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 center dot 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 center dot 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.