Transformation of sulfadimethoxine and trimethoprim in VUV radiated aqueous solutions

The combination of trimethoprim and sulfonamides (e.g., sulfadimethoxine) is often used as a growth promoter and antibiotic in animal husbandry. In this work, the efficiency of the low pressure mercury vapour (LPM) lamp, emits at 254 and 185 nm (UV/VUV185 nm lamp) and Xeexcimer lamp, emits at 172 nm (VUV172 nm) photons were compared in the transformation of sulfadimethoxine (SDM) and trimethoprim (TRIM). Both light sources were effective on the transformation of both components. Although the VUV photon flux of the excimer lamp was significantly higher than of LPM lamp, there was no significant difference between the transformation rates of organic substances. The reason was most probably the extreme inhomogeneity of 172 nm radiated solution. VUV185 nm photolysis increased the initial rate of transformation comparing to that determined in UV (254 nm) radiated solution mainly in the case of TRIM, and just slightly for SDM, probably because the direct UV photolysis is also effective for SDM transformation, opposite to the TRIM. The VUV172 nm photolysis was found to be more effective in mineralization, for both compounds than UV/VUV185 nm photolysis. Dissolved O2 has significant effect only in the case of the UV/VUV185 nm photolysis of TRIM.