Scielo RSS <![CDATA[Water SA]]> vol. 35 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Flow-gauging structures in South African rivers part 1</b>: <b>an overview</b>]]> Accurate hydrological information is of paramount importance in a dry country such as South Africa. Flow measurements in rivers are complicated by the high variability of flows as well as by sediment and debris loads. It has been found necessary to modify and even substitute certain internationally accepted gauging structure designs to overcome local practical problems and improve accuracies. This, Part 1 of a paper in 2 parts, concentrates on the attributes of different types of gauging structures and the information provided on the different structures will assist the reader with the selection of an appropriate structure. The historical development of the gauging structure network in South African rivers is briefly discussed. Gauging structures used in South African rivers and basic design criteria for the preferred structures at this stage, based on past experience, are discussed: • Crump weirs • Sharp-crested weirs • Sluicing flumes. This paper reflects the lessons that have been learnt by DWAF and other South African organisations and should be of value to others who have to perform flow measurements under similar climatic conditions. Factors that may adversely impact on gauging accuracy are also pointed out in the conclusion. Part 2 of the paper contains information on the calibration theory and techniques to rate the preferred gauging structures. <![CDATA[<b>Flow-gauging structures in South African rivers part 2</b>: <b>calibration</b>]]> Accurate hydrological information is of paramount importance in a dry country such as South Africa. Flow measurements in rivers are complicated by the high variability of flows as well as by sediment loads and debris. It has been found necessary to modify and even substitute certain internationally accepted gauging station designs to overcome practical problems and to improve accuracies. Part 1 of this paper concentrated on the attributes of different types of gauging structures and provided guidance on the design criteria applicable for selected structures. Part 2 of this paper in 2 parts contains information required to rate or calibrate the gauging structures that are most likely to be selected in the foreseeable future: • Crump weirs • Sharp-crested weirs • Sluicing flumes. This paper and its linked predecessor reflect the lessons that have been learnt by DWAF and other South African organisations and should be of value to others who have to perform flow measurements under similar conditions. The problems associated with the use of compound weir structures to gauge discharge and techniques that may be used to overcome some of these problems are also discussed. <![CDATA[<b>A catchment-scale irrigation systems model for sugarcane part 1</b>: <b>model development</b>]]> In South Africa, the demand for water exceeds available supplies in many catchments. In order to justify existing water requirements and to budget and plan in the context of growing uncertainty regarding water availability, a model to assist in the assessment and management of catchment water supply and demand interactions, and the associated impacts on the profitability of irrigated sugarcane, has been developed. The model, ACRUCane, operates as a submodel within the ACRU agrohydrological model and simulates the water budget of a field of irrigated sugarcane. The water budget is based on the integration of several widely accepted algorithms and concepts, accounts for different irrigation system types performing at different levels of uniformity and different water management strategies. Furthermore, it can simulate a wide variety of water availability scenarios and constraints through its link with ACRU simulated hydrology. The crop yield algorithms used in the model were verified using data from three different irrigation trials with widely varying irrigation treatments, where the model was shown to adequately distinguish the impacts of different watering strategies on crop yields. A description of the model algorithms and results from verification studies are presented in this paper. Application of the model is presented in a companion paper. <![CDATA[<b>A catchment-scale irrigation systems model for sugarcane part 2</b>: <b>model application</b>]]> In the face of growing uncertainty regarding water availability to irrigated agriculture in South Africa, a computer simulation model, ACRUCane, has been developed to provide management information to irrigators of sugarcane and catchment water managers. ACRUCane can be used to simulate catchment hydrology, sugarcane yield, irrigation water requirement and water supply. The development and verification of the model is described in a companion paper. In order to illustrate the application of the model, it was configured to represent a catchment in northern KwaZulu-Natal (Pongola) with runoff feeding into a dam which supplied water for a dragline irrigation system. Various 'what if' scenarios representing potential changes to the irrigation system or management practice were assessed. Analysis of the simulated scenarios showed the interdependencies between irrigation application uniformity and irrigation scheduling. Improved application uniformities needed to be combined with improved scheduling to obtain maximum benefit, estimated to be approximately R3 000/ha. Improved scheduling resulted in fewer seasons with water shortages and crop yield reductions. Replacing the dragline system with subsurface drip (SSD) resulted in gains in the proportion of applied water used beneficially and a small increase in crop yields. However, the amount of water applied using both types of irrigation system and the impacts on the dam storage levels were very similar. The increased capital cost of the SSD system relative to the dragline system resulted in marginally lower profits. <![CDATA[<b>Nitrogen dynamics in land cleared of alien vegetation (<i>Acacia saligna</i>) and impacts on groundwater at Riverlands Nature Reserve (Western Cape, South Africa)</b>]]> Woody invading alien plants, many of which are nitrogen-fixing legumes (Fabaceae family), are currently cleared in South African catchments to reduce water loss and preserve streamflow, and for the restoration of the ecosystem. This study tested the hypothesis that clearing invasive alien vegetation may disturb the vegetation-micro-organism-soil N cycling system by producing a large once-off input of fresh tree litterfall rich in N and by eliminating a large N sink. Three experimental plots were established at the Riverlands Nature Reserve (Western Cape, South Africa): a site invaded by Acacia saligna to be used as control; a site cleared of Acacia saligna; and a site with natural vegetation to be used as background. Nitrogen concentrations in soil and groundwater, volumetric soil water contents, root density and weather conditions were measured during 2007. Oxidised forms of nitrogen, in particular NO3-, were dominant in the system. Recharge and leachate were simulated with the HYDRUS-2D model and used as inputs into Visual MODFLOW to predict the spatial distribution of nitrate plus nitrite (NOx) in groundwater. NOx levels in soil and groundwater were higher in alien-invaded areas compared to fynbos-covered land. A quick release of NOx into groundwater was observed due to high residual N reserves in the rooting zone, decreased evapotranspiration and increased recharge in the treatment cleared of alien vegetation. In the long run, high NOx concentrations in groundwater underlying cleared land will last only until all the excess nitrogen has been leached from the soil. A decrease in NOx concentration in groundwater can be expected thereafter. Clearing land of alien invasive legumes may therefore have a beneficial effect by reducing groundwater contamination from NOx and reducing water losses in catchments. <![CDATA[<b>Social capital, community-based governance and resilience in an African artisanal river fishery</b>]]> This is a study of a community-based fishery on the Rovuma River that forms the border between Mozambique and Tanzania. We postulate a relationship between social capital and community-based governance over access to and the use of the fish resource. In historical times social capital was high and community-based governance regulated access to and use of the fishery as a common property resource. Transforming forces particularly colonial administration, advocating Christianity, war and an emerging market economy undermined social capital, which in turn affected community-based governance. The deconstruction of social capital has resulted in attitudes and behaviours that challenge governance processes with dire consequences for sustainable resource utilisation. Harvesting of fish stocks occurs at levels that are no longer sustainable and inappropriate practices are being adopted. While the Mozambique government policy promotes community-based fisheries management in artisanal fisheries, we argue that under current conditions of ineffective community-based governance, a strong focus on reconstruction of social capital will be required before a community-based resource management process can be effectively implemented. The findings are discussed in the context of resilience in social ecological systems. We suggest that given the historical context in which community-based natural resource management is promoted within southern Africa such a focus may have wide relevance. <![CDATA[<b>River flow response to changes in vegetation cover in a South African fynbos catchment</b>]]> Mountain fynbos catchments in the Western Cape region of South Africa are prone to substantial changes in land cover due to invasion by exotic tree species (and their clearing), fires, and vegetation response to inter-annual variations in rainfall. While small catchment experiments and modelling studies have pointed to reductions in river flow as catchment biomass increases, there is little empirical evidence of land cover change affecting river flow in large catchments that are important sources of water for the region. Monitoring changes in above-ground green biomass in multiple large catchments is challenging, but may be accomplished using a remotely sensed spectral vegetation index. It was hypothesised in this study that annual river yield (river flow as a fraction of rainfall) in the Molenaars catchment near Paarl, South Africa co-varies with an index of green vegetation cover derived from satellite data (the normalised difference vegetation index, NDVI). The catchment was partitioned into 'upland' and 'lowland' zones and the relationship between annual river yield and summer NDVI was determined for each zone over an 18-year period. There was a statistically significant negative linear relationship between annual river yield and the NDVI of the lowland zone when three outliers were excluded from the analysis. These outliers corresponded to periods with prolonged drought conditions when river yield appeared to be decoupled from vegetation water use in the lowland zone. There was no relationship between river yield and changes in the NDVI in the upland zone where plants were unlikely to have sustained access to adequate soil water for transpiration. The importance of considering the location of land cover changes in a catchment, and inadequacies in high-elevation measurements of rainfall in this mountainous region, were highlighted in the study. <![CDATA[<b>Water in nutritional health of individuals and households</b>: <b>an overview</b>]]> This paper gives an overview of human water requirements (Part 1) and water quality for nutritional health (Part 2). A balance between water input and water output is needed to maintain a normal hydration status. Water requirements of individuals differ in different stages and circumstances in the healthy life cycle, e.g. childhood, pregnancy and lactation as well for the elderly. Various sources of dietary water as well as water consumption of the South African population are discussed. Water is needed to maintain a normal hydration status, yet the non-water ingredients of beverages may also have hydration and non-hydration-related (ill-) effects, mostly in the longer term. Furthermore, water quality can affect nutrition-related health. Water is a source of nutrients, with fluoride being the most important from a nutritional perspective. Water is needed for hygiene and there are various transmission routes for diseases related to water i.e. water-borne, water-washed, water-based and water-related. In South Africa, 2.6% of all deaths and disability adjusted life years (DALYs) are attributable to unsafe water, sanitation and hygiene. The figures are much higher for children under 5 years of age. Of the diseases associated with water, those that precipitate with diarrhoea remain among the most important causes of global childhood mortality and morbidity. There is some evidence that certain chronic diseases are associated with water-related pathogens. Water has a role to play in holistic multi-sectoral interventions addressing nutritional problems. <![CDATA[<b>Environmental life cycle assessments for water treatment processes a South African case study of an urban water cycle</b>]]> The objective of this study was to generate information on the environmental profile of the life cycle of water, including treatment, distribution and collection and disposal (including recycling), in an urban context. As a case study the eThekwini Municipality (with its main city Durban) in South Africa was used. Another aim of the study was to compare the environmental consequences for the provision of normal, virgin potable water vs. recycled water to industry in Durban. Therefore, a series of environmental life cycle assessments (LCAs) were performed and environmental scores were calculated for the processes involved in the treatment, recycling and disposal of water and wastewater. In order to enable the addition of these scores the same approach was adopted and the same methodology was used and a final environmental profile was produced. This study shows that a system approach as well as a process approach is needed for the integral assessment of the environmental performance in the provision of water and wastewater services. From the LCAs of individual processes involved in the provision of water and wastewater in the eThekwini Municipality, it emerged that the process with the highest contribution is the activated sludge process - used in the treatment of wastewater. However, when considering the entire system and including the losses in the distribution network for potable water, the process with the highest contribution became the distribution itself. An improvement analysis was performed and is presented. It takes into account a series of possible interventions and their consequences. Most notably, one conclusion of this study is that recycling as currently undertaken in Durban, has positive environmental impacts. <![CDATA[<b>Suitability of total coliform </b>β<b>-D-galactosidase activity and CFU counts in monitoring faecal contamination of environmental water samples</b>]]> Total coliforms are a group of bacteria found in high numbers in mammalian intestines; hence their presence in water indicates the possible contamination with faecal material. Total and faecal coliform counts were monitored over a period of 18 months using mFC, m-Endo and CM1046 media together with enzymatic assays on 215 environmental water samples obtained from the Eastern Cape Province of South Africa. A positive correlation, with an R² value of 0.9393 was observed between faecal and total coliform colony units employing mFc and m-Endo media, and 0.8818 using CM1046 media. Also, a positive correlation was observed between Escherichia coli colony-forming units and β-d-galactosidase (B-GAL) activity (R²=0.8542). Overall, this study indicated that faecal contamination of environmental water samples could be monitored by measuring total coliform β-galactosidase activity and total coliform colony-forming units. <![CDATA[<b>Adsorptive removal of various phenols from water by South African coal fly ash</b>]]> South African coal fly ash (SACFA) was used to effectively remove phenol, 2-nitrophenol and 4-nitrophenol from wastewater. The rate of adsorption follows first-order kinetics before attaining equilibrium with the sorption rate (Kad) obtained being the highest for 4-nitrophenol (p-nitrophenol) (7.0 x 10³/h), followed by phenol (1.2 x 10³/h) and 2-nitrophenol (o-nitrophenol) (1.0 x 10³/h). Batch studies were performed to evaluate the adsorption process, and it was found that the Freundlich isotherm effectively fits the experimental data for the adsorbates better than the Langmuir model, with the fly ash having the highest adsorption capacity of 6.51 X 10-2 mg/g for 4-nitrophenol, 6.00 x 10-2 mg/g for 2-nitrophenol and 6.31 x10-2 mg/g for phenol. The fly ash was found to adsorb 90.2% of phenol, 88.9% of 2-nitrophenol and 92.6% of 4-nitrophenol at an initial concentration of 20 mg/ℓ. The desorption studies suggested that the desorption of 4-nitrophenol was the most difficult of the three adsorbates to be desorbed. The desorption efficiency was 17.9% for phenol, 18.8% for 2-nitrophenol and 10.2% for 4-nitrophenol. This work proved that SACFA can be used as an efficient adsorbent material for removal of phenol from water and wastewater. <![CDATA[<b>Performance of a water defluoridation plant in a rural area in South Africa</b>]]> The fluoride concentration of a borehole water supply in a rural area (Madibeng Local Municipality, North West Province, South Africa) varies between 5 and 6 mg/ℓ. This water is therefore not suitable for potable purposes because the high fluoride concentration may cause mottling of tooth enamel in children and fluorosis in adults. Therefore, the fluoride concentration should be reduced to less than 1.5 mg/ℓ to make the water suitable for potable purposes. The activated alumina and reverse osmosis processes are both processes that can be very effectively applied for water defluoridation. The activated alumina process, however, is considered to be a more simple and robust process for water defluoridation, especially in a rural area. Therefore, the activated alumina process was selected for water defluoridation. An activated alumina plant was designed, constructed and commissioned in the rural area. Fluoride in the feed water is removed from 6 to 8 mg/ℓ to less than 1.5 mg/ℓ. No reduction in plant output was experienced over 6 service cycles. Therefore, it appears that fouling of the activated alumina should not be a problem. Plant output varied between 940 and 1 296 m³ to a fluoride breakthrough of approximately 2.0 mg/ℓ. No significant operational problems were experienced during commissioning and the plant is performing satisfactorily. Spent regenerant is disposed of into evaporation ponds. It was demonstrated that a 1st world technology could be effectively applied in a rural area with proper training and supervision of the operators. The capital and operational costs of the 200 m³/d defluoridation plant are estimated at approximately R1.2m. and R0.7/m³ treated water. <![CDATA[<b>Anoxic and aerobic values for the yield coefficient of the heterotrophic biomass</b>: <b>determination at full-scale plants and consequences on simulations</b>]]> The present study aims at optimising the nitrification and denitrification phases at intermittently aerated process (activated sludge) removing nitrogen from municipal wastewater. The nitrogen removal performance recorded at 22 intermittently aerated plants was compared to the results obtained from the simulations given by the widely used ASM1. It is shown that simulations with a single value for the heterotrophic yield with any electron acceptor over-predict the nitrate concentration in the effluent of treatment plants. The reduction of this coefficient by 20% for anoxic conditions reduces the nitrate concentration by 10 g N·m-3. It significantly improves the accuracy of the predictions of nitrate concentrations in treated effluents compare to real data. Simulations with dual values (aerobic and anoxic conditions) for heterotrophic yield (modified ASM1) were then used to determine the practical daily aerobic time interval to meet a given nitrogen discharge objective. Finally, to support design decisions, the relevance of a pre-denitrification configuration in front of an intermittently aerated tank was studied. It is shown that when the load of BOD5 is below the conventional design value, a small contribution of the anoxic zone to nitrate removal occurs, except for over-aerated plants. When plants receive a higher load of BOD5, the modified ASM1 suggests that the anoxic zone has a higher contribution to nitrogen removal, for both correctly and over-aerated plants. <![CDATA[<b>Use of compost bacteria to degrade cellulose from grass cuttings in biological removal of sulphate from acid mine drainage</b>]]> The study focused on the use of compost bacteria to degrade cellulose from grass cuttings as energy and carbon sources for sulphate-reducing bacteria (SRB) in a biological reactor. The fermentation of grass cuttings was carried out by anaerobic bacteria isolated from compost, thereby producing volatile fatty acids (VFA) and other intermediates, which were used as carbon and energy sources for sulphate reduction by SRB. Grass was added daily to the reactor in order to obtain maximum production of chemical oxygen demand (COD) and VFA. The results indicated that daily addition of grass is essential for the efficient VFA production, sulphate reduction and for the cell growth of the microbial biomass. Sulphate reduction of 38% was achieved with an average reactor chemical oxygen demand/sulphate (COD/SO4) ratio of 0.56 mg/ℓ. These results showed that 25 g of grass could produce enough VFA for a sulphate load of 25 g, which is a cost-effective method for sulphate removal. <![CDATA[<b>Humic acid as a model for natural organic matter (NOM) in the removal of odorants from water by cyclodextrin polyurethanes</b>]]> Current practices in some water-treatment facilities have reported that natural organic matter (NOM) blocks the adsorption sites of activated carbon resulting in lower geosmin and 2-methylisoborneol (2-MIB) removal. Humic acid has been reported to compete with geosmin and 2-MIB removal in the same way. The removal of odour chemicals such as geosmin and 2-MIB is important for potable-water treatment by water supply companies and municipalities. We have previously demonstrated that cyclodextrin polyurethanes are capable of removing a number of organic pollutants from water, but are not able to reduce the levels of NOM significantly. We wished to determine if the polymers would selectively remove geosmin and 2-MIB, despite the presence of NOM. Humic acid was chosen as a model for NOM since NOM constitutes about 70% of humic acid. Results obtained from this study indicate that the presence of humic acids at different concentrations could not affect the removal of geosmin and 2-MIB when cyclodextrin polymers were used since 90% removal was achieved. However the UV-Vis analysis showed a low removal of humic acids (3 to 20%). <![CDATA[<b>Monitoring natural organic matter and disinfection by-products at different stages in two South African water treatment plants</b>]]> Natural organic matter (NOM) is a complex organic material present in natural surface water. NOM can cause problems during water treatment most notably the formation of toxic disinfection by-products. This study was undertaken in order to assess the effectiveness of some of the water treatment techniques employed by selected water supply companies in South Africa in dealing with NOM. Total organic carbon (TOC) and ultra violet (UV) absorbance at wavelength of 254 nm were measured and used to calculate specific ultra violet absorbance (SUVA), which was used to determine the changes in NOM concentration throughout the water treatment train. Other parameters measured include pH, turbidity, chemical oxygen demand (COD) and conductivity. Water samples were collected from two water treatment plants in South Africa, namely Sedibeng (Balkfontein) and Midvaal. The overall TOC reduction after the water treatment processes was 33% and 30% at Midvaal and Sedibeng, respectively. SUVA values were generally low (<2 ℓ∙mg-1∙m-1) indicating the presence of aliphatic compounds and less 'aromaticity' in NOM of the water samples. Water insoluble β-cyclodextrin (β-CD) polyurethanes were then applied to the water to compare TOC reduction in addition to 'normal' water treatment processes, and were found to provide up to 19% additional TOC decrease, and UV absorbance reduction was up to 78%. Results obtained using gas chromatography-mass spectrometry (GC-MS) analysis after chlorination, revealed that the water had the potential to form halomethane compounds with chloroform being the most dominant. Again, water-insoluble β-CD polyurethanes were applied to the water as a treatment to remove trihalomethanes (THMs) and were found to efficiently remove up to 95% of THMs formed during the disinfection step. The treatment processes studied have limited ability in dealing with NOM and are not individually effective in NOM removal. Results obtained indicate that the application of β-CD polyurethanes in addition to the water treatment processes may enhance NOM removal in water and significantly reduce the THMs formed. <![CDATA[<b>The use of hydrodynamic disintegration as a means to improve anaerobic digestion of activated sludge</b>]]> Disintegration by hydrodynamic cavitation has a positive effect on the degree and rate of sludge anaerobic digestion. By applying hydrodynamic disintegration the lysis of cells occurs in minutes instead of days. The intracellular and extracellular components are set free and are immediately available for biological degradation which leads to an improvement of the subsequent anaerobic process. Hydrodynamic disintegration of the activated sludge results in organic matter and a polymer transfer from the solid phase to the liquid phase, and an increase in COD value of 284 mg∙ℓ-1 was observed, i.e. from 42 mg∙ℓ-1 to 326 mg∙ℓ-1. In addition the degree of disintegration changed from 14% after 15 min disintegration to 54% after 90 min of disintegration. A disruption of bacterial cells by hydrodynamic cavitation has a positive effect on the degree and rate of excess sludge anaerobic digestion. The cells of the activated sludge micro-organisms rupture and addition to the digestion process leads to increased biogas production. The hydrodynamic disintegration of activated sludge leads to a higher degree of degradation and higher biogas production. Adding the disintegrated sludge (10%, 20% and 30% of volume) to fermentation processes resulted in an improvement in biogas production of about 22%, 95% and 131% respectively. <![CDATA[<b>Fertiliser value of human manure from pilot urine-diversion toilets</b>]]> Ecological sanitation is a system that, unlike the traditional waterborne sewerage and pit toilet systems, regards human excreta as a resource to be recycled rather than as a waste. There is, however, little or no information on the fertiliser value of human excreta in South Africa. This study, therefore, evaluated the effectiveness of human manure as a source of nutrients using cabbage as a test crop at Ntselamanzi location, Alice, South Africa as part of a project intended to generate knowledge and good practice in ecological sanitation. Treatments were arranged in a randomised complete block design with 4 replications and consisted of a control, 100 kg N∙ha-1 as goat manure, and 4 non-zero rates of human manure and NPK fertiliser applied to supply the equivalent of 50, 100, 200, and 400 kg N∙ha-1. Human manure resulted in higher cabbage yields than goat manure but was out-yielded by inorganic fertiliser. The greater effectiveness of human manure when compared with goat manure was attributed to the fact that it was a better source of K and P for plants as it maintained higher levels of these nutrients in soil than goat manure. For greater agronomic effectiveness, the human manure should be co-applied with some inorganic N fertiliser as it proved to be a poor source of nitrogen. The human manure increased soil pH and therefore has potential for improving crop growth in acidic soils through its liming effects as well. The dry human manure was evaluated as comparable to Type B sludge in South Africa with respect to microbial content and could therefore be used to fertilise some crops/plants provided stipulated restrictions to minimise human exposure are adhered to.