Mitigating perfluorooctanoic acid inhibition in electrochemically-assisted spiral upflow anaerobic membrane reactor for wastewater treatment: EPS interaction-desorption dynamics and metabolic pathway reconstruction

The widespread occurrence of perfluorooctanoic acid (PFOA) in industrial wastewater poses a major challenge to anaerobic treatment systems due to its chemical stability and persistence. Here, an electrochemical spiral upflow anaerobic membrane reactor (EC-SU-AnMBR) was developed by integrating a Ru-Ir/Ti-mesh-wrapped hollow-fiber membrane anode and a spiral Ti-mesh cathode to facilitate PFOA desorption and detoxification. PFOA readily accumulated in tightly bound extracellular polymeric substances (EPS) under open-circuit mode via hydrophobic interactions and electrostatic adsorption, disrupting anaerobic granular sludge (AnGS) structure and impairing microbial functionality. Electrochemical regulation (closed-circuit) effectively alleviated PFOA inhibition, achieving COD removal of 80.7 % (vs. 66.7 %) and a 1.5-fold higher CH₄ recovery (227.7 vs. 140.8 mL/g COD/d). Electric field-migration and bioanode-membrane interception/oxidation together weakened PFOA-AnGS binding capability by altering EPS structural stability and interaction-desorption dynamics, decreasing PFOA retention rate in the bioreactor from initial 60.4 % to 2.1 % (p < 0.01) and reinforcing sludge regranulation. Further analysis demonstrated that the bioelectrocatalysis upregulated the relative abundance of functional genes involved in glucose metabolism (pfk, por, and ackA) and methanogenesis (fwd, mtr, and mcr) by selectively enriching hydrolytic/acidogenic bacteria and syntrophic-methanogenic consortia (Smithellaceae, Kosmotogaceae, and Methanotrichaceae) at both bioelectrodes. This study proposes a promising EC-SU-AnMBR system for the sustainable treatment of PFOA-contaminated wastewater and elucidates the metagenome-informed metabolic adaptation mechanisms under PFOA stress.