Degradation of atenolol by UV/peroxymonosulfate: Kinetics, effect of operational parameters and mechanism

• DO can influence SO4--based AOPs remarkably.
• HA-induced absorption and indirect photolysis was vital at the early reaction stage.
• Four attacking ways were involved in the degradation mechanisms.

Photoactivation of peroxymonosulfate (PMS) with UV (254 nm) irradiation was used to generate the SO4--based advanced oxidation process, which was adopted to degrade atenolol (ATL) in water. The second-order reaction rate constants of ATL with HO and SO4- were determined, and the effects of operational parameters (dose of PMS, solution pH, HCO3-, humic acids (HA), and N2 bubbling) were evaluated as well. Finally the main transformation intermediates were identified and possible degradation pathways were proposed. The results showed that there was a linear positive correlation between the degradation rate of ATL and specific dose of PMS (1–16 M PMS/M ATL). Increasing solution pH from 3 to 9 promoted elimination of ATL due to the pH-dependent effect of PMS photodecomposition, while further pH increase from 9 to 11 caused slowing down of degradation because of apparent conversion of HO to SO4-. 1–8 mM HCO3- exerted no more than 5.3% inhibition effect on ATL destruction, suggesting HCO3- was a weak inhibitor. Absorption (or complexation) and photosensitized oxidation induced by HA improved ATL degradation during the first minute of degradation process, whereas photon competition and radical scavenging effects became the leading role afterward. Bubbling with nitrogen enhanced the degradation rate due to the stripping of dissolved oxygen. Hydroxylation of aromatic ring, cleavage of ether bond, oxidation of primary and secondary amine moieties, and dimerization were involved in the degradation mechanism of ATL by UV/PMS.