Manure Digesters Richard Ballenger. Overview Cattle Basics Cattle Basics Manure Management Manure Management Digester Overview Digester Overview Digester.

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