Methane Promotion of Waste Sludge Anaerobic Digestion: Effect of Typical Metal Meshes on Community Evolution and Electron Transfer

Anaerobic digestion of waste activated sludge (WAS) to produce methane is a promising pathway for biomass energy recovery. However, a slow organic biodegradation rate and weak microbial cooperation between fermentation bacteria and methanogens lead to low methane production from WAS. Considering the reuse of conductive materials for the regulation of microbial communities, this study chose three kinds of high-mesh metal materials (nickel, copper, and stainless steel) to promote the anaerobic digestion process. All three kinds of metal mesh could effectively increase methane production, and the highest methane production was increased by 61%, reaching 77.52 mL gVSS−1. The poor biocompatibility of the stainless steel mesh was the least effective in promoting methane production compared to the biocompatible copper mesh and nickel mesh. The microbiological analysis found that the metal mesh with good biocompatibility can effectively induce and promote the enrichment of key microorganisms in the process of synergistic methane production, and the direct electron transfer process (DIET) of microorganisms on the metal surface contributes to the further improvement of the methane production efficiency. Therefore, the application of metal conductive materials in sludge anaerobic fermentation is feasible to achieve the retention of syntrophic bacteria and methanogens in the system.