Migration of heavy metals and microbial metabolic regulation mechanisms in the co-fermentation of coal slime and sawdust

Heavy metals (HMs) significantly affect the anaerobic fermentation of coal slime (CS), while sawdust serves as a promising substrate for methane bioconversion and an effective adsorbent for HMs. To explore the migration of HMs and improve the conversion efficiency of CS and sawdust to biomethane, experiments were conducted on the co-fermentation of CS and sawdust with different mass ratios. FT-IR, ICP-MS, SEM-EDS, and metagenomic sequencing were employed to elucidate the regulation mechanism of microorganisms after adding sawdust in altering the toxicological environment. The results revealed that the optimum mass ratio of CS to sawdust was 2:1. Oxygen-containing functional groups in CS were removed, and the fatty structure was degraded. Addition of sawdust promoted the further degradation of CS and migration of various HMs. Metal elements such as Fe, Mg, Co, and Cd had also been detected on its surface. <i>Bacillota</i> (39.05%) was significantly enriched, which effectively improved the microbial community structure. The abundance of species with metal detoxification functions increased. The types and abundance of transporters related to toxic metal ions increased in families such as ATP-binding Cassette Superfamily (ABC) and Resistance-Nodulation-Cell Division Superfamily (RND), which would further aid in cellular homeostasis. Moreover, the addition of sawdust promoted the expression of metal resistance genes (MRGs). Multi-MRGs were primarily linked to Cu, As, and Zn, with an increased abundance of bacterial species contributing to key MRGs such as <i>copA</i>, <i>ziaA</i>, and <i>actP</i>. These findings offer valuable insights that support the clean and efficient utilization of CS and sawdust.