Scielo RSS <![CDATA[Water SA]]> vol. 38 num. 1 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>The chemical oxidation of lignin found in Sappi Saiccor dissolving pulp mill effluent</b>]]> Sappi Saiccor (situated in Durban, South Africa) dissolving pulp mill effluent, produced from an acid bisulphite pulping process, uses acacia and eucalyptus hardwoods to produce a unique and different blend of lignin that has not been previously studied. The chemical oxidation of lignin found in Sappi Saiccor's effluent has been investigated using a number of different chemical oxidising agents, such as nitrobenzene, oxygen with and without the presence of a copper sulphate pentahydrate catalyst, and hydrogen peroxide. The reaction products were extracted with acid and identified using GC-MS and LC-MS techniques. Nitrobenzene is a good oxidising agent but tends to produce many toxic by-products and would not be acceptable on an industrial scale. Oxygen oxidation has previously been shown to produce aldehyde-type compounds, and in this work has produced good yields of both vanillin and syringaldehyde compared to previous oxygen oxidation reactions. Hydrogen peroxide is a strong oxidising agent that tends to over-oxidise the lignin during long reaction times. <![CDATA[<b>Removal and transformation of hexavalent chromium in sequencing batch reactor</b>]]> The objectives of this study are to evaluate the efficiency of removal of hexavalent chromium (Cr(VI)) in a sequencing batch reactor (SBR) and to ascertain the fate of Cr(VI) in the treatment process. An SBR was operated with the FILL, REACT, SETTLE, DRAW and IDLE periods in the time ratio of 2:12:2:1.5:6.5 for a cycle time of 24 h. The study was divided into 5 phases with the addition of 0.5, 2.0, 3.0 and 5.0 mg/ℓ of Cr(VI) in Phases II, III, IV and V for a duration of 46, 75, 43 and 16 operational cycles, respectively. The Cr(VI) removal efficiencies for SBR were found to be 79.8, 88.4 and 99.8% in Phases III, IV and V, respectively. The results revealed that Cr(VI) removal efficiency improved with acclimated activated sludge. Determination of Cr in the suspended sludge showed that around 95% of the Cr species were Cr(III). Determination of Cr concentration profiles during the FILL and REACT periods showed that the predominant species was Cr(III) as Cr(VI) was bio-reduced. The proposed Cr(VI) removal mechanism involves bioreduction to Cr(III) which was subsequently precipitated and adsorbed by activated sludge. Precipitation rather than sorption is envisaged to be the main path of removal of Cr(III) from the solution. <![CDATA[<b>Diffusive gradient in thin-films (DGT) as risk assessment and management tools in the Central Witwatersrand Goldfield, South Africa</b>]]> Diffusive gradient in thin-films (DGT) technology was used to monitor bio-available metals and the tool was developed for risk-based pollution assessment and liability apportionment in the Witwatersrand Goldfields, South Africa, where there is widespread mine-related pollution. DGT technology is a passive sampling technique whereby metal species are selectively diffused from polluted water through a diffusion layer and trapped by an inner chelating resin, giving rise to time-weighted average concentrations. The results show that the concentrations of most hazardous metals recorded from grab samples are higher than values recorded from DGT samplers, resulting in inaccurate input information to risk assessors, the public and decision makers. DGT samplers deployed along upper, middle and lower reaches of Elsburgspruit, a stream southeast of Johannesburg, provided data which could assist in evaluating the source and evolution of metals along the stream length. DGT samplers deployed in 5 augers at different depths around a tailings dam showed that liming and trenching fails to contain deep seep age of trace metals. The results highlight the potential of using DGT samplers as a monitoring tool for providing accurate metal pollution information, assessing source and evolution of metals in streams or rivers for apportionment of liabilities, and evaluating the success of current contaminant containment methods. <![CDATA[<b>Application of magnesium hydroxide and barium hydroxide for the removal of metals and sulphate from mine water</b>]]> The proposed magnesium-barium-oxide process consists of metal removal with Mg(OH)2, magnesium and sulphate removal with Ba(OH)2 and calcium removal with CO2. The raw materials, Mg(OH)2 and Ba(OH)2 are recovered from the BaSO4 and Mg(OH)2 sludges that are produced. Laboratory studies showed that metals are removed to low levels. This includes iron(II), the dominant metal ion in mine water, which is first oxidised to iron(III), whereafter it precipitates as Fe(OH)3 resulting in residual levels of Fe(II) in the mine water of less than 20 mg/ℓ. Sulphate is also removed to less than 25 mg/ℓ. The final sulphate concentration is a function of the amount of Ba(OH)2 dosed, as the amount of sulphate removed is stoichiometrically equivalent to the Ba(OH)2 dosage. During CO2-dosing, CaCO3 is precipitated to the saturation level of CaCO3. <![CDATA[<b>Identification of metal-tolerant organisms isolated from the Plankenburg River, Western Cape, South Africa</b>]]> The ability of biofilms to resist pollutants makes them advantageous for use in bioremediation. The objective of this investigation was to isolate metal-tolerant micro-organisms from a site along the Plankenburg River. Microbial biofilms cultivated in multi-channelled flow cells were exposed to varying concentrations of aluminium (Al), iron (Fe), copper (Cu), manganese (Mn), nickel (Ni) and zinc (Zn), stained with the BacLightTM viability probe, visualised using epifluorescence microscopy and analysed using ScionImage. Exposure to the highest Al, Fe, Cu and Mn concentrations increased the percentages of dead cells. A difference in live and dead cells after exposure to varying Zn and Ni concentrations was not evident. When exposed to the lowest concentrations, no notable difference could be detected in comparison with the untreated control. Possible metal-tolerant micro-organisms were identified from the exposed flow cells using polymerase chain reaction (PCR) and deoxyribonucleic acid (DNA) sequencing, followed by ClustalX alignment and phylogenetic analysis. Phylogenetic analysis identified a variety of organisms, including Bacillus sp., Pseudomonas sp., Delftia tsuruhatensis strain A90, Kocuria kristinae strain 6J-5b, Comamonas testosteroni WDL7, Stenotrophomonas maltophilia strain 776, Staphylococcus sp. MOLA:313, Micrococcus sp. TPR14, Sphingomonas sp. 8b-1 and Microbacterium sp. PAO-12. Two major clusters could be distinguished based on their Gram-reactions. <![CDATA[<b>A comparative assessment of chemical contaminant removal by three household water treatment filters</b>]]> This study was aimed at modifying the design of, constructing, evaluating and comparing chemical contaminant removal efficiency by, 3 household water treatment filters. The filters were: 1) biosand filter (BSF); 2) the ceramic candle filter (CCF); 3) bucket filter (BF). The filters were evaluated for their efficiency in removal of calcium, magnesium, iron and arsenic, nitrates, phosphates, fluorides, total organic carbon and turbidity, by determining levels of these contaminants in water before and after filtration through the filters. The effects of chlorophyll a concentration (mg/m³) of intake water, as well as the effects of turbidity of intake water, on the flow rates of the filters was quantified and recommendations on the quality of water that could be filtered through these filters were made. Chlorophyll a concentrations in intake water had a positive correlation with the turbidity of the unfiltered water (r = 0.607).The flow rates of the filters were 0.8 ℓ/h - 6.48 ℓ/h (BSF), 0.05 ℓ/h - 2.495 ℓ/h (CCF) and 106.5 ℓ/h - 160.5 ℓ/h (BF). Because of the large particle size materials used in constructing the BF and the design, which caused it to be a rapid sand filter, the biosand filter (BF) was found to have flow rates significantly higher than those of BSF and CCF (p > 0.05). There was no difference in the efficiency of removal of metals (average 40% - 50%) by the filters (p > 0.05), as the same removal mechanisms (straining, ammonification, fixation and adsorption) were believed to be taking place in all of the filters. The CCF removed total organic carbon (TOC) (up to 39%) better than the BSF and BF (p < 0.05). The filters removed turbidity effectively with the BSF having the highest reduction (70%). The average turbidity reduction efficiency was in the order BSF (70%) > BF (51%) > CCF (44%). The BSF, CCF and BF reduced turbidity and other contaminants even after filtering a total cumulative volume greater than 1 000 ℓ. <![CDATA[<b>A case study to determine the efficacy of ozonation in purification processes</b>]]> The aim of this study was to determine the efficacy of ozone in water purification processes at the Midvaal Water Company, which uses the hypertrophic Middle Vaal River for source water. It was found that pre- and intermediate ozonation had no significant effect on pH, conductivity, dissolved organic carbon (DOC) and total organic carbon (TOC). Chlorophyll-a, total chlorophyll, spectral absorbance coefficient (SAC 254) and total algal cells were not influenced by pre-ozonation (as desired) but were greatly reduced after intermediate ozonation. The dissolved air flotation step which occurs after pre ozonation and prior to intermediate ozonation contributed to an average total chlorophyll removal of 74%. The effect of ozonation on the removal of manganese, iron and aluminium could not be determined during this study since these elements were present in relatively low concentrations in the source water. Intermediate ozonation had variable effects on the removal of Cyanophyceae, Dinophyceae, Euglenophyceae and Chlorophyceae, but Chrysophyceae, Bacillariophyceae and Cryptophyceae were greatly reduced after this stage. <![CDATA[<b>The hydrodynamic response of a semi-arid headwater wetland to technical rehabilitation interventions</b>]]> Loss of wetland extent continues to be documented as a significant problem and this is true for the headwaters of the Sand River system in the north-east of South Africa. Here wetlands are undergoing severe down-cutting by erosion gullies (dongas) leading to desiccation of the system and loss of viable substrate that is used for subsistence agriculture. The Manalana sub-catchment was the focus of an integrated wetland rehabilitation programme between 2004-2009, a major focus of which was the stabilisation of such erosion gullies by large retaining structures. This paper presents findings of a hydrological monitoring study of the shallow groundwaters to determine the wetland';s hydrodynamic behaviour and the extent to which this had degraded as a result of erosion. Furthermore, whether technical rehabilitation could ameliorate any degradation in the wetland';s hydrological condition was also assessed. The findings show that the wetland groundwater hydrology is strongly controlled by the distribution of clays within it, facilitating distinct hydrological micro-regions within the wetland spatially and vertically. Based on these findings it is revealed that the loss of these clays impacts severely on the system';s hydrology. The installation of an impermeable buttress weir was able to restore these hydrodynamics as observed through the reversal of the hydraulic gradients between groundwater observation stations, but the precise placement of the structure was shown to be crucial for this effect. This finding demonstrated the requirement of informed, or wise, technical rehabilitation principles based on hydro-geomorphic understanding of the system. A downstream pervious gabion dam was also monitored for its effect on restoring the wetland';s hydrology, but observed responses showed little change, and, in fact, the wetlands hydrology here remained intact, attributed to the presence of a clay plug that was saved from erosion by the placement of this structure. <![CDATA[<b>Comparison of methods for determining unsaturated hydraulic conductivity in the wet range to evaluate the sensitivity of wetting front detectors</b>]]> The design of passive lysimeters or wetting front detectors determines the tensions at which they collect a water sample from an unsaturated soil. When deployed in the field to help manage irrigation, it is necessary to know the minimum flux of water that can be sampled by a passive lysimeter and how this relates to the drainage flux at field capacity. This requires a good estimate of the unsaturated hydraulic conductivity characteristic, K (h), in the wet range (< 10 kPa). We compared various field, laboratory and theoretical approaches for obtaining the K (h) function and compared these to a reference K (h) function derived by applying inverse modelling approaches to field drainage experimental data. The Van Genuchten model and three of the pedotransfer models produced K (h) functions with a root mean square error of less than 5% compared to the reference, and appear to be simple methods of obtaining a reasonable estimate of unsaturated hydraulic conductivity. However, despite the goodness of fit, there can be a 10-fold difference in conductivity at a given tension < 10 kPa estimated from the different methods. Moreover, water content at field capacity depends entirely on whether field capacity is defined as time elapsed after saturation, a set tension or a minimum flux. <![CDATA[<b>The effect of crop residue layers on evapotranspiration, growth and yield of irrigated sugarcane</b>]]> A layer of harvest residues from the previous crop can reduce wasteful evaporation from the soil surface and thereby increase the efficiency of use of limited water resources for agricultural production. The practice of harvesting sugarcane green and leaving crop residues in the field, as opposed to burning the residue, has been re-adopted in many sugarcane industries worldwide. However, a better understanding of the dynamic impacts of residue layers on various aspects of the cropping system is required to (1) enable the formulation of sets of best management practices for specific production scenarios, and (2) promote the use of residue layers in areas where it is desirable and has not been adopted, such as irrigated sugarcane production in South Africa. The objective of this study, therefore, was to quantify the effect of 2 different types of residue layers on crop growth, cane yield and evapotranspiration of fully irrigated sugarcane. A layer of cane tops and dead leaves (Trash) and a layer of green tops (Tops) were applied to the soil surface of sugarcane crops (plant crop and first ratoon crop of variety N14) grown on lysimeters at Pongola, South Africa. Observations of crop growth (stalk population, stalk height, canopy cover), cane yield and evapotranspiration for these treatments were compared to that of a bare soil treatment. The data were also used to derive values of crop evaporation coefficients for different development phases and these were compared to FAO56 recommendations. Initial stalk population in the plant crop and radiation capture in the plant and ratoon crop were affected negatively by crop residue layers, but without significantly reducing final stalk population and cane yield. Peak stalk population occurred later in crops grown in residue layers, but peak and final stalk populations were unaffected. Evapotranspiration was reduced by both residue layers, mainly due to a slower developing canopy (reduced transpiration) and reduced evaporation from the soil, during the pre-canopy phases. Increased drainage was observed under residue layers, emphasising the importance of accurate irrigation scheduling to avoid water logging. The FAO56 methodology for calculating crop evaporation coefficient values for the initial, development and late season phases are supported by the results obtained here. Crop evaporation coefficient values were significantly reduced by residue layers. It is important that irrigation scheduling practices be adjusted to realise the potential water savings of sugarcane production systems that make use of residue layers. This study provides the information required to do that. The information could also be used to improve the ability of the crop models to accurately simulate crop growth and evapotranspiration in a residue layer cropping system. <![CDATA[<b>River water quality in the northern sugarcane-producing regions of South Africa and implications for irrigation</b>: <b>a scoping study</b>]]> Sustainable cultivation of crops under irrigation requires water of appropriate quality, especially with regards to salinity and sodicity. Agriculture can impact negatively on water quality, often through the export of nutrients (particularly nitrogen (N) and phosphorus (P)) from the root zone, resulting in eutrophication of surface water and pollution of groundwater. Sugarcane is the major irrigated crop with regards to area cultivated in the Crocodile, Komati-Lomati and Pongola River catchments. Increasing demand for and use of water resources in these catchments has led to concerns about deterioration in water quality. In this study, chemical water quality data obtained from the South African Department of Water Affairs was used to assess the quality of river water in the above catchments. Electrical conductivity (EC) data show an increase in salt concentration along the river course as a result of various anthropogenic activities in the catchment. Irrigators located further downstream will therefore generally have to pay more attention to the quality of their irrigation water and on-farm salinity management. For the lower parts of the Komati-Lomati and Pongola River catchments, hazards due to sodicity will also need attention. Interestingly, acidifying effects of mine water drainage are potentially being countered by high salt input from agricultural return flow. Nutrient enrichment was evident at many of the river sampling points. Increasing salt, sodicity, N and P over time for most of the rivers studied is also a concern that requires action to ensure the sustainability of irrigation activities in these catchments. More intensive monitoring, including measurement of organic N and P fractions, is recommended to improve understanding of the contribution of different anthropogenic activities to river water pollution and to develop effective mitigation strategies. <![CDATA[<b>Nutrient limitation of phytoplankton in five impoundments on the Manyame River, Zimbabwe</b>]]> Nutrient limitation was investigated in the Manyame lakes, namely, Harava Dam, Seke Dam, Lake Chivero, Lake Manyame and Bhiri Dam, during 2004-05. Selenestrum capricornutum was used as the test organism in one group of bioassays and the lakes' natural phytoplankton population in the other. Nitrogen was indicated to be the primary limiting nutrient in Harava Dam, Seke Dam and Lake Manyame. Phosphorus was found to be the primary limiting nutrient in Bhiri Dam while no nutrient was indicated to be limiting the growth of phytoplankton in Lake Chivero; instead, light was implicated to be limiting the growth of phytoplankton. Harava Dam and Seke Dam showed signs of enrichment, relative to 1977, attributed to sewage discharge from expanding urban settlements in Ruwa and surrounding areas. Lake Chivero has remained much the same in the last 30 years and was indicated to be acting as a nutrient trap, since the dams downstream of it were not found to be as eutrophic. Lake Manyame, Seke Dam and Harava Dam were concluded to be mesotrophic, Bhiri Dam oligotrophic and Lake Chivero eutrophic. <![CDATA[<b>Promoting uptake and use of conservation science in South Africa by government</b>]]> This paper aims to analyse how to encourage science uptake, here defined as the uptake and use of scientific research products (including journal articles, scientific reports, tools, expert knowledge, etc.), in the South African context. While science uptake into implementation is a very case- and context-specific process, the authors propose that a general framework for analysis of the policy-making context in South Africa needs to be considered when analysing how to promote science uptake in specific cases. In this paper, the National Freshwater Ecosystem Priority Areas (NFEPA) project is used as an example to illustrate how to apply this framework and how science projects in South Africa can be better positioned for impact and use. The paper starts by introducing the framework for conceptualising the complex set of dynamic processes and actors that can be involved in science uptake by government in South Africa, i.e., the policy-making context. From this theoretical platform the authors analyse to what extent the NFEPA project will be able to support more effective implementation of existing environmental and water legislation. This is done by exploring the challenges that hinder the uptake of science in government departments and then offering recommendations on how to address these. <![CDATA[<b>The role of statutory and local rules in allocating water between large- and small-scale irrigators in an African river catchment</b>]]> This paper presents a case study of large- and small-scale irrigators negotiating for access to water from Nduruma River in the Pangani River Basin, Tanzania. The paper shows that despite the existence of a formal statutory water permit system, all users need to conform to the existing local rules in order to secure access to water. The spatial geography of Nduruma is such that smallholder farmers are located upstream and downstream, while large-scale irrigators are in the midstream part of the sub-catchment. There is not enough water in the river to satisfy all demands. The majority of the smallholder farmers currently access water under local arrangements, but large-scale irrigators have obtained state-issued water use permits. To access water the estates adopt a variety of strategies: they try to claim water access by adhering to state water law; they engage with the downstream smallholder farmers and negotiate rotational allocation; and/or they band with downstream farmers to secure more water from upstream farmers. Estates that were successful in securing their water access were those that engaged with the local system and negotiated a fair rotational water-sharing arrangement. By adopting this strategy, the estates not only avoid conflict with the poor downstream farmers but also gain social reputation, increasing chances of cooperative behaviours from the farmers towards their hydraulic infrastructure investments. Cooperative behaviours by the estates may also be due to their dependence on local labour. We further find diverging perspectives on the implementation of the state water use permits - not only between the local and state forms of water governance, but also between the differing administrative levels of government. The local governments are more likely to spend their limited resources on 'keeping the peace'; rather than on enforcing the water law. At the larger catchment scale, however, the anonymity between users makes it more difficult to initiate and maintain cooperative arrangements. <![CDATA[<b>The extent of on-site leakage in selected suburbs of Johannesburg</b>]]> This study investigated on-site leakage on 182 properties with relatively new municipal water meters in well-established suburbs of Johannesburg. A methodology was developed to estimate the on-site leakage rate from readings taken from these municipal water meters, which was then adjusted to account for metering errors. The results were analysed in 2 categories: 'Residential'; properties, which consisted of single houses on individual stands, and 'Other'; properties, which consisted of non-residential users and blocks of flats. A high incidence, 64%, of measurable on-site leakage was found. The average on-site leakage rates on 'Residential'; and 'Other'; properties were found to be 12 and 29 kℓ/month per property, respectively. In both cases, this represented 25% of measured consumption. Apparent losses due to on-site leakage were determined to be 10% of the on-site leakage, or 3% of total consumption. <![CDATA[<b>Swimming pools and intra-city climates</b>: <b>influences on residential water consumption in Cape Town</b>]]> Water demand management can be effective as a resource management approach if demand estimation is accurate and consumption determinants are defined. While determinants such as household income, regional climate, water price, property size and household occupancy have been comprehensively studied and modelled, other determinants such as swimming pools and intra-city climates have not. This study examines residential water consumption in the City of Cape Town in 2008/2009, under property size regimes, to separately determine whether the presence of pools or occurrence of different intra-city precipitation patterns have an influence on water consumption. A sample of 14 233 properties is analysed, with 20.86% having swimming pools within their boundaries. Overall, those properties with swimming pools used 37.36% or 8.85 kℓ per month more water than those without, with pools having a larger influence on household consumption on smaller properties. These results were statistically significant. Different precipitation patterns occurred over the study period, and while there were indications that consumption may be lower if there is more rainfall, limited evidence was found to support the hypothesis. <![CDATA[<b>Effects of free-surface on design charts for open channels</b>]]> Normal depth is an important parameter for the design of channels and canals. For rectangular, trapezoidal, and circular channel sections it is possible to express normal depth by a trial-and-error procedure or analytically. However, the effects of free-surface on the design charts for determination of the normal depth are not investigated. In this paper, graphical solutions of normal depth for the rectangular, trapezoidal, and circular cross-sections have been obtained in the non-dimensional form. To evaluate the resistance effects of the free-surface in the calculation of the normal depth, the dimensionless-form of Manning';s equation with free-surface weight factor is introduced herein. The design charts reported previously were modified. <![CDATA[<b>On modifying the Arrhenius equation to compensate for temperature changes for reactions within biological systems</b>]]> In this communiqué, we discuss the use of the Arrhenius relationship to describe the temperature dependence of reacting biological systems, such as those treating wastewater. We also discuss the use of the modified Arrhenius function, and those instances where its applicability is limited. We show that the error when using the modified relationship is 7% at 30ºC, 15% at 40ºC and 25% at 50ºC. We conclude that whilst the modified relationship is acceptable at lower temperatures, in those applications where higher temperatures are reached (above 25ºC) the error with using the relationship may not be acceptable. We present an Arrhenius equation for use in biological systems, which is applicable for all temperature ranges.