Enhancing Methane Production from Lignite via Pyrite-Electrochemical Coupling and Microbial Community Restructuring

Coalbed methane enhancement technologies are critical for clean and efficient utilization of low-rank coal resources. However, current biological conversion efficiencies remain limited because of low electron transfer rates and insufficient activity of methanogenic bacteria. In this study, a synergistic enhancement strategy combining pyrite addition and electrical stimulation was proposed to improve methane production from brown coal during anaerobic fermentation by promoting microbial electron transport and metabolic activity. Gradient experiments were conducted under varying pyrite dosages (0-32%) and voltage conditions (0-6 V), coupled with 16S rRNA high-throughput sequencing to systematically analyze gas production, key physicochemical parameters, and microbial community shifts. The results indicated that the combined treatment (16% pyrite + 3 V) increased the cumulative methane yield to 4220 mL over a 30 day fermentation period, representing a 767% increase compared with the untreated control. Concurrently, the relative abundance of Methanobacterium increased from 1.42% to 9.13%. Pyrite functioned as an Fe²⁺/S^2- electron shuttle to facilitate direct electron transfer, whereas electrical stimulation enhanced H₂ production and jointly optimized the hydrogenotrophic methanogenesis pathway. A threshold effect was also identified, whereby excessive pyrite or high voltage induced Fe³⁺/S^2- toxicity and water electrolysis side reactions, compromising system stability. This synergistic strategy achieved a 7-fold increase in methane yield without the addition of conventional chemical additives such as nutrients, enzymes, or synthetic mediators, highlighting its potential for application in the biological intensification of low-rank coal exploitation.