Improving the prediction of ammonium nitrogen removal through struvite precipitation

Both an optimization statistical model and a chemical thermodynamic equilibrium computer model were proposed to develop, improve, and optimize struvite precipitation process. The NH(4)-N in synthetically prepared wastewater was removed using struvite precipitation technology. A quadratic statistical modeling, response surface methodology (RSM), was applied to investigate the improvement availability for high-level removal of ammonium-nitrogen by struvite precipitation. Then, a chemical equilibrium model, Visual MINTEQ, was used to calculate the equilibrium speciation and saturation index in aqueous solution and solid phases. In addition, the availability of Mg(2+), NH (4) (+) , and PO (4) (3-) ions as a function of pH was modeled. The predicted and experimental data indicated that the two models might describe the experiments well. The results showed that pH was an important parameter in ammonium-nitrogen removals at low initial NH(4)-N concentration. P/N molar ratio was a limiting factor on struvite precipitation at high initial NH(4)-N concentration. Within the ranges of the investigated factors, Visual MINTEQ program can be proposed to predetermine the concentration of ammonium precipitated by struvite, and RSM can be used to predict total NH(4)-N removal by both struvite precipitation and ammonia volatilization from our investigated system operated at high pH and opened to the atmosphere.