Recovery of high-quality struvite fertilizer product from swine wastewater using fluidized bed homogeneous crystallization

Recovering phosphorus (PO43-) and nitrogen (NH4+) from swine wastewater is critical because their excess release can trigger eutrophication, severely harming aquatic ecosystems. This study introduces a pioneering fluidized-bed homogeneous crystallization (FBHC) process for single-step co-recovery of PO43- and NH4+. The method ensures compliance with discharge standards and produces a reusable nutrient product. Preliminary jar-test experiments were performed to identify the feasibility of struvite (MgNH4PO4<middle dot>6H(2)O) precipitation and to define the appropriate range for key operational parameters. Subsequently, operational parameters including pH, reaction time, up-flow velocity, cross-sectional loading, and bed height were systematically optimized. Under optimal conditions with a working medium at pH 9, reaction time of 24 min, up-flow velocity of 36 m h(-1), cross-sectional loading of 0.27 kg m(-2) h(-1), and bed height of 10 cm, the total removal efficiencies reached 97.42% for PO43- and 86.55% for NH4+. The corresponding crystallization ratios were 95.55% and 83.18%, respectively. The FBHC process exhibited high crystallization efficiency (>95%), contributing to reduced impurity levels and improved energy efficiency compared to conventional fluidized bed and chemical precipitation methods. The recovered product was identified as high-purity struvite (94.3%), predominantly comprising particles smaller than 0.75 mm. These results demonstrate the effectiveness of the FBHC strategy for simultaneous nutrient removal and resource recovery through the production of a value-added fertilizer.