Characterization of gas sorption and pore structure alterations of sludge bio-seeding coals: an experimental study

This study examines the impact of sludge-based bio-treatment on gas sorption and pore structure modification in subbituminous and lignite coals, aiming to enhance methane-rich biogas production from coal waste. We previously reported the promising results for biogas production from batch reactors using coal as the primary feedstock and sludge as the bio-seeds. In this study, methane and CO₂ gas sorption experiments, along with pore structure characterization, were performed to quantify the changes in gas sorption capacity induced by bio-reaction and modifications to the pore structure. The results reveal significant capacity increases post-bio-treatment, with CH₄ adsorption improving by 40 % for subbituminous coal and 42 % for lignite, and CO₂ adsorption increasing by 53 % and 24 %, respectively. The pore structure characterization confirmed enhanced pore volume and surface area, suggesting active microbial-induced modifications, primarily on macropore surfaces. These changes contribute to improved gas sorption and present promising implications for bio-enhanced coalbed methane recovery and CO₂ sequestration. This study affirmatively confirmed that bio-reaction induced microbial activities actively modified the pore structure. Future investigations will be needed to quantify the localized aqueous-gas equilibrium for optimizing sludge bio-seeding coal conversion.