Development of Hybrid Adsorbent for Selective Fluoride Removal from Contaminated Drinking Water

Abstract

Contamination of drinking water due to fluoride is a severe health hazard problem. Excess of fluoride (>1.5 mg/l) in drinking water is harmful to the human health. Various treatment technologies for removing fluoride from groundwater have been investigated in the past. Activated alumina and nanohydroxyapatite both have different physical and chemical characteristics regard to sorption behaviour for fluoride among other materials. Activated alumina has chemical stability, mechanical stability, selectivity, low cost, favourable hydraulic properties while nanohydroxyapatite possesses properties like high chemical reactivity, low selectivity, high surface area to volume ratio but it is non-regenerable. So the attempt is being made to take the advantage of their properties for defluoridation of ground water. The nanoparticle lacks chemical stability and mechanical strength. Though they are highly reactive yet exhibit a high pressure drop or head loss in fixed bed column operation hence they are not suitable for any continuous systems. Also nanoparticles have the tendency of aggregation; this reduces the high surface area to volume ratio and subsequently reduces the efficiency of process. By precipitating nano particles of within a host material, these scantinesses can be beaten out without compromising the parent properties of nanoparticles. So an effort to synthesise a hybrid adsorbent, exploiting the properties of both activated alumina and nanohydroxyapatite was made by precipitating the hydroxyapatite within the nanosized pores of host material, activated alumina. Validation of this hybrid material was carried out in both, batch mode (adsorption isotherm) and continuous mode (column) at fluoride concentration 3mg/L to 10 mg/L having the background of Chloride(100 mg/L), sulphate(50 mg/L), bicarbonate(120 mg/L) and pH 7.5. Effect of different background condition was also studied and its applicability in real life was validated through its column performance. Up to 3 regeneration the adsorbent showed no decrease in its defluoridation capacity and it has more potential for fluoride removal if used after more regeneration.