Field Experience of Fluoride Nilogon:A Method of Fluoride Removal from Groundwater

Field trial of a patented fluoride removal method, based on precipitation–adsorption, has been carried out in some villages of Assam, North East India, with groundwater sources containing 1.8–20 mg/l initial [F^–] at small community (220 l) and household (15 l) levels. Pre-acidified water containing 0.68 mM phos-phoric acid was treated in a crushed limestone bed (1–20 mm) for 3 h and filtered through a sand–gravel filter to retain a desired 0.7 mg/l [F^–] with pH of 7.44–7.9 and relevant water quality parameters meeting WHO guidelines. A slightly higher dose can totally remove fluoride. The fluoride removal has been found to be independent of initial [F^–]. The units have been showing consistent results till now for over five and half years and 4625 batches of use without requiring any interventions like reactivation, replacement or re-plenishment of the limestone bed. With consistent re-moval of fluoride from any initial concentration to a desired concentration, a recurring cost of only Rs 0.005/l of water and an estimated life of the lime-stone bed of about 50 years or 39,000 batches, this safe, environment-friendly and simple method without requiring electricity, has been gaining popularity as Fluoride Nilogon.