(139d) Electroautotrophic Synthesis of Acetate and Methane

Electroautotrophic synthesis of chemicals from CO₂ offers an attractive way of producing fuels that would be sustainable, domestic and environmentally benign, particularly in relation to climate change.  Autotrophic rates of acetate and methane production by microbes with hydrogen gas as an electron donor have been demonstrated in the multiple kg m^-3 h^-1 range.  However, this approach requires a source of hydrogen.  Generation of hydrogen by electrolysis, or direct delivery of electrons through an electrode, could serve as the source of hydrogen if sustainable energy, such as solar or wind, is used to drive the production of electrical energy.  The overall method becomes even more attractive if the use of rare earth elements is avoided and only microbial catalysts are employed.  This approach is especially advantageous if the microbes operate within the electrolysis/electrochemical cell.  Using a community of microorganisms selected from a brewery waste we have produced high amounts of methane and acetate from reductive electrical current in electrochemical cells with only microbial catalysts.  The data thus far indicate that the generation of both products is dependent upon the biological catalysts associated with the electrodes, and the production rates observed for both products exceed any published rates as of the time of this submission.  The electromethane could readily be dropped into existing natural gas infrastructure and used as a transportation fuel.  Acetate is a commodity chemical but is also a building block that may be used to produce other fuels.  We are attempting to convert that acetate into alcohols (ethanol and butanol) with communities of microbes selected within the electrochemical cells.  The rates of production, electrochemical data associated with the catalysis, reactor design, microbial catalyst identification and community characteristics (examined metagenomically) will be discussed.