Transcript The George Washington University Washington, DC

“Anaerobic digestion”
Azra Vajzovic
April 29th, 2008
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
 Wastewater 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 bacteria
Acidogenesis
Acetogenic bacteria
Acetogenesis
Methanogenic bacteria
Methanogenesis
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, 0-3
H 2S
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) enginegenerator, 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
 1 cow »about 4km
(2.5 miles) on the train
 Sweden has779
biogas buses
The biogas train might eventually
replace diesel or electric trains
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/bioma
ss/digester_landfill.html
 http://www.avatarenergy.com/index.php?option=com_fro
ntpage