Scielo RSS <![CDATA[Water SA]]> vol. 39 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Kinetic, equilibrium and thermodynamic modelling of the sorption of metals from aqueous solution by a silica polyamine composite</b>]]> Batch sorption studies were conducted to assess the potential of a phosphonated silica polyamine composite (BPAP) to remove metals (Co, Cu, Fe, Mg, Mn, Ni, U and Zn) from mine waters. The metal adsorption showed a good Langmuir isotherm fit. Ni and Mn fitted both the Freundlich and Langmuir isotherms. The activation energies (Ea) of Co, Mg and Ni ranged between 5 and 40 kJ-mol-1, signifying physisorption while U showed a chemisorption type of adsorption (with Ea > 50 kJ-mol-1). Cu and Fe on the other hand gave negative Ea values, indicating their preference to bind to low-energy sites. The pseudo-second-order kinetic model provided the best correlation of the experimental data, except for Mg and Ni for which the pseudo-first-order model and the Elovich model gave a better fit, respectively. Adsorption was almost constant over a wide pH regime and increased with time. Adsorption increased with concentration of the metals with the exception of Co, Fe and Ni which displayed about a 40% drop at a concentration of 200 mg.l-1. Desorption experimental data gave poor results except for U which showed 99.9% desorption. <![CDATA[<b>Removal of waterborne bacteria from surface water and groundwater by cost-effective household water treatment systems (HWTS)</b>: <b>A sustainable solution for improving water quality in rural communities of Africa</b>]]> In this study 5 household water-treatment devices/systems (HWTS) were constructed using inexpensive local materials (sand, gravel, zeolites and clays). They included the silver-impregnated porous pot filter (SIPP), the ceramic candle filter (CCF), the conventional biosand filter (BSF-S), a modified biosand filter with zeolites (BSF-Z), and a bucket filter (BF). Their ability to remove turbidity and pathogenic bacteria (Vibrio cholerae, Salmonella typhimurium and Shigella dysenteriae) from synthetic sterile water, groundwater and surface-water sources was evaluated. The flow rates ranged from 0.05ℓ∙h-1 to 2.49ℓ∙h-1 for SIPP; 1ℓ∙h-1 to 4ℓ∙h-1 for CCF; 0.81ℓ∙h-1 to 6.84ℓ∙h-1 for BSF-S; 1.74ℓ∙h-1 to 19.2ℓ∙h-1 for BSF-Z; and from 106.5ℓ∙h-1 to 160.5ℓ∙h-1 for BF. The highest (64% to 98% (0.74 to 1.08 NTU)) and lowest (14% to 76% (2.91 to 7.19 NTU)) average percentage turbidity removals were noted for SIPP and BF, respectively. The SIPP was the only device that consistently removed 100% of all target pathogens throughout the study. Its performance was found to be significantly superior (p<0.05) compared to that of the other four devices. Sixty (60%) to 100% bacterial removals were observed for BSF-S; 90% to 100% for BSF-Z; 90% to 100% for CCF; and 40% to 99.9% for BF. Based on the findings of this study the SIPP can be recommended for use by rural communities as it consistently produced high-quality water that complied with the SANS 241 turbidity and microbiological limits for drinking water. <![CDATA[<b>Fluctuations of indicator and index microbes as indication of pollution over three years in the Plankenburg and Eerste Rivers, Western Cape, South Africa</b>]]> The Plankenburg and Eerste Rivers (Western Cape) have been reported to be contaminated with faecal coliforms. Water is drawn from both rivers for irrigation of fresh produce. The potential risk in the use of these rivers as irrigation sources was assessed by determining the fluctuations of 'indicator' and 'index' microbes over 3 years. Selected physico-chemical (water temperature, pH, COD, conductivity and alkalinity) and microbiological parameters, including coliforms, faecal coliforms, Escherichia coli and enterococci, as 'indicators' of faecal pollution, and Salmonella, Listeria and Staphylococcus, as 'index' of the presence of potential pathogens, were monitored. No correlation was found between water temperature and COD (r² = 0.0003), whereas for temperature and pH a significant trend (p = 0.0004), but low correlation (r² = 0.108), was observed. With the exception of the faecal coliforms (E. coli), no significant trends and no correlations between temperature and the dependent variables were found. For the faecal coliforms there was a significant trend (p = 0.0289) with temperature but not a good correlation (r² = 0.0434), but the impact of temperature over time was significant (p = 0.0047). This is important, when the World Health Organisation (WHO) and South African Department of Water Affairs (DWA) guidelines for faecal coliforms are applied, as it indicates that temperature does impact the faecal coliform numbers. The presence of indicator organisms did not only indicate unsanitary conditions, but also the presence of potential pathogens such as Staphylococcus, Klebsiella, Listeria and Salmonella. Based on these results the microbial quality of these rivers was found to be unacceptable and does not meet the WHO and DWA guidelines for safe irrigation. There was also a high risk of exposure to human pathogens when water from these rivers is used to irrigate produce that is consumed without further processing. <![CDATA[<b>Development and assessment of a daily time-step continuous simulation modelling approach for design flood estimation at ungauged locations</b>: <b>ACRU model and Thukela Catchment case study</b>]]> The estimation of design floods is necessary for the design of hydraulic structures. Commonly used event-based approaches to design flood estimation have several limitations, which include the estimation of antecedent soil moisture conditions and the assumption that the exceedance probability of the design flood is the same as the exceedance probability of the design rainfall. Many of the limitations of event-based approaches may be overcome by the use of continuous simulation modelling for design flood estimation. This paper contains a brief summary on the development and assessment of a continuous simulation modelling system for design flood estimation in ungauged catchments. These developments include an investigation into the appropriate spatial scale of model configuration for optimum performance of the system, the temporal disaggregation of daily rainfall for hydrograph generation, flood routing in ungauged catchments and the use of radar information and rain-gauge data to improve the estimation of catchment rainfall. Results from the application of the system for design flood estimation in the Thukela Catchment in South Africa are presented and discussed. The results from the study highlight the challenges of hydrological modelling in an operational catchment and the need for reliable rainfall and runoff data. From the results obtained, it is concluded that reasonable and consistent estimates of design floods in the Thukela Catchment, particularly in smaller sub-catchments, can be obtained using the ACRU model. <![CDATA[<b>Population dynamics of the invasive fish, <i>Gambusia affinis,</i> in irrigation impoundments in the Sundays River Valley, Eastern Cape, South Africa</b>]]> The alien invasive Gambusia affinis is one of the most widely introduced fish species on the planet, and has established in freshwater ecosystems across South Africa. The invasion ecology and, in particular, the population dynamics of the species in this country are, however, poorly understood. In this study the relative abundance and population dynamics of G. affinis were quantified in 5 interconnected irrigation impoundments within the Sundays River Valley, Eastern Cape. Four fish surveys were conducted from early summer (February 2012) to early winter (June 2012). Repeated-measures ANOVA analyses on the catch per unit effort (CPUE) of G. affinis between sampling events and dams revealed significant differences in population dynamics among dams, although an overall trend of rapid increase followed by plateau in summer, with a rapid decline in winter was seen in most dams. A general linear model assessing the role of biotic and abiotic factors on G. affinis CPUE found that water temperature and the presence of the native fish Glossogobius callidus had significant effects on the CPUE of G. affinis. While winter drops in temperature are likely to have caused mortality in G. affinis populations, and may act as the primary regulator of G. affinis establishment success in South African impoundments, the negative effect of G. callidus densities on G. affinis suggests competitive or predator-prey interactions with the native species. <![CDATA[<b>On the use of electrical resistivity methods in monitoring infiltration of salt fluxes in dry coal ash dumps in Mpumalanga, South Africa</b>]]> One of the principal environmental concerns relating to coal combustion waste disposal is the potential for groundwater contamination from salt fluxes and trace elements that may be leached into the underlying groundwater system. Since changes in moisture and salt concentrations usually provide contrasts in electrical properties against the host media, electrical resistivity methods can be used to monitor ingression of solute plumes as well as to detect any preferential flow paths within the ash medium. In this study, 2D electrical resistivity tomography was used to monitor brine (10% NaCl) water ingression through the unsaturated zone of a dry coal ash dump at a power station, Mpumalanga, South Africa. This was after the initial laboratory determination of the relation between electrical resistivity and moisture/salt content for the ash dump. The results showed that infiltration plume progression was more pronounced in the vertical direction, suggesting that moisture movement is mainly due to gravitational pull. There was no evidence of preferential flow within the ash medium, although the different infiltration rates for different sites suggested different permeability within the unsaturated zone. <![CDATA[<b>Oestrogen, testosterone, cytotoxin and cholinesterase inhibitor removal during reclamation of sewage to drinking water</b>]]> Namibia is the driest sub-Saharan country in Africa. Namibia's capital, Windhoek, reclaims sewage water for domestic use at the Goreangab Water Reclamation Plant (GWRP). Risks associated with sewage effluent and reclaimed sewage should be closely monitored; therefore water at the Gammams Sewage Treatment Plant (GSTP) inlet and outlet, as well as reclaimed water from the GWRP, were assayed using selected bioassays. Samples collected were analysed using enzyme-linked immunosorbent-assays and chromogenic tests for steroid hormones, neurotoxicity, cytotoxicity and inflammatory activity. Estradiol level at the sewage treatment inlet was 78 pg/mℓ and the treated sewage level showed an 83% to 95% reduction in this, while after reclamation the level was below detection limit. Estrone concentrations at the sewage treatment inlet ranged from 10 to 161 pg/mℓ. Sewage treatment reduced estrone by between 85% and 92%. After reclamation the level of estrone was below detection limit. Testosterone ranged between 162 and 405 pg/mℓ at the sewage plant inlet. Sewage treatment removed 96% of the initial testosterone. The residual testosterone was effectively removed by processes in GWRP and after reclamation no testosterone was detected in water. Acetylcholinesterase (AChE) inhibition at the sewage treatment inlet was 50% while it was only 27% after sewage treatment. After reclamation AChE inhibition was not detected. Only water at the sewage inlet in March and February showed cytotoxicity. High inflammatory activity was detected at the sewage plant inlet. Sewage treatment reduced inflammatory activity by 64%. After reclamation low inflammatory activity was induced. Treated sewage used for reclamation tested positive for most of the biomarkers and can pose a risk to human health. However, reclamation successfully removed these contaminants. Due to the presence of contaminants in the intake water at the reclamation plant, it is essential to routinely monitor the water produced by the reclamation plant for potential residues that can adversely affect human health. <![CDATA[<b>Municipal sludge as source of nitrogen and phosphorus in perennial pasture <i>Eragrostis curvula</i> production</b>: <b>Agronomic benefits and environmental impacts</b>]]> Land application of sludge has been shown to improve soil properties and aid crop growth, but the possibility of constituent nutrients such as nitrogen and phosphorus reaching environmentally toxic levels has caused governing authorities to set limits to how much sludge can be applied to agronomic land. The high nitrogen utilisation potential of pasture grasses suggests that more sludge can be used in this cropping system without the risk of excess nitrates. This study investigates the effect of exceeding the South African sludge application limit on hay yield, soil nitrates and phosphorus. Field plots were arranged in a complete block design comprising 4 replications of 4 treatments planted to Eragrostis curvula. The treatments consisted of 0, 4, 8 and 16 Mg∙ha-1 anaerobically digested sludge. Soil samples were collected before treatment application and at the end of each growing season for N, P, NO3-, NH4+, and Bray-1P analyses. Plant samples were collected at flowering stage for hay yield and N and P uptake determination. Statistical analyses were conducted using analysis of variance (ANOVA) and general linear model (GLM) procedures of Windows SAS 9.0 to evaluate the effect of sludge application rates on hay yield. Results over 4 growing seasons indicate that exceeding the recommended limit increased hay yield by 4% in a dry season (11.7 vs. 12.36 Mg∙ha-1) and by 16% in a wet season (14.19 vs. 17.31 Mg∙ha-1) and also increased nitrogen uptake by 15%. Sludge applied at double the recommended limit did not cause the accumulation of nitrate and ammonium in the soil, however, both total and Bray-1P were doubled. The study shows that the potential long-term environmental risk of doubling the sludge application rate norm would be from labile P accumulation in the soil profile despite a sludge P:Fe molar ratio of less than unity. <![CDATA[<b>Removal of copper(II) ion from aqueous solution by high-porosity activated carbon</b>]]> The removal of copper(II) ion from aqueous solution by the granular activated carbon, obtained from hazelnut shells (ACHS) (Corylus avellana L. var. lunga istriana), was investigated. The ACHS was prepared from ground dried hazelnut shells by specific method carbonisation and water steam activation at 950ºC for 2 h. The granular activated carbon produced from hazelnut shells has a high specific surface area (1 452 m²·g-1) and highly developed microporous structure (micropore volume: 0.615 cm³·g-1). In batch tests, the influences of solution pH, contact time, initial metal ion concentration and temperature on the sorption of copper(II) ion on ACHS were studied. The results indicate that sorption of copper(II) ion on ACHS strongly depends on pH values. The adsorption data can be well described by the Langmuir isotherm and Redlich-Peterson model. The monolayer adsorption capacity of the ACHS-copper(II) ion, calculated from the Langmuir isotherms, is 3.07 mmol·g-1. The time-dependent adsorption of copper(II) ion could be described by the pseudo second-order and Elovich kinetics, indicating that the rate-limiting step might be a chemical reaction. The intra-particle diffusion model indicates that adsorption of copper(II) ions on ACHS was diffusion controlled. <![CDATA[<b>Assessing and forecasting groundwater development costs in Sub-Saharan Africa</b>]]> Greater use of groundwater in Sub-Saharan Africa is a pre-requisite for improved human welfare; however, the costs associated with groundwater development are prohibitively high and poorly defined. This study identifies and disaggregates the costs of groundwater development in 11 Sub-Saharan African countries, while the cost factors that most strongly affect drilling expenditures are traced. Further, the institutional and technical constraints impeding groundwater development are also explored while a time-series analysis forecasts future drilling expenditures. The results indicate that mobilisation and demobilisation costs, together with well development costs, factors that are difficult to change, are most significantly affecting the total costs of drilling. Further, the nature of the hydrogeological formation (which is largely a site characteristic), along with the often-aged machinery (which can be controlled), are also major impediments to lowering the cost of drilling. All countries are forecasted to have a slight to considerable drilling cost decrease for the next decade which offers encouragement for future groundwater development. Greater attention to the individual cost factors and to forecasting analysis could help to design more coherent and consistent groundwater development policies in Sub-Saharan Africa. <![CDATA[<b>Hydrologic-economic appraisal of life-cycle costs of inter-basin water transfer projects</b>]]> This article describes research that compares actual water transfers of an inter-basin transfer (IBT) scheme with its original, appraisal stage, prediction. Transfers are shown to be significantly less and also more variable than predicted. Further research reveals that the state of the receiving system has a large bearing on year-to-year decisions regarding water transfers. Past appraisals, following what is called the Incremental Approach, do not adequately consider the stochastic nature of the likely future inter-basin transfer operating regime. Examination of six case studies, four South African, one Chinese and one Australian, shows that the Incremental Approach is still in general use - despite tools available for an improved approach. A new approach, called the Comprehensive Approach, is proposed to upgrade estimations of variable costs associated with water transfers - often substantial life-cycle cost components of IBTs. A demonstration of the Comprehensive Approach, by means of an example of an IBT with significant pumping costs associated with water transfers, is provided. Uncertainty regarding future water transfers and associated variable costs are provided for by stochastic simulation modelling. The Incremental Approach is shown to be severely biased with respect to variable costs and it is shown that this bias leads to significantly different estimations of likely life-cycle project costs. Such differences conceivably lead to suboptimal decision-making. <![CDATA[<b>Unit Reference Value</b>: <b>Application in appraising inter-basin water transfer projects</b>]]> Unit Reference Value (URV) is a common measure in South Africa to assess the economic efficiency of proposed water projects. This is a companion article to an earlier one establishing that the current approach of appraisal of inter-basin water transfer projects (IBTs) with significant pumping costs overestimates likely future water transfers and thereby variable operational costs. Those findings are taken further and it is established that the URV, as currently applied, fails as a suitable measure to appraise such IBTs. From rooting URVs in fundamental cost effectiveness analysis theory a revised URV approach is proposed that provides for a conceptual separation between water transfers affecting operating costs and water transfers used as a proxy measure for effectiveness. The prominent effect of the revised URV approach is demonstrated by means of the example of the proposed Thukela Water Project in South Africa. <![CDATA[<b>Modelling the filling rate of pit latrines</b>]]> Excreta (faeces and urine) that are deposited into a pit latrine are subject to biodegradation, which substantially reduces the volume that remains. On the other hand, other matter that is not biodegradable usually finds its way into pit latrines. The net filling rate is thus dependent on both the rate of addition of material and its composition. A simple material balance model is presented which represents the faecal sludge as a mixture of biodegradable organic material, un-biodegradable organic material and inorganic material. Measurements made on 2 pits in eThekwini, South Africa, were used to determine parameters for the model. Model predictions were then compared with data from 15 other pits in the same area and filling rate data from previous South African studies, which exhibit a 20th to 80th percentile range of 200 to 453ℓ·pit-1·yr-1. These comparisons indicated that the pits studied exhibited relatively low filling rates resulting from orderly disposal practices. The average composition of the pit (COD, biodegradable material and inorganic fraction) changes with age, which will impact on any subsequent sludge treatment process. Pit filling rates are greatly affected by the disposal of solid waste in addition to the faecal material. For the pits studied, the model predicts that the filling time could have been extended from 15 years to over 25 years if all solid waste had been excluded from the pit. <![CDATA[<b>Classification and quality of groundwater supplies in the Lower Shire Valley, Malawi - Part 1</b>: <b>Physico-chemical quality of borehole water supplies in Chikhwawa, Malawi</b>]]> This paper presents data on the physico-chemical quality of groundwater supplies in Chikhwawa, Malawi. Eighty-four water samples were collected and analysed for a range of chemical constituents (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, Se, V, Zn, K, Na,Cl-, F-, NO3-, SO4(2-)), pH, temperature, electrical conductivity and turbidity, from 28 boreholes located in 25 remote, rural villages (n=3 per village) distributed along the east (n=15) and west (n=10) banks of the Shire River. Samples were collected every 2 months during the wet season, over a period of 5 months (December to April). Results were compared with national (Malawi Bureau of Standards Maximum Permissible Levels (MBS MPL)) and international (World Health Organization Guideline Values (WHO GV)) drinking-water standards. In general, most parameters complied with the Malawi Bureau of Standards Maximum Permissible Levels (MBS MPL) for borehole water supplies. The MBS MPL standards for iron, sodium and nitrate were slightly exceed at a few boreholes, technically rendering the water supply unwholesome but not necessarily unfit for human consumption. In contrast, significantly high nitrate (<200 mg/ℓ) and fluoride (< 5 mg/ℓ) concentrations at levels which constitute a significant risk to the health of the consumer were detected in borehole samples in a number of villages and warrant further investigation. Water committee members complained of problems associated with taste (saltiness or bitterness) and appearance (discoloured water) primarily on the west bank, presumably as a result of the high sodium and chloride levels, and precipitation of soluble iron and manganese, respectively. This resulted in some water collectors reverting to the use of surface water sources to obtain drinking-water, a practice which should be dissuaded through the education of water and village health committees. <![CDATA[<b>Classification and quality of groundwater supplies in the Lower Shire Valley, Malawi - Part 2</b>: <b>Classification of borehole water supplies in Chikhwawa, Malawi</b>]]> This paper compares data gathered from a study of the chemical and bacteriological quality of drinking-water from 28 rural borehole supplies in Chikhwawa, Malawi, with a tiered classification scheme (Class 0 being ideal through to Class III being unsuitable for drinking without prior treatment) developed by investigators from the Institute for Water Quality Studies, Department of Water Affairs and Forestry, South Africa. In general, the majority of borehole water supplies were classified as Class 0 or Class I supplies based upon the chemical analysis and bacteriological examination. However the classification of a borehole water supply was variable and depended upon the parameter, date of sampling and whether or not it was based on the mean or individual concentration. A number of boreholes were classified as II or III as they contained elevated levels of fluoride and nitrate suggesting that consumption over short or prolonged periods of time may lead to adverse or serious health effects, such as skeletal fluorosis in adults and methaemoglobinaemia in infants. Research is required to develop practicable, affordable and sustainable methods to enable villagers to treat Class II/III water supplies and improve the quality of their drinking-water to a class suitable for human consumption. <![CDATA[<b>Development of a gradient tube method for examining microbial population structures in floating sulphur biofilms</b>]]> Floating biofilms occur in thin layers of between 50 µm and 500 µm on the surface of certain organic, sulphidic aquatic environments and, at times, may only be several cells deep. While these structures may be important in terms of energy flow pathways, and possibly also in wastewater treatment operations, little is known about their structural/functional properties. This is due, in part, to their flimsy nature but also to methodological constraints related to their sampling and manipulation. We have investigated floating sulphur biofilms that appear as white layers on the surface of anoxic sulphidic organic wastewaters and describe here the development of a novel gradient tube method for investigating these systems. This approach enables testing of the hypothesis that these floating sulphur biofilms are complex well-differentiated structures rather than disordered dispersions of microbial biomass as has been previously thought. Furthermore, if the former is correct, they would seem to resemble the structure and functionality of comparable complex bioflms that are attached to solid substrates. The gradient tube method involves the establishment of apposing gradients of sulphide and oxygen that are expanded across a tube of agarose 10 cm in length; this simulates the oxic/anoxic interface that occurs over only several micrometres in the natural biofilm system. A plug of sulphide-enriched agarose is first placed in the base of the tube. Samples of the floating sulphur biofilm are then mixed into agarose growth medium and, before it sets, this is overlaid on top of the plug. The tubes are then open capped and incubated. A variety of different microbial populations may thus become established in the separate physiological niches that are set up in this way within the gradient tube. The populations may be quite robustly sampled by extruding and then sectioning the agarose plug. This expansion of the biofilm enables more detailed molecular phylogenetic studies of the populations found in the various niches within the biofilm and also measurement of physico-chemical parameters within the system. <![CDATA[<b>Estimating evapotranspiration using remote sensing and the Surface Energy Balance System - A South African perspective</b>]]> Remote sensing-based evapotranspiration (ET) algorithms developed in recent years are well suited for estimating evapotranspiration and its spatial trends over time. In this paper the application of energy balance methods in South Africa is reviewed, showing that the Surface Energy Balance Algorithm for Land (SEBAL) model is the most widely used, but highlighting the potentials of the Surface Energy Balance System (SEBS) model. The SEBS model is then reviewed in the international literature and lessons learned from South African examples are expanded upon. The SEBS model has been extensively used for teaching and training purposes and has been applied in research projects across many different environments. However, there are discrepancies in the reported accuracy of the SEBS model due to known model sensitivities. It is therefore recommended that any further research using the SEBS model in South Africa should be limited to agricultural areas where accurate vegetation parameters can be obtained, where high resolution imagery with low sensor zenith angles is available, and where canopy cover is complete.