Scielo RSS <![CDATA[Water SA]]> vol. 46 num. 3 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>A preliminary fish survey of the estuaries on the south-east coast of South Africa, Kei Estuary to Mdumbi: A comparative study</b>]]> A preliminary ichthyofaunal and physico-chemical survey of estuaries on the south-east coast of South Africa from the Kei Estuary to the Mdumbi Estuary was undertaken between October and November 1997. Twenty-seven (27) estuaries were surveyed along this stretch of coastline and these were grouped into three estuary types: small (< 10 ha) predominantly closed estuaries, moderate to large (&gt; 10 ha) predominantly closed estuaries and predominantly open estuaries. Multivariate analyses revealed significant differences between predominantly closed estuaries and predominantly open estuaries in terms of both their physico-chemical characteristics and their fish communities. There was no difference between small and moderate to large predominantly closed estuaries. A significant relationship was also observed between the physico-chemical characteristics of the estuaries and their fish communities. The estuaries in the study area fall within the warm-temperate biogeographic region; temperate species dominated the fish communities of all the estuaries. This survey represents one of the few fish surveys undertaken along this little-studied section of the coastline. <![CDATA[<b>A regional flow type classification for South African perennial rivers</b>]]> Flow classification provides a statistically robust method of defining an expected range of variability for flow metrics describing frequency, magnitude, duration and timing of events. Here, we characterised reference mean daily flows for 1950-1999 for all 5838 quinary catchments of South Africa based on 150 metrics. Using a two-tiered approach, where sub-catchments were classified into similar flow types using principal components and cluster analyses, we defined 6 to 12 flow types for each of 8 hydrological regions reflecting rainfall seasonality. Redundancy between variables was 87% on average, so that site variability could be accounted for using 8-28 metrics. In general, flow volume metrics accounted for Axis 1 variability, while coefficients of dispersion had 1.8 times less leverage in Axis 2. With the incorporation into a spatial product and an associated database, this study provides a basis for defining statistically robust reference flow conditions for multiple flow metrics, against which current observed flows at specific sites may be compared. <![CDATA[<b>Evaluating the use of iron-coated tubes for wetland delineation in South Africa: A pilot study in the Kruger National Park</b>]]> The identification of hydric soils is important for wetland delineation and protection. South Africa currently uses the Department of Water Affairs and Forestry (DWAF) wetland delineation guidelines which can be subjective in certain contexts. A robust technical standard that can be legally conclusive is therefore required and should be developed for South African conditions. The National Technical Committee of Hydric Soils (NTCHS, 2007) in the United States of America has accepted the Indicator of Reduction in Soils (IRIS) tube methodology as a technical standard, but this had not yet been tested in South Africa. It is proposed that the NTCHS (2007) be adapted for use in South Africa. These Fe-coated tubes are installed into the soil and if reducing conditions are present, the Fe coating is removed. The aim of this study was to evaluate the use of IRIS tubes as a technical standard for wetland delineation in South Africa. The study took place in three different wetland systems (Malahlapanga, Nshawu and the Tshuthsi spruit) in the Kruger National Park. Piezometers were installed in triplicate in each zone, and the water table, pH and Eh were recorded monthly. Soils were classified, soil wetness indicators identified, and vegetation described. The study took place from September 2012 to August 2013. The areal percentage of paint removed from the top 300 mm of the IRIS tubes was quantified by scanning the tubes and then compared to the DWAF wetland indicators. It was found that the DWAF indicators and the IRIS tube method were mostly in agreement; however, the conditions at the Tshutshi spruit were not favourable for Fe reduction, and hence the use of IRIS tubes, due to the high pH values recorded. The IRIS tubes were therefore a useful tool for wetland delineation in the majority of conditions, but are not recommended in high pH, sodic environments. Further research is recommended over a wider geographical area as well as testing the MIRIS methodology (Manganese Indicators of Reduction in Soils) in wetlands that would inhibit Fe reduction. <![CDATA[<b>Estimation of surface depression storage capacity from random roughness and slope</b>]]> Depression storage capacity (DSC) models found in the literature were developed using statistical regression for relatively large soil surface roughness and slope values resulting in several fitting parameters. In this research, we developed and tested a conceptual model to estimate surface depression storage having small roughness values usually encountered in rainwater harvesting micro-catchments and bare soil in arid regions with only one fitting parameter. Laboratory impermeable surfaces of 30 x 30 cm² were constructed with 4 sizes of gravel and mortar resulting in random roughness values ranging from 0.9 to 6.3 mm. A series of laboratory experiments were conducted under 9 slope values using simulated rain. Depression storage for each combination of relative roughness and slope was estimated by the mass balance approach. Analysis of experimental results indicated that the developed linear model between DSC and the square root of the ratio of random roughness (RR) to slope was significant at p < 0.001 and coefficient of determination R² = 0.90. The developed model predicted depression storage of small relief at higher accuracy compared to other models found in the literature. However, the model is based on small-scale laboratory plots and further testing in the field will provide more insight for practical applications. <![CDATA[<b>Nutritional yield and nutritional water productivity of cowpea (<i>Vigna unguiculata</i> L. Walp) under varying irrigation water regimes</b>]]> There is a need to mainstream traditional crops in sub-Saharan Africa, in order to tackle food and nutritional insecurity through incorporating nutritional quality into crop water productivity, in the wider context of the water-food-nutrition-health nexus. The objective of the study was to determine the effect of irrigation water regimes on the nutritional yield (NY) and nutritional water productivity (NWP) of cowpea under Moistube irrigation (MTI) and subsurface drip irrigation (SDI). We hypothesized that NY and NWP of cowpea were not different under MTI and SDI and that deficit irrigation improved NWP. The experiment was laid as a split-plot design arranged in randomized complete blocks, replicated 3 times, with 3 irrigation water regimes: 100% of crop evapotranspiration (ETc), 70% of ETc, and 40% of ETc. Irrigation type and water regime did not significantly (p &gt; 0.05) affect the nutritional quality of cowpea. Similarly, NWP of crude fat (28.20-39.20 g∙m-3), ash (47.20-50.70 g∙m-3) and crude fibre (30.70-48.10 g∙m-3) did not vary significantly. However, protein and carbohydrate NWP showed significant (p < 0.05) differences across irrigation water regimes and irrigation type. The highest protein NWP (276.20 g∙m-3) was attained under MTI at 100% ETc, which was significantly (p < 0.05) higher than SDI (237.1 g∙m-3) and MTI (189.8 g∙m-3) at 40% ETc. Cowpea is suited for production in water-scarce environments; however, there are trade-offs with carbohydrate NWP. This should not be of concern as often diets are already energy-dense but lacking in other micronutrients. <![CDATA[<b>Application of logistic model to estimate eggplant yield and dry matter under different levels of salinity and water deficit in greenhouse and outdoor conditions</b>]]> Eggplant is an important product in greenhouse cultivation in the world. However, much of its production is done on the farm. Few studies have been conducted on modelling of its growth and yield. Considering the simplicity of the logistic models, only the temperature and dry matter data during the growing season are needed to calibrate them. Hence, we evaluated the performance of the logistic model in growth and yield prediction of eggplant in greenhouse and farm conditions. Eggplants were planted in 2012 and 2013 under different treatments of irrigation and salinity with a complete randomized block statistical design. Irrigation frequency treatments consisted of: daily (I1), weekly, (I2) and every 2 weeks of irrigation (I3). Each pot was irrigated to field capacity level. Four levels of salinity treatments are as follows: electrical conductivities (EC) of 0.8 (J1); 2.5 (J2); 5.0 (J3) and 7.0 (J4) dS∙m-1. The amount of plant dry matter was measured during the growing season (DM) and the amount of product (Y) at the end of the growing season. The logistic model was calibrated with the first-year data and validated with the second-year data. Logistic equation coefficients and harvest index were estimated as a function of the depth and electrical conductivity of irrigation water. The results showed that the accuracy of the logistic model for estimating DM during the growing season was good and predicted the product at the end of the growing season with acceptable accuracy. Also, the model's agreement with the measured DM and Y was good. <![CDATA[<b>Investigating stable isotope effects and moisture trajectories for rainfall events in Johannesburg, South Africa</b>]]> This study investigated the isotopic composition of daily rainfall in Johannesburg from November 2016 to October 2018. The moisture sources and trajectories for rainfall events of extreme isotopic signatures were deduced using the Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT). The results from time series and regression analysis show temperature and amount effects, with low coefficient of determination (R²) values of 0.21 and 0.12, respectively. The rainfall with amounts of <20 mm yielded a meteoric water line (MWL) with a slope of +6.9 and deuterium excess (d-excess) of +11.9‰. Rainfall with amounts of ≥20 mm had slope and d-excess values of +8.2 and +18.6‰, respectively. The lower slope in rainfall of <20 mm indicated the preferential occurrence of sub-cloud re-evaporation on light rainfall. Considering the lack of re-evaporation in heavy rainfall (≥20 mm), its slope and d-excess were approximated to those of incoming or in-cloud moisture prior to condensation. Therefore, a high d-excess of +18.6‰ in incoming moisture indicates evaporation that mainly occurs under warm sea surface temperature and low relative humidity. HYSPLIT shows that the moisture for the most depleted and the most enriched rainfall originates in the higher latitudes but differs in trajectory. The moisture for the most depleted rainfall had long residence in the higher latitudes following a semi-direct trajectory to Johannesburg, over the Atlantic and Indian Oceans. The most enriched rainfall followed a curved anticlockwise trajectory with long residence in the lower latitudes over the Indian Ocean. Circulation of saturated moisture over the warm Indian Ocean leads to a loss of light isotopes, thereby enhancing enrichment in the moisture that moves further inland. HYSPLIT indicated the importance of atmospheric conditions along the moisture trajectory on the signature of Johannesburg rainfall. <![CDATA[<b>Climate trends in the Cape Town area, South Africa</b>]]> Climatic conditions near Cape Town, South Africa (34°S, 19°E) are analysed for historical trends in station measurements in the 20th century and in modern satellite-blended datasets. Despite the variety of datasets and record lengths, all show a steady drying trend. Faster rates of warming, 0.1°C∙yr-1, are found in land surface temperatures during the period 2000-2017. Drying trends are most acute to the northwest of the Hottentots Holland mountains. Hydrology station measurements in the Upper Berg River catchment since 1956 reveal a decline in streamflow of −0.012 m³∙s-1∙month-1, and an upward slope in potential evaporation of +0.020 W∙m-2 ∙month-1. Rainfall has declined most in May and September, indicating a shorter winter wet season. Features supporting the drying trend include an increase of easterly winds and low-level subsidence during summer. The clockwise circulation trend around Cape Town entrains dry air from the Karoo interior and the south coast upwelling zone, leading to negative sensible heat flux, a capping inversion and diminished orographic rainfall. <![CDATA[<b>Pre-disaster planning and preparedness: drought and flood forecasting and analysis in Zimbabwe</b>]]> A situational analysis of future drought and flood impacts in Zimbabwe is outlined in this present study. The assessment under different scenarios is carried out using Aqueduct Global Flood Analyzer in which all the analyses are based on the gross domestic product (GDP), population, and the present and future (2030) urban damage. In this study, to effectively estimate future changes, three scenarios were employed, namely, IPCC Scenario A2, the Representative Concentration Pathways (RCP) scenario which represents climate change, and the Shared Socio-economic Pathways (SSP) scenario which represents socio-economic change. All these scenarios were employed from the Intergovernmental Panel on Climate Change 5th Assessment Report. To determine current mean monthly precipitation, 1981-2010 data were used and Meteonorm V7 software was employed for the generation of the mean monthly precipitation from 2011 to 2100. The level of flood protection employed is a 10-year one which is used to identify the population at risk, the effects of this event on the GDP and to determine the rate at which urban damage is happening. Utilizing Meteonorm V7 software, average monthly precipitation is predicted. This study determined that, in any year, the majority of Zimbabwe has a low to medium (2-3% probability) flood occurrence in which a 10-year flood has a 10% occurrence probability in any given year. If there is no flood protection employed, this 10-year flood could cause around 74.9 million USD affected GDP, 119 thousand affected population and 49.5 million USD urban damage. As much as it is impossible to eliminate drought and flood events, a diminution approach and proper planning and preparation before their occurrence reduce the economic and social losses. <![CDATA[<b>Experimental investigation on the effect of different slot shapes and configurations on scour dimension downstream of flip buckets</b>]]> Flip buckets at the end of a spillway can dissipate the flood discharge energy. Compared to other energy dissipators, this is a cost-effective structure. The formation of a scour hole downstream of a flip bucket is a topic of interest among hydraulic engineers. The current study investigated scouring downstream of a flip bucket under two major scenarios: (i) free conditions, and (ii) slotted conditions with rectangular and triangular slots configured differently under four different discharge rates. In total, 20 experiments were conducted in this study. Results showed that the use of a deflector slot greatly affected the scour extent and depth, resulting in a greater scour reduction (53%) in the labyrinth rectangular slotted bucket compared to the solid bucket. The results were compared to empirical equations, and a high correlation was observed between them. In comparison, the Taraimovich equation produced more accurate results in control experiments, and the Damle-A and Damle-B equations produced more accurate results in experiments corresponding to labyrinth rectangular and triangular slotted buckets. <![CDATA[<b>Design optimization of water distribution networks: real-world case study with penalty-free multi-objective genetic algorithm using pressure-driven simulation</b>]]> Water distribution systems are an integral part of the economic infrastructure of modern-day societies. However, previous research on the design optimization of water distribution systems generally involved few decision variables and consequently small solution spaces; piecemeal-solution methods based on pre-processing and search space reduction; and/or combinations of techniques working in concert. The present investigation was motivated by the desire to address the above-mentioned issues including those associated with the lack of high-performance computing (HPC) expertise and limited access in developing countries. More specifically, the article's aims are, firstly, to solve a practical water distribution network design optimization problem and, secondly, to develop and demonstrate a generic multi-objective genetic algorithm capable of achieving optimal and near-optimal solutions on complex real-world design optimization problems reliably and quickly. A multi-objective genetic algorithm was developed that applies sustained and extensive exploration of the active constraint boundaries. The computational efficiency was demonstrated by the small fraction of 10-245 function evaluations relative to the size of the solution space. Highly competitive solutions were achieved consistently, including a new best solution. The water utility's detailed distribution network model in EPANET 2 was used for the hydraulic simulations. Therefore, with some additional improvements, the optimization algorithm developed could assist practitioners in day-to-day planning and design <![CDATA[<b>Sensitivity analysis on a three-phase plant-wide water and resource recovery facility model for identification of significant parameters</b>]]> Water and resource recovery facility (WRRF) mathematical models have been advancing towards their widespread application for sizing and operation of treatment plants to minimize energy consumption and cost while maximizing nutrient recovery and effluent quality. Effective utilisation of these models requires that they are well calibrated. However, difficulties (with important parameters not identified and uncertainties in interpretation of model output results) can be experienced in model calibration, especially due to (i) the intricate relationships of model output variables with model input factors (where parameters are inter-related to various model outputs), resulting in non-linearity, and (ii) the limitations (due to expensive and/or time-consuming experimental methods) experienced in procuring and reconciling data required for determination of the model input factors. This paper presents the performance of a sensitivity analysis, reinforced with expert-based reasoning, on a three-phase (aqueous-gas-solid) plant-wide model (PWM_SA, Ikumi et al., 2015), for identification of significant parameters, and highlights the ones requiring experimental determination, specific to the system. The sensitivity analysis exercise was performed using two methods - i.e., Morris screening (screening method) and standardised regression coefficient (SRC; based on regression). This process was useful towards detection of the parameters, which are not normally measured at WRRFs, but may require attention for future application of mathematical models in decision-making processes for WRRFs. These included the influent fractions of unbiodegradable and readily biodegradable organics, the kinetic constants for hydrolysis of biodegradable particulates, the elemental composition of the organics and the specific growth rate of autotrophic nitrifying biomass. <![CDATA[<b>An analytic hierarchy process model for selecting adsorbent for heavy metal ion removal from wastewater</b>]]> This paper provides an analytic hierarchy process (AHP) model for the selection of an adsorbent to adhere with multiple types of metal ions from wastewater. Experimental literature is surveyed to estimate the entries for comparison matrices. The model allows the user to combine the degree of importance of the adsorption of each ion type to the degree of importance of both technical and non-technical criteria. A case study is provided to select among three adsorbents and three types of ions. Results illustrate the usability of the model in handling experimental problems; chitosan is selected for its high technical qualities, that sludge is preferred for its availability and low cost, and that pH-level and adsorbent-dosage are the most influential sub-criteria to control to enhance adsorption efficiency. Moreover, sensitivity analysis shows that the decision is impacted by the relative importance of technical criteria and by the degree of importance of ions. <![CDATA[<b>Photocatalytic degradation of a basic dye in water by nanostructured HPEI/TiO</b><b><sub>2</sub> containing membranes</b>]]> A photocatalytically active membrane was synthesized through the embedding of HPEI/TiO2 nanocomposite in PES membrane for the removal of methyl orange (MO) dye from water. Membranes were characterized using scanning electron microscopy coupled with energy dispersive X-ray, atomic force microscopy, water contact angle measurements and water flux analysis. PES/HPEI/TiO2 membranes showed improved hydrophilicity and were effective in the photodegradation of MO. The reaction rate for MO degradation was 11.6 x 10−³ min−¹, and the degradation was accompanied by the generation of sulphate ions as degradation by-products. <![CDATA[<b>Development of a paper-based microfluidic device for the quantification of ammonia in industrial wastewater</b>]]> Ammonia is a toxic pollutant increasingly found in urban and industrial wastewater and unprotected surface water. Industry discharges and fertilizer run-off release ammonia into sewers and streams, overloading wastewater treatment plants and causing fish deaths in surface water such as rivers, sea and lakes. The purpose of this study was to develop and evaluate the effectiveness of the microfluidic paper-based device (µPAD) for the quantification of ammonia in wastewater. The µPAD fabricated had an oval-shaped pattern which was designed using CorelDraw software. The hydrophilic zones were created by printing a chromatographic paper with a Xerox wax printer (Xerox colorqube 8570). The modified version of the colorimetric method using Nessler reagent was combined with microfluidic technologies to create a low-cost monitoring system for detection of ammonia in wastewater. The method allows for ammonia determination in the range of 0-5 ppm (mg/L) with a limit of detection of 3.34 ppm. This study indicated that a µPAD was successfully used to quantify the concentration of ammonia in wastewater. <![CDATA[<b>SPE-LC-PDA method development and application for the analysis of selected pharmaceuticals in river and wastewater samples from South Africa</b>]]> The occurrence of pharmaceutical compounds in the environment has been a growing concern. However, there is little information on the concentration levels of pharmaceuticals in African countries. This indicates the need and the importance to develop sensitive methods that can detect these compounds at trace levels (ng/L-µg/L). This work reports on the development of solid phase extraction followed by liquid chromatography-photo diode array (SPE-LC-PDA) analysis. The method was then applied for the analysis of pharmaceutical compounds (ibuprofen, fenoprofen, naproxen, carbamazepine and diclofenac) in river and wastewater samples. The SPE recoveries obtained at 10 000 ng/L spike concentration ranged from 89-120% in distilled water, 79-110% in river water and 78-94% in wastewater. The LODs and LOQs ranged from 10.9-20.4 ng/L and 36.2-60.7 ng/L, respectively. Concentrations of the pharmaceuticals obtained in river water samples ranged from 60 to 32 900 ng/L; in wastewater they ranged from 70 to 66 900 ng/L. Higher concentrations of pharmaceuticals were detected in winter compared to the spring season. <![CDATA[<b>Modelling of chlorophyll-<i>a</i> and <i>Microcystis aeruginosa</i> decay under the effect of different oxidants in culture media</b>]]> Blooms of the cyanobacterium Microcystis aeruginosa are common in many eutrophic freshwater bodies and pose a serious threat to water quality, potentially giving rise to high turbidity, food web alterations, increased production of toxic microcystin (MC-LR) and odorous compounds. The comparative effectiveness of oxidant treatment of M. aeruginosa cells in culture media was evaluated by applying a mathematical model of chlorophyll-a (Chl-a), cells and MC removal. The oxidants were chlorine (1-5 mg∙L-1), hydrogen peroxide (HP: 50-150 mg∙L-1), percitric acid (PCA: 10-50 mg∙L-1), and peracetic acid (PAA: 1.5-7.5 mg∙L-1). The Weibull distribution model was applied to assess the degree of inactivation of M. aeruginosa viability under different oxidant treatments. First-order kinetics was successfully applied to the experimental data for Chl-a decay. Using the Weibull model, it was possible to predict the required exposure time (Tr) for oxidants to achieve a 99.9% reduction in viable M. aeruginosa cells with respect to the initial value. 5 mg∙L-1 chlorine produced a 81% degradation of [D-Leu¹] MC-LR after 72 h, with an exposure time (Tr) of 141 h. Among the peroxide treatments (HP, PCA and PAA), PCA (10-50 mg∙L-1) produced the highest level of [D-Leu¹] MC-LR degradation (39-79%), with low exposure times (Tr = 119-125 h). Chl-a concentration and M. aeruginosa counts for each oxidant treatment were highly correlated and successfully linked by a cubic polynomial. This is the first modelling report of M. aeruginosa decay by oxidant treatments. <![CDATA[<b>Comparison of the physicochemical and microbiological quality of different brands of bottled water with well water in Lesotho using principal component analysis</b>]]> Water, though vital for life, is also the route for transmission of water-borne diseases. Bottled water is consumed worldwide for its accessibility and the public perception of purity. However, this perception is usually not based on experimental results to confirm or invalidate it, especially where the sample commodity is not adequately tested for quality. In this study, different bottled water brands in Lesotho were compared to tap and well water samples sourced locally. The standard water testing methods were used to assess the physicochemical and microbiological quality of these samples. The physicochemical parameters such as hardness, alkalinity, pH, chloride, conductivity and nitrate content were below WHO acceptable limits for all water samples tested. Upon the employment of multivariate statistics, one of the bottled water samples (C) was completely indistinguishable from the two well water samples collected in the local village. On the other hand, microbiological analysis indicated that the water samples designated as C (bottle water brand), F (tap water), G (Ha-Mafefooane) and H (Roma community water) had a high microbial load and were contaminated with Escherichia coli, while A, B, D and E samples contained Staphylococcus spp. The presence of such indicator organisms suggests possible poor hygiene during processing. It is therefore recommended that stricter policy measures be taken to regularly monitor bottled water quality, before and after production and storage, to fulfil the basic water quality standards of WHO. Public awareness should also be created that bottled water may still be impure, despite appearing attractive and convenient. <![CDATA[<b>Drying of faecal sludge from VIP latrines through a medium infrared radiation process</b>]]> In order to treat faecal sludge from ventilated improved pit (VIP) latrines, eThekwini Municipality (Durban, South Africa) developed an infrared dryer, 'LaDePa' (Latrine Dehydration Pasteurization). Parameters that influence its operation were investigated using a laboratory-scale replica of the full-scale machine. For this, faecal sludge collected from VIP latrines was pelletized and dried under different operating conditions. Drying curves were obtained by plotting medium wave infrared intensity (MIR), height of emitters above the belt, air flowrate and pellet diameter against the residence time. These curves were then used to determine the drying rate and energy consumption. The results show that the drying rate increased while the energy consumption decreased by increasing the power of the MIR emitters and decreasing the size of the pellets. For example, the drying time to get a moisture content of 0.8 g water/g dry solid was shortened from 27 to 6 min while the energy consumption for this reduced from 1.5 to 0.8 kWh after increasing the MIR power from 1.5 to 3.3 kW. Similar drying curves were obtained by varying the distance between the pellets and MIR emitters, and adjusting intensity of the MIR radiation to obtain the same temperature in the drying zone. It was also observed that higher airflow rates enhanced mass transfer rates, but led to a cooling effect. No effect on the drying rate was observed after pre-drying the sludge or adding sawdust. The study shows that for the process to be efficient, the MIR intensity should be high enough for fast drying to occur (T ≥ 150°C), but without causing thermal degradation (T ≤ 220°C). The height of emitter above the belt and the pellet size should be as small as possible (8 mm); airflow rate should be optimised to maximize the mass transfer rate and minimize the cooling effect.