832r10005 (evaluation of energy conservation measures for wastewater treatment facilities)

8/7/2019 832R10005 (Evaluation of Energy Conservation Measures for Wastewater Treatment Facilities)

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Evaluation of

Energy Conservation

Measuresfor Wastewater Treatment Facilies


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Evaluation of Energy Conservation Measures ii September 2010

U.S.EnvironmentalProtectionAgency

OfficeofWastewaterManagement

1200PennsylvaniaAvenueNW

Washington,DC20460

EPA832R10005

September2010

Coverphoto:

BucklinPointWWTF,MA. PhotocourtesyofNarragansettBayCommission.

Coverinsertphotos(lefttoright):

HighSpeedMagneticBearingTurboBlowerattheDePereWTF,WI. PhotocourtesyofGreenBay

MetropolitanSewerageDistrict.

OxidationDitchwithAerationRotorattheCityofBartlettWWTP#1,TN.PhotocourtesyofCityof

BartlettWastewaterDivision.

VariableOutletVaneDiffuser. PhotocourtesyofTurblex,Inc.


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Evaluation of Energy Conservation Measures iii September 2010

Preface

TheU.S.EnvironmentalProtectionAgency(EPA)ischargedbyCongresswithprotectingthenations

land,air,andwaterresources.Underamandateofenvironmentallaws,theAgencystrivestoformulate

andimplementactionsleadingtoabalancebetweenhumanactivitiesandtheabilityofecosystemsto

supportandsustainlife.Tomeetthismandate,theOfficeofWastewaterManagement(OWM)provides

informationandtechnicalsupporttohelpsolveenvironmentalproblemstodayandtobuildthe

knowledgebasenecessarytoprotectpublichealthandtheenvironmentwellintothefuture.This

documentwaspreparedundercontracttoEPA,byTheCadmusGroup. Thedocumentprovides

informationoncurrentstateofdevelopmentasofthepublicationdate;however,itisexpectedthat

thisdocumentwillberevisedperiodicallytoreflectadvancesinthisrapidlyevolvingarea. Exceptas

noted,information,interviews,anddatadevelopmentwereconductedbythecontractor.Whilethere

aremanyproven,costeffectiveenergyconservationpracticesandnumerousnewtechnologiesor

modificationsofexistingtechnologiesavailablefordetailedstudy,thecasestudiesinthisdocument

wereselectedonthebasisofspecificcriteria.Thecriteriaincludedtheabilitytoprovideasleastoneyearoffullscaleoperatingandperformancedata,capabilityofprovidingdetailedcapital,operations,

andmaintenancecostbreakdowns,andtheabilitytoprovidethedatawithinthetimeframeestablished

forcompletingthedocument.Itisanticipatedthatasthedocumentisupdated,additionalcasestudies

onnewtechnologiescouldbeincluded.

DisclaimerThisinformationrepresentsnew,innovativeoremergingapproaches,techniques,ortechnologiesthat

mayassistutilityownersandoperatorsreducethecapitaloroperatingcostsofwastewatertreatment.

Someoftheinformation,especiallyrelatedtoemergingtechnologies,wasprovidedbythe

manufacturer

or

vendor

of

the

equipment

or

technology,

and

could

not

be

verified

or

supported

by

a

fullscalecasestudy. Insomecases,costdatawerebasedonestimatedsavingswithoutactualfield

data. Whenevaluatingtechnologies,estimatedcosts,andstatedperformance,effortsshouldbemade

bythereadertocollectcurrentandmoreuptodateinformation.

Thementionoftradenames,specificvendors,orproductsdoesnotrepresentanactualorpresumed

endorsement,preference,oracceptancebyEPAorthefederalgovernment.Statedresults,conclusions,

usage,orpracticescontainedhereinmaybedifferentdependingonspecificsiteconditionsanddonot

necessarilyrepresenttheviewsorpoliciesofEPA.

ThisdocumenthasbeenreviewedinaccordancewithEPAspeerandadministrativereviewpoliciesand

approvedforpublication


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Evaluation of Energy Conservation Measures iv September 2010

AcknowledgementsThisdocumentwaspreparedbyTheCadmusGroup,Inc.(Cadmus)underEPAContractNo.GS10F

0273KC/I1,TaskOrder311. TheCadmusTeamwasledbyLauraDufresneandStephenCoutureof

CadmusandDavidReardonandKennethHendersonofHDR. EPAtechnicaldirectionandoversightwereprovidedbyJamesWheelerandPhilZahreddine,EPAOfficeofWastewaterManagement.

Theprojectwassupportedbyatechnicalexpertpanelconsistingofthefollowingindividuals:

KathleenOConner,NewYorkStateEnergyResearchandDevelopmentAuthority

JoeCantwell,SAIC

MikeWilson,CH2MHill

SteveBolles,ProcessEnergyServices

AndreSchmidt,LosAngelesCountySanitationDistrictsEnergyRecoveryEngineeringServices

JessBurgess,ConsortiumforEnergyEfficiency

Aformalpeerreviewofthedraftdocumentwasconductedbythefollowingindividuals:

ThomasE.Jenkins,JenTechInc.

JuliaGass,Black&Veatch

GeorgeLawrence,EfficiencyVermont

GeorgeCrawford,CH2MHILL

AdditionalreviewwasprovidedbyDavidRedmonofRedmonEngineeringCompany,AndrewShawof

Black&Veatch,andAndrewTrumanofBlack&Veatch.

WhileeveryeffortwasmadetoaccommodateallofthePeerReviewcomments,theresultsand

conclusionsdonotindicateconsensusandmaynotrepresenttheviewsofallthereviewers.

Theauthorssincerelyappreciatethereviewandguidanceprovidedbythetechnicalexpertpanel

membersandpeerreviewers.


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Evaluation of Energy Conservation Measures v September 2010

Acronyms and Abbreviations

ACEEE AmericanCouncilforanEnergyEfficientEconomy

APPA AmericanPublicPowerAssociation

ASCE AmericanSocietyofCivilEngineers

ASE AlliancetoSaveEnergy

AWWA AmericanWaterWorksAssociation

BEP BestEfficiencyPoint

bhp BrakeHorsepower

BNR BiologicalNutrientRemoval

BOD BiochemicalOxygenDemand

CCCSD CentralContraCostaSanitaryDistrict

CEC CaliforniaEnergyCommission

CEE ConsortiumforEnergyEfficiency

CFO CostFlowOpportunity

CHP CombinedHeatandPower

DCS DistributedControlSystem

DO DissolvedOxygen

DOE DepartmentofEnergy

DSIRE DatabaseofStateIncentivesforRenewablesandEfficiency

ECM EnergyConservationMeasure

EPACT EnergyPolicyAct

EPC EnergyPerformanceContracting

EPRI ElectricPowerResearchInstitute

ESCO EnergyServicesCompany

GBMSD GreenBay(Wisconsin)MetropolitanSewerageDistrict

gpm Gallonsperminute

hp HorsepowerI&I Inflowandinfiltration

IOA InternationalOzoneAssociation

IUVA InternationalUltravioletAssociation

kW Kilowatt

kWh Kilowatthour

LPHO LowPressureHighOutput

MBR MembraneBioreactor

mg MillionGallons

mgd MillionGallonsperDay

MLE ModifiedLudzackEttingerprocess

MPN MostProbableNumber

NAESCO NationalAssociationofEnergyServiceCompanies

NEMA NationalElectricalManufacturersAssociation

NYSERDA NewYorkStateResearchandDevelopmentAuthority

PG&E PacificGasandElectric

PLC ProgrammableLogicController

PSAT PumpSystemAssessmentTool

psi PoundsperSquareInch

psig PoundsperSquareInchGauge


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Evaluation of Energy Conservation Measures vi September 2010

rpm RevolutionsperMinute

SRT SolidsResidenceTime

TDH TotalDynamicHead

TSS TotalSuspendedSolids

TVA TennesseeValleyAuthority

UV UltravioletLight

UVT UVtransmittance

VFD VariableFrequencyDrive

W Watt

WEF WaterEnvironmentFederation

WEFTEC WaterEnvironmentFederationTechnicalExhibitionandConference

WERF WaterEnvironmentResearchFoundation

WMARSS WacoMetropolitanAreaRegionalSewerSystem

WPCP WaterPollutionControlPlant

WRF WaterResearchFoundation

WSU WashingtonStateUniversity

WWTP WastewaterTreatmentPlant


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Evaluation of Energy Conservation Measures vii September 2010

Contents1. Introduction ............................................................................................................... 11

1.1

Background

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

1

1

1.2 PurposeandAudience........................................................................................ 12

1.3 ReportOrganization............................................................................................ 13

1.4 SummaryofInnovativeandEmergingECMS..................................................... 14

1.5 References.......................................................................................................... 16

2. RecommendedApproachtoEnergyManagement ........................................................ 21

2.1 Introduction........................................................................................................ 21

2.2 RecommendedApproach................................................................................... 21

2.3 ToolsforEnergyManagement........................................................................... 24

2.4 FinancingResources............................................................................................ 24

2.5 OtherECMsandResources................................................................................. 26

2.6 References.......................................................................................................... 27

3. EnergyConservationMeasuresforPumpingSystems.................................................... 31

3.1 Introduction........................................................................................................ 31

3.2 PumpingSystemDesign...................................................................................... 33

3.3 Motors ............................................................................................................... 35

3.3.1 MotorEfficiencyandEfficiencyStandards............................................ 36

3.3.2 MotorManagementPrograms.............................................................. 37

3.3.3 InnovativeandEmergingTechnologies................................................. 38

3.4

Power

Factor

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

3

9

3.5 VariableFrequencyDrives(VFDs)..................................................................... 310

3.5.1 EnergySavings..................................................................................... 311

3.5.2 Applications......................................................................................... 311

3.5.3 VFDStrategiesforWastewaterPumpingStations.............................. 312

3.6 References........................................................................................................ 313

4. DesignandControlofAerationSystems......................................................................... 41

4.1 Introduction........................................................................................................ 41

4.2 ECMsforAerationSystems................................................................................ 41

4.2.1 ECMsforDiffusedAerationSystems..................................................... 42

4.2.2 ECMsforMechanicalAerators.............................................................. 45

4.3 ControloftheAerationProcess......................................................................... 47

4.3.1 AutomatedDOControl.......................................................................... 47

4.3.1.1DOMeasurementEquipment.................................................. 410

4.3.1.2AdvancesinDOControlStrategies.......................................... 413

4.3.2 EmergingTechnologiesUsingControlParametersotherthanDO.....415

4.4 InnovativeandEmergingControlStrategiesforBiological

NutrientRemoval.............................................................................................. 418


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Evaluation of Energy Conservation Measures viii September 2010

4.5 References........................................................................................................ 420

5. BlowerandDiffuserTechnologyforAerationSystems................................................... 51

5.1 IntroductionandComparisonofBlowerTypes.................................................. 51

5.2 HighSpeedGearless(Turbo)Blowers................................................................ 55

5.3 SingleStageCentrifugalBlowerswithInletGuideVanesandVariable

DiffuserVanes................................................................................................... 511

5.4 NewDiffuserTechnology.................................................................................. 515

5.5 References........................................................................................................ 519

6. InnovativeandEmergingEnergyConservationMeasuresforSelected

TreatmentProcesses....................................................................................................... 61

6.1 Introduction........................................................................................................ 61

6.2 UVDisinfection................................................................................................... 61

6.2.1 Design.................................................................................................... 63

6.2.2 OperationandMaintenance.................................................................. 65

6.3 MembraneBioreactors(MBRs).......................................................................... 66

6.4 AnoxicandAnaerobicZoneMixing.................................................................... 68

6.4.1 HyperbolicMixer.................................................................................... 68

6.4.2 PulsedLargeBubbleMixing................................................................. 612

6.5 References........................................................................................................ 613

7. EnergyConservationMeasuresforSolidsProcessing..................................................... 71

7.1 Introduction........................................................................................................ 71

7.2 Digestion............................................................................................................. 71

7.3

Incineration

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

7

4

7.4 ThermalDrying................................................................................................... 76

7.5 References.......................................................................................................... 79

8. SummaryofFacilityCaseStudies.................................................................................... 81

8.1 Introduction........................................................................................................ 81

8.2 Approach............................................................................................................. 81

8.3 SummaryofResults............................................................................................ 83

AppendixA: FacilityCaseStudies

AppendixB: WebResources


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Evaluation of Energy Conservation Measures ix September 2010

ListofTablesTable11. InnovativeandEmergingECMs.......................................................................... 15

Table31. PumpSystemEfficiency...................................................................................... 32

Table51. OverviewofBlowerTypesofAerationofWastewater...................................... 52

Table52. ManufacturerCostRangesforSelectBlowerTypes........................................... 53Table53. TypicalBlowerEfficiencies.................................................................................. 54

Table53. ExamplesofTurboBlowerManufacturersintheNorthAmericanMarket.......58

Table54. NetPresentWorthofBlowerSelectionsfortheCityofOneida(2003$).........514

Table61. DisinfectionEquipmentPowerandCostEstimates(55mgdPeakFlow,

38mgdAverageFlow,65%DesignUVT)............................................................ 64

Table81. SummaryofFacilityCaseStudies....................................................................... 84


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Evaluation of Energy Conservation Measures x September 2010

ListofFiguresFigure11. TypicalEnergyUseProfilefor10mgdSecondaryTreatmentProcesses...........12

Figure21. StepsinthePlanDoCheckActManagementSystemsApproach..................... 22

Figure31. VectorRelationshipofACPower........................................................................ 39

Figure32. WastedEnergyinAlternativeControlSchemesComparedto ...............................

VariableFrequencyDrives................................................................................ 311

Figure41. EimcoWaterTechnologiesCarrouselSystemExcellAeratorII........................ 46

Figure42. CommonCascadeSystemforAutomatedDOControl..................................... 410

Figure43. OpticalDOSensorOperation............................................................................ 412

Figure44. IntegratedAirFlowControlSystemforAutomatedDOControl...................... 414

Figure45. FlowThroughRespirometryCell...................................................................... 416

Figure46. RepresentationofBIOSProcess....................................................................... 417

Figure47. RepresentationoftheBiosProcess.................................................................. 419

Figure51. ExampleofHighSpeedTurboBlowerwithAirBearings(HIS)........................... 56

Figure52. ExampleofHighSpeedTurboBlowerwithMechanicalBearings

(Atlas

Copco)

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

5

6

Figure53. ComparisonofPowerDrawforOldandNewBloweratBurlington,VT..........511

Figure54. ExampleofSingleStageCentrifugalBlowerwithInletGuideVanesand

VariableDiffuserVanesbyTurblex................................................................. 511

Figure55. ExampleofSingleStageCentrifugalBlowerwithInletGuideVanesand

VariableDiffuserVanesbyDresserRoots........................................................ 511

Figure56. VariableOutletVaneDiffuserfromTurblex................................................... 512

Figure57. UltrafinePoreMembraneAerationPanel....................................................... 515

Figure58. AeroStripDiffuserbytheAerostripCorporation............................................ 516

Figure61. ExampleUVLampConfigurationsforWastewaterTreatment.......................... 62

Figure62. TypicalInstallationofaHyperboloidMixer........................................................ 69

Figure63. ConventionalHydrofoilMixer........................................................................... 611

Figure64. TypicalBioMixTMInstallation............................................................................. 612

Figure71. VerticalLinearMotionMixerbyEnersaveFluidMixers,Inc.............................. 73

Figure72. SchematicRepresentationofMultipleHearthIncineratorEnergyEfficiency

ImprovementsatWSSCWesternBranchWWTP............................................... 76

Figure73. ExampleofSolarDryerbyParkson..................................................................... 78


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EvaluationofEnergyConservationMeasures 11 September2010

1.Introduction

1.1 Background

Providingreliablewastewaterservicesandsafedrinkingwaterisahighlyenergyintensive

activity

in

the

United

States.

A

report

prepared

for

the

Electric

Power

Research

Institute

(EPRI)

in

1996

estimatedthatbytheendofthatyear,theenergydemandforthewaterandwastewaterindustry

wouldbeapproximately75billionkilowatthours(kWh)peryear,orabout3percentoftheelectricity

consumedintheU.S.(Burton1996). TheConsortiumforEnergyEfficiency(CEE)nowestimatesthe

annualenergyusageatapproximately100billionkWhperyear(Burton1996,extrapolatedbyCEE). At

anaverageenergycostof$0.075perkWh,thecostforprovidingsafedrinkingwaterandproviding

effectivewastewatertreatmentisapproximately$7.5billionperyear.

Energyisusedthroughoutthewastewatertreatmentprocess;however,pumpingandaeration

operationsaretypicallythelargestenergyusers(seeFigure11foratypicalenergyuseprofilefora

mediumsizedwastewatertreatmentplant). Energycostsinthewastewaterindustryarerisingdueto

manyfactors,including:

Implementationofmorestringenteffluentrequirements,includingenhancedremovalofnutrientsandotheremergingcontaminantsofconcernthatmay,insomecases,leadtotheuse

ofmoreenergyintensivetechnologies.

Enhancedtreatmentofbiosolidsincludingdrying/pelletizing. Agingwastewatercollectionsystemsthatresultinadditionalinflowandinfiltration,leadingto

higherpumpingandtreatmentcosts.

Increaseinelectricityrates.Asaconsequenceoftheserisingcosts,manywastewaterfacilitieshavedevelopedenergymanagement

strategiesandimplementedenergyconservationmeasures(ECMs).Usingthefiguresprovidedearlierin

thissection,improvingtheenergyefficiencyofAmerica'sdrinkingwaterandwastewatersystemsby10

percentcouldsavemorethan10billionkWheachyear,representingacostsavingsofapproximately

$750millionannually.

Chapter1covers:

1.1 Background

1.2 PurposeandAudience

1.3 ReportOrganization

1.4 SummaryofInnovativeandEmergingECMs

1.5 References


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Figure11.TypicalEnergyUseProfilefor10mgdSecondaryTreatmentProcesses.

Source:WEF2009,Figure7.1.Usedwithpermission.

Note:energyuseforvarioustreatmentprocesseswillvarygreatlyfromplanttoplant. Advancedtreatment

processesmayrequiremoreenergythanconventionaltreatmentprocessesandmaynotberepresentedinthis

figure.

1.2 PurposeandAudienceThepurposeofthisreportistoencouragetheimplementationofECMsatpubliclyowned

treatmentworks(POTWs)byprovidingaccurateperformanceandcost/benefitinformationforsuch

projects.Thereportsfocusismainlyonenergyefficientequipmentreplacement,operational

modifications,andprocesscontrolenhancementsthatleadtoimprovedenergyefficiencyandcost

savingswithreasonablepaybackperiods(10yearsorless). Thescopeofthereportdoesnotinclude

cogenerationtechnologies(alsoknownascombinedheatandpower,orCHP)oralternative/renewable

energytechnologies,astheinformationonthesetopicsisbeingdevelopedbyEPAunderseparate

projects.ThemainaudiencesforthisreportarePOTWmanagers,owners,andoperatorswhomaybe

consideringtheimplementationofECMsandstatesorotheragencieswhomaybeinterestedin

supportingsuchprojects.

ThisreportincludessummaryinformationonconventionalECMsthatareinuseintheU.S.and

haveastrongtrackrecordofsuccesswithrespecttoenergyconservation;however,thefocusis

identificationofinnovativeandemergingECMs. Forthepurposesofthisdocument,innovativeand

emergingaredefinedasfollows:

Innovative: technologiesthatmaybeestablishedoverseasandhaveeitherbeentestedintheU.S.asafullscaledemonstrationprojectorinstalledataU.S.wastewatertreatmentplant


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(WWTP)foratleastoneyearbutnotmorethan5years. Foratechnologythatmeetstheabove

criteriatobeconsideredinnovativeratherthanemerging,independenttestdatashowing

energysavingsmustbepresentedintheliteratureordocumentedinthisreportinoneofthe

facilitycasestudies.Innovativetechnologiesincludemodificationsandnewapplicationsfor

establishedtechnologies.

Emerging:technologiesinthedevelopmentortestingstageintheU.S.andthatshowpotentialforenergysavingsandrelativelyshortpaybackperiods,butforwhichindependentfullscale

demonstrationoroperatingdataarenotyetavailable.

SeeSection1.4forasummaryofinnovativeandemergingECMsidentifiedinthisreport.

ThisreportbuildsuponanextensiveliteraturereviewoftheeffectivenessandcostsofECMsfor

municipalwastewatertreatmentandsolidsprocessing.Additionally,apaneloftechnicalexperts

providedinputontheimplementationofvariousECMs.Detailedfacilityassessmentsofninewastewater

treatmentfacilitiesareprovided,includingdetailedinformationonECMimplementation,energy

savings,andcostdata.

1.3 ReportOrganization

Thereportisorganizedintoninechaptersandtwoappendicesasfollows:

Chapter1,Introduction,presentsbackground,purpose,audience,andorganizationforthereport.

Chapter2,RecommendedApproachtoEnergyManagement,presentsacomprehensiveapproachtoenergymanagementatawastewatertreatmentutility,includingdevelopingan

energymanagementprogram.Itlistsavailabletoolsandfinancingresourcesthatcanhelp

utilitiesimplementtheirprograms.ItalsolistsotherECMsthatshouldbeconsideredby

wastewaterutilitiesbutarenotthefocusofthisreport.

Chapter3,EnergyConservationMeasuresforPumpingSystemsprovidesanoverviewofconventionalECMsrelatedtopumpingdesign,variablefrequencydrives(VFDs),andmotorsand

refersthereadertoindustrystandardsandweblinksforadditionalguidance.

Chapter4,DesignandControlofAerationSystems,providesdetailedinformationonECMsrelatedtothedesignofaerationsystemsandautomatedaerationcontrol,including

conventionalcontrolbasedondissolvedoxygen(DO)measurementsandemergingcontrol

strategies.Innovativeandemergingtechnologiesforautomatedcontrolofbiologicalnitrogen

removalarealsodiscussed.

Chapter5,BlowerandDiffuserTechnologyforAerationSystems,describesinnovativeECMsrelatedtobloweranddiffuserequipment.Itincludesasummaryofvariousblowertypessuchas

singlestagecentrifugal,highspeedturbo,andscrewcompressorsinadditiontonewdiffuser

technology.

Chapter6,InnovativeandEmergingEnergyConservationMeasuresforSelectedTreatmentProcesses,providesadiscussionofECMsforadvancedtechnologies(UVdisinfection,


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membranes,andanoxiczonemixing)andpresentsfullscaleplanttestresultswhereavailable.

ForECMsthataretechnicallyfeasibleandpromisingfortheindustrybutwhereoperatingdata

arenotavailable,manufacturersinformationisprovided.

Chapter7EnergyConservationMeasuresforSolidsProcessing,describesinnovativeEMSfordigestion,incineration,andthermaldryingandprovidessupportingdatafromcasehistories.

Chapter8,SummaryofFacilityCaseStudies,describestheapproachusedtoselecttheninefacilitycasestudiesandsummarizescasestudyfindingsinnarrativeformandinsummary

tables.

AppendixA,FacilityCaseStudies,containsdetailedinformationandresultsfromninefacilitycasestudies.

AppendixB,WebResources,providesresourcesforfurtherinformation.Categoriesofwebresourcesincludebooksavailablefromonlineretailers;governmentpublicationsthroughU.S.

DepartmentofEnergy(DOE)andU.S.EnvironmentalProtectionAgency(EPA);information

availablefromnonprofitorganizations,stateprograms,WaterEnvironmentResearch

Foundation(WERF)andWaterResearchFoundation(WaterRF);andonlinejournalsand

conferenceproceedings.

1.4 SummaryofInnovativeandEmergingECMs

Table11liststheinnovativeandemergingECMsidentifiedinthisreportandreferencesthe

specificreportsectionformoreinformation. AsstatedinSection1.2,independentdemonstrationor

fullscaleoperatingdatadocumentingenergysavingsarerequiredforanewtechnologytobe

consideredinnovative;otherwise,itwasclassifiedasemerginginthisreport. Notethatthisreport

describesmanyotherconventionalECMsthatcanachievesignificantenergysavings.


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Table11. InnovativeandEmergingECMs

Chapter ECMName ECMCategorization

andReportSection

4DesignandControl

ofAerationSystems

IntermittentAeration Emerging4.2.1

DualImpellerAerator(mechanicalmixing) Emerging4.2.2

Integratedairflowcontrol Innovative4.3.1

AutomatedSRT/DOControl Innovative 4.3.1

Respirometryforaerationcontrol Emerging4.3.2

Criticaloxygenpointcontrol Emerging4.3.2

Offgasmonitoringandcontrol Emerging4.3.2

Onlinemonitoringandcontrolofnitrification

usingnicotinamideadeninedinucleotide(NADH)

(Symbioprocess)

Emerging4.4

BioprocessIntelligentOptimizationSystem(BIOS) Emerging4.4

5 BlowerandDiffuser

Technologyfor

AerationSystems

Highspeedgearless(Turbo)blowers Innovative5.2

Singlestagecentrifugalblowerswithinletguide

vanesandvariablediffuservanes

Innovative5.3

Ultrafinebubblediffusers Emerging5.4

Newdiffusercleaningtechnology Emerging5.5

6Innovativeand

EmergingEnergy

ConservationMeasures

forSelectedTreatment

Processes

LowpressurehighoutputlampsforUV

disinfection

Emerging6.2.1

AutomatedchannelroutingforUVdisinfection Emerging6.2.2

Membraneairscouralternatives Emerging6.3

Hyperbolicmixers Innovative6.4.1

PulsedLargeBubbleMixing(e.g.,BioMx) Innovative6.4.2

7EnergyConservation

MeasuresforSolids

Processing

Verticallinearmotionmixer Innovative7.2

Upgradingmultiplehearthfurnacesto

incorporatewasteheatrecovery/combustionair

preheating

Innovative7.3

Solardrying Emerging7.4


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1.5 References

Burton,FranklinL.1996.WaterandWastewaterIndustries:CharacteristicsandEnergyManagement

Opportunities.BurtonEnvironmentalEngineering,LosAltos,CA.PreparedfortheElectricPower

ResearchInstitute.PaloAlto,California.ReportCR106941.September,1996.

Carns,K.,2005.BringingEnergyEfficiencytotheWater&WastewaterIndustry:HowDoWeGetThere?

InWEFTEC2005Proceedings.

WaterEnvironmentFederation(WEF).2009.ManualofPractice(MOP)No.32:EnergyConservationin

WaterandWastewaterFacilities.PreparedbytheEnergyConservationinWaterandWastewater

TreatmentFacilitiesTaskForceoftheWaterEnvironmentFederation.McGrawHill,NewYork.

USEPA.2008.EnsuringaSustainableFuture:AnEnergyManagementGuidebookforWastewaterand

WaterUtilities.January2008.Availableonline:

http://www.epa.gov/waterinfrastructure/pdfs/guidebook_si_energymanagement.pdf


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2.RecommendedApproachtoEnergyManagement

2.1 Introduction

Equipmentupgradesandoperationalmodificationstoreduceenergyuseshouldnotbeone

timeevents,butshouldbeincorporatedintoacomprehensiveenergyreviewandmanagementstrategy.

Section2.2presentsEPAsrecommendedapproachtoenergymanagementforwastewaterutilities. On

linetoolsandfinancingresourcesareavailabletoutilitiesinterestedindevelopinganenergy

managementstrategyandaredescribedinSections2.3and2.4respectively.

AsexplainedinChapter1,thescopeofthisdocumentisenergyconservationmeasures(ECMs)

relatedtoequipmentupgradesandoperationsstrategies,withafocusoninnovativeandemerging

technologies.Theseareonlyasubset,however,oftheECMsavailabletowastewaterutilities.Section

2.5listsothertypesofECMs(mainlyconventional)andprovidesreferencesforadditionalinformation.

2.2 RecommendedApproach

Tooptimizeenergysavingsatawastewatertreatmentplant(WWTP)nowandinthefuture,

ECMsshouldbeevaluatedandimplementedaspartofacomprehensiveenergymanagementprogram.

Inordertoassistutilitiesindevelopingsuchaprogram,theEPAOfficeofWastewaterManagement

developedaguidebookentitledEnsuringaSustainableFuture: AnEnergyManagementGuidebookfor

WastewaterandWaterUtilities(USEPA,2008a)

http://www.epa.gov/waterinfrastructure/pdfs/guidebook_si_energymanagement.pdf,whichnotesthat:

Moreandmoreutilitiesarerealizingthatasystematicapproachformanagingthefullrangeof

energychallengestheyfaceisthebestwaytoensurethattheseissuesareaddressedonan

ongoingbasisinordertoreduceclimateimpacts,savemoney,andremainsustainable(EPA

2008,p.3).

ThisEPAguidebookrecommendstheplandocheckactmanagementsystemapproachforenergy

conservationandmanagementasshowninFigure2.1. Thisbasicapproachisapplicabletoallutility

operationsandnotsolelytoenergymanagementactivities.However,theapproachhasbeenexpanded

andtailoredtowaterandwastewaterutilitiesinasimple9stepapproachshowninthetextbox

followingFigure2.1. Thesekeystepsforsuccessarebasedonexperienceofwaterandwastewater

utilitiesthathavegonethroughtheprocessofidentifyingandimplementingECMs. Notethatinthe9

stepapproach,identifyingECMsdoesnotcomeintoplayuntilStep6,DeviseaPlan.

Chapter2covers:

2.1 Introduction2.2 RecommendedApproach2.3 ToolsforEnergyManagement2.4 FinancingResources2.5 OtherECMsandResources2.6 References


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Figure21.StepsinthePlanDoCheckActManagementSystemsApproach

Source: USEPA2008b


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Recommended9StepApproachtoEnergyManagement

1. CreateanEnergySustainabilityTeam. Identifyanenergyprogrammanagementteamwithresponsibilityforimplementingtheimprovementprogramfromstarttofinish. Createacore

teamwithrepresentativesfromallaspectsofoperations,maintenanceandmanagement.

ConsiderappointinganEnergyManagerwhoseonlyresponsibilityisenergyconservation(andpossiblyrecovery)foryourfacility.

2. GatherData. Gatherdataonenergyuse(e.g.,fromgas,fueloilandelectricitybills). Makethisdataavailabletotheteam.

3. BenchmarkPerformance. Createabaselineofenergyperformanceagainstwhichyoucanmeasureimprovementsovertime. YoucandothisusingENERGYSTARsPortfolioManagerfor

wastewatertreatmentplants,availableonlineat

http://www.energystar.gov/index.cfm?c=water.wastewater_drinking_water.Portfolio

Managerhasthebenefitofconvertingalltypesofenergyuse(e.g.,naturalgas,fueloil,and

electricity)

to

a

common

unit

so

that

they

can

be

added

together,

and

provides

an

estimate

of

greenhousegasemissions. Youmayalsobeabletocompareyourutilitysperformanceto

similarutilitiesifyoumeetcertaincriteria.

4. ConductanEnergyAudit. Determinetheenergyuseofvariousprocessesandidentifyopportunitiesforenergyusereduction.

5. DevelopGoals. Identifyquantifiableenergyimprovementgoalsthatcomplementyourutilitysmission,goals,andstrategicdirection.

6. DeviseaPlan. IdentifyEnergyConservationMeasures(ECMs)anddevelopaplanforimplementing

them.

Start

with

low

hanging

fruit

and

focus

on

energy

intensive

operations

suchasaerationandpumping. Considerrenewableenergyoptionsandopportunitiesfor

energygenerationusingalternativemethods. Determinecostsandpaybackperiodsfor

variousoptions.

7. ImplementImprovements. Assignresponsibilitiesandestablishdeadlines. Consideralternativefinancingapproaches. Fullyengageandtrainyouroperationsstaff.

8. MonitorandMeasureResults. Trackperformance,reviewprogresstowardsenergygoals,anddevelopaplanformaintainingenergyefficientequipment. Reevaluateyourgoalsinlightof

newinformationandpriorities,andmakechangestoyourprogramasnecessary.

9. CommunicateSuccess. Communicatethesuccessesofyourenergymanagementprogramtoemployees,utilitymanagement,andyourcommunity.


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2.3 ToolsforEnergyManagement

Anumberoftoolshavebeendevelopedtohelpwastewaterutilitiesimplementanenergy

managementprogram. Datamanagementtoolsthatareavailableonlineinclude:

The

ENERGY

STAR

benchmarking

tool

Portfolio

Manager

provides

a

way

for

utilities

to

track

theirenergyuseaswellascomparetheirperformancetoutilitieswithsimilarsizeand

treatmentgoals.Itisavailablefreeonlineat

http://www.energystar.gov/index.cfm?c=water.wastewater_drinking_water.See

http://www.energystar.gov/index.cfm?c=business.bus_internet_presentationsfordetails

regardingregularwebbasedtraining.

Pumpandmotormanagementtools(seeChapter3formoreinformation):- ThePumpingSystemAssessmentTool(PSAT),developedbytheDepartmentofEnergy

(DOE)andavailablefreeonlineat

http://www1.eere.energy.gov/industry/bestpractices/software_psat.html

can

help

users

determinetheefficiencyoftheirexistingpumpingsystemsandcalculateenergyandcost

savingsforupgrades.

- MotorMaster+isamotorselectionandmanagementtool,availableforfreeonlineathttp://www.motorsmatter.org/.Itincludesinventorymanagementfeatures,maintenance

logging,efficiencyanalysis,savingsevaluation,andenergyaccounting.Itincludesacatalog

of17,000motorsfrom14manufacturers,includingNEMAPremiumefficiencymotors,and

motorpurchasinginformation.

2.4 FinancingResources

Fundingenergyconservationprojectsisanimportantcomponentofanenergymanagement

program,particularlyduetolimitedresourcesavailabletoutilitiesandtheneedtomeetmultiple

environmentalobjectivesandregulatoryrequirements. Anumberoffundingoptions,however,are

availabletoautility. TheCaliforniaEnergyCommission(CEC)notesthat:

Ashortageofinternalfundsneednotbeabarriertoimplementingenergyefficiencyprojects.

Thereareplentyoffinancingsources,programsandoptionsavailabletoserveyou.Realbarriers

areduetothelackofawarenessorunderstandingofthe:

1) manybenefitsofinvestinginenergyefficiencyprojects.Thesebenefitsincludeenergycostsavings,increasedrevenues,improvedworkercomfortandproductivity,

reducedmaintenancecostofold,inefficientequipment,andreductionof

environmentaldegradationand


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2)manyprogramsforfinancingenergyefficiencyprojects(CEC2000)1.

Capitalprojectsforpublicallyownedwastewaterutilitieshavehistoricallyreceivedfundingfrom

grantsandloans;however,thirdpartyfinancing(e.g.,stateenergyoffices,energyservicescompanies)is

becomingmorecommon.InmanypartsoftheU.S.,energyperformancecontracting(EPC)hasbeen

usedtofinanceenergyefficiencyimprovements(Zobler2009).Properlystructuredperformance

contractscanbeconsideredintheutilitysoperatingbudgetinsteadofasacapitalexpense.Examples

includeenergyserviceproviderbasedfinancingandtaxexemptleasepurchaseagreements.

Oneoptiontostreamlinetheaudit,financing,andimplementationstepsofanenergy

managementprogramistohireanEnergyServicesCompany(ESCO).ESCOsusuallydevelopandmanage

EPCs,manageawiderangeoftasks,andassumesomeormostofthetechnicalandperformancerisk

associatedwiththeproject.SeetheNationalAssociationofEnergyServiceCompanies(NAESCO)

websiteathttp://www.naesco.org/formoreinformationandalistofserviceprovidersinyourarea.

AdditionalguidanceisavailableintheCECsHandbook,HowtoHireanEnergyServicesCompany(CEC

2000),availableonlineathttp://www.energy.ca.gov/reports/efficiency_handbooks/40000001D.PDF.

Inadditiontotheaboveresources,otherfreetoolsandresourcesareavailabletohelp

wastewaterutilitiesfinanceECMs.Examplesareprovidedbelow.

TheCleanWaterStateRevolvingFund(CWSRF),offeringlowinterestloans(average2.2percent)forwastewatertreatmentimprovements.Theprogramisadministeredbyindividual

statesAlistofregionalandstatecontactsisavailableonlineat

http://www.epa.gov/owm/cwfinance/cwsrf/contacts.htm.

FinancingguidancefromENERGYSTAR,availableonlineathttp://www.energystar.gov/index.cfm?c=business.bus_financing.Includesaspreadsheetbased

CashFlowOpportunity(CFO)Calculatorthatcanhelpplantmanagerscalculatesimplepayback

aswellascostofdelay,whichisthelostopportunitycostiftheprojectisdelayed12monthsormore.

DatabaseofStateIncentivesforRenewablesandEfficiency(DSIRE),availableonlineathttp://www.dsireusa.org/isacomprehensivesourceofinformationonstate,local,utility,and

federalincentivesandpoliciesthatpromoterenewableenergyandenergyefficiency.

Establishedin1995,DSIREisanongoingprojectoftheNorthCarolinaSolarCenterandthe

InterstateRenewableEnergyCouncil,whichisfundedbytheU.S.DepartmentofEnergy(DOE).

ReportbytheCECtitledHowtoFinancePublicSectorEnergyEfficiencyProjects(CEC2000),availableonlineathttp://www.energy.ca.gov/reports/efficiency_handbooks/40000001A.PDF.

Includesadescriptionofcosteffectivenesscriteriaandoptionsforfinancingenergyefficiency

projects.

1Formoreinformation,seetheCECreport,HowtoFinancePublicSectorEnergyEfficiencyProjects.January2000.

Availableonlineathttp://www.energy.ca.gov/reports/efficiency_handbooks/40000001A.PDF


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2.5 OtherECMsandResources

Althoughthefocusofthisdocumentistoreportoninnovativeandemergingequipmentand

operationsrelatedECMs,otherECMs(bothinnovativeandconventional),havebeenusedsuccessfully

atWWTPstosaveenergyandassociatedcosts,suchas:

Lighting,HVAC,andotherbuildingimprovements. ReducingtheloadingtotheWWTPsby:

- Collectionsystemimprovementstoreduceinfiltrationandinflowtoreducestormrelatedpeaks

- Waterconservation- Useofequalizationbasinstoattenuatepeakflowsandloadings

UseofSupervisoryControlandDataAcquisition(SCADA)softwareforprocessmonitoringandoperationalcontrol. SCADAhasmanyoperationalbenefits,including:

- Itcanprovidedataforprocessmodelingandenergyuseoptimization- Itcanprovideimmediatedetectionofproblemsthroughdiagnosticdisplays,enabling

quickinterventionforfastresolutions

- Itcanallowoperatorstocompensateforseasonalflowandwetweatherbyautomaticallyadjustingsetpoints(USEPA2006).

Implementingcogenerationtechnologytogenerateelectricityandrecoverableheatonsiteusingmethaneoffgasfromanaerobicdigesters.

Implementingenergymanagementstrategiessuchas- Hiringanenergymanager- Realtimepowermonitoring- Peakelectricdemandreduction- Submeteringtoidentifythemostenergyintensiveprocesses

OtherECMsthatcanoffermodestimprovementsandmaybeeasyforasystemtoimplementinclude

pumpcoatingstoreducefrictionorinstallingavortexgritremovalsysteminsteadofonethatuses

aeration.

ECMsshouldalwaysbeconsideredwhenaplantisfacingamajor20or30yearupgrade. Atthis

time,thereareopportunitiestoreconfiguretheplantforenergysavings. NotedinChapters3and4of

thisdocumentbutworthreiteratingistheimportanceofproperlydesigningforenergyefficiency.

Maximizingequipment(blowerandpump)turndowncapacityanddesigningforplantupgradesinstages

(i.e.,rightsizing)cangoalongwaytomeetenergyefficiencygoals. Anotherimportantdesign

conceptistousehydraulicheadwheneverpossibletoreducetheneedtopump. TheConsortiumfor

EnergyEfficiency(CEE)hasrecentlyissuedguidanceonhowtoincludeenergyefficiencyinrequestsfor

qualifications(RFQs)andRequestsforProposals(RFPs). Thisguidanceisavailablefreeonlineat

http://www.cee1.org/ind/motsys/ww/rfp/index.php3.


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AppendixBofthisreportprovidesacomprehensivelistofwebreferencesforenergy

conservation.OtherimportanttechnicalreferencesincludetheWaterEnvironmentFederation(WEF)

ManualofPractice(MOP)No.32:EnergyConservationinWaterandWastewaterFacilities(WEF2009)

andthereportbytheElectricPowerResearchInstitute(EPRI),QualityEnergyEfficiencyRetrofitsfor

WastewaterSystems(EPRI1998).TheWEFMOP8,DesignofMunicipalWastewaterTreatmentPlants

(WEFandASCE2010)providesguidanceondesigningenergyefficientwastewatertreatmentplant

components.TheWERFreport,EnergyEfficiencyinWastewaterTreatmentinNorthAmerica:A

CompendiumofBestPracticesandCaseStudiesofNovelApproaches,providesrecommendationson

energyefficiencyimprovementsboththroughoptimizationofcurrentprocessesandthroughadoption

ofnovelapproaches.ThereportisscheduledtobepublishedinJanuary2011.Lastly,theWERFreport,

BestPracticesforSustainableWastewaterTreatment:InitialCaseStudyIncorporatingEuropean

ExperienceandEvaluationToolConcept(2009),highlightsEuropeancasestudiesrelatedtoenergy

efficiencyinwastewatertreatment.

Additionalonlineresourcesforcomprehensiveenergymanagementinclude:

EnsuringaSustainableFuture: AnEnergyManagementGuidebookforWastewaterandWaterUtilities(USEPA2008a). Thisdocumentprovidesastepbystepmethodforenergyconservation

basedonthePlanDoCheckActmanagementapproach.Itisavailableonlineat:


EPAsWastewaterManagementFactSheet:EnergyConservation(USEPA2006),availableonlineat:http://www.epa.gov/owm/mtb/energycon_fasht_final.pdf. This7pagefactsheetdescribes

possiblepracticesthatcanbeimplementedtoconserveenergyataWWTP.

TheFlexYourPowerBestPracticesGuideforLocalGovernments,WastewaterSector,availableonlineat: http://www.fypower.org/bpg/module.html?b=institutional&m=Water_Use. This

guidecontainsa4stepapproachtoreducingenergyuseataWWTPandincludeslinksto

additionalonlineresources.

WisconsinFocusonEnergysWaterandWastewaterEnergyBestPracticeGuidebook(FocusonEnergy2006),availableonlineat:

http://www.werf.org/AM/Template.cfm?Section=Home&TEMPLATE=/CM/ContentDisplay.cfm&

CONTENTID=10245. ThisguidebookcontainsbenchmarkingresultsfromselectedWisconsin

wastewaterfacilities,bestpracticeapproachestoongoingmanagementofenergyuse,best

practicefundingandfinancingopportunities,andreferencesforfurtheropportunitiesin

water/wastewatersystemenergyefficiencyandpowerdemandreduction.

2.6 References

CaliforniaEnergyCommission(CEC).2000.HowtoFinancePublicSectorEnergyEfficiencyProjects.

January2000.Availableonlineathttp://www.energy.ca.gov/reports/efficiency_handbooks/40000

001A.PDF

Cantwell,J.,J.Newton,T.Jenkins,P.Cavagnaro,andC.Kalwara.2009.RunninganEnergyEfficient

WastewaterUtilityModificationsThatCanImproveYourBottomLine.WEFWebcast.June19,2009.


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EnergyStar.2010.EnergyStarGuidelinesforEnergyManagement.U.S.EnvironmentalProtection

AgencyandtheU.S.DepartmentofEnergy.Accessed1March2010.

http://www.energystar.gov/index.cfm?c=guidelines.guidelines_index

EPRI.1998.QualityEnergyEfficiencyRetrofitsforWastewaterSystems.ElectricPowerResearch

Institute.ProjectManager:KeithCarns.CR109081.

FocusonEnergy.2006.WaterandWastewaterEnergyBestPracticeGuidebook.Reportpreparedby

ScienceApplicationsInternationalCorporation.Availableonlineifrequestedat

http://www.focusonenergy.com/Business/IndustrialBusiness/Guidebooks/

Ishida,C.,E.Garvey,S.Dent,S.Deslauriers,andH.S.McDonald.2008.Optimo:AnInnovative

WastewaterMasterPlanOptimizationModelThatImprovesSystemEfficiency,ReducesRisks,andSaves

CapitalandO&MCosts.PresentedatUtilityandManagement2008.Tampa,FL.WEF.

USDOE.2007. MotorMaster+:MotorDrivenSystems,version4.0.6.U.S.DepartmentofEnergy.

http://www1.eere.energy.gov/industry/bestpractices/software_motormaster.html

USDOE.2008.PumpingSystemAssessmentTool(PSAT).U.S.DepartmentofEnergy.

http://www1.eere.energy.gov/industry/bestpractices/software_psat.html

USEPA.2006.WastewaterManagementFactSheet:EnergyConservation.July2006.EPAOfficeofWater

832F06024.Availableonline:http://www.epa.gov/owm/mtb/energycon_fasht_final.pdf

USEPA.2008a.EnsuringaSustainableFuture:AnEnergyManagementGuidebookforWastewaterand

WaterUtilities.January2008.Availableonline:


USEPA.2008b.EPAEnvironmentalManagementSystems:BasicInformation. Lastupdated17June

2008.Availableonline:http://www.peercenter.net/toolkit/

WEFandASCE.2010.DesignofMunicipalWastewaterTreatmentPlantsWEFManualofPractice8and

ASCEManualsandReportsonEngineeringPracticeNo.76,5thEd.WaterEnvironmentFederation,

Alexandria,VA,andAmericanSocietyofCivilEngineersEnvironment&WaterResourcesInstitute,

Reston,Va.

WEF.2009.MOPNo.32:EnergyConservationinWaterandWastewaterFacilities.Preparedbythe

EnergyConservationinWaterandWastewaterTreatmentFacilitiesTaskForceoftheWater

EnvironmentFederation.McGrawHill,NewYork.

WERF.2009.BestPracticesforSustainableWastewaterTreatment:InitialCaseStudyIncorporating

EuropeanExperienceandEvaluationToolConcept.Alexandria,VA:WERF.Availableonline:http://www.werf.org/AM/Template.cfm?Section=Search&Template=/CustomSource/Research/Publicati

onProfile.cfm&id=OWSO4R07a


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3.EnergyConservationMeasuresforPumpingSystems

3.1 Introduction

Pumpingoperationscanbeasignificantenergydrawatwastewatertreatmentplants(WWTPs),

inmanycasesaresecondonlytoaeration.Pumpsareusedformanyapplications. Attheplant

headworks,theymaybeusedtoprovidehydraulicheadforthetreatmentprocesses.Withintheplant,

theyareusedtorecycleandconveywasteflows,solids,andtreatedeffluenttoandfromavarietyof

treatmentprocesses.Pumpsarealsofoundinremotelocationsinthecollectionsystemtohelpconvey

wastewatertotheplant.

Theoverallefficiencyofapumpingsystem,alsocalledthewiretowaterefficiency,isthe

productoftheefficiencyofthepumpitself,themotor,andthedrivesystemormethodofflowcontrol

employed.Pumpsloseefficiencyfromturbulence,friction,andrecirculationwithinthepump(WEF

2009).Anotherlossisincurrediftheactualoperatingconditiondoesnotmatchthepumpsbest

efficiencypoint(BEP).1 Thevariousmethodsforcontrollingflowratedecreasesystemefficiency.

Throttlingvalvestoreducetheflowrateincreasesthepumpinghead,flowcontrolvalvesburnhead

producedbythepump,recirculationexpendspowerwithnousefulwork,andVFDsproduceaminor

amount

of

heat.

Of

these

methods,

VFDs

are

the

most

flexible

and

efficient

means

to

control

flow

despitetheminorheatlossincurred.Table31summarizestypicalpumpsystemefficiencyvaluesnote

thatinefficiencyinmorethanonecomponentcanaddupquickly,resultinginaveryinefficientpumping

system.

1BEPistheflowrate(typicallyingallonsperminuteorcubicmetersperday)andhead(infeetormeters)thatgivesthe

maximumefficiencyonapumpcurve. Forbasicinformationonpumpsystemdesign,seetheWEFManualofPracticeNo.32,

EnergyConservationinWaterandWastewaterFacilities(WEF2009),orthesixpartseries,UnderstandingPumpSystem

FundamentalsforanEnergyEfficientWorld(PumpZone2008and2009),availableonlineathttp://www.pump

zone.com/pumps/pumps/understandingpumpfundamentalsforanenergyefficientworld.html

Chapter3covers:

3.1 Introduction

3.2 Pumping

System

Design

3.3 Motors

3.4 PowerFactor

3.5 VariableFrequencyDrives(VFDs)

3.6 References


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Table31.PumpSystemEfficiency

Pump SystemComponent

Efficiency

Range Low Avg High

Pump 30 85 % 30 % 60 % 75 %1

Flow Control2

20 98 % 20 % 60 % 98 %Motor

385 95 % 85 % 90 % 95 %

Efficiency of System 5 % 32 % 80 %1. For pumping wastewater. Pump system efficiencies for clean water can be higher.2. Represents throttling, pump control valves, recirculation and VFDs.3. Represents nameplate efficiency and varies by horsepower. See Section 3.4 for more information

Inefficienciesinpumpingoftencomefromamismatchbetweenthepumpandthesystemit

servesduetoimproperpumpselection,changesinoperatingconditions,ortheexpectationthatthe

pumpwilloperateoverawiderangeofconditions.Signsofaninefficientpumpingsysteminclude:

Highly

or

frequently

throttled

control

valves

Bypassline(recirculation)flowcontrol

Frequenton/offcycling

Cavitationnoiseatthepumporelsewhereinthesystem

Ahotrunningmotor

Apumpsystemwithnomeansofmeasuringflow,pressure,orpowerconsumption

Inabilitytoproducemaximumdesignflow

Formoreinformation,refertothePumpSystemBasicAssessmentGuide(PumpSystemsMatterTM

2010),availableonlineathttp://www.pumpsystemsmatter.org/content_detail.aspx?id=3334.

The

literature

provides

several

examples

of

plants

reducing

pumping

energy

by

as

much

as

50

percentthroughpumpsystemimprovements(FocusonEnergy2006).Energysavingsresultfrom

loweringofpumpingcapacitytobettermatchsystemdemands,replacinginefficientpumps,selecting

moreefficientmotors,andinstallingvariablespeedcontrollers.Generallyspeaking,energyconservation

measures(ECMs)forpumpingareconventionalanddonotrepresentanareawhererecenttechnology

innovationhasplayedapartinimprovingenergyconservationandefficiency.PumpingECMsare,

however,stillextremelyimportanttoreducingandoptimizingenergyuseatwastewatertreatment

plants.ThischapterprovidesanoverviewofconventionalECMsrelatedtopumpingdesign,variable

frequencydrives(VFDs),andmotorsandrefersthereadertoindustrystandardsandweblinksfor

additionalguidance.

WastewaterutilitiesshouldconsiderimplementingpumpingECMsaspartofalongtermpump

testingandmaintenanceprogram.Pumpsshouldbetestedeverytwotothreeyearstoensurethatthey

areoperatingefficiently.Utilitiesshouldtestforflow,head,andpowerconsumptionandthencalculate

efficiencyforeachpumpsystem.Ifoverallsystemefficiencyislow(lessthan60or70percentfor

centrifugalwastewaterpumps,lessthan72percentforcleanwaterpumps2),amoredetailedevaluation

iswarranted.Thistypeofprogramcangivetheplantearlywarningwhenpumpcomponentsarefailing

andcanpreventcatastrophicfailures.Itisimportantthatallcomponentsbeevaluatedandaddressed

2EmailcommunicationfromKenHenderson,September8,2010.


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holisticallysothattheentiresystemisenergyefficient.Stateandlocalrequirementsforredundancy

(e.g.,thecommonrequirementthatapumpstationcanpumppeakflowswiththelargestpumpoutof

service)andsafetyfactorsmaylimitavailableefficienciesinsomecases.

Severaltoolsareavailablefreeonlinetoassistwastewaterutilitiesindevelopingapumptesting

andmaintenanceprogram.PumpSystemsMatterTM,aneducationprogramconceivedbytheHydraulic

Institute,providestechnicalreferences,downloadabletools,tipsheets,andwhitepapersontheir

websiteathttp://www.pumpsystemsmatter.org/default.aspx.TheDepartmentofEnergy(DOE)has

developedandsupportsthePumpSystemAssessmentTool(PSAT),availablefreeonlineat

http://www1.eere.energy.gov/industry/bestpractices/software_psat.html,tohelpusersdeterminethe

efficiencyoftheirexistingpumpingsystemsandcalculateenergyandcostsavingsforupgrades.The

WaterEnvironmentFederation(WEF)providesguidanceonlifecyclecosting,operationand

maintenancepractices,andmeasurementequipmentintheirMOPNo.32(WEF2009).

3.2 PumpingSystemDesign

Appropriatesizingofpumpsiskeytoefficientoperationofwastewatertreatmentplants.Pumps

sizedforpeakflowconditionsthatoccurinfrequentlyor,worse,inthefuturetowardstheendofthe

pumpsservicelifeoperatethemajorityofthetimeatareducedflowthatisbelowtheirBEP. Peakflow

istypicallyseveraltimesgreaterthanaveragedailyflowandcanbeanorderofmagnitudedifferent

thanminimumflow,especiallyforsmallsystemsorsystemswithsignificantinflowandinfiltration(I&I).

Insomesystems,theseprojectedfutureflowsareneverreachedduringthedesignlifeofthepump.

Forexistingtreatmentplants,utilitiesshouldevaluatetheoperationofexistingpumpsand

identifyopportunitiesforenergyreduction.Agoodstartingpointistodeterminetheefficiencyof

existingpumpingsystems,focusingfirstonpumpsthatoperateforthemosthoursandhavepotential

problemsasidentifiedbythebulletlistinSection3.1(presenceofbypasslines,throttledvalves,etc.).

Plantsshouldcollectperformanceinformationontheflowrate,pressure,anddeliveredpowertothe

pumps.

Field

measurements

may

be

necessary

if

the

plant

does

not

regularly

record

this

information.

Pumpandsystemcurvescanthenbeconstructedtodeterminetheactualoperatingpointsofthe

existingsystem.Operatingpointsmorethan10percentdifferentthantheBEPsignalroomfor

improvement.DetailedguidanceonpumpsystemassessmentisprovidedinthePumpSystemsMatter

publication,PumpSystemBasicAssessmentGuide,availableonlineat

http://www.pumpsystemsmatter.org/content_detail.aspx?id=3334

Toimproveefficiency,utilitiesshouldconsiderreplacingoraugmentinglargecapacitypumps

thatoperateintermittentlywithsmallercapacitypumpsthatwilloperateforlongerperiodsandcloser

totheirBEP. Whenreplacingapumpwithasmallerunit,boththehorsepowerandefficiencychange. A

quickwaytoestimatetheannualenergycostsavingsistoapproximatecostbeforeandafterthe

improvementanddeterminethedifferenceusingthefollowingequation:

AnnualEnergySavings($)=[hp1xL1x0.746xhrxE1xC][hp2xL2x0.746xhrxE2xC] Eq.31

Where:

hp1=horsepoweroutputforthelargercapacitypump

hp2=horsepoweroutputforthesmallercapacitypump

L1=loadfactoroflargercapacitypump(percentageoffullload/100 determinedfrompump

curve)


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L2=loadfactorofsmallercapacitypump(percentageoffullload/100 determinedfrompump

curve)

hr=annualoperatinghours

C=energy(electricpower)rate($/kWh)

E1=efficiencyofthelargercapacitypump

E2=efficiencyofthesmallercapacitypump

SeeExample31forhowtheTownofTrumbullwasabletosavemorethan$1,500peryearbyaddinga

smallpumptooneofitsexistingsewagepumpingstations.Whenappliedcorrectly,replacementof

standarddriveswithVFDscanalsoyieldsignificantimprovements(seeSection3.3foradditional

discussion).

Forgreenfieldplantsand/ornewpumpstations,utilitiesshouldconsiderandplanforstaging

upgradesoftreatmentcapacityaspartofthedesignprocess.Forexample,multiplepumpscanbe

specifiedtomeetafuturedesignflowinsteadofonelargepumpsothatindividualpumpscanbe

installedasneeded,sayatyearzero,yearten,andyeartwenty.TheStateofWisconsinsFocuson

Example31 TownofTrumbull,CT,ImprovesEfficiencyatReservoirAvenuePumpStation

BACKGROUND:WastewaterfromtheTownofTrumbull,insouthwesternCT,iscollectedand

conveyedtoaWWTPinBridgeportviatensewagepumpstations. Oneofthese,theReservoirAvenue

Pumpstation,consistingoftwo40hpdirectdrivepumpsdesignedtohandleanaveragedailyflowof

236gallonsperminute(gpm). Eachpumpwasoperatedatareducedspeedof1320rpmat50.3feet

oftotaldynamichead(TDH)withadutypointofapproximately850gpm. Abubblertypelevelcontrol

systemwasusedtoturnthepumpsoffandon. Onepumpcanhandletheentirepeakinflow(usually


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Energybestpracticesguidebook(FocusonEnergy2006)estimatesthatstagingoftreatmentcapacity

canresultinenergysavingsbetween10and30percentoftotalenergyconsumedbyaunitprocess.

3.3 Motors

Thecostofrunningelectricmotorscanbethelargestfractionofaplantstotaloperatingcosts.

WEFestimatesthatelectricmotorsmakeup90percentoftheelectricenergyconsumptionofatypical

wastewatertreatmentplant(WEF2009). Inefficientmotors,operationoutsideofoptimalloading

conditions,andmechanicalorelectricalproblemswiththemotoritselfcanleadtowastedenergyatthe

plantandareopportunitiesforsavings.

Thepercentenergysavingsresultingfromreplacingoldermotorswithpremiummotorsis

modest,typicallybetween4and8percent(NEMAStandardMG1.2006).Savingscanbehigherwhen

energyauditsrevealthatexistingmotorsachieveverylowefficiencies,orwhenexistingmotorsare

oversizedand/orunderloaded.Manyplantshavecoupledmotorreplacementswithupgradesfrom

fixedspeedtovariablespeeddrivesforsignificantlyhigherenergysavings.

Ingeneral,upgradingmotorsisaconventionalECMthathasbeenpracticedatwastewater

treatmentplantsforsometime.Becausethemainfocusofthisreportisinnovativeratherthan

conventionaltechnologies,thissectioncontainsonlyabriefoverviewofmaterial,anddirectsthereader

tootherpublicallyavailablewebsitesandreferencesfordetailedinformation.Specifically,Section3.3.1

describesmotorefficiencyandsummarizescurrentmotorefficiencystandards,andSection3.3.2

provideslinkstomotormanagementtoolsandsoftware.Theexceptiontoconventionalpracticesisthe

emergenceofnew,ultraefficiencymotors,whicharedescribedinSection3.3.3.

Inadditiontotoolsandreferencesidentifiedinsubsequentsections,thereaderisreferredto

thefollowingwebsitesfortechnicalinformationonmotors:

TheU.S.DOEprovidesextensiveinformationaspartoftheirMotorChallengesProgram.Publicationsincludedownloadablebooks,tipsheets,andfactsheetsontechnicalandeconomic

topicsrelatedtomotors.See

http://www1.eere.energy.gov/industry/bestpractices/techpubs_motors.html foralistof

publishedmaterialandrelevantweblinks.

TheConsortiumforEnergyEfficiency(CEE)providestechnicalmaterial,links,andfactsheets

underitsMotorsandMotorSystemsIndustrialProgram(http://www.cee1.org/ind/mot

sys/mtrmsmain.php3).


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3.3.1 MotorEfficiencyandEfficiencyStandards

Motorefficiencyisameasureofmechanicalpoweroutputcomparedtoelectricalpowerinput,

expressedasapercentage.

Motorefficiency=Pm/Pe Eq.32

Where:

Pm=mechanicalpoweroutputofthemotorinWatts

Pe=electricalpowerinputtothemotorinWatts(WEF2009)

Nomotoris100percentefficientallmotorsexperiencesomepowerlossduetofriction,electrical

resistancelosses,magneticcorelosses,andstrayloadlosses.Smallermotorsgenerallyexperience

higherlossescomparedtolargermotors.

TheUnitedStatesCongress,intheEnergyPolicyAct(EPACT)of1992,setminimumefficiency

standardsforvarioustypesofelectricmotorsmanufacturedinorimportedtotheUnitedStates.

Minimumnominal,fullloadefficienciestypicallyrangefrom80to95percentdependingonsize(i.e.,

horsepower)andothercharacteristics.Motorsmanufacturedsince1997wererequiredtocomplywith

EPACTstandardsandtobelabeledwithacertifiedefficiencyvalue.

TheNationalElectricalManufacturersAssociation(NEMA)premiumefficiencystandardhas

existedsince2001(NEMA2006)asavoluntaryindustrystandardandhasbeenwidelyadopteddueto

itspower(andthuscost)savingsoverEPACT1992compliancestandards.The2007EnergyActraised

efficiencystandardsofmotorstoNEMApremiumefficiencylevelsandsetnewstandardsformotorsnot

coveredbypreviouslegislation.The2007act,whichcomesintoforceinDecember2010,issummarized

onlineathttp://www.motorsmatter.org/resources/gen_legislation.html.

Submersible

motors

are

commonly

used

in

wastewater

treatment

plants.

They

serve

specialized

applicationsinenvironmentsthatarenotsuitedforNEMAmotors. Thereiscurrentlynoefficiency

standardforsubmersiblemotorsandtheirefficiencyislessthanNEMAmotors. Additionally,their

powerfactorisusuallylower. Theirselectionisusuallydrivenbytheapplication,thoughsome

applicationshavealternativesthatuseNEMAmotors. Efficiencyshouldbeconsideredintheevaluation

ofalternativesintheseapplicationsasitaffectsthelifecyclecostusedintheselectionprocess.

Operatingefficiencyinthefieldisusuallylessthanthenominal,fullloadefficiencyidentifiedby

themotormanufacturer.Onereasonforthisistheoperatingload.Asaruleofthumb,mostmotorsare

designedtooperateatbetween50and100percentoftheirratedload,withmaximumefficiency

occurringatabout75percentofmaximumload.Forexample,amotorratedfor20horsepower(hp)

shouldoperatebetween10and20hpandwouldhaveitsbestefficiencyaround15hp.Largermotors

canoperatewithreasonableefficiencyatloadsdowntothe25percentrange(USDOE1996).Motors

operatedoutsideoftheoptimalloadingloseefficiency.Otherfactorsthatreduceefficiencyinthefield

includepowerquality(I.e.,propervoltage,amps,andfrequency)andtemperature.Motorsthathave

beenrewoundtypicallyarelessefficientcomparedtotheoriginalmotor.

Accuratelydeterminingtheefficiencyofmotorsinserviceataplantischallengingbecausethere

isnoreliablefieldinstrumentformeasuringmechanicaloutputpower.Severalmethodsareavailable,

however,toapproximatemotorefficiency.Forasummary,seetheU.S.DepartmentofEnergyfactsheet


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onthesubject(USDOE2005),availableonlineat

http://www1.eere.energy.gov/industry/bestpractices/pdfs/estimate_motor_efficiency_motor_systemts

2.pdf.OnemethodistousefieldmeasurementsandtechnicaldataintheMotorMaster+softwaretool

toestimateefficiency.Section3.3.2providesadditionalinformationonthistool.

3.3.2 MotorManagementPrograms

Wastewaterutilitiesshouldconsiderpurchasingnewenergyefficientpremiummotorsinstead

ofrewindingolderunitswhenreplacingequipmentandwhenmakingmajorimprovementsattheplant

(seethetextboxinthissectionforadditionalrecommendations). Motorreplacementisbestdoneas

partofaplantwidemotormanagementprogram.Afirststepinprogramdevelopmentistocreatean

inventoryofallmotorsattheplant.Theinventoryshouldcontainasmuchinformationaspossible

includingmanufacturersspecifications,nameplateinformation,andfieldmeasurementssuchas

voltage,amperage,powerfactor,andoperatingspeedundertypicaloperatingconditions.Followingthe

datagatheringphase,plantmanagersshouldconductamotorreplacementanalysistodeterminewhich

motorstoreplacenowandwhicharereasonablyefficientandcanbereplacedinthefutureorattimeof

failure.

Akeyinputtoanymotorreplacementanalysisiseconomics.Asimpleapproachistocalculate

theannualenergysavingsofthenewmotorcomparedtotheoldunitanddeterminethepaybackperiod

inyears(inotherwords,whenwillthecumulativeenergysavingsexceedtheinitialcosts).Thefollowing

simpleequationcanbeusedtodetermineannualenergysavings:

AnnualEnergySavings($)=hpxLx0.746xhrxCx(Ep Ee) Eq.33

Where:

hp=horsepoweroutputofmotor

L=loadfactor(percentageoffullload/100)

0.746=conversionfromhorsepowertokWunits

hr=annualoperatinghours

C=energy(electricpower)rate($/kWh)

Ee=existingmotorefficiencyasapercentage

Ep=premiummotorefficiencyasapercentage

WhenShouldPlantsConsiderBuyingNewEnergyEfficientMotors?

Fornewinstallations

Whenpurchasingnewequipmentpackages

Whenmakingmajormodificationstotheplant

Insteadofrewindingolder,standardefficiencyunits

Toreplaceoversizedand/orunderloadedmotors

Aspartofapreventivemaintenanceorenergyconservationprogram

Source: MotorChallengeFactSheet:BuyinganEnergyEfficiencyElectricMotor. Availableonline

athttp://www1.eere.energy.gov/industry/bestpractices/pdfs/mc0382.pdf


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Simplepaybackinyearscanthenbecalculatedasthenewmotorcost(capitalplusinstallation)

dividedbytheannualenergysavings.Whencomparingbuyingapremiummotorinsteadofrewinding

anexistingone,thecostofrewindingtheexistingmotorshouldbesubtractedfromthemotorcost.Any

cashrebatefromyourlocalelectricutilityorstateenergyagencyshouldalsobesubtractedfromthe

costofthenewmotor. Whenreplacingpumps,motors,orcontrolsystems,upgradingtheelectrical

service,wiring,transformers,andothercomponentsoftheelectricalsystemshouldbeconsideredin

calculatingenergysavingsandlifecyclecosts. Utilitiesshouldalsoconsidertheimportanceofreliability

andenvironmentalfactorswhenmakingmotorreplacementdecisions.Morerobusteconomicanalyses

suchasnetpresentvaluelifecyclecostanalysisshouldbeconsidered,especiallyforlargeexpenditures.

TheENERGYSTARCashFlowOpportunity(CFO)calculatorisaneasytousespreadsheettool

thatcanhelpplantmanagerscalculatesimplepaybackaswellascostofdelay,whichisthelost

opportunitycostiftheprojectisdelayedtwelvemonthsormore.Thelastsheetoftheworkbook

providesasummarythatcanbegiventoseniormanagersanddecisionmakerstohelpconvincethemof

thefinancialsoundnessofenergyefficiencyupgrades.TheCFOcalculatorandotherfinancialtoolsare

availableforfreedownloadathttp://www.energystar.gov/index.cfm?c=assess_value.financial_tools.

Thetaskofmotorinventorymanagementandreplacementanalysisismadesignificantlyeasier

bypublicallyavailablesoftwaretools.DevelopedbytheDOEIndustrialTechnologiesProgram,

MotorMaster+isamotorselectionandmanagementtool,availablefreeonlineat

http://www.motorsmatter.org/.Itincludesinventorymanagementfeatures,maintenancelogging,

efficiencyanalysis,savingsevaluation,andenergyaccounting.Itincludesacatalogof17,000motors

from14manufacturers,includingNEMAPremiumefficiencymotors,andmotorpurchasing

information.InadditiontoMotorMaster+software,thesponsorsoftheMotorDecisionsMatter

campaigndevelopedaspreadsheettooltoassistplantmanagerswithmotorreplacement/repair

decisionmaking.Thetoolistitledthe1*2*3ApproachtoMotorManagementandisavailableforfree

downloadathttp://www.motorsmatter.org/tools/123approach.html.

3.3.3

Innovative

and

Emerging

Technologies

SiemensEnergyandAutomationincooperationwiththeCopperDevelopmentAssociationhas

developedultraefficientcopperrotorsquirrelcagetypeinductionACmotors.Thesemotorsexceed

NEMApremiumfullloadefficiencystandardsbyupto1.4percent;however,theyareonlycurrently

availableinoutputsupto20hp.Inadditiontousinghighconductivitycopperrotorsinplaceof

aluminum,thenewmotorshavethefollowingefficiencyimprovements:

Optimizedrotorandstatordesign

Lowfrictionbearings

Improvedcoolingsystem

Polyureabasedgrease

Dynamicallybalancedrotors

Precisionmachinedmatingsurfacesforreducedvibration

ThemotorsinsulationisdesignedtobecompatiblewithVFDs(USDOE2008).

TheU.S.DepartmentofEnergy(USDOE),incooperationwithBaldorElectricCompanyandother

privatepartners,isdevelopinganewgradeofUltraEfficientandPowerDenseElectricMotors,withthe

goalofa15percentreductioninmotorenergylossoverNEMApremiummotors.Forexample,ifa


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NEMApremiummotorwithparticularcharacteristicsandoutputhorsepowerwas92percentefficient

andthushad8percentloss,thisnewgradeofmotorwouldreducelossby0.15*8%=1.2percent,fora

newoverallefficiencyof93.2percent.Thenewgradeofmotorwillalsobe30percentsmallerinvolume

and30percentlowerinweight,leadingtodecreasedmotorcostduetolowermaterialscosts(USDOE

2009).Formoreinformation,seeDOEswebsiteat

http://www1.eere.energy.gov/industry/intensiveprocesses/pdfs/electric_motors.pdf.

3.4 PowerFactor

Powerfactorisimportantbecausecustomerswhoseloadshavelowpowerfactorrequire

greatergenerationcapacitythanwhatisactuallymetered. Thisimposesacostontheelectricutility

thatisnototherwiserecoveredbytheenergyanddemandcharges. Therearetwotypesofpowerthat

makeupthetotalorapparentpowersuppliedbytheelectricutility. Theirrelationshipisshownin

Figure31. Thefirstistheactivepower. MeasuredinkW,itisthepowerusedbytheequipmentto

producework. Thesecondisthereactivepower. Thisisthepowerusedtocreatethemagneticfield

necessaryforinductiondevicestooperate. ItismeasuredinkVARs.

Figure31. VectorRelationshipofACPower

Powerfactoristheratiooftheactivepowertotheapparentpower. Thepowerfactoroffully

loadedinductionmotorsrangesfrom80to90percentdependingonthetypeofmotorandthemotors

speed. Powerfactordeterioratesastheloadonthemotordecreases. Otherelectricaldevicessuchasspaceheatersandolderfluorescentorhighdischargelampsalsohavepoorpowerfactor. Treatment

plantshaveseveralmotors,numerouslamps,andoftenelectricheaters,which,combined,lowersthe

facilitysoverallpowerfactor.

Powerfactormaybeleadingorlagging. Voltageandcurrentwaveformsareinphaseina

resistiveACcircuit. However,reactiveloads,suchasinductionmotors,storeenergyintheirmagnetic

fields. Whenthisenergygetsreleasedbacktothecircuititpushesthecurrentandvoltagewaveforms

outofphase. Thecurrentwaveformthenlagsbehindthevoltagewaveform. Whentheloadis

capacitive,theoppositeoccurs,andthecurrentwaveformleadsthevoltagewaveform.

Improvingpowerfactorisbeneficialasitimprovesvoltage,decreasessystemlosses,frees

capacitytothesystem,anddecreasespowercostswherefeesforpoorpowerfactorarebilled. Power

factorcanbeimprovedbyreducingthereactivepowercomponentofthecircuit. Addingcapacitorsto

aninductionmotorisperhapsthemostcosteffectivemeanstocorrectpowerfactorastheyprovide

reactivepower. Synchronousmotorsareanalternativetocapacitorsforpowerfactorcorrection.

Synchronousmotorscanberunatlagging,unity,orleadingpowerfactorbycontrollingtheirfield

excitation. Whenthefieldexcitationvoltageisdecreased,themotorrunsinlaggingpowerfactor. This

conditioniscalledunderexcitation. Whenthefieldexcitationvoltageismadeequaltotherated

voltage,themotorrunsatunitypowerfactor. Themotorrunsatleadingpowerfactorwhenthefield

Active Power,kW

ReactivePower,kVAR

ApparentPower,kVAR


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excitationvoltageisincreasedabovetheratedvoltage. Thisconditioniscalledoverexcitation. When

overexcited,theycanprovidesystempowerfactorcorrection. Synchronousmotorsabove300hpand

below1200rpmareoftenlessexpensivethanacomparableinductionmotor(ThumannandDunning,

2008).

Thefeasibilityofaddingcapacitorsdependsonwhethertheelectricutilitychargesforlow

powerfactor. Correctivemeasuresareinfrequentlyinstalledsincemanyelectricutilitiesdonotcharge

smallcustomersforpoorpowerfactorbutratherpriceitintotheelectricalratesasacostofbusiness.A

costevaluationisneededtodeterminethetypeofcorrectionequipmenttouse. Theevaluationshould

includemotortype,motorstarter,exciter(forsynchronousmotors),capacitorsandswitchingdevicesif

needed,efficiency,andpowerfactorfees(IEEE1990). Manufacturersshouldbeconsultedbefore

installingcapacitorstoreducedvoltagesolidstatestartersandVFDsastherecanbeproblemsifthey

arenotproperlylocatedandapplied.

3.5 VariableFrequencyDrives(VFDs)

VFDsareusedtovarythespeedofapumptomatchtheflowconditions. Theycontrolthe

speedofamotorbyvaryingthefrequencyofthepowerdeliveredtothemotor. Theresultisaclose

matchoftheelectricalpowerinputtothepumpwiththehydraulicpowerneededtopumpthewater.

AsillustratedbytheredareasinFigure32,othermethodsusedtocontrolflowexpendmoreelectrical

powerthanthehydraulicpowerneeded. Throttlingvalvesdecreaseflowbymovingtheoperatingpoint

onthepumpscurvetotheleft.Thisisachievedbyartificiallyincreasingtheheadagainstwhichthe

pumpworks. Bypasscontrolreturnsaportionofthewaterpumpedbacktothesuctionsideofthe

pump,whichwastesaportionoftheenergyusedtorecirculatethewaterwithnousefulwork.

Stop/startcontrolisindicativeofanoversizedpumpthatpulsestomatchflow. Whilethisachieves

thesameamountofworkasasmallerpumpoperatingcontinuously,itdoessoatahigherpower(kW)

demand. VFDsareaproventechnologythatismoreefficientthanthesecontrolmethodsandare

ideallysuitedinsituationswheretheflowrateishighlyvariable.


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Figure32.WastedEnergyinAlternativeControlSchemesComparedtoVariableFrequencyDrives

Source:providedcourtesyofPumpSystemsMatterandtheHydraulicInstitute,Parsippany,NJ

www.PumpSystemsMatter.org

3.5.1 EnergySavings

VFDshavebeenusedbymanywastewaterutilitiestoconserveenergyandreducecosts.A

literaturereviewfoundnumeroussuccessstorieswithenergysavingsrangingfrom70,000kWh/yrfor

smallerWWTPs(i.e.averagedailyflowof710mgd)to2,800,000kWh/yrforlargerWWTPs(i.e.average

dailyflowof80mgd)(EPRI1998;EfficiencyPartnership2009;USDOE2005c).VFDsarenowmore

availableandaffordable,andpaybacksforVFDsrangefromsixmonthstofiveyearsdependingonthe

existinglevelofcontrolandannualhoursofoperation(FocusonEnergy,2006).

Toapproximatethepotentialenergysavings,utilitiesshoulddevelopacurveofactualflowin

hourlyincrementsduringaday.Usingthecurve,energyconsumedbyaconstantspeedmotorand

throttlingvalvecanbeestimatedandcomparedtoenergyconsumedbyaVFDsystemthatmatchthe

hourlyflowratetopowerused.

3.5.2 Applications

VFDscanbeinstalledatremotecollectionsystempumpingstations,atliftstations,onblowers,

andonoxidationditchaerationrotordrives.AcommonapplicationofVFDsisforpumpsthatexperience

alargevariationindiurnalflow,suchasatwastewaterpumpingstations. However,ifVFDsarenot

selectedandappliedcorrectly,theycanwasteenergy. Operatingbelow75%forfullload,VFDscanhave

verylowefficiencies. InselectingaVFD,informationshouldbeobtainedfromtheVFDmanufacture

showingtheefficiencyatdifferentturndownrates.


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VFDsarenotapplicableinallsituations.VFDsmaynotbeeffectivewhenalargestatichead

mustbeovercomeorwherethereislittlevariationintheflowrate(WEF2009).Additionally,some

motorsarenotsuitedforusewithVFDs.Whenthedrivereducesthefrequencytothemotorthevoltage

decreases.However,theamperageincreaseswhichcangenerateheat.Morecommonly,voltagespikes

thatdevelopfromthenonsinusoidalwaveformproducedbyVFDscandamagemotorinsulationifnot

properlyfiltered.Conductorswithinthemotorshouldbeproperlyinsulatedandthemotorsshouldbe

capableofdissipatingtheheat.

3.5.3 VFDStrategiesforWastewaterPumpingStations

VFDscanbecostlytoinstallinanexistingpumpstationandrequirespaceintheelectricalroom.

Therangeofflow,numberofpumps,andhoursofoperationalsoneedtobeconsideredwhen

evaluatingtheimplementationofVFDcontrol.AlthoughequippingallpumpswithVFDsprovides

maximumoperationalflexibility,thiscanbecostlyand,inretrofitprojects,notalwaysfeasible.Often

therewardsofhavingVFDscanbeachievedatlesscostwithhalforasfewasonepumpbeing

equipped.

OneVFDcanbefeasibleinsmallstationswheretwopumpsareruninduty/standbymode

becausethedutypumprunsthemajorityofthetime,reapingthesavingswiththeVFD.Insituations

wherebothpumpsareruninthelead/lagmodetocovertherangeofflowencountereditisusually

beneficialtohavebothpumpsequippedwithVFDs.Thisallowsthepumpstoalternatetheleadposition,

whichbalancestheirhours,anditsimplifiesthecontrolsasbothpumpscanbeoperatedinthesame

manner.

Inthecaseoflargerstationswiththreeormorepumpsofthesamesizeoperatedinlead/lag

mode,thenumberofVFDsneededdependsontherangeofflowandthespaceavailable.Ifonepump

runsthemajorityofthetimewithinfrequentassistancefromtheothers,thenoneVFDwouldlikely

suffice.However,ifthesecondpumpoperatesfrequently,thenatleasttwoVFDsarerecommended.In

thetwoVFDscenario,whenaninfrequentpeakflowisneeded,thethirdconstantspeedpumpcan

providethebaseloadwhilebothVFDdrivenpumpsadjusttomeetthedemand.Dependingonthesize

ofthepumps,itcouldbemorebeneficialtoinstallasmallerpumpinsteadandrunitwithaVFD.This

maximizestheefficiencyofthesystembecausewhenthelargepumpsarerun,theyareneartheirBEP

withouttheheatlossesgeneratedbyVFDs.

Largestationswithmultiplepumpsofdifferentsizesneedtobeevaluatedonacasebycase

basis.Typically,VFDsareplacedonthesmallerpumpssothattheycanbeusedtofillinthepeaks

beforeanotherlargepumpisturnedon.Thecontrolsaresimpleandsequencingiseasytomaintain

whenapumpisdownforservice.Additionally,thecostislowerassmallVFDsarelessexpensivethan

largeones.

Itisimportanttoruneachpumpperiodically. Bearingsinpumpsthatsittoolongcanbe

damagedfrombrinnellingandstuffingboxescandryoutandleak. ItisbeneficialfromanO&M

standpointtoexerciseequippedatintervalsrecommendedbytheequipmentmanufacturertoensure

theirreliabilitywhencalledupon. Energywise,itisbesttodothisduringoffpeakelectrichourssuchas

morningoronweekends.


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USDOE.1999.MotorChallengeProjectFactSheet.CityofMilfordPumpOptimizationProjectYields

$96,000NetPresentValue.U.S.DepartmentofEnergy,OfficeofIndustrialTechnologiesEnergy

EfficiencyandRenewableEnergy.

http://www1.eere.energy.gov/industry/bestpractices/pdfs/milford.pdf

USDOE.BuyinganEnergyEfficientElectricMotor.OfficeofIndustrialTechnologies,EnergyEfficiency

andRenewableEnergy.DOE/GO10096314

http://www1.eere.energy.gov/industry/bestpractices/pdfs/mc0382.pdf

USDOE.2000.PerformanceImprovementsatWastewaterTreatmentPlants.OfficeofIndustrial

Technologies,EnergyEfficiencyandRenewableEnergy.

http://www1.eere.energy.gov/industry/bestpractices/pdfs/fairf.pdf

USDEO2005a.MotorSystemsTipSheet#2:EstimatingMotorEfficiencyintheField.Industrial

TechnologiesProgram,EnergyEfficiencyandRenewableEnergy.DOE/GO1020052021.

http://www1.eere.energy.gov/industry/bestpractices/pdfs/estimate_motor_efficiency_motor_systemts

2.pdf

USDOE.2005b.CaseStudyTheChallenge:ImprovingSewagePumpSystemPerformance,Townof

Trumbull.U.S.DepartmentofEnergy,EnergyEfficiencyandRenewableEnergy.

http://www1.eere.energy.gov/industry/bestpractices/case_study_sewage_pump.html

USDOE.2005c.OnondagaCountyDepartmentofWaterEnvironmentProtection:ProcessOptimization

SavesEnergyatMetropolitanSyracuseWastewaterTreatmentPlant.U.S.DepartmentOfEnergy,Energy

EfficiencyandRenewableEnergy.

http://www1.eere.energy.gov/industry/bestpractices/pdfs/onondaga_county.pdf

USDOE.2008.NewMotorTechnologiesBoostSystemEfficiency.UnitedStatesDepartmentofEnergy

IndustrialTechnologiesProgram.PublishedintheSummer2008issueofEnergyMatters

http://www1.eere.energy.gov/industry/bestpractices/energymatters/archives/summer2008.html#a284

USDOE.2009.UltraEfficientandPowerDenseElectricMotors.UnitedStatesDepartmentofEnergy,

EnergyEfficiencyandRenewableEnergyDivision.

http://www1.eere.energy.gov/industry/intensiveprocesses/pdfs/electric_motors.pdf

WashingtonStateUniversity(WSU)CooperativeExtensionEnergyProgram.2003.MotorMaster+

Version4.0UserGuide. DevelopedfortheU.S.DepartmentofEnergy.Availableonlineat

http://www1.eere.energy.gov/industry/bestpractices/pdfs/motormaster_user_manual.pdf

WaterEnvironmentFederation(WEF),2009.ManualofPractice(MOP)No.32:EnergyConservationin

WaterandWastewaterFacilities.PreparedbytheEnergyConservationinWaterandWastewater

TreatmentFacilitiesTaskForceoftheWaterEnvironmentFederation.McGrawHill,NewYork.


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Evaluation of Energy Conservation Measures 4-1 September 2010

4. DesignandControlofAerationSystems

4.1 IntroductionTheaerationprocesscanaccountforthelargestenergydemandofanyoperationatthefacility.

Althoughthedemandissitespecificandcanvarywidelyfromplanttoplant,thefractionofenergyused

foraerationrangesfrom25toasmuchas60percentoftotalplantenergyuse(WEF2009). Becauseof

thehighenergyuseassociatedwithaeration,energysavingscanbegainedbydesigningandoperating

aerationsystemstomatch,ascloselyaspossible,theactualoxygendemandsoftheprocess. Through

improvedunderstandingoftheoxygendemandsofaparticularwastewaterandhowthosedemands

fluctuatewithtimeofdayandseason,wastewatertreatmentplants(WWTPs)canbuildflexibilityinto

theiraerationsystemssothatoperationcanaddressrealtimedemandsefficiently.

Section4.2inthischapterdescribesenergyconservationmeasures(ECMs)foraerationsystems.

Section4.3followswithadiscussionofaerationcontrol,includingconventionalcontrolbasedon

dissolvedoxygen(DO)measurementsandinnovativecontrolstrategies. Innovativeandemerging

technologiesforcontrolofbiologicalnitrogenremovalarediscussedinSection4.4. SeeChapter5for

innovativeECMsrelatedtonewcommerciallyavailablebloweranddiffuserequipment.

4.2 ECMsforAerationSystemsWastewaterisaeratedbyeitherbub

832r10005 (evaluation of energy conservation measures for wastewater treatment facilities)

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