REMOVING ARSENIC AND FLUORIDE FROM HOT SPRING WATER BY ELECTROLYSIS

Abstract

Currently in Japan, there are many hot springs containing fluoride and arsenic with high concentration. Although the national minimum effluent standard for arsenic and fluoride is 100 µg/L and 8 mg/L, respectively, they are not applied to the hotels with hot spring since no appropriate treatment techniques are available. The objective of this research is to reduce fluoride and arsenic in hot spring wastewater by using electrolysis technique to meet the national minimum effluent standards. The electrolysis system with an anode bath and a cathode bath separated by a diaphragm was adopted. Fluoride and arsenic co-precipitate with magnesium hydroxide formed in the cathode bath in which pH value increases as the electrolysis progresses. The Gero hot spring containing fluoride and arsenic as 17 mg/L and 120 µg/L, respectively, was used as a model effluent. Since Gero hot spring water contains almost no magnesium, magnesium chloride was added as a magnesium source. The addition of 100-200 mg/L could reduce the fluoride concentration to less than 8 mg/L. The arsenic concentration decreased to less than 10 μg/L. 1040 C/L of electricity was required for the operation. The electrolysis system successfully reduces the fluoride and arsenic concentrations below the national minimum effluent standards.