S146: Conversion of CO2­ to chemicals by autotrophic microorganisms at a negatively poised electrode

Microbial electrosynthesis is the conversion of CO₂­ to chemicals by autotrophic microorganisms using reducing equivalents from a negatively poised electrode.  The technology has the potential to be a sustainable, carbon-consuming platform for industrial chemical production.  In order for microbial electrosynthesis systems to become commercially relevant, long-term operation and improved rates must be demonstrated. In order to address this, bioelectrochemical reactors were operated chronoamperometrically at a cathode potential of -590 mV vs. SHE for over 200 days using a mixed microbial consortium (microbiome).  Current consumed was directly related to the formation of hydrogen, acetate, and/or methane.  Rates of acetate production were repeatedly observed over 10 mMl/L cathode liquid volume/day, and reached a maximum of 17.25 mM/day (1.04 g/L/d) with accumulation to 175 mM (10.5 g/L) over 20 days.  Hydrogen was also produced at high rates by the biocathode, reaching 100 mM/d (0.2 g/L/d) and a total accumulation of 1164 mM (2.4 g/L) over 20 days.  Other products observed were formate, propionate, and butyrate.  Acetobacterium spp. dominated the active microbial population on the cathodes (50-60%), with members of Sulfurospirillum and the Rhodobacteraceae also prevalent.  Utilization of microbiomes for microbial electrosynthesis has the potential to produce commodity chemicals, gaseous and liquid fuels, and bioplastics from CO₂.  The production of acetate in this study approach that reported for bioreactors pressurized with H2:CO₂, indicating that electrodes deliver electrons to autotrophic microorganisms effectively. This study demonstrated sustained long-term performance of an electrosynthetic microbiome.