Synergistic disinfection of Escherichia coli by the UVA/Fe(III)/sulfite system via multi-target oxidative damage

UVA-driven iron-mediated sulfite advanced oxidation processes have demonstrated high efficiency in degrading organic pollutants, yet their potential for microbial inactivation remains underexplored. This study systematically investigates the disinfection performance and mechanism of a UVA/Fe(III)/sulfite system using Escherichia coli ( E. coli ) as a model bacterium. The ternary system exhibited synergistic bactericidal activity, achieving complete inactivation of 10 6 CFU/mL E. coli within 45 min at pH 5.6, significantly outperforming individual or binary controls. Radical quenching and electron paramagnetic resonance (EPR) analyses identified sulfate radicals ( SO 4 • − ) , hydroxyl radicals ( • OH ) , superoxide ( O 2 • − ) , and peroxymonosulfate radicals ( SO 5 • − ) as the primary reactive species, generated via a sustained photochemical Fe(II)/Fe(III) redox cycle. Mechanistic investigations revealed a multi-target oxidative cascade: initial disruption of cell envelope integrity and lipid peroxidation facilitated intracellular radical influx, leading to rapid adenosine triphosphate (ATP) depletion, inactivation of antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)), and oxidative deoxyribonucleic acid (DNA) lesions. Disinfection efficiency increased with decreasing pH, and was promoted by elevated dissolved oxygen. While chloride and nitrate exhibited moderate interference, phosphate and humic acid severely inhibited inactivation through Fe(III) precipitation and radical scavenging/light screening, respectively. These findings elucidate the inactivation pathways of the UVA/Fe(III)/sulfite system, establishing a theoretical foundation for its application as a cost-effective, solar-driven water disinfection strategy.