Selection of locally available soil adsorbents for the development of household defluoridation unit

Four locally available soil materials namely Crushed burnt clay pot, Household ash, Keren soil, and Adigerghish soil were studied in batch defluoridation in Keren, a fluorosis endemic place in Eritrea. Their adsorption capacities for fluoride uptake were compared for the development of a household defluoridation unit. The comparison of the adsorbent materials based on the fluoride removal efficiency revealed that crushed burnt clay pot has superior fluoride removal capacity than the other three adsorbents. Its average fluoride removal capacity was about 0.26 mg F-/g of the medium compared to the other three adsorbents which ranged from 0.08-0.1 mg/g for the same mass of 7g. Crushed burnt clay pot was thus selected for further defluoridation tests carried out in a mini column unit for the development of the household defluoridation unit. The result from the mini column indicated that optimum removal of fluoride was obtained at a bed depth of 25 cm and a flow rate of 2.5 ml/min, treating 7.3 litres of water meeting the WHO drinking water guideline of less than 1.5 mg/L of fluoride concentration. The set-up of the mini column was scaled-up and a pilot scale defluoridation test was carried out. The pilot scale managed to treat 324 litres of water while satisfying the WHO standards of fluoride concentration. The performance of the pilot column based on crushed burnt clay pot agreed with that obtained from the mini column and therefore can be upgraded for larger scale defluoridation practice.