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anaerobic digestion
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The Suitability of Different The Suitability of Different Feedstocks for Anaerobic Feedstocks for Anaerobic
DigestionDigestion
[email protected]@aquaenviro.co.uk
2525thth September 2007 September 2007
ObjectivesObjectives
Renewable Obligations Renewable Obligations The need for a ‘clean’ feedstockThe need for a ‘clean’ feedstock Potential sources of contaminationPotential sources of contamination Sources of waste/energySources of waste/energy Waste characteristicsWaste characteristics Nutrient balancingNutrient balancing
Renewable ObligationsRenewable Obligations
An incentive to encourage renewable energyAn incentive to encourage renewable energy Mandatory requirement increasing to 15% by Mandatory requirement increasing to 15% by
20152015 1 ROC = 1 MWh of electricity generated from 1 ROC = 1 MWh of electricity generated from
eligible sourceseligible sources Current value ~£40, but variableCurrent value ~£40, but variable
ROCsofVolumeTotal
SizeObligationOveralliceBuyoutvalueROC
...
..*Pr.
Ofgem ROC RegisterOfgem ROC Register
(Source: DEFRA, 2007)(Source: DEFRA, 2007)
Variable
Stable
Levelised CostsLevelised Costs
(Source: DEFRA, 2007)(Source: DEFRA, 2007)
Levelised Costs 2020Levelised Costs 2020
(Source: DEFRA, 2007)(Source: DEFRA, 2007)
The Fractional \ Multiple ROC The Fractional \ Multiple ROC SystemSystem
Established Sewage gas, landfill gas, co-firing of non-energy crop biomass
0.25 ROCs/MW
h
Reference Onshore wind, hydro-electric, co-firing of energy crops, energy from waste with CHP
1.0 ROCs/MW
h
Post Demonstratio
n
Offshore wind, dedicated regular biomass 1.5 ROCs/MW
h
Emerging Wave, tidal, advanced conversion techniques, (gasification, pyrolysis and AD), dedicated regular biomass with CHP, solar, geothermal
2.0 ROCs/MW
h
(Source: DEFRA, 2007)(Source: DEFRA, 2007)
MethanogenesisMethanogenesis
Organic matter Organic matter Methane & Carbon DioxideMethane & Carbon Dioxide
CCxxHHxxOOxx CHCH4 4 ++ COCO22
Inorganic ContaminantsInorganic Contaminants
Source: Scottish Enterprise, 2006 – ‘Digestate Standard Project’ (Heslop & Collins) Source: Scottish Enterprise, 2006 – ‘Digestate Standard Project’ (Heslop & Collins)
Organic ContaminantsOrganic Contaminants
Source: Scottish Enterprise, 2006 – ‘Digestate Standard Project’ (Heslop & Collins) Source: Scottish Enterprise, 2006 – ‘Digestate Standard Project’ (Heslop & Collins)
Suitable Energy Sources for ADSuitable Energy Sources for AD Feedstock – any substrate that can be converted into Feedstock – any substrate that can be converted into
methane by anaerobic bacteria. methane by anaerobic bacteria.
Methane concentration
COD: Volatile Solids
Potential energy yield (KWh) from 1kg of
volatile solids
Fats ~70-75% As high as 2.9: 1 10.3
Proteins ~60% ~1.4: 1 5.0
Simple Carbohydrat
es
~50% As low as 1.1:1 3.9
Lignocellulose
Sources, Composition & Sources, Composition & BiodegradabilityBiodegradability
(Source: Steffen (Source: Steffen et alet al, 1998, ‘Feedstocks for Anaerobic Digestion’), 1998, ‘Feedstocks for Anaerobic Digestion’)
AmmoniaAmmonia
Important nutrient for cell growthImportant nutrient for cell growth Inhibition >3000 mg/lInhibition >3000 mg/l More likely at higher pH’s (>8)More likely at higher pH’s (>8) High protein wastes increase riskHigh protein wastes increase risk Offset by balancing feedstocksOffset by balancing feedstocks
Agricultural FeedstocksAgricultural Feedstocks
(Source: Steffen (Source: Steffen et alet al, 1998, ‘Feedstocks for Anaerobic Digestion’), 1998, ‘Feedstocks for Anaerobic Digestion’)
Feedstocks cont..Feedstocks cont..
(Source: Steffen (Source: Steffen et alet al, 1998, ‘Feedstocks for Anaerobic Digestion’), 1998, ‘Feedstocks for Anaerobic Digestion’)
Achieving a balanceAchieving a balance
Retention timeRetention time Carbon: nitrogen: PhosphorusCarbon: nitrogen: Phosphorus Percentage volatile solidsPercentage volatile solids Methane content of the biogasMethane content of the biogas Organic loading rateOrganic loading rate Contaminants in the feedstockContaminants in the feedstock InhibitorsInhibitors
Know your waste – determine the Know your waste – determine the methane potential in advancemethane potential in advance
COD, VS & TKN analysis Biomethane potential testing Bench scale testing
The Impact of Waste HandlingThe Impact of Waste Handling
How is the waste collected?How is the waste collected? What is the transport distance?What is the transport distance? How long is the waste degrading How long is the waste degrading
before AD?before AD? Is pre-treatment required?Is pre-treatment required?
