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Seattle, WA, United States

Westerman P.W.,North Carolina State University | Bowers K.E.,Multiform Harvest Inc | Zering K.D.,North Carolina State University
Applied Engineering in Agriculture | Year: 2010

Tests for phosphorus reduction by increasing magnesium and pH to form struvite (magnesium ammonium phosphate hexahydrate (MgNH4PO 4·6(H2O)) were conducted using effluent from a covered earthen anaerobic digester for swine manure. A cone-shaped crystallizer system was constructed in the field and operated with direct pumping of covered digester liquid at a flow rate of 5.4 L/min (1.43 gal/min). Using the field system, 24 combinations of pH increase (0- to 1.5-pH units) and magnesium (Mg) addition (0, 20, 40, and 60 mg/L) were tested in short-term (30-min) tests. Up to 80% of the total phosphorus (TP) could be removed with the highest increases in pH and Mg. About 65% of TP was removed with the combination of 0.5-pH unit increase and addition of 40 mg/L of Mg. To test performance over longer periods, this combination was utilized in 40 tests each of 2-h duration during the period of September 2007 through October 2008. Reductions averaged 55 ± 10% (mean ± standard deviation) removal of TP and 65 ± 5% removal of orthophosphate phosphorus (OP). Analyses of samples of the solids removed from the crystallizer on six different dates indicated that N, P, and Mg were lower on average than theoretical values for pure struvite (5.71% N, 12.62% P, and 9.90% Mg) by 9.9%, 4.4%, and 6.2%. The solids included 1.8% calcium, indicating calcium compounds were being included in the formed material. Costs and returns were estimated for a commercial scale system and chemical costs and TP removal were estimated at selected levels of Mg addition and increase in pH. The net annual cost of the system for 60% removal of TP from digester effluent for a 1000-sow farrow-to-finish operation was estimated to be $0.0146/kg of live hog marketed. © 2010 American Society of Agricultural and Biological Engineers. Source

Zhang T.,Washington State University | Bowers K.E.,Multiform Harvest Inc | Harrison J.H.,Washington State University | Chen S.,Washington State University
Water Environment Research | Year: 2010

Being a non-renewable resource and a source of potential water pollution, phosphorus could be recovered from animal manure in the form of struvite (MgNH4PO4·6H2O) to be used as a slow-release fertilizer. It was found recently that the majority of phosphorus in anaerobically digested dairy effluent is tied up in a fine suspended calcium-phosphate solid, thus becoming unavailable for struvite formation. Acidification and use of a chelating agent were investigated for converting the calciumassociated phosphorus in the digested effluent to dissolved phosphate ions, so that struvite can be produced. The results demonstrated that the phosphorus in the effluent was released into the solution by lowering the pH. In addition, the phosphorus concentration in the solution increased significantly with increased ethylenediaminetetraacetic acid (EDTA) concentration, as EDTA has a high stability constant with calcium. Most of the phosphorus (91%) was released into the solution after adding EDTA. Further, the freed phosphorus ion precipitated out as struvite provided that sufficient magnesium ions (Mg 2+) were present in the solution. Furthermore, the phase structure of the solid precipitate obtained from the EDTA treatment matched well with standard struvite, based on the data from X-ray diffraction analysis. These results provide methods for altering the forms of phosphorus for the design and application of phosphorus-removal technologies for dairy wastewater management. Source

Shen Y.,Virginia Polytechnic Institute and State University | Ogejo J.A.,Virginia Polytechnic Institute and State University | Bowers K.E.,Multiform Harvest Inc
Transactions of the ASABE | Year: 2011

Phosphorus (P) can be recovered as struvite from liquid dairy manure as a way to recycle and reuse P. One of the factors that can inhibit struvite precipitation is the calcium (Ca) concentration in dairy manure. This study used modeling and laboratory experiments to investigate acidification and addition of Ca sequestering compounds (ethylenediaminetetraacetic acid and oxalic acid) as means of enhancing the precipitation and recovery of struvite from dairy manure. The Visual MINTEQ model was used to determine the desirable pH of manure at which all the particulate inorganic phosphates are released into solution and predict the quantities of struvite and other minerals that can be formed. The model results were validated experimentally using synthetic liquid and dairy manure. Both the model and experimental results showed that struvite can be precipitated from dairy manure with a high calcium-to-magnesium molar ratio (Ca:Mg) of 1.46 by acidifying manure to pH 4.5, adding EDTA or oxalic acid, and then raising the pH to 7.5. Adding magnesium to lower the Ca:Mg ratio was not effective in struvite precipitation. In addition, reducing the total suspended solids concentrations supported better struvite precipitation. © 2011 American Society of Agricultural and Biological Engineers. Source

Agency: Department of Agriculture | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 79.61K | Year: 2005

Over-application of phosphorus to cropland surrounding dairy farms is an increasing concern nationwide. Dairy farms often irrigate crops with wastewater from their lagoons. The wastewater phosphorus content can exceed crops' needs, resulting in soil phosphorus accumulation. Accumulation eventually leads to runoff into surrounding streams and lakes, degrading water quality. This project will test the feasibility of using a new type of crystallizer for removing phosphorus from wastewater.

Multiform Harvest Inc | Date: 2012-02-03

Methods and compositions for chemical drying and for producing struvite.

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