| Iodinated X-rays contrast media（ICM）are triiodide derivatives on positions 2,4,and 6 of the benzene ring.The introduction of side chains at other positions on the benzene ring can increase water solubility and reduce toxicity.They are mainly divided into ionic and non ionic compounds.As a typical representative of non ionic compounds,iopamidol（IPM）is of great significance in the study of its removal and degradation.Atrazine（ATZ）is a triazine herbicide that can cause cancer even in low concentrations in water,posing a significant risk to human health.It is difficult to efficiently degrade ATZ in conventional water treatment technologies.As a common advanced treatment technology,the solar/chlorine system in advanced oxidation method can effectively remove difficult to degrade organic micro pollutants.In this study,IPM and ATZ were used as target pollutants.The degradation kinetics of IPM and ATZ by solar/chlorine system were investigated,and a series of studies were conducted on the oxidation products and degradation paths in the degradation process.The main work includes the degradation effect of two target substances in the solar/chlorine system,the degradation kinetics study under the influence of different water background components,and the identification of the contribution rate of the active species（HO·,Cl·,Cl O·,Cl2·,O3）produced in the solar/chlorine system to the degradation of IPM and the change of steady-state concentration.The degradation products of the two targets in the system were detected and the reaction path was introduced.The changes of acute toxicity during the degradation of IPM and ATZ in the solar/chlorine system were analyzed and the possible risks were determined.Finally,the unit energy consumption(EEO)of the two targets in the solar/chlorine system were calculated and analyzed.By comparing the controlled experimental conditions,it was found that under the presence of sodium hypochlorite alone as an oxidant,IPM and ATZ did not degrade.Sunlight alone had a certain degradation effect on the two target substances,and the degradation rate of the two target substances was greatly improved under the conditions of sunlight combined with chlorine oxidation.During the experiment,with the increase of the concentration of oxidant Na Cl O,the degradation rates of IPM and ATZ both steadily increased.As the concentration of the target substance increases,the efficiency of IPM degradation in the solar/chlorine system significantly decreases.The change in solution p H will affect the presence of HCl O in the solution,thereby affecting the degradation of the target substance in the solar/chlorine system.As the p H increases,the degradation of IPM and ATZ is inhibited,while in acidic solutions,the degradation effect of the two target substances is significantly enhanced.After adding Cl-in the solar/chlorine system,the degradation of IPM was promoted by microscopy,while the degradation of ATZ was inhibited.After the addition of HCO3-,the rate of IPM degradation in the solar/chlorine system was slightly inhibited,and the inhibitory effect gradually weakened with the increase of HCO3-concentration.During the degradation of ATZ,the addition of HCO3-significantly inhibited its degradation.HCO3-competes with ATZ in the system to react with free radicals such as HO·and Cl·,resulting in a decrease in the number of free radicals reacting with ATZ.The addition of natural organic matter（NOM）to the system will capture some active species and have a certain shading effect on the solution,reducing the penetration ability of sunlight,thereby inhibiting the degradation of IPM and ATZ by the solar/chlorine system.Experimental analysis in different actual water bodies shows that the degradation effect of IPM and ATZ in actual water bodies is not as good as in ultrapure water.In the process of degradation of IPM in solar/chlorine system,nitrobenzene（NB）,benzoic acid（BA）and dimethoxybenzene（DMOB）are added into the solution as probe compounds.NB reacts with HO,NB reacts with HO·and Cl·,and DMOB reacts with HO·,Cl·,Cl O·and O3.The steady-state concentrations of HO·,Cl·,Cl O·and Cl2-·in the solar/chlorine system([HO·]ss,[Cl·]ss,[Cl O·]ss and[Cl2-·]ss)were calculated.Furthermore,the contribution rates of solar,O3,HO·,Cl·,Cl O·,Cl2-·to the degradation of IPM in the solar/chlorine system were calculated.During the degradation of ATZ by solar/chlorine,NB was added as a probe to calculate the contribution rates of solar,O3,HO·,and RCS to the degradation of ATZ.Total organic carbon（TOC）was detected during the degradation of IPM and ATZ,and the oxidation products of IPM and ATZ were detected by high performance liquid chromatography mass spectrometry（LC-MS/MS）,and the possible degradation path was speculated.The reaction pathway of IPM can be divided into deiodination,side chain cleavage,and oxidation of amino（-NH2）to nitro（-NO2）.The reaction path of ATZ is mainly through electron transfer reaction,hydrogen abstraction reaction and addition reaction to generate oxidation products,which are ultimately decomposed into small molecules.The acute toxicity during the degradation of IPM and ATZ in the solar/chlorine system was analyzed by the change of luminescence value of luminous Bacillus.The results showed that IPM itself was not toxic during the degradation of IPM in the solar/chlorine system,and the toxicity of its degradation products did not change significantly.In the process of degradation of ATZ by solar/chlorine,the toxicity of ATZ decreases first,then increases and then decreases,indicating that the intermediate products produced by ATZ in the degradation process have certain toxicity,while the toxicity of degradation by sunlight/chlorine system eventually becomes smaller. |
