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Onsite Defluoridation Systems for Drinking Water Production

  • Author(s): Wong, Elaine
  • Advisor(s): Stenstrom, Michael K
  • et al.
Abstract

Fluoride in drinking water has several effects on the teeth and bones. At concentrations of 1-1.5 mg/L, fluoride can strengthen enamel, improving dental health, but at concentrations above 1.5 to 4 mg/L can cause dental fluorosis. At concentrations of 4 -10 mg/L, skeletal fluorosis can occur. There are many areas of the world that have excessive fluoride in drinking water, such as China, India, Sri Lanka, and the Rift Valley countries in Africa. Treatment solutions are needed, especially in poor areas where drinking water treatment plants are not available. On-site or individual treatment alternatives can be attractive if constructed from common materials and if simple enough to be constructed and maintained by users. This dissertation investigates using calcium carbonate as a cost effective sorbent for an onsite defluoridation drinking water system. Batch and column experiments were performed to characterize F- removal properties. Fluoride sorption was described by Freundlich, Langmuir and Dubinin- Radushkevich isotherm models, and it was found that the equilibrium time was approximately 3 hours, with approximately 77% of equilibrium concentration reached within 1 hour. Granular calcium carbonate was found to have comparable F- removal abilities to the commercial ion exchange resins and possessed higher removal effectiveness compared to calcium containing eggshells and seashells. It was also found that the anion Cl- did not compete with F- at typical drinking water concentrations, having little impact on the effectiveness of the treatment system. A fluoride removal system is proposed that can be used at home and can be maintained by users. Different calcium phosphate systems were also analyzed to find ways to improve fluoride removal rates. Adding phosphoric acid and calcium carbonate were effective in increasing fluoride removal rates. However, there would need to be a significant amount of phosphoric acid and initial pH would need to be approximately 1.5 or less to have optimal removal rates. We found the best results by using Ca(OH)2 and NaH2PO4,with fluoride concentrations decreasing to 0.003 mg/L F-. Through this work, we can be a step closer to bringing safe drinking water to those that do not have access to it.

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