O
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-016 May 1982
Project Summary
Evaluation and Control of
Sidestreams Generated in
Publicly Owned Treatment
Works
Roy Ball, Michael Harris, and Kevin Deeny
The document on which this project
summary is based provides methodol-
ogies and considerations for evaluat-
ing and controlling sidestreams
generated in publicly owned treat-
ment works (POTW's). The methodol-
ogies are structured in algorithms.
These algorithms are used initially
to determine whether one or more
sidestreams are impacting on main-
stream process performance. Once an
impact on process performance is
determined, additional algorithms
present operational procedures for
controlling the impact of the side-
stream, either at the mainstream-pro-
cess or at the source of the
sides tream.
Through the proper use of the algo-
rithms, a point is reached where all
applicable operational methods to
reduce the sidestream impact have
been performed. Decision points
included in the algorithms refer the
user to design methods to control
sidestream impacts in the event that
all of the operational methods have
been unable to reduce the impacts to
acceptable levels.
In addition, sidestream characteri-
zation data are appended to the full
report to provide available informa-
tion for design purposes.
The methodologies for evaluating
and controlling sidestreams in
POTW's are not intended to represent
all of the available means, nor are they
each intended to apply to all POTW's.
The algorithms are somewhat com-
plex so they can be applied to a wide
range of treatment plants with differ-
ing design and operational features.
The ultimate user willtailor and apply
the algorithms to the individual treat-
ment plant; therefore, the complexity
of the algorithms will be directly
related to the specific treatment plant
for which they are used.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory,
Cincinnati, OH, to announce key find-
ings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
POTW's have been mandated by the
Federal Water Pollution Control Act
Amendments of 1972 (Public Law 92-
500) and the Clean Water Act of 1977
(Public Law 92-215) to discharge only
effluents that have attained certain lev-
els of treatment. In general, the treat-
ment processes required to meet these
discharge standards are a combination
of unit operations and unit processes.
In general, the more stringent the dis-
charge standard, the greater are the
amounts and types of sludges gener-
ated by a POTW. This results in many
types of sludge handling or treatment
operations and processes being
-------
required to ensure proper overall sys-
tem performance. In addition to produc-
ing sludges that must be adequately
disposed of, sidestreams are generated
that must also be treated.
Many performance problems at
POTW's are allegedly the result of recy-
cling these sidestreams within the
POTW. Sidestreams often carry signifi-
cant quantities of organic and inorganic
materials either in solution or sus-
pended form. Although the volume of
these sidestreams is generally small as
compared with the influent flow of the
POTW's, returning these sidestreams
to the influent of the POTW can signifi-
cantly increase the organic and solids
loading to the POTW. The significance
of the potential impact on mainstream
processes depends on a number of fac-
tors that include the percent of plant
design capacity in service, combina-
tions of processes used, and specific
design and operating features of the
plant. Generally, however, most main-
stream processes should be capable of
handling any sidestream generated at a
POTW.
Once the matrix was completed,
definitive procedures to assess the
impact of sidestreams had to be devel-
oped to be applied at POTW's. Following
the assessment, specific operational
methodologies and design information
had to be developed to use in reducing
the impact of sidestreams on POTW's.
The first step in evaluating and con-
trolling sidestream impact is to define
whether a sidestream is indeed respon-
sible for an observed loss in perform-
ance in a mainstream process.
Since POTW's may differ significantly
in the number and type of processes
that are used at the facility, a flexible,
systemized approach for evaluating
sidestream impacts was developed.
This approach uses algorithms that are
similar to logic flow diagrams. An algo-
rithm developed for each of the main-
stream processes considered in this
report is to be used as a guideline in
evaluating the impact of sidestreams on
the mainstream processes.
To determine whether sidestreams
are responsible for losses in perform-
ance, the user must select the approp-
riate algorithm for the specific POTW
and complete the work outlined in the
algorithm before any other activity is
initiated. In the event that a sidestream
impact is confirmed through the use of
the evaluation procedure outlined in the
algorithm, the user is referred to opera-
tional methods and design information
(contained in the report) that can be
used to control the impact. The system-
ized approach using algorithms is also
used to present operational methods to
control the sidestreams impact.
The overall approach for using the
information in this report is shown
graphically in Figure 1 and briefly dis-
cussed below.
Algorithms applicable to the specific
POTW are selected by the user and used
as guidelines in determining whether
sidestreams are impacting mainstream
processes. Impacts, once determined
are recorded on a checklist for refer-
ence. At this point, the user must deter-
mine whether any of the impacts had
been previously considered or are new
to the checklist. If the impacts have not
been previously considered, the user is
directed to operational information (in
algorithm format)to assist in controlling
the impact(s). A checklist for opera-
tional information is used to keep track
of recommended activity. Ultimately,
the recommendations are to be carried
out at the POTW.
To determine whether the recom-
mended changes have been partially or
fully successful in controlling the
Mainstream Treatment Process
Evaluation Algorithms
Primary Treatment I Secondary Treatment
Evaluation I Evaluation
Evaluation Algorithm
Checklist
I Anything New Added? | • >| End of Evaluation I
Yes
|n
Design Modification
Matrix
Operational Mitigation Design Modification
Algorithm Checklist I Matrix Checklist
No
J
Has Everything Been Implemented?
I Ranking
Implementation |
Figure 1. Summary of the evaluation processes.
-------
impact, the processes must then be re-
evaluated by using the original evalua-
tion algorithm. This time, however, if a
problem still exists (and knowing that
operational methods have been tried to
correct the condition), the user is refer-
enced to design modifications to control
the impact.
Methodology
A process matrix was developed to
categorize sidestream volumes and
strengths typical of various types of
POTW's. From this matrix, the impact of
the sidestreams on overall POTW per-
formance and effluent quality was
determined, and operational evaluation
and control procedures and design
information to minimize their impact
were developed.
The process matrix contains the fol-
lowing mainstream treatment pro-
cesses and sidestream generators:
Mainstream treatment processess
• Primary clarification-IP)
• Activated sludge-(AS)
• Trickling filter-(TF)
• Rotating biological contactor-(RBC)
Sidestream generator/sidestream
• Gravity thickener-(GT)/super-
natant
• Dissolved air flotation-(DAF)/sub-
natant
• Anaerobic digestion-(AnD)/super-
natant
• Aerobic digestion-(AeD)/super-
natant (decant)
• Vacuum filter-(VF)/filtrate
• Centrifuge-(C)/centrate
Table 1. Process Matrix
• Belt filter press-(BF)/filtrate
• Sand drying bed-(SB)/under-
drainage liquor
• Sludge lagoon-(LA)/supernatant
• Heat treatment-(HT)/liquor
• Wet air oxidation-(WAO)/liquor
• Pressure filter (filter press)-(FP)
/filtrate
• Purifax-(PX)/supernatant, filtrate,
subnatant, or under-drainage liquor
It was necessary to develop a matrix
(Table 1) of typical wastewater treat-
ment processes/sidestreams from
which operational strategies and
design information could be developed.
The treatment processes and side-
stream generator elements of the
matrix were selected through a com-
plete prioritization procedure that took
into account such factors as numbers in
use, the number and type of side-
streams in typical treatment plants, and
the sidestream's character. As part of
the development of the matrix, data on
the character of specific sidestreams
were accumulated by means of a litera-
ture search; these data were used m
mathematical process models to predict
the overall impact of sidestreams on
typical treatment plants.
Table 2 presents information
gathered on sidestream characteristics
during the literature search. Table 3 is
an example of a summary of sidestream
characteristics that have been pre-
dicted through the use of mathematical
models.
It was necessary to assign priorities
to the information to develop a matrix of
Sidestream Generator
Primary
(P)
this type (Table 1) because of the differ-
ent combinations of processes that can
possibly be found in POTW's. As an
example, from the matrix shown in
Table 1, over 1,300 plant-wide side-
streams are possible with potentially
different characteristics. Additionally, if
other factors are considered (e.g.,
separate digestion and/or thickening
for primary treatment processes, or
thickening before and after digestion),
the number of possible sidestreams
with potentially different characteris-
tics could grow into the tens of
thousands.
Results and Discussion
This project developed the general
methodology to assess and control the
impact of sidestreams on mainstream
processes. The methodology developed
in the report is presented in the form of
algorithms, similar to logic flow dia-
grams, which allow this information to
be applicable to various site specific
situations.
Two types of algorithms were devel-
oped - evaluation and control
algorithms.
Evaluation algorithms were devel-
oped to evaluate mainstream treatment
processes primarily with respect to the
impact of sidestreams. The mainstream
processes that were considered
included the primary and secondary
treatment processes shown in the
matrix in Table 1. Secondary clarifica-
tion was considered as part of each
secondary treatment process. As an
Treatment Process
Activated
Sludge
(AS)
Trickling
Filter
ITF)
Rotating
Biological
Contactor
(RBC)
Gravity thickener (GT)
Dissolved air flotation (DAF)
Anaerobic digestion (AnD)
Aerobic digestion (Aed)
Vacuum filter (VF)
Centrifuge (C)
Belt filter press (BF)
Sand drying bed (SB)
Lagoon (LA)
Heat treatment (HT)
Wet air oxidation (WAO)
Pressure filter (Filter press, FP)
Pur if ax (PX)
O
O
•
O
O No evaluation required. These process combinations were not considered typical for POTW's and, therefore, were not used for
plant-wide sidestream predictions and evaluations.
• Evaluation required.
-------
example. Figure 2 illustrates a portion
of the algorithm that is used to evaluate
the impact of sidestreams on primary
clarification.
Co/tfro/algorithms were developed to
be used as guides in making operational
changes at the mainstream and side-
stream processes to control the impact
of the sidestreams. Algorithms were
developed for each of the mainstreams
and sidestreams shown in the matrix in
Table 1.
An example of a control algorithm for
gravity thickeners is shown in Figure 3.
In the event that operational modifi-
cations are not sufficient to reduce the
sidestream impact, design information
is presented that will assist in the con-
trol of sidestream impacts. An example
of design information suggested for a
specific sidestream impact is presented
in Table 4.
Summary
The full report presents methods to
evaluate whether mainstream treat-
ment processes are being impacted by
sidestreams occurring within a POTW.
In the event that an impact is deter-
mined, methods are established to con-
trol the impact(s) operationally or, if
required, through design modifications.
The methodologies presented in the
report for the evaluation and control of
sidestreams in POTW's are not
intended to represent all of the available
means nor are they each intended to
apply to all POTW's. The report format,
utilizing individual algorithms, is
intended to be flexible so that the infor-
mation can be tailored and applied to
each individual POTW.
The full report was submitted in ful-
fillment of Contract No. 68-03-2775 by
Roy F. Weston, Inc., under the sponsor-
ship of the U.S. Environmental Protec-
tion Agency.
Table 2. Sidestream Characteristics, Summary of Literature Review
Sidestream
Generator
Numbers
In Use*
Solids
Retention,
BODs,
mg/L
SS,
mg/L
Gravity
thickening
Dissolved
air
flotation
Anaerobic
digestion
Aerobic
digestion
Vacuum
filtration
Centrifugation
Belt filter
press
Sand drying
beds
Lagoons
Heat
treatment
Wet air
oxidation
Pressure
filter
Pur/fax
940 80-95
314 70-99.9
6,796 —
4,750 —
1,912 80-99.5
368 30-98
132
10,939
797
170
13
157
69
22-99.8
85-100
90-99+
100-400 98-2,500
50-3,950 20-2.440
2-11,014 100-32,400
5-6,350 10-41,800
10-10,000 160-20.OOO
173-10,000 100-20,000
46-146 30-3,400
6-6,000
150
90-99+ 3,000-10,000
20-800
71
1,600-15,000 50-11.400
20-500
96-WO 1.000-6,500 100-1,926
— 1OO-350 50-150
a Source: 1978 Needs Survey Data (Updated), U.S. Environmental Protection Agency.
4
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Table 3. Example Summary of Sidestreams Characteristics
'Loading. Ib/Day
Concentration, mg/L
Sidestream
Vacuum filtration
Solid bowl scroll
centrifuge
Basket centrifuge
Belt filter
Process Description*
P + AnD + VF
P + AS + GT + AnD + VF
P + AS + DAF + AnD + VF
P+ AS+ DAF+ AeD+ VF
P+ TF+ GT+ AnD + VF
P+ TF+ DAF + AnD + VF
P+ RBC+ GT+ AnD+ VF
P + RBC + DAF + AnD + VF
P + SBSC
P + AS + GT + AnD + SBSC
P + AS + DAF + AnD + SBSC
P + AS + DAF + AeD + SBSC
P+ TF+ GT+ AnD+ SBSC
P+ TF+ DAF + AnD + SBSC
P + RBC + GT+ AnD + SBSC
P + RBC + DAF + AnD + SBSC
P+ BC
P+ AS+ GT+ AnD+ BC
P + AS+ DAF + AnD + BC
P + AS + DAF + AeD + BC
P+ TF+ GT+ AnD+ BC
P+ TF+ DAF + AnD + BC
P+ RBC+ GT+ AnD+ BC
P + RBC + DAF + AnD + BC
P + AnD + BF
P + AS + GT + AnD + BF
P + AS + DAF + AnD + BF
P + AS + DAF + AeD + BF
P+ TF+ GT+ AnD + BF
P+ TF+ DAF + AnD + BF
P+ RBC + GT+ AnD+ BF
P + RBC + DAF + AnD + BF
Flow.
gpm
3.471
5.210
4,400
5,190
3.480
3,750
3,660
3,780
1,660
2.500
2,350
611
1,210
1,410
1,320
1.440
184
1,720
1.220
2,050
658
899
823
934
5.710
13.100
1 1,900
15,400
6,630
7,750
7.050
7.510
TBOD*
7.4
16.9
14.9
34.4
9.1
10.6
10.3
11.1
46.0
26.0
17.0
6.4
11.8
13.3
13.0
14.1
3.9
8.2
5.8
6.9
3.0
4.1
3.8
4.3
5.9
17.6
15.6
40, ?
7.5
9.0
8.6
9.3
TSSC
37.9
114
86.7
95.7
56.0
64.9
62.1
66.1
90.1
146
137
15.3
65.4
76.2
71.6
77.9
7.7
25.1
17.8
15.4
9.3
12.7.
11.7
13.2
20.7
78.9
71.4
101.5
33.6
40.0
36.2
38.9
TBOD
254
389
406
794
314
339
337
351
3,320
1,250
867
1,250
1,170
1,140
1,180
1,180
2,570
575
570
411
550
546
557
556
124
161
158
312
136
139
146
147
TSS
1,310
2.620
2,360
2,210
1,930
2,080
2,030
2,100
6,500
7,000
7.000
3,000
6,500
6,500
6,500
6,500
5,000
1,750
1.750
9OO
1,700
1,700
1.7OO
1,700
434
724
719
789
608
618
616
620
P, primary clarification; AnD, anaerobic digestion; VF, vacuum filter; AS, activated sludge; GT, gravity thickener; DAF, dissolved air
flotation; AeD, aerobic digestion; TF, trickling filter; RBC, rotating biological contactor; SBSC, solid bowl scroll centrifuge; BC,
basket centrifuge
b Total biochemical oxygen demand
c Total suspended so/ids
-------
Table 4. Primary Clarifiers Operational Impact
Observed Operational
Impact Parameter
Alternative Design
Modifications)
Design Criteria for
Modification(s)
Solids loading (TSSJ
Hydraulic loading (Q)
Effluent dissolved
oxygen concentration
(DO)
1. Add conditioning chemicals:
• Organic polyme,
• Inorganic salts (aiurn,
ferric chloride, lime)
2. Increase clarifier area by
clarifier addition
3. Increase overflow weir
length
1. Increase clarifier area by
clarifier addition
2. Install variable speed
influent pumping to reduce
flow variation
1. Increase or install grit
chamber aeration
1. Provide for 1-5 minutes
mixing at 100-200 seconds
(flocculation for 15-30
minutes at seconds'1),
and a chemical dosage of:
• 0-10 milligrams per liter (mg/Lj
• 0-500 mg/L for salts
Surface overflow rate of less
than 1,000 gallons per day per
square foot with a hydraulic
detent/on time of 90-120 min
Weir loading rate of less than
10,000 gallons per day per
linear foot of weir
Surface overflow rate of less
than 1,000 gpd/ft2 with a
hydraulic detention time of
90-120 min
Continuous influent flow at
2.
3.
1
2.
headworks
1. Standard cubic feet per min
of air per linear foot
-------
0
Are Primary
Clarifier Effluent
Solids Greater
than 100 mg/L?
© ,
Yes
Calculate
Influent
Design Solids
Loading fW/0
Sidestream) on
Clarifier =
solids/ 'd/sq ft.
© <
Is Inf. Solids
Loading Less
than Design
Loading?
© J
Yes
Calculate Inf.
Solids Loading
(W/Sidstream)
on Clarifier
= solids/ d/sq ft
©
Is Total Inf.
Solids
Less than
Design Loading?
i
r
/vJ
>J No Impact
Original Clarifier
Design
., Deficiencies
^ and/or ^,
Collection
System
Enforcement
Problems Exist
© Yes
Have T_^
Operational ^
.. Methods to \
£ Reduce Impact of
Sidestream \
Solids been 1
Implemented? L.
Yes No
No Further
Evaluation
of this
Parameter is
Possible. Go to
(72)
©
Implement
Design
Methods 17]
and
Continue
Algorithm _^
Evaluation. (/2j
Goto \-s
©
Implement
Operational
Methods to
Reduce Impact
of Sidestream
Solids
/j\ Continue
^^r X"X
Evaluation. \2}
Goto ^"^
•*•
©
Measure Inf.
Flow
Rate W/O
Sidestream
(/5)
Calculate
Clarifier
Weir Overflow
Rate = gpd/ft
© <
Is Inf. Overflow
Rate Less than
Design
Overflow
Rate?
©
Yes
Calclate Total
(W/ Sidestream)
Clarifier Weir
Overflow Rate
(75)
Is Total Weir
Overflow Rate
Less than
Design
Overflow Rate?
i
(/5) (75)
Original Clarifier
Design
Deficiencies
[^and/or ^
Collection
System
Enforcement
Problems Exist.
®v
Yes
Have
Operational *
... Methods to
^Reduce the
Impact
of Sidestream
Hydraulics been ^
Implemented?
Yes No
No Further
Evaluation of
this
Parameter is
Possible. Go to
(22)
[20)
Implement
Design
Methods j?]
and
Continue
Algorithm ^-^
Evaluation. (22)
Goto v-^
2n
Implement
Operational
Methods to
Reduce Impact o
Sidestream y^
Hydraulics \f
Continue
Evaluation. (22\
Goto \~S
*•
->•
*•
vS
Figure 2. Example of an evaluation algorithm to evaluate Sidestream impacts on primary clarification.
-------
Is Dilution Water
Used at
Thickeners?
No
Yes
Eliminate or
Minimize Use of
Dilution
Are Primary and
Waste Activated
Sludges.
Discharged to
Separate
Thickeners?
No
Yes
Measure the
Suspended Solids
Concentrations in
the Thickener
Overflows.
Are the Overflow
Solids
Concentrations
Unequal (±10%).
No
Yes
Consider Blending1
Sludges to
Increase Overall
Thickener
Performance
Perform Jar Tests
to Evaluate
Thickener
Performance with
Blended Sludges.
Will Sludge
Blending Increase
Thickener
Performance (i.e..
Result in a
Decrease in the
Average
Thickener
Overflow Solids
Concentration}
Based on Jar
Tests Performed
Above?
No
Operate
Thickeners with
Blended Sludges.
Are the Thickeners
Equpped with
Chemical
Conditioning
Facilities?
No
Yes
Evaluate
Thickener
Flocculant Aids by
Performing Jar
Tests and Utilize if
Effective
Where
Reduce the Solids
Retention Time in
the Thickenerfs)
to Minimize Septic
Conditions. Take
Unneeded Units
Out of Service if
Required.
I
Is the Plant
Equipped with an
Aerated Grit
Chamber?
No
Yes
Where Possible
Redirect the
Thickener
Overflow
Upstream of the
Grit Chamber to
Elevate the D.O.
Before Entering
the Clarifier.
Minimize the
Sludge Retention
Time in the
Primary Clarifiers.
Reduce the
Variability in the
Thickener
Overflow Rate by
Scheduling the
Pumping of
Primary and
Secondary
Sludges on a More
Continuous Basis.
Likewise,
Schedule Sludge
Pumping from the
Thickener(s) on a
More Continuous
Basis.
I
For Plants
Equipped with
Variable Rate
Sludge Pumping:
I
For Plants
Equipped with
Constant Rate
Sludge Pumping
Adjust Sludge
Pumping from the
Thickener(s) to
be Continuous.
I
Adjust Sludge
Pumping from the
Thickener(s) to
Occur More
Frequently but for
Shorter Periods of
Time.
Return to
Appropriate
Evaluation of
Sidestream Impact
Algorithm.
Possibilities are:
Primary
Activated
Sludge
Trickling
Filter/RBC
0
Figure 3. Example of a control algorithm which outlines operational methods to reduce the impact of gravity thickeners.
8
-------
ROY Ball, Michael Harris, and Kevin Deeny are with Roy F. Weston, Inc., West
Chester, PA 19380.
Jon H. Bender is the EPA Project Officer (see below).
The complete report, entitled "Evaluation and Control ofSidestrearns Generated
in Publicly Owned Treatment Works," (Order No. PB 82-195 272; Cost:
$18.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
: 1982 — 559-092/3405
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