Abstract: The effects of processing conditions on NH₄⁺-N(ammonia-nitrogen) removal to form struvite(magnesium ammonium phosphate, MAP) were studied in a laboratory scale. MAP precipitation was carried out by adding phosphoric acid and MgO. The effect of pH was significant and the highest removal was obtained at pH 9.0. A PO₄^3-∶Mg²⁺ ∶NH₄⁺ molar ratio of 1 ∶ 1.5 ∶1 was found to be beneficial for the higher removal of NH₄⁺-N and the higher recovery of ammonia to form struvite. In addition, the feedin sequence of material significantly affects NH₄⁺-N removal. It was shown that a highest NH₄⁺-N removal of 99.1% and an ammonia recovery of 80.1% could be obtained by a two-step precipitation process.

Key words: ammonia-nitrogen wastewater, struvite, magnesium ammonium phosphate, wastewater treatment, recovery, fertilizer