Results from recent research at North Carolina State University showed that a chemically treated effluent had less odor intensity and irritation than either flushed wastes or the separated liquid. Solid-liquid separation processes do not necessarily produce fewer odors. Additional treatment may be necessary. Theoretically, the separation of the solid and liquid portions of animal manure can reduce odor from subsequent storage and treatment facilities. If the separated liquid contains less solids and organic matter, it is likely that it will generate less odor and gases when stored.
Physical separation has generally little effect on the dissolved fraction of liquid manure.
Addition of chemicals to manure can significantly enhance the P content in the separated solids. Potassium and ammonia are not significantly affected by mechanical separation, as they are mostly dissolved within the liquid. A mechanical solid-separator can be expensive. It is possible that ownership costs per hog could be reduced if the separator is installed on a farm with more hogs on inventory. Therefore storage, handling and spreading techniques for both liquid and solid manure are required.