An approach to residual aluminium control at Nisiya purification plant, Water Works Bureau, Yokohama

In Yokohama Water Works Bureau, the target value for aluminium control in purified water is set to 0.05 mg/L. In this study, we examined the effects of pH and water temperature on the water solubility of aluminium during purification processes, and obtained a solubility curve of aluminium in water based on these parameters. The result indicated that the water solubility of aluminium increases as water temperature or pH increases. In addition, it was calculated from this solubility curve of aluminium in water, that the level of residual aluminium in purified water can be controlled at approx. 0.04–0.05 mg/L by adjusting pH of coagulated water to approx. 7.1–7.4 depending on water temperature. Furthermore, as a result of pH control according to actual coagulated water temperatures based on this assumption, it was demonstrated that the target value for aluminium control in purified water, (0.05 mg/L) is achievable.