A Fenton-like degradation mechanism for 1,4-dioxane using zero-valent iron (Fe0) and UV light

In this study, the degradation mechanism of 1,4-dioxane using zero-valent iron (Fe0) in the presence of UV light was investigated kinetically. The degradation of 1,4-dioxane in Fe0-only, photolysis, and combined Fe0 and UV reactions followed the kinetics of a pseudo-first-order model. The degradation rate constant (19 × 10−4 min−1) in the combined reaction with UV-C (4.2 mW cm−2) and Fe0 (5 mg L−1) was significantly enhanced compared to Fe0-only (4.8 × 10−4 min−1) and photolytic reactions (2.25 × 10−4 min−1), respectively. The removal efficiency of 1,4-dioxane in combined reaction with Fe0 and UV within 4 h was enhanced by increasing UV intensity at UV-C region (34% at 4.2 mW cm−2 and 89% at 16.9 mW cm−2) comparing with the removal in the combined reaction with Fe0 and UV-A (29% at 2.1 mW cm−2, and 33% at 12.6 mW cm−2). It indicates that 1,4-dioxane was degraded mostly by OH radicals in the combined reaction. The degradation patterns in both Fe0-only and combined reactions were well fitted to the Langmuir–Hinshelwood model, implying that adsorption as well as the chemical reaction occurred. The transformation of Fe0 to Fe2+ and Fe3+ was observed in the Fe0-only and combined reactions, and the transformation rate of Fe0 was improved by UV irradiation. Furthermore, the reduction of Fe3+ was identified in the combined reaction, and the reduction rate was enhanced by an increase of UV energy. Our study demonstrated that the enhancement of 1,4-dioxane removal rate occurred via an increased supply of OH radicals from the Fenton-like reaction induced by the photolysis of Fe0 and H2O, and with producing less sludge.