Degradation metabolic pathway of low-rank coal using single hydrolytic bacteria

The hydrolysis process is the rate-limiting step of coal anaerobic fermentation, and the selection of highefficiency hydrolysis bacteria determines the hydrolysis of coal efficiency. To optimize the hydrolysis of the coal, five different single hydrolytic bacteria were extracted from long-flame coal for hydrolysis and gas production experiments. The solid-liquid two-phase products after hydrolysis were analyzed by using the Fourier Transform Infrared Spectrometer test (FTIR), three-dimensional Excitation Emission Matrix test (3D-EEM), and Gas Chromatography Mass Spectrometer test (GC-MS). The metabolic differences of the two strains with better degradation effects were analyzed. The results showed that the metabolites in the hydrolysis stage of coal to methane were mainly aromatic compounds and organic acids. The gas production cycle of coal samples without microbial hydrolysis treatment was 27 days, while that with microbial hydrolysis treatment was significantly shortened. The cumulative methane production capacities of the Bacillus polymorpha and Bacillus sphaericus strains were 4.28 mL/g and 3.75 mL/g, respectively. After the coal was degraded by Bacillus polymorpha bacteria, the methane production rate of coal samples was 58.6 %, with the degradation rate constant k was 0.488. Strain Bacillus sphaericus had better transport capacity for amino acids, proteins, and the degradation solution contained more soluble organic matter. The methanogenesis process was dominated by methylamine conversion. The Bacillus polymorpha could degrade aromatic carbon, and its degraded products had the highest content of polymer compounds, organic acids, benzene, and its derivatives. The reaction process could secrete more coenzymes. The methanogenic process mainly involved acetic acid decarboxylation conversion, and its hydrolysis effect was the best. Bacillus polymorpha and Bacillus sphaericus strains screened in this experiment can be used as highly efficiency hydrolytic bacteria to promote anaerobic fermentation to produce methane, which could significantly improve the hydrolysis efficiency. In practical applications, a more suitable on-site hydrolytic bacteria expansion method should be considered, and the feasibility of pure strain application should be fully considered to make it better applied to the bioengineering site of Coalbed methane.