Manure Manure DigestersDigestersRichard BallengerRichard Ballenger
OverviewOverview
Cattle BasicsCattle Basics Manure ManagementManure Management Digester OverviewDigester Overview Digester ChemistryDigester Chemistry Digester FlowDigester Flow ReactorsReactors Crave Farm Case StudyCrave Farm Case Study Future DigestersFuture Digesters
Cattle BasicsCattle Basics
Produce up to 100 lbs of milk/day ~10-12 galProduce up to 100 lbs of milk/day ~10-12 gal Milked three times each day - 24 hr/day operationMilked three times each day - 24 hr/day operation Creatures of habitCreatures of habit
Eat up to 90 lbs of food/dayEat up to 90 lbs of food/day Drink 200-400 lbs of water/day ~20 25-50 galDrink 200-400 lbs of water/day ~20 25-50 gal Mass balance: 200-400 lbs of waste/dayMass balance: 200-400 lbs of waste/day These numbers are staggering considering These numbers are staggering considering
there can be thousands of cattle per farmthere can be thousands of cattle per farm
Manure ManagementManure Management
How to handle the large amount?How to handle the large amount? Where does it go?Where does it go? How does it get there?How does it get there? What are its uses?What are its uses?
Typical Manure Typical Manure ManagementManagement
Some farms have slatted floorsSome farms have slatted floors Manure is gravity fed to a Manure is gravity fed to a
holding lagoonholding lagoon Can be used as fertilizerCan be used as fertilizer
High organic N content – can’t be High organic N content – can’t be spread on live plantsspread on live plants
Can only be spread before plantingCan only be spread before planting OdorOdor
Manure CompositionManure Composition
Moisture content:Moisture content: 88-91%88-91% Total solids (TS):Total solids (TS): 9-12%9-12% Volatile solids (VS):Volatile solids (VS): 7-9%7-9%
Digester OverviewDigester Overview
Converts methane from manure into Converts methane from manure into powerpower
Completely removes odorCompletely removes odor Separates solid from liquid wasteSeparates solid from liquid waste
Solids can be sold as potting mixSolids can be sold as potting mix Solids can be used as cattle beddingSolids can be used as cattle bedding Liquid can be used as fertilizer on green Liquid can be used as fertilizer on green
plantsplants Reduces manure management Reduces manure management
problemsproblems
Digester MythsDigester Myths
Does not reduce manure volumeDoes not reduce manure volume Liquid does not have reduced Liquid does not have reduced
nutrientsnutrients ***Phosphorus exception***Phosphorus exception
Digester ChemistryDigester Chemistry
Anaerobic Process (No oxygen)Anaerobic Process (No oxygen) VS contain fasts, carbohydrates, VS contain fasts, carbohydrates,
proteins, and miscellaneous other proteins, and miscellaneous other nutrientsnutrients
Two stage processTwo stage process Acid-forming stageAcid-forming stage Methane forming stageMethane forming stage
Acid Forming StageAcid Forming Stage
Performed by acid formersPerformed by acid formers VS + bacteria = fatty acidsVS + bacteria = fatty acids Not very sensitive to temperature Not very sensitive to temperature
and pHand pH Excess acid formers lower the pHExcess acid formers lower the pH
Methane Forming StageMethane Forming Stage
Performed by methane formersPerformed by methane formers fatty acids + bacteria = methane fatty acids + bacteria = methane
and carbon dioxideand carbon dioxide Optimal Temperature ~ 95-100 °FOptimal Temperature ~ 95-100 °F Optimal pH ~ 6.8-7.4Optimal pH ~ 6.8-7.4
Lime sometimes added at startup to Lime sometimes added at startup to control pH from excess acid formerscontrol pH from excess acid formers
General Digester FlowGeneral Digester Flow
Manure enters floor slats and is Manure enters floor slats and is gravity fed to underground tankgravity fed to underground tank
Manure fed into digesterManure fed into digester Methane and carbon dioxide collect Methane and carbon dioxide collect
under the digester cover under the digester cover Fed to combustion engine for electricity Fed to combustion engine for electricity
generationgeneration Solids and liquids are separatedSolids and liquids are separated
Solids stored in barnSolids stored in barn Liquids stored in a lagoonLiquids stored in a lagoon
Flow DiagramFlow Diagram
ReactorsReactors
Three typesThree types Covered LagoonCovered Lagoon Plug FlowPlug Flow Complete MixComplete Mix
Covered Lagoon DigesterCovered Lagoon Digester
Make by covering Make by covering your holding your holding lagoonlagoon
Simplest type, but Simplest type, but least effectiveleast effective
In cold climates In cold climates only used for odor only used for odor controlcontrol
Plug FlowPlug Flow
Middle of the road Middle of the road digesterdigester
Can be used in Can be used in warm or cold warm or cold climatesclimates
Has problems with Has problems with pluggingplugging
Completely MixedCompletely Mixed
Best technology, Best technology, but most expensivebut most expensive
Warm and cold Warm and cold climatesclimates
Usually cylindrical Usually cylindrical towers made of towers made of concrete or concrete or stainless steelstainless steel Up to about 90 ft in Up to about 90 ft in
diameterdiameter
Case StudyCase Study
Crave Brothers Farm – Waterloo, WICrave Brothers Farm – Waterloo, WI Installation by Clear Horizons, a Installation by Clear Horizons, a
division of Peeper Electricdivision of Peeper Electric Complete Mix DigesterComplete Mix Digester 1,000 head of cattle1,000 head of cattle Approximate energy production 200 Approximate energy production 200
kWkW
StructureStructure
84 ft outside (82 ft 84 ft outside (82 ft inside) diameterinside) diameter
Stainless steel Stainless steel constructionconstruction 304 Stainless for 304 Stainless for
solid contactsolid contact 316 Stainless for 316 Stainless for
Biogas contactBiogas contact Wrapped in Wrapped in
insulationinsulation
RoofRoof
Double membraneDouble membrane Rigid outsideRigid outside Floating insideFloating inside
Blower regulates pressure between Blower regulates pressure between the two membranesthe two membranes
Allows for differences in methane Allows for differences in methane productionproduction
Heat ControlHeat Control
Inside temperature Inside temperature 95-100 °F95-100 °F
Regulated by Regulated by temperature coilstemperature coils
Heat required Heat required comes from the comes from the combustion enginecombustion engine
AgitationAgitation
Agitated by one large and three small Agitated by one large and three small submersible motorssubmersible motors
PumpingPumping
Manure pumped in just below Manure pumped in just below solid/liquid levelsolid/liquid level
Methane pumped off the topMethane pumped off the top As bacteria break down manure, the As bacteria break down manure, the
density increases as sinks to bottomdensity increases as sinks to bottom Solid/liquid pumped off bottom and Solid/liquid pumped off bottom and
separatedseparated Maximum retention time ~ 3 daysMaximum retention time ~ 3 days
EngineEngine
Internal combustion engineInternal combustion engine 200 kW200 kW Effluent from digester is 60% methane Effluent from digester is 60% methane
40% carbon dioxide40% carbon dioxide Electricity and Heat are utilizedElectricity and Heat are utilized
Electricity pumped back into power gridElectricity pumped back into power grid Heat used to heat the digesterHeat used to heat the digester Excess heat can be used for hot water Excess heat can be used for hot water
on the farmon the farm
DCSDCS
DCS (Distributed Control System) DCS (Distributed Control System) controls and trends all aspectscontrols and trends all aspects
Completely automatedCompletely automated Only needs to be checked about Only needs to be checked about
once per weekonce per week
Cost AnalysisCost Analysis
Barely economical in the United Barely economical in the United StatesStates $0.06/kw-hr$0.06/kw-hr $1.5 million capital cost$1.5 million capital cost Pay back period of 7-8 yearsPay back period of 7-8 years
Very economical in EuropeVery economical in Europe $0.30 - $0.40/kw-hr$0.30 - $0.40/kw-hr Carbon creditsCarbon credits
Carbon CreditsCarbon Credits
New concept – Linked to KyotoNew concept – Linked to Kyoto Destroy green house gas and receive Destroy green house gas and receive
creditscredits Less greenhouse gasses emitted with Less greenhouse gasses emitted with
digesterdigester Companies that emit lots of Companies that emit lots of
greenhouse gasses can purchase greenhouse gasses can purchase carbon creditscarbon credits ““Reduces” their output by only spending Reduces” their output by only spending
moneymoney
Crave Farm AgreementCrave Farm Agreement
Crave farm agrees to provide Crave farm agrees to provide manure for ten yearsmanure for ten years
Clear Horizons pays the bill for the Clear Horizons pays the bill for the digesterdigester They get all profits from sale of They get all profits from sale of
electricity and solidelectricity and solid Crave farm gets the liquid fertilizer Crave farm gets the liquid fertilizer
and any excess heat from the and any excess heat from the combustioncombustion
Clear Horizon - Financial Clear Horizon - Financial Risk?Risk?
Clear horizons investment – Not riskClear horizons investment – Not risk Get tax cut for green energyGet tax cut for green energy With no change they will make their With no change they will make their
money back in 8 yearsmoney back in 8 years If energy costs increase, pay back If energy costs increase, pay back
period a little shorterperiod a little shorter If US needs carbon credits, pay back in If US needs carbon credits, pay back in
about 1-2 yearsabout 1-2 years
Why not own the Why not own the digester?digester?
For a farm $1.5 million is a lot of For a farm $1.5 million is a lot of money to finance for about 8 yearsmoney to finance for about 8 years
Farm has to do all of the work and Farm has to do all of the work and upkeep instead of Clear Horizonsupkeep instead of Clear Horizons
Already getting a tax break because Already getting a tax break because they are a farmthey are a farm
Future of DigestersFuture of Digesters
Everything about a digester helps a Everything about a digester helps a farmfarm
Only problem is costOnly problem is cost Clear horizons is virtually Clear horizons is virtually
eliminating cost issueeliminating cost issue Not signing on because farmers like to Not signing on because farmers like to
be in total controlbe in total control Some farmers use sand bedding which Some farmers use sand bedding which
doesn’t work well with the digesterdoesn’t work well with the digester
Special Thanks To:Special Thanks To:
Karl CraveKarl Crave Crave Brothers FarmCrave Brothers Farm Clear HorizonsClear Horizons
SourcesSources http://www.extension.umn.edu/capacity/afe/http://www.extension.umn.edu/capacity/afe/
components/PowerPoints/SchmidtAndigest.pdfcomponents/PowerPoints/SchmidtAndigest.pdf http://www.manuremanagement.cornell.edu/http://www.manuremanagement.cornell.edu/
Docs/Food%20Waste%20fact%20sheetDocs/Food%20Waste%20fact%20sheet%202.pdf%202.pdf
http://www.rcmdigesters.comhttp://www.rcmdigesters.com http://muextension.missouri.edu/explore/http://muextension.missouri.edu/explore/
agguides/agengin/g01881.htmagguides/agengin/g01881.htm http://www.weltec-biopower.dehttp://www.weltec-biopower.de http://www.banffpork.ca/proc/2004pdf/p193-http://www.banffpork.ca/proc/2004pdf/p193-
West.pdfWest.pdf http://www.clearhorizonsllc.comhttp://www.clearhorizonsllc.com