Module for Phosphorus Separation and Recycling From Liquid Manures.

A method has been developed to extract and concentrate soluble phosphates from livestock wastewater.  The research was conducted over a 10 year period and went from initial bench studies and discovery, to pilot module development, to full-scale demonstrations of the P module in swine farms (4400 to 5200 finishing pigs/farm) and current licensing and commercialization by industry.  The process is based on the distinct chemical equilibrium between phosphorus and calcium ions when natural buffers in the manure -ammonia and carbonate alkalinity- are eliminated by biological nitrification, which substantially reduces chemical lime addition to precipitate phosphate, and increases P concentration of the product. The precipitated P is recovered in a marketable form; the concentration grade obtained during full-scale demonstration was 24.4 ± 4.5% phosphorus pentoxide (P₂O₅).  The recovered P can be recycled into plant fertilizer without further processing due to its high content (> 90%) of plant available P (citrate extraction). It can be pelletized by standard grinding and compaction techniques. The process has several positive implications. Removing P from wastewater can cut down on any excess, which is not absorbed from the soil by plants and instead washes away as runoff into streams and rivers. Large amounts of the nutrient can lead to oxygen depletion in water bodies. During processing, hydrated lime precipitates most of the P in the wastewater as a solid and converts it into a marketable calcium phosphate fertilizer. This P could be very useful to the fertilizer industry, because world reserves of the nutrient are limited. Another benefit is that the high pH achieved by the P module destroys disease-causing pathogens present in the leftover manure liquid.