Bioelectrochemical methane production from CO2 by Methanosarcina barkeri via direct and H2-mediated indirect electron transfer

Electromethanogenesis is a promising strategy for bioconversion of CO2 to CH4 via direct electron transfer (DET) and/or H2-mediated indirect electron transfer (IET). However, specific contribution ratios of DET or H2-mediated IET are unclear. Here, pathway preferences were firstly calculated in the “cage” type cathode colonized by Methanosarcina barkeri. The highest CH4 production rate of 4.4 μmol cm−2•day−1 was detected from 36 to 72 h at −1.2 V. The average ratios of H2-mediated IET were calculated as 59.73 ± 8.29%, 69.45 ± 20.75%, 69.55 ± 18.30% and 82.97 ± 16.13% at −0.6, −0.8, −1.0 and −1.2 V (vs SHE), respectively. While above −0.4 V, only the DET pathway was detected. The real time polymerase-chain reaction amplification at the transcriptional level of ccdA and frhB showed the similar trend for the pathway preference in CH4 production. Results provide specific ratios and preference of CH4 production via these two pathways, which may be used for parameter reference for industrial applications. [Display omitted] •New “cage” type cathode was designed to calculate pathway preference.•Ratios of CH4 via DET are 40–18% at −0.6∼-1.2 V, the remaining are H2-mediated IET.•Almost no CH4 was found via H2-mediated IET below −0.4 V.•The expression level of ccdA and frhB gene were assessed by newly designed primers.