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

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 degrees 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-, No-3(-), 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 center dot(-) and HO center dot) 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. (C) 2019 Elsevier Ltd. All rights reserved.