Development of a crumb rubber adsorbent for the sorption of lead and copper from waste water: Optimization of sorption in a binary component system
- Authors: Hlabana,Relebohile Gladys
- Date: 2022-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/59688 , vital:62356
- Description: Waste tyre is becoming a global environmental problem due to challenges in its disposal management and the fact that it poses fire hazards and metal leaching risk. Waste tyre can also breed mosquitos if it traps water thereby becoming an environmental health problem. There is also a portion of unused tyre in a waste tyre that is valuable and should be recycled. In South Africa waste tyre recycling is in three industries, one of which is crumb rubber where waste tyre is applied into various sized particles called crumb rubber. Crumb rubber can be applied in environmental remediation as an organic and inorganic pollutants’ adsorbent. Considering the fact that South Africa’s environment is loaded with heavy metal pollutants due to contributions by mining and agriculture as examples, it is postulated that crumb rubber produced in South Africa could be used to remediate the environment of these toxic metals. In this study adsorption of Pb (II) and Cu (II) from the synthetic waste water using waste tyre crumb rubber produced in South Africa was studied. Crumb rubber was activated using aqueous NaOH (0.02%) to make crumb rubber wettable followed by it being treated with 0.02 % acidified KMnO4 for modification of its ability to sorp positively charged metal species. Trial sorption experiments on 50 mg / L Cu (II) were successful with sorption of over 70% in 250 minutes. Final optimization of the sorption of combined Pb (II) and Cu (II) was studied using a full factorial design and optimum conditions of sorption were found to be pH 5.4; [metal] 0.617 mmol / L for Pb (II); and pH 5.4; the optimization of Cu (II) was found to be pH 5.4; [metal] 0.777 mmol / L. In Pb (II) sorptions the mechanism of adsorption on the activated crumb rubber was found to be following the Freundlich model indicating that the adsorption seemed to occur on a multilayer adsorbent, while the mechanism of copper(II) adsorption on to the activated crumb rubber was found to be following Langmuir model, indicating that the adsorption seemed to occur on a monolayer. With adsorption percentages ranging from 98.2 % to 100.0 %, for Pb (II), the crumb rubber produced under the conditions of this study, can be used in South Africa for selective removal of Pb (II). , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2022
- Full Text:
- Date Issued: 2022-12
- Authors: Hlabana,Relebohile Gladys
- Date: 2022-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/59688 , vital:62356
- Description: Waste tyre is becoming a global environmental problem due to challenges in its disposal management and the fact that it poses fire hazards and metal leaching risk. Waste tyre can also breed mosquitos if it traps water thereby becoming an environmental health problem. There is also a portion of unused tyre in a waste tyre that is valuable and should be recycled. In South Africa waste tyre recycling is in three industries, one of which is crumb rubber where waste tyre is applied into various sized particles called crumb rubber. Crumb rubber can be applied in environmental remediation as an organic and inorganic pollutants’ adsorbent. Considering the fact that South Africa’s environment is loaded with heavy metal pollutants due to contributions by mining and agriculture as examples, it is postulated that crumb rubber produced in South Africa could be used to remediate the environment of these toxic metals. In this study adsorption of Pb (II) and Cu (II) from the synthetic waste water using waste tyre crumb rubber produced in South Africa was studied. Crumb rubber was activated using aqueous NaOH (0.02%) to make crumb rubber wettable followed by it being treated with 0.02 % acidified KMnO4 for modification of its ability to sorp positively charged metal species. Trial sorption experiments on 50 mg / L Cu (II) were successful with sorption of over 70% in 250 minutes. Final optimization of the sorption of combined Pb (II) and Cu (II) was studied using a full factorial design and optimum conditions of sorption were found to be pH 5.4; [metal] 0.617 mmol / L for Pb (II); and pH 5.4; the optimization of Cu (II) was found to be pH 5.4; [metal] 0.777 mmol / L. In Pb (II) sorptions the mechanism of adsorption on the activated crumb rubber was found to be following the Freundlich model indicating that the adsorption seemed to occur on a multilayer adsorbent, while the mechanism of copper(II) adsorption on to the activated crumb rubber was found to be following Langmuir model, indicating that the adsorption seemed to occur on a monolayer. With adsorption percentages ranging from 98.2 % to 100.0 %, for Pb (II), the crumb rubber produced under the conditions of this study, can be used in South Africa for selective removal of Pb (II). , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2022
- Full Text:
- Date Issued: 2022-12
Spatial and temporal analysis of the critical zone in the Western rift valley corridor: towards earth stewardship science in East Africa
- Authors: Miller, Warren David
- Date: 2022-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/59771 , vital:62423
- Description: Over the coming decades, Africa is expected to experience disturbing effects due to climate change and increased land cover change due to human influences presenting a significant concern for the future well-being of human and biological systems, the latter being the foundation of ecosystem services supplied to humanity. Therefore, unprecedented transdisciplinary cooperation, coordination, and integration amongst researchers, government, and civil society are necessary to increase the resiliency of these systems. This study aims to provide an outline of the Africa Alive Corridors (AAC) as an essential model for the encouragement of sustainable development through Earth Stewardship science. These aims are accompanied by the quantification and forward modelling for land cover change of the Critical Zone over 10 Great Lake Basins across one of the AAC, the Western Rift Valley Corridor (WRVC), in East Africa between the years 2018 and 2060. This approach provides the foundation for implementing improved regional governance, better encouragement of sustainable development beyond the 2030 United Nations Sustainable Development Goals, and education programs, such as the AAC, that promote socio-ecological resilience through Earth Stewardship Science. The AAC archives a portion of East Africa as the WRVC, a corridor along the western branch of the East African Rift System that highlights twenty heritage nodes, primarily great lakes, mountain ranges, national parks, and biological hotspots. These heritage entities are associated with ca. 12-million-years of evolution and transformation of the East African topography and related African Great Lake (AGL) systems. The thesis defines the study area by delineating AGL basins intersected by the WRVC. Across these basins, land cover change analysis provides a platform for an integrated assessment of the projected health of the corridor region. Existing land cover datasets provide the initial conditions of the study area for 2008 and 2013. Land cover between 2008 and 2013 is cross-tabulated using the Land Cover Module in the Terrset software, followed by the iii delineation of sub-models and driver variable identification. The Multi-Layer Perceptron algorithm provides the transition potentials between tree cover, urban area, cropland, wetland, and open area classes. Change quantification and prediction using Markov Chain analysis are then established for 2018, 2030, and 2060. The model successfully simulated future land cover change and concluded that: (1) proximity to existing human activity, proximity to existing tree cover, and population are the primary drivers of change; (2) the dominant land cover of the ten lake basins for 2018 was cropland at ca. 48%, followed by tree cover at ca. 33%; (3) total anthropogenic change over the coming four decades equates to over ca. 52 000 km2 (5 200 000 ha), and particularly (4) an urban area is expected to increase by >130%. This assessment ultimately provides a platform for regional governance development at the basin scale and Earth Stewardship science in East Africa. These changes require transdisciplinary action from researchers to civil society. The AAC provides the foundation for understanding the dynamics of the systems that support life across broader spatial and temporal resolutions in Africa, highlighting the need for future generations to build socio-ecological resilience to anticipate challenges such as biodiversity loss posed by climate change and excessive land cover change. , Thesis (DSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-12
- Authors: Miller, Warren David
- Date: 2022-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/59771 , vital:62423
- Description: Over the coming decades, Africa is expected to experience disturbing effects due to climate change and increased land cover change due to human influences presenting a significant concern for the future well-being of human and biological systems, the latter being the foundation of ecosystem services supplied to humanity. Therefore, unprecedented transdisciplinary cooperation, coordination, and integration amongst researchers, government, and civil society are necessary to increase the resiliency of these systems. This study aims to provide an outline of the Africa Alive Corridors (AAC) as an essential model for the encouragement of sustainable development through Earth Stewardship science. These aims are accompanied by the quantification and forward modelling for land cover change of the Critical Zone over 10 Great Lake Basins across one of the AAC, the Western Rift Valley Corridor (WRVC), in East Africa between the years 2018 and 2060. This approach provides the foundation for implementing improved regional governance, better encouragement of sustainable development beyond the 2030 United Nations Sustainable Development Goals, and education programs, such as the AAC, that promote socio-ecological resilience through Earth Stewardship Science. The AAC archives a portion of East Africa as the WRVC, a corridor along the western branch of the East African Rift System that highlights twenty heritage nodes, primarily great lakes, mountain ranges, national parks, and biological hotspots. These heritage entities are associated with ca. 12-million-years of evolution and transformation of the East African topography and related African Great Lake (AGL) systems. The thesis defines the study area by delineating AGL basins intersected by the WRVC. Across these basins, land cover change analysis provides a platform for an integrated assessment of the projected health of the corridor region. Existing land cover datasets provide the initial conditions of the study area for 2008 and 2013. Land cover between 2008 and 2013 is cross-tabulated using the Land Cover Module in the Terrset software, followed by the iii delineation of sub-models and driver variable identification. The Multi-Layer Perceptron algorithm provides the transition potentials between tree cover, urban area, cropland, wetland, and open area classes. Change quantification and prediction using Markov Chain analysis are then established for 2018, 2030, and 2060. The model successfully simulated future land cover change and concluded that: (1) proximity to existing human activity, proximity to existing tree cover, and population are the primary drivers of change; (2) the dominant land cover of the ten lake basins for 2018 was cropland at ca. 48%, followed by tree cover at ca. 33%; (3) total anthropogenic change over the coming four decades equates to over ca. 52 000 km2 (5 200 000 ha), and particularly (4) an urban area is expected to increase by >130%. This assessment ultimately provides a platform for regional governance development at the basin scale and Earth Stewardship science in East Africa. These changes require transdisciplinary action from researchers to civil society. The AAC provides the foundation for understanding the dynamics of the systems that support life across broader spatial and temporal resolutions in Africa, highlighting the need for future generations to build socio-ecological resilience to anticipate challenges such as biodiversity loss posed by climate change and excessive land cover change. , Thesis (DSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-12
The co-evolution of Africa’s eastern margin and its primate fauna: implications for hominin evolution
- Authors: Mambalu, Philasande
- Date: 2022-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/59755 , vital:62418
- Description: I investigated potential links between the diversification of African primate lineages and the physical evolution of the continent. I compared published phylogenetic trees based on mitochondrial and nuclear DNA for five clades: (a) Lorisoidea (galagos and pottos); (b) arboreal guenon monkeys (Cercopithecus and its allies); (c) living apes (including humans); (d) Papionini (baboons); and (e) savanna or “vervet” monkeys (Chlorocebus). I compared primate divergence dates with the ages of tectonic events, patterns of climatic change, and their palaeo-vegetational consequences. Based on present primate distributions, I estimated likely geographic locations of the divergence events. Finally, I compared the phylogenetic patterns of the primate clades with hominin evolutionary scenarios. Phylogenetic comparisons indicated three time periods when rates of speciation increased across the five primate clades: the Eocene – Oligocene transition (34 – 32 Ma); the mid-late Miocene (10 – 5 Ma); and the Pliocene – Pleistocene transition (2.7 – 2.3 Ma). Concentrated bursts of lineage splitting indicate a broadscale causal relationship between environmental change and lineage divergence. Human evolution followed similar biogeographic patterns to those of other primate clades. Tectonic events, climatic changes and palaeo-vegetational shifts are intimately connected, and have synergistic effects on biotic diversity. Tectonic events influence climatic change through their effects on oceanic circulation, planetary temperatures and rainfall patterns. Additionally, tectonic uplift and erosion may create geographic barriers to organismal dispersal across the continent, increasing the likelihood of geographic separation of populations and speciation. Recently evolved primate species show high levels of hybridisation for several generations after their initial divergence. Genus Homo generated ~10 species over 2.5 Ma. The emergence of these taxa likely involved substantial hybridisation, as demonstrated by the presence of Neanderthal genes within the H. sapiens genome. I suggest that this hybridisation contributed to the difficulties palaeoanthropologists often experience in distinguishing fossil hominin taxa. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-12
- Authors: Mambalu, Philasande
- Date: 2022-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/59755 , vital:62418
- Description: I investigated potential links between the diversification of African primate lineages and the physical evolution of the continent. I compared published phylogenetic trees based on mitochondrial and nuclear DNA for five clades: (a) Lorisoidea (galagos and pottos); (b) arboreal guenon monkeys (Cercopithecus and its allies); (c) living apes (including humans); (d) Papionini (baboons); and (e) savanna or “vervet” monkeys (Chlorocebus). I compared primate divergence dates with the ages of tectonic events, patterns of climatic change, and their palaeo-vegetational consequences. Based on present primate distributions, I estimated likely geographic locations of the divergence events. Finally, I compared the phylogenetic patterns of the primate clades with hominin evolutionary scenarios. Phylogenetic comparisons indicated three time periods when rates of speciation increased across the five primate clades: the Eocene – Oligocene transition (34 – 32 Ma); the mid-late Miocene (10 – 5 Ma); and the Pliocene – Pleistocene transition (2.7 – 2.3 Ma). Concentrated bursts of lineage splitting indicate a broadscale causal relationship between environmental change and lineage divergence. Human evolution followed similar biogeographic patterns to those of other primate clades. Tectonic events, climatic changes and palaeo-vegetational shifts are intimately connected, and have synergistic effects on biotic diversity. Tectonic events influence climatic change through their effects on oceanic circulation, planetary temperatures and rainfall patterns. Additionally, tectonic uplift and erosion may create geographic barriers to organismal dispersal across the continent, increasing the likelihood of geographic separation of populations and speciation. Recently evolved primate species show high levels of hybridisation for several generations after their initial divergence. Genus Homo generated ~10 species over 2.5 Ma. The emergence of these taxa likely involved substantial hybridisation, as demonstrated by the presence of Neanderthal genes within the H. sapiens genome. I suggest that this hybridisation contributed to the difficulties palaeoanthropologists often experience in distinguishing fossil hominin taxa. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-12
A case study on the incidence and extent of medullated and coloured fibres in the commercially produced South African wool clip 2010 – 2017
- Authors: Zietsman, Jolandrie
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55445 , vital:52002
- Description: No formal study on the incidence and extent of medullated and coloured fibres has been performed in South Africa. The purpose of this research project was to investigate the validity of the claims that there has been an increase in the production of wool contaminated with medullated and coloured fibres. Therefore, the main aim of this study was to determine whether the incidence and extent of medullated and coloured fibres in the South African wool clip have changed over time. Secondly, the study aimed to determine whether the incidence and extent of medullated and coloured fibres have a distinct geographic distribution. This study explored eight years of wool production records (2010 to 2017) obtained from BKB, the largest wool broker in South Africa. For the purpose of this research, the wool-producing areas of South Africa were divided into 6 regions, according to average annual rainfall, vegetation type and major farming practices applied in the area. Statistical analysis of the data included descriptive statistics, analysis of variance and post-hoc tests, as well as regression analyses. This study succeeded in quantifying the extent and prevalence of contamination with medullated and coloured fibres in the South African wool clip. The overarching conclusions were: • Floating kemp is the most important contaminant of wool in South Africa, with the incidence of harsh kemp and coloured fibres being very low. • Generally, the most important areas that need attention in combatting contamination in the South African wool clip, are the Mixed Farming Summer Rainfall Region, the Semi-Arid Grassveld and the High Rainfall Grassland. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: Zietsman, Jolandrie
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55445 , vital:52002
- Description: No formal study on the incidence and extent of medullated and coloured fibres has been performed in South Africa. The purpose of this research project was to investigate the validity of the claims that there has been an increase in the production of wool contaminated with medullated and coloured fibres. Therefore, the main aim of this study was to determine whether the incidence and extent of medullated and coloured fibres in the South African wool clip have changed over time. Secondly, the study aimed to determine whether the incidence and extent of medullated and coloured fibres have a distinct geographic distribution. This study explored eight years of wool production records (2010 to 2017) obtained from BKB, the largest wool broker in South Africa. For the purpose of this research, the wool-producing areas of South Africa were divided into 6 regions, according to average annual rainfall, vegetation type and major farming practices applied in the area. Statistical analysis of the data included descriptive statistics, analysis of variance and post-hoc tests, as well as regression analyses. This study succeeded in quantifying the extent and prevalence of contamination with medullated and coloured fibres in the South African wool clip. The overarching conclusions were: • Floating kemp is the most important contaminant of wool in South Africa, with the incidence of harsh kemp and coloured fibres being very low. • Generally, the most important areas that need attention in combatting contamination in the South African wool clip, are the Mixed Farming Summer Rainfall Region, the Semi-Arid Grassveld and the High Rainfall Grassland. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-04
Classification and clustering based methods for outlier detection of solar resource data
- Authors: Abrahams, Waldo
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55423 , vital:51996
- Description: Almost 90% of the primary global energy demand is serviced from the burning of fossil fuels (Abas, Kalair & Khan, 2015). Owing to the detrimental environmental impact of this, a global energy transition to the use of renewable energy, including solar energy, is needed (Gielen et al., 2019). An important aspect that inhibits the growth of solar energy is accurate solar resource data. Such data is needed because knowledge of the future reliability and quality of energy production is required to analyse a system’s performance and determine financial implications (Sengupta et al., 2017). Existing methods used to detect outliers in solar resource data do not efficiently identify outliers and an accurate and robust approach is required (Eastwood, 2019). Using simulated and real-world data, this study investigates the use of several classification methods, along with a two-stage clustering-classification approach to accurately identify outliers in solar resource data. The Treebag method proves to be an adequate outlier detection method for solar resource data. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: Abrahams, Waldo
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55423 , vital:51996
- Description: Almost 90% of the primary global energy demand is serviced from the burning of fossil fuels (Abas, Kalair & Khan, 2015). Owing to the detrimental environmental impact of this, a global energy transition to the use of renewable energy, including solar energy, is needed (Gielen et al., 2019). An important aspect that inhibits the growth of solar energy is accurate solar resource data. Such data is needed because knowledge of the future reliability and quality of energy production is required to analyse a system’s performance and determine financial implications (Sengupta et al., 2017). Existing methods used to detect outliers in solar resource data do not efficiently identify outliers and an accurate and robust approach is required (Eastwood, 2019). Using simulated and real-world data, this study investigates the use of several classification methods, along with a two-stage clustering-classification approach to accurately identify outliers in solar resource data. The Treebag method proves to be an adequate outlier detection method for solar resource data. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2022
- Full Text:
- Date Issued: 2022-04
Effect of fire severity on Afrotemperate forest tree survival
- Authors: Giddey, Brandon Louis
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55385 , vital:51988
- Description: Weather patterns have changed globally with increased fire danger weather conditions, along with poor management and fire suppression, likely contributing to the increase in prevalence of large wildfires. Ecosystems such as temperate broadleaved forests, where fire is limited by climatic conditions, are particularly at risk of altered fire regimes related to climate change. It is thus important to monitor the effects of fire in these ecosystems. Satellite remote sensing is a cost-effective way to assess spatial variability of fire effects on a landscape scale and has become an increasingly used tool for studying fire severity. In the southern Cape of South Africa during October-November 2018, a large wildfire burnt patches of Southern Cape Afrotemperate Forest (hereafter ‘Afrotemperate forest’). This provided an opportunity to investigate the accuracy of a satellite index for fire severity and the effect of fire on Afrotemperate forest survival. The first objective was to verify through field observations the accuracy of the differenced Normalised Burn Ratio (dNBR) as an index of fire severity derived from Sentinel 2 images in Afrotemperate forest. The second objective was to investigate the effect of fire severity and tree size on the post-fire survival of Afrotemperate forest tree species. For the first objective, stem fire severity, estimated from observed damage to the main stem, was recorded for 1 648 trees in 87 plots and linear regression used to test whether the observed measure of fire severity was related to dNBR. For the second objective, stem fire severity and tree survival 19-24 months post-fire were recorded for 40 species and 1 378 trees in 88 plots. Trees were considered to have survived if they resprouted from the main stem or had green foliage in the canopy. The survival response was assessed in relation to stem fire severity and tree size for all trees collectively and for 10 species (with sample size > 40) individually, using logistic regression. A strong linear relationship between dNBR and stem fire severity (r2 = 0.69, p < 0.001) confirmed the accuracy of dNBR as a measure of fire severity in Afrotemperate forest. In the fire investigated, 4 628 ha of Afrotemperate forest burnt of which 67% burnt at low severity, 21% at medium severity and 12% at high severity. The dNBR values associated with fire severity categories were comparable between Afrotemperate and North American forests, suggesting that dNBR values are relatively standard across forest types. Information on the distribution of fire severity facilitates investigation of further questions regarding past and future fire regimes and the fire ecology of Afrotemperate forest. The post-fire survival rate of Afrotemperate forest trees was 45% which is comparable to that in coniferous forests of North America but lower than that in temperate forests of Australia and Portugal and the neighbouring dune thicket which shares several species with Afrotemperate forest. Fire severity had a significant negative effect on survival and tree size a significant positive effect. Total variance explained by the model (for species collectively) was 40.8%, of which fire severity and tree size combined explained 13.2%, and species as random factor, 27.6%. Respective tree species showed differential survival responses – four species showed high survival (> 60% of individuals), while five species showed low survival (< 40%). This study was the first post-fire assessment of the resprouting ability of Afrotemperate forest trees and a third of the trees surveyed (for species collectively) resprouted from the stem. This suggested that resprouting from the stem is a primary means of post-fire recovery in Afrotemperate forest trees, in contrast with previous assertions that several common canopy species, including Podocarpus latifolius, Afrocarpus falcatus, Scutia myrtina, Scolopia mundii and Rapanea melanophloeos, are unable to resprout. Varying resilience to fire among species supports previous suggestions that fire affects species’ composition and diversity in these forests and calls for careful management of fire regimes in the face of global change. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2022
- Full Text: false
- Date Issued: 2022-04
- Authors: Giddey, Brandon Louis
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55385 , vital:51988
- Description: Weather patterns have changed globally with increased fire danger weather conditions, along with poor management and fire suppression, likely contributing to the increase in prevalence of large wildfires. Ecosystems such as temperate broadleaved forests, where fire is limited by climatic conditions, are particularly at risk of altered fire regimes related to climate change. It is thus important to monitor the effects of fire in these ecosystems. Satellite remote sensing is a cost-effective way to assess spatial variability of fire effects on a landscape scale and has become an increasingly used tool for studying fire severity. In the southern Cape of South Africa during October-November 2018, a large wildfire burnt patches of Southern Cape Afrotemperate Forest (hereafter ‘Afrotemperate forest’). This provided an opportunity to investigate the accuracy of a satellite index for fire severity and the effect of fire on Afrotemperate forest survival. The first objective was to verify through field observations the accuracy of the differenced Normalised Burn Ratio (dNBR) as an index of fire severity derived from Sentinel 2 images in Afrotemperate forest. The second objective was to investigate the effect of fire severity and tree size on the post-fire survival of Afrotemperate forest tree species. For the first objective, stem fire severity, estimated from observed damage to the main stem, was recorded for 1 648 trees in 87 plots and linear regression used to test whether the observed measure of fire severity was related to dNBR. For the second objective, stem fire severity and tree survival 19-24 months post-fire were recorded for 40 species and 1 378 trees in 88 plots. Trees were considered to have survived if they resprouted from the main stem or had green foliage in the canopy. The survival response was assessed in relation to stem fire severity and tree size for all trees collectively and for 10 species (with sample size > 40) individually, using logistic regression. A strong linear relationship between dNBR and stem fire severity (r2 = 0.69, p < 0.001) confirmed the accuracy of dNBR as a measure of fire severity in Afrotemperate forest. In the fire investigated, 4 628 ha of Afrotemperate forest burnt of which 67% burnt at low severity, 21% at medium severity and 12% at high severity. The dNBR values associated with fire severity categories were comparable between Afrotemperate and North American forests, suggesting that dNBR values are relatively standard across forest types. Information on the distribution of fire severity facilitates investigation of further questions regarding past and future fire regimes and the fire ecology of Afrotemperate forest. The post-fire survival rate of Afrotemperate forest trees was 45% which is comparable to that in coniferous forests of North America but lower than that in temperate forests of Australia and Portugal and the neighbouring dune thicket which shares several species with Afrotemperate forest. Fire severity had a significant negative effect on survival and tree size a significant positive effect. Total variance explained by the model (for species collectively) was 40.8%, of which fire severity and tree size combined explained 13.2%, and species as random factor, 27.6%. Respective tree species showed differential survival responses – four species showed high survival (> 60% of individuals), while five species showed low survival (< 40%). This study was the first post-fire assessment of the resprouting ability of Afrotemperate forest trees and a third of the trees surveyed (for species collectively) resprouted from the stem. This suggested that resprouting from the stem is a primary means of post-fire recovery in Afrotemperate forest trees, in contrast with previous assertions that several common canopy species, including Podocarpus latifolius, Afrocarpus falcatus, Scutia myrtina, Scolopia mundii and Rapanea melanophloeos, are unable to resprout. Varying resilience to fire among species supports previous suggestions that fire affects species’ composition and diversity in these forests and calls for careful management of fire regimes in the face of global change. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2022
- Full Text: false
- Date Issued: 2022-04
Encapsulation of flame retardants for lithium-ion battery safety
- Authors: Ntombela, Nompilo Princess
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55412 , vital:51993
- Description: Lithium-ion technology takes the lead in electric mobility systems, resulting in an increase in the global demand for Li-ion batteries; however, these batteries are associated with numerous safety concerns. Additionally, there are high costs, high energy and power issues which are some of its key limitations. Research efforts are focused on overcoming these obstacles, with different approaches being explored, such as the investigation of more stable salts, modification of active materials and organic solvents, and the use of electrolyte additives. This study focused specifically on electrolyte additives since the electrolyte is one of the most unstable components of the battery. The electrolyte’s decomposition is one of the reactions that occur inside a battery, which may occur due to overcharging or due to an internal short circuit, amongst others. The electrolyte’s decomposition occurs at the early stages of the thermal runaway process and forms part of the reactions that lead to fires and explosions. Thus, this research aims to develop suitable electrolyte additives to improve the safety aspects of Li-ion batteries. Flame retardant additives show great promise in reducing the flammability of the electrolyte in Li-ion batteries, since they serve to suppress the chemical reactions associated with battery ignition. They retard the fires by scavenging the active radical species formed during the decomposition reaction. In this study, the use of flame retardants was investigated. Flame retardant additives have shown to have flame impeding properties inside a battery; however, their direct addition to the electrolyte tends to cause adverse effects on the ionic conductivity and electrochemical performance of the cells. This study investigated an alternative option - the option to microencapsulate such additives into a neutral compound to ensure that the flame retardant has minimal/no effect on the performance of the battery. This investigation looked at tris(2-butoxyethyl) phosphate (TBP) and bis(2,2,2-trifluoroethyl) methylphosphonate (BFP) as flame retardant additives for the electrolyte. The TBP and BFP flame retardants were microencapsulated in poly(urea formaldehyde) (PUF) coating material via in situ polymerization method. The capsules were characterized using various analytical techniques - to prove it was successfully encapsulated. Electrochemical studies were further done on the capsules and neat flame retardants inside a coin cell. Self-extinguishing time (SET), which is the flammability test, proved that the additives have flame retarding abilities. Opto-digital microscopy (DSX) and scanning electron microscopy (SEM) did confirm the spherical shape of the microcapsules, where SEM also showed the smooth outer layer of the microcapsules and its hollow inner side. Fourier transform infrared spectroscopy (FTIR) proved the presence of the TBP and BFP inside the PUF resin by showing that the chemical composition of microcapsules consisted of both the PUF and flame retardant additives. Simultaneous DSC-TGA (DST) was also performed which showed that the microcapsules were stable before 200 °C, which indicates it would not decompose before the thermal runaway events are occurring. TGA analysis did show that the microcapsules underwent multiple decomposition steps upon heating. Additionally, 31P nuclear magnetic resonance (NMR) was used to quantify the amount of flame retardants additives encapsulated inside PUF shell, and also confirmed the stability of the microcapsules for one month in the electrolyte and at temperatures up to 200 °C. The ionic conductivity was vastly decreased when the flame retardants were added directly to the electrolyte. However, adding the flame retardants in a form of capsules had minimal effect on the ionic conductivity. The cycle capacities of the capsules were also improved when the capsules were added to the cell compared to that of neat flame retardants. The same effect was also noticed when doing Electrochemical Impedance Spectroscopy (EIS). This shows that microencapsulation improves the resistance of the cell caused by the flame retardant in comparison to when added directly to the electrolyte of the cell. , Thesis (MSC) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: Ntombela, Nompilo Princess
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55412 , vital:51993
- Description: Lithium-ion technology takes the lead in electric mobility systems, resulting in an increase in the global demand for Li-ion batteries; however, these batteries are associated with numerous safety concerns. Additionally, there are high costs, high energy and power issues which are some of its key limitations. Research efforts are focused on overcoming these obstacles, with different approaches being explored, such as the investigation of more stable salts, modification of active materials and organic solvents, and the use of electrolyte additives. This study focused specifically on electrolyte additives since the electrolyte is one of the most unstable components of the battery. The electrolyte’s decomposition is one of the reactions that occur inside a battery, which may occur due to overcharging or due to an internal short circuit, amongst others. The electrolyte’s decomposition occurs at the early stages of the thermal runaway process and forms part of the reactions that lead to fires and explosions. Thus, this research aims to develop suitable electrolyte additives to improve the safety aspects of Li-ion batteries. Flame retardant additives show great promise in reducing the flammability of the electrolyte in Li-ion batteries, since they serve to suppress the chemical reactions associated with battery ignition. They retard the fires by scavenging the active radical species formed during the decomposition reaction. In this study, the use of flame retardants was investigated. Flame retardant additives have shown to have flame impeding properties inside a battery; however, their direct addition to the electrolyte tends to cause adverse effects on the ionic conductivity and electrochemical performance of the cells. This study investigated an alternative option - the option to microencapsulate such additives into a neutral compound to ensure that the flame retardant has minimal/no effect on the performance of the battery. This investigation looked at tris(2-butoxyethyl) phosphate (TBP) and bis(2,2,2-trifluoroethyl) methylphosphonate (BFP) as flame retardant additives for the electrolyte. The TBP and BFP flame retardants were microencapsulated in poly(urea formaldehyde) (PUF) coating material via in situ polymerization method. The capsules were characterized using various analytical techniques - to prove it was successfully encapsulated. Electrochemical studies were further done on the capsules and neat flame retardants inside a coin cell. Self-extinguishing time (SET), which is the flammability test, proved that the additives have flame retarding abilities. Opto-digital microscopy (DSX) and scanning electron microscopy (SEM) did confirm the spherical shape of the microcapsules, where SEM also showed the smooth outer layer of the microcapsules and its hollow inner side. Fourier transform infrared spectroscopy (FTIR) proved the presence of the TBP and BFP inside the PUF resin by showing that the chemical composition of microcapsules consisted of both the PUF and flame retardant additives. Simultaneous DSC-TGA (DST) was also performed which showed that the microcapsules were stable before 200 °C, which indicates it would not decompose before the thermal runaway events are occurring. TGA analysis did show that the microcapsules underwent multiple decomposition steps upon heating. Additionally, 31P nuclear magnetic resonance (NMR) was used to quantify the amount of flame retardants additives encapsulated inside PUF shell, and also confirmed the stability of the microcapsules for one month in the electrolyte and at temperatures up to 200 °C. The ionic conductivity was vastly decreased when the flame retardants were added directly to the electrolyte. However, adding the flame retardants in a form of capsules had minimal effect on the ionic conductivity. The cycle capacities of the capsules were also improved when the capsules were added to the cell compared to that of neat flame retardants. The same effect was also noticed when doing Electrochemical Impedance Spectroscopy (EIS). This shows that microencapsulation improves the resistance of the cell caused by the flame retardant in comparison to when added directly to the electrolyte of the cell. , Thesis (MSC) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2022
- Full Text:
- Date Issued: 2022-04
Hydraulic vulnerability of Subtropical Thicket to drought : a remote sensing and physiological perspective
- Authors: Buttner, Daniel Harry
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55455 , vital:52017
- Description: Water availability is one of largest constraints on plant survival, growth, and species distribution globally. The recent escalation in tree mortality coupled with declining precipitation and amplified temperatures has implicated drought as a major cause behind many large-scale dieback events observed across the world. Raising the question, what makes some species more resistant and persist while others dwindle and vanish from the landscape? The observed variability in species drought susceptibility demonstrates the complexity of physiological responses of plants to changes in water availability. Hydraulic dysfunction in plants has been purported to be the key mechanism behind drought-induced mortality provoking interest in hydraulic traits and critical thresholds of xylem physiological function. The capability of species to maintain hydraulic functionality under drought strongly influences the survival and general productivity towards water deficits. Hence, two core objectives, and subsequently aims, of this thesis are firstly to investigate the effect of drought on Subtropical Thicket vegetation health and productivity, and secondly to examine the underpinning physiological mechanisms and functional thresholds relaying speciesspecific drought vulnerability within this semi-arid biome. In first data chapter, this thesis offers an assessment of vegetation change under drought and its influence on plant physiological function and productivity across a subsection of Subtropical Thicket distribution. Additionally, this chapter provides a regional scale perspective of drought on Subtropical Thicket flora in the Eastern Cape of South Africa. A severe anomalous dieback event, which coincided with extreme, accumulative drought conditions was observed in 2020. Employing a combination of field-based approaches and remote sensing, this chapter aimed to provide a comprehensive report of the extent and severity of crown defoliation and canopy dieback following this event, additionally describing predisposing and compounding factors. Based on Standardized Precipitation Evapotranspiration and Standardized Precipitation Indices this event began in 2015 and coincided with amplified temperatures, exacerbating evaporative demand. Aerial UAV surveys and field-based investigations were undertaken. Remotely sensed (RS) indices provided an avenue for extensive spatiotemporal investigations to uncover the extent of drought-related impact on vegetation productivity and discuss potential underpinning mechanisms behind drought-induced mortality in Subtropical Thicket. Leveraging long-term time series RS data, Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI), from Moderate Resolution Imaging Spectroradiometer (MODIS) satellites as a proxy vegetation physiological status in combination with SPI and SPEI describing drought condition and groundbased surveying defining canopy vitality condition this study incidentally addressed the aim of endeavoring to link drought-induced mortality and early warning symptoms observed in the field with RS time series data to describe drought impacts across Subtropical Thicket. Furthermore, the findings of this chapter demonstrate the spatial and temporal heterogeneity in drought impacts on Subtropical Thicket. The recent drought of 2015 till 2021 is the longest documented period for the past 50 years in which there has been no accumulated net positive water availability, this apparently perpetual state of water deficiency has enacted a high cost for vegetation productivity and growth for the study area, exhibited well by average NDVI values of less than -0.5 for over 70% of the research site. The findings of this chapter report, to the contrary of anecdotal suggestions in the literature, on the intrinsic tolerance of Subtropical Thicket and that ii drought has a far more significant role on overall vegetation productivity, growth, and mortality in this region. The second data chapter assess whole-plant physiological functionality during a drought event in the Eastern Cape, South Africa. This is the first study in Subtropical Thicket to quantify in situ hydraulic functional integrity under a natural drought event testing the leading hypothesis describing tree mortality – hydraulic dysfunction. This chapter firstly, investigates hydraulic traits (e.g., turgor loss point) and describe key physiological thresholds (e.g., P50) for maintaining function during drought. Secondly, levels of native embolism were determined under drought conditions and combined with measurements of xylem vulnerability to embolism providing an estimation of degree of hydraulic dysfunction experienced by six dominant woody canopy species in Subtropical Thicket – to quantify interspecific drought tolerance and susceptibility. Subtropical Thicket species exhibited remarkable tolerance towards desiccation (TLP from as low as -3MPa) and hydraulic functional resistance to embolism (P50 value as low as -7.89MPa). The observed unexpected drought resilience of subtropical derived lineages highlights the intrinsic evolutionary role aridification had, selecting for greater embolism resistance and community-level conservatism in drought resistance of Subtropical Thicket. The level of native embolism and hydraulic safety margins identified two species (Schotia latifolia and Polyagla myrtifolia) that were the most vulnerable, and a third (Pappea capensis) moderately vulnerable, then the remaining studied species – this could result in community-level adjustments in species composition and structure under future projected climate change scenarios where, increased frequencies of drought events are anticipated. This retrospective assessment of canopy vigor with physiological functional thresholds evokes hydraulic dysfunction as the principal mechanism of observed Subtropical Thicket dieback to drought. This chapter provides crucial in situ data for predictive assertions around drought-induced mortality risk in a phylogenetically diverse and climatically unique biome of southern Africa; and is the first to identify critical hydraulic thresholds for tree species within this region. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: Buttner, Daniel Harry
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55455 , vital:52017
- Description: Water availability is one of largest constraints on plant survival, growth, and species distribution globally. The recent escalation in tree mortality coupled with declining precipitation and amplified temperatures has implicated drought as a major cause behind many large-scale dieback events observed across the world. Raising the question, what makes some species more resistant and persist while others dwindle and vanish from the landscape? The observed variability in species drought susceptibility demonstrates the complexity of physiological responses of plants to changes in water availability. Hydraulic dysfunction in plants has been purported to be the key mechanism behind drought-induced mortality provoking interest in hydraulic traits and critical thresholds of xylem physiological function. The capability of species to maintain hydraulic functionality under drought strongly influences the survival and general productivity towards water deficits. Hence, two core objectives, and subsequently aims, of this thesis are firstly to investigate the effect of drought on Subtropical Thicket vegetation health and productivity, and secondly to examine the underpinning physiological mechanisms and functional thresholds relaying speciesspecific drought vulnerability within this semi-arid biome. In first data chapter, this thesis offers an assessment of vegetation change under drought and its influence on plant physiological function and productivity across a subsection of Subtropical Thicket distribution. Additionally, this chapter provides a regional scale perspective of drought on Subtropical Thicket flora in the Eastern Cape of South Africa. A severe anomalous dieback event, which coincided with extreme, accumulative drought conditions was observed in 2020. Employing a combination of field-based approaches and remote sensing, this chapter aimed to provide a comprehensive report of the extent and severity of crown defoliation and canopy dieback following this event, additionally describing predisposing and compounding factors. Based on Standardized Precipitation Evapotranspiration and Standardized Precipitation Indices this event began in 2015 and coincided with amplified temperatures, exacerbating evaporative demand. Aerial UAV surveys and field-based investigations were undertaken. Remotely sensed (RS) indices provided an avenue for extensive spatiotemporal investigations to uncover the extent of drought-related impact on vegetation productivity and discuss potential underpinning mechanisms behind drought-induced mortality in Subtropical Thicket. Leveraging long-term time series RS data, Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI), from Moderate Resolution Imaging Spectroradiometer (MODIS) satellites as a proxy vegetation physiological status in combination with SPI and SPEI describing drought condition and groundbased surveying defining canopy vitality condition this study incidentally addressed the aim of endeavoring to link drought-induced mortality and early warning symptoms observed in the field with RS time series data to describe drought impacts across Subtropical Thicket. Furthermore, the findings of this chapter demonstrate the spatial and temporal heterogeneity in drought impacts on Subtropical Thicket. The recent drought of 2015 till 2021 is the longest documented period for the past 50 years in which there has been no accumulated net positive water availability, this apparently perpetual state of water deficiency has enacted a high cost for vegetation productivity and growth for the study area, exhibited well by average NDVI values of less than -0.5 for over 70% of the research site. The findings of this chapter report, to the contrary of anecdotal suggestions in the literature, on the intrinsic tolerance of Subtropical Thicket and that ii drought has a far more significant role on overall vegetation productivity, growth, and mortality in this region. The second data chapter assess whole-plant physiological functionality during a drought event in the Eastern Cape, South Africa. This is the first study in Subtropical Thicket to quantify in situ hydraulic functional integrity under a natural drought event testing the leading hypothesis describing tree mortality – hydraulic dysfunction. This chapter firstly, investigates hydraulic traits (e.g., turgor loss point) and describe key physiological thresholds (e.g., P50) for maintaining function during drought. Secondly, levels of native embolism were determined under drought conditions and combined with measurements of xylem vulnerability to embolism providing an estimation of degree of hydraulic dysfunction experienced by six dominant woody canopy species in Subtropical Thicket – to quantify interspecific drought tolerance and susceptibility. Subtropical Thicket species exhibited remarkable tolerance towards desiccation (TLP from as low as -3MPa) and hydraulic functional resistance to embolism (P50 value as low as -7.89MPa). The observed unexpected drought resilience of subtropical derived lineages highlights the intrinsic evolutionary role aridification had, selecting for greater embolism resistance and community-level conservatism in drought resistance of Subtropical Thicket. The level of native embolism and hydraulic safety margins identified two species (Schotia latifolia and Polyagla myrtifolia) that were the most vulnerable, and a third (Pappea capensis) moderately vulnerable, then the remaining studied species – this could result in community-level adjustments in species composition and structure under future projected climate change scenarios where, increased frequencies of drought events are anticipated. This retrospective assessment of canopy vigor with physiological functional thresholds evokes hydraulic dysfunction as the principal mechanism of observed Subtropical Thicket dieback to drought. This chapter provides crucial in situ data for predictive assertions around drought-induced mortality risk in a phylogenetically diverse and climatically unique biome of southern Africa; and is the first to identify critical hydraulic thresholds for tree species within this region. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-04
Potential suppressive effects of alien Acacia melanoxylon on Afrotemperate Forest tree recruitment
- Miles, Bayleigh, Baard, Johan
- Authors: Miles, Bayleigh , Baard, Johan
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55391 , vital:51989
- Description: Acacia melanoxylon R.Br. is a prominent alien and invasive species in many parts of the world and evidence exists of its adverse effects on indigenous forest community composition through allelopathy and alteration of light regimes. The species also occurs extensively in Southern Cape Afrotemperate Forest (South Africa) and is thought to suppress indigenous Afrotemperate Forest tree seedlings through various mechanisms such as the alteration of natural light regimes or allelopathy, although this has not been rigorously verified. This study aimed to investigate whether Acacia melanoxylon has a suppressive effect on Afrotemperate Forest tree recruitment. Firstly, we assessed the potential allelopathic effect of Acacia melanoxylon and an indigenous Afrotemperate Forest species Olea capensis macrocarpa (C.H.Wright) I.Verd. on the germination of Acacia melanoxylon and three prominent indigenous tree species’ seedlings in a nursery trial. Germination of the indigenous species failed; however, we were able to compare the germination of Acacia melanoxylon among the three treatments, namely Acacia melanoxylon leachate, Olea capensis leachate, and no leachate. The average germination of Acacia melanoxylon was 67% and germination was marginally higher under Acacia melanoxylon leachate and Olea capensis leachate, respectively, than under the control. This suggested that germination of the species is improved, or at the least, unaffected, by leachates of itself or that of a common indigenous canopy species. We then critically evaluated the germination requirements of the indigenous test species to determine probable reasons why their germination failed in our trial. The most plausible explanation for the germination failure could be that the trial period did not encompass an entire winter season and may not have provided adequate cold stratification. We concluded that the lack of sensitivity of Acacia melanoxylon to leachates of itself or a common indigenous overstorey species likely contribute to its success as an invasive species in Southern Cape Afrotemperate Forest. Secondly, we investigated, through field surveys, whether Acacia melanoxylon affects indigenous Afrotemperate Forest tree sapling composition and light regimes underneath its canopy. Using a paired plot design, we compared light intensity, tree sapling species richness, diversity, and density underneath 30 overstorey Acacia melanoxylon trees and 30 indigenous counterparts. We recorded 2506 indigenous tree saplings from 29 species in the 60 plots and found that there were no significant differences in richness, diversity, or v density of saplings underneath Acacia melanoxylon compared to that under indigenous counterparts. Light intensity did not differ significantly underneath Acacia melanoxylon and indigenous canopies, however light intensity varied significantly more underneath the canopies of Acacia melanoxylon. Canonical correspondence analysis of the abundance of sapling species confirmed that sapling composition was not largely determined by the overstorey species. We concluded that Acacia melanoxylon does not significantly alter indigenous tree species composition underneath its canopy at the typical densities (<3 trees per hectare) at which it occurred in the forests of the Garden Route National Park that we surveyed. Nevertheless, populations of Acacia melanoxylon in the forest interior still act as a source of propagules for invasion in forest margins, riparian areas, and neighbouring fynbos shrubland. These invasive attributes need to be considered in the management of the species in the region at large. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: Miles, Bayleigh , Baard, Johan
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55391 , vital:51989
- Description: Acacia melanoxylon R.Br. is a prominent alien and invasive species in many parts of the world and evidence exists of its adverse effects on indigenous forest community composition through allelopathy and alteration of light regimes. The species also occurs extensively in Southern Cape Afrotemperate Forest (South Africa) and is thought to suppress indigenous Afrotemperate Forest tree seedlings through various mechanisms such as the alteration of natural light regimes or allelopathy, although this has not been rigorously verified. This study aimed to investigate whether Acacia melanoxylon has a suppressive effect on Afrotemperate Forest tree recruitment. Firstly, we assessed the potential allelopathic effect of Acacia melanoxylon and an indigenous Afrotemperate Forest species Olea capensis macrocarpa (C.H.Wright) I.Verd. on the germination of Acacia melanoxylon and three prominent indigenous tree species’ seedlings in a nursery trial. Germination of the indigenous species failed; however, we were able to compare the germination of Acacia melanoxylon among the three treatments, namely Acacia melanoxylon leachate, Olea capensis leachate, and no leachate. The average germination of Acacia melanoxylon was 67% and germination was marginally higher under Acacia melanoxylon leachate and Olea capensis leachate, respectively, than under the control. This suggested that germination of the species is improved, or at the least, unaffected, by leachates of itself or that of a common indigenous canopy species. We then critically evaluated the germination requirements of the indigenous test species to determine probable reasons why their germination failed in our trial. The most plausible explanation for the germination failure could be that the trial period did not encompass an entire winter season and may not have provided adequate cold stratification. We concluded that the lack of sensitivity of Acacia melanoxylon to leachates of itself or a common indigenous overstorey species likely contribute to its success as an invasive species in Southern Cape Afrotemperate Forest. Secondly, we investigated, through field surveys, whether Acacia melanoxylon affects indigenous Afrotemperate Forest tree sapling composition and light regimes underneath its canopy. Using a paired plot design, we compared light intensity, tree sapling species richness, diversity, and density underneath 30 overstorey Acacia melanoxylon trees and 30 indigenous counterparts. We recorded 2506 indigenous tree saplings from 29 species in the 60 plots and found that there were no significant differences in richness, diversity, or v density of saplings underneath Acacia melanoxylon compared to that under indigenous counterparts. Light intensity did not differ significantly underneath Acacia melanoxylon and indigenous canopies, however light intensity varied significantly more underneath the canopies of Acacia melanoxylon. Canonical correspondence analysis of the abundance of sapling species confirmed that sapling composition was not largely determined by the overstorey species. We concluded that Acacia melanoxylon does not significantly alter indigenous tree species composition underneath its canopy at the typical densities (<3 trees per hectare) at which it occurred in the forests of the Garden Route National Park that we surveyed. Nevertheless, populations of Acacia melanoxylon in the forest interior still act as a source of propagules for invasion in forest margins, riparian areas, and neighbouring fynbos shrubland. These invasive attributes need to be considered in the management of the species in the region at large. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2022
- Full Text:
- Date Issued: 2022-04
Spatial modelling of accessibility to tuberculosis treatment: the case of Ngaka Modiri Molema District
- Authors: Ramotsongwa, Karabo Naome
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55435 , vital:52000
- Description: Accessibility to healthcare refers to the availability, or the provision of healthcare-byhealthcare professionals and stakeholders and individuals' ability to obtain care and treatment. It affects overall physical, social, and mental health; disease and disability prevention; detection and treatment of health conditions; standard of living; preventable death; and life expectancy, and it is crucial to the performance of health care systems around the world. If healthcare services are available and are in sufficient supply, people will be able to seek health care, and a population will have access to services. The leading cause of death globally is Tuberculosis (TB) and South Africa is amongst the top 5 countries most affected by TB. This is aggravated by high HIV/AIDS statistics. Children belowthe age of 4, between the ages of 4- 15, and women and men of working ages are highly affected by TB and it is the primary cause of death in these groups in the Ngaka Modiri Molema District. This study used study tools like Spatial Modelling, Geographic Information Systems and software like ArcGIS 10.5, TerrSet IDRISI 18.30, and secondary data from the North West Departmentof Health (Tier.net &DHIS) and also TB patients’ home addresses to investigate the accessibility of TB treatment in Ngaka Modiri Molema, in order to spatially visualize the distribution of a communicable disease like TB and public healthcare facilities in the Ngaka Modiri Molema (NMM) District and suggest optimum sites for hospital facilities. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: Ramotsongwa, Karabo Naome
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/55435 , vital:52000
- Description: Accessibility to healthcare refers to the availability, or the provision of healthcare-byhealthcare professionals and stakeholders and individuals' ability to obtain care and treatment. It affects overall physical, social, and mental health; disease and disability prevention; detection and treatment of health conditions; standard of living; preventable death; and life expectancy, and it is crucial to the performance of health care systems around the world. If healthcare services are available and are in sufficient supply, people will be able to seek health care, and a population will have access to services. The leading cause of death globally is Tuberculosis (TB) and South Africa is amongst the top 5 countries most affected by TB. This is aggravated by high HIV/AIDS statistics. Children belowthe age of 4, between the ages of 4- 15, and women and men of working ages are highly affected by TB and it is the primary cause of death in these groups in the Ngaka Modiri Molema District. This study used study tools like Spatial Modelling, Geographic Information Systems and software like ArcGIS 10.5, TerrSet IDRISI 18.30, and secondary data from the North West Departmentof Health (Tier.net &DHIS) and also TB patients’ home addresses to investigate the accessibility of TB treatment in Ngaka Modiri Molema, in order to spatially visualize the distribution of a communicable disease like TB and public healthcare facilities in the Ngaka Modiri Molema (NMM) District and suggest optimum sites for hospital facilities. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2022-04
The use of psychometric test systems as a pre-selection tool for identifying successful harvesting machine operators
- Authors: Schwegman, Kylle
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/55246 , vital:51102
- Description: A shift towards fully mechanized forest activities, such as harvesting and, more recently, silviculture, has occurred from the early 2 000’s. The reason for mechanizing these activities differs for each country, although for most countries there is concern relating to the health and safety of forest workers. With mechanization in harvesting, the forest worker has moved away from the physical intensity of having to fell, debranch, debark and cross-cut trees into logs using either an axe or chainsaw, to operating a machine. Studies revolving around the human element (operator) have been conducted specifically relating to the ergonomics of the machines and how operators may influence machine productivity. Results showed that due to the repetitive nature of the work, the operators are exposed to associated stresses for longer periods. Typical injuries associated to these kinds of stressors are whole body vibrations (WBVs), repetitive hand and arm movements, non-neutral body postures and manual lifting, which lead to musculoskeletal symptoms in the lower back, neck and shoulders. However, as machine technology improves so does the ergonomic conditions which are experienced by machine operators. Machine productivity can be influenced by various factors, with the most influential being tree volume. However, a recent study showed that over 40% of variation in machine productivity has been observed amongst different machine operators operating similar machines. The specific reason for these differences has yet to be determined. However, decision making, motivation, planning capacity, concentration, memory, motor coordination, pattern recognition, logic reasoning, and spatial perception are abilities that have been described as important for successful harvesting work. The pre-selection of operators using psychometric and cognitive tests is not new to forestry, although very little information is available relating to the aptitude test known as the Vienna test system as well as the best possible demographic associated with successful harvesting operators. The overall aim of this study was to determine whether the high variation found amongst harvesting machine operators could be reduced initially through a preselection process which involves the use of aptitude tests (Vienna Test System) and demographic questionnaires. A study was implemented in Zululand, South Africa, testing whether there were significant productivity differences between nine machine operators. , Thesis (PhD) -- Faculty of Science, School of Natural Resource Management, 2022
- Full Text:
- Date Issued: 2022-04
- Authors: Schwegman, Kylle
- Date: 2022-04
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/55246 , vital:51102
- Description: A shift towards fully mechanized forest activities, such as harvesting and, more recently, silviculture, has occurred from the early 2 000’s. The reason for mechanizing these activities differs for each country, although for most countries there is concern relating to the health and safety of forest workers. With mechanization in harvesting, the forest worker has moved away from the physical intensity of having to fell, debranch, debark and cross-cut trees into logs using either an axe or chainsaw, to operating a machine. Studies revolving around the human element (operator) have been conducted specifically relating to the ergonomics of the machines and how operators may influence machine productivity. Results showed that due to the repetitive nature of the work, the operators are exposed to associated stresses for longer periods. Typical injuries associated to these kinds of stressors are whole body vibrations (WBVs), repetitive hand and arm movements, non-neutral body postures and manual lifting, which lead to musculoskeletal symptoms in the lower back, neck and shoulders. However, as machine technology improves so does the ergonomic conditions which are experienced by machine operators. Machine productivity can be influenced by various factors, with the most influential being tree volume. However, a recent study showed that over 40% of variation in machine productivity has been observed amongst different machine operators operating similar machines. The specific reason for these differences has yet to be determined. However, decision making, motivation, planning capacity, concentration, memory, motor coordination, pattern recognition, logic reasoning, and spatial perception are abilities that have been described as important for successful harvesting work. The pre-selection of operators using psychometric and cognitive tests is not new to forestry, although very little information is available relating to the aptitude test known as the Vienna test system as well as the best possible demographic associated with successful harvesting operators. The overall aim of this study was to determine whether the high variation found amongst harvesting machine operators could be reduced initially through a preselection process which involves the use of aptitude tests (Vienna Test System) and demographic questionnaires. A study was implemented in Zululand, South Africa, testing whether there were significant productivity differences between nine machine operators. , Thesis (PhD) -- Faculty of Science, School of Natural Resource Management, 2022
- Full Text:
- Date Issued: 2022-04
A critical exploration of the attitudes towards and knowledge of natural resource management amongst first-year Natural Resource Management students
- Authors: Jooste, Eileen
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's , text
- Identifier: http://hdl.handle.net/10948/53666 , vital:45688
- Description: Available literature suggests that there is a need to gain more understanding of what students’ environmental attitudes and knowledge are and how they are developed by education systems. Education, in general, plays an important role in students’ attitudes and their knowledge of the world around them. It can shape students’ awareness of their natural environment and contribute to their understanding of environmental issues. Education can also strengthen students’ critical thinking, build awareness, stimulate problem solving, and promote sustainable practices. It has the potential to empower students to address global challenges from their own diverse perspectives and prepare them to uphold the economy. Education can improve and maintain societal wellbeing and can help students to maintain the natural environment, along with achieving sustainable development. Environmental education, specifically, can play a big role in how students deal with the natural environment. The primary aim of this qualitative research study was to examine first-year students’ environmental attitudes and knowledge in the School of Natural Resource Management at the Nelson Mandela University George Campus, South Africa. First-year students’ environmental attitudes and knowledge were examined as they entered the university, and then again at the end of the first semester once they had completed a module in ecology. More specifically, at the outset of the research the objectives were (1) to establish an understanding of the baseline environmental attitudes and knowledge of first-year students who were undertaking three ecological modules being offered by the School of Natural Resource Management; (2) to assess the changes in the first-year students’ environmental attitudes and knowledge, using a post-intervention strategy; (3) to understand what type of teaching approaches were used by the lecturers teaching the ecological modules; and (4) to evaluate how the teaching approaches of the lecturers influenced the baseline environmental attitudes and knowledge of the student group. This research took place in the midst of the Corona Virus pandemic, which had significantly influenced the teaching and learning environment. Multiple education systems, including those of the Nelson Mandela University George Campus, had to rapidly transition to online teaching and learning. So, although unplanned for, this research could not ignore the rapid transition to online teaching and learning and the role it played in shaping the first-year School of Natural Resource Management students’ environmental attitudes and knowledge. It also impacted the teaching approaches of the environmental lecturers. An additional objective in response to the rapid transition to online teaching and learning was, therefore, added: (5) to understand the experiences of the first-year School of Natural Resource Management students and the three environmental lecturers who had to rapidly transition to online teaching and learning. Data was collected via questionnaires and semi-structured interviews with students and staff in the School of Natural Resource Management at Nelson Mandela University George Campus within three different natural resource management programs, namely Agriculture, Nature Conservation, and Forestry. Baseline questionnaires were conducted with 107 students for a baseline assessment as the students entered the university. An online post-intervention questionnaire was conducted with 33 of the initial group of students at the end of the semester for a post-intervention assessment. In-depth semi-structured interviews were conducted with three environmental lectures before they taught their three ecology modules in each of the programs. Additional online semi-structured interviews were also done with the same three environmental lectures after the rapid transition to online teaching and learning took place. The significant findings from this research were analyzed and discussed. This included the baseline environmental attitudes and knowledge of the student body upon arrival at the university and the changes in their environmental attitudes and knowledge after they were exposed to the ecology modules taught in each of the programs. The discussion also included the teaching approaches adopted by the environmental lecturers and the influence their teaching approaches had on the students’ environmental attitudes and knowledge. In addition, the results shed light on the experiences of students and lecturers during the rapid transition to online teaching and learning. The main conclusions reached were that the first-year School of Natural Resource Management students did not have a deep understanding of ecological concepts prior to arriving at university, but they did show a concern for the natural environment. Their lack of understanding was reduced as the students progressed with the ecology module. A greater understanding resulted in a change in students’ perspectives on the ecological module, their program, and the industry they were preparing to enter after being exposed to the ecology module. The environmental lecturers’ teaching approaches contributed to improving the students’ environmental attitudes and knowledge. When it came to the rapid transition to online teaching and learning, both the first-year School of Natural Resource Management students and environmental lecturers experienced benefits and challenges. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Jooste, Eileen
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's , text
- Identifier: http://hdl.handle.net/10948/53666 , vital:45688
- Description: Available literature suggests that there is a need to gain more understanding of what students’ environmental attitudes and knowledge are and how they are developed by education systems. Education, in general, plays an important role in students’ attitudes and their knowledge of the world around them. It can shape students’ awareness of their natural environment and contribute to their understanding of environmental issues. Education can also strengthen students’ critical thinking, build awareness, stimulate problem solving, and promote sustainable practices. It has the potential to empower students to address global challenges from their own diverse perspectives and prepare them to uphold the economy. Education can improve and maintain societal wellbeing and can help students to maintain the natural environment, along with achieving sustainable development. Environmental education, specifically, can play a big role in how students deal with the natural environment. The primary aim of this qualitative research study was to examine first-year students’ environmental attitudes and knowledge in the School of Natural Resource Management at the Nelson Mandela University George Campus, South Africa. First-year students’ environmental attitudes and knowledge were examined as they entered the university, and then again at the end of the first semester once they had completed a module in ecology. More specifically, at the outset of the research the objectives were (1) to establish an understanding of the baseline environmental attitudes and knowledge of first-year students who were undertaking three ecological modules being offered by the School of Natural Resource Management; (2) to assess the changes in the first-year students’ environmental attitudes and knowledge, using a post-intervention strategy; (3) to understand what type of teaching approaches were used by the lecturers teaching the ecological modules; and (4) to evaluate how the teaching approaches of the lecturers influenced the baseline environmental attitudes and knowledge of the student group. This research took place in the midst of the Corona Virus pandemic, which had significantly influenced the teaching and learning environment. Multiple education systems, including those of the Nelson Mandela University George Campus, had to rapidly transition to online teaching and learning. So, although unplanned for, this research could not ignore the rapid transition to online teaching and learning and the role it played in shaping the first-year School of Natural Resource Management students’ environmental attitudes and knowledge. It also impacted the teaching approaches of the environmental lecturers. An additional objective in response to the rapid transition to online teaching and learning was, therefore, added: (5) to understand the experiences of the first-year School of Natural Resource Management students and the three environmental lecturers who had to rapidly transition to online teaching and learning. Data was collected via questionnaires and semi-structured interviews with students and staff in the School of Natural Resource Management at Nelson Mandela University George Campus within three different natural resource management programs, namely Agriculture, Nature Conservation, and Forestry. Baseline questionnaires were conducted with 107 students for a baseline assessment as the students entered the university. An online post-intervention questionnaire was conducted with 33 of the initial group of students at the end of the semester for a post-intervention assessment. In-depth semi-structured interviews were conducted with three environmental lectures before they taught their three ecology modules in each of the programs. Additional online semi-structured interviews were also done with the same three environmental lectures after the rapid transition to online teaching and learning took place. The significant findings from this research were analyzed and discussed. This included the baseline environmental attitudes and knowledge of the student body upon arrival at the university and the changes in their environmental attitudes and knowledge after they were exposed to the ecology modules taught in each of the programs. The discussion also included the teaching approaches adopted by the environmental lecturers and the influence their teaching approaches had on the students’ environmental attitudes and knowledge. In addition, the results shed light on the experiences of students and lecturers during the rapid transition to online teaching and learning. The main conclusions reached were that the first-year School of Natural Resource Management students did not have a deep understanding of ecological concepts prior to arriving at university, but they did show a concern for the natural environment. Their lack of understanding was reduced as the students progressed with the ecology module. A greater understanding resulted in a change in students’ perspectives on the ecological module, their program, and the industry they were preparing to enter after being exposed to the ecology module. The environmental lecturers’ teaching approaches contributed to improving the students’ environmental attitudes and knowledge. When it came to the rapid transition to online teaching and learning, both the first-year School of Natural Resource Management students and environmental lecturers experienced benefits and challenges. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2021
- Full Text:
- Date Issued: 2021-12
A data-driven decision-making model for the third-party logistics industry in Africa
- Authors: Moyo, Faith
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53875 , vital:46022
- Description: Third-party logistics (3PL) providers have continued to be key players in the supply chain network and have witnessed a growth in the usage of information technology. This growth has enhanced the volume of structured and unstructured data that is collected at a high velocity, and is of rich variety, sometimes described as “Big Data”. Leaders in the 3PL industry are constantly seeking to effectively and efficiently mature their abilities to exploit this data to gain business value through data-driven decision-making (DDDM). DDDM helps the leaders to reduce the reliance they place on observations and intuition to make crucial business decisions in a volatile business environment. The aim of this research was to develop a prescriptive model for DDDM in 3PLs. The model consists of iterative elements that prescribe guidelines to decision-makers in the 3PL industry on how to adopt DDDM. A literature review of existing theoretical frameworks and models for DDDM was conducted to determine the extent to which they contribute towards DDDM for 3PLs. The Design-Science Research Methodology (DSRM) was followed to address the aim of the research and applied to pragmatically and iteratively develop and evaluate the artefact (the model for DDDM) in the real-world context of a 3PL. The literature findings revealed that the challenges with DDDM in organisations include three main categories of challenges related to data quality, data management, vision and capabilities. Once the challenges with DDDM were established, a prescriptive model was designed and developed for DDDM in 3PLs. Qualitative data was collected from semi-structured interviews to gain an understanding of the problems and possible solutions in the real-world context of 3PLs. An As-Is Analysis in the real-world case 3PL company confirmed the challenges identified in literature, and that data is still used in the 3PL company for descriptive and diagnostic analytics to aid with the decision-making processes. This highlights that there is still room for maturity into using data for predictive and prescriptive analytics that will, in turn, improve the decision-making process. An improved second version of the model was demonstrated to the participants (the targeted users), who had the opportunity to evaluate the model. The findings revealed that the model provided clear guidelines on how to make data-driven decisions and that the feedback loop and the data culture aspects highlighted in the design were some of the important features of the model. Some improvements were suggested by participants. A field study of three data analytics tools was conducted to identify the advantages and disadvantages of each as well as to highlight the status of DDDM at the real-world case 3PL. The limitations of the second version of the model, together with the recommendations from the participants were used to inform the improved and revised third version of the model. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Moyo, Faith
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53875 , vital:46022
- Description: Third-party logistics (3PL) providers have continued to be key players in the supply chain network and have witnessed a growth in the usage of information technology. This growth has enhanced the volume of structured and unstructured data that is collected at a high velocity, and is of rich variety, sometimes described as “Big Data”. Leaders in the 3PL industry are constantly seeking to effectively and efficiently mature their abilities to exploit this data to gain business value through data-driven decision-making (DDDM). DDDM helps the leaders to reduce the reliance they place on observations and intuition to make crucial business decisions in a volatile business environment. The aim of this research was to develop a prescriptive model for DDDM in 3PLs. The model consists of iterative elements that prescribe guidelines to decision-makers in the 3PL industry on how to adopt DDDM. A literature review of existing theoretical frameworks and models for DDDM was conducted to determine the extent to which they contribute towards DDDM for 3PLs. The Design-Science Research Methodology (DSRM) was followed to address the aim of the research and applied to pragmatically and iteratively develop and evaluate the artefact (the model for DDDM) in the real-world context of a 3PL. The literature findings revealed that the challenges with DDDM in organisations include three main categories of challenges related to data quality, data management, vision and capabilities. Once the challenges with DDDM were established, a prescriptive model was designed and developed for DDDM in 3PLs. Qualitative data was collected from semi-structured interviews to gain an understanding of the problems and possible solutions in the real-world context of 3PLs. An As-Is Analysis in the real-world case 3PL company confirmed the challenges identified in literature, and that data is still used in the 3PL company for descriptive and diagnostic analytics to aid with the decision-making processes. This highlights that there is still room for maturity into using data for predictive and prescriptive analytics that will, in turn, improve the decision-making process. An improved second version of the model was demonstrated to the participants (the targeted users), who had the opportunity to evaluate the model. The findings revealed that the model provided clear guidelines on how to make data-driven decisions and that the feedback loop and the data culture aspects highlighted in the design were some of the important features of the model. Some improvements were suggested by participants. A field study of three data analytics tools was conducted to identify the advantages and disadvantages of each as well as to highlight the status of DDDM at the real-world case 3PL. The limitations of the second version of the model, together with the recommendations from the participants were used to inform the improved and revised third version of the model. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text:
- Date Issued: 2021-12
A spatial assessment of riparian vegetation density and implications for streambank erosion in relation to land tenure in the Mgwalana Catchment, Eastern Cape Province, South Africa
- Authors: Maxama, Asakhile
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53864 , vital:46026
- Description: Riparian vegetation provides an array of various ecosystem functions and has significantly shaped the conditions of catchments. It has strong controls on fluvial geomorphology and erosion processes. The Mgwalana catchment has been intensively studied over the years and the current environmental condition of the study has been linked to land use history. The catchment has been subjected to land use/cover changes (LUCC) over the years. However, spatial variations in riparian vegetation, their implications for stream bank stability and the contribution of land tenure systems to stream channel degradation are poorly understood. The study sought to assess the implications of the spatial variations in riparian vegetation density for stream bank erosion in relation to land tenure on a catchment scale. Land tenure units comprising the catchment of study are traditional and betterment villages (communal lands), and former white commercial farms. A three-pronged approach using GIS and remote sensing, field investigations and laboratory procedures for soil analysis was employed in this study. Variations of riparian vegetation density in the catchment were mapped using ArcGIS for the two land tenure units to assess the spatial variations of riparian density along stream reaches and to determine the spatial relationship between land tenure units and riparian vegetation diminution. Other mapped shape files include sediment accumulation zones to analyse the spatial relationship between riparian vegetation density and sediment sinks. LUCC classification and analysis of the Normalized Difference Vegetation Index (NDVI) were carried out in IDRISI Selva, using Landsat 8 TM imagery of 2018 to represent the current spatial riparian vegetation variations in the catchment. Field investigations were conducted to determine the coupling among hillslope gully erosion, riparian vegetation density and sink areas; and to assess physical characteristics of soil. This would permit an assessment of the implications of riparian vegetation for stream bank erosion and sediment accumulation within the tenure units. Soil samples were taken from scantily and densely vegetated stream reaches, as well as measurements of channel widths and depths. Analyses of soil physical properties viz; grain size distribution, bulk density, soil texture and aggregate stability were done. Results demonstrated that a sparse riparian vegetation distribution was consistent with the communal villages, confined to the upper catchment area. Dense riparian vegetation distribution was consistent with former commercial farms in the lower catchment area. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Maxama, Asakhile
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53864 , vital:46026
- Description: Riparian vegetation provides an array of various ecosystem functions and has significantly shaped the conditions of catchments. It has strong controls on fluvial geomorphology and erosion processes. The Mgwalana catchment has been intensively studied over the years and the current environmental condition of the study has been linked to land use history. The catchment has been subjected to land use/cover changes (LUCC) over the years. However, spatial variations in riparian vegetation, their implications for stream bank stability and the contribution of land tenure systems to stream channel degradation are poorly understood. The study sought to assess the implications of the spatial variations in riparian vegetation density for stream bank erosion in relation to land tenure on a catchment scale. Land tenure units comprising the catchment of study are traditional and betterment villages (communal lands), and former white commercial farms. A three-pronged approach using GIS and remote sensing, field investigations and laboratory procedures for soil analysis was employed in this study. Variations of riparian vegetation density in the catchment were mapped using ArcGIS for the two land tenure units to assess the spatial variations of riparian density along stream reaches and to determine the spatial relationship between land tenure units and riparian vegetation diminution. Other mapped shape files include sediment accumulation zones to analyse the spatial relationship between riparian vegetation density and sediment sinks. LUCC classification and analysis of the Normalized Difference Vegetation Index (NDVI) were carried out in IDRISI Selva, using Landsat 8 TM imagery of 2018 to represent the current spatial riparian vegetation variations in the catchment. Field investigations were conducted to determine the coupling among hillslope gully erosion, riparian vegetation density and sink areas; and to assess physical characteristics of soil. This would permit an assessment of the implications of riparian vegetation for stream bank erosion and sediment accumulation within the tenure units. Soil samples were taken from scantily and densely vegetated stream reaches, as well as measurements of channel widths and depths. Analyses of soil physical properties viz; grain size distribution, bulk density, soil texture and aggregate stability were done. Results demonstrated that a sparse riparian vegetation distribution was consistent with the communal villages, confined to the upper catchment area. Dense riparian vegetation distribution was consistent with former commercial farms in the lower catchment area. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2021
- Full Text:
- Date Issued: 2021-12
A value alignment smart city stakeholder model
- Van der Hoogen, Anthea Vivian
- Authors: Van der Hoogen, Anthea Vivian
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/54129 , vital:46309
- Description: The concept of a Smart City has evolved over the last three decades and has attracted the increasing interest of the scientific research community. Unfortunately, many Smart City projects and initiatives do not provide the value expected by all the stakeholders. Many of the reasons for this relate to a lack of data management, data integration, data access and stakeholder participation. People are an integral part of any city’s ecosystem, and the Smart City concept was introduced to address the challenges of an ever-growing global population leading to the risk of depletion of economic, environmental and social resources. The problem addressed in this study is based on the challenges preventing the creation of the value of smart cities or stakeholders. Limited research has been published on the status of Smart City initiatives or on the impact of various success factors on the potential value creation for stakeholders including citizens. Studies on initiatives in developing countries, such as South Africa are even less. Whilst some challenges and constraints related to smart cities in Africa have been reported, there are no studies reporting on initiatives across the data value chain that consider all types of stakeholders, nor the impact of these initiatives. This study addressed this gap in research and designed a theoretical Value Alignment Smart City Stakeholder (VASCS) Model based on a Systematic Literature Review and a review of related theories. The model has important components that should form part of any Smart City project or Smart City initiative. These five main components are: 1) nine Smart City dimensions with related success factors; 2) four stakeholder roles (enablers, providers, utilisers and users); 3) the data value chain; and 4) the five phases of stakeholder benefits/value realisation that can be linked to; 5) stakeholder value alignment. This study applied the VASCS Model to Smart City initiatives in two case studies in the Eastern Cape Province of South Africa, which were the Nelson Mandela Bay and Buffalo City to investigate and understand the status of such initiatives and the alignment of value thereof. The stakeholder interviews were conducted in two rounds with various stakeholders of Smart City initiatives, referred to as cases in the two case studies. An expert review of the VASCS Model was conducted with eight experts in the field of Information Systems and Smart Cities. The findings of this review served to confirm the components of the model, with only minor improvements recommended. It was confirmed that all of the components need to be considered in planning Smart City projects. The first round consisted of six interviews with enablers and providers and the second round consisted of 22 interviews with users, utilisers and citizens. The interviews investigated the value and impact experienced by stakeholders of these initiatives, with a particular focus on the users, utilisers and citizens of the cases. The interview data was transcribed and qualitatively analysed by using Atlas.tiand Excel. The data was analysed according to the Technological, Organisational and Environmental theory constructs and other identified themes. The interview analysis findings revealed several drivers for these initiatives, which were primarily cost reduction, integration and quality assurance. The results also highlighted access to resources, such as technical skills as a challenge. Another challenge identified was connectivity related to access to data and the digital and physical divide that can impact decision making. The main benefits of Smart City initiatives highlighted were the provision of infrastructure, education and training and digitalisation. The theoretical contribution of this study is the VASCS Model, which can assist other researchers and practitioners with knowledge of the factors, drivers, challenges and value obtained in Smart City initiatives. The model has two supplementary components: A Stakeholder Classification Model and a Smart City Success Factor Evaluation Template. The practical contribution of this study is the potential use of the VASCS Model by practitioners, city management, researchers and other stakeholders, who can use the model, with the related model and template for planning and evaluating Smart City initiatives. The model can be used to classify the digital activities according to a Smart City’s success factors while evaluating the value created by these activities. The impact of these initiatives can then be assessed through value realisation and alignment for stakeholders. The scientific contribution is the adoption of the model to the cases in the Eastern Cape. To reveal in depth, rich, interview findings that provide important lessons learnt relating to the value created for the stakeholders and the addition of these findings to the body of knowledge. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Van der Hoogen, Anthea Vivian
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/54129 , vital:46309
- Description: The concept of a Smart City has evolved over the last three decades and has attracted the increasing interest of the scientific research community. Unfortunately, many Smart City projects and initiatives do not provide the value expected by all the stakeholders. Many of the reasons for this relate to a lack of data management, data integration, data access and stakeholder participation. People are an integral part of any city’s ecosystem, and the Smart City concept was introduced to address the challenges of an ever-growing global population leading to the risk of depletion of economic, environmental and social resources. The problem addressed in this study is based on the challenges preventing the creation of the value of smart cities or stakeholders. Limited research has been published on the status of Smart City initiatives or on the impact of various success factors on the potential value creation for stakeholders including citizens. Studies on initiatives in developing countries, such as South Africa are even less. Whilst some challenges and constraints related to smart cities in Africa have been reported, there are no studies reporting on initiatives across the data value chain that consider all types of stakeholders, nor the impact of these initiatives. This study addressed this gap in research and designed a theoretical Value Alignment Smart City Stakeholder (VASCS) Model based on a Systematic Literature Review and a review of related theories. The model has important components that should form part of any Smart City project or Smart City initiative. These five main components are: 1) nine Smart City dimensions with related success factors; 2) four stakeholder roles (enablers, providers, utilisers and users); 3) the data value chain; and 4) the five phases of stakeholder benefits/value realisation that can be linked to; 5) stakeholder value alignment. This study applied the VASCS Model to Smart City initiatives in two case studies in the Eastern Cape Province of South Africa, which were the Nelson Mandela Bay and Buffalo City to investigate and understand the status of such initiatives and the alignment of value thereof. The stakeholder interviews were conducted in two rounds with various stakeholders of Smart City initiatives, referred to as cases in the two case studies. An expert review of the VASCS Model was conducted with eight experts in the field of Information Systems and Smart Cities. The findings of this review served to confirm the components of the model, with only minor improvements recommended. It was confirmed that all of the components need to be considered in planning Smart City projects. The first round consisted of six interviews with enablers and providers and the second round consisted of 22 interviews with users, utilisers and citizens. The interviews investigated the value and impact experienced by stakeholders of these initiatives, with a particular focus on the users, utilisers and citizens of the cases. The interview data was transcribed and qualitatively analysed by using Atlas.tiand Excel. The data was analysed according to the Technological, Organisational and Environmental theory constructs and other identified themes. The interview analysis findings revealed several drivers for these initiatives, which were primarily cost reduction, integration and quality assurance. The results also highlighted access to resources, such as technical skills as a challenge. Another challenge identified was connectivity related to access to data and the digital and physical divide that can impact decision making. The main benefits of Smart City initiatives highlighted were the provision of infrastructure, education and training and digitalisation. The theoretical contribution of this study is the VASCS Model, which can assist other researchers and practitioners with knowledge of the factors, drivers, challenges and value obtained in Smart City initiatives. The model has two supplementary components: A Stakeholder Classification Model and a Smart City Success Factor Evaluation Template. The practical contribution of this study is the potential use of the VASCS Model by practitioners, city management, researchers and other stakeholders, who can use the model, with the related model and template for planning and evaluating Smart City initiatives. The model can be used to classify the digital activities according to a Smart City’s success factors while evaluating the value created by these activities. The impact of these initiatives can then be assessed through value realisation and alignment for stakeholders. The scientific contribution is the adoption of the model to the cases in the Eastern Cape. To reveal in depth, rich, interview findings that provide important lessons learnt relating to the value created for the stakeholders and the addition of these findings to the body of knowledge. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text:
- Date Issued: 2021-12
Applying a systems analysis approach to support marine spatial planning in Algoa Bay, South Africa
- Authors: Vermeulen, Estee Ann
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/54121 , vital:46312
- Description: Ocean health provides the foundation for human health through the provisioning of ecosystem services. Increasing demands on ocean space and resources are, however, resulting in a decline in ocean health, with direct and indirect knock-on effects on marine uses and ultimately on human health. In response, there is a growing need to acknowledge and better manage complex human-ocean interactions. This has been recognised in global sustainable development goals and in integrated ocean management processes, leading to widespread endorsement of an ecosystem-based marine spatial planning (MSP) process, including in South Africa. In support of the national MSP process, significant progress has been made in understanding the spatial extent of marine activities and associated marine pressures, but the temporal dynamics of marine activities and interconnections with the marine environment are less well understood. To plan for the growth of marine activities and associated user conflicts, the drivers of these temporal dynamics and associated feedback effects need to be analysed and potential policy and management interventions identified and tested. To support South Africa’s national MSP process, this study adopts a systems analysis approach, using system dynamics modelling, to explore the temporal change in marine uses under alternative growth scenarios in Algoa Bay. Algoa Bay is an appropriate study area because it is experiencing a rapid expansion of marine activities, coupled with a growing uncertainty regarding marine sustainability outcomes. To assist future marine management decisions, the Algoa Marine Systems Analysis Tool (Algoa MSAT) was developed, comprising seven sub-models. Five of the sub-models represent selected marine uses in Algoa Bay, whereas the sixth and seventh integrate the outputs from each marine use in terms of sustainable management indicators (marine health, marine wealth and marine labour). Model development primarily adopted an expert-based model ling approach, although the involvement of stakeholders, through a collaborative modelling process, assisted in integrating knowledge on different marine sectors’ activities, impacts and planning visions into the model framework. Model results were generated under different scenarios to investigate changes in the growth of marine activities and marine sustainability indicators under different levels of ocean governance. Under the baseline (or business-as-usual) model scenario, marine activities were shown to grow increasingly within their respective management limits, with an increase in marine wealth and labour and a consequential decrease in marine health. This scenario particularly highlights that current ocean governance practices are ineffective in sustaining the projected growth of the marine uses, particularly for those that are vulnerable to negative changes in marine health. Conversely, sectors that hold more value in marine wealth and are more resilient to changes in marine health, may continue to grow regardless of negative knock-on effects of the health of the marine environment and on other uses in the bay. This emphasises that an alternative governance strategy is needed to achieve the long-term goal of an ecosystem-based MSP process, as required by South African MSP legislation. To achieve this will require multiple, adaptive cross-sectoral management interventions that are directed towards the ‘deeper leverage points’ that are able to maintain the growth of marine activities within appropriate limits defined by marine health. Using the model interface developed in this project, decision-makers and stakeholders can use the model to explore the temporal dynamics in marine activities under different governance scenarios. Although the model is limited to Algoa Bay, the model boundary can be adapted to assist in marine planning processes at national or trans-national scales. Such analytical assessments and tools are critical to progress the ecosystem-based management approach in MSP, as is required to achieve global sustainable development goals. , Thesis (PhD) -- Faculty of Science, Coastal and Marine Research Unit, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Vermeulen, Estee Ann
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/54121 , vital:46312
- Description: Ocean health provides the foundation for human health through the provisioning of ecosystem services. Increasing demands on ocean space and resources are, however, resulting in a decline in ocean health, with direct and indirect knock-on effects on marine uses and ultimately on human health. In response, there is a growing need to acknowledge and better manage complex human-ocean interactions. This has been recognised in global sustainable development goals and in integrated ocean management processes, leading to widespread endorsement of an ecosystem-based marine spatial planning (MSP) process, including in South Africa. In support of the national MSP process, significant progress has been made in understanding the spatial extent of marine activities and associated marine pressures, but the temporal dynamics of marine activities and interconnections with the marine environment are less well understood. To plan for the growth of marine activities and associated user conflicts, the drivers of these temporal dynamics and associated feedback effects need to be analysed and potential policy and management interventions identified and tested. To support South Africa’s national MSP process, this study adopts a systems analysis approach, using system dynamics modelling, to explore the temporal change in marine uses under alternative growth scenarios in Algoa Bay. Algoa Bay is an appropriate study area because it is experiencing a rapid expansion of marine activities, coupled with a growing uncertainty regarding marine sustainability outcomes. To assist future marine management decisions, the Algoa Marine Systems Analysis Tool (Algoa MSAT) was developed, comprising seven sub-models. Five of the sub-models represent selected marine uses in Algoa Bay, whereas the sixth and seventh integrate the outputs from each marine use in terms of sustainable management indicators (marine health, marine wealth and marine labour). Model development primarily adopted an expert-based model ling approach, although the involvement of stakeholders, through a collaborative modelling process, assisted in integrating knowledge on different marine sectors’ activities, impacts and planning visions into the model framework. Model results were generated under different scenarios to investigate changes in the growth of marine activities and marine sustainability indicators under different levels of ocean governance. Under the baseline (or business-as-usual) model scenario, marine activities were shown to grow increasingly within their respective management limits, with an increase in marine wealth and labour and a consequential decrease in marine health. This scenario particularly highlights that current ocean governance practices are ineffective in sustaining the projected growth of the marine uses, particularly for those that are vulnerable to negative changes in marine health. Conversely, sectors that hold more value in marine wealth and are more resilient to changes in marine health, may continue to grow regardless of negative knock-on effects of the health of the marine environment and on other uses in the bay. This emphasises that an alternative governance strategy is needed to achieve the long-term goal of an ecosystem-based MSP process, as required by South African MSP legislation. To achieve this will require multiple, adaptive cross-sectoral management interventions that are directed towards the ‘deeper leverage points’ that are able to maintain the growth of marine activities within appropriate limits defined by marine health. Using the model interface developed in this project, decision-makers and stakeholders can use the model to explore the temporal dynamics in marine activities under different governance scenarios. Although the model is limited to Algoa Bay, the model boundary can be adapted to assist in marine planning processes at national or trans-national scales. Such analytical assessments and tools are critical to progress the ecosystem-based management approach in MSP, as is required to achieve global sustainable development goals. , Thesis (PhD) -- Faculty of Science, Coastal and Marine Research Unit, 2021
- Full Text:
- Date Issued: 2021-12
Coordination polymers for denitrogenation of fuel oils
- Authors: Dembaremba, Tendai O
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/53630 , vital:45682
- Description: In this thesis, we present adsorptive removal of nitrogen-containing compounds from fuel oil as an alternative to complement conventional hydrotreatment to obtain ultra-low sulfur and nitrogen levels. This is in cognizance of the challenges nitrogen-containing compounds pose to the hydrotreatment process, particularly their inhibition and/or poisoning of the catalysts used in the process, of which basic nitrogen-containing compounds are the major culprits. Selectivity is the biggest challenge for adsorptive removal of nitrogen-containing compounds. We explore reticular synthesis of metal organic frameworks and the use of coordinatively unsaturated metal sites in 1-dimensional coordination polymers to achieve good selectivity for nitrogen-containing compounds. In the first part of the thesis, reticular synthesis of metal organic frameworks to control the size of the cavity, and strategically use the linkers and metal centres was envisaged. In this work we explored variation of the metal centres in the secondary building units (SBUs of the MOFs as the first step to the testing and implementation of the design strategies. Carbazole, representing carbazoles which the major compounds that remain in hydrotreated fuel, was the target compound. Four MOFs of zinc (Zn-CDC-bpe), copper (Cu-CDC-bpe), nickel (Ni-CDC-bpe) and cobalt (Co-CDC-bpe) based on the formation of a dinuclear metal paddlewheel SBUs with the ligand 9H-Carbazole-3,6-dicarboxylic acid (H2CDC) and occupation of the axial positions of the paddlewheel by 1,2-Bis(4-pyridyl)ethane (bpe) to form porous networks were synthesized. A fifth MOF containing only CDC which forms a [Zn4O(O2C-R)5(O2HC-R)] SBU was also synthesized (Zn-CDC). The ligand H2CDC was inspired by the possibility of improving selectivity for carbazole via π–π interactions through the more preferred parallel-offset stacking as well as the possibility for further substitution of the carbazole N-H to add groups that improve selectivity. The sizes of the MOF cavities can then be controlled by choosing different lengths of ligands analogous to 1,2-Bis(4-pyridyl)ethane (bpe), e.g. 4,4’-bipyridine and pyrazine. All the MOFs showed good selectivity of carbazole. The Zn-CDC MOF also had good selectivity for the basic nitrogen-containing compounds tested: quinoline, isoquinoline, quinaldine and 1-naphthylamine. Its uptake of carbazole was also slightly higher. This was attributed to the presence of an unsaturated Zn site in the SBU. Adsorption in all the MOFs was primarily due to physisorption. It was concluded that the role of the metal centre does not play a significant role in the adsorption of carbazole besides providing a template for reticular synthesis. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text: false
- Date Issued: 2021-12
- Authors: Dembaremba, Tendai O
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/53630 , vital:45682
- Description: In this thesis, we present adsorptive removal of nitrogen-containing compounds from fuel oil as an alternative to complement conventional hydrotreatment to obtain ultra-low sulfur and nitrogen levels. This is in cognizance of the challenges nitrogen-containing compounds pose to the hydrotreatment process, particularly their inhibition and/or poisoning of the catalysts used in the process, of which basic nitrogen-containing compounds are the major culprits. Selectivity is the biggest challenge for adsorptive removal of nitrogen-containing compounds. We explore reticular synthesis of metal organic frameworks and the use of coordinatively unsaturated metal sites in 1-dimensional coordination polymers to achieve good selectivity for nitrogen-containing compounds. In the first part of the thesis, reticular synthesis of metal organic frameworks to control the size of the cavity, and strategically use the linkers and metal centres was envisaged. In this work we explored variation of the metal centres in the secondary building units (SBUs of the MOFs as the first step to the testing and implementation of the design strategies. Carbazole, representing carbazoles which the major compounds that remain in hydrotreated fuel, was the target compound. Four MOFs of zinc (Zn-CDC-bpe), copper (Cu-CDC-bpe), nickel (Ni-CDC-bpe) and cobalt (Co-CDC-bpe) based on the formation of a dinuclear metal paddlewheel SBUs with the ligand 9H-Carbazole-3,6-dicarboxylic acid (H2CDC) and occupation of the axial positions of the paddlewheel by 1,2-Bis(4-pyridyl)ethane (bpe) to form porous networks were synthesized. A fifth MOF containing only CDC which forms a [Zn4O(O2C-R)5(O2HC-R)] SBU was also synthesized (Zn-CDC). The ligand H2CDC was inspired by the possibility of improving selectivity for carbazole via π–π interactions through the more preferred parallel-offset stacking as well as the possibility for further substitution of the carbazole N-H to add groups that improve selectivity. The sizes of the MOF cavities can then be controlled by choosing different lengths of ligands analogous to 1,2-Bis(4-pyridyl)ethane (bpe), e.g. 4,4’-bipyridine and pyrazine. All the MOFs showed good selectivity of carbazole. The Zn-CDC MOF also had good selectivity for the basic nitrogen-containing compounds tested: quinoline, isoquinoline, quinaldine and 1-naphthylamine. Its uptake of carbazole was also slightly higher. This was attributed to the presence of an unsaturated Zn site in the SBU. Adsorption in all the MOFs was primarily due to physisorption. It was concluded that the role of the metal centre does not play a significant role in the adsorption of carbazole besides providing a template for reticular synthesis. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text: false
- Date Issued: 2021-12
Corrosion and hydrogen resistant modified zirlo surfaces for nuclear fuel cladding
- Authors: Ngongo, Sinoyolo
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/54077 , vital:46252
- Description: Zirconium (Zr) alloys are used as fuel cladding material in all modern water cooled commercial nuclear reactors. Zr alloys have many desirable properties for the nuclear reactor core environment, however, it also has a weakness in that overheated zirconium alloy fuel rods react with hot steam resulting in the release of hydrogen. High temperatures increase the oxidation rate and hence the hydrogen production rate which in turn increase the risk of a hydrogen gas explosion such as what is surmised to have happened in the 2011 Fukushima Daiichi nuclear plant incident. The some of the hydrogen produced will also diffuse into the zirconium alloy and form zirconium hydrides which will weaken the original zirconium alloy material. The development of accident tolerant fuel became a major focus area after the Fukushima event in March 2011 with the U.S. congress directing the U.S. Department of Energy to develop fuel with enhanced accident tolerance at high temperatures. The main objective in the case of zirconium alloy cladding has been the modification of cladding surface layers by coating or doping in order to reduce the oxidation rate and hydrogen generation rate by the reaction of steam with zirconium alloy cladding at high temperatures. This thesis focuses on two surface modifications to decrease the surface corrosion rate of ZIRLOTM (the Zr alloy used in this study) and reduce hydrogen uptake by ZIRLO. The first modification involves an oxidation-resistant nano-crystalline diamond (NCD) film deposited on ZIRLO. The NCD layer was deposited in a microwave plasma-enhanced linear antenna chemical vapor deposition (MW-LA-PECVD) system after immersion of the ZIRLO tubes in a water-based solution containing nanodiamonds. ZIRLO tube samples were coated with 200 nm and 500 nm thick NCD layers. The 200 nm thick NCD coated ZIRLO was kept as control sample whereas the 500 nm thick NCD coated ZIRLO was exposed to steam oxidation at 360 °C for 90 days. The results revealed that the NCD exfoliated in some areas leaving the ZIRLO exposed to the steam. In the areas where the diamond did not exfoliate, the diamond was still attached to the ZIRLO with an amorphous carbon layer present between the NCD and the zirconium oxide layer.The transmission electron microscopy (TEM) results of this study indicate the presence a sp3 – hybridised diamond phase for the NCD layer as well as an intermediate amorphous carbon layer between the NCD and ZrO2 layers. Analyses of the area where the NCD layer had exfoliated showed no evidence of an NCD layer. It is possible that the amorphous carbon layer between the diamond and the zirconium oxide is responsible for weak interfacial bonding leading to partial exfoliation during oxidation in steam 360 °C for 90 days. In the second modification, the effectiveness of a Cr doped ZrO2 layer to reduce the migration rate of hydrogen in ZrO2 was investigated. The ZIRLO tube used for this part of the study did not have a thin oxide passivation surface layer. Two different procedures were used to create chromium doped zirconium oxide surface layers on ZIRLO. The ZIRLO surface was coated with chromium using cathodic arc deposition followed compression plasma flow (CPF) treatment to facilitate intermixing of the Cr and the ZIRLO. In procedure 1, the surface modification was achieved through the incorporation of chromium into the zirconium surface layer using a compression plasma flow (CPF) technique, followed by the oxidation of the chromium doped zirconium. The oxidation process was conducted at 500 °C for 6 hours. In procedure 2, the chromium was incorporated into the zirconium oxide layer again using the CPF technique. Hydrogen desorption was measured from pure ZIRLO and CPF modified samples using a special gas reaction controller system. The key finding of the results is that the chromium doped (incorporated) zirconium oxide layer on ZIRLO sample exhibited the lowest hydrogen desorption rate of all the samples analysed. This indicates that H in the Cr doped zirconium oxide layer had the lowest mobility of all the samples investigated. This is consistent with the theoretical predictions that the doping of ZrO2 by Cr reduces the solubility of hydrogen in ZrO2. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text: false
- Date Issued: 2021-12
- Authors: Ngongo, Sinoyolo
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/54077 , vital:46252
- Description: Zirconium (Zr) alloys are used as fuel cladding material in all modern water cooled commercial nuclear reactors. Zr alloys have many desirable properties for the nuclear reactor core environment, however, it also has a weakness in that overheated zirconium alloy fuel rods react with hot steam resulting in the release of hydrogen. High temperatures increase the oxidation rate and hence the hydrogen production rate which in turn increase the risk of a hydrogen gas explosion such as what is surmised to have happened in the 2011 Fukushima Daiichi nuclear plant incident. The some of the hydrogen produced will also diffuse into the zirconium alloy and form zirconium hydrides which will weaken the original zirconium alloy material. The development of accident tolerant fuel became a major focus area after the Fukushima event in March 2011 with the U.S. congress directing the U.S. Department of Energy to develop fuel with enhanced accident tolerance at high temperatures. The main objective in the case of zirconium alloy cladding has been the modification of cladding surface layers by coating or doping in order to reduce the oxidation rate and hydrogen generation rate by the reaction of steam with zirconium alloy cladding at high temperatures. This thesis focuses on two surface modifications to decrease the surface corrosion rate of ZIRLOTM (the Zr alloy used in this study) and reduce hydrogen uptake by ZIRLO. The first modification involves an oxidation-resistant nano-crystalline diamond (NCD) film deposited on ZIRLO. The NCD layer was deposited in a microwave plasma-enhanced linear antenna chemical vapor deposition (MW-LA-PECVD) system after immersion of the ZIRLO tubes in a water-based solution containing nanodiamonds. ZIRLO tube samples were coated with 200 nm and 500 nm thick NCD layers. The 200 nm thick NCD coated ZIRLO was kept as control sample whereas the 500 nm thick NCD coated ZIRLO was exposed to steam oxidation at 360 °C for 90 days. The results revealed that the NCD exfoliated in some areas leaving the ZIRLO exposed to the steam. In the areas where the diamond did not exfoliate, the diamond was still attached to the ZIRLO with an amorphous carbon layer present between the NCD and the zirconium oxide layer.The transmission electron microscopy (TEM) results of this study indicate the presence a sp3 – hybridised diamond phase for the NCD layer as well as an intermediate amorphous carbon layer between the NCD and ZrO2 layers. Analyses of the area where the NCD layer had exfoliated showed no evidence of an NCD layer. It is possible that the amorphous carbon layer between the diamond and the zirconium oxide is responsible for weak interfacial bonding leading to partial exfoliation during oxidation in steam 360 °C for 90 days. In the second modification, the effectiveness of a Cr doped ZrO2 layer to reduce the migration rate of hydrogen in ZrO2 was investigated. The ZIRLO tube used for this part of the study did not have a thin oxide passivation surface layer. Two different procedures were used to create chromium doped zirconium oxide surface layers on ZIRLO. The ZIRLO surface was coated with chromium using cathodic arc deposition followed compression plasma flow (CPF) treatment to facilitate intermixing of the Cr and the ZIRLO. In procedure 1, the surface modification was achieved through the incorporation of chromium into the zirconium surface layer using a compression plasma flow (CPF) technique, followed by the oxidation of the chromium doped zirconium. The oxidation process was conducted at 500 °C for 6 hours. In procedure 2, the chromium was incorporated into the zirconium oxide layer again using the CPF technique. Hydrogen desorption was measured from pure ZIRLO and CPF modified samples using a special gas reaction controller system. The key finding of the results is that the chromium doped (incorporated) zirconium oxide layer on ZIRLO sample exhibited the lowest hydrogen desorption rate of all the samples analysed. This indicates that H in the Cr doped zirconium oxide layer had the lowest mobility of all the samples investigated. This is consistent with the theoretical predictions that the doping of ZrO2 by Cr reduces the solubility of hydrogen in ZrO2. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text: false
- Date Issued: 2021-12
Effect of coal and microalgae biomass co-firing on CO2, SO2 and NOx emissions: An experimental evaluation
- Authors: Magida, Nokuthula Ethel
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53817 , vital:45984
- Description: There is increasingly stringent legislation on the environmental impact of energy production from coal combustion, and this has led to growing pressure to reduce the emission of greenhouse gases (GHGs). Thus, there is a significant need to develop and implement clean coal combustion technologies that would reduce the environmental gas pollutants. For power generation, the co-firing of biomass fuels at conventional coal-fired power stations is recognised as one of the low-cost, low-risk options to achieve significant reductions in GHG emissions. When coal is co-utilized with biomass there is added attractiveness because the biomass is CO2 neutral, and there is interest in using waste biomass and microalgae. Thus, the co-combustion of coal and biomass for energy production results in pollutant reduction, especially in the emissions of NOx, SOx, volatile organic compounds and polyaromatic hydrocarbons. The synergistic activity observed for toxic organic emissions is not well understood and is thought to involve chemical interaction between the volatiles from each fuel coupled with possible catalytic activity from the inorganic constituents of the fuels. The characterization of co-firing products and gases emitted from coal and microalgae (particularly the Scenedesmus strain) co-combustion has received limited attention. Therefore, this study seeks to understand possible interactions occurring during co-combustion of coal and Scenedesmus microalgae (Coalgae®). Additionally, the study aims to determine the effect of co-firing coal and Scenedesmus microalgae on CO2, SO2 and NOx emissions. The term “Coalgae®” refers to the mixture of coal and microalgae biomass. The study looks at physico-thermal characteristics as well as CO2, SO2 and NOx emissions of various coal-microalgae blending ratios by mass; 100:0 (coal), 95:5 (Coalgae® 5%), 90:10 (Coalgae® 10%), 85:15 (Coalgae® 15%) and 80:20 (Coalgae® 20%). Characterization techniques carried out included proximate and ultimate analyses, Fourier-transform infrared (FT-IR) and Scanning electron microscopy and X-ray energy dispersive spectroscopy (SEM/EDS). For combustion studies two techniques were applied. Low heating rate was obtained through a Thermogravimetric-Mass spectrometer analysis (TG-MS). Other combustion experiments were performed on the five lumpy fuels (coal and Coalgae® 5% - 20%) exposed to the flame in a fixed-bed combustion reactor. The emission concentrations of CO2 (%), NOx (ppm) and SO2 (ppm) of coal and Coalgae® blends were measured during the combustion of the five materials using a Lancom 4 portable flue gas analyser. The mass reduction (g) and temperature (°C) at the reactor exit were recorded during the combustion tests to compare the combustion behaviour of the four mixtures to that of raw coal. TG-DTG curves of coal and microalgae confirmed that the combustion behaviour of these materials was different. Coal showed one reaction during the combustion process, while microalgae and the Coalgae® blends showed three reactions. A significant reduction in activation energies of 160.4 kJ/mol, 159.6 kJ/mol, 151.3 kJ/mol, and 134.2 kJ/mol for Coalgae® 5% - Coalgae® 20%, respectively, compared to coal (161.3 kJ/mol) was achieved. The lowering of activation energy could be attributed to the relative fixed carbon content. SEM morphology images of ash obtained from the combustion of coal and Coalgae® 5% - 20% confirmed changes in devolatilization and combustion behaviour of solid raw fuel. The ash of Coalgae® blends had higher fluxing elements (Fe, Ca, K and Mg) than coal and this shows possibility of slagging and fouling in combustion systems. The Coalgae® blends showed a synergistic effect due to different combustion characteristics of coal and Scenedesmus microalgae. The combustion results obtained from the fixed-bed reactor showed significant reductions in concentrations of CO2, SO2 and NOx emissions for Coalgae® blends compared to baseline coal. Microalgae reduced CO2 emissions from baseline coal by 14.9%, 19.5%, 23.5% and 31.4% for Coalgae® 5%, 10%, 15% and 20%, respectively. SO2 reductions of 1.9%, 10.6%, 15.8% and 18.2%, and NOx reductions of 22.4%, 26.1%, 24.4% and 16.9% were achieved with Coalgae® 5%, 10%, 15% and 20%, respectively. Moreover, the combustion efficiency of Coalgae® blends increased significantly by up to 14.5% from baseline coal (86.4%) to Coalgae® 20% (98.9%). Based on the above findings, the co-firing of coal and Scenedesmus microalgae biomass was necessary for the reduction of CO2, SO2, and NOx emissions. As such, Coalgae® blends can be considered as alternative fuels in any coal driven process for energy generation. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Magida, Nokuthula Ethel
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53817 , vital:45984
- Description: There is increasingly stringent legislation on the environmental impact of energy production from coal combustion, and this has led to growing pressure to reduce the emission of greenhouse gases (GHGs). Thus, there is a significant need to develop and implement clean coal combustion technologies that would reduce the environmental gas pollutants. For power generation, the co-firing of biomass fuels at conventional coal-fired power stations is recognised as one of the low-cost, low-risk options to achieve significant reductions in GHG emissions. When coal is co-utilized with biomass there is added attractiveness because the biomass is CO2 neutral, and there is interest in using waste biomass and microalgae. Thus, the co-combustion of coal and biomass for energy production results in pollutant reduction, especially in the emissions of NOx, SOx, volatile organic compounds and polyaromatic hydrocarbons. The synergistic activity observed for toxic organic emissions is not well understood and is thought to involve chemical interaction between the volatiles from each fuel coupled with possible catalytic activity from the inorganic constituents of the fuels. The characterization of co-firing products and gases emitted from coal and microalgae (particularly the Scenedesmus strain) co-combustion has received limited attention. Therefore, this study seeks to understand possible interactions occurring during co-combustion of coal and Scenedesmus microalgae (Coalgae®). Additionally, the study aims to determine the effect of co-firing coal and Scenedesmus microalgae on CO2, SO2 and NOx emissions. The term “Coalgae®” refers to the mixture of coal and microalgae biomass. The study looks at physico-thermal characteristics as well as CO2, SO2 and NOx emissions of various coal-microalgae blending ratios by mass; 100:0 (coal), 95:5 (Coalgae® 5%), 90:10 (Coalgae® 10%), 85:15 (Coalgae® 15%) and 80:20 (Coalgae® 20%). Characterization techniques carried out included proximate and ultimate analyses, Fourier-transform infrared (FT-IR) and Scanning electron microscopy and X-ray energy dispersive spectroscopy (SEM/EDS). For combustion studies two techniques were applied. Low heating rate was obtained through a Thermogravimetric-Mass spectrometer analysis (TG-MS). Other combustion experiments were performed on the five lumpy fuels (coal and Coalgae® 5% - 20%) exposed to the flame in a fixed-bed combustion reactor. The emission concentrations of CO2 (%), NOx (ppm) and SO2 (ppm) of coal and Coalgae® blends were measured during the combustion of the five materials using a Lancom 4 portable flue gas analyser. The mass reduction (g) and temperature (°C) at the reactor exit were recorded during the combustion tests to compare the combustion behaviour of the four mixtures to that of raw coal. TG-DTG curves of coal and microalgae confirmed that the combustion behaviour of these materials was different. Coal showed one reaction during the combustion process, while microalgae and the Coalgae® blends showed three reactions. A significant reduction in activation energies of 160.4 kJ/mol, 159.6 kJ/mol, 151.3 kJ/mol, and 134.2 kJ/mol for Coalgae® 5% - Coalgae® 20%, respectively, compared to coal (161.3 kJ/mol) was achieved. The lowering of activation energy could be attributed to the relative fixed carbon content. SEM morphology images of ash obtained from the combustion of coal and Coalgae® 5% - 20% confirmed changes in devolatilization and combustion behaviour of solid raw fuel. The ash of Coalgae® blends had higher fluxing elements (Fe, Ca, K and Mg) than coal and this shows possibility of slagging and fouling in combustion systems. The Coalgae® blends showed a synergistic effect due to different combustion characteristics of coal and Scenedesmus microalgae. The combustion results obtained from the fixed-bed reactor showed significant reductions in concentrations of CO2, SO2 and NOx emissions for Coalgae® blends compared to baseline coal. Microalgae reduced CO2 emissions from baseline coal by 14.9%, 19.5%, 23.5% and 31.4% for Coalgae® 5%, 10%, 15% and 20%, respectively. SO2 reductions of 1.9%, 10.6%, 15.8% and 18.2%, and NOx reductions of 22.4%, 26.1%, 24.4% and 16.9% were achieved with Coalgae® 5%, 10%, 15% and 20%, respectively. Moreover, the combustion efficiency of Coalgae® blends increased significantly by up to 14.5% from baseline coal (86.4%) to Coalgae® 20% (98.9%). Based on the above findings, the co-firing of coal and Scenedesmus microalgae biomass was necessary for the reduction of CO2, SO2, and NOx emissions. As such, Coalgae® blends can be considered as alternative fuels in any coal driven process for energy generation. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text:
- Date Issued: 2021-12
Engineering nanocatalysts using mixed metals for hydrodesulfurization of fuel oil
- Authors: Majodina, Siphumelele
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53861 , vital:46021
- Description: Crude oil is a complex blend containing thousands of hydrocarbons, non-hydrocarbon compounds and heavy metals. These hydrocarbons are mixed with variable quantities of sulfur-, nitrogen-, and oxygen-containing compounds. The combustion of fuel containing organosulfur compounds results in the emission of sulfur oxides (SOx) into the atmosphere. These toxic gases escape into the atmosphere resulting in air pollution, which is a large contributor to global warming. Air pollution also causes pulmonary diseases, allergies and may even lead to human death. It can also cause harm to other living organisms such as animals and food crops. Thus, mandating the reduction of sulfur in organosulfur compounds in fuel to <10 ppmS by the environmental protection agency. Several studies have been conducted to remove sulfur from fuels, most of which have focused on removing refractory sulfur compounds due to the difficulty in removing sulfur in these compounds. However, the currently employed hydrodesulfurization (HDS) catalysts suffer in producing fuels complying with the future standards of fuels quality. Generally, HDS catalysts are made up of metallic components, Co (Ni) and Mo (W), on porous supports, the catalytic activity of these catalysts strongly depends on the amount of NiWS (CoMoS) phases in it and to the extent in which these phases are exposed on the catalyst support surfaces and this is engineered using chelating agents and size of catalysts. To this end, nanosized materials (nanocatalysts) are considered most suitable, as reported active phases of HDS catalysts are exposed, hence improving the hydrodesulfurization of sulfur-containing compounds in fuels. Nanocatalysts results in nanoparticles and when impregnated on a support will results in high surface area, and enhances electronic property, which increases the activity of the catalyst allowing the most refractory sulfur to be removed. The addition of chelating agents such as EDTA, acetic acid, and citric acid further improves the activity of the catalysts by producing more active phases on the catalyst. In this research project, nanocatalysts will be synthesised using mixed metals with and without chelating agents and tested for HDS activity and selectivity towards sulfur using refractory organosulfur compounds in fuels under industrial HDS conditions. This work was divided into two sections, and this dissertation summarizes the research outcomes of each phase. The first section examines the effect of chelating ligands, namely, ethylenediaminetetraacetic acid (EDTA), citric acid (CA), and acetic acid (AA), on CoMo HDS activity and the sulfidation mechanism. In this study, chelating ligands seem to have a beneficial effect on HDS activity. Detailed mechanistic aspects of interactions between chelating ligands and metallic species (Co-chelating ligands) were also studied. Characterization by SC-XRD revealed that the presence of the chelating ligand result in the formation of complex with cobalt, and the effect of this complex was shown by TG-DSC analysis. This showed that the presence of chelating ligand leads a to delay of cobalt sulfidation as the complex decomposes at higher temperatures, which was the main cause of improving HDS activity. It was also shown that chelating ligands play a role in dispersion of metal oxides and sulfided metal oxides (TEM and XPS). XPS results showed low MoS2 phase for CoMo/Al2O3 (45%), while CoMo-EDTA/Al2O3 (63%) catalyst resulted in high MoS2 phases. From all the catalysts, CoMo-CA/Al2O3 (98%) gave the highest catalytic activity, and the increase in activity could be attributed to the formation of octahedral molybdenum oxides as they are easily reducible during sulfidation and result in more dispersed active phases and weak metal-support interaction. The second section examines the effect of a promoter (Rh) and different chelating ligands (EDTA, AA, and CA) on the catalyst RhMo supported with alumina. In this phase, rhodium was used as promoter, the following trend for catalytic activity was observed: RhMo/Al2O3 (88%) > RhMo-AA/Al2O3 (73%) > RhMo-CA/Al2O3 (72%) > RhMo-EDTA/Al2O3 (68%). This could be that the addition of chelating ligand complexed both metallic species retarding sulfidation of both metals, hence lowering the HDS activity. Studies show that it is possible for the citric acid to complex with both promoter and an active metal (Mo), and this might result in the formation of molybdenum dimers, trimers and tetramers which are difficult to sulfide. XPS analysis showed that unchelated catalyst have more MoS2 phases of 63%, hence higher dispersion than the chelated catalyst, this could be the reason for high activity in RhMo/Al2O3 (88%) catalyst. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Majodina, Siphumelele
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53861 , vital:46021
- Description: Crude oil is a complex blend containing thousands of hydrocarbons, non-hydrocarbon compounds and heavy metals. These hydrocarbons are mixed with variable quantities of sulfur-, nitrogen-, and oxygen-containing compounds. The combustion of fuel containing organosulfur compounds results in the emission of sulfur oxides (SOx) into the atmosphere. These toxic gases escape into the atmosphere resulting in air pollution, which is a large contributor to global warming. Air pollution also causes pulmonary diseases, allergies and may even lead to human death. It can also cause harm to other living organisms such as animals and food crops. Thus, mandating the reduction of sulfur in organosulfur compounds in fuel to <10 ppmS by the environmental protection agency. Several studies have been conducted to remove sulfur from fuels, most of which have focused on removing refractory sulfur compounds due to the difficulty in removing sulfur in these compounds. However, the currently employed hydrodesulfurization (HDS) catalysts suffer in producing fuels complying with the future standards of fuels quality. Generally, HDS catalysts are made up of metallic components, Co (Ni) and Mo (W), on porous supports, the catalytic activity of these catalysts strongly depends on the amount of NiWS (CoMoS) phases in it and to the extent in which these phases are exposed on the catalyst support surfaces and this is engineered using chelating agents and size of catalysts. To this end, nanosized materials (nanocatalysts) are considered most suitable, as reported active phases of HDS catalysts are exposed, hence improving the hydrodesulfurization of sulfur-containing compounds in fuels. Nanocatalysts results in nanoparticles and when impregnated on a support will results in high surface area, and enhances electronic property, which increases the activity of the catalyst allowing the most refractory sulfur to be removed. The addition of chelating agents such as EDTA, acetic acid, and citric acid further improves the activity of the catalysts by producing more active phases on the catalyst. In this research project, nanocatalysts will be synthesised using mixed metals with and without chelating agents and tested for HDS activity and selectivity towards sulfur using refractory organosulfur compounds in fuels under industrial HDS conditions. This work was divided into two sections, and this dissertation summarizes the research outcomes of each phase. The first section examines the effect of chelating ligands, namely, ethylenediaminetetraacetic acid (EDTA), citric acid (CA), and acetic acid (AA), on CoMo HDS activity and the sulfidation mechanism. In this study, chelating ligands seem to have a beneficial effect on HDS activity. Detailed mechanistic aspects of interactions between chelating ligands and metallic species (Co-chelating ligands) were also studied. Characterization by SC-XRD revealed that the presence of the chelating ligand result in the formation of complex with cobalt, and the effect of this complex was shown by TG-DSC analysis. This showed that the presence of chelating ligand leads a to delay of cobalt sulfidation as the complex decomposes at higher temperatures, which was the main cause of improving HDS activity. It was also shown that chelating ligands play a role in dispersion of metal oxides and sulfided metal oxides (TEM and XPS). XPS results showed low MoS2 phase for CoMo/Al2O3 (45%), while CoMo-EDTA/Al2O3 (63%) catalyst resulted in high MoS2 phases. From all the catalysts, CoMo-CA/Al2O3 (98%) gave the highest catalytic activity, and the increase in activity could be attributed to the formation of octahedral molybdenum oxides as they are easily reducible during sulfidation and result in more dispersed active phases and weak metal-support interaction. The second section examines the effect of a promoter (Rh) and different chelating ligands (EDTA, AA, and CA) on the catalyst RhMo supported with alumina. In this phase, rhodium was used as promoter, the following trend for catalytic activity was observed: RhMo/Al2O3 (88%) > RhMo-AA/Al2O3 (73%) > RhMo-CA/Al2O3 (72%) > RhMo-EDTA/Al2O3 (68%). This could be that the addition of chelating ligand complexed both metallic species retarding sulfidation of both metals, hence lowering the HDS activity. Studies show that it is possible for the citric acid to complex with both promoter and an active metal (Mo), and this might result in the formation of molybdenum dimers, trimers and tetramers which are difficult to sulfide. XPS analysis showed that unchelated catalyst have more MoS2 phases of 63%, hence higher dispersion than the chelated catalyst, this could be the reason for high activity in RhMo/Al2O3 (88%) catalyst. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text:
- Date Issued: 2021-12