APPLICATIONOFFUZZYCONTROLSINSEWAGETREATMENT

APPLICATIONOFFUZZYCONTROLSINSEWAGETREATMENTWEI-LUZHU,HUI-QIONGDENG,SHUAIWANGCollegeofElectricalEngineering,HebeiUniversityofScienceandTechnology,Shijiazhuang050018,ChinaE-MAIL:[e-mail],[e-mail],[e-mail]:Fortheshortagesofthetraditionalflowprogramcontrolandtimeprogramcontrolintheprocessofsewagetreatment,thispaperadoptsaFuzzyprogrammingmethodbasedonPLC.ThePLCanditsgeneralI/OmoduleareinvolvedinformingtheModuleControllerinhardware.WeusetheDOandthesludgerefluxratioasthemaincontrolparameters,andinferthebestcontrolvariablesbyPLCdiscretecalculationandlook-uptableonline.Notonlycanweensurethequalityofpurifiedwater,butalsosaveenergybyusingthisfuzzycontrollerintheprocessofsewagetreatment.Keywords:SewageTreatment;ProgramControl;FuzzyControl;DO;Sludgerefluxratio1.IntroductionBiologicalSewageTreatmentSystemisacomplexdynamicsystem,whichregardsmicrobetreatmentascorpusandhasmultipleinputsandoutputs.Ithasseveralcontroltasks,suchaswaterquality,BNR,protectingfromsludgebulking,decreasingoperatingexpenseandsoon[1].Becauseoftherandom,timevaryingandnonlinearofthechangeinvolumeandqualityofthewastewater,itishardtobuildthemathematicalmodelwhichisinlinewithrealityaccordingtotheactualdata.Soourclassicalcontroltheory(PIDcontrol)can'tbeusedtocontroleffectually.Asabranchofintelligentcontrol,fuzzycontrolhasmanyadvantagesinthecontrolofrandom,timevarying,nonlinearcomplexsystem[2],andithasbeenusedmoreandmorewidelyinthesewagetreatment.2.Theprocedureofsewagetreatment2.1.ThebasicprocessofsewagetreatmentAtpresentmostofthesewagetreatmentadoptactivatedsludgeprocess.Atfirst,separatethewastewaterthatflowsintotheNo.1settlingtankfromsuspendedmatterandletitenterintotheaerationtank.Atthesametime,theactivatedsludgethatreflowsfromthebottomoftheNo.2settlingtankalsoentersintotheaerationtank,andcombineswiththesewagetoformmixture.Andthen,bymixingandaerating,theactivatedsludgetoucheswiththesewageadequatelyandacquiresenoughDO(dissolvedoxygen).Thesolubleorganicpollutantsinthesewagewouldbeadsorbedbyactivatedsludgeanddecomposedbymicrobeintheactivatedsludge.Finally,thesewagewouldbepurifiedandflowfromtheNo.2settlingtank.ThesuspendedmatterwouldbesettledintheNo.2settlingtank,andmostofthesludgewouldreflowtotheNo.1settlingtank,littlewouldbedischarged.(SeeFig.1)Figure1.Activatedsludgesewagetreatment2.2.ControlmethodofsewagetreatmentThetraditionalcontrolmethodismainlyaboutflowprogramcontrolandtimeprogramcontrol,inwhichfixedflowandfixedtimeisinvolvedasbasiccontrolparameters.Butinfact,notonlythevolumeandconsistenceofsewagebutalsothequalityofactivatedsludgeistimevarying,sothetraditionalmethodiseasytocausepoorqualityofwaterorawasteofenergy.Thetwomethodscan'tadjustwithactualchange,sotheycanhardlyachievetheoptimalcontrol.3.ApplicationofFuzzyControlinSewageTreatment3.1.ThechoiceofcontrolparametersinfuzzycontrolsystemInbiologicalsewagetreatmentsystem,therearemanycontrolledvariables,suchasthevalueofaeration,thesludgerefluxratio,theemissionofsludgeandsoon[4].AndtheKEYtosolvetheproblemistosearchthecontrolsparameters,whichcanbemonitoredonlineandreflecttheprocessof22082010IEEE978-1-4244-6527-9/10/$26.00©ProceedingsoftheNinthInternationalConferenceonMachineLearningandCybernetics,Qingdao,11-14July2010reaction.ThemicrobeinthereactordecomposesorganicpollutantswithDOfromaeration.AndthecontentofDOdependsonconsistenceofsewage,valueofaerationandconsistenceofsludge.Studiesshowthat[5-8]thechangeofDOcanreflecttheprocessoforganicsdecomposingandBNRincertainway,sowecanuseitasthecontrolparameter.Inpractice,weuseblowertoputairintoreactiontanktoaddtheconcentrationofDO,sobyadjustingthenumberofblower,wecanchangetheconcentrationofDO.Figure2.Fuzzycontrollerstructure3.2.TheconstructionoffuzzycontrollerWewouldbuildtwoindependentcontrollers,fuzzycontrollerofDOconcentrationandfuzzycontrollerofsludgerefluxratio.Eachofthemhasdoubleinputandsingleoutput.TheformerusesthedeviationofDO'sconcentrationandthevalueofwastewaterasitsinputandtheairvolumeofblowersasitsoutput.Whilethelatterusesthedeviationofsludgerefluxratioandthevalueofsewageasitsinputandtheairvolumeofblowersasitsoutput.Tothetwooutputs,wechoosethebiggeronetokeeptheconcentrationofDO.Asaresultwecanensurethequalityofpurifiedwater.Theconstructionoffuzzycontrolsystemisshownasbelow(Fig.2).3.3.DomaintransformationIftheactualinputis0x,itsvariationrangeis[maxmin,xx],therequesteddomainis[maxmin,xx],bylineartransformation,asaresult,thereis,maxminmaxmin00-)22xxxxxkx++=+˄(1)Here,kisthescalefactor,maxminmaxmin()/()kxxxx=++.Inoutplant,thedesignvalueofDOis9.3mg/L.Thesludgerefluxratiois1.2andtheDOdeviationoffuzzycontrollerintimedomainCdois{-2.0,-1.5,-1.0,-0.5,0,0.5,1.0,1.5,2.0}.FuzztoED,thenitbecomesinto{-4,-3,-2,-1,0,1,2,3,4},thedeviationofsludgerefluxratioCmudisƸ{-0.2,-0.15,-0.1,-0.05,0,0.05,0.1,0.15,0.2}.FuzzintoEM,itbecomesinto{-4,-3,-2,-1,0,1,2,3,4},thevariationrangeofwastewaterflowLsis{1.8,2.1,2.4,2.7,3,3.3,3.6,3.9,4.2}×1000m3/h.FuzzintoES,itbecomesinto{-4,-3,-2,-1,0,1,2,3,4}.Thenumberofblowernfis{0,1,2,3,4,5,6,7,8,9}.