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ABSTRACT
Fluoride contaminated water sources are found in many parts of the world and the consumption of such water is causing dental and skeletal fluorosis in humans, especially in developing countries. Hybrid sorbent-ultrafiltration (UF) systems are proposed for the removal of fluoride from water for the first time in this study. Laterite and bone char were selected as they are low cost, accessible sorbents in developing countries. The performances of the laterite-UF and bone char-UF systems were compared in terms of fluoride removal and membrane permeability under varying fluoride concentration, solution pH, and sorbent load. For equilibrium fluoride concentration of 1.5 mg/L, the World Health Organization guideline for safe drinking water, the sorption capacity of bone char (1.1 mg/g) was larger than that of laterite (0.40 mg/g) and this was attributed to the larger surface area of bone char. For the laterite-UF system, increase in fluoride concentration resulted in a decline in UF permeability whereas for the bone char-UF system there was no influence of fluoride concentration on membrane permeability. The optimal solution pH at which the systems are operated at maximum sorption capacity while avoiding membrane fouling was determined as pH 5-6 for the laterite-UF and pH 7 for the bone char-UF system. For both systems, the permeability declined in a similar manner as the sorbent load increased. Although both systems require further optimization, they showed to be viable defluoridation technologies.
Acknowledgements
The authors would like to thank Godfrey Mkongo from Ngurdoto Defluoridation Research Station for providing the bone char, Millipore Corporation for kindly supplying the membranes used for the experiments, Dr. Enzo Mangano, the University of Edinburgh for conducting surface area and micro-pore volume analysis of laterite and bone char and interpretation of the results, Marie Weckert, Jenny Gilbertson, and Elodie Varennes for helping in some of the experimental work and Dr. Otar Akanyeti, the University of Florida for proof reading. Helen Cope, the University of Edinburgh, is specially thanked for assisting with surface charge analysis of laterite, helping to conduct some of the experiments and proof reading. Prof. Andrea I. Schäfer, Karlsruhe Institute of Technology is also acknowledged for initiating the project and valuable scientific discussions.