tnvironmenial Protection
Agency
Municipal Environmental
Laboratory
Cincinnati OH 45268
EPA 600 2 79 157
November 1979
and Development
Sequential
NJtrification-
Denitrification in a
Plug Flow Activated
Sludge System
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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 deve10pment 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
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<4
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8
9
Environmental Health Effects Research
Environmental Protection Ter.hnology
Ecological Research
Environmental Monitoring
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Interagency Energy-Environment Research and Development
Special" Reports
Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment. and methodology to repair or prevent en-
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EPA-600/2-79-l57
November 1979
SEQUENTIAL NITRIFICATION-DENITRIFICATION
IN A
PLUG FLOW ACTIVATED SLUDGE SYSTEM
by
James A. Heidman
EPA-DC Pilot Plant
Washington, D.C. 20032
Contract No. 68-03-0349
Project Officer
Irwin J. Kugelman
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGZNCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
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 welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solution
and it involves defining the problem, measuring its impact, and searching for
solutions. The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment, and management
of wastewater and solid and hazardous waste pollutant discharges from
municipal and community sources, for the preservation and treatment of public
drinking water supplies, and to minimize the adverse economic, social, health,
and aesthetic effects of pollution. This publication is one of the products
of that research; a most vital communications link between the researcher and
the user community.
The study summarized in this report demonstrates that the carbon sources
naturally present in municipal wastewater can be effectively utilized to
provide the energy required for the dissimilatory reduction of NO;-N in a
process using a single nitrification-denitrification cycle.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
iii
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ABSTRACT
The use of the carbon sources present in municipal wastewater to provide
the energy required for nitrification-denitrification was evglua~ed on a pilot
plant scale in a simulated plug flow reactor. The majority of this report is
devoted to the results from operation of a nine-pass activated sludge system.
Results from the operation of a four-pass and an eight-pass reactor are also
briefly summarized. The nine-pass reactor received primary effluent from the
District of Columbia wastewater treatment plant. The first two passes and the
last pass were aerated whereas the remaining passes were mechanically mixed.
Nitrification could occur in the aerated passes and denitrification could
occur in the others.
The nine-pass reactor was operated for over a year with nitrification-
denitrification routinely achieved. B~ maintaining a sufficiently low process
loading, nearly all of the ~ncomi~g llli4-N could be oxidized in the first two
passes with most of ~he (N02 + N03)-N subsequently_denit~ified in the next six
passes. Residual NH4-N levels of 0.1 mg/l and (N02 + N03)-N levels of
1.0 mg/l were obtained with both steady state and a diurnal flow cycle. When
th~ loading to the first two passes was sufficiently high to prevent all
NH4-N from being oxidized prior to exiting the second pass, there was a
corresponding rise in the effluent nitrogen residuals. FeC13 addition to the
ninth pass of the system during a portion of the study increased the P removal
to approximately 90% with no discernible impact on the nitrification-
denitrification performance.
Downflow dual media filters were fed clarified effluent during the period
of FeC13 addition. Filter~d effluent quality w~s as follows: BOD=1.5 mg/l;
SS=2 mg/l; P=0.25 mg/l; NH4-N=0.2 mg/l; and (N02 + NO )-N=0.9 mg/l. The
filter with the larger medla produced an effluent qua1ity identical to that
attained with smaller media but run lengths were 50% longer.
Nitrification and denitrification rates measured during laboratory
kinetic studies were found to correlate well with actual process performance.
The length of the initial aeration period exerted a marked impact on the
subsequent denitrification rates. When the aeration period was not excessive,
there was no apparent advantage in utilizing a flow-splitting approach with
part of the primary effluent bypassed directly to denitrification. Accelerated
denitrification rates were obtained in laboratory studies with added KNO
during the period of soluble COD removal from primary effluent. However;
other.studie~ ~ndic~ted that. the soluble COD was normally rem~ved under
aeroblc condltlons In less tlme than required for complete NH4-N oxidation.
iv
-------
The use of chemical addition for the
was studied and chlorine appeared to have
autotrophic nitrifying organisms than did
control of filamentous organisms
fewer adverse effects on the
H202'
This report was submitted in fulfillment of Contract No. 68-03-0349 by
the Government of the District of Columbia under the sponsorship of the
U.S. Environmental Protection Agency. This report covers the period
September, 1974 to July, 1976, and work was completed as of January, 1977.
v
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CONTENTS
iii
iv
viii
Foreword
Abstract
Figures
Tables
Acknowledgments
References
Appendix
x
xiii
l.
2.
3.
4.
5.
6.
1
3
4
5
9
15
15
17
30
67
81
85
7.
Introduction
Conclusions
Recommendations
Background Considerations
Experimental Systems and Procedures
Results
Four-Pass Reactor
Eight-Pass Reactor
Nine-Pass Reactor
Kinetic Studies
Sludge Settling Characteristics
Discussion
93
95
vii
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FIGURES
Number
Page
1
Three general flow schemes for achieving nitrification-
denitrification using internal carbon sources. . . . .
. . . .
7
2
Schematic diagram of the nine-pass reactor used in the present
investigation. . . . . . . . . . . . . . . . . . . . . . . .
. . . .
10
3
Schematic diagram of downflow dual media filter
11
. . . .
. . . .
4
16
Schematic diagram of four-pass oxygen system
5
Laboratory kinetic study of nitrification followed by
denitrification with and without supplemental primary effluent
18
6
Laboratory kinetic study with a single nitrification-
denitrification cycle. . . . . . . . . . . . . . . .
. . . . . . . .
20
7
Laboratory kinetic study with multiple nitrification-
denitrification cycles . . . . . . . . . . . . . . . . .
21
8
Reactor solids levels and effluent TKN and (NO; + NO;)-N levels
from May 28 to July 9, 1976 . . . . . . . . . . . . . . . . . .
31
9 Diurnal flow pattern . . . . . . . . 35
10 Reactor solids levels from July 11 to September 22, 1975 " . . 39
11 Effluent suspended solids from July 11 to September 22, 1975 ' " 41
12
Effluent TKN and (NO; + NO;)-N from July 11 to September 22, 1975 . .
43
13
Reactor solids levels from September 23 to December 2, 1975
. . . . .
45
14
Increase in rate of denitrification with primary effluent
addition. . . . . . . . . . . . . . . . . . . . . . . . .
. . . . .
68
15
Denitrification kinetic rate with recycle solids on May 25, 1976
69
16
Denitrification kinetic rate with recycle solids and primary
effluent on May 25, 1976 . . . . . . . . . . . . . . . . .
. . . . .
70
17
Denitrification kinetic rate with recycle solids on May 28, 1976
71
viii
-------
Number
A-l
18
Denitrification kinetic rate with recycle solids and primary
effluent on May 28, 1976 . . . . . . . . . . . .
. . . .
19
Denitrification kinetic rate with recycle solids after
60 minute's aeration on June 10, 1976 . . . . .
. . . .
20
Nitrification-Denitrification cycle with recycle solids and
primary effluent on June 10, 1976 . . . . . . . . . .
. . . .
21
Nitrification-Denitrification cycle with recycle solids and
filtered primary effluent on June 10, 1976 . . . . . . . . .
. . . .
22
Comparison of denitrification rates using filtered and
unfiltered primary effluent. . . . . . . . . . . . .
. . . .
23
Comparison of soluble COD removal rate and the time required
for nitrification (Test No.1) . . . . . . . . . . . . . . .
. . . .
24
Comparison of soluble COD removal rate and the time required
for nitrification (Test No.2) . . . . . . . . . . . . . . .
. . . .
25
Mixed liquor settling velocity vs. suspended solids concentration
26
SVI vs. suspended solids concentration. . .
. . . .
. . . . . . . .
27
Nitrification and denitrification kinetic rates from laboratory
studies vs. temperature. . . . . . . . . . . . . . . . . . .
Effect of H202 dosage on rate of nitrification in first laboratory
test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A-2 Effect of H202 dosage on rate of nitrification in second laboratory
test . . . . . . . . .
A-3 Effect of Clorox addition on rate of nitrification . .
A-4
Reactor solids and (NO; + NO;)-N levels in a complete mix reactor
during and after Clorox addition. . . . . . . . . . . . . . . . .
ix
Page
72
74
75
76
77
78
79
83
84
87
96
97
99
102
-------
Number
TABLES
1
Summary of Nitrification and Denitrification Kinetic Rates With
and Without Supplemental Primary Effluent. . . . . . . . . .
2
Selected Characteristics for the Eight Pass Reactor from
December 20, 1974 to January 18, 1975 . . . . . . .
. . . . .
3
Selected Characteristics for the Eight Pass Reactor from
January 28 to February 20, 1975 . . . . . . . . . .
. . . . .
4
Selected Characteristics for the Eight Pass Reactor from
March 23 to April 14, 1975 . . . . . . . . . . . . . . . . . . . .
5
Summary of Reduction in Denitrification Kinetic Rates Following
Extended Aeration. . . . . . . . . . . . . . . . . . . . . .
6
(NO; + NO]-)-N Concentrations in the Nine Pass Reactor at Selected
Times on anuary 23 and January 30, 1975 . . . .
7
Nitrification and Denitrification Kinetic Rates in the Nine Pass
Reactor on January 23 and January 30, 1975 .. . . . . . . . . . .
8
Process Characteristics for the Nine Pass Reactor from May 28 to
July 9, 1975 . . . . . . . . . . . . . . .
9 Influent and Effluent Characteristics for the Nine Pass Reactor
from May 28 to July 9, 1975 33
10 Relationships Among Flow Meter, Flow Recorder and Actual Flow
During Operation With a Diurnal Flow . 36
11
Process Characteristics for the Nine Pass Reactor from July 11 to
September 22, 1975 . . . . . . . . . . . . . . . . . . . . . . . .
12
Influent and Effluent Characteristics for the Nine Pass Rector
from July 11 to September 22, 1975 . . . . . . . . . . . . .
13
Comparison of TOC Loading Based on Arithmetic vs. Flow-Proportioned
Averages. . . . . . . . . . . . . . . . . . . . . . . . . .
14
Summaries of Process Characteristics with the Nine Pass Reactor for
Three Time Periods During September-December, 1975 . . . . . . . .
x
Page
19
23
24
25
27
28
29
32
37
38
42
46
-------
Number
15
Influent and Effluent Characteristics for the Nine Pass Reactor
from September 24 to December 2, 1975 . . . . . . . . . . . . .
16
Influent and Effluent Characteristics for the Nine Pass Reactor
from September 24 to October 31, 1975 . . . . . . . . . . . . .
17
Influent and Effluent Characteristics for the Nine Pass Reactor
from October 9 to November 20, 1975 . . . . . . . . . . . . . .
18
Process Characteristics for the Nine Pass Reactor from November 1
to December 2, 1975 . . . . . . . . . . . . . . . . . . .
19
Influent and Effluent Characteristics for the Nine Pass Reactor
from November 1 to December 2, 1975 . . . . . . . . . . . . . .
20
Effect of Filtration on the Clarified Effluent from the Nine
Pass Reactor from October 9 to November 20, 1975 . . . . . . . . . .
21
Filter Operation and Performance
. . . .
. . . .
. . . . .
. . . . .
22
Process Characteristics for the Nine Pass Reactor from December 4-
December 23, 1975 . . . . . . . . . . . . . . . . . . . .
23
Influent and Effluent Characteristics for the Nine Pass Reactor
from December 4-23, 1975 . . . . . . . . . . . . . . . .
24
Process Characteristics for the Nine Pass Reactor from January 16
to February 10, 1976 . . . . . . . . . . . . . . . . . . . . .
25
Influent and Effluent Characteristics for the Nine Pass Reactor
from January 16 to February 10, 1976 . . . . . . . . . . . . .
26
Process Characteristics for the Nine Pass Reactor from February 26
to April 5, 1976 . . . . . . . . . . . . . . . . .
27
Influent and Effluent Characteristics for the Nine Pass Reactor
from February 26 to April 5, 1976 . . . . . . . . . . . . . . .
28
Process Characteristics for the Nine Pass Reactor from April 15
to May 10, 1976 . . . . . . . . . . . . . . . . . .
29
Influent and Effluent Characteristics for the Nine Pass Reactor
from April 15 to May 10, 1976 . . . . . . . . . . . . . .
30
Process Characteristics for the Nine Pass Reactor from June 1 to
July 1, 1976 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
Influent and Effluent Characteristics for the Nine Pass Reactor
from June 1 to July 1, 1976 . . . . . . . . . . . . . . .
xi
Page
47
48
49
50
51
53
54
55
56
58
59
60
61
63
64
65
66
-------
Number
A-l
A-2
32
+ - -
NH4-N, (N02 + NO )-N and COD Concentrations in the Nine Pass
Reactor at Selecied Times on July 1, 1976 . . . . . . . . . . . . . .
33
Summary of Mixed Liquor Settling Velocities from the Last Pass
of the Eight or Nine Pass Reactor. . . . . . . . . . . . . . . . . .
34
Summary of Observed Cell Yields, F/M Ratios and Process SRT's for
Selected Periods. . . . . . . . . . . . . . . . . . . . . . .
+ --
NH4-N and (N02 + N03)-N Levels in a Simulated Plug Flow System
During Clorox Additlon (September 17-18, 1975) ........
+ --
NH4-N and (N02 + N03)-N Levels in a Simulated Plug Flow System
During Clorox Additlon (March 24-25, 1976). . . . . . . . . . .
. . . 100
. . . 101
xii
Page
80
82
89
-------
ACKNOWLEDGMENTS
A project of this duration reflects the efforts of the entire EPA-DC
Pilot Plant staff. Paul Ragsdale supervised the mechanics and instrumentation
personnel. Calvin Taylor served as chief operator. Laboratory analyses were
performed under the direction of David Rubis. Laboratory kinetic studies were
performed by Jerry Ballangee.
The efforts of all of the mechanics, technicians, crew chiefs, operators,
and laboratory personnel are gratefully acknowledged.
xiii
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SECTION 1
INTRODUCTION
Nitrogen removal from wastewater can be accomplished by a number of
alternative biological and/or physical-chemical treatment sequences. The
choice of the most effective process or combination of process sequences can,
of course, only result from a thorough engineering evaluation of the various
options based on the characteristics of the water to be treated in conjunction
with the degree and reliability of treatment required. Options available to
satisfy nitrogen removal criteria have been summarized in considerable length
in a process design manual for nitrogen control (1).
Biological removal of nitrogenous materials in activated sludge systems
beyond that obtaine$ as a ~esult of cellular synthesis can be achieved by
oxidation of the NH4 to NOj-N followed by the dissimilatory reduction of the
nitrate to nitrogen gas (also NO or NO). In the days prior to emphasis on
nutrients in discharge waters, this ptenomenon was often mentioned in the
context of a nuisance associated with rising sludge in the ~econdary clarifiers.
In recent years, however, the dissimilatory reduction of N03-N has been
deliberately exploited as a viable methodology for nitrogen removal. In most
biological denitrification systems an external carbon source such as methanol
has been added to accomplish dissimilatory nitrate reduction. Although this
technique is quite effective and easy to control, the cost of the external
carbon source can be considerable and extra biological sludge is produced. In
an effort to reduce costs, attention has recently been turned to systems
which use internal carbon sources (the organics already in the waste and
endogenous metabolism) for biological denitrification.
The use of internal carbon sources and/or endogenous respiration to
achieve dissimilatory NO; reduction is certainly not a new concept. A number
of investigators have examined alternative flow processes/schemes to achieve
this objective. Ludzack and Ettinger (2) reported on a sequence to accomplish
internal denitrification in 1962. A flow sequence very similar to that
utilized in the present investigation was reported by Wuhrmann in 1964 (3).
A summary of the available literature on biological denitrification was
presented by Christensen and Harremoes (4) and updated through early 1975 by
these authors (5) at the August 1975 IAWPR specialized conference. That
conference was devoted to nitrogen as a water pollutant, and the conference
proceedings (6) contain an excellent compilation of much of the current work
on single stage systems for nitrification-denitrification. The literature
reviews (4,5) conference proceedings (6) and EPA Design Manual (1) provide
considerable information and literature references on biological approaches to
nitrification-denitrification and there is little point in repeating this
1
-------
information
aspects and
be familiar
here. However, a very brief summary of some of the more fundamental
considerations will be presented in Section 4 for those who may not
with the basic details.
In the study reported on here, a pilot plant evaluation of the efficacy
of the system originally proposed by Wuhrmann was conducted. In this system
a plug-flow activated sludge reactor is operated with three zones in series.
In the first, oxidation of exogenous carbon and nitrogen takes place; in the
second reduction of nitrate with oxidation of endogenous or adsorbed carbon
takes place; in the third oxidation of residual carbon and nitrogen is
accomplished.
2
-------
SECTION 2
CONCLUSIONS
1. A multipass reactor can be reliable operated to allow the incoming
ammonia to be oxidized to nitrate at the head of the reactor. When the mixed
liquor is then sent to the anoxic sections of the reactor, denitrification
will occur. A terminally aerated pass/section in the reactor is desirable to
degasify the mixed liquor prior to clarification, and to oxidize any residual
ammonia to nitrate.
2. Use of a nine-pass reactor to provide a single nitrification-
de¥itrification cycle followed by a_final_aeration step produced effluent
NH4-N residuals of 0.1 mg/l and (N02 + N03)-N concentrations of ,~ 1.0 mg/l
when treating District of Columbia primary effluent. These results were
achieved with both steady and diurnal flow patterns.
3. Nitrification and denitrification kinetic rates measured in
laboratory ptudies were found to correlate well with actual process performance.
Laboratory kinetic studies also indicated that bypassing a portion of the
primary effluent directly to denitrification was not needed to insure good
denitrification, provided the length of the initial aeration period was not
excessive. Aeration beyond that needed to achieve nitrification resulted in a
noticeable decline in the subsequent denitrification rate.
4. FeC13 addition directly to the mixed liquor in the last reactor paSS
increased phosphorus removals to near 90%. No detrimental impact on the
nitrification-denitrification performance was observed.
5. When parallel downflow dual-media filters with differing filtering
media were fed clarified effluent, they produced filtered effluents of
identical quality. However the increased run lengths achieved with the larger
media (64 cm of 2.0 mm ES anthracite and 38 cm of 0.9 mm ES silica sand)
clearly indicated that this filter was superior to the one with smaller media
(64 cm of 1.3 mm ES anthracite and 38 cm of 0.65 mm ES silica sand).
6. Low activated sludge settling velocities and high SVI's were
encountered with the single stage system used in this study. These are
typical of results with most single stage systems.
7 -
nuisance
to offer
If chemical addition is to be used for the control of heterotrophic
growths without impacting the nitrifying organisms, chlorine appears
a much greater potential for success than does H 0 .
2 2
3
-------
SECTION 3
RECOMMENDATIONS
The previous results of Wuhrmann (3), Christensen et al. (7), and the
results from the present study clearly indicate that a single nitrification-
denitrification approach can reliably produce high nitrogen removals. Sim-
ilarly a number of other approaches involving internal carbon sources have
also been shown to be effective. A major difficulty is attempting to
extrapolate the particular flow/concentration/temperature characteristics of
a given wastewater into the most effective process configuration for that
particular set of circumstances. Further careful experimentation is needed
to better define the denitrification rates as a function of all the variables
involved. If this could be done, it may be possible to reduce the lO-fold
range of kinetic values considered "typical" of single state systems into
better design procedures for the amount of denitrification capacity needed.
One difficulty with this system was the need for very large clarifiers
because the activated sludge has poor sedimentation properties. During
periods when iron was added to precipitate phosphorus, significant improvement
in clarification was achieved. The use of other weighing agents to improve
clarification in these types of systems should be evaluated.
4
-------
SECTION 4
BACKGROUND CONSIDERATIONS
Oxidation of ammonia to nitrite is accomplished by the chemoautotrophic
Nitrosomonas organisms. The subsequent conversion of the nitrite to nitrate
is the result of the chemoautotrophic Nitrobacter species. Although a number
of heterotrophic bacteria can also oxidize inorganic nitrogen, there is no
indication that they playa significant role in wastewater treatment (8).
The combined result of the nitrogen transformations brought about by
Nitrosomonas and Nitrobacter can be summarized as follows:
+
NH4 + 2 02
~
N03 + 2 H+ + H20
,
The stoichiometric oxyge~ requirement is 4.57
oxidized. Each mg of N03-N formed results in
of 7.14 mg of alkalinity as CaC03.
+
mg of 02 per mg of NH4-N
the corresponding destruction
In the absence of dissolved oxygen, a number of facultative heterotrophic
bacteria commonly present in wastewater treatment systems are able to utilize
NO; as a terminal electron acceptor with the resultant formation of nitrogen
gas (also NO or N20). The electron donor (carbonaceous energy source) can
either be added as an external carbon source such as methanol or one can
utilize a system in which the carbon source naturally present in the waste-
water also serves in the dissimilatory nitrogen reduction p~ocess. The
stoichiometric quantity of alkalinity produced per mg of N03-N reduced to N2
gas is 3.57 mg as CaC03. Hence denitrification partially offsets the
alkalinity loss caused by nitrification.
In municipal and domestic wastewater, the nitrogen entering the treatment
plant is predominantly organic nitrogen and ammonia nitrogen. NO- may be
present in low concentrations in some cases. However in most ins~ances, such
as at the District of Columbia Wastewater Treatment Plant where this study
was conducted, the nitrate initially present has already been reduced by the
time the wastewater arrives at the treatment plant. Hence the normal
situation is that the nitrogen must first be oxidized to NO; before it can be
reduced to NZ gas. It should be noted that t~ere are certaln industrial
waste situatlons where large quantities of N03 and degradable organic
material may be initially present in the wastewater and in this case the
dissimilatory reduction of the NO; to nitrogen gas may be accomplished in an
initial anoxic biological treatment step (9). Alternatively in a municipal
wastewater plant with aerobic sludge digestion there is the likelihood of
5
-------
encountering a waste stream high in N03
for the dissimilatory reduction of this
step should this be desired.
and this also may present an option
material with an anoxic treatment
General process alternatives available to achieve nitrification-
denitrification using internal carbon sources are shown in Figure 1. In
the first process scheme both carbonaceous oxidation and nitrification occur
in the first basin with endogenous denitrification in the second basin. This
general flow sequence mayor may not include a terminally aerated chamber but
some aeration time should be provided to at least degasify the mixed liquor
and improve the sludge settling characteristics. A major advantage of this
process is its' inherent simplicity and ease of operation. An additional
option with this general approach is to bypass a portion of the raw or
primary sewage directly to the denitrification chamber to accelerate the rate
of denitrification. This, of course, results in the introduction of unoxidized
organic compounds and ammonia nitrogen into the process. These reduced
nitrogen forms cannot be removed in the denitrification reactor. The use of
a terminally aerated chamber can allow for the conversion of this residual
nitrogen to nitrate nitrogen and insure the oxidation of any remaining
unmetabolized carbonaceous materials introduced with the bypassed wastewater.
In the ~econd general process sche~e shown in Figure 1, mixed liquor in
which the NH4-N has been oxidized to NO -N is recycled back and mixed with
the incoming sewage in the lead denitriiication reactor. This flow sequence
insures a ready supply of external carbon to accelerate the denitrification
rate in the first reactor but requires recycling of the second basin mixed
liquor at a rate which may be several times that of the incoming flow. The
second basin is operated to provide for nitrification and associated
carbonaceous oxidation. This basin can be followed by additional denitri-
fication and nitrification basins to further reduce the nitrate level froln
the second basin. In this case, reliance is placed on endogenous denitri-
fication for NO; reduction in the second denitrification basin.
In the third general process sequence carbonaceous oxidation, nitri-
fication and denitrification all occur in "one" basin. This an be accomplished
by careful positioning of surface aerators to provide aerobic and anaerobic
zones; by alternating the flow and/or air supply to different basin sections;
or by use of the Pasveer system, the Carrousel plant or the Orbal plant to
provide alternating aerobic and anaerobic zones.
It can be seen that a number of process options are available to achieve
denitrification without reliance on external carbon sources such as methanol.
All of the process schemes discussed above have been employed in actual
practice and the literature reviews by Christensen and Harremoes (4,5) and
the 1975 IAWPR specialized conference proceedings (6) serve as a ready guide
to this information.
There are a few generalizations which can be made concerning all three
of the process schemes presented in Figure 1. No matter what system is
utilized it is necessary to provide a sufficiently long solids retention time
(SRT) to insure the growth of nitrifying organisms, a sufficient aerated
6
-------
1
RAW or PRU1ARY
-----------
(Optional)
PRIMARY
C + N
D
r-,
I I
A
I I
L_.J
RAW or
RECYCLE
2
MIXED
LI~UOR
RAW or
PRIMARY
D
C + N
r-, r-'
, " I
D r-+I A
I " I
L_.J L_...J
RECYCLE
3
PRIMARY
C + N + D
RAVl or
RECYCLE
Figure 1.
Three general flow schemes for achieving
nitrification-denitrification using internal
carbon sources.
7
-------
basin volume at a dissolved oxygen (D.G) level adequate for nitrification to
occur, and an anaerobic basin or anaerobic section for dissimilatory nitrate
reduction. Obviously no matter what flow scheme is considered, the designer
must attempt to reconcile the divarications inherent in combining both
nitrification and denitrification into one process. Long aeration times and
high D.O. levels promote nitrification at the expense of the carbon source
available for denitrification. Alternatively. the anaerobic conditions
necessary for denitrification provide an environment in which the nitrifying
organisms cannot grow. Also as conditions are changed to allow for more and
more unmetabolized carbon source to be present to accelerate the denitrification
rate, there will be a correspondin~ increase in the concentration of NH4-N
which must first be oxidized to NO} prior to it's availability for disslmilatory
reduction. As noted by Christensen et al. (7), a certain amount of brinksman-
ship is needed in order to achieve high nitrogen removal.
Because of the generally favorable economic position of nitrification
and denitrification for nitrogen removal compared to other available
physical-chemical processes, the use of these biological processes would
normally be considered as part of any design where nitrogen removal is
required. In some cases toxicity considerations or the need to provide
nitrogen removal only at certain selected times of the year may provide
sufficient constraints to discount the usefulness of biological processes.
Where this is not the case, a single stage system has the potential of
playing an integral part in the final process design as either the basic
treatment process or as a system component in a more complex nitrogen control
strategy.
8
-------
SECTION 5
EXPERIMENTAL SYSTEMS AND PROCEDUR~S
The experimental systems selected for evaluation in the present study
were adaptations of the first general flow scheme presen~ed ip FjgUre 1. The
actual process configuration that was investigated throughau~most of the
study is shown in Figure 2. The reactor consisted of nine compartments
connected in series. The first eight passes were constructed by making minor
modifications to two side-by-side oxygen activated sludge pilot system
reactors. The ~irst eight passes were of equal size with a total liquid
volume of 6l.3m (16,200 gal). The ninth ~ass was constructed from other
tankage and held a liquid volume of 7.04 m (1860 gal). The first, second,
and ninth passes were aerated by discharging compressed air into 2.5 cm (1 in)
PVC perforated pipe sections placed at the bottom of each reactor pass. The
air flow rate to each pass was controlled manually with a ball valve in each
air line. Mechanical energy for mixing passes 3 thru 8 was supplied by
individual Philadelphia Gear mixers located above each pass and turning a
long mixer shaft with a 30 cm (12 in) impeller. Each of the nine passes was
open to the atmosphere.
Flow from the ninth pass went through a splitter box and on2to two 2
center feed clarifiers each with a cross-sectional area of 7.2 m (78 ft )
based on clarifier diameter. Underflow solids were returned to the head of
the process with variable speed }loyno pumps. Sludge wasting was controlled
by manually diverting each recycle stream to a calibrated drum once or twice
per day depending upon the waste volume desired.
Influent flow consisted of primary effluent pumped with a centrifugal
pump through a magnetic flow meter to the first reactor pass. During the
study with an imposed diurnal flow, a Data-Trak programmer was used in
conjunction with a pneumatically controlled valve to provide the desired flow
pattern. Flow meter accuracy was checked once per week by diverting the
metered flow to a calibrated drum. The actual flow was manually recorded
once per day from a flow totalizer connected to the magnetic flow meter and
the results from the weekly flow meter checks were used to correct the
recorded values when necessary.
During a portion of the study, FeC13 was added to the ninth pass of the
reactor by means of a simple peristaltic pump. Since this portion of the
study was conducted with a steady influent flow, a constant chemical feed
rate was maintained. Also during the period of FeCl addition, a portion of
the effluent from one of the clarifiers was pumped t6 two gravity downflow
filters as shown in Figure 3.
9
-------
I-'
o
D.C.
Primary
Figure 2.
PASS
PASS
1
PASS
PASS
Recycle No.2
PASS
PASS
t:':I
'"Zj
'-rj
PASS
2
3
4
5
6
PASS
PASS
Recycle No.1
7
8
9
t:':I
'"Zj
.""7j
TO FILTERS
(Optional)
Schematic diagram of the nine-pass reactor used in the present investigation.
-------
FLOW CHECK
BOX
INLET
PIPE
J.
15
.,~ em
.: :;:. :.:.:: .;::: ..:.:.::. T
~~~R \.~!1~ f'~Jl~ ~
l "~""':"" .
1~ :~/'""O;:"""~":):' ~
(;~'~m) :yr:")"
AIR WASH
EFFLUENT
- ANTHRAC I TE
(64 em)
--
AIR SPARGER
TO
DRAIN
-
BACKWASH
WATER
Figure 3.
Schematic diagram of downflow dual media filter.
- INTERFACE
FLOWJ:1ETER
CLARIFIER NO.1
EFFLUENT
11
-------
The filters were constructed of 35.6 cm (14 in) diameter clear plexiglass
columns appro2imate12 2.4 m (8 ft) in length, each having a lateral surface
area of 0.1 m (1 ft). Taps were provided at 7:6 cm (3 in) ~nt~rvals to
monitor the differential pressure across the medla. A 0.14 m /mln (5 scfm)
air wash system was installed for use during backwash. For backwashing of
the filters, tap water was pumped from a holding tank upward through the
media and discharged to drain. The support media consisted of approximately
15 cm (6 in) of 1.3 cm (0.5 in) diameter stone, above which was placed 10 cm
(4 in) of 0.3 cm (.125 in) diameter garnet to prevent the overlying sand
from penetrating the support media. The filter media consisted of
approximately 38 cm (15 in) of sand under 64 cm (25 in) of anthracite coal.
As the differential pressure increased across the filter media, the
height of the water increased in the column to maintain constant flow. A
maximum of 3 m (10 ft) of total head was available, although backwash operations
were initiated when the head exceeded 2.5 m (8.3 ft). The backwash sequence
was as follows:
(1)
(2)
(3)
l.min. of air scour at 1.5 m3/min/m2 (5 scfm/ft2).
partial filter drainage to top of media. 3 2
1 min. air2scour with 2 min. low flow, 0.4 m /min/m
(10 gpm/ft ) backwash. 3 7 2
10 min. of high flow, 1.2 m /min/m~ (30 gpm/ft )
backwash.
(4)
Throughout the study samples of mixed liquor from the last reactor pass were
periodically removed and settling tests were run in 2.3 m x 0.15 m (7.5 ft
x 6 inches) diameter stirred columns. The stirring mechanism consisted of
two 0.64 cm (1/4 inch) diameter rods which extended the length of the column
and rotated around the vertical axis at a rate of 15 rph. Settling rates in
which the recycle solids were mixed in varying proportions with the
clarified process effluent were also determined on two occasions.
The process was operated on a 24-hour a day, 7-day a week schedule.
The only interruptions in the normal operating sequence resulted from
mechanical malfunctions and these were normally of short duration. No process
data are presented in this paper from any period with excessive mechanical
malfunctions.
Grab samples of reactor influent and both clarified effluents (and
filter influent and effluents during their operation) were manually taken
every four hours, and grab samples of mixed liquor and recycle solids were
manually obtained every eight hours for the laboratory analyses described
below. The grab samples were composited over a 24-hour period on Tuesday,
Wednesday and Thursday; samples collected on Friday-Saturday and on Sunday-
Monday were composited over the 48-hour period. The single exception to this
was that the samples for BOD~ measurement were always 24-hour composites and
the analysis was always started within a few hours (4-10 hours) after the
last sample for each 24-hour composite had been collected. All samples
were refrigerated at 20C prior to analysis. In addition, all samples except
those taken for BODS or suspended solids analysis were preserved with one
12
-------
drop of H2S04 per 30 ml of sample while they were being held in storage. All
laboratory analyses (except BOD) were performed on a Monday through Friday
schedule. 5
The following analyses were performed in the District of Columbia Pilot
Plant laboratories according to the procedures specified in Standard Methods
(10): suspended solids, volatile suspended solids, BODS' COD and TKN. Also
BODS analyses of effluent samples were performed with nitrate production
inhlbited by the addition of 0.5 mg/l of allyl thiourea (11). The procedures
sp~cified in the EPA Manual (12) were use~ for the determination of (NO; +
N03)-N with a Technicon autoanalyzer. NH -N was measured by a Technicon
analyzer using modifications of the metho~s of Scheiner (13) or Kamphake (14).
The method of Ga!es et_al. (15) w~s used for the determination of total
phosphorus. (NO + N03)-N and NH4-N measurements during laboratory kinetic
studies were bot~ made with Technlcon analyzers following the procedures in
the EPA Manual (12).
In addition to collecting grab samples and compositing them for
subsequent laboratory analysis, the operating personnel also: (a) checked
the mixed liquor dissolved oxygen levels in the aerated passes every four
hours with a portable Delta Scientific field probe and adjusted the air flow
rates as needed to attempt to maintain a D.O. concentration of 2-4 mg/l in the
first, second and ninth passes; (b) obtained selected solids samples for 30-
minute sludge volume determinations in one-liter cylinders; (c) measured
temperature, pH and alkalinity of selected samples; (d) measured the depths
of the sludge blankets in the clarifiers with a photoelectric cell; (e)
checked the FeC13 feed rate during this portion of the study; and (f) recorded
the pressure drop across the filters and backwashed when necessary.
On numerous occasions batch kinetic studies to determine nitrification
and/or denitrification kinetic rates were undertaken in the laboratory with
process solids withdrawn from the recycle stream of the nitrification-
denitrification system. Although the laboratory studies employed varied
methodologies, a few generalizations can be made. A water bath was always
used to insure that the temperature of the culture during the kinetic analysis
remained the same as that which existed in the process at the time. All
nitrification studies were conducted with diffused-air aeration sufficient to
maintain a D.O. > 2.0 mg/l. All denitrification studies were performed in
flexible plastic cube containers which were always filled to the top prior to
putting on the plastic cap. A glass rod was fitted through a hole in the cap
and extended into the container. A large magnet and magnetic stirrer were
used to mix the contents. Samples were withdrawn by squeezing the container
and forcing the contents out through plastic tubing attached to the glass rod.
Clamping the tubing prev~nted any ~ir fr~m flowing back into the container.
Samples withdrawn for NH4-N or (N02 + N03)-N analyses were gravity filtered
through Whatman No.1 paper immediately after collection. Typical filtration
times were 1-2 minutes. Any samples taken for soluble COD analysis were
vacuum filtered through Reeve Angel 984 H Glass Fiber Filters without use of
the cellulose pad backing.
13
-------
Since nuisance heterotrophic growths are characteristic of high SRT
operation with D.C. wastewater, a few preliminary studies were undertaken
to assess the potential usefulness of H202 or HOCl addition to a nitrifying
activated sludge mixed liquor. The objective of these studies was to gain
some idea of the dosages which could be employed to potentially obviate
nuisance growth conditions without impairing the metabolism of the nitrifying
organisms. None of these special studies involved any chemical addition
directly to the single-stage process. Since information on the use of H202
or HOCl in nitrifying systems is scarce, the procedures and results from
these few brief studies have been summarized in the Appendix.
14
-------
SECTION 6
RESULTS
The major objective of this report is to summarize the kinetic and
process data obtained during operation of the nine-pass reactor illustrated
in Figure 2. The system was operated in this mode from May 15, 1975 to
July 2, 1976. Prior to this time the single nitrification-denitrification
approach was examined in two other process configurations and some preliminary
data about possible system performance with flow-splitting approaches was
gathered. The initial process configurations and preliminary data will be
briefly summarized before proceeding to a discussion of the nine-pass reactor.
FOUR-PASS REACTOR
A four-pass oxygen activated sludge system was operated at the pilot
plant during the summer of 1974. The system received D.C. secondary effluent,
lime for pH control to 7.0 in the last reactor pass, and was operated to
provide complete nitrification. At the end of September, the system was
modified as shown in Figure 4. Inlet oxygen was fed to the void space at the
top of the first pass with an external manifold used to transfer the overlying
gas directly to the void space over the fourth pass where it was vented to
atmosphere. No attempt was made to optimize oxygen utilization. The second
and third passes were mechanically mixed. Lime addition was continued to
maintain the pH in the last pass near 7.0. Although an attempt was made to
maintain the D.O. between 2-4 mg/l in the aerated passes, the actual D.O.
level was frequently 10-12 mg/l. This provided far from an optimum system for
a single nitrification-denitrification cycle followed by terminal aeration.
Nonetheless the average process performance from November 3 to December 7, 1974.
resulted in the influent TKN being reduced from an average of 28.4 mg/l to an
effluent TKN value of 1.5 mg/l and effluent (NO; + NO;)-N of 7.2 mg/l. This
represented an overall average nitrogen removal of 7070.
At this time it was felt that there could be considerable merit in
sending 60-80% of the primary effluent to the head of a plug flow biological
process for nitrification with the remaining 40-20% being bypassed to a
denitrification section to provide accelerated denitrification rates. i
sufficiently large terminally aerated chamber could then oxidize the NH -N
introduced by bypassing a portion of the sewage and result in overall n~trogen
removals of 70-80%.
This concept was briefly evaluated in two kinetic studies using recycle
biological solids from the four-pass syst~m. The solids were mixed with
primary effluent and aerated until all NH4-N had been oxidized. Since the lag
15
-------
n.,
- - --1
I
I
02 RECYCLE
LIME
f-'
'"
Figure 4.
GAS TRANSFER
)'
)
~
SLUDGE RECYCLE
EXHAUST GAS
WASTE
SLUDGE
lliill
Schematic diagram of four-pass oxygen system.
-------
time between sample collection and readout from the Technicon autoanal+zer
was about 15-20 minutes, the aeration period necessary for complete NH4-N
oxidation was estimated from the first 3-4 samples and aeration was continued
for a brief period beyond the calculated time required. Following aeration
(D.O. of 2-6 mg/l), the sample was divided into two parts with additional
primary effluent introduced into one of the two sub samples. Each of the two
sub samples was then denitrified in a closed cube container as described in
Section 5. A 25% primary addition corresponds to the addition of 250 ml to
each initial 1000 ml of the primary. In actual practice this would correspond
to splitting the influent flow with 80% going to the head of the process and
20% being added downstream after nitrification was complete. Results from one
of the experiments are shown in Figure 5 and both studies are summarized in
Table 1 (10/29/74 and 10/30/74). In order to centralize this type of kinetic
data, Table 1 includes all results obtained throughout the project from this
kind of experiment.
The first two studies indicated that if the aeration time was not
excessive, the addition of moderate amounts of supplemental primary to
ac~elerate denitrification was not especially advantageo¥s in view of the
NH4-N being introduced at this point. Removal of the NH4-N added to
denitrification with the primary effluent would, of course, require an
additional nitrification-denitrification cycle.
An additional laboratory experiment was conducted in which a single
nitrification-denitrification cycle was compared with several air on-off
cycles where the periods of no dissolved oxygen were selected to try to
maximize the denitrification rate. Results are presented in Figures 6 and 7.
The first denitrification rate in the air cycling system was almost double
that of the alternate system. However, by the third cycle the rate decreased
to less than the rate prevailing in the system with complete nitrification
followed by denitrification. In terms of the overall time requirement for
nitrogen removal, there appeared to be little advantage in going to a complex
air cycling system.
EIGHT-PASS REACTOR
On the basis of these initial experiments, a decision was made to
evaluate a "plug-flow" reactor operated with a single nitrification-
denitrification cycle followed by terminal aeration. On December 10 the
four-pass oxygen activated sludge system was expanded to an eight-pass
system. Air lines were installed for aeration of passes 1, 2, and 8. Flow
from the eighth pass went through a splitter box and then directly to the
two clarifiers (Figure 2). The system was changed to air aeration to provide
better D.O. control over that attainable by manual adjustment of the oxygen
feed rates and also to eliminate the need for lime addition to maintain a
pH > 6.5 in all passes.
The reactor MLVSS were maintained near 3,000 mg/l from mid-December
through February 1975. Since lime was no longer added, a large quantity of
inert solids previously introduced with the lime was slowly wasted from the
system, and the MLSS declined from near 7,000 mg/l to 4,000 mg/l by the end
of January.
17
-------
I-'
00
20
18
.--1
----
00
~
1
(NO; + NO;) - N in Unit With
No Additional Primary
MLVSS = 4660 mg/l
~
Z
10
,-.
1("/
o
Z
+
8
IN
o
Z
'-'
H
o
Z
6
I
+"-'t
;:r::
Z
30
240
330
180
270
300
60
90
120
150
210
Turn, minutes
Figure 5.
Laboratory kinetic study of nitrification followed by denitrification with
and without supplemental primary effluent.
-------
TABLE 1. SUMMARY OF NITRIFICATION AND DENITRIFICATION KINETIC RATES WITH AND WITHOUT SUPPLEMENTAL PRIMARY EFFLUENT.
Denitrification Rate Initial COD Increase
Initial Aeration Time) m1n~ mg(NO; + NO;)-N Ratio of in Denit.
Primary Nitrification hr gMLVSS Primary Eff. Additional Rate With
Initial Effluent RequireJ Rate Without With Vol. Primary Additional
,Temp MLVSS COD f~r mg(NO; + NO;)-N Extra Additional Recycle Effluent Primary
oC mg/l mg/l NH -N Vol. mg/1 %
Date Odi~ation Actual hr . MLVSS Pr ima ry Primary
Rate % Added
10/29/74 '''23 4660 80 <1~0 2.9 1.0 1.2 20 20
10/30/74 22-23 4840 80 < 105 2.7 0.89 1.2 50 35
11/05/74 23 3930 80 90 3.3 0.98
12/19/74 18-20 4100 202 80 85 3.4 1.3 1.5 25 2:1 173 15
01/22/75 16.5 2960 163 80 90 2.7 1.4 1.6 25 2:1 14
01/29/7S 17 2480 135 100 110 2.9 0.90 1.1 25 2:1 135 22
.......
I.() 02/14/75 16 2850 162 90 110 2.0 0.83 1.0 33 2:1 143 20
03/25/75 17 2540 120 90 100 2.8 0.83 0.94 33 2:1 120 13
06/25/75 26 2290 100 30 70 6.7 1.1 1.4 33 2:1 27
09/16/75 24.S 1520 138 40 50 6.9 1.3 1.5 11 3:1 129 15
10/16/75 23 2410 144 40 50 5.5 1.0 1.3 33 122 30
10/22/75 23 2100 208 70 70 4.7 1.5 1.8 33 3:1 202 20
11/20/75 21 2370 248 90 90 3,1 1.1 1.3 33 3:1 253 18
12/19/7S 17 3030 75 80 2.4 0.94 1.1 33 3:1 17
02/20/76 17 2930 70 80 2.3 0.80 1.1 33 2:1 38
03/12/76 17.5 2180 15 90 2.9 1.1 2:1
01/02/16 25.S 21S0 244 40 40 5.7 2.0 2,S 33 2:1 244 25
-------
20
AERATION ~< DENITRIFICATION
11/5/74
Temp. = 230e
1 MLVSS = 3930 mg/l
M 14
--
00
S
. (NO; + NO;) - N
z L'
----
I C")
0 LO
z
+
IC'J
tV 0 8
0 z
'-'
!-<
0
z 6
+--::r-
::r:: 4 +
z NH - N
4
30
270
300
330
minutes
Figure 6.
Laboratory kinetic study with a single nitrification-denitrification
cycle.
-------
20
AIR AIR AIR I AIR
18 ON OFF OFF ON OFF
11/5/74
16 Temp. = 230e
MLVSS = 3800 mg/l
.--1
---
OJ) 14
~
. NH+ - N
z
4
12
r--.
\C'f")
0
Z
+ 10
N IN
0
I--' Z
'--'
8
H
0
Z
I 6
+--1" - -
::r:: (N02 + N03) - N
z
4
30
60
90
120
150
180
210
240
270
300
330
TilIE, minutes
Figure 7.
Laboratory kinetic study with multiple nitrification-denitrification cycles.
-------
Prior to January 18, 1975 the main D.C. treatment plant operated with
all elutriation water and thicke~er overflow r3tu~ned back to. the head of3 .
the plant. This flow was approxlmately 39.4 m /mln (15 mgd) In the 790 m /mln
(300 mgd) plant. After January 18 the District modified the plant flow so
that the elutriation and thickener overflow was sent directly to the head of
the secondary activated sludge system. As a result, the TKN in the primary
effluent available to the pilot plant decreased by an average of 8 mg/l.
Because of this large change in wastewater characteristics and the system
transition characteristics prevailing at this time there is not much general
information to be gained from the average process performance during December
or January. A few system parameters for the 30 day period of December 20-
January 18 are noted in Table 2. The nitrogen removal averaged 70% with
most of the effluent TKN associated with the 20 mg/l of effluent suspended
solids. During this time period there was a great deal of Nocardia production
and the final clarifiers were frequently covered with floating solids. This
is not unique to the single stage process and has been frequently observed
in secondary systems treating D.C. wastewater (16).
From Januar~ 28-February 20, 1975 the process flow was steady and
averaged 171.5 m /day (45,300 gpd). Influent and effluent parameters were
also steady during this period and a few general system characteristics have
been summarized in Table 3. Each of the clarifier recycle streams was
sampled individually and are so differentiated in the Table.
3
From February 21-23, the flow was reduced to 136.3 m /day (36,000 gpd)
because the clarifier bed (sludge blanket) level reached the level of the
effluent weirs. During the last week of February and the first two days of
March digester and elutriation water was periodically sent back to the D.C.
primary clarifiers while new piping was instatled on the main D.C. plant.
This resulted in large temporary surges in NH4-N and BOD loadings and makes
evaluation of composite samples meaningless. This problem was eliminated on
March 3. System operation continued at steady flow until May 15.
Good system performance prevailed from March 25-April 14 and a few
selected data from this period are summarized in Table 4. The heavy
Nocardia concentrations which had been present up to this time produced
enough foam/scum on the surfaces of the stirred passes (3,4,5,6, and 7) to
essentially eliminate oxygen diffusion into the denitrification section of
the reactor. However, during the last two weeks of April and the first two
weeks of May, the Nocardia concentrations decreased to the point where no
foam was present and excessive oxygen transfer into the denitrification
passes resulted in poor nitrogen removals.
The information of primary value obtained during the period of operation
of the eight-pass reactor was that derived from laboratory and/or process
kinetic studies. Because of the usefulness of this information it was decided
to describe the general process operation in the preceeding paragraphs.
As shown in Table 1, several additional laboratory studies were conducted
with recycle solids obtained from the eight-pass reactor. Since previous
studies of this type had been conducted with warm wastewater ( ~ 230C), there
remained the question as to whether a flow-splitting arrangement might not
22
-------
TABLE 2.
SELECTED CHARACTERISTICS FOR THE EIGHT PASS REACTOR
FROM DECEMBER 20, 1974 TO J~NUARY 18, 1975
Parameter
Value
-
3
Influent Flow, m /day
153.3
Influent Flow, gpd
40,500
Total Reactor Detention Time, hrs
9.6
Aerated Reactor Detention Time, hrs
3.6
MLVSS (Standard Deviation), mg/l
3,040 (95)
F/M Ratio, gBOD5 Applied/g MLVSS
0.10
Influent
Effl~lent
BOD, mg/l
124
13
COD, mg/l
262
31
TKN, mg/l
(NO; + NO;)-N, mg/1
28.7
2.4
o
6.0
Temperature, °c
17.6
23
-------
TABLE 3.
SELECTED CHARACTERISTICS FOR THE EIGHT PASS
REACTOR FROM JANUARY 28 TO FEBRUARY 20, 1975
Parameter
3
Influent Flow, m /day
Influent Flow, gpd
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
MLSS (Std. Dev.), mg/l
MLVSS (Std. Dev.), mg/1
F/M Ratio, gBOD5 App1ied/day/g MLVSS
Recycle No.1 VSS (Std. Dev.), mg/1
Recycle No.1 TKN (Std. Dev.), mg/1
Recycle No.2 VSS (Std. Dev.), mg/1
Recycle No.2 TKN (Std. Dev.), mg/l
Percent TKN in Recycle VSS (No.1), %
Percent TKN in Recycle VSS (No.2), %
Influent
BOD, mg/1
COD, mg/1
TKN, mg/1
+
NH4-N, mg/l
(NO; + NO;)-N, mg/1
SS, mg/1
104
225
19.7
15.4
o
89
Temp, °c
16.7
Value
171. 5
45,300
8.6
3.2
4,130 (156)
2,840 (108)
0.10
7,950
745
8,170
787
(256)
(55)
(288)
( 61)
9.4
9.6
Effluent
10.7
27.5
1.7
0.3
2.5
17
24
-------
TABLE 4.
SELECTED CHARACTERISTICS FOR THE EIGHT PASS REACTOR
FROM HARCH 23 TO APRIL 14, 1975
Parameter
3
Influent Flow, m /d~
Influent Flow, gpd
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
MLSS (Std. Dev.), mg/l
MLVSS (Std. Dev.), mg/l
F/M Ratio, gBOD5 Applied/day/ g MLVSS
Recycle No.1 VSS (Std. Dev.), mg/1
Recycle No.1 TKN (Std. Dev.), mg/l
Recycle No.1 P (Std. Dev.), mg/l
Recycle No.2 VSS (Std. Dev.), mg/l
Recycle No.2 TKN (Std. Dev.), mg/1
Recycle No.2 P (Std. Dev.), rng/l
Percent TKN in Recycle VSS (No.1), %
Percent TKN in Recycle VSS (No.2), %
Percent P in Recycle VSS (No.1), %
Percent P in Recycle VSS (No.2), %
Influent
BOD, mg/l
COD, mg/l
TKN, mg/l
+
NH4 - N, mg/l
(N02 + NO;)-N, mg/l
SS, rng/l
Temp, °c
112
225
21. 7
16.1
o
87
16.9
Value
-
161. 3
42,600
9.1
3.4
4,250 (96)
2,890 (117)
0.10
7,110 (470)
713 (104)
266 (23.3)
7,290 (265)
739 (148)
277 (21. 7)
10.0
10.1
3.7
3.8
Effluent
8.5
23.5
1.5
0.2
3.4
11
25
-------
prove necessary under wintertime conditions. In the five laboratory studies
conducted from December 1974 through March 1975 the aeration time was closely
controlled to b.f only slightly in excess of that req~i~ed for "comple;e"
« 0.5 mg/l) NH -N oxidation. In all cases, the add1t1on of 25 or 33% more
primary effluen~ did accelerate the subsequent denitrification rate, but
the increase was only 15-20%. It was felt ~hat this small increase in rate
was not worth the penalty of introducing NH4-N into the third pass of the
eight-pass reactor by splitting the influent flow to both these reactor
passes.
With a perfect plug flow reactor, one could theoretically control the
aeration pe+iod to be just sufficient to complete the oxidati~n ~f.the.
incoming NH -N with the remainder of the tankage used for den1tr1f1cat1on.
Of course, 1n actual practice this is not possible. Therefore, an additional
question at this time was what happened to the subsequent denitrification
rate w~en the initial aeration period was extended beyond the time required
for NH4-N oxidation. This was briefly investigated in the laboratory by
aerating a large sample of recycle solids and primary effluent and trans-
ferring subsamples to closed stirred containers for denitrification at
various times during the aeration period. All results from this type of
laboratory experiment have been centralized in Table 5. Because of a
temperature increase in the unit removed after 110 minutes on February 13
(temperature bath malfunction), the denitrification rate may be somewhat
higher than normal. This study (and the others which will be discussed
later) did indicate that the length of the aeration period was closely
connected with the ensuing denitrification rate.
The last major question remaining at this time was whether or not these
laboratory studies were indicative of what was actually occurring in the
pilot plant system. Samples from each of the eight passes wer.f collected at
var~ous t~mes on January 23 and Ja~uary ~O and analyzed for NH4-N and
~N02 + N03)-N. Results of the (N02 + N03)-N determ~nations are presented
1n Table o. In both cases from 1.5 to 4 mg/l of NH4-N remained unoxidized
in the second pass. It is immediately obvious that aeration of pass 8 was
cre~ting ~erobic conditions/backmixing in pass 7. The increase in measured
(N02 + N03)-N l.fvels between passes 6 and Z was Earalled by a decrease in
the measured NH4-N concentration. The (NO + N03)-N levels in passes 2
and 3 were also the "same" in all cases, w5ich reflected the influent mixed
liquor (to pass 3) at 2-4 mg/l D.O. in addition to any mixing between this
aerated and stirred set of passes. The differences in (NO- + NO-)-N
2 3
levels between passes 1 and 2, 3 and 4, 4 and 5, and 5 and 6, can be used
to calculate system kinetic rates by assuming a series arrangement of
completely mixed reactors. The results of these calculations are summarized
in Table 7. The estimated nitrification kinetic rates of 2.9 and 2.7 mg
N/hr/g VSS agree very closely with the results obtained in the laboratory
st¥dies on January 22 and 29 (Table 1). There was sufficient exogenous
NH4-N l~ft in pass 2 of th~ reactor to treat the kinetic rate in this
system 1ndependently of NH4-N concentration. The denitrification kinetic
rates were also calculated by taking the difference between passes and these
rates ~lso agree well with the denitrification rates without added primary
shown 1n Table 1 for the same time period.
26
-------
TABLE 5. S~~Y OF REDUCTION IN D~NITRIFICATION KINETIC RATES FOLLOWING EXTENDED AERATION
Aeration time, min. Nitrification Denitrification
Initial Rate Rate Initial Ratio
Primary Required
Initial Effluent for mg(NOZ + NO-)-N m~(N02 + NO-)-N Primary Eff. Vol
Temp MLVSS COD NH; - N 1 1 Recycle Vol.
Date °c mg/1 mg/1 Oxi~ation Ac tua1 hr gMLVSS hr . gHLVSS
2/13/75 17-22 110 1.2
16.5 2840 166 90 2.2 2:1
17.0 155 0.67
9/10/75 57 1.9
25 1420 117 38 102 8.6 1.4 3:1
147 1.4
N
'-.I
10/2/75 45 1.3
22.5 1810 37 105 6.1 0.89 3:1
165 0.72
2/26/76 60 0.96
17 3280 60 105 2.2 0.79 2:1
150 0.74
6/25/76 35 1.3
24.5 2270 27 5.8 2:1
95 1.0
-------
TABLE 6. (NO; + NO;)-N CONCENTRATIONS IN THE NINE PASS REACTOR AT SELECTED TIHES ON
JANUARY 23 AND JANUARY 30, 1975
(NO; + N03)-N, mg/1
Date Time Inf. Pass 1 Pass 2 Pass 3 Pass 4 Pass 5 Pass 6 Pass 7 Pass 8
1/23/75 1100 0 4.9 10.2 9.7 7.8
1155 0 6.1 4.6 6.3 6.8
1355 0 4.2 10.1 10.5 8.7 6.8 5.5 6.9 7.5
1530 0 9.9 9.9 7.5 8.2
N
00
1/30/75 1300 0 4.5 9.8 9.4 7.2 4.9 3.2 4.6 4.5
1500 0 4.1 9.4 9.2 7.3 5.0 3.5 4.5 5.0
Date 1/23/75 1/30/75
Average Influent Flow, l/min 121.5 117.3
Total Recycle Flow, l/min 62.4 62.4
Average MLSS, mg/1 4,000 4,080
Average MLVSS, mg/1 2,800 2,765
-------
TABLE 7. NITRIFICATION AND DENITRIFICATION KINETIC RATES IN THE NINE PASS
REACTOR ON JANUARY 23 AND JANUARY 30, 1975
(NO; + NO;)-N Kinetic Rate
Average mg(NO; + NO;)-N
Difference Difference
Date Time Passes mg/1 mg/1 hr g HLVSS
1/23 1100 2-1 5.3 5.6 2.9
1355 2-1 5.9
1/30 1300 2-1 5.3 5.3 2.7
1500 2-1 5.3
1/23 1100 3-4 1.9 1.85 0.96
1355 3-4 1.8
1/23 1355 4-5 1.9 1.9 0.98
1/23 1155 5-6 1.5 1.4 0.72
1355 5-6 1.3
1/30 1300 3-4 2.2 2.05 1.05
1500 3-4 1.9
1/30 1300 4-5 2.3 2.3 1.17
1500 4-5 2.3
1/30 1300 5-6 1.7 1.6 0.82
1500 5-6 1.5
29
-------
Studies of this type were also used to verify that the poor denitrifi-
cation performance during the last two weeks of April and the first two
weeks of May was the result of oxygen transfer into the stirred passes after
the foam/scum layer disappeared. A sample withdrawn from the fifth pass
denitrified in a sealed container at a rate of 0.7 mg N/hr/g VSS but p~ss to
pa~s measurements showed that there was virtually no change in the (N02 +
N03)-N levels in the reactor.
NINE-PASS REACTOR
In an effort to overcome some of the mixing/oxygen diffusion problems,
the system configuration was changed on May 15 to the nine-pass configuration
shown in Figure 2. This eliminated the backmixing/aeration problem between
the seventh and eighth passes. Fortunately, the Nocardia concentration
began to rebuild in the middle of May and the resulting foam/scum in passes
3-7 effectively eliminated the oxygen diffusion problem for the remainder of
the project. Since the mixed liquor exited from the "top" of pass 8, the
scum could not build up on this pass.
3
The system was operated at a steady average flow of 167.3 m /day
(44,200_gpd) !rom May 28 through July 9. Reactor solids and effluent TKN
and (N02 + NO )-N values are shown on a daily basis in Figure 8. Other
system parame~ers are summarized in Tables 8 and 9. The nitrification-
denitrifica~ion performance of the system was excellent with an average
res~dual ~H4-N concentration of 0.1 mg/l and an average residual
(N02 + N03)-N concentration of just 0.75 mg/l. From a practical point of
view, the system delivered as good an effluent quality during this period
as one could realistically hope for with the present flow arrangement.
The MLSS declined from around 4,000 mg/l during the first half of the
period summarized in Table 8 to about 3,400 mg/l during July. Also the
clarifier bed levels exhibited a gradual reduction during June and July. The
system SRT based on the total solids in the nine passes of the reactor was
28 days and it was 9.2 days based on the solids in the aerated passes
(1, 2 and 9) only. The observed net solids production for this period was
0.58 g SS/g BOD5 applied and 0.40 g VSS/g BOD5 applied. In view of the
general decline in reactor solids and the clarifier bed level, these sludge
production numbers reflect some wasting from "storage."
If the influent mass of phosphorus is divided by the effluent plus waste
total mass, the ratio is 1.12. Considering that there was a decline in solids
concentration, one would expect to calculate a ratio slightly less than 1.
There were no difficulties with the influent flow meter during this period
and the deviation of the P mass balance from unity presumably reflects mostly
error in the P determination. The materials balance approach is useful in
single stage nitrification-denitrification since it enables the amount of
nitrogen removed by denitrification to be calculated. If one assumes a
perfect N mass balance, the amount of nitrogen removed through denitrification
averaged 12.9 mg/l. Taking the nitrification rate of 6.7 mg (NO; + NO;)-N/
hr/g MLVSS from 6/25/75 (Table 1) in conjunction with a 79 l/min (21 gpm)
recycle flow and a 117 l/min (31 gpm) influent flow, it can be calculated
that up to 22.7 mg/l of NH4-N could be oxidized (neglecting concentration
30
-------
rl
........
~ 4000
UJ
q
~ 3000
o
UJ
~
~ 2000
u
1.0
H
~
~
i:LI
. . . .
MLSS
. . . .
OTKN
~ (NO; + NO;) - N
0.5
31 4 '3 12 16 20 24 28 2 6 10
MAY ~I( JUNE >'1< JULY >1
DAY, 1975
Figure 8. Reactor solids levels and effluent TKN and (NO; + NO;)-N levels from
May 28 to July 9, 1976.
-------
TABLE 8.
PROCESS CHJL~CTERISTICS FOR THE NINE PASS REACTOR
FROM HAY 28 TO JULY 9, 1975
Parameter
Value or
Average
9.8
3.2
44,200
167.3
19-23
72-87
285
11. 6
3820
2610
250
0.09
9270
1), mg/l 6300
625
231
8790
2), mg/l 5940
587
215
3.7
3.6
9.9
9.9
Standard
Deviation
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, gpd
3
Influent Flow, m /day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
2
Clarifier Overflow Rates, gpd/ft
Clarifier Overflow Rates, m/day
MLSS, mg/l
MLVSS, mg/l
SVI, ml/gm
F/N Ratio, gBOD5 Applied/day/g MLVSS
Recycle Suspended Solids (No.1), mg/l
Recycle Volatile Suspended Solids (No.
Recycle TKN (No.1), mg/l
Recycle P (No.1), mg/l
Recycle Suspended Solids (No.2), mg/l
Recycle Volatile Suspended Solids (No.
Recycle TKN (No.2), mg/l
Recycle P (No.2), mg/l
Percent P in Recycle VSS (No.1), %
Percent P in Recycle VSS (No.2), %
Percent TKN in Recycle VSS (No.1), %
Percent T~~ in Recycle VSS (No.2), %
249
145
10
665
340
73
24
398
252
67
22
32
-------
TABLE 9.
INFLUENT AND EFFLUENT CHARACTERISTICS FOR THE NINE PASS REACTOR
FROM MAY 28 TO JULY 9, 1975
Nean
Influent
Standard
Deviation
Clarifier No.1 Effluent
Standard
Deviation
Mean
Clarifier No.2 Effluent
Standard
Deviation
Mean
Parameter
BOD, mg/l 96 15.5 8.9 1.6 9.8 2.1
Inhibited BOD, mg/1 3.6 1.1 4.3 1.4
COD, mg/l 198 23.8 23.8 4.5 28.0 5.5
w
w SS, mg/1 79 16.6 11.3 2.5 14.1 6.2
VSS, mg/1 60 11. 8 8.0 2.4 9.9 5.5
TKN, mg/1 18.0 2.2 1.3 0.31 1.6 0.44
+
NH4 - N, mg/1 13.0 1.1 0.1 0.08 0.1 0.08
(NO; + NO;)-N, mg/l 0 0.8 0.17 0.7 0.17
Total P, mg/l 4.8 0.59 3.2 0.52 3.3 0.46
Temp., °c 24.5 1.3
-------
dependence at low concentrations) in the first two reactor passes at ~VSS
of 26l0_mg/l.- On July 1 a series of measurements were ~ade of the NH4-N
and (NO + NO )-N levels in each pass. The influent NH4-N concentratlon
during Ehe pe~iod of the measurements was so low that nltrification was
nearly completed in the first pass. The_average denitrification rate !rom
pa2ses 3 to 4 and 4 to 5 (passes with N03-N > 1.0 mg/l) was 1.3 mg (N02 +
NO )-N/hr/g MLVSS and this rate also agrees well with the results of
la~oratory measurements on 6/25 (Table 1).
Because of the excellent system response under steady state flow
conditions, it was decided to place more stress on the system by imposing a
diurnal flow cycle. On July 10, the diurnal flow pattern shown in Figure 9
was imposed on the system. This flow pattern varies f30m 76 l/min (20 gpm)
tb 170 l/min (45 gpm) and averages approximately 170 m /day (45,000 gpd).
The system was operated with a diurnally varying flow until September 22,
1975.
The relationships between the flow meter, the flow recorder and the
actual process flow are summarized in Table 10. There was essentially no
trouble with the Data-Trak system so the metered flow to the system con-
sistently followed the pattern shown in Figure 9. From the initiation of the
diurnal flow through about September 2, there were no major discrepancies
between metered, recorded and actual flow. Since the relationships among
the three values changed at each flow level on any given day, it was
extremely difficult to correct the recorded values and determine the true
flow. 3ven with no major problems during August, the recor~ed flow averaged
162.4 m /day (42,900 gpd) for the first 18 days and 184.7 m /day (48,800 gpd)
for the last 13 days. The flow problem was particularly bad during the
middle of September where the actual flow was 38-45 l/min (10-12 gpm) higher
than the recorded or metered flow. At this time, the flow varied from about
114 to 227 l/min (30 to 60 gpm) although the flow pattern (time of maximum
and minimum flows) continued to follow that shown in F~gure 1. Also at this
time the flow was being underrecorded by around 60.6 m /day (16,000 gpd).
In view of all the difficulties encountered in trying to record the
actual flow while operating with the diurnal pattern, the best approach to
data analysis appeared to be to treat the data as one large block. Operation
over the 74-day period is summarized in Tables 11 and 12. The average
influent flow was determined by using the information in Table 103to arrive
at a "best guess" of the real average flow. The value of 185.5 m /day
(49,000 gpd) was used in all calculations involving flow, e.g. loading,
SRI', etc.
Washington, D.C. experienced a very wet summer in 1975 and stormwater
flows/infiltration comprised a large part of the total plant flow during
this period. The influent BODS only averaged 81 mg/l and the influent TKN
was just 16.9 mg/l for the 74-aay period summarized in Tables 11 and 12.
The variation in reactor MLSS and MLVSS is shown in Figure 10. Each value
represents the average from three separate composite samples (passes 1, 5
and 9) and should represent a realistic average in spite of the diurnal flow.
It can be seen that the solids levels gradually declined until mid-August
34
-------
50
40
160
120
30 ~
-,-1
S S
p.. ---
00 r-I
~ ~
~ ~
o 0
H H
Lv ~ 80 ~
V1 20
10
o
2
4
8
6
Figure 9.
40
10
12
18
20
22
24
14
16
TIME, hours
Diurnal flow pattern.
-------
TABLE 10. RELATIONSHIPS AMONG FLOW METER, FLOW RECORDER AND ACTUAL FLOW DURING
OPERATION WITH A DIURNAL FLOW
Flow, gpm Flow, gpm
Date Meter Recorded Actual Date Meter Recorded Actual
7/10 22 20 23.3 8/25 48 51 47.5
33 32 33.7 30 30 31.8
44 44 42.0 10 8 13.4
7/14 25 23 28.3 9/2 55 58 59.4
10 8 14.9 33 33 35.7
20 19 22.8
7/21 31 30 32.0 9/8 51 53 57.1
41 39 38.8 42 44 48.3
26 25 29.1
7/28 10 6 11.8 9/15 50 53 66
25 22 24.0 41 44 55.5
31 32 43.0
21 21 30.5
8/4 20 18 21.1 9/22 56 58 56.1
30 27 28.1 36 37 38.6
25 24 28.8
8/11 40 38 35.6
19 15 18.4
8/18 50 46 45.7
40 37 38.3
30 27 30.3
20 16 21.8
36
-------
TABLE 11.
PROCESS CHARACTERISTICS FOR THE NINE PASS REACTOR FROM
JULY 11 TO SEPTEMBER 22, 1975
Parameter
Value
or
Average
Standard
Deviation
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, 3
m /day
Influent Flow, gpd
Total Recycle Flow, l/min
Total Recycle Flow, gpm
Clarifier Overflow Rates, m/day
Clarifier Overflow Rates, gpd/ft 2
MLSS, mg/l
MLVSS, mg/l
F/M Ratio,g BODS Applied/day/g MLVSS
Recycle Suspended Solids(No. 1), mg/l
Recycle Volatile Suspended Solids (No.
Recycle TKN (No.1): mg/l
Recycle P (No.1), mg/l
1), mg/l
Recycle Suspended Solids (No.2), mg/l
Recycle Volatile Suspended Solids (No.2), mg/l
Recycle TKN (No.2), mg/l
Recycle P (No.2), mg/l
Percent P in Recycle VSS (No.1), %
Percent P in Recycle VSS (No.2), %
Percent TKN in Recycle VSS (No.1), %
Percent TKN in Recycle VSS (No.2), %
8.8
2.9
185.5
49,000
68-76
18-20
12.8
314
2830
1900
0.12
393
255
7210
4780
1285
825
97
480
188
35
985
7210
4810
615
78
30
500
193
3.9
4.0
10.0
10.4
37
-------
TABLE 12. INFLUENT AND EFFLUENT CHARACTERISTICS FOR THE NINE PASS
REACTOR FROM JULY 11 TO SEPTEMBER 22, 1975
Influent Clarifier No. 1 Effluent Clarifier No. 2 Effluent
Standard Standard Standard
Parameter Hean Deviation Mean Deviation Mean Deviation
BOD, mg/1 81.0 14.2 7.8 2.2 8.8 2.7
Inhibited BOD, mg/1 2.8 1.3 3.4 1.9
COD, mg/1 187 27. Lf 22.1 2.9 25.5 4.4
w SS, mg/1 88 15.5 11. 2 4.9 15.3 5.8
CJ:)
VSS, mg/1 64 12.5 7.4 3.3 10.5 4.7
TKN, mg/1 16.9 2.7 1.4 0.70 1.4 0.49
+
NH4 - N, mg/1 11. 9 2.3 0.1 0.15 0.1 0.14
(NO; + NO;)-N, mg/1 0.88 0.22 0.85 0.22
Total P, mg/1 4.7 0.78 2.9 0.52 2.9 0.39
Temp., °c 26.2 1.1
-------
4000
.-!
--
00
s
w
'"
.
CJ)
o
H
H
o
CJ) 2000
p:::
o
E-i
u
<:
w
p:::
1000
10
1<
..~
. . .
15
20
25
30
4
9
14
19
24
2:'
3
8
13
18
23
JULY
*
AUGUST
;1<
SEPTEMBER
~
DATE, 1975
Figure 10.
Reactor solids levels from July 11 to September 22, 1975.
-------
and then held generally steady for the remainder of the period summarized.
Underflow wasting was varied to maintain the desired MLSS levels and varied
from 757 l/day (200 gpd) from July 11-31 down to no wasting between
August 27-September 8. Using the solids actually deliberately wasted each
day in conjunction with the waste rate for each day yields an average daily
waste for the 74-day period of 2040 g VSS/day. At 49,000 gpd and 9.0 mg/l
VSS in the effluent, the overflow wasting amounted to 1670 g VSS/day. This
indicates that calculations of SRT and sludge production are extremely sensi-
tive to effluent solids levels. The presence of Nocardia caused erratic
solids levels in the effluent as shown in Figure 11. The average SRT was
35 days with net solids production values of 0.37 g SS/g BODS applied and
0.25 g VSS/g BODS applied.
Neither the influent or effluent composite sample volumes were flow
proportioned. Continuous TOC analyses of primary effluent feed were
available during part of September (furnished by W. Schuk) and selected
results from 5 day's analyses are presented in Table 13. The reported TOC
values were those at the times the six daily grab samples for the laboratory
composite sample were taken. It can be seen that there is no difference
between the flow proportioned averages and the arithmetic averages when
following the flow pattern shown in Figure 9.
The daily average effluent TKN and (NO; + NO;)-N values are shown in
Figure 12. The variability in ef*luent TKN reflects the variability in efflu-
ent suspended solids since the NH4-N ~oncen!rations were extremely low at all
times (average of 0.1 mg/l). The (N02 + N03)-N levels averaged 0.9 mg/l over
this 74-day period and once again these res~dual levels were as low as one
can realistically hope to attain with this type of single stage process.
Furthermore the effluent quality was essentially the same as observed at
steady flow, thus indicating that the system could handle reasonable f!ow
vaEiations and still perform well. At nitrifica~ion rates of 7 mg (N02 +
N03)-N/hr/g MLVSS (Table 1), one could accept NH4-N concentrations of 18 mg/l
at 50 gpm and 1900 mg/l VSS and still attain "complete" nitrification prior
to denitrification. Again it should be noted that this calculatio~ neglects
concentration dependent kinetics encountered with low exogenous NH4-N levels.
Two kinetic studies were performed with the recycle solids during the
period of diurnal flow operation. Results are presented in Tables 1 and 5.
Once again it was observed that there was no obvious advantage in switching
to a flow-splitting arrangement, and overaeration beyond that required
for nitrification still resulted in satisfactory denitrification rates for
operation at the warm wastewater temperatures.
On September 23, 1975, the primary effluent flow to the single stage
system was set at a steady 132 l/min (35 gpm). FeC13 addition to the ninth
pass of the reactor+~as initiated with the dosage set at 35 mg/l. This is
equivalent to an Fe dosage of 12.0 mg/l or an Fe:P mole ratio of 1.3 at an
influent P concentration of 5 mg/l. Parallel dual-media filters were placed
downstream from the No.1 clarifier in early October. FeC13 addition was con-
tinued until December 2, 1975. The next period of process and kinetic data
to be :onsidered will summarize the period of FeC13 addition and filter
operat~on.
40
-------
40
CLARIFIER NO. 1
30
20
...-!
-
bD 10
s
.
U)
A
H
H
0
U)
A CLARIFIER NO. 2
.po. w 40
A
t-' Z
W
p....
U)
p 30
U)
E--<
Z
W
p 20
H
~
~
w
10
10
~
15
20
JULY
25
30
~
4
14
AUGUST
24
3
8
18
23
13
9
19
29
>1.(
SEPTEMBER
~
DATE, 1975
Figure 11.
Effluent suspended solids from July 11 to September 22, 1975.
-------
TABLE 13.
COMPARISON OF TOC LOADING BASED ON ARITHMETIC
VS. FLOW-PROPORTIONED AVERAGES
I n f 1 u e n t T 0 C, mg/l
Flow Time D a t e
gpm l/min 9/10 9/11 9/12 9/13 9/17
20 76 0630 53 59 55 54 60
26 98 1030 37 40 37 38 40
45 170 1430 52 43 47 39 43
31 117 1830 65 61 60 64 65
35 132 2230 72 68 59 68 72
30 113 0230 68 71 60 58 69
Arithmetic Average
57.8
57.0
53.0
53.5
58.1
Flow Proportioned Average
58.5
56.4
53.0
53.1
57.6
42
-------
3.5
3.0
2.5
r-I
---
co
S
~ 2.0
~
H
1.5
1.0
.p..
w
r-I
--- 1.5
co
s
~
z 1.0
I
,-...
I ("')
0
z
+ 0.5
I N
0
Z
'-'
18
23
~
10
to<
15
20
JULY
25
30
>f~
4
9
14
AUGUST
24
29
3
~
8 13
SEPTEMBER
19
DATE, 1975
Figure 12.
Effluent TKN and (NO; + N03)-N from July 11 to September 22, 1975.
-------
The FeC13 had an immediate impact on the effluent P concentration
which decreased to < 0.5 mg/l by September 24. There was no noticeable
impact on the nitrification-denitrification cycle. Operation during the
remainder of September and all of October posed no problems. The influent
flow was always near 132 l/min (35 gpm) and the chemical feed rate was very
stable. Placing the chemical feed in the last pass did not depress the mixed
liquor pH below 6.5. As shown in Figure 13, the MLSS increased considerably
during this period. Filters "N" and "p" (arbitrary designations) were placed
in operation on October 6. All effluent from the No.1 clarifier was directed
to an overflowing 208 1 (55 gal) drum from which the filter influents were
pumped at a steady 19 l/min (5 gpm) to each filter. Sample collection was
initiated after the first operating cycle was completed. The filter samples
were composited in accordance with the same schedule as all other influent
and effluent samples.
Operation during November and December 1-2 was not as stable as during
October. By November 18, the clarifier bed levels were very near the surface
and periodic flow reductions from 132 l/min to 113 l/min (35 to 30 gpm) were
made whenever the clarifier bed started to overflow the weirs. This flow
reduction caused the beds to drop back below the effluent weirs and collection
of effluent samples was postponed a few minutes if necessary until the bed
had dropped below the weir. No filter data are reported for any period where
the clarifier bed overflow resulted in a surge of solids onto the filters.
Also during November and December 1-2, the chemical feed rates were somewhat
more erratic as were the effluent P concentrations.
The changes in waste rates, reactor solids concentrations, clarifier bed
levels, flow rate, etc. preclude any period from being considered representa-
tive of steady-state operation. The reactor VSS were deliberately increased
in anticipation of cold wastewater temperatures which did not develop. In
fact, the wastewater temperature was still 20°C at the end of November. The
increase in MLVSS was accompanied by the considerably higher MLSS which
included the effects of the chemical sludge from FeC13 addition.
The system characteristics have been summarized in four separate ways in
Tables 14 thru 19. Very heavy rains at the end of September produced an
abnormally weak wastewater for several days. This is reflected in the low
average influent loading for the period of September 24-0ctober 31. This
period was summarized separately because the flow and chemical doses were
most stable during this time. The 35 mg/l FeCI] dose resulted in an average
residual phosphorus concentration of less than 0.5 mg/l. Even during the
period with somewhat more variability in flow and dosage (November 1-
December 2), the average residual phosphorus concentration was only 0.64 mg/l;
this also reflects the lower Fe:P mole ratio which resulted from the higher
average influent phosphorus concentrations.
Operation during the period of October 9-November 20 has also been
summarized separately since this is the period of good filter operation.
There were enough temporary bed upsets on the No.1 clarifier after
November 20 to make it impossible to calculate solids loadings to the
filters. Results from the filter operation during the 43-day period of
44
-------
6000
5000
r-1
--
co
S
~ 4000
rJ)
Q
H
H
0
rJ)
.j::'- ~
V1 0
H
U
~ 3000
~
MLVSS
2000
rnc:tfb .
25 30 5 10 15 20 25 30 4 9 14 19 24 29 4
~ SEPT >1< OCTOBER ~I< NOVEMBER >r- DEC
DATE, 1975
Figure 13.
Reactor solids levels from September 23 to December 2, 1975.
-------
TABLE 14.
SUMMARIES OF PROCESS CHARACTERISTICS WITH
THE NINE PASS REACTOR FOR THREE PERIODS
DURING SEPTEMBER-DECEMBER, 1975
Parameter
September 24 - December 2 (70 Days)
Value or
Average
Standard
Deviation
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, ggd
Influent Flow, m /day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
Clarifier Overflow Rates,
Clarifier Overflow Rates,
MLSS, mg/l
MLVSS, mg/l
F/M Ratio, g BODS Applied/day/g MLVSS
FeC13 Dose*, mg/l
Fe:P Mole Ratio
September 24 - October 31 (38 Days)
8.4
2.8
51,300
194.2
18-20
68-76
329
13.4
5020
2740
0.09
34.1
1. 35
2
gpd/ ft
m/day
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, g1d
Influent Flow, m /day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
Clarifier Overflow Rates,
Clarifier Overflow Rates,
MLSS, mg/l
MLVSS, mg/l
F/M Ratio, g BODS Applied/day/g MLVSS
FeC13 Dose*, mg/l
Fe:P Mole Ratio
October 9 - November 20 (43 Days)
8.1
2.7
53,300
201. 8
18-20
68-76
342
13.9
4510
2430
0.10
34.7
1. 55
2
gpd/ft
m/day
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, ggd
Influent Flow, m /day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
Clarifier Overflow Rates,
Clarifier Overflow Rates,
MLSS, mg/l
MLVSS, mg/l
F/M Ratio, g BODS Applied/day/g MLVSS
FeC13 Dose*, mg/l
Fe:P Mole Ratio
*Based on Average Influent Flow for Period
8.7
2.9
49,600
187.8
18-20
68-76
320
13.0
5450
2920
0.09
34.9
1.25
2
gpd/ft
m/day
878
471
4.2
817
369
2.0
495
327
4.8
46
-------
TABLE 15. INFLUENT AND EFFLUENT CHARACTERISTICS FOR THE NINE PASS
REACTOR FROM SEPTEMBER 24 TO DECEMBER 2, 1975
Influent Clarifier No. 1 Effluent Clarifier No. 2 Effluent
Standard Standard Standard
Parameter Mean Deviation Mean Deviation N':CdJl Deviation
BOD, mg/1 88.4 16.6 4.8 1.8 4.7 1.3
Inhibited BOD, mg/1 2.8 1.1 2.7 0.72
COD, mg/1 191 34.0 19.2 2.3 20.2 3.3
-I'-
-...J
SS, mg/1 88 18.6 10.9 3.6 12.9 4.7
VSS, mg/1 64 10.0 6.3 2.3 7.2 2.9
+ mg/1 12.3 2.4 0.2 0.20
NH4-N, 0.2 0.20
(NO; + NO;)-N, mg/1 0.8 0.30 0.8 0.26
Total P, mg/1 4.8 1.2 0.52 0.17 0.55 0.16
Temp., °c 21.8 1.2
-------
TABLE 16. INFLUENT AND EFFLUENT CHARACTERISTICS FOR THE NINE PASS
REACTOR FROM SEPTEMBER 24 TO OCTOBER 31, 1975
Influent Clarifier No. 1 Effluent Clarifier No. 2 Effluent
Standard Standard Standard
Parameter Mean Deviation Mean Deviation Mean Deviation
BOD, mg/1 79.1 16.1 4.4 1.2 4.9 1.3
Inhibited BOD, mg/1 2.3 0.55 2.4 0.49
COD, mg/1 175 34.2 18.6 2.0 19.5 2.3
+:-
Cf)
SS, mg/1 84 17.1 10.9 3.54 14.0 3.96
VSS, mg/1 61 9.2 6.0 2.3 7.5 2.3
+ 11. 8
NH4-N, mg/1 2.9 0.2 0.15 0.2 0.19
(NO; + NO;)-N, mg/1 0.8 0.29 0.8 0.28
Total P, mg/1 4.3 1.1 0.43 0.10 0.48 0.12
Temp., °c 22.6 0.50
-------
TABLE 17. INFLUENT AND EFFLUENT CHARACTERISTICS FOR THE NINE PASS
REACTOR FROM OCTOBER 9 TO NOVEMBER 20, 1975
Influent Clarifier No. 1 Effluent Clarifier No. 2 Effluent
Standard Standard Standard
Parameter Mean Deviation Mean Deviation Mean Deviation
BOD, mg/1 91. 2 12.7 4.6 1.7 4.6 1.4
Inhibited BOD, mg/1 2.5 0.9 2.5 0.63
+-- COD, mg/1 206 20.9 19.1 1.9 20.1 2.3
1.0
SS, mg/1 86 13.6 11.0 3.6 13.1 4.9
VSS, mg/1 65 9.3 6.3 2.4 7.3 3.2
+
NH4-N, mg/1 13.0 1.3 0.2 0.23 0.2 0.23
(NO; + NO;)-N, mg/1 0.8 0.36 0.8 0.30
Total P, mg/l 5.4 0.98 0.58 0.17 0.60 0.13
Temp., °c 22.0 0.91
-------
TABLE 18.
PROCESS CHARACTERISTICS FOR THE
NINE PASS REACTOR FROM NOVEMBER 1
TO DECEMBER 2, 1975
Parameter
Value
or
Average
Standard
Deviation
Influent Flow, gpd
3
Influent Flow, m /day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
8.8
2.9
48,900
185.1
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
2
Clarifier Overflow Rates, gpd/ft
Clurifier Overflow Rates, m/day
MLSS, mg/l
MLVSS, mg/l
18-20
68-76
314
12.8
5680
3140
357
205
F/M Ratio,g BODS Applied/day/g MLVSS
Recycle Suspended Solids (No.1), mg/l
0.09
16,100
1062
Recycle Volatile Suspended
(No.1); mg/l
Recycle P (No.1), mg/l
Recycle Suspended Solids (No.2), mg/l
Solids
8800
711
691
80
17,360
1601
Recycle Volatile Suspended Solids
(No.2), mg/l
Recycle P (No.2), mg/l
Percent P in Recycle VSS (No.1)
Percent P in Recycle VSS (No.2)
FeC13 Dose*, mg/l
Fe:P Mole Ratio
9410
711
8.1
793
88
7.6
33.3
1.15
5.0
*
Based on Average Influent Flow for Period
50
-------
TABLE 19.
INFLUENT AND EFFLUENT CHARACTERISTICS
FOR THE NINE PASS REACTOR FROM NOVEMBER 1
TO DECEMBER 2, 1975
Clarifier No. 1 Clarifier No. 2
Parameter Influent Effluent Effluent
Mean Standard Mean Standard Hean Standard
Deviation Deviation Deviation
lJ1 BOD, mg/1 100 7.9 5.2 2.3 4.4 1.2
I--'
Inhibited BOD, mg/1 3.2 1.4 3.0 0.84
COD, mg/1 212 20.1 20.0 2.5 21.0 4.2
SS, mg/1 93 19.6 10.8 3.7 11.5 5.1
VSS, mg/1 68 9.9 6.6 2.4 6.9 3.5
+ 12.7
NH4-N, mg/1 1.1 0.2 0.23 0.2 0.20
(NO; + NO;)-N, mg/1 0.8 0.32 0.7 0.22
Total P, mg/1 5.5 1.0 0.63 0.17 0.64 0.17
Temp., °c 20.8 1.0
-------
October 9-November 20 are summarized in Tables 20 and 21. The No.1 clari-
fier effluent was sampled again after being pumped to the top of the filters
and both results have been summarized in Table 20. The effluent quality from
the two filters was identical. As indicated in Table 21, the average run with
filter "p" was 72 hours with a minimum run length of 50 hours. Average solids
capture per run was also 50% greater than with filter "N." These results are
cansis.tent with previous observations when the two media were compared (17).
It can be seen that an excellent effluent quality was obtained.
There were no problems with FeC13 additi~n in terms_of ni!:rification-
denitrification performance. The effluent NH -N and (NOZ + N03)-N
levels continued to be very low and not signi~icantly different than those
levels observed from June to September during the period of no FeC13 addi-
tion. During the last five days 0t operation considered here (after 65 days
of ~eC13 ~ddition) the residual NH~-N averaged 0.2 mg/l and the effluent
(NO + NO )-N concentration was 0.9 mg/l. The clarifier bed level problem
at the en~ of November (compounded by a 20% underrecording of influent flow
for a week) was minor and would not have existed at just slightly lower
hydraulic loadings. In retrospect, the solids levels were also higher than
needed because the anticipated drop in wastewater temperature did not occur.
Four laboratory studies were also conducted with the recycle solids
during the period of FeC13 addition. The potential advantage of influent
flow-splitting appeared to be minimal (Table 1). The denitrification rate
was again shown to be dependent on the length of the aeration period
(Table 5).
On December 3, 1975, the FeC13 addition was terminated and the influent
flow increased to 132 l/min (35 gpm). At this time the intent was to stress
the system during wintertime operation. Beginning on December 25, the
clarifier bed levels began to drop dramatically and the level in the No.2
clarifier decreased 2.lm (7 ft) over a 3-day period. The system was
examined repeatedly over the next few days but the problem was not discovered
until January 6. At this time, it was found that one of the drive-box gears
on the No. 1 clarifier had worn to the point that the clarifier scraper
mechanism was no longer turning. This was missed in the earlier inspections
of the system since the drive motor was still running as usual. The influent
flow was reduced to 64 l/min (17 gpm) and all process effluent was diverted
to the No.2 clarifier. The No.1 clarifier was pumped down during the
night of the 6th. Examination of the No.1 clarifier on the morning of the
7th revealed that all of the "lost" solids were lying on the bottom of the
clarifier. The visual appearance and odor characteristics of these solids
was such that it was decided to return them to the reactor rather than waste
them to drain. A replacement gear was installed and the flow was increased
to 114 l/min (30 gpm). T~is resulted in a 3000 mg/l increase in reactor
MLSS, and the effluent NH4-N levels which had averaged 4 mg/l from
January 4-6 were reduced to 0.1 mg/l by January 10, 1976.
The process characteristics from December 4-December 23 have been sum-
marized in Tables 22 and 23. The effluent P concentrations slowly rose
over this period from about 1 mg/l on December 4 to near 3 mg/l by
December 23. The wastewater temperatures decreased from 20°C to l6.5°C by
52
-------
TABLE 20.
EFFECT OF FILtRATION ON THE CLARIFIED EFFLUENT
FROM THE NINE PASS REACTOR FROM OCTOBER 9 TO
NOVEMBER 20. 1975
Clarifier No. 1 Filter Filter "N" Filter "p"
Parameter Effluent Influent Effluent Effluent
Mean Std. Mean Std. Mean Std. Mean Std.
Dev. Dev. Dev. Dev.
BOD, mg/1 4.6 1.7 5.0 1.7 1.6 0.86 1.5 0.73
VI
VJ
Inhibited BOD, mg/! 2.5 0.9 2.9 1.0 1.4 0.62 1.4 0.61
S8, mg/! 11.0 3.6 14.8 5.1 2.2 0.77 2.2 0.95
VSS, mg/1 6.3 2.4 8.3 2.8 1.6 0.56 1.6 0.79
P, mg/1 0.58 0.17 0.64 0.19 0.25 0.09 0.25 0.08
+ 0.2 0.23 0.2 0.27
NH4-N, mg/1 0.2 0.20 0.2 0.18
(NO; + NO;)-N~ mg/1 0.8 0.36 0.8 0.31 0.9 0.30 0.9 0.29
-------
TABLE 21.
FILTER OPERATION AND PERFORMANCE
Parameter
Filter "N"
Filter "p"
Number of Runs
22
14
Mean Length of Run (Std. Dev.), hrs
47.5 (9.7)
71.5 (16.2)
Minimum Run Length, hrs
34
50
Maximum Run Length, hrs
68
104
2
Filtration Rate, gpm/ft (cm/min)
5.0 (20.4)
104 (264)
5.0 (20.4)
98 (249)
Mean Headloss to Backwash, inches (cm)
Minimum Headloss to Backwash, inches (cm)
95 (241)
109 (277)
78 (198)
Maximum Headloss to Backwash, inches (cm)
114 (290)
Average Initial Headloss (Std. Dev.),
inches
11.6 (1.4)
29.5 (3.6)
8.7 (1.4)
22.1 (3.6)
Average Initial Headloss (Std. Dev.), cm
2
Average Solids Capture, lb/ft /run
1.50
2.26
2
Average Solids Capture, kg/m /run
7.32
11. 03
Filter "N"
64 cm anthracite
ES = 1. 3 rom
DC = 1. 5
38 cm silica sand
ES = 0.65 rom
DC = 1. 4
Filter "p"
64 cm anthracite
ES = 2.0 rom
DC = 1. 5
38 cm silica sand
ES = 0.9 rom
DC = 1. 4
54
-------
TABLE 22.
PROCESS CHARACTERISTICS FOR THE NINE
PASS REACTOR FROM DECEMBER 4-23, 1975
Parameter
Value
or
Average
Standard
Deviation
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, gpd
Influent Flow, m3/day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
2
Clarifier Overflow Rates, gpd/ft
Clarifier Overflow Rates, m/day
SVI, ml/gm
MLSS, mg/l
MLVSS, mg/l
Total Reactor SRT, days
F/M Ratio, g BOD5 Applied/day/g MLVSS
Recycle Suspended Solids (No.1), mg/l
Recycle Volatile Suspended Solids
(No.1), mg/l
Recycle P (No.1), mg/l
Recycle Suspended Solids (No.2), mg/l
Recycle Volatile Suspended Solids
(No.2), mg/l
Recycle P (No.2), mg/l
Percent P in Recycle VSS (No.1), %
Percent P in Recycle VSS (No.2). %
8.2
2.7
52,700
199.5
19
72
338
13.8
191
5210
3220
11.3
417
167
20
0.10
15,510
931
9590
640
16,300
322
68
456
10,110
656
6.7
6.5
492
77
55
-------
TABLE 23.
INFLUENT AND EFFLUENT CHARACTERISTICS FOR THE
NINE PASS REACTOR FROM DECEMBER 4-23, 1975
Clarifier No. 1 Clarifier No. 2
Parameter Influent Effluent Effluent
Mean Standard Mean Standard Mean Standard
Deviation Deviation Deviation
BOD, mg/1 115 17.1 5.6 1.1 6.0 1.7
Inhibited BOD, mg/1 3.7 0.5 3.9 1.0
\..Jl
0"
COD, mg/1 238 19.6 23.8 3.9 23.3 4.1
SS, mg/1 98 15.1 12.1 7.5 11.4 7.1
VSS, mg/1 76 10.9 6.8 4.3 6.2 4.8
+ mg/1 13.0 0.91 0.3 0.17 0.3 0.12
NH4-N,
(NO; + NO;)-N, mg/1 1.6 0.4 1.5 0.4
Total P, mg/1 5.4 0.46 2.0 0.49 2.0 0.33
Temp.. °c 18.2 0.9
-------
the 23rd. The combinatiQn of a decline in wasteWater temperature and a higher
process loading resulted in a residual (NO; + NO;)-N conc~ntration of 1.6
mg/l. This occurred because the initial aeration period was insufficient to
oxidize all of the NH!-N and this unoxidized fraction was not oxidized until
reaching the terminal aeration chamber.
There was a gradual decline in the MLSS levels during the 20-day period
from December 4-23 as the chemical sludge was slowly wasted from the system.
The volatile suspended solids concentration and clarifier bed levels remained
generally uniform but the calculated 20-day SRT and net VSS production of
0.48 g VSS/g BODS applied may not be very close to the true equilibrium
values at the average loading of 0.10 g BOD applied/g MLVSS. The one
laboratory kinetic evaluation conducted dur~ng December (Table 1) produced
a typical response. A nitrification rate of 2.4 mg N/hr/g VSS, MLVSS of
3220 mg/l, and an influent flow of 139 l/min (36.6 gpm) allow a maximum
(NO; + NO;)-N formation of 14.3 mg/l (undiluted with recycle) in the first
two passes. This was very close to the average influent NH!-N concentration
in the composited samples. Although the hydraulic loading was constant
during this time, the NH+-N loading cycled with the hourly changes in
wastewater strength (Tab1e 13) resulting in insufficient aeration time in
the first two passes for complete NH+-N oxidation during part of each day.
4
The interruption in system operation because of the clarifier drive
failure makes it extremely difficult to interpret the results after the
system was repaired and returned to normal operation. The question that
cannot be answered is whether the period of time in which a substantial
fraction of the biological solids lay in the No.1 clarifier was sufficient
to alter the normal relationships between viability of nitrifying organisms,
viability of heterotrophic organisms, and system MLVSS. Hence the next
period of operation to be summarized must be considered with this question
in mind.
system operation from January l6-February 10 is summarized in Tables
24 and 25. This time frame was selected since the effluent characteristics
and reactor solids were quite uniform during this 26-day period. The
aeration time in passes 1 and 2 was insufficient to oxidize all incoming
NHt-N. The higher than normal P content in the recycle solids indicates
that there were still chemical solids in the system from the FeC13 addition
and of course a substantial fraction of the solids which had lain at the
bottom of the No.1 clarifier. The total reactor SRT was 33 days with net
VSS production of 0.38 g VSS/g BODS applied. The system continued to nitrify
and denitrify well during this cola weather operation, but little more can
be prudently said.
The effluent NH:-N concentration decreased in mid-February to ~ 0.3 mg/l.
The process temperature, influent flow rate and volumetric waste rate were
stable from February 26-April 5, 1976, and operating results from this
period are summarized in Tables 26 and 27. The nitrification rates on
2/20/76 (Table 1) and 2/26/76 (Table 5) were quite close to those seen the
year before on 2/13/75 (Table 5) and 2/14/75 (Table 1) at the same waste-
water temperatures. This would indicate that the response during the
57
-------
TABLE 24.
PROCESS CHARACTERISTICS FOR THE
NINE PASS REACTOR FROM JANUARY 16
TO FEBRUARY 10, 1976
Parameter
Value
or
Average
Standard
Deviation
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, gpd
3
Influent Flow, m /day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
2
Clarifier Overflow Rates, gpd/ft
Clarifier Overflow Rates, m/day
SV I, ml / gm
MLSS, mg/l
MLVSS, mg/l
Total Reactor SRT, days
F/M Ratio, g BODS Applied/day/g MLVSS
Recycle Suspended Solids (No.1), mg/l
Recycle Volatile Suspended
(No.1), mg/l
Recycle P (No.1). mg/l
Recycle Suspended Solids (No.2), mg/l
Solids
Recycle Volatile Suspended Solids
(No.2), mg/l
Recycle P (No.2), mg/l
Percent P in Recycle VSS (No.
Percent P in Recycle VSS (No.
1), %
2), %
9.5
3.1
45,700
173.0
19
72
293
11. 9
182
4.5
196
5380
3660
33
141
0.08
14,370
1022
9720
506
14,190
654
89
801
9580
506
5.2
5.3
504
46
58
-------
TABLE 25.
INFLUENT AND EFFLUENT CHARACTERISTICS FOR
THE NINE PASS REACTOR FROM JANUARY 16 TO
FEBRUARY 10. 1976
Clarifier No. 1 Clarifier No. 2
Parameter Influent Effluent Effluent
Mean Standard Hean Standard Mean Standard
Deviation Deviation Deviation
BOD, mg/1 114 20.5 6.9 3.0 7.6 2.4
\Jl Inhibited BOD, mg/1 4.6 1.8 5.1 1.5
'"
COD, mg/1 230 26.2 26.0 4.8 28.1 8.9
SS, mg/1 98 13.2 11.8 6.1 12.2 7.1
VSS, mg/1 76 13.0 7.5 4.5 7.6 6.2
+ 11. 7 1.8 0.8
NH4-N, mg/l 0.5 0.8 0.4
(NO; + NO;)-N, mg/1 0.3 0.3 1.6 0.4 1.4 0.4
Total P, mg/1 5.5 0.98 2.7 0.36 2.7 0.46
Temp., °c 15.3 0.55
-------
TABLE 26.
PROCESS CHARACTERISTICS FOR THE
NINE PASS REACTOR FROM FEBRUARY 26
TO APRIL 5, 1976
Parameter
Value
or
Average
Standard
Deviation
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, gpd
3
Influent Flow, m /day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
Clarifier Overflow Rates, gpd/ft2
Clarifier Overflow Rates, m/day
SVI, ml/gm
MLSS, mg/l
MLVSS, mg/l
Total Reactor SRT, days
F/M Ratio, g BODS Appliedfday/g MLVSS
Recycle Suspended Solids (No.1), mg/l
Recycle Volatile Suspended
(No.1), mg/l
Recycle P (No.1). mg/l
Recycle Suspended Solids (No.2), mg/l
Solids
Recycle Volatile Suspended
(No.2), mg/l
Recycle P (No.2), mg/l
Recycle VSS % P (No.1)
Recycle VSS % P (No.2)
Solids
10.2
3.3
42,400
160.5
19.3
73
272
11.1
180
4900
3530
12
517
346
35
0.09
13,310
1242
9590
418
874
70
11,160
1764
8060
360
4.4
4.5
1157
90
60
-------
TABLE 27.
INFLUENT AND EFFLUENT CHARACTERISTICS FOR
THE NINE PASS REACTOR FROM FEBRUARY 26 TO
APRIL 5, 1976
Clarifier No. 1 Clarifier No. 2
Parameter Influent Effluent Effluent
Mean Standard Mean Standard Mean Standard
Deviation Deviation Deviation
BOD, mg/1 131 16.6 10.9 3.7 11. 8 5.1
0'\ Inhibited BOD, mg/1 7.2 3.6 7.8 3.9
I-'
COD, mg/1 246 19.5 33.2 11. 6 35.0 10.0
SS, mg/1 103 14.2 14.8 7.6 14.7 8.6
VSS, mg/1 81 9.4 9.7 5.3 9.8 5.9
+ 12.8 0.91 0.3 0.13 0.3 0.13
NH4-N, mg/1
(NO; + NO;)-N, mg/1 1.0 0.33 0.9 0.26
Total P, mg/1 5.6 0.75 3.5 0.53 3.5 0.71
Temp., °c 17.6 0.6
-------
period of February 26-Apr:U 51 1976, shpuld have been "typ;i.cal" and npt
influenced by the clarifier failure at the end of December.
At an average nitrification rate of 2.5 mg (NO; + NO;)-N/hr/g VSS, MLVSS
of 3530 mg/l and an influent flow of 111 l/m~n (29:~ gpm) , one c~ul~. .
potentially oxidize 20.3 mg/l of incoming NH4-N prlor to the ddenltrlfl~a~l~n
sequence. Hence system operation during this period was geare to maxlmlzlng
nitrogen removal through a single nitrificatio¥-denitrificat~on cycle. This
is in fact what occurred and the effluent NH4-N concentratl0n was 0.3 mg/l
, ,
and the effluent (NO- + NO-)-N concentration was < 1.0 mg/l during the period
summarized in Tables226 and 27.
The P content of the recycle solids was still somewhat higher than
normal because of the remaining chemical sludge. The influent mass of
phosphorus divided by the effluent plus waste total mass was 1.13 which is a
reasonably good balance. Net solids production was 0.46 g SS/g BODS applied
and 0.33 g VSS/g BOD applied.
On April 6 the influent flow was increased to a steady rate of 151 l/min
(40 gpm). Flow was stable at this level until May 11 when one of the con-
struction crews on the main D.C. plant severed the power supply to the pilot
plant and all flows and mixing equipment were off for 27 hours. There was
about a 9-day transition period following the flow increase on April 6 in
which the effluent NH4-N level was ~ 1.0 mg/l. Process characteristics were
generally stable from April 15-May 10 and the response during this 26-day
period is summarized in Tables 28 and 29. The loading to the+first aerated
chambers during this period was high enough to prevent all N¥4-N from being
oxidized at this point during the part of the day of high NH4-N concentra-
tions. However, the oxidation was essentially completed in the terminally
aerated chamber with the result that the effluent (NO;+NO;)-N concentration
averaged 1.4 mg/l. No laboratory kinetic studies were conducted during this
period. Previous studies indicate the nitrification rate would have been on
the order of 3 mg (NO; + NO;)-N/hr/g MLVSS, and at the average solids and
flow conditions existlng during this po~tion of the project one could only
expect to oxidize a maximum incoming NH4-N concentration of 14.6 mg/l in the
first two aerated passes of the reactor.
The loss of power on May 11 effectively terminated a defined transition
to steady state operation at the higher loading. Following restoration of
the severed power supply on May 12, the influent flow was set at 132 l/min
(35 gpm) and the system was operated without further incident at constant
flow and waste rates until July 2 when the study was terminated and the
system drained. The brief disruption in system operation had no marked
impact on subsequent system performance since the effluent quality returned
to normal by May 14. The major effort from the 14th to the conclusion of the
study was devoted to several laboratory experiments, and the process was
simply operated to provide a good quality effluent and serve as a source
of biological solids for the laboratory st¥dies. For example, during the
last 31 days_of op~ration, the effluent NH4-N averaged 0.1 mg/l with
effluent (N02 + N03)-N concentrations of 1.1 mg/l (Tables 30 and 31).
62
-------
TABLE 28.
PROCESS CHARACTERISTICS FOR THE
NINE PASS REACTOR FROM APRIL 15
TO MAY 10, 1976
Parameter
Value
or
Average
Standard
Deviation
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
7.1
2.3
Influent Flow, gpd
3
Influent Flow, m /day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
60,600
229
19
Total Reactor SRT, days
F/M Ratio, g BODS Applied/day/g MLVSS
Recycle Suspended Solids (No.1). mg/l
72
390
15.9
4080
3030
26
323
251
2
Clarifier Overflow Rates, gpd/ft
Clarifier Overflow Rates, m/day
MLSS, mg/l
MLVSS, mg/l
0.13
12,780
855
Recycle Volatile Suspended Solids
(No.1), mg/l
Recycle P (No.1), mg/l
Recycle Suspended Solids (No.2). mg/l
9390
378
12,590
614
72
1,108
Recycle Volatile Suspended
(No.2). mg/l
Recycle P (No.2). mg/l
Recycle VSS % P (No.1)
Recycle VSS % P (No.2)
Solids
9,320
380
4.0
848
79
4.1
63
-------
TABLE 29. INFLUENT AND EFFLUENT CHARACTERISTICS FOR
THE NINE PASS REACTOR FROM APRIL 15 TO
MAY 10, 1976
-- -~ -- --~--
- ---- - ----
Clarifier No. 1 Clarifier No. 2
Parameter Influent Effluent Effluent
Mean Standard Mean Standard Mean Standard
Deviation Deviation Deviation
BOD, mg/l 120 22.0 10.5 3.6 11. 3 3.5
Inhibited BOD, mg/1 7.3 3.3 8.2 3.5
'"
.i'-
COD, mg/l 237 31 29.3 7.2 30.5 6.1
SS, mg/l 97 9.0 11.8 7.8 16.1 11.1
VSS, mg/1 76 8.4 7.5 4.1 11.6 7.8
+ mg/1 12.1 0.57 0.3 .14 0.3
NH4-N, .15
(NO; + NO;)-N, mg/1 0 0 1.4 0.44 1.4 0.47
Total P, mg/1 5.1 0.62 3.2 0.34 3.2 0.31
Temp., °c 20.6 1.0
-------
TABLE 30.
PROCESS CHARACTERISTICS FOR THE
NINE PASS REACTOR FROM JUNE 1
TO JULY 1, 1976
Parameter
Value
or
Average
Standard
Deviation
Total Reactor Detention Time, hrs
Aerated Reactor Detention Time, hrs
Influent Flow, gpd
Influent Flow, m3/day
Total Recycle Flow, gpm
Total Recycle Flow, l/min
8.4
2.7
51,600
195.3
20.5
78
331
2
Clarifier Overflow Rates, gpd/ft
Clarifier Overflow Rates, m/day
MLSS, mg/1
MLVSS, mg/1
13.5
3200
240
180
Total Reactor SRT, days
F/M Ratio, g BOD5 App1ied/day/g MLVSS
Recycle Suspended Solids (No.1), mg/1
Recycle Volatile Suspended Solids
(No.1). mg/1
Recycle P (No.1), mg/1
Recycle Suspended Solids (No.2), mg/1
2370
32
0.12
9030
534
6740
272
8460
378
35.8
547
Recycle Volatile Suspended
(No.2), mg/1
Recycle P (No.2), mg/1
Recycle VSS % P (No.1)
Recycle VSS % P (No.2)
Solids
6290
241
394
21.8
4.0
3.8
65
-------
TABLE 31.
INFLUENT AND EFFLUENT CHARACTERISTICS FOR
THE NINE PASS REACTOR FROM JUNE 1 TO
JULY 1, 1976
Clarifier No. 1 Clarifier No. 2
Parameter Influent Effluent Effluent
Mean Standard Mean Standard Mean Standard
Deviation Deviation Deviation
BOD, mg/1 97 14.0 6.5 2.2 7.8 2.1
0'
0' Inhibited BOD, mg/1 3.2 1.6 4.9 1.6
COD, mg/l 210 18.4 21. 7 3.8 23.6 3.7
SS, mg/1 81 12.1 7.9 4.5 9.0 4.6
VSS, mg/l 64 10.6 5.4 3.3 6.1 3.6
+ mg/l 11.4 0.83 0.09 0.03 0.1 0.05
NH4-N,
(NO; + NO;)-N, mg/l 1.1 0.11 1.1 0.12
Total P, mg/l 4.9 0.40 3.4 0.40 3.4 0.29
Temp., °c 24.7 1.3
-------
KINETIC STUDIES
Three similar kinetic studies were preformed during the last 10 days of
May according to the following experimental protocol:
(a)
Recycle solids were used to partially fill each of two cube
containers.
(b)
KN03 was added to give a desired N03 concentration.
One of the cube containers was filled with recycle solids and
the other was filled with primary effluent.
(c)
(d)
of mixing, samples were withdrawn for
elapsed time between the addition of
of the first sample was approximately
After about
filtration.
N03 and the
2 minutes.
30 seconds
The total
withdrawal
(e)
Samples for N03 analysis were gravity filtered through Whatman
paper.
(f)
Samples for COD analyses were vacuum filtered through 984 H Reeve
Angel glass fiber filters without the cellulose pads.
The first experiment (Figure 14) established once again !he linearity
of the denitrification reac!ion d~wn to very low levels of N03. A den~tri-
fication rate of 6.6 mg (N02 + N23)-N/~r/gm VSS was observed ln the unlt
receiving primary vs. 1.6 mg (N02 + NO )-N/hr g VSS in the control system.
The soluble COD in the unit recelving ihe primary was reduced from 85 mg/l
to 50 mg/l within 15 minutes.
A higher NO; concentration was used in the second study (Figures 15 and
16) and the initlal denitrification rate in the unit receiving primary
effluent was 6.5 mg (NO; + NO;)-N/hr/g VSS. The kinetic rate decreased
after 24-31 minutes (depending upon what one considers the lines of best
fit). The rate associated with the dashed line in Figure 16 is 4.1 mg
(NO- + NO;)-N/hr/g VSS. The soluble COD removal rate was essentially the
sam~ as in the previous experiment with the readily degradable soluble COD
being removed in about 20 minutes.
The third study was carried out over a somewhat longer time period
(Figures 17 and 18). Three denitrification rates are shown for the system
receiving primary effluent. As in the previous study. different curves could
also be fit through the data points. Once again, the initial denitrification
rate corresponds very well to the other two studies. Similarly the readily
degradable soluble COD was removed in about 20 minutes.
The results presented in Figures 16 and 18 are of interest in inter-
preting the past kinetic studies summarized in Table 1. A typical kinetic
study consisted of mixing influent to recycle in a 2:1 ratio, aeration, and
then primary addition to simulate 1/4 of the total influent flow being
bypassed directly to denitrification. In this case, the additional primary
67
-------
~
Z
I
""""
I ("')
o
z
+
I C'J
o
Z
'--'
r-i
--
bJ}
s
RECYCLE SOLIDS AND
PRIMARY EFFLUENT
5.0
MLSS = 2315 mg/1
MLVSS = 1770 mg/1
TEMPERATURE = 22°C
4.0
6.6 mg (NO; + NO;)-N
hr . g MLVSS
3.0
2.0
1.0
5
10
15
20
Figure 14.
RECYCLE SOLIDS ONLY
MLSS = 8750 mg/1
MLVSS = 6540 mg/1
TEMPERATURE = 22°C
1.6 mg (NO; + NO;)-N
hr . g MLVSS
5
10
15
20
TIME, minutes
Increase in rate of denitrification with primary
effluent addition.
68
-------
RECYCLE SOLIDS
16 TEMPERATURE = 22°C
MLSS = 9370 mg/1
14 MLVSS = 7130 mg/l
.--I 12
.......
00
S
~ 10
z
I 1. 1 mg (NO; + NO;)-N
,-...,
1M
0 hr . g MLVSS
z 8
+
IN
0"'> 0
\0 Z 6
'-'
4
2
10
20
30
40
50
60
70
80
90
TIME, minutes
Figure 15.
Denitrification kinetic rate with recycle solids
on May 25, 1976.
-------
18
16 RECYCLE PLUS PRIMARY 90
TEMPERATURE ~ 22°C
MLSS ~ 2580 mg/l
14 MLVSS = 2020 mg/l 80
mg (NO; + NO;)-N
12 hr . g HLVSS 70
.-1
--
.-1 bO
-- S
bO 10 60
s ~
~ A
o
Z U
I (NO; + NO;)-N
;--.. 8 3.0 mg 50 w
I ("") H
o hr . g HLVSS ~
'-J Z ~
o + H
o
6 40 Cf.)
IN
0
Z
'-/ SOLUBLE COD
4 30
2 20
10
20
30
40
50
TIME, minutes
Figure 16.
Denitrification kinetic rate with recycle solids and primary
effluent on May 25, 1976.
-------
16 RECYCLE SOLIDS
TEMPERATURE = 22°C
MLSS = 9660 mg/1
14 MLVSS = 7240 mg/1
12
.--i
-----
bO
S 10
.
z 1.6 mg (NO; + NO;)-N
I
,......, hr . g MLVSS
1C'i 8
o
z
~ +
I-'
IN 6
0
z
'-"
4
2
10
20
30
40
50
60
70
TIME, minutes
Figure 17.
Denitrification kinetic rate with recycle solids on May 28, 1976.
-------
14
6.6 mg (NO; + NO;)-N
hr . g MLVSS
RECYCLE PLUS PRIMARY
TEMPERATURE = 22°C
MLSS = 3660 mg/l
~~VSS = 2775 mg/l
PRIMARY EFFLUENT COD=224 mg/l
12
~
Z
I
I"-"'(V") 8
o
Z
-...J
N +
I N 6
o
z
'-'
(NO; + NO;)-N
. g MLVSS
SOLUBLE COD
4
(NO; + NO;)-N
. g MLVSS
2
10
20
30
40
50
60
70
TIME, minutes
Figure 18.
Denitrification kinetic rate with recycle solids and primary effluent on May 28, 1976.
90
80
70
.--i
----
bO
60 s
.
o
o
u
50 ~
.....:1
P=I
~
.....:1
40 g
30
20
-------
would have ~ncreased the readily degradable soluble COD by about 10 mg/1.
At the COD removal rates indicated in the three previous kinetic studies,
this material would have been removed in approximately 5 minutes. Since the
primary was added to an aerated system (2-6 mg/1 residual D.O.) and since
3-4 minutes were required after supplemental primary addition to transfer
this material to a cube container, stir and begin collecting samples, any
initial high rate during soluble COD removal would only have lasted about
5 minutes and would never have been observed.
Three laboratory studies were conducted on June 10 with the results
presented in Figures 19 thru 21. In one case (Figure 19), recycle solids
were aerated for 60 minutes, KN03 was then added, and the denitrification
rate measured. In the second case (Figure 20) recycle solids were mixed
with primary effluent, aerated for 60 minutes, and then the denitrification
rate was measured. In the third case (Figure 21) filtered primary effluent
was added. The denitrification rates were 1.2, 2.1 and 1.7 mg N/hr/g VSS,
respectively. The soluble COD removal rates were the same, within experi-
mental error, in units receiving primary or filtered primary. Although
the degradable soluble COD was removed in the third unit well before the
end of the aeration period, the endogenous denitrification rate was enhanced
over that observed in the control unit but not to the extent observed in
the unit receiving unfiltered primary. It is apparent that the colloidal
material in the unfiltered primary (an extra 90 mg/1 as COD) did not
influence the denitrification rate beyond what could be attributed simply
to more initial COD.
In a study on the following day, filtered and unfiltered primary effluent
and KNO were added to recycle solids and the denitrification rates were
measure~. Results are presented in Figure 22. Once again the soluble COD
was removed very rapidly. The initial denitrification rates of 7.0 and
7.2 mg N/hr/g VSS were the same within experimental error. The subsequent
denitrification rates were only marginally higher in the unit receiving
unfiltered primary indicating that the extra 95 mg/1 of particulate COD was
apparently being degraded rather slowly.
On June 24 two studies were conducted in which recycle solids were
added to primary effluent and then aerated until nitrification was complete
(Figures 23 and 24). Concurrent measurement of soluble COD removal showed
that the degradable component of the mate~ia1 was removed in less time than
was required to completely oxidize the NH4-N. This same observation was
essentially m~de when_the_actual process was sampled several days later;
results of NH4-N, (NOZ+N03)-N, and COD analyses are presented in Table 32.
It can be seen that n1trification was essentially complete in the first
pass and the soluble COD was also reduced to its residual level by this
point. An accurate determination ~f the nitrification kinetic rate is not
possible from these data as the NH4-N oxidation rat~ is_not zero order when
the concentration is below 1 mg/1. The average (N02+N03)-N reduction from
passes 3 to 4 and 4 to 5 corresponds to a denitrification kinetic rate of
1.55 mg (NO;+NO;)-N/hr/g VSS. This rate agrees well with denitrification
rates obtained 1n the various batch kinetic tests.
73
-------
16
SOLIDS
AERATED
>,
"-J
+--
,....,
-.....
00
S
~1 0
z
I
,.--..
IC'"'J
~ 8
+
1.2 mg (NO;~Q;2-N
hr . g MLVSS
RECYCLE SOLIDS
TEMPERATURE = 23.50C
MLSS = 7550 mg/1
MLVSS = 5800 mg/1
14
12
IN
~ 6
'-"
2
30
60
90
120
150
180
TIME, minutes
Figure 19.
Denitrification kinetic rate with recycle solids after 60 minute's aeration
on June 10, 1976.
-------
AERATION >+< DENITRIFICATION >-
9
8
M
- 7
bO
f3
..
Z
I 6
,......
I C"")
0
z
+ 5
IN
0
Z
'-'
-.J
\Jl 4
H
°
z 3
I
+~
~
2
30
8
A
8
RECYCLE PLUS PRIMARY
TEMPERATURE = 23.50C
MLSS = 2480 mg/l
MLVSS = 1925 mg/1
PRIMARY EFFL. COD = 223 mg/1
SOLUBLE COD @ 15 min = 24.1 mg/1
SOLUBLE COD @ 30 min = 17.8 mg/1
60
2.1 mg(NO; + NO~)-N .
hr . g MLVS
90
120
150
180
TIME, minutes
Figure 20.
Nitrification-Denitrification cycle with recycle solids and primary
effluent on June 10, 1976.
-------
9
8
rl
--...
bJ) 7
S
~
Z
I
,....., 6
I (">')
o
z
+
IN 5
o
z
'-"
-.J 4
0' H
0
Z
I 3
+-.:t
~
2
1
AERATION
>1<
6
6
8.
DENITRIFICATION
RECYCLE PLUS FILTERED
TEMPERATURE = 23.50C
MLSS = 2560 mg/1
MLVSS = 1975 mg/1
FILTERED PRIMARY COD =
SOLUBLE COD @ 15 min =
SOLUBLE COD @ 30 min =
l!S.
1.7 mg(NO; + NO;)-N
hr . g MLVSS
+
NH -N
4
\
30 60
90
120
150
180
TINE, minutes
>-
PRIMARY
133 mg/l
19.5 mg/1
18.7 mg/l
210
Figure 21.
Nitrification-Denitrification cycle with recycle solids and filtered primary
effluent on June 10, 1976.
-------
RECYCLE PLUS FILTERED PRIMARY
14 MLSS = 2250 mg/1 MLVSS = 1790 mg/1 140
FILTERED PRIMARY COD = 156 mg/1
TEMPERATURE = 23.50C
12 !;:;.
120
r-I 7.0 mg (NO; + NO;)-N
- hr
00 . g MLVSS
S 10 100 r-I
-
~ 00
:z; S
I
,-.., (NO; + NO;)-N ~
IC"') 8 80 A
o
:z; . g MLVSS 0
u
+ ~
IN ~
6 60 ~
o ;:::J
:z; ~
'-"" 0
Cf)
4 SOLUBLE 40
COD 2.2 mg
hr
2 20
4
RECYCLE PLUS UNFILTERED PRIMARY
}~SS = 2440 mg/1 MLVSS = 1920 mg/1
UNFILTERED PRIMARY COD = 251 mg/1
FILTERED RECYCLE COD = 38.4 mg/1
SOLUBLE
COD
140
120
100 r-I
~
00
E!
~
80 p
o
u
~
~
60 ~
;:::J
~
o
Cf)
mg (NO;+NO~)-N 40
r . g MLV S
20
b
30 40 50 60 70 80 90
(NO; + NO;)-N
. g MLVSS
14
12
r-I
........
W 10
~
:z;
I
I'-"'C"') 8
o
:z;
+
I N 6
o
:z;
'-""
(NO; + NO;)-N
. g MLVSS
2
10
20
Figure 22.
TIME, minutes
Comparison of denitrificatiGn rates using filtered
and unfiltered primary effluent.
77
-------
110
TEMPERATURE = 250C
8 MLSS = 2740 mg/1
MLVSS = 2110 mg/l
7 6.3 mg
hr
M
--- 80
00 6
s
z 70
I .--1
~ 5 ---
1M 00
0 s 60
z
.
+ Q
4 0
IN U 50
0
z ~
-....J '-' H
OJ I'Q
H ;=J 40
0 3 H
0
Z u:J
I
+-
-------
TEMPERATURE = 260C
9 MLSS = 2330 mg/l
MLVSS = 1780 mg/l
8 80
H 7 70
--
00
S
.
z 6 H 60
I --
,....., 00
1M S
0
z .
+ 5 Q 50
0
IN U
0 ~
z ,...4
-..-J '-" 4 6.1 mg(NO-+NO-)-N ~ 40
\D :::J
!-< hr . g m:VS~-~ ,...4
0 0
z UJ
I 3 30
+-:t
::r::
z
2 20
6.3 mg NH+-N
1 hr 'g ML~SS 10
.
11.
~
10
20
30
40
10
20
30
TIME, minutes
TIME, minutes
Figure 24.
Comparison of soluble COD removal rate and the time required for nitrification (Test No.2).
-------
TABLE 32. + - -
NH -N, (NO + NO )-N AND COD CONCENTRATIONS
IN4THE NINt PASS3REACTOR AT SELECTED TIMES
ON JULY 1, 1976 *
Time Influent Pass Pass Pass Pass Pass Pass Pass Pass
1 2 3 4 5 6 7 8
+ mg/l
~ - N,
1230 9.9 0.1 0.2 0.2 1.1 0.7 1.1 1.1 1.1
1350 12.8 0.6 1.1
1530 13.9 0.9 0.9
(NO; + NO;)-N
CJ:) 1230 6.6 6.9 6.8 4.6 2.3 1.3 0.8 0.7
o
1350 7.0 7.0 7.4 4.7 2.4 0.9 0.8
1530 8.1 8.4 8.2 6.0 3.4 1.3 0.8 1.2
Soluble COD, mg/l
1350 22.4 23.9 ( R e c y c 1 e 1 9 . 7 )
1420 104
1530 95.8 20.8 18.5
a
*Process Temperature = 27 C
*Average MLSS = 3,230 mg/l
*Average MLVSS = 2,470 mg/l
*Recycle Flow = 78.0 l/min (20.6 gpm)
*Influent Flow = 127.2 l/min (33.6 gpm)
*Detention Time per Pass Based on Total Flow = 37.4 min
-------
The effects of overaeration were evaluated on June 25 (Table 5) when a
mixture of recycle and influent was aerated until nitrification was complete.
Part of the mixture was then allowed to denitrify immediately with the
remainder aerated an additional 60 minutes prior to denitrification. The
overaeration resulted in a denitrification rate of 1.0 mg (NO-+NO;)-N/hr/g
VSS compared to a rate of 1.3 in the sample that was denitrif!ed at the end
of the nitrification cycle.
In the last kinetic test performed, a sample was nitrified, split into
two parts, and 33% additional primary added to one of the two parts prior to
denitrification (Table 1). As previously observed over the last 1-1/2 years,
the increased denitrification rate resulting from the additional primary
addition was not sufficiently large to justify a more complex flow-splitting
scheme. COD values were: primary effluent, 244 mg/l; soluble primary, 138
mg/l; soluble recycle, 42.8 mg/l; soluble component after 20 and 30 minutes
aeration, 39.0 and 32.3 mg/l, respectively.
SLUDGE SETTLING CHARACTERISTICS
Throughout the course of this investigation, the mixed liquor from the
last aerated reactor pass was periodically removed and the settling velocity
determined in the stirred .15 m (6") column previously described. These
velocities are summarized in Table 33. The results appear generally typical
of other single stage systems. Nocardia is a filamentous organism and this
is reflected in the low settling velocities encountered especially at low
temperatures and high solids. The FeCI addition increased the settling
velocities compared to a system at simiiar MLSS levels, but obviously this
came at the expense of having to maintain higher MLSS because of the lower
percentage of volatile solids. On balance these two factors tended to be
offsetting.
Two batch flux settling tests were run and the results are shown in
Figure 25. The higher settling velocities in December primarily reflect
the FeC13' When these tests were conducted, a subsample was placed in a
I-liter unstirred cylinder for determination of the 30-minute sludge volume.
This was used in conjunction with the suspended solids data from each test
to compute the SVI as shown in Figure 26. This response is rather typical
where filamentous organisms are present and shows that one can attain a
range of SVI values depending upon the suspended solids level.
81
-------
TABLE 33. SUMMARY OF MIXED LIQUOR SETTLING VELOCITIES FROM
THE LAST PASS OF THE EIGHT OR NINE PASS REACTOR
Settling Volatile Settling Volatile
Date Temp MLSS Velocity Solids Date Temp MLSS Velocity Solids
°c mg/1 ft/hr m/hr % °c mg/1 ft/hr m/hr %
2/11/75 17 3800 5.3 1.6 70 8/28/75 27 2200 16 4.9 67
2/21/75 17.5 3700 4.3 1.3 70 9/11/75 24.5 2900 11. 3 3.4 67
3/6/75 18 3700 6.5 2.0 70 9/18/75 24.5 2600 10.2 3.1 69
3/11/75 17 3400 5.3 1.6 71 9/30/75 23 2800 4.2 1.3 55
3/20/7 5 16 4100 2.7 0.82 68 10/07/75 23 4200 4.0 1.2 54
3/25/75 17 4000 3.3 1.0 67 10/22/75 22 5200 3.9 1.2 52
00 4/01/75 18 4200 3.5 1.1 67 10/31/75 22 5500 3.7 1.1 53
N 4/8/7 5 17.5 4300 3.3 1.0 68 11/20/75 21 6100 2.6 0.79 55
4/15/75 18 4500 3.1 0.94 70 11/24/75 20 6400 3.1 0.94 56
4/25/75 18.5 4700 1.7 0.52 71 12/16/75 18.5 4700 4.5 1.4 62
5/06/75 19 3900 1.9 0.58 71 12/24/75 17 4900 4.2 1.3 67
5/13/75 21 3800 2.5 0.76 68 1/27/76 16 5100 3.6 1.1 69
5/20/75 22 4000 3.2 0.98 70 2/10/76 16 5800 3.5 1.1 69
5/27/75 23.5 4100 3.9 1.2 69 2/19/76 18 5700 3.1 0.94 70
6/20/75 26 4000 3.8 1.2 68 3/01/76 18.5 5200 3.9 1.2 70
6/26/75 25.5 3700 4.5 1.4 69 3/08/76 18.5 5100 3.9 1.2 72
7/08/75 26 3200 4.8 1.5 70 3/15/76 18.5 4900 4.5 1.4 72
7/14/75 24 3500 4.0 1.2 69 3/29/76 19 4200 9.8 3.0 73
7/22/75 26 3500 6.0 1.8 66 4/06/76 18 3600 6.2 1.9 72
7/31/75 27.5 3100 6.6 2.0 66 5/24/76 22 3700 7.7 2.3 73
8/12/75 27 2500 9.1 2.8 67 6/10/76 24.5 3200 6.5 2.0 76
8/22/75 27 2000 16 4.9 67 6/30/76 26 3000 7.2 2.2 73
-------
Stirring Speed
40
/::, 3/27/75
o 12/02/75
30
20
H
..c:
---
.jJ
lH
~ 10
~
H
U 8.0
0
H
~
:>
CCJ 6.0
z
H
H
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E-<
~ 4.0 A
(J)
15 rph
16°C
19°C
2.0
1.0
o
o
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o
o
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o
o
o
~
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o
o
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o
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~
o 0
o 0
o 0
~
~
00 0
'""""
N
M
~
LJ") \.0
SUSPENDED SOLIDS, mg/l
Figure 25.
Mixed liquor settling velocity vs. suspended
solids concentration.
83
-------
600
A 3/27/75
o 12/02/75
500
400
A
I \
I \
/ \
\
/ \
/ \
t!.b \ \
.~
'\
S
DO
-
r-1
S
300
~
H
:>
UJ
200
100
o
o
2000
4000
6000
3000
SUSPENDED SOLIDS, mg/l
Figure 26.
SVI vs. suspended solids concentration.
84
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SECTION 7
DISCUSSION
Based on the results presented in the previous section, it can be seen
that acceptable nitrification-denitrification performance was routinely
achieved with the nine pass+reactor. For many of the steady state_per!ods
summarized, the effluent NH4-N was < 0.5 mg/l and the_effluent (N02+N03)-N
conce~tra~io~ wa~ ~ 1 mg/l. Occasional c~ecks !or N02-N were always
negatlve lndlcatlng that the measured (N02 + N01)-N was essentially all
N03-N. This was the expected result since for the set of conditions pre-
valling in these studies the Nitrosomonas kinetics essentially control the
nitrification response. The overall process response was the result of a
number of interacting variables. In fact, there are so many variables that
it is impossible to disaggregate the data to a level where the influence of
each factor can be examined individually.
The decision to use primary effluent in place of raw sewage provided a
lower C:N ratio to the system than would have prevailed without use of a
primary clarifier. The BOD:TKN ratio from June-September 1975 was 5:1.
Because of reduced laboratory staffing, the TKN analyses were discontinued
after September. However, the 5:1 ratio should be representative of that
prevailing after September 1975. This value was sufficiently high to exceed
the critical ratio required for denitrification (5).
The soluble COD measurements made during the initial aeration periods of
some of the laboratory kinetic studies show that the readily degradable
soluble material was essentially removed in every case prior to the minimum
time required for complete nitrification. If raw sewage and not primary
effluent had been applied to the single-stage system, this presumably would
have happened even faster because of an increased heterotrophic:nitrifying
organism ratio. Since perhaps 50% of the BOD in primary effluent is
colloidal or larger in size, this material cannot be metabolized as rapidly
as the "soluble" material and would be expected to provide some contribution
to "endogenous denitrification." Clearly the use of raw sewage in place of
primary would provide even larger amounts of particulate material (~ 30% BOD
removal is common for a primary settler) available for slower degradation.
Intuitively, one would expect different denitrification rates with the single
nitrification-denitrification approach using raw instead of primary sewage
because of the increase in essentially all particulate matter.
The two kinetic studies summarized in Figures 19 thru 22 are somewhat
conflicting in their interpretation. The increase in the denitrification
rate of 0.5 mg/l/hr in the unit receiving the filtered primary (COD=133 mg/l)
85
-------
and the increased rate of 0.9 mg/l/hr in the unit receiving the unfiltered
primary (COD=223 mg/l) over the rate prevailing in the control unit (Figure 19)
indicates no need to differentiate the potential influence of different car-
bonaceous molecular sizes on the subsequent denitrification rates. On the
other hand, the results shown in Figure 22 imply that the colloidal fraction
is not used very rapidly and may be quite important in the "endogenous
denitrification." This is an area where further studies are needed.
The denitrification rate observed when using a single nitrification-
denitrification cycle was obviously very dependent on the length of the
initial aeration period as shown in Table 5 and Figure 7. Aeration beyond
the minimum time needed to accomplish nitrification clearly reduced the
subsequent denitrification rate. The results shown in Table 5 for 9/10, 10/2,
and 2/26, indicate that the decline in the denitrification rate is not a
simple function of the length of the aeration period. The decline in the
denitrification rate with extended aeration is significant enough that one
would need to have a uniform length of aeration period to provide a meaning-
ful direct comparison of denitrification rates of the type shown in Table 1.
Since the denitrification rates are a function of the initial COD, the
length of the aeration period, temperature, and presumably the soluble:
particulate organics ratio, one must exercise considerable caution in inter-
preting denitrification rates and comparing them to the results of others.
When the denitrification rates in Table 1 from 1/22/75 onward for the units
receiving no additional primary, the rates from the shortest aeration times
in Table 5, and the rate from Figure 20 are plotted as a function of tempera-
ture, as shown in Figure 27, there is no obvious relationship. The rates of
0.8 to 2.0 mg (NO; + NO;)-N/hr/gm MLVSS are quite consistent with the rates
summarized by Chrlstensen and Harremoes (5) for various nitrification-
denitrification processes. In view of the variability in aeration times,
temperatures, and initial COD values used in the laboratory studies to deter-
mine the denitrification rates, it is not possible to define the denitrifica-
tion rates as a function of each of these variables on the basis of the data
at hand.
The maximum denitrification rates observed by mixing primary effluent
and recycle solids and then adding KN03 were 6.5-7.2 mg (NO-+NO-)-N/hr/gm
MLVSS, and these rates prevailed only as long as there was ~ re~dily available
exogenous supply of soluble COD. These rates exceed the 2-3 mg N/hr/gm VSS
upper limit indicated by Christensen and Harremoes (5). However, it is obvious
that special care must be taken to find this initial rapid rate. Barnard (18)
rerorted a very rapid initial rate lasting from 5 to 15 minutes of 13 mg
N03-N/hr/g SS. This was attributed to the reduced state of the anaerobic raw
sewage. This rapid rate was not observed here, but it should be noted that
the primary influent is pumped from an aerated grit chamber so the same con-
di~ions did not prevail. The intermediate denitrification rates of ~ 3.5 mg
N03-N/hr/g MLSS described by Barnard agree very well with the rates observed
here.
The
are also
tionship
nitrification kinetic rates with solids
plotted as a function of temperature in
between kinetic rate and temperature is
from the 8 or 9 pass system
Figure 27. Here the rela-
more obvious. However, a
86
-------
8.0
6
6.0
4.0
6
2.0 0 00
o 0
0 aD
0 0 0
1.0 ~ 0
0.8 0
0.6
~
~
E--<
~ 0.4
u
H
E--<
~
Z
H
:::<:
0.2 ~ NITRIFICATION KINETIC RATES
o DENITRIFICATION KINETIC RATES
16
17
18
19
20
21
22
23
24
25
26
o
TEMPERATURE, C
Figure 27.
Nitrification and denitrification kinetic rates
from laboratory studies vs. temperature.
87
-------
major problem in data interpretation is that the nitrification rat~ is bas~-
cally expressed in terms of the non-nitrifying mass of heterotroph1c organ1sms.
Since net heterotrophic yield is a function of temperature (19,20) and SRT,
the ratio of nitrifying to carbonaceous organism observed yields may c~ange
during the year and imply a larger temperature function than really eX1sts.
The data in Figure 27 indicate a 3-fold change in the nitrification rates
with the temperature range encountered with D.C. wastewater.
Various periods of steady state operation have been summarized in
Table 34. A 30-day reactor SRT corresponds to an SRT of 9.8 days in the
aerated portion of the reactor. Knowles, et al. (21) proposed that the
relationship between maximum specific gr~wth rate and temperature for
Nitrosomonas could be expre~sed as 1~g10~ = 0.0413 (T) - 0~94~. Accordingl
to this expression, the maX1mum spec1flc growth rate at 15 C 1S 0.47 days.
Since SRT is the inverse of the growth rate, the minimum SRT required is
2.1 days. Hence at all times, the "aerated SRT" was substantially in excess
of the minimum theoretical value needed.
Except for the period of July 11 to September 22, the other steady
state operating periods summarized in Table 34 are only equivalent to about
1 SRT in length. During winter operation, the clarifier bed levels also
tended to be high such that the "total SRT" of reactor and clarifier could
have been perhaps double the reactor SRT's. This must be considered when
evaluating observed sludge production as a function of loading. Clearly
the short periods of operation summarized in Table 34 (~ 1 SRT) offer the
possibility of estimating sludge production values far from true equilibrium
conditions. This was previously mentioned when the data from 5/28-7/9 were
discussed and was also the case for the period of 2/26-4/5 where there were
declining MLVSS levels and presumably some wasting from storage. The change
was so great for the period of September 23 to December 2 (Figure 13), that
this period was not summarized in Table 34.
The overall cell yield coefficient when treating DC primary effluent has
been previously estimated_f16) at 0.79 g VSS/g BOD5 applied. The decay
coefficient was 0.064 day. For a 30-day SRT the expected observed cell
yield would be 0.79/[1 +0.064(30)] or 0.27 g VSS/g BOD applied. This
assumes a 30-day aerated SRT which was obviously not t~e case in the present
investigation. Nonetheless the value of 0.27 agrees favorably with the
values reported in Table 34.
The P mass balance was never unity and this presumably reflects either
overestimation of the average influent concentration or an underestimate of
the average concentration in the clarified effluent. The sludge P content
was generally constant (where there was no FeCl influence) and the recorded
underflow waste volumes gave observed cell yiel~ values which were quite
consistent with expectations. Since the accuracy of the influent flow meter
was checked weekly, the estimate of influent flow for all periods of steady
flow should not be in error by more than 3-4%. The method of" underflow
wasting also makes it extremely unlikely that the waste volumes were not
measured correctly to within 10% and in all probability the error was no more
than 5%.
88
-------
TABLE 34.
SUMMARY OF OBSERVED CELL YIELDS, F/M RATIOS
AND PROCESS SRT'S FOR SELECTED PERIODS
Dates Number Average SRT Observed Yield F/M P
of Days Temp days g SS/day g VSS/day g BODS App1. Mass Balance
0c g BODS App1. g BODS App1. day. g MLVSS In/Out
5/28-7/9 43 24.5 28 0.58 0.40 0.09 1.12
00 7/11-9/22 74 26.2 35 0.37 0.25 0.12 1.41
\D
11/1-12/2 32 20.8 27 0.43 0.09
12/4-12/23 20 18.2 20 0.48 0.10
2/26-4/5 40 17.6 35 0.46 0.33 0.09 1.13
4/15-5/10 26 20.6 26 0.40 0.29 0.13 1.21
6/1-7/1 31 24.7 32 0.37 0.27 0.12 1.17
-------
If one has a perfect N halance, ~t ~~ possible tg take. the TKN~n~TKNQut
-(NO- + NO-)-N and cqlculate the nitrogen removal resultlng from the
nitrtficatlon-8~~itrification cycle plus whatever nitrogen removal oc~u:s
through denitrification in the final clarifier. The loss in ~he clarlf~er
can be significant especially with high clarifier bed levels. When this
calculation was applied to the system parameters for the period of.5/28 to
7/9, it was determined that 12.9 mg/l of the incoming 18 mg/l of nltrog:n
were removed in the nitrification-denitrification process. Of the remalnder,
2.2 mg/l of N passed into the effluent and the equivalent of 2.9 mg/l of
incoming nitrogen was removed in the waste activated slu~ge: .Hen~e th:
high nitrogen removal is the result of nitrification-denltrlflcatlon wlth
sludge wasting accounting for only 16% of the N removal as a result of the
low observed cell yields encountered in high SRT processes.
The laboratory kinetic studies were shown to provide an accurate
indication of what was occurring in the actual process. In ~ll cases the
nitrification kinetic rates were independent of exogenous NH4-N concentra-
tions down to < 1 mg/l. The saturation constant for Nitrosomonas has been
reported (8) t~ be in the range of 0.1 to 1.0 mg/l depending on the person
conducting the study and the experimental conditions. If the growth rate is
assumed to follow the expression ~ = ~ SiCK + S), the growth rate would
be 91% of the maximum value with an ex~~~nous NH!-N concentration of 1 mg/l
and K of 0.1 mg/l. If K were as high as 1.0 mg/l, the growth rate would
only ~e 50% of the maxim~ value at S = 1.0 mg/l. Obviously an accurate
determination of K would req¥ire a concentrated effort to evaluate the
biological respons~ at low NH4-N levels coupled with the use of an analytical
procedure accurate at these low levels. Since this study did not include any
attempt to estimate K and since the values reported in the literature vary
by a factor of 10, th~re is no obvious reason for attempting to compare the
observed system responses and laboratory kinetic data on the basis of
Michaelis-Menten kinetics when using an undetermined saturation constant.
Rather the simple application of linear rates to the initial two complete mix
passes is sufficient to+describe general process nitrification response as
long as the residual NH4-N concentration in the second pass is > 1.0 mg/l.
The denitrification rates occurring in the process (Tables 7 and 32)
were also found to be comparable with the rates observed in the laboratory
kinetic studies. Since the COD loading cycled throughout the day, the
process denitrification rate should also vary during the day. For this
reason, the denitrification rate calculated at a given point in time should
not necessarily agree with a laboratory rate unless the aeration period and
organic loading were comparable in each unit.
The laboratory studies of the type shown in Table 1 consistently
indicated that there was no apparent advantage to a flow-splitting approach
as long as the length of the aeration period was not substantially in excess
of the time required to attain "complete" nitrification. The average 22%
increase in the denitrification rate with supplemental primary addition was
not suffici~nt, for the purposes of this study, to warrant increasing the
~ffluent N03-N levels. This increase in NO;-N would occur because the NH+-N
In!rod~ced lnto the denitrification section would be subsequently oxidize~ to
N03-N ln the terminally aerated section of the reactor. This residual NO-
3
90
-------
could be eliminated in an additional nitrification-denitrification cycle, but
there is no apparent advantage to this approach over the one utilized.
The nitrification and denitrification kinetic rates in Tables 1 and 5
summarize some of the more obvious advantages and disadvantages of the single
nitrification-denitrification approach to nitrogen removal. For a waste-
water such as that in Washington, D.C. with the temperature varying from
around 15°C in the winter to around 26°C in the summer there will be an
apparent 3-fold change in nitrification kinetic rates from winter to summer
(Figure 27). There is also the probability in most design situations that
one must deal with a diurnal flow/concentration cycle. If one has a modest
3:1 maximum:minimum flow variation synchronous with a 3:1 concentration
change coupled with a long range 3:1 influence of temperature, then there is
actually a 27-fold difference in the combination of aeration time and solids
levels which are required during the year to provide the optimum conditions
(aeration just sufficient for "complete" nitrification) in a perfect plug
flow reactor. In many small plants a 6-7:1 maximum:minimum flow variation
is not unusual and this could mean a 50-100 fold difference in producing
optimum conditions in a perfect plug flow reactor during the course of a
year. As shown in Table 5, the penalty for always providing sufficient
aeration time/solids to meet the peak loading for a day is a reduction in the
subsequent denitrification rates which will prevail under lower loading
conditions. The lower rates will be offset by lower (NO;)-N concentrations
to be biologically reduced with the time available for dlssimilation
determined by the hydraulic flow characteristics of the plant. Obviously.
the use of complete mix tanks and flow equalization can attenuate the impact
of incoming flow/concentration changes considerably.
The single stage nitrification-denitrification process can clearly be
operated to handle the concentration variations which occur during the day.
This was demonstrated in the long period of operation of the process.
Also, the results of the July II-September 22 operation (Tables 11 and 12)
show that the system can respond to moderate diurnal flow changes and still
produce an effluent low in total N. The application of the laboratory
kinetic rates to estimate the amount. of N that could be oxidized in the
first two passes was shown to produce results which agreed closely with the
amount of (NO; + NO;)-N in the final effluent. Where insufficient aeration
time was aV$ilable ln the initial aeration sequence to oxidize all £f the-
incoming NH4-N, there was a corresponding rise in the effluent (N02 + N03)-N
level reflecting oxidation of this material in the terminal aeration step.
The results obtained from the system during the period of FeCI addition
indicate that this metal salt can effectively remove the influent p~osphorus
with no impact on the nitrifying organisms. This has been shown by several
other investigators so the result was expected. The FeC13 dosage was selected
to maintain a pH of > 6.5 in the terminal aerated chamber. At the rather
moderate dosages utilized, the P removal for the entire 70-day period of
FeCl addition was 89% with most of the effluent P associated with particulate
matt~r/biological solids. Filtration of the clarified effluent over the
43-day period of October 9-November 20 reduced the effluent P from 0.61 mg/l
to 0.25 mg/l. The FeCl addition resulted in the build-up of a large amount
of chemical sludge with3a reduction of the MLVSS to near 50% of the MLSS.
91
-------
This necessitated carrying highe}:" MLSS in the ;r;e",ctox to maintain the desired
process loading. The settling velQcities (Table 33) were abQu~ the samea,s
encountered at similar temperatures with no feC13' The.F:C13 ~m~roved the
mixed liquor settling velocities over what would be antlclpat:d ln a
comparable biological system (equal MLSS) without FeCl~ additlon. On
balance the increased in MLSS needed to maintain a sUltable SRT was
largely' compensated for by the increased settling velocities.
As shown in Tables 20 and 21, filtration of the clarified effluent
produced a final effluent of excellent quality. The desirability of using
the larger media can clearly be seen. Each of the filters produced an
effluent of identical quality but the run lengths with filter "p" were
substantially longer than when using filter "N." These results are
consistent with previous observations made during an in-depth evaluation
of these filter media (17).
The few brief studies summarized in the Appendix indicate that C12
addition is potentially more useful than.is.HZ02 ~or controllin~ nu~sance
heterotrophic growths in systems where nltrlflcatlon must be malntalned.
H ° dosages near the minimum values reported to be useful against
ftl~mentous forms (22) had a marked impact on nitrification. In contrast,
moderate HOCl dosages to the recycle solids were not detrimental to
nitrification. Obviously, the usefulness of C12 in any given situation will
depend on the resistance of the heterotrophic organisms causing the problems
and the dosages and point of application (especially because of the potential
for chloramine formation).
The results summarized in the previous section indicate that a single
nitrification-denitrification approach in a "plug-flow" reactor is a reliable
means of achieving nitrogen removal beyond that attributable to cellular
sy¥thesis. This approach is best suited to relatively uniform flows and
NH4-N concentrations but this is not a requirement of the system. Flow
equalization or use of alternative approaches such as shown in Figure 1 can
help overcome non-uniform loadings. Depending upon the discharge standards
which have to be met, one could construct a multipass system such as used
here with sufficient flexibility to vary the number of aerated passes. In
winter operation the number of aerated passes could be sufficient to provide
complete nitrification and whatever denitrification could be attained in the
remaining stirred passes. In warm weather operation the increased nitrifi-
cation kinetic rates and improved settling velocities make possible the
use of a reduced number of aerated passes. Even where the discharge standards
are more stringent than can be reliably achieved by single stage systems, the
use of these systems should not be automatically precluded. If the system
used in this study were combined with an additional staged denitrification
sequence using methanol, for example, one could operate the first process
in a way to insure complete nitrification at all times with some variation
in available denitrification capacity and still obtain a substantial savings
in the methanol requirement in the subsequent denitrification step.
92
-------
REFERENCES
1.
Process Design Manual for Nitrogen Control, Technology Transfer, U.S.
Environ. Proto Agency, October, 1975.
2.
Ludzack, F. J. and Ettinger, M. B., "Controlling Operation to Minimize
Activated Sludge Effluent Nitrogen," Jour. Water Poll. Control Fed.,
34, 920, 1962.
3.
Wuhrmann, K., "Nitrogen Removal in Sewage Treatment Processes,"
Internat. Verein. Limnol., XV, 580, 1964.
Verh.
4.
Christensen, M. H. and Harremoes, P., "Biological Denitrification in
Water Treatment," Rep. 2-72, Dept. of Sanitary Engineering, Tech. Univ.
of Denmark, 1972.
5.
Christensen, M. H. and Harremoes, P., "A Literature Review
Denitrification of Sewage," IAWPR Specialized Conference,
Copenhagen, Denmark, August, 1975.
of Biological
Vol. 3,
6.
Conference on Nitrogen as a Water Pollutant, IAWPR
ference, Vol. 3, Copenhagen, Denmark, August, 1975.
Specialized Con-
7.
Christensen, M. H., Harremoes, P. and Jensen, O. R., "Combined Sludge
Denitrification of Sewage Utilizing Internal Carbon Sources," IAWPR
Specialized Conference, Vol. 3, Copenhagen, Denmark, August, 1975.
8.
Poduska, R. A., "A Dynamic Model of Nitrification for the Activated
Sludge Process," Ph.D. Thesis, Clemson Univ., Clemson, South Carolina,
1973.
9.
Bridle, T. R. Climenhage, D. C. and Stelzig, A., "Start Up of Full
Scale Nitrification-Denitrification Treatment Plant for Industrial
Waste," Proc. 31st Annual Purdue Industrial Waste Conference, 807, 1976.
10.
Standard Methods for the Examination of Water and Wastewater, 13th
Edition, American Public Health Assoc. Inc., Washington, D.C., 1971.
11.
Young, J. C., "Chemical Methods for Nitrification Control," Jour. Water
Poll. Control Fed., ~, 637, 1973.
12.
Methods for Chemical Analysis of Water and Waste, Technology Transfer,
U.S. Environ. Proto Agency, EPA-625-6-74-003, 1974.
93
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13.
Scheiner, D., "Determination of Ammonia and Kjeldahl Nitrogen by Indo-
phenol Hethod," Water Research, 10, 31, 1976.
14.
Kamphake, L. J., Personal Communication, 1971.
15.
Gales, M. Jr., Julian,
Determination of Total
Assn., ~, 1363, 1966.
E. and Kroner, R., "Method for Quantitative
Phosphorus in Water," Jour. Amer. Water Works
16.
Heidman, J. A., "Pilot Plant Evaluation
Systems, " Environ. Proto Tech. Series,
2-77-108, 1977.
of Alternative Activated Sludge
Environ. Proto Agency, EPA~600/
17.
Bowker, R. P. G., "Downflow Granular Filtration of Activated Sludge
Effluents," Environ. Proto Tech. Series, Environ. Prot. Agency,
EPA-600/2-77-l44, 1977.
18.
Barnard, J. L. and Meiring, P. G. J., "Sources
their Effects on Denitrification Rates," IAWPR
Vol. 3, Copenhagen, Denmark, August, 1975.
of Hydrogen Donors and
Specialized Conference,
19.
Muck, R. E. and Grady. C. P. L., "Temperature Effects on Microbial
Growth in CSTR's," Jour. Env. Eng., Proc. Amer. Soc. Civil Eng., 100,
1147, 1974. ---
20.
Gujer, W. and Jenkins, D., "The Contact Stabilization Activated Sludge
Process - Oxygen Utilization, Sludge Production and Efficiency," Water
Res.,9, 553, 1975.
21.
Knowles, G., Downing, A.
Constants for Nitrifying
Electronic Computer," J.
L. and Barrett, H. J., "Determination of Kinetic
Bacteria in Mixed Culture with the Aid of an
Gen. Microbio~, ~, 263, 1965.
22.
Cole, C. A., Stamberg, J. B. and Bishop,
Filamentous Growth in Activated Sludge,"
Environ. Proto Agency, EPA-670/2-73-033,
D. F., "Hydrogen Peroxide Cures
Environ. Proto Tech. Series,
1973.
94
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APPENDIX
As indicated in Section 5, a few laboratory studies were undertaken to
assess the potential usefulness of H202 or HOCI for the control of hetero-
trophic nuisance growths without impairing the nitrifying organisms also
present.
In the first study with H202' 500-ml of recycle solids from the single
stage nitrification system were added to each of 5 beakers. H 02 (Becco 35%
obtained from FMC Corporation) was added to each beaker to yietd the following
concentrations: 0, 18.9, 37.7, 75.4 and 113 mg H202/l. The contents of each
beaker were mixed and after 1-3 minutes, 1 liter of D.C. primary effluent was
added to each system to yield final H202 concentrations of 0, 6.3, 12.6, 25.1
and 37.7 mg/l. This mode of peroxide aadition simulated to some degree what
would occur if the H202 was added to the recycle line of an actual process.
Each of the beakers was aerated after the primary effluent was added, and
samples were withdrawn periodically for (NO; + NO;)-N analysis. Results are
presented in Figure A-I. No affect was observed at the lowest dosage. How-
ever, initial dosages of 37.7 and 75.4 mg H202/l produced rates which were
only 53% and 18% of the control respectively. Hence nitrification was
severely reduced at a final simulated concentration in a reactor (recycle
plus primary) of 25 mg/l.
In an attempt to more closely define the inhibitory dosage and to
eliminate the possible effect of an initially high concentration of H202'
an additional series of studies was undertaken in which the peroxide was
added to a mixture of recycle and primary effluent simulating addition
directly to the mixed liquor of a process. Results are presented in Figure
A-2. The peroxide began to inhibit nitrification at a dosage between 10 and
20 mg/l, and a 64% inhibition was observed at 40 mg/l. The results reported
by Cole, et al. (22) indicated that a minimum dosage for filamentous organism
control presumably lies between 10 and 40 mg H202/l. Better results for many
filamentous forms were obtained with dosages of 100-250 mg/l. The laboratory
studies, therefore, indicate that there would be little chance of filamentous
control by H ° without the concurrent elimination or severe inhibition of
nitrificatio~.2 If peroxide were tried in an actual process, close control of
the dosage would be required.
Since these two studies indicated that H202 had little po~ential.for
controlling the filamentous organisms frequently encountered wlth actlvated
sludge systems treating D.C. wastewater, the remaining studies were focused
on the potential of chlorine. In all cases Clorox was used, and the equiva-
lent C12 dosage was determined by the procedure in Standard Methods (10).
95
-------
9
8
7
6
.-I
........
bO
~
. 5
z
I
~
1M
\D 0 4
0\ Z
+
IN
0 3
z
'-'
2
1
H202 Dosage, mg/1
AFTER
PRIMARY
INITIAL
o 0
\1 18.9
o 37.7
~ 75.4
o 113
o
6.3
12.6
25.1
37.7
30
60
90
120
150
180
210
TIME, minutes
Figure A-I.
Effect of H202 dosage on rate of nitrification in first laboratory test.
-------
9
8
7
,...., 6
.......
b()
S
.
z 5
I
""'
1C""1
0
Z
+ 4
IN
0
Z HZOZ Dosage, mg/l
'-' 3
o 0
2 7 10
0 20
1 b. 30
0 40
30 60 90 120 150 180
'"
......
TIME, minutes
Figure A-2.
Effect of H202 dosage on rate of nitrification in second laboratory test.
-------
Clorox (equivalent C12 = 112 mg Cl2/mll was ~dded to five samples of
recycle from the single stage system at equivalent Cl2 doseR of 0, 1, 2, 4
and 8 mg/l. Th€ recycle samples were stirred for seve:a1 s~cp~ds and then
primary effluent was added in a 2:1 ratio to produc~ f1na! equ~valent C12
doses of 1/3 the above values. The increase in (N02 + N03)-N was ~oni~ored
in each of the five aerated samples and the results are presented ln Flgure
A-3. There was no apparent inhibitory affect on the nitrifying organisms.
The same type of experiment was conducted the following day with equi:alen~
C12 doses to the recycle of 0, 10, 20, 30 and 40 mg/l.. ~he decrease ln NH4-N
was monitored and once again there was no apparent inhlbltory affect on the
nitrifying organisms. Based on these two brief studies, it appeared that one
could potentially control filamentous growth with C12 in a nitrifying system
without affecting nitrification. This hypothesis was further tested on a
larger scale with three additional studies.
A 28.9 m3 (7630 gal) reactor consisting of eight completely mixed passes
in series (16) was operated at the pilot plant during the summer of 1975.
This activated sludge system was receiving D.C. primary effluent and was
operated at a sufficiently high SRT to achieve complete nitrification. C1orox
was fed to the recycle stream of this system at a point immediately prior to
its entering the reactor for a 19-hour period. The steady feed rate of
13.5 ml/min (86 mg Cl /m1 equivalent strength) corresponded to a Clz dosage
of 8.8 mg/l based on the steady 132 l/min (35 gpm) influent flow. As shown
in Table A-l, the system continued to nitrify throughout the period of Clorox
addition. The data suggests a reduction in the nitrification rate of about
20%.
An additional study was conducted with the 8-pass reactor in March 1976
using an applied C12 dosage near the upper limit of values commonly reported
in the literature for the control of filamentous growth. Clorox (106 mg
C12/ml) was added for 19.5 hours at a steady rate of 21.4 ml/min. which
resulted in an equivalent chlorine dosage to the process of 20.3 mg/l based
on the steady 112 l/min (29.5 gpm) influent flow. Again the Clorox was added
to the recycle stream immediately prior to the point where it entered the
reactor. As shown in Table A-2, the system continued to nitrify throughout
the period of Clorox addition with no obvious impact on the nitrification
rate.
The final pilot plant study to be reported was conducted with a
completely mixed activated sludge system operating on D.C. primary effluent.
The system was operated at a steady flow of 114 l/min (30 gpm) for a reactor
detention time of 4.31 hours based on influent flow. The recycle flow rate
was 49 l/min (13 gpm). Clorox with an equivalent C12 concentration of III mg
C12/ml was added at a steady flow of 10.9 ml/min. Tne Clorox was added to
the recycle stream immediately ahead of the reactor. Based on the average
114 l/min (30 gpm) influent flow, the Clorox addition corresponded to a C12
dosage of 10.6 mg/l. The dosage was started at 1300 hours on March 15 and
continued for 24 hours. Reactor D.O._was m~intained above 3 mg/l. The
reactor solids concentrations ~nd (N02 + NO )-N concentrations are summarized
in Figure A-4. The reactor NH4-N concentra€ion remained below 1 mg/l
throughout the period of Clorox addition and for the additional day that
monitoring was continued.
98
-------
10
9
8
r-I
....... l:::.
bO 7
s
~
Z
I
/"', 6
1("')
0
Z
+
IN 5
0
z
'-'
4
EQUIVALENT
3 C12' mg/1
o 0
6 1
2 0 2
'V 4
1 <> 8
20
40
60
80
100
TIME, minutes
Figure A-3.
Effect of C1orox addition on rate of nitrification.
99
-------
TABLE A-1. NH+-N AND (NO- + NO-)-N LEVELS IN A SIMULATED
PLtlG FLOW SYStEM DU~ING CLOROX ADDITION
(SEPTEMBER 17-18, 1975)*
C 0 nee n t rat ion, m g / 1
Date Time MLVSS Parameter Pass Pass Pass Pass
mg/l 1 2 3 4
NH + -N < 1.0
9/17 1330 1,250 (NO; +4NO;)-N 4.3 6.9 9.1 10.9
NH+-N 2.7
9/17 1520 1,260 (NO; +4NO;)-N 4.6 7.5 9.1 11.5
I-' NH+-N 7.1
o (NO; +4NO;)-N
0 9/17 2100 1,070 4.7 7.5
+ 3.2
NH -N
9/18 0100 1,260 (NO; +4NO;)-N 5.6 9.2
NH+-N 1.3
9/18 1000 1,240 (NO; +4NO;)-N 5.3 8.6
* Clorox Addition Started on 9/17 at 1400 hours
* Clorox Addition Ended on 9/18 at 0850 hours
* Influent Flow = 132 l/min (35.0 gpm)
* 0
Temperature = 25 C
* Recycle Flow = 42.4 l/min (11.2 gpm)
-------
TABLE A-2.
+ --
NH4-N AND (N02 + N03)-N LEVELS IN A SIWJLATED
PLUG FLOW SYSTEM DURING CLOROX ADDITION '/~
(MARCH 24-25, 1976)
Date/Time + mg/1 (NO; + NO;)-N, mg/1
NH4-N,
Pass Pass Pass Pass Pass
6 2 4 6 8
3/24
1100 < 0.2 5.1 7.8 7.7 8.0
1500 < 0.2 6.0 11.2 11.8 11. 5
2000 < 0.2 6.4 11.8 13.1 13.7
3/25
0200 0.4 5.1 10.1 11.1 11.4
0800 0.8 6.0 8.6 9.1 9.5
1300 < 0.2 6.7 9.3 9.3 8.8
*Inf1uent Flow = 112 l/min (29.5 gpm)
*Recyc1e Flow = 60 l/min (15.9 gpm)
*Temperature = 180C
*C1orox Addition Started @ 1100 hours on 3/24
*C1orox Addition Ended @ 0630 hours on 3/25
101
-------
M
---...
DO
8
.
Z
I 12
/'"'.
1M
0
Z
+ 10
IN
a
Z
.........
1< CL) fed @ 10.c) mg/l ,
3600
3400 MLSS
M
---...
00
S
f-' U) 3200
a
N Q
H
H
a
U) 3000
~
0
E-<
U
~ 2800
~ -G--
~ --G-
--{]- -0
2600 / !J MLVSS
1200 2000
~ 3-15-76 ~<
0400
1200
3-16-76
2000
0400 1200
)o~ 3-17-76 ~
Figure A-4.
TIME (hour) and DATE
Reactor solids and (NO; + NO~)-N levels in a complete mix reactor
during and after Clorox addition.
-------
These brief studies indicated that chlorine dosages in the range
commonly utilized for the control of many nuisance filamentous forms can
be applied without any drastic impact on the nitrifying organisms. The
effect of continuous chlorine addition over long time periods was not
examined, and hence the ClZ dosages successfully used here may not be
feasible for extended operation. However, continous ClZ addition at low
dosages was stated to be effective for control of sludge bulking at the
Central Contra Costa plant without impairing nitrification efficiency (1).
103
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TECHNICAL REPORT DATA
(Please read InsJrnctions on the reverse before completing)
1. REPORT NO. 12. 3. RECIPIENT'SACCESSIONoNO.
EPA-600/2-79-l57
4. TITLE AND SUBTITLE 5. REPORT DATE
SEQUENTIAL NITRIFICATION-DENITRIFICATION IN A November 1979 (Issuing Date)
PLUG FLOW ACTIVATED SLUDGE SYSTEM 6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S) 8. DERFORMING ORGANIZATION REPORT NO.
James A. Reidman
9. PERFORMING ORGANIZATION NAME AND ADDRESS . 10. PROGRAM ELEMENT NO.
Government of the District of Columbia IBC611
Dept. of Environmental Services 11. CONTRACT/GRANT NO.
EPA-DC Pilot Plant, 5000 Overlook Avenue S.W.
Washington, D.C. 20032 68-03-0349
12. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED
Municipal Environmental Research Laboratory-Cin., OR FINAL REPORT 10/74-7/76
Office of Research and Development 14. SPONSORING AGENCY CODE
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268 EPA/600/l4
15. SUPPLEMENTARY NOTES
Project Officer: Irwin J. Kugelman (513) 684-7633
16. ABSTRACT The use of' the carbon sources present in municipal wastewater to provide the
energy required for nitrification-denitrification was evaluated on a pilot plant scale
in a simulated plug flow reactor. Most of this report is devoted to the results from
operation of a nine-pass activated sludge system receiving primary effluent. The first
two passes and the last pass were aerated whereas the remaining passes were mechanicall~
mixed. Nitrification occured in the aerated passes and denitrification in the others.
By maintaining a sufficiently low process loading, nearly all of the incoming ammonia
was oxidized in the first two passes+with most of the nitrate subs~quent~y denitrified
in the next six passes. Residual NR4-N levels of 0.1 mg/l and (N02 + N03)-N levels
of 1.0 mg/l were obtained with both steady state and diurnal flow. FeCl addition
during a portion of the study increased the P removal to approximately 9d% with no
dis'cernible impact on the nitrification-denitrification performance.
Nitrification and denitrification kinetic rates measured during laboratory
studies were found to correlate well with actual process rates. These rates were
obtained under varying conditions of temperature, available COD, length of initial
aeration period, etc.
I If chem1cal add1t1on 1S to be used for the control of f1lamentous organ1sms i
~without impairing the autotrophic nitrifying organisms, chlorine appeared to offer a ~
~ much.g.r.eat.er._.po.tentiaL_f.o.r~...succ.essthan. did .HZ~~-."__'c~------~---_..._~._-----_._._-:
C KEY WORDS AND DOC T ANAL YSIS
a. DESCRIPTORS rD'N~-"R"O"N 'ND
-------
United States
Environmental Protection
Agency
Environmental Research Information
Center
Cincinnati OH 45268
Postage and
Fees Paid
E nvironmenMl
Protection
Aqpncv
FPA 33S
Official Business
Poniilty for Private Use. $300
l Fourth Clriss Rjte
Book
the
or co$»y. ami return to th«
Mt ham3 corner
H you cfc not «w»r) to f®c«iv« th««« reports CHf CK
detach or c<^>y rhis cov®f ami return to th» ad«Jr»fs 10 the
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EPA-600/2-79-157
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