Influent phosphate concentration

Figure 5 shows the effect of phosphate concentration on crystallization rate Rg. Crystallization rate was obtained by weighing seeds in the reactor periodically, in which phosphate concentration drop in the bed was low enough, not to produce concentration distribution, by making the depth of the bed thin. Solubility of hydroxyapatite is so low, that the influent phosphate concentration is equal to super saturation dC. As shown in Figure 5, crystallization rate was proportional to 1.1th order of supersaturation. 

Figure 2 shows the outline of fluidized bed process. Seeds are fluidized by the upflow of influent and recirculated water. Recirculation is necessary to maintain water quality of the influent average, lower phosphate concentration in the influent, and also to obtain flow rate for fluidization. 

In this experiment, tap water with added phosphate was used as influent. Concentration of phosphate was adjusted to an adequate range from 2 to 23 mg/jg. Calcium chloride and sodium hydroxide solution were added to maintain calcium concentration from 70 to 100 mg/jg and pH of the effluent from 9.0 to 9.5. Using this equipment, we performed experiments to obtain efficiency of phosphate removal, relationship between phosphate concentration, and crystallization rate and factors affecting phoshate removal. 

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