Laboratory Studies of Ammonia Nitrogen Removal in Wastewater from Ammonia Industry by Struvite Precipitation

A laboratory scale study was conducted to precipitate the high concentration of ammonia-nitrogen (NH₄-N) in wastewater to form magnesium ammonium phosphate(struvite) by applying such chemicals as Na₂HPO₄·12H₂O and MgCl₂·6H₂O. Synthetic ammonia-nitrogen wastewater was prepared with NH₄Cl solution. The reaction conditions such as pH, the molar ratios of Mg/P and P/N, and the molar ratios NH₄-N:PO₄-P:Mg (that is N:P:Mg) have been studied. The removal efficiencies of NH₄-N, PO₄-P and Mg were studied simultaneously. The results showed that the optimum pH value was about 9. The optimal molar ratios of Mg/P and P/N were about 1.0-1.1. When the molar ratio of N:P:Mg was 1:1:1.1, the removal efficiencies of NH₄-N, PO₄-P and Mg was 87.5, 99.7 and 93.8%, respectively, the concentration of NH₄-N, PO₄-P and Mg in effluent was 125, 5.7 and 116 mg/L, respectively. Precipitation was analyzed with scanning electron microscope and X-ray diffraction (XRD) analysis and the result indicated struvite precipitation was formed. The primary treatment wastewater was discharged into municipal wastewater treatment plant for further treatment.