Browsing by Faculty "Faculty of Engineering and the Built Environment"
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- ItemOpen Access25cc HCCI engine fueled with Diethyl Ether(2009) Lemberger, Ian; Floweday, Gareth; Yates, AndrewThis research forms part of an ongoing HCCI study at the SASOL Advanced Fuels Laboratory to investigate and understand engine configuration and fuel chemistry effects on combustion in HCCI engines. This project continues from a previous project where a small Progress Aero Works (PAW) 6.5cc high speed model "diesel" aeroplane engine was found to operate in HCCI mode with surprising ease and flexibility. A 25cc, four-stroke, single cylinder Honda GX25 engine, possessing 2-valves with an overhead cam and separate oil sump lubrication system was used. This research aimed to provide insight with respect to which engine characteristics such as size, heat transfer, speed and fuel blending effects, play the primary role in operational differences between the Honda GX25, conventional HCCI engines and the remarkable operational flexibility of the PAW engine.
- ItemOpen Access3-Phase gate-turn off thyristor inverter(1986) Kleyn, D AThe requirements of a standard 3-phase Induction Motor driven by a Voltage Source Inverter (VSI) are studied. A full 3-phase Variable Speed Drive (VSD) and its controller have been designed, constructed and tested. Gate Turn-Off Thyristors (GTO's) are used as the main switching elements in the Inverter stage of the Drive. The drive requirements of GTO's are studied in detail.
- ItemOpen AccessA 3-phase Z-source inverter driven by a novel hybrid switching algorithm(2007) Malengret, Jean-Claude; Braae, MartinA 3-phase Z-source inverter has been researched, designed, simulated, builtand tested. The purpose of the inverter is to deliver 3-phase 400 VAC from aDC supply that can vary over a range of 20 to 70 Vdc. This is done with a Zsourceinverter topology which is a single conversion method with no additionalDC to DC boost converter. A novel DSP control algorithm allows the inverter toachieve the following:· Run Space Vector Pulse Width Modulation (SV-PWM) for maximum DCbus voltage utilization while boosting the DC bus during zero space vectorstates using shoot through.· Seamless transition between modulation control and modulation / shootthrough control.· Optimised efficiency and DC bus utilisation using Hybrid Space VectorBoost Pulse Width Modulation (HSVB PWM) which is unique to thisdissertation.Such a system is particularly suited to fuel cell and particularly wind turbineapplications where the DC bus voltage is varies over a wide range resulting inthe need for a DC to DC buck/boost to regulate the DC bus to maintain a steady3-phase sinusoidal output. A further application could be for general purpose 3-phase inverter capable of operating on different DC standard bus voltages ( e.g.24, 36, 48 VDC).The benefits of a Z-source topology for the above purposes are a reduction inhigh power semi-conductor components (e.g. power MOSFET). There is also areduction in switching losses and inherent shoot through protection.Furthermore, the inverter is more robust in the sense that it is not vulnerable to spurious shoot through, which could be disastrous in the case of a traditionalvoltage fed inverter.
- ItemOpen Access3D model reconstruction using photoconsistency(2007) Joubert, Kirk Michael; Nicolls, Fred; De Jager, GerhardModel reconstruction using photoconsistency refers to a method that creates a photohull, an approximate computer model, using multiple calibrated camera views of an object. The term photoconsistency refers to the concept that is used to calculate the photohull from the camera views. A computer model surface is considered photoconsistent if the appearance of that surface agrees with the appearance of the surface of the real world object from all camera viewpoints. This thesis presents the work done in implementing some concepts and approaches described in the literature.
- ItemOpen Access3D property objects in South African local government: the necessity of representing and managing the third dimension in the City of Cape Town property management system(2021) Humby, Lara; Whittal, Jennifer; Simon HullThe objective of this research was to analyse whether there is a need for a form of 3D Land Administration System (LAS)in South Africa (SA) based on the land administration functions of land tenure, land use, land development and land value. The investigation can be divided into two key focus areas that align with subsystems of the LAS: (i) the Land Tenure System (LTS) that is responsible for land tenure; and (ii) the Property Management System (PMS) that is responsible for land use, development and value. These two key areas fall within the SA LAS and make use of the cadastre as a foundation. Humby (2014) focussed on the first subsystem and found that there may be a significant need within the LTS for a 3D cadastral record or a 3D legal property object (LPO). The second subsystem is the focus of this study. To analyse the need for 3D in the PMS, the City of Cape Town (CCT) was adopted as a single case study, and modelled using systems thinking tools. The model focussed on the definition, use and management of property information, or the conceptual 3D property management object (PMO), to fulfil the land administration functions of land use, development and value within the CCT PMS. Established land administration theory, including the Land Management Paradigm, the good governance principles and RRR requirements, was used as a foundation against which the CCT PMS was analysed. This allowed for an increased understanding of the current CCT PMS's ability to achieve its land administration goals, policies and sustainable development. Following this, the current use of 3D within the CCT PMS was presented and analysed, along with the potential resulting benefits, uses and challenges of introducing 3D into that system. Semi-structured in-depth interviews, documentation evidence and participant and direct observations were employed in this section of the research. Furthermore, international land administration and 3D experiences, as presented in the literature review, were incorporated in this analysis. This study concludes that introducing a third dimension into the CCT PMS would have its challenges, but the uses and benefits that have been seen globally and that are recognised within the CCT, may outweigh those challenges. The research illustrates how a 3D Property Management Object would clarify the records and aid the land administration functions. Preferably, 3D would be introduced into the cadastre and LTS initially, and the PMS could then adopt that real RRRs LPO record as a foundation for the PMO records. However, the LTS has fallen behind in technology and it appears the CCT PMS will have to take the lead in introducing 3D into the SA LAS. It is recommended that a full cost-benefit analysis is conducted prior to any further research or development within the CCT.
- ItemOpen Access3D reconstruction and camera calibration from 2D images(2000) Henrichsen, Arne; De Jager, GerhardA 3D reconstruction technique from stereo images is presented that needs minimal intervention from the user. The reconstruction problem consists of three steps, each of which is equivalent to the estimation of a specific geometry group. The first step is the estimation of the epipolar geometry that exists between the stereo image pair, a process involving feature matching in both images. The second step estimates the affine geometry, a process of finding a special plane in projective space by means of vanishing points. Camera calibration forms part of the third step in obtaining the metric geometry, from which it is possible to obtain a 3D model of the scene. The advantage of this system is that the stereo images do not need to be calibrated in order to obtain a reconstruction. Results for both the camera calibration and reconstruction are presented to verify that it is possible to obtain a 3D model directly from features in the images.
- ItemOpen Access3D visualisation of the laetoli footprints on the internet(2000) Taylor, SimonBibliography: p. 84-86.
- ItemOpen AccessA 500kHz-5MHz CW stepped frequency borehole tomographic imaging system(2001) Isaacson, Adam Rhett; Inggs, MichaelThis dissertation involves a study of Cross-Borehole Tomography. The mathematical physical models of the Radon Transform are reviewed. The entire Cross-Borehole Tomographic process is simulated, based on these physical models of the Radon Transform. The system specifications for the final design are based on the results from the simulation. Finally, the final design is built, and tested. The phase yields a better quality of image reconstruction when compared to amplitude, and hence a coherent system is a good choice. The system is frequency to frequency coherent for the entire transmit frequency range, which satisfies the main aim of this dissertation.
- ItemOpen Access9-Phase inverter driven motor(1983) Hoffman, Keith PaulThe behaviour of a 9-phase squirrel cage induction motor is studied when it is excited with unmodulated and chopper modulated quasi-square phase voltages. A 9-phase bridge inverter, which produces the quasi-square waveforms, and its digital controller have been constructed and tested. A theoretical analysis is included, which shows the influence of phase current harmonics upon output torque.
- ItemOpen AccessA Case Study on the Viability of Electricity Generated from a Solar PV Installation as an Alternative or Supplement to Traditional Electricity Supply in Existing Buildings(2020) Jooste, Van Wyk; Le Jeune, Karen; Nurick, SaulThis research study emphasizes the global responsibility and the importance of employing alternative sources of energy that are climate-friendly. It argues against coal-based energy creation and explains why it is not a long-term sustainable solution to the global energy demand. Many countries have embraced green energy initiatives and are adopting progressive strategies to limit its carbon footprint. The research explores and compares various methods of generating renewable energy and motivates the identification of solar energy as a suitable candidate to contribute on a much larger scale to the energy demand for South Africa and abroad. The paper further researches the history of solar energy, barriers preventing large scale implementation and the solutions to bridge those barriers. The aim of this paper is to determine to what extent technology has developed for small scale property owners to generate its own electricity supply from solar energy resources in South Africa and whether the supply generated would be sufficient to warrant consistent and uninterrupted flow compared to traditional coal-based energy resources. The cost of installation and maintenance of solar PV technology together with its financial return is investigated as well as the possibility to generate excess electricity that can be fed back into the grid. The result of the research sheds light on whether it makes financial sense to small scale building owners or managers to install a rooftop solar PV system to either generate its own stream of electricity supply or to merely supplement the traditional electricity supply from Eskom, the national electricity supplier. The research study chose to analyse a single case study and conducted semi~structured interviews with a number of stakeholders. The case study comprised a solar PV system that has been mounted on a rooftop of a building tenanted by a private school. The financial data from the installation in addition to qualitative data arrived at the conclusion that it is financially viable for building owners or managers to install a suitably sized PV system to supplement traditional electricity supply in existing buildings.
- ItemOpen AccessA Case Study to Determine if Micro-Unit Developments Create Another Step Along the Housing Ladder for Low-Income Homeowners in Soweto(2022) van Eeden, Marile; Viruly, FrancoisThe South African government has been providing subsidised housing for decades, yet a large portion of the population live in inadequate housing. More recently, it has been found that many residents earn more than what is allowed to qualify for a housing subsidy; however, they earn too little to enter the formal market. These residents, therefore, turn to the informal market, where they obtain housing in informal settlements or housing in backyards. A new housing development trend is emerging in the form of backyard micro-unit developments. This research proposal examines the potential of backyard micro-unit development to address the low-income housing demand and how these developments can be used as a means to climb the housing ladder. An exploratory case study is undertaken to understand housing trends within Soweto, South Africa. A mixed research approach was used together with both quantitative and qualitative data. The COVID-19 pandemic, however, posed a significant limitation on fieldwork; therefore, the study relied on secondary data sources. The analysis indicates that the backyard micro-unit developments mimic the formal market, and the backyard micro-unit developments provide an adequate housing option for low-income earners. Furthermore, the demand for affordable accommodation results in the commercialisation of the informal rental market and presents the opportunity for homeowners to move up the housing ladder, and it addresses the mounting housing backlog in Soweto. Furthermore, the analysis indicates the significance of a title deed for residents in townships and its role in their ability to climb the housing ladder.
- ItemOpen AccessA CFD framework for aeroelastic gust load calculations(2018) Man, William Liw Tat; Malan, ArnaudA Computational Fluid Dynamics (CFD) framework for the simulation of the aeroelastic response of aircraft flying under gust loading was developed. The multiphysics, Finite Volume, VertexCentered code Elementaltextsuperscript{textregistered} was employed and calculations were performed for the transonic flow regime. In the structural domain, the fuselage was treated as rigid and the wing was considered for aeroelastic calculations. The latter was represented by a beam stick model using Timoshenko beam theory in Elementaltextsuperscript{textregistered}'s structural module. The case under consideration was the NASA Common Research Model (CRM) flying at Ma = 0.86 with a 30 ft gust applied over the aircraft. Key contributions of this work included implementation of a computationally efficient gust model as well as the development of a fluidstructure interface. The latter was to transfer forces from a deforming wing skin to the wing-beam in a conservative manner while reflecting the resulting displacements on the wing surface. An interface library was developed for this purpose and 3rd order accurate Bezier curves used to recover a smooth deformed wing. The various sub-components of the aeroelastic model were rigorously validated. Following this, the developed framework was applied to the CRM under gust load conditions.
- ItemOpen AccessA CFD Model for a Fixed Bed Reactor for Fischer Tropsch Reaction using Ansys(2023) Chitranshi, Vidushi; Moller, KlausFischer-Tropsch (FT) is a process which can convert synthesis gas derived from natural gas, coal or even biomass to a variety of products including saturated and unsaturated hydrocarbon chains, while keeping the emission of greenhouse gases minimum. Among various types of reactors used for commercial FT, fixed bed tubular reactors are among the most common type of reactor. However, there is a big challenge faced by these tubular reactors. FT is a highly exothermic process and therefore, heat removal in these reactors is needed to be highly efficient to avoid a thermal runaway. To improve the heat transfer in any reactor, it is necessary to estimate the heat production correctly. Therefore, the kinetics in the FT system needs to correctly represent the heat transfer behaviour in the system. This requires an effective description of the reaction kinetics. FT is a polymerisation reaction, so the rate expressions must be able to retain the chain reaction behaviour. This is not possible with a lumped approach model which is used by most researchers in literature. Therefore, a partial equilibrium approach was employed, where thermodynamic and kinetic models were coupled, and the reaction rates depended on the concentration of reactants as well as products. The kinetic model employed in the current project was taken directly from the work of Davies and Moller. The abovementioned partial equilibrium kinetics was used to develop a CFD model for the FT reaction system. This model was reproduced using COCO simulator for a plug flow reactor for same operating conditions as Ansys to compare the results from both the softwares. The results showed a close agreement and hence, assured that the CFD model could be used for further testing. The other challenge with the FT in FBRs is the heat dissipation. To avoid the thermal runaway, some innovations in reactor design have been studied in literature. In terms of heat transfer capabilities, when shell and tube heat exchangers are compared with the plate and frame heat exchangers, various sources in literature claim that the latter is found to be more effective. However, plate type reactors have not yet been explored in detail for their heat transfer capabilities. Taking an idea from this, the CFD model developed for the tubular reactors was adapted for plate type reactors. The heat transfer capabilities of the plate type reactors were compared relative to the tubular reactors. The tube reactor and plate type reactor were compared on the basis of two criteria. One criterion was based on physical similarity between the reactors. It included having equal Reynolds Number and equal surface area available per unit volume for both type of reactors. For a plate with plate spacing t and a tube with diameter D, the latter condition resulted in the expression, D = 2t. The factors that Reynolds number for a packed bed depends on were all same for both the geometries, so by default, the Reynolds Number was identical for both cases. The other criterion was based on catalyst packing. It included having equal tube-to-particle diameter ratio for both geometries. For tube reactors, diameter is an important parameter that determines the heat dissipation behaviour, so a parametric study was carried out to study the effect of a diameter and plate spacing on heat transfer behaviour for the same set of operating conditions. It was found that the plate type reactor had a hotspot temperature which was less than the hotspot temperature of corresponding tube reactor at all plate spacings. This indicated that the heat dissipation in a plate type reactor is better than in the corresponding tube reactor. Since the tube reactors observed higher temperatures than corresponding plate reactors, the CO conversion observed in the tube reactors was higher. When the product distributions for the two geometries were compared at isothermal conditions, the results almost overlapped for the two geometries. But when they were compared for non- isothermal conditions, significant differences were observed. This showed that heat dissipation mechanisms in the system had a huge role in bringing out different performances for the two geometries. Effect of temperature and conversion on the product distribution were also studied. On the basis of tube to particle diameter ratio criterion, tube reactor was found to outperform the plate reactors in terms of temperature control when compared using the tube-to-particle diameter ratio. Therefore, the superiority of one reactor over the other was dependent on the criterion they are being compared for. The plate type reactor was then represented in PFR model by tuning the heat transfer coefficient of the tubular model in COCO. The difference between the CO conversions achieved between the plate type reactor in Ansys and the representative model in COCO was found to be very little. Hence, the plate type reactor representation could be successfully achieved in COCO. There can be a lot of further research that can be done using the current model. The areas of reaction kinetics and reactor design were highlighted in this regard. The current model can be extended to a larger number of species, for a better representation of the FT product spectrum. Formation of liquids was completely neglected in the current project. It can be taken into account as presence of liquid can affect the FT reactor system by imposing internal and external mass transfer limitations to the reactions. The current model can also be used to study the HTFT process and also to study the isomeric products in the LTFT which were assumed to be not present in the current project. In the areas of reactor design, the geometry of catalyst particles can be included in the reactor geometry. This model can also be used for plates of other shapes and sizes to study the effect of shape and size on heat transfer capabilities. Different types of corrugated plates are used in the Plate and Frame Heat exchangers nowadays. The corrugations increase the surface area available and also increase mixing. Using the current model, such modifications can be studied for their effect on the reactions in a reactive system.
- ItemOpen AccessA city walkable: [Re]Imagining spatial justice through access and public space in North End, East London(2023) Hendricks, Lerys; Ewing, Kathryn; Crooijmans, HedwigA city walkable is about re-imagining spatial justice through access and public space in North End, East London, South Africa. The research questioned the state of East London's public space, its inner-city decay, and its vehicular dependency. East London lacks good quality public space that is walkable and accessible. A city walkable has streets that are comfortable, safe, interesting and offer choice. The urban environment must foster walkability. Before Apartheid, North End was a mixed-race community that was spatially integrated with the city because of its proximity to the CBD and its urban fabric. North Enders never needed to own a vehicle to access amenities. People could access their everyday amenities on foot and felt safe walking day or night. North End was a walkable, mixed-use neighbourhood. However, due to the Group Areas Act of 1950, people were forcibly removed from the city and relocated to what is now known as townships. Due to this removal people are forced to rely on public transport or private vehicle for mobility. Townships are not mixed-use, and streets do not foster walkability. By removing people from the city, Apartheid removed walkability. The fundamentals of living in a city are access to the convenience of amenities and work. Denying access to the city is a spatial injustice. This denial has resulted in a lack of walkable streets, unsafe public spaces, and car dependency. Since the forced removals of 1950' North End has been rezoned as a light industrial area. The research aimed to unlock the potential for walkability in East London. North End is re-imagined not only a walkable neighbourhood, but as a neighbourhood that is integrated with both township areas and the CBD. The links used to create linkages are a series of urban mixed-use corridors. Thus, creating a city that is spatially just. This makes North End a strategic place in the city which has the potential to become East London's 'knuckle'. Through various interventions, spatial strategies, and framework a more just, walkable city is envisioned.
- ItemOpen AccessA cleaner production assessment of the ultra-fine coal waste generated in South Africa(2007) Reddick, J F; Von Blottnitz, H; Kothuis, BThe South African coal mining industry is currently disposing of about 10 million tons of ultra-fine coal (<150 µm) per year. Once discarded, these sulphur-containing ultra-fines contribute to several environmental problems. As part of a project initiated by the Water Research Commission to investigate the use of Cleaner Production (CP) in the mining industry, a study was carried out to determine whether a CP approach could be used to identify opportunities to reduce this coal waste, and to determine which of these opportunities would be most feasible. In order to do this, a CP assessment was conducted at three case study collieries in the South African Witbank coalfield. Mass-balancing and sampling, followed by laboratory characterisation tests and site surveys, were used to determine the quantity, quality and sources of the ultra-fine coal at the three collieries. Literature reviews, brainstorming sessions and interviews then followed to generate the CP options. An environmental, economic and technical feasibility assessment was then prepared for each option, to determine the most viable interventions for implementation. A number of opportunities were identified through the assessment. By preventing coarser coal from being discarded with the ultra-fine coal, the quantity of coal disposed of could be decreased at all three collieries, and by up to 24% in one case. Increasing the crusher top size would reduce the amount of coal that is milled to less than 150 µm, so that less is wasted. The ultra-fines that have already been disposed of on slurry dams can be completely reclaimed and converted into a valuable product, which can be sold as power station feedstock. The newly processed ultra-fines could be beneficiated using flotation and exported together with the coarser coal. The results of the assessments thus suggested that workable CP opportunities to reduce ultra-fine coal wastage exist at the sites investigated, and that their feasibility is colliery-specific. The associated financial benefits of the proposed options suggested that CP is a realistic approach to addressing environmental problems.
- ItemOpen AccessA commentary on the intellectual health of the nation(2007) Vaughan, Christopher L; Reddy, B Dayanand; Noakes, Timothy D; Moran, V CThe record of high-quality research at South African universities is not as impressive as we may have thought, according to some international rankings. Whatever we might think of these assessments, we have to take them seriously. We suggest ways in which our universities and other institutions of higher learning might raise the level of their game.
- ItemRestrictedA common heritage / an appropriated history: The Cape Dutch preservation and revival movement as nation and empire builder(2007) Coetzer, NicThe Cape Dutch architectural revival at the time of the Union of South Africa in 1910 points to more than just an emerging interest in building preservation and the Arts and Crafts rural ideal germane to English architectural circles of the time. Cape Dutch architecture, and the gable of Groot Constantia in particular, was used as a symbol to establish a common European heritage that could transcend the animosities of English and Afrikaans South Africans and help forge a new white 'nation'. A closer reading reveals that Cape Dutch architecture, as history and as style, was appropriated by English architects at the Cape as the contribution South African architecture could make to the British Empire.
- ItemOpen AccessA Comparative Analysis of the Performance and the Microbial Ecology of Biological Sulphate Reducing Reactor Systems(2020) Hessler, Tomas; Huddy, Robert; Harrison, SusanAcid rock drainage (ARD) is defined as acidic waste-water contaminated with sulphate and heavy metals which is generated through the oxidation of sulphidic ores in the presence of water and oxygen. Mining activities accelerate this process by bringing these ores to the surface where they are further crushed and, eventually end up in waste rock dumps and tailing impoundments where they continue to generate ARD into perpetuity. Active mining operations are mandated to prevent the discharge of ARD into the environment. This ARD is commonly remediated by expensive yet highly effective active treatment strategies such as high-density sludge processes and reverse osmosis. South Africa has an extensive history of gold and coal mining which has left abandoned mine workings with associated waste rock dumps throughout northern and eastern parts of the country. As many of these mines have long been abandoned, the responsibility to mitigate the environmental impact of the generated ARD lies solely with government. Although these diffuse sites often generate smaller volumes of less aggressive ARD compared to that generated through mine water rebound, the sheer number and the continual ARD generation from these sites is a severe threat to South Africa's already poor water security. Biological sulphate reduction (BSR) has long been considered an attractive option for the longterm remediation of these low-volume sources of ARD – but its implementation has shown mixed success. BSR is a process catalysed through the innate metabolism of sulphate-reducing bacteria (SRB) which coexist within complex microbial communities. SRB themselves are a highly diverse group of anaerobic microorganisms which use sulphate as a terminal electron acceptor. The sulphide and bicarbonate produced during BSR can be used to precipitate heavy metals and aid in the neutralisation of the ARD, respectively. The implementation of BSR is, therefore, a comprehensive remediation strategy for diffuse sources of ARD. The study of BSR, using various reactor configurations and operating conditions shows much promise. However, the microbial ecology of the complex communities within BSR systems, and their links to the performance of BSR processes, has received far less attention in published literature. This is not a result of underappreciation of the role microbial communities but rather a historical lack of tools, specifically high-throughput techniques, available to assess complex microbial consortia. It is asserted that the success of a sustainable BSR process developed for the long-term remediation of ARD requires an in-depth understanding the microbial communities associated with this process. The identification of the microorganisms which are key to the process, thosewhich threaten the stability of the community and the optimal growth conditions of these microorganisms, can be used to inform how these bioreactors are designed and operated. This study investigated the performance and microbial ecology of several continuous BSR reactors using culture-independent metagenomic sequencing approaches. The performance and microbial ecology of these reactors were evaluated at a range of hydraulic residence times (HRT) over the course of approximately 1000 days of continuous operation, from five- through to one-day(s). The tested reactor configurations included a continuous stirred tank reactor (CSTR), an up-flow anaerobic packed bed reactor (UAPBR) and a linear flow channel reactor (LFCR) that were each operated in duplicate and supplemented with either lactate or acetate as an electron donor. The different reactor configurations and supplied electron donors, as well as the varied applied HRT, generated a range of microenvironments which were hypothesised to lead to the divergence of the initial microbial community of the inoculum and generate numerous distinct microbial communities throughout and across the reactor systems. 16S rRNA gene amplicon sequencing was used to assess the microbial community structure of the numerous populations across the reactor systems and monitor how these communities responded to the change in the applied HRT. Genome-resolved metagenomics was employed in parallel to recover the genomes of all predominant microorganisms identified through gene amplicon sequencing. This allowed the interrogation of the composition of the respective microbial communities as well as the genetic potential of each microorganism and encompassing the communities represented within specific reactor environments. The CSTRs were selected as these systems are characterised as well-mixed, support solely suspended biomass and kinetic equilibriums are achieved rapidly. This allows the performance of these reactors to be predictable and provides a benchmark to which the LFCRs and UAPBRs could be compared. The lactate-supplemented CSTR performed largely as anticipated based on available literature, demonstrating a maintained sulphate conversion of approximately 55% over the course of the study. The reactor achieved a maximum observed volumetric sulphate reduction rate (VSRR) of 17 mg/ℓ.h at a one-day HRT. The system supported a low SRB diversity, constituted almost entirely by a Desulfomicrobium and two Desulfovibrio operational taxonomic units (OTUs). The acetate-supplemented CSTR was able to maintain sulphate reducing performance at HRT where complete washout of SRB had been predicted based on literature. This reactor exhibited a maximum VSRR of 10.8 mg/ℓ.h at a 1.5-day HRT and was dominated by the same Desulfovibrio and Desulfomicrobium observed in the lactate-supplemented CSTR, along with several other SRB genera at lower abundance. The LFCRs demonstrated an approximately ten-fold greater biomass retention than the corresponding CSTRs. This was facilitated through the incorporation of carbon microfibres, whichfacilitated microbial colonisation and biofilm formation within the reactors. Surprisingly, the lactate-supplemented LFCR, underperformed compared to the lactate-supplemented CSTR, achieving a maximum VSRR of 14.8 mg/ℓ.h at a one-day HRT. This reduced performance, in spite of the enhanced biomass retention, was concluded to result from the out-competition of lactateoxidising SRB in the reactor by Veillonella and Enterobacter OTUs. The acetate-supplemented LFCR exhibited a period of underperformance before recovering and subsequently demonstrated a maximum VSRR of 17.1 mg/ℓ.h at a one-day HRT. Evaluations of the microbial communities of this system during the HRT study revealed a dramatic shift in the SRB communities from being dominated by Desulfatitalea and Desulfovibrio to being dominated predominantly by Desulfomicrobium and Desulfobacter. The UAPBRs are governed by plug-flow which resulted in the generation of gradients of decreasing substrates and increasing products throughout the height of the reactors. This, as hypothesised, resulted in the stratification of the microbial communities throughout the height of these reactors. This allowed many associations to be made between specific microorganisms and their ideal growth environments. Both UAPBRs demonstrated competitive sulphate reducing performance. The lactate-supplemented UAPBR proved especially successful as this system was able to maintain >95% sulphate conversion at one-day HRT, corresponding with a VSRR of 40.1 mg/ℓ.h. The performance of this reactor was attributed to the significant quantity of retained biomass and the successful harbouring of lactate-oxidising SRB towards the inlet zone of the reactor as well as propionate- and acetate-oxidising SRB towards the effluent zones of the reactor. The acetatesupplemented UAPBR exhibited a maximum VSRR of 23.2 mg/ℓ.h at a one-day HRT and a maximum sulphate conversion of 79% at a 2.3-day HRT. The stratification of the microbial communities within the acetate-supplemented UAPBR was less pronounced than the lactatesupplemented UAPBR, as a result of the fewer available volatile fatty acid species. However, the stratification which was observed in this system could be used to postulate the growth kinetics associated with the identified SRB – a Desulfobulbus was associated with rapid acetate oxidation in the inlet zone while a Desulfatitalea and a Desulfosarcina could be implicated in sulphate scavenging in the effluent zone of this reactor. This proved particularly valuable for elucidating the roles of these same SRB in the well-mixed reactor systems. Genome-resolved metagenomics was employed to recover the genomes of the microorganisms identified in these systems and determine the metabolic potential of these microorganisms. Hydrogen-evolving hydrogenase genes were found to be widespread in genomes not capable of sulphate reduction. In contrast, hydrogen-consuming hydrogenases as well as autotrophic gene pathways were common amongst SRB genomes. The ubiquity of hydrogenase genes in these environments indicated that inter-species hydrogen transfer was an important feature within thesemicrobial communities. The dual consumption of both acetate and hydrogen was concluded to have facilitated the maintained sulphate reducing performance of the acetate-supplemented reactor systems at short HRT where system failure had been predicted. Indices of replication (iRep) were used to estimate the instantaneous growth rates of the microorganisms from metagenomic shotgun sequencing datasets. This revealed that, at a four-day HRT, the microorganisms within the biofilms were comparably active to planktonic microorganisms. This, together with the dynamic changes in the composition of these biofilms during the HRT study, suggests these biofilms are even more active and competitive than previously thought. The combined use of next-generation gene amplicon sequencing and genome-resolved metagenomics has given unprecedented insights into the microbial communities of BSR reactor systems. Using this approach, it was possible to uncover a seldom discussed form of hydrogen cycling within BSR systems and has shown that there is no ‘one-size-fits-all' approach when inoculating BSR reactors. The SRB within these systems were often highly specialised to particular environments, specific electron donors and each showed differing growth kinetics. The success of long-term, semi-passive BSR reactor systems would benefit greatly from the tailoring of SRB inoculums informed by the chosen reactor configuration and operating conditions. The outcomes of the kinetic reactor experiments have led to several recommendations for the design and operation of these systems.
- ItemOpen AccessA comparative study of the access to and use of electricity by farmworker households in the Free-State(1996) Hofmeyer, Iilne-Mari
- ItemOpen AccessA Comparative Study on Shear Strength Testing of Single and Multi-layer Interfaces using Large Direct Shear Apparatus(2021) Muluti, Shade; Kalumba, Denis; Sobhee-Beetul, LaxmeeGeotechnical structures such as composite liner systems in landfills consist of multiple interfaces, which include a broad range of geosynthetics in conjunction with soil, rocks and any other related materials. This results in the introduction of many interface planes into the structure, which can potentially create instability especially along the slope and ultimately result in failure. To date, many laboratories use single interface testing instead of multi-layer interface testing to determine geosynthetic shear design characteristic values that are used in the design of structures such as landfill liners. A topic of discussion remains the preferred interface testing configuration and only a few studies have substantiated and quantified the significance of varying the different interface shear testing configurations. This study, therefore, aimed to evaluate and compare the effects of the use of the two interface test configurations on the shear strength of soil/geosynthetic and geosynthetic/geosynthetic interfaces. Furthermore, it was intended to identify the test configuration that provides the most critical shear strength results, while also understanding the fundamental mechanisms responsible for the shear strength observed. In this study, three geosynthetics were used: geotextile (GTX), geomembrane (GMB) and geosynthetic clay liner (GCL), which generally constitute the critical interface components of a lining system in a modern South African landfill liner. Two soils were utilised as a part of the materials required for the investigation and they were: river sand and red clay. The laboratory tests were conducted under saturated conditions in accordance with the ASTM D5321 and ASTM D6243 standards, using a 305 mm x 305 mm large direct shear box. The tests were carried out over a range of applied normal pressures of 50, 100, 200 and 400 kPa. A constant shear rate of 1.0 mm/min was used in the interface tests that did not involve GCLs or clay specimens and therefore no excess pore pressure was anticipated at the interface. On the other hand, for all other interface tests involving either clay or GCLs samples, a shearing rate of 0.1 mm/min was utilized. The results showed that nonlinear behaviour of the shear stress versus shear displacement responses was exhibited in both the single and multi-layer interface tests, regardless of the normal stress applied. However, it was noted that with an increase in normal stress applied, the deviation in mobilized shear stress between the two test configurations increased, with single interface tests yielding higher shear stress values compared to multi-layer interface tests. In single interface tests, the high shear stresses could be related to the clamping that confined each of the test specimens during shearing to one end of the shear block. On the other hand, only the top and bottom test specimens were clamped in multi-layer interface tests, thus allowing failure to have occurred at the weakest of the available interfaces. Moreover, for single interface tests, peak strengths were generally 9% lower for the range of normal stresses considered, whereas Large Displacement (LD) strengths were generally 24 % lower for the single interface tests, compared to the peak and LD strength values for multi-layer interface tests. This was particularly observed at low normal stresses between 50 and 200 kPa, and it could probably have been caused by the rigid clamping of the geosynthetics which results in some tensile strains in the geosynthetics. In addition, it was observed in multi-layer interface tests that a transfer of shear stresses within the system could have occurred, which could have led to higher overall shear resistance of the composite. As a result, single interface tests yielded a conservative estimate of the peak and LD shear strengths for the tested interfaces compared to multi-layer interface tests. This may be attributed to higher displacement along with the critical interface in single interface tests than in multi-layer interface tests. To allow the investigator to observe the displacement, as well as the possible transfer of shear stresses within the system during the shearing of the various geosynthetics, it was recommended that real-time monitoring of the displacement mobilization should be carried out in multi-layer interface tests during shearing.