Microbial communities from the Huaibei Coalfield alter the physicochemical properties of coal in methanogenic bioconversion

The relationships among the production of methane, the physicochemical properties of coal, and the composition of microbial communities are poorly understood in methanogenic bioconversion. In this study, we investigated the changes in microbial communities during the methanogenic process of coal based on culture dependent methods as well as the physicochemical properties of the coal samples. The process of methane production could be clearly divided into four phases (lag, log, peak, and stationary phases). The initial bacterial communities in the cultivation were predominantly Bacteroidales, Actionmycetales, and Bacillales; the archaeal community was present at values below the detection limit. However, distinct changes in bacterial communities were noted at the log phase of methane production. Bacteroides species accounted for > 80% of the total bacterial community, and acetotrophic Methanosarcina was the only archaeal community. Interestingly, Clostridiales increased considerably during the first 2 weeks, but decreased thereafter, indicating that Clostridiales may play a unique role during the initial stage of methanogenic coal bioconversion. Furthermore, the final coal sample showed decreased C and O contents and increased N and H contents. Volatile and ash contents as well as microporosity were also higher than those in the initial state. These results suggested that methanogenic coal bioconversion was a complex biochemical process and that the physicochemical properties of coal were altered in methanogenic bioconversion. Moreover, these findings may facilitate the development of strategies to improve the production of biomethane utilizing coal.