April 29th, 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.SoilsStreamsOceansWastewater sludge and organic waste

treatment

Why anaerobic digestion? Pollution

The natural ecosystems replaced

The harmful effects treated

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

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

Process (2)

Bacterial Hydrolysis

Acidogenic bacteriaAcidogenesis

Acetogenic bacteria Acetogenesis

Methanogenic bacteriaMethanogenesis

C6H12O6 → 3CO2 + 3CH4

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

End products

Biogas for energy Digestate-acidogenic full of

lignin Wastewater-further treated

Matter  %

Methane, CH4 50-75

Carbon dioxide, CO2

25-50

Nitrogen, N2 0-10

Hydrogen, H2 0-1

Hydrogen sulfide, H2S

0-3

Oxygen, O2 0-2

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

Feedstocks

Biodegradable waste materials

Waste paper Grass clippings Leftover food Animal waste Sludge from municipal

sewage

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

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.

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

The biogas train might eventually replace diesel or electric trains

1 cow »about 4km (2.5 miles) on the train

Sweden has779 biogas buses

Volvo S80

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

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