134-Treatment of Fluoride Chemical Industry Wastewater for Defluoridation.

Abstract

Effluent from industrial processes constitutes a major source of contamination of fluoride in water. Wastewater containing fluoride are commonly treated with lime or calcium salt along with aluminium salt to bring down the fluoride below 1.5 mg/L in the effluent to be discharged in water bodies. Fluoride react with calcium to form sparingly soluble calcium fluoride precipitate. The wastewater does not always behave ideally because of the presence of interfering anions. The studies on fl uoride removal from wastewater generated from fluorine based chemical industries have been carried out by using lime and alum. The characterisation of waste generated from individual chemical unit were carried out to diagnose the exact nature of the problem. The treatability studies using lime followed by alum were conducted on mixed effluent collected in tank to bring down the fluoride below 1.5 mg/L in the effluent. The lime in combination with alum could bring down the fluoride concentration below 1.5 mg/L in treated effluent. A large variation was observed in effluent quality depending upon the different working units and quantity of effluent generated. The variation in alum dose to bring down the fluoride was due to change in effluent quality with respect to silica and fluoride concentration.