Abstract
Wastewater containing fluoride is released by various industries. In 2001, the effluent standard for fluoride was revised from 15 to 8 mg·l-1 in Japan. The aim of this study was to develop a simplified method for high-quality treatment of fluoride in wastewater. The calcium fluoride method is one of the conventional methods of removing fluoride from wastewater. However, the concentration of fluoride in the effluent obtained by this method has not been considered suitable based on the new effluent standard. In this paper, the effect of CO2 in the atmosphere on the reaction between calcium ion and fluoride ion was assessed based on chemical equilibrium. It is found that CO2 in the atmosphere interferes with fluoride removal efficiency and produces a large amount of sludge by forming calcium carbonate. In order to confirm these phenomena, experiments using real wastewater under normal and degassed conditions were carried out not only by measuring the fluoride concentration in the wastewater, but also by characterizing the properties of the formed sludge. As a result, the calcium fluoride method under degassed conditions is suggested to be a very promising method for treatment of wastewater containing fluoride from the viewpoint of minimum emission.
