Browsing by Author "Wilbard, Lilian"

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    Investigation on water defluoridation using corals
    (University of Dar es Salaam, 2015) Wilbard, Lilian
    The effectiveness of dry corals in reducing the concentration of fluoride ions in fluoride-rich water to the acceptable limits for drinking water was determined. Characterization of the corals using XRD analysis and SEM revealed that they are mainly composed of CaCO3 in the form of aragonite and their exoskeleton is non-porous. The percentage composition of calcium in the corals as determined by XRF spectrometry was 53.03 % to 53.10 %. CaCO3 contained in the corals decomposed to CaO at the temperature range of 628 °C to 754 °C as evidenced by TGA and DTG. Batch type defluoridation studies were conducted where by the effect of contact time, acidification of the water, particle size, coral amount, initial fluoride ion concentration of the water and reusability were tested. Results revealed that using the raw fresh corals in direct defluoridation of water with an initial fluoride ion concentration of 5.0 mg/L gave a percentage defluoridation of only 18.5 %. Moreover, results on defluoridation using thermally activated corals showed that corals activated at 800 °C gave a percentage defluoridation of 83 % with the pH of 11.6. Results on defluoridation of pre-acidified (by oxalic acid) fluoride-rich water using dry fresh corals showed that a percentage defluoridation of 87.7% was obtained with a pH of 7.2. The same amount of corals was able to give acceptable concentration of fluoride in drinking water which is below 1.5 mg/L when reused five times but saturated when it was reused for the sixth time. From the results obtained, a procedure for defluoridation of fluoride-rich water utilizing dry fresh corals was adapted and successfully tested on natural water samples. The sample of natural water from Maji ya Chai village, Ngurdoto, Arusha region, having a concentration of 12.5 mg/L fluoride was defluoridated to 1.2 mg/L.