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The Suitability Of Different Feedstocks For Anaerobic Digestion

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The Suitability Of Different Feedstocks For Anaerobic Digestion

  1. 1. The Suitability of Different Feedstocks for Anaerobic Digestion [email_address] 25 th September 2007
  2. 2. Objectives <ul><li>Renewable Obligations </li></ul><ul><li>The need for a ‘clean’ feedstock </li></ul><ul><li>Potential sources of contamination </li></ul><ul><li>Sources of waste/energy </li></ul><ul><li>Waste characteristics </li></ul><ul><li>Nutrient balancing </li></ul>
  3. 3. Renewable Obligations <ul><li>An incentive to encourage renewable energy </li></ul><ul><li>Mandatory requirement increasing to 15% by 2015 </li></ul><ul><li>1 ROC = 1 MWh of electricity generated from eligible sources </li></ul><ul><li>Current value ~£40, but variable </li></ul>
  4. 4. Ofgem ROC Register <ul><li>(Source: DEFRA, 2007) </li></ul>Variable Stable
  5. 5. Levelised Costs <ul><li>(Source: DEFRA, 2007) </li></ul>
  6. 6. Levelised Costs 2020 <ul><li>(Source: DEFRA, 2007) </li></ul>
  7. 7. The Fractional Multiple ROC System (Source: DEFRA, 2007) 2.0 ROCs/MWh Wave, tidal, advanced conversion techniques, (gasification, pyrolysis and AD), dedicated regular biomass with CHP, solar, geothermal Emerging 1.5 ROCs/MWh Offshore wind, dedicated regular biomass Post Demonstration 1.0 ROCs/MWh Onshore wind, hydro-electric, co-firing of energy crops, energy from waste with CHP Reference 0.25 ROCs/MWh Sewage gas, landfill gas, co-firing of non-energy crop biomass Established
  8. 8. Methanogenesis <ul><li>Organic matter Methane & Carbon Dioxide </li></ul><ul><li>C x H x O x CH 4 + CO 2 </li></ul>
  9. 9. Inorganic Contaminants <ul><li>Source: Scottish Enterprise, 2006 – ‘Digestate Standard Project’ (Heslop & Collins) </li></ul>
  10. 10. Organic Contaminants <ul><li>Source: Scottish Enterprise, 2006 – ‘Digestate Standard Project’ (Heslop & Collins) </li></ul>
  11. 11. Suitable Energy Sources for AD <ul><li>Feedstock – any substrate that can be converted into methane by anaerobic bacteria. </li></ul>Lignocellulose 3.9 As low as 1.1:1 ~50% Simple Carbohydrates 5.0 ~1.4: 1 ~60% Proteins 10.3 As high as 2.9: 1 ~70-75% Fats Potential energy yield (KWh) from 1kg of volatile solids COD: Volatile Solids Methane concentration
  12. 12. Sources, Composition & Biodegradability <ul><li>(Source: Steffen et al , 1998, ‘Feedstocks for Anaerobic Digestion’) </li></ul>
  13. 13. Ammonia <ul><li>Important nutrient for cell growth </li></ul><ul><li>Inhibition >3000 mg/l </li></ul><ul><li>More likely at higher pH’s (>8) </li></ul><ul><li>High protein wastes increase risk </li></ul><ul><li>Offset by balancing feedstocks </li></ul>
  14. 14. Agricultural Feedstocks <ul><li>(Source: Steffen et al , 1998, ‘Feedstocks for Anaerobic Digestion’) </li></ul>
  15. 15. Feedstocks cont.. <ul><li>(Source: Steffen et al , 1998, ‘Feedstocks for Anaerobic Digestion’) </li></ul>
  16. 16. Achieving a balance <ul><li>Retention time </li></ul><ul><li>Carbon: nitrogen: Phosphorus </li></ul><ul><li>Percentage volatile solids </li></ul><ul><li>Methane content of the biogas </li></ul><ul><li>Organic loading rate </li></ul><ul><li>Contaminants in the feedstock </li></ul><ul><li>Inhibitors </li></ul>
  17. 17. Know your waste – determine the methane potential in advance <ul><li>COD, VS & TKN analysis </li></ul><ul><li>Biomethane potential testing </li></ul><ul><li>Bench scale testing </li></ul>
  18. 18. The Impact of Waste Handling <ul><li>How is the waste collected? </li></ul><ul><li>What is the transport distance? </li></ul><ul><li>How long is the waste degrading before AD? </li></ul><ul><li>Is pre-treatment required? </li></ul>
  19. 19. <ul><li>Thank you </li></ul><ul><li>[email_address] </li></ul>

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