Continuous electromethanogenesis of propionate wastewater: Effect of external voltage and hydraulic retention time

Conventional anaerobic digestion (AD) may be inhibited by the accumulation of intermediate metabolites, thereby disrupting the stability of the AD process. The emerging electromethanogenesis system opens up a new opportunity to enhance the efficiency of biogas technology. In this study, the potential mechanism of the combined impact of applied external voltage and hydraulic retention time on continuous propionate digestion was investigated for the first time. The methane yield was increased up to 98.6 %, while the methane content was enhanced up to 48.0 % with an external voltage of 1.0 V, compared with the control. The cyclic voltammetry results suggested that the external voltage facilitated faster growth, stronger resistance to hydraulic shock, and higher electrochemical activity of electroactive biofilms with a thickness of approximately 10 mu m. Further analysis via a three-dimensional excitation-emission matrix confirmed the external voltage-boosted EPS secretion comprised of protein-like substances, acting as the electron mediator between Smithella and Methanosaeta.