EPA 670/2-73-042
February 1974
ACTIVATED SLUDGE PROCESS
USING
PURE OXYGEN
BY
Edward A. Wilcox
Samuel 0. Akinbami
Contract No. 14-12-846
Project 101/11010 FRN
Program Element 1B2033
Project Officer
Doll off 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
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 95 cents
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ABSTRACT
An evaluation of the pure oxygen activated sludge system (UNOX) has
been underway since May, 1970. During the first 16 months of test
operation on the 100,000 gpd facility at the Blue Plains Wastewater
Treatment Plant, over five different phases of operation were tested to
demonstrate the performance of the system under varying conditions.
The oxygen activated sludge system (UNOXJ consisted of a unique,
four stage, gas tight biological reactor that employed cocurrent gas-
liquid contacting. In less than 1.85 hours of oxygenation, the system
removed 90 percent of the influent BODg and utilized over 95 percent
of the supplied oxygen. The effluent quality was as good or better
than that obtained from a 3.6 hour step aeration system operating in
parallel with the oxygenation system.
The microbial organisms visually were essentially the same as those
found in a typical conventional system. Their rate of activity,
however, was greater than those of the air system. The total solids
production was significantly less than the similarly operating
diffused air system. Solids production averaged between 0.2 and 0.5
Ib. solids wasted per Ib. BOD removed.
Satisfactory solid-liquid separation was achieved at clarifier overflow
rates varying between 300 and 1940 gallons per day per square foot.
The clarifier underflow concentrations varied from 1.0 to 2.4 percent
and mixed liquor suspended solids were maintained between 4000 and
7600 mg/1. The MLSS increased to over 8000 mg/1 when operated with
alum addition for phosphorus removal.
This report was submitted in fulfillment of Project 101/11010 FRN and
Contract No. 14-12-846 by the Union Carbide Corporation, Linde Division
under the sponsorship of the Environmental Protection Agency. Work
was completed as of December, 1970.
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CONTENTS
Section Title
ABSTRACT
LIST OF TABLES vi
LIST OF FIGURES vii
I SUMMARY AND CONCLUSIONS 1
Summary 1
Conclusions 1
II RECOMMENDATIONS 3
III INTRODUCTION 5
Background-History 5
Purpose of Project 5
Proposed Study 6
Authorization, Scope and Content of Report 6
IV OXYGEN ACTIVATED SLUDGE 9
Pilot Plant Facilities 9
Influent Wastewater 12
Process Monitoring 12
Mode of Operation 12
Analytical Procedures 17
V PROCESS OPERATION AND PERFORMANCE 19
Description of Phase Operations and 19
Performance
Substrate Removals 29
Nutrient Removals 36
Biomass Characteristics 36
Sludge Production 38
Organic Loading 38
Oxygen Utilization 38
Clarifier Performance 40
VI ACKNOWLEDGEMENTS 45
VII REFERENCES 47
iii
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TABLES
No. Title Page
1 INFLUENT WASTEWATER CHARACTERISTICS 13
2 OPERATING PHASES 20
3 PERFORMANCE SUMMARY 21
4 OPERATING PARAMETERS 22
5 PERFORMANCE DATA 23
6 BIOCHEMICAL OXYGEN DEMAND 25
6A EFFLUENT SOLUBLE BIOCHEMICAL OXYGEN DEMAND 26
7 ALUM ADDITION 28
8 CHEMICAL OXYGEN DEMAND 30
9 SUSPENDED SOLIDS 31
10 NITROGEN AND PHOSPHORUS 32
11 SOLIDS BALANCE 39
12 OXYGEN CONSUMPTION 41
13 OXYGEN USAGE COMPARED TO COD BALANCE 42
14 DIURNAL FLOW OPERATION 43
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Figures
No.
1
2
3
4
5
6
7
Title
"UNOX" PILOT PLANT FACILITY
CENTERFEED CLARIFIER UNIT
INFLUENT BOD, PROBABILITY OF OCCURRENCE
DIURNAL FLOW VARIATION
BOD REMOVAL, PROBABILITY OF OCCURRENCE
EFFLUENT BOD, PROBABILITY OF OCCURRENCE
BOD CONTENT OF EFFLUENT SUSPENDED SOLIDS
Page
10
11
14
16
33
34
35
EFFECT OF ALUM DOSAGE ON PHOSPHORUS REMOVAL 37
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SECTION I
SUMMARY AND CONCLUSIONS
Summary
In May 1970, an evaluation of the oxygen activated sludge system (UNOX)
was begun at the Blue Plains Wastewater Treatment Facility to demonstrate
the ability of the oxygen system to operate at high mixed liquor solids and
short retention times and produce effluents of comparable quality with the
conventional activated sludge of relatively lower solids and longer retention
times.
Because the Potomac stream standards require about 98 percent phosphorus
removal from the wastewater before discharge, an evaluation of phosphate
removal by chemical addition to the pure oxygen system was conducted.
Nitrification, though not of primary interest, was also studied.
During this program, the pilot plant was operated at relatively steady flow
as well as with a diurnal flow pattern both with and without alum addition.
In addition, the initial peripheral feed clarifier was modified to a center-feed
clarifier on August 14, 1970. However, the clarifier overflow rates experienced
were much higher than those in conventional practice. A description of the
pilot plant facilities, characterization of the wastewater, mode of operation
and process information are discussed in the report.
Conclusions
1. An oxygen aeration system (UNOX) employing a gas tight biological
reactor has been in operation at the Blue Plains facility since May 1970.
During this entire period a high quality effluent was produced while
operating the system at high mixed-liquor solids levels and retention
times of less than 2 hours.
2 . Good quality effluent was produced with an average biomass loading
of 0.30 Ib. BOD per Ib. MLVSS and a maximum value of 0.45 while the
system was not stressed. Later operation showed effective treatment
at loads as high as 1.3 Ib. BOD/lb. MLVSS as reported by John B.
Stamberg, et al (13).
3. The clarifier for the oxygen aeration system was operated for the
majority of this program at average overflow rates of 1000 to 1300 GPDPSF
with frequent periods of diurnal variations achieving 12 hour sustained
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peak overflow rates of 1700 to 1900 GPDPSF. The oxygenation system
demonstrated the ability to maintain MLSS levels of 4000 to 7000 mg/1
even while operating at these high hydraulic loadings.
4. The oxygenation system demonstrated the ability to produce a con-
centrated recycle sludge. At these high overflow rates, the recycle sludge
concentration was about 1.5 percent suspended solids. During this phase
with alum addition, the concentration averaged about 2.3 percent suspended
solids .
5. The addition of alum to the fourth stage of an oxygen activated sludge
system was demonstrated to be a practical method of removing phosphorus.
Average phosphorus residuals of 1.8 mg/1 as P with alum dosage of 1.4
Al to P by weight were achieved.
6 . Nitrification was achieved by the oxygenation system during the
summer and fall periods when process conditions and temperature were
mutually established in the range where nitrification would be expected.
7. Based upon the influent and exhaust gas flow, over 95 percent of
the oxygen was consistently utilized.
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SECTION II
RECOMMENDATIONS
During the late winter and early springtime operation of the oxygenation
system at Blue Plains it was noted that the settling characteristics of
the mixed-liquor were not as good as had been observed in the previous
summer and fall operation. During this period a filamentous culture was
present at times in the mixed-liquor and waste temperature was of course
lower than in the summer-fall period. It is postulated that either or both
of these factors may have influenced the settling characteristics. It is
recommended that full pilot plant operations be continued at Blue Plains
to determine the factors affecting biomass settling characteristics.
Since this study was done at relatively high clarifier loadings (average
of about 1300 GPDPSF), it is recommended that more studies be done
at the same overflow rate as most clarifiers that are in operation at present.
This would mean an overflow rate of 600 to 800 GPDPSF. Under these
conditions, it should be possible to maintain a recycle sludge with solids
concentrations of 2 to 3 percent consistently.
It is recommended that the study be continued to more accurately determine
the actual oxygen requirement under a wider range of operating conditions,
to be able to distinguish between the oxygen consumed, e.g. with and
without nitrification, endogenous respiration, and leakages if oossible.
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SECTION III
INTRODUCTION
Background-History
The use of pure oxygen within the activated sludge process dates back
some 20 years. Pirnie (1) proposed a system of predissolving pure oxygen
in high concentrations in the influent wastewater before entering a non-
aerated mixed reactor. The process was termed "a bioprecipitation system".
Biological success was achieved by Okun (2) in bench scale tests and later
by Budd and Lambeth (3) on a pilot scale, but oxygen utilization efficiencies
of 20 to 25 percent were too costly. Okun and Lynn (4) and later Okun (5)
showed an increase in the effective sludge activity in the mixed liquor by
reducing or eliminating anaerobic periods such as can occur in clarification.
McKinney and Pfeffer (6) more recently reviewed the use of oxygen in
activated sludge. Increased metabolism rates, produced by eliminating
periods of zero dissolved oxygen,would increase treatment efficiencies
in overloaded plants and reduce the size required for new plants. Thus,
potential reductions in capital investment were viewed possible for oxygen
systems.
Union Carbide recently developed the UNOX System (7) which is an oxygen-
aeration-activated sludge system with an oxygen utilization of over 90
percent. This oxygen-activated sludge process (UNOX) is presently being
piloted in several locations and several, full-scale plants utilizing the
pure oxygen process (UNOX) are under construction and will soon be in
operation.
Purpose of Project
The District of Columbia must upgrade the existing Blue Plains Water
Pollution Control Plant so that the effluent from the plant meets the
Potomac River Water Quality standards. Furthermore , the plant is to
be expanded so that it will be capable of treating an average flow of
309 MGD. The area of land available for expansion is limited and
previous studies have shown that the available land may not be enough
to provide adequate treatment for 420 MGD wastewater flow.
The use of pure oxygen in activated sludge enhances the transfer of
oxygen into the wastewater for biochemical usage resulting in the ability
of the system to support a high biomass in the wastewater. The rate of
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removal of biochemical oxygen demand (BOD) is proportional to the product
of biomass (measured as MLVSS) and the time of reaction. If the biomass
is increased, the time required for a given BOD removal can be reduced thereby
reducing the area of land required for the reactor. It can be seen that a pure
oxygen system which can maintain a higher biomass will offer a possible
solution to the problem of land requirement.
The other problem is the removal of phosphates in the wastewater by
chemical addition to precipitate the phosphates and then remove them by
sedimentation. Since an activated sludge process requires sedimentation,
a further reduction in land requirement can be achieved if the two systems
can be combined by adding the chemical to the activated sludge system
and removing BOD and phosphates in the same operation.
Proposed Study
The proposed study was to demonstrate the performance of the pure
oxygen system with regard to high mixed liquor suspended solids concentration
and short retention times as compared to a step aeration system.
The pilot plant was to be operated on steady flow and diurnal
variation simulation of flow at high mixed liquor suspended solids (MLSS)
concentration.
In order to evaluate the degree of phosphate removal that can be achieved
in the activated sludge system, alum was to be added under various oper-
ating conditions. 90 percent phosphate removal has been reported in
literature but 98 percent removal is required at Washington, D.C. This
test was to provide a basis for the decision on how adequate phosphate
removal can be achieved.
Authorization, Scope and Content of the Report
The studies covered in this report were undertaken by the Environmental
Protection Agency, Washington, D.C. , with Union Carbide under contract
to provide the engineering and the equipment required for the study, train
the EPA operators and reduce data furnished by the EPA. The contract was
signed on February 13 , 1970 under section 302 (C)(15) of the Federal
Property and Administrative Services Act of 1949, as amended, and Section
(5) of the Federal Water Pollution Control Act, as amended. The contract
was for $55,900 for engineering and equipment and for data reduction and
the final report.
The ultimate goal of the project was to evaluate the oxygen-activated sludge
process (UNOX) by determining process performance and operating requirements
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for the Washington, D.C. primary effluent wastewater. The basic facilities
and equipment for the UNOX System test program are described in Section
IV.
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SECTION IV
OXYGEN ACTIVATED SLUDGE SYSTEM
Pilot Plant Facilities
The- UNOX System couples the use of pure oxygen with a highly effective
mass transfer and contacting system to biologically remove organic
contaminants. The EPA-DC pilot plant employs a unique gas-tight
biological reactor with four stages operating in series. The reactor
operated initially with a peripheral feed clarifier which was later
modified to a conventional centerfeed gravity clarifier. A schematic
diagram of the pilot plant facility is shown in Figure 1.
The gas tight biological reactor consists of four cocurrent gas-liquid
stages . Each stage contains a sparge impeller contacting device.
The sparger consists of rotating spokes equipped with orifices, whereas
the primary liquid pumping device is a marine type impeller. Each of
the stages is a completely mixed unit with the overall system approximating
plug flow. The influent waste and the return sludge were mixed prior
to entering the first stage. The wastewater feed and sludge return lines
are both equipped with magnetic flow meters which are periodically
calibrated.
The clarifier initially was a peripheral feed center take-off clarifier
with a rapid sludge return type sludge removal system. The influent
channel around the periphecy of the clarifier was separated from the
upflow area by an apron which extended 70 inches below the water level.
This clarifier was later modified to a centerfeed clarifier, but the apron
was not removed. This resulted in a clarifier with a total area of 107
square feet and an upflow area of 78 square feet. This means that the
total area of the clarifier is 37 percent greater than the upflow area
as compared to full scale units where the difference is only 5 percent
or less. Therefore, the upflow area was used in clarifier overflow rates
in this report. Since the apron did not extend down to the compaction
zone of the clarifier, the total clarifier area (107 sq. ft.) was used for
clarifier solids loadings.
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FIGURE 2
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
INITIAL CLARIFIER UNIT
46-]
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132"
140"
14"
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11
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Influent Wastewater
Throughout the pilot plant study, the biological reactor influent was
obtained from the effluent of the full-scale primary clarifiers. The
quantitative variability of the clarified wastewater is shown in Table
I. As noted, the daily BOD5 varied between 50 and 170 mg/1 with
an overall average of about 114 mg/1. 80 percent of the time, the
BOD was between 80 and 150 mg/1 with the higher and lower ranges
each occurring 10 percent of the time. A probability curve of influent
BOD is shown in Figure 3. The average COD/BOD ratio was about
2.3. Suspended solids varied between 40 and 200 mg/1 with an
average of about 108 mg/1; the volatile content averaged 80 percent.
The total Kjeldahl nitrogen and total phosphorus each averaged 26 mg/1.
The lowest sustained influent waste temperature was 66°F. Periodically
during the study, a filamentous type culture was noted in the wastewater.
Microscopic analysis showed that this same culture was present on the
full-scale primary clarifier weirs .
Process Monitoring
In addition to the routine monitoring of gas and liquid flow rates by
appropriate recording and metering equipment, several basic parameters
are measured in order to obtain a process performance evaluation.
Daily composite samples are formed for six (6) grab samples taken at
four (4) hour intervals for the biological reactor influent, the clarifier
effluent and the recycle sludge. Mixed liquor composites are formed
from three (3) grab samples taken at eight (8) hour intervals. All of
the grab samples taken are volumetrically proportional according to
the pilot plant influent. Settling information is collected daily through
graduate cylinder settling tests. Solids are normally wasted four (4)
to six (6) times per day (or as required) and the volume wasted is
measured. Waste sludge solids concentration is the same as clarifier
underflow concentration. Most of the analytical procedures are
conducted as outlined in the 12th Edition of Standard Methods. All
analytical tests are performed by the EPA'-DC personnel
at Blue Plains , and these results, together with the monitoring
information are sent to Union Carbide to be reduced for use in this
report.
Mode of Operation
The EPA-DC Pilot Plant has been in operation since May 1970. Primary
effluent from the District of Columbia's plant is fed to the oxygen reactor
either with a steady flow or with a predetermined daily cycle or diurnal
12
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TABLE I
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
INFLUENT WASTE CHARACTERISTICS
PARAMETER
Chemical Oxygen Demand , mg/1
Biochemical Oxygen Demand, mg/1
Total Suspended Solids, mg/1
Volatile Suspended Solids, mg/1
Total Kjeldahl Nitrogen, mg/1
Total Phosphorus, mg/1
pH
Temperature, °F
24-HOUR COMPOSITES
95% Occurrence
Range
160-340
50-170
40-200
40-140
15-35
16-35
6.8-7.7
66-87
Average
267
114
108
81
26
26
7.3
75
13
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variation, normally with a 2.3:1 (45-105 gallons per minute) daily flow
variation (Figure 4) . The four stage system with 8,100 gallons capacity
provides 1.94 hours of retention time at the nominal influent flow of
100,000 gallons per day. At the peak daily flows, the retention time
is 1.3 hours.
The reactor is sealed to prevent loss of oxygen and includes submerged
hydraulic entrances and exits as well as simple water-sealed mixing
equipment. It is divided into stages to provide the proper tank geometry
for efficient mixing and oxygen usage.
The efficient oxygen usage is achieved by cocurrent contacting of the
mixed-liquor and oxygen gas through the various stages. The addition of
pure oxygen to the reactor is controlled by a pressure regulator. An inlet
oxygen control valve actuated by the pressure regulator maintains the
overhead gas at a selected pressure usually between 1" and 4" of water.
Even with large instantaneous fluctuations in oxygen consumption, the
oxygen control valve easily maintains the selected pressure. The overhead
gas pressure is normally selected to produce an oxygen concentration at
approximately 50 percent in the exhaust gas .from the reactor. Pure oxygen
is introduced to the first stage where the peak oxygen demand occurs. As
the oxygen is used in biological metabolism, nitrogen stripped from the
wastewater and the respirated carbon dioxide reduces the oxygen concentration
in the overhead gas flowing cocurrently with the mixed liquor through the
succeeding stages. The successive decrease of both oxygen supply and
demand produces efficient oxygen use before the residual gas is exhausted
from the reactor.
The dissolved oxygen level in the mixed liquor is controlled between 4.0
and 8.0 mg/1 by adjusting the recirculation rate of the oxygen enriched gas
within the individual stage. The compressor in each stage pumps the
overhead gas through the rotating mixer impeller to provide efficient
dispersion and mixing of the recirculated gas. The recirculation rate in
each stage may be set either manually on the basis of a dissolved oxygen
analysis or automatically in the first stage using a control system with a
dissolved oxygen probe as a sensor.
In order to cope with foaming problems, water spray nozzles were installed
at the exit from each stage. The spray nozzles are turned on as required to
spray jets of water to dissipate the foam. A flap gate was also installed at
the weir in stage 4 so that the liquid level in the reactor could be lowered.
If the spray nozzles do not completely dissipate the foam, it could be
removed from the reactor by lowering the liquid level.
15
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Analytical Procedures
To evaluate the oxygen activated sludge process, appropriate samples
were manually composited over a 24 hour period. Samples were stored
at 3°C to minimize biological activity.
The 5-day biological oxygen demand (BOD) of the composite samples was
determined by the probe method (10) and the ammonia (10) and nitrate-
nitrite (11) on a Technicon Automatic Analyzer. The total phosphorus (12)
was determined by the persulfate method. All other analyses employed
Standard Methods (9). Soluble phosphorus and soluble BOD were filtered
through a standard glass suspended solids filter before analyses.
17
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SECTION V
PROCESS OPERATION AND PERFORMANCE
The pilot plant operation which started in May 1970 is still in progress.
This report covers only the first six months of operation which can be
divided into five operating phases. The different phases of operation
are described in the following discussion and tabulated in Table 2 for
easy reference. Table 3 summarizes the phase performances, and
Tables 4 and 5 show the weekly summary of data obtained.
Phase I (May 24 to July 17, 1970)
This was primarily a startup period. In two weeks, the mixed liquor
suspended solids (MLSS) had increased from 700 to 6000 mg/1 and the
influent flow increased to 65 gallons per minute (gpm). Sludge volume
index (SVI) averaged 35. However, on May 31, the biomass was lost
from the system when a waste sludge valve was inadvertently left
open. In rebuilding the mixed liquor solids, a filamentous culture
developed. By reducing the flow from 65 to 30 gpm, the filamentous
growth was eliminated and flow was gradually increased to 80 gpm
with a retention time of 1. 66 hours.
The clarifier, shown in Figure 2, was originally a peripheral feed clar-
ifier. The effluent from the UNOX reactor entered the feed channel
located on the periphery of the clarifier at one point and is distributed
by inlet ports at the bottom of the feed channel. With all the flow going
in one direction, it means that some of the flow has to travel 360°
around the clarifier which lessens the chance of equal distribution. In
addition, some of the inlet orifices were plugged, thus aggravating
any mal-distribution and causing short circuiting. This resulted in
relatavely high effluent suspended solids which averaged 43 mg/1.
Effluent BOD averaged 15 mg/1 at a biomass loading of 0. 28 Ib. BOD
per Ib. MLVSS. Average retention time was 2. 5 hours and clarifier
overflow rate averaged 770 gallons per day per square foot (GPDPSF).
Phase II (July 18 to August 13, 1970)
A steady flow of 75 gpm was maintained during this period of operation.
Retention time was 1. 8 hours. MLSS averaged 5200 mg/1 with biomass
loading averaging 0. 33 Ib. BOD per Ib. MLVSS. Solids retention time
(SRT) averaged seven days.
19
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TABLE 2
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
OPERATING PHASES
II
III
Period of Operation
May 24 to July 17, 1970
July 18 to August 13, 1970
August 14 to Sept. 30, 1970
IV
V
October 1 to October 25, 1970
October 26 to November 21, 1970
Mode of Operation
Steady flow varying from 30
to 80 gpm with peripheral-
feed clarifier
Steady flow of 75 gpm with
peri'pheral-feed clarifier
The peripheral feed clarifier was
modified to a center-feed clarifier
on August 14, 1970. Steady flow
of 75 gpm was maintained until
August 26, 1970 when a diurnal
flow pattern averaging 75 gpm was
initiated.
Alum addition with diurnal flow
averaging 75 gpm with center-
feed clarifier
Steady flow varying from 50 to
70 gpm with center-feed clarifier
20
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The peripheral feed clarifier showed a little improvement over Phase I
operation but effluent suspended solids averaged 36 mg/1 at an overflow
rate of 1000 GPDPSF. Effluent BOD averaged 18 mg/1 even though the
soluble effluent BOD was practically nil (see Tables 6 and 6A). With
better clarification, a lower effluent BOD could be achieved. It was de-
cided, therefore, to convert the peripheral feed clarifier to a centerfeed
clarifier because of the operation problems described in Phase I.
Phase III (August 14 to September 30, 1970)
The first two weeks of this phase was run at steady flow with the new
centerfeed clarifier. The flow was maintained at 75 gpm and when it was
apparent the system had stabilized, a diurnal flow pattern, shown in
Figure 4, was initiated. As shown, the reactor retention time varied
between 1.3 and 3.0 hours with an average of about 1. 8 hours. The
daily flow variation was normally from 45 to 105 gpm. This diurnal
pattern was the expected pattern for dry weather flow of the District of
Columbia's future plant.
MLSS averaged 5800 mg/1 with a volatile content of about 80 percent.
Biomass loading was 0. 30 Ib. BOD^ per Ib. MLVSS per day and solids
retention time averaged 10 days. Limited graduate cylinder tests showed
settling velocities greater than 8 feet per hour.
In modifying the peripheral feed to a centerfeed clarifier, the baffle
which extended 70 inches below the weir was left in place. In addition,
a relatively large centerwell was installed (see Figure 2) so that the
clarification zone available for upflow (the upper 70 inches of the
clarifier) had an area of only 78 square feet as compared to the total
area of 107 square feet in the thickening zone. Therefore, the clarifier
overflow rate was based on the area available for upflow while the
solids loading was based on the area available for thickening (107
square feet).
The clarifier overlow rate averaged 1380 GPDPSF during this phase
of operation with a peak of 1940 GPDPSF at the peak flow of 105 gpm.
As shown in Figure 4, the diurnal flow pattern includes a sustained
10 hour flow of 90 gpm giving an overflow rate of 1670 GPDPSF.
Clarifier mass loading varied from 40 to 100 Ib. per day per square
foot. At these high loadings, the recycle sludge averaged 1. 4 percent
suspended solids and effluent suspended solids averaged 24 mg/1.
Effluent BOD and COD were 15 and 50 mg/1, respectively, on the
average. Sludge retention time averaged 10 days.
24
-------
TABLE 6
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
BIOCHEMICAL OXYGEN DEMAND
Date
(wk.of)
5-24-70
5-31-70
6-7-70
6-14-70
6-21-70
6-28-70
7-5-70
7-12-70
7-19-70
7-26-70
8-2-70
8-9-70
8-16-70
8-23-70
8-30-70
9-6-70
9-13-70
9-20-70
9-27-70
10-4-70
30-11-70
10 18-70
10-25-70
11-1-70
11-8-70
11-15 70
Influent
Range
109-147
85-142
56-140
56-112
64-195
47-114
58-105
39-114
47-129
80-115
49-112
27-114
77-153
58-115
93-114
94-140
74-163
99-127
96-144
100-138
104-130
70-132
75-146
89-152
101-137
93-154
BOD5, mg/1
Average
130
129
102
88
109
89
77
86
94
98
72
80
112
86
101
107
102
107
119
124
117
100
121
120
120
128
Effluent BOD5, mg/1
Range Average
5-21
11-16
11-23
7-35
8-37
11-27
15-21
8-22
17-21
5-26
13-30
10-19
9-17
13-24
11-18
5-15
10-17
12-19
15-21
11-17
9-21
7-19
9-24
10-26
13-37
8-16
11
14
16
15
22
18
17
18
19
17
20
16
14
18
14
12
12
15
17
14
14
10
15
17
22
12
Average
Removal, %
92
89
84
83
80
80
78
79
80
82
72
80
88
79
86
89
88
86
86
89
88
90
88
86
82
91
25
-------
TABLE 6A
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
BIOCHEMICAL OXYGEN DEMAND
DATE EFFLUENT BODs . mg/1
8-11-70
8-25-70
8-26-70
9-1-70
9-15-70
9-21-70
9-28-70
9-29-70
11-2-70
11-9-70
11-10-70
11-16-70
11-17-70
11-23-70
11-24-70
TOTAL
17
16
18
11
11
19
15
15
12
37
25
9
11
27
SOLUBLE
0.2
0.1
1.9
1.2
nil
1.2
0.2
2.4
2.5
2.5
3.1
0.6
nil
nil
3.4
26
-------
Phase IV (October 1 to October 25, 1970)
During this phase of operation, alum was added in order to obtain
phosphorus removal. The same diurnal pattern as for Phase III was
maintained throughout this phase but due to inconsistency of the feed
pump, average daily retention varied from 1.9 to 2.3 hours with a
phase average of 2.05 hours.
Solid-liquid separation was improved by alum addition. The mixed
liquor suspended solids averaged 8000 mg/1 but the volatile fraction
decreased from 78 percent in Phase III to 66 percent. These relatively
high mixed liquor solids levels resulted in clarifier mass loadings
ranging from 75 to 120 Ib. per day per square foot (based on total
clarifier area of 107 square feet). The recycle sludge concentrations
went up to 3,0 percent with an average of 2.4 percent suspended
solids. The clarifier overflow rate during this phase averaged 1230
GPDPSF. Effluent BOD averaged 13 mg/1 and the removal averaged
about 90 percent. Soluble BOD remained very low indicating that
the alum did not hinder biochemical activity.
A summary of alum addition data is presented in Table 7. As noted,
the alum addition did not correspond to the variability of the phosphorus
feed. A rapid drop in mixed liquor pH was observed starting on
October 20, 1970. Poorly flocculated mixed liquor was observed at the
same time, resulting in poorer settling. This situation may have been
the result of an excessive alum dosage to the system. Therefore
alum addition was discontinued on October 25, 1970.
Phase V (October 26 to November 11, 1970)
Most of this phase was transitional operation. After alum addition
was stopped, flow was reduced to 50 gpm to allow the system to
stabilize and then gradually increased to 70 gpm. Mixed liquor sus-
pended solids were decreased to about 6000 mg/J. Volatile fraction
increased to about 70 percent. On the whole, retention time averaged
2. 19 hours and biomass loading was 0. 28 Ib. BOD/day/lbMLVSS and
a solids retention time of nine days was maintained. Solids wasting
averaged about 0. 2 Ib. solids per Ib. BOD removed.
Although this phase of operation was mostly transitional, good perfor-
mance was maintained. Effluent suspended solids was about 34 mg/1
and effluent BOD averaged 16 mg/1. Clarifier overflow rate remained
very high with an average of 1170 GPDPFS.
27
-------
TABLE 7
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
ALUM ADDITION
Phosphorus
Applied (as P)
Date
10/1/70
10/2/70
10/3/70
10/4/70
10/5/70
10/6/70
10/7/70
10/8/70
10/9/70
10/10/70
10/11/70
10/12/70
10/13/70
10/14/70
10/15/70
10/16/70
10/17/70
10/18/70
10/19/70
10/20/70
10/21/70
10/22/70
10/23/70
10/24/70
10/25/70
Ib/day
10.4
9.2
8.6
-
-
7.0
8.1
7.5
8.1
7.2
7.3
7.5
7.8
7.4
6.4
5.7
6.9
7.1
9.1
6.8
5.8
6.5
8.0
8.2
6.4
.
Alum Added
Ib/dav
11.1
79.6
78.1
134.4
124.6
116.5
92.5
147.5
117.5
94.0
135.5
22.0
102.0
63.5
105.5
112.5
60.0
82.5
56.0
64.5
108.5
116.7
112.1
97.0
127.5
Aluminum
Added
Ib/dav
1.0
4.5
7.0
12.1
11.2
10.5
8.3
13.3
10.6
8.5
12.2
2.0
9.2
5.7
9.5
10.1
5.4
7.4
5.0
5.8
9.8
10.5
10.1
8.7
11.5
Lb Aluminum
Added/
Lb Phosphorus pH
Applied
0.10
0.49
0.81
-
-
1.50
1.02
1.77
1.31
1.18
1.67
0.27
1.18
0.77
1.45
1.77
0.77
1.05
0.56
0.87
1.65
1.70
1.27
1.08
1.76
Units
6.6
7.2
7.3
6.5
6.1
6.35
6.8
6.7
7.1
6.9
6.0
6.2
7.1
6.6
7.45
6.3
7.3
7.3
6.7
6.1
6.5
6.2
6.2
5.8
6.0
% P
Removal
44
56
69
-
-
38
81
87
83
82
87
83
75
72
75
-
74
75
50
84
77
92
90
83
80
28
-------
Substrate Removals
A summary of the performance of the oxygen aeration system is shown
in Table 3. A good quality effluent was produced throughout the oper-
ation with weekly average residual BOD varying between 10 and 22
mg/1. The soluble residual BOD shown in Table 6 averaged less than
3 mg/1 indicating that most of the residual BOD in the effluent was
associated with the effluent suspended solids. When proper clarifi-
cation was provided, BOD removal averaged 92 percent with effluent
BOD being below 10 mg/1 90 percent of the time (see Figure 6).
The chemical oxygen demand (COD) removal varied between 66 and 85
percent with residuals between 36 and 138 mg/1. The removal of COD
was also dependent on the solids removal as evidenced by the results
which show that with low effluent solids, COD removal averaged 84
percent with residuals ranging from' 36 to 50
The effluent suspended solids were relatively high in the first six
months of this study partly because of excessively high overflow rates
that were maintained in the clarifiers. Overflow rates ranged between
600 GPDPSF at low flow periods to 1940 GPDPSF at high flow periods,
with a 10 hour period at about 1700 GPDPSF resulting in effluent solids
which averaged 20 to 40 mg/1. Since the completion of this program,
operation of the plant at lower overflow rates (700 GPDPSF with a peak
of about 1100 GPDPSF) has shown that effluent suspended solids can
be maintained consistently below 20 mg/1.
29
-------
TABLE 8
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
CHEMICAL OXYGEN DEMAND
Date
(wk. of)
5-24-70
5-31-70
6-7-70
6-14-70
6-21-70
6-28-70
7-5-70
7-12-70
7-19-70
7-26-70
8-2-70
8-9-70
8-16-70
8-23-70
8-30-70
9-6-70
9-13-70
9-20-70
9-27-70
10-4-70
10-11-70
10-18-70
rO-25-70
11-1-70
11-8-70
11-15-70
Influent
Range
215-448
200-279
114-302
194-288
205-322
211-337
214-359
169-255
162-304
180-278
202-258
181-297
247-306
208-369
187-337
179-316
220-289
239-284
132-305
259-366
256-330
247-388
248-470
226-337
214-321
241-372
COD, mg/1
Average
288
248
241
256
261
266
278
221
229
224
228
237
275
270
286
246
265
267
266
293
300
295
329
282
264
298
Effluent COD, mg/1
Range
33-51
18-59
24-60
35-40
31-50
55-80
35-128
45-164
21-78
37-94
32-84
16-59
36-61
39-86
29-57
37-57
34-98
39-54
35-87
41-169
40-129
33-117
51-264
46-94
61-128
23-60
Average
45
50
46
41
41
65
66
101
50
63
54
46
49
50
49
43
53
48
59
88
70
61
138
67
85
44
Average
Removal, %
84
80
81
84
84
76
76
54
78
72
76
81
82
81
83
83
80
82
78
70
77
79
58
76
68
85
30
-------
TABLE 9
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
SUSPENDED SOLIDS
Date
(wk. of)
Influent Suspended
Solids, mg/1
Effluent Suspended
Solids, mg/1
5-24-70
5-31-70
6-7-70
6-14-70
6-21-70
6-28-70
7-5-70
7-12-70
7-19-70
7-26-70
8-2-70
8-9-70
8-16-70
8-23-70
8-30-70
9-6-70
9-13-70
9-20-70
9-27-70
10-4-70
10-11-70
10-18-70
10-25-70
11-1-70
11-8-70
11-15-70
Range
TSS
74-970
104-168
46-116
92-146
88-138
61-468
78-208
90-162
8-132
60-122
80-148
76-122
68-111
58-126
70-136
78-158
80-126
68-136
86-116
82-110
86-214
100-156
74-124
76-184
56-128
86-102
Average
TSS
253
127
94
115
115
149
114
114
89
91
111
100
102
80
115
112
98
104
103
99
157
121
101
130
92
92
vss
121
87
96
79
92
68
72
82
67
67
78
80
80
52
88
77
73
82
84
83
117
75
77
85
72
72
Range
TSS
5-78
7-31
21-77
12-96
14-66
23-101
15-110
22-122
10-71
14-64
10-78
14-30
8-34
16-38
12-39
7-40
10-62
16-26
21-30
9-24
25-91
10-53
30-224
14-68
30-100
13-21
Average
TSS
33
22
45
32
31
51
44
75
34
45
42
21
21
25
23
22
27
23
25
18
46
36
86
39
56
16
VSS
10
12
17
15
22
23
25
50
19
29
29
15
15
17
16
13
18
18
20
12
32
21
49
34
39
8
Average TSS
Removal, %
87
83
52
72
73
66
61
34
62
51
62
79
79
69
80
80
72
78
76
81
71
70
15
70
39
83
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Nutrient Removals
Nitrogen
In the warmer periods of the year (July to October) 70 to 90 percent of the
total Kjeldahl nitrogen (TKN) was removed as compared to about 30 percent
for the rest of the year. The increase in effluent nitrate during the period
of high TKN removal showed that the increased removal was due to nitri-
fication which occurred mostly at solids retention time of eight days or
higher. This is in accord with various other work that has been done on
nitrification and shows the ability of the pure oxygen system to nitrify
as well as a conventional activated sludge system.
Phosphorus
In October 1970, alum was added to the fourth stage mixed liquor so that
the phosphorus present in the wastewater could be removed by precipita-
tion as phosphates. After the initial startup of this phase, phosphorus
removals increased to about 80 to 90 percent. This removal was achieved
at an alum dosage of about 1. 4 to 1. 8 lb. aluminum added to 1 Ib. phos-
phorus present in the wastewater. Figure 8 shows the effect of alum
dosage on phosphorus removal. It is apparent from Figure 8 that in order
to maintain a 90 percent removal, about 1.8 lb. aluminum must be added
for every pound of phosphorus present in the waste. The addition of
alum, however, causes about 40 percent increase in the sludge production,
and sludge wasting must be adjusted to accommodate this extra sludge pro-
duction. It was observed that there was a rapid drop in the mixed liquor
pH from about 6. 7 on October 19, 1970 to 6. 0 by October 25. This
may have been caused by an excessive dosage of alum to the system.
This resulted in a dispersed biomass. Thus, alum addition was stopped to a
allow the mixed liquor to recover.
Biomass Characteristics
The mixed liquor suspended solids were similar visually to the micro-
organisms in conventional activated sludge. The mixed liquor biota
was normally very well bioflocculated with active stalked ciliates
growing on the bacterial mass. Zooflagellates and free swimming
ciliates, although few in number, remained adjacent to or within the
flocculated particles. Several varieties of large active rotifiers were
plentiful. A few nematodes existed in the sludge. Normally, fila-
mentous growth was not apparent. There was almost a complete
absence of fragmented debris or unflocculated bacteria between the
discrete particles.
36
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Sludge Production
The total sludge production per pound of BOD applied, including the
waste and effluent solids, was directly related to the solids retention
time (SRT). The solids production in the pure oxygen system decreased
with increasing SRT while the solids production in the step aeration
sludge system increased with SRT up to 9.5 days and then started to
decrease. At an SRT of 6 days or higher, the solids production in the
pure oxygen system was significant, y lower than in the step aeration
system. Solids production at 9.5 days SRT was at a maximum of one
pound solids per pound BOD applied for the step aeration system
compared to 0.5 pound solids per pound BOD applied for the oxygen
system. Indeed, the total solids production decreased to 0.35
pounds solids per pound BOD applied at an SRT of 13 days in the
pure oxygen system. The initial increase in solids production of
the step aeration system was due to increased BOD removals
by assimilation into the biomass.
Organic Loading
The performance of the pure oxygen system has amply demonstrated
the ability of this system to operate efficiently at various loading con-
ditions. Through this period of operation, effluent BOD has been main-
tained consistently below 20 mg/1. The soluble effluent BOD was
negligible indicating extensive endogenous activity. This means that
the system could have been operated successfully at biomass loadings
higher than the 0. 5 Ib. BOD/day/lb. MLVSS that was experienced during
this operation. As has been noted before, it is apparent that complete
assimilation of BOD into the biomass is achieved even at low retention
times. Sludge production was very low because of the auto oxidation
resulting from endogenous activity.
Oxygen Utilization
Consistently over 90 percent of the feed oxygen was utilized
throughout this pilot plant operation. The vented stream usually
contained 50 percent oxygen or less.
The oxygen consumption ratios shown in Tables 3 and 4 are very high
compared to other available data on oxygen systems. This is due to
a combination of the following factors:
1. The System operated at relatively low loading rates which resulted
in extensive endogenous respiration.
38
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TABLE 11
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
SOLIDS BALANCE
Date
CWk. ofl
7/5/70
7/12/70
7/19/70
7/26/70
8/2/70
8/9/70
8/16/70
8/23/70
8/30/70
9/6/70
9/13/70
9/20/70
9/27/70
10/4/70
10/11/70
10/18/70
10/25/70
11/1/70
11/8/70
11/15/70
Influent
Solids,
Effluent
Solids,
Waste
Ib/day Ib/day lb/
SS
102.5
90.3
82.0
82.4
102.3
87.6
91.0
70.5
99.4
95.9
86.1
92.5
89.9
86.2
124.8
99.3
80.4
91.7
69.5
91.7
VSS
64.3
64.5
62.7
60.8
72.2
69.7
71.2
46.0
75.7
66.0
64.1
72.0
70.8
22.1
93.3
61.2
61.3
60.6
53.4
58.2
SS
39.5
57.9
32.1
35.9
38.9
18.7
18.5
21.8
19.7
18.6
23.1
20.0
22.2
15.3
35.7
29.5
67.9
29.0
40.6
12.9
VSS
22.7
38.5
17.1
26.1
27.1
12.9
13.1
15.1
13.6
11.0
15.8
15.9
17.2
15.3
24.4
17.6
38.1
25.3
27.9
6.2
ss_
0
20.7
12.3
35.9
28.5
14.6
9.2
34.6
17.3
27.2
23.6
26.2
67.3
67.8
98.5
-
4.5
33.1
14.0
Solids ,
'day
VSS
_
0
12.5
8.6
23.0
21.7
8.6
7.1
25.9
13.5
21.5
19.0
21.1
47.4
45.5
64.1
-
3.1
24.3
10.2
Solids Accumulation
lb TSS/
lb BODp
.
1.03
0.76
0.65
1.56
0.99
0.38
0.51
0.72
0.44
0.65
0.54
0.54
0.88
1.28
1.72
-
0.44
1.02
0.28
lb TSS/
lb CODR
• A
0.62
0.31
0.47
0.33
0.16
0.16
0.26
0.21
0.26
0.27
0.23
0.27
0.47
0.57
0.66
-
0.21
0.57
0.13
39
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2 . There was nitrification which accounted for some of the extra
oxygen. It should benoted that about 4.6 Ibs. of oxygen is required
to convert 1 Ib. of nitrogen to nitrate.
3. Leakages were found at various times during the operation and
Table 13 shows that it amounted to 8 to 20 percent of the oxygen
required by COD balance (assuming COD =1.4 volatile suspended solids
because COD analysis of the waste sludge was not done) .
Table 12 shows consumption ratio on the basis of applied BOD and COD.
Table 13 shows that oxygen supplied was more than required by
theoretical calculation using a COD balance. It can be seen from Table 12
that as the study progressed, the oxygen requirement decreased. This
was due to the fact that the endogenous respiration decreased and
nitrification decreased with decreasing temperature.
Clarifier Performance
The purpose of this section of this report is to present, in a nut shell, a
detailed report of the clarifiers that were employed with the oxygen acti-
vated sludge system.
Initially, a peripheral feed clarifier was used. The clarifier influent
entered the influent channel at one point and was directed one way all around
the clarifier to distribute the flow. However, since some flow is imme-
diately introduced into the clarifier upon entering the influent channel,
while some of the flow had to go all the way around the clarifier in the
influent channel before entering the clarifier, the hydraulic distribution
through the clarifier is likely to be uneven. This will result in poor
clarification which was observed in the first two phases of operation
when this clarifier was used.
When the clarifier was converted to a centerfeed, the clarification im-
proved as evidenced by the decrease in the effluent suspended solids
concentration in the last three phases of operation covered in this report.
The initial clarifier design necessitated a baffle that extended 70 inches
below the weir all around the clarifier as shown in Figure 2. When the
clarifier was modified, this baffle was left in place with the result that
the area available for upflow (in the clarification zone) was only 78
square feet while the total area of the clarifier was 107 square feet.
This reduction in clarification area means that the average flow rates
were 1000 to 1300 GPDPSF in the clarification zone. During periods
of diurnal flow variations, a peak overflow rate of 1940 GPDPSF was
sustained for 2 hours and 1700 GPDPSF was sustained for 10 hours. Even
at these high overflow rates, the average effluent suspended solids were 24,
33, and 34 mg/1 respectively, during phases III, IV and V.
40
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TABLE 12
PURE OXYGEN SYSTEM
BLUE PLAINS WASTE TREATMENT PLANT
OXYGEN CONSUMPTION
Date
(Week of)
7/5/70
7/12/70
7/19/70
7/26/70
8/2/70
8/9/70
8/16/70
8/23/70
8/30/70
9/6/70
9/13/70
9/20/70
9/27/70
10/4/70
10/11/70
10/18/70
10/25/70
11/1/70
11/8/70
11/15/70
Lb O2/lb BODA
2.19
1.77
2.06
2.38
2.85
2.98
1.90
2.39
2.12
2.03
2.15
2.23
1.89
1.65
1.79
1.61
1.16
1.30
1.16
1.32
Lb O2/lb CODA
0.60
0.72
0.90
0.98
0.76
0.76
0.74
0.88
0.82
0.89
0.84
0.70
0.69
0.55
0.43
0.55
0.53
0.56
41
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Subsequent operation of the pilot plant which will be reported on
separately soon, showed that at more conventional overflow rates
(700 gpdpsf average and 1100 gpdpsf maximum) a suspended solids
effluent concentration below 20 mg/1 can be consistently maintained.
This has been documented in the paper presented by J. B. Stamberg,
D. F. Bishop, and G. W. Kumke. (14)
The total clarifier area (107 sq. ft.) was used to compute the solids
loading in the clarifier. The loadings varied from 40 to 60 Ibs . per
day per square foot at average condition with peak loads of 70 to
90 Ibs. solids per day per square foot.
Clarifier underflow concentrations averaged 1.4 percent solids nor-
mally and increased to 2.2 percent during the period of alum addition,
Subsequent operation of this pilot plant at lower overflow rates have
shown clarifier underflow concentrations of 2.0 to 2.7 percent as
reported by John B. Stamberg, et al 03).
These results show the excellent solid-liquid separation character-
istics of the pure oxygen system. As a result, the mixed liquor
suspended solids of 5000 to 7000 mg/1 were maintained. Further
work is in progress to evaluate the effect that temperature may have
on solid-liquid separation.
44
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SECTION VI
ACKNOWLEDGEMENTS
This project was conducted under the auspices of the Linde Division
Development and Engineering Facilities at Tonawanda, New York
(M.L. Kasbohm - Director) and the Federal Water Pollution Control
Association, Department of the Interior, Washington, D.C.
In the course of this project, the efforts of F.D. Bishop, Project
Officer, and his staff at the Blue Plains Waste Treatment were greatly
appreciated.
45
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SECTION VII
REFERENCES
1. Pirnie, M. , Presentation at Twenty-First Annual Meeting of Sewage
Works Associations, Detroit, Mich. , October 18-21, 1948.
2. Okun, D. A. , Sewage Works Journal, 21. (1949).
3. Budd, W. E. , and Labeth , G. F. , Sewage and Industrial Waste,
29., 253 (1957).
4. Okun, D. A. , and Lynn, W. R. , "Preliminary Investigation into
the Effect of Oxygen Tension on Biological Sewage Treatment,"
in "Biological Treatment of Sewage and Industrial Wastes: Vol. I,
Aerobic Oxidation," Reinhold Publishing Corp. , New York (1956).
5. Okun, D. A. , Sewage and Industrial Wastes, 29 , 253 (1957).
6. McKinney, R. E. , and Pfeffer, J. T. , Water and Sewage Works,
October (1965).
7. Alberts son, J. G., McWhirter, J. R. , Robinson, E. K. and
Vahldieck, N. P., "Investigation of the Use of High Purity
Oxygen Aeration in Conventional Activated Sludge Process ,"
FWQA Department of the Interior Program No. 17050 DNW,
Contract No. 14-12-465, May (1970).
8. Stamberg, John B. , Bishop, Dolloff F. ,Kumke, G. W., "Activated
Sludge Treatment with Oxygen", AIChE Sym. Series 124, Vol.68, 1972
9. "Standard Methods for the Examination of Water and Wastewater,"
12th Edition, American Public Health Association, New York,
(1965).
10. "FWPCA Methods for Chemical Analysis of Water and Wastes ,"
U. S. Department of the Interior, Federal Water Pollution Control
Administration, Cincinnati (November 1969).
11. Kamphake, L. Hannah, S., and Cohen, J. , Water Resources, j^,
205 (1967).
12. Gales, M. , Julian E. , and Kroner, R. , Journal of American
Waterworks Association, 58., 1363 (1966).
47
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REFERENCES CONTD.
13. Stamberg, John B., et al, "Systems Alternatives in Oxygen
Activated Sludge", presented at the 1972 WPCF Conference
at Atlanta, Ga.
48
«U.S. GOVERNMENT PRINTING OFFICE-1974 546-318/378 1-3
-------
SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
w
4, Tn!c
ACTIVATED SLUDGE PROCESS USING PURE OXYGEN
Wilcox, Edward A. and Akinbami, Samuel 0.
UNION CARBIDE CORPORATION
Linde Division
P.O. Box 44
Tonawanda, New York 14150
11010 FRN
14-12-846
aal- "'
Environmental Protection Agency Report, EPA-670/2-73-042, February 1974.
The oxygen activated sludge system (UNOX) consisted of a unique, four stage,
gas tight biological reactor that employed co-current gas-liquid contacting.
In less than 1.85 hours of oxygenation, the system removed 90 percent of the
influent 6005 and utilized over 95 percent of the supplied oxygen. The
microbial organisms visually were essentially the same as those found in a
typical conventional system. Their rate of activity, however, was greater
than those of the air system. Satisfactory solid-liquid separation was
achieved at clarifier overflow rates varying between 300 and 1940 gallons
per day per square foot. The clarifier underflow concentrations varied from
1.0 to 2.4 percent and mixed liquor suspended solids were maintained between
4000 and 7600 mg/1. Solids production averaged between 0.2 and 0.5 lb,_
solids wasted per Ib. BOD removed.
17s. Descriptors
* Oxygen Requirements
Activated Sludge
Micro-organism
BOD Sedimentation Rates
17b Identifiers
* Oxygen Activated Sludge
Plug Flow Reactor
Mixed Liquor
Alum Addition
Phosphorus Removal
05D
* Dissolved Oxygen
Endogenous Respiration
Sludge Production
Se&tttitg Cletss,
22, Pnte*
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
US DEPARTMENT OF THE INTERIOR
WASHINGTON, D C 2O24O
Dolloff F. Bishop
Environmental Protection Agency
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