Ammonium Nitrogen Removal from Urea Fertilizer Plant Wastewater via Struvite Crystal Production

Elimination of ammonium concentration from urea fertilizer plant wastewater through struvite crystal (NH₄MgPO₄.6H₂O) formation by adding MgCl₂, KH₂PO₄, and KOH were studied. This method of elimination has two benefits, namely, reducing ammonium nitrogen content in the wastewater, as well as production of a valuable material (struvite crystal). Struvite is known as a slow-release fertilizer and less soluble. This report presents the ammonium removal efficiencies during struvite formation. The growth of struvite production under different molar ratios of Mg²⁺:NH₄⁺:PO₄^3- and solution pH is also discussed. To find the efficiencies and measure the growth rates, lab-scale experiments were conducted in a batch crystallizer-reactor. SEM, XRD, and FTIR observation were also applied to investigate the characteristics of struvite. The reactant molar ratios of Mg²⁺:NH₄⁺:PO₄^3- of 1.2:1:1, 1:1:1.2, and 1:1:1 were evaluated. Each of the molar ratios was treated at the solution pH of 8, 9, and 10. It was found that, the highest ammonium removal efficiency was 94.7% at the molar ratio of 1.2:1:1 and pH of 9. Primarily, the growth rate of struvite formation complied with a first-order kinetic model. The rate constants (k₁) were calculated to be 2.6, 4.3, and 5.0 h^-1 for solution pH of 8, 9, and 10, respectively. The findings of the study provide suggestion for an alternative sustainable recovery of ammonium nitrogen content in a urea fertilizer plant effluent.