A novel strategy for enhancing electron transfer by adding BC/AQS in the anaerobic digestion of agriculture waste: Focusing on the interaction between quinone/C=O and microbes

Low interspecies electron transfer efficiency among microorganisms is a critical factor limiting anaerobic digestion performance. In this study, conductive and stable biochar (BC) was combined with redox-active anthraquinone-2-sulfonate (AQS) to enhance electron transfer efficiency through their synergistic effects, thereby improving the efficiency of anaerobic digestion. Results showed that cumulative methane production (CMP) reached 176.34 mL/g VS under optimal conditions, including an AQS impregnation concentration of 1 mmol/L, a BC/AQS addition of 5 %, and a total solid (TS) content of 10 %. The addition of BC/AQS enriched Proteiniphilum and Methanobacterium , which shifted the methanogenic pathway from acetoclastic to hydrogenotrophic, significantly improving volatile fatty acid conversion and total organic carbon degradation. Redundancy analysis (RDA) and changes in key enzyme-encoding genes indicated that BC/AQS enhances the synergistic interaction between Proteiniphilum and Methanobacterium through the redox activity of quinone/C=O functional groups, which may play a key role in the formation of direct interspecies electron transfer (DIET). This study provides a promising strategy to enhance microbial electron transfer mechanisms in anaerobic digestion by leveraging the complementary properties of meso-materials, offering new insights into the utilization of agricultural waste for energy production.