Oxidation of flumequine in aqueous solution by UV-activated peroxymonosulfate: Kinetics, water matrix effects, degradation products and reaction pathways

Abstract

The degradation of flumequine (FLU) in aqueous solution by ultraviolet (UV)-activated peroxymonosulfate (PMS) was investigated in this work. Under the conditions of [PMS]0:[FLU]0 = 1:1, T = 25 ± 2 °C, pH = 7.0 ± 0.1, nearly complete removal of FLU was achieved after 60 min. The effects of various operating parameters, including oxidant doses, pH, the presence of typical ions (NH4+、Mg2+、Fe3+、Cl−、NO3−、HCO3−) and humic acid were evaluated. It was found that the pseudo-first-order rate constants of FLU degradation increased with increasing PMS dosage and decreasing solution pH. The presence of Mg2+ could accelerate FLU removal, while Fe3+, HCO3−, NO3− and HA inhibited the reaction. Moreover, the degradation of FLU in different water matrices were also explored, and the removal followed the order of Tap water > Ultrapure water > River water > Secondary clarifier effluent. According to the control and radical quenching experiment results, direct photolysis and reactive radicals (SO4- and HO) contributed mainly to FLU degradation in the UV/PMS system. Initial FLU molecule underwent reactions such as hydroxylation, hydroxyl substitution, demethylation, decarboxylation/decarbonylation and ring opening, leading to the formation of nineteen oxidation products. The effective degradation by UV/PMS suggests a feasible technology for treating FLU in waters and wastewaters.