TY - JOUR
T1 - Biomass segregation between biofilm and flocs improves the control of nitrite-oxidizing bacteria in mainstream partial nitritation and anammox processes
AU - Laureni, Michele
AU - Weissbrodt, David G.
AU - Villez, Kris
AU - Robin, Orlane
AU - de Jonge, Nadieh
AU - Rosenthal, Alex
AU - Wells, George
AU - Nielsen, Jeppe Lund
AU - Morgenroth, Eberhard
AU - Joss, Adriano
PY - 2019
Y1 - 2019
N2 -
The control of nitrite-oxidizing bacteria (NOB) challenges the implementation of partial nitritation and anammox (PN/A) processes under mainstream conditions. The aim of the present study was to understand how operating conditions impact microbial competition and the control of NOB in hybrid PN/A systems, where biofilm and flocs coexist. A hybrid PN/A moving-bed biofilm reactor (MBBR; also referred to as integrated fixed film activated sludge or IFAS) was operated at 15 °C on aerobically pre-treated municipal wastewater (23 mg
NH4-N
L
−1
). Ammonium-oxidizing bacteria (AOB) and NOB were enriched primarily in the flocs, and anammox bacteria (AMX) in the biofilm. After decreasing the dissolved oxygen concentration (DO) from 1.2 to 0.17 mg
O2
L
−1
- with all other operating conditions unchanged - washout of NOB from the flocs was observed. The activity of the minor NOB fraction remaining in the biofilm was suppressed at low DO. As a result, low effluent NO
3
−
concentrations (0.5 mg
N
L
−1
) were consistently achieved at aerobic nitrogen removal rates (80 mg
N
L
−1
d
−1
) comparable to those of conventional treatment plants. A simple dynamic mathematical model, assuming perfect biomass segregation with AOB and NOB in the flocs and AMX in the biofilm, was able to qualitatively reproduce the selective washout of NOB from the flocs in response to the decrease in DO-setpoint. Similarly, numerical simulations indicated that flocs removal is an effective operational strategy to achieve the selective washout of NOB. The direct competition for NO
2
−
between NOB and AMX - the latter retained in the biofilm and acting as a “NO
2
-sink” - was identified by the model as key mechanism leading to a difference in the actual growth rates of AOB and NOB (i.e., μ
NOB
< μ
AOB
in flocs) and allowing for the selective NOB washout over a broad range of simulated sludge retention times (SRT = 6.8–24.5 d). Experimental results and model predictions demonstrate the increased operational flexibility, in terms of variables that can be easily controlled by operators, offered by hybrid systems as compared to solely biofilm systems for the control of NOB in mainstream PN/A applications.
AB -
The control of nitrite-oxidizing bacteria (NOB) challenges the implementation of partial nitritation and anammox (PN/A) processes under mainstream conditions. The aim of the present study was to understand how operating conditions impact microbial competition and the control of NOB in hybrid PN/A systems, where biofilm and flocs coexist. A hybrid PN/A moving-bed biofilm reactor (MBBR; also referred to as integrated fixed film activated sludge or IFAS) was operated at 15 °C on aerobically pre-treated municipal wastewater (23 mg
NH4-N
L
−1
). Ammonium-oxidizing bacteria (AOB) and NOB were enriched primarily in the flocs, and anammox bacteria (AMX) in the biofilm. After decreasing the dissolved oxygen concentration (DO) from 1.2 to 0.17 mg
O2
L
−1
- with all other operating conditions unchanged - washout of NOB from the flocs was observed. The activity of the minor NOB fraction remaining in the biofilm was suppressed at low DO. As a result, low effluent NO
3
−
concentrations (0.5 mg
N
L
−1
) were consistently achieved at aerobic nitrogen removal rates (80 mg
N
L
−1
d
−1
) comparable to those of conventional treatment plants. A simple dynamic mathematical model, assuming perfect biomass segregation with AOB and NOB in the flocs and AMX in the biofilm, was able to qualitatively reproduce the selective washout of NOB from the flocs in response to the decrease in DO-setpoint. Similarly, numerical simulations indicated that flocs removal is an effective operational strategy to achieve the selective washout of NOB. The direct competition for NO
2
−
between NOB and AMX - the latter retained in the biofilm and acting as a “NO
2
-sink” - was identified by the model as key mechanism leading to a difference in the actual growth rates of AOB and NOB (i.e., μ
NOB
< μ
AOB
in flocs) and allowing for the selective NOB washout over a broad range of simulated sludge retention times (SRT = 6.8–24.5 d). Experimental results and model predictions demonstrate the increased operational flexibility, in terms of variables that can be easily controlled by operators, offered by hybrid systems as compared to solely biofilm systems for the control of NOB in mainstream PN/A applications.
KW - Biomass segregation
KW - Hybrid system
KW - IFAS
KW - Mainstream anammox
KW - Mathematical modelling
KW - Nitrite sink
KW - NOB washout
KW - Partial nitritation/anammox
UR - http://www.scopus.com/inward/record.url?scp=85061635723&partnerID=8YFLogxK
U2 - 10.1016/j.watres.2018.12.051
DO - 10.1016/j.watres.2018.12.051
M3 - Article
AN - SCOPUS:85061635723
SN - 0043-1354
VL - 154
SP - 104
EP - 116
JO - Water Research
JF - Water Research
ER -