xvEPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
EPA-600/2-80-154
August 1980
Research and Development
A Study of Nitrate
Respiration in the
Activated Sludge
Process
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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-Enyironment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned tp 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 trea* snt
of pollution-sources to meet environmental quality standards.
This document is available to theipublic through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-80-154
August 1980
A STUDY OF NITRATE RESPIRATION
IN THE ACTIVATED SLUDGE PROCESS
by. .
Carl Beer
New York State Department of Environmental Conservation
Albany, New York 12233
Grant No. 17050 EDL
Project Officer
Richard C. Brenner
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 Labora-
tory, U.S. Environmental Protection-Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or recommendation
for use.
ii
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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 wel-
fare of the American people. Noxious air, foul water, and spoiled land are
tragic testimony to the deterioration of our natural environment. The com-
plexity of that environment and the interplay between its components require
a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution and
it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technolpgy and systems for the prevention, treatment, and management
of wastewater and solid and hazardous waste pollutant discharges from munici-
pal and community sources, for the preservation and treatment of public drink-
ing water supplies, and to minimize the adverse economic, social, health, and
aesthetic effects of pollution. This publication is one of the products of
that research; a most vital communications link between the researcher and
the user community.
This report describes a successtul effort to develop a modification of the
activated sludge process that removes a high percentage of nitrogen from
municipal sewage without the addition of an organic carbon source like
methanol.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
iii
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ABSTRACT
In an experimental, 570-m /day (0.15-mgd) activated sludge plant treating
domestic wastewater from a correctional facility, 76 to 87 percent nitrogen
removal was obtained via sludge synthesis and biological denitrification
using endogenous H-donors. Between 27 and 48 percent of the influent nitro-
gen was removed by denitrification and between 37 and 49 percent via sludge
synthesis. The process was operated for 8 mo under comprehensive analytical
control. Ferric chloride (Fed-}) was used to enhance phosphorus removal. •
The lowest winter temperature measured in the aeration tank was 15.9 C. An
in-line surge tank was employed for flow equalization. Primary settling was
not utilized in the first 5 mo of operation during the 1974-75 winter. A
turbid effluent developed in the fifth month of operation, however. This
condition was finally brought under control by adding primary settling to the
flow scheme and dosing FeClg to the influent of the primary settler. This
change in treatment strategy reduced nitrogen removal from 82 percent to 78
percent by reducing sharply the amount of nitrogen removed via sludge syn-
thesis. The portion of nitrogen removed by denitrification was not affected.
This type of operation was used for 3 mo^
The surge tank was used as part of the activated sludge system, for short
periods of time. Pulsating aeration by a floating aerator controlled by a
time clock in the surge tank allowed the direct use of wastewater carbon as
the H-donor in biological denitrification. Nitrogen removal efficiency was
thereby increased, but a bulking sludge problem developed.
By chlorinating excess activated sludge or a mixture of primary and excess
activated sludge to pH 2.5 and using the pipeline from the chlorinator to the
sludge drying bed as a reactor, a 50 percent increase in sludge filterability
was obtained.
The feasibility of utilizing a chlorine contact chamber as a multiple tray
second-phase settling tank featuring a cross-flow arrangement of settling
surfaces was investigated. An incremental suspended solids1 removal of 33
percent was obtained. -
This report was submitted in fulfillment of Grant No. 17050 EDL by the New
York State Department of Environmental Conservation under the partial spon-
sorship of the U.S. Environmental Protection Agency and covers the period
from November 1973 to July 1975. • • .
iv
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CONTENTS
Foreword ill
Abstract iv
Figures vi
Tables . . viii
Abbreviations and Symbols . . . xi
Acknowledgements xvi
1. Introduction 1
2. Conclusions 6
" 3. Recommendations .'. 9
4. Stoichiometric and Kinetic Considerations , '.. . . 12
5. Analytical Methods and Sampling Procedures , 34
6. Treatment Facilities, Operating Procedures, and Plant Measure-
ment Procedures , 36
7 . Raw Sewage Characteristics . .. . 46
8. Results and Discussion 51
9. Design Considerations for Activated Sludge Systems Employing
Compartmentalized Aeration Tanks 126
References , 137
Publications and Patents 140
Appendices 141
v
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FIGURES
Number .. Page
1 Coxsackie Experimental Sewage Treatment Plant-Plan of Facilities 2
2 Numbering Scheme for Aeration Cells 4
3 Aeration Patterns in Compartmentalized Reactors 19
4 Two-Step Feeding of Compartmentalized Reactors 21
5 Effluent Ammonia Concentration (S-) vs. Imposed Nitrifier
Growth Rate (unr) • • 25
6 Ammonia Profiles in a Plug Flow Reactor Illustrating Table 6 ... 31
7 Surge Tank .• 37
8 Sideweir Structure 39
9 Section View of Aeration Tank 41
10 Section View of Final Settler 41
11 Chlorine Contact Chamber/Second-Phase Settler Combination 43
12 Raw Sewage Flow Pattern (11/9/73-12/9/73) 49
13 Process Schematic for Flow Sheets I-and II 52
14 Aeration Train Dissolved COD Profiles for Flow Sheet I 55
15 Aeration Train Dissolved Orthophosphorus Profiles for Flow
Sheet I f 56
16 Daily Final Settler Effluent Total COD Profiles for Flow
Sheet I 58
17 Daily Final Settler Effluent NO~+NO~-N Profiles for Flow
Sheet I J 59
18 Process Schematic for Flow Sheet III 63
19 Process Schematic for Flow .Sheet IV 67
20 Process Schematic for Flow Sheet V 68
21 Process Schematic for Flow Sheet VI 69
22 Monthly Nitrogen Balance Bar Diagrams for Flow Sheets IV, V,
and VI 88
23 Flow Sheet I Nitrogen Profiles (11/14/73) 96
24 Flow Sheet I Nitrogen Profiles (11/27/73) 97
VI
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FIGURES (continued)
Number ' •.'•••
25 Flow Sheet I Nitrogen Profiles (12/5/73 98
26 Flow Sheet IV Nitrogen Profiles (9/18/74) 99
27 .Flow Sheet IV Nitrogen Profiles (10/10/74) 100
28 Flow Sheet IV Nitrogen Profiles (11/14/74) .. 101
29 Flow Sheet VI Nitrogen Profiles (6/12/75) . . .' 102
30 Flow Sheet I Ammonia and Nitrate Bar Diagram Profiles (11/14/73). 103
31 Flow Sheet I Ammonia and Nitrate Bar Diagram Profiles (11/27/73). 104
32 Flow Sheet I Ammonia and Nitrate Bar Diagram Profiles (12/5/73).. 105
33 Flow Sheet VI Ammonia and Nitrate Bar Diagram Profiles (6/12/75). 106
vii
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TABLES
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Coxsackie Experimental Sewage Treatment Plant - Main Dimensions
of Major Treatment Units and Characteristics of Equipment
Characteristic Features of 'Flow Sheets I ,Through VI
Endogenous Nitrate Respiration Stoichiometric Relationships ....
Stoichiometric Projection of Nitrogen Removal via Sludge
Synthesis and Endogenous Nitrate Respiration
Substrate Nitrate Respiration and Anoxic Synthesis
Effect on Basic Kinetic Values of Applying Safety Factor of 2 ,to
Plug Flow Reactor • .
Flow-Weighted, Annual-Average Raw Sewage and Surge Tank Effluent
Characteristics of Year Ending July 31, 1975 (Flow Sheets IV,
V, and VI)
Flow-Weighted, Monthly-Average Raw Sewage Characteristics for
12 Months Ending July 31, 1975 (Flow Sheets IV, V, and VI)
Raw Sewage Characteristics for November and December 1973
(Flow Sheet I) „
Average Values of Operating Parameters for Flow Sheet I
Average Chlorine Contact Chamber Effluent Values for Flow Sheet
I
Operating and Effluent Data for Flow Sheet II . . .
Operating and Effluent Data for Flow Sheet III
Air Flow to Plant and DO in Aeration Cells During Flow Sheet
IV, V, and VI Operations
Monthly Hydraulic Surge Tank, Primary Settler, and Chlorine
Contact Chamber Data for Flow Sheets IV, V, and VI
Monthly-Average Aeration Tank and Final Settler Detention
Times for Flow Sheets IV, V, and VI
Monthly-Average Final Settler Overflow and Solids Loading Rates
for Flow Sheets IV, V, and VI
Flow-Weighted, Monthly-Average Surge Tank Effluent Character-
istics for Flow Sheets IV, V, and VI
- -r'^a. .-
3
5
16
17
19
30
47
48
50
53
54
62
65
70'
71
72
73
74
viii
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TABLES (continued)
Number
Page
19 Monthly-Average Aeration Tank Loading Rates and Solids
Retention Times for Flow Sheets IV, V, and VI 75
20 Monthly-Average Mixed Liquor Characteristics for Flow Sheets
IV, V, and VI 76
21 Monthly-Average Excess Activated Sludge Characteristics for
Flow Sheets IV, V, and VI 77
22 Monthly-Average Solids Production Data for Flow Sheets IV,
V, and VI . 78
23 Flow-Weighted, Monthly-Average Final Settler Effluent Char-
acteristics for Flow Sheets IV, V, and VI 79
24 Monthly-Average COD and BOD Removal Efficiencies for Flow
Sheets IV, V, and VI . 80
25 Monthly Treatment System Nitrogen Balances (Excluding Surge
Tank and Chlorine Contact Chamber) for Flow Sheets IV, V,
and VI 81
3+
26 Monthly Treatment System Fe Balances (Excluding Chlorine Con-
tact Chamber) for Flow Sheets IV, V, and VI 82
27 Monthly Treatment System Phosphorus Balances (Excluding Surge
Tank and Chlorine Contact Chamber) for Flow Sheets IV, V,
and VI .. . 83
28 Effect of Ferric Chloride Addition on Process Phosphorus
Removal and Iron Concentration in Return Sludge: Flow Sheet
IV 84
29 Flow-Weighted, Monthly-Average Chlorine Contact Chamber
Effluent Characteristics for Flow Sheet IV 85
30 Flow-Weighted, Monthly-Average Primary Settler Effluent
Characteristics for Flow Sheets V and VI 86
31 Flow-Weighted, Monthly-Average Chlorine Contact Chamber
Effluent Characteristics for Flow Sheets V and VI 87
32 Average Contaminant Load on Aeration Train During Flow Sheet
IV and VI Operations - 93
33 Comparison of Sludge Production and Organic Load Data for
Flow Sheets IV and VI 94
34 Stoichiometric Data Abstracted from Nitrogen Profiles for
Flow Sheets I, IV, and VI .„;... 109
35 Kinetic Data Abstracted from Nitrogen Profiles for Flow Sheets
I, IV, and VI Ill
36 Monthly Rates of Denitrification Abstracted from Monthly
Nitrogen Balances for Flow Sheets IV, V, and VI 113
ix
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TABLES (continued)
Number
37
38
39
40
41
42
43
44
45
Page
Monthly Actual vs. Predicted Volatile Sludge Production for
Flow Sheets IV, V, and VI 115
Monthly Growth Rates Abstracted from Monthly Nitrogen Balances
for Flow Sheets IV, V, and VI 116
j
Monthly-Average Return Sludge Characteristics for Flow
Sheets IV, V, and VI 118
Effect of Chlorine Contact, Chamber/Second Phase Settler
Combination on Suspended Solids Removal 119
Chlorine Dosages Used During Sludge Chlorination Experiments
122
Effect of Sludge Chlorination on Solids Concentration,
Filterability, and pH . . . .• 123
Effect of Sludge Chlorinatiion on Slurry Filtrate Quality 124
Quality of Sludge Dewatering Bed Underflow During Sludge
Chlorination Experiments .. 125
Forms of Nitrogen and Mass of Newly Formed Biomass as Affected
by Residence in the Five Zones of the Reactor of the Process
Design Example • 135
x
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ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS
alk. alkalinity
A.S. activated sludge
CC chlorine contact
CCC chlorine contact chamber
CM completely mixed
CRT cell residence time
diss. dissolved
DO dissolved oxygen
EAS excess activated sludge
ENR endogenous nitrate respiration
EOR endogenous oxygen respiration
EPA U.S. Environmental Protection Agency
EPA PDM Process Design Manual for Nitrogen Control, published by EPA
F/M food-to-microorganism ratio
HM . heterotrophic matrix
MCRT mean cell residence time
ML mixed liquor
MLSS mixed liquor suspended solids; mixed liquor suspended solids con-
centration
MLVSS mixed liquor volatile suspended solids; mixed liquor volatile sus-
pended solids concentration
N nitrogen
n. nitrifier or nitrifiers
N.AP. not applicable
N.AV. not available
OUR oxygen uptake rate
P phosphorus
.PF plug flow
xi
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ABBREVIATIONS AND SYMBOLS (continued)
Q.R. questionable result |
RSSS return sludge suspended solids; return sludge suspended solids con-
centration
RSVSS return sludge volatile suspended solids; return sludge volatile sus-
pended solids concentration
SF safety factor
SRT solids residence time (= CRT)
SS total suspended solids; total suspended solids concentration
SVI sludge volume index
SWD side water depth
VSS volatile suspended solids; volatile suspended solids concentration
SYMBOLS USED IN EQUATIONS
(units given in parentheses)
b Fractional rate of biomass destruction in a particular endogenous
respiration reaction (mg of biomass destroyed per mg of initial
biomass).
b(day ) Microorganism decay factor in endogenous oxygen respiration (mg/mg/
day) .
bj Biomass destruction factor in endogenous nitrate respiration (mg
biomass destroyed/mg N074-N07-N gasified) .
C (mg/&) Monthly flow weighted average of any contaminant concentration
(C
m
Z C Q. /Z Q ).
n n n
C (mg/5,) Contaminant concentration, 24-hr composite, n
,
day of the month.
JENR
Stoichiometric efficiency factor in endogenous nitrate respiration
(mg N removed from procejss water/mg NO~+NO~-N gasified) .
Fraction of nitrifier biomass in total biomass-of mixed liquor or
return sludge. | ,
Fraction of substrate us!ed for energy in a biological substrate
removal process.
Percent of Fe found in mixed liquor or return sludge solids.
Fraction of substrate used for synthesis of new biomass in a bio-
logical substrate remova|l process.
k,(day ) Specific endogenous nitrate respiration reaction rate (mg NO-+NO--N
gasified/mg MLVSS/day). , J
K (mg/&) Michaelis-Menten constant in nitrification corresponding to prevail-
ing temperature (mg/£ Ntft-N) .
Fe(%)
f
XII
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ABBREVIATIONS AND SYMBOLS (continued)
AN(mg/£) or
AN (mg/fc)
Nd(mg/£)
N^mg/A)
N0(mg/£)
AN (mg/Jl)
w
Q(£/day)
Qn (Jl/day)
Qr(£/day)
(^(ft/day)
S(mg/£)
ASC(mg/£)
SDT(day)
SDTd(day)
SDT (day)
SDT (day)
SF '
n
S±(ing/A)
S0(mg/£)
sssv30(mg/Ji)
SV30(m&)
Qr/Q)
Mass of nitrifiers wasted per liter of reactor space.
Mass of nitrifiers present per liter of reactor space.
Nitrifier biomass produced per liter of sewage treated.
Nitrogen gasified in endogenous nitrate respiration per liter
of sewage treated.
Effluent biodegradable nitrogen concentration.
Influent biodegradable nitrogen concentration. ,
Mass of nitrifiers present per liter of reactor space at time
t = 0.
Nitrifier biomass wasted per liter of sewage treated.
Plant flow.
Plant flow, n day of month. *
Return sludge flow.
Waste sludge flow.
Sludge recycle ratio (r =
Substrate concentration.
BOD,, removed in a process per liter of sewage treated.
Sewage detention time in entire reactor (SDT = V/Q).
Sewage detention time in denitrification (anoxic) reactor
(SDTd = Vd/Q). . . *
Sewage detention time in nitrification (aerobic) reactor
(SDTfl = Vn/Q). .
Sewage detention time in purge cell of aerobic-anoxic reactor
(SDTp = Vp/Q).
Safety factor, denitrification reactor.
Safety factor, nitrification reactor.
Initial NH.-N concentration after dilution of SQ by the recycle
flow: S. = (S0 + r S1)/(l + r) (In the influent pipe of a re-
actor or at the head end of a plug flow tank).
NH.-N concentration in the effluent of a reactor.
4
NHj~-N concentration in the influent wastewater.
Suspended solids concentration in the space occupied by settled
sludge at the end of a 30-min settled volume test.
Volume occupied by sludge at the end of a 30-min settling test
for a 1—liter test volume of mixed liquor.
xiii
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ABBREVIATIONS AND SYMBOLS (continued)
SV60(mJl)
SVI(mJl/g)
t(day)
tm(day)
tn(day)
T(C)
vd(£)
Vol. (%)
wn(day
AX(mg/S,)
Y
Y'
\
0
yhr(day~1)
Volume occupied by sludge at the end of a 60-min settling test
for a 1-liter test volume of mixed liquor.
Sludge volume index.
Time. <
Flowthrough time in plug flow nitrification reactor necessary
to achieve prescribed effluent NH.-N concentration.
Flowthrough time in plug flow nitrification reactor
[tn = SDTn/(l + r)].
Temperature. ,
Fractional volatility of mixed liquor solids (v = VSS/SS) ; final
fractional volatility of mixed liquor solids at the end of a
particular endogenous respiration period.
Volume of reactor .
Volume of denitrification (anoxic) reactor.
Volume of nitrification (aerobic) reactor.
Fractional volatility of mixed liquor or return sludge solids
at the beginning of endogenous respiration.
Percentage of volatility of mixed liquor solids or of return
sludge solids (Vol. |= 100 v) .
Volume of purge compartment of aerobic-anoxic reactor.
Specific nitrif ier biomass wasting rate (mg/mg/day) .
Mixed liquor volatile suspended solids concentration (biomass
concentration) .
Net biomass production (mg VSS synthesized less mg VSS destroyed
in EOR and ENR) per 'liter of sewage treated.
Biomass wasted (mg VSS) per liter of sewage treated.
Yield factor, BOD,- removal (mg VSS produced/mg BOD,, removed
at zero cell residence time) .
Adjusted aerobic yield factor, BODg removal (mg VSS produced/mg
6005 removed at zero cell residence time less aerobic decay:
Y' = Y - b X SDT /ASC) .
Yield factor, nitrification (mg nitrif ier biomass produced/mg
NHt-N oxidized) .
Theta, base of exponential factor used as temperature coeffi-
cient in the Arrhenius-Phelps-Streeter equation that describes
the effect of temperature on rate of biological reactions.
Specific growth rate of the heterotrophic matrix prevailing in
the system (y = AX/X SDT) .
xiv
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ABBREVIATIONS AND SYMBOLS (continued)
max
(day
J
Un(day
y' (day"1)
LLd
ynr(day
Maximum specific nitrifier growth rate, within the context of
the Monod function, corresponding to prevailing temperature, DO,
and pH.
Specific instantaneous nitrifier growth rate corresponding to
prevailing NH't-N concentration and environmental conditions.
Average specific nitrifier growth rate computed for one reaction
cycle of a plug flow reactor.
Average specific nitrifier growth rate in a plug flow reactor
computed for one reaction cycle, neglecting effect of sludge
recirculation.
Specific nitrifier growth rate to be imposed on system in
accordance with effluent requirements and applicable process
kinetics.
Specific nitrifier growth rate selected by designer for imposi-
tion on the system (y , = y /SF ).
nd nr n
Summation over the days of 1 mo,
xv
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ACKNOWLEDGEMENTS
In the area of conceptual contributions, the help received from Dr. Ross
McKinney (University of Kansas) and Dr. L. Wang (Rensselaer Polytechnic In-
stitute) is gratefully acknowledged. Dr. McKinney called attention to the
lack of release of ammoniacal nitrlogen during the anoxic treatment intervals
experienced at Coxsackie; he stipulated the chemical equation used in this
report to describe endogenous nitrate respiration. Dr. Wang helped with
formulating some of the stoichiometric equations used in Section 4.
In the area of professional and administrative encouragement, thanks are due
to Richard Brenner and James Heidman (EPA), Dr. L. J. Hetling (New York State),
D. F. Metzler (State of Kansas), and Dr. McKinney.
In the area of technical support, Jthe help of Italo Carcich, John McKinney,
Lee Flocke, and Gordon Langlois - |all with New York State - is gratefully
acknowledged, as well as the efforts of the staff members at the Coxsackie
Research Center. '
Special thanks are due to Helen Rest and Virginia Capano for their untiring
efforts and never-failing good spirits while typing the manuscript and taking
care of the seemingly endless revisions.
J. Tofflemire and J. Bloomfield (New York State) read part of the manuscript
and called attention to certain deficiencies. Many thanks to them.
Special gratitude is due to Richard Brenner and James Heidman (EPA) for their
editorial help. Without their massive assistance, this report could not have
been written.
xvi
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SECTION 1
INTRODUCTION
This project was initiated in the summer of 1966 when the New York State De-
partments of Correction and Health agreed to undertake a program of research
and development in the area of sewage treatment at one of its correctional
facilities. With a view to the impending program of sewage treatment plant
construction in New York State, it was decided to build an experimental sew-
age treatment plant and a research laboratory on the grounds of the Coxsackie
Correctional Facility at West Coxsackie, New York. The plant was intended to
treat the wastewater of that penal facility and to be devoted to research in
the area of activated sludge. It was felt that the activated sludge process
would be the principal process underlying the plants to be constructed in the
State. Assistance in conducting this research program was-sought from the
Federal Water Pollution Control Administration, and a grant application was
finally approved by that agency in July 1968.
The Coxsackie Correctional Facility is an institution for young male delin-
quents aged 16 to 21. The average age of the inmates is 18. , Design inmate
population is 750. During the period covered by the full analytical data of
this report, the inmate population was near capacity. In addition to the
inmates, approximately 350 prison personnel are in daytime or nighttime resi-
dence at the facility. A 306-ha (750-ac) farming operation is part of the
correctional facility. Farm products are milk, vegetables, apples, and beef.
The institution is located on U.S. Route 9W, 39 km (24 mi) south of Albany.
The effluent of the sewage plant is discharged to the Coxsackie Creek, a short
tributary of the Hudson River. The Coxsackie Creek is classified as an inter-
mittent stream. The New York State effluent requirements for sewage treatment
plant discharging to intermittent streams are as follows:
max. 5 mg/£
max. 2 mg/£
min. 7.5 mg/£
DO
The facilities which comprised the research installation are shown in Figure
1. The main dimensions of the major treatment units employed on this project
are summarized in Table 1.
The experimental sewage treatment planlf was placed in operation in July 1972.
The first year of operation did not furnish any data because of frequent oper-
ational catastrophies resulting from the breakdown of improperly installed
-------
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TABLE 1. COXSACKIE EXPERIMENTAL SEWAGE TREATMENT PLANT - MAIN DIMENSIONS
_ OF MAJOR TREATMENT UNITS AND CHARACTERISTICS OF EQUIPMENT _ __
AVERAGE DAILY FLOW: . s
570 m3 (0.15 mgd)
SCREENS:
Two manually raked screens in series; 25 and 13 mm spacing of bars
GRIT REMOVAL:
Some grit removal occurs in surge tank and flow control structure
(Side weir structure)
SURGE TANK: ' , .
9.76 m diameter; approximately 215 m^ working capacity; equipped
with floating aerator with direct-coupled, propeller- type impeller,
7.45 kw/1150 rpm; outpumping by submersible fixed-speed, torque-
flow pumps to flow control structure
CONTROL OF FLOW TO TREATMENT UNITS:
Manual, by varying opening of submerged orifice in constan't head
device
PRIMARY SETTLER (Optional Use):
1.83 m wide; 7.32 m long; 2.44 m sidewater depth; 32.7
13.4 m.2 area; 1.83 m weir
AERATION TANK:
volume;
12 compartments, each 1.53 x 3.05 m in plan; sidewater depth 2.31
or 2.61 m, adjustable; volume under aeration 129 or 146 -or', INKA
aeration grids mounted near floor, 3.2 mm diam. airholes; one
double compartment equipped with 0.25 kw/350 rpm mixer; compart-
ments in series
AIR BLOWER:
Centrifugal type; 3.2 to 14.16 m3/min; 15 kw
FINAL SETTLING TANK:
Peripheral entry; 4.88 m diameter; 3.05 m sidewater depth; 57 m3
volume; 18.70 m^ area, 12.81 m weir
SLUDGE RETURN PUMPS:
Plunger Type
CHLORINE CONTACT CHAMBER:
15.9 m^ volume
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equipment.
problem.
Also, operations were isomewhat handicapped by a sludge disposal
In the fall of 1973, Flow Sheet No1. I was implemented as the first of a
series of six flow sheets evaluated, all characterized by the use of anoxic
zones in a plug flow (PF) aeration tank and by the use of ferric chloride to
enhance phosphorus removal and flocculation. The main emphasis of this re-
search was on nitrogen removal without use of an external organic carbon
source. Table 2 contains a description of the six flow, sheets evaluated, and
Figure 2 depicts aeration cell numbering.
Return Sludge
6
I
5
T 7/8
4
9
3
10
2
II
12 '
^ Raw Sewage or Primary Effluent
Mixed Liquor
Figure 2. Numbering scheme for aeration cells.
A PF regime was achieved in the aeration tank by providing 11 compartments or
cells arranged in series. Raw sewage or primary effluent was introduced into
Cell 1 along with the return sludge. Ten of the 11 compartments were of
equal size; Cell 7/8 was double the size of the other compartments.
-------
TABLE 2. CHARACTERISTIC FEATURES OF FLOW SHEETS I THROUGH VI
I
Fig. 13
II
Fig. 13
III
Fig. 18
IV
Fig. 20
V
Fig. 21
VI
Fig. 22
Period
Nov. 1973 to
March 1974
inclusive
1
April 26 to
May 6, 1974
May 7 to
June 21, 1974
June 22, 1974
to March 31,
1975
April 1975
May to July
1975 inclu-
sive
Surge Tank
Anoxic ,
sludge
scraper used
Aerobic ,
floating
aerator on
full time
Used as part
of the acti-
vated sludge
system
Aerobic,
floating
aerator on 2
min, off 18
m In
Same as Flow
Sheet IV
Same as Flow
Sheet IV
Primary
Settler
In use
In use
By-p'assed
By-passed
In use
In use, in
conjunction
with
chemical
addition
Scheme of
Aeration
Return sludge & primary
effluent introduced into
Cell 1 - Cells 1, 7/8,
9, 10, 11 anoxic -
FeClo dosed to primary
effluent (1)
Same as Flow Sheet I -
Cells 1, 7/8, 9, 10, 11
anoxic (1)
Return sludge & raw
sewage introduced into
surge tank - Cells 5, 6,
7/8, 9, 10 anoxic -
FeClg dosed to ML leav-
ing surge tank (1)
Return sludge and raw
sewage introduced into
Cell 1 - Cells 5, 6,
7/8, 9, 10 anoxic -
FeCl3 dosed to either
surge tank effluent and/
or ML leaving aeration •
tank (2)
Return sludge & primary
effluent introduced into
Cell 1, otherwise same
as Flow Sheet IV (2)
Return sludge & primary
effluent introduced into
Cell 1 - same aeration
pattern as Flow Sheet
IV but also alternating
aerobic and anoxic
zones - FeCl3 addition
to primary influent & ML
leaving aeration system
(2)
(1) Aerator Volume used: 129 m^
(2) Aerator Volume used: 146 m"
-------
SECTION 2
CONCLUSIONS
Three forms of nitrate respiration may be postulated to occur in single-
sludge activated sludge (A.S.) systems designed for nitrogen removal. In all
three forms, the reaction is mediated by the heterotrophic microbial biomass
that makes up the bulk of the mix^d liquor suspended solids (MLSS) of the
system, to wit: I
i
a) Substrate nitrate respiration:! the interaction, under anoxic conditions,
of organic wastewater carbon compounds with nitrates, the carbon com-
pounds serving as the hydrogen donor. Organic wastewater carbon compounds
are present in the liquid phase of the process water.
b) Endogenous nitrate respiration (ENR): the interaction, under anoxic con-
ditions, of the heterotrophic biomass itself with the nitrates, the bio-
mass serving as the hydrogen donor. Biodegradable carbon compounds are
absent from the liquid phase of the process water.
c) Adsorbed carbon nitrate respiration: the interaction, under anoxic con-
ditions, of organic carbon compounds adsorbed by the biomass with ni-
trates, the adsorbed matter serving as the hydrogen donor. Biodegradable
carbon compounds are absent from the liquid phase of the process water.
An in-line surge tank, operated as part of an A.S. system and subjected to
pulsating aeration, can be used to stimulate substrate nitrate respiration to
occur directly in the surge tank. Pulsating aeration may be provided by a
floating, direct-drive surface aerator, operated on a 10 min "on", 10 min
"off" cycle. i
ENR can be effected in an A.S. sysjtem by providing a compartmentalized reac-
tor and operating the compartments to produce an aerobic-anoxic-aerobic pat-
tern of aeration for a PF hydraulic regime. The aerobic period at the
effluent end of the reactor is provided to nitrify any ammonia released by the
biomass in the preceding anoxic compartments and to purge the gaseous nitro-
gen that clings to the A.S. floe.
Adsorbed carbon nitrate respiration seems to occur in conjunction with ENR if
the preceding aerobic period is kept as short as possible. The following
additional conclusions can be drawn with respect to ENR:
1) ENR may be used instead of endogenous oxygen respiration (EOR) for bio-
mass destruction and for conditioning the A.S. floe for liquid-solids
-------
separation in the final settler. Analysis of sludge production data
under this project points to a biomass destruction rate of 2.2 mg/mg N
removed.
2) ENR is accompanied by generation of alkalinity, in part compensating for
destruction of alkalinity during nitrification. Five alkalinity and
nitrogen profiles through the compartmentalized reactor developed during
the project indicated alkalinity generation of 2.6 to 3.9 mg/mg NCL-N
gasified, alkalinity being expressed as CaCCL.
3) ENR is accompanied by ammonia gas release. The extent of that release
varies considerably with the treatment situation and is generally far
below the extent predicted by stoichiometric theory. Based on an assumed
biomass composition of C,.H709N, the stoichiometric release of ammonia in
ENR is 0.25 mg/mg NO~-N gasified. Five nitrogen profiles through the
compartmentalized reactor, developed for three different treatment
schemes, indicated ammonia release varying between 0.03 and 0.17 mg/
mg NO~-N gasified. It was concluded that adsorbed carbon nitrate respira-
tion contributed to the difference between actual and theoretical NH.-N
release and that the assumed biomass composition formula - CJS-O-N - might
not be correct.
4) For a particular pattern of aeration, the specific nitrate reduction rate
(mg NO~-N gasified to N2/mg MLVSS/day) is:
- independent of cell residence time (CRT) within the 4- to 9-day
range used on the project,
— independent of nitrate nitrogen concentration down to 1 mg/&
NO" + NO~-N, and
- independent of the MLSS concentration within the range used in this
project, i.e., 2500-4000 mg/fi, .
5) Within the ranges indicated in the preceding paragraph, ENR may be re- .
. garded as a zero order reaction with respect to N0~ + NO~-N and MLVSS.
6) Incorporation of ENR into an A.S. process does not necessarily affect
nitrification unfavorably.
With respect to nitrification in a single-sludge A.S. system in a compart-
mentalized reactor, the following conclusions are based on observations made
during the project:
1) At the very beginning of the aerobic reaction period, a short interval of
inhibition of nitrate generation occurs. However, ammonia removal is not
impaired. This phenomenon cannot be observed by examining the ammonia
profile; it is visible in the nitrate profile. The phenomenon does not
seem to be caused by a deficiency of dissolved oxygen (DO) in the process
water. During this period of inhibition, NH^-N is taken up by the heter-
otrophic biota.
-------
2) Alkalinity destruction during nitrification is very near the theoretical
(stoichiometric) value of 7.14^mg/mg NffJ~-N nitrified.
3) Except for the short inhibition period referred to above, the nitrate pro-
file has the shape of a Monod curve, as generally maintained in the
literature (1).
4) Providing a larger CRT for the ;heterotrophic matrix will increase the
amount of nitrifiers and the rate of nitrification, as predicted by kinet-
ic theory.
5) The monthly nitrifier growth rates computed on the basis of the growth
rates of the heterotrophic matrix imposed on the A.S. system appear to be
considerably higher than the growth rates that should have occurred in
accordance with kinetic theory :and kinetic coefficients found in the lit-
erature .
The use of a compartmentalized aeration tank allows the allocation of treat-
ment time to aerobic and anoxic periiods in accordance with seasonal require-
ments .
Excessive preaeration of untreated sewage in a surge tank results in a turbi,d
(milky) effluent' from the downstream A.S. system.
Chlorination of sludge (both excess activated and primary) to a pH of 2.5 in
a pipe reactor of 4-min detention time will effectively improve drainage
properties of the sludge to an extent comparable to that obtainable in com-
mercial sludge chlorination reactors.
Under aerobic conditions, heterotrophic bacteria prefer organically bound
nitrogen to ammonia as a source of nitrogen.
-------
SECTION 3
RECOMMENDATIONS
When designing sewage treatment plants for nitrogen removal, consideration
should be given to single-sludge AlS. systems utilizing ENR as a means of de-
nitrification and biomass destruction. The following detailed recommendations
apply to the design of such plants:
1) Compartmentalized aeration tanks should be utilized with provisions for
both the aerobic as well as anoxic mode of operation in most compartments.
Compartmentalization will achieve an approximation of PF, which from a
kinetic standpoint is a more efficient hydraulic regime than a completely
mixed (CM) regime. In contrast to theoretical PF, Compartmentalization
will provide a measure of damping of shock loads depending upon the size
of the first compartment. Compartmentalization also will provide flexi-
bility of the aeration pattern allowing adaptation to fluctuating loads
and reaction rates.
I
2) The last compartment in a compartmentalized reactor should be an aerobic
compartment for the stripping of nitrogen gas bubbles clinging to the
A;S. floe and for nitrifying the ammonia released in the preceding anoxic
compartments.
3) If maximum utilization of wastewater carbon compounds for nitrogen re-
moval is intended, the plant should be designed without primary settling.
This will make more biomass available for the N02 + N03~N destruction
that occurs in ENR.
4) To consistently achieve an effluent BOD^ concentration of 10 mg/1 or \Less,
an overall mean cell residence time (MCRT) of at least 10 days should be
provided for. At shorter CRTs, it is difficult to achieve the required
good flocculation of the A.S. floe.
Experience from this project points to the need for additional kinetic re-
search in the area of nitrification. The average monthly nitrifier growth
rates observed differed from those predicted for the prevailing treatment
conditions on the basis of recommended kinetic theory and coefficients. Also,
the nitrate.profiles through a PF reactor were not found to fully follow
the Monod function, stipulated frequently as. the relationship governing
nitrification. These discrepancies are understandable when conside'ring that
the present kinetic theory of nitrification is largely built on the behavior
of pure cultures maintained in river (Thames) water. The bulk of the recom-
mended additional research should be undertaken with mixed cultures (derived
-------
from municipal sewage treatment plants) using CM reactors. By keeping the
wasting rates for the reactors constant and maintaining uniform environmental
conditions and ammonia nitrogen loads, it should be possible to obtain real-
istic growth rate data as a function of prevailing substrate concentration
and environmental conditions which would be applicable to sewage treatment
plants. Kinetic research on CM reactors should be supplemented by research
in fill-and-draw reactors also u^ing mixed cultures. This research should
lead to an improved functional equation relating the effluent ammonia con-
centration of PF reactors to the imposed growth rate of the nitrifiers. That
equation would include influent ammonia nitrogen (N) concentration, influent
BOD5 concentration, and the ratio of sludge recirculation to sewage flow as
variable operational parameters.
There is a dearth of data supporting yield coefficients for aerobic respira-
tion/synthesis and nitrate respiration/synthesis. Yet these yield coeffi-
cients are vitally important for the sizing of single-sludge A.S. plants.
Research should be undertaken with fill-and-draw reactors to remedy this de-
ficiency. In the aerobic process, the onset of biomass destruction via EOR
may be pinpointed by observing the substrate (TOG) and ammonia profiles, pro-
vided nitrification is suppressed. Operating the process in this manner
should not only furnish yield data but also data regarding initial sludge
volatility, another kinetic coefficient for sizing and operating single-
sludge A.S. plants. In the anoxic process, disappearance of nitrates will
pinpoint the end of substrate nitrate respiration.
Further research is recommended with respect to the biomass destruction
(decay) coefficient prevailing with PF regimes under both aerobic and anoxic
conditions at various temperatures. This coefficient is needed for sizing
single-sludge A.S. plants designed for N removal. This research should be
conducted in fill-and-draw reactors which simulate PF systems. Sludge fil-
terability should be determined a|t the end of the reaction; this is an impor-
tant factor for judging cost effectiveness of a process. Results of this
research would also furnish the following data, all important in sizing and
operating the reactors: percent of biomass destruction as a function of
percent sludge volatility, practical limits of biomass destruction, biomass
destruction as a function of N03-N gasification, and ammonia and alkalinity
release in various treatment schemes.
Promising results were achieved using a chlorine contact chamber (CCC) as a
second-phase final settler. A multiple-tray cross flow configuration was
employed. Further research and development work to perfect this concept is
recommended. The essence of this1 work should be the development of suitable
corrugated profiles for the trays[ of the settler. Flat sheets were used on
this project.
Experience gained on this project;points to greater SS and BOD removal capac-
ities for A.S. plants employing nitrate respiration as compared with single-
sludge A.S. plants of the fully aerobic type. However, sufficient time was
not available to produce quantitative data reflecting the effect of nitrate
respiration on removal efficiencies. Research in parallel reactors to pro-
duce such data should be undertaken. Incorporation of a certain measure of
nitrate respiration in all A.S. processes seems indicated. The extent of
10
-------
this measure should also be a subject of the suggested parallel-reactor re-
search.
Further research is also recommended concerning the utilization of a surge
tank as part of an overall A.S. system operated for nitrogen removal. The
surge tank should be operated in a pulsating aeration mode, thus stimulating
substrate nitrate respiration to take place directly in the surge tank. The
surge tank, in turn, should be followed by a compartmentalized reactor employ-
ing ENR. Excellent overall system removals were achieved with this arrange-
ment during the project; however, the investigation could not be completed
because of sludge bulking.
The BOD and SS removal capabilities of an A.S. process is directly related to
the flocculating characteristics of its MLSS. For plant operating purposes,
as well as for comparative purposes, it would be desirable to have a simple
flocculating test available. Such a test should be developed and standard-
ized. It could consist simply of determining the SS concentration in the
supernatant of a suitably sized laboratory settler after 30 min of settling.
In the course of this study, it became clear that two basic patterns of
aeration are available for the operation of single-sludge A.S. systems in .
compartmentalized reactors: the "block" pattern and the "alternating zones"
pattern. A comparative evaluation of the two approaches under conditions of
changing loads and reaction rates is recommended. The "alternating zones"
approach may require less operator adjustment to adapt the process to chang-
ing loads and reaction rates; however, project results related to this sub-
ject are inconclusive.
11
-------
SECTION 4
STOICHIOMETRIC AND KINETIC CONSIDERATIONS
In this section, certain aspects of single-sludge A.S. systems, using nitrate
respiration are discussed in order to present a working theory for the pro-
cesses investigated under this project. The discussion is based on data
found in the literature, particularly in the Process Design Manual for Nitro-
gen Control (1) published by the U.S. Environmental Protection Agency (EPA
PDM). The material covered in this section does not coincide with the scope
of the related sections of the EPA PDM, and the approach taken here differs
in many respects from the approach of that manual.
Section 4 represents an attempt to postulate models of certain complex bio-
logical processes. As in other attempts of .this nature, a good measure of
idealization and simplification had to be used.
The term "substrate" as used here, and throughout this project report, refers
to matter that is dissolved or suspended in the liquid phase of the process
water. "Substrate" does not refer, to matter already adsorbed to the surface
of the biomass.
The term "anoxic" refers to the DO concentration of the liquid phase of the
process water. Anoxic conditions prevail if the DO of the process water is
approximately 0.5 mg/& or less. Nitrates may or may not be present under
anoxic conditions.
NITRATE RESPIRATION IN SINGLE-SLUDGE ACTIVATED SLUDGE SYSTEMS
Four routes of nitrogen removal seem to be available in single-sludge A.S.
sludge systems. These routes are:; «
a) Sludge synthesis: this may occur either under aerobic or anoxic condi-
tions. The stoichiometric equation describing sludge synthesis is the
same for both conditions. ..In the course of the synthesis reaction,
ammoniacal or organically-bound nitrogen is removed from the substrate by
the biomass and incorporated into new biomass. The energy deficiency of
the synthesis reaction is covered by the energy surplus of aerobic or
nitrate (substrate) respiration.
I
b) Substrate nitrate respiration:! the interaction of nitrates with organic
wastewater carbon compounds mediated by the biomass. This reaction al-
ways accompanies sludge synthesis under anoxic conditions. Nitrates are
utilized as the hydrogen acceptor, organic wastewater carbon compounds
as the hydrogen donor. This l!s an energy reaction. Nitrogen is released
12
-------
to the atmosphere. During this reaction, biodegradable carbon compounds
are present in the liquid phase of the process water.
c) Endogenous nitrate respiration: the interaction of nitrates with the
sludge biomass itself under anoxic conditions„ Nitrates are utilized as
the hydrogen acceptor; the biomass itself serves as the hydrogen donor.
This too is an energy reaction. Nitrogen is released to the atmosphere
and ammonia is released to the process water. During ENR, biodegradable
carbon compounds are absent from the liquid phase of the process water.
Adsorbed carbon nitrate respiration often accompanies ENR. Because the
chemistry of the biomass and of adsorbed carbon compounds is not well
known, it is often impossible to differentiate quantitatively between ENR
and adsorbed carbon nitrate respiration. In later sections of this re-
port, the term ENR is, therefore, used to cover both denitrification based
on biomass destruction and denitrification based on the utilization of
adsorbed carbon compounds as the hydrogen donor.
d) Adsorbed carbon nitrate respiration: the interaction, under anoxic con-
ditions, of nitrates with organic carbon compounds adsorbed by the bio-
mass and occurring while the liquid phase of the process water is already
devoid of biodegradable carbon compounds. The adsorbed carbon compounds
are utilized as the hydrogen donor by the biomass; nitrates serve as the
hydrogen acceptor. This too is an energy reaction. Nitrogen is released
to the atmosphere. The reaction occurs in conjunction with ENR and is
accompanied by a measure of sludge synthesis. The stqichiometry of this
reaction is probably similar to that of substrate nitrate respiration,
but not enough data are available to a'llow the postulation of stoichio-
metric equations. For reactor design purposes, the kinetic equations
describing ENR can be easily adapted to reflect the occurrence of
adsorbed carbon nitrate respiration. This is shown in following sections.
The stoichiometry and kinetics of adsorbed carbon nitrate respiration are
not discussed further in this report.
Stoichiometric and Metabolic Assumptions
This Stoichiometric discussion rests on the following basic assumptions:
1) The composition of the biomass produced in the A.S. process is C,.H O^N (2).
2) The composition of the carbon source in domestic- sewage is CL JH.. „() N (3).
3) The energy/synthesis ratio (f :f ) for aerobic biological removal of the
carbon source is 0.54:1.
4) The energy/synthesis ratio (f :f ) for anoxic biological removal of the
carbon source is 1.86:1.
5) The BOD.-/COD ratio of the carbon source is 0.45:1.
J
The fe:fs ratio is the ratio of substrate utilized for energy to substrate
utilized for synthesis in a reaction of zero CRT, i.e., in a reaction in which
no endogenous respiration occurs. The nomenclature fe:fs is due to McCarty (3)
13.
-------
The carbon source does not include free ammonia in the domestic sewage. The
energy/synthesis ratio for the aerobic process is a rounded version of the
ratio stipulated by Forges et al. (2); the fe = fs ratio for the anoxic process
was estimated on the basis of data reported by Barnard (4).
It is readily conceded that the experimental basis of the assumptions used
leaves much to be desired. This applies in particular to the assumptions made
regarding biomass composition and the fe:fs ratio for the anoxic process.
Yet, it was felt that available data are good enough to serve as a basis for
a working theory.
l
From the assumptions listed, several conclusions may be readily drawn, to wit:
1) The yield factor Y based on BODs (mg MLVSS produced/mg BOD5 removed) in
aerobic substrate utilization is 1.02; Y is o.46 in terms of COD.
2) During anoxic substrate utilization, Y is 0.55 in terms of 6005, 0.25 in
terms of COD.
3) One mole of the carbon source in domestic sewage (C..nH-joO N) has a COD of
400 g, a BOD5 of 180 g, and a TOG of 120 g and weighs 201 g.
4) One mole of the biomass (MLVSS) produced has a COD of 160 g, weighs 113 g,
and contains 12.4 percent nitrogen.
5) The stoichiometric equation for sludge synthesis under aerobic as well as
anoxic conditions is:
C10H19°3N
NH
2'5 C0
2.5
(1)
It should be noted that NH^-N is assumed to be the source of the addition-
al nitrogen needed, even under anoxic conditions.
6) The stoichiometric equation for aerobic (oxygen) respiration in the pres-
ence of substrate is:
Usually this reaction is simply referred to as "respiration."
7) The stoichiometric equation for substrate nitrate respiration is:
(2)
C10H19°3N
10 NaN°
10 C02 + 3 H20 + NH3 + 10 NaOH + 5
(3)
8) The stoichiometric equation for aerobic removal (synthesis + respiration)
of the carbon source reads:
C10H19°3N
4'375 °
°'625 NH
1.875
4.75
1.625
(4)
14
-------
9) The stoichiometric equation for anoxic removal (synthesis + respiration)
of the carbon source reads:
6-5 NaN(
0.125 NH + 5.625 C02 + 0.875
+6.5 NaOH + 3.25 N +3
(5)
In Equations 3 and 5, NaNO« stands for all the nitrates present.
Construction of Equations 1 to 5 is based on the half-reaction equations orig-
inally proposed by McCarty (3). The heuristic strategy of looking on all
biological substrate removal processes as composed of a respiration (energy)
reaction and a synthesis (sludge production) reaction was introduced into
sanitary engineering by Forges et al. (2).
Additional details on the subject of.this subsection may be found in Reference
5.
Endogenous Nitrate Respiration (ENR)
ENR was introduced to sewage treatment in 1964 by Wuhrmann of Zurich (6) who
inserted an anoxic reactor between the,aeration tank and final settler of a
conventional A.S. system (see Figure 5-15 of the EPA FDM). The anoxic treat-
ment tank was equipped with mixing devices to keep the biomass in suspension.
Equations 6 and 7 describe endogenous oxygen respiration (EOR) and ENR, re-
spectively. Equation 6 has been stipulated by Forges et al. (2) and Equation 7
by McKinney (7) and Christensen et .al. (8). From Equations 6 and 7, Equa-
tions 6a and 7a were derived by considering the reactions between C02, NH3,
and NaOH that may be predicted to occur in the process water (for further
details, see .Reference 5).
C_H_0«N + 5 0,, —»- 5 CO,, + NH,, + 2 H00 (6)
(6a)
5 C02 + NH3 + 2 N2 + 4 NaOH
4 NaHC0
(7)
(7a)
The same amount of ammonia nitrogen is released in both the EOR and ENR reac-
tions. In the aerobic reaction, the ammonia nitrogen is immediately nitrified.
This is not the case in the anoxic reaction. Extra aerobic reactor space must
be provided if it is desired to oxidize the ammonia nitrogen formed during
ENR. This was not done by Wuhrmann.
The release of ammonia nitrogen by the biomass gives rise to a slight momentary
increase in alkalinity. In the anoxic reaction, additional alkalinity is re-
leased due to the reduction of nitrates (3.57 mg alkalinity as CaC03/mg N03~N
15
-------
gasified). This is one-half of the amount used up in the nitrification of
1 mg of ammonia nitrogen. Once the nitrates are exhausted, the plant operator
will be confronted with unneeded reactor space if the anoxic zone is too
large.
From Equation 7a, the values of Table 3 have been abstracted.
TABLE 3. ENDOGENOUS NITRATE RESPIRATION STOICHIOMETRIC RELATIONSHIPS
1 mg of NO,-N gasified 2 mg of biomass destroyed
1 mg of N03~N gasified 0.25 mg of NH^-N released to the liquid
phase of the process water due to bio-
mass destruction
1 mg of NO,-N gasified 1.07 mg of biomass carbon destroyed
1 mg of NO_-N gasified
4.46 mg of total alkalinity produced:
3.57 mg due to reduction of NO-j-N, 0.89
mg due to biomass destruction
1 mg of N03~N gasified 0.75 mg of N removed from the liquid
phase of the process water: 1 mg of
NOg-N is gasified, but 0,.25 mg of NH+-N
is added
1 mg of N removed* 2.69 mg of biomass destroyed
1 mg of N removed* 1.43 mg of biomass carbon destroyed
1 mg of N removed*
1.33 mg of NO -N gasified
* From the liquid phase of the process water.
Of particular importance with ENR are two stoichiometric relationships:
a) For 4 mg of NO~-N gasified, 1 mg of NH^-N is released back to the process
water.
b) Two mg of biomass are destroyed for each mg of NO~-N reduced; 2.69 mg of
biomass are destroyed for each mg of N removed.
Table 3 concerns a single-stage reaction. All N removed in this reaction
from the mixed liquor (ML) is removed by gasification of NO^-N. But the
amount of NO^-N gasified is larger than the net amount of N removed from the
liquid phase of the process water. The difference is the ammoniacal N re-
leased by the biomass that was destroyed during ENR.
If it is desired to remove the residual ammonia nitrogen generated during ENR,
a cascade approach would have to be followed if the basic scheme suggested by
Wuhrmann is used. The NH^-N released in the first ENR zone would be nitrified
16
-------
in a following aerobic zone. The nitrate nitrogen generated'there would be
reduced in a second ENR zone. This would result in a second NHt-N residual,
amounting to approximately one-quarter of the first residual. Repeated applica^
tion of the cascade approach would result in an overall process in which mg
of_N removed from the liquid phase of the process water would equal mg of
NO«-N gasified. .
Nitrogen Removal by ENR and Aerobic Sludge Synthesis
The effect of increasing rates of biomass destruction via ENR is shown in
Table 4. It is assumed that 100 mg of BOD5 are removed and that the initial
sludge volatility is 80 percent. The first column represents a theoretical
process with no biomass destruction. _ Nitrogen removal is 12 mg, due only to
sludge synthesis. The 80 percent volatility stays unchanged. In the second
column, 42 percent biomass destruction occurs, resulting in a final sludge
'volatility of 70 percent. A part of this biomass destruction is assumed to
be due to EOR, with no benefit for nitrogen removal. Ten percent of the ini-
tial biomass of 100 mg, or 10 mg, is assumed -to have been lost in this way.
The nitrogen removal in this process is 19 mg. If EOR had been used for bio-
mass destruction, the removal would have been 7 mg. The third column repre-
sents a process with 63 percent biomass destruction. Ten percent of the
original biomass of 100 mg is lost again in EOR. The final sludge volatility
is 60 percent; nitrogen removal is 24 mg. If EOR had been used throughout,
nitrogen removal would have been 4 mg.
In Table 4, it was assumed that 2.69 mg of biomass were destroyed for each mg
of N removed.
TABLE 4. STOICHIOMETRIC PROJECTION OF NITROGEN REMOVAL VIA SLUDGE
SYNTHESIS AND ENDOGENOUS NITRATE RESPIRATION *
Final sludge volatility
Biomass destruction
Initial biomass
Biomass used in ENR
Biomass lost in EOR
Biomass final
N removed in sludge
N removed via ENR
N removed total
(%) 80
(%) ~
(mg) 100
(mg)
(mg)
(mg) 100
(mg) 12
(mg)
(mg) 12
70
42
100
32
10
58
7
12
19
60
63
100
53
10
37
4
20
24
* Based on 100 mg of BOD5 removed and 80 percent initial sludge
volatility.
17
-------
The assumed 80 percent value for initial volatility is probably conservative.
The actual value may be somewhat higher; 82 percent volatility, for instance,
was reported for the Newtown Creek return sludge at a CRT of 3 days with pure
oxygen operation (9). On the other hand, initial volatility might be much
lower than 80 percent due to metal salt addition for phosphorus removal. The
final volatility of 60 percent is not unattainable. A manufacturer of aera-
tion equipment for oxidation ditches (10) lists 55 percent volatility as
attainable and as characteristic of "completely mineralized" sludge which
does not require further stabilization. Efficient nitrogen removal by ENR
goes hand in hand with substantial; destruction of the volatile biomass gener-
ated during BOD removal. This should favorably affect the cost of sludge
disposal.
The relationship between biomass destruction and change in sludge volatility
may be expressed by the following two equations:
V1 -
1 - b v
(8)
V0 "
where:
'0
b
vQ(l - v)
final fractional sludge volatility
initial fractional sludge volatility
fractional rate of biomass destruction.
(9)
The validity of these equations may be recognized by considering for instance
that the inert mass of sludge containing 60 percent VSS was originally asso-
ciated with 160 mg of VSS
example:
if VQ was 0.8, as illustrated in the following
In the course of an endogenous respiration procedure, 200 mg
of sludge solids of 80 percent initial volatility (VQ = 0.80)
are reduced by 100 mg. Assuming that the entire weight reduction
was with respect to volatile solids, the composition of the
solids at the end of the procedure will be 40 mg fixed and 60
mg volatile (v = 0.60). The destruction of the volatile biomass
amounts to 100 mg. This is (100/160) 100 =62.5 percent biomass
destruction. Using Equation 9 furnishes the same result, to wit:
0.80 - 0.60
0.80(1 - 0.60)
= 0.625 or 62.5 percent
In the operation of systems using; ENR and aerobic sludge synthesis for N re-
moval, two conditions must obviously be avoided or minimized: anoxic resi-
dence time in the absence of nitrates and loss of wastewater carbon in EOR.
To minimize the occurrence of these conditions, it appears advisable to use
a compartmentalized reactor, equipped with aeration and mixing equipment in
such a. way that the bulk of the compartments may easily be switched over from
18
-------
the aerobic to the anoxic condition and vice versa.
Two basic aeration patterns are conceivable, the block approach and the al-
ternating zones approach, as shown in Figure 3. A compartmentalized reactor
equipped with dual equipment (aeration and mixing) in most compartments would
allow the use of either approach. In both approaches, the last cell should
be an. aerobic cell to nitrify ammonia nitrogen released in preceding cells
and to strip gaseous nitrogen clinging to the floe.
ALTERNATING ZONES
BLOCK APPROACH
Blank Cells: aerobic
Crossed Cells! anoxic
Figure 3. Aeration patterns in compartmentalized reactors.
If a reasonable number of cells are provided under the block approach, the
daily aeration pattern could be modified in response to changes in load and-
reaction rates. When using the alternating zones approach, such adjustments
might not be necessary.
Nitrogen Removal by Substrate Nitrate Respiration and Anoxic Sludge Synthesis
The stoichiometric equation for anoxic synthesis and substrate nitrate respir-
ation combined in the ratio of 0.54:1 was listed as Equation 5. From that
equation, the following table was abstracted.
TABLE 5. SUBSTRATE NITRATE RESPIRATION AND ANOXIC SYNTHESIS
Species
Reduction of 1 mg of NO§-N is related to
Action
TOG
BOD5
COD
Biomass
TKN
NH+-N
Alkalinity (CaC03)
Removed
Removed
Removed
Produced
Metabolized
Released
Released
1.32
1.98
4.40
1.09
0.13
0.02
3.57
19
-------
Approximately 2 mg of 800$ are needed for the gasification of 1 mg of NOg-N.
This process of gasification also produces 1.09 mg of biomass, metabolizing
thereby 0.13 mg of TKN. Whether or not NH^-N is released in the reaction de-
pends on the nitrogen content of the organic carbon source. Assuming that
the organic carbon source has the composition CiQHi'gOsN, the net release of N
to the process water (in the form of NH^-N) is 0.02 mg per mg of NO-j-N gasi-
fied. The biomass generated during substrate nitrate respiration and anoxic
synthesis, obviously, could be used for nitrogen removal via an ENR anoxic
reactor further downstream.
Substrate nitrate respiration is sbmewhat more difficult to implement in a
single-sludge A.S. system than endogenous nitrate respiration. It becomes
necessary to arrange for contact between nitrate nitrogen and untreated pro-
cess water. But nitrates only become available after the process water has
received a considerable measure of; treatment. However, the carbon source in
the substrate is removed from the process water after a very short length of
treatment, this phenomenon being the basis of the contact stabilization pro-
cess. .
There seems to exist, basically, tjiree ways to overcome these apparently con-
tradictory requirements, to wit:
\ '
1) By step feeding the untreated process water to the reactor as illustrated
in Figure 4. Only a portion of the carbon source in the wastewater is
utilized for substrate nitrate, respiration in this process, which is dis-
cussed at some length in Reference 5.
The process water is divided iftto two or more portions. The first por-
tion is fed, together with the return sludge, into the first aerobic cell
of a compartmentalized aeration tank. The remaining portions are fed
into anoxic cells further downstream. Interaction between the organic
carbon source in these streams with nitrates generated in preceding aero-
bic cells brings about substrate nitrate respiration.
2) By mixed liquor recirculation, as suggested by Ludzak and Ettinger in
1962 (11). This procedure is now used in the first two reactors of the
patented Bardenpho process (4) (12) (see Figure 5-21 of the EPA PDM).
The stoichiometry of this process is also discussed in detail in Refer-
ence 5. :
3) By pulsating aeration. The untreated process water is introduced into
a basin which is alternately abrated and mixed anoxically. At the end of"
the aerobic period, the nitrogen of the process water will.be mostly in
the nitrate form. During the ensuing anoxic period, substrate nitrate
respiration will occur via interaction between the inflowing untreated
process water and these nitrates. However, the inflowing ammonia will
remain nearly intact during the anoxic period. Nitrifiers are inactive.
at very low DO's. One way to prevent substantial bleedthrough of NH^-N
would be to place a nitrification reactor after the pulsating aeration
basin. To obtain an effluent very low in NOg-N, some ENR will have to be
provided as an additional step. For domestic wastewater, ENR does not
occur in the pulsating aeration basin itself. During the anoxic periods,
20
-------
the available NC^-N Is completely utilized by the organic wastewater
carbon source present. At the end of the anoxic period, the nitrates will
be exhausted but some organic wastewater:, carbon source will still be
available. In order for ENR to occur, NO^-N must be present but substrate
must be absent. Several implementations of the pulsating aeration con-
cept are discussed in the EPA PDM (see Figures 5-19 and 5-22 of that man-
ual) . . '
One cannot compare the nitrogen removal capacity (mg N removable/mg BOD5 re-
moved) of ENR with the removal capacity of substrate nitrate respiration per
se. Removal capacities are comparable only in the framework of projected
flow sheets. According to the third column of Table 4, the limit of the. ni-
trogen removal capacity of ENR plus aerobic sludge synthesis is not far above
0.24 mg N/mg BOD removed. Reference 4 indicates that the Bardenpho flow sheet
has approximately twice this nitrogen removal capacity. Under that flow sheet,
the bulk of the nitrogen is removed via substrate nitrate respiration.
r///x
Anoxic
Cells
6
1
'//y
/-t/
5
%/,
%
?&
Raw Sewage or Primary Effluent
"i
%
4&
2
/ \ | /
^///
r J.
2
12
Return Sludge
Mixed Liquor
To Final Settler
Figure 4. Two-step feeding of compartmentalized reactor.
NITRIFICATION KINETICS
In an A.S. system, the mass of the heterotrophic matrix per liter of reactor
space (X, mg/Jl) can be controlled directly by the operator by varying certain
operational procedures, in particular the sludge recycle ratio (r) and.the
volume of the return sludge wasted per day (Qw, A/day). If the operator de-
cides that his plant should be operated at a certain heterotrophic biomass
concentration, Xa, he can implement this decision within fairly narrow limits,
provided that adequate operating and measuring facilities have been provided.
For single-sludge A.S. systems designed for nitrification or nitrogen removal,
the mass of nitrifiers per liter of reactor space (N, mg/£) cannot be deter-
mined with presently available analytical procedures in a practical way. The
nitrifiers (n.) are inseparably admixed to the heterotrophic matrix. The frac-,
tional content of the nitrifiers in this mixture varies. It. follows that N
cannot be controlled directly by the plant operator in the same way that he
can control X.
21
-------
As a measure of indirect control, the operator imposes a constant specific
daily wasting rate on the n., thus: causing them to vary in mass in response
to load fluctuations and to assume [a specific rate of growth which approaches,
on the average, the imposed specific daily wasting rate. This fluctuating
mass of n. would provide near constant quality effluent, i.e., NH^-N concen-
tration, if load fluctuations were. sufficiently slow. By overdesigning the
reactor with respect to average treatment requirements, effluent fluctuations
under field conditions are kept within acceptable bounds. In the following
paragraphs, "rate of growth" will be used frequently in place of "specific
rate of growth." Also, the symbol X and the expression heterotrophic matrix • .
(HM) will be used to designate the mixture of heterotrophic microbes and ni-
trifiers. The fraction of n. in the mixture (as estimated by research methods)
is so small that X can be regarded as representing the heterotrophs only.
Nitrification in Completely Mixed (CM) Reactors
In CM reactors, the entire life span of the n. evolves under the influence
of only one substrate concentration, the effluent NH^-N concentration (Si).
Under otherwise constant environmental conditions, S-^ dictates the nitrifier
growth rate G-O in accordance with a rate of growth vs . substrate concentra-
tion function (fn(S)) determined experimentally:
y = f (S)
Kn n '
The definitional equation for y is:*
' ft) (*
(10)
(11)
This equation is valid for situations where the mass of nitrifiers is not af-
fected by wasting.
The physical meaning of yn can be visualized by envisioning a CM reactor oper-
ated at constant N, constant environmental conditions, and constant S^ and
utilizing a pure culture of n. N is kept constant by continuously wasting
the biomass produced. The mass of n*. wasted in one day per mass of n. present
equals yn at the chosen S-^. ;
This case may be described by the following two equations:
N = N,
J = w
n n
(12)
(13)
where:
N =
w m
n
n. concentration at time 0, mg/&
n. concentration, mg/£
specific n. wasting rate, day
* The EPA PDM uses y in a somewhajt different sense.
22
-------
The definitial equation for w is:
w = r^T
n V N
/d(n)\
. day
-1
(14)
where: d(n) = mass of n. wasted during dt per liter of reactor space, mg/&.
Both yn and w are mass ratios referred to time. Equation 12 is also valid
for .those situations where w ^ y . Whenever w £ 0, the definitial Equation
11 for y becomes: n n n
n
-
\dtj
w
n
(Ha)
The EPA PDM prescribes that the Monod function be regarded as the function
(fn). That recommendation is followed in this report. Equation 15, therefore,
describes the functional relationship between un and S:
,. /ox
- fn(S) =
rnax
(15)
where: y = maximum n. growth rate, in accordance with prevailing envi-
ronmental conditions of wastewater temperature (T), pH, and
DO, day" (Uma . is approached by yn at high S's, but it is
never equalled 'by y )
n
K = Michaelis-Menten constant, in accordance with prevailing T,
S mg/5. of NH+-N. j
The following values for y and K are used in this report, in accordance
with recommendations of the EPA PDM:
K
10
(0.051T - 1.158)
(16)
y = 0.47 e
max
[0.098(T - 15)]
DO
1.3 + DO
[1 - 0.8333(7.2 - pH)], day
(17)
-1
For a CM reactor, the functional relationship between y and S.. can, therefore,
be described by either one of the following equations, provided that steady
state conditions have been reached:
y
max
K + S-
s 1
(CM reactor)
(18)
y K
nr s
j - y
max nr
(CM reactor)
(19)
23
-------
where: u = n. growth rate to be imposed on a reactor to satisfy given
effluent requirements, day~l.
In a CM reactor, the average daily growth rate equals the instantaneous rate
of growth occurring anytime during ;the day, steady state conditions prevailing.
Equation 15 is plausible as growth ;is a consequence of biota-substrate inter-
action, and the rate of this reaction per mg of biota can be expected to in-
crease with increasing substrate concentration. Equation 19 follows mathemat-
ically from Equation 18, but one can visualize quantitatively quite easily
that it is indeed possible to produce a near constant effluent concentration
in a CM reactor by imposing a constant rate of growth (ynr) on the biota
therein, to wit: Assume that a steady state treatment situation has been
reached. The rate of n. wasting per liter of sewage treated (AN /N)n equals
the rate of n. production per liter of sewage treated (ANp/N)Q for any length
of time. Now the influent NH^-N concentration (SQ) is suddenly raised and
kept at the increased value. N has to be assumed to stay unchanged, initially.
Sj_ will rise as illustrated in one of the following paragraphs. This will
cause a rise in ANp/N per Equation 12. The rate of n. production will now be
larger than rate of n. wasting as the latter is kept constant by the operator.
This leads to an increase in N, which in turn will cause a decrease in ND/N.
N will increase until AN /N has reached again the initial value of (AN /N;0,
which is equal to (ANW/N)0. P
If S-, is determined only after steady state conditions have been reestablished
following a change in load, it will be found that S-L depends only on the VL
imposed on the reactor and on environmental conditions as defined by Equations
13, 14, and 16, but not on SQ, the rate of flow (Q) , or the ratio of sludge
recirculation (r) . In the transition periods, S-^ will be higher than pre-
dicted by Equation 19 if the load was increased and lower if the load was de-
creased. The functional relationship between S-, and yi under steady state
conditions is illustrated by Figure 5 for 15 C and 10 C. If the wastewater
temperature falls while ji stays constant, S-^ will increase.
Based on the assumption that SQ - S^ represents indeed the amount of NHA-N
nitrified in the process, N may be computed for a given Sn, sewage detention
time (SDT ), and H by using Equation 20:
Y(C _ C \
V O^v OT I
n 0 1 /r,n\
U : (20)
nr N SDT
n
where: Y = nitrification yield coefficient, in terms of NH.-N
SDT - sewage detention time (nominal detention time) in the nitri-
fication reactor, day.
Equation 20 is a translation of defsinitional Equation 11 into steady state con-
ditions. Y (SQ - S-^) represents the mg of n. mass produced per liter of sew-
age treated. 1/SDT represents the liters of sewage treated per day per liter
of reactor space. For all-aerobic systems, SDTn may be replaced by SDT. Ac-
cording to the EPA PDM, Y has the value of 0.15. ,
: 24
-------
10
0
10
CSI
d
CSI
d
in
d
C!
O
•K
4J
s
4J
§
o
0
O
O
PO
O
5
H-l
w
(U
I
25
-------
The following definitial equations apply to SDT and SDT:
SDT
n
SDT
VQ
V/Q
(21)
(22)
where: Q = plant flow or compartment flow, a/day
V = capacity of nitrification reactor or compartment,
V - capacity of entire reactor in all-aerobic systems,
For a treatment situation characterized by pH = 7.2, DO = 3 mg/&, T = 15 C
and S^ = 1 mg/&, a ynr of 0.2357 day"-1- would be required. For SQ = 14.5 mg/&
and SDT = 0.25 day, N would be 34. J4 mg/&. If the flow was increased to
double the original value, SDT would be reduced to 0.125 day and N would in-
crease to 68.8 mg/&. If SQ was increased to 29 mg/&, N would increase to
71.3 mg/fc, again based on a SDT of 0.25 days. It should be noted however
that a CM reactor operating at constant ynr cannot accommodate changes in
environmental conditions of T, pH, and DO without a change in S±.
Nitrification in Plug Flow (PF) Reactors
As a slug of MLSS travels through a PF reactor, the ammonia nitrogen concen-
tration in the surrounding process water changes from a high of S-^ (initial
NH^-N concentration after dilution of -SQ by the recycle flow) at the head end
of the tank to a low of S^ near the effluent end. yn varies in accordance
with Equation 15 from a high of ymax siAKs + si^ to a low of Vimax sl/(Ks + sl)
An average n. growth rate (yna) will result, assuming that all NHt'-N defined
by Sj[ -
cation:
na
is oxidized and that there is no addition to
via ammonifi-
n
(23)
N t
n
where: t = flowthrough time (mixed liquor detention time) in the nitri-
fication reactor, day.
By using the following obvious equalities:
1 + r
(24)
t =
n
SDT
n
1 + r
(25)
nr
y (PF reactor)
ll ci
(26)
Equation 23, therefore, becomes identical with Equation 20. yna is the con-
trollable growth rate of nitrifying reactors and forms the-basis of kinetic
equations.
26
-------
A second approximating assumption is usually made when developing kinetics
for PF reactors: that ft stays constant during tn. This simplification, made
to facilitate the mathematics of the (process,^ tends to understate the effi-
ciency of the process by perhaps 3 to 5 percent.
For PF reactors, it is impossible to set forth a counterpiece,to Equation 19.
However, a counterpiece to Equation 18 may be written, to wit (13):
y (sn - s,)
max 0 1
so - si H
- (1
+ r) K In
S
so
(i
+ rsi
+ r) S1
-i (PF reactor)
(27)
Derivation of this equation can be found in Appendix A.
Contrary to CM reactors, PF reactors are affected by changes in r and SQ. An
increase in SQ will bring about a decrease in Si- An increase in r will bring
about a deterioration of the effluent. Further aspects of the relationship
expressed by Equation 27 can be recognized by observing Figure 5. For the PF
reactors in this figure, an SQ of 12 mg/& was assumed.
That figure also provides a comparison between PF and CM, to wit :
a) CM generally requires a lower u^ than PF to achieve the same Sj_; this
means larger reactors with the CM regime.
b) The advantage of PF diminishes with an increasing prescribed S^, with an
increasing r used, and with a lower prevailing operating temperature.
c) PF is more sensitive to changes in
than CM.
Due to the higher prevailing average reaction rate (ynr/Yn) , PF reactors need
somewhat less biomass than CM reactors for the same treatment situation.
The following data were computed for PF reactors. Corresponding data have
been computed for CM reactors in the preceding subsection.
In order to provide an S^ of 1 mg/£ at SQ = 14.5 mg/&, r = 0.5, T = 15 C, pH
=7.2, and DO = 3 mg/&, it is necessary to provide a ynr of 0.30 day L for PF.
For an SDT of 0.25 day, N will establish itself at 27 mg/5,. If S0 is raised
to 29 mg/&, S-L will be reduced to 0.2 mg/£ and N will increase to 38 mg/£. If
the flow is doubled at SQ = 14.5 mg/&, SDT will drop to 0.125 day and N will
double from 27 to 54 mg/&. These changes will occur, provided the n. biomass
is given enough time to grow to the new ft concentrations and Unr is maintained
at 0.30 day
"1
Imposing the. Nitrif ier Growth Rate
The plant operator imposes wasting rates on the HM, i.e., the MLSS. By doing
so, he also imposes wasting rates on the mass of n. . The imposed n. wasting
rates cause the n. to assume compatible growth rates over a period of time.
Momentary n. growth rates cannot be controlled in CM reactors under .conditions
27
-------
of fluctuating loads. In PF reactors, momentary n. growth rates cannot be
controlled at all.
The identity of n. and MLSS wasting rates are based on the equation:
ANw/N = AXw/X
(28)
where:
• !
ANw = n. wasted per liter of sewage treated, mg/£
AXw = MLVSS wasted per | liter of sewage treated, mg/&
X = MLVSS concentration, mg/£ .
This equality holds because it can be assumed that the fraction of n. in the
MLVSS is the same as in the waste sludge. Under steady state conditions,
X is a constant.
To arrive at a convenient equationfor ynr in terms of AX, X, and SDT, one
makes use of the following obvious equalities which are valid at steady state
conditions :
AN
n
AN = AN
p w
(29)
(30)
Combining Equations 20, 28, 29, and 30 furnishes the following equation for
:Cti
AX
ynr in CM and PF reactors:
nr
X SDT
(31)
n
where:
AX = MLVSS produced per liter of sewage treated, mg/Jl.
Similarly, the growth rate imposed on the HM (y, ) is:
AX
hr
X SDT
(32)
For all-aerobic reactors, ynr is the same as the growth rate imposed on the
For aerobic-anoxic reactors, the following relationship between
y
nr
and
prevails, which follows readily from Equations 31 and 32.
y,
nr
y
hr
f SDT\
SDT }
\ n/
(33)
It must be emphasized that AX refers to the biomass production in the entire
reactor, not only to the biomass production in the aerobic part. It will make
no difference whether AX/X is based on MLSS or MLVSS.
Equation 31 may also be interpreted in the following way, which might look
more plausible to some engineers. If f stands for the fraction of nitrifiers
28
-------
in the mixed liquor solids, f (AX) (Q) stands for the daily production of n.
mass, and f (X) (Vn) stands for the .mass of n. in the aerobic portion of the
reactor; in order to obtain yn, the daily n. production must be related to the
n. mass present in the aerobic portion of the reactor only. Nitrifiers pres-
ent in the anoxic portion and in the settling tank must be regarded as dormant,
not participating in growth. If they are not excluded from consideration, the
values of the kinetic coefficients (Equations 16 and 17) could not be.used.
These coefficients were determined in all-aerobic reactors. Also, the defini-
tional equation for yn (Equation 11) would not apply. Thus, it follows again:
f AX Q
f X V
AX
n
X SDT
n
Safety Factor (SF) and Quantity of Nitrifier Biomass (N)
In this report, SF shall mean the ratio of ynr to the design nitrifier growth
rate (yna) selected by the designer for imposition on the nitrification reac-
tor, to wit:
SF =
nr
y
nd
(34)
The application of an SF* means reducing ynr necessary to achieve a prescribed
average Si under a given treatment situation to a smaller value. This will
result in a lower S-^ for that treatment situation than prescribed.
For a PF reactor and a treatment situation characterized by S0 = 14.5 mg/&,
r = 0.5, pH= 7.2, and DO = 3 mg/&, a ynr of 0.30 will be required to achieve
an Sx of 1 mg/£ NHj-N. Applying an SF of 2 will result in a ynd of 0.15 and a
new S;L of practically 0 mg/&. For the same treatment situation and SF applica-
tion, S]_ for a CM reactor will decrease from 1 mg/& to 0.23 mg/& as the
growth rate is reduced from 0.24 day"1 to 0.12 day~l.
Looking now at Equation 31, to wit:
AX
nr
X SDT
n
it can be seen that there are three ways to reduce ynr> once all design param-
eters have been tentatively chosen:
a)
b)
Increase
by increasing the size of the nitrification reactor.
Decrease AX by measures taking effect outside of the nitrification reactor.
Improving or providing primary settling or improving or providing ENR are
two measures that might be taken. The first measure would reduce the
* This SF concept differs from the SF concept of the EPA PDM as defined by
Equation 3-29 on Page 3-20 of that manual.
29
-------
BODe to be removed in the activated sludge system, which in turn would
decrease AX; the second measure would provide for a greater biomass de-
struction, also decreasing AX:
c) Increase X. :
If either route b or c is taken, the application of an SF will cause an in-
crease in ft (from the value associated with ynr) by a factor slightly larger
than the SF. This can be recognized by considering Equation 20, to wit:
V.
nr
Yn
-------
(VI — — — — .=.
H-
vO.
•3
I
4J
O
+J
O
I
bo
•H
CO
-------
Data points for Profiles A, B, and C were determined by evaluating Equation
35, which follows readily from Equations 23, 24, and 27.
t =
n
U N
max
- s
(35)
where: S - the ammonia nitrogen concentration in the reactor at time t;
note that S becomes S^ for t = tn. For Profiles A and B, N is
the n. mass that has developed under the steady state operating
conditions of these profiles. For Profiles C and D, N is the
n. mass that has developed under the steady state conditions
of Profile B.
N for Profile A was determined by using Equation 20; S-, for Profile B was de-
termined by using Equation 27 and |'for the computation of N for that profile,
Equation 20 was used again. To determine S^ for Profiles C and D, Equation
36 was used. In that equation, N1is the n. mass developed under the steady
state conditions of Profile B. Note that SDT = (1 + r) t
n
n
SDT = -
n R
n
max
N
(36)
Because of the slight difference in S-^ (9.7 vs. 9.8 mg/£), Curve B, read on
tank scale II, represents Profile;D only approximately.
To project the effect of a sudden increase in ammonia nitrogen load on a CM
reactor, it is necessary to solve,quadratic Equation 37 for S.. :
SDT N
max n
n
+ K
- S» K =0
0 s
(37)
In this equation, which follows readily from Equations 18 and 20, N is the n.
mass developed under the steady state conditions preceding the imposition of
the transient load; the other parameters reflect transient load conditions.
With respect to buffering capability by application of an SF, CM reactors are
somewhat less efficient than PF reactors. The following four values are
obtained, respectively, for S^ in a CM reactor for the four treatment situa-
tions of Profiles A, B, C, and D: 1.00, 0.23, 1.01, and 0..92 mg/& NH+-N.
The preceding discussion illustrates how the application of an SF will keep
the effluent NHJ^-N concentration below the prescribed steady state design
requirement when a sudden increase in NH^-N load occurs. If the increase in
load is maintained for some time, the effluent NH^-N concentration will start
to decrease from the higher value experienced at the imposition of the trans-
ient load. This drop is in response to the increase in n. mass that will
take place.
However, the effect of the SF on the effluent NIfy-N concentration as discussed
32
-------
is based on a simplification, an approximation to reality: it is based on
the concept of a steady state load which does not exist in reality.
It should also be noted that the SF concept described does not fully corre-
spond to the SF concept in other f,ields of engineering. Generally, the SF
is the ratio of a selected design parameter value to the value of the same
parameter computed in accordance to design requirements. If it were desired
to use the same procedure for the computation of y ,, influent NHt-N and BODc
loads would have to be known to the designer as mass vs. time functions and
the required SQ, likewise, would be defined in the design requirements with
respect to time and rate of flow, perhaps as the flow weighted average over
24 hr. From these data, Vlnr would be determined with the help of a computer
program, taking fluctuations in n. mass during the design period into con-
sideration. To the ynr thus determined, an SF would then be applied. In such
a procedure, the SF would protect the plant against unforeseeable upsets.
Load fluctuations would be accommodated in the determination of u itself.
nr
CONCLUSIONS
This kinetic discussion of nitrification indicates that PF reactors are more
efficient than CM reactors, particularly if a low effluent ammonia nitrogen
concentration is desired and if sludge recycle rates can be kept low. Com-
partmentalization will minimize carbon loss via EOR in the warmer season if
great .fluctuations in wastewater temperature are expected. Compartments
should be small at the effluent end of a PF reactor to minimize tankage oper-
ating at low ammonia nitrogen concentrations and, therefore, low reaction
rates. Compartments at the head end of the reactors may be larger because
the Monod function furnishes a near zero order reaction rate for NH7VN con-
centrations above 2 to 3 mg/£.
33
-------
SECTION 5
ANALYTICAL METHODS AND SAMPLING PROCEDURES
ANALYTICAL METHODS
In general, Standard Methods (13th edition) (14) or methods recommended or
approved by EPA (15) were used.
When determining dissolved phosphorus forms, 0.45 ym membrane filters were
used. Paper towels were employed when determining the chlorine residual in
the filtrate of chlorinated sludge. Glass fiber filters were used for all
other dissolved parameters.
BOD samples were processed every day, 7 days a week. The same is true of SS
and VSS samples. All other samples were processed during the 5 working days
of the week. Refrigeration was employed for all samples that could not be
processed immediately. Sulfuric acid was used to preserve samples collected
on weekends and holidays that could not be processed on the day taken.
Chemical Oxygen Demand (COD)
In addition to the procedure described in Standard Methods, the autoclave
method described by Albertson et al. (16) and a modified standard method
were used. The autoclave method was used for 24-hr COD profiles of the final
settler effluent.
On March 21, 1975, the standard COD method was modified by omitting the use
of mercuric sulfate. This was prompted by .a review of British standard
methods (17) and by the difficulties encountered in obtaining HgS04 and dis-
posing of laboratory wastes containing mercury. According to the British
standards, the addition of HgSO, is not required for samples containing less
than 100 mg/A Cl . All the institutional sewage samples tested contained
less than 50 mg/£. Cl .
Nitrite + Nitrate Nitrogen, Ammonia Nitrogen, and Orthophosphorus in
Filtered Samples
These parameters were determined with a Technicon Autoanalyzer II using
Technicon Industrial Methods Nos. 100-70W, 98-70W, and 94-70W, respectively•
(Technicon 1971).
Oxygen Uptake Rate (OUR)
OURs were determined immediately aifter sample collection. A 500-ml sample' -
34
-------
was brought to the laboratory in a stoppered 1000-ml fleaker 5 shaken for
30 sec, and poured into a 300-ml BOD bottle. The DO drop in mg/& over 3 min
was determined and furnished the basis for the determination of the OUR. A
BOD bottle DO probe, equipped with an agitator, was utilized. OUR was re-
ferred to MLSS.
Total Organic Carbon (TOG)
TOG was determined on a Beckman Model 915 Total Organic Carbon Analyzer.
Alkalinity
Mixed liquor (ML) alkalinity was determined on filtered samples.
Filterability
The simple test described in the Gulp-Gulp textbook "Advanced Wastewater
Treatment" (18) was used. The md of filtrate produced in 30 sec were deter-
mined using a 9-cm (3.5-in.) Buchner funnel and Wo. 1 Whatman paper. The
vacuum was kept at approximately 58 cm (23 in.).
Chlorine Residual
Chlorine residual on the filtrate of chlorinated sludge was determined by
Standard Method 114A (lodpmetric); all other chlorine residual determinations
were made using Standard Method 114C (Orthodoline).
SAMPLING PROCEDURES
Two types of sampling methods were employed for collecting composite samples.
a) Samples were taken every hour and composited in accordance with flow.
Refrigerated Serco samplers^) were utilized for this method, which was
employed for collecting raw sewage samples only.
b) Samples were taken every hour and composited as taken. The same amount
of sample was collected every time. If the flowthrough rate was changed,
a new compositing container was started. Shop-made, refrigerated
samplers were used for this procedure, taking 170 ml of sample every hour.
Composite sampling was used for all main stream samples under Flow Sheets IV,
V, and VI. For Flow Sheets I, II, and III, the mode of sampling used is in-
dicated in the tables reporting the results of operations. ML and return
sludge samples were taken as grab samples, twice daily.
In general, daily sampling was employed until the end of October 1974 includ-
ing weekends. From then on, weekend sampling of raw sewage was discontinued.
BOD,- determinations on CCC effluent were also discontinued.
(1) Product of Corning Glass, a capped beaker.
(2) Product of Sanford Products Corp., 2355 Rand Tower, Minneapolis, MN 55402
35
-------
SECTION' 6
TREATMENT FACILITIES, OPERATING PROCEDURES, AND PLANT MEASUREMENTS
TREATMENT FACILITIES AND OPERATING PROCEDURES
Pretreatment
The pretreatment units consist of two hand-raked screens in series. The first
screen is equipped with bars of 25-mm (1-in.) spacing, the second with bars
of 13-mm (1/2-in.) spacing. The original installation included two commi-
nuters instead of the finer screens. The comminuters were taken out of
service due to the high incidence of rags, pencils, and toothbrushes in the
raw sewage. The comminuters could not cope with these materials.
Flow Equalization
The surge tank (Figure 7) is 9.76 m (32. ft) in diameter. Sludge accumulation
at the bottom of the tank is prevented by either one of two procedures: (1)
by operating a sludge scraper in conjunction with continuous recirculation of
raw sewage or (2) by operating a floating aerator part of the time, also in
conjunction with continuous recirculation of sewage.
The floating aerator is controlled;by a time clock and equipped with a pro-
peller-type impeller, coupled directly to a 7.45-kW (10-hp), 1150-rpm motor.
I
Operation of the sludge scraper results in somewhat better utilization of the
surge tank space than provided by the floating aerator. When using the
sludge scraper, the minimum liquid volume of the surge tank was 68.1 m3
(18,000 gal); when using the floating aerator, the surge tank could be drawn
down only to 90.8 mj (24,000 gal). The maximum liquid volume of the surge
tank in both cases was 295.2 m3 (78,000 gal).
Sewage is pumped from the surge tank by submerged, torque-flow type, constant-
speed pumps to the sideweir structure shown in Figure 8. Due to the varying
water level in the surge tank, the rate'of pumping to the sideweir varies,
with an average of 12.6 £/sec (200 |gpm). The sideweir returns part of the
sewage to the surge tank and releases a constant but controllable flow to
the plant. Flow to the plant from jthe sideweir is by gravity and is con-
trolled by an adjustable submerged Isluice gate opening.
Operation of a surge tank imposes a certain operational burden on the plant
operator. A surge tank equalizes flow fluctuations that occur within a 24-hr
period automatically, but it is obviously desirable to adjust the outpumping
36
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rate to fluctuations that occur from day-to-day. These nondiurnal fluctua-
tions may be due to changes in water consumption from one weekday to the next,
to changing rates of groundwater infiltration, or to changes of air tempera-
ture. At West Coxsackie, nondiurnal flow fluctuations are such that the
highest 24-hr inflow rate to the plant is approximately double that of the
lowest 24-hr inflow rate. The surge tank is equipped with two arrangements
intended to compensate, if needed, for the selection of faulty outpumping
rates: one is a low level pump cutout, device, the other a bypass. The cut-
out device stops the pumps delivering sewage from the surge tank to the side-
weir structure as soon as the fluid level in the surge tank falls below a
certain level. The bypass allows settled and chlorinated sewage to be dis-
charged to the receiving water whenever the overflow point is reached or in
the event of a prolonged power outage. Settling and chlorination take place
in the wet well shown in Figure 7. The wet well also serves as a backup or
standby unit for the surge tank.
The net outpumping rate is controlled by manually varying the height of the
sluicegate opening in the sideweir structure. Increments.of 13 mm (1/2 in.)
are used. The smallest sluicegate opening height used is 51 mm (2 in.), cor-
responding to a 4.5-&/sec (71-gpm).plant flow. The largest opening is 114 mm
(4-1/2 in.), corresponding to a plant flow of 9.1 £/sec (144 gpm). At the
higher flow rates, discharge from the submerged sluicegate is no longer free,
i.e., the opening in the sluicegate' becomes a submerged orifice.
Primary Settling Tank
The primary settler is of conventional, rectangular design, 1..83 m (6 ft)
wide by 7.32 m (24 ft) long with a :sidewater depth (SWD) of 2.44 m (8 ft).
The sludge scraper-skimmer flights iare chain operated. Sludge withdrawal is
from a hopper at the head end of the tank. The sludge pump is a horizontal
torque-flow pump, operated by a time clock. The original design provided a
time clock allowing a minimum sludge pumping interval of 2 hr and a minimum
period of pumping of 2 min. Only this arrangement was available for Flow
Sheet I. Sludge pumping was at the rate of 12.6 &/sec (200 gpm). For Flow
Sheets V and VI (the only other flow sheets incorporating primary settling),
adequate sludge pumping facilities were provided.
Aeration Tank
The aeration tank used is divided into 11 cells, numbered 1, 2, 3, 4, 5, 6,
7/8, 9, 10, 11, and 12 for the purpose of this presentation. Each cell,
except Cell 7/8, is 1.52 m x 3.05 m (5 ft x 10 ft) in plan, with an SWD of
approximately 2.3 m (7-1/2 ft) or 2.6 m (8-1/2 ft) depending on the height of
the outfall round weir used. The 2.6-m (8-1/2 ft) SWD corresponds to 146 m3
(38,500 gal) under aeration, the 2.^-m (7-1/2 ft) SWD to 129 m3 (34,000 gal)
under aeration (see Figure 9). Cel|L 7/8 is 3.05 m x 3.05 m (10 ft x 10 ft)
in plan. Figure 2 illustrates the numbering scheme used. .
Each cell, except Cell 7/8, is equipped with an INKA aeration grid of PVC
pipe featuring 3.2-mm (1/8-in.) diameter air holes. Each grid "covers 46 per-
cent of the area of its cell. The grids are mounted 0.3 m (1 ft) from the
bottom of the cells. They are attached to the floor of the aeration tank
38
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(Figure 9) .
Cell 7/8 is equipped with a 0.25-kW (1/3-hp), 350-rpm mixer.* Anoxic condi-
tions in other cells were achieved by throttling the air flow. Ports between
the aeration cells are at the bottom of the partition walls and are simple
slots 102 mm (4 in.) high by 305 mm (12 in.) wide. They are arranged in me-
andering fashion.
ML proceeds from Cell 1 to Cell 12 in PF fashion. However, there is a valved
cros's connection between Cell 5 and Cell 7/8 for use at higher flows. Both
raw sewage and return sludge are admitted to Cell 1. ML is withdrawn from
Cell 12.
Final Settling Tank, Sludge Recirculation, and Solids Management
The final settler is of conventional design with a 4.88-m (16-ft) diameter,
a 3.05-m (10-ft) SWD, and peripheral-tangential entry of the ML. Tangential
ML entry imparts a slow rotating motion to the entire sludge mass of the
settler. A sludge blanket develops on the bottom of the settler and in the
raceway between the skirt and peripheral wall; the blanket extends upward in
the raceway to within approximately 0.4 m '(1.3 ft) of the water level (Figure 10) .
The height of the sludge blanket at the bottom of the settler was determined
twice daily with the help of a Keene Model 8000 Sludge Blanket Finder. When
the sludge blanket finder enters the sludge blanket, a.slight modification of
the audible signal occurs. The quality of this signal modification is indic-
ative of the density of the sludge blanket and of the range of SS concentra-
tion in the effluent. A sharp change in tone indicates good flocculation and
few SS.
For wasting of excess activated sludge (EAS) and for sludge recirculation,
plunger pumps are used, the two pumps riding on the same suction line. The
wasting pump is activated by a time clock at intervals of 2 hr. The quantity
of sludge wasted on the project was varied by varying the sludge wasting
periods; the shortest period used was 2 min every 2 hr. Occasionally, auto-
matic wasting was replaced or supplemented by manual wasting. The amount of
sludge wasted was governed by a general policy of maintaining a sludge
blanket of 30-60 cm (1-2 ft) height.
Sludge Disposal
Two methods of sludge disposal are used:
a) Sludge chlorination to a pH of 2.5 followed by dewatering and drying of
the chlorinated sludge on sand beds and disposal of the air-dried sludge
on a landfill site. The sludge reacts with the chlorine for approximately
4 min in the pipeline that carries it from the point of chlorination to
the sludge drying beds. This method is used during the months of May to
October.
* This corresponds to a specific power of 10 W/m .
40
-------
HEADER
INKA
AERATION
GRID
8'7" SWD
Figure 9. Section view of aeration tank.
IIIIIIIIIU
MIXED
LIQUOR
2.0 FT AV
EFFLUENT
10 FT SWD
NOTE: I FT =0.31 M
SLUDGE
WITHDRAWAL
Figure 10. Section view of final settler.
41
-------
During the initial period of operations, a Purifax machine, manufactured
by BIF, Providence, RI, was used for sludge chlorination. In early 1974,
however, the reaction vessel of the machine was plugged by a rubber
stopper and the pipeline leading to the sludge drying beds was employed
as sole reactor from then on. ,
2 2
The total area of the sludge drying beds is 595 m (6400 ft ), composed
of 149 m^ (1600 f t ) of standard sand drying beds previously used to dry
anaerobically digested Imhoff tank sludge and 446 m (4800 ft ) of sludge
drying area constructed on the top surfaces of two trickling filters, now
out-of-service.*
I
b) Aerobic sludge stabilization and disposal of the treated sludge in a
wooded area. This method is used during the remainder of the year,
November to April. No supernatant recycle streams are directed back to
the head end of the plant from the aerobic digester. The stabilized
sludge is not decanted prior to disposal in the wooded area; however,
sludge is thickened by gravity before being placed into the digester.
When thickening EAS, a cationic polymer was used as a flocculation aid.
Mixtures of EAS and primary sludge were thickened without such aid.
Ferric Chloride Feeding Procedure
Liquid ferric chloride solution of! 42° Be' was purchased and fed as such with
chemical feed pumps actuated by time clocks (percentage timers) on a 1-min or
2-min feeding cycle. Rates of feed were set in terms of mg/& Fe based on
sewage flow through the submerged sluice gate in the sideweir structure.
Rates of dosing, in mg/min, were adjusted concurrently with the sewage flow.
The rate of ferric chloride addition was based on the treatment goal of
obtaining an effluent phosphorus concentration of less than 1 mg/& .
Chlorine Contact Chamber (CCC)/Secbnd-Phase Settler Combination
The combined treatment unit, illustrated by Figure 11, consists of mixing
chamber, influent plenum, flowthrough chamber, and effluent plenum.
In the CCC mixing chamber, chlorine solution-is admixed to the final settler
effluent. The chamber is equipped with a 0.25-kW (1/3 hp), 330-rpm mixer.
The two plenums serve to distribute the process water over the cross section
of the flowthrough chamber with the help of two orifice plates mounted at
the entrance and exit of that chamber. Each orifice plate carries 40 ori-
fices of 12.7 mm (1/2 in.) diameter. The flowthrough chamber is 1.52 m x
1.52 m (5 ft x 5 ft) in cross section and 4.88 m (16 ft) long.
On June 18, 1975, two baffle cages in series were installed in the flow-
through chamber. The baffle cagesj carry plexiglass baffle's 3.2 mm (1/8 in.)
thick that are inclined by 60° to the horizontal and spaced 152 mm (6 in.) on
center or 305 mm (12 in.) vertically.
* Approximately 30 cm (12 in.) of stone was replaced by sand and gravel.
42
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The treatment unit is also equipped with a sludge scraper and sludge with-
drawal means.
PLANT MEASUREMENTS :
Surge Tank Detention Time
This parameter was determined by dividing the surge tank effluent flow into
the average sewage volume of the surge tank, on a daily basis. The average
daily sewage volume of the surge tank was determined from a level recorder
chart.
Ferric Chloride Feed Rate
3+
This chemical feed rate, expressed as mg/& Fe~" , was computed daily on the
basis of a feed pump calibration curve and the surge tank effluent flow.
Main Stream Flow Measurements
The main stream flow was measured at two points, upstream of the surge tank
and at the effluent point of the flow control device (sideweir structure) that
controlled the flow to the treatment system downstream of the surge tank. The
latter flow measurement, the surge tank effluent flow, was used for all compu-
tations in the report except for the arithmetic compositing of the raw sewage
samples.
It should be noted that the reported raw sewage flows are approximately 20
percent higher than the .surge tank effluent flows. The surge tank efflijent
flows were measured with a magnetic flow meter which was volumetrically cali-
brated with the help of stopwatch and the primary settler. The raw sewage
flows were also measured with a magnetic flow meter. However, there was no
possibility to calibrate that meter volumetrically.
Return Sludge Recycle Rate
Return sludge flow was measured with a magnetic flow meter which was cali-
brated volumetrically with the help of stopwatch and aerobic digester.
Aeration Tank Air Flow
Total air flow to the aeration tank was measured with an amperemeter. Air
flow to the individual cells was not measured on this project. Ampere read-
ings were taken daily.
Excess Activated Sludge (EAS) Production
The time-clock operated plunger pikmps employed for wasting EAS were calibrated
routinely. The volume of EAS per'day was obtained by multiplying pumping time
by delivery rate. EAS suspended solids concentrations were regarded as con-
stant over 24-hr periods. . - ;
44
-------
Aeration Cell DO ..".'.
The DO level in the various cells was determined once or twice per day with
a Yellow Springs DO meter.
45
-------
SECTION 7-
RAW SEWAGE CHARACTERISTICS
Although the Correctional Facility has a separate sanitary sewer system, in-
filtration occurs during rainy periods. In the fall, silo drainage (corn
silage) enters the sewer system.
The institutional sewage is domestic in type but it is somewhat stronger,
much fresher, and contains more rags than municipal wastewater. The raw
sewage phosphorus concentration was somewhat higher during the study, approx-
imately 4 mg/& higher, than normally encountered in municipal sewage due to
extensive use of an anticorrosion agent in the water treatment plant. ML
temperature was also somewhat higher, approximately 7 C higher during .the
cold season, than in typical municipal sewage treatment plants, due to the
very short sewer lines and the high water consumption in the institutional
laundry. During winter, the sewage is cooled down several degrees during
passage through the surge tank.
Annual average raw sewage and surge tank effluent characteristics for the
12 mo of August 1974 through July 1975 are presented in Table 7. Table 8
breaks down most of the same raw sewage characteristics on a monthly basis
for the same 1-yr period. These data are based on 24-hr composites. The
freshness of the sewage may be deduced from the comparatively low ammonia
nitrogen and orthophosphorus content. Table 9 summarizes several raw sewage
parameters for the fall of 1973.
During the cold season, the average influent flow was 5-10 percent lower than
in the summer, with some increase in contaminant concentration (Table 8). The
mass flow of contaminants stayed fairly constant. The major portion of the
phosphorus in the raw sewage originates in the Correctional Facility's water
treatment plant.
The raw sewage diurnal flow pattern is characterized by sudden changes in rate
of flow, as shown in Figure 12. Minimum flow occurs in the early morning
hours with three short peaks appearing throughout the day. Peaks I, II, and
III reflect dishwashing and clean-up periods after meals| Peak III also re-
flects the use of showers. The instantaneous flow rate fluctuates between 2
Vsec (32 gpm) and 25 £/sec (396 gpm). The usage of showers affects the
daily flow rate. Under the present liberal shower use policy, the daily flow
rate increases considerably on hot weather days.
The iron content of the raw sewage fluctuated between 0.2 and 1.8 mg/fi,.
higher values may have been caused by either sewage maintenance work or
46
The
-------
TABLE 7. FLOW-WEIGHTED, ANNUAL-AVERAGE RAW SEWAGE AND SURGE TANK
EFFLUENT CHARACTERISTICS FOR YEAR ENDING JULY 31 1975
(FLOW SHEETS IV, V, AND VI)
Parameter
COD (mgM)
BOD5 (mg/A)
Diss. BOD5 (mgM)
Diss. BOD5 as % of BOD5
BOD5 as % of COD
SS (nig/ A)
VSS as % of TSS
Temp, of Sewage (C)
DO (mgM)
PH
Alkalinity (mg/A as CaC03)
NHt-N (mgM)
TKN (mg/A)
NH^-N as % of TKN
Diss. Orthophosphorus (mg/&)
Diss. Phosphorus (mg/&)
Total Phosphorus (mg/£)
COD/TKN
Raw
Sewage
530
240
125
52%
45%
233
84%
25.3
5.1
7.4
175
9.7
26.9
36%
4.4
6,,3
9.7
20
Surge
Tank
Effluent
420
185
65
35%
44%
243
22.4
0.3
7.4
200
12.7
27.1
47%
4.8
5.0
9.8
16
Change
-110
-55
-60
+10
-2.9
-4.8
0
+25
+3.0
+0.2
+0.4
-1.3
+0.1
Change
/Xof\
\Raw / Comments
-21%
-23%
-48%
+4% '
Sept., Oct.,
& Nov. 1974
only
0
+14%
+31%
+0.7% (1)
+9
-21% 9 mo. only
+1% (1)
(1) These increases appear to be caused by imperfect sampling or analytical
47
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48
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49
-------
TABLE 9. RAW SEWAGE CHARACTERISTICS FOR NOVEMBER AND DECEMBER 1973
(FLOW SHEET I)
Parameter
Number of Tests
Mean (mg/£)
COD
6
470
BOD_
5
i
3 '
233
SS Total P
5 2
211 9.5
TKN
5
28
N0~ + NO~-N
2 3
6
0.1
farming operations. The raw sewage contains minimal grit, but it contains a
noticeable amount of Anthrafilt, originating in the water filtration plant.
When backwashing the multimedia filter, some Anthrafilt is carried along with
the washwater. The carriage water used by the Correctional Facility is sur-
face water, drawn by gravity from an impounding reservoir located nearby. At
times, the Anthrafilt in the raw sewage caused serious clogging problems in
the sewage treatment plant.
During dry weather, all the nitrogen contained in the raw sewage is present
as organically bound nitrogen and ammonia. At times of heavy infiltration,
the nitrate-nitrite nitrogen content of the influent rises to 3-4 mg/£.
50
-------
SECTION 8
RESULTS AND DISCUSSION
OPERATING RESULTS: FLOW SHEET I
This flow sheet, as shown schematically in Figure 13, was characterized by
two anoxic zones in the aeration tank, by the incorporation of the primary
settler in the flow regime, by the anoxic operation of the surge tank, and by
ferric chloride addition to the effluent of the primary settler. The raw
sewage flow was somewhat smaller than experienced under subsequent flow sheets
due to a smaller inmate population.
The sampling technique available during Flow Sheet I operations was poor,
especially during cold weather when many sampler breakdowns occurred. Also,
removal efficiencies for the primary settler were quite low for this phase
due to an unsatisfactory mode of wasting primary sludge. On the other hand,
the low average influent sewage flow and the anoxic detention time provided
in the treatment train seemed to affect treatment results favorably, erratic
as they may appear. The erratic results achieved under this flow sheet were
likely due not to an unreliable process, but rather to poor operation and
process monitoring.
Results achieved and operating conditions prevailing under Flow Sheet I are
reported in Tables 10 and 11. The nitrogen removal aspects of this flow
sheet are discussed in the subsection on Nitrogen Profiles, beginning on
page 95.
jiiurge Tank Operation
Detention time in the surge tank was approximately 9 hr. Because the surge
tank aerator was not utilized during this phase, a slight sewage odor was
always noticeable near the surge tank. Considerable floating matter was
visible in the surge tank. The color of the sewage in the surge tank and in
the primary settler was milkish white.
Primary Settler Operation
Detention time in the primary settler was approximately 1.7 hr. Due to
faults of design, there was always some floating sludge from the sludge hopper
on the settler surface.
51
-------
CO
LU
O
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-------
TABLE 10. AVERAGE VALUES OF OPERATING PARAMETERS FOR FLOW SHEET I
Parameter
Detention Times Based on
Raw Sewage Flow
Surge Tank (hr)
Primary Clarifier (hr)
Secondary Clarifier (hr)
Aeration Tank (hr)
Detention Time Based on
Mixed Liquor Flow
Aeration Tank (hr) •
Loadings and Overflow Rate
*0rganic Loading Rate,
Aeration Tank - F/M
(kg BOD5/day/kg MLVSS)
^Volumetric Loading Rate,
Aeration Tank
(kg BOD5/day/m3)
(Ib BOD5/day/1000 ftj)
December January
1973 1974
February March
1974 1974
Sewage Flow (i
Sewage Flow (i
nT/day)
(0.122)
461
(0.130)
492
(0.124)
469
(0.127)
' 481
Overflow Rate,
(m3/m2/day)
(gpd/ft2)
Final Settler
11
1.7
3.0
6.7
5.0
0.22
0.56
(35)
24.8
(609)
Mixed Liquor and Sludge Production
Data
Sludge Retention Time (days) 5.8
kg VSS produced per kg BOD removed 0.75
MLSS (mgM) 3900
Volatility [(MLVSS/MLSS) X 100] 64%
Rate of Sludge Return 33%
7
1.6
2.8
6.3
4.8
0.25
0.68
(42)
26.4
(648)
6.3
0.61
3900
70%
30%
9
1.7
2.9
6.6
5.0
0.28
0.66
(41)
25.1
(615)
4.1
0.84
3300
71%
31%
10
1.6
2.9
6.5
4.9
0.29
0.68
(42)
25.7
(629)
4.9
0.68
3400
68%
33%
* Loading rates are based on kg of BOD5 introduced into the aeration system.
53
-------
TABLE .11.. AVERAGE CHLORINE CONTACT CHAMBER EFFLUENT VALUES FOR FLOW SHEET it
Parameter
December January February March
1973 1974 1974 1974
PH
(Number of Observations)
BOD5(mg/A)* I
(Number of Grab Samples) ;
SS (mg/£) ;
(Number of Grab Samples) ;
TKN (mg/A)
(Number of Grab Samples) i
NO^+NO'-N (mg/£)
(Number of Grab Samples)
Soluble Orthophosphorus (mg/& P)
(Number of Grab Samples)
7.3
(8)
3.0
(6)
4.0
(15)
1.38
(6)
2.1
(9)
0.16
(9)
7.0
(21)
3.8
(18)
7.4
(8)
1.55
(14)
2.1
(17)
0.33
(17)
7.0
(17)
4.8
(13)
5.5
(17)
3.36
(17)
0.6
(17)
1*09
(17)
7.0
(19)
5.8
(7)
6.3
(11)
3.45
(4)
2.1
(16)
0.25
(17)
t Average chlorine dose was 9.5 mg/&.
* BOD samples were seeded before analysis.
Aeration Train Operation
Nominal detention time'averaged approximately 6.5 hr, r 32 percent, and MLSS
concentration 3500 mg/&.
Aeration Train Profiles
On November 14, November 27, and December 5, 1973, profile sampling was con-
ducted through the aeration train. Samples were drawn from the individual
cells in sequence, spacing the sample taking at intervals corresponding to
an ML flowthrough time of 29 min per cell (58 min for Cell 7/8). The re-
sulting profiles are shown in Figures 14, 15, 23, 24, and 25. Zero time
samples were not collected. The first samples were drawn from Cell 1, repre-
senting the effluent from that cell and the influent of Cell 2. For tabula-
tion of profile data, see Appendix B.
Pattern of Aeration
The first cell was kept anoxic because it was felt that such an arrangement
would contribute to keeping the sludge volume index (SVI) down, with a view
to the work of Chudoba et al. (19). On the basis of their laboratory in-
vestigation, Chudoba and his coworkers came to the conclusion that a steep
54
-------
I20T
NO
100
90
80
12/5/73
Plant Influent Total COD 475mg/l
Primary Effluent Total COD 356mg/l
/ \fc-~11/14/73
12/5/73
Xi*. * * \
^...__.___../ v_
4 56 7/8
Aeration Cell Numbers
10 II 12
Figure 14. Aeration train dissolved COD profiles for Flow Sheet I.
55
-------
11/27/73
-12/5/73
2
6
7/8 ' 9 " 10 J II ' 12
Aeration Cell Numbers
Figure 15. Aeration train dissolved orthophosphorus profiles for Flow Sheet I.
56
-------
organic carbon gradient at the head end of the aeration tank would discourage
sludge bulking due to filamentous organisms.
Final Settler Effluent Profiles
Total COD and N03-N 24-hr profiles were run on the final settler effluent for
3 days in November and December of 1973. These are depicted in -Figures 16
and 17.
Carbon Removal
The profile tables (Tables B-l, B-2, and B-3 in Appendix B) and Figure 14
indicate definite trends for the first half of the aeration train:
1) Nearly all of the particulate COD in the primary effluent is adsorbed in
the first cell, the anoxic cell, by the MLSS. This is indicated by the
low SS concentration in the supernatant of the first cell ML (see Tables
B-l, B-2, and B-3). For approximate SS content of primary effluent, see
Table 32.
2) A very rapid reduction of soluble COD takes place in the upstream portion
of the aeration tank, consisting of the anoxic cell and the first two to
four aerobic cells. This reduction brings the soluble COD concentration
of the process water down to practically the final effluent soluble COD
concentration.
3) After the original rapid reduction of soluble CODs in the aeration train,
an increase in this parameter occurred, indicating perhaps release of
organics from the ML biomass. On two of the three occasions depicted in
Figure 14, subsequent anoxic treatment in double Cell 7/8 resulted in
resorption of the released COD, but the data for the following anoxic
cells are somewhat diffuse.
Soluble Orthophosphorus Removal
The aeration train profile shown in Figure 15 indicates that approximately
7 mg of soluble orthophosphorus were adsorbed to or absorbed by the ML sludge
in Cell 2, the first aerobic cell. This shows very clearly that the aerobic
portion of the activated sludge process itself was responsible for phosphorus
removal. It should be noted that the activated sludge was in full contact
with soluble orthophosphorus in Cell 1; however, no phosphorus removal occur-
red there. The bulk of the remaining soluble orthophosphorus was removed in
Cell 3. Of further noteworthiness was the lack of any phosphorus release in
anoxic Cells 7/8, 9, 10, and 11. . .
The mechanisms of phosphorus removal via FeCl3 addition did not become clear
under this research project. Total phosphorus in the raw sewage averaged
approximately 10 mg/£. During the time the aeration tank profiles were! taken,
only 13 mg/& of Fe3+ were needed to achieve nearly complete transfer of the
phosphorus to the sludge. Stoichiometric requirements were 18 mg/£. Removal
of some particulate phosphorus with the primary sludge and biological
57
-------
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4-1
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-------
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o
u
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CM
ro
CO
CO
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phosphorus removal in the aeration tank to satisfy synthesis requirements may
account for the efficient performance at lower-than-stoichiometric iron dose-
ages. Also, the anoxic conditions in the first aeration cell and/or in the
surge tank may have created a treatment situation favorable to luxury uptake
of phosphorus.
The ML sludge underwent a visible color change with rising ferric chloride
dosing rate, becoming darker and reddish-brown, indicating an accumulation of
ferric hydroxide or hydrated ferric oxide. Also, when standing anaerobically
in a glass bottle in the laboratory, the sludge turned black within a few
days. This suggests formation of ferrous sulfide as the result of a re'action
betxjeen ferric hydroxide and hydrogen sulfide.
Final Effluent Oxidized Nitrogen Profiles
Figure 17 depicts three 24-hr NO~+NO~-N profiles of the final settler efflu-
ent. These around-the-clock cross sections indicate a very pronounced oxi-
dized nitrogen peak at the late afternoon hour, probably reflecting a morning
nitrogen peak load on the plant due to kitchen and bathroom use. The load-
equilization performance of the surge tank, obviously, leaves much to be
desired.
Sludge Characteristics
For the 3 days of the aeration train profiles, the SVI averaged approximately
100 mfc/g- ML volatility was about 65 percent. With other conditions remain-
ing "unchanged, percent volatility will mirror the iron content of sludge,
decreasing as the iron concentration increases.
Oxygen Uptake Rates (OURs)
In conjunction with the profile of December 5, 1973, OURs on the ML were
conducted with the following results:
Cell No. 1 2 3456
OUR (mg/02/hr/g MLSS) 22.3 9.1 11.1 9.4 7.5 6.5
Cell No.
10
7.1
11
5.4
12
6.0
OUR (mg/02/hr/g MLSS) 7.9
Underlined cells were anoxic.
Turbulence in Anoxic Cells
In Cell 7/8, the floe particles were clearly visible and distinguishable from
the supernatant. That was not the case with respect to the other anoxic
cells. The same condition prevailed in later flow sheets. In Cell 7/8, ML
solids were kept in suspension by a mixer. In the other anoxic cells,
throttled air was used.
60
-------
OPERATING RESULTS: FLOW SHEET II'
This was the first flow sheet under which the 7.45-kW (10-hp) floating aerator
was utilized'in the surge tank. The sludge scraper used with Flow Sheet I
had been dismantled. The surge tank aerator was operated continuously during
the 1 wk Flow Sheet II was evaluated. All other operating aspects of Flow
Sheet II were identical to Flow Sheet I (see Figure 13).
Rationale
It had been hoped that the lengthy preaeration period provided by the surge
tank would greatly improve the overall performance of the treatment system
by:
a) Nearly saturating the influent to the primary settler with DO, thereby
alleviating the rising sludge problem in that unit.
b) Effecting a considerable reduction in BOD in the process water, thereby
reducing the organic load on the A.S. aeration system and improving its
performance. This was supported by literature reports on the effects of
preaeration (20). ,
The improvements hoped for would be brought about without additional tankage.
Results . - . .
Utilization of the surge tank for preaeration had a very unfavorable effect
and had to be discontinued after a few days. The chlorinated final effluent
became "milky," containing a high concentration of SS with correspondingly
high BOD5 and COD concentrations. Some of the analytical results for Flow
Sheet II are shown in Table 12.
Full-time aeration of the surge tank was accompanied by heavy foam formation
in that treatment unit. The process water in the surge tank and primary
settler became more transparent and assumed a brownish tint.
33iscussion
It is believed that the "milky" effluent.was due to dispersed growth, that
full-time aeration in the surge tank, where the average detention time was
9 hr, greatly increased biological action in the surge tank, stimulating
bacterial growth there. But the physiological state of the bacterial growth
developed therein was such that they did not flocculate nor could they be
captured by the A.S. floe.
61
-------
TABLE 12. OPERATING AND EFFLUENT DATA FOR FLOW SHEET II
Chlorinated
Date
1974
4/29
4/30
5/1
5/2
5/3
5/6
5/7
TSS
7.0
24.0
40.0*
21.0*
52.0*
110.0
26.0*
BOD5**
(mg/JO
8.5
13.7*
15.0*
18.0*
24.0*
' 8.5
28*
Effluent1"
COD
N.A.
65*
69*
91*
80*
N.AV.
83*
Mixed Liquor
, TKN
(mg/A)
6.3
9.0*
13.2*
13.4*
8.4*
2.9
5.3*
TSS
(me/A)
2240
2790
2455
2000
2380
3850
3085'
SVI
98
87
99
100
92
117
91
Vol.
68.8
66.2
68.8
70.0
69.6
60.0
67.0
1* Average chlorine dose was 9.5 mg/&.
* Values determined on 24-hr composite samples; values not starred
determined as grab samples.
**
samples were seeded before analysis.
OPERATING RESULTS: FLOW SHEET III
This flow sheet, depicted schematically in Figure 18, was characterized by
the use of the surge tank as part of the activated sludge system and by the
absence of primary settling. Raw sewage and return sludge were both intro-
duced to the surge tank, which was. operated with the 7.45-kW (10-hp) aerator
as an aeration device. The entire compartmentalized aeration tank was also
part of the aeration system. The surge tank continued to function as a flow
equalization unit.
Rationale
It was felt that using the surge tank as part of the activated sludge system
would increase the MLSS mass by approximately 125 percent, thereby drastically
lowering the F/M load on the system and improving carbonaceous oxidation and
nitrification. Since the surge tank would continue to be used for equaliza-
tion, this improvement could be brought about without additional capital cost.
The additional cost of the floating aerator and larger pumping equipment
would be offset by eliminating the cost of the sludge scraper.
Results
The above rationale proved to be correct but not sufficiently comprehensive.
62
-------
ANOXIC CELLS
F77777I
PULSATING AERATION
AERATION TANK
SCREEN CHANNEL
7/8
PLANT
INFLUENT
MIXED LIQUOR,
FINAL
SETTLER
RETURN SLUDGE
^WASTE SLUDGE
SECONDARY EFFLUENT
CHLORINE CONTACT CHAMBER
PLANT EFFLUENT
Figure 18. Process schematic for Flow Sheet III.
63
-------
Effluent quality at the beginning of this phase was excellent. However, the
process soon became unmanageable due to a rising SVI, which reached nearly
500 m)l/g within- 6 wk as indicated in Table 13 . The effect of the new flow
sheet on sludge settleability had not been taken into consideration.
Sludge bulking was caused by gramrnegative filamentous organisms. A greatly
increased population of stalked ciliates was also noticeable. It is believed
that the sludge bulking may have been initiated by the switch to a system
that included as a first treatment unit a CM reactor of about 9 hr sewage
detention time. The combination bf a relatively high DO concentration and a
low COD concentration in the process water may have triggered a population
explosion of the filamentous organisms.
The floating aerator was first operated full time for the first 2 days of
Flow Sheet III. Full-time operation of the aerator resulted in a final ef-
fluent nitrate concentration of near 10 mg/Jl N. Under the prevailing oper-
ating conditions, this high nitrate nitrogen concentration was accompanied by
problems of floating and rising sludge in the final settler. After the first
2 days, the floating aerator was put on a 10 min "on", 10 min "off" cycle.
This change in aeration pattern immediately solved the problem of excessive
nitrates in the final effluent by allowing substrate nitrate respiration to
occur directly in the surge tank.. Improved nitrogen removal was accomplished
by making use of the wastewater organic carbon. Reduction of the aeration
"on" time also obviated a foaming problem in the surge tank. The 10 min "on",
10 min "off" aerator cycle was selected because it was felt that settling of
the activated sludge floe would just about be completed in 10 min at low pro-
cess water levels in the surge tank. The biomass must be in suspension in
order for substrate nitrate respiration to occur.
Removals were of course greatly affected by the poor settling qualities of
the sludge which frequently resulted in high TSS, BOD^, and TKN concentra-
tions in the final effluent (see 'Table 13). Apart from this, the results
indicate the probability limits to which nitrogen removal can be pushed in a
one-sludge system without a supplemental carbon source. TKN probably cannot
be reduced below 1.5 to 2.0 mg/JL NO^ + NO^-N probably cannot be consistently
reduced to below 0.5 mg/S.. Such performance will require utilization of a
manageable sludge blanket in the :final settler, not the bulking high sludge
blanket experienced in this phase.
Conclusions
The utilization of a surge tank as part of an aerobic-anoxic A.S. system ap-
pears to be a viable arrangement, particularly for smaller plants. The surge
tank provides both flow equalization, which is important for effective final
settler operation, and substrate nitrate respiration, which is important for
effective nitrogen removal. Provisions for coping with sludge bulking must
be made, however.
The floating aerator should be activated by a time clock and have a direct
drive. Gear-driven aerators are not suited for the "on-off" operation
required.
64
-------
TABLE 13. OPERATING AND EFFLUENT DATA FOR FLOW SHEET III
f
Mixed Liquor
Date
1974
5/8
5/9
5/10
5/13.
5/14
5/15
5/16
5/17
5/20
5/21
5/22
5/23
5/24
5/27
5/28
5/29
5/30
5/31
6/3
6/4
6/5
6/6
6/7
6/10
6/11
6/12
6/13
6/14
6/17
6/18
6/19
6/20
6/21
Flow
(m3/day)
416
454
416
568
378
341
341
341
341
N.AV.
530
530
492
492
454
530
530
568
568
530
568
568
530
530
606
568
568
568
606
530
606
530
568
MLSS
2040
2140
2675
2090
2840
3750
2990
1695
985
3900
2890
3390
4000
N.AV.
4385
4260
3520
2705
4150
3410
3995
1450
2840
3200
2940
2960
3060
3270
3005
2235
2405
2395
1945
SVI
83
77
83
86
92
186
193
100
102
210
250
208
68
N.AV.
220
370
320
245
234
276
242
207
N.AV.
294
310
318
307
291
N.AV.
425
401
401
478
Effluent:, Chlorine Contact Chamber''
TSS
2.0
8.0*
12.4
16.0
21.5*
23.0*
13.0*
11.5*
6.2
314*
69*
9*
75*
N.AV.
3.0
6.5
7.0*
8.5*
14.0
115*
7.2*
14.5*
6.0*
3.0*
44.0*
9,0*
4.2*
24.0*
6.0
33.0*
26.0*
36.0*
195.0*
BOD5**
(mgM)
8.0
15.0
25.0*
8.5
13,7
16.0*
N.AV.
12.0*
N.AV.
N.AV.
N.AV.
N.AV.
N.AV.
N.AV.
3.4
14*
7*
10*
6.0
10.3*
15.0*
12.0*
8.0*
6.9
36.0*
12.0*
5.0*
15.0*
10.0
22.0*
23.0*
25.0*
N.AV.
TKN
N.AV.
3.4*
2.2*
2.5
2.9*
2.5*
2.1*
2.0*
1.7
22.9*
3.6*
1.1*
1.7*
N.AV.
0.8
0.7
1.4*
1.5*
1.2
2.2*
N.AV.
2.1*
1.1
0.8
3.78*
1.68*
1.7*
2.1*
1.8
2,2*
4.3*
2.4*
14.6*
N02+N03-N
OnsM)
10.9
8.5*
2.4*
5.0
3,9*
2.8*
0.7*
1.8*
3.6
1.4*
0.01*
0.01*
0.2*
N.AV.
0.2
0.1
0.4*
0.4*
0.1
0.2*
0.2*
0.6*
0.5
0.4
0.2*
0.7*
0.7*
0.4*
0.3
0.3*
0.2*
0.2*
0.2*
"f" Average chlorine dose was 9.0 mg/£. ,
* Values determined on 24-hr composite samples; values not starred determined
on grab samples.
** BOD,, samples were seeded before analysis.
Average detention time in surge tank: approximately 9 hr.
65
-------
The surge tank pumps should be suitable for pumping ML. They have to accom-
modate both the plant flow as well as the return sludge flow.
TERMINOLOGY USED IN TABLES DESCRIBING PERFORMANCE OF FLOW SHEETS IV, V9 AND VI
The bulk of data describing the operating conditions and performance results
for Flow Sheets IV, V, and VI (Figures 19, 20, and 21, respectively) are con- '
tained in Tables 14 through 31 and Figure 22. The following remarks explain
how some of these data were computed.
"Daily Flow" is the daily flow introduced into the primary settler or the
aeration tank via the variable sluice gate in the sideweir structure, averaged
over one calendar month. The daily flows for the month were added and the
sum divided by the number of days in the month.
"Mean Sewage Detention Time," for all units except the surge tank, is the
average monthly nominal fluid retention time. It was found by dividing the
"Daily Flow", as described above, into the volumetric capacity of the treat-
ment unit. "Monthly High (Low) Sewage Detention Times" were determined by
dividing the highest (lowest) daily plant flow of the calendar month into the
capacity of the treatment unit.
Similar procedures were followed when determining the other hydraulic param-
eters based on plant flow: surface overflow rate and weir overflow rate.
"Mean Sewage Detention Time" for the surge tank was determined as the flow
weighted monthly average of the daily sewage detention time in the surge tank
using the same method of computation utilized for determining the monthly
flow weighted average of substrate concentrations found in the process water.
"High" and "Low" sewage detention times for the month were found simply by
inspecting the list of daily detention times for the calendar month under
consideration. Determination of the surge tank daily sewage detention time
is described in Section 6.
"Mixed Liquor Detention Time" was computed by dividing, the average monthly
ML flow into the capacity of the aeration tank. ML flow is the sum of sewage
flow and sludge recycle flow.
Monthly flow weighted average concentrations C were determined by using the
equation: . m
:n^n
m
(38)
n
where: C = concentration, 24-hr composite, n day of the month, mg/.Jl
Q = daily flow, n day of the month
S = summation for the days o'f the month.
66
-------
ANOXIC CELLS
FeCl3 (ALTERNATE)
AERATION TANK
SCREEN CHANNEL
SURGE TANK
PLANT'
INFLUENT
MIXED LIQUOR
FeCI3
FONAL
SETTLER
)-
RETURN SLUDGE
WASTE SLUDGE
SECONDARY EFFLUENT
CHLORINE CONTACT CHAMBER
PLANT EFFLUENT
Figure 19. Process schematic for Flow Sheet IV.
67
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The same computational procedure was applied to temperatures and MLSS and .
RSSS concentrations.
The volatility of MLSS and RSSS in an A.S. system using iron and aluminum
salts for phosphorus removal cannot readily be compared with the volatility
of sludge occurring .in a system not using this procedure. This was commented
upon by Mulbarger (22). To permit better comparison of the volatilities
achieved, the column "% Vol. Adjusted" was provided in Table 21. It was
assumed that all iron in the sludge was present in the form of Fe(OH)_ and
that the molecular weight of Fe(OH) is equal to 1.91 times the molecular
weight of Fe (107/56 =1.91).
The following equation was used for computing the values in the column headed
"% Vol. Adjusted":
Vol. Adjusted =
% Vol.
100 - % Fe x 1.91
100
(39)
where: % Vol. = percent volatile solids determined
3+
% Fe = percent Fe found in (total) MLSS or RSSS.
In other words, the volatile solids mass is related to the total solids mass
minus the mass of the assumed iron 'compound therein.
OPERATING RESULTS: SURGE TANK
The effect of the surge tank on raw .sewage characteristics was shown pre-
viously in Table 7. Sewage detention times in the surge tank are presented
in .Table 15. Dissolved BOD,, decreased by 60 mg/&; particulate BOD increased
by 5 mg/&. The change in BOD,, components indicates biological oxidation of
dissolved BOD by dispersed biota, with the emphasis on respiration. Alka- •
linity increased by 25 mg/&.
Over extended periods, inflow to and outflow (outpumping) from an inline
surge tank must balance each other. This can be arranged in basically two
ways:
a) By adjusting the outpumping rate once or twice a day. At the same time,
the sludge recycle rate must be adjusted if that rate is generally kept
at a moderate percentage of the inflow. This method of flow control re-
quires constant attention on the part of the plant operator.
b) By adjusting the outpumping rate only to the seasonal and perhaps to the
weekend fluctuations of inflow and relying otherwise on the low-level
cutout mechanism of the discharge pumps. Controls should be provided
that would stop sludge wasting and preferably also effluent chlorination
during cutout periods. The sludge blanket in the final settler must
generally be kept low under this mode of operation.
89
-------
By and large, operation of the surge tank, was trouble free. ,, A certain amount
of disturbances were caused by rags that tended to "ball up" from time-to-
time in the submersible torque-flow pump and lodge between the housing and
the impeller. Rags also tended to collect around the columns supporting the
motor of the floating aerator. Once a block of wood jammed the impeller of
the aerator. The surge tank had to be dewatered several times in order to
remove 6-cm (2-1/2 in.) diameter can tops from the 10-cm (4 in.) pipeline
that connects the center well of the surge tank with the pump pit.
OPERATING RESULTS: FLOW SHEET IV • : - '
This flow sheet, shown diagrammatically in Figure 19 and characterized by the
omission of primary settling and the utilization of a single anoxic zone in
the aeration train comprising Cel|._| 5,' 6, 7/8, 9, and 10, was evaluated from
August 1974 through March 1975. The aerator in the surge tank was on a 2 min
"on", 18 min "off" cycle. Several modes of ferric chloride dosing were
employed. This was the first flqV sheet under which a rather complete samp-
ling and analytical program was ii| force.
Operating conditions and performance results for Flow Sheet IV are .reflected
in Tables 14-29 and Figure 22. Certain aspects of nitrogen removal and sludge
production are discussed in two .later subsections.
BOD,., Suspended Solids, and Nitrogen (N) Removal'
t
Provided that a system has sufficient N removal capacity via sludge synthesis
and denitrification, N removal efficiency will depend on the flocculating
properties of the sludge and will;parallel SS and BOD removals. Poor floc-
culating properties will be reflected in high SS in the effluent,, paralleled
by high BOD_ and TKN concentrations. This was observed on this project and
may be seen by examining the respective tables.
It appears that a change in the nature of the wastewater being treated
occurred during December 1974, resulting in increased final effluent BOD ,
SS, and TKN. The effluent became "milky" again, thus creating a very
unsightly appearance in the final settler. ,The fine SS could be filtered out
by a 0.45 ym membrane filter, but not by a glass fiber filter. This led to
numerous attempts to remedy the situation, among others the relocation of the
FeCl3 dosing point from the surge tank effluent to the final settler influent.
That measure improved the situation somewhat, but not to a satisfactory level.
Consistently low SS concentrations in the final effluent were established
only under Flow Sheet VI by adding 8 mg/5, of Fe3+ in the form of FeClj to the
influent of the primary settler. !
It was theorized that some new constituent in the process water had an un- .•
favorable effect on flocculation. 1 Nitrification and denitrification were not
seriously affected, .but phosphorus; removal suffered considerably. The de- ',
terioration of SS removals was not caused by the somewhat lower winter tern-"
peratures of the process water; such deterioration was not observed in the
preceding winter season. ...._,...
90
-------
The occurrence of the "milky" effluent was accompanied by heavy foaming in
the aeration train and also in the mixing chamber of the CGC. In general,
a poor effluent, in terms of BOD and SS, was associated with the heavy foam-
ing.
Ferric Chloride Addition and Phosphorus Removal
3+
Ferric chloride dosage, in terms of mg/£ Fe and Fe/P molar ratio, is shown
in Table 28. The Fe/P molar ratio varied between 0.43 and 0.79. Up to
September 20, ferric chloride was dosed to the effluent of the surge tank.
On that day, the.dosing, point was relocated to the effluent of the aeration
train. This brought about a drastic decrease in FeCl^ requirements and
explains the low FeCl_ dosages in October, November, and December. On Febru-
ary 7, Fed addition was discontinued for 2 wk because Fe appeared in the
effluent ana because the ML assumed an unusual color. Ferric chloride addi-
tion was reinstituted on February 28, this time again to the surge tank
effluent. ,
Disregarding December*, satisfactory phosphorus removal (i.e., 1 mg/5, final
effluent P, or less) was achieved only in September and October. In addi-
tion, 80 percent or better P removal was also achieved in August, September,
and March. During February, ferric chloride feeding had been discontinued
for 20 days. This explains the poor P-removal results in February.
In general, P removal efficiency paralleled SS removal efficiency. The same
unknown wastewater constituent that adversely affected SS removal also af-
fected P removal unfavorably.
Efficient P removal by metal addition to the A.S. process is predicated on
the general soundness of the process, as observable in SS removal. When
clarification efficiency is impaired due to wastewater characteristics, in-
creased metal dosage generally will not help. ,
OPERATING RESULTS: FLOW SHEET V
Except for changes in the aeration train aeration pattern, the mode of ferric
chloride addition, and the pattern of'surge tank aeration, Flow Sheet V, as
seen schematically in Figure 20, was identical to Flow Sheet II. The aeration
pattern utilized was the same as employed with Flow Sheet IV. Ferric chloride
was dosed in a "split" fashion, 4 mg/Jl Fe3+ to the ML leaving the aeration
train, the rest to the primary effluent. The surge tank aerator was operated
in the cyclic pattern adopted in Flow Sheet IV, rather than the full "on"-time
mode used with Flow Sheet II.
Since Flow Sheet II, several mechanical modifications had been made to the
primary settler: the sludge wasting appurtenances had been improved and a
25-mm x 25-mm (1-in. x 1-in.) coarse mesh screen had been installed in the
effluent trough. ' .
* The December results are not significant because the secondary plant was in
operation only part of the month.
91
-------
Operating conditions and performance results for this flow sheet are pre-
sented in Tables 14-27, 30 > and 31 and Figure 22. Certain aspects of nitro-
gen removal and sludge production are discussed in a later subsection.
Final effluent BOD5» dissolved BOD^, and SS concentrations were similar to
the average values achieved during Phase IV. However, average effluent COD
and dissolved COD were 35 and 49 percent higher, respectively. Also, total
N removal efficiency deteriorated to unsatisfactory levels and the Phase V
run was discontinued at the end of April 1975 after 1 mo of operation. It is
possible that the operating period was too short to allow performance to be
optimized.
OPERATING RESULTS: FLOW SHEET VI
As depicted schematically in Figure 21, Flow Sheet VI was characterized by the
use of the primary settler and split ferric chloride addition (8 mg/& Fe3* to
the influent of the primary settler and 5-6 mg/& Fe3+ to the aeration tank
effluent). Experimentation with the aeration train aeration pattern, intended
to improve denitrification, was carried out during this final phase which
lasted 3 mo (May-July 1975). The1 cyclic 2 min "on!1, 18 min "off" operating
mode for the surge tank aerator was continued.
Operating conditions and performance results for this flow -sheet are reflected
by the data in Tables 14-27, 30, and 31 and Figure 22. Certain aspects of N
removal and sludge production areidiscussed in two later subsections.
01 "
The increase in Fe dosing rate and the forward (upstream) movement in one
of the split Fe3+ dosing points were based on the idea that the upstream addi-
tion of ferric chloride, an acidic compound, would help to .alleviate the
detrimental effects of the unknown institutional contaminant that inhibited
complete flocculation in the A.S. process, thus resulting in periodic solids
removal problems. It was assumed that these contaminants originated either
in the kitchen or the laundry. The upstream dosing would allow the ferric
chloride to react with the process water outside of the A.S. tank. The change
in the ferric chloride dosing procedure was not related to phosphorus removal
considerations. Experimentation with the aeration pattern was initiated only
to counteract anticipated effects!of the change in the ferric chloride dosing
scheme on N removal.
Operating Conditions
The average hydraulic load on the aeration system was somewhat higher, 575
m3/day (0.15 mgd) vs. 506 m3/day (0.13 mgd), in Phase VI than in Phase IV.
The average process water temperature was 25 C.
Table 32 compares contaminant concentrations in the influent to the aeration
tank for Flow Sheets IV and VI. Aeration system influent BOD5 and SS concen-
trations for Flow Sheet VI were only 55 and 65 percent, respectively, of those
for Flow Sheet IV. Influent TKN concentration, however, changed little.
The decrease in influent BODc and SS concentrations had the effect of halving
sludge production in terms of the mass of solids produced in the A.S. system
92
-------
TABLE 32. AVERAGE CONTAMINENT LOAD ON AERATION TRAIN
DURING FLOW SHEET IV AND VI OPERATIONS
Parameter
Flow Sheet IV*
(me/ft)
Flow Sheet VI**
ss
COD
BODjj
NHf-N
TKN
Total
Diss.
Phosphorus
Orthophosphorus
245
422
196
12.2
27.0
10.1
4.9
160
287
107
13.8
24.1
6.9
2.6
* Surge Tank Effluent,
** Primary Settler Effluent.
per liter of sewage treated as.seen in Table 22. Solids produced per mg of
BOD5 removed, on the other hand4 ,did not change significantly. The volatility
of the sludge did not increase in Phase VI as one would have expected con-
sidering the removal of inert solids in the primary settler. The lack of
increase in ML volatility may have been due to the higher Fe3+ content of the
sludge. The BOD5 reduction brought about by primary settling plus FeCl. addi-
tion in Phase VI was 28, 30, and 38 percent, respectively, in the months of
May, June, and July of 1975.
The effect of primary settling assisted by metal addition on sludge production
and SRT is shown in the comparison of Flow Sheet IV (no primary settling) and
Flow Sheet VI (primary settling with FeCl3 addition) data in Table 33 below.
Aeration Pattern*
Several measures were taken with the goal of improving aeration train N re-
moval. These included the following:
1) Cell 11 was converted to anoxic operation to extend the anoxic detention
time of the aeration train. This resulted in the retention of only one
cell, Cell 12, for aerobic polishing following denitrification. This
attempt at extending the anoxic portion of the aeration train had to be
abandoned. One cell at the end of the train was not sufficient to nitrify
all the ammonia nitrogen released during the anoxic part of the cycle.
2) Cell 4 was also converted to an anoxic operating mode, again to increase
the denitrification period. It was found that the first three cells of
the train nitrified all the ammonia nitrogen in the primary effluent.
This was a beneficial, permanent change.
* See Table 14 for plant air flows and aeration cell DO'i
93
-------
TABLE 33. COMPARISON OF SLUDGE PRODUCTION AND ORGANIC
LOAD DATA FOR .FLOWSHEETS IV AND VI .
Parameter
Flow Sheet IV Flow Sheet VI
Solids Production (mg of EAS and final
effluent SS produced per mg of BQD^
removed)
Solids Production (mg of EAS and final
effluent SS produced per liter of
sewage treated)
Liquid EAS Production (liter per
liter of sewage treated)
Solids Residence Time Based on
MLSS (days)
Daily BOD5 Load on MLSS (kg/kg)
1.15
211
0.017
4.7
0.20
1.20
123
0.008
8.0
0.11
3)
An alternating pattern of aeration-mixing was tried in July 1974 with
the idea of promoting some substrate nitrate respiration to occur. After
initially promising results, the success of this trial was not decisive.
The attempt was abandoned after 1 mo. DO in the aeration cells must be
rigidly controlled to assure good denitrification in the anoxic cells.
Too high a DO concentration in an aerobic cell followed by an anoxic cell
will yield an-unfavorably high DO in the anoxic cell and adversely affect
denitrification in that cell. Also, it appeared that the aerobic-anoxic
pattern had a deteriorating effect on denitrifying ability, decreasing
the fraction of facultative anaerobes present. The alternating pattern
used was as follows:
Cell 1
Cell 2 Cell 3
Cell 4 Cell 5
Cell 6
aerobic anoxic aerobic anoxic aerobic anoxic
Cell 7/8
anoxic
Cell 7/8
anoxic
Cell 9
Cell 10 Cell 11 . Cell 12
aerobic anoxic
anoxic
aerobic
4) An attempt was made to increase sludge production in the aeration train
(and associated N removal) by keeping DO concentrations in the aerobic
cells low. This experiment also had no readily discernible success.
Treatment Results [
Final effluent BOD5 and SS residuals decreased to their lowest sustained , ..
levels of the project, 7 and 8 mg/&, respectively, on the average. Effluent.
94
-------
COD increased slightly, however, compared to Flow Sheet IV, 55 mg/£ vs. 49
mg/&, due to a 40 percent increase in residual dissolved COD. Total N re-
moval also deteriorated slightly to approximately 2 percent less than the 80
percent target. The denitrification rate stayed about the same as under Flow
Sheet IV, but N removal via incorporation in EAS fell sharply due to the
lower F/M loading and the resulting lower total EAS production. This decrease
in N removal via EAS production was not fully compensated for by the addi-
tional N removed in the primary sludge. :
A second, very pronounced, change in process behavior was the increase in the
rate of nitrification. Nitrification remained complete, despite the facts
that, compared to Flow Sheet IV, 13.6 percent more unoxidized N entered
the aeration train on a mass loading basis and the initial (as opposed to
polishing) nitrification step was accomplished in three cells instead of four.
Another new phenomenon observed with this .flow sheet was the sizeable re-•
lease of ammonia nitrogen during the anoxic period. Obviously what occurred
here was a shift from adsorbed carbon nitrate respiration to true ENR.
Conclusions
The reaction time provided by Flow Sheet VI was not sufficient, under the
prevailing operating conditions, to provide adequate denitrification of the
increased nitrate nitrogen load on the anoxic zone of the aeration system.
An additional ML detention time of at least 1 hr would have been required for
ENR to be carried to completion. The increased CRT employed with this flow
sheet (8-9 days) significantly enhanced SS and BOD,, removals.
NITROGEN PROFILES: FLOWSHEETS I, IV, AND VI
From'data collected in aeration train profile sampling (see Appendix Tables
B-l to B-7), the N profiles of Figures 23-29 were drawn. These graphs show,
in an idealized way, the concentration changes of the various forms of dis-
solved N for a slug of process water traversing the aeration train. Actually,
these changes appear to occur in the form of concentration jumps due to the
CM nature of the individual compartments. For each cell depicted, two, values
of N concentrations are shown, the influent values at .the left side, the ef-
fluent values at the right side. The influent values were obtained by
analyzing the sample of the preceding cell, the effluent values by analyzing
the cell sample itself. For the profiles of June 12, 1975 (Figure 29 - Flow
Sheet VI), the first sample was taken from a mixing chamber where primary
effluent was admixed to return sludge. These profiles, therefore, reflect
the reactions in the entire aeration train. For the other profile graphs,
the first sample was taken from the first cells; reactions occurring in the
first cell are, therefore, not depicted in these other profile graphs. Solu-
ble, organically bound N is represented by the distance between the TKN and
NH+-N curves.
The bar diagrams of Figures_30-33 indicate via the use of graphic symbols-
changes in NH+-N and NO~+NO,,-N concentrations for the individual cells, de-
picted as nitrification, denitrification, uptake by the biomass, release by
the biomass, and ammonification.
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Shape of Dissolved Total Nitrogen Curves
Figures 23-29 all .show at least one period of concentration increase in the
first half of the process, as follows:
Figure
23
24
25
26
27
28
29
Flow Sheet
IV
IV
IV
VI
Cell in which
increase in
dissolved total
N occurred
4, 5
4, 6
This occurrence indicates solubilization of particulate substrate N, mainly te
NHj-N. A small amount of organically' bound N was also released. The positiot
of this release seems to indicate the efficiency of the aerobic process, an
earlier occurrence tending toward greater efficiency. Note that Cell 3 was
the second aerobic cell in Flow Sheet I but the third aerobic cell in Flow
Sheet IV. This rise in dissolved N w4s apparently due to the interaction of
'biota with particulate nitrogenous matter adsorbed by the biota on contact
with primary effluent or surge tank effluent.
In all profiles except Figure 28, a second rise of dissolved total N occurs
toward the end of the process, due to the release of biomass N as NHT-N.
The ammonia nitrogen is immediately nitrified in the following aerobic cells.
Shape of Bar Diagrams
In aerobic cells, the following reaction combinations are apparent:
1) Decrease of NH.-N not matched by nitrification. The difference is taken
up by the biomass and is indicated by hatching in the graphs.
2) Nitrification not matched by decrease in NH^-N. The difference is due ,to
NHJ~-N released by the biomass or to ammonification, both reactions being
followed by nitrification. This is indicated by stippled areas in the
figures.
In anoxic cells, release of ammonia nitrogen occurs; this is indicated by a
black arrow.
Absorption of Ammonia Nitrogen by Biomass vs. Nitrification
The bar diagrams indicate that absorption may be greater than nitrification
and occurs in the first one or two aerobic cells. Intensity and forward loca-
tion of this phenomenon may be indicative of the rate of aerobic synthesis.
Preference of Biota for Organically Bound Nitrogen
The distance between the TKN and NH.-N curves narrows at the beginning of the
process. No significant increase in distance occurs further down the cells.
Particulate N is utilized very early in the process; most of the particulate
matter in the influent is quickly adsorbed by the biomass.
107
-------
Ammonia Release During Endogenous Nitrate Respiration
Table 34 indicates that the amount of NH.-N released during ENR was generally
much smaller than predicted by stoichiometric theory, which calls for a re-
lease of 0.25 mg NHj-N/mg N gasified, or 25 percent. The highest release
rate encountered was 17 percent. Two profiles for Flow Sheet I exhibit prac-
tically no NHj-N release.
To explain the lack of ammonia nitrogen released, one might hypothesize.as
follows:
a) Adsorbed carbon compounds, or storage carbon not yet assimilated into the
biomass, may have been used as the hydrogen donor. This reaction would
resemble substrate nitrate respiration and would be accompanied by some
sludge production. The release of NH~j~-N would be minimal.
b) Lack of ammonia nitrogen release may not be real. Nitrification may go
on simultaneously with denitrification preventing an increase in iw,
concentration.
may gc
NHT-N
c) The bacterial biomass may contain less nitrogen than indicated by the
formula CJHUO^N, which has been stipulated by Forges et al. (2).
d) The facultative organisms engaged in nitrate respiration may have utilized
some substrate carbon, perhaps deflocculated matter.
The variability of the ammonia nitrogen release observed indicates that more
than one of the factors listed above was involved.
Alkalinity Release During Endogenous Nitrate, Respiration
The theoretical release of alkalinity during ENR is 4.46 mg/mg NO_-N gasified,
3.57 mg of which is due to the reduction pf nitrate nitrogen and 6.89 mg to
the release of ammonia nitrogen by the biomass. All of the five profiles for
which alkalinity data are available (see TaBle 34) show a lesser release of
alkalinity. Three profiles indicate a release near the 3.57 mg level, hinting
at the effect of adsorbed carbon respiration; the other two profiles depict
a release even below the 3.57 mg level, indicating perhaps nitrification
occurring in the anoxic cells.
Alkalinity Destroyed During Nitrification
Table 34 indicates that destruction of alkalinity during nitrification was in
fair agreement with the stoichiometric prediction of 7.14 mg/mg NH.-N oxidized.
Rates of Nitrification ;
The changing rates of nitrification can best be observed by examining the
aerobic portions of the NO~+NO~-N curves. The NHl"-N curves are not suitable
for this purpose because tne decrease in NHJ~-N may have been due to sorption
by the heterotrophic biomass.
108
-------
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The rate of nitrification appears to have been inhibited in the beginning
phase of the process. The extent of this inhibition or retardation seems to
have depended on the overall nitrification efficiency. At high rates of over-.
all efficiency, the retardation was of short duration, not more than 30 min.
This retardation seems to be accompanied by intense sorption of NHJ"-N on part
of the heterotrophs. On the other hand, an oxygen deficiency was never noted
in any of the aerobic cells. One might therefore theorize that the retarda-
tion was due to transport difficulties with respect to ammonia nitrogen, the
heterotrophic organisms competing with the n. for NH^-N and gaining the upper
hand during a short period of the process. In three of the four bar graphs
(Figures 30-33), sorption of NHt-N was greater than nitrification across
the first aerobic cell.
Once this period of retardation was overcome, ,the nitrification curves had
the shape of the Monod profiles illustrated previously in Figure 6. The high-
est rate tended to occur right after' the inhibition period; the rate stayed
nearly constant down to approximately 2 mg/& NHt-N.
The drastic increase in nitrification rates for the profile of June 12, 1975
(Figure 29) reflects the increase of CRT provided for Flow Sheet VI. This
increase is in basic agreement with kinetic theory.
The N profile curves (Figures 23-29) reflect the mg/&/time rates, not these
rates referred to 1 mg/5. MLVSS. The nitrification rates appear as the slope
of the NO-J+ NO^-N profiles for the aerobic cells. It is logical to inspect
the nitrification rates as they appear in the aeration train profiles for it
can be assumed that the active biomass does not change appreciably during one
reaction period. Also, when comparing different profiles with each other, it
should be remembered that the kinetic theory of nitrification in single-sludge
A.S. systems indicates that the mass of n. is independent of MLSS concentra-
tion; it is dependent only on the ammonia nitrogen load, environmental condi-
tions, and the growth rate imposed on the MLSS. The average and highest ni-
trification rates associated with the seven aforementioned profiles of Figures
23-29 are summarized in Table 35, on the bases of both mass/volume/time and
mass/mass/time.
Rates of Endogenous Nitrate Respiration (Denitrification)
In the aeration train profiles (Figures 23-29), ENR reaction rates are given
in terms of mg NOI+NOo-N gasified/liter reaction volume vs. time and appear
as the slope of tne NOr+NOo-N profiles.for the anoxic cells. In Table 35,
rates of denitrification are shown per unit volume of reactor/time and per
unit mass VSS/time.
The significance of the ENR rates observed is considerably diminished by the
variability of the operating conditions .that prevailed. Obviously, ENR rates
are affected by the DO concentration of the process water and, if it occurs,
by the exhaustion of NO^+NOI-N. The latter condition may largely be avoided
by proper utilization of compartments. Most cells were kept anoxic by
throttling the air flow to the aeration grids located near the bottom of the
cells. This type of operation, of course, is not the best way to maintain
minimum DO concentrations. With a view to these factors, the highest
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denitrification rates observed, between 0.040 and 0.049 mg NO?+NO"~-N gasified/
mg MLVSS/day, are probably more significant than the mean rates computed.
This range of highest .rates was encountered in all flow sheets profiled.
[
Several other factors that might affect denitrification rates were not investi-
gated including:
a) Effect of adsorbed carbon, if any
b) Effect of water temperature
c) Effect of CRT
d) Effect of the aeration pattern and sludge management procedures on the
share of denitrifying biota in the biomass.
The substantial uniformity of the ENR rates observed nevertheless seems to
indicate that the share of the denitrifying biota was little affected by the
small changes in aeration pattern implemented, by the change in CRT that
occurred in going from Flow Sheet IV to Flow Sheet VI, or by the adsorbed
carbon which probably was present under Flow Sheet I.
Evaluation of Flow Sheets I, IV, and VI
Flow Sheet I provided too little denitrification time; too much NO~-N was left
in the process water at the end of|the anoxic period.
/ ' '
Flow Sheet IV provided too little nitrification time, within the framework
of the prevailing n. growth rate, and too much denitrification time. At the
end of the main nitrification period, a considerable amount of NtTJ~-N was left
in the process water; the denitrification period contained two idle cells in
which practically no reaction occurred.
Flow Sheet VI provided too little denitrification time. A cascade arrangement
for nitrification and subsequent denitrification of the ammonia nitrogen re-
leased during the first anoxic period might have- improved overall N removal
performance.
ANALYSIS OF MONTHLY NITROGEN BALANCES: FLOW SHEETS IV, V, AND VI
Rates of Denitrification
The denitrification rates in Tablei36, obtained by analysis of the mass bal-
ance data in Table 25, appear to be higher on the average than the kinetic
rates developed in Table 35 from the nitrogen profiles of Figures 23-29. This
might be due to denitrification occurring in the final settler. A 2 mg/& de-
nitrification effect attributable to the final settler would explain much of
the difference encountered. Furthermore, it should be noted that the mg/£
shown as denitrified in Table 25 were not actually measured, but rather com-
puted by deduction. They are, therefore, subject to considerable error. The
rates for Flow Sheet IV have been shown for flow-through-times based on both
four and six anoxic compartments. Comparing the denitrification rates for
112
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August 1974 with those for January 1975, a theta value (0) of 1.08 could be
computed, with respect to a reference temperature of 20 C.
1 1 ,
The theta symbol is used here in its usual sense: it denotes the base of an
exponential factor employed to describe the temperature dependency of a bio-
logical reaction rate; a reference temperature has to be selected for which
the exponential factor assumes the value one; equation 50 illustrates the use
of 0 as here defined; in that equation, 0 has the value 1.06 and the refer-
ence temperature selected is 20C. The exponent of 0 is always the difference
between reaction temperature and reference temperature. The type of func-
tional dependency between reaction rate and temperature described by equation
50 was stipulated by Arrhenius-Phelps-Streeter. For a given reaction, 0 may be
determined mathematically if the reaction rates for two temperatures are
known. For such a determination, knowledge of the reaction rate at the ref-
erence temperature is not required.
Sludge Production
Actual sludge production for 12 mo is compared in Table 37 with projected
sludge production, the latter based on a EOD^ yield coefficient of 0.9 and a
biomass destruction factor of 2.15 mg biomass destroyed/mg N removed via ENR.
The results indicate fair agreement, particularly for Flow Sheet IV when the
primary settler was not used.
The BODs yield coefficient of 0.9 mg/mg and the biomass destruction factor
of 2.15 mg/mg were selected in a trial-and-error procedure to produce good
agreement between actual sludge production and sludge production computed .on
the basis of these two biological coefficients. The BOD^ yield factor is
close to the theoretical yield factor developed in Section 4. The biomass
destruction factor of 2.15 mg/mg is considerably smaller than the theoretical
value of 2.69 mg/mg developed in Section .4 for ENR. The difference probably
reflects the effect of adsorbed carbon nitrate respiration. „
Nitrif ier Growth Rates Based on Nitrogen Balances
In the preparation of this table, ,a simplified equation was employed to com- .
pute the average PF n. growth rate corresponding to influent and effluent
ammonia nitrogen concentrations and environmental conditions, to wit:
na
(S0 -
(S0 -
Ks ln
This simplified equation disregards the sludge recycle ratio (r) . The EPA
PDM accepts disregarding r if it i^s under 1.0, and in this case, it was con-
sistently under 0.5. The pH was assumed to be 7.2. Because of the simplifi-
cation described, the symbol y1 was employed instead of the y used in
equation 27 of Section 4 .
The y1 values determined are juxtaposed in Table 38 to the n. growth -rates
imposea on the system via sludge wasting of the HM. Significant discrepancies
114
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116
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will be noted. • •
SOLIDS MANAGEMENT ASPECTS OF FLOW SHEETS IV, V, AND VI
The Relationship Between SVI, RSSS, and MLSS Concentrations; Effect of BOD
Load on RSSS Concentrations
The sludge concentration in the space occupied by the settled sludge at the
end of a 30-min settled volume test (SS_,^) is related to the SVI as follows:
SV30
ss
SV30
10
SVI
(40)
This equation follows immediately from the definition of the SVI and from
geometrical considerations.
SS
SV30
has been regarded traditionally as approximately equal to the RSSS
concentration, provided there is no substantial compaction or dilution of
return sludge in the final settler. Such a condition would prevail if the
final settler were operated with a rather shallow sludge blanket. SS
might be regarded as the maximum safe RSSS concentration that is achievable.
In many situations, it will be more practical to operate with a smaller
RSSS concentration, i.e., with a higher sludge recycle rate than corresponds
t0 SSSV30'
Using Equation 40, Table 39 was prepared. The table indicates that SS
!V30
indeed was approximately equal to RSSS concentration, but that the corre-
lation was generally poor. The March 1975 value of the RSSS concentration
for instance was 139 percent of the corresponding SS
value, while the
„
January 1975 RSSS concentration was only 84 percent of the corresponding
The RSSS concentration hovered around 12,000 mg/Jl for the period during which
the primary settler was bypassed and near 15,000 mg/£ for the period during
which primary settling was employed. Table 39 illustrates the beneficial
effect of lowered organic load and increased SRT on RSSS concentration and
SVI .
Tabel 20 which lists the ratios SV60/SV30 for the 10 mo of August 1974-May
1975 indicates that compaction in the second 30 min of the settled volume
test is considerably larger for sludges with a high SVI (in the 90-110 mA/g
range) - approximately 25 percent - than for sludges with a low SVI (under
70 m£/g) - approximately 10 percent.
OPERATING RESULTS: CHLORINE CONTACT CHAMBER/ SECOND-PHASE SETTLER COMBINATION
Baffle cages were installed in the combined chlorine contact chamber /second-
phase final settler unit (refer to. Figure 11) on June 18, 1975. The data in
Table 40 for the 5-wk period of June 28-August 1, 1975, indicate an average
33 percent reduction in SS from 5.4 mg/& down to 3.6 mg/£ was achieved across
the unit . ,
117
-------
TABLE 39. MONTHLY-AVERAGE RETURN SLUDGE CHARACTERISTICS
FOR FLOW SHEETS IV. V. AND VI
Month
Aug.
Sept.
Oct.
Nov.
Dec.
Jan.
Feb.
Mar.
Apr.
May
June
July
Year
1974
1974
1974
1974
1974
1975
1975
1975
1975
1975
1975
1975
RSSS
(mg/A)
11,400
11,100
13,300
12,000
13,300
13,100
11,300
12,700
15,000
14,200
14,500
16,600
SVI
(ml/g)
108
91
93
76
64
64
75
110
73
88
68
59
SSSV30
(mg/£)
9,300
11,000
10,800
13,200
15,600
15,600
13,300
9,100
13,700
. 11,400
14,700 •
16,900
SRT Based
on MLSS
(days)
4.4
3.7
5.5
3.8
4.8
6.1
4.5
5.2
6.2
8.1
7.0
9.0
Daily
BOD5 Load
on MLVSS
(kg/kg)
0.35
0.37
0.26
0.34
0.28
0.26
0.28
0.27
0.23
0.17
0.19
0.17
During the 5 wk ending August 1, 1975, the following operating conditions
prevailed: ,
•3
Average daily flow: 629 m /day (166,000 gpd)
Average flow rate: 7.28 £/sec (0.255 cfs)
Average flow velocity taken over the 1.525-m x 1.525-m ,
(5-ft x 5-ft) cross section: 0.0031 m/sec (0.0102 ft/sec)
Average flow-through-time for 4.88-m (16-ft) length: 26 min
It is believed the operation of the subject combination unit could be improved
by using corrugated sheets instead of the flat Plexiglass sheets as baffles.
Using corrugated sheets would drastically cut down the accumulation time of
the solids on the baffles. Solids accumulate on the baffles until a certain
thickness is reached. At that point, the solids slide off; if the accumula-
tion time is too long, a danger exists that the solids will become septic and-
float to the top. Chlorination, of course, retards biological action.
The orifice plates had to be cleaned periodically of scraps of papers and
bits of rags. In order to prevent such a manual operation, a combined second-
phase settler/chlorine contact chamber should be'protected by a travelling
screen.
SLUDGE CHLORINATION
Data generated during 19 batches of sludge chlorination are summarized in
Tables 41, 42, and 43. Characteristics of the underflow from the sludge
118
-------
TABLE 40. EFFECT OF CHLORINE CONTACT CHAMBER/SECOND-PHASE SETTLER
COMBINATION ON SUSPENDED SOLIDS REMOVAL
Date
1975
June 28
29
30
July 1
2
3
4
5
6
7
8
9
10
11
.12
13
14
15
Influent
SS (mg/A)
2.0
5.1
7.3
5.2
3.8
N.AV.
7.9
5.5
6.3
4.5
5.6
6.8
5.0
5.4
5.1
3.8
6.0
4.8'
Effluent
SS (mg/A)
2.6
3.4
3.1
N.AV.
2.7
2.7
1.3
4.7
5.1
3.9
4.7
4.5
4.5
3.7
3.5
3.3
4.4
3.5
Date
1975
July 16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Aug. 1
Ave .
Influent
SS (mg/A')
3.6
4.2
6.2
3.8
6.3
5.1
5.5
6.7
7.6
7.2
4.9
5.8
11.4
5.4
4.3
4.9
6.9
5.4
Effluent
SS (mg/A)
2.7
2.9
2.9
2.7
4.5
3.8
3.9
4.6
5.9
4.5
4.0
3.7
•3.7
4.1
3.1
3.8
3.9
3.6
119
-------
I
dewatering beds for nine of those batches are presented in Table 44.
The batch size varied somewhat according to the solids concentration of the
sludge treated and also according to the sludge storage space available. A
typical batch consisted of 34 m3 (9000 gal) applied to 111 m2 (1200 ft2) of
sand bed, resulting in an average sludge slurry dose of 0.31 m (1 ft). How-
ever, such a depth was never attained because drainage occurred immediately
upon application. At most, approximately 15 cm (6 in.) of chlorinated sludge
slurry were seen standing on the bed. Usually, all visible liquid had drained
away by the morning following application.
The slurry was treated at a rate of approximately 2.5 &/sec (40 gpm). The
weighted average of the chlorine dosage was 830 mg/& or 10 percent of the
dry weight of the sludge chlorinated. The chlorine dosage was adjusted to
produce a pH of 2.3 to 2.8 in the chlorinated slurry. The pH of the unchlori-
nated slurry indicates that considerable nitrification had occurred on,some
batches before treatment.
During chlorination, samples of unchlorinated and chlorinated sludge slurry
were withdrawn and subjected to the tests reflected in Tables 41, 42, and 43.
Glass fiber filters were used to determine some of the parameters in Table 44.
There x^ras only a slight reduction in SS due to chlorination, approximately 5
percent. It should be noted in this connection that solids reduction due to
acidification with E^SO^ to pH 2 was found to be between 50 and 60 percent in
unrelated laboratory tests on the waste sludge of this plant.
There was an approximate 2 percent! increase in the VSS concentration, probably
attributable to experimental error.
The increase in filterability, 49 percent on the average, was of course the
most important change in sludge characteristics brought about by sludge chlo-
rination. The~increase of filterability was greater for sludges of a low
initial filterability. The weighted average filterability was increased from
52 to 101 m&/30 sec. The mechanisms of this increase remain to be explained.
The changes in nutrient concentration were somewhat erratic but on the average
negligible, i.e., under 3 mg/& .
The chlorine residual in the chlorinated sludge was approximately 150 mg/& .
A significant increase in the TOC of the sludge supernatant was observed from
a range of 11-150 mg/£ to a range .of 46-188 mg/& .
The sludge dewatering beds underflow did not impose any significant load on
the A.S. system. The following constituent ranges were determined:
SS
VSS
pH
Chlorine Residual
TOC
COD
9-76-mg/fi,
2-43 mg/&
5.2-6.9
0.1-5.3 mg/5,
39-60 mg/Jl
142-241 mg/5,
' 120
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Alkalinity
N02+N03-N
Dissolved Orthophosphorus
42-130 mg/£ as CaCO,
6-36 mg/£ J
1-17 mg/Jl
0.4-1.8 mg/£
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o r-
os oo
rH CM
st st
CM i-H
st rH
st to
rH CO
O to
r-. oo
vo IO
O\ CM
rH
O 'O»
st
rH 10
rH VO
O> vO
Ft pq
H CO
CJ CO
10 vo
rH rH
O O CO
rH rH rH
CM 00 IO
rH H
IO rH VO
rH CM
CO CM r-»
r^ to CM
H
OO Os rH
t*** ON rH
H rH CM
* •
> >
o
§
^*
•K
125
-------
SECTION 9
DESIGN CONSIDERATIONS FOR ACTIVATED SLUDGE SYSTEMS
EMPLOYING COMPARTMENTALIZED AERATION TANKS
BASIC DESIGN ALTERNATIVES
The reactor should be designed as a compartmentalized tank to produce a near
PF hydraulic regime and to allow for flexibility in the aeration pattern. All
biological reactions deviate from the zero order reaction mode in the area of
low substrate or hydrogen acceptor (NO^+NOg-N) concentration, and such low
concentrations are often prescribed under today's more stringent effluent re-
quirements. The PF hydraulic regime is obviously superior to the CM hydraulic
regime for all reactions of an order greater than zero. Aeration pattern
flexibility is important to achieve full reactor utilization in all seasons.
The block arrangement of aerobic-anoxic cells is one of the two basic patterns
of aeration cells that seems to be available, as illustrated previously in
Figure 3. The other arrangement is the alternating zones approach. Flexible
mechanical design will allow the use of either approach in the same reactor.
The alternating zones pattern was not tested for a sufficient period of time
on this project to adequately assess its potential. However, the alternating
zones approach, if used in a reactor of generous overall design, might make
it unnecessary to adjust the aeration pattern to seasonal changes of operating
conditions.
A recommended cell size is 9.1 m x 9.1 m x 9.1 m SWD (30 ft x 30 ft x 30 ft),
equivalent to a cell volume of 754 m3 (202,000 gal). For gentle mixing,, a
power input of 10 W/m3 is required according to Bradley (23). The inlet and
outlet ports have to be near the bottom because the solids are not uniformly
dispersed throughout the tank cells.. The size of these ports should be care-
fully computed so as not to cause undue differences in the SWD of the cells.
DO control equipment should be provided for any cell where aeration equipment
is installed. An excessive DO concentration, over 3 mg/£ , will impair the
efficiency of the following anoxijc cell.
i • . "
A large sludge recycle rate will depress the substrate gradient in a compart-
mentalized reactor; this is kinetfLcally disadvantageous because the average
substrate concentration in a PF reactor determines its removal rate. On the
other hand, a high recycle rate often makes management of the solids in the
final settler easier.
Exclusive of the aeration system itself,'a decision must be made whether to
provide either primary settling or flow equalization or both. To cope with
load fluctuations, the designer has the choice, in many cases, between a
126
-------
larger aeration tank and flow equalization. In a PF aerobic-anoxic reactor,
extension of flow-through time up to a certain point will not cause the re- .
lease of nutrients nor deterioration of the effluent via deflocculation,
assuming that P is controlled by metal salt addition; it will, however, re-
sult in decreasing sludge production. The designer should also be cognizant
that flow equalization imposes a certain measure of complexity on the opera-
tion and 'maintenance of a plant.
It is, therefore, recommended that increasing the reactor size be given
priority consideration unless there are other factors beside the secondary
system that can only be resolved by flow equalization. If flow equalization
is not included in the design, a deep secondary settler must be provided to
accommodate diurnal expansion of the sludge blanket. Similar considerations
apply to the design of the primary settler. Another point to cdnsider is that
systems not equipped with primary settling will possess greater N removal
capacity.
In both aeration patterns, the last cell prior to the final settler should be
an aerobic cell to nitrify any ammonia nitrogen released in the preceding
anoxic cells and to purge any nitrogen gas clinging to the floe. If such an
aerobic cell is not provided, settling difficulties may occur.
REACTOR SIZING EQUATIONS
In this discussion, reactor volumes are expressed in terms of sewage detention
times. The.dimension is day. SDT, SDTn,.SDTd, and SDT refer to the entire
reactor, nitrification reactor, denitrification reactor? and purge reactor
respectively. By multiplying sewage detention time values by the daily plant
flow, the. various reactor volumes are obtained. If the plant flow is
expressed as nrVday, plant capacity is calculated as m3, etc. The purge re-
actor serves to nitrify NH+-N released during SDTd. There is no need to de-
termine a reactor size requirement for aerobic respiration/synthesis. That
reaction occurs during nitrification. Many of the kinetic coefficients ap-
pearing in the design equations have been insufficiently researched so far.
The design equations suggested should, therefore, be used only to determine
design parameters for a pilot plant. The design of a municipal plant should
be preceded by fairly large-scale pilot plant studies, preferably on the site
of the proposed facility. Values of kinetic coefficients suggested on the '
basis of this project are listed in the following subsection which presents a
design example.
Consistent with Section 4 and the EPA PDM, no decay coefficient for nitrifiers
is used in the reactor design equations presented in the following paragraphs'
however, a decay coefficient (b) for the heterotrophic biqmass is employed in
the conventional way to account for biomass destruction through auto-oxidation
in.'aerobic cells.
Equations 41 to 46 are suggested for the computation of SDTn, SDTd, SDT ', and
SDT, to be used in the sequence listed. Except as regards SDTD, the design
equations are the same for both the block and the alternating zones approach.
Under the block approach, the purge reactor has to nitrify all the NH~-N
127
-------
released during SDTd- Under the alternating zones approach, only the NH4-N
released in the last anoxic zone has to be nitrified during SDTp.
[ASC Y -
SDT
X
(1 - n b[d) + b SF
(41)
AX =
SDT V X'
n nr
SF
n
N. - N_ - N - AX n
d U J- .
(42)
(43)
SDT.
kdx
(44)
SDT = N, b, n
d d
SDT = SDT + SDT, + SDT
n d p
.SDT
n
(45)
(46)
where:
SFn
ASC
NC
N,
N.
SF.
1
X
AX
safety factor, nitrification reactor
BODS removed (during SDTn) per liter of sewage treated,
biomass (VSS) destroyed per mg of NO~-N reduced in ENR,
mg/mg
biodegradable nitrogen in the influent, mg/&
Biodegradable njLtrogen in the effluent, mg/5,
decimal nitrogen fraction in the wasted biomass
microorganism decay factor in EOR, day
= NCf-N reduced to gaseous nitrogen during SDTd per liter of
sewage treated, mg/A
= safety factor, denitrif ication reactor (ENR)
= specific ENR reaction rate (mg NO~-N reduced/rag MLVSS/day) ,
' * -1 J
day •*•
= nitrification reactor influent NH^-N concentration, mg/&
= nitrification reactor effluent Nlfr-N concentration, mg/£
= mixed liquor volatile suspended solids concentration (bio-
mass concentration in the ML), mg/&
- Net biomass production (mg VSS synthesized less mg VSS
destroyed in EOR and ENR) per liter of sewage treated.
128
-------
Y = yield factor, BOD_ removal (mg VSS produced/mg BOD,.
removed at zero cell residence time), mg/mg
nr
nsl
specific n. growth rate to be imposed on a reactor to
satisfy given effluent requirements, day
specific n. growth rate corresponding to assumed NH.-N con-
centration in effluent of CM purge reactor;, day"!.
To make the mathematics manageable, the small amount of biomass destruction
that occurs in the purge reactor was neglected in the development of the above
equations. The effect of this omission is estimated in the following sub-
section.
Remarks Regarding Kinetic Coefficients and SF,
Regarding b, —
The ENR biomass destruction factor is difficult to measure directly in pilot
plant experiments. However, b, may be determined indirectly by using the
following equation, which follows readily from the definition of b,:
bd =
mg NH.-N released/mg NO.,-N reduced
nitrogen fraction in wasted biomass
(47)
Regarding u —
The calculation of y was discussed at some length in Section 4. If the
nitrification reactor is a PF reactor, S , S-, and r must be given or assumed.
If the nitrification reactor is a CM reactor, only S.. must be known.
Regarding (1 - n b,) —
This expression indicates the stoichiometric efficiency (EFNR) of ENR, which
will vary in accordance with the adsorbed carbon utilized.
ENR
N removed in ENR
NO~-N reduced in ENR
= 1 - n b
(48)
Regarding b —
_-i
A wide range of values for b, from 0.048 - 0.2 day """, is listed in the litera-
ture (3)t (13) (24) (25). The dependency ,of b on temperature is not discussed
in connection with these data listings. This might be due to the fact that b
is usually measured as it manifests itself in the form of net sludge produc-
tion Y' per Equation 49, to wit:
Y'
Y - b
X SDT
r
ASC
(49)
If Y is also dependent on temperature, the temperature dependency of b might
129
-------
not become evident. Some researchers (26) have determined a theta (0) of
1.07 for b, with respect to the Streeter-Phelps version of the Arrhenius equa-
tion. :
Regarding k, —
The product k, b, might be called the anoxic counterpiece of b.
ing equation is suggested as describing the temperature depend
The follow-
dependency of k
, :
d20
. (T-20)
(50)
In other words, a 0 of 1.06 is suggested.
Regarding SFd —
It seems to make little sense to use a large SF^. Heterotrophs are not as
easily inhibited as nitrifiers. The anoxic reactor -is somewhat shielded from
upsetting substances by the preceding aerobic reactor. Also, it is important
to keep the anoxic residence time a? short as possible so as not to damage
the sensitive nitrifiers.
Choice of Design Parameter Values
An analysis of Equations 41 to 46 indicates that X is the only design variable
which may be selected by the designer, once he has chosen the effluent NH^-N
concentration of the nitrification reactor (S.,) and r if a PF reactor is
involved. While the choice of X affects SDT and SDTd, the ratio SDT /SDTd
and the values of AX and N, are not! affectedly X, once r and S^ have been
chosen.
Derivation of Equations ;
Equation 41 —
This equation for SDT was obtained by combining the following equations:
SF AX
(51)
AX n
AX = ASC Y1 - N, b,
d d
X SDT
Y - b
n
ASC
(52)
(53)
(49)
130
-------
where: Y1 = net yield coefficient in nitrification reactor (VSS pro-
duced/mg BOD5 removed taking biomass destruction due to EOR
into consideration), mg/mg.
Equation 51 follows readily from Equations 31 and 34. Equation 52 is a
material balance equation with respect to nitrogen, taken over SDTn and SDTd.
Equation 53 is a material balance equation*for biomass, taken over the same
two reactors-. Equation 49 is the well known equation for sludge production
in an aerobic process, accounting for biomass generation by synthesis and
for biomass destruction by auto-oxidation.
Equation 44 — ' '
This equation expresses the position that ENR can be regarded as a zero order
reaction both with respect to the available NO~-N concentration and the amount
of biomass available for bio-oxidation.
Equation 45 —
This equation for the calculation of SDT was obtained by combining the
following two equations: p
N, b , n
d d
SDT
. P
'V.
nsl
n
N
(54)
N =
Yn
-------
Nitrification reactor:
First denitrification reactor:
First purge reactor:
Second denitrification reactor:
Second purge reactor: ;
•TOTAL: !
SDT = 0.192 day =
SDT = 0.167 day =
SDTpl = 0.020 day =
SDT = 0.159 day =
SDT = 0.020 day =
SDT = 0.558 day or
4.62 hr
4.0.0 hr
0.48 hr
3.82 hr
0.48 hr
13.39 hr
STEP VIII. To check the results of computation Steps II to VI, trace the
fate of the nitrogen forms and the newly formed biomass through
the various zones of the reactor, as illustrated by Table 45.
NOTES (Table 45): . .
(1) For the synthesis reaction which produces 150.00 mg/& new biomass,
12.00 mg/5, of N must be removed from the process water. The reactor in-
fluent contains 10.00 mg/5, of:organic N and 15.00 mg/& of ammonia N.
Obviously, one has to make an assumption as to the shares of these two
forms in the 12.00 mg/£ of N that are metabolized in the synthesis reac-
tion. It has been assumed here that all the influent organic N is metab-
olized (10.00 mg/&) and that the influent ammonia nitrogen contributes
only 2.00 mg/A to the total N'amount needed for synthesis. It is gener-
ally accepted that all particulate matter in a reactor's influent is
very quickly adsorbed by the biomass in an aerobic process. The nitro-
gen profiles of this report indicate that a portion of the dissolved
organic influent nitrogen is removed quickly from the process water,
while the balance of this nitrogen form remains unchanged through the
remainder of the process; apparently this balance can be regarded non-
biodegradable. In this design example, the presence of non-biodegrad-
able N compounds has been disregarded.
(2) Biomass destruction: b X SDT^
(3) A small amount of organic N is first metabolized, then later released
as NH*-N. Due to SF , S1 is practically zero.
(4) 11.02 = 0.022 (3000) (0.167) \
(5) 1.69 = 2.19 - 0.50. The corresponding size of the purge reactor would
be 0.020 day. '
(6) The gasification capacity of the second anoxic reaction is 0.022 (3000)
(0.159) = 10.49 mg/Jl . Due to SF,, only a part of this capacity is
utilized under design conditions.
(7) 1.30 - 1.80 - 0.50. The corresponding size of the purge reactor would
be:
"30 [edit
188 (0.192)
(15 - 0) (1.1
(.015 day = 0.36 hr.
134
-------
w
1
CO
Pi
!><
pq_^
Q EC
[V| t^
o §
PC* i>
P31! PC
^ 6?-
co ci
<, w
CO
CO pt
S co
O CO
M fL.
P3 CJ
q
Q Pi
[VT p.
2 Ed
S B
pet H
§ °
g c
E*
P-t tJ
O -, cu cd ^-.
rH 0 Q b
|5 !-l O E
CU O -H ^
13 *
CU x*>
•H =*
M S "bt
CO E
cd O
0
•K
CO J-*.
CO «=?
a & g "M
•H CU 6 E
!a -H *-*
cu
4-1 -K
cd <>-x
!-l o?
1 -H CO "b
& CO
CU
4-1 -K
cd x-s
1 0 co b
4"? 'rl ,0. g
§ CO
CU
CJ ti *
•H JO x-s
S S £°*
CO -rl -t-1 — »
bO «> 6)
0 ^ 'SvS
CO
=
IT
1 —
o
o
rH
J
S
H
-t
M
O VO
O to
O ^i"
10 CO
rH 1
O VO
o r-.
CM CM
r-H 1
VO
ir
4!
O vo VO
t^Jl f^iifc |>>^
CM CM ir
1 + r^
1
o
o .
CD
rH
1
Nitrification Reactor:
Synthesis (1)
Nitrification Reactor:
Biomass destruction (2)
Nitrification Reactor:
Nitrification (3)
*s
ir
p.
^.
-sf
CM
o\
VO
IO
O
Balance
o
c^
^s
1
CM
O
rH
"t~
O^
r-
|
CM
•o
*
H
^
O\
cs
4-
First Anoxic Reactor:
Gasification of N (4)
First Anoxic Reactor:
Biomass destruction
c
oo
oo
CM
.O
r-
1—1
IO
o
r-
r--
-------
(8) Due to the effect of SF , the overall nitrogen removal result is slightly
better than required: 1^ = Ij8 mg/£ (computed) vs. N, = 2.0 mg/Jl (pre-
scribed). However, the effect of neglecting biomass destruction in the
purge reactors remains to be investigated. AX and N^ in Table 45 differ
by minute amounts from the values computed under Steps III and IV, re-
spectively, again due to the effect of SF
n
STEP IX.
Compute the aerobic and anoxic reactor sizes for the same treatment
situation, but for 20 C.
Using the procedures of Steps II to VI, the following values were obtained.
For comparison, the 10 C values are also listed in parentheses.
SDT
n
SDT.
c
SDT
0.105 day (0.192)
0.164 day (0.326)
0.029 day (0.040)
AX = 91.6 mg/j> (72.2)
N, = 15.7 mg/Jl (17.2)
d
Biomass lost in EOR =18.9 mg/& (34.56)
= 0.61 (0.48)
TOTAL 0.298 day (0.558)
The required SDT is 87 percent longer at 10 C than at 20 C, or in other words,
only 53 percent of the reactor volume designed for 10 C is needed for treat-
ment at 20 C. The excess reactor capacity available during higher tempera-
ture periods could be used for biomass destruction. In other words, much
greater safety factors are inherent to summertime operation. Reduction of X
or taking some reactor space out of service are two possible ways of adjust-
ing operations to the higher biological reaction rates that prevail during
the warmer season.
In the preceding discussion, biomass destruction in the purge reactor was
neglected. In the following paragraph, the effect of this omission on over-
all N removal is estimated. ;
In Step VI, the size of the purge reactor was computed to be 0.040 day at
10 C. This SDTp would cause a biomass destruction = b (X) (SDTp) = 0.06
(3000) (0.040) =7.2 mg/5, sewage treated, thereby releasing (biomass de-
stroyed) (n) - 7.2X(0.08) = 0.58 n^g/5, NHJ-N. Half of this amount would be
released in the first section of tihe purge reactor and would be nitrified
instantaneously. In the following second denitrification reactor, these
0.29 mg/& NO^-N would be gasified ;as this reactor zone has excess N reduction
capacity due to its safety factor | (SFd). This gasification is accompanied by
the release of bd (NOg-N) (n) = 2.5 (0.29) (0.08) =0.06 mg/X, NHJ-N resulting
from biomass destruction. The total increase in effluent N would, therefore,
be equal to the NH^-N released and nitrified from biomass destruction in the
second purge reactor plus the NH^-N released in the preceding second denitri-
fication reactor (which would also, of course> be nitrified in the second
purge reactor) = 0.29 + 0.06 = 0.35 mg/£, an insignificant amount partially
offset by the excess removal effect discussed under Step VIII.
136
-------
REFERENCES
3.
4.
5.
6.
7.
8.
9.
10.
Process Design Manual for Nitrogen Control, U.S. Environmental Protec-
tion Agency, Office of Technology Transfer, October 1975.
Forges, N., Jasewiez, L., and Hoover, S. R., "Principles of Biological
Oxidation," In: Biological Treatment of Sewage and Industrial Wastes,
Vol. 1, Ed. by J. McCabe and W. W. Eckenfelder, Jr., Reinhold Publishing
Corporation, New York City, p. 35, 1956.
McCarty, P. L., "Energetics and Bacterial Growth," In: Organic Com-
pounds in Aquatic Environments, Ed. by S. D. Faust and J. V. Hunter,
Marcel Dekker, Inc., New York City, p. 495, 1971. See also:
Christensen, D. B. and McCarty, P. L., "Multi-Process Biological Treat-
ment Model," Water Pollution Control Federation, Vol. 47, p. 2652,
November 1975.
Barnard, J. L., "Biological Nutrient Removal Without the Addition of
Chemicals," Water Research, Vol. 9, p. 485, May/June 1975.
Beer, C. and Wang, L. K., "Activated Sludge Systems Using Nitrate
Respiration - Design Considerations," Journal Water Pollution Control
Federation, Vol. 50, p. 2120, September 1978.
Wuhrmann, K., "Stickstoff und Phosphorelimination, Ergebnisse von
Versuchen im technischen Masstab," Schweiz. Z. Hydrol., Vol. 26, p. 520,
1964.
Private communication with R. E. McKinney, University of Kansas,
Lawrence, Kansas, September 1975.
Christensen, M. H^ .and Harremoes, P., "Biological Denitrif icat.ion in
Water Treatment," Report No. 72-2, Department of Sanitary Engineering,
Technical University of Denmark, Lyngby, 1972.
Brenner, R. C., "Federal Government Activities in Oxygen Activated
Sludge Process Development," In: Applications of Commercial Oxygen to
Water and Wastewater Systems, Ed. by R. E. Speece and J. F. Malina, Jr.,
Proceedings, Water Resources Symposium No. 6, Center for Research in
Water Resources, Austin, Texas,1 p.. 135, 1973.
Beloit - Passavant Corporation Bulletin No. 5300, "Magna Rotor,"
Birmingham, Alabama.'
137
-------
11. Ludzak, F. J. and Ettinger, ML B., "Controlling Operation to Minimize
Activated Sludge Effluent Nitrpgen," Journal Water Pollution Control
Federation, Vol. 34, p. 920, September 1962.
12. United States Patent No. 3,964,998, Issued to J. L. Barnard, June 22,
1976.
13. Lawrence, A. W. and McCarty, P. L., "A Kinetic Approach to Biological
Wastewater Treatment Design and Operation," Technical Report No. 23,
Cornell University Water Resources and Marine Sciences Center, Ithaca,
New York, 1969.
14. "Standard Methods for the Examination of Water and Wastewater," 13th Ed.,
American Public Health Association, 1971.
15. "Methods for Chemical Analysis of Water and Wastes," U.S. Environmental
Protection Agency, Washington, B.C., 1974.
16. Albertson, J. G. et al., "Investigation of the Use of High Purity
Oxygen Aeration in the Conventional Activated Sludge Process.," Water
Pollution Control Research Series Report No. 17050 DNW 05/70., U.S.
Department of the Interior, Federal Water Quality Administration,
Washington, D.C., May 1970.
17. Analysis of Raw, Potable and Waste Waters, Department of the Environment,
H.M.S. Office, London, 1972.
18. Gulp, R. L. et al., Advanced IWastewater Treatment, Van Nostrand
Reinhold Publishers, New York,, New York, 1971.
19. Chudoba, J. et al., "Control[of Activated Sludge Filamentous Bulking,"
Wat;er Research, Vol. 7, p. 1163, August 1973.
20. Setter, L. R., "Modified Sewage Aeration," Sewage Works Journal, July
1943. ;
21. Antonie, R. L. et al., "Operating Experience with Bio-Surf Process
Treatment of Food Processing Wastes," Proceedings, 28th Annual Industrial
Waste Conference, Purdue University, West Lafayette, Indiana, 1973.
22. Mulbarger, M. C., "The Three Sludge Systems of Nitrogen and Phosphorus
Removal," Presented at the 44th Annual Conference of the Water Pollution
Control Federation, San Francisco, California, October 1971.
23. Private communication with P. R. Bradley, Mixing Equipment Company,
Rochester, New York, December 1976.
24. Metcalf & Eddy, Inc., Wastewater Engineering, McGraw Hill, New York City,
1972. ;
25. Kalinske, A. A., "Comparison of Air and Oxygen Activated Sludge Systems,"
Journal Water Pollution Control Federation, Vol. 48, p. 2472, November 1976.
138
-------
26. Wuhrmann, K., "Factors Affecting Efficiency and Solids Production in the
Activated Sludge Process," In: Biological Treatment of Sewage and
Industrial Wastes, Vol. 1, Ed. by J. McCabe and W. W. Eckenfelder, Jr.,
Reinhold Publishing Corporation, New York City, p. 49, 1956.
139
-------
PUBLICATIONS AND PATENTS
PUBLICATIONS :
Beer, C., Wang, L. K., and Hetlingi L. J., "Full-Scale Operation of Plug Flow
Activated Sludge Systems," Journal'of the New England Water Pollution Control
Association, Vol. 9, No. 2, September 1975.
Beer, C., Hetling, L. J., and Wangi, L. K., "Full-Scale Operation of Plug Flow
Activated Sludge Systems," Technical Paper No. 42, New York State Department
of Environmental Conservation, Albany, New York, 1975.
Beer, C., and Hetling, L. J., "Nitrogen Removal and Phosphorus Precipitation
in a Compartmentalized Aeration Tank," Technical Paper No. 32, New York State
Department of Environmental Conservation, Albany, New York, 1974.
Beer, C., and Wang, L. K., "Process Design of Single-Sludge Activated Sludge
Systems Using Nitrate Respiration,!", Technical Paper No. 50, New York State
Department of Environmental Conservation, Albany, i New York, 1977. Presented
at the 49th Annual Meeting of the New York Water Pollution Control Associa-
tion, New York City, January 17-19, 1977; see Ref. 5, p. 137.
Beer, C., "Tests for Nitrifying and Denitrifying Ability of Activated Sludge,"
Bulletin of Environmental Contamination and Technology, Vol. 18, No. 5,
p. 558, 1977.
Beer, C., Bergenthal, J. F., and Wang, L. K., "A Study of Endogenous Nitrate
Respiration of Activated Sludge," I Proceedings, 9th Mid-Atlantic Industrial
Waste Conference, Bucknell University, Lewisburg, Pennsylvania 1977.
PATENTS
United States Patent No. 3,517,810, Liquid Waste Treatment Process, Issued to
C. Beer, June 30, 1970. This patent covers a two-stage activated sludge
process not investigated under this project. The process concept was de-
veloped in the course of preparing this grant application.
140
-------
APPENDICES
A. Derivation of Equation 27 142
B. Data from Aeration Train Profile Samplings ^ 144
Table B-l. Aeration Train Profile Data for Flow Sheet I
(11/14/73) 144
Table B-2. Aeration Train Profile Data for Flow Sheet I
(11/27/73) 145
Table B-3. Aeration Train Profile Data for Flow Sheet I
(12/5/73) 146
Table B-4. Aeration Train'Profile Data for Flow Sheet IV
(9/18/74) 147
Table B-5. Aeration Train Profile Data for Flow Sheet IV
(10/10/74) , 148
Table B-6. Aeration Train Profile Data for Flow Sheet IV
(11/14/74) :...; 149
Table B-7. Aeration Train Profile Data for Flow Sheet VI
(6/12/75) :.-......- 150
141
-------
APPENDIX A
DERIVATION OF EQUATION 27
Equation 27, to wit:
U
(so -
nr
SQ - BI + (1 + r) Ks In
SQ + r
(1 + r)
1) Monod function for growth:
N
y s
max
S)
2) Relationship between growth and substrate removal:
dt
n Vd
3) Monod function for substrate removal:
JL
4) Formulate the derivative of the inverse of the Monod function for sub-
strate removal:
dt
dS
Y /K + S\
n ( s \ _
N \p Sj
^ max '
Y
n
N y
max
(s ) i 1
sJ
5) Integrate dt/dS between S = S. and S = S. to obtain the treatment time
required to transform S. into S-:
n
n
max
N
S. - S, + K In
i 1 s
fV
\*1.
142
-------
6) Express t in terms of y , N, Y , and S. - S, per Equation 23:
"• HH H 1 _L
n
n
7) Combine Steps 5 and 6, eliminating t , Y , and N:
n . n
Si-Sl
na
U
max
/S.'
S. - S. + K In ( -^
x 1 s S
8) Solve for y :
na
U
y (s. - s.)
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-80-154
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
A STUDY OF NITRATE RESPIRATION IN THE ACTIVATED SLUDGE
PROCESS '
5. REPORT DATE
August 1980 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Carl Beer
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
New York State Dept. of Environmental Conservation
50 Wolf Road
Albany, New York 12233
10. PROGRAM ELEMENT NO.
35B1C, D.U.B-124, Task D-1/1C
11. CONTRACT/GRANT NO.
Grant No. 17050 EDL
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research .Laboratory—Cin., OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final, July 1968-Julv 1975
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: Richard C. Brenner (513-684-7657)
16. ABSTRACT • ~ ' '
In an experimental, 570-m3/day (0.15-mgd) activated sludge plant treating domestic
wastewater from a correctional facility, 76 to 87 percent nitrogen removal was
obtained via sludge synthesis and biological denitrification using endogenous H-
donors in a compartmentalized reactor with alternating aerobic and anoxic zones.
Between. 27 and 48 percent of the influent nitrogen was removed by denitrification
and between 37.and 49-percent via sludge synthesis. The process was operated for
8 mo under comprehensive analytical control. Ferric chloride (FeCl3) was used to
enhance phosphorus removal. The lowest winter temperature measured in the aeration
tank was 15.9 C. An in-line surge tank was employed for flow equalization. Primary
settling was not utilized in the first 5 mo of operation during the 1974-75 winter.
A turbid effluent developed in the fifth month of operation, however. This condition
was finally brought under control by adding primary settling to the flow scheme and
dosing FeCl3 to the influent of the primary settler. This change in treatment strat-
egy reduced nitrogen removal from 82 percent to 78 percent by reducing sharply the
amount of nitrogen removed via sludge synthesis. The portion of nitrogen removed
by denitrification was not affected. This type of operation was used for 3 mo.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Grbup
*Sewage treatment, ^Activated sludge pro-
cess, *Nitrification, *Chemical removal
(sewage treatment), Iron chlorides,
Aerobic processes, Chlorination
*Nitrate respiration,
^Compartmentalized reac-
tor, *Denitrification,
Endogenous hydrogen
donor, Anoxic, Sludge
synthesis, Flow equaliza-
tion
13B
8. DISTRIBUTION STATEMENT
Release to Public
19: SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
167
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
151
GOVERNMENT PRINTING OFFICE: 1980--657-165/0124
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