African Journals Online
WaterSA

Volume 27, Issue 1, 2001
ABSTRACT

Adsorption of Cu(II) and Cr(VI) ions by chitosan: kinetics and equilibrium studies

Schmuhl, R.; Krieg, H.M.; Keizer, K.

Abstract: The ability of chitosan as an adsorbent for Cu (II) and Cr (VI) ions in aqueous solution was studied. The experiments were done as batch processes. Equilibrium studies were done on both cross-linked and non-cross-linked chitosan for both metals. Cr (VI) adsorption behaviour could be described using the Langmuir isotherm over the whole concentration range of 10 to 1000 mg·l^-1 Cr. The maximum adsorption capacity for both types of chitosan was found to be 78 mg·g^-1 for the non-cross-linked chitosan and 50 mg·g^-1 for the cross-linked chitosan for the Cr (VI) removal. For the Cu (II) removal the Freundlich isotherm described the experimental data over the whole concentration range of 10 to 1000 mg·l^-1 Cu (II). The maximum adsorption capacity for both types of chitosan can be estimated to be greater than 80 mg·g^-1. Cr (VI) removal was the highest at pH 5 but pH did not have a large influence on Cu (II). From these results it is clear that the adsorption of heavy metals is possible with chitosan, but that with this method, end concentrations of below 1 mg·l^-1 can hardly be obtained.

Equilibrium and kinetics of nitrate removal by protonated cross-linked chitosan

Jaafari, K.; Elmaleh, S.; Coma, J.; Benkhouja, K.

Abstract: Nitrate, contained in surface or groundwater, can be removed by sorption on protonated cross-linked chitosan gel beads. The sorption capacity is pH-dependent and large enough to meet the standard of drinkable water. The isothermal equilibrium curves are straight lines, which implies that the removal is independent of the initial concentration. The main reactive process, which probably depends on the secondary ammonium groups, involves the total bead volume and not only its surface. If required, the sorption capacity is easily recovered by increasing the pH to 12. The main competitor is fluoride but, even in its presence, the sorption capacity of nitrate remains significant. The sorption kinetics, which can be represented by a mass transfer equation, is not limited by pore or by film diffusion.

Biosorption of Ni(ii) and Pb(ii) by Phanerochaete chrysosporium from a binary metal system – kinetics

Haluk Ceribasi, I.; Yetis, Ulku

Abstract: The biosorption kinetics of Ni(II) and Pb(II) by the resting cells of a lignolytic white-rot fungus, Phanerochaete chrysosporium, from a binary metal system were investigated. Kinetic studies revealed that biosorption takes place in two stages: a rapid surface adsorption, within the first 30 min, and a slow intracellular diffusion till the end of the 3 h contact time. In the first minutes of contact solution pH decreased sharply, parallel to the fast metal uptake, probably because of the protons released by the biosorbent. As sorption equilibrium was reached, solution pH also reached an equilibrium level. Metal biosorption capacities increased as the initial metal concentrations (C_i) increased, independent of initial pH (pH_i) and generally the metal with higher C_i had a higher uptake capacity. The results also show that some portion of the metal ions sorbed by P. chrysosporium was readily released to solution with a decrease in pH. At equilibrium, the maximum total metal uptake of P. chrysosporium was 109.5 mg/g and was reached at pH_i 5. Under these circumstances Ni(II) and Pb(II) uptake capacities were 55.9 mg Ni/g and 53.6 mg Pb/g, respectively.

Surfactants and the attachment of Pseudomonas aeruginosa to 3CR12 stainless steel and glass

Cloete, T.E.; Jacobs, L.

Abstract: Five non-ionic and three anionic surfactants were evaluated using 4'6-diamidino-2-phenylidole (DAPI) staining, scanning electron microscopy (SEM) and spectrophotometry for their efficacy in preventing adhesion and removing Ps. Aeruginosa attached to 3CR12 stainless steel coupons and glass. All the surfactants tested gave more than 90% inhibition of adhesion to the surfaces tested with no significant difference between the effectivity of the different anionic surfactants (p > 0.18) nor between the effectivity of the non-ionic surfactants (p > 0.16). The non-ionic and anionic surfactants resulted in more than 80% and 63% removal of attached Ps. Aeruginosa cells, respectively. The non-ionic surfactants were significantly more effective in removing attached bacteria, than the anionic surfactants (p < 0.001). The prevention of attachment of Ps. Aeruginosa cells to a glass surface, using the surfactants, was also monitored spectrophotometrically. There was no significant difference (p = 0.437) when comparing the DAPI - staining technique with spectrophotometric evaluations.

The generation and use of cumulative probability distributions in flood risk assessment for the Mfolozi flood-plain

Du Plessis, L.A.

Abstract: The traditional method of presenting flood damage is to calculate the mean annual flood damage. This approach does not explicitly point out the risk of floods and communities do not have an indication of what the risk implications of various floods are. A clearer picture of the uncertainty of flood damages as well as the damage implications can be created by constructing and using cumulative probability distribution curves. The inclusion of flood damage on a stochastic basis is most definitely an extension of previous flood research, which only used deterministic analysis. With this approach, flood-plain dwellers can comprehend better the nature, scope and potential effects of the risk invalued. The main aim of this paper is to explain better the potential risk of floods to flood-plain dwellers by constructing and using cumulative probability distribution curves.

Loss functions for structural flood mitigation measures

Berning, C.; Du Plessis, L.A.; Viljoen, M.F.

Abstract: The paper aims at discussing the methodology used to develop loss functions for flood mitigation measures, using historic data of flood damage to infrastructure. The main determinants of the extent of damage are the size of the flood and the length of the infrastructure within the boundaries of the flood-line. In regression analysis, flood peak was used as the independent variable in the Cobb-Douglas functions to depict the relationship between damage and flood peak. The Mfolozi flood-plain in Northern KwaZulu-Natal served as the study area. Loss functions for infrastructure, for ex ante estimation of damage to infrastructure, were developed for inclusion in a flood damage simulation model (FLODSIM) developed by the Department of Agricultural Economics of the University of the Orange Free State in collaboration with the Water Research Commission. Loss functions were determined for spillways, levees, tramlines, public roads, drains and bridges.

The quality of the Florisbad spring-water in relation to the quality of the groundwater and the effects of rainfall

Douglas, R.M.

Abstract: The spring-water, groundwater and rainfall were examined as part of a study to determine aspects of the environment in which faunal remains at Florisbad were fossilised. A 1988 analysis of the Florisbad spring and exploration pit-water showed a 27% higher TDS in the pit-water after a high rainfall period, despite the two being located only 22 m apart. An extended qualitative water-sampling programme in 1999 confirmed a difference, but in this instance the TDS of the same exploration pit was 49% lower than that of the spring-water after a low rainfall period. This was contrary to the norm where high recharge usually results in low TDS and low recharge results in high TDS. Results also showed extreme TDS variations of up to 6 times higher between individual pit-waters 54 m apart. The fluctuation in the quality of the pit-water, in relation to the stable spring-water, led to the conclusion that the two should be separate entities. It was further concluded that the mineralisation of the pit-water originated either directly, or indirectly, from a source other than the spring-water. Long-term rainfall appears to have only a slight effect on the quality of the spring-water and possibly no effect on the quality of the pit-water, while short-term rainfall appears to have little effect on the spring-water quality, but has a decided influence on the pit-waters. Aspects relating to water quality and water monitoring at Florisbad are discussed and a comprehensive historic record of the spring-water quality and composition is also given. Investigations on the origin/s of the groundwater mineralisation are continuing. The results clearly indicate that the spring-water does not currently carry sufficient mineralisation for fossilisation.

SOLAIR disinfection of coliform bacteria in hand-drawn drinking water

Meyer, V.; Reed, R.H.

Abstract: SOLAIR is an alternative disinfection method utilising natural sunlight (specifically UV-A and UV-B radiation) and oxygen (from atmospheric air) to damage, inactivate and / or kill the coliform bacteria found in contaminated water. It is a natural process (virtually self-purification) with no need to add any potentially hazardous chemicals or to use sophisticated and expensive equipment.

The SOLAIR process was applied in a typical South African scenario, i.e., a rural informal village where water for domestic use is drawn from an unlined and heavily contaminated well. Results obtained showed significant reduction (99.99%) in both the faecal and total coliform counts within 4 to 6 h, with no subsequent reactivation of growth after 24 h. The disinfected water complied in terms of bacteriological quality, with both the South African Bureau of Standards (SABS), drinking water standards and the South African Water Quality Guidelines (SAWQG) for domestic use as prescribed by the Department of Water Affairs and Forestry (DWAF). The rate of bacterial reduction depended on various parameters including the type and colour of plastic containers used, the initial concentration of micro-organisms in the drawn water, the irradiation levels of UV-A and UV-B rays, the oxygen concentration and distribution in the water containers, and the presence of visible turbidity.

In South Africa where more than 8 m. people are still using water obtained directly from alternative sources such as rivers, streams, boreholes, wells, community taps and dams, SOLAIR could prove to be an efficient and an economically feasible method to be used for disinfection of hand-drawn water to an acceptable potable standard.

Allozyme variation in a Johnston's topminnow, Aplocheilichthys johnstoni, population from the Zambezi River system

Steenkamp, M.K.J.; Engelbrecht, G.D.; Mulder, P.F.S.

Abstract: Twenty five specimens of Aplocheilichthys johnstoni (Günther, 1893) were collected from the Cuando River in the Zambezi River system. Protein electrophoresis was used to analyse the genetic structure of this population. Seven of the 20 loci studied, (15% using the 95% criterion) revealed polymorphism. The heterozygosity value obtained (H_O = 0.050) compare favourably to those recorded for other fish species. Observed allele frequencies deviated from expected Hardy-Weinberg proportions at the EST-3, GPD-1 and GPI-2 protein coding loci. The results from the genetic analysis of A. johnstoni are discussed in relation to its role in mosquito larval control.

Ubiquity of the water-borne pathogens, Cryptosporidium and Giardia, in KwaZulu-Natal populations

Jarmey-Swan, C.; Bailey, I.W.; Howgrave-Graham, A.R.

Abstract: The prevalence of the diarrhoea disease caused by the water-borne pathogens Cryptosporidium and Giardia in KwaZulu-Natal, was determined from pathology laboratory data. Cryptosporidium and Giardia were found to be endemic in KwaZulu-Natal with laboratory-confirmed incidences ranging from 2.9 to 3.7% and 2.9 to 3.0% respectively of diarrhoea samples submitted for protozoan parasite analysis. Increases in the number of samples submitted for Cryptosporidium or Giardia analysis were independent of the actual incidence of either protozoan pathogen. Female and male patients tested for cryptosporidiosis had similar positive percentages while giardiasis was more prevalent in female patients. Cryptosporidium and Giardia prevalence in children under 5 years indicated that Cryptosporidium was most prevalent (39.3%) in the Giardia was most prevalent in the 3 to 4 year age group (38.5%). A low percentage of Cryptosporidium and Giardia positive cases were recorded in symptomatic (4.5% and 5.3% respectively) and asymptomatic (2.4% and 0.8% respectively) HIV patients. The incidence of Cryptosporidium and Giardia did not appear to correlate (Pearson's correlation test) with climatic factors such as rainfall, season or year, possibly indicating that water-borne transmission is not the predominant route and other factors such as personal hygiene, potable water supply, sanitation and education probably have a more significant impact.

Current-use insecticides, phosphates and suspended solids in the Lourens River, Western Cape, during the first rainfall event of the wet season

Schulz, Ralf; Peall, Sue K.C.; Dabrowski, James M.; Reinecke, Adriaan J.

Abstract: Pesticide contamination resulting from agricultural runoff depends on the time period between application and rainfall. In Western Cape orchard areas, the last pesticide application of the growing season in summer takes place at the end of February. Pesticides, total phosphates and total suspended solids (TSS) were measured in the Lourens River at the beginning of April 1999 prior to the first rainfall of the rainy season and in the middle of April during high discharge following the first rainfall of 9.6 mm/d. Pre-runoff samples indicated only contamination with total endosulfan (α, β, sulphate) at levels up to 0.06 µg/l. Runoff during the first rainfall event resulted in an increase in the levels of endosulfan, chlorpyrifos and azinphos-methyl, to 0.16,

Plant-soil interactions of sludge-borne heavy metals and the effect on maize (Zea mays L.) seedling growth

Henning, B.J.; Snyman, H.G.; Aveling, T.A.S.

Abstract: The use of sewage sludge as an organic fertiliser under South African conditions is an alternative disposal route to sacrificial land disposal. However, the lack of research done under South African conditions and the conservative nature of the heavy metal guidelines, when interpreted as total metal content is limiting the agricultural use of sludge. A glasshouse experiment, which forms part of a greater project, was conducted to characterise soil-plant interactions of the main sludge-borne heavy metals (Pb, Cd, Zn and Cu) in two sludges (low metal and high metal) to different soil types (clayey, loamy and sandy) on maize seedlings. Growth differences, heavy metal accumulation in plant parts and soil-metal concentrations (total and potentially available) were determined. The low metal sludge treatment showed the highest yield for maize seedlings when compared to controls (soil unamended and inorganic fertiliser added). The amendment of sludge to the soil did indicate higher heavy metal content, although the increase was not as predicted, owing to the difficulty of obtaining a representative sample in the soil. Except for Cd, heavy metal values in the soils (at the beginning and end of experiment) exceeded guidelines due to very high background values in the soil. No negative effects of heavy metal contamination in plant parts of the crops could be proven. Results showed that application of sludge to different soils could be useful in order to increase crop growth over a 28 d period in the glasshouse. Soil, plant and water quality monitoring, together with the prevention of metals entering the plant, is a prerequisite in order to prevent potential health hazards of sludge application to agricultural land.

Mixing studies in an Orbal activated sludge system

Burrows, L.J.; West, J.R.; Forster, C.F.; Martin, A.

Abstract: Orbal multi-channel oxidation ditches have received relatively little attention and thus knowledge of their characteristics is not as highly advanced as for other oxidation ditch systems. Dye tracer and dissolved oxygen measurements have been undertaken to elucidate the mixing characteristics of a three-channel Orbal system treating 80 Ml/d. The dissolved oxygen concentrations showed a complex variation in space due to the input, approximating a continuous line source, non-uniform distribution of turbulence and secondary flows caused by channel configuration. Consideration of the DO measurements and the dye tracing results suggest that the flow could be treated as 2 CSTRs in the outer channel and a single CSTR in each of the two inner channels.

Potamonautid river crabs (Decapoda, Brachyura, Potamonautidae) of KwaZulu-Natal, South Africa

Gouws, G.; Stewart, B.A.

Abstract: The recent descriptions of Potamonautes dentatus, P. clarus and P. lividus have brought the number of species recorded from KwaZulu-Natal (South Africa) to five, with P. depressus depressus and P. sidneyi having long been known from the province. To determine and quantify levels of genetic differentiation between these species, 14 populations were analysed using allozyme electrophoresis of 14 presumptive loci. Interspecific genetic identity-values ranged between 0.224 and 0.793 (D = 0.233 to 1.495), with between one and ten fixed allele differences present among species. Morphometric differentiation between species was examined using discriminant function analyses of seven carapace and eight pereiopod variables. Species were found to be well defined along the first two canonical variables, in terms of carapace and pereiopod morphometrics. Results are discussed in light of genetic and morphometric differentiation documented for the genus. The distribution of each species was determined, using data from 220 collection localities, plotted, and discussed. A key for the identification of the species occurring in the province is provided.

Uptake and distribution of a copper, iron and zinc mixture in gill, liver and plasma of a freshwater teleost, Tilapia sparrmanii        99

Wepener, V.; Van Vuren, J.H.J.; Du Preez, H.H.

Abstract: Since polluted environments contain mixtures of different contaminants, the aim of this study was to investigate the time-integrated uptake of individual metals by a freshwater teleost, Tilapia sparrmanii following exposure to a metal mixture containing Cu, Fe and Zn. The metal concentrations used during the bioassays were chosen to represent ecologically relevant concentrations as found in the Olifants River, Kruger National Park, South Africa. The concentrations used in the bioassay were 0.16 mg·ℓ^-1, 4.3 mg·ℓ^-1 and 1.003 mg·ℓ^-1 for Cu, Fe and Zn respectively. Gill, plasma and liver were sampled at 0, 2, 4, 6, 12, 24, 24, 48, 72, 96 h and four weeks. Gill tissue is the initial site of accumulation of water-borne metals. Although the fish were exposed to a metal mixture, the interactions between metals and the external gill surface, as well as the subsequent uptake rate, were associated with the particular chemical properties of individual metals. The tendency of the individual metals in the metal mixture to bind to the external gill surface via ionic bonds, and to gill cytosolic compounds via covalent bonds, was Cu > Fe > Zn. The ensuing uptake rates into the extracellular compartment (blood) and intracellular compartment (liver tissue) were Zn > Fe > Cu. The toxic effects of Cu and Fe were, therefore, primarily exerted on the gill surface and in the gill cytosol, whereas the toxic action of Zn was primarily limited to the internal organs.

Dynamic model simulations as a tool for evaluating the stability of an anaerobic process

Azeiteiro, C.; Capela, I.F.; Duarte, A.C.

Abstract: The association of a wall growth factor with a dynamic model based on Andrews' work (1969), without pH restrictions, is used herein to study the inhibition of methanogenesis by high concentrations of volatile acids. The model considers the methanogenic bacteria as being representative of the biological phase of the anaerobic digestion, and assumes a continuous feed of acetic acid to the continuously stirred anaerobic reactor. The model can be used for simulations on transient conditions, namely the effect of initial conditions on the start-up of a digester, as well as for studying the significant improvements in stability when wall growth occurs in the reactor. The effect of changing the feed characteristics to a digester was studied in two situations: with and without wall growth. The presence of wall growth allows a better behaviour of an anaerobic process in any case, namely when a step increase in the feeding substrate concentration or in flow rate is performed.