Bioelectrochemical Upgrading of Anaerobic Digestion Biogas Spyros G. - PowerPoint PPT Presentation

Bioelectrochemical Upgrading of Anaerobic Digestion Biogas Spyros G. Pavlostathis School of Civil & Environmental Engineering Georgia Institute of Technology Atlanta, GA 30332 ‐ 0512, USA NAXOS 2018 6th International Conference on Sustainable Solid Waste Management Naxos Island, Greece 14 June 2018 1

Municipal Wastewater Treatment  Opportunities for CO 2 reuse and energy recovery in municipal wastewater treatment plants (WWTP), now referred to as Water Resource Recovery Facilities (WRRF) 2

Anaerobic Digestion Biogas (CO 2 , CH 4 , trace gases) Complex organic compounds Carbohydrates, Proteins, Lipids Hydrolysis Simple organic compounds Sugars, Amino acids, Fatty acids Acidogenesis Organic acids and alcohols Acetogenesis H 2 , CO 2 Acetate Methanogenesis CO 2 , CH 4 Liquid digestate, Biosolids 3

Anaerobic Digestion – Biogas Composition Assumes complete mineralization; ignores microbial growth Gujer and Zehnder, Water Sci. Technol. , 1983 Mean Oxidation State of Carbon (OS) = 4 - 1.5(COD/TOC) CH 4 (%) = 100 - 12.5 (OS + 4) 4

CO 2 Capture & Sequestration  Absorption  Chemical (MEA, caustic, etc.)  Physical (Selexol, Rectisol, etc.)  Adsorption  Alumina, zeolite, activated carbon  Cryogenics  Membrane separation  Gas separation (Polyphenyleneoxide, polydimethylsiloxane)  Gas absorption (Polypropelene)  Ceramics 5

CO 2 Conversion & Valorization Roadmap of Valorization Technologies for Captured CO 2 Pan et al. Crit. Rev. Environ. Sci. Technol ., 2018 Microbial CO 2 Fixation (Microalgae, Phototrophic Bacteria) CO 2  Biomass  Products Bioelectrochemical Systems (BES) for Direct CO 2 Conversion BES CO 2 CH 4 , Acetate, C 3 , C 4 …. 6

Biomethane Valorization – New Concepts (2018) 7

Bioelectrochemical Systems (BES) Microbial Fuel Cell (MFC) Produces electrical current Reduction Oxidation Microbial Electrolysis Cell (MEC) Produces hydrogen (H 2 ) Microbial Electromethanogenesis Produces methane (CH 4 ) Microbial Electrosynthesis (MES) Produces 1+ carbon compounds A, Resistor (MFC) or applied potential (MEC) (e.g., acetate, etc.) B, Proton exchange membrane R1, Reactant in the anode (oxidation half reaction) 2H + + 2e ‐ → H 2 P1, Product in the anode E H °' = ‐ 0.414 V R2, Reactant in the cathode (reduction half reaction) P2: Product in the cathode CO 2 + 8H + + 8e ‐ → CH 4 + 2H 2 O E H °' = ‐ 0.244 V CO 2 + 4H 2 → CH 4 + 2H 2 O Δ E°' = 0.170 V 8 At 25 °C, 1 atm, pH 7.

Electron Transfer Mechanisms in Biocathode e ‐ H + CO 2 CH 4 (1) Direct Electron (3) Non ‐ H 2 ‐ Mediated Transfer (DET) Electron Transfer CO 2 CH 4 M ox H 2 O M red H 2 (2) H 2 ‐ Mediated CH 4 CO 2 CO 2 CH 4 Electron Transfer (MET) M red H 2 M ox H 2 O 9

BES Performance Geppert et al., Trends Biotechnol ., 2016  BES performance depends on:  Electron donor (anode)  Cathode potential  System design (e.g., PEM surface area, electrode type and surface area)  Inoculum type  Reactor type (One ‐ vs. two ‐ chamber systems; batch vs. continuous flow)  Operational parameters (e.g., pH, temperature)  Methane production rate depends on  Cathode potential (V)  Current density (A/m 2 )  Current ‐ to ‐ methane efficiency (%) 10

Biocathode Performance – Effect of Inoculum Biocathode methanogenic inocula: MM, mixed; EHM, pre ‐ enriched hydrogenotrophic 50 MM-B A MM-biocathode 4 EHM-B EHM-biocathode 40 (mg COD/L) ACETATE 3 CURRENT (mA) 30 2 20 1 10 0 CURRENT DENSITY MM-B 20 B 0 EHM-B 15 -10 (A/m 2 ) 10 -20 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 5 VOLTAGE (V) 0 Final Biofilm Mean CH 4 Production MM-B C HEADSPACE CH 4 3 Biomass (mmol CH 4 /mg biomass ‐ EHM-B Biocathode (mg) day) (mmol) 2 MM ‐ 0.54 ± 0.07 0.15 ± 0.01 inoculated 1 EHM ‐ 0.64 ± 0.19 0.59 ± 0.03 0 inoculated 0 5 10 15 20 TIME (d) Dykstra, C.M.; Pavlostathis, S.G. 2017. Methanogenic biocathode microbial community development and the role of Bacteria. Environ. Sci. Technol. 51(9) 5306 ‐ 5316. 11

Biocathode Performance – Effect of Inoculum Biocathode methanogenic inocula: MM, mixed; EHM, pre ‐ enriched hydrogenotrophic Archaea Bacteria 100 100 RELATIVE ABUNDANCE (%) RELATIVE ABUNDANCE (%) 80 80 60 60 Bacteroidetes Protoebacteria Actinobacteria 40 Firmicutes 40 Spirochaetes Synergistia Thermotogae 20 Anaerolineales 20 Acidobacteria Deferribacteres Chloroflexi 0 Unclassified MM MM-biocathode EHM EHM-biocathode 0 MM MM-biocathode EHM EHM-biocathode Methanobrevibacter spp. Methanogens Methanobrevibacter arboriphilus Cell lysis Methanoculleus spp. • MM ‐ biocathode enriched in Methanolinea spp. products CH 4 Spirochaetes and other non ‐ Methanomethylovorans spp. Methanosaeta spp. exoelectrogenic, fermentative Methanobacterium spp. Exoelectrogen Cathode • Biocathode archaeal communities Bacteria converged on the same phylotypes, • EHM ‐ biocathode enriched in Methanobrevibacter arboriphilus e ‐ , H + , Proteobacteria , exoelectrogens CO 2 • Inoculum pre ‐ enrichment with H 2 /CO 2 and putative producers of CO 2 , selects for methanogens that are also electron shuttle mediators Oxidized selected for by biocathode conditions carbon (faster biocathode start ‐ up) Dykstra, C.M.; Pavlostathis, S.G. 2017. Methanogenic biocathode microbial community 12 development and the role of Bacteria. Environ. Sci. Technol. 51(9) 5306 ‐ 5316.

Biocathode Performance – Effect of H 2 S Cathode Headspace H 2 S (1% v/v) Cathode Headspace H 2 S (0 ‐ 6%) 80 A CURRENT DENSITY BES1 (Control) Headspace CE CCE 60 BES2 (H 2 S amended) H 2 S (% v/v) (%) (%) (A/m2) 0 11 100 40 4 19 99 20 5 58 13 0 6 58 15 0 5 10 15 20 8 B CE, Coulombic efficiency METHANE (mmol) 6 CCE, cathode capture efficiency 4 2 0 0 5 10 15 20 TIME (d) Two competing effects: • Depression of CH 4 production ( ≥ 4% H 2 S): Inhibition of methanogens? • Enhancement of CH 4 production ( ≤ 3% H 2 S): What is/are the process(es) involved? 13

Biocathode Performance – Effect of H 2 S Cathode e ‐ CH 4 CO 2 20% H 2 S H 2 S is the 80% CO 2 most toxic of H 2 S HS ‐ S 2 ‐ Neutral pH CH 4 the sulfide e ‐ species High local pH H + CO 2 H 2 S The methanogenic biocathode is protected from sulfide inhibition by biofilm formation and a local high pH at the cathode surface. 14

Biocathode Performance – Effect of H 2 S Anode e ‐ Potential anode H 2 S oxidation products CO 2 N 2 S 0 2 ‐ 2 ‐ S x S 4 O 6 S 2 O 3 2 ‐ SO 4 2 ‐ Sun et al., ES&T 2009 N 2 H 2 S CO 2 2 ‐ SO 4 CO 2 Acetate SRB Acetate • Low H 2 S → more electrons donated to the anode → higher biocathode CH 4 production • High H 2 S → s � mulate sulfur cycling → divert acetate eeq from the anode → lower biocathode CH 4 production 15

Biocathode Performance – Effect of H 2 S Anode Cathode 100 100 Bacteroidetes B A RELATIVE ABUNDANCE (%) 90 RELATIVE ABUNDANCE (%) Proteobacteria 90 Actinobacteria 80 80 Firmicutes 70 70 Spirochaetes 60 60 Synergistia 50 50 Unclassified 40 40 30 30 20 20 10 10 0 0 BES1 BES2 BES1 BES2 Biofilm Susp. Biofilm Susp. Biofilm Susp. Biofilm Susp. Control H 2 S ‐ amended Control H 2 S ‐ amended • Deltaproteobacteria were not detected in any anode or cathode biofilm or suspended growth samples, except in the BES2 anode biofilm. • SRB phylotypes in the BES2 anode biofilm represented 32% of Deltaproteobacteria and 1% of total Bacteria. • Identified SRB phylotypes include Desulfobulbus propionicus , Desulfovibrio sp. and Syntrophobacterales spp. 16

Methanogenic BES Performance  Methane production rate (L CH 4 /L reactor/day) 0.27 ‐ 27 calculated assuming a current density of 1 ‐ 100 A/m 2 (Geppert et al., 2016)(High ‐ rate anaerobic digesters 1.4 ‐ 9.8 L CH 4 /L reactor/day)  Cell voltage From ‐ 0.7 to ‐ 1.5 V  Current ‐ to ‐ methane efficiency 23 to 99% (>100% microbially induced cathode corrosion)  Energy (electrical) input (Wh/L CH 4 ) Water anode electron donor: 19 calculated; 74 ‐ 97 observed (Geppert et al., 2016) Acetate anode electron donor (observed; Dykstra & Pavlostathis, 2017) CO 2 ‐ fed System Wh/L CH 4 Control BES 27.0 BES with 3% H 2 S 31.0 BES with 1 g/L ZVI a 7.6 a ZVI, zero valent iron added to the biocathode 17

Methanogenic BES – Remaining Challenges  Choice of anode electron donor  Reduction of energy losses (internal resistance; cathode overpotential)  Reduction of gas transport through the membrane  New electrode materials  Increase of methane production rate  Scale ‐ up 18

BES AD Biogas Upgrading ≤ ‐ 0.8 V CH 4 CO 2 Acetate Biogas (CH 4 + CO 2 ) PEM 19

Acknowledgement  Experimental data presented here are from Dr. Christy Dykstra’s PhD dissertation entitled “Bioelectrochemical Conversion of Carbon Dioxide to Methane for Biogas Upgrading”.  This material is based in part upon work supported by the US National Science Foundation Graduate Research Fellowship under Grant No. DGE ‐ 1148903. 20

Bioelectrochemical Upgrading of Anaerobic Digestion Biogas Spyros G. Pavlostathis School of Civil & Environmental Engineering Georgia Institute of Technology Atlanta, GA 30332 ‐ 0512, USA NAXOS 2018 6th International Conference on Sustainable Solid Waste Management Naxos Island, Greece 14 June 2018 21

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