BioProject

The hydrolysis efficiency of coal has long been regarded as an important factor restricting the production of biomethane. More...

The hydrolysis efficiency of coal has long been regarded as an important factor restricting the production of biomethane. Supercritical carbon dioxide (Sc-CO2) has received extensive attention due to its unique extraction ability. In order to investigate the effect of Sc-CO2 pretreatment on biomethane, in this study, coal samples of four different coal ranks were selected for the combined experiment of supercritical CO2 extraction and anaerobic digestion (Sc-CO2-AD). Methanogenic efficiency, coal-derived elements, key intermediate liquid phase products, and functional genes in microbial community structure and key metabolic pathways were assessed in Sc-CO2-AD and AD systems. The results show that the promotion effect of Sc-CO2 on coal-based biomethane is positively correlated with the degree of coal metamorphism. With the increase in coal rank, the increase of Sc-CO2 to coal biomethanation was 19.21%, 58.80%, 69.92%, and 102%, respectively. Sc-CO2 extraction can significantly shorten the stagnation time of methane production of medium and high-rank coal. After Sc-CO2 extraction, the stagnation time of methane production by anaerobic fermentation of four coal samples was shortened by 5.97%, 27.5%, 22.38%, and 32.87%, respectively. Furthermore, in the hydrolysis stage of anaerobic digestion, the content of tryptophan, fulvic acid, and humic acid in the fermentation broth increased, and the content of dissolved organic matter (DOM), and the abundance of hydrocarbons and esters available for microbial consumption increased. In addition, Sc-CO2 is more likely to act on the phenols, alcohols, and ethers in the coal molecules, making them fall off and become the metabolic substrates of microorganisms. The abundance of key enzymes involved in biomethane synthesis increased by 1~4 times, and the microbial community structure tended to be stable. Sc-CO2 extraction makes up for the deficiency of microbial degradation of coal, increases the hydrolysis efficiency and bioavailability of coal in the AD system, and promotes the production of biomethane. This study provides an experimental basis for improving coalbed methane recovery. Less...