Experimental study on the mechanism of biological hydrogen sulfide generation from organic sulfur-rich coal.

Abstract

Whether of primary or secondary origin, the presence of hydrogen sulfide (H₂S) in coalbed methane (CBM) is commonly attributed to sulfate reduction facilitated by sulfate-reducing bacteria (SRB). However, the sulfate content in high-sulfur coal is exceptionally low, insufficient to function as a substrate for sulfate-reducing bacteria (SRB). In this study, an anaerobic digestion experiment was conducted with high-organic-sulfur coal collected from the Late Permian Longtan Formation in Guangxi Province as both the carbon and sulfur sources. The formation mechanism of H₂S is revealed from the evolution rules of gas components, liquid organic matter, and microbial communities during the anaerobic digestion process. The findings indicate three distinct mechanisms contributing to the biological formation of H₂S in coal seams: firstly, the degradation of readily degradable organic sulfur in coal by microorganisms possessing denitrification capabilities, primarily attributed to the activity of the bacteria Wolinella; secondly, The symbiotic system between SRB and Pseudomonas and denitrifying bacteria（Thiobacillus） to metabolize SO₄^2- and produce H₂S; thirdly, Methylotrophic methanogens employ the methyl groups of organic sulfides to produce CH₄ and H₂S simultaneously. Therefore, biological H₂S can be generated under the presence of a sulfur source, appropriate temperature, and conducive environmental conditions. This comprehension will contribute valuable insights to the discourse on the generation and enrichment patterns of H₂S in natural coalbed methane. Additionally, it can offer practical avenues for the prevention and control of H₂S through technological approaches.