Sustainable Electro-Fenton Antifouling Strategy Simultaneously Improves Nitrogen-Removal Efficiency of Anammox in Membrane Bioreactors.

Abstract

Membrane bioreactors (MBRs) are promising for wastewater treatment, especially for anaerobic ammonia oxidation (anammox), but membrane fouling remains a challenge. Current antifouling strategies often fail to improve treatment performance, necessitating dual-functional solutions. Here, we integrated a simple electro-Fenton system into an anammox MBR to concurrently achieve sustainable fouling mitigation and enhanced nitrogen removal. At 0.05 mA/cm², the system demonstrated: (1) exceptional hydroxyl radical (•OH) generation for foulant degradation and bacterial inactivation on membranes, and (2) highly selective electrocatalytic nitrate (NO₃^-) reduction to nitrite (NO₂^-, >90% selectivity) with minimal ammonium production. Implemented in an anammox MBR through cathodic iron mesh integration on the membrane module, it achieved remarkable performance over 151 days of operation: 84.1% longer fouling cycles, 93.9% nitrogen-removal efficiency, 19.4% energy savings, and 22.5% lower antifouling costs compared to the control. Mechanistic analysis revealed that the system's dual benefits stem from synergistic •OH-mediated fouling control and enhanced nitrogen removal through selective NO₃^--to-NO₂^- conversion coupled with NO₂^- recycling in the anammox process, boosting treatment efficiency by 9.1%. This work presents a groundbreaking and sustainable electro-Fenton approach that simultaneously addresses membrane fouling and enhances nitrogen removal, advancing energy-efficient anammox processes in mainstream wastewater treatment while inspiring multifunctional MBR antifouling strategies.