Ammonia removal from aqueous solutions by MgNH4PO4o6H2O precipitation

Ammonia removal from aqueous solutions as magnesium ammonium phosphate, MgNH4PO4-6H2O (struvite, MAP), was investigated and thè parameters, pH and ammonium/magnesium/phosphate molar ratio, for optimization of thè ammonia precipitation were determined. The pH of thè solution containing thè calculated amounts of NH4C1, MgCl2 and NaH2PO4 (initial pH 4-5) was slowly adjusted to thè fixed value (in thè range 8.5-10.5) with thè use of a concentrated NaOH solution. About 3 min. after thè struvite precipitation, thè solid was filtered off on a cellulose filler. By this method, under strictly controlied conditions (pH, N/Mg/P molar ratio and reaction rime), thè NH4+ removal in high yield (up to 99% for concentrations > 1000 mg/L) was performed In most experiments performed thè ammonium ion content in thè filtrate has been reduced to a level lower than 15 mg/L with a single treatment.