Doctoral Degrees (Civil Engineering)

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Browsing Doctoral Degrees (Civil Engineering) by browse.metadata.advisor "Brink, I. C."

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    Development and optimization of a combined small scale low cost point of use water treatment system
    (Stellenbosch : Stellenbosch University, 2019-12) Siwila, Stephen; Brink, I. C.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT:Access to safe drinking water is still limited in many rural and suburban areas of developing countries. Point-of-use (PoU) water treatment is the most feasible solution to fight waterborne diseases which pose a serious threat in such areas. Only user friendly, affordable and grid-independent but effective approaches are deemed feasible for poorer communities. Although efforts to develop cost-effective PoU technologies are underway globally, challenges still exist. This study was aimed at developing a combined small-scale low-cost gravity-driven PoU system able to provide bacteriologically safe and aesthetically acceptable drinking water. A range of PoU system configurations were developed and tested. Knowledge gained culminated in the development of a final novel PoU system incorporating silver-coated ceramic granular media (SCCGM) for filtration and inbuilt disinfection, geotextile for pre-filtration (to significantly reduce particulate loads in the water before it passes through the SCCGM thereby increasing pathogen contact with the silver), granular activated carbon (GAC) as an adsorption media (for improving aesthetic aspects and removal of selected heavy metals), and a built-in storage compartment for treated water. No chemical addition is needed. It is a replicable, scalable, and user and environmentally friendly cost-effective technology primarily for particle and bacterial removal and aesthetic improvement. Geotextile and GAC filtration steps enhanced the system’s ability to treat a broader variety of raw water and extended filter runs. Laboratory tests on the system showed high potential for significant E.coli and fecal coliforms removal (>99.99%) at an optimum flow of 2 L/h. In addition, the system exhibited substantial improvements of aesthetic aspects (color, odor and taste) with average turbidity removals of 99.2%. Mathematical modelling was done using E.coli as an indicator organism to aid in optimization of the final novel PoU system and to support future research in terms of configuration, process combination, flow rate, material combination, etc. The system was modelled as a series of three compartments using suitable disinfection kinetic models for silver inactivation and specialized colloidal filtration theory models for fibrous and granular filtration. The modelling demonstrated that suitable removal mechanisms can be applied integrally to model a combined PoU system to predict overall effluent bacterial quality. Such modelling can be used to optimize similarly combined systems by allowing engineers to systematically vary design parameters until desired system effectiveness is attained. The system was developed after investigation and evaluation of local treatment materials and approaches over a period of 18 months, which resulted in three simple, yet innovative water treatment systems namely the: (i) modified intermittently operated slow sand filtration system incorporating geotextile and GAC (ISSFGeoGAC), (ii) eight-layer four-pot bidim sequential filtration (BidimSEQFIL) system, and (iii) wood filtration system combined with GAC (WFSGAC). The ISSFGeoGAC and WFSGAC were designed for removal of bacteria, particles, color, taste, odor and selected heavy metals while BidimSEQFIL was designed for particle and bacterial removal. These were then comparatively evaluated alongside two commercially available PoU systems using a comparison framework developed in this study for evaluating low-cost PoU technologies. The findings will be helpful to engineers, NGOs, etc. for possible application of the novel systems, modelling and optimization of combined PoU systems, and comparative evaluation of low-cost PoU systems.
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    Modelling breakthrough curves and investigating the impact of models and numerical properties on parameter estimation
    (Stellenbosch : Stellenbosch University, 2019-04) Silavwe, Davy Danny; Brink, I. C.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: The research investigated and applied several Eulerian numerical methods of the advection-dispersion model (AD-Model) for the analysis of concentration-time curves, also known as breakthrough curves (BTCs), to develop empirical models for predicting stream longitudinal dispersion coefficients. Typically, measured BTCs are analysed to estimate solute transport parameters which are then used to develop empirical equations by correlating optimised longitudinal dispersion coefficients with the bulk flow and channel properties. The investigation attempted to determine the impact of numerical methods and nondimensional numerical properties on optimised parameters and subsequently on constructed empirical models for predicting longitudinal dispersion coefficients. Four concerns related to the construction of empirical models for estimating stream longitudinal dispersion coefficient based on estimates by numerical methods were addressed. (a) Dependence of estimated parameter values on the method used. (b) Influence of numerical properties on values of estimated parameters (c) Identification of model structure, and (d) Characterising model performance. To address the concern (a), six optional numerical methods were assessed using a set of synthetic BTCs simulated for a hypothetical stream reach. This was followed by a selection of three numerical methods for the analysis of observed BTCs to determine parameter values for the development of empirical models. The selected numerical methods are well-known methods, namely, Backward-time/centred space (BTCS), Crank-Nicolson, Implicit QUICK, QUICKEST, MacCormack and third-order upstream-differencing methods. Shortlisted methods were Crank-Nicolson, MacCormack and QUICKEST methods. To address issue (b) parameter values for the development of empirical models were obtained over a range of numerical properties. To address issue (c) dimensional analysis and least-squares regression was used. To address issue (d) a combination of several model performance measures focusing on several features were used for a broad evaluation of models. The study shows that optimal parameter values of the AD-Model determined by Eulerian numerical methods vary with numerical methods and model resolution, such that there is a possibility of overestimating or underestimating parameter values, especially the dispersion coefficient. Consequently, in this research, the Crank-Nicolson and the MacCormack methods were observed to overpredict the dispersion coefficient with an increase in Peclet number, while the the QUICKEST method was observed to underpredict dispersion coefficients with increase in Peclet number. Consequently, structures of developed empirical models and predictions varied with solution method used and nondimensional numerical parameters under which optimised parameters were determined. Based on performance analysis measures, adequate and comparable empirical models were developed for a range of 0.599 – 12.818 of the Peclet number. However, the quality of concentration predictions using predicted dispersion coefficients requires the use of numerical methods and model resolutions under which empirical models were developed. Therefore, empirical models may be well-founded within their calibrated conditions and channel characteristics.