Biochar-microorganisms hybrid enhanced anaerobic digestion: Innovative insight considering electron transfer potential and functional network of microorganisms

Immobilizing microorganisms on biochar is potential method to regulate the electron transfer capacity. This study developed biochar-microorganism hybrids via pre-coupling for anaerobic digestion (AD) of high-load organic wastewater. Compared with uncoupled groups, the methane yield of pre-coupled groups increased by 26.4 %-36.9 %, the lag phase shortened from 4.45-5.62 days to 0.85–1.06 days, and soluble chemical oxygen demand removal efficiency increased from 60.8 %-63.8 % to 92.4 %-96.4 %. Microscopic analysis showed that pre-coupling enhanced microbial activity and abundance, reduced the bacteria-archaea spatial distance, and promoted direct interspecies electron transfer. Synergistic microbes (Syntrophobacter and Syntrophomonas) were enriched, potentially establishing syntrophic relationships with methanogens to promote organic degradation. Functional prediction indicated the potential abundance of metabolic modules including M00009, M00173, M00144, M00620, and M00374 increased. These findings provided microscopic explanations for the enhanced AD performance. The developed biochar-microorganism hybrid demonstrated the potential to reduce hydraulic retention time and improve AD efficiency, offering valuable guidance for practical applications.