Characteristics of microbial communities in water from CBM wells and biogas production potential in eastern Yunnan and western Guizhou, China

The study of microbial communities in the produced water of coalbed methane (CBM) wells is an important aspect of microbial-enhanced methane production. Water produced from 15 CBM wells in four synclines in eastern Yunnan and western Guizhou was collected. Through the use of 16S ribosomal RNA (16S rRNA) amplicon sequencing and realtime fluorescence quantitative polymerase chain reaction (PCR), the characteristics of bacterial and archaeal communities before and after enrichment culture were studied. The methanogenic pathways of secondary biogas were discussed, and potential microbial-enhanced methane production was preliminarily evaluated. The results showed that the bacterial DNA content in uncultured produced water was low, so it is difficult to detect. After enrichment, the dominant bacteria phyla were Proteobacteria, Bacteroidetes, and Firmicutes. A total of seven phyla were detected in the uncultured produced water, and the dominant archaeal phylum was Euyarchaeota. Methanogens were the main component of archaea. The dominant archaeal genera were Methanobacterium, Methanoculleus and Methanobrevibacter. The community structure of the archaea changed noticeably after four days of enrichment culture. The relative abundance of Euryarchaeota increased to 99% in most samples after enrichment culture. It was found that there was a transition from Methanoregula to Methanobacterium within genera. The relative abundance of Methanobacterium increased, which can produce hydrogenotrophic methane. Combined with the isotopic composition of the produced water and gas, it is considered that the CBM in the Tucheng and Enhong synlines consists of a mixture of thermogenic gas and biogas. The proportion of secondary biogas in the Tucheng and Enhong synlines are estimated to range from 10.89% to 49.62%. There are mainly hydrogentrophic methanogens in the study area, and CO 2 reduction is the main way of microbial gas production. After enrichment culture of produced water in the study area, the hydrogenotrophic methanogens were enriched. These two areas have strong potential for microbial-enhanced methane production.