sample on
the worksheet.
2) A minimum of three slides per sample should be examined.
3) Scan each slide and count the number of microorganisms in each
group.
4) Provide a mark for each microorganism counted in the appropriate
group space on the worksheet.
5) After completing the examination of the three slides, total the
number of organisms counted in each group.
6) The three higher totals are interpreted as the predominating
organisms.
Microscopic examinations of the activated sludge should be made three
times per week during peak flow periods. If a consistent trend of pre-
dominating organisms is established during normal operating conditions,
the frequency of examinations should be decreased to one time per week.
Flow
Accurate flow
measurements
are essential.
Flow
measurements
are very
Important.
A physical measurement of the in-plant flows is essential for true process
control. Without these flow measurements, it is impossible to compute hy-
draulic and organic loadings, F/M ratios, air requirements, detention periods,
recycle flows, clarifier underflows, or sludge wasting rates. Without the above
parameters to regulate the treatment processes, the operator is left with only
a "seat of the pants" approach to process control. Without a measurement of
in-plant flows, it is impossible to competently evaluate the operation of the
individual treatment units. The measurement of the plant flows also provides
a basis for computing costs for billing, estimating chemical needs, predicting
the future need for plant expansion or modification, and evaluating the
effect of the plant effluent on the receiving stream. Reference to Figure IV-2
will indicate locations of typical in-plant flows that should be measured for
process control.
IV-25
-------
ACTIVATED SLUDGE PROCESS
SECTION IV - LABORATORY CONTROL
FIGURE IV-8
WORKSHEET FOR
MICROSCOPIC EXAMINATION OF
ACTIVATED SLUDGE
DATE:
BY:
TIME:
TEMP:
AM
PM
°C
SAMPLE LOCATION:
MICROORGANISM
GROUP
AMOEBOIDS <&Z
FLAGELLATES WJjp
FREE ^v
SWIMMING (ffi
CILIATES
STALKED ^^X
ClLlATES 11;^' — ^v
ROTIFERS ^^^&M
WORMS .^-/
SLIDE
NO. I
SLIDE
NO. 2
SLIDE
NO. 3
TOTAL
RELATIVE PREDOMINANCE:
I.
2.
3
IV-26
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
How to measure
flow without a
flow meter.
In many of the smaller plants, only the plant influent flow and possibly the
plant effluent flow are metered. In these cases, the operator will have to
measure the in-plant flows by other means. For instance, a pumped flow may
be estimated by multiplying the pump capacity (gpm) times the minutes of
pumping time per day.
gpd = (gpm)(m in/day)
Often, pump capacity may be estimated by measuring the volume of liquid
pumped from or to a structure in a timed period. No unmetered flows into or
out of the structure must be permitted during the test period. Metered flows
into or out of a structure during the test must be taken into account when
computing the volume of liquid pumped.
gpm = (Area, sq.ft.) (Depth, ft.) (7.48 gal/cu.ft.)= metered flow, gpm
minutes
The metering instrumentation must be properly maintained and calibrated on
a regular and routine basis to insure that their measurements are accurate
and usable in process control and performance evaluation.
Sludge Blanket Measurement
The level of the
sludge blanket
can be
measured with
optical or
electronic
equipment.
Types of
blanket finders.
Within the secondary clarifier, a separation of the liquid and solids takes place.
The solids settle to the bottom of the clarifier while the settled liquid is dis-
placed over the clarifier effluent weirs. If the settled solids are not removed
from the tank at a rate equal to or greater than solids input by the aeration
effluent flow, a blanket of sludge will accumulate until eventually the solids
are washed out in the clarifier effluent flow.
The location of the sludge blanket in relation to the clarifier depth may be
determined by various types of devices. Some are commercially available
while others must be improvised by the operator. Figure IV-9 shows several
variations of sludge blanket finders. The following are some of the different
types of blanket finders:
1) A series of air lift pumps mounted within the clarifier at various depths.
2) Gravity flow tubes located at various depths.
3) Electronic sludge level detector—a light source and photo-electric
cell attached to a graduated handle or drop cord. The photo-electric
cell actuates a meter, buzzer, light, etc.
4) Sight glass finder—a graduated pipe with a sight glass and light
source attached at the lower end.
5) Plexiglass core sampler.
6) Some type of portable pumping unit with a graduated suction pipe or
hose.
IV-27
-------
ACTIVATED SLUDGE PROCESS
SECTION IV - LABORATORY CONTROL
«Air
AIR LIFT PUMP
•v:)!
'
SIGHT GLASS
ELECTRONIC
SLUDGE BLANKET INDICATORS
FIGURE IV-9
IV-28
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Use the sludge
blanket
thickness to
contorl RAS
flow.
Determining the sludge blanket depth in the secondary clarifier in conjunction
with other measurements such as the influent flow, MLSS, SVI, and the RAS
flow and suspended solids concentration provides valuable information that
can be used to control the RAS flow rates. Additionally, this test can be used
to evaluate the operation of multiple units, for instance the sludge blanket
depth in two clarifiers operating in parallel (both receiving flow from same
aeration basin) having equal RAS flow rates should be comparable. If the
sludge blanket in one clarifier was rising while the blanket in the other clarifier
was falling, it could be concluded that the aeration tank effluent flow is
unevenly distributed to the clarifiers. A rising blanket may indicate an in-
adequate sludge return rate, unbalanced distribution of aeration tank effluent
flow, inadequate sludge wasting rates, or a poorly settling sludge. The presence
of a poorly settling sludge could be verified with the SVI value. To correct a
rising blanket, the operator first determines the reasons by a review of the lab
test results, operational logs, and process control parameters. After deter-
mining the possible reason for the increased blanket depth, the operator
should then take the appropriate corrective measures.
Run a profile to
determine
average blanket
thickness.
Exercise
caution.
Precautionary Procedures
The following precautionary procedures should be followed in the per-
formance of the sludge blanket measurement:
1) Select a measuring station located at a point where the blanket
depth represents an average of the entire blanket depth. Such a
location can be selected by running a profile of the clarifier's entire
blanket depth. Thereafter, the selected location should always be
used.
2) The sludge blanket finding devices must be used with care. The
electronic devices must be lowered slowly until the blanket is
located.
3) Procedures and techniques must be uniform for all operations and
for all measurements.
Centrifuge Test
Quick method
to determine
SS.
Test results
vary often.
The centrifuge test provides a quick and convenient method of roughly deter-
mining the suspended matter (SS) concentrations of the mixed liquor and
return sludge. The centrifuge test results can be used to calculate a mass
(solids) balance and to develop various graphs for control and monitoring of
the return sludge flow rates, adjustment of the sludge wasting rates, clarifier
and aeration sludge detention times, and solids distribution ratios. How to
use the centrifuge test results for controlling the activated sludge process is
discussed futher in Section 2.04, "SLUDGE QUALITY CONTROL"
Due to changing sludge settling and compaction characteristics, the results
of the centrifuge test will often vary for similar suspended matter concentra-
tions. The sludge characteristics as reflected by the 30-minute settling test
must be considered when interpreting or using the results of the centrifuge test.
IV-29
-------
ACTIVATED SLUDGE PROCESS
SECTION IV-LABORATORY CONTROL
Precautionary Procedures
A generalized procedure is described below:
1) Collect a representative sample.
2) Thoroughly mix sample and fill each centrifuge tube exactly to the
full mark. The sample must be thoroughly mixed before each pour-
ing. It is recommended that no less than three tubes be run on
each sample.
3) Centrifuge samples for 15 minutes with the speed adjustment set
at full speed. It is of utmost importance that the samples are
centrifuged for the same speed setting each time to promote con-
sistent compaction and meaningful test results.
4) Remove one tube at a time and read the amount of suspended
matter concentrated in the bottom of the tube. The results should
be recorded for future reference.
5) Use the results of the centrifuge test directly for control and
monitoring of the activated sludge process as described in Section
2.04, "SLUDGE QUALITY CONTROL" or convert to suspended
matter concentration as described below.
Comparisons of
centrifuge and
SS tests must
be made.
Plot SS and
centrifuge test
results on graph
to obtain
relationship.
Turbidity
checks
operational
performance.
Suspended Matter Correlation
A correlation between the centrifuge test results and the actual filtered
suspended matter concentration may be made on a daily basis by per-
forming a centrifuge test and a suspended matter test on the same sample
of mixed liquor. A 5-day moving average of the spin ratio (SS concentration
mg/l/centrifuge sludge concentration, %) should be used to minimize the
effect of any variation in this relationship. Another method sometimes
used to correlate the results of the two tests is to plot the SS concentra-
tion/centrifuge sludge concentration relationship on a graph. After the
various points are plotted on the graph, a line of best fit is drawn as shown
on Figure IV-10. Since this relationship varies as sludge characteristics
change, the line of best fit must be periodically checked and corrected by
comparing the graph readout with the results of an actual filtered sus-
pended matter test.
Turbidity
Turbidity refers to the interference of light passage through water. Fine
particles of suspended matter hinder the passage of light by scattering and
absorbing the rays. Turbidity in the secondary effluent is chiefly due to bio-
logical floe that has carried over in the clarifier effluent.
The turbidity measurement of the secondary effluent is a quick and easy
method of checking the operation and performance of the activated sludge
process. In recent years, some turbidity analyzers have been permanently
installed at the secondary clarifier to continuously measure and indicate the
clarity of the secondary effluent. A properly operated activated sludge process *
generally produces an effluent with a turbidity between 1.0 and 3.0 JTU
(Jackson Turbidity Unit). An increasing effluent turbidity indicates an unfavor-
able trend in process operation which should be promptly investigated and
corrected.
IV-30
-------
• Samples Measured for
Suspended Solids and
Centrifuge Sludge Reading
Line of Best Fit-
4.0
<
CO
10
o
c
o
0)
CT>
T3
OO
0)
t-
4->
O
500
1000
1500 2000 2500
Suspended Solids , mg/1
3000
3500
4000
CORRELATION OF CENTRIFUGE AND SUSPENDED SOLIDS CONCENTRATIONS
FIGURE IV-10
w
m
O
3D (/)
•< m
s ~°
O 3D
Z O
H O
3D m
O c/>
r- W
-------
ACTIVATED SLUDGE PROCESS
SECTION IV - LABORATORY CONTROL
Recommended
way of
expressing
turbidity.
A photo-electric turbidimeter with an automatic readout in either Jackson
Turbidity Units (JTU) or Formazin Turbidity Units (FTU)* is the recommended
method of measuring the turbidity of the secondary effluent.
Precautionary Procedures
When performing the turbidity test, the following procedures should be
followed in conjunction with the procedures outlined in Standard Methods.
1) Hold' the turbidimeter test vial near the top. The test vial must be
kept clean, both on the inside and the outside.
2) Calibrate the turbidimeter using a standard in the range of the
turbidity expected.
3) Stir the sample before pouring. Pour the sample slowly into the
test vial, being careful not to create or trap air bubbles.
4) Be sure the outside of the test vial is dry before inserting it into
the turbidimeter.
5) After allowing any air bubbles to escape, promptly read the results.
6) Replace any test vials that are scratched or damaged.
"Jackson Turbidity Units and Formazin Turbidity Units, although not identical, are
almost the same for practical purposes.
REFERENCES
APHA, AWWA, WPCF, Standard Methods for Examination of Water and Wastewater,
14th Edition, 1976.
California Water Pollution control Association, Laboratory Procedures for Operators
of Water Pollution Control Plants, 1970.
Kerri, Kenneth D., et al., A field Study Training Program, Operation of Wastewater
Treatment Plants, (Chapters 6 and 14), Sacramento State College Department of
Civil Engineering.
Ministry of the Enviornment - Activated Sludge Process Anaylses and Interpretation
Workshop Manual, Training, Certification, and Safety Section, Toronto, Ontario,
M4V LP5.
New York State Department of Health Laboratory Procedures for Waste-Water
Treatment Plant Operators, Health Education Service, Albany, N.Y.
U.S. Environmental Protection Agency, Technology Transfer - Handbook for Analytical
Quality Control in Water and Wastewater Laboratories, Analytical Quality Control
Laboratory, National Environmental Research Center, Cincinnati, Ohio, June, 1972.
The Texas Water Utilities Association, Manual of Wastewater Operations.
Water Pollution Control Federation, Simplified Laboratory Procedures for Wastewater
Examination, Publication No. 18,1971.
IV-32
-------
TRICKLING FILTER PROCESS
TABLE OF CONTENTS
Topic Page
SECTION I-TROUBLESHOOTING
1.01 INTRODUCTION 1-1
1.02 TROUBLESHOOTING GUIDES 1-1
No, 1-Filter Flies I-2
No. 2-Odors I-3
No. 3-Ponding I-5
No. 4-High Effluent Suspended Solids I-6
No. 5-Freezing I-8
SECTION II-PROCESS CONTROL
2.01 INTRODUCTION 11-1
2.02 OPERATIONAL GUIDES 11-1
No. 1-Trickling Filter II-2
No. 2-Secondary Clarifier II-5
No. 3 - Pumping Equipment and Piping II-6
2.03 PERFORMANCE AND EVALUATION II-7
Review of In-Plant Recycled Flows 11-7
2.04 PROCESS CONTROL 11-9
Staging 11-9
Recirculation 11-9
Sludge Removal 11-12
2.05 LOADING PARAMETERS 11-14
Organic Loading 11-15
Hydraulic Loading 11-16
Surface Overflow Rate 11-17
2.06 OPERATIONAL PROBLEMS 11-18
Filter Flies 11-19
Odors II-20
Ponding 11-21
High Effluent Suspended Solids II-23
Freezing II-24
SECTION III-FUNDAMENTALS
3.01 INTRODUCTION III-1
Definitions Hl-2
3.02 PROCESS DESCRIPTION III-3
Rotary Distributor III-3
Fixed-Nozzle Distributors MI-6
Dosing III-6
Media III-6
Underdrain III-9
Ventilation 111-10
Natural Ventilation 111-10
Forced Ventilation 111-10
Final Sedimentation 111-10
-------
TRICKLING FILTER PROCESS
TABLE OF CONTENTS (continued)
3.03 TRICKLING FILTER CLASSIFICATION 111-12
Low-Rate Trickling Filters 111-12
High-Rate Trickling filters 111-13
Aero-Filter 111-14
Bio-Filter 111-14
Accelo-Filter 111-15
Roughing-Rate Trickling Filters 111-15
SECTION IV-LABORATORY CONTROL
4.01 INTRODUCTION IV-1
4.02 LABORATORY SAMPLING AND TESTING PROGRAM IV-1
Grab Samples IV-1
Composite Samples IV-3
Laboratory Control Program IV-4
Low-Rate Trickling Filter Process IV-4
High-Rate Trickling Filter Process IV-4
Roughing Filters/Biological Towers IV-6
4.03 LABORATORY CONTROL GUIDES IV-6
Biochemical Oxygen Demand IV-7
Chemical Oxygen Demand IV-8
Soluble COD and BOD \ IV-9
Settleable Matter IV-9
Total Suspended Matter IV-10
Nitrite Nitrogen IV-11
Nitrate Nitrogen IV-12
Ammonia Nitrogen IV-12
Total Phosphorous IV-13
Dissolved Oxygen IV-13
Hydrogen Ion Concentration IV-14
Temperature IV-15
Flow IV-15
-------
TRICKLING FILTER PROCESS
LIST OF FIGURES
Figure No. Description Page
11-1 Typical Trickling FilterTrend Plots II-8
II-2 Staging of Filters 11-10
111-1 Typical Trickling Filter Process 111-1
III-2 Typical Trickling Filter in Cross Section III-4
III-3 Rotary Distributor III-5
III-4 Fixed-Nozzle Distribution System III-7
III-5 Redwood Lath Media III-8
III-6 Plastic Media III-9
III-7 Low-Rate Trickling Filter Layout 111-12
III-8 High-Rate Trickling Filter Layout 111-14
III-9 Trickling Filter Variations 111-16
111-10 Typical Roughing Filter Installation 111-17
111-11 Oxidation (Biological) Towers 111-18
IV-1 Wastewater Sampling Guidelines IV-2
IV-2 Sampling and Testing Program for Trickling Filter IV-5
-------
TRICKLING FILTER PROCESS
LIST OF TABLES
Table No. Page
11-1 Guide to Successful Process Control \ 11-1
111-1 Filter Classification and Characteristics 111-11
-------
TRICKLING FILTER PROCESS
SECTION I-TROUBLESHOOTING
Select the
measure with
least adverse
effect.
Know the
process.
1.01 INTRODUCTION
This section of the manual presents troubleshooting procedures for solving
the common operating problems experienced in the trickling filter process.
With each problem, or observation, is included a list of probable causes,
procedures to determine the cause, and the suggested corrective measures
listed in the order to be considered. You, the operator, must determine and
select one or more of the corrective measures that will restore the process
to an efficiency level which will produce the best final effluent quality. In
order to evaluate the problem and select the best corrective measure, you
must be thoroughly familiar with the trickling filter process and how it fits
into the overall treatment plant operation. In addition, you must be familiar
with the influent wastewater characteristics, plant flow rates and patterns,
design and actual loading parameters, performance of the overall plant and
individual processes, and current maintenance procedures.
1.02 TROUBLESHOOTING GUIDES
There are five problems that frequently occur in the operation of a trickling
filter process. These problems are listed below and are referenced to the
troubleshooting guides which are presented on the following pages:
INDEX TO TROUBLESHOOTING GUIDES
Troubleshooting
Guide No.
1
2
3
4
5
Problem Indicator
Filter Flies
Odors
Ponding
High Effluent Suspended Solids
Freezing
1-1
-------
TRICKLING FILTER PROCESS
TROUBLESHOOTING GUIDE I — Filter Flies
OBSERVATION
1. Filter Flies.
a. Gnat-sized moth-like
flies.
b. Dark brown, worm-like
larvae in filter slime
growth.
PROBABLE CAUSE
A. Poor distribution of waste-
water, especially along the
filter wall.
B. Hydraulic loading insuf-
ficient to keep fly eggs and
larvae washed from filter
bed.
NECESSARY CHECK
1. Visually check.
1 . Calculate hydraulic loading.
Hydraulic loadings greater
than 200 gpd/sq. ft. are
usually required.
REMEDIES
1) Unclog spray orifices or
nozzles.
2) Provide orifice openings at
end of distributor arm to
spray walls or open dump
gates slightly for a spray
effect on filter wall.
1) Prevent completion of the
filter fly life cycle in the
order of the following
remedies:
a) Increase recirculation
rate.
b) Flood, Filter for several
hours each week during
fly season or,
c) Chlorinate filter influent
for several hours each
week maintaining a 1 to
2 mg/l residual at the
distributor outlet.
d) Spray filter walls and
other areas where flies
rest with a residual-type
insecticide— if not pro-
hibited by State or local
regulatory agencies. DO
NOT spray surface of
media.
REFERENCES
pg n-19
pg M-19
pgii-19
-------
TRICKLING FILTER PROCESS
TROUBLESHOOTING GUIDE 2-ODORS
OBSERVATION
1 . Odors
(Anaerobic decomposition
within the filter.)
PROBABLE CAUSE
A, Excessive organic loading.
a. Industrial wastes.
NECESSARY CHECK
1 . Calculate organic loading.
a. Check industries for
unusual waste discharge.
REMEDIES
1) Utilize a commercial mask-
ing agent while making the
appropriate corrections.
2) Encourage aerobic condi-
tions in pre-treatment
units — try pre-chlorination,
aeration, or recirculation
during low night flows.
3) Enforce industrial waste
ordinance.
4} Improve operation of pri-
mary sedimentation tanks.
5) Increase recirculation rate
to dilute organic strength
and improve oxygen
transfer.
6) Chlorinate filter influent for
for several hours each day
during low flow maintaining
a 1 to 2 rng/t residual at
distributor outlet.
7) If design loading is being
exceeded, plant expansion
may be required.
REFERENCES
pgll-15&ll-20
Pi 11-20
pg n-9
pg H-20
pg n-15 & 11-7
-------
TRICKLING FILTER PROCESS
TROUBLESHOOTING GUIDE 2 - ODORS (continued)
OBSERVATION
PROBABLE CAUSE
B. Poor Ventilation.
C. Poor housekeeping.
NECESSARY CHECK
1. If provided see that vent
pipes are clear in filter.
2. Check underdrain system
is not obstructed or flowing
more than half full.
3. Check filter media voids
are not filled with biological
growths.
1. Visually check.
REMEDIES
1) Unclog vent pipes.
2) Remove all debris from
filter effluent channel and
flush obstructive materials
from underdrain.
3) If underdrain system is
flowing more than half full,
reduce filter recirculation
if possible.
4) Improvise a mechanical
means of improving venti-
lation if natural ventilation
is inadequate.
5) Increase circulation to
flush out the excess bio-
logical growths.
1) Remove all debris from
filter media surface.
2) Wash down distributor
splash plates and the
side walls above the media.
REFERENCES
pg 111-10
pglli-9
pg 111-10
pg M-9
pg Il-2
pg n-2
-------
TRICKLING FILTER PROCESS
TROUBLESHOOTING GUIDE 3 - PONDING
OBSERVATION
1. Ponding of water over
filter media.
PROBABLE CAUSE
A. Excessive biological
growth in media voids.
B. Media is . nonuniformly
sized, disintegrating or
too small.
C. Poor housekeeping.
NECESSARY CHECK
1 . Check records for increases
in organic loading and/or
decreases in hydraulic
loading or if dosing inter-
vals has been decreased.
1. Visually inspect.
1. Visually inspect.
REMEDIES
1) Loosen surface layer of
rock, media.
2) Flush the area with high
pressure stream of water.
3) Increase recirculation.
4) Dose the filter influent with
Chlorine for 2-4 hours to
obtain 1-2 mg/l residual at
distributor outlet.
5) If possible, flood the filter
for 24 hours.
6) If possible, shut down TF -
dry media and wash out.
1) Dry out filter and check
media. Replace nonuni-
formly sized, or damaged
media.
1) Remove all leaves, paper,
sticks, and other
debris accumulating on
filter media surface.
REFERENCES
pg 11-21
pg 11-21
pg n-9
pg 11-21
pg n-21 &III-9
pg 11-21
p 11-21 &III-6
pgii-2
-------
TRICKLING FILTER PROCESS
TROUBLESHOOTING GUIDE 4 - HIGH EFFLUENT SUSPENDED SOLIDS
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
1. Increase in Clarifier Ef-
fluent Suspended Solids.
A. Excessive sloughing from
filter.
1. Check seasonal changes
that would affect micro-
organisms.
2. Check organic loading.
a. Industrial wastes.
o>
B. Denitrif ication in clarif ier.
C. Final Clarifier hydraulically
overloaded.
1. Check to see if filter ef-
fluent is nitrified and sludge
floats in clumps.
1. Calculate Clarifier surface
overflow rate. (Should not
exceed 1200 gpd/sq. ft. at
peak flow.)
1) Wait for season to change
or try polymer addition.
1) If there is a high rate of
loading, decrease by using
more filters, if available.
2) Enforce industrial waste
ordinance.
3) Increase Clarifier under-
flow rate.
4) Plant expansion may be
necessary.
1) Increase Clarifier under-
flow rate.
1) If due to recirculation,
reduce recirculation rate
during peak flow periods.
2) Additional clarifiers may
be required.
pg H-23
pgll-15
pg M-23
pg 11-12
pg 11-12 &II-23
pg 11-17, II-7&II-9
pg 11-17
-------
TRICKLING FILTER PROCESS
TROUBLESHOOTING GUIDE4-HIGH EFFLUENT SUSPENDED SOLIDS (continued)
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
D. Equipment malfunction in
final clarif ier.
E. Temperature currents in
final clarifier.
1. Check for broken sludge
collection equipment
2, Check for broken baffles.
3. Check for uneven flows
over eff uent weirs.
1. Make temperature survey
of the clarifier using a
temperature probe on a DO
meter.
1) Replace or repair broken
equipment.
2) Adjust effuent weirs to an
equal elevation.
1) Install baffles to stop
short-circuiting.
pg II-23
pgll-23&ll-5
pg li-23
-------
TRICKLING FILTER PROCESS
TROUBLESHOOTING GUIDE 5- FREEZING
OBSERVATION
PROBABLE CAUSE
NECESSARY CHECK
REMEDIES
REFERENCES
1. Freezing.
A. Low temperatures.
1. Check atmospheric
temperatures.
oo
1) Decrease recirculation.
2) Operate two-stage fiters in
parallel.
3) Adjust orifices and splash
plates for coarse spray,
4) Construct windbreak.
5) If using intermittent dos-
ing, open bleeder valve on
the distribution main.
6) Partially open dump gates
at outer end of distributor
arms to provide stream
along retaining wall in-
stead of a spray.
7) Cover pump sumps and
dosing tanks.
8) Manually remove ice
formation.
pg n-9
pg n-9
pgll-24, III-3&III-6
Pfl MI-6
pglll-6
-------
TRICKLING FILTER PROCESS
SECTION I-TROUBLESHOOTING
REFERENCES
Environmental Protection Agency, Technology Transfer, Process Design Manual for
Upgrading Existing Wastewater Treatment Plants, October, 1974.
Kerri, Kenneth D., et al., A Field Study Training Program, Operation of Wastewater
Treatment Plants, (Chapter 6), Sacramento State College Department of Civil
Engineering.
Lohmeyer, George T., Trickling Filters and Their Operation, Water & Sewage Works,
September, 1958.
New York State Department of Health, Manual of Instruction for Sewage Treatment
Plant Operations.
The South Carolina Water and Sewage Works Association, Correspondence Course
Manual for Sewage Plant Operators, Class C, 1962.
The Texas Water Utilities Association, Manual of Wastewater Operations, (Chapter
12), 1971.
Water Pollution Control Federation, Operation of Wastewater Treatment Plants,
Manual of Practice No. 11,1970.
I-9
-------
TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Importance of a
properly
controlled
operation.
Acceptable
ranges are
given herein.
2.01 INTRODUCTION
The trickling filter process is reliable and can treat shock organic loads. It
requires much less monitoring and control then the activated sludge process.
However, proper operation and control is still required to achieve peak per-
formance and to avoid operational problems such as ponding, odors, flies,
and freezing. Table 11-1 presents guidelines to achieving successful process
control.
The operating parameters given in this section are intended as acceptable
ranges to guide the operator in achieving operational control at his plant.
Operation and control of a trickling filter process should be based on its re-
sponse and performance. The success or failure in achieving the best possible
performance from the treatment process is dependent on the operator.
TABLE 11-1
GUIDE TO SUCCESSFUL PROCESS CONTROL
REQUIREMENT
REFERENCE
1. Sound operational and preventive
maintenance measures.
Section 2.02,
OPERATIONAL GUIDES
2. Laboratory monitoring
Section 4.02,
LABORATORY SAMPLING AND
TESTING PROGRAM
3. Accurate, up-to-date records.
Appendix A,
OPERATIONAL RECORDS
4. Evaluation of operational and laboratory
data.
Section 4.03,
LABORATORY CONTROL TESTS
5. Application of data evaluation to adjustment
of the process.
Section 2.04,
PROCESS CONTROL
6. Troubleshooting problems before they
become serious.
Section 1.02,
TROUBLESHOOTING GUIDES
2.02 OPERATIONAL GUIDES
Operational guides are provided on the following pages to aid the operator in
establishing routine operational procedures for his trickling filter process.
Performance of the routine operational procedures is not complete without a
competent preventive maintenance program. Every item of operating equip-
ment requires frequent attention with particular emphasis on lubrication and
other preventive maintenance requirements to ensure trouble-free operation
and minimum maintenance costs. A good preventive maintenance program
helps to improve process control by ensuring that the equipment remains
operational.
1-1
-------
TRICKLING FILTER PROCESS
OPERATIONAL GUIDE 1 - TRICKLING FILTER
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
A. ROTARY DISTRIBUTOR
1. Check that distributor rotates smoothly.
2. Clean clogged orifices.
3. Hose slime growths off splash plates.
4. Check oil in bearing assembly for water
contamination.
5. Maintain bearing assembly and drive
unit if so equipped.
6. Adjust guy rods.
7. Winter operation (Freezing conditions).
1a) Visually observe.
1b) Jumpy operation could denote bearing
damage and/or malfunction of pumps.
2a) Shut off the flow to the filter.
2b) WAIT for arms to stop rotating before
proceeding.
2c) Be CAREFUL when walking on media
surface—it is extremely slippery.
2d) Remove obstructive materials from
orifices.
2e) Open end dump gates and flush the.
distributor arms.
21) Return unit to normal service.
3a) Excess growths can affect uniform
spreading action of plates.
4a) Water contamination denotes a badly
worn or defective seal.
4b) A leaky seal should be repaired immedi-
' ately to avoid bearing damage.
5a) Follow manufacturer's instructions.
5b) A competent preventive maintenance
program is essential for good operation.
6a) Should be adjusted with seasonal
temperature changes to keep distribu-
tor arms leveled.
7a) See Troubleshooting Guide No. 5.
Daily
Daily
Daily
pgin-3
pgiil-3
pgin-3
Seasonally
pglll-3
pg II-24
-------
TRICKLING FILTER PROCESS
OPERATIONAL GUIDE 1 - TRICKLING FILTER (continued)
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
B. FIXED-NOZZLE DISTRI-
BUTION SYSTEM
C. DOSING SIPHON
1. Clogged nozzles.
2, Flush all dead ends in the distribution
piping.
3. Winter operation (Freezing conditions).
1. Check operation.
2. Clean and lubricate float-actuated
counters, etc.
3. Wash down tank walls.
4. Clean tank and inspect piping apparatus.
5. Winter operation (Freezing conditions).
1a) Shut off flow to lateral.
1b) Be CAREFUL when walking on media
surface—it is extremely slippery.
1c) Disassemble and clean clogged nozzles.
1d) Open valve, or remove nozzle, at end of
lateral and flush obstructive materials
which may be in the lateral.
1e) Return to service.
2a) May not be possible with some systems.
3a) See Troubleshooting Guide No. 5.
1a) Observe a dosing cycle. If it is not work-
ing properly, check for a clogged siphon
vent or a leak in the piping.
2a) Follow manufacturer's instructions.
3a) To prevent odors and unsightly accum-
ulation of grease and slime.
4a) Replace badly corroded piping.
5a) Cover tank to minimize loss of heat.
Daily
pg lfl-6
Weekly
Daily
pglli-6
Daily
Bi-annually
-------
TRICKLING FILTER PROCESS
OPERATIONAL GUIDE 1 - TRICKLING FILTER (continued)
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
D. MEDIA
E. UNDERDRAW
1. Visually check.
2. Remove all debris from filter surface.
1. Inspect.
1a) Check for any indication of ponding,
filter flies, and windblown debris.
1a) When needed, flush out obstructive
growths and debris.
1b) Remove any obstructive materials in
effluent channel.
1c) Underdrain conduits and effluent chan-
nel should not be flowing more than
half full.
Daily
Daily
pg n-18
pglll-9& 111-10
F. WALLS
Q. HYDRAULIC LOADING
ON FILTER
1. Wash down side walls above media.
1. Control recirculation rates for optimum
performance.
Daily
1a) Review records to determine the lowest
recirculation ratio yielding good process
performance (based on BOD or COD of
the final effluent).
1 b) The recirculation ratio should be great
enough to avoid the problems of pond-
ing, odors, and filter flies.
pgll-7,11-15 & 11-16
-------
TRICKLING FILTER PROCESS
OPERATIONAL GUIDE 2 - SECONDARY CLARIFIER
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
A. TANK
1. Inspect for proper operation.
2. Perform daily wash down.
01
3. Maintain sludge collection equipment
and drive units.
4. Inspect baffles and effluent weirs.
5. Check sludge withdrawal rate and
frequency.
1a) Mechanical equipment.
1b) Presence of floating sludge—see
Troubleshooting Guide No. 4.
2a) Hose down the influent channels, tank
walls—especially at the water line, ef-
fluent weir and launders, effluent chan-
nel, and sight sludge box or hopper-if
so provided.
3a) Follow manufacturer's instructions.
4a) Maintain baffles in sound condition.
4b) Maintain effluent weirs at an equal
elevation.
5a) Sludge should be removed before it be-
comes septic and floats to the surface,
preferably on a continuous basis.
Twice/shift
Daily
pg 11-12 &II-23
Daily
Twice/shift
pgll-23
pg 11-12
-------
TRICKLING FILTER PROCESS
OPERATIONAL GUIDE 3 - PUMPING EQUIPMENT AND PIPING
EQUIPMENT
SUGGESTED STEP PROCEDURES
DETAILS
FREQUENCY
REFERENCE
A. PUMPS
O>
1. Check operation of the pumps and
motors.
2, Alternate pumps in service.
3. Maintain pumping units.
4, Fully open and close all valves.
5. Check operation of air vacuum/relief
valves, flow meters, ect.
1a) Check for excessive vibration, unusual
noises, lubricant leakage, and
overheating.
1 b) Check oil reservoir level—if so equipped.
1c) Check oil feed rate—if so equipped.
1d) Check packing or mechanical seals-
make adjustments per manufacturer's
instructions.
1e) Check for proper position of suction
and discharge valves.
3a) Follow manufacturer's instructions.
4a) Make necessary adjustments or repairs.
4b) Maintain valves and operators according
to manufacturer's instructions.
5a) Maintain according to manufacturer's
instructions.
Twice/shift
Daily
Monthly
Weekly
-------
TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Competent
process control
Includes
evaluation of
process
performance.
Many factors
affect filter
performance.
Importance of
complete and
accurate
records.
2.03 PERFORMANCE EVALUATION
Evaluation of process performance is an essential part of competent process
control and operation. The evaluation is helpful in determining process re-
sponse to various modes of operation, developing performance trends, and
identifying the causes of operational problems. For trickling filters, perform-
ance evaluation consists of reviewing the COD, BOD, suspended solids, and
ammonia nitrogen removal efficiencies in relationship to the mode of opera-
tion, loading parameters, and plant recirculation flows. The review and
application df lab testing results is further discussed in Section IV "TRICKLING
FILTER LABORATORY CONTROL" and "APPENDIX A".
Trickling filter performance is affected by many factors, such as hydraulic
and organic loadings, depth and physical characteristics of the media, method
of wastewater distribution, ventilation, characteristics of applied wastewater
(temperature, pH, toxicants, etc.), and the hydraulic loading upon the subse-
quent sedimentation unit. An effective means of reviewing your plant per-
formance is to maintain daily charts or graphs reflecting such data against
time. The charts presented in Figure 11-1 serve as visual aids in identifying the
optimum control parameters and make any trends or changes immediately
evident. The preparation and use of these trend charts are discussed further
in "APPENDIX A"
Conclusions reached during the process evaluation are then applied to the
adjustment of the process (selection of recirculation rates and modes of
operation) for efficient and economical operation. Whenever possible, only
one process adjustment should be made at a time to allow sufficient time
between each change for the process to respond and stabilize.
Complete and accurate records of all phases of plant operation and mainten-
ance are essential for accurate performance evaluation and process control.
The preparation of operational records is discussed further in "APPENDIX A".
Recycled flows
may cause
overloading.
Review of In-Plant Recycled Flow
In evaluating the performance of the process or solving problems, a careful
consideration should be given to all in-plant recycled flows. Often, in-plant
recycled flows are the cause of organic or hydraulic overloading. The sludge
processing operations may return decants from digesters, thickeners, centri-
fuges, or vacuum filters. The waste backwash water from effluent sand filtra-
tion processes may also cause hydraulic overloading or other process control
problems. The recycled flow from improperly loaded and operated sludge
processing units may account for as much as 25 percent of the total plant
organic loading. Usually, the majority of recycled flows are returned to the
primary sedimentation units where it is hoped organic solids will settle out.
In most cases this practice is the major cause of overloading secondary pro-
cesses due to poor removal of solids in the recycled flows sent to the primary
sedimentation units.
The additional loading then results in a greater sludge production, and subse-
quently an increased loading upon the sludge processing operation. In the
trickling filter process, excessive COD or BOD loadings will eventually reduce
effluent quality and cause anaerobic conditions to occur in the filter.
I-7
-------
TRICKLING FILTER PROCESS
SECTION II - PROCESS CONTROL
o
3
§
>-) I
a
a ft
H
U,
3°.
< c
3?
j ^
u a
So
O
H
H
3
u
K
zoo
100
30
HIGH RATE TRICKLING FILTER
(Five-day moving average trend plots)
FIGURE II-1
TYPICAL TRICKLING FILTER TREND PLOTS
11-8
-------
TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Minimize the
effect of
recycled flows.
Some guidelines that will reduce the effects of recycled flows on the trickling
filter process include the following:
1) Add flow continuously or during low night flows to avoid shock loads.
2) Improve efficiency of sludge handling process.
3) Utilize a lagoon or drying bed for poor quality decants from sludge
processing operations.
4) Avoid pumping excess water in underflow fed to sludge handling
processes.
5) Aerate or pretreat recycled flows to reduce oxygen demands.
Select
operating
parameters for
best
performance
with least cost.
2.04 PROCESS CONTROL
Operational control of the trickling filter process primarily consists of reviewing
operating logs and lab test results to select the proper operational parameters
(recirculation rates, hydraulic loading) and modes that yield the required
performance at the least cost. The plant operator must be cost conscious
and concerned with the conservation of power, and the production of effluent
that will meet discharge requirements. For example, to conserve power and
minimize operational costs, the operator should select and utilize the lowest
recirculation rate that will provide the required performance, but not result in
ponding, odors, filter flies, or other problems.
Staging
Staging refers to
operating filters
The term staging refers to the operation of trickling filters in series. The
purpose of staging is to produce a higher quality effluent by using the first
filter in the series as a roughing filter.
Modified
concept.
An approach that has been used successfully in England involves alternating
the filters, that is, the leading filter is alternated between the two filters
operating in series. This practice is referred to as Alternating Double Filtration
(A.D.F.). The primary advantage of this approach is that the slime thickness is
controlled in both filters by the alternate loading which tends to reduce clog-
ging problems. Unless the filter process is designed to operate with A.D.F.,
this flexibility in the operational mode is usually non-existent. Basically the
mode of staging is dictated by design rather than operational control. As
shown in Figure II-2, both filters (stages) are generally constructed the same
size with several options for recirculation incorporated into the design. The
selection of the recirculation scheme should be based upon process perform-
ance. Use the scheme which produces the best effluent.
Recirculation
Why Is
recirculation
used?
Recirculation is practiced in all high-rate trickling filter plants and to some
degree in low-rate trickling filter plants. Recirculation is utilized in high-rate
trickling filter plants basically to maintain a constant hydraulic loading to
prevent clogging the voids in the filter media. In the low-rate trickling filter
plant, recirculation may be utilized to maintain a sufficient dosing rate during
low flows. Various recirculation arrangements are shown on Figure II-2.
II-9
-------
ALTERNATE
RECIRCULATION
RECIRCULATION
FIRST STAGE
TRICKLING FILTER
INTERMEDIATE
CLARIFIER
SECOND STAGE
TRICKLING FILTER
SECONDARY
CLARIFIER
PRIMARY
CLARIFIER
EFFLUENT
(I) ~\
m 30
P
O r-
Z z
= 2)
-"
8
m
w
en
00
§s
5 w
SLUDGE
SLUDGE
SLUDGE
FIGURE II- 2
STAGING OF FILTERS
-------
TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Consider
hydraulic
loadings.
Base control on
filter response
and
performance.
When selecting the recirculation flow scheme and rate, the hydraulic loading
on the filter and affected clarifiers must be considered as well as the hydraulic
limitations of the distribution and underdrain systems. As a rule of thumb,
the underdrain conduits and effluent channels should not flow more than
one-half full.
Usually, the recirculation ratio has a greater effect on filter performance than
the recirculation flow scheme. Recirculation ratios may be defined as parts of
recirculated flow per part of raw wastewater flow. Therefore, a ratio of 0.5 is
equivalent to one half gallon of recirculated flow for each gallon of wastewater
to be treated. Although some experimentally based equations have been
developed to calculate the amount of recirculation needed, it is recommended
that operational control be based on filter response and process performance.
In high-rate trickling filters, recirculation ratios (R/Q) usually range from 0.5 to
4.0 with higher ratios considered to be economically unjustifiable. Common
engineering practice is to design the high-rate trickling filter process for ratios
of 0.5 to 2.0. Trickling filters utilizing synthetic media employ recirculation as
a means of maintaining a minimum wetting rate, i.e., a hydraulic loading
(gpm/sq ft) which will maintain biological growth throughout the media depth.
The recirculation ratio is determined as shown below:
Example Calculation
A. Data Required
1. Recirculation flow = 0.2 mgd
2. Raw wastewater flow = 0.4 mgd
B. Determine the recirculation ratio (R/Q).
R/Q =
recirculation flow
raw wastewater flow
_ 0.2 mgd
0.4 mgd
Recirculation
can minimize
operational
problems and
Improve filter
performance.
= 0.5
Recirculation is often utilized to improve filter performance and to minimize
operational problems. Some of the advantages of recirculation include the
following:
1. Maintains biological growth throughout synthetic media depth.
2. May improve operation of primary and final sedimentation units during
low flow periods by reducing septicity.
3. Dilutes high strength or toxic wastes to make them treatable.
4. Minimizes hydraulic and organic loading variations.
5. Improves distribution of the wastewater over the filter surface.
6. Minimizes odors, ponding, and filter fly breeding by increasing hydraulic
loading to encourage continuous sloughing and reduce slime thickness.
7. Prevents biological growth from drying out during low flows.
1-11
-------
TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Be aware of
possible
adverse effects.
Know your
system.
Although the advantages of recirculation generally outweigh the disadvan-
tages, recirculation may result in the following adverse effects:
1. Reduces the wastewater temperature and therefore lowers the rate of
biological activity. In extremely cold climates, recirculation may
increase the potential for ice formation.
2. Recirculation through a sedimentation unit at rates exceeding hydrau-
lic design limits may reduce efficiency.
3. Increases operational costs due to higher pumping rates.
4. If excessive, it may decrease the organic removal efficiency of the
process.
The operator should be familiar with all the modes of recirculation available
to him at his plant. Some of the common modes of recirculation are shown on
Figure II-2. The mode most favorable to your particular operation should be
selected. Operating costs should also be considered in the selection of
recirculation modes and rates.
Sludge Removal
Trickling filter
sludge requires
thickening.
Withdraw
sludge before
it becomes
septic.
Increase
sludge
withdrawal
during periods
of heavy
sloughing.
Sludge removal
frequency is
important.
Sludge
characteristics
and production.
Underflow (secondary sludge) from the final sedimentation units is often
returned to the primary sedimentation units for resettling with the primary
sludge. This method is commonly practiced to thicken the secondary sludge
and reduce the volume of water pumped to the processing or sludge disposal
facilities. The sludge withdrawal from the final sedimentation tank may be
intermittent or continuous. Consideration to remove the sludge before it
becomes septic in the sedimentation tank should be made. Usually, visual
inspection of the sludge characteristics is sufficient to determine if the with-
drawal rate should be increased or decreased. Due to periodic sloughing of
biological growth from the filter media, the amount of solids settling in the
final sedimentation unit will vary. Sludge from a low-rate trickling filter is
relatively stable, and periodic removal at 3 to 24 hour intervals, depending
upon operational conditions, is usually sufficient. During warm summer
weather and periods of heavy sloughing, removal at 3 to 6 hour intervals may
be required. Sludge from a high-rate trickling filter has a higher oxygen de-
mand, and therefore, it must be removed from the sedimentation tank within
a short time, preferably on a continuous basis.
Occasionally, sludge is transferred directly to digestion units, and the fre-
quency and rate of pumping must be set to maintain reasonable sludge
concentrations without permitting septic conditions to develop. Rising and
floating sludge would indicate that the frequency of pumping should be
increased, or that the continuous pumping rate should be increased.
Trickling filter sludge is usually a dark brown, humus material with little or no
odor when aerobic. Generally, trickling filters treating domestic wastewater
produce 500 to 750 pounds of settleable solids per million gallons of waste-
water treated. The sludge produced by a low-rate filter usually has a total dry^
solids content of one to seven percent after settling in the sedimentation
tank. The sludge produced by a high-rate filter is lighter and fluffier with a
total dry solids content ranging from one-half to three percent.
11-12
-------
Simple method
to calculate
sludge
pumping
frequency.
TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
There are several methods of estimating the volume of sludge that must be
removed from a trickling filter process. The simplest method is based on a
settleable solids test (Imhoff Cone Test) of a composite sample* of the filter
effluent. The volume of sludge to be removed may be estimated as follows:
Example Calculation
A. Date Required
•1. Filter effluent settleable solids = 4ml/l
(Average of a series of grab samples)
2. Flow to clarifjer = 900,000 gpd
B. Determine the volume of sludge in gallons per day.
(a) Sludge vol., - (Settleable Sol., ml/l) (flow, gpd)
gpd " 1,000 ml/I
_ (4 ml/l) (900,000 gpd)
1,000 ml/l
OR
= 3600 gpd
(b) Sludge vol., = Sludge Volume, gpd_
gpd 1,440 min/day
3600 gpd
1,440 min/day
= 2.5 gpm
C. Determine pump control.
(a) Percent time on =
(Sludge Volume, gpd) (100%)
(Pumping Rate, gpm) (1,440 min/day)
(3600gpd)(100%)
(50 gpm) (1,440 min/day)
= 5%
OR
(b) Minutes per
hour
_ (Percent Time On) (60 minutes/hr)
100%
(5%) (60 minutes/hr)
100%
= 3 minutes/hr
'Composite sample - Refer to Section 4.02 for discussion.
11-13
-------
TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Alternate
method to
calculate
sludge
pumping rate.
Trickling filters
are designed
with
loading criteria
for operation.
A second method of estimating the volume of sludge is based on measurement
of the sedimentation unit influent and effluent suspended solids, the percent
total dry solids in the sludge, and the flow to the clarifier. The volume of
sludge to be removed may be estimated as follows:
Example Calculation
A. Data Required
1. Filter effluent suspended solids = 90 mg/l
(composite sample)
2. Sedimentation unit effluent = 30 mg/l
suspended solids
3. Flow to sedimentation unit = 0.9 mgd
4. Desired sludge concentration = 1.5%
(Some allowance should be made for
the irregularity in the filter sloughings)
B. Determine the suspended solids removed by the sedimentation
unit in mg/l.
SS removed, mg/l = SSjnf|v mg/l -sseffl., mg/l
= 90-30
= 60 mg/l
C. Determine the volume of sludge in gallons per day.
Sludge Vol., gpd = (Flow, mgd) (SS removed, mg/l)
Desired Sludge Cone., %
_ (0.9 mgd) (60 mg/l) (100%)
1.5%
= 3600 gpd
2.05 LOADING PARAMETERS
A trickling filter process is designed with loading parameters as criteria for
operation. Operation of the process within these parameters is essential if
design performance is to be achieved and discharge requirements met on a
continuous basis. The process control parameters for trickling filters are
generally based on organic loading and hydraulic loading. In considering the
trickling filter process, the filter or filters and the following sedimentation
unit should always be considered as one unit in both design and operationr
The process control parameter for sedimentation units is generally based on
the surface overflow rate. Exceeding the design parameters of any unit pro-
cess will eventually result in a poor quality effluent.
11-14
-------
TRICKLING FILTER PROCESS
SECTION II - PROCESS CONTROL
BOD loading in
recirculation
flow should be
ignored.
Organic Loading
The organic loading is commonly expressed as pounds of BOD applied per
day per 1,000 cubic feet, cubic yard, or acre-foot of media. Where recirculation
is practiced, an additional organic load is contained in the recirculated flow.
This added loading is included in the calculations by some operators and
omitted by others since it is included in the influent load. The Water Pollution
Control Federation Manual of Practice No. 6., Units of Expression for Waste-
Water Treatment, expresses BOD loading as Ib BOD/day/1,000 cu. ft. excluding
the additional BOD load contributed by the recirculated flow in the high-rate
filter plant. To eliminate confusion in making data comparisons with other
plants, it is suggested that the BOD of the recirculated flow be ignored. The
BOD loading is determined as follows:
How to
calculate BOD
loading for
trickling filters.
Example Calculation
A. Data Required
1. Primary effluent BOD = 132mg/l
2. Raw wastewater flow = 0.4 mgd
3. Diameter of filter = 50 ft.
4. Depth of filter media = 3 ft.
B. Determine pounds of BOD applied per day.
BOD Applied Ibs/day = (BOD, mg/l) (Flow, mgd) (8.34 Ibs/gal)
= (132 mg/l) (0.4 mgd) (8.34 Ibs/gal)
= 440
C. Determine the filter surface area in square feet.
Surface Area, sq. feet = (0.785) (Dia., ft.) (Dia., ft.)*
= (0.785) (50 ft.) (50 ft.)
= 1963.5
'Surface Area = x Dia. x Dia. = (0.785) (dia.) (dia.) or 0.785 (Dia)2
D. Determine the volume of filter media in 1000 cubic feet.
Vol. of Media, 1000 cu. ft. =
(Surface Area, sq. ft.) (Depth, ft.)
1000 units
(1962.5 sq.ft.) (3 ft.)
1000 units
= 5.88 or 5.9 thousand cubic feet
11-15
-------
TRICKLING FILTER PROCESS
SECTION II - PROCESS CONTROL
E. Determine the BOD loading.
r,«r^, .,. ,L. r,«r^-, , BCJD applied, Ibs/day
BOD Loading, Ibs BOD/day/ = — —-
1000 cu. ft Volume of Media, 1000 cu. ft.
440, Ibs/day
5.9 thousand cu. ft.
= 75
Hydraulic
loading can be
limited by filter
distribution and
underdrain
systems.
How to
calculate
hydraulic
loading for
trickling filters.
Hydraulic Loading
The WPCF Manual of Practice No. 6 expresses hydraulic loading as gallons
waste flow (including recirculation) per day per square foot of surface area
(gpd/sq. ft.). Often, the hydraulic loading of a trickling filter is limited by the
hydraulic capacity of either the distribution or underdrain systems. The
hydraulic loading on the super-rate trickling filters (synthetic media-filled
towers) is commonly expressed as gallons per minute per square foot of
surface area (gpm/sq. ft.). The hydraulic loading may be determined as follows:
Example Calculation
A. Data Required
1. Raw wastewater flow = 0.4 mgd = 400,000 gpd
2. Recirculation flow = 0.2 mgd = 200,000 gpd
3. Diameter of filter = 50ft.
B. Determine the total flow applied to the filter in gallons per day.
Total Flow, gpd = Raw Wastewater Flow, gpd + Recirc. Flow, gpd
= 400,000 + 200,000
= 600,000
C. Determine the surface area of the filter in square feet.
Surface Area, sq. ft. = (0.785) (Dia., ft.) (Dia., ft.)*
= (0.785) (50) (50)
= 1963.5
11-16
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TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
D. Determine the hydraulic loading.
Hydraulic Loading, = Total Flow, gpd
gpd/sq. ft. Surface Area, sq, ft.
Hydraulic Loading,
600,000
1963.5
= 306
"Surface Area =^li(Dia.)(Dia.) = 0.785 (Dia.)(Dia.) or 0.785 (Dia,)2
4
Surface Overflow Rate
Importance of
hydraulic
loading on
sedimentation
units.
The surface overflow rate is the parameter commonly used to measure the
hydraulic loading on the sedimentation units. The surface overflow rate is
expressed as gallons waste flow per day per square foot of surface area
(gpd/sq. ft.). The surface overflow rate is directly related to the sedimentation
unit's ability to effectively remove settleable solids. Normally, if the surface
overflow rate is within the design range, it can be assumed that the detention
time and weir overflow rates are also within the design range. However, con-
sideration should be given to flow distribution which can cause short circuit-
ing of flow through the unit. Sedimentation units which follow low and high
rate trickling filters are commonly designed with maximum surface overflow
rates of 1000 gpd/sq. ft. and 800 gpd/sq. ft., respectively.
The surface overlow rate is determined as shown below:
How to
calculate
surface
overflow rate.
Example Calculation
A. D.ata Required
1. Peak hour influent wastewater flow = 600,000 gpd
2. Recirculated flow from sedimentation = 300,000 gpd
unit effluent
3. Diameter of sedimentation unit = 40ft.
B. Determine the total flow in gallons per day.
Total Flow, gpd = Influent Wastewater Flow, gpd + Recirculated
Flow, gpd
= 600,000 4- 300,000
= 900,000
1-17
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TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
C. Determine the surface area of the sedimentation unit in square feet.
Surface Area, sq.ft. = (0.785) (Dia., ft.)(Dia., ft.)*
= (0.785) (40) (40)
= 1256
D. Determine the surface overflow rate.
Flow, gpd
Surface Overflow Rate, =—
gpd/sq.ft. Surface Area, sq. ft.
900,000
•Surface Area =
1256
= 717
(Dia.) (Dia.) = (0.785) (Dia.) (Dia.) or 0.785 (Dia.)2
Common
problems with
trickling filters.
Good
operational
practices
minimize
problems.
2.06 OPERATIONAL PROBLEMS
There are five problems which commonly occur in trickling filter operations:
1) Filterflies
2) Odors
3) Ponding
4) High effluent suspended solids
5) Freezing
Each of these problems is disucssed in the following sections. Although the
trickling filter process does not require complicated or stringent process
control measures, it does require daily attention and maintenance for an
efficient and trouble-free operation. Some of these practices are listed below:
1) Keep the distributor orifices or spray nozzles free of obstructions.
2) Keep excessive growths hosed off the distributor splash plates and
the side walls above the media.
3) Keep the distributor arm system in good repair and leveled to ensure
the wastewater is applied uniformly over the filter bed.
4) Keep all obstructive materials removed from the filter surface, the
underdrain conduits and effluent channel.
5) Avoid expected problems by implementing preventive measures on a
routine basis.
6) Do not allow problems to become serious before correcting.
11-18
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TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Filter Flies
Beneficial
when in small
numbers.
Filter flies may
become a
serious
nuisance during
summer months.
The filter fly is a gnat-sized, moth-like fly that often breeds in the slimes of a
trickling filter. Its dark brown, worm-like larvae live in the trickling filter slime
performing a useful function by consuming the dead and decaying biological
slime growths. At the completion of metamorphosis, the larvae emerge from
the filter as adult flies and they create a considerable nuisance when present.
In addition to being unsanitary, the flies get into the eyes, nose, and ears, and
cause a-great deal of physical discomfort and irritation. During the cooler part
of the year, filter flies usually exist in numbers which do not present problems.
But in the warmer summer months, due to their shorter life cycle (7 days or
possibly less), the flies emerge from infested filter beds in vast numbers,
presenting a serious nuisance. Although the flies are capable of flying only a
short distance, they may be carried by the wind over considerable distances
to residential areas.
Implement
preventive
measures.
Prevent
completion of
the flies life
cycle.
Corrective
measures for fly
problems.
Proper
maintenance Is
Important.
Possible
solution when
the
reclrculatlon
rate can not be
reduced.
Can the
hydraulic
loading be
Increased by
reclrculatlon?
Possible
control
measure if filter
design permits
flooding.
For these reasons, preventive measures should be implemented as a routine
program to avoid the development of a nuisance problem and subsequent
complaints. Unfortunately, the filter fly and its larvae are not easily destroyed.
The most effective means of control is to prevent the completion of its life
cycle.
Some probable causes for filter fly problems include the following:
1. Poor distribution of influent wastewater, espeically along the filter
wall.
2. Hydraulic loading rates are insufficient to keep fly eggs and larvae
washed from the filter media.
3. Preventive measures program not being implemented on a routine basis.
One or more of the following corrective measures may be needed to control
fly problems in any given situation. The measures best suited to your particular
operation with the least adverse effect on the quality of the plant's final
effluent should be selected. The measures are listed in the suggested order
of consideration.
• The distribution system should be properly maintained so that waste-
water is uniformly applied over the media. Keep distributor orifices or
spray nozzles free of all obstructions. Keep the biological growths
adhering to the splash plates hosed off. If distributor arms are not
equipped with spray nozzles at the outer end to keep the media adjacent
to the wall and the inside surface of the wall wet, either tap the ends of
the distributor arm or open dump gates slightly for a spray effect.
• Slow down the distributor arm rotation by reversing some of the spray
nozzle directions. This will act to brake the rotating arm.
• Increase the recirculation rate to help wash fly larvae from the filter
bed. Hydraulic loadings in excess of 200 gpd/sq. ft. will often minimize
filter fly problems.
• On a routine weekly basis, flood the filter for several hours to prevent
completion of the filter fly life cycle. When this measure is used, con-
sideration should be given to the resultant hydraulic loading placed on
the filters remaining in service. Care should be exercised in releasing
the wastewater from the flooded filter such that the hydraulic design
capacity of the secondary sedimentation units is not exceeded, result-
ing in the washout of settleable solids.
11-19
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TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Unwise use of
chlorine may
lower effluent
quality.
First check
with State and
local regulatory
agencies.
On a routine weekly basis, preferably during a period of low flow, dose
the filter influent for several hours (no more than 8 hours at a time) with
sufficient chlorine to maintain a 1 to 2 mg/l residual at the distributor
outlet. The application of chorine will cause sloughing of the upper
layer of media slime where fly larvae and pupae reside. Caution should
be exercised during prolonged chlorine application at higher residuals.
This could cause too much of the slime layer to slough off and reduce
filter performance.
If not prohibited by State of local regulatory agencies, spray filter walls
and other areas where the flies rest with a residual-type insecticide.
Do not spray insecticide onto the filter media, as the insecticide may
harm the slime growth and contaminate the receiving waters. Insecticide
treatment should be repeated at intervals of two or four weeks. Alternate
the type of insecticide used to avoid developing a resistant strain of
the fly.
Odors
Causes for
odors.
Indication that
other
operational
problems may
exist.
Foul odors coming from a filter are generally due to anaerobic conditions
occurring within the slime growth of the filter. When the available dissolved
oxygen is consumed by the microorganisms, conditions which cause an-
aerobic decomposition will occur. It is normal for the innermost slime layer
next to the media to be anaerobic, because of inhibited diffusion of oxygen
through the outer slime layer. However, the outer slime layer must be com-
pletely aerobic; and therefore, a continuous and adequate supply of oxygen
(dissolved) is necessary for an efficiently operating filter. Foul odors do not
commonly occur when aerobic conditions are maintained in the filter. When
odors do occur, it is a good indication of inadequate operational and process
control procedures.
Improve primary
treatment.
Some probable causes of odor problems include the following:
1. Excessive organic loading due to the following: an unusually high
BOD in the efluent wastewater; an overloaded or poorly operated primary
sedimentation unit; overloaded or poorly operated sludge processing
operations resulting in an in-plant recycle flow with a high BOD loading;
or inadequate dilution by recirculation.
2. Poor ventilation due to the following: a submerged underdrain system;
clogged vent pipes (vertical pipes from underdrain around inner
circumference of periphery walls); obstructed underdrain channels;
natural ventilation is poor; or void spaces between media is filled with
excessive gray to black biological growths. ,v
3. Filter is operating at or over its hydraulic and/or organic loading
capacity.
4. Poor housekeeping practices. Accumulation of debris on meida surface.
The following measures should be implemented to resolve odor problems:
• Evaluate the operation of the primary sedimentation tanks for possile-
means of improving efficiency. An influent baffle may be needed to
prevent short-circuiting, or an improvement in the scum baffle may be
necessary to prevent the loss of grease particles from the tank.
II-20
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TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Maintain good
public relations.
Maintain
aerobic
conditions in
upstream
treatment units.
Good
housekeeping.
Recirculation
rate may need
increasing.
Chlorlnatlon
lessens the
problem.
Utilize one of the commercially available masking agents to make
odors less noticeable, thereby avoiding complaints. This should not
be considered as a solution to the operational problem, but only as a
means to avoid a public relations problem while the source of the
problem is located and appropriate corrections are made.
Maintain aerobic conditions in the wastewater collection system, and
in primary and secondary sedimentation units (prevent septicity). Re-
circulation of filter effluent, or final effluent, through the primary
sedimentation units during low night flows would be helpful in reducing
septicity. The same principle can be utilized by recirculating effluent
through the secondary sedimentation units.
Remove all debris (leaves, sticks, paper, etc.) from the surface of the
filter media.
Check to see that vent pipes are clear.
Remove all debris from filter effluent channel and periodically flush
obstructive materials from the underdrain system.
Increase recirculation to the filter to dilute the strength of the applied
wastewater, to flush out the excess biological growths, and to improve
oxygen transfer. The hydraulic loading applied to the filter should not
be so great that the underdrain system is flowing more than one-half full.
On a daily basis, dose the filter influent for several hours, preferably
during a period of low flow, with sufficient chlorine to maintain a 1 to
2 mg/l residual at the distributor outlet. Prolonged chlorine application
at higher residuals may reduce filter performance. Chlorination only
lessens the problem until a permanent solution such as plant expan-
sion, improved operation, or a larger recirculation pump can be provided.
Ponding
Conditions In'
(liter which can
and will lead to
ponding.
Ponding also known as pooling, is the formation of pools of wastewater on
the filter surface due to clogging of the void space between the media. The
voids may be clogged by excessive biological growths, accumulated debris,
non-uniformly sized media, or disintegrated media fragments. Clogging of the
media voids will inhibit air and wastewater passage, thereby reducing filter
performance and resulting in anaerobic conditions which are responsible for
foul odors. The potential for ponding can be minimized by use of a sufficient
hydraulic loading (relative to the organic loading) to keep excess biological
growths flushed from the media voids on a routine basis, and by removing any
debris which may accumulate on the media surface.
Some probable causes of ponding problems include the following:
1. Application of a high-strength waste with inadequate dilution by
recirculation.
2. Inadequate hydraulic loading in relation to the organic loading to keep
media voids flushed.
3. Non-uniformly sized media where smaller particles fill the void space
between larger particles. This inhibits air ventilation and passage of
wastewater.
4. Disintegrating media resulting in clogging of the void space.
1-21
-------
TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Corrective
measures for
filter ponding.
Practice good
housekeeping.
Improve
condition and
prevent
recurrence.
Cure for minor
ponding.
Cure for serious
ponding when
loading does
not permit
removal of a
filter from
service.
When filter
design permits
flooding and
extra filters are
available.
Flooding not
possible.
Defective media.
5. Uniformly-sized media which is too small to provide adequate void
space for air and wastewater passage at current loadings.
6. An accumulation of moss, snails, leaves, sticks, or other such materials
which clog filter voids.
One or more of the following corrective measures may be needed to control
ponding depending on the cause and seriousness of the problem. The meas-
ures are listed in the suggested order of consideration. The measures best
suited to your particular operation with the least adverse effect on the quality
of the plant's final effluent should be selected.
• Remove all leaves, paper, sticks, and other debris accumulating on the
media surface.
• Increase recirculation to reduce influent strength and improve the
hydraulic flushing of media voids.
• Agitate and flush the affected portion of the filter surface with a high
pressure stream of water.
• Loosen the surface layer of rock in the affected area by raking or forking.
• Dose the filter influent for 2 to 4 hours (preferably during low flow) with
sufficient chlorine to maintain a 1 to 2 mg/l residual at the distributor
outlet. Residuals of 20 to 50 mg/l may be needed when ponding is
serious and it is necessary to unload the majority of the biological
growth. Significant unloading of the slime layer will reduce the treat-
ment efficiency until a biological balance is re-established. If the treat-
ment facility lacks provisions for application of chlorine to the filter
influent flow, chlorinated lime (34%) or HTH powder (70%) may be
applied to the affected area at a dosage of 8 to 10 pounds of chlorine
per 1,000 square feet of filter surface.
• If the construction of the filter permits, flood the filter, keeping the
media submerged for about 24 hours. When utilizing this method, con-
sideration should-be given to the resultant loading placed on the filter
units remaining in service. To prevent surcharging of the secondary
sedimentation units, release the wastewater from the flooded filter
slowly, preferably during the low night flow period.
• Remove the filter from service allowing the slime growths to dry out.
When placed back into service, the loosened growths drop from the
media and wash out with the filter effluent. The length of drying required
depends on the weather and the thickness of the growths. A few hours
of drying may be adequate to slough the excess growths, while for more
seriously clogged media, one or more days of drying time may be
required. Portions of a filter media may be dried out by closing off
individual distributor arm orifices.
• In the event each of the above measures fail to relieve the problem,
remove some of the media for cleaning and inspection. If the media is
found to be in satisfactory condition and uniformly-sized (3 to 5 inches)
it can be carefully placed back into the filter. If the media is defective
or too small, it must be replaced.
CAUTION: All filter underdrain systems can be easily damaged by the.
weight of heavy equipment or careless placement of media.
II-22
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TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
High Effluent Suspended Solids
Removal of
settleable
sloughings is
the k«y to good
performance.
Causes for high
effluent
suspended
solids.
Things to look
for when
experiencing
high effluent
solids.
Check
hydraulic
loading.
Check surface
overflow rate.
Perform
temperature
profile.
The efficiency of the trickling filter process is dependent on the removal of
filter sloughings in the final sedimentation units. A high suspended solids
concentration in the sedimentation unit effluent is usually indicative that a
problem exists in this portion of the trickling filter process.
Some probable causes for high effluent suspended solids include the following:
1. The unit is hydraulically overloaded due to excessive flow rates in
conjunction with recirculated flow rates, or the flow is unevenly dis-
tributed between multiple units.
2. Sludge collection equipment needs adjustment or repair.
3. Baffles or skirts need repair.
4. Effluent weirs not at an equal elevation.
5. Temperature currents.
6. Rate of sludge withdrawal or frequency is inadequate.
7. Heavy sloughing caused by temperature and biological activity. Shock
loadings due to toxic wastes or organic and/or hydraulic overloads.
The following measures should be implemented to determine as well as
resolve the problem.
• Check for broken welds, bolts, supports, and/or holes in the baffles
and make any needed repairs.
• Check that effluent weirs are set at an equal elevation and make any
needed adjustments.
• Check that the sludge collection equipment is operating properly. The
condition of the sludge scrapers or flights should be checked and the
clearance between the floor and scraper adjusted if needed.
• The operator should check the hydraulic loading on each clarifier (see
Surface Overflow Rate) by either measuring the flow to each clarifier or
by estimating the flow balance between multiple units as indicated by
the depth of flow over the weirs in each of the clarifiers. Overloading
can result from excessive flow or unevenly distributed flow between
multiple units.
• Compare the calculated surface overflow rate with the design rate. If
the current rate exceeds the design rate, the unit is overloaded and
efficient operation can be restored if additional sedimentation facilities
are provided. The installation of baffles in the existing unit may im-
prove settling.
• A temperature profile of the sedimentation unit will identify the presence
of any temperature currents. The temperature probe on a dissolved
oxygen meter is an excellent tool for this procedure. To make the
survey, the temperature profile is measured and recorded at the head,
one quarter, one half, three quarters and end of a rectangular or square
unit, or at the quarter points across a circular unit. At each point, the
temperature is measured at the surface and the quarter points down to
the bottom of the tank. Be careful that the temperature probe and wires
do not get entangled in the sludge collection equipment. If the deeper
temperatures are consistently cooler by 1 to 2° or more, temperature
currents are present. The settling will be improved if baffles are installed
to break up the currents and stop the turbulence.
II-23
-------
TRICKLING FILTER PROCESS
SECTION II - PROCESS CONTROL
Check the
sludge removal
rate.
Chemical
addition may be
required
temporarily.
Check for
industrial
discharges
which hinder
process
performance.
Check for shock
hydraulic
loadings.
If the sludge floats to the sedimentation unit surface in clumps with
numerous small bubbles attached, the problem is most likely related
to septicity or denitrif ication. This problem is best resolved by increasing
the sludge removal rate to draw the solids out of the unit more rapidly.
Polymer addition to the sedimentation unit influent flow may improve
the capture of suspended solids. The type of polymer and initial dosage
should be determined in the lab by jar tests. It has been reported that a
1 to 2 mg/l dosage of cationic polymer has been effective in some
circumstances. The polymer dosage should be periodically adjusted on
the basis of the most effective solids capture with the least amount of
chemical addition. The rate of sludge removal should be increased
during periods of chemical addition and heavy sloughing.
Conditions such as abnormal pH's, temperatures, or toxic chemicals
can be best controlled by enforcing strict industrial waste discharge
ordinances. Increasing the recirculation rate will help to buffer the
effect of shock loads. However, harmful industrial dumps should be
stopped or neutralized at their source whenever possible. If possible,
a toxic shock load (usually characterized by an abnormally low or high
pH) should be diverted to a holding basin and returned to the plant
influent at a very low rate to minimize its effect on the biological pro-
cesses in the treatment plant (digesters as well as trickling filter
processes).
Frequent hydraulic shock loads may justify the addition of flow equal-
ization basins. These basins should be aerated and mixed to prevent
septicity and settling of the solids. In some cases, hydraulic shock
loads can be buffered by using the influent wet well and adjoining in-
fluent pipe for equalization and controlling the influent wastewater
pumps to level out the peak flows. The practice of holding wastewater
in the influent sewer for more than a brief period must be avoided.
Freezing
Freezing
generally
limited to
climatic
conditions.
Conditions
which create
freezing
problems.
Things to help
reduce freezing
problems.
This problem is limited to those areas of the country that experience freezing
weather conditions. Wastewater that is exposed as a thin film or is not in
motion is very susceptible to temperature loss and subsequent freezing. To
some extent, ice formation can be minimized by appropriate operational
procedures.
Causes of freezing problems include the following:
1. Loss of temperature in the applied wastewater due to recircuiation
(the filter acts like a cooling tower).
2. Strong prevailing winds which increase heat loss.
3. Wastewater standing in the distribution system which may freeze
when intermittent dosing is practiced.
4. A thin film of spray which freezes more readily than a coarse stream
of spray.
The potential for ice formation can be reduced by the following measures:
• Decrease recirculation as much as possible to reduce cooling effects
upon the wastewater.
II-24
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TRICKLING FILTER PROCESS
SECTION II-PROCESS CONTROL
Operate two-stage filters in parallel to reduce cooling effects by
making fewer passes through the filters.
Adjust orifices and splash plates for a coarser spray effect.
Construct a windbreak to protect the filter from prevailing winds and
reduce heat losses.
Where intermittent dosing is practical, open the bleeder valve in the
lower end of the distribution main slightly. This will drain the system
between doses.
Partially open the dump gates at the outer end of the distributor arms
to provide a stream rather than a spray along the retaining wall.
Cover open pump sumps and dosing tanks to reduce heat losses.
Break up and remove ice formations which may obstruct operation.
REFERENCES
Eckenfeder, W.W., Biological Waste Treatment, Pergamon Press, New York, 1961.
Hawks, H.A,, The Ecology of Waste Water Treatment, Pergamon Press, Oxford, 1963.
Kerri, Kenneth D., et al., A Field Study Training Program, Operation of Wastewater
Treatment Plants, (Chapter 6), Sacramento state College Department of Civil
Engineering.
Lohmeyer, George T., Trickling Filters and Their Operation, Water & Sewage Works,
September 1958.
McKinney, Ross E., Microbiology for Sanitary Engineers, McGraw-Hill Book Company
Inc., 1962.
National Research Council, Sewage Treatment at Military Installations, Sewage Works
Journal, 18, No. 5,1946.
The South Carolina Water and Sewage Works Association, Correspondence Course
Manual for Sewage Plant Operators, Class C, (Chapter 16) 1962.
The Texas Water Utilities Association, Manual of Wastewater Operations, (Chapter
12), 1971.
Water Pollution Control Federation, Operation of Wastewater Treatment Plants,
Manual of Practice No. 11.
Water Pollution Control Federation, Sewage Treatment Plant Design, Manual of
Practice No. 8,1959.
Water Pollution Control Federation, Units of Expression for Wastewater Treatment,
Manual of Practice No. 6,1976.
li-25
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Why popular.
Trickling filter
process.
3.01 INTRODUCTION
The trickling filter process was first used in the United States in 1908, and has
remained a popular form of wastewater treatment since that time. Inexpensive
aeration and process stability are the primary reasons that the trickling filter
has remained a popular treatment process. As energy costs increase, the
usage of trickling filters as roughing filters is likely to increase.
The trickling filter process consists of a trickling filter and a sedimentation
unit. The filter structure is filled with media which provides surface area for
the microorganisms to attach themselves. The wastewater is applied at the
surface of the trickling filter, and it trickles or splashes over and through the
voids of the media where the microorganisms are attached. After the waste-
water passes through the filter, it is collected in an underdrain system below
the media. Solids which reamin in the wastewater are then settled and removed
from the sedimentation unit. A portion of the filter effluent may be recirculated
to the head of the filter as shown on Figure 111-1.
RECIRCULATION EFFLUENT
DIRECT RECIRCULATION
SECONDARY
CLARIFIER
TRICKLING
FILTER
'1
I
I
j EFFLUENT
BIOLOGICAL
SLUDGE
TYPICAL TRICKLING FILTER PROCESS
FIGURE 111-1
Total amount of
microorganisms
Is called the
blomass.
Surface
microorganisms
are aerobic-Sub-
surface
anaerobic.
Capable of
withstanding
shock loads.
The total amount of microorganisms attached to the trickling filter media is
called the biomass. The biomass includes algae, bacteria, fungi, protozoa,
and higher life forms of organisms such as worms, snails, and insect larvae.
Facultative bacteria are the microorganisms responsible for the majority of
the treatment which occurs in the trickling filter. The surface microorganisms
are aerobic while the microorganisms immediately attached to the media sur-
face or where dissolved oxygen is absent are anaerobic.
Because they contain vast numbers and varieties of microorganisms, trickling
filters are capable of adapting to changes in environmental conditions and
loadings. For this reason shock organic loads have less effect on this process
than on some modes of the activated sludge process.
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Definitions
Operation of the trickling filter process requires a basic understanding of
some key words commonly used by operators. The following provides a
framework for understanding what a trickling filter consists of and what makes
it function as a treatment unit.
• MEDIA is placed in a structure to provide a surface for the micro-
organisms to attach themselves. The media frequently consists of
rocks, plastic sheeting and redwood laths.
• DISTRIBUTOR ARM is the most common method of evenly applying
the wastewater over the media in the structure. The arm is generally
propelled by the momentum or force of wastewater being sprayed
from orifices located on the arm.
• BIOMASS refers to the total mass of microorganisms attached to the
media. In concept, the biomass is similar to the Solids Inventory used
in activated sludge terminology to describe the total amount of micro-
organisms in an activated sludge system.
• RECIRCULATION refers to the pumping of the filter effluent back to
the head end of the trickling filter. Recirculation evens out variations
in the hydraulic loading.
• SLOUGHING is the process by which the excess growth of the micro-
organisms falls off of the filter media. When the thickness of the
biological growth is too great, the excess microorganisms are washed
off of the media and discharged with the filter effluent.
• FILTER UNDERDRAIN consists of a sloped floor under the filter media
which allows the wastewater and sloughings to collect in a channel.
From the channel the wastewater and sloughings (filter effluent) are
transferred to the sedimentation unit for settling and removal.
• HYDRAULIC LOADING refers to the amount of wastewater applied to
the surface of the trickling filter media. The hydraulic loading is calcu-
lated by dividing the average daily influent flow by the surface area of
the filter media. The loading parameter is commonly expressed as
gallons per day per square foot of surface area (gpd/sq. ft.).
• ORGANIC LOADING refers to the amount of BOD or COD applied per
unit volume of filter media per day. The organic loading is commonly
expressed as pounds of BOD applied per day per 1000 cu. ft. (Ib BOD/
day/1000 cu. ft.).
• LOW RATE TRICKLING FILTERS are operated with an organic loading
of 5 to 25 Ib BOD applied/day/1000 cu. ft. The low rate filter will fre-
quently produce a nitrified effluent, and low rate filters are becoming
slightly more popular because of this capability.
• HIGH RATE TRICKLING FILTERS are operated with organic loadings
of 25 to 100 Ib BOD applied/day/1000 cu. ft.
• ROUGHING FILTERS are operated at loading rates above 100 Ib BOD
applied/day/1000 cu. ft. A roughing filter is used to reduce the amount
of BOD and/or COD in the wastewater.
• BIOLOGICAL TOWERS refer to the type of trickling filters that are
synthetic media-filled, tower-like structures. These towers are some-
times referred to as oxidation or roughing towers. Because of their
high hydraulic loading, they are often classified as Super-Rate trickling
filters.
I-2
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
STAGING refers to operating trickling filters in series. Staging is
practiced to produce an effluent with a lower BOD and/or COD con-
centration.
Waste Is
absorbed by
slime growth.
Slime growth
sloughs off
media.
Sloughlngs are
captured In the
clarlfler.
Principle
components of
process.
3.02 PROCESS DESCRIPTION
The trickling filter process consists of spraying the wastewater over a bed of
media, such as crushed rock, cynders, slate, redwood laths, or molded plastic
materials to form a biological slime layer. This slime, or zoogleal film, is com-
posed primarily of bacteria, protozoa, and fungi, and at times includes worms,
fly larvae, rotifiers, and snails. Usually sunlight promotes an algal growth on
the bed's upper surface. As the wastewater trickles downward through the
voids of the media, organic matter and dissolved oxygen are absorbed into
the film and at the same time, the metabolic end products such as carbon
dioxide, water, nitrates and sulfates are released.
When the slime layer loses its ability to continue clinging to the media, usually
due to either the excess thickness of the slime layer and/or the scouring effect
of the wastewater flow, portions of the slime layer slough off into the waste
flow. The waste flow containing the metabolic end products and sloughings
flows into an underdrain system which supports the media and permits air
circulation. The underdrain system has a sloping bottom conveying the waste
flow into a main effluent channel.
In a single stage system, the collected trickling filter effluent is conveyed to
a sedimentation unit for the removal of the settleable sloughings. In a multi-
stage system, final sedimentation would follow the last trickling filter stage.
In some cases the system may have intermediate sedimentation units between
the trickling filter stages.
The principal components of the trickling filter process consist of the following:
1. The distribution system through which the wastewater is applied to
the filter media.
2. The filter media which provides surface area for the microorganisms
to grow.
3. The underdrain system which supports the media and provides drainage
of the waste flow to a collection channel while permitting air circulation.
A final sedimentation tank for the removal of the filter sloughings.
4.
A cross-section of a typical circular trickling filter is shown on Figure
with the principal components identified.
I-2
Rotary Distributor
The rotary distributor consists of two or more horizontal arms that are mounted
what makes the on a turntable assembly anchored to a center column, as shown on Figure
distribution arm MI-3. The wastewater is uniformly distributed over the media by orifices
rotate? located in the side of the distributor arms. Usually, the reaction force of the
wastewater spray from the orifices provides the force needed to rotate the
distributor assembly. In some cases, the distributor assembly is motor driven.
I-3
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
TYPICAL TRICKLING FILTER IN CROSS SECTION
FIGURE HI-2
1-4
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Maintenance
provisions.
Distributor arm
rotation speed.
The turntable rests upon and revolves on a ball bearing assembly which
operates in an oil bath with a mechanical-type seal between the rotating
turntable and the stationary base to eliminate oil leakage and contact with
the wastewater.
The distributor arms are commonly braced by horizontal tie rods. To maintain
the distributor arms in the horizontal position and permit seasonal adjustment,
the arms are supported vertically by adjustable guy rods from a center mast.
A dump gate is provided at the outer end of each arm for flushing the
obstructive materials from inside the arm. Often, an orifice is provided in the
dump gate to spray the edge of the media to discourage fly breeding. Usually,
a drain plug is provided in the center column to facilitate shutdown procedures
and prevent damage due to freezing.
The distributor arms are sized to prevent velocities in excess of 4 feet per
second (fps) at maximum flow. Generally, the rotation speed of the reaction
driven unit will vary with the flow rate in the range of 0.1 to 2.0 rpm. The four-
arm distributors are often equipped with weir boxes at the center column to
confine the flow to two arms at minimum flow rates. This feature is provided
to maintain proper reaction force for the rotation of the distributor arms from
a minimum flow to a maximum flow.
Figure III-3
Rotary Distributor
III-5
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Uncommon in
newer plants.
Found mostly
in older plants.
Uniform spray
application.
Deep bed filter.
Fixed Nozzle Distributors
In the rock-filled filters, fixed-nozzle distribution systems are uncommon and
are usually found at older facilities. The distribution system consists of
stationary pipes placed in the filter bed with inverted nozzles located at
strategic points fora relatively uniform coverage of spraying wastewater over
the media. Special nozzles constructed with a deflector for a flat spray pattern
are usually used in these filters. Dosing tanks are utilized to provide an inter-
mittent wastewater application. The dosing tanks are usually designed to
provide a minimum rest period of 30 sec. at maximum flow. Figure 111-4 illu-
strates the fixed nozzles, a dosing tank and distribution system.
The dosing tanks also provide a varying head so that the spray falls first at a
maximum distance from the nozzle and then at a decreasing distance as the
head drops. This technique provides a relatively uniform application.
With the introduction of synthetic media, construction of deep-bed, fixed-
nozzle filters provide greater contact time and higher wetting rates of waste-
water applied. The nozzles are strategically located at points along pipes
spraying downward over the bed.
Dosing
Dosing by
siphon, pumps
or gravity.
The hydraulic head required for operation of the distribution system may be
provided by dosing tanks, pumps, or by gravity discharge from the preceding
treatment unit.
Dosing tanks are usually equipped with an automatic siphon controlling the
maximum and minimum head conditions. They also provide an intermittent
dosing frequency. A typical dosing siphon is shown in Figure 111-4.
Media
Media does not
filter
wastewater but
must be
durable,
Insoluble and
uniformly-sized.
The media in a trickling filter does not provide a straining or filtering action as
implied by the name, but provides a surface area for the growth of a slime
film which is responsible for the removal of organic matter. The media may be
crushed rock, slag, coal, bricks, redwood blocks or laths, molded plastic, or
any durable, insoluble and uniformly-sized material. Uniformity in media size
is required to provide adequate void spaces for air circulation and to avoid
flow restriction resulting in a condition known as ponding. The size range of
rock media is usually 3 to 5 inches in diameter depending upon the hydraulic
loading that the filter has been designed for. High-rate filters use a larger
media than the low-rate filters. The durability, cost, and availability are some
of the factors that determine the type of media used. The depth of media in
rock-filled filters range from 3 to 8 feet with the majority of the biological
activity occurring in the upper 3 feet.
In recent years, several forms of manufactured media have been introduced.*
The manufactured media provides a greater surface area per a specific volume
upon which the zoolgeal film may grow while providing ample void space for
the free circulation of air. Additional advantages are: a uniform media for
better liquid distribution, light-weight material allowing construction of
111-6
-------
DEFLECTOR'
co
o
FIXED NOZZLE DISTRIBUTION SYSTEM
FIXED-NOZZLE DISTRIBUTJON SYSTEM
FIGURE 111-4
2 -D
m 3)
z o
H O
> m
i— en
U) Ui
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TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Advantages of
synthetic media.
Redwood lath
media.
Plastic media.
deeper beds; a greater BOD removal in a given volume of media; chemically
resistant; and an ability to handle high-strength wastes, such as those from
the food processing industry.
One type of manufactured media is redwood laths constructed into 4x4 foot
racks with spacer rails between layers and space between the laths allowing
for air circulation and water flow. The racks are stacked vertically with laths
and spacer rails. The rough-sawn texture of the redwood enhances the reten-
tion of slime growths. Figure 111-5 illustrates the redwood lath media.
The molded plastic media consists of modules of interlocking or bonded
corrugated sheets of plastic arranged somewhat like a honeycomb. The
modules of media are stacked so that they interlock and fit the filter configur-
ation. The corrugated surface of the plastic media enhances the retention of
the slime growths. Filters utilizing plastic media are often constructed 15 to
30 feet deep, thus the terms biological or oxidation tower has been introduced
to identify these installations. The synthetic media have a higher miminum
wetting rate (i.e., rate of flow per unit area) which will maintain a slime growth
throughout the media depth for optimum performance. This rate of flow may
range from 0.5 to as high as 2.0 gpm/sq. ft. (30 to 125 mgd/acre) depending
upon the type and configuration of the media. Design parameters for a specific
media are available from the manufacturer. A typical example of plastic media
is shown in Figure III-6.
REDWOOD LATH
REDWOOD LATH MEDIA
FIGURE III-5
I-8
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
PLASTIC MEDIA
FIGURE 111-6
Filter
underdrain
system must
provide
adequate
removal of
effluent and
provide
adequate air
circulation for
efficient
operation.
Underdrain
The underdrain system collects the filter effluent and transfers it to the
subsequent filtration stage or sedimentation tank. The system consists of
braces which support the filter media. The floor is sloped to collect the filter
effluent in a channel. The underdrain braces may be spaced redwood stringers
or slotted blocks constructed of concrete or more commonly, vitrified clay.
The underdrain also allows air to circulate through the media to provide the
oxygen transfer necessary to maintain aerobic conditions essential to efficient
filter operation. Ample underdrain capacity is necessary for rapidly discharg-
ing the effluent, and for air circulation and aeration. With natural ventilation,
the underdrain system and effluent channel are usually sized such that not
more than 50 percent of its cross-sectional area will be submerged at peak
hydraulic loading. Some trickling filters have vertical vent pipes around the
inner circumference of the structure wall to provide ample ventilation. Other
trickling filters have drainage ducts extended through the filter structure wall
to provide ventilation.
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Ventilation
Proper filter
ventilation is
a must.
Adequate ventilation is very important in achieving efficient filter operation.
Usually, with an adequately sized underdrain system, the difference in air and
wastewater temperature will provide adequate natural ventilation. However,
forced ventilation may be necessary in some of the following instances:
A. Filters with extremely deep beds, such as the biological towers.
B. Filters situated below grade.
C. Heavily loaded filters.
D. Filters covered by a dome for winter protection, or odor control.
Natural
ventilation
occurs by
differences in
temperature.
Natural Ventilation
Natural ventilation occurs by gravity due to the temperature differential
between the wastewater temperature and the outside air temperature.
The heating or cooling of the air will cause a density change resulting
in an air movement (heated air rises and cooled air falls). Therefore, the
direction of air flow will depend on the temperatures of the air and waste-
water. If the air temperature is warmer than the wastewater temperature,
the cooled-air flow will be downward through the filter. If the air tempera-
ture is lower than the wastewater temperature, the warmed-air flow will be
upward through the filter.
Forced Ventilation
Forced air
ventilation
should be in the
same direction
as natural air
current.
Usually, forced ventilation systems are designed to provide an air flow of
1 cfm/sq. ft. of filter area with air flow in either direction. The fans should
be operated to circulate the air in the same direction as the natural air
current. The ventilation units must be equipped with air-tight seals to avoid
corrosion problems. At some locations, the air is exhausted through
scrubbing towers for the removal of odorous and corrosive gases that are
formed in treating the wastes. This is true particularly from food-processing
industrial wastewater. During freezing or low air temperatures, it is a wise
practice to restrict the air flow to minimize freezing. The volume of air
required to sustain an aerobic filter operation is in the vicinity of 0.1 cfm/
sq. ft. of filter area. However, this rate will vary depending on the organic
loading and microorganism activity in the filter.
Final Sedimentation
Final
sedimentation
tank Is an
Important unit
In the trickling
filter process.
Design is
similar to
primary tanks.
The final sedimentation unit is an essential component since trickling filters
convert the organic matter to a settleable biomass which periodically or
continuously slough (drops) from the filter media. Therefore, the efficiency of
the trickling filter process is dependent upon the removal of this sloughed
biomass in the final sedimentation unit.
The design and construction of the sedimentation unit is similar to that of
primary sedimentation tanks. Determination and review of the clarifier loading
parameters is discussed in Section 2.05.
111-10
-------
TRICKLING FILTER PROCESS
TABLE Ill-l
FILTER CLASSIFICATIONS AND CHARACTERISTICS
PARAMETER
Type of Media
Media Depth
Organic'
Loading
Hydraulic
Loading
Recirculation
Ratio
Sloughings
Clanfier
Surface
Overflow Rate
BOD Removal
(Includes Sedimentation)
UNITS
ft.
m
i- w
(ft (ft
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Three general
classes of
trickling filters.
Common
ways to
express
trickling filter
loading.
3.03 TRICKLING FILTER CLASSIFICATION
Trickling filters are generally classified as low-rate, high-rate, or roughing-
rate. These classifications are related to the application rate of the hydraulic
and organic loadings on the filters. Loading parameters and other operational
characteristics for various filter classifications are given in Table 111-1. Trickling
filters may be further categorized as follows:
A. Depth
B. Number of Stages
C. Media Type
D. Recirculation Flow Scheme
E. Distribution-Fixed or Revolving
F. Dosing Frequency - Intermittent or Continuous
The organic load on a filter is usually expressed as the measurement by
weight of BOD applied per unit volume of filter media. The Water Pollution
Control Federation Manual of Practice No. 6, expresses organic loading as
pounds of BOD per day (in waste applied) per 1000 cubic feet of filter media
volume (Ib BOD/day/1000 cu. ft.).
Low-Rate Trickling Filters
How trickling
filters came
about.
RAW
SEWAGE
Trickling filters probably originated from the use of intermittent sand filters.
The wastewater was allowed to pass through two or more feet of coarse sand
where the microorganisms converted the organic matter into stable end
products. The need for greater removal per unit volume of filter media prompted
the innovation of contact filters which were basins filled with rock.
The famed Lawrence Experiment Station of the Massachusetts State Board
of Health is generally credited with setting up the first experimental trickling
filter. They demonstrated that a slow movement of wastewater through a
gravel media coated with a biological slime would produce an increase in
removing BOD from the wastewater. This concept was improved by an English-
man, Joseph Corbett, by the innovation of a spray distribution system and a
false bottom underdrain system.
EFFLUENT .
SLUDGE
SLUDGE
LOW-RATE TRICKLING FILTER
FIGURE III-7
1-12
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
How a low-rate
filter operates.
Biological
activity and
efficiency of a
low-rate filter.
Odors and flies
common to
process.
Concepts of a
high-rate filter
process.
How a high-rate
filter operates.
A high-rate filter
sloughs almost
continuously.
Low-rate filters are not usually equipped for recirculation except for the
return of the sedimentation unit underflow (sludge) to the plant headworks.
Some plants do practice recirculation, however, mostly during low flow periods.
Recirculation prevents the biological slime from drying out and thus improves
filter performance. Generally, a thick, heavy biological growth is developed
on the filter media with only a periodic sloughing. A seasonal change in
temperature or wastewater application rate will cause large amounts of the
biological growth to drop from the filter media. Such an unloading is especially
noticeable in the spring and fall. The filter sloughings are usually well oxidized
and settle readily.
Most of the biological activity in a low-rate filter occurs in the upper three
feet of the filter-bed allowing the autotrophic nitrifying bacteria to grow in the
lower portion of the filter. A properly loaded and operated low-rate trickling
filter process will consistently produce a high-quality, well-nitrified effluent
with a BOD and a suspended solids content in the range of 20 to 25 mg/l.
The low-rate filter is a highly reliable biological process with the ability to
consistently produce a high quality effluent even with fluctuating loading
rates. Proper control measures must be taken to minimize nuisances, such as
odors and filter fly breeding which are common to low-rate filters.
High-Rate Trickling Filters
By using in-plant recjrculation to dilute the influent organic strength and to
keep the media voids flushed, high-rate trickling filters allow greater BOD
loadings per volume of media. Recirculation also results in the return of active
microorganisms to seed the filter and aids in the prevention of odors and
flies. High-rate filters may be either single-stage or two-stage. The two-stage
design is capable of achieving the same removal rates as the low-rate filter.
However, nitrification does not generally occur unless the BOD loading to the
second stage is sufficiently reduced.
High-rate trickling filters are generally designed to receive a continuous flow
of wastewater. All high-rate filters are equipped for recirculation, although
some utilize this feature only during periods of low flow (See Figure 111-8 for
typical recirculation schemes for High-Rate Trickling Filters). The recirculation
system is commonly designed to provide a ratio of 0.5 to 2. Some systems,
however, utilize recirculation to maintain a constant hydraulic loading on the
filter. The depth of media in a high-rate filter ranges from three to eight feet,
with most filters in the three to five foot range. To avoid clogging and improve
ventilation, a larger size media is used. The media is usually relatively uniform
and in the range of three to five inches.
Due to the greater hydraulic loading, the excess biological growths are
flushed from the media on a nearly continuous basis. This sloughed material
is not fully oxidized, and has a high BOD content which can cause problems
in the sedimentation unit. Although not as dense as the low-rate filter, the
high-rate filter sloughiags still settle readily. A single-stage, high-rate filter
process usually has a BOD removal efficiency of 65 to 85 percent and seldom
exhibits any significant degree of nitrification. A two-stage, high-rate filter
process may attain BOD removal efficiencies of 75 to 90 percent with varying
degrees of nitrification which depends on the organic loading, filter depth,
and wastewater temperature.
1-13
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
ALTERNATE
RECIRCULATION
EFFLUENT.
SLUDGE
SLUDGE
HIGH-RATE TRICKLING FILTER
FIGURE 111-8
There are a number of patented modifications of recirculation schemes to the
high-rate trickling filter process. Some of these recirculation schemes are
shown on Figure 111-9. A brief discussion of these modifications follows:
Recirculation
to front of filter
during low flows.
Aero-Filter
The distinguishing feature of this process is the method of spraying the
wastewater over the media. Specially designed distributors are usually
utilized to provide a "raindrop" application on a maximum surface area at
one time. Recirculation (from the final sedimentation tank to the filter
influent) is practiced only during periods of low flow to maintain a mini-
mum hydraulic loading of 13 mgad. This procedure allows for an efficient
distributor operation. A deep media bed of 8 feet is recommended for the
Aero-Filter with a minimum depth of 6 feet. The second filter of a two-
stage system may have a minimum depth of 5 feet.
Recirculation
to front of
primary
sedimentation
tank.
Bio-Filter
The Bio-Filter has a relatively shallow media bed of 3 to 5 feet. The dis-
tinguishing feature of this process is the method of recirculation. Filter
effluent, or final sedimentation tank effluent, is returned to the head of
the primary sedimentation tank. This method of recirculation requires
larger sedimentation units than normal; however, better sedimentation
operation can be attained during periods of low flow.
1-14
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Reclrculatlon to
front of filter
continuously.
Accelo-Filter
The Accelo-Filter has a relatively deep bed depth, generally about 6 feet.
The distinguishing feature of this process is the method of recirculation.
The filter effluent is returned to the inlet of that filter or a preceding
filter where it mixes with the raw wastewater. A recirculation ratio of 2 to 1
is recommended. This method of recirculation reduces filter odors and fly
breeding, and increases the dissolved oxygen concentration. The recir-
culation also continuously reseeds the influent filter flow with active
microorganisms sloughed from the fiter without affecting the hydraulic
loading on the primary or final sedimentation tanks.
Roughing-Rate Trickling Filters
Roughing filters
are used to
buffer high
loadings on
subsequent
biological
processes.
See Figure 111-11
for towers.
Roughing
towers can
buffer the
activated
sludge
process.
Roughing
tower is also
capable of
producing
high-quality
effluent.
Roughing filters are usually designed as an intermediate stage of treatment,
and many times precede activated sludge treatment or second-stage filters.
Their primary function is to reduce high organic loadings on a subsequent
treatment process. Often, roughing filters are utilized at plants receiving
high-strength industrial wastes. A roughing filter may be either a rock-filled
filter or a synthetic media-filled tower receiving a very high organic loading.
Roughing filters have a very high BOD removal efficiency. Generally, a BOD
removal of 40 to 70 percent can be expected from a roughing filter process
that includes sedimentation.
Figure 111-10 shows a typical roughing filter installation.
With the introduction of various types of synthetic media, a new concept in
trickling filters has been developed. The synthetic media possesses a greater
surface area and void space than the conventional crushed rock media. This
allows a greater growth of biological slime per unit volume and permits
greater hydraulic loadings on the filter without obstructing air flow and
oxygen transfer. The synthetic media is lightweight, permitting the construc-
tion of deeper filter beds, resulting in smaller diameter units. The increased
depth Is required to provide sufficient contact time at the higher hydraulic
loadings. As the recommended bed depths for synthetic media are 15 to 30
feet, the resulting tower-like structures are sometimes referred to as biological
oxidation or roughing towers. The most important application of the biological
towers has been as roughing units to absorb toxic or unusually strong in-
dustrial wastes and high soluble BOD wastes from food processing industries.
At San Pablo, California, a roughing tower buffers the activated sludge process
by absorbing shock loads. Toxic wastes occasionally kill the organisms in the
upper portion of the roughing tower; however, the following activated sludge
process is protected and the roughing tower readily recovers.
The synthetic media filters are not limited to use as roughing filters; they are
capable of producing a high-quality effluent with BOD loadings in the high-
rate range. Biological towers utilizing plastic packing at 50 to 100 Ibs BOD/
1000 cu. ft./day are capable of achieving approximately the same performance
as rock-filled filters with an organic loading of 30 to 60 Ibs BOD/1000 cu. ft./day.
-15
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
RECIRCULATION
AERO-FILTER
RECIRCULATION
BIO-FILTER
RECIRCULATION
ACCELO-FILTER
TRICKLING FILTER VARIATIONS
FIGURE IE-9
1-16
-------
RECIRCULATION (OPTIONAL]
INTERMEDIATE
CLARIFIER
SLUDGE
SLUDGE
AERATION BASIN
RETURN ACTIVATED SLUDGE
SECONDARY
CLARIFIER
w
TYPICAL ROUGHING FILTER INSTALLATION
FIGURE 111-10
O
E O
Is
.
m 3)
z o
H O
> m
r- en
w to
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
Reclrculatlon is
used to
maintain
biological
growth
throughout
depth of media.
Figure 111-11 is a photograph showing the oxidation (biological) towers used at
Fairfield, California to buffer and reduce the organic loading of high-strength
brewery waste on the activated sludge process. The air scrubber towers
(center) are used to avoid odor nuisances. These oxidation towers are covered
and utilize forced ventilation for exhausting the foul air through the scrubbing
towers.
Recirculation is utilized to provide the hydraulic wetting rate that will main-
tain the growth of a biological slime throughout the depth of the media. This
minimum wetting rate depends on the type and shape of the media. The BOD
removal efficiency of a biological tower is greatly dependent on the main-
tenance of a healthy biological slime throughout the media depth, as well as
the wastewater characteristics, mode of recirculation, and type of synthetic
media. A decrease in BOD removal may accompany wetting rates that are
greatly above or below the minimum wetting rate. Modes of recirculation may
include one or a combination of the following:
1. Return of the tower effluent to the tower influent to seed the media
slime growth with suspended biological (sloughings) growths.
2. Return of the clarifier effluent to the tower infuent to dilute the strength
of the influent wastewater.
3. Return the sedimentation unit underflow to the tower influent for the
build-up of microorganisms to absorb shock loads, and to improve
efficiency. Sometimes, the underflow may be reaerated prior to re-
turning in the tower influent. This will provide additional buffering for
periods of shock loading.
Figure 111-11
Oxidation (Biological) Towers
111-18
-------
TRICKLING FILTER PROCESS
SECTION III-FUNDAMENTALS
REFERENCES
Eckenfelder, W.W., Biological Waste Treatment, Pergamon Press, New York, 1961.
Environmental Protection Agency, Process Design Manual for Upgrading Existing
Wastewater Treatment Plants, 1974.
Hammer, Mark J., Water and Waste-Water Technology, John Wiley & Sons, Inc.,
New York 1975.
Hawkes, H.A., The Ecology of Waste Water Treatment, Pergamon Press, Oxford, 1963.
Kerri Kenneth D., et al., A Field Study Training Program, Operation of Wastewater
Treatment Plants, (Chapter 6), Sacramento State College Department of Civil
Engineering.
Lohmeyer, George T., Trickling Filters and Their Operation, Water & Sewage Works,
October 1958.
McKinney, Ross E., Microbiology for Sanitary Engineers, McGraw-Hill Book Company
Inc., New York, 1962.
Metcalf & Eddy, Inc., Wastewater Engineering, McGraw-Hill, New York, 1972.
Minch, V.A., Egan, John T., and Sandlin, McDewain, Design and Operation of Plastic
Media Filters, Journal WPCF, Vol. 34, No. 5, May 1962.
Public Works Journal Corporation, Handbook of Trickling Filter Design, 1970.
Reynolds L.B., and Chipperfield, P.N.J., Principles Governing The Selection of Plastic
Media for High-Rate Biological Filtration, 1970.
Schulze, K.L, D. Sc., Trickling Filter Theory, Water & Sewage Works, R256, October,
1960.
The Texas Water Utilities Association, Manual of Wastewater Operations, (Chapter
12), 1971.
Water Pollution Control Federation, Manual of Practice No. 6, Units of Expression
for Wastewater Treatment, 1976.
1-19
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
4.01 INTRODUCTION
Laboratory
control is an
essential tool.
An essential tool for proper process control is frequent and accurate sampling
and laboratory control tests. By relating the lab test results to operation, the
operator can select the most effective operational parameters, determine the
efficiency of his treatment processes, and identify developing problems
before they seriously affect effluent quality. Therefore, laboratory facilities
play an important role in the control of an aerobic biological treatment facility.
4.02 LABORATORY SAMPLING AND TESTING PROGRAM
Good sampling
procedures are
essential.
Good sampling procedures are the key to meaningful laboratory analyses. A
typical sample represents only a small fraction of the total flow, and great
care must be exercised to ensure that the sample is representative. If this
is not accomplished, the subsequent analytical data is worthless for process
control. Therefore, the importance of good and accurate sampling techniques
cannot be overstressed.
Two types of
samples.
24-hour
composite
sampling is
preferred.
The exact location of sampling points within a given treatment plant cannot
be specified because of the varying conditions and the plant design. However,
it is possible to present certain general guidelines which are presented on
Figure IV-1.
Two types of samples may be collected, depending upon the purpose of
sampling. The first is a dip or "grab" sample which consists of a single por-
tion collected at a given time. The second type of sample is a "composite"
sample that consists of portions taken at known times and then combined in
volumes that are proportional to the flow at the time of sampling. These
combined portions produce a sample which is representative of the wastewater
characteristics over the entire sampling period.
The preferred sampling procedure, except for certain lab or field tests which
must be run immediately (Dissolved Oxygen, Temperature, pH), is to collect
hourly samples over a day, having sample volumes that are in proportion to
the wastewater flow rate. When available and where possible, automatic
sampling devices should be employed. The sample containers and sample
lines should be thoroughly cleaned each time to prevent sample contamina-
tion. The hourly grab samples should be composited into a labeled plastic
gallon bottle and kept refrigerated at 3 or 4° C. to prevent bacterial decom-
position. For some tests (such as the nitrogen tests), other methods of
preservation may be needed, refer to Standard Methods for recommended
preservation procedures. A final composited sample volume of 2 to 3 liters is
usually sufficient to perform all routine tests. Where collection of an hourly
sample is not feasible, a 2 or 3 hourly sampling procedure is the next best
alternative. The sampling method and time of sampling should be noted upon
the lab record (log) sheet as reference for later data review and interpretation.
If only grab
samples are
collected, the
operator must
sample during
peak flow
conditions.
Grab Samples
Grab samples are representative of the instantaneous characteristics of the
wastewater. If it is only possible to collect grab samples, they should be
collected when the treatment plant is operating at peak flow conditions.
IV-1
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
Sampling point should be readily
accessible and adequate safety
precautions should be observed.
No deposits or materials should be
collected from the side walls or
the water surface.
Sample must be taken where the
wastewater 1s mixed and of
uniform composition.
MIXED
Large or unusual particles should
not be collected with routine
samples.
S»C-4»C
Sample should be delivered and
analyzed as soon as possible.
Stored samples must be
refrigerated at 3 to 4° C.
WASTEWATER SAMPLING GUIDELINES
FIGURE IV-1
IV-2
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
24-Hour
composites are
the best for
determining
organic loading
and
performance.
Sample collection should be conducted systematically at various sampling
locations during the flow sequence through the plant. Grab sampling times
may be systematically staggered to account for the respective hydraulic
detention time of each unit process. In this manner, a slug of water may be
theoretically followed through the treatment plant. For example, if the hy-
draulic detention period through a particular unit process is two hours,
then the grab sample of the effluent from this unit should be collected two
hours after the influent sample. In this manner, the samples can be assumed
to be representative of the wastewater before and after treatment.
Composite Samples
Composite samples generally represent the wastewater characteristics over
a specified period of time. The ideal procedure incorporates the use of 24-hour
composite samples consisting of hourly grab samples proportioned to the
flow at the time of sampling. This procedure is only feasible in treatment
facilities with 24-hour attendance or where automatic samplers are warranted.
Adequate results, however, can generally be obtained from analysis of com-
posite samples collected over a shorter period. In those facilities where
automatic samplers are not available, collection of composite samples
during the number of shifts worked would be sufficient as long as peak flow
periods are included. A total composited sample volume of approximately
three liters is generally sufficient to perform the routine process control tests.
The total amount of sample required, the number of samples required, the
rate of flow at the time of sampling, and the estimated average daily flow rate,
can be used to calculate the amount of sample to be collected during each
sampling period to represent the daily flow from the following equation:
Amount of sample to collect, ml =
Calculation for
composite
sampling.
(Rate of flow, mgd @ time of sampling) (Total sample required, ml)
(Number of samples collected) (Average daily flow, mgd)
Example Calculation
A. Data Required
1. Rate of flow at time of sample colle'ction = 1.5 mgd
2. Total sample volume required = 3 liters or 3000 ml
Note: ml = (liters) (1000)
3. Number of samples to be collected = 8
4. Average daily flow = 0.9 mgd
B. Determine the amount of sample to be collected for the present
flow rate in milliliters.
IV-3
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
(Rate of flow, mgd) (Total sample required, ml)
Amount of sample = -^ •—— T~T~^ T—
to collect, ml (Number of samples) (Ave. daily flow, mgd)
_ (1.5 mgd) (3000 ml)
(8) (0.9 mgd)
= 625 ml
Lab control
requires
adequate
facilities and
technical skills.
Laboratory Control Program
The specific laboratory tests and frequency which they are performed for
process control and performance evaluation will vary from plant to plant
depending on the type of trickling filter process, plant size, laboratory facilities,
available manpower, and technical skills. Minimum sampling and testing
programs for typical trickling filter processes are presented on Figure IV-2.
Minimum tests
for low-rate
filters.
Minimum tests
for high-rate
filters.
Low-Rate Trickling Filter Process
The low-rate trickling filter process does not require complicated or
stringent process control measures. However, the process does require
daily attention to maintain efficient and trouble-free operation. At a
smaller plant, the following tests would be sufficient in evaluating the
performance of a low-rate filter process:
• BOD
• Settleable Matter
• Suspended Matter
• Temperature
• pH
• Dissolved Oxygen
At a larger plant, the laboratory control program should also include
ammonia and nitrate nitrogen determinations. The presence of 2 to 15
mg/l of nitrate nitrogen in the filter effluent usually indicates a high
degree of stabilization. A typical sampling and testing program may be
developed for a low-rate filter process by referring to Figure IV-2.
High-Rate Trickling Filter Process
Like the low-rate trickling filter process, the high-rate process requires
limited daily maintenance for an efficient and trouble-free operation. The
recirculation flow scheme and rate should be regulated to attain the best
possible performance at the least expense. At single-stage trickling filter
plants, the following tests would be sufficient in evaluating the filter
performance:
• BOD
• Settleable Matter
• Suspended Matter
• Temperature
• pH
• Dissolved Oxygen
IV-4
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
SECONDARY
CLARIFIER
EFFLUENT.
SLUDGE
SAMPLE LOCATIONS FOR TYPICAL TRICKLING FILTER PROCESS
DESCRIPTION
FLOW
BOD
COD
SUSPENDED SOLIDS TOTAL
SUSPENDED SOLIDS VOLATILE
SETTLEABLE SOLIDS
AMMONIA*
NITRITE •
NITRATE * •
PHOSPHORUS
D O
pH
TEMPERATURE
TOTAL & VOLATILE SOLIDS
LOCATION OF SAMPLE
0
SETTLED SEW*
IPHMAHY
EFFLUENTI
CR
,x
jxr
jxC
rxr
ZXL
^xl
.x,
CD
z
D
_l
-
X
X
©
SLUDGE
[UNDER FLOWI
-
^xd
^X^
©
SECONDARY
CLARIFIER
EFFLUENT
1 CR
^XT
jixr
jx^
X
;><
<><,
>^
^XT
?><
;><
(4)
0
o
2
Ł>
-
1 /W
1/W
1/W
1 /W
D
2/M
2/M
2/M
2 /M
1/W
D
D
1/W
5 MGD AND
LARGER
-
2 /W
2/W
2/W
2/W
D
1 /W
1 /W
1/W
1/W
2/W
D
D
2/W
TYPE OF
SAMPLE
-
c
c
c
c
c
c
c
c
c
G
G
G
C
METHOD
OF TEST
-
AM
AM
AM
AM
AM
AM
AM
AM
AM
AM
AM
AM
AM
APPLICATION
OF TEST
P
P
P
P
P
P
P
P
P
P
P
s
s
P
NOT APPLICABLE TO SINGLE-STAGE .HIGH-RATE AND ROUGHING-RATE FILTERS
CODE DESCRIPTION
SAMPLE
&^ TEST RESULTS CALCULATED
0 DENOTES SAMPLE LOCATION
C COMPOSITE
D DAILY
G GRAB
P PROCESS CONTROL
S SURVEILLANCE
W WEEK
M MONTH
AM ANALYTICAL MEASUREMENT
Cfl CONTINUOUSLY RECORDED AND TOTALIZED
MM MAKE MEASUREMENT
PM PHYSICAL MEASUREMENT
SAMPLING AND TESTING PROGRAM FOR
TRICKLING FILTER PROCESS
FIGURE IZ-2
IV-5
-------
TRICKLING FILTER PROCESS
SECTION IV - LABORATORY CONTROL
At two-stage filtration plants where nitrification is being achieved, the
laboratory control program should also include ammonia and nitrate
nitrogen determinations. For development of a typical sampling and testing
program, refer to Figure IV-2.
Minimum tests
for roughing
towers.
Roughing Filters/Biological Towers
The following laboratory tests will be valuable in performance evaluation
of a filter being operated as a roughing unit:
• BOD
• Temperature
• pH
• Dissolved Oxygen
Minimum tests
for a biological
tower.
Process control
concept.
If solids sedimentation occurs, the following tests should also be included
to monitor the sludge removal and effectiveness of the sedimentation
unit:
• Settleable Matter
• Suspended Matter
For development of a typical sampling and testing program refer to Figure
IV-2.
In a biological tower where the sedimentation unit underflow (settled
matter) is returned to the tower influent, process control is somewhat
more difficult and requires a more stringent monitoring program. The mix-
ing of these flows results in a biological mass similar to that of mixed
liquor in the activated sludge process. The following laboratory tests
would be valuable in performance evaluation and process control:
• Suspended matter and BOD of the influent and effluent flows.
• Suspended matter concentration of the tower effluent flow.
• Suspended matter concentration of return sludge flow.
• Settleability (settlometer) test of the tower effluent flow.
• Dissolved oxygen of tower effluent and before effluent weir in
clarifier.
Process control primarily consists of the operator selecting and maintain-
ing the recycle rates and the suspended matter concentration in the
tower effluent flow that produces a sludge with good flocculating and
settling characteristics, and consequently an acceptable quality of
effluent. The excess filter sludge (amount of sludge equal to that produced
each day) is usually wasted from the system on a daily basis. For labora-
tory and process control procedures, and sampling and testing program
refer to the "ACTIVATED SLUDGE PROCESS" division, Sections II and IV.
4.03 LABORATORY CONTROL TESTS
This section of the manual is provided to increase understanding and to
develop an appreciation of laboratory control tests.
IV-6
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
Sampling and
analyses must
be Increased
when the
process Is upset.
Typical
worksheets
provided.
The tests discussed are those necessary for routine process control when the
biological system is operating properly. Additional analyses and increased
frequency of analysis for the routine analysis may be required for abnormal
conditions. Specific suggestions are made for abnormal operation in Section
I, "TROUBLESHOOTING." However, the operator must rely upon his own
judgment to determine which analyses he needs to conduct to supply the
information that he desires.
Typical worksheets have been provided in Appendix A to assist the operator
in developing systematic data collection, calculation, and recording. Pre-
cautionary procedures are presented for each of the tests presented in this
section to make the operator aware of the common pitfalls. Except where a
specific note is made, all analyses are referenced to the fourteenth edition
of "Standard Methods for the Examination of Waters and Wastewaters."
The 5-Day BOD.
Calculating
removal
efficiency.
Biochemical Oxygen Demand (BOD)
The biochemical oxygen demand is determined by incubating a sample of
known volume in the presence of microorganisms, excess nutrients, and
dissolved oxygen. A properly conducted BOD analysis will have organic
matter as the growth limiting substance. If oxygen is limiting, the analysis
is not meaningful.
The BOD is an index of the amount of oxygen that will be consumed by the
decomposition of the organic matter in a wastewater. The analysis consists
of measuring the initial dissolved oxygen concentration, incubation for five
days at 20° C, and measuring the final dissolved oxygen. The difference in
dissolved oxygen concentration corrected for the initial dilution is called the
BOD. The BOD test is related to both the organic loading upon the biological
process as well as the removal efficiency of the process. The difference be-
tween the BOD applied and the BOD leaving the process is equal to the BOD
removed by the process. The difference is part of the data required to deter-
mine the loading upon the process. For example, the organic loading upon
the trickling filter process is expressed as the pounds BOD applied per day
per 1000 cubic feet of filter media. Historically the organic loading on a
trickling filter has been expressed as BOD applied. The efficiency of the
process is determined by the following formula:
BOD applied, Ib/day - BOD leaving, Ib/day x 100 = the remova| efficiency, %
BOD applied, Ib/day
In this determination, the combined efficiency of the trickling filter and
clarif ier are considered.
Minimum of two
dilutions, at
least 2 mg/l D.O.
used—must be
at least 2 mg/l
left after 5-days.
Precautionary Procedures
When performing BOD analyses the following procedures should be
followed in conjunction with the procedures outined in Standard Methods.
1) A minimum of two dilutions per sample should be used. Only
analyses with oxygen depletions of greater than 2 mg/l but with no
less than a residual of 2.0 mg/l after five days of incubation at 20° C
should be used to calculate the BOD. Generally, the highest value
calculated should be used to represent the BOD.
IV-7
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
Mix samples
well.
Avoid aeration
during bottle
filling.
Note 5-Days
mean 120 Hours.
Toxic slide.
Primary
standard made
from glucose-
glutamic acid.
Useallythrlourea
to inhibit
nitriflers.
2) Samples should be well mixed before the dilutions are made. A
wide tip pipette should be used for making the dilutions. The wide
tip does not clog with suspended solids.
3) Samples and the dilution water must be carefully added to the
BOD bottle to avoid aeration and the possibility of entraining
bubbles in the solution.
4) The BOD incubator must be maintained at 20° ± 1° C for the entire
5 day (Note: 120 hours) period. Record the temperature of the
incubator from a NBS certified thermometer placed in a beaker of
water in the incubator.
5) IF the BOD value of the more dilute sample is always greater, this
may indicate that there is some toxic material in the wastewater,
which is inhibiting the bacteria. A series of dilutions should be set
up and run. If the BOD is increasing with higher dilution, this may
indicate a condition known as a toxic slide. Further analyses
should be conducted to determine the nature of the toxic material,
and if it appears that the concentration of the toxicant is significant,
efforts should be initiated to identify the source and reduce the
concentration of the toxicant in the wastewater.
6) Use of a primary standard is strongly recommended. The standard
should be made of glucose—glutomic acid mixture—and it should
be made up at a BOD near those levels in the treatment plant
influent. The primary standard should be made up and analyzed
weekly. Any significant variation (more than ± 20%) should cause
the operator to be suspicious. Efforts should be undertaken to
review the laboratory procedure, and find out what is causing the
problem. Each operator should analyze the standard and the results
should be within ±10%. Operators not falling within this range
should review their laborator techniques and make the appropriate
adjustments.
7) Wastewaters that have been partially nitrified may produce high
BOD results. The increased oxygen demand results from the oxi-
dation of ammonia to nitrate. The use of allylthiourea in the dilution
water will inhibit the nitriflers and alleviate this problem.
Chemical Oxygen Demand (COD)
COD is fast and
reproducible.
The COD is
better for
process control.
The COD is an estimate of the total oxygen demand that results from the de-
gradable organic matter. The analysis consists of oxidizing the organic matter
with potassium dichromate in a heated strongly acidic solution.
While the BOD analysis is an index of the biodegradable organic matter, it is
not very useful for process control because of the five day lag in time. The
COD test is rapid (3-4 hours); it is not subject to interferences from toxic
materials; and it is not affected by ammonia oxidation.
The COD removal of a biological process is directly relatable to the amount of*
biological growth that can result from this removal. The COD analysis suffers
from the disadvantage that it does not measure the rate of biodegradability
of matter removed and therefore it is difficult to predict the effects of effluents
on the oxygen resources of receiving waters and the treatability of a particular
wastewater.
IV-8
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
The analyst
must establish
his variability.
Precautionary Procedures
When performing the COD test, the following procedures should be
followed in conjunction with those outlined in Standard Methods.
1) Initially, the analyst should run triplicate samples to establish the
variability of his analyses. Once this variability is established,
samples can be analyzed without replication.
2) Use a wide tip pipette to ensure that a representative sample is
taken.
3) Glassware used for the COD analyses must be washed with hy-
drochloric acid, hot washed, and rinsed three times with distilled
water.
4) Extreme caution and safety precautions should be practiced when
handling the chemical reagents for the test. Goggles, a rubberized
apron and asbestos gloves are essential equipment.
5) If a sample mixture turns green during or immediately following
the heating period, the analysis is not valid and should be re-
examined in a more dilute sample. If the problem reoccurs then
the laboratory technique should be reevaluated and the sample
should be checked for likely interferences, such as high chloride
concentration or the presence of a strong base.
6) A primary standard consisting of potassium acid phtalate should
be analyzed on a weekly basis to ensure that the analyses are con-
sistent. The COD concentration of the standard should be near
the level of the COD of the wastewater. (See Standard Methods.)
Soluble COD and BOD
Soluble COD
and BOD.
The discussions on BOD and COD have been limited to the measurement of
the total COD and BOD. The soluble BOD and COD are more meaningful for
measuring performance. The soluble BOD or COD is determined in exactly
the manner descried above, except that the sample is filtered through a mem-
brane filter prior to the analysis. The use of this filtering apparatus is discussed
underthe suspended matter analysis.
Settleable Matter
How to make a
quick check on
Sedimentation
Unit operation.
Symptoms-
highlighted by
settleabillty
test.
The settleable matter test (also known as the Imhoff Cone Test) is a measure
of the volume of solid matter that settles to the bottom of an Imhoff cone in
one hour. The volume of settled solids is read as milliliters per liter (ml/l)
directly from the graduations at the bottom of the Imhoff cone.
This test is of value in providing a quick and efficient check of a sedimentation
unit. Additionally, a rough estimate of the volume of solids removed by the
sedimentation unit can be made. Only a trace of settleable solids should
remain in the secondary effluent, and very little should remain in the primary
effluent. Poor settleable matter removal may indicate the following related
problems which may occur in sedimentation basins:
Primary and Secondary
1) Hydraulic overload.
2) Irregular flow distributions to multiple units.
IV-9
EPA
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
3) Excessively high velocity currents.
4) Effluent weirs of uneven height - short circuiting.
5) Improper sampling technique.
6) Improper raw sludge removal rates.
Secondary Only
1) Biological upset.
Precautionary Procedures
When performing the settleable solids test, the following procedures
should be followed in conjunction with those outlined in Standard Methods.
1) Take a sample volume greater than one liter.
2) Use grab samples for this analysis.
3) Fill the Imhoff cone exactly to the one liter mark in one rapid
pouring without stopping.
4) After the sample has settled for 45 minutes, either gently tap the
sides of the cone or gently spin the cone between the palms of
your hands to settle those solids adhering to the sides of the cone
above the compacted settled layer at the bottom of the cone.
5) Read and record the volume of settled matter (ml/l) at the end of
one hour. Read the graduation at the average solids depth and not
at a peak or void area on the surface of the settled solids.
Measure of the
filterable
solids.
Use of this test.
Total Suspended Matter
The suspended matter test refers to the solids in suspension that can be
removed by standard filtering laboratory procedures. The suspended matter
is determined by filtering a known volume of sample through a weighed
glass-fiber or membrane filter disc in an appropriate filtering apparatus. The
filter with the entrapped solids is oven-dried at 103° -105° C and then cooled
in a desiccator and subsequently weighed. The increase in fitter weight
represents the suspended matter.
The significance of the suspended matter test is generally dependent on the
type of treatment process and the location of measurement within that pro-
cess application. Results of the test have the following uses in process
control:
1) Evaluating the organic strength of the wastewater.
2) Evaluating clarifier solids loading.
3) Determine the sludge recycle rate by calculation.
4) Calculating clarifier solids capture.
5) Estimating the solids inventory.
Precautionary Procedures
When performing the suspended matter test, the following procedures*
should be followed in conjunction with the procedures outlined in Standard
Methods.
1) The sample must be thoroughly mixed prior to taking a sample
aliquot.
IV-10
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
Use wide tipped
pipette.
Temperature
between 103-
105°C.
2) Do not use a small-tipped pipette to measure the sample aliquot.
A wide-tipped pipette should be utilized to permit passage of the
larger solids and to facilitate rinsing. An alternate method of
obtaining a sample aliquot would be to pour it into a graduated
cylinder.
3) Rinse all adhering solids from graduate (or pipette) with distilled
water. Pour rinse water through the filter.
4) Test results that appear faulty or questionable should be dis-
regarded.
5) It is important to always maintain a temperature of between 103 -
105° C in the drying oven. The temperature must be monitored and
recorded in a record book.
6) Be sure that the paper filter is properly seated in the filtration
apparatus before pouring the sample. This is easily accomplished
by wetting the filter paper with distilled water, then applying
vacuum to the filtration apparatus.
7) Samples containing high solids levels may require more than one
hour to completely dry.
8) Be consistent in the length of time the filter apparatus and paper
are allowed to cool in the dessicator both before and after filtering.
9) Use Whatman GF/C filters and a millipore filter apparatus with
sintered glass seat for this analysis.
Nitrite Nitrogen
NO2 a partially
oxidized form of
nitrogen.
High NO2
concentrations
Imply
incomplete
nitrification.
Analyze as soon
as possible.
Sample must be
cool.
Nitrite (NO2) is an intermediate oxidation state of nitrogen between ammonia
nitrogen and nitrate nitrogen. Nitrite is transatory and readily amenable to
both bacterial oxidation to nitrate or reduction to nitrogen gas depending
upon environmental factors such as dissolved oxygen and microbial conditions.
The nitrite concentration can be used to monitor how well nitrification is
progressing in a treatment process. High nitrite concentrations indicate in-
complete nitrification, and could lead to problems, such as high chlorine and
oxygen demands.
Precautionary Procedures
When performing the nitrite nitrogen test, the following procedures should
be followed in conjunction with the procedures outlined in Standard
Methods.
1) Use extreme caution in handling the chemical reagents to avoid
injury or damaged clothing.
2) Due to the instability of nitrite (NO2), the composite samples used
for the nitrite analysis should be preserved by one of the following
methods: (a) freezing, or (b) 5 ml of chloroform per liter of sample.
3) The samples must be cool when the analysis is performed or
erroneous results will be measured.
4) Deviation from standard procedure may yield erroneous results.
Be consistent in your laboratory technique.
IV-11
-------
TRICKLING FILTER PROCESS
SECTION IV - LABORATORY CONTROL
NO3alully
oxidized form of
nitrogen.
Typical in low
rate trickling
filters.
Use the Brucine
Method.
Nitrate Nitrogen
Nitrate is seldom found in raw wastewater or primary effluent, because facu-
ltative microorganisms can readily use nitrate as an oxygen source. In the
biological treatment process, the ammonia nitrogen can be microbiologically
oxidized to nitrite and then to nitrate depending on the microorganisms
present and the environmental factors such as pH, temperature, and dissolved
oxygen.
Secondary effluent may contain from 0 to 50 mg/l nitrate nitrogen depending
on the total nitrogen content in the raw wastewater and conditions of treat-
ment. Low-rate trickling filters with relatively deep beds can produce highly
nitrified effluents, while a single-stage, high-rate trickling filter will rarely be
capable of nitrifying.
Precautionary Procedures
When performing the nitrate nitrogen test, the following procedures
should be followed in conjunction with the procedures outined in Standard
Methods.
1) Use the Brucine method for routine analysis.
2) Analyze the sample as soon as possible to avoid bacterial reduc-
tion of the nitrate.
3) Preserve samples that cannot be analyzed immediately by either
freezing or by the addition of 5 ml of chloroform per liter of sample.
Ammonia Nitrogen
A measure of
the form of
nitrogen that
causes high
chlorine
demands and
fish toxicity.
This test measures the nitrogen present in the wastewater as ammonia.
Ammonia nitrogen in domestic wastewater is generally between 10 and 40
mg/l. Primary treatment may increase the ammonia nitrogen content slightly
due to decomposition of some protein compounds during treatment. In
secondary treatment process, ammonia can be oxidized to nitrite then to
nitrate in varying degrees depending on factors, such as the residence time
of the microorganisms, wastewater temperature, and oxygen reliability.
The significance of this test is associated with the oxygen demand required
to oxidize ammonia in the biological treatment process or receiving stream.
Theoretically, the oxidation of one pound of ammonia nitrogen requires 4.6
pounds of oxygen. This test is also valuable in evaluating the performance of
a treatment process designed to nitrify. Other significant problems relating
to ammonia are high chlorine demands, fish toxicity, and high oxygen demand
on receiving waters.
Precautionary Procedures
When performing the Ammonia Nitrogen test, the following procedures
should be followed in conjunction with the procedures outlined in Standard
Methods.
1) Use extreme caution in handling the chemical reagents to avoid
injury or damaged clothing.
2) Deviation from standard procedures may yield erroneous results.
Consistency in laboratory techniques is essential.
IV-12
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
Total Phosphorus
Essential to
biological
growth.
Phosphorus is one of the nutrients essential to biological growth in secondary
treatment processes. Most wastewaters have more phosphorus available
than is required for biological growth and assimilation of the carbonaceous
BOD. A deficiency of phosphorus may result from high waste loading from
industries, such as canneries which generally have wastes that are high in
carbohydrates and low in nutrients. Such a phosphorus defficiency may limit
biological g'rowth and lead to poor BOD removals.
Typical raw domestic wasteweter contains approximately 10 mg/l of phosphorus
of which 20 to 30 percent may be removed by the growth of microorganisms
which are wasted from the process. Greater removals may be obtained by
various processes involving addition of a metal ion such as iron or aluminum
to chemically precipitate iron or aluminum phosphate. Other removal pro-
cesses involve pH adjustment by addition of lime or other means and chemical
precipitation of a calcium phosphate.
Precautionary Procedures
When performing the total phosphorus test, the following procedures
should be followed in conjunction with the procedures outlined in Standard
Methods.
1) Use extreme caution in handling the chemical reagents to avoid
injury or damaged clothing.
2) Record specific procedures used for pretreatment of sample and
measurement of phosphorus concentration with test results. Also,
clearly indicate the expression of the test results, P or PO4. (Note:
1.00 mg/l P equals 3.06 mg/l PO4.)
3) Deviation from standard procedure may yield erroneous results.
Be consistent in your laboratory technique.
Dissolved Oxygen
An Important
parameter.
Dissolved oxygen (DO) is that oxygen dissolved in liquid and is usually ex-
pressed as milligrams per liter (mg/l). There are various tests to determine
the DO content of water. Generally, the iodometic methods and the membrane
electrode (DO probe) are best suited for the domestic wastewater application.
The azide modification of the iodometric method (also known as Winkler
Method) is recommended for most wastewater and stream samples. When
determining the DO in trickling filtereffluent and other biological floes which
have a high oxygen utilization rate, the copper sulfate-sulfamic acid floccula-
tion modification should precede the azide modification to retard biological
activity and to flocculate suspended solids. The membrane electrode method
is becoming increasingly more popular because of its speed, ease of opera-
tion, and adaptability to process control instrumentation. The membrane
electrodes must be properly maintained and calibrated on a daily basis to
ensure that their measurements are accurate and usable for process control.
IV-13
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
DO
measurement
can be used to
control aeration.
Use special care
in sampling.
Perform
immediately
after sampling.
The significance of the DO test in process control is in its measurement of
the dissolved oxygen available for and essential to aerobic decomposition
of the organic matter; otherwise, anaerobic decomposition may occur with
the possible development of nuisance conditions. The DO test is also used
in the determination of BOD as discussed previously. Fish and most aquatic
life require dissolved oxygen to sustain their existence and the DO test is an
important measurement in plant effluents and receiving water quality.
Precautionary Procedures
When performing the DO test, the following procedures should be allowed
in conjunction with the procedures outlined in Standard Methods.
1) Use extreme caution in handling the chemical reagents to avoid
injury or damaged clothing.
2) The use of special DO sampling equipment is preferable for col-
lecting samples. The samples should be taken with the sample
container completely immersed and without aeration of the sample
or entrapment of any air bubbles.
3) Perform DO test immediately following collection of sample.
4) The following substances will interfere in the azide modification
of the iodometric DO analysis: iron salts, organic matter, excessive
suspended matter, sulfide, sulfur dioxide, residual chlorine,
chromium, and cyanide.
Hydrogen Ion Concentration (ph)
An important
measure for the
microorganism.
The intensity of acidity or alkalinity of a solution is numerically expressed by
its pH. A pH value of 7.0 is neutral, while values 7 to 14 are alkaline and values
0 to 7 are acid. pH can be measured colorimetrically or electrometrically. The
electrometric method (pH meter) is preferred in all applications because it is
not as subject to interference by color, turbidity, colloidal matter, various
oxidants and reductants as is the less expensive colorimetric method.
The pH measurements are valuable in process control because pH is one of
the environmental factors that affect the activity and health of microorganisms.
Sudden changes or abnormal pH values may be indicative of adverse industrial
discharge of a strongly acid or alkaline waste. Such discharges are detrimental
to biological processes as well as to the collection system and treatment
equipment, and should be either stopped or neutralized prior to discharge.
Generally, the pH of the secondary effluent will be close to 7. A pH drop may
be noticeable in a biological process achieving nitrification because alkalinity
is destroyed and carbon dioxide is produced during the nitrification process.
Use grab
samples-
analyze
Immediately.
Precautionary Procedures
When performing the pH test, the following procedures should be followed
in conjunction with the procedures outlined in Standard Methods.
1) Grab samples should be used for the pH measurement. The pH
test should be performed on the samples immediately following
collection before the temperature or dissolved gas content can
change significantly. Do no heat or stir the pH sample as a change
in temperature or dissolved gas content will affect the pH value.
IV-14
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
Calibrate the pH
meter daily.
Exercise
extreme care
with electordes.
2) Do not contaminate the buffer by pouring the used buffer solution
back into the buffer container.
3) Calibrate the pH meter daily with a buffer solution of approximately
the same temperature and pH as the sample to be tested. Adjust
the pH meter's temperature compensator for each pH measurement.
4) Avoid fouling the electrodes with oil or grease.
5) Erratic results or drifting should prompt an investigation of the
electrodes.
Temperature
affects growth
of
microorganisms.
Temperature
In process control, accurate temperature measurements are helpful in evalu-
ating process performance because temperature is one of the most important
factors affecting microbial growth. Generally stated, the rate of microbial
growth doubles for every 10° C increase in temperature within the specific
temperature range of the microbe. Temperature measurements can be helpful
in detecting infiltration/inflow problems and illegal industrial discharges.
Thermometers are calibrated for either total immersion or partial immersion.
A thermometer calibrated for total immersion must be completely immersed
in the wastewater sample to give a correct reading, while a partial-immersion
thermometer must be immersed in the sample to the depth of the etched
circle around the stem for a correct reading.
If a Fahrenheit thermometer is used its readings may be converted to Centi-
grade by the following formula:
= — (° F-
9
32C
Measure
Immediately.
Precautionary Procedures
When obtaining the temperature of a sample, the following procedures
should be followed in conjunction with the procedures outlined in Standard
Methods.
1) To attain truly representative temperature measurement, it is
necessary either to take the temperature reading at the point of
sampling or immediately following sample collection. A large
sample volume should be used to avoid a temperature change
during the measurement.
2) The accuracy of the thermometer used should be occasionally
verified against a precision thermometer certified by the National
Bureau of Standards (NBS).
3) The thermometer should be left in the sample while it is read.
Flow
Accurate flow
measurements
•re essential.
A physical measurement of the in-plant flows is essential for true process
control. Without these flow measurements, it is impossible to compute
hydraulic and organic loadings, detention periods, recycle flows, and clarifier
underflows. Without the above parameters to regulate the treatment processes,
IV-15
-------
TRICKLING FILTER PROCESS
SECTION IV - LABORATORY CONTROL
Flow
measurements
are very
important.
How to
measure flow
without a flow
meter.
the operator is left with only a "seat of the pants" approach to process control.
Without a measurement of in-plant flows, it is impossible to competently
evaluate the operation of the individual treatment units. The measurement of
the plant flows also provides a basis for computing costs for billing, esti-
mating chemical needs, predicting the future need for plant expansion or
modification, and evaluating the effect of the plant effluent on the receiving
stream. Reference to Figure IV-2 will indicate locations of typical in-plant
flows that should be measured for process control.
In many of the smaller plants, only the plant influent flow and possibly the
plant effluent flow are metered. In these cases, the operator will have to
measure the in-plant flows by other means. For instance, a pumped flow may
be estimated by multiplying the pump capacity (gpm) times the minutes of
pumping time per day.
gpd = (gpm)(min/day)
Often, pump capacity may be estimated by measuring the volume of liquid
pumped from or to a structure in a timed period. No unmetered flows into or
out of the structure must be permitted during the test period. Metered flows
into or out of a structure during the test must be taken into account when
computing the volume of liquid pumped.
gpm = (Area, sq.ft.) (Depth, ft.) (7.48 gal/cu. ft.) = metered flow, gpm
minutes
The metering instrumentation must be properly maintained and calibrated on
a regular and routine basis to insure that their measurements are accurate
and usable in process control and performance evaluation.
IV-16
-------
TRICKLING FILTER PROCESS
SECTION IV-LABORATORY CONTROL
REFERENCES
APHA, AWWA, WPCF, Standard Methods for Examination of Water and Wastewater,
14th Edition, 1976.
California Water Pollution Control Association, Laboratory Procedures for Operators
of Water Pollution Control Plants, 1970.
Kerri, Kenneth, D., et al., A Field Study Training Program, Operation of Wastewater
Treatment Plants, (Chapters 6 and 14), Sacramento State College Department of
Civil Engineering.
New York State Department of Health, Laboratory Procedures for Wastewater Treat-
ment Plant Operators, Health Education Service, Albany, N.Y.
New York State Department of Health, Manual of Instruction for Sewage Treatment
Plant Operators, Health Education Service, Albany, N.Y.
The Texas Water Utilities Association, Manual of Wastewater Operations, Texas State
Department of Health, 1971, Austin, Texas.
U.S. Environmental Protection Agency, Estimating Laboratory Needs for Municipal
Wastewater Treatment Facilities, Office of Water Program Operations, Publica-
tion No. 4301 9-74-002, Washington, D.C.
U.S. Environmental Protection Agency, Technology Transfer, Handbook for Analytical
Quality Control in Water and Wastewater Laboratories, Analytical Quality Control
Laboratory, National Environmental Research Center, Cincinnati, Ohio, June, 1972.
Water Pollution Control Federation, Simplified Laboratory Procedures for Wastewater
Examination, Publication No. 18,1971.
IV-17
-------
APPENDIX A
OPERATIONAL RECORDS
TABLE OF CONTENTS
Topic Page
1.01 INTRODUCTION A-1
1.02 OPERATIONAL PERFORMANCE RECORDS A-1
Daily Records A-1
Monthly Records A-3
1.03 COMPUTER AIDED DATA MANAGEMENT A-9
1.04 INTERPRETATION OF RECORDS A-9
Trend Plots A-11
-------
APPENDIX A
OPERATIONAL RECORDS
LIST OF FIGURES
Figure No. Description Page
A-1 B.O.D. Worksheet A-4
A-2 C.O.D. Workshe.et A-5
A-3 Suspended Solids Worksheet A-6
A-4 30-Minute Settling Test A-7
A-5 Monthly Process Control and Performance Logs A-8
A-6 Trend Plots A-13
-------
APPENDIX A
OPERATIONAL RECORDS
LIST OF TABLES
Table No. Description Page
A-1 Weekly Computer Report of Process Parameters A-10
A-2 Summary of Laboratory Test Applications for Process Control A-12
and Performance Evaluation
-------
APPENDIX A - OPERATIONAL RECORDS
Accurate
records are the
key to
consistent
process control.
1.01 INTRODUCTION
The quantity of records to be kept will depend upon the size and type of the
wastewater treatment facility. A small plant may not require the number of
variety of records required for a large plant. The specific records required will
be determined by the size and number of unit processes within the treatment
facility. Generally, these records are categorized as follows:
1) Operational Performance and Process Control
2) Inventory
3) Maintenance
4) O & M Costs
5) Personnel
For the purpose of this manual, only the Operational Performance and Process
Control records will be discussed. Several references are listed at the end of
this appendix which will provide detailed information concerning other
records outlined above. Operational Performance and Process Control records
at most wastewater treatment facilities are kept daily and on a monthly
basis. Averages for the month of operation are normally recorded on the
monthly log.
Performance
records
document the
operations and
provide the
information for
process control.
1.02 OPERATIONAL PERFORMANCE RECORDS
Complete and accurate records of all phases of plant operation and mainten-
ance are essential for the evaluation and control of a biological wastewater
treatment facility. Such records are valuable for justifying expenditures, and
for making recommendations concerning operational changes, modifications,
and expansions. These records are also used to verify compliance with
effluent quality requirements. Records should be systematically logged by
unit process and filed in a calendar sequence. Generally, the minimum
amount of record keeping required includes the following:
1) Daily Log
2) Daily Laboratory Work Sheets
3) Influent and/or effluent flow rates
4) Organic and hydraulic loading rates of each unit process
5) Amount and dosage of chemicals used
6) Power consumption
7) Unusual happenings such as bypasses, floods, storms, complaints,
other significant events that could be possibly needed in the future
for legal and administrative purposes.
Daily Records
Be sure to enter
time of day and
Initial your
entries.
A daily log or diary should be maintained to record events and operations
during each shift of plant operation. In larger treatment plants, it may be
beneficial to maintain such a log for each unit process. The log may be a
standard (81/2 x 11) spiral notebook or a standard daily diary made for that
purpose.
A-1
-------
The information entered in the plant log should be pertinent only to plant
functions. Log entries must include the time, the day of the week, the date,
Daily records the year, and the weather conditions. The names of the operators working at
areusedto the plant, and their arrival and departure times should also be included. Log
°bserve 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
happenings. 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 cases. An example
of one day's log entries in a small trickling filter plant is outlined below:
Tuesday, January 6,1976 Weather: Clear, Temp. 73° F, Wind-NW
J. Doakes, Operator; A. Smith, Assistant Operator.
G. Doe, Maintenance Helper.
8:20 AM Made plant checkout, changed flow charts, No. 2 super-
natant tube plugged on No. 2 digester, cleared tube.
9:00 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 mainten-
ance, put No. 2 filter reciruclation pump on, took No. 1
pump off.
10:00AM 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.
10:30 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 refrigerator 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.
A-2
-------
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 ahlorine container
on line, in case No. 1 should run empty during the night.
In addition to maintaining a daily log of plant operations daily laboratory data
should be kept and transferred to the monthly log form. The daily records
should be systematic so that later references can be, made. Example daily
laboratory worksheets are presented on the following plages.
Monthly Records
Monthly
records indicate
trends and
averages.
How to
construct a log.
Monthly records should report the totals and the, averages of the values
recorded daily. It is also beneficial to show the 'maximum and minimum
daily results, such as maximum and minimum daily flows.
Daily recorded data are usually transferred onto the monthly data sheets. The
monthly data sheet is designed to meet the reporting needs of a particular
plant. It should have all important data recorded that may be used later for
the preparation of monthly or annual reports.
The monthly data sheet may be a single 81/2 x 11 sheet for a small treatment
plant, or it may be a number of sheets pertinent to various treatment units
within the 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
from 1 to 31 to cover the days in the month. Then from left to right across the
sheet are columns to record daily information. These columns should contain
the day of the week, weather conditions, plant flows, wastewater temperatures,
pH, settleable solids, BOD, quantity of sludged pumped, DO, and other per-
tinent information applicable to various unit processes. A space for remakes
is helpful to record and explain unusual events. Typical column headings for
-an activated sludge plant and trickling filter plant are presented in Figure
A-5. Figure A-5 is designed so that it may be composited to fit the needs of a
particular plant. Therefore, the operator may develop a monthly log by using
Figure A-5 as an example.
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 to maintain proper plant operation. In
addition, he can develop the form to fulfill the requirements of his agency as
well as the appropriate regulatory agencies. Generally, these sheets can be
classified as an operational performance log and process control log as
illustrated in Figure A-5.
In addition to routine daily operation, maintenance, and wastewater char-
acteristics, 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 maintenance procedures.
A-3
-------
B.C. D. WORKSHEET
Date of Sample:
Incubation
Date In: Date Out:
1 . Bottle No.
2. ml of sample used
3. Initial D. O.
4. D. O. after 5 days
5. D. O. depletion (diff. )
6. Factor (factor x diff. )
7. B. O. D. mg/1
8. Avg. B. O. D. mg/1
Primary
Standard
Blank
Sample
Primary
Effluent
Final
Effluent
Dilution Water initial D. O.
After 5 days incubation
Dilution Water D. O. depletion
CALCULATIONS:
(Initial D. O. , mg/l-D. O. after incubation, mg/1) (Bottle capacity, ml)
(ml of sample used)
= B. O.D. , mg/1
FIGURE A-1
-------
C.O.D. WORKSHEET
Date of Sample:_
Date of Analysis:
1. Reflux Sample No.
2. ml of sample used
3. ml FAS for blank
4. ml FAS for sample
5. Difference FAS
6. FAS normality
7. C. O. D. mg/l
8. Avg. C. O. D. mg/l
Primary
Standard
Blank
Sample
-
Primary
Effluent
Final
Effluent
CALCULATIONS:
(ml FAS blank - ml FAS sample) x FAS normality x 8, 000 = COD mg/l
ml sample use
FIGURE A-2
-------
FIGURE A-3
SUSPENDED SOLIDS WORKSHEET
Sample by:
Date:
Time:
Type of Sample:
Location:
Analysis by:
Date:
Time:
Method used - Crucible/Filter
(Circle One)
Run Number
A Wt. of crucible/filter,
and dry solids, gm
B Wt. of crucible/filter, gm
'X
C Wt. of dry solids, gm
D ML of sample
**
E Suspended solids, mg/1
A Wt. of crucible/ filter,
and dry solids, gm
B Wt. of crucible/ filter,
and ash, gm
*
C Wt. of vol. solids, gm
D ML of sample
>!
E Vol. suspended solids, mg/1
Calculations ^
* A - B = C
Cxi, OOP, OOP)
D
= E
A-6
-------
FIGURE A-4
DAILY LABORATORY ANALYSIS
30-MINUTE SETTLING TEST
Date
GRAB SAMPLE
Test Set Up:
Temp. ' C
Min.
ML/L
0
5
10
15
20
25
30
40
50
60
SDI or SVI =
OBSERVATIONS:
Day
GRAB SAMPLE
Test Set Up:
Temp. °C
Min.
pm
ML/L
0
5
10
15
20
25
30
40
50
60
SDI or SVI =
OBSERVATIONS:
CALCULATIONS:
30 min ML/L
SVI =
MLSS mg/1
x 1,000
SDI =
100
SVI
A-7
-------
oo
PLANT NO.
I
i
.
'
•
»
,
•
10
,,
,1
l>
14
„
»
"
.-
1.
10
„
»
«
»
»
»
»
2*
»
»
>'
i
TOTA!
•""—
•°"»"»
AVERAGE
MONTHLY PROCESS CONTROL LOS . "".ScTS™""*1 MOUTH or
FOR A TYPICAL ACTIVATED SLUDOE PROCESS Jol'S" HE^.TED
POUNDS PTM DAT
REMOVED
«,„ | coo
UNDEB
AERATION
HA
M
Tld
i
••••
••••
a
™
«.
*•
*•
»T
TEMP.'C
PM.
EFFL.
SEC.
AERATION BASIN RETURN ACTIVATED SLUDGE SYSTEM NITROGEN HVL PHOSPHORUS SECONDARY CLARIFIER
MHTOLBUOB SUSPENDED SOUDS DET ^ «" ^p'SS^S,^'^ WASTE SUSPENDED SOLIDS .TKN *H f* NO^-Ii W.-N AS PMC/L „„, iipiiT npQ ^ ^
MONTHLY PERFORMANCE LOG
FOR A TYPICAL WASTEWATER TREATMENT FACILITY
(ACTIVATED SLUDGE PROCESS OR TRICKLING FILTER PROCESS)
E'MCD | ' „.,, /HR .,,., " ' ' 1 ur/LVOI.-r,, t 1 POUNDS Pth [ TT7 1 POUNDS PER | 7^7, f POUNDS PER 1 1 1
E MCD ML/L/HR MO/L TOTAL MC/L VOLATILE DAYREMOVED "='L DAY REMOVED MC'L DAY REMOVED fc
rl II 1 1 II |"TT"H In hi rr ill i—i-pr-l II •|-r"T"T"i II 1 1 1
"*
I MICRO. 1 [REMARKS
I EXAM. 1 1
MLSS || * *
1 * II
-
CHLORINATION REMARKS
P"E POST *„„«,,., »m/r,n invrt^r "
L63/HA-I DOSACE RESIDUA). LBS/DAT LXJSAGE RESIDUAL "'TIME"' LABORATORY "aATA^HEOljiHED °
MONTHLY PROCESS CONTROL LOG
FOR A TYPICAL TRICKLING FILTER PROCESS
(INCLUDE WITH PREFORMANCE LOG )
TRICKLING FILTER SECONDARY CLAfMFIER "HOSPHORUS NITROGEN M6 /L
«
•
LHSQOf
PER
1000 FT
1 ŁŁŁ RECItt. HEMOVED FLO» PEJ TIME MG/L PBL SEC. PRI. ] SEC. PHI. SEC. SEC. SEC.
[ f
i
i
•
•
.
•
10
I,
II
..
,1
'•
"
,.
„
in
*
l"
„
«
,0
'"
MONTHLY PROCESS CONTROL AND PREFORMANCE LOGS
FIGURE A-5
-------
1.03 COMPUTER AIDED DATA MANAGEMENT I
An Important
new tool.
Low cost data
processing.
A good
reference.
Note the format
In Table A-1.
The computer
can fill In
performance.
Reports to
regulatory
agencies.
Easily used tool.
Interpretation—
The main
purpose of
keeping records.
Use your
records
frequently.
The computer is an economical aid for data collection and analysis. The
computer can be used to tabulate and analyze all of the data needed to
perform routine and non-routine process control operations. The computer
can also be used to inventory equipment, to log maintenance requirements,
and to provide completed report forms for regulatory agencies.
Typical operations costs for process control data management would be less
than $250 per month. These costs include terminal rental and computer
time. A nominal initial cost would be involved to generate the programs used
for a particular treatment plant.
A recent article* described the operation of a computer program used to
tabulate and analyze the operating data needed to monitor the operation of
an activated sludge plant. Table A-1 (from the article) presents the minimum
data required to properly operate and monitor an activated sludge treatment
plant. Note that the data are tabulated on a daily basis, although process
control is based upon averaged data.
The data format used in Table A-1 makes the data easily usable. It is strongly
recommended that the data shown on Table A-1 be tabulated in this format,
because of the general usefulness of these data in treatment plant operations.
These fifteen data entries can be used as a starting point for the proper
operation and monitoring of any plant.
Additional use of the computer include the generation of monthly perform-
ance reports to regulatory agencies, and cataloging maintenance operations
and equipment inventory. The computer can be used to prompt or remind
operations personnel that scheduled maintenance operations are due. The
computer can continue to catalog outstanding maintenance operations until
the operator responds with a signal that the duty is completed. *
The computer is an easily used tool that can be programmed to perform
routine data tabulation and analysis. With minimal effort, operations personnel
can readily learn to use and depend on the computer, freeing their time to
perform other necessary functions.
*Trussel, R., et al., "Computer Assisted Operation of an Activated Sludge
Plant", October, 1974.
1.04 INTERPRETATION 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 can enable the operator to determine operation and main-
tenance needs of his plant. The information shown by the records should
also indicate to him and to his supervisor the treatment 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.
A-9
-------
TABLE A-1
WEEKLY REPORT OF PROCESS PARAMETERS
WEEK ENDING 10/2/74
^**********************************************************************
* 0 * LOADING *
* A ******************************************************************
* T * FL0W * C0D * C0D * SS * SS *
* E * MOD * MG/L * UBS * MG/L * LBS *
************************************************************************
* 9/26* 2.73 * 349. 7946. * 1 5S . * 35?7. *
* 9/27* 2.68 * 434. 9700. 148. * 3308. *
* 9/28* 2.70 434. 9773. 455. * 10246.
* 9/29* 2.85 434. 10334. 102. * 242»,
* 9/30* 2.80 357« S337. 112. * 2615.
*10/ 1* 2.96 374. 9242. 108. * 2669.
*10/ 2* 2.74 376. 8598. 127. * 2904.
************************************************************************
* AVG * 2.78 * 394. * 9133. * 173. * 3967. *
*********
* D *
* A ***
* T *
* E *
*********
* 9/26*
* 9/27*
* 9/28*
* 9/29*
* 9/30*
*10/ 1*
*10/ 2*
********
********
F/M
********
0.40
0.50
0.97
8.94
0.41
o.st
0.78
*****
*****
*
*
*****
*
*
*
*
*
*
*
********
*******,
SRT
DAYS
*******>
20.2
86.9
37.3
24.2
7i.2
51.4
36.9
***************
C0NTRBL
***************
* S0LIDS
* LBS
***************
* 19996.
* 19433.
* 10088.
* 10970.
* 20184.
* 17947.
* 10966.
*****
>***<
*
*
H***4
*
*
*
*
*
*
*
I***********
************
SETT'LY *
X o
************
51.0 <
36.0 4
32.0
30.0
59.0
82.0
37.0
**************
*
K*************
i- SVI *
» ML/GM *
**************
t 225. *
« 168. *
192. *
169. *
173. *
270. *
198. *
****************************************************$*****$$ j**^*,,,,,^*^*
* AVG * 0.65 * 47.9 * 15655. .* 46.7 * 199. *
*************** ******************************* + ,Ł*************,,$.(,********
* D *
* A **
* T *
* E *
PERFORMANCE
*********************
TURBIDITY
*******************
* 9/26*
* 9/27*
* 9/28*
* 9/29*
* 9/30*
*10/ 1 +
*10/ 2*
2.7
3.3
5.4
5.6
SS
MG/L
******
*
*
***********
SS
S REM0VEO
IT***
*
*
***********************
C0D * C0D
MG/L * X REM0VED
*
k*
***************************************************
14.0
11. 0
12.0
23.0
5.6 * 16.0
5.6 * 19.0
6.1 * 18.0
*
*
*
*
*
*
*
91.1
92.6
97.4
77.5
85.7
82.4
85.8
*
*
*
*
*
*
*
47.
54.
54.
54.
78.
48.
58.
86.5
87.6
87.6
87.6
78.2
87.2 •
84.6
************************************************************************
* AVG * 4.9 * 16.1 * 87.5 * 56. * 85.6 *
************************************************************************
A-10
-------
Look for trends.
Look for sudden
variations.
Laboratory analyses performed on various samples provide essential tools to
aid in the control and evaluation of a biological treatment process. Table A-2
presents a list of the analyses and their use in performance evaluation and
process control.
Records should not only be analyzed as a single piece of data, but any vari-
ation should be looked upon for its relation to another source of data. For
example, a sudden rise in temperature of the influent might be accompanied
by greatly increased flows. This could indicate a large industrial discharge.
This discharge could also influence the BOD and suspended solids concen-
trations 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 sudden variations in
data, an expected range of values has to be determined for the particular
treatment unit under consideration. This range must be based upon expected
or past performance. For example, if average daily flows during weekdays
were around two million gallons per day and suddenly a flow of 0.5 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
wastewater.
An excellent way to facilitate review of daily records and detect sudden
changes or trends are prepared charts showing values plotted against days
or time. Unless results are plotted, slight changes and trends can go unde-
tected. The deviation from the expected .values may have been caused by
unusual circumstances or an error in observation oranalysis.
Plotting your
data increases
in value.
Use of average
data.
Trend Plots
Plotting data on graphs is very helpful to illustrate trends in the operation of
a wastewater treatment facility. Regular plotting of data may reveal unexpected
trends which could provide insight to prevent an operational upset of a unit
process. In addition, this approach could be utilized to justify budget require-
ments, and to show the need for plant modifications or expansion. To look
for or show a trend, plot the value or values against time as illustrated in
Figure A-6. The important concepts relevant to plotting trend charts are
discussed below:
1. Plotting daily data will not provide good process control interpret-
tions. A 5-day moving average method is suggested for normal opera-
tions. In cases where data is not taken daily, the collected data can
still be used to generate moving averages. Each day a new set of data
is included and-one data set is deleted from the group of five to be
averaged.
A-11
-------
TABLE A-2
SUMMARY OF LABORATORY
CONTROL TEST APPLICATIONS FOR
PROCESS CONTROL AND PERFORMANCE EVALUATION
TEST /SAMPLE
BOD - COD
PRIMARY EFFLUENT
SECONDARY EFFLUENT
SUSPENDED SOLIDS
TOTAL
PRIMARY EFFLUENT
MIXED LIQUOR
SECONDARY EFFLUENT
RAS/WAS
VOLATILE
MIXED LIQUOR
SECONDARY EFFLUENT
RAS/WAS
NITROCEN-KJEDAHL
PRIMARY EFFLUENT
SECONDARY EFFLUENT
AMMONIA
PRIMARY EFFLUENT
SECONDARY EFFLUENT
NITRITE
PRIMARY EFFLUENT
SECONDARY EFFLUENT
NITRATE
PRIMARY EFFLUENT
SECONDARY EFFLUENT
PHOSPHORUS
PRIMARY EFFLUENT
SECONDARY EFFLUENT
30-MINUTE SETTLING
MIXED LIQUOR
DO
HAW WASTEWATER
MIXED LIQUOR
PH
PRIMARY EFFLUENT
MIXED LIQUOR
TEMPERATURE
PRIMARY EFFLUENT
MIXED LIQUOR
SECONDARY EFFLUENT
SETT LEA BLE SOLIDS
PRIMARY EFFLUENT
FILTER EFFLUENT
SECONDARY EFFLUENT
MICROSCOPIC EXAMINATION
MIXED LIQUOR
FLOW
SLUDGE BLANKET
SECONDARY CLARIFIER
ACTIVATED SLUDGE PROCESS
TRICKLING
• ORGANIC I-OAD APPLIED
• ORGANIC LOAD REMOVED
0 F/M RATIO DETERMINATIONS
FILTER PROCESS
O RECIRCULATION RATE REQUIREMENTS
ORGANIC LOAD APPLIED
ORGANIC LOAD REMOVED
EVALUATE PROCESS PERFORMANCE
SOLIDS LOADING ON SECONDARY CLARIFIEH
MASS BALANCE DETERMINATIONS
0 HAS/WAS RATES
O MLVSS LEVELS IN AERATION BASIN
0 MCRT DETERMINATIONS
0 SLUDGE REMOVAL HATES FROM CLARIFIER
• NITRIFICATION 1
• NUTRIENT BALANCE 1
0 SLUDGE QUALITY AND SETTLING CHARACTERISTICS
0 SVI
0 SDI
o SLUDGE REMOVAL RELATIVE TO DENITRIFICATION
• TOXIC SHOCK LOAD I
• OXYGEN DEMAND FOR CHANGES IN ORGANIC LOADING 1
0 AERATION REQUIREMENTS
0 HECIRCULATION RATE REQUIREMENTS
WASTE DISCHARGES ADVERSE TO
BIO LOGICAL SYSTEM
• DETECTION OF INFILTRATION-INFLOW
• REFLECTS CONDITION OF BIOLOGICAL ACTIVITY
• REFLECTS CONDITIONS OF NITRIFICATION
• EFFICIENCY OF CLAHIFIEH ]
0 ASSIST IN MCHT DETERMINATIONS
0 OPERATIONAL PROBLEMS RELATIVE TO
FILAMENTOUS ORGANISMS
0 EVALUATE SLUDGE QUALITY
o SLUDGE REMOVAL RATES FROM CLARIFIEH
• DETERMINE APPLIED LOADS 1
• HYDRAULIC DETENTION TIME |
o SOLIDS DISTRIBUTION
0 USE TO DETERMINE RAS FLOW RATES
0 EVALUATE HYDRAULICS
• APPLICABLE TO BOTH BSD LOGICAL PROCESSES
A-12
-------
2
O
H
<
Pi
W
Q
W
>
O
W
«
§
u
O
H
Q
o
g
H
2
Z.OOO
1,500
1,000
500
0.6
0.5
0. 4
0. 3
600
400
ZOO
0
150
100
50
10
15
DAY
20
25
30
ACTIVATED SLUDGE PROCESS
(Five-day moving average trend plots)
FIGURE A~6
A-13
-------
How to generate
a 5-day moving
average.
For example, 5-day moving averages for a 2-day period (January 5 and 6, 1976)
are calculated as follows:
Date
1-1-76
1-2-76
1-3-76
1-4-76
1-5-76
Total
1-6-76
Initial Data
Group
BODmg/l
120
118
124
122
121
605 •=- 5 = 121
avg. for 1-5-76
Total
Sequential
Data
Group
BOD mg/l
Deleted
118
124
122
121
123 added
608 + 5 = 122
avg. for 1-6-76
Plot process
control data:
F/M
MCRT
MLVSS
Effluent SS
Effluent BOD
Etc.
Learn to plot
accurately and
meaningfully.
2) All data used for process control should be plotted on a daily, weekly,
and monthly basis. Daily plots showing large variations indicate that
either shock loadings or errors in operation and/or calculation have
occurred. Weekly and monthly plots will show long-term changes and
indicate whether the control exerted by the process control techniques
is suited to operating conditions.
3) The operator must familiarize himself with the techniques of graph-
ically displaying data, in order to get the maximum amount of informa-
tion out of the data. Trend observation is probably the singlemost
important tool that the operator has to prevent catastrophic upset of
the biological processes.
A-14
-------
REFERENCES
New York State Department of Health, Laboratory Procedures for Wastewater Treat-
ment Plant Operators, Health Education Service, Albany, N.Y.
New York State Department of Health, Manual of Instruction for Sewage Treatment
Plant Operators, Health Education Service, Albany, N.Y.
Recommended Standards for Sewage Works, 1973 Revised Edition, Published by
Health Education Service, Albany, N.Y.
Sacramento State University, Operation of Wastewater Treatment Plants A Field
Study Program, Sacramento, California.
Texas Water Utilities Association, Manual of Wastewater Operations, Texas State
Department of Health, 1971, Austin, Texas.
Trussell, R.R., Bravo, A., Kermit, P., and Nichels, C., Computer Assisted Operation of
an Activated Sludge Plant, Presented at the 47th Annual Convention of the Water
Pollution Control Federation, October, 1974.
A-15
-------
APPENDIX B-PLANT VISTS
The wastewater treatment plants included in this appendix were visited to establish
the state-of-the-art for process control of aerobic biological wastewater treatment
facilities throughout the United States.
A statistical breakdown of the types and methods of operation for each plant visit
is included.
B-1
-------
CITY OF AMARILLO, TEXAS
General Description
The River Road Wastewater Treatment Plant consists of screening, primary sedimen-
tation, primary effluent holding pond (balancing), secondary treatment by the activated
sludge process, and post chlorination. The activated sludge process has the flexibility
of operating in the following modes: (1) conventional, (2) step-feed or variations
therein: reaction, contact stabilization and Kraus. Currently, the reaction mode is
used throughout the" year.
Performance and Process Control
They have the flexibility of wasting activated sludge by wasting from the return sludge
flow and/or wasting mixed liquor from the channel conveying the aeration effluent
to the secondary clarifiers. They utilize both wasting modes simultaneously. The
waste RAS is returned to the plant influent for sedimentation with the primary sludge.
The mixture of primary sludge and waste RAS is pumped to a gravity thickener. The
RAS wasting rate remains at a fairly constant rate (the rate is based upon achieving the
desired effect in the primary sludge thickener) while mixed liquor wasting rate is
varied as needs dictate. The digester sludge is pumped to clay-bottom drying beds
with the decant liquor returned to the plant influent.
In order to balance the wastewater flows to the secondary treatment process, the plant
personnel constructed an earthen primary effluent holding pond. It should be noted
that this wastewater treatment facility is situated in the country with no nearby
neighbors to complain about the odors or appearance. This type of flow balancing has
been effective and quite satisfactory.
The plant utilized the conventional mode of the activated sludge process prior to the
City obtaining a new source of water supply from a lake. The lake water possesses a
high sulfate and chloride content with wide swings in the water temperature through-
out the year. After the lake water was used as the City's water source, the plant
began to experience severe bulking problems (probably due to high sulfates and
swings in wastewater [55 - 80° F] temperature). The sludge reaeration mode of operation
was tried with three hours in the reaeration zone and three hours in the aeration
zone. They concluded that the reaeration mode was effective in minimizing their bulk-
ing problems. They now use the reaeration mode throughout the year.
The WAS rates are based upon the maintenance of a constant MLSS concentration.
Response of the process and past experience are basically the guides used to in-
creasing or decreasing the MLSS level. This procedure seems to work quite satis-
factorily in conjunction with the balancing of the primary effluent flows.
The RAS rate was adjusted upon the basis of a daily sludge blanket depth measure-
ment. An electronic sludge blanket detector is utilized to measure the sludge depth
in theclarifier.
DO's of 2-3 mg/l are maintained-at the outlet of aeration basins. DO's greater than
3.5 mg/l are avoided because filamentous organism tend to predominate in the activated
sludge.
B-2
-------
WASTE
ACTIVATED
SLUDGE
ANAEROBIC
SUPERNATANT
SECONDARY
CLARIFIERS
PLANT FLOW DIAGRAM
CITY OF AMARILLO, TEXA-, iVER ROAD PLANT
CONVETIONAL ACTIVAl.J SLUDGE
CURRENT PLAW IN OPERATION - IV68
PLANT FLOW
PLANT DESIGN
AERATION BASINS
CLARIFIERS
AVG DRY WEA'IHER.MGD
MAX DAY,MOD
PEAK HOUR,MOD
X INDUSTRIAL -
14.2
22.0
10.9
14.2
22.0
10.
PLANT LOADING
NUMBER
LENGTH, FT
WIDTH,FT
DEPTH,FT
AREA-EACH,SF
AERATION SYSTEM
2
0.
0.
0.
0.
NUMBER
DIAMETER,FT
DEPTH,FT
AREA-EACH,SF
WEIR LENGTH,FT
WEIR TYPE
SLUDGE REMOVAL
73.
10.5
4418.
430.
V-NOTCH
PLOW
AF.RATION BASINS DESIGN TYPICAL
INF BODB.MG/L I 20. 120.
IMF SS.MU/L 60. 50.
F/M.LP BOD3 REM/Ln MLVSS/DAY 0.2b 0.24
MCRT.DAYS 3.b 3.3
SLUDGE AGE,DAYS 3.0 9.1
MLSS.MG/L 2000. 2000.
MAX MLSS.MG/L 2400.
MIH MLSS.MG/L 1300.
* VOLATILE 8U.
D.o. LEVELS,MG/L 2.0 2.0
AIR APPLIED,SCF/GAL I .5
AIR APPLIED.SCF/LB BODb REM 165V.
RtlURK, X 60. 60.
MAX RETURN, X 78.
DET. TIME.* AVG FLOW,HOURS 6.0 6.0
UbT. TIME.rt A.F.+RETURii.HoURS 3.V 4.1
Db'T. TIMb",«J M.F.+RETURN,HOURS 3.6 3.5
SYSTEM DIFFUSED
TYPE SPARGER
MAX SCFM 14000.
AVG SCFM I I 000.
PLANT PERFORMANCE
EFF BODb.MG/L
% BODS REMOVAL
EFF SS.MG/L
» SS REMOVAL
SVI.ML/GRAM
SO I,GRAM/1OOUL
Ib.O
88.
I 0.0
84.
TYPICAL
Ib.O
88.
10.0
83.
200.
0.50
SECONDARY CLARIFIERS
TYPICAL
MAX DAY
AVG
SURFACE LOADING,GAL/bF/OAY 804. 07V. 804. 017.
WEIR LOADING,GAL/F1/UAY 8256. 0977. 82b6. 6337.
DETECTION TIME.H1IJRS 2.3 2.8 2.3 3.1
SOLIDS LOADING,LRS/SF/HOUR 0.81 0.73 0.81 0.68
B-3
-------
CITY OF AUSTIN, TEXAS
General Description
At the Govalle Wastewater Treatment Plant there are four activated sludge plants fed
from a common influent diversion structure. The accumulated data only pertain to "D"
plant, the newest and most modern. The splitting of the influent flows to A, B, C, and D
plants is accomplished by motorized sluice gate valves at the influent diversion struc-
ture. The contact stabilization mode of the activated sludge process preceded by
screening and grit removal is utilized at "D" plant. There are three feed points into
the aeration basin which function as a means to control the detention time in contact
zone. They attempt to maintain a detention time of 20-30 minutes in the contact zone.
The operator claims that a sludge with optimum settling characteristics is attained by
a contact detention time of approximately 30 minutes.
Performance and Process Control
Excess activated sludge is wasted from the stabilization zone (sludge reaeration) of
the aeration basin and discharged to an aerobic digester with a one-day detention time.
The digester liquor is transferred to 191 acres of oxidation ponds. Except for the
underflow from the chlorine contact tank, there are no recycled flows at "D" plant.
They vary the WAS rates to maintain a suspended solids concentration in the RAS of
3,500-5,000 mg/l. They would also increase the WAS rate if they had an increase in
sludge blanket depth without an increase in SVI. The suspended solids concentration
of the return sludge governs the suspended solids concentration in the stabilization
zone. They use the following ratio to indicate if they need to increase or decrease
WAS rate:
BOD of return sludge, mg/l _
— DU.& TO U. (
Suspended Solids of return sludge, mg/l
The above ratio would seem to indicate the degree of stabilization, which in turn is
related to the sludge age and F/M ratio.
The RAS rates are adjusted to maintain the desired suspended solids concentration
(stabilization zone) while maintaining less than two feet of sludge blanket in the
secondary clarifiers. Small air lifts installed in the clarifiers at fixed two-foot intervals
indicate sludge blanket depth.
They maintain a DO of 1 to 2 mg/l at the outlet of the aeration basin. Aeration rates
also are controlled to maintain a DO of 0.5 mg/l in the secondary clarifiers just prior to
the effluent weir to avoid septicity In the return sludge.
Wastewater temperature is as high as 84° F in the summer and as low as 69° F in the
winter. In the winter, they increase the suspended solids level to compensate for
slower biological activity. Also, they decrease the air rates to avoid excessive DO's
and subsequent filamentous organism growth.
Storm flows are diverted around the activated sludge processes through a bar screen
to a storm overflow clarifier, chlorinated and discharged to the outfall. The underflow
from the clarifier is pumped to the influent diversion structure. The storm overflow
clarifier also serves as the chlorine contact tank for "D" plant.
B-4
-------
I RAW
SEWAGE
STORM WATER OVERFLOW
CONTACT BASIN
STABLIZATION BASIN
WASTE
ACTIVATED
SLUDGE
SECONDARY
CLARIFIERS
SECONDARY
CLARIFIERS
RETURN ACTIVATED SLUDGE
CLARIFIER UNDERFLOW
CHLORINE
CONTACT
AND
CLARIFIER
PLANT FLOW DIAGRAM
EFFLUENT
CITY OF AUSl'IH, TEXAS - W1VALLE PLArtT
CONTACT STABILIZATION
CURRENT PLANT III OPERATION 1«71
PLANT FLOW
PLANT OESIOi<
AERATION BAS1US
CLAB1F1EBS
AVG DRY WEAfHER.MGD 10,0
KAX DAY,MOD 15.0
PEAK HOUR,MOD 15.0
X INDUSTHIAL
PLANT LOADING
9,0
15.0
15.0
10.
NUMBER
LEriCTH.FT
HI DTK,FT
DEPTH,FT
AREA-EACH,SF
IS'.
(3500.
AERATION SYSTEM
hUHHER
DIAMETER,FT
DEPTH,FT
AREA-EACH,SF
HEIR LENGTH,FT
HEIR TYPE
SLUDOE REMOVAL
2
I 10.
12,0
VD03.
6-30,
V-HUTCH
PLCM
AERATION BASINS DESIGN TYPICAL
INF BO05,MG/L 180. 160.
INF SS.MG/L '80, 160.
FVW.LB BODS REU/LB MLVSS/DAY O.?b O.b5
MCBT.DAYS 12.0 18.0
SLUDGE AOE.DAYS 5.3 2.1
MLSS.MC/L 2SOO, JOOU.
MAX ULSS.MO/L 2300.
KIN tilSS,MG/L 1SOO.
X VOLATILE 80.
D.O. LEVELS,MC/L 1.5 I.5
AIR APPLIED,SCF/OAL 2-
AIR APPLIED,SCF/LB BODS BEM 1540.
RETURN, X «4. **•
MAX RETURN, % 67.
DET. TIME.fl AVO FLOW,HOURS 3.6 4.0
DET. TIME,a A.F.+RETURN.HOURS 2.6 2.0
OET. TIME.fl M.F.+RETURn,HOURS I.V I.V
SYSTEit DIFFUSED
TYPE SPAROER
MAX SCFM 17700.
AVO SCFS 11800.
PLANT PERFORMANCE
EFF 0005.MGA.
X BODa REMOVAL
EFF SS,;ffi/L
S SS REMOVAL
SHI,ML/GRAM
SDI.ORMH/IOOML
DESIGN
20.0
US.
20.0
8V.
13.0
yj.
14.0
91 .
no.
0.91
SECONDARY CLARIFIERS
SURFACE L(IAOIMO,OAL/SF/DAY
WEIR LOAUIHU.CAL/FT/DAY
DGTENTIUrt TWE.HDURS
SOLIDS LOADINC.LBS/Sf/IKHM
789.
IS3S.
2.7
0.87
S26.
7692.
4.1
O.o4
MAX DAY
789.
11538.
2.7
0.6V
AVO
474.
6V23.
4,3
0,48
B-5
-------
CITY OF CARSON CITY, NEVADA - WASTEWATER TREATMENT PLANT
General Description
The Carson City Wastewater Treatment Plant is a two-stage trickling filter plant with a
design capacity of 3.75 mgd ADWF. The plant was originally put into operation in 1961
as a primary treatment facility with 1.5 mgd design flow capacity, expanded to the
secondary treatment (as the same design flow) in 1968, and expanded to the current
design flow capacity in 1974. The current ADWF at the plant is approximately 2.1 mgd.
The principal unit processes of the plant are as follows: comminution grit removal via
a grit cyclone, primary sedimentation, flow measurement with Parshall flumes a pri-
mary stage trickling filter, intermediate clarification (with recirculation of the inter-
mediate clarifier overflow to the primary trickling filter), a second stage trickling filter
(with recirculation of unsettled effluent), final clarification, chlorination, and effluent
disposal. Primary and secondary sludges are thickened, centrifuged, and incinerated
at on-site facilities. Centrate is returned to the thickener, and thickener overflow is
returned to the primary sedimentation basins. Effluent disposal is either to the Carson
River or to reclamation at a nearby golf course. In either case, the effluent is held in an
effluent storage pond prior to disposal. Excess flow to the plant during storms is by-
passed from a manhole prior to the plant headworks and from the wet well of the
primary stage trickling filter feed pumps to an oxidation pond. This stored overflow
is recycled back to the plant headworks during dry weather for retreatment. Additionally,
some excess stormwater can be bypassed around the primary stage trickling filter to
the secondary stage trickling filter.
Performance and Process Control
The treatment plant operator has no control over the mode or rate of recirculation
around either trickling filter stage. In both cases, recirculated flow is returned to the
wet wells of the filter feed pumps by gravity flow. The water level in these wet wells
are in turn controlled by level-actuated constant speed pumps. This method of re-
circulation results in a relatively constant hydraulic loading rate to each filter. However,
the organic loading rate to each filter is highly dependent on the hydraulic influent
flow rate to the plant.
B-6
-------
CLARIFIER UNDERFLOW
EFFLUENT ,
4 jSECONDARY
CLARIFIERS
FIRST STAGE
TRICKLING
FILTER
SECOND STAGE
TRICKLING
FILTER
RAW
SEWAGE
PLANT FLOW DIAGRAM
CARSOH CUV, NEVADA
HUH DATE TRICKLINii FILTER
CURRENT PLANT IN OPERATION - IV6B
PLANT FLOW
PLANT DESIGn
TYPICAL
TRICKLIwG FILTERS
CLARlFIERb
AVG DRY HEATHER,MOD
MAX DAY.MGU
PEA< HOUR,MOD
% INDUSTRIAL
7.b
V.S
3.0
1.0
1.1
0.
NUMBER
DIAMETER, FT
DEPTH. FT
AREA-EACH, SF
VOL-EACII.CF
2
80.
7.0
b027.
35186.
NUMBER
DIAMETER, FT
DEPTH, fl
AREA-EACH, SF
HEIR LENGTH, FT
WEIR TYPE
SLUDGE REMOVAL
2
7'j.
12.0
4413.
2bJ.
V- NOTCH
PLO'.','
PLAh'T LOADlHG
PLANT PERHJR.V.AJCE
T'lICKLING FRIERS
Inf DODb,MG/L
IMF Si,MU/L
ORii LOAU,LFiW)D-J/IOL)OCF/DAY
HYD LOAD, MOD/ACRE
RECIRCULA'IIUN.S
50.
110.
I 10.
50.
3V.
bO.
FFF po[)3,MU/L
% BOOS REMOVAL
EFF SS.MC/L
% SS REMOVAL
DEbIGN
24 .u
bo.
21.0
30.0
7v.
20.0
80.
SfCOnDARY CLARIFIERS
SUHhACE LOADINU,GAL/SF/DAY
MhIR L()ADIHG,GAL/Fl/DAY
DElFHlION TIME,HOURS
DESIi;,i
MAX DAY AVG
1698.
30000.
1.3
849.
15000.
2.J
TYPICAL
MAX DAY AVG
900.
loOOO.
2.4
079.
12000.
3.2
B-7
-------
CITY OF DALLAS, TEXAS - CENTRAL PLANT
General Description
The Dallas Central Wastewater Treatment Plant consists of two trickling filter plants—
the older Dallas Wastewater Treatment Plant with single stage standard rate T.F., and
the White Rock Wastewater Treatment Plant with roughing T.F. followed by high-rate
T.F. At both plants, the trickling filters are preceded by screening, grit removal, and
primary sedimentation. '
Performance
The sludge from the final clarifiers is returned to the plant influent for sedimentation
with the primary sludge. The control of sludge withdrawal rates from the final clarifier
is determined by visual observation. The mixture of primary and trickling filter sludge
is pumped to anaerobic digesters for stabilization. The digester liquor is transferred
to another plant for disposal, thus there is no supernatant recycle flows at these plants.
At both plants, final clarifier effluent is returned to the trickling filters to provide
continuous dosing and reasonably constant hydraulic loading. The recirculation rates
are based on maintenance of a specific total flow to the trickling filters. This procedure
seems to be simple and effective.
Process Control
They performed an extensive lab monitoring program; however, the lab results are not
primarily for trickling filter process control. Process control is based on maintaining
a constant hydraulic loading via recirculation of the settled trickling filter effluent.
Operational problems have been experienced with filter flies which have been effec-
tively controlled by flooding each filter (except roughing T.F.) once per week during the
fly season (March to November). It appears that the weekly flooding (especially for
standard rate T.F.) is the explanation for the absence of ponding or odor problems
with the filter operation.
The Dallas Wastewater Treatment Plant (standard rate T.F.) is operating at design
capacity, while the White Rock Wastewater Treatment Plant (high rate T.F. preceded
by roughing T.F.) is operating considerably beyond its design capacity.
B-8
-------
ANAEROBIC
SUPERNATANT
PRIMARY CLARIFIERS
SECONDARY
CLARIFIERS
RECIRCULATION
PLANT FLOW DIAGRAM
CITY OF OALLAS, TEXAS - CiNfBUL PLANT
STO. RATE TRICKLING FILTER
CURftfc'hr PLANT Iri OPERATION - 1940
PLANT FLOW
PLANT DESICh
TYPICAL
TRICKLING FILTERS
CLARIMERS
AVG DRY WEATHER,MOD 32.0
MAX DAY,MOD 60,0
PEAK HOUR,MOD 60.0
% INDUSTRIAL
31.0
60.0
60.0
20.
NUMBED
DIAMETER,FT
DEPTH, FT
AREA-EACH,SF
VOL-EACH.CF
16
176.
7.:
24328.
I 82464.
nUMBEB
LErtClK.FT
WIDTH,FT
DEPTH,FT
AREA-EA.CH,SF
WEIR LENGTH,FT
WEIR TYPE
SLUDGE REMOVAL
j
103.
7s.
ti .2
7SOU.
150.
V-N01CH
FLIGHT
PLANT LOADING
PLAIir PERFORMANCE
TRICKLING FILTERS DESIGN TYPICAL
INF BOD9.MO/L 210, 210.
IMF SS.MO/L 94. 94.
(180 LOAD,LBB()D5/IOOOCF/OAY 19. 19.
HYD LOAD, MOO/ACRE 6. 6.
RECIRCULATION,% 60. 60.
EFF BID5,«0/L
» BODS REMOVAL
EFF SS.MG/L
X SS REMOVAL
25.0
42.0
55,
TYPICAL
2S.O
W,
42.0
5S>.
SECONDARY CLARIFIERS
SURFACE LOADING,GAL/SF/OAY
WEIR LOAD INC,GAL/FT/DAY
DETENTION TIME,HOURS
DESIGrf
MAX DAY
2667,
133333,
O.o
1422.
11)11.
i .4
TYPICAL
MAX DAY
2667.
133333.
O.t
1378.
6 8889,
B-9
-------
CITY OF FORT LAUDERDALE, FLORIDA - PLANT A
General Description
The wastewater treatment plant is a conventional activated sludge plant. The plant is
also designed to operate in the step feed aeration mode. Aeration is provided by
multiple low speed surface aerators. The depth of aerator submergence is varied with
a weir that Increases or decreases the mixed liquor depth. Varying the mixed liquor
depth provides control of the aeration rate.
Waste solids are processed in a wet air oxidation system. The centrate from the oxi-
dized sludge is returned to the headworks. When the wet air oxidation system is
operating, the primary effluent often has a higher BOD concentration than the raw
sewage.
The plant treats wastewaters from light industrial and domestic areas. Average dry
weather flow is 7 mgd of which 60% is due to industry. Peak flows occur in the
summer during tourist season. The plant effluent is discharged to an estuary.
Performance
Effluent concentrations of BOD and SS are typically 25 and 15 mg/l, respectively. The
settled sewage has a BOD of 125 mg/l when the wet airoxidation system is in use.
Process Control
The F/M Is held around 0.15 to 0.2 Ibs BODs removed/lb MLVSS/day. Actual wasting is
controlled to maintain constant MLSS. The organic loading is nearly constant, and a
constant MLSS fixes the F/M. D.O. is maintained around 2 mg/l by adjusting the mixed
liquor depth.
Settleability of the mixed liquor was improved by continual dosing of the return acti-
vated sludge with 4 mg/l of Cl2- Settleability also Improved by over aerating the
biological solids in the aeration basin at night.
B-10
-------
RETURN ACTIVATED SLUDGE
EFFLUENT
SECONDARY
CLARIFIER
SECONDARY
CLARIFIER
PLANT FLOW DIAGRAM
CITY Oh FT. LAUDERDALE, FLORIDA - PLANT A
CONVENTIONAL ACTIVATED SLUDGE
CURRENT PLAN"! IN OPERATION -'1971
PLAIIT FLOW
OESKII
PLANT DESIGi,
AFRATIOl. BASINS
CLARIFIERS
AVG DRY WEATHER,MOD 8.2
MAX DAY,MOD 3.2
PEAK HOUR,MUD 12.0
» INDUSTRIAL
PLANT LOADING
7.0
8.0
12.0
60.
NUMBER
LENGTH,FT
WIDTH.FT
DEPTH,FT
AREA-EACH,SF
2
165.
55.
13.
AERATION SYSTEM
NUMBER
DIAMETER,FT
DEPTH,FT
AREA-EACH,SF
WEIR LENGTH,FT
HE in TYPE
SLUDGE REMOVAL
2
B'j.
12.u
5674.
270.
V-IJOTCH
VACUUM
AERATION BASINS DESIGN TYPICAL
INF BOD5,MG/L 100. 100.
INF SS,MC/L 100. 100.
F/M.LD BODS REM/LH MLVSS/DAY 0.35 0.15
MCHT.DAYS 7.4 7.7
SLUDGE AGE,DAYS 5.3 6.3
MLSS.MG/L 2500. 2500.
MAX MLSS.MG/L 2800.
MIN MLSS,MG/L 2200.
% VOLATILE 75.
D.O. LEVELS,MG/L 2.0 2.0
RETURN, % 64. 46.
MAX RETURN, % I 18.
DET. TIME.8 AVG FLOW,HOURS 5.1 6.1
DET. TIME," A.F.+RETURN.HOCJRS 3.3 4.2
DET. TIME,8 M.F.+RETURN,HOURS J.3 3.8
SYSTEM
TYPE
NUMBER
HP-EACH
MAX LO 02/DAY
AVG LB 02/DAY
MECHANICAL
SURFACE
6
60.
720.
641 .
PLANT PERFORMANCE
EFF BOD5.MG/L
% BOD5 REMOVAL
EFF SS./UG/L
X SS REMOVAL
SVI,ML/GRAM
SDI.GRAH/IOOML
10.0
•JO.
10.0
90.
30.0
70.
20.0
00.
7b.
1.33
SECONDARr CLARIFIERS
SURFACE LOADING,GAL/SF/DAr
WEIR LOADING,GAL/FT/DAV
DETENTION TIME,HOURS
SOLIDS LOADING,LRS/SF/HOUR
MAX DAY
727.
Ib278.
3.0
0.98
DESIGM
AVG
727.
16278.
3.0
O.V8
TYPICAL
MAX :>AV
705.
14815.
3.1
0.86
AVG
617.
12963.
3.5
0.78
B-11
-------
CITY OF FREMONT, NEBRASKA
General Description
Fremont's treatment facilities consist of two primary clarification, followed by fixed-
nozzle trickling filters or roughing filters, followed by intermediate clarification, acti-
vated sludge, final clarification, chlorlnatlon, and discharge. The Fremont, Nebraska
Wastewater Treatment Plant went Into operation in March 1975, and, to date, the
operators have had very few problems with their aerobic treatment units. The plant
design allows a great deal of flexibility in flow schemes. Each unit from the primary
clarlfiers to the final clarlfiers is duplicated; that is, there are two primary ciarifiers,
two trickling filters, two intermediate ciarifiers, etc. The plant piping is such that
effluent from each unit joins at a splitter box where it is combined, then resplit to
flow to each of the two following units. The splitter boxes are designed so that flow
can be split evenly to each unit or any one unit can be taken off line, such as one
aeration tank or final clarifier or intermediate clarifier, and all of the flow can be
routed through the duplicate unit. There have been some mechanical equipment fail-
ures whereby it was necessary to use this capability to reroute the flow around one of
the aeration basins.
Performance and Process Control
Normally, 2.0 mg/l minimum dissolved oxygen (D.O.) is controlled by adjusting the air
flow rate to the diffusers beneath the turbine generators. Control of air flow is accom-
plished manually.
To date, Fremont, Nebraska has not had foaming problems in the aeration basins
other than the normal foaming encountered during start-up. They have had no toxic
loads and no bulking sludge to date. They have had some problems with rising sludge.
Their solution to that problem Is to increase their return rate and to lower the mixed
liquor concentration by wasting sludge. Effectively, this cuts the sludge age down and
tends to inhibit nitrification.
The plant is controlled on the basis of suspended solids balance. A mixed liquor
suspended solids between 3,000 and 4,000 mg/l is the goal that they strive for. The
sludge is wasted based upon the siudge blanket depth in the ciarifiers. Sludge is
wasted to lower the depth of the sludge blanket. The sludge blanket's depth is meas-
ured regularly by means of a flashlight on a long pole.
The return sludge system can be operated in an automatic or manual mode. In the
automatic mode, the return sludge rate may be set proportionally to influent flow.
They have had problems with flow proportional RAS In the low plant influent flow
ranges. The flow rate is set by throttling RAS with a motor-operated butterfly valve.
This valve and a magnetic flow meter are in the gravity line between the clarifier and
the RAS sump. The RAS flows by gravity to a sump where it is picked up by a pump
and returned to the aeration basin. The pumping rate is determined by sump level. The
present method of operating is to set the return sludge rate manually at some fixed rate.
Sludge is wasted with a system similar to the RAS system. A butterfly valve on a
gravity line is manually set to waste at a fixed rate through a mag meter to a WAS sump.
WAS is pumped from the sump to a gravity thickener where it is mixed with inter-
mediate sludge and primary sludge. An alternative wasting point is the primary
clarifier. The solids handling facilities have the potential of affecting the activated
sludge process in that they may limit the rate of sludge wasting and thus affect the
suspended solids level In the aeration basins under certain conditions.
B-12
-------
WASTE ACTIVATED SLUDGE
PLANT FLOW DIAGRAM
CITY OF t'-RF.-UMT,
COMPLETE HX AC1IVATED SLUDGE KITH ROUGHING HLTERS
CURRENT PLAHT IN OPERATION - 1975'
PLANT FLOW
PLAHf DESIGN
OSS IOn
TYPICAL
AERATION BASINS
CLARIKIEIKi
AVG DRY IIFATHEU.MGD 7,3
KAX DAY,MOO IO.S
PEAK HUUH,«00 10.0
•4 INDUSTRIAL
PLANT LOADING
TRICKLING FILTERS DESIGN
INF BODs.MG/L 000.
INF SS.MO/L 400.
ORG L»AO,LSBODs/l OOOCF/DAY i>80.
HYD LOAD, MOD/ACRE 127,
RECIRCULATION,* IbO.
4.0
o.O
a.o
40.
TYPICAL
600.
400.
311.
6B.
ISO.
NUMBER
LENOM.Fl
KIUTH.FT
DEPTH, Ff
AI1EA-?SCH,SF
2
100.
100.
8.a
10000.
NUMHER
AERA1KIN SYSTk.M
ijYSTE'J MECHANICAL
TYPE TUHOIHE
MUMBER 8
HP-EACH SO.
MAX LB D2/OAY 480.
AVG LB 02/DAY 480.
DEPTH, FT
AREA-EACH, SF
WEIR LEHCTH.Ff
WEI1? TYPE
SLUDUE BEMHVAL
1'RICKLING FILTERS
2
VI).
10,0
0302.
b2/.
V-MJTCH
VACUUM
NUMBER
LENGTH,FT
HIDTH.FT
DEPTH,FT
2
80,
40.
10.0.
AREA-EACH,SF 3217.
VI1L-EACH.CF 32170.
AERATION BASICS
IHh D()D3,MO/L
I (IF SS.MO/L
F/rt,LP BflDb BEh/LB ML^SS/DAY
HCRT.DAYS
SLUD06 AGE,DAYS
XLSS.MG/L
MAX MLSS.MG/L
MIN MLSS.MG/L
X VOLATILE
D.O. LEVELS,HG/L
RETURN, *
MAX RETURN, %
DŁT. TIME.o AVG FLOW,HOURS
DEI. TIME.8 A.F.+RETURH.HOURS
DET. TI«E,« H.F.*RETURN,HOURS
SECIMDABY CLARIFIERS
SURFACE LOADIHU.uAL/SFXDAY
HFIS LOADING,GAL/Ff/DAY
DETEHTION TIME.HlIUnS
SOLIDS LOADING,LBS/SF/HOUR
DESlGil
ZOO.
100.
0,40
0,
S.6
3400.
2.0
7S.
250.
3.8
2.7
2.1
DESIGN
MAX DAY
825.
9961. 7
2,2
1 ,2S
TYPICAL
180.
90.
0.20
li .7
11 .6
3500.
7000.
3000.
60.
1 .0
IbO.
7.2
2.9
2.4
MO
580.
1 16.
3.0
0.98
PLANT
EFF BOOb.HG/L
X BODS REMOVAL
EFF SS,HO/L
% SS REMOVAL
SV I. ML/GRAM
SD I. ORAM/ 100 ML
TYPICAL
«AX DAY AVO
472. 314.
s«M. 379S.
3,8 5,7
1.15 0.90
PEHFORMANCE
DESIGN
40.0
93.
20.0
95.
II ,0
98,
15.0
96.
100.
1 ,00
B-13
-------
INDIANAPOLIS, INDIANA - WASTEWATER TREATMENT PLANT NO. 2
SOUTHPORT ROAD AND WHITE RIVER
General Description
The activated sludge system can be operated as conventional, step aeration or bio-
absorption process. Various processes are run throughout the year, and are depend-
ent upon waste strength and influent flow characteristics.
Hydraulic monitoring, control, and distribution is the primary operating features. All
force main type process flows are controlled by means of magnetic flow meters with
remote readout and remotely-actuated valves. Likewise, gravity (open channel) flow is
monitored and controlled by Parshall flumes with flow indicators and remotely-actuated
slide gates. One exception to the above is that gravity flows to the various points in
the aeration basins are distributed by manually-operated slide gates.
Performance
Process balancing is facilitated by the ability to transfer RAS or WAS flows between
unit processes within the plant. Another unique design feature is that primary sludge
can be introduced into the secondary clarifiers. As a safety feature only, influent
wastewater flows can be bypassed to other in-plant processes.
Process Control
Fundamentally the plant is operated simply by the sludge blanket in the secondary
clarifier. The RAS vs. WAS proportion is determined by the current BOD loading on the
aeration basins. The sludge draw-off is adjusted once to twice a day based on diurnal
flow, and/or upon the observation of shock loading.
B-14
-------
RAW
SEWAGE
WASTE SLUDGE
EFFLUENT
AERATION BASINS
MIXED LIQUOR
RETURN ACTIVATED SLUDGE
SECONDARY
CLARIFIERS
PLANT FLOW DIAGRAM
WASTE
ACTIVATED
SLUDGE
CITY OF INDIANAPOLIS, IIIDIAHA - SOUTHPOR1 PLANT
CONVENTIONAL ACTIVATED SLUDOE
CURRENT PLANT IN OPERATION - 1968
PLANT FLOW
PLANT DESIGN
DESIGN
TYPICAL
AERATION BASINS
CLARIFIERS
AVJ DRY WEATHER,MOD 28.0
MAX DAY,MOD 42.0
PEAK HOUR,MOD 42.0
% INDUSTRIAL
PLANT LOADING
35.0
4b.O
00.0
86.
NUMBER
LENGTH,FT
WIDTH,FT
DEPTH,FT
AREA-EACH,SF
4
752.
30.
15.u
22560.
AERATION SYSTEM
NUMBER
DIAMETER,FT
DEPTH,FT
AREA-EACH,SF
WEIR LENGTH,FT
HEIR TYPE
SLUDGE REMOVAL
100.
8.0
7854.
314.
V-NOTCH
PLOW
AERATION BASINb DESIGN TYPICAL
INF BOD5.MG/L 240. 110.
INF SS.MG/L I 12. 75.
h/M.LB BODS REM/LO MLVSb/DAY O.bO 0.27
MCRT.DAYS 7.5 o.b
SLUDGE AGE,DAYS 5.8 o.7
MLSS.MU/L 1800. 1725.
MAX MLSS.MG/L 2000.
HIM MLSS.MG/L 1300.
X VOLATILE 70.
D.o. LEVELS,MG/L
-------
CITY OF KENOSHA, WISCONSIN
General Description
The water pollution control plant facilities at Kenosha, Wisconsin consist essentially
of a conventional activated sludge process, with solids treatment incorporating flota-
tion thickening, anaerobic digestion, and dewatering by pressure filters.
This plant is designed to handle an average dry weather flow of 23 mgd. Currently, the
industrial contribution is averaging 67 percent of the average dry weather flow. Since
the combined sewer system contributes high hydraulic loads on the facilities during
rainfall, the utility also placed in operation the world's first biosorption treatment
system. This is a 20 mgd project to demonstrate the biological treatment of combined
sewer overflows during periods of rainfall.
Performance and Process Control
The activated sludge system consists of four single-pass basins, with return activated
sludge applied at the influent channel. Variations of RAS application other than at the
influent channel are insignificant in importance. The alternate application points are
at the beginning and end of the first aeration basin. Dissolved oxygen in the various
basins .are maintained at a level of 1 to 2 mg/l. Air feed rates are generally not
varied, due to difficulty in manually adjusting these rates.
The four final clarifiers are the peripheral feed, center suction sludge discharge variety.
A common header with connections to each clarifier is used for pumping. Each pump
is variable speed; however, only three pumps are provided for the four tanks, thus
making controlled takeoff difficult. Although the pumps are variable speed, the RAS
flow rates are not varied. The rate of flow is controlled through the use of a magnetic
flow meter in the line returning to the aeration basin.
The amount of waste activated sludge (WAS) is controlled by the MLSS concentration
level in the aeration basin. WAS is taken from the RAS line and fed to an open aerated
pit, where eventually the sludge will be fed to the flotation thickeners. Rate is varied
to maintain an MLSS level between 2,500 to 3,000 mg/l.
The most serious control problem is that associated with the hydraulic distribution of
flow to the four secondary clarifiers. The problem arises from the fact that the last
expansion added a secondary clarifier which itself is approximately 50 percent larger
than the initial three secondary clarifiers. The distribution channels were designed
solely to feed the initial three clarifiers; therefore, flow to the new and larger clarifier
is much below design capacity. Consequently, during large increases in flow, the
remaining three clarifiers tend to be hydraulically overloaded.
B-16
-------
ANAEROBIC
SUPERNATANT
RETURN
PRIMARY CLARIFIERS
SECONDARY
CLARIFIERS
PLANT FLOW DIAGRAM
CITY OF KENOSHA, WISCONSIN
CONVENTIONAL ACTIVATED SLUDGE
CURRENT PLANT IK OPERATION - 1972
PLANT FLOW
DESIGN
TYPICAL
PLANT DESIGN
AERATION 1ASIN5 CLARIFIERS
AVG DRY HEATHER,MOD 23.0
MAX DAY,MOD 26.0
PEAK HOUR,MOD 30.0
% INDUSTRIAL
PLANT LOADING
AERATION BASINS
INF BODb,MG/L
INF SS.MG/L
F/M.LB BODb REM/L1 M.V55/DAY
MCRT.DAYS
SLUDGE AGE,DAYS
MLSS.MG/L
MAX MLSS.MG/L
MIN MLSS.MG/L
X VOLATILE
D.O. LEVELS,MG/L
AIR APPLIED,SCH/GAL
AIR APPLIED.SCF/LB BODS REM
RETURN, %
MAX RETURN, %
DET. TIME,* AVG FLOH,HOURS
DET. TIME,» A.F.+RETURN.HOURS
DET. TIME,8 M.F.+RETURN .HOURS
SECONDARY CLARIFIERS
SURFACE LOADING,UAL/SF/DAY
WEIR LOAD ING,GAL/FT/DAY
DETENTION TIME, HOURS
SOLIDS LOAD ING,LBS/SF/HOUR
20.0
23.0
30.0
67.
NUMBER
VOLUME,
CU FT
AERATION SYSTFM
NUMBER
DIAMETER,FT
DEPTH,FT
AREA-EACH,SF
WEIR LENGTH,FT
HEIR TYPE
SLUDGE REMOVAL
100.
I I .0
7854.
25o.
V-NOTCH
VACUUM
G
DESIGN
80.
7b.
0.13
0.
7.b
2500.
2.0
54.
47.
3.8
2.6
2.4
DESIGN
MAX DAY AVG
828. 732.
25391 . 22461 .
2.4 2.7
TYPICAL
73.
75.
0.16
B.O
8.8
3600.
4000.
2000.
63.
1 .5
0.6
I 121 .
46.
4.4
3.0
2.7
MAX
828
22461
2
1.01 0.93 1
SYSTEM DIFFUSED
TYPE SPARGER
MAX SCFM 13350.
AVG SCFM 8700.
PLANT
EFF BODS, MG/L
% K1D3 REMOVAL
EFF SS.MG/L
% SS REMOVAL
5V I, ML /GRAM
SDI, GRAM/100 ML
TYPICAL
DAY AVO
637.
19531 .
.7 3.1
.29 1.17
PERFORMANCE
DESIGN
10.0
87.
10.0
87.
6.0
92.
31 .0
59.
I lo.
0.86
B-17
-------
LAS VEGAS, NEVADA-CLARK COUNTY SANITATION DISTRICT NO. 1
TREATMENT PLANT
General Description
In 1956 Clark County Sanitation District No. 1 put their 12 mgd trickling filter in service.
In 1974 an addition to the original plant was put into operation, increasing the capacity
to a total of 32 mgd. At this time, solids incineration was added.
Performance and Process Control
The treatment plant has had few operating problems, being a high-rate single-stage
filter plant. The main problems have been mechanical maintenance problems rather
than serious operational problems. There is enough capacity in process units to pro-
vide standby/backup capability when necessary. Here again, operation of the plant is
not significantly affected by the weather. One problem experienced at this plant has
been large amounts of freshwater snails accumulating in the chlorine contact tank.
Anticipating a continuation of this problem, a traveling bridge collector was installed
in the new chlorine contact tank, but the problem has been diminishing steadily since
the new portion of the plant has been put into operation. There have been operations
problems with the incinerator which have no effect on the operation of the trickling
filter plant.
B-18
-------
RAW
SEWAGE
AEROBIC DIGESTER SUPERNATANT
PRIMARY
CLARIFIERS
CLARIFIER
UNDERFLOW
PLANT FLOW DIAGRAM
LAS VEOAS, NEVADA - CLARK COUNTY PLANT
STANDARD RATE TRICKLING FILTER
CUBBErfT PLANT IH OPERATION - 1974
PLANT FLOW
PLAOT DBS I Gil
fBICKLING FILTERS CLAPIFIEHS
AVO DRY HEATHER, UDD 32.0
MAX DAY,MOD 53.0
PEAK HOUR,MOD S3.0
* INDUSTRIAL
27,0
34.0
34.0
0.
14UHBER 5
DIMEfER.FT 190.
DEPTH,FT 5.0
ARI-A-EACH.SF 283S3,
WL-EMM.CF 141744,
NUMBER
DIAMETER,FT
DEPTH,FT
AREA-BACH,SF
HEIR LEMCTH.FT
NEIR TYPE
SLUDUE
100.
y.s
78S4.
020.
V-NOTCH
PLOW
PLANT LOADING
PLANT PERFORMANCE
TRiCKLINC FILTERS DF.SIOi) TYPICAL
IHF BOOa,MG/L 147. 74.
INF SS.Mli/L 88. 220.
ORG L()AD,LBBOD5/IOOOCF/DAY 5b. 24.
ma LOAD, MOO/ACRE 2V. 37.
RECIRCULA1! <)«,!Ł 190. 340.
EFF note,MG/L
X BODb REMOVAL
EFF SS,im/L
S SS REMOVAL
20.0
86.
20.0
77.
TYPICAL
7.4
VO.
22.0
90.
SECONDARY CLAfHFrEDS
SURFACE LIIADING.GAL/5F/DAY
WEIR LOADING,UAL/Ff/DAY
DF.fEnTHW flHE,HOURS
DESIGN
1350.
17097.
1.2
TYPICAL
MAX JAY AVG
10323.
2.0
loves.
) .v
688.
8710.
2.4
B-19
-------
LOWER POTOMAC POLLUTION CONTROL PLANT, LORTON, VA.
General Description
The wastewater treatment plant is a conventional activated sludge plant utilizing the
contact stabilization mode of operation. Diffused aeration is provided by positive
displacement blowers. Each aeration basin has three passes with the first pass used
for reaeration.
Waste solids are transferred to gravity thickeners followed by vacuum filters and
incineration. Thickener effluent, filtrate, and spent cooling water are returned to the
plant headworks.
The plant treats wastes primarily from domestic sources. Average dry weather flow is
15.0 mgd. Design average flow is 18.0 mgd. Effluent is discharged to a creek.
Performance
Effluent concentrations of BOD and suspended solids are typically 14 and 13 mg/l,
respectively. Settled wastewater has a typical BOD concentration of 220 mg/l. The
side stream flows, being transferred to the plant headworks, causes higher organic
loadings.
Process Control
The primary control parameter for this plant is the Sludge Compaction Ratio (SCR)
method. The SCR is computed by obtaining mean values of 24 30-minute settling tests
and 24 spin(centrifuge) tests of hourly MLSS grab samples. The SCR is equal to the
settling mean value divided by the spin mean value times 83.4. The number for opera-
tional control is computed by multiplying the SCR by 100 and adding the settling mean
value. For this plant, the control number of 500 appears provide optimum operation.
The control number is maintained by solids wasting and is also used as an indicator
for the addition of polymers. At this time no correlation of the control number has
been made to other process controls such as F/M, MCRT, etc.
B-20
-------
tWASTE
SLUDGE
PRIMARY
CLARIFIERS
AERATION BASINS
SETTLED SEWAGE
RETURN ACTIVATED SLUDGE
FILTRATE RETURN
SECONDARY
CLARIFIERS
WASTE
ACTIVATED
LSLUDGE
RAW
SEWAGE
PLANT FLOW DIAGRAM
CITY OF LORTUil. VIRGINIA - LOWER POTOMAC PLANT
STEP FEED ACTIVATE!! SLUDOE
CURRENT PLANT II) OPERATION - 1973
PLAMT FLOW
DESIGII
TYPICAL
PLANT DESIGN
AERATION 3ASINS CLARIFIERb
AVU DRY WEATHER,MOD 18.0
MAX DAY,MUD 20.0
PKflK HOUH.MGD 22.0
X INDUSTRIAL
Ib. I
20.0
22.0
30.
PLANT LOADING
NUMBER
LENGTH,FT
WID1H.FI
DEPTH,FT
AREA-EACH,SF
AERATION SYSTEM
2
0.
0.
0.
0.
HUMHER
DIAMETER,FT
DEPTH,FT
AREA-EACH,SF
HEIR LENGTH,FT
HEIR TYPE
SLUDGE REMOVAL
3
120.
12.0
I 1310.
367.
V-NOTCH
VACUUM
AERATION OASIHS DESIGN TYPICAL
INF BOD5,JIG/L 200. 200.
INF SS.MG/L 200. 200.
FAI.Ln 8005 REM/L3 MLVSS/DAY 0.30 I.3B
MCRf.DAYS 5.0 1.5
SLUDGE AGE,DAYS 0.6 0.8
MLSS.MG/L o25. 625.
MAX MLSS.MG/L 800.
Mill MLSS.MG/L 500.
Ł VOLATILE 8i.
D.O. LEVELS,MG/L 1.5 2.0
AIR APPLIED.SCF/GAL 1.2
AIR APPLIED,SCF/LB BODS REM 804.
RETURN, i 46. 46.
MAX RETURN, % 199.
DET. TIME.e AVG FLOW,HOURS 5.1 6.0
DET. TIME,a A.F.+RETURN.HOURS 3.6 4.1
[JET. TIME,«i M.H'.+RETURrt.HOURS 3.4 3.4
SYSTEM DIFFUSED
TYPE SOCK
MAX SCFM 31000.
AVG SCFM 13000.
PLAMT PERFORMANCE
EFF BODS,MG/L
X BODS REMOVAL
EFF SS.MG/L
% SS REMOVAL
SVI,ML/GRAM
SDl.GRAH/IOOML
DESIGII
lb.0
93.
15.0
93.
TYPICAL
15.0
93.
15.0
93.
ISO.
0.56
SECONDARY CLARIFIERS
SURFACE LOADING,UAL/SF/DAY
HEIR LOAD ING,GAL/FT/DAY
I3EIENTION TIME,HOURS
SOLIDS LOADING,LRS/SFAIOUR
DESIGN TYPICAL
MAX DAY AVG MAX DAY AVG
589. 531. S89. 443.
18165. 16349. 18165. 13715.
3.7 4.1 3.7 4.8
0.17 0.16 0.17 0.14
B-21
-------
CITY OF MADERA, CALIFORNIA
General Description
The wastewater treatment plant incorporates the activated biofiltration (ABF) mode of
operation. An alternate mode, single-stage high-rate filtration, is also available. The
normal mode of operation is with the activated biofiltration process. The ABF process
consist of loading two parallel filters at rates of approximately 560 gpm/ft2 followed
by sedimentation. Solids from the settling tanks are returned at a 2:1 ratio, and mixed
with primary effluent before being applied to the filters. Waste solids are transferred
to the plant headworks and settled in the primary clarifiers. The plant treats waste-
water primarily from domestic sources and receives industrial wastes during the
canning season. Average dry weather flow is 2.7 mgd with maximum day peaks of
3.5 mgd. Effluent is discharged to evaporation-percolation ponds.
Performance
Effluent concentrations of BOD and suspended solids are typically 30 and 11 mg/l,
respectively.
Solids concentrations from the filter effluent are typically 2,600 mg/l. Control of these
solids are maintained by the amount of solids wasted from the system.
Process Control
The only process control currently used is maintaining the filter effluent solids at
optimum concentrations for various wastewater characteristics during specific times
of the year. This control is maintained by wasting solids from the system.
B-22
-------
RAW SEWAGE
PRIMARY CLARIFIERS
WASTE
SLUDGE
RETURN
SLUDGE
WASTE SLUDGE
RECIRCULATION
EFFLUENT
PLANT FLOW DIAGRAM
SECONDARY
CLARIFIER
SECONDARY
CLARIRER
CITY OF MADERA, CALIFORNIA
ACriVATED BIO-FILTER
CURRENT PLANT IN OPERATION - 1972
PLAUT FLOW
PLAN!' DEMON
TRICKLINO FILTERS
CLARIFIERS
AVO DRY HEATHER,MOD 7.0
MAX DAY,MOD II.0
PEAK HOUR,MOD 1 I .0
% INDUSTRIAL
2.7
3.5
5.0
50.
NUMBER
LENGTH, FT
WIDTH,FT
DEPTH,FT
AREA-EACH,SF
VOL-EACH.CF
2
60.
60.
12.0
3739.
44871 .
HUMRER
DIAMETER,FT
DEPTH,FT
AREA-EACH,SF
WEIR LENGTH,FT
WEIR TYPE
SLUDGE REMOVAL
2
73.
12.0
4413.
236.
V-NOTCH
VACUUM
PLANT LOADING
PLANT PERFORMANCE
TRICKLINO FILTERS DESIGN
INF BOD5.MG/L I 10.
INF SS.MO/L 110.
ORG LUAD.LRBOD5/1000CF/DAY 75.
HYD LOAD. MOD/ACRE 160.
RECIRCULATION,* 200.
97.
90.
24.
47.
200.
EFF BOD5.MG/L
% BODS REMOVAL
EFF SS.MG/L
X SS REMOVAL
DESIGN
30.0
73.
30.0
73.
TYPICAL
20.0
79.
22.0
76.
SECONDARY CLARIFIERS
SURFACE LOADING,GAL/SF/DAY
WEIR LOADING,GAL/FT/DAY
DETENTION TIME,HOURS
DESIGN
MAX DAY
TYPICAL
MAX DAY
1245.
23355.
1.7
792.
14862.
2.7
396.
7431.
5.4
306.
5732.
7.0
B-23
-------
CITIES OF NEENAH-MENASHA, WISCONSIN - SEWAGE TREATMENT
PLANT
General Description
The treatment facilities are designed to operate primarily as a conventional activated
sludge (CAS) or contact stabilization system. The contact stabilization mode has been
tried periodically, and the results have been unsatisfactory. Tapered aeration was
tried but resulted in clogged diffusers. Therefore, CAS is the only feasible mode of
operation.
Performance
The primary facilities are designed to discharge only 13 mgd to the activated sludge
system. Although the aeration facilities are designed to handle 18 mgd, the RAS held
constant at 9.0 mgd make the ADWF to the system near 22 mgd. Flow in excess of 13
mgd out of the primaries is hydraulically diverted to the interceptor sewer.
The RAS enters a wet well and is controlled by a telescopic valve arrangement. RAS
and WAS are pumped from the wet well. The WAS is flotation thickened and pumped
to a holding tank. RAS is returned to the head of each of the two aeration basins.
Process Control
Contrary to practice in most plants, the desire in operation is to achieve a relatively
high sludge level in the final tanks (correlates with the high SVI average of 210-220
ml/g). Denser sludge blankets are particularly susceptible to lifting, with subsequent
poor effluent quality. Standard practice at this facility is to maintain a level of sludge
near the effluent weirs. The high SVI level is achieved by maintaining 3-4 mg/l DO in
the effluent from the aeration basin.
High DO in the aeration basin is desirable, since at lower levels odor problems persist.
B-24
-------
RAW
SEWAGE
FILTRATE
AERATION BASINS
WASTE
SLUDGE
WASTE ACTIVATED SLUDGE
RETURN ACTIVATED SLUDGE
SECONDARY
CLARIFIERS
EFFLUENT
PLANT FLOW DIAGRAM
CITIES OF iJFGHAH-MENOSHA, WISCONSIN
CONVENTIONAL ACTIVATED SLUDOE
CURRENT PLANT IN OPERATION - 1967
PLANT FLOW
DESIGN
PLANT DESIGN
AERATION BASINS CLARIFIERb
AVU DRY WEAIHER.MGD 18.0
MAX DAY.MGD 30.0
PEAK HOUR,MOD 4O.O
» INDUSTRIAL
PLANT LOADING
13.7
30.0
46.0
60.
NUMBER
LENGTH,FT
WIDTH,FT
DEPTH,FT
AREA-EACH,SF
2
540.
30.
16.0
I 0200.
AERATION SYSTEM
NUMBER 2
DIAMETER,FT 120.
DEPTH,FT 11.6
AREA-EACH,SF I I 310.
WEIR LENGTH,FT 377.
WEIR TYPE V-NOTCH
SLUDGE REMOVAL VACUUM
AERATIO.I BASINS DESIGN TYPICAL
I* 3003,HG/L 144. 123.
IliF SS.MG/L 100. 78.
F/M.LB DODb REM/LB HLVSS/DAY 0.22 0.12
rfCHT.DAYS 0. 0.7
bLUDGE AGE.DAYS 7.D I4.b
MLSS.MG/L 3iOO. 4000.
MAX MLSS.MU/L i>000.
Mill f
-------
CITY OF PALO ALTO, CALIFORNIA
General Description
Due to the inability of the primary plan to meet the more strict discharge requirements,
in 1966 it was decided to expand the plant and also treat the wastes from the cities of
Mountain View and Los Altos by the activated sludge process.
A regional plant was.constructed with primary treatment, activated sludge secondary
treatment and solids incineration, the capacity being 35 MGD dry weather flow and
53 MGD wet weather flow. The regional plant was placed in operation in 1972. Plans
for the future include expansion to 75 MGD dry weather flow and separate treatment
of toxic industrial wastes.
Operation
The plant normally operates in the Complete Mix mode, but has the capability of
operating in the Reaeration or Contact Stabilization mode. Reaeration has been tried
at the plant, with little success. Sludge (RAS) is returned from the final clarifier with a
portion being wasted. Waste sludge and primary sludge are thickened prior to de-
watering and incineration.
B-26
-------
SETTLED SEWAGE
RAW SEWAGE
PRIMARY
CLARIFIERS
WASTE
SLUDGE
I
RETURN
ACTIVATED
SLUDGE
WASTE
ACTIVATED
SLUDGE
AERATION
BASINS
J
WASTE
ACTIVATED
SLUDGE
MIXED LIQUOR
SECONDARY
CLARIFIERS
PLANT FLOW DIAGRAM
I EFFLUENT
PLANT FLOW
CITY OF PALO ALTO, CALIFORNIA
WIMPLETE MIX ACTIVATED SLUDGE
CURMENT PLA.JT IN OPERATION - 1971
PLANT DESIGN
TYPICAL
AERATION BASINS
CLARIHERS
AVG DRY WEATHER,MOD 3b.O
MAX DAY,MOD 70.0
PEAiC HOUR,HOD 70,0
X INDUSTRIAL
PUH1 LOADING
20.5
33,0
7u.o
50,
NUMBER
LENGTH, ft
WIDTH, FT
DEP1H.FT
AREA-EACH,SF
135.
120.
15.0
10200.
AERATION SYSTEM
NUMBER
LENGTH,KI
WIUTH.F1
DECTH.H:
AREA-EACH.Sf
WEIR LENGTH,FT
HEIR TYPE
SLUDGE REMOVAL
I Its,
1 1 ,0
1322!).
448.
y-NOTCH
VACUUM
AERATION BASIHS DESIGN TYPICAL
INF ROD5.MG/L loO, 100
INF SS.MO/L 84. 60
F/M.LR BODS REniXLB MLVSS/DAY 0.30 0,26
MCRJ'.DAYS 12,0 3 a
SLUDGE AGE,DAYS 0. 6,9
MLSS,MU/t 2600. 1600,
MAX MLSS.Mli/L 1800.
HIH MLSS.MG/L 1000.
* VOLATILE 80
U.I). LEVELS,KC/L \ ,b 20
RETURN, % 130. 60.
MAX RETURN, * j 30.
DEI. TIME.d AVG FLUW.HOUSS S.O 6.6
PET. TIMŁ,t» A.F.*RETURH,!K)URS 2,S 4 I
DET, TIME.* «.F.*BETUR»,HOURS 1.7 36
SYSTEM MECHANICAL
TYPE TURBINE
rtUKBER 16
HP-EACH 50.
HAX L3 HZ/DAY 20000.
AVG LH 02/DAY 20000,
PLANT PERFOEHAriCE
EFF BODb,MO/L.
S BOD5 REMOVAL
EFF SS.MG/L
% SS REMOVAL
SVI,ML/GRAM
SOI.GRAM/IOOML
DESIGN
20.0
88.
2U.O
71 .
IYPICAL
14.0
86.
14.0
77.
2 00,
0,50
SECONDARY CLARIFIERS
SURFACE LOADING,GAL/SF/DAY
WEIR LOADING,GAL/i-'l/QAY
DEl'ENlIOn 1'WE. HOURS
SOLIDS LOADINO.LRS/SF/HDUn
DESIUN
MAX DAY
i 323.
39O63.
I . 78
«o2.
19531.
3.0
MAX DAY
624.
18415.
3.2
0.1S
AVG
501 .
I 4781).
3.V
0.42
B-27
-------
CITY OF PHOENIX, ARIZONA - 91st AVENUE SEWAGE TREATMENT
PLANT
General Description
Initially, a 5 mgd trickling filter plant was located at the 91st Avenue site. This plant
treated wastewater from Glendale and the west side of Phoenix until late in 1964 when
Stage I of the 91st Avenue activated sludge plant was put into operation. The capacity
of this first stage was 45 mgd and was part of a five-city (regional) wastewater project.
In 1969 a 15 mgd Stage II was put into operation, giving the plant a total capacity of
60 mgd. At present, the 91st Avenue Sewage Treatment Plant is treating wastewater
from the cities of Glendale, Phoenix, Tempe, Scottsdale, Mesa, and Sun City. Young-
town and Peoria will be contributing their flows to the plant in the near future. Con-
struction is underway to expand the plant further, and future plans call for an eventual
capacity of 240 mgd.
Performance and Process Control
The plant is currently being operated in the conventional mode, but has the capability
of being operated in the step-feed mode. The 91st Avenue plant has experienced much
the same type of problem with frothing in the aeration basins as the City of Tucson,
and they solved it in the same manner by reducing the MLSS level to the 1,200 -1,600
mg/l range. As in the case of the Tucson plant, this, along with a low sludge age of
2 to 4 days, seems to remedy the frothing problem.
B-28
-------
ANAEROBIC
SUPERNATANT
RETURN
RETURN ACTIVATED SLUDGE
AERATION BASINS
RAW
SEWAGE
WASTE
ACTIVATED
SLUDGE
SECONDARY
CLARIFIERS
EFFLUENT
PLANT FLOW DIAGRAM
CITV OF PHOENIX, ARIZONA
CONVENTIONAL ACTIVATED SLUDGE
CURRENT PLANT III OPERATION - I 9o9
PLANT PLOW
PLANT DESIGU
TYPICAL
AE BAT ION BASINS
CLARIFIERS
AVG DRY HEATHER,,MOD 60,0
MAX DAY,MOO 90.0
PEAK HOUR,MOD 105,0
X INDUSTRIAL
PLANT LOADING
60.0
90,0
105.0
50.
NUMBER
LENGTH,FT
WIDTH,FT
DEPTH,FT
AREA-EACH,SF
4
310,
100.
15.4
31000.
AERATION SYSTEM
NUMBER
LENGTH,FT
WIDTH,FT
DEPTH,FT
AREA-EACH,SF
WEIR LENOTH.FT
WEIR TYPE
SLUDGE REMOVAL
24
ei.
47,
8.0
4254.
300.
V-NOTCH
FLIGHT
AERATION BASINS DESIGN TYPICAL
INF BOD5.1M/L 235. 118.
INF SS.MG/L lib, 45.
F/M.LB BODS REM/LB MLVSS/DAY 0.67 0.39
MCHT.DAYS 2.7 2.2
SLUDGE ACE,BAYS 3.2 5.2
MLSS.MG/L 2000. 1400.
MAX M_SS,MQ/L 1«00.
KIN MLSS,«0/L 1200.
% VOLATILE n-
D.O. LEVELS,MG/L 2.0 2.O
AIR APPLIED,SCF/OAL 1.7
AIR APPLIED,SCF/LB BOD5 I?EM 21 14.
RETURN, % 53. 30.
MAX RETURN, * 80.
DET. TIHE,« AVG FLOW,HOURS 5.8 5.8
DET. TI«E,« A.f.-»BETURN,HOUffS 3.8 4.5
DET. TIME,* H.F.tRETURN,HOURS 2.8 3.2
SYSTEM DIFFUSED
TYPE SPAROER
MAX SCFM 7B600.
AVG SCFM 72000.
PLANT PERFORMANCE
EFF BODS,MG/L
% BODS REMOVAL
iFF SS.MG/L
X SS REMOVAL
SVI,ML/GRAM
SDI.GRAH/IOOW.
DESIGN
20.0
91 .
29.0
SO.
TYPICAL
20.0
83.
52.0
20.
100,
1.00
SECONDARY CLARIFIERS
SURFACE LOADING,GAL/SF/DAY
HEIR LOADING,GALXFT/DAY
DETENTION TIKE,HOURS
SOLIDS LOADING,L8S/SF/Hf!UR
MAX DAY
882.
12500.
1.6
0.83
AVO
588.
8333.
2.4
0.63
TYPICAL
MAX DAY
882.
12500.
1.6
0.51
AVG
588.
8333.
2.4
0.37
B-29
-------
VILLAGE OF RIDGEWOOD, NEW JERSEY
General Description
The wastewater treatment plant is a conventional activated sludge plant. Design flexi-
bility of the plant allows the contact stabilization mode which is the current mode of
operation. Diffused aeration is provided by low pressure centrifugal blowers.
Waste solids are processed by gravity thickening and anaerobic digestion. Additional
side stream flows such as digester supernatant and filtrate from the sludge vacuum
filters are transferred to the thickener. The thickener effluent undergoes separate
aeration before being returned to the treatment process thus limiting additional
BOD loads.
The plant treats primarily domestic wastes. Average dry weather flow is 3.1 mgd with
a design average of 5.0 mgd. Plant effluent is discharged to a river.
Performance
Effluent concentrations of BOD and suspended solids are typically 16 and 13 mg/l,
respectively. The settled wastewater has a BOD of 130 mg/l.
Process Control
The F/M is held around 0.17 to 0.25 Ibs BOD/day/lb MLVSS. The organic loading is
nearly constant and by wasting to maintain a constant MLSS fixes the F/M. D.O. is
maintained around 2 mg/l by adjusting the blower air rates.
B-30
-------
DILUTED
ANAEROBIC
SUPERNATANT
CONTACT BASIN «B
STABILIZATION BASIN
WASTE ACTIVATED SLUDGE
RETURN
ACTIVATED
SLUDGE
STABILIZATION BASIN
CONTACT BASIN
AHH^
SECONDARY
CLARIFIER
SECONDARY
CLARIFIER
PLANT FLOW DIAGRAM
VILLAGE OF RIDCEHOOD, NErt JERSEY
COrfTACT STABILIZATION
CURRENT PLANT IN OPERATION - 1966
PLAiiT FLOW
PLANT DESIGN
AVG DRY HEATHER,MOD
MAX DAY,MOD
PEAK HOUR,MOD
% INDUSTRIAL
5.0
7.b
7,5
3.0
4.0
6.0
50.
AERATION BASIMS
ft'UMBER I
VULUKE, 0.
CU FT 81,300.
AERATION SYSTEM
CLARIFIERS
h UMBER
DIAMETER, cT
DEPTH,FT
AREA-EACH ,51-'
WEIR LENGTH,FT
WEIR TYPE
SLUDGE REMOVAL
2
75.
10.6
4418.
424.
V-NOTCHE
PLOW
AERATION BASINS
PLArtT LOADING
INF BOD5.MG/L 135.
INF SS.MG/L to.
F/M.LB 90D5 REM./L? MLVSS/DAY 0.58
«CBT,OAYS 0.
SLUDGE AGE,DAYS 0.4
MLSS.MG/L 2000,
MAX MLSS.MO/L
MIN MISS.MG/L
Ł VOLAflLE
D.I). LEVELS,MO/L 2.0
AIR APPLIED.SCF/GAL
AIR APPLIED,SCF/L1 BODS RE«
RETURN, X 43.
MAX RETURH, X 0.
DET. TIME,* AVO h'LOM,HOURS 2.9
DEf. TIME,* A.F.tRETURN.HOURS 2.3
DET. TIKE,* M.F.tRETURti,HOURS 1.7
TYPICAL
135.
85.
0.33
0.3
5.0
2100,
2300.
1800.
8a.
I .5
0.9
856.
43.
4.9
3.4
2.3
SYSTEM
TYPE
MAX SCF«
AVO SCFM
DIFFUSED
SOCK
6000,
1800.
PLANT PEDFORMANCE
DESIGN
EFF BOD5.MG/L
% 80D5 REMOVAL
EfF SS.MG/L
% SS REMOVAL
SVI,ML/GRAK
SOI,ORAM/100ML
15.0
90.
10.0
90.
14.0
90.
10.0
as.
100.
1 .00
SECONDARY CLARIFIEBS
SUtlHACE LI>ADIl(0,GAL/SF/DAY
HEIR LOADIrtO.OAL/Fr/DAY
DETENTION TIME, HOURS
SOLIDS LOAD INC, LnS/SF/HDUR
MAX DAY
349,
P844.
2,2
0,69
AVG
566.
5890.
3.4
0.50
TYPICAL
MAX DAY
349,
471 7.
4.2
0.44
AVO
340.
3538.
5.6
0.36
B-31
-------
ST. PAUL, MINNESOTA - METROPOLITAN WASTEWATER TREATMENT
PLANT
General Description
The current facilities were designed to operate as a high rate activated sludge process
or step aeration activated sludge process, depending on influent conditions of the
plant. Design average dry weather flow influent conditions are 218 mgd, 250 mg/l BOD,
and 315 mg/l suspended solids.
This plant presently operates at or in excess of its design capacity. Existing sludge
disposal facilities are also operating at design capacity. These factors combined
result in the plant failing to meet effluent standards.
Performance
Probably one of the most serious problems with the plant is its inability to operate in
the step aeration mode. The inability is due to (1) the loss of the incremental feed pipes,
and (2) not enough air capacity.
Another problem which directly relates to the aerobic process is the fact that the
gravity thickeners operate under an overloaded condition. This results in poor capture
efficiencies in the thickeners and consequently adds a solids burden on the aeration
system. Related to the above is'the problem that more solids handling inventory
capacity is required in the secondary system and flexibility for process control is very
limited.
B-32
-------
RAW SIWAQE
PRIMARY CLARIFiERS
WASTE SLUDGE
c-
AERATION BASINS
SETTLED
SEWAGE
MIXED
LIQUOR
SECONDARY
CLARIFIERS
EFFLUENT .
RETURN ACTIVATED SLUDGE
WASTE
ACTIVATED
SLUDGE
PLANT FLOW DIAGRAM
CITY OF ST. PAUL, uHWIEbOTA - METROPOLITAN PLANT
CONVENTIONAL ACTIVATED SLUDOE
CURRENT PLAMT IN OPERATlOU - 1974
PLArIT FLOW
PLAMT DESIGN
HPICAL
AERATIUli BASINS
CLARIFIERS
AVO DRY KEAnfEil,
KAX DAV,»UD
PEAK lIOUD.ttGD
X INDUSTRIAL
218,0
322,0
391.0
PLAiJT LOADING
230.0
345.0
460,0
33.
NUMBER 8
LENG'M.HT 315.
WIDTH, FT 120.
DEPI'H.FT 15.0
AREA-EACH,SF 43000.
AERATION SYSTEM
hUSBER
LENGTH,FT
HI D1H, FT
DEPTH,FT
AREA-EACH,SF
WEIR LENGTH,FT
WEIR TYPE
SLUDGE REMOVAL
12
242.
7j,
II .0
19660.
82V.
/-NOTCH
PLOW
AERATION BASWS DESIGN
INF B()DS,HG/L I(W.
INF SS.MO/L 122>
K/M.LD RODS [IB,',/LB WLVSS/DAr 0.60
HCRT.DAYS 0.
SLUDCE AOE.UAYS 2-a
MLSS.MO/L 3000.
MAX MLSS.MG/L
HIM ,'ilLSS,MO/L
X VOLATILE
D.I). LEVELS,M/L 2.0
AIR APPLIED,SCF/GAL
AIR APPLIED,SCF/LR BODS HEW
RETURN, X '*•
MAX RETURN, % -*9.
DET. TIME,'? AVG FLOW,HOURS 4.-I
DEI. TIME," A.F.+RETUDM,HI)U1S 3.B
DET. TIME,a H.h.*RETUni,,HOUSS 2.V
TYPICAL
[60.
I 10.
O.S4
4.8
2.4
1500.
800.
2200.
B6.
I .i
I .0
977.
I /.
4.2
3.6
2.'J
SYSTEM DIFFUSED
TYPE SPARGER
MAX SCFM 80000,
AVG SCFM 60000.
PLAHT PERFORMANCE
EFF BODb.MG/L
% BODS REMOVAL
EFF SS.MG/L
% SS REMOVAL
SVI,ML/GRAM
SDI.GRAM/IOOML
PESIGf!
32.0
83.
31.0
75.
37.0
77.
38.0
65.
110.
0.51
SECONDARY CLABIFIERS
SURFACE LHAUIWG.OAL/SF/DAY
WEIR LOADb
-------
SAN PABLO SANITARY DISTRICT, CALIFORNIA
General Description
The San Pablo Sanitary District, California operates a 12.5 mgd wastewater treatment
plant designed for year-round complete nitrification. The original plant consisted of a
primary treatment plant with effluent chlorination and anaerobic digestion for solids
processing. Additions completed in 1972 included additional primary treatment facili-
ties, a new plastic media roughing trickling filter, new aeration-nitrification tanks, new
secondary clarifiers, an additional chlorine contact tank, new dissolved air flotation
thickener, and two new anaerobic digesters. A primary design consideration in laying
out the plant for nitrification was the presence of a significant volume fraction (11 to 13
percent) of potentially toxic industrial wastes in the influent wastewater. Tank truck
washing residues and the waste from a manufacturer of organic peroxide and phenol
formaldehyde are the major industrial waste sources. The roughing filter is used in the
treatment plant to protect the nitrifying organisms from influent wastewater toxicity.
Toxic dumps have caused severe sloughing and loss of growth on the media in the
roughing filter, but nitrification remained unaffected.
Performance
Effluent BOD5 and suspended solids concentrations are typically 5 mg/l. Complete
nitrification is obtained year round with a secondary effluent ammonia nitrogen con-
centration of less than 0.2 mg/l. The roughing filter converts influent organic matter
to biological organisms. This is indicated by data which shows that the total BOD5 and
total COD remain relatively unaffected by the roughing filter operation while the
soluble BOD5 and soluble COD are reduced with a corresponding increase in total
suspended solids.
Process Control
Control of the process is by maintaining an F/M of 0.15 Ib BOD5/lb MLVSS or an MCRT
of around 13 days. The MLVSS concentration is checked each day and the waste rate
is adjusted to give desired MLVSS concentration range based on desired F/M and
previous months BOD and flow data.
Air rates are adjusted twice a day to maintain DO of 3.0 mg/l in aerator effluent. A
timer is used to shut-off one blower at night.
RAS is controlled using a program cam in proportion to flow. The RAS flow is then
modified by a ratio station to give approximately 5,000 mg/l solids in return.
B-34
-------
RAW SEWAGE
PRIMARY CLARIFIERS
I
SLUDGE
ANAEROBIC
SUPERNATANT
RETURN
ACTIVATED
SLUDGE
WASTE
ACTIVATED
SLUDGE
AERATION
BASINS
SECONDARY
CLARIFIERS
PLANT FLOW DIAGRAM
CITY OF SAN PABLO, CALIFORNIA
CONVENTIONAL ACTIVATED SLUDGE WITH ROUGHING FILTER
CURRENT PLANT IN OPERATION - 1972
PLANT FLOW
DESIGN
TYPICAL
PLANT DESIGN
AERATION BASINS CLARIFIERS
AVG DRY WEATHER,MOD 12.0
MAX DAY,MOD 16.5
PEAK HOUR,MOD 16.5
% INDUSTRIAL
6.5
15.5
19.5
15.
NUMBER
LENGTH,FT
WIDTH,FT
DEPTH.FT
AREA-EACH,SF
2
252.
50.
15.0
12600.
AERATION SYSTEM
NUMBER
LENGTH, FT
WIDTH,FT
DEPTH.FT
AREA-EACH,SF
WEIR LENGTH,FT
HEIR TYPE
SLUDGE REMOVAL
2
I BO.
60.
8.0
10800.
240.
V-NOTCH
FLIGHT
PLANT LOADING
TRICKLING FILTERS
INF BOD5.MG/L
INF SS.MG/L
ORG LOAD.LBBOD5/1000CF/DAY
HYD LOAD, MOD/ACRE
RECIRCULATION.X
AERATION BASINS
INF ROD5.MG/L
INF SS.MG/L
F/M.LR BODS REM/LB MLVSS/DAY
MCRT.DAYS
SLUDGE ACE,DAYS
MLSS.MG/L
MAX MLSS.MG/L
MIN MLSS.MG/L
X VOLATILE
D.O. LEVELS,MG/L
AIR APPLIED,SCF/GAL
AIR APPLIED.SCF/L3 BODS REM
RETURN, %
MAX RETURN, %
DEI". TIME,8 AVG FLOW,HOURS
DET. TIME,* A.F.*RETURN,HOURS
DET. TIME,8 M.F.*RETURN,HOURS
SECONDARY CLARIFIERS
SURFACE LOADING,GAL/SF/DAY
WEIR LOADING,GAL/FT/DAY
DETENTION TIME,HOURS
SOLIDS LOADING,LOS/SF/HOUR
DESIGN
130.
130.
350.
840.
TYPICAL
120.
120.
I 70.
453.
SYSTEM
TYPE
MAX SCFM
AVG SCFM
DIFFUSED
SPARGER
24000.
1 I 000.
fHJ .
DESIGN
no.
1 10.
0.30
7.0
3.0
1500.
2.0
55.
128.
5.7
S 4.3
S 3.4
DESIGN
*;*»u.
TYPICAL
100.
100.
. O.I 7
24.1
7.4
1700.
2000.
1400.
75.
3.0
2.4
3044.
31 .
10.4
8.0
3.9
PLANT
EFF BOD5.MG/L
% BOD5 REMOVAL
EFF SS.MG/L
X SS REMOVAL
SV I, ML /GRAM
SDI, GRAM/I 00 ML
TYPICAL
PERFORMANCE
DESIGN
1 1 .0
91.
11.0
VI-
MAX DAY AVG MAX DAY AVG
764. 556
34375. 25000
1.9 2
0.49 0
764.
32292.
.6 2.
.38 0.
301 .
13542.
0 4.8
48 0.23
TRICKLING FILTERS
NUMBER I
DIAMETER,FT 52.
DEPTH.FT 18.0
AREA-EACH,SF 2124.
VOL-EACH.CF 38227.
TYPICAL
4.0
97.
3.0
97.
100.
I .00
B-35
-------
CITY OF TUSCON, ARIZONA
General Description
The first primary treatment plant was constructed in 1928 and expanded in 1942. Pri-
mary effluent was used for irrigation. In 1951 the first 12 mgd activated sludge plant
was put into operation, secondary effluent being sold for irrigation. In 1960 a high-rate
trickling filter plant was added in parallel to the existing activated sludge plant,
increasing total capacity to 24 mgd. A second activated sludge plant was placed in
operation in 1968, in parallel with the other two plants. With the addition of this third
plant, the total treatment capacity was increased to 37 mgd. At the present time, the
three plants are treating in excess of 33 mgd, but the plants are hydraulically over-
loaded 12-18 hours per day.
Performance and Process Control
The two activated sludge plants are basically conventional plug flow processes. There
is not enough flexibility in the plant to make other modes of operation feasible.
The plants are operated with a low MLSS, under 1,000 to prevent frothing from becoming
a problem. The sludge age is kept to 1.5 - 2 days to control frothing problems. The
activated sludge processes are controlled to sludge age and MLSS. Wasting and return
rates are adjusted as needed to control to the appropriate sludge age and MLSS.
Operations are not significantly affected by changes in weather or other environmental
changes. The erratic flow characteristics, which hydraulically overload the plant for
12 - 18 hours per day, cause the most serious chronic operational problems for the
operators. There is a solids washout problem in the secondaries when the hydraulic
overload condition exists.
B-36
-------
RETURN ACTIVATED SLUDGE
SECONDARY
CLARIFIERS
ANAEROBIC
SUPERNATANT
PLANT FLOW DIAGRAM
CITY OF TUCSON, ARIZONA - PLANT «
CONVENTIONAL ACTIVATED SLUtKE
CURREifl PLANT IN OPERATION - 1968
PLANT FLOW
DESIGN
PLAMT DESIGN
AERATION BASIilS
CLARIFiERS
AVC 0BY IHEATHER.MCD 13.0
MAX DAY,HOD 14.0
PEAK HiJUR.lWD 22.0
* lilOUbTHIAL
PLAWT LOADING
12.4
14.0
22.0
SO.
NUMBER
LENOTH.FT
MI DTK,FT
DEPTH, FT
AREA-EACH,SK
AERATION SYSTEM
4
0.
0.
0.
0.
NUMBER
DIA«ETER,FT
DEPTH,FT
AREA-EACH,SF
WEIR LENGTH,FT
WEIR TYPE
SLUDGE REMOVAL
2
103.
10.0
8659,
330.
V-flOTCH
VACUUM
AERAHOn BASIilb
II.F 0005, MG/L
1HF SS.HC/L
F/st,LB BODi) lib'M/LB MLVSS/DAV
MCBl'.DAYS
SLUOGE AGE, DAYS
«LSS,MO/L
MAX SLSS.MU/L
HIM «LSS,HO/L
"& VOLAilLE
D.O. LEVELS, MO/L
AID APPLIED, SWAJAL
AIR APPLIED, SCb'/LO BOOS REK
WAX RETURN, a
DEI'. 11 Mb,* AVC FLOW, HOURS
DET. TIME,;! A.r.+RETURN.IIOURS
DET. TIME,.* M.F.+BErURn, HOURS
DESIGN
150.
100.
0.40
0.
4.4
2000.
31 .
58.
4.8
3.7
3.3
14V.
87.
0.71
2,b
2.7
1100.
1400.
500.
77.
3.0
0.9
868.
30.
3.0
3.V
3.5
SYSTEM DIFFUSED
TYPE SPARGER
MAX SCFM 10000.
AVO SCF'A 8100.
PLAHf PERFORMANCE
EFF BOD5.MG/L
% B(JK> REMOVAL
EFF SS.MG/L
X SS REMOVAL
SV I,ML/GRAM
SDI.GRAM/IOOML
DESIGN
15.0
90,
10.0
yo.
22.0
Si).
21 .0
76.
235.
0.43
SECONDARY CLARIFIERS
SURFACE LOADI«0,GAL/iF/DAY
HKIR LOADING,OAL/Ff/UAY
DEi'EitTIOJI TIKE.1WURS
SOLIDS LOADING,LSS/SF/HOUB
MAX DAY
808.
21212.
2.2
0.72
1 9697.
2.4
0.6d
TYPICAL
MAX DAY
808.
21212.
2.2
0.39
AVG
716.
18788.
2.5
0.36
B-37
-------
NORTHWEST BERGEN CO. SEWER AUTHORITY, WALDWICK NEW
JERSEY
General Description
The wastewater treatment plant a conventional activated sludge plant utilizing the
step feed aeration mode of operation. Diffused spiral roll aeration is provided by posi-
tive displacement blowers. MLSS is settled in rectangular clarifiers with sludge with-
drawal from a trough at the midpoint of each tank. Waste solids are transferred to
gravity thickeners followed by centrifucation and incineration.
The plant treats wastewater primarily from domestic sources with an average daily flow
of 4.6 mgd. Design average dry weather flow is 8.5 mgd. Effluent is discharged to a river.
Performance
Effluent concentrations of BOD and suspended solids are typically less than 5 mg/l.
Settled wastewater has a typical BOD concentration of 100 mg/l.
Process Control
F/M is held around 0.13 to 0.25 Ibs BOD/day/lb MLSS. Actual wasting is controlled to
maintain a constant MCRT of about 6 days. The mode of process control is by main-
taining a constant MCRT which varies the MLSS and F/M. D.O. is maintained around
4.0 mg/l.
B-38
-------
PRIMARY
CLARIFIERS
STABILIZATION BASINS
7
SECONDARY
CLARIFIERS
EFFLUENT
RETURN ACTIVATED SLUDGE
WASTE
ACTIVATED
SLUDGE
PLANT FLOW DIAGRAM
CITY OF WALDWICK, NEW JERSEY - NE BERGEN CO. PLA«I
CONTACT STABILIZATION
CURRENT PLANT IN OPERATION - 1975
PLANT FLOW
DESIGN
PLANT DESIGN
AERATION BASINS CLARIKIERb
AVO DRY WEATHER,MGD 8.5
MAX DAY,MGD 21.0
PEAK HOUR,MGD 25.0
% INDUSTRIAL
4.6
8.0
25.0
50.
NUMBER
LENGTH,FT
WIDTH, FT
DEPTH, FT
AREA-EACH,SF
3
205.
20.
15.0
4100.
AERATION SYSTEM
NUMBER
LENGTH,FT
WIDTH,FT
DEPTH,FT
AREA-EACH.SF
WEIR LENGTH,FT
HEIR TYPE
SLUDGE REMOVAL
3
160.
32.
10.0
5120.
384.
V-NOTCH
VACUUM
PLANT LOADING
AERATION BASINS
INF ROD5,MG/L
INF SS.MG/L
F/M.LB BODS REM/LB MLVSS/DAY
MCRT,DAYS
SLUDCE AGE, DAYS
MLSS.MG/L
MAX MLSS.MG/L
MIN MLSS.MG/L
X VOLATILE
D.O. LEVELS,MG/L
AIR APPLIED,SCF/OAL
AIR APPLIED.SCF/LB BODS REM
RETURN, X
MAX RETURN, X
DET. TIME,* AVO FLOW,HOURS
DET. T1ME.O A.F.«RETURN.HOURS
DET. TIME,* M.F.«RETURN,HOURS
SECONDARY CLARIFIERS
SURFACE LOADING,GAL/SF/DAY
WEIR LOADING,GAL/FT/DAY
DETENTION TIME,HOURS
SOLIDS LOAD ING,LnS/SF/HOUR
10
DESIGN
275.
275.
1 .10
0.
1 .2
2000.
2.0
85.
65.
3.9
i 2.7
i 1 .3
DES IGN
MAX DAY AVO
1367. 553.
18229. 7378.
1.3 3.2
TYPICAL
1 16.
80.
0.26
4.7
6.8
1800.
2000.
1500.
75.
4.5
1 .2
1274.
18.
7.2
6.1
3.8
SYSTEM DIFFUSED
TYPE SOCK
MAX SCFM 19050.
AVG SCFM 3800.
PLANT
EFF BOD5.MO/L
% BHD5 REMOVAL
EFF SS.MG/L
X SS REMOVAL
SV I, ML/GRAM
SDI.ORAM/IOOML
TYPICAL
PERFORMANCE
DESIGN
20.0
95.
20.0
95.
MAX DAY AVG
1367.
6944.
3.
1.13 0.56 0.
299.
3993.
4 6.0
36 0.22
TYPICAL
4.0
97.
4.0
95.
258.
0.39
B-39
-------
APPENDIX C-LABORATORY EQUIPMENT
Outlined on the following pages are suggested laboratory equipment, supplies and
chemical reagents required to perform the process control tests for typical aerobic
biological treatment facilities.
In addition, optional equipment, and/or methods have been included for certain tests.
All test methods are referenced to "Standard Methods for the Examination of Water
and Wastewater," 14th Edition, 1976, APHA, AWWA, WPCF.
Additional equipment required in conjunction with the following tests include:
1. Standard type refrigeration for sample storage
2. Fume hood
3. Bottles for collecting and storing of samples or use with automatic samplers.
4. An appropriate carrying device for sample bottles if samples are collected
manually
5. Sample bottle tongs with extended handle
BOD TEST
A. Equipment and supplies
1. Incubator (BOD) Capacity, 13 cu. ft., ambient air thermostatically controlled
at 20 ± 1 ° C
2. Bottles (BOD), meet APHA specifications, numbered in sequence, 300 ml
capacity, 2 cases (48 bottles suggested)
3. Buret, Straight Stopcock, with side tube stopcock for filling, 50 ml capacity,
0.1 ml subdivisions
4. Support, Buret Double, with holder
5. Bottle, reagent, 1000 ml capacity, with tubulature near bottom
6. Bottles (4), Dropping Assembly, 250 ml capacity
7. Bottle, carboy, 5 gal
8. Tubing, polyethylene, 10 ft.
9. Pipets, volumetric, assorted sizes, 1 to 25 ml, color coded, 0.1 ml subdivisions
10. Balance, Triple Beam, 600 grams, sensitivity 0.1 gram
11. Hot Plate/Magnetic Stirrer
12. Flasks erlenmeyer, 500 ml capacity
B. Chemical Reagents
1. Distilled water
2. Sodium Thiosulfate solution
3. Concentrated Sulfuric Acid
4. ManganousSulfate solution
5. Alkaline iodide-sodium azide solutions
6. Starch solution
7. Phosphate buffer solution
8. Magnesium Sulfate solution
9. Calcium Chloride solutions
10. Ferric Chloride solution
C-1
-------
C. Optional Equipment/Method
1. Polargraphic Dissolved Oxygen Meter, self contained, with BOD agitator
and probe assembly
COD TEST
A. Equipment and Supplies
1, Extraction Apparatus, 6 unit, complete with support rods, clamping brackets,
and rod clamps, 115 Volt ac
2. Condensers, reflux with § ground joint both top and bottom, and drip tip at
bottom, length 350 mm
3. Flasks, boiling, flat bottom, short neck, with! joint, 250 ml capacity
4. Cylinder, graduated, 50 ml capacity
5. Pipet Filler, Polypropylene, Nalgene, safety, for use with volatile, corrosive
and poisonous liquids
6, Pipets, Volumetric, color coded, 25 ml capacity, 0.1 ml subdivisions
7. Tubing, polyethylene, 25 ft,
8. Buret, Straight Stopcock, with side tube stopcock for filling, 50 ml capacity,
0.1 ml subdivisions
9. Support, Buret Double, with holder
10. Bottle, Reagent, 1000 ml capacity, with tabulature near bottom
11. Potable water source
12. Rubber gloves and apron
13. Clamp, Flask, Safety Tongs
14. Safety glasses
15. Beads, glass
16. Balance, Triple Beam, 600 grams, sensitivity 0.1 gram
B. Chemical Reagents
1. Standard Potassium Dichromate Solution
2. Sulfuric Acid-Silver Sulfate Solution
3. Standard Ferrous Ammonium Sulfate Solution
4. Ferroin Indicator
5. Silver Sulfate, powder
6. Mercuric Sulfate, analytical grade crystals
SUSPENDED SOLIDS TEST
I. TOTAL SUSPENDED SOLIDS
A. Equipment and Supplies
1. Filter, holders, membrane assembly for vacuum filtration
2. Flasks, filtering, 1000 ml capacity
3. Tubing, Vacuum, 10ft.
4. Forceps, specimen
5. Pump, Air Pressure and vacuum type
6. Paper, filter, glass fiber, 47 mm diameter
C-2
-------
7. Vacuum, manifold with four connections and stopcocks
8. Oven, drying, with forced draft; thermostatically controlled to maintain
103 ± °C
9. Cabinet, Desiccator, for vacuum drying and storage
10. Balance, Analytical, automatic, digital, single pan; readout to 0.1
milligram
11. Cylinder, graduated, assorted sizes (25 to 100 ml capacity)
B. Chemicals
1, Desiccant, silica gel air dryer
I!. VOLATILE SUSPENDED SOLIDS
A. Equipment and Supplies
1. Furnace, muffle, 115 Volt ac; thermostatically controlled to maintain
600 ± ' C
III. OPTIONAL EQUIPMENT/METHOD
A. Gooch crucible method with 2.4 cm glass fiber filter
SETTLEABLE SOLIDS TEST
A. Equipment and Supplies
1. Cones, Imhoff, 1000 ml capacity
2. Stand, Imhoff cone
3. Rod, stirrer, glass
4. Timer, interval, range 15 minutes to 2 hours, 115 Volt ac
NITROGEN-KJELDHAL (TKN)
A. -Equipment and Supplies
1. Bulbs, connecting, spherical, 65 mm diameter
2. Tubes, delivery, with safety bulb
3. Flasks, 800 ml capacity
4. Stopper, rubber, 800 ml Flask size
5, Spectrophotometer, 400 to 425 mju with light patch of 1 cm or longer
6. Distillation Apparatus, 6 unit, Kjeidhal, 115 Volt ac
7. Beads, glass
8. Flasks, erienmeyer, 500 ml capacity
9. Cylinders, graduated, 50 to 500 ml capacity
10. Balance, triple beam, 600 grams, sensitivity 0.1 gram
11. Rubber gloves and apron
12. Safety glasses
B. Chemical Reagents
1. Distilled Water
C-3
-------
2. Potassium Sulfate
3. Concentrated Sulfuric Acid
4. Red Mercuric Oxide
5. Phenophalien Indicator Solution
6. Sodium Hydroxide
7. Sodium Thiosulfate, 5 parts water
8. Methyl Red Indicator
9. Ethyl Alcohol
10. MethyleneBlue
11. Indicating Boric Acid Solution
C. Optional Equipment/Method
1. Filter Photometer, with maximum transmittance at 400 to 425 mM and light
path of 1 cm or longer
2. Messier Tubes, matched, 50 ml capacity, tall form
AMMONIA-NITROGEN TEST
(Nesslerization Method)
A. Equipment and Supplies
1. Spectrophotometerforuseat 400 to 500 m/uand light path of 1 cm or longer
2. Beakers, assorted sizes, 25 to 200 ml
3. Pipet, fillers, for use with corrosive liquid
4. Pipets, assorted sizes, 1 to 25 ml, color coded, 0.1 ml subdivisions
5. Cylinders, graduated, assorted sizes 25 to 200 ml
6. Bottles, reagent, 1000 ml capacity
7. Balance, triple beam, 600 grams, sensitivity 0.1 gram
8. Rubber gloves and apron
9. Safety glasses
B. Chemical Reagents
1. Ammonia free water
2. Potassium Dihydrogen Phosphate
3. Dipotassium Hydrogen Phosphate
4. Dechlorination agent - Thiosulfate
5. Sodium Hydroxide, 0.3N
6. Sodium Arsenite
7. Sodium Sulfite
8. Sulfuric Acid
9. Zinc Sulfate
10. Mercuric Iodide
11. Potassium Iodide
12. Ammonium Chloride, Anhydraus
13. Hydrochloric Acid
14. Potassium Chloroplatinate
15. Cobaltous Chloride
C-4
-------
C. Optional Equipment/Method
1, Filter Photometer with maximum transmittanee at 400 to 425 HIM lightpath
of 1 cm or longer
2. NessierTubes, matched, 50 ml, tall form
3 . pH meter, equipped with high pH electrode
4. Phenate Method (Tentative)
NITRITE - NITROGEN TEST
A. Equipment and Supplies
1, Spectrophotometer, for use'at 400 to 500 HIM and lightpath of 1 cm or longer
2. Beakers, assorted sizes, 25 to 200 ml
3, Pipet, fillers, for use with corrosive liquids
4. Pipets, assorted sizes, 1 to 25 ml, color coded, 0.1 ml subdivisions
5. Cylinders, graduated, assorted sizes, 25 to 200 ml
6. Bottles, reagent, 1,000 ml capacity
7, Balance, Triple Beam, 600 grams, sensitivity 0,1 gram
8. Rubber Gloves and Apron
9, Safety Glasses
B, Chemical Reagents
1. Nitrite-Free Water
2. Potassium Permanganate
3. Calcium Hydroxide
4, Orthotolidine
5. Concentrated Sulfuric Acid
6. Manganese Sulfate
7, Ammonium Oxalate
8. EDTA Reagent
9, Sulfanilis Acid
10. Hydrochloric Acid
11. Naphthylamine Hydrochloride
12. Sodium Acetate
13. Sodium Nitrite
C. Optional Equipment/Method
1. Filter Photometer, with maximum transmittanee near 500 m^ and light path
of 1 cm or longer
2. Nessler Tubes, matched, 50 ml, tall form
NITRATE NITROGEN TEST
(Brucine Method)
A. Equipment and Supplies
1. Spectrophotometer, for use at 400 to 500 m/u and light path of 1 cm or longer
2. Beakers, assorted sizes, 25 to 200 ml
3. Pipet, fillers, for use with corrosive liquids
4. Pipets, assorted sizes, 1 to 25 mi, color coded, 0.1 ml subdivisions
C-5
-------
5. Cylinders, graduated, assorted sizes, 25 to 200 ml
6. Bottles, reagent, 1,000 ml capacity
7. Balance, Triple Beam, 600 grams, sensitivity 0.1 gram
8. Rubber Gloves and Apron
9. Safety Glasses
10. Test Tube Rack
11. Test Tubes, 2.5 x 15cm
B. Chemical Reagents
1. Potassium Nitrate, anhydrous
2. Sodium Arsenite
3. BrucineSulfate
4. Sulfanilic Acid
5. Concentrated Hydrochloric Acid
6. Concentrated Sulfuric Acid
7. Sodium Chloride
C. Optional Equipment/Method
1. Filter Photometer, with violet filter, having maximum transmittance between
400-425 HIM and light path of 1 inch
2. Zinc Reduction Method
3. Cadmium Reduction Method
4. Phenoldisulfanic Acid Method
5. Chromotropic Acid Method
TOTAL PHOSPHORUS (AS P)
(Ascorbic Acid Method)
A. Equipment and Supplies
1. Spectrophotometer, for use at 400 to 500 m/x and light path of 1 cm or longer
2. Beakers, assorted sizes, 25 to 200 ml
3. Pipet, fillers, for use with corrosive liquids
4. Pipets, assorted sizes, 1 to 25 ml, color coded, 0.1 ml subdivisions
5. Cylinders, graduated, assorted sizes, 25 to 200 ml
6. Bottles, reagent, 1,000 ml capacity
7. Balance, Triple Beam, 600 grams, sensitivity 0.1 gram
8. Rubber Gloves and Apron
9. Safety Glasses
10. Cylinder, mixing 100 ml capacity
11. Hot Plate/Magnetic Stirrer, combination
B. Chemical Reagents
1. Ascorbic Acid
2. Antimon Potassium Tartrate
3. Hyrochloric Acid
4. Sulfuric Acid
5. Ammonium Malybdate
C-6
-------
6. Ammonium Persulfate
7. Potassium Phosphate, dibasic
8, Potassium Phosphate, monobasic
9. Sodium Hydroxide
10. Phenolphthalein
C. Optional Equipment/Method
1. Filter Photometer, with red color filter and light path of 0.5 cm or longer
2. Vanadamolybdaphasphoric Acid Colorimetric Method
3. Stannous Chloride Method
30-MINUTE SETTLING TEST
(One Liter Graduated Cylinder Method)
A. Equipment and Supplies
1. Cylinders, graduated, one liter (1,000 ml) capacity; glass cylinders rec-
ommended.
2. Rod, glass, stirrer
3. Interval Timer, 1 minute to 2 hours, 115 volt ac
4. Bottles, sample, wide mouth, 1 gallon capacity
B. Optional Equipment/Method
1. Mallory Direct Reading Settlometer, 2,000 ml capacity
DISSOLVED OXYGEN TEST
(Winkler Method)
A. Equipment and Supplies
1. Bottles (BOD), meet APHA specifications, numbered in sequence, 300 ml
capacity, 2 cases (48 bottles suggested)
2. Buret, straight stopcock, with side tube stopcock for filling, 50 ml capacity,
0.1 ml subdivisions
3. Support, Buret Double, with holder
4. Bottle, reagent, 1,000 ml capacity, with tubulature near bottom
5. Bottles (4), dropping assembly, 250 ml capacity
6. Tubing, polyethylene, 10 ft.
7. Pipets, volumetric assorted sizes, 1 to 25 ml, color coded, 0.1 ml subdivisions
8. Balance, Triple Beam, 600 grams, sensitivity 0.1 gram
9. Hot Plate/Magnetic Stirrer
10. Flasks, erlenmeyer, 500 ml capacity
B. Chemical Reagents
1. Distilled Water
2. Sodium Thiosulfate Solution
3. Concentrated Sulfuric Acid
4. Manganous Sulfate Solution
5. Alkaline Iodide-Sodium Azide Solutions
6. Starch Solution
C-7
-------
7. Sulfamic Acid, technical grade
8. Copper Sulfate
9. Concentrated Acetic Acid
C. Optional Equipment/Method
1. Polarographic Dissolved Oxygen Meter, self contained, with probe assembly
pH TEST
(Electrometric Method)
A. Equipment and Supplies
1. pH Meter
2. Electrode, reference
3. Electrode, glass
4. Beakers, 100 ml capacity
5. Bottle, wash, 250 ml capacity
6. Tissue Paper
B. Chemical Reagents
1. BufferSolution, pH 4.0
2. BufferSolution, pH 7.0
3. BufferSolution, pH 10.0
4. Filling Solution, for reference electrode
5. KCL Solution, saturated
C. Optional Equipment/Method
1. Colorimetric Method (not recommended for wastewaters)
2. pH Paper (provides quick estimate)
TEMPERATURE
A. Equipment and Supplies
1. Combination Thermometers,-20° to+150° C, +20° to 220° F
2. Thermometer, 0° to + 120° C, with metal armored case and nylon cord
B. Optional Equipment/Method
1. Telethermometer
2. Thermistor Probe
C-8
-------
REFERENCES
APHA, AWWA, WPCF, Standard Methods for the Examination of Water and Waste-
water, 14th Edition, 1976 - APHA New York, N.Y.
Ministry of the Environment, Activated Sludge Process Analyses and Interpretation
Workshop Manual, Training, Certification, and Safety Section, Toronto, Ontario,
M4V, LP5.
Nagano, J., Laboratory Procedures for Operators of Water Pollution Control Plants,
California Water Pollution Control Association, October 2,1970.
U.S. Environmental Protection Agency, Estimating Laboratory Needs for Municipal
Wastewater Treatment Facilitiesm, Office of Water Program Operations, Publica-
tion No. 4301 9-74-002, Washington, D.C.
U.S. Environmental Protection Agency, Estimating Laboratory Needs for Municipal
Wastewater Treatment Facilities, Office of Water Program Operations, Publica-
tion No. 4301 9-74-002, Washington, D.C.
Water Pollution Control Federation, Simplified Laboratory Practices for Wastewater
Examination, Manual of Practice No. 18,1971.
C-9
-------
APPENDIX D- GLOSSARY
Absorption The taking up of one substance into the body of another.
Activated Sludge Sludge floe produced in raw or settled wastewater by the growth of
organisms (including zoogleal bacteria) in the presence of dissolved oxygen. The
term "activated" comes from the fact that the sludge is teaming with active, or
living, microorganisms.
Activated Sludge Loading The pounds of biochemcial oxygen demand (BOD) in the
applied liquid per unit volume of aeration capacity or per pound of activated
sludge per day.
Activated Sludge Process A biological wastewater treatment process in which a mix-
ture of wastewater and activated sludge is agitated and aerated. The activated
sludge is subsequently separated from the treated wastewater (mixed liquor) by
sedimentation and wasted or returned to the process as needed.
Adsorption The adherence of a gas, liquid, or dissolved material on the surface or
interface zone of another substance.
Aeration The bringing about of intimate contact between air and a liquid by one or
more of the following methods: (a) spraying the liquid in the air, (b) bubbling air
through the liquid, and (c) agitating the liquid to promote surface absorption of air.
Aeration Period The theoretical time, usually expressed in hours, during which mixed
liquor is subjected to aeration in an aeration tank while undergoing activated
sludge treatment. It is equal to the volume of the tank divided by the volumetric
rate of flow of the wastewater and return sludge.
Aerobic (1) A condition in which "free" or dissolved oxygen (62) is present. (2) Re-
quiring, or not destroyed by, the presence of free oxygen.
Alkalinity Buffering, or acid neutralizing, capacity of water due primarily to its car-
bonate, bicarbonate, and hydroxide content.
Ambient Temperature Temperature of the surroundings.
Anaerobic (1) A condition in which "free" or dissolved oxygen (62) is not present.
(2) Requiring, or not destroyed by, the absence of free oxygen.
Assimilation The process by which food is converted to cell protoplasm.
Autotrophic Having the ability to utilize CO2 as sole source of carbon.
Available Oxygen The quantity of dissolved oxygen available for oxidation of organic
matter in a water body.
Bacteria Singe celled microorganisms of primary importance in most biological
wastewater treatment processes.
Batch Reactor Reactor in which flow is neither entering nor leaving on a continuous
basis.
Biochemical Oxygen Demand (BOD) A standard test indicating the quantity of oxygen
utilized by wastewater under controlled conditions of temperature and time.
Bioassay Estimating the toxicity of an effluent by testing its effects on living
organisms.
Biodegradation The destruction or mineralization of organic materials by micro-
organisms.
Bioflocculation A condition whereby organic materials tend to be transferred from
the dispersed form in wastewater to settleable material by mechanical entrap-
ment and assimilation.
Biological Examinations A microscopic survey of the types of microorganisms
present in a sample.
D-1
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Biological Filter A bed of sand, gravel, broken stone, or other medium through which
wastewater flows or trickles that depends on biological action for its effectiveness.
Biological Filtration The process of passing a liquid through a biological filter, thus
permitting contact with zoogleal films attached to the media that adsorb and
absorb fine suspended, collodial, and dissolved solids and release end products
of biochemical oxidation.
Biological Wastewater Treatment Forms of wastewater treatment in which bacterial
or biochemcial action Js intensified to stablize the unstable organic matter
present and remove non-settling solids. Intermittent sand filters, contact beds,
trickling filters, and activated sludge processes are examples.
Biological Reactor The site(s) in a wastewafer treatment plant where the principal
biochemical reactions take place.
Biomass Active or dead microorganisms present in a particular area of a biological
treatment plant.
BOD See Biochemical Oxygen Demand.
BODs Five-day biochemcial oxygen demand; the oxygen demand exerted after five
days of a BOD test. (See Biochemcial Oxygen Demand)
BOD Load The BOD content, usually expressed in pounds per unit of time, of waste-
water passing into a waste treatment system.
Bulking Sludge An activated sludge that settles poorly because of low-density floe.
Carbonaceous Oxidation Biochemical process by which heterotrophic microorganisms
derive energy from organic wastes, rendering more stable organics or inorganics
as end-products.
Catalyst A substance that speeds up a chemical reaction without being altered itself.
Chemical Oxygen Demand (COD) A measure of the oxygen-consuming capacity of
inorganic and organic matter present in wastewater. It is expressed as the
equivalent amount of oxygen required as determined using a chemical oxidant in
a standard test. It does not differentiate between stable and unstable organic
material and thus does not necessarily correlate with biochemical oxygen
demand (BOD).
Chlorination The application of chlorine or chlorine compounds to water or waste-
water, usually for disinfection, but frequently to obtain other biological or chemi-
cal results.
Chlorine Contact Chamber A detention basin provided primarily to secure the diffusion
of chlorine through the liquid.
Chlorine Demand The difference between the amount of chlorine added to water or
wastewater and the amount of residual chlorine remaining at the end of a specified
contact period.
Ciliate A type of protozoan characterized by short, filamentous cilia used for motility
and/or capturing food.
Coagulation The clustering of suspended solids into larger particles or floes caused
by the addition of a chemical (coagulant) or by biological processes.
COD See Chemical Oxygen Demand.
Coliform-Group Bacteria A group of bacteria found in the intestines of man which are
used as indicators of fecal pollution and the presence of pathogenic bacteria in
water and wastewater. ,
Colloids Finely divided, non-settleable solids which may be removed by coagulation
or biochemcial action.
Complete Mix Idealized continuous flow reactor in which fluid particles are immedi-
ately dispersed throughout the reactor.
D-2
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Complete Treatment In an imprecise and general sense, the processing of domestic
and some industrial wastewaters by means of primary and secondary treatment.
It may include other specialized types of treatment and disinfection. A high
percentage removal of suspended, colloidal, and dissolved organic matter is
implied.
Composite Samples Samples collected at regular intervals, sometimes in proportion
to the existing flow, and then combined to form a sample representative of flow
overa period of time.
Concentration (1) The amount of a given substance dissolved or suspended in a unit
volume of solution. (2) The process of increasing the solids per unit volume in a
liquid.
Contact Aerator A biological unit consisting of stone, cement-asbestos, or other sur-
faces supported in an aeration tank, in which air is diffused up and around the
surfaces and settled wastewater flows through the tank.
Contact Stabilization Process A modification of the activated sludge process in which
wastewater is aerated with a high concentration of activated sludge for a short
period, usually less than 60 minutes, to obtain BOD removal. The solids are
subsequently separated by sedimentation and transferred to a stabilization tank
where aeration is continued, starving the activated sludge before returning it to
the aeration basin.
Conventional Activated Sludge Process Activated sludge process utilizing plug-flow
through the aeration basin with primary effluent and activated sludge fed at the
head end and uniform aeration throughout.
Cytoplasm Contents of a biological cell excluding the nucleus.
Degradation The conversion of a substance to simpler compounds.
Density Mass per unit volume of any substance.
Design Parameters Various criteria used to determine size, shape, quantity, and/or
methods in the design of units and processes in a treatment plant.
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 (volume divided by
flow rate).
Dewater To extract a portion of the water present in a sludge or slurry.
Diffused Air Aeration The process by which air is compressed and discharged below
the mixed liquor surf ace through some type of air diffusion device.
Diffuser A device (porous plate, tube, bag) used to break the air stream from a blower
system into fine bubbles in a liquid.
Disinfection The process by which pathogenic (disease-causing) microorganisms
are killed. Chlorination is the most frequently used method in wastewater
treatment.
Dissolved Oxygen (DO) Molecular or "free" oxygen (62) dissolved in water or waste-
water.
Dissolved Solids Very small, non-settling particles defined by the method of measure-
ment (see Standard Methods).
Distributor A mechanical device used for spreading wastewater over the surface of a
trickling filter. A rotary distributor is usually used.
Ditch Oxidation A modification of the activated sludge process or the aerated pond,
in which the mixture under treatment is circulated in an endless ditch and aeration
and circulation are produced by a mechanical device.
Diurnal Flow Flow that shows marked and regular variations through the course of a
day.
D-3
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Domestic Wastewater Wastewater derived principally from dwellings, business
buildings, institutions and other non-industrial sources.
DO See Dissolved Oxygen.
Dosing Ratio The maximum rate of wastewater application to a filter divided by the
average rate.
Dry Suspended Solids The weight of the suspended matter in wastewater or other
liquid after drying for 1 hr. at 103° C.
Ecology The branch of biology dealing with the relationships between organisms and
their environment.
Effluent Wastewater or other liquid flowing from a basin, treatment process, or treat-
ment plant.
Enzymes Substances produced by living organisms that speed up chemical changes.
Endogenous Respiration Utilization internal cellular material as food under aerobic
conditions when an adequate external food supply is unavailable.
Excess Activated Sludge The quantity of activated sludge above that needed for
process operation.
Extended Aeration A modification of the activated sludge process utilizing very long
aeration periods.
F/M Ratio Food to microorganism ratio; the amount of food (organic matter as BOD
or COD) available per unit mass of microorganisms.
Facultative (1) A condition in which "free" or dissolved oxygen (O2) is present only
in some places. (2) Able to function both in the presence or absence of free
oxygen.
Filamentous Bacteria Bacteria that grow in a thread or filamentous form.
Filter Flooding The filling of a trickling filter to an elevation above the top of the
medium by closing all outlets, in order to control nuisance of filter flies.
Floe Groups or "clumps" of bacteria that have come together and formed a small
gelatinous mass. Found in aeration tanks and secondary clarifiers.
Flocculation An action resulting in the gathering of fine particles to form larger
particles.
Grab Sample A single sample of wastewater taken all at one time from one place.
Head A term used in expressing the pressure or energy of fluids in terms of the height
of a verticle column of water.
Head Loss Energy lost, expressed in head, from flowing fluids due to friction and
turbulence.
Heterotrophic A term describing organisms which use organics as the source of cell
carbon.
High-Rate Filter A trickling filter operated at a high average daily dosing rate, usually
between 100 and 1000 gpd/sq. ft.
Hydraulic Detention Time The theoretical time required to displace the contents of a
tank or unit at a given discharge rate (volume of tank divided by discharge rate).
Hydraulic Loading The volume of wastewater applied to a unit in a given time.
Industrial Wastewater Wastewater in which wastes from industrial processes pre-
dominate.
Influent Wastewater or other liquid flowing into a reservoir, basin, treatment process,
or treatment plants.
Intermittent Filter A trickling filter which is dosed intermittently rather than continu-
ously.
D-4
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Kessener Brush A cylindrical metal brush used to maintain circulation and provide
oxygen in the activated sludge process.
Kinetic Data Recorded measurements used to determine rates of microorganism
growth and substrate removal.
Kraus Process A modification of the activated sludge process in which liquid from
anaerobic digesters is added to the aeration basins as a source of additional
nutrients.
Log Growth Phase The period of time when the mass of microorganisms is doubling
at regular intervas.
Low-Rate Filter A trickling filter designed to be operated with a hydraulic load of 25
v to 100 gpd/sq. ft. of filter surface. Also called standard-rate filter.
Mean Cell Residence Time Average period that a cell is held in the activated sludge
process; also known as solids retention time.
MechanicalAeration A class of processes by which the surface of an aeration tank is
mechanically agitated to cause spray or wave resulting in aeration of the liquid.
Metabolism The life-process in which food is utilized.
Micronutrients Inorganic nutrients required in only trace amounts.
Microorganism 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 Liqour The mixture of activated sludge and wastewater in an aeration tank.
Mixed Liquor Suspended Solids (MLSS) Defined by testing method (see Standard
Methods). May be roughly defined as non-filterable solid particles in mixed liquor.
Mixed Liquor Volatile Suspended Solids (MLVSS) Defined by testing method (see
Standards Methods). May be roughly defined as that part of the mixed liquor
suspended solids that is combustible.
Motile Capable of movement.
Nematode Unsegmented worm.
New Growth Rate The rate of increase in the mass of live microorganisms calculated
by subtracting the death rate from the synthesis rate.
Nitrification The biochemcial conversion of unoxidized nitrogen (amonia and organic
nitrogen) to oxidized nitrogen (usually nitrate).
Nutrients Elements which are needed to support living cells such as carbon, hydrogen,
oxygen, nitrogen, and phosphorus.
Organic Matter High Energy carbon compounds, usually from plant or animal sources,
but sometimes synthetic.
Oxidation A chemical reaction, usually involving the addition of oxygen and the
release of energy.
Oxygen Uptake Rate The rate at which oxygen is transferred to wastewater under
aeration.
Oxygen Utilization The oxygen consumed to support aerobic biological treatment
processes.
Parshall Flume A device which measures the critical depth to determine flow.
Peak Load The maximum rate of flow to a wastewater treatment plant.
pH An expression of the intensity of the alkaline or acidic strength of a water.
Photosynthesis The use of sunlight to obtain the energy necessary to synthesize
new cell material.
Pin Floe Very fine floe particles with poor settling characteristics.
Plain Sedimentation Sedimentation without the aid of chemicals.
D-5
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Plug Flow Reactor Idealized continuous flow reactor in which fluid particles are
discharged in the same order In which they entered.
Ponding The formation of pools or ponds of wastewater as a result of surface clogging
in trickling filters.
Preaeration A preparatory treatment of wastewater consisting of aeration to remove
gases, add oxygen, promote flotation of grease, and aid coagulation.
Pretreatment The use of racks, screens, communitors, and grit removal devices to
remove metal, rocks, sand, eggshells, and similar materials which may hinder
the operation of a treatment plant.
Primary Treatment The first phase of wastewater treatment, consisting of separating
the readily settleable or floatable solids by sedimentation and skimming.
Protoplasm The material of a living cell.
Protozoa Animal-like microorganisms.
Psychoda The generic name of filter flies.
Raw Wastewater Wastewater before it receives any treatment,
Reactor Any vessel in which a chemical, biochemical, or physical reaction takes place.
Recirculation The return of a portion of the wastewater which has already passed
through a trickling filter for a second passage.
Respiration The process by which a cell takes up oxygen and gives off the carbon
dioxide formed in energy-producing reactions.
Rising Sludge A problem in secondary settling tanks generally attributed to denitri-
fication in the sludge blanket.
Rotary Distributor A movable distributor made up of horizontal arms that extend to
the edge of the circular filter bed, revolve about a central post, and distribute
liquid over the bed through holes or jets in the arms.
Rotlfar A small, multi-celled animal that gets its name from the rotating action of
rows of cilia near its mouth.
Roughing Filter A trickling filter of relatively coarse material operated at high rate to
afford preliminary treatment,
Scum Collector A mechanical device for skimming and removing scum from the
surface of a settling tank.
Secondary Treatment Phase of wastewater treatment in which dissolved or suspended
material is converted into a form more readily separated from the wastewater.
Sedimentation The process of settling suspended solids by gravity.
Septic A condition produced by growth of anaerobic organisms.
Settleable Matter See Settleable Solids.
Settleable Solids That matter In wastewater which will not stay in suspension during
a preselected settling period, either settling to the bottom or floating to the top.
Settled Wastewater Wastewater from which most of the settleable solids have been
removed by sedimentation.
Sewage Spent water of a community.
Shock Load The arrival at a plant of a waste which is toxic to organisms in sufficient
quantity or strength to cause operating problems. Organic or hydraulic overloads
can also cause a shock load.
Side Water Depth (SWD) The depth of water measured along a vertical exterior wall.
Sloughing The dropping or washing off of slime from trickling filter media.
Sludge The solids separated from liquids during processing,
Sludge Age A measure of the length of time a particle of suspended solids has been
undergoing aeration. •
D-6
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Sludge Blanket A layer of sludge suspended within an enclosed body of wastewater,
such as a settling tank.
Sludge Bulking Poor settling due to low density floe in the activated sludge process.
Sludge Digestion A process by which organic matter in sludge is converted into a
more stable form by anaerobic or aerobic organisms.
Sludge Density Index The reciprocal of the sludge volume index (SVI) multiplied by
100 (i.e. 1/SVI x 100).
Sludge Volume Index The ratio of the volume in milliliters of sludge settled from a
1,000-ml sample in 30 min to the concentration of mixed liquor in milligrams per
liter multiplied by 1000.
Solids Retention Time (SRT) The average residence time of suspended solids in a
biological waste treatment system, equal to the total weight of suspended solids
in the system divided by the total weight of suspended solids leaving the system
per unit time.
Solids Loading The weight or mass of solids applied to a treatment process per unit
time.
Soluble Capable of dissolving readily.
Stabilization Conversion to a form that resists change.
Stage A process which is followed or preceded by a similar process.
Standard-Rate Filter See Low-Rate Filter.
Step Aeration Same as step feed.
Step Feed Adding wastewater at points along the length of an aeration basin rather
than just at the head end.
Supernatant Liquid removed from settled sludge.
Substrate The substance being used by microorganisms in suspension.
Suspended Matter See Suspended Solids.
Suspended Solids (SS) Defined by testing method (see Standard Methods), but may
be roughly defined as all non-dissolved solids that take a certain minimum time
to settle in still water.
Synthesis The creation of new material from elementary building blocks.
Tapered Aeration An aeration method whereby the quantity of air added varies along
the aeration basin with a maximum at the head end and a minimum at the outlet
end.
Toxicity The ability of a waste to poison organisms.
Trickling Filter A biological treatment process in which the wastewater trickles
through a bed of slime-covered media and is treated by the action of the micro-
organisms in the slime layer.
Trickling Filter Media The solid material in a trickling filter which provides a surface
for a biological film of microorganisms. Crushed stone is the most commonly
used media, but plastics are gaining popularity.
Turbidity Cloudiness of wastewater due to suspended solids.
Virus The smallest form capable of producing diseases in man or other higher
organisms.
Volatile Matter See Volatile Solids.
Volatile Solids Defined by testing method (see Standard Method), but may be roughly
defined as combustible solids.
Wastewater The used water and solids that flow to a treatment plant.
D-7
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Zooglea A jelly-like coating developed by bacteria.
Zooleal Matrix The floe or slime formed by zoogleal bacteria.
(Definitions principally from Glossary of Water and Wastewater Engineering, APHA,
ASCE, AWWA, and WPCF (1969); "Operation of Wastewater Treatment Plants," EPA
(1970); Wastewater Engineering, Metcalf & Eddy (1972); Biology of Microorganisms,
Brock (1974).)
D-8
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METRIC SYSTEM REFERENCE
THERE ARE THREE BASIC METRIC UNITS AND THEY ARE: METERS UHICH MEASURE LENGTH; GRAMS HHICH MEASURE WEIGHT (MASS);
AND LITERS HHICH MEASURE VOLUME OR CAPACITY. THE METRIC SYSTEM IS BASED ON THE NUMBER 10 WITH PREFIXES TO
SPECIFY THE MULTIPLE OR FRACTION OF THE BftSIC UNIT. THE PREFIXES COMMONLY USED «RE:
Prefix
mega, M
kilo, k
hecto, n
deca, da
Prefix
deci, d
centi, c
milli, m
micro, u
CONVERSION FACTORS
ENGLISH UNIT
ere
cre-f eet
ub i c feet
ubic feet ,
ubic feet/gallon
ubic feet/ pound
ubic yard
feet
gal 1 on
ga 1 1 on
gallon per day/sq foot
gallon per minute/sq foot
pound
pounds/1,000 cubic feet
pound/day/cubic foot
pound/million gallon
million gallon
million gal 1 ons/day
million gallons/day
pounds/cubic foot
pounds/square foot
pounds / soua re inch
square feet
square inch
SYMBOL
ac
acre-ft
cu ft
cu ft
cu ft/gal
cu ft/lb
cu yd
ft
gal
gal
gpd/sq ft
gpm
gpm/sq ft
Ib
lb/1 ,000 sq ft
Ib/day/cu ft
Ib/mil gal
mil gal
mgd
mgd
pcf
psf
psi
sq ft
sq i n
ENGLISH TO
METRIC
MULTIPLY BY
4046.9
1233.5
0.02832
28.32
7.482
0.06243
0.7646
0.3048
3.785
0.003785
0.04074
0 . 06308
0.67902
0.4536
16.02
16.02
0.1198
3785.0
3785.0
0.0438
16.02
4.882
0.0703
0.0929
645.2
METRIC TO
ENGLISH
MULTIPLY BY
0.0002471 1
0.0008107
35.315
0.035315
0.0001336
16.02
1 .308
3.281
0.2642
264.2
24.55
15 85
1 .473
2.205
0.06243
0.06243
8.344
0.0002642
0.0002642
22.83
0.06243
0.2048
14.22
10.76
0.00155
METRIC UNITS
square mete s
cubic meter
cubic meter
1 i ters
1 1 ters/cubi meter
cubic meter /kilogram
cubic meter
meters
liters
cubic meters
cubic meter/sq meter per day
liters/sq meter per second
ki 1 ograms
grams/cubic meter
ki 1 ograms/cu meter per day
grams/cubic meter
cubic meters
cubic meters/day
cubic me ters / second
kilograms/cubic meter
ki 1 ograms/ squa re meter
ki 1 ograms force/sq centimeter
square meter
square mi 1 1 ime ter
SYMBOL
m2
m3
m3
1 ,
1/m3
m3/kg
n.3
m
1
m3
m3/m2-d
i / <-
1
1/m -s
kg
g/m3
kg/m -d
g/m3
m3
m3/day
m3/s
kg/m3
kg/m2
kg f/cr/
m2
mm 2
RECOMMENDED WASTEWATER UNITS OF EXPRESSION
DESCRIPTION
Hastewater Fl ow
Organ i c Load i ng
Aera ti on Period
Ai r Requi rement
Air Flow
Vol ume
ENGLISH UNIT
million gallons per day
gal 1 ons per mi nute
pounds of BODj (or COD) applied per day per pound of
mixed liquor volatile suspended solids (MLVSS)under
aera ti on
hours of detention in aeration tank excluding
return sludge (RAS) flows
cubic feet of air per pound of 6005 (or COD) removed
cubic feet of air per gallon of wastewater treated
cubic feet per minute
million gallons, cubic feet, or gallons
METRIC UNIT
cubic meters per second
cubic meter per day
liters per second
meter of vo 1 ume
kilograms of BOOc (or COO) applied per day
MLVSS under aera ti on
per cubic
per ki 1 ogram
same as Engl i sh units
cubic meters of air per kilogram of BODs (o
removed
Liters of air per cubic meter of wastewater
treated
r COD)
cubic meters per second or liters per second
cubic meters or liters
U.S. GOVERNMENT PRINTING OFFICE: 1980 — 677-014/1109 RT.CIOK SO. 8
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