Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2022
Publication Date: 4/13/2022
Citation: Rotz, C.A., Reiner, M.R., Fishel, S.K., Church, C. 2022. Whole farm performance of centrifuge extraction of phosphorus from dairy manure. Applied Engineering in Agriculture. 38(2):321-330. https://doi.org/10.13031/aea.14863.
Interpretive Summary: Dairy manure contains nutrients that are beneficial for crop production, but transportation of bulk manures can be a constraint to returning those nutrients to the land producing feed leading to poor distribution of those nutrients. Because phosphorus runoff from farms contributes to eutrophication of streams and other water bodies, farmers are experiencing increasing pressure and regulation to not over-apply manure nutrients to fields. A possible solution to overloading soils is to remove some of the phosphorus from manure before it is applied. A few farms are currently using a combined screw press and centrifuge system to remove phosphorus from manure, but the whole-farm implications on performance, environmental benefits, and economics have not been fully evaluated. A comprehensive evaluation showed that extraction of a portion of the phosphorus provides a better ratio of nitrogen and phosphorus contents in the remaining manure for use on nearby cropland and reduces transport costs for nutrients applied to more distant cropland. The extraction process provides a concentrated material that can be transported from the farm for other uses, but the cost of producing this phosphorus rich material is greater than phosphate fertilizer prices. Thus, a centrifuge provides a useful tool for extracting and concentrating manure phosphorus providing long-term environmental benefit, but economic benefit depends upon other manure handling practices and the end use of the extracted material.
Technical Abstract: As the size of dairy farms has increased, feeds produced on the farm and those purchased from off-farm sources can be transported long distances to feed the herd. Transporting the manure back to the cropland producing the feed can be difficult and uneconomical. Technology such as a centrifuge can be used to extract nutrients into a more concentrated form for more efficient transport. A farm in Pennsylvania with distant cropland was simulated with the Integrated Farm System Model to evaluate the feasibility of extracting phosphorus (P) to reduce transport requirements on farm or to produce a concentrated P product for off-farm use. Phosphorus extraction with a centrifuge was found to be more practical and economical when used with manure scraped from the barn floor than with flushed manure because much less material was handled. Moving less material through the centrifuge improved extraction efficiency and reduced electricity consumption providing more economical P extraction. On a large dairy farm where manure must be transported to distant cropland to obtain uniform distribution, P extraction with a centrifuge provided a better ratio of nitrogen and P contents for use on nearby cropland and reduced transport costs for nutrients applied to more distant cropland. To avoid long-term accumulation of soil P on farms where substantial portions of feed are imported, use of centrifuge extraction provided a material with a high P concentration exported from the farm for other uses. Extracting the P for off-farm use cost about $2.51/kg P, which was greater than the price of phosphate fertilizer, but the extract also includes other nutrients and micronutrients of value to crops. A centrifuge provides a useful tool for extracting and concentrating manure P, but economic benefit depends upon other manure handling practices and the end use of the extracted material.