Treatment by adsorption on a dual-layer filter of hyperfluoridated brackish water from the Ndamatou borehole in Touba, Senegal

Fluorine is a common component of natural water and plays an important role in many metabolic processes, when present in small quantities in the human body. A concentration higher than 1.5 mg/L, as set by the World Health Organisation (WHO), can cause serious health problems, such as dental or bone disorders, Alzheimer’s disease and infertility. Various methods have often been used to remove excess fluoride from water, but their cost and difficulty of application are barriers to accessibility for middle-income populations. The aim of this study is to apply adsorption technology by superimposing two adsorbents, namely zircon and carbon made from filao litter, activated with calcium chloride. The treated samples were taken from the Ndamatou borehole in Touba (Senegal), and raw water characterisation has led to the conclusion that this water is brackish and hyperfluorinated. A 500 mL sample was passed through a double-layer filter with a contact time of 10 minutes, resulting in a 66.45% reduction in fluoride ions, from a concentration of 4.65 to 1.56 mg/L. Analysis of the other constituents of natural water showed reductions of 25.22% for bicarbonates. On the other hand, increases were noted for chlorides (104.28%), sulphates (65.89%), nitrates (46.87%), calcium (1141.76%), magnesium (323.80%), sodium (13.93%) and potassium (41.43%). These results demonstrate the mixed filter’s ability to retain certain pollutants and release others. In most cases, the concentrations obtained in the filtrate meet the standards or do not present a risk to human health. The increase in chlorides and calcium can be attributed to the activating agent.