Phosphorus removal and recovery from wastewater by highly efficient struvite crystallization in an improved fluidized bed reactor

Phosphorus is the crucial factor causing eutrophication in the aquatic ecology. The high phosphorus loading in water bodies may result from the direct disposal of untreated wastewater. In this study, a fluidized bed reactor (FBR) was specially developed to remove and recover phosphorus effectively and efficiently via struvite crystallization. Different physiochemical and hydraulic conditions, including hydraulic retention time (HRT), pH, and molar ratios of Mg : P, N : P and Ca : Mg, were explored to optimize the performance of this improved FBR. For the continuous operating trials, promising removal and recovery efficiencies were achieved at the phosphorus concentration of 25.0 mg/L: > 90% of phosphorus could be removed under the optimum condition (pH=9, HRT=12 h, Mg : P=1.25 and N : P=7.5). Increasing the recycle flow rate and prolonging the contact time could also enhance the FBR efficiency. The crystal products obtained in FBR were analyzed in terms of composition and structure. Results indicated that almost pure struvite (> 99%) was achieved at low calcium concentrations, which could be considered as a high quality fertilizer.