Degremont水处理手册(第7版)-3

5METHODSANDMEANSOFANALYSIS1GENERALAnalysisisabsolutelynecessarytodesignawatertreatmentinstallationprojectaswellastomonitoritsoperationandtoevaluatethequalityofthetreatedwater(plantoutlet,systems,naturalenvironment).Therelentlessprogressofanalyticaltechniquesmakesitpossibletoimproveourknowledgeoftheconstituentsofthedifferenttypesofwaterandtheireffects.Qualitystandardsareincreasinglyrigorous,treatmentsareincreasinglysophisticatedandmonitoringneedstobeallthemorepreciseandreliable.1.1PRECISIONTheprecisionofamethodincludesseveralcriteria.Accuracyisthedifferencebetweentruevalueandtheaverageoftheresults.Itdependsonsystematicerrors(interferences,sampling,calibrating).Reliabilityisdeterminedbyrepeatability(sameproceduralconditionsforthesameoperator)andreproducibility(differentproceduralconditionswithdifferentoperators).Thestatisticalexpressionoftechniquesmakesitpossibletoimproveourknowledgeoftheconstituentsofthedifferenttypesofwaterandtheireffects.Qualitystandardsareincreasinglyrigorous,treatmentsareincreasinglysophisticatedandmonitoringneedstobeallthemorepreciseandreliable.thesedeviationsisprovidedbythestandarddeviation.Sensitivityisdeterminedbythemeasurabledeviationcomparedtothevaluetobemeasured.Detectionlimitistheminimumconcentrationthatcanbedetectedwith95%probability.Forallspectrometricmeasurements,thedetectionlimitofanelementistheconcentrationcorrespondingtotwicethesignalduetothebackgroundnoiseoftheapparatus.Statisticalmethodsthataremoreadvancedmakeitpossibletointerveneincasesofsystematicerrors,tochooseanalyticalmethods,toelaboratesamplingpolicies(locationsandfrequency),etc.Chap.5:Methodsandmeansofanalysis1.2.LABORATORYANALYSESANDON-SITEANALYSESLegislationonwaterqualityiscontinuallydeveloping.Thegrowingnumberofqualityparameters(62fortheEEC,forexample)andthelowlevelofcertainguidelevels(GL)compellaboratoriestorevisethemethodsandequipmentused.Thegrowingnumberofverificationstheoperatorsandhealthorganizationsareimposingonthemselvescompelthepersonsinchargetoinvestinsophisticatedanalyticalequipment(chromatograph,atomicabsorptionoremissionspectrometer,insomecasesevenmassspectrometer,etc.).Thisanalyticalequipmentisobviouslynotsuitedtoon-siteanalysesrequiring:-aninvestigationwithsimple,sturdyanalyticaltechniques(follow-upofsmallplantsorstudyforthedesignofaninstallation),-theuseofportable,self-contained,compactmultisensorswithdataprocessing,-continuousmonitoring(warningunitforrawwater,qualitysensorsfortreatedwater).1.3.COMPUTERIZATIONOFTHELABORATORYProgramscurrentlymakeitpossibletoprocessanalysisinformationanddataforadministrativeandtechnicalpurposes.AutomatedadministrativemanagementofthelaboratorySoftwarecanfollowasamplefromitsarrivalinthelaboratoryuntiltheresultsreportisissued.Itispossibletoverifythecoherenceofsaidresultsinordertoautomaticallyconfirmtheanalysis.treatmentTechnicalmanagementTheresultsstoredcanbeprocessedinstatisticalmannertoestablishqualityassessments,theevolutionofparameterswithtime,correlationsbetweenparametersandinformation(climatology,treatmentsthewaterhasundergone,reagentdosages),waterqualitymapsinthesystems.Itisalsopossible-toimprovetreatmentlines,-tochooseintermediatetreatmentpointsinthesystem(rechlorination,forexample),-toestablishhistorical,mathematicalmodelstohelpwithdecidinginchoicesof.2.Samples2.SAMPLESTheprimaryobjectiveofsamplingistoobtainsamplesrepresentativeoftheelementthatonewishestoanalyze(water,material,sludge,deposit,gas,reagent,etc.).Samplesofwatermustbetakeninparticularlycleanbottlesrinsedseveraltimeswiththewatertobeexamined,unlessthebottle,originatingfromthelaboratory,containsachemicalagent:forexample,achlorineremovingagent(bacteriology)orpreservativeacid(metals),etc.Inmostphysical-chemicalanalysesofwaterintendedforsupply(systemwater,drillingwater,etc.),itisnecessarytowaittheneededamountoftimetoobtainaconstantwaterquality.Withregardtolakeorreservoirwater,thechoiceofsamplingsitesmusttakeintoaccountthevariationsintheparameterstobemeasuredinrelationtodepth,season,winds,rains,etc.2.1.SAMPLINGMODE2.1.1.GrabsamplingThisisthesamplingmodeusedmostoften.Thebottlesarefilledwithoutshakingthewateruponcontactwiththeair.Itisthereforenecessarytouseatubeadaptedtothesamplerandimmerseittothebottomofthebottle,toreplacethecontentsofthebottleseveraltimesandthentostopperthebottleimmediately.Certainanalyses(oxygen,carbondioxide,pH,etc.)requireanyshakingorcontactwithairtobeavoided.Samplesforbacte-Chap.5:Methodsandmeansofanalysisriologicalanalysesareconductedinsterilebottlesafterhavingsterilizedthedrawingpoint(metaltap)byflameandhavingletthewaterflowatconstantflowforaboutoneminuteundertheprotectionoftheflamebeforetakingthesample.Itisabsolutelynecessarytorecordthedate,originandnatureofthewateroneachsample.Forwastewater,dailyvariationsinquantityandqualitymakegrabsamplesinsufficientlyrepresentativeofthepollutingflow.Isolatedsamplesaretakenwhenthepresenceofunusualorundesirableelementsorconcentrationsisnoted.Forexample:-toxicresiduessuchascyanides(bysmelling),chromium,copper(bycolouration),-oilsandgreases,-concen