Browsing by Author "Katima, Jamidu"

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    Diurnal Cycles of Variation of Physical–Chemical Parameters in Waste Stabilization Ponds
    (Elsevier, 2002) Kayombo, S.; Mbwette, T. S. A.; Mayo, Aloyce W.; Katima, Jamidu; Jørgensen, S. E.
    Diurnal fluctuations of pH, dissolved oxygen (DO), water, air temperature and sunlight intensity were investigated in the waste stabilization ponds at the University of Dar es Salaam. The variation of these parameters followed the diurnal pattern of light intensity. The rate of oxygen production based on first order linear regression analysis was between 0.02 and 0.36 mg/l per h with high production rate being observed in secondary facultative ponds. The rate of utilization of dissolved oxygen (total respiration) during the night by the microbial population in the pond ranged between 0.016 and 0.435 mg/l per h. The average rate of increase of pH during the day was 0.0006–0.243 units of pH per h, and the rate of decrease was 0.0003–0.101 units of pH per h. The ponds receiving low organic loading showed high diurnal variation of physical–chemical parameters. The relationship between average hourly DO and pH followed a polynomial trend with the coefficient of regression (R2) ranging from 0.76 to 0.82. It may be concluded that the diurnal variation of the parameters in the WSPs is due to hourly and daily variation of light intensity.
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    Modelling Diurnal Variation of Dissolved Oxygen in Waste Stabilization Ponds
    (Elsevier, 2000) Kayombo, S.; Mbwette, T. S. A.; Mayo, Aloyce W.; Katima, Jamidu; Jørgensen, S. E.
    The dissolved oxygen sub model was developed in order to depict the combined influence of light, pH, temperature and carbon dioxide on the processes of dissolved oxygen (DO) production and utilization in secondary facultative waste stabilization ponds (SFWSP). The model was formulated based on Chen and Orlob (Chen, C.W., Orlob, G.T., 1975. In: Patten, B.C. (Ed.), Systems Analysis in Ecology, Vol. 3. Academic Press, New York, pp. 476–588.), and was modified to include the influence of pH and carbon dioxide. The forcing functions to the DO model were light intensity, carbon dioxide, temperature and pH. It was found that temperature, light and pH influence the process of photosynthesis based on the multiplicative formulation of forcing functions. The model was calibrated and validated by using the average daily data from SFWSP1 and 11. The model yielded a linear regression coefficient of 0.87 during calibration and 0.78 during validation. Based on the model results the rate of production of DO with relation to dry algal biomass was 1.599 mg DO/mg dry weight, which is equivalent to 35.905 mg DO/mg chlorophyll-a. Such correlation between the observed data and model prediction indicates that the assumption inherent in the mathematical model formulation of the processes is valid for the description of DO production and usage in the ponds.
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    Modelling Nitrogen Transformation and Removal in Primary Facultative Ponds
    (Elsevier, 2002) Senzia, M. A.; Mayo, Aloyce W.; Mbwette, T. S. A.; Katima, Jamidu; Jørgensen, S. E.
    This paper presents a dynamic rational model for nitrogen transformation in primary facultative ponds. The results show that, the dominant mechanism for nitrogen removal was sedimentation of organic nitrogen (9.7%). The major nitrogen transformation route was through mineralization (19.2%) followed by ammonia uptake by microorganisms (17.4%) and nitrification (2.4%). Denitrification process was another possible route for removal of nitrogen (4.1%), but volatilisation played a negligible role (0.1%). Approximately 38.8% of nitrogen flowing to primary facultative pond did not undergo any transformation. It was further found out that 8.3% of influent nitrogen was unaccounted for, which might be lost through seepage to the ground or evaporation. Nitrogen contained in microorganisms accounted for 50% of the total nitrogen in the final effluent.
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    Solvent-Free MgO-Functionalized Mesoporous Catalysts for Jatropha Oil Transesterification
    (Hindawi Publishing Corporation, 2015) Andrew, Anamagreth; Katima, Jamidu; Lee, Keat T.; Epiphan, James; Mdoe, Gabriel
    A convenient solvent-free technique was employed in the functionalization of Micelle-Templated Silica using Cashew Nut Shell Liquid (MTS-CNSL) as a template and magnesium nitrate as a precursor salt. Magnesium oxide species was highly dispersed in MTS-CNSL by manually grinding the precursor salt and the as-synthesized mesoporous silica followed by calcination. The resultant modified mesoporous silicas MgO/MTS-CNSL were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR, N2 adsorption/desorption), and scanning electron microscopy/energy dispersive X-ray (SEM/EDX). MgO/MTS-CNSL (30) having small specific surface area of 16.7 m2 /g and larger pore volume of 0.02 cm3 /g, presented higher activity of 81.45% for jatropha oil under optimized conditions (200∘ C, 4 h, 36 : 1 methanol : oil ratio, 500 rpm, and 6% wt of catalyst). This method of catalyst development has an advantage of being highly energy- and time-efficient.