Electric field-driven methanogenesis from low-rank coal: Deciphering synergistic role of direct interspecies electron transfer and conventional microbial pathways.

Low-rank coal represents a challenging substrate for biomethane production due to its low biodegradability, limiting conventional bioconversion efficiencies. This study employed an Electric Field-driven Anaerobic Digestion (EFAD) system to enhance methane production from lignite by stimulating both direct interspecies electron transfer (DIET) and classical methanogenic pathways (hydrogenotrophic and acetoclastic). Batch experiments demonstrated a 3.8-fold increase in methane yield under EFAD compared to conventional anaerobic digestion, with DIET accounting for approximately 22 % of methane production. Electrochemical impedance spectroscopy revealed reduced charge transfer resistance and enhanced redox activity, indicating improved electron transfer in the EFAD system. Microbial community analysis showed enrichment of electroactive bacteria and methanogens. Selective inhibition of methanogenic pathways confirmed the participation of targeted methanogens and highlighted the EFAD system's ability to mitigate pathway suppression via DIET enhancement. These results provide mechanistic insights that advance the potential of bioelectrochemical methods for efficient, scalable biomethane recovery from low-rank coal.