Dual cathode configuration and headspace gas recirculation for enhancing microbial electrosynthesis using Sporomusa ovata

High-rate production of acetate and other value-added products from the reduction of CO2 in microbial electrosynthesis (MES) using acetogens can be achieved with high reducing power where H-2 appears as a key electron mediator. H-2 evolution using metal cathodes can enhance the availability of H-2 to support high-rate microbial reduction of CO2. Due to the low solubility of H-2, the availability of H-2 remains limited to the bacteria. In this study, we investigated the performances of Sporomusa ovata for CO2 reduction when dual cathodes were used together in an MES, one was regular carbon cathode, and the other was a titanium mesh that allows higher hydrogen evolution. The dual cathode configuration was investigated in two sets of MES, one set had the usual S. ovata inoculated graphite rod, and another set had a synthetic biofilm-imprinted carbon cloth. Additionally, the headspace gas in MES was recirculated to increase the H-2 availability to the bacteria in suspension. High-rate CO2 reduction was observed at-0.9 V vs Ag/AgCl with dual cathode configuration as compared to single cathodes. High titers of acetate (up to similar to 11 g/L) with maximum instantaneous rates of 0.68-0.7 g/L/d at-0.9 V vs Ag/AgCl were observed, which are higher than the production rates reported in the literatures for S. ovata using MES with surface modified cathodes. A high H-2 availability supported the high-rate acetate production from CO2 with diminished electricity input.