A NOVEL Treatment System to Remove Phosphorus from Liquid Wastes.

Lowering the total phosphorus (P) content of animal manures is one means of addressing concerns over excessive P addition to soils and P runoff following land application of animal manure. We sought to develop a treatment system for liquid manures that conserves the manure nitrogen (N) content while removing most of the manure P content. Initial evaluation of a treatment system involving manure liquid-solid separation and precipitation of dissolved P with an alkaline salt (Ca(OH)₂) resulted in poor liquid/solid separation and poor dissolved P removal and created conditions promoting ammonia-N (NH₃-N) volatilization. As a result, we developed a four stage system with iterative solid removal and acid salt (ferric sulfate – Fe₂(SO4)₃) precipitation of dissolved P: (1) removal of bulk solids; (2) removal of intermediate sized solids (>25 μm); (3) chemical treatment to convert dissolved P; (4) final removal of fine solids and chemically precipitated P. When tested on manure slurries from 150 and 2700 cow dairies, 96-99% total P was removed, resulting in a liquid manure filtrate with approximately 400:1 N:P ratio. While costs of treatment were roughly $38 kg^-1 P removed, equivalent to $750 cow^-1yr^-1, we anticipate that refinement of the process and beneficial uses of the solid materials (bedding, compost, etc.) will improve cost-efficacy considerably.