Anaerobic Co-digestion of
Biomass for Methane Production :
Recent Research Achievements
Wei Wu
CE 521
Introduction
Anaerobic Digestion
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Anaerobic digestion (AD)
Organic Matter + H2O + Bacteria
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CH4 + CO2 + NH3 + H2S
Traditionally
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Single substrate and single purpose
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Manure was digested to produce energy
Sewage sludge should be stabilized
Industrial waste water should be pre-treated
Recently
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Co-digestion of two or more substrate and multi-purpose
Co-digestion
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Co-digestion
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Two or more substrates
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Major amount of a main basic substrates (e.g.
manure or sewage sludge) + Minor amount of a
singe, or a variety of additional substrates
Multi-purpose process serving at the same
time
Waste upgrading
 Energy production
 Improvement of fertilizer quality
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Co-digestion—Cont.
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Factors impact the production of biogas
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The type of waste being digested
Its concentration
Its temperature
The presence of toxic materials
The pH and alkalinity
The hydraulic retention time
The solids retention time
The ration of food to microorganism
The rate of digester loading
The rate at which toxic end products of digestion are
removed
Benefits of Co-digestion
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Improved nutrient balance and digestion
performance
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A nutrient ratio of TOC:N:P = 300:5:1 to
achieve optimal digestion performance
Manure
Crop or Crop residues
Low C/N ratio– high ammonia
High alkalinity
Rich in macro/micro
nutrient
High C/N ratio– high carbon content
Low alkalinity
Lack of macro/micro
nutrient
Improve the C/N ratio, buffering capacity and more biodegradable substrate
Benefits of Co-digestion
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Effective utilization of digester volumes
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Help to utilize the availability of free capacities
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Co- digestion of energy crops and manure resulted
in the doubling of the plant capacity from 500 kW
to 1000 kW retaining the digester volume
(Lindorfer et al., 2007)
The wide distribution of sewage treatment
plants minimizes transportation costs
Equalization of particulate, floating,
settling, acidifying etc. wastes, through
dilution by manure
Co-digestion
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Types of digester
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Mesophilic AD
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Approximately 30-35° C
Retention time of
15 – 30 d
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Thermophilic AD
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Exceed 55 ° C
Retention time of
12-14 d
Continuously stirred tank reactors (CSTRS) under mesophilic conditions
Co-digestion
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Source of organic waste streams can be codigested with manure
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Food Industry
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Grain Industry
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Damaged grain
Paper Industry
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Waste from potato, sugar beet, meat, and dairy processing
Newspaper and recycled paper
Domestic Wastes
Livestock Wastes
Crop Residues
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Corn stover and switchgrass
Case 1
Increased by 65 %
Manure + 30% sugar beet tops
Cow manure alone
Increased by 58 %
Manure + 30% grass
Cow manure alone
Increased by 16 %
Manure + 30% oat straw
Cow manure alone
Lehtomaki et al., 2007
Case 2
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Whey co-digestion with diluted poultry manure
 For an hydraulic retention time of 18 days at
35 ° C and organic loading rate of 4.9 g COD/L
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Biogas production increased by 40%
Gelegenis et al., 2007
Case 3
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Co-digestion of solid slaughter house waste,
fruit-vegetable wastes, and manure
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Possibility to treat combined waste of
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Manure (cattle and swine)
Solid slaughterhouse wastes (rumen, paunch content,
and blood from cattle and swine)
Fruit-vegetable wastes
Alvarez et al., 2007
Drawbacks of Co-digestion
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Increased digester effluent chemical
oxygen demand (COD)
Additional pretreatment requirements
Increased mixing requirements
Wastewater treatment requirements
High utilization degree required
Conclusion
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Co-digestion offers several possible ecological,
technological, and economical advantages
There is very limited research, specifically in the
U.S., that characterizes the digestibility of a
number of the waste streams
The potential economic impact of fully utilizing
alternative waste streams with AD of manure
seems to be great, but economic analysis must
be done to quantify this information