A double-chamber microbial electrolysis cell improved the anaerobic digestion efficiency and elucidated the underlying bio-electrochemical mechanism

Abstract

Bioelectrochemical regulation has been proven to enhance the traditional anaerobic digestion (AD) of biowastes. However, most of the research has been conducted using a single-chamber reactor that could not explain the underlying mechanism and/or role of electrodes in CH4 production. Herein, a double-chamber microbial electrolysis cell integrated anaerobic digestion system (MEC-AD) was fed with corn stover (CS) and was exposed to 0.0 V to 1.5 V to elucidate the possible effects of cathode and anode on the AD performance. It was shown that CH4 yield was enhanced by 80.41% at 0.6 V, however, there was a sharp decline in methanogens at 0.9 V, which finally resulted in acidification. Interestingly, electroactive bacteria of Enterococcus were enriched on the electrode at 0.6 V which accelerated the degradation of CS, and thus, enhanced the subsequent mixotrophic methanogenesis dominated by Methanosarcina in the bulk solution of the anode chamber. While, Enterococcus and Methanobacterium were shown to be the dominating microbes in the cathode chamber, which were found syntrophically associated to enhance hydrogenotrophic methanogenesis via the direct interspecies electron transfer process. The synergistic stabilization of both anode and cathode chambers resulted in the final performance improvement in the MEC-AD system. This MEC-AD system provided a deeper understanding for methane enhancement, which will facilitate the scale-up application of the double-chamber systems.