Oxidation of benzotriazole and benzothiazole in photochemical processes: Kinetics and formation of transformation products

Abstract

The oxidation of two industrial chemicals abundant in the environment, i.e., benzothiazole (BTH) and 1H-benzotriazole (BTA) was investigated in UV and UV/H2O2-systems using polychromatic mercury lamp. Experiments were performed in Milli-Q™ water solutions of BTH and BTA at pH 5, 7 and 9 and in synthetic wastewater spiked with BTH and BTA pre-treated in membrane bioreactors (MBRs). Results showed that polychromatic UV-radiation is an efficient oxidative agent for BTH and BTA abatement in water and wastewater. In the kinetic study direct photolysis quantum yields at pH 7 were calculated as 0.022 and 0.051 for BTH and BTA, respectively, and the second-order rate constant for the reaction between investigated compounds and hydroxyl radicals (OH) were determined to be (9.5±1.7)·108M−1s−1 and (2.7±0.1)·109M−1s−1, for BTH and BTA at pH 7, respectively. Identification of transformation products performed with liquid chromatography coupled with high resolution tandem mass spectrometry provided information about 6 and 5 transformation products formed during the photodegradation of BTH and BTA, respectively. The Microtox bioassay showed that direct photolysis is efficient to detoxify BTH and BTA in aqueous solutions.