差分光谱与DBPs生成之间的联系

WaterResearch36(2002)3273–3282CorrelationsbetweendifferentialabsorbanceandtheformationofindividualDBPsGregoryV.Korshin,WellsW.Wu,MarkM.Benjamin*,OanaHemingwayDepartmentofCivilandEnvironmentalEngineering,UniversityofWashington,Box352700,Seattle,WA98195-2700,USAReceived1August2001;receivedinrevisedform1December2001AbstractThisstudyexaminedcorrelationsbetweenthedifferentialabsorbanceat272nm(DA272)andtheformationofdisinfectionby-products(DBPs)inchlorinatedwaterfromtheToltRiver,awatersourceforSeattle,WA.TheDBPsinvestigatedincludedchloroform(CHCl3),dichlorobromomethane(CHCl2Br),mono-,di-andtrichloroaceticacids(MCAA,DCAA,andTCAA,respectively),chloralhydrate(CH),dichloroacetonitrile(DCAN)and1,1,1-trichloropropanone(TCP).WhereasthekineticsofDBPformationarecomplexandarenon-linear,thesameDBPdatarepresentedasafunctionofDA272arequitesimple.Absorbancedecreaseswhenthewaterischlorinated,i.e.,DA272isalwaysnegative.TheDBPvs.
DA272correlationscanalmostalwaysbequantifiedbylinearequations,atleastabovesomethresholdvalueof
DA272;withR2values0.95.TheonlyDBPthatdidnotfollowthistrendwasCH,forwhichanexponentialrelationshipbetterdescribedthedata.TCPandDCANwereunstableatpH7and8,butatpH6linearcorrelationsbetweentheirconcentrationsand
DA272wereasstrongasthoseforthemorestableDBPs.Thethreshold
DA272valueisapproximatelythesameformanyoftheDBPsstudied,supportingthehypothesisthatindividualDBPsarereleasedfollowingtheformationofacommonintermediate,oratleastasmallgroupofsimilarintermediates.TheDBPvs.
DA272correlationsmayhavepracticalvaluesincetheyprovideanalternativeapproachformonitoringtheformationofindividualDBPspecieson-line,butthegeneralityoftherelationshipsneedstobefurtherexamined.r2002ElsevierScienceLtd.Allrightsreserved.Keywords:Differentialabsorbance;Chlorination;DBPS1.IntroductionTheformationofnumerousdisinfectionby-products(DBPs)whendrinkingwaterisdisinfectedwithchlorineiswellestablished[1–3].TherateandyieldoftheDBPformationreactionsareaffectedbyseveralparameters,includingtheidentityandconcentrationofthehalogen-atingagentandthereactivesitesintheorganicprecursormolecules,solutionpHandtemperature,andtheconcentrationsofbromideandammoniainsolution(e.g.[2,4]).Forinstance,theyieldoftrihalo-methanes(THMs)iswidelyreportedtoincreasewithincreasingpH[1,3,5–8],whilethatofhaloaceticacids(HAAs)andtotalorganichalogen(TOX)decreases.ThelattertrendsarelessuniversalthanthetrendforTHMs[5,7,9–13].SeveralphenomenologicallybasedexpressionshavebeenproposedtorelatemajorwaterqualityparametersandhalogenationconditionstotherateorultimateamountofDBPformation[14–17].However,theintrinsiccomplexityofthereactionsmakestheformoftheserelationshipsverydifficulttoascertain.Topartiallycircumventthesedifficulties,severalresearchershaveattemptedtocorrelateDBPformationwithwaterqualityparametersandthechlorinationconditionsvia*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](M.M.Benjamin).0043-1354/02/$-seefrontmatterr2002ElsevierScienceLtd.Allrightsreserved.PII:S0043-1354(02)00042-8non-mechanistic,statisticalequations[2,4,18–23].Theequationsproposedbythedifferentresearchershavedifferentfunctionalforms,andthefittingparametersintheequationsmustbedeterminedbysite-specifictesting.Therefore,thecalibrationoftheequationsrequiresanextensivestudyofDBPformationinthesystemofinterest.Inaddition,frequentrecalibrationmightbenecessarytoidentifyseasonalorlonger-termchangesinthevaluesofthefittingparameters[24].OneofthemotivationsfordevelopingpredictiveequationsforDBPformationistoreducetheneedfordirectanalysesoftheDBPs,inlightofthetime,effort,andcostthatthoseanalysesrequire.IfamuchlesscomplexandcostlytoolcouldbedevelopedtoevaluateDBPformation,theneedtorelyoneitherphenomen-ologicalorstatisticalequationswoulddiminishsub-stantially.Overthepastseveralyears,wehavedemonstratedtheuseofsuchatoolforanalysisofTOX[25–28].Thistoolisbasedonmeasurementofthedifferentialabsorbancespectrumofthewater,definedasshowninEq.(1)DAl¼Achll
Ainitl;ð1ÞwhereAchllandAinitlaretheabsorbanceoflightatwavelengthlpriortoandafterchlorination,respec-tively,andDAlisthedifferentialabsorbanceatthatwavelength.Thesignificanceofthedifferentialabsorbanceisrelatedtothefactthattheultravioletabsorbanceofnaturalwatersisattributableoverwhelminglytothediversepopulationoforganicmoleculesinthewaterreferredtocollectivelyasnaturalorganicmatter(NOM).WhentheNOMmoleculesreactwithoxidants,DBPsareformedand,simultaneously,theabsorbanceoftheNOMchanges,givingrisetothedifferentialabsorbancespectrum.PreviousresearchhasshownthatthedifferentialspectrageneratedwhenNOM-containingwatersarechlorinatedhaveseveralcommonfeatures.First,thesignofthedifferentialabsorbanceisvirtuallyalwaysnegative,i.e.,chlorinationdecreasestheabsorbanceoftheNOMandthereforeofthesolution.Second,theshapeofthedifferentialUVspectraofchlorinatedNOMisreproduciblefordifferentwatersourcesandchlorinationconditions.Inparticular,allsuchdiffer-entialspectrahaveawell-definedpeaknear272nm,incontrastwiththeconventionalabsorbancespectraofNOMeitherpriortoorafterch