Nitrogen amendment enhances the biological methanogenic potential of bituminous coal

Abstract

Improving the bioavailability of coals is an effective way to increase the production of secondary biogenic coalbed methane (CBM); however, information on the influence of different elements on the biological methane yield is lacking. In this study, the effect of high nitrogen amendment on biological methane yield was analyzed by indoor anaerobic culture experiments with two samples from different coal seams in a mining area. The results showed that the methanogenic rate increased by 1.89–3.43 times after 40 days under the high nitrogen amendment. The high nitrogen amendment changed the microbial community structure and increased 40.78% of the metabolites in the coal samples, 62 of which were related to methane metabolism, degradation of aromatic compounds, fatty acid degradation, polycyclic aromatic hydrocarbon degradation, and degradation of other benzene series. Metagenomic analysis showed that high nitrogen amendment also caused significant changes in functional gene composition and increased the abundance of functional genes related to methane metabolism, β-oxidation and the degradation of toluene and phenol. In addition, the high nitrogen amendment increased the relative abundance of methanogenic Methanosarcina and Methanoculleus and some bacterial taxa belonging to orders Clostridiales and Thermoanaerobacterales. Among them, a total of 17 metagenome assembled genomes (MAGs) were reconstructed, most of which can produce hydrogen and have the ability to degrade aromatic compounds into acetate. In summary, this study indicated the importance of nitrogen as a single element in biological methanogenesis that helps to stimulate biological methane yield for the exploration and development of CBM.