Abstract:
During coalbed methane (CBM) drainage and production processes, both high-sulfur coal and high-sulfate coal seam water are prone to generate epigenetic biogenic H
2S. The organic sulfur in high-sulfur coal is converted into sulfate by microbial degradation, and then reduced to H
2S 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 H
2S inhibition effects of gradient additions of sodium tungstate and sodium molybdate were compared.The results demonstrated that while sodium molybdate could inhibit H
2S production, it almost simultaneously suppressed CH
4 generation at 1.0 g/L concentration (cumulative H
2S production H
2S is 0.03 mL/g, cumulative CH
4 production is 0.08 mL/g). Sodium tungstate showed minimal impact on CH
4 production, with 0.8 g/L identified as the optimal concentration. Under optimal conditions, the peak gas-phase H
2S 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 H
2S production decreased from 5.72 mL/g to 1.88 mL/g (67.1% reduction), while cumulative CH
4 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 CH
4 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, H
2S production by
Wolinella using sulfite as an electron acceptor and symbiotic H
2S 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 H
2S 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.