First investigation of microbial diversity and biogenic methane potential in coal mines located in the Red River Basin, Vietnam

Abstract The generation of biogenic methane from coal mines is considered a sustainable approach for enhancing the recovery of natural gas from coalbeds. This study aims to provide the first quantitative data about the characteristics of coal samples, microbial community, and biogenic methane potential in coal mines located in the Red River Basin (RRB), Vietnam. Coal samples from the RRB were characterized and classified into Lignite B and Subbituminous A. Formation water (FW) and coal samples from the investigated boreholes were also analyzed and characterized for microbial communities. Bacterial communities were found to be more dominant (65.8%) than archaea (34.2%) in the FW sample. Four bacterial phyla, including Proteobacteria, Firmicute, Actinobacteria, and Bacteroidetes, were found in the FW sample, in which Proteobacteria were the most abundant phylum, accounting for 56% of total identified bacteria. In the Proteobacteria phylum, only Alphaproteobacteria, Deltaproteobacteria, and Gammaproteobacteria were found in the FW sample; and Gammaproteobacteria were the most abundant class (50.5%). At the genus level, more than 30 microbial genera were detected in the FW sample with the relative abundance >0.1%, in which Shewanella was the most abundant genus, followed by uncultured Rhodobacteraceae, Paracoccus, and Pseudomonas. The microbial population in the coal sample was less diverse than that in the FW sample. The final methane yields after 21 days of incubation with coal samples varied from 2.51 to 5.21 mL of methane per gram coal, exhibiting the great potential for the biotransformation of coal to methane. The results of this study have shown that the presence of indigenous microbial consortia along with available substrates can play an important role in the generation of biogenic methane in coal mines.