Photodegradation of sulphadimethoxine in water by medium pressure UV lamp

The photodegradation rate of sulphadimethoxine (SMT) in water was studied under polychromatic UV light, in a bench scale apparatus. SMT photolysis was carried out at pH levels of 2.5, 6.5 and 10 to study the impact of acid base properties on the degradation of SMT. The highest SMT photolysis fluence based rate was found at pH = 2.5 (k=7.22 × 10⁻⁴ cm²/mJ) and the lowest rate at pH = 10 (k=4.72 × 10⁻⁴ cm²/mJ), thus the reaction rate decreases with an increase in pH between pH values of 2.5–10. Results indicated that direct photolysis is not satisfactory for degradation of SMT by polychromatic UV lamp as a fluence of approximately 7,000 mJ/cm² is needed to break down 99% of SMT at pH 6.5. The photodegradation products of SMT were studied at various pH values. Photodegradation of SMT results in dissimilar relative amounts of intermediates formed at different pH values which may exert a photon demand and impact on SMT photodegradation rate.