Magnesium potassium phosphate hexahydrate (MgKPO4 center dot 6H(2)O, MPP) crystallization is a promising approach to recover phosphorus (P) and potassium (K). Achievement of large MPP crystal size is still critical for the MPP products utilization. We performed a pilot-scale fluidized bed reactor (FBR) with treatment of synthetic source-separated urine to capture the MPP crystallization. Using the optimized FRR. operational parameters, as pH of 10.5, Mg:P molar ratio of 1:1, supersaturation ratio of 3.0, and superficial velocity of 350 cm/min, pellets of high purity (86 +/- 2%) with a maximum size of 4 mm were achieved. The removal efficiencies of K and P reached 20-35% and 80-90%, respectively. Furthermore, we proposed a kinetic model to describe the pellet growth. The pellet growth rate was determined as G = 5.046 X 10(-9)SV(0.88)S(1.96). The model combined with mass balance approach could predict P and K removal efficiencies of the FBR well.