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Thesis (MTech (Chemical engineering))--Cape Technikon, Cape Town, 2001 / Approximately 40% of the surface waters of South Africa, and the surface waters of Lesotho, are soft and acidic with low calcium, alkalinity and carborrate species concentration. Distribution of such waters results in aggressive attack of cement concrete pipes and linings, and corrosive attack of metal pipes. valves, etc. within the distribution network. The impact of such attack is usually significant, and usually includes the loss of water, the need for expensive repairs and deterioration in drinking-water quality. Water conditioning to prevent aggression and/or corrosion (termed stabilization) is conventionally achieved by the addition of lime (Ca(OH)2) and carbon dioxide (C02). Although this process is well documented and understood, it has a number of drawbacks which include the use of troublesome lime, high chemical operating costs, and the need for high quality white lime which is currently in short supply in South Africa. An alternative stabilization process is stabilisation via contact with limestone (solid calcium carbonate), which has been shown to have many advantages over Iime-mediated stabilization. However, the use of limestone mediated stabilization has hitherto been limited to smaller water treatment works as a result of the large contact tanks required. Use of limestone for larger water treatment works was made viable by the development by CSIR of the limestone mediated Sidestream Stabilisation Process (SSP). The SSP consists of taking a sidestream of approximately 2 - 5% of the unstabilised water, dosing high levels of C02, and then contacting the COr acidified stream with limestone. The acidified sidestream takes up considerable amounts of calcium carbonate (CaC03), increasing the alkalinity and the calcium concentration.

D.Ing. / The use of dissolved air flotation (DAF) as a water clarification process has gained momentum over the past two decades. Despite its increased application there is a lack of information concerning the understanding of the underlying principles of the process. Plants are being designed based mainly on empirical guidelines, especially with respect to the bubble production system. Bubbles are generated in the DAF process when water, supersaturated with air under pressure, is released under atmospheric conditions. The efficiency of air dissolution and precipitation determines the quantity of air available for flotation and thus, to a large extent, the success of the whole DAF process. The first part of this thesis deals with a rational model for predicting the air transfer efficiency in packed saturators which are used in most modern DAF plants to dissolve air into water. The model assumes the Lewis-Whitman two-film theory for interfacial mass transfer and uses the Onda correlations to estimate the mass transfer coefficient. The model provides good insight into the effects of key design parameters on the air transfer efficiency. The experimental verification of the model required a method for predicting the saturator air composition and a technique to practically determine the air transfer efficiency in the packed bed of an operating saturator. Both methods are described in detail in this study. The verification of the mass transfer model showed a close agreement of experimental and theoretical results and the model thus provides a powerful tool for the design of packed saturators. The second part of the thesis deals with air precipitation and the quantity of air released after depressurization. Based on a literature review on this subject it was assumed that the air release is incomplete and that it would be a function of the operating conditions of the saturation system as well as of the design of the injection nozzle across which the pressure is released. Since the injection nozzles play an important role in the DAF process numerous experiments were carried out which measured the released air volume for different nozzle configurations and saturator pressures. The results of this study showed that the air release after depressurization is indeed incomplete and that it takes a long time for all the excess air to come out of solution. It was found that the efficiency with which the air was released is a function of the saturator pressure and the nozzle design. The experimental observations led to the formulation of a two-step air release model, which explains the precipitation process in terms of a slow and fast release step. The mathematical framework for quantification of the model is provided. Once the model is quantified it will be possible to compare the performance of different injection nozzles solely with regard to their design features and independent of any parameters influencing the air release downstream of the nozzle. This model may then help to further the understanding of the precipitation process and could lead to the development of some rational guidelines for nozzle design and prediction of nozzle performance.

The presence of organic contaminants in water has caused great concern over their potential adverse health impact on humans and animals. Organic contaminants found in water are both naturally occurring and synthetic. Various chemical and physical water treatment processes are being used to remove organic contaminants. Conventional water treatment methods include the utilization of activated carbon for the removal of organic contaminants. It is generally conceded that activated carbon owes its adsorptive properties primarily to its large surface area, as well as to its pore size. Although activated carbon is nonselective against most of the water contaminants, it does not remove the concentration of organic contaminants to acceptable levels i.e. ppb. Moreover, activated carbon also absorbs moisture from the air and as a result loses its absorptive effectiveness. For this reason attention has been being given to alternative methods for water treatment especially for the removal of organic pollutants. In this study, cyclodextrin polymers that were water insoluble were synthesized and tested for their ability to remove organic species in water. Cyclodextrins (CDs) and their corresponding derivatives have been used in a wide range of applications including pharmaceutical and pesticide removal and catalysis. Cyclodextrins are cyclic oligosaccharides derived from enzyme degradation of starch. They are known as molecular hosts capable of including of forming inclusion complexes, with a degree of selectivity, with a range of guest molecules via a noncovalent interaction in their hydrophobic cavities. Although the interaction between cyclodextrin and an organic molecule is the basis for absorption or separation of various organic agents, the solubility of cyclodextrin in water and organic solvents impose limitations to the application of cyclodextrins in water treatment. Therefore, polymerizing a cyclodextrin monomer with an excess of a bifunctional linker produces an insoluble polymer which can form inclusion complexes with guest molecules. In this project, the synthesis of a number of cyclodextrin polymers was performed by reacting cyclodextrin with bifunctional linkers. / Dr. B. B. Mamba Dr. R. W. M. Krause Dr. T. J. Malefetse

M. Tech. / The study assessed the risk of infection introduced by containers in which households collect water from different sources. The study area was in rural villages in the Vhembe region of the Limpopo Province. Each village had its own unique water sources consisting mainly of untreated ground waters and untreated surface waters. Randomly selected household members use their containers to collect water from these different sources. Two of the three villages received new small water supply systems within the study period, proving the villagers with water of good health-related microbial quality. The remaining village continued to use contaminated water from their untreated surface water sources. The water supply intervention in two of the three villages provided the opportunity to assess the impact these interventions would have on the risk of infection i.e. whether the risk could be reduced for the villagers no having access to good quality water. A customized quantitative microbial risk assessment was done based on the health-related quality of the water that people ingested before and after the intervention. This assessment was based on exposure of, consequence to and impact on an individual water consumer. Exposure included variables such as daily quantities of unheated drinking water consumed per individual (in litres) available at the point of use (in the dwelling) for ingestion, numbers of diarrhoeagenic E. coli (Dec) per litre in water sampled from containers derived from water samples positive for indicator E. coli and daily doses of DEc per litre ingested by an individual in the target population. Consequence was assessed by calculating the probability of infection per day from diarrhoeagenic E. coli for an individual and from there the annual infection per individual. The impact of the small water supply system was determined by assessing changes in annual individual risk of infection from before to after the interventions per village. In terms of daily water volumes consumed per individual, there were no significant differences in consumption amongst the three villages. At 1.26 ℓcd (at the upper limit of the 95% confidence interval) the consumption was slightly higher than the one litre suggested by WHO 2003. The container water collected from sources before the intervention in the two villages was significantly more contaminated by indicator E. coli (iEc) and diarrhoeagenic E. coli (DEc) than their container waters after the intervention. In terms of impact, the risk of infections was substantially reduced by the interventions. For Village 1 the risk of infection was reduced from 646 infections to 135 infections per 10,000 of the population. If these are converted to 10% as disease manifesting, then there could have been 65 cases of enteric disease attributable to water before the intervention, which was then reduced to 14 cases after the intervention. For Village 2 the population risk was reduced from 110 to 67 cases after the intervention. For Village 3 the population risk remained at 2,778 infections or 278 cases of enteric waterborne disease because of their continued use of untreated water. The study findings indicated that for Village 1, the population risk of infection would be 135 infections per 10,000, for Village 2 it would be 167 and for Village 3 - 234. If the hypothetical conversion rate of one case of enteric waterborne disease for every 10 infections of Howard et al. (2006) is used, then this would mean 14 cases of disease per 10,000 for the population for Village 1, 17 cases for Village 2 and 24 cases for Village 3. Relating this to the WHO (2003) suggestion of one case per 1,000 as an acceptable, it would mean 1.3 cases for Village 1, 1.7 for Village 2 and 2.4 for Village 3. For Village 1 the risk of contracting waterborne enteric disease was close to acceptable, but not at all acceptable for the other two villages, even for Village group 2 after the intervention. The water system in Village 2 failed often during the study which was probably the cause of the persistently higher risk of disease. It can be concluded that providing a well maintained small water supply system reduced the risk to and maintained it at an acceptable level. Table

Bioflocculants produced by two identified bacteria: Actinobacterium sp. Mayor and Methylobacterium sp. Obi were investigated with regard to their physicochemical and flocculating characteristics. The two strains were later combined to form a consortium for further studies. The optimum culture conditions for the bioflocculant production were similar for all strains except in the case of Actinobacterium sp. Mayor and the consortium, where glucose was replaced by sodium carbonate as a carbon source. Multi-nitrogen source was the best nitrogen source compare to individual sources for both strains. The divalent cation, Ca2+ proved to be a better flocculating activity stimulus for all produced bioflocculants in this study. The optimum flocculating activities obtained for both individual strains and the consortium were all at alkaline pH. The yield of purified bioflocculant produced by the consortium was 8.203 g/l, while 4.190 g/l and 4.610 g/l were recovered for single strains of Actinobacterium sp. Mayor and Methylobacterium sp. Obi respectively. Further characterization of pure bioflocculants revealed that a bioflocculant dosage of 0.3 mg/ml resulted in the highest flocculating activity for both individual strains while 1.0 mg/ml of the bioflocculant produced by the consortium was required to enhance maximum flocculating efficiency. These bioflocculants proved to be all thermo stable at a temperature range of 20 to 900°C with a heating rate of 10oC/min under a constant flow of nitrogen gas. The presence of functional groups normally required for bioflocculation such as hydroxyl, carboxyl and amino was also detected. The findings of this study suggest that the producedbioflocculants can be utilized as excellent substitutes for harmful synthetic flocculants in both water and wastewater treatments as well as in other industrial applications.