Photodegradation of the antibiotic sulphamethoxazole in water with UV/H2O2 advanced oxidation process.

Photodegradation of the antibiotic sulphamethoxazole (SMX) in water using a medium-pressure UV lamp combined with H2O2 (UV/H2O2) was used to generate the advanced oxidation process (AOP). The photodegradation process was steadily improved with addition of H2O2 at relatively low to moderate concentrations (5 to 50 mg L(-1)). However, the addition of H2O2 to the photolysis process at higher concentrations (50 to 150 mg L(-1)) did not improve the degradation rate of SMX (in comparison with 50 mg L(-1) H2O2). Addition of H2O2 to the UV photolysis process resulted in several processes occurring concurrently as follows: (a) formation of HO* radicals which contributed to the SMX degradation, (b) decrease in the available light for direct UV photolysis of SMX, and (c) scavenging of the HO* radicals by H2O2, which was highly dominant at moderate to high concentrations of H2O2. It is clear that these factors, separately and synergistically, and possibly others such as by-product formation, affect the overall difference in SMX degradation in the AOP process at different H2O2 concentrations.