Effiency And Mechanism Of Iopamidol Degradation By UV-Based Oxidation Processes

Iodinated X-rays contrast media(ICM)has been commonly used to facilitate the medical imaging of organs and blood vessels.Due to its considerable production and high stability,ICM has been frequently detected in effluents of wastewater treatment plants and surface waters.Compared to conventional water treatment technology,UV-based advanced oxidation technology as a common deep treatment technology can effectively remove the refractory pollutants.Although ICM itself is nontoxic to human body,iodide can be released during oxidative treatment of IPM,which raises the potential risk of producing iodinated disinfection byproducts(I-DBPs)in disinfection process.Therefore,it is necessary to further explore its degradation pathways in UV-based advanced oxidation technology and the potential formation of I-DBPs.In this study,the degradation kinetics of iopamidol(IPM)by three different UV-based oxidation processes including UV/hydrogen peroxide(H2O2),UV/persulfate(PDS)and UV/chlorine(NaClO)were examined and the potential formation of I-DBPs in these processes followed by sequential chlorination was comparatively investigated.Increasing pH led to the decrease of IPM degradation rate in UV/NaClO,while it showed negligible impact in UV/PDS and UV/H2O2.Common background constituents such as chloride ion,carbonate and natural organic matter inhibited IPM degradation in UV/H2O2 and UV/PDS,while IPM degradation in UV/NaClO was only suppressed by natural organic matter but not chloride ion and carbonate.The contributions of reactive species to IPM degradation by three UV-based oxidation processes were distinguished.It was found that the contribution of hydroxyl radical(HO·)and UV direct photolysis in UV/H2O2 technology to IPM degradation was equivalent,while the UV/PDS by HO and sulfate radical(SO-4·)and UV/NaClO technology was dominated by reactive chlorine speices(RCS).The differences in transformation products of IPM treated by HO·,SO-4·,as well as RCS generated in these processes,respectively,were also analyzed.The results suggested that HO· preferred to react with IPM by addition reaction led to the formation of hydroxylated derivatives.S-4·preferred to oxidize amino group of IPM to nitro group,while RCS favored the reaction with IPM or intermediates of IPM by addition and substitution reaction to generate chlorine-containing products.Moreover,specific I-DBPs(i.e.,iodoform(IF)and monoiodacetic acid(MIAA))were detected in the three processes followed by chlorination.The addition of natural organic matter had little effect on IF formation of three processes,while MIAA formation decreased in all processes except UV/H2O2.Given that the formation of I-DBPs in UV/NaClO was less than those formed in the other two processes,UV/NaClO seems to be a more promising strategy for effectively removing IPM with alleviation of I-DBPs in treated water effluents.This work for the first time compares the degradation efficiency of IPM and the potential of producing toxic I-DBPs in different UV-based oxidation processes,which has important implications for their application...