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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
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