Highly efficient phosphorus and potassium recovery from urine via crystallization process in a fluidized bed reactor system

Human urine consists of large amounts of phosphorus (P) and potassium (K), which are essential chemical elements for living species and plants growth. In this study, we investigate the effects of reflux rate on crystallization promotion to simultaneously recover P and K from urine. The effects of potassium ion presence in the formation of magnesium ammonium phosphate (MAP) in the fluidized bed reactor (FBR) is also studied. The largest removal efficiency of P at 96.57% and K at 68.40% can be achieved under the optimal conditions of: pH 9.5, P:Mg:N molar ratio of 1:1.4:1.2, and reflux rate of 12 L min(-1). The purity of produced MAP and magnesium potassium phosphate (MPP) are both promoted, owing to the improved formation frequency among particles, when reflux rate is increased. During the MAP production process, MgKPO4 is initially nucleation and growth under turbulence environmental in FBR. Afterwards, with the presence of NH4+ in solution, K+ ion can be replaced by NH4+ and formed the MAP due to more stability of MgNH4PO4 compound than MgKPO4. The cost analysis demonstrates that FBR system can provide a profit of $2.01/m(3) on urine treatment. The investigation can shed lights on efficient removal and recovery process of P and K elements from urine through changing various reflux rates for further development.