An electrochemical anaerobic dynamic membrane bioreactor for enhanced sludge digestion: Unveiling molecular interactions and microbial mechanisms

This study investigated the effects of stepwise external voltages on an electrochemical anaerobic dynamic membrane bioreactor (EC-AnDMBR) for anaerobic digestion of waste activated sludge. Increasing the applied voltage greatly mitigated membrane fouling, reduced the transmembrane pressure increase rate and enhanced both volatile solids digestion and biogas production. The dynamic membrane structure became looser with fewer biofouling substances, attributed to a 42.6 % increase in the sludge-membrane interaction energy barrier at higher voltages. Electrochemical analysis revealed improved electroactivity of the anaerobic sludge, as evidenced by increased conductivity and reduced internal resistance. The proton-coupled electron transfer (PCET) pathway was promoted, indicated by a significant increase in the hydrogen/deuterium kinetic isotope effect from 616 to 25,990. Molecular simulations of dissolved organic matter (DOM) showed an enrichment of amide and quinone groups, along with stronger hydrogen-bonding and π-cation interactions, which may contribute to the PCET process. Moreover, elevated voltages promoted more deterministic microbial community assembly and reduced upstream microbial immigration. Gene upregulation in organic metabolism, electron/proton transport, and methanogenesis further supported enhanced digestion performance via PCET pathway. These findings offer valuable insights into the molecular mechanisms and microbial ecology of EC-AnDMBR systems, advancing the development of more efficient and sustainable sludge treatment technologies.