Advancedcompactwastewatertreatmentbasedoncoagulati

ADVANCEDCOMPACTWASTEWATERTREATMENTBASEDONCOAGULATIONANDMOVINGBEDBIOFILMPROCESSESHallvardØdegaard**FacultyofCivilandEnvironmentalEngineering,NorwegianUniversityofScienceandTechnology(NTNU),N-7491Trondheim,NorwayABSTRACTAdvancedcompactwastewatertreatmentprocessesarebeinglookedforbycitiesallovertheworldaseffluentstandardsarebecomingmorestringentandlandavailablefortreatmentplantsmorescarce.Inthispaperitisdemonstratedthataverysubstantialportionofthepollutantsinmunicipalwastewaterappearsasparticulateandcolloidalmatter.Pre-coagulation,therefore,givesveryefficientpre-treatmentthatresultsinconsiderablesavinginthetotalspacerequiredbytheplant,especiallywhencombinedwithabiofilmprocessfortheremovalofthesolublematter.Anewbiofilmprocessforthispurposeisdescribed.Themovingbedbiofilmprocessisbasedonplasticcarriers,thatmoveinthereactor,onwhichbiomassattachandgrow.Thecarriersarekeptwithinthereactorbyasievearrangementandbiomassthatissloughingoffthecarriersisseparatedbeforeeffluentdischarge.Inadditiontocombiningthemovingbedbiofilmprocesswithpre-coagulation,thepaperdiscussesalsotheuseofahigh-ratemovingbedprocesscombinedwithcoagulationdirectlyafterthebiofilmreactorinordertoenhanceseparability.Thisresultsinverycompacttreatmentplantsforsecondarytreatmentandpossiblyphosphateremoval.KEYWORDSWastewater,characteristics,coagulation,biofilmreactor,organicloading,performance,kineticsINTRODUCTIONThereareseveralfactorsthathavetobetakenintoaccountwhenevaluatingdifferenttreatmentmethodsforwastewatertreatment,suchas;(1)treatmentefficiency,(2)cost,(3)arearequirement,(4)sludgeproductionand(5)sustainability(e.g.ecologicalimpactandenergyuse).Withrespecttotreatmentefficiency,onehassofarbeenfocusingonoxygenconsumingmatter(organicmatterandammonium)andnutrients(PandN).Thishasleadtomoreinterestbeingdevotedtoremovalofsolublematterthanparticles.Inthefuture,however,itisreasontobelievethatmorefocuswillbeonmicrobialcontamination(suchashelmintheggs,parasiticprotozoa,bacteriaandviruses)andmicropollutants(heavymetalsaswellasorganicmicropollutants).Averyconsiderablefractionofthesepollutants,aswellasoforganicmatter,arepresentinmunicipalwastewaterasparticlesorcolloidsorstronglyassociatedtosuch.Thisoughttoleadtoashiftintheresearchinterestfromremovalofsolublemattertoremovalofparticles.Thecostofwastewatertreatmentisdependentonlocalcircumstances.Inthebigcities,however,thespacerequiredfortheplantisverydeterminingfortheinvestmentcost.Compacttreatmentalternativesmethodsareconsequentlymoreandmorebeingfavoured.Biofilmsystemsarereplacingactivatedsludgesystemsandhigh-rateseparationtechniquesarereplacingtraditionalsettlingtanks.Thedisposalofsludgerepresentsanincreasinglyhigherportionofthetotalcostofwastewatertreatment.Methodsarelookedfor,therefore,thatminimisestheamountofsludgeproduced.Thesludgedoesrepresentaresource,however.Itcontainsbothanenergypotentialthatcanbeutilisedaswellasspecificcompoundsthatarelimitedintheworld,suchasphosphorous.Itisarequirementtodaythattreatmentofwastewatershouldbesustainable.Thismeansthatthetreatmentshouldconsumeaslittlematerials,chemicals,energyandlandaspossibleandmakereuseofthewater,thenutrients,theenergyandthechemicals.Thedevelopmentofwastewatertreatmenthastoaverylargeextentbeenhamperedbytradition.Afterthediscoveryoftheactivatedsludgeprocess,biologicaltreatmentbasedonthisprocesshasbecomethedominantoneforanumberofpurposes.Fromthestartthemainobjectivewasremovalofoxygenconsumingmaterialsuchasorganicmatterandammonium.Latertheprocesshassuccessfullybeendevelopedalsotobeabletoremovethenutrientsphosphorousandnitrogen.Traditionallytheactivatedsludgestephasbeenfollowingaprimarytreatmentstepbasedonsettling.Inmanycountries,however,(Denmark,Hollandetc)extremelylow-loadedsystemswithoutpre-treatmenthavebeenpreferred,partlybecauseoftheambitiontominimisesludgeproductionbyin-reactoraerobicstabilisation.Itcanbequestioned,however,iflow-loadedactivatedsludgeplantsaresustainable.Theyconsumealotofmaterials(e.g.concrete)becauseoftheirlargetankvolumes,theyusequitealotofenergyforaeration,theyconvertmostoftheorganicmattertouselessCO2andtheresourcesofthewastewatercannotoptimallybereusedInthispaperweshalldiscusswastewatertreatmentinviewofmybasicwastewatertreatmentphilosophy(seeFigure1).Accordingtothisphilosophy,oneshouldfirstremoveasmuchoftheparticulatematteraseconomicallyfeasible(byenhancedprimarytreatment,e.g.pre-coagulation)andthendealwiththesolublematterafterwardsinacompactbioreactor(e.g.abiofilmreactor).Theorganicconcentrateshouldbemadeuseofbyproducingenergy(intheformofbiogas)andcarbonsourcethatcanbeusedinthesolubleremovalpartoftheprocess,ifnecessary.Othervaluableresourcesofthesludgeshouldberecycledsuchasphosphorousandpossiblymetals.EnhancedprimaryRemovalofsolublesOrganicconcentrateCarbonsourceBiogasTakeouttheparticlesfirstMakeuseoftheconcentrateThendealwiththesolublesUtilizetheresoucesfromtheconcentrateNutrientsFigure1MybasicwastewatertreatmentphilospophyWASTEWATERCHARACTERISTICSANDITSINFLUENCEONTREATMENTAlreadyinthefiftiestherewerestudiescarriedoutinordertodividethe