Simulation study on the biological methanation of CO2 sequestered in coal seams

The technologies for the bioconversion of CO2 to CH4 by microorganisms are clean and safe and have attracted extensive attention in the field of energy conservation and emission reduction in recent years. A series of biological gas production experiments were carried out using bituminous coal D and indigenous bacteria from the Qianqiu coal mine, with the addition of NaHCO3 to simulate CO2 sequestration in coal seams, to explore the feasibility of biomethanation of CO2 sequestered in coal seams. Changes in the characteristics of both the gas and liquid phases during the fermentation process were studied. The results showed that the methane production follows a low-high-low trend with an increase in the bicarbonate concentration. During the fermentation process, the pH and chemical oxygen demand (COD) values of the fermentation solution initially increased and later decreased. In the early stage of the fermentation experiment, the microorganisms mainly degraded the ethers; the alcohols were degraded in the later stage. Identification of the microbial community structure showed that although bicarbonate inhibits the growth of some microorganisms, it increases the hydrolysis capacity of the fermentation process and also enriches the hydrogenotrophic methanogens associated with the bioconversion process of CO2 to CH4. This indicates that the composition of the archaea in the fermentation solution transforms to support the bioconversion of CO2 to CH4. The results show that the CO2 sequestered in the coal seams can be converted into CH4 by indigenous bacteria, which can reduce greenhouse gas emissions and the re-leakage risk of CO2 and also produce clean energy.