Potential for Potential for Anaerobic Digestion of Anaerobic Digestion of Crop ResiduesCrop Residues

Ron Fleming & Malcolm MacAlpine (Ridgetown Campus of University of

Guelph), Jim Todd (OMAFRA)

CSBE09-706

FundingFundingOMAFRA – Alternative Renewable

Fuels Plus programU of Guelph/OMAFRA Agreement

ObjectivesObjectivesSuitability of various agricultural by-

products, mainly related to vegetable production and processing, as feedstocks for AD

Feedstock handling, processing and storage requirements

Optimum conditions to maximize methane production

Economic potential of using vegetable wastes as energy feedstocks

Nutrient quality of digestate

OverviewOverview3 year project – 2008 to 2010Use a pilot scale anaerobic digester Potential in Ontario to use organic

“waste” materials common in agriculture to produce energy through the use of an anaerobic digester◦Consider livestock manure as an input◦Look at crop residuals from various

field crops

Top 10 Vegetable Crops for Top 10 Vegetable Crops for Marketed Production in Marketed Production in OntarioOntario

Example: Tomato WasteExample: Tomato WasteAvailable for 8 weeks –

August/SeptemberWaste represents 3 to 13% of

total harvested3 types of processing wastes:

◦Pomace (mostly skins) – 800 t in 2008

◦Lye sludge (+/- 94% water) and Screenings (stems, seeds, etc) – 16,000 to 19,000 t

Potential Biogas YieldsPotential Biogas Yields

100 200 300 400 600

25 36

Liquid cattle manure

Liquid swine manure

93 103

155 171

195 202

Fodder beetsGrass

Green maize, dough stageCorn silage, dough stage, high-grain

Grass silage, first cutCorn silage, waxy stage, high-grain

35 39

68 90

291

220 400

469 486

552 600

657

Food waste

Potato mash, freshWhey

Potato peelingsSilage from sugar beet leafs

Brewer`s grain silage

Skimmed greaseMolasses

Waste breadCanola cake, 15 % fat

Waste greaseBaking wastes

(m3 biogas/tonne)

Description of AD SystemDescription of AD System152 cm diameter, 130 cm depth,

flexible domed top, total volume = 2.7 m3; liquid volume = approx. 1.8 m3

Complete-mixed mesophilic system

Mobile Anaerobic DigesterMobile Anaerobic Digester

Feeding Hopper and Feeding Hopper and AugerAuger

Auger Tube OutletAuger Tube Outlet

Mixing Paddle and Heating Mixing Paddle and Heating CoilsCoils

Electric and Heating Electric and Heating SystemsSystems

Gas Analyzer and Flow Gas Analyzer and Flow MeterMeter

Flare and Pressure Relief Flare and Pressure Relief TubeTube

Test MethodTest MethodVarious materials/mixtures

testedApprox. 4 weeks for each recipeDaily Monday to Friday:

◦Gas samples analyzed◦Gas volume recorded◦Gas flared◦Mixer started◦Material added

Loading rateLoading rateRanged from 0.5 to 1.2 kg VS/m3

digester capacityAverage hydraulic retention time

ranged from 21 to 40 days

Input #1 Input #1 Sugar beets + swine manureSugar beets + swine manure

www.extension.umn.edu/.../DC7715.html

Adding mixture of sugar beets and manure to feed hopper

Input #2Input #2Liquid swine manureLiquid swine manureHad been stored for several

monthsRepresents an input that is

plentiful

Input #3Input #3Sweet potatoesSweet potatoesChopped fineAdded to

digestate, mixed and added to digester as a slurry

No new liquids added

Input #4Input #4Sweet potatoes + (fresh) Sweet potatoes + (fresh) swine manureswine manure

Digestate removedSweet potatoes mixed with fresh

swine manure

Input #5Input #5Swine manureSwine manureFreshly produced manure

Input #6Input #6Dried tobacco Dried tobacco Nicotine-free tobacco leaves

(dry)Mixed with digestate before

adding to digester as a slurry

Sample AnalysisSample AnalysisBiogas:

◦Methane (CH4), Carbon Dioxide (CO2)

Inputs and outputs: ◦N, P, K, pH, NH4-N, C, ash

◦Calculated C:N ratio◦Calculated Volatile Solids

Results for 2008Results for 2008

Example of Daily Inputs and Methane Example of Daily Inputs and Methane Production – Sweet Potatoes & Swine Production – Sweet Potatoes & Swine manuremanure

Example of Cumulative Gas Production Example of Cumulative Gas Production and VS Inputs – Sweet Potatoes & Swine and VS Inputs – Sweet Potatoes & Swine manure manure

Sugar beets & swine manure – poor gas production – but – first test for the unit & problems with temperature control

Fresh swine manure yielded twice as much methane as older swine manure

Dried tobacco was the most difficult to mix

Digestion led to a decrease in DM and an increase in NH4-N

Input Biogas Methane content

Swine manure + sugar beets

57%

“Older” swine manure 64%

Sweet Potatoes 48%

Sweet Potatoes + manure

56%

“Fresh” swine manure 63%

Nicotine-free tobacco leaves

49%

Input Methane Produced (L/kg VS)

Swine manure + sugar beets

233

“Older” swine manure 336

Sweet Potatoes 547

Sweet Potatoes + manure

585

“Fresh” swine manure 670

Nicotine-free tobacco leaves

358

Advantages of this test Advantages of this test setupsetupCan change recipe fairly easily Don’t need huge quantities of

inputsIs a good demonstration unit –

technology transfer

LimitationsLimitationsCurrently only able to add inputs 5

days per weekA few design problems – e.g. input

auger not sufficient for many materials – some re-design needed

Initial difficulty keeping temperature constant – has been resolved

Assumes gas production stabilized within 4 weeks

This yearThis yearContinue testing – vegetable

wastes + other farm organic materials

Document logistical considerations for various materials

Document economic considerations

Questions?Questions?