Degradation of selected emerging contaminants by UV-activated persulfate: Kinetics and influence of matrix constituents

The degradation of five selected emerging contaminants (ECs) including 1H-benzotriazole (BZ), N,N-diethyl-m-toluamide or DEET (DT), chlorophene (CP), 3-methylindole (ML), and nortriptyline hydrochloride (NH) in aqueous solutions by UV-activated persulfate (UV/PS) has been investigated. Selected ECs were not effectively degraded by direct UV photolysis or dark PS. However, their photodegradation efficiency significantly increased with addition of PS due to the generation of SO4− and HO. Second order rate constants for the reaction between SO4− and each EC were determined by competition kinetics, being the values at pH 7 2.0 × 1010, 1.2 × 1010, 1.8 × 109, 1.1 × 109 and 9.5 × 108 M−1 s−1 for NH, ML, CP, BZ and DT, respectively. While the dose of PS exerted a positive influence on the degradation of ECs, the highest degradation rate was observed at near neutral pH. With respect to the influence of background water matrix constituents, bicarbonate showed an inhibition effect on the removal of DT, BZ and NH and promoted the degradation of CP and especially of ML, which can be explained by their high reaction rate with carbonate radicals. The presence of humic acids inhibited the degradation of selected ECs, probably due to light screening and radical scavenging. Both radical species SO4− and HO exert an important role on the oxidation of the ECs investigated by the UV/PS system, being the contribution of SO4− predominant for those compounds that present high reactivity with this radical. Although the presence of inorganic and organic matter in real water matrices decreased the degradation rate of selected ECs, UV/PS process is an efficient option for their removal from contaminated waters.