School of Civil & Environmental Engineering (ETDs)

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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
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.
The removal of diclofenac, cypermethrin, ibuprofen and naproxen from wastewater using advanced membrane technology
(University of the Witwatersrand, Johannesburg, 2024) Ngwamba, Pamela Nadia; Biyela, Precious
In recent years, emerging contaminants (ECs) such as pharmaceuticals, personal care products, endocrine-disrupting compounds, industrial additives, pesticides, nanomaterials, surfactant retardants, surfactants, and their metabolites and transformation products have been widely detected in both wastewater and water bodies. These compounds originate from a diverse range of point and non-point sources, consistently introducing them into wastewater and directly and/or indirectly introducing them to water bodies and the broader environment. The ECs have garnered attention due to their potential environmental impact and potential to induce adverse health effects. Conventional wastewater treatment processes are often not adequate to efficiently remove these compounds, thus leading to residual concentrations entering aquatic ecosystems and eventually, reaching drinking water systems. Although extensive research has been done over the past decade, there is limited literature covering the effects of long-term exposure to ECs, especially their metabolites and by-products, their fate, and toxicity levels. Consequently, additional research is imperative to establish limits and facilitate the regulation of these ECs. Advanced treatment methods, including ozonation, activated carbon filters, and membranes, have proven effective in eliminating ECs from wastewater. It must be noted that the efficiency of these advanced processes varies significantly. Despite extensive testing of various technologies, limitations still exist. Although most of the advanced treatments are highly effective, none of them have the ability to remove a mixture of ECs effectively. This variation is attributed to the nature of the compounds (e.g., hydrophobicity/hydrophilicity and solubility) and operational parameters like temperature, hydraulic retention time, and solids retention time. Nanocomposite membranes have been identified as a viable technology for the removal of ECs from wastewater due to their unique properties and enhanced performance when compared to conventional membranes. They are highly selective and efficient, additionally, they can be designed to specifically remove ECs such as pharmaceuticals, pesticides, and endocrine disruptors. Furthermore, they show greater antifouling properties, reducing the accumulation of contaminants on the membrane surface and extending the lifespan of the membrane, thereby lowering maintenance costs and improving operational efficiency. The aims and objectives of the research report were to compile a comprehensive literature review that highlights the importance of removing ECs from the environment; prepare and characterise four different flat-sheet membranes using polyvinylidene fluoride (PVDF) and imidazolium-based polymeric ionic liquids (PILs) and testing the membranes to determine the retention time and effectiveness of the prepared membranes in removing four different iv pharmaceutical products which are diclofenac, cypermethrin, ibuprofen, and naproxen. The hypothesis assumed that the imidazolium-based PILS/PVDF flat sheet membranes would yield a removal efficiency greater than 90%. This expectation was achieved, and all the membranes achieved a removal efficiency greater than 90%. Various studies have shown that nanocomposite membranes yield high removal rates. The synthesised membranes had better features than PVDF alone. The PVDF alone was found to have the largest pore size and the least retention time, although the removal efficiency was high. The blended membranes lead to higher porosity and retention times. They had smaller pore sizes as compared to plain PVDF; hence, the retention time was increasing. The higher the concentration of the imidazolium, the lower the contact angle measured; this is an indication of a more hydrophilic membrane surface. Hydrophilic membranes are less prone to fouling. The method investigated in this report is simple and can be easily reproduced. Based on the findings of this research report, the methods employed are precise, accurate, highly sensitive, and rapid.
Determining the parameters for the sizing of sediment traps in the city of Johannesburg
(University of the Witwatersrand, Johannesburg, 2024) Raliengoane, Mankoe Francis; Fitchett, Anne
Urban land practices usually involve soil compaction and vegetation removal as cities expand and grow. This has led to increased flood peak flows and high stormwater runoff volumes associated with sediments, nutrients and other pollutants that load downstream water resources. To address these issues, there has been a growth of practices involving Sustainable Drainage Systems (SuDS) for managing stormwater runoff quantity and quality from urban areas. For example, this involves the application of attenuation ponds, and wetlands which temporarily store urban stormwater runoff, thereby reducing the sediment loads, pollutants, and release of peak flows to the downstream water resources at flow rates that mimic the pre-development flow patterns. This practice is gaining momentum in South African urban areas, which are supported by the policies and legislation set up by local authorities to address stormwater management. However, these stormwater application practices often do not perform according to their design capacities because they get filled with sediments and their effectiveness in attenuating peak flows is reduced. Therefore, it is important to reduce sediments coming into these structures by applying sediment traps and basins located at the head of such structures. The sediment trap’s main function is to slow down the stormwater runoff and help in the reduction of sediments before stormwater runoff is discharged out of the construction site and other disturbed areas. The City of Johannesburg Stormwater Management By-laws and Stormwater Design Manual have limited information for the management of sediment using sediment traps and basins and which parameters need to be considered when sizing sediment traps. Therefore, the main aim of the current research was to determine the parameters that should be considered when sizing sediment traps specifically for the city of Johannesburg. The following parameters: design rainfall, daily rainfall, catchment area, evaporation, land cover and land use, percentage of permeable and impermeable areas, topographical data, peak flow, runoff volume, catchment topography, soil types and infiltration characteristics, sediment particle size distribution, sediment settling velocity, sediment loading rate/yield were modelled through Personal Computer Stormwater Management Model (PCSWMM), ArcSWAT ArcGIS, and Excel Spreadsheet Models. Further, the sensitivity analysis was undertaken using different values of imperviousness and infiltration rates while observing peak flow and runoff volume changes in PCSWMM outputs. Modelling in PCSWMM showed that peak flows and runoff volumes increased due to an increase in the values of the imperviousness used. However, the range of infiltration rates for the soils in both sub- catchments S22 and S23 did not change the peak flows and runoff volumes. Though it was not the scope of the current study, it was observed that higher infiltration rates than the ones that were determined from the sub-catchments S22 and S23 indeed reduced peak flows and runoff volumes. On the other hand, particle settling velocity showed that gravel particles took a short time to settle and required a smaller sediment trap iii storage capacity. In comparison, silt particles took longer to settle and required a larger sediment trap storage capacity. Lastly, sediment yield from both sub-catchments S22 and S23 showed that sediment yield is driven by rainfall, whereby months with high rainfall had higher sediment yield than the months with low rainfall. It is therefore, concluded that the following parameters: design rainfall, daily rainfall, evaporation, land cover and land use, percentage of permeable and impermeable areas, topographical data, contributing catchment area, peak flow, runoff volume, catchment topography, soil types and infiltration characteristics, sediment particle size distribution, sediment settling velocity, sediment loading yield should be considered by the engineers, designers and planners when sizing sediment traps in the City of Johannesburg and possibly in other places as well.
The impact of incorrectly sized bulk meters on water consumption and municipal revenue
(University of the Witwatersrand, Johannesburg, 2024) Rabé, Magdeleen; Ilemobade, A.
South Africa is a water-scarce country, characterised by lower-than-average rainfall and high water consumption rates, with Non-Revenue Water increasing despite water conservation efforts. Literature shows that bulk water meters are often incorrectly sized, increasing Apparent Losses from metering inaccuracies, resulting in revenue loss and negating the municipality’s water conservation and water demand management initiatives. This study investigates the impact of incorrectly sized bulk water meters (sized 40mm – 150mm installed at non-residential and multi-residential facilities) on municipal revenue by analysing flow logging data and metered consumption characteristics of 42 users. The methodology combines flow logging to analyse actual water consumption characteristics, assessment of meter operating flow ranges for optimal sizing, calculation of weighted accuracy for Apparent Loss estimation, and literature review on meter sizing and alternatives to consider regarding fire demand requirements. Highlights from this study are (a) the consumer profiling findings underscore the importance of aligning meter size with consumer water use patterns: consumption below the meter’s starting flow is observed at 50% of the stands analysed in the dataset, indicating over-sized meters; (b) 57% of the stands had on-site leakage, occurring at low flow rates where meters are most inaccurate; (c) two examples demonstrate the impact of incorporating fire demand, resulting in meter size changes from a 15mm to 100mm, and a 25mm to 150mm, respectively; (d) resizing meters for 35 stands is estimated to result in an additional municipal revenue gain of R636,876.92 within one year. Overall, the study highlights the importance of accurate meter sizing for reducing Non-Revenue Water, improving revenue generation, and enhancing water conservation efforts.
Assessment of in-service durability performance of natural draft cooling towers in a petrochemical environment
(University of the Witwatersrand, Johannesburg, 2024) Shaw, Kyle Lloyd; Otieno, Mike
Effective temperature control is an important operation requirement in petrochemical processes, where Cooling Towers (CT) play a key role in efficiently lowering water temperature for reuse in various chemical processes. Natural draft cooling towers function as heat extraction systems, dissipating thermal energy from hot water into the atmosphere through cold air. However, many reinforced concrete cooling towers have exhibited signs of deterioration over time, such as cracking, corrosion, and structural misalignment, posing the risk of structural failure. To address these issues, structural condition assessment programs, aiming to inspect, repair, and monitor cooling towers to prevent structural collapse are of significant importance. The focus of this study investigates the durability of natural draft cooling towers in an aggressive petrochemical environment. With a focus on Sasol Secunda Natural Draft Cooling Towers, the research aims to identify and characterize the various concrete deterioration mechanisms, quantify durability parameters, and explore mitigation measures for both new and existing cooling towers. Concrete deterioration is a significant concern in structures exposed to harsh environments, affecting their global stability and service life. The study examines the role of cover concrete quality in resisting corrosive agents and assesses durability using South Africa's three durability index (DI) tests, including water sorptivity, chloride conductivity, and oxygen permeability. The study comprised of on-site assessments and laboratory testing methods to determine the durability performance of cooling towers. The approach includes the three durability index tests. On-site assessments include visual inspections and non-destructive testing (NDT) near areas displaying signs of deterioration. The significance of this research relies on the operational efficiency of cooling towers in petrochemical plants, their vulnerability to harsh conditions, and the need for durability design considerations at Front End Loading (FEL) engineering and planning. It aims to shift from prescriptive to performance-based design approaches and provide insights for maintenance and mitigation strategies. This study contributes to the knowledge of concrete durability in challenging environments, aiming to enhance the longevity and performance of critical industrial infrastructure, particularly natural draft cooling towers.
Unlocking Sustainability: An Exploration of the Potential for Food Waste Conversion into Energy and Value-Added Products for Effective Landfill Diversion in South Africa
(University of the Witwatersrand, Johannesburg, 2024) Pereira, Gabriel Philip Alves; Fitchett, Anne
This research report examines the potential for transforming food waste into energy and value-added products as a sustainable strategy for diverting waste from landfills in South Africa. The study uses a social cost-benefit framework to evaluate various waste conversion technologies, including anaerobic digestion, aerobic composting, vermicomposting, and black soldier fly larvae, within South Africa's unique socio- economic and environmental landscape. The study combines quantitative waste composition analyses with technology evaluations, revealing significant landfilling costs and underscoring the economic and environmental urgency of strategic food waste diversion. Highlighting gate fees' critical role, the findings advocate adjusting these fees to incentivise sustainable waste management practices. Notably, Black Soldier Fly larvae and Vermicomposting technologies emerge as dual-benefit strategies for waste reduction and resource recovery. The report calls for policy and infrastructure advancements to enable the broad adoption of these technologies, emphasising their importance in achieving sustainability and economic objectives.
The Impact of South Africa’s Response to Informal Settlements and Affordable Housing Development when compared to the responses adopted in Brazil and India
(University of the Witwatersrand, Johannesburg, 2024) Mlotsa, Cebile; Biyela, Precious
In South Africa, informal settlements are prevalent in all the major urban centers, including some long-established informal settlements, such as ones within Alexandria township in the City of Johannesburg, Nyanga in the City of Cape Town and Kennedy Road in the City of eThekwini. New informal settlements are continuing to develop across South Africa’s urban centers. Various policies and interventions have been implemented to address this phenomena. This study aimed to investigate the impact and effectiveness of South Africa’s policies and interventions on informal settlements and compared them to policies and interventions of India Brazil. The study begins with a literature review of the policies and strategies of the three countries alongside best practices recommended by international organizations such as UN-Habitat and the World Bank. The effectiveness of the policies was assessed, and the general issues that affect informal settlements globally were identified. Research questions were formulated based on the literature review to gain further insights into South Africa's response strategies. Semi-structured Interviews were conducted with three professionals working in organizations addressing informal settlements across different provinces, focusing on current strategies, their impact and effectiveness, and potential improvements. A field visit to Mahlakong informal settlement in Limpopo was also carried out which included interviews with two residents to understand challenges and interventions underway to address them. The study found some progressive policies and strategies underway in South Africa, such as the strong emphasis on participation and approval by residents of informal settlements when interventions are carried out, and incremental construction of infrastructure in informal settlements. The study also identified areas that if addressed can improve South Africa’s response to informal settlements, such as recognizing multi-storey inner city buildings as informal settlements, encouraging private developers to invest in affordable housing development, and diversifying tenure legalization option.

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