Combined electrocoagulation and electroflotation for removal of fluoride from drinking water

A combined electrocoagulation (EC) and electroflotation (EF) process was proposed to remove fluoride from drinking water. Its efficacy was investigated under different conditions. Experimental results showed that the combined process could remove fluoride effectively. The total hydraulic retention time required was only 30 min. After treatment, the fluoride concentration was reduced from initial 4.0-6.0 mg/L to lower than 1.0 mg/L. The influent pH value was found to be a very important variable that affected fluoride removal significantly. The optimal influent pH range is 6.0-7.0 at which not only can effective defluoridation be achieved, but also no pH readjustment is needed after treatment. In addition, it was found that SO42-had negative effect; Ca2+had positive effect; while Cl-had little effect on the fluoride removal. The EC charge loading, EF charge loading and energy consumption were 3.0 Faradays/m3, 1.5 Faradays/m3, and 1.2 kWh/m3, respectively, under typical conditions where fluoride was reduced from initial 4.0 to 0.87 mg/L.