Microbial community development on different cathode metals in a bioelectrolysis enhanced methane production system

Abstract Methane production enhanced by electrode respiring microorganisms is a recently developing technology for bioelectrolysis assisted anaerobic digestion. The direct interspecies electron transfer between electrodes and microbe has been recognized as the core mechanism for methanogenesis in this coupled system. However, the detailed mechanisms of methane electrosynthesis on cathodes need in-depth investigation. This work is to evaluate the effects of hydrogen evolution capacity of cathode on methane production and biocathode community that developed on commonly used cathode materials (copper, nickel and stainless steel). Integrated reactors with nickel cathode exhibited a maximum methane yield of 59.2 mL CH4/gVSS with a higher current density of 9 A/m2 compared to copper electrode and stainless-steel electrode. About 40% increase of methane production rate is achieved in the coupled reactors with nickel electrode compared to traditional anaerobic digestion technique. Analysis of microbial community structure reveals that the bioelectrolysis cathode persuades the whole system towards the hydrogenotrophic methanogenic pathway. A methanogenic system derived from Methanobacterium is formed on metal electrodes, which simultaneously utilizes both electrons and hydrogen to produce methane. However, higher hydrogen evolution reaction capacity leads to higher electrochemical contribution for methane synthesis, which results in an improved conversion efficiency.