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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

Dairy Manure Management:
Technologies for Treating Dairy Manure

Solid-Liquid Separation

Crop Nutrient Management Removal of Nutrients & Salts Anaerobic Digestion/ Thermal Conversion Composting Dairy
Blue boxes indicate processes. Green boxes indicate products with economic value. *Current practice on
California dairies or pilot project in place. Flow Diagram, PDF (1 pg, 12K) About PDF

Solid-liquid separation removes organic and inorganic matter from the dairy waste stream, which is primarily liquid, especially on a flush dairy. Separation facilitates utilization of solids for bedding and compost, allows for transport off-site, makes liquid transfer more efficient, and reduces volatile emissions. The remaining liquids should have fewer solids that are smaller and less likely to settle.

Solid-liquid separation devices may use gravity flow with few moving parts and require little management effort, or they may incorporate pumps and motors and require intensive management. Gravity separators include settling basins, ponds, and weeping walls. Mechanical separation technologies include stationary inclined screen; vibrating screen; rotating flighted cylinder; rotating cone; piston; liquid cyclone; and roller, belt, screw, or filter presses (Reference 1). Chemical precipitants have been used with other types of waste to precipitate or flocculate specific solids to increase removal efficiency and may be the most effective method of removing excess phosphorous from the waste stream. Precipitation or flocculation in a treatment cell allows for harvesting the precipitated material, whereas precipitation in a storage lagoon provides no mechanism to harvest the material.

Separation efficiency depends on many factors, including the size distribution of particles in the influent, which in turn depends on bedding source and quantity, parlor water addition, and seasonal changes in biological activity in storage ponds. The characteristics of the treatment technology, including treatment time and facility design and operation, also affect separation efficiency. For example, any treatment prior to separation, such as storage in a lagoon, will reduce particle size, making it more difficult to remove the particles. For another example, flushing animal housing with 1,500 to 2,200 gallons per minute of recycled wastewater ("flush water") is standard practice on California dairies. If the flush water sump is relatively small, the flush water will flow through separation devices at a high volume, reducing separation efficiency. Greater sump capacity allows for a reduced flow rate, increasing separation efficiency.

Pilot Projects

Separators of varying types are found on almost all California dairies. The various separation devices have different infrastructure needs and fixed costs associated with installation. They also differ in maintenance costs well as the ongoing resources needed to collect and manage separated solids. Site-specific parameters will determine what type(s) of separators may be used and the separator location. As parameters change over time, the facility operator should reevaluate separation options and make changes as needed to optimize performance.

References

1. Moore, J. 1989, "Dairy Manure Solid Separation," in: Proceedings from the Dairy Manure Management Symposium, Syracuse, NY, February 22-24, NRAES 31, Northeast Regional Agricultural Engineering Service, pp.178-192.

"Separation processes," section 8.2, pp., 329-337, in: C.H. Burton and C. Turner. 2003. Manure Management: Treatment Strategies for Sustainable Agriculture, 2nd edition. Silsoe Research Institute, Silsoe, UK. 451 pp.

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