Biological methane production coupled with sulfur oxidation in microbial electrosynthesis system without organic substrates

Methane is produced in microbial electrosynthesis system (MES) without organic substates. However, relatively high applied voltages are required to proceed the bio-electrical reaction. In this study, we demonstrated that electrotrophic methane production at the biocathode was performed even at a very low voltage of 0.1 V in a MES, in which abiotic HS- oxidation to SO42- occurred at a anodic carbon-cloth surface coated with platinum powder. In addition, microbial community analysis revealed the most probable pathway for methane production from electrons. First, electrotrophic H2 was yielded by syntrophic bacteria such as Syntrophorhabdus, Syntrophobacter, Syntrophus, Leptolinea and Aminicenantales with a direct acceptance of electrons at the biocathode. Subsequently, the most of yielded H2 was converted to acetate by Clotrodium and Spirochate of homoacetogen. In conclusion, the main methane production was indirectly performed by a high population of acetoclastic methanogens of Methanosaeta via acetate. The methane production via H2 was also performed by hydrogentronophic mathenogens of Methanobacterium and Methanolinea.