Mechanism of Ammonium Chloride Enhanced Microbial Degradation of Coal: A Metagenomic Perspective

Microbial anaerobic degradation of coal matrix to produce methane is an important way to realize green development and clean utilization of coal. However, the extremely high carbon-nitrogen ratio of coal leads to the limitation of microbial metabolic activity. In this study, a comparative experiment was set up between the basic inorganic salt medium (control) and the addition of 1.5 g/L ammonium chloride (treatment). Using metagenomic sequencing technology, the regulation of nitrogen source addition on coal degradation process was deeply analyzed from the two dimensions of species succession and metabolic functional gene abundance. The results showed that the community diversity was significantly improved, and the addition of nitrogen sources broke the nutritional bottleneck, and the Shannon index of the microbial community in the control group was significantly increased to 5.1. PCoA showed that the PC1 interpretation rate of the two groups of community structure was 75.72 %. Species composition analysis showed that the abundance of core degrading bacteria (Clostridium, Bacillus) and methanogens (Methanosarcina, Methanothrix) increased significantly in the treatment group. STAMP difference analysis showed that the Xylene degradation and Naphthalene degradation pathways directly related to coal skeleton degradation in the treatment group were significantly activated. At the same time, the enhancement of oxidative phosphorylation, cofactor biosynthesis and quorum sensing pathway provide enough energy support and enzyme system guarantee for the cleavage of coal macromolecules. This study elucidates the molecular mechanism of nitrogen source enhanced coal biotransformation, which has important reference value for optimizing the production technology of underground coalbed methane project.