Anaerobic assignment

,ingininpri-of(lis-usefterlip-agelustbythisintil)er-re-;lowinand achor-ptlyandntalfilersssedusener-pikenowtaleck-heiriclesrto leariall,ovaluld-re-ead-rees,erylingsflicecol-lo-ruc-and-tails;lice.-satlingstheroflent,Di-hreefol-ions, cific1964°y5-1AnaerobicWasteTreatmentFundamentals112-PERRYL.McCARTYAssociateProfessorofSanitaryEngineeringStanfordUniversityTHEanaerobicprocessisinmanywaysidealforwastetreatment.Ithasseveralsignificantadvan-tagesoverotheravailablemethodsandisalmostcertainlyassuredofincreasedusageinthefuture.An-aerobictreatmentispresentlyem-ployedatmostmunicipaltreatmentplants,andisresponsibleforthemajorportionofwastestabilizationthatoccursthere.However,inspiteofthepresentsignificanceandlargefuturepotentialofthisprocess,ithasnotgenerallyenjoyedthefav-orablereputationittrulydeserves.Theprimaryobstaclehasbeenalackoffundamentalunderstandingoftheprocess,requiredbothtoex-plainandcontroltheoccasionalup-setswhichmayoccur,andtoextendsuccessfullythisprocesstothetreatmentofawidevarietyofin-dustrialwastes.Anincreasingrealizationofthepotentialsofanaerobictreatmentisevidentfromthereportingeachyearoflargernumbersofresearchinvestigationsonthisprocess.Al-ready,significantadvanceshave.beenmadeextendingtheprocesssoitcanbeusedsuccessfullyonmanymoreorganicwastes.Thisseriesofarticlesisintendedtosummarizeourpresentknowledgeofanaerobictreatmentandtopointouttheim-PUBLICWORKSforSeptember,1964Thisi%thefirstofaseriesoffourarticlesonaprocessofwastetreatmentthathasnotbeentoowellunderstoodandcon-sequentlyhasnotbeenaswidelyusedasitmightdeserve.PartOnediscussestheadvantagesanddisadvantagesofanaerobicwastetreatment,conventionalpracticesandthepresentconceptsofthemicrobiologyandchemistryinvolved.PartsTwoandThreewillcovertheenvironmentalrequirementsforachievingcontroloftheanaerobicprocessandpreventingorcorrectingtoxicityinthesystem.PartFourwilloutlinetheapplicationofthesevariousconceptsintreatmentplantdesign.portantparametersfordesign,oper-ation,andcontrol.Thisfirstarticleisconcernedwithageneraldescrip-tion,togetherwiththechemistryandmicrobiologyoftheprocess.Thesubsequentthreearticleswilldealwithtreatmentcontrolanddesign.AdvantagesTheadvantagesofanaerobictreatmentcanbestbeindicatedbycomparingthisprocesswithaerobictreatment.Inaerobictreatment,asrepresentedbytheactivatedsludgeandtricklingfilterprocesses,thewasteismixedwithlargequanti-tiesofmicroorganismsandair.Microorganismsusetheorganicwasteforfood,andusetheoxygenintheairtoburnaportionofthisfoodtocarbondioxideandwaterforenergy.Sincetheseorganismsobtainmuchenergyfromthisoxi-dation,theirgrowthisrapidandalargeportionoftheorganicwasteisconvertedintonewcells.ThePARTONEIChemistryandMicrobiologyportionconvertedtocellsisnotactuallystabilized,but'issimplyenangedinform.Althoughthesecellscanberemovedfromthewastestream,thebiologicalsludgetheyproducestillpresentsasignificantdisposalproblem.1Inanaerobictreatment,thewasteisalsomixedwithlargequantitiesofmicroorganisms,buthere,airisexcluded.Undertheseconditions.bacteriagrowwhicharecapableofconvertingtheorganicwastetocarbondioxideandmethanegas.Unlikeaerobicoxidation,thean-aerobicconversiontomethanegasyieldsrelativelylittleenergytothemicroorganisms.Thus,theirrateofgrowthisslowandonlyasmallportionofthewasteisconvertedtonewcells,themajorportionofthedegradablewastebeingcon-vertedtomethanegas.Suchcon-versiontomethanegasrepresentswastestabilizationsincethisgasisinsolubleandescapesfromtheTable1-AdvantagesofAnaerobicTreatment1.Ahighdegreeofwastestabilizationispossible.2.Lowproductionofwastebiologicalsludge.3.Lownutrientrequirements.4.Nooxygenrequirements.5.Methaneisausefulendproduct.I107stages.1Eachstagerepresentstheculminationofgrowthofapopula-tionofmethaneformerscapableoffermentingoneparticulargroupofcompounds.Theprocessisnotcom-pletelyoperationaluntilallthegroupsofmethaneformersarefinallyestablished.Thismaytakeseveralweeksiftheprocessisstartedwithoutthebenefitofseedsludgecontainingtheme-thaneformersrequiredforthespecificacidspresent.Whiletherearemanydifferentmethaneformingbacteria,therearealsomanydifferentacidformingbacteria.Waste,],r!~ilizationre-quiresabalanceamongalltheseorganisms.Theestablishmentandmaintenanceofthisbalanceisnor-mallyindicatedbyoneofthemostimportantcontroltests,thatfortheconcentrationofvolatileacids.ThevolatileacidsaretheshortchainorganicacidsindicatedinTable2.Theacidsshownarethemajorin-termediatesproducedbythefirststageconversion.Theyrepresenttheintermediatecompoundsofmostimportanceinanaerobictreatment,andmostofthemethaneformedfromthisprocessresultsfromfer-mentationoftheseacidsbythemethanebacteria.Whenthesystemisinbalance,themethanebacteriausetheacidintermediatesasrapidlyastheyappear.However,ifthemethanebacteriaarenotpresentinsuitablenumbers,orarebeingsloweddownbyunfavorableenvironmentalcon-ditions,theywillnotusetheacidsasrapidlyastheyareproducedbytheacidformers,andthevolatileacidswillincreaseinconcentration.Thus,anincreaseinacidconcen-trationindicatesthemethaneform-ersarenotinbalancewiththeacidformers.Ananalysisfortheindividualacidspre