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On Farm Anaerobic Digestion

These plants are low profile low cost and simple Anaerobic Digestion plants designed to accept the organic wastes, and possibly also a mix of bio-crop feedstock created substantially just by the farm itself. The facility would normally be expected to by owned and operated by the farmer/farm business, but on occasions may be part of a co-operative venture and community funded or aided.

Frequently these plants would avoid the more stringent regulation of larger plants, and often would not be approved to accept Animal By-Products.

Table 1 - Simple On-Farm Anaerobic Digestion Schematic Diagram

Central Anaerobic Digestion

These plants are larger and more complex than On Farm Anaerobic Digestion Plants. They will serve a number of livestock farms and usually be PPC Permitted by the environmental regulator. They will usually accept Animal By-Products wastes for digestion and be licensed by the state veterinary service to do so.

Table 2 - Simple Central Anaerobic Digestion Schematic Diagram

Diagrams provided courtesy of DEFRA: Ref - AEAT/ENV/R/2104; Assessment of Methane Management and Recovery Options for Livestock Manures and Slurries. Report for: Sustainable Agriculture Strategy Division,Department for Environment Food and Rural Affairs,London SW1P 3JR.

Centralised Anaerobic Digestion in Denmark

In Denmark there are over 20 centralised Anaerobic Digestion plants in operation and more than 60 farm scale Anaerobic Digestion in operation.

Technically well operating many have been operating for more than 15 years. They are economically viable and most operate as co-digestion plants with slurries, in additional to food industry, brewing industry etc wastes. The slurries do not add a great deal of gas production, and accepting the sludges is more valuable a a disposal method than a biogas creator. The comparative gas yield figures are:

• 1 tonne liquid manure 5% Dry Mass (DM) = 20 m³ biogas
• 1 tonne organic waste = 0 –1000 m³ biogas

More Danish Agricultural Anaerobic Digestion information is in a .pdf file here.