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.