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Reducing the Effects of Calcium on Struvite Precipitation in Liquid Dairy Manure

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2010 Pittsburgh, Pennsylvania, June 20 - June 23, 2010  1009212.(doi:10.13031/2013.29830)
Authors:   Yanwen Shen, Jactone Arogo Ogejo, Keith Bowers
Keywords:   Struvite precipitation; Calcium inhibition; EDTA; Oxalate; Dairy manure; Phosphorus recovery from manure; Calcium to magnesium ratio.

Phosphorus (P) recovery as magnesium ammonium phosphate ( struvite, MgNH4PO46H2O) from wastewater has gained interest over the past decade. This study focuses on struvite recovery from liquid dairy manure. Two of the challenges that need to be overcome to recover struvite from liquid dairy manure are (1) low soluble ortho-P to total P (SOP/TP) ratio and (2) relatively high calcium concentration. The present study investigated the effectiveness of oxalic acid and EDTA to reduce the calcium inhibitory effects to enhance struvite precipitation. First, a chemical equilibrium model (Visual MINTEQ 2.60) was used to predict the operating pH and reagent dosage needed at different stages. Then, bench-scale experiments were conducted to validate the modeling results. Oxalic acid and EDTA addition enhanced struvite precipitation from the manure with total suspended solids (TSS) concentration less than 4,000 mg/L.

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