Enhanced Anaerobic Digestion Effluent Treatment by an Electrochemical Membrane Bioreactor: Synergistic Roles of Forward Osmosis and Microbial Electrosynthesis

Abstract

Anaerobic membrane bioreactors (AnMBRs) have demonstrated great potential for carbon neutrality operation among numerous wastewater process technologies, but current progresses only emphasize energy recovery rather than capturing and converting CO 2 from wastewater. In this study, a novel anaerobic osmosis membrane bioreactor coupled with microbial electrosynthesis (AnOMBR-MES) was proposed for simultaneous anaerobic digestion (AD) effluent treatment and CO 2 capture. As the experiment progressed, the AnOMBR-MES system elicited an excellent and stable pollutant removal efficiency, and the raw biogas was in situ-upgraded by a CO 2 reduction reaction (CO 2 RR) in the MES. A combination of factors (cathodic CO 2 RR, slight alkalization, and versatile methanogenetic pathways) contributed to the enhanced CO 2 -to-CH 4 conversion in the AnOMBR-MES system compared to the AnOMBR. Microbial community analysis revealed that the enrichment of Methanobacterium at the biocathode surface and Methanosaeta in the bulk solution was favorable for the conversion of CO 2 and organic matter into CH 4 via establishment of indirect electron transfer chains. Consequently, the CH 4 yield (0.31 m 3 /kg-COD removal ) and energy recovery (0.82 kWh/kg-COD) of the AnOMBR-MES system at 1.0 V were comparable to those of AnMBRs previously reported in the literature. Overall, our results indicate that the AnOMBR-MES system could be a low-carbon-intensity system and realize energy-positive AD effluent treatment.