PhD Theses

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Man-made lakes: their social economic and ecological impacts: the case in Tanzania
(University of Dar es Salaam, 1977) Kaduma, Josephine Diana
The creation of man-made lakes have become a popular method of developing the water resources of river basins the world over. The purposes for their creation vary from flood control, irrigation, navigation, fishing and hydro-electric power production. Their impacts to the people and areas in their vicinity are similar. The planning, construction, operation and maintainance procedures are also similar. Hence earlier cases provide useful lessons to the later ones. This study examines the influence of man-made lakes on man's environment and on his social and economic ways of life. While man-made lakes have been constructed successfully in some developed nations, in Africa, their planning has omitted many social and environmental aspects. Consequently, various problems to both the people and the economic and / or ecological planners have been experienced. By studying five large man-made lakes in other African countries, the thesis shows how their planning and problems are similar to those of man-made lakes in Tanzania. Nyumba ya Mungu lake, the first man-made lake in Tanzania is studied in detail showing similarities to the five lakes. Its planning and implementation processes are examined showing omissions, failures, successes and achievements. An attempt is made to show where Nyumba ya Mungu experiences are being used in the planning of other man-made lakes in Tanzania and where similar mistakes are being made. The thesis observes with concern that in spite of earlier experiences, planning of new man-made lakes in Tanzania still places a great deal of emphasis on the production of hydroelectric power at the expense of other water requiring activities. The multi-purpose approach is used only as a means of satisfying the economic justification analysis. Pangani and Rufiji river projects are used to illustrate the adherence to this tendency. In an economic analysis, costs and benefits are given monetary values to facilitate comparisons. In a country like Tanzania, it is difficult and sometimes impossible to quantify many benefits accruing from a water resource development project hence the relevance of the analysis becomes questionable.
Enhancement of heat tranfer by corona wind
(University of Dar es Salaam, 1987) Kadete, Henry
The mechanism of heat transfer enhancement across solid gaseous interfaces by corona wind directed towards the heat transfer surface is investigated. Basic principles of heat transfer, negative dc corona and the nature of corona wind are studied. Voltage-current characteristics of negative dc corona in geometries which create corona wind are measured. The velocity distribution and velocity characteristics of corona wind are measured by Pitot-tube and by hot-wire constant-temperature anemometer. Corona wind is visualized by Toeplers children measurements. Corona wind is also visualized by the injection of carbon dioxide generated mist into the flow. Heat transfer measurements with and without corona wind reaching an upward facing heat transfer surface are made. Voltage-current characteristics of a corona triode are measured. The corona triode is used to generate corona wind and to control the magnitude of current which reaches the heat transfer surface. Heat transfer measurements in this corona triode geometry are made. Conclusions are that corona wind may adequately be described by the Navier-Stokes equations of motion. The Coulombion drag forces transferred to the neutral gas background create corona wind. The corona current is a function of the applied voltage and the electrode gap geometry. The average corona wind turns out to be proportional to the square root of the corona current. The corona wind velocity distribution is bell shaped with a maximum of about 5 m/s.The electro kinetic conversion efficiency is of the order of one percent. The enhancement of heat transfer by corona wind insignificant. Heat convection enhancement by up to 90 percent is measured. The enhancement of convective heat transfer by corona wind blowing on a heat transfer surface turns out to be proportional to the 0,3Power of the corona current. It turns out that the enhancement of convective heat transfer is only due to the augmentation of the hydrodynamic flow of the air. The corona wind is laminar, less turbulent than a mechanically created jet, has a small spread with a cross-section area of about 2x4 on-1i and has a long reach of up to 25cm which makes it superior to mechanically created jets for enhancement of heat convection by blowing towards heat transfer surfaces. The Langmuir-Child equation for space charge limited Current [SCLC] in vacuum is expressed in a general form in a gaseous media.
A pre-feasibility study of micro hydropower plant at Kiirila and Kibengwe Falls
(University of Dar es Salaam, 1990) Kibira, Medrad Rwegasira
A study has been made in Kagera Region with particular emphasis on Kyamato river basin in Bukoba rural district for potential micro-hydropower sites Forty six potential micro-hydropower sites have been identified from topographical maps for micro-hydropower development in the region. Sever sites have been identified in Kyamato basin but only two sites Kibengwe and Kiirila have been studied in detail and earmarked for development. The hydropower potential of Kyamato basin has been assessed using the line potential method. The ultimate power potential of Kyamato river basin was estimated at 1.2 MW and realizable power potential was estimated at 645 kW. A Fortran computer programme to process meteorological data into monthly run developed. The developed procedure for converting meteorological data into run off was used on Kibengwe and Kiirila falls a case study. The annual mean discharge for Kibengwe was found to annual mean discharge for Kiirila was found to be 0.1m3/s. Flow duration curves for Kibengwe and Kiirila were then drawn and at 50 percent exceedance, power was calculated to be 75 kW and 10 kW respectively. The development procedure was then tested on the gauged stream, Ndembera. A flow duration curve of Ndembera river using meteorological data derived from Madibira Meteorological station was drawn and compared with flow duration cuvers drawn by using actual readings obtained from Madibira gauging station. The results were quite satisfactory. The study gives initial estimates of main components and capital costs for the proposed micro-hydropower plants. The estimated capital cost for Kibengwe was Tshs. 32,303,503/= or $ 2154.0 per kW. The estimated cost for Kiirila was Tshs. 10,476,840/= or $ 5238.0 per kW. Use of stone masonry and burnt bricks instead of concrete blocks for construction of civil structures, use of locally manufactured machinery, use of local skills and standardization of machinery and civil structures were suggested as means of reducing capital costs. Finally, cross-flow turbines have been recommended for use of micro-hydropower projects because of their simplicity in manufacture and higher part load efficiencies.
Performance Prediction of Electronic Energy Converters in Connection with Intermittent Energy source: With Special Attention to Wind and Insolation Energies
(University of Dar es Salaam, 1991) Nzali, Aggrey Hezron Stephen Jifike
To encounter the problems accompanying the use of insolation energy and wind energy separately. In this thesis a new method which involves harnessing the two types of energies simultaneously in a combined manner is proposed. Since separately the two types of energies are unreliable, irregular and stochastic in nature, in the thesis. Performance prediction of electronic energy converters when operated in intermittent energy sources of wind and insolation combined has been done by simulations. To prepare the work of simulating. Simulation models for the wind energy conversion system. Insolation energy conversion system and storage batteries system were first developed. The simulation results, which involved four types of wind turbine system, one type of solar cells modules and one type of storage batteries showed that in some months when the two energy source are to a high degreed complementary, the resulting demand on storage batteries and the number of solar cells modules was reduced while in the months when the two were not, the performance prediction results were poor. To examine whether the newly proposed method was economically superior to the existing methods, a systems life-cycle counting method was used. The results showed that of the four alternative methods namely wind only, isolation only. Wind and diesel system, and a combined wind and insolation energy conversion systems taking into account the life –cycle costs of the systems for a period of twenty years, the method that of the systems for a period of twenty year, the method that used a combined wind and insolation energy conversion system was the cheapest and more reliable alternative compared to the others. Additionally in the thesis it is shown that a part from the cloudy activity, the available insolation energy throughout the year is constantly high for most places in Tanzania and that because of the technological advances. Made in the field of power electronics, solar cells and wind turbines, engineering, the energy problems in the rural areas of developing nations can eventually be weakened by employing these technologies to harness efficiently the alternative energy sources of wind and insolation simultaneously.
An improved computer aided engineering method for the design analysis of diesel engine pistons
(University of Dar es Salaam, 1996) Mshoro, Idrissa Bilali
Considering the high performance targets imposed on modern reciprocating Internal Combustion Engines (ICE), critical assessment of piston life has been a major problem area. Currently, transient piston temperature and strain for use in the fatigue assessment are predicted by the finite elements method. However, the Heat Transfer Coefficients (HTC) required in the computation of temperature are determined empirically, which affects the prediction accuracy during conceptual design. From the sensitivity analysis, the HTC on the piston crown and between the piston and liner were found to have the greatest influence on temperatures and are highly influenced by piston geometry, and hence required more accurate modelling. In the present study, the former was computed from in-cylinder fluid flow analysis using Finite Volume (FV) formulations. For this purpose, a parametric FV model generator was developed to optimise the mesh, and the blending factor in the convective flux discretisation. The HTC between the piston and liner was predicted from the analysis of clearances between them. With these approaches, less than 2.1 % deviations between predicted and measured temperatures were observed, as compared to 5 - 20 % when employing existing methods. The computation efficiency was also enhanced. Currently, it could take 25 man weeks to obtain accurate temperatures on a model with 3000 elements, whilst the same can be obtained in 10 - 12 man weeks (4 man days for a repeat analysis) with the improved method. As a test case, piston temperatures and stresses were predicted for a load cycle from 156 kW at 2500 rev/min to no load at 650 rov/nzin. The bowl lip experienced the highest temperature and stress gradients of 300° C/min and 73 MPn/mint, respectively. Subsequently, a piston life of 244292 hours was predicted. By employing existing methods in the computation of thermal loading, Char (1993) and Sivarajah (1993) predicted 208321 and 199027 hours, respectively. Although the design analysis method for pistons has been improved significantly, further work is still required to allow analysis of engine with more than two ports per cylinder under fired engine conditions. Interactive analysis of HTC and clearances between the piston and liner is also required since both are temperature-dependent. Due to computer memory limitations, the same was not performed in the present study
Some methodologies for facts controllers
(University of Dar es Salaam, 1997) Mwinyiwiwa, Bakari M. M.
Flexible AC Transmission Systems (FACTS) have been conceived to increase the transmissibility of electric power without the necessity of building new transmission lines. An important family of controllers proposed for FACTS are based on high power solidstate switches, such as the gate-turn-off thyristor (GTO), which is presently rated at 6kV, 6kA. The FACTS controller operates at the transmission voltage, in the order of SOOkV, and it must be rated at hundreds of MVA. The research of this thesis contributes in developing the methodologies necessary for the integration of the solid-state switches so that the FACTS controllers have the voltage withstand and the current carrying capacity. The methodologies followed in the thesis are based on organizing the solid-state switches firstly in the forms of: (a) 2-level, voltage-source converter modules or (b) multilevel, voltage-source, converter modules. Thereafter, the modules are connected in series and/or in parallel. Switching strategies such as: (i) the phase-shifted triangle carrier technique and (ii) the fundamental frequency switching, are shown to be promising. The thesis addresses the methodologies of uniting the modules: (i) in parallel, (ii) in series and (iii) in parallel groups of series-connected modules. Series connections require magnetic transformers. Transformers also enable 6-phase and 12-phase ac systems to be produced from the standard 3-phase ac utility supply. The thesis has initiated research in incorporating the multi-phase ac systems to the multi-modular, multi-level converters. The thesis has also developed the interface methodology for digital (digital signal processor, DSP) control of the array of modules in real-time. The methodologies of the thesis have been proven in digital simulations and experimentally in laboratory models
Development and application of a GIS-based regional hydrological variability and impact assessment system (RHVIAS) for Southern Africa Region
(University of Dar es Salaam, 1999) Berhanu, Fanta Alemaw
Local or regional water resources planning and management is a complex problem. Clearly, hydrologic aspects constitute the major component. In addition, hydrological assessment of the existing and the future water-resources availability of a region is an important aspect. Assessing the environmental impact of the indisputable possible global climate change on regional water resources is another fundamental global concern. This calls for the development of a distributed hydrological model that accounts for the spatial variation and regional distribution of the various natural resources and environmental assets of a region. For this purpose, a GIS-based regional hydrological variability and environmental impact assessment system (RHVIAS) is developed. The system links the different components for analysis of regional water resources availability, variability and environmental impact assessment (EIA) of possible climate change on water resources at a regional scale. The system developed in this work has three components: variability analysis subsystem (VAS), a hydrological modeling subsystem (HMS), and an environmental impact assessment subsystem (EAS). The Southern African subcontinent, the SADC region, is considered for this study. The variability analysis subsystem (VAS) is composed of a system of time series models for hydrological variability analysis. It constitutes sub-modules for: (i) studying the annual and seasonal river runoff variability of 665 rivers, (ii) detection of possible climate change using a century-record of annual precipitation and temperature, and (iii) attribution study of climate change in terms of El Nino effects on river runoff variability using correlation analysis. VAS is externally coupled with ArcView~GIS for portraying the spatial coherence of identified temporal variability in the river runoff regimes. The hydrological modeling subsystem (HMS) is a system comprising a distributed GISbased hydrologic model (DGHM). It considers the geo-referenced distributed ground and satellite-based information such as soil, vegetation and other hydro-climatic information. DGHM simulates regional water balances such as runoff, soil moisture acid evapotranspiration for any grid, using GIS based temporal information and coupling with stochastic weather generation models (WGMs) for weather disaggregation. The WGM for rainfall has been built from a network of 760 rain gauge stations consisting of daily rainfall of length 2-91 years recorded in this century throughout the Southern African region. Both descriptive ability and predictive ability statistical tests have revealed the potential applicability of the model to generate rainfall at any selected grid in the region. The environmental impact assessment subsystem (EAS) constitutes a module for EIA of climate change on the water resources. It uses DGHM and it is externally coupled with a set of global climate models (GCMs) and simulated regional climate change scenarios. A coupling procedure is formulated to make a link in EAS between the GCM derived climates and DGHM through WGMs. Three GCMs are coupled in EAS selected from a suite of 14 GCMs tested - based on the IPCC 1992 emissions scenario (IS92a) and associated global warming with respect to the baseline 1961-90 climatology of the region. The selected GCMs represent relatively wet, dry and moderate scenarios, and they are the Oregon State University (OSU) model, the Hadley Centre 1994/95 model (HADCM2), UK Hadley Centre 1992 model (UKTR). Each component of RHVIAS, viz. VAS, HMS and EAS, has been tested individually, and finally integrated as interactive user-interface package to undertake an integrated water resources assessment. The approach used in VAS provided an excellent environment for undertaking variability analysis in temporal horizons and portraying attributes in a spatial context using GIS tools, for 665 gauged catehments in Southern Africa. River runoff declines since mid of 1970s have been prevalent in central and southern part of the SADC region. In the 20th century, temperature rises at a rate of 0.09° C per decade, and rainfall variation of mainly ±20% have been investigated. A correlation analysis of seasonal El-Nino/Southern Oscillation (ENSO) indices (that occurred since mid of 1950s to 1998) and annual discharge of selected rivers in the region is carried out. It reveals that a significant variance is accounted for by the ENSO episodes that suggest possible El Nino contribution to the natural variability of runoff. The HMS provides an excellent tool for simulating regional water balances at georeferenced grids of 0.5° resolution covering the region. It simulates the 1961-90 monthly runoff, evapotranspiration and soil moisture regimes of the SADC region. EAS provides a means of portraying regional water resources availability for the current and post-climate change conditions as a result of the simulated set of regional climate change scenarios predicted by GCMs. The 1961-90 average mean annual runoff from the land catchments in Southern Africa, generated using the developed model, in the region is about 151 mm per year, although there is a significant inter-regional variation among the SADC countries. Surface water availability in the region will be less reliable, and runoff changes are expected to be within ±20% in the 2050s; however, decision-makers should,be aware of the sub-regional variations and uncertainties associated with GCM-based climate change projections in formulating strategies to cope with the risks of climate change. Integrated water management at the river basin level remains the key action to alleviate water scarcity in the region. Potential actions to mitigate fossil fuel emissions such as increased agro-forestry and energy conservation & efficiency, employment of renewable energy systems and use of alternative fuels are suggested. Measures taken to reduce GHGs simultaneously reduce local and regional pollution. Designing the right response, in the region or a particular country, however, presents a tough challenge; while benefits accrue to the whole world, the costs accrue to the country where the investment or policy change takes place. The author has explored the implication of global efforts in abating or mitigating climate change - from the formation GEF to the Kyoto Protocol - and the provision of the UNFCCC framework for countries to address the treat of climate change.
Development of semi-distributed physically based hydrologic model for Usangu fans.
(University of Dar es Salaam, 2000) Seifu, Leulseged Abayneh
A semi-distributed physically based hydrologic model is developed to simulate the process of wave propagation from the high catchment over the fan-shaped catchment of Usangu plains and estimate the outflow from the fans into the swamp. The model is developed based on the propagation of flow wave from the high catchment on the fans as a function of state space conditions that includes daily state of soil moisture, rainfall and other meteorological conditions of the fans. Implicit finite difference scheme of kinematic wave equation coupled with state water balance equation was used. An alternative model, which is based on the USDA-SCS Curve Number technique, is also developed for the purpose of model output comparison. Both models were applied to the Usangu fans that do not have definite river channel. The input data to the models include rainfall, the inflow from upper catchment, potential evapotranspiration, topographic and soil-water parameters. Since there is no observed flow data at the outlet of the each fan, calibration of the model is impossible. Therefore, an attempt was made to derive the representative physical parameters for each of the fan from various sources. The result obtained from both models show that there is a considerable amount of water loss within the fan. However, the SCS model over estimates the loss as compared to the kinematic wave model. For those fans, which have definite river channel, only channel routing model was applied. The channel flow routing model is developed based on the Muskingum-Cunge method with lateral inflow. It is coupled with the kinematic wave model.
Investigation of the mechanisms of defluoridation of drinking water by using locally available magnesite.
(University of Dar es Salaam, 2000) Singano, Josephat J.
The locally available magnesite at Chambogo, Same district was investigated as a media for fluoride removal from drinking water. The objective is to find a suitable mechanism of defluoridation using Magnesite. Media preparation involved crushing and calcination of magnesite at different temperatures and durations. Jar tests and pH chemostat experiments in batch and continuous flow on fluoride removal ability of the media were carried out. The results showed that, magnesite can be used in drinking water defluoridation when calcined at the right temperature and duration. High fluoride removal capacity was found to be 65 mg F/g in batch experiments. Adsorption of fluoride has a maximum value at optimum pH range of 10.5 to 11.0. The higher initial fluoride concentration reduced the dissolved magnesium and thus the total hardness residue. A fluoride removal capacity of 27 mg F/g was revealed in a bucket fill and draw method when using naturally fluoridated water with initial fluoride of 21 mg F/L. It was also found that fluoride removal capacity in a continuous flow is very low (at the optimum of 3.5 mg F/g) compared with a capacity of 26 mg F/g in a batch system. The process of fluoride uptake using calcined magnesite involves a combination of two or more reactions depending on the fluoride concentration in the solution, pH, alkalinity and dosage of magnesia. The process portrays a lag time at the end it is evident the process is not a simple sorption or chemisorption. Because of lack of direct correlation between changes in alkalinity and fluoride removal, it is concluded that the reaction is not a simple ion exchange. The main mechanism of removal is the uptake of fluoride by the first step of hydrolysis product of magnesia by water to form a complex component of magnesium mono-hydroxyl-fluoride.
Densification, relaxation, and combustion characteristics of densified Biomass fuels: a comparative study with wood combustion.
(University of Dar es Salaam, 2001) Rajabu, Hassan M.
Densification of loose biomass waste such as agricultural, forest and industrial residues to form Densified Biomass Fuels (DBF) is an attractive option in areas where these resources remain unutilized. The potential of DBF to substitute fuelwood or coal in industrial combustion systems depends on how closely its handling and combustion behaviour match the existing facilities. In this work, experiments were conducted to study densification, relaxation, and combustion characteristics of rice straw and sawdust DBF. Experiments on wood combustion were also conducted for comparison to DBF. Densification tests were performed in uniaxial closed-die mode. Die diameters of 2.5 and 3.8 cm were used with die pressure up to 134 MPA. Results showed that an exponential relationship in the form: P=Ae(Bp), seems to best represent the uniaxial densification process for the material tested. Where: P is the die pressure, and p is the density of DBF. The values for coefficients `A' and `B' depend on die size, material type, and storage relative humidity. The relaxation behavior of DBF was studied in low, medium, and high, relative humidity conditions. DBF made of rice straw showed 52-68% increase in length in the pressure range tested, which is 6-18% higher than for sawdust. DBF from the larger diameter die showed 3-9% higher expansion compared to the smaller die. DBF showed higher percentage increase in length when stored in high humidity conditions. The change of moisture content of DBF during storage delays the stabilization period and increases their expansion considerably. Combustion tests were carried out in an isothermal thermogravimetric analyser. Results demonstrate that, during pyrolysis the cylindrical particles of both DBF and wood loose mass in a thin reaction zone. DBF were found to expand during combustion by up to 50% of its original volume. The anisotropic properties in wood have an influence on the direction of volatile gases coming out of the particle during pyrolysis. Model predictions show that drying and pyrolysis overlaps. Model predictions on the advancement of pyrolysis zone in radial and axial directions, and burning rate of the particle are in good agreement with experiment results.
Development of low flow prediction models for southern Africa
(University of Dar es Salaam, 2002) Mngodo, Raymond Julius
Hydrological Network does not cover all catchments in the Southern Africa region. There are many ungauged catchments that could have the potential for water resources development. A database was established for 638 river flow stations from 11 Southern Africa countries, covering an area of 6,929,826 km2. Spatial database consisting of river basins, gauged catchments, national boundaries; river; rainfall; potential evaporation; wetlands; and geology was established using ARC-INFO. The objective of this study was to develop low flow prediction models. The low flow index Q70 from flow duration curve was used to describe flow regime and map spatial variability of mean annual runoff, temporal variability of annual runoff, temporal variability of annual runoff and base flow contributions to river flow. About 25% of the rivers are ephemeral, 30% are intermittent and the remaining 45% are perennial rivers. Linear regression models were developed to predict Q70 for ungauged catchments in the nine primary basins of Southern Africa using catchment area, MAR, AAR, BFI and their GIS coverage’s. The BFI has a strong influence in estimation of Q70. For Tanzania, a non-linear regression equation was obtained by including geology indices. Eight homogeneous regions of 10-day annual minimum flows for Tanzania were delineated using a simple test based on the variability of at-site values of Cv: The L-moment ratio diagrams and the goodness of fit test of Hosking and Wallis are used to assess the suitability of selected distributions as regional parent distributions. The LLG distribution provides a good fit to low flows in one region while the LN distribution fits well in seven regions. The GEV-4 and non-parametric kernel estimation models were explored as other possible methods of low flow analysis. The GEV-4 models and the NKE when compared with Weibull models for its predictive and descriptive ability tests showed better results.
Modelling of constructed wetlands for polishing on-site anaerobically pre-treated domestic wastewater.
(University of Dar es Salaam, 2002) Kaseva, Mengiseny
This research work has been carried out to assess the performance of the Horizontal Sub-Surface Flow Constructed Wetland (HSSFCW) system in polishing pre-treated wastewater from the Upward Flow Anaerobic Sludge Blanket (UASB) and Septic Tank (ST) systems. Four different experimental set-ups of serially operated pretreatment and tertiary treatment systems were carried out. The HSSFCW units were designed and operated with a hydraulic loading of approximately 0.1 m3/m2/day and a hydraulic retention time (HRT) of approximately two days. The first experimental set up (UASB-HSSFCW) consisted of three CW units (A, B and C). The first unit was used as a control while the second and third units were planted with Phragmites mauritianus and Typha latifolia, respectively. Results obtained in this experimental set-up indicated a final BODs effluent quality of 29.2 mg/1 in unit B that corresponds to a removal of 73.8%, while in the second experimental set up (ST-HSSFCW) a BOD5 effluent quality of 27.45 mg/1, or equivalent to a removal of 74%, was obtained. In the UASB-HSSFCW set-up, slightly higher TC (56.35%) and FC (67.9%) removal rates were-recorded in wetland units B and C compared to the control unit A. Wetland unit B performed better in terms of FC removal while unit C had a better TC removal rate. Results obtained in ST-HSSFCW planted with Typha latifolia indicated a mean TC removal of 75% while the mean FC removal was 66.1 %. In the third experimental set up (UASB-VRF-HSSFCW), the mean FC removal was 98.8%, while the TC mean removal was 98.3% and COD removal was 74.8%. In the STHSSFCW the COD removal was 70%. In the UASB-HSSFCW system, NH4-N removal rates of 1.0, 0.91 and 0.45 g/m2/day for units B, C and A; respectively were achieved during the initial six months (phase 1) of the study. These removal rates were higher than those obtained during the last six months (phase II) of the study (0.44, 0.35 and 0.43 g/m2/day for units B, C and A). In the UASB-VRF-HSSFCW system, NH4-N mass loading removal rate in VRF was 0.91 g/m2/day, which was comparable to the removal rates obtained in the UASBHSSFCW system but was higher than the 0.6 g/m2/day obtained in ST-HSSFCW. However, a much higher removal rate (1.54 g/m /day) was obtained in UASB-VRF'HSSFCW system suggesting further that a serially operated UASB-VRF-HSSFCW can perform better than a UASB-HSSFCW and ST-HSSFCW system alone. In the fourth experimental set-up, which consisted of the UASB and HSSFCW, packed with fine gravel and sand FC in the influent which was in the magnitude of 7 logs, was reduced to 3 logs, which were within the WHO and FAO guidelines for wastewater recycle and re-use in agriculture and aquaculture. Model results for BOD5, and bacteria dynamics in the first experimental set up indicated that out flow BOD5 and BOD decomposition plays an important role in the removal of BOD5. The obtained results suggest that the developed model has been able to simulate and can thus be used to predict the removal mechanisms of BOD5, and bacteria in the HSSFCW. The model can also be used for designing HSSFCW systems.
Production and characterisation of coffee husks particleboards.
(University of Dar es Salaam, 2002) Ogola, Wilson Otieno
Tanzania has an economy based on agriculture. The agricultural activities produce wastes that are normally burnt while preparing the farms for the next season, consequently causing environmental pollution. Very little of these wastes are economically found useful due to lack of technological knowhow. Research developments have revealed that agricultural wastes could be used to make useful engineering materials for roofing, panelling, sheathing and furniture. Also, naturally occurring binders, abundantly available in Tanzania, could be used in the binding of the materials instead of the synthetic binders that are non-available and expensive. In this research, particleboards have been processed from coffee husks, a by-product from coffee processing with a naturally occurring hydrolyzed tannin adhesive and some of the existing synthetic adhesives such as urea formaldehyde, phenol formaldehyde as binders. A blend of coffee husks and wood particles with the above resins were also processed. The processing techniques used in industry were simulated in the laboratory to produce the boards. The resulting boards were characterized by determining their physical and mechanical properties by using ASTM Standards D1037-93 part A and DIN 53456 standards. A comparison of their properties were made with the data of the wood art 2-1989 for grade Cl type (general purpose) article boards and from CAN 3-01883-M82 Grade Y-Canadian Standards for Exterior particleboards. Results indicate that coffee husks particle sizes were between 850 mm to 2 mm in diameter and the moisture content was between 9 to 13 %. The optimum physical and mechanical properties were obtained with 12-14% of hydrolyzed tannin resin content, 7-8% of urea formaldehyde and 10% phenol formaldehyde resin content, based on the dry weight of the coffee husks. Coffee husks particleboards had the following optimum physical properties: For coffee husks/hydrolyzed tannin particleboards of density1035 kg/m3, thickness swelling after one hour was 6% which compared well with the BS standards 5669 part 2, of 8.4%. It had water absorption of 8.4% for the same period. The water absorption and thickness swelling for coffee husks/urea formaldehyde particleboard of density 1033 kg/m3 were 24% and 20% respectively. The specific heat capacity was 1260, 1508, 1670, 1651 Jkg-1 ºC-1 for coffee husks/urea formaldehyde, coffee husks/phenol formaldehyde, coffee husks/tannin, wood/tannin particleboards at room temperature respectively. Coffee husks particleboards had the following optimum mechanical properties: For coffee husks/tannin particleboards of density 1035 kg/m3, the modulus of elasticity (MOE) was 1216 MPa, the modulus of rupture (MOR) was 6 MPa, the tensile strength parallel to the surface was 2 MPa, the impact strength was 11.3 kJ/m, a shear strength parallel to the surface of 0.51 MPa, work done on impact of 1.1 J, screw withdrawal forces of 2300 N (face), and 638 N(edge), nail withdrawal forces of 497 N(face)and 282 N (edge), compression strength parallel to the surface of 6 MPa and a nail head pull through of 1787 N. The corresponding coffee husks/urea formaldehyde particleboard had MOE and MOR of 1089 MPa and 5 MPa respectively. The impact streght was 3.4 kJ/m2, a tensile streght parallel to the surface of 0.7 MPa, work done of 3J, and nail head pull through of 387 N. The results indicated that, it was possible to produce particleboards using these locally available materials for general applications. This would help in reducing the current pressure on wood and also help in reducing deforestation and conservation of the rainforests as well as wild life survival. A blend of coffee husks with wood particles improved the mechanical properties and lowered the mphysical properties of coffee husks particleboards. The resulting particle boards, had physical and mechanical properties which compared well with those of particleboards made from other agricultural wastes such as maize cobs, maize husks and rice husks. However, the properties were lower than those from BS Standards 5669 part 2 type C1 (general purpose) and CAN 3-01883M82-Grade Y-Canadian Standards for Exterior particleboard. This was due to the limited particle sizes of the coffee husks that could not allow for much improvement in the physical and mechanical properties as well as their smooth waxy surfaces that could not allow for good interfacial adhesion.
Optimisation of bone char filter column for defluoridating drinking water at household level in Tanzania.
(University of Dar es Salaam, 2002) Mjengera, Hassani Juma
Excessive fluoride concentration in drinking water is a major problem in many regions of the world, especially in developing countries, which are facing financial constraints and the technology to treat the water to acceptable fluoride levels. Excessive fluoride in potable water has been found to be the cause of dental, skeletal and crippling fluorosis. With these facts in mind water with excessive fluoride should be treated, although simplicity applicability, acceptability and affordability of these are yet to be verified. This project therefore is aimed at developing an efficient and affordable method of producing drinking water with acceptable fluoride concentrations. The use of bone char media has been considered and tested. In this research charring temperatures, contact time and fluoride binding capacity were investigated. A series of raw cattle bones were charred at different durations for a temperature of 600°C, followed by charring for 20 minutes within temperature range of 300°C to 800°C. All the bone samples prepared were crushed and sieved to different sieve sizes. Natural water with initial fluoride concentration in the range of 3.2 to 22 mg/L was used in the investigations since this is a common range of fluoride concentration in Tanzania. Make up water was prepared using sodium fluoride with concentration levels in the range of 10 to 100 mg/L. Using these waters various relationships were observed and established. This study therefore, reveals that thermally activated bone at temperatures of 400 - 600 °C, produce bones of good quality required for defluoridating water for drinking and cooking. Two systems for defluoridation of water have been developed and set for practical tests in Kitefu and Ngurdoto Villages in Arumeru District Arusha Region in Tanzania. Initial tests have shown that the media produced water of acceptable quality with 0.3-mg/L residue fluorides. The units have operated well for a period of 12 months with residual fluoride contents of 0.3 mg/L from initial fluoride levels in the range of 2.8, 10 and 15.6 mg/L. The beneficiaries have accepted the technology without any difficulty.
Development of a decision support system for the rufiji river basin - Tanzania
(University of Dar es Salaam, 2003) Yawson, Daniel Kwesi
Three stand-alone Decision Support System (DSS) models have been developed at three critical locations within the Rufiji River Basin in Tanzania. The models are the Usangu Basin Model (UsaBaMod) for the headwaters of the Great Ruaha River, which is the main contributor to the Mtera-Kidatu Reservoir System, the Mtera- Kidatu Simulation Model (MteKid) for the optimal operational procedure of the reservoir system, and the Rufiji River Basin Flood Warning System (RBFWS) for the Rufiji floodplain and the Delta. For the UsaBaMod, dry season irrigation was found to be the main cause of the drying up of the Great Ruaha River among the numerous possibilities considered, and that if the dry season irrigation abstractions are restricted to crop water requirements, for example, instead of the constant abstraction methods being employed, then the river would be able to sustain flows during the dry season. Investigations about the possible cause of the failure of the reservoir system have shown that the actual amount of water that was being released from the Mtera Reservoir as spill must have been much higher than what had been recorded. It was also evident from the investigation that while Mtera Reservoir was “struggling” to get refilled in certain years the Kidatu Reservoir recorded large amounts of spill more enough to bring the Mtera Reservoir to its full condition. RBFWS in a form of a user-friendly computer package to generate flood forecasts within the Rufiji River at Stiegler’s Gorge and at Mloka as well as showing the extent of flood inundation in the floodplain with the corresponding flow magnitude had also been developed.
Investigation of performance characteristics of multi-phase thermal pump
(University of Dar es Salaam, 2004) Chami, Francis Augustine
A multi-phase thermal pump has been investigated. Basically the pump is a metal tube, which on one end has separate water and steam inlets and a water outlet on the other end. Non-return valves are employed on all inlets and outlet. Experimental methods coupled with mathematical modeling were done. The results indicated that the discharge head of the pump increased linearly with steam pressure. The temperature of the inlet water influenced significantly the volumetric discharge rate. The discharge rate increased with steam pressure to a maxima and decreased thereafter, for a given inlet water temperature. Except for very low steam pressures, the discharge volume per stroke of the pump was found to be higher than the volume of the smaller cylinder, an observation that did not support the sudden expansion theory of operation of the pump with two cylinders. Further investigations of the pump to establish operating characteristics for steam gauge pressure between 0.05 and 0.5 bar indicated the existence of substantial suction head and a maximum developed head was measured. Entry and exit losses accounts were made of the developed head. The process of pumping was found to be a sensitive one and highly dependent on heat transfer from the steam. Both heat loss through the pump walls and to the water being pumped contributed in creating conditions for condensation and this in turn initiated the filling of the pump with water ready for another pumping stroke. Experiments were conducted to find the influence of operating parameters on the performance of the pump, with the focus on the optimum parameters for a given condition. Observation of the results revealed that pump diameter did not have significant influence on the flow rate. It was also observed that each pump has at least one common cycle time where different discharge heads produced the same flow rate. Modeling of the pump has revealed the existence of dimensionless parameters that influence the operation of the pump. These are Reynold’s, Prandtl’s dimensionless numbers and length to diameter ratio of the pump. Conditions necessary for the reversal of the pump caused by the involved forces have been established. A novel idea has been worked out on the application of the multi-phase thermal pump in refrigeration system. This idea has introduced a new refrigeration system to the refrigeration industry, which involved a principle different from that of conventional refrigeration systems. A coefficient of performance (COP) of 8.3 and the overall heat energy balance of the system has been calculated and a working model has been produced. Recommendations are made for more efforts to be directed in the application of the pump in the refrigeration industry using different environmentally friendly refrigerants and improving the system.
Modeling of coupled dynamic roughing filters and horizontal subsurface flow constructed wetlands to tertiary treatment of waste stabilization pond effluents
(University of Dar es Salaam, 2004) Kimwaga, Richard Joseph
This study which was investigated in different times from May 2000 to March 2002 was conducted to determine the potential use of coupled Dynamic Roughing Filters (DyRFs) and Horizontal Subsurface Flow Constructed Wetlands (HSSFCW) as a cheaper and yet effective and appropriate alternative technology of treating domestic wastewater in tropical environments like Tanzania. Pilot set ups of coupled DyRF and HSSFCW were constructed at the outlet of the Waste Stabilisation Pond (WSP) at the University of Dar es Salaam. One set of a DyRF- HSSFCW was placed downstream the Primary Facultative WSP (PFWSP) and the other was located downstream the Maturation WSP (MWSP). The study was carried out in a 2.2-m long, 0.7-m wide and 0.7-m deep DyRF as a first stage, using three different fractions of gravel ranging from 8mm to 32mm, respectively from the top to the bottom. In the second stage, there was a HSSFCW with 0.6-m wide, 1.75-m long and 0.6-m deep planted with Phragmites mauritianus. The optimised combination of the operational and design variables yielding the highest purification efficiency of DyRF was at a filtration rate of 2 - 3m/h, a filter material size range of 8 - 25mm, and the filter media thickness of 0.7m. A further study was conducted to compare the environmental conditions, performance and first order removal rates kinetics of TSS, BOD5, COD and Faecal Coliforms (FC) for a coupled DyRF and HSSFCW placed downstream of the Primary Facultative Waste Stabilisation Ponds (PFWSP) and that after Maturation Waste Stabilisation Ponds (MWSP). The best location of DyRF - HSSFCW for the achievement of higher removal rates of 0.56 d*1 (TSS), 0.75 d'1 (BODs), 0.79 d’1 (COD) and 0.85 d'1 (FC) was found to be after the MWSP. In the final phase of the study, an ecological model was also developed to simulate the retention and removal of Total Suspended Solids (TSS) in a coupled DyRF and HSSFCW treating effluents from PFWSP system. The model was based on the application of the deep - bed filtration models for drinking water purification with an extension term that incorporates biological activities (i.e. biodegradation). The simulations were performed using STELLA™ II software. The model found out that the sedimentation process was the major removal route of the TSS in the DyRF accounting for a mean removal of 63.7% (26.67 gTSS/m2/d) of the total removal followed by the filtration process mean removal rate of 22.1% (9.25 gTSS/m2/d). However, the filtration process was the major route of removal of the TSS in the HSSFCW accounting for a mean removal of 77.4% (7.23gTSS/m2/d) followed by bio-degradation, which accounted for a mean removal of only 16.2% (1 52gTSS/m2/d).
Estimation of motor vehicle fuel consumption and the corresponding greenhouse gas emissions in a developing country city
(University of Dar es Salaam, 2004) Bundara, Malima Manyasi Patroba
Urban road transport is a major consumer of fuel and a major source of both carcinogenic and polluting greenhouse gases. As a result, developed countries have and continue carrying out studies to control vehicular fuel consumption and the corresponding emissions. Having the largest population of motor vehicles in Tanzania, the Dar es Salaam road network was studied to formulate a model for estimating the city’s vehicular fuel requirements and establish the corresponding gas emission factors by collecting and analysing the 1980 - 1999 historical data and year 2000 field data. The resulting model and findings on the contribution of traffic conditions, mode of transport and behaviour of drivers are presented and discussed. Three conclusions are made. First, a city’s vehicular fuel requirements can be obtained from accurate data on the number of motor vehicles and length and type of roads with a margin of error of ±6%. Second, in Dar es Salaam city, traffic conditions, mode of transport and behaviour of drivers considerably increase vehicular fuel consumption and emissions. Third, vehicular greenhouse gas emission factors in Dar es Salaam city are higher than those specified by WHO (WHO, Geneva, 2000) especially for CO and NOx whose factors are higher by more than 500 and 100 times respectively. Adoption of the formulated model and changing the mode of public transport are recommended to enable city authorities to put in place appropriate measures for controlling and reducing fuel consumption and emissions. The use of improved data collection methods and/or relating the vehicle-kilometre-travelled per day with the physical length of the city’s road network can improve accuracy of the model.
Modeling project management processes for sustainability.case studies in Tanzania.
(University of Dar es Salaam, 2005) Makalle, Albinus Mketa Pastory
A sustainable project must contribute to economic and social welfare without depleting natural resources, destroying the environment or harming human health. However, the current project management system focuses on project economic objectives as the primary objective instead of the resulting social transformation and environmental changes. Building upon basic sustainability principles, the problem was addressed in this thesis by a critical review and analysis of project management processes, development and the use of sustainability indicators. With this understanding, a system approach was used to conceptualize a paradigm shift in project management system for sustainability incorporating Environmental Impact Assessment (EIA), Cause- effect chain and the Social Economic Resource models. Using a multi-evidence research methodology of four case studies in Tanzania, at different phases of project cycle, it was established that success of the case projects and facilities, have depended on financial and technical aspects. In order to move towards sustainability, project management processes were restructured based on developed project sustainability indicator models and management integration framework for sustainability referred to as ‘Project Management Integration Framework’. The framework provides a holistic approach to integrate economic, environmental and social concerns into project cycle which are difficult or not adequately addressed in modern project impact assessment methods. The sustainability indicators, as general systems.
Effect of plastification on the buckling behaviour of non-linear structural two-dimensional reinforced concrete frames
(University of Dar es Salaam, 2005) Salim, Wanjala Ramadhan
This Thesis deals with non-linear finite element analysis of structural 2-D reinforced concrete frames. It explores the effect of progressive material failure due to flexural actions on axial load carrying capacity of the frame. A plane stress field is assumed to describe the behaviour of frame members. The thesis proposes a new finite beam-column element that takes into consideration non-linear geometrical and material response. The non-linear incremental formulation is based on the Principle of Virtual Work. The equilibrium equations are derived using the Updated Lagrange Formulation. The material behaviour of concrete is described by failure surface described by Kupfer/Tusuji et al. The modified model of Hognestad is used for the concrete stress- strain relation. The material behaviour of rebar is described by Von Mises yield criterion while the stress-strain relation is modelled as bilinear elastic work hardening plastic material. Typical structures have been analyzed and results presented. The results show that consideration of plastification in a 2-D reinforced concrete frame, when the effect of cracking is taken into account, leads to a lower axial load carrying capacity of the structure. Thus the study results show that the effects of plastification on axial load carrying capacity of structures are important and should always be included in finite element models for predicting response of reinforced concrete members.

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