Q IWA Publishing 2010 Water Science & Technology—WST | 61.8 | 2010
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Syntrophy of aerobic and anaerobic ammonia oxidisers
B. Wett, M. Hell, G. Nyhuis, T. Puempel, I. Takacs and S. Murthy
ABSTRACT
Deammonification is known as an efficient and resource saving sidestream process option to
remove the nitrogen load from sludge liquors. The transfer of the intermediate product nitrite
between both syntrophic groups of organisms – aerobic and anaerobic ammonia oxidizers (AOB)
– appears very sensitive to process conditions such as temperature, dissolved oxygen (DO) and
operating nitrite level. Growth kinetics for aerobic and anaerobic AOBs differ by one order of
magnitude and require an adequate selection of sludge retention time. This paper provides
measurement- and model-based results on how selected sludge wasting impacts population
dynamics in a suspended growth deammonification system. Anammox enrichment up to a
doubled portion in mixed liquor solids can substantially improve process stability in difficult
conditions. A case-study on low temperature operations outlines two possible strategies to
balance syntrophic consumption of ammonium and nitrite.
Key words
| anammox, AOB, cyclone, deammonification, DEMON, sidestream, sludge liquor
B. Wett (corresponding author)
Department of Environmental Engineering,
University of Innsbruck,
Technikerstr.13, A-6020 Innsbruck,
Austria
E-mail: [email protected]
M. Hell
Achental-Inntal-Zillertal Wastewater Cooperation,
HNr.150, A-6261 Strass i.Z,
Austria
G. Nyhuis
Cyklar-Stulz GmbH,
Rietwiesstrasse 39, CH-8737 Gommiswald,
Switzerland
T. Puempel
Department of Microbiology,
University of Innsbruck,
Technikerstr.23, A-6020 Innsbruck,
Austria
I. Takacs
EnviroSim Europe,
15 Impasse Fauré, 33000 Bordeaux,
France
S. Murthy
DCWASA, DWT,
5000 Overlook Ave., SW
Washington, DC 20032,
USA
INTRODUCTION
Single- and two-stage systems have been developed where
allow advanced acclimation to toxic ammonia levels
aerobic and anaerobic ammonia oxidation processes are
(Turk & Mavinic 1989).
catalysed either by suspended or fixed biomass. A fast
† Another group – anoxic heterotrophic biomass (AHB) –
growing number of successful full-scale implementations
plays a minor role due to limited availability of organic
contribute operational experience and build up confidence
carbon but can help to reduce residual nitrate
in these innovative technologies.
(11% stoichiometric nitrate production from deammo-
Basically four different microbial consortia are involved
in nitrogen removal processes (Figure 1):
† One out of these – nitrite oxidisers (NOB) – need to be
nification according to Strous et al. 1998). The main
microbial players in deammonification process coexist in
close syntrophy:
repressed by taking advantage of their higher oxygen
† Anaerobic AOB depend on aerobic AOB producing
half saturation concentration and different temperature
nitrite which serves as electron acceptor but turns into a
sensitivity (Arrhenius coefficient) compared to aerobic
toxic compound when exceeding a certain level.
ammonia oxidisers. Moreover free ammonia inhibition
Strous et al. (1999) allude to the negative influence of
can out-compete NOB as long as sludge age does not
nitrite concentration and exposure time on anammox
doi: 10.2166/wst.2010.969
B. Wett et al. | Aerobic and anaerobic ammonia oxidisers
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Water Science & Technology—WST | 61.8 | 2010
Activity (mg NO2-N/gTSS/h)
16
14
12
Underflow
10
MLSS
Overflow
8
6
4
2
0
0
10
20
30
40
50
Time (d)
Figure 5
|
Development of anaerobic AOB (anammox) activity after process restart comparing mixed liquor, overflow and underflow of the cyclone used in the DEMON process for
biomass separation.
almost complete ammonia conversion is feasible and set-
process conditions. Due to slower life cycles at lower
points of pH-control need to be set to a higher level – to 8.0
temperature the simulated anammox biomass tends to
in current case study (Figure 3).
decrease at same mixed liquor solids concentration while
Sudden temperature drop from 30 to 208C caused rapid
SRT is still sufficient for complete establishment of aerobic
nitrite accumulation. Corresponding to process temperature
AOB. Therefore temperature driven population dynamics
drop by 108C the oxygen uptake rate (OUR) decreased by
during an adaptation period cannot help to reconcile
50% and the aeration rate had to be reduced in order to
syntrophic balance of aerobic and anaerobic AOB.
maintain DO levels below 0.3 mg/L. At stepwise decrease of
Figure 4 presents simulation results from an instan-
operating temperature the biomass would adapt to new
taneous drop of temperature from one operation cycle to
SBR Total suspended solids
SBR Volatile suspended solids
5,500
5,000
4,500
Concentration (mg/L)
4,000
3,500
3,000
2,500
2,000
1,500
1,000
500
7
7
00
/
2
3/
11
/1
11
7
7
00
2
0/
/1
11
11
/2
2
4/
/
12
12
/
2
8/
7
12
/1
2
5/
7
00
00
00
00
2
1/
7
7
7
00
00
2
7/
12
/2
2
2/
00
2
9/
/2
12
Time
Figure 6
|
Dynamic TSS- and VSS profiles during a 1 month simulation period after implementation of the cyclone model (same wastage flow) followed by 1 month simulation at a
3-fold wastage flow.
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B. Wett et al. | Aerobic and anaerobic ammonia oxidisers
crucial for the robustness of the system and has been
investigated numerically. The BioWinY ASDM model with
2-step nitrification and anaerobic ammonia oxidation was
used to calculate the biomass composition in the reactor at
Water Science & Technology—WST | 61.8 | 2010
† Gas-lift for gravimetrical granule separation (Van
Dongen et al. 2001)
† Biofilm showing an uncontrolled biomass separation
driven by diffusion limitation
steady state. Then the 2 selectivity parameters of the
cyclone-model have been calibrated to solids flux- and
Substantially higher accumulated mass of anaerobic AOB
anammox activity measurements (99% of AOB, NOB,
in the system compensates for slower kinetics of these
AHB and endogenous products in the waste stream and
organisms compared to aerobic ones. Model results
84% of anammox biomass and inorganic matter in the
indicate doubling of the anammox to aerobic AOB mass
recycled stream) and the dynamic transition to a new
ratio. Selective sludge wasting at sidestream treatment
steady biomass composition with selected SRT has been
systems can be used to tackle the following process
simulated. Selection of a higher share of inorganic matter
engineering goals.
and anammox in the cyclone underflow caused VSS
reduction (Figure 6) and anammox enrichment in the
reactor (Figure 7).
Due to the recycled underflow total solids in the reactor
increased and the anammox concentration profile showing
† Low temperature operations: Anammox enrichment to
overcome temperature sensitivity of anaerobic organisms
† Stable repression of NOB: Accumulated anammox
compete for generated nitrite
a steep slope during the 1 month simulation run. Then a
† Process robustness against disturbance: Over-capacity of
threefold increase of the wastage rate was assumed resulting
anaerobic AOB improves tolerance for operational
in a sharp decrease in solids down to 3.5 g/L but anammox
failures like over-aeration
biomass was maintained at a high level. The calculated
† High COD- or solids loads in the influent flow:
steady state anammox portion increased from initially 8 to
Insignificant impact on anammox retention time due to
15% of total solids while the aerobic AOB portion remained
selected sludge wasting
constant at 5% (Table 1). The final SRT for anaerobic AOB
was almost 6 times higher than for aerobic AOB.
Investigation of impacts of the cyclone on process
† Savings in volume requirement: Same selected SRT for
anaerobic AOB at lower mass of total solids or reactor
volume, respectively
robustness at low temperature operation will require
detailed monitoring and frequent activity tests during the
cold season. Last winter two DEMON plants in Switzerland
have been equipped with a cyclone. The deammonification
system in Thun – where an uncovered sidestream reactor is
operated – has experienced temperatures of 208C without
loss in operational stability (Nyhuis 2009).
CONCLUSIONS
Long retention time for slowly growing anaerobic AOB and
short acclimation periods for aerobic AOB seem to be
contradicting control targets. This dilemma can be solved by
measures separating these functional groups of ammonia
oxidisers.
† Cyclone making use of centrifugal forces to select
appropriate SRT for each AOB population
REFERENCES
Fux, Ch. 2003 Biological nitrogen elimination of ammonium-rich
sludge digestion liquids. PhD thesis, Swiss Federal Institute of
Technology.
Innerebner, G., Insam, H., Franke-Whittle, I. & Wett, B. 2007
Identification of anammox bacteria in a full-scale
deammonification plant making use of anaerobic
ammonia oxidation. Syst. Appl. Microbiol. 30(5),
408– 412.
Jones, R. M., Dold, P., Takács, I., Chapman, K., Wett, B., Murthy, S.
& O’Shaughnessy, M. 2007 Simulation for operation and
control of reject water treatment processes. In: Proceedings
WEFTEC, San Diego.
Nyhuis, G. 2009 Personal communication.
Rosenwinkel, K. H. & Cornelius, A. 2005 Deammonification in
the moving bed process for the treatment of wastewater
with high ammonia content. Chem. Eng. Technol. 28(1),
49 –52.