晶析型脱リン材のリン除去能に及ぼす水中のカルシウム濃度および除去環境温度の影響

抄録

In order to prevent the eutrophication phenomenon in closed waters such as lakes and inner bays, it is essential to establish a method for removing substances such as phosphorus and nitrogen which cause eutrophication. We have developed a crystallization type phosphorus remover on gypsum and CaCO₃. In this study, the effects of the amount of calcium ion concentration in water and removal environment temperature at the time of removal on the phosphorus removal capacity were investigated. The phosphorus remover was obtained from a CaCO₃-Ca(OH)₂-gypsum composite by carbonating under CO₂ gas pressure of 0.4 MPa after impregnation with a saturated aqueous solution of NaHCO₃. When the amount of calcium concentration in water was large, the phosphorus removal rate was high in the initial stage of phosphorus removal, but the rate decreased with the passage of the removal time. In the initial stage of phosphorus removal, large amount of calcium ions increased the degree of supersaturation of calcium phosphate, and therefore nucleation and crystal growth of calcium phosphate on the surface of calcium carbonate was probably promoted, resulting in the increase in phosphorus removal rate. However, the phosphorus removal rate would decrease with the passage of the removal time due to the rapid decreased in the phosphate ion concentration in the initial stage. As removal environment temperature increased, the phosphorus removal rate increased in the initial stage of phosphorus removal, but the rate decreased as the phosphorus removal progressed, and consequently the lower the removal environment temperature, the higher the removal rate. When the temperature is high, the amount of dissolved calcium was large, and as a result, the phosphorus removal rate would increase in the initial stage of removal. However, the rapid consumption of phosphate ions in the initial stage would lead to the decrease in the removal rate with the progress of phosphorus removal.