EPA-600/2-76-180
October 1976
EXPERIMENTAL EVALUATION
OF
OXYGEN AND AIR ACTIVATED SLUDGE NITRIFICATION SYSTEMS
With and Without pH Control
by
James A. Heidman
Government of the District of Columbia
Department of Environmental Services
EPA-DC Pilot Plant
Washington, DC 20032
Contract No. 68-03-0349
Project Officer
Irwin J. Kugelman
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
.... fP^FClW! ASCTCV
r:. J- i!d-l?
-------
DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. 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.
-------
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 municipal 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 study described in this report relates the performance of
biological nitrification systems to several parameters subject to
engineering control. The reliable oxidation of the ammonia present in
wastewater can result in a substantial decrease in the ultimate oxygen
demand exerted in the receiving aqueous environment.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
-------
CONTENTS
Page
Foreword i i i
List of Figures vi
List of Tables v11
Acknowledgment 1X
I Introduction 1
II Summary 2
III Conclusions 3
IV Recommendations 4
V Experimental 5
A. Oxygen Nitrification Systems 5
B. Air Nitrification System 7
C. Influent Flow 7
D. Biological System Clarifiers 7
VI Methods and Procedures 8
VII Results 10
A. Introduction 10
B. Phase I (October-December 1973) 10
C. Phase II (January-May 1974) 13
D. Phase III (June-September 1974) 22
E. Supplemental Studies and Analyses 29
VIII Discussion 49
IX References and Notes 55
-------
LIST OF FIGURES
Number Page
1 Oxygen Aeration System 6
2 Reactor Solids and Effluent Nitrogen for the Oxygen Nitrification
System Without pH Control (Days 275-365, 1973) 11
3 D.C. Secondary Effluent Temperature and Reactor pH for the Oxygen
Nitrification System Without pH Control (Days 275-365, 1973). . . 12
4 Effluent TKN and NH4-N for the Oxygen Nitrification Systems With
and Without pH Control (Days 1-150, 1974) 16
5 Reactor MLSS Concentrations for the Oxygen Nitrification Systems
With and Without pH Control (Days 1-150, 1974) 17
6 Reactor MLVSS Concentrations for the Oxygen Nitrification Systems
With and Without pH Control (Days 1-150, 1974) 18
7 D.C. Secondary Effluent Temperature and Reactor pH Values for the
Oxygen Nitrification Systems With and Without pH Control (Days
1-150, 1974) 19
8 Reactor MLSS and MLVSS Concentrations in the Air and Oxygen
Nitrification Systems (Days 155-265, 1974) 30
9 Effluent COD, TKN and NH4-N for the Air and Oxygen Nitrification
Systems (Days 155-265, 1974) 33
10 Reactor pH Values for the Air and Oxygen Nitrification Systems
(Days 155-265, 1974) 34
11 Settling Velocities of Air and Oxygen Nitrification Solids as a
Function of MLSS Concentrations 35
12 Laboratory Determination of Nitrification Kinetic Rate 43
13 Nitrification Kinetic Rate vs Temperature for the Oxygen
Nitrification System With pH Control 51
14 Average Daily Dissolved Oxygen Concentrations in the Air and
Oxygen Nitrification Systems (Days 186-265, 1974) 53
-------
LIST OF TABLES
Number Page
1 Process Characteristics for the Oxygen Nitrification System
Without pH Control (Days 317-351, 1973) . 14
2 Influent and Effluent Characteristics for the Oxygen Nitrifica-
tion System Without pH Control (Days 317-351, 1973) 15
3 Process Characteristics for the Oxygen Nitrification System
With pH Control (Days 51-150, 1974) 20
4 Influent and Effluent Characteristics for the Oxygen Nitrifica-
tion System With pH Control (Days 51-150, 1974) 21
5 Effluent Characteristics of the Oxygen Nitrification System
With pH Control for March and May, 1974 23
6 Influent and Effluent Characteristics for the Oxygen Nitrifica-
tion Systems With and Without pH Control (Days 56-85, 1974). . . 24
7 Process Characteristics for the Oxygen Nitrification System
Without pH Control (Days 26-85, 1974) 25
8 Influent and Effluent Characteristics for the Oxygen Nitrifica-
tion System Without pH Control (Days 26-85, 1974) 26
9 Process Characteristics for the Oxygen Nitrification System
Without pH Control (Days 115-141, 1974) 27
10 Influent and Effluent Characteristics for the Oxygen Nitrifica-
tion System Without pH Control (Days 115-141, 1974) 28
11 Process Characteristics for the Air and Oxygen Nitrification
Systems With pH Control (Days 186-265, 1974) 31
12 Influent and Effluent Characteristics for the Air and Oxygen
Nitrification Systems With pH Control (Days 186-265, 1974) ... 32
13 Nitrification Kinetic Values for the Oxygen Nitrification System
Without pH Control 36
14 Comparison of the Kinetic Rates for the Oxygen Nitrification
Systems With and Without pH Control 37
vii
-------
LIST OF TABLES (CONTINUED)
Page
15 Comparison of the Kinetic Rates for the Oxygen Nitrification
Systems With and Without pH Control on the Basis of MLVSS,
Protein and ATP 38
16 Effect of pH on Nitrification Kinetic Rate from the Oxygen
System Without pH Control 39
17 Suspended Solids Concentrations and NH4-N for the Oxygen
Nitrification System Without pH Control (Day 94, 1974) 40
18 Summary of Air and Oxygen Nitrification System Kinetic Studies . 41
19 Summary of MLVSS and Protein Values for Selected Kinetic Tests . 45
20 Mixed Liquor Suspended Solids Settling Velocities for the Air
and Oxygen Nitrification Systems 47
21 Oxygen Uptake Values for Selected Grab Samples With the Oxygen
and Air Nitrification Systems 48
22 A Comparison of Oxygen Consumption in the Air and Oxygen Nitri-
fication Systems With pH Control (Days 186-265, 1974) 54
vm
-------
ACKNOWLEDGMENT
The pilot system was maintained and operated by the EPA-DC Pilot Plant staff
under the direction of Calvin Taylor, Chief Operator, and Paul Ragsdale, head
of instrumentation and mechanical repair. Laboratory analyses were performed
under the direction of David Rubis.
The assistance of all the District of Columbia operators, technicians and
laboratory staff at the EPA-DC Pilot Plant is gratefully acknowledged.
-------
SECTION I
INTRODUCTION
Within the past few years, the use of commercial oxygen activated sludge
systems has become increasingly popular for secondary biological treatment.
A logical extension of the oxygen process is its application for the biolog-
ical nitrification of the ammonia present in wastewater. The nitrification
process can be incorporated directly in the secondary treatment process by
maintaining a sufficiently high sludge retention time (SRT) or it can be
added as a separate treatment stage.
In wastewaters with a relatively low alkalinity, such as the District of
Columbia, the nitric acid produced by biological nitrification results in a
noticeable pH depression. This depression is intensified with gas-tight
staged oxygen systems where the carbon dioxide produced by biological activ-
ity is retained as the process gas is recirculated within the stages before
discharge to the atmosphere. Since the optimum pH for the nitrifying bacteria
has been reported to be in the alkaline range, the pH depression may not be
conducive to optimum nitrification rates.
A few preliminary studies conducted at the pilot plant suggested that the
reduced pH was retarding the degree of nitrification normally encountered in
systems operated at pH 7. Since these preliminary studies utilized an oxygen
activated sludge system, there was also some concern that oxygen toxicity
could influence the observed process performance.
The primary objectives of the study described herein were twofold:
A. To evaluate the performance of oxygen nitrification systems
with and without pH control.
B. To compare the performance of oxygen and air nitrification
systems operated under similar conditions.
To accomplish these objectives, three discrete biological processes were
operated for varying lengths of time. Two of the processes were oxygen acti-
vated sludge systems. The pH was controlled in one of these systems but not
in the other. The third biological process was an air activated sludge
system operated at controlled pH. For all three systems the feed was second-
ary effluent from the District of Columbia biological treatment plant. Thus
all systems were separate-stage nitrification reactors.
-------
SECTION II
SUMMARY
The nitrification capabilities of two oxygen activated sludge systems receiv-
ing District of Columbia secondary effluent at a steady state flow of 190 m /
day (50,000 gpd) were evaluated. The pH of one system was controlled to main-
tain a pH of 7.0 in the last reactor pass of the four pass system. The pH of
the second system was uncontrolled and reactor pH values of 5.5-6.0 were com-
mon. Also parallel air and oxygen nitrification systems both with pH control
were evaluated under similar operating conditions. Parameters used to compare
the systems included effluent quality, sludge settling rates, lime dosage,
sludge production and nitrification kinetic rates.
The effluent quality of the oxygen nitrification system with pH control was
excellent throughout 8 months of investigation. The effluent NH.-N concen-
tration averaged about 0.2 mg/1. The effluent NH.-N of the oxygen process
without pH control was normally 1 mg/1 or less. However this system did not
show the day-to-day stability that was achieved with pH control.
The carbonaceous and nitrogenous effluent quality of the air and oxygen nitri-
fication systems operated at the same loadings with pH control to 7.0 in the
last reactor pass of each system was identical. However three times the lime
dosage was required in the oxygen system. This resulted in a larger percent-
age of inert material in the oxygen system and increased sludge production.
It also required maintaining higher MLSS levels to achieve the same MLVSS in
each system. The improved settling characteristics of the oxygen sludge com-
pensated for the increased solids loading to the clarifier. Both systems
produced excellent effluent quality.
-------
SECTION III
CONCLUSIONS
1. Nitrification of District of Columbia secondary effluent can be achieved
in oxygen activated sludge systems with or without pH control.
2. The nitrifying organisms were estimated to comprise less than 5 per cent
of the total MLSS.
3. The nitrification kinetic rates determined for the oxygen system with pH
control exhibited an excellent correlation with wastewater temperature.
4. Oxygen nitrification with pH control to 7.0 in the last quarter of the
reactor produced an effluent of excellent quality with an 8-month average
effluent NH.-N concentration of just 0.2 mg/1. The lime dose required to
maintain the pH control was 125 nig/1 as CaO.
5. The effluent NH.-N concentration from the oxygen activated sludge process
without pH control was normally 1 mg/1 or less. However this system did
not show the day-to-day stability that was achieved with pH control. The
pH normally ranged from 5.5 to 6.0 in the last quarter of this reactor.
6. The carbonaceous and nitrogenous effluent quality from the air and oxygen
activated sludge systems operated with pH control and at the same loadings
were identical.
7. Because the C0? produced by biological activity is recirculated within
the stages of the oxygen system before discharge to the atmosphere, this
system required three times the lime dosage needed in the air system to
maintain a pH of 7.0 in the last reactor pass.
8. During the period of parallel operation of the oxygen and air systems, the
MLVSS were 36% and 58% of the MLSS, respectively. This resulted from
inert material in the lime and any chemical precipitates formed in the
neutralization reaction.
9. Due to the greater degree of inorganic solids produced, the MLSS in the
oxygen nitrification reactor were higher than in the air nitrification
system. However this produced no sludge separation problem because the
sludge with the higher inert content had superior settling characteristics.
-------
SECTION IV
RECOMMENDATIONS
It would be of interest to compare the nitrification performance of oxygen
and/or air nitrification systems where the pH of one system is controlled at
7.0 and the pH of the other system is controlled at successively lower values.
On the basis of the results obtained here and reported elsewhere, it appears
that maintaining an acclimated system at pH 6.0 will produce nitrification
rates which are equivalent to those from a system maintained at pH 7.0.
There is further evidence that the nitrification rates begin to decline below
pH 5.9-6.0 even for a system acclimated to lower values. The stability of
the oxygen process operated at pH 6.0 should be determined. The stability
of the air nitrification system without pH control should be determined. The
effect of pH on nitrification at lower SRT values than those used here should
be quantified. Furthermore, the trade-offs between process stability, declin-
ing nitrification kinetic rates, reduced sludge production and reduced lime
dosages need to be established.
-------
SECTION V
EXPERIMENTAL
A. Oxygen Nitrification Systems
A schematic diagram of tne oxygen activated sludge process without pH control
is presented in Figure 1. The reactor consisted of four passes of equal size,
in series, with a total volume of 30.6 m^ (8100 gal). The reactor was sealed
to prevent loss of oxygen arid included submerged hydraulic entrances and exits
as well as simple water-sealed mixing equipment. Sampling ports were located
at mid-depth for each reactor pass.
The addition of oxygen to tne void space overlying the first pass of the reac-
tor was controlled by a pressure regulator. The regulator activated the inlet
oxygen control valve to maintain the overhead gas at a selected pressure which
was maintained between 2.5-10 cm (1 to 4 inches) of water. The manual valve
on the exhaust gas line was set to bleed off the exhaust gas from the void
space above the fourth reactor stage at a rate sufficient to maintain an oxygen
concentration of 30-50% in the exhaust line. Sample taps were installed at
several locations within the system with lines leading to a Beckman oxygen
analyzer for determination of the gaseous oxygen concentrations.
A series of compressors were located above each reactor pass. The gas in the
overlying void space was recirculated tnrough the compressors and down through
the rotating hollow mixer shafts wnere it was discharged through perforated
stainless steel diffusers. The diffusers were welded to the end of the mixer
shafts about 30 cm (12 inches) below tne impellers. The rate of gas recircu-
lation and hence the dissolved oxygen concentrations was controlled by varying
the number of compressors in use at any time and/or by the use of a control
valve on the suction side of the compressors.
Mechanical energy was supplied to maintain the biological solids of each pass
in the reactor in a suspended state. A single Philadelphia Gear Mixer was
located directly above each pass and it was used to turn a 35 cm (14-inch)
marine impeller attached to the mixer shafts.
The reactor configuration of the oxygen activated sludge system with pH con-
trol was essentially the same as shown in Figure 1. In this system, however,
the influent flow and the recycle flow were mixed in a 208 1 (55 gal) drum
prior to entering the first pass of the reactor. A lime feeder was installed
directly above the drum and dry lime was added as required to maintain a pH
of 7.0 in the last reactor pass. The lime feed control strategy varied from
the use of a flow proportioned feed forward - first pass pH feed back digital
control program to the use of a simple timing mechanism to turn on the lime
-------
LU
O)
GO
(C
cu
c
O)
CD
>>
X
o
O)
S-
C7)
-------
feeder for a preset number of seconds each minute. Because of severe and
rapid slime growth on the pH electrodes, better control was obtained by the
use of the simple timing mechanism.
B. Air Nitrification System
The air nitrification reactor was constructed by modifying one of the oxygen
nitrification reactors. The mechanical mixers were removed and air lines were
installed. These lines discharged air into PVC perforated pipe diffusers
located at the bottom of each reactor pass. Removal of the mixers resulted
in each pass being open to the atmosphere. This system also received dry lime
for pH control. A screw feeder was located directly above the first pass of
the air system, and lime was added by using a timing mechanism. Sufficient
lime was added to maintain a pH of 7.0 in the last pass of the reactor.
C. Influent Flow
In all cases, the influent flow consisted of District of Columbia secondary
effluent obtained from the effluent channel of the 762 m3/nrin (290 mgd) D.C.
Blue Plains Wastewater Treatment Plant. The flow rate was maintained near
132 1/min (35 gpm) at all times providing a daily flow of about 191 m3/day
(50,400 gpd). The flow passed through a magnetic flow meter and the actual
flow was recorded once per day from a flow totalizer attached to the magnetic
flow meter. A pneumatically controlled valve in the influent feed line to
each system was adjusted as required to maintain the flow at the desired rate.
D. Biological System Clarifiers
The discharge from either the air or oxygen nitrification systems flowed to
center-feed clarifiers with surface areas of 7.2 m2 (78 ft2). This provided
for an overflow rate of 26.3 m/day (645 gpd/ft^) at the steady 132 1/min
(35 gpm) flow. The recycle flow rate was varied as operating conditions
warranted.
-------
SECTION VI
METHODS AND PROCEDURES
Each process was monitored on a 24-hour a day, 7-day a week schedule. The
only interruptions in the normal operating sequence resulted from mechanical
difficulties and necessary repairs were always made within a short time. Grab
samples of reactor influent and clarified effluent were taken every four hours,
and grab samples of mixed liquor and recycle solids were obtained every eight
hours for the laboratory analyses described below. The grab samples were com-
posited over a 24-hour period on Tuesday, Wednesday and Thursday; samples
collected on Friday-Saturday and on Sunday-Monday were composited over the
48-hour period. The single exception to this was that the samples for BODs
measurement were always 24-hour composites and the analysis was always started
within a few hours (4-10 hours) after the last sample for each 24-hour compos-
ite had been collected. All samples were refrigerated at 2ฐC prior to analysis.
In addition, all samples except those taken for BOD5 or suspended solids anal-
ysis were preserved with one drop of H2S04 per 30 ml of sample while they were
being held in storage. All laboratory analyses (except 6005) were performed
on a Monday through Friday schedule.
The following analyses were performed in the District of Columbia Pilot Plant
laboratories according to the procedures specified in Standard Methods (1):
suspended solids, volatile suspended solids, BODs, COD and TKN. Also, 6005
analyses were performed with nitrate production inhibited by the addition of
0.5 nig/1 of allylthiourea (2). The procedures specified in the EPA Manual (3)
were used for the determination of NH4-N, N03-N and N02-N with a Technicon
autoanalyzer. The method of Gales et al. (4) was used for the determination
of total phosphorus. Calcium concentrations were measured by atomic absorp-
tion with a Perkin-Elmer Model 303 Spectrometer.
In addition to collecting grab samples and compositing them for subsequent
laboratory analysis, the operating personnel also: (a) checked the mixed
liquor dissolved oxygen levels in the appropriate reactors every four hours
and adjusted the oxygen recirculation rates or air flow rates as necessary
to keep a D.O. of 5-12 mg/1 in the oxygen systems and 2-4 mg/1 in the air
nitrification system; (b) obtained solids samples for 30-minute sludge volume
determinations in one-liter cylinders; (c) measured temperature, pH and alka-
linity of selected samples; (d) measured the depth of the sludge blankets in
the clarifiers; and (e) adjusted the lime feed rates if needed.
Sludge wasting was done manually by diverting the sludge recycle flow to a
calibrated drum. When the waste rate was 0.19 m3/day (50 gpd) or less, the
wasting was done once per day. For waste rates in excess of 0.19 m3/day
(50 gpd), wasting of approximately equal increments was done twice per day.
8
-------
Throughout the year, samples of mixed liquor were removed periodically and
settling tests were run in 2.3 m x 0.15 m (7.5 f t x 6 inches) diameter stirred
columns. The stirring mechanism consisted of two 0.64 cm (1/4 inch) diameter
rods which extended the length of the column and rotated around the vertical
axis at a rate of 10-14 rph. Settling rates in which the recycle solids were
mixed in varying proportions with process effluent were also occasionally
evaluated.
On numerous occasions, batch kinetic studies were undertaken in the labora-
tory to determine nitrification kinetic rates. The nitrification studies were
performed by mixing 1-2 liters of recycle solids with District of Columbia
secondary effluent. A water bath was normally employed to insure that the
temperature of the kinetic analysis remained the same as that which existed
in the process. For those systems where pH control was practiced, the initial
pH in the kinetic study was adjusted with lime to a value similar to that
existing in the first pass of the process under investigation. Special studies
in which the pH was controlled at some constant value during the kinetic test
were also performed. During the kinetic test the sludge from the oxygen
systems was aerated with pure oxygen with sufficient mechanical stirring sup-
plied with a magnetic stirer and stirring bar to maintain the solids in
suspension. The D.O. was maintained between 5 and 12 mg/1. Diffused air was
added to the air nitrification sludge and the D.O. was maintained between 2
and 4 mg/1. The decrease in NH^-N was monitored by automated analysis. In
all cases, the Nfy-N removal followed zero order kinetics until the exogenous
NH4-N levels dropped to near 1 mg/1.
The kinetic rates were always expressed per unit of MLVSS. In some cases, the
rates were also expressed per unit of sludge protein or per unit of sludge
ATP. Sludge protein was estimated by the Folin procedure (5). Interferences
by non-proteinaceous material are common with this procedure (6), but this
was not of concern for the purposes of this study. Biological solids were
disrupted on a Bronson Sonifier prior to analysis. Sludge ATP was extracted
by boiling the cells for five minutes in tris buffer, and the concentrations
were measured in a Biospherics Biometer. Samples for protein and ATP were
frozen immediately after collection and maintained in this state until the
analyses were performed. The MLVSS determinations were always performed
immediately after the kinetic test.
Dissolved oxygen uptake rates were periodically measured by withdrawing a
sample of mixed liquor from the reactor pass of interest and immediately
measuring the decrease in dissolved oxygen as a function of time. The studies
were performed in mechanically stirred 6005 bottles with a Delta Scientific
D.O. probe inserted into the tapered bottle neck.
-------
SECTION VII
RESULTS
A. Introduction
The oxygen activated sludge system with no pH control was placed on stream at
the end of September 1973 and operated until the later part of May 1974. The
original research plan called for running the pH controlled oxygen activated
sludge system during the same time period. However this system was not started
until January 1974 because of delays in procuring needed equipment. In view
of this period of nonoverlapping operation, the results from the oxygen acti-
vated sludge studies will be presented in two discrete phases. The first
phase covers the results obtained when just the oxygen activated sludge system
with no pH control was in operation; this period extends from October thru
December 1973. The second phase of operation presented covers the period when
both oxygen nitrification systems were in operation (January thru May 1974).
A third phase of operation will be presented which covers the period when the
oxygen and air nitrification systems were being compared. These results were
obtained from June thru September 1974 and are summarized under Phase III.
B. Phase I (October-December 1973):
A step-feed oxygen activated sludge system receiving D.C. primary effluent at
the rate of 379 m3/day {100,000 gpd) was operated at the pilot plant during
the Fall of 1973. On September 28 (day 271) the system was temporarily shut
down and reconverted to an oxygen aeration system receiving D.C. secondary
effluent as illustrated in Figure 1. Sufficient nitrifying organisms were
present in the sludge to produce immediate complete nitrification.
The variation in mixed liquor solids and effluent TKN and Nh^-N from the
oxygen aeration system is presented in Figure 2. The data points shown repre-
sent 5-day averages. There was no deliberate wasting from the system during
October. However, the change in influent wastewater from primary to secondary
effluent was accompanied by a gradual decline in mixed liquor solids until
the latter part of the month. From days 302-316 there was repeated failure
of the influent flow controller resulting from the inadvertent cross-connection
of pneumatic and hydraulic control lines. This resulted in extreme flow vari-
ations and the effluent quality during this period is not amenable to meaning-
ful analysis. From days 317-351, the process ran under stable influent flow
and with a constant volumetric waste rate. As shown in Figure 2, there was a
gradual rise in effluent NH4-N during this period. The increased effluent
NH4-N corresponds to reduced nitrification kinetic rates resulting from the
decline in wastewater temperature as shown in Figure 3.
10
-------
0>
5.0
4.0
3.0
2.0
1.0
<
DC
HI
O
O
O
5000
4000
3000
2000
1000
0
A Effluent TKN
o Effluent NH4-N
280 290 300 310 320 330 340 350 360
DAY, 1973
Figure 2. Reactor Solids and Effluent Nitrogen for the Oxygen
Nitrification System Without pH Control (Days 275-365, 1973).
11
-------
0>
cu
o>
a
E
O
o
X
a
o
(0
0)
(0
a.
4
CO
^^
LL
O
2
o
CO
O
cu
-P CO
1^
s- cr>
re uo
CLIO
CO
s~ i
O LT>
-i-> r-
O CM
to
,
to
O O
r~ ซ--i_^ป
to
cu "o
S- S-
3 4->
t-> c
(O O
i- O
cu
CM
OS
o
CM
q
o
.
E Q.
3
4-> O
E J=
Ol !->
4- E
LU Oป
n3 to
O O
O !-
00 rd
O
O M-
ป|
Q i.
co
(I)
CD
12
-------
Results obtained from the operation during days 317-351 are summarized in
Tables 1 and 2. It can be seen that the District of Columbia secondary efflu-
ent, which serves as the influent to the oxygen nitrification process, is of
poor quality with an average 6005 of 61 mg/1 and a COD of 141 mg/1. To a
large extent this poor quality results from hydraulic overload of the secondary
clarifiers resulting in a relatively high suspended solids in the effluent. No
nitrification occurs in the D.C. secondary treatment process.
o
Flow to the oxygen nitrification system averaged 186 m /day (49,100 gpd) for
a corresponding detention time of 3.9 hours. The volumetric waste rate was
maintained at a constant value. The resulting SRT (7) was approximately
28 days. As indicated in Figure 3, the reactor pH during this period dropped
to around 5.7 in the fourth reactor pass. The pH data shown represent the
median pH values for each 5-day period. The last pass reactor pH frequently
reached pH 5.5 and there were a few occasions when it was reduced to 5.3.
The clarifier blanket rose slowly during the month of December and by day 352
it was necessary to reduce the flow to maintain the blanket within the clari-
fier. During the last 14 days of the year (days 351-365) the flow was stable
and averaged 156.7 m^/day (41,400 gpd) with a reactor detention time of 4.7
hours. This reduced the clarifier overflow rate to 21.6 m/day (530 gpd/ft^).
The additional detention time and the possibility of increased acclimation
to the colder temperature resulted in a reduction of the residual effluent
NH4-N concentration to less than 1 mg/1.
C. Phase II (January-May 1974)
On the second of January, the flow to the oxygen nitrification system was
increased to 191 m3/day (50,400 gpd). This did not produce any problems with
the clarifier blanket level which remained 0.9-1.5 m (3-5 ft) below the clari-
fier surface. On both the 7th and 8th of January, 1.9 m3 (500 gal) of recycle
solids were removed from the oxygen system and used to seed the oxygen nitrifi-
cation system with pH control. The removal of 3.8 m3 (1000 gal) of solids,
which was 17 times the normal volumetric wasting, resulted in a temporary
increase in effluent NH^-N (Figure 4, day 10). However the system recovered
rapidly and the solids levels and residual NH/j-N levels returned to their
previous levels by the last third of the month.
Flow to the oxygen nitrification system with pH control was at steady state
and averaged 185 m3/day (48,900 gpd) during the last half of January. By the
end of the month the MLSS concentration had increased to 5000 mg/1 and at
this time the full sampling sequence for laboratory analysis was initiated.
The variations in effluent TKN and NH4-N, MLSS, MLVSS and temperature and pH
for both oxygen systems are shown in Figures 4 thru 7, respectively. The data
points shown represent five-day averages. As shown in Figure 6, the MLVSS con-
centration in the system with pH control remained reasonably constant from
days 51-150. The operational characteristics of the system during this 100-day
time period and the influent and effluent quality are summarized in Tables 3
and 4, respectively. The effluent NH4-N concentration was extremely low and
exhibited only a small daily variation. Other effluent parameters eg. COD and
13
-------
1- S-
tO O
T3 $-
C S-
CO UJ
4->
CO
CM O ซ3-
10 LO tr> co co
CO CM t-H CM CM
co
>-
co
o o
to 'ฃ>
(O >
+J m
CO O
IO
co o>
CO CM
CO LO
CO tTl CM
O
O CO
Cฃ. CO
UJ i-H
CD LO
>- CO
X I
o r-
i-H
LlJ CO
I co
en. eC
o o
CU en
3 tO
i S- S-
to o cu
VD
00
i-H
O
O
t 1
CD
VO
LO
CO CM
O
CO
o
CD
IO
CO
o
CD
CM
0
O
LO
T 1
LO
CM
i 1
i 1
00
i )
0
LO
CM
rH
00
CM
CO
t-H
0
00
CM
CM
O
CD
r--
LO
co _i
o o
I-H o:
I h-
co 2:
I-H O
o; o
LU
I in
o o.
4J
C
O)
=c =>
:r o
co
CO
UJ
o
o
CQ
CM
>>
(O
-a
oo
co
-a
Q.
en
o
-o
CO
ป*
o
r
U_
4J
C
cu
p_
<4-
c
t t
T3
Q.
cn
n
O
LZ
+j
c
cu
3
^
M-
ฃ3
i
S_
3
O
-c
n
r
1
C
o
r
+J
ซ3
s_
0)
=C
ier Overflow Rate,
<+-
*^
s-
i1
ซ\
oo
co
_i
si
en
%
00
oo
>
_i
2!
^-*
cn
E
co
co
cu
r*
0
>Nj
U
cu
en
rt
CO
CO
cu
I '
0
>^
0
cu
en
A
z
i^
1
cu
r
U
>J
o
cu
en
E
*s
Q
o
cu
^
U
>^
o
cu
CO
to
-a
ซ*
i
o:
00
^~ c
>> 0
(T3 -r-
-o -ปJ
-~^ 0
LO 3
/") ~u
O O
CO S-
CL.
cn
^ (/)
" *l~~
O
r- 0
-P OO
(O
Cฃ
s:
>xซ^
U-
!
tO
+J
O
h-
Solids Production,
r
fO
4->
o
h-
O
O
Q-
co
r-
O
co
M-
O
c:
cu
o
s_
O)
14
-------
o
S- S-
*T3 O
-D S-
C S-
(O LU
co
CO
CO
C_3
-p
c
a;
c
T5 O
S- !-
o re
10 >
4-> CL>
co o
13 CO
>- r-.
X CTi
O -<
E
to
CO
00
CO
CT>
LO
CM
CM
Cป
51-
:r ^H
I LO
co
o: i
O r^-
LU iI
co
co
c_> co
ii >-
1-cC
co Q
Ct
LU I
H- O
o o:
< o
IE CJ
C_3
n:
1 Q-
LU h-
_J O
cn
M
O)
-o
S- S-
10 O
"TD 5^
c s-
co
c
"O O
S- -r-
(O >
co o
e\j
oo
co
cvj
CVJ
CO
cr>
CO
o
CO
00
CO
CO
CO
LU
U3
IO
CTl
CM LO
ii CO
LO
O
03
0)
CO
O
CO
o
to
o
Q
o
CQ
Q
O CO
o oo
CO
co
CM to
O -^ +
re
15
-------
C/l
>>
oo
O
r- CTl
S- T-H
^ o
in
C iI
cu i
CT)i-H
X c/)
o >>
O Q
+->
s- 'o
O S-
z o
I O
T3 4->
E 3
03 O
+-> -a
c c
cu fa
M- !-
LU 3
0)
l/6iu
16
-------
o
O
o
10
o
CO
o
CN
O
o
O)
ป
<
s >
o
K
O
o
o
o
o
n
o
CN
(O
U
s- r^
*-> cr>
c o
0) LO
C7)r I
-C 03
-P Q
i.
O r
^O
to 4->
C C
O O
i- O
s- Q.
o o
a 4J
o -i-
oo
5- J=
O 4->
-(-> -I-
O 3
o;
uo
01
en
T
Ll_
O
o
o
00
0
O
o
K
o
o
o
o
o
o
o
m
O
0
o
^~
o
0
o
n
o
o
o
CM
o
o
o
rซ~
o
I/BUI '
17
-------
O
CO
o
cs
o
o
o hป
00 g>
o Q
o
en
O
CN
to
>>
oo
c
o
(O
O
+-> CTi
C O
CD Lf>
P Q
i.
O
to 4->
O O
r- O
rt3 ^
i- Q.
O) 3
u o
oo
00
S- -M
O -i-
-M 3
O
(O
a>
D;
O)
O
O
O
o
o
o
CO
o
o
o
CM
o
o
o
'SSA1IAI
18
-------
Q O
O
<*)
O
O
O)
O r-
oo
n
e <
K o
o
o
o
CO
o
r-
CTi
S- i-H
O
oo in
QJ i I
=5 I
(O
to
Q.Q
S-
O i
4-> O
o s-
(O -l->
0) C
a: o
o
o
c 3:
to Q-
OJ -(->
S- 3
3 O
i-> ^:
10 4->
cu is
Q.
E -O
01 C
t (C
C -(->
C/l
**- E
UJ O)
+->
>, 00
S- >>
03 1/5
-a
c c:
o o
o -i-
-------
-o
S- i.
-
oo
-P CO
OO'Q
Vฃ> O O
co oo 1-1 in I-H oo
CM CO CO CM If) IT)
en CM ซd- CM CM co
en
>- o
X If)
O i-H
O)
cu
CD
tO
i- S-
(O O 0)
=c
CM
o
o
co
00 CO
" O
co
o
CM
O O
<ฃ> CM
10 10
O O
LO LO
IO i-l
*ป *s
00 00
o
cxi
on
CVI
IT)
oo
ฃ>
CM
CTl
Q_ Q
to
O _J
I-H O
I QC
00 I
i i s:
cc o
c
cu
3
< D.
CJ I
oo
oo
LU
C_3
O
o:
Q.
CO
LU
_J
CO
CM
oo
oo
-0
OO
A
LZ
-M
C
CU
3
!
M-
C
Q.
CD
A
O
LZ
^^
C
cu
3
l|_
5
s-
o
A
P
C
o
4ปj
_l
E
A
oo
oo
cu
"o
o
s
E1
ซ\
oo
oo
>
cu
r
o
o
ฃ
CD
E
ft
1
0)
o
o
cu
a:
r
iฐ
A
Q
o
C_5
CO
o
0
s
,
(0
^_j
\
1
o:
oo
_1
CD
LO
Q
o
CO r
CD en
A n
o cu
-13
<0
o:
^
LL.
(/)
o
cu
^
r-
lids Production, mg/
O
oo
r*_
H3
2
n
C
O
ฃ
O
3
O
s-
"o
oo
^_
to
M
O
C
o
r
O
3
o
O
o.
'o
oo
V-^
C
cu
0
S-
D.
20
-------
^
LU
1
oo
oo
,
o
(
7"j
* '
Ll_
l I
01
l i
1 1 i
.._,
x ซ3-
0 r-.
1 1 1 t_~i
f ซ
o
o: LO
o ซ-H
LL_ 1
OO LO
11 oo
00
+-> Q}
00 Q
c
(O
ai
s
-
CT
E
E
CU
3
^~
C
t <
D
S- S-
(O 0
o s-
c s-
fO LU
4-*
oo
-o o
S- <-
(0 -(->
o ซ
C -r-
05 >
oo Q
C
to
CU
SI
moooooovoiO' it ico ซJD
LocovoLOซ^-oO' 10 r-~
OCDCJOOCDOOO O
LO r-ซ CO
COi l
-------
SS were also quite low and indicate that the oxygen process with pH control
reliably produces a high quality effluent. Average values in March and May
are compared in Table 5 to illustrate the increased carbonaceous effluent
quality which was obtained during the warmer weather. The reduced concen-
tration of suspended solids in the effluent, in all likelihood, represented
an increase in clarification efficiency resulting from the warmer wastewater.
To maintain a pH of 7.0 in the last pass of the reactor required an average
lime dose of 126 mg/1 of Warner High Ca Lime (8). The inert materials con-
tributed by the lime required that higher MLSS concentrations be maintained
as compared to the system with no pH control in order to maintain the same
level of reactor MLVSS.
On day 86 and on one and possibly two occasions thereafter there were large
inadvertent solids losses from the oxygen nitrification system without pH
control because of a malfunctioning valve. These solids losses produced a
large decrease in reactor solids and the large temporary increase in the
effluent NH.-N concentration shown in Figure 4. This solids loss limits the
time period for which a meaningful direct comparison of the two oxygen systems
can be made to days 56-85, a period of 30 days. During this period the MLVSS
in the system without pH control averaged 2620 mg/1 (Standard Deviation = 241)
compared to an average of 2690 mg/1 (Standard Deviation = 199) in the system
with pH control. As shown in Table 6, the system with pH control provides an
effluent of somewhat better quality. The better carbonaceous quality can be
explained by an increase in clarification efficiency resulting from the high
lime dosage. The residual Wty-N level is also somewhat lower with pH control
but the difference is small. The pH adjustment results in a 50 mg/1 increase
of calcium ion.
The operating characteristics of the system without pH control have been
summarized for the 60 day period of days 26-85 (Tables 7 and 8). The oper-
ating characteristics from days 115-141 have also been summarized (Tables 9
and 10). In this case, however, the time period was insufficient to insure
that equilibrium operation existed. For this reason, the SRT has not been
determined. Nonetheless, the results indicate that the process performed
well (average effluent Nfy-N <1.0 mg/1) at the low reactor solids levels.
D. Phase III (June-September 1974)
On the 148th day of the year (May 28), the recycle pump to the oxygen nitrifi-
cation system without pH control was turned off while leaving the influent flow
on. The mixing equipment was removed during the morning of day 149, the reac-
tor was drained, and diffusors for compressed air aeration were installed.
Also a dry lime feeder was installed to feed lime directly into the first pass
of the reactor. The unit was placed on stream by the afternoon of day 149 at
a flow of 132 1/min (35 gpm). The amount of solids saved in the clarifier dur-
ing system modification was insufficient. Consequently, 1.5 m3 (400 gal) of
recycle solids from the oxygen nitrification system with pH control were added
to the air system on day 154. This produced reactor solids of 3000 mg/1 and
resulted in a completely nitrified effluent by day 156.
The removal of the 1.5 m3 (400 gal) of recycle solids from the oxygen system
22
-------
a to
C 'I-
O
CO
o
o
o
CM
O
r->-
o
CO ซ-H
O i-l
i-ป
o
CO i 1
CO
01
o
U3
o
r-. vo
CO i-H
in
in
IS)
8
ro
o
o
C\J
CM
CO
ซ-H
o
CO
CO
ro
CM
iI
CO
x ;
o
LU
1C
a:
o
cc
oo o
o u.
oo o
I-H Qi
Cฃ. I
LU -Z.
\ o
O CJ)
a: i
o
LU
Ln
LU
co
2
Standard Standard
i.
0
i.
LU
O
ID
(0
CM
r--. LD o i o
O O i-< 0 O
f 1 i-H
o 01 ซrf- Ln ซ i
ซ* CM un o o
Ln o CM
in co r-i
CO O
i I CO CO I-H O
CM
o
o
CO
o
I-H
CO
r-H
CM i-H i-H ซ3-
O i-H i-H i-H
O1 i 1 CO r-H
O un Ln r*.
CO CM
CO I-H 01 CO
Q
O
ca
T3
OJ
O jc O
O C O
OQ ii C_>
I
CO 10
i s
o
2: Q-
I CM CO
d- o o
oo +
oo ca
> o
23
-------
co
s:
LU
I
CO
CO
^^
o
1 1
1
1
C_5
ti
5
1
1 1- .
r*^
2: en
1 1 1 ,__(
0
^^" *^
X LO
O 00
i
1 1 i (^5
rc LO
I
co
rv' >_
( ) cฃ
U_ Q
*ป *
CO
O _l
I-H CD
1 OL
col
I-H ^
i-v o
UJ C_J
,
o
i S-
^^ 4J
O) ฃZ
E 0
0
rv
-i-> rc
ฃ= Q.
3 -l->
i 3
t ฐ
1 1 1 ฑj
5
i r
--. o
CD S-
E -!->
ซ O
4-> O
c~
cu rc
3 Q.
^~
^ -<""
M- -(->
UJ T-
"^Z
S- S-
re O
~O S-
ฃ S-
rc UJ
4^
CO
c
-o o
S- -i-
ro !->
"O fO
rc >
-i-> eu
CO Q
c
re
CO
TD
S- S-
rc O
c s-
rc UJ
4_3
co
c
-o o
S- !-
rc 4J
"O ro
ฃ *r
rc >
<-> CU
CO Q
C
rc
ฃ
^3" t l
OO LO CM ซ3- O ซ 1 t 1
O O I-H CM CM O O
CM CM i 1 CO
CM 1 .CO 1 LO
^J" CM LO i-H t 1 O O
CM ซ* CM
^J- to ซd"
1 LO IO O
CM en ซsi- CM CM CM o
en CM
r**. LO en o ป i o o
O O O r-H i-H O O
LO O
en oo oo i i CM ^- i i
ปป
CO CM *d" LO LO O O
en o I-H
r^. ^j- Y- H
CO T- 1 CM
I-H oo co I-H cn I-H co
00
I-H
O
0
en
o
CO
CO
I 1
^~
I 1
0
r**"*
o
CM
CO
I 1
1 1
o
UO
o
en
*
CM
0
00
o
co
CO
LO
o
00
CM
VO
o
CO
CM
I 1
^J-
Id
**o
CM
CO
o:
oo
CTl
-o
i. S-
rC O
-a s-
c s-
(C UJ
CO
CM
CO
CO
ID
CO
CO
ro
CD
CM
*
o
LO
o
LU
Q I
UJ
cu
r
M-
-o o
ro +>
T3 ro
rC '>
-P 0)
CO O
CM
to
CO
CM
en
r--
CM
c
ro
0>
UD
00
vo
CO
CM
CO PO
UJ
_J
CO
cP
O
on
a
cu
i *
2ฐ^
LO
00
I
o
JT)
LO -i-
Q j= Q
O C O
CO i-i O
co
co co
CO >
if I
*^ Q_
rO
O
rC
Q
24
-------
S- S-
03 O
"O i-
c s-
oo
CM ซd" 11
ซ . VD LO i i
vo r~- oo LO co vo
ro CM i i i i CNJ CNJ
UJ
(O >
-u d)
oo a
co CM
o o
ooio
co i i
CU
01
>
to
CO
S
O
0)
3
S
O
CU
3
(O
S_
CD
>,
to
O)
>
o
s-
ฃ!
4-
_i
E
A
oo
cu
'o
>i
o
cu
^
oo
>.
cu
f
o
>>
o
cu
g
I
cu
o
>,
0
cu
^
Q
c_>
cu
r
o
>,
0
O)
01
rO
TQ
A
1
Cฃ.
O
O
CT)
01
o
"O
O
C
O
"O
O
o
!-
4->
o
3
-O
O
s_
a.
(/)
-O
Q- D- I
to
T3
.f-
r-
o
oo
r
ro
-M
o
oo
i
(0
-M
o
O
+->
U
i-
a>
(X
25
-------
^r-
<^_
LU
i
r
oo
oo
z.
o
1 1
1
~ r^
x -
*~ ~i t_j
i ^_ ^
uo
Di O
LU CฃL
\ \
1 r~
0 Z
< o
o: o
n: in
O Q.
h- 1
LU O
=> 31
_J 1
Ll_ i i
LL. 3
LU
Q
=1
1
z.
LU
r
Dl
+J
C3
cu
3
pi~
<ป-
(*-
LU
T3
c_ c^_
(O O
-a s-
C i-
tO LU
00
c
"O O
s- -
10 -ป
T3 ro
C -r-
(O >
4-J CU
c
(O
CD
^^
,
^^^
CT
E1
A
4->
C
OJ
3
r^
t(-
I-H
T3
s- s-
10 O
"c s-
(O LU
oo
c
o o
i. T-
(O -(->
*O fO
C !-
(0 >
-t-) CU
CO Q
c
(O
^
CT* CTป
CM 10 +
O .*: +
CM
-------
"O
S_ $_
03 O
-O S-
c s-
03 LlJ
+J
oo
CM
co
IO
ID
O
ro VD
oo
ro 4->
"O rO
C <-
rO >
4->
OO Q
oo
OO O
CM LO
U3
CO
-CM
co tn
CTi
>- si-
X I
O I
LO
O) O
CD O
3 re CTs I-H OOLOLO LOO
i S^S- CTi > O CM C\J OO ii i( O OO
rOOCU COcn lO *3" 00 ^3" OO rj> O O
^ป > iI ^" OO CM tO 'I *I VD **^ LO P""*. <"^
oo
Qi >-
o <;
U. Q
oo
O _J
i-i O
h- o:
oo I
UJ
o:
>.
T3
"O
-"H^
CO
E
ri
3
O
LZ
40
c
(D
3
^~
14-
C
i i
T3
Q.
CD
n
^
O
LZ
-l_>
c
QJ
^
r
4
c~
i i
l/l
S-
~^
0
-C
r\
d)
E
^
C
o
r
+J
fC
S-
1
**s^
CD
E
A
oo
CO
J
s:
i
x^
O^
E
n
CO
CO
^>
1
s:
i
"s^^
en
E
rt
oo
00
O)
^~
o
;>^
O
O)
o:
r
v*^
CD
E
A
OO
oo
^ป
O)
p-^
o
>^
u
O)
Q:
,_
v*^
CD
E
A
~^l
***s
1
O)
r
0
o
0)
Cฃ
r~>
"-^
CD
E
n
CZ1
o
^_3
O)
"o
o
0)
Cฃ
(O
o
LO
Q
o
co
CD
^/
f\
o
4^
fG
rs
s:
u_
27
-------
oo
>-
oo
OOJO OJ
Ci-ซ LO
T3 fO c ^ f"^ c^j ^D 00 ^^ ^^ c^i
(->
LO CO OJ
00 LO
C_3 ^H
1 1 1 1
I
oo oo
Ct et
LU O
1 ^ ^
0
c_> ^ 01
0 E
H- 0
py" ft
LU 31 -4-J
^ O- ฃ=
_1 CU
U_ 1 3
u. ro r
LU O 4-
^ c
Q 1 I-H
< s
1
"ZZ.
LU
^
_J
LJ_
^
1 1
-^
03 O CO
-o s-
C S- OJ
03 LU
oo
E
T3 O
S- !-
03 4-> LO
T3 03
E -t- i-H
03 > "-H
-M Q)
00 Q
03
0) 00
s: LO
O"! t-H Ol LO CO
ซa- co oj o o
i-H 00 LO
CO VjO
LO LO ซJ"
OJ i 1 i 1 OJ t-H
OO LO
CO
1 LO O> CTl < 1 LO
i ป~H r^ LO oj t-n
OJ
00
o
I--.
o
LO
CO
OJ
CO
co
cr>
LO
ca
<:
O
00
-a
a>
LO
a
o
oa
a
o oo
O 00
oo
oo
^^
co
0
OJ
0
z
_
3
S-
o
Q.
CO
o
r
Q_
^
4^
P"
"03
f^
ซ=t
CO
o
0
03
O
CO
+ "^
03
0 *
28
-------
had no noticeable impact on product quality. The effluent COD for the month
of June averaged 19.7 mg/1 and the Nfy-N level was 0.19 mg/1.
The MLSS and MLVSS levels in the air and oxygen nitrification systems are
shown in Figure 8. It can be seen that the MLVSS levels were generally within
10 per cent of each other. This is not true of the MLSS concentrations because
of the difference in lime requirement to maintain pH 7.0 in the last pass.
The process characteristics for each of the two systems for the 80 day period
from days 186-265 are summarized in Tables 11 and 12. The carbonaceous efflu-
ent quality and the residual Nfy-N and TKN levels are the same (Figure 9).
The increased phosphorus removal in the oxygen system relative to the air
system apparently results from the higher lime dosage needed to maintain a
fourth pass reactor pH of 7.0 in the oxygen system. As shown in Figure 10,
the fourth pass reactor pH values were essentially identical in both systems
but there was a larger pH drop across the four passes of the oxygen system
than occurred in the air system. The higher pH in the first pass of the
oxygen system compared to the air system produced the increased phosphate
precipitation.
The average SRT values for the 80 day period summarized in Table 11 were
essentially the same. During July, August and September, the respective SRT
values for the air and oxygen systems were 11.1 and 12.2; 10.5 and 11.7; and
7.9 and 6.5 days. The lower SRT values in September reflect the increased
wasting which was applied to the system during the last month of operation.
Sufficient time was not available to characterize these two systems under
extended equilibrium operation at these relatively low SRT's.
The only drawback to the air nitrification system was the poorer settling
properties of its sludge compared to the oxygen system. The average SVI for
the air system from days 186-265 was 194 ml/gm whereas it was only 55 ml/gm
for the oxygen system. Results of batch settling tests in the 0.15 m (6 inch)
diameter column over a range of solids concentrations are presented in Figure
11. The increased settling velocities in the oxygen system more than compen-
sated for the increase in MLSS which were carried in this system to maintain
the same MLVSS level as in the air system. As previously indicated the dif-
ference in the percent volatile solids reflects inert material resulting from
the differing lime dosages for pH control.
E. Supplemental Studies and Analyses
Throughout the course of the study, nitrification kinetic rates were determined
by laboratory batch kinetic studies. Although the interpretation of kinetic
values can be misleading (see Discussion), it is felt that these studies pro-
vided a useful tool for comparison of the various processes. The results
obtained from all kinetic evaluations are presented in Tables 13 thru 18.
In all cases the laboratory studies yielded zero order kinetic constants. The
results of a typical kinetic analyses are presented in Figure 12.
As shown in Table 14, the laboratory kinetic rates in the system without pH
control were consistently somewhat higher than in the pH controlled system on
29
-------
8000
o
X
i
7000
6000
O)
ฃ 5000
r*
(A
o
(/) 4000
3000
2000
1000
150
\
AP"ฐ*'0"0''OV
^thw^2^-
V
GJ MLSS Oxygen System
v MLSS Air System
A MLVSS Oxygen System
o MLVSS Air System
I i i
170
190 210
DAY, 1974
230
250
Figure 8. Reactor MLSS and MLVSS Concentrations in the Air and
Oxygen Nitrification Systems (Days 155-265, 1974).
30
-------
GO
GO
z.
O
tC
\-
o
E
M
to
OO
E
O)
Dl
>h.
X
O
a
s_
03
o
E
to
1 *
OO
s-
o
cu
r_
to
E
O
t
(O
>
Q
CD
cn
to co
j_
cu co
> cn
^-
cn
0
I 1
o
o
CM r~ LO
ปco vo in
i 1 VO LO CO
LO CO CM CO VO
CTi
LO
CO
o
VO
CM
CM
o
^o
CO
VO
o
in
CO
>
o
*
o
vo in
^" VO
I 1 t-H
O
^^
O O
* t^
*fr CM
il t 1
in
in
CM
CM
o
^f"
CM
ป
CO
1 1
O VO
tI iI iI O
VO
o co
CM r-- ti
i-H CTi CO
1
1 1
2:
^' ^-
\ \ \ f"**.
ocn
x cu
0 - +>
LO CO
Q VO >,
Z:CM oo
-
^S
E
a o
S- -i-
(0 4J
a to
E !-
(0 >
-(-> CU
00 Q
S-
o a>
cn o
O) tO CM O
3 S- CTi
CU O
IO > O CM
5> ซa: CM in
f^.
CTi
co
co o
r^ co CTI
^^ ^^ co
CO CM CO CO
LO
1 1
CM
O
^^
CM
CM
O O
iI CM CO
vo CO ^d- co
iI CTi CTi iI
O O
co LO
<* O O VO
" VO CTi " CTi i-H
CO ^f CM CO
i-H CTi CTi i-H CTI O
CM
in
CM rป.
. co
CTI CT> ii
CTt
c
cu
oo
oo
LU
o
o
a:
Q.
UJ
_l
CO
CM
4J
to -^.
-a T3
. Q.
E cn
to
-a
CO
o
cu
3
T3
a.
en
4->
cu
10
3
0
to
cu
cu
4->
to
cu
o
cu
S-
tO
CU
tO
a:
s-
cu
o
S-
cu
S-
<0
cn
oo
oo
cn
oo
oo
cu
a
to
CD
o o
cn
ft
00
oo
cu
o
cu
a:
cn
00
oo
cu
75
o
cu
OL
cn
1
cu
o
u
cu
OL
cn
Q
o
o
cu
75
o
cu
a:
CO
to
-a
i-^
cc
oo
OO *- Lf)
00 CM VO
> i-H CM
_I CM 1
s: i co
VO I-H
cn co CM
^ i-H
"^ to
2? i2 ^
tO >> tg
^o ^J f^.^
LO
Q <~
o ^.
CQ *v. cn
cn E
cn E
* *
O CU CU
r- (O CO
^"^ CD CD
ro Q Q
oc
^T" g ฃ1
^v, *r- *r
Ll_ _l _l
E
o
r
o
"O
a.
to
o
To
oo
i *
o
i-
al Solids Production, Ib/MG
-M
o
1
cent of Solids Production in
S-
cu
Q-
Chemstone Hydrated Chemical
Warner High Calcium Lime
*
*
*
31
-------
CO
s:
LU
1
CO
>-
co
z.
o
^-1
<
(_j
l r
Lu
l i
o;
i
i i
z.
LU
CJ3
>-
X
O
Q -
Z. *&
< r^
CT>
CXL I-H
1 I
-
C_5 cC
^Hง
1
co
1 1 1
r^ _J
o: o
LU CC
1 1
C_> Z
^C C^
ry O
<ฃ
ic in
0 Q.
| ;E
Z I
LU l-H
^> 2
I
Lu
Lu
1 1 1
C
O
r-
+J
03
O
r-
^
r
s_
.)_)
^-
z.
i-
5
C
O
r-
4->
(O
O
t
p-
S-
4->
Z.
E
O)
CD
>>
X
o
r^
*"^^
01
E
9\
-!->
E
(11
3
M
if-
LU
r"~
"*ซ^
cn
E
ปป
-P
c
XI 1
u^
3
4^
M-
LU
^
Ol
E
n
+J
E
OJ
3
^^
-3ฐ
=ฃ
raLU
+J
CO
E
T3 O
S- -r-
03 -M
"O 03
E !-
03 >
4->
CO
E
-a o
S- T-
03 +J
n (o
<^j "j"
c 'd
03 >
4-> Ol
CO Q
E
03
0)
s
T3
S- S-
03 O
T3 S-
E S-
O3 LU
_l_)
co
c
T3 O
S- -r-
03 -ป->
O 03
E -r-
t 1 LO CO CTi CO *3"
1^ < l CO CO Cxi O
O O O O O O
O
c\j co ^3- ^- in co
1C < 1 CO CO CM O
*! VO
ซd- CM CM o
O O
ซ-l CO CM (ฃ3 * i-H
ซ 1 CO O CTl "* CO
^1- <-l CO CM CM O
O O O O O O
CO
IO i-H VO IO ซ 1 CM
CO i-l CM CM CM O
IO ^~
00 LD i-H CO CTl
o
00 CO CM CO ^" O
si-
<* CM CO LO CO
*
i 1 CM t 1 i 1 O
cn to LO i i
CO
ซ-l CO LO CO
ซ 1 i 1 i 1 i I CM
CM
O
O
IO
I 1
0
CD
t 1
,
o
CM
O
o
0
CM
O
CT)
i-H
,
O
CO
CM
O
^t-
CM
^t-
i 1
o
CM
i l
un
CM
i-H
CO
I 1
0
CM
i 1
VO
CO
i-H
I 1
o
LO
O
o
*d-
i-H
o
IO
o
53-
co
1 1
o
r-.
0
CO
S
E
O3
VO
un
O
CO
in
ID
O-)
CM
in
un
LT>
CM
ii
LU
_l
co
LO
Q
O
CO
Q
O
CO
-o
O)
-(->
_Q
IE Q
E O CO
i i o co
^
t
CO
o
z.
1 CM
CO Z. ^J- O
co ^: ic ^
> 1 Z ^
to
3
S-
o
.E
Q.
CO
O
JZ
Q-
32
-------
30
O) 20
O
o
o
10
^ 3.0
O)
^ 2.0
z"
H ]-ฐ
0
1, "
- 2.0
ซ
X.
Z
1.0
0
150
170
o Air System
A Oxygen System
o Air System
A Oxygen System
A
oAir System
A Oxygen System
190
210
230
DAY, 1974
250
Figure 9. Effluent COD, TKN and NH,-N for the Air and Oxygen
Nitrification Systems (Day! 155-265, 1974).
33
-------
a
cc
O
O
<
m
cc
CO
<
a.
CO
DC
E
a>
CO _
c
0)
O)
O
<
E
0)
CO
o -
DC
O
O
<
LU
OC
(/)
CO
<
a.
DC
O
o
K
CN
O
ซn
CN
O
CO
CM
o
CN
03
U
Ol
CT>
X
o
0)
s
<
o
o
oป
o
ts
CM
O LT>
M- UT)
r-H
to
,
i
-------
'AjpO|9A
cs
o
o
o
CN
O
o
o
o
o
o
00
o
o
o
o
o
o
o
o
o
CN
to
-a
o
to
c
o
4J
C
r- O
O
r !
+-> 4J
i- O
O C
O 3
i U_
a>
CD 10
-p
ai
to
O
CO
o
CM
35
-------
co
>-
co
+_>
(O
a:
o
!Jo
01
.r-
(O
o
r^
1
3T
Z
cn
CO
co
>
_i
cn
LO
vo
0
0
CT>
^j-
O
o
vo
LO
o
o
1^ CM
^f ^J-
O O
O O
CD
CM
O
O
f*>.
CM
O
O
O
CO
O
O
cn
co
o
o
(O
c 3:
r- Q.
U3
vo
.
vo
vo
CvJ
vo
co
vo
LO
LO
LO
LO
c
3:
i- CL
C
1 1
1 10
| *
1 VO
vo r^- vo
vo vo vo
vo
vo
^- vo
vo vo
vo
vo
O O
co
UJ
~^
J
<
31
Q.
1
=>
O
Q.
ฃ
^
O
0
O
o
CM
O
LO
O
r- en
1t ซ 1
o
LO
*
CD
1 1
o
LO
oo
f 1
o
vo
1 1
o
LO
r <
o
LO
LO
I 1
&
*
vo
ซ 1
O (
^
o
1 1
I
1
LO
CD
LO
CO
LO
co
LO
CO
to
CO
(O
o.
c\j
#
vo
O I-H
.
VO VO
CM
VO
CO
VO
Csl
VO
01
LO
LO
LO LO
CM <-l
O i-l ^- O
CO rH i-l CM CM
LO
a
0 O O O
O Z -ZL -Z.
O O O C
CU CU Q)
-------
Date
TABLE 14. COMPARISON OF THE KINETIC RATES
FOR THE OXYGEN NITRIFICATION SYSTEMS
WITH AND WITHOUT pH CONTROL
Temp
Kinetic Rates
Kinetic Rate
Difference
100
Feb 1
15
26
Mar 5*
5
6*
6
7*
7
Mar 22*
28*
Apr 19
24
30
May 7
10
16
21
ฐC
17
15
15.5
17-17.5
17-17.5
16.5-17
16.5-17
17.5-18
17.5-18
16.5-17
17.0
19.5
19.5-20
22.0
21-22
21.0
23.0
22.0
Kg NH4-N/day/Kg MLVSS
Without
pH Control
(A)
0.064
0.059
0.071
0.116
0.103
0.094
0.107
0.088
0.114
0.094
0.110
0.146
0.116
0.126
0.144
0.113
W1 th
pH Control
(B)
0.053
0.047
0.060
0.062
0.063
0.071
0.065
0.079
0.070
0.103
0.104
0.100
0.109
0.088
RA)-(B)1
L
-------
oo ttป
s: 4->
LU (O
oo
> o
C/1CL -
2:=s; co
o c
H-lQ -r-
12: ^
{ ^
U. I-H
1 i LU
Cฃ\
(0
I-H CC
Z.CL.
UJOO
CJ3 00
"^~ ^> r-
X_l 2: (i
os: i :
^r
LULL. 3: 1
3:0 2: c
t Q
QiM
OOO
u-o:
CQ
oo
UJ LU
1 3:
o;
00
[Zl _j
UJO
3 2:
o
LiJ C_5
13:
o.
1 |
LJL.
Oh-
py ฃ^
03:
oo h-
I-H 1 1
0:3
Q. Q
^r ^_
1 -g~
^J^x.
31 D-
^ S-
^^^_
31 O
2: E
>j
(O
o
z.
1
3:
2T
cn
s
a .ฃ
> cu ป
^ ' * mm
J ซ^* f"
= (0 -
uocc
C
r- r-
0) ป
4-) C
O ฃ
s_
Q.
r"
CL. "*
h- C
4J
o
a.
en
Q.
1
<
CD
E
oo
oo
>
_l
s:
en
XX
^
^
J>
**
7)
?
ซ^
3>
i i
i i
i i
00 oo
oo
00 i-H
10
vo oo
CM CM
1 1
0 0
X X
i-H 0
CTl LO
VD en
r*^. co
CM cn
I 1 r-H
LO 1
|
O 1
r-H 1
O OO
r^>
O I-H
ID O
CM O
0 0
P*"^ P*"-
VD 00
LO LO
0 1
LO 1
CM CM
1 1
O O
X X
00 OO
O 0
00 I-H
0 *3-
i 1 i-H
CM LO
CM cn
r-H
VO CTl
* CT*
l*x. i-H
f^
*j- cn
^J" O
o o
OO 00
cn LO
vo o
i i
*3- LO
f*^ i-H
LO i-H
I-H
CM CM
1 1
O O
X X
O OO
en LO
O LO
(X3 OO
-H OO
i 1 CM
ID i 1
OO 00
1 1
1 1
1 1
00 CO
r-H CO
0 O
r*ซป f***
to en
OO iD
^O i-H
CM LO
^1- 00
1 1
1 t
1 1
CTl O
1^ CTl
r^. 00
r-H
o
3!
h-
LO I-H
LU
a.
E o
cuo
h-
E
CU
I \
in
oo
CM CM
CM CM
jc
-J -7
o- a.
CM CM
CMCM i-H i 1 OOOO CMCM
II CM CM CM CM CM CM
i-H i-H
CM CM
T- r- T- T" ~I~ "T" "T" T
^L- ^^ ^L. L- 1*. 1~ ^ 1-*
Q.Q. Q.Q. 0-0. 0.0.
Z.-3. 2:3 2T3 2:3
r i~
0 4->
S- C
r-> O
C 0
o
u 3:
0.
3;
ฐ"5
O T-
C S
3: 3:
0- 0-
S
LO LO LO
CVJ
LO
38
-------
TABLE 16. EFFECT OF pH ON NITRIFICATION KINETIC RATE
FROM THE OXYGEN SYSTEM
WITHOUT pH CONTROL
Date
Nov. 15*
Nov. 16
Nov. 20
Jan. 16
Jan. 16
Feb. 28
Feb. 28
Apri 1 4
April 4
April 4
April 4*
Temp.
ฐC
17.5
18.5
19
17
17
15
15
17.5-18
17.5-18
17.5-18
17.5-18
Kinetic
Initial pH
6.6
7.5ฑ0.1
7.3ฑ0.2
6.6ฑ0.1
5.8ฑ0.1
6.U0.05
5.510.02
5.910.05
5.610.05
5.510.05
6.6
Study
Final pH
6.65
7.5+0.1
7.310.2
6.610.1
5.810.1
6.1+0.05
5.510.02
5.910.05
5.6+0.05
5.510.05
5.9
Kinetic Rate
Kg NH4-N/day
Kg MLVSS
0.049
0.048
0.048
0.038
0.032
0.091
0.057
0.135
0.120
0.114
0.139
pH not controlled
39
-------
CD
E
CO
a
o
oo
a>
-o
E
cr>
oo
o
^i-
cr>
o
o
o
CM
LO
o
o
LO
CT>
o
CTt
LO
O
oo I
z oo
o >-
ii oo
< 2=
Cฃ O_l
I i-iO
z. I o;
LU <; h
OO2T
CTi
O Li_ O !-
O >i S-
a; :n a.
oo I a. -=c
Q I-H
cn
o z o
oo uj ^
CJ3 t
a >- I-H >,
LU X 3 (B
Q O Q
a.
00
00
2
01
o
c
o
CO
CO
ta o
Q- 2:
CO
CO
CO
(O O
a. -z.
CM
CO
CO
to O
Q- 2T
CO
CO
to o
C IT)
CD CTi
3
r O
in
1I
o
o
CM
o
O
O
in
uo
o
CM
o
rH
CM
LO
cr>
CM
o
LO
O
o
LO
CM
CM
O
10
O
CM
O
10
O
LO
CM
o
C\J
O O LO
LO O <*
oo 01
-------
oo
UJ
l-H
Q
- >
1
oo
o
i i
h-
UJ
z.
\ i
in
ฃ
t LO ^" i-H
O *d- 'CM
S_ O t-H
Q- ii oo i-H en
E
oo
oo o LO vo co
> CM en CM o
o o o o
en
r^ CM I-H iv. i^ CM co CM co rv i i
. . . . . . . . . . it
CO^l- CMCM OO^J- CO^- CMO II
i If \ t-H i 1 i 1 t-H l-H i 1 i 1 i-H II
OCO LOป-H T-Hi-H i-H^l- LOI^ COCM
VOCM ^i-rv LOVO voi co^- COLO
oo oo oo oo oo oo
LU
I
OO
>-
oo
r- S-
(O CU .C
(O
a: ^-.
CO
ซd- O
en 10
ซฃ> o
ซ i i i
.
en en
oo en
t i
.11
co f-n
oo
en 1-1
co
en
co
LO O O LO
^^ ^^ ^^
^^
vo co rv I-H
o
CD
>-
X
O
Q
Z.
=C
CtL
H-I
<
o i"
D-
O LO
vo cn
i-H
O LO
i-H CM
VO 00
O O LO LO
^ซ *st~ rv co
vo vo vo cn
O LO
cn vo
vo cn
LO LO
o en
O LO
CO I-H
ซ* CO
i i
i i
i i
oo
oo
I O LO
VO LO
-1 CM
LO LO
CM r^
CO ^^
t-H i 1
LO O
rv I-H
oo rv
i-H i-H
LO LO
LO VO
oo -
o;
oo
00
Q. LO
E O
COO 00
I CM
oo
CM
LO
CM
VO
CM
vo
CM
VO
CM
LO
CM
LO
CM
CO
<
0)
4->
in
CUCU
CD o>
.t% ฃ5?
-------
co -o
iI CO
CQ -t-i
c
S- !-
_c cu
\ 4-> CM 1 II O ซฑ LOCM
Z O LO 1 1 VO CTป
IS- -CO II O O
^J- O CT* t~H 1 1 r**- Ot t-H t-H
^ E
to CD
CU CD
rซ
U
(U >>
C fO
i- TD CO
iti ^ c/7 ซa- co COLO CM r-ป 01 co
Z > CM LO CT> ^J" CTi CM CM CO
1 1 i It 1 O t 1 Ot-H t It 1
31 OO OO OO OO
Z CD
i S-
ro O) ^: co r^LO ซ^-r~~ oco
> 4-J ***^ co * r^- co co r^. LO *
3* O fO ^ *"~* CO
E o; . vo > i s^ot cocf) LO < i
cu cr>
c:
r-i OO II LOCO LOt-H
CU~-^ COO II OCO CM i I
4-^ CD LO CPi 1 1 LO O"> LO CO
O E *"~^
CL
COi LOO LOLO OLO OO
CO1^^ LO^l- LOtJ" O*d" COCT>
>CD t-Hf^. i 1 LO OCO CMP-
Q. O O O LO
E 0
GJ^^ f"*** **O CO *s^
1 CVJ CM CM CM
E c c c c
cu cu cu cu cu
4-> CD CD CD CD
to ฃ->> S->^ S->> S->1
>, !- X !- X -I- X !- X
CO =tO co
r 1
o o
00 LO
co rป-
LO
^~
CM
cu
CD
^ x"
<0
CM
1
o
42
-------
HI
CO
>"
(/>
< K
O CO
II
DC
<
CO
LU
5
LU
__ o
Ol
ns
o:
o
OJ
r-
M
o
e<3
o
M-
O
fO
c
O)
-M
a
(C
O
J3
(O
CD
en
i^
u_
I/Bui 'N-
43
-------
the basis of MLVSS. The values on March 5, 6 and 7 represent duplicate
studies in which pure oxygen aeration was compared with aeration with a small
portion of the actual process gas. It is apparent that the use of oxygen in
the laboratory does not affect the kinetic rate. In addition to the volatile
solids determination the sludge protein and ATP content were also measured in
a few selected cases. A comparison of the kinetic rates on the basis of all
three parameters is presented in Table 15. There is no consistent pattern
with respect to the rates per unit of protein. The rates per unit of ATP
were considerably higher in the pH controlled system. However, this differ-
ence is difficult to interpret because of the differing F/M ratios at which
the systems were operating when these comparative kinetic studies were per-
formed. Although the influent flow rates were quite similar at this time,
the MLVSS concentration in the system without pH control was approximately
half that in the pH controlled system (Figure 6, days 100-140).
A few laboratory batch kinetic studies in which the pH was controlled are
presented in Table 16. Although the number of studies is limited, they do
provide some insight into the effect of pH on a system acclimated to low pH
conditions. Above a pH of 6.0-6.1, there appears to be little advantage in
increasing the pH. Below a pH of 6, there is a decline in the kinetic rate
with decreasing pH. Considerable nitrification still occurs at pH 5.5. How
low the pH can be reduced before nitrification ceases is unknown.
The values presented in Table 16 for day 94 (April 4) represent the result
of a series of studies to confirm that the laboratory kinetic studies are
representative of actual process potential. The value for uncontrolled pH
was determined in the laboratory in the normal manner, i.e. oxygen aeration
with no pH control. The three additional kinetic values reported were
obtained in the following manner. A sample of mixed liquor from a given
reactor pass was withdrawn and the pH was carefully measured. Next NH^Cl
was added to the sample to produce an NH4-N concentration of about 10 mg/1.
The sample was then aerated with a portion of the gas stream that was being
used for that particular pass in the actual process. Lime was added as
required to maintain the pH within ฑ0.05 pH units of the initial pH. The
kinetic rate at pH 5.9 was the same as that measured in the laboratory kinetic
test with oxygen aeration. The kinetic rate declined with further decreases
in pH.
Samples of process influent and of reactor mixed liquor were analyzed through-
out the day that the above mentioned studies were performed. The results are
presented in Table 17. Influent flow during this period was 143.5 1/min
(37.9 gpm) and the recycle flow was 49.6 1/min (13.1 gpm) yielding a total
flow through the process of 193.1 1/min (51.0 gpm). Each reactor pass has a
volume of 7.65 m3 (2020 gal) yielding a detention time of 0.66 hours at the
193 1/min (51 gpm) total flow. The soluble NH^N concentration of the re-
cycle flow was 1.1 mg/1. Using the average of all NH4-N concentrations
measured in the influent and in the first pass, the average influent NH^-N
concentration (proportioned to include mixing with recycle) was 8.78 mg/1
and the average Pass No. 1 NH4-N concentration was 2.08 mg/1. Average solids
were 2000 mg/1 and were 84.4% volatile. By treating the first pass as a com-
pletely mixed, continuous flow reactor with no backmixing, the kinetic rate
44
-------
for NH4-N removal was 0.144 gm NH4-N/day/gm MLVSS. When using those values
between 0850 hours and 1450 hours (which corresponds to the period of steady
influent Nfty-N) the kinetic rate is 0.141 gm NH^-N/day/gm MLVSS. It can be
seen that this kinetic rate (0.141) is essentially the same as shown in Table
16 for the kinetics test with Pass No. 1 (0.135) or that obtained in the regu-
lar kinetics test (0.139). The process kinetic rate determined by the differ-
ence in influent and Pass No. 1 values could be biased slightly toward the
high side because of a small amount of backmixing with the second pass of the
reactor. However, this is not felt to be significant.
Observation of the results of all the batch kinetics tests indicates that the
NH4-N removal rate in short-term studies is independent of exogenous Nlfy-N
concentrations above a concentration of about 1 mg/1. Hence, the rate meas-
ured in Pass No. 1 is concentration independent. This is not the case, how-
ever, for the kinetic rate in the second pass. Using the average of all
values for Pass No. 1 and Pass No. 2 and treating Pass No. 2 as an ideal
complete mix reactor, yields an NH4-N removal of 1.63 mg/1 and a kinetic rate
of 0.037 gm NH4~N/day/gm/MLVSS. This kinetic rate is only 26% of that rate
measured in the first pass and reflects the change from a concentration
independent kinetic rate to a concentration dependent rate. The kinetic tests
at various pH values indicate that the main factor is truly concentration with
the lower pH playing a minor role (in the pH ranges explored in this study).
Examination of the concentrations reported for Passes 3 and 4 reveals a con-
tinuing decline in kinetic rate as the concentration decreases. This is
exactly what is expected.
Since the air and oxygen nitrification systems were operated under similar
loading conditions throughout the period when their performance was being
compared, their kinetic rates can be directly compared in a more meaningful
way. The kinetic rates obtained during this period of operation are sum-
marized in Table 18. The protein concentrations, as estimated by the Folin
Procedure, were a constant percentage of the MLVSS within both systems
(Table 19). In all cases the kinetic rates were similar on any given day.
Furthermore there was no tendency for either of the systems to have kinetic
rates consistently higher or lower than the other.
On several occasions during the study, the mixed liquor from the fourth pass
of the systems was removed for a determination of the settling velocity in
the 0.15 m (6 inch) column. The results of these determinations are summar-
ized in Table 20. The lime addition caused a large amount of non-volatile
material to be carried in the oxygen system with pH control. For example, the
average mixed liquor volatile solids concentration in this system for days
186-265 was only 36%. Hence high MLSS concentrations were necessary to main-
tain the MLVSS concentrations desired. Nevertheless, the increased settling
velocity resulting from the lime addition compensated for the higher MLSS
levels which were needed in the pH controlled oxygen system compared to the
levels in the air nitrification system with pH control (average MLVSS con-
centration of 58% from days 186-265) or the oxygen system with no pH control.
On a few occasions during the study, the oxygen uptake rates in the oxygen or
air system were measured. These rates are summarized in Table 21. The lower
than normal rates on July 31 reflect the presence of storm water in the was.te-
water.
45
-------
00
oo
LU
oo ii
00 H-
s:
LU
oo
00
o
1 1
1
r^
0
i i
LJL,
i i
DC
\ i
*^.
Z.
LU
CD
X
o
z.
1 1
LU O
O 1^*
OC *f
o.
^^
^-,
t 1
LU i LO
I ^ en
O C7> t-H
a: E I-H
o_
OO r LO
oo ^^, ^^
> CT) LO
J E CM
LO ซ* i 1 CO
vo f^ vo i^
*J- CO LO *d"
LO O LO LO
CM ซ3- CO VO
oo vo cn en
LO O LO O
t-^ ซ i vo ^~
1^ 1^ VO CD
ซ 1 t 1 t-H CM
i i ^- r^ LO LO co
t i r^ I-H co vo en
LO LO LO LO LO LO
LO LO O CO i-H CO
en ซ i o oo I-H ซ*
r^- oo en en o o
i i i i
LO O O LO O O
LO CM ซa- * en vo
LO ^j* r^. oo t^ f^*
rH t 1 i 1 i 1 ซ-H i 1
o o
LU
>- I
oc c_)
eg; Q LU
SI "Z. I
S
-------
TABLE 20. MIXED LIQUOR SUSPENDED SOLIDS SETTLING VELOCITIES
FOR THE AIR AND OXYGEN NITRIFICATION SYSTEMS
Oxygen Nitrification System
Without pH Control (March-
April) and Air Nitrification
System
Oxygen Nitrification System
With pH Control
Month
March
April
May
June
July
August
September
Temp
ฐC
16.5
17.5
17.5
17.0
24.0
26.5
26.5
27.0
27.0
27.0
25.0
26.0
25.0
23.0
MLSS
mg/1
3200
3200
3000
2000
4500
4600
3900
4100
4000
4500
3700
3900
3600
2800
Settling
Velocity
ft/hr
12.5
11.4
12.3
15.0
7.8
6.9
7.7
8.6
6.8
8.8
6.8
7.6
6.4
9.0
m/hr
3.8
3.5
3.7
4.6
2.4
2.1
2.3
2.6
2.1
2.7
2.1
2.3
2.0
2.7
Temp
17.5
17.5
17.5
17.5
17.5
20.0
21.5
22.0
23.0
23.0
24.0
24.0
26.5
26.5
27.0
27.0
24.0
25.0
MLSS
mg/1
5000
5100
5100
5200
4200
6500
6900
6900
7400
5000
6500
6400
6300
5300
7100
8400
5400
5800
Settling
Velocity
ft/hr
14.3
14.1
11.7
11.9
11.6
9.4
9.6
15.9
10.0
16.8
10.9
10.6
6.6
9.1
9.7
9.7
12.4
12.9
m/hr
4.4
4.3
3.6
3.6
3.5
2.9
2.9
4.8
3.0
5.1
3.3
3.2
2.0
2.8
3.0
3.0
3.8
3.9
47
-------
E
OJ
to
00
c
o
p
o
oo
00
ens:
P H
O>
c
o
o
CO
CO
CM
CO O"i CP>
en
O CO LO CM
IT) O OO i1
CM CM CM CM
oo oo
s:
CO LU
""C 1
<2 oo
CD >
oo
Q
LU ^
1 O
O i i
LU H-
J - LU
X ^
0 1
(/)
E
0>
>>
oo
c:
o
o
c
f
a
_*->
'^
c~
0)
CT
X
o
p_
o
S-
4-^
E
o
C_5
~T"
Q.
4->
O
1 *
i
,
0
S-
1 ^
E
O
n:
oo
s- oo
.c: >
CDS! CM CM OO
E CM t-i i 1 10
E
CD
S-
_E
\ LO
r
. o 10 r~~. r~-
CD VO OO OO t 1
E
OO
s- oo
-C >
"^^ 1 ^t*
^^ J ^-i
CO ^^" OO
E CM cr> co r^.
E
cn
r^ซ i^ i i
co CM ot r^*. co ^t* *& oo oo
C\J CM CM
CMCOI~~-IO CMOOID*3- CMI--.IOIO
OO>-H VOOCM ^ฑLOCO
ป
r^CMCOr-. OOCMCMCM ooiovo
tncMi II-H if'' ii 1< i ijocMซ ir i
LOOIDLO OLOOOCO UDCOl^LO
r~-Locrioo r^iฃ>LOi i cnr^-ซd-ซ-<
CM CM i 1 i 1 CM CM i IT 1 CM CM i I t 1
CM
CQ
CO
CM LD OO CT>
Id CM CM iI
CO O <* LO
*
OO CM CM iI
COCOCM
OO O OO ป LO
CM i-l 1 tI
to
t/)
1 CM OO
1 CM OO
1 CM OO
CM OO
0) <*
4-> r-~.
(O CTl
Q <-t
o
s-
O-
<
CT>
rO
O
CM
oo
3
"3
-------
SECTION VIII
DISCUSSION
The effluent NH.-N levels from the oxygen nitrification system with pH control
were extremely Tow throughouc the period of study. By comparison, the oxygen
system without pH control did not exhibit the same stability (e.g. Figure 4,
Days 30-50) and the residual Nfy-N levels tended to run somewhat higher. Yet
even without the pH control, the NH4-N level was normally 1 mg/1 or less.
Also good recovery of nitrification was experienced with this system after
the loss of a large portion of the solids due to a mechanical failure at the
end of March.
To achieve pH control at 7.0 in the last pass required a lime dose of about
125 mg/1. This resulted in considerably more inorganic sludge production
than in the process with no pH control and a 50 mg/1 increase in calcium ion
in the process effluent.
It is apparent that the nitrifying organisms can acclimate to and function
well at relatively low pH values. Haug and McCarty (10) found good growth
at pH 6.0 following a suitable period of acclimation. Similarly, Stankewich
(11) observed consistent nitrification in his oxygen nitrification studies
at a pH of 5.8-6.0. For the oxygen system with no pH control in this study,
the normal range in reactor pH was from 5.5-6.0. It was not uncommon for
the pH in the last pass to fall to 5.3. Nitrification still occurred at
these pH values although the data in Table 16 do show that the kinetic rate
starts declining below a pH of 5.9-6.0 even in a system acclimated to lower
pH conditions. Additional studies to more carefully define the nitrifica-
tion rate as a function of pH would be of interest. At this time it would
appear that if pH control is to be employed in an oxygen system to insure
the degree of stability that was attained in this study with pH control, one
could probably maintain a pH of just 6.0 in the final pass with no detri-
mental effects on the nitrification rate.
The cell yield coefficients for Nitrosomonas and Nitrobacter reported in the
literature are variable. Poduska (12) summarized reported values and con-
cluded that using 0.05 gm Nitrosomonas formed per gm Nfy-N oxid'ized and
0.02 gm Nitrobacter formed per gm N02~N oxidized were reasonable estimates
of sludge yield. Lawrence and Brown (13) using the estimates of Downing
et. al. (14) also utilized the above mentioned yield coefficients in their
kinetic evaluations.
Using an influent NH^-N concentration of 16 mg/1 as being typical of Blue
Plains secondary effluent and neglecting that fraction of the NH^-N or
organic nitrogen metabolized into carbonaceous organisms, produces a daily
49
-------
yield of nitrifying organisms of roughly 212 gm/day [(50,000)(3.785)(16)(0.07)
(10'3)J. Using a conservative estimate of carbonaceous sludge production of
0.35 gm solids/gm of BOD5 applied yields a daily carbonaceous sludge production
with a 65 mg/1 influent BOD5 of 4305 gm/day f(50,000)(3.785)(65)(0.35)(10-3)].
This corresponds to a sludge production of 22.8 mg/1 (190 Ib/MG). The sludge
production value reported in Table 1 for high SRT operation and similar load-
ing conditions was also 22.8 mg/1 (190 Ib/MG). In this case the nitrifying
organisms would comprise only 4.7 per cent of the total cell population.
While these numbers can be altered by including cell maintenance coefficients,
correcting for nitrogen metabolized into carbonaceous organisms or organic
nitrogen converted to ammonia, etc., the basic point which must be considered
is that the nitrifying organisms comprise a very small percentage of the
sludge mixed liquor. Hence, for this study, when the kinetic rates are
evaluated per unit of MLVSS or per unit of protein, the rates are actually
being expressed almost entirely as a function of the mass of carbonaceous
organisms present. So long as this is clearly understood, the evaluation of
nitrification kinetic rates per unit of MLVSS or protein can provide valuable
insights into system performance. However the direct comparison of nitrifi-
cation kinetic rates per unit of system mass between systems receiving differ-
ent influent wastewaters or even between systems receiving the same influent
wastewater but operated under different conditions can lead to erroneous con-
clusions unless all variables impacting on total system mass as well as the
variables affecting the nitrification rate per unit of nitrifying organisms
are considered.
The kinetic rates reported in Table 14 show that the nitrification kinetic
rates obtained in the laboratory were consistently somewhat higher for the
oxygen nitrification sludge in the system with no pH control. However the
differences are small and could easily reflect other factors not related to
nitrification, eg. different predominating heterotrophic populations because
of the difference in pH with slightly different yield coefficients. The
kinetic rates give no evidence that operation at the uncontrolled pH ranges
observed in this study is detrimental to the development of a nitrifying
population with capabilities equivalent to that from the pH controlled system.
Obviously the response of any particular process will depend on the rate
decline as a function of pH (as illustrated in Table 16) in conjunction with
the excess capacity of the process for complete nitrification as described in
Table 17. In this case (Table 17), the rate decline which occurs in the
fourth pass because of the lower pH is overshadowed by the low rate resulting
from the very low residual NH^-N concentration. This relationship of residual
NH4-N and substrate removal is predicted by Monod kinetics and has been dis-
cussed by a number of authors previously.
The oxygen nitrification system with pH control was not operated at widely
varying F/M loadings during the study. Since pH was also controlled, the
major factor affecting the nitrification kinetic rate was the process temper-
ature. The laboratory batch kinetic rates are presented as a function of
temperature in Figure 13. Both the linear and exponential regression equa-
tions are presented. It can be seen that an excellent correlation was obtained.
As indicated in Table 12, there was no difference in carbonaceous or nitrogen-
ous effluent quality when parallel air and oxygen systems were examined.
50
-------
00
CM
CM
o
CM
in
CM
CM
CO
CM
CM
O
o
V*
111
QC
ซ nj
a.
o
CN
UJ
00
(U
O)
a>
S- r-
3 O
4J S-
rtf )->
S- E
o to
r- >,
4->
-------
Similarly as shown in Table 18, the kinetic rates were essentially the same.
The sludge yield coefficients and decay coefficients were reported by Humineck
and Ball (15) to be essentially the same under aeration or oxygenation.
Others (16) have questioned this conclusion.
A total of 24 dissolved oxygen readings were taken daily in each of the two
nitrification systems, and the average daily levels are shown in Figure 14.
The mean D.O. level in the air system was 3.0 mg/1. The mean level in the
oxygen system was 8.1 mg/1, but the variation was considerably larger than
encountered in the air system. However, the mean D.O. in the oxygen system
was less than 6 mg/1 on just 7 of the 80 days under consideration here.
The assumption of equal yields and equal decay coefficients during the period
of parallel operation of the air and oxygen systems is firmly supported by the
volatile solids sludge production data and the calculated net oxygen utiliza-
tion. Although the total solids production reported in Table 11 is substan-
tially higher for the oxygen system, this is due to the greater lime dosage.
The total production of volatile suspended solids was 34.6 mg/1 for the air
system and 35.5 mg/1 for the oxygen system. This difference of just 2.6 per
cent is negligible and well within experimental error. The systems can also
be compared by calculating the oxygen utilization based on the COD and (NOp +
N03)-N data. Grab samples of effluent from both systems were periodically
analyzed for N02-N, but none was ever found. Hence the reported (N02 + N03)-N
effluent values are actually N03-N. The net oxygen demand of each system was
calculated as shown in Table 22. Again it can be seen that the difference
between the two values is only 1.9 per cent which is well within experimental
error. These data indicate that the kinetic rates per unit of protein or VSS
reported in Table 18 should be directly comparable.
Maintaining the last pass of the oxygen and air systems at pH 7.0 required
nearly 3 times the lime dosage in the oxygen system. This apparently was
responsible for the slightly enhanced phosphorus removals. The large lime
dosage did result in a better settling sludge with a much lower average SVI.
It, of course, also resulted in much higher sludge production.
52
-------
ฃ
"5
^^
CO
C
.2
to
o
'vl
z
,^j
<
I
O
.. <] O
^4 xt)
^1 t)
jO 0
*%ซ*ซ,, ฐ\
^k $ ~*
XT' ft *
\* . 0 ฐฐ -
r- ^ vl O
1 * ซ ป
H ^ ^
CO ^i^l O
C <] "^ ง
^3 ^J ^^ ^^J
*"* ^l ^)
w <^ %
E " ^ งฐ _
ft^ ^J ^*i
** ^1 ^i Q
* .. <1 o
^^ XI ^0
X^^l Ci/
^^ (^
^^ ^1 O
*?J C/
x] Q _
xi ^T"^ /^ฎ
^^^ ง
^gl lO
^i O
<<1
C *3-
*^~ r^*ซ
01
to ซ i
o ซ
f LO
ns e>j
+J VO
C 00
CJ ri
u
C CO
0 >,
C_> (O
Ol
en co
^k ^r
-o cr
X O)
O +->
"S (/?
>
'o o
CO 4->
5 5
^ si
OJ
CO C
fO 0)
S- en
CD >>
> X
< O
ซ^-
ซ (
OJ
S-
^3
en
ปr
LJ_
CN
GO
CN
l/6uj '
paA|ossiQ
53
-------
tQ
T3
CM
O
: oo
D_ oo
2: >
=> 00
oo
z. -z.
o o
CJ HH
z <
LU <_> _J
O I-H O
>- U- CC
X 1-1 H-
o a; -z.
h- O
U. I-H O
o -z.
1C
z z: Q.
O LU
to CD 3:
I-H >- I
Qฃ X 1-1
<: o s
a.
CVI
CVJ LU
CO
CTi
LO
10
cvi
00
oo
>-
CM
O
CD
CVJ
O
CD
O O O
CO i-H LO
O i-H LO
in
CM
co
rtJ
"O
CVJ
O
CD
O
O
CO
E
OJ
4-)
(/)
>^
CO
c
o
4^
(O
o
r
M-
*^~
r-
y*
f_
i~
'5.
LO
CO
^
CO
^c
O
o
en
A
Od
un
N_-*
J
F"
^
to
"^3
^^
CM
0
E
CD
O
o
CM
CM
O
I
4J
to
N
r-
i
*r
4->
Z5
C
fc
>^
0
1 ซ
0)
z.
O)
to
oo
c
o
1
to
o
ซฃ
r
i-
+>
r~
21
j^
0)
CD
ฃ
CD
CM
O
ฃ
O
I 1
ซl
LO
CM
II
LO
CO
CO
^z.
0
o
CM
i 1
LO
^_^
"x
CO
|
O
f 1
^x
o
CO
t i
3:
,ฃ!
LL.
X
Q
O
P
O)
3
ql
C
i i
CM
O
E
CD
O
CO
cr>
ซ*
CO
II
LO
CO
1*-
co
v
o
o
i-H
A
[
LO
ป -
*^*n
CO
1
o
I 1
to"
o
CM
"-^
3
J2.
u_
X
f)
o
o
+J
c
3
<ฃ
t-
LU
CM
O
E
CD
O
CM
O
m
cn
ii
LO
CO
CO
o
o
r t
i-H
LO
^X
CO
|
O
1^ J
*ซ^^
*
I-H
^^_
CO
^
U3
CO
>-H
LZ
X
CM
O
1
co
o
Z:
v_^
^_>
C
.
0
CM
00
r-l
g
LZ
CD
to
10
^
X
Q
O
0
0)
to
(0
3
>j
*O
"O
CM
0
E
CD
O
o
LO
CM
CM
C
o
tffm
*->
N
r-
i
r
!->
=3
e
&
0
4J
CD
Z
54
-------
SECTION IX
REFERENCES AND NOTES
1. Standard Methods for the Examination of Water and Wastewater, Thirteenth
Edition, 1971.
2. Young, J. C., "Chemical Methods for Nitrification Control," Jour. Water
Poll. Control Fed., 45_, 637, 1973.
3. Methods for Chemical Analysis of Water and Waste, EPA, 1971.
4. Gales, M. Jr., Julian, E. and Kroner, R., "Method for Quantitative Deter-
mination of Total Phosphorus in Water," Jour. Amer. Water Works Assn.,
58, No. 10, 1363, 1966.
5. Ramanathan, M., Gaudy, A. F. Jr. and Cook, E. E., "Selected Analytical
Methods for Research in Water Pollution Control," Publication M-2 of the
Center for Water Research in Engineering, Oklahoma State University,
1968.
6. Smit, C. J. B., et. al_. "Determination of Tannins and Related Poly-
phenols in Foods; Comparison of the Loewenthal and the Folin-Denis
Methods," Analytical Chemistry, 27_, 1159, 1955.
7. Defined as (MLVSS)(Reactor Volume) - QWaste VSS)(Waste Flow) + (Effluent
VSS)(Process FlowQ.
8. Warner High Calcium Lime. According to the manufacturer, the lime con-
tains a minimum of 94% CaO and 0.9% MgO.
9. Chemstone Hydrated Chemical Grade Lime is stated by the manufacturer to
have an equivalent minimum CaO content of 72%.
10. Haug, R. T. and McCarty, P. L., "Nitrification with the Submerged Filter,"
Technical Report No. 149, Stanford University, 1971.
11. Stankewich, M. J. Jr., "Biological Nitrification with the High Purity
Oxygenation Process," Engineering Bulletin of Purdue University, Proceed-
ings of the 27th Industrial Waste Conference, Extension Series No. 141,
pg 1, 1972.
12. Poduska, R. A., "A Dynamic Model of Nitrification for the Activated Sludge
Process," Ph.D. Thesis. Clemson University, Clemson, South Carolina, 1973.
55
-------
13. Lawrence, A. W. and Brown, C. G., "Biokinetic Approach to Optimal Design
and Control of Nitrifying Activated Sludge Systems," Presented at the
Annual Meeting of the New York Water Pollution Control Association, New
York City, January 1973.
14. Downing, A. L., Painter, H. A. and Knowles, G., "Nitrification in the
Activated Sludge Process," Jour. Inst. Sew. Purif., Part 2, pg 130,
1964.
15. Humineck, M. J. and Ball, J. E., "Kinetics of Activated Sludge Oxygen-
ation," Jour. Water Poll. Control Fed., Vol. 46, pg 735, 1974.
16. Drnevich, R. F. and Stuck, J. D., "Error Sources in the Operation of
Bench and Pilot Scale Systems used to Evaluate the Activated Sludge
Process," 30th Annual Purdue Industrial Waste Conference, Lafayette,
Indiana, 1975.
56
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO.
EPA-600/2-76-180
3. RECIPIENT'S ACCESSIOf+-NO.
4. TITLE AND SUBTITLE
EXPERIMENTAL EVALUATION OF OXYGEN AND AIR ACTIVATED
SLUDGE NITRIFICATION SYSTEMS
With and Without pH Control
5. REPORT DATE
October 1976 (Issuing date)
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
James A. Heidman
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Government of the District of Columbia
Department of Environmental Services
EPA-DC Pilot Plant
5000 Overlook Ave. S.W. Washington, D.C.
10. PROGRAM ELEMENT NO. 1
ROAP 21 ASR TASK 026
20032
11. CONTRACT/GRANT NO.
Contract No. 68-03-0349
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final Report - 10/73-09/74
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The nitrification capabilities of two oxygen activated sludge systems receiving Distric
of Columbia secondary effluent at a steady state flow of 190 m3/day (50,000 gpd) were
evaluated. The pH of one system was controlled to maintain a pH of 7.0 in the last re-
actor pass of the four-pass system. The pH of the second system was uncontrolled and
reactor pH values of 5.5-6.0 were common. Also parallel air and oxygen nitrification
systems both with pH control were evaluated under similar operating conditions. Para-
meters used to compare the systems included effluent quality, sludge settling rates,
lime dosage, sludge production and nitrification kinetic rates.
The effluent quality of the oxygen nitrification system with pH control was excellent
throughout 8 months of investigation. The effluent NH4-N concentration averaged about
0.2 mg/1. The effluent NH4-N of the oxygen process without pH control was normally
1 rng/1 or less. However this system did not show the day-to-day stability that was
achieved with pH control.
The carbonaceous and nitrogenous effluent quality of the air and oxygen nitrification
systems operated at the same loadings with pH control to 7.0 in the last reactor pass
of each system was identical. However three times the lime dosage was required in the
oxygen system. This resulted in a larger percentage of inert material in the oxygen
system and increased sludge production.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Nitrification
Activated Sludge
Oxygenation
Ammonia
Lime
Sewage Treatment
b. IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Parallel Systems
Nitrification Rates
Sludge Production
Settling Rates
13B
13 DISTRIBUTION STATEMENT
Release to Public
19 SECURITY CLASS (This Report)
Unclassified
21 NO OF PAGES
67
20 SECURITY CLASS /This page}
Unclassified
22. PRICE
EPA Form 2220-1 (9-73) 57
^ U y bOVtRNMENT PRINTING OFFICE. 1976-757-056/5
------- |