2008 USC-UAM Conference on biofiltration for air pollution control Long Beach, October 2008 OPERATIONAL ASPECTS OF THE BIOLOGICAL SWEETENING OF ENERGY GASES MIMICS IN A LAB-SCALE BIOTRICKLING FILTER M. Fortuny; A. Gonzalez-Sánchez; C. Casas; D. Gabriel; J. Lafuente M. A. Deshusses Xavier Gamisans Duke University Dep. Civil & Environmental Engineering Universitat Autònoma de Barcelona Departament d’Enginyeria Química Universitat Politècnica de Catalunya Escola Politècnica Superior d’Enginyeria de Manresa.

2008 USC-UAM Conference on biofiltration for air pollution control Outline Introduction Background Previous results Objectives Materials & Methods Setup Methodology Results & Discussion EBRT Intermittent substrate supply Trickling liquid velocity pH Conclusions INTRODUCTION 2/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Background ENERGY capacity of doing, transforming or moving Renewable Non-Renewable INTRODUCTION 3/18 2008 USC-UAM Conference on biofiltration for air pollution control

Background BIOGAS Biogas energy recovery needs clean up H2S, halogenated compounds, other RSC, etc. (1-3 %) CH4 & CO2 (97-99 %) H2S tipical concentrations 500-2,000 ppmv but can reach up to 2% (20,000 ppmv) Biogas energy recovery needs clean up INTRODUCTION 4/18 2008 USC-UAM Conference on biofiltration for air pollution control

Background E Chemical processes (dry and wet scrubbing technologies) Biological RSC oxidation Sulfur Oxidizing Biomass + CO2 + Nutrients Biomass + By-products H2S +1/2 O2 → S0 + H2O E SO4= + 2H+ → + 3/2 O2 E E H2S +2 O2 → SO4= + 2H+ Successfully applied for H2S abatement at low concentrations and low pH (Gabriel and Deshusses, 2003, PNAS-USA) Successfully applied for H2S abatement at high concentrations and high pH (Buisman et al., 1989, Acta Biotechnol.) Successfully applied for H2S abatement at high concentrations and neutral pH (Fortuny et al., 2008; Chemosphere, 71, 10-17) INTRODUCTION 5/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Previous results USC-TRG CONFERENCE 2006, L.A., USA. (Fortuny et al., 2008, Chemosphere, 71 (1): 10-17) Interesting alternative with high removal efficiencies for high inlet concentrations (>80 and 90% for 10,000 and 6,000 ppmv respectively) Sulfur production and accumulation at very high (>6,000 ppmv) is the main handicap O2 availability is the most important and limiting factor Proved system robustness pH plays a main role BIOTECHNIQUES 2007, A Coruña, SPAIN Improved O2 supply considerably reduces sulfur accumulation Efficient start-up and inoculation pH control implementation Study on the O2/H2S supply ratio and sulfur speciation Preliminary research on the EBRT and maximum Elimination Capacity INTRODUCTION 6/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Objectives To further study some of the operational parameters influencing the process performance: - EBRT - Substrate supply shutdowns - Liquid recirculation velocity - pH changes INTRODUCTION 7/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Experimental setup B Setup Schematic of the lab-scale reactor 1: Main reactor 2: Air supply compartment 3: Gas inlet 4: Gas outlet 5: HCO3- supply 6: Gas monitoring 7: MM supply 8: Recirculation pump 9: pH control 10: Liquid monitoring 11: Air supply 12: Level control 13: Liquid purge MATERIALS & METHODS 8/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Setup Parameter Normal value Inlet concentration (ppmv) 2000 Loading rate g H2S m-3 h-1 55.6 Operational pH 6.5 – 7 Packing material HD Q-PAC Specific surface area (m2 m-3) 433 Reactor packed volume (L) 2.0 Reactor liquid volume (L) 4.5 ± 0.2 Fresh liquid flow (L d-1) 2.5 ± 0.2 Recirculation velocity (m h-1) 3.8 EBRT gas (s) 180 HRT liquid (h) 24 - 48 HD Q-PAC (Lantec Products, CA, USA) MATERIALS & METHODS 9/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Methodology Effect of the EBRT: Stepwise decrease from 180 s. down to 25 s at an inlet H2S = 2,000 ppmv => LR from 55 up to 400 g H2S m-3h-1. Effect of an intermittent substrate supply: Gas and carbonate supply shutdown with liquid recirculation, purge and make-up water on. pH control kept on as an indirect measure of biological activity. Effect of the trickling velocity Step-wise increase from 0.52 up to 19.5 m h-1 every 48h (5 HRT) at a LR of 83.5 g H2S m-3 h-1 (3,000 ppmv), an O2/H2S supply ratio of 23.5 (v v-1) and an EBRT of 180 s. Effect of pH changes Initial imposition of a pH drop down to 2.5 with HCl 1M for a 34 h period and resumption of normal pH 6-6.5. Afterwards, imposition of a pH increase up to 9.5 with NaOH 1M for a 24 h period before returning to pH 6-6.5. MATERIALS & METHODS 10/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control EBRT and maximum EC Object: reduce the design EBRT of 180 s. and increase pollutant mass transfer Run 3: after 10 days of gas flow reversion: Max. EC = 145 ± 2 g H2S m-3 h-1 Stimulation of biomass growth for a short period of time is not a good strategy to improve the mass transfer Run 1: shortly after inoculation: Max. EC=125 ± 3 g H2S m-3 h-1 Run 2: after over a year’s operation: Max EC= 144 ± 4 g H2S m-3 h-1 No biological limitation (no H2S accumulation) means improved mass transfer RESULTS & DISCUSSION 11/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Methodology Effect of the EBRT: Stepwise decrease from 180 s. down to 25 s at an inlet H2S = 2,000 ppmv => LR from 55 up to 400 g H2S m-3h-1. Effect of an intermittent substrate supply: Gas and carbonate supply shutdown with liquid recirculation, purge and make-up water on. pH control kept on as an indirect measure of biological activity. Effect of the trickling velocity Step-wise increase from 0.52 up to 19.5 m h-1 every 48h (5 HRT) at a LR of 83.5 g H2S m-3 h-1 (3,000 ppmv), an O2/H2S supply ratio of 23.5 (v v-1) and an EBRT of 180 s. Effect of pH changes Initial imposition of a pH drop down to 2.5 with HCl 1M for a 34 h period and resumption of normal pH 6-6.5. Afterwards, imposition of a pH increase up to 9.5 with NaOH 1M for a 24 h period before returning to pH 6-6.5. MATERIALS & METHODS 10/18 2008 USC-UAM Conference on biofiltration for air pollution control

Intermittent substrate supply Object: assess the capacity to overcome substrate shutdowns pH control: indicates changes in bio-activity gas supply shutdown  acidification gas supply resumption  basification and loss of RE few hours after resumption  acidification RE: small and brief (< 7 %) decrease on day 86.6 ORP and sulfur balance: continuity in the biological activity by S0 oxidation A pH control can be used as a biological activity assessment tool S0 “maintains” biological activity RESULTS & DISCUSSION 12/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Methodology Effect of the EBRT: Stepwise decrease from 180 s. down to 25 s at an inlet H2S = 2,000 ppmv => LR from 55 up to 400 g H2S m-3h-1. Effect of an intermittent substrate supply: Gas and carbonate supply shutdown with liquid recirculation, purge and make-up water on. pH control kept on as an indirect measure of biological activity. Effect of the trickling velocity Step-wise increase from 0.52 up to 19.5 m h-1 every 48h (5 HRT) at a LR of 83.5 g H2S m-3 h-1 (3,000 ppmv), an O2/H2S supply ratio of 23.5 (v v-1) and an EBRT of 180 s. Effect of pH changes Initial imposition of a pH drop down to 2.5 with HCl 1M for a 34 h period and resumption of normal pH 6-6.5. Afterwards, imposition of a pH increase up to 9.5 with NaOH 1M for a 24 h period before returning to pH 6-6.5. MATERIALS & METHODS 10/18 2008 USC-UAM Conference on biofiltration for air pollution control

Trickling liquid velocity (I) Object: effect on by-products and biomass accumulation RE not affected (0.51 to 19.1 m h-1 and LR of 83.5 g H2S m-3 h-1) Main effect on the O2 transfer Oxygen availability increase Interesting operational advantage since elemental sulfur accumulation is diminished without an air supply increase RESULTS & DISCUSSION 13/18 2008 USC-UAM Conference on biofiltration for air pollution control

Trickling liquid velocity (II) Biomass or S0 liquid concentration and trickling velocity not related Increasing trickling velocity not efficient to reduce accumulated S0 (short run) A high trickling velocity recommended (in this system) since increases O2 availability thereby reducing S0 production RESULTS & DISCUSSION 14/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Methodology Effect of the EBRT: Stepwise decrease from 180 s. down to 25 s at an inlet H2S = 2,000 ppmv => LR from 55 up to 400 g H2S m-3h-1. Effect of an intermittent substrate supply: Gas and carbonate supply shutdown with liquid recirculation, purge and make-up water on. pH control kept on as an indirect measure of biological activity. Effect of the trickling velocity Step-wise increase from 0.52 up to 19.5 m h-1 every 48h (5 HRT) at a LR of 83.5 g H2S m-3 h-1 (3,000 ppmv), an O2/H2S supply ratio of 23.5 (v v-1) and an EBRT of 180 s. Effect of pH changes Initial imposition of a pH drop down to 2.5 with HCl 1M for a 34 h period and resumption of normal pH 6-6.5. Afterwards, imposition of a pH increase up to 9.5 with NaOH 1M for a 24 h period before returning to pH 6-6.5. MATERIALS & METHODS 10/18 2008 USC-UAM Conference on biofiltration for air pollution control

pH Object: effect in case of pH control failure pH drop: no effect on RE slightly affects biomass activity (25% reduction on SO4= production) fast recovery of sulfate production (biological activity) pH rise: significant reduction of RE important reduction of biological activity sulfide accumulation and chemical production of thiosulfate Slower recovery of biological activity Bioreactor much more susceptible to high pH than to low pH conditions RESULTS & DISCUSSION 15/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Conclusions The EBRT could be reduced from 180 s. to 90 s. without affecting the removal of H2S, but drastically reducing the investment costs of a full-scale reactor The main rate limiting process was found to be mass transfer of H2S which was not affected by a full colonization of the packed column by bacteria Gas supply shutdowns for up to 5 days are not a concern if make-up water supply is kept on, since elemental sulfur oxidation ensures continuous biological activity A high liquid trickling velocity is recommended because it favors sulfate production through a better use of the supplied DO. There may be a small effect on the biomass activity from a short (34h) and sharp pH drop down to a value of 2.5. However, a pH rise of only 24 hours up to a value of 9.5 has a significant effect on the overall reactor performance. CONCLUSIONS 16/18 2008 USC-UAM Conference on biofiltration for air pollution control

2008 USC-UAM Conference on biofiltration for air pollution control Long Beach, October 2008 OPERATIONAL ASPECTS OF THE BIOLOGICAL SWEETENING OF ENERGY GASES MIMICS IN A LAB-SCALE BIOTRICKLING FILTER Marc Fortuny; A. Gonzalez-Sánchez; C. Casas; D. Gabriel; J. Lafuente M. A. Deshusses Xavier Gamisans Duke University Dep. Civil & Environmental Engineering Universitat Autònoma de Barcelona Departament d’Enginyeria Química Universitat Politècnica de Catalunya Escola Politècnica Superior d’Enginyeria de Manresa.