Phosphorus recovery in a fluidized bed crystallization reactor

A process for recovering phosphorus from wastewater in form of magnesium ammonium phosphate (MAP) crystals using a fluidized bed reactor was investigated. The phosphorus recovery ratio was found to be influenced by the particle size of the MAP crystals, as well as the reaction pH, inlet ammonium and phosphorus concentration. The optimum operation conditions for the fluidized bed reactor to achieve the maximum recovery rate of phosphorus were organized in terms of the supersaturation ratio and reaction pH. The best supersaturation ratio was found to be 3.7. The optimum reaction pH depended on the inlet phosphorus concentration and was found to be 7.9 when the inlet PO₄-P was 230 mg·L^-1. A continuous treatment of filtrate from digested sludge was performed based on these optimum operation conditions and using a newly proposed fluidized bed system. The fluidized bed system has a seeder, which allowed control of the particle size distribution inside the crystallization tower. A recovery ratio higher than 90% was achieved for a long period of the demonstration test in this new fluidized bed system.