DEFLUORIDATION OF WATERS OF DIFFERENT ALKALINITIES USING ALUM-CHARCOAL SLURRY

Abstract

Fluoride ion in drinking water has great significance from physiological point of view. Several methods of defluoridation were suggested. Most of them suffer from one or the other drawbacks. To overcome these, In India, a technique was devel-oped which is referred as Nalgonda Technique. However, even the use of this other-wise simple technique has some limitations. To overcome these problems, Mekenen, (2000) suggested use of alum-PAC in place of alum. Defluoridation of 41 Test water Samples of fluorides concentrations rang/ing from 4 to 21 mg/L and alkalini ties concentrations varying from 4 00 to 1070 mg/L as CaCO3 was studied using Al, (SO4)3.161-120-PAC or Al2 (SO4)3.16 H2O - PAC-Al C13. Experiments were conducted using jar test apparatus. Rapid mixing was done at 100-120 rpm for 40 minutes and slow mixing at 30-40 rpm for 20 minutes. Characteristics of various test water sample prepared and defluoridated water sam-ples were analysed as per Standard Methods (1998). Doses of chemicals required for various concentrations of fluoride and alkalin-ity in test water samples were found to bring the fluorides level in treated water to acceptable limit of 1.5 mg/L. The proportion of fluoride removed per unit quantity of alum varied considerably with test water. characteristics. Alkalinity remaining con-stant, the proportion of fluoride removed per unit amount of alum increased with test water fluoride concentration. Use of alum-PAC or alum-PAC-A1C13 resulted in ad-vantages namely (i) Reduction in alum dose (ii) Residual sulfate concentration were found within 400 mg/L. The mechanism of fluoride removal by alum could not be concluded as either due to adsorption or co-precipitation on the basis of these stud-ies. The precise mechanism of fluoride removal still remains to be understood.