Browsing by Author "Gebreyohannes, Netsanet"

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    Assessment of contamination level of a Tanzanian river system with respect to trace metallic elements and their fate in the environment
    (IWA Publishing, 2022-04-01) Gebreyohannes, Netsanet; Rwiza, Mwemezi; Mahene, Wilson
    The quality of water and sediments from a marginally-studied river was investigated with respect to As, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn including their fractionation behavior and environmental risk. Samples were collected along the Kou River that flows across two districts in the Manyara region of Tanzania. The leaching behavior of Fe was studied using sequential extraction fractionation and kinetics approach. The Kou water failed to meet the irrigation, aquatic, and biological life standards with respect to one of more trace metallic elements (TMEs). Fe concentration in the river water ranged from 4.1 to 5.38 mg/L, exceeding all the three standards. Six pollution indices were applied to assess the contamination and ecological risks of the nine trace metallic elements in the sediments. Overall, the metals were found to moderately contaminate the sediments. Cr, Fe, and Mn fell under the ‘severely polluted’ sediment quality class. Fe was the only metal that was found to significantly pollute both the river water and sediments. The Fe fractions in the sediments were in the order of residuals.Fe-Mn bound.or ganic bound.carbonate bound.water soluble.ion exchangeable; 7.8% of the total Fe content was bioavailable with a low potential to leach from the sediments. Under natural conditions, the sharpest release of the non-residual mobile fractions of Fe were identified to occur within the first 24 hours with the maximum Fe leached being 0.14% on the 12th day. None of the metals in the sediments were found with a poten tial to pose ecological risk
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    Contamination assessment and optimization of coagulation-flocculation-sedimentation water treatment process for Kou river in northern Tanzania
    (NM-AIST, 2022-06) Gebreyohannes, Netsanet
    The Babati Urban Water Supply and Sanitation Authority (BAWASA) in northern Tanzania supplies water from the Kou River to Magugu town for domestic purpose, where its Fe (3.64 mg/L) and turbidity (87 NTU) concentrations were found in excess beyond their acceptable limits. A coagulation-flocculation-sedimentation water treatment plant was planned to be installed for treating the water, where the system’s performance is negatively influenced due to inadequate applications, hence requiring optimization. The quality of sediment and water of the Kou River was examined for physicochemical parameters and 9 metallic elements. The water did not meet the requirements for aquatic, biological life, and irrigation purposes for at least 1 metallic ion. Furthermore, pollution levels of the 9 metals in the river sediments were evaluated using 6 pollution indices and a moderate contamination was found, hardly posing ecological risk. A coagulation-flocculation-sedimentation water treatment system was optimized to respond to coagulant dose, pH, mixing rates, mixing time, and settling time in the removal of Fe and turbidity using jar-test. The optimum dose and conditions were: 30 mg/L alum, an initial mixing rate of 150 rpm for 5 minutes, slow mixing rate of 20 rpm for 30 minutes and settling time for 30 minutes which was validated using scale-up pilot test and resulted in 98.25% turbidity and 97.5% Fe removal. Furthe research on developing enhanced time-saving optimization method and developing a dose indicator technology to assign alum dose requirement based on the fluctuating characteristics of the raw waters (turbidity) is recommended.