Anaerobic Digestion 101

1 Anaerobic Digestion 101 November 2, 20171:00 3:00 pm EasternWEF Plant Operations and Maintenance CommitteeHow to Participate Today Audio Modes Listen using Mic & Speakers Or, select Use Telephone and dial the conference (please remember long distance phone charges apply). Submit your questions using the Questions pane. A recording will be availablefor replay shortly after EdgecombGilbert Neely Wastewater Reclamation FacilityProject ManagerToday s ModeratorToday s SpeakersMatthew Higgins, , Civil andEnvironmental EngineeringBucknell UniversityMatt Van Horne, and SawyerPeter Loomis, SmithDave Parry, Digestion 101 Matthew Higgins, W. Carlson Chair in Environmental EngineeringBucknell UniversityLewisburg, PA 17837 Big PictureActivated SludgeInfluentPlant EffluentSecondary ClarifierPrimary ClarifierWaste Activated SludgePrimary SludgeThickeningThickeningAnaerobicDiges tionDewateringBiogasCHPWhy Anaerobic Digestion ?

2 One of the approaches to meeting EPA 503 Requirements for biosolids:1. Vector Attraction Reduction (VAR) requirements-reduces the organics in the sludges so it is stable 2. Reduces pathogens-Meets EPA Requirement as Process to Significantly Reduce Pathogens Why Anaerobic Digestion ?3. Produces a renewable energy source biogas (55-70% methane) uses:-Combined heat and power systems (CHP)-Digester heating-Vehicle fuel-Put into natural gas grid4. Produces a excellent soil amendment product, rich in:-carbon-nitrogen-phosphorus -micronutrientsBig Picture of Anaerobic Digestion Process1. Organics In4. Organics Out3. biogas Out (CH4+ CO2)2. Microbial Degradation of OrganicsOrganics InFeed StocksTypical Feed Total Solids ConcentrationsWaste Activated Sludge (WAS)4-6%Primary Sludge (PS)4-6%Primary/Secondary Blends4-6%Food Wastes5-15%Fats, Oils and Grease (FOG)Highly variableLots of other organic wastesvariableMicrobial ConversionsParticle DisintegrationOrganic Particles(floc)Complex PolymersProteins, Carbohydrates and LipidsHydrolysisAmino Acids,Sugars, Fatty AcidsFermentation(acidogenesis)Volatile FattyAcids and Hydrogen Gas (H2)

3 AcetatePropionateButyrateValerateH2 Microbial ConversionsAceticlasticMethanogenesisAce tatePropionateButyrateValerateH2CH3 COOHH2CO2+ CH44H2+ CO22H2O + CH4 HydrogenotrophicMethanogenesisMicrobial DegradationTypical Parameters for Expressing Degradation1. Volatile Solids Reduction (VSR)2. Chemical Oxygen Demand Reduction (CODR)Mass of VS InMass of VS outVSR= 100* =Qin*VSin=Qout*VSoutMicrobial DegradationVSR by Van Kleek Equation Van Kleek assumes inert solids are constant in and out of the digester, no settling of grit Inert Solids = TS VS (also called fixed solids or ash ) Equation uses the volatile solids fraction (VSF) = VSFin= VSFout= Microbial DegradationVolatile Solids Reduction by Van Kleek EquationVSFout= VSR by Van Kleek = 100 * VSFin= Typical VSRsFeed StocksVSRW aste Activated Sludge (WAS)25-40%Primary Sludge (PS)

4 40-65%Food Wastes75-85%Fats, Oils and Grease (FOG)80-95%01020304050607005101520253035 VSR (%)SRT (d)Operational Parameters Affecting VSR - SRTS olids Retention Time (SRT) = average time a particle spends in the digester SRT = = Typical Design &Operation RangePrimary SludgeWaste ActivatedOperational Parameters Affecting VSR -TemperatureMesophilic Range: 25-45 oCThermophilic Range: 50-65 oCOperational Parameters Affecting VSR -Temperature303540455055051015202530 VSR (%)SRT (d)40 C35 C25 CTypical Mesophilic OperatingTemperature35-38 oCDigester Operational Parameters Organic Loading RatesKg VSind m3 Volatile Solids Loading Rates = mass of VS fed per day per unit volume of Textbook Values: a.

5 Kg VSinper day per cubic meter of digester volume (1-3 kg VS/d-m3)b. lb VSinper day per cubic ft of digester volume ( lb VS/d-ft3)OLR don t consider:a. What is in your digesterb. Nature of wastesc. Operational conditionsHigher OLRs can be readily achieved with good operationsDigester Operational Parameters Specific Organic Loading RatesSpecific Organic Loading Rate considers biomass in digester= grams of CODinper day, per gram of VS in digesterSOLR = Guideline: Anaerobic Digestion Operational ParametersParameterImportanceStable OperatingRangespHMaster variable for digester buffer pH changes>1000 mg/L as CaCO3 VFAs or VAsIncrease in concentrations an indicatorof potential upset<300 mg/LVA / A l k a l i n i t yRatio of Volatile Fatty Acids to Alkalinity Ratio, increases mean process changes< (CH4/CO2 Ratio)

6 Decreases in CH4content can mean process changes and inhibition>55%Stoichiometry of Anaerobic DigestionCnHaObNc+ H2O xCH4+ yCO2+ zHCO3-+zNH4+x, y and z are a function of n, a, b, and cmethaneproductionbiogasproductiondigest erpHpotentialinhibitionOrganic FeedstockTheoretical General Equation (Buswell, 1952)digester alkalinityStoichiometry of Anaerobic DigestionTypeFormulaSourceWaste Activated Data (average of 8 plants)Primary Data(average of 5 plants)Food WasteC17H30O6 NBucknell Data (average of 3 different FWs)FatsC16H32O2 Rittman and McCartyCarbohydrateC6H10O5 Rittman and McCartyProteinC16H24O5N4 Rittman and McCartyBiogas ProductionFeed StockMethane Yield Methane Yield VSRP rimary Sludge66036055%Waste Activated62525040%Food Waste65056080%FOG (Fats, Oil, Grease)98088090%Sugars44040090%Protein58 052090%27 Notes on EPA Regulatory RequirementsClass B Biosolids: assumes pathogens are present site restrictions are used for land application to ensure public safety product is stable, vector attraction reduction is metSeveral Options for Demonstrating Class B Requirements1.

7 VSR > 38% for vector attraction reduction2. Monitor fecal coliforms: < 2 million per gram dry solids3. Demonstrate Digestion meets time and temperature requirement = 15 days at > 35 oC28 Notes on EPA Regulatory RequirementsClass A Biosolids: pathogens levels below detection no site restrictions for beneficial reuse stable product that meets vector attraction reductionSeveral Options for Demonstrating Class B Requirements1. >38% VSR for vector attraction reduction2. Monitor fecal coliforms: < 1000 per gram dry solids3. Monitor Salmonella: < 3 MPN/gram dry solids29 SummaryAnaerobic Digestion is a sustainable approach to treating organic wastes: produces renewable energy produces a product that recycles organics and nutrients can be used to meet EPA requirements for biosolids stable operations require regular monitoring and good practices 14 years experience Specializes in biosolids, energy management and wastewater treatment facilities Principal Investigator for WE&RF project on the operational impacts of co-digestionMatt Van Horne, PEAgenda What is co- Digestion ?

8 Why consider co- Digestion ? System configuration System control Lessons learnedWhat is Co- Digestion ?Co- Digestion at a WRRFP rimary SludgeWaste Activated SludgeExternal Organic MaterialsAnaerobic DigesterWhat Are Possible External Sources of Material? Fats/oils/grease (FOG) Pre-consumer food waste Post-consumer food waste Industrial waste organicsWhat Are Possible External Sources of Material?Why Consider Co- Digestion ?First Lets Take a Step feedstocksDigester gasIncreasing Gas production More incoming organics can result in more digester gas produced More change the economics of beneficial utilizationIncrease Utility Revenue Tipping fees More biosolids to sell More energy to sell externallyCollection System Benefits Remove problematic materials (FOG)

9 From collection system with appropriate outletSystem ConfigurationOverall System ComponentsTr u c k UnloadingDepackagingand SlurryingScreening and Debris RemovalGrinding and MaceratingHeatingStorageTruck UnloadingDepackaging/SlurryingScreening/ Debris RemovalGrinding/MaceratingHeatingStorage FeedingSample FOG Facility Sample FOG Facility Sample FOG FacilitySample FOG FacilitySample Food Waste FacilityTr u c k tipping floorDepackagerShredderPumping well with recirculation pumpDigester feed pumpDilution waterWaste materialDigester Considerations Increased solids content mixing Increased organic loading gas handling and foaming/RVE control Digested solids productionKey Points Can be many new steps Harsh characteristics of material Odor management Design for reliability Design for maintenance accessSystem ControlWhat Are We Really Trying to Control?

10 Digester performance is key Loading rates Quality of materials for Digestion Mixing system performanceHow Do We Monitor and Control This? Feedstock monitoring pH Total solids Volatile solids Toxicity Take samples from each batch received!How Do We Monitor and Control This? Digester monitoring pH Volatile acid concentrations Alkalinity Foaming Temperature Feed rates Volatile solidsBut What Does This Really Mean? Continue normal digester monitoring and sampling Maybe small expansion of parameters Become familiar with received materials Understand how the digesters react to different materials Can be simple flow rate controlLessons LearnedWE&RF Has a Significant Research Program on Co-DigestionDetailed SurveyWhat Do Plants Monitor?