Intermittent Aeration Suppresses Nitrite-Oxidizing Bacteria in Membrane-Aerated Biofilms: A Model- Based Explanation

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1 upplementary information Intermittent Aeration uppresses NitriteOxidizing Bacteria in MembraneAerated Biofilms: A Model Based Explanation Yunjie Ma, Carlos DomingoFélez, Benedek Gy. Plósz, and Barth F. mets* Department of Environmental Engineering, Technical University of Denmark, Miljøvej building 3, 2800 ongens Lyngby, Denmark. * Corresponding Author: bfsm@env.dtu.dk, Tel: Fax: Current address: Department of Chemical Engineering, University of Bath, Claverton Down, BA2 7AY Bath, United ingdom. Number of Pages: 7 Figures: 0 Tables: 8

2 Table. Reaction stoichiometry matrix for the multispecies nitrifying biofilm model N4 O2 NO2 NO3 N2 CO3 CO2 X X I X X X Growth g COD m 3 g N m 3 g O 2 m 3 g N m 3 g N m 3 g N m 3 µmol/l µmol/l µmol/l g COD m 3 g COD m 3 g COD m 3 g COD m 3 g COD m 3 i NXB Y Y Y Y 000 7Y inxb. 4 Y Y Y Y B Y i NXB Y Y B Y inxb Y.7Y 000( Y ) Y.7Y.7Y B B 4 B Y inxb Y 2.86Y 000 ( Y ) Y 2.86Y 2.86Y B B 4 ydrolysis Decay f i f i f i f i B f i f i Buffer Reaction 2

3 Table 2. Process rates for the biological/chemical processes in the multipopulation biofilm model Growth Rate µ X FA O2 ifna, FA, + FA+ FA FA ifa, O2, + O2 ifna, + FNA µ X FNA O 2 ifa, FNA, + FNA+ FNA FNA ifna, O2, + O2 ifa, + FA B µ X + O 2 +, O 2, O 2 B on nitrite µ X η, anoxic, + NO 2, NO 2 + NO 2 O 2, O 2, + O 2 B on nitrate µ X η, anoxic +, NO3 + NO3, NO3 O2, O2, + O2 ydrolysis Decay b X b X B b X Buffer Reaction (, ) 0 7 3

4 Table 3. Oxygen (O 2 )/carbon dioxide (CO 2 ) mass transfer coefficients in PDM silicon membrane ymbol: Parameter k M : membrane mass transfer coefficient (m/day) ml,o2 : oxygen partition coefficient in the membraneliquid interface in clean water k M,O2,clean :k M ml,o2, oxygen mass transfer coefficient of the membrane in clean Value 0.55±0.04 a 7.2 a 3.9±0.3 a water (m/day) ml,co2 : carbon dioxide partition coefficient in the membraneliquid interface in clean water.32 b k M,CO2 :k M ml,co2, carbon dioxide mass transfer coefficient of the membrane in clean water or with biofilm (m/day) 0.73±0.06 c E: enhancement factor of the oxygen partition coefficient in the membraneliquid interface with biofilm 4.3 a,c,d k M,O2 : oxygen mass transfer coefficient of the membrane with biofilm, evaluated based on oxygen flux (m/day) e 6 a Values referred to the study of PellicerNàcher et al.. (The same PDM membrane and the same inoculum were used in these 2 studies). b CO 2 partition coefficient in the membraneliquid interface was assumed to be the same with the partition coefficient in the gasliquid interface, i.e. the enry s constant (.32). c We assumed biofilm activity had no effect on CO 2 mass transfer in the PDM membrane, which was different form O 2 transfer. d E was dependent on the characteristics of the system, i.e. membrane material, thickness, etc. e Oxygen flux was calculated by oxygen needed for the oxidized Nitrogen species measured in the bulk. (, = (.. ) =, (,, ) 4

5 Table 4. Evaluation of DO limitation effect based on predicted and measured O 2 concentrations biofilm thickness O 2 Concentration DO limitation effect (µm) predicted measured 2 / Note: DO limitation was evaluated by ; predicted oxygen concentrations; 2 measured oxygen concentrations; oxygen affinities for and were 0.6 and.2 mg/l, respectively. 5

6 Table 5. ummary of experimental data used in model calibration and validation Model calibration Model validation. Micro profiles (N 4 +, NO 2, NO3 and DO) in the first aeration hour at steady state in the MABR Experimental condition (this work nitritation biofilm): AL = 0.5 gn/m 2 /day, C N4 +,in = 75 mgn/l Buffer capacity in the influent (CO 3 )/(N 4 + ) = 2. Intermittent aeration: 6hour aeration + 6hour nonaeration. Micro profiles (N 4 +, NO 2, NO3 and DO) in the last aeration hour at steady state in the MABR Experimental condition (this work nitritation biofilm): Bulk measurements (N 4 +, NO 2, NO3 and p) in a 2hour aeration and nonaeration cycle at steady state in the MABR Experimental condition (this work nitritation biofilm): 2 Bulk measurements (N 4 +, NO 2 and NO3 ) in the batchmode operation of the MABR Experimental condition (completely mixed system nitritation and nitratation): + C N4,initial = 300 mgn/l, C NO2,in = C NO3,in = 0 mgn/l Buffer capacity (CO 3 )/(N 4 + ) = 2. Initial biomass: 0.3 gv/l enriched nitrifying biomass, : was assumed to be 5:3 (Figure 8) Continuous aeration 3 Bulk measurements (N 4 +, NO 2, NO3 and p) in MABR2 Experimental condition (nitritation biofilm under 4 different ALs): Day 0~87.5: AL = 30 gn/m 2 /day, C N4 +,in = 200 mgn/l Buffer capacity in the influent (CO 3 )/(N 4 + ) =.0 Day 87.5~94: AL = 5 gn/m 2 /day, C N4 +,in = 65 mgn/l Buffer capacity in the influent (CO 3 )/(N 4 + ) =.2 Day 94~99: AL = 6 gn/m 2 /day, C N4 +,in = 28 mgn/l Buffer capacity in the influent (CO 3 )/(N 4 + ) = 2. Day 99~05: AL = 0.5 gn/m 2 /day, C N4 +,in = 75 mgn/l Buffer capacity in the influent (CO 3 )/(N 4 + ) = 2. Intermittent aeration: 6hour aeration + 6hour nonaeration AL: ammonium surface loading; 2 During the batch startup phase, biofilm was not yet substantially developed and minor biomass was attached to the membrane. ence a completely mixed system was assumed. The calibrated kinetic parameters and could be evaluated in this experimental data fitting; 3 The same inoculum, membranes and reactor system were used in MABR2 as in the studied MABR. Except for different influent, operational conditions were also the same in these two MABRs, considering the intermittent aeration strategy, air pressure in the membrane lumen and bulk recirculation rate, etc. Thus the performance in MABR2 was representative to this type of counterdiffusion biofilms. With this data set, the simulation scenarios of suppression in intermittently aerated MABRs with higher, medium or lower residual N + 4 concentrations could be validated. 6

7 Table 6. Detailed description of each simulation scenario cenario to validate the model with experimental data Validation with experimental data in MABR With calibrated parameters, MNBM was run in intermittent aeration (6hour aeration and 6hour nonaeration) until steady state. Validation with experimental data in batch mode In this data fit, continuousfeeding biofilm compartment in intermittent aeration was replaced by a completely mixed reactor compartment in continuous aeration with an initial N + 4 at 300 mg N/L (batch mode). All the biological/chemical processes and kinetic parameters remained unchanged, with the exception of membrane transfer coefficients of O 2 and CO 2. k M,O2 and k M,CO2 were set as.2 and 0.5 m/d, respectively, considering contributions to the overall transfer resistance from membrane (in clean water without biofilm) and boundary layer (k l =.69 m/d). The initial concentration of enriched nitrifying biomass in the batch mode simulation was 300 mgv/l, and the ratio of to was 5:3 (Figure 8). Validation with experimental data in MABR2 In this modeldata fit, MNBM was run in intermittent aeration (6hour aeration and 6hour nonaeration) under 4 different ALs (Table 5). All the kinetic parameters and membrane transfer coefficients of O 2 and CO 2 in MABR2 scenario were assumed to be the same as in MABR scenario. Only buffer capacity was changed under each relevant AL. cenario 2 to clarify why suppression occurred after switching from continuous to intermittent aeration and explain the observation of suppression in PellicerNàcher et al. 2 The model was run in continuous aeration to achieve a nitrifying biofilm, followed with intermittent aeration (6+6) to study the process of suppression. Variation of relevant influencing factors in intermittent aeration was compared with the effects in continuous aeration. Oxygen and ammonium surface loadings remained unchanged in the whole simulation. cenario 3 to find an optimal operational window for nitritation in intermittently aerated MABRs (Table 8) Evaluate aeration intermittency in suppression MNBM was run in continuous aeration (200 days) to achieve a nitrifying biofilm. Afterwards aeration was switched to different intermittent aeration strategies but with the same influent. The nitritation efficiencies during the suppression phase (e.g. day 25) were recorded. Evaluate of residual N + 4 (FA) concentrations in suppression MNBM was run in continuous aeration (200 days) to achieve a nitrifying biofilm. Afterwards aeration was switched to intermittent aeration (6hour aeration and 6hour nonaeration) with different combinations of influent N + 4 concentration and buffer 7

8 capacity. The nitritation efficiencies during the suppression phase (e.g. day 25) were recorded. Table 7. Modelbased evaluation of ammonium removal rate (ARE) and nitritation efficiency (NE) in simulations with different oxygen mass transfer coefficients. Effluent Conc. (mgn/l) Reactor performance k M,O2 * N 4 + NO 2 NO 3 ARE NE * As k M,O2 in this study (6 m/day, calculated based on oxygen balance in table 3) was higher than the reported values of this kind silicone membrane (.5~3 m/day),,3 lower values were tested. 8

9 Table 8. Predicted nitritation efficiencies (NE, %) in various intermittent aeration strategies Influent 2 Effluent (Bulk) imulation Case Aeration intermittency Residual N + 4 /FA + N 4 in (mgn/l) + Buffer N 4 FA 4 5 p NE % NE capacity 3 normalized (mgn/l) (mgn/l) continuous ± 7.22 ± ± 7.2 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 7.2 ± ± ± ± ± Aeration strategy 6+6 meant a 2hour intermittent aeration cycle consisting of a 6hour aeration phase and a 6hour nonaeration phase. 2 Ammomium surface loading in simulations was between 4.2~2.2 gn/m 2 /day. 3 Buffer capacity in the influent was recorded as the molar ratio of bicarbonate (CO 3 ) to ammonium (N + 4 _N). 4 FA was calculated with the averaged concentrations of N + 4 and p during a full aeration cycle (equation 6). 5 For a clear comparison, NE was normalized to the Nitritation efficiency in the default simulation case A (NE = 48.5%). MNBM was run in continuous aeration (200 days) to achieve a mature nitrifying biofilm, followed by various intermittent aeration strategies with different aeration intermittency or influent concentrations. NEs in the process of suppression in intermittent aeration were recorded (e.g. at day 25) (Table 6). In simulations, oxygen loadings varied proportionally with ammonium influent concentrations to provide the similar amount of oxygen source per unit of ammonium loading. 9

10 Figure. chematic of membraneaerated biofilm reactors. 0

11 Figure 2. ensitivity ranking of kinetic parameters with default values, considering the sum of reactor performances in the bulk (A) and within the biofilm (B).

12 Figure 3. ensitivity ranking of kinetic parameters with default values, considering the individual reactor performance in terms of ammonium (A), nitrite (B) and nitrate (C) within the biofilm. As the sensitivity regarding performance within the biofilm was higher than the bulk performance, sensitivity ranking considering the individual reactor performance in the bulk was not shown. (D) RME in the trialanderror parameter estimation process for. The grey contours refer to RME=0.5 region. The red points refer to RME=0. region. The 95% confidence regions of the estimates were within the grey contours. =,, =0. where J crit was the critical value, J opt was the minimized objective function, N data was the number of measured data points, p was the number of estimated parameters, and,, was the value of the F distribution for α, p and N data p. 4 2

13 Figure 4. (A) Model validation with experimental data in MABR batchmode operation. (B) Model validation with experimental data in MABR2 under different ammonium surface loadings. 3

14 Figure 5. Predicted dynamic changes of DO (A), p (B), FA (C), FNA (D) within the biofilm at different time intervals during the 6hour aeration at day 5. Red dots represent concentrations in the bulk. 4

15 Figure 6. Dynamic variations of bulk N from continuous aeration (time < 200 days) to intermittent aeration (time > 200 days) Figure 7. Change patterns of individual limitation/inhibition effect within the biofilm in a 6hour aeration period at day 220. Intermittent aeration effects (e.g.,, ) was normalized by continuous aeration effects (,, ). 5

16 Figure 8. Copies of different phylogenetic groups (approximating functional guilds) in the inoculum and mature biofilm measured in quantitative PCR assays. The biofilm could not be sampled during the operation. The primers used for the quantification of bacterial numbers referred to PellicerNàcher et al. (204). 5 Figure 9. Measured bulk N concentrations during the entire operation process. 6

17 Figure 0 Predicted Nitritation efficiencies (normalized) and concentrations of bulk N 4 + and N 3 in MNBM simulations with different influent concentrations (N 4 + or buffer CO 3 ) in intermittent aeration (6+6). The curve (NE ~ bulk FA) shows that bulk FA may give a simple indicator of the nitritation potential in MABRs. References () PellicerNàcher, C.; DomingoFélez, C.; Lackner,.; mets, B. F. Microbial activity catalyzes oxygen transfer in membraneaerated nitritating biofilm reactors. J. Memb. ci. 203, 446, (2) PellicerNàcher, C.; un,.; Lackner,.; Terada, A.; chreiber, F.; Zhou, Q.; mets, B. F. equential aeration of membraneaerated biofilm reactors for highrate autotrophic nitrogen removal: experimental demonstration. Environ. ci. Technol. 200, 44 (9), (3) Lackner,.; Terada, A.; mets, B. F. eterotrophic activity compromises autotrophic nitrogen removal in membraneaerated biofilms: results of a modeling study. Water Res. 2008, 42 (4 5), (4) Dochain, D.; Vanrolleghem, P. Dynamical modelling and estimation in wastewater treatment processes; IWA Publishing, London, U. IBN , 200. (5) PellicerNàcher, C.; Franck,.; Gülay, A.; Ruscalleda, M.; Terada, A.; Aloud, W. A.; ansen, M. A.; ørensen,. J.; mets, B. F. equentially aerated membrane biofilm reactors for autotrophic nitrogen removal: Microbial community composition and dynamics. Microb. Biotechnol. 204, 7 (),