Recent progress in improving the yield of microbially enhanced coalbed methane production

Microbially enhanced coalbed methane (MECBM) production has drawn significant interest worldwide in recent years since the direct combustion of fossil energy sources including oil and coal, would cause global environmental pollution and have detrimental effects on human health. MECBM shows great potential in producing biomethane and thus reducing fossil fuel related pollution. Although much progress has been achieved in understanding the mechanism of how coal is converted into biomethane, studies have shown that the biodegradation efficiency is still low. The present review mainly focuses on discussing recent advances in enhancing the biomethane yield and affecting key factors. Strategies aimed at improving coal solubility or coal bioavailability, stimulating bacterial growth, changing bacterial communities, and altering metabolic pathways or activity of functional genes of microbacteria exert a significantly positive effect on the yield of biomethane production. Coal rank, coal maceral, coal structure, microbial community, culture condition and culture nutrient are key factors that determine the coal degradation efficiency. Expanded investigations on determining key microorganisms that play decisive roles in the conversion of coal to biomethane and what components of coal are consumed by these bacteria will help to clarify the mechanism underlying the MECBM and provide guidance for future in-situ biostimulation of coalbed-methane production from coal seam.