Kinetic profiles and efficiency disparities in biomethane production mediated by indigenous versus exogenous...

Biomethane is a clean, renewable, and eco-friendly unconventional natural gas resource that has attracted widespread global attention. However, the differences in biomethane generation and the constraining factors under the drive of indigenous versus exogenous microorganisms remain unclear. To address this, anaerobic fermentation experiments simulating coal‑derived biomethane generation were conducted using two distinct microbial sources: indigenous microorganisms enriched from fresh coal samples from the study area and exogenous microorganisms optimized under laboratory conditions. Five representative coal samples from the Wuguantun and Baode mining areas were used as carbon substrates. The efficiency of biomethane production was evaluated based on gas chromatography and analysis using four kinetic models. By integrating methods including coal petrographic and proximate analyses, 16 S rRNA high-throughput sequencing, and Fourier transform infrared spectroscopy, principal component analysis and metabolic pathway analysis were applied to systematically elucidate the main controlling factors and synergistic mechanisms governing biomethane generation. The results indicate that although both indigenous and exogenous microorganisms follow a similar three‑stage process during coal‑degrading methanogenesis, their gas production efficiencies differ significantly. Bioaugmentation with exogenous microbial consortia systematically optimized the biomethane generation process, increasing the maximum methane potential (A₀) by approximately 80% on average, shortening the lag phase (λ) by about 55% on average, and significantly enhancing the maximum methane production rate (µ_m). Coal chemical structure was identified as the primary factor controlling gas‑production variability, with high H/C, and a high aliphatic structures (A_al/A_ar, CH₂/CH₃), and moderate O/C serving as the most critical predictors, demonstrating excellent bioavailability. Coal physicochemical structure, microbial functional potential, and methanogenic pathway distribution govern biomethane output. The physicochemical structure of coal sets the upper limit of potential; the predicted functional gene abundance of the initial microbial community serves as an indicator of substrate degradation potential; and the distribution of downstream methanogenic pathways ultimately governs biomethane conversion efficiency. This study not only deepens the understanding of the complex biogeochemical process of coal bioconversion but also provides key scientific evidence for refining theoretical models of biomethane generation.