Field studies on defluoridation using magnesium oxide

Abstract

By far the most serious natural groundwater-quality problem in India derives from high fluoride, arsenic and iron concentrations. Fluoride removal from contaminated groundwater is practiced by pump and treat method; treatment is generally accomplished by addition of an aluminium sulfate–lime mixture to the pumped water or by permeating water through column of activated alumina. A magnesium-oxide-based method (termed the IISc method) has been developed to remove fluoride from drinking water. The IISc method relies upon the precipitation–sedimentation–filtration technique. Magnesium oxide addition to the contaminated groundwater removes fluoride ions through chemical reactions. The alkaline pH induced by magnesium oxide addition is neutralised by the addition of sodium bisulfate solution to the treated water. Interference from bicarbonate ions towards pH neutralisation is minimised by the addition of lime and calcium chloride solution to the untreated water. The IISc method has several advantages: chemicals used in the process are non-toxic, the process does not involve a recharge process and avoids the generation of corrosive and toxic wastes. This study reports experimental results and experience gathered during the course of a field investigation spread over a 10 month period using the IISc method for treating fluoride-contaminated drinking water in a village in Karnataka.