Effect of recirculation and hydraulic loading rate on ammonium and phosphate recovery from fertilizer industry wastewater

This study aimed to determine the optimum recirculation ratio and hydraulic loading rate for the recovery process of ammonium and phosphate, and study the formation, morphology, and structure of struvite crystals. This study provides a crystallization method to treat fertilizer wastewater using a continuous system and recirculation, including a fluidized bed reactor (FBR). Ammonium and phosphate were recovered from fertilizer industry wastewater using a continuous FBR under different recirculation ratios (3, 6, and 9) and loading rates (0.39 L/min, 0.59 L/min, and 0.79 L/min). MgCl₂ was used as the precipitant with a 1.5:1 molarity ratio [Mg²⁺]:[PO₄³⁻]. The results showed that 55.71% phosphate and 49.69% ammonium could be recovered at recirculation ratio and hydraulic loading rate were 9 and 0.39 L/min, respectively. Scanning electron microscopy-energy diffraction X-ray analysis showed that the formed crystals comprised 80% struvite. Further, a high recirculation ratio and low loading rate resulted in higher ammonium and phosphate recovery efficiencies. These results indicated that a long detention time of treated wastewater can increase the nutrient recovery.