Efficiency And Mechanism Of Iodinated X-ray Constrast Media Degradation In Chlorination Enhanced By Ultraviolet Or Ultrasound

Water pollution has always been one of the focus of water resources security in China.Although a series of introduced and implemented macro-management methods and norms of water resources,including the river chief system,ecological compensation for water environment and the most stringent water resources management system and so on,have gained success,solving specific water pollution cannot be separated from the support of efficient micro-treatment technology.Therefore,it is of great significance to carry out researches on water pollution control technology to alleviate water pollution and improve the water environment in China.In addition,with the rapid development of human economy and society,the control of conventional and specific indicators in the current water environmental quality standards has not been able to fully safeguard water safety.The frequent detection in water environment of emerging pollutants represented by Pharmaceutical and Personal Care Products(PPCPs)has gradually become one of the focus of water environment problems.Iodinated X-ray constrast media(ICM),a class of iodine-containing organic compounds,has been widely used in aid medical testing.Because of its high water solubility and chemical inertness,ICM can not be removed by traditional wastewater treatment effectively and is frequently detected in surface water,underground water and even drinking water at home and abroad.ICM residue and incomplete transformation may be the cause of the formation of iodine disinfection by-products(I-DBPs),which poses a potential threat to human water safety,so it is of great scientific and practical significance to carry out ICM pollution control research in water environment.In this paper,iopamidol(IPM),a typical non-ionic ICM in water,was studied.UV photolysis and chlorination of IPM were compared.And IPM degradation by UV/chlorine and US/chlorine process were respectively investigated,including influencing factors(operational parameters and water quality indicators),main products and degradation pathways.Besides,the comparative toxicity of products during IPM degradation by UV photolysis,chlorination,UV/chlorine and US/chlorine process was assessed based on toxicology genomics.The main contents of this paper include:(1)UV photolysis and chlorination of IPM.When the initial pH and temperature respectively was 5.8 and 25?,59.5%of IPM was removed in 60 min under the 6-W low-pressure mercury lamp irradiation.And other conditions were the same,with chlorine dosage of 0.12 mmol/L,IPM removal was 28.5%.UV photolysis and chlorination of IPM followed the pseudo-first-order reaction kinetics.IPM removal decreased with the increase of its initial concentration.The effect of the initial pH(5.8-11.1)on UV photolysis and chlorination of IPM was not obvious.The activation energy of UV photolysis and chlorination of IPM was 14.4 and 75.6 kJ/mol,respectively.The increase of chlorine dosage(0.03-0.24 mmol/L)enhanced the chlorination of IPM.Results of effect of main inorganic anions showed that Cl-and CO32-had no obvious effect on UV photolysis of IPM,while Cl-promoted and CO32-inhibited the chlorination of IPM.SO42-with lower concentration inhibited UV photolysis of IPM,while had a certain role in promoting with higher concentration,and there was no significant effect of SO42-on IPM chlorination.NO3-,I-and Br-significantly inhibited UV photolysis of IPM.HCO3-?PO43-?NO3-?I-?Br-adversed to UV photolysis of IPM.HCO3-and NO3-had no obvious effect on its chlorination,while PO43-?I-?Br-inhibited.The mechanism of UV photolysis of IPM mainly included its direct photolysis and self-sensitization photolysis,and the contribution of direct photolysis,HO-and 1O2 was 48.66%,14.67%and 36.67%,respectively.(2)UV/chlorine effectively improved the photolysis and chlorination of IPM.UV/chlorine treatment achieved 99.5%IPM removal in 60 min under the following conditions:initial pH=5.8,6-W low-pressure mercury lamp,initial IPM concentration of 10 mg/L,chlorine dosage of 0.12 mmol/L,the temperature of 25?.During IPM degradation,secondary free radicals(e.g.Cl2-· and ClO·)were more important than Cl-and HO·,the contribution of HO·,reactive chlorine species(RCS),chlorination and UV photolysis was 2.03%,74.72%,6.32%and 16.93%,respectively.Activation energy of IPM degradation by UV/chlorine process was 19.8 kJ/mol,which was significantly lower than 75.6 kJ/mol of chlorination.UPLC-QTOF-MS/MS showed that 22 main products,including chlorine-and iodine-containing organics,were produced during IPM degradation by US/chlorine.Among all identified products,iodine-containing compounds were dominant.The degradation pathways mainly included dehydrogenation,deiodine,hydrolysis,addition,substitution and ammonia oxidation(3)Ultrasound also effectively enhanced the chlorination of IPM.When the initial pH,temperature,chlorine dosage and ultrasound power respectively was 5.8,25?,0.12 mmol/L and 28.5 W,removal of IPM(10 mg/L)obtained 85.8%in 60 min.In US/chlorine process,the effect of ultrasound irradiation was negligible,and the contribution of chlorination,HO· and RCS was 16.47%,4.71%and 78.82%,respectively.Activation energy of IPM was 59.03 kJ/mol,which was higher than 19.8 kJ/mol of UV/chlorine.Compared with UV/chlorine,8 main products were produced during IPM degradation by US/chlorine,and the degradation pathways mainly included substitution,hydrolysis and deiodine reaction(4)Humic Acid(HA)showed a certain degree of inhibition effect on IPM degradation by UV irradiation,chlorination,UV/chlorine,while its effect in US/chlorine process was associated with IPM concentration.Results of EEM spectra showed that HA was also removed in the degradation of IPM by four comparative processes with some new fluorescent substances produced.The potential of four processes on HA removal was UV/chlorine>US/chlorine>chlorination>UV irradiation(5)Identification and comparison of toxicity of products during IPM degradation by diferent processes.Results of toxicity assessment based on toxicology genomics showed that from the point of view of changes in the expression of stress-reactive genes,the toxicity of products changed during IPM degradation by UV irradiation,chlorination,UV/chlorine and US/chlorine,respectively.After 30 minutes reaction time,comparsion of toxicity of IPM degradation products obtained from four comparative processes was UV/chlorine>chlorination>US/chlorine>UV irradiation,while UV/chlorine>US/chlorine>chlorination>UV irradiation after 60 minutes.