Browsing by Author "Mbwette, T. S. A."

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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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    Effects of Substrate Concentrations on the Growth of Heterotrophic Bacteria and Algae in Secondary Facultative Ponds
    (Elsevier, 2003) Kayombo, S.; Mbwette, T. S. A.; Katima, Jamidu H. Y.; Jørgensen, S. E.
    This paper presents the effect of substrate concentration on the growth of a mixed culture of algae and heterotrophic bacteria in secondary facultative ponds (SFPs) utilizing settled domestic sewage as a sole source of organic carbon. The growth of the mixed culture was studied at the concentrations ranging between 200 and 800 mg COD/l in a series of batch chemostat reactors. From the laboratory data, the specific growth rate (m) was determined using the modified Gompertz model. The maximum specific growth rate (mmax) and half saturation coefficients (Ks) were calculated using the Monod kinetic equation. The maximum observed growth rate (mmax) for heterotrophic bacteria was 3.8 day 1 with Ks of 200 mg COD/l. The mmax for algal biomass based on suspended volatile solids was 2.7 day 1 with Ks of 110 mg COD/l. The mmax of algae based on the chlorophyll-a was 3.5 day 1 at Ks of 50 mg COD/l. The observed specific substrate removal by heterotrophic bacteria varied between the concentrations of substrate used and the average value was 0.82 (mg COD/mg biomass). The specific substrate utilization rate in the bioreactors was direct proportional to the specific growth rate. Hence, the determined Monod kinetic parameters are useful for the definition of the operation of SFPs.
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    Managing University Crises
    (1996) Ishumi, Abel G.M.; Mbwette, T. S. A.
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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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    Use of Coupled Dynamic Roughing Filters and Subsurface Horizontal Flow Constructed Wetland System as Appropriate Technologyfor Upgrading Waste Stabilisation Ponds Effluents in Tanzania
    (2004) Kimwaga, Richard; Mashauri, Damas A.; Mbwette, T. S. A.; Katima, Jamidu H. Y.; Jørgensen, S. E.
    As a part of a comprehensive evaluation of post-treatment techniques for upgrading Waste Stabilization Pond (WSP) effluents, coupled Dynamic Roughing Filters (DyRF) and Subsurface Horizontal Flow Constructed Wetland System (HSSFCW) system was evaluated in Tanzania. Coupled DyRF and HSSFCW were considered as cheaper and yet effective and appropriate alternative technology for upgrading WSP effluents in tropical environments like Tanzania. The main objective of the study was to determine the performance treatment of coupled DyRF and HSSFCW for upgrading WSP effluents with respect to organic compounds (TSS and BOD5) and pathogen (FC). A pilot of coupled DyRF and HSSFCW was constructed at the outlet of the Maturation WSP at the University of Dar es Salaam, Tanzania. The study was carried out in a 2.2 m × 0.7 m × 0.7 m deep DyRF as a first stage, using three different fractions of gravel ranging from 8mm to 32mm, from the top to the bottom respectively. In the second stage, a HSSFCW planted with Phragmites Mauritianus with 0.6-m wide, 1.75-m long and 0.6 - m deep was used. The DyRF – HSSFCW system achieved TSS load reduction by 89.35% which is 15.97 gTSS/m2/day, while BOD5 load reduction by 84.47% which is 9.29 gBOD5/m2/day was achieved. The FC mean removal rate of 99.99 % was also achieved. By achieving mean effluent TSS (12.63  4.12 mg/l), BOD5 (14.12  3.84 mg/l), and mean effluent FC concentrations of 790 FC/100ml it was concluded that application of coupled DyRF and HSSFCW in the tropics can be considered technically one of the most appropriate technology for upgrading WSP effluents.
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    Waste Stabilization Ponds and Constructed Wetlands Design Manual Acknowledgement
    (2005) Kayombo, S.; Mbwette, T. S. A.; Katima, Jamidu H. Y.; Ladegaard, N.; Jørgensen, S. E.
    Waste Stabilization Ponds (WSP) and Constructed Wetlands (CW) have proven to be effective alternatives for treating wastewater, and the construction of low energy-consuming ecosystems that use natural processes, in contrast to complex high-maintenance treatment systems, will hopefully lead to more ecologically-sustainable wastewater treatment in the future. CWs and WSPs also have the capability of meeting the demand for a high percentage removal of pathogenic organisms, compared to conventional technologies. CWs and WSPs combined, and joined with other technologies, may be important for even more improved performance of water cleaning systems. WSP’s and CW’s are now well-established methods for wastewater treatment in tropical climates. Their many advantages include: simplicity, low cost, low maintenance, low energy consumption, robustness, and sustainability. While WSPs are most commonly used for treating domestic wastewaters, they are also successfully used for treating industrial wastewater, including water that contains agro-industrial wastes. One of the potential advantages of using constructed wetlands is that they do not allow mosquitoes to breed (sub-surface flow wetland). The process of designing WSPs and wetlands, and predicting their performance, is improving rapidly as we gain more experience with these systems.