Recognition And Transformation Mechanisms Of Iodinated Disinfection By-products During Disinfection Of Drinking Water

Disinfection of drinking water is one of the most important aspects for drinking water treatment.The concentrations of Br^-and I^-are naturally present in source water due to seawater intrusion near sea coast of china,iodinated disinfection by-products（I-DBPs）can produced after disinfection with iodide-containing raw water by chlorine,chlorine dioxide or chloramine.a Results showed that I-DBPs shown to be more cytotoxicity and genotoxicity than their brominated and chlorinated analogues.Therefore,the rule of I-DBPs forms during drinking water disinfection process,which mainly intermediate generated and reaction mechanism.Investigate their formation and futher transformation mechanisms during drinking water disinfection process is very important for the control and evaluate health risk cause by I-DBPs and to ensure the safety of drinking water.The main contents and results are summarized as follows:（1）Two analytical methods for the detection of iodinated-Trihalomethanes（I-THMs）in drinking water by purge and trap（P&T）with gas chromatography-mass spectrometry（GC/MS）or liquid-liquid extraction with gas chromatography-electron capture detection（LLE-GC/ECD）were compared.Results showed that the LLE-GC/ECD method using methyl tert-butyl ether（MTBE）as extractant was more suitable for qualitative and quantitative analysis of I-THMs.The linearity was observed in the range 0.5–1000μg/L for 6 I-THMs with correlation coefficients（R²）values of>0.99.The developed LLE-GC/ECD method showed good repeatability,with relative standard deviations（RSD,n=7）between 3.9%and 6.4%,as quantified by internal standard.Limits of detections（LODs）varied between 0.05 and 0.11μg/L.Recoveries of I-THMs for surface water,filtered source water,and tap water at the spiked levels of 0.5,2.0,and 10.0μg/L were in the range of 81.2%-108.6%,with RSDs of 2.6%～7.5%.The method was simple,rapid,sensitive,and could be well suited for the determination of I-THMs in drinking water.（2）Systematic investigations were performed of factors,including reaction time,p H,bromide and iodide ion concentrations,NH₂Cl dose,chloramine application models,and natural organic matter（NOM）,that influence the formation of iodinated disinfection by-products（e.g.,trihalomethanes（THMs）,haloacetic acids（HAAs）,and haloacetamides（HAc Ams））in drinking waters.Furthermore,the kinetic model involved in the evolution of reactive iodine species during chloramination was developed.Among the investigated I-DBPs,iodoform（CHI₃）,iodoacetic acid（IAA）,diiodoacetic acid（DIAA）,triiodoacetic acid（TIAA）,and diiodoacetamide（DIAc Am）,were major species observed during chloramination of iodide-containing synthetic and natural water samples.During chloramination,longer reaction times led to continued formation of CHI₃,IAA and DIAA,TIAA,whereas DIAc Am reached a peak then decreased with longer times.Maximum yields of I-DBPs occurred at p H 8,but acidic conditions favored the formation of IAA,DIAA,TIAA and DIAc Am.The mode of chloramination exhibited the largest impact on I-DBPs formation,and followed the order:preformed NH₂Cl>pre-ammonification>pre-chlorination 5 min>pre-chlorination 20 min.Increasing the bromide/iodide ratios enhanced the formation of Br-substituted I-DBPs.Finally,on the basis of a comparison of 18model compounds,molecules with carboxylic groups were shown to favor the formation of the I-DBPs investigated,and low-SUVA₂₅₄ NOM moieties were more reactive with iodine than high-SUVA₂₅₄.Tentative proposals are presented for pathways for I-THM,I-HAA and DIAc Am formation from chloramination of NOM based on a combination of current measurements and previously published information.（3）This study compared the decay of disinfectants,the formation and transformation of secondary disinfectants during different pre-oxidation by chlorine,chlorine dioxide（Cl O₂）,potassium permanganate（KMn O₄）and ferrate（K₂Fe O₄）.Four kinetic models involved in the evolution of reactive iodine species were developed.Various impact factors were evaluated,including the different oxidation time,iodide concentration,bromide and iodide ion ratio,p H,iodide concentration,oxidant dose and type of NOM,that influence the formation and species of iodinated disinfection by-products.The results showed that reactive iodine species is the vital parameter of I-DBPs formation during disinfection.As the reaction time went,DBPs formation increased with the decay of disinfectants.The presence of bromide increased Br-DBPs but decreased the formation of I-DBPs due to the conversion of iodide to iodate during chlorination.However,bromide can not affect on disinfection process using Cl O₂,KMn O₄ and K₂Fe O₄.Oxidant dose and type of NOM showed significant influence on formation of I-DBPs.The order with respect to I-DBPs formation potential form model compounds during pre-oxidation was phenol>citric acid>butenol>glycine.Finally,taken raw filtrated water,the effect of different pre-oxidation process on DBPs formation at different bromide/iodide ratios was evualted,the corresponding theoretical cytotoxicty was caculated based on the THMs and HAAs formed,result showed that high cytotoxicty induced by the formation of DBPs during pre-chlorination in presence of bromide.However,for Cl O₂ and KMn O₄oxidation process,the presence of iodide significantly increased the cytotoxicty.