Charles BanksCharles BanksUniversity of SouthamptonUniversity of Southampton

School of Civil Engineering and the EnvironmentSchool of Civil Engineering and the Environment

ChinaChina--UK Sustainable Agriculture Innovation NetworkUK Sustainable Agriculture Innovation Network

2007 YANGLING INTERNATIONAL AGRI2007 YANGLING INTERNATIONAL AGRI--SCIENCE FORUMSCIENCE FORUM

Integration of energy production Integration of energy production and nutrient management in and nutrient management in

farmingfarming

Lecture overviewLecture overview:

• Crop farming for biogas production in Europe

• Incentives and drawbacks

• Example of energy crop farming and potential conflicts to nutrient management

• Agricultural waste and the larger nutrient cycle

• Integration of urban waste management into energy and nutrient recycling

Anaerobic digestion in its simplest formAnaerobic digestion in its simplest form

• Closed reactor

• System of gas collection

• Production of biogas

• Production of digestate

Anaerobic reactor

Gas storage

Energy

Heat

Energy use

excess

Product

Product use

Crop farming for biogas in EuropeCrop farming for biogas in Europe

• Stimulated by the EU renewable energy targets

• Makes use of surplus agricultural land

• Different incentives in different EU countries

• Subsidies for electricity production in some countries and reduction in fuel tax in others

• In Germany, Austria and the UK biogas used mainly for electricity production

• In Scandinavian countries biogas is used mainly as a vehicle fuel

Crops used for biofuel productionCrops used for biofuel production• for biodiesel

– oilseed rape

– sunflower

– linseed

– soya

– peanut

• for bioethanol

– wheat

– sugar beet

– maize

– sugar cane

– sweet sorghum

– lignocellulosic material

• for biogas– barley– cabbage– carrot– cauliflower– clover– elephant grass– flax– fodder beet– giant knotweed– hemp– horse bean– jerusalem

artichoke– kale– lucerne– lupin– maize– marrow kale

– meadow foxtail– miscanthus– mustard– nettle– oats– pea– potato– rape– reed canary

grass– rhubarb– ryegrass– sorghum– sugar beet– triticale– turnip– verge cuttings– fetch– wheat

Biogas yields (mBiogas yields (m3 3 wet tonnewet tonne--11))

195Total plant grain silage

391Corn cop mix (5.3% fibre)

597Milled grain

183Grass silage

190Maize silage

98Meadow grass

Biogas yieldAgricultural energy crops

Biogas production from maize and Biogas production from maize and vegetable wastevegetable waste

Energy inputs into bioEnergy inputs into bio--energy productionenergy production

biofuel production

crop production

biomass feedstock

direct energy inputs

indirect energy inputs

energy by-products

indirect energy inputs

other agricultural

inputs

Fossil fuels or substitute fuels

from the production

process

machinery

labour

Energy balance ?Energy balance ?

Energy balance for a maize fed digesterEnergy balance for a maize fed digester

36%

20%1%

22%

4%

14%3%

crop energy requirement

nitrogen fertiliser

crop transport

parasitic heat requirement

parasitic electricity

digester embodied energy

digestate disposal energy

GJ/year49,932energy production

GJ/ha157

m32,331,092biogas produced

m31,398,655methane

GJ/ha30

GJ/year9566total energy requirement

ha318crop area

m32000digester capacity

unitvalue

Crop production inputsCrop production inputs

0 1 2 3 4 5 6 7 8 9

fuel

machinery

fertiliser

pesticides

labour

Energy requirement GJ ha-1

sugar beetmaizewheatsoyalucerne

Nutrient recycling in crop based Nutrient recycling in crop based biogas productionbiogas production

Crop biomass

digestion

Biogas

Crop biomass

Fertilisation window for maizeFertilisation window for maize

Fertilisation window for grassFertilisation window for grass

Nutrient requirements of grassland [%]

481834

271756

N P2O5 K2O

Nutrient composition of maize digestate [%]

Nutrients applied if N=100% [%]

Nutrients applied if K2O=100% [%]

100 175 285

34 57 100

Example of nutrient balance on digestate Example of nutrient balance on digestate application to alternative cropsapplication to alternative crops

Energy crop and agricultural waste Energy crop and agricultural waste biogas productionbiogas production

• Large production of animal manure in EU – 1250 million tonnes per year

• Environmentally damaging

• Potential energy yield per tonne is low for biogas production

• It can be economically used for biogas production if treated with energy crops or high energy value waste (co-digestion)

Biogas yields (mBiogas yields (m3 3 wet tonnewet tonne--11))

93Poultry

18Pig

34Fattening cattle

20Dairy cattle

Biogas yieldManure & slurry

50 tonnes d-1

ODM 8%

48 tonnes d48 tonnes d--11

2 tonnes / day biogas

= 1566 m3

= 862 m3 CH4

357 kW potential energy357 kW potential energy

125 kW 125 kW electricityelectricity

134 kW 134 kW surplus heatsurplus heat

45 kW 45 kW parasitic parasitic heatheat

Volume 1500 m3

30 day HRT

Load 2.7 kg ODM m-3 d-1

Volumetric gas production = 1.04 m 3 m-3

50 tonnes /day

ODM 8%

50.5 tonnes d50.5 tonnes d--11

4 tonnes / day biogas

= 3348 m3

= 2020 m3 CH4

837 kW potential energy837 kW potential energy

293 kW 293 kW electricityelectricity

374 kW 374 kW surplus heatsurplus heat

45 kW 45 kW parasitic parasitic heatheat

Volume 1500 m3

27.5 day HRT

Load 4.1 kg ODM m-3 d-1

co-digestate

4.5 tonnes / day

ODM 36%

Volumetric gas production = 2.23 m 3 m-3

•• UK farm based UK farm based

coco --digestion digestion biogas plantbiogas plant

Digestion plant

maize silage

maize crop

Maize 230 hectares

400 dairy cows

3000m3 digester

370 kW output CHP

Energy crop and food productionEnergy crop and food production

Crop biomass

digestion

Biogas

Livestock

Fertiliser

disposal

biomass

Animal husbandry and waste importAnimal husbandry and waste import

Crop biomass

digestion

Biogas

Livestock

Fertiliser

disposal

biomass

CoCo--digestion food processing wastes digestion food processing wastes with cattle slurrywith cattle slurry

Food processing pig slurry with market Food processing pig slurry with market wastewaste

Energy and food productionEnergy and food production

Crop biomass

digestion

Biogas

Livestock

biomass

Pre-treatment and post treatment are minimised

Green wasteMarket wasteKitchen waste

Food processing waste

Digester

Final product

Biogas from urban source Biogas from urban source segregated wastesegregated waste

UKUK’’s first demonstration plant for s first demonstration plant for food waste biogas productionfood waste biogas production

Concept based on collection of Concept based on collection of domestic food wastedomestic food waste

• Separated in the household

in separate lined bin

• Uncooked and cooked food

• Vegetables and meat

• Bones

• NO garden waste

• Moisture content > 75%

• 150 -200 kg per household per year

Process flow for food waste digestionProcess flow for food waste digestion

Domestickitchenfoodwaste

Commercial food waste

Equalisation

storagetank

Maceratorpump

Digester

Digestate storagetank

Gas collector

CHP

Waste

digestate

Pasteur-isation

unit

DOMESTIC KITCHEN WASTE (23%TS)

230 kg TS

770 kg H2O

1000 kg Total

DIGESTER

75% destruction of organic material

BIOFERTILISER (7.8% TS)

60 kg TS

770 kg H2O

830 kg Total

BIOGAS

60 kg CH4

110 kg CO2

170 kg Total (140m3 biogas)

CHP

UNIT

ELECTRICITY

275 kW.hr Gross

250 kW.hr Net

HEAT

440 kW.hr Gross

220 kW.hr Net

Mass balance for 1 tonne of source Mass balance for 1 tonne of source segregated domestic catering wastesegregated domestic catering waste

Food waste digestate characteristicsFood waste digestate characteristics

BDL: below the detection limit. Cd-1mg kg-1 TS, Hg-0.01mg kg-1 TS, Pb-10mg kg-1 TS

Zn (mg kg-1 TS)Pb (mg kg-1 TS)Ni (mg kg-1 TS)Hg (mg kg-1 TS)Cu (mg kg-1 TS)Cr (mg kg-1 TS)Cd (mg kg-1 TS)TP (g kg-1 TS)TK (g kg-1 TS)TN (g kg-1 TS)

PAS110 upper limit

Digestate fibre

Digestate liquor

400130160200BDLBDL5010401.0--200204010010501.5BDLBDL

1112184755115

DIGESTATESMaizeCattle slurryGrassPig slurryPoultry manureKitchen wasteBloodwhole crop cereal

CROPSMaizeSugar beetPotatoesBeans & PeasGrassCereals – wheat, barley, rye

Management challenges for nutrient Management challenges for nutrient recycling:recycling:

Nutrient compositions in digestate may not reflect crop requirements

K2O %

P2O 5%

N%

Finland Finland –– small scale integrated small scale integrated farming systemfarming system

Kalmari Farm

Raw slurry storageDigestate

storage

Biogas vehicle fuel pump

Crop drying

Farm house

Silage store

Animal housingAnaerobic

digester

Research supported by:Research supported by:

• UKRC – Rural Economy and Land Use (RELU) Programme

• EU Sixth Framework Programme

• UK Government’s Department for Environment Food and Rural Affairs