Influence of Acidic pH on Hydrogen and Acetate Production by an Electrosynthetic Microbiome

Production of hydrogen and organic compounds by an electrosynthetic microbiome using electrodes and carbon dioxide as sole electron donor and carbon source, respectively, was examined after exposure to acidic pH (similar to 5). Hydrogen production by biocathodes poised at -600 mV vs. SHE increased > 100-fold and acetate production ceased at acidic pH, but similar to 5-15 mM (catholyte volume)/day acetate and >1,000 mM/day hydrogen were attained at pH similar to 6.5 following repeated exposure to acidic pH. Cyclic voltammetry revealed a 250 mV decrease in hydrogen overpotential and a maximum current density of 12.2 mA/cm(2) at -765 mV (0.065 mA/cm(2) sterile control at -800 mV) by the Acetobacterium-dominated community. Supplying -800 mV to the microbiome after repeated exposure to acidic pH resulted in up to 2.6 kg/m(3)/day hydrogen (approximate to 2.6 gallons gasoline equivalent), 0.7 kg/m(3)/day formate, and 3.1 kg/m(3)/day acetate (= 4.7 kg CO2 captured).