Browsing by Author "Masamba, W. R. L."

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    Breakthrough Characteristics and Flow-Rate Interaction in Water Defluoridation with a Bauxite-Gypsum-Magnesite Composite Filter
    (2012-11) Thole, Bernard; Mtalo, Felix W.; Masamba, W. R. L.
    Water defluoridation in a fixed bed column may be optimized through choice of flow rate. This, however, affects breakthrough characteristics. In any fixed bed system an understanding of flow rate and breakthrough interactions is therefore important to guide choice of design velocity. Consequently interactions between flow rate and break through characteristics were determined in a fixed bed column in defluoridation with a composite filter of bauxite, gypsum and magnesite. This was an attempt to optimize defluoridation with the three materials. Lower flow rates obtained longer service times but higher residual concentrations of sulphates and chlorides. Higher flow rates registered lower residual sulphate and chloride concentrations but obtained lower service times. There were no significant differences in residual concentrations of aluminium, iron, calcium and magnesium among the different flow rate regimes. Adsorbent exhaustion rates and critical bed depths increased with increase in flow rates, indicating that lower flow rates offered better technical system performance. Critical bed depths ranged from 5.23 to 10.89 cm for flow rate range of 0.68 to 1.25 ml/s. Operating lines were polynomic with generic form δ = C1 t2 - C2 t + C3, where δ is adsorbent exhaustion rate and t is empty bed residence time. Choice of flow rates, in this system requires a balance between service-time optimisation and water quality.
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    Effect of Particle Size on Loading Capacity and Water Quality in Water Defluoridation with 200°C Calcined Bauxite, Gypsum, Magnesite and their Composite Filter
    (College of Engineering and Technology, University of Dar es Salaam, 2012-01-12) Thole, Bernard; Mtalo, Felix W.; Masamba, W. R. L.
    Defluoridation was carried out with bauxite, gypsum, magnesite and their composite calcined at 200°C to determine relationship between particle size, capacity and water quality, in an attempt to formulate a composite filter in the ratio of loading capacities. Particles of 0.5 to 1.0, 1.0 to 1.4, 1.4 to 2.0 and 2.0 to 3.0 mm diameter were employed in batch defluoridation. Color, hardness, pH,   3 2 F ,Cl , Al ,Fe were determined hourly until fluoride equilibrium was obtained. Results showed that capacities were inversely correlated to particle size obtaining polynomial, linear and logarithmic relations of capacity (mg/g) to particle size (mm); Cs   Pz Pz 2 ( ) (composite, gypsum), Cs  Pz  (bauxite) and Cs   ln Pz  (magnesite). Bauxite, gypsum and composite decreased but magnesite increased pH. Particle size and pH changes were positively correlated, highly for bauxite (r2 = 0.915), fairly for composite and magnesite (r2 = 0.855 and 0.853, respectively) and lowly correlated for gypsum (r2 = 0.562). Smaller particles obtained higher apparent colour, hardness, alkalinity and sulphate. There was no relationship between particle size and  3 2 Cl , Al ,Fe . Sorption capacities of these materials increase with decrease in particle size, however decrease in particle size enhances colour, hardness and sulphate levels. In optimizing the materials for defluoridation particle size can be decreased while monitoring colour, hardness, alkalinity and sulphate levels. Particles of diameter 2 mm were optimum in the present experiments.
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    Water Defluoridation with 150–300oC Calcined Bauxite-Gypsum-Magnesite (B-G-Mc) filters
    (WIT, 2011) Thole, Bernard; Mtalo, Felix W.; Masamba, W. R. L.
    Research on water defluoridation with composite filters of bauxite, gypsum and magnesite was carried out at Ngurdoto Research Station to determine capacity, nature of fluoride-sorbent interaction and changes in water quality. The objective was to identify an optimum composite filter that would not alter the water quality beyond World Health Organisation recommendations. The three materials were characterized through X-Ray Fluorescence. The major components were Al2O3 (30.33%) for bauxite, CaO (28.09%) for gypsum and MgO (34.57%) for magnesite. The materials were calcined at temperatures of 150, 200, 250 and 300o C. Six composite filters were prepared for each calcine temperature of bauxite:gypsum:magnesite in the ratios 1:2:3, 1:3:2, 2:1:3, 2:3:1, 3:1:2 and 3:2:1. The highest capacity, 11.77 mg F/g, was obtained with the 3:1:2–200o C calcine. The optimum filter was however the 1:2:3–200o C calcine with capacity of 10.19 mg F/g. This filter did not alter the water quality beyond the considered WHO limits. The fluoride-sorbent interaction could best be described by Langmuir isotherm for the 200 and 300o C, and Temkin isotherm for the 150 and 250o C composites. Most composites changed water quality beyond WHO standards in Al3+, Fe2+, and 2 SO4 , however a composite filter of these materials is plausible.