Kinetics and Modeling of Degradation of Ionophore Antibiotics by UV and UV/H₂O₂

Ionophore antibiotics (IPAs), one of the major groups of pharmaceuticals used in livestock industry, have been found to contaminate agricultural runoff and surface waters via land application of animal manures as fertilizers. However, limited research has investigated the means to remove IPAs from water sources. This study investigates the degradation of IPAs by using ultraviolet (UV) photolysis and UV combined with hydrogen peroxide (UV/H₂O₂) advanced oxidation process (AOP) under low-pressure (LP) UV lamps in various water matrices. Three widely used (monensin, salinomycin, and narasin) and one model (nigericin) IPAs exhibit low light absorption in the UV range and degrade slowly at the light intensity of 3.36 × 10^–6 Einstein·L^–1·s^–1 under UV photolysis conditions. However, IPAs react with hydroxyl radicals produced by UV/H₂O₂ at fast reaction rates, with second-order reaction rate constants at (3.49–4.00) × 10⁹ M^–1·s^–1. Water matrix constituents enhanced the removal of IPAs by UV photolysis but inhibited UV/H₂O₂ process. A steady-state kinetic model successfully predicts the impact of water constituents on IPA degradation by UV/H₂O₂ and determines the optimal H₂O₂ dose by considering both energy consumption and IPA removal. LC/MS analysis of reaction products reveals the initial transformation pathways of IPAs via hydrogen atom abstraction and peroxidation during UV/H₂O₂. This study is among the first to provide a comprehensive understanding of the degradation of IPAs via UV/H₂O₂ AOP