Crystallization of struvite family crystals from cow urine: analysis, characterization, and effects of crystallization method, retention time, rate of mixing, and competing ions

Phosphorus recovered from cow urine rich in nutrients serves as an alternative form of fertilizer when recovered as magnesium ammonium phosphate termed as struvite (MgNH 4 PO 4 ·6H 2 O). Extraction of struvite was investigated through bench scale experiments, and its yield was measured by surface spread method and plain sedimentation method. Magnesium (Mg): phosphorus (P) ratio of 5: 1 yielded 77.5 mg/L and 10 mg/L of struvite by surface spread method and plain sedimentation method, respectively. A 15-fold increase in phosphorus recovery was obtained through plain sedimentation method. The mean width and length of struvite crystals obtained from plain sedimentation method were 4.4 µm and 18.4 µm, respectively. Struvite crystal size decreased by 77.78% when the rate of mixing was increased from 40 to 120 rpm. SEM analysis depicted the needle-like and lath-shaped morphology of struvite crystals. EDS analysis revealed the presence of Ca 2+ and Na + ions, and the XRD results confirmed the co-precipitation of other magnesium phosphates such as bobierrite and newberyite and sequential precipitation of K-struvite.