Rural Electricity Resource Council

Typical manure sources include large dairy farms and swine production facilities. Poultry operations can be adapted to methane recovery, but the manure collection system and use of floor litter do not lend themselves as well to biogas production.

Livestock facilities collect and store manure because of sanitary, environmental, and farm operational requirements. The waste is collected and stored as either liquids, slurries, semi-solids, or solids. The characteristics of each are detailed below:

Raw Manure has a solids content of 8% to 25%, depending upon animal type. It can be diluted by various process waters or thickened by air drying or by adding bedding materials.

Liquid Manure has been diluted to a solids content of less than 3%. This manure is typically "flushed" from where it is deposited by using fresh or recycled water. The manure and flush water can be pumped to treatment and storage tanks, ponds, lagoons or other suitable structures before land application. Liquid manure systems in "warm" climates can be adapted for biogas production and energy recovery. Locations subject to freezing temperatures (or below) typically use methane recovery for odor control and flare the gas off, unless a heat source is provided.

Slurry Manure has been diluted to a solids content of about 3% to 10%. Slurry manure is usually collected by a mechanical "scraper" system. The slurry can be pumped, and is often treated or stored in tanks, ponds, or lagoons prior to land application. Some amount of water often becomes mixed with the manure to create a slurry. Manure managed in this form may be used for biogas recovery and energy production, depending on climate and dilution factors

Semi-Solid Manure has a solids content of 10 to 20%. This manure is typically scraped. Water is not added to the manure, and the manure is typically stored in a covered structure until it is spread on local fields. Fresh scraped manure (less than 1 week old) can be used for biogas and energy production in all climates, because it can be heated to promote bacterial growth.

Solid Manure having a 20% or greater solids content is most often handled by a scoop loader. Aged solid manure or manure that is left "unmanaged" (i.e., left in pastures by animals or accumulated in animal pens and allowed to dry) is not suitable for biogas recovery.

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