The evaluation of different persulfate activation methods (UV, solar light, electron, Fe(II)) on the degradation of sulfaclozine was investigated along with the effect of persulfate concentrations. UV/TiO2/K2S2O8 resulted in the highest degradation rate regardless persulfate concentrations. However, persulfate addition on the UV/TiO2 system was not as efficient as expected and the use of radical scavengers showed that pH played an important role in the distribution of dominant radicals. It was found that at pH 7, hydroxyl and sulfate radicals were involved in the degradation of sulfaclozine, whereas at pH 11 no contribution of sulfate radicals was observed. Following the formation of the six by-products of the first generation formed in UV/TiO2 system, we obtained the formation of two by-products out of six in the UV/K2S2O8 system and four in the UV/TiO2/K2S2O8 system but with different concentrations, confirming the hypothesis suggested about the intervention of O-2(center dot-) in the degradation mechanism of sulfaclozine. The second order rate constant of the reaction between sulfaclozine and SO4 center dot- radicals was determined by a competitive kinetics method and two values of 7.5 x 10(9) M-1 s(-1) and 1.7 x 10(10) M-1 s(-1) were obtained depending on the references used, and found to be close to those obtained between sulfaclozine and (OH)-O-center dot radicals (7.2 x 10(9) M-1 s(-1) and 5.9 x 10(9) M-1 s(-1)). (C) 2016 Elsevier B.V. All rights reserved.