the potential of anaerobic digestion technology to treat ......mexico’s coffee industry generates...

Theoretical Framework Biogasyieldisbasedonpreviousresearchresultsof131m3ofbiogaspertonoffreshcoffeepulp(Gauthoetal).Theestimatedmethanepercentageofthebiogasissetat65%.MostADplantswithathermophilicCSTRaredesignedtohaveahydraulicretentiontime(HRT)of10days(Stafford).Thedigestedsolidfertilizervalueissetat$50perton(thisandallfollowingvaluesareinUSDollars),at50%moisture,thepriceofcompostedcoffeepulpinHuatusco.Thedigestedliquidfertilizercontains0.68kgofnitrogen/m3.Therefore,itsvalueisbasedon$1.02/kgnitrogen,thecurrentpriceforureanitrogen.Thebiogaspriceisbasedonmethane(CH4)content.Methanegasisvaluedat$10/MMBTU,theprojectedaveragepriceforHuatusco(PemexGas).

Conclusions Themodelproveseconomicallyfeasibleattheconditionsstudied.Afteryear10,AD-CWSwillstartmakingaprofit.AD-CWSwillnotonlyeliminatecoffeeprocessingwastedischargeintowaterways,butbecauseofitslocationinawelldevelopedagriculturalarea,ifwillalsogeneraterevenuethroughfertilizerandmethanesales.Byminimallyprocessingthebiogasandusingitasafueltodrycoffeebeans,themodeliseconomicallyfeasible.Whilethepossibilitytogenerateelectricityfrombiogasexists,generatorcapitolcostandgridaccessibilitymakethisalessattractiveoption.Atthistime,furtherstudiesareneededtoverifythebiogasyieldfromcoffeepulpatthermophilictemperatures(above55°C)inordertoproperlyforecastrevenues.EnforcementofenvironmentallawsinMexicowillresultinfinestothecoffeeindustryfordischargingcoffeewasteintowaterways,increasingcoffeeprocessingoperatingcosts.AD-CWScanhelpthecoffeeindustrycomplywithenvironmen-talregulationsandavoidfines.

Results and Discussion

AD-CWSisdesignedtohaveaworkinglifeof15years,2yearsforconstructionandset-up,thenthe3rdyeartheplantwillstartoperating(figure2).TheeconomicanalysisofbuildingtheAD-CWSyieldedacapitalcostof$0.97million(thisandallfollowingvaluesareinUSDollars),andyearlyoperatingcostof$0.28million.Capitalcostpaybackis10.3years.Afteryear2,revenueexpectstobe$0.78millionayear.Therateofreturnofthewholeprojectis14%.ThemostsignificantfindingisthatAD-CWSnotonlyprovidesrevenuetothecoffeeplantbyproducingmethaneandfertilizer,butalsoeliminatestheneedtodisposeofwastewa-terandcompostcoffeepulp,bothofwhichcontributetowaterpollution.

ThesuccessofADitinitsabilitytosellsolidandliquiddischargeasfertilizer.Huatuscohasthebenefitofbeinglocatedinanagriculturalarea,withawell-developedfertilizermarketandproximitytocrops,diminishingtransportationcosts.InmanyotherregionswhereADhasbeenproposed,liquiddischargeasfertilizercannotbedevelopedduetohightransportationcosts.Theeconomicmodelchargesafeeof$0.05/kgofcoffeewaste.Thisrepresentsonly3%ofthecoffeeprocessingcost.However,whentheMexicangovernmentbeginsfiningthecoffeeindustryforcoffeewastedischarge,ADtechnology–liketheproposedAD-CWS-willbecomeevenmoreattractive.

Abstract Theaimofthisstudyistotheoreticallyevaluateananaerobicdigestionsystemforcoffeewaste.

•Thefirstobjectiveofthestudyistodeterminethedesignfeasibil-ityofanAnaerobicDigestion(AD)plantsystemtotreatcoffeewastefromSolidaridad Cafetalera,acoffeeprocessingplantinHuatusco,VeracruzState,Mexico,calledAD-CoffeeWasteSystem(AD-CWS).

•ThesecondobjectiveistobuildaneconomicmodelforAD-CWSinHuatusco.TheAD’seffluentswillbemarketablefertilizerandthebio-gaswillbesoldtodrycoffeebeansandfordomesticuse.

Throughtheoreticalframework,AD-CWSwillproduce131m3ofbiogaspertonoffreshcoffeepulp(Gauthoetal).AD-CWSproduces3,010m3/dayofbiogas,1.58t/daydbofsolidfertilizerand104.45m3/dayofliquidfertilizer.Theeconomicmodelshowsrevenuestartingthe7thyearofoperationwithatotalrateofreturnof14%.Basedonthisdata,AD-CWSisagoodoptiontotreatcoffeewasteforSolidaridaCafetelerainHuatusco.

Acknowledgements ThisresearchwasmadepossiblethankstothesupportofDrLi,directorofOUInternationalDevelopmentStudies,andDrBotteandDrPaxtonmembersofmythesiscommittee,ProfessorSalvador D�az C�rdenas atSalvadorD�azC�rdenasatUniversidad Autónoma Chapingo,in Huatusco. I am also gratefulnHuatusco.IamalsogratefulforthesupportfromDr.Teodoro Espinosa Solares fromTeodoroEspinosaSolaresfromUniversidad Autónoma Chapingo, and West Virginia State University visiting professor, andandWestVirginiaStateUniversityvisitingprofessor,andJohnBombardiere,WestVirginiaStateBioplexProjectassistantmanager. SpecialaknowledgementtothemembersofUniónRegionaldePequeñosProductoresdeCafé,Agropecuaria,ForestalydelaAgroindustriadeHuatusco,(UR)whoarethe owners and workers atheownersandworkersatSolidaridadCafetalerainHuatusco,Mexico

ReferencesCastillo,M.,H.Baily,P.Violle,P.Pommares,andB.Sallee.1993.CoffeewastewatertreatmentintheCoatepecriverbasin,Veracruz,Mexico. Turrialba43,(2)(October18):143-150.Gautho,B.,P.Rantala,andR.Maatta.1991.Coffeeindustrywastes.WaterScienceandTechnology24,(1):53-60.InternationalCoffeeOrganization(ICO).Tradestatistics.London,England,2006[citedJanuary/172006].Availablefromhttp://www.ico.org/ trade_statistics.asp.Pandey,A.,C.R.Soccol,P.Nigam,D.Brand,R.Mohan,andS.Roussos.2000.Biotechnologicalpotentialofcoffeepulpandcoffeehuskforbiopro-cesses.BiochemicalEngineeringJournal6,(2)(Oct1):153-162.PemexGas.HistorynaturalgaspricesMexico,2006[citedApril/202006].Availablefromhttp://www.gas.pemex.com/PEMEX_GasStafford,D.A.,RexHorton,andDennisL.Hawkes.1980.Methaneproductionfromwasteorganicmatter.BocaRaton,Fla.:CRCPress.

Introduction Coffeeisanimportantcropindevelopingcountries.In2004,6,985,680tonsofcoffeebeanswereproducedworldwide(ICO).However,coffeeproducingcountriesfaceseriousproblemsindispos-ingofcoffeeprocessingwaste.2milliontonsofcoffeewasteisgen-eratedyearly(Pandeyetal).In2004,Mexicoproduced232,020tonsofcoffeebeans,andwasthe7thleadingworldwidecoffeeproducer(ICO).Mexico’scoffeeindustrygenerates13.2millionm3ofwaste-water,equivalenttothesewageofacityof5.6millioninhabitants(Castilloetal).

AnaerobicDigestion(AD)technologyisworthevaluatingasanalternativecoffeewastedisposalsolution.TheaimofthisstudyistoevaluatetheeconomicfeasibilityofusingADtotreatcoffeewaste,byproposingasystemthatusesthecoffeewastetogeneratebiogasandfertilizer,calledAD-CoffeeWasteSystem(AD-CWS).AD-CWSisbaseduponSolidaridad Cafetalera,acoffeeprocessingplantinHuatusco,VeracruzState,Mexico.TheAD-CWSisbasedonamedi-umsizecoffeeplant,processing45tonsofcoffeecherriesaday.TheADwillrun100days,duringtheharvestperiod,fromSeptembertoMarch.AD-CWSusesaContinuousStirredTankReactor(CSTR)atthermophilicconditions(above55°C).Theoretically,AD-CWSwillpro-cess22.98tonsofcoffeepulp,3.54tonofmucilageand73.62m3ofwastewaterperday(figure1).

ThePotentialofAnaerobicDigestionTechnologytoTreatCoffeeWasteinHuatusco,Mexico

YsabelBombardiere1,Dr.GerardineBotte2,Dr.JuliaPaxton3,Dr.JieliLi41MAIA,DevelopmentStudies,2ChemicalEngineering,3Economics,4Sociology,OhioUniversity,Athens,Ohio

Coffee CherriesCoffee Plantation

Ripe Coffee Cherries

Pico Orizaba near HuatuscoLocation of Huatusco