Hydrogen consumption and methanogenic community evolution in anodophilic biofilms in single chamber microbial electrolysis cells under different startup modes

Abstract

In microbial electrolysis cells (MECs), methanogenic communities were sensitively affected both by hydrogen production rate, which were regulated by external voltages, and by initial cathodes, which were determined by reactor startup mode. Hydrogenotrophic methanogens, such as Methanobacterium, Methanococcus, Methanocorpusculum, and Methanoculleus, were enriched in the anode biofilm with a high voltage (0.7 V), which promoted a hydrogen production rate of 0.99–1.10 mL H₂ per mL reactor in a 24 h batch operation, compared to 0.08–0.09 mL H₂ per mL reactor at low applied voltage (0.3 V). Acetoclastic methanogens were only obtained from Methanosarcina, which competed with anode respiring bacteria in the anode biofilm, and they were largely detected in open circuit reactors (control). GeoChip analysis revealed that MECs with the largest hydrogen yields had the highest microbial diversity of methanogens. The cathodic products (hydrogen, methane) can simultaneously make the anodophilic community structure comprehensive and diverse despite the use of only a single substrate (acetate) in MECs. The results indicated that the evolution of microbial communities was substantially affected by external voltage and initial operational modes, but methanogen communities were inevitably affected by cathodic products. Higher applied voltage positively affected the relative abundance of cytochrome gene among the overall detected genes, and methanogens were consequently promoted by high coulombic efficiency and fast hydrogen production rate. This research can help in understanding of improving or regulating the quality of products from MEC reactors in the future.