Anaerobic Co-digestion of Biomass for Methane Production : Recent Research Achievements

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Anaerobic Co-digestion of Biomass for Methane
Production Recent Research Achievements

• Wei Wu
• CE 521

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Introduction
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Anaerobic Digestion

• Anaerobic digestion (AD)
• Organic Matter H2O Bacteria
• CH4 CO2 NH3 H2S
• Traditionally
• Single substrate and single purpose
• Manure was digested to produce energy
• Sewage sludge should be stabilized
• Industrial waste water should be pre-treated
• Recently
• Co-digestion of two or more substrate and
  multi-purpose

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Co-digestion

• Co-digestion
• Two or more substrates
• 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-digestionCont.

• Factors impact the production of biogas
• 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

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Benefits of Co-digestion

• Improved nutrient balance and digestion
  performance
• A nutrient ratio of TOCNP 30051 to achieve
  optimal digestion performance

Manure Low C/N ratio high ammonia High
alkalinity Rich in macro/micro nutrient
Crop or Crop residues High C/N ratio high
carbon content Low alkalinity Lack of
macro/micro nutrient
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Benefits of Co-digestion

• Effective utilization of digester volumes
• Help to utilize the availability of free
  capacities
• 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

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Co-digestion

• Types of digester
• Mesophilic AD
• Approximately 30-35 C
• Retention time of
• 15 30 d

• Thermophilic AD
• Exceed 55 C
• Retention time of
• 12-14 d

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Co-digestion

• Source of organic waste streams can be
  co-digested with manure
• Food Industry
• Waste from potato, sugar beet, meat, and dairy
  processing
• Grain Industry
• Damaged grain
• Paper Industry
• Newspaper and recycled paper
• Domestic Wastes
• Livestock Wastes
• Crop Residues
• Corn stover and switchgrass

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Case 1
Lehtomaki et al., 2007
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Case 2

• 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
• Biogas production increased by 40

Gelegenis et al., 2007
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Case 3

• Co-digestion of solid slaughter house waste,
  fruit-vegetable wastes, and manure
• Possibility to treat combined waste of
• Manure (cattle and swine)
• Solid slaughterhouse wastes (rumen, paunch
  content, and blood from cattle and swine)
• Fruit-vegetable wastes

Alvarez et al., 2007
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Drawbacks of Co-digestion

• Increased digester effluent chemical oxygen
  demand (COD)
• Additional pretreatment requirements
• Increased mixing requirements
• Wastewater treatment requirements
• High utilization degree required

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Conclusion

• 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

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