Anaerobic bacteria Microorganisms that live and reproduce in an environment containing no “free” or dissolved oxygen.

Anaerobic digester Avesselandassociatedheatingandgascollectionsystemsdesignedspecificallytocontainbiomass

undergoingdigestionanditsassociatedmicrobiallyproducedbiogas.Conditionsprovidedbythedigesterinclude:anoxygen-freeenvironment,aconstanttemperature,andsufficientbiomassretentiontime.

Anaerobic digestion Abiologicalprocessinwhichmicrobesbreakdownorganicmaterialinanoxygen-freeenvironmentwhile

producingbiogasasaby-product.

Anaerobic lagoon Aholdingpondforlivestockmanurethatisdesignedtoanaerobicallystabilizemanure,andmaybedesignedto

capturebiogaswiththeuseofanimpermeable,floatingcover.

Annual capital cost The equivalent annual capital cost converts the total capital costs into an annual charge. The equivalent annual

capital cost is calculated according to the formula EAC=pv/(1/r-1/(r*(1+r)^n))where“pv”isthepresentvalueortotalcapitalinvestmentintoday’sdollars,risthe

discount rate, and n is the life of the capital investment.

Biogas Forthepurposesofthisdocument,therawandun-cleanedgasproducedbyadigester,consistingofmainly

methane(~60%),carbondioxide(~40%),watervapor,andhydrogensulfide.

Biological Oxygen Demand (BOD) Theamountofoxygenrequiredbyaerobicmicroorganismstodecomposetheorganicmatterinasampleof

water,suchasthatpollutedbysewage.Itisusedasameasureofthedegreeofwaterpollution.

British Thermal Unit (Btu) TheEnglishSystemstandardmeasureofheatenergy.IttakesoneBtutoraisethetemperatureofonepound

ofwaterbyonedegreeFahrenheitatsealevel.

Capital cost Aone-timefixedcostincurredonthepurchaseofbuildingsandequipment.Adigester’scapitalcostincludes

the purchase of land the system is on, permitting and legal costs, the equipment needed to run the digester, costofdigesterconstruction,thecostoffinancing,andthecostofcommissioningthedigesterpriortosteady-state operation of the digester.

Carbon dioxide (CO2) Acolorless,odorless,non-flammablegasfoundinbiogas.

ANDIGDecember, 2012

Anaerobic Digestion Glossary of Terms

Carbon to Nitrogen Ratio (C/N) Therelationshipbetweencarbonandnitrogenthatfacilitatesbiogasproduction.AC/Nratioof30permits

digestiontoproceedatanoptimumrate,assumingotherconditionsarefavorable.

Centralized digester Ananaerobicvesselwhichusesfeedstocksfromseveralfarmsand/orotherbiomasssources,withinarelatively

proximate distance to the digester location.

Co-generation Thesequentialuseofenergyfortheproductionofelectricalandusefulthermalenergy.Thesequencecanbe

thermalusefollowedbypowerproductionorthereverse,subjecttothefollowingstandards:(a)Atleast5%oftheco-generationproject’stotalannualenergyoutputshallbeintheformofusefulthermalenergy.(b)Whereusefulthermalenergyfollowspowerproduction,theusefulannualpoweroutputplusone-halftheusefulannualthermalenergyoutputequalsnotlessthan42.5%ofanynaturalgasandoilenergyinput.

Combined Heat and Power (CHP) Thesequentialorsimultaneousgenerationoftwodifferentformsofusefulenergy–mechanicalandthermal

–fromasingleprimaryenergysourceinasingle,integratedsystem.CHPsystemsusuallyconsistofaprimemover,agenerator,aheatrecoverysystem,andelectricalinterconnectionsconfiguredintoanintegratedwhole.

Complete mix digester Ananaerobicvesselthatismixedwithoneormoremixingtechniques.

Covered lagoon digester Thissystemcapturesbiogasunderanimpermeablecover,whiletakingadvantageofthelowmaintenance

requirementofalagoon.Twolagooncellsareneededforthesystemtooperateefficiently.

Dewater Todrainorremovewaterfromanenclosure.Dewateralsomeansdrainingorremovingwaterfromsludgeto

increase the solids concentration.

Digester Anenclosedtankinwhichanaerobicdigestionoforganicwastestakesplace.

Digestate Effluent;Materialremainingaftertheanaerobicdigestionofabiodegradablefeedstock.Digestateisproduced

bothbyacidogenesisandmethanogenesis,andeachhasdifferentcharacteristics.

Discount rate Theinterestrateusedindiscountingfuturecashflows.

Distributed generation Adistributedgenerationsysteminvolvessmallamountsofgenerationlocatedonautility’sdistributionsystem

forthepurposeofmeetinglocal(substationlevel)peakloads.

Distribution system (electric utility) Thesubstations,transformersandlinesthatconveyelectricityfromhigh-powertransmissionlinesto

consumers.

Effluent Digestate;MaterialexitingtheADvessel.

Emission Thereleaseordischargeofasubstanceintotheenvironment;generallyreferstothereleaseofgasesor

particulates into the air.

End-use sectors The residential, commercial, transportation and industrial sectors of the economy.

Engine-Generator set Thecombinationofaninternalcombustionengineandageneratortoproduceelectricity;maybesingleordual

fueled depending on the location and set up.

Feedstock Anyorganicmaterialwithbiogasproductionpotential.

Filtrate Liquid component of the digestate after separation.

Fiber Solid component of the digestate after separation.

Fixed film digester Acolumnpackedwithmedia,suchaswoodchipsorsmallplasticrings,whichfacilitatesmicrobialcolonization

enablingthedigestertohaveasmallerfootprintandreducingHRT.

Flare Adeviceusedtosafelycombustsurplusorunusedbiogas.

Greenhouse Gas (GHG) Agas,suchascarbondioxideormethane,whichcontributestoawarmingactionintheatmosphere.

Grid Theelectricutilitycompanies’transmissionanddistributionsystemthatlinkspowerplantstocustomers

throughhighpowertransmissionlineservice;highvoltageprimaryserviceforindustrialapplications;mediumvoltageprimaryserviceforcommercialandindustrialapplications;andsecondaryserviceforcommercialandresidentialcustomers.Gridcanalsorefertothelayoutofgasdistributionsystemofacityortown.

High solids digestion Alsoknownas“dryfermentation”,highsolidsdigestionisusedtotreatstackablematerialssuchasfood

scraps,yarddebris,andmunicipalsolidswastes.Asthenameimplies,highsolidsdigestersworkwithmaterialsthathaveasolidscontentof25-50%.

High strength waste Feedstocks,suchasfats,oils,andgreasesorotherorganiccomponents,thathaveahighBiologicalOxygen

Demand.Thesefeedstocksgeneratealotofbiogasbutcanalsomakeadigestergosourifnotmanagedcorrectly.

Hydraulic retention time (HRT) The length of time material remains in the digester.

Hydrogen sulfide (H2S) Atoxic,colorlessgasthathasanoffensiveodorofrotteneggs.Hydrogensulfidehasseriousnegative

implicationsforthewearofgashandlingequipmentforananaerobicdigestersystem.

Hydrolysis Abiologicaldecompositionprocessinvolvedintheanaerobicdigestionoforganicmaterial.

Influent Biomassonthein-flowsideofatreatment,storage,ortransferdevice.

Installed capacity Thetotalcapacityofelectricalgenerationdevicesinapowerstationorsystem.

Kilowatt-hour (kWh) Themostcommonlyusedunitofmeasureoftheamountofelectricpowerconsumedovertime.Thestand-

aloneunitindicatesonekilowattofelectricitysuppliedforonehour.

Loading rate Meteringfeedstocksintoadigesterataregular,calculatedrateovertime.

Lagoon Inwastewatertreatmentorlivestockfacilities,ashallowpondusedtostorewastewaterwherebiological

activitydecomposesthewaste.

Manure Thecombinationofurineandfeces.

Mesophilic Of,relatingto,orbeingatamoderatetemperature(35-40˚C).

Methane (CH4) Aflammable,explosive,colorless,odorless,gas.Methaneisthemajorconstituentofnaturalgas,andalso

usuallymakesupthelargestconcentrationofbiogasproducedinananaerobicdigester.

Methanogens Activeinphase3ofthedigestionprocess,acids(mainlyaceticandpropionicacids)producedinphase2are

convertedintobiogasbymethane-formingbacteria.

Microturbine Asmallcombustionturbinewithapoweroutputrangingfrom25-to500-kW.Microturbinesarecomposedofa

compressor,combustor,turbine,alternator,recuperator,andgenerator.

Net generation Grossgenerationminustheenergyconsumedatthegenerationsiteforuseinmaintainingenergyneeds(heat

orelectric).

Net Present Value (NPV) Thepresentvalueofaninvestment’sfuturenetcashflowminustheinitialinvestment.Generally,iftheNPVof

aninvestmentispositive,theinvestmentshouldbemade.

Operation and Maintenance (O&M) costs Operatingexpensesareassociatedwithrunningafacility.Maintenanceexpensesaretheportionofexpenses

consistingoflabor,materials,andotherdirectandindirectexpensesincurredforpreservingtheoperatingefficiencyorphysicalconditionofafacility.

Plug-flow digester Adesignforananaerobicdigesterinwhichthematerialentersatoneendandistheoreticallypushedinplugs

towardstheotherend,wherethematerialexitsthedigesterafterbeingdigestedoverthe design HRT.Present value The current value of one or more future cash payments, discounted at some appropriate interest rate.

Rate of return The annual return on an investment, expressed as a percentage of the total amount invested.

Siloxane Anyofaclassoforganicorinorganicchemicalcompoundsofsilicon,oxygen,andusuallycarbonand

hydrogen,basedonthestructuralunitR2SiOwhereRisanalkylgroup,usuallymethyl.

Slug Alargeinjectionoffeedstockintoadigester.

Slurry Thecontentsofadigesterundergoinganaerobicdigestion.Whenremovedfromthedigester,slurryisknownas

digestate.Digestatecaneitherbelandappliedasacropnutrientsource,orfurtherprocessedandseparatedintofiltrateandfiber.

Sour digester condition Adigestergoes“sour”whenfermentingbacteriaareproducingmoreorganicacidsthanmethanogenscan

convertintomethane,causingthepHoftheslurrytodrop.WhenthepHdropsbelow6.8,methanogensdieoffand methane production ceases.

Stabilization Occurswhenthevolatilesolidscontentofafeedstockisbiologicallyreducedviadetentiontimes,mixingand

interactionwithfermentingbacteria.

Thermophilic Of,orrelatingto,orbeingatarelativelyhightemperature(50-60˚C).

Thermal sink Astructurethatabsorbsheat.

Tipping fees Moniesthatarepaidtoasitethatisacceptingoutsidesourcesoforganicmaterial(non-farmbiomass).

USDA/NIFA National Facilitation Project The Role of a 21st Century Engaged University

Thispublicationisavailableonlineat:http://blogs.extension.org/andig1/files/2013/01/ANDIG-Glossary.pdf

On-linetrainingprogramsonbioenergyandsustainability,on-farmenergyconservationandefficiency,andanaerobicdigestionareavailableonlineat:http://fyi.uwex.edu/biotrainingcenter

Treatment volume Insidevolumeofananaerobicdigesterthat,undernormaloperatingconditionswouldbefullofmaterial

undergoinganaerobicdecomposition.

Turbine Adeviceforconvertingtheflowofafluid(air,steam,water,orhotgases)intomechanicalmotion.

Volatile solids Thosesolidsinwaterorotherliquidsthatarelostonignitionofthedrysolidsat550degreesCentigrade.

Glossary definitions come from the following sources:

Gooch,C.AandJ.L.Pronto.2009.CapitalizingonEnergyOpportunitiesonNewYorkDairyFarms.ParticipantBriefingPaper:ReferenceDocument.PreparedbyCurtA.GoochP.E.andJenniferL.ProntoforDairyPowerNewYorkSummit:CreatingaGreener,CleanerFuture,October29-30,2009.Availableat:

http://www.usdairy.com/Public%20Communication%20Tools/Sustainability%20GHG%20Projects/Dairy%20Power/Dairy%20Power%20New%20York%20Summit%20Participant%20Brief%20-%20Reference%20Docu-ment%20-%20FINAL%2010%2020%2009.pdfverified12/2012

LezbergS.,M.C.GouldandM.Jungswirth(eds.).2013.IntroductiontoAnaerobicDigestionCourse.On-line Curriculum.BioenergyTrainingCenter.Availableat:http://fyi.uwex.edu/biotrainingcenterverified12/2012

Sourcesofadditionalenergytermsusedintheanaerobicdigestionindustrycanbefoundat:• PublicInterestEnergyResearch.2006.Glossaryofenergyterms.Availableat: www.pierminigrid.org/glossary.htmlverified12/2012• Kramer,J.2009.WisconsinAgriculturalBiogasCasebook.PreparedforFocusonEnergy.Availableat: http://www.focusonenergy.com/files/Document_Management_System/Renewables/biogas09_casestudy.pdf verified12/2012