Environmental Protection Technology Series
Alum Addition To Activated Sludge
With Tertiary Solids Removal
\
LU
CD
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Monitoring, Environ-
mental Protection Agency, have been grouped into five series. These
five broad categories were established to facilitate further develop-
ment and application of environmental technology. Elimination of
traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The five series
are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the Environmental Protection Technology
Series. This series describes research performed to develop and demon-
strate instrumentation, equipment and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution.
This work provides the new or improved technology required for the
control and treatment of pollution sources to meet environmental
quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the Office of Research and Monitoring,
EPA, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
-------
EPA 670/2-73-037
August 1973
ALUM ADDITION TO ACTIVATED SLUDGE WITH
TERTIARY SOLIDS REMOVAL
By
Alan B. Hais
John B. Stamberg
Doll off F. Bishop
D.C. Department of Environmental Services
and
EPA-DC Pilot Plant
Washington, D.C. 20032
Contract No. 14-12-818
Project 11010 EYM
Program Element 1B2033
Project Officer
Dolloff F, Bishop
Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, V.S. Government Printing Office, Washington, D.C. 20402 - Price 66 cents
-------
ABSTRACT
Pilot treatment of District of Columbia primary effluent in the EPA-DC
Pilot Plant consisted of four pass step aeration, alum addition in the
final aeration pass for phosphorus removal, secondary clarification
and multi-media filtration for tertiary solids separation.
The activated sludge system was operated with 4.0 hours aeration time
(based on the influent flow) and an overflow rate in the secondary
settler of 425 gal/(day)(sq.ft.). Alum (A12(SO.)3.14 H^O) was dosed
assuming an influent phosphorus concentration of 8.15 mg/1 as P. Lime
(25 mg/1) was added to the mixed liquor to stabilize the wastewater
during periods of low alkalinity. The dual-media filter (24-inch bed
depth) and the tri-media filter (40-inch bed depth), each loaded at
2.4 gal/(min.) (sq.ft.), regularly exhibited filter runs between 24
and 32 hours.
When operating with the usual final stage mixed liquor pH (6.7-6.9),
the complete system with tri-media filtration removed 92% of the
suspended solids, 96% of the BOD and 93% of the phosphorus from the
primary effluent. Daily fluctuations in the final pass pH, however,
corresponded to similar fluctuations in phosphorus removal. Further-
more, the removal of suspended solids, BOD and phosphorus all increased
to 97% during those periods when the final pass pH was between 6.3 and
6.6. Operation with a relatively low mixed liquor pH (less than 6.2),
caused an upset in the activated sludge.
This report is submitted in partial fulfillment of Project 11010 EYM
and Contract No. 14-12-818 by the Department of Environmental Services,
Government of the District of Columbia under the sponsorship of the
Office of Research and Monitoring, Environmental Protection Agency.
Work was completed as of October 1971.
-------
CONTENTS
Page
Abstract ii
List of Figures iv
List of Tables v
Acknowledgments vi
Sections
I Conclusions 1
II Recommendations 2
III Introduction 3
IV Description of Pilot Plant and Procedures 4
V Operation of Activated Sludge Process 7
VI Results and Discussions 11
Pollutant Residuals 11
Filter Media Comparison 16
Effect of pH 16
Summary 18
VII References 22
VIII Publications 23
IX Glossary 24
-------
FIGURES
No. Page
1 Pilot Process for Phosphorus Removal 5
2 Settling Test Interface Versus Settling Time 9
3 BOD Removal 13
4 Suspended Solids Removal 14
5 Phosphorus Removal 1~
6 Phosphorus Removal and pH Variation 19
7 Correlation Between Phosphorus Residual and
Fourth Stage pH 20
IV
-------
TABLES
No. Page
1 Operating Conditions for Pilot System 6
2 Activated Sludge Characteristics 8
3 Occurrence of Nitrification in Step Aeration 10
4 Residuals in Effluents 12
5 Filtration Residuals 17
-------
ACKNOWLEDGMENTS
The pilot system was constructed, maintained and operated by the
EPA-DC pilot plant staff under the direction of Robert A. Hallbrook,
chief mechanic; Walter W. Schuk, head instrument technician;
George D. Gray, chief operator; and Howard P. Warner, chief analytical
chemist.
-------
SECTION I
CONCLUSIONS
1. Step aeration with alum addition followed by secondary
sedimentation and tri-media filtration with the fourth pass mixed
liquor pH typically between 6.7 and 6.9 produced filtered effluent
residuals of 5 mg/1 of BOD (96% removal), 8 mg/1 of suspended solids
(92% removal) and 0.6 mg/1 of total phosphorus (as P, 93% removal)
for three months of stable operation.
2. When operating with a fourth pass pH between 6.3 and 6.6 the
system (with tri-media filtration) removed 97% of the suspended solids,
BOD and total phosphorus from the primary effluent. The pollutant
residuals after filtration for twenty days of continuous operation in
this pH range were 4 mg/1 of suspended solids, 3.6 mg/1 of BOD and
0.23 mg/1 as P of total phosphorus.
3. Dual-and tri-media filtration both provided effective tertiary
solids separation; however, the tri-media filter consistently removed
between 5% and 10% more of the pollutant residuals from the secondary
effluent than did the dual-media filter.
4. Filter runs between 24 and 32 hours were maintained on a regular
basis, while filter runs exceeding 48 hours were possible with a
high quality secondary effluent.
5. Fluctuations in the residuals of suspended solids and phosphorus
corresponded to similar fluctuations in the fourth pass mixed liquor
pH. A definite relationship between pH and phosphorus residual was
established indicating that above pH 6.6 a rapid increase in the
phosphorus residual occurred with increasing pH at a given Al/P ratio.
6. Inasmuch as operation with a mixed liquor pH of less than 6.2
caused an upset in the activated sludge, it appeared that optimum
performance of the mineral addition activated sludge process is
achieved by maintaining an average final pass pH between 6.3 and 6.6.
-------
SECTION II
RECOMMENDATIONS
In the present study the feasibility of mineral addition to the
activated sludge process for phosphorus removal was demonstrated. A
sequence of unit processes was established and information concerning
basic operational parameters and chemical dose rates was determined.
The study, however, was not intended to provide complete design
criteria due to the nature of the pilot system itself. It is therefore
recommended that mineral addition to activated sludge with pH control
and filtration included in the system be operated on a larger scale to
determine important design parameters such as realistic clarifier
overflow rates, air requirements and the effect of a diurnal flow and
loading variation on the system (i.e. parameters which cannot be
meaningfully evaluated in a 2000 gallon per day pilot system.)
Maintenance of the final pass pH in the relatively narrow range between
6.3 and 6.6 was required to produce consistently'low phosphorus
residuals. Equipment to automatically monitor and adjust pH to the
proper value will have to be developed and piloted to establish the
controllability of pH and chemical requirements, as well as ,to confirm
the product quality observed in this study. In areas of relatively
low wastewater alkalinity, such as the District of Columbia, pH control
will require facilities to dose with both acid and base. For
applications in areas where the wastewater alkalinity is sufficiently
high to insure that an excessive drop in pH will not occur at the
normal alum dosing rates, provisions for the addition of acid will be
all that is required.
-------
SECTION III
INTRODUCTION
The insolublization of phosphate ions in wastewater by the addition of
aluminum salts to the activated sludge process is a low capital cost
method for phosphorus removal. Barth and Ettinger (1) reported that
sodium aluminate added to the aeration basin of an activated sludge
pilot plant removed 95% of the phosphorus from a supplemented waste-
water (0.5 mg/1 as P in the clarified effluent) at an aluminum to
phosphorus weight ratio of 1.5:1. While an aluminum dose somewhat
in excess of the stoichiometric weight ratio of 0.87:1 was necessary
to obtain low phosphorus residuals, aluminum salt (mineral) addition
to activated sludge had the advantage of a lower precipitant dosage
than was required for an aluminum salt process incorporating a
separate tertiary step for phosphorus removal. The improved settling
characteristics of the combined biological and chemical sludge was
also an advantage of mineral addition.
In a similar bench-scale pilot study, Eberhardt and Nesbitt (2)
observed the effect of pH and filtration on phosphorus removal during
mineral addition to the activated sludge process. In studies with
domestic wastewater, operation with a mixed liquor pH of 6.0 and an
aluminum to phosphorus weight ratio of 1.8:1 produced the greatest
phosphorus removal after secondary clarification, averaging residuals
of 0.5 mg/1 as P (96% removal).
Greater phosphorus residuals in the secondary effluent were recorded
when operating with a mixed liquor pH between 6.1 and 6.8. However,
laboratory filtration of the effluent samples increased phosphorus
removals to greater than 99%, except when the pH was 6.8.
Miele (3) further confirmed the observation that phosphorus removal
efficiency depended on pH. Short-term operation of a 1.8 million
gal/day activated sludge plant with an average aluminum to phosphorus
weight ratio between 1.4:1 and 1.8:1 produced phosphorus removals in
excess of 95%. Jar tests indicated that greater phosphorus removal
occurred with decreasing pH in the pH range of 5-8.
In the present study, alum (aluminum sulfate) was dosed at a constant
rate to a 2,000 gal/day activated sludge pilot plant. In addition to
conventional secondary settling, filtration was used to remove
residual organic solids and particulate phosphorus. The effect of pH
on phosphorus removal was established.
-------
SECTION IV
DESCRIPTION OF PILOT PLANT AND PROCEDURES
The pilot plant process (Figure 1) consisted of step aeration, clari-
fication, and filtration. Primary effluent from the main District
of Columbia sewage treatment plant was fed at a constant rate of
2QQO gpd to a four pass step-aeration system. A splitter box
distributed equal portions of the primary effluent to each of the
final three aeration passes. The fourth pass mixed liquor flowed
by gravity to a circular settler, where it entered through a single
port on the periphery of the clarifier and was baffled downward.
The secondary settled solids were returned to the head of the first
pass for reaeration. Because of the relatively small capacity of
the clarifier, solids were wasted from the first pass.
The overflow from the secondary clarifier was pumped to two pressurized
plexiglas filter columns (6.5-inch i.d.) which were operated in parallel.
One filter had a dual-media bed, packed with 18 inches of 0.9 mm. coal
on top of 6 inches of sand (equal quantities 0.40-0.45 mm. sand and 0.8-
1.20 mm. sand). The other filter was a "Neptune Microfloc"* multi-media
filter consisting of 25 inches of coal followed by ten inches of sand
and five inches garnet (manufacturer's designation MF197). The flow
rates, detention times, and hydraulic loadings for the processes are
described in Table 1.
Alum (A12(S04)3 ' 14O) in an aqueous solution was added to the fourth
pass mixed liquor to precipitate phosphate ions from the sewage. With
the exception of one short period, alum was dosed at a constant rate
for the entire operation. The alum dose was based on a 2:1 A1:P weight
ratio and an influent phosphorus concentration of 8.2 mg/1 as P. An
emergency lime feed system was installed after the third month of
operation to increase the buffer capacity of the wastewater during
periods of low alkalinity by adding 25 mg/1 of lime to the first pass
mixed liquor.
Analytical Procedures
All samples for analysis were manually composited over 24 hours. During
compositing, all samples were stored at 3°C to minimize additional
biological activity.
In the laboratory, the total phosphorus were determined by the
persulfate method (4), BOD's by the probe method (5), ammonia (5)
and nitrate-nitrite (6) were determined on the Technicon Automatic
Analyzer, and the total organic carbon (TOC) was measured on a Beckman
Carbonaceous Analyzer (7). All other analyses employed Standard Methods
(8).
* Mention of a product does not constitute EPA endorsement of the
product.
-------
PRIMARY
Fl
~i
•ALUM
WASTE
* EFFLUENT*
Figure 1. Pilot Process for Phosphorus Removal
-------
Table 1. Operating Conditions for Pilot System
Process Flow Loading Rate
Secondary Settling 1.45 gal/min. 425 gal/(day)(sq.ft.)
Filtration 0.56 gal/min. 2.4 gal/(day)(sq.ft.)
Aeration Time - 4.0 hours (based on 1.45 gal/min. flow)
Return Solids Rate - 42%
-------
SECTION V
OPERATION OF THE ACTIVATED SLUDGE PROCESS
The alum activated sludge process was started in August 1970, using
primary effluent from the District of Columbia plant and seed
biological solids from an existing step aeration process. Two weeks
later, alum addition was begun; scheduled wasting of secondary settled
solids began in the last week of August.
The operation of the activated sludge for the five-month period
following the month of start-up is summarized in Table 2. During the
study, the Solids Retention Time (SRT) in aeration was operated at or
above 5 days because operation of activated sludge on the District
of Columbia wastewater produced filamentous growth and bulking solids
for operation with SRT's between two and five days. The average MLSS
for the first four months t>f operation was 6,600 mg/1. In January,
increased solids wasting reduced the MLSS to less than 5,000 mg/1.
and the SRT to 5.0 days. The percent volatile solids in the mixed
liquor stabilized at approximately 60%. With an average sludge volume
index of 45 for the entire operation, the.solids were readily settleable,
Because of the relatively small scale of the system, meaningful
clarification rates were not produced in the secondary clarifier.
Settling rates were determined in one liter graduate cylinders. In a
typical settling test, at a mixed liquor temperature of 48°F(lowest
operating temperature), the initial portion of the subsidence was
characterized by unhindered settling (Figure 2). After approximately
3.5 minutes, zone settling developed with a rate (based on the initial
portion of hindered .settling) of 13.2 ft/hr. (2,380 gal/(day)(sq.ft.)).
The presence of almost 8 mg/1 of NO^-N in the secondary effluent
during September (Table 3) indicated that substantial nitrification was
possible in a mineralized activated sludge with a final stage pH of
less than 7. Gradually decreasing nitrate concentrations with
corresponding increases in NH3-N were recorded as the temperature
dropped during October and November. An upset in the activated sludge
system in November destroyed many of the nitrifying organisms and
nitrification was greatly reduced. The cold temperatures experienced
during December and January prevented the recovery of the nitrifiers
and nitrification never returned to the levels seen prior to the upset.
-------
Table 2. Activated Sludge Characteristics
September, 1970
October, 1970
November, 1970
December, 1970
January, 1971
Temp.
°F
81°
75°
680
630
54°
MLSS
(% volatile)
mg/1
6900 (59%)
6560 (59%)
5720 (60%)
7080 (59%)
4930 (60%)
SVI
65
36
37
44
44
SRT
days
6.5
8.7
6.4
7.4
5.0
F/M
(Ib.BOD used/day
Ib. MLVSS
0.15
0.16
0.19
0.18
0.24
CO
-------
1000
800
CO
£ 600
400
i
200
0
i i i i
T I n|~~l I I I | I I I TT
I I I iTT
I i i i i I
1000 ML = 1.15 FT.
TEMPERATURE - 9°C.
MLSS = 3980 MG/L
i i i i I i i i i I i i i i I i i i i I i i i i I i i i i
5
10
15
MINUTES
20
25 30
Figure 2. Settling Test Interface Versus Settling Time
-------
Table 3. Occurrence of Nitrification in Step Aeration
September, 1970
October, 1970
November, 1970
,_» December, 1970
o
January, 1970
Temp.
°F
81°
75°
68°
63°
54°
SRT
days
6.5
8.7
6.4
7.4
5.0
Total Nitrogen
Primary Influent
mg/1
25.8
27.8
26.2
27.1
26.5
TKN
mg/1
8.5
12.6
13.2
16.8
16.6
Residuals
NH--N
mg/i
6.9
10.2
11.0
15.1
14.3
NO--N
mg/1
7.9
7.4
6.5
3.8
3.4
-------
SECTION VI
TEST RESULTS AND DISCUSSIONS
Pollutant Residuals
The activated sludge system with mineral addition performed well during
the entire operation (Table 4). The slightly reduced performance of the
system in November was caused by an upset in the activated sludge.
Good secondary treatment with filtration on stream was obtained during
October, December and January. During these three months, secondary
treatment alone removed 89% of the primary effluent BOD with filtration
increasing the total removal to 96%. These treatment efficiencies
produced average BOD values of 11.9 mg/1 in secondary effluent and
5.0 mg/1 in the filtered (tri-media) effluent. An average TOC residual
of 17.1 mg/1 in the secondary effluent represented 82% removal from the
primary effluent. Filtration (tri-media) increased the TOC removal by
5% producing water containing an average of 11.8 mg/1 of TOC. Similarly,
secondary treatment and filtration (tri-media) removed 82 and 90% of
the influent COD, respectively, with COD residuals of 48.9 mg/1 in the
secondary effluent and 27.4 mg/1 in the filtered effluent.
Secondary treatment removed 68% of the suspended solids from the primary
effluent for an average residual of 33 mg/1. Filtration (tri-media)
removed an additional 24% of the suspended solids with an average
residual of 8 mg/1. Total phosphorus residuals averaged 1.9 mg/1 as P
(78% removal) in the secondary effluent and 0.61 mg/1 (93% removal)
after filtration (tri-media).
Operations during December provide an indication of typical variability
in pollutant removal. BOD residuals ranged from 6.8 to 19.2 mg/1 in the
secondary effluent with an average of 12.0 mg/1 for the month (Figure 3).
Similarly, daily BOD residuals in the filtered (tri-media) effluent
varied from 10.5 to less than 1 mg/1 for a monthly average of 4.9 mg/1.
The suspended solids in the secondary effluent (Figure 4) exhibited
greater daily variability than residual BOD ranging between 12 and 54
mg/1 (33 mg/1 average). Filtration (tri-media) reduced the solids to an
average of 8 mg/1, although the quality of the filtered (tri-media)
effluent (daily residuals from 1 to 29 mg/1) reflected the variation in
amount of suspended solids carried over from the secondary clarifier.
The phosphorus removal exhibited an even greater daily variability than
did the solids removal, with residuals ranging between 0.9 and 4.6 mg/1
as P in the secondary effluent and between 0.07 and 2.9 mg/1 as P after
tri-media filtration (Figure 5). Nevertheless, phosphorus residuals
averaged 1.9 mg/1 as P in the secondary effluent and 0.65 mg/1 as P in
the filtered effluent.
11
-------
Table 4. Residuals in Effluents
September
Primary
Secondary
October
Primary
Secondary
Filtered (tri-media)
November
Primary
Secondary
Filtered (tri-media)
December
Primary
Secondary
Filtered (tri-media)
January
Primary
Secondary
Filtered (tri-media)
BOD
mg/1
107
12.2
121
16.2
5.2
128
17.8
8.1
140
12.0
4.9
127
13.5
5.0
TOC
mg/1
99
11.3
101
17.5
12.1
92
20.8
13.6
91
16.4
11.4
85
17.7
11.9
COD
mg/1
260
33.9
304
54.3
28.1
280
58.7
32.6
260
47.0
26.0
255
45.5
28.1
SS
mg/1
105
19
120
41
9
97
50
16
94
33
8
96
26
7
P
mg/1
8.2
1.4
9.1
2.2
0.58
8.7
2.9
0.97
8.5
1.9
0.65
8.2
1.6
0.61
12
-------
160
140
120
100
80
60
40
20
0
1
15 20
DECEMBER
Figure 3. BOD Removal
30
-------
5
10
15 20
DECEMBER
30
Figure 4. Suspended Solids Removal
-------
10
0
10 15 20
DECEMBER
Figure 5. Phosphorus Removal
25
30
-------
Filter Media Comparison
Comparing the different filters, tri-media filtration removed between
5 and 10% more of the pollutant residuals from the secondary effluent
than did dual-media filtration (Table 5). For the four months of filter
operation, the tri-media effluent averaged 10 mg/1 of suspended solids
and 0.7 mg/1 as P of total phosphorus; the dual-media effluent,13 mg/1
of suspended solids and 0.89 mg/1 as P of total phosphorus. The
phosphorus concentration in the tri-media filter effluent regularly
duplicated the "soluble" phosphorus residual as determined by 0.45 >u
millipore filtration.
Similar differences in effluent quality from the two types of filters
were observed with respect to the organic residuals (BOD, TOC, and COD).
The residuals of BOD, TOC, and COD in the tri-media filter effluent
averaged 5.8, 12.2, and 28.7 mg/1, respectively, the same residuals
after dual-media filtration averaged 6.9, 13.2, and 34.4 mg/1.
With good quality secondary,effluent (25-40 mg/1 suspended solids),
filter runs between 24 and 32 hours occurred regularly. Filter runs in
excess of 48 hours were possible during those periods when good
phosphate precipitation and effective secondary solids capture in the
settlers produced a very high quality secondary effluent (15-20 mg/1
suspended solids). During high solids carryover from the settlers
(> 50 mg/1), filter runs of 24 hours permitting solids breakthough
still selectively removed phosphorus.
The Effect of pH
The fourth pass mixed liquor pH for the five months of operation
normally varied between 6.7 and 6.9. However, lower residuals of
suspended solids and prganics, as well as phosphorus, were recorded
in the secondary and filtered effluents when operating with a fourth
pass mixed liquor pH of less than 6.6. As an example of favorable pH
operation, the twenty-day period from October 21 to November 9, at a
pH of approximately 6.5 in the fourth pass mixed liquor, averaged
filtered residuals of 4 mg/1 for suspended solids, 3.6 mg/1 for BOD,
and 0.23 mg/1 as P for total phosphorus.
As the fourth pass pH increased to 7 and above, a deterioration of
effluent quality was observed visually as well as by increased
pollutant residuals. Operation at a relatively high pH (greater than
6.9) generally produced a fine turbid haze in the secondary effluent
which was difficult to remove by filtration. During periods of high
pH operation, the greatest increases were recorded in the residuals of
suspended solids and phosphorus while the residual organic concentrations
were less affected.
Using the January fourth pass pH and filtered phosphorus residual- as
references, a steady increase in the phosphorus residual corresponded
16
-------
October
Table 5. Filtration Residuals
BOD TOC COD SS P
mg/1 mg/1 mg/1 mg/1 mg/1
Dual-media 5.2 11.7 35.5 14 0.68
Tri-media 5.2 12.1 28.1 9 0.58
November
Dual-media 10.4 15.6 36.8 19 1.2
Tri-media 8.1 13.6 32.6 16 0.97
December
Dual-media 6.3 12.6 28.6 11 0.97
Tri-media 4.9 11.4 26.0 8 0.65
January
Dual-media 5.8 12.8 32.6 8 0.75
Tri-media 5.0 11.9 28.1 7 0.61
17
-------
to a similar rise in pH (Figure 6). Furthermore, many local peaks in
the residual phosphorus concentration reflected similar peaks in the
pH. Inasmuch as alum was fed at a constant rate, the only changes in
the A1:P ratio were caused by normal fluctuations in the influent
phosphorus concentration and the A1:P ratio randomly oscillated about
the 2:1 value chosen for the study, averaging 1.99:1 for the month.
A definite relationship between the fourth pass pH and the filtered
phosphorus residual is indicated by the smooth curve drawn through the
data (Figure 7). The figure clearly defines the steady rise in
phosphorus residual with pH. Furthermore, this increase in phosphorus
residual is particularly rapid above pH 6.6.
Operation at pH below 6.2, however, produced an upset in the biological
system. This upset occurred in November when the decreased buffer
capacity of a rain-diluted sewage caused an excessive drop in pH at the
2:1 A1:P ratio being used for the study. Fourth pass pH values of 6.1
or less were recorded on several occasions during the second week in
November. The pH values of the other mixed liquor passes, which
normally exhibited the pH of the influent wastewater, were also reduced
to the same level as the fourth pass pH.
On November 12, the A1:P ratio was reduced to stabilize the pH above
6.5 until the buffer capacity of the sewage returned to normal levels.
However, the activated sludge mixed liquor had already been upset.
When viewed under a microscope, the mixed liquor during this period
appeared to be poorly bio-flocculated and the MLSS dropped from
7200 mg/1 to a low of 3850 mg/1 on November 22. The emergency lime
feed system was installed shortly thereafter and prevented a similar
occurence during a period of heavy rainfall in December.
The information derived from this study indicates that pH control is
essential to consistently produce low phosphorus residuals from the
alum addition activated sludge process. The control of pH in the
relatively narrow range between 6.3 and 6.6 would necessitate alternate
dosing of acid and base as required by the prevailing conditions of pH
and alkalinity. With proper pH control, it is likely that efficient
phosphorus removal can be achieved using an Al:P ratio considerably
less than 2:1.
Summary
Step aeration with alum addition followed by secondary-sedimentation
and tri-media filtration with the fourth pass mixed liquor pH typically
between 6.7 and 6.9 produced filtered effluent residuals of 5 mg/1 of
BOD, 12 mg/1 of TOC, 27 mg/1 of COD, 8 mg/1 of suspended solids, and
0.6 mg/1 of total phosphorus (as P) for three months of stable operation.
These residuals correspond to removals of 96, 87, 90, 92 and 93%,
respectively, of the pollutants in the influent primary wastewater.
18
-------
7.0
6.5
,' DOSED MIXED LIQUOR
cs
ts>
1.0
1 5
15
JANUARY
20 25
30
Figure 6. Phosphorus Removal and pH Variation
-------
6.0 6.2
Figure 7. Correlation Between Phosphorus Residual
and Fourth Stage pH
20
-------
When operating with a fourth pass pH between 6.3 and 6.6,the pilot
system (with tri-media filtration) removed 97% of the suspended solids,
BOD, and total phosphorus from the District of Columbia primary
effluent. The pollutant residuals after filtration for the twenty days
of continuous operation in this pH range were 4 mg/1 of suspended solids,
3.6 mg/1 of BOD and 0.23 mg/1 as P of total phosphorus.
Dual and tri-media filtration both provided effective tertiary solids
separation, however, the tri-media filter consistently removed between
5 and 10% more of the pollutant residuals from the secondary effluent
than did the dual-media filter. Filter runs between 24 and 32 hours
were maintained on a regular basis. Furthermore, with high quality
secondary effluent, filter runs exceeding 48 hours were possible.
Fluctuations in the residuals of suspended solids and phosphorus
corresponded to similar fluctuations in the fourth pass mixed liquor
pH. A definite relationship between pH and phosphorus removal was then
established, indicating that above pH 6.6 a rapid increase in the
phosphorus residual occurred with increasing pH. However, operation
with a mixed liquor pH of less than 6.2 caused an upset in the
activated sludge. Therefore, it appears that optimum performance of
the mineral addition activated sludge process is achieved by main-
taining an average fina1 stage pH between 6.3 and 6.6.
21
-------
SECTION VII
REFERENCES
1. Barth, E.F., and Ettinger, M.B., Journ. Water Poll. Control Fed.,
39, 1362, 1967.
2. Eberhardt, W.A., and Nesbitt, J.B., Journ. Water Poll. Control
Fed., 40_, 1239, 1968.
3. Miele, R., "PO^ Removal by Aluminum Addition to Activated Sludge."
Report from FWPCA at Pomona Water Renovation Plant No. 1
(July 1968).
4. Gales, M., Julian, E., and Droner, R., Journ. of Am. Water Wks.
Assoc., 58, 1363 (1966).
5. "FWPCA Methods for Chemical Analysis of Water and Wastes", U.S.
Dept. of the Interior, Fed. Water Poll. Control Adm., Cincinnati
(November 1969).
6. Kamphake, L., Hannah, S., and Cohen, J., Water Res., ]_, 205 (1967).
7. Schaeffer, R.B., et al., Journ. Water Poll. Control Fed., 37_, 1545
(1965).
8. "Standard Methods for the Examination of Water and Wastewater."
12th Ed., American Public Health Association, New York (1965).
22
-------
SECTION VIII
PUBLICATIONS
Hais, A.B., Stamberg, J.B., and Bishop, D.F., "Alum Addition to Activated
Sludge with Tertiary Solids Removal." Presented at the 68th National
Meeting of the AIChE, Houston (March 1971).
Hais, A.B., Stamberg, J.B., and Bishop, D.F., "Alum Addition to Activated
Sludge with Tertiary Solids Removal, "Chemical Engineering Progress
Symposium Series, 68, (1972).
23
-------
SECTION IX
GLOSSARY
Biochemical Oxygen Demand (5 day, BODr) - Measure of the quantity of
carbonaceous organic material usable 3s a source of food by aerobic
organisms present in a water.
Chemical Oxygen Demand (COD) - Measure of the Quantity of chemically
oxidizable compounds present in a water.
Total Organic Carbon (TOC) - Measure of the soluble and particulate
organic carbon present in a water as determined by the amount of COg
formed by combustion at 950°C.
Total Kjeldahl Nitrogen (TKN) - Measure of the ammonia-nitrogen and
organic nitrogen present in a water.
Suspended Solids (SS) - Measure of the solids retained by a standard
glass fiber filter and dried to constant weight, at 180°C.
Activated Sludge - The contacting of a liquid waste with a biological
floe to convert one or more of the soluble wastewater components to a
particulate form.
Mixed Liquor - The mixture of biological floe and wastewater in an
activated sludge reactor.
Mixed Liquor Volatile Suspended Solids (MLVSS) - Measure of the mixed
liquor suspended solids combusted after ignition at 600°C; measures
the organic fraction of the suspended solids concentration and is an
approximation of the quantity of micro-organisms present.
Step Aeration - An activated sludge process in which the influent
wastewater is fed in equal volumes at 1/4, 1/2 and 3/4 points along
the length of the reaction basin.
Sludge Volume Index (SVI) - The volume in mi Hi liters occupied by
1 gram of activated sludge after settling the mixed liquor for
30 minutes.
Zone Settling - The type of sedimentation displayed by flocculant
suspensions of intermediate concentration in which the particles are
close enough together to permit interparticle forces to hold the
particles in a fixed position relative to each other.
Bulking Solids - An activated sludge mixed liquor which, primarily due
to the shape of the particles in the floe, displays poor compaction
characteristics upon settling.
24
-------
Primary Effluent - Raw wastewater from which the settleable and
floatable matter has been removed by sedimentation.
Nitrification A biological process in which ammonia is converted
first to nitrite and then to nitrate.
Solids Retention Time - Ib. VSS under aeration
(Ib. VSS leaving system in underflow
wasting and secondary effluent)/day
U. S. GOVERNMENT PRINTING OFFICE : 1973--5I»6-310/79
25
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
| !„ Report No,
3. Accession No.
w
4. Title
Alum Addition to Activated Sludge with Tertiary
Solids Removal
?. Author(s)
Hais, Alan B., Stamberg, John B. and Bishop, Dolloff F.
EPA-DC Pilot Plant
Department of Environmental Services
Government of the District of Columbia
5000 Overlook Ave. S.W.
Washington, ..P.p.... .2.0032.. _,,,„„ ....... „..,
5. Report Date
6.
8. Perfofinittg Organization
Repoyf Na,
10.- Project No.
11010 EYM
12.
15. Supplementary Notes
11. Contract/Grant No.
.^ 14-12-818.
I', fyjje of-Report and
IHsied Covered
Environmental Protection Agency report number EPA-670/2-73-037,
August 1973.
'the activated sludge system was operated with 4.0 hours aeration time (based on the
influent flow) and an overflow rate in the secondary settler of 425 gal/(day)(sq.ft.).
Alum was dosed assuming an influent phosphorus concentration, of 8.15 mg/1 as P. Lime
(25 mg/1) was added to the mixed liquor to stabilize the wastewater during periods of
low alkalinity. The dual-media filter (24-inch bed depth) and the tri-media filter
(40-inch bed depth), each loaded with secondary effluent at 2.4 gal/(min.)(sq.ft.),
regularly exhibited filter runs between 24 and 32 hours.
When operating the step aeration with the usual final stage mixed liquor pH (6.7-6.9),
the complete system with tri-media filtration removed 92% of the suspended solids,
96% of the BOD and 93% of the phosphorus from the primary effluent. Daily fluctu-
ations in the final pass pH, however, corresponded to similar fluctuations in
phosphorus removal. Furthermore, the removal of suspended solids, BOD and phosphorus
all increased to 97% during those periods when the final pass pH was between 6.3 and
6.6. Operation at pH below 6.2 caused an upset in the activated sludge.
17a. Descriptors
Hydrogen Ion Concentration
Activated Sludge
Filtration
Phosphates
17b. Identifiers
Aluminium Phosphate Precipitation
Alum Addition*
Step Aeration*
Filtration of Secondary Effluent*
Multi-media Filters
lie. COWR.R Field & Group
05D
Wastewater Treatment
B.O.D.
Suspended Solids
3.8, Availability
19, Security Class.
(Report)
20. Security Class,
(Page)
21, No. of
Pagss
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D.C. 20240
Abstracts Dolloff F. Bishop
Institution
Environmental Protection Agency
WRSIC 102 (REV. JUNE 1971}
------- |