THE USE OF A SEQUENCING BATCH REACTOR (SBR) FOR THE REMOVAL OF ORGANICS AND NUTRIENTS WHEN SUBJECTED TO INTERMnTENT LOADING Kenneth Allen Haggerty P.Eng. A thesis submitted in conformity with the requirernents for the degree of Master of Applied Science Graduate Department of Civil Engineering University of Toronto O Copyright b y Kenneth Haggerty, 1 997
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THE USE OF A SEQUENCING BATCH REACTOR (SBR) FOR THE
REMOVAL OF ORGANICS AND NUTRIENTS WHEN SUBJECTED TO
INTERMnTENT LOADING
Kenneth Allen Haggerty P.Eng.
A thesis submitted in conformity with the requirernents
for the degree of Master of Applied Science
Graduate Department of Civil Engineering
University of Toronto
O Copyright b y Kenneth Haggerty, 1 997
National Library I * m of Canada Bibliothèque nationale du Canada
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THE USE OF A SEQUENCNG BATCH REACTOR (SBR) FOR THE REMOVAL OF
ORGANICS AND NUTRENTS WHEN SUBJECTED TO INTERMITTENT LOADNG
by Kenneth Allen Haggerty P.Eng.
A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Graduate Department of Civil Engineering,University of Toronto
A synthetic waste water has been treated with lab scale sequencing batch reactors (SBRs)
operating in a mode designed to remove organics and nutrients (nitrogen and phosphoms). These
SBRs were subjected to starvation under differing operational conditions for between 58 and 1 17
days. The ability of an SBR to maintain its capability to remove organics and nutrients d e r
periods of inactivity was determined. By not decanting the SBR at the end of the cycle preceding
starvation, and allowing the SBR to remain quiescent during the starvation period, the retention
of the treatment capability was substantial d e r 58 days at 22" C. Survival of treatment capability
is fùrther enhanced by operating the SBR pior to starvation in a mode with an extended anoxic
period (3.5 hr) during and after fiIl. Conversely the process survival is significantly reduced if the
SBR is decanted after the last cycle preceding starvation, and is further reduced by mixing, and or
aerating the remaining rnixed liquor . Higher temperatures appear to reduce the process
survivability .
ACKNOWLEDGMENTS and DEDICATION
1 would like to express my gratitude to my supervisor Professor David M.
Bagiey for his insightfùl guidance throughout this work, and his encouragement
throughout my studies.
1 thank my uife Eeva: without who's forbearance, encouragement, and
understanding , 1 would never have been able to maintain the resolve necessas. to
complete this project .
I dedicate this work to my brother Gordon, whose untimeiy death caused me
to examine and repriorize rny objectives.
TABLE OF CONTENTS
Page
Abstract
Acknowledgments and Dedication
Table of Contents
List of Tables
List of Figures
Nomenclature
Chapter 1 Introduction
1 . 1 The Wastewater Treatment Problern
1.2 The Effects of Inactivity on the Operating Performance of an SBR
1.3 Objectives
Chapter 2 Literature Survey
2.1 Some Aspects of Bacterial Growth and Starvation Responses
2.1.1 Introduction
2.1.2 The Ce11 Cycie
2.1.3 Starvation Regulon
2.1.4 Viability
2.1.5 General S tarvat ion Responses
2.1.6 Resuscitation
2.1.7 Ce11 Death
2.1.8 Nutnent Uptake Systems
2.1.9 Intracellular inclusions, PHA and Polyphosphates
2.1.10 Extra Cellular Products
2.1.1 1 Starvation Related Experimental Observations in Wastewater Treatrnent
2.1.12 Observations
2.2 Nutrient Removal Mechanisms
2.2.1 Ammonia and Nitrate Removal
2.2.1.1 Introduction
2.2.1 -2 Arnmonia Removd
2.2.1.3 Nitrification
2.2.1.4 Denitrification
2.2.2 Biological Phosphorus Removd
2.2.2.1 f ntroduction
2.2.2.2 Prescription
2.2.2.3 Description
2.3 Sequencing Batch Reacton
Chapter 3 Materials and Methods
3.1 Overview
3.2 Experimental Setup
3 -3 SBR Construction
3.4 Artificial Wastewater
3 -5 SBR Operation
3 -6 Starvation
3 -7 Restart After Starvation
3.8 Sampling and Analytical methods
Chapter 4 Results and Discussion:
4.1 Pre-Starvztion Result s and Discussion
4.1.1 SBR Stari-up Problems
4.1 -2 Pre-Starvation SBR Operation
4.1.2.1 Organics Removal
4.1.2.2 PO: - P Release
4.1.2.3 PO: - P Uptake
4.1 -2.4 NH,' - N and NO,' - N Removal
4.1.2.5 Discussion
4.2 Starvation
4.2.1 CODf During Starvation
4.2.2 NH,+ - N and NO; - N During Starvation
4.2.3 PO:' - P Dunng Starvation
4.2.4 Status at End of Starvation
4.2.5 Discussion
4.3 Starvat ion Recovery
4.3.1 CODf During Starvation Recovery
4.3.2 NH,' - N and NO, - N Dunng Starvation Recovery
4.3 -3 PO,> - P Durhg Starvation Recovery
4.3.4 Nitrate Attenuation of PO,% - P Removal Capability
4.3 -5 Discussion
Chapter 5 Summary, Conclusions and Recommendations
5.1 Summaxy
5.2 Conclusions
5.3 Recornmendations for Further Study
References
Appendix A Expenmental Data
vii
List of Tables
Table - Table 1 Baîtery 1 SBR Operation
Table 2 Battery 2 SBR Operation
Table 3 Starvation Conditions
Table 4 SBR Operating Schedules for Restart
Table 5 Parameters During CODf Uptake
Table 6 CODf in Anoxic Period and in Effluent
Table 7 CODf in Anoxic Penod (28 rpm Mu<)
Table 8 PO,)' P Yield
Table 9 PhosphatdAcetate Ratios fiom the Literature
Table 10 COD Requirements for Denitrification During Fil1
Table 1 1 Mixed Liquor Prior to Restarting SBRs
Table 12 CODf Removal During Starvation Recovery
Page
39
40
41
42
48
56
57
59
60
63
73
75
. . . Vlll
List o f Fipures
Fipu re
Figure 1 Chiorophyll vs Nutrient Concentrations
Figure 2 Overview of SBR Arrangement
Figure 3 SBR with Level Probes
Figure 4 SBRs 2 and 3 in Battery 1
Figure 5 Level Control Circuitry
Figure 6 Subarate Flow Diagrarn
Figure 7 Expenmental Setup
Figure 8 SBR 1 Tracking Study Aug. 13, 1996
Figure 9 SBR 1 Tracking Smdy Aug. 13, 1996
Figure 10 CODf and DO Uptake Study for SBR 1
Figure 1 1 SBR 1 Tracking Study Onober 8, 1996
Figure 12 SBR 2 Tracking Study Oaober 24, 1 996
Figure 13 SBR 3 Tracking Smdy Novernber 12, 1996
Figure 14 SBR 4 Tracking Smdy November 7, 1996
Figure 1 5 SBR 5 Tracking Smdy November 12, 1996
Figure 16 SBR 6 Tracking Study November 12, 1996
Figure 17 PO,; P Release vs NO,' N Denitnfied
Figure 18 Battery 1 CODf During Starvation
Figure 19 Battery 2 CODf During Starvation
Figure 20 CODf vs Duration of Starvation
Figure 2 1 NO; - N During Starvation (Battery 1)
Figure 22 NO; - N During Starvation (Battery 2)
Figure 23 PO,= - P During Starvation (Battery 1 )
Figure 24 PO^^ - P During Starvation (Battery 2)
Figure 25 SBRs 1 and 2, NO; - N and PO: - P
Figure 26 Efnuent CODf patteries 1 and 2)
Figure 27 Effluent NH,* - N and NO,- - N (Battery 1 )
Figure 28 Effluent NH,' - N and NO,' - N (Battery 2)
Figure 29 Effluent PO: - P During Starvation Recovery
Figure 30 SBR 4 PO,* - P During Starvation Recovery
Figure 3 1 PO,% - P and NO; - N in SBR 4 After Restart
AODC
A w w
BPR
COD
CODf
CODt
DO
DVC
HRT
ML
mss
MLVSS
ORE'
OUR
P A 0
PHB
PT
PWQO
RBCOD
SBR
Nomenclature
acradine orange direct count
artificial wastewater
biological phosphorus removd
chernical oxygen demand
COD of filtrate (soluble COD)
total COD
dissolved oxygen
direct viable count
hydraulic retention time
mixed liquor
mixed liquor suspended solids
mixed liquor volatile suspended solids
oxidation reduction potential
oxygen uptake rate
polyphosphate accumulating organism
polyhydroxybu~~ate
total phosphorus
provincial water quality objectives
readily biodegradable COD
sequencing batch reactor I
SRP
SRT
SS
u
VBNC
VFA
VSS
WWTP
soluble reactive phosphoms
solids retention time
suspended solids
substrate uptake rate
viable but non cultureable
volatile fatty acid
volatile suspended solids
wastewater treat ment plant
xii
CHAPTER 1
INTRODUCTION
1.1 The Wastewater Treatment Problem
Soluble reactive phosphorus (SRP), or orthophosphate (PO,%- P) is generdly
the Iimiting nutrient in the oligotrophic lakes in Precarnbrian regions, and
eutrophication is often attendant its addition [Hutchinson, 19731. Figure 1 (repnnted
with permission) clearly shows this close relationship between eutrophic status and
( 1 ) Calcolated losscs duc IO denitrificatiai during anoxic paiod have betn dtduaed
Table 9 PhosphatdAcetate Release Rntios from the Literature
Wentzei
Anrn
Mino
Wentzel
A m n
Corneau
Smolders, Y,,, = 0.19pH - 0.85
Release Ratio@-moUC-mol)
The PO4& - P concentrations in the ML at the start of the study were in every
case higher than the concentration in the effluent at the end of the tracking study.
NO,' - N concentrations in the ML were reduced fiom that in the effluent, but only
SBRs 5 and 6 were O. This is somewhat different fiom results reported by Shin et
a1.(1992), who only reported PO,% - P release d e r al1 of the NO,' - N was removed.
Examination of the tracking studies indicates that ail NO; - N was removed by the end
of fil1 in al1 SB& except for SBR 4, which took 1 hr for complete denitrification to
occur. The relationship between PO,% - P yield and overall NO,' - N losses is quite
strong indicating that the COD used for denitrification was related to the PO,> - P
energetics. The maximum PO: - P released during the anoxic period varied inversely
with the NO,' - N denitrified during the anoxic fil1 penod, and can be charactenzed by
the relationship mg PO,= - P released /L = 9.23 - 2.34 x (mg NO,' - N denitrified)
(? = 0.92). This is shown in Figure 17, it is indicative of an RE3COD shortage, and can
ody be considered as specific to the systems used in these experiments. It is clear fiom
the PO,> - P release observed for SBRs 5 and 6 in which significant denitrification
ocnirred prior to fill, that endogenous carbon stores, which are thought to have been
consumed during denitrification, were not limiting to the PO,> - P release.
Figure 17 PO4 P Release w NO3 N Denitrified
There was no observed relationship between PO: - P yield or concentration
and KRT.
4.1.2.3 PO," - P Uplprake.
An examination of the tracking study results plotted in Figures 1 1 to 16
indicates that the PO: - P uptake rate had essentially reached O for SBRs 1, 2, 4, and
6 by the end of the aeration cycle. SBR 3 was still exhibiting PO: - P uptake d e r
4.5 hours aeration. This SBR however, had only been operating in a PO,% - P removai
cycle for 2 weeks pnor to this study. SBR 5 was receiving aeration for 3 hours, and
would have probably benefited nom additional aeration time, or a higher rate of
aeration. Within the overall cycle this could have been accomrnodated as this SBR
exhibited the highest release rate of any in the study as it did not require al1 of the
anoxic cycle for complete P release.
1.1.2.4 NH,' - N a n d N O i - N .
The concentration of NO,' - N in the effluent was expected to vary with HRT,
being higher for shorter HRTs as the initial NH,' - N concentration would be higher
due to the lower dilution by the ML rernaining fiom the previous cycle. This was not
the case. The effluent concentration averaged 8.4 mg/L + 0.7 mgL. For al1 SBRs an
average of 70% of the NH,' - N applied was removed (standard deviation 2%).
In every case, except for SBR 4, NO,' - N concentrations in the effluent were
higher than in the ML at the start of the cycle (Table 10). indicating that the NO,' was
acting as an electron acceptor and denitnfication was occurring. Concurrently the
NH,+ - N in the ML was higher than in the effluent. This was of special note in SBR 5
where over 3 different tracking studies the NH,' - N increased from undetectable ( les
than 0.1 m a ) in the effluent to a level of 5 m a in the ML before fill. In spite of the
COD required for denitrification, CODf was always higher in the ML at the start of
the cycle (before fill) than in the effluent. Endogenous processes were no doubt
responsible for this effect, but the actual mechanisms were not determined. As
previously mentioned ail NO,' - N was removed by the end of fiil in dl SBRs except
for SBR 4, which took 1 hr for complete denitrification to occur. The efnuent NH,' -
N was uniformiy near O. Table 10 summarizes the NO,' - N removed during fil1 by
denitrification and the contribution of this process to COD removai dunng fill.
Table 10 COD Requirements for Denitrification During Fill - -
f arameter SBR
(1) CaIcuIated at 2.84 mgCODDmg NO; - N darivified (Scaion 2.2.1.4)
In order to be assured of the extent of biological NH,' - N removal, a study
NO; - N in emuent, mg/L
NO; - N in ML before fiIl, mg/L
COD Required for denitrification, mgLu)
was conducted to determine whether air stripping was a factor. Using the same type of
aerator devices and airstones as were used in the SBRs, air was bubbled into a jar test
vesse1 containing 2 L of tapwater with 9.4 mgL NH,' - N at 20 OC and at pH 7. Over
a 25 hour study period NH,' - N was found to be lost at a rate of 0.068 mg/L.h (12
samples, i = 0.87). Over a 4 hour aeration period this rate projects a loss of 0.27
mg/L, and confirms that air stripping was not a signifiant factor in accounting for any
NH; - N losses, as this represents less than 2.6% of the NH,' - N in any of the SBRs.
1
8.3
3.6
5.8
3
9
5.1
7.2
2
9.2
3.6
3.8
1
8
9.8
13.9
5
8.8
O
O
6
7.2
O
O
4.1.2.5 Discussion 90% o f the CODf in the AWW was removed, and this was
unafliected over the range of HRTs studied. However, an unexpected CODf removal
profile was observed, whereby 57% of the CODf was captured by the end of fill
without a concurrent PO4$ - P release. This is attnbuted to the high DO in the AWW
(z 8 mg/L), and is not expeaed to be representative of normal residential wastewater.
The CODf removed dunng fill is suspected to be =COD which would othexwise
have been available for use by the PAOs. The relationship between NO, - N
denitrified during fill. and PO: - P release indicates that the p04> - P release observed
in this study wîs limited by a shortage of available RBCOD. Denitrification funher
reduced the RBCOD, and hence caused the reduction in PO,> - P release during the
anoxic period. Since denitrification occurred in SBRs 5 and 6 prior to fill and they
both achieved higher PO,* - P release than the other SBRs it can be concluded that
shortage of endogenous stores was not a factor in PO," - P release, nor were
endogenous stores significantly involved in denitnfication during the anoxic cycle.
Nitrification was not dependent on HRT and was easily achieved within the
aeration time provided. On average 70% of the applied N in the AWW was removed.
Dunng the course of the experiments it was thought that the CODf captured
represented CODf which was not easily degraded, and hence was not able to play a
role in the PO,> - P release. Subsequent analysis has led to the conclusion that other
causes discussed above were at least panly responsible. Had there been adequate time
during the experiments the question of RBCOD availability could have been resolved
by testing the AWW for short chah fatty acids, or RBCOD. Additionaily, measures to
maintain a low DO in the AWW (< 1 mgL) could have been employed. It may be that
the complex AWW used simply contained less RBCOD than normal residential
wastewater.
In order to operate at steady-state and produce an effluent with low PO: - P
concentration it is necessary to remove sludge or ML fiom the system after the
PO,* - P uptake is completed (Section 2.2.2.2), and before any subsequent release
commences. The problems encountered in achieving PO: - P release coupled with
time constraints prevented this fiom being accomplished in these studies.
The ability of SBRs 5 and 6 to completely denitrify afler decant and pnor to fil1
without significant PO: - P release represents a phenornenon which merits further
study due to tbe favorable effect on PO,& - P release. It is not understood why this did
not occur to the sarne extent in the other SBRs.
4.2 Starvation
The SBRs were tested for CODS NH, - N, NO,' - N, and PO:' - P several
times during the course of starvation. Each of the parameters characterized is
considered in one of the following sections. It should be remembered that SBRs 4 and
5 were not stirred during the sampling process so as not to jeopardize the overall non
- mixed expenmental status. Therefore the parameters measured in these SBRs may
represent non-homogeneous conditions.
4.2.1 CODf Durina Starvation
The CODf rose significantly within the initial 2 to 3 days of starvation as can
be seen in plots of the CODf readings for batteries 1 and 2 (Figures 18 and 19
respectively). In Battery 1 higher levels of CODf were reached and maintained in SBR
2 (aerated and decanted) than in SBR 1 (stirred and decanted). The levels in SBR 3
(stirred, but not decanted) were sirnilar to those in SBR 1, indicating that CODf
concentration was a function of DO availability. When factored to account for the fact
that the SBRs were decanted, the levels in 1 and 2 were lower than those in 3. The
overall upward trend in CODf level with increased starvation time for SBRs 1 and 3
appears to confirm that diffusion supplied DO was the limiting factor.
In Battery 2 the CODf levels for SBR 5 showed an initiai spike, then dropped
(this may not have been a representative sample due to no mixing), and increased over
time, whereas the levels in SBR 4, and 6 dropped slightly with time after the initial
increase.
Figure 18 Battery 1 CODf D u ~ g Starvation
Figure 19 Battery 2 CODf During Stsivation
flCOM: end 1 o COM: day 1
50 60 70 80 90 100 110 120 13C
s tarvation duration, days
Figure 20 CODfvs Duration of Starvation
The overall general trend of CODf with duration of starvation which appears in
Figures 18 and 19 and is summarized in Figure 20 is that CODf starts at approxirnately
the same level (avg. 24 mg/L) in al1 SBRs, and except for SBR 4, reaches a maximum
level of 70 to 100 mgL. Note that SBRs 1 and 2 were decanted prior to the onset of
stwation, and given the resulting higher biomass concentration at the start, they will
therefore possibly have higher CODf concentrations than would be the case if they had
not been decanted.
4.2.2 NH,' - N and NO; - N Durine Starvation
During the course of starvation nitrate concentrations increased in dl SBRs.
Concentrations in SBRs 1 and 2 (decanted) were much higher than in the others, with
SBR 2 having the highest concentration of d l . Data shown in Figures 2 1 and 22
suggest that the production of nitrate is lirnited by either the interna1 stores of available
N andor pH, and is a fûnction of the availability of oxygen. Afier o b s e ~ n g the rapid
nitrate formation and an associated drop in pH in SBRs 1 and 2, additional aikalinity
was added to SBR 3 (500 mglL of both N%CO,, and NaHCO,) at the onset of
starvation. This was excessive and raised the pH to 9.1 which is above the optimal
level for nitrification. D u ~ g the course of starvation and associated nitrification the
pH did not drop below 8.5 in SBR 3.
Figure 21 NO3 - N During Starvation (Battety 1)
The nitrate reading for SBR 6 of 28.2 mg/L a the end of its 84 day starvation
penod was similar to the 2 1 mgL for SBR 3 after 71 days starvation. However the
concentrations in SBRs 5 and 6 at 55 days starvation were only 4 mg/L and 4.5 mg/L
respectively. Whereas the concentration in SBR 6 increased thereafter, that in SBR 5
was reduced to O f ier 78 days. Concurrent with this NH, - N levels were 4 mg/L in
SBR 5 and 1.3 mgL in SBR 6. The rasons for this nitrification/denitrification
difEerence between these SBRs is thought to be due to SBRs 4 and 5 not being mixeci.
In battery 2 the pH remained near 7.
Figure 22 NO3 - N Durhg Staivation (Battery 2)
4.2.3 PO:- P durine starvation
Al1 SBRs exhibited PO: - P release aller the onset of starvation. The PO: - P
concentration reached a maximum shortly f i er starvation commenced, and there was
virtually no increase thereafter. This is shown clearly for Batteries 1 and 2 in Figures
23 and 24.
A SBR 1 4 ...
O O SBR 2
B ~ R 3
th starved, d
Figure 23 P04 - P DuMg Stawation (Battery 1)
O 20 40 60 80 lot
the starved, d
Figum 24 PO4 -P During Starvation (Battery 2)
The PO,% - P release rate for SBR 2 of 0.8 [email protected] was double that of 0.4
mg/l.hr for SBR 1. Both SBRs 1 and 2 had a total P content of approximately 88
rngL before decant, which converts to after decant total concentrations of 176 mgL
for SBR 1, and 234 mg/L for SBR 2. The maximum PO,& - P measured in SBR 1
was 17.6 mg& or 10 % of the total P. The maximum PO,$ - P measured in SBR 2
was 119 mgL or just over 50% of the total P. The average PO,& - P for al1 SBRs
except SBR 3 at the end of starvation was 13.3 mg/L.
The progress of the changes in PO: - P concentrations for SBRs 1 and 2 in
relation to their NO; - N concentration is compared in Figure 25. The PO,> - P
concentration in SBR 2 increased at roughly the same rate as that of the NO; - N, and
reached its maximum concurrent with the NO; - N concentration starting to level oE
NO, - N formation in SBR 1 is subject to a lag of 8 days before measurable
concentrations are observed.
It is no? known why the concentration of POP - P in SBR 2 was so much
higher than in al1 of the others. It would appear that this difference is related to
aeration. One possibility is that a precipitate is forming in al1 SBRs at a slow rate, and
the PO: - P release rate in SBR 2 is much greater than this rate. The PO: - P
concentration simply overtakes the precipitate formation. Later on when the PO,* - P
formation has ceased, the precipitate formation continues and the PO:- - P
concentration is gradually reduced until it equilibrates at the same level as in the other
SB&. ,
Figure 25 SBR's 1 and 2, NO3 - N and PO4 - P
4.2.4 Status at end of Starvation
Prior to restarting the SBRs the characteristics of the ML were recorded
before the addition of substrate. These were as show in Table 1 1 .
Table 11 Mixed Liquor Prior to Restarting SBRs
SBR # DAYS STARVED, (T) CODf
mg/L
NO; - N
mgn,
PO, - P
mg/L
4.2.5 Discussion
Endogenous decay occumed during starvation and was dependent on
availability of DO as was evident from the progression of CODf and NO; - N
concentrations with tirne. NO,' - N formation was highest in the decanted SBRs (1 and
2), lower in the mixed SBRs (3 and 6), and lowest in the non-mixed SBRs (4 and 5). It
is likely that the low pH in SB& 1 and 2 was inhibitory to further nitrification, and
possibly to other endogenous processes. The high pH in SBR3 may have dso had an
inhibitory eEect. PO: - P release appeared to be a fùnction of endogenous processes,
however the total quantity of PO,% - P released was not determined.
4.3 Starvation Recovery
4.3.1 CODf Dunne Starvation Recovery
When the SBRs were restarted, the rate at which the effluent CODf stabilized
varied among the SBRs as shown in Figure 26, and Table 12 which sumrnarizes the
key points. The effluent CODf from the decanted SBRs started at a higher level and
was reduced at a slower rate than the others (excluding SBR 5, see 4.3.2).
The temperature diflerence between Batteries 1 and 2 appears to have been
the other detennining factor in the rate of recovery of CODf removal capability.
Starvation at the 5°C higher temperature (Battery 1) resulted in generally slightly
higher CODf Iwels dunng the recovery period. Aithough SBR 3 reached its
prestarvation CODf level after the second day, this was a high level as this SBR had
been converted fiom a series of other cycles 2 weeks pnor to the onset of stamation
and had not stabilized. At the end of starvation it had a CODf of 70 m a , which was
6 mg/L below its level at the start of starvation.
From the standpoint of recovery of CODf removal capability SBR 4 performed
the best, followed by SBR6, and then SBRS which expenenced aeration problems
(Section 4.3 -2).
7 14 2 1
Tme aaer s t a ~ t i a n , dayo
Figure 26 Emuent CODf
Table 12 CODf Removal During Starvation Recovery
NR - not reached.
days to 2.5X prestarvation lcvel
days to 40 m g L lcvcl
days to 30 mgL level
9 1 O O 1 2 3
9 10 4 1 9 3
NR 15 NR 1 14 8
4.3.2 NH: - N and NO; - N Durinn Starvation Recoverv
Dunng the period when starvation recovery was monitored neither SBR 1, nor
SBR 2 recovered the ability to nit* (Figure 27). However, during a tracking study
done after 14 days of recovery, SBR 1 showed a 2 mg/l reduction in NH,' - N which
may have partiy been due to growth, and an NO; - N concentration of 0.5 mg/L . SBR
3 showed decreased NH,' - N on the 6th day, and NO; - N was measurable on the 7th
day. By the 19th day nitrification was complete for both SB& 3 and 4. SBRs 4, 5, and
6 (Figure 28) showed abiiity to nitnfy on the first cycle d e r restart. Unfortunately a
blizzard delayed receipt of testing reagents and there is a 12 day gap in the effluent
data for SBR 4. M e r 14 days the effluent nitrate level had reached 2.4 mgL, and
after 17 days was removing virtually al1 of the NH,' - N (0.2 mg/L). SBR 5 was found
to exhibit erratic NH,' - N etfluent levels. This was eventually traced to a problem in
the timer which activated the aerator. Its battery was low, and although it showed the
time properly, it occasionally did not trip the relay to start the aerator as scheduled,
resulting in varying NH; - N concentrations in the effluent. This also probably
affected the CODf discussed in the previous section. SBR 6 demonstrated irnrnediate
MI,' - N removai capability which gradually increased after a 3 day lag, unti1 after the
10th day NH,* - N levels were at 1 -8 mg& and NO; - N was at 6 mg/L
7 14 2 1
T i after starvation, days
Figure 27 Emwnt NH4 - N & NO3 - N (Batte y 1)
7 14 2 1
T m after starvation. days
Figure 28 Effluent NH4 - N & NO3 (Battery 2)
4.3.3 PO^^ - P durina starvation recoverv
It was decided to restart SBR 4 first because of its pre-starvation performance
wherein it had shown negligible PO,' - P release or uptake, but had shown good
organics removal as weii as nitrification-denitrification (Figure 14). During starvation
recovery PA0 activity in this SBR became evident during a tracking study of the 7th
cycle (2 days). This is discussed more fully in Section 4.3.4.
20
SBR 1
~ S B R 2
A SBR3
O SBR4
)IC S8R 5
V SBRG
7 14 2 1
T I after starvation. days
Figure 29 Effluent P M - P During Starvation Recovery
None of the SBRs in Battery 1 exhibited effluent PO,^ - P reduction to low
levels during the period monitored (Figure 29). However, SBR 1 did show a
differential of 1.8 m a PO,)' - P between the end of anoxic mix and the end of
aeration in a tracking study &er 14 days recovery. SBR 2 showed a reduction in
effluent PO: - P commencing on the 15th day, and a tracking study on the 20th day
revealed a differential of 6.8 mgL PO,% - P between the end of anoxic mix and the end
of aeration. SBR 3 showed no evidence of PO,* - P release or uptake in effluent or in
tracking studies.
AU of the SBRs in Battery 2 exhibited reduced PO,* - P concentrations in
their eflluent (Figure 29) during the course of starvation recovery. After 2 days SBR 4
showed a PO^* - P differential of 2.5 mg& between the end of anoxic mix and the end
of aeration in a tracking study, and after 14 days effluent PO,' - P was reduced to 0.4
mg/L . SBR 5 showed reduced levels of PO,> - P in the effluent after 2 days and
reached a level of 1.9 mg/L &er 5 days, a e r which the level commenced to rise. SBR
6 showed reduced effluent PO,* - P d e r 1 day of operation, thereafter levels dropped
progressively until the end of the study (10 days) when a level of 0.68 m a PO: - P
was reached.
4.3.4 Nitrate Attenuation of PO: - P Removal Capability
During the starvation recovery studies it was observed that PO,* - P release
and uptake was achieved and then graduaily lost, particularly in SBRs 4 and 5.
Whereas the problems with the aerator control in SBR 5 make it difficult to be certain
as to the cause of the variations, there was no such problem with SBR 4, and the loss
of PO,% - P removal capability was observed in a senes of tracking studies (Figure 30).
These studies clearly show the recovery of the capability to release and subsequently
take up PO: - P, and thereafter the gradua1 decline in this capability.
O 1 2 3 4 5 6 7 8
Tirne f mm start of cy cle. hr
Figure 30 SBR 4, P04 - P During Staivation Recovery
The progression of NO,' - N and PO,% - P concentrations for days 14, 18, and
36 is show in Figure 3 1
As with the prestarvation studies it is evident that as the NO,- - N
concentration to be denitrified increased, the PO,* - P released decreased. In addition
the length of time taken for denitrification increased as the NO,- - N concentration
increased. This served as a further demonstration that the systems studied were short
of RBCOD available for PA0 use.
O 1 2 3 4 5 6 7 8 Time from start of cycle. hi.
Figure 31 fO4 - P, & NO3 - N in SBR 4 After Restart
4.3.5 Discussion
There were two main factors which affected the ability of the SBRs to recover
organic and nutrient removal capabilities after starvation.
(1) Endogenous substrate utilkation, which was dependent on the avaiiability of DO,
was detrimentai to recovery of CODf removai capability, nitrification, and PO,* - P
release and uptake capability. This was demonstrated in SBR 2 which was decanted
and aerated, and to a lesser extent in SBR 1 which was lefl in the decanted state, and
would have therefore had a higher DO concentration than SBR 3 which was in the
same battery, but was not decanted and recovered quicker. SBR 3 responded less
quickly in developing CODf removal capability, but very much the same for NH, - N
removal as did SBR 4 which was 5°C cooler, but otherwise on the same cycle.
(2) SBR 6 had a longer anoxic period prior to starvation than did SBR 4, and this
appears to have selected for nitrifiers which better survived starvation. This longer
anoxic cycle also appeared to enhance the ability to recover Po,* - P release and
uptake as SBR 6 recovered removal capability quicker than any other SBR
The attenuation of PO,$ - P release and uptake observed prior to the onset of
starvation (Section 4.1.2.2) was observed to develop in SBR 4 during recovery fiom
starvation. The snidy clearly showed that as nitrification development proceeded (it
comrnenced not long prior to the study on day 14), there was a concurrent loss of
PO,= - P release and uptake capability, and an increase in PO,> - P in the effluent.
CHAPTER 5
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
5.1 Summary
HRT did not have a measurable effect on effluent quality over the range
studied (10.7 - 32 hr). AU of the SBRs were capable of removing at Ieast 90% of
applied CODf and producing an effluent with a CODf of 18.4 m a . 70% of the
applied NH, - N was removed and the remainder was completeiy nitrified in the
emuent which had an average NO; N concentration of 8.4 m a , . The HRT did not
influence the NO; N concentration in the effluent.
There was a shortage of RBCOD in the anoxic stage. This is believed to have
been partly a consequence of high DO in the AWW, which led to 57 % of the CODf
being captured during fil1 without a concurrent PO,% - P release. Due to the RBCOD
shortage, the presence of nitrate in the ML before fil1 was found to have a severe
negative impact on the ability to release and take up phosphate. PO,)' - P released was
reduced by 2.34 mg/rngNO; - N denitrified during anoxic fill. There was no
relationship between PO f - P released and HRT.
Dunng starvation endogenous processes were dependent on the availability of
oxygen. Consequently those SBRs which were not decanted recovered more quickly
than those which were decanted. The non-decanted SBRs were al1 capable of reducing
effluent CODf to below 40 mg/L within 4 days. The recoveiy of nitrification capability #
took considerably longer. SBRs with 3.5 hr anoxic cycles appeared to recover
complete nitrification capability more quickly (1 0 ci) than did those with 2 hr cycles
(1 7d- 19d). The same effiect was observed for recovery of PO,% - P release and uptake
capability which took 10 days to develop in SBR 6 (3.5 h) vs 14 days in SBR 4 (2h).
5.2 Conclusions
An SBR operated to treat AWW in a marner which will result in the removai
of organics, and nutnents is capable of recovenng its process capability afler periods
of starvation up to at least 84 days at 22°C.
The survival capability of the SBR treatment process depends to a large extent
on the condition which the SBR is lefi in at the onset of starvation and to a lesser
extent on the operating sequence of the SBR prior to starvation. Quiescent conditions
during starvation allowed for the most rapid recovery of treatrnent capability, and a
longer anoxic stage in the operating cycle was observed to enhance this effect.
5.3 Recommendations for Further Study
Research to resolve the following issues needs to be completed in order to
enhance the applicability of this technology.
(1) Determine the effect of temperature on starvation recovery over the ranges
encountered in typical field applications.
(2) The effects of longer HRTs employing longer anoxic and aeration stages
dunng restart need to be known in order to reduce the time taken for full process
recovery. This could assist in the optimization of an operating strategy which wouJd
result in the release of a high quaiity efluent after restart.
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APPENDIX A
EXPERIMENTAL DATA
Table 1 SOLIDS DATA AT TIME OF TRACKING STUDY SBR 1
TIME, h 2 3 4 AVERAGE a
MLSS, m%L 2130 2780 2050 2320 326
MLVSS, m@ 1760 2270 1680 1903 261
Table 2 SOLIDS DATA AT TIME OF TRACKING STUDY SBR 2
TIME, h 2 5 AVERAGE O
MLSS, mg/L 2910 2700 2805 105
MLVSS, mg/L 2580 21 10 2345 235
Table 3 SOLIDS DATA AT TIME OF TRACKING STUDY SBR 3 - - -- . --
TIME, h 2 5 AVERAGE 6
MLSSmgfL 1220 770 995 225
MLVSS, mg& 1050 700 875 175
TabIe 4 SOLIDS DATA AT TIME OF TRACKING STUDY SBR 4
m, h 2 5 6.5 AVERAGE d
MLSS, m@ 1170 1100 1190 1153 39
W S S , mgîL 1010 930 990 977 34
Table 5 SOLIDS DATA AT TIME OF TRACKING STUDY SBR 5
MLSS, mfl 2230 2160 2195 35
MLVSS, mg& 1890 1820 1855 35
Table 6 SOLIDS DATA AT TIME OF TRACKING STUDY SBR 6
TIME, h 2 5 AVERAGE d
MLSS, m g L 2800 2570 2685 115
MLVSS, mgL 2290 2070 2180 110
IMAGE EVALUATION TEST TARGET (QA-3)
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