Enhanced struvite (MgNH4PO4.6H2O) granulation and separation from synthetic wastewater using fluidized-bed crystallization (FBC) technology

Struvite (MgNH4PO4.6H2O) could be recovered from wastewater containing phosphorus and showed high po-tential as an alternative source of phosphorus fertilizer. A comparison of batch experiment and continuous crystallization processes was carried out using batch reactor and fluidized bed reactor (FBR) methods, respec-tively. The continuous crystallization processes for phosphorus granulation were conducted both in a seeded (FBC) and unseeded (FBHC) system. Various seed materials such as dolomite-(CaMg(CO3)2), CaHPO4, and SiO2 were applied as seed material in FBC. In the batch reactor, the operating parameters, including pH, [Mg]0/[P]0 molar ratio, and initial phosphorus concentration were first optimized. The effects of the coexisting ions (SO42 , Cl , NO3 , Na+, K+, Ca2+) and organic pollutants (Ethylenediaminetetraacetic acid-EDTA, and Citric acid) on phosphorus-containing wastewater treatment were also examined. The hydraulic parameters of FBR (Fluidized -bed reactor), including effluent pHe, and cross-sectional surface loading (L, kg m 2 h 1) were investigated to recover phosphorus and ammonium as struvite pellets. Under optimum conditions (pHe 8.8, [Mg]0/[P]0 = 1.3/1, L = 2.4 kg-P m 2 h 1), FBC using dolomite as seed resulted in higher phosphorus removal efficiency than the FBHC system with total removal (TR) = 93.0 % and a crystallization ratio (CR) = 85.0 %. As confirmed by the XRD pattern, the solid products consist of magnesium ammonium phosphate (MgNH4PO4.6H2O) from both FBC and FBHC processes. The high crystallization ratio (CR = 85 %) and the recovery of crystal pellets (>1 mm) in the FBC process reduce the production of sludge compared to traditional chemical precipitation and FBHC processes.