Efficiency And Mechanism Of Iopamidol Degradation By Ozone/peroxymonosulfate

Recently,X-ray constrast media?ICM?are widely detected in the environment with high stability and can not be effectively removed by conventional water treatment processes.Although ICM can be oxidized by traditional advanced oxidation process,the unknown morphology of the iodine intermediates leads to a high risk of iodine by-products generation in disinfection process.Iodine disinfection by-products are highly toxic and have a great impact on the quality of drinking water,which has aroused people's attention.Iopamidol?IPM?is a nonionic contrast media,most widely used and most frequently detected in all kinds of water.A new advanced oxidation process,O₃/PMS was used to remove IPM in this work.It was compared with traditional O₃ processes?i.e.,O₃ and O₃/H₂O₂?in many ways.O₃/PMS system was found to display good performance for the degradation of IPM.Faced with complex background components in water,the diverse oxidizing species?i.e.,O₃,HO·,and SO4·-?have the advantage of multiple degradation and risk diversification.In addition,SO4·-has a better de-iodide ability with a high iodate production,which shows a better effect on controlling the formation of disinfection by-products.HO· and SO4·-were identified as the main active species in O₃/PMS system by trapping experiments.The apparent second-order rate constants?kapp,M-1s-1?for the reactions of O₃,HO·,and SO4·-with IPM were determined by competition kinetics methods and were 0.26?2.58×109and 5.18×109M-1s-1,respectively.Further experiments investigated the impacts of oxidants doses and several environmental factors?i.e.,p H,carbonate ion,chloride ion,and natural organic matters?on the degradation efficiency of IPM by O₃/PMS.In addition,the contributions of HO· and SO4·-were also calculated to indicate the relative importance of these two radicals.The results indicated that PMS could efficiently enhance the degradation rates of IPM by O₃ as well as the contribution of SO4·-.The degradation of IPM and the contribution of SO4·-both increased with the increase of p H.In contrast,carbonate ions inhibited the degradation of O₃ and IPM due to its ability to capture HO· and SO4·-forming more selective carbonate radical.Under neutral condition,chloride ion has slight impacts on the degradation of O₃,and it has a weak capturing ability towards HO· but a strong ability towards SO4·-.Natural organic matters could greatly enhanced O₃ degradation as well as the degradation rate of IPM,but the final degradation extents of IPM were decreased under these conditions,indicating a lower total utilization efficiency of oxidant.The degradation of IPM by O₃/PMS system in Harbin groundwater was then conducted.The groundwater containing high levels of carbonate ions,chloride ions and natural organic matters,which could trap HO·and SO4·-,leading a lower degradation efficiency of IPM.The results also indicated that carbonate displayed certain ability towards IPM but weaker than those of HO· and SO4·-.The iodide ions released from IPM in the O₃ system existed in a stable form as iodate?IO₃-?.Under similar conditions,O₃/PMS system has the greatest IPM degradation rate and IO₃-formation levels.IPM has a large molecular structure,the long chain structure is first oxidized to attack the iodine.Therefore,the iodide release increased rapidly with the degradation of IPM.The degradation pathways of IPM by O₃,HO·,and SO4·-included?i?the cleavage of amide bond of branched chain into carboxyl,amide bond,and amino,and?ii?the oxidation of amino to nitro and hydroxyl to aldehyde.SO4·-was found to be more easily to induce deiodide of IPM by electron transfer pathway,HO· led to less deiodie products for its weak deiodide ability via addition reaction.Compared with traditional O₃ processes,the removal rate of IPM is higher in O₃/PMS process.The comparison of iodide release and production under different processes indicated that SO4·-has the best deiodide efficiency of IPM,O₃ followed,and HO· has the weakest performance of de-iodide,showing a better effect on controlling the formation of disinfection by-products.