Phosphorus and nitrogen distribution of screw press separated dairy manure with recovery of bedding material

The distribution of P and N after dairy manure is separated into solids and liquids was determined using an on-farm screw press separator. The farm used separated solids for bedding, and when bedding material was needed, the outlet plate of the separator was adjusted to increase resistance to produce drier solids. At all other times the separator was set to result in solids that were less dry and spread on fields for fertilizer. On seven occasions the separator was operated to produce solids for bedding and spreading for 20 min each, resulting in 14 sample collections. At each collection event, the amount of dry matter (DM) of the manure processed was estimated from volume, specific gravity, and DM content. The DM amount of separated solids was calculated from wet weight and DM content, and the amount of DM of liquids was calculated as the difference between the amount processed and the amount recovered in solids. The distribution of N and P in solids and liquids was calculated based on the DM amounts and nutrient concentrations. The recovery in solids was 48.2% and 51.4% for DM, 12.5% and 15.1% for P, and 22.7% and 25.7% for N, when manure was processed to produce solids for bedding and spreading, respectively. Most of the P and N remained in liquids after dairy manure was separated, and adjusting the separator to produce drier solids suitable for bedding resulted in even lower recoveries of these nutrients in solids.