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.