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April 29 th , 2008

April 29 th , 2008. “Anaerobic digestion”. Azra Vajzovic. Outline. Anaerobic digestion History Process Applications Examples. Anaerobic digestion. Process in which microorganisms break down biodegradable material in the absence of oxygen producing biogas. Soils Streams Oceans

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April 29 th , 2008

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  1. April 29th, 2008 “Anaerobic digestion” Azra Vajzovic

  2. Outline • Anaerobic digestion • History • Process • Applications • Examples

  3. Anaerobic digestion • Process in which microorganisms break down biodegradable material in the absence of oxygen producing biogas. • Soils • Streams • Oceans • Wastewater sludge and organic waste treatment

  4. Why anaerobic digestion? • Pollution • The natural ecosystems replaced • The harmful effects treated

  5. History • XVI-R.Boyle and S.Hale, sediments • 1859-1st anaerobic digester in Bombay • 1930s-academic recognition in the discovery of anaerobic bacteria • 1930-40s optimization of growth conditions for methanogenic bacteria (Germany & France-manure) • 1970’s reserves of fossil fuels finite

  6. Process (1) • Processing • Decomposition (hydrolysis)-sugars • Conversion of decomposed matter to organic acids • Conversion of acids to methane gas • Conditions • Temperature, 35°C- 40°C • pH • Loading rates • 14-40 days Crucial for material break down

  7. Process (2) Bacterial Hydrolysis Acidogenic bacteria Acidogenesis Acetogenic bacteria Acetogenesis Methanogenic bacteria Methanogenesis C6H12O6 → 3CO2 + 3CH4

  8. Anaerobic digesters • Batch or continuous • Temperature • Mesophilic 37°-41°C • Thermophilic up to 70°C • Solids content • High solids • Low solids • Complexity • Single stage • Multistage an airtight container

  9. End products • Biogas for energy • Digestate-acidogenic full of lignin • Wastewater-further treated

  10. Use of biogas • Heat/electricity with a microturbine • Fuel for cars, buses, and trains-replacing fossil fuels • Reducing methane emission from landfills • In natural gas grid • Digestate used as fertilizer • Smell - reduced up to 80% • Attract subsidies/renewable energy

  11. Feedstocks • Biodegradable waste materials • Waste paper • Grass clippings • Leftover food • Animal waste • Sludge from municipal sewage

  12. Estimated Cost • For a 1,500 cow dairy • Biogas ~60% methane • Estimated Costs per 1,000 ft3 biomethane • Capital Cost ~$3.10 • Operating Cost ~$0.60

  13. California - Royal Farms No. 1 • From waste to energy • Fuels a 70-100 kilowatt (kW) engine-generator, able to meet electricity and heat monthly demand.

  14. Sweden-first biogas train • Run 600km (372 miles), reached 130km/h (80mph) • Sweden's east coast between Linkoeping and Vaestervik. (September 2005) • 54 passengers, two biogas bus engines organic sludge from farm • 1 cow »about 4km (2.5 miles) on the train • Sweden has779 biogas buses The biogas train might eventually replace diesel or electric trains

  15. Volvo S80

  16. Pros and cons of biomethane fuel Pros: • An alternative to fossil fuel • Sourced from waste • Reduces greenhouse gas • Clean emissions • Good fuel efficiency • Better performance than liquid fuels • Higher octane rating Cons: • Infrastructure is nonexistent • Requires cars to be converted • No government support

  17. References • http://news.bbc.co.uk/2/hi/europe/4112926.stm • http://en.wikipedia.org/wiki/Anaerobic_digestion • http://www.consumerenergycenter.org/renewables/biomass/digester_landfill.html • http://www.avatarenergy.com/index.php?option=com_frontpage

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