UV Photodegradation of Enoxacin in Water: Kinetics and Degradation Pathways

Fluoroquinolones, such as enoxacin, are poorly removed by common sewage-treatment processes, leading to their discharge into the environment, where they have unknown, and potentially serious, impacts on plants and aquatic organisms. The aim of the research reported in this paper was to understand the degradation of enoxacin by direct UV (ultraviolet) photolysis and advanced oxidation processes (AOPs) involving UV/H2O2 and photo-Fenton [UV/H2O2/Fe(II)], which may provide an alternative method of removing this compound from water in a treatment plant. Aqueous samples of enoxacin (0.06mM) were irradiated at 254nm (Io=2x1016photons-1). The presence of H2O2, as well as the addition of FeSO47H2O (photo-Fenton process) both resulted in faster degradation kinetics compared to direct irradiation, with all of these systems leading to significant mineralization of enoxacin [>80% removal of total organic carbon (TOC)] within 30min. The kinetics for the degradation of enoxacin in the presence of natural organic matter (NOM) isolates were also evaluated. Analysis of reaction byproducts by liquid chromatography-mass spectrometry (LC-MS) suggested that photolysis of enoxacin results in hydroxylation, defluorination, and formation of a geminal diol. Proton nuclear magnetic resonance was used for further verification. In addition, the rate constant for the hydroxyl radical (center dot OH) reaction with enoxacin was determined by pulse radiolysis studies to be (5.91 +/- 0.08)x109Lmol-1s-1. These results suggest that center dot OH may play an important role in the photoinduced removal of enoxacin from water, and these systems may be used to remove this compound in treatment plants.(C) 2015 American Society of Civil Engineers.