Aerobic Digestion,or,Its a Bug eat Bug WorldBrett WardMunicipal Technical Advisory ServiceThe University of TennesseeAerobic DigestionContinuation of the Activated SludgeProcessSuper Extended AerationNo food is addedReduction of Volatile Solids through: Endogenous Respiration Bacterial Cells use their own protoplasm for energy Some cells die and become food for othersBiological ChemistryBOD, Bug Food, Organic Pollution Test of the organic strength of sewage Organic- from plants and animals Protein, carbohydrates, fats Fecal matter, food scrapes, paper, industrialwaste ofplantor animal origin.NormalBacteriological RespirationBOD + BOD Bugs + O2 = More BOD+ CO2 + H20 + NH3BugsRespiration/ OxidationRespirationWe call it breathingScientifically it is therelease of energyThe Bugs want the energy in the BOD Energy to live and growThe Bugs are teeny tiny chemical factories They split complex organic compounds into simple oxidized compounds.Respiration / OxidationNormal Bacteriological RespirationBOD + BOD Bugs + O2 = More BODGlucoseC6H12O6+ BOD Bugs+ O2 = More BOD+ CO2 + H20 +NH3BugsBugs+CO2+ H20ProteinC3H7O2N + BODBugs+ O2= MoreBODBugs+CO2+ H20 +NH3SewageTreatmentSewage, BOD Carbs, Protein, FatsAdd air and mix wellBugs grow And Grow And GrowWasteexcessBugs to DigesterWith out wastingMLSS goes up, up, and OUT!upWaste today whatgrew todayBiological ChemistryDigesters receive no food or BOD Endogenous RespirationBOD+O2 = Less BOD+CO2 + H2O+ NH3BugsBugsBugs use stored energySome die, and become food for othersReduction of Volatile SolidsDigestion GoalsThicken WasteControl Odors, Reduce SludgeActivated Sludge: DecantingKeep it aerobicVolume, EndogenousResp.Meet Disposal Requirements Land Fill Land ApplicationAerobicAdvantagesLow ConstructionCostEasy to OperateHigh QualitySupernatantSafer process, no methaneAerobic vs AnaerobicSupernatantAerobicAnaerobicBOD 1000-10000BOD 500 mg/Lmg/LTSS100-300 mg/LTSS 5000- 15000mg/LAmmonia 500-1000mg/L T. Phos 300-1000mg/LTKN 170 mg/LT.Phos98 mg/LAerobic DisadvantagesHigh Aeration Costs, electricityDigested Sludge more difficult to dewaterProcess affected by temperature changesMore Sludge produced for disposalAerobic DigesterDesignVarious SizesVarious Aeration Diffused air Surface MechanicalVarious DecantFixed ValvesMoving Arms Telescoping Valves Suspended PumpsOperating StrategyComplete MixedBatch, Fill and DrawSeries, Parallel or combinationBiosolidsBiosolidsWASPrimary& WASPrimarySecondary DigestersBiosolidsDigester OperationsOperational StrategyTools you haveBasinsDecant or supernatantAerationPersonnelequipmentDestinationLand FillLand ApplicationOther FacilityDigesterMonitoringDaily to WeeklyDissolved OxygenSettleometer pH, Alkalinity Nitrate503 tests, Prior to usedisposalorSOURTemperatureFecalDigester MonitoringSupernatant MonitoringMonitor forsystem.affectsonthewatertreatmentFlowBOD Ammonia TSSNitrate (NO3) PhosphorusLandFillSpecial Waste PermitDivision of SolidWaste ManagementNo Free Water, AKA paint filter testNo Toxic Lecheate, TCLP, Toxic Characteristics Lecheate ProceedureLand FillPrimary ConcernsOdor Control, too little O2, tooSludgemuchfeedOxygenMaintain Oxic environment Sacramento Manual, 1-2 mg/L DO What works for you 0.5 mg/L, can be more cost effective >2.0 mg/Lwastes electricitycan cause low pHcan contribute to foamingLand FillDewateringAvoid excessive long aeration timesLong times decrease floc and particle sizeGreater than 20 days, Capillary Suction Time(CST) greatly increases Lower CST means better dewatering.LandApplication503 RequirementsMetal accumulationNitrogen managementPathogen Destruction Class A or BVector Requirements38% Red. of V.S.SOURBench top testTime and Temp.Land ApplicationConcernsOdorsPathogen ReductionVector Attraction Red.Land ApplicationClass B Geometric Mean of seven samples is less2,000,000 cfu/gRequires Total Solids Test for CalculationsthanNatural Die off in Digester Intestinal organisms Air Off cycles appear to assist in reduction.Land ApplicationClass B, PSRP Aerobic Digestion MCRT, 40 days at 20 C60 days at 15 CLand ApplicationVector Attraction Reduction38% Reduction of VS, Van Kleeck Equation Works best where there is Primary Sludge feedBench Top Aerobic DigestionSOUR Test, dont thicken above 2% TSAll are tests to document Sludge Stability Low BOD (food), Low energy, highly oxidizedSludge StabilizationRequires Time and Air Low Temperature Slows the process High Temps speed the processTN Design Criteria 12.5.2.2Hydraulic detention time at20 Cshould be 15- 25 days depending on typeSludge StabilizationThis may not be enough. VariablesFeed Sludge, WAS, Primary, CombinationWe all have Winter TemperaturesDesign for 20 C guarantees failure in WinterAeration equipment and location can warm your digester in the winter.Aerobic Digester TipsLow Temperature Slows Pathogen Reduction Slows Volatile Solids ReductionHigh Temperature Speeds Pathogen Reduction Speeds Volatile Solid ReductionAerobic Digester TipsLow DOdoes notdoes notslowslowpathogen reductionvolatile solids reductionHigh DO Will cause pHto decrease Will waste electricityDigester pHManagementEndogenous RespirationBOD+O2 = Less BOD+CO2 + H2O +NH3BugsBugsAmmonia is producedDigester pHManagementWhere there is Ammonia,be nitrification Elements of NitrificationThereissuretoAmmonia PresentOld Sludge AgeAdequateAdequateAdequateOxygenTemperatureAlkalinityDigester pHManagementNH3+NH3+ O2 + Alk.= More NH3+NO3BugsBugs1 Part4 Parts7 PartsNitrification is an expensive processIf you aerate continuously for long times, alkalinity may drop and pH drop.Digester pHManagementIf pH drops,If nitrates are presentTurn the aerationOff and Denitrify!Oxygen Usage HierarchyFree Dissolved OxygenAerobic or OxicTreatmentLittle or No free Oxygen, but NO3 presentAnoxic TreatmentSulfate, SO4 is the next choice of the BugsAnaerobic conditions are beginning. ODORS fm. H2S12DenitrificationNormal Bacteriological RespirationBOD +BODBugs + O2 = More BOD+ CO2 + H20 +NH3Bugs1 Part1.25 PartsBOD +BODBugs + O2 = More BOD+ CO2 + H20 +NH3BugsDenitrificationNH3+NH3+O2 + Alk.= More NH3+ NO3BugsBugsNitrogen gasBOD + BODBugs + NO3 =More BODBugs+ CO2 + H20 + N2 + Alk1 Part0.3 Parts3.5 PartsDenitrifying returns alkalinity to the basin and stops pH dropAgronomicLoadingRatesNitrogen Fertilizervalue of the BiosolidsThe lower the nitratethe more can be applied per acre.Agronomic Loading RatesAgronomic Loading RatesAgronomic LoadingRatesNitrate Levels Digester #1, 5700 mg/L Digester #2, 22,000 mg/LDigester #2 Sludge requires 30% more landfor application.Actual Land Application CaseBiosolids Nitrate 4000-7000 mg/L Not enough land to apply at the presentLoading RateInitiated Off- On aeration 8 hours ON, 16 hours OFFBiosolids Nitrate 100-1000 mg/L, 75-98 % reductionAgronomic Application rates up and no need for more land.Benefits of DenitrificationPrevent pH drops by recycling AlkalinitySave money by recycling Oxygen Apply Biosolids at higher rates Improved Dewatering characteristics Reduce sludge volumeSelect against filamentsDenitrification reduces theAerobic DigesterHigh Aeration Costs, electricity, ReducedDigested Sludge more difficult to dewater, ImprovedProcess affected by temperature changesMore Sludge produced for disposal, ImprovedDisadvantagesDigester Case StudyTwo Stage Aerated 24/7, odors, odors, odors First Stage, primary and WASStage Two Low pH, as low as 6.0 s.u. and under, What would you do?On More IssueFoamingThis looks likenocardiaform foamIf it is a problem Microscopic Exam Surface chlorinate1% Cl2 liquid spray on the foam when the air is OFFMore than once per day is better.MoreFoamLight smelly foamPrimary Sludge Feed Not filaments Microscopic Exam Small solids Paper fibersAerobicDigestersQuestions?