Environmental Protection Technology Series
Hydrogen Peroxide Cures Filamentous
Growth In Activated Sludge
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
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mental Protection Agency, have been grouped into five series. These
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This report has been assigned to the Environmental Protection Technology
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EPA 670/2-73-033
October 1973
HYDROGEN PEROXIDE CURES FILAMENTOUS GROWTH
IN
ACTIVATED SLUDGE
by
Charles A. Cole
John B. Stamberg
Dolloff F. Bishop
Contract No. 14-12-818
Project 11010 FYM
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 DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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ABSTRACT
Laboratory tests at the Dupont Experimental Station substantiated by
tests at the EPA-DC Pilot Plant in Washington, D.C. revealed that
H202 offered a solution to filamentous bulking caused by Sphaerotilus
growth. The addition of H-yOj eliminated the free-growing filaments
£ £
while not deteriorating the spherical aerobic floe. The #2^2 a^-so
released oxygen which was beneficial in maintaining a purely aerobic
environment. Bulking activated sludge units could be brought under
control by doses of H20 from 20-200 mg/1 for less than one to
several days. The sludge volume index of the systems was reduced
substantially. The H2°2 treated aeration process could then be
brought under control by maintaining proper plant operation.
This report is submitted in partial fulfillment of Project 11010 FYM
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 July-1971.
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CONTENTS
Page
Abstract ii
List of Figures iv
Acknowledgments v
Sections
I Conclusions 1
II Recommendations 2
III Introduction 3
IV Laboratory Tests 5
V Experimental Plan and Results 6
VI Pilot Plant Aeration 10
VII Oxygen Activated Sludge 16
VIII Economics IS
IX References 19
X List of Publications 20
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FIGURES
No.
1 Sludge Concentration Indexes in the Bench Scale Tests 7
2 Photograph of Bench Scale Clarifier Prior to HO 8
Treatment
3 Photograph of Bench Scale Clarifier After the Addition 9
of 200 mg/1 of HO
4 Sludge Volume Indexes During February HO Treatment 12
in the Pilot Plant Step Aeration Process
5 Photo-Micrograph of Free-Growing Filamentous Growth 13
(Sphaerotilus) in the Pilot Plant Step Aeration Process
6 Photo-Micrograph After the Elimination of Filamentous 14
Growth by HO Addition in the Step Aeration Process
7 Sludge Volume Indexes During April and May HO 15
Treatment in the Step Aeration Process
8 Sludge Volume Indexes During HO Treatment in the 17
Oxygen Activated Sludge Process
IV
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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.
The cooperation and support of Dr. C.A. Cole and the Electrochemicals
Department of E.I. du Pont de Nemours is gratefully acknowledged.
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SECTION I
CONCLUSIONS
1. The addition of #£0.2 *-° the sludge recycle in filamentous bulking
activated sludge processes reduced the SVI to controllable levels in
laboratory tests on Penns Grove, New Jersey, wastewater and in pilot
tests of step aeration and oxygen activated sludge processes on the
District of Columbia wastewater. The filamentous organisms in the
step aeration and oxygen system were identified as Sphaerotilus.
2. The effective dose of ^2^2 was a function of time and concentration.
The optimum dosage and time were not determined and may vary from plant
to plant.
3. Once the SVI was below 200 and controllable settling was possible,
continued addition of #2^9 was not re
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SECTION II
RECOMMENDATIONS
The effectiveness of HO for reducing bulking caused by filamentous
organisms other than Sphaerotilus should be determined. Optimum
dosage periods and concentrations of HO to eliminate bulking
should be determined for Sphaerotilus and other filamentous organisms.
The product of the activated sludge effluent during treatment should
be compared to other alternative methods of reducing bulking such as
chlorine addition.
Accurate economic evaluations of all alternative solutions to bulking
should be made.
The operational conditions and the influent substrates that cause the
heavy propagation of the filamentous organism should be investigated.
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SECTION III
INTRODUCTION
Bulking or nonsettling activated sludge has intermittently disrupted
operation of sewage treatment plants for years. One of the most
common causes of bulking is the proliferation of filamentous growth
(1) (2) (3) (4). The establishment of filamentous growth is generally
believed to be caused by conditions under which the filamentous
organism propagates as fast or faster then the more desirable spherical
aerobic (floe forming) bacteria. Since the free growing filamentous
organisms have a higher area to volume ratio than spherical aerobic
growth. Pipes (1) suggests that the filamentous organisms have the
metabolic advantage in activated sludge reactors with high soluble
organic substrates, low dissolved oxygen concentrations or low
nutrient conditions.
Smith and Purdy (2) suggest that several types of filamentous organisms
cause the bulking, but generally the Sphaerotilus species is the most
common cause. Recently, Farquhar and Boyle (3) (4) verified the
presence of filamentous organisms at various activated sludge plants.
They developed techniques for identifying the various filamentous
species and found that the Sphaerotalis and Thiothrix were most
commonly associated with bulking.
The control of filamentous organisms and the prevention of bulking in
the activated sludge process are important factors in achieving
present and future water quality and effluent discharge requirements.
The filamentous growth not only reduces product quality of the
secondary effluent but also decreases the quality of subsequent
tertiary treatment effluents (5) (6) (7) (8).
Imhoff and Fair (9) report that the treatments used to reduce the
sludge volume index of the bulking sludge include reduction of the
amount of return sludge and wasting more sludge in an attempt to build
up a new microbiological population, increasing air supply, by-passing
or diluting influent sewage to change the loading rate, addition of
flocculating chemicals to improve the settling characteristics of the
sludge, and chlorination of the return sludge to destroy the
filamentous organisms. Chlorine, which is the most common treatment
for elimination of filamentous organisms, has the disadvantage that
it also destroys the desirable spherical bacteria.
These treatment techniques used to control bulking produce slow or
poor response. A new method is clearly needed to eliminate the
filamentous growth without extensive damage to the normal spherical
aerobic population. In addition, operational procedures are needed to
minimize reoccurrence of the filamentous condition in the activated
sludge process.
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This work describes the use of HO in laboratory and pilot activated
sludge systems to eliminate filamentous growth. The laboratory
studies were performed at the Dupont Experimental Station in Wilmington,
Delaware. The pilot studies with step aeration and pure oxygen
activated sludge were performed at the EPA-DC Pilot Plant in Washington,
D.C. Operating conditions to prevent the reestablishing of the
bulking sludge in the D.C. wastewater were also evaluated.
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SECTION IV
LABORATORY TESTS
The bench scale tests were performed in an activated sludge system in
the laboratory. The completely mixed aerator and the clarifier had
detention times of 3.34 hrs. and 2.0 hrs., respectively, based on a
feed rate of 12.5 cc/min. The sludge recycle rate was 100% of the feed
flow.
The feed used for the experiment was a settled primary domestic sewage
from Penns Grove, New Jersey. Both diffused and mechanical aeration
were used to maintain the dissolved oxygen concentration above 5 mg/1.
Typical parameters were used for evaluation of waste treatment
efficiency including a modified sludge volume index which was termed
"sludge concentration index"- The sludge concentration index was
determined by using a 25 ml graduated cylinder for the settling tests
rather than the standard liter cylinder. The small volume was
necessary because of the scale of the laboratory experiments. The
sludge concentration index, however, was calculated as a SVI and
reported as the volume in milliliters occupied by 1 gram of dry
suspended solids. The sludge concentration index obtained for the
bench scale experimental work in the 25 ml cylinder were not comparable
with the conventional SVI probably because of wall effects and the
increase in the ratio of the diameter of the floe to the diameter of
the cylinder. The sludge concentration index, however, was useful as
a relative indicator of bulking conditions for the laboratory
experiments.
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SECTION V
EXPERIMENTAL PLAN AND RESULTS
After seeding the laboratory unit, the activated sludge unit was
operated for approximately one week before data for analysis were
recorded. After start-up, the sludge concentration index increased
steadily. The food to micro-organism ratio increased from 0.3 to
0.7 Ib of BOD /lb of MLSS and the sludge concentration index (Figure 1)
increased to near 1000. Microscopic examination of the sludge
revealed the presence of numerous free-growing filamentous organisms.
The effluent quality deteriorated from a turbidity of 3 Jackson
Turbidity Units (JTU) and 2 mg/1 of suspended solids to 13 JTU and
24 mg/1 of suspended solids just prior to the addition of HO on the
eleventh day.
HO at a concentration of 200 mg/1 was added in the recycle line for
a 24-hour period. The sludge concentration index immediately
decreased from 1000 to 400-500. The sludge depth (Figures 2 and 3) in
the clarifier also decreased after HO treatment. This reduction of
concentration index was observed to correspond to nearly complete
elimination of the free-filamentous growth. The effluent quality
improved to 3 JTU and to about 1 mg/1 of suspended solids.
Operating at the same retention time and food to micro-organism ratio,
filamentous growth reestablished within ten days after termination of
H~0 addition. The sludge concentration index increased again to near
1000 within five days even with the continuous addition of 10 mg/1 of
HO in the recycle stream. The effluent quality deteriorated to
33 JTU and 52 mg/1 of suspended solids. However, when the HO dosage
was increased to 40 mg/1, the sludge concentration index again
decreased to below 400 within two days. The effluent quality improved
to 4 JTU and 1 mg/1 of suspended solids. Continued application of
HO for an additional four days did not lower the concentration index
further. The studies on controlling filamentous bulking with HO
were then continued at the EPA-DC Pilot Plant in Washington, D.C.
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x
Ld
Z
tr
i-
z
LJ
o
O
U
O
§
1000
900
800
700
600
500
400
300
200
100
0
I0mg/l 40mg/l 200mg/l
j 1
8 12 16 20 24 28 32 36 40
DAYS
FIGURE 1 - Sludge concentration indexes observed
in the bench scale tests
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Figure 2. Photograph of Bench Scale Clarifier Prior to t^O Treatment
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Figure 3. Photograph of Bench Scale Clarifier After the Addition
of 200 mg/1 of H0
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SECTION VI
PILOT PLANT AERATION
At the EPA-DC Pilot Plant, the aeration process was operated as step
aeration or contact stabilization. The step aeration effluent was
fed to subsequent treatment stages of nitrification and denitrification.
The nominal capacity of step aeration was 100,000 gpd with a 2.3:1
maximum to minimum diurnal flow variation at an average detention time
of 3.6 hours. The secondary clarifier had an average overflow rate of
650 gpd/ft with daily .peaks of 975 gpd/'ft .
In the summer of 1970, the step aeration plant performed well producing
an effluent and suspended solids concentration of 16 mg/1 and 25 mg/1,
respectively. The system was operated with high mixed liquor concen-
trations (over 2500 mg/1) and with minimum solids wasting. The
operation produced a solids retention time (SRT) of between 8 and 12
days at a loading of less than 0.3 Ib. BOD /lb. of MLVSS. The high
SRTs indicate the process was operated with endogenous metabolism
(Equation 1).
(lb. vol. solids under aeration) (%)
(lb. vol. solids wasted/day) + (lb. eff. vol. solids/day)
In October of 1970, high solids wasting was programmed to minimize
nitrification in order to provide the maximum ammonia concentration
for the subsequent independent nitrification system. This mode of
operating the step aeration process produced lower mixed liquor
concentrations, less endogenous respiration and an SRT of 3 to 5 days
at a loading of approximately 0.5 lb. BOD^/lb. of MLVSS. As with
earlier operation on D.C. wastewater in the 3-5 SRT range (10), heavy
filamentous growth developed in the aeration tank. The organisms were
identified (11) as Sphaerotilus. The effluent quality deteriorated to
32 mg/1 of BOD and 48 mg/1 of suspended solids and the SVI increased
to over 300.
The dissolved oxygen was then maintained above 1 mg/1 and the wasting
of solids was reduced to the minimum level which would prevent the
clarifier blanket from overflowing. This combination of techniques
failed to substantially reduce the SVI below 300 through the winter
period to mid-February. Chlorine addition was avoided to protect the
subsequent nitrifying activated sludge from both free chlorine and the
long-term heavy organic (BOD) loading stress caused by the deterioration
of secondary effluent during chlorination. The HO was then employed
based on the success of the laboratory studies at the Dupont Labora-
tories.
The addition of HO in moderate dosages was applied in mid-February.
The HO was added to the sludge recycle (50% of the influent flow)
10
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at a dose equal to 20 mg/1 of the influent flow for 2 days. The
dosage was then increased to 40 mg/1 for 12 additional days. As seen
in Figure 4, the addition of HO quickly reduced the SVI from the
300-400 range to less than 200. Solids wasting was reduced as the
settling qualities of the mixed liquor improved. The SVI then
steadily improved to 60 and remained at that level. As shown in the
photo-micrographs (Figures 5 and 6), the long free growing filamentous
strands were quickly reduced and eventually eliminated as the SVI
improved.
The improved settling properties permitted continuous operation at
higher solids concentrations and an SRT above 5 days. During the
HO addition, the poor effluent quality (80 mg/1 of BOD and 90 mg/1
of SS) did not deteriorate further but steadily improved to 25 mg/1
BOD and 20 mg/1 SS.
In late April, equipment tank modifications required the step aeration
process to be transferred to temporary tankage. The available
temporary aeration tank was too large and wooden baffles were used to
section the tank to the desired size. However, the baffles had
uncontrollable leaks. The leakage of mixed liquor out of the aeration
tank was sufficient to lower the SRT to the point where filamentous
growth was reestablished. The SVI rapidly increased to well over 300.
fl_0 was again added to the recycle but this time at a high dosage
(equivalent to 200 mg/1 in the influent flow) for a 1 day period. An
immediate reduction in SVI to less than 150 occurred (Figure 7). The
effluent BOD of 67 mg/1 before treatment improved to less than 40 mg/1
for several Says immediately after the. addition of HO .
Normally with the improvement in settling characteristics, the bulking
condition could be permanently controlled in D.C. wastewater by build-
ing solids and operating at a higher mixed liquor solids concentration
and a higher SRT. With the uncontrolled mixed liquor wasting through
the wooded baffles, however, the SRT and mixed liquor concentrations
could not be increased. Thus the filamentous growth gradually
reappeared and the effluent BOD deteriorated to its previous levels.
11
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500
400
^ 300
e
200
100
0
H202
20mg/l 4-Omg/l
5 7 9 II 13 15 17 19 21 23 25 27 I 3 5
FEBRUARY MARCH
FIGURE 4 - Sludge volume indexes observed during February
HO treatment in the pilot plant step aeration
process
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Figure 5. Photo-Micrograph of Free-Growing Filamentous Growth
(Sphaerotilus) in the Pilot Plant Step Aeration Process
13
-------
i
Figure 6. Photo-Micrograph After the Elimination of Filamentous
Growth by tC^ Addition in the Step Aeration Process
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Ul
500
400
! 300
X.
"e
> 200
100
0
2345 67 8 910 II
MAY
FIGURE 7 - Sludge volume indexes observed during April and May
treatment in the pilot plant step aeration process.
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SECTION VII
OXYGEN ACTIVATED SLUDGE
The oxygen ("UNOX") activated sludge process at the EPA-DC Pilot Plant
during the study had a nominal capacity of 100,000 gpd and operated
with an average reactor time of 1.5 hours and a clarifier overflow
rate of 650 gpd/ft2. The reactor dissolved oxygen was maintained
between 6 and 10 mg/1.
The system developed filamentous growth during a period of reactor
modification where the operating conditions produced an SRT of less
than 5 days and where periods of low dissolved oxygen occurred. Once
the filamentous growth was established and SRT was maintained below
5 days (0.6 Ib. BOD /lb. of MLVSS), the growth continued to propagate
in the high dissolved oxygen concentrations. As in step aeration
systems, the SVI ranged between 300 and 500. The growth was also
identified as Sphaerotilus (12). Initially the flow was decreased from
100,000 gpd to 45,000 gpd to lower the loading and overflow rate in
an attempt to increase the SRT. However, improvement in SVI was only
slight for the four days prior to HO treatment (Figure 8).
#0 treatment was then employed. The initial treatment consisted of
aading 200 mg/1 (based on the influent flow) to the recycle (70%)for
24 hours followed by four hours of an increased dose of 400 mg/1. The
reduction of free growing filaments occurred but not as drastically as
in step aeration, perhaps because the organism was acclimated to a
high oxygen environment where the relative change in oxidation-
reduction potential with the HO addition was less. During the high
dosage period (400 mg/1), deflocculation of the spherical aerobic mass
also was noticed. The SVI, however, decreased to nearly 200 after
the HO treatment.
£ £
A second treatment of HO was tried 11 days later. The dosage was
200 mg/1 for one day. The treatment initially produced a modest
improvement, and the SVI dropped below 200. The SVI then steadily
decreased to 60 as solids could be retained in the system without
further HO addition.
At low influent flow and low overflow rates, the effluent quality
remained satisfactory. The effluent BOD remained below 10 mg/1 during
the entire test period, even during HO treatment.
16
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6
500
400
300
200
100
0
H202200mg/l
nj
400 ing/I
25 29
MAY
H202
200 mg/|
10
14 18
JUNE
22 26 30
FIGURE 8 - Sludge volume indexes observed during ff,0? treatment
in the pilot plant oxygen activated sluage process.
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SECTION VIII
ECONOMICS
The chemical cost for treatment with HO as employed in this study
to eliminate filamentous bulking is estimated as $548.00 per million
gallons of plant flow. This cost assumes treatment at a dosage of
200 mg/1 based upon influent plant flow and applied to the recycled
sludge for a 24-hour period. The cost for HO (13) is $0.23 per
pound of 70% by weight HO ($0.33 per pound of pure HO) in tank
truck lots FOB freight equalized to the nearest source of production.
This cost does not necessarily reflect optimum treatment requirements
and costs but does indicate that continuous application of HO even
at low doses to control filamentous bulking is not likely to be
economically practical. Thus HO, as an immediate cure for bulking
conditions, requires subsequent operation of the treatment plant to
prevent or to minimize the number of recurrences of the bulking
filamentous condition.
Since other techniques to eliminate bulking have shown slow or poor
response and continue to permit poor quality treatment for extended
periods, these techniques and their costs are not comparable to HO
as an effective treatment approach for Sphaerotilus bulking.
18
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SECTION IX
REFERENCES
1. Pipesf W.O., "Bulking of Activated Sludge"', Advances in Applied
Microbiology, 9_, 185 (1967).
2. Farquhar, G.J. and W.C. Boyle, "Identification of Filamentous
Micro-organisms in Activated Sludge", Journal of Water Pollution
Control Federation", 43_, 604 (1971).
3. Farquhar, S.J. and W.C. Boyle, "Occurrence of Filamentous Micro-
organisms in Activated Sludge", Journal of Water Pollution Control
Federation, 43, 779 (1971).
4. Smith, R.S. and W.C. Purdy, "The Use of Chlorination of Correction
of Sludge Bulking in the Activated Sludge Process", Sewage Works
Journal, 8_, 223 (1936).
5. O'Farrell, T.P., J.B. Stamberg, D.F. Bishop, "Carbon Adsorption
of Lime Clarified RAw, Primary and Secondary Wastewaters".
Presented at the 68th AIChE, Houston, Texas, March 1971.
6. O'Farrell, T.P. D.F. Bishop, "Lime Precipitation in Raw, Primary
and Secondary Wastewater", AIChE Symposium Series 124 Water-1971,
68, 43 (1972).
7. Stamberg, J.B., D.F. Bishop, G. Kumke, "Activated Sludge Treatment
with Oxygen", AIChE Symposium Series 124 Water-1971, 68, 25 (1972).
8. Stamberg, J.B., D.F. Bishop, "Separate Stage Nitrification and
Denitrification of Municipal Wastewater". Presented at the 68th
National Meeting of the AIChE, Houston, Texas, March 1971.
9. Imhoff, K. and G.M. Fair, "Sewage Treatment", John Wiley and Sons,
Inc., N.Y., p. 160 (1956).
10. Dahl, B. "District of Columbia Internal Report on the Use of
Minerals within a 2000 gpd Activated Sludge System'1, July (1969).
11. Lewis, R.F., Taft Center, Environmental Protection Agency,
Cincinnati, Ohio, Private Communication, February 1971.
12. Lewis, R.F.,Taft Center, Environmental Protection Agency,
Cincinnati, Ohio, Private Communication, June 1971.
13. Oil Paint and Drug Reporter, June 1973.
19
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SECTION X
PUBLICATIONS
Presented at the 5th Mid-Atlantic Industrial Waste Conference,
Philadelphiaf Pennsylvania, November 1971.
Cole, C.A., J.B. Stairiberg, and D.F. Bishop, "Hydrogen Peroxide Cures
Filamentous Growth in Activated Sludge", Journal of Water Pollution
Control Federation, 45, 829, 1973.
20
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report No.
w
4. Title
HYDROGEN PEROXIDE CURES FILAMENTOUS GROWTH IN
ACTIVATED SLUDGE
Author(s)
Cole, Charles, Stamberg, John B.r and Bishop, Dolloff F.
5. Report Date
t.
S. I riormi f, Orga. zation
Report No.
Plant
Department of Environmental Services
Government of the District of Columbia
5000 Overlook Ave. S.W.
P.g.
ojr. r fo
11010 FYM
-f i'£,-.-lTf NO.
I.< Type . f Repo. and
Period Covered
12. Srr"JSOrin; O'rgani-ation
ENVIRONMENTAL PROTECTION AGENCY
Environmental Protection Agency report number EPA-670/2-73-033
October 1973.
16. Abstract
Laboratory tests at the Dupont Experimental Station substantiated by tests at the
EPA-DC Pilot Plant in Washington, D.C. revealed that HJO. offered a solution to
filamentous bulking caused by Sphaerotilus growth. The addition of tf O eliminated
the free-growing filaments while not deteriorating the spherical aerboic floe. The
H_O also released oxygen which was beneficial in maintaining a purely aerobic
environment. Bulking activated sludge units could be brought under control by doses
of H O2 from 20-200 mg/1 for less than one to several days. The sludge volume index
of the systems was reduced substantially. The HO treated aeration process could
then be brought under control by maintaining proper plant operation.
17a. Descriptors
Activated Sludge
*Sphaerotilus
Sedimentation
17b. Identifiers
* Hydrogen Peroxide
Bulking
17c. COWRR Field & Group
If. Availability
"Security Class.
(Repoi )
Se<-
(Page)
21.
No. of
Pages
Pi t :e
Semi To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
John B. Stamberg
Environmental Protection Agency
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