Personal Research Database

Title: Water SA

Full Journal Title: Water SA; Water SA

ISO Abbreviated Title: Water SA

JCR Abbreviated Title: Water SA

ISSN: 0378-4738

Issues/Year: 4

Journal Country/Territory: South Africa

Language: Multi-Language

Publisher: Water Research Commission

Publisher Address: PO Box 824, Pretoria 0001, South Africa

Subject Categories:

Water Resources: Impact Factor: 0.592, 25/46 (1999); Impact Factor: 0.263, 42/47 (2000); Impact Factor: 0.427, 33/50 (2001); Impact Factor: 0.464 (2004)

? Ekama, G.A. and Marais, G.V.R. (1978), Adsorption in activated sludge process. Water SA, 4 (1), 39-48.

Full Text: 1960-80\Wat SA4, 39.pdf

Abstract: Investigations into the phenomenon of storage of substrate in the activated sludge process indicate that this phase is preceded by an adsorption phase, which requires the expenditure of energy. Incorporation of the adsorption mechanism into the general model of the activated sludge process by Ekama and Marais (1977) allowed the reinstatement in their model of the widely accepted Monod formulation for nitrification. Application of the modified model to processes with imposed dynamic loading conditions operated at long and short sludge ages gave improved predictions of the process response variables, i.e. oxygen consumption rate, effluent total Kjeldahl nitrogen (TKN) and nitrate concentrations.

? Ekama, G.A. and Marais, G.V.R. (1979), Adsorption in the activated sludge process - Reply. Water SA, 5 (1), 57-60.

Full Text: 1979\Water SA5, 57.pdf

? Fox, V.G. (1979), Letter to the editor with regard to the paper adsorption in the activated sludge process. Water SA, 5 (1), 57.

Full Text: 1960-80\Wat SA5, 57.pdf

? Saucedo, I., Guibal, E., Roussy, J., Roulph, C. and Le Cloirec, P. (1993), Uranium sorption by glutamate glucan: A modified chitosan. Part I. Equilibrium studies. Water SA, 19 (2), 113-118.

Full Text: 1993\Wat SA19, 113.pdf

Abstract: Chitosan, a natural polymer, is modified by an oxo-2-glutaric acid substitution and a subsequent reduction to form glutamate glucan. This modified chitosan is then used to examine uranium sorption. The main parameters that play an important part in sorption mechanisms are the pH and the total metal concentration. Other parameters such as temperature, agitation and particle size of the sorbent show a restricted effect on the sorption equilibrium.The maximum uptake capacity, obtained at pH 5 to 6, reaches approximately 500 mgU, g. At pH 5, a sorption monolayer is predominant; at higher pH, the sorption becomes more complicated. A surface precipitation model of uranium sorption is proposed.

Keywords: Adsorption, Ascorbic-Acid, Chitosan, Glutamate Glucan, Metal, Particle Size, Reduction, Sorption, Temperature, Uranium, Water

? Guibal, E., Saucedo, I., Roussy, J., Roulph, C. and Le Cloirec, P. (1993), Uranium sorption by glutamate glucan: A modified chitosan. Part II. Kinetic studies. Water SA, 19 (2), 119-126.

Full Text: 1993\Wat SA19, 119.pdf

Abstract: The kinetics of uranium sorption by glutamate glucan, a modified chitosan polymer, were studied. The effects of the particle size of sorbent, pH, metal concentration, temperature and agitation were investigated. Diffusion mechanisms were predominant in rate-controlling steps: external mass transfer seemed to have a restricted effect on kinetic behaviour, on the other hand intraparticle diffusion was the main resistance model. Metal concentration, pH and particle size of the polymer were the major parameters, showing a great effect on the rate ratio of the intraparticle diffusion model and on diffusion coefficient D’i, whose value varied between 1,5 and 3610^-12 m², min.

Keywords: Activated Carbon, Adsorbents, Adsorption, Chitosan, Diffusion, Functional Polymers, Glutamate Glucan, Highly Phosphorylated Derivatives, Kinetics, Metal, Partially Deacetylated Chitin, Particle Size, Removal, Sorption, Temperature, Uranium, Water

Gaid, A., Kaoua, F., Mederres, N. and Khodjsa, M. (1994), Surface mass transfer processes using activated date pits as adsorbent. Water SA, 20 (4), 273-278.

Full Text: 1994\Wat SA20, 273.pdf

Abstract: The factors affecting the initial rate of adsorption of some organic compounds onto activated date pits, have been investigated in detail. Phenol, aniline, Methylene Blue, procion red and humic substances were employed to test this adsorbent.

The applicability of the Langmuir isotherm for the present system has been tested and the surface mass transfer coefficient and the surface diffusion coefficient at 20-degrees-C determined. The kinetics of adsorption indicates that the process is diffusion controlled.

Keywords: Removal, Adsorption, Carbon, Dye

Notes: highly cited

? Carliell, C.M., Barclay, S.J., Naidoo, N., Buckley, C.A., Mulholland, D.A. and Senior, E. (1995), Microbial decolorization of a reactive azo dye under anaerobic conditions. Water SA, 21 (1), 61-69.

Full Text: 1995\Wat SA21, 61.pdf

Abstract: Water-soluble azo dyes are used extensively in the textile industry and are known to be problematic with respect to the removal of colour from textile waste waters. Under anaerobic conditions azo dyes can be utilised as terminal electron acceptors in microbial respiration, and are reduced and decolourised concurrently with re-oxidation of reduced flavin nucleotides. The microbial decolourisation of an azo dye (C.I. Reactive Red 141) was investigated with respect to the kinetic order of azo reduction and rate-controlling factors of the reaction. Decolourisation of C.I. Reactive Red 141 was found to be first order with respect to dye concentration, although increasing the initial dye concentration in the serum bottles resulted in decreasing k values of -0.441/h (100 mg/l of C.I. Reactive Red 141), -0.316/h (150 mg/l) and -0.252/h (200 mg/l). The presence of labile carbon in the anaerobic systems was found to be essential in order to obtain an acceptable rate of decolourisation. The k value obtained for decolourisation of the azo dye without a supplemental carbon source (glucose) was -0.012/h, in comparison to a k value of -0.441/h when supplemented with glucose (1 g/l). The presence of nitrate in the anaerobic system was found to inhibit decolourisation, while the presence of sulphate was found to have no discernible effect on the rate of decolourisation. A low redox potential (-450 to -500 mV) was found to be conducive to rapid decolourisation of C.I. Reactive Red 141. AC.I. Reactive Red 141 degradation product was positively identified as 2-aminonaphthalene-1,5-disulphonic acid, confirming that azo reduction was responsible for decolourisation of the azo dye. A toxicity assay was performed which showed that C.I. Reactive Red 141 was inhibitory to the anaerobic microbial community at concentrations > 100 mg/l, but that prior exposure of the biomass to the dye increased the resistance to previously inhibitory dye concentrations.

Keywords: Growth-Inhibition, Bacillus-Subtilis, Basic-Dyes, Reduction, Degradation

? Guibal, E., Roussy, J. and Le Cloirec, P. (1996), Photochemical reaction of uranium with glucosamine, acetylglucosamine and related polymers: Chitin and chitosan. Water SA, 22 (1), 19-26.

Full Text: 1996\Wat SA22, 19.pdf

Abstract: Uranyl ions can interact with amino-ligands and polymers such as chitin and chitosan by complexation and adsorption. This reaction can be affected by certain circumstances, such as a direct exposure to visible light, to give photoreactions. Among the main photoreduction mechanisms, sensitised photoactivation (SP) and charge transfer to mass (CTTM) are thought to explain the various responses obtained under several experimental conditions, where the nature of the ligand and the aerobic or anaerobic media are all changed. It seems that a preliminary complexation of uranium by ligand is required to optimise the reduction rate. The pH of the solution is significantly affected by the photoreaction, depending on the experimental procedure, and a precipitate appears after a duration. Elemental analysis and infra-red studies enable the structure of the precipitates to be determined as dihydrated uranate forms.

Keywords: Adsorption, Biosorption, Chitosan, Glutamate Glucan, Mechanism, pH, Photo-Oxidation, Photoreduction, Reduction, Sorption, Uranyl Ions, Water

Sharma, D.C. and Forster, C.F. (1996), Removal of hexavalent chromium from aqueous solutions by granular activated carbon. Water SA, 22 (2), 153-160.

Full Text: 1996\Wat SA22, 153.pdf

Abstract: Batch absorption trials were used to assess the effectiveness of using activated carbon as a sorbent for the removal of hexavalent chromium from solution. The results show that, although the pH for maximum efficiency varied slightly with the concentration of Cr(VI) being applied, the most effective pH was in the range 2.5 to 3.0. Based on linear regression analysis, the data obtained from the batch studies showed a good compliance with both the Langmuir and the Freundlich equations. The values obtained for the isotherm constants showed that the maximum adsorption capacity. X_m, was 145 mg/g. An examination of the adsorption kinetics was also made and an analysis of the data shows that pore diffusion is not the only factor governing the sorption rate.

Keywords: Peat, Moss

Ho, Y.S., Wase, D.A.J. and Forster, C.F. (1996), Removal of lead ions from aqueous solution using sphagnum moss peat as adsorbent. Water SA, 22 (3), 219-224.

Full Text: 1996\Wat SA22, 219.pdf

Abstract: The use of sphagnum moss peat for the removal of lead from aqueous solution has been studied in batch experiments. Investigations include the effect of pH and temperature and kinetics of adsorption. The adsorption equilibria data were found to follow Langmuir models. It was found that the efficiency of lead removal using sphagnum moss peat as adsorbent depended very little either on the reaction temperatures (10 to 40°C) or on the initial pH values (4.0 to 6.0). Kinetic data suggested that the adsorption process was endothermic and pore diffusion was not the only rate-determining step.

Keywords: Cross-Flow Microfiltration, Heavy-Metals, Adsorption, Effluents, Waste, Clay

Grebenyuk, V.D., Linkov, N.A. and Linkov, V.M. (1998), Removal of Ni and Cu ions from aqueous solutions by means of a hybrid electrosorption/electrodialysis process. Water SA, 24 (2), 123-127.

Full Text: 1998\Wat SA24, 123.pdf

Abstract: The hybrid adsorption/electrodialysis process was shown to be effective in the removal of Ni Cu ions from aqueous solutions imitating electroplating effluents. Adsorption of the ions on the cation-exchange and amphoteric resins packed in the desalination compartment of the electrodialysis cell with (electrosorption) with without the influence of electrical current was studied. In the case of the ion-saturation operation carried out before the electrosorption process, no direct relationship between the type of resin and the ion-removal efficiency was found; the process performance was affected by over-equivalent adsorption resulting from electrochemical reactions taking place in the boundary layer between the resin and the solution. Under the influence of electrical current as high as sixfold higher metal ion extraction than in a conventional adsorption process was observed. The presence of ion-exchange resins in the desalination compartment also affected the performance of ion-exchange membranes used in the cell. The method was found more applicable to Cu containing solutions.

Keywords: Electrodialysis, Separation

Atkinson, B.W., Bux, F. and Kasan, H.C. (1998), Considerations for application of biosorption technology to remediate metal-contaminated industrial effluents. Water SA, 24 (2), 123-127.

Full Text: 1998\Wat SA24, 129.pdf

Abstract: Inorganic contaminants present in waste streams may be removed by one of three methods, viz. physical, chemical or biological. Chemical and physical techniques have traditionally been employed to remediate such streams. However, due to the crisis of rapidly deteriorating potable water quality, legislation governing the levels of contaminants is becoming progressively stricter. Therefore, alternative methods for treatment have been investigated. Biosorption technology, utilising any natural form of biomass to passively adsorb and immobilise solubilised heavy metals or radionuclides, offers such an alternative. However, the technology needs to effectively compete both on a cost and performance basis with existing methods before industry will accept and implement it. A pilot-plant feasibility study, using waste activated sludge to bioremediate a metal plating effluent, showed that the currently used method of chemical precipitation is more cost-effective. This paper describes the factors that must be considered when selecting bioremediation as a cleanup technology for inorganics.

Ning, Z., Kennedy, K.J. and Fernandes, L. (1998), pH dependency of 2,4-chlorophenol dechlorination by acclimated anaerobic granules. Water SA, 24 (2), 1153-1156.

Full Text: 1998\Wat SA24, 1153.pdf

Abstract: The pH dependency of anaerobic dechlorination of 2,4-dichlorophenol by acclimated anaerobic granules was investigated. The results showed that the dechlorination could be performed by these granules at a wide pH range of 6.8 to 7.9, but dechlorination rate increased as pH value went up. The data analysis considering the effect of sorption indicated that the increase of the dechlorination rate was due to pH dependence of metabolic activity of the acclimated anaerobic granules.

Notes: highly cited

Quek, S.Y., Wase, D.A.J. and Forster, C.F. (1998), The use of sago waste for the sorption of lead and copper. Water SA, 24 (3), 251-256.

Full Text: 1998\Wat SA24, 251.pdf

Abstract: Sago processing waste, which is both a waste and a pollutant, was used to adsorb lead and copper ions from solution. The sorption process was examined in terms of it equilibria and its kinetics. The effect of pH, contact time, sorbate concentration, particle size and sorbent mass were also studied. The most effective pH range was found to be 4 to 5.5 for both metals. The equilibrium data for both metals fitted both the Langmuir and the Freundlich models and, based on the Langmuir constants, the sage waste had a greater sorption capacity for lead (46.6 mg/g) than for copper (12.4 mg/g) The kinetic studies showed that the sorption rates could be described better by a second-order expression than by the more commonly applied Lagergren equation.

Keywords: Sphagnum Moss Peat, Aqueous-Solution, Removal, Adsorption, Ions, Adsorbent, Cadmium, Water

Srinivasan, P.T., Viraraghavan, T. and Subramanian, K.S. (1999), Aluminium in drinking water: An overview. Water SA, 25 (1), 47-55.

Full Text: 1999\Wat SA25, 47.pdf

Abstract: Aluminium (Al) is one of the trace inorganic metals present in drinking water. In addition to the naturally occurring Al in raw waters, use of Al-based coagulants especially Al₂(SO₄)₃ (alum) often leads to an increase in treated water Al concentrations. A high (3.6 to 6 mg/l) concentration of Al may precipitate as aluminium hydroxide giving rise to consumer complaints. Al is also a suspected causative agent of neurological disorders such as Alzheimer’s disease and presenile dementia. During conventional water treatment processes, Al undergoes various transformations (also called ‘speciation’ of Al) which are influenced by factors such as pH, turbidity, temperature of water source, and the organic and inorganic ligands present in water. Chemical precipitation, reverse osmosis, electrodialysis and cation exchange methods are efficient in AI removal from water. This paper gives an overview of the presence of Al in drinking water with reference to its speciation, removal (treatment methods), water supply and health problems, and the regulation of its levels in drinking water.

Keywords: Aqueous Aluminum

? Lahav, O. and Green, M. (2000), Bioregenerated ion-exchange process: The effect of the biofilm on ion-exchange capacity and kinetics. Water SA, 26 (1), 51-57.

Full Text: 2000\Wat SA26, 51.pdf

Abstract: A new process for ammonium removal from wastewater using zeolite has been developed. The zeolite (chabazite) serves the dual purpose of an ion exchanger and a physical carrier for nitrifying bacteria which bio-regenerate the ammonium-saturated mineral. The entire process is carried out in a single, compact reactor and takes place in two phases: ion-exchange phase and bioregeneration phase.

This paper describes the effects of the biofilm on ion-exchange capacity and kinetics. Batch and continuous experiments showed a reduction of about 25 to 30% in the ion-exchange rate in biofilm covered chabazite as compared to virgin chabazite, while the ion-exchange capacity did not change. Experiments conducted indicated that the rate-controlling step for ion exchange shifted from pore diffusion in the virgin chabazite to dim diffusion in the biofilm-covered chabazite. The diffusion rate of NH₄⁺ inside biofilms is of the same order of magnitude as diffusion rate of NH₄⁺ in water and 3 to 4 orders of magnitude greater than typical pore diffusion rates reported in zeolites. Therefore, the biofilm coverage of the chabazite was originally not expected to affect the ion-exchange rate. In addition, chemical precipitation a as experimentally found not to be the cause for the ion-exchange rate reduction.

It was hypothesised that the rate-limiting factor for ion exchange was caused by the part of the biofilm adjacent to the chabazite which differs from the rest of the biofilm and is characterised by a much higher density which impedes diffusion.

Yan, G.Y. and Viraraghavan, T. (2000), Effect of pretreatment on the bioadsorption of heavy metals on Mucor rouxii. Water SA, 26 (1), 119-123.

Full Text: 2000\Wat SA26, 119.pdf

Abstract: Different chemicals were used to study the effect of pretreatment of Mucor rouxii biomass on bioadsorption of Pb²⁺. Cd²⁺; Ni²⁺; and Zn²⁺. Pretreatment with detergent and alkali chemicals such as NaOH, Na₂CO₃, and NaHCO₃, were found to improve or maintain the bioadsorption capacity in comparison with live M. rouxii biomass. Acid pretreatment using HCl, H₂SO₄ and C₂H₄O₂ resulted in a significant reduction in the bioadsorption capacity. Pretreatment using CaCl₂ and NaCl slightly reduced the bioadsorption capacity. All the pretreatment methods resulted in a reduction in biomass in comparison with autoclaved biomass. In addition, M. rouxii biomass pretreated with chemicals without autoclaving was still viable, even after boiling. To improve the bioadsorption capacity for metal ions by dead biomass, alkali pretreatment is an effective method, but the loss of biomass after the pretreatment should be taken into consideration while assessing the bioadsorption performance.

Keywords: Dilute Aqueous-Solutions, Aspergillus-Niger, Biosorption, Biomass, Removal, pH, Wastewaters, Mechanisms, Biosorbent, Recovery

Woolard, C.D., Petrus, K. and van der Horst, M. (2000), The use of a modified fly ash as an adsorbent for lead. Water SA, 26 (4), 531-536.

Full Text: 2000\Wat SA26, 531.pdf

Abstract: Coal fly ash was modified by hydrothermal treatment with NaOH solutions of varying concentrations. During the modification the zeolites, NaP1 and hydroxysodalite, were synthesised. Increasing base concentration led to hydroxysodalite being the preferred product. Elemental analysis revealed that the modification treatment preferentially leached Si from the fly ash at low base concentrations. Elevated base concentrations, however, resulted in Al being leached as well as the inclusion of Na in the zeolite product. The modification activated the fly ash significantly with respect to specific surface area (SSA) and cation exchange capacity (CEC). SSA increased from 1.0 m².g^-1 to a maximum of 62.7 m².g^-1 while CEC rose from 25 mmol/100 g to a maximum of 300 mmol/100g. Metal sorption studies were performed with lead as the metal choice. Adsorption experiments at pH = 5, revealed that all modified ash samples adsorbed significantly more Pb than the raw ash. The best adsorption was obtained for ash, modified with 3M NaOH. 3M NaOH-modified ash also proved the most effective sorbent when adsorption was determined as a function of pH.

Keywords: Zeolite, Removal, Ions, Clay, Peat

Notes: highly cited

Schmuhl, R., Krieg, H.M. and Keizer, K. (2001), Adsorption of Cu(II) and Cr(VI) ions by chitosan: Kinetics and equilibrium studies. Water SA, 27 (1), 1-7.

Full Text: 2001\Wat SA27, 1.pdf

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.l^-1 for the non-cross-linked chitosan and 50 mg.l^-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.l^-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.

Keywords: Metal-Ions, Recovery, Sorption, Chitin

Jaafari, K., Elmaleh, S., Coma, J. and Benkhouja, K. (2001), Equilibrium and kinetics of nitrate removal by protonated cross-linked chitosan. Water SA, 27 (1), 9-13.

Full Text: 2001\Wat SA27, 9.pdf

Abstract: Nitrate, contained in surface or groundwater, can be removed by sorption on protonated cross-linked chitosan gel beads. The sorption capacity iu 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.

Keywords: Adsorption, Acid

Çeribasi, I.H. and Yetis, Ü. (2001), Iosorption of Ni(II) and Pb(II) by Phanerochaete chrysosporium from a binary metal system: Kinetics. Water SA, 27 (1), 15-20.

Full Text: 2001\Wat SA27, 15.pdf

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.

Keywords: Heavy-Metals, Saccharomyces-Cerevisiae, Aqueous-Solutions, Removal, Biomass, Mechanisms, Adsorption, Effluents, Recovery, Copper

? Contreras, E., Bertola, N. and Zaritzky, N. (2001), The application of different techniques to determine activated sludge kinetic parameters in a food industry wastewater. Water SA, 27 (2), 169-176.

Full Text: 2001\Wat SA27, 169.pdf

Abstract: In the present work, a continuous-feed system under steady state conditions (classical method) and a respirometric technique based on oxygen consumption measurements, were used to compare microbial parameters using a wastewater model system of a potato processing plant. The effects of the operating conditions in the continuous aerobic reactor on microbial growth and nora composition were also analysed.

Continuous-feed experiments allowed for the calculation of the following biodegradation parameters. maximum substrate consumption specific rate (q(Smax)) = 0.19 mgCOD (mgVSS)^-1.h^-1, saturation constant (Ks) = 8.3 mgCOD.t(1), biomass yield (Y-X/S) = 0.61 mgVSS (mgCOD) ^-1, biomass decay constant (kd) = 0.04.h^-1 and maximum oxygen consumption specific rate (q(O2max)) = 0.03 mgCOD (mgVSS) ^-1.h^-1.

The respirometric technique als allowed for the calculation of kinetic parameters. However. these parameters depended on dilution rate (D) and/or on dissolved oxygen concentration (DO). Values of q(O2max) and Ks increased with D; q(O2max) ranged between 0.05 and 0.13 mgO(2) (mgVSS) ^-1.h^-1 and Ks between 2 and 26 mgCOD.t(1) for D values varying between 0.01 and 0.15.h^-1.

Microscope observations showed that sludge composition was a function of dilution rate. Low D values (low soluble organic matter (Ss) and high DO concentrations) yielded sludges mainly formed by floc-forming bacteria: high D values (high Ss and low DO concentrations) yielded sludges mainly formed by filamentous micro-organisms.

Since the low substrate/biomass ratios used in the respirometric method limit the growth of micro-organisms maintaining the initial physiological state of the original biomass, the observed differences in the respirometric parameters reflected the actual microbial composition.

Keywords: Filamentous Organism Bulking, Model System, Storage, Biodegradability, Nitrification, Water

Dilek, F.B. and Bese, S. (2001), Treatment of pulping effluents by using alum and clay: Colour removal and sludge characteristics. Water SA, 27 (3), 361-366.

Full Text: 2001\Wat SA27, 361.pdf

Abstract: The effect of clay addition during alum coagulation, on the removal of colour from pulp-and-paper industry wastewaters, was investigated. Four types of clay, namely beige-and brown-sepiolites, calcium- and sodium-bentonites of different mesh sizes were used, Different quantities of alum and clay were applied, either singly or in combination, to the effluents of the wood-based pulp-and-paper mill. Colour of the treated wastewater, the sludge volume index (SVI) and sludge cake resistance (SCR) of the sludge produced were monitored. It was observed that the clays tested were not efficient in colour removal when they were applied on their own. When clay was added along with alum, a certain increase in colour removal efficiency was obtained as compared to alum alone. When alum was used in conjunction with clay, settling characteristics of the sludge produced improved substantially, in terms of both SVI and SCR. Acid activation of the clays did not improve the colour removal efficiency further. However, acid activation of sodium bentonite caused the SVI and SCR values to improve considerably compared to virgin sodium bentonite. Use of different, mesh sizes of clays did not exert any significant effect on the colour removal. However, it did exert significant effects on SVI and SCR values as such that the increase in mesh size caused the SVI values to decrease and the SCR values to increase.

Keywords: Kraft

Darbi, A., Viraraghavan, T., Butler, R. and Corkal, D. (2002), Batch studies on nitrate removal from potable water. Water SA, 28 (3), 319-322.

Full Text: 2002\Water SA28, 319.pdf

Abstract: A sulphur/lime stone autotrophic denitrification process was used to achieve the biological removal of nitrate from groundwater. The feasibility of the system was evaluated under anaerobic conditions using laboratory scale batch reactors. The optimum sulphur/limestone ratio was determined to be 1.1 (wt/wt). Different initial nitrate-nitrogen concentrations (94, 57, and 10 mg.NO₃ N/l) were used during the batch tests to examine nitrate removal efficiencies. The results showed that the higher the initial concentration, the longer it takes before nitrate removal commences. Both total suspended solid (TSS) and mean size of particles increased with time, which may be related to bacterial growth in the system.

Keywords: Autotrophic Denitrification, Drinking-Water, Sulfur

Krishnan, K.A. and Anirudhan, T.S. (2003), Removal of cadmium(II) from aqueous solutions by steam-activated sulphurised carbon prepared from sugar-cane bagasse pith: Kinetics and equilibrium studies. Water SA, 29 (2), 147-156.

Full Text: 2003\Wat SA29, 147.pdf

Abstract: Removal of cadmium(II) from aqueous solutions was studied using steam activated sulphurised carbon (SA-S-C) prepared from bagasse pith (a sugar-cane industry waste). Batch adsorption experiments were performed as a function of solute concentration, contact time, adsorbent dose, pH, temperature and ionic strength. The maximum removal took place in the pH range of 5.0 to 9.0. The maximum adsorption of 98.8 % (24.70 mg/g) took place by SA-S-C with 8.9 % sulphur content at pH 6.0 from an initial Cd(II) concentration of 50 mg/dM³. The sorption process follows pseudo-second-order kinetics. Kinetic parameters as a function of initial concentration and temperature were determined to predict the adsorption behaviour of Cd(II) onto SA-S-C. Decrease in ionic strength of the solution was found to improve the adsorption capacity of the adsorbent. The equilibrium data could be best fitted by the Langmuir adsorption isotherm equation over the entire concentration range (50 to 1000 mg/dm³). The effectiveness of the SA-S-C for Cd(II) removal was examined and compared with other adsorbents reported in the literature, At solution pH of 6.0, the maximum adsorption capacity of SA-S-C calculated by the Langmuir isotherm is 149.93 mg/g at 30degreesC. Acid regeneration was tried for several cycles with a view to recover the sorbed metal ions and also to restore the sorbent to its original state.

Keywords: Adsorption Dynamics, Langmuir Equation, Cd(II) Removal, Sulphurised Carbon, Desorption, Waste-Water, Metal-Ions, Coconut Husk, Adsorption, Sorption, Cd(II), Peat, Lead, Mercury

Thirunavukkarasu, O.S., Viraraghavan, T. and Subramanian, K.S. (2003), Arsenic removal from drinking water using granular ferric hydroxide. Water SA, 29 (2), 161-170.

Full Text: 2003\Wat SA29, 161.pdf

Abstract: This paper examines the use of granular ferric hydroxide (GFH) to remove both arsenate [As(V)] and arsenite [As(M)] present in drinking water by conducting batch and column studies. The kinetic studies were conducted as a function of pH, and less than 5 g/l was achieved from an initial concentration of 100 g/l for both As(III) and As(V) with GFH at a pH of 7.6, which is in the pH range typically encountered in drinking water supplies. In the isotherm studies, the observed data fitted well with both the Freundlich and the Langmuir models. In continuous column tests (five cycles) with tap water using GFH, consistently less than 5 g/l of arsenic was achieved in the finished water for 38 to 42 hours of column operation, where the influent had a spiked arsenic concentration of 500 g/l. High bed volumes (1260 and 1140) up to a breakthrough concentration of 5 g/l were achieved in the column studies. The adsorptive capacities for GFH estimated from the column studies were higher than that of activated alumina reported in the previous studies. Speciation of a natural water sample with arsenic showed the dominance of As(III) species over As(V). Batch and column studies showed that granular ferric hydroxide (GFH) can be effectively used in small water utilities to achieve less than 5 g As/l in drinking water.

Keywords: Adsorption, Drinking Water, Arsenic Removal, Granular Ferric Hydroxide, Arsenic Speciation, Amorphous Iron Hydroxide, Oxide-Coated Sand, West-Bengal, Adsorption, Groundwater, Ferrihydrite, Bangladesh, Coagulation, Kinetics

Fu, Y.Z. and Viraraghavan, T. (2003), Column studies for biosorption of dyes from aqueous solutions on immobilised Aspergillus niger fungal biomass. Water SA, 29 (4), 465-472.

Full Text: 2003\Wat SA29, 465.pdf

Abstract: Biosorption is becoming a promising alternative to replace or supplement the present dye removal processes from dye wastewaters. Based on the results of batch studies on biosorption of the dyes on powdered fungal biomass, Aspergillus niger, an immobilised fungal biomass was used in column studies for removal of four dyes, Acid Blue 29, Basic Blue 9, Congo Red and Disperse Red I from aqueous solutions. For each dye, the effectively pretreated powdered fungal biomass was immobilised in a polysulphone matrix in the form of spherical beads. In column studies, adsorption and elution tests were conducted for each dye and the regeneration and reuse for Acid Blue 29 were carried out. The breakthrough data from column studies could be described by the Thomas model. Results of t-tests indicated that the Thomas model constants were statistically significant at 95% confidence level for Acid Blue 29 and Basic Blue 9, but not for Congo Red and Disperse Red 1. The beads had adsorption capacities of 64.7 mg/g for Acid Blue 29, 8.3 mg/g for Basic Blue 9, 1.1 mg/g for Congo Red, and 0.1 mg/g far Disperse Red 1, respectively. In the elution tests, Acid Blue 29 and Basic Blue 9 were easily desorbed from the beads, but Congo Red and Disperse Red I were minimally desorbed. The beads in the column retained a high adsorption capacity (91%) for Acid Blue 29 in the second cycle, which suggested that the system using A. niger biomass can be developed for the removal of certain dyes.

Keywords: Aspergillus niger, Immobilisation, Acid Blue 29, Basic Blue 9, Congo Red, Disperse Red 1, Waste-Water, Color Removal, Heavy-Metals, Decolorization, Wastewaters, Mechanism, Effluents

Huang, W.J., Chen, C.Y. and Peng, M.Y. (2004), Adsorption/reduction of bromate from drinking water using GAC: Effects on carbon characteristics and long term pilot study. Water SA, 30 (3), 369-375.

Full Text: 2004\Wat SA30, 369.pdf

Abstract: This study investigated the feasibility of using granular activated carbon (GAC) to remove bromate (BrO₃^-) from drinking water through batch experiments, rapid small-scale column tests (RSSCT) and a pilot-scale study. The results indicated that the GAC capacity for BrO₃^- removal was dependent on the GAC surface characteristics and empty-bed contact time (EBCT). The GAC with a high number of basic groups and higher pH(pzc) values showed an,increased BrO₃^- removal capacity. On the other hand, BrO₃^- removal was improved by increasing EBCT. In the GAC pilot plant, a GAC column (operating with 15 min EBCT) preload for 12 months achieved a BrO₃^- and assimilable organic carbon (AOC) removal rate ranging between 7 and 96% and between 41 and 85%, respectively. The amount of BrO₃^- removed was found to be proportional to the influent BrO₃^- concentration. Based on the results of our long-term experiment, the BrO₃^- and AOC removal rate during the transition from initial GAC to biological activated carbon (BAC) was calculated as 0.12% w/w and 0.27% w/w, respectively. However, the BrO₃^- removal rate apparently decreased with increasing operating time (after 3 months). This may be a result of the contribution of the bacterial biomass being adsorbed on the GAC surface which hindered BrO₃^- reduction by GAC, either by blocking the pores or adsorbing on the activated sites for BrO₃^- reduction.

Keywords: Granular Activated Carbon, Biological Activated Carbon, Bromate, Assimilable Organic Carbon, Assimilable Organic-Carbon, Removing Bromate, Activated Carbon, Ozonation, Bromide

Demirbas, E., Kobya, M., Senturk, E. and Ozkan, T. (2004), Adsorption kinetics for the removal of chromium(VI) from aqueous solutions on the activated carbons prepared from agricultural wastes. Water SA, 30 (4), 533-472.

Full Text: 2004\Wat SA30, 533.pdf

Abstract: The batch removal of Cr(VI) from aqueous solution using low-cost adsorbents such as cornelian cherry, apricot stone and almond shell under different experimental conditions was investigated in this study. The influences of initial Cr(VI) ion concentration (20 to 300 mg·l^-1), pH (1 to 4) and particle size (0.63 to 1.60 mm) have been reported. Adsorption of Cr(VI) is highly pH-dependent and the results indicate that the optimum pH for the removal was found to be 1 for all types of carbon. A comparison of kinetic models applied to the adsorption of Cr(VI) ions on the adsorbents was evaluated for the pseudo first-order, the pseudo second-order, Elovich and intraparticle diffusion kinetic models, respectively. Results show that the pseudo second-order kinetic model was found to correlate the experimental data well.

Keywords: Adsorption, Cr(VI), Adsorption Kinetics, Low-Cost Adsorbents, Aqueous Solution

? Goswami, S. and Ghosh, U.C. (2005), Studies on adsorption behaviour of Cr(VI) onto synthetic hydrous stannic oxide. Water SA, 31 (4), 597-602.

Full Text: 2005\Wat SA31, 597.pdf

Abstract: Hydrous stannic oxide (HSO) was synthesized in the laboratory and its systematic Cr (VI) adsorption behaviour was studied by means of batch experiments. The particle size of HSO used was in the range of 140 to 290 µm. The variable parameters viz. the effects of pH, concentration of Cr (VI) and time of contact etc. are here reported. The optimum pH and time of contact required for maximum adsorption was found to be 2.0 and nearly 90 min, respectively. The experimental equilibrium adsorption data are tested for the Langmuir, Freundlich, Temkin and Redlich-Peterson equations. Results indicate the following order to fit the isotherms equations: Redlich- Peterson > Temkin > Freundlich > Langmuir. Different kinetic models have been applied to fit the experimental kinetic data. The results are compared, and indicated that the best fit is obtained with the Lagergren or pseudo first-order and the power-function models. A discussion on the adsorption mechanism with respect to the thermodynamic parameters leads to two possible interpretations: One is the exothermic nature of the adsorption process and the other is the ion-ion type electrostatic interaction between the adsorbent and adsorbate ion.

Keywords: Cr(VI), Adsorption Mechanism, Hydrous Stannic Oxide(HSO), Isotherm, Kinetics, Thermodynamic Parameters

? Singh, T.S., Parikh, B. and Pant, K.K. (2006), Investigation on the sorption of aluminium in drinking water by low-cost adsorbents. Water SA, 32 (1), 49-54.

Full Text: 2006\Wat SA32, 49.pdf

Abstract: Aluminium is one of the trace inorganic metals present in drinking water. High aluminium concentrations (3.6 to 6 mg/L) may precipitate as aluminium hydroxide affecting aquatic life. Aluminium is also a suspected agent of neurological disorders such as Alzheimer’s disease and senile dementia. The present investigation aims at the sorption of aluminium from drinking water using a low-cost adsorbent. Rice husk char and activated rice husk char were prepared and characterised for various physicochemical properties. The performance of rice husk char (RHC) was compared with other low-cost adsorbents for their aluminium removal capacity. The effect of pH, initial concentration, contact time and temperature was studied for adsorption of aluminium from water under batch conditions. The maximum adsorption capacity was observed with rice husk char at an optimal pH of 4.2. The adsorption of aluminium follows the Freundlich adsorption isotherm. The rate of aluminium adsorption was successfully described by a first-order kinetic model. The thermodynamic study revealed that aluminium adsorption is an exothermic process and the adsorption decreases with an increase in temperature.

Keywords: Aluminium Adsorption, Batch, Kinetics, Thermodynamics, Rice Husk Char

? Salipira, K.L., Mamba, B.B., Krause, R.W., Malefetse, T.J. and Durbach, S.H. (2008), Cyclodextrin polyurethanes polymerised with carbon nanotubes for the removal of organic pollutants in water. Water SA, 34 (1), 113-118.

Full Text: 2008\Wat SA34, 113.pdf

Abstract: Organic compounds are some of the major pollutants of water worldwide. They can be toxic or carcinogenic even at low concentrations. The non-reactivity of these species makes it difficult to remove them from water, particularly when present at concentration levels of nanograms per litre (ng center dot l(-1)) or lower. Reasonably inexpensive yet effective methods for the removal of these organic pollutants to below ppb levels are therefore required. Insoluble cyclodextrin polyurethanes have demonstrated the ability to remove organic species from water at concentration levels of nanograms per litre. Carbon nanotubes have also been reported to efficiently adsorb some organic molecules such as dioxins and polychlorinated dibenzo-furans. However, these nanotubes are currently too expensive to be used on their own in water treatment. An investigation into the use of cross-linked cyclodextrin polyurethanes copolymerised with functionalised multiwalled carbon nanotubes as adsorbents for organic pollutants has yielded very useful results which may have an impact in future water treatment applications.

Keywords: Adsorption, Africa, Carbon Nanotubes, Cyclodextrins, Emerging Contaminants, Endocrine Disruptors, Exposure, Impact, Multiwalled Carbon Nanotubes, Polymer Composites, South-Africa, Trichloroethylene, Water

? Brown, R., Mills, A.J. and Jack, C. (2008), Non-rainfall moisture inputs in the Knersvlakte: Methodology and preliminary findings. Water SA, 34 (2), 275-278.

Full Text: 2008\Wat SA34, 275.pdf

Abstract: Dew, fog/mist and water vapour adsorption, the 3 vectors by which non-rainfall water can be added to soil water, may play a critical role in ecosystem function in arid zones. This paper explores a methodology for overcoming the challenges of measuring small daily inputs of non-rainfall water in the harsh environment of the Knersvlakte on the West Coast of South Africa. An automatic micro-lysimeter (MLS) - an experimental arrangement of a sensitive electro-mechanical load cell, suitable electronic amplification and signal conditioning, and a microcontroller was developed. A microcomputer was employed for overall system control and data logging. Initial field work took place between late September and November 2006 on Arizona Farm, 30 km north of Vanrhynsdorp. In March 2007, subsequent work began at the Ratelgat BIOTA observatory. Manual soil weight sampling corresponded well with theoretical dew maximums, with measured maximum and minimum dew/fog of 0.4 mm and 0.08 mm (+/- 0.08 mm) (both in September 2006). Measurements from the first prototype MLS were marred by large (+/- 0.24 mm) error figures, signal dropout from the analog to digital converter, and insufficient range at the required resolution. The subsequent prototype (field tested in March 2007 and still in use) provides much smaller errors (+/- 0.05 mm). Calibration testing at Ratelgat indicates maximum overnight dew/fog contributions of 0.35 rum (+/- 0.05 mm), which corresponds with theoretical calculations as well as field measurements in other arid zones. Maximum dew/fog derived soil water occurs between 07:00 and 09:15. Surprisingly, soil weight, as a consequence of dew/fog inputs, starts to increase shortly after 17:20. These are preliminary findings and longer term testing and validation are ongoing at present. The role of quartz pebbles and small succulent plants in the interception of non-rainfall water is still to be explored.

Keywords: Adsorption, Africa, Desert, Dew, Dew Formation, Environment, Evaporation, Fog, Fog, Knersvlakte, Methodology, Micro-Lysimeter, Non-Rainfall Water, Soil, South-Africa, Water, West Coast

? Potgieter, J.H., Bada, S.O. and Potgieter-Vermaak, S.S. (2009), Adsorptive removal of various phenols from water by South African coal fly ash. Water SA, 35 (1), 89-96.

Full Text: 2009\Wat SA35, 89.pdf

Abstract: South African coal fly ash (SACFA) was used to effectively remove phenol, 2-nitrophenol and 4-nitrophenol from wastewater. The rate of adsorption follows first-order kinetics before attaining equilibrium with the sorption rate (K(ad)) obtained being the highest for 4-nitrophenol (p-nitrophenol) (7.0 x 10(-3)/h), followed by phenol (1.2 x 10(-3)/h) and 2-nitrophenol (o-nitrophenol) (1.0 x 10(-3)/h). Batch studies were performed to evaluate the adsorption process, and it was found that the Freundlich isotherm effectively fits the experimental data for the adsorbates better than the Langmuir model, with the fly ash having the highest adsorption capacity of 6.51 X 10(-2) mg/g for 4-nitrophenol, 6.00 x 10(-2) mg/g for 2-nitrophenol and 6.31 x 10(-2) mg/g for phenol. The fly ash was found to adsorb 90.2% of phenol, 88.9% of 2-nitrophenol and 92.6% of 4-nitrophenol at an initial concentration of 20 mg/l. The desorption studies suggested that the desorption of 4-nitrophenol was the most difficult of the three adsorbates to be desorbed. The desorption efficiency was 17.9% for phenol, 18.8% for 2-nitrophenol and 10.2% for 4-nitrophenol. This work proved that SACFA can be used as an efficient adsorbent material for removal of phenol from water and wastewater.

Keywords: Activated Carbon, Adsorption, Adsorption-Desorption, Aquatic Systems, Aqueous-Solution, Batch Study, Biosorption, Chlorophenols, England, Fly Ash, Isotherm, Kinetics, Model, Nitrophenols, Organic Pollutants, P-Nitrophenol, Phanerochaete-Chrysosporium, Phenol, Power-Plant, Sorption, South-Africa, Waste-Water, Water

? Schoeman, J.J. (2009), Performance of a water defluoridation plant in a rural area in South Africa. Water SA, 35 (1), 97-101.

Full Text: 2009\Wat SA35, 97.pdf

Abstract: The fluoride concentration of a borehole water supply in a rural area (Madibeng Local Municipality, North West Province, South Africa) varies between 5 and 6 mg/l. This water is therefore not suitable for potable purposes because the high fluoride concentration may cause mottling of tooth enamel in children and fluorosis in adults. Therefore, the fluoride concentration should be reduced to less than 1.5 mg/l to make the water suitable for potable purposes. The activated alumina and reverse osmosis processes are both processes that can be very effectively applied for water defluoridation. The activated alumina process, however, is considered to be a more simple and robust process for water defluoridation, especially in a rural area. Therefore, the activated alumina process was selected for water defluoridation. An activated alumina plant was designed, constructed and commissioned in the rural area. Fluoride in the feed water is removed from 6 to 8 mg/l to less than 1.5 mg/l. No reduction in plant output was experienced over 6 service cycles. Therefore, it appears that fouling of the activated alumina should not be a problem. Plant output varied between 940 and 1 296 m(3) to a fluoride breakthrough of approximately 2.0 mg/l. No significant operational problems were experienced during commissioning and the plant is performing satisfactorily. Spent regenerant is disposed of into evaporation ponds. It was demonstrated that a 1(st) world technology could be effectively applied in a rural area with proper training and supervision of the operators. The capital and operational costs of the 200 m(3)/d defluoridation plant are estimated at approximately R1.2m. and R0.7/m(3) treated water.

Keywords: Activated Alumina, Adsorption, Africa, Children, Costs, Drinking-Water, Electrodialysis, Fluoride, Fluoride Removal, Performance, Plant Performance, South-Africa, Training, Water, Water Defluoridation

? Mamba, B.B., Krause, R.W., Malefetse, T.J., Sithole, S.P. and Nkambule, T.I. (2009), Humic acid as a model for natural organic matter (NOM) in the removal of odorants from water by cyclodextrin polyurethanes. Water SA, 35 (1), 117-120.

Full Text: 2009\Wat SA35, 117.pdf

Abstract: Current practices in some water-treatment facilities have reported that natural organic matter (NOM) blocks the adsorption sites of activated carbon resulting in lower geosmin and 2-methylisoborneol (2-MIB) removal. Humic acid has been reported to compete with geosmin and 2-MIB removal in the same way. The removal of odour chemicals such as geosmin and 2-MIB is important for potable-water treatment by water supply companies and municipalities. We have previously demonstrated that cyclodextrin polyurethanes are capable of removing a number of organic pollutants from water, but are not able to reduce the levels of NOM significantly. We wished to determine if the polymers would selectively remove geosmin and 2-MIB, despite the presence of NOM. Humic acid was chosen as a model for NOM since NOM constitutes about 70% of humic acid. Results obtained from this study indicate that the presence of humic acids at different concentrations could not affect the removal of geosmin and 2-MIB when cyclodextrin polymers were used since 90% removal was achieved. However the UV-Vis analysis showed a low removal of humic acids (3 to 20%).

Keywords: 2-Methylisoborneol (2-MIB), Activated Carbon, Adsorption, Africa, Cyclodextrin Polymers, Geosmin, Geosmin, Humic Acids, MIB, Model, Simultaneous Adsorption, South-Africa, Water

? Mamba, B.B., Dlamini, N.P. and Mulaba-Bafubiandi, A.F. (2009), Acidithiobacillus caldus, Leptospirillum spp., Ferroplasma spp. and Sulphobacillus spp. mixed strains for use in cobalt and copper removal from water. Water SA, 35 (3), 301-306.

Full Text: 2009/Wat Sa35, 301.pdf

Abstract: Bacteria from the genus Acidithiobacillus, Leptospirillum and Ferroplasma, Sulphobacillus are often associated with water remediation. In this study a consortium of Acidithiobacillus caldus, Leptospirillum spp., Ferroplasma spp. and Sulphobacillus spp. was cultured and used to remove Cu²⁺ and Co²⁺ from synthetic aqueous sulphate solutions. The influence of experimental conditions such as pH, temperature, time, volume and metal concentration on the efficiency of the biosorption process was investigated. Biosorption of 54 to 67% Cu (pH 2, 37°C, 24 h) and 23-70% Co (pH 2, 37°C, 24 h) was observed from solutions containing 3.86 g.l^-1 Cu²⁺ ions and 3.36 g.l^-1 Co²⁺ ions. Such findings suggest that if optimal conditions for biosorption of the metals by micro-organisms are achieved, this should afford a cost-effective method of removing metal species from water and aqueous solutions.

Keywords: Adsorption, Adsorption, Aqueous-Solution, Arrhizus, Biosorption, Biosorption, Cadmium, Cobalt, Copper, Equilibrium, Ions, Lead(II), Pb(II), Sorption, Synthetic Solution

? Mamba, B.B., Nyembe, D.W. and Mulaba-Bafubiandi, A.F. (2009), Removal of copper and cobalt from aqueous solutions using natural clinoptilolite. Water SA, 35 (3), 307-314.

Full Text: 2009\Wat SA35, 307.pdf

Abstract: Southern African clinoptilolite capability as an ion-exchanger with respect to Cu²⁺ and Co²⁺ was investigated in order to consider its possible application at removing metals from aqueous solutions. The column method was used in the cation-exchange processes with synthetic solution concentrations of 0.07 M (3.86 g/l), 0.33 M (19.31 g/l) and 0.66 M (38.63 g/l) of Cu²⁺ solution and 0.07 M (3.34 g/l), 0.33 M (16.69 g/l) and 0.66 M (33.37 g/l) of Co²⁺ solution. Synthetic non-mixed sulphate solutions of copper and cobalt recorded maximum cation uptakes of 79% and 63% with 0.02 M HCl-activated clinoptilolite respectively. From the Cu/Co mixed solutions, both cobalt and copper recorded a 79% uptake with 0.02 M HCl-activation. The 0.04 M HCl activation gave percentage removals of 79% and 77% for Co²⁺ and Cu²⁺ respectively. In the ion-exchange evaluation part of the study, it was found that in every concentration range, the adsorption mass ratio of clinoptilolite to metal concentration conformed to both Langmuir and Freundlich adsorption isotherms. However, the non-mixed aqueous solutions of Cu(2+) and Co(2+) fitted mainly the Langmuir equation. It was found that the adsorption process depends on the hydrated radius of the cation being exchanged, the concentration of the acid that activates the clinoptilolite and the concentration of the targeted cation in solution.

Keywords: Adsorption, Africa, Capacity, Cation Exchange, Cations, Clay, Clinoptilolite, Cobalt, Copper, Evaluation, Heavy-Metals, Ion-Exchange, Isotherms, Selectivity, Sorption, South-Africa, Wastewater, Water, Zeolites

? Bajpai, S.K. and Jain, A. (2010), Removal of copper(II) from aqueous solution using spent tea leaves (STL) as a potential sorbent. Water SA, 36 (3), 221-228.

Full Text: 2010\Wat SA36, 221.pdf

Abstract: In this work spent tea leaves were used as a non-conventional, cost-effective sorbent for removal of Cu(II) from aqueous solutions in batch systems. The sorbent was characterised with respect to surface area, pore volume, density, etc. The equilibrium sorption data were applied to various sorption isotherm models, and the order of fitness was: Langmuir > Temkin > Freundlich. The maximum sorption capacity Q₀ was found to be almost 90.9 and 68.4, as evaluated using Langmuir isotherms at 27ºC and 37ºC respectively. The observed decrease in sorption capacity with temperature indicated the exothermic nature of the uptake process. The kinetic uptake data were best interpreted by a pseudo second-order kinetic model with values of rate constants of adsorption of 1.47×10^-2 and 3.01×10^-2 g/mg.min, respectively, for the initial sorbate concentrations of 10 and 20 mg. l^-1 at 27ºC. The sorption mean free energy was determined from the Dubinin Radushkevich (DR) isotherm model and was found to be 9.91 kJ.mol^-1, indicating ion exchange/chemisorption nature of uptake process. The Cu(II) uptake was found to increase with the pH of the sorbate solution and maximum sorption was observed in the pH range of 1.0 to 4.8. Finally, thermodynamic parameters like ΔG, ΔH, ΔS were also evaluated.

Keywords: Adsorbents, Adsorption, Adsorption-Kinetics, Aqueous Solution, Aqueous Solutions, Batch, Biosorption, Capacity, Copper(II), Cost-Effective, Cr(VI), Cu(II), Data, Energy, Equilibrium, Exothermic, Fitness, Freundlich, Industry Waste, Ions, Isotherm, Isotherm Model, Isotherms, Kinetic, Kinetic Model, Langmuir, Langmuir Isotherms, Langmuir Model, Model, Models, Pb(II), pH, Pore Volume, Potential, Pseudo Second Order, Pseudo Second-Order, Pseudo-Second-Order, Rate Constants, Removal, Sawdust, Second Order, Second-Order, Solution, Solutions, Sorbate, Sorbent, Sorption, Sorption Capacity, Sorption Isotherm, Spent Tea Leaves, Surface, Surface Area, Systems, Temperature, Thermodynamic, Thermodynamic Parameters, Uptake, Volume, Work

? Dlamini, N.P., Mamba, B.B. and Mulaba-Bafubiandi, A.F. (2010), The effect of silica concentration on the biosorption of Cu²⁺ and Co²⁺ from aqueous solutions mediated by strains of Bacillus. Water SA, 36 (4), 445-450.

Full Text: 2010\Wat SA36, 445.pdf

Abstract: Bacillus strains were isolated from a mine tailings dump in Nigel town, south-east of Johannesburg. These were then grown at 37(+/- 0.5) degrees C in a trace element-agitated liquid media. The effects of pH, contact time, initial ion concentration and the presence of co-cations were studied to ascertain the optimal conditions for biosorption to take place. Test solutions contained 0.002 M, 0.07 M and 0.2 M of either copper or cobalt ions. The Bacillus strains removed the copper and cobalt more efficiently from solutions of low concentration (0.002 M and 0.07 M) than from solutions of high concentration (0.2 M) over a 48 h period. Maximum biosorption was obtained at pH 6.5 and 5.5 for copper and cobalt solutions, respectively. The presence of silica led to an initial increase in both copper and cobalt biosorption, though higher concentrations of silica resulted in a decrease in metal uptake by Bacillus strains.

Keywords: Africa, Bacillus, Binary, Biosorption, Cobalt, Copper, Copper(II), Equilibrium, Ions, Lead(II), Metals, Pb(II), Silica, Single, Sorption, South-Africa, Surfaces, Waste, Water

? Onyango, M.S., Masukume, M., Ochieng, A. and Otieno, F. (2010), Functionalised natural zeolite and its potential for treating drinking water containing excess amount of nitrate. Water SA, 36 (5), 655-662.

Full Text: 2010\Wat SA36, 655.pdf

Abstract: An excess level of nitrate in drinking water is responsible for methemoglobinemia, or 'blue baby' disease. Consequently, management of nitrate in drinking water is universally of public health interest. In this study, clinoptilolite functionalised with cationic surfactant hexadecyltrimethyl ammonium (HDTMA) was used for the removal of nitrate from drinking water. The effects of surfactant loading, adsorbent dosage, pH, coexisting ions, temperature and environmental water quality on the adsorption of nitrate were investigated. It was found that adsorption was optimum when the initial concentration of the functionalising surfactant was 3 000 mg.l(-1). An increase in adsorbent dosage raised the percentage removal of nitrate. The valency of the coexisting anion had a major effect on nitrate removal, with the presence of phosphate (a trivalent anion) leading to the lowest removal ability. Temperature and pH had negligible effects on adsorbent performance. Environmental water samples (natural groundwater samples from Limpopo Province, South Africa) were tested and it was found that the World Health Organisation (WHO) regulatory compliance can be achieved even when the initial concentration of nitrate exceeds 300 mg.l(-1). Equilibrium data was modelled using the Freundlich and Langmuir isotherms and the data conformed well to the Freundlich isotherm, indicating the heterogeneous nature of the active sites. Kinetically, nitrate adsorption was best described by the pseudo-second rate equation.

Keywords: Adsorption, Adsorption, Africa, Aqueous-Solution, Capacity, Clinoptilolite, Compliance, Equilibrium, Groundwater, Hdtma-Modified Zeolite, Ion-Exchange, Ions, Isotherm, Isotherms, Kinetics, Natural Zeolite, Nitrate, Public Health, Removal, Reverse-Osmosis, Sorption, South-Africa, Water, Who, Zeolite

? Noubactep, C. (2010), The fundamental mechanism of aqueous contaminant removal by metallic iron. Water SA, 36 (5), 663-670.

Full Text: 2010\Wat SA36, 663.pdf

Abstract: Contaminant co-precipitation with continuously generated and transformed iron corrosion products has received relatively little attention in comparison to other possible removal mechanisms (adsorption, oxidation, precipitation) in Fe(0)/H₂O systems at near neutral pH values. A primary reason for this is that the use of elemental iron (Fe(0)) in environmental remediation is based on the thermodynamic-founded premise that reducible contaminants are potentially reduced while Fe(0) is oxidised. However, co-precipitation portends to be of fundamental importance for the process of contaminant removal in Fe(0)/H₂O systems, as the successful removal of bacteria, viruses and non reducible organic (e.g. methylene blue, triazoles) and inorganic (e.g. Zn) compounds has been reported. This later consideration has led to a search for the reasons why the importance of co-precipitation has almost been overlooked for more than a decade. Three major reasons have been identified: the improper consideration of the huge literature of iron corrosion by pioneer works, yielding to propagation of misconceptions in the iron technology literature; the improper consideration of available results from other branches of environmental science (e.g. CO₂ corrosion, electrocoagulation using Fe(0) electrodes, Fe or Mn geochemistry); and the use of inappropriate experimental procedures (in particular, mixing operations). The present paper demonstrates that contaminant co-precipitation with iron corrosion products is the fundamental mechanism of contaminant removal in Fe(0)/H₂O systems. Therefore, the 'iron technology' as a whole is to be revisited as the 'know-why' of contaminant removal is yet to be properly addressed.

Keywords: Adsorption, Carbon-Dioxide Corrosion, Co-Precipitation, Corrosion, Elemental Iron, Environmental Science, Granular Iron, Groundwater Remediation, Iron, Iron Corrosion, Iron Oxhydroxides, Literature, Long-Term Performance, Mild-Steel, Natural-Waters, Permeable Reactive Barriers, Plattnerite) Reductive Dissolution, Primary, Review, South-Africa, Water, Zero-Valent Iron, Zerovalent Iron

? Moodley, K.M., Singh, R., Musapatika, E.T., Onyango, M.S. and Ochieng, A. (2011), Removal of nickel from wastewater using an agricultural adsorbent. Water SA, 37 (1), 41-46.

Full Text: 2011\Wat SA37, 41.pdf

Abstract: Chemical wastewater streams may contain toxic compounds which are non-biodegradable, and therefore require advanced treatment techniques such as adsorption. However, application of adsorption processes is often limited by the cost of adsorbents. In this study, the adsorption capacity of a low-cost adsorbent (pine sawdust) was investigated by treating wastewater containing nickel (II) and other heavy metal ions. Results were analysed using response surface methodology and a factorial design was employed to determine the interactive effects of the various factors on the adsorption capacity. Furthermore, Langmuir and Freundlich adsorption isotherms were fitted to experimental data to characterise the adsorption of the nickel ions by the pine sawdust. As a result, the highest adsorption capacity was attained at the combined effect of low adsorbent dose, high pH and high initial concentration. On the other hand, the Freundlich isotherm fitted the experimental data better than the Langmuir isotherm. Results of this study indicate that the use of pine sawdust could be a promising solution to the elimination of nickel ions from multi-component aqueous solutions.

Keywords: Activated Carbon, Adsorption, Adsorption, Africa, Aqueous-Solutions, By-Products, Heavy-Metals, Ions, Isotherm, Isotherms, Langmuir Isotherm, Methodology, Nickel Ions, Optimization, Pb(II), Process Variables, Response-Surface Methodology, Sawdust, Sawdust, South-Africa, Wastewater, Water