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
