Simulation and comparative study on the oxidation kinetics of atrazine by UV/H2O2, UV/HSO5- and UV/S2O82-

This study comparatively investigated atrazine (ATZ) degradation by irradiation at the wavelength of 254 nm in the presence of peroxides including hydrogen peroxide (H2O2), peroxymonosulfate (HSC5-), and persulfate (S2O82-) at various initial ATE concentrations and oxidant dosages. The effects of water matrix, such as carbonate/bicarbonate (HCO3-/CO32-), chloride ions (Cl-), and natural organic matter (NOM), were evaluated on these three advanced oxidation processes. A simple steady-state kinetic model was developed based on the initial rates of ATE destruction, which could well describe the apparent pseudo-first-order rate constants (k(app), s(-1)) of ATE degradation in these three processes. The specific roles of reactive species (i.e., HO center dot, SO4-center dot, CO3-center dot, and Cl-2(-center dot)) under various experimental conditions were quantitatively evaluated based on their steady-state concentrations obtained from this model. Modeling results showed that the steady-state concentrations of HO center dot and SO4-center dot decreased with the increase of CO32-/HCO3- concentration, and the relative contribution of HO center dot to ATE degradation significantly decreased in UV/H2O2 and UV/HSO5- systems. On the other hand, the scavenging effect of HCO3-/CO3- on the relative contribution of SO4-center dot to NE degradation was lower than that on HO center dot. The presence of Cl- (0.5 -10 mM) significantly scavenged SO4-center dot but had slightly scavenging effect on HO center dot at the present experimental pH, resulting in greater decrease of k(app) in the UV/S2O82- than UV/H2O2 and UV/HSO5- systems. Higher levels of Cl-2(-center dot) were generated in the UV/S2O82- than those in the UV/H2O2 and UV/HSO5- systems at the same Cl- concentrations. NOM significantly decreased kapp due to its effects of competitive UV absorption and radical scavenging with the latter one being dominant. These results improve the understanding of the effects of water constituents for ATZ degradation in the UV-based oxidation processes. (C) 2015 Elsevier Ltd. All rights reserved.