Permanganate with a double-edge role in photodegradation of sulfamethoxazole: Kinetic, reaction mechanism and toxicity

In this study, the double-edge role of permanganate in sulfamethoxazole (SMX) photodegradation with a recyclable catalyst was revealed for the first time. The role of the catalyst under different UV wavelength, the role of permanganate in the treatment process, the effects of permanganate dosage and solution pH on the removal efficiency were investigated. Moreover, the transformation products, TOC reduction and the toxicity of the treated final product to Chlorella vulgaris and Artemia saline were determined. Sole permanganate showed no effect in SMX degradation, while its introduction to the photocatalytic process doubled the reaction rate at the optimal dosage. It is interesting to find that the reaction rate showed a fluctuation trend in terms of permanganate dosage due to the summation of positive effect of permanganate oxidation and the negative effect of the formed MnO2 at the surface of the catalyst, as well as the light attenuation due to overdosed permanganate. The determined intermediates, the higher inorganic ions release and TOC reduction provided a clue on a higher mineralization compared to SMX degradation in the same process without permanganate. Permanganate above 1 mu M may pose a threat to the algae growth, therefore a good monitoring and control of residual permanganate dosage should be incorporated into the process design. A good toxicity reduction to A. saline was observed in the treated effluent; a longer detention is suggested for the complete removal of toxicity. (C) 2017 Elsevier Ltd. All rights reserved.