Electrochemical Control of Redox Potential Arrests Methanogenesis and Regulates Products in Mixed Culture Electro-Fermentation

This study demonstrates the feasibility of using solid electrodes as an alternative source or sink of electrons to regulate the redox potential of mixed culture anaerobic reactors, so tunable fermentation products can be generated. The product spectrum was characterized under the working potentials of −1.0, −0.6, and −0.2 V (versus Ag/AgCl), which spans the electron flow direction from cathodic current to anodic current. Results show that in neutral pH a more negative working potential led to higher production of CH4, H2, and acetic acid, while increasing the potential from −1.0 to −0.2 V (versus Ag/AgCl) greatly reduced methanogenesis by 68% and acetic acid generation by 33%. Lowering initial pH to 6.2 reduced such effects by electrical potential. The decrease of working potential slightly decreased butyric acid production and showed little impact on propionic acid under both pH conditions. When the reactor switched from poised conditions to open circuit condition, more propionic acid and acetic acid while less butyric acid production was observed. This redox-potential-based control presents a new approach to regulate the mixed culture fermentation and improve product tunability.