LAUSR

Abstract The degradation of the antibiotic sulfamethoxazole (SMX) was studied by several oxidation processes in the same reactor and under identical experimental conditions. The evolution of SMX concentration and mineralization degree, as well as toxicity of the treated solutions were the parameters considered to assess the efficiency of the different oxidation processes. The formation of molecular, radical and ion intermediates was also monitored. Ozonation was the most efficient process in SMX degradation, while photo–ozonation, with or without H2O2, led to the highest mineralization (83% after 3 h), confirming the synergistic effect when ozone and light were applied together. The results suggested that the first intermediate formed during the degradation of SMX was 3-amino-5-methylisoxazole, the direct O3 attack being then the main responsible for its degradation. During the photolysis process p-benzoquinone was formed, although after 3 h of reaction this intermediate was no longer detected. The formation of two refractory acids, oxalic (OXL) and oxamic (OXM), was confirmed during SMX degradation and the presence of O3 and radiation together was mandatory to remove these compounds. When O3 and light were combined, all nitrogen and sulphur present in SMX molecule were converted into NH4+, NO3− and SO42−, respectively. Although photo-ozonation was the most efficient process in converting SMX, a considerable toxicity was developed in the treated solution, suggesting the formation of intermediates more toxic than the parent molecule.