EPA-600/2-77-088
August 1977
Environmental Protection Technology Series
FULL-SCALE OPERATION
OF A SINGLE-STAGE
NITRIFICATION-DENITRIFICATION PLANT
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
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
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-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-77-088
August 1977
t-ULL-SCALE OPERATION OF A SINGLE-STAGE
NITRIFICATION-DENITRIF1CATION PLANT
Donald E. Schwlnn
Donald F. Storrler
Stearns & Wheler, C1v1l and Sanitary Engineers
Cazenovia, New York 13035
and
Daniel G. Thome
Water and Sewer Department
Town of Owego, New York 13827
Grant No. 803618-01
Project Officer
E. F. Barth
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
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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.
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. The complexity of that environment and
the Interplay between Its components require a concentrated and Integrated
attack on the problem.
Research and development 1s that necessary first step 1n problem solu-
tion and 1t 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, treat-
ment, 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 publica-
tion 1s one of the products of that research; a most vital communications
link between the researcher and the user community.
The work reported herein shows that by modification of operational con-
trol a large degree of total nitrogen removal can be obtained at municipal
wastewater treatment facilities. The report highlights those features of
plant design and operational control necessary to obtain nitrogen removal in
a single-stage activated sludge plant treating normal strength domestic
wastewater.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
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ABSTRACT
The major objective of this study was to operate the single-stage
n1tr1f1cation-denltrlfication process on a full-scale to determine the
feasibility and reliability of the process, the design features needed and
the operating techniques to ensure optimum performance. Because
n1tr1f1cation-denltrlfication can become difficult to operate under extremely
cold wastewater temperatures, a full-scale plant at Owego, New York, was
selected where wastewater temperatures range from 8° to 22°C. Alternating
aeroblc-anoxic conditions were achieved 1n completely mixed reactors by the
on-off cycling of mechanical aerators.
The following results and conclusions were determined from these studies:
1. Nitrogen removals of from 76 to 86 percent were normally accom-
plished with hydraulic retention times of 13 to 27 hours,
depending upon wastewater temperature and strength. BOD and sus-
pended solids reductions were well above 90 percent.
2. Wastewater organlcs were found to be a suitable carbon source for
the denltrlfication process 1n lieu of supplemental carbon addition.
3. Solids inventory must be reduced at higher temperatures to prevent
premature carbon consumption and subsequent reductions in denltrl-
fi cation efficiency. Nitrogen removal was reduced to 67 percent
for a 2- to 3-week period during summer operation because of
excessive solids Inventory but was restored Immediately by reducing
the solids Inventory.
4. Strong supernatant returns resulting from an outage of one anaero-
bic digester and excessive storage of solids 1n the one remaining
digester adversely affected the n1trif1cation-denitrif1 cation
process. Because of these strong supernatant returns, nitrogen
removal was reduced to 58 percent during the last month of the study.
5. Sludge settling rates measured during the study showed no differences
1n settleabillty compared to both conventional and extended aeration
operation that preceded the study.
6. Less power 1s consumed than for single-stage nitrification only.
7. Nitrogen removal can be achieved in many existing plants at little
or no capital cost by Implementing single-stage nitrif1cat1on-
denltriffcation 1f the design conditions and wastewater character
lend themselves to the control option studied at Owego, New York.
This report was submitted 1n fulfillment of Grant No. 803618-01 by the
Town of Owego, New York, under the partial sponsorship of the U.S. Environ-
mental Protection Agency. Research work was conducted May to September 1975
and February to May 1976 under the direction of Stearns & Wheler, Civil and
Sanitary Engineers, who served as a subcontractor to the Town of Owego.
1v
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CONTENTS
Foreword iii
Abstract 1v
Figures v11
Tables v111
Acknowledgments ix
1. Introduction 1
2. Summary of Conclusions and Recommendations 3
3. Background 6
4. Description of Treatment Facilities 8
5. Process Modifications and Monitoring 12
Experimental Plan 12
Operational Programs 12
Sampling and Analytical Procedures 16
Sampling and Storage 16
Analytical Techniques 19
Special Tests 21
6. Process Control and Performance 22
General 22
Phase I - Warm Weather Operation 22
Phase IA - All Aeration Tanks 1n Service 22
Phase IB - One Aeration Tank 1n Service 26
Phase II - Cold Weather Operation 27
Start-Up 27
Phase IIA - All Aeration Tanks 1n Service 28
Phase I IB - One Aeration Tank 1n Service 29
7. Discussion of Results. . 36
Nitrogen Removal 36
Biochemical Oxygen Demand, Chemical Oxygen Demand, and
Suspended Sol Ids Removals 37
Process Monitoring 37
F/M and Solids Retention Time 39
Dissolved Oxygen 42
Sludge SettleablHty 42
Sludge Wasting and Recycling Rates 43
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CONTENTS (CONTINUED)
Anaerobic Digester Supernatant 47
Kinetic Rate Tests 47
Oxygen Requirements 53
COD/TKN 53
Mixing 55
Phosphorus Removal 55
Septage and Siphon Flushing. . . " 55
8. Design and Operating Considerations 57
Primary Settling Tanks 57
Reactor Design 57
Aeration and Mixing Equipment 58
Final Settling Tank : 58
Sludge Processing 59
Process Operation and Control 59
9. Future Research 60
References 62
Appendi x
VI
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FIGURES
Number page
1 Owego Water Pollution Control Plant No. 2 9
2 Schematic Flow Diagram, SIngle-Stage N1trif1cation-
Den1tr1f1cation, Owego Water Pollution Control Plant
No. 2 10
3 Alternating Aerob1c-Anox1c Cycles 1n Compartments N-l
and S-l 15
4 Dissolved Oxygen Test 1n Compartment S-l 24
5 Typical Aerobic-Anoxic Cycle 25
6 Influent Wastewater Samples Before and After Digester
Supernatant Return Point 31
7 Samples in Figure 6 After 30-Minute Settling 31
8 Column Settling Test (Warm Weather) 44
9 Column Settling Test (Cold Weather) 45
10 Floating Solids 1n Column Settling Vessel 46
11 N1tr1f1cat1on-Denitr1ficat1on Rate Test 48
12 Observed Nitrification Rates at Various Locations 51
13 Effect of Temperature on Peak Den1tr1 ft cation Rates
With Wastewater as Carbon Source 52
14 Proposed Process Modifications for Evaluation in Future
Research at Town of Owego WPCP No. 2 61
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TABLES
Number Page
1 Single-Stage N1tr1f1cat1on-Denitr1f1cation Process and
Operational Variables 1
2 Major Plant Components 11
3 Sequence of Events , , 17
4 Process Loading Characteristics 32
5 Operational Characteristics. . 33
6 Nitrogen Removal 34
7 Treatment Efficiency 35
8 Relative Degree of Nitrification and Alkalinity Removal. . . 38
9 Orion Probe Vs. Wet Chemistry for NH^-N Measurements .... 40
10 Secondary Digester Supernatant Characteristics 47
11 Laboratory Batch Nitrification-Denltrification
Kinetic Rates 50
12 Oxygen Requirements 54
13 Septage and River Siphon Flushing 56
vi ii
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ACKNOWLEDGMENTS
The Interest and support of Mr. Will 1am E. Engelhard, Supervisor for the
Town of Owego, and the members of the Town Board 1s acknowledged with sincere
thanks. Employees of the Water and Sewer Department of the Town of Owego
who carried out the major share of plant operation and control included
Mr. Daniel G. Thome, Chief Plant Operator, and Mr. Burton E. Schoonover,
Laboratory Technician. Our gratitude 1s also expressed to Mrs. Dale Y.
Williams and Mrs. Esther L. Swartz for assistance 1n monitoring project
costs.
Supplemental Information and advice were given during the study by
several U.S. Environmental Protection Agency research and development per-
sonnel, Including Mr. Edwin F- Barth and Dr. James A. Heidman. Mr. Barth
served as Project Officer for the Office of Research and Development.
Analytical services were provided by Water Testing Laboratory, Inc.,
supervised by Mr. Michael P. Quirk. Bradford G. Wheler of Stearns & Wheler,
C1v1l and Sanitary Engineers, participated 1n much of the field work and
data analysis.
Monitoring equipment, including specific 1on probes and meter, was
loaned for field testing to the Town of Owego by Orion Research, Inc.
1x
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SECTION 1
INTRODUCTION
In many areas of the United States, water quality criteria require the
removal of nutrients from wastewater treatment plant effluents. Nitrogen
and phosphorus are the two major nutrients of concern 1n wastewater efflu-
ents. This study was addressed to Improving nitrogen removal at an existing
activated sludge plant by modification of operational control.
Nitrogen removal facilities can cost considerably more to construct
and operate as compared to conventional secondary treatment. This Increased
cost is largely due to the fact that the most reliable biological system
available necessitates three separate stages of activated sludge treatment
(2, 5, 10), with different types of process control in each of the three
stages. Additionally, methanol must be added to multi-stage systems for
nitrogen removal. Within the past two years the energy situation has
resulted 1n methanol shortages and much higher costs.
Recent research (3, 4) has Indicated that the functions of the three
different stages can be combined 1n a single treatment stage under controlled
operating conditions, and can achieve 75 percent or more nitrogen removal
without the addition of methanol. However, there is a lack of detailed
design and operating data for engineers and operators to implement single-
stage nitrif 1 cation-den1tr1f1cation. It was the major objective of this
study to operate a full-scale plant to determine the feasibility and
reliability of the process, to identify design features needed to be incor-
porated by engineers, and to develop operating techniques to ensure optimum
performance. Process and operational variables that warrant study are
listed 1n Table 1. Because n1tr1f1cat1on-denitr1f1cation can become more
difficult to operate under extremely cold wastewater temperatures, a full-
scale plant at Owego, New York, was selected which performs under wastewater
temperatures ranging from 8° to 22°C.
TABLE 1, SINGLE-STAGE NITRIFICATION-DENITRIFICATION
PROCESS AND OPERATIONAL VARIABLES
Wastewater TemperatureFood/Mass (F/M)
Nitrification and Den1trification Kinetics Solids Retention Time
COD/TKN Dissolved Oxygen Ranges
Hydraulic Retention Time Aerobic-Anoxic Cycling Time
Sludge Recycle Rate Aeration Tank Volume
Sludge Wasting Rate Sludge Settling Properties
MLSS and MLVSS
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For the initial portion of the study, operation as extended aeration
activated sludge was chosen because the longer aeration time associated with
this variation of the activated sludge process 1s more conducive to success
of single-stage n1tr1ficatlon-denltrlfication. The plant selected, however,
1s capable of operation at shorter detention periods; therefore, these
shorter periods were also Investigated under various conditions.
An additional reason for Initial operation under the extended aeration
process was that there are many extended aeration plants in the nation which
have the capability for nitrification and denltrlfication, and furthermore,
many such plants are under design or construction. Thus, a significant
improvement in national water quality could be achieved at very little cost
by the use of single-stage n1tr1f1cat1on-den1trification, especially in
water quality limited areas where nitrogen removal 1s necessary.
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SECTION 2
SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS
1. Single-stage n1tr1f1cat1on-den1tHf1 cation, using an intermittently
aerated compartment followed by a continuously aerated compartment,
normally provided total nitrogen removals of 76 to 86 percent under
wastewater temperatures varying from 8° to 22°C. BOD and suspended
solids reductions of well over 90 percent were simultaneously obtained.
It 1s believed that similar performance can be obtained in many other
similarly designed plants by a few simple physical and operational
changes.
2. The process was operated under the wide Influent load variations found
in smaller plants. The absence of primary settling and the presence
of significant shock loads from septic tank trucks and river siphon
flushings did not adversely affect process operation and performance.
3. At wastewater temperatures ranging from 11° to 22°C, successful opera-
tion was achieved at F/M ratios of 0.06 to 0.13 g BODs/day/g MLVSS and
solids retention times of 13 to 70 days. At temperatures of 8° to
12°C, F/M ratios of 0.07 to 0.08 g BODs/day/g MLVSS and solids reten-
tion times of 20 to 32 days were successfully utilized. Generally,
these corresponded to hydraulic retention times of 13 to 27 hours at
the higher temperatures and 20 to 24 hours at the low temperatures.
4. Wastewater organlcs were suitable as a carbon source for denitrifica-
tion. However, at higher wastewater temperatures 1t was necessary to
significantly reduce the mixed liquor suspended solids inventory to
prevent premature carbon consumption and loss of denitrification.
Nitrogen removal was reduced to 67 percent for a 2- to 3-week period
during summer operation because of excessive solids Inventory but was
restored immediately by reducing the solids Inventory.
b
5. Strong digester supernatant returns resulting from an outage of one
anaerobic digester and excessive storage 'of solids in the one
remaining digester occurred during that portion of the test program
when colder wastewater was being treated. The return of excessive
digester solids necessitated an Increase 1n the sludge wasting rate
causing a significant reduction in solids retention time and a marked
change 1n the nature of the mixed liquor solids, which led to a loss
of nitrification. Nitrogen removal was reduced to 58 percent during
the last month of study because of these supernatant returns.
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6. Sludge settling rates measured during the study ranged from 0.46 to
1,04 m/hr in summer and from 0.18 to 0.49 m/hr in winter. When compared
to both conventional and extended aeration operation which preceded
the study, no differences 1n settleabillty were noted.
7. Although some separation of liquid from solids took place near the
surface of the intermittently aerated compartments during the aerator
off cycle, the shortness of the off cycle (30 minutes) and the number
of cycles occurring provided ample opportunity for denitriflcation.
It is possible, however, that the lack of mixing of organlcs entering
the tank during the off cycle was a limiting factor in achieving a
higher degree of denitrlfication.
8. The amount of oxygen, and thus the energy Input, required to operate
the process was significantly less than the theoretical amount required
for single-stage nitrification without denltrification. This is due
to the fact that, under anoxic conditions, the oxygen that was pre-
viously supplied to form nitrates is used during denltrification to
oxidize a substantial portion of the influent carbon. Thus, during
denitrification, nitrate is the final electron acceptor rather than
oxygen supplied by aeration equipment.
9. During the aerobic cycle, dissolved oxygen levels of about 0.7 to
1.0 mg/1 appeared most compatible with process objectives. Lower
concentrations appeared to inhibit nitrification, while higher concen-
trations delayed the onset of denitrlfication when the aerator was
turned off.
10. At no time was there any Indication of rising solids due to denitrl-
fi cation 1n the final settling tanks. This may be attributed to the
use of continuous aeration Immediately prior to final settling which
provided the following benefits: (1) oxidation of residual carbona-
ceous material to minimize available carbon and (2) increased dissolved
oxygen levels to avoid anoxic conditions in the settling tanks.
11. Nitrification and denitrlfi cation kinetic rate test results correlated
reasonably well with published data from other studies. However,
additional research 1s necessary to perfect test procedures and to
establish design procedures based upon the use of kinetic rates.
12. The process was responsive and straightforward to operate. Once
nitrification was established, cycling of the aerators provided
immediate denltrification Indicating that denitrifying organisms
are present in substantial numbers even when only carbonaceous
oxidation and nitrification are employed.
13. In addition to an understanding of the fundamentals of activated
sludge, the operator must also be trained 1n the basic biology of
nitrification and denitrlfication to achieve effective performance
under all conditions.
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14. Removal of alkalinity correlated sufficiently well with the degree
of nitrification to enable the use of alkalinity measurements as an
operating tool to monitor the nitrification portion of the process.
However, alkalinity differences with and without denitrlflcation
were slight, and thus alkalinity could not be used effectively to
monitor denitrification.
15. Experiments were conducted to evaluate the use of specific ion probes
for process monitoring of nitrification and denitrification. The
ammonia-nitrogen probe results correlated well with wet chemistry
analyses indicating that the probe is an excellent tool for
monitoring nitrification. The nitrite probe and cadmium reduction
column technique for nitrate measurement could not be fully evaluated
due to difficulties with the reduction column. More test work is
needed to establish this technique.
16. A number of special design considerations were Identified during the
study. These have been, presented in a separate section of the report.
17. The results of this study, along with recent research by others,
Indicate that single-stage n1trlf1cat1on-den1tr1f1cation is capable of
80 to 90 percent nitrogen removal at significantly lower capital and
operating costs compared to other nitrogen removal processes. These
potential savings warrant further research to expand the applicability
of the process concepts in both existing and new plants. Additional
research subjects identified during the studies reported herein have
been summarized 1n a special section of this report.
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SECTION 3
BACKGROUND
Considerable research has been reported on biological processes for
nitrification and denitrlflcation to provide nitrified effluents or nitro-
gen removal from wastewater (10, 11). Three basic classes of organisms are
required to achieve the removal of carbonaceous and nitrogenous materials
in a suspended growth biological reactor. Aerobic heterotrophs provide
carbonaceous removal by nrlcrobial assimilation and oxidation. Aerobic
autotrophs, collectively known as nitrifiers, provide oxidation of nitrogen
in a two-step microbial reaction: first, ammonia is converted to nitrite
by Nitrosomonas; and then, nitrite 1s converted to nitrate by Nitrobacter.
Facultative heterotrophs provide denltHfication by nitrate respiration,
i.e., the microbial reduction of nitrate to nitrogen gas. The nitrate
radical acts as the electron acceptor and organic carbon sources serve as
electron donors under anaerobic or anoxlc conditions. Facultative organisms
are also capable of oxidizing carbonaceous material under aerobic conditions
Optimum environmental and operating conditions for each of these
classes of bacteria differ from one another. Nitrifying bacteria have
more specific environmental requirements than the heterotrophic bacteria
responsible for carbon removal. The nitrification rate in the activated
sludge process reportedly (3) reaches a maximum at dissolved oxygen (DO)
concentrations of approximately 2 mg/1 or above, and decreases to zero as
the DO concentration decreases to zero. Although some denltrification can
occur 1n aerobic systems, maximum denltHfi cation rates occur at DO concen-
trations near zero, when ample organic carbon 1s available. Because of the
varying conditions best suited for each type of bacteria, two-stage and
three-stage systems for n1trif1cat1on-den1trif1cation with supplemental
carbon addition received the most attention initially. However, because
multi-stage systems have high capital and operating costs, the search
for more economical alternates has Intensified.
The most significant and recent single-stage nitriflcatlon-
den1tr1f1cation studies were conducted at the USEPA Blue Plains Pilot Plant
in Washington, D.C. Bishop, et al., (3) achieved 75 to 84 percent nitrogen
removal from primary wastewaters 1n a single-stage activated sludge process
without the use of supplemental organic carbon. Aeration cycles of
30 minutes were alternately applied to each pass of a two-pass biological
reactor to achieve aeroblc-anoxlc conditions. The data suggested that
Increases in the COD/TKN ratio above 10 would further Increase nitrogen
removal. Reducing the COD/TKN ratio to 7.5 decreased nitrogen removal to
67 percent. Laboratory kinetic studies Indicated that the den1tr1f1cation
kinetic rate controlled the reactor design. Further studies were conducted
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by Heidman, et al., 14) at the Blue Plains Pilot Plant to establish an
optimum set of operational conditions for a single-stage nltrification-
denitrlflcation activated sludge system. Successful operation of the system
was attributed to the long solids retention time (SRT) which establishes a
relatively high and constant ratio of n1tr1f1ers to heterotrophs. In con-
trast to the system used 1n the initial study which employed intermittent
air pulsation throughout the reactor, the latter study employed a plug flow
biological reactor in which the head end was aerated, the middle section was
stirred, and the end section was aerated. Preliminary cost comparisons
indicated that this system can achieve comparable process performance results
to the three-stage system at a significant reduction in cost.
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SECTION 4
DESCRIPTION OF TREATMENT FACILITIES
Owego Water Pollution Control Plant No. 2 (Figure 1) is located 1n the
Hamlet of Apalachin, Town of Owego, 1n the southern portion of Central
New York State near Blnghamton. The Town of Owego and the treatment plant
Itself are located on the banks of the Susquehanna River. The plant 1s
designed for a year 1990 flow of 7,600 cu m/day (2.0 mgd) and was placed 1n
operation 1n 1971.
Flexibility was provided 1n the design to allow for operation during
the Initial low flow years as an extended aeration plant and to allow opera-
tion 1n the conventional activated sludge or contact stabilization mode as
wastewater flows increase over the design life of the plant. During the
year previous to start-up of the single-stage n1tr1f1cation-denitr1f1cat1on
study, the plant had been operated as a low-loaded conventional activated
sludge treatment plant. Currently, plant flow 1s approximately 1,900 cu m/day
(0.5 mgd). A schematic flow diagram of the treatment facilities is shown 1n
Figure 2. A summary of key plant components 1s presented in Table 2.
The wastewater at Owego is typically domestic 1n character. While
operating in the conventional activated sludge mode prior to Initiation of
the study, the plant had been achieving BOD5 and suspended solids (S3)
removals above 90 percent.
8
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FIGURE 1. OWEGO WATER POLLUTION CONTROL PLANT NO. 2
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NOTE: PRIMARY SETTLING TANKS NOT IN
SERVICE DURING RESEARCH STUDY.
WASTE SLUDGE
FINAL
EFFLUENT
NT
P
1
1
O-
C(
FINAL
SETTLING
ILORINE^- •*)
)NTACT -*'
•^
(
'(\
9
,*'
>
\
r fc RETURN SLUDGE
| '
«„.,-)
$ 1
|t
^
^.•v
t
t
N-2
CONTINUOUS
AERATION
ZONE
••-
S-2 *•
CONTINUOUS
AERATION
ZONE
N-l
AEROBIC -ANOXIC
ZONE
~m~
— S-l f
AEROBIC- ANOXIC
ZONE
1
4
w
!
r
-4
ADMINISTRATION
BUILDING
INFLUENT
CHAMBER
WASTEWATER
DISTRIBUTION
STRUCTURE
PRIMARY SETTLING TANKS
SLUDGE
DIGESTERS
DIGESTED SLUDGE
TO TANK TRUCK
FIGURE 2. SCHEMATIC FLOW DIAGRAM, SINGLE-STAGE NITRIFICATION-
DENITRIFICATION, OWEGO WATER POLLUTION CONTROL
PLANT NO. 2
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TABLE 2. MAJOR PLANT COMPONENTS
Component
Bar Rack, Hand Cleaned
No. of Units
Unit Capacity
Comnvlnutor
No. of Units
Unit Capacity
Grit Separators
Cyclone Degrltter, Primary Sludge
Cyclone Size
Flow Meters
Parshall Flume
Flow Range
Flow Tube (Return Sludge)
Flow (Waste Sludge)
Flow Tube (Thickened Sludge)
Primary Settling Tanks
No. of Units
Total Surface Area
Diameter
Average Depth
Aeration Tanks
No. of Tanks
No. of Compartments Per Tank
Volume of Compartments
First Compartment IN-l and S-l)
Second Compartment (N-2 and S-2)
Depth
No. of Mechanical Aerators Per
Compartment
Aerator Horsepower
Return Sludge Rate
Final Settling Tanks
No. of Rectangular Units
Length
Width
Average Depth
Surface Area
Total Volume
Chlorine Contact Tanks
No. of Rectangular Units
Length
Width
Depth
Total Volume
Sludge Digestion Tanks
No. of Units
Diameter
Sldewall Operating Depth
Sludge Thickening Tank
No. of Units
Diameter
Sldewater Depth
Sludge Disposal
Tank Truck
Tank Capacity
Emergency Open Sludge Drying Areas
Total Area
ISU
1 I
19,000 cu m/day 5 mgd
1 1
19,000 cu m/day 5 mgd
1
0.3 m
0.23 m
0-19,000 cu m/day
1
1
1
2
230 sq m
12 m
2.7 m
2
2
1,190 cu m
760 cu m
3.7 m
1
11 kw
1,900-5,700 cu m/day
2
26 m
4.4 m
2.6 m
240 sq m
630 cu m
1
27 m
4 m
1.8 m
200 cu m
2
12 m
9 m
1
7.3 m
2.4 m
1
7.6 cu m
2
4,050 sq m
1
12 1n.
9 1n.
0-5 mgd
1
1
1
2,500 sq ft
40 ft
9 ft
2
2
42,000 cu ft
27,000 cu ft
12 ft
1
15 hp
0.5-1.5 mgd
2
85 ft
14.5 ft
8.5 ft
2,600 sq ft
167,000 gal
1
88 ft
13 ft
6 ft
52,000 gal
2
40 ft
30 ft
1
24 ft
8 ft
1
2,000 gal
2
1 acre
11
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SECTION 5
PROCESS MODIFICATIONS AND MONITORING
EXPERIMENTAL PLAN
To achieve single-stage n1trlf1cation-den1trlf1cation in an activated
sludge system utililizing wastewater organics as the carbon source for deni-
trification, the plan was to provide alternating aerobic-anoxic conditions
within the reactor and to provide sufficient S.RT to obtain a stable
nitrifying population within the mixed liquor.
To provide alternating aerobic-anoxic conditions, the mechanical
aerators in Compartments N-l and S-l (see Figure 2) were each to be cycled by
installing automatic timers. No additional mixing was to be provided during
the anoxic stage when the aerator was off; however, it was anticipated that
the residual rolling action caused by mechanical aeration would keep the
solids suspended to a reasonable extent during the off cycle. In addition,
by keeping the anoxic cycle relatively short, liquid-solids separation would
be minimized. Mechanical aerators 1n Compartments N-2 and S-2 were to pro-
vide continuous aeration to oxidize residual ammonia (Nfy-N) and carbonaceous
material and to prevent sludge bulking 1n the secondary clariflers caused by
denltrlfication of nitrified mixed liquor.
To Increase the concentration of solids, and thereby Increase the SRT,
it was anticipated that the sludge wasting rate would have to be signifi-
cantly reduced. Mixed liquor was settled in two rectangular final settling
tanks with middle- and front-end hoppers. The return sludge piping layout
was such that the same pump was used to return sludge from both sets of
hoppers to the head of the reactor.
The study was divided Into two phases: warm weather operation and
cold weather operation. Shorter hydraulic retention times (HRT's) were
Investigated during each .phase of the study once the process had-been
established at longer HRT's, assuming that sufficient SRT was provided
throughout. Operation 1n the winter was of particular Interest because
cold weather was considered to be the critical controlling environmental
factor of the study.
OPERATIONAL PROGRAMS
In preparation for the change to the single-stage nitrlflcation-
den1tr1f1cation process, the mixed liquor suspended solids (MLSS) concen-
tration was increased. Starting 1n November 1974 sludge wasting was
12
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discontinued. The MLSS concentration Increased from 1,000 mg/1 1n mid-
November to 3,600 mg/1 1n early January 1975. On January 7 both aeration
tanks were put into service to fully establish the extended aeration process.
The HRT in the aeration tanks was Increased from approximately 12 hours to
24 hours. The process of building up the MLSS Inventory was continued.
The major operating modification necessary to initiate the study was
the bypassing of raw wastewater directly Into the aeration tanks, rather than
through the primary settling tanks as normally done. Beginning January 27,
the influent was piped directly to the aeration tanks to enhance the
carbon/nitrogen ratio entering the aeration tanks. This was done 1n line
with the finding at the Blue Plains pilot single-stage system that a rela-
tively high BOD/TKN ratio is needed for effective denitrification.
One of the most important features of process development and operation
Was the creation of alternating periods of aerobic and anoxic conditions.
Computations Indicated that the aerators installed at Owego could supply the
oxygen required for carbonaceous oxidation and for nitrification, even when
operating on a 50 percent on-off cycle. This would then allow adequate time
for denitrification to occur during the off cycle. As the aerators are of
the variable submergence type, the oxygen required could be provided in a
short aerobic cycle at high submergence, or during a long aerobic cycle at
low submergence. This would allow the duration of the aerobic and anoxic
cycles to be balanced 1n accordance with nitrification and denitrification
kinetic rates.
All major interior and exterior equipment items had been well maintained
and were in excellent operational condition at the time of start-up for the
study. The only operational difference noted as a result of the pre-study
modifications was a moderate Increase of scum in the final tanks, but the
scum baffle effectively prevented the scum from entering the final weir box.
Prior to initiation of cycling the aerators, the following program was
outlined for the start-up period beginning March 18:
a. Continue existing operation for background base line data.
b. Collect 6-hour composites manually until automatic samplers are
operational. Sample raw wastewater (downstream of, supernatant
return) and unchlorinated effluent.
c. Check out plant laboratory and independent commercial laboratory
with reference samples.
d. Modify recycle rate to optimize clarifier performance and reduce
rate if possible whenever 30-minute return sludge settling sample
shows excess supernatant.
e. Waste activated sludge to control MLSS at 3,000 mg/1.
f. Characterize settling velocity of MLSS in each aerator.
13
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g. Determine deoxygenatlon rate and oxygenation rate with manual
control of surface aerators.
h. Inspect and make operational the movable weirs on aeration tanks
so oxygen transfer capacity of surface aerators can be varied.
1. Characterize the quality of digester supernatant.
j. Sample mixed liquor between large and small aeration compartments
periodically.
In addition, the following equipment modifications were made:
a. Automatic timer Installation on motors of mechanical aerators.
b. Install automatic sampler housings.
c. Repair aeration tank weir drives.
d. Install manual bar screen at aerator Influent channel to minimize
rag accumulations on aerator blades.
e. Install flow splitter at aerator Influent.
f. Balance flows to final tanks.
g. Repair of solenoids on return sludge suction valves.
h. Order and Install laboratory equipment and minor electrical
and physical equipment.
Once all of the above tasks had been completed, Phase I (warm weather
operation) of the s'tudy was ready to begin. On May 5, the timers on the
aerators in Compartments S-l and N-l were pulsed on a 30-mlnute staggered
on-off cycle. The aerators 1n Compartments S-2 and N-2 were set to remain
running continuously. Figure 3 shows Compartment S-l 1n Its aerobic cycle
and Compartment N-l 1n Its anoxlc cycle. S-2 can be seen 1n the foreground.
This Initiated the denitrlflcation phase of the single-stage n1tr1f1cation-
denitriflcation process utilizing wastewater organics as the carbon source
for denitrlfication. The process was operated in this manner for the
remainder of the study period, varying only the aeration tankage in service
and the submergence of aerator blades. No attempt was made to fine tune the
process by optimizing the aerator on-off cycles. Sludge disposal was as
normally practiced, employing two-stage digestion of thickened sludge
followed by ultimate disposal to the land.
The critical phase of the project, Phase II, took place during the
late winter and spring of 1976 when cold temperature performance was studied.
14
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FIGURE 3. ALTERNATING AEROBIC-ANOXIC CYCLES IN COMPARTMENTS N-l AND S-l
-------
The sequence of events for the entire pre-study and study periods 1s
shown 1n Table 3, which can be conveniently subdivided Into the following:
- Pre-Study Period - Process modifications beginning 1n
November 1974.
- Phase I Start-Up (March 18-May 4) - Final preparations for warm
weather operation (ll°-22eC) Including equipment modifications and
checkout, initiation of sampling program and laboratory checkout.
- Phase IA (May 5-July 16) - First portion of the warm weather phase
using all aeration tank capacity.
- Phase IB (July 17-September 8) - Second portion of the warm weather
phase at half the aeration tank capacity to explore the effects of
reduced tankage on process performance.
- Standby Period (September 9-February 2) - Study was temporarily dis-
continued, to be reinstated in February to evaluate plant performance
during cold weather. In the Interim, a 9- to 11-hour aeration period
With on-off aerator cycling was maintained. Process monitoring and
analyses were discontinued and Intermittent checks were made to
ensure that both nitrification and denltriflcation were occurring.
- Phase II Start-Up (February 3-March 9) - Initiation of cold weather
operation (8°-13°C) phase of the study.
- Phase IIA (March ID-April 30) - First portion of the cold weather
phase using all aeration tank capacity.
- Phase IIB (May 1-May 28) - Second portion of the cold weather phase
using half the aeration tank capacity to explore the effects of
reduced tankage on process performance.
SAMPLING AND ANALYTICAL PROCEDURES
Sampling and Storage
The gathering of data on a 5-day basis for the single-stage
n1tr1f1cat1on-denitr1f1cation study began 1n late March during the start-
up period. Much of the analytical work was performed by the treatment
plant laboratory. COD, nitrogen, phosphorus, and certain other special
analyses were performed by a commercial testing laboratory. During the
start-up period, plant laboratory personnel performed and familiarized
themselves with the additional analyses required for the study. These
were checked by analysis of split samples by the commercial testing labora-
tory. Log sheets for analytical and operating data and time and expenses
related to the study were developed. During the first four weeks of data
gathering, a Technlcon Auto-Analyzer was used for COD and nitrogen analyses.
Suspicious results, especially for organic nitrogen, necessitated a change
to manual analytical techniques. Analytical procedures were checked on
unknown samples provided by the Environmental Protection Agency.
16
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TABLE 3. SEQUENCE OF EVENTS
Pre-Study
November 1974
January 7, 1975
January 27, 1975
March 1, 1975
Phase I Start-Up
March 18, 1975
March 24, 1975
April 18, 1975
Phase IA
May 5, 1975
May 28, 1975
June 13, 1975
Phase IB
July 17, 1975
August 1975
September 8, 1975
October 1975 thru
January 1976
January 28, 1976
Phase II Start-Up
February 3, 1976
February 12, 1976
Phase IIA
March 10, 1976
March 1976
Phase IIB
"ay 1, 1976
May 28, 1976
Sludge wasting discontinued
Second aeration tank put 1n service
Primary clarltiers taken off line
Grant funded
Initiation of operational and equipment modifications
Nitrogen series analysis started
Changed labs (Technicon Auto-Analyzer to wet chemistry)
Air pulsed on 30-minute cycle
Aerator blade submergence Increased to 5 inches
Aerator blade submergence increased to 7 inches
North aeration tank (N-l and N-2) taken out of service
Primary digester malfunction--taken out of service
Discontinued study until cold weather period
Monitored on random basis
Hydraulic washout of sol Ids
Aerator blade submergence decreased to 5 inches
Measures taken to reestablish process; north aeration
tank put 1n service; all aerators placed in continuous
operation
Pulsing started; resumed monitoring program
Began cleaning out primary digester
North aeration tank (N-l and N-2) taken out of service
Study terminated
17
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The following analyses were performed by the commercial testing
laboratory and plant laboratory during the study period.
Five-Day Basis -
Influent and Effluent: BODs, COD, SS, Org-N, NH4-N, N02-N, N03-N,
Alkalinity (Composite Samples)
Temperature, pH, Settleable Sol Ids (Grab Samples)
Mixed Liquor: MLSS, pH, Settleable Solids, SVI (Grab Samples)
Return Sludge: Settleable Solids, Total Solids (Grab Samples)
Random Basis -
Influent and Effluent: VSS, Total-P (Grab Samples)
Mixed Liquor: MLVSS, COD, DO, Temperature (Grab Samples)
Mixed Liquor Supernatant: BODs, COD> ss> VSS, Org-N, NH4-N, N02-N,
N03-N (Grab Samples)
Return Sludge: COD, SS, VSS, Org-N, NH4-N, N02-N, N03-N (Grab Samples)
Secondary Digester Supernatant: BODs, COD, SS, Org-N, NH4-N, N02-N,
N03-N, Total-P, Alkalinity (Grab Samples)
Primary and Secondary Digester Sludge: pH, Total Solids, Total Volatile
Solids, Alkalinity (Grab Samples)
Because of problems 1n obtaining delivery of two automatic samplers and
operating difficulties experienced with one or both of the samplers, con-
tinuous 24-hour sampling could not always be obtained. Laboratory results
of 24-hour automatically composited samples were examined against results
for 6- and 8-hour manually composited samples. COD, BODs, SS, and N-series
results were compared 1n periods when both sampling methods were utilized,
and no discernible differences were found. Samples were not taken on Satur-
days, Sundays, or holidays. Influent samples were collected at the entrance
to the aeration tanks to include the contributions of digester supernatant
and septic wastes. Effluent samples were collected at the effluent weir of
the final settling tanks prior to chlorlnation.
Tests of acidified versus non-ac1d1f1ed samples were conducted the
latter part of May and the middle of June 1975 to determine the more
effective method 1n preserving samples to be sent to the commercial labora-
tory. After one week of refrigeration, the samples were analyzed for NH4-N
and nitrate (N03~N) and compared to the fresh sample that had been analyzed
shortly after being collected. The values for the sample with acidification
Were closer to those of -she fresh sample. Thereafter all Influent and
effluent samples to be sent to the commercial laboratory for COD and nitrogen
analyses were acidified with concentrated sulfurlc add to pH 2.0 and stored
18
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at 4°C until analyzed. All samples to be analyzed by plant personnel were
refrigerated only and determinations were performed within 24 to 48 hours of
collection.
A specific 1on meter, Orion Research lonalyzer Model 407A, was obtained
to assist plant operators 1n evaluating process performance. The analyzer
was evaluated specifically for two reasons:
1. To compare the accuracy of the analyzer to wet chemistry
techniques for NH4-N and N03-N measurements.
2. To evaluate Its use as a plant process control and moni-
toring tool.
Analytical Techniques
Owego Water Pollution Control Plant No. 2 Laboratory—
All analytical procedures were 1n accordance with the procedures
authorized in Standard Methods for the Examination of Water and Wastewater
(1), 13th edition, unless otherwise specified.
p_H_— The glass electrode method was used as outlined 1n Standard Methods,
pages 276-281. The plant used a Corning Model No. 7 pH meter.
Temperature—Measurements were taken with a mercury-filled thermometer
as outlined 1n Standard Methods, pages 348-349.
Dissolved Oxygen—DO measurements were taken with a Yellow Springs DO
meter, Model No. 57. The instrument was calibrated against the modified
Winkler method.
Alkalinity—The total alkalinity determinations were performed as
outlined in Standard Methods, pages 52-55, using the potentiometric method.
Solids—Sludge Volume Index (SVI)--The SVI's were performed as outlined
1n Standard Methods, page 561.
Settleable Sol Ids—The settleable sol Ids were determined as
outlined in Standard Methods, page 539.
Suspended Solids—The SS content was determined using the
method outlined 1n Standard Methods, pages 537-538.
Total Solids—The total solids content was determined using
the procedure outlined 1n Standard Methods, page 538.
Biochemical Oxygen Demand—The 5-day BOD determinations were made as
outlined in Standard Methods, pages 489-494, employing the azide modifica-
tion of the Winkler test, as described 1n Standard Methods, pages 477-489.
19
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Commerci al Laboratory—
All analytical procedures were 1n accordance with the procedures out-
lined 1 n Standard Methods for the Examination of Water and wastewater (1),
13th edition, or the USEPA's Manual of Methods for Chemical Analyses of
Water and Wastes (9), 1974 edition, unless otherwise specified.
Chemical Oxygen Demand^~The dlchromate reflux method, as presented 1n
Standard Methods, pages 495-499, was the procedure used for all COD deter-
minations with one minor variation. The 30 ml of sulfuric add reagent were
added directly into the Erlenmeyer flask and not through the condenser.
Sulfanrlc acid (0.12 g) was added to every liter of standard 0.25 N potassium
dlchromate solution. A 20 ml sample or a sample diluted to 20 ml with dis-
tilled water was used for analysis.
Nitrogen—Nitrate-Nitrogen—The N03-N determinations were made as
outlined in the USEPA Manual of Methods, pages 197-200,
employing the brudne method.
Nitrite-Nitrogen—The nitrite-nitrogen (NC^-N) determina-
tions were made as outlined in the USEPA Manual of Methods,
pages 215-216.
Ammonia Nitrogen—The Nfy-N concentration was determined
using the method for organic nitrogen (Org-N) as des-
cribed in Standard Methods, pages 246-247, with the
elimination of the digestion step. Distillation of the
ammonia fraction was accomplished on a Lab-Con-Co, distilla-
tion apparatus with final ammonia measurement by titration.
Organic Nitrogen—Org-N concentrations were determined by
digestion and distillation of the residue from the Nlfy-N
determination, as outlined 1n Standard Methods, pages 246-247.
Biochemical Oxygen Demand—The 5-day BOD determinations were made
as outlined 1n Standard Methods, pages 489-494. An oxygen probe was employed
1n making Initial and final oxygen determinations. It should be noted that
IDO's were taken on each BOD bottle no matter what the initial volumes of
samples were. The DO meter (Yellow Springs Instrument, Model No. 57) was
standardized against the azlde modification of the Wlnkler test.
Solids—Suspended Solids--The SS content was determined using
Procedure 224C as outlined 1n Standard Methods, pages 537-538.
Volatile Suspended Solids—Volatile suspended solids (VSS) were
determined by Procedure 224D as outlined in Standard Methods,
page 538.
Total Solids— The total solids content was determined using
Procedure 224A as outlined 1n Standard Methods, pages 535-536.
Total Volatile Solids—The total volatile solids were determined
by Procedure 224B as outlined 1n Standard Methods, page 536.
20
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Alkalinity—The total alkalinity determinations were performed as out-
Uned 1n Standard Methods, pages 52-55, using the potentiometric method.
Specific Ion--An Orion Research Ammonia Electrode (Model No. 95-10) and
an Orion Specific Ion Meter (Model No. 407A) were used 1n
a comparison study between wet chemistry and the electrode
method.
An OH on Research N1trite Electrode (Model No. 95-46-02)
and an OH on Specific Ion Meter (Model No. 407A) were used
1n a comparison study between wet chemistry and the elec-
trode method. Samples to be analyzed by the Nitrite
Electrode were first passed through a cadmium reduction
column to reduce N03-N to N02-N.
Special Tests
Special tests were conducted periodically to assist 1n monitoring and
evaluating process performance and to help 1n determining design and
operating criteria.
1. DO profiles were performed 1n aeration tanks using a DO
meter and probe 8 to 10 feet below the water!ine to deter-
mine the rates of oxygenatlon and deoxygenation during
on-off cycling of the mechanical aerators in N-l and S-l.
2. Batch settling tests were conducted to determine the
settling rate of mixed liquor solids. During Phase I a 1-1
graduated cylinder was utilized for this purpose; and during
Phase II a 10.5-cm (4-l/8-1n.) diameter column, 122 cm
(.48 1n.} long was used. Stirring was not provided in either
case.
3. Laboratory scale batch n1tr1f1cat1on-den1trification kinetic
studies were performed to determine the kinetic rate at which
each biological reaction occurs. These studies were performed
by batch mixing 5 1 of return sludge with 5 1 of influent,
aerating with the laboratory air supply, and extracting
samples at !5-m1nute Intervals for a 2-hour period. At the
end of 2 hours, aeration was discontinued and 3 1 of fresh
Influent were added to the remaining mixed liquor. The solu-
tion was then gently mixed and samples were extracted every
15 minutes for the next hour. The temperature of the mixed
liquor was measured throughout the test, but a water bath
was not used to maintain a constant temperature. Samples
were analyzed for COD and nitrogen constituents. From
these data, the kinetic rate constants of nitrification and
denHHflcation were determined.
21
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SECTION 6
PROCESS CONTROL AND PERFORMANCE
GENERAL
The purpose of this section is to describe the operating techniques
and controls employed during both major phases of the study and to present
the operational loadings and process performance observed. The tables which
present these operating and performance data have been included at the end
of this section to avoid unnecessary fragmentation of the data and to enable
the reader to more.readily review the results of the entire study, by
referring to Tables 4, 5, 6 and 7.
PHASE I - WARM WEATHER OPERATION
In early May 1975, the installation of the timers for the mechanical
aerators was completed. By that time, laboratory sampling and analytical
procedures had been checked and plant personnel had been oriented to the
additional demands of the study. In addition, essentially complete nitrifi-
cation had been established.
Laboratory results on influent samples collected during the start-up
operations showed a large variation in the influent strength. These varia-
tions were attributed to three major factors: (1) the periodic flushing of
a siphon under the Susquehanna River, (2) the inflow of digester supernatant
when sludge was wasted, and (3) the dumping of septic waste by commercial
septic tank pumpers. As such situations are normally encountered in prac-
tice, no attempt was made to shield the process from their effects.
Phase IA - All Aeration Tanks in Service
On May 5, pulsing of the S-l and N-l aerators, on the 30-minute on-off
cycle was started to establish suitable conditions for denitrification.
Cycling of the timers reduced the operating DO level in aeration basins
N-l and S-l from 5 to 1 mg/1. The average DO level for Phase IA in con-
tinuously aerated Compartments S-2 and N-2 was approximately 3.6 mg/1. The
response of the process to cycling was immediateTy apparent as the final
effluent N03-N concentration decreased from 12 mg/1 to approximately 5 mg/1
as a result of denitrification during anoxic conditions. Effluent quality
remained constant and floating scum normally observed in the aeration and
final settling tanks disappeared. Towards the latter part of May the
residual NH4-N, and thus, the residual total nitrogen (Total-N) concentration
increased. This was attributed to insufficient DO levels (approximately
0.5 mg/1) attained during the aerator on cycle. An increase in wastewater
temperature resulted in less oxygen transfer as well as a higher bacterial
22
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metabolism rate. To Increase the amount of oxygen supplied, the aerator
blade submergence was Increased on May 28 by raising the weir levels 2.5 cm
(1 1n.) for both tanks. Effluent NH4-N levels returned to levels consistent
with previous results. Anticipating the warmer summer temperatures, the sub-
mergence of the aerator blades was increased by 5.1 cm (2 1n.) on June 13 to
further Increase the oxygen supplied. Durinq the course of the entire study,
DO concentrations were periodically checked (Figure 4) for an entire on-off
aerator cycle. Figure 5 is a plot of typical DO concentrations occurring
during one complete cycle. This pattern varied depending on temperature,
solids inventory, and wastewater characteristics.
Nitrogen removals for May averaged 76.4 percent and for June averaged
80.6 percent. In the last week of June, however, residual N03-N levels began
to increase. Previous to this, effluent NOs-N concentrations were approxi-
mately 5 mg/1. By July 1, effluent HO^-H had risen to 11 mg/1 and remained
at that level or above for the period of July 1-16, indicating that little
denltrification was being achieved. Total-N removal for this period
decreased to approximately 67 percent.
Because Influent wastewater temperatures had risen significantly during
June, while maintaining a constant solids inventory, 1t was believed that
the lack of denltrification was being caused by complete oxidation of organic
carbon during the aerobic cycle. This in turn reduced the carbon available
for denltrifi cation during the anoxic cycle. This condition was Intensified
by a lower than usual COD/TKN ratio during early July. To prevent the
premature consumption of carbon 1t was decided to reduce the mixed liquor
solids inventory within the system. It was possible to accomplish this in
one of two ways:
1. By gradual wasting of MLSS to the digesters until denltrifica-
tion was restored.
2. By removing one aeration tank, and Its mixed liquor solids,
from service.
A series of calculations was made that indicated that 1t should be
possible to sustain nitrification and denltrifi cation at the same mixed
liquor solids concentration with one-half of the aeration tankage. The
calculations also indicated that the aerator oxygenation capacity of one
tank would be somewhat less than the theoretical amount needed to accomplish
carbonaceous and nitrogenous oxidation. However, because much of the oxygen
used for nitrification is reused for carbonaceous oxidation during denitrl-
flcatlon, 1t was believed that the aerator oxygenation capacity could be
adequate.
Upon review of the factors Involved 1t was decided to remove one-half
of the aeration tankage, and Us contents, from service. Incidental to the
decision was the observation that the mixed liquor solids inventory had been
reduced by about 20 percent during late June and early July with no Improve-
ment 1n denitrification. Therefore, on July 16, the north aeration tank
(Compartments N-l and N-2) was Isolated from the treatment process. This
change constituted the end of Phase IA and the beginning of Phase IB.
23
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ro
FIGURE 4. DISSOLVED OXYGEN TEST IN COMPARTMENT S-l
-------
ro
tn
JULY 17,1975
TANK TEMP = I9°C
PROBE DEPTH = 2.4-3.0m (8-10')
S-l AERATION COMPARTMENT
PROBE LOCATION = CENTER OF S-l
10 15
ANOXIC
40 45
AEROBIC
AERATOR
OFF
AERATOR
ON
TIME (MINUTES)
AERATOR
OFF
FIGURE 5. TYPICAL AEROBIC-ANOXIC CYCLE
-------
A complete tabulation of the operational loadings and process perfor-
mance during Phase IA is Included 1n the tables at the end of this section.
As may be seen, excellent removals of BOD, COD and SS were consistently
achieved under loading conditions typical for an extended aeration system,
while simultaneously achieving a high degree of nitrification and nitrogen
removal.
Phase IB - One Aeration Tank in Service
By Inactivating the north aeration tank and the MLSS contained therein,
the HRT was reduced from 28 hours 1n Phase IA to 14 hours for Phase IB and
the operational SRT was reduced from more than 40 days to less than 20 days.
The F/M ratio was increased from about 0.06 g BODs/day/g MLVSS to about 0.13.
An Immediate improvement in nitrogen removal took place while BOD, COD, and
SS removals remained constant. The operating DO levels for Phase IB
generally ranged from 0.8 to 1.0 mg/1 1n Compartment S-l and was approxi-
mately 2.2 mg/1 in S-2. Effluent NOa-N values were immediately reduced from
11-13 mg/1 to 1-3 mg/1 and remained low for the remainder of Phase IB during
which the warmest wastewater temperatures of the study (18° to 22°C) were
recorded. A higher degree of denitrlflcation was achieved in Phase IB as
effluent N03-N concentrations were lower. Total-N removals during this
period were consistently around 85 percent and on several days exceeded
90 percent. The results confirmed that the decrease in nitrogen removal 1n
the latter portion of Phase IA was caused by a deficiency of carbon source.
Total-N removal for the first week in September decreased to 77.1 per-
cent due to the combination of lower influent Total-N and a slight Increase
in effluent Total-N.
Excellent BOD§, COD, and SS removals were maintained throughout this
phase. BODs and SS residuals were consistently less than 10 mg/1, while
COD removals averaged slightly less than 90 percent.
During Phase IB, HRT's 1n the aeration tanks averaged 13 to 16 hours,
and SRT's averaged 13 to 19 days. Wastewater flow rates did not signifi-
cantly change from Phase IA; therefore, the surface overflow rate (SOR) and
HRT 1n the final settling tanks remained in the same ranges. The BOD5
loading approximately doubled, and the F/M ratio Increased but did not double
due to higher MLSS levels. Values of SVI were not .quite as high in July and
August probably because of the improved sludge settling properties caused by
warmer temperatures and the change in mode of operation. Results of
30-minute settleabillty tests were generally better than those in Phase IA.
In August an operational problem potentially detrimental to the process
was created when the emergency overflow on the fixed cover primary digester
plugged. Continued waste sludge pumping caused failure of the anchor bolts
and brackets which held the cover in place. The tank was removed from ser-
vice and operation of the secondary digester was modified to allow it to
function as a primary digester. -A sludge recir-culation pump was used to
provide mixing within .the digester. The pump was turned off to allow liquid-
soli ds separation prior to the introduction or removal of sludge. Digester
supernatant from this tank was returned to the influent of the aeration tanks.
26
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Based upon the quantity of sludge wasted Immediately prior to the
digester cover failure, calculations were made to determine the adequacy of
the remaining digester. These Indicated that the tank capacity would be
adequate, as long as digested sludge was removed regularly to avoid deterio-
ration of supernatant quality. Plans were made to empty and repair the
primary digester 1n the fall of 1975 and to place 1t 1n service prior to the
cold weather portion of the study which was planned for February, March and
April of 1976.
In early September 1t was concluded that the objectives of the warm
weather study had been achieved. On September 8, the study was suspended
to be reinitiated 1n February under cold weather conditions. During the
Interim period until winter conditions prevailed, the plant was operated
to maintain n1tr1f1cat1on-den1tr1f1cat1on. The south aeration tank con-
tinued 1n operation with pulsed aeration on the 30-m1nute on-off cycle,
while the north aeration tank remained out of operation. MLSS were held
1n the range of 4,000 to 5,000 mg/1. Dally sampling and monitoring were
discontinued except for alkalinity measurements. During the fall and winter,
spot nitrogen analyses were made to prove that nitrification and den1tr1f1ca-
tion were maintained. Laboratory results for 2 to 3 samples per month for
November and December indicated approximately 68 percent and 78 percent
Total-N removal, respectively, while the temperature had decreased to 11°C.
Destruction of alkalinity continued to be high. Wastewater flow rates
significantly increased during this period reducing the aeration tank HRT to
approximately 10 to 11 hours, yet good BOD, COD, SS, and nitrogen removals
were still achieved. The plant was operating well, and conditions appeared
to be ideal for the anticipated start-up of Phase II at the beginning of
February 1976.
Daily wastewater temperatures in January 1976 ranged from 7° to 10°C.
Dally alkalinity data indicated that essentially complete nitrification was
maintained. Although NOo-N analyses were not performed, the combination of
high alkalinity drop, pulsed air operation, and low temperature conditions
Inhibiting premature carbon consumption was indicative that denitHfication
should also be occurring.
Extremely high flows were encountered towards the end of January. Pre-
cipitation and thawing snow during unseasonably warm temperatures caused
groundwater infiltration and Inflow Into sewers under construction. The
total plant flow Increased from 2,200 cu m/day (0.59 mgd) on January 26 to
4,000 cu m/day (1.06 mgd) on January 27 to 5,000 cu m/day (1.31 mgd) on
January 28, causing flooding conditions and a hydraulic washout of solids.
The MLSS concentration dropped from 4,100 mg/1 on January 26 to 1,400 mg/1
on January 28. Shortly thereafter, a large decrease in alkalinity destruc-
tion occurred, Indicating the probable loss of nitrifying bacteria.
PHASE II - COLD WEATHER OPERATION
Start-Up
Phase II start-up was Initiated February 3, 1976, with full resumption
of the dally monitoring program for n1tr1f1cat1on-den1tr1f1cat1on with one
27
-------
aeration tank 1n service. The planned work to repair the primary digester
had not been done; therefore, the plant continued to operate with a single
digester. Although the mixed liquor solids level had Increased substantially
since the washout, analyses for the period of February 3-11 confirmed that
nitrification had been lost. Good removals of COD, BOD, and SS were obtained
during this period, indicating that the microorganism population for car-
bonaceous oxidation had been quickly reestablished. However, the influent
NH4-N concentration was 18.5 mg/1, and the effluent NH4-N concentration was
15.7 mg/1, while Total-N removal was only 24 percent. The SRT was estimated
to be 10 days during the first two weeks of February, which may not have
been sufficient for the nitriflers to reestablish themselves at the lower
temperature. Flows had stabilized, and the aerator HRT was 10.2 hours.
During this period, plant records indicated for the first time evidence
of a problem 1n digester operation. On February 9-11, heavy supernatant
returns were observed caused by insufficient winter withdrawals of digested
sludge from the one operating digester. Daily composite sampling was dis-
continued on February 12, until nitrification was restored.
The following procedures were Initiated on February 12 to restore
nitrification:
1. To maximize SRT, the north aeration tank was returned to
service and sludge wasting was discontinued.
2. To assess the degree of nitrification, alkalinity drop from
Influent to effluent was closely monitored.
3. To further enhance nitrification, all mechanical aerators
were placed 1n continuous operation and the aeration tank
effluent weirs were adjusted to provide an operating DO con-
centration of 2 to 4 mg/1.
By the first week in March, the MLSS in both tanks exceeded 3,000 mg/1
and the alkalinity measurements indicated that nitrification had been
restored. At this time, the mechanical aerators 1n Compartments N-l and S-l
were returned to timer control on the 30 minutes on, 30 minutes off cycle.
Phase IIA - All Aeration Tanks in Service
On March 10, daily composite sampling was resumed to evaluate the first
portion of cold weather operation, I.e., extended aeration operation with
both aeration tanks in service and wastewater temperatures in the 8° to 10°C
range. Laboratory results indicated that the nitrifying and denitrifying
bacterial populations had been reestablished, as essentially complete
nitrification and 77 to 79 percent Total-N removal were achieved. Total-N
removal (efficiencies in March and April were approximately equal to those
achieved during Phase IA when the plant operated under similar process
loading conditions but at warmer wastewater temperatures. Higher flow
rates 1n Phase IIA resulted in slightly lower HRT's, but no detrimental
effect on the process was apparent. The operating DO level in Compartments
S-l and N-l ranged from 0.7 to 1.0 mg/1. DO readings were not recorded in
28
-------
S-2 or N-2 1n Phase IIA. Excellent BODs, COD and SS removals were main-
tained. Floating solids were observed 1n the final settling tank, but
effluent quality was not Impaired.
During March the F/M ratio and SRT were maintained at about the same
levels as for Phase IA with MLSS concentrations approaching 4,000 mg/1.
In April, MLSS concentrations were Intentionally reduced to about 3,000 mg/1
to assess operation under somewhat higher F/M ratios. A corresponding
reduction 1n SRT from 32 to 20 days was noted. This reduction 1n SRT was
greater than.had been anticipated, probably due to Increasing amounts of
digested solids being returned 1n the digester supernatant which 1n turn
necessitated Increased wasting to maintain a relatively constant MLSS con-
centatlon. In March, plant personnel began to clean out the primary digester
which had been Idle for several months. Sludge from the digester was trucked
away to land disposal areas. Because only one truck and limited manpower
were available for this maintenance operation, less digested sludge from the
one functional digester was removed as previous to Phase IIA. The net effect
was a buildup of solids, Inadequate Hquid-soHds separation, and an increase
1n supernatant strength. In general, this accounted for the higher sludge
wasting rate and lower SRT observed In Phase IIA as compared to that during
Phase IA.
Nitrogen removals 1n April were erratic compared to other periods.
During the week of April 11, extremely high nitrogen removals in excess of
90 percent were achieved, while the following week only 63 percent Total-N
was removed. Although essentially complete nitrification was achieved
throughout April, effluent N03-N concentrations ranged from traces to
20 mg/1 and tended to increase towards the latter part of the month. At
that time, 1t was thought that the increase in effluent N03-N was probably
the result of a deficiency 1n wastewater organics for use as a carbon source
during the denltrlflcation step, as had occurred 1n early July in Phase IA
when the temperature increased and the COD/TKN ratio unaccountably decreased.
As had been done in Phase IA, the north aeration tank was removed from
service 1n an attempt to improve Total-N removal and to study the process
at reduced retention times under cold weather conditions. By reducing the
solIds inventory, it was anticipated that sufficient wastewater organics
would remain unoxldlzed to be used as a carbon source during denltriflcation.
Phase IIB - One Aeration Tank 1n Service
Utilizing one aeration tank, the second portion of the cold weather
phase was conducted during the month of May with wastewater temperatures 1n
the range of 11° to 13°C. Operation of the plant was similar to that during
Phase IB with a few noticeable differences. These included: (1) lower
influent wastewater temperatures; (2) higher flow rates, giving lower reten-
tion times in the aeration and final settling tanks, and higher surface
overflow rates in. the final settling tanks; (3) slightly lower MLSS levels
and correspondingly higher F/M ratios and lower SRT's; (4) stronger super-
natant returns resulting from the loss of the primary digester and its
subsequent cleaning, causing an Inability to remove digested sludge from the
secondary digester because of a shortage of vehicles and manpower.
29
-------
Sludge production during this period was higher than Phase IIA, as
would be expected at an Increased F/M ratio, but was also significantly
higher than sludge production 1n Phase IB. This was primarily a reflection
of solids contributions from the stronger digester supernatant returns.
The SVI's were high 1n the first part of May and typical of previous
plant experience at lower temperatures. Lower SVI's that occurred 1n late
May were the result of a change 1n sludge settling characteristics caused
by Inert solIds returned 1n digester supernatant.
Excellent BOD5, COD, and SS removals were maintained at first in
Phase IIB. In the final portion, May 10-28, good removals were obtained; but
the treatment efficiency for all these constituents decreased. A similar
pattern was observed in nitrogen removals, but the decrease in efficiency
from May 10 to 28 was even more noticeable and was due primarily to deterio-
rating nitrification caused by markedly shortened SRT's resulting from
excessive returns of digester supernatant solids. Visible evidence of these
effects was provided by the Jet black nature of the MLSS. Figure 6 1s a
picture of influent wastewater samples before and after the point of digester
supernatant return. Figure 7 is a picture of the same samples after
30 minutes of settling. The large mass of dark settleable solids returned 1n
digester supernatant is readily apparent. The data suggested that denitri-
f1cation improved with the reduction to one aeration tank, but before
sufficient data could be gathered, the nitrification process had started to
fail. By the last week in May, effluent NH/j-N levels had Increased to about
15 mg/1 and Total-N removals had decreased to about 50 percent.
Because of the loss of nitrification and the fact that completion of
the primary digester cleaning and repair was not anticipated to be completed
for several months more, further testing and process evaluation were termi-
nated. Although difficult to accurately determine, it appeared that a
certain degree of den1tr1f1cation was being achieved up to the time that
monitoring was discontinued.
Another operational problem experienced 1n Phase IIB was the extremely
wide daily variations in MLSS. These wide variations were the direct result
of the sludge return piping layout. Front-end and midpoint sludge hoppers
1n the final settling tanks are joined in the same suction line for the
return sludge pumps rather than separate lines with separate pumps. Mal-
functions 1n the solenoid valve system used to provide individual, timed
withdrawals from each hopper resulted 1n sludge being drawn from both sets
of hoppers. When uneven resistance was encountered, the pump drew the more
dilute sludge and, at times, returned essentially only effluent to the aera-
tion tanks. At other times, very heavy sludges were returned from either
hopper. This uneven return sludge pumping was probably the main cause for
the wide dally variation of MLSS in the aeration tank and may have adversely
affected process performance. Although the same piping arrangement was used
in Phases IA, IB, and IIA, the same problem was not observed because the
sludges for those phases were not as compactlble due to the absence of large
quantities of anaeroblcally digested solids.
30
-------
-
FIGURE 6. INFLUENT WASTEWATER SAMPLES BEFORE AND AFTER
DIGESTER SUPERNATANT RETURN POINT
FIGURE 7. SAMPLES IN FIGURE 6 AFTER 30-MINUTE SETTLING
31
-------
TABLE 4. PROCESS LOADING CHARACTERISTICS
Wastewater Flow
Aeration Tank
Final Settling Tank
tSi
mgd
Time Period
1975
PHASE IA-
May 5-31
June
July 1- 16
PHASE m -
July 17-31
Aug.
Sept. 1-8
1976
PHASE IIA -
Mar. 10-31
Apr.
PHASE IIB -
May 1-9
May 10-28
Avg.
0.483
0.456
0.379
0.392
0. 435
0.463
0.628
0.526
0.530
0.523
Range
0.21-0.69
0.38-0.64
0.32-0.44
0.28-0.47
0.33-0.62
0.37-0.55
0.50-1.00
0.33-0.80
0.41-0.64
0.38-0.74
cu m/day
Avg.
1,830
1.730
1,430
1,480
1,650
1,750
2,380
1,990
2,010
1,980
Range
800-2,610
1,440-2,420
1,210-1,670
1,060-1,780
1,250-2,350
1,400-2,080
1,890-3,790
1,250-3,030
1,550-2,420
1,440-2,800
BOD5 Loading
Ibs/day/
1, 000 cu ft
11.9
10. 1
7.5
19.7
20.4
18. 1
13.4
12; 3
20. 1
23.5
kg/day/
cu m
191
162
120
316
327
290
215
197
322
376
HRT*1' SOR
(hrs)
25.7
27.3
32.8
15.9
14.3
13.4
19.8
23.6
11.7
. 11.9
gpd/sq ft
183
173
144
148
165
175
238
199
201
198
mW-d
7.5
7.0
5.9
6.0
6.7
7. 1
9.7
8. 1
8.2
8. 1
HRT
(hrs)
7.8
8.3
10.0
9.7
8.7
8.2
6.0
7.2
7.2
7.2
SS Loading
Ibs/day/
sq ft
5. 1
4. 7
3.2
4.0
3.6
5.8
-
7.7
4.4
5.4
5.0
kg/day/
sq m
81.7
75.3
51.3
64. 1
57.7
92.9
123.3
70.5
86.5
80. 1
(1) 61 percent of the HRT is associated with the pulsed aeration compartments.
39 percent of the HRT is associated with the continuously aerated compartments.
-------
TABLK 5. OPERATIONAL CHARACTERISTICS
MLSS
F/M( 1>
SRT
Recycle Rate Sludge Production SVI
Time Period
1975
PHASE IA -
May 5-31
June
July 1-16
PHASE IB -
July 17-31
co Aug.
CO
Sept. 1-8
(mg/1)
3,340
3,260
2,660
3,250
3,810
3,990
(g BODK/day/g MLSS)
0
0.057
0.049
0.045
0.097
0.085
0.073
(g BOD,./day/g MLVSS)
o
0.079
0.068
0.063
0. 130
0. 120
0.099
(days)
69
41
44
19
18
13
<%Q)
177
190
209
231
190
187
(gig BODg Rem, ) (ml/gm)
209
0.44(2) 276
305
216
0.76(2) 214
242
1976
PHASE 1IA -
Mar. 10-31 3,860
Apr. 3,020
PHASE HB -
May 1-9
May 10-28
3,200
3,020
0.055
0.065
0. 100
0.120
0.069
0.081
32
20
12
10
138
164
163
165
258
212
(1) SS and VSS analyses of mixed liquor samples from Compartments N-2 and S-2 for Phases IA and IIA;
from Compartment S-2 for Phases IB and IIB.
(2) Average for phase.
-------
TABLE 6. NITROGEN REMOVAL
(1)
Influent
Waste water
Temp. (°C)
Time Period
1975
PHASE IA -
May 5-31
June
July 1-16
PHASE IB -
July 17-31
Aug.
Sept. 1-8
1976
PHASE HA -
Mar. 10-31
Apr.
PHASE IIB -
May 1-9
May 10-28
Avg.
14
16
18
19
20
19
9
10
12
12
Range
11-16
15-18
17-19
18-20
18-22
18-21
8-10
9-12
11-12
12-13
NH4-N
(mg/1)
Inf.
27.9
30.4
34.4
31.7
33.2
26.1
16.9
21.1
22.0
19.7
Eff.
2.2
1.3
1.7
2.1
1.9
1.5
0.6
0.3
1.0
7. 1
Org-N
(mg/1)
Inf.
12.5
12.0
12.4
13.2
13.0
11.6
16.6
16.1
14.4
15.5
Eff.
2.5
2.2
2.7
2.3
2.4
3.2
1.7
1.4
1.5
1.4
N02-N+
NOa-N (mg/1)
Inf.
0.3
0.3
0.3
0.6
0.4
0.3
1.4
0.8
0.4
1. 1
Eff.
4.9
4.8
11.3
1.9
2.7
4.0
5.3
6.9
7.6
5.1
Total -N
I
Avg.
40.7
42.7
47.1
45.5
46.6
38.. 0
34.9
38.0
36.8
36.3
Inf.
S. D.(2) Range
•
14.6
13.5
8.3
7.4
8.9
7.5
4.6
6.1
10.7
3.3
17.6-88.1
22.5-80.5
37.6-68.6
34.6-59.4
32.8-69. 1
32.3-52.3
30.0-45.2
22.6-50.4
26.3-47.6
28.5-41.8
Avg.
9.6
8.3
15.7
6.3
7.0
8.7
7.6
8.6
10. 1
13.6
(mg/1)
Eff. %
S.D.(2) Range
3.0
3.7
1. 1
1.2
2.3
1. 1
2.4
5. 1
1. 1
2.7
-
3. 1-13.5
2.2-13.7
14.3-17.5
4.2- 7.8
2.1-10.6
7.4- 9.9
2.5-10.4
2.4-22.0
9.4-11.2
9. 1-17.4
Red.
76.4
80.6
66.7
86.2
85.0
77. 1
78.6
77.4
71.2
57.8
(1) For complete daily nitrogen data see Appendix.
(2) S. D. = Standard Deviation.
-------
TABLE 7. TREATMENT EFFICIENCY
PHASE IA - 1975
PHASE IB - 1975
PHASE IIA - 1976
00
en
Parameter
BOD5 (mg/1)
Inf. - Avg.
S.D. (1)
Range
Eff. - Avg.
Range
% Reduction
COD (mg/1)
Inf. - Avg.
S. D. ( 1}
Range
Eff. - Avg.
S.D. (1)
Range
% Reduction
SS (mg/1)
Inf. - Avg.
Range
Eff. - Avg.
Range
% Reduction
May 5-31
204
124
56-519
18
10
3-37
91.2
522
491
136-2,425
63
50
12-201
87.9
228
204
68-820
13
14
1-54
94.3
June
183
126
68-671
5
2
2-11
97.3
474
515
170-2,650
57
29
16-112
88.0
187
123
96-708
4
3
1-12
97.9
July 1-16
163
49
96-261
5
1
3-8
96.9
293
8.1
196-423
55
16
24-82
81.2
155
76
50-336
4
2
1-7
97.4
July 17-3 1
208
85
113-360
6
2
4-12
97. 1
423
196
246-916
35
15
19-58
91.7
234
132
108-456
5
4
1-12
97.9
Aug.
194
87
89-422
8
4
3-19
95.9
467
148
204-796
58
24
18-102
87.6
241
182
64-908
6
4
1-12
97.5
Sept. 1-8
162
49
88-218
11
4
7-16
93.2
391
119
232-517
78
10
67-93
80. 1
198
44
140-268
7
3
2-10
96.5
Mar. 10-31
176
46
99-301
11
3
5-16
93.8
346
118
183-706
35
22
10-71
89.9
149
45
162-204
17
19
3-69
88.6
Apr:
194
50
124-308
7
2
4-11
96.4
388
102
199-634
48
23
10-90
87.6
163
52
90-272
6
7
1-27
96.3
May 1-9
157
25
142-186
9
6
5-16
94.3
351
17
331-817
36
15
22-51
89.7
156
22
135-178
6
2
5-8
96.2
May 10-28
186
37
145-273
26
6
18-37
86.0
374
49
300-430
63
20
27-84
83.2
209
159
116-774
15
10
3-34
92.8
(1) S. D. = Standard Deviation.
-------
SECTION 7
DISCUSSION OF RESULTS
NITROGEN REMOVAL
Single-stage biological nitrification-denitrification was shown to be
a viable nitrogen removal process under full-scale plant operation for both
summer and winter conditions. Suitable environmental conditions for nitrogen
removal were created by simple operational changes and without the supple-
mental addition of methanol. Wastewater organics proved to be adequate as
a carbon source for denitrification in lieu of methanol. By operating at
sufficiently low F/M ratios and correspondingly high SRT's under warm and
cold weather conditions at HRT's of about 13 to 16 hours and 20 to 24 hours,
respectively, stable carbonaceous oxidizing, nitrifying, and denitrifying
bacterial populations were maintained. With reference to Table 6, it may be
seen that the largest constituent of Total-N 1n the effluent was generally
N03-N. Influent and effluent N02-N concentrations were negligible. With
the exception of the latter part of Phase IIB, effluent Nfy-N levels varied
from 0.3 to 2.2 mg/1, Indicating a high degree of nitrification. Good
removals of Org-N were also consistently achieved. Excluding the period of
July 1-16 when lack of available carbon impaired denitrification, nitrogen
removals during Phase I averaged 76 to 81 percent with both aeration tanks 1n
service and 77 to 86 percent with one aeration tank in service. In Phase
IIA, with two tanks in operation, nitrogen removals averaged about 78 per-
cent. Nitrogen removal was good 1n the early portion of Phase IIB (one tank
in operation) but rapidly dropped to about 50 percent due to the impact of
supernatant returns from the overloaded anaerobic digester.
Careful operational control of solids Inventory was found to be a major
factor in obtaining efficient year-round nitrogen removal. Other Important
factors were influent characteristics and loadings, including wastewater
temperature, COD/TKN ratio, excessive wet weather wastewater flow rates
and excessive solids 1n digester supernatant returns. In late June of
Phase IA, the combination of a higher bacterial metabolism rate resulting
from Increasing temperature, and a lower COD/TKN ratio, resulted in a
deficiency of available carbon for denitrifi cation. To reduce the rate at
Which carbon was consumed during the aerobic cycle, and thus to increase the
amount of carbon available during the anoxlc cycle, the north aeration tank
was removed from service. This resulted 1n an Immediate return of denitri-
fi cation to previously observed values.
Some problems were encountered in attempting to restore nitrification
following a solids washout due to high settling tank loading rates resulting
from Infiltration/Inflow problems in the collection system 1n late January
36
-------
between Phases I and II. Although solids were rapidly built back up and the
blomass responsible for carbonaceous removal was rapidly reestablished, the
nltrlfiers were not reestablished until approximately four weeks after the
washout. Conversely, denitrifying bacteria were found to be highly respon-
sive and readily established. It appeared that when conditions were
favorable for good nitrification efficiency and when an anoxlc period and
adequate carbon source were provided, a high degree of den1tr1f1cation was
readily achievable.
The failure of the process to efficiently remove nitrogen 1n Phase IIB
is believed to be primarily attributable to the digester problems causing the
return of excessive inert solids 1n digester supernatant and not to tempera-
ture effects at lower retention times. Data from the standby period between
Phase I and Phase II suggest that single-stage n1tr1f1cat1on-den1trif1cat1on
at SRT's of less than 2C days are feasible during winter conditions with
adequate operational control. Spot checks indicated that n1tr1f1cat1on-
denitrlfication at such SRT's was maintained at wastewater temperatures as
low as 11°C with one aeration tank in service until the hydraulic washout of
sol Ids 1n late January. Insufficient data, however, was collected during
this standby period to fully evaluate the process under such conditions.
Additional research 1s needed to determine minimum reactor volume under
winter conditions.
BIOCHEMICAL OXYGEN DEMAND, CHEMICAL OXYGEN
DEMAND, AND SUSPENDED SOLIDS REMOVALS
Process modifications and operational changes performed to create
suitable environmental conditions for the n1tr1f1cation-den1trif1cat1on
process did not adversely affect the plant's ability to remove BOD, COD,
and SS. Removal efficiencies were equal or superior to previous plant per-
formance. As shown 1n Table 7, excellent removals of these three contami-
nants were consistently achieved throughout the study period until near the
end of Phase II when strong digester supernatant returns caused a slight
decrease 1n treatment efficiency. 6005 removal efficiency normally ranged
from 94 to 97 percent, except during Phase IIB when the efficiency decreased
to 86 percent. Effluent COD values over various time periods averaged
between 35 and 78 mg/1. As effluent BODc values were consistently less than
10 jng/1, the data suggest that residual COD consisted of mostly refractory
material. SS removals generally exceeded 95 percent. On many occasions,
equipment and piping objects located 6 to 8 feet below the water surface of
the final settling tanks could clearly be seen.
PROCESS MONITORING
Process evaluation prior to Initiation of Phase IA was complicated by
reliance upon a commercial laboratory for analytical services that utilized
a Technlcon Auto-Analyzer for COD and nitrogen analyses. After changing to
another commercial laboratory, employing manual analytical techniques,
results of analyses were much more consistent and reproducible. Excellent
correlations on USEPA reference samples were found for analytical results by
both the plant laboratory and the second commercial laboratory. Sampling and
storage techniques used 1n the study were evaluated and found to be satis-
factory 1n providing reliable and representative results.
37
-------
Although no distinguishable differences were found 1n comparing 24-hour
automatically composited samples with 6- and 8-hour manually composited
samples, 6- and 8-hour composite samples were collected only as a matter of
necessity. It was Intended that all Influent and effluent samples throughout
the study period be 24-hour composites. Unfortunately, the automatic
samplers were not delivered as scheduled at the start of the study and
operating difficulties were experienced with these samplers when they were
put on Hne. Repeated attempts to obtain servicing of the samplers, although
promised by the equipment manufacturer, were rarely successful. This
experience points to the importance of the proximity of service facilities
as a major criterion to consider 1n selecting the supplier for any type of
process monitoring equipment.
The results of this study indicated that a greater degree of operator
supervision, as compared to normal activated sludge system operation, 1s
required as well as a basic understanding of the chemistry and biology of
the processes involved. Adequate operational flexibility and controls are
necessary to consistently obtain good biological nitrificatlon-
den1tr1f1 cation. As nitrification appears to be the most critical of the
several processes involved, the operator's attention must be focused on
maintaining essentially complete nitrification as a first priority. Once
this has been established, attention can be turned to maintaining the correct
DO cycle and MLSS concentration needed to produce denltHfl cation.
To assist operators 1n evaluating process performance for dally opera-
tional control purposes, simple daily monitoring techniques readily available
to plant operators are needed. As alkalinity determinations are straight-
forward and readily performed by plant personnel, daily tests were run on
Influent and effluent samples by plant personnel to evaluate its use as
3 process monitoring tool. Alkalinity destruction was found to be a good
general indicator of the degree of nitrification, as shown 1n Table 8, and
became a useful operating tool. Approximately, 4.2 to 5.4 pounds of alka-
linity were destroyed per pound of Nfy-N removed. The table shows an
overlap in the percentage of alkalinity destroyed for the degree of nitrifi-
cation. This probably reflects the formation of alkalinity by denltrifica-
tlon, as the data collected Included samples on days with and without
den 1tr1f1 cation. Based upon a review of alkalinity data obtained for the
entire study, 1t appeared that changes in alkalinity resulting from denitrl-
f1 cation were too slight to be used as an Indicator of the degree of
denitrifl cation obtained. The ranges 1n alkalinity removal shown apply to
Owego and will vary from one location to another, depending on the buffering
capacity of different wastewaters.
TABLE 8. RELATIVE DEGREE OF NITRIFICATION AND ALKALINITY REMOVAL
Degree of Nitrification
(Percent NH4-N Removed) (Pecent Removed)
90+
60-90
30-60
45-65
30-50
20-35
38
-------
As Indicated 1n Table 9, the NH4-N probe data correlated very well with
wet chemistry techniques. As the meter would be used by operators 1n more
of a qualitative rather than quantitative manner, the accuracy of the meter
for Nfy-N analysis 1s more than adequate to be recommended as a dally process
performance test.
In contrast, the results were not as encouraging when the analyzer was
used to measure NOa-N. The manufacturer of the meter and probe (Orion
Research) advised that an NOs-N probe could not be used because 1t was
designed for very low concentrations of organic matter. In order to verify
this, the manufacturer was supplied with effluent samples for testing using
the N03-N probe. These results showed that effluent samples, even though
efficiently treated, contained sufficient organic matter to render the probe
unusable. To measure NOs-N, the manufacturer recommended that a N02-N probe
be used with the meter. This necessitated that the sample first had to be
passed through a cadmium reduction column to reduce N03-N to N02-N. Several
attempts were made to construct a cadmium column as specified 1n the manu-
facturer's manual (7), but the column did not function properly. Even after
1t was modified, based upon the work of other researchers, it did not effec-
tively reduce N03-N to N02-N. Moreover, the NCfc-N probe Itself did not
function properly when used to measure standards. Although 1t was impossible
to completely evaluate this method because of the difficulties experienced
With the cadmium column, the entire procedure appears to be unsuitable for
use as a dally monitoring tool for plant operators at this time. These
difficulties were as follows:
1. Difficulty in controlling the sample flow rate at a
specified constant rate as the liquid level in the
column varies (flow rate determines contact time
ands therefore, degree of reduction).
2. If the contact time is too short, Inefficient reduc-
tion 1s obtained. If the contact time is too long, a
portion of the NCL-N reduced to N02-N is further reduced
to N2 gas.
3. Frequent flushing with water 1s required and stan-
dards have to be run through the column every fifth
or sixth sample.
In summary, a specific 1on meter was found to be an excellent monitoring
tool for plant operators to evaluate process performance for nitrification;
but not for denitriflcation.
F/M AND SOLIDS RETENTION TIME
The F/M ratio and SRT were found to be Important considerations for the
design and control of the single-stage n1trlficat1on-den1tr1f1cat1on system.
With both aeration tanks in service, effective nitrogen removal was obtained
at an F/M of .06 to .08 g BOD5/day/g MLV5S in Phase IA (11° to 16°C) and at
an F/M of .07 to .08 g BOD5/day/g MLVSS 1n Phase IIA (8° to 12°C). With one
aeration tank 1n service, effective nitrogen removal was obtained at an F/M
39
-------
TABLE 9. ORION PROBE
VS. WET CHEMISTRY FOR NH4-N MEASUREMENTS
Date
11/19/75
12/5/75
12/15/75
12/19/75
3/10/76
3/11/76
3/12/76
3/15/76
3/16/76
3/17/76
3/18/76
Wet Chemistry
23.5*
1.5
23.4
1.5
30.0
0.5
26.5
0.8
23.7
1,0
17.2
N/A
17.9
1.0
16.5
0.7
15.6
0.5
16.0
0.5
20.5
0.7
NH4-N (ir
Probe
22.0
1.3
25.0 .
1.2
32.0
< 1.0
29.0
< 1.0
27.0
1.7
20.0
1.2
21.0
1.0
17.5
< 1.0
15.5
< 1.0
16.5
< 1.0
20.0
< T.O
ig/D
Date
3/19/76
3/22/76
3/23/76
3/24/76
3/25/76
3/26/76
4/5/76
4/6/76
4/7/76
4/8/76
4/9/76
Wet Chemistry
15.5
0.5
14.5
0.8
15.6
0.3
18.5
0.4
20.0
0.4
14.5
0.2
15.1
0.6
23.9
1.3
22.3
0.7
19.7
0.7
24.2
0.7
Probe
16.0
15.0
16.0
18.0
20.0
15.0
13.8
24.0
21.0
19.0
22.0
< 1.0
*For each date first entry is raw wastewater, and second entry is final
effluent.
40
-------
of .10 to .13 g BOD5/day/g MLVSS 1n Phase IB (18° to 22°C) while Inefficient
nitrogen removal was obtained 1n Phase I IB (11° to 13°C). Although the
period of operation in each phase was not equivalent to three times the esti-
mated operational SRT for that period as required by the rule of washout
curves to establish stable operation, essentially stable operation was Indi-
cated 1n Phases IA, IB, and IIA by the consistency of effluent parameters
such as COD and NH4-N. Based upon this, the data suggest that SRT's between
41 and 69 days 1n Phase IA, between 20 and 32 days in Phase IIA, and between
13 and 19 days in Phase IB resulted 1n effective nitrogen removal. Stable
operation was not achieved In Phase IIB at an estimated SRT of 10 to 12 days.
The lower SRT's during Phase II, particularly during Phase IIB, were due pri-
marily to the Increased rate of sludge wasting necessitated by inefficient
anaerobic digester operation and return of digester solids to the aeration
tank. By maintaining the MLSS at the desired level of approximately
3,000 mg/1, the input of digester solids probably resulted 1n a lower frac-
tion of active microblal mass during Phase IIB and, thus, a net loss of some
nitrifying bacteria. Due to plant staffing problems, no measurements were
made to determine the volatile fraction of MLSS during this period. It 1s
doubtful that such data, even if available, would have been useful because
the type of volatile solids 1n the system was far different than during
normal process operation.
The loss of nitrification 1n Phase IIB with one aeration tank in service
at colder temperatures appears to have been due to Inadequate sol Ids inven-
tory or SRT. Calculations, based upon the bench scale determination of
kinetic rate at 12°C, Indicated that the solids inventory was marginal for
complete nitrification to occur. A decrease 1n the fraction of active mass
because of the digester solids returns would have dictated an Increase 1n
the solids Inventory required for complete nitrification, assuming sufficient
SRT. It seems unlikely that the system failed because of insufficient SRT
at 12°C, causing a washout of the nitrlfiers. A previous steady-state
laboratory study (6) found that the limiting value of minimum SRT for nitri-
fication is approximately four days at 8°C. During May 1976 the Owego plant
was operated at SRT's of 10 to 12 days at temperatures of 11° to 13°C.
Results from other full-scale studies (11) Indicated that at 12°C, SRT's of
10 to 12 days should have been adequate.
Nevertheless, 1t 1s Important that a sufficient Inventory of aerated
sol Ids based upon aerobic cycles be provided with an adequate safety factor
(6) to ensure complete nitrification at the lowest temperature conditions to
be encountered.
The results Indicate that single-stage n1trif1cat1on-den1tr1f1cation can
be operated over a wide range of SRT's with only a minimal amount of moni-
toring required and only minor adjustments 1n plant operation for most of
the year. At temperatures of 8° to 16°C during Phases IA and IIA, the plant
was effectively operated at SRT's ranging from 20 to 69 days. At higher
temperatures, a major reduction 1n solIds Inventory was required to achieve
effective den1tr1f1cation.
In summary, 1t appears that SRT's between 20 and 30 days were best for
wastewater temperatures between 8C and 15°C. For temperatures between 15°
41
-------
and 22°C, SRT's of 15 to 20 days were sufficient. The process functioned
well at longer SRT's (40 to 69 days) except during peak summer temperatures
when carbon deficiency problems occurred due to excessively rapid carbon
removal during the aerobic cycle. Operation at longer SRT's in warm weather
may be feasible by reducing the aerobic cycle time and increasing the anoxic
cycle time. However, the success of this1 approach would depend upon the
ability to maintain adequate aerobic HRT for nitrification. Although addi-
tional research 1s needed to determine the optimum F/M ratio and SRT under
various conditions, the results at Owego appear to compare reasonably well
with other recent studies for single-stage nitrogen removal.
DISSOLVED OXYGEN
Operational variables related to oxygen supply Include DO ranges and
aerator cycling times. DO profiles were routinely performed to assist 1n
monitoring and evaluating process performance. The DO levels in Compartments
N-l and S-l were generally maintained between 1 and 2 mg/1 during the on-
cycle 1n the early phases of the study period; As the study proceeded, 1t
appeared that DO levels nearer to 1 mg/1 were preferable and gave somewhat
superior performance as this did not appear to Inhibit nitrification, but
enhanced denitrification by shortening the lag period to reach anoxic condi-
tions during the off cycle.
The mechanical aeration equipment was operated so that periodic adjust-
ments could be made to compensate for gradual changes 1n temperature, which
affected aerator oxygenatlon rates. As wastewater temperatures increased,
biological activity increased and oxygenatlon capacity decreased causing a
gradual drop-off of DO during the aerobic cycle. Additional oxygenatlon was
readily obtained by raising the aeration tank effluent weir level.
DO levels of less than 1 mg/1 during the aerobic cycle may be adequate,
depending on seasonal conditions. An operating DO level of 0.7 to 1.0 mg/1
appeared to be satisfactory, but time did not permit extensive study of this
aspect, and additional work to optimize DO levels may be worthwhile.
SLUDGE SETTLEABILITY
Excellent removals of SS were consistently achieved throughout the
entire study indicating that the process did not adversely affect solids
removals. Column settling tests were conducted periodically to monitor
changes in settleability and to provide data for estimating settling tank
capacity in future designs.
It 1s worth noting that a sludge bulking condition had developed 1n
July 1974, about six months prior to the process changes that were made in
January 1975 in anticipation of the study. Prior to July 1974, 30-minute
sludge settling tests in a 1-1 graduated cylinder normally resulted 1n
Interface levels of 200 to 500 ml. For no apparent reason, these increased
to 900 to 1,000 ml in July 1974 and, regardless of the process changes made
prior to and during the study, remained 1n the same range. Thus, the effect
of single-stage n1trif1catlon-denitrlflcation on sludge settleability,
Whether positive or negative, could not be determined.
42
-------
The results of typical column settling tests under warm and cold weather
conditions are shown 1n Figures 8 and 9, respectively. During Phase I, a
1-1 graduated cylinder was used for settling tests. The curve in Figure 8
shows that the floe settled well and that the settling rate was 0.8 m/hr
(2.7 ft/hr) in warm weather. During Phase II, a 10-1 column was used for
settling tests. The curve 1n Figure 9 shows that there was an apparent
bulking condition during cold weather. Typically, there was a 30- to 60-
mlnute delay before the solids would begin to settle, and the rate was much
lower than during summer. Although on occasion floating solids were observed
1n the final settling tanks, they did not escape over the weirs. Figure 10
1s a picture of a column settling test showing the floating solids.
Under warm weather conditions and at MLSS concentrations of 2,500 to
3,500 mg/1 sludge settling rates fell between 0.46 and 1.04 m/hr (1.5 and
3.4 ft/hr). However, no correlation between MLSS concentration and settling
rate was observed.
Based on settleability data observed after the 30- to 60-m1nute delay
period at similar MLSS levels during winter conditions, sludge settling
rates ranged from 0.18 to 0.49 m/hr (0.6 to 1.6 ft/hr). The lower values,
When converted directly to equivalent surface overflow rates, indicated that
the sludge should not have settled at the rates actually occurring 1n the
settling tank. However, no loss of solids from the tanks was observed
Indicating that the 6- to 7-hour tank detention time was an Important factor
in sol Ids capture.
SLUDGE WASTING AND RECYCLING RATES
Sludge wasting procedures were Intended to maintain a MLSS level of
3,000 mg/1, although in actual operation MLSS normally ranged between
3,000 and 4,000 mg/1. The required sludge wasting rate for Phase IA was
estimated to be 0.44 g/g BOD5 removed. In Phase IB, the sludge production
rate Increased to 0.76 g/g BOD5 due to the reduction 1n sol Ids Inventory and,
consequently, the SRT. Sludge wasting rates in Phase IIA and IIB were
estimated to be 0.71 g/g BODs removed and 0.98 g/g BODs removed, respec-
tively. Although the plant was operated at similar F/M ratios during both
phases, the sludge wasting rate had to be increased in Phase II to maintain
the desired MLSS levels. This Increase in sludge wasting was probably neces-
sitated primarily by the increased return of Inert solids in digester
supernatant, as well as by the usual increase 1n synthesized carbon which
usually occurs at colder temperatures.
The sludge recycle flow was held fairly constant over the entire
study period. No attempt was made to determine the effects of a range
of recycle rates on nitrogen removal. The data suggest that increased
nitrogen removal can be attained at higher sludge recycle ratios. Analysis
of data collected during the study showed that additional nitrification
was achieved 1n the continuously aerated compartments following the cycled
compartments. Since little denitrlflcation occurred in the plant after that
point, NOs-N was normally the largest constituent of Total-N irr the effluent.
By Increasing the sludge recycle rate, additional denitrlficatlon of nitrates
contained 1n the return sludge supernatant may be achieved, thereby
43
-------
JULY 24,1975
TANK TEMP. = 20°C
S-2 AERATION COMPARTMENT
MLSS = 3436 rv.g/l
SETTLING RATE = 0.82m/hr.
12.7 f t./hr.l
400
10 15
TIME (MINUTES)
FIGURE 8. COLUMN SETTLING TEST [WARM WEATHER!
44
-------
APRIL 15,1976
TANKTEMR=8°C
S-2 AERATION COMPARTMENT
MLSS - 2824 mg/l
SETTLING RATE = 0.24m/hr.
I0.8ft./hr.)
2.2
40 60
TIME (MINUTES)
FIGURE 9. COLUMN SETTLING TEST [COLD WEATHER)
45
-------
FIGURE 10. FLOATING SOLIDS IN COLUMN SETTLING VESSEL
46
-------
increasing the quantity of nitrates removed across the plant. Additional
research is needed to investigate the benefits of high recycle rates as a
tool to increase denitrification.
ANAEROBIC DIGESTER SUPERNATANT
Samples were randomly taken from the digesters to determine the strength
of digester supernatant returns. As shown in Table 10, analyses of samples
collected in Phase I indicated that the digesters were operating well and
a weak supernatant was being returned to the head of the aeration tanks. No
detrimental effects were observed. On an average weekly basis, the super-
natant return contributed at most an additional 4 percent to the normal
Influent 6005, COD, and SS loadings. TKN from supernatant returns con-
tributed an additional 5 to 13 percent to the normal influent TKN loading.
Similar analyses during Phase IIB indicated that supernatant returns had
become stronger due to the cessation of digested sludge removal from the one
digester. During Phase IIB it was estimated that digester supernatant
returns accounted for an additional 31 to 36 percent increase in the normal
influent BOD5, TKN, and SS loadings and approximately an 18 percent increase
in the normal COD loading. Of course, the supernatant returns were a shock
loading because sludge wasting, with corresponding equal volume displacement
pf supernatant, and subsequent return to the head of the aeration tank was
normally practiced three times per week over a period of a few hours. Thus,
during the actual period of wasting, the supernatant return represented a
300 to 600 percent Increase in the total loading on the aeration tanks.
TABLE 10. SECONDARY DIGESTER SUPERNATANT CHARACTERISTICS
Phase
IA
IB
IIA
IIB
Number Average Concentration (mg/1)
Of Samples BOD5 COD SS TKN
2
8
0
1
120
200
— __
1,160
380
371
»- — — .
1,490
53 235
155
— .... — _ _
1,240 217
The digester supernatant problems that occurred during Phase IIB are a
classic example of the Importance of avoiding excessive storage of solids in
digestion tanks and the adverse effects of heavy supernatant returns on the
operation of biological treatment systems.
KINETIC RATE TESTS
Several batch laboratory n1tr1f1cation-denitrification kinetic rate
tests were conducted during the study. Data obtained from one such test
performed under summer conditions are plotted 1n Figure 11. The Figure
clearly shows the occurrence of nitrification during the aerobic stage
and denitrifi cation during the anoxic stage. The sudden changes in N03-N
47
-------
AUGUST 21,1975
TEMP = 2I°C
30 60 90
NITRIFICATION
MLVSS = 2340mg/l
TIME (MINUTES)
TECHNIQUE: REFER TO "SPECIALTESTS, ITEM*3','pg. 21
FIGURE II. NITRIFICATION-DENITRIFICATION RATE TEST
48
-------
and NH4-N concentrations at T = 120 minutes, resulting in the discontinuous
curves, reflect the addition of fresh Influent wastewater at that point to
provide a source of carbon for den1tr1f1cation.
Two preliminary tests were conducted prior to the August 21, 1976 test
to establish rate testing procedures. The data obtained from these tests
has not been presented, as samples were taken only at 1-hour Intervals and,
therefore, did not provide an adequate number of data points for kinetic
rate determinations. In all subsequent tests, sampling was conducted at
15-minute Intervals.
Data from the 15-minute Interval tests are presented 1n Table 11. As
expected, the nitrification rates observed at lower temperatures were lower
than those observed at higher temperatures. To the contrary, the denltHfi-
cation rate observed at 14°C was higher than that observed at 21°C. Three
factors appeared to contribute to this phenomenon:
1. As the reduction of NOs-N in any given test varies considerably
from a straight-line slope, the denltriflcation rate calculated
can vary depending upon which portion of the test data 1s used.
For example, 1n the August 21, 1975 test plot shown, the cal-
culated rate Included the flatter portion of the curve from
150 to 180 minutes. If only the steep portion (T = 135 to
150 minutes) had been used, the calculated rate would have
been approximately trebled.
2. In comparing the kinetic studies conducted, residual COD values
varied widely from test to test during the denitriflcation step.
Thus, the unexpected results in the calculated denitrlflcation
rates may be due to differences 1n available carbon. Beginning
at T = 150 minutes of the August 21, 1975 test, COD values
decreased to a level approaching that of plant effluent COD.
This suggests that the more readily oxidlzable carbon had been
utilized during the aerobic stage, leaving little available
carbon for denitriflcation. In the other tests conducted,
residual COD values during the denitrification step were
higher, indicating that greater amounts of unoxidized carbon
were available for denitriflcation.
3. The August 21, 1975 test was conducted 1n a 9.5-1 (10-qtJ pall,
while the April 29, 1976 test was conducted in a 10.5-cm
dlam x 122-cm high (4-1/8-in. diam x 48-in.) plexiglass column.
It 1s conceivable that denitrifi cation 1n the pail, which was
stirred during the anoxic portion of the test, could have been
slowed by the Introduction of atmospheric oxygen into the pall
while it was being stirred.
49
-------
TABLE 11. LABORATORY BATCH NITRIFICATION-DENITRIFICATION KINETIC RATES
Kinetic Rate Constant*
Date
Tempera- Nitrification (9
ture. °C
g MLVSS
Denltr1f1 cation (g
g MLVSS
8/21/75
3/23/76
4/29/76
21
12
14
0.064
0.032
0.047
0.097
—
0.170
* Cycle of aeroblc-anoxic operat1on--2 hours aerobic, 1 hour anoxlc.
With reference to Figure 11, 1t can be seen that nitrification continued
during the first 15 minutes of the anoxic portion of the test. This can be
explained by the fact that residual DO was available for nitrification for
a short time after aeration was stopped. This DO was soon utilized, and no
significant nitrification occurred during the remainder of the anoxlc cycle.
The data from this test also suggest that the den1tr1f1 cation rate decreased
as the supply of readily oxidizable wastewater organlcs was depleted. At
T = 120 minutes, after the addition of fresh influent, the COD was 146 mg/1;
and at T = 150 minutes the COD was 67 mg/1. In addition, the relatively low
concentration of NOa-N (approximately 4 mg/1) available for denitrifi cation
may have also affected the kinetic rate.
Several limitations were encountered with the methodology employed for
batch kinetic studies. Because a large laboratory reaction vessel was needed
to provide adequate sample volumes for analytical purposes, a water bath
could not be used to maintain a constant temperature in the reaction vessel.
With warmer wastewater the temperature remained fairly constant; however,
during the winter the temperature Inside the vessel gradually increased over
the 3-hour test period. A second limitation of the testing procedure was
that nitrification continued during the beginning of the anoxlc cycle
utilizing the residual DO, thereby Increasing the N03-N concentration. At
the same time, some denitrifi cation had started, thereby decreasing the N03-N
concentration. Thus, the observed decrease in NOa-N concentration used to
determine the kinetic rates may have been larger than was apparent. DO con-
centrations during the aerobic cycle in the laboratory reaction vessel were
significantly higher than those in the aeration tanks due to the relative
shallowness of the laboratory test vessels. The need to control laboratory
air flow to maintain sufficient agitation for liquid-solids contact resulted
in higher DO levels in the test vessels.
Observed nitrification and denitrifl cation rates from these studies are
compared to the results of similar studies (11) in Figures 12 and 13. Con-
sidering the variability of wastewater fron one location to another and the
Inherent limitations of the methodology employed, the kinetic rates deter-
mined are 1n reasonable agreement. As pointed out in other studies (6), a
kinetic rate based upon MLVSS is of limited usefulness as a general design
criterion for nitrification and denitrifi cation systems. Since the pre-
dominant fraction of a mixed bacterial culture 1n a single-stage system
consists of carbonaceous heterotrophic organisms, and only a small fraction
50
-------
0.7
0.6
FIGURE 12. OBSERVED NITRIFICATION RATES AT VARIOUS LOCATIONS
o
Q
\ 0.1
•Q 0.4
•S«$ 0.3
O
Owego, New York
pH 7.5, BOD5/TKN = 4.7
Blue Plains, pH 6.8 to 7.2 (Air System)
(ref. 7 ) BOD5/TKN = 1.3
Srlborough, Mass.
(ref. 62) BOD5/TKN = 3.(
i 1 1 1 ^—
-I-
Blue Plains, pH 7.0 (Oxygen System)
( ref. 8) BOD5/TKN = 3.0
H 1-
10 II 12
13 14 15 16 17 18 19 2O 21 22 23 24 25 26 27 28 29 3O
TEMPERATURE, C
(]} Source: USEPA "Process Design Manual For Nitrogen Control" (11).
-------
FIGURE 13. EFFECT OF TEMPERATURE ON PEAK DENITRIPICATION
RATES WITH WASTEWATER AS CARBON SOURCE
O.I5
(1)
CO
co
•Q
6
O.IO
x
o
-------
of the MLVSS are nitrifiers and deiritriflers, the proportion of nltHflers
and denitrlflers in the sludge mass cannot be accurately estimated and 1s
largely dependent upon the Influent COD/TKN ratio and process loading condi-
tions. Even for Identical systems operating under similar temperature
conditions, measurements will vary from one location to another, depending
on Influent wastewater characteristics. Thus, the use of kinetic rates as
a design criterion 1s dependent upon local conditions. Notwithstanding these
limitations, the data indicate that nitrification, and not denitrlfication,
1s the rate limiting step and will exert the greatest impact on reactor
sizing.
OXYGEN REQUIREMENTS
Calculations of the theoretical oxygen demand necessary for carbonaceous
oxidation and nitrification are compared to estimates of the actual amounts
of oxygen supplied by the mechanical aerators 1n Table 12, based upon actual
BGDs and TKN removals. The results indicated that the actual amounts of
oxygen supplied exceeded theoretical amounts required 1n Phases IA and IIA
with both aeration tanks 1n service; but 1n Phases IB and I IB with one aera-
tion tank 1n service, the actual amounts of oxygen supplied were less than
theoretical requirements. Nevertheless, efficient removal of BODs and
efficient nitrification were achieved 1n Phase IB, and DO levels were ade-
quate indicating that the oxygen supply to the system was not deficient.
As would be expected for a system of this type, the data indicate that
the amount of oxygen required for single-stage nitr1fication-denitr1f1cation
is less than that required in a nitrifying activated sludge system. Calcula-
tions of theoretical oxygen requirements did not take Into account the fact
that a portion of the Influent organic carbon acted as the electron donor
and was stabilized during the denitrlfication process, while the nitrate
radical acted as the electron acceptor. Thus, oxygen supplied by the
mechanical aerators for nitrification is reused during denitrlfication to
oxidize a substantial portion of the Influent organic material. The resul-
tant reduction in energy Input required represents a potential operating cost
savings when employing both nitrification and denitrification in a single-
stage system.
COD/TKN
The ratio of carbonaceous material to nitrogenous material as reflected
by the ratios of BODs/TKN and COD/TKN 1s believed to have a significant
effect upon single-stage n1tr1f1cation-denitr1f1cation. The primary settling
tanks were removed from service prior to the start of the study to Increase
the COD/TKN ratio and, therefore, maximize the availability of carbon needed
for denltrlffcation. Previous studies (3) had found that when the COD/TKN
ratio was reduced from 10 to 7.5, nitrogen removal was reduced. Although
no attempt was made to vary the COD/TKN ratio to study Its effects, an
unexplained temporary decrease 1n the COD/TKN ratio 1s believed to have been
a contributing cause to a reduction 1n the degree of denitrlfi cation achieved
1n Phase IA. From July 1-16, the COD/TKN ratio was 6.4, compared to a normal
COD/TKN ratio of about 10. The unusally low influent COD loading probably
contributed to the carbon deficiency during denitrlfication noted during this
53
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TABLE 12. OXYGEN REQUIREMENTS
Theoretical
BOD*
Time Period
1975
PHASE IA -
May 5-31
June
July 1-16
PHASE m -
July 17-31
Aug.
Sept. 1-8
1976
PHASE HA -
Mar. 10-31
Apr.
PHASE Iffi -
May 1-9
May 10-28
Ibs/day
1,020
1,020
730
1,020
1,010
870
1,290
1,230
1,050
1,210
kg/day
463
463
331
463
458
395
585
558
476
549
Theoretical
NOD**
Ibs/day
600
680
620
610
700
590
770
710
650
520
kg/day
272
308
281
277
318
268
349
322
295
236
Total O2
Demand
Ibs/day
1,620
1,700
1,350
1,630
1,710
1,460
2,060
1,940
1,700
1,730
kg/day
735
771
612
740
776
663
934
880
771
785
Actual O2
1st
Ibafday
740
710
830
420
420
420
820
820
410
410
Stage
^ kg/ day
336
322
376
191
191
191
372
372
186
186
2nd
Ibs/day
1,480
1,410
1,670
830
830
830
1,650
1,650
820
820
Supplied
Stage
kg/ day
671
640
757
376
376
376
748
748
372
372
Total
Ibs/day
2,280
2,120
2,500
1,250
1,250
1,250
2,470
2,470
1,230
1,230
kg/day
1,007
962
1, 133
567
567
567
1, 120
1, 120
558
558
Ratio of
Actual to
Theoretical
1.41
1.25
1.85
0.77
0.73
0.86
1.20
1.27
0.72
0.71
* Theoretical Carbonaceous 02 Demand = 1. 5 x BODg Removed.
** Theoretical Nitrogenous O2 Demand = 4. 6 x TKN Removed.
-------
period. However, because the changeover from two to one aeration tanks on
July 16 resulted in such an abrupt improvement in denitrification, it is
believed that excess biomass was the more important cause of the temporary
loss of denitrification.
MIXING
One of the initial concerns of the study related to the loss of liquid-
solids contact during the anoxic denitrification cycle due to partial
settling of mixed liquor 1n the aeration tanks when the mechanical aerators
were off. During the 30-m1nute anoxic cycle the liquid-solids interface sub-
sided to a depth of approximately 0.6 to 1.2 m (2 to 4 ft) 1n warm weather
and 0.3 to 0.6 m (1 to 2 ft) 1n cold weather. The residual rolling action
remaining from the aerator on cycle was sufficient to suspend the floe to
a large extent. Adequate I1qu1d-sol1ds contact for efficient denltriflcation
was achieved under both winter and summer conditions because of the number
of cycles influent wastewater underwent prior to discharge from the aeration
tanks. Under the worst conditions, I.e., 11 quid-sol ids Interface depth at
1.2 m (4 ft) and one aeration tank 1n service, the probability that each
influent particle of water came Into contact with solids for at least one
anoxic cycle is greater than 99 percent. Therefore, the partial lack of
liquid-solids contact did not appear to adversely affect denitrification even
during warm weather when the contact zone was shallowest.
PHOSPHORUS REMOVAL
Total phosphorus analyses were conducted on a 5-day basis for the period
of April 24, 1975 to June 4, 1976 to determine the effects of single-stage
nitrif1cation-denitrification on phosphorus removal. As anticipated, there
was no discernible effect of the process on phosphorus removal. Prior to
pulsing of the aerators, phosphorus was reduced from an average of 9.9 mg/1
to 5.5 mg/1, or 44 percent removal, based upon seven composite samples
analyzed. After pulsing, phosphorus was reduced from an average of 9.6 mg/1
to 4.7 mg/1, or 51 percent removal, based upon 22 composite samples analyzed.
This apparent improvement was not considered significant because of the wide
variations in both influent and effluent samples.
SEPTA6E AND SIPHON FLUSHING
In addition to digester supernatant returns and high flow rates from
Infiltration and .Inflow, shock loads were contributed to the aeration tanks
by septic tank truck dumping and periodic flushing of the Susquehanna River
siphon. Table 13 lists the quantities of septic wastes received at the
treatment plant and the frequency of flushing the Susquehanna River siphon.
No adverse effects from septage and siphon flushing were apparent on the
n1trl f1cation-den1tri f1cation process.
55
-------
TABLE 13. SEPTAGE AND RIVER SIPHON FLUSHING
Septage Siphon
Month
April 1975
May 1975
June 1975
July 1975
August 1975
September 1975
October 1975
November 1975
December 1975
January 1976
February 1976
March 1976
April 1976
May 1976
cu m/month
45.8
89.4
82.5
46.2
21.6
51.9
39.8
50.4
26.9
23.9
37.9
40.9
22.7
22.3
gal /month
12,100
23,600
21 ,800
12,200
5,700
13,700
10,500
13,300
7,100
6,300
10,000
10,800
6,000
5,900
(times flushed/month)
—
—
0
3
2
1
14
12
14
13
12
14
13
12
56
-------
SECTION 8
DESIGN AND OPERATING CONSIDERATIONS
Although more research work 1s necessary to provide additional data
and process methodology for design, a number of Important design and
operating considerations were revealed by the study.
PRIMARY SETTLING TANKS
In determining whether or not to use primary settling tanks ahead of a
single-stage n1tr1f1cat1on-den1tr1f1cation system, the following should be
considered:
1. The use of primary settling will reduce the COD/TKN ratio
of the aeration tank Influent and thus may reduce the
degree of denitrification attainable. However, It 1s
possible that soluble COD may be of considerably more
Importance than total COD. If so, the removal of
particulate COD 1n primary tanks may not have an adverse
effect on denitrification.
2. Reduction 1n biological reactor volume requirements.
3. Reduction 1n rag accumulations on aeration equipment.
4. Reduction in scum accumulations 1n biological reactor and
final settling tanks.
5. Benefits associated with capture of sol Ids from septic tank
wastes, digester supernatant, thickener overflow, and sewer
flushings.
REACTOR DESIGN
The following considerations are offered relative to reactor sizing
and configuration:
1. Reactor volume must be adequate for complete nitrification.
Additional volume must be allowed for denitrification, as well
as for lag periods while DO is being depleted at the Initiation
of denitrifi cation.
2. Provision should be made for maintaining DO 1n the final
settling tank influent at all times.
57
-------
3. If wastewater temperatures vary seasonally, flexibility should
be provided to adjust operating reactor volume to maintain
optimum process performance.
4. Each reactor should be compartmentalized to segregate aerobic
from anoxic or alternating anoxic-aerobic sections. Provision
should be made to introduce feed to each compartment and to divide
feed among compartments.
AERATION AND MIXING EQUIPMENT
1. Aeration equipment must be sized to provide the amounts of
oxygen necessary for complete carbonaceous and nitrogenous
oxidation, and have the flexibility to deliver the total
amount of oxygen needed into the tankage on-line under each
seasonal situation.
2. Although surface mechanical aeration will achieve satisfac-
tory results, consideration should be given to aerator
designs that will provide mixing during the anoxic cycle to
ensure complete contact with unoxldized carbon entering the
reactor.
3. Automatic controls must be provided to control the duration
of the aerobic and anoxic cycles. For surface mechanical
aerators, simple 1- to 2-hour repeat cycle timers appear ade-
quate. For diffused or combined turbine-sparger systems,
timed valve controllers can be used to rotate the air feed
from one tank to another, or to start and stop air blowers.
FINAL SETTLING TANK
1. Tanks must be provided with low surface overflow rates to
prevent solIds washout at high flows and be sufficiently
deep to allow for diurnal blanket level variations without
solids carryover due to weir velocity effects. Current
design criteria for extended aeration settling tanks (12)
should not be exceeded and more conservative criteria may
be warranted.
2. Separate sludge return pumps and suction lines should be
provided for each settling tank.
3. Return sludge capability of 200 percent appears desirable
with systems employing MLSS operating levels above 3,000 mg/1.
4. Flow meters should be provided for both return and waste
sludge.
5. Multiple effluent weir designs which create high velocities
between weir troughs, or between the trough and the tank
wall, should be avoided.
58
-------
SLUDGE PROCESSING
1. Although well-operated anaerobic digesters should pose no
problem, consideration should be given to aerobic digestion
as the character of aerobic digester supernatant returns
may be more compatible with process operation.
2. Allowance should be made 1n reactor design for the TKN
content of returns from sludge processing operations.
PROCESS OPERATION AND CONTROL
1. Essentially complete nitrification must be achieved at
all times.
2. The existence of nitrification can be monitored by alkalinity
measurements or preferably by the use of an NH^-N meter and
probe.
3. The presence of denltrification 1s best monitored by nitrate
analysis, but alkalinity changes may be of assistance as an
Indication. The most desirable tool would be a reliable and
simple probe-type measuring device for N03-N.
4. Solids inventory and attention to solids wasting are the main
factors in maintaining proper F/M and SRT.
5. DO concentrations of greater than 1 mg/1 during the aerobic
cycle do not appear necessary. Substantially lower levels
may inhibit nitrification while higher levels may delay the
onset of denltrification at the beginning of the anoxlc cycle.
6. Clarifler sludge blanket level measurement as well as 30-minute
settling tests on return sludge are desirable to avoid under-
pumping of return sludge.
7. Operators must understand the fundamentals of each major process
involved and the basic process interrelationships. Normally,
once the proper solids inventory, wasting rate, cycle time and
oxygen level have been established, the process appears to per-
form 1n a stable manner.
59
-------
SECTION 9
FUTURE RESEARCH
In reviewing the overall procedures and results of this study, several
areas can be identified where additional research would be of great assis-
tance in a better understanding of the process and an improvement in design
and operating techniques.
At Owego, the following additional research objectives appear desirable:
1. Potential improvements in nitrogen removal by feeding and
intermittently aerating the second compartment (see Figure 14).
2. Examine the effect of primary settling on nitrogen removal.
3. Evaluate nitrogen removal at high sludge recycle rates.
4. Evaluate benefits of continuous mixing during anoxic cycle.
5. Obtain additional data on process design criteria and cold
weather performance.
6. Evaluation of cadmium reduction column and N02-N probe to
monitor denitrlfication.
Before a new concept such as single-stage n1trif1cation-denitrification
will be accepted by the design profession as a viable alternate to currently
established nitrogen removal processes, proof of the universal merits of the
process, by testing at other full-scale plants, is highly desirable. In
addition to providing additional data on process reliability, performance,
and design technology, the selection of appropriate, existing plants could
also provide the following information:
1. The adaptability of diffused aeration equipment to the process.
2. The degree of nitrogen removal achieved by "ditch-type"
activated sludge plants and the development of design tech-
niques to maximize removals.
3. performance levels attainable by turbine-sparger aeration
equipment.
4. For very warm climates, whether or not premature carbon con-
sumption can be controlled to avoid the loss of denitrlfication.
60
-------
WASTE SLUDGE
TO THICKENER
FINAL
SETTLING
NOTE:
RETURN SLUDGE
N-2 A
<>
S-2
ALT.
4
4-
RAW INFLUENT OR
PRIMARY EFFLUENT
s~1
ALT. '
« '
1. ADD PART OF INFLUENT WASTEWATER TO AERATORS N-2 & S-2
2. ALL AERATORS INTERMITTENTLY OPERATED.
3. TIMED OPERATION OF AERATORS N-2 & S-2 WOULD BE
STAGGERED TO ENSURE SOME DISSOLVED OXYGEN IN
FEED TO SETTLING TANK'AT ALL TIMES.
FIGURE 14. PROPOSED PROCESS MODIFICATIONS FOR EVALUATION
IN FUTURE RESEARCH AT TOWN OF OWEGO WPCP NO.2
-------
REFERENCES
1. American Public Health Association, American Water Works Association
and Water Pollution Control Federation. Standard Methods for the
Examination of Water and Wastewater. 13th Edition. American Public
Health Association, Washington, D.C., 1971.
2. Earth, E. F., R. C. Brenner, and R. F. Lewis. Chemical Control of
Nitrogen and Phosphorus 1n Wastewater Effluent. J. Water Pollution
Control Federation, Vol. 46, No. 12, 2040, 1968.
3. Bishop, D. F., J. A. Heldman, and J. B. Stamberg. SIngle-Stage
N1trif1cation-Den1trif1cation. J. Water Pollution Control Federation,
Vol. 48, No. 3, 520, 1976.
4. Heldman, J. A., I. J. Kugelman, and E. F- Barth. Plug Flow Single-
stage N1trif1cat1on-Denitr1ficat1on Activated Sludge. Presented at:
49th Annual Conference of the Water Pollution Control Federation,
Minneapolis, Minnesota, October 3-8, 1976.
5. Kugelman, I. J. Status of Advanced Waste Treatment. Presented at:
Long Island Marine Resources Council, Hauppauge, Long Island, New York,
June 10, 1971.
6. Lawrence, A. L., and C. 6. Brown. Blokinetic Approach to Optional
Design and Control of Nitrifying Activated Sludge Systems. Presented
at: Annual Meeting of the New York Water Pollution Control Association,
New York, New York, January 23, 1973.
7. Orion Research. Instruction Manual: Nitrogen Oxide Electrode
Model 95-46. Orion Research, Inc., Cambridge, Massachusetts, 1975.
8. Ryan, B. W., and E. F. Barth. Nutrient Control by Plant Modification
at El Lago, Texas. EPA-600/2-76-104, U. S. Environmental Protection
Agency, Cincinnati, Ohio, 1976.
9. U. S. Environmental Protection Agency, Office of Technology Transfer.
Manual of Methods for Chemical Analysis of Water and Wastes. Environ-
mental Monitoring and Support Laboratory, Cincinnati, Ohio, 1974.
10. U. S. Environmental Protection Agency, Office of Technology Transfer.
Nitrification and Denitrification Facilities. Prepared by: Metcalf &
Eddy, Consulting Engineers, Boston, Massachusetts, August 1973.
62
-------
11. U. S. Environmental Protection Agency, Office of Technology Transfer.
Process Design Manual for Nitrogen Control. Prepared by: Brown and
Caldwell, Consulting Engineers, Walnut Creek, California, October 1975.
12. U. S. Environmental Protection Agency, Office of Technology Transfer.
Process Design Manual for Upgrading Existing Wastewater Treatment
Plants. Prepared by: Metcalf & Eddy, Consulting Engineers, Boston,
Massachusetts, October 1974.
63
-------
APPENDIX
DAILY NITROGEN DATA
64
-------
DAILY NITROGEN DATA - MAY 1975
CT>
Date
1
2
3
4
Phase IA
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Wastewater
Temp. (°C)
12
12
12
12
12
13
12
13
13
14
15
15
15
15
15
15
15
15
16
Org-N
Inf.
9.5
24.6
4.5
10.0
9.0
11.7
9.8
19.5
10.9
9.5
12. 1
11.8
11.4
15.6
10.6
10.6
2.5
8.5
34.7
(mg/1)
Eff.
2.8
3.5
3.3
2.9
3.5
4.5
3.0
2.6
Tr.
Tr.
3.4
3.9
3.5
Tr.
2.0
1.6
1.8
1.6
2.7
NH4-N
Inf.
28.2
24.0
12.5
9.8
29.5
16.7
23.9
27.0
45.9
33.4
27.5
27. 1
24.3
29.9
26.7
30.2
34.3
25.6
53.3
(mg/1)
Eff.
0.4
0.9
0.8
0.5
1. 1
0.7
1.5
0.5
0.5
4. 1
1.3
5.6
9.8
6.8
3.2
1.3
1.8
1. 1
0.5
TKN (mg/1) N02-N(mg/l) NOg-N (mg/1)
Inf. Eff. Inf. Eff. Inf. Eff.
37.7
48.6
17.0
19.8
38.5
28.4
33.7
46.5
56.8
42.9
39.6
38.9
35.7
45.5
37.3
40.8
36.8
34. 1
88.0
3.2
4.4
4. 1
3.4
4.6
5.2
4.5
3. 1
0.5
4. 1
4.7
9.5
13.3
6.8
5.2
2.9
3.6
2.7
3.2
0.32
1. 10
0.64
0.76
0. 19
0. 14
0. 12
0.25
0.05
0.04
0.09
0. 14
0.06
0.09
0. 18
0.24
0.22
0. 10
0. 12
5.00
5.60
4.00
4.80
4.20
6.00
5.00
5.25
2.60
3.25
3.80
3.95
4.40
4.80
6.20
3.80
7.60
6.80
5.80
Total-N (mg/1)
Inf. Eff.
38.0
49.7
17.6
20.6
38.7
29.5
33.8
46.7
56.8
42.9
39.7
40.0
35.8
45.6
37.5
41.0
40.0
34.2
88. 1
8.2
10.0
8. 1
8.2
8.8
11.2
9.5
8.4
3. 1
7.4
8.5
13.5
17.7
11.6
11.4
6.7
11.2
9.5
9.0
-------
DAILY NITROGEN DATA - JUNE 1975
crv
Date
1
2
3
4.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Wastewater
Temp. (°C)
16
15
16
16
15
15
16
16
16
16
17
17
17
17
17
17
17
17
17
17
18
Org-N (mg/1)
Inf. Eff.
11.6
37.5
10.9
5.5
22.2
9.7
11.4
11.4
10.5
10.9
10. 1
10.9
15.0
8.3
6.0
5.3
9. 1
6.5
8.5
17.7
12.2
2.2
1.7
1.8
1.5
2.3
2.5
2.6
2.4
1. 1
1.5
2.1
1.2
1.3
2.0
3. 1
2.5
2.5
2.8
3.3
3. 1
2.8
NH4-N
Inf.
24.2
43. 1
40.3
16.6
48.7
24.2
32.8
32.3
23.9
17. 1
19.2
28.5
25.2
33.2
32.5
32.3
29.5
30.5
34. 1
39.8
29.8
(mg/1)
Eff.
0.9
0.7
4.6
1.8
1.9
0.6
0.5
0.6
1.0
0.6
0.5
1.3
0.5
1.9
2.2
2.3
0.7
0.9
1.3
1.2
0.8
TKN (mg/1) NO2-N (mg/1) NOg-N
Inf. Eff. . Inf. Eff. Inf.
35.8
80.6
51.2
22. 1
70.9
33.9
44.2
43.7
34.4
28.0
29.3
39.4
40.2
41.5
38.5
37.6
38.6
37.0
42.6
57.5
41.8
3.1
2.4
6.4
3.3
4.2
3.1
3. 1
3.0
2.1
2. 1
2.6
2.5
1.8
3.9 --
5.3
4.8
3.2
3.7
4.6
4.3
3.6
0. 14
0.26
0.30
0. 40
0.60
0.42
0.43
0.45
0.08
0. 14
0. 10
0. 10
0.08
0. 10
0. 16
0. 14
0.20
0. 10
0.30
0.50
0.30
(mg/1)
Eff.
9.00
4.80
6.80
4.40
4. 10
4.40
4. 10
4.30
0. 10
0.20
0.64
2.40
0.40
3.60
4.80
5.90
5.90
6.80
9. 10
9. 10
9.00
Total-N (mg/1)
Inf. Eff.
35.9
80.5
51.5
22.5
71.5
34.3
44.6
44.2
34.5
28. 1
29.4
39.5
40.3
41.6
38.7
37.7
38.8
37. 1
42.9
58.0
42. 1
12. 1
7.2
13.2
7.7
8.3
7.5
7.2
7.3
2.2
2.3
3.2
4.9
2.2
7.5
10. 1
10.7
9. 1
10.6
13.7
13.4
12.6
-------
DAILY NITROGEN DATA - JULY 1975
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Phase IB
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Wastewater
Temp. (°C)
17
17
18
18
18
18
18
19
18
18
19
19
19
19
20
20
19
20
19
19
19
19
20
Org-N
Inf.
10.0
9.9
15.9
12. 1
14.1
13.0
10. 1
15.3
9.9
14.4
14.3
10.0
14.5
15. 1
9.5
10.4
15.9
9.3
22. 1
16.8
10.0
9.9
12.0
(mg/1)
Eff.
3.4
3.8
3.2
2.9
3.2
2. 1
3. 1
?..o
1.6
2.2
2.0
2.5
2.5
1.9
2.2
2.0
0.9
2.0
2.0
1.9
2.4
2. 1
4.5
NH4-N
Inf.
37. 1
27.2
29. 1
35.0
40.0
32.6
31.7
53.0
31.5
28.5
37. 1
29.8
31.7
35.7
25.7
33.2
32.8
25.3
37.2
29.8
27.3
38.4
31.6
(mg/D
Eff.
1.0
1.0
1.3
3.0
1.5
1.5
1.3
1.3
1.5
1.5
1.4
3.6
1.3
0.7
2.7
2.3
2.2
1.0
3.0
4.3
1.9
3. 1
1.0
TKN (mg/1)
Inf. Eff.
47.1
37. 1
45.0
47.1
54! 1
45.6
41.8
68.3
41.4
42.9
51.4
39.8
46.2
50.8
35.2
43.6
48.7
34.6
59.3
46.6
37.3
48.3
43.6
4.4
4.8
4.5
5.9
4.7
3.6
4.4
3.3
3. 1
3.7
3.4
6. 1
3.8
2.6
4.9
4.3
3. 1
3.0
5.0
6.2
4.3
5.2
5.5
NO0-N (mg/1) NO--1S
£t ij
Inf. Eff. Inf.
0.30
0.50
0.34
0.32
0.34
0.32
0.32
0.30
0.30
0.22
0.50
0.30
0.40
0.40
0.38
0.2G
0.22
0.023 0.002 0.01
0.013 0.014 0.04
o.ooa o.^tu 3.40
0.006 0.580 1.00
O.Olb 0.010 0.13
0.072 Tr. 0.38
1 (mg/1)
Eff.
11.0
11.0
10.0
10.2
10.2
10.4
10.6
11.0
14. 0
11.8
13.4
11.4
2.2
1.6
1.0
3.0
2.3
1.0
1.4
1. 1
o. a
1.7
1.7
Total-N (mg/1)
Inf. Eff.
47.4
37.6
45.3
47.4
54.4
45.9
42. 1
68.6
41.7
43. 1
51.9
40.2
46.6
51.2
35.6
43.9
48.9
34.6
59.4
50.0
38.3
48.4
44. 1
15.4
15.8
14.5
16. 1
14.9
14.0
15.0
14.3
17.1
15.5
16.8
17.5
6.0
4.2
5.9
7.3
6. 1
4.0
6.4
7.8
5.7
6.9
7.2
-------
DAILY NITROGEN DATA - AUGUST 1975
oo
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Waste water
Temp. (°C)
20
20
20
20
20
20
*
21
22
21
20
21
20
20
20
20
20
21
21
20
20
20
Org-N (mg/1)
Inf. Eff.
16.9
8.0
9.5
—
21.1
15.5
14.5
9.2
12. 1
15.9
12.2
12.7
13.4
9.4
12.9
11.4
12.2
11.7
9.5
19.8
12.8
2.9
2.5
2.5
3. 1
2.5
Tr.
2.2
2.2
1.2
2. 1
2.8
Tr.
2.2
2.4
2.5
2.6
1.9
2. 1
2.2
2.7
2.6
NH4-N
Inf.
32.9
28.2
32. 1
—
47.8
44.5
34.2
26.3
37.7
29.5
34.0
32.0
35.2
36.5
37.5
33.6
24.2
29.3
23.0
39.5
26.3
(mg/1)
Eff.
0.3
0.4
2.1
0.6
0.7
1. 1
2.5
3.1
3.2
1.3
2.3
3.6
2.5
3. 1
1. 1
0.5
5.5
0.5
3.0
0.8
0.8
TKN (mg/1)
Inf. Eff.
49.8
36.2
41.6
—
68.9
60.0
48.7
35.5
49.8
45.4
46.2
44.7
48.6
45.9
50.4
45.0
36.4
41.0
32.5
59.3
39. 1
3.2
2.9
4.6
3.7
3.2
1. 1
4.7
5.3
4.4
3.4
5. 1
3.6
4.7
5.5
3.6
3. 1
7.4
2.6
5.2
3.5
3.4
N02-N (mg/1)
Inf. Eff.
0.072
0.050
0.053
0.068
—
—
—
--
--
0.018
0.032
0.032
0.054
0.030 ,
0.028
0.041
0.050
0.039
Tr.
0.028
0.032
Tr.
0.070
Tr.
0.050
--
—
-.
--
--
0.070
0.010
0.010
0.050
0.050
Tr.
Tr.
0.085
Tr.
Tr.
0.010
Tr.
NOg-N
Inf.
0.38
0. 16
0.28
0.31
0. 16
0.02
0.68
0.68
0.36
0.48
0.81
0.60
0.38
0.36
0.38
0.36
0.38
0.36
0.30
0. 12
0.20
(mg/1)
Eff.
1.35
0.65
0.36
0.65
1.40
1.00
0. 15
1. 10
1.90
4.60
4.20
3.30
5.80
4.50
5.50
3.90
2.30
2.60
3.40
3.90
3.70
<
Total-N (mg/1)
Inf. Eff.
50.2
36.4
41.9
—
69. 1
60.0
49.4
36.2
50.2
45.9
47.0
45.3
49.0
46.3
50.8
45.4
36.8
41.4
32.8
59.5
39.3
4.6
3.6
5.0
4.4
4.6
2. 1
4.9
6.4
6.3
8. 1
9.3
6.9
10.6
10. 1
9. 1
7.0
9.8
5.2
8.6
7.4
7. 1
-------
DAILY NITROGEN DATA - SEPTEMBER 1975
Date
1
2
3
4
5
6
7
8
Stand-py
9
10
11
Wastewater
Temp. (°C)
18
21
20
19
19
20
Org-N
Inf.
9.0
9.7
8.4
13.3
17.5
11.7
(mg/1)
Eff.
2.7
2.8
2.4
3.4
3.8
4. 1
NH4-N
Inf.
23.5
26.7
23.8
25.7
34.6
22.0
(mg/1)
Eff.
0.9
2.6
1.2
0.5
1.5
2.3
TKN
Inf.
32.5
36.4
32.2
39.0
52. 1
33.7
(mg/1)
Eff.
3.6
5.4
3.6
3.9
5.3
6.4
NO2-N
Inf.
0.032
0.035
0.032
0.024
0.032
0.039
(mg/1)
Eff.
0.030
0. 160
0. 175
0. 120
0.085
0. 140
N03-N
Inf.
0.54
0. 19
0.09
0. 18
0.20
0. 12
(mg/1)
Eff.
3.80
3.50
3.65
4.60
4.20
3.40
Total-N
Inf.
33. 1
36.6
32.3
39.2
52.3
33.9
(mg/1)
Eff.
7.4
9. 1
7.4
8.6
9.6
9.9
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
-------
DAILY NITROGEN DATA - FEBRUARY 1976
-j
o
Wastewater
Date Temp. (°C)
1
2
Phase H - Start- Up
3 9
4 9
5 8
6 8
7
8
9 8
10 8
11 9
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Org-N (mg/1) NH4-N (mg/1) TKN (mg/1) NC>2-N (mg/1) NOg-N (mg/1) Total-N (mg/1)
Inf. Eff. Inf. Eff. Inf. Eff. Inf. Eff. Inf. Eff. Inf. Eff.
15.0 3.1 22.7 10.2 37.7 13.3 0.056 0.680 0.24 2.50 38.0 16.5
9.7 Tr. 19.6 13.7 29.3 13.7 0.196 0.750 0.78 2.00 30.3 16.5
16.7 Tr. 20.0 12.9 36.7 12.9 0.112 0.630 1.22 1.20 38.0 14.7
Tr. Tr. 15.5 15.9 15.5 20.9 0.126 0.370 1.16 0.90 16.8 21.7
6.4 19.7 14.5 21.0 20.9 40.7 1.260 2.800 0.05 0.05 22.2 43.6
13.4 1.3 24.0 18.0 27.4 19.3 0.800 2.900 0.04 0.05 38.2 22.3
8.9 1.5 13.5 18.0 22.4 18.5 0.400 0.900 0.06 0.04 22.9 19.4
-------
DAILY NITROGEN DATA - MARCH 1976
Date
1
2
3
4
5
6
7
8
9
Phase IIA
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Waste water
Temp. (°C)
9
8
8
8
8
8
9
8
9
9
9
9
9
10
10
10
Org-N
Inf.
17.6
18.0
16.7
15.5
14.6
14.4
18.2
14.1
14.8
15.7
25.0
13.5
14.6
14.9
22.4
16.8
(mg/1)
Eff.
—
1.9
1.9
1.5
2.5
1.8
2.5
2.0
1.7
2.0
1. 1
1.3
1.3
1.6
1.3
1.7
NH4-N
Inf.
23.7
17.2
17.9
16.5
15.6
16.0
20.5
15.5
14.5
15.6
18.5
20.0
14.5
14.5
19.9
16.9
(mg/1)
Eff.
--
1.0
1.0
0.7
0.5
0.5
0.7
0.5
0.8
0.3
0.4
0.4
0.2
1.3
0.4
0.4
TKN (mg/1)
Inf. Eff.
41.3
35.2
34.6
32.3
30.2
30.4
38.7
29.6
29.3
31.3
43.5
33.5
29. 1
29.4
42.3
33.7
—
2.9
2.9
2.2
3.0
2.3
3.2
2.5
2. 5
2.3
1.5
1.7
1.5
2.9
1.7
2. 1
NO2-N (mg/1)
Inf. Eff.
0. 128
0. 102
0. 120
0.060
0.056
0.074
0.084
0.096
0.096
0.066
0.084
0.086
0.092
0.084
0.084
0.062
1.200
1.700
1.900
0.620
0.400
0.510
0.590
0.450
0.370
0. 180
0. 130
0. 120
0. 100
0.030
0.030
0.030
NOg-N (mg/1)
Inf. Eff.
1.08
2.40
1.60
1.26
1.26
1.30
1. 12
1.30
1.70
1.60
1.66
1.42
1.66
0.48
0.33
0.26
3.20
4.00
3.20
4.30
2.90
4.30
6.60
6.30
6.80
6.60
6.30
8.00
8.60
1.60
0. 80
2. 25
Total-N (mg/1)
Inf. Eff.
42.5
37.7
36.3
33.3
31.5
31.8
39.9
31.0
31. 1
33.0
45.2
35.0
30.9
30.0
42.7
34.0
--
8.6
8.0
7. 1
6.3
7. 1
10.4
9.3
9.7
9. 1
7.9
9.8
10.2
4.5
2.5
4.4
-------
DAILY NITROGEN DATA - APRIL 1976
PO
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Wastewater
Temp. (°C)
10
9
10
10
10
10
9
9
9
9
10
11
12
12
11
11
10
10
11
12
Org-N (mg/l)
Inf. Eff.
12.6
18.4
12.9
24.3
22.2
22.5
15.4
17.8
16.5
16.3
18.4
14.3
16.8
10.3
11.7
15.5
13.8
11.8
12.3
17.3
1.3
1.6
1.6
1.7
1.9
2.0
1.2
1.2
1.3
1.6
1.5
1.4
1.2
1. 1
1.1
1.2
1.2
1.4
1.6
1.5
NH4-N
Inf.
9.5
15. 1
23.9
22.3
19.7
24.2
17.3
21.0
17.6
19.7
23.7
22.0
24.2
24. 1
21. 1
21.2
17.6
37.6
21.0
19.9
(mg/l)
Eff.
0.4
0.6
1.3
0.7
0.7
0.7
0. 1
0. 1
0.8
0.3
0.1
0.1
0.1
0.1
0. 1
0.1
0. 1
0.2
0. 1
0. 1
TKN (mg/l)
Inf. Eff.
22. 1
33.5
36.8
46.6
41.9
46.9
32.7
38.8
34. 1
36.0
42. 1
36.3
41.0
34.4
32.8
36.7
31.4
49.4
33.3
37.2
1.7
2.2
2.9
2.4
2.6
2.7
1.3
1.3
2. 1
1.9
1.6
1.5
1.3
1.2
1.2
1.2
1.3
1.6
1.7
1.6
NO2-N (mg/l)
Inf. Eff.
0.062
0.070
0.056
0.090
0.084
0.088
0.084
0.066
0.080
0.094
0.078
0. 136
0. 138
0. 158
0. 110
0.076
0.076
0.076
0.086
0.098
0.038
0.040
0.020
0.020
0.020
0.020
0.020
0.040
0.035
0.050
0.020
.0.200
0.200
0.200
0.200
0.200
0.004
0.004
0.006
0.010
N03-N (mg/l)
Inf. Eff.
0.42
0.08
0.02
0. 10
0.02
0.04
1.00
0.84
0.74
0.82
0.90
0.90
0. 10
0.70
0.94
1.24
1.02
0.94
1.'12
1.20
2.20
0. 14
0.09
0.09
0. 12
0. 10
11.00
6.00
12.00
20.00
13.00
6.40
6.00
6.50
7.30
8.80
9.30
9.70
10.00
7.80
Total-N (mg/l)
Inf. Eff.
22.6
33.7
36.9
46.8
42.0
46.8
33.8
39.7
35.0
36.9
43. 1
37.3
41.2
35.3
33.9
38.0
32.5
50.4
34.5
38.5
3.9
2.4
3.0
2.5
2.7
2.8
12.3
7.3
14. 1
22.0
14.6
8.1
7.5
7.9
8.7
10.3
10.5
11.3
11.7
9.4
-------
DAILY NITROGEN DATA - MAY 1976
CO
Date
1
2
Phase nB
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Wastewater
Temp. (°C)
11
11
12
12
11
12
12
12
12
12
12
12
12
12
12
12
12
13
13
13
Org-N
Inf.
i
10.4
11.7
26.4
14.9
21. 1
15.6
15.5
15.1
15.5
17. 1
17.1
14.6
14.1
15.0
15.8
--
--
--
__
._
(mg/1)
Eff.
0.9
2.0
—
--
1.5
1.6
0.8
1.6
1. 1
0. 1
1.6
1.6
1.3
2. 1
2.5
--
—
--
--
--
NH4-N
Inf.
15.5
24.5
23.9
19.4
26. 1
21.6
23.6
17.7
17.8
20.3
23.6
20. 1
18.8
15.0
18.5
24.0
20.8
25.0
31.0
19.3
(mg/l)
Eff.
0.5
._
-_
0.6
1.8
8.1
4.9
3.0
4.0
2.8
9.8
9.5
6.6
10.2
12.2
14. 1
12.3
15. 1
14.4
13.7
TKN (mg/1)
Inf. Eff.
25.9
36.2
50.3
34.3
47.2
37.2
39.1
32.8
33.3
37.4
40.7
34.7
32.9
30.0
34.3
__
—
—
—
--
1.4
.-
--
2.6
3.3
9.7
5.7
4.6
5.1
2.9
11.4
11. 1
7.9
12.3
14.7
--
--
—
--
--
NO2-N
Inf.
0.024
0.012
0.030
0.018
0.022
0.026
0.029
0.037
0.038
0.042
0.035
0.030
0.034
0.038
0.043
--
—
--
--
--
(mg/1)
Eff.
0.005
0.010
__
--
0.070
0.160
0.190
0. 170
0.030
0.028
0.470
0.270
0.310
0.290
0.240
--
--
--
--
--
NO.-N
J
Inf.
0.34
0.32
0.48
0.32
0.40
1.24
0.98
1.36
1.22
1.24
1.04
0.58
0.58
1. 10
1. 10
--
--
--
--
--
(mg/1)
Eff.
9.8
5.8
--
--
8.0
4.4
5.3
7.4
6.6
6.2
4.4
3.7
4.7
4.0
2.5
--
--
--
--
--
Total-N (mg/1)
Inf. Eff.
26.3
36.5
50.8
34.6
47.6
38.5
40.1
34.2
34.6
38.7
41.8
35.3
33.5
31. 1
35.4
--
--
--
--
—
11.2
9.4
-_
—
9.4
14.3
11.2
12.2
11.7
9.1
16.3
15. 1
12.9
16.9
17.4
--
--
--
__
--
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-77-088
3. RECIPIENT'S ACCESSION>NO.
4. TITLE AND SUBTITLE
FULL-SCALE OPERATION OF A SINGLE-STAGE NITRIFICATION-
DEN I TRIF I CAT I ON PLANT
5. RFPORT DATE
August 1977(Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Donald
Donald
Daniel
E.
F.
6.
Schwlnn
Storrier
Thome
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Town of Owego
Town Hall
20 Court Street
Owego, New York 13827
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
803618-01
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—Gin., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final 3/1/75 - 11/29/76
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
E. F. Earth, Project Officer
(513) .684-7641
16. ABSTRACT
The major objective of this study was to operate a full-scale single-stage
nitrification-denitrification plant without methanol addition to determine the
feasibility and reliability of the process, the design features needed to be
incorporated by engineers, and the operating techniques to be employed to ensure
optimum performance. Because nitrification-denitrification can become more difficult
to operate under extreme cold wastewater temperatures, a full-scale plant located at
Owego, New York, was selected which performs under wastewater temperatures ranging
from 8° to 22°C. Alternating aerobic-anoxic conditions were achieved in completely
mixed reactors by the on-off cycling of mechanical aerators.
The following results and conclusions were determined from these studies:
1. Single-stage n1tr1ficat1on-den1tr1f1cation is a viable nitrogen
removal process.
2. Nitrogen removals of from 76 to 86 percent were normally
accomplished with hydraulic retention times of 13 to 27 hours,
depending upon wastewater temperature and strength. BOD and
suspended solids reductions were well above 90 percent.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Waste water*, Activated Sludge Process,
Nitrification*
b.lDENTIFIERS/OPEN ENDED TERMS
Den1tr1f1cation*, Single
Stage, Settling Rates,
Anaerobic Digestion,
Temperature Variation,
Phosphorus Removal
c. COSATI Field/Group
13B
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport/
UNCLASSIFIED
21. NO. Ol
84
20. SECURITY CLASS (TMspage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
74
.S. GOVERNMENT PRINTING OFFICE: 1977- 757-056/6485
------- |