Internal driving mechanism of microbial community and metabolic pathway for psychrophilic anaerobic digestion by microbial electrolysis cell

The system that microbial electrolysis cell coupled anaerobic digestion (termed MEC-AD) with metal organic framework-modified cathode was operated under different voltage levels (0-1.2 V) at 20 degrees C. The maximum methane yield increased to 0.23 +/- 0.01 LCH4 g(-1)COD at 0.9 V, with 28% improvement compared to 0 V (0.18 +/- 0.01 LCH4 g(-1)COD). Moreover, total volatile fatty acid and propionate accumulation decreased by 32% and 15% at 0.9 V, indicating the system has potential to alleviate acidity suppression. Acidogens and electroactive microorganisms was clearly enriched with increasing applied voltage. Specifically, the abundance of Smithella increased, which could degrade propionate to acetate. Methanosaeta was dominant, accounting for ca. 40.1%similar to 55.1% of the archaea community at 0.3-1.2 V. Furthermore, the system reinforced psychrophilic methanogenesis by activating important enzymes involved in related metabolism pathways. Overall, this study provides perspective on the future practical application for the regulation of psychrophilic AD in electrochemically integrated bioreactors.

Automated summary

The MEC-AD system with metal organic framework-modified cathode was operated at different voltage levels (0-1.2 V) and 20 degrees C. Increasing the applied voltage to 0.9 V resulted in a 28% improvement in methane yield and a decrease in volatile fatty acid and propionate accumulation. Acidogens and electroactive microorganisms were enriched with increasing voltage, particularly the abundance of Smithella and Methanosaeta. The system also enhanced psychrophilic methanogenesis and related metabolism pathways. This study provides insights into the practical application of electrochemically integrated bioreactors for psychrophilic AD regulation.