Field experience of Fluoride Nilogon: a method of fluoride removal from groundwater

摘要

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 phosphoric 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 replenishment of the limestone bed. With consistent removal 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 limestone 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.