Scielo RSS <![CDATA[Water SA]]> http://www.scielo.org.za/rss.php?pid=1816-795020100001&lang=en vol. 36 num. 1 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Measurement of grassland evaporation using a surface-layer scintillometer</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100001&lng=en&nrm=iso&tlng=en A dual-beam surface-layer scintillometer (SLS) was used to estimate sensible heat flux (H) every 2 min for a path length of either 50 or 101 m, for more than 30 months in a mesic grassland in eastern South Africa. The SLS method relies on Monin-Obukhov similarity theory, the correlation between the laser beam signal amplitude variances and the covariance of the logarithm of the beam signal amplitude measured using 2 laser detectors. Procedures for checking SLS data integrity in real-time are highlighted as are the post-data collection rejection procedures. From the H estimates, using SLS and measurements of soil heat flux and net irradiance, evaporation rates were calculated as a residual of the shortened energy balance equation and compared with grass reference evaporation rates (ETo). Inconsistent hourly ETo values occur in the late afternoon due to the incorrect assumption that the soil heat flux is 10% of net irradiance. The SLS estimates of H and the estimates of evaporation rate as a residual compared favourably with those obtained using the Bowen ratio and eddy covariance methods for cloudless days, cloudy days and days with variable cloud. There was no evidence for the eddy covariance measurements of H being underestimated in comparison to the Bowen ratio and SLS measurements. On many days, the diurnal variation in SLS H was asymmetrical, peaking before noon. <![CDATA[<b>Surface renewal method for estimating sensible heat flux</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100002&lng=en&nrm=iso&tlng=en For short canopies, latent energy flux may be estimated using a shortened surface energy balance from measurements of sensible and soil heat flux and the net irradiance at the surface. The surface renewal (SR) method for estimating sensible heat, latent energy, and other scalar fluxes has the advantage over other micrometeorological methods since the method requires only measurement of the scalar of interest at a point and the method may be applied close to the canopy surface, thereby reducing fetch requirements. The SR analysis for estimating sensible heat flux from canopies involves high-frequency air-temperature measurements (typically 2 to 10 Hz) using unshielded and naturally-ventilated 25- to 75-mm diameter fine-wire thermocouples. The SR method is based on the premise that a parcel of air connected to the surface, after it has been enriched or depleted, is renewed by an air parcel from above. There are 2 SR analysis approaches: the ideal SR analysis approach which presumes a constant αfactor; and a set of SR approaches that avoid the use of the α calibration factor. The weighting factor α depends on measurement height, canopy structure and stability conditions since it depends on the capability of the highest frequency eddies to mix the scalar within the air parcels renewed by coherent structures. A combination approach using SR and either similarity theory, that requires friction velocity or wind-speed measurements, or dissipation theory, has also been used to estimate H. The combination SR and dissipation method only requires high-frequency air-temperature data and may be considered not to require calibration. The ideal SR and combination SR/dissipation approaches are the least expensive micrometeorological methods for estimating sensible heat flux and also latent energy flux if one forces closure of the surface energy balance. However, application of SR analysis using slow data-loggers require some expertise since high-frequency air temperature data are not usually stored with the slower data-loggers. Some structure functions can be stored for post-processing and determination of ramp amplitude and ramp period, but the appropriate time lags have to be chosen a priori. Fortunately, modern data-loggers avoid this problem and complex SR analysis approaches can now be applied. However, for routine purposes, applications using the ideal SR analysis approach with slow data-loggers may be of interest since it is a very affordable method. <![CDATA[<b>Characterisation of rainfall at a semi-arid ecotope in the Limpopo Province (South Africa) and its implications for sustainable crop production</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100003&lng=en&nrm=iso&tlng=en Detailed knowledge of rainfall regime is an important prerequisite for agricultural planning. Despite the importance of rain-fed agriculture to food security in the semi-arid regions of South Africa, studies to understand the spatial and temporal variability of rainfall are not widely documented. Twenty-three years (1983 to 2005) of rainfall data were analysed in order to study the basic statistical rainfall characteristics at the University of Venda ecotope. Annual and monthly rainfall was fitted to theoretical probability distributions. The Anderson-Darling goodness-of-fit test was used to evaluate best fit models. Probability of receiving annual and monthly rainfall was predicted using the appropriate probability distribution functions. The chance of experiencing dry spells of different durations was determined. Cumulative frequency analysis of daily rainfall amounts and depths was characterized. It was found that the distribution of daily rainfall was highly skewed with high frequency of occurrence of low-rainfall events. The distribution of daily rainfall depths was also highly skewed, a comparatively small proportion of rainy days supplying a high proportion of the rainfall. <![CDATA[<b>Crop production management practices as a cause for low water productivity at Zanyokwe Irrigation Scheme</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100004&lng=en&nrm=iso&tlng=en Generally, smallholder irrigation schemes (SIS) in South Africa have performed poorly and have not delivered on their development objectives of increasing crop production and improving rural livelihoods. Limited knowledge of irrigated crop production among farmers has been identified as one of the constraints to improved crop productivity, but research that investigates the relationship between farmer practices and productivity is lacking. A monitoring study was therefore conducted at the Zanyokwe Irrigation Scheme (ZIS) in the Eastern Cape to identify cropping systems and management practices used by farmers and to determine how these were related to performance. Evidence from 2 case studies showed that water management limited crop productivity. Irrigation application and system efficiencies were below the norm and irrigation scheduling did not take crop type and growth stage into account. Monitoring of 20 farmers over a 3-yr period showed that cropping intensity averaged only 48% and that the yields of the 2 main summer crops, grain maize (Zea mays L.) and butternut (Cucurbita moschata) averaged only 2.4 and 6.0 t·ha-1, respectively. In addition to poor water management, other main constraints to crop productivity were inadequate weed and fertiliser management and low plant populations. The results indicated that a lack of basic technical skills pertaining to irrigated crop production among farmers was a possible cause of inadequate management. In this regard, it is expected that farmers could benefit from 'back to basics' training programmes in the areas of crop and irrigation water management. Research needs to focus on labour-saving production technologies, establishing farm-specific fertiliser recommendations, the identification and use of affordable sources of nutrients, as well as strategies to improve plant population in maize by preventing bird damage to newly-planted stands. <![CDATA[<b>Modelling the economic tradeoffs between allocating water for crop production or leaching for salinity management</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100005&lng=en&nrm=iso&tlng=en Salinisation threatens the sustainability of irrigation agriculture and needs to be managed through leaching practices. Under conditions of water scarcity a tradeoff exists between allocating water for salinity management and production. Currently no model in South Africa is able to model explicitly the impact of salinity management through leaching on the economic efficiency of irrigation farming, taking the opportunity cost of water under limited water supply conditions into consideration. The main objective of this paper is to develop a robust non-linear optimisation model that is able to determine endogenously the impact of declining irrigation water quality on the economic efficiency of irrigation farming. A data envelopment framework was used to integrate recently developed soil water salinity crop-yield production functions and leaching functions to model the complex interactions involved in water allocation decisions. Results showed that it is profitable to reduce the area irrigated under limited water supply conditions in order to release water for leaching purposes. When more water, but still a limited amount of water, is allocated to the farmer, his willingness to pay for water will increase if irrigation water deteriorates. Thus, the conclusion is that leaching is profitable irrespective of the water supply conditions. <![CDATA[<b>Quantifying the annual fish harvest from South Africa's largest freshwater reservoir</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100006&lng=en&nrm=iso&tlng=en South African inland fisheries are poorly developed and their contribution to near-shore communities is poorly understood. This study is the first comprehensive assessment of recreational and subsistence angling undertaken in an inland fishery in South Africa. The study was conducted on the 360 km² Lake Gariep, South Africa's largest freshwater reservoir. A total of 508 anglers were interviewed between February 2007 and January 2008. Of those interviewed, 67% were subsistence anglers and 33% recreational anglers. Catch per unit effort (CPUE) did not differ significantly between sectors. CPUE fluctuated seasonally, ranging between 0.37 (95% CI= 0.26 to 0.51) kg·angler-1·h-1 in winter and 0.88 (0.67 to 1.17) kg·angler-1·h-1 in summer. The duration of a fishing day ranged from 5.99 (5.24 to 6.74) h in mid-winter to 7.26 (6.88 to 7.63) h in early summer. Expected end-of-day catch (CPUE × fishing-trip duration) ranged from 2.2 to 6.4 kg·angler-1·d-1 depending on the season. The number of anglers ranged from 22 (8 to 53) anglers·d-1 in June/July to 74 (25 to 176) anglers·d-1 in April. Total annual catch from the roving creel survey was estimated at 71.4 (57.4 to 91.4) t·yr-1. Another 7.5 t·yr-1 were landed during recreational angling competitions. The resultant total catch divided by the lakeshore population equated to a per capita fish supply of 11.1 kg·yr-1. More than 70% of the catch was the alien invasive carp Cyprinus carpio and there was no evidence of overfishing. The fish resource of Lake Gariep is of significant recreational and subsistence value. As a result of the low fish price (ZAR5.72 ± 2.60·kg-1) subsistence fishing was considered a low-revenue activity that mainly augmented food security in lakeshore communities. The relatively high CPUE indicated that the fishery may be an important safety-net during periods when alternate sources of livelihoods are limited. Consequently, we recommend that the importance of angling to local communities needs to be taken into account when planning fisheries development and developing an inland fisheries policy. <![CDATA[<b>Generating high-resolution digital elevation models for wetland research using Google Earth<sup>TM</sup> imagery</b>: <b>an example from South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100007&lng=en&nrm=iso&tlng=en Digital elevation models (DEM) generated in geographical information systems (GIS) have proven to be useful tools in hydrological research, aiding, amongst others, the delineation of catchment areas, identification of drainage patterns and flow pathways as well as for runoff determinations. They are of particular value in areas of comparatively flat topography, where such tasks are often difficult to perform. However, owing to the fact that elevation differences in wetlands typically fall below or just into the range of contour intervals of standard topographic maps being generally 20 m, and 5m for some areas, the latter fail to give enough detail. This means that sufficiently detailed relief information is often difficult to obtain for wetland research. Site-specific, high-resolution relief surveys are too expensive, relative to many research budgets, to constitute a viable alternative. Based on an approximately 12 km² study area surrounding a karst-related peatland, this paper presents a method to retrieve the required high-resolution elevation data at 1 m intervals, at low cost, from satellite imagery in Google EarthTM. The paper describes procedures used to capture and process the data using GIS ArcDesktopTM to produce a high-resolution contour map and DEM. For quality assurance purposes the generated map is visually compared to 5 m and 20 m contour intervals of standard topographic maps (1:50000) issued by the Chief Directorate Surveys and Mapping (CDSM). After correcting an off-set of 5 m it was found that the deviation of the generated contour map based on Google data from CDSM contours was in the same order as the deviation between the 2 CDSM contour sets. Finally, all 3 contour maps were compared to a contour map of 0.5 m-interval resolution specifically generated for the study area using aerial photography from an airborne survey. This too confirmed the overall good reliability of the generated, Google EarthTM-based, contour map. Although Google EarthTM's contour models are based on data of the Shuttle Radar Topography Mission (SRTM), the direct use of freely available SRTM data for localised, high-resolution DEM yielded unsatisfactory results. This may be due to (unspecified) procedures, or unknown data sources employed by Google EarthTM that enhance the quality of relief data. With updating intervals of 2 to 4 years, satellite imagery in Google EarthTM offers the additional advantage of containing much more recent information on relevant hydrological features than the outdated topographic maps available for the study area. It is concluded that the presented method allows the generation of high-resolution DEMs especially for areas of flat topography where adequate relief information is either not available or too costly to generate. These DEMs are useful for further wetland research. <![CDATA[<b>Threats and opportunities for post-closure development in dolomitic gold mining areas of the West Rand and Far West Rand (South Africa)</b> <b>- </b><b>a hydraulic view part 1: mining legacy and future threats</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100008&lng=en&nrm=iso&tlng=en For long periods in the history of South Africa gold mining formed the backbone of an otherwise agriculturally-dominated economy, initiating rapid urbanisation in often remote and underdeveloped farming areas. This paper explores examples from a mined-out goldfield west of Johannesburg (West Rand), where consequences of mine closure can currently be observed, as well as from an active goldfield on the Far West Rand. Both areas are linked by the Wonderfonteinspruit, a stream drawing much national and international media attention for its high levels of radioactive pollution. Dating back more than 120 years, the impacts of gold mining and later uranium mining on the natural environment are profound and complex, perhaps most affecting the rich groundwater resources found in the exceptionally well-karstified dolomite that underlies most of the catchment area. Mining-related impacts such as large-scale land degradation associated with dewatering of karstic aquifers and widespread pollution of surface water and groundwater systems are discussed. Based on this, potential threats and opportunities for post-mining scenarios are identified in a series of 3 papers. Part 1 of this series outlines impacts of mining, particularly on the natural water resources, and possible consequences associated with the future re-watering of currently de-watered dolomitic compartments. The need for a regionally-integrated approach to the closure of highly interconnected mines is stressed and timelines of the closure process estimated. In Part 2 the emphasis is on identifying possible opportunities for post-mining development centred mainly around the utilisation of exceptional karst features and associated water resources. Part 3 aims to quantify uncertainties associated with planning in mining-dominated environments by comparing historical predictions with factual developments. <![CDATA[<b>Threats and opportunities for post-closure development in dolomitic gold-mining areas of the West Rand and Far West Rand (South Africa)</b> <b>- </b><b>a hydraulic view part 2: opportunities</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100009&lng=en&nrm=iso&tlng=en Largely dependent on gold mines for their economic survival, many mining towns in the Far West Rand fear the effects of the inevitable impact of mine closure, not only on the economy but also on social stability. Large-scale environmental degradation in the form of sinkholes and widespread radioactive pollution exacerbate such fears. Based on an analysis of mining impacts and potential threats for post-mining developments provided in Part I, this 2nd paper in a 3-part series aims to stimulate thought, through the discussion of potential opportunities centred on the rich water resources of the area. This is in full recognition of a subsequent need to assess the economic and technical feasibility of identified opportunities in more detail. Many opportunities are based on the concept that perceived mining liabilities may have the potential to be turned into assets. Examples include the restoration of dewatered karst aquifers and their use for storing large volumes of water, protected from evaporation losses, combined with artificial groundwater recharge and harvesting as well as underground generation of hydropower. This could well be complemented by other water-based developments such as aquaculture, agriculture and different forms of tourism relating to water, karst and mining. Possibilities for using waste land such as sinkhole areas and slimes dams include the establishment of a large game reserve on donated land as well as using tailings for biofuel production and generating solar- and wind-based electricity. Lastly, the re-establishment of a uranium-related industry is explored; this could capitalise on existing infrastructure and former expertise and benefit from the envisaged development of uranium as a strategic resource in SA. In view of the current media attention given to negative environmental and health effects, it is, however, questionable whether such development would be acceptable to local residents. <![CDATA[<b>Threats and opportunities for post-closure development in dolomitic gold mining areas of the West Rand and Far West Rand (South Africa)</b><b> - </b><b>a hydraulic view part 3: planning and uncertainty - lessons from history</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100010&lng=en&nrm=iso&tlng=en Mining is exposed to geological uncertainty as well as to economic forces beyond its control, such as commodity prices and exchange rates that govern profitability. Predictions of future scenarios in mining areas are thus inherently difficult and unreliable. This uncertainty is exacerbated by the long time periods required for pro-active planning of post-mining developments often spanning several decades. This paper presents examples from a gold mining area in the Far West Rand (South Africa) illustrating the variance between predicted scenarios and reality. The facts are embedded in a historical recount of events crucial for the design and approval of mine-closure plans, as well as post-mining development. It is argued that historical arrangements and data need to be understood and preserved in order to avoid the repetition of (costly) mistakes made in the Far West Rand. Owing to the pivotal role of water in the semi-arid area and the fact that some of the most important groundwater resources of South Africa were impacted on by deep-level mining, this paper in 3 parts adopted a largely hydraulic perspective. The loss of 'institutional memory' and local expertise has been identified as the main threat to planning. Part 3 presents an attempt to counteract such loss by providing an account of the events of 5 decades, as witnessed by the first author. <![CDATA[<b>The link between Movability Number and Incipient Motion in river sediments</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100011&lng=en&nrm=iso&tlng=en The concept of incipient motion has been of continuing interest to researchers and engineers working with sediment movement in rivers. This paper takes a new look at the use of the Movability Number for the prediction of Incipient Motion - which is here defined in terms of Intensity of Motion. A relationship between Movability Number and Intensity of Motion is developed for flow with turbulent boundaries, using data from other researchers for Particle Reynolds numbers up to nearly 12 000. This allowed for a firmer definition of Incipient Motion as well as a new bedload transportation equation. Additional laboratory experimentation for Particle Reynolds number over the range 0.12-486 facilitated the improved prediction of Incipient Motion from a plot of the critical Movability Number vs. Particle Reynolds number for a wide range of boundary conditions from laminar to turbulent. <![CDATA[<b>A falling-head procedure for the measurement of filter media sphericity</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100012&lng=en&nrm=iso&tlng=en Filter media sphericity is normally determined experimentally in a laboratory filtration column. The pressure drop is measured across a bed of known depth while the filtration rate is kept constant. The sphericity is then calculated from a theoretical headloss relationship using the Ergun equation. This paper proposes a method along similar lines, but suggests a much simpler experimental procedure. Instead of having to maintain a constant flow rate and measuring both the flow rate and the pressure, the column is filled and the water then allowed to drain through the bed. The only measurement to be taken is the time it takes for the water level to drop through a known distance, which is called a falling-head procedure. The full theoretical development of the method is provided, as well as a detailed experimental procedure. The practicality of the method is demonstrated with tests performed on a variety of filter media, and a fully-worked example is presented. <![CDATA[<b>Cr(VI) generation during sample preparation of solid samples</b>: <b>a chromite ore case study</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100013&lng=en&nrm=iso&tlng=en South Africa holds more than 70% of the world's viable chromite ore reserves and produces ~46.2% of the world's high carbon ferrochrome. It was recently reported that beneficiated South African chromite ores contained significant amounts of Cr(VI). If this is true, it could have serious consequences for South African chromite mines and the local environment. Currently none of these mines make any provision for Cr(VI) leaching from their mined ores. The data obtained in this study proved that the Cr(VI) content of chromite samples is influenced by the sample preparation technique employed prior to chemical analysis, more specifically, that pulverising of chromite samples in a normal atmospheric environment resulted in Cr(VI) formation. No Cr(VI) was liberated when pulverising was conducted in an inert atmosphere. The presence of Cr(VI) in South African chromite ores therefore seems unlikely. The results also suggest that the perceived threat of Cr(VI) contamination of groundwater and surface water, originating from chromite ore stockpiles, is improbable. <![CDATA[<b>A comparison of five extraction methods for extracellular polymeric substances (EPS) from biofilm by using three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100014&lng=en&nrm=iso&tlng=en Two physical methods (centrifugation and ultrasonication) and 3 chemical methods (extraction with EDTA, extraction with formaldehyde, and extraction with formaldehyde plus NaOH) for extraction of EPS from alga-bacteria biofilm were assessed. Pretreatment with ultrasound at low intensity doubled the EPS yield without significant modification of the composition of EPS. Extraction with EDTA or extraction with formaldehyde plus NaOH increased yield by about 1 order of magnitude compared with other methods. However, the protein and polysaccharide content in EPS prepared with EDTA or formaldehyde plus NaOH were low. Two fluorescence peaks belonging to protein-like peaks and 2 fluorescence peaks belonging to humic acid-like substances were found in 3DEEM fluorescence spectra of all the EPS samples prepared using different methods. Fulvic-like fluorescence was detected only in the EPS extracted with formaldehyde plus NaOH. Location of, and fluorescence intensity at, each peak were clearly affected by the extraction methods. Dialysis was also found to be an important factor influencing the yield, composition and fluorescence characteristics of EPS. <![CDATA[<b>Phthalate ester plasticizers in freshwater systems of Venda, South Africa and potential health effects</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100015&lng=en&nrm=iso&tlng=en Phthalate ester plasticizers were determined in rivers and dams of the Venda region, South Africa. Liquid-liquid extraction, column chromatographic clean-up and capillary gas chromatography were the methods used for the quantitative analyses. Levels of phthalates in water samples from the rivers and dams ranged from 0.16 mg/ℓ to 10.17 mg/ℓ and varied between 0.02 mg/kg and 0.89 mg/kg in sediments. Generally, the highest concentrations of phthalates were found as DBP and DEHP, which is consistent with their common use in plastic materials and other industrial chemicals. The phthalate levels found in the water samples were much higher than the criterion of 3 µg/ℓ phthalates recommended by the United States Environmental Protection Agency (USEPA) for the protection of fish and other aquatic life, and higher than the Suggested No-Adverse Effect Levels (SNAEL) of 7.5 to 38.5 µg/ℓ for drinking water. The health risk-assessment studies on the phthalates found in the water systems suggested potential carcinogenic and other toxic effects they may pose to communities downstream which might be exposed either through drinking untreated water from the rivers, through dermal absorption or by using the freshwater sources to water their vegetable gardens. DEHP posed the highest risk potential of all the phthalates and the water use or exposure pathway that appeared to pose the highest potential health risk for carcinogenic as well as toxic effects was vegetable watering. The results for phthalates in the water samples give cause for environmental concern as people's health downstream is at stake if rural populations use this water. <![CDATA[<b>Monitoring bacterial faecal contamination in waters using multiplex real-time PCR assay for <i>Bacteroides </i>spp. and faecal enterococci</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100016&lng=en&nrm=iso&tlng=en Monitoring of sanitary quality or faecal pollution in water is currently based on quantifying some bacterial indicators such as Escherichia coli and faecal enterococci. Using a multiplex real-time PCR assay for faecal enterococci and Bacteroides spp., the detection of faecal contamination in non-treated water can be done in a few hours, reducing the analysis time to 2 h. The conventional method based on cultures was compared with a multiplex assay procedure for Bacteroides spp. and faecal enterococci with an internal inhibition control. Out of 74 water samples from different sources analyzed, using both procedures, 54 were true positives and 6 true negatives, 12 samples were real-time PCR positive and culture-negative whereas 2 were real-time PCR negative and culture-positive. In conclusion, 89.2% of the samples were found to be positive with real-time PCR and 75.7% with plate cultures. Detection levels were much higher when using the multiplex real-time PCR assay, based on the higher number of positive samples in comparison with conventional microbiology. The feasibility of multiple reactions in the monitoring of faecal contamination has been demonstrated along with fast quantification of the faecal load. Such procedure can be performed in less than 3 h. This work extends the use of multiplex real-time PCR for environmental analysis, demonstrating the feasibility of these procedures in monitoring faecal pollution of water samples. <![CDATA[<b>Effect of phenolic compounds on the rapid direct enzymatic detection of β</b><b>-D-galactosidase and β</b><b>-D-glucuronidase</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100017&lng=en&nrm=iso&tlng=en β-D-Galactosidase and β-D-glucuronidase are 2 marker enzymes used in the rapid detection of total coliforms and E. coli, respectively. A range of bioprobes and biosensors have recently been developed for the rapid, direct and in situ detection of these enzymes. Chromogenic substrates are often used to assay for these enzymes and result in phenolic products being formed. However, phenolic compounds may also be present in water due to industrial activity. In this study, the effect of 11 US EPA priority pollutant phenols (PPP) on these enzyme assays were investigated and it was shown that over- and under-estimation of β-D-galactosidase and β-D-glucuronidase activities may occur due to inhibition or activation of these enzymes in the presence of these phenolic compounds. The types of inhibition as well as inhibition constant (Ki) values were established for the inhibited activities. Wastewater treatment plant and other effluents (e.g. tannery effluents) may contain these phenolic compounds at concentrations high enough to inhibit or activate the activities of the marker enzymes, therefore influencing the rapid and direct enzymatic measurement of faecal contamination using these metabolic marker enzymes. <![CDATA[<b>Organic matter and heavy metals in grey-water sludge</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100018&lng=en&nrm=iso&tlng=en Grey-water intended for non-potable reuse is being intensively studied, but little attention has been given to the associated solid fraction, the grey-water sludge. In this study grey-water sludge originating from bathroom grey-water has been screened with respect to organic matter; particles; short-chain fatty alcohols and acids; selected metals and basic parameters as well as characterization of the organic matter content by oxygen utilization rate (OUR). The grey-water sludge contains metal loads comparable to Danish sewage sludge, and it exceeds the Danish quality criteria for spreading on agricultural land for cadmium and nickel. If dewatered and managed as soil it would be classified as 'Class 3; polluted soil' with respect to cadmium, copper and nickel. The OUR results indicate that the grey-water biological sludge contains an equivalent amount of readily degradable organic matter compared to municipal activated sludge. But it contains 35% more readily, and 90% more slowly, hydrolysable organic matter than municipal sludge. <![CDATA[<b>Hierarchical clustering of RGB surface water images based on MIA-LSI approach</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100019&lng=en&nrm=iso&tlng=en Multivariate image analysis (MIA) combined with the latent semantic indexing (LSI) method was used for the retrieval of similar water-related images within a testing database of 126 RGB images. This database, compiled from digital photographs of the various water levels and similar images of surface areas and vegetation, was transferred into an image matrix, and reorganised by means of principal component analysis (PCA) based on singular value decomposition (SVD). The high dimensionality of original images given by their pixel numbers was reduced to 6 principal components. Thus characterised images were partitioned into clusters of similar images using hierarchical clustering. The best defined clusters were obtained when the Ward's method was applied. Images were partitioned into the 2 main clusters in terms of similar colours of displayed objects. Each main cluster was further partitioned into sub-clusters according to similar shapes and sizes of the objects. The clustering results were verified by the visual comparison of selected images. It was found that the MIA-LSI approach complemented with a suitable clustering method is able to recognise the similar images of surface water according to the colour and shape of floating subjects. This finding can be utilised for the automatic computer-aided visual monitoring of surface water quality by means of digital images. <![CDATA[<b>Initial testing of electrospun nanofibre filters in water filtration applications</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S1816-79502010000100020&lng=en&nrm=iso&tlng=en The aim of this study was to evaluate the use of nanofibre microfiltration membranes, spun by an innovative electrospinning technique, in water filtration applications. As such, this study bridges the gap between developments in electrospinning techniques for the production of flat-sheet membranes and the application of these membranes in water filtration. Three different applications were examined. Firstly, the use of the membrane (functionalised or non-functionalised) for the removal of pathogens was investigated. Secondly, the electrospun flat-sheet membranes were applied for wastewater treatment in a laboratory-scale submerged membrane bioreactor (MBR). In addition to these applications, physical properties such as clean water permeability (CWP) and strength were also examined. The tests showed that the electrospun membranes can be used for water filtration applications, but that further improvements are necessary before these membranes can be practically employed. In particular, the level of functionality and the properties of irreversible fouling require further research.