It is sometimes desirable to separate the solid and liquid portions of livestock manure. Livestock manure is placed in a still basin to allow solids to settle to the bottom. A detention time as short as 30 minutes can be used to settle out solids from dilute waste waters such as open-lot runoff. Septic tanks installed ahead of leach fields and settling basins used with vegetative infiltration areas are examples of settling systems. Solids must be removed regularly to maintain treatment efficiency of settling systems and to recharge the storage capacity.
Centrifuges increase the effect of gravity by spinning the manure at high speeds.
Centrifuges are surprisingly small and can produce a solids cake from 15 percent to 40 percent solids. This equipment requires routine maintenance. Filtering and screening systems use a medium to hold solids as the liquid moves through. Gravity, vacuum, or pressure can be used to move the liquids through the media. Liquid-solid separators that use stationary and vibrating screens remove solids from flushing water.