Environmental Protection Technology Series
ALUM ADDITION AND STEP-FEED STUDIES
IN OXYGEN-ACTIVATED SLUDGE
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
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The nine series are:
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3. Ecological Research
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This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
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provides the new or improved technology required for the control and treatment
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This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-77-166
September 1977
ALUM ADDITION AND STEP-FEED STUDIES
IN
OXYGEN-ACTIVATED SLUDGE
by
Dolloff F. Bishop, James A. Heidman, Richard C. Brenner
and
John B. Stamberg
EPA-DC Pilot Plant
Washington, D.C. 20032
Contract No. 68-01-0162
Project Officer
Dolloff F. Bishop
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
This study was conducted in cooperation
with
the Government of the District of Columbia
Department of Environmental Services
Washington, D.C. 20004
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recommendation for use.
11
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FOREWORD
The Environmental Protection Agency was created because of increasing public
and government concern about the dangers of pollution to the health and
welfare of the American people. Noxious air, foul water, and spoiled land
are tragic testimony to the deterioration of our natural environment. The
complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution and
it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment, and management
of wastewater and solid and hazardous waste pollutant discharges from muni-
cipal and community sources, for the preservation and treatment of public
drinking water supplies, and to minimize the adverse economic, social, health,
and aesthetic effects of pollution. This publication is one of the products
of that research; a most vital communications link between the researcher and
the user community.
The use of pure oxygen in the activated sludge process for removal of organic
pollutants from wastewater and thus from the aqueous environment is being
employed in an increasing number of treatment plants. This work describes
firstly the use of mineral (alum) addition within the oxygen-activated sludge
process to increase the removal of the phosphorus nutrients from the waste-
water and secondly, an alternate process configuration for contacting the
oxygen and the wastewater.
Francis T. Mayo
Director
Municipal Environmental Research Laboratory
iii
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ABSTRACT
A plug flow, (^-activated sludge process was operated with alum addition to
remove phosphorus and with lime addition to prevent the process pH from
decreasing below 6.4. The G£ reactor was operated at F/M ratios between
0.18 to 0.24 gm of BOD5/gm of MLVSS/day with the SRT varying from 4.7 to 6.0
days in a typical co-current C^-liquid contacting system.
The average alum (Al2(804)3 ' -^ H2°) dosages for the five steady-state
operating periods increased from 84 mg/1 to 184 mg/1 with the M/P weight
ratios increasing from 1.1 to 2.66. The amount of lime required to maintain
the process pH at 6.4 or above varied from 15 mg/1 to 58 mg/1 as CaO. The
lime demand was related to both the alum addition and to partial nitrification
occurring in the oxygen reactor.
The pollutant removals from the primary effluent ranged from 82 to 92% for
BOD5 (7.4 to 19 mg/1 of residual BOD5), from 52 to 84% for suspended solids
(17 to 56 mg/1 of residual SS), and from 54 to 86% for phosphorus (1.05 to
3.26 ™g/l of residual P). The optimum P removal occurred at a 1.8 to 1
average Al/P ratio with an average total residual P of 1.05 mg/1.
In a second study, the 02 process was operated in a step-feed configuration
consisting of a sludge oxygenation stage followed by three stages of oxygen
aeration with equal portions of the primary effluent fed to each stage. In
typical operation, the process with a F/M ratio of 0.23 exhibited a MLSS
concentration profile in the four stages of 10,700 mg/1; 7,060 mg/1; 5,020
mg/1; and 4,150 mg/1. The step configuration clearly reduced the solids
loading to the clarifier and provided an average process MLSS of more than
6,500 mg/1.
The step operation produced excellent BOD^ removals (89% from the primary
effluent) with an effluent BOD5 of 10 mg/1 and a soluble (filtered) effluent
BOD5 of less than 3 mg/1. The COD and suspended solids residual averaged
43 mg/1 and 23 mg/1, respectively.
Oxygen balances, based upon inlet and outlet 02 measurements and alternately
upon 02 uptake rates and upon the amount of 02 in the outlet gas, revealed
an 02 usage of approximately 50%. The 02 usage in the step configuration was
significantly less than the 90% typically achieved in co-current contacting.
This report was submitted in partial fulfillment of Contract No. 68-01-0162 by
the government of the District of Columbia, Department of Environmental Services
under the sponsorship of the U.S. Environmental Protection Agency. This report
covers experimental work conducted during the period October 1972-October 1973.
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CONTENTS
Foreword iii
Abstract , . iv
List of Figures vi
List of Tables vii
Acknowledgements viii
1. Introduction 4
2. Conclusions 1
3. Recommendations 3
4. Pilot System 6
5. Analytical Procedures 8
6. Alum Addition Studies 9
7. Step-Feed Studies 21
References 30
Publications 31
v
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FIGURES
Number Page
1 Oxygen Aeration System 7
2 Phosphorus Removal by Alum Addition in
(^-Activated Sludge 14
3 Initial Settling Velocities of Oxygen MLSS as a
Function of Concentration 16
4 Typical Step-02 MLSS Settling 23
5 D.O. Uptake as a Function of Time-Stage No. 1 and 2 27
6 D.O. Uptake as a Function of Time-Stage No. 3 and 4 28
vi
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TABLES
Number Page
1 Reactor Operating Conditions for (^-Activated Sludge
with Alum 10
2 Clarifier Operation and Sludge Production of 02~Activated
Sludge with Alum Addition 11
3 Effluent Quality of 02~Activated Sludge with Alum Addition 13
4 Settling Rates for 02-Activated Sludge with Alum Addition 15
5 Filtration System on Alum-Qr, Secondary Effluent 18
6 Filter Performance on Alum-0« Secondary Effluent 19
7 Step-Feed, 02~Activated Sludge Operating Conditions 22
8 Initial Settling Velocities of Step-Feed,
02-Activated Sludge 24
9 Step-Feed, 02-Activated Sludge Effluent Quality 25
vii
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ACKNOWLEDGEMENTS
The assistance of the operators, technicians and laboratory staff at the
EPA-DC Pilot Plant is gratefully acknowledged.
viii
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SECTION 1
INTRODUCTION
The oxygen-activated sludge process with more than 90% utilization of oxygen
has developed in recent years into a significant competitor with conventional
aeration for removal of BOD,- from xvastewater. The process has been studied
since 1970 at the EPA-DC Pilot Plant1'2 in Washington, D.C.; the study has
revealed several advantages over conventional aeration.
The high oxygen transfer rates with pure Q^ produce high dissolved oxygen (D.O.)
concentrations and permit the use of high mixed liquor concentrations and thus
small reactors. The high D.O. in the reactor minimizes periods of lowD.O.,
such as occur in clarification, and increases Oo transfer into the center of
the sludge mass. The process exhibits apparently higher metabolic rates and
good resistance to shock organic loadings. The high oxygen transfer rates
provide process flexibility for minimizing sludge production through easily
increased endogenous respiration in the reactor.
In evaluating oxygen applications, the process stability and reduced reactor
size must be weighed against the cost of the oxygen and the mechanical systems
employed in its utilization. In addition, the increased mixed liquor concen-
trations possible in the oxygen process increases the mass loading on the
clarifier, which increases clarifier size. Finally, sludge reduction through
increased endogenous respiration requires a stoichiometric amount of 02 for
each unit amount of COD destroyed. The final design of the oxygen process and
its solids-handling system requires the consideration and balancing of these
factors with the ultimate cost benefit to be fully determined in the market
place over the next few years.
With the current usage of the 02~activated sludge process, consideration of
its compatibility with other wastewater treatment processes and development of
techniques to reduce mass loading on the oxygen clarifier are needed. In pre-
vious work, alum addition1 to remove phosphorus (Equation 1) was applied to
the Q£ process on a wastewater of moderate alkalinity (130 mg/1 as CaCO-j).
With the recirculation of 0^ within each reactor stage, the CO™, increasing in
recirculated process gas, normally suppressed the Washington, B.C. effluent pH
to a range of 6.4 to 6.6 without alum addition. In the study with alum addi-
tion, the Al/P weight ratio was incrementally increased from 1.1:1 to 1.85:1
during a period of approximately one month. At an Al/P weight ratio of 1.85:1,
the acid produced (Equation 2) by the hydrolysis of excess Al further
reduced the 02 process wastewater pH from its normal 6.4 to 6.6 range to less
than 6.0.
Al + P04 -> A1P04 (1)
3HOH -» A1(OH)3 + 3H+ (2)
1
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At the low pH, the process immediately removed more than 90% of the P
but within three days exhibited a dispersion of the biological and chemical
solids into the final effluent. At a 1.4:1 Al/P ratio, the process waste-
water pH and alkalinity decreased only slightly and the bio-mass dispersion
did not occur but the alum addition removed only 80% of the P. During the
alum addition, the chemical precipitates increased the amount of solids in
the reactor and the solids loading to the final clarifier.
Therefore, two studies on the activated sludge process were
performed at the EPA-DC Pilot Plant: one, to further evaluate alum addition
for phosphorus removal using lime for pH control; the other, to evaluate a
step-feed configuration without mineral addition to reduce the solids loading
to the final clarifier.
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SECTION 2
CONCLUSIONS
ALUM ADDITION STUDIES
In earlier work with alum addition in the oxygen-activated sludge process on
D.C. wastewater, increasing the Al/P dosage weight ratio to 1.85:1 depressed
the process pH from approximately 6.4 to below pH 6. Within three days, the
process exhibited a dispersion of both chemical and biological solids into
the process effluent. In the current study on alum addition for phosphorus
removal, lime slurry added to the influent wastewater maintained the effluent
pH above 6.4 and prevented sudden dispersion of the biological and chemical
solids in the clarifier.
The alum addition in the oxygen-activated sludge process, evaluated at four
average levels of Al/P dosage weight ratios (1.1:1, 1.45:1, 1.8:1, and 2.66:1),
produced a maximum phosphorus removal of 86% at the 1.81 Al/P weight ratio.
At the 1.8:1 Al/P weight ratio, the process exhibited maximum removals of
BOD5 (92%) and suspended solids (84%), with an average BOD5 residual of 7.4
mg/1 and a suspended solids residual of 17 mg/1.
At an average Al/P weight ratio of 2.66, the process exhibited a gradual in-
crease of nonbiological solids in the process effluent. The excessive amounts
of Al (OH)-} accumulated during 14 days of operation gradually increased
clarifier instability and forced discontinuance of the alum feed.
The average lime dose required to maintain the process pH of 6.4 was 15 and
37 mg/1 at respective Al/P weight ratios of 1.8 and 2.66:1. Based upon a 1:1
molar Al/P requirement for precipitation of the phosphorus, these lime dosages
corresponded approximately stoichiometrically to the milli-equivalents of acid
produced by the hydrolysis of excess Al"1"^" ions to A1(OH)_.
Lime dosages above the stoichiometric requirements for hydrolysis of excess
Al"*""*"^ ions were also required to neutralize the HNO^ produced when the process
was partially nitrifying.
Solids production of 02~activated sludge with alum addition increased over
that for operation of the biological process without mineral addition. During
operation with Al/P weight ratios ranging from 1.1:1 to 2.66:1 and for an
overall Al/P weight ratio of 1.53:1, the solids production averaged approxi-
mately 1.34 gm of solids per gm of applied BODtj, of which 0.99 gm of solids
per gm of applied BODr was in the wasted sludge.
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STEP-FEED STUDIES
The 02~activated sludge process operated in a step-feed configuration, as when
operated in the conventional "plug" flow configuration, removed essentially
all soluble substrate, with the soluble effluent BOD 5 averaging less than
3 mg/1.
The step-feed configuration exhibited a MLSS profile that decreased from
nearly 10,000 mg/1 in the first stage to about 4,000 mg/1 in the fourth stage
and averaged 6,500 mg/1. The 4,000 mg/1 MLSS in the fourth stage produced a
desirable and modest solids loading [clarifier flux of about 115 kg/d/m
(23 Ib/d/ft )]. Thus, the step-feed configuration permitted a high average
MLSS without a high flux loading to the clarifier.
The step-feed configuration for the 0? process, however, achieved only a 50%
utilization of the C>2 gas feed compared to the typical 90% utilization for
the "plug" flow configuration. If further work confirms the 50% G£ utilization
efficiency, the step-feed configuration will not be an economical alternative
in the 0?-activated sludge process as practiced at the EPA-DC Pilot Plant.
The solids production in the step-feed configuration at an SRT of approxi-
mately 11 days was 0.5 gm of solids produced per gm of applied BOD-, with
approximately half of the solids production leaving the process in the
secondary effluent.
The Deactivated sludge process in the step-feed configuration produced
approximately 70% nitrification of the TKN at an SRT of 11 days and removed
approximately 40% of the total nitrogen.
The settling velocities of oxygen-activated sludge mixed liquor in the step-
feed configuration were good. At a MLSS of approximately 4,000 mg/1, the
solids exhibited initial settling velocities of 5.2 m/hr (17 ft/hr) which was
typical of summer time settling of 0~-activated sludge solids.
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SECTION 3
RECOMMENDATIONS
ALUM ADDITION STUDIES
In the study, the oxygen-activated sludge system functioned satisfactorily at
an average alum dosage (Period 3) which corresponded to an Al/P weight ratio
of 1.8. Increasing the average alum dosage to correspond to an Al/P weight
ratio of 2.66 (Period 4), even with pH control, produced a gradual process
failure. In addition, without continuous phosphorus analyses on the primary
wastewater, the control of the daily and instantaneous Al/P ratio was not
very good. Thus, the process behavior and the lower limit of the effluent
residual P concentration needs further study in a system with effective
instantaneous Al/P dosage control at Al/P weight ratios between 1.8 and 2.66.
STEP-FEED STUDIES
While the step-feed configuration on the oxygen-activated sludge process
reduced the mass loading to the final clarifier and also achieved efficient
BOD,- removal, the observed poor oxygen utilization efficiency would prevent
in the step-feed configuration practical applications of the oxygen contacting
system employed in the EPA-DC Pilot Plant. Confirmation of the observed
oxygen utilization efficiency is needed. Work on alternate oxygen contacting
approaches should also be performed to determine if practical (reasonable
oxygen utilization) operations can be achieved for an oxygen step-feed acti-
vated sludge configuration.
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SECTION 4
PILOT SYSTEM
In the EPA-DC Pilot Plant, the oxygen-activated sludge equipment (Figure 1)
consisted of a four-stage reactor of 30.5 nr* (8,080 gallon) liquid volume,
and two center-feed gravity settlers with 7.25 m^ (78 ft^) of clarification
area in each settler and water sidewall depth of 3.4 m (11.1 ft.). The gas-
tight reactor included submerged hydraulic entrances and exits with water
seals where the mixing equipment enters the reactor.
The reactor was divided into four mixing stages. Oxygen was introduced into
the first stage; its flow controlled by a pressure regulator to maintain a
pre-selected reactor gas pressure, usually between 2.54 cm (1 inch) and
9.16 cm (4 inches) of water. The oxygen flowed from the first through the
fourth stage and for normal "plug" flow operation was co-current to the mixed
liquor flow. Compressors on each stage recirculated the overhead gas through
a rotating diffusion-impeller to provide mixing of the bio-mass and to disperse
the recirculating gas. Variations in the compressor recirculation rate,
selected manually by the operator, were used to control the dissolved oxygen
level for plug flow between 4 and 8 mg/1.
In the center-feed settlers, two sludge withdrawal mechanisms were employed:
one settler mechanism employed a hydraulic syphon; the other, a. conventional
plow to force the sludge into a central sludge well. Sludge recirculation
was achieved by variable-speed Moyno sludge pumps.
In the study of mineral addition, the reactor was operated with various
diurnal flow patterns in a "plug" flow configuration with District of Columbia
primary effluent as the process feed. Lime slurry was added to the wastewater
at the reactor influent and alum was added at the reactor discharge. The lime
slurry dosage was controlled in a flow-proportioned (feedforward), pH error
(feedback) analog control loop by a submerged pH probe located in the first
reactor stage. The pH set point was manually altered by the operator to main-
tain the final process effluent pH in the range of 6.3 to 6.8. The manually-
selected alum dosage was proportioned to flow by using a pneumatically
controlled metering pump.
In the step-feed study, the District of Columbia primary effluent was divided
by a splitter box into three separate equal streams and pumped at a steady
flow into the last three stages of the reactor. Alum was not added to the
process. In the step-feed study, the 02 reactor employed the normal contacting
procedures and gas flow configuration.
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02
O2 RECYLE
•1
l
i
INFLUENT
db
ob
cb
SLUDGE RECYCLE
••-EXHAUST GAS
JT
I L
EFFLUENT
WASTE
Figure 1. Oxygen aeration system.
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SECTION 5
ANALYTICAL PROCEDURES
In the evaluation of the process performance, BOD samples were always
manually composited proportional to flow over a 24-hour period. All other
appropriate samples were composited for 24-hour periods on Tuesday through
Thursday and for 48-hour periods on Friday through Monday. All samples
were stored at 3°C to minimize biological activity. All samples except
for BOD and suspended solids were also acidified with 1 ml of t^SO^ per
600 ml of sample.
The 5-day biological oxygen demand (6005) of the composite samples was de-
termined by means of the probe method^; the ammonia^ and nitrate-nitrite^
by use of a Technicon Automatic Analyzer. The total organic carbon (TOC)
was measured on a Beckman Carbonaceous Analyzer. The total phosphorus" was
determined by means of the persulfate method. All other analyses employed
Standard Methods^. Soluble phosphorus and soluble BOD were filtered through
a standard-glass suspended-solids filter before analyses.
Batch settling tests on the process mixed liquor were periodically conducted
in a stirred 15.3 cm (6-inch) diameter by 3.3 m (10 feet) long "plexiglas"
settling column. The slope of the interface height versus time provided
the initial settling velocity of the mixed-liquor suspended-solids con-
centration at the existing wastewater temperature.
Dissolved oxygen uptake rates on samples of the mixed liquor from various
reactor stages were conducted as appropriate. In the test, the mixed
liquor sample, usually with 4 to 8 mg/1 of D.O., was placed in a
standard BOD bottle; and the dissolved oxygen concentration was continuously
measured with a D.O. meter as a function of time. The oxygen uptake rate
was then calculated as the slope of the D.O. versus time plotted for the
mixed liquor solids concentration in the sample.
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SECTION 6
ALUM ADDITION STUDIES
The operation of the process during alum addition studies was divided into
five operating periods (Table 1) and a two-week period in February (period 4a
and 4b) for correcting an accumulation of excess solids in the clarifier. The
combination of reactor contact time and average MLVSS provided relatively
constant F/M (0.18 to 0.24 gm of BOD5/gm of MLVSS/day) and SRT (4.7 to 6.0
days) operation during the five operating periods. The diurnal flows (Table 2)
were usually varied for an approximate 1.5:1 peak to average flow ratio,
although in November the variation was 2:1 and in December 1.2:1. During the
study, the influent pH averaged 7; the effluent pH was maintained at or above
pH 6.4 with the addition of lime slurry.
During the first four periods, the average alum dose was increased from a 1.1
to a 2.66 Al/P weight ratio. During the last period (March 1-20), the Al/P
weight ratio was averaged at 1.78. Surprisingly, the lime dosage (Table 1)
decreased with increasing alum dosages in the first four periods. Actually, in
the first period (November) with little excess Al ions, HN03 production by
nitrification within the 02 process produced part of the lime demand. In
December, a combination of partial nitrification, an elevated effluent pH of
6.7 with corresponding C02 neutralization (the normal operating pH is approxi-
mately 6.4 for Oo-activated sludge in Washington, D.C.), and the hydrolysis
of the excess Al ions (Equation 2) all contributed to the 58 mg/1 CaO dosage.
In January, the elevated pH of 6.6 and the hydrolysis of the excess Al ions
determined the lime requirement.
In the last two periods (February 1-14 and March 1-20) with the effluent pH at
6.4 and without nitrification, the lime dosages (15 ing/1 of CaO at a 1.78 Al/P
ratio and 37 mg/1 at a 2.66 Al/P ratio) corresponded almost stoichiometrically
to the amount of acid produced by the hydrolysis of the excess Al ions
(Equation 2). Clearly, only modest lime doses were required to prevent pH
depression caused by the addition of excess mineral salts for efficient phos-
phorus removal in the Q£ process. It should be emphasized, however, that the
combination of partial nitrification and elevated effluent pH (above that
normally produced without mineral addition by CO,., adsorption in the process
wastewater) significantly increased the lime dosage.
During the entire study, the sludge production (Table 2) averaged 1.34 gm of
solids/gm of BOD,- applied. The average operating conditions corresponding to
the sludge production was an influent BOD^ of 101 mg/1, an Al/P of 1.53, and
an alum dose of 115 mg/1. In January, the decreased concentration of sludge
at the bottom of the clarifiers and the increased capture of solids produced an
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TABLE 1. REACTOR OPERATING CONDITIONS FOR DEACTIVATED SLUDGE WITH ALUM
Period
Date
Reactor Detention hrs
F/M gra BOD5
(gm MLVSS) (day)
SRT days
MLSS
mg/1
% Vol.
CaO Dose
mg/1
PH
^ In
0 Out
Alkalinity as
CaC03, mg/1
In
Out
Alum Dose , mg/1
Al/P Weight Ratiob
(N03 4- N02) - N,
mg/1 in Eff.
1
Nov '72
2.6
0.21
5.8
6915
65
50.7
7.0
6.4
127
99
84
1.1
7.28
2
Dec '72
2.5
0.22
5,5
6840
61.3
58.0
7.0
6.7
116
134
105
1.45
3.53
3
Jan '73
2.76
0,20
6.0
6760
61
38.7
7.0
6.6
130
136
142
1.82
0.46
4
Feb 1-14
2.95
0.18
5.4
7060
58.5
37.4
7.0
6.4
114
101
184
2.66
0.25
4a
Feb 15-22C
3.43
0.16
3.5
6950
62.5
20
7.0
6.7
121
152
0.14
4b
Feb 23-28d
3.0
0.28
4.5
5380
66
15
7.0
6.5
130
126
105
1.1
5
Mar 1-20
3.0
0.24
4.7
5375
65.6
15.1
7.0
.6.4
129
116
136
1.78
0.15
aAlum as Al-CSO,)- ' 14H Q average daily dosage 115 mg/1.
DAverage daily Al/P £01? November^March 1.53..
'Alum addition discontinued; heavy wasting applied to remove accumulated chemical solids.
Alum addition resumed at a 1..1 Al/P weight ratio; darifier bed level reestablished at
usual 5-6 ft. depth.
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TABLE 2. CLARIFIER OPERATION AND SLUDGE PRODUCTION OF 0 ACTIVATED SLUDGE WITH ALUM ADDITION
Period
1
z..
3
4
4a
4b
5
Date
Nov. 1972
Dec. 1972
Jan. 1973
Feb. 1-14
Feb. 15-22
Feb. 23-28
Mar. 1-20
Average
Clarifier
Overflow
(m/d)
19.2
19.9
18.3
17.1
14.7
16.7
16.8
Peak to
Average
Flow
2
1.2
1.45
1.6
1.0
1.6
1.55
SVI
(nnl/g)
44
41
47
48
58
56
58
Recycle
Rate (%}
43
47
52
52
47
46
50
Underflow Solids (%)
Plow
2.39
2.15
2.04
2.0
2.43
1.57
1.63
Tow-Bro
2.19
2.14
2.04
2.04
2.34
1.76
1.83
Solids Production
(gm solids/gm BOD applied)
Produced3-
1 . 24
1.33
0.91
1.68C
2.83°
1.30°
1.34
Wastedb
.93
1.05
0.73
1.34
1.88
.88
.82
a The average sludge production for the study was 1.34 gm/gm of applied BOD5. The average operating
characteristics corresponding to the sludge production were an applied BODs of 101 mg/1, an Al/P of 1.53,
and an alum dose of L15 mg/1.
The average sludge wasted for the study was 0.99 gm/gm of applied
under conditions as in note 1.
The average sludge production for Feb. 1-28 was 1.92 gm/gm applied BOD .
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increasing inventory of solids in the clarifiers. Although' increased wasting
rates were employed in early February, the high alum dosage for February 1-14
further increased the total solids inventory and the height of the sludge
blanket in the clarifiers. Increasing amounts of solids, chiefly chemical
solids, appeared in the clarifiers' overflow. To eliminate the increased
solids inventory and the excessive carryover of solids in the effluent, the
alum addition was discontinued for eight days in February (15-22) and heavy
wasting was applied to the process. Thus, while solids production during the
first two periods (November and December) and last period (March 1-20) repre-
sented production at approximate equilibrium conditions, the sludge production
in January was lower and in February was higher than expected production at
equilibrium conditions.
The BOD, COD, SS, and P removals (Table 3) generally increased with Al/P dosage
ratios until the 2,66 Al/P ratio was applied. The best removals occurred at
the 1.8 Al/P ratio. As indicated earlier, at the 2.66 Al/P ratio the process
exhibited a gradually increasing carry-over of chiefly chemical solids. The
accumulated solids from January and the high Al/P dosage caused increased
sludge blanket depth within the clarifier and contributed to the deterioration
in effluent quality. The average pH was maintained at 6.4 and the increased
solids carry-over did not result from low pH. The solids in the process did
not disperse suddenly; but even with an increased wasting of sludge, the con-
tinued addition of a large excess alum caused further deterioration. The alum
feed was discontinued on February 15 and high wasting rates were applied to the
process to eliminate the excess sludge. After eight days of operation, the
sludge blanket level was restored to the normal operating level and alum dosing
was resumed, but at a 1.1 Al/P ratio. During the heavy wasting, heavy solids
carry-over occurred in the clarifier. Although the BOD removal declined only
moderately (from about 90% to 81%), COD, SS, and phosphorus removals declined
markedly. Thus, many of the materials in the effluent were biologically
difficult to degrade or were chemical solids.
With the resumption of alum addition, the process exhibited satisfactory BOD
removals of about 85%, but high solids, COD, and P continued to appear in the
effluent for the remainder of the study. Clearly, the last period (March 1-20)
of the study did not represent typical product quality for mineral addition
in the 02 process.
The process influent and effluent exhibited a wide daily variation in phos-
phorus content during the operation from November through January. Since the
alum dosage was proportioned to flow, the daily variation in phosphorus content,
with some drift in the alum metering pump, produced the range of Al/P shown in
Figure 2. This figure clearly revealed not only the decrease in P with in-
creasing Al/P dosage ratio, but also a wide variation in daily P removal. With
the combined sewers in the District of Columbia causing the wide daily variation
in influent P, we decided that improved Al/P dosage control would be useful.
During the study, fully automatic control, however, was not employed because it
required the development of a continuous analyzer for influent P.
12
-------
3. EFFLUENT QUALITY OF 02 ACTIVATED SLUDGE WITH ALUM ADDITION3
BOD(mg/l)
'c-rlod Al/P
1 1.1
2 1 . 45
3 1.82
4 2.66
4,,
4b 1.1
5 1.78
In
104
100
97
91
100
91
108
Out
19.1
9.5
7.4
10.2
19.3
12.7
16
% Rem.
82
90
92
89
81
86
85
COD(mg/l)
In
238
241
246
220
247
249
246
Out
48
49
39
45
103
82
76
% Rem.
80
80
84
80
58
63
69
In
112
116
110
104
110
104
117
SS(mg/l)
Out
33
30
17
31
96
49
56
% Rom.
70
74
84
70
13
53
52
P(mg/l)
In
6.98
6.75
7.24
6.45
7.22
8.55
7.12
Out
1.84
1.72
1.05
1.32
4.64
4.05
3.26
% Rem.
74
75
86
79
36
53
54
N(mg/l)
In
23.8
26.9
25.9
23.2
22.8
23.5
25.0
Out
12.7
13.3
18.8
18.0
20.9
19.5
19.6
•\ Re,
48
36
28
22
8
17
'V ' '
aPercentage removals has eld upon primary effluent.
-------
10
8
Q.
CO 6
O)
CO
I4
Q_
CO
03
0.
1-
o
00°
o
o INFLUENT
• EFFLUENT
6.2—6.8pH range
11/72-1/73
o
o
° oo
8
o
° oo
89)
o
o o
o
o CD °° ° oo
o o 00°
o o
o o
o
o o
o
o
o
o
o
.4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
AI/P WEIGHT RATIO
Figure 2. Phosphorus removal by alum addition in O^
activated sludge.
14
-------
When alum addition to the 0* process improved the solids capture in the
clarifier, it also may have moderately improved the initial settling velocities
for any given MLSS and wastewater temperature. The initial settling velocities
(Table 4) of the MLSS fall within the range of previously observed settling
velocities (Figure 3) for oxygen-activated sludge without alum addition.
However, in earlier work2 at the EPA-DC Pilot Plant, the initial settling
velocities of the MLSS without alum addition during similar seasons (November-
February) tended to fall within the lower portions of the observed range. In
the current study, the initial settling velocities of the MLSS with alum
addition clustered in the upper portion of the observed range. Unfortunately,
without a control (parallel D£ process without alum addition) for direct com-
parison, it was not possible to determine whether the apparent (compared to
earlier observations) improvement was related to alum addition, and whether
this improvement in initial settling velocities was great enough to compensate
for the increased clarifier mass-loading caused by the precipitated chemical
solids. In contrast to the apparent increase in the settling velocities of the
MLSS, the underflow solids concentration in the clarifiers decreased with
increasing alum dosage (Table 2). (The thickening characteristics in the last
half of February and March should not be considered representative because of
the heavy wasting in mid-February).
Finally, filtration of the alum-C^ process effluent through dual and multi-media
filters was performed as an additional compatibility study. The filtration
study, unfortunately, was conducted during the operation with the highest Al/P
dosage range (2.66:1) and did not correspond to the period of best alum
addition-C>2 operation. Thus, the solids concentration entering the filter were
higher than those during the most efficient process operation. Two filter media
were employed (Table 5), a dual media and a multi-media. In the multi-media,
two different coals, one of specific gravity 1.4 and the other of specific
gravity 1.6, were used to produce a four media bed. Laboratory Millipore
filtration (0.45u) of the effluents was performed for comparison with the in-
depth pilot filtration. In the brief tests, the filters were backwashed after
a headless of 3.18 meters (125 inches) of water occurred across the filter. The
filter cycles averaged approximately 10 hours with a backwash requirement of 15%
of the product volume. The solids loading per filter cycle (in kg of solids per
square meter of filtration area) ranged from 18.8 to 28.2 (.38 to .58 Ib of
solids/ft^) and were similar to typical loadings for filtration of other min-
eralized activated-sludge effluents in the pilot plant"' ^ .
The filter study revealed filtration performance (Table 6) on mineralized 02
process effluent similar to performances observed in earlier EPA-DC pilot
studies-^ of mineralized step-aeration activated-sludge effluent. Although the
media specifications in the two studies were different, the solids removals of
60 to 75% in the current study compared well with the 62 to 78% removals of the
earlier work^ on the alum-air activated sludge effluent. With higher Al/P
ratios and a lower effluent pH, the phosphorus residuals in the current study
were lower than the average residuals reported in the earlier work but were
similar to those residuals observed in that earlier work when the effluent pH
of the air system was in the 6.4 to 6.5 pH range.
15
-------
TABLE 4. SETTLING RATES
DATE
11/1/72
12/15/72
12/22/72
12/27/72
1/10/73
1/12/73
1/29/73
2/7/73
2/27/73
3/7/73
3/14/73
TEMP
(°c)
20.0
16.7
15.0
16.0
16.7
17.2
15.0
15.7
14.5
15.5
16.0
FOR 00 ACTIVATED SLUDGE WITH
SVI
(ml/gm)
46
41
--
37
42
51
51
48
51
71
54
MLSS
(mg/1)
5800
6540
8010
6650
7480
7340
5820
6870
5540
5740
4860
ALUM ADDI
ISV
(m/hr)
2.9
3.1
4.1
2.7
2.4
3.1
2.6
2.2
2.4
2.3
3.0
-------
TABLE 5. FILTRATION SYSTEM ON ALUM-CL SECONDARY EFFLUENT
Media Specifications
Dual-media
Coal
Sand
Multi-media
Coal I
Coal 11
Sand
Ilmenite
Operating Conditions
Depth (m)
. 0.61
0.305
0.406
0.203
0.229
0.076
Size (mm)
1.24-1.44
0.6-0.7
1.5-1.6
1.0-1.1
0.4-0.5
0.2-0.35
Specific Gr
1.5
2.6
1.4
1.6
2.6
4.65
Diurnal flow cycle, peak to average 1.6:1
Average flow (m/min) 0.196
Average cycle time (hours) 10
Head loss at backwash (m) . _ 3.18
Backwash requirement (% of product) 15
Backwash rate (m/min) 0.81
Surface wash rate (m/min) 0.12
Filter solids loading kg/m2/cycle 18.8-28.:
17
-------
5.00
u 1.00-
O
o
z
LU
to
0.50-
0.10-
0.05-
oALUM ADDITION
+ STEP FEED
EPA-DC PILOT PLANT
OBSERVED SETTLING
LIMITS (2)
OXYGEN SLUDGE
OBSERVED SETTLING
LIMITS (8)
UNION CARBIDE
5 lb
MLSS CONCENTRATION (gm/l)
50
100
Figure 3
Initial settling velocities of oxygen
MLSS as a function of concentration.
18
-------
TABLE 6. FILTER PERFORMANCE ON ALU.M-0 SECONDARY EFFLUENT
Pilot. Filters
Date
2/6/7*
2/7/74
2/14/74
Millioore
Sample
Inf. (mg/l)
Dual Eff. (mg/l)
/o Remova 1
7.'u Hi Eff. (mg/1)
% Removal
Inf. (mg/l)
Dual Eff. (mg/l)
% Removal
-Multi Eff. (mg/l)
/j Remova 1
Inf. (mg/l)
Dual Eff. (mg/l)
,°o Removal
Multi Eff. (mg/l)
% Removal
Filtration
Eff. P
°< Removal
SS
25
6
72
6
72
27
11
60
--
--
32
12
62
9
72
2/6/74
0.652
19
BOD
7.3
4.7
35
3.3
55
7.0
4.5
36
3.3
53
12.0
6.9
43
4.8
60
COD
36
29
19
19
47
35
25
29
19
46
54
32
41
32
41
2/7/74
0.74
20
P
0.805
0.365
55
0.346
57
0.926
0.405
56
0.150
33
2.06
0.531
74
0.346
83
Al/P
Ratio
3.95
4.13
1.99
2/14/74
1.72
17
19
-------
With the snail data base of the current study, a meaningful comparison between
media types cannot be made. However, comparison between the pilot in-depth
filtration and the laboratory Millipore filtration is appropriate. Filtration
through the in-depth dual and multi-media filters removed more than 50% of the
residual P. Filtration through the 0.45ji laboratory Millipore filters removed
only approximately 20% of the residual P. These results confirmed similar
observations during extensive filtration studies on the effluent from the
three-stage activated sludge pilot system in the EPA-DC Pilot Plant. The in-
depth filtration improved the removal of phosphorus, either because of
increased precipitation and flocculation on the filter bed or because of
adsorption of the P on the Al (OH)., and other materials in the filter bed.
20
-------
SECTION 7
STEP-FEED STUDIES
In the step-feed study, the operation of the (^-activated sludge process with
an equal split of the feed into the last three reactor stages was initiated
(Table 7) in late June at a steady flow with a reactor detention time of about
1.85 hours and with a steady clarifier overflow rate of approximately 27.5 m/d
(675 gpd/ft ). Mineral addition was not employed. Data acquisition was ini-
tiated on July 20, 1973. The process was first operated at an F/M of about
0.23 gm BOD5/gm MLVSS/day and at an SRT of 11 days. Later the F/M was
increased to 0.32 gm BOD5/gm MLVSS/day.
The important advantage of the step-feed configuration was the MLSS profile
(Table 7) through the reactor stages. The MLSS decreased from nearly 10,000
mg/1 in the first stage to about 4,000 mg/1 in the last stage and averaged
around 6,500 mg/1. Thus, the step-feed configuration produced a desirable and
modest solids loading (clarifier flux) of about 115 kg/d/m2 (23 lb/day/ft2)
and a high average MLSS without a high flux loading to the clarifier.
At the operating SRT of 11 days, the process exhibited a low sludge production
of about 0.5 gm of solids/gm BOD,- applied, with about half of the solids pro-
duction in the waste sludge stream and the rest in the secondary effluent. The
MLSS entering the clarifier exhibited typically excellent settling velocities
for summer operation (Figure 4). The initial settling velocities in the 15.25
cm diameter by 2.44 m high column ranged from 5.3 to 8.3 m/hr (17.4 to 27.2
ft/hr) (Table 8) and, as typical of warm-water settling rates, clustered in the
upper portion of the earlier observed settling velocities (Figure 3).
The effluent quality from the step-feed operation was excellent (Table 9).
With nitrification in the process, an allyl-thiourea inhibited BOD^ (0.5 mg/1
of allyl-thiourea) and an uninhibited filtered BODtj were obtained on the final
effluent. As in conventional plug-flow Oo-activated sludge1, the process
operated in the step-feed configuration reduced the soluble BODcj to less than
3 mg/1 and the total residual BOD5 (inhibited) to less than 10 mg/1. The
step-feed process also efficiently removed COD (78 to 85%) and suspended
solids (70 to 87%). Without alum addition, the process removed from 17 to 42%
of the total P. At the high SRT, the system partially nitrified, converting
about 70% of the TKN to nitrate, and provided a total nitrogen removal of about
40%. The nitrification and C02 reduced the effluent pH to 6.3. As expected,
the nitrification also reduced the effluent alkalinity.
The step-feed configuration, because of treatment efficiency and clarifier
loading characteristics, is especially well suited to the oxygen-activated
sludge process. However, the key to its application is the efficiency of
21
-------
TABLE 7. STEP-FEED, 0 -ACTIVATED SLUDGE OPERATING CONDITIONS
REACTOR
to
ro
F/M
Detention gm BOD Average MLSS
Period Time SRT MLSS (mq/l)
1973 (hr.l
July 20-31
Aug. 1-31
Sept. 13-26
CLARIFIER AND
Period
1973
July r-0-31
Any. 1-31
Sept. 18-26
1.81
1.84
1.88
SLUDGE
Flow
Rate
(m3/d)
405
399
390
(qm MLVSS)(day) (days) (mq/l) (% Vol.) Staqe 1 Staqe 2 Staqe 3
0.26 10.7 6500 73 9800 6720 5180
0.23 11.5 6730 74 10,700 7060 5020
0.32 5830 74 8970 6040 4570
PRODUCTION
Clnrifier '_, * Underflow Solids Recycle . . . /
„ ,., Flux „.._ ,,,,-. n ' gm solids/gm
Overflow ,., SVI (A.) Rate 3 '^
(m/d) (kq/d/;;O (ml/q) Plow Tow Bro ("') Produced
28.0 120 50 2.06 1.70 53 0.49
27.5 115 37 2.15 1.84 51 0.50
27.0 102 49 2.16 1.78 42
Staqe 4
4310
4150
3760
BOD applied
Wasted
0.19
0.24
-------
2.2
2.0
1.8
1.6
1 12
O l"*
tu
1 1.0
0.8
0.6
0.4
0.2
SLOPE = 5.3 m/hr.
MLSS, 3880mg/l
TEMP., 26.7°C
.25
.50
1.25
.75 1.0
TIME (hrs)
Figure 4. Typical step-O2 MLSS settling.
1.50
23
-------
to
TABLE 8. INITIAL SETTLING VELOCITIES3 OF
STEP-FEED, DEACTIVATED SLUDGE
SVI (ml/g) TEMP (°C) MLSS (mg/l) ISV (m/hr)
70
53
60
39
34
24.5
25.0
24.7
26.7
26 . 2
2620
4360
3860
3880
4510
6.9
5.5
8.3
5.3
5.5
aDynamic settling in 15.25 cm dia. by 2.44 m long settling column
mixed at 10 rph.
-------
TABLE 9. STEP-FEED, DEACTIVATED SLUDGE EFFLUENT QUALITY3
CARBON AND SOLIDS
to
t-n
BODc, Filt. BODC ^^
Period In
1973 (mq/l)
July 20-31
Aug. 1-31 88.5
Sept. 18-26 111
PHOSPHORUS AND NITROGEN
PH
Period , ~ .
1973 In °Ut
July 20-31 6.9 6.3
Aug. 1-31 6.9 6.3
Sept. 18-26 7.0 6.3
Out Rem.
(mq/l) (%}
9.7 89
8.3 93
Alkalinity
In Out
(mq/l) (mq/l)
126 74
129 80
' 154 94
\j
Eff.
(mg/1)
—
2.8
2.4
Total
In
(mq/l)
5.78
5.51
7.45
In
(mq/l)
208
208
248
P
Out
(mq/l)
4.77
4.40
4.27
Out
(mq/l)
46
43
38
TKN
In
(mq/l)
20.2
20.6
24.5
Rem.
f
-------
utilization of the. Q2 gas feed to the process. Prior to the step~feed study,
the equipment was completely renovated and the 02 recirculation compressors
were replaced.
During the summer operation with the new and renovated equipment, the system
exhibited unknown oxygen losses. Finally in September, all leaks were elimi-
nated and brief oxygen balances were performed on the process. Two approaches
to the oxygen balances were employed. One approach was employed to compare
the measured 0~ in the inlet gas flow with the Oj in the outlet gas flow and
in the effluent stream (D.O.). The second approach was employed to compare
measured inlet 02 with the oxygen used as measured by dissolved oxygen uptake
rates (Figures 5 and 6) in each of the process stages. Both approaches to
the oxygen balance (Table 10) revealed about a 50% utilization of the inlet 02.
Further work is needed to confirm these 02 balances and in particular to assess
the increase in mechanical energy input needed to decrease the percent oxygen
in the exhaust gas. However, if confirmed, oxygen usage of about 50% will
eliminate the step configuration as a practical alternative to the 02 process
as practiced at the EPA-DC Pilot Plant.
26
-------
2.0H
1.0
0.0-
SEPT. 25, 1973
MLSS = 8,115mg./l.
STAGE NO.l
UPTAKE = 96.8
RUN NO. 1
RATE = 11.64 mg02/l/hr
gm MLSS
RUN NO. 2
RATE = 12.2 mgO2/l/hi
gm MLSS
23
TIME (min)
O)
£
O
•
Q
6.0
5.0
4.0
3.0
2.0
1.0
0.0
STAGE NO. 2
MLSS = 5400mg/l
UPTAKE = 83.7
•RUN NO. 1
RATE = 15.4 mgO2/l/hr
gm MLSS
RUN NO. 2
RATE = 15.5
mg
gm MLSS
01 2345
TIME (min)
Figure 5. D.O. uptake as a function of time stage
No. 1 and 2.
27
-------
7.0
6.0
= 4.0-
O)
— 3.0-
2.0-
1.0-
0
1.0-
DILUTE MLSS-
=1875 mg/l
RATE=15.45 mgO2/l/hr
gm MLSS
SEPT. 25, 1973
STAGE NO. 3
UPTAKE=69.4
mgO2/|/hr
,MLSS=4,290 mg/l
RATE=16.88 mgO2/l/hr
gm MLSS
1.0
4.0
5.0
2.0 3.0
TIME (min)
STAGE NO.4
DILUTE MLSS 2015 mg/l UPTAKE=57 2
;RATE=16.4mg02/l/hr mgo2'/|/hr
"^ gm MLSS
MLSS=3560 mg/l
RATE=15.75 mgO2/l/hr
gm MLSS
1.0 2.0 3.0 4.0 5.0
TIME (min)
Figure 6. D.O. uptake as a function of time stage No. 3 and 4.
28
-------
TABLE 10. STEP-FEED, 0 -ACTIVATED SLUDGE OXYGEN USAGE
to
Time Period
Sept. 25*
09:28-17:09
12:27-15:35
Sept. 27b
10:03-18:24
15:10-18:24
°2
In
(kq)
33.6
12.9
49.0
21.2
Out
(kq)
16.6
6.3
25.6
11.4
°2
Usage
(o'\
\/°)
50
52
48
54
°9
D.O. Uptake
(kq)
18.0
7.4
21.1
8.5
02
Usage
(%}
54
57
44
40
a
Average % 0 in effluent gas 46%.
b ^
Average % 0 in effluent gas 49%.
-------
REFERENCES
1. Stamberg, J.B,, Bishop, D.F, and Kumke, G. "Activated Sludge Treatment
With Oxygen," AIChE Symposium Series 124, Water 1971, 68. 25 (1972)
2. Stamberg, J.B., Bishop, D.F, Hais, A.B., and Bennett, S.M., "System
Alternatives in Oxygen Activated Sludge/' presented at the 45th Annual
Conference of Water Pollution Control Federation, Atlanta, Georgia,
October 1972.
3. "FWPCA Methods for Chemical Analysis of Water and Wastes/' U.S. Dept.
of the Interior, Fed. Water Poll. Control Adm., Cincinnati, Ohio
(November 1969).
4. Kamphake,L., Hannah, s. and Cohen, J., "Automated Analysis for Nitrate by
Hydrazine Reduction," Water Res., 1, 205 (1967)
5. Schaeffer, R.B., et al., "Application of a Carbon Analyzer in Waste Treat-
ment/' Jour. Water Poll. Control Fed., _37, 1545 (1965).
6.- Gales, M., Julian E., and Kroner, R., "Method for Quantitative Determi-
nation of Total Phosphate in Water,," Jour, of Am. Water Wks. Assoc., 58,
1363 (1966)
7. "Standard Methods for the Examination of Water and Wastewater." 12th ed.,
American Public Health Association, New York (1965)
8. Linde Division, Union Carbide Corp., "Operating Experiences and Design
Criteria for Unox Wastewater Treatment Systems." prepared for U.S. EPA
Technology Transfer Program^ Design Seminar for Waste Treatment Facilities,
New York, New York, February 29-March 1, 1972.
9. O'Farrell, T.P., and Bishop S., "Filtration of Effluent from Staged
Nitrification-Denitrification Treatment/1 presented at the 76th National
Meeting of AIChE, Tulsa, March 10-13. 1974.
10. Hais, A.B., Stamberg J.B, and Bishop D.F,, "Alum Addition to Activated
Sludge with Tertiary Solids Removal/' AIChE Symposium Series 145, Water
1974, 71, 252 (1975).
30
-------
PUBLICATIONS
Heidman, J. A., Bishop, D. F., and Stamberg, J. B., "Carbon, Nitrogen,
and Phosphorus Removal in Staged Nitrification-Denitrification Activated
Sludge Treatment," AIChE Symposium Series 145, Water 1974, 71, 264 (1975)
31
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-77-166
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Alum Addition and Step-Feed
Activated Sludge
Studies in Oxygen-
5. REPORT DATE
September
1977 (Issuing Date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Dolloff F. Bishop, James A. Heidman, Richard C.
Brenner, and John B. Stamberg
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORG -XNIZATION NAME AND ADDRESS
Government of the District of Columbia
Department of Environmental Services
EPA-DC Pilot Plant
5000 Overlook Avenue, S.W., Washington, D.C.
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/HHXHXNO.
68-01-0162
20032
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—Gin., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final Report - 10/72 to 10/73
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: Dolloff F. Bishop (513-684-7628)
16. ABSTRACT
A plug flow, 02~activated sludge process was operated with alum addition to remove
phosphorus and with lime addition to prevent the process pH from decreasing below 6.4.
The 02 reactor was operated at F/M ratios between 0.18 to 0.24 gm of BOD5/gm of MLVSS/
day in a typical co-current 02~liquid contacting system. The alum dosages for the fiv
steady-state operating periods increased from 84 mg/1 to 184 mg/1 was used to maintain
the process pH at 6.4. The pollutant removals from the primary effluent ranged from
82 to 92% for BOD5 (7.4 to 19 mg/1 of residual 6005) and from 54 to 86% for phosphorus
(1.05 to 3.26 mg/1 of residual P). The optimum P removal occurred at a 1.8 to 1 aver-
age Al/P mole ratio with an average total residual P of 1.05 mg/1.
In a second study, the 02 process was operated in a step-feed configuration consisting
of a sludge oxygenation stage followed by three stages of oxygen aeration with equal
portions of the primary effluent fed to each stage. In typical operation, the process
with a F/M ratio of 0.23 exhibited a MLSS concentration profile in the four stages of
10,700 mg/1; 7,060 mg/1; 5,020 mg/1; and 4,150 mg/1. The step configuration clearly
reduced the solids loading to the clarifier and provided an average MLSS of more than
6,500 mg/1. The step operation produced excellent BOD5 removals (89% from primary).
The 02 usage in the step configuration was significantly less than the 90% typically
achieved in co-current contacting.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*0xygenation
*Activated Sludge Process
Sedimentation
Aluminum Sulfate
Sewage Treatment
Calcium Oxides
*Liquid Oxygen
Oxygen Consump-
tion
pH Control
*0xygen activated sludge
Phosphorus removal
*Mineral addition
Step-feed operation
EPA-DC Pilot Plant,
Washington, DC
Dissolved Oxygen
13B
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
•21. NO. OF PAGES
40
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
32
* U.S. GOVEBSMEKT PSIKU1IG OFFICE 1977- 75 7-0 56 /6 542
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