Abstract: Sulfa antibiotics are widespread antimicrobial agents in aquatic environments, and their primary degradation pathway is photodegradation. Through the research on the photochemical kinetics of sulfamethazine (SAD) and sulfamethoxazole (SMZ), the self-sensitized photodegradation of two sulfa antibiotics in pure water and the effects of aqueous dissolved organic matter fulvic acids (FA) on photodegradation were investigated. In pure water, the photodegradation of the two sulfa antibiotics follows pseudo-first-order kinetics, but with different mechanisms. In addition, the photodegradation of the sulfa antibiotics are significantly influenced by the concentration of aqueous fulvic acids. For sulfamethazine, high concentrations of FA (20, 50, 100 mg/L) are favorable for the photodegradation of SAD while low concentrations of FA (2 mg/L) would inhibit the photodegradation. For sulfamethoxazole, the presence of low concentration of FA (02, 2 mg/L) slightly accelerates the degradation, whereas high concentrations of FA (20, 50, 100 mg/L) decrease the degradation rate of the compound.

Key words: sulfa antibiotics, ultraviolet–visible irradiation, self-sensitized photodegradation, fulvic acids