| Iohexol is one of the most widely used lodinated Contrast Media(ICM),which is used in the detection and diagnosis of blood vessels,soft tissue and viscera in the medical field of magnetic resonance imaging.It is a new type of PPCPs in water contaminants which was frequently detected.This type of material has unique biological stability,and iohexol is difficult to be completely removed in the conventional process,and its effective removal methods are seldom reported.In addition,iodinated contrast agents have also been shown to be important precursors of iodinated disinfection by-products(I-DBPs),so their continued accumulation in water will cause water eco-environmental safety risks and threaten human health.In this study,the removal efficiency of iohexol in water was studied by using silicate-based inorganic membrane catalyzed ozone oxidation(O3/silicate-based inorganic membrane combined process)technology,and in order to explore the feasibility of degradation of iodinated contrast agents by this advanced oxidation technology.The synergistic relationship between the silicate-based inorganic membrane and the catalytic ozone oxidation was investigated by the comparative experiment.The self-decomposition rate constant of O3(kO3)in the separately O3 system was 0.0007 s-1,which can be increased to 0.0012 s-1 in the O3/silicate-based inorganic membrane combined process,and the combined process can also has higher oxidation efficiency of iohexol,which can be increased by 20%.It was shown that the silicate-based inorganic membrane can improve the mass transfer of O3 in water and promote the decomposition of O3 in contact with membrane,then that will enhance the oxidation and removal rate of iohexol.In the static experiment,the influence factors of O3/silicate-based inorganic membrane combined process for the treatment of iohexol were investigated on the basis of dynamic study.It was found that that when pH = 4.51,5.73,7.22,8.64,the apparent rate constants kobs of iohexol degradation were 0.0071,0.0071,0.0110,0.0171,0.0344 L/(mol·s).Because the alkaline conditions can promote the decomposition of O3,indicating that the·OH or other high oxidation performance of free radicals generated by O3 indirect reaction play a leading role in degradation of iohexol.In addition,the effects of bicarbonate alkalinity,the addition of tert-butanol,the temperature,the reuse of silicate-based inorganic membrane on the degradation efficiency of iohexol in O3/silicate-based inorganic membrane combined process were investigated through the contrast experiment.In this study,the intermediates produced by the degradation of iohexol were tested and analyzed.The forming rules of iodate were studied,and 14 kinds of intermediate compounds of iohexol were detected.8 kinds of these products were quantitatively analyzed.According to the product research results,the degradation mechanism of iohexol was analyzed,and the possible degradation pathways were deduced.In order to simulate the actual water treatment project,The degradation efficiency of iohexol by the combination of O3/silicate-based inorganic membrane combined process in continuous flow mode was studied.And the experiments also investigated the effects of hydraulic retention time,ozone concentration,initial concentration of iohexol,water temperature,water quality background and other factors.Therefore,this study can provides support that combined process application of iodinated contrast media such as iohexol in the actual water treatment. |
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