Browsing by Subject "civil engineering"

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    Open Access
    A framework for the evaluation of the structural safety of existing concrete gravity dams
    (2019) Dankers, Clyde Lleland; Moyo, Pilate
    Addressing the aging and deterioration of dams is a relatively new challenge in the dam engineering field in South Africa. The average life expectancy of a dam is approximately 50 years, but they can normally be used for much longer periods than this. Maintenance and rehabilitation are vital to ensure that they achieve their design service lives and for the extension of their service lives. The rehabilitation of dams to extend their service lives and/or to ensure that they comply with modern stability criteria can be an extremely lengthy and costly exercise. It would therefore be valuable to do some research into the process of evaluating the structural safety of dams. The focus of this research study is specifically on the evaluation of the structural safety of large concrete gravity dams. The purpose of the research is to investigate the most commonly used and accepted methods to evaluate the structural safety of concrete gravity dams and develop a framework that can be used for the evaluation of the structural safety of concrete gravity dams. For the purpose of this research study, an existing large concrete gravity dam was evaluated as a case study. The dam is approximately 93 years old and provides water to the nearby local municipality for domestic purposes. According to the first and second Dam Safety Evaluation (DSE) reports the dam does not comply with modern stability criteria for concrete gravity dams. The findings of these dam safety evaluation reports led to the dam being labelled as essentially “unsafe” in the case of the occurrence of a large flood. Typically, this would mean that the dam must be rehabilitated to improve its safety. However, some engineers believe that this is not the case and that major rehabilitation is not necessary. In this research study a framework for the evaluation of the structural safety of existing concrete gravity dams was developed based on lessons learnt from the literature review and the case study. This recommended framework can be useful as a guide for future safety evaluations of existing concrete gravity dams. The potential benefits of using this recommended framework includes avoiding unnecessary rehabilitation work, as well as significant time and cost savings.
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    A review on the efficiency of different supplementary cementitious materials as a partial replacement for Portland cement in concrete
    (2022) Taiwo, Ridwan A; Alexander, Mark; Leo, Emmanuel
    The effects of global warming and climate change are important and have attracted the attention of many researchers. Global warming is a result of the presence of increasing amounts of greenhouse gases in the atmosphere. Carbon dioxide, which is largely emitted into the atmosphere during the manufacture of cement clinker, is one of the greenhouse gases. Hence, researchers have explored the use of some waste materials and naturally occurring minerals as a partial replacement for cement in concrete. These materials are often referred to as supplementary cementitious materials (SCMs). Apart from the potential benefits of these SCMs for the properties of concrete, they also bring about a reduction in the amount of waste in landfill sites, as these wastes can cause land, water, and air pollution, thereby posing threats to human health. However, despite the potential benefits of SCMs in the cement and construction industry, they have not been fully utilized especially in developing countries in Africa. This may be due to low awareness of the potential benefits of SCMs among the stakeholders in the construction industry, and also limited availability. Nevertheless, due to extensive research into the usability of different materials as SCM, various materials are available in the construction market as binder systems. Thus, selecting the appropriate binder system to get the desired result for a particular concrete might be difficult for construction personnel. Hence, this study presents a review of the effects of various SCMs on the mechanical and durability properties of concrete. Six SCMs are reviewed. These SCMs include fly ash, silica fume, which are industry by-products; metakaolin, limestone calcined clay, which are naturally occurring minerals; rice husk ash, which is an agricultural waste material; and limestone-fly ash, which is a combination of an industrial by-product and a naturally occurring material. Firstly, an overview of the mechanical and durability properties of concrete is presented. This includes the presentation of general factors affecting the mechanical and durability properties of concrete. Subsequently, the effect of the various SCMs on mechanical (such as strength, elastic modulus, creep, and shrinkage) and durability properties (freeze-thaw, acid attack, sulphate attack, chloride-induced corrosion, carbonation-induced corrosion, and alkali-silica reaction) of concrete are presented. The review shows that the inclusion of appropriate dosage of these SCMs in concrete or mortar enhances their properties. Certain limitations of these SCMs are also discussed. This study also identifies areas of further research in relation to the properties of concrete produced with the SCMs.
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    An investigation of the pollution contribution of catchments surrounding the Knysna Estuary, with implications for stormwater management
    (2019) Harvey, Alice Lindiwe; Armitage, Neil
    The Knysna Estuary is ranked highest in South Africa for conservation importance and is a haven for endemic marine species. The ecosystem services provided by the estuary include significant biodiversity value and amenity value for residents and tourists. The economy of Knysna is reliant on tourism, which in turn is dependent on ecosystem services. The health of the Knysna Estuary is currently threatened by poor water quality. If the water pollution can be addressed, ecosystems can be protected and significant social and economic costs of environmental degradation can be avoided. The pollution contribution of runoff from catchments to the estuary is imperfectly understood. Mitigation measures designed based on imperfect knowledge may be inappropriate or fail to address the pollution concerns. A poor understanding of the world views of stakeholders could lead to the design of socially unacceptable solutions. This study aimed to improve knowledge of the catchments surrounding the estuary, and stakeholders within these areas, to inform solutions. Surface water sampling and testing and analysis of national and municipal databases were used to assess the pollutant contribution of catchment runoff. High nutrient concentrations were conducive to eutrophic or hypertrophic conditions at most sites. Total Inorganic Nitrogen (TIN) concentrations exceeded 5 mg/ℓ at 60% of the sites. Ammonium concentrations made up a disproportionate fraction of the TIN readings, with most fractions exceeding 20%, and many exceeding 70%. Student t tests indicated that TIN concentrations at the Bongani River were significantly higher than historical data. Total Suspended Solid (TSS) concentrations at some sites were lower than historical data. E. coli spikes of over 30,000 CFU/100 mℓ were measured at nine sites in October 2018. The Bongani River catchment was identified as a significant source of elevated nutrients and E. coli. Elevated nutrients and TSS were also recorded in the effluent from the Knysna Waste Water Treatment Works (WWTW) with mean values of 36 and 24 mg/ℓ for Total Ammonia Nitrogen (TAN) and TSS respectively. A Kendall correlation analysis indicated significant positive trends in TIN and TAN, and negative trends in Soluble Reactive Phosphorus. A hydrological model was built for the Bongani Catchment. Data input to the model was obtained from site visits, literature, and a desktop study of available catchment information. The model was calibrated against observed data at two water level monitoring points. The model was used to estimate pollutant loads for large storms, and can be used to inform possible pollution mitigation strategies. Further water management challenges and pollution sources were identified through stakeholder interviews. A decision support tool was used to understand how stakeholder world views and values can inform the selection of socially acceptable solutions. Stakeholder interviews identified sewage leaks as a water management concern. This corresponds well with the elevated nutrient and E. coli concentrations measured in many catchments. Other identified pollutants were litter and TSS.
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    Open Access
    Assessing the effectiveness of reduced parking requirements in facilitating transit-oriented development: a case study of “PT areas” in Cape Town
    (2022) Sasman, Nicola Anne; Behrens, Roger
    There has been a paradigm shift in thinking about parking provision, as government policy has favoured public transport and non-motorised transport (NMT), to limit and manage its supply in cities. This has been informed by sustainability principles, the understanding of “transit-oriented development” (TOD), and the “triple access” system thinking. This thinking has been applied in various ways in different cities, and its application in the literature is explored here, including case study lessons. This dissertation aims to answer the question: Recognising the current car-centric nature of the modern city (both in the Global North and South) on the one hand, and the sustainability and social equity imperatives on the other, can reduced parking provision and improved parking management be used to support the restructuring of the city over time, in support of public transport and of transit-oriented development? Cape Town is used as a case study, by assessing the effectiveness of the implementation of a tool adopted by the City of Cape Town, called “public transport areas” (“PT areas”), which allows reduced off-street parking supply in centres which are well-served by public transport. The research quantifies the number of parking bays not supplied as a result of the uptake of this PT offering, and locates this geographically. This was undertaken in 2 phases: the municipality conducted a pilot study of a small sample of centres, led by the author. The lessons learnt from this then informed the methodology for the full analysis, with the City providing the data to the author for analysis in her capacity as a student. The results of the quantitative research show that there was a significant nett saving of 9 662 parking bays in all centres, resulting in the freeing up of at least 18ha of developable land for more productive use. This does not include the additional gross lettable area potential created by reduced parking requirements, specific to each erf and land use. The research concludes that a tool such as the “PT offering” can have an impact on land use intensification, but its effectiveness is dampened if a good public transport system is not in place to enable positive travel behaviour change. It recommends that the moment is right, due to changing behaviour as a result of the COVID-19 pandemic, for authorities to take actions to reduce parking demand and supply, and related management, in support of more people- and planet-orientated cities.civil
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    Assessment of development form and its impact on the modal split and trip generation for low-income commercial developments
    (2018) Botha, Marlyn Lloyd; Zuidgeest, Marcus
    This topic of research was motivated through my extensive interaction in the development field and a key element which was recognized with numerous development assessments within the City of Cape Town, was the fact that our current legislation or standards applied in South Africa do not accurately inform commercial developments within low-income areas. It was observed that the South African standards and policies rely heavily on international standards which focus on private vehicle movement and networks planning which is geared for mobility, whereas South Africa and in particular metropolitan Cape Town has unique characteristic due to the City Planning Structure which was shaped by a flawed political system. The objective of this dissertation is therefore firstly to assess the impact which the built environment (TOD and TND) has on the modal split and trip generation for low income commercial developments, secondary to draw a comparison between the actual operation of low income developments and the accepted trip generation rates used in South Africa, thirdly, to assess the unique characteristics of low income developments within a local context. With this problem statement in mind the aim of this dissertation is therefore to, firstly, to establish a better understanding of the modal split and trip generation for low income commercial developments, secondly, to establish a trip generation rate which is more compatible with developments within low-income communities; and lastly to establish the benefits which can be attained through appropriate development form implementation within the low-income. The literature review section of this dissertation will review academic literature as well as recent policy documents which investigate the relationship between the development form and the impact on traffic patterns, trip generation and modal splits of development. The literature review also establishes common trends and understandings when investigating/reviewing complex data of this nature. It is also the aim of the literature review to set a foundation for the site investigation and analysis process which will be undertaken as part of this dissertation. A critical aspect of this research was the site selection process as this has a direct bearing on the outcomes of the analysis and the accuracy of the results. It is therefore critical to note that the three sites selected for this research were selected based on stringent criteria. With the site selection approach it was a key aspect to keep as many of externalities or external factors constant (Ceteris Paribus) and in this way the results would emphasize the impact of the development form on the trip generation, traffic patterns and the modal split of these developments (if any). The data collection process was done using two distinct survey methods based on the level of technology available at the sites investigated. The first method used was data collection using recorded camera surveillance footage obtained from the centre management. The second method was a manual survey method done by individuals employed at the sites and this was used where electronic data was not available. The survey/data collection process was also broken up into 4 phases, of which the first of these processes was a pilot survey which was undertaken at one of the sites earmarked for the investigation. The aim of this pilot survey was to identify the any shortcoming in the data collection process and it was at this point where all adjustments could be made to eliminate any future errors in the data set. The pilot survey also indicated whether or not the relevant data could be extracted from the camera angles available. The second critical phase of the survey process was that a full week survey was done, this was done to establish the critical peak day which would eventually be used to calculate the critical peak hour for the centres analysed as well as the peak hour factors. The aim of establishing a peak day for the various centres was to eliminate unnecessary data collection and cost, also to focus the study on peak data which will later be compared against prescribed peak rates for these types of developments. Once the peak day was established, phase three was to undertake the final surveys for each individual site and phase four was implemented in order to strengthen the outcomes of the data set, the approach of a repetitive assessment approach (three separate surveys at each site) was used. Based on the weekly peak analysis done, it is evident that the Saturday peak is to be considered the critical/maximum peak for the week. A further conclusion of the weekly peak analysis is that the weekend (Saturday and Sunday) traffic pattern differs from the weekday pattern as it is structured around a single critical morning to midday peak, with the no secondary peaks encountered as with the weekday traffic patterns. The analysis done indicates that TND development principals have a greater impact on the modal split (or preferred mode choice) than TOD as the number of pedestrian trips far exceeds the number of public transport trips generated. This trend was conclusive for all 3 sites used as part of the investigation. A firm conclusion can be drawn from modal split analysis when assessing these developments. When the development form is adequately structured around a pedestrian movement and accessibility (TND type developments), one of the main benefits are increased pedestrian traffic. The outcomes of the modal split analysis also show a positive trend when using the TOD design approach, with the benefits of increased public transport trips. When assessing all the results achieved in the trip generation comparative analysis, it can be concluded that the COTO rate is an accurate prediction for low income shopping centre developments which are built along a transport corridor (TOD design element) and which are pedestrian friendly developments (TND design element). The NDoT calculated rates are not considered appropriate for these developments as they are way in excess of the actual rates recorded.
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    Open Access
    Case study analysis of integrated public transport networks in five South African cities
    (2019) Manuel, Mikhail; Behrens, Roger
    In 2007, 13 South African cities embarked on implementing Integrated Public Transport Networks (IPTN’s) guided by the Public Transport Strategy and Action Plan (PTSAP) published by the National Department of Transport (NDoT). The PTSAP sought to reform public transport industries across South Africa by 2020 to ward off increasing congestion, passenger dissatisfaction with overcrowding, long travel times, high travel costs, and safety concerns. Of the 13 cities, Nelson Mandela Bay Metropolitan Municipality (NMBM), City of Tshwane (CoT), City of Johannesburg (CoJ), City of Cape Town (CoCT), and George Local Municipality (GLM) had progressed the furthest by the end of 2017. However, all five Cities had experienced delays in achieving their IPTN project objectives. This dissertation investigates the underlying factors causing the delays. The research was guided by a framework of analysis developed by three core questions - the impact of the minibus-taxi industry negotiations, the impact of government’s capacity to implement, and the impact of South Africa’s urban form. The literature review begins with the fundamentals of reform of the three dimensions of the public transport industry: service characteristics, operator business structure, and competition. It then continues with a review of the history of attempts at reform in the minibus-taxi industry and bus industry, and a breakdown of the PTSAP. The literature review concludes with the fundamentals of mass transit use with an emphasis on the influence of urban form. Data were collected from media sources, government and academic publications, and qualitative semi-structured face-to-face interviews. The data were used to evaluate each IPTN system’s outcome and develop a chronology of each project’s implementation. In NMBM, Libhongolethu was delayed due to the strained relationship between the local minibus-taxi industry and the NMBM, and the alleged mismanagement of resources. It was concluded that alack of political will and a lack of capacity-to-implement were the underlying factors. In CoT, A Re Yeng was delayed due to difficulty in developing adequate IPTN plans, and lack of foresight on the long-term impact of political decisions. It was concluded that weak planning capacity and poor political decision making were the underlying factors. In CoJ, Rea Vaya benefitted from the external pressure of hosting the World Cup, as well as strong political leadership in the minibus-taxi industry and CoJ during Phase 1A. However, the project still grappled with animosity between local minibus-taxi associations, the influence of national mother- bodies on local associations, distrust of government within the minibus-taxi industry, industry transformation compensation benchmarking, and uncertainty following the 2016 local government elections. Therefore, it was concluded that politics within the minibus-taxi industry and government were the underlying factors. In CoCT, MyCiTi was delayed due to the inappropriate nature of BRT for Cape Town’s spatial form, higher than expected industry transition costs, budgetary cycles of government financial planning, and the moderation of services to improve financial sustainability. Therefore, it was concluded that an overall inappropriate solution to the public transport problem, prudent political leadership and adequate capacity-to-implement within the CoCT were the underlying factors. In GLM, GoGeorge was delayed because of inappropriate design restrictions imposed by the NDoT and changes in political leadership in quick succession at a vital stage of the project. Therefore, it was concluded that a lack of capacity within the NDoT and leadership instability were the underlying factors. In conclusion, all three core questions were found to be determinants of success or delay, while in addition, political will was also found to be a fundamental factor to success or delay. Analysis of the case-specific causes of delay found thatall cases were ultimately delayed due to five fundamental factors: an inappropriately ambitious implementation timeframe, the incongruency between gold-standard BRT design and South African urban form, the difficulty of overcoming the complexity of trust between the minibus-taxi industry and government, political will, and government’s lack ofcapacity to implementa reform programme as complex as the PTSAP.
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    Challenges and Opportunities for Sustainable Urban Mobility (Non-Motorised Transport): A Case Study of Eveline Street in the Windhoek Municipality, Namibia
    (2019) Kamundu, Erwin; Vanderschuren, Marianne
    Windhoek has several inherited structural challenges that include a trend of decreasing densities of urban settlements, along with social inequalities and highly skewed levels of access and mobility. The most vulnerable members of the society in Windhoek currently carry the majority of the transportation costs and inconveniences. Non-Motorised Transport (NMT) in Eveline Street forms a significant part of the daily activity of people as they commute to and from public transport stops and stations, places of work, places of education and walking to water collection points and means of creating a living. The implementation of Non-Motorised Transport (NMT) facilities as a manner of supporting NMT trips has been largely neglected in Eveline Street thus, exposing NMT users to road accidents. Non-Motorised Transport (NMT) is a core aspect in the development of a sustainable transport system for the City of Windhoek. Its importance derives from the high percentage of persons in Windhoek who depends on NMT, as well as its economic and ecological efficiency compared to Motorised Transport (MT) on distances up to approximately 5 km. Approximately 20% of Windhoek's households can afford to own a car, therefore roads alone are not enough to secure social sustainability and only worsens already existing income inequality (Araes, 2007). Non-Motorised Transport (NMT) supplements public transport, contributes to lively urban quarters and is an integral part of the transport system of Windhoek. Low income households in Windhoek spend up to one quarter (25%) of their income on transport (Zwicky et al., 2013). Non-Motorised Transport (NMT) users are the most vulnerable traffic-group, often involved in severe accidents and there is a need for special attention and provision to enable, strengthen and develop NMT as a proper and feasible mode of transport in Windhoek. Non-Motorised Transport (NMT) has an important role to play in greening the economy in the context of providing and promoting more sustainable transport options, forming part of more cost-effective solutions in establishing a sustainable transport system to improve economic progression for the residents of Windhoek. The main motivating reason for this research was to investigate the current opportunities and challenges being experienced that affects the promotion of the Non-Motorised Transport (NMT) in providing a sustainable urban mobility within Eveline Street in the Windhoek Municipal area, Namibia. This study further seeks to examine the potential and sustainability for effective transportation planning for Non-Motorised Transport (NMT) and its effects in the reduction of Motorised Transport (MT) congestion in the area. In Windhoek, the main types of Non-Motorised Transport (NMT) users are pedestrians (majority type) and cyclists (minority type). The research paper aims to come up with the conclusive proposals and possible intervention measures that will help in the provision and management of Non-Motorised Transport (NMT) infrastructure to ensure a sustainable urban transport system. Thus, helping Windhoek municipality, Namibian government, stakeholders and practitioners to make better informed decisions when addressing the transport challenges of NMT users in urban areas. The scope of the research was limited to Non-Motorised Transport (NMT), more specifically, walking and cycling as a mode of transport in the infamous Eveline Street in the high density suburb of Greenwell Matongo in the area of Katutura in the greater Windhoek municipality. Eveline Street being used as a case study to understand what potential value NMT trips could be for Windhoek. There are various benefits to Non-Motorised Transport (NMT) as a mode of transport. Safety benefits of successful NMT facilities include lower risk of road collisions, injuries and fatalities, while there are also several health benefits of NMT trips, which include lowered levels of stress, obesity and other Non-Communicable Diseases (NCDs). NonMotorised Transport (NMT), as a mode of transport, is one of the most sustainable modes of transport, as it does not rely on fuel and, is one of the cleanest modes of transportation. Furthermore, Non-Motorised Transport (NMT) trips have various socio-economic benefits that help to address equality concerns, which are highly relevant for pedestrians in Windhoek. An example, of how improved NMT trips could address equality issues, would be increasing the mobility and accessibility of vulnerable members of society. This can be for socio-economic reasons or physical and mental abilities that influence the individual's ability to commute. The research methodology involved the review of literature, primary and secondary data collection, validation and analysis, interpretation and subsequent recommendations to address urban mobility challenges and policy recommendations to promote NMT for Windhoek Municipality. The methodology comprises surveys, traffic counts; direct observation and behavioral studies. The tools used included questionnaires, tally sheets, walkability audit tool, maps and photographs. The secondary data was obtained mainly through the literature review of the existing work by academic and researchers on NMT, land use and transport planning, institutional setup and policy administration. Other sources of secondary data included universities, libraries, internet, GIZ Studies, MVA Namibia, SUTMP, Local authorities records, Namibia Statistics Agency, and Government documents on transport and environment. The data was collected by administering roadside questionnaire, direct observations of behavior and the walkability of the area, interviewing key informants, photographs and Global Positioning Systems (GPS) locations.
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    Open Access
    Comparing the Metcalf and Eddy and UCT steady state guidelines for sizing of biological nutrient removal activated sludge wastewater treatment plants
    (2020) Murphy, Katelyn; Ekama, George A; Ikumi, David
    This dissertation aims to provide both a qualitative and quantitative comparison of two steady state activated sludge (AS) design guidelines - the University of Cape Town (UCT) guideline used in South Africa and the Metcalf and Eddy (M&E) guideline used in North America and other parts of the world. It looks at the key similarities and differences between the two steady state AS design guidelines and how, under dynamic conditions, a system that is sized using a particular guideline (i) compares to its steady state results and (ii) performs under these dynamic conditions. In order to achieve the aims and objectives of this dissertation, an AS steady state model was created in a Microsoft Excel spreadsheet for the UCT guideline and M&E guideline respectively, and the models were analysed in terms of the key similarities and differences in the design guidelines in terms of inputs, equations, approaches and assumptions used. The results produced from each model were also analysed by setting the influent wastewater characteristics the same for each guideline and then analysing the results. The systems that were sized using the steady state AS models were then input into an AS system dynamic simulation software program, UCTOLD (which predicts virtually identical results as ASM1), together with a full set of diurnal influent data, to predict the behaviour of the system under steady state and dynamic conditions and compare the steady state predictions to those calculated in the steady state models and assess how the steady state model sized systems perform under dynamic loading conditions. The results of the analyses found that the two guidelines are similar in terms of organic material removal, nitrification and the sizing of the secondary settling tank, but differ significantly in the sizing of the anoxic reactor to achieve a certain nitrate removal. The key findings are: (1) Both UCT and M&E guidelines close the COD and N flux balances within 1%. (2) For organics removal only, at the same SRT, sludge production and oxygen demand are about 5% higher and lower respectively for the M&E guideline than the UCT guideline. When a UCT and M&E sized fully aerobic system is simulated with ASM1, this difference is repeated. The UCT guideline results are closely correlated with the ASM1 results but the M&E results deviate from those of ASM1. These differences arise because the M&E guideline assigns different values to the kinetic, stoichiometric and temperature sensitivity constants. If these constants in the M&E guideline are assigned the same values as the UCT guideline, virtually identical results are obtained. (3) For nitrification under fully aerobic conditions, the M&E guideline calculates a slightly shorter minimum aerobic SRT for nitrification than the UCT guideline. Again, the M&E guideline assigns different values to the nitrification kinetic (μAm20, bA20), stoichiometric (YA, Kn20) and temperature sensitivity constants (θμAm, θbA, θKn) than the UCT guideline. The M&E guideline calculates the minimum sludge age for nitrification, Rsm, using a fixed maximum specific growth rate of nitrifiers at 20oC (μAm20) at 0.90 g/(g.d), and after correcting for temperature, DO concentration in the aerobic reactor and assigning a safety factor (Sf = 1.5), the minimum sludge age for nitrification is slightly shorter than for the UCT guideline for a selected maximum specific growth rate of nitrifiers at 20oC (μAm20) of 0.45 g/(g.d) and assigning Sf = 1.25. In the M&E guideline the mass of nitrifiers is added to the reactor MLSS concentration which increases the MLSS mass in the reactor by about 1-3%. This is not done in the UCT guideline to maintain the COD balance for organics removal. At the same SRT in a fully aerobic system (i.e. aerobic SRT = system SRT), the oxygen demand for nitrification is closely similar in the two guidelines. This is because the calculated concentrations of nitrate produced by nitrification (called nitrification capacity Nc in the UCT guideline) are closely similar – the difference in the sludge production of the two guideline make little difference to the N taken up for sludge production. (4) If fully aerobic nitrifying reactors sized with the M&E and UCT guidelines are simulated with ASM1 at the same SRT, the same differences as with organic removal are observed. Hence the main difference in the sizing for nitrification in fully aerobic reactors in the two guidelines is the shorter aerobic SRT for nitrification in the M&E guideline (as a result of the different nitrification kinetics and safety factors) than in the UCT guideline. (5) Significant differences between the two guidelines emerge when adding an anoxic reactor for denitrification, such as for the anoxic aerobic nitrification - denitrification (ND) Modified Ludzack-Ettinger (MLE) system. This is because (5.1) the nitrifiers are assumed to behave differently under anoxic conditions in the two guidelines and (5.2) the effective specific denitrification rates of the OHO biomass in the anoxic reactor are much higher in the M&E guideline than in the UCT guideline. (6) With regard to difference (5.1), in the UCT guideline, the nitrifiers are assumed to grow only in the aerobic reactor but die in both the anoxic and aerobic reactors. In the M&E guideline, the nitrifiers are assumed to die (and grow) only in the aerobic reactor, i.e. they neither grow nor die in the anoxic reactor. Hence in the M&E guideline, the MLE system is sized based on an aerobic SRT, which excludes the mass of sludge in the anoxic reactor as in (3) above, but in the UCT guideline the MLE system is sized based on a system SRT, which includes the mass of sludge in the anoxic reactor. (7) With regard to difference (5.2), the faster specific denitrification rate determined with the M&E guideline yield much smaller anoxic reactors by at least 50% to achieve the same nitrate removal. (8) The consequence of these two differences is that the system SRT of the MLE system determined with the UCT guideline is considerably longer than that determined with the M&E guideline leading to larger anoxic, aerobic and system reactor volumes. This difference widens as the influent TKN/COD concentration ratio increases, i.e. as the concentration of nitrate to be denitrified increases. (9) When simulating the UCT sized MLE systems (under steady state conditions) with ASM1, very similar reactor MLVSS and MLSS concentration, effluent ammonia and nitrate concentrations and total oxygen demands are obtained with ASM1 and the UCT guideline. This indicates that the denitrification kinetics of the UCT guideline are well aligned with ASM1. This is not the case when simulating with ASM1 M&E guideline sized MLE systems under steady state conditions – while the effluent ammonia concentration compares well, the effluent nitrate concentration is far higher (increases from 6 mgNO3-N/l to above 20 mgNO3-N/l). This indicates that even though the denitrification kinetics of the M&E guideline were derived in part from ASM1 simulations, the denitrification kinetics of the M&E guideline are very poorly aligned with ASM1. (10) When the fmanx,M&E of the denitrification MLE system in (9) is increased to fmanx,UCT of 0.318 (but keeping the SRT = SRTsys,M&E) and simulated with ASM1, the effluent nitrate concentrations reduce from around 20 mgNO3-N/ℓ to around 6 mgNO3-N/ℓ, which is aligned with the UCT guideline ASM1 results. (11) The enhanced biological phosphorus removal (EBPR) parts of the UCT and M&E guidelines were not compared. While the EBPR part of the UCT guideline is complete and accounts for the phosphorus accumulating organisms (PAO) and their polyphosphorus content in the VSS and TSS calculations, as well as the differences in the denitrification kinetics in NDEBPR system compared with ND systems, which aligns the UCT NDEBPR guideline with ASM2, this is not the case in the M&E guideline. Because there is insufficient information in the M&E guideline to execute a complete NDEBPR system design calculation, the EBPR parts of the guidelines could not be compared. (12) The M&E overflow rates can be aligned with the UCT 1DFT to determine very similar SST surface areas. The lower resultant reactor MLSS of the M&E sized systems when simulated with ASM1 means that the SSTs will operate at a lower than designed for MLSS and thus under peak conditions (fq is 2.5 or greater) the SST will operate at a higher than permissible overflow rate. This is because the M&E SST sizing procedure does not include a 1DFT flux rating of 0.80 (as the UCT guideline does), which has the effect of increasing the SST surface area estimated by the 1DFT by 25%.
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    Open Access
    Dissolved air (pressure) flotation
    (1973) Bratby, John Raymond; Marais, G.v. R.
    It appears that, in the past, little attempt has been made to establish the basic parameters influencing the flotation process, or their inter-relationships, on a quantitative basis for the purpose of developing rational design procedures. This thesis investigates those parameters influencing solids removal and thickening by dissolved-air (pressure) flotation and the criteria pertaining to the design of flotation tanks for solids removal and thickening. A review of pertinent literature on flotation is presented. The historical development of flotation is given together with the theory of bubble-particle adhesion. Four common methods of flotation are compared and their inherent advantages and disadvantages are discussed. Dissolved-air (pressure) flotation, the method used in this investigation, is considered in greater detail by presenting established practical considerations for design. A pressure-saturation unit was developed in which all the compressed air supplied is dissolved into the saturator feed by continously recycling the air through a sparger, i.e. there is no air wastage. The air circulating pump operates within the pressurized circuit so that it pumps only against the hydrostatic head of water in the saturator. A vertical flow type flotation unit was developed which provides a counter current flow regime and a stable interface between the clear liquid and rising agglomerates. The accumulated agglomerates discharge freely and without mechanical assistance at the top of the unit.
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    Dynamic performance of pre-cast prestressed beams – cast in-situ slab composite bridges
    (2013) Leo, Emmanuel; Moyo, P; Beushausen, H. D
    Most bridge management systems still rely on visual inspections for condition assessment of bridges; this means that damage in inaccessible parts of the structure such as shear connectors in concrete composite bridges remain undetected until catastrophic failure occurs. Localized non-destructive techniques such as ultrasonic techniques, radar method, impact testing, magnetic based methods and proof load tests are limited to small areas, time consuming and require prior knowledge of the damaged zone. These limitations can be overcome by using dynamics-based techniques. The main objective of this work is to investigate experimentally the effectiveness of dynamics-based techniques in assessing the condition of shear connectors in concrete composite bridges consisting of pre-cast prestressed beams and a cast in-situ slab based on measurements taken from the surface of the accessible deck slab. In this research, shear links of 8mm bars extended from beam to the slab are used to stimulate shear connectors in real bridges. The experimental work involved building five concrete composite beams each with different number of shear connectors. The testing procedure consisted of measuring the dynamic properties in both the undamaged and damaged beams. Damage was introduced by accelerating corrosion to a group of shear connectors near the supports in each composite beam. Push-off test was conducted in order to determine the shear capacity of the shear connectors in both undamaged and damaged state. The modal tests were successfully executed and from the modal analysis results it was observed that a beam with large number of shear connectors produce high frequencies and high amplitudes of frequency response functions (FRFs) compared to the one with less number of shear connectors. After the shear connectors were damaged all beams showed similar results. In the FRFs, the frequency peaks shifted to the left and the peaks amplitudes changed, the natural frequencies generally dropped indicating the existence of damage. In an attempt to locate regions with damaged shear connectors, the Coordinate Modal Assurance Criteria (COMAC), change of flexibility, change of curvature and strain energy method were used. All methods showed positive and negative results. The change of flexibility method showed minimum negative results compared to other methods in locating regions with damaged shear connectors. Generally, Results show that dynamics-based techniques can be used to detect and localize regions with damaged shear connectors in pre-cast prestressed beams - cast in-situ slab composite bridges by only taking vibration measurements from the surface of the accessible deck slab.
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    Enabling equitable access to public transport information to enhance hybrid system use in Cape Town, South Africa
    (2022) Ryseck, Bianca Beatrice; Behrens, Roger
    Though previously unscheduled public transport services were often seen as incompatible with equitable mobility goals, emerging cities are increasingly seeking to integrate these with new scheduled services to form hybrid public transport systems. In contrast to the abundance of services available, there is little information available to plan multimodal journeys across the hybrid system, limiting users' abilities to best use the system to meet their needs. This thesis investigated, through mixed research methods framed within Amartya Sen's capability approach, how to enable equitable access to public transport information on the hybrid system through information and communications technology. The research focussed on captive public transport users in the context of Cape Town, South Africa. Using (n=22) semi-structured interviews, candidate passenger information types for planning hybrid journeys across various scenarios were identified. A best-worst scaling study was undertaken (n=413) to gain a representative understanding of the least and most useful information types. A stated preference choice model was applied (n=501) to investigate what minimum information is required to make use of the hybrid network to access mobility opportunities in non-routine scenarios. The most useful information types were represented as different levels of certainty. These information types were: (1) frequency, (2) fare cost, (3) departure time, (4) arrival time, (5) safety walking to/from a station/stop, (6) safety onboard, and (7) safety while waiting at a stop. A further passenger survey (n=536), together with available secondary data, was analysed to gauge access to technologies and skills related to transport information use cases. This research found that none of the information types at the quality level desired is currently evenly available across the hybrid system, and no official information sources have the capacity to equitably reach captive users given current technological capabilities. The combination of gaps in information provision and adequate communication methods hinders users' informational capabilities to plan journeys that best meet their needs and preferences, and consequentially limits their access to opportunities through mobility. Strategies for understanding information needs, collecting the data necessary, and opening this data to the public through portals provide the adaptability and flexibility needed to deliver sustainable solutions.
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    Energy optimisation on wastewater treatment plants focusing on different aeration technology
    (2020) Strassberger, Divan; Ekama, George
    With ever more pressure being exerted on South Africa to reduce its carbon emissions and their sole energy producer, Eskom, on the verge of collapse, electricity cost in South Africa are set to increase drastically. It is therefore important that electrical consumption be reduced throughout all sectors and wastewater treatment is no exception. With reduction of electrical consumption of WWTPs in mind, this thesis focused on the costing and viability of replacing less efficient aeration technology (slow speed surface aeration) with more efficient technology (fine bubble diffused aeration). The main objective of the investigation was to calculate the total cost (capital, maintenance and operational) of the two technologies, with the input of the varying inflow rates and wastewater characteristics, and find the inflow rate where the total cost of the two technologies are the same. This intersection was titled the Viability Threshold Point. With this point known it is possible to advise designers and investors as to when and where which aeration technology should be implemented. Different data groups were established with varying wastewater characteristics (see table below) as well as inflow rates varying from 1.0 Mℓ/d to 12.0 Mℓ/d. An inflow COD concentration of 750 mg/ℓ was chosen as a benchmark group and the other inflow characteristics were calculated to represent typical values based on this COD concentration.
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    Establishing the environmental and economic benefits of applying advanced thermal hydrolysis to existing anaerobic digesters in the Western Cape, South Africa
    (2021) Potts, Wesley; Ekama, George
    The treatment of sewage by wastewater treatment works (WWTW) generates a solids byproduct stream requiring treatment and disposal. The waste sludges generated are rich in essential nutrients and energy, and present an opportunity to turn a waste stream into a resource. Retrofitting a thermal hydrolysis process (THP) to existing anaerobic digestion (AD) sludge treatment has proven itself globally as a reliable means of increasing treatment capacity and creating a final product that is non-hazardous. This allows for more sustainable sludge disposal options. However, THP has not yet been proven in a South African context. This research carried out a comparative desktop case study of the existing AD facility at the Cape Flats WWTW in the Western Cape, South Africa. The facility's equipment is due for an upgrade and it was investigated if an improved process could be created. The base case of maintaining existing conventional mesophilic anaerobic digestion (MAD) was compared against the case of retrofitting THP. This would increase capacity and improve final product quality. The site would become a regional sludge facility importing additional sludge from some of the surrounding WWTWs. This would divert sludge from landfill and create more sustainable disposal options. Steady-state models were developed for the conventional MAD and THP-MAD. These models were developed to include a kinetics section, stoichiometry section and a weak acid/base chemistry section. The kinetics section used hydrolysis as the rate limiting step when applying saturation kinetics. A stoichiometry section takes input from the kinetics conversion and used the elemental compositions of both substrate and biomass while predicting the amounts of other AD products formed. The weak acid/base chemistry predicted pH and took into account corrections for ionic strength and temperature, which were found to be particularly applicable in the case of high solids THP digestion with the elevated dissolved concentrations. Many of the WWTW's in Cape Town make use of nitrification-denitrification biological excess phosphorous removal (NDBEPR) activated sludge (AS) treatment, often preceded by primary sedimentation. The modelling thus considered a 60:40 mixture of NDBEPR wasted activated sludge (WAS) and primary sludge (PS). AD modelling accounted for the breakdown of polyphosphate (PP) with the uptake of readily biodegradable COD to form poly3- hydroxybutyrate (PHB). The models also predicted the extent of spontaneous magnesium ammonium phosphate (struvite) precipitation inside the digester, and as well as the effect this would have on digester alkalinity and pH. Results showed that when THP is retrofitted 2.5 times more sludge could be processed using the existing digesters' volume i.e. without building any additional digesters. This results in sludge treatment throughput increasing from 60 dry tonnes of solids per day for conventional digestion to 153 dry tonnes per through advanced THP digestion. Modelling has shown in each case that important AD parameters, such as free ammonia concentration, pH, alkalinity, and methane production are within the correct range for stable digester operation while sludge stability was achieved. Major operating expenses and savings were evaluated. It was estimated that retrofitting THP created a saving of over R70mil/annum, largely due to savings in sludge disposal, and produce 2.7MW of surplus electrical energy. Carbon emissions were assessed for each case with THP digestion reducing significantly more emissions than conventional digestion. Additional investment required to upgrade conventional digestion to THP digestion specifically at the Cape Flats WWTW site would create a payback of between 5 to 6 years.
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    Groundwater quantity and quality assessment for aquifer recharge in Ohangwena region, Namibia
    (2022) Ndakola, Hilja; Okedi, John
    The high population growth rate and changing climatic conditions for the Ohangwena region create increasing pressure on the local water balance. As groundwater demands increase and availability declines, sustainable groundwater management is required for the Ohangwena region. This thesis assessed the suitability of using runoff for aquifer recharge to augment groundwater in the Ohangwena region and minimize the lowering of water table. The Geographical Information System (GIS) and groundwater flow models were used in this study to assess the water resources in the study area. A multicriteria approach using a weighted rating was used in this study to generate a map showing areas suitable for groundwater recharge. The resultant groundwater potential recharge zones map was produced based on the overall weights of seven influential factors for groundwater recharge namely lithology, land use/land cover, lineaments, drainage, slope, geology, and soil type. The results of the assessment indicated that 85% of the Ohangwena region is characterized by high groundwater recharge zones, while 25% is characterized by very high groundwater recharge zones. The very high groundwater recharge zones are mostly found in the central part of the region, on the far upper western side and the eastern side of the region. The recorded recharge rates for the region in the range of 40 – 60 mm/year were introduced to an established model using the MODFLOW software, to assess the impact of Aquifer Recharge on the groundwater levels. The impact was assessed with both the steady-state model to approximate aquifer recharge under controlled conditions, and the transient state model for close representation of recharge in reality at four wells namely, WW201045, WW201637, WW201634, and WW20267, where it was evaluated by the hydraulic heads and water budget analysis. The steady state model results indicated a change in groundwater levels in the range of -0.10 - 0.70 m. In the same manner, the transient state model results show a gradual increase in groundwater levels in the range of 9.2 - 12.10 meters for the 350 m deep Ohangwena aquifer. The groundwater levels can be improved locally by infiltrating runoff into the KOH-II aquifer via the injection wells or infiltration basins during the rainy season (November to April) when there is plenty of runoff and flood in the region. The high soil infiltration rates in the region make runoff to be suitable for Aquifer Recharge implementation in the region. Transferring runoff to the aquifer aims at making use of the large aquifer storage space and limiting evaporation loss. The study also employed particle tracking and MT3DMS to assess the transport of contaminants associated with runoff within the aquifer. This was assessed at two wells thatserved as injection wells in the model, and four contaminants namely chloride, Electrical Conductivity, Total Dissolved Solids, and E-coli were studied. The outcomes of this assessment indicated that both Chloride, Electrical conductivity, Total Dissolved Solids, and E-coli concentrations decrease from 1000 mg/l to 0.01 mg/l, 532 mS/s to 0.1, 478.56 mg/l to 0.01 mg/l, and 9.58 to 0.01 respectively as timesteps increase, and it takes 20 timesteps (94672800 seconds) for them to disperse further into the aquifer. The dispersion of Chloride, EC, TDS, and E-coli within the aquifer covers a maximum distance of 12.1, 9.6, 8.7, and 6.7 km respectively.
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    Heat transfer through anaerobic digester concrete tank walls
    (2018) Davis, Owen S; Alexander, Mark
    This dissertation is a study of the heat transfer through concrete walls in anaerobic digester facilities. In the biogas industry, the term “heat loss” is synonymous with heat transfer. The dissertation identifies the reasons why heat is critical in the operations of these facilities. Concrete has traditionally been a material used for the retention of liquid-based products and additionally provides good thermal insulating properties. It combines the benefits of being relatively cost effective for the construction of large tanks and requiring low maintenance during the operational life span. The research focuses on the thermal properties of the various constituents of concrete and the influence these have on the overall thermal properties of the concrete tank. The constituents forming part of the study are cement, corex slag, water, fine and coarse aggregate. The study showed that the aggregates have a greater influence on the thermal conductivity than the other constituents. It also showed that the mineral composition of the aggregates has a greater effect on the thermal conductivity than the porosity of the aggregates. The study also looked at the influence of the interfacial transition zone around the aggregate and this was found to be not significant and generally can be ignored as a contributor to the thermal conductivity of normal / structural concrete. The effects of the porosity of the binder paste does affect the thermal conductivity specifically when aqueous solutions are being retained. The capillary pores of the paste can be filled with liquid (mainly water) and less with air. Due to water having a higher thermal conductivity than air, the thermal conductivity of the binder paste is significantly increased. The effects of reinforcement on the thermal conductivity of concrete was also investigated. Different types and arrangements of reinforcement could have a big influence. Steel fibres and reinforcement if aligned in the direction of the thermal gradient will greatly increase the thermal conductivity. However, it was found that the reinforcement used in the sample wall did not increase the thermal conductivity significantly as it was mainly aligned perpendicularly to the direction of the thermal gradient. Similarly, no steel fibres were used in the concrete. Once the thermal conductivities of the constituent materials were determined, the effective thermal conductivity of the concrete could be calculated using the effective medium theory. The subsequent heat losses, which are a function of the thermal conductivity, the temperature gradient between the internal and external faces of the concrete wall, the contact surface area and the heat transfer coefficient, could be calculated as a function of time. The New Horizons Waste to Energy Project in Cape Town was used as a reference project and the research was based on the materials used in the construction of the concrete anaerobic tanks. The project was also used for the measurement of the temperature gradients and subsequent calculation of actual heat losses at various points along the concrete walls. Furthermore, a computational model was developed using Abaqus to compare the results with those derived from the theoretical model. The heat loss from the computational model compares very well with that of the theoretical model.
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    Modelling public transport mode choice for low-income residential suburbs in Harare, Zimbabwe
    (2023) Mapfurira, Masimba Tutsirai; Zuidgeest, Marcus
    Modern-day life in developing urban cities is structured around the need to access goods and services outside the vicinity of residential areas, and transportation facilitates access to such services. Like many other African cities, most of the residents in Harare sorely rely on public transport, and while the government of Zimbabwe acknowledges the need for efficient public transportation systems in the country's urban environments, insufficient commitment and political will have been directed towards developing strategic plans with clear and well-defined objectives. The development of public transport plans and policies requires a good understanding of the passengers' service quality needs and willingness to pay for service quality improvements. In this study, we use stated choice preference data collected from five high-density suburbs in Harare (n = 361) to investigate the influence of service quality indicators to travel mode choice decisions. Multinomial, mixed, and latent class logit models are developed under the random utility maximisation framework and compared to identify the best model. The model is used to evaluate the willingness to pay indicators for public transport service improvements and outline the contributions of the findings to possible policy directives. The results suggest that latent class models better explain observed choices than mixed and multinomial logit counterparts. With regards to public transport mode choice behaviour, the study classifies the population into two distinct groups on the basis of gender, income, employment status, and location. The willingness to pay indicators shows a substantial difference in the value of all the public transport attributes between the groups, except for waiting time. The willingness to pay for improvements in waiting time, which relates to service frequency, is standard at Z$65 per hour. Noteworthy is the classification of the suburbs between the groups; the posterior analysis indicates that Chitungwiza residents have the highest willingness to pay and Budiriro, the least. This research is of value to ZUPCO and other potential private players in identifying service quality deficiencies and understanding the requirements of public transport service provision at the suburban level. The strong inertia towards kombis emphasises the general dissatisfaction with ZUPCO service quality levels while providing insights into lagging areas that future policy deliberations could address. The research presents a potential performance framework to the Harare city council against which the public transport service provision can be assessed. Most importantly, the findings might be useful in further understanding the public transport landscape in other cities in Zimbabwe, similar to the high-density suburbs used as study areas in this research.
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    Modelling toll impacts using congested highway assignment software – a case study of the proposed N2 - R72 link road in east London, South Africa
    (2021) Duze, Fezekile; Zuidgeest, Marcus
    Traffic congestion has become a growing burden on society. Various approaches to model transportation do not scale efficiently due to its complex nature. The estimate of the locality and quantity of traffic that passes through, leaves or enters a study area are arrived at by assumption. There could be an increase in congestion if investments in infrastructure are done based on inaccurate transport modelling. Furthermore, outside the study area, the effects of changes in infrastructure are unknown. Hence, it is necessary to model transportation networks at a larger scale than previously required. Governments all over the world are faced with continual challenges of providing infrastructures with basic amenities to their citizens. In every financial year, government budgets are always overstretched, which leaves very little for infrastructure maintenance, especially in less developed countries such as South Africa. Tolling road is one option to overcome this challenge. This thesis, therefore, studies toll road modelling options for the proposed N2-R72 link road in East London, South Africa. The proposed N2/R72 Link Road is approximately eight kilometres long and includes a longspan bridge across the Buffalo River as well as a number of interchanges/intersections within an urban environment. Tolling in urban areas is not uncommon in South Africa and is typically associated with mainline plazas supported by several ramp plazas. The strategy presumably for the N2/R72 Link Road involves a mainline plaza constructed on the N2/R72 Link Road just before or after the Buffalo River Bridge. Traffic will be attracted from the existing roads depending on the benefits and toll on the proposed link. The research problem addressed in this thesis arose from the fact that TomTom Traffic Index in South Africa identified East London as the third most congested city in South Africa. The morning and evening commuters experience a massive increase in travel times. Globally, it has been shown that congestion level does not necessarily get reduced as a result of an increase in road capacity. At the same time, there is a need for a possible of diversion to the proposed link road, which can be a choice of a road user's willingness to pay toll fees. The challenge that arises is that diversions can result in gains and losses in terms of revenue for toll agencies if travellers' chose alternative, lower class, existing routes. Now, based on the above the Buffalo City Metropolitan Municipality (BCMM) approached SANRAL to construct a new link with a bridge. In order to finance that (with the benefit of managing traffic as well) the idea is to toll the new link. Knowing that the road user preferences are different. especially there is a need to understand the impact of tolling on traffic flows in the area. The main research question is What the impact of tolling is on the use of the upgraded link knowing that there is heterogeneity amongst users in terms of sensitivity to user costs for transport? The effect of tolling on the proposed N2-R72 link roads is being tested using the congested highway assignment software called SATURN. The way the problem is although preferably VISSUM as a ‘proper' micro model in that they model on a real-time, behavioural level. EMME models on a macro level and could have been used to accommodate all four steps in conventional models. It is tricky to use SATURN on a meso and micro level, as the micro level can distort the trip assignment if only a small (but key) part of the network is simulated (i.e. the assignment results in trips diverting around the simulation by using the buffer network). SATURN as employed in this study can operate at the meso level (buffer networks) with the junction simulation component operating at the micro level (somewhat). This report cautions against confusing the concepts of micro, meso and macro traffic models. In order to understand how the transport network may react to the proposed changes, a modelling approach is proposed. To achieve this, a traffic model was developed to represent the existing situation. This model provides the benchmark against which any proposal will be compared. This study will compare results between the existing and proposed situation in order for an informed decision can be taken on whether to proceed with the proposal based on the impact it will have on the existing network. In transport planning, various transport models are used to forecast impacts and evaluate options. This study investigates and reports on the impact of tolling should SANRAL construct a new road linking two national roads knowing that there is heterogeneity amongst users in terms of sensitivity to user costs for transport. To undertake this study a congested highway assignment model will be used based on a known case study and available old model. The literature review illustrates that with a growth of Public-Private Partnership (PPP) projects, toll roads would increase incessantly. Route choice by users is greatly influenced by toll and can sometimes also have effects on trip departure time and choice of mode. To model toll roads, users' willingness to pay (WTP) or Value of Time (VOT) has an important role, and generally, worker's wages is considered to be equivalent to VOT. This study also acknowledges that there is a distinguished difference between urban toll schemes and congestion pricing. The GFIP e-toll scheme is not congestion pricing, but rather a way to generate revenues for road upgrading and network expansion. It is not meant to suppress trip demand; in fact, it has the opposite effect when upgrades are made, and the network is expanded. The “user-pay” principle is viewed as a traffic demand measure, not as a means by which to raise funds for road building. The obvious questions are: What is the “user-pays” principle? How is the amount that the user must pay determined? Congestion pricing is meant to reduce congestion by suppressing demand. The objectives of congestion pricing are to reduce congestion, to reduce the environmental impact of vehicles by reducing harmful exhaust emission, and to improve the space for public and Non-Motorised Transport (NMT) modes. Revenue from congestion pricing should be used for public transport provision and not upgrading and/or building new roads. The results of the model analysis show that, since traffic growth on toll roads is increasing somewhere in the range of 2% and 6%, the impact on income cannot be negative. There is, notwithstanding, a risk of heightening maintenance charges if heavy vehicles continue to increase at an expense twice that of light vehicles. While not a single verification utilized in sight in the literature that toll roads in South Africa are looking to alleviate clog, it very well may be presumed that growth of light vehicle (Class 1) exacerbate congestion. It is the research candidate's view that research on the perception of Value of Time (VOT) by road-user needs to be found and on toll diversion, being able to classify and predict future traffic and volumes will be essential for the national roads agency and other provincial road authorities on roads they are in control for.
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    Questions of resilience in municipal finance response to a shock event: a case study of the Cape Town drought
    (2019) Cooke, Kayleen; Cirolia, Liza
    The gaining prominence of resilience in urban policy has meant that urban decision makers are increasingly being asked to exhibit foresight and preparedness in how the urban system is planned and managed. The City of Cape Town has accepted this principle of resilience as a key means of driving collective understanding and action within the urban system in a time of growing uncertainty. Cape Town recently experienced the worst natural disaster in the history of its city-dom, in the form of a three-year drought. The impact of this drought on the municipal budget has been formidable. In terms of expenditure, considerable adjustments to the planned expenditure had to be made in order to source the funds required for large-scale infrastructure projects designed to increase resilience within the municipal water supply. In terms of revenue, there is significant concern around the fiscal sustainability of the municipality as more and more households are developing their own water supply in the form of rainwater tanks and boreholes, which is anticipated to decrease the municipal revenue gained from water tariffs dramatically (CCT, 2018f). The story of how the municipal budget system was affected by and reacted to the drought provides an opportunity to observe the application of the City’s understanding of resilience to a complex system, where many actors undertake simultaneous and independent activities, and the impact of these activities is evident at multiple levels and across multiple systems and sub-systems.
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    The development and operation of plant microbial fuel cells using municipal sludge
    (2019) Gulamhussein, Mohamedjaffer; Randall, Dyllon
    Wastewater treatment accounts for 3-5% of the total electricity demand in developed countries. However, wastewater is estimated to have 9.3 times more energy than which is required to treat it. A sediment microbial fuel cell (SMFC) can potentially be used to treat wastewater and produce electricity by utilising the organics found in the wastewater. The challenge associated with using SMFCs is efficiency and longevity. Literature has shown that the efficiency can be increased by growing plants in a SMFC. Plants release organics and oxygen into the rhizosphere which can increase microbial growth and increase oxygen at the cathode. This research undertook to design a batch plant microbial fuel cell (PMFC) and operate it on three different municipal sludge streams namely, thickened waste activated sludge (WAS), liquid WAS and primary sludge (PS). In addition, three indigenous South African plant species, namely, C. papyrus nanus, W. thyrsiflora and P. australis were tested based on their power output potential and organic removal potential. The highest PPD (1036 ± 59 mW/m3 ) was obtained from the system using thickened WAS as substrate and planted with W. thyrsiflora. This was followed by liquid WAS as substrate planted with W. thyrsiflora (290 ± 21 mW/m3 ) and the lowest in the unplanted system using PS (119 ± 31 mW/m3 ). It was also found that COD utilisation for power generation was most efficient when using WAS. Thickened WAS produced 1330 mW/m3 per gram of COD consumed followed by liquid WAS with 508 mW/(m3 ·gCOD) and the lowest conversion in PS i.e. 124 mW/(m3 ·gCOD). Based on these factors WAS was chosen as the most suitable feed for a PMFC. Furthermore, it was found that utilising the PS in an anaerobic digestion would have over 500 times more power output making its use in a PMFC not viable. The highest organic removal efficiencies were observed when systems were planted with C. papyrus. When using WAS, C. papyrus achieved 62.2 ± 12.8%, 62.8 ± 9.6%, 58.5 ± 14.0%, 75.4 ± 8.4%, 95.3 ± 2.8% and 94.4 ± 3.5% removal efficiencies of VSS, COD, TKN, TP, FSA and OP respectively. When using PS, C. papyrus achieved 59.4 ± 9.7% 45.7 ± 10.4%, 82.0 ± 3.3%, 65.6 ± 3.2%, 97.4 ± 2.4% and 78.5 ± 2.8% removal efficiencies of VSS, COD, TKN, TP FSA and OP respectively. Therefore, it was noticed that W. thyrsiflora produced the highest power densities, but the C. papyrus produced the highest organic removal. The decision between the two plants was made based on the plant species ability to grow in sludge. It was noticed that the W. thyrsiflora died in thickened WAS. When using liquid WAS and PS, the old roots died, and new roots grew on the surface for W. thyrsiflora. Given the uncertainty of the plants ability to survive in the long term, C. papyrus was chosen as the most suitable plant species as it was able to grow in all three sludge types. Using WAS and C. papyrus, three more optimisation experiments were conducted. In the first one, it was found that using a separator between the electrodes increased the power density by 35%. The power output increased from 141 ± 16 mW/m3 to 191 ± 16 mW/m3 when a separator was used. It was noticed that the separator system had more horizontal root growth along the top surface just under the cathode of the PMFC as the separator limited vertical root growth. This may be the reason for higher power densities since more roots meant more oxygen release that can be consumed by the cathode. The second optimisation experiment focused on the use of multiple electrodes. It was found that using multiple electrodes was more efficient than single electrodes. Furthermore, it was noticed that connecting the multiple electrodes in parallel within a set-up was more efficient than connecting them in series. The peak power densities followed the order of: parallel connection 443 mW/m3 , series connection 296 ± 46 mW/m3 and 156 ± 17 mW/m3 for the control. The third optimisation experiment was focused on varying electrode distance. It was noticed that the highest peak power density was achieved when the electrode distance was halved (664 ± 122 mW/m3 ) followed by the system with 1.5 times electrode spacing which produced 453 ± 74 mW/m3 and the lowest for the standard design (290 mW/m3 ). From the three optimisation experiments, it was noticed that some variables have a larger impact on the performance of the PMFC than others. Halving the electrode distance increased the PPD 2.3 times, while doubling the electrodes increased it 2.8 times. Adding a separator only increased it by 1.4 times. This indicates that more focus should be attributed to the electrode distance and number of electrodes. In summary, this research found that, of the three plant species investigated, using C. papyrus with WAS substrate was the most practical and best performing combination for a PMFC. Furthermore, having a separator between the electrodes, having multiple electrodes connected in parallel within a set-up and decreasing the electrode distance to half all increased the power production.
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    The development of counter-surveying as a methodology to document forced removals: case studies of District Six and Die Vlakte
    (2025) Mokomane, Tlotliso; Motala, Siddique
    Nearly 30 years post-apartheid, many victims of forced removals remain displaced, their sense of place and identity fractured. The methodology of counter-surveying, though underdeveloped, has been proposed to identify sites of forced removals and engage with affected communities. According to Motala and Bozalek (2022), counter-surveying is a method that uses traditional surveying techniques to temporarily mark and engage with demolished sites, particularly in the contexts of dispossession and forced removals. This study further develops, enhances and describes the counter-surveying methodology through an interdisciplinary approach, integrating Geographic Information Systems (GIS), archival research, site visits, interviews, and hauntology to map forced removal sites. It seeks to document the lives and spaces of those displaced, asking: How can counter-surveying be optimised to capture and document the stories of forced removals? The research centres on ex-residents of District Six and Die Vlakte as they revisit the locations where their former homes once stood. It highlights the danger of oversimplifying the complex ordeals faced by a group and the erasure of individual experiences. The analysis of interviews with ex-residents reveals significant work needed towards reparations for victims of forced removals. Additionally, the results emphasise the importance of ‘exact place' and using non-traditional methods to engage with the past, preserving, and giving life to historical events. This research aims to provide a framework for addressing historical injustices through an innovative methodological approach highlighting the ongoing impacts of past injustices.