Achieving clean coal utilization via microbially enhanced coalbed methane technology: Progress, critical assessment and future perspectives

Abstract As a predominant global fossil fuel, the conventional utilization of coal is characterized by low energy conversion efficiency, intensive carbon emissions, and significant environmental pollution. Microbially Enhanced Coalbed Methane (MECBM) technology, which leverages microbial processes to transform coal into clean biomethane, offers a promising paradigm for the sustainable and green utilization of coal resources. This paper provides a comprehensive review of the critical factors influencing methane yields, encompassing coal matrix properties and microbial environmental parameters. Building on this foundation, we categorize and synthesize the principal technological pathways of MECBM: coal pretreatment (physical, chemical, and biological), nutrient stimulation, and microbial enhancement. The underlying mechanisms, enhancement efficacy, and inherent limitations of these technologies are rigorously analyzed. Notably, a carbon emission accounting approach based on IPCC guidelines is applied to quantify the carbon reduction contributions of various technological routes. Under a direct carbon displacement accounting framework, various MECBM technologies are evaluated, among which nutrient stimulation exhibited the highest theoretical mitigation efficiency (ranging from 0.75% to 6%, excluding indirect emissions from reagent production, energy consumption, and microbial cultivation). Furthermore, lignite is identified as an experimental substrate with substantial potential for carbon footprint reduction. However, the overall carbon reduction contribution remains well below theoretical limits, primarily because of low methane conversion rates. Finally, this review summarizes the prevailing scientific and engineering challenges facing MECBM and proposes future research trajectories, including dynamic adaptive studies, integrated technological strategies, and life cycle carbon reduction assessments.