Optimization of fluoride removal process in drinking water using natural adsorbents.

Currently, in Tanzania, fluoride removal from drinking water is treated mostly using the bone char method. The method has poor acceptability in some religious communities such as Muslims, Hindus and Buddhists and also causes water quality deterioration in taste and odour if the bones preparation is under performed. The use of natural adsorbents as an alternative is feasible with limitations of high levels of sulphate and iron in treated water. The study was conducted to determine the removal efficiency, optimum calcination temperature and composite ratio of the three adsorbents bauxite, gypsum and magnesite for the removal of fluoride in drinking water with concentration of 16.7mg/L of fluoride. The adsorbent materials calcined at different temperatures ranging between 3500C and 6000C, sieved to obtain particle sizes of 0≥0.075mm to ≥1mm. Batch experiment were performed and samples were collected at different contact time intervals of 2 minutes to 60minutes, and residual fluoride was determined. Bauxite had the highest fluoride removal efficiency compared to gypsum and magnesite, the best calcination temperature was found to be 3500C, 4000C, 6000C for gypsum, bauxite and magnesite respectively. The optimum calcination temperatures were used to prepare a composite at different ratios of 1:2:3, 2:3:1 and 3:2:1, bauxite: gypsum: magnesite respectively. All the ratios gave low sulphate level within the recommended standards and very low iron level. Other selected water quality parameters were not altered beyond the recommended standards. The composite ratios lowered fluoride level to 1.53mg/L, 2.07mg/L, 2.60mg/L for 1:2:3, 2:3:1, 3:2:1 ratios respectively. In conclusion the study reveals that, it is possible for composite made of adsorbent calcinated at different optimum temperatures to give good results in fluoride removal from drinking water.