Doctoral Degrees (Civil Engineering)
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Browsing Doctoral Degrees (Civil Engineering) by browse.metadata.advisor "Brink, Isobel"
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- ItemAn investigation into untreated greywater as supplementary household water source to augment potable municipal supply with consideration of associated risks.(Stellenbosch : Stellenbosch University, 2022-04) Nel, Nicole; Jacobs, Heinz Erasmus; Brink, Isobel; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Despite the available body of research regarding supplementary household water sources and in particular, greywater use, there is a critical gap when it comes to understanding the uptake of untreated greywater in suburban areas and the trade-off between the risks and potential water savings. This dissertation focuses on untreated greywater use in residential, fully serviced houses equipped with regular water use appliances and with conventional waterborne sewers. The main objective is to gain an improved understanding of the uptake of untreated greywater and the potential for use and application in suburban areas by exploring the trade-off between expected water savings (associated with quantity) and potential risks (associated with quality) as related to untreated greywater use. This study starts with addressing on-site supplementary household water sources with a focus on groundwater abstraction, rainwater harvesting, and greywater use as available non-potable supplementary water sources to residential consumers. The legal position in South Africa and an end use model to assess the theoretical impact of these sources on water demand in formal residential areas, is presented. The model provides valuable strategic direction and indicates a significant theoretical reduction in potable municipal water demand of between 55% and 69% for relatively large properties with irrigated gardens when supplementary household sources are maximally utilised (when compared to exclusive municipal use as a baseline). This load reduction on piped reticulation systems could be an advantage through augmenting municipal supply. However, water service planning and demand management are complicated by the introduction, and possible future decommissioning, of any household water source. The trade off between the advantages and disadvantages of this load reduction defines whether there is a nett positive benefit linked to the use of the household water sources. Groundwater is the household water source considered to have the most notable penetration and intensity to impact potable water demand in residential areas and is coupled to a relatively low risk in terms of water quality relative to other uses such as greywater use. Groundwater, however, has the biggest barrier to entry and requires the highest capital investment of the three supplementary household water sources. The distinct trade off between the advantages and disadvantages of untreated greywater, particularly in comparison to the other supplementary household water sources, provides justification towards it being the focus of this study. Untreated greywater use at household level is an accessible water source to supplement non-potable water requirements in times of emergency water curtailments, but poses various risks to the consumer, the wider community, infrastructure and the environment. Little is known about unregulated, untreated greywater use practices in suburban communities where consumers have become accustomed to reliable potable water supplied via a pressurised, piped distribution system. There is a lack of knowledge regarding the sources of greywater used, collection methods, -storage and -distribution, the application points, the level of treatment (if any) and the perceived risks related to the greywater use. The City of Cape Town was selected as a case study site for research into greywater use under the threat of “Day Zero” and stringent water restrictions, implemented during the 2017/2018 summer season. A consumer survey and analysis of relevant online forums was conducted in order to obtain the necessary information. Greywater use practices from a sample group of 351 consumers were identified and classified. Untreated greywater use was found to be common, mainly for garden irrigation and toilet flushing. The results point to high-risk activities in the study group. By using these reported ad hoc greywater use practices identified through the Cape Town case study, the volume of untreated greywater used by households in formal residential settings was evaluated by means of a stochastic end use model. Untreated greywater use practices (e.g. bucketing) were found to reduce water consumption in a single person suburban household by less than 10%, which is lower than values reported in literature. This relatively low volume weighed up against the high risk of using untreated greywater may result in a negative nett benefit, providing decision making insights for both water service providers and consumers. This quantification of the volumes associated with untreated ad hoc greywater use is the first step in understanding the trade-off between expected water savings (quantity) and potential risks (quality) of untreated greywater use. The second component of the water saving-risk trade off involved an investigation of untreated greywater quality and related risks, through a statistical analysis of greywater quality results, as sourced from South African studies. Greywater sources included were the bathroom, kitchen, laundry, mixed and general residential sources. Variability in terms of each of the reported physical, chemical and microbiological constituents by source and between result sets was noted. Statistically significant differences were evident between the pH, conductivity and phosphorous values of certain sources. A risk assessment undertaken for each of the constituents revealed further variability. The constituent with the highest number of high-risk samples was total dissolved solids, although further research into specific constituent elements that are of real danger to humans is warranted here. The finding that water savings due to untreated greywater through manual collection methods is <10% is markedly less than the water savings through the use of multiple household water sources (up to 69% for large properties). This coupled with the relatively high risk and high consequences in greywater practices in terms of public health, the environment, and infrastructure, given its variability, provide insight into the quality-quantity space. There is a need for a more nuanced view of the potential potable savings associated with greywater use and a need for improved risk management. Risk management and drivers of consumer decision making in the water use space were therefore explored further. As a result, a decision-making matrix was designed as an interim conceptual tool to assist consumers when faced with water use decisions during emergency drought conditions. This research is unique in that while the use of greywater with purpose-built infrastructure and treatment systems has been studied for a number of locations and configurations, the practices used by individuals in the absence of such infrastructure was not well understood. This study has shed light on the reported volume of untreated greywater used by households in formal residential settings, based on reported ad hoc greywater use practices and on the extent of these potentially risky practices. A novel holistic picture of the risks and trade-offs associated with untreated greywater use was developed, allowing for advancement of knowledge in the field.
- ItemInvestigation of novel deflector shapes for uncontrolled spillways(Stellenbosch : Stellenbosch University, 2024-02) Wright, Henry John; Bosman, Adèle ; Brink, Isobel ; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: The hydraulics of stepped spillways are generally well understood, although numerous fundamental hydraulic aspects remain inadequately explored. Critical knowledge gaps persist, including aerated flow hydraulics, hydraulics of embankment flows, hydraulics of stepped spillways for steep gravity dams, environmental hydraulics as well as turbulent interactions between cavity flow and skimming flow. Notably, the elusive safe unit discharge limits for stepped spillways remain undefined, with conflicting findings in the literature. The majority of stepped spillways have been designed for a maximum unit discharge of 25 to 30m3/s/m due to the risk of cavitation damage. It has further been reported that the critical velocity of approximately 20 m/s for the inception of cavitation on stepped spillways is obtained at a unit discharge of 25 m3/s/m. Further research in the field revealed that a bottom aerator becomes imperative for discharges greater than 30m3/s/m. However, discrepancies persist, with other researchers suggesting that the safe unit discharge is lower, quoting 11.5 m3/s/m to 14 m3/s/m for step heights of 0.6 m to 1.2m, respectively. Therefore, the exact limits of stepped spillways remain unquantified when water flows on the downstream slope. In China, the Flared Gate Pier (FGP) has been used on stepped spillways, particularly the X-type and Y-type piers. These piers support the crest gates and have been customised to contract the flow rapidly into a high-velocity jet. These piers have been used at, amongst others, the Dachaoshan Dam, a 111 m high Roller Compacted Concrete (RCC) gravity dam, with a maximum unit discharge designed of 193m3/s/m. These piers redirect flow into high-velocity jets, achieving efficient energy dissipation without relying on the stepped spillway face. Although historically utilised exclusively with gated spillways, FGPs hold potential as deflector-type energy dissipaters and were used as the basis for the novel deflector investigations in this research. To date, a variety of aerators have been fitted to improve spillway performance. Other aeration methods, such as the use of Roberts splitters, rectangular protrusions and triangular protrusions have been proposed, with some of these designs being successfully implemented. However, research has noted that these methods yield only marginal increases in the safe unit discharge of stepped spillways. The main concern regarding stepped spillways is the cavitation risk during high discharges, with a critical cavitation parameter of 0.5 compared to 0.2 for smooth chutes. This limits the maximum allowable unit discharge. While cavitation pitting has not been reported on prototype spillways, the exact conditions under which cavitation on stepped spillways may occur remain uncertain. The current research investigated the feasibility of a novel deflector form aimed at increasing the safe discharge capacity of spillways by deflecting the flow away from the spillway slope. The research incorporated a comprehensive approach, comprising a series of numerical models to simulate the hydrodynamic environment as well as four physical models. Numerical model simulations were undertaken with FLOW-3D HYDRO® and ANSYS FLUENT® computational fluid dynamics (CFD) software to optimise the deflector geometries before being tested with a physical model. A 1:50 scale physical model was constructed to investigate the influence of different deflector shapes. The investigation spans a range of prototype unit discharges ranging from 50 to 200m3/s/m and evaluates factors such as water surface profiles created by the deflector and pressure distribution on the deflector. A regression analysis was performed on the collected physical model data to develop equations that predict the jet's inner and outer trajectory and jet breakup length. The proposed novel deflectors developed in this study proved to be effective at various flow rates when the flow trajectory and threshold pressures were considered. These deflectors could be used for dams higher than 150 m and unit discharges ranging between 100 and 200 m3/s/m. Further research is required to improve, amongst others, deflector geometries, to study variables and to undertake additional measurements to conform and improve the efficiency of the novel deflectors, using this research as a basis.
- ItemPlant biofiltration for urban stormwater runoff purification in South Africa(Stellenbosch : Stellenbosch University, 2022-04) Jacklin, Dylan Michael; Brink, Isobel; Jacobs, Shayne Martin; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: A major consequence of urbanisation is the large-scale conversion of pervious to impervious surfaces, which significantly alters the natural hydrological cycle in terms of both hydrology and quality. Together with climate change, urbanisation and the associated stormwater runoff are regarded as major threats to water resource security worldwide, due to the variety of pollutants generated and transported. Conventional urban stormwater management rapidly collects and transports runoff for discharge into the nearest watercourse, triggering a plethora of public and ecological health concerns. In response, the Water Sensitive Urban Design (WSUD) concept, of which plant biofiltration is a component, is increasingly preferred as a sustainable alternative to conventional systems as it considers stormwater as a resource to protect rather than a substance of which to dispose. Plant biofiltration promotes a spatial network of passive, ecologically sound treatment solutions to the diffused nature of urban stormwater pollution, for discharge into existing drainage systems or watercourses. South Africa, one of the most rapidly urbanising countries in Africa, experiences some of the worst environmental deterioration globally. Stormwater runoff discharge, together with aging and defective conventional treatment systems, threaten the country’s already limited freshwater resources. Therefore, the South African Water Research Commission seeks to promote the adoption of WSUD, thus representing a significant shift from the linear drainage strategy currently adopted at local level to a holistic management approach of the urban water cycle and its integration into urban design. Although the value of ecosystem services is increasingly recognised, WSUD and particularly plant biofiltration as one of its components, is under-utilised, as the current framework in South Africa only provides broad philosophical guidance lacking scientific premise for practical design considerations. Variable performances have been reported in standard and modified plant biofilters, stagnating treatment optimisation knowledge. The difficulty of plant biofilter optimisation stems from the complex pollutant removal processes, which vary between physical designs and operational conditions. Therefore, appropriate design demands that both engineering hydrology and the scientific functioning of natural elements be considered; however, the latter is not currently included in the training of the civil engineer who can be the professional responsible for plant biofilter planning and design. Furthermore, current plant biofilter models insufficiently account for design modification and its associated removal processes. Limited local research and design specifics are currently available, which has resulted in injudicious plant selection and erroneous plant biofilter design, inhibiting treatment performance and threatening the recipient site’s natural biodiversity. Thus, the main aim of this research is to advance knowledge in stormwater plant biofiltration for improved urban water management in South Africa. This research initially presents potential phytoremediators, plants for the in situ treatment of pollutants, which are indigenous to the Western Cape, South Africa, as an aid to the practicing engineer for use in local plant biofiltration initiatives. Although chosen plant species were from the local Western Cape area for logistic reasons (the University is situated in the Western Cape), the techniques presented to identify species are transferable to other biogeographic areas. Informed by this undertaking, a phyto-guide is developed for identifying novel phytoremediators, adept at adjusting to the recipient habitat’s dynamic conditions and further incentivised by South Africa’s extensive biodiversity. The initial approach to plant biofilter optimisation investigated four engineered materials as potential growth media amendments, promoting attapulgite combinations for use in small-scale stormwater biofilters in the spatially constrained urban area. Progressing with plant biofilter optimisation, nine indigenous South African biofilters were investigated as effective yet sustainable alternatives to exotic phytoremediators, and Prionium serratum, among others, was found to exhibit enhanced removal capabilities. Physically modifying the plant biofilter as the final component to optimisation, following growth media and plant species, showed that combining standard biofiltration techniques with upflow filtration, plenum aeration and anaerobic zone saturation is the most efficient solution; removing on average 96% of synthetic stormwater loads. The novel sequential modifications between designs highlighted pollutant-specific removal processes and proffered plant biofilter designs for optimised treatment performance. Empirical findings based on the data captured by the preceding investigations contribute statistical output for future local in-depth modeling endeavours. Additionally, in developing the conceptual deterministic plant biofilter model for stormwater treatment, possible applications of existing models for the various nutrient, and potentially heavy metal, removal processes are summarised. In conclusion, this research contributes physical design specifics and both experimental and mathematical models to urban stormwater treatment researchers and practitioners, constantly improving the understanding of plant biofilter complexity.
- ItemStormwater runoff treatment from automobile workshops in Nigeria using combined rice husk, gravel and activated carbon filters.(Stellenbosch : Stellenbosch University, 2022-11) Ataguba, Clement Oguche; Brink, Isobel; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Stormwater runoff from automobile workshops is a major source of pollutant mass flow to rivers, which pose a risk to aquatic ecosystems. An investigation into pollution of stormwater runoff from selected automobile workshops, the development of low cost treatment technologies using granular activated carbon (GAC), rice husk (RH) and river gravel filters (GR) for removal of metals from polluted stormwater runoff from automobile workshops and the application of Langmuir and Freundlich isotherm models in predicting the removal of lead and iron were carried out. A comparative study using the low cost treatment technologies and conventional oil & grease trap (COT) in the removal of oil & grease was also done. Furthermore, a sustainability assessment of the low cost treatment technologies of GAC-RH and GR-GAC was included using a triple bottom line approach (economic, environmental and social impacts). These investigations indicated that stormwater runoff from automobile workshops was highly polluted with concentrations above the permissible discharge limits in Nigerian and American standards. Additionally, the developed low cost treatment technologies were found to lower the high concentrations of metals, indicating their potential successful use in the treatment of the stormwater runoff. This specifically with the GAC-RH filter material combination exhibiting high metals removal efficiencies when compared with GR-GAC and RH treatment filters. The research also indicated that the low cost treatment technologies compared favourably well with the COT in the removal of oil and grease (O&G). The order of oil and grease removal efficiencies of the treatment technologies was GAC-RH > RH > GR-GAC > COT. Langmuir isotherm model was found to predict the removal of lead and iron as favourable adsorption process while the Freundlich isotherm model predicted the removal of lead and iron as a chemisorption process. During adsorption testing, the adsorption capacity of the GAC-RH and GR-GAC filter material combinations decreased with increased dosages of the adsorbents. The overall sustainability assessment of the GAC-RH and GR-GAC technologies indicated that the GAC-RH filter showed a slightly higher overall sustainability score when compared to the GR-GAC filter application. Finally, a centralized auto-mechanic village was proposed for major towns and a hypothetical design for stormwater detention system was also presented in a proposed Design Guide for Stormwater Management: Application to Auto-Mechanic Villages in Nigeria.