The characteristics of thermophilic anaerobic bacteria in coal and its methanogenesis mechanism

Abstract

The research on the characteristics and metabolism of thermophilic methanogens in coal under high temperature conditions is helpful to the development and utilization of deep coalbed methane, improving the potential of microbial methanogenesis and carbon dioxide emission reduction, and expanding the application scope of Coalbed Gas Bioengineering. Therefore, the lean coal in central and southern region of Henan, China with abnormal ground temperature was used as the substrate, and the microorganisms in coal seam water were used as the source of bacteria. The experiments were carried out at 50 °C, 55 °C, 60 °C, 65 °C and 70 °C, respectively. The results showed that hydrogenotrophic methanogenesis was the primary pathway of methane generation by thermophilic anaerobic digestion of coal. The hydrolysis products were consumed by hydrolysis bacteria Coprothermobacter, Acetomicrobium and acetic acid oxidizing bacteria Tepidanaerobacter to produce a large amount of H₂ and CO₂. Then CO₂ was reduced to CH₄ by the hydrogenotrophic methanogen Methanothermobacter. From all aspects, 55 °C was the most suitable for coal thermophilic anaerobic digestion to produce methane. At this temperature, the biomethane production at the peak of biogas production could reach 0.45 mL/g, and the cumulative production was 1.81 mL/g. The content of glycosyl transferases (GTs) was found to be the lowest in the anaerobic digestion system operating at 50 °C, resulting in the lowest coal degradation rate. In the 60 °C and 65 °C systems, cellular processes and the utilization of organic compounds exhibited lower activity compared to the 55 °C system, resulting in reduced methane production. Pyruvate metabolism and glycine metabolism were strongest at 70 °C, which could easily lead to acid accumulation and ammonia inhibition. The comprehension of this concept will establish a foundation for mitigating detrimental factors during the implementation process of Coalbed Gas Bioengineering under elevated temperatures.