REMOVING FLUORIDE FROM A HOT SPRING USING AN ELECTROLYSIS SYSTEM

Abstract

A high concentration of fluoride in the wastewater from hot springs is an environmental issue
in Japan, since some of the wastewater exceeds the national minimum effluent standards of 8 mg/l. However,
an effective treatment for fluoride removal has not yet been developed. Accordingly, the temporal effluent
standards of 15mg/l - 50 mg/l have, so far, been applied to the wastewater from hot springs.
In this study, an electrolysis system consisting of an anode bath and a cathode bath separated by a
diaphragm made of a clay panel was tested for the removal of fluoride. In an electrolysis system, fluoride is
removed by co-precipitation with magnesium hydroxide formed in a cathode bath under a high pH condition.
As a pretreatment of wastewater, 100 mg/l of magnesium was added to water from Gero hot spring, Gifu,
Japan, to enhance the formation of the precipitation of magnesium hydroxide, since water from Gero hot
spring contains less than 1 mg/l of magnesium. Water from Gero hot spring to which 100 mg/l of magnesium
had been added was treated by an electrolysis system with a flow rate of 10 l/day and a current of 120 mA.
The electrolysis system reduced the fluoride concentration from 16.6 mg/l to 6.4 mg/l, which meets the
national minimum effluent standards of 8 mg/l.