Scielo RSS <![CDATA[Water SA]]> vol. 44 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>The effect of anaerobic baffled reactor effluent on nitrogen and phosphorus leaching from four soils in a laboratory column experiment</b>]]> Leaching of nitrogen and phosphorus from soil columns during application of anaerobic baffled reactor effluent was evaluated. The soils used were from Inanda (Ia), Cartref (Cf), and Sepane (Se) forms, and a silica sand (SS). Each was packed into duplicate columns (103 mm internal diameter; 200 mm length), four each for up-flow and down-flow leaching. Effluent was delivered continuously for 6, 8 and 35 days at high (32 mm·h-1), medium (16 mm·h-1), and low (2 mm·h-1) rates, respectively. At each flow rate, 9 pore volumes were collected. Leachates were analysed for pH, electrical conductivity (EC), nitrate and phosphate. Leachate pH from all soils was lower than the original effluent (6.4). Leachate EC varied between 0.5 and 0.9 dS·m-1 compared to the effluent EC of 0.84 dS· m-1. At high flow rate, the amount of nitrogen leached was similar from all soils. At low and medium rates, more nitrogen was leached from the coarser-textured SS and Cf than the finer-textured Ia and Se, at both flow directions. Flow direction had a greater effect on nitrogen leaching from finer- than coarser-textured soils. Phosphorus concentrations were higher than the original effluent at medium and high flow rates indicating that the soils were a source of phosphorus. At low flow rate, phosphorus concentrations were much lower than the original effluent, indicating soil retention. Phosphorus leaching was greater from coarser- than finer-textured soils in the up-flow columns, but the opposite occurred in the down-flow columns. <![CDATA[<b>Development of a coupled dispersive liquid-liquid micro-extraction with supported liquid phase micro-extraction for triclosan determination in wastewater</b>]]> As attention is drawn towards the monitoring of the so-called emerging pollutants, some common household chemicals are not well researched. Household antimicrobials can also present wastewater treatment challenges if not taken cognisance of. Herein we report the application of a recently reported coupled dispersive liquid-liquid micro-extraction (DLLME) with supported liquid phase micro-extraction (LPME) for the extraction of triclosan from wastewater. A univariate approach was used to investigate various parameters amenable to DLLME while no attempt was made to optimise the LPME, achieving the following optimum conditions: 25 µL of a 1:1 toluene-chloroform mixture with 10% sodium chloride into 1 mL aqueous triclosan solutions and extraction time of 15 min achieving an enrichment efficiency 167 times the reference solution prepared with distilled water, good linearity (R² = 0.9946) with the estimated limit of detection at 0.013 µg/mL and good repeatability (%RSD ≤ 10). The method showed considerable ruggedness with a similar linearity (R² = 0.9957) and repeatability (%RSD < 10), with only the limit of detection being compromised (0.31 µg/mL) when applied to a wastewater sample using a matrix-matched standard addition approach. Although the GC-FID method detected triclosan in the wastewater sample, the results were negated by those from the GC-MS; as such it therefore could not be concluded with confidence whether the water contained any triclosan or not. However, the results demonstrated the potential of this method in determination of triclosan in water-based samples when the extraction was coupled to a more rugged system such as a GC-MS. <![CDATA[<b>Assessing the clogging and permeability of degrading packed bed reactors</b>]]> In South Africa, the need for water treatment is increasing, especially in the mining sector. As active water treatment technologies are expensive, the mining sector has an increasing need for passive water treatment technology, with low maintenance and operating costs, yet efficient water treatment ability. Literature on passive water treatment suggests that these systems only offer a narrow range of treatment capabilities. Therefore, hybrid water treatment systems could be a solution to low-cost water treatment in South Africa. The degrading packed bed reactor (DPBR) is one of the units comprising the hybrid treatment group. The DPBR's main action is to convert sulfates into sulfides and alkalinity, since this reduces the impact on the environment by increasing the pH and reducing the salinity. In this study, 6 small-scale DPBRs were constructed. Each was classified according to its unique organic source (manure, straw, vegetable food processing waste, wood shavings, chicken litter and a combined sample with layers of all the carbon sources). Synthetic acid mine drainage (AMD) was fed through the 6 bioreactors for a period of 3 months. Permeabilities, leachate samples and effective void volumes were measured from the DPBRs. From the experiments conducted, it was found that the manure and combination bioreactors (with equal layers of manure, straw, compost, wood shavings and chicken litter) had the lowest overall permeabilities, with straw and compost having the highest permeabilities. Linked to this, the experiments showed that the manure and combination bioreactors had the largest decreases in effective porosity with straw and compost having the least. Hydraulically, the combination bioreactor performed the best by incorporating the best attributes from each carbon source. Wood shavings preformed almost as well. Chicken litter clogged within 18 days after the initiation of the experiment and thus was the least effective substrate. <![CDATA[<b>Toxicity and biodegradability of caffeic acid in anaerobic digesting sludge</b>]]> Caffeic acid in waste comes from a variety of industries, and its disposal is likely to increase due to emerging processes such as graphene production and use in healthcare products. The current sustainable option to treat waste caffeic acid and prevent its natural transformation in soil to greenhouse gases, is anaerobic digestion. However, little is known about the toxic and inhibitory effects of caffeic acid on biogas production as well as its ultimate anaerobic biodegradability; or about the reactive-adsorptive processes taking place with caffeic acid in sludge, metabolic intermediates, thermodynamic limitations and the effects on extracellular polymeric substances (EPS). Standard methods revealed that 80% of biogas production (EC80) from a readily digestible biomass was inhibited at 389 mg caffeic acid·g-1 VSS. Up to 52% of caffeic acid was biodegraded. β-oxidation and reductive dehydroxylation were the initial activation reactions transforming caffeic acid into typical polyphenol structural units (protocatechuic acid and 4HBA). Adsorption of caffeic acid (53.3% and 28.6%) to the sludge occurred even at inhibitory concentrations. The EPS structure remained unchanged regardless of the increase in concentration of caffeic acid. Reasonable concentrations of caffeic acid could be co-digested with a similar readily digestible biomass with an expected reduction in biogas production. It is feasible to treat waste caffeic acid by anaerobic digestion and adsorption of its derivates, in order to reduce the contribution to global warming and to protect the environment. <![CDATA[<b>Evaluation of the effectiveness of the National Benchmarking Initiative (NBI) in improving the productivity of water services authorities in South Africa</b>]]> Water shortages, public demonstrations and lack of service delivery have plagued many South African water services authorities (WSAs) for a number of years. From 2004-2007 the National Benchmarking Initiative (NBI) was implemented to improve the performance, efficiency and sustainability of WSAs. The current study demonstrates the use of data envelopment analysis (DEA) and the Malmquist productivity index (MPI) for the assessment of the effectiveness of the NBI in achieving these goals. Furthermore, the MPI is used to assess the impact that the termination of the NBI had on the efficiency of the WSAs in the years that followed. In conclusion, the MPI is identified as a valuable tool for regulators and policy makers that wish to assess the performance of their benchmarking initiatives. <![CDATA[<b>Associations between stormwater retention pond parameters and pollutant (suspended solids and metals) removal efficiencies</b>]]> Presented in this paper are the results of correlational analyses and logistic regression between metal substances (Cd, Cu, Pb, Zn), as well as suspended solids removal, and physical pond parameters of 19 stormwater retention pond case studies obtained from the International Stormwater BMP database. Included are cross-correlations between metals and solids in pond influent, effluent and removals. The findings provide insights fundamental to further development of improved models and design guidelines for stormwater ponds. Indications were that (i) pond efficiencies differed between high and low influent concentrations and masses, (ii) concentration was an invalid indicator of correlations between substances in pond influent and effluent as well as the fractions of substances removed within ponds, (iii) total cadmium, copper, lead, zinc and total suspended solids (TSS) were associated in surface runoff and similarly removed within ponds, (iv) statistically significant correlations were often only found in data groups either above or below a specific statistic (quartile value, median) for specific pond parameters, indicating that removals may have been differently influenced by pond parameters over different data ranges, and (v) the volume within the permanent pool was of greater importance to pond efficiencies than the volume captured during storm events. <![CDATA[<b>An updated water balance for the Grootfontein aquifer near Mahikeng</b>]]> The Grootfontein Aquifer, part of the important North West dolomite aquifers, supplies about 20% of Mahikeng's domestic water needs. Over-abstraction caused the large natural spring draining the aquifer to disappear in 1981, and groundwater levels have since fallen nearly 30 m in the vicinity of the former spring. Analysis of water levels and a water balance using recent assessments of groundwater abstractions confirm past work describing the hydrogeological functioning of the aquifer, and suggest that current abstractions need to fall by between 19 and 36 ML/day (7 and 13 Mm³/a) to bring the aquifer back into long-term balance. Continued over-abstraction at Grootfontein implies increasing risk to Mahikeng's water supply, and illuminates the larger challenge of ensuring groundwater use in the North West dolomites that is sustainable and in the public interest. <![CDATA[<b>A glimpse into the littoral nutrient dynamics of a lake system connected to the sea</b>]]> In South Africa more than 80% of estuaries are small, dynamic and predominantly linear systems. Nutrient characteristics in these systems are mostly influenced by external catchment processes, except during extended periods of closure. However, a small percentage of the country's estuaries (< 3%) comprise larger estuarine lakes mostly evolved from drowned river valleys. The physical properties of these systems suggest relatively low flushing rates, and the potentially stronger influence of in-situ processes on nutrient characteristics. This study investigates dissolved inorganic nutrient dynamics in the littoral zones of these estuarine lake systems, and potential influencing factors, using the Wilderness Lake System as a case study. Comparison of inter-annual and seasonal trends in dissolved inorganic nutrients (NOx-N, NH4-N and PO4-P) in river inflow and in the three lakes confirmed that external catchment fluxes are most likely not the sole, or even the dominant drivers of average long-term or seasonal dissolved inorganic nutrient patterns in the lake littoral zones. Relatively low NOx:NH4 ratios (mostly less than 1) in the lakes (especially in Eilandvlei and Langvlei) indicated a stronger influence of in-situ processes, such as bacteriological remineralisation, similar to observations in other lake type systems with low flushing rates. Low NO3:NH4 ratios are known to stimulate cyanobacteria, having the metabolic ability to potentially produce microcystins. Therefore, incremental dissolved inorganic nutrient and organic matter enrichment may cause these systems to tip into eutrophic, possibly toxic, aquatic states that will be difficult, if not impossible, to reverse given their weak flushing mechanisms. The findings from this study highlight the importance of appropriate water resource management, both in the catchments and within the floodplains of estuarine lake systems. <![CDATA[<b>Severe weather over the Highveld of South Africa during November 2016</b>]]> November months are notorious for severe weather over the Highveld of South Africa. November 2016 was no exception and a large number of severe events occurred. Very heavy rainfall, large hail and tornadoes were reported. The aim of this paper is to compare the synoptic circulation of November 2016 with the long-term mean November circulation and to investigate some sounding derived parameters. Furthermore, a few of the severe weather events are described in detail. The surface temperatures and dewpoint temperatures were found to be higher than normal resulting in increased conditional instability over the Highveld. Low-level moisture originated over the warm Mozambique Channel and the 500 hPa temperature trough was located favourably over the Highveld; further east than normal. The combination of these factors and weak steering winds resulted in flash flooding on the 9th while favourable wind shear conditions caused the development of a tornado on 15 November. The favourable circulation patterns and moisture gave rise to an atmosphere in which severe weather was a possibility, and the awareness of such factors is used as one of many tools when considering the severe weather forecast. The consideration of the daily variables derived from sounding data were good precursors for the prediction of severe thunderstorm development over the Highveld during November 2016. It is recommended that an operational meteorologist incorporates upper air sounding data into the forecasting process and not to rely on numerical prediction models exclusively. <![CDATA[<b>Case study modelling for an ettringite treatment process</b>]]> Several technologies have been developed to treat acid mine drainage (AMD) and attention is shifting towards the removal of sulphate. The formation of ettringite, a hydrous calcium aluminium sulphate mineral, is an option to treat AMD and can reduce the sulphate concentration to well below the discharge specifications. The process modelled in this study includes the formation of ettringite and the recovery of gibbsite through the decomposition of recycled ettringite. The modelling of this process was done using PHREEQC and the results presented in this paper are based on the outcome of different case studies that investigated how the process is affected by a change in parameters. These include, changing the feed water pH, altering the split fractions in the hydrocyclone for the gibbsite recovery and varying the pH for ettringite formation. <![CDATA[<b>Development and assessment of rules to parameterise the ACRU model for design flood estimation</b>]]> Design flood estimation (DFE) is essential in the planning and design of hydraulic structures. In South Africa, outdated methods are widely applied for DFE. In this paper the potential of a continuous simulation modelling (CSM) approach to DFE in South Africa, using the daily time-step ACRU agrohydrological model, is investigated. The paper focuses on the links and similarities between the SCS-SA and ACRU models and the subsequent preliminary investigations that were undertaken to account for and incorporate the land cover classes, including land management practices and hydrological condition, of the SCS-SA model into the ACRU CSM approach. The approach to this study was to investigate how design volumes simulated by the SCS-SA model for various land management practices or conditions could be simulated by the ACRU model. Since peak discharge estimation in both models is directly dependent on simulated volumes, this preliminary study focused only on design runoff volumes, with subsequent investigations on peak discharge required in future research. In the absence of observed data, design runoff volumes and changes in design runoff volumes, as simulated by the SCS-SA model, were used as a substitute for observed data, i.e., as a reference, to achieve similar design runoff volumes and changes in design volumes in the ACRU model. This was achieved by adjusting relevant input parameters in the ACRU model to represent the change in management practice or hydrological condition, as represented in the SCS-SA model. Following a sensitivity analysis of relevant ACRU parameters, calibration of 2 selected parameters against SCS-SA CN values for selected land cover classes was performed. A strong linear relationship (R² = 0.94) between these ACRU parameters and SCS-SA CNs for selected land cover classes was found and consequently specific rules and equations were developed to represent SCS-SA land cover classes in ACRU. Recommendations are made to further validate and verify the approach and to further the development of a CSM system for DFE in South Africa. <![CDATA[<b>Effect of sodium adsorption ratio and electric conductivity of the applied water on infiltration in a sandy-loam soil</b>]]> Infiltration measurements using a double-ring infiltrometer were conducted on a sandy-loam soil located in Saudi Arabia. The measurements were performed for an undisturbed soil. The effect of sodium adsorption ratio (SAR) and electric conductivity (EC) of the applied water on infiltration rate was examined. The infiltration rate at the initial time was high, in the order 305 > 240 > 137 > 104 > 65 mm/h for SAR of 3.34, 3.52, 4.14, 4.18, and 7.60, respectively. The results showed that 180 min after the initial time of measurement in the sandy-loam soil, the final infiltration rates were in the range of 21.1-44.0 mm/h for the different qualities of water considered in this study, with an average value of 33.8 mm/h. Hence, the infiltration rate is sensitive to the SAR of the applied water. The final infiltration rate (IRf) and the final cumulative infiltration depth (Zf) after 180 min could be predicted using the following equations: IRf (mm/h) = 49.399 + 6.691 × EC (dS/m) - 6.740 × SAR (-) R² = 0.939 Zf (mm) = 148.198 + 20.074 × EC (dS/m) - 20.221 × SAR (-) R² = 0.9387 <![CDATA[<b>Determination of oestrogen hormones in raw and treated water samples by reverse phase ultra-fast liquid chromatography mass spectrometry - a case study in Johannesburg South, South Africa</b>]]> Hormones in water samples have been classified as 'emerging pollutants' and may pose a potential risk for humans. Hormones can be found in both surface and ground water at low concentrations. These compounds enter water streams through wastewater treatment plants (WWTP) and may elicit endocrine disruption to organisms. As a result of the low concentrations, a suitable analytical methodology is essential for their determination. In the past, residues of oestrogens in aqueous and solid environmental samples have commonly been analysed by gas chromatography (GC) equipped with mass spectrometry (MS). However, the necessary derivatisation steps are not only time consuming and laborious but also tedious. The first part of this case study was to develop a method to determine trace concentrations of the estrone (E1), 17α-estradiol (E2α), 17-β-estradiol (E2β) and 17-α-ethinylestradiol (EE2) hormones using reverse phase ultra-fast liquid chromatography mass spectrometry (RP-UFLC). Using the developed method, the second part of the case study was to determine the concentrations of the hormones in raw and treated potable water samples from the Vaal River catchment area in the south of Johannesburg, South Africa. Analytes were extracted by solid phase extraction (SPE C18 sorbent) cartridges and subsequently injected into ultra-fast liquid chromatography with the reverse phase column coupled to mass spectrometry (UFLC-MS) for analyte determinations. The limits of quantification were in the range of 0.24 to 0.32 ng·L-1 for the analytes. Accuracy was 95.6, 93.8, 97.6 and 100.9% for EE2, E2α, E2β and E1, respectively. In raw water samples taken during the rainy wet season, estrone was detected at concentrations of 0.90 and 4.43 ng·L-1. However, treated potable water samples did not contain detectable levels of hormones. This is potentially due to the ability of a water treatment process to remove endocrine disruptors during water purification. <![CDATA[<b>Distribution of primary and secondary currents in sine-generated bends</b>]]> The secondary circulation in a meandering channel redistributes the velocity over the bend. However, the shift of primary flow by secondary currents is not quantitatively understood, due to the difficulty in isolating the role of curvature-driven secondary flow from that of topography-driven secondary flow in bed-deformed meanders. The influences of curvature-driven and topography-driven secondary currents on the redistribution of primary flow in sine-generated meandering channels were examined by CCHE2D. The model is calibrated using data measured in two sets of laboratory experiments including flat-bed flow and mobile-bed flow. Analysis indicated that topography-induced current mainly contributes to the redistribution of primary flow from inner to outer bank in the curved channels, rather than the secondary flow driven by curvature. <![CDATA[<b>Analysis of water use by gated communities in South Africa</b>]]> Gated communities (hereafter GCs) are popular in many countries, including South Africa, because added security and lifestyle improvements are offered relative to homes built on freestanding properties. One of the key factors for the popularity of GCs is the availability of amenities to support the demands of the residents, such as gymnasia, walkways, golf courses, play parks and polo fields. Further benefits include the improved management of infrastructure such as telecommunication services, roads, water, sewer, electrical and stormwater assets. GCs are often governed by trustees or homeowners' associations, responsible for the operation and the maintenance functions of the infrastructure, as well as implementing and adhering to legislation that pertains to the GC. As part of this study, the monthly water-use records of 2 888 GCs in 3 different South African cities were analysed. Water use was evaluated for each GC as a whole, and also per household in each case. The average number of homes per GC was 33 households/GC, with the smallest GC in the study sample containing 3 houses and the largest 524 houses. One of the study sites was in the winter rainfall region, while 2 sites were in the summer rainfall region. The average annual water use of individual households in each GC was plotted against current guidelines and was found to be relatively low. The average annual daily demands of all properties in the winter rainfall region was 0.63 kL/d, compared to 0.66 kL/d and 0.49 kL/d for the two study sites in the summer rainfall region. The results highlighted peculiarities in the water use of GCs that have not been reported on before, in particular the relatively low water use and the differences between GC homes' water use in the various rainfall regions. <![CDATA[<b>Effect of landcover/land-use changes on water availability in and around Ruti Dam in Nyazvidzi catchment, Zimbabwe</b>]]> The aim of this study was to quantify the upstream land-use and landcover changes and assess their effect on Ruti Dam levels and water availability in Nyazvidzi catchment. Remote-sensing techniques, hydrologic modelling and statistical inference were applied. Spatial landcover dynamics were derived from Landsat satellite data for the years 1984, 1990, 1993, 1996, 2003, 2008, and 2013 using the maximum likelihood classification technique. Results showed that forests and shrubs decreased by 36% between 1984 and 2013 whilst cultivated areas increased by 13% over the same period. The HEC-HMS rainfall-runoff model was used to simulate steamflow for the Nyazvidzi catchment, Zimbabwe. For the calibration period (2000-2001), a satisfactory Nash-Sutcliffe efficiency (NSE) model peformance of 0.71 and relative volume error (RV E) of 10% were obtained. Model validation (1995-1997) gave a NSE of 0.61 and RV E of 12%. We applied the Mann-Kendall trend test to assess for monotonic trends in runoff over the study period and the results showed that there were significant decreases in observed runoff at Station E140 (monthly time scale) and at Stations E62 and E140 (seasonal time scale). Results showed that the wet season (Nov-Feb) had higher mean water balance values with an excess runoff of 8.12 mm/month. The dry season (April-Sept) had lower mean water balance values, with the lowest at 0.04 mm/month. Strong positive relationships (r²) between dam levels and land-use changes were obtained as follows: bare (0.95), cultivation (0.76) and forests (0.98). The relationship between runoff generated and land-use changes was found to be relatively weaker (0.54 for forests, 0.51 for bare and 0.14 for cultivation). Findings of this study underscore the relevance of applying hydrological models, remote sensing and statistical inference in quantifying and detecting environmental changes, as well as how they affect the availability and the quality of water resources in space and time.