Browsing by Author "Kayombo, S."
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Item 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.Item 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.Item 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.Item 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.Item Wastewater Treatment for Pollution Control(2012) Nzabuheraheza, F. D.; Katima, Jamidu H. Y.; Njau, K. N.; Kayombo, S.; Niyigena, N. A.Performance of a Dynamic Roughing Filter (DRF) coupled with a Horizontal Subsurface Flow Constructed Wetland (HSSFCW) in the treatment of a wastewater was studied in tropical conditions. The results show that in HSSFCW planted with Cyperus papyrus and Phragmites mauritianus in series, the removal rates of TDS, TSS, COD and BOD5 were 72.07%, 80.01%, 81.22% and 78.37%, respectively, while in the second HSSFCW planted with Cyperus papyrus only, the removal rates were 71.00%, 79.00%, 73.76 and 75.78%, respectively. HSSFCW planted with mixed macrophytes, performed better than a HSSFCW planted with single macrophyte. This was attributed to synergetic effects of Cyperus horizontal roots and Phragmites vertical plant roots weaved and entangled in cell 1 providing a good filter mat and a better bacterial attachment. Thus the use of two macrophytes planted in series was recognized to be responsible for better performance of HSSFCW cell 1 in pollutants removal from wastewater.