Biogas upgrading via microbial electrolysis cell-integrated anaerobic digestion: A critical review of stabilization strategies towards practical application.

Biogas produced by conventional anaerobic digestion (AD) requires upgrading due to its elevated CO2 content. The microbial electrolysis cell coupled with anaerobic digestion (MEC-AD) facilitates in-situ biogas upgrading by enhancing microbial metabolism through bioelectrochemical processes. However, the performance of MEC-AD in treating real organic wastes is often constrained by challenges such as complex electron flow competition, mass transfer limitations, and instability within the microbial ecosystem. This review begins by elucidating the mechanisms through which MEC-AD achieves CO2 reduction and methane enrichment, primarily via hydrogenotrophic methanogenesis and direct electromethanogenesis. It then critically examines the performance gaps and underlying causes of these limitations when transitioning from ideal substrates to real waste streams. To address these challenges, the paper systematically evaluates three synergistic enhancement strategies: optimizing electrode systems to improve electron transfer, manipulating microbial syntrophic networks to enhance electron utilization, and precisely controlling operational parameters to direct electron flow. Finally, future research directions are proposed, emphasizing the necessity for cross-scale precise regulation of electron transfer, intelligent reactor design, and comprehensive assessments of energy efficiency to facilitate the engineering application and carbon reduction potential of MEC-AD technology.