April 29 th , 2008

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