This study tested the hypothesis that the hydantoin-hydrolysing enzymes of a novel Pseudomonas putida, RUKM3s, with high-levels of activity of a non-stereoselective hydantoinase, and an L-selective N-carbamyl amino acid amidohydrolase (NCAAH), could be optimally extracted, partially purified for characterisation, stabilised by immobilisation, and applied as a biocatalyst for production of amino acids from 5-mono-substituted hydantoin substrates. Experiments were devised to optimise conditions for the production of RUKM3s biomass with high levels of hydantoin hydrolysing activity, and to evaluate techniques of protein extraction, enzyme isolation, purification and characterisation. The NCAAH ofRUKM3s is a dimer of approximately 60 k:Da, .with two subunits of approximately 30 k:Da each. The hydantoinase · is approximately 210 kDa. Methods of enzyme immobilisation were investigated and operational parameters of the immobilised biocatalysts were evaluated. Stabilisation of biocatalysts by immobilisation revealed that among five methods of immobilisation used, covalent coupling to Eupergit® C provided the most suitable biocatalyst formulation of the RUKM3s enzymes. A model of the hydantoinase reaction based on the stabilised biocatalyst was developed and tested by empirical studies in a bioreactor system. In the system, the high hydantoinase activity from RUK.M3s was coupled with the high NCAAH activity of a mutant Agrobacterium tumefaciens strain, RUOR-PNI, to enhance the overall product yield. It was . demonstrated that the combined bioreactor system could achieve close to 100 % conversion yields of amino acid, operating in a continuous substrate-feed mode.

Talc is a naturally floatable gangue material common in South African platinum bearing (PGM) ore bodies. Long chain polysaccharide depressants are effective in depressing talc flotation and improving the grade of the concentrates of those ores with talc as a gangue constituent. This thesis describes an investigation into the surface interactions of two types of long chain polysaccharide depressants (carboxymethylcellulose and guar gum) with pure talc and with Merensky PGM ore (which is known to contain talc as a gangue constituent). Specifically, the objectives of this thesis were as follows: 1. To characterize the differences in the depressants selected. 2. To examine the effects that polymeric structure and molecular weight of the depressant have on the hydrophobicity of talc. 3. To extrapolate the findings from highly controlled laboratory conditions to batch flotation tests with Merensky PGM ore. During the course of the experiments, it became clear that ionic conditions were an important factor in this system and they were therefore incorporated into the work done. Overall, the molecular weight of the depressants was not seen to be an important factor in their ability to depress talc. The molecular structure did appear to impact depressant efficiency, but only under conditions oflow ionic strength in the microflotation system. III Ionic conditions were found to be a pivotal factor in the performance of the CMC depressants in reducing the flotation of talc. It was also found that the ions adsorbed onto the talc surface in the absence of depressants - leading to a reduction in talc floatability. Divalent cations were more effective than monovalent cations in enhancing the effectiveness of the CMC depressants - suggesting stronger adsorption under these conditions. Guar depressants appeared to be unaffected by varying ionic conditions. The batch flotation tests, and the microflotation tests at the higher ionic strengths, showed that similar depressing ability was obtained for the CMCs and the guars. However, the batch floats indicated that increasing dosage led to improved depressant performance while the microflotation tests indicated that a maximum level of depression was achieved at fairly low dosages

Many attempts have been made in studying the structural behaviour of cooling tower shells, focusing more on the effect of wind on the structure and shape imperfections. However, little has been investigated on the most basic loading condition, i.e. self-weight load. This thesis focuses on a cooling tower with uniform thickness where several geometric parameters like the hyperbolic axis ratio (bla), top opening angle , offset parameters (A), and scale of the structure are varied one at a time, to investigate the effect these parameters have on the meridional and hoop stresses. A general-pwpose finite element programme, ABAQUS, was used to create models of the cooling tower structure. The model results were verified using closed-form analytical membrane solutions as reported by Zingoni. The model considers constraining the base against rotation in all directions while the top is made to be free. The predicted numeric meridional and hoop stresses compare favourably well with the closed-form analytical results, except at the critically stressed zone near the base that exhibits some bending disturbances. Parametric investigation shows that an increase in the hyperbolic axis ratio, the top opening angle, and offset paramete also increases meridional and hoop stresses. It is concluded that lower blao, and zero offset parameters be adopted for preliminary design purposes. Finally, recommendations are made on the need for further investigations.

Power system stability is defined as the condition of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a finite disturbance. In the evaluation of stability, the focus is on the behavior of the power system when subjected to both large and small disturbances. Large disturbances are caused by severe changes in the power system, e.g. a short-circuit on a transmission line, loss of a large generator or load, loss of a tie-line between two systems. Small disturbances in the form of load changes take place continuously requiring the system to adjust to the changing conditions. The system should be capable of operating satisfactorily under these conditions and successfully supplying the maximum amount ofload. Power system stability is defined as the condition of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a finite disturbance. In the evaluation of stability, the focus is on the behavior of the power system when subjected to both large and small disturbances. Large disturbances are caused by severe changes in the power system, e.g. a short-circuit on a transmission line, loss of a large generator or load, loss of a tie-line between two systems. Small disturbances in the form of load changes take place continuously requiring the system to adjust to the changing conditions. The system should be capable of operating satisfactorily under these conditions and successfully supplying the maximum amount ofload. This dissertation deals with the use of Power System Stabilizers (PSS) to damp electromechanical oscillations arising from small disturbances. In particular, it focuses on three issues associated with the damping of these oscillations. These include ensuring robustness of PSS under changing operating conditions, maintaining or selecting the structure of the PSS and coordinating multiple PSS to ensure global power system robustness. To address the issues outlined above, a new PSS design/tuning method has been developed. The method, called sub-optimal Hoo PSS design/tuning, is based on Hoo control theory. For the implementation of the sub-optimal Hoo PSS design/tuning method, various standard optimization methods, such as Sequential Quadratic Programming (SQP), were investigated. However, power systems typically have multiple "modes" that result in the optimization problem being non-convex in nature. To overcome the issue of non-convexity, the optimization algorithm, embedded in the 111 University of Cape Town sub-optimal Hoo PSS design/tuning method, is based on Population Based Incremental Learning (PBIL). This new sub-optimal Heo design/tuning method has a number of important features. The method allows for the selection of the PSS structure i.e. the designer can select the order and structure of the PSS. The method can be applied to the full model of the power system i.e. there is no need for using a reduced-order model. The method is based on Heo control theory i.e. it uses robustness as a key objective. The method ensures adequate damping of the electromechanical oscillations of the power system. The method is suitable for optimizing existing PSS in a power system. This method improves the overall damping of the system and does not affect the observability of the system poles. To demonstrate the effectiveness of the sUb-optimal Hoo PSS design/tuning method, a number of case studies are presented in the thesis. The sub-optimal Hoo design/tuning method is extended to allow for the coordinated tuning of multiple controllers. The ability to tune multiple controllers in a coordinated manner allows the designer to focus on the overall stability and robustness of the power system, rather than focusing just on, the local stability of the system as viewed from the generator where the controllers are connected.

The minerals processing industry in South Africa produces significant tonnages of waste material which are disposed of commonly in dedicated waste depositories. These deposits pose a potential to pollute the environment if leachate is generated within the deposit and released to the surroundings. Leachate generation is generally investigated using laboratory columnar experiments which attempt to mimic the physical and chemical processes which occur in the deposit. These experiments, termed lysimeter experiments, are time consuming in that they typically last for at least a few months and can last for up to three years. Lysimeter experiments are also costly to conduct. Because of restrictions such as these, relatively few deposits have been characterised to determine the leachate which they generate and thus the risk which they pose to the environment. There is an urgent need to be able to estimate the environmental risks associated with existing waste deposits. The first step towards assessing this risk would be an ability to predict leachate generation within a specific deposit. Such an ability could be used to identify which of the existing deposits produce significant leachate and thus pose a potential hazard to the environment. Equally, if leachate generation from new deposits could be estimated as a function of waste material and characteristics of the waste deposit, this information could be used to improve the engineering design of waste deposits. The work presented in this thesis involved identifying suitable modelling strategies which could be used to determine leachate generation within waste deposits which contain waste material typical of that produced by the minerals processing industry. Two modelling strategies have been investigated. The first modelling strategy involved a macroscopic model in which all effects such as intrinsic chemical kinetics, intra-particle diffusion, external mass transfer and hydrodynamic considerations are lumped into a single parameter. The result of this approach is an effective reaction rate for the release of hazardous constituents from a volume element of the waste deposit. The effective reaction rate is determined by fitting the model to experimental data based on lysimeter tests. The main advantage of this model is that it eliminates the need for a detailed understanding of the individual factors which contribute to leachate generation. This model was investigated both for its inherent simplicity and for use in cases where insufficient information with respect to the intrinsic chemical reaction rates, intra-particle diffusion, external mass transfer or hydrodynamic aspects exist. The main disadvantage of this model is that it has a limited predictive ability in that the individual significance of any one factor which contributes to leachate generation cannot be determined. For this reason a second, more detailed model, termed the heterogenous columnar model, has also been investigated. The heterogenous columnar model describes the release of hazardous constituents at the single particle level and relates this information to the overall leachate generation within the deposit. This is achieved by calculating the release of hazardous constituents from the size distribution of particles to the bulk fluid between these particles. The release of hazardous constituents from individual particles is determined by making use of a particle-scale chemical reaction 'model. This particle-scale model is sufficiently detailed to be able to determine the relative contribution to the overall release of hazardous constituents from the particles of intrinsic chemical kinetics of the reactions to the effects of diffusion of the fluid reagent into each particle. The heterogenous columnar model can also be used to determine whether the effective rate of release of hazardous constituents from the particles (which include intrinsic kinetic and diffusional contributions) or the flow of fluid reagent through the deposit limits the release of hazardous constituents from the deposit. This information can be used to determine the main factors which affect the release of hazardous constituents from waste deposits and can thus be used to improve the design of waste deposits. Probably the most important attribute of the heterogenous columnar model is that methods have been investigated to determine the model parameters from a simple continuously stirred tank reactor (CSTR) type experiment. The ability of the heterogenous columnar. model to predict leaching behaviour has been investigated using data on precious metal leaching found in the literature. The results are encouraging in that the model can accurately predict the leaching behaviour of precious metals. A preliminary investigation into determining suitable particle-scale model parameters for a sample of waste from a CSTR experiment has been conducted. This too has yielded encouraging results. However, the application of using the heterogenous columnar model using these parameters to describe leachate generation within waste deposits or lysimeter experiments still needs to be demonstrated. Once the heterogenous columnar model has been verified against data pertaining to leachate generation from a waste deposit it may start to provide the minerals processing industry with the information which it so desperately requires in order to dispose of wastes in a manner which minimises the impact on the environment.

The principal objective of this investigation was to enquire in what measure calcium phosphate precipitation and luxury biological uptake contributes to excess removal of phosphorus in activated sludge systems, i.e. removal in excess of the basic biological requirement for metabolic purposes. This objective was pursued by imposing conditions in which one or the other of the two mechanisms had negligible influence. From the series of batch and continuous activated sludge experiments the following conclusions are made regarding excess phosphorus removal.

The Zandvlei estuary is the only functional estuary on the False Bay coastline which forms part of the southeast boundary of the City of Cape Town (CCT) on the southwest coast of South Africa. It provides an important habitat for fledgling fish species in the area and is a popular recreational site for birdwatchers, sailors and conservation-enthusiasts. The estuary has experienced water quality problems for many years. It drains three upstream sub-catchments which are largely comprised of conventional drainage systems which carry stormwater pollutants into the watercourses that then drain into the estuary. Of the many pollutants that flow into the estuary, elevated nutrient levels (specifically phosphorus and nitrogen) are a major concern because they can lead to eutrophication and excessive plant growth. In recent years the estuary has experienced algal blooms resulting in adverse effects on local plants, and animal and human life. Sustainable Drainage Systems (SuDS) are holistic drainage practices that address, amongst other things, water quality issues like those experienced by the Zandvlei estuary by treating the stormwater. The aim of this study was to identify areas of raised nutrient concentrations and model various SuDS measures to improve the water quality of runoff. Surface water sampling in the catchment and a study of historical water quality data was undertaken to identify areas with higher nutrient concentrations. Phosphorus concentrations, in the form of SRP, was found to be above the eutrophic threshold in most samples, while nitrogen concentrations, in the form of TIN, were found to mostly be beneath the eutrophic threshold. The locations of higher nutrient concentrations coincided with suspected sources of raised nutrients based on a desktop study of the catchment that identified agricultural areas, golf courses that use treated effluent for irrigation, and commercial/industrial areas. Water level sensors were developed and placed in each sub-catchment to compare nutrient concentrations during storms to stream flow during storms. A hydrological and hydraulic model was built representing two of the river systems feeding into the Zandvlei estuary – the Keysers and Westlake River sub-catchments. The PCSWMM software package developed by CHI, which uses the SWMM engine developed by USEPA, was employed. Data regarding historical rainfall, land use, stream flow, surface cover, soil types, geology and historical temperatures were used to construct the model. The model was calibrated against historical stream flow data obtained from CCT. Various SuDS measures were modelled and grouped into three scenarios: Scenario 1 modelled local controls targeting the suspected source areas, Scenario 2 involved modelling large-scale regional controls, and Scenario 3 was a combination of the first two. The local controls modelled were swales and bioretention areas. The regional controls modelled were wetlands, primarily because the study area already contains wetland areas that are currently disconnected from the river systems. Wetlands were modelled with upper and lower limit treatment equations. The simulated wetlands were able to reduce the SRP and TIN concentrations to below the eutrophic threshold (below 0.25 mg/ℓ and 2.5 mg/ℓ respectively) for three years out of the 8-year simulation period. The various scenarios achieved pollutant reductions ranging from approximately 25-80%. The CCT requires a TP reduction of 45% and a TSS reduction 80%. For TP, this was achieved throughout the simulation period when wetlands are functioning efficiently (i.e. the upper treatment limit); while for TSS, this requirement was only achieved in some years when the wetlands are functioning efficiently. Scenario 1 showed the least pollutant removal overall, while Scenario 2 and 3 showed similar pollutant removal and flow reduction, suggesting that the effect of the proposed local controls is insignificant compared to that of the large-scale regional controls.

Rapid urbanization and advancement in concrete technology in the world has led to excessive exploitation of natural sand resources for use in the construction industry. This excessive utilization has led to the depletion of natural sand resources; for instance, in countries such as India and Indonesia, sand mafia and destruction of beaches due to illegal sand mining have been reported. These trends have forced the construction industry to adopt the use of alternative construction materials such as recycled aggregates into new construction as a measure to deal with this growing challenge. Currently, in South Africa, a blend of different types of sand is used for construction purposes due to variations in the sand quality and over exploitation of nearby deposits of natural sand resources. However, the adoption of recycled fine aggregates has been a challenge due to properties such as higher water absorption and lower relative densities of the aggregates along with the variation of material sources which attributes to the lower durability performance of concrete made with recycled fine aggregates. Durability of concrete with recycled fine aggregates is largely affected by the transport mechanisms which is influenced by the presence of residual mortar on the surface of recycled fine aggregates. This research involves an investigation on both mechanical properties such as compressive strength as well as durability properties such as resistance to penetration of aggressive ions, of concrete made with partial replacement of recycled fine aggregates.

Increasing urbanisation and population growth are making it difficult for governments to achieve sustainable development. Provision of clean energy is among the seventeen sustainable development goals, as it reduces reliance on fossil fuels. In recent years, Namibia has rapidly increased her reliance on sustainable energy. The renewable energy sources (RESs), including wind and solar energy, can be described as clean sources which have lesser negative environmental impact compared to conventional energy sources. Amongst the pressing challenges today is finding solutions on efficient solar and wind energy production. It is imperative to work out the optimum location of RESs before installing them. This can significantly improve performance and establishes the foundation for studying both solar and wind power in a site selection problem. This study aims to determine potential locations for wind and solar photovoltaic (PV) energy plants installation using one of the multi-criteria decision-making (MCDM) methods, the analytical hierarchy process (AHP), and a geographic information system (GIS) within the Central North Regional Electricity Distributor (CENORED) supply area. Combining GIS with MCDM results in a powerful technique for selecting potential sites, since GIS provides effective analysis, manipulation, and visualization of geospatial data, whereas MCDM provides consistent weighing of criteria. In the evaluations of the location: topographical, environmental, climatic and regulations constraints were considered as factors that may facilitate or hinder the deployment of solarwind energy power plants. For solar PV energy plant, the highest potential areas are in the north-west, south-west and study area's southern regions, whereas for the wind power plant, only the northwest part is a highly suitable location for wind energy plants installation. These findings can be used to determine most favourable location of interest for solar PV and wind power plant development or to support the integration of electrical grid expansion and off-grid electrification strategies.

Electronic waste (e-waste) has emerged as a rapidly growing waste stream, growing at a global rate of 2 Mt per annum and is expected to exceed 74 Mt by 2030. E-waste contains a high content of precious and base metals which can be recovered for economic benefit. This has made the recycling of this waste stream of interest, with particular emphasis on the recovery of metals from waste Printed Circuit Boards (PCBs) as they contain a high content of copper as well as a significant quantity of precious metals such as gold, silver, and palladium. The major economic driver for the beneficiation of PCBs is the recovery of these precious metals followed by the recovery of copper which can constitute more than 20% of the value share. In the South African context, 5-7% of e-waste generated is collected and formally recycled. There exists potential to increase the proportion of e-waste recycled through the development of accessible beneficiation techniques that can be implemented by small scale industries. This study builds on previously completed research on alkaline ammonia leaching for the recovery of copper from waste PCBs that have undergone various physical or chemical pretreatment processes for metal liberation. Some PCB manufacturing processes employ a similar alkaline ammonia oxidative leaching system as one of the key process-steps in the manufacturing of PCBs as is evident by the case study of a local PCB manufacturing company. There exists an opportunity to utilize waste etchant from the manufacturing process as lixiviant for the recovery of copper from waste PCBs. This will enhance resource efficiency in line with the United Nations sustainable development goal 12, responsible consumption and production by extracting value from both the copper loaded waste etchant and waste PCBs. The potential to recover copper from both waste PCBs and the waste etchant through a leach circuit that utilizes the excess lixiviant contained in the waste etchant is explored. To do this, the copper distribution of a custom-made 4-layer PCB is established through a breakdown of the readily accessible top and bottom surface copper, referred to as the “surface copper” as well as the tightly laminated inner layer copper inaccessible to the lixiviant. Pre-treatment utilizing chemistry from the PCB manufacturing desmear process is then explored as a viable pretreatment method for liberating the inner layer copper with a key focus on solvent swelling with N-Methyl-2-pyrrolidone (NMP) and NMP based solvent (Solvent B). The characterization of the custom-made PCB determined that 47.2% of the copper was located on the surface of the PCB and 52.8% in the inner layers. The success of the solvent swelling pre-treatment is measured by the extent to which this 52.8% is unlocked for access by the lixiviant. The degree of metal liberation by the chemical pre-treatment method employed was determined by diagnostic column leaching using primarily samples of waste etchant from a local PCB manufacturing factory as well as synthetic etchant modelled after a typical waste etchant stream. Solvent swelling yielded good recoveries above 90%, with NMP solvent swelling at 150C achieving the highest copper recovery of the two solvents at 93.4%. It was found that the PCBs that did not undergo solvent swelling yielded recoveries mostly from the surface copper with a recovery of 50% from boards that had been soaked in sodium hydroxide for removal of the solder mask coating. A combination of both physical and chemical pretreatment by combining 6 pass shredding with solvent swelling yielded a copper recovery of 68.9% using Solvent B. This was comparable to 88.4% obtained from solvent swelling with the same solvent. Solvent swelling alone was found to be an effective method for liberating copper from the inner layers and combining swelling with mechanical shredding was found to yield lower copper recoveries as a result of the preg-robbing phenomenon. Three lixiviant systems were analyzed for performance, namely ammonium sulphate, waste etchant and synthetic etchant. Of the three, ammonium sulphate with initial copper concentration of 100 ppm was significantly outperformed in leaching rate by waste etchant and synthetic etchant which required shorter leaching times to recover the readily accessible surface copper, however waste etchant was found to have limitations of copper saturation leading to precipitation due to its high copper content.