High-efficiency degradation of nanofiltration concentrates using an iron-modified self-breathing electrode in electro-Fenton systems

Abstract

The homogeneous electro-Fenton(EF) technique is widely recognized in water treatment for its efficient generation of hydroxyl radicals (·OH). However, its drawbacks, such as iron sludge formation and strict pH requirements, constrain its practical applications. To overcome these limitations, this study developed an iron-modified self-breathing electrode (Fe₃O₄/MGF_if) through impregnation and filtration, characterized it, and applied it to construct a heterogeneous EF system for treating nanofiltration concentrates (NFCs). Under optimal conditions, the Fe₃O₄/MGF_if electrode achieved COD and TOC removal efficiencies of 74.2 ± 1.8 % and 81.6 ± 1.7 %, respectively, within 2 h. Moreover, the modified electrode demonstrated degradation efficiency in the heterogeneous EF system comparable to that in the homogeneous EF system, while eliminating iron sludge formation and expanding the applicable pH range. Radical scavenging, quenching experiments and electron paramagnetic resonance (EPR) technique demonstrated that the electrode generated substantial ·OH and minor amounts of superoxide radicals (·O₂⁻) during NFCs degradation. The ultraviolet fluorescence spectra and three-dimensional fluorescence spectra indicated that reactive radicals efficiently degraded humic substances in NFCs, reduced aromatization, and significantly enhanced biochemical properties. This study resolves the challenges of iron sludge formation and pH constraints in homogeneous EF-based NFCs treatment and proposes a novel pathway capable of efficiently degrading recalcitrant organic pollutants by self-breathing.