Recovery of phosphorus from synthetic wastewaters by struvite crystallization in a fluidized-bed reactor: Effects of pH, phosphate concentration and coexisting ions.

The crystallization of struvite in fluidized-bed crystallizer (FBC) was performed to treat synthetic wastewaters that contain phosphorous. Under optimal conditions (pH 9.5, molar ratio Mg/N/P = 1.3/4/1, struvite seed dose (53-297 μm) = 30 g L-1, total flow rate = 12 ml min-1, reflux = 120 ml min-1), the removal of phosphate (PR) and the crystallization ratio (CR) were 95.8% and 93.5%, respectively. Based on a thermodynamic prediction, the supersaturation, which was obtained from the difference between the theoretical solubility and phosphate concentration, predominated the crystallization efficiency and the properties of the struvite pellets, such as their morphology, particle size and apparent density. Coexisting ions NO3- (80, 160 ppm), CH2COOH- (260, 520 ppm), F- (650, 1300 ppm) and SO42- (650, 1300 ppm), were utilized to prepare P-containing wastewaters. Of these ions, SO42- (1300 ppm) remarkably reduced the capability of FBC to remove phosphate from solution. In the presence of NO3- and CH3COO- (for synthesizing TFT-LCD wastewater), and F- and SO42- (for synthesizing semiconductor wastewater), CR% was lower than in pure water, although the ultimate PR% did not differ significantly.