Evaluation of Fluoride Removal From Water Using Baked Ando Soils

Abstract

Ingestion of excess amount of fluoride leads to dental and skeletal fluorosis. Because there is no cure for fluorosis, prevention measures such as the reduction of elevated fluoride concentrations from potable water is critical. While several methods for defluoridation exist, accessibility and sustainability challenges such as prohibitive costs and inappropriate technology are major hindrances for removal of fluoride from water among low-income communities. On the other hand, locally available materials such as Ando soil may have potential for removal of fluoride from water. Moreover, soil calcination could enhance the adsorption properties of the soil material in removal of fluoride from solution. This study evaluated baked Ando soil as an adsorbent material for fluoride through batch adsorption tests with the untreated soil as control. Fluoridated water samples were collected from boreholes in Naivasha Town with fluoride concentrations of 7.1 to 7.9 mg/l that exceeded the WHO guideline concentration of 1.5 mg/l for drinking water. Simulated fluoride water samples with fluoride concentrations of 4.4 to 18.4 mg/l were prepared from stock solution. Ando soils samples were collected from Kavutiri in Embu County and subjected to heat treatment at 100 to 700oC for three hours. The highest reduction in fluoride concentration was achieved from 7.1 to 0.5 mg/l in 30 minutes at a dosage 40 g soil L-1 borehole water and calcination temperature 350oC. Even though calcination marginally improved fluoride removal rate; nevertheless, it resulted in a more stable adsorption of fluoride ions than the untreated soils. The adsorption data fitted Langmuir adsorption isotherm with the correlation coefficient (R2) of 0.9769 indicating the calcined soil was a homogeneous adsorbent. The study concluded that baked Ando soil provides a viable alternative for removing fluoride from groundwater sources in Kenya