Long-term open circuit microbial electrosynthesis system promotes methanogenesis

Abstract Microbial electrosynthesis (MES) can potentially provide a mean for storing renewable energy surpluses as chemical energy. However, the fluctuating nature of these energy sources may represent a threat to MES, as the microbial communities that develop on the biocathode rely on the continuous existence of a polarized electrode. This work assesses how MES performance, product generation and microbial community evolution are affected by a long-period (6 weeks) power off (open circuit). Acetogenic and H 2 -producing bacteria activity recovered after reconnection. However, few days later syntrophic acetate oxidation bacteria and H 2 -consuming methanogens became dominant, producing CH 4 as the main product, via electromethanogenesis and the syntrophic interaction between eubacterial and archaeal communities which consume both the acetic acid and the hydrogen present in the cathode environment. Thus, the system proved to be resilient to a long-term power interruption in terms of electroactivity. At the same time, these results demonstrated that the system could be extensively affected in both end product generation and microbial communities.