Recent progress on the biological degradation and solubilization of coal

Coal mining and coal combustion for energy generation will continue in the medium term and remain a primary source of pollutants. Its complex structure renders coal a recalcitrant material and relatively few bacteria and fungi can thus degrade this carbonaceous substrate. In this review, we assess research progress on the biological degradation and solubilisation of coal, waste coal, discard and gangue from 2014 to 2024, the period following the publication of our 2013 critical appraisal of this topic. We focus on the continued need for studies on coal biodegradation and bio-solubilization. We explore and, where appropriate, evaluate some of the more important recent advances in coal bio-solubilization research to illustrate progress in this field. Of particular significance are the ever-increasing number of bacterial and fungal biocatalysts identified as possessing coal degrading potential, the role of microbial consortia in this process, the aerobic and anaerobic mechanisms of coal utilisation, and progress in elucidating the underlying molecular and biochemical events involved. Also reviewed are advances in the application of industrial products derived from coal, including biomethane, coal-bed methane, and humic substances, and the use of waste and discard coal-derived humics as technosols for soil restoration and the commercial-scale rehabilitation of coal mining-affected land. It is concluded that an understanding of the mechanisms underpinning coal biodegradation is critical in combating many of the detrimental impacts of mined coal, exposed coal seams and stockpiled coal mine waste and that the outputs from these studies must be incorporated into the development of diversified production technologies and strategies for both socio-economic and ecological gain.