Ammonia removal from aqueous solutions by MgNH4PO4•6H2O precipitation

Ammonia removal from aqueous solutions as magnesium ammonium phosphate, MgNH4PO4. 6H(2)O (struvite, MAP), was investigated and the parameters, pH and ammonium/magnesium/phosphate molar ratio, for optimization of the ammonia precipitation were determined. The pH of the solution containing the calculated amounts of NH4Cl, MgCl2 and NaH2PO4 (initial pH 4-5) was slowly adjusted to the fixed value (in the range 8.5-10.5) with the use of a concentrated NaOH solution. About 3 min. after the struvite precipitation, the solid was filtered off on a cellulose filter. By this method, under strictly controlled conditions (py N/Mg/P molar ratio and reaction time), the NH4+ removal in high yield (up to 99% for concentrations greater than or equal to 1000 mg/L) was performed. In most experiments performed the ammonium ion content in the filtrate has been reduced to a level lower than 15 mg/L with a single treatment.