Enhanced methanogenic co-degradation of propionate and butyrate by anaerobic microbiome enriched on conductive carbon fibers.

•Carbon fibers improved methanogenic co-degradation of propionate and butyrate.•Methanogenesis rate increased by 6.7 times.•Various electroactive bacteria were abundant in carbon fibers amended bioreactor.•Methanosaeta were dominant over Methanosarcina.•Significance of direct interspecies electron transfer (DIET) was discussed.