| Iodine X-ray contrast agent(ICM)is an organic compound containing iodine,which is widely used to enhance the imaging of human organs and blood vessels.Because of its high stability,it has been detected in sewage treatment plant effluent,surface water and groundwater.ICM will release inorganic iodine ions in the oxidation process,and the subsequent disinfection oxidation will produce iodine disinfection by-products(I-DBPs).In this paper,the non-ionic ICM-Iopamidol(IPM)and ionic ICM-Sodium Diatrizoate(DTZ)were taken as the research objects,and the degradation effect of NaClO catalyzed by Fe(Ⅱ)was studied based on the advanced oxidation technology of reactive chlorine free radicals(RCS),so as to provide some reference for the effective treatment of ICM-containing wastewater.The main contents are as follows:(1)Fe(Ⅱ)can effectively catalyze NaClO to oxidize IPM.When NaClO concentration is 6mM,450r/min,initial pH=3.00(0.2),25℃,initial IPM concentration is 0.015mM,Fe(Ⅱ)concentration is 1 mM and 60 min,the degradation rate of IPM oxidized by Fe(Ⅱ)/NaClO reaches 87.54%,which is 5.81 and 2.92 times higher than that of single Fe(Ⅱ)and NaClO system.The degradation rate of IPM increases with the increase of temperature(15℃-45℃),and the activation energy was 29.47kJ/mol.Taking the degradation rate of IPM as the response value,combined with the three influencing factors of solution pH,Fe(Ⅱ)and NaClO concentration,the response surface optimization model is established.The results show that the determination coefficient of the model was 0.9961,and the fitting degree was good,which could well predict the degradation effect of IPM by Fe(Ⅱ)/NaClO.Cl-,HCO3-,NO3-,Br-and Ihave different promoting and inhibiting effects on IPM degradation in the range of 0-10mM and HA promoted or inhitited IPM oxidation in the concentration range 0-1mg/L.Fe(Ⅱ)/NaClO can remove IPM in wastewater treatment plant effluent and lake water with the degradation rate achieving 90.36%and 75.03%respectively.which indicated that Fe(Ⅱ)/NaClO can be used to remove IPM in actual water.(2)The free radical experiments showed that secondary chlorine free radicals(such as C1O·and Cl2·-etc.)were the main active species for IPM degradation in Fe(Ⅱ)/NaClO system,with the contribution reaching 64.02%.HPLC/MS/MS analysis indicated that nine products are were formed in Fe(Ⅱ)/NaClO system.IPM was degraded in three ways:substitution,amide hydrolysis and deiodination.The results of iodotrihalomethanes(I-THMs)showed that a small amount of chloroiodomethane(DCIM)and triiodomethanes(TIM)were detected when NaClO and Fe(Ⅱ)/NaClO oxidized IPM,and the yields of the two systems were 0.5608 μg/L and 0.3129 μg/L,respectively.Fe(Ⅱ)/NaClO was safer than NaClO alone.(3)Fe(Ⅱ)/NaClO can also effectively degrade ionic ICM-DTZ with the degradation rate of DTZ of 84.86%under the same experimental condition.DTZ degradation rate increased firstly,then decreased with Fe(Ⅱ)concentration.The degradation rate achieved the highest at pH=3.02.The degradation of DTZ increases with the temperature(15℃-45℃),and the activation energy was 19.75kJ/mol.The results of free radical analysis show that ClO·and Cl2·-are the main active species in the oxidation of DTZ by Fe(Ⅱ)/NaClO,and their contribution rate reaches 65.18%.Relatively,ionic ICM-DTZ was more easier to degrade in Fe(Ⅱ)/NaClO system.The results of iodotrihalomethanes(I-THMs)showed that a small amount of chloroiodomethane(DCIM)and triiodomethanes(TIM)were detected when NaClO and Fe(Ⅱ)/NaClO oxidized IPM,and the yields of the two systems were 0.3308 μg/L and 0.2988μg/L,respectively.Therefore,ionic ICM-DTZ is easier to degrade and safer. |
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