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Communities in WIReDSpace
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- This community is for all faculties and schools' research outputs and publications by Wits academics and researchers.
- This community hosts traditional outputs such as published and unpublished research articles, conference papers, book chapters and other research outputs authored by Wits academics and researchers. Items in this collection are also mapped to relevant collections within the Faculties/Schools/Departments communities for more specific browsing and searching.
- This Community hosts a collection of electronic theses and dissertations (ETDs) submitted by doctoral and masters' students of Wits University.
- This community is for all faculties and schools' theses and dissertations by masters and doctoral students.
Recent Submissions
Prospects of gibbsite-rich laterite as a source of aluminosilicates in geopolymerisation
(University of the Witwatersrand, Johannesburg, 2024) Gilayeneh, Victor Saye; Nwaubani, Sunday; Otieno, Mike
Laterite, an iron-rich soil widely found in the tropical and subtropical regions of the world, has shown promise for the development of eco-friendly construction materials through geopolymerisation. However, this material varies greatly in composition based on location, prevailing climate conditions, and even in depth within a given lateritic profile. The top layer of most lateritic profiles is usually low in kaolinite but rich in aluminium or iron hydroxide minerals. Despite these variations, research on the use of laterite in geopolymerisation has predominantly focused on materials rich in kaolinite. Therefore, this study explores the potential of aluminium-rich laterite as a source of aluminosilicates in geopolymerisation. In this study, the reaction kinetics, setting times, flow behaviour, strength development, phase composition, and pore structure of geopolymer derived from aluminous laterite were examined. This study also considered both calcined and uncalcined laterite as well as the influence of calcium minerals, namely calcium carbonate (CaCO3) and Portland cement, which replaced 40% of the laterite. In addition, the influence of the laterite’s properties on the performance of the derived geopolymer was also examined. The flow behaviour of the paste was found to be influenced by the viscosity of the activating solution, while the setting times and heat of reaction varied according to the type of laterite and the presence of calcium carbonate or Portland cement, which reduced the setting times and accelerated the rate of heat liberation within the first hour of the isothermal calorimetry test. The geopolymer mix based on calcined laterite displayed the highest amount of heat liberated, while its uncalcined laterite counterpart showed the lowest. All mixes within the calcined laterite series exhibited higher compressive strength than those in the uncalcined series, but only the calcined laterite mixes containing calcium minerals achieved structural strength. The uncalcined laterite mixes experienced strength regressions, with samples of the uncalcined laterite mix containing calcium carbonate developing cracks and subsequently disintegrating. The phase assemblage, porosity and pore structure were also influenced by the type of laterite and the presence of calcium carbonate or Portland cement. However, the presence of calcium carbonate also led to severe efflorescence and subflorescence, which negatively impacted the porosity and structural integrity. Also, the dissolution of gibbsite initiated the development of unstable phases in the uncalcined laterite mixes within the geopolymer and hybrid categories. Conversely, in the absence of activators, especially sodium hydroxide, as demonstrated in the binary mix containing uncalcined laterite, the dissolution of gibbsite is inhibited, resulting in the formation of stable phases.
Improving bulk water pump station policies and operations in conditions of uncertain and changing demand
(University of the Witwatersrand, Johannesburg, 2024) Mudau, Thendo David
South Africa is facing growing and complex changes in water demand; furthermore, acute water scarcity challenges due to drought and degradation of surface water resources threaten its ability to manage the demands. Industrial and power generation sectors in some regions are plagued with water shortages, requiring inter-basin transfer schemes for bulk water transfer to these regions. The complexity in the water demand is further exacerbated when the demand that bulk water transfer systems are designed to manage varies from the demand projections. This has resulted in inefficient pumping operations and unnecessary costs, which are causing great concern as a result of the current water crisis and the increasing cost of electricity in South Africa. This was an investigation to find out how the increasing energy costs and inefficiencies due to uncertainties in demand could be mitigated in bulk water transfer schemes in South Africa. This was done through determination of the impact demand changes and uncertainties have on bulk water transfer pump stations’ adherence to the operational policy, performance, and costs. Approaches to reduce costs associated with the changes in the demand and improve the operational performance of the pump station were proposed. The Jericho pump station in the Mpumalanga province, South Africa, was used as a case study to assess the impact demand changes have on the pump station’s operation and control, as well as the operational energy costs. The results of the assessment showed that all these three aspects of the pump station had been negatively affected by the variability in the demand, particularly the energy costs with operational costs due to pumping operations during peak periods contributing to 33% of the estimated energy costs during the study period. Optimal pump scheduling and a capital investment in the form of a booster pump station to assist the Jericho pumping system and changes to the pump station control policy are proposed, and it is determined that they would ensure a 17.02% saving in annual energy costs. Furthermore, it is shown that operational costs due to pumping operations during peak Time- of-Use (TOU) periods are more than three times the standard and off-peak tariffs, and as such pumping operations during peak periods should be minimized. This research report showed the significance of optimal pump scheduling and how operational policies of bulk water transfer systems should continuously be reviewed and improved if required, especially with the ever-changing demands.
Using a hybrid adsorption-membrane filtration system to produce biologically stable drinking water
(University of the Witwatersrand, Johannesburg, 2024) Omalanga, Landry Sendango; Biyela , Precious; Simate, Geoffrey S.
The purpose of water treatment is to produce clean and safe drinking water, for consumers. Water quality, both during treatment and distribution, is greatly affected by the presence of natural organic matter (NOM). The presence of NOM affects the effectiveness of water treatment processes and sometimes increases the cost of water treatment and leads to operational problems. Furthermore, the presence of biodegradable organic matter (BOM), which is a fraction of NOM, can degrade water quality during distribution resulting in the loss of biological stability. The excessive presence of BOM can be addressed using advanced water treatment processes or by relying on systems which combine multiple water treatment processes to increase treatment efficiency. The main aim of this study was to evaluate the effectiveness of a hybrid adsorption- membrane filtration system in lowering the bacterial regrowth potential in water. Ready-made multi-walled carbon nanotubes (MWCNTs) were used as adsorbents in this study. MWCNTs were chosen because they exhibit high adsorption properties mainly because of their fibrous shape and external surface accessibility. MWCNTs have hydrophobic characteristics and a propensity to aggregate due to the presence of electrostatic interactions among them, therefore, functionalization of MWCNTs was required to improve their dispersion in the organic and inorganic solvents. A non-covalent functionalization process was employed using cetyltrimethylammonium bromide (CTAB) as a cationic surfactant to ameliorate the stability and dispersibility of MWCNTs in aqueous solution. The non-covalent functionalization was preferred to sustain the functionalities needed for BOM capture enhancement and environmental safety. Polysulfone (PSF) membranes were produced by phase inversion method using N, N- dimethylformamide as solvent for the removal of BOM from water. The phase inversion method was chosen in this study due to its simple processing, flexible production scales, and low cost. The MWCNTs and PSF membranes were characterized using microscopy techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), X ray diffraction (XRD), Raman spectroscopy, tensile strength test, and the hydrophilicity (contact angle) test. These techniques were selected because they enable the evaluation of the morphology, composition, physical characteristics, and dynamic behavior of nanostructured materials. iv Batch adsorption experiments were employed to investigate the adsorption properties of functionalized MWCNTs for BOM removal. Four different concentrations of functionalized MWCNTs were tested to determine the ideal conditions for the adsorption of two forms of BOM; assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC), from water. The concentrations of functionalized MWCNTs used were 4, 8, 12, and 16 mg in 100 mL of BOM solution. Furthermore, the cross-flow filtration mode, also known as tangential flow filtration, was used to separate the remaining BOM in water by passing water along the surface of the NF membrane using pressure difference. Cross-flow filtration was chosen because it removes the buildup from the surface of the membrane and provides the benefit of an improved membrane lifespan by helping to prevent irreversible fouling. A mathematical model of membrane filtration process in continuous system was also developed to better understand the correlations between the different variables of the membrane filtration process such as the inlet (feed) concentration (Cin) and flow rate (Qin), and the outlet (retentate) concentration (Cout) and flow rate (Qout), and the permeate concentration Cp. Results obtained after the functionalization process of MWCNTs showed an improvement in their stability and dispersibility in aqueous solution. The characterization of both MWCNTs and PSF membranes showed some interesting features. For example, morphological and structural studies show that MWCNTs possess fibrous shapes with a high aspect ratio, and a hollow structure with an inner diameter. The finger-like structures found on the surfaces of PSF membranes play a crucial role in their adsorption capabilities. These structures, which vary in pore size, contribute to the overall capacity of the membranes to absorb BOM from water. During adsorption experiments, it was observed that the removal of BOM from water increased with an increase in the adsorbent (functionalized MWCNTs) concentration. This is likely due to high concentration gradient which acts as a driving force to overcome resistances to mass transfer of dye ions between the aqueous phase and the solid phase. However, the maximum removal of both AOC and BDOC was recorded at a concentration of functionalized MWCNTs of 12 mg, at a contact time of 4 hours and at an agitation speed of 180 rpm. The PSF membrane produced by phase inversion method demonstrated the highest flux of 0.0091 ml/cm2.min at room temperature (25°C) and after a filtration time of 90 minutes. The selectivity and permeate flux were increased with forward flushing and backwashing processes of the PSF membranes because it flushes out accumulated debris and particles on the surface and inside the pores of the membranes. After using the hybrid adsorption-membrane v filtration system, BDOC concentrations dropped to an average of 65% of the initial raw water BDOC and the AOC concentrations dropped to approximately 80% of the initial raw water AOC. Outputs from the mathematical model demonstrated that the change in initial conditions (Cin and Qin) is responsible for the transient response (changes from one steady state to another) in these membranes. The adsorption and membrane nanofiltration hybrid system adopted in this study, effectively removed both AOC and BDOC from water, and can therefore be used to produce biologically stable drinking water. The outcome of this study could be the application of the combination of BOM targeting strategies and residual disinfection to better control bacterial regrowth in drinking water distribution systems (DWDSs). This in turn could help water utilities with meeting distribution systems, water quality guidelines, and protect public health
Recommendations for improved research(er) visibility to maximize impact
(University of the Witwatersrand, Johannesburg, 2025-07) Matizirofa, Lazarus Gallant; Wits Libraries - Open Scholarship & Research Visibility Unit
South Africa's move towards open science. The Draft National Open Science Policy, by the South African government with stakeholders in 2022, is an encouraging step forward as it aims to promote the practice of open, application ORCID in South Africa. Proposal for all publicly funded research to be disseminated via open-access platforms, including data-supporting publications – as mandated by most global funders.
A decision support framework for grading of civil engineering contractors and evaluation of infrastructure project performance
(University of the Witwatersrand, Johannesburg, 2024) Chiloane-Nwabueze, Salome
The construction sector plays a key role in the economic development of a country. The management of this sector is thus crucial in maximising the performance of the sector and the economy. The South African construction sector performance has some level of inefficiencies that could be improved to enhance the sector’s performance outputs. Therefore, the study aimed to develop a framework for grading civil engineering contractors and the evaluation of project performance. To achieve this, the study reviewed the literature on relevant key concepts and CIDB processes and systems. The government of South Africa has mandated the registration and grading of contractors to the Construction Industry Development Board (CIDB). The CIDB grade is a license for trading with the government. It certifies contractors who are graded as capable of delivering projects up to a pre-determined contract value in each class of work. Currently, the grading system is based on two key determinants, which are the contractor’s track record (i.e., completed projects) and available capital. Presently, a contractor grade does not denote the contractors’ capabilities. However, contractor grading and performance evaluation should be a multi-criteria decision-making process. A questionnaire was developed and distributed to the key participants in the industry to establish whether there is a need for enhancing the current registration, grading, and performance evaluation of contractors in the construction sector and to establish relevant criteria. Of the 149 respondents, the results of the study have revealed that most of the respondents (88.6%) agree that enhancing the current construction sector entry requirements could assist in improving contractors’ capabilities. Moreover, 90.6% of the respondents have indicated that enhancing the current construction sector entry requirements will assist in improving the performance outputs of the construction sector. A multicriteria decision-making methodology using the Analytical Hierarchy Process (AHP) based on seven main criteria with seventeen sub-criteria was carried out for iii grading of contractors and performance evaluation of contractors. Thereafter, using the results obtained from the AHP, an enhanced framework was developed for registering, grading, and evaluating the performance of contractors. Relevant scenarios and CIDB grading scenarios were applied to test and validate the developed framework. The construction sector entry requirements have been proposed by the study based on the literature reviewed and results of the state of practice survey to improve the sector performance. One way of improving the sector’s performance is through entry regulation. Organisations and some countries worldwide have some form of entry regulation to manage the construction sector. To minimise business failure and poor performance, new entrants need to have at least a recognised technical qualification in the aspiring field of work. This will ensure that new entrants have the relevant knowledge of the field in which they aspire to enter. Having entry regulations and improved grading and performance evaluation systems may assist in improving the sector’s performance. Proposals on the enhancements that may be considered by the CIDB are made which may assist in improving the industry’s performance.