Electrochemically Sustained Iron-Activated Sulfite Process for Rapid Contaminant Degradation and Intrinsic Bromate Suppression at Near-Neutral pH

Remediating persistent organic contaminants in near-neutral aquatic environments remains a challenge for conventional homogeneous Fe(II,III)-mediated sulfate radical-based advanced oxidation processes (SR-AOPs), which typically require acidic pH or generate hazardous byproducts. This study introduces an electro-activated sulfite process (Fe-EC/S(IV)) employing sacrificial iron electrodes to overcome these limitations. Continuous anodic Fe 2+ release sustains active FeHSO 3 + complexes, enabling efficient S(IV) activation at pH 4−6. Mechanistic analysis identifies SO 4 •− as the dominant oxidant, formed via inner-sphere electron transfer within FeHSO 3 + complexes, followed by aerobic chain reactions (SO 3 •− → SO 5 •− → SO 4 •− ). The system achieves rapid oxcarbazepine degradation (pseudo-first-order constant, k obs = 1.15   min −1 ), representing a 57.5-fold kinetic enhancement over standalone Fe-EC at pH 6. Notably, the process intrinsically suppresses the carcinogenic BrO 3 − formation (<1   μg   L −1 ) through the S(IV)-mediated reductive quenching of bromine intermediates, substantially outperforming Fe-EC/peroxomonosulfate systems (11.3   μg   L −1 BrO 3 − ). Demonstrating >70% removal in natural waters without pH adjustment or added electrolytes, and broad-spectrum efficacy (77.9–91.7%) across contaminant classes, this electrochemically sustained process offers a novel AOP paradigm integrating the radical-based oxidation with inherent byproduct control for complex water remediation scenarios.