Ureolytic phophate precipitation from wastewater

MAPLE and PHREEQC were used for modelling phosphate precipitation from wastewater as struvite. Our simulations showed that relative high concentrations of ammonium and magnesium ions are necessary to precipitate the phosphate as struvite: to reduce phosphate-P concentration from 20 to 6 ppm relative concentrations of Mg 2+ , phosphate-P and NH4 + of 4.6/1/8 are necessary. An ureolytic method previously developed for the precipitation of calcium-ions from wastewater as calcite, was adapted to the precipitation of phosphate as struvite. When a synthetic wastewater or wastewater from a vegetable processing company, urea and a source of magnesium ions were added to ureolytic sludge, struvite was formed; meanwhile the phosphate concentration of the wastewaters decreased and pH increased to about 8.5. Using a continuous reactor with a hydraulic retention time of 2.4 h and relative molar excesses of 4.6 and 2.6 to phosphate of magnesium ions and urea respectively it was possible to decrease the phosphate concentration from 30 to 4 ppm phosphate-P. The reactor worked relatively stable under a broad range of experimental conditions.