Enhanced biomethanation in anaerobic membrane bioreactor: decarbonization efficiency, carbon mass flow, and microbial dynamics.

Methanation of carbon dioxide (CO₂) is a key process for improving carbon utilization technology. In this study, we investigated a novel approach to biomethanation from hydrogen (H₂) and CO₂ using an anaerobic membrane bioreactor under mesophilic conditions. System performance was evaluated by varying carbon loading rates, with a focus on decarbonization efficiency, carbon mass flow, and microbial dynamics. The results demonstrated stable operation and strong resilience, achieving a decarbonization efficiency higher than 84 % and a methane (CH₄) flow-out rate of 1.1 L/L/d at a carbon loading rate of 1.0 g-C/L/d. Carbon mass balance showed that CH₄ accounted for 43.8-82.4 % of influent carbon. Microbial analysis indicated a clear shift from a diverse consortium to a Methanobacterium-dominant community, with its relative abundance increasing from 4.2 % to 47.8 %. Gene expression analysis revealed upregulation of key methanogenesis genes (fwd, mtr, and mcrA). Our findings provide valuable insight into the development of scalable ex-situ biomethanation systems.