African Journals Online
WaterSA

Volume 29, Issue 2, 2003
ABSTRACTS

A seeded ambient temperature ferrite process for treatment of AMD waters: magnetite formation in the presence and absence of calcium ions under steady state operation

Morgan, B.E; .Lahav, O.; Hearne, G.R.; Loewenthal, R.E.

Abstract: An ambient temperature ferrite process has been developed for the removal of iron and non-ferrous metals from AMD waters. The process involves the controlled formation of magnetite (Fe₃O₄) that has the capacity to substitute divalent and trivalent cations as part of the lattice, thus forming a stable easy-to-separate ferrite. This paper reports on continuous operations of the process in the absence and presence of Ca²⁺, which is well known to impede ferrite formation. In the first instance, the process involves the precipitation of hydroxy-metals at pH 10.5 and their subsequent adsorption onto magnetite seed in a contact stabilisation reactor. Second, liquid-solid separation is effected and the solid fraction is subsequently treated in an oxidising reactor in which a fraction of the ferrous species is oxidised to an intermediate ferric precipitate. Finally, both ferrous and ferric species undergo crystalchemical processing and are incorporated into stable magnetite. Results indicate that Ca²⁺ interference can be overcome by maintaining a high ratio of precipitated ferrous species to dissolved Ca²⁺. It was found that in order to attain the required high Fe²⁺:Ca²⁺ ratio, the solid ferrous-hydroxy species concentration in the oxidation reactor should be maintained at above 1 200 mg Fe/l. Ferrous to calcium ratios greater than 3 were found to favour magnetite formation. In the absence of Ca²⁺, a solid ferroushydroxy species concentration of approximately 500 mg/l was sufficient for magnetite formation. Operating the process at ferroushydroxy concentrations of lower than 1 200 and 500 mg/l in the presence and absence of calcium respectively enhanced the formation of other iron oxides, primarily goethite. In all experiments the iron concentration in the effluent was less than 1 mg/l, the sludge volume index (SVI) extremely low (< 4 ml/g) and the percentage of ferrous-hydroxy species in the sludge can be reduced to about 1%. These features, together with the potential to incorporate heavy metals into a stable compound, make the process very promising for AMD treatment.

Keywords: Ferrite process, Magnetite seed, Calcium interference, Acid mine drainage

A proposed chemical mechanism for biological phosphate removal in activated sludge treatment of wastewater

Van der Post, D.C.; Schutte, C.F.

Abstract: This paper presents an alternative for the "all biological" phosphate removal model. It is postulated that a chemical substance in wastewater reacts with orthophosphate under anaerobic conditions to make the so-called luxury uptake of phosphorus possible in biological nutrient removal (BNR) activated sludge plants. Experimental evidence indicates that the reaction product, an organic phosphate, is the phosphate species that is taken up by organisms in the process of biological phosphate removal. The research on which this paper is based, forms part of a Ph.D. study and further research to confirm the initial observations and to identify the chemical agent involved in biological phosphorus removal is continuing.

Treatment of a textile dye in the anaerobic baffled reactor

Bell, Joanne; Buckley, Chris A.

Abstract: Synthetic organic colourants, the majority of which are recalcitrant in nature, are used in many different manufacturing processes. The dyes are released into the environment in industrial effluents and are highly visible even at low concentrations (< 1 mg/l). Decolorisation of the dye CI Reactive Red 141 was investigated in a laboratory-scale anaerobic baffled reactor (ABR). The results of the physical decolorisation tests suggested significant decolorisation due to adsorption to the biomass; however, it is possible that the dye chromophores were reduced due to the low redox potential environment within the test bottles. No dye breakthrough, due to adsorption saturation, was observed during operation of the reactor. COD reduction was consistently > 90 %. Colour reduction averaged 86 %. The biomass showed acclimation to the dye, with increased methanogenic activity with each increase in dye concentration. The reactor operation was stable, even with increases in the dye concentration. This investigation has shown that successful treatment of a highly coloured wastewater is possible in the ABR.

Keywords: Anaerobic baffled reactor, Textile dyes, CI Red 141

Household chemicals and personal care products as sources for xenobiotic organic compounds in grey wastewater

Eriksson, E.; Auffarth, K.; Eilersen, A-M.; Henze, M.; Ledin, A.

Abstract: Despite contributing 75% of the total wastewater flow to domestic sewers, little is currently known concerning the detailed production patterns and characteristics of grey wastewater. In this study, an inventory of the consumption of household chemicals including a diary survey of water-consuming activities was carried out over seven consecutive days in a block of flats. In total 290 parameters in 92 household chemicals were registered in the inventory in which 30 out of 38 tenants participated. The study was accompanied by quantitative analyses of selected parameters and a screening for organic components in grey wastewater. More than 190 individual components were identified by GC-MS. Identified substances were grouped into eight substance classes based on their application and their concentrations were semi-quantitatively assessed. Several fragrances like citronellol, hexyl cinnamic aldehyde and menthol as well as some preservatives, e.g. citric acid and triclosan, were identified. The measurements also showed that unwanted and unexpected compounds like drugs and pesticides could be present, as well as chemicals not directly deriving from household chemicals or personal care products, e.g. flame-retardants. The inventory provided detailed information about the consumption of various types of household chemicals, but no information on compound concentrations could be assessed due to the limited data in the list of contents of the household chemicals. It was shown that tracking of potentially toxic compounds used in households was possible.

Keywords: Characterisation, Diary survey, Greywater, Inventory, Screening, Xenobiotic

Removal of cadmium(II) from aqueous solutions by steam-activated sulphurised carbon prepared from sugar-cane bagasse pith: kinetics and equilibrium studies

Krishnan, K. Anoop; Anirudhan, T.S.

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 1 000 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 30°C. 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

An empirical study of factors influencing lime slaking. Part II: lime constituents and water composition

Potgieter, J.H.; Potgieter, S.S.; De Waal, D.

Abstract: Chloride, carbonate and sulphate ions are common constituents of many waters and are often found in high concentrations in water used for the slaking of lime. Furthermore, magnesium oxide is a common constituent of many limestones and can, after calcining, also affect the hydration rate of the lime if it is present as magnesium oxide. The purpose of this investigation was to assess quantitatively the effect of these various chemical influences, whether it be from a geological origin or present in the slaking water, on the slaking rate of lime. It was found that the presence of chloride ions in the slaking water increased the lime reactivity, while sulphate and carbonate ions in the slaking water retarded the hydration reaction. Magnesium oxide also had a detrimental effect on the slaking rate of lime.

Keywords: Lime, Slaking, Chloride, Sulphate, Carbonate

Arsenic removal from drinking water using granular ferric hydroxide

Thirunavukkarasu, O.S.; Viraraghavan, T.; Subramanian, K.S.

Abstract: This paper examines the use of granular ferric hydroxide (GFH) to remove both arsenate [As(V)] and arsenite [As(III)] present in drinking water by conducting batch and column studies. The kinetic studies were conducted as a function of pH, and less than 5 mg/l was achieved from an initial concentration of 100 mg/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 mg/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 mg/l. High bed volumes (1260 and 1140) up to a breakthrough concentration of 5 mg/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 mg As/l in drinking water.

Keywords: Adsorption, Drinking water, Arsenic removal, Granular ferric hydroxide, Arsenic speciation

The effect of a water-hygiene educational programme on the microbiological quality of container-stored water in households

Nala, N.P.; Jagals, P.; Joubert, G.

Abstract: This study investigated whether a water-handling hygiene education programme could improve the health-related microbiological quality of container water stored and used in households in a dense urban settlement in the Free State Province. Previous studies in the area indicated that stored container water became contaminated during the process of fetching from communal standpipes and then storing and handling the water at home, which exposed the study population to a potential risk of microbiological infection. A water-hygiene education programme was implemented together with a health-related microbiological water quality assessment programme. Members of selected households participated in a series of domestic water-handling hygiene education training sessions over a period of eight months and the quality of their stored water monitored for improvement in tandem over the same period. The results were compared to those of similar tests done during previous studies in the same area. Turbidity, heterotrophic bacteria numbers and total coliform bacteria were used as indicators of general microbial water quality while E. coli bacteria were used to indicate faecal pollution. While the results generally reflected significant improvements for all the indicators from the previous studies, a potential risk of infection was still indicated for consumers. Based on education programme attendance profile, the study sample was divided into frequent, intermittent and never groups. No significant changes were found in water quality between the three groups, even though the frequent group attended most of the training sessions. This implies that the programme did not have a particular influence on any one group. Container-stored water was still being contaminated in the domestic environment despite the water-handling hygiene education programme. An improved hygiene-education programme appears to be needed to change deep-rooted inherent behaviours such as hand- washing prior to water handling as well as proper protection of container-stored water from environmental contamination.

Keywords: Water-hygiene education, Container-stored water quality, Turbidity, Heterotrophic bacteria, Total coliforms, E. coli, Infection risk

Detection of viable toxigenic Vibrio cholerae and virulent Shigella spp. in environmental waters by pit-stop seminested polymerase chain reaction assays

Du Preez, M.; Venter, S.N.; Theron, J.

Abstract: A rapid and sensitive assay was developed for the detection of low numbers of viable Vibrio cholerae and Shigella spp. cells in environmental and drinking water samples. Water samples were filtered, and the filters were enriched in a non-selective medium. The enrichment cultures were prepared for polymerase chain reactions (PCR) by a rapid and simple DNA extraction procedure consisting of boiling. Seminested PCR, based on specific amplification of the cholera toxin operon of V. cholerae and the invasion plasmid antigen gene (ipaH) of virulent Shigella spp., was performed and the PCR products were visualised by agarose gel electrophoresis. The assay allowed the detection of as few as 1 cfu/100 ml of V. cholerae and 8 cfu/100 ml of Shigella cells. A comparison of the PCR method and culturing methods by using environmental water samples showed that the PCR method has a higher level of sensitivity than culturing methods. As an application of the PCR detection protocol, environmental water samples were screened for the presence of V. cholerae and Shigella spp. Positive amplifications resulted from V. cholerae and Shigella species in environmental samples. The results obtained indicate that the described seminested PCR has the advantage of a rapid turn-around time and fulfils the requirements of sensitivity for use in an environmental laboratory.

Keywords: Vibrio cholerae, Shigella, Water-borne pathogens, Polymerase chain reaction, Environmental waters, Drinking water, Detection

Pollution assessment in the Keiskamma River and in the impoundment downstream

Fatoki, O.S.; Gogwana, P.; Ogunfowokan, A.O.

Abstract: The Keiskamma River and the impoundment, downstream were characterised over a one-year period by using standard physicochemical methods to assess their present qualities. The pH levels are normal in the river and in the impoundment but turbidity values and the levels of electrical conductivity are high in both water systems. Also, the nutrient levels in both systems are eutrophic. The DO and BOD levels exceeded EU guideline values for the protection of the aquatic ecosystem. The Keiskammahoek Sewage Treatment Plant (KSTP) was identified as a pollution point source into the receiving river and the impoundment. Its treatment performance was investigated. Significant pollution of the river and the impoundment from the KSTP was indicated for electrical conductivity, nutrients and oxygen-demanding substances.

Keywords: Pollution point source, River impoundment

The application of geographic information systems (GIS) in the analysis of nutrient loadings from an agro-rural catchment

Mtetwa, S.; Kusangaya, S.; Schutte, C.F.

Abstract: A large amount of data is usually generated during environmental monitoring programmes. The data need to be transformed into useful information that can be used for interpretation and analysis of problems. This paper outlines the feasibility of using geographic information system (GIS) techniques in the analysis of catchment nutrient yields with the aim of providing a knowledge base for effective decision-making. In this case the spatial and temporal distributions of the nutrient yields in the catchment were analysed. Interpolation with the GIS packages (Arc View Version 3.1 and Arc View Spatial Analyst) enabled the estimation of yields in areas without actual measurement thereof.

Verification of rainfall forecasts for the Vaal Dam catchment for the summer rainfall seasons of 1994 to 1998

Marx, H.G.; Dyson, L.L.; Van Heerden, J. 

Abstract: Rainfall forecasts compiled by the South African Weather Service (SAWS) are used daily by agriculture, industry, sportsmen and the general public. Because of the importance of the rainfall forecast, it is of considerable interest to know how reliable these forecasts are. The SAWS evaluates the rainfall forecasts issued by the Central Forecasting Office (CFO) on a daily basis. A hit score is determined in each of 19 rainfall districts throughout South Africa. This renders a result of approximately 60% correct forecasts for all 19 districts. This paper investigates the accuracy of the predicted rainfall percentages or rainfall classes. The 24h rainfall forecasts are verified for the summer months (October to March) of 1994 to 1998 for the Vaal Dam catchment. The rainfall distribution classes were chosen to represent no-rain, isolated rain, scattered rain and widespread rain. Results indicate that the percentage of correct forecasts is less than the values obtained by using the SAWS's hit score method. The predicted widespread rain class is less than 25% correct. The tendency exists to forecast scattered rain whenever any rain event is predicted. A rain event is seldom missed (3%), but some rain is often forecast (45%) for days, which then remain dry days. A more comprehensive rainfall forecast evaluation system is recommended.

Keywords: Rainfall forecasts, Verification, Rainfall distribution classes, Vaal Dam catchment

Structure and precursors of the 1992 / 93 drought in KwaZulu-Natal, South Africa from NCEP reanalysis data

Dube, Lawrence T.; Jury, Mark R.

Abstract: The historical context and potential causes and structure of the 1992/93 drought in KwaZulu-Natal are analysed using NCEP reanalysis data. The analysis indicates that increased westerly winds with surface marine lows and continental highs prevailed over Southern Africa. Anomalous divergence and subsidence occur over the eastern subcontinent, coupled with reduced tropical moist inflows. Mid-latitude confluence, anticyclonic vorticity and upper level convergence suppressed convection over KwaZulu/Natal. The precipitable water field reflects a SE-NW orientated stationary wave-train pattern over Southern Africa with KwaZulu-Natal anti-phase with the Zambezi valley. A meridional overturning cell is seen as a driving mechanism behind the 1992/93 drought over South Africa. The velocity potential shows a dipole between the Zambezi and the SW Indian Ocean, and it appears that the kinematic structure was more important than the thermodynamic. Impacts include a reduction in crop yield and streamflows, and a slowing of economic activity.

Control options for river water quality improvement: a case study of TDS and inorganic nitrogen in the Crocodile River (South Africa)

Deksissa, Tolessa; Ashton, Peter J.; Vanrolleghem, Peter A.

Abstract: Using a simple conceptual dynamic river water quality model, the effects of different basin-wide water quality management options on downstream water quality improvements in a semi-arid river, the Crocodile River (South Africa) were investigated. When a river is impacted by high rates of freshwater withdrawal (in its upstream reaches), and receives polluted side-stream inflows and wastewater effluent discharges (in the middle reaches), river water quality can deteriorate seriously over time. This study focused on two water quality problems: Progressive increases in the concentrations of total dissolved solids (TDS) as a measure of salinity, and the concentrations of nitrate-plus-nitrite and ammonia (as inorganic nitrogen) as a measure of eutrophication. Based on a lowflow analysis for the period prior to construction of the Kwena Dam (1960 to 1979), the 7d low flows that could be expected to occur every 10 years (7Q10) are generally very low (< 0.5 m3·s-1), both in the upstream (Montrose Weir) and the downstream (Kruger National Park) sections of the Crocodile River. During such critical periods of low river flow, very low effluent standard limits would be required to prevent adverse river water quality. However, these options are not economically feasible. Furthermore, inflows from the highly polluted tributary stream, the Kaap River, which drains an area where considerable gold mining takes place, govern water quality in the Crocodile River downstream of the Crocodile-Kaap confluence. Subsequently, two additional water quality control options (setting limits for maximum water withdrawal and low-flow augmentation) were analysed. The results show that a decrease in maximum water withdrawal could reduce the TDS concentration. Furthermore, controlling water release patterns from a dam at the Montrose Weir can have a remarkably positive effect on the downstream river water quality. On the basis of the 1989/90 monitoring data, a minimum flow of 5 m3·s-1 at the Montrose Weir can reduce concentrations of TDS and ammonia nitrogen by about 20% and 60%, respectively, in the Kruger National Park (at the downstream point of the considered river). However, this management option does not reduce nitrate nitrogen concentrations. The proposed model used in this study is relatively simple and can be used as a tool for the evaluation of short-term (monthly) basin-wide water quality management options.

Keywords: Dynamic model, Flow regulation, Water quality management, Tank in series model

The accuracy of fluoride measurement in water and its implications for water fluoridation: rapid communication

Haarhoff, Johannes

Abstract: The accurate measurement of the fluoride concentration in water is an essential prerequisite to stay within the allowable dosing tolerances required by the South African water fluoridation legislation. In the absence of reliable error estimates for fluoride measurement in natural water samples, a study was conducted utilising data from interlaboratory comparison studies conducted by the CSIR, the SABS and MEDUNSA. This study shows that:

• natural samples are more difficult to measure than synthetic samples;
• technology advances over the last 25 years did not reduce the measurement error significantly;
• all analytical methods suffer to some extent when natural samples are analysed; and
• the measurement error will have to be appreciably reduced if the legal requirements of the pending water fluoridation are to be met.

Keywords: Water fluoridation , Fluoride measurement , Accuracy, Natural samples , Measurement error

Evaluation of the Cape Town Protocol for the isolation of Campylobacter spp. from environmental waters: short communication

Diergaardt, S.M.; Venter, S.N.; Chalmers, M.; Theron, J.; Brozel, V.S.

Abstract: Campylobacter is recognised as one of the major causes of bacterial gastro-enteritis world-wide. In addition to poultry products, milk and water have also been implicated as possible sources of infection. Methods for the detection and isolation of this organism have been developed specifically for the medical field and select for Campylobacter jejuni and C. coli, excluding all other species of Campylobacter, whereas the filter-based Cape Town Protocol reportedly yields most Campylobacter spp. The Cape Town Protocol was evaluated for possible use in analysis of environmental water samples. It yielded only 0.1% of the total number of actively growing C. jejuni and C. coli cells, whereas the selective medium mCCDA yielded 10%. Analysis of 60 water samples yielded 221 putative Campylobacter isolates, but only four could be confirmed as Arcobacter butzleri and none as Campylobacter. Our results indicated that neither the Cape Town Protocol nor mCCDA can be used for the direct enumeration or isolation of Campylobacter spp. from environmental water samples.

Keywords: Campylobacter, Arcobacter, Water-borne pathogens