Liquid manure is undigested solids and liquid excreted by animals and mixed with waste feed and process generated wastewater such as flush water, milking parlor wastewater and wash water used to clean livestock and poultry facilities. For example, as excreted, dairy manure has 12-14% total solids but when diluted with water used to flush manure alleys, it reduces to 3-4% solids.
The two most common liquid manure treatment methods are solid-liquid separation and biological treatment of manure in lagoons. Many animal feeding operations combine these two treatment methods by directing liquid manure to a solid-liquid separator before it enters a lagoon for storage and further treatment.
The two most prevalent techniques for separating solids from liquid manure are sedimentation that occurs in long, wide, free-draining, and shallow structures that allow some solids to settle out by gravity, and mechanical separation, achieved by gravity and a mechanical screen or belt and screw type presses.
Anaerobic lagoons are frequently used by animal feeding operations as liquid manure storage and treatment structures. In a lagoon, organic waste is diluted with water and bacteria decompose the organic matter. During decomposition, solids that cannot be liquified by bacteria settle out as sludge. The treated liquid and dilution water, called effluent, are used by livestock and poultry producers as fertilizer. Effluent also can be recycled for manure handling in a flush system.
