Environmental Protection Technology Series
PARALLEL EVALUATION OF CONSTANT AND
DIURNAL FLOW TREATMENT SYSTEMS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-600/2-78-034
March 1978
PARALLEL EVALUATION
OF
CONSTANT AND DIURNAL FLOW TREATMENT SYSTEMS
by
Jon H. Bender
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
11
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment and management
of wastewater, solid and hazardous waste pollutant discharges from municipal
and community sources, for the preservation and treatment of public drinking
water supplies, and to minimize the adverse economic, social, health, and
aesthetic effects of pollution. This publication is one of the products of
that research; a most vital communications link between the researcher and
the user community.
This report describes the results of studies performed to define the
effects of diurnal flow variations on typical activated sludge system
performance. These hourly fluctuations in wastewater strength and flow
can adversely affect primary treatment as well as secondary treatment
process units. The results are compared to data from a similar system
operated at a constant flow.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
in
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ABSTRACT
Pilot plant studies were performed to evaluate the effects of an imposed
diurnal flow pattern on a conventional activated sludge treatment plant.
These results were compared against data generated on a similar system
treating a constant flow. Effects on primary clarifier and final clarifier
performance as well as soluble organic removals were evaluated. Other
effects on general plant stability were noted.
There were essentially no differences between the diurnal and constant
flow systems at the 1.5/1, 2.0/1, and 2.5/1 peak-to-average diurnal flows
imposed. Intensive sampling over a 24 hour diurnal flow cycle did not alter
this basic conclusion. General plant stability was not affected except for
some sludge blanket level problems at the 2.5/1 peak-to-average flow phase.
This report was submitted in fullfillment of Task 02, program element
1BC611, SOS 2A. This report covers the period from January 20, 1974 to
June 1, 1975 and work was completed June 1, 1975.
IV
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CONTENTS
Disclaimer ii
Foreword iii
Abstract iv
Figures vi
Tables ix
Acknowledgements x
1. Introduction 1
2. Conclusions 4
3. Recommendations 4
4. Plant Descriptions 5
5. Results , 9
Phase I - Peak-to-average ratio at 1.5/1 9
Phase II - Peak-to-average ratio at 2.0/1 15
Phase III - Peak-to-average ratio at 2.5/1 23
Intensive 24-hr sampling studies 30
Effects on plant stability 48
FeCl3 addition results 55
Summary 58
References 60
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FIGURES
Number Page
1 Typical Influent Wastewater Flow Pattern 2
2 Schematic of Parallel Activated Sludge Pilot Treatment Systems . . 6
3 Diurnal Flow Pattern for Phase I; Peak-to-Average Diurnal Ratio
at 1.5/1 10
4 Daily Variation of Raw Wastewater TSS for Phase I; Peak-to-
Average Diurnal Ratio at 1.5/1 12
5 Daily Variation of Raw Wastewater TBODs for Phase I; Peak-to-
Average Diurnal Ratio at 1.5/1 13
6 Daily Variation of Constant Flow System Primary Effluent TSS;
Peak-to-Average Dirunal Ratio at 1.5/1 14
7 Daily Variation of Constant Flow System and Dirunal Flow
System Final Effluent TSS for Phase I; Peak-to-Average
Diurnal Ratio at 1.5/1 16
8 Daily Variations of Constant Flow System and Diurnal Flow
System Final Effluent TBOD5 for Phase I; Peak-to-Average
Diurnal Ratio at 1.5/1 17
9 Diurnal Flow Pattern for Phase II; Peak-to-Average Diurnal
Ratio at 2.0/1 18
10 Daily Variation of Raw Wastewater TSS for Phase II; Peak-to-
Average Diurnal Ratio at 2.0/1 20
*
11 Daily Variation of Raw Wastewater TBOD5 for Phase II; Peak-to-
Average Diurnal Flow at 2.0/1 21
12 Daily Variation of Constant Flow System and Diurnal Flow
System Primary Effluent TSS for Phase II; Peak-to-Average
Diurnal Ratio at 2.0/1 22
13 Daily Variations of Constant Flow System and Diurnal Flow
System Final Effluent TSS for Phase II; Peak-to-Average
Diurnal Ratio at 2.0/1 24
VI
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Number Page
14 Daily Variation of Constant Flow System and Diurnal
Flow System Final Effluent TBOD5 for Phase II;
Peak-to-Average Diurnal Ratio at 2.0/1 ... 25
15 Diurnal Flow Pattern for Phase III; Peak-to-Average
Diurnal Ratio at 2.5/1 ......... 26
16 Daily Variation of Raw Wastewater TSS for Phase III;
Peak-to-Average Diurnal Ratio at 2.5/1 ...... 28
17 Daily Variation of Raw Wastewater TBOD5 for Phase III;
Peak-to-Average Diurnal Ratio at 2.5/1 . . 29
18 Daily Variation of Constant Flow System and Diurnal Flow
System Primary Effluent TSS for Phase III; Peak-to-
Average Diurnal Ratio at 2.0/1 31
19 Daily Variation of Constant Flow System and Diurnal Flow
System Final Effluent TSS for Phase III; Peak-to-
Average Diurnal Ratio at 2.5/1 . 32
20 Daily Variation of Constant Flow System and Diurnal
Flow System Final Effluent TBOD5 for Phase III;
Peak-to-Average Diurnal Ratio at 2.5/1 ... 33
21 Results of Intensive 24-hr. Sampling Study for Phase I;
Raw Wastewater TCOD 35
22 Results of Intensive 24-hr. Sampling Study for Phase I;
Raw Wastewater TSS ........... ... 36
23 Results of Intensive 24-hr. Sampling Study for Phase I;
Primary Effluent TCOD ........ ....... 37
24 Results of Intensive 24-hr. Sampling Study for Phase I;
Primary Effluent TSS ............... 38
25 Results of Intensive 24-hr. Sampling Study for Phase I;
Final Effluent TCOD 39
26 Results of Intensive 24-hr. Sampling Study for Phase I;
Final Effluent TSS 40
27 Results of Intensive 24-hr. Sampling Study for Phase II;
Raw Wastewater TCOD 42
28 Results of Intensive 24-hr. Sampling Study for Phase II;
Raw Wastewater TSS ...................... 43
Vll
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Number Page
29 Results of Intensive 24-hr. Sampling Study for
Phase II; Primary Effluent TCOD 44
30 Results of Intensive 24-hr. Sampling Study for
Phase II; Primary Effluent TSS 45
31 Results of Intensive 24-hr. Sampling Study for
Phase II; Final Effluent TCOD 46
32 Results of Intensive 24-hr. Sampling Study for
Phase II; Final Effluent TSS 47
33 Results of Intensive 24-hr. Sampling Study for
Phase III; Raw Wastewater TCOD 49
34 Results of Intensive 24-hr. Sampling Study for
Phase III; Raw Wastewater TSS . , 50
35 Results of Intensive 24-hr. Sampling Study for
Phase III; Primary Effluent TCOD 51
36 Results of Intensive 24-hr. Sampling Study for
Phase III; Primary Effluent TSS 52
37 Results of Intensive 24-hr. Sampling Study for
Phase III; Final Effluent TCOD 53
38 Results of Intensive 24-hr. Sampling Study for
Phase III; Final Effluent TCOD 54
Vlll
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TABLES
Number Page
1 Average Performance Values for Phase I; 1.5/1
Peak-to-Average Flow (1-20-74 to 3-16-74) 11
2 Average Performance Values for Phase I; 2.0/1
Peak-to-Average Flow (10-6-74 to 11-12-74) 19
3 Average Performance Values for Phase III; 2.5/1
Peak-to-Average Flow (4-6-75 to 5-12-75) 27
4 Results of Fed3 Addition Study During Phase II;
2.0/1 Peak-to-Average Flow 56
5 Results of FeCl3 Addition Study During Phase II;
2.5/1 Peak-to-Average Flow 57
6 Summary of Average Performance Values for Phases I,
II, and III 59
IX
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ACKNOWLEDGEMENTS
Appreciation is extended to the following people for their efforts
throughout the conduct of this project:
Burney N. Jackson supervised the operation of the pilot plant and the
analytical laboratory and the compilation and reduction of project data.
Glenn R. Gruber, Leo J. Fichter, Mark C. Meckes, Mark C. Fischer, and
Kevie A. Stahl operated and maintained the pilot plant on a 24-hour per
day, 7 days per week basis. In addition, Ms. Stahl assisted Mr. Jackson
in data compilation and reduction.
Robert N. Bloomhuff, William Chaney, and Harold L. Sparks performed
daily laboratory analyses for all project samples.
Richard C. Brenner was the Project Officer during experimental data
collection and also assisted in the review of this report.
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SECTION 1
INTRODUCTION
Wastewater treatment facilities generally receive a dry-weather waste-
water flow that varies in strength and volume at various hours of the day.
These variations are related to water use in the community by both its private
and industrial sectors. This daily cyclic nature of wastewater flows and
strengths are known as diurnal variations. An example of the diurnal
variation of a treatment plant wastewater flow is shown in Figure 1. The
magnitude of the diurnal flow variation is related to the ratio of dry-weather
peak-to-average flow. This is also defined by others as the ratio of the
dry-weather peak flow to minimum flow.
To handle diurnal variations in flow, unit process design may be based on
either average flows or peak flows. When the design is based on average
flows, unit processes may have poor performance during peak flows. However,
designs based on peak flows may result in substantially increased treatment
plant costs for required increased reactor sizes.
When the magnitude of the diurnal flow variation is large, flow
equalization may be an economical alternative for adequate treatment of the
entire flow. Flow equalization dampens out flow fluctuations by providing
storage during times of peak flows which are pumped through the plant during
periods of less than average flows. This permits the design and operation
of the treatment processes based on a more constant flow. Also,
concentration fluctuations may be dampened, providing a more uniform loading
of wastewater components to the treatment plant unit processes.
Several benefits have been attributed to the use of flow equalization.
Primary clarification, theoretically, should be improved since elimination
of peak overflow rates would?provide lower and more uniform effluent
quality. LaBrega and Keenan found that primary effluent suspended solids
removal increased from 23 to 47 percent before and after flow equalization;
however, organic removals across the primary were essentially the same.
Activated sludge secondary clarifiers should also theoretically receive the
same benefits. However, Boon and Burgess3 and Foess et al.,4 found that
variations in sludge settleability had a greater effect on final clarifier
performance than periods of peak flow. Other potential benefits include
increased uniformity in concentration and mass flow of organics and
nutrients to biological treatment units as well as dampening of any shock
loads of toxic materials.
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PEAK FLOW
Q.
o
o
_l
u.
tt
IS*
<
£
<
ot
37.8
00)
10 12 14 16
HOUR OF DAY
Figure 1. Typical influent wastewater diurnal flow pattern
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The purpose of this study was to evaluate the effects of imposing a
diurnal flow to a pilot scale activated sludge wastewater treatment system.
Variations in primary and secondary clarifier performance as well as
soluble organic removals were evaluated against a similar system treating a
constant wastewater flow. Secondary objectives were to evaluate the
effects on general plant stability, ability to maintain dissolved oxygen (DO)
in the aeration basins, and secondary clarifier sludge blanket levels
during the diurnal cycle. During the three successive phases of the study,
the effects of diurnal flow variations (peak/average) of 1.5/1, 2.0/1, and
2.5/1 were evaluated. The constant flow system was operated to simulate a
flow-equalized plant. However, fluctuations in organic and nutrient loads
were not dampened since the constant flow system received the same raw
wastewater source as the diurnal flow system. Therefore, fluctuating organic
and nutrient concentrations were received by the constant flow system which
would have been dampened in a true flow equalization situation.
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SECTION 2
CONCLUSIONS
1. At the diurnal flow variations examined in this study (1.5/1, 2.0/1,
2.5/1 peak-to-average), the constant and diurnal flow systems performed
essentially the same.
2. There were no clear trends in primary clarifier performance between
the constant and diurnal systems during any phase of this study.
3. Soluble organic removals were essentially the same for the two
systems.
4. Final clarifier performance did not vary significantly between the
diurnal and constant flow systems.
5. Intensive sampling over the 24 hr. diurnal flow cycles revealed no
significant trends in system performance between the constant and diurnal
flow systems.
6. No differences in treatment plant stability were observed between
the two systems, although sludge blanket problems occurred periodically
with the diurnally varied system during the 2.5/1 peak to average diurnal
flow pattern.
7. Accurate flow proportioned sampling is essential to obtaining
accurate results in diurnal flow studies. As the magnitude of the diurnal
cycle increases, the lack of representative flow-proportioned samples will
bias the evaluation in favor of the diurnal system.
SECTION 3
RECOMMENDATIONS
1. Additional pilot plant flow equalization studies should be performed
incorporating in-line and/or side-line storage of incoming wastewater. The
damping effect on mass loadings afforded by the storage technique represents
a potential benefit of flow equalization which could not be evaluated in this
project due to equipment limitations. The cumulative effect of hydraulic
equalization and mass load damping could enhance the attractiveness of flow
equalization from a process stability standpoint beyond the neutral position
presented in this report.
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SECTION 4
PLANT DESCRIPTION
All of the experimental work for this study was performed at the pilot
plant in the Experimental Wing of the Robert A. Taft Sanitary Engineering
Center- Cincinnati, Ohio, using two parallel activated sludge treatment
systems and associated equipment.
Two sources of raw wastewater were utilized for this study. Phase I
(1.5/1 peak-to-average flow) used a primarily domestic wastewater from the Mt.
Washington area of Cincinnati, Ohio. This is a combined sewer system which
at times produces a very weak wastewater. Phases II and III (2.0/1 and 2.5/1
peak-to-average flow, respectively) used a different wastewater source from
another area of eastern Cincinnati with a large industrial contribution.
Wide fluctuations in pH are characteristic of this wastewater. No pH control
was provided.
The experimental pilot plant consists of the two parallel treatment
systems shown schematically in Figure 2. Raw wastewater from one of the two
sources described previously is comminuted and screened before being pumped
to the primary clarifiers.
Raw wastewater flow control to the constant flow system (CFS) is
provided by a Fischer and Porter* analog flow controller. The controller
compares the flow signal from a Fischer and Porter magnetic flow meter to
the controller set point which generates an error signal that is integrated
over time by the controller. A diaphragm flow control valve is then
adjusted by the controller to compensate for the error signal, thereby
controlling flow.
The diurnal flow pattern was imposed with a Fischer and Porter flow
programmer. This unit generates a 0-100 percent signal which can be
programmed to alter the controller set-point with time. The flow is
controlled at various set-points at various times of the day. The rest of
the control loop is the same as the CFS.
Two identical primary clarifiers were used in parallel in the diurnal
flow system (DPS). Each unit has a surface area of 1.1 m2 (12 ft2) and a
volume of 3,975 1 (1,050 gal) providing a surface overflow rate (SOR) of
48.9 m3/day/m2 (1,200 gpd/ft2) and a detention time of 1.75 hr., respectively,
at an average unit influent flow rate of 37.8 1/min (10 gpm). The depth of
*Fischer and Porter Company. Warminster, Pennsylvania
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CONSTANT FLOW SYSTEM
PRIMARY SLUDGE
30 GPM
(CONSTANT)
RAW WASTEWATER
? :
PRIMARY
CLARIFIER
:LOW CONTROL
/ALVE
1
AERA
TION B>
\SIN
RETURN SLUDGE
20 GPM
/AVERAGE -'
( DIURNALLY
\ VARIED ,
FLOW CONTROL VALVE
10 GPM TO DRAIN
(CONSTANT)
DIURNAL FLOW SYSTEM
FINAL EFFLUENT
WASTE ACTIVATED SLUDGE
10
GPM
PRIMARY
CLARIFIER
10 GPM
PRIMARY
CLARIFIER
AERATION BASIN
FINAL \ FINAL EFFLUENT
CLARIFIER
RETURN SLUDGE
PRIMARY SLUDGE
WASTE ACTIVATED SLUDGE
Figure 2. Schematic of parallel activated sludge pilot treatment systems.
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these units are 3.96 m (13 ft.)- Floating scum is removed manually in each
unit. Mechanical sludge scraping is not provided in these primaries.
The CFS utilized one primary clarifier with a controlled influent flow
of 113.5 I/rain (30 gpm). This unit has a surface area of 3.3 m2 (36 ft2),
providing an SOR of 48.9 m3/day/m2 (1,200 gpd/ft2) at 113.5 1/min (30 gpm).
The depth of the unit is 2.74 m (9 ft.). A liquid volume of 7,230 liters
(1,910 gal.) yields a detention time of 1.06 hr. at 113.5 1/min (30 gpm)-
Only 75.7 1/min (20 gpm) of the effluent from this primary clarifier was
needed as feed to the CFS aerator; the other 37.8 1/min (10 gpm) was wasted
directly to drain. A 113.5 1/min (30 gpm) raw wastewater flow rate was
employed to provide the same average primary clarifier overflow rate as
imposed on the DPS primaries. This primary unit is equipped with mechanical
sludge scraping and scum removal equipment.
The aeration systems are identical for both systems. Each aeration
basin is a rectangular tank separated into three compartments. The total
volume of each basin is 18,960 liters (5,010 gal.) with a 2.1 m (7 ft.)
liquid depth. At the average system flow rate of 75.7 1/min (20 gpm), the
nominal detention time of each aerator is 4.2 hr. Each basin contains
non-clog, coarse-bubble air diffusers supplied with 376 1/min (15 scfm) of
compressed air.
Each system has identical center-feed, peripheral-weir, circular final
clarifiers. These units are 2.3 m (7.5 ft) in diameter with a 2.7 m (9 ft.)
side water depth. With a usable surface area of 3.4 m2 (36.6 ft2) [20 cm
(8 in.) of the 2.3 m (7.5 ft.) diameter is taken up by the peripheral weir],
the SOR is 31.9 m^/day/m2 (785 gpd/ft2) at the average flow of 75.7 1/min
(20 gpm). Mechanical sludge scrapers are provided, but scum removal is
manual.
Return sludge flow is accomplished by variable speed centrifugal pumps
and measured with Fischer and PorterR magnetic flow meters. During this
study, sludge recycle flow rates were varied manually between 30 to 50
percent of the raw wastewater flow to maintain mixed liquor suspended
solids (MLSS) at about 3000 mg/1. Further, recycle rates on the DPS were
adjusted manually throughout the day to maintain an approximate constant
percentage of the diurnal influent flow pattern.
Both activated sludge systems were operated to maintain an F/M ratio of
between 0.2 and 0.4 kg TBOD^/day/kg MLVSS. Operational experience indicated
that 3000 mg/1 of MLSS would result in an F/M in the required range.
All raw wastewater, primary effluent, and final effluent samples were
composited over each 24-hr, period. Each sample cycle was initiated by a
flush of the sample lines to drain with the wastewater to be sampled. The
sample flows were then diverted to refrigerated containers. Samples
collected on the DPS were automatically proportioned to flow by actuating
*Fischer and Porter Company, Warminster, Pennsylvania
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the sampler solenoid valves once every 3,785 liters (1,000 gal.) of
throughput rather than once every hour as was done on the CFS.
Analyses were performed by the operations staff of the pilot plant in
accordance with Standard Methods.5
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SECTION 5
RESULTS
This study was performed in three phases. A different peak to average
diurnal flow variation was imposed during each phase on one of the treatment
systems. During all three phases the other parallel treatment system
received the same constant flow rate. Both systems treated the same total
volume of wastewater daily. Each phase consisted of several months of
operation. Periods of instability were encountered during each phase due to
a combination of operating problems and slug loads of biological inhibitory
materials in the wastewater. Therefore, a period of six to eight weeks was
selected from each phase for presentation and evaluation when both systems
were experiencing simultaneous stable operation.
PHASE I PEAK-TO-AVERAGE DIURNAL RATIO AT 1.5/1
A 1.5/1 peak to average (P/A) diurnal flow was imposed on the DPS
during Phase I of this project. The flow pattern for this phase is shown in
Figure 3.
Table 1 shows the averages for the various parameters measured during
the 8 weeks of Phase I. The raw wastewater was weak with an average total
suspended solids (TSS) of 98 mg/1, an average 5-day total biochemical oxygen
demand (TBODr) of 106 mg/1 and an average total chemical oxygen demand (TCOD)
of 156 mg/1. Daily variations of the raw wastewater TSS and TBODr are shown
in Figures 4 and 5.
With a P/A of 1.5, the DPS primary clarifiers operated at an SOR of
48.9 m3/day/m2 (1,200 gpd/ft2) at the average flow and 73.3 m3/day/m2
(1,800 gpd/ft2) at the peak flow. The DPS produced an average primary
effluent of 67 mg/1 TSS, 84 mg/1 TBOD5, and a TCOD of 116 mg/1. The CFS
during the same period produced an average primary effluent of 84 mg/1 TSS,
93 mg/1 TBODs, and 134 mg/1 TCOD. Average removals across the diurnal
primary clarifier were 12 percent higher for TCOD, 8 percent higher for
TBODr, and 18 percent higher for TSS. Daily variations in primary effluent
TSS for the CFS and DPS are shown in Figure 6. No explanation can be given
the higher quality primary effluent produced by the DPS during Phase I.
The DPS final clarifiers during Phase I was operated at an SOR of
31.9 m3/day/m2 (785 gpd/ft2) at the average flow and 48.1 m3/day/m2
(1,180 gpd/ft2) at the peak flow. Final effluent from the DFS showed an
average of 10 mg/1 TSS, 16 mg/1 TBOD5, and 34 mg/1 TCOD. The CFS final
effluent showed an average TSS of 9 mg/1, TBOD5 of 16 mg/1, and a TCOD of
31 mg/1.
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226.8
(60)
189
^ (50)
O
£ 151.4
(40)
CO
LU
^
in
113.6
(30)
75.7
(20)
37.8
(10)
PEAK FLOW
AVERAGE FLOW
i i i i
i i
8 10 12 14 16 18 20 22 24
HOUR OF DAY
Figure 3. Diurnal flow pattern for Phase I,-peak to average diurnal ratio
at 1.5/1.
10
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TABLE 1. AVERAGE PERFORMANCE VALUES FOR PHASE I: 1.5/1 PEAK-TO-AVERAGE FLOW
(1-20-74 to 3-16-74)
RAW
WASTEWATER
PRIMARY
EFFLUENT
DIURNAL SYSTEM
PRIMARY
EFFLUENT
CONSTANT SYSTEM
FINAL
EFFLUENT
DIURNAL SYSTEM
FINAL
EFFLUENT
CONSTANT SYSTEM
TOTAL
COD
(mgA)
156
116
134
34
31
TOTAL SOLUBLE
COD COD
REMOVED (mg/1)
00
55
26+
14+
77j: «
n: «
TOTAL
BOD5
(mg/1)
106
84
93
16
16
TOTAL
BOD5
REMOVED
(%)
20+
12+
81*
85+
83*
85+
SOLUBLE SOLUBLE
BODs BOD5
(mg/1) REMOVED
00
26
94°
5 95A
95°
5 95*
TOTAL
SUSPENDED
SOLIDS
(mg/1)
98
67
84
10
9
TOTAL
SUSPENDED
SOLIDS
REMOVED
(%)
32+
14+
85*
90+
89*
91+
VOLATILE
SUSPENDED
SOLIDS
(mg/1)
77
50
64
8
7
F/M
(kgTBODq/day)
(kg MLVSS)
0.26
0.27
+ Based on raw wastewater
* Based on primary effluent
0 Based on TBODj of primary and SBOD5 of final effluent
A Based on TBOD5 of raw wastewater and SBODs of final effluent
-------
O) 300-
K5 250-
LU 200
150-
100-
50-
0
CO
I
10
1 1 '
20
30
i
40
DAYS STUDIED PHASE 1
50
60
Figure 4. Daily variation of raw wastewater TSS for Phase I;peak to average diurnal ratio at 1.5/1
-------
i 300-,
^ 250-
UJ
<
150 -
s/i
<
50
0
1
10
I ... I I ... , J ...... , , , , , ,
20 30 40
DAYS STUDIED PHASE 1
i
50
60
Figure 5. Daily variation of raw wastewater TBOD5 for Phase Irpeak to average diurnal ratio at 1.5/1.
-------
o>
E 300-,
250-
200-
150-
5
a:
100-
50-
0
1 I'
10
CONSTANT FLOW SYSTEM
DIURNAL FLOW SYSTEM
20 30 40
DAYS STUDIED PHASE 1
50
60
Figure 6. Daily variation of constant flow system primary effluent TSS for Phase I; peak to average
diurnal ratio at 1.5/1.
-------
Total plant removal efficiencies for these parameters were approximately
equal for both systems. Even though the CFS aerator received a stronger
primary wastewater than the DPS aerator the final effluent levels between the
constant and diurnal systems were essentially the same. Final effluent
soluble BOD5 concentration for the DPS and CFS were identical and indicated
a high degree of biological treatment efficiency. Both systems were operated
at an average F/M of 0.26 kg TBOD5/kg MLVSS/day. Figures 7 and 8 show the
daily variations in final effluent TSS and TBODs, respectively.
Conclusions regarding comparison of secondary treatment performance are
difficult to make since the primary effluent feed to each system was
different. Based on the final effluent characteristics, both systems appear
equal. However, the percentage of solids and organics removed through the
constant flow activated sludge system averaged 2-6 percent higher than the
diurnal flow secondary system. The differences in performance are not large
enough to substantiate, on the average, any distinction between the constant
and diurnal flow systems operations during the 1.5/1 P/A phase.
PHASE II PEAK-TO-AVERAGE DIURNAL RATIO AT 2.0/1
For Phase II, the imposed diurnal flow was increased to 2.0/1 peak-to-
average as illustrated in Figure 9, while still maintaining an average
influent flow over a 24 hr. period of 75.7 1/min. (20 gpm). The CFS
continued to receive the same flow as in Phase I.
Table 2 summarizes the averages for the various parameters measured
during the six weeks of Phase II. As mentioned previously, the raw wastewater
source was changed at the beginning of Phase II from a primarily domestic
wastewater to a combined industrial-domestic wastewater. Industrial
contributions increased the magnitude and fluctuation in wastewater strength
significantly for the rest of the study. Phase II raw wastewater averaged
244 mg/1 TSS, 170 mg/1 TBOD5, and 354 mg/1 TCOD. Figures 10 and 11 plot the
daily variations in raw wastewater TSS and TBOD^, respectively.
At a P/A diurnal flow ratio of 2.0/1, the DPS primary clarifiers were
operated at an SOR OF 48.9 m^/day/m2 (1,200 gpd/ft2) at the average flow of
75.7 1/min. (20 gpm) and 97.8 m3/day/m2 (2,400 gpd/ft2) at the peak flow
of 151.4 1/min. (40 gpm). DPS produced a primary effluent that averaged
200 mg/1 TSS, 148 mg/1 TBOD5, and 330 mg/1 TCOD. During this same period the
CFS primary effluent averaged 203 mg/1 TSS, 151 mg/1 TBOD5 and 342 mg/1 TCOD.
Percent removals averaged 4 percent and 2 percent, respectively, for
TCOD and TBOD5 across the diurnal primary clarifier. TSS removal was 3 percent
higher for the constant flow primary clarifier. These variations
in removals between the systems are not as large as in Phase I but the
removal efficiencies for both primaries were substantially lower. Figure 12
shows the daily variations in primary effluent TSS for the diurnal and
constant flow systems during this 6 week period.
The daily fluctuations in primary clarifier performance show that the
diurnal primary clarifiers at times produced a substantially higher quality
effluent. Overall in Phase II, the DPS primary clariifers exhibit less daily
15
-------
E
60-
50-
10
CONSTANT FLOW SYSTEM
DIURNAL FLOW SYSTEM
DAYS STUDIED PHASE 1
Figure 7. Daily variation of constant flow system and diurnal flow system final effluent TSS for
Phase I;peak to average diurnal ratio at 1.5/1.
-------
Q
O
u.
LU
<
Z
70 -
60 -
50-
40-
30
20
10
10
CONSTANT FLOW SYSTEM
DIURNAL FLOW SYSTEM
1 I
20
30
1 i
40
50
60
DAYS STUDIED PHASE 1
Figure 8. Daily variations of constant flow system and diurnal flow system final effluent TBOD5 for
Phase I;peak to average diurnal ratio at 1.5/1.
-------
AVERAGE FLOW
0
2 4 6 8 10 12 14 16 18 20 22 24
HOUR OF DAY
Figure 9. Diurnal flow pattern for Phase II;peak to average diurnal ratio
at 2.0/1.
18
-------
TABLE 2. AVERAGE PERFORMANCE VALUES FOR PHASE II: 2.0/1 PEAK-TO-AVERAGE FLOW
(10-6-74 to 11-12-74)
RAW
WASTEWATER
PRIMARY
EFFLUENT
DIURNAL SYSTEM
PRIMARY
EFFLUENT
CONSTANT SYSTEM
FINAL
EFFLUENT
DIURNAL SYSTEM
FINAL
EFFLUENT
CONSTANT SYSTEM
TOTAL TOTAL SOLUBLE
COD COD COD
(mg/1) REMOVED (mg/1)
354 131
330 7+
342 3+
77 ill 5S
74*
89 71+ 56
TOTAL
BOD5
(mg/1)
170
148
151
19
24
TOTAL
BOD5
REMOVED
13+
11+
87*
89+
84*
86+
SOLUBLE SOLUBLE TOTAL
BODS BODs SUSPENDED
(mg/1) REMOVED SOLIDS
W (mg/1)
67 244
200
203
10 q^A 22
q-zO
11 946 30
TOTAL VOLATILE
SUSPENDED SUSPENDED
SOLIDS SOLIDS
REMOVED (mg/1)
191
18+ 142
21+ 152
89* Ifi
91+ 16
85* 21
88+ ^
F/M
(kpTBOD.q/day)
(kg MLVSS)
0.51
0.39
+ Based on raw wastewater
* Based on primary effluent
0 Based on TBOD5 of primary effluent and SBOD5 of final effluent
A Based on TBODs of raw wastewater and SBOD5 of final effluent
-------
o>
E
uu
450-
400-
400-
350-
300-
250-
200-
150-
100-
50-H
1 » r "
10 20 30
DAYS STUDIED PHASE 11
Figure 10. Daily variation of raw wastewater TSS for Phase II,-peak to
average diurnal ratio at 2.0/1.
40
20
-------
o>
E
o
O
UJ
400
350
300
250
200
150
100-
50-
o-
0
10
1 ITU r r j i "iT^IJIT
20 30
DAYS STUDIED PHASE 11
40
Figure 11. Daily variation of raw wastewater TBOD^ for Phase II;peak to
average diurnal ratio at 2.0/1.
21
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CO
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s
400-
350-
300-
250-^
200-
150
100
50-
CONSTANT
FLOW SYSTEM
DIURNAL
FLOWSYSTEM
1 I
1 I I I 1 T 1
III I I I I F I I I I I
10 20 30
DAYS STUDIED PHASE 11
40
Figure 12. Daily variation of constant flow system and diurnal flow system
primary effluent TSS for Phase II;peak to average diurnal ratio
at 2.0/1.
22
-------
performance variability than the single CFS primary clarifier. Theoretically;
a primary clarifier operated at a constant flow should have less effluent
variability than one experiencing diurnal flow fluctuations.
The DPS final clarifier during Phase II was operated at an SOR of
31.9 m3/day/m2 (785 gpd/ft2) at the average flow and 64.0 m3/day/m2
(1,570 gpd/ft2) at the peak flow. DPS final effluent averaged 22 mg/1 TSS,
19 mg/1 TBOD5, and 77 mg/1 TCOD. Final effluent quality from the CFS was
less averaging 30 mg/1 TSS, 24 mg/1 TBOD5, and 89 mg/1 TCOD.
Both total system and secondary system removal efficiencies averaged
3-4 percent higher for the DPS during this phase of the study, even though
the constant flow activated sludge system was operated at an F/M of
0.39 kgBOD5/day/kgMLVSS as compared to 0.51 for the diurnal flow activated
sludge system. Soluble organic removals were equivalent in the two
systems; therefore, the difference in overall secondary system performance in
this phase can be attributed to less efficient solids capture in the CFS
final clarifier.
Figures 13 and 14 show the daily variations in final effluent TSS and
TBODs, respectively., for the constant and diurnal flow systems. These
figures along with the average data for this phase from Table 2 support the
observation that the DPS produced a slightly better effluent than the CFS.
Based on Phase I and Phase II results, it appears that equalization of flows
without dampening of pollutant loads does not offer any potential for
improved average treatment performance at P/A diurnal variations of 2.0/1
or less.
PHASE III PEAK TO AVERAGE DIURNAL RATIO AT 2.5/1
Phase III of this study investigated imposing a 2.5/1 peak to average
(P/A) diurnal flow variation to the DPS with the same 75.7 1/min. (20 gpm)
constant flow as used in Phases I and II to the CFS. The diurnal flow pattern
for this phase is shown in Figure 15.
Table 3 summarizes the averages of the parameters measured during the
7 wks. of Phase III. The source of raw wastewater was the same as that for
Phase II. During this period, the raw wastewater averaged 167 mg/1 TSS,
137 mg/1 TBODs, and 255 mg/1 TCOD. Daily variations of TSS and TBOD5 are
shown in Figures 16 and 17, respectively. Fluctuation in waste strengths
were not as large as in Phase II.
With a P/A flow variation of 2.5/1, the DPS primary clarifiers operated
at an SOR of 48.9 m3/day/m2 (1,200 gpd/ft ) at the average flow of
75.7 1/min. (20 gpm) and 122.2 m3/day/m2 (3000 gpd/ft2) at the peak flow of
189.3 1/min. (50 gpm). The diurnal flow primaries produced an average
effluent quality of 117 mg/1 TSS, 95 mg/1 TBOD5, and 220 mg/1 TCOD. Primary
effluent from the constant flow primary averaged 121 mg/1 TSS, 86 mg/1 TBOD5,
and 195 mg/1 TCOD.
23
-------
CONSTANT
FLOW SYSTEM
0)
V)
DIURNAL
FLOW SYSTEM
,.,.,.,,..,,
10 20 30
DAYS STUDIED PHASE 11
Figure 13. Daily variations of constant flow system and diurnal flow system
final effluent TSS for Phase II;p'eak to average diurnal ratio
at 2.0/1.
24
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O
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00
70
60
50-
40-
30
20-
10-
CONSTANT
FLOW
SYSTEM
DIURNAL
FLOW SYSTEM
|I|I|||I||IIITI»I||I III | I T
10 20 30
I I II II I 7 I
40
DAYS STUDIED PHASE 11
Figure 14. Daily variation of constant flow system and diurnal flow system
final effluent TBOD5 for Phase Iljpeak to average diurnal ratio
at 2.0/1.
25
-------
AVERAGE FLOW
8 10 12 14 16 18 20 22 24
HOUR OF DAY
Figure 15. Diurnal flow pattern for Phase III; peak to average diurnal ratio
at 2.5/1.
26
-------
TABLE 3. AVERAGE PERFORMANCE VALUES FOR PHASE III; 2.5/1 PEAK-TO-AVERAGE FLOW
(4-6-75 to 5-12-75)
RAW
WASTEWATER
PRIMARY
EFFLUENT
DIURNAL SYSTEM
PRIMARY
EFFLUENT
CONSTANT SYSTEM
FINAL
EFFLUENT
DIURNAL SYSTEM
FINAL
EFFLUENT
CONSTANT SYSTEM
TOTAL
COD
(mg/1)
255
220
195
60
50
TOTAL SOLUBLE TOTAL
COD COD BOD 5
REMOVED (mg/1) (mg/1)
(*)
94 137
14+ 95
24+ 86
v7+ 40 20
80+ 32 19
TOTAL
BODr
REMOVED
31 +
37 +
79*
85+
78*
86+
SOLUBLE SOLUBLE TOTAL
BODr BOD5 SUSPENDED
(mg/1) REMOVED SOLIDS
(%) (mg/1)
40 167
117
121
94°
6 %A 24
97°
3 ggA 19
TOTAL
SUSPENDED
SOLIDS
REMOVED
30+
28+
80*
86+
84*
87+
VOLATI LE
SUSPENDED
SOLIDS
(mg/1)
114
76
81
16
13
F/M
(kgTBODfi/day)
(kg MLVSS)
0.24
0.20
+ Based on raw wastewater
* Based on primary effluent
0 Based on TBOD5 of primary effluent and SBODg of final effluent
A Based on TBOD5 of raw wastewater and SBOD5 of final effluent
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to
c*
LU
<
350-1
300-J
250
200
150
100-
1
C
) 10
20
30
40
50
DAYS STUDIED PHASE 111
Figure 16. Daily variation of raw wastewater TSS for Phase HI; peak to average diurnal ratio
at 2.5/1.
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§ 200-
CQ
o: 150 -
Uj
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100-
50 -
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10 20 30
DAYS STUDIED PHASE 111
111111 i
40
n
50
Figure 17. Daily variation of raw wastewater TBOD5 for Phase III; peak to average diurnal ratio
at 2.5/1.
-------
Removals of TCOD and TBOD5 averaged 10 and 6 percent higher, respectively,
across the constant flow primary clarifier, representing a reversal in
efficiency patterns observed in Phases I and II. The diurnal flow primary
clarifier removed on the average 2 percent more TSS than the constant flow
primary. Daily variations in primary effluent TSS levels, as shown in Figure
18, indicate some fluctuation between constant and diurnal primary clarifier
performance but there was no significant trend.
During this phase the DPS final clarifiers were operated at an SOR of
31.9 m3/day/m2 (785 gpd/ft2) at the average flow and 80.0 m3/day/m
(1,963 gpd/ft2) at the peak flow. On the average, the DPS final effluent
showed a TSS of 24 mg/1, TBOD5 of 20 mg/1, and TCOD of 60 mg/1. Final effluent
average values from the CFS were 19 mg/1 TSS, 19 mg/1 BOD5, and 50 mg/1 TCOD.
Both secondary systems removed essentially the same percentage of TCOD and
TBOD5. However, on a total system basis, TCOD removal was 4 percent higher
for the CFS. Soluble BODs and TSS removals were 3 and 4 percent higher
respectively, for the CFS on a secondary system basis only and virtually equal
on a total system basis. Figures 18 and 19 depict the daily variations in
final effluent TSS and TBOD^, respectively-, for the two systems. Final
effluent TSS exhibited greater variance at times from the diurnal flow
clarifier, but no detectable trend was evident. No significant differences
between the daily TBODs levels of the constant and diurnal flow final effluents
were shown. The results from Phase III indicate that no discernible
differences in performance trends between the two systems could be
quantified at the 2.5/1 P/A diurnal cycle.
INTENSIVE 24 HR SAMPLING STUDIES
During one 24 hr. period of each phase of this study, an intensive
sampling schedule was initiated. Grab samples from the raw wastewater,
primary effluent, and secondary effluent were collected every 2 hrs. from
both the DPS and CFS. From these grab samples, incremental total mass
loadings were calculated for the 2 hr. period that the grab sample
represented. Cumulative mass loadings were then calculated by summation of
the 2 hr. incremental mass loadings. The cumulative mass plots show the
progression of the influent and effluent system loadings and represent the
total mass loading for the system at any time during the 24 hr. period.
The purpose of flow equalization is to provide treatment plant process
units with a relatively constant flow and mass loading. Flow equalisation
is accomplished through use of a basin with sufficient volume to store raw
wastewater flows in excess of the constant flow supplied to the treatment
plant. This storage volume also allows the diurnally fluctuating wastewater
concentrations to be combined such that a relatively constant concentration
can be supplied to the treatment plant. Therefore, if true flow
equalization was provided to the CFS, incremental mass loadings would be
essentially equal and the cumulative mass loading would be essentially a
straight line with a constant slope. The DPS would have diurnally
fluctuating incremental mass loadings which could affect the shape of the
cumulative mass loading plots. Since both systems were operated so as to
process the same total volume of wastewater per day, the cumulative mass
30
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300-1
250-
200-
150 -
100
CONSTANT FLOW SYSTEM
DIURNAL FLOW SYSTEM
10 20 30 40
DAYS STUDIED PHASE 111
:igure 18. Daily variation of constant flow system and diurnal flow system primary effluent TSS
for Phase III;peak to average diurnal ratio at 2.0/1.
-------
DIURNAL FLOW SYSTEM
O>
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to
CO
u- 30 -
<
Z
CONSTANT
FLOW SYSTEM
0
DAYS STUDIED PHASE 111
Figure 19. Daily variation of constant flow system and diurnal flow system final effluent
system TSS for Phase III;peak to average diurnal ratio at 2.5/1.
-------
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10
Q
O
oo
70-
60-
50-
40-
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20-
10-
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SYSTEM
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10
CONSTANT FLOW SYSTEM
I I I I I I I II I I I | I^T I I T ^ I T I I f T 1 'TT^ '
20 30 40
DAYS STUDIED PHASE 111
50
Figure 20. Daily variation of constant flow system final effluent TBOD^ for Phase III; peak to
average diurnal ratio at 2.5/1.
-------
loadings for the raw wastewater at the end of the 24 hr. cycle, theoretically,
should be the same for both the DFS and CFS.
The CFS did not completely simulate flow equalization since raw waste-
water storage was not provided. Therefore, the CFS received a constant flow
of a diurnally fluctuating raw wastewater. This could result in the CFS
receiving a higher or lower total mass loading over a 24 hr. period than the
DPS. For instance, if high wastewater concentrations occurred during periods
of low flow in the diurnal cycle, the incremental mass loading for the CFS
would be substantially higher than that for the DPS, thus possibly showing
the cumulative mass loading at the end of the 24 hr. cycle to be higher than
that for the DPS. Since both systems may have received different total waste
loads over the 24 hr. intensive sampling period, process unit effluent quality
may have been affected.
Phase I - Peak-to-Average Diurnal Ratio at 1.5/1
Figures 21 and 22 show the raw wastewater concentrations, incremental
mass loadings and cumulative mass loadings for TCOD and TSS, respectively,
calculated for the intensive 24 hr. sampling study performed during Phase I
of this study. The effect of the imposed diurnal flow pattern is shown on
the incremental and cumulative mass loading plots for the CFS and DPS. At a
1.5/1 P/A diurnal cycle, TCOD incremental and cumulative mass loadings were
essentially the same. However, the DPS received a 25 percent less TSS total
mass loading over the 24 hr. cycle.
Primary effluent concentrations, incremental and cumulative mass loadings
are shown in Figure 23 and 24 for TCOD and TSS, respectively. The diurnal
primary effluent TCOD concentrations were consistently, though only slightly
below those of the constant flow primary. No consistent trend was observed
for TSS. Cumulative TCOD mass loading for the CFS and DPS primaries showed
both systems producing essentially the same effluent total mass over the 24
hr. period. The DPS primary effluent cumulative mass loading for TSS was
approximately 25 percent less than the CFS. The difference appears to
correspond with the difference in influent TSS loadings to the CFS and DPS
primaries. Incremental mass TCOD and TSS loadings for the DFS primaries show
only small diurnal fluctuation over that observed with the CFS. The slope of
the cumulative mass loading plots substantiates this result since both plots
had essentially the same slope. This indicates that the imposed diurnal flow
at the 1.5 P/A ratio did not substantially affect primary effluent mass loading
rates over the 24 hr. period studied.
Figures 25 and 26 show the final effluent TCOD and TSS concentrations,
incremental mass loadings, and cumulative mass loadings, respectively, for
the 24 hr. period sampled during Phase I of this study. There were no
significant trends between the CFS and DFS secondary effluent TCOD and TSS
concentrations. The incremental mass loadings for final effluent TCOD did
show a significant increase over the six hours of peak diurnal flow. Over
the entire 24 hr. sampling period, the incremental mass loadings for final
effluent TSS were essentially the same. The cumulative mass loadings for
the DFS final effluent TCOD were slightly higher than those observed from
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Figure 22. Results of intensive 24 hr. sampling study for Phase I; raw
wastewater TSS.
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Figure 23. Results of intensive 24 hr. sampling study for Phase I; primary
effluent TCOD.
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effluent TSS.
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effluent TCOD.
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Figure 26. Results of intensive 24 hr. sampling study for Phase I; final
effluent TSS.
40
-------
the CFS. Final effluent TSS cumulative mass loadings were essentially the
same for both systems and the 24 hr. sampling period.
The results from the Phase I intensive 24 hr. sampling study indicate
that the DPS primary clarifier and activated sludge secondary treatment
performance were essentially unaffected by the 1.5/1 P/A diurnal flow ratio,
as compared to the CFS operated at a constant flow.
Phase II - Peak-to-Average Diurnal Ratio at 2.0/1
Figures 27 and 28 show the raw wastewater concentrations, incremental
mass loadings, and cumulative mass loadings for TCOD and TSS, respectively,
calculated for the intensive 24 hr. sampling study performed during Phase II
of this study. The incremental mass loadings plots for both TCOD and TSS
show that the DPS was receiving mass loadings that had a substantial diurnal
fluctuation. Mass loadings to the CFS were essentially constant. The
cumulative mass loading plots for both TCOD and TSS also showed the
diurnally fluctuating mass loadings to the DPS. However, for both TCOD and
TSS the DPS received a total mass loading 12 percent less than the CFS, over
the 24 hr. period.
CFS and DPS primary effluent concentrations, incremental mass loadings,
and cumulative mass loadings for TCOD and TSS are shown in Figures 29 and 30,
respectively. There were no significant trends in primary effluent TCOD or
TSS observed between the CFS and DPS. The incremental mass loading plots
showed that the DPS primary effluent mass loadings for TCOD had a significant
diurnal fluctuation corresponding to peak diurnal flows. However, the diurnal
flow primary had only small fluctuations in effluent TSS mass loadings during
the peak diurnal flows. The constant flow primary had relatively constant
effluent mass loading for both TCOD and TSS over the 24 hr. period sampled.
Cumulative mass loading plots for TCOD showed both the CFS and DPS primary
effluent TCOD mass loadings to be equivalent over the 24 hr. period. The TSS
cumulative mass loading for the DPS primary effluent was 18 percent less
than the CFS over the 24 hr. sampling period.
Figures 31 and 32 show the final effluent TCOD and TSS concentrations,
incremental mass loadings, and cumulative mass loadings, respectively, for
the 24 hr. period sampled. There were no significant trends between the
CFS and DPS secondary effluent TCOD and TSS concentrations. The incremental
mass loadings for DPS final effluent TCOD and TSS did show significant
fluctuations corresponding to the diurnal flow pattern. Final effluent
incremental mass loadings for the CFS were essentially constant over the
24 hr. sampling period. The final effluent cumulative mass loadings for the
DPS were 10 percent and 5 percent for TCOD and TSS, respectively, less than
those for the CFS.
The results from the Phase II intensive 24 hr. sampling study indicate
that both the primary clarifier and activated sludge secondary treatment
performance were essentially unaffected by the 2.0/1 P/A diurnal flow imposed
on the DPS as compared to the CFS operated at a constant flow. Lack of
equalization of the raw wastewater TCOD and TSS concentrations to the CFS
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wastewater TCOD.
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primary effluent TCOD.
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^" '~*
/ \
/ \
v \
_/
^^^-"^
CONSTANT FLOW
0 _
300.
O)
250_
to
to
ac
a.
CONSTANT FLOW SYSTEM
DIURNAL FLOW SYSTEM
Figure 30. Results of intensive 24 hr. sampling study for Phase II; primary
p-f-Flnpnt TSS .
45
-------
DIURNAL FLOW SYSTEM
Q
O
< £
Oc
X
z < -1
- 5 £ <
* O z
2.27
(5)
1.82
(4)"
1.36
(3)
0.908
(2)"
0.454
0)
01
DIURNAL FLOW SYSTEM
CONSTANT FLOW SYSTEM
DIURNAL FLOW
CONSTANT FLOW
ui
5
Q
O
u
<
Z
150_
100_
50_
DIURNAL FLOW SYSTEM
CONSTANT
FLOW SYSTEM
I I I I I I I I I I I I
0 2 4 6 8 10 12 14 16 18 20 22 24
HOURS
Figure 31. Results of intensive 24 hr. sampling study for Phase II: final
effluent TCOD.
46
-------
DIURNAL FLOW SYSTEM
0.454
(1)"
> D (_ LXJ U1
Z < z o m 0.227
s 2 Q, it ~ (o.sf
o z
0_J
DIURNAL FLOW SYSTEM
CONSTANT FLOW
SYSTEM
DIURNAL FLOW
CONSTANT FLOW
30
20_
CONSTANT FLOW
SYSTEM
DIURNAL FLOW SYSTEM
<
Z
H o
c
1
2
1
4
1
6
1
8
1 1
10 12
1
14
1
16
1
18
1
20
1
22
1
24
HOURS
Figure 32. Results of intensive 24 hr. sampling study for Phase II; final
effluent TSS.
47
-------
may have caused primary and final effluent total mass loadings for this
system to be slightly higher than the DPS.
Phase III - Peak-to-Average Diurnal Ratio at 2.5/1
Figures 33 and 34 show the raw wastewater concentrations, incremental
mass loadings, and cumulative mass loadings for TCOD and TSS, respectively,
calculated for the intensive 24 hr. sampling study performed during Phase III
of this study. The incremental mass loading plots for both TCOD and TSS
show that the DPS was receiving mass loadings that fluctuated significantly
over the diurnal cycle. Mass loadings to the CFS were essentially constant
except during large fluctuations in raw wastewater concentrations. Cumulative
mass loading plots for both TCOD and TSS showed that both systems were
receiving essentially the same total mass over the 24 hr. sampling period.
CFS and DPS primary effluent concentrations, incremental mass loadings,
and cumulative mass loadings for TCOD and TSS are shown in Figures 35 and 36,
respectively. The DPS primary effluent quality for both TCOD and TSS was
consistently less than the CFS, except for effluent TCOD during the last six
hours of the intensive sampling study. No explanation for this difference in
primary effluent quality is apparent. DPS primary effluent incremental mass
loading plots for both TCOD and TSS show large diurnal fluctuations while the
CFS primary effluent had a relatively constant mass loading. The primary
effluent TCOD cumulative mass loading plots showed no siginficant difference
between the two systems. However, the TSS total mass loading over the
24 hr. sampling period was 15 percent less for the DPS primary than the CFS
primary. This is related to the better performance of the DPS primary
clarifier during this 24 hr. study.
Figures 37 and 38 show the final effluent TCOD and TSS concentrations,
incremental mass loadings, and cumulative mass loadings, respectively, for
the 24.hr. period sampled. The CFS TCOD final effluent quality was better
than that of the DPS for most of the 24 hr. period. The DPS final effluent
TSS concentrations were more variable than the CFS and followed the diurnal
flow pattern as would be expected at this 2.5/1 P/A diurnal ratio. The
incremental mass loadings for the DPS final effluent TCOD and TSS showed
large fluctuations corresponding to the diurnal flow pattern. Final effluent
incremental mass loadings for the CFS were essentially constant over the
24 hr. sampling period. The final effluent cumulative mass loadings for TCOD
and TSS were 25 percent and 21 percent higher, respectively, for thg DPS than
for the CFS.
The results from the Phase III intensive 24 hr. sampling study indicate
the 2.5/1 P/A imposed diurnal flow variation significantly affected the DPS
activated sludge secondary clarifier performance when compared to the similar
CFS operated at a constant flow. However, since this represents only one day
of intensive sampling, it is difficult to make any definite conclusions re-
garding the effects of the 2.5/1 P/A imposed diurnal flow ratio on the treat-
ment system over extended periods of time.
48
-------
CONSTANT FLOW SYSTEM
z *-
w
-
iu . .
< m
5
£
< *
$
5
<
5
O
u_ .
" ^
^
5
LU y
11
5
9.08
(20)
6.81
(15)~
4.54
(10)~
2.27
(5)~
0 _
226.8
(60)~
189
(50)
151.4
(40)
113.6
(30)~
75.7
(20)
37. 8_
(10)
0 _J
D) 600
500 _
CONSTANT FLOW SYSTEM
DIURNAL FLOW SYSTEM
CONSTANT FLOW
TCOD
CtL
LU
<
LU
^
t/>
5
a.
400 _
300 _
200 _
100 _
0
^V_ /x
^-^_ /
v /
^-~^^J
\\\\\\\\\\\\
0 24 6 8 10 12 14 16 18 20 22 2-
HOURS
Figure 33. Results of intensive 24 hr. sampling study for Phase III; raw
wastewater TCOD.
49
-------
DIURNAL FLOW SYSTEM
uo
CO A CjJ
_1 |_ 4.31_
O J a: (10)
'?""_
i O £ 5 ">
! Q - 5 ^ 2.27
j -1 « « (5)"
: in 3- < 0>
0 _
DIURNAL FLOW SYSTEM
CONSTANT FLOW SYSTEM
a: 5
S*
<0
CONSTANT FLOW
^ 200_
o
£
V>
VI
I- 150_
CK
LJJ
I
<
5 ioo_
LJJ
h-
tO
> 50_
i i i i r r i i i i i i
2 4 6 8 10 12 14 16 18 20 22 24
HOURS
Figure 34. Results of intensive 24 hr. sampling study for Phase III; raw
wastewater TSS.
50
-------
o
o
Z Z
31.8
(70)"
27.2
(6of
22.7
|5of
1B.2
(40)"
13.6
(30)"
9.08
|20"
4.54
(10)"
0 -J
CONSTANT FLOW
SYSTEM
DIURNAL FLOW SYSTEM
o
O
So 2
"- s
6.81
(15)"
4.54
(10)"
2.27_
(5)
226.8
(60)"
189
(50)"
151.4
(40)"
113.6
(30)"
75.7
(20)"
37.8_
(10)"
O
O
300 _
100 _
^CONSTANT FLOW SYSTEM
DIURNAL FLOW SYSTEM
I I I I I I I I I T I I
0 24 6 8 10 12 14 16 18 20 22 24
HOURS
Figure 35. Results of intensive 24 hr. sampling study for Phase III;
primary effluent TCOD.
51
-------
DIURNAL FLOW SYSTEM
< -
_i O > i-
55^5-
_1 O!
, X
'
Sos
" 5
o-
4.54
(10)"
2.27
(5)"
01
CONSTANT FLOW SYSTEM
DIURNAL FLOW SYSTEM
I- O-
< O
<
Of
226.8
(60)"
189
(50)"
151.4
(40)'
113.6
(30)"
7S.7
(20)"
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(10)"
0I
CONSTANT FLOW
O)
S
§
a.
150-,
100
50-
DIURNAL FLOW SYSTEM
I I I I I I I I I I I I
0 2 4 6 8 10 12 14 16 18 20 22 24
HOURS
Figure 36. Results of intensive 24 hr. sampling study for Phase III;
primary effluent TSS.
52
-------
6.81
CONSTANT FLOW SYSTEM
1.36
(3)'
-I X > - 0 908
< Z oc
h- ~ UJ _- |9i
z Q i_ Z co Ul
m < Z "J m
so - 2 i
Z < -
-sS|
0.454
(1)'
CONSTANT FLOW
O
u
Z
LU
Z)
<
Z
100_
50.
DIURNAL FLOW SYSTEM
CONSTANT FLOW SYSTEM
i r i i i i i i i i i i
0 2 4 6 8 10 12 14 16 18 20 22 24
HOURS
Figure 37. Results of intensive 24 hr. sampling study for Phase III;
final effluent TCOD.
53
-------
o
z
Q
o £
-11-
VI UJ I/T
i I"
LU LU CT)
> -.*
5?
^ u_
s
CONSTANT FLOW SYSTEM
_J >"
l/l CS _,
< o: <
S O z
0.454
(1.0)
0.227
(0.5)"
0'
DIURNAL FLOW SYSTEM
CONSTANT FLOW SYSTEM
I ^
CONSTANT FLOW
O)
S.
20
10
DIURNAL FLOW SYSTEM
I I I I I T 1 I I I I I
0 2 46 8 10 12 14 16 13 20 22 24
HOURS
Figure 38. Results of intensive 24 hr. sampling study for Phase III;
final effluent TSS.
54
-------
EFFECTS ON PLANT STABILITY
Diurnal flow variations could also have some impact on other areas of
plant stability. These would be generally related to variations in aeration
basin dissolved oxygen (DO) concentrations and final clarifier sludge
blanket levels during periods of peak flows.
The lack of continuous on-line DO measurement made quantifying diurnal
DO levels in the aeration basins difficult. During this study, DO
levels were measured 6 times daily. However, data relating DO levels to
the imposed diurnal flow pattern were not collected. Generally, the
operations staff did not observe any regular fluctuation of DO levels
during the peak flows of the diurnal cycle.
Sludge blanket levels would theoretically vary during the diurnal
flow cycle. These variations would be caused by fluctuating upflow veloci-
ties in the diurnal flow final clarifier. Data on sludge blanket levels
was collected. However, these data could not be related to the diurnal
flow pattern and are not included in this report. The operations staff
noted consistently high sludge blanket levels in the DPS clarifier only
during the 2.5/1 P/A phase of the study. The DPS effluent solids levels
were not adversely affected by the high blanket seen except when the
blanket would come over the weirs. The frequency levels of high effluent
solids due to high sludge blanket was not recorded.
FeCl3 ADDITION RESULTS
Earlier investigations (3,4) into flow equalization concluded the
mixed liquor settleability was a more important factor in final clarifier
performance than diurnal peak flows. During Phases II and III of the
study, 10 mg/1 of FeCl3 was added periodically to the mixed liquor just
before entering the final clarifiers to stabilize sludge settleability.
Though these FeCl3 additions were performed only for 2 to 3 week intervals,
they provide insight into final clarifier performance under conditions
of very stable sludge settleability.
Table 4 shows the averages of data collected over a 4 week period
during Phase II of this study. Primary effluent data are similar to that
previously reported at the 2.0/1 P/A diurnal ratio. CFS activated sludge
performance, however, improved considerably in contrast to the DPS with
mineral addition. TBODs and TSS levels were 50 percent higher in the
DPS final effluents than in CFS final effluent. However, final effluent
soluble BODs levels were the same for both systems.
Similar data with FeClj addition was collected during 2 weeks of the
Phase III 2.5/1 P/A diurnal flow study. As shown in Table 5, final
effluent TCOD and TBOD5 levels were 3 times greater for the DPS as
compared to the CFS. Final effluent TSS values were 4 times greater for
the DPS, and final effluent soluble BOD5 was 3 times greater.
55
-------
TABLE 4. RESULTS OF FeCls ADDITION STUDY DURING PHASE II: 2.0/1 PEAK-TO-AVERAGE FLOW
(6-30-74 to 7-23-74)
TOTAL
COD
RAW
WASTEWATER
PRIMARY
EFFLUENT 290
DIURNAL SYSTEM
PRIMARY
EFFLUENT 315
CONSTANT SYSTEM
FINAL
EFFLUENT 64
DIURNAL SYSTEM
F INAL
EFFLUENT 40
CONSTANT SYSTEM
TOTAL
COD
REMOVED
40+
35+
78*
87 +
87*
92+
SOLUBLE TOTAL
COD BODr
(mg/1) (rag/1)
123 225
123
140
48 21
35 11
TOTAL
BOD 5
REMOVED
45+
38+
83*
91 +
92*
95+
SOLUBLE SOLUBLE TOTAL
BOD5 BOD5 SUSPENDED
(mg/1) REMOVED SOLIDS
(%) (mg/1)
51 288
168
159
97°
99A 19
2'5 11° 9
TOTAL
SUSPENDED
SOLIDS
REMOVED
42+
45 +
89*
93+
94*
97+
VOLATILE
SUSPENDED
SOLIDS
(mg/1)
238
133
114
13
6
F/M
(kpTBOD^/day)
(k MLVSS)
C>
0.31
0.33
+ Based on raw wastewater
* Based on primai-y effluent
c Based on primary effluent TBODg and final effluent SBODS
A Based on raw wastewater TBOD5 and final effluent SBOD5
-------
TABLE S. RESULTS OF FeClj ADDITION STUDY DURING PHASE III: 2.5/1 PEAK-TO-AVERAGE FLOW
(2-16-75 to 3-1-75)
TOTAL
COD
(rag/1)
RAW
WASTEWATER
PRIMARY
EFFLUENT 233
DIURNAL SYSTEM
-J PRIMARY
EFFLUENT 189
CONSTANT SYSTEM
FINAL
EFFLUENT 95
DIURNAL SYSTEM
FINAL
EFFLUENT 36
CONSTANT SYSTEM
TOTAL SOLUBLE TOTAL
COD COD B0r>5
REMOVED (mg/1) /n
(mg/1) lmg/1J
96 122
0+ 117
19+ 101
n: - -
n: * -
TOTAL
BOD5
REMOVED
4+
17+
77*
78+
90*
92+
SOLUBLE SOLUBLE TOTAL
BOD5 BOD5 SUSPENDED
(mg/1) REMOVED SOLIDS
(%) (mg/1)
54 128
95
90
97°
10 g~A 44
070
3.5 ^A 10
TOTAL
SUSPENDED
SOLIDS
REMOVED
(%)
26
30
54*
66+
89*
92+
VOLATILE
SUSPENDED
SOLIDS
(mg/1)
92
68
66
29
7.S
F/M
(kgTBODc;/day)
(kg MLVSS
0.41
0.27
+ Based on raw wastewater
* Based on primary effluent
0 Based on primary effluent TBOD5 and final effluent SBODS
A Based on raw wastewater TBOD5 and final effluent SBODr
-------
These results indicate that FeCl^ addition had significantly better
stabilizing effect on the CFS than the DPS during periods of biological
upset. Broad generalization cannot be made from these limited results,
however mixed liquor settleability does appear to have a greater influence
on final clarifier performance than the range of diurnal flow patterns
imposed for this study.
Summary
The treatment plant average performances are summarized in Table 6 for
all phases of this study. Data collected during the 3 long term phases of
this project indicated that the DPS overall and individual treatment unit
performance was unaffected up to and including a 2.5/1 P/A diurnal flow
variation when compared to the CFS performance. Results from the intensive
24 hr. sampling studies essentially substantiated these results. The 2.5/1
P/A intensive study did show the CFS final effluent cumulative mass loadings
for both TCOD and TSS to be significantly lower than the DFS over the 24 hr.
period studied. These results could indicate a possibility that at a P/A
diurnal ratio above 2.5/1 significant differences between the CFS and DFS
would be observed. However, the extrapolation of long term treatment plant
performance data from one day of data is very difficult.
Several factors affected the data and the conclusions that can be
made from this report. The major factor was the lack of true flow
equalization for the CFS and the resultant diurnally fluctuating organic
and solids loadings to the CFS which may have altered the performance of
the two systems in favor of the DFS. The biological stability could have
also altered the results related to secondary clarifier performance.
The settling properties of the activated sludge could have varied between
the various phases and even between the CFS and DFS. These variations in
sludge settleability would directly impact the maximum diurnal variation
that the plant could receive. Adknowledging the impact of sludge settleability,
the maximum diurnal flow variation that the treatment plant can receive
would be related to the peak overflow rate imposed on the final clarifiers
and its duration.
58
-------
TABLS 6. SUMHARY OF AVERAGE PERFORMANCE VALUES FOR PHASES I, II, AND III
RAM
KASTEVATER
PWJttKY
EFFLUENT
DIURHAL
SYSTEM
PRIMARY
EFFLUENT
CONSTANT
SYSTEM
FOAL
EFFLUENT
DIURNAL
SYSTEM
FEIAL
EFFLUENT
CONSTANT
SYSTEM
PHASE
1.5/1
2.0/1
2.5/1
2.0/1
2.5/1
l.S/1
2.0/1
2.5/1
2.0/1
CF«C13)
2.5/1
l.S/1
2.0/1
2.5/1
2.0/1
(F«d3)
2.5/1
(F«Cl3)
I. I/I
2.0/1
2.5/1
2.0/1
(F«C13)
2.5/1
U'cCl;}
1.5/1
2.0/1
2.5/1
2.0/1
2.5/1
TOTAL
CaiA)
156
354
2SS
403
233
116
330
220
290
233
134
342
195
315
139
54
77
60
64
95
31
39
SO
40
36
TOTAL SOLUBLE TOTAL
COO COO BOO;
REMOVED (at/1) (a«/l)
26*
7*
14*
40-
0-
14*
I*
24.
35-
19-
71*
78*
77*
78*
73*
76*
78*
87.
59*
59*
77*
30*
74*
74*
74*
76*
37*
92*
83'
33*
SS
131
9«
1Z3
96
23
55
40
48
33
24
56
40
35
27
106
170
137
225
122
84
143
95
123
117
93
151
36
140
101
16
19
20
21
27
16
24
23
11
10
TOTAL SOLUBLE SOLUBLE TOTAL
BCD; BOO; BOO; SUSPENDED
REMOVED (as/1) REMOVED SOLIDS
26
47
40
51
54
20*
13*
31*
45*
4*
12*
11.
37.
33-
17*
31*
35-
S7* 10
89* l°
79* .
as- 6
83'
91.
£ »
s: s
84*
86* "
78*
36* J
92* , .
95- *'3
9«J*
92* i-5
98
244
167
283
123
67
200
117
163
95
84
203
121
159
90
9S4 10
94A a
964 24
99^ 19
» 1A
92
95? ,
95
94^ M
97°
99^ 9
97* l°
TOTAL VOLATILE F/M
SUSPENDED SUSP'ENDED Ct-TBOD^/dav)
SOLIDS RE- SOLIDS (fci MLVSS)
MOVED (1) (ag/1)
32*
18*
30-
42*
26-
14*
21*
23-
45*
30*
85*
90*
89*
91.
80*
36*
39-
93*
54*
46-
39*
91*
3S»
88-
84-
37*
94*
97.
89*
92*
77
191
114
233
92
50
142
76
133
63
64
152
31
114
66
3
16
16
13
29
7
21
13
6
7.S
0.26
0.51
0.24
0.31
0.11
0.27
0.39
0.2
0.33
0.27
* 3*j«d on raw uutmctr
3u*d
a Bu«d
& B-J-J
on yeioMry
on prlsBP^
on raatf VMM
' tffllMBt
' «£flu«nt
₯M»**V Tt
TBODS and
inn. *nrf «
final
n«i *;
affluent
CTtt-M. «C
5BCD;
im_
59
-------
REFERENCES
1. Flow Equalization, Technology Transfer Seminar Publication, U.S.
Environmental Protection Agency, 21 pp, May 1974.
2. LaGrega, Michael D., and Keenan, John D., "Effects of Equalizing
Wastewater Flows," JWPCF, VOL. 46, No. 1, pp 123-132, January 1974.
3. Boon, A.G., and Burgess, D.R., "Effects of Diurna'l Variations in Flow
of Settled Sewage on the Performances of High Rate Activated Sludge
Plants," Water Pollution Control, Vol. 71, No. 5, pp 493-522, 1972
4. Foess, Gerald W., Meenahan, James G., and Harjee, Michael, J., "Evaluation
of Flow Equalization at a Small Wastewater Treatment Plant." U.S.
Environmental Protection Agency Contract No. 68-03-0417, EPA-600/2-76-181,
September 1976.
5. Standard Methods for the Examination of Water and Wastewater, 13th Edition,
American Public Health Association, 1971.
60
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-78-054
3. RECIPIENT'S ACCESSI ON- NO.
4. TITLE AND SUBTITLE
Parallel Evaluation of Constant and Diurnal Flow
Treatment Systems
5. REPORT DATE
March 1978 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Jon H. Bender
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Municipal Environmental Research Laboratory - Cinti., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as Above
13. TYPE OF RE PORT AND PERIOD COVERED
In-house
14. SPONSORING AGENCY CODE
EPA-600/14
15. SUPPLEMENTARY NOTES
Project Officer:
Richard C. Brenner 513/684-7721
EPA-MERL-WRD Cincinnati, Ohio 45268
16. ABSTRACT
Pilot plant studies were performed to evaluate the effects of an imposed
diurnal flow pattern on a conventional activated sludge treatment plant.
These results were compared against data generated on a similar system
treating a constant flow. Effects on primary clarifier and final clarifier
performance as well as soluble or organic removals were evaluated. Other
effects on general plant stability were noted.
There were essentially no differences between the diurnal and constant
flow systems at the 1.5/1, 2.0/1, and 2.5/1 peak-to-average diurnal flows
imposed. Intensive sampling over a 24 hour diurnal flow cycle did not alter
this basic conclusion. General plant stability was not affected except for
some sludge blanket level problems at the 2.5/1 peak-to-average flow phase.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDEDTERMS
c. COSATI Field/Group
Performance
Primary Clarifier
Secondary Clarifier
Activated Sludge Treat-
ment
Diurnal Flow Variations
13B
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
71
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
61
U.S. GOVERNMENT PRINTING OFFICE: 1978-757-140/6809 Region No. 5-11
------- |