Chemical Phosphorus Removal for Separated Flushed Dairy Manure

Abstract

The objective of this study was to determine effective and economical dosages of chemicals to remove phosphorus (P) from liquid dairy manure, the corresponding chemical and polymer dosages to treat manure in a full-scale case study at the Virginia Tech dairy, and the cost of manure treatment and land application of P-rich sludge produced. Ferric chloride (FeCl36H2O), ferric sulfate (Fe2[SO4]35H2O), aluminum chloride (AlCl36H2O), aluminum sulfate (Al2[SO4]313H2O, alum), and five cationic polyacrylamides were evaluated at varying dosages using jar tests on liquid manure of approximately 0.87% and 1.5% total solids (TS) concentration. Treated manure settled in Imhoff cones and sludge volume was measured; supernatant was analyzed for total P, solids, and pH. FeCl36H2O, alum, and Superfloc 4512 (an ultra-high molecular weight polyacrylamide) were selected for further testing. Polymer addition enhanced floc size and settleability of sludge and improved P removal. Jar tests using a combination of chemical and polymer provided more than 97% P removal from liquid dairy manure obtained from one of Virginia Tech's storage tanks showing the potential for high P removal. As a case study, a storage tank containing 1,860 m3 of manure with 1.2% TS and 157 mg P/L was treated in batch using 200 mg/L AlCl3 as Al and 100 mg/L of Superfloc 4512 polymer. Approximately 84% of the total P was sequestered in a P-rich sludge. A portion of the sludge (600 m3) was transported off the farm for land application. The total cost of treating manure and transporting the P rich sludge was $4.09/m3 ($0.02/gal). This study demonstrated the feasibility of using chemicals and polymer to treat large volumes of manure in batch for P-based nutrient management for a dairy.