High efficiency treatment of ammonium-nitrogen wastewater via high-purity ammonium magnesium phosphate technology

ABSTRACT

Schematic of MAP precipitation principle, listing the key factors including temperature, pH, ion dosing order, precipitant types, and molar ratio.

In the practical application of magnesium ammonium phosphate (MAP) precipitation technology for the removal of aqueous ammonium from wastewater, achieving precise control over reaction conditions to produce high-purity MAP remains a significant challenge. In order to solve the above problems, we have carefully explored the influence of multi-dimensional factors, including ion injection order, pH, agent ratio, precipitant combination, and temperature, on the crystallization process of MAP. It was found that more than 99% removal efficiency of ammonia nitrogen from simulated wastewater could be achieved using the combination of MgCl2·6H2O and Na2HPO4·12H2O agents at 25 °C and pH = 9. Furthermore, the obtained MAP crystals were also generated under these process conditions with high purity by SEM, XRD, and FTIR characterization. Then the optimized process was applied to treat actual wastewater from the coking plant of Ningxia for further validation, and it could achieve an ammonia removal efficiency of 98.05%, which proved the stability of the optimized conditions. This research has achieved the dual goals of deep purification of wastewater and resource recovery by scientifically regulating the precipitation path, providing key technical support for the transformation of MAP technology from laboratory to engineering, and bridging the gap between laboratory research and industrial implementation.