Degradation of di-n-butyl phthalate by a homogeneous sono–photo–Fenton process with in situ generated hydrogen peroxide

•The sono–photo–Fenton process was superior to the constituent processes.•The US/Fe2+ process was more efficient in utilizing Fe2+.•Synergistic effect was found when adding Fe2+ to the direct UV254 irradiation.•DBP degradation was found inversely related to initial pH.•DBP degradation was found greatest at an optimal Fe2+ concentration. The merits of a homogeneous sono–photo–Fenton treatment process (US/UV/Fe2+) were investigated using di-n-butyl phthalate (DBP) as the model compound. The process involved ultrasound at 400kHz and UV irradiation at 254nm, and hydrogen peroxide generated in situ from the ultrasonic process was used as the exclusive source. The properties of the constituent processes, that is, the US/Fe2+, US/UV, and UV/Fe2+ processes, were examined and compared. The treatment performance of the US/UV/Fe2+ process was superior to the constituent processes and synergistic mechanisms in the US/UV/Fe2+ process were the result of the promotion of hydroxyl radical generation. For the constituent processes, the US/Fe2+ process was found to be more efficient in utilizing Fe2+ compared to the conventional Fenton reaction. It was also observed that the addition of Fe2+ to the test solution undergoing UV254 irradiation (UV/Fe2+ process) substantially improved DBP degradation, an effect which has been hardly reported previously; the mechanisms responsible for the synergistic effect have been proposed for the first time in this study. For the US/Fe2+, UV/Fe2+ and US/UV/Fe2+ processes, the influence of initial solution pH (2–9) and Fe2+ dosage (0–0.5mM) on DBP treatment performance was examined. DBP degradation was found to be inversely related to pH, and greatest at an optimal Fe2+ concentration, which was 0.1mM for the US/UV/Fe2+ process.