PHOSPHATE REMOVAL BY ACTIVATED SLUDGE
Amenability Studies at
Indianapolis, Indiana
by
L. H. Myers, J. A. Horn, L. D. Lively,
J. L. Witherow, and C. P. Priesing*
*The authors are, respectively, Research Chemist, Research Sanitary
Engineer, Research Chemist, Research Sanitary Engineer, and Acting
Chief, Treatment and Control Research Program, Robert S. Kerr Water
Research Center, Federal Water Pollution Control Administration,
U. S. Department of the Interior, Ada, Oklahoma.
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TABLE OF CONTENTS
Item Page
ABSTRACT ill
INTRODUCTION 1
RESULTS AND DISCUSSIONS 4
Plant Characteristics 4
Plant Monitoring 6
Aeration Jug Studies 15
Sewage Characterization 34
Microbiological Studies 34
SUMMARY 35
CONCLUSIONS 37
RECOMMENDATIONS 39
i
APPENDIXES 40
Appendix I - Analytical Procedures 40
Appendix II - Plant Performance and Operating Data . . 44
ACKNOWLEDGMENT 45
REFERENCES 46
GLOSSARY 47
TABLES
Plant Monitoring - Phosphate and Solids 16
MLSS Variation - Components ; 17
MLSS Variation - Results 17
BOD Load Variation - Components 18
BOD Load Variation - Results 18
Phosphate Variation - Components 25
Phosphate Variation - Results . 27
Chemical Variation - Components 28
Chemical Variation - Results 30
Component Variation - Components 30
Component Variation - Results 31
Acclimation-Control Comparison 33
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TABLE OF CONTENTS (Continued)
Item Page
FIGURES
Southwest Sewage Treatment Plant,
Indianapolis, Indiana 5
Dye Detention in Aeration Tanks - Step Feed 8
Dye Detention in Aeration Tanks - Conventional Feed . 10
Dye Detention in Final Clarifier 11
Dissolved Oxygen in Aeration Tank - Conventional
Feed 13
Dissolved Oxygen in Aeration Tank - Step Feed .... 14
MLSS Variation - Phosphate 20
MLSS Variation - Supernatant and Sludge Phosphate . . 21
BOD Variation - Phosphate 23
BOD Variation - Phosphate Removal and SNVOC 24
Phosphate Variation - Phosphate 26
Chemical Addition - Phosphate 29
Component Variation - Phosphate 32
ii
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ABSTRACT
Phosphate removal by activated sludge was investigated in pilot and
plant scale research conducted at the Indianapolis, Indiana, Southwest
Sewage Treatment Plant. These studies show that the aeration tanks
were averaging 20 percent removal of the orthophosphate in the tank
influent. The conditions were different from those found in the
San Antonio Rilling Plant:
1. Primary effluent BOD and orthophosphate (as P) levels
were much lower, averaging 90 and 5.5 mg/1, respectively;
2. MLSS concentrations were higher, ranging from 1,500 to
1,800 mg/1;
3. BOD loadings were much lower, ranging from 0.09 to 0.16
Ib/lb. MLSS/day; and
4. Final clarifiers had deeper sludge blankets and lower
dissolved oxygen concentrations, and the mixed liquor aeration
time and dissolved oxygen concentrations exceeded those normally
found in the Rilling Plant.
Pilot investigations were made to determine the amenability of
the waste and activated sludge to phosphate removal. Removal
gradually increased with increasing oxygen demanding substrate or
hardness concentration. Ferrous iron or aluminum salts removed 3
high levels of orthophosphate, which agrees with previous studies. '
Variation in MLSS or orthophosphate concentration did not cause a 3
significant change in removal in contradiction of previous studies.
Following an acclimation period of 16 to 40 hours, orthophosphate
removal increased to 78 percent which, excluding the chemical
addition studies, was the maximum removal efficiency obtained. The
waste and sludge were classified as moderately amenable to phosphate
removal.
The plant is recommended to demonstrate phosphate removal.
111
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INTRODUCTION
Research studies conducted at San Antonio, Texas, ' indicated
the ability of the activated sludge process to remove a high per-
centage of orthophosphate from municipal and industrial sewage.
The investigation concluded that mixed liquor suspended solids
in the aeration tanks were capable of removing phosphorus from the
soluble phase. The removal capability of this process was dependent
upon detention time, biochemical oxygen demand (BOD) loading, mixed
liquor suspended solids and dissolved oxygen concentrations, phosphate
loading, rapid solid-liquid separation in the final clarifier, fast
transfer of return sludge to the aeration tank, and separate disposal
of waste phosphate-laden sludge.
As a part of a continuing research program to investigate phosphate
removal capabilities by activated sludge plants in different regions
of the United States, under different loading and climatic conditions,
a study was initiated at the Southwest Sewage Treatment Plant,
Indianapolis, Indiana.
The purposes of this and other studies were:
1. To determine the feasibility of phosphate removal by
activated sludge plants located in different regions of the United
States. These plants, operating under differing conditions due to
populations served, mixed wastes from industries and municipal
applications, and different properties of the potable water supply
represent problems encountered in sewages and their effect on the
phosphate removal capabilities of the activated sludge process.
2. To locate a minimum of six activated sludge plants in
different regions of the United States capable of demonstrating
phosphate removal in the activated sludge process by the parameters
identified in the San Antonio study.2
3. To locate one activated sludge plant, representing mixed
sewage with the operational and design, flexibility possible to
further study the phosphate removal process with respect to future
engineering design.
4. To validate the phosphate removal parameters identified by
the San Antonio study.2 The use of the aerated jugs under control
conditions is ideally suited to verify these parameters and to aid
in the search for new parameters.
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2 3
Prior pilot studies ' demonstrate the use of five-gallon polyethylene
carboys in representing aeration tanks on a pilot scale. Control of
operating parameters during the studies is a must, and these controls
are possible by using the carboys. Of importance in the phosphate
removal process is the control of dissolved solids concentrations,
suspended solids levels, phosphate variations, chemical additions,
dissolved oxygen, BOD loading, and aeration time.
The pilot studies, in conjunction with a plant survey, are undertaken
to meet the described purposes and may be used in design and operation
changes to control phosphate levels in a specific plant effluent.
Experimental Procedures
Plant Analysis
Design, operation, sampling, and analytical procedures concerning
the Southwest plant were discussed with the plant superintendent and
plant personnel. The plant records were reviewed for sewage flow,
BOD loading and removal, total suspended solids levels, air flow
rates, and other pertinent chemical and physical parameters. Operating
data during this study period obtained from the plant chemist are
found in Appendix II.
Tracer studies were conducted using Rhodamine WT* dye on the aeration
tanks and final clarifiers to determine characteristics such as
detention, short circuiting, and degree of longitudinal mixing.
Grab samples were collected throughout the plant to determine
orthophosphate removal, dissolved oxygen concentrations, and total
and volatile suspended solids levels. The slug-flow method of
sampling was normally used to compensate for process flow-through
time.
Samples were transported to the Robert S. Kerr Water Research Center
for further analyses to characterize the wastes. These analyses
included metals, chemical oxygen demand (COD), total phosphate,
sulfate, organic nitrogen, nitrite, and nitrate. When needed, the
samples were fixed in accordance with Standard Methods.^ Analytical
procedures are described in Appendix I. Sampled sources were:
raw, primary effluent, various points throughout the aeration tanks,
return sludge, and final effluent.
*LBS Rhodamine WT Solution (20%), E. I. DuPont de Nemours Company,
Organic Chemicals Department, Dye and Chemical Division, de Nemours
Building, Wilmington, Delaware 19898.
-------
Aeration Jug Studies
To obtain the desired range of total suspended solids in the
five-gallon polyethylene carboys, a mixed liquor was synthesized.
Return sludge or plant mixed liquor was mixed with primary effluent
or raw sewage to obtain the desired suspended solids levels. To
produce a consistent suspended solids charge for each jug, the
return sludge was thickened by a pilot air flotation device. The
total suspended solids concentration of the return sludge was
estimated by centrifuging 10 ml for 5 minutes and comparing the
compacted volume to the measured total suspended solids. Thereafter,
centrifugation provided an estimate of TSS. All jugs were started
at the same time. The thickened return sludge was kept under
aeration until used as the makeup for the jugs.
A portable electric air compressor provided air for the jugs. The
air was delivered through a manifold containing individual needle
valves for each jug. Rotometers measuring liters of air per minute
were connected to the valves, and the controlled air was directed
to the bottom of the jugs and out through polyethylene tee fittings
which simulated diffusers. Air flow was constant through each study
period except where noted.
The jugs were monitored for dissolved oxygen concentration and
temperature by immersing a dissolved oxygen meter probe in each
jug during the study.
At predetermined intervals, samples were withdrawn from the jugs for
chemical analysis. The sample was withdrawn through a plastic tube
into a clean and dry four-ounce polyethylene bottle. The first sample
was returned to the respective carboy, and a second sample was with-
drawn for the desired analysis. If supplemental analyses were desired,
a 250 ml sample was taken.
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RESULTS AND DISCUSSIONS
Plant Characteristics
The Southwest Indianapolis Water Pollution Control Plant is a 28 mgd
activated sludge plant which treats the excess flows from the main
Indianapolis Water Pollution Control Plant. The Southwest Plant
receives about 20 percent of the total sewage flow from the city
of Indianapolis. Sewers in the city of Indianapolis carry both
sanitary wastes and storm water flows.
Significant industrial waste contributions include those; from the
processing of starch, penicillin, meats, and poultry. Industry
minimizes such contributions; however, the plant is occasionally
upset by slugs of such wastes. The organic loading (BOD) contri-
buted by industry is estimated at 50 percent.
The Southwest Plant, completed in June 1966, is located approximately
10 miles southwest of downtown Indianapolis. An expansion program
is under way which will provide a parallel plant of equal capacity.
Operation of the existing plant will not be interrupted except during
connection of the new plant to the existing raw sewage lift station.
All of the sewage flow from the city of Indianapolis passes through
the screens and grit chambers of the main plant. About 25 mgd of
this sewage is then pumped through a 10-mile interceptor sewer to the
Southwest Plant with a travel time of two hours. Treatment facilities
at the Southwest Plant provide screening, grit and scum removal,
primary settling, and biological removal by the activated sludge
process. The removal of total suspended solids arid BOD throughout
the plant consistently exceeds 90 percent. The plant effluent
discharges into the White River. Figure 1 is a schematic drawing
of the treatment units.
Primary clarification facilities consist of four circular units; each
has a 95-foot diameter and a 10-foot side wall depth. Primary effluent
flows by gravity from the clarifiers into an aerated channel. Gate
control structures regulate the channel flow into each aeration tank.
The aeration units consist of four 4-pass, rectangular tanks. Each
pass is 188.5 feet long, 30 feet wide, and 15 feet in liquid depth.
Piping is available to allow step feeding of primary effluent at
the one-quarter points and the inlet end. Aeration is accomplished
by coarse diffuser tubes mounted on "swing" headers which are
positioned uniformly along the tank length. Seven blowers having a
total capacity of 50,000 cfm provide the process air. Final
clarification consists of four circular tanks, each 100 feet in
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Sewer From Main Plant
Screen
Pump Station
Preaeration Grit
Removal
Primary Clarifiers
Primary Eff.
Aeration Tanks-1-^
B-2
A-2
Final Eff.
Final Clarifiers
FIGURE I - SOUTHWEST SEWAGE TREATMENT PLANT
INDIANAPOLIS , IND.
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diameter and having an 8-foot liquid depth. The weir length of each
tank is 314 feet. The final clarifiers are equipped with inlet
baffles.
Six variable speed return sludge pumps have a maximum combined
capacity of 21 mgd. Two of these pumps are for standby purposes.
The secondary treatment facilities can be operated as two independent
plants. The 14 mgd plant on the east is referred to as the "A" plant,
and the one on the west is called the "B" plant (See Figure 1). The
return sludge flow from each final clarifier may be monitored at the
sludge wells adjacent to the final clarifiers. Return sludge is
pumped back directly to the inlet end of the aeration tanks. If
desired, return sludge can be diverted and mixed with primary effluent
prior to entering the aeration tanks. During such diversion, the
secondary facilities could not be divided into two independent plants.
Step feeding is practiced when slugs of waste upset the conventional
flow-through process.
Indicating, recording, and totalizing meters monitor (1) total raw
sewage flow, (2) the combined air supplied to Passes Nos. 1 and 2
and that supplied to Passes Nos. 3 and 4 in the aeration tanks, (3)
return sludge flow to each aeration tank, and (4) waste activated
sludge. There are no meters available to measure the primary
effluent flow to each aeration tank.
Nine sludge lagoons, having a total area in excess of 45 acres, are
available for disposal of screenings, grit, primary and waste
activated sludge, oil, and grease. Less than one-half of the lagoon
area contains this material. There was no return flow from the
lagoons to the plant. These lagoons are located west of the plant
and adjacent to the White River.
Plant Monitoring
During the study period of June 12 to 21, 1967, the "B"-battery
aeration tanks were operating in conventional flow-through fashion
while the "A"-battery aeration tanks received primary effluent by
step feed. The method of step feeding was varied during the study
period. Emphasis was placed on monitoring the conventional process
("B" battery) since it provided the greater average mixed liquor
aeration time and more closely simulated plug-flow conditions.
General Plant Operation
Normal sewage flow averages 25 to 28 mgd. Diurnal flow variation
was insignificant since it did not exceed 10 percent. The return
sludge varied from 53 to 60 percent of the sewage flow. The unit
-------
amount o;': air applied ranged from 1.7 to 2.7 cu. ft. per gallon of
primarv effluent. An average of 500,000 gallons or 3.5 percent of
the activated sludge was wasted daily.
The Mf.SS concentrations in the aeration tanks ranged from 1,625 to
2,343 mg/1 during the study period. The unit organic loading in the
aeration tanks varied from 9 to 16 pounds BOD per 100 pounds of MLSS
per day. Return sludge total suspended solids ranged from 2,700 to
4, SOO rr,g/l. Tht: primary effluent had concentrations of BOD and total
suspended solids averaging 90 and 85 mg/1, respectively, during the
study pt'iiud. The final effluent contained about 10 mg/1 BOD and
15 mg/1 total suspended solids. These results were determined by
plant personnel utilizing 24-hour composite samples. The average
removal of BOD and suspended solids through the activated sludge
facilit ies was 90 and 80 percent, respectively. Plant operation
and performance data are given in Appendix II.
Dye Tracer Studies
F1 ow Pi st. r i but ion - At 12: 15 p.m. on June 12, 1967, 10 liters of
20 percent Rhodamint- WT dye was added to the primary effluent to
determine the flow division and the detention times in the aeration
tanks. Samples were collected from the one-half point and effluent
of the "B"-battery tanks and from the effluent of the "A"-battery
tanks. The comparison of dye recoveries indicated that Aeration Tank
B-l received 29 percent of the sewage flow. Aeration Tanks B-2,
A-l, and A-2 received 23, 25, and 23 percent, respectively. These
results were used to compute the hydraulic loading to each aeration
tank during subsequent studies.
Afcial i.)i.i Tank i.; (Battery "A''J - Figure 2 is a plot of dye concentration
versus elapsed time after dye addition on July 12 for the Battery "A"
aeration tanks. During this study period, these aeration tanks were
operated DV step feed with the settled sludge returned to the inlet
end of the tank and the primary effluent in equal proportions added
to the one-quarter and one-half points. The average flow rates of
return sludge and primary effluent are given in Figure 2. The
theoretical displacement time of the primary effluent is also shown.
Computation oi area under the dye curve shows that 8 percent and 34
percent of the primary effluent flow received less than 2 and 3 hours
of aeration, respectively.
Aerat.ionTanks (battery "B") - At 9:00 a.m. on June 15, 2.5 liters of
20 percent Rhodamine WT dye was added at the inlet of Aeration Tank
B-2 to determine its hydraulic characteristics. Primary effluent and
return sludge entered only the inlet, and samples were collected from
the one-half and outlet points of this tank. Samples were also
collected from the one-half and effluent points of Aeration Tank B-l
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Q.
Q.
cc
H
Z
Ul
O
z
O
O
100
~ 80
o 60
40
20
STEP FEED METHOD:
1/2 PE (3.4 MGD) TO 1/4 PT.
1/2 PE (3.4 MGD) TO 1/2 PT.
RS (3.8 MGD) TO INLET
TANK A-l (EFFLUENT)
TANK A-2
(EFFLUENT)
Theor. Displacement Time ><-vA.
" PE
^ 1
TO l/2pt. PE '
Q 1/4 pt.
D 1 2 3 4 5 6
0
i i
7 8
TIME (MRS.)
FIGURE 2 - DYE DETENTION IN AERATION TANKS-STEP FEED
-------
to determine the background dye concentration caused by the return
of dyed sludge to the aeration tanks. Sampling was discontinued at
8:00 p.m. since the effluent dye concentration was approaching the
background concentration. These study results were used in preference
to those of June 12 because correction was made for background dye
concentration.
The average mixed liquor flow rate through the 2.5 million-gallon
aeration tank was 9.9 mgd during the study; therefore, the theoretical
displacement time was 6.1 hours. Flow did not vary significantly
during the study. The four-pass aeration tank has a length to width
ratio of 25:1. The average amount of air applied was 10,100 cfm or
1.5 cu. ft, per gallon of mixed liquor. Dye concentration above
background at the one-half and outlet points versus elapsed time after
dye addition is plotted in Figure 3 along with a percent flow-through
curve The modal and median detention times were 4,8 and 5.4 hours,
respectively. The times of 10 percent (t-^0) and 90 percent (tg0)
flow through were 3.5 and 7.9 hours, respectively, which resulted in
a dispersion index (tgo/^K)) °f 2.25. The modal detention time (t-^)
is equal to 78 percent of the theoretical displacement time (t^).
The dye lecovery was within 10 percent of the amount added.
The corresponding value of tgQ/t,Q for the aeration tanks of the
San Antonio Rilling Plant was 3.5. This indicates that the
Indianapolis aeration tanks exhibit less longitudinal mixing and
better plug-flow characteristics than do the Rilling tanks. Since
the Indianapolis tanks are four-pass with a 25:1 length to width
ratio as compared to two-pass with a 20;1 length to width ratio for
the Rilling tanks, the physical configuration of the Indianapolis
tanks is more favorable to plug-flow simulation. Referring to Figure
), the flow-through characteristics of the Indianapolis B-aeration
tanks are such that all of the flow receives at least two hours'
aeration, and only 3 percent receives Less than 3 hours' aeration.
The rates ,of phosphate removal observed in pilot and plant investi-
gations '"^ indicate that the hydraulic characteristics of the
Indianapolis aeration tanks are adequate for phosphate removal.
Although plug-flow characteristics are diminished by step feeding
(split equally between, the one-quarter and midpoints), detention
times are sufficient to allow phosphate removal.
Final Clarifiers - At 1:45 p.m. on June 19, 0.5 liter of 20 percent
Rhodamine WT dye was added to the inlet well of Final Clarifier B-2
to determine the flow-through characteristics of the overflow and
return sludge. Samples of the clarifier overflow were collected at
5- to 30-minute intervals. The return sludge was sampled at the
adjacent sludge well. Dye concentration versus elapsed time after
dye addition for both the overflow and the return sludge are depicted
in Figure 4.
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10
O
LJ
UJ
CO
z
O
S
o:
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s
UJ
>-
Q
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ro
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a:
NOIlVaiN3DNOO 3AQ
M01J !N3Dy3d
-------
11
220
RETURN SLUDGE
OVERFLOW
0
1.5
2.5
TIME (MRS.)
FIGURE 4 - DYE DETENTION IN FINAL CLARIFIERS
-------
12
Assuming an equal flow split between the "B"-battery clarifiers, the
average mixed liquor inflow to the 470,000-gallon clarifier was 11
mgd. The return sludge flow averaged 3.6 mgd. Based on the overflow
rate of 7.4 mgd, the theoretical displacement time was 1.5 hours. The
modal detention time of the clarifier overflow was slightly more than
1 hour (70 percent of the theoretical displacement time). Such a
relationship is indicative of normal circular clarifier performance.
A sharp peak in the dye concentration of the return sludge occurred
within five minutes after dye addition. This peak represents short
circuiting of mixed liquor directly to the return sludge outlet. Dye
concentrations dropped off rapidly after this peak was experienced.
Comparison of areas under the return sludge dye curve shows that
about 50 percent of the return sludge flow was mixed liquor which had
short-circuited. This high degree of short circuiting substantially
reduces the return sludge suspended solids concentrations.
Dissolved Oxygen and Sludge Depth Measurements
Aeration Tanks - The dissolved oxygen in the aeration tanks was
monitored at various times throughout the study period. Dissolved
oxygen profiles for one of the Battery "B" aeration tanks are shown
in Figure 5. The concentrations are quite variable, especially
during the latter half of the aeration tanks. The DO values were
1 to 2 mg/1 at the midpoint and 2.5 to 4 mg/1 at the effluent.
Air supply varied from 2.0 to 2.7 cu. ft. per gallon of primary
effluent. Specific values for each survey period are shown in
Figure 5. According to previous plant investigations, '" the blower
capacity is sufficient to maintain dissolved oxygen concentrations
satisfactory for phosphate removal.
Two slug-flow DO profiles were taken in the Battery "B" tanks
on June 20, 1967, at times corresponding to slug-flow orthophosphate
surveys. The DO increased gradually to about 1.5 mg/1 at the three-
quarter point and then rapidly to about 4 mg/1 at the tail.
A typical DO profile of Aeration Tank A-l having step feed is shown
in Figure 6. The effect of step feeding at the 1/4, 1/2, and 3/4 points
is readily apparent from this profile. As in the "B" tanks, the
DO rapidly increased during the last quarter of the tank. The
dissolved oxygen levels were sufficient for phosphate removal.
Final Clarifiers - The dissolved oxygen in the final clarifiers
ranged from 0.5 to 0.9 mg/1. Sludge blanket depths, estimated by
use of an optical density sensor, were 12 inches at the side wall
and 2 to 4 feet in the center. The plant superintendent has found
that such sludge blanket depths cannot be avoided with the present
sludge scraper performance. The return sludge dissolved oxygen
concentration varied from 0.2 to 0.6 mg/1. The low DO concentrations
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DATE
1967
TIME PE FLOW
PM
MGO
13
AIR APPLIED
CFM CU. FT/GAL.
6/15
6/17
6/19
6/21
I'OO
4=00
4=30
5=30
6.4
4.8
6.4
5.8
10,100
9,000
9,100
10, 300
2.28
2.71
2.05
2.55
o>
E
z
UJ
o
>
X
o
o
UJ
CO
o
1/8
1/4 3/8 1/2 5/8 3/4
LOCATION IN TANK B-2
7/8
EFF.
FIGURE 5- DISSOLVED OXYGEN IN AERATION TANK-
CONVENTIONAL FEED
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14
5 h
MIXED LIQUOR AERATION
6/21/67 6'00 PM
1/4 pt. 1/2 pt.
LOCATION IN TANK A-l
3/4pt.
EFF.
FIGURE 6 - DISSOLVED OXYGEN IN AERATION TANK
STEP FEED
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15
in the final clarifiers are apparently caused by the sludge blanket.
Such an environment caused phosphate release as seen by the increase
of orthophosphate in the final clarifier.
Phosphate and Solids Monitoring
The plant was monitored to determine phosphate removal and suspended
solids concentrations. The raw sewage (raw), primary effluent (PE),
return sludge (RS), and final effluent (FE) were sampled along
with Aeration Tanks Nos. 1 and 2 in "B" battery (B-l, B-2) at the
inlet (in), half-point (1/2), and outlet (out). The data for the
"B" plant are shown in Table 1. Many of the samples taken on
June 14, 15, 17, and 20 were staggered in proportion to the modal
detention times to follow a "slug" of waste through the unit
processes.
The plant was not obtaining significant phosphate removal, and a
sampling program was not undertaken to more accurately determine
removals. From the available data, removals were estimated at 10
percent from the primary to final effluents and at 20 percent
through the aeration tanks. The average phosphate as P concen-
trations of PE and FE were 5.4 and 4.7 mg/1, respectively.
The suspended solids varied from 3 to 5 thousand mg/1 in the return
sludge and from 1.5 to 2 thousand mg/1 in the mixed liquor and had
a volatile content ranging from 70 to 85 percent.
Aeration Jug Studies
A series of experiments were devised to test the sewage and sludge
of selected plants with regard to orthophosphate removal. Factors
previously shown to effect the rate and magnitude of ortho-
phosphate removal in the aeration tank are: suspended solids, DO,
BOD, and orthophosphate concentrations; concentration of metal
precipitants and sludge conditions. These experiments are devised
to evaluate plants for future process demonstration.
MLSS Variation
A battery of seven jugs was prepared on June 13, 1967, to determine
the optimum mixed liquor suspended solids concentration for soluble
phosphorus removal. Jug components used in this study are presented
in Table 2.
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16
Table 1
Plant Monitoring - Phosphate and Solids
Southwest Indianapolis Sewage Treatment Plant
Sample
Time
0-PO,.
(mg/l-P)
6/12/67
Raw
PE
RS
B-l (in)
B-l (1/2)
B-l (out)
FE (B-l)
B-2 (in)
B-2 (1/2)
B-2 (out)
FE (B-2)
6/13/67
RS
PE
FE
6/14/67
PE
FE
RS
RS
RS
B-2 (in)
B-2 (1/2)
B-2 (out)
FE
6/15/67
PE
RS
RS
B-l (in)
B-l (1/2)
B-l (out)
B-2 (out)
B-2 (out)
B-2 (out)
2:30
2:30
2:30
2:30
2:30
2:30
2:30
2:30
2:30
2:30
2:30
11:30
12:00
12:30
10:30
10:30
10:30
12:30
6:20
12:00
2:15
6:15
6:25
9:30
9:30
4:00
9:00
9:30
10:00
10:00
2:30
3:45
pm
pm
pm
pm
pm
pm
pm
pm
pm
pm
pm
am
N
pm
am
am
am
pm
pm
N
pm
pm
pm
am
am
pm
am
am
am
am
pm
pm
4
4
7
5
5
5
5
5
5
5
5
3
4
2
6
4
5
4
5
5
4
4
7
7
9
-
-
-
-
5
5
.8
.6
.0
.9
.9
.4
.9
.5
.6
.2
.8
.0
.8
.8
.0
.7
-
.5
.9
.8
.4
.4
.4
.4
.3
.1
-
-
-
-
.1
.1
TSS VSS
(mg/1) (mg/1)
__.
3290 2820
1620 1270
1650 1130
1620 1140
4030
32
82
2600
4890
1600
1720
1850
1690
1560
Sample
Time
0-PO,
(mg/l-ft
TSS
(mg/1)
6/16/67
PE
PE
RS
9:30
6:00
9:45
am
pm
am
4.3
5.3
4.2
76
6/17/67
Raw
PE
PE
RS
RS
B (in)
B (out)
FE
2:00
11:30
2:00
11:30
12:15
2:00
2:00
3:00
pm
am
pm
am
pm
pm
pm
pm
5.5
7.0
7.2
7.0
5.8
6.8
7.0
54
3080
6/20/67
Raw
Raw
PE
PE
PE
RS
RS
B-2
B-2
B-2
B-2
B-2
B-2
FE
FE
(in)
(in)
(1/2)
(1/2)
(out)
(out)
9:00
10:00
10:30
11:30
4:20
10:30
11:30
10:30
11:30
1:00
2:00
3:30
4:30
4:20
4:30
am
am
am
am
pm
am
am
am
am
pm
pm
pm
pm
pm
pm
3.0
3.7
4.3
4.0
4.4
4.3
4.3
5.4
4.8
3.9
4.1
4.3
4.0
3.5
3.6
248
186
3800
2010
2170
1760
-------
17
Table 2
Mixed Liquor Suspended Solids Variation
Components of Aeration Jugs*
Jug No.
1
2
3
4
5
6
7
PE
(liter)
10
10
10
10
10
10
10
Cone. RS
(liter)
0.4
0.8
FE
TSS
1.1
1.5
1.9
2.6
3.4
4.6
4.2
3.9
3.5
3.1
2.4
1.6
453
1,241
1,676
2,246
2,470
3,445
4,760
*Aeration rate = 17.5 liters per minute
VSS
(liter) (mg/1) (mg/1)
268
608
932
1,316
1,748
2,130
3,060
A constant volume of primary effluent was used in each jug to limit
the effect of BOD variation. Final effluent was used to bring the
volume of each jug to 15 liters. Analyses of the jug components are
given in Table 1, and the study results in Table 3.
Table 3
Aeration
Time (hrs.)
0 (12:30 p.m.)
1
2
3
4
MLSS Variation - Results
Soluble Orthophosphate (mg/l-P)
Jug No.
3.8
3.0
2.8
2.0
2.2
2.1
2.0
3.8
2.9
2.4
2.1
2.1
1.9
1.8
3.7
2.7
2.3
2.0
2.0
1.8
1.8
3.8
3.0
2.3
2.0
2.0
1.9
1.9
4.4
4.5
3.8
2.4
2.1
2.1
2.1
4.6
3.2
2.3
2.0
2.1
1.9
2.1
4.4
4.8
3.2
2.2
2.2
2.1
2.3
% Removal
TSS (mg/1)
47
453
52
1,241
51
1,676
50
2,246
52
2,470
54
3,445
47
4,760
-------
18
Figure 7 illustrates variation of soluble orthophosphate concentration
with respect to aeration time. Maximum soluble phosphate removal was
accomplished in the first three hours of aeration after which little
change was noted. During the study, removals varied from 47 to 54
percent; therefore, it was concluded that suspended solids concentra-
tions in the range studied had no significant effect on phosphate
removal. Total suspended and volatile suspended solids concentrations
show no correlation with orthophosphate removal. An intermediate MLSS
level of 2,500 mg/1 was chosen for use in future studies.
The temperature increased from 25 to 30°C during the initial 3-hour
aeration period due to absorption of heat from sunshine on the jugs
in the afternoon. After 3 hours, the temperature exceeded 30°C.
After 6 hours' aeration, the air supply was terminated, and jug
contents were permitted to settle for 30 minutes. Figure 8 shows
soluble and total phosphate data for the supernate and settled sludge.
The total phosphate is incorporated in the solids and effectively
removed by settling. The greater orthophosphate concentration in the
sludge compared to that in the supernatant indicates release from the
solid to the water in the simulated return sludge. The orthophosphate
concentration in the supernate is essentially equal to that in the jug
mixed liquor after 6 hours' aeration, indicating no release in the
simulated final effluent within the 30-minute quiescent settling
period.
Organic Load Variation
A battery of six jugs was prepared on June 14, 1967, to determine
the effect of variation in the substrate BOD concentration on ortho-
phosphate removal.
Jugs in this experiment contained solids (2.5 liters of concentrated
sludge diluted with an equal volume of final effluent) and a BOD
source which will be called substrate to distinguish it from plant
primary effluent. This substrate volume was 10 liters for each jug.
Jug No. 2 was the control and contained 10 liters of plant primary
effluent as substrate and«was the 100 percent reference point.
According to plant records, the average annual BOD of the primary
effluent is 150 mg/1. The primary effluent used for jug makeup
was assumed to have this BOD concentration.
Substrate BOD load was reduced to about 50 percent in Jug No. 1 by
using 5 liters of primary effluent and 5 liters of final effluent.
Approximately 125, 165, and 250 percent substrate BOD loads were
established in Jugs Nos. 3, 4, and 5, respectively, by the addition
-------
JUG NO. TSS (mg/l)
19
o>
E
UJ
X
CL
(/>
O
I
Q.
O
X
I-
cc
o
NO. 3
TIME (MRS.)
FIGURE 7-MLSS VARIATION - PHOSPHATE
-------
20
CL
i
LU 5
o
Q
CO
H
<
z
oc
UJ
Q.
O)
2
I
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0
0-PO/i IN SLUDGE
T-P04 IN SLUDGE
X-T-P04 IN SUPER. _
' ^
200
150
o»
100
50uj
a.
^
(O
0-P04 IN SUPER
I
I
1000 2000 3000 4000
MLSS (mg/ I )
5000
FIGURE 8-MLSS VARIATION-SUPERATANT ft SLUDGE PHOSPHATE
-------
21
of a BOD supplement (Metrecal*) to 10 liters of primary effluent.
The jug components and test results are shown in Tables 4 and 5.
Mixed liquor from the head of Aeration Tank B-2 was used in Jug No.
for comparison with the synthetic mixed liquor of the other jugs.
Table 4
BOD Load Variation - Components
Jug No.
Component
PE (liters)*
Cone. RS (liters)
FE (liters)
ML (liters)
Metrecal (ml)**
Analysis (mg/1)
TSS
Est. Substrate
BOD (mg/1)
Est. Substrate
BOD load (%)
5.0
2.5
7.5
10.0
2.5
2.5
10.0
2.5
2.5
1.3
10.0
2.5
2.5
3.5
10.0
2.5
2.5
7.8
15
2,755 2,675 2,825 2,675 2,890 1,195
75 150 190 250 375 150
50 100 125 165 250
*For analyses of components, see Table 1.
**Metrecal contains 1.1 mg/ml O-PO^ as P and 290 mg/ml BOD.
Table 5
BOD Load Variation - Results
0-P04 (mg/l-P)
Analysis
0-PO/,
(mg/l-P)
6.0
6.5
4.7
Aeration
Time (Mrs)
0 (11:00 a.m.)
1
2
3
4
5
% Removal
1
4.8
3.9
3.4
3.4
3.4
3.4
29
2
6.1
4.4
3.7
3.4
3.3
3.3
46
Jug
3
6.3
5.1
4.0
3.4
3.4
3.4
46
No.
4
6.6
6.1
4.3
3.3
3.2
3.3
50
5
6.6
5.4
3.7
3.0
2.9
2.8
58
6
6.1
5.1
4.5
4.0
3.9
3.6
41
*See page 43.
-------
22
Orthophosphate removal with respect to aeration time is shown in
Figure 9. As in the suspended solids variation study, the maximum
removal took place in the first 3 hours. Initial orthophosphate
values for Jugs Nos. 1 through 5 agree with theoretical values based
on volumes of jug components within 10 percent.
Soluble nonvolatile organic carbon (SNVOC) determinations were made
on jug mixed liquor filtrate at the start of the experiment. These
data are plotted against estimated substrate BOD to show the increase
in carbon load from Jugs Nos. 1 through 5 (Figure 10).
Percent orthophosphate removal with respect to estimated substrate
BOD concentration was plotted in Figure 10. Both magnitude and percent
orthophosphate removal increased as the substrate BOD concentration
increased. The plant mixed liquor (Jug No. 6) removed almost as
much phosphate as its synthetic BOD equivalent (Jug No. 2).
An additional experiment was performed on June 15, 1967, for verifi-
cation of BOD influence. Two jugs (Nos. 2 and 5) were prepared using
concentrated return sludge and primary effluent. Fifteen milliliters
of Metrecal were added to Jug No. 5 to increase the substrate BOD to
about 375 percent of that in the control Jug No. 2. The jug components
and analytical results are shown in Tables 6 and 7, respectively. The
control jug removed 23.0 percent of the soluble phosphate while Jug No. ]
removed 49 percent. Mixed liquor from the head of Aeration Tank B-2
(Jug No. 1 in Table 7) removed 11 percent during this aeration period.
Phosphate release was noted in the heavily-loaded BOD jug during the
first hour of aeration. San Antonio aeration tanks at high organic
and hydraulic loading had a similar pattern of release.1
These experiments lend further support to the conclusion that ortho-
phosphate removal increases with increasing substrate BOD concentration.
Phosphate Variation
A set of four jugs was prepared on June 15, 1967 to determine the
effect of soluble phosphorus concentration on orthophosphate removal.
Jug components and analytical results are shown in Tables 6 and 7.
Jug No. 1 contained mixed liquor from the head of Aeration Tank B-2
and served as the plant reference. Jugs Nos. 3 and 4 were set up
to contain one-half and twice the initial phosphate concentration of
Jug No. 2, respectively. Jug No. 2 served as a control.
Since phosphate removal was found to increase with increasing substrate
BOD, this experiment was set up to simulate conditions which would
result from bypassing a portion of the primary clarifiers. The amount
of BOD substrate was increased by using larger quantities of primary
effluent. Simulation of raw sewage BOD concentration was not selected
since direct dosing of raw sewage to the aeration tanks would result
-------
23
JUG NO. MLSS (mg/l)
0.
i
0>
E
UJ
Q.
CO
O
X
Q.
O
X
I-
oc
O
2
3
4
5
6
2,755
2,675
2,825
2,675
2,890
1,195
NO. 5
NO.
0 1
2 3
AERATION TIME
4
(MRS.)
5
6
FIGURE 9-BOD VARIATION- PHOSPHATE
-------
24
60-
o
5
UJ
a:
UJ
V)
O
Q.
O
OC
O
50
£ 40
30
20
10
0
PLANT MIXED LIQUOR
100 200
ESTIMATED SUBSTRATE
BOD
300
(mg/l)
FIGURE 10-BOD VARIATIONS-PHOSPHATE REMOVAL 8 SNVOC
-------
25
iri grease and scum accumulation in the final clarifiers which are not
equipped with skimming facilities.
Table 6
Phosphate Variation - Components
Jug No.
Components
PE (liters)
Cone. RS (liters)
FE (liters)
ML (liters)
Metrecal (ml)
K HP04 (mg/l-P)
City Water (liters)
TSS (mg/1)
*BOD Variation Study
12.5
2.5
6.3
2.5
12.5
2.5
15
1,600 2,765
3.0
6.0
6.2
2,940 3,095
12.5
2.5
15.0
3,040
Note: For analyses of components, see Table 1.
Jug No. 3 containing about half of the normal phosphate concentration
removed 55 percent of the soluble phosphate in the initial three hours
of the study and then exhibited phosphate release. After 6 hours'
aeration, the overall removal was 28 percent. Similar results were
observed in Jugs Nos. 2 and 4. Jug No. 2 removed 32 percent after
.3 hours' aeration, but only 23 percent in 6 hours. Jug No. 4 removed
27 percent in 3 hours and 23 percent after 6 hours' aeration. Jug
No. 1, containing plant mixed liquor, removed 11 percent of the
soluble phosphate during the 6-hour period. Figure 11 is a plot of
phosphate removal versus aeration time.
Table 7 reveals that although percent removal is not affected
significantly by initial phosphate concentration in the range
6.5 to 12.4 mg/l-P, there is a slight increase in the weight
removed with increasing initial phosphate concentration. In
order of increasing phosphate concentration, Jugs Nos. 3, 2, and
4 removed 1.1, 1.5, and 2.9 mg/l-P, respectively, after 6 hours'
aeration.
-------
26
12
a
, 10
8
o 6
Q.
O
I
I-
rr
o
NO. 4 (200% P04 )
NO. I (PLANT ML)
NO. 2 (NORMAL P04 )
NO. 3 ( 50 % P04 )
0
234
AERATION TIME
FIGURE II- PHOSPHATE VARIATIONS - PHOSPHATE
-------
Table 7
27
Aeration
Time (Hrs)
0 (10:30 a.m.)
1
2
3
4
5
6
Phosphate Variation - Results
0-P04 (rag/l-P)
Jug No.
5*
6.5
6.0
5.8
5.5
5.6
5.8
5.8
% Removal 11
* BOD Variation Study
6.5
5.5
4.5
4.4
4.2
4.8
5.0
23
4.0
2.8
2.2
1.8
2.3
2.7
2.9
28
12.4
10.5
9.8
9.0
9.0
9.4
9.5
23
7.7
8.8
7.5
6.2
5.5
4.2
3.9
49
Chemical Variation
Five jugs were set up on June 16, 1967, to determine the effect
of chemical addition and variation in hardness on phosphate removal.
Jugs were prepared using 13 liters of primary effluent rather than
10 liters to increase the BOD substrate. The MLSS concentration
varied from 2,900 to 3,100 mg/1.
Two jugs were set up to determine the effect of ferrous iron and
aluminum salts on phosphate removal. Orthophosphate concentration
was determined on primary effluent. Then, Jugs Nos. 2 and 3 were
dosed with 25 mg/1 of ferrous and aluminum ion, respectively. After
chemical addition and thorough mixing, the soluble orthophosphate
concentration was immediately determined. Return sludge was then
added to these jugs to produce mixed liquor, and orthophosphate was
again determined. The jugs were aerated and monitored for 6 hours.
Table 8 lists the jug components.
Two jugs were set up to determine the effect of variation in hardness
on phosphate removal. The primary effluent used for jug makeup
contained 420 mg/1 total hardness as CaCOn. Jug No. 4 was set up
to have a 200 mg/1 hardness by dilution with deionized primary
effluent. Jug No. 5 was dosed with calcium chloride to simulate a
hardness of 500 mg/1.
Jug No. 6 served as a control for both the chemical addition and
hardness variation studies. Jug No. 1 contained acclimated sludge
and is listed under "Acclimation Studies."
-------
28
Table 8
Chemical Variation - Components
Jug No.
Components
PE (liters) 13.0 13.0 13.0* 13.0 13.0
Cone. RS (liters) 2.0 2.0 2.0 2.0 2.0
FeSO, (mg/l-Fe) 25.0 -
A12(S04)3 (mg/l-Al) - 25.0
CaCl2 (mg/l-Ca) - 26.0
Air (ft3/m) 17.5 17.5 17.5 17.5 17.5
TSS (mg/1) 3,040 3,060 2,860 2,980 3,120
*Consisted of 6.5 liters of PE + 6.5 liters of PE after mixed bed
deionizer treatment.
Note: For analyses of components, see Table 1.
The results are shown in Table 9 and Figure 12. The addition of
iron and aluminum salts immediately reduced the orthophosphate
concentration by 79 and 95 percent, respectively. The addition of
return sludge to provide a MLSS concentration of about 3,000 mg/1
increased the initial orthophosphate concentrations to 1.7 and 0.4
mg/1 in Jugs Nos. 2 and 3, respectively. The lower concentration of
orthophosphate in Jug No. 3 was attributed to precipitation of the
phosphate by residual aluminum ion prior to mixed liquor sampling.
After 6 hours' aeration, the orthophosphate decreased from 1.7 to
0.9 mg/1 in the mixed liquor containing iron. The jug containing
aluminum reduced the concentration from 0.4 to 0.2 mg/L during the
same period. The increase in orthophosphate concentrations which
occurred during the last three hours of aeration was greater in the
jug containing iron.
Jug No. 4 containing 200 mg/1 hardness showed a 25 percent removal
of soluble phosphate, while Jug No. 5, containing 500 rag/1 hardness,
removed 33 percent soluble phosphate. The control jug containing
420 mg/1 hardness removed 31 percent. Release occurred in each of
the jugs although not to the extent noticed in the suspended solids
and BOD studies.
-------
29
Q.
i
o>
£ 4
x
w 3
O
X
Q.
O
X
NO. 4 (LOW HARDNESS)
NO. 283
NO. 6 (NORMAL HARDNESS)
NO. 5 (HIGH HARDNESS)
AERATION PERIOD
RETURN SLUDGE ADDED
CHEMICAL ADDED
2 3
AERATION TIME
FIGURE 12 - CHEMICAL ADDITION - PHOSPHATE
-------
30
Table 9
Chemical Variation - Results
0-P04 (mg/l-P)
Jug No.
Aeration
Time (Hrs)
0 (PE only) (11:00 a.m.)
0 (PE + chemical
addition)
0 (after RS addition)
1
2
3
4
5
6
7<> Removal (during
aeration)
I Removal (after
chemical addition)
Chemical
2
m.) 4.3
0.2
1.7
0.6
0.5
0.4
0.6
0.7
0.9
Addition
3
4.3
0.1
0.4
0.1
0.1
0.1
0.2
0.2
0.2
Hardness
4
4.3
4.7
5.9
4.9
4.5
4.2
4.3
4.4
4.4
Variation
5
4.3
4.4
5.5
4.4
3.9
3.6
3.5
3.5
3.6
6
4.3
4.7
5.5
4.4
4.1
3.8
3.6
3.7
3.8
47
79
50
95
25
33
31
Both iron and aluminum are effective agents for removing orthophosphate,
Percent orthophosphate removal increased with increasing hardness
concentration. The results are not conclusive due to the limited
tests but indicate potential for additional investigations.
Component Variation
A battery of four jugs was prepared on June 21, 1967, to evaluate
the effect of different components used for preparation of mixed
liquors on orthophosphate removal. Jug components and results are
shown in Tables 10 and 11, respectively.
Table 10
Component Variation - Components
Jug No.
Component
(liters)
Raw
PE
Cone. RS*
ML
Cone. ML**
TSS (mg/1)
1
-
-
2
10.0
6.0
3
10.0
-
6.0
4
10.0
-
15
1,530
2,650
2,620
5.0
2,800
* Return sludge concentrated 2:1 by settling.
**Mixed liquor from head of Aeration Tank B-2 concentrated 6:1 with
cationic polymer.
-------
31
Jug No. 1 (plant mixed liquor) was used as the control and removed
42 percent of the initial orthophosphate. About the same percent
removal was observed in Jug No. 2 using PE as the BOD source. In
Jug No. 3, raw sewage was used instead of primary effluent and
resulted in 53 percent" orthophosphate removal. Jug No. 4 containing
concentrated mixed liquor plus PE exhibited 72 percent removal of
soluble orthophosphate. The most notable difference between these
jugs was the soluble nonvolatile organic carbon content. Phosphate
removal increased with increasing initial organic carbon concentra-
tion, thus substantiating the results of the BOD variation experiment.
Table 11
Component Variation - Results
SNVOC (mg/1) 0-P04 (mg/l-P)
Aeration Jug No. Jug No.
Time (Hrs) 2 3 4 1 2 3 4
0 (11:30 a.m.) 59.0 81.2 116 6.4 6.0 5.7 6.3
1 -
2 ...
3 31.5 35.5 41.0
4 ...
5 22.7 27.5 28.7
% Removal 61 66 75 42 40 53 72
.Figure 13 displays orthophosphate concentration versus aeration time
for Jugs Nos. 1 through 4. None of the jugs exhibited release in
contrast to data from previous studies.
The soluble nonvolatile organic carbon and orthophosphate concentra-
tions in Table 11 indicate the higher the SNVOC initial concentration
(organic load) the higher the phosphate removal. The rates of SNVOC
and phosphate reduction are similar; both decrease more rapidly
during the initial 3 hours of aeration.
Acclimation Study
At 6:00 p.m. on June 14, a study was started to acclimate the plant
sludge to orthophosphate removal under controlled conditions. The
contents of Jug No. 3 of the BOD variation study was allowed to
settle for one hour, after which 10 liters of supernatant were
decanted and replaced with 10 liters of primary effluent. Metrecal
solution was continuously fed overnight to simulate a high unit BOD
load. Supplemental phosphate was added, and the jug was aerated at
17.5 liters per minute.
5.1
4.4
4.4
4.1
3.7
4.5
4.0
4.0
3.7
3.6
4.1
3.3
3.2
2.8
2.7
5.0
3.5
2.9
2.2
1.8
-------
32
Q.
i
o>
E
LJ
X
O.
-------
33
At 9:30 a.m. on June 15, 1967, the contents were again settled for
45 minutes, the supernatant decanted, and 7.5 liters of primary
effluent was added. Three milliliters of Metrecal were added to
supplement the BOD load to typical plant conditions. Aeration was
started and the acclimated and control jugs were monitored from
10:30 a.m. to 4:30 p.m. (Table 12). At 1:00 p.m. (2.5 hours), an
additional 5 milliliters of Metrecal were added to increase BOD
loading because analysis showed a low carbon content. The jug was
fed 421 milliliters of Metrecal-phosphate solution overnight with an
aeration rate of 17.5 liters per minute. The overall orthophosphate
load during the 16-hour overnight aeration periods was about 25 mg/1
as phosphorus (including the initial jug concentration).
At 9:00 a.m. on June 16, 1967, aeration was again stopped and the
contents allowed to settle. The supernatant was decanted and replaced
with 8.5 liters of primary effluent and 2.5 milliliters of Metrecal.
Aeration of the mixed liquor was initiated at 11:00 a.m. and continued
for 6 hours.
The analytical results for the acclimation and control jugs are
shown in Table 12. The acclimated jugs removed 78 percent of the
phosphate during both 6-hour aeration periods, whereas the control
jugs removed 23 and 31 percent.
The results from these experiments offer evidence that Indianapolis
sludge can be acclimated to high levels of soluble orthophosphate
removal.
Aeration
Time (Hrs)
0
1
2
3
4
5
6
7o Removal
MLSS (mg/1)
* Components:
**Components:
Table 12
Acclimation-Control Comparison
June 15-16, 1967
0-PO^ as P (mg/1)
6/15/67
6/16/67
Acclimated
Jug
6.9
6.1
3.7
3.2
2.3
1.4
1.5
78
3,230
Control
Jug*
6.5
5.5
4.5
4.4
4.2
4.8
5.0
23
2,765
Acclimated
Jug
4.9
4.5
4.0
3.3
2.4
1.3
1.1
78
3,810
Control
Jug**
5.5
4.4
4.1
3.8
3.6
3.7
3.8
31
3,120
Jug No. 2, Table 6.
Jug No. 6, Table 8.
Note: Aeration rate
per minute.
= 17.5 liters
-------
34
Sewage Characterization
A related purpose of the amenability analytical program was to
characterize samples from the various unit processes of activated
sludge plants with regard to selected chemical parameters. Additional
samples from an aeration jug study were included in the characteriza-
tion scheme. Such samples were taken from a jug study whose constituents
and operation resulted in maximum phosphate removal. Primarily, the
intention was to search for trends or correlatable functions within or
between various chemical parameters "which would be useful in defining
the phosphate removal process. Frequently, phosphate removal realized
from jug aeration was higher than that occurring in the aeration tanks.
During such instances, the probability of identifying the significant
differences in chemical composition was enhanced.
The samples were analyzed with and without solids to differentiate
between the quantity of each chemical parameter associated with the
solids from those associated with the liquid. Separation was accom-
plished by first decanting, then subjecting the resulting supernatant
to further solids removal using a Sharpies Ultra Centrifuge.*
The significance of the results will not be discussed in this report
since the basic purpose was for comparison with similar data from
other studies. The data are presented and compared under separate
cover .5
Microbiological Studies
This study was divided into two sections. The first section was
total plate counts of the various unit processes and aeration jug
samples. The second section included the selection of predominant
colonies, transfer of these colonies to agar slants, and shipment
to the Ada laboratory for identification.
There is no apparent correlation between plate counts, phosphate
removal capabilities, and total or volatile suspended solids content
of the mixed liquor. If such a relationship does exist, it was not
detected by the methods employed.
6
A separate report presents the data and discusses the microbiological
studies conducted during the amenability investigations.
*See page 43.
-------
35
SUMMARY
Studies conducted on the activated sludge facilities at the Southwest
Sewage Treatment Plant, Indianapolis, Indiana, from June 12 to 21,
1967, indicate orthophosphate removal averaging 20 percent through
the aeration tank, but only 10 percent from primary to final effluent.
The diurnal variation of BOD concentration in the raw sewage entering
the plant is typical; however, arrival of peak concentrations are
delayed until the early afternoon period due to the 2-hour flow time
from the main plant to the Southwest Plant.
The aeration tanks are four-pass with a length to width ratio of
25:1. Dye tracer studies conducted during conventional flow-through
conditions show that the tank effluent has a dispersion index (tgo/t^o)
of 2.25 and a modal detention time equal to 78 percent of the displace-
ment time. All of the mixed liquor flow receives more than two hours
of aeration, and only 3 percent of the flow receives less than 3
hours' aeration.
Dye tracer studies conducted during step-feeding conditions (equal
splitting of primary effluent between quarter and half points) show
that the detention time is reduced compared to conventional flow-
through operation. Eight percent of the mixed liquor flow receives
less than 2 hours of aeration and 34 percent less than 3 hours.
Dye tracer studies of the circular final clarifiers indicate that the
overflow has a modal detention time of 1 hour, and half of the return
sludge flow consists of short-circuited mixed liquor.
The plant MLSS concentration ranged from 1,625 to 2,343 mg/1, and the
return sludge ranged from 2,710 to 4,600 mg/1 of TSS. The return
sludge is typically 55 percent of the primary effluent. The primary
effluent flow is usually controlled from the main plant at between
25 and 28 mgd. The diurnal flow variation does not normally exceed
10 percent of the average daily inflow. About 500,000 gallon per
day of activated sludge is wasted.
The amount of air supplied ranges from 1.7 to 2.7 cubic feet per gallon
of waste treated, which resulted in a dissolved oxygen concentration
of 2.5 to 4 mg/1 in the aeration tank effluent. The dissolved oxygen
in the final clarifiers averaged 0.5 to 0.9 mg/1. Sludge blanket
depths in the final clarifiers varied from 12 inches at the side wall
to a range of 2 to 4 feet at the center. Blanket depth cannot be
reduced with the present sludge scraper performance.
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36
Plant monitoring during the study period shows that phosphate
concentrations (mg/l-P) in the waste streams were as follows:
Source
Raw
PE
FE
RS
Ortho
Total
Min.
4.8
4.3
4.4
3.0
Max. Min.
Max.
5.5
7.4
7.0
9.1
9.3
4.6
2.7
58.0
10.9
8.1
10.0
147.5
Avg. Ortho/Total
0.51
0.83
0.92
0.06
Daily orthophosphate and BOD loadings in the aeration tanks ranged
from 2.3 to 4.0 pounds phosphorus per day per 100 pounds MLSS and
from 9 to 16 pounds BOD per day per 100 pounds MLSS, respectively.
Pilot studies were conducted in aerated jugs to determine the
effect on orthophosphate removal caused by (1) variation in MLSS,
BOD, orthophosphate, and hardness concentration, (2) addition of
ferrous iron and trivalent aluminum, and (3) sludge acclimation.
The MLSS concentration and phosphate removal were not highly
correlated as the MLSS was increased from 453 to 4,760 mg/1; the
removal varied from 47 to 54 percent. Excluding this MLSS study,
the mixed liquor in the jugs was synthesized from 2,600 to 3,100
mg/1 suspended solids. As the substrate BOD was increased from
50 to 250 percent of the normal primary effluent, the removal
increased from 29 to 58 percent. Variation in orthophosphate
loading from 50 to 200 percent of the primary effluent concentration
did not significantly effect phosphate removal. Removal increased
from 25 to 33 percent as hardness concentration was increased from
200 to 500 mg/1.
Addition of 25 mg/1 iron or aluminum to primary effluent resulted
in 79 percent removal with iron and 95 percent with aluminum.
After acclimating for a period of 16 to 40 hours, the return sludge
removed 78 percent of the orthophosphate in the acclimated jugs
whereas 23 and 31 percent were removed in the control jugs.
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37
CONCLUSIONS
Plant Studies
1. Limited plant studies indicate that the activated sludge
facilities at the Southwest Indianapolis Sewage Treatment Plant are
not removing high levels of orthophosphate.
2. The BOD and orthophosphate concentrations in the primary
effluent are about 50 to 60 percent and 60 to 70 percent, respectively,
of that prevalent in the San Antonio wastes.
3. When step feeding is not being practiced, the aeration
tanks exhibit less longitudinal mixing and better plug-flow
characteristics than those of the San Antonio Rilling Plant.
4. Sufficient aeration time is provided for high orthophosphate
removal in both the conventionally-fed and step-fed tanks.
5. The concentrations of the dissolved oxygen present in the
aeration tanks are sufficient to allow phosphate removal.
6. Conditions found in the final clarifiers indicate an
environment which would be conducive to high levels of phosphate
release due to low dissolved oxygen levels and excessive sludge
detention time. The plant cannot be operated for optimum phosphate
removal until rapid sludge removal is provided.
Jug Studies
1. Orthophosphate removal does not vary significantly nor
correlate with variation in MLSS concentration.
2. At constant MLSS concentration, orthophosphate removal
increases as the substrate BOD concentration increases.
3. At constant MLSS and BOD concentrations, percent ortho-
phosphate removal does not change significantly with variation
in initial orthophosphate concentration.
4. At constant MLSS, BOD,and orthophosphate concentrations,
orthophosphate removal increases as the hardness increases.
5. Ferrous iron and aluminum salts are effective removal
agents of soluble orthophosphate. Aluminum was more effective
than iron.
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38
6. Bacterial plate count does not correlate with soluble
orthophosphate removal.
7. The waste and sludge are amenable to phosphate removal.
After a period of acclimation, the sludge is capable of removing
2.5 to 3 times as much orthophosphate as the unacclimated sludge.
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39
RECOMMENDATIONS
1. It is recommended that the Southwest Plant be considered
as a site for demonstrating phosphate removal by activated sludge.
Although amenability of the sludge to high levels of phosphate
removal was conclusive only after acclimation, the following
advantages justify the above recommendation: (1) presence of a
controlled plant inflow exhibiting only minimum diurnal flow
variation; (2) use of a relatively new and reliable physical plant;
(3) flexibility of plant operation; (4) minimum aeration tank short
circuiting; (5) absence of return flows since primary and waste
activated sludges are lagooned; and (6) interest in nutrient
removal exhibited by plant personnel.
2. The following changes may be necessary to optimize
operating parameters considered essential to obtain high levels
of soluble phosphate removal:
a. Increase the primary effluent BOD concentration by
removing one or two of the primary clarifiers from service and/or
b. Waste a larger quantity of return sludge to increase
the unit BOD loading (Ib./day/lb. MLSS) and decrease the sludge age.
c. Maintain a readily-settleable mixed liquor and returning
the sludge rapidly to minimize sludge detention in the final clarifiers.
This may require replacement or modification of the sludge removal
mechanism.
d. Adjust aeration rates to maintain a residual dissolved
oxygen concentration in the final clarifiers sufficient to minimize
release of phosphate into the effluent.
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40
APPENDIXES
Appendix I
Analytical Procedures
by
B. L. DePrater
Sample Preparation
Samples collected for analyses in the field were processed as
outlined in the respective analytical test procedures.
Samples returned to the Robert S. Kerr Water Research Center are
referred to as whole, centrate, whole fixed, and centrate fixed.
The following table lists the treatment each type received prior
to shipment to Ada.
Sample Treatment
1. Whole Shipped as is with no treatment.
2. Whole Fixed Shipped as is plus 1 ml cone, sulfuric
acid per liter of sample.
3. Centrate The sample was passed through a
Sharpies* motor driven laboratory
model continuous centrifuge, equipped
with a clarifier bowl driven at 23,000
rpm. The sample was delivered to the
centrifuge by a peristaltic pump at a
feed rate of 150 ml/min. The bowl
was cleaned and rinsed with distilled
water after each sample.
4. Centrate Fixed The centrate sample plus 1 ml/1 cone.
sulfuric acid.
All samples were shipped in either 250 ml plastic bottles or 1,000
ml cubetainers.**
*See page 43.
**Hedwin Corporation, 1600 Roland Heights Avenue, Baltimore, Maryland
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41
Chemical Tests
1. Orthophosphate
In the field, initial samples for Orthophosphate were
filtered immediately using Schleicher and Schuell* No. 588 paper.
Subsequent analysis by the stannous chloride procedure in Standard
Methods included the use of a B&L Spectronic 20* at 690 my.
A continuous automatic sampling device, built specifically
to support jug-study phosphate analyses, supplied whole samples to
a Technicon AutoAnalyzer platformed according to the method by
Gales and Julian. The manifold and reagents were modified, however,
to more closely approximate Standard Methods. The arrangement, in
order of sequence, was as follows:
a. A six-port peristaltic pump circulating jug mixed liquor
continuously.
b. An open-shut solenoid valve system selectively sampling
the flow from a T-connection in each circulating jug line.
c. A stepping relay alternately activating one of six jug
sample solenoids or the solenoid to a distilled wash water supply.
d. A master timer regulating the stepping relay at two-
minute intervals.
e. A Technicon* proportioning pump providing the flow of
samples and distilled water to a Technicon continuous filter. This
pump also diluted filtered samples with distilled water in the ratio
of 1:40, respectively.
Whole plant samples were run on the Technicon AutoAnalyzer
using a Technicon Sampler II and a continuous filter with samples
reaching the filter within thirty minutes. No significant ortho-
phosphate bleedback occurred in unfiltered samples during this
period.
2. Total Phosphate
Analyses were conducted on fixed whole samples at the Ada
laboratory within 15 days of sample collection. Initially whole
*See page 43,
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42
samples were blended for three to five minutes in a Waring Blendor*
and then analyzed by the persulfate procedure of Gales and Julian.
The procedure was modified to more closely approximate the Standard
Methods procedure for orthophosphate in that the samples were
neutralized after digestion. Also the manifold design and reagents
for the AutoAr.alyzer were adjusted to deliver approximately the
amount of reagents per sample outlined by Standard Methods.
3. Total Carbon and Total Nonvolatile Organic Carbon
Whole samples were run in the field using the methods of
Van Hall, et al. ' A Beckman Carbonaceous Analyzer* was used.
Preliminary homogenization with a Waring Blendor provided represen-
tative syringe sampling of whole samples. As the whole acidified
sample was further purged with nitrogen gas for five minutes,
results were reported as total nonvolatile organic carbon. Acetic
acid standards were used for instrument calibration.
4. Total Oxygen Demand
10
Whole samples were run by the method of Stenger, et al.,
using the instrument and techniques described therein. Preliminary
homogenization with a Waring Blendor was practiced. Sodium acetate
standards were used.
5. Total Hardness
In the field, hardness was determined by EDTA. titrimetry
according to Standard Methods (Method B, pages 147-152).
Physical Tests
1. Solids
Tests for total suspended and total volatile suspended
solids were conducted according to Standard Methods (Methods C & D,
pages 424-425). Reeve Angel" 2.4 cm. glass fiber filters, Grade
934AH, were used in lieu of asbestos mats. Gooch crucibles were
fired at 600°C, cooled, the mats placed in the crucibles and dried
at 103°C for at least 1 hour before initial weighing. At intervals,
crucibles with filters were subjected to 600 C furnace temperatures
to check for weight loss due to the filter. Total and total volatile
solids were determined according to Standard Methods (Methods A & B,
pages 423-424).
*See page 43.
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2. Dissolved Oxygen
Measurements were made in situ with a YSI Model 51 Oxygen
Meter* equipped with a Model 5103 oxygen/temperature probe. The
meter was calibrated against the Azide Modification of the Winkler
Method described in Standard Methods^ (Method A, pages 406-410).
The meter was also calibrated against saturated air at the temperature
of the test medium.
3. Hydrogen Ion Concentration
All pH measurements were made using a line current Beckman
Zeromatic II* equipped with glass and calomel electrodes. Measure-
ments were made on whole-untreated samples.
4. Temperature
Temperature measurements were made with a battery powered
thermistor-thermometer.
^Mention of products and manufacturers is for identification only
and does not constitute endorsement by the Federal Water Pollution
Control Administration or the U. S. Department of the Interior.
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44
Appendix II
Southwest Indianapolis Sewage Treatment Plant
June 12-21, 1967
Plant Performance Data-
12
13
14
15
16
17
18
19
20
21
12
13
14
15
16
17
18
19
20
21
BOD Concentration
(mg/1) Total Susp.
Solids (mg/1) Overall % Removal
Raw Pri. Final Raw Pri. Final BOD TSS
Sewage Eff. Eff. Sewage Eff. Eff.
162 92 15 195 70 11 90.7 94.3
239 121 6 225 72 16 97.4 93.1
200 93 4 245 126 13 98.2 94.5
200 80 13 255 86 27 93.7 89.6
183 56 7 270 88 20 96.9 92.7
158 75 13 115 60 17 91.7 85.6
68 60 4 165 70 21 94.8 87.2
122 92 22 125 108 21 82.3 83.2
169 122 19 375 94 15 88.7 96.0
124 89 12 365 80 16 90.7 95.7
Operating Data - Activated Sludge Plant:
Flow
Pri.
Eff.
27.2
27.8
23.9
25.2
14.3**
20 . 6**
20.4**
28.0
26.2
25.1
Ret.
Sludge
14.5
15.0
14.5
14.9
14.4
14.9
14.0
15.3
14.7
14.1
% Ret.
Sludge
53.3
54.0
60.8
59.2
101.0
72.2
68.6
54.5
56.0
56.2
Air
Applied
CF/gal.PE
1.7
2.0
2.3
2.3
3.6
2.5
2.4
1.9
2.2
2.7
MLSS
(mg/1)
1,731
1,897
1,832
2,343
1,975
2,073
1,828
1,636
1,783
1,625
RS
(mg/1)
4,600
4,190
4,150
4,450
3,925
2,710
3,455
3,005
3,585
3,065
*Based on analysis of 24-hour composite samples consisting of equal
portions of grab samples collected hourly by means of automatic
samplers. Samples are refrigerated during the compositing period.
**Bypassed waste causing atypical operation.
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45
ACKNOWLEDGMENT
We wish to acknowledge the help of Mr. Ed Dougherty, Plant
Superintendent, and his fine staff for the assistance they gave
us before, during, and after the study period. Without this help,
our job would have been much more difficult.
We also wish to acknowledge the guidance of Mr. Oral H. Hert,
Chief of Sewage Section, Division of Engineering, Indiana State
Health Department, during our preliminary survey of Indiana's
activated sludge plants to select a plant for phosphate amenability
study.
The extra hours of analysis excellently performed by Mr. B. E.
Bledsoe, Chemist; Mr, B. D. Newport, Physical Science Technician;
and Mr. S. C. Yin, Microbiologist, along with their interest and
devotion to their respective professions, made this study possible.
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46
REFERENCES
1. Priesing, C. P., et al. , "Phosphate Removal by Activated Sludge--
Plant Research," Presented October 11, 1967, New York Water
Pollution Control Federation Meeting, New York, USDI, FWPCA,
Robert S. Kerr Water Research Center, Ada, Oklahoma.
2. Priesing, C. P., et al., "Phosphate Removal by Activated Sludge--
Pilot Research," Presented October 11, 1967, New York Water
Pollution Control Federation Meeting, New York, USDI, FWPCA,
Robert S. Kerr Water Research Center, Ada, Oklahoma.
3. Scalf, M. R., et al., "Phosphate Removal by Activated Sludge,
Amenability Studies at Baltimore, Maryland," Internal Report,
USDI, FWPCA, Robert S. Kerr Water Research Center, Ada,
Oklahoma.
4. Standard Methods for the Examination of Water and Wastewater,
12th Edition. 1965.
5. Lively, L. D., et al., "Phosphate Removal by Activated Sludge,
Waste Characterization," Internal Report, USDI, FWPCA, Robert S.
Kerr Water Research Center, Ada, Oklahoma. 1968.
6. Moyer, J. E., et al., "Survey of Activated Sludge Treatment
Plants for Predominant Bacterial Types," Internal Report,
USDI, FWPCA, Robert S. Kerr Water Research Center, Ada,
Oklahoma. 1968.
7. Gales, M. E. and Julian, E. C., "Determination of Inorganic
Phosphate or Total Phosphate in Water by Automatic Analysis."
Presented at the 1966 Technicon Symposium on Automation in
Analytical Chemistry.
8. Van Hall, C. E., et al., "Rapid Combustion Method for the
Determination of Organic Substances in Aqueous Solutions,"
Analytical Chemistry 35:3, 315. 1963.
9. Van Hall., C. E., et al., "Elimination of Carbonates from Aqueous
Solutions Prior to Organic Carbon Determination," Analytical
Chemistry 37:6, 769. 1965.
10. Stenger, V. A. and Van Hall, C. E., "Rapid Method for Determination
of Chemical Oxygen Demand," Analytical Chemistry 39:2, 207. 1967.
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47
GLOSSARY
AT Aeration tank
FE Final effluent
ft3 Cubic feet
Mrs Hours
mgd Million gallons per day
mg/1 Milligrams per liter
mg/l-P Milligrams per liter phosphorus as the element
ml Milliliters
MLSS Mixed liquor suspended solids
P Phosphorus as the element
PE Primary effluent
ppb Parts per billion
RS Return sludge
SNVOC Soluble nonvolatile organic carbon
TC Total carbon
TOG Total organic carbon
TOD Total oxygen demand
TSS Total suspended solids
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