Nutrient Removal and Recovery: Hazenite Precipitation From Livestock Manure Wastewater.

This study investigates simultaneous nutrient removal and recovery from nondigested livestock manure wastewater. To manage high suspended solids, chitosan-mediated coagulation was utilized as a pretreatment for effective solid-liquid separation. Subsequent precipitation experiments evaluated the influence of pH, initial molar ratios, temperature, and multi-ionic interference. Optimal conditions were identified at pH 9.5, a Mg:N:P molar ratio of 1.2:1:1, and 30°C, achieving aqueous reductions of 95% for PO4-P, 91% for Mg, and 97% for NH4-N. The primary scientific contribution of this study is the identification of Hazenite (KNaMg2(PO4)2.14H2O) as the recovered solid phase, rather than conventional magnesium ammonium phosphate (struvite). Structural characterizations via XRD and SEM-EDX revealed the absence of nitrogen in the recovered precipitate. These analyses indicate that the elevated background potassium and sodium concentrations drove the crystallization of this specific alkali-magnesium phosphate. Thermodynamic and elemental analyses indicate that the extensive depletion of aqueous NH4-N was primarily driven by pH-induced ammonia volatilization rather than solid-phase recovery. Furthermore, ionic competition and kinetic inhibition restricted both ammonium and calcium integration into the crystal lattice. These findings demonstrate that in complex, alkali-rich effluents, the precipitation pathway fundamentally shifts from standard struvite toward Hazenite recovery, providing an alternative for nutrient upcycling into high-value mineral phases.