Enhancing Biomethane Yield and Metabolic Pathways in Kitchen Waste Anaerobic Digestion Through Microbial Electrolysis Cell Integration

This study developed a system (MEC-AD) by integrating a single-chamber microbial electrolysis cell (MEC) with anaerobic digestion (AD), aiming to enhance the conversion efficiency of kitchen waste (KW) into biomethane and optimize metabolic pathways. The performance and microbial metabolic mechanisms of MEC-AD were investigated and compared with those of conventional AD, through inoculation with original inoculum (UAD) and electrically domesticated inoculum (EAD), respectively. The results show that the MEC-AD system achieved a CH4 yield of 223.12 mL/g VS, which was 31.27% and 25.24% higher than that of conventional UAD and EAD, respectively. The system also obtained total solid (TS) and volatile solid (VS) conversion rates of 82.32% and 83.39%, respectively. Furthermore, the MEC-AD system enhanced the degradation of soluble chemical oxygen demand (SCOD) and mitigated biogas production stagnation by reducing the accumulation of volatile fatty acids (VFAs) as intermediate products. Microbial metagenomics analysis revealed that the MEC-AD system enhanced microbial diversity and enriched functional genera abundance, facilitating substrate degradation and syntrophic relationships. At the molecular level, the system upregulated the expression of key enzyme-encoding genes, thereby simultaneously strengthening both direct interspecies electron transfer (DIET) and mediated interspecies electron transfer (MIET) pathways for methanogenesis. These findings demonstrate that MEC-AD significantly improves methane production through multi-pathway synergies, representing an innovative solution for efficient KW-to-biomethane conversion.