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It is commonly accepted that biogenic coalbed methane (CBM) is formed by anaerobic bacteria and methanogens via coal biodegradation. While the syntrophic cooperation between fungi and methanogens has been well-established in the production of methane from rumen, little is known about the role that fungi play in the formation of biogenic CBM. Miseq sequencing and mcrA gene library were employed to investigate the fungal, archaeal, and bacterial communities in produced water from Qinshui Basin, a major site for CBM exploitation in China. The syntrophic relationship between fungi degrading coal and methanogens producing methane was also investigated. A diversity of fungal communities was found in produced water from different coal seams with the dominance of Ascomycota and Basidiomycota. Hydrogenotrophic methanogens, Methanobacterium, were also found to be predominant in produced water as revealed by Miseq sequencing and mcrA gene library analysis. Bacterial communities with potential to degrade coal were also recovered in produced water. Large yields of methane were produced in incubations with produced water and coal. Incubations that included antibiotics achieved 62.24% to 97.53% of the methane production as compared to the incubations without antibiotics. These results confirmed that most of the biogenic gas was produced by hydrogenotrophic methanogens and demonstrated the important role that fungi play in the biodegradation of coal.

Microorganisms are essential for the formation of biogenic coalbed methane (CBM) and the application of microbially enhanced CBM (MECoM). Anthracite-degrading methanogenic microflora was cultivated by enrichment and subculture from produced water obtained in Qinshui Basin where CBM is explored commercially. The maximum methane yield was 255 μmol/g of coal after 23 days of cultivation at 35 °C, 1.1–1.2% of salinity, <0.15 mm of coal particle size, pH 8–9, and 5 mL of inocula/g of coal. Microflora archaea, as revealed by MiSeq, were mainly composed of Methanosaeta, an acetic acid-consuming methanogen, followed by Methanocella, a hydrogen-consuming methanogen, suggesting a diversity of methanogenic pathways with a dominance of acetoclastic methanogenesis. The bacteria mainly included Enterobacter, Acetoanaerobium, Macellibacteroides, Clostridium, and Ercella. FTIR analysis showed that the oxygen-containing groups and aliphatic groups were the main targets for microbial degradation. XRD analysis indicated that crystal nucleus structures of coal decreased after degradation. The concentrations of aliphatics were shown to increase over the incubation period based on GC–MS analysis, while the concentrations of dissolved aromatics decreased. These results show the potential for enhancing CBM production by stimulating the activity of methanogenic consortia in situ in Qinshui Basin as well as other high-rank coal reservoirs.

Isotopic studies have shown that many of the world’s coalbed natural gas plays are secondary biogenic in origin, suggesting a potential for gas regeneration through enhanced microbial activities. The generation of biogas through biostimulation and bioaugmentation is limited to the bioavailability of coal-derived compounds and is considered carbon positive. Here we show that plant-derived carbohydrates can be used as alternative substrates for gas generation by the indigenous coal seam microorganisms. The results suggest that coalbeds can act as natural geobioreactors to produce low carbon renewable natural gas, which can be considered carbon neutral, or perhaps even carbon negative depending on the amount of carbon sequestered within the coal. In addition, coal bioavailability is no longer a limiting factor. This approach has the potential of bridging the gap between fossil fuels and renewable energy by utilizing existing coalbed natural gas infrastructure to produce low carbon renewable natural gas and reducing global warming.

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