Browsing by Author "Siwila, Stephen"

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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 of Escherichia coli removal by a low-cost combined drinking water treatment system
    (IWA Publishing, 2020-08) Siwila, Stephen; Brink, Isobel C.
    ENGLISH ABSTRACT: This work presents mathematical modelling of Escherichia coli (E. coli) removal by a multi-barrier point-of-use drinking water system. The modelled system is a combination of three treatment stages: filtration by geotextile fabric followed by filtration and disinfection by silver-coated ceramic granular media (SCCGM) then granular activated carbon (GAC) filtration. The presented models accounted for removal mechanisms by each treatment stage. E. coli was modelled as a microbial particle. E. coli inactivation by SCCGM was modelled using the Chick’s, Chick-Watson, Collins-Selleck and complete mix system bacterial inactivation kinetic models, which were considered adequately representative for describing the removal. Geotextile removal was modelled using colloidal filtration theory (CFT) for hydrosol deposition in fibrous media. The filtration removal contributions by the SCCGM and GAC were modelled using CFT for removal of colloidal particles by granular media. The model results showed that inactivation by silver in the SCCGM was the main bacterial removal mechanism. Geotextile and GAC also depicted appreciable removals. The theoretical modelling approach used is important for design and optimization of the multi-barrier system and can support future research in terms of material combinations, system costs, etc. Collector diameter, particle size, filtration velocity and contact time were identified as critical parameters for E. coli removal efficiency.
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    A novel low-cost multi-barrier system for drinking water treatment in rural and suburban areas
    (IWA Publishing, 2020-03) Siwila, Stephen; Brink, Isobel C.
    A low-cost multi-barrier drinking water system incorporating geotextile fabric for pre-filtration, silver-coated ceramic granular media (SCCGM) for filtration and disinfection, granular activated carbon (GAC) as an adsorption media and a safe storage compartment for treated water has been developed and tested. The developed system offers a novel concept of point-of-use drinking water treatment in rural and suburban areas of developing countries. The system is primarily aimed at bacterial and aesthetic improvement and has been optimised to produce .99.99% E. coli and fecal coliforms removal. Although particular emphasis was placed on the elimination of bacteria, improvement of the acceptability aspects of water was also given high priority so that users are not motivated to use more appealing but potentially unsafe sources. This paper discusses key system features and contaminant removal performance. A system using SCCGM only was also tested alongside the multi-barrier system. Strengths and weaknesses of the system are also presented. Both the developed and SCCGM-only systems consistently provided .99.99% E. coli and fecal coliforms removal at an optimum flow of 2 L/h. The developed system significantly recorded improvements of aesthetic aspects (turbidity, color, taste and odor). Average turbidity removals were 99.2% and 90.2% by the multi-barrier and SCCGM-only systems respectively.