Synthesis of Biofuels on Biocathodes Alfred M. Spormann Departments of Chemical Engineering, and of Civil & Environmental Engineering Stanford University
Source: The National Academies http://needtoknow.nas.edu/energy/interactive/energy-system.php
Current bioenergy efforts on nontraditional biomass Source: The National Academies http://needtoknow.nas.edu/energy/interactive/energy-system.php
Microbial electrosynthesis Source: The National Academies http://needtoknow.nas.edu/energy/interactive/energy-system.php
Synthesis of -neutral Electrofuels H 2 O, waste e - (atmospheric) Usage Solar Wind Nuclear Microbial Cathodic Biofuel Reactors -neutral Transportation fuels Commodity/Fine Chemicals
Energetics of Bio-Electrochemical Systems Microbial fuel cell <CH 2 O> Anode e - G<0 (useful) Cathode Redox potentials - G<0 G>0 ½ O 2 H 2 O Energy production +
Energetics of Bio-Electrochemical Systems Microbial fuel cell <CH 2 O> ½ O 2 Anode e - G<0 (useful) Cathode H 2 O Energy production Redox potentials - G<0 G>0 + Microbial electrosynthesis <CH 2 O> Anode A Cathode e - Anode B H 2 O ½ O 2 Hydrocarbons, Chemicals G>0 (solar, renewable, nuclear) Energy consumption
Exoelectrogenic Bacteria Cathode Cathode Cathode Actinobacillus succinogenes Sporomusa ovata -325mV (vs SHE) Med ox Fumarate Succinate Coulombic Efficiency: Not Available Med red (Park et al. 1999) -400mV (vs SHE) Acetate Coulombic Efficiency: 85% (Nevin et al. 2010) Methanobacterium palustre - 700mV - 900mV (vs SHE) Methane Coulombic Efficiency: 80-96% (Cheng et al. 2010) (Vilano et al. 2010)
Research Focus in Microbial Electrosynthesis e - Anode Cathode C reduced C e - oxidized Hydrocarbons, Chemicals Uptake of cathodic electrons and integration into cellular metabolism reduction and designer fuels/chemicals pathways Engineering stable microbial communities Delivery and activation of electrons to cathode
Bio-Electrochemical Reactor
Cathode Our research platform Cathode Cathode Cathode Methanogenic archaea Homoacetogenic bacteria Methane Acetate Shewanella oneidensis -500mV (vs SHE) Med ox Med red Fumarate (Surrogate) Succinate Escherichia coli -600mV (vs SHE) Med ox Fumarate (Surrogate) Med red Succinate
Fumarate, Succinate Mediator-controlled cathodic electron consumption by S. oneidensis MR1 Expected stoichiometry: Fumarate + 2e - + 2H + Succinate mmol L -1
Electrode attached biofilm of S. oneidensis MR1 Current consumption coupled to fumarate reduction fumarate addition -360 mv vs. SHE
Electrode attached biofilm of S. oneidensis MR1 Current consumption coupled to fumarate reduction Expected stoichiometry: Fumarate + 2e - + 2H + Succinate
Electrode attached biofilm of S. oneidensis MR1 Cyclic voltammetry of abiotic and biofilm electrode with fumarate
Concentration (mm) OD(600) Mediator-controlled cathodic electron consumption by E. coli using fumarate 45 40 Fumarate 0.25 35 0.20 30 25 20 15 0.15 0.10 Fumarate Succinate Malate Series4 10 0.05 5 Succinate 0 0.00 0 50 100 150 200 Time [min]
Synthesis of -neutral Electrofuels H 2 O, waste e - (atmospheric) Usage Solar Wind Nuclear Microbial Cathodic Biofuel Reactors -neutral Transportation fuels Commodity/Fine Chemicals
Spormann bioelectrofuels team Liliana de la Paz Ann Lesnefsky Svenja Lohner Holly Sewell Anne-Kristin Kaster Blaise Pinaud Jamarillo lab Dr. Yi Cui Stanford Funding: GCEP Dr. Bruce Logan Penn State
Power densities reported on MFCs (normalized to electrode-projected surface) Logan 2009
Current [ma] Shewanella oneidensis MR-1 (AS84) Cell suspension, 0, 0.1, 0.5 mm MV (prereduced) 0 mm MV 0.05/0.1 mm MV 0.1 mm MV 0.5 mm MV Time [h]
Cathode Cathode Cathode Sporomusa ovata Exoelectrogenic Bacteria -400mV (vs SHE) Coulombic Efficiency: 85% Acetate (Nevin et al. 2010) Geobacter sulfurreducens (Gregory et al, 2010) -300mV (vs SHE) Methanobacterium palustre Fumarate/PCE Succinate/TCE, cdce Coulombic Efficiency: 65% (Dumas et al. 2010) - 700mV - 900mV (vs SHE) Methane Coulombic Efficiency: 80-96% (Cheng et al. 2010) (Vilano et al. 2010)
Current Expected Data Addition of e - -acceptor Concentration Reactant, Product Time
Escherichia coli: e - + fumarate
Electrons [mmol] Shewanella oneidensis Electron Balance 0.5 0.4 e - consumed by fumarate reduction 0.3 0.2 0.1 0 Cathodic e - consumed 0 2 4 6 Time [h]
Future Work - Outlook Identify molecular mechanism of electron transport into the cell Optimize shuttle mediated electron transport Explore other mediators & cathode potentials Work with other (engineered) target microorganisms Construct microbial communities, interspecies electron transfer Scale up
Microbial Fuel Cell Microbially catalyzed Bio-Electrochemical Systems Chemically catalyzed Microbial Electrosynthesis Chemically catalyzed Microbially catalyzed Organics Anode O 2 H 2 O H + H 2 Product Electron acceptor Cathode Hydrocarbons, chemicals - + - + Energy production Energy consumption adapted from Rabaey & Rozendal, 2010
Mediators/Electron shuttles Methyl Viologen Neutral Red Redox potential: -440mV Oxidized: Transparent Reduced: Blue Redox potential: -330mV Oxidized: Red Reduced: Transparent
Electrons [mmol] Shewanella oneidensis Electron Balance 1.6 e - consumed by fumarate reduction 1.2 0.8 Cathodic e - consumed 0.4 0-0.4 0 5 10 15 20 25 Time [h]
Methane (peak Area) 100 Methanothermobacter marburgensis measured results -500 mv -500 mv 80 60 40 Sparging /N 2 Sparging /N 2 Sparging /N 2 20 0 0 1 h 4 h 0 o/n 0 t
Fumarate, Succinate Shewanella oneidensis MR-1 WT (AS579 ) Cell suspension, 0.5 mm MV (added last) Pregrown on 50mM lactate, 70mM + CAA fumarate anaerobically for app. 18h, OD: app. 0.8, -700mV vs Ag/AgCl
Candidate Microorganisms for Microbial Electrosynthesis Homoacetogens Methanogens Engineered microorganisms (Acetate) alkane precursor CH 4 (Methane) Constructed microbial communities
Exoelectrogenic Bacteria Cathode Cathode Cathode Sporomusa ovata -400mV (vs SHE) Coulombic Efficiency: 85% Acetate (Nevin et al. 2010) Shewanella oneidensis -500mV (vs SHE) Med ox Fumarate (Surrogate) Spormann lab Med red Succinate Escherichia coli -600mV (vs SHE) Med ox Fumarate (Surrogate) Spormann lab Med red Succinate