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Technical background on small scale anaerobic digestion of food waste Iemke Bisschops, Els Schuman, Kasia Kujawa, Henri Sp...
<ul><li>Anaerobic digestion </li></ul>
What is anaerobic digestion <ul><li>A chain of biological processes </li></ul><ul><li>Carried out by different groups of m...
Types of digesters <ul><li>Completely mixed </li></ul><ul><li>Plug flow </li></ul><ul><li>Batch </li></ul><ul><li>Fed-batc...
Slurry digestion <ul><li>Digestion of animal manure is the most widespread AD application worldwide. It produces: </li></u...
Digesters <ul><li>Rural communities: typically small-scale units </li></ul><ul><ul><li>Nepal 50,000 digesters; China > 8 m...
Digesters <ul><li>Western countries: normally medium- to large-scale </li></ul><ul><li>Germany, Austria and Switzerland ar...
AD systems - Suitability <ul><li>Small plants used in developing countries seem attractive from engineering point of view ...
AD systems - Suitability <ul><li>Current systems used for AD of organic solid waste </li></ul><ul><ul><li>Large to very la...
Small scale AD interest growing <ul><li>http://www.patervis.com/sintex.html </li></ul>
<ul><li>Anaerobic digestion of food waste </li></ul>
Food waste <ul><li>Main substrate considered in project with CCN </li></ul><ul><li>Weekly production on average 3 kg per h...
Anaerobic Conversion of Organic Matter CH 4  / CO 2 Methanogenesis Acetogenesis Suspended, colloidal organic matter Hydrol...
Biological stability - Acidification <ul><li>Overloading may lead to process deterioration –  </li></ul><ul><li>A vicious ...
Biological stability - Acidification 50% inhibition by acetic acid Methanogenic  capacity  exceeded Poor  buffering capaci...
Food waste as AD substrate <ul><li>Characteristics of reactor feed and as a result the reactor performance depend on: </li...
Food waste as AD substrate <ul><li>In principle suitable substrate for AD </li></ul><ul><li>Challenging for a small system...
Examples of regulations <ul><li>Animal by-product regulation (ABPR) </li></ul><ul><li>Environmental permitting rules </li>...
Legislation - ABPR <ul><li>Animal by-product regulation (ABPR) regulates all waste from animal origin including kitchen wa...
Digestate <ul><li>Organic nitrogen is converted into ammonia </li></ul><ul><ul><li>Directly available to crops </li></ul><...
Digestate use – Practical <ul><li>When all regulations are complied with, the digestate can be used as fertiliser </li></u...
Biogas <ul><li>Composition (most important compounds) </li></ul><ul><ul><li>Methane </li></ul></ul><ul><ul><li>Carbon diox...
Biogas use on small scale <ul><li>In developing countries very common, e.g. cooking and lighting </li></ul><ul><li>In West...
<ul><li>Proposed system concept </li></ul><ul><li>for CCN project </li></ul>
Summary of system criteria <ul><li>Digester volume fixed at 1 m 3 </li></ul><ul><ul><li>Amount of waste will be made to fi...
Process design  <ul><li>Biodegradability </li></ul><ul><li>Hydrolysis rate of substrates ( particle size!) </li></ul><ul><...
Proposed system concept Simplified process flow diagram, not to scale. Dashed connecting lines: slurry/liquid flow could b...
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Technical Background Small Scale Biogas production

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Presentation by Iemke Bisschops of Lettinga Associates Foundation (LeAF) held at the biogas information seminar in Wageningen the Netherlands, 4 October 2009, organized by the Wageningen Environmental Platform & the Community Composting Network

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Technical Background Small Scale Biogas production

  1. 1. Technical background on small scale anaerobic digestion of food waste Iemke Bisschops, Els Schuman, Kasia Kujawa, Henri Spanjers
  2. 2. <ul><li>Anaerobic digestion </li></ul>
  3. 3. What is anaerobic digestion <ul><li>A chain of biological processes </li></ul><ul><li>Carried out by different groups of microorganisms </li></ul><ul><li>In absence of oxygen </li></ul><ul><li>Products: biogas and digestate </li></ul><ul><li>Different digester configurations are employed </li></ul><ul><ul><li>depending on substrate and local conditions/preferences </li></ul></ul>
  4. 4. Types of digesters <ul><li>Completely mixed </li></ul><ul><li>Plug flow </li></ul><ul><li>Batch </li></ul><ul><li>Fed-batch </li></ul><ul><li>Percolation systems (type of batch system) </li></ul>
  5. 5. Slurry digestion <ul><li>Digestion of animal manure is the most widespread AD application worldwide. It produces: </li></ul><ul><ul><li>Valuable fertiliser </li></ul></ul><ul><ul><li>Biogas </li></ul></ul><ul><li>Farm-scale digestion plants </li></ul><ul><ul><li>widespread use throughout the world </li></ul></ul><ul><ul><li>plants in both developing and technically advanced countries </li></ul></ul>
  6. 6. Digesters <ul><li>Rural communities: typically small-scale units </li></ul><ul><ul><li>Nepal 50,000 digesters; China > 8 million. </li></ul></ul><ul><li>These small plants are generally used for providing gas for cooking and lighting for a single household. </li></ul>(images references in CCN phase 1 report)
  7. 7. Digesters <ul><li>Western countries: normally medium- to large-scale </li></ul><ul><li>Germany, Austria and Switzerland are leading countries </li></ul><ul><ul><li>Farm-scale digesters: Germany > 2000; Austria ~ 120; Switzerland > 70. </li></ul></ul>
  8. 8. AD systems - Suitability <ul><li>Small plants used in developing countries seem attractive from engineering point of view </li></ul><ul><ul><li>relatively simple design, construction, operation </li></ul></ul><ul><li>Not suitable for use in </li></ul><ul><li>Western Europe </li></ul><ul><ul><li>Regulations to meet </li></ul></ul><ul><ul><li>Temperature too low </li></ul></ul><ul><li>At low temperature </li></ul><ul><ul><li>Very large systems needed </li></ul></ul><ul><ul><li>And/or heating </li></ul></ul>
  9. 9. AD systems - Suitability <ul><li>Current systems used for AD of organic solid waste </li></ul><ul><ul><li>Large to very large scale systems </li></ul></ul><ul><ul><li>Usually batch systems with percolation & recycling of leachate </li></ul></ul><ul><li>Percolation systems not suitable for very small scale </li></ul><ul><ul><li>Technically too difficult </li></ul></ul><ul><ul><li>Moving parts, risk of clogging,… </li></ul></ul><ul><li>Slurry digester seems most feasible option </li></ul><ul><ul><li>Technically quite simple </li></ul></ul><ul><ul><li>Experience exists at small scale </li></ul></ul>
  10. 10. Small scale AD interest growing <ul><li>http://www.patervis.com/sintex.html </li></ul>
  11. 11. <ul><li>Anaerobic digestion of food waste </li></ul>
  12. 12. Food waste <ul><li>Main substrate considered in project with CCN </li></ul><ul><li>Weekly production on average 3 kg per household </li></ul><ul><li>Complex substrate </li></ul><ul><ul><li>carbohydrates </li></ul></ul><ul><ul><li>proteins </li></ul></ul><ul><ul><li>lipids </li></ul></ul><ul><ul><li>nutrients, minerals </li></ul></ul><ul><li>Usually very concentrated </li></ul><ul><li>and highly degradable </li></ul>
  13. 13. Anaerobic Conversion of Organic Matter CH 4 / CO 2 Methanogenesis Acetogenesis Suspended, colloidal organic matter Hydrolysis Acidogenesis volatile fatty acids alcohol H 2 / CO 2 acetic acid proteins carbohydrates lipids amino acids sugars free fatty acids glycerol ammonia
  14. 14. Biological stability - Acidification <ul><li>Overloading may lead to process deterioration – </li></ul><ul><li>A vicious circle </li></ul>Overloading Methanogenic capacity exceeded Poor buffering capacity VFA increase pH decrease Unionised VFA increase Methanogenic toxicity increase
  15. 15. Biological stability - Acidification 50% inhibition by acetic acid Methanogenic capacity exceeded Poor buffering capacity VFA increase pH decrease Unionised VFA increase Methanogenic toxicity increase 30000 8 3000 7 300 6 30 5 Concentration (mg/l) pH
  16. 16. Food waste as AD substrate <ul><li>Characteristics of reactor feed and as a result the reactor performance depend on: </li></ul><ul><ul><li>composition </li></ul></ul><ul><ul><li>particle size </li></ul></ul><ul><ul><li>storage time </li></ul></ul><ul><li>Fast acidification, already starting during storage </li></ul><ul><li>Acidification continues inside reactor </li></ul><ul><ul><li>Careful process operation is essential </li></ul></ul>
  17. 17. Food waste as AD substrate <ul><li>In principle suitable substrate for AD </li></ul><ul><li>Challenging for a small system without advanced monitoring and control </li></ul><ul><li>But: </li></ul><ul><li>Normally contains waste from </li></ul><ul><li>animal origin </li></ul><ul><li>-> regulatory barriers </li></ul>
  18. 18. Examples of regulations <ul><li>Animal by-product regulation (ABPR) </li></ul><ul><li>Environmental permitting rules </li></ul><ul><li>Planning regulations </li></ul><ul><li>Regulations for fertiliser use </li></ul><ul><li>Rules on gas safety </li></ul><ul><li>etc… </li></ul><ul><li>Important factor! </li></ul>
  19. 19. Legislation - ABPR <ul><li>Animal by-product regulation (ABPR) regulates all waste from animal origin including kitchen waste </li></ul><ul><ul><li>Classified as “category 3 catering waste” </li></ul></ul><ul><li>Hygienisation of kitchen waste necessary </li></ul><ul><li>Treatment standards for category 3 catering waste: </li></ul><ul><ul><li>minimum 57°C for 5 hours, maximum particle size 50 mm </li></ul></ul><ul><ul><li>70°C for 1 hour, maximum particle size 60 mm </li></ul></ul>
  20. 20. Digestate <ul><li>Organic nitrogen is converted into ammonia </li></ul><ul><ul><li>Directly available to crops </li></ul></ul><ul><ul><li>Possibly higher ammonia emissions from the field </li></ul></ul><ul><li>Reduced viability of pathogens and weed seeds </li></ul><ul><li>Legislation </li></ul><ul><ul><li>Important to ensure safe use </li></ul></ul><ul><ul><li>Probably largest barrier </li></ul></ul><ul><li>Quality protocols </li></ul><ul><ul><li>e.g. UK: “Quality Protocol for the Production and Use of Quality Compost from Source-Segregated Biowaste” </li></ul></ul><ul><ul><li>Defines the point at which the material ceases to be a waste and instead becomes a product. </li></ul></ul>
  21. 21. Digestate use – Practical <ul><li>When all regulations are complied with, the digestate can be used as fertiliser </li></ul><ul><li>It should be worked into the soil to prevent ammonia emissions </li></ul><ul><li>Separation in liquid and solid fraction </li></ul><ul><ul><li>Solid fraction can be composted together with green waste (might be more attractive) </li></ul></ul><ul><ul><li>Liquid fraction can be used as liquid fertiliser </li></ul></ul><ul><ul><li>Will still contain solids and salts, this might limit its application in drip systems. </li></ul></ul>
  22. 22. Biogas <ul><li>Composition (most important compounds) </li></ul><ul><ul><li>Methane </li></ul></ul><ul><ul><li>Carbon dioxide </li></ul></ul><ul><ul><li>Hydrogen sulphide </li></ul></ul><ul><li>Examples of uses: </li></ul><ul><ul><li>Heating </li></ul></ul><ul><ul><li>Steam production </li></ul></ul><ul><ul><li>CHP: electricity and heat </li></ul></ul><ul><ul><li>Transport fuel (e.g. car, lift truck, city busses) </li></ul></ul><ul><ul><li>Supply to normal natural gas network (so called Green Gas) </li></ul></ul><ul><li>End use determines the needed gas quality </li></ul>
  23. 23. Biogas use on small scale <ul><li>In developing countries very common, e.g. cooking and lighting </li></ul><ul><li>In Western Europe not common </li></ul><ul><ul><li>gas quality upgrading normally necessary </li></ul></ul><ul><ul><li>economy of scale </li></ul></ul><ul><li>But: starting to gain interest </li></ul>
  24. 24. <ul><li>Proposed system concept </li></ul><ul><li>for CCN project </li></ul>
  25. 25. Summary of system criteria <ul><li>Digester volume fixed at 1 m 3 </li></ul><ul><ul><li>Amount of waste will be made to fit system size </li></ul></ul><ul><li>Robust and easy to build </li></ul><ul><li>Steel and plastic as preferred building materials </li></ul><ul><li>Focus on kitchen waste as a substrate </li></ul>
  26. 26. Process design <ul><li>Biodegradability </li></ul><ul><li>Hydrolysis rate of substrates ( particle size!) </li></ul><ul><li>Applied conditions </li></ul><ul><ul><li>Temperature (mesophilic / thermophilic) </li></ul></ul><ul><ul><li>Retention time </li></ul></ul><ul><ul><li>Presence of toxic or inhibitory compounds </li></ul></ul><ul><li>All combined determine overall process performance </li></ul><ul><ul><li>Stability of process and products </li></ul></ul><ul><ul><li>Biogas production </li></ul></ul>
  27. 27. Proposed system concept Simplified process flow diagram, not to scale. Dashed connecting lines: slurry/liquid flow could be done manually

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