Scielo RSS <![CDATA[Water SA]]> vol. 41 num. 3 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Reduction of microbial biofilm formation using hydrophobic nano-silica coating on cooling tower fill material</b>]]> A cooling tower is a heat removal device, which extracts waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers are frequently associated with biofilm problems and Legionnaires disease outbreaks. Where biofilms can cause clogging and corrosion, reduction of biofilms is important for operational reasons and public health. Therefore, effective anti-biofilm strategies are needed in practice. The aim of the present study was to reduce biofilm formation using a nano-hydrophobic coating on cooling tower fill materials - polypropylene cooling tower fill material was coated with nano-silica. The effectiveness of the hydrophobic coating was investigated for a 6-month test period in a model cooling tower system, by monthly counting of the surface-associated bacteria using an epifluorescence microscope. A significant reduction (up to 4 log) in surface-associated bacteria was observed on coated test samples in comparison to uncoated control coupons. This study is the first report regarding the use of nano-silica coatings on cooling tower fills. The coating can be easily fabricated and the range of possible applications can be expanded to include a variety of conditions. <![CDATA[<b>Water footprint assessment to inform water management and policy making in South Africa</b>]]> One method to inform decisions with respect to sustainable, efficient and equitable water allocation and use is water footprint assessment (WFA). This paper presents a preliminary WFA of South Africa (SA) based on data for the period 1996-2005. Crop production was found to contribute about 75% of the total water footprint of national production. The total water footprint of crop production is mainly composed of five crops: maize, fodder crops, sugarcane, wheat and sunflower seed, which account for 83% of the crop water footprint. The average water footprint of a South African consumer is 1 255 m³/yr, below the world average of 1 385 m³/yr, and is dominated by the consumption of meat (32%) and cereals (29%). About one fifth of this water footprint of consumption is external to SA. While SA is a net virtual water importer, the virtual water trade analysis revealed that a large share of blue water consumption is related to export. Sustainability concerns are that the major river basins face severe blue-water scarcity for extended periods of the year, and that water pollution levels related to nitrogen and phosphorus were found to be unsustainable in all river basins in SA. Efficient allocation and use of water is investigated by means of comparing the consumptive water footprint to global benchmark values, as well as the economic green- and blue-water productivity and the economic land productivity of the crops cultivated in SA. Furthermore, crops with specific potential for biofuel production are assessed. Lastly, recommendations to address the identified issues are given. <![CDATA[<b>Characterisation of surface uptake and biosorption of cationic nuclear fission products by sulphate-reducing bacteria</b>]]> The treatment of radioactive fission products - 90Sr2+, 60Co2+ and 137Cs+ - from simulated nuclear wastewater was evaluated using locally-isolated sulphate-reducing organisms. In this study, sulphate-reducing bacteria (SRB) were used as biosorbents for removal of the cationic fission products. The cultures achieved 90%, 100%, and 80% removal of Sr2+, Co2+ and Cs+, respectively, for a 75 mg×ℓ-1 solution of each metal under a low ionic strength of 0.01 M. Increasing the ionic strength of the solution to 0.5 M resulted in a decreased metal uptake to 80%, 65% and 70% for Sr2+, Co2+ and Cs+, respectively. Approximately 68% of the adsorbed fraction on cell surfaces was exchangeable (i.e., was desorbed under acidic conditions). Using surface complexation models and equilibrium modelling analysis, reaction sites on the cell walls of the cultures were determined to belong to the -COOH and -H2PO4 groups (pKa = 4-5 and 7-8, respectively). The distribution of the isoelectric equilibrium points for cell surfaces was consistent with the composition and characteristics of the identified microbial species in the culture which was dominated by the Gram(+ve) Bacilli - Lysinicibacillus boronitolerans AB199591 - and biofloc-forming Gram(-ve) SRBs, such as Desulfomonile tiedgei AF418162, Syntrophobacter wolinii X70905, and Desulforhopalus vacuolatus L42613. The high exchangeable fraction on the cells and the higher removal rates under lower ionic strength indicates that metal binding was non-electrostatic which was consistent with outer-sphere complexation behaviour. <![CDATA[<b>Modelling mid-span water table depth and drainage discharge dynamics using DRAINMOD 6.1 in a sugarcane field in Pongola, South Africa</b>]]> Determining optimal subsurface drainage design parameters through monitoring of water table depth (WTD) and drainage discharge (DD) at various combinations of drain depth and spacing is expensive, both in terms of time and money. Thus, drainage design simulation models provide for a simplistic and cost-effective method of determining the most appropriate subsurface drainage design parameters. In this study, the performance of the DRAINMOD model (Version 6.1) in predicting WTDs and DDs was investigated for a 32 ha sugarcane field in Pongola, South Africa. Water table depths were monitored in 1.7 m deep piezometers installed mid-way between two drains by using an electronic dip meter with a beeper, while DDs were measured at drain lateral outlet points, using a bucket and a stop watch. Both WTDs and DDs were monitored from September 2011 to February 2012. Results of the DRAINMOD model evaluation in predicting WTD, during calibration period, showed that there was a very strong agreement between simulated and observed WTDs with a goodness-of-fit (R²) of 0.826 and a mean absolute error (MAE) of 5.3 cm. Similarly, simulated and observed DDs during the model validation period also showed very strong agreement, with an R² value of 0.801 and an MAE of 0.2 mm∙day-1. Results of simulated WTDs at various combinations of drain depth and spacing indicated that in clay soil a WTD of 1.0 to 1.5 m from the soil surface can be achieved by installing drain pipes at drain spacing ranging from 25 to 40 m and drain depth between 1.4 and 1.8 m. On the other hand, in clay-loam soil, the same 1.0 to 1.5 m WTD can be achieved when the drain pipes are installed at drain depths ranging from 1.4 to 1.8 m and corresponding drain spacing ranging from 55 to 70 m. Based on these results, it was concluded that DRAINMOD 6.1 can reliably be used as a subsurface drainage design tool in the Pongola region. This would simplify the design of subsurface drainage systems and the formulation of subsurface drainage design criteria for different crops and soil types found in the area and possibly throughout South Africa. <![CDATA[<b>Conceptual framework for sewer pump problems allowing for fuzzy logic application</b>]]> Sewer pump station problems in separate sewer systems (separate from stormwater drainage systems) were investigated in order to derive a conceptual framework for decision making. Notwithstanding the fundamental service that efficient sewage pumping provides to a community, it was apparent that limited research has been published on the topic. Research was undertaken to identify, investigate and classify problems at existing operational sewage pump stations by means of site visits, interviews, and an extensive knowledge review. A conceptual framework for sewer pump problems was subsequently derived. The application of the framework is illustrated by means of a fuzzy logic approach to one of the problem classes identified. This study sets the scene for further research into fuzzy-based efficiency indices pertaining to different sewer system components and the ultimate application in sewer system decision support tools. <![CDATA[<b>Influence of selected biotopes on chironomid-based bioassessment of the Swartkops River, Eastern Cape, South Africa</b>]]> Impact of pollution on aquatic biota is usually assessed by comparing the assemblage at an impacted site with those at a control or reference site. In South Africa, except in rivers where not all biotopes are represented, the characterisation of a macroinvertebrate-based pollution effect is usually based on samples collected from three distinct biotopes, i.e., stones, vegetation and sediments. In this study, the influence of reducing the numbers of biotopes on chironomid-based bioassessment of pollution in the Swartkops River was investigated. This paper addresses the following questions: (i) can the chironomid species assemblage from any single distinct biotope analysed separately provide sufficiently accurate results similar to those of the composite-biotope group assemblage, and (ii) can chironomid community types be identified based on their biotope preferences? Chironomid larvae were sampled seasonally from three distinct biotopes: stones (stone-in-and-out-of-current), vegetation (marginal and aquatic), and sediment (gravel, sand and mud, GSM) at one upstream control site, i.e., Site 1, and three downstream sites, i.e., Sites 2, 3 and 4. Site 2 in Uitenhage was impacted by diffuse pollution sources including runoff from road networks. Site 3, also in Uitenhage, was impacted by wastewater effluent discharges as well as diffuse pollution sources, while Site 4 in Despatch was about 2.5 km downstream of Site 3. The multivariate analysis of similarity (ANOSIM) indicated that the chironomid species assemblages based on the composite biotopes were significantly different between all site pairs in terms of species composition and abundance. However, when the assemblages were analysed separately for each of the three distinct biotopes, only the stone-based assemblage indicated significant differences between all of the site pairs similarly to those of the composite biotopes. Thus, the results suggest that, when resources are limited, sampling only the stony benthos could still provide bioassessment results similar to benthos from all three biotopes combined. <![CDATA[<b>Adaptive capacity and water governance in the Keiskamma River Catchment, Eastern Cape Province, South Africa</b>]]> South Africa, being a semi-arid country, faces water resource constraints. The projected impacts of climate change in the Keiskamma River Catchment, Eastern Cape Province, are, for example, changes in rainfall with effects on streamflow, salt water intrusion, decreasing water quality due to runoff and erosion, and droughts. This paper uses an existing framework, the Adaptive Capacity Wheel (ACW), complemented by two additional dimensions: adaptation motivation and adaptation belief. The objectives were, first, to assess the adaptive capacity of water governance in the study region, and, second, to show how the ACW can be used as an approach and a communication tool with stakeholders to identify strengths and weaknesses. Based on this, recommendations can be drawn that could help water experts and stakeholders in the future. The results depict a 'medium' score for adaptive capacity. However, it is important to look closely at each dimension assessed by the ACW. The key recommendations are: to overcome the implementation gap, to ensure better coordination across and within governmental levels; to raise awareness, capacity and skill among decision makers and the public; and to increase the political will to overcome adaptation barriers. <![CDATA[<b>Thermochemical reduction of pelletized gypsum mixed with carbonaceous reductants</b>]]> The recovery of better quality waste gypsum during acid mine drainage (AMD) neutralization is one step closer to achieving downstream waste gypsum beneficiation for recovery of valuable materials. This can facilitate recovery of treatment costs and prevention of environmental pollution from gypsum waste-dumps. Thermal reduction using rotary kilns to recover valuable materials from waste gypsum remains a critical and controversial process because of waste gypsum handling problems, environmental pollution due to dust and gaseous emissions and poor conversion yields. In order to mitigate these problems and improve waste gypsum conversion yields, pelletization of waste gypsum in the presence of binders (starch and cellulose) was investigated. A laboratory-scale disc pelletizer was used to produce pellets from a mixture of coal and commercial gypsum or waste gypsum, generated during AMD neutralization, with starch and micro-crystalline cellulose used as binders. The pellets were subjected to high-temperature thermal treatment in a tube furnace to generate calcium sulphide (CaS), an important intermediate for waste gypsum beneficiation. The kinetics of thermal conversion of pelletized waste gypsum to CaS were found to be highly dependent on furnace temperature. Results also showed that pelletization affords improved handling of waste gypsum while use of binders as additives significantly improved the CaS yield, with starch giving the better yield compared to cellulose. <![CDATA[<b>Yield-reliability analysis and operating rules for run-of-river abstractions for typical rural water supply: Siloam Village case study</b>]]> The study focused on yield-reliability analysis and operating rules for optimum scheduling of run-of-river (ROR) abstractions for typical rural water supply schemes using Siloam Village, Limpopo Province, South Africa, as a case study. Efficient operation of water supply systems requires operating rules as decision support tools. System operation methods have hardly been developed or applied to water supply to rural communities that depend on ROR abstractions. Simulated runoff was used to derive unregulated river yield at different levels of assurance of supply (LAS) for Nzhelele River at Siloam Village using 1-day flow duration curves. Yield-reliability analysis results were used to derive operating rules. The results show that Nzhelele River can meet domestic and low-flow requirements at 50-80% (1:2-1:5) LAS. The low-flow and domestic water requirements can be partially met at 90% (1:10) LAS. The generic operating rules for ROR abstractions were consequently derived from the procedure used in developing operating rules for Nzhelele River. This enables generation of operating rules for ROR abstractions in any typical rural water supply system. <![CDATA[<b>Evaluation of an automated struvite reactor to recover phosphorus from source-separated urine collected at urine diversion toilets in eThekwini</b>]]> In the present study we attempted to develop a reactor system to recover phosphorus by struvite precipitation, and which can be installed anywhere in the field without access to a laboratory. A reactor was developed that can run fully automated and recover up to 93% of total phosphorus (total P). Turbidity and conductivity signals were investigated as automation proxies for magnesium dosage, thus making laboratory phosphate measurements to determine the exact magnesium dosage unnecessary. Conductivity is highly influenced by the dosing parameters (molarity and pump speed) and turbidity is affected by particle size distribution issues. Algorithms based on both conductivity and turbidity signals were not able to detect the precipitation endpoint in real time. However it proved possible to identify the endpoint retrospectively from the conductivity signal, and thereafter to dose an algorithm-calculated volume of urine to use up the excess magnesium dosed. <![CDATA[<b>Performance of regional flood frequency analysis methods in KwaZulu-Natal, South Africa</b>]]> Estimates of design floods are required for the design of hydraulic structures and to quantify the risk of failure of the structures. Many international studies have shown that design floods estimated using a regionalised method result in more reliable estimates of design floods than values computed from a single site or from other methods. A number of regional flood frequency analysis (RFFA) methods have been developed, which cover all or parts of South Africa. These include methods developed by Van Bladeren (1993), Mkhandi et al. (2000), Görgens (2007) and Haile (2011). The performance of these methods has been assessed at selected flow-gauging sites in the province of KwaZulu-Natal (KZN), South Africa. It is recommended that the limitations of available flow records to estimate extreme flow events need to be urgently addressed. From the results for KZN the JPV method, with a regionalised GEV distribution with the veld zone regionalisation, generally gave the best performance when compared to design floods estimated from the annual maximum series extracted from the observed data. It is recommended that the performance of the various RFFA methods needs to be assessed at a national scale and that a more detailed regionalisation be used in the development of an updated RFFA method for South Africa. <![CDATA[<b>The applicability of nanofiltration for the treatment and reuse of textile reactive dye effluent</b>]]> The main aim of the study was to test the feasibility of using nanofiltration (NF) processes for the treatment of reactive dye-bath effluents from the textile industry, in order to recover the water and chemicals (salts) for reuse purposes. The study of the reusability of nanofiltered water for dyeing has been given little or no attention. About 30% of reactive dyes remain unfixed on fibres; the unfixed dyes are responsible for the colouration in effluents. Membrane processes were employed to treat reactive dye-bath effluents to recover the salts and water. Investigations were conducted firstly with ultrafiltration (UF) used as a pre-treatment for NF. Secondly, evaluations were performed for 2 types of NF membranes (SR90 and NF90), in terms of quality of permeate produced and fluxes achieved for 2 different samples of effluent. The effect of cleaning on membrane performance was assessed. A reusability test was carried out on both permeate samples for dyeing light and dark shade recipes. The use of UF as pre-treatment to NF resulted in rejection of colloidal substances > 90% and a 15% flux improvement. Permeate from NF90 had a conductivity of 76 µS/cm and total organic carbon (TOC) of 20 mg/ℓ, as compared to SR90 which had a conductivity of 8.3 mS/cm and a TOC of 58 mg/ℓ. Light shade from NF90 gave satisfactory results on dyeing, with no colour difference. However a variation in colour was noticed when the medium sample was used to dye the light shade. Both NF permeates gave satisfactory results when used to dye the dark shades. Permeate from NF90 was within the accepted range for reuse, while permeate from SR90 had a higher salt recovery. Chemical cleaning resulted in 80% flux recovery. From the reusability test it was concluded that permeate from NF90 met the reuse criteria for feed water to the dye bath. <![CDATA[<b>A gap analysis of the South African innovation system for water</b>]]> This paper draws on the innovation literature to analyse the South African system of innovation for water. Two major approaches to science and innovation from the innovation systems literature are described and compared: the neoclassical or 'market-failure' linear model of innovation, and the more complex and more recent innovation systems approach. It is argued that the innovation systems approach is a useful basis of analysis because of its emphasis on the diffusion of knowledge and the factors which tend to affect it - in comparison with the neoclassical model's assumption of perfect knowledge transfer. An analysis of gaps was undertaken using an interactive web-based puzzle-building activity with participants in the water sector. The primary gaps identified are not those that state actors continue to focus on in policy interventions; instead, they include the need to enable effective demand by end users, to facilitate more direct interaction between users and researchers, and to involve the private sector much more strongly in water innovation. Human capacity needs were highlighted, as was the need for strong leadership and openness in data sharing. The argument is made that those gaps that are seen as least important by practitioners and researchers in the sector are the very gaps that South African water innovation policy continues to focus on, while the gaps in cognitive capacity, in structures allowing the articulation of societal needs, and in industry involvement are largely un(der)addressed. This suggests that a linear, or neo-classical understanding of innovation may underlie innovation policy for water in South Africa. Recommendations for future policy directions include promoting knowledge-related infrastructure and data sharing; reorganising the research environment within universities; strengthening support for entrepreneurs; and creating centres of competency with strong industrial-design and economic- and market analysis capabilities. <![CDATA[<b>Investigation into increasing short-duration rainfall intensities in South Africa</b>]]> Extreme storms in South Africa and specifically in the Western Cape have been responsible for widespread destruction to property and infrastructure, even leading to displacement and death. The occurrences of these storms have been increasingly linked to human-induced climate change that is expected to cause more variable weather. Studies on climate circulation models for future climate conditions project that rainfall in the Western Cape and wider South African region is to become more intense and extreme. Sub-daily rainfall for 3 stations in the Western Cape and 4 stations in the rest of South Africa were analysed in order to determine if any trends towards more intense and extreme rainfall are observed and whether the trend is unique to the Western Cape or indicates a wider trend. This study explores this expectation by using historical short-duration rainfall (less than 24 h) for 7 stations in the Western Cape and South African region. Digitised autographic and automatic weather station 5-min rainfall data were combined to extend the effective record length. Both the magnitude and frequency of occurrence of rainfall events were analysed to assess if rainfall intensities are showing any evidence of increasing over time. For the magnitude of rainfall events, extreme value theory was applied to non-stationary sequences, using both a parametric and non-parametric approach for both event maxima and peaks over threshold modelling. The frequency analysis entailed measuring the frequency of exceedance of rainfall events over a certain threshold value. Both the magnitude and frequency analysis indicated that the combination of the two record types influenced the results of some of the stations, while the others showed no consistent evidence of changing rainfall intensities. This led to the conclusion that, from the available observed short-duration record, no evidence was found of trends or indications of changes in rainfall intensities. <![CDATA[<b>Active biomonitoring of a subtropical river using glutathione-S-transferase (GST) and heat shock proteins (HSP 70) in <i>Oreochromis niloticus</i> as surrogate biomarkers of metal contamination</b>]]> The aim of this study was to establish the level of water quality impairment along a mine effluent receiving river, Pote River in Zimbabwe, using Oreochromis niloticus (Nile tilapia) as an indicator organism. Glutathione-S-transferase (GST) enzyme and heat shock protein (HSP 70) expression in the stomach tissue of Nile tilapia were used as biomarkers of heavy metal pollution. Water and fish samples were collected at three sites in the Pote River. Metal concentration in tilapia tissues and water were measured using flame acetylene absorption spectrophotometry while enzymatic activity was determined using ultra-violet spectrophotometry. The concentration of Ni and Zn in water was significantly high compared to the World Health Organization aquatic effluent standards. Cd and Zn were strongly associated with high GST activity and low HSP 70 protein concentrations in fish tissues. Results of this study show that HSP 70 protein and GST enzyme activity can be useful biomarkers of metal contamination in lotic systems.