Photodegradation of tylosin tartrate by advanced oxidation processes

Tylosin tartrate, a macrolide antibiotic, is one of a class of emerging contaminants that have been detected in natural bodies of water since they are not easily removed by conventional treatment processes. In this study, the direct and indirect photodegradation of tylosin tartrate was analyzed to understand the role of reactive oxygen species and organic matter that may be present in surface waters. While direct photolysis caused negligible degradation (k = (9.4 ± 1.8) × 10^-5 s^-1), the addition of 0.4 M hydrogen peroxide (k = (2.18 ± 0.01) × 10^-4 s^-1) or usage of the photo-Fenton process (k = (2.96 ± 0.02) × 10^-4 s^-1) resulted in greater degradation. The degradation was maximized by combining tylosin tartrate with an experimentally determined optimal concentration of humic acid (15 mg/L), which readily produced singlet oxygen and increased the overall degradation (k = 1.31 ± 0.05) × 10^-3 s^-1) by means of indirect photolysis. Absolute pseudo-first-order bimolecular reaction rate constants for tylosin tartrate were measured with singlet oxygen [(4.7936 ± 0.0001) × 10⁵ M^-1 s^-1] and hydroxyl radical [(5.2693 ± 0.0002) × 10⁹ M^-1 s^-1] using competition kinetics, and when combined with data on concentration of the reactive oxygen species, showed that the hydroxyl radical makes a contribution to the degradation that is approximately eleven orders of magnitude greater than singlet oxygen.