748 continuous monitoring of volatile organic compounds in industrial waste water
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8/8/2019 748 Continuous Monitoring of Volatile Organic Compounds in Industrial Waste Water
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AN-924 / AXIOM ANALYTICAL, INC.
TeauthoriswithAxiomAnalytical,Inc.,17751-BSkyParkCircle,Irvine,Caliornia92614.W.M.Doyle’[email protected].
1. Introduction
Te discharge o organic chemicals into waste water is anendemicprobleminchemicalprocessing.Asaresult,mostplantsemployremediationacilitiestopuriytheirwastewaterbeoredischargingitintotheenvironment.However,theseacilitiescanbeeasilyoverloadedbyalargespill.Convention-aldetectionmethodswhichinvolvetheperiodiccollectionosamplesandlaboratoryanalysisbyrelativelyslowtechniques
suchasGCorGC/MS,suerromanumberolimitations;
1. Inabilitytodetectamajorspillbeoreitcanreach–and possiblydamage–theremediationacility.
2. Failuretodetectmanyshorttermspillsduetothelow samplingrequency.
3. Inaccuraciessuchasunderreportingoconcentrations duetoevaporationovolatilepollutantsbetweensample collectionandmeasurement.
4. Inabilitytodetectspillsrapidlyenoughtotakeeective remedialaction.
5. Frequentinabilitytodeterminethesourceoagiven chemicalspill. We have developed a ully automated system or the
Continuousmonitoringofvolatileorganiccompoundsin
industrialwastewater
Walter M. Doyle
Tispaperoutlinesanintegratedsystemwhichprovidesrapid,ully-automatic,monitoringoselectedvolatileorganicsinwastewater.Manyprioritypollutants,suchaschlorinatedhydrocarbonsandaromaticsarecharacterizedbylowsolubilityandhighvaporpressure,makingthemdiculttomeasureusingtraditionaltechniques.Tewastewateranalyzeremploysthesparging-inraredmethod,coupledwiththelatestinprocessanalyticalsotware,toovercometheselimitations,makingpossiblethesimultaneousmeasurementomultiplespecieswithdetectionlimitsinthelowppbrange,andupdatedresultseveryewminutes.
continuousmonitoringovolatileorganicpollutantsbasedonthesparging-inraredtechnique.Tistechniqueusesastreamoairbubblestotranserthepollutantsromaxedvolumeo watertoanairstream,wheretheconcentrationscanbemea-suredquicklyandeasilyusinginraredspectroscopy.1 Tespeedothesparging-inraredtechniqueenablesittoovercomeeachothelimitationsotheprevioussystemsout-linedabove.Inaddition,sincethesystemisullyautomated,it
greatlyreducesmanpowerrequirements,resultinginsubstan-tialcostsavings.Finally,byprovidingatime-resolvedchemicalsignatureoeachspill,itmakesitpossibletotraceaspilltoits exact location so that action can be taken to prevenarecurrence.2. SystemDescription
Tekey hardwareelementso the sparging-IRwastewateanalysis system are illustrated inFigure 1.Tese include aspargingvessel,alowvolumeIRgascell(AxiomAnalyticalLF-210),anF-IRspectrometer(BrukerIRCube),awa-terpump,anairpump,andvariousvalvesandsensors.Tese
arecontrolledbytheSymbion-DX™processanalyticalsot- waresuite(SymbionSystems,Inc.).Symbion-DX™controlsandsequencestheoperationothespectrometer,pumps,andvalvesandprovidesortheanalysis,display,alarming,andarchivingodata.Tesystemisdesignedorcontinuous,un-attended24/7operationwith reportingand alarmingvia aplant-widedatanetwork.
8/8/2019 748 Continuous Monitoring of Volatile Organic Compounds in Industrial Waste Water
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Tesystemtypicallymakesadiscretemeasurementeverytwotothreeminutes.Temeasurementcycleinvolvesrstpump-
inga200mLsampleowastewaterromtheplant’seu-entstreamintothespargingvessel.Airisthenpumpedintothebottomothevesselataconstantfowrateviaaspargingnozzle.Tesolutecontainingairemergingromthevesselisdirectedtothegascellwhereitisanalyzedbythespectrome-teroperatinginconjunctionwiththeSymbion-DX™sotwareandamultivariateanalysisprogram.
3. PrinciplesofOperation
Teoperationothesparging-IRsystemisbasedontheactthateachorganicchemicalspecieshasauniqueinraredspec-
trum,orngerprint(Figure2).Despitetheuniquenesso
eachngerprint,thedirectmeasurement o lowconcentrationsovolatileorganicsinliquidwaterismadeextremely
dicultbythepresenceoverystrongandbroadwaterab-sorption in thengerprintspectral region.Te sparging-IRsystemsolvesthisproblembytranserringtheorganicsromthewatertoavaporstream.Telowsolubilityomanyvola-tileorganics, combinedwith the act that theirvaporpressuresaretypicallymuchgreaterthanthatowater,leadstoadramaticenhancementotheirrelativeconcentrationsinthevaporstream.Forthechlorinatedhydrocarbonsandaromaticogreatestenvironmentalconcern,therelativeconcentrationcanbemanyordersomagnitudegreaterthanintheliquid water.Atthesametime,thespectralabsorptionsowaterva-porarearweakerandnarrowerthanthoseoliquidwater.
Asaresult,theseabsorptionsgenerallydonotoverlapthoseothespeciesointerestandhencedonotlimitthesystem’sensitivity.
4. TypicalResults
Tewastewateranalysissystemwillusuallybecalibratedtoreportonthosevolatileorganicsthatmaybepresentinagivenplantenvironment.ypically,thiswillbeasmallnumberocomponents.However,wehavemeasuredasmanyasteendierentspeciessimultaneouslyduringlabsimulation.Inrou-tineoperation,themeasuredconcentrationsarereportedvia
theplant’snetwork.Foranalyticalpurposes,thetimedepen-dentdepletioncurvescanbemonitoredonthesystem’svideodisplay.AtypicalresultisshowninFigure3. Tesensitivityothesystemormeasuringindividualspeciesdependsonthesolubilityandvaporpressureoeachspe-ciesaswellasvariousactorsrelatedtotheoperatingrequire-mentssuchasnumberospeciestobemonitored,requiredspeed,andtypeoinrareddetectoremployed.AnexampleomeasurementlimitsoraparticularsetocomponentsisgiveninableI.
Figure1.MajorelementsotheSparging-IRwastewateranalysissystem.
Figure2.Vaporphasengerprintregionspectraochloroorm(red),DCM(green),andoluene(blue).
Data
System
Gas
CellSparging
System
FTIR
Spectrometer
Optical
Conduits
Sample Air
Flow
ExhaustPlant Air Clean Water
Control
Signals
Concentrations, Alarms,
Messages, Data
StorageWaste Water
Sample
Loop
Data
System
Data
System
Gas
Cell
Gas
CellSparging
System
Sparging
System
FTIR
Spectrometer
FTIR
Spectrometer
Optical
Conduits
Sample Air
Flow
ExhaustPlant Air Clean Water
Control
Signals
Concentrations, Alarms,
Messages, Data
StorageWaste Water
Sample
Loop
8/8/2019 748 Continuous Monitoring of Volatile Organic Compounds in Industrial Waste Water
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AN-924 / AXIOM ANALYTICAL, INC.
5. ImplementationandConclusion
Terstullyautomatedsparging-IRwastewatersystemhasbeenincontinuousoperationoroverayearatamajorchemi-cal manuacturing complex (Figure 4). It has successullydetectedsignicantspillsonanumberooccasionsintimeorappropriateactiontobetaken.Severaladditionalbenetshaveresultedromtheuseothissystem.Notonlyhasiteliminated the costs associatedwithmajor spills, but ithasalsomadeitpossibletoeliminatetheverysignicantcostsas-sociatedwiththepreviousapproachodiscretedailysamplingando-lineanalysis.Teuseocontinuouson-linemonitor-ingalsorevealedinaccuraciesinherentintheprevioussystem.
Teseresultedromtheevaporationothevolatilepollutantsbetweenthetimeasamplewasgatheredanditseventualanalysis.Finally,byprovidingachemicalsignatureoeachspillthesystemhasmadeitpossibletotracethespilltoaparticularplantlocation.Asaresultothesebenets,thisparticulaacilityhasnowchangedovertocompletedependenceonthenewsparging-IRwastewatersystem.
References
1. W.M.Doyle,“ContinuousMonitoringoOrganicPollutants
inWaterbySparging-Inrared”,AxiomAnalytical,Inc.
echnicalNoteAN-907.
TABLEI
SELECTEDDETECTIONLIMITS
Contaminant DetectionLimit(ppb)
Benzene 5
Carbon tetrachloride 0.5
Chloroform .5
,-Dichloroethylene 5
,2-Dichloroethylene 2
cis-Dichloroethylene 7
trans-Dichloroethylene 4
Ethyl benzene 6
Styrene 5
Tetrachloroethylene
Toluene 4
,,-Trichloroethane
,,2-Trichloroethane 25
Trichloroethylene 0.6
Figure4.A ully automatic Sparging-IR system or 24/7 on-lineoperation.
Figure3.Depletionplotsoourorganicspeciesinwaterobtainedduringlaboratorysimulation.Tey-axisunitsareppm.