Magnetic bioelectrochemical anode for suspended community electron collection to amplify methane production

Bioelectrochemical systems have been widely studied as an enhanced anaerobic digestion (AD) technology for regulating electron transfers during organic degradation and methane production using bioelectrodes. However, owing to their limited interactions with bioelectrodes, suspended microbial communities are relatively less effective than biofilm communities. In this study, a magnetic composite electrode-driven bioelectrochemical reactor is constructed and the synergistic optimization mechanism of magnetic-field-coupled magnetite particles is elucidated. The combined effects of magnetic fields and Fe₃O₄ particle–anode contact on methane production were examined using five membrane-free reactors with different magnetic and particle-size conditions. The magnetic field with 20–40 mesh Fe₃O₄ shortened the start-up time to 48.7 d (32.8% less than the control) and achieved the highest methane rate (1.70 mol CH₄/(m³·d)), chemical oxygen demand (COD) removal (94.34%), and current-driven methane conversion efficiency (68.1%). Electrochemical analysis showed improvements in direct and mediated electron transfer due to increased Fe₃O₄ active site exposure, with cathode coulombic efficiency rising by 90.3%. Microbial analysis revealed that fine particles promoted rapid transfer mediated by Proteobacteria, whereas coarse particles enriched Desulfobacterota through stable mineral–microbe interfaces. These findings demonstrate that regulating magnetic particle–anode interfaces can accelerate start-up, enhance electron transfer, and improve the stability of bioelectrochemical methane production. (Figure presented.)