Seth Lynne Wei Tech Report

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Technical Report No: ND08 - 08

HYDRAULIC AND KINETIC MODELING OF A

FULL-SCALE MOVING BED BIOFILM REACTOR

FOR TERTIARY NITRIFICATION

by

Seth N. Lynne

Wei Lin

Dept. of Civil Engineering, North Dakota State University

Fargo, North Dakota

November 2008

North Dakota Water Resources Research Institute

North Dakota State University, Fargo, North Dakota


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Technical Report No: ND08 - 08

HYDRAULIC AND KINETIC MODELING OF AFULL-SCALE MOVING BED BIOFILM REACTOR

FOR TERTIARY NITRIFICATION

by

Seth N. Lynne1

Wei Lin2

WRRI Graduate Research Fellow1

and Associate Professor2

Department of Civil EngineeringNorth Dakota State University

Fargo, ND 58105

November 2008

The work upon which this report is based was supported in part by federal funds provided by

the United States of Department of Interior in the form of ND WRRI Graduate Research

Fellowship for the graduate student through the North Dakota Water Resources Research

Institute.

Contents of this report do not necessarily reflect the views and policies of the US Department

of Interior, nor does mention of trade names or commercial products constitute their

endorsement or recommendation for use by the US government.

Project Period: March 1, 2004 February 28, 2005

Project Number: 2004ND52B

North Dakota Water Resources Research Institute

Director: G. Padmanabhan

North Dakota State University

Fargo, North Dakota 58105


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ACKNOWLEDGEMENT

StipendsupportfortheResearchFellow,SethLynne,wasprovidedbytheNorthDakota

WaterResourcesResearchInstitute.WethanktheCityofMoorhead,MN,forproviding

opportunitiesandadditionalfinancialsupportforthisproject. Wewouldalsoliketoacknowledge

Dr.Zimmerman,CityEngineerofMoorhead,andtheMoorheadWastewaterTreatmentFacilitystafffortheirtime,supportandassistance.

ABSTRACT

Afullscalemovingbedbiofilmreactor(MBBR),utilizedforseparatestagenitrification,was

examinedforthefirst24monthsfollowingsystemcommencement. Toevaluatethefactors

affectingtheperformanceoftheMBBR,amonitoringprogramwasdeveloped. Monitoringdata

revealedthattheMBBRprocessmeteffluentammoniadesigncriteriaduringbothcoldandwarm

weatherperiods. Evaluationsindicatedthatsystemperformanceishighlydependentuponthe

proceduresforreturningbiosolidssupernatanttothefacilityheadworks. Becauseofhigh

ammoniaconcentrationsassociatedwiththesupernatant,equalizedflowwasrecommendedtoreducethevariabilityininfluentammonialoadingdistributedtotheMBBR.

ToinvestigatethehydrauliccharacteristicsoftheMBBRbasin,traceranalyseswereperformed.

TraceranalysesindicatedthattheMBBRcanbesimulatedastwocontinuousflowstirredtank

reactorsinserieswithhydraulicdeficienciesrepresentedasbypassflow. Inadditiontothetracer

studies,aseriesofammoniadistributionmonitoringwasconductedtofurtherevaluatethe

hydrauliccharacteristicsoftheMBBR. Hydraulicanalysesdemonstratedthatbasinperformance

couldbeimprovedbyoptimizinginfluentflowdistribution,therebyreducingtheprobabilityfor

shortcircuiting.

Laboratorybenchscaleanalyses,designedtosimulatethefullscalesystem,wereconductedto

evaluatenitrificationkineticsoftheMBBR. Ammoniareductiondatafromthebenchscaletests

werestatisticallyfittoanattachedgrowthMonodtypemodel. Althoughthekineticparameters

providedanexcellentfittotheobserveddata,variabilityexistedbetweenthemeasuredkinetic

valuesforeachbenchscaletest.

Utilizingthefullscalemonitoringresults,thehydraulicsimulation,andthekineticparameters

obtainedfromthebenchscaleanalyses,acombinedmodelforthefullscaleMBBRsystemwas

developed. FullscalemodelsimulationsindicatedthattheMBBRprocessperformancewas

affectedmoresignificantlybybasinphysicalcharacteristics,asopposedtonitrificationkinetics,

whenconsiderablehydraulicdeficienciesexist. However,whentheMBBRsystemwasoptimized

withrespecttohydraulics,theprocessperformancewasobservedtobehighlydependentupon

nitrificationkinetics. Considerationmustbegiventobothkineticandhydrauliccharacteristicsto

ensuremaximumperformanceforMBBRsystems.

Keywords:MovingBedBiofilmReactor(MBBR),Nitrification,Ammonia,KineticModel

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TABLEOFCONTENTS

ACKNOWLEDGEMENT ii

ABSTRACT...................................................................................................................................ii

TABLEOF

CONTENTS

..................................................................................................................

iii

LISTOFTABLES..........................................................................................................................iv

LISTOFFIGURES........................................................................................................................iv

INTRODUCTION..........................................................................................................................1

DescriptionofWaterProblemAddressed......................................................................... 1

Objectives........................................................................................................................... 2

BACKGROUND............................................................................................................................3

SelectionofNitrificationProcess....................................................................................... 3

MoorheadMBBRNitrificationSystem..........4

PreviousMBBRAnalysis..................................................................................................... 7

INVESTIGATIVEAPPROACH.......................................................................................................10

ExperimentalDesign......................................................................................................... 10

MaterialsandMethods.................................................................................................... 10

RESULTSANDMODELDEVELOPMENT.......................................................................................12

AnalysisoftheFullScaleMBBRMonitoringDiscussion..................................................12

HydraulicAnalysis............................................................................................................. 16

TracerStudies............................................................................................................................ 17

NH3NDistributionintheMBBR............................................................................................... 19

HydraulicAnalysisDiscussion................................................................................................... 21

NitrificationKinetics......................................................................................................... 21

FullScaleMBBRSimulation............................................................................................. 25

SUMMARYANDCONCLUSIONS................................................................................................32

REFERENCES.............................................................................................................................34

iii


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iv

LISTOFTABLESTable Page

Table1.EffluentNH3NLimits............................................................................................... 2

Table2.MBBRDesignCriteria............................................................................................... 7

Table3.TracerEvaluationSetup......................................................................................... 11Table4.SeasonalMBBRPerformance................................................................................. 13

Table5.MBBRConditionsDuringSupernatantReturn.......................................................15

Table6.MBBRFlowConditionsDuringTracerAnalysis......................................................17

Table7.FullScaleTracerAnalysisSummary....................................................................... 18

Table8.MBBRConditionsDuringNH3NDistributionAnalysis..........................................20

Table9.SummaryofLaboratoryBenchScaleAnalysis.......................................................24

Table10.FullScaleMBBRDatafortheDateofEachBenchScaleAnalysis.......................25

LISTOFFIGURESFigure Page

Figure1.Moorhead,MN,WWTFFlowDiagram................................................................... 5

Figure2.MoorheadMBBRSchematic................................................................................... 6

Figure3.FullScaleMBBRInfluentNH3N.............................................................................. 8

Figure4.FullScaleMBBREffluentNH3N............................................................................. 8

Figure5.PreviousFullScaleSimulation................................................................................ 9

Figure6.MBBRNH3NMonthlyAverageData.................................................................... 13

Figure7.SupernatantReturnFlowandMBBRPerformance..............................................14

Figure8.JanuaryMarch2004SupernatantFlowandMBBRResponse............................15

Figure9.TracerTestNo.4Response(at6.60MGDand4,500scfm).................................18

Figure10.EffectiveVolumeasaFunctionofInfluentFlow................................................19

Figure11.NH3NDistributionNo.1(at4.40MGDand4,500scfm)...................................20

Figure12.LaboratoryBenchScaleData.............................................................................. 24

Figure13.FullScaleMBBRModel....................................................................................... 26

Figure14.FullScaleSimulation,January2004................................................................... 26

Figure15.FullScaleSimulation,June2004........................................................................ 27

Figure16.EffluentNH3NasaFunctionofInfluentNH3NandBypassFlow.....................28

Figure17.MaximumSubstrateUtilizationRateSensitivity,BypassFlow=0%....................29Figure18.MaximumSubstrateUtilizationRateSensitivity,BypassFlow=30%..................29

Figure19.HalfSaturationConstantSensitivity,BypassFlow=0%......................................30

Figure20.HalfSaturationConstantSensitivity,BypassFlow=30%....................................31


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INTRODUCTION

Thisresearchsoughttoidentifythefactorsaffectingtheperformanceofafullscalemoving

bedbiofilmreactorutilizedfornitrification. Amonitoringplanwasdevelopedtoevaluatethe

parametersaffectingthestabilityoftheprocess. Utilizingthemonitoringdata,inconjunction

withbasinhydraulicanalysesandkineticparameters,amodeloftheprocesswaspresented,whichcanbeutilizedtoexamineoperationalproceduresastheyrelatetoafullscalenitrifying

system.

DescriptionofWaterProblemAddressed

Highconcentrationsofammoniainwastewaterdischargeshavebeenshowntobetoxictofish

andmarinebiotaaswellastocausedissolvedoxygen(DO)depletioninreceivingstreams,

especiallyduringperiodsoflowriverflow. Becauseammoniaisalsoanutrient,dischargecan

contributetoalgalbloomsandeutrophicationinaquaticsystems. WhentheCityofMoorhead

WastewaterTreatmentFacility(WWTF)wasdesignedintheearly1980s,noammoniadischarge

limitwasimplemented,andtreatmentprocessesweredesignedwithoutconsiderationforammoniaremoval. SinceoperationoftheMoorheadWWTFbeganin1983,thetypicaldischarge

concentrationofammonianitrogen(NH3N)totheRedRiveroftheNorthwasnear19milligrams

perliter(mg/L).

Inthemid1990s,thereachoftheRedRiveroftheNorthfromthecitiesofMoorhead,MN,

andFargo,ND,totheconfluencewiththeBuffaloRiverinMinnesotawasidentifiedasimpaired

forbothammoniaanddissolvedoxygen(i.e.,violatingwaterqualitystandardsforthese

parametersatlowriverflow)(Zimmermanetal.,2003). In1994,aworkgroupwasformedto

addressthisimpairmentandprepareaTotalMaximumDailyLoad(TMDL)studytoestablish

allowableloadingsoffivedaycarbonaceousbiochemicaloxygendemand(CBOD5)andammonia

dischargedfromthecitiesofFargoandMoorheadwastewatertreatmentfacilitiesand

correspondingpermitlimitsforthetreatedwastewaterdischarges. In1999,theUSEPArevisedits

waterqualitycriterionforammonia. Thepreviousammoniacriterionwasbasedondissolved

oxygenlevelsaswellastoxicity. Thecriterionwasrevisedforammoniatoxicityandunrelatedto

dissolvedoxygenimpactsassociatedwithammoniadischarges. TheMinnesotaPollutionControl

Agencysubsequentlyadoptedasitespecificstandardforammoniafortheimpairedreachofthe

RedRiveroftheNorthbasedonthenewcriteriaanddevelopedanewdischargelimitfortheCity

ofMoorhead. ThelimitisseasonalandbasedonflowintheRedRiveroftheNorth. Compliance

ismaintainedonlyduringthemonthsofJunethroughSeptemberwhenflowintheRedRiveris

commonlylow. AlthoughtheeffluentNH3Nconcentrationlimitof19mg/Lremainsconstantfor

allriverflows,themasslimitissignificantlyreducedatlowriverflows(lessthanfiftycubicfeet

persecond). Therefore,inadditiontoeffluentNH3Nconcentration,theWWTFmustalsomonitor

NH3NloadingtotheRedRiver. BecausetheeffluentflowfromtheWWTFisrelativelyconstant

duringperiodsoflowriverflow,themassloadinglimitationequatestoaneffluentNH3Nconcentrationofapproximately8mg/L. TheNationalPollutantDischargeEliminationSystem

permitforthefacilitycontainstheeffluentNH3NlimitsshowninTable1.

AcompliancedateofSeptember30,2003,wasalsoestablished. TheCityofMoorhead

developedafacilityplanand,basedonthatplan,constructedaninnovativeprocess,theattached

growthmovingbedbiofilmreactor(MBBR),tomeetthenewlimitsatacostof$3.3millionin

2002.

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Table1.MoorheadWastewaterTreatmentFacilityEffluentNH3NLimits.

EffectivePeriod ApplicableRiverFlow LimitType Limit

JuneSeptember Allriverflows CalendarMonthAverage 19mg/L

Greaterthan1.42m3/sec

(50cfs1)

CalendarMonthAverage 647kg/day

(1,427lb/day)

Lessthan1.42m3/sec

(50cfs1)

CalendarMonthAverage 108kg/day

(238lb/day)1cfs=Cubicfeetpersecond.

Atthetimeofconstruction,theprocesswastheonlyfullscaleseparatestagenitrifyingMBBR

inthecountry. TheMBBRprocessutilizesfloatingmediaplacedinanaerationbasin. Inthebasin,

anaerationsystemsuppliesoxygenandprovidesmixingfortheprocesswhilethemediasupply

thenecessarysurfaceareaforattachedgrowthofnitrifyingbacteria.

Assessmentofthisnew,innovativeprocessisnecessarytoevaluatetheoperational

parametersaffectingtheperformanceoftheMBBRsystem. Abetterunderstandingofthe

processgainedbystudyingthekeyparametersviaakineticmodelwillresultinimproved

operationalstabilityandreducedeffluentconcentrationsofammonia,thusimprovingtheoverall

waterqualityoftheRedRiveroftheNorth.

ResearchObjectives

Theultimategoalofthisresearchistoidentifyandevaluatethecriticaldesignandoperational

parametersaffectingthenitrificationrateinafullscaleMBBRprocess. Toaccomplishthisgoal,

theprimaryobjectivesoftheresearchinclude:

1. collectandevaluatefullscalemonitoringdatafortheMBBRsystemundervariousflowand

ammonialoadingconditions;

2. evaluatethehydrauliccharacteristicsofthebasintobetterunderstandtheflowof

wastewaterthroughthesystemandselectanappropriatehydraulicmodel;

3. studynitrificationkineticsandchooseasuitablemodeltoevaluatethepertinentkinetic

parametersoftheprocess;and

4. utilizethemonitoringdataincombinationwiththehydraulicandkineticparametersto

developanappropriatemodelforthefullscaleMBBRsystem.

ImprovedunderstandingofthetertiarynitrifyingMBBRsystemisnecessarytoenhancethe

operationalstabilityofthefullscalesystemandthus,optimizetheeffluentammonia

concentrationdischargedtotheRedRiveroftheNorth.

Otherbenefitsincludedinthestudyarerelatedtotheuniquenessoftheprocess. This

researchwillbewidelyapplicabletotheMBBRprocessingeneral,andthus,expandthebodyofcurrentknowledgeassociatedwiththenewandinnovativeprocess. Asmentionedearlier,atthe

timeofconstructiontheMoorheadprocesswastheonlyseparatestagenitrifyingmovingbed

biofilmreactorinthecountry. AttentionhasbeengrowingwithregardtotheMBBRprocess. Asa

separatestagesystem,anopportunityispresentedtostudyandevaluatethefullscalesystem,

andthus,providevaluableoperationalanddesigninformationwhichmaybeutilizedinsimilar

systems;notonlyforseparatestagesystems,butalsoincombinationwithactivatedsludge.

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BACKGROUND

InthissectionthehistoryregardingthenitrificationstudiesattheMoorheadWWTFis

portrayedandtherationaleusedbytheCityofMoorheadtoultimatelyselectMBBRasthe

treatmentsystemispresented. PreviousanalysisoftheMoorheadMBBRsystemisalso

summarized.

SelectionofNitrificationProcess

TheissueofammoniareductionhasbeenstudiedextensivelybytheCityofMoorheadWWTF

andatNorthDakotaStateUniversity. TheCityofMoorhead,Minnesotaoperatesanadvanced

WWTFwithadesignflowof22,710m3/d(6mgd)andcontinuousdischargetotheRedRiverofthe

North. TheWWTFservesthecommunitiesofMoorhead,Dilworth,andtheTownofOakport,MN.

Theliquidtreatmentprocessesincludebarscreens,aeratedgrittanks,flowequalization,primary

clarification,highpurityoxygenactivatedsludgesecondarytreatment,finalclarification,polishing

ponds,andchlorination/dechlorinationdisinfection. BecauseoflowpHandshortsludge

retention

time

(SRT)

in

the

high

purity

oxygen

activated

sludge

system,

nitrification

was

not

achievableundertheexistingtreatmentsystemattheMoorheadWWTF.

Klecker(1998)studiedthefeasibilityofusingtheexistingpolishingpondsattheMoorhead

WWTFfornitrification. TheresultsofKleckersstudyindicatedthepolishingpondsprovidedan

appropriatedetentiontime,butthelowbiomassconcentrationinthepondslimitedtheremoval

efficiencyofthenitrificationprocess. Kleckerrecommendedthatmodifiedoperationbe

evaluatedtoachievenitrificationonafullscale.

BasedonKleckersstudy(1998)andtheresearchofZimmerman(2003),itwasdeterminedto

convertoneoftheexistingpolishingpondsattheMoorheadWWTFtoanitrificationbasin.

Feasibilityofthefullscalenitrificationprocesswasevaluatedbyapilotscalestudyusinga

separatestageattachedgrowthprocess. Fromthestudy,Zimmermanetal.,(2003)foundthe

additionofthemediatothebasinallowedforthedevelopmentofasuitablebiomasspopulation.

Basedontheresultsofthisstudy,aMBBRwasselectedfornitrificationattheMoorheadWWTF.

TheMBBRisaninnovative,attachedgrowthprocessthatusessmallplasticmediatoprovidea

surfaceforthegrowthofbacteria. TheMBBRsystemisflexibleandcanberetrofitintoalmostany

sizeorshapeoftank. Mechanicalmixersoraerationsystemsareutilizedformixingthereactor.

Screensareusedtocontainthemediawithinthereactor. Returnflowisunnecessaryand

backwashingofthescreensisnotrequired. Coarsebubbleaerationiscommonlyusedinthe

reactor. Mediavolumeinthereactoriscontingentonorganicandhydraulicloading,temperature,

theoxygentransfercapabilityoftheaerationsystem,andtherequiredleveloftreatment. The

MBBRprocessisrelativelynew,withthefirstinstallationin1990(RustenandNeu,1999). Asof

2000,about100installationswerereportedwithmostoftheselocatedinEurope(Water

EnvironmentResearchFoundation,2000).

BecausereturnactivatedsludgeflowisnotrequiredfortheMBBRprocess,thedesignismorestraightforwardthanthedesignofcombinedattachedandsuspendedgrowthsystems(i.e.,

integratedfixedfilmactivatedsludgeorIFASprocess). TheMBBRdesigncanbecomplicated,to

someextent,becausethereisnogenerallyacceptedcomprehensivemodel. Therefore,system

designisnormallylimitedtoempiricalrelationships,andoften,sitespecificpilottesting.

Fortypicaldesign,thefullscaleMBBRcanachieve90%ammoniaremovalatNH3Nloadingsof

1.0grampersquaremeterofmediasurfaceareaperday(g/m2/d)withadissolvedoxygen(DO)

concentrationgreaterthan5mg/LandaneffluentNH3Nconcentrationgreaterthan3mg/L. For

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90%removalatDOconcentrationsgreaterthan5mg/L,buteffluentNH3Nconcentrationsless

than3mg/L,thedesignloadingdropsto0.45g/m2/d(degaardetal.,1994).

OveralltheMBBRprocesswasselectedbasedonanumberofconsiderations. Theprocesswas

foundtobeacosteffectivealternativeinreducingeffluentammoniaconcentrations. Thedesign

servedasthemostefficientintermsofexpansionofthefacilitybecausenoadditionalamountof

landwasrequiredtocomplywiththeammoniatreatmentrequirements,andtheMBBRprocess

alsodemonstratedtheabilitytoreducetheeffluentammoniaconcentrationstoalimitbelowthe

permittedlevel(Zimmermanetal.,2004).

MoorheadMBBRNitrificationSystem

In2003,theMoorheadWWTFwasupgradedtoincludeaseparatestagefullscaleMBBR

nitrificationprocesstocomplywiththeseasonaleffluentNH3Nlimits. TheMBBRprocesswas

constructedbyconvertingtheeasthalfoftheexistingPolishingPondNo.1toanaerationbasin. A

flowdiagramforthefacilitywiththenewMBBRisshowninFigure1.Aschematicdiagramofthe

MBBRisshowninFigure2,anddesigncriteriaforinitialandfuture(year2020)conditionsare

providedinTable2. ThedesignNH3NeffluentinTable2isbaseduponeffluentmassloadingto

theRedRiver,thusexplainingthevariationinlistedeffluentconcentrations.

AsystemtobypasstheMBBRexistsbetweenPolishingPondNo.1andControlStructureNo.1.

Thebypassisautomaticathighflows(greaterthan7.5mgd)toavoidfloodingthebasin. The

configurationalsoallowstheWWTFtocompletelybypasstheMBBRandprovidestheabilityto

feedonlyaportionofthetotalplanteffluentflowtothebasin. Bypassoccursduringperiodsof

highflowwhenammoniaconcentrationsaresignificantlybelowaverageduetodilution.

MediainthebasinaremanufacturedbyHydroxylPac(HydroxylSystems,Sidney,British

Columbia,Canada). Themediaelementsaremadeofultravioletresistant,highdensity

polyethylene;havedimensionsofapproximately22mmindiameterby15mminlength;andhave

aspecificsurfaceareaof388m2/m3. Thesurfaceareaofthemediasouterportionisnot

considered,duetothelackofnitrifyingorganisms,asaresultofthecollisionsoccurringbetween

theindividualmediaelementswithinthebasin. Therefore,thespecificsurfaceareaisdefinedasthesurfaceareaofonlytheinner,protectedportionofthemediaelement. Themediaare

buoyantandhaveaspecificdensityof0.96g/cm3.

TheHydroxylPacmediawasselectedbasedontheyearlongpilotstudythattested

performancecriteria,theabilitytoacquirethemedia,andtheinstallationofacosteffectivebasin

withtheflexibilitytohandlefutureloading. Thefillfractionofmedia(volumeofthereactor

occupiedbymedia)inthebasinisabout32%. FutureNH3Nloadingconditionscanbeaddressed

bytheadditionoffurthermedia(approximately40%byvolumebasedonthemanufacturers

recommendation).

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Subnatant

WasteActivatedSludge

Primar

y

Digester2

Primary

Digester1

GasHold

ing

Digester3

Thickened

W.A.S.

Primary

Clarifier

Sludge

Final

Clarifier

Effluent

Outfallto

RedRiver

D.A.F.

Thickener

2

D.A.F.

Thickener

1

Equalization

Bas

in

3

Equalization

Bas

in

2

Eq.

Basin

1

Grit 1

Grit 2

Primary

Clarifier1

Primary

Clarifier2

HighPurityOxygen

ActivatedSludge1

HighPurityOxygen

ActivatedSludge2

Final

Clarifier

1

Final

Clarifier

2

Final

Clarifier

3

Final

Clarifier

4

ReturnActivatedSludge

Chlorination/

DechlorinationBuilding

Polishing

Pond1

(1.1acres)

Po

lishingPond2

(3.0acres)

PolishingPond3

(4.9acres)

Air

Blower

Bldg.

Cl2

Contact

Cl2

Chlorine

Mix

PondEffluent

SulfurDioxide

Nitrification

MBBR

Biosolids

Storage

Digested

Biosolidsfrom

Digester3

Decantto

Equalization

Basin1

Land

Applied

Biosolids

Screw

Pumps

BarScreens

Influent

Decantfrom

BiosolidsStorage

DigestedBiosolids

toBiosolids

Storage

F

igure1.

Moorhead,

MN,

WWTFFl

owDiagram.

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Figure2.MoorheadMBBRSchematic.

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Table2.MBBRDesignCriteria.

Parameter

Initial

Annual

Average

Initial

Maximum

Month

2020

Annual

Average

2020

Maximum

Month

BasinDimensions(LxWxD),m(ft) 42x24.4x2.9(138x80x9.5)

BasinVolume,m3(ft3) 2,970(104,880)

MediaVolume,m3(ft3) 950

(33,560)

950

(33,560)

1,604

(57,000)

1,604

(57,000)

MediaVolume,%fill 32 32 54 54

Flow,m3/d(mgd1) 18,173

(4.8)

24,610

(6.5)

22,710

(6.0)

34,075

(9.0)

InfluentNH3N,mg/L 17 17 17 17

InfluentNH3N,kg/d(lb/day) 308

(680)

417

(920)

385

(850)

578

(1,275)

InfluentNH3N,g/m2/d 0.84 1.13 0.62 0.93

Predictedremoval,% 64.7 74.1 71.8 81.2

EffluentNH3N,mg/L 6.0 4.4 4.8 3.2

EffluentNH3N,kg/d(lb/day) 108

(238)

108

(238)

108

(238)

108

(238)

Oxygenrequired,kg/d(lb/day) 1,185

(2,614)

1,428

(3,149)

1,363

(3,006)

2,156

(4,755)

Airforoxygenrequirements,standard

m3/min(scfm2)

125

(4,418)

151

(5,322)

144

(5,082)

228

(8,038)1mgd=Milliongallonsperday.

2scfm=Standardcubicfeetperminute.

PreviousMBBRAnalysis

ThefullscaleMBBRprocesswasplacedintooperationonApril1,2003. Atthetime,effluent

flowfromPolishingPondNo.1wasdirectedthroughtheMBBRbasin. Noseedbiomasswasused

fortheMBBRstartup(Zimmermanetal.,2004). WhenMBBReffluentNH3Nconcentrationsfell

to6.0mg/Lorless,thestartupphasewasconsideredcomplete. Influentandeffluentammonia

nitrogen,asmeasuredacrosstheMBBRbasinsincestartupin2003,areshowninFigures3and4,

respectively. Designandaveragemonthlyconcentrationsaswellasmaximumandminimum

monthlyvalues(representedbyupperandlowerbars)arealsoshowninthefigures.

AsevidentbytheeffluentNH3Ndata,thesystemrequiredapproximatelytwomonthsto

developastablenitrifyingbiomass(Zimmermanetal.,2004). Althoughtheinfluent

concentrationshavebeenvariableandconsistentlyexceededthedesignvalue(17mg/L),the

systemhasachievedthedesigneffluentconcentrationduringthemonthswhenpermitlimitsare

applicable. Duringsystemstartup,Zimmermanetal.(2004)notedthatthevariabilitywasthe

resultofatleasttwofactors:occasionalwetweatherflowwhichdilutesinfluentNH3N

concentrationsandoperationalproceduresforreturningsupernatant(typicalNH3N

concentrationsbetween1,500and2,000mg/L)fromthebiosolidsstoragefacilitytotheWWTF

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headworks(refertoFigure1). Performancewasonlyslightlyreducedduringcolderweather

monthswhenpermitlimitswerenotineffect(Zimmermanetal.,2004).

0

10

20

30

40

50

60

70

80

Apr0

3

May

03

Jun0

3Jul0

3

Aug03

Sep03

Oct0

3

Nov0

3

Dec03Jan

04

Feb0

4

Mar04

Apr0

4

May

04

Jun0

4Jul0

4

Aug04

Sep04

Oct0

4

Nov0

4

Dec04Jan

05

Feb0

5

Mar05

Apr0

5

InfluentNH3

N(mg/L)

Avg Design

Figure3.FullScaleMBBRInfluentNH3N.

0

10

20

30

40

50

60

70

Apr0

3

May

03

Jun0

3Jul0

3

Aug03

Sep03

Oct0

3

Nov0

3

Dec03Jan

04

Feb0

4

Mar04

Apr0

4

May

04

Jun0

4Jul0

4

Aug04

Sep04

Oct0

4

Nov0

4

Dec04Jan

05

Feb0

5

Mar05

Apr0

5

EffluentNH3

N(mg/L)

Avg Design

Figure4.FullScaleMBBREffluentNH3N.

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Basedupontheresultsofthepilotstudy,Zimmerman(2003)andhiscoinvestigators

suggestedthenitrificationrateoftheMBBRcouldbesimulatedasanempiricalfirstorderdecay

modelasshownbelow.

)1(maxkL

L eRR

= , (23)where RL=NH3NremovalrateatloadingL,g/m

2/d

L=NH3Nloading,g/m2/d

Rmax=maximumNH3Nremovalrate,g/m2/d

k=removalratecoefficient,(g/m2/d)1

Basedonthedatagatheredfromthepilotstudy,Rmaxandkwerefoundtobe1.30g/m2/dand

0.93(g/m2/d)1,respectively. TheequationwasderivedfromaverageNH3Nloadingsrangingfrom

0.45to1.58g/m2/dandforaverageeffluenttemperaturesrangingfrom15to21C. Forthefull

scalesystem,Zimmermanetal.,(2004)dividedtheresultsintotwotemperatureregimes,onefor

coldweatherperiods(11to14C)andoneforwarmweatherperiods(17to21C). TheresultsofthemodelaredisplayedinFigure5.

TheempiricalrelationshipinEquation(23)impliesnitrificationintheMBBRisprimarily

dependentuponNH3Nloading. However,anumberofotherparameterswererecognizedas

affectingtheprocess. FurtherresearchofthenewMBBRprocesswasrecommendedtoresolve

unansweredquestionsregardingthenitrificationrateanditsrelationshiptoammonia

concentration,dissolvedoxygenconcentration,basinconfiguration,anddetentiontime,aswellas

influentloading(Zimmermanetal.,2004). Theseparameters,aswellasbasinalkalinity,

temperature,nitrificationkinetics,biomasscharacteristics,andsystemhydraulicswillbeexplored

astheyrelatetothenitrificationefficiencyoftheMBBR.Developingdefinitiverelationships

requireevaluationwheretheseparametersaremaintainedasindependentvariables.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40

NH3NLoading(g/m2/d)

NH3

NRemoval(g/m2/d)

Pilot(1521C) Actual(1721C) Actual(1114 C)

100%Removal 80%Removal 60%Removal

o o o

Figure5.PreviousFullScaleSimulation.

9


15/39

INVESTIGATIVEAPPROACH

AdescriptionofthemonitoringprogramdevelopedtostudythefullscaleMBBRsystemis

presented. Testingproceduresaswellashydraulicandkineticexperimentaldesignsandmethods

aredetailedwithin.

ExperimentalDesign

ToeffectivelymonitortheMBBRbasinandestablishanunderstandingofthesystem,a

detailedmonitoringplanwasdevelopedandmaintained. Thefullscalesystemwascontinuously

monitoredsinceoperationalstartupthroughthepresenttime. Effluentflowrate,aswellas

airflowandairpressuretothebasinhasbeencontinuouslymonitored. Regularmonitoringhas

beencarriedoutforMBBRtemperature,DO,pH,CBOD5,solubleCBOD5(SBOD5),totalsuspended

solids(TSS),totalKjeldahlnitrogen(TKN),NH3N,nitritenitrogen(NO2N),nitratenitrogen(NO3

N),andalkalinity. Periodicgrabsampleanalysis,conductedfivedaysperweek,hasbeenutilized

fortemperature,DO,andpH. Allotherparameterswerebasedon24hourflowcomposite

samples

and

were

performed

at

a

rate

varying

from

once

per

week

to

four

times

per

week.

ToinvestigatethehydrauliccharacteristicsoftheMBBRbasin,severaldyetestswere

performed. Byanalyzingthetracer(dye)concentrationpresentinthebasineffluentandfitting

theoreticaltraceroutputresponsecurvestothefieldmeasuredeffluentdyedata,thehydraulic

performanceoftheMBBRcanbedetermined. TheMBBRbasinwasassumedtoperform

hydraulicallyasaseriesofcontinuousflowstirredtankreactors(CFSTR).

Inadditiontothetracerstudies,NH3Ndistributionmonitoringthroughoutthebasinwas

conductedtofurtherevaluatethehydrauliccharacteristicsoftheMBBR. Todetermineifthe

MBBRbasinwasexperiencingzonesofpoormixingorshortcircuiting,NH3Nconcentrationswere

examinedacrossandthroughoutthebasin.

ThenitrificationratekineticsoftheMBBRbasinwereevaluatedbyconductingseveralbench

scalebatchanalyses. Eachkineticexperimentwasdesignedtorepresentthenitrificationprocess

occurringwithinthefullscaleMBBR. NH3Noxidationwasanalyzedasafunctionofmedia

specificsurfaceareawhilekeepingallothervariables(i.e.,temperatureandDO)relatively

constant. ByfittingtheNH3Nreductioninthebenchscaletests,anappropriatemodelforthe

nitrificationkineticsoccurringinthefullscaleMBBRcanbeselected.

MaterialsandMethods

ThesampleanalysesofMBBRtemperature,DO,pH,CBOD5,SBOD5,TSS,TKN,NH3N,NO2N,

NO3N,andalkalinitywereallperformedattheMoorheadWWTFlaboratory. Allanalyseswere

conductedaccordingtotheStandardMethodsfortheExaminationofWaterandWastewater

(APHAetal.,1998). Whereapplicable,proceduresestablishedforlaboratorycertificationthrough

theMinnesotaDepartmentofHealth(1990)werealsoutilized. Qualityassuranceandquality

controlprocedureswereusedduringallanalysesandincludedatleastonereagentblankper

analysisset,atleastoneduplicateanalysispersetwithatleasttenpercentofallsamplesbeing

duplicateanalyses,andatleastonespikedsampleanalysispersetwithatleasttenpercentofall

samplesbeingspikedsampleanalyses.

Atotaloffourtracer(dye)studieswereconductedtoevaluatethehydrauliccharacteristicsof

theMBBRbasin. Fourdifferentinfluentflowratesandtwodifferentair(mixing)flowrateswere

utilizedtoevaluatethehydraulicimpactsassociatedwithdifferentflowandmixingrates. The

10


16/39

tracerevaluationswereperformedusingapulseinputof208L(55gallons)ofRhodamineWTdye

(Norlab,Inc.,Amherst,Ohio). Dyewasaddedatasinglepointneartheinfluentpipeinthreeof

thetests. Inafourthtest,designedtoevaluateinfluentflowdistribution,influentflowwassplit,

aswellasdye,andinjectedintothebasinattwopoints,oneattheinfluentpipeandonedirectly

oppositetheinfluentpipe. Dyewasaddedduringnormaloperationwithcontinuousflowthrough

theMBBRbasinforallfourtests. Aftertheadditionofdye,effluentsampleswerecollectedfrom

theMBBReffluentcontrolstructureatselectedtimeintervals. Theabsorbanceoffilteredeffluent

sampleswasmeasuredatawavelengthof555.6nmonaspectrophotometer(HachCompany,

Loveland,Colorado). Thedyeconcentrationwasdeterminedbaseduponacalibrationcurvefor

dyeconcentrationversusabsorbance(alsoatawavelengthof555.6nm)developedfromknown

dilutionsofdyeinfilteredPolishingPondNo.1effluent. Table3specifiesthesetupforeachof

thefourtracerstudies. Influentflowisreportedforthedurationofeachtestperiod.

Table3.TracerEvaluationSetup.

TestNo. InfluentFlowRate

m3/d(mgd1)

Airflow

standardm3/min(scfm2)

InjectionPoint

1

16,656

(4.40)

127

(4,500)

Influent

pipe

2 17,942(4.74) 127(4,500) Influentpipe&

directlyopposite

3 20,214(5.34) 212(7,500) Influentpipe

4 24,984(6.60) 127(4,500) Influentpipe1mgd=Milliongallonsperday.

2scfm=Standardcubicfeetperminute.

AnalysisofNH3Ndistributionwithinthebasinwasconductedtofurtherexaminethehydraulic

characteristicsoftheMBBRsystem. Grabsampleswerecollectedandanalyzedfromthebasinat

tendifferentsamplelocationsaroundtheperimeter. RefertoFigure2forsamplelocationsand

identifications. TheproceduresforthegrabsampleanalysesfollowedandwereconductedaccordingtotheprovisionsoftheStandardMethodsfortheExaminationofWaterand

Wastewater(APHAetal.,1998).

FromDecember2003throughMay2005,thirteenlaboratorybenchscalebatchtestswere

conductedtoevaluatethenitrificationratekineticsoftheMBBRprocess. Samplesofmediawere

collecteddirectlyfromthefullscaleMBBRtoensureanestablishedpopulationofnitrifying

biomass. Themediawasplacedin15Liter(4gallon)benchscalebatchreactorscontainingnon

nitrifiedeffluentfromPolishingPondNo.1. Themediafillfractioninthevarioustestsranged

fromlessthanonepercent(


17/39

RESULTSANDMODELDEVELOPMENT

Monitoringandexperimentalresultsareprovidedwithintoillustratethedesignand

operationalparametersidentifiedasaffectingtheperformanceofthefullscaleMBBRsystem.

Fullscalemonitoring,basinhydraulicanalysis,andnitrificationkinetictestingresultsand

discussionsareincluded.

AnalysisoftheFullScaleMBBRMonitoringData

TheaveragemonthlyinfluentandeffluentNH3NconcentrationsfromApril2003toApril2005

areshowninFigure6. NH3NremovalefficiencythroughtheMBBRbasinisillustratedinthe

figure. AsevidentbytheremovaldatainFigure6,theefficiencyofnitrificationintheMBBRwas

reducedduringperiods(JanuarytoMarch2005)ofhighinfluentTSSandCBOD5concentrations.

WhentheCBOD5concentrationswereelevatedintheMBBRduringtheseperiods(>20mg/L),

competitionfromheterotrophicbacteriareducedthegrowthandefficiencyofnitrifying

microorganisms. TheperiodsofelevatedTSSandCBOD5wereassociatedwithpoorsettlinginthe

finalclarifiersandactivatedsludgesystemupsets.AsindicatedbythedataintheFigure6,theinfluentNH3NconcentrationstotheMBBRbasin

commonlyexceededthedesigninfluentconcentrationof17.0mg/L. Despitethehigherthan

expectedinfluentconcentrations,theaverageeffluentNH3Nwaswellbelowthe8.0mg/Llimit

permittedduringsummermonths. Table4providesaseasonalandoverallcomparisonofthe

MBBRbasinforthefirst24monthsofoperation.

TheNH3NremovalacrosstheMBBRbasinwasreducedduringcoldweathermonthswhen

comparedtowarmermonths. Duringthecoldweathermonths,theaverageinfluentNH3N

concentrationswereslightlyelevated,howeverastheaverageloadingremainedrelatively

unchangedduringcoldandwarmweathermonths,thedataappearedtoindicatetemperature

hadaneffectontheperformanceoftheMBBR.

Theoperationalproceduresandschedulingofbiosolidssupernatantreturnflowhasbeen

erratic. ThereturnflowofthesupernatanttotheWWTFheadworksappearedtodirectlyaffect

theperformanceoftheMBBRbasinastheNH3Nconcentrationofthesupernatantwastypically

between1,500and2,000mg/L.

12


18/39

0

5

10

15

20

25

30

35

Apr03M

ay03Jun

03Jul03Au

g03Se

p03Oct03No

v03De

c03Jan04Feb

04M

ar04Apr04M

ay04Jun

04Jul04Au

g04Se

p04Oct04No

v04De

c04Jan05Feb

05M

ar05Apr05

NH3

N

(mg/L)

0

10

20

30

40

50

6070

80

90

100

NH3

N

Removal(%

)

InfluentNH3N EffluentNH3N

EffluentNH3NSummerLimit(8mg/L) InfluentNH3NDesign(17mg/L)

NH3NRemoval Figure6.MBBRNH3NMonthlyAverageData.

Table4.SeasonalMBBRPerformance.

Parameter JuneSeptember

(warmweather)

DecemberMarch

(coldweather)

Overall

(24months)

EffluentTemperature,C 18.7 12.0 15.3

InfluentNH3N,mg/L 20.8 24.4 22.3

NH3NLoading,g/m2/d 0.98 0.96 0.97

NH3NRemoval,% 88.0 63.6 75.2

EffluentNH3N,mg/L 2.75 10.0 6.84

AsillustratedbythedatainFigure7,periodsofsupernatantreturnalsocorrelatedwithperiodsofhighinfluentNH3Nconcentrations. Theinformationcontainedinthefollowingfigures

soughttoprovideaclearerunderstandingoftheimpactofsupernatantreturnonthe

performanceoftheMBBRsystem. Figure8showedthetotalMBBRbasinNH3Nloading,the

portionoftheNH3Nloadingcontributedbythesupernatant,influentandeffluentNH3N,and

headworkssupernatantreturnflowdatafortheperiodofJanuarytoMarch2004. Asevidentby

thedatainthefigure,thesupernatantloadrepresentedasignificantportionofthetotalMBBR

NH3Nloading.

13


19/39

0

10

20

30

40

50

60

70

80

A

pr03

M

ay03

Jun

03Jul03

Aug

03

Sep

03

O

ct03

Nov

03

D

ec03Jan

04

Feb

04

M

ar04

A

pr04

M

ay04

Jun

04Jul0

4

Aug

04

Sep

04

O

ct04

Nov

04

D

ec04Jan

05

Feb

05

M

ar05

A

pr05

NH3N(mg/L)

5

10

15

20

25

30

35

40

45

SupernateFlow(GP

M)

InfluentNH3N EffluentNH3N SupernateFlow

Figure7.SupernatantReturnFlowandMBBRPerformance.AtthebeginningofJanuary2004,theCityofMoorheadWWTFwasreturningbiosolids

supernatanttotheheadworksatarateofapproximately26gallonsperminute(GPM).

Coincidently,theNH3NloadingandinfluentandeffluentconcentrationsintheMBBRbasinwere

abovethepreviouslyreportedaveragevalues(approximately0.97g/m2/d,22mg/L,and7.0mg/L,

respectively).

However,whentheWWTFceasedsupernatantreturnflowonJanuary9,2004theloadingas

wellasinfluentandeffluentNH3NconcentrationsintheMBBRreturnedtoaveragelevels.

January2004wasalso(aspreviouslyreported),onaverage,thecoldestmonthsincetheoperation

oftheMBBRbegan,indicatingthebasinisimpactedmoreprofoundlybysupernatantreturnthan

temperature. InFebruary2004,supernatantwasagainflowingandtheMBBRbasinNH3Nloading

andconcentrationsrespondedbyincreasingaboveaveragelevels. Theflowofsupernatantwas

heldrelativelyconstantduringthemiddleofFebruary2004andtheMBBRbasinappearedto

acclimateastheeffluentNH3Nconcentrationsplateauandeventuallydecline. However,as

evidentbythedata,whensupernatantflowwasincreasedthroughoutMarch2004theNH3N

againascendedbeyondaverageconditions. TheMBBRbasinNH3Nloadingandconcentrations

respondedalmostimmediatelyoncethesupernatantreturnflowwasreducedonMarch21,2004.

Becauseofthelowgrowthrateofnitrifyingorganisms,theMBBRisnotabletorespond

immediatelytotheadditionalNH3Nloadingassociatedwiththesupernatantreturn. However,

followingperiodsofconsistent,steadyreturnflowrates,itappearsthenitrifiersareabletoadapttotheincreasedNH3Nconditions. Itshouldbenoted,theMBBRcannotachievethesame

effluentNH3Nconcentrationsatlowerloadings,whencomparedtohigherloadings,duetolower

nitrifiergrowthratesatreducedloadings(degaardetal.,1994).Whensupernatantreturnwas

occurringduringthesixmonthperiodin2004,theflow,NH3Nloading,andNH3Ninfluent

concentrationsforboththeMBBRbasinandthesupernatantareshowninTable5.

14


20/39

0

5

10

15

20

25

30

35

40

45

50

1Jan0

4

8Jan0

4

15Jan

04

22Jan

04

29Jan

04

5Feb

04

12Feb

04

19Feb

04

26Feb

04

4Mar0

4

11Ma

r04

18Ma

r04

25Ma

r04

NH3

N(mg/L)and

SupernateFlow(G

PM)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

NH3NLoading(g/m

2/d)

SupernateFlowrate InfluentNH3N

EffluentNH3N TotalMBBRNH3NLoading

SupernatantNH3NLoading

Figure8.JanuaryMarch2004SupernatantFlowandMBBRResponse.

Table5.MBBRConditionsDuringSupernatantReturn.

Parameter

TotalMBBR

Conditions

Supernatant

Conditions

Flow

Minimum

Average

Maximum

3.53mgd1

4.22mgd

8.22mgd

1.00gpm2

22.5gpm

41.0gpm

InfluentNH3N

Minimum

Average

Maximum

13.4mg/L

27.1mg/L

42.9mg/L

1,254mg/L

1,813mg/L

2,149mg/L

NH3NLoading

Minimum

Average

Maximum

0.57g/m2/d

1.18g/m2/d

1.98g/m2/d

0.13g/m2/d

0.78g/m2/d

1.30g/m2/d1mgd=Milliongallonsperday.

2gpm=Gallonsperminute.

Asevidentbytheabovedata,timesofsupernatantreturncorrelatedwithperiodsofNH3N

loadingthatexceededtheMBBRdesignmaximumvalueof1.13g/m2/d. Theimpactsfromthe

additionalNH3Nloadingassociatedwiththesupernatantreturnwereintentionallyexcluded

duringthedesignoftheMBBR. Duringmonthswhenpermitlimitsareenforced,theWWTF

establishedoperationalprocedurestoceasesupernatantreturnactivitiestoavoidNH3N

15


21/39

dischargeviolations. Althoughthereturnofsupernatantistemporarilyhaltedwhenpermit

limitationsareenforced,toimprovetheoperationalstabilityoftheMBBRandreducetheoverall

NH3NconcentrationsdischargedtotheRedRiver,theMoorheadWWTFshouldexploreequalized

returnflowofsupernatant.

TheMoorheadMBBRbasinwasmonitoredundervariousflowandloadingconditionstogain

animprovedunderstandingofthesystemandtoevaluatethecurrentoperationalpractices. Flow

throughtheMBBRhadvariedinresponsetowetweatherconditions,butduringtheremainderof

thetwentyfourmonthperiodsinceoperationwasinitiated,theflowremainedrelativelystable

andwellwithinthedesignconditions. TheMBBRdemonstratedthecriteriaofaneffectivetertiary

nitrifyingsystemeventhoughtheaverageinfluentloading(0.97g/m2/d)hadbeenconsistently

greaterthanaveragedesignloading(0.84g/m2/d). DespitethehigherthananticipatedNH3N

loadings,theNH3Nremovalefficiencyofthebasinwasonaverage75.2%;morethan10%higher

thanthepredictedrate(refertoTable2).

Sinceoperationbegan,theoverallperformanceoftheMBBRbasinhadbeenvariable. Colder

temperaturesappearedtoreducethenitrificationrateinthebasin. Althoughtheremoval

efficiencywasreducedincoldweathermonthstheMBBRbasinconsistentlyremovedmorethan

64%oftheinfluentNH3Nreceivedduringthecolderperiods. Therefore,thesystemhas

demonstratedtheabilitytooxidizeammoniaevenatlowtemperatures. BecausethesystemrarelyexperiencedpHshifts,thenitrifyingorganismswithintheMBBRappearedtoacclimateto

thelowerthanoptimumpHcondition.

InregardtothefullscaleMBBRbasinmonitoring,theoperationalreturnofsupernatantfrom

thebiosolidsstoragefacilitytotheheadworksoftheWWTFhasbeenshowntohavethegreatest

impactontheoverallperformanceoftheMBBRbasin. Asevidentbythedata,thesupernatant

loadrepresentsasignificantportionofthetotalMBBRNH3Nloading. Becauseofthelowgrowth

rateofnitrifyingbacteria,theMBBRbasinwasunabletorespondimmediatelytotheelevated

NH3Nloadingassociatedwiththesupernatantreturnflow. Becauseofthevariabilityininfluent

NH3Nconcentrationsandloadingsduetothereturnofsupernatant,equalizedandregularly

scheduledsupernatantflowshouldbeimplementedattheMoorheadWWTF. Theproposed

actionwill

result

in

more

consistent

loading

to

the

basin

and

would

allow

for

greater

treatment

efficiencyacrosstheMBBR,duetotheobservedadaptabilityofnitrifyingbacteriainthesystem.

BecauseequalizedreturnflowwillonlystabilizetheNH3NloadingtotheMBBR,sidestream

treatmentofthesupernatantcouldalsobeexploredtoreducethepotentialforoverloadingthe

system. SidestreamtreatmentwillreducetheadditionalNH3Nloadingassociatedwiththe

supernatant;howevertheincreasedcoststotreatthesupernatantseparatelymayprohibitthis

action. Theadditionofmediatothebasincouldalsobeexplored,astheadditionalsurfacearea

willallowforgreaterbiomasswithintheMBBR.

HydraulicAnalysis

To

examine

the

hydraulic

characteristics

and

select

an

appropriate

hydraulic

model

to

simulate

thefullscaleMBBRsystem,tracerstudieswereperformed. Additionally,NH3Ndistributioninthe

MBBRwascarriedouttoevaluateflowthroughthebasinandevaluatethepotentialforbasin

shortcircuitingand/ordeadzones.

16


22/39

TracerStudies

Formodelingpurposes,anunderstandingofflowthroughtheMBBRbasinwasnecessaryto

determinehowthereactorbehaveshydraulically. Toevaluatethehydrauliccharacteristicsofthe

MBBRbasin,aseriesofpulseinputtracerstudieswereperformed. Atotaloffourtracerstudies

wereconductedatfourinfluentflowratesandtwodifferentair(mixing)flowrates. Variousflow

rates,measuredforthedurationofeachtest,wereutilizedtoevaluatethechangeinbasin

hydrauliccharacteristicsassociatedwithflow. Increasedmixingwasalsoexaminedtodetermine

ifelevatedaeration(mixing)reducedthepotentialfordeadzoneswithintheMBBR. Inonetest,

flowwasequallysplitbetweenopposingendsoftheinletsideoftheMBBRbasintoevaluatethe

impactsassociatedwithimprovedinfluentflowdistribution. Theflowconditionsforallfourtracer

analysesaredisplayedinTable6.

Table6.MBBRFlowConditionsDuringTracerAnalysis.

Test

No. OperationalConditions

Air(Mixing)

Flow(scfm1)

Influent

Flow(mgd2)

1 Averagedailyflow,normalmixing 4,500 4.402 Splitinfluentflow,normalmixing 4,500 4.74

3 Elevatedaeration(mixing)rate 7,500 5.34

4 Peakflow,normalmixing 4,500 6.601scfm=Standardcubicfeetperminute.

2mgd=Milliongallonsperday.

Basedupontheeffluenttracerdataobtainedfromthestudies,thehydrauliccharacteristicsof

theMBBRbasinwereevaluatedbyassumingthesystemperformedasanumberofequalvolume,

continuousflowstirredtankreactors(CFSTRs)inseries. Thetrendingoftracerdataindicatedthe

systembehavesmoresimilartoaseriesofCFSTRsasopposedtoasingleCFSTRoraplugflow

reactor. TosimulatethetracerresponsethroughtheseriesofCFSTRs,thefollowingnonreactive

pulseinputtracerequationwasutilizedassuggestedbyTchobanoglousandSchroeder(1987).

= n

tn

oT e

n

t

n

CC /

1

/)!1(

, (42)

where CT=theoreticaleffluentdyeconcentrationattimet,mL/L

Co=initialdyeconcentration,mL/L

t=time,min

n=numberofCFSTRsinseries

=

hydraulic

detention

time,

min

=totalreactorvolume/flowrate

UsingEquation(42),theactualeffluenttracerresponsecurvewasstatisticallyfittoa

theoreticaleffluenttracerresponsecurvebyadjustingtheeffectivebasinvolumetominimizethe

errorbetweentheactualandtheoreticalcurves,utilizingthemethodofleastsquares. The

effectivebasinvolumedoesnotcontainthereactorvolumeassociatedwithstagnantflow,or

deadzones(i.e.,effectivevolume=totalvolumestagnantvolume). Asaresult,thepotentialfor

17


23/39

flowtoshortcircuitorbypasstheMBBRbasinisrepresentedbythedeadvolumeofthebasinfor

eachflowrateandmixingcondition.

TheresultofatypicaltracerstudywaspresentedinFigure9.Theactualfullscalefield

measuredbasineffluentdyeconcentrations,theoreticaltracerresponsecurvesfor2and3ideal

CFSTRs,andbestfittracerresponsecurveswithassumedeffectivevolumeswereincludedinthe

figure. Table7summarizestheresultsofthefourfullscaletracerstudies.

0.00

0 50 100 150 200 250 300Time(min)

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

EffluentDyeConcentration(mL/L)

Actual 2CFSTRs 2CFSTRs,92%effectivevolume 3CFSTRs

Figure9.TracerTestNo.4Response(at6.60MGDand4,500scfm).

Table7.FullScaleTracerAnalysisSummary.

Test

No.

Influent

Flow

Condition

Air

(Mixing)

Flow

(scfm1)

Influent

Flow

(mgd2)

Theoretical

HDT3

(hours)

Effective

Volume

(%)

Effective

HDT3

(hours)

R

1 Normaloperation 4,500 4.40 4.3 76 3.3 0.86

2 Splitflow 4,500 4.74 4.5 85 3.8 0.72

3 Normaloperation 7,500 5.34 3.5 81 2.9 0.91

4 Normaloperation 4,500 6.60 2.8 92 2.6 0.871scfm=Standardcubicfeetperminute.


3HDT=Hydraulicdetentiontime.

TheresultsofthetracerstudiesindicatedtheMBBRbasincouldbehydraulicallymodeledas

twoequalvolumeCFSTRsinserieswithaneffectivevolumelessthanthefullbasinvolume. The

traceranalysisimpliedtheMBBRbasinwassubjecttosomedegreeofshortcircuitingbetween

18


24/39

theinfluentpipeandeffluentcontrolstructure. Tofurtherillustratethedegreeofshortcircuiting

asitrelatestoflowthroughtheMBBR,thebasineffectivevolumeasafunctionofflowratewas

presentedinFigure10. Asevidentbytheresults,alinearrelationshipexistedbetweenbasinflow

andeffectivevolumefornormaloperationwithrespecttoinfluentflowdistribution. Thesplit

flowconditionwasperformedtoevaluatethehydraulicimpactsassociatedwithimproved

influentflowdistribution,andtherefore,wasexcludedfromtherelationshipcalculation.

y=0.0723x+0.435

R2=0.9851

0%

10%

20%

30%40%

50%

60%

70%

80%

90%

100%

4.0 4.5 5.0 5.5 6.0 6.5

Flowrate(MGD)

Effective

MBBRVolume(%)

7.0

NormalOperation SplitInfluent Increased(Air)Mixing

Figure10.EffectiveVolumeasaFunctionofInfluentFlow.Theshortcircuitingofinfluentflowtotheeffluentstructureappearedtoberelatedtotheinlet

pipingarrangementwhichdischargestheinfluentflowinadirectiontransversetoflowthrough

theMBBRbasin. AsapparentbythedatainFigure10,higherflowrates,withgreater

momentums,distributedinfluentflowsfurtheracrosstheinfluentendofthebasin(Figure2)

resultinginbetterdistributionandanincreasedeffectivebasinvolume. Enhancedmixing

intensityintheMBBRbyincreasedairflowdidnotappeartoimprovethebasineffectivevolume,

asshownbytheincreasedmixingdatumpointinFigure10. Bysplittingtheinfluentflow

betweenthetwoopposingsidesattheinfluentendoftheMBBRbasin,thedataindicatedan

increaseineffectivevolumeduetoimprovedinfluentflowdistribution,asevidentbythesplit

influentdatumpointinFigure10.

NH3NDistributionintheMBBR

TofurtherexaminethehydrauliccharacteristicsoftheMBBR,NH3Ndistributiontestingwas

performed. NH3Nconcentrationswereexaminedacrossandthroughoutthebasintodetermine

iftheMBBRwasexperiencingzonesofpoormixingorshortcircuiting. TheNH3Ndistribution

analyseswereperformedatthreeseparateflowratesandtwodifferentaeration(mixing)rates.

Theelevatedmixingscenariowasperformedtodetermineifincreasedaerationloweredthe

19


25/39

potentialforzonesofpoormixingwithintheMBBR. ConditionsintheMBBRbasinduringeachof

thethreeNH3NdistributiontestsarelistedinTable8.

Table8.MBBRConditionsDuringNH3NDistributionAnalysis.

Test

No.

OperationalConditions

Air(Mixing)

Flow(scfm1)

Influent

Flow(mgd2)

Influent

NH3N

(mg/L)

Basin

Temp.(C)

1 Averagedailyflow,normalmixing 4,500 4.40 13.9 14.2

2 Elevatedaeration(mixing) rate 7,500 5.34 15.5 16.9

3 Peakflow,normalmixing 4,500 6.60 15.5 16.91scfm=Standardcubicfeetperminute.


OneoftheNH3NdistributionresultsaredisplayedinFigure11. Theinletpipeislocatedat

SamplePoint2,andtheeffluentstructureispositionedadjacenttoSamplePoint6inthe

followingfigure. ThecorrespondingsamplelocationsarealsoidentifiedinFigure2.

EastMiddle

West

0

1

2

3

4

5

6

7

8

NH3N(mg/L)

2

3

4

5

6

1

10

98

7

Figure11.NH3NDistributionNo.1(at4.40MGDand4,500scfm).

AllofthedistributiondataindicatedhigherNH3Nconcentrationsatornearthebasininlet

(SamplePoint2). DuringnormalMBBRbasinoperationatlowerinfluentflowrates,asteepNH3N

concentrationgradientexistedattheinletendtransversetotheflowthroughtheMBBR. An

increaseinaeration(mixing)rateoranincreaseininfluentflowhadthepropensitytomovethe

highestNH3Nconcentrationtowardthemiddleoftheinfluentendindicatingaslight

improvementwithregardtoinfluentdistribution. Forallthreescenarios,aconsiderable

differenceinNH3Nconcentrationsexistedbetweenpairedsamplepointslocatedalongthe

longitudinalsidesoftheMBBRbasin. NH3Nconcentrations,alongthelongitudinalsideofthe

basincontainingtheinletpipe,weremeasurablygreaterthanthosealongtheopposite(east)side

ofthebasin. Thetrendconfirmedinfluentflowshortcircuitedalongtheinletsideofthebasin

andcontributedtoanincreasedeffluentNH3Nconcentration.

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HydraulicAnalysisDiscussion

ToevaluatethedesignandoperationalparametersofthefullscaleMBBR,NH3Ndistribution

resultswereusedincombinationwiththehydraulictracerevaluations. Tracerstudiesindicated

theMBBRsystemcanbesimulatedasanumberofCFSTRsinserieswithaneffectivevolumeless

than

that

of

the

total

basin

volume.

Recognizing

the

influent

piping

arrangement

to

the

MBBR

basindischargesflowinadirectiontransversetotheflowofwastewaterthroughthebasin,the

NH3Ndistributionresultsindicatedhigherflowrates,withelevatedvelocitiesandmomentum,

drovetheflowtowardsthecenteroftherectangularbasin,andtherefore,appearedtoimprove

thedistributionofflowacrosstheinfluentendofthebasin. Byimprovingtheflowdistribution,

theentirebasinvolumewasmoreeffectivelyutilized,therebyincreasingtheeffectivebasin

volumeandreducingtheprobabilityforbypassfloworshortcircuiting.

Byimprovingthedistributionofinfluentflowacrosstheinletsideofthebasinandmore

effectivelyusingtheentirebasinvolume,thenitrificationperformanceoftheMBBRcouldbe

improved. FortheMoorheadMBBRconfiguration,severalalternativesforenhancedinfluent

distributionareavailablesuchastheinstallationofabaffleattheinletpipeortheintroductionof

influentatmultiplepointsacrosstheinletsideofthebasin. TheNH3Ndistributiondatarevealed

increasedmixingalone,throughtheuseofhigheraerationrates,withintheMBBRdidnot

improvetheinfluentflowdistribution. However,anincreaseinmixingfocusedsolelyattheinlet

wasnotexaminedduringtheproject.

TheresultsofthehydraulicevaluationsindicatedthatMBBRsystemscanbeoptimizedby

ensuringevendistributionofinfluentflowtomoreeffectivelyutilizetheentirereactorvolume. In

additiontoimprovedinfluentpipingarrangements,areactorwithagreaterlengthtowidthratio

mayalsoimproveinfluentflowdistribution. Cautionshouldbeusedwhendesigningbasinswith

highlengthtowidthratiosastheseratiosmayresultinelevatedflowthroughvelocitiesandthus

promotemediamigrationtowardstheeffluentendofthereactor,potentiallyresultinginan

unevendistributionofmediathroughoutthebasin.

NitrificationKinetics

TheMBBRisanattachedgrowthnitrificationsystem. Inattachedgrowthsystems,substrateis

consumedatthesurfaceofthebiofilm(MetcalfandEddy,2003). Becauseofthebiofilmlayer

characteristicsonthemedia,theinnerbiomasscanbeconsideredinactivewithrespecttotherate

ofnitrification(GradyandLim,1999). Therefore,foranalyticalpurposes,theassumptionis

implementedthatonlythesurfaceareaofthebiofilmpresentonthemediaisactiveand

contributingtonitrification.

Datafrombenchscalebatchtestscanbeusedtoindirectlyanalyzenitrificationkineticswith

thefollowingattachedgrowthsaturationorMonodtyperelationship(MetcalfandEddy,2003):

NK

N

N

m

+= , (43)

where =nitrifierspecificgrowthrate,d1

m=maximumnitrifierspecificgrowthrate,d1

N=NH3Nconcentration,g/m3

21


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KN=halfsaturationconstant,g/m3

Basedontheabovegrowthkinetics,thenitrificationrateinabatchreactorcanbewrittenas:

Y

X

NK

Nr

dt

dN

N

m

n+

== , (44)

where rn=nitrificationrate,g/m3/d

X=activebiomassconcentrationinthereactor,g/m3

Y=nitrifieryield,gbiomass/gsubstrateutilized

Forbiofilmsystems,theactivebiomassconcentrationcanbewrittenas:

V

hAX ab

=

, (45)

where A=totalmediasurfacearea,m2

b=biomassdensity,g/m3

ha=activebiomassthickness,m

V=volumeofthereactor,m3

Assumingthebiomassdensityandactivebiomassthicknessremainrelativelyconstantthroughout

thebatchtests,Equation(44)canbemodifiedto:

s

N

m ANK

Nr

dt

dN

+= ' , (46)

where rm=maximumsubstrateutilizationrate,g/m2/d

= abm hY

As =specificmediasurfaceareainthereactor,m2/m3

=V

A

BasedonEquations(44)and(46),rnisafunctionofthetotalmediasurfaceareainthereactor.

IntegratingEquation(46)betweentheinitialNH3Nconcentration(No)andtheNH3N

concentrationattimet(Nt),thefollowingrelationshipisdeveloped(Tchobanoglousand

Schroeder,1987):

)(ln' tot

oNsm NN

N

NKtAr +

= (47)

Assumingthequantityofactivenitrifyingbiomasswasdirectlyrelatedtothemediasurface

areaprovidedwithinthereactor,theexpressioneliminatestheneedtomeasuretheactive

22


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nitrifyingbiomass. UsingEquation(47),thebenchscaleNH3Ndatawasplottedasafunctionof

timetodeterminethenitrificationkineticparameterswherebyrmwasexpressedasgNH3

N/m2/min. Thehalfsaturationconstant,KN,iscommonlyreportedas1.0mg/Lfornitrifying

systemswithaveragetemperaturesrangingbetween10and20C(USEPA,1993). Therefore,the

halfsaturationconstantfortheMBBRbasinwasreasonablyassumedas1.0mg/L. Withthis

assumption,thermvaluewasstatisticallyfittotheobserveddatafromthebenchscaletestsusing

linearregressiontechniques.

Aspreviouslydemonstrated,nitrificationwithintheMBBRbasinappearstobeaffectedby

temperature. Lowerwatertemperaturesinhibittheactivityandgrowthofnitrifying

microorganisms(USEPA,1993). Therateofnitrificationhasalsobeenshowntobedependent

upontemperaturebyaffectingtherateofsubstratediffusiontothebiomass(GradyandLim,

1999). Usingthefollowingequation(TchobanoglousandSchroeder,1987),rmfromthebench

scaleanalysiswasadjustedto20C.

)20(

20 ''T

mTm

o

rr=

]

, (48)where rm20=maximumsubstrateutilizationrateat20C,g/m2/d

rmT=maximumsubstrateutilizationrateattemperatureT,g/m2/d

=temperaturecoefficient:

=1.047(4 T 20C)

=1.056(T>20C)

AlthoughmostmicroorganismsgrowpoorlyoutsidethepHrangeof6to8,nitrifyingbacteria

areparticularlysensitive(Quinlan,1984). Therateofnitrificationreachesamaximumarounda

pHof8.5anddeclinesforlowervalues(GradyandLim,1999). Conversely,ifasystemhas

acclimatedtoalowpH,rmislesseffectedthanifthepHissuddenlyshifted(USEPA,1993). The

followingequationcanbeutilizedtosimulatetheinfluenceofpHonthemaximumsubstrate

utilizationrate(Siegrist,1987):

[ 1)5.6(101'' += pHmom rr , (49)where rm=maximumsubstrateutilizationrateatagivenpH,g/m

2/d

rmo=maximumsubstrateutilizationrateatanoptimumpHof8.5,g/m2/d

Atypicalcurveforammoniareductionversustimeforoneofthethirteenlaboratorybench

scalekineticanalysesisshowninFigure12. Equation(47)wasutilizedtofittheobservedNH3N

datatotheMonodtyperelationship. Resultsfromallthirteenbenchscaleanalysesare

summarizedinTable9. Thedateforeachbenchscalestudywasintendedtorepresenta

relativelysteadystateperiodofoperationforthefullscaleMBBR. Toillustratetheoperationof

thefullscaleMBBRduringandprecedingthebenchscaleanalyses,Table10providesfullscale

MBBRdataforthedayofeachanalysis.

Asindicatedbythecoefficientofdetermination(R2)valuesinTable9,allofthelaboratory

benchscaledataprovidedanexcellentfittotheMonodtyperateexpression. However,the

maximumsubstrateutilizationrate,afteradjustingtoacommontemperatureandpH,exhibited

variation,rangingfrom2.024to4.418g/m2/dwithanaverageof3.370g/m2/d. Aspecific

investigationintothepotentialfactorscausingthevariationwasnotconducted. However,the

23


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variationmayhavebeenrelatedtotheconditionsinthefullscaleMBBRatthetimeeachtestwas

conducted(i.e.,NH3Nloading,DOversusNH3Nratelimitingconditions)and/ortheassumption

thequantityofactivenitrifyingbiomasswasdirectlyrelatedtothemediasurfaceareaprovided

withintheMBBRbasin.

rm=0.0015g/m2/min

MediaFill=30%

Date=4/05/2005

R2=0.9979

0

2

4

6

8

10

12

14

16

0 20 40 60 80 100 120 140

NH3

N(mg/L)

Time(min)

BatchData Simulation Figure12.LaboratoryBenchScaleData.

Table

9.

Summary

of

Laboratory

Bench

Scale

Analysis.

Date Measured

rm

g/m2/min

Media

Fill

Fraction

%

rmT=20C

pH=8.5

g/m2/min

rmT=20C

pH=8.5

g/m2/d

R2

12/08/030.0018


30/39

Table10.FullScaleMBBRDatafortheDateofEachBenchScaleAnalysis.

Date

Flow

mgd1

Influent

NH3N

mg/L

Influent

NH3N

g/m2/d

Effluent

NH3N

mg/L

Effluent

Temp

C

Effluent

DOmg/L

EffluentpH

12/08/03 4.49 12.7 0.59 0.12 13.0 5.4 7.22

09/22/04 4.91 12.1 0.61 0.30 18.3 8.6 7.24

09/30/04 4.61 21.5 1.02 4.90 18.1 6.3 7.13

04/05/05 4.56 14.6 0.68 1.00 16.0 4.3 7.04

05/03/05 4.25 27.5 1.20 7.70 15.0 4.1 6.95

05/12/05 4.62 24.6 1.17 7.50 14.0 5.9 6.911mgd=Milliongallonsperday.

FullScaleMBBRSimulation

Tofurtherexploreandevaluatethecriticaldesignandoperationalparametersoftheseparate

stagenitrifyingMBBR,amodelofthesystemwasdevelopedutilizingthedatafromthehydraulic

andbenchscalekineticstudies. AsimulationprogramconsistingoftwoCFSTRsinserieswithan

effectivevolumelessthanthetotalreactorvolumecouldbeutilizedtosimulatethehydraulic

characteristicsoftheMBBRbasin. However,toincorporatetheresultsofthekineticevaluations

themodelwasmodifiedtoasystemcontainingtwoCFSTRsinserieswithabypassflow

representinghydraulicinefficiencies. Figure13containsavisualrepresentationofthecombined

model.

Theaveragermvalueof3.37g/m2/dobtainedfromthelaboratorybenchscalekineticanalyses

alongwiththeassumedKNconcentrationof1.0mg/Lwereutilizedformodelinput. Toevaluate

theunknownbypassflowinthemodel,tworelativelysteadystateperiodsofoperationwere

selected. Onecoldweatherperiod(January2004)andonewarmweatherperiodwereevaluated(June2004).Toinitiatethemodel,rmwasadjustedfromthevalueof3.37g/m

2/d(pH=8.5and

temperature=20C)toreflecttheactualeffluenttemperatureandpHconditionspresentinthe

fullscaleMBBR,usingEquations(48)and(49). SimulatedeffluentNH3Nconcentrationswere

matchedtoactualeffluentNH3NconcentrationsfortheactualinfluentflowandinfluentNH3N

concentrationbyadjustingbypassflowratesasapercentageoftheinfluentflow. Theaverage

bypassflowvaluewasthencalculatedandinputintothemodel. Effluentconcentrations

predictedbythemodelarecomparedtoactualeffluentNH3NconcentrationsinFigures14and

15,respectively.

25


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Qbypass,Ci

Q,Ci Q,Ce

Q

Qbypass,Ce1

Q

Qbypass,

Ce2

where, Q = Influentflow,m3/d

Qbypass= Bypassedflow,m3/d

Ci= InfluentNH3Nconcentration,g/m3

H = DetentiontimeineachCFSTR,days

Ce1=EffluentNH3NconcentrationfromCFSTR1

andInfluentNH3NconcentrationtoCFSTR2,g/m3

Ce2= EffluentNH3NconcentrationfromCFSTR2,g/m3

CFSTR

= Continuous

flow

stirred

tank

reactorKN = Halfsaturationconstant,g/m

3

r m = Maximumsubstrateutilitzationrate,g/m2/d

Ce= EffluentNH3Nconcentration,g/m3

As= Specificmediasurfaceareawithinthereactor,m2/m3

(Ce1 Ce2)(KN +Ce2)

r mA s Ce2 H = H =

(Ci Ce1)(KN +Ce1)

r mA s Ce1

CFSTR1 CFSTR2

Figure13.FullScaleMBBRModel.

FortheperiodanalyzedinFigure14,thecomputeddailybypassflowsforthefullscaleMBBR

rangedfrom10%to26%oftheinfluentflowwithanaveragevalueof17%. Influentflowsranged

from3.6mgdto3.9mgdwithanaverageof3.7mgd. BasedonFigure10,theaverageflowrate

wouldcorrespondtoapredictedbasindeadvolumeof30%.

0

5

10

15

20

25

8Jan 13Jan 18Jan 23Jan 28Jan 2Feb

Date(2004)

NH3

N

(mg/L)

0

1

2

3

4

5

Flow

(mgd)

Influent Effluent Sim ulatedEffluent Flow

Figure2.FullScaleSimulation,January2004.

26


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ForthetimeexaminedinFigure15,therangeofcalculatedbypassflowswas0.2%to2.6%of

theinfluentflowwithanaverageof1.2%. Influentflowsrangedfrom4.0mgdto4.7mgdwithan

averageof4.3mgd. FromFigure10,theaverageflowratewouldcorrespondtoabasindead

volumeof25%. Althoughadirectcorrelationwasnotestablished,thegeneraltrendbetween

influentflow,bypassflow,andMBBRdeadvolumeisconsistent;wherebyhigherinfluentflow

ratesreduceboththepredicteddeadvolumeandthecomputedbasinbypassflow.

0

5

10

15

20

25

NH3

N

(mg/L)

0

1

2

3

4

5

Flow

(mgd)

7Jun 12Jun 17Jun 22Jun 27Jun 2Jul

Date(2004)

Influent Effluent Simulated Flow

Figure15.FullScaleSimulation,June2004.

Byadjustingtheaveragebypassflowasapercentageofthetotalbasinflow,themodel

providedanexcellentfittothefullscaleMBBReffluentNH3Ndata.Additionally,themodelofthe

fullscaleMBBRwasusedtofurtherevaluatetheeffluentNH3Nconcentrationsresultingfrom

improvedhydraulicefficiencyachievedbyimprovedinfluentdistribution(reducedshortcircuiting

orbypassflowpercentages). EffluentNH3Nconcentrationsweremodeledasafunctionof

influentNH3Nconcentration(andloading)forvariousbypassflowpercentagesassumingan

influentdesignflowof4.8mgd(resultinginaHDTof3.9hours),effluenttemperatureof15C,

effluentpHof7.0,KNvalueof1.0mg/L,andtheaveragermvalueof3.37g/m2/d.

ThefullscaleMBBRisdesignedtooperateataminimumDOconcentrationof5mg/L. Based

onthereportedratioof3.2(Szwerinskietal.,1986)signifyingthechangebetweentheoxygenand

ammonialimitingregimefornitrification,thetransitionfromDOratelimitingconditionstoNH3N

ratelimitingconditionswasassumedtooccurataneffluentNH3Nconcentration,inthesecond

CFSTR,ofapproximately1.6mg/L(refertoFigure13). Thedashedlineinthefollowing

simulations(Figures16to20)representsthetransitionpointbetweenDOratelimitingconditionsandNH3Nratelimitingconditions. ThetransitionlinewasdevelopedassumingeffluentNH3Nof

1.6mg/LwasthecriticalconcentrationwithinthemodelCFSTRs. Whenbypasswasequaltozero

(hydraulicallyidealconditions),theCFSTRNH3NequaledMBBReffluentNH3N,andthereforethe

transitionlinewasverticalat1.6mg/L. Whenbypassflowexisted,duetolessthanidealhydraulic

conditions,theweightedaverageeffluentconcentrations,asaffectedbybypass,wasplotted.

TheresultsofthevariablebypasssimulationwerepresentedinFigure16. Theresults

indicatedhydraulicimprovementinthefullscaleMBBRcouldsignificantlyincreasetheallowable

27


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34/39

0

5

10

15

20

25

3035

40

45

50

0 5 10 15 20 25 30 35 40

EffluentNH3N(mg/L)

InfluentNH3

N(m

g/L)

0.0

0.5

1.0

1.5

2.0

2.5

NH3

NLoading(g/m

2/d)

1g/m2/d 2g/m2/d 3g/m2/d 4g/m2/d

DORateLimiting

rm=

Figure17.MaximumSubstrateUtilizationRateSensitivity,BypassFlow=0%.

0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8 10 12 14 16 18 20EffluentNH3N(mg/L)

InfluentNH3

N(mg/L)

0.0

0.5

1.0

1.5

2.0

2.5

NH3

NLoading(g/m

2/d)

1g/m2/d 2g/m2/d 3g/m2/d 4g/m2/d

NH3NRateLimiting

DORateLimiting

rm

=

Figure18.MaximumSubstrateUtilizationRateSensitivity,BypassFlow=30%.

29


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Atabypassflowof0%(maximumhydraulicefficiency),DOratelimitationcontrolledall

effluentNH3Nconcentrationsgreaterthanapproximately1.6mg/L.FortheeffluentNH3N

concentrationof1.6mg/L,therangeofrmvaluesmeasuredinthelaboratorystudiespredicted

allowableinfluentNH3Nconcentrationsof20to40mg/L(loadingof1.0g/m2/dto2.0g/m2/d).

Therefore,withaproperlydesignedsystem,processperformancewasverysensitivetorm.

Conversely,withabypassflowof30%andaneffluentNH3Ngoalof6mg/L,theallowableinfluent

NH3Nconcentrationwouldhavebeenapproximately20mg/L(loadingof1.0g/m2/d)forthe

rangeof rmvaluesmeasuredinthelaboratorystudies. The20mg/Linfluentconcentration(1.0

g/m2/dloading)conditionwouldplacetheoperationjustinsideoftheDOratelimitingregime.

Withsignificantbypassflows,processperformanceisnotsensitivetonitrificationkinetics,but

rather,isgovernedbythehydraulicoperationofthebasin.

Forrmvalueslessthanthosemeasuredinthelaboratorystudies( 2g/m2/d),predicted

nitrificationperformancedropsoffsignificantlyforeitherbypassscenario(Figures17and18).

Tofurtherexaminethesensitivityofthemodel,withrespecttonitrificationkinetics,thehalf

saturationconstantwasalsoevaluated. TheKNvaluewasvariedbasedonreportedrangesfor

aerobicattachedgrowthnitrifyingsystems(USEPA,1993). Thefullscalemodelwasevaluatedin

termsofKNforbothidealandlessthanidealhydraulicconditions. NH3Nconcentrationswere

modeledasafunctionofinfluentNH3Nconcentration(andloading)forvariousKNvaluesassuminganinfluentflowof4.8mgd(HDTof3.9hours),effluenttemperatureof15C,effluentpH

of7.0,rmvalueof3.37g/m2/d,andbypassflowpercentagesof0%and30%. Theresultsofthe

modelsimulationsforbothhydraulicsituationswerepresentedinFigures19and20,respectively.

0

5

10

15

20

25

30

35

40

45

50

0 5 10 15 20 25 30 35 40EffluentNH3N(mg/L)

InfluentNH3N(mg/L)

0.0

0.5

1.0

1.5

2.0

2.5

NH3NLoading(g/m2/d)

0.5mg/L 1.0mg/L 1.5mg/L 2.0mg/L

DORateLimiting

KN = Figure19.HalfSaturationConstantSensitivity,BypassFlow=0%.

30


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0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8 10 12 14 16 18 20

EffluentNH3N(mg/L)

InfluentNH3N(mg/L)

0.0

0.5

1.0

1.5

2.0

2.5

NH3NLoading(g/m2/d)

0.5mg/L 1.0mg/L 1.5mg/L 2.0mg/L

NH3NRateLimiting

DORateLimiting

KN = Figure20.HalfSaturationConstantSensitivity,BypassFlow=30%.

AsevidentbythemodelingresultsdisplayedinFigures19and20,thesimulationwaslargely

independentofthehalfsaturationconstantfortheEPAreportedvalues. Utilizingthermvalueof

3.37g/m2/dobtainedfromthebench scaleanalyses,thenitrificationintheMoorheadMBBRwas

generallyunaffectedbythevalueofKNasthepredictedeffluentNH3Nconcentrationsvariedby

lessthan3.0mg/LforbothhydraulicscenariosatallsimulatedinfluentNH3Nconcentrations.

Therefore,theassumedKNvalueof1.0mg/LfortheMBBRsystemisacceptableformodeling

purposes.

ThemodelanalysesindicatedtheMBBRprocesswashighlydependentonbothhydraulic

considerationsandthemaximumsubstrateutilizationrate,rm,describingthenitrificationprocess. Thelaboratorybenchscaleanalysesconductedaspartofthisstudyindicatedaccurate

measurementofthermparametermayhavebeconfoundedbyseveralfactorsincluding

conditionsinthefullscaleMBBRatthetimeofanalysisand/ortheassumptionthequantityof

activenitrifyingbiomasswasdirectlyrelatedtothemediasurfaceareaprovided.

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SUMMARYANDCONCLUSIONS

Theprimarygoalofthisresearchwastoidentifyandevaluatethecriticaldesignand

operationalparametersaffectingnitrificationinafullscaleMBBRprocessutilizedbythe

Moorhead,MinnesotaWWTF. AnimprovedunderstandingofthetertiarynitrifyingMBBRsystem

wasnecessarytoenhancetheoperationalstabilityofthefullscalesystemandthus,optimizetheeffluentammoniaconcentrationdischargedtotheRedRiveroftheNorth. Toaccomplishthis

goal,thesystemwasevaluatedundervariousflowandammonialoadingconditions. Hydraulic

andnitrificationkineticparametersoftheMBBRwerealsoexaminedtodevelopanappropriate

fullscalemodelthatwasusedinconjunctionwiththemonitoringdatatoexaminethedesignand

operationalparametersaffectingtheprocessperformance. Fromtheresultsobtainedduringthis

study,thefollowingconclusioncanbedrawn:

1. ThefullscaleMBBRsystemhasachievedthedesignobjectivesestablishedfortheprocessand

hasproventobeanappropriateandeffectiveseparatestagenitrifyingapplicationatthe

MoorheadWWTF. Althoughtherateofnitrificationappearedtobereducedduringcold

weathermonths,overall,thesystemdemonstratedtheabilitytooxidizeammoniainboth

coldandwarmweatherperiods. WhiletheinfluentNH3Nconcentrationsandloadingshave

typicallyexceededthedesignvaluesof17mg/Land0.84g/m2/drespectively,theMBBRbasin

achievedanaverageeffluentNH3Nconcentrationof6.84mg/L. Duringwarmweather

months,whentheeffluentNH3Npermitlimitswereineffect(JunethroughSeptember=8.0

mg/L)theeffluentconcentrationwasreducedevenfurtherbytheMBBRsystem,onaverage

2.75mg/L.

2. Theoperationalreturnofsupernatantfromthebiosolidsstoragefacilitytotheheadworksof

theWWTFhasbeenshowntoimpacttheoverallperformanceoftheMBBRbasin. The

supernatantloadrepresentedasignificantportionofthetotalMBBRNH3Nloading. Because

ofthevariabilityininfluentNH3Nconcentrationsandloadingsduetothereturnof

supernatant,equalizedandregularlyscheduledsupernatantflowshouldbeimplementedat

theMoorheadWWTF. TheMBBRsystemhasdemonstratedtheabilitytoadapttothehigherNH3Ninfluentloadingconditionsandappearedtooxidizeammoniaeffectivelyaslongas

consistent,steadysupernatantflowwasmaintained. Sidestreamtreatmentforthe

supernatantortheadditionofmediatotheMBBRshouldalsobeexploredtoeliminatethe

impactsassociatedwiththeadditionalNH3Nloading.

3. TheresultsofthehydraulicanalysesindicatedtheMBBRprocesscouldbesimulated

hydraulicallyasanumberofCFSTRsinserieswithaneffectivevolumelessthanthatofthefull

basin. Theresultsofthehydraulicanalysesalsodemonstratedshortcircuitingoccurredalong

theinletsideofthebasinbetweentheinfluentpipeandthebasineffluentstructure. The

performanceofthesystemcouldbeimprovedbyincreasedflowrates(withgreater

momentums)whichdrivetheinfluentflowsfurtheracrosstheinletendofthebasinresulting

in

improved

flow

distribution,

thereby

reducing

the

propensity

for

bypass

within

the

basin.

SeveraldesignoptionsareavailableforimprovedbasinflowdistributionforsimilarMBBR

systemsincluding:baffleinstallation,multipleinletpoints,orincreasedlengthtowidthratios.

Increasedmixingalone,throughtheuseofhigheraerationrates,withintheMBBRdidnot

improvetheinfluentflowdistribution. However,anincreaseinmixingfocusedsolelyatthe

inletwasnotexaminedduringthisproject.

4. Laboratorybenchscalekineticanalyseswereconductedtoevaluatethemaximumsubstrate

utilizationrate,rm,forthenitrifyingbiomassinthefullscaleMBBRprocess. Assumingahalf

32


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saturationconstant,KN,of1.0mg/L,rmwasestimatedbystatisticallyfittingtheobserveddata

toanattachedgrowthMonodrateexpression. Thedataprovidedanexcellentfittothe

Monodrateexpression. However,thermvaluesexhibitedvariation,rangingfrom2.024to

4.418g/m2/dwithanaverageof3.370g/m2/d. Althoughaspecificinvestigationintothe

potentialcausesforthevariationwasnotconducted,anaccuratedeterminationofrmmaybe

confoundedbytheconditionsinthefullscaleMBBRatthetimetheanalysiswasconducted.

Assumingthequantityofactivenitrifyingbiomasswasdirectlyrelatedtothemediasurface

areamayhavealsoledtothevariationinrm.

5. Utilizingthehydraulicsimulationandthekineticparametersobtainedfromthebenchscale

analyses,acombinedmodelforthefullscaleMBBRsystemwasdeveloped. Thehydraulic

deficienciesofthesystemwereincorporatedinthemodelasasimulatedbypassflow. The

modelresultsindicatednitrificationperformanceintheMBBRwashighlydependentuponthe

physicalconfigurationandhydrauliccharacteristicsofthebasin. Hydraulicimprovementsin

thefullscaleMBBRcansignificantlyincreasetheinfluentNH3Ncapacityofthesystemfora

particulareffluentNH3Nconcentrationgoal. TheMBBRprocessperformancewasfoundto

becontingentonbasinphysicalcharacteristics,asopposedtonitrificationkinetics,when

considerablehydraulicdeficienciesexist. However,whentheMBBRsystemwasmaximized

withrespecttohydraulicstheprocessperformancewasgovernedbynitrificationkinetics. Inahydraulicallyoptimizedbasin,thesimulationsillustratedMBBRprocessperformancewas

greatlydependenton,andsensitiveto,themaximumsubstrateutilizationratefornitrifying

bacteria,rm. Appropriateconsiderationmustbegiventobothkineticandhydraulic

characteristicstoensuremaximumperformancepotentialforanyMBBRsystem.

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REFERENCES

AmericanPublicHealthAssociation,AmericanWaterWorksAssociation,WaterEnvironment

Federation.(1998)StandardMethodsfortheExaminationofWaterandWastewater.20th

ed.,Washington,D.C.

Grady,Jr.,L.,andLim,H.(1999)BiologicalWastewaterTreatment.NewYork,NewYork.Klecker,J.(1998)FeasibilityStudyofAchievingAmmoniaRemovalbyNitrificationinPolishing

Ponds. MasterofScienceThesis,CivilEngineering,NorthDakotaStateUniversity,Fargo,

NorthDakota.

MetcalfandEddy,Inc.(2003)WastewaterEngineering:TreatmentandReuse.NewYork,NY.

MinnesotaDepartmentofHealth.(1990)Laboratories,AccreditationRequirements.State

RegistrationMinnesotaRules,Chapter4740,14,1874,St.Paul,Minnesota.

degaard,H.,Rusten,B.,andWestrum,T.(1994)ANewMovingBedBiofilmReactor

ApplicationsandResults.WaterScienceTechnology,29,10/11,157.

Quinlan,A.(1984)PredictionoftheOptimumpHforAmmoniaNOxidationbyNitrosomonas

EuropeainWellAeratedNaturalandDomesticWastewaters.WaterResource,18,561.

Rusten,B.,andNeu,K.(1999)DowntoSize.WaterEnvironmentTechnology,11,27.

Siegrist,T.,andGujer,W.(1987)DemonstrationofMassTransferandpHEffectsonNitrifying

Bacteria.WaterResource,21,1481.

Szwerinski,H.,andArvin,E.,Harremos,P.(1986)pHDecreaseinaNitrifyingBiofilm.Water

Resource,20,971.

Tchobanoglous,G.,andSchroeder,E.(1987)WaterQuality.Davis,California.

U.S.EnvironmentalProtectionAgency.(1993)NitrogenControlManual.EPA625/R93/010,

OfficeofResearchandDevelopment,Washington,D.C.

WaterEnvironmentFederation.(2000)AerobicFixedGrowthReactors.Alexandria,Virginia.

WaterEnvironmentResearchFoundation.(2000)InvestigationofHybridSystemsforEnhanced

NutrientControl.Alexandria,Virginia.

Zimmerman,R.,Richard,D.,Bradshaw,A.,andCraddock,P.(2003)PilotScaleEvaluationof

SeparateStageNitrificationUsinganAttachedGrowth,MovingBedMediaProcess.WaterEnvironmentResearch,75,422.

Zimmerman,R.,Richard,D.,andCostello,J.(2004)Design,Construction,Startup,andOperation

ofaFullScaleSeparateStageMovingBedBiofilmReactorNitrificationProcess.

Proceedingsofthe77thAnnualWaterEnvironmentFederationTechnicalExhibitionand

Conference[CDROM],NewOrleans,Louisiana,Oct.26,WaterEnvironmentFederation,

Alexandria,Virginia.

Zimmerman,R.,Richard,D.,Lynne,S.,andLin,W.(2005)IsYourMBBRRunningOnAllCylinders?

Proceedingsofthe78thAnnualWaterEnvironmentFederationTechnicalExhibitionand

Conference[CDROM],Washington,D.C.,Oct.29Nov.2,WaterEnvironmentFederation,

Alexandria,Virginia.

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