Heat-activated persulfate oxidation of sulfamethoxazole in water

Heat-activated persulfate to produce highly reactive sulfate radicals (SO4 center dot) to oxidize sulfamethoxazole (SMX) in water was studied. The SMX degradation rate was significantly influenced by the reaction temperature, persulfate dose, initial pH, and co-existing anions. Higher temperature achieved higher degradation rate. The calculated activation energy for hot persulfate oxidation of SMX was approximately 130.93 kJ/mol. The degradation rate constant was proportional to the persulfate dose. An alkaline condition favored the SMX degradation. Effects of anions on the SMX degradation were species-dependent. Cl-, SO42- and NO3- inhibited the SMX degradation, to different degrees. In contrast, HCO3- accelerated the treatment. The SMX decomposition was associated with hydroxylation, sulfonamide bond breakage, and oxidation of the amine groups. Toxicity tests revealed production of more toxic products. Therefore, appropriate post-treatments need to be considered to address the undesirable byproducts.