Enhanced bio-methanation of coal through direct interspecies electron transfer mediated by nano-magnetite.

This study sought to improve the bioconversion efficiency of coal to biomethane through the addition of nano-magnetite. By integrating process performance evaluation, electrochemical characterization, and microbial functional analysis, this study provides mechanistic insight into the role of nano-magnetite in enhancing coal anaerobic digestion. An anaerobic digestion (AD) system mediated by nano-magnetite and utilizing lignite as the substrate was established to evaluate methane production performance and associated metabolic responses. The results demonstrated that the incorporation of nano-magnetite significantly accelerated methane production and increased biomethane yield, with the highest enhancement observed at an optimal dosage of 2 g, resulting in a 62.14% increase compared to the control group. Electrochemical and biochemical indicators suggested enhanced microbial electron transfer activity in the nano-magnetite–amended system. Microbial community analysis indicated that nano-magnetite enrichment increased the abundance of electroactive microorganisms, including Sphaerochaeta, Desulfomicrobium, Geobacter, and Geovibrio, thereby facilitating both the acetoclastic pathway and the hydrogenotrophic CO₂-reduction pathway in methanogenesis. Variations in key gene abundance suggest a potential for DIET between Geobacter, Geovibrio, and Methanothrix, which may be associated with the observed increase in biomethane production from coal. The addition of nano-magnetite to potentially facilitate DIET may represent an effective strategy for promoting biomethane production from coal.