Phosphorus Removal from Animal Waste with SWAN-Gypsum

The PI’s on this project are Drs. Gary Felton and K.J. Hughes. The sponsor is Millenium Inorganic Chemicals Inc. at a funding level of $175,000. The project duration was 1999-2000. We: (1) developed a single tank phosphorus treatment system, suitable for agricultural use, that utilized chemical precipitation with SWAN-gypsum (a locally produced industrial byproduct with an extremely high P sorbing capacity in a neutral pH environment ) as a means of removing soluble phosphorus from animal wastewater; (2) determined the suitability of the solids generated in the precipitation tank and poultry litter amended with SWAN-gypsum as a soil amendment in terms of both soluble P in leachate and basic soil fertility; and (3) demonstrated, on-farm, the viability of the design under day-to-day operational conditions.

The process generates a liquid effluent and solid waste that is sustainable and economically feasible in terms of both time and money and is easily incorporated into existing farm wastewater treatment and handling systems. The resulting products maintain the nitrogen fertilizer value of both liquid and solid animal waste and are an agronomically valuable soil amendment that can be applied to local agricultural land based on crop nitrogen requirements. In the poultry producing regions of Delaware, Maryland, and Virginia, long-term application of poultry litter as the primary crop nitrogen source has resulted in elevated soil phosphorus (P) levels and is suspected of being a source of dissolved phosphorus in surface waters. Dissolved P is the most readily available form for algal uptake in receiving waters, and hence may disproportionately contribute to eutrophication. One potential solution to this problem that would allow farmers to continue land applying poultry litter is to amend manure with high-P-affinity materials. Two high P-affinity materials produced in the titanium dioxide manufacturing process, secondary gypsum (SG) and filter cake (FC) were investigated as potential poultry litter amendments. Both are rich in iron, and SG also contains a significant quantity of calcium and sulfates, primarily in the form of gypsum. Laboratory experiments were conducted to investigate: (1) the appropriate ratio of litter to amendment, (2) the effect of 1, 2, and 4 week incubations on soluble P, and (3) the effect of amendments on poultry litter pH. Four treatments were investigated: (1) poultry litter only, and poultry litter amended with: (2) SG, (3) FC, and (4) a mixture (MIX) of SG and FC. The pH of the amended poultry litter decreased from an initial pH of 8.3 to a pH of 6.2 to 7.0. Amendment-to-litter ratio had the most profound impact on water-extractable phosphorus (WEP). All treatments significantly reduced WEP as compared to the control samples. Poultry litter to amendment mixtures at a 1:1 (mass basis) rate reduced WEP by 98%. The reduction dropped to 90% for the 2:1 mix, approximately 74% for the 4:1 mix, and 40% to 60% for the 8:1 mix.

For more information, contact Dr. Gary Felton

Last updated: 02/6/2008