Phosphorus and potassium recovery from human urine using a fluidized bed homogeneous crystallization (FBHC) process

Most of nutrients in municipal wastewater originate from human urine. In this study, a novel fluidized-bed homogeneous crystallization process was developed for the simultaneous recovery of phosphorus (P) and potassium (K) from synthetic human urine. The operational variables including pH, Mg:K ratios and up-flow velocity were tested in the laboratory. The total removal of P and K (TR%) reached 98.4% and 70.5%, respectively, and the crystallization ratios (CR%) were 86.5% and 62.3%, respectively, at conditions of pH 10 +/- 0.2, molar ratio Mg:K = 1.25, initial concentrations 850 mg P/L and 1830 mg K/L. The SEM and XRD analyses showed that the fluidized bed homogeneous crystallization (FBHC) product was pure magnesium potassium phosphate (K-struvite) (average size = 0.85 mm; purity = 95 +/- 3%). The modelling of minimum fluidization velocity (MFV) resulted in values of up-flow 1.5-2.0 times the MFV for the effective fluidization. The profit of the recovery of P and K from human urine via FBHC process could be $0.26/m(3) -urine.