Substrate Composition Effects on the Microbial Enhancement of Biogenic Methane Production from Coal

The conversion of coal to biomethane is an environmentally friendly and sustainable method of coal utilization, and algae is a nutrient additive that enhances the economic sustainability of coal-to-biomethane production. The key regulatory factors and interaction mechanism of methane production were studied by carrying out anaerobic fermentation experiments on coal and microorganisms. Spearman correlation analysis, multiple linear regression, random forest and principal component analysis (PCA) were used to evaluate the effects of 14 coal-quality and microorganism composition parameters on methane production. The results showed that the hemicellulose content of microorganisms was significantly positively correlated with methane production, while total sugar and total fat significantly reduced the gas production. The protein content of microorganisms in a reasonable range could promote methane production. Among the coal-quality parameters, the C/H ratio (β = 0.43) and dry volatile matter (β = 0.17) had a weak positive contribution to methane production, while a high carbonization degree (C% > 80%; vitrinite reflectance > 1.2%) significantly inhibited the fermentation activity. The higher the maturity of the coal, the lower the methane production. The optimal methanogenic performance was concentrated in the combination of a low degree of coalification in coal (PC1 < −1.5) and high hemicellulose in microorganisms (PC2 > 1.8). In this study, a process optimization strategy was put forward, and the combination of low-rank coal with vitrinite reflectance < 0.5%, volatile matter > 35%, microorganisms with hemicellulose > 4.5%, and total sugar < 20% was optimized in an anaerobic fermentation experiment of coal and microorganisms. The results provide theoretical support for the directional control of anaerobic digestion of coal enhanced by microorganisms.