Synergistic methane production via anaerobic co-digestion of coal slime and sawdust: From substrate interactions to microbial functional responses

Anaerobic digestion represents a promising technology for the resource utilization of coal slime (CS). To enhance biomethane conversion efficiency, anaerobic co-digestion experiments of CS and sawdust were conducted. Methane production kinetics were analyzed to assess the promoting effect of co-digestion. Substrate physicochemical transformations were characterized via FTIR and SEM, while metagenomic sequencing coupled with functional annotation using the CAZy and KEGG databases were performed to compare microbial community structure and the expression of key metabolic enzyme genes across different substrate systems. Results showed that adding 10 g sawdust to three types of CS significantly increased cumulative methane yield by 125.44 %, 101.39 %, and 58.00 %, respectively. Methane production lag phases were further shortened, with degradation of lipid structures and hydroxyl groups in CS observed. Microbial communities were optimized, with enrichment of hydrolytically active genera such as Mobilitalea and Sphaerochaeta. Genes encoding hydrolytic enzymes including GHs, GTs, and CBMs, as well as key enzymes involved in cellulose degradation and acetate synthesis, exhibited increased abundance. The relative contribution of acetoclastic methanogenesis was also enhanced. These findings provide theoretical support and practical insight into improving the bioconversion efficiency of CS and sawdust, offering a sustainable pathway for the valorization of solid wastes.