Synergistic Effects of Magnetic Fields and Magnetite on Anaerobic Digestion: Enhancing Methane Production and Microbial Activity.

Methane production rate has been a major obstacle hindering the widespread adoption of anaerobic digestion (AD) process. This study investigated the synergistic effects of magnetite and an external magnetic field on anaerobic sludge, with a focus on methane production, volatile fatty acids (VFAs), and microbial community structure. The group treated with both magnetite and a magnetic field (DM) exhibited the highest methane yield (69.16 ± 5.56 mL/g biomass), nearly double that of the blank control group (BC, 37.50 ± 1.59 mL/g biomass), along with the shortest lag phase in kinetic modeling (0.96 ± 0.13 d vs 1.52 ± 0.13 d by BC), indicating a faster microbial response. DM treatment also resulted in more rapid VFAs consumption, especially of acetic acid and propionic acid, suggesting enhanced metabolic activity and substrate conversion efficiency. The dominant genera in all the groups were Enterococcus, Proteiniphilum, Acetomicrobium, and Candidatus Caldatribacterium. Diversity analysis, simper analysis, and network attribute difference analyses have all indicated that the overall microbial community structure in the bulk sludge remained stable, and magnetite had influenced microbial activity on its surface. These research findings have demonstrated that magnetite and magnetic fields synergistically enhanced AD efficiency by stimulating microbial activity without altering the microbial community structure. These outcomes have provided valuable insights for developing bioaugmentation strategies for enhanced biogas production.