African Journals Online
WaterSA

Volume 28, Issue 4, 2002
ABSTRACTS

Fog-water harvesting along the West Coast of South Africa: a feasibility study

Olivier, J.

Abstract: Many parts of the West Coast of South Africa experience severe water shortages throughout the year. Despite the meager rainfall, however, the region is subject to a high incidence of fog which might provide water for water-poor communities. This paper investigates the fog water potential of the area. Since fog water collection rates are to some extent dependent upon the spatial and temporal characteristics of fog, these aspects were investigated. Pilot fog collectors were erected at six West Coast sites and the water collection rates measured over a three to four year period. It was found that the incidence of fog is mostly confined to the coastal zone below the 200 m contour line with fog frequency decreasing with latitude within this zone. The highest water collection rates were recorded at Cape Columbine where volumes in excess of 2.5 l/m2 of collecting surface can be expected to be collected per day. Of this, approximately 90% is due to fog deposition alone, while rainfall contributes to the remaining 10%. The quality of the water is good and fit for human consumption.

January and July climate simulations over the SADC region using the limited-area model DARLAM

Engelbrecht, F.A.; Rautenbach, C.J. deW.; McGregor, J.L.; Katzfey, J.J.

Abstract: High-resolution climate simulations of near-surface variables are presented for January and July over the Southern African Developing Countries (SADC) region using the CSIRO Division of Atmospheric Research Limited-Area Model (DARLAM) nested within a General Circulation Model (GCM). The model domain includes tropical (north and south of the equator) and subtropical (Southern Africa) regions. Objective measures of skill are used to assess the quality of model simulations, and the performance of the model is verified over various subregions of the model domain. South of the tropics, DARLAM fields are not only superior to those produced by the GCM, but also compare well with mesoscale observations. This is particularly true for the spatial distribution of rainfall and screen temperature simulations. DARLAM, however, severely over-estimates rainfall totals over regions of steep orography.

A hydrogeomorphological approach to quantification of groundwater discharge to streams in South Africa

Xu, Y.; Titus, R.; Holness, S.D.; Zhang, J.; Van Tonder, G.J.

Abstract: In South Africa, the flow requirements for maintaining the normal functioning of aquatic ecosystems is termed the "ecological reserve", and these should be determined when a licence application for water allocation is processed. Determination of the ecological reserve entails investigation of the relationship between the major interactive components of the hydrologic cycle, namely groundwater and surface water bodies including rivers, lakes and estuaries. Information on groundwater discharge towards surface water bodies is critical for the water resource manager to make a decision regarding the amount of groundwater allocation that can be licensed without causing a negative impact on aquatic ecosystems. Existing techniques of hydrograph-separation are too subjective either due to the fact that assumptions of the techniques cannot be met in reality or that the parameters used in models do not have physical meanings. This paper presents a geomorphologic framework under which the quantification of groundwater from a hydrograph is discussed. A focus is placed on hydrogeomorphological typing that can be used to guide a process of separating groundwater discharge time series from hydrographs where a monthly groundwater discharge time series is required for comparison with instream flow requirements. For generating monthly groundwater discharge time series, a generic procedure is proposed, which is applied in a case study.

Measuring evaporation from soil surfaces for environmental and geotechnical purposes

Blight, G.E.

Abstract: There are many reasons for the need to assess rates and quantities of evaporation or evapotranspiration from natural soil surfaces, the surfaces of deposits of mine or industrial waste, or soil-covered waste surfaces. These include assessing water balances for nearsurface soil strata, landfills, tailings dams and waste dumps and suitable deposition or application intervals for hydraulic fill tailings dams, or for the disposal of liquid wastes on land. The surface energy balance is probably the most widely used method for assessing evaporation, although other methods are also available. The surface energy balance method is studied in this paper. The surface energy balance is by no means a new method (it was proposed by Bowen in 1926), but appears to be almost unknown to civil engineers, and in particular to those engaged in geotechnical engineering or waste management. The aim of this paper is to draw attention to this useful technique and to show how it can be applied in many aspects of environmental geotechnics and waste management. The paper describes the measurements made to assess the surface energy balance as well as its analysis, and presents the results of typical measurements. It also presents numerical values of the parameters and constants needed for the analysis. The experimental difficulties of the analysis are described and examined, and the method's accuracy is assessed by means of laboratory and field measurements. The paper is intended to be both informative and a practical guide to measuring evaporation in the field.

Spectrophotometric determination of pK_a values for fluorescein using activity coefficient corrections

Smith, S.A.; Pretorius, W.A.

Abstract: The absorbance of the organic water tracer compound fluorescein is known to be pH dependent but differences between the reported PK_a values make it difficult to predict these absorbance changes. A new pK_a determination method, which incorporated activity corrections, was used to calculate the pK_a values of fluorescein. Several published pK_a values were re-evaluated and were in agreement once activity corrections were applied.

The conservative behaviour of fluorescein

Smith, S.A.; Pretorius, W.A.

Abstract: Failure to account for fluorescein absorbance changes with pH may be responsible for some of the apparent non-conservative behaviour of this easily detectable tracer compound. While it is possible to calculate an accurate absorptivity value for fluorescein at every pH, this calculation is not necessary if the sample pH is increased above pH 9 before measuring the absorbance. Intense sunlight degrades fluorescein quickly but even hot samples are stable if kept in the dark.

Analysis of the structural diversity of the microbial community in a paper-mill water system

Van der Merwe, Thea; Riedel, Karl-Heinz; Wolfaardt, Francois

Abstract: Microbial populations in paper-mill water systems are usually enumerated using microbiological techniques such as plate counts and the most probable number technique. These conventional methods can only quantify a limited percentage of the microbial populations and the microbial numbers are, therefore, generally underestimated. One possible alternative to these methods involves the analysis of signature lipid biomarkers to study the structural diversity of microbial populations. The aim of this study was, therefore, to evaluate the applicability of signature lipid biomarker analysis in a paper-mill water system. Samples from the sessile and planktonic phases were collected over a period of one year at the Sappi Cape Kraft paper-mill. The samples were subjected to analysis of signature lipid biomarkers as well as conventional culturing. Analysis of the phospholipid fatty acids revealed the presence of a large diversity of micro-organisms. The same trends in the number of cultured cells and the counts obtained with signature lipid biomarker analysis were observed, although the numbers obtained with signature lipid biomarker analysis were at least 1 000 times higher. Profiles of signature lipid biomarkers reflected changes in production and water management practices, which could not be detected with culturing techniques. The analysis of signature lipid biomarkers provided more information for the characterisation of microbial communities in paper-mill water systems and has potential for application in other industrial water systems.

Commercial production of crops irrigated with gypsiferous mine water

Jovanovic, N.Z.; Annandale, J.G.; Claassens, A.S.; Lorentz, S.A.; Tanner, P.D.; Aken, M.E.; Hodgson, F.D.I.

Abstract: The use of gypsiferous mine water for irrigation of agricultural crops is a promising technology that could add value through agricultural production and utilise mine effluent. Crop response to irrigation with gypsiferous mine water, as well as the impact on soil and groundwater resources were investigated in a three-year field trial set up at Kleinkopje Colliery (Witbank, Mpumalanga Province, South Africa). Sugar-beans, maize and wheat were irrigated with four centre pivots on virgin and rehabilitated land, under three irrigation management regimes using two qualities of mine water. Good crop yields were obtained compared to dry-land cropping. Waterlogging in certain areas of the fields indicated that especially rehabilitated land should be properly prepared and, where necessary, waterways built to prevent yield reduction. Soil salinity increased over the duration of the trial due to high concentrations of Ca²⁺, SO₄^2- and Mg²⁺ in the irrigation water, but this never reached levels critical to yields of most crops. Exchangeable Ca²⁺ and Mg²⁺ in the soil increased with time, whilst K⁺ decreased. Plant analyses indicated possible nutrient deficiencies, which should be easily managed through corrective fertilisation. The groundwater impact was limited based on borehole measurements, indicating the presence of a buffer zone between the cropped soil profile and groundwater, but this should be monitored over a longer period. Commercial production of crops under irrigation with gypsiferous mine water is feasible and the resulting environmental impact is limited, but further research is required to confirm these findings over a longer period.

Model evaluation and optimisation of nutrient removal potential for sequencing batch reactors

Artan, N.; Wilderer, P.; Orhon, D.; Tasli, R.; Morgenroth, E.

Abstract: Performance of sequencing batch reactors for simultaneous nitrogen and phosphorus removal is evaluated by means of model simulation, using the activated sludge model, ASM2d, involving anoxic phosphorus uptake, recently proposed by the IAWQ Task group. The evaluation includes all major process configurations with different aerobic, anoxic, anaerobic sequences, and fill conditions. Basic relationships between modelling and design based on overall process stoichiometry are established for the interpretation of nutrient profiles associated with different operation modes. A similar approach is also used for the assessment of the effect of major operating parameters on system performance.

Metal concentrations in Clarias gariepinus and Labeo umbratus from the Olifants and Klein Olifants River, Mpumalanga, South Africa: zinc, copper, manganese, lead, chromium, nickel, aluminium and iron

Coetzee, L.; Du Preez, H.H.; Van Vuren, J.H.J.

Abstract: The upper catchment of the Olifants River, from its origin near Bethal to its confluence with the Wilge River, north of Witbank, and its tributaries are being subjected to increasing afforestation, mining, power generation, irrigation, domestic and industrial activities. These activities have a profound effect on the water quality. The major point sources of pollution in the study area include mines, industries and very importantly, combined sewage purification works that are located alongside the river. In addition to oxidizable material, these sources contain detergents, nutrients and metals. It was therefore necessary to determine the extent to which these activities affect the water quality of the system. The bioaccumulation of zinc (Zn), copper(Cu), manganese (Mn), lead (Pb), chromium (Cr), nickel (Ni), aluminium (Al) and iron (Fe) in the skin, muscle, liver and gill tissues of Clarias gariepinus and Labeo umbratus from the Upper Olifants River and Klein Olifants River was investigated over the period February 1994 to May 1995. The highest concentrations of these metals were found in the gill and liver tissues of both species, with lower concentrations in the skin and muscle tissues. Bioaccumulation patterns were found to vary according to the species of the fish, mainly according to their different feeding habits and the routes of metal uptake. It also varied as a function of the different localities. Accumulation was size specific, with higher concentrations of metals found in smaller fish.

Checklist of free living nematodes recorded from freshwater habitats in Southern Africa

Heyns, J.

Abstract: A checklist is given of about 150 species of aquatic and semi-aquatic free living nematodes recorded from freshwater as well as from mud and wet soil adjoining water bodies, from South Africa, Botswana and Namibia.

Bioassays for coastal water quality: an assessment using the larval development of Haliotis midae L

Shackleton, A.L.; Schoeman, D.S.; Newman, B.K.

Abstract: The United States Environmental Protection Agency (USEPA) has established a suite of methods that use coastal invertebrate species as bioassay organisms to test industrial and domestic effluent as well as coastal waters for potential toxicity. Although these methods are used globally, the potential of such toxicity tests has not been adequately explored for South African coastal waters. This study serves to describe a simple, cost-effective and relatively quick testing procedure using the development of Haliotis midae larvae as a bioassay of coastal water quality. This test is based on the sensitivity of these larvae to low concentrations of zinc (Zn). Its performance in a field trial demonstrates not only that this test has the potential to identify coastal waters of poor quality, but also that such identification could be of value in attempts to restock natural abalone populations, which are under extreme pressure from legal and illegal exploitation. Further work in this line should focus on the refinement of the methodology for this and other local species and should aim to contribute to the development of suitable criteria for the management of coastal water quality in South Africa.

A modified method to determine biomass concentration as COD in pure cultures and in activated sludge systems

Contreras, Edgardo M.; Bertola, Nora C.; Giannuzzi, Leda; Zaritzky, Noemi E.

Abstract: A simple technique to determine biomass concentration as chemical oxygen demand (COD) was developed as an alternative to the standard volatile suspended solid (VSS) method. The proposed technique for biomass measurement as COD is based on the determination of the biomass COD (COD_B) as the difference between total COD (COD_T) and the soluble COD (COD_S) of the sample. The obtained results show that this technique was quicker and simpler than the traditional VSS method. The validity of the proposed methods was tested with pure cultures of a filamentous micro-organisms (Sphaerotilus natans), a floc-forming bacteria and activated sludges. The method was also used for estimating the conversion factor (f_CV) from VSS to COD units. A modification of the standard VSS technique was also proposed using two membranes in the filtration device; this technique allowed the biomass determination in 1 ?m size bacteria cultures that cannot be detected by the standard VSS method because cells are not retained by the 1.5 mm diameter pore glass-fibre filter.