Development of biocathode during repeated cycles of bioelectrochemical conversion of carbon dioxide to methane.

Functioning biocathodes are essential for electromethanogenesis. This study investigated the development of a biocathode from non-acclimated anaerobic sludge in an electromethanogenesis cell at a cathode potential of −0.7 V (vs. standard hydrogen electrode) over four cycles of repeated batch operations. The CO 2 -to-CH 4 conversion rate increased (to 97.7%) while the length of the lag phase decreased as the number of cycles increased, suggesting that a functioning biocathode developed during the repeated subculturing cycles. CO 2 -resupply test results suggested that the biocathode catalyzed the formation of CH 4 via both direct and indirect (H 2 -mediated) electron transfer mechanisms. The biocathode archaeal community was dominated by the genus Methanobacterium , and most archaeal sequences (>89%) were affiliated with Methanobacterium palustre . The bacterial community was dominated by putative electroactive bacteria, with Arcobacter , which is rarely observed in biocathodes, forming the largest population. These electroactive bacteria were likely involved in electron transfer between the cathode and the methanogens. [ABSTRACT FROM AUTHOR]