Supporting Information. A Modeling Study. Dame, 156 Fitzpatrick Hall, Notre Dame, IN USA. Julianalaan 67, 2628 BC Delft, The Netherlands

Transcription

1 Supporting Information Hydroxylamine Diffusion an Enhance N 2 O Emissions in Nitrifying Biofilms: A Modeling Study Fabrizio Sabba 1, ristian Picioreanu 2, Julio Pérez 2,3, Robert Nerenberg 1* 1 Department of ivil and Environmental Engineering and Earth Science, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN USA 2 Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 67, 2628 B Delft, The Netherlands 3 Department of hemical Engineering, Universitat Autonoma de Barcelona, Engineering School, Ed. Q, 08193, Bellaterra, Spain *orresponding author: Robert Nerenberg, Phone: ; fax ; rnerenbe@nd.edu The following are included as supporting information for this paper: Number of pages: 19 Number of supplementary sections: 2 Number of figures: 6 Number of tables: 4 S1

2 SI 1. Methods Numerical model The model for N 2 O production in biofilms developed here is based on traditional diffusionreaction material balances for the relevant chemical species in the biofilm and in continuous ideally-mixed reactor, by incorporating the existing AOB kinetic model from Ni et al. (2014). A one-dimensional stationary biofilm with fixed thickness L F was assumed in all cases, thus without including any biomass growth, attachment or detachment. The model was constructed in a planar geometry, except for the case evaluating N 2 O production in granular (spherical) biofilms. For the standard case, only ammonia-oxidizing microorganisms (AOB) were considered, with biomass uniformly distributed throughout the biofilm and constant concentration F,XAOB (kg biomass/m 3 biofilm). 1. Solute balances in the biofilm Six model solutes (index i) were included, with concentrations F,i (mol/m 3 biofilm): dissolved oxygen (O 2 ), ammonia (NH 3 ), hydroxylamine (NH 2 OH), nitrite (NO - 2 ), nitric oxide (NO) and nitrous oxide (N 2 O). Time-dependent mole balances for all solutes in the biofilm (eq.(1)) included rates of reaction and transport by diffusion: t D r Fi, 2 F, i F, i i (1) with x for planar and 2 x x x for spherical biofilms. The effective diffusion coefficients in the biofilm, D F,i, were chosen smaller (typically 50%) than those in aqueous phase, D aq,i. The net rates for each soluble component, r i, result from the process stoichiometry and kinetics (according to the AOB reaction model from Ni et al., 2014), as provided in the supplementary information, Table S1 and Table S2. For example, the net N 2 O S2

3 production rate was expressed as rn2o 0.5r4 0.5r6, and the net hydroxylamine rate was r r r. NH2OH 1 2 The boundary condition at the biofilm support or at the granule center (x=0) was set as zero-flux for all solutes, eq. (2): D Fi, x Fi, x 0 0 (2) For simplicity of model analysis, the external mass transfer resistance (diffusion boundary layer) was neglected for all solutes. Therefore, the concentration at the biofilm surface (x=l F ) was equal with that in the reactor bulk liquid, eq. (3): F, i F B, i x L (3) with B,i in mol/m 3 liquid. 2. Redox mediator balances in the biofilm The redox mediator concentrations in the biofilm, F,Mox and F,Mred (mol/kg biomass) were calculated from the time-dependent balances, eq. (4). The mediator balances only include the net reactions r i (with i Mred or Mox) and no transport because these compounds are immobilized in the stationary microbial phase: t Fi, r i F, XAOB (4) As explained in Ni et al. (2014), results are independent of the constant value chosen for the total mediator concentration F, MedT F, Mox F, Mred because the affinity coefficients were all scaled with this concentration. S3

4 3. Solute balances in the bulk liquid With the exception of oxygen, set by aeration at a constant value B,O2, the solute concentrations in bulk liquid resulted from the time-dependent balance, eq. (5) (i=nh 3, NH 2 OH, NO 2 -, NO): Bi, Q A in, i B, i J i t V V B F B (5) For N 2 O, assumed to be stripped by aeration, an additional transfer term was included in the N 2 O balance in liquid, such that: B, N2O Q A J k a H t V V B F in, N2O B, N2O N2O L G, N2O N2O B, N2O B (6) The influent flow rate Q, influent concentrations in,i, liquid volume V B and biofilm surface area A F were constant (Table S3). The flux exchanged with the biofilm was calculated at the biofilm surface as J D, (, / dx ), for all solutes including N 2 O. i F i F i x L F 4. N 2 O balance in the gas An additional balance equation, eq. (7), was solved for the gas phase concentration of N 2 O, G,N2O (mol/m 3 gas). Q V 0 B, N2O kla G, N2OH N2O B, N2O t V V G, N2O G L G G (7) The gas flow rate Q G, head gas volume V G, gas-liquid mass transfer coefficient k L a and Henry coefficient H N2O were all constant. As initial values, all concentrations in biofilm, bulk liquid and gas were chosen equal to the corresponding influent concentrations. S4

5 5. Model solution The model was implemented in OMSOL Multiphysics (v4.4, omsol Inc., Burlington, MA). Although the model analysis could have been entirely executed in the more familiar AQUASIM computer package (Reichert et al, 1994), OMSOL was chosen for its flexible modeling interface, superior high numerical capabilities, data processing and visualization. Model equations were solved with variable time step on a biofilm domain discretized with a maximum mesh size of 1 m. The simulation times were in the order of seconds per case. All reported steady state results were in all conditions obtained after maximum 3 days. SI 2. Methods Experimental setup The pilot plant was an airlift granular sludge reactor with a capacity of 150 L. Previous to the N 2 O measuring campaign, the reactor had been operating for ca. 100 days oxidizing ca. 95% of the influent ammonium to nitrite, with negligible production of nitrate. The hydraulic retention time (HRT) was maintained within the range of d and the sludge residence time (SRT) was kept at 50 d. The nitrogen loading rate (NLR) of 0.85 g N/L/d at 30º, a biomass concentration of 5 g MLVSS/L, and a mean granule size of 0.5 mm (Tora et al., 2013). More details about the reactor, start-up and reactor operation can be found in Tora et al. (2013). The wastewater contained TAN mg N/L, total organic carbon (TO) mg /L (although only 5% was biodegradable OD), total inorganic carbon (TI) mg /L, total nitrite nitrogen (TNN=NO - 2 -N + HNO 2 -N) 2 7 mg N/L, NO mg N/L, MLSS mg/l, MLVSS mg/l; ph S5

6 Table S1. Stoichiometry matrix of the reaction model (according to Ni et al., 2014) omponents Reactions O 2 NH 3 NH 2 OH N 2 O NO NO 2 - NO 3 - M red M ox Rates 1. Ammonia oxidation (AMO) 2. Hydroxylamine oxidation (HAO) 3. Nitric oxide oxidation 4. Nitric oxide reduction (NOR) 5. Oxygen reduction 6. Nitrite reduction (NirK, NOR) r r r r r r6 Table S2. Reaction rates for the model of Ni et al. (2014) Reactions Rates 1. Ammonia oxidation (AMO) 2. Hydroxylamine oxidation (HAO) 3. Nitric oxide oxidation 4. Nitric oxide reduction (NOR) 5. Oxygen reduction 6. Nitrite reduction (NirK, NOR) r k 1 AOB, NH3, ox F, XAOB r k 2 AOB, NH2OH, ox F, XAOB r k 3 AOB, NO, ox F, XAOB r k 4 AOB, NO, red F, XAOB r k 5 AOB, O2, red F, XAOB r k F, O2 F, NH3 F, Mred K K K AOB, O2, NH3 F, O2 AOB, NH3 F, NH3 AOB, Mred, 1 F, Mred F, NH2OH F, Mox K K AOB, NH2OH F, NH2OH AOB, Mox F, Mox F, NO F, Mox K K AOB, NO, ox F, NO AOB, Mox F, Mox F, NO F, Mred AOB, NO, red F, NO AOB, Mred, 2 F, Mred K K F, O2 F, Mred AOB, O2, red F, O2 AOB, Mred, 3 F, Mred K K F, NO2 F, Mred 6 AOB, NO2, red F, XAOB 2 K AOB, NO2 F, NO2 F, NO2 / K AOB, I, NO2 K AOB, Mred, 4 F, Mred S6

7 Table S3. Model parameters in the base case Parameter Symbol Value Units Source Maximum rate coefficients - NH 3 oxidation, AOB k AOB,NH3,ox mmol g -1 h -1 Ni et al. (2014), Law et al. (2012) - NH 2 OH oxidation, AOB k AOB,NH2OH,ox mmol g -1 h -1 Ni et al. (2014), Law et al. (2012) - NO oxidation, AOB k AOB,NO,ox mmol g -1 h -1 Ni et al. (2014), Law et al. (2012) - O 2 reduction, AOB k AOB,O2,red mmol g -1 h -1 Ni et al. (2014) - NO - 2 reduction, AOB k AOB,NO2,red 3.06 mmol g -1 h -1 Ni et al. (2014) - NO reduction, AOB k AOB,NO,red mmol g -1 h -1 Ni et al. (2014) Half-saturation rate coefficients - O 2 in NH 3 oxidation, AOB K AOB,O2,NH mmol L -1 Ni et al. (2014), Law et al. (2012) - NH 3 oxidation, AOB K AOB,NH mmol L -1 Ni et al. (2014), Law et al. (2012) - NH 2 OH oxidation, AOB K AOB,NH2OH 0.05 mmol L -1 Ni et al. (2014), Law et al. (2012) - NO oxidation, AOB K AOB,NO,ox mmol L -1 Ni et al. (2014), Law et al. (2012) - O 2 reduction, AOB K AOB,O2,red mmol L -1 Ni et al. (2014), Law et al. (2012) - NO - 2 reduction, AOB K AOB,NO mmol L -1 Ni et al. (2014), Law et al. (2012) - NO reduction, AOB K AOB,NO,red mmol L -1 Ni et al. (2014), Law et al. (2012) - M ox in NO oxidation, AOB K AOB,Mox 0.01 T,Med mmol L -1 Ni et al. (2014), Pan et al. (2013) - M red in NH 3 oxidation, AOB K AOB,Mred, T,Med mmol L -1 Ni et al. (2014) - M red in NO reduction, AOB K AOB, Mred, T,Med mmol L -1 Ni et al. (2014), Pan et al. (2013) - M red in O 2 reduction, AOB K AOB,Mred, T,Med mmol L -1 Ni et al. (2014) - M red in NO - 2 reduction, AOB K AOB,Mred, T,Med mmol L -1 Ni et al. (2014) - NO - 2 inhibition, AOB K AOB,I,NO mmol L -1 Ni et al. (2014) Diffusion coefficients in water at 30 - oxygen D aq,o m 2 s -1 R Handbook (2014) (b) - ammonia D aq,nh m 2 s -1 R Handbook (2014) (a) - hydroxylamine D aq,nh2oh m 2 s -1 Zare et al. (2007) - nitrous oxide D aq,n2o m 2 s -1 R Handbook (2014) (b) - nitric oxide D aq,no m 2 s -1 Zacharia and Deen (2005) - nitrite D aq,no m 2 s -1 R Handbook (2014) (a) Reduction factor diffusion coefficients in biofilm Oxygen concentration in influent and bulk liquid Ammonia concentration in influent f diff in,o2, O2 in,nh to 5 (varied) 80 (base case) 40, 160 (varied) mg L -1 mgn L -1 various Horn and Morgenroth (2006) typical range typical values main stream treatment Hydroxylamine, nitrous oxide, nitric oxide, nitrite, nitrate in influent in,i 0 mg L -1 chosen Initial concentrations 0,i in,i mg L -1 chosen S7

8 Biomass concentration in the biofilm oncentration total redox mediators Biofilm thickness F,XAOB 50 (base case) g L -1 typical value, Wanner et al (2006) T,Med 0.01 mmol g -1 Ni et al. (2014), Pan et al. (2013) L F 100 (base case) 2, 20, 50, 200 (varied) m typical values Liquid flow rate Q 11 ml min -1 reactor F. Sabba Liquid volume in the reactor V B 4 L reactor F. Sabba Biofilm surface area A F 0.5 m 2 reactor F. Sabba Gas volume V G 3.5 L reactor F. Sabba Gas flow rate Q G 2 L min -1 reactor F. Sabba Gas-liquid mass transfer coeff. k L a 100 h -1 chosen Henry gas-liquid coefficient N 2 O (30 º) H N2O mol/mol R Handbook (2014) (c) S8

9 Table S4. Model parameters changed for comparison with experimental data from Pijuan et al. (2014) Parameter Symbol Value Units Source Oxygen concentration in influent and bulk liquid Ammonia concentration in influent Set ammonia concentration in bulk liquid (controlled by flow rate) in,o2, O2 0.5 to 8 mg L -1 experimental in,nh3 730 mgn L -1 experimental as for side stream treatment NH3 40 mgn L -1 experimental AOB biomass concentration in F,XAOB 100 g L -1 experimental the biofilm Average granule radius L F 250 m experimental Liquid flow rate Q variable L min -1 varied to control bulk NH 3 concentration Liquid volume in the reactor V B 135 L experimental Biofilm surface area A F 90 m 2 experimental Gas volume V G 10 L experimental Gas flow rate Q G 50 L min -1 experimental S9

10 (a) (b) A fs =3A fp L fs =3L fp Figure S1. omparison of N 2 O production rates, per unit reactor volume and time, as a function of bulk DO for planar and spherical biofilms of different thicknesses. (a) A spherical biofilm (e.g. aerobic granular sludge) with the same thickness and total biomass volume as an equivalent planar biofilm would have a 3-times larger surface area, thus allowing for more NH 3 conversion, less NH 3 in the bulk liquid and narrower N 2 O production peak. However, if the spherical biofilm has the same total volume and area as the planar one (i.e., by increasing 3 times the granule radius), the N 2 O production would be comparable with the planar case (inner regions are inactive in both planar and spherical biofilms). (b) Spherical biofilms of variable size were analyzed here, while keeping same total biomass in the reactor by changing the number of granules. Because the smaller the granule size the more area would result when reaching the same biomass amount, more NH 3 conversion is possible leading to NH 3 limitation below a certain biofilm thickness (20 m here). No N 2 O production peak can be observed at the limit (2 m) corresponding to suspended biomass. Results for a similar planar biofilm case are presented in Figure 2a. S10

11 3 3 (a) (d) (b) (e) (c) S11

12 Figure S2. (a-c) Effect of the set dissolved oxygen concentration at different influent ammonia concentrations (40, 80 and 160 mg N-NH 3 /L). (a) N 2 O production rate (per L reactor volume), (b) % N-N 2 O produced per N-NH 3 converted, (c) NH 3 concentration in the bulk liquid. (d-e) Effect of the set dissolved oxygen concentration at different controlled NH 3 concentrations in bulk liquid (2.5, 5 and 10 mg N-NH 3 /L, from 80 mg N-NH 3 /L in influent). (d) N 2 O production rate (per L reactor volume), (e) % N-N 2 O produced per N-NH 3 converted. The NH 3 concentration in bulk c b,nh3 was controlled by varying the flow rate Q following the method proposed in Jemaat et al. (2013): Q Q0 1 a cset, NH3 cb, NH3 / c set, NH3. The set NH 3 concentrations c s,nh3 were 2.5, 5 and 10 mg N-NH 3 /L, the reference flow rate Q 0 was 1 ml/min and a sufficiently high value of a was chosen for a fast control action, a= S12

13 (a) NH 3 (b) NO 2 - (c) r N2O (d) M red (e) O 2 (f) NH 2 OH Figure S3. The net rate of N 2 O production is effectively determined by the availability of reduced mediators in the biofilm with not limiting ammonia and nitrite. (a) ammonia concentration; (b) nitrite concentration; (c) N 2 O net rate; (d) M red concentration; (e) O 2 concentration; (f) NH 2 OH concentration. All results were obtained in the standard case conditions. S13

14 (a) omponent concentrations (b) omponent rates NO 2 - NH 2 OH N 2 O O 2 NH 3 O 2 NH 2 OH N 2 O NO (c) Reaction rates (d) Electron rates total e- production , total e- consumption Figure S4. Solute concentrations and rates in the biofilm. (a) omponent concentrations, (b) net component rates, (c) reaction rates, and (d) electron rates over the biofilm depth. Results are for the standard case conditions at a bulk DO of 2 mg/l. ompare these results with those obtained at DO 1 mg/l in Figure 4. S14

15 (a) (b) Figure S5. Effect of effective diffusivity on the N 2 O production rates at different dissolved oxygen concentrations. (a) Reduced diffusion coefficients for all components in the biofilm (D f ), compared to diffusivities in water (D aq ), would allow less oxygen penetration, thus widen the DO interval with large N 2 O production. (b) A 10-times decrease in the NH 2 OH diffusion coefficient only, eliminates the peak of N 2 O production at low DO. In this case, which would be possible if NH 2 OH did not diffuse outside cells, the NH 2 OH does not reach into the anoxic biofilm zone. Hydroxylamine diffusion in the biofilm appears to be essential for a surge in N 2 O production. S15

16 a) b) Figure S6a,b: Sensitivity analyses for the kinetic parameters in the AOB rate expressions r1 (a) and r2 (b). The parameters was either left as in the base case, increased two-fold, or reduced by one half. S16

17 c) d) Figure S6c,d: Sensitivity analyses for the kinetic parameters in the AOB rate expressions r3 (c) and r4 (d). The parameters was either left as in the base case, increased two-fold, or reduced by one half. S17

18 e) f) Figure S6e,f: Sensitivity analyses for the kinetic parameters in the AOB rate expressions r5 (e) and r6 (f). The parameters was either left as in the base case, increased two-fold, or reduced by one half. S18

19 REFERENES R Handbook of hemistry and Physics, 95 th Edition, (a) Section 5: Ionic onductivity and Diffusion at Infinite Dilution, (b) Section 6: Diffusion of gases in water, (c) Section 5: Solubility of selected gases in water. Online at Horn, H.; Morgenroth, E. Transport of oxygen, sodium chloride, and sodium nitrate in biofilms. hemical Engineering Science. 2006, 61(5): Jemaat, Z.; Bartoli, A.; Isanta, E.; arrera, J.; Suarez-Ojeda, M.E.; Perez, J. losed-loop control of ammonium concentration in nitritation: onvenient for reactor operation but also for modeling. Bioresource Technology. 2013, 128, Law, Y.; Ni, B. J.; Lant, P.; Yuan, Z. Nitrous oxide (N 2 O) production by an enriched culture of ammonia oxidizing bacteria depends on its ammonia oxidation rate. Water Research. 2012, 46(10) Ni, B.; Peng, L.; Law, Y.; Guo, J.; Yuan, Z. Modeling of nitrous oxide production by autotrophic ammonia-oxidizing bacteria with multiple production pathways. Environmental Science and Technology. 2014, 48 (7), Pan, Y.; Ni, B.J.; Yuan, Z. Modeling electron competition among nitrogen oxides reduction and N 2 O accumulation in denitrification. Environmental Science and Technology. 2013, 47(19), Reichert, P. AQUASIM, a tool for simulation and data analysis of aquatic systems. Water Science and Technology. 1994, 30(2): Tora, J.A.; Moline, E.; arrera, J.; Perez, J. Efficient and automated start-up of a pilot reactor for nitritation of reject water: From batch granulation to high rate continuous operation. hemical Engineering Journal. 2013, 226: Wanner, O.; Eberl, H.J.; Morgenroth, E; Noguera, D.; Picioreanu,.; Rittmann, B.E.; Van Loosdrecht, M..M. IWA Task Group on Biofilm Modeling. Mathematical Modeling of Biofilms. IWA Scientific and Technical Report No.18, IWA Publishing, ISBN Zacharia, I.G.; Deen, W.M. Diffusivity and solubility of nitric oxide in water and saline. Annals of Biomedical Engineering 2005, 33, Zare, H.R.; Sobhani, Z.; Mazloum-Ardakani, M. Electrocatalytic oxidation of hydroxylamine at a rutin multi-wall carbon nanotubes modified glassy carbon electrode: Improvement of the catalytic activity. Sensors and Actuators B, 2007, 126(2), S19