Electrodialysis Combined With Ultraviolet Pretreatment Technology For Total Organic Halogen Analysis Based On Ion Chromatography

Total organic halogen(TOX)is a surrogate bulk organic parameter of all halogenated organics in water.Because it is convenient to evaluate the total amount of disinfection by-products(DBPs)in water,TOX provided a powerful tool for the treatment and monitoring of DBPs.However,the existing TOX analysis methods mainly use activated carbon adsorption to separate organic halogen.The adsorption capacity of different activated carbon are different,and the phase transformation in the adsorption and separation process has a great impact on the organic halogen,which may significantly affect the stability and accuracy of the analysis,and limits the normal application of the TOX analysis method.In this study,a electrodialysis combined with ultraviolet pretreatment technology for TOX analysis based on ion chromatography was proposed,which can be used together with ion chromatography to accurately and stably analyze the total organic halogen in water.Through verification and application,this dissertation had obtained the following findings.An efficient separation of TOX and halides was realized by immobile ED technology.A 120 min of ED treatment can remove four kinds of halides(fluoride,chloride,bromide and idodide)of 10.0 mg/L in water samples by more than 99.5%.Even if the initial concentration of chloride went up to 1000.0 mg/L,the residual level of chloride after treatment can be lowered to about 15.0μg/L.Therefore,the purpose of high efficiency removal of halides had been achieved.In terms of organic matter recovery,the recoveries of trichlorophenol,trichlorome thane,trichloroacetic acid and trichloroacetonitrile were relatively low.Through investigating the loss of these four substances,the main loss paths of these substances were identified to be adsorption,volatilization,ion exchange and decomposition.Ho wever,after the system optimization,the average recovery of 14 kinds of typical DBPs can reached over 85.6%.In addition,for the surface water and sewage samples,their UV absorption spectra were consistent before and after electrodialysis,and the recoveries of total organic carbon was greater than 80%.The recoveries of total polar chlorinated and brominated DBPs measured by high performance liquid chromatography electrospray ionization mass spectrometry(HPLC-ESI-tq MS)could reach 79.7%and 83.6%.The dehalogenation method of vacuum ultraviolet advanced oxidation coupled with ultraviolet reduction can realize the efficient dehalogenation of TOX in water.A rapid dehalogenation of TOX can be achieved within 2 hours by using an advanced oxidation process based on UV185nm(VUV)irradiation for mostly halogenated DBPs in simulated and real water samples.Unexpectedly,VUV could oxidize iodide into high valent species,which is undesirable for the detection of iodide with ion chromatography.Given that UV254nm photolysis in alkaline condition could help reduce iodate to iodide,the dehalogenation process was optimized by applying VUV irradation at normal condition for 60 min and then an additional UV254nm irradation for 30 min after adjusting p H to 10.5.Eventually,the recoveries of halides from common DBPs were achieved by over 85.5%.In a certain range,the reliability of dehalogenation was not interfered by initial DBPs concentration(0～1.0mg/L),p H value(7.0～12.0),carbonate(10.0 mg/L),nitrate(10.0 mg/L)and other coexisting compounds.Subsequently,the dehalogenation experiments of surface water and sewage samples showed that more than 95.0%of total organic carbon was converted into inorganic carbon,and 96.4%of total polar halogenated DBPs measured by HPLC-ESI-tq MS were dehalogenated.A new method of TOX analysis based on electrodialysis,vacuum ultraviolet and ion chromatography detection was established.The analysis of DBPs,and TOX in tap water,sewage and other samples showed that the method has good stability and accuracy.Comparing the new method with the traditional AOX method,the two methods showed good linearities for the tap water and sewage samples with different dilution factors,with their fitting linear correlations(R~2)being greater than0.9.The new method exhibited a better recovery performance for volatile halogenated DBPs.For example,the recoveries of trichloromethane by new method and the traditional approach were 98.9%and 67.0%,respectively.Therefore,the comparison results show that the new method of TOX analysis established in this study is feasible.The new method was used in study of the formation potential of TOX.The results showed that the new method can be used to analyze a series of lake water samples with different molecular weight ranges and chlorination dosages.From the perspective of MW of DBPs precursor,the fraction of compounds with MW<1 k Da in the selected water was the dominant fraction,and its corresponding formation potential of TOX was dominant too.Although the absolute amount of TOX generated by the fraction of compounds with MW<1 k Da of two water samples were different,the ratios of typical DBPs measured by gas chromatography to TOCl were similar(ranging from 4.7 to 5.0).The amount of halogenated DBPs and total organic chlorine(TOCl)increased more obviously than that of total organic bromine(TOBr).