Scielo RSS <![CDATA[Water SA]]> vol. 41 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Impacts of fish on phosphorus budget dynamics of some SA reservoirs: Evaluating prospects of 'bottom up' phosphorus reduction in eutrophic systems through fish removal (biomanipulation)</b>]]> Data on fish standing stocks in 7 South African reservoirs were used to assess prospects of reducing in-lake amounts of total phosphorus (TP) through remedial biomanipulation - the removal of fish to deplete internal stocks of biomass-incorporated TP and especially to restrict enhancement of TP availability through internal 'bottom up' recycling by fish. Literature-derived conversion functions were used to estimate the quantity of TP stored in fish biomass, recycled by fish through excretion, and released from bottom sediments through carp and catfish bioturbation. This provided a quasi mass-balance assessment of these contributory influences of fish on TP budgets of reservoirs ranging from mesotrophy to hypertrophy in trophic status (annual mean TP levels of 0.04-0.51 mg/l). Absolute contributions of fish were inevitably related directly to reservoir-specific fish stock abundance, both total-fish and coarse-fish biomass levels which increased with trophic status, generating parallel absolute increases in TP sinks and internal TP loading fluxes. On overall average, total fish stock sequestered 2.2 kg TP/ha in biomass, recycled 13.8 kg TP/ha/yr through excretion, and mobilized 8.0 kg TP/ha/yr through sediment bioturbation. Average values relative to external loadings in 5 reservoirs amounted to 3.8% (biomass), 22.8% (excretion) and 11.8% (bioturbation), totalling 38.4%. Most pertinently, the relative importance of fish in reservoir TP budgets declined progressively with rising trophic status, with corresponding averages less than half (1.4, 8.7 and 5.4%, total = 15.4%) in 3 hypertrophic reservoirs (> 0.10 mg TP/ℓ). While total fish eradication plausibly reduces average internal phosphorus by some 40% relative to external load, the corresponding average reduction in hypertrophic reservoirs in greatest need of nutrient reduction is far less (~ 15%). 'Bottom-up' bioremediation accordingly offers little help in the management of nutrient-enriched reservoirs, and is essentially futile where high external nutrient loading persists. <![CDATA[<b>Removal of hard COD, nitrogenous compounds and phenols from a high-strength coal gasification wastewater stream</b>]]> The objective of this study was to identify the factors affecting the suspended and fixed biomass in the removal of hard COD, nitrogenous compounds and phenols from a coal gasification wastewater (CGWW) stream using a hybrid fixed-film bioreactor (H-FFBR) process under real-time plant operational conditions and actual wastewater composition. The composition of the influent and effluent was studied to determine which compounds were not removed by hydrolysis (bacterial activity) and how this correlated to the suspended and fixed biomass activity, COD and phenol removal. A H-FFBR with 12 gm-3 attached biomass and 440 mg-ℓ¹ suspended biomass achieved 78% phenol removal and 49% COD removal but insignificant removal of nitrogenous compounds. During the operation period, fixed biomass concentration was higher than the suspended biomass. Parameters such as pH, phenols, alkalinity, metal ions, conductivity, total dissolved solids and aeration rate affected the fixed biofilm properties such as adhesion, thickness and structure. It can be concluded that the composition of the effluent had a direct effect on the fixed biomass properties and thus a direct effect on the removal of phenols, COD and nitrogenous compounds in the wastewater. <![CDATA[<b>Fouling mechanism and cleanability of ultrafiltration membranes modified with polydopamine-graft-PEG</b>]]> Membrane surface modification via grafting poly(ethylene glycol) (PEG) onto the coated polydopamine (PD) layer is an attractive strategy because it can improve the hydrophilicity of the membrane surface. Sodium alginate (SA), bovine serum albumin (BSA), and humic acid (HA) were used as model foulants to investigate the fouling mechanism and cleanability of modified membranes. The modification narrowed or blocked the membrane pores, which led to a reduction in the permeability of ultrafiltration membranes. A Hermia model was used to explore the fouling mechanism of the modified membranes. PD-g-PEG modified membranes exhibit a lower adsorption for the model foulants and a better cleanability than the unmodified membranes. <![CDATA[<b>Removal of nutrient and heavy metal loads from sewage effluent using vetiver grass, <i>Chrysopogon zizanioides </i>(L.) Roberty</b>]]> Urban cities in many developing nations face the challenge of relieving the pressure exerted on overloaded sewage treatment works. Apart from limited financial capacity, complementary treatment methods like phyto-extraction of pollutants from the effluent have not been fully exploited, particularly in southern Africa. A study was conducted in Harare, Zimbabwe, to assess the potential of vetiver grass, Chrysopogon zizanioides, in removing N, P, Zn, Mn and Ni loads in sewage effluent from primary clarification, under hydroponic conditions. Vetiver grass was grown from tillers on floating trays suspended in effluent, and the total concentrations of selected parameters were monitored in both effluent and vetiver grass at 0, 7, 14 and 21 days of retention in effluent. Higher pollutant reduction (62-100%) in effluent, with respect to all parameters, under vetiver grass compared to no vetiver treatment (9-27%), was recorded by Day 21. Effluent pH remained stable at 7.44-7.64. Smaller changes were found for N (9.8 from 27.5 mg.ℓ-1) and P (2.0 from 5.3 mg.ℓ-1) than for the heavy metals. Vetiver grass dry biomass accumulated at 3.8-4.7 g-tiller-1-week-1, while heavy metal extraction (up to 6.2 mg Zn, 3.3 mg Mn and 0.06 mg Ni tiller-1) by root uptake increased with time at an exponential rate (R², 0.73-0.83). The study established that, while root uptake was a significant feature of the clean-up process, the corresponding high reduction of heavy metals in effluent suggests multiple removal mechanisms, including bio-sorption by microorganisms producing an immobilised microbial biomass on the container wall. A deliberate lowering of effluent pH may increase root uptake thereby possibly reducing the clean-up time and improving effluent quality. There is potential for application of this technology in cities struggling with the cost of conventional sewage treatment. <![CDATA[<b>Incorporating seepage losses into a 1D unsteady model of floods in an ephemeral stream</b>]]> Zangemar River is an ephemeral river located in the northwestern part of Iran. Maku and Poldasht are hydrometric stations located upstream and downstream of Zangemar River, respectively. The measured flood hydrograph indicates that the output hydrograph volume from Poldasht station is significantly less than the input hydrograph for Maku station, though there are no lateral outflow branches and the amount of evaporation and direct removal from the river reach during flood events is negligible. These transmission losses can be caused by infiltration into the streambed and floodplain. Due to transmission losses and lack of initial flow, flood routing in these rivers is impossible to achieve through conventional methods and it is essential to develop new flood routing methods. Therefore, in this study a computer model for natural river cross-sections has been developed in which partial differential equations of non-uniform unsteady flow (Saint-Venant equations) are solved by finite difference methods. These equations have been developed by adding Muskat's equation in such a way that seepage losses can be calculated simultaneously. The results showed that with consideration of seepage losses the developed model can predict the output hydrograph with good accuracy, compared to the field data. The results of flood routing for 13 input hydrographs showed that the seepage loss volume in the river reach is about 74% of the input hydrograph volume, on average. The model predicts seepage losses with a mean error of about 9.93% and the maximum error is less than 20%. <![CDATA[<b>Water use characteristics of a bambara groundnut <i>(Vigna subterranea </i>L. Verdc) landrace during seedling establishment</b>]]> Bambara groundnut is slow to establish and this has negative implications for total water use. Consideration of bambara groundnut as a water-efficient crop for dry areas will benefit from an understanding of water use efficiency and water use characteristics during establishment. We investigated whether there is an association between seed-coat colour of bambara groundnut seeds and water use efficiency. A secondary objective was to determine physiological and metabolic responses of bambara groundnut to terminal water stress during seedling establishment. Bambara groundnut seedlings showed reduced seedling canopy growth, increased root length and root: shoot ratio, as well as increased total soluble sugars and tissue water potential with decreasing water availability - traits associated with drought avoidance mechanisms. Consequently, seedling water use efficiency improved with decreasing water availability. Acclimation to water stress was observed under terminal stress; previously stressed seedlings responded better than previously non-stressed seedlings. Dark-coloured seeds had higher levels of phenolics which may have led to their enhanced performance during seedling emergence as well as improved drought tolerance and seedling WUE. <![CDATA[<b>Optimal design of trapezoidal lined channel with least cost: Semi-theoretical approach powered by genetic programming</b>]]> In this paper the effects of the aspect ratio (width to depth ratio, b/d) on the cost of a trapezoidal concrete-lined channel (either power channel or irrigation channel) are analysed. The recommended b/d ratios given in the literature and their limitations are also discussed. Efforts are made to derive an equation for determining the optimal depth of the water from known parameters such as discharge, velocity and bed slope for concrete-lined channels. An equation for finding the minimum possible discharge within a specific velocity and bed slope is developed based on a semi-theoretical approach. The same approach is followed to obtain another formula for finding the maximum possible velocity for a specific discharge and bed slope. The obtained equations eliminate the iteration process commonly involved in finding the dimensions of a trapezoidal channel. A relation is developed for finding the aspect ratio in response to a given discharge and bed slope by using linear genetic programming techniques. The results show that the proposed model can be successfully applied in the design of lined channels as an alternative to existing methods. <![CDATA[<b>Establishing a conversion factor between electrical conductivity and total dissolved solids in South African mine waters</b>]]> Total dissolved solids (TDS, in mg/ℓ) can be estimated from measurements of electrical conductivity at 25°C (EC, in μS/cm) by applying a conversion factor f. This factor is commonly reported to range from 0.54 to 1.1. For 45 South African mine-water samples, factors between 0.25 and 1.34, with a median of 0.85, were determined. The samples cover an EC-range of 70- 16 000 μS/cm and TDS of 50-14 000 mg/ℓ. Linear regression for the entire dataset yields a conversion factor of 0.88 but for samples with EC < 5 000 μS/cm, a conversion factor of 0.97 is recommended. However, both of these factors allow only estimates of TDS and for accurate TDS values it is necessary to determine the conversion factor specifically for each site. Besides spatial variations, temporal variations of conversion factors were also observed. <![CDATA[<b>A scoping study on the prevalence of <i>Escherichia coli </i>and <i>Enterococcus </i>species in harvested rainwater stored in tanks</b>]]> Rainwater harvesting (RWH) is a relatively inexpensive technology that has the potential to provide safe water in communities where conventional technologies are difficult to implement. In this study, the microbiological quality of rainwater harvested from rooftops and ground-surface runoff was evaluated based on the concentrations of Escherichia coli, total coliforms and enterococci. Samples were collected from 15 roof-harvested rainwater (RHRW) tanks, 4 ground-surface runoff rainwater harvesting (GRWH) tanks, 3 rivers and 1 spring water source in the Eastern Cape Province of South Africa, and 14 RHRW tanks in Gauteng Province. In the Eastern Cape Province E. coli and enterococci were detected in 7 and 4 of the 15 RHRW tanks, respectively. Enterococci were detected only from one river whereas E. coli was detected in all three rivers; in spring water neither enterococci nor E. coli were detected. Samples from GRWH tanks were positive for E. coli and enterococci in 2 and 3 of the 4 tanks, respectively. In Gauteng Province, E. coli, coliforms and enterococci were detected from 6, 6 and 9 of the 14 rainwater tanks, respectively. On average, E. coli and enterococci were detected in 44.8% of the RHRW tanks, although enterococci concentrations were several times higher than those for E. coli. We further evaluated the significance of urban pigeons as the likely sources of contamination by isolating 156 enterococci from 30 pigeon faecal samples and 208 enterococci from RHRW samples collected from Gauteng Province. Matrix-assisted laser desorption ionisation identification of the various enterococci revealed 4 species - E. faecalis (20.5%), E. mundtii (20.51%), E. faecium (23.1%) and E. casseliflavus (17.3%) - to be dominant in faecal samples, whereas E. casseliflavus (34.6%) and E. mundtii (33.2%) were dominant in RHRW. <![CDATA[<b>An investigation of the effect of pit latrine additives on VIP latrine sludge content under laboratory and field trials</b>]]> Sludge content in VIP latrines is degraded mainly under anaerobic conditions and the process is relatively slow. At varying stages of digestion within pit latrines, sludge accumulates and odour and fly nuisance may occur which could pose risks to public health and the environment. Management of accumulated sludge in pit latrines has been a major problem facing a number of municipalities in South Africa and is also a global issue. Manufacturers of various commercial pit latrine additives claim that by addition of this product to pit content, accumulation rate and pit content volume can be reduced, thereby preventing the pit from ever reaching capacity. This paper presents a comprehensive study conducted to determine the effects of additives on pit contents under laboratory and field conditions. By conducting both laboratory and field trials, it was possible to identify whether there is any acceleration of mass or volume stabilisation as a result of additive addition, and whether any apparent effect is a result of biodegradation or of compaction. The results indicated that neither laboratory trials nor field trials provided any evidence that the use of pit additives has any beneficial effect on pit contents. The reasons why additives seem to not have any beneficial effects are also discussed. <![CDATA[<b>A demand-based management option to address boat congestion at the Sundays River Estuary, Eastern Cape, South Africa</b>]]> The Sundays River Estuary situated in the Eastern Cape is an example of a South African Estuary experiencing congestion externalities, mainly vis-à-vis motorised boat use. This paper employs a choice model to estimate people's preferences for less boat congestion on the Sundays River Estuary. The results show that visitors to the estuary are willing to trade off a levy of ZAR 35/a (in addition to what they already pay) for a reduction of boat congestion during peak periods (only). This paper proposes that this amount be set as a user charge to manage excess recreational boat use. <![CDATA[<b>Application of hydropedological insights in hydrological modelling of the Stevenson-Hamilton Research Supersite, Kruger National Park, South Africa</b>]]> Soil information is increasingly sought after for hydrological modelling, as the importance of soil in the hydrological cycle is understood better. In this paper the output of a digital soil mapping exercise was used as the soil input into a distributed hydrological model (ACRU) for a test site within the Stevenson-Hamilton Research Supersite, Kruger National Park (South Africa). The aim was to determine the effect of parameterising a hydrological model with increased levels of soil information, at different scales. To accommodate this aim, ACRU was run in 3 different modes, each with increasing levels of input, on 3 catchments, including a 1st, 2nd and 3rd order catchment. The outputs evaluated included both streamflow and soil water content at selected soil profiles. Simulation accuracy increased with higher levels of soil input, as well as with increasing catchment size. The improved accuracy with increased soil input underscores the value of detailed soil information in modelling, while the improved results with increased catchment size show that the optimal scale for including soil information has not yet been reached. <![CDATA[<b>Chemical and thermal properties of VIP latrine sludge</b>]]> This study investigated the chemical and thermal properties of faecal sludge from 10 dry VIP latrines in Bester's Camp in the eThekwini Municipality, Durban, South Africa. Faecal sludge samples were selected at different depths and from the front and back sections of 10 VIP latrines during a manual emptying process. The samples were analysed for: moisture content; volatile solids; chemical oxygen demand; ammonia; total Kjeldahl nitrogen; pH; orthophosphate; thermal conductivity; calorific value and heat capacity. These properties will facilitate the design of faecal sludge emptying and treatment equipment. A manual sorting of the pit contents was carried out to determine the categories and amounts of household waste present. There was a significant difference in the moisture, volatile solids, chemical oxygen demand, ammonia, total Kjeldahl nitrogen and orthophosphate content of the faecal sludge between the front and back sections of the pit. There was minimal change in the thermal properties within the pit. The median values through the pit of each property analysed were: moisture content - 0.81 g water/g wet mass; volatile solids - 1.5 g VS/g ash; COD - 1.7 g COD/g ash; ammonia nitrogen - 10 mg NH3-N/g dry mass; TKN - 39 mg N/g dry mass; pH - 8.03; orthophosphate - 0.06 mg PO4/g dry mass; thermal conductivity - 0.55 W/m K; calorific value - 14 kJ/g dry mass; heat capacity - 2.4x10³ kJ/kg K. On average, 87% of pit content is faecal sludge; the remainder consists of wastes such as paper, plastics and textiles. <![CDATA[<b>Assessing the relationship between youth capabilities and food security: A case study of a rainwater harvesting project in South Africa</b>]]> Rainwater harvesting presents a viable option for securing water availability in order to increase food production. The study focuses on rural youth in Luphisi and Dwaleni villages in the Mpumalanga Province and considers the relationship between youth capabilities and food security. The study uses qualitative data collected from focus group discussions and quantitative data from a baseline survey within the context of an integrated rainwater harvesting project. The indicators tapped into attributes related to trust, social cohesion, inclusion and sociability, and examined these within the context of the 'capability approach', to consider whether and in what ways these attributes can be linked to food security. Results show that youth have high levels of certain capabilities such as trust, social cohesion and inclusion, co-operation, self-esteem, and meaning. However, in other dimensions there are fewer opportunities, like access to networks, access to knowledge and information and sociability, which are lacking among youth and restrict opportunities for them to engage with issues around food and water security. The Chi-square test was used to investigate the relationship between youth capabilities and food security and at p<0.05 results showed that there was no relationship between youth capabilities and food security in Dwaleni. There were however three capabilities showing significant statistical relationships between youth capabilities and food security in Luphisi: collective action and co-operation, social cohesion and self-esteem. We argue that there are opportunities to build on existing capabilities and that, overall, the potential of youth for engaging in water resources management is not being tapped into. <![CDATA[<b>A stable isotopic study of the diet of <i>Potamonautes sidneyi </i>(Brachyura: Potamonautidae) in two coastal lakes of the iSimangaliso Wetland Park, South Africa</b>]]> Potamonautes sidneyi Rathbun 1904, is a dominant freshwater crab in KwaZulu-Natal, South Africa. Recent flood events in the iSimangaliso Wetland Park have allowed a substantial range expansion of this species, including previously hypersaline and desiccated areas. A stable isotope study was conducted to examine the feeding habits of the populations from Lake Sibaya and Mpophomeni Stream, two contrasting sites in the iSimangaliso Wetland Park. Juveniles from Mpophomeni Stream were more depleted in δ13C and more enriched in δ15N compared to adults, indicating a more carnivorous diet and higher trophic position. A general shift in diet was observed at both sites, with consumption of aquatic invertebrates and sedimentary organic matter more prevalent in the wet summer months, while greater proportions of detritus and microphytobenthos were consumed in autumn/winter. No significant difference was observed between adults from the two sites despite the abiotic variations. The species appears to play a complex role in the trophic web, by acting as an intermediate consumer facilitating the flow of nutrients across levels and by breaking down decomposing organic matter, allowing for rapid recycling of nutrients within its ecosystem. <![CDATA[<b>Distribution of polychlorinated biphenyl residues in several tissues of fish from the North End Lake, Port Elizabeth, South Africa</b>]]> The concentrations and distribution of 6 PCB indicator congeners (IUPAC nos. 28, 52, 101, 138, 153, and 180) were measured in 236 organ samples of fish (Cyprinus carpio and Oreochromis mossambicus) from the North End Lake in Port Elizabeth, South Africa. Polychlorinated biphenyls (PCBs) were extracted from the fish muscles, gills, gonads and livers using USEPA method 8082, followed by a clean-up using concentrated sulphuric acid and florisil column chromatography. Analysis was achieved by gas chromatography-mass spectrometry (GC/MS) using the internal standard method. The concentrations of total PCBs in the liver, gonads, gills and muscle were 95.69, 57.49, 44.63, 34.14 ng-g-1 lipid weight (lw) in C. carpio and 119.73, 59.21, 49.78, 34.63 ng-g-1 (lw) in O. mossambicus, respectively. These values were relatively low compared to those reported in the literature. PCB levels were predictably highest in the lipid-rich livers. Individual congeners were not distributed homogeneously within the investigated organs. PCBs 153 and 138 were present at higher concentrations than other PCB congeners for both species. PCB contaminants in fish act as indicators of pollution in aquatic ecosystems and are a potential threat to human health when consumed. <![CDATA[<b>Water footprint of growing vegetables in selected smallholder irrigation schemes in South Africa</b>]]> Crop water footprint (WF) is the volume of fresh water used to produce a certain crop in all the steps in the production line. The CROPWAT model was used to calculate crop evapotranspiration, differentiating green and blue water in Zanyokwe (ZIS), Thabina (TIS) and Tugela Ferry (TFIS) Irrigation Schemes. Green beans had the highest water footprint in all three irrigation schemes with 3 535.7 m³/t in TIS, 2 753 m³/t in TFIS and 2 407.6 m³/t in ZIS. Cabbage had the lowest water footprint. The highest water footprint for growing cabbage was 254.5 m³/t in TFIS, followed by 223.1 m³/t in TIS, and the lowest was 217.8 m³/t in ZIS. Green WF represented the highest percentage of water use at ZIS (50.5%), followed by blue water at 26.5% while grey water constituted 22.9%. At TFIS blue, green and grey water use was 23.1%, 56.7% and 20.2%, respectively. The differences observed in the WF of different crops and different schemes were attributed to the differences in weather and environmental characteristics. Green beans had the highest grey water footprint, i.e., 373 m³/t and the lowest was cabbage with 37 m³/t. Potato, spinach and tomatoes had footprints of 156 m³/t, 214 m³/t and 132 m³/t, respectively. For future research it is necessary to consider the possibility and trade-offs of shifting production of each crop to the places where it is most efficient, and to focus on blue water scarcity in each of the case study locations <![CDATA[<b>Recent developments in biological nutrient removal</b>]]> Biological nitrogen (N) and phosphorus (P) removal from municipal wastewater with the activated sludge (AS) system has been the preferred technology for the last 40 years. While several questions remain to be answered for more consistent, reliable and stable performance for enhanced biological P removal (EBPR), recent developments in this technology have focused on (i) increasing capacity and reducing the plant space footprint and (ii) improving N removal. To increase capacity and reduce AS system space, (a) integrated fixed-film activated sludge (IFAS), (b) external nitrification, (c) membrane, (d) aerobic granulation BNR systems and (e) more efficient N removal bioprocesses (anammox and nitrite shunt) have been developed. With IFAS, fixed media are added to the aerobic activated sludge reactor to make nitrification independent of the suspended AS sludge age. With external nitrification, nitrification is achieved in a side-stream fixed media reactor, which removes the size-defining nitrification process from the suspended AS system and halves its sludge age, improves sludge settleability and increases capacity. With membranes, secondary settling tanks are replaced with in-reactor membranes for solid-liquid separation. With aerobic granulation, the activated sludge process is controlled to form fast-settling granules comprising heterotrophs, nitrifiers, denitrifiers and phosphorus-accumulating organisms (PAOs) in a sequencing batch (SBR) type reactor - the granules not only settle fast but the SBR-type operation also removes the need for secondary settling tanks allowing higher reactor solids concentrations and hence smaller reactors. To achieve N removal more efficiently, methods are being developed to (i) short-circuit nitrification-denitrification (ND) by preventing nitrate formation and enforcing ND over nitrite - this requires less oxygen and organics than ND over nitrate allowing lower N concentrations to be achieved for the same influent organics concentration and oxygen supply, and (ii) encouraging the growth of anammox bacteria in the activated sludge which remove N autotrophically by combining ammonia and nitrite to form nitrogen gas - this halves oxygen demand for nitrification and requires no organics. These recent developments in BNR technology are briefly reviewed in this paper.