Aeration-control-of-a-wastewater-treatment-plant-using-hybrid-NMPC

ComputersandChemicalEngineering35(2011)638–650ContentslistsavailableatScienceDirectComputersandChemicalEngineeringjournalhomepage:www.elsevier.com/locate/compchemengAerationcontrolofawastewatertreatmentplantusinghybridNMPCS.Cristea∗,C.dePrada,D.Sarabia,G.GutiérrezDepartmentofSystemsEngineeringandAutomaticControl,FacultyofSciences,UniversityofValladolid,c/RealdeBurgoss/n,47011Valladolid,SpainarticleinfoArticlehistory:Received16November2009Receivedinrevisedform25May2010Accepted16July2010Availableonline3August2010Keywords:HybridnonlinearModelPredictiveControlWastewatertreatmentplantsReal-timeoptimizationabstractIntheoperationofwastewatertreatmentplantsakeyvariableisdissolvedoxygen(DO)contentinthebioreactors.Asoxygenisconsumedbythemicroorganisms,moreoxygenhastobeaddedtothewaterinordertocomplywiththerequiredminimumdissolvedoxygenconcentration.Thisisdoneusingasetofaeratorsworkingon/offthatrepresentsmostoftheplantenergyconsumption.Inthispaperahybridnonlinearpredictivecontrolalgorithmisproposed,basedoneconomicandcontrolaims.Specifically,thecontrollerminimizestheenergyusewhilesatisfyingthetime-varyingoxygendemandoftheplantandconsideringseveraloperationconstraints.Aparameterizationofthebinarycontrolsignalsintermsofoccurrencetimeofeventsallowstheoptimizationproblemtobere-formulatedasannonlinearprogramming(NLP)problemateverysamplingtime.Realisticsimulationresultsconsideringrealperturbationsdatasetsfortheinletvariablesarepresented.©2010ElsevierLtd.Allrightsreserved.1.IntroductionBiologicalwastewatertreatmentisessentialtokeeptheeco-logicalbalanceoftheenvironmentandnowitisfrequentlyusedinindustriesandurbanareas.Mostbiologicaloxidationprocessesfortreatingwastewaterhaveincommontheuseofoxygen(orair)andmicrobialaction.Inparticular,aerobicallyactivatedsludgepro-cessesare,nowadays,themostextensivelyusedsystemtocleanwastewater.Thebasisoftheprocessliesinmaintainingamixtureofseveralmicroorganismstransformingthebiodegradablepollu-tants(substrate)intonewbiomass.Asinthisoperationoxygenisconsu