Ammonia removal from aqueous solutions by MgNH4PO4 center dot 6H(2)O precipitation

Ammonia removal from aqueous solutions as magnesium ammonium phosphate, MgN H4PO4. 6H(2)O (struvite, MAP), was investigated and the parameters, pH and ammonium/magnesium/phosphate molar ratio, for optimization of the ammonia p recipitation were determined. The pH of the solution containing the calcula ted amounts of NH4Cl, MgCl2 and NaH2PO4 (initial pH 4-5) was slowly adjuste d 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 wa s filtered off on a cellulose filter. By this method, under strictly contro lled 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 sing le treatment.