WATER POLLUTION CONTROL RESEARCH SERIES • 17010 EIP 10/71
Soluble Phosphorus Removal
in the Activated Sludge Process
Part II
Sludge Digestion Study
U.:
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes
the results and progress in the control and abatement
of pollution in our Nation's waters. They provide a
central source of information on the research, develop-
ment, and demonstration activities in the Environmental
Protection Agency, through inhouse research and grants
and contracts with Federal, State, and local agencies,
research institutions, and industrial organizations.
Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Chief, Publications
Branch, Research Information Division, Research and
Monitoring, Environmental Protection Agency, Washington,
D. C. 20460.
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SOLUBLE PHOSPHORUS REMOVAL IN THE ACTIVATED SLUDGE PROCESS
PART II
SLUDGE DIGESTION STUDY
by
The Soap and Detergent Association
New York, N. Y. 10016
for the
Office of Research and Monitoring
ENVIRONMENTAL PROTECTION AGENCY
Project #17010 EIP
October 1971
For sale by tho Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 65 cents
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EPA Review Notice
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents neces-
sarily 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.
ii
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ABSTRACT
Sludges containing aluminum phosphorus precipitates from an acti-
vated sludge wastewater treatment plant were digested in a high-
rate digester. Sodium aluminate and liquid alum were used to pre-
cipitate the phosphorus from the wastewater. Analyses on both raw
and digested sludges showed that once precipitated from the waste-
water and incorporated into a sludge the phosphorus did not redis-
solve while undergoing anaerobic digestion. Most of the soluble
phosphorus in both the raw and digested sludges was in the ortho-
phosphate form, and the addition of the inorganic aluminum phosphorus
complexes did not adversely effect the anaerobic digester. High
concentrations of soluble aluminum ion did not appear in the anaero-
bic digester, and the use of alum for phosphorus removal caused no
additional hydrogen sulfide production during sludge digestion.
Analyses also indicated the addition of aluminum compounds enhanced
the dewatering properties of the raw sludges.
This report was submitted in fulfillment of Project Number 17010 EIP
under the partial sponsorship of the Environmental Protection Agency.
111
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TABLE OF CONTENTS
Page
ABSTRACT. iii
LIST OF FIGURES vii
LIST OF TABLES viii
CONCLUSIONS 1
RECOMMENDATIONS 3
INTRODUCTION 5
ORIGIN AND IMPORTANCE OF THE STUDY 5
STATEMENT OF THE PROBLEM 6
EXPERIMENTAL FACILITIES AND PROCEDURES 7
EXPERIMENTAL FACILITIES 7
Sampling Technique 11
Flow Measurements 12
Sludge Flows 12
Supernatant Return 14
Gas Volume o 14
ANALYTICAL TESTS AND PROCEDURES 14
Aluminum 14
Alkalinity 16
Dewatering of Sludges 16
Filtration 16
Gas Analysis 16
pH 16
Phosphorus 16
Solids 17
Sulfate 17
Volatile Acids 17
EXPERIMENTAL RESULTS AND DISCUSSION 19
PHOSPHORUS BALANCE 19
DIGESTER OPERATION 24
pH 30
ALKALINITY AND VOLATILE ACIDS 30
GAS PRODUCTION AND VOLATILE SOLIDS DESTRUCTION 35
SULFATE 38
ALUMINUM 42
SLUDGE DEWATERING 42
GENERAL DISCUSSION 47
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TABLE OF CONTENTS (continued)
Page
ACKNOWLEDGEMENTS 53
BIBLIOGRAPHY 55
APPENDIX 57
vi
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LIST OF FIGURES
Figure Page
1 FLOW DIAGRAM OF WASTEWATER THROUGH THE TREATMENT FACILITY . 8
2 FLOW DIAGRAM OF SLUDGE THROUGH THE TREATMENT FACILITY ... 9
3 CUMULATIVE TOTAL PHOSPHORUS BALANCE OF THE DIGESTER .... 20
4 CUMULATIVE TOTAL SOLUBLE PHOSPHORUS AND ORTHOPHOSPHATE
BALANCES OF THE DIGESTER 22
5 DIGESTER PROFILE OF THE SOLIDS LEVELS IN THE PRIMARY
DIGESTER ..... 25
6 DIGESTER PROFILE OF THE SOLIDS LEVELS IN THE SECONDARY
DIGESTER 26
7 DIGESTER PROFILE OF THE TOTAL PHOSPHORUS CONCENTRATIONS
IN THE SECONDARY DIGESTER 27
8 DIGESTER PROFILE OF SOLUBLE PHOSPHORUS CONCENTRATIONS IN
THE SECONDARY DIGESTER ON JULY 30, 1969 28
9 CUMULATIVE TOTAL SOLIDS BALANCE OF THE DIGESTER 29
10 a&b pH VALUES OF VARIOUS SLUDGES THROUGHOUT THE STUDY PERIOD. . 31
11 a&b ALKALINITY AND VOLATILE ACIDS OF DIGESTED SLUDGE DURING THE
STUDY PERIOD 33
12 a&b DIGESTER GAS PRODUCTION AND VOLATILE SOLIDS LOADING .... 36
13 a&b DIGESTER GAS PRODUCTION AND REDUCTION OF VOLATILE SOLIDS. . 39
14 QUANTITATIVE ANALYSIS OF DIGESTER GAS ..... 41
15 SULFATE ION CONCENTRATIONS OF THE SLUDGES 43
16 ALUMINUM ION CONCENTRATIONS OF THE SLUDGES 44
17 TIME OF VACUUM BREAK AS A FUNCTION OF FERRIC CHLORIDE
CONCENTRATIONS ADDED TO WASTE ACTIVATED SLUDGE 48
18 TIME OF VACUUM BREAK AS A FUNCTION OF FERRIC CHLORIDE
ADDED TO A 75 PERCENT WASTE ACTIVATED 25 PERCENT RAW
SLUDGE MIXTURE 49
19 TIME OF VACUUM BREAK AS A FUNCTION OF FERRIC CHLORIDE
ADDED TO A 50 PERCENT WASTE ACTIVATED 50 PERCENT RAW
SLUDGE MIXTURE ..... 50
20 A TYPICAL PLOT OF t/V (TIME/VOLUME) AGAINST V (VOLUME)
FROM RESULTS OF DEWATERING STUDIES, RUN NO. 1, 9/2/69. . . 59
vii
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LIST OF TABLES
Table Page
1 COMPARISON OF SOLUBLE ALUMINUM ION CONTENT OF DIGESTED
SLUDGES BY SPECTROCHEMICAL ANALYSIS VS. THE RAPID
MODIFIED ERIOCHROME CYANINE R METHOD 15
2 COMPARISON OF TOTAL PHOSPHORUS CONTENT OF SLUDGES
DETERMINED BY A MODIFIED ALKALINE ASH PROCEDURE VS.
THE POTASSIUM PERSULFATE METHOD 18
3 TOTAL SOLUBLE PHOSPHORUS IN THE DIGESTED SLUDGE 23
4 SPECIFIC RESISTANCE AND TOTAL SOLIDS OF SLUDGES 46
viii
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CONCLUSIONS
The conclusions which were drawn from this investigation are:
1. Most of the soluble phosphorus in both the raw and digested
sludges was in the orthophosphate form.
2. Once precipitated from the wastewater and incorporated into a
sludge the phosphorus did not redissolve while' undergoing
anaerobic digestion, even during a digester upset.
3. The addition of inorganic aluminum phosphorus complexes did
not adversely effect the anaerobic digestion process.
4. The use of alum for the removal of phosphorus from waste-
water caused no additional hydrogen sulfide production during
sludge digestion.
5. High concentrations of soluble aluminum ion did not appear in
the anaerobic digester, and aluminum ion toxicity was not
apparent.
6. The addition of aluminum compounds for the removal of phos-
phorus enhanced the dewatering properties of the raw sludges.
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RECOMMENDATIONS
During this investigation, it became apparent that further study
in the following areas might prove beneficial:
1. A laboratory scale study to determine the maximum aluminum
phosphate precipitate concentration which can be tolerated
under an anaerobic environment.
2. A study to investigate the effects of the phosphorus enriched
sludge on crops and its economic potential as a commercial
fertilizer.
3. A study to investigate the economic feasibility of dewatering
and wet oxidation of raw sludge containing the chemical pre-
cipitates, as a means of sludge disposal.
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INTRODUCTION
ORIGIN AND IMPORTANCE OF THE STUDY
The effects of excessive eutrophication in bodies of water has
pointed to the need for controlling nutrient additions in water
courses. The control of excessive eutrophication as indicated by
Leibig's Law of the minimum points to the limitation of some
nutritional requirement (14). Phosphorus removal from wastewater
treatment plant effluents has been suggested as a means of con-
trol by many people (5) (11) (14) (15). Currently, the removal of
phosphorus from wastewater discharges is a major area of investi-
gation and research in the field of environmental pollution con-
trol. Nesbitt (11) reviewed phosphorus removal methods and showed
the method of chemical treatment as most economical because of the
ability to incorporate existing treatment facilities in effecting
phosphorus removal.
The removal of phosphorus from wastewater by means of chemical
precipitation requires the use of a positively charged cation.
Five commonly investigated precipitants include lime, aluminum
sulfate (alum), sodium aluminate, ferric chloride, and ferric
sulfate. All of these coagulants will form a precipitate in
which the phosphate ion will bind to the positively charged
cation and settle out of solution. Once the phosphorus has been
precipitated from solution and incorporated in the sludge, the
problems of treatment, handling, and disposal remain. The phos-
phorus enriched sludge must be treated and/or disposed of in a
suitable manner before the problem of nutrient phosphorus removal
is effectively solved. This solution requires a knowledge of the
effects of this inorganic phosphorus cation precipitate upon
methods of sludge treatment, and the effects of sludge treatment
on the inorganic phosphorus precipitate.
Controlled anaerobic decomposition of organic raw sludges has been
a widely practiced process in wastewater treatment, and the addition
of inorganic compounds such as a cation-phosphorus complex into the
raw sludges could alter this process, The redissolving of the cation
during the digestion process may cause a toxic condition which
the bacterial population could not tolerate. Soluble forms of heavy
metals, high concentrations of metals, and high concentrations of
various salts have been shown to hinder the anaerobic digestion
process (9) (12) (13) (20).
Rudolfs et al. (13) reported a retardation in the digestion of some
sludges containing iron compounds, while Earth and Ettinger (2) re-
ported acceptable sludge digestion in a pilot plant study using
aluminum compounds.
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Along with the toxic effect of a metal cation the introduction of
excessive amounts of soluble sulfate ion into the digester has
caused concern because of the possible production of hydrogen
sulfide gas. Although studies utilizing aluminum sulfate for
phosphorus removal have been reviewed (1) (2) (5) (23), no results
on hydrogen sulfide production were reported.
The dissolving of the cation is not the only area of concern in
chemical treatment of wastewaters to achieve phosphorus removal.
If the cation-phosphorus precipitate were to redissolve in the
digester, the phosphorus could be returned to the wastewater
treatment system via the supernatant return and the entire phos-
phate removal scheme negated. However, various studies to date
indicate that the phosphorus precipitate remains insoluble during
anaerobic digestion (2) (22) (23).
Finally, to help reduce sludge disposal cost, sludge dewatering
may be practiced. The addition of an aluminum compound to acti-
vated sludge for removal of phosphorus may also act as a beneficial
preconditioning step if vacuum filtration is used for this dewat-
ering.
STATEMENT OF THE PROBLEM
This investigation was conducted on sludges fed to a treatment
plant digester, which included precipitates formed by the addition
of sodium aluminate [liquid, Na2Al2C>4] or alum [liquid, Al2(804)3]
to the wastewater being treated in an activated sludge system.
Specific objectives of this research were:
1. To determine the effects of the inorganic precipitate on the
anaerobic digestion process.
2. To determine if the aluminum-phosphorus precipitate is harmful
to the digestion process.
3. To determine the identity of the different forms of phosphorus,
and the effects of anaerobic digestion on them.
4. To determine if the excess sulfate ion, released into solution
during phosphate removal utilizing alum, increases the produc-
tion of hydrogen sulfide.
5. To determine effects of the aluminum-phosphorus precipitate on
the dewatering properties of raw sludges.
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EXPERIMENTAL FACILITIES AND PROCEDURES
EXPERIMENTAL FACILITIES
The sludge digestion system used in this study was a two-stage
system located at the Pennsylvania State University Wastewater
Treatment Plant. The plant is designed to accommodate flows of
4 mgd, and receives and treats nearly equal wastewater flows
from both the Pennsylvania State University and the Borough of
State College. The flows from the University and the Borough
are split, and the plant is set up to treat each separately,
although flows can be diverted from one flow stream to the other
(Fig. 1).
The facility treating Borough wastewater consists of the following:
1. Barminutor
2n Grit chamber
3. Primary aeration and settling tank
4. Secondary aeration and settling tank
5. Common chlorine contact tank
Waste activated sludge removed from the primary and secondary set-
tling tanks flows to a flotation sludge thickener. From there
the thickened sludge goes to a sludge well before being pumped to
the primary digester. Fig. 2 represents the sludge flow through
the plant.
The facility treating University wastewater consists of the following:
1. Barminutor
2, Preaeration and prechlcrination tank
3. Primary settling tank
4. High rate trickling filters
5. Final aeration tanks
6. Final settling tanks
7. Common chlorine contact tank
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CO
t t
BOROUGH INFLUENT UNIVERSITY INFLUENT
FLOW SPLITTER
BARMINUTOR
PRIMARY
SETTLING
TANKS
PRECHLORINATION
AND
PREAERATION
TANKS
PRIMARY
AERATION-
SETTLING
TANKS
SECONDARY
AERATION-
SETTLING
TANKS
HIGH RATE
TRICKLING
FILTER
No. 2
HIGH RATE
TRICKLING
FILTER
No. 1
FINAL
SETTLING
TANKS
FINAL
AERATION
TANKS
co
FIGURE 1: FLOW DIAGRAM OF WASTEWATER THROUGH THE TREATMENT FACILITY
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PRIMARY
AERATION-
SETTLING
TANKS
SUPER-
NATANT
STORAG
SLUDGE
STORAGE
TANK
WASTE
SLUDGE
WELL
SECONDARY
DIGESTER
1
1
PRIMARY
TANKS
SLUDGE WELL
DIGESTED
SLUDGE
FINAL
SETTLING
TANKS
FINAL
AERATION
TANKS
LEGEND
RAW UNIVERSITY SLUDGE
RAW BOROUGH SLUDGE — - —•
DIGESTED SLUDGE *•
SUPERNATANT RETURN /- * '
WASTE ACTIVATED SLUDGE (UNIV.) —
SAMPLING POINTS /e\ Cl Imnc
\\) oLUUbt
(
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The sludge from this system is comprised of raw sludge from the
primary settling tank and waste activated sludge from the final
settling tanks. Waste activated sludge is removed from a waste
sludge well and returned to the influent end of the plant prior to
the preaeration tank. The waste activated sludge is thus combined
with the raw sludge from the primary settling tank and is pumped
to the digesters with this sludge. Raw primary sludge can be
pumped directly to the primary digester or to a sludge concentration
tank prior to entering the primary digester (Fig. 2).
During these studies, chemical was added only to the system treating
University wastewater. Chemical additions were based on phosphorus
removal requirements and are discussed in detail in a separate
report (8). The exact location of the addition was varied, but in
all cases was either in the final aeration tanks or in the channel
carrying aeration tank effluents to the final settling tanks. Alum
was first added to aeration tank #2 on January 27, 1969. This
addition was the beginning of Phase I of the study which was designed
to determine what precipitant to use, how much to use and where to
add it. On February 21, 1969, alum addition was begun in aeration
tank //I, and continued in both tanks until May 19, 1969. Sodium
aluminate additions began in both tanks on Hay 28 and continued
through August 11, 1969, the end of Phase 1. During the entire test
period the coagulants dosage was varied, because of the requirements
of this phase of the study. Starting on August 21, 1969, alum was
added to only aeration tank //I and aeration tank //2 was kept as a
control. This mode of operation constituted Phase 2 of the study
and lasted through August 20, 1970.
The digesters were operated as a two-stage system, with each stage
having a capacity of 37,925 cubic feet. There was no recirculation
of sludge from the secondary digester to the primary digester
during the test period. The primary digester used a Pearth gas
recirculation system to keep it operating as a high rate digester.
It has a heat exchanger, and the pumping capacity is 150 gpm. The
secondary digester was operated as a conventional digester with
supernatant being withdrawn when it was formed. During the period
from January 1969 through May 1969, the secondary digester was non-
stratified, supernatant was withdrawn infrequently, and all of the
sludge removed from the digester was hauled by truck to University
farm land and disposed of by spraying. A small percentage was
returned as supernatant to the supernatant liquor storage tank at
times when flow and hauling schedules dictated. During this period
both digesters were operated at a capacity of about 36,000 cubic
feet, which resulted in a detention time of approximately 19 days.
Starting in the early part of June 1969 and continuing throughout
the remainder of the study, raw sludge from the University plant
was pumped to a sludge storage tank which concentrated it before
it was added to the primary digester (Fig. 2). This procedure re-
duced sludge volumes and increased the digestion time to approxi-
mately 38 days. During this operation sludge supernatant from both
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the raw sludge storage tank, and the secondary digester was pumped
to the supernatant liquor storage tank, and then to the primary
aeration tank. The pumping of sludges varied with operational
changes at the plant but raw sludge from the University primary
tank was generally pumped to the digester at 2 AM, 10 AM, and 6 PM
daily. Excess activated sludge from the Borough flow was thickened
in a flotation type thickener and stored in a sludge well located
in the thickener building. It was fed to the primary digester along
with the University raw sludge.
The secondary digester was stratified and operated as a conven-
tional digester. The supernatant was returned to the supernatant
liquor storage tank or was hauled by truck along with the bottom
digested sludge from the secondary digester for land disposal.
This method of operation was continued throughout the test period.
Sampling Technique
The location of sampling points for sludge samples is shown on
Fig. 2. Each of the samples was collected and composited in a
different manner.
Samples of Borough raw sludge were taken either from the screw
transporting the thickened sludge from the thickener to the storage
tank in the thickener building or from the storage tank itself, A
one liter sample was taken at the same time the digested sludge
was sampled.
Samples of University raw sludge, which included the waste activated
sludge, were taken from a sludge well located next to the primary
settling tanks. The samples were taken at the pumping times earlier
mentioned. Sample volumes of approximately one liter were collected
at each pumping and composited into a representative 500 ml sample.
The samples were taken on the same days that the Borough raw sludge
samples were collected.
Samples of digested sludge being withdrawn for land disposal were
collected in 500 ml plastic bottles at three separate times during
the withdrawal period. These samples were taken when approximately
one-sixth, one-half, and five-sixths of the sludge had been with-
drawn. These three samples were then combined into one sample,
representing the digested sludge. Digested sludge samples generally
were taken on every Monday and Wednesday, but periodically the sampling
was done on other days of the week. Analyses were run only on com-
posite samples, and no composits of longer time periods were made.
Supernatant samples were collected at varying intervals as there was
not a specific pumping and hauling schedule for the secondary digester
supernatant. For hauled supernatant, during Phase I of the study,
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samples were collected approximately weekly, while during Phase 2 the
sampling frequency was twice weekly. Whenever supernatant was being
pumped back through the plant rather than hauled for land disposal,
samples were collected at each time of pumping. Similar analyses
were run on both supernatant and digested bottom sludge.
Samples used for digester profiles were collected using a weighted
Kemmerer type sampler.
Samples used in dewatering tects were collected from two points.
Waste activated sludge was obtained from the waste sludge well
located next to the final clarifiers in the plant treating university
wastewater, and raw sludge from the sludge well located next to the
primary clarifiers in the same plant.
Gas samples were collected in two aspirator bottles. A non-gas
absorbing sodium sulfate solution was used in the bottles to insure
preservation of the sample prior to analysis. The point of col-
lection was a sampling port located on the gas meter in the digester
control building.
Flow Measurements
During Phase 1, flow measurements were taken from records maintained
at the treatment plant. There were no direct measurements of the
sludge flows in and out of the digesters. The daily sludge additions
and removals were calculated from a gage which indicated the rise and
fall of the digester covers, while the hauled sludge volumes were
measured by multiplying truck volume times the number of trips.
Supernatant recycle also was measured using a level gage on the
supernatant storage tank. The flows were determined in the following
manner:
Sludge Flows
Waste sludge from the Borough activated sludge system was measured
using a flow meter located ahead of the sludge thickener. Waste
activated sludge solids concentrations were measured and an average
value determined. Total solids added to the sludge thickener were
then computed using the relationship:
TS(in) " Q x P x 8'35
where: TS, . = total pounds of solids into the sludge thickener
Q = flow of waste activated sludge in gallons per day
P = percent solids in the waste activated sludge
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The sludge thickener was assumed to recover 100% of the solid
material. This value has been observed by plant personnel and
is believed to be valid. Using the solids concentration of the
thickened sludge the flow out of the thickener can be computed
as :
TS
[2]
L J
. .
8.35 x P, ,
(out)
where: Q = flow of raw Borough sludge to the primary digester
Boro . , ,
in gallons
TS... , = total pounds of solids into the sludge thickener
p/ t\ = percent total solids in the thickened sludge
The total sludge addition was measured from the change in elevation
of the digester covers, and the quantity of University raw sludge
computed as:
QUniv
where: Q . = Flow of the University raw sludge into the primary
digester in gallons
Q = Total sludge flow into the primary digester in gal-
lons
Q = Flow of the raw Borough sludge into the primary
xBoro . . 1 & "
digester in gallons
During Phase 2, the University raw sludge was measured directly from
the drawdown at the raw sludge well during each pumping period. The
total sludge flow was measured from the rise in the digester covers.
The raw Borough sludge quantities were then calculated as:
QBoro = QT ~ QUniv
where: Q = Flow of the raw Borough sludge into the primary
Boro . , . , ,
digester in gallons
Q = Total sludge flow into the primary digester in
gallons
0,, . = Flow of the University into the primary digester
Univ . . .
in gallons
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Supernatant Return
Supernatant return volumes were obtained by computing the dif-
ference between the volume of total raw sludge added and the
volume of digested sludge hauled.
Gas Volume
Gas volume was recorded utilizing a gas meter located in the
digester control building.
ANALYTICAL TESTS AND PROCEDURES
The following sections include a summary of the tests performed
and the procedure used throughout this investigation.
Aluminum
Soluble aluminum ion was measured utilizing the "Rapid Modified
Eriochrome Cyanine R Method for the Determination of Aluminum in
Water" as suggested by Shull and Guthan (19). Samples were also
sent to the Mineral Constitution Laboratory, at The Pennsylvania
State University for spectrochemical analysis. The analyses were
carried out using atomic absorption.
Samples tested using the Modified Eriochrome Cyanine R Method,
were first centrifuged at 13,300 x g for 15 minutes then filtered
using glass fiber filter pads. The samples were then diluted.
The diluted samples were turbid and the samples containing Borough
wastewater were known to contain fluoride. The fluoride ion inter-
feres with the Eriochrome Cyanine R Method causing the results to
be low. In order to determine the error in the tests, samples were
analyzed spectrochemically and the results compared with results
from the Modified Eriochrome Cyanine R Method. In addition, a
sample was ultracentrifuged at 100,000 x g for 60 minutes in order
to remove turbidity. While ultracentrifuging removed most of the
suspended particles, inspection of the centrifuged sample with a
Tyndal beam revealed some turbidity still remained. The results
of the tests are shown in Table 1. Samples 1 and 2 were taken
June 24, 1969, and the results show the Eriochrome Cyanine R Method
to be low compared to the spectrochemical analysis. Samples 3 and
4 were taken August 5, 1969, and sample 3 shows higher soluble
aluminum readings by the Eriochrome Cyanine R Method, than by spec-
trochemical analysis, while the results from sample 4 are oppo-
site. Filtering did not produce a sample which contained only
soluble aluminum. Some suspended particles which contained alumi-
num compounds passed through the filter pad. The low pH in the
Eriochrome Cyanine R Method may have caused the suspended precipi-
tated aluminum to redissolve in the test. This phenomenon probably
14
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TABLE 1: COMPARISON OF SOLUBLE ALUMINUM ION
CONTENT OF DIGESTED SLUDGES BY
SPECTROCHEMICAL ANALYSIS VS. THE
RAPID MODIFIED ERIOCHROME CYANINE
R METHOD
SAMPLE:
ALUMINUM ION MEASURED
(mg AL+++/D
ERIOCHROME R
METHOD
SPECTROCHEMICAL
ANALYSIS
1.
2.
3.
4.
PRIMARY DIGESTER
SECONDARY DIGESTER
SECONDARY DIGESTER
SECONDARY DIGESTER
(ULTRACENTRIFUGED)
0.48
1.90
2.0
0
9.27
7.35
0.79
0.08
15
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occurred in all filtered samples. The sample which most truly
represents only soluble aluminum ions is sample 4, which recorded
very low values; however, it too is probably high because there was
suspended material remaining in sample 4 after ultracentrifuging.
Alkalinity
Alkalinity determinations were carried out utilizing the procedure
given in Standard Methods (21).
Dewatering of Sludges
Dewatering tests were carried out in the laboratory using the method
of Coackley (3). Buchner funnel tests used Whatman No. 40 filter
paper with the vacuum applied through an adjustable vacuum pump.
From these tests, the specific resistance of the sludges was compu-
ted, using the Coackley formula discussed in the Appendix.
Filtration
Filtration of sludges for sample analysis, excluding dewatering
tests, was performed using 5.5 cm dia. Reeve-Angel glass fiber
filter pads. In most cases in order to achieve necessary filtrate
volumes the sludge samples were centrifuged prior to filtration.
Samples were centrifuged for 15 minutes at 13,300 x g.
Gas Analysis
Gas samples were passed through a Hewlett and Packard 5750 F&M Research
Chromatograph for analysis. The relative percentages of methane,
carbon dioxide, nitrogen, and hydrogen sulfide were recorded by
analyzing a 0.5 ml. sample. Analyses were run using a 1/8-inch
diameter, 6-foot long, stainless steel column packed with Porapak Q;
helium carrier gas; a 60°C column oven temperature; and a thermal
conductivity cell with a bridge current of 150 ma. Other temperatures
were: detector - 250°C, auxiliary - 250°C, and injection port - 150°C.
The chart speed was 0.5 in/min.
PH
pH measurements were made using a pH meter after (21).
Phosphorus
The Stannous Chloride Method for Orthophosphate (21) was used for
all of the phosphorus determinations. The test was conducted in an
16
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incubator controlled at 20°C, and ten minutes were allowed for
color development before readings were taken. Readings were taken
at a wave length of 690 my using a Bausch and Lomb Spectronic 20
spectrophotometer and a 2.54 cm light path. The methods of sample
preparation varied as indicated below.
Total phosphorus determinations followed a modified alkaline ash
procedure used by Eberhardt and Nesbitt (5). In a review of methods
for total phosphorus analysis, Harwood et al. (6) found the dry-
ashing procedure the most reliable. A comparison between the modi-
fied alkaline ash and potassium persulfate method (7) was run and
the results are given in Table 2. It would appear that the modified
alkaline ash method gave consistantly higher values for digested
sludge, while both methods gave similar readings for raw sludge.
Though it was the longer test, the modified alkaline ash method was
used throughout this study.
Total soluble phosphorus determinations used a modification of the
binary acid wet-ash procedures (5). Orthophosphate determinations
followed the previously mentioned Standard Methods procedure. Both
total soluble phosphate and soluble orthophosphate were determined
on samples that were filtered prior to testing. Total phosphorus
samples were not filtered. Total phosphorus samples, following
initial dilution, were blended for two minutes at high speeds to
insure uniform sampling.
Solids
Total, volatile, and fixed solids analyses were conducted following
the procedure outlined in Standard Methods (21).
Sulfate
Sulfate analysis followed the Turbidimetric Method (21), using a
Beckman D.B. Spectrophotometer, and a 4 cm light path. All samples
were filtered and diluted prior to analysis.
Volatile Acids
Volatile acids were determined by the method of direct titration as
presented by Di Lallo and Alberson (4). Samples were centrifuged,
but not filtered prior to analysis.
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TABLE 2: COMPARISON OF TOTAL PHOSPHORUS CONTENT
OF SLUDGES DETERMINED BY A MODIFIED
ALKALINE ASH PROCEDURE VS. THE
POTASSIUM PERSULFATE METHOD
PHOSPHORUS CONTENT
(mg P/l)
1.
2.
3.
4.
5.
OHI'irLC .
DIGESTED SLUDGE
DIGESTED SLUDGE
DIGESTED SLUDGE
RAW BOROUGH SLUDGE
RAW UNIVERSITY SLUDGE
ALKALINE ASH
METHOD
605
605
648
578
600
POTASSIUM PERSULFATE
METHOD
539
539
485
605
581
ON A BASIS OF THREE REPLICATE SAMPLES
18
-------
EXPERIMENTAL RESULTS AND DISCUSSION
PHOSPHORUS BALANCE
To find the identity of the phosphorus during anaerobic digestion,
a phosphorus balance was calculated by tracing the types of phos-
phorus entering and leaving the digester. The balance assumed a
steady state flow condition. While daily plant hauling and pumping
schedules did vary, the recorded daily sludge flow into the digester
was assumed to be the valid, steady state, flow measurement. The
amount of sludge removed from the digester during a particular time
period was assumed to be equal to the equivalent inflow for that
period. The average daily pounds of phosphorus entering or leaving
the digester for a one-month period was determined by the following
relationship:
Pounds of phosphorus = C.. x P x Q [5]
where: GI = 0.834 x 10 pounds per gallon
P = average monthly value for phosphorus in the sludge
samples collected, expressed as mg P/l
Q = average daily flow of sludge in gallons for a one-
month period
The average daily phosphorus values for a one-month period, were
calculated using Equation 5 and then used in the phosphorus balance.
The total cumulative phosphorus entering and leaving the digester is
presented in Fig. 3.
The total phosphorus balance (Fig. 3) showed that less phosphorus
was removed from the digester than had been added. Initially, as
the phosphorus enriched sludge was first added, the phosphorus in
the raw feed sludge was greater than that in the digested sludge.
By comparing the slopes of the plotted values of cumulative phos-
phorus for a given time period the increase or decline of phosphorus
in the various sludges was observed. Equal slopes indicate the phos-
phorus going into the digester was the same as that being removed.
For the month of February, 1969, the slope of the plotted values
showed the cumulative phosphorus fed to the digester was greater
than that removed from it. Following one detention period, or
approximately March 1, 1969 (week 5), both raw and digested sludge
plots theoretically should be parallel. Beginning in March and
continuing through July 1970 (week 78), the plotted lines were di-
verted rather than parallel. The plot of the phosphorus in the raw
feed sludge had a slope equal to 61°, while the plot of the phosphorus
19
-------
CO
Z5
O
1/1
_o
co
=>
o:
o
Q.
CO
o
Q-
ID
^
Z)
O
10
70
60
50
40
30
20
10
WEEK OF STUDY
30 40 50
60
70
T
T
T
TOTAL PHOSPHORUS IN
TOTAL PHOSPHORUS OUT
a UNACCOUNTED PHOSPHORUS
b BUILD UP WITHIN DIGESTER
o
D-
-O
-a
a -
FMAMJJASONDJFMAMJJ
MONTHS
FIGURE 3: CUMULATIVE TOTAL PHOSPHORUS BALANCE OF THE DIGESTER
20
-------
in the digested sludge had a slope of 45°. At no time during the
entire study was the amount of total phosphorus entering the diges-
ter equal to the amount in the digested sludge which was removed.
At the end of the study period the total discrepancy between phos-
phorus fed into and removed from the digester was approximately
32,800 Ibs. The equilibrium phosphorus within the digester during
the detention period was estimated to be 3,200 Ibs. and is shown
graphically on Fig. 3. Thus a total of 29,600 Ibs. of phosphorus
as P remained unaccounted for during the study period.
Fig. 4 shows the total soluble phosphorus and orthophosphate
balances. The relationship between soluble phosphorus fed into the
digester and the amount removed in the digested sludge is closer
than the relationship shown in Fig. 3. During the first three months,
total soluble phosphorus and orthophosphate removed from the digester
equalled or slightly exceeded that being fed. During the rest of
phase 1, the phosphorus removal was less than that being fed. This
finding indicates that the aluminum phosphorus precipitate, when
incorporated into the raw sludge, does not redissolve while under-
going anaerobic digestion. Apparently, soluble phosphorus also
precipitated during digestion particularly after the phosphorus
rich sludge had accumulated within the digester for one detention
period. From Fig. 4, it was evident that most of the soluble
phosphorus, in both the raw feed and digested sludges, was in the
orthophosphate form.
The variations in the phosphorus levels of the sludges used in
calculating the phosphorus balances partly accounts for the variance
in the total phosphorus balance. However, errors resulting from
these variations should be compensating. It seems more likely that
the unaccounted for phosphorus resulted from an inability to collect
a representative sample, particularly in the sludge being removed
from the digester. Various techniques in sample collection, pre-
paration, and phosphorus analysis were tried during the study, however,
the phosphorus discrepancy in the total phosphorus balance remained
unchanged. A further discussion of this discrepancy and its relation
to sampling will be given later in the section on digester operation.
Table 3 gives the concentration of the total soluble phosphorus of
the digested sludge observed during the study period. The soluble
phosphorus values were generally lower during phase 1, than in
phase 2. During phase 2, phosphorus was removed from only one
half the University wastewater flow, as the remaining flow was
used as a control. Consequentially, there was less sludge con-
taining hydroxy aluminum phosphate and less total aluminum ion
available to precipitate soluble phosphorus in the untreated raw
University sludge. Therefore the higher soluble phosphorus values
during phase 2 were expected. These phosphorus concentrations varied
from 13 mg P/l to 171 mg P/l, however, there was not a significant
increase in phosphorus levels during any period of the investigation.
21
-------
10
20
WEEK OF STUDY
30 40 50
60
70
CO
o
in
CO
CC.
§
Q.
CO
O
CL
TOTAL SOLUBLE PHOSPHORUS IN
TOTAL SOLUBLE PHOSPHORUS OUT G>-
ORTHOPHOSPHATE IN
ORTHOPHOSPHATE OUT Q
MAMJJASONDJFMAMJJ
MONTHS
FIGURE 4: CUMULATIVE TOTAL SOLUBLE PHOSPHOF;US AND ORTHOPHOSPHATE
BALANCES OF THE DIGESTER
22
-------
TABLE 3: TOTAL SOLUBLE PHOSPHORUS IN THE DIGESTED SLUDGE
WEEK OF PHOSPHORUS WEEK OF PHOSPHORUS WEEK OF PHOSPHORUS
STUDY DATE mg P/1 STUDY DATE mg P/l STUDY DATE mg P/l
1
2
3
4
5
6
7
8
9
10
Jl
12
13
14
15
16
17
18
19
20
21
22
23
2k
25
26
27
PHASE 1
Feb. 5, 1969
12
19
26
March 5
12
19
26
April 2
9
16
23
30
May 7
14
21
28
June 6
11
18
26
July 2
9
16
23
30
Aug. 6
PHASE 1 (CONTINUED)
108
92
79
114
36
33
60
72
53
69
68
Ik
43
66
85
73
90
52
66
81
34
20
13
29
59
72
105
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
Aug. 13, 1369
20
Aug. 27, 1969
PHASE 2
Sept. 3, 1969
10
17
2k
Oct. 1
8
15
22
29
Nov. 5
12
19
26
Dec. k
10
17
23
31, 1969
Jan. 7, 1970
14
21
28
97
88
112
105
114
121
113
112
116
124
106
109
60
92
93
87
59
79
86
85
93
92
111
101
110
53
5k
55
56
57
58
59
60
61
62
63
6k
65
66
67
68
69
70
71
72
73
7k
75
76
77
78
79
80
81
PHASE 2 (CONTINUED)
Feb. k, 1970
11
18
25
March k
11
18
25,
Apr! l 1 ,
8
15
22
29
May 6
13
20
27
June 3
10
17
2k
July 1
8
16
22
29
Aug. 5
12
19, 1970
95
90
82
90
92
126
90
77
72
98
101
106
99
125
142
136
128
140
152
128
147
160
92
171
142
-
-
-
151
-------
This fact is considered important, as a digester upset occurred
at the end of May. During this upset period evidence of precipi-
tated phosphorus redissolving in soluble phosphorus forms was not
found. The relative insolubility of the precipitated phosphorus
is shown by both the values in Table 3, and the phosphorus balances
shown in Fig. 4. The digester upset will be discussed in greater
detail in following sections.
DIGESTER OPERATION
As stated previously, the digester was operated as a two stage
unit, with the primary digester utilizing gas recirculation for
mixing. Fig. 5 shows the results of five digester profiles run on
the primary digester. These profile results show that for the most
part, the primary digester was operating as a high rate digester
with fairly little change in solids level from top to bottom.
Note, however, that top scum layers and heavier bottom sludges
did accumulate at times. The secondary digester, which was
designed to behave as a conventional digester without mixing,
maintained a rather constant solids level in the sludge at dis-
tances of from 4 to 12 feet above the digester floor. The pro-
files for the secondary digester, shown in Fig. 6, indicate that
this digester was stratified. This stratification, which consisted
of a thicker bottom sludge and a thicker scum layer existed
throughout the entire study period.
Figs. 7 and 8 show the profiles of total phosphorus and total solu-
ble phosphorus concentrations in the secondary digester. A trend
toward higher total phosphorus in the heavier bottom sludge is
indicated. The soluble phosphorus concentrations remained rela-
tively constant throughout the digester even though the digester
was stratified. The relationships between total and soluble phos-
phorus and solids level may help to explain the discrepancy in the
total phosphorus balance. While the soluble phosphorus level is
relatively independent of solids content, a relationship between
total phosphorus and total solids does exist as expected. There-
fore, because of the uneven distribution of solids, a sample could
be collected which was not a true composite of the sludge removed,
thus causing an error in the total phosphorus balance. Also, in
this same sample, there would be less of an effect on the total
soluble and orthophosphate balances.
In an effort to determine the cause of error in the total phosphorus
balance, a total solids balance was calculated, Fig. 9. This
balance plotted the cumulative solids in, cumulative solids out,
and cumulative solids destroyed. The value for volatile solids
reduction was obtained from Sawyer and Grumbling (16), based on the
percent volatile solids in the raw sludge feed, and the digester
detention time.
24
-------
o
co
a:
UJ
Q
O
18
16
14
12
10
OO
•—i c
Q 6
O Q 4/ 2/68
O O ll/ 1/68
A A 8/12/69
V V 2/ 5/70
El D 4/16/70
0246 8
PERCENT SOLIDS
FIGURE 5: DIGESTER PROFILE OF THE SOuIDS LEVELS IN THE PRIMARY
DIGESTER
25
-------
18 _
o
DQ
re
2:
o
DC
OO
16 -
14
12
10
O 4/ 2/68
O • O IV 1/68
CD D 7/24/69
_£ 7/30/69
V 4/21/70
246
PERCENT SOLIDS
8
FIGURE 6: DIGESTER PROFILE OF THE SOLIDS LEVELS IN THE SECONDARY
DIGESTER
26
-------
o
CQ
O
a:
I/)
»—I
o
18
16
14
12
10
0
250
10/21/68
7/24/69
7/30/69
4/21/70
500
1250
750 1000
mg P/l
FIGURE 7: DIGESTER PROFILE OF THE TOTAL PHOSPHORUS CONCENTRATIONS
IN THE SECONDARY DIGESTER
27
-------
o
CO
a:
t/o
UJ
CD
O
a:
18
16
14
12
10
o—
El ORTHOPHOSPHATE
O TOTAL SOLUBLE
PHOSPHORUS
I
20 40 60 80 100
mg P/l
FIGURE 8: DIGESTER PROFILE OF SOLUBLE PHOSPHORUS CONCENTRATIONS IN
THE SECONDARY DIGESTER ON JULY 30, 1969
28
-------
10
20
WEEK OF STUDY
30 40 50
60
4 -
o
o
o
o
o
in
LO
Q
O
LO
2 -
CUMMULATIVE TOTAL SOLIDS
INTO DIGESTER
CUMMULATIVE TOTAL SOLIDS
OUT OF DIGESTER
CUMMULATIVE TOTAL
SOLIDS OUT + VOLAT
SOLIDS DESTROYED
DURING DIGESTION
I l I l I l I I I I
FM AMJJASONDJFMAM
MONTHS
FIGURE 9: CUMMULATIVE SOLIDS BALANCE OF THE DIGESTER
29
-------
As with the total phosphorus balance (Fig. 3), the total solids
balance (Fig. 9) showed that more solids entered the digester than
were both reduced in and removed from the digester. Theoretically,
these two values should be equal, but they are not. The average
slopes of the lines in Fig. 9 (solids balance) are close to those
of the lines in Fig. 3 (total phosphorus balance). This similarity
indicates that the samples of digested sludge obtained were not
representative of the sludge removed from the digester. Sludge
samples were taken only twice a week. This frequency was adequate
for the raw sludge which was fairly uniform in quality. However,
for the digested sludge it appears that insufficient samples were
taken of the thicker bottom sludge.
pH
Figs. lOa and lOb show the pH values of the University raw sludge,
Borough raw sludge, and the digested sludge recorded during the
study period. The digested sludge maintained a pH between 7.0 to
7.4 until the end of May 1969 (week 15), when the pH began to drop.
The decrease of pH values continued until a value of 6.3 was
reached on June 5, 1969 (week 18). Correspondingly, the pH of
both raw sludges varied between 6.0 and 7.1 from February 1969
(week 1), until mid-May 1969 (week 14). Each of the raw sludges
showed a decline in pH which preceded the pH decrease of the di-
gested sludge by approximately two weeks.
After June 5, 1969 (week 18), the pH values of the digested sludge
increased until a value of 7.0 was reached at the end of June 1969
(week 22). The pH then generally remained above 7.0 for the rest
of the study period. However, the pH values of the raw sludges did
not return to their pre-upset levels until the fall of 1969 (week
33). These continued lower pH values can be attributed to a change
in operation at the plant. Starting in June (week 19), the raw
University sludge was fed into a sludge concentrator prior to pump-
ing to the digester and this procedure was continued throughout the
rest of the study. Feedings were also reduced from three times
daily to only once daily during the summer months of 1969 and twice
daily during the summer of 1970. These changes in operation could
have caused higher volatile acids and thus lower pH values to be
present in the raw sludge fed to the digester.
While the change of operation can account for the continued lower
pH values of the raw sludges, the initial mid-May decrease is un-
explained and may have been related to the cause of the digester
upset.
ALKALINITY AND VOLATILE ACIDS
Figs, lla and lib show the alkalinity and volatile acid values of
the sludges for the study period. The results indicate the digester
30
-------
X
Q.
O
<
LU
O
O
CJ
UJ
O
O
ct
Q
CD
O
WEEK OF STUDY
20 25
A DIGESTED SLUDGE
D UNIVERSITY RAW SLUDGE
O O BOROUGH RAW SLUDGE
MARCH
APRIL
MAY
JUNE
JULY
AUGUST SEPTEMBER
OCTOBER
FIGURE lOa: pH VALUES OF VARIOUS SLUDGES THROUGHOUT THE STUDY PERIOD
-------
CO
t-0
IE
c.
<
o:
o
o
o
CD
o
cr
Q
o
o
45
WEEK OF STUDY
60
DIGESTED SLUDGE
UNIVERSITY RAW SLUDGE
BOROUGH RAW S
5 ~
4 _
NOVEMBER DECEMBER JANUARY FEBRUARY MARCH
MONTHS
FIGURE I Ob: pH VALUES OF VARIOUS SLUDGES THROUGHOUT THE STUDY PERIOD
APRIL
MAY
JUNE
JULY
-------
3.5
- 2.5
3.0
- 2.0
CO
ID
O
2.5
O)
2.0
Q
2
<
O
X
E
CO
Q
<
.5
.0
<
<
I .5
<
o
0.5
L- O.Oi
A-
Q-
MARCH
15
T
I
-A ALKALINITY
-D VOLATILE ACIDS
WEEK OF STUDY
20
25
I
30
35
J_
APRIL
MAY
JUNE
JULY
AUGUST SEPTEMBER OCTOBER
FIGURE Ma : ALKALINITY AND VOLATILE ACIDS OF DIGESTED SLUDGE DURING THE STUDY PERIOD
-------
45
50
WEEK OF STUDY
55 60
65
70
75
3.5
I- 2.5
3.0
- 2.0
32.5
o
I .5
'2.0
en
CO
Q
O
.0
<
_j
<
I .5
0.5-
O1- O.O
D-
I
I
-D
ALKALINITY
VOLATILE ACIDS
I
I
_L
I
I
NOVEMBER DECEMBER
MAY
JANUARY FEBRUARY MARCH APRIL
MONTHS
FIGURE Mb: ALKALINITY AND VOLATILE ACIDS OF DIGESTED SLUDGE DURING THE STUDY PERIOD
JUNE
JULY
-------
upset occurred at the same time the pH of the digested sludge de-
creased. Alkalinity decreased slowly through March 1969 (week 7)
and April 1969 (week 16) and then dropped suddenly at the end of
May 1969 (week 18). The alkalinity returned to 3,000 mg/1 on June
25, 1969 (week 20), when lime was added to the digester to help
correct the digester upset and then remained about 2,500 mg/1
through November 1969 (week 45) with an exception during week 40.
Lime addition ceased during the latter part of June 1969 (week 22)
and the fluctuation in alkalinity may be attributed to the strati-
fication in the secondary digester.
The level of volatile acids remained fairly constant until the May
1969 digester upset (week 17). During the upset, volatile acids
increased from 250 mg/1 to 3,220 mg/1. As the upset was corrected
the volatile acids level returned to the pre-upset level of 250 mg/1.
While the upset period from mid-May 1969 (week 17) through the end
of June 1969 (week 24) produced conditions of high volatile acids,
lower pHs, and reduced alkalinity, the concentration of soluble
phosphorus in the sludge removed from the digester was lower than
the mean value for the remainder of the study period. The mean
value for the upset period was 66 mg P/l, while the value for
phase 1 was 71 mg P/l, and Phase 2 was 108 mg P/l. Thus it appears
that even during a digester upset, with its corresponding increased
acid levels, the precipitated phosphorus does not become soluble.
This result would be expected as the optimum pH for precipitation
of phosphate with aluminum was shown to be between 5.5 and 6,0 (5).
GAS PRODUCTION AND VOLATILE SOLIDS DESTRUCTION
Gas production and volatile solids loading for the study period are
shown in Figs. 12a and 12b. A normal relationship existed between
volatile solids loading and the corresponding gas production. Begin-
ning in February 1969 (week 1) and extending through the end cf May
1969 (week 18), the plots of gas production and volatile solids
loading are generally parallel showing a relatively stable level of
digestion was achieved in the digester. The sharp reduction in both
volatile solids loading and gas production at the end of March 1969
(week 10) can be related to the reduced student population between
the winter and spring terms.
As was shown in the sludge pH, alkalinity, and volatile acids
analyses, a digester upset is also noted in the gas production
values. Beginning in the latter part of May 1969 (week 18) and
continuing until mid-June 1969 (week 22), gas production values were
significantly reduced- Once the upset was noted, an effort to re-
duce the loading on the digester was begun. This effort involved
the hauling of raw sludges to a sludge lagoon. The decreased student
population in mid-June, also aided in the reduction of volatile
solids loadings. Since the reduced gas production preceded the re-
duction in volatile solids loading, the initial reduction of gas pro-
duction was caused by the digester upset, and not the reduced volatile
solids loading.
35
-------
10
WEEK OF STUDY
15 20
25
30
35
7 _
60
A-A-^
50h Q
?5
CO
^^'\
r*
CO
O
\
t
40
Q
O
(X
Q.
CD
20
i/i.
^A
CD
o
<
o.
CO
Q
O
CO
±12
o
GAS PRODUCTION A
VOLATILE SOLIDS LOADING 0-
G
10
k
0
I
I
I
^.
H3-Q-Q
FEBRUARY MARCH APRIL MAY JUNE
FIGURE I2a: DIGESTER GAS PRODUCTION AND VOLATILE SOLIDS LOADING
JULY
AUGUST
SEPTEMBER
-------
40
45
50
WEEK OF STUDY
55 60
65
70
60
!50
to
I 40
2 30
o
Q
CO
o 20
o
(0
JD
Q
<
O
O
to
UJ
O
0
GAS PRODUCTION A
VOLATILE SOLIDS LOAD ING
_L
OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY MARCH
MONTHS
APRIL
MAY
JUNE
JULY
FIGURE I2b: DIGESTER GAS PRODUCTION AND VOLATILE SOLIDS LOADING
-------
Gas production and volatile solids reduction are shown in Figs.
13a and 13b. Gas production, volatile solids loading (V.S.L.)
and volatile solids reduced (V.S.R.) appear to be lower than
those found in the literature (18), but agree well with those
calculated for digester operation from January 1968 through
December 1968 before the study was begun. During this period,
no phosphorus enriched sludge was added to the digester, and it
can be considered a semi-control period. During 1968 gas pro-
duction values averaged 5.3 ft3/lb V.S.L. and 8.2 ft3/lb V.S.R.
In phase 1 of the study, gas production averaged 6.1 ft-Vlb
V.S.L. and 8.7 ft3/lb V.S.R., while phase 2 had 5.8 ft3/lb V.S..L.
and 7.9 ft3/lb V.S.R. Thus, the addition of the chemical bio-
logical sludge to the digester had no effect on these digestion
parameters. Figs. 12a, 12b, and 13a and 13b, showed that the gas
production response followed both the volatile solids loading
and the volatile solids reduction.
Analyses to determine the methane, carbon dioxide, and hydrogen
sulfide content of the digester gas were made and are plotted in
Fig. 14. These analyses were only run during phase 1 of the study.
Methane comprised slightly more than 60 percent and carbon dioxide
slightly less than 40 percent of the gas sample volume. These
results agree with the range expressed by Sawyer and McCarty (17)
who state that the methane content of digester gas ranges from 55
to 65 percent, while carbon dioxide content varies from 33 to 38
percent. Exceptions to these ranges occurred during the "upset
period" when the methane content was reduced. This reduction is
expected as the high concentrations of volatile acids and corres-
ponding drop in pH decreases the growth rate of the methane forming
organisms.
SULFATE
Another purpose of this study was to determine whether the sulfate
ion introduced into the system when the phosphate was precipitated
with alum would find its way into the digester and be reduced to
hydrogen sulfide gas. This excess hydrogen sulfide could cause
corrosion and odor problems in the treatment plant. Sulfate
analyses of sludges were conducted during phase 1, as this period
had the highest concentrations of sulfate ions. At no time during
the study were any measurable quantities of hydrogen sulfide found.
Even during the digester upset, measurable quantities of hydrogen
sulfide were not shown in the analyses, although trace hydrogen sul-
fide odors were observed in the digester buildings.
Samples collected on 5, 10, and 12 June 1969 showed higher hydrogen
sulfide values, however, these values were still too small to be
significant.
38
-------
10
15
WEEK OF STUDY
20
25
30
GAS PRODUCTION A A
VOLATILE SOLIDS REDUCTIONQ
FEBRUARY MARCH
APRIL
MAY J UNE
MONTHS
FIGURE I3a: DIGESTER GAS PRODUCTION AND REDUCTION OF VOLATILE SOLIDS
JULY
AUGUST
SEPTEMBER
-------
40
45
50
WEEK OF STUDY
55 60
65
70
75
60
50
I 40
o
o
Q_
CD
20
10
0
- GAS PRODUCT I ON A A
VOLATILE SOLIDS REDUCTION E
-El
I
I
I
I
OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY MARCH
MONTHS
FIGURE I3b: DIGESTER GAS PRODUCTION AND REDUCTION OF VOLATILE SOLIDS
APRIL
MAY
JUNE
JULY
-------
70
60
50
40
30
A
CARBON DIOXIDE Q ---- Q
GV/ \ >*t3
^ OQ /
-NO MEASURABLE HYDROGEN SULFIDE-
MARCH APRIL
FIGURE 14: QUANTITATIVE ANALYSIS OF DIGESTER GAS
MAY JUNE
MONTHS
JULY AUGUST
-------
Fig. 15 shows the sulfate ion concentration of the sludges recorded
during phase 1 of the study period. The sulfate concentrations in
the digested sludge through May 28, 1969 were higher than the
levels recorded in June. This was expected as alum was added to
the system until May 28, 1969, then sodium aluminate additions
began. Note, that even with alum additions, a large increase of
sulfate ion was not observed in the sludges. The levels of sul-
fate ion in both the raw sludges are approximately equal, although
raw Borough sludge had no alum additions. It appears that chemical
precipitation of phosphorus from wastewater, utilizing alum, will
not stimulate production of hydrogen sulfide gas during anaerobic
digestion, because the sulfate ion is not incorporated in the sludge
to any extent and thus does not enter the digester.
ALUMINUM
Fig. 16 shows the values obtained for soluble aluminum ion utilizing
the Rapid Modified Eriochrome Cyanine R Method after Schull and
Guthan (19) and run during Phase 1 of the study. The values are
quite low for the raw sludges and reach a maximum of only 2.5 mg/1
in the digested sludge. Even during the digester upset a marked
increase in the soluble aluminum ion concentration did not occur.
For the reasons pointed out in the discussion of this method on
pages 14-16 the values obtained are probably higher than the actual
ion concentrations. It is the authors' contention that there was
very little soluble aluminum, and that values measured represented
mostly redissolved aluminum compounds.
It is very unlikely that the digester upset was caused by "aluminum
ion toxicity" because of the low aluminum ion concentrations, the
fact that the upset occurred four months after the introduction of
the aluminum compound into the digester, and the fact that the
digester recovered without a cessation in the aluminum addition.
SLUDGE DEWATERING
During this investigation, dewatering tests were conducted to deter-
mine the effect of the aluminum phosphate complex on sludge dewater-
ing. Analyses were run only on raw University sludge as a digested
sludge which did not contain the aluminum phosphate was unavailable
to use for a control. Therefore, comparison of raw sludges gave a
better indication of the sludge conditioning properties of the phos-
phate precipitate. Data and calculations of test results from the
dewatering studies are included in the Appendix.
Two sets of analyses were carried out on sludges containing precipi-
tates formed when sodium aluminate was being added, the first on
June 26, 1969, and the second on July 23, 1969. On September 2, 1969,
sludge which contained no chemical additions, and sludge containing
-------
OJ
o
oo
o;
160
140
120
100
z 80
o
•z.
2 60
UJ
-------
4.0
3.0
i1
•a:
cc.
8 2.0
1.0
1 1 1
0 -0
Qm
nj
y V
** ^
- \ /
>io-^B<8^8^Srl
i i I
SECONDARY DIGESTED SLUDGE
BOROUGH RAW SLUDGE
UNIVERSITY RAW SLUDGE
P'^"\ ' \ ' \ / -
* \ A / \ /
V \ "^ /
A . I \ 1
v ° V
\ i *
_ .a R-EK. \ /
^-o-e^-o ; ^ -o- - o^Dp^e^—^^o^
MARCH APRIL
FIGURE 16: ALUMINUM ION CONCENTRATIONS OF THE SLUDGES
MAY JUNE
MONTHS
JULY
AUGUST
-------
precipitates from the addition of alum were tested. The sludge
which contained no chemical addition was used as a control sample.
The raw University sludge did contain small amounts of precipitate
as the waste activated sludge was recycled to the influent end of
the plant, but the amount recycled was small and should have little
effect on the sludge characteristics. These sludges were analyzed
as 100 percent waste activated sludge, a mixture of 25 percent raw
University sludge and 75 percent waste activated sludge, and a
mixture of 50 percent raw University sludge and 50 percent waste
activated sludge. All mixtures were composited by volume and all
composite samples totaled 200 ml. Table 4 shows the specific
resistance and total solids of the various sludges. The specific
resistance is an indication of the dewaterability of a sludge; with
a low specific resistance indicating easier dewatering (3).
Samples tested on June 26, showed increasing values of specific
resistance as the percentage of raw sludge was increased, but
these changes were quite small.
Samples tested on July 23 contained aluminum phosphate compounds
formed from the addition of sodium aluminate to the activated
sludge. These samples showed almost no change in specific resis-
tance values for the three composite sludges. In fact, a slight
decrease in specific resistance and an increase in total solids
was noted as the percentage of raw sludges in the sample was in-
creased. This difference may be explained by the fact that the
average total phosphorus indicates that less precipitate was avail-
able to precondition the waste activated sludge. The specific
resistance values for the waste activated sludges of June 26, 1969
and July 23, 1969, also supports this statement.
During this stage of the study, sodium aluminate was added to both
of the aeration tanks, so that a control sample was not available.
On September 2, 1969, the sample collected from aeration tank No.
1 contained precipitate formed from the addition of alum while the
activated sludge sample from aeration tank No. 2 contained no chemi-
cal precipitate. In these samples the specific resistance increased
as the percentage of raw sludge increased. Comparison of the con-
trol sample and the sample containing precipitate formed from the
addition of alum showed at least one order of magnitude difference
for the 100 percent activated sludge and the 75 percent activated
sludge and 25 percent raw sludge samples. A smaller difference was
found between the 50 percent activated sludge and 50 percent raw
sludge sample and the control samp.le. It is concluded that under
these conditions alum addition to wastewater for the removal of
phosphorus also produces a waste activated sludge which is easier
to dewater. Also, when this sludge is combined with raw primary
sludge, the resulting mixture again shows an increased ability to
be dewatered.
While sludges containing precipitate formed from the addition of
sodium aluminate could not be compared against a control taken at
45
-------
TABLE 4: SPECIFIC RESISTANCE AND TOTAL SOLIDS OF SLUDGES
SAMPLE:
6/26/69
SODIUM
ALUM I NATE
7/23/69
SODIUM
ALUMINATE
9/2/69
ALUM
9/2/69
NO CHEMICALS
ADDED
100% AS3
100% AS .
75%AS-25%RS D
50%AS-50%RS
100% AS
75%AS-25%RS
50%AS-50%RS
IQOJ: AS
75%AS-25%RS
50%AS-50%RS
100% AS
75%AS-25%RS
50%AS-50%RS
SPECIFIC RESISTANCE TOTAL
2. SOLIDS
sec /gm ^
0.84xlOQ
0.70x10*
1.28x10*
2.01x10*
2.88xlOQ
2.78x10*.
2.31x10*
0.38x1 OQ
0.63x10*
2.78x10*
5.06x10?
9.15x10*
10.04x10*
3.08
3.14
2.72
2.60
2.20
2.80
3.50
1.09
1.20
1.41
1.84
1.78
1.79
'AS-WASTE ACTIVATED SLUDGE
'RS-RAW UNIVERSITY PRIMARY SLUDGE
46
-------
the same time as the samples, the relative values of specific resis-
tance for these samples (Table 4) suggests that a similar ease of
dewatering was obtained with sodium aluminate treatment.
Along with the specific resistance analyses, additional tests were
run in which ferric chloride was added as a preconditioner prior
to filtration. The amount of ferric chloride varied from 50 to
500 mg/1 in a 200 ml sludge sample. The time of vacuum break was
plotted against ferric chloride added, and the results shown in
Figs. 17, 18 and 19. Samples containing precipitate formed from
the addition of alum may be compared directly against the control
samples having no chemical addition. Samples in which sodium
aluminate was added did not have a direct control, but again may
be compared with the other control without serious error.
In all cases, sludges treated with alum required less ferric chloride
to condition than did the other sludges. The minimum time to vacuum
break for this sludge occurred with concentrations of 125 mg/1 of
ferric chloride, while the control contained 250 mg/1. Sludges con-
taining precipitate formed by the addition of sodium aluminate de-
watered more readily than did the control for the alum sludge. The
sludges treated with sodium aluminate also had a shorter time to
vacuum break after a sufficient quantity of ferric chloride was
added. Whether this was caused by the precipitate or was due to
intrinsic sludge properties could not be determined in these studies.
In view of specific resistance values and results from the increasing
dosages of ferric chloride, it appears that sludges which have been
treated with alum to remove phosphorus are dewatered more easily
than those which are not treated. These results also indicate that
this statement may be true for sludges treated with sodium aluminate.
GENERAL DISCUSSION
The foregoing data indicate that a biological sludge containing a
complex aluminum phosphate precipitate can be processed in an anaero-
bic digester without harm to the digestion process and without the
process causing any phosphorus to be returned to the liquid waste
stream. Although the total phosphorus balance indicated that all the
phosphorus leaving the digester was not accounted for, the analyses
appeared to be in error because of the uneven distribution of the
solids in the digester which resulted in a non-representative sample
being collected of the sludge leaving the digester.
The balance of soluble forms of phosphorus showed a better agreement
although less phosphorus left the digester than entered it. This
better agreement can be related to a more even distribution through-
out the digester (Fig. 8). The unaccounted for soluble phosphorus
was probably removed from the untreated sludge through precipitation
or adsorption reactions with the insoluble hydrous aluminum phosphate.
The soluble phosphorus balance also showed that most of the soluble
47
-------
(U
OL
CO
T
T
o-
B-
- -O
D
A
SLUDGE WITHOUT
CHEMICAL ADDITION
SLUDGE CONTAINING
PRECIPITATE FROM ALUM
SLUDGE CONTAINING
PRECIPITATE FROM
SODIUM ALUMINATE
I
125 250 375
FERRIC CHLORIDE, mg/1
500
FIGURE 17: TIME OF VACUUM BREAK AS A FUNCTION OF FERRIC CHLORIDE
CONCENTRATIONS ADDED TO WASTE ACTIVATED SLUDGE
48
-------
7-
c
i
OtL
CO
6-
5-
4-
SLUDGE WITHOUT
CHEMICAL ADDITION
SLUDGE CONTAINING
PRECIPITATE FROM ALUM
SLUDGE CONTAINING
PRECIPITATE FROM
SODIUM ALUMINATE
3
0
250 375
FERRIC CHLORIDE, mg/1
500
FIGURE 18: TIME OF VACUUM BREAK AS A FUNCTION OF FERRIC CHLORIDE
CONCENTRATIONS ADDED TO A 75 PERCENT WASTE ACTIVATED
25 PERCENT RAW SLUDGE MIXTURE
49
-------
o
7-
T
0
SLUDGE WITHOUT
CHEMICAL ADDITION
SLUDGE CONTAINING
PRECIPITATE FROM ALUM
SLUDGE CONTAINING
PRECIPITATE FROM
SODIUM ALUMINATE
I
125 250 375
FERRIC CHLORIDE, mg/1
500
FIGURE 19: TIME OF VACUUM BREAK AS A FUNCTION OF FERRIC CHLORIDE
CONCENTRATIONS ADDED TO A 50 PERCENT WASTE ACTIVATED
50 PERCENT RAW SLUDGE MIXTURE
50
-------
phosphorus was in the orthophosphate form. No evidence was found
that the precipitated phosphorus redissolved while undergoing
anaerobic digestion. This is in agreement with findings of Earth
and Ettinger (2) and Zenz and Pivnicka (23). Further, during a
digester upset with the lowering of the digester pH, the precipi-
tated phosphorus remained insoluble.
The measurement of several digestion parameters (alkalinity, vola-
tile acids, pH, gas production, volatile solids destruction) showed
that a relatively stable digestion period existed from the beginning
of February 1969 until the end of May 1969. Beginning in the latter
part of May 1969, a digester upset developed. This digester upset
was probably related to a drop in the pH of the raw sludges beginning
about mid-May. The reason for this pH reduction on both raw sludges
could not be established, but was corrected by mid-July 1969, by
reducing the volatile solids loadings and adding lime to the raw
feed sludges.
Quantitative analyses of digester gas and sulfate ion in the various
sludges showed that sulfate ion added during the removal of phos-
phorus from wastewaters using alum, did not cause a detectable
amount of hydrogen sulfide to be produced during anaerobic digestion.
A high soluble aluminum ion concentration did not occur in the
sludges even during the digester upset period.
In comparing these various parameters, it appears that removal of
phosphorus from wastewater by means of chemical precipitation using
either alum or sodium aluminate and the addition of these phosphorus
rich sludges to an anaerobic digester, will not cause adverse effects
upon the anaerobic digestion process.
Finally, a series of dewatering tests run on waste activated sludge,
and combinations of waste activated and raw University primary
sludge showed that a sludge which incorporates the precipitates of
the chemical additives dewaters more readily than a sludge which
does not include these precipitates.
During phase 1, phosphorus was removed from only half of the total
plant flow. The amount of precipitated phosphorus which entered the
digester during this period was only approximately half that which
can be expected in a plant treating all of its wastewater for phosphorus
removal. During phase 2, phosphorus was removed from only one-fourth
of the wastewater flow and the resulting sludge was only one-fourth
of that which could be expected in a plant removing phosphorus from
all of its flow. Zenz and Pivnicka (23) showed that in a plant
treating all of the wastewater flow for phosphorus removal, the
average difference in total phosphorus levels between the sludge
containing phosphorus and the control sludge was 593 mg P/l. In this
study the difference between the phosphorus level in the digested
sludge prior to chemical additions and those after phosphorus removal
51
-------
began was calculated to be 353 rag P/l. However, although a higher
phosphorus level would be expected in a waste treatment removing
phosphorus from its total flow, the distribution and effects of the
phosphate precipitate should be no different from those recorded in
this study.
52
-------
ACKNOWLEDGMENTS
This study was done and this report was prepared by Mr. James C.
O'Shaughnessy under the guidance of Prof. John B. Nesbitt and
Instructor David A. Long of the Department of Civil Engineering of
Pennsylvania State University, University Park, Pennsylvania.
The valuable advice and assistance of the late Professor R. Rupert
Kountz is sincerely acknowledged.
Acknowledgment is also given to Messrs. Lloyd Niemann and Lawrence
Williams and to their operating staff at the University Wastewater
Treatment Plant for their assistance during the course of the inves-
tigation. The writer would also like to acknowledge the technical
assistance of Mrs. Francine Klein and Messrs. David Smith and
Michael Schimerlik.
This project was supported and financed in part by The Soap and
Detergent Association, New York, New York, and in part by a Research
and Development Grant from the Federal Water Pollution Control Admin-
istration, Department of the Interior, pursuant to the Federal Water
Pollution Control Act. The assistance provided by the EPA Project
Officer, Dr. Robert L. Bunch, Advanced Waste Treatment Research
Laboratory, Cincinnati, Ohio, and the Phosphorus Committee of The
Soap and Detergent Association is acknowledged with sincere thanks.
53
-------
BIBLIOGRAPHY
1. Earth, E. F., Brenner, R. C., and Lewis, R. F., "Chemical-
Biological Control of Nitrogen and Phosphorus in Wastewater
. Effluent," Journal of the Water Pollution Control Federation,
Vol. 40, No. 12, Dec. 1968, pp. 2040-2054.
2. Barth, E. F., and Ettinger, M. B., "Mineral Controlled Phos-
phorus Removal in the Activated Sludge Process," Journal of
the Water Pollution Control Federation, Vol. 39, No. 8, Aug.
1967, pp. 1362-1368.
3. Coackley, P., "Laboratory Scale Filtration Experiments and
Their Application to Sewage Sludge Dewatering," Biological
Treatment of Sewage and Industrial Wastes, 1st ed., Vol. 2,
Reinhold, New York, 1958, pp. 270-306.
4. DiLallo, R., and Alberson, 0. E., "Volatile Acids by Direct
Titration," Paper, New England Sewage & Industrial Waste
Association, May 1960, Water Pollution Control Federation,
Washington, D. C.
5. Eberhardt, W. A., and Nesbitt, J. B., Chemical Precipitation
of Phosphorus Within a High Rate Activated Sludge Process,
Engineering Research Report, The Pennsylvania State University,
Dept. of Civil Engineering, March 1968.
6. Harwood, J. E., van Steenderen, R. A., and Kuhn, A. L., "A
Comparison of Some Methods for Total Phosphate Analyses,"
Water Research, Vol. 3, No. 6, June 1969, pp. 425-432.
7. Jankovic, S. G., Mitchell, D. T., and Buzzell, J. C., "Measure-
ment of Phosphorus in Wastewater," Water and Sewage Works, Vol.
114, No. 12, Dec. 1967, p. 474.
8. Long, D. A., Nesbitt, J. B., Kountz, R. R., "Soluble Phosphate
Removal in the Activated Sludge Process - A Two Year Plant
Scale Study," presented at 26th Annual Purdue Industrial Waste
Conf., May 4, 5, and 6, 1971.
9. McCarty, P. L., and McKinney, R. E., "Salt Toxicity in Anaero-
bic Digestion," Journal of the Water Pollution Control Federa-
tion, Vol. 33, No. 4, April 1961, pp. 399-415.
10. McDermott, G. N., et al., "Copper and Anaerobic Sludge Digestion,"
Journal of the Water Pollution Control Federation, Vol. 35, No.
5, May 1963, pp. 655-662.
11. Nesbitt, J. B., "Removal of Phosphorus from Municipal Sewage
Plant Effluents," Engineering Research Bulletin, B-93, Feb.
1966, The Pennsylvania State University, University Park, Pa.
55
-------
12. Pagano, J. F., Teweles, R., and Buswell, A. M., "The Effect of
Chromium on the Methane Fermentation of Acetic Acid," Sewage
and Industrial Wastes, Vol. 22, No. 3, March 1950, pp. 336-345.
13. Rudolfs, W., Setter, L. R., and Baumgartner, W. H., "Effects of
Iron Compounds on Sedimentation, Digestion, and Ripe Sludge
Conditioning," Sewage Works Journal, Vol. 1, No. 4, July 1929,
pp. 398-410.
14. Sawyer, C. N., "Cause, Effects, and Control of Aquatic Growths,"
Journal of the Water Pollution Control Federation, Vol. 34, No.
3, March 1962, pp. 279-287.
15. Sawyer, C. N., "Some New Aspects of Phosphates in Relation to
Lake Fertilization," Sewage and Industrial Wastes, Vol. 24,
No. 6, June 1952, pp. 768-776.
16. Sawyer, C. N., and Grumbling, J. S., "High Rate Digestion,"
Jol. S.E.D., A.S.C.E., Vol. 86, No. SA2, March 1960, pp. 49-63.
17. Sawyer, C. N., and McCarty, P. L., Chemistry for Sanitary Engi-
neers, 2nd ed., McGraw-Hill, New York, 1967.
18. Sawyer, C. N., and Roy, H. K., "A Laboratory Evaluation of High
Rate Sludge Digestion," Sewage and Industrial Wastes, Vol. 27,
No. 12, Dec. 1955, pp. 1356-1363.
19. Shull, K. E., and Guthan, G. R., "Rapid Modified Eriochrome
Cyanine R Method for the Determination of Aluminum in Water,"
Paper, 87th Annual Conference of the American Water Works
Association, June 1967, Suburban Water Company, Bryn MaVr,
Pa.
20. Smith, D. T., et al., Bacteriology, llth ed., Appleton-Century-
Crofts, New York, 1957, p. 81.
21. Standard Methods for the Examination of Water and Wastewater, 12th
ed., American Public Health Association, New York, 1965.
22. Thomas, E. A., "Phosphatfallung in der Klaranlage von Uster und
Beseitigung des Eisen-Phosphat-Schlammes (1960 und 1963),"
Vierteljahrsschrift der Naturforschenden Gesellschaft in Zurich,
Vol. Ill, Dez. 1966, pp. 309-318.
23. Zenz, D. R., and Pivnicka, J. R., "Effective Phosphorus Removal
by the Addition of Alum to the Activated Sludge Process," Paper,
24th Annual Purdue Industrial Waste Conference, May 1969, Purdue
University, Lafayette, Ind.
56
-------
APPENDIX - SLUDGE DEWATERING DATA
This Appendix contains the data and calculations for the dewatering
tests run during the investigation.
The method used for measuring the dewatering potential of a sludge
was the specific resistance as presented by Coackley (3) .
[6]
l J
yc
2
where: r = specific resistance (sec per gm)
b = slope of the plot of time divided by the volume of
filtrate vs volume of filtrate
2
P = pressure vacuum across the filter membrane (gm per cm )
2
A = filter area (cm )
y = the filtrate viscosity (poises)
c = solids content (gm per ml)
The specific resistance of a sludge can be determined and compared
numerically with values obtained from other sludges to give a rela-
tive indication of the sludge dewaterability.
The following example shows a typical calculation for specific resis-
tance.
Example: Date - 9/2/69
Run - No. 1
Sample - 100% waste activated sludge, alum precipitates
incorporated
Temp, of filtrate (T) - 26°C
Viscosity of filtrate (y) - 0.00875 poises
Total solids content of sludge (X) - 1.09%
Solids content of the filter cake (Y) - 6.0%
2
Area of the filter - 95.0 cm (a constant value)
2
Pressure of the vacuum (P) - 790.6 gm/cm (a constant value)
57
-------
Filter Run Data:
time filtrate volume
(sec) (ml)
t_ V t/V
15 70 0.214 Cb =
30 105 0.386 brea* recorded
45 125 0.36Q at 85
60 145 0.414
75 163 0.460
90 172 0.523
The value of b^ which is the slope of the plot of t/V
against V was obtained from Fig. 20.
98.91
^ - ^ 1.09
_ 2bPA2 = 2(.00291)(790.6)(95.0)2 a 9
r " PC (.00875K.0133) =0.384x10
58
-------
o
OJ
(/I
0.7
0.6
0.5
0.4
0.3
0.2
0.1
T
VACUUM BREAK
b = 0.45/160 = 0.00291
50 100 150
V VOLUME, ml
200
FIGURE 20: A TYPICAL PLOT OF t/V (TIME/VOLUME) AGAINST V (VOLUME)
FROM RESULTS OF DEWATERING STUDIES, RUN No. 1, 9/2/69
59
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report Ho.
3. Accession No.
w
4. Title SOLUBLE PHOSPHORUS REMOVAL IN THE ACTIVATED SLUDGE
PROCESS, PART II, SLUDGE DIGESTION STUDY,
7. Author(s) 0' Shaughnessy, James C., Nesbitt, John B., Long,
David A., and Kountz, R. Rupert
9. Organization
Department of Civil Engineering, The Pennsylvania State
University, University Park, Pennsylvania 16802
12. Sponsoring Organization
15. Supplementary Notes
5. Report Date
6.
8. Performing Organization
Report No.
W. Project No.
11. Contract/Grant No.
17010 EIP
13. Type of Report and
Period Covered
16. Abstract
Sludges containing aluminum phosphorus precipitates from an activated sludge waste-
water treatment plant were digested in a high rate digester. Sodium aluminate and
liquid alum were used to precipitate the phosphorus from the wastewater. Analyses
on both raw and digested sludges showed that once precipitated from the wastewater
and incorporated into a sludge the phosphorus did not redissolve while undergoing
anaerobic digestion. Most of the soluble phosphorus in both the raw and digested
sludges was in the orthophosphate form, and the addition of the inorganic aluminum
phosphorus complexes did not adversely effect the anaerobic digester. High concen-
trations of soluble aluminum ion did not appear in the anaerobic digester, and the
use of alum for phosphorus removal caused no additional hydrogen sulfide production
during sludge digestion. Analyses also indicated the addition of aluminum compounds
enhanced the dewatering properties of the raw sludges.
17a. Descriptors
^Activated Sludge, ^Chemical Waste Treatment, ^Phosphate, ^Phosphorus, *Sludge,
^Sludge Digestion,
Eutrophication, Nitrification, Nutrients
/ 76. Identifiers
^Aluminum, Sludge Gases, Sludge Dewatering Alkalinity, Volatile Acids
17c. COWRR Field & Group 05D
18. Availability
19. Security Class.
(Report)
20. Security Class.
(Page)
21. No. of
Pages
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 20240
Abstractor J> c< pi shaughnessy | institution pept. of Civil Engrg., Penn State Univ.
WRSIC 102 (REV. JUNE 1971)
GPO 913.28t
------- |