Experimental study on in-situ inhibition mechanism of epigenetic biogenic H₂S in coal seam

During coalbed methane (CBM) drainage and production processes, both high-sulfur coal and high-sulfate coal seam water are prone to generate epigenetic biogenic H₂S. The organic sulfur in high-sulfur coal is converted into sulfate by microbial degradation, and then reduced to H₂S by sulfate-reducing bacteria (SRB). Sulfate in high sulfate coal seam water is directly reduced by SRB. These two pathways share the same mechanism but differ in substrate sources. In this common issue, the Jincheng Taiyuan Formation No.15 high-sulfur coal and indigenous bacteria were employed as the experimental system, and the H₂S inhibition effects of gradient additions of sodium tungstate and sodium molybdate were compared.The results demonstrated that while sodium molybdate could inhibit H₂S production, it almost simultaneously suppressed CH₄ generation at 1.0 g/L concentration (cumulative H₂S production H₂S is 0.03 mL/g, cumulative CH₄ production is 0.08 mL/g). Sodium tungstate showed minimal impact on CH₄ production, with 0.8 g/L identified as the optimal concentration. Under optimal conditions, the peak gas-phase H₂S concentration decreased from 240×10⁻⁶ on day 12 in the control group to 27×10⁻⁶ on day 3, representing an approximately 88.8% reduction with significantly earlier peak occurrence. The cumulative H₂S production decreased from 5.72 mL/g to 1.88 mL/g (67.1% reduction), while cumulative CH₄ production increased from 4.25 mL/g to 4.50 mL/g (a decrease of 5.9%), with the gas production peak advancing by 3 days. These findings indicate that sodium tungstate addition does not inhibit and may even slightly promote CH₄ production. In systems supplemented with sodium tungstate, tungstate is transported into cells via TupABC/ModABC transporters, where it competes with ATP sulfurylase to form unstable APW (adenosine 5'-phosphotungstate), blocking the initial activation from \mathrmSO_4^2- to APS (adenosine 5'-phosphosulfate). This manifests as an increase rather than decrease in \mathrmSO_4^2- concentration throughout the fermentation process. Metagenomic and microbial community analyses revealed a decrease in the relative abundance of hydrolytic bacteria Macellibacteroides, slowing the upstream supply of organic sulfur to sulfate. The abundance of SRB (Desulfitibacter) and key genes (sat/aprAB/dsrAB) decreased, while tungstate transporter genes (tupABC/modABC) increased. The relative abundance of acetoclastic methanogen Methanosaeta increased by 55.51% compared to the control, with more substrate (Volatile Fatty Acids, VFA) directed toward methanogenic pathways. Additionally, H₂S production by Wolinella using sulfite as an electron acceptor and symbiotic H₂S production by methylotrophic methanogens were identified. However, the SRB pathway remains the primary and controllable target. This study provides an effective technology for in-situ inhibition of epigenetic biogenic H₂S in fracturing and drainage stages, which can avoid passive desulfurization after coalbed methane production. It not only has significant economic benefits, but also is conducive to the maintenance of extraction pipelines.