Research Articles (Civil Engineering)
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- ItemModelling 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.
- ItemBaseline adjustment methodology in a shared water savings contract under serious drought conditions(Water Research Commission, 2020-01) Jacobs, H. E.; Du Plessis, J. L.; Nel, Nicole; Gugushe, S.; Levin, S.ENGLISH ABSTRACT: Baselines are often employed in shared water saving contracts for estimating water savings after some type of intervention by the water service company. An adjustment to the baseline may become necessary under certain conditions. Earlier work has described a number of relatively complex methods for baseline determination and adjustment, but application in regions faced with relatively limited data becomes problematic. If the adjustment were determined before finalising the contractual matters, it would be possible to gather the required data in order to determine the adjustment. However, in cases where no adjustment was fixed prior to the contract, a method is required to determine an adjustment mid-contract based on whatever data are available at the time. This paper presents a methodology for baseline adjustment in an existing shared water savings contract and explains how adjustment could be determined mid-contract, under conditions of limited data. The adjustment compensates for expected reduced water consumption due to external influences induced by serious water restrictions, typically introduced during periods of drought. The fundamental principle underpinning the baseline adjustment methodology presented in this paper involved segregating real water losses from the actual consumption of end-users, preferably by analysing the minimum night flow. In the absence of recorded night flows, an alternative procedure involving the minimum monthly consumption pre- and post-baseline was employed. The baseline adjustment method was subsequently applied in a South African case study, reported on separately. This technique is helpful because adjustments could be determined without adding unnecessary complexity or cost, and provides a means to resolve disputes in cases where unexpected savings occur mid-contract.
- ItemGarden footprint area and water use of gated communities in South Africa(Water Research Commission, 2020-04) Du Plessis, Jacques L.; Knox, Ashley J.; Jacobs, Heinz E.Gated community homes in South Africa are popular amongst property buyers in urban environments such as cities and metropoles due to the increased security and lifestyle improvements offered. Garden design and layout requirements are prescribed in architectural guidelines compiled by the homeowners associations of these communities. Garden footprint area in gated community homes is of importance to researchers and planners, because of the influence on water use. This study used a quantitative approach to evaluate the spatial data of garden footprint area as a percentage of total plot area for 1 813 gated community homes in different regions of South Africa. The research reviewed how garden footprint area is prescribed and how it is applied in gated community homes. The impact of garden footprint area on water use was also analysed. The results were compared to relevant information lifted from specific architectural design guidelines developed for each gated community. Data from 11 gated communities were analysed and the average garden footprint area was found to be 36% of the total plot area. Gated community homes with a garden area smaller than 100 m2 were found to have limited influence on monthly water consumption, while the water use of gated community homes with a larger garden footprint area increased proportionally with garden footprint area. The seasonal fluctuation of water use is illustrative of garden irrigation and other outdoor water use. The results provided useful input for incorporation in outdoor water use modelling of gated community homes.
- ItemThe potential use of plant species within a Renosterveld landscape for the phytoremediation of glyphosate and fertiliser(Water Research Commission, 2020-01) Jacklin, D. M.; Brink, I. C.; De Waal, J.ENGLISH ABSTRACT: In South Africa, fertiliser and herbicide pollutants resulting from agricultural practices indirectly lead to the degradation of surface freshwater and groundwater quality. Nitrogen and phosphorus, and glyphosate, derived from agricultural fertiliser and herbicide applications, respectively, contribute to watercourse toxicity. Adjacent to many of the surface freshwater systems are some of South Africa's most productive agricultural lands, where natural ecosystems are converted to croplands, resulting in the degradation of natural vegetation and deterioration of freshwater quality. The critically endangered status of some Renosterveld vegetation types is the product of agricultural expansion, nutrient loading through fertilisation and the spraying of herbicides. A buffer of Renosterveld vegetation along river corridors may contribute to the remediation of agricultural pollutants prior to entering watercourses. The utilisation of wetland plants occurring within Renosterveld for agricultural pollutant extraction can increase river corridor biodiversity, creating indigenous refuges and facilitating habitat connectivity. A laboratory phytoremediation system was designed and constructed to investigate the pollutant-removal potential of indigenous species occurring in Renosterveld vegetation (amongst other areas), compared with commonly used invasive alien plants (IAP) in floating wetland designs. Five pollutant parameters - ammonia, nitrate, orthophosphate and two glyphosate concentrations - reflect environmental stresses on 14 wetland species naturally occurring within Renosterveld vegetation. Effluent analyses indicated significant removal efficiencies for the indigenous vegetation across both fertiliser and herbicide pollutants, with the two most effective species identified as Phragmites australis and Cyperus textilis, with 95.87% and 96.42% removal, respectively. All wetland species displayed greater pollutant removal than the unvegetated soil control and when compared to an IAP and palmiet assemblage, indicated similar pollutant-removal efficiencies, justifying their use as an acceptable alternative.
- ItemBaseline adjustment methodology in a shared water savings contract during severe water restrictions - a case study in the Western Cape, South Africa(2020-01) Jacobs, H. E.; Du Plessis, J. L.; Nel, Nicole; Gugushe, S.; Levin, S.A novel method for baseline adjustment in a shared water savings contract under serious drought conditions was presented in a companion paper. The newly developed baseline adjustment method was subsequently applied to a case study, as discussed in this manuscript. The case study involved application of the method to 24 relatively complex sites, spread over the Western Cape Province in South Africa. The sites included, for example, military bases, naval dockyards, an airforce base, prison facilities, large multi-storey blocks of flats and administrative office buildings. Baseline adjustment became essential mid-contract during the serious water restrictions in Cape Town at the time. The restrictions were linked to the 'Day Zero' scenario in 2018 when water supply would potentially run out, and resulted in water savings at baseline sites that were ascribed to external factors. The study incorporated a comprehensive review of the approved baseline reports with site visits to 12 of the properties. The baseline adjustment method provided a robust means to obtain adjustments for sites with relatively limited data. The minimum data requirement was a record of monthly water consumption per site. The adjustments varied between 0% and 64% of the original baseline value for the different sites in the study sample. The relatively higher adjustments were linked to sites where outdoor irrigation and pool water use was prevalent during the baseline-setting period, but was banned during the drought. Zero adjustments were found for sites with exceptionally high leakage flows that had subsequently been repaired; leaks dwarfed actual use in these cases. The results for all 24 sites were accepted by the contracting parties as being reasonable and fair.