748 continuous monitoring of volatile organic compounds in industrial waste water

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’se-mailaddressismdoyle@goaxiom.com.

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.

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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

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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.