A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of a Master of Science degree in Chemistry. University of the Witwatersrand, May 2013 / The pollution of water sources by chemical and biological species has created a serious water crisis all over the world. Such pollution has placed severe strains on the limited water sources resulting in the spread of waterborne diseases, which continue to be the leading causes of deaths in developing countries. Pollution by organic species still poses a serious health and environmental problem. Attempts to mitigate this problem are on-going and a number of methods are employed currently. Activated carbon and reverse osmosis are some of the current techniques that are used for the removal of organics in water. However, these techniques are limited in the removal of pollutants at lower concentrations (ng/L). Recent studies demonstrated the efficient removal of organics by nanoporous cyclodextrin (CD) polymers, a class of nanomaterials with great potential in absorbing organic pollutants from water. This project reports on the synthesis of β-cyclodextrin (β-CD) based polymer nanocomposite materials (nanocomposites) that have been blended with nitrogen-doped carbon nanotubes (N-CNTs) and silver (Ag) nanoparticles for water treatment. Prior to this study, the synthesis of these nanocomposites has been based on a conventional method that involves heating the reactants in a round bottom flask for 16 – 24 h. In this study a new method that is efficient, greener and time saving is reported. This facile method involved synthesizing the polymer nanocomposites under microwave irradiation wherein complete synthesis of the polymer nanocomposites was achieved in 10 min. N-CNTs were first synthesized via modified chemical vapour deposition method (CVD) using a 10wt% Fe-Co/CaCO3 catalyst. The N-CNTs were found to contain ~ 2% nitrogen by CN and XPS analysis. The N-CNTs were of high purity and were oxidized with acid functional groups (-COOH, -C=O, -OH) using nitric acid under reflux. Zeta potential studies indicated that the quantity of acid functional groups increased with increase in acid treatment time. The functionalised N-CNTs (fN-CNTs) were then decorated with Ag nanoparticles using microwave irradiation and further polymerized with β-CD using hexamethylene diisocyanate (HMDI) as the linker in an industrial microwave under an inert gas atmosphere of N2. Two types of polymer nanocomposites were synthesized namely, N-CNTs/β-CD and Ag/N-CNTs/β-CD. Different synthesis parameters such as microwave power and time were varied during the synthesis of these composites to study their effect on the result materials. Different level of power, 400 W, 600 W and 800 W were tested and surface area and morphology data indicated that all these powers can be used in synthesising the polymer composites. The optimum power used was 600 W, which gave highly porous, less densely packed morphology and a higher surface area of the polymers. The synthesis time was varied for 10 min, 15 min and 30 min. An irradiation time of 10 min was found to be sufficient for the synthesis of the nanocomposites. The polymers showed an efficient removal of p-nitrophenol, bisphenol A and trichloroethylene (TCE) from spiked water as confirmed by UV-Vis spectroscopy and GC/MS analysis.

Thesis (M.Sc.(Civil Engineering))--University of the Witwatersrand, Faculty of Engineering, 1989.

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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Drinking water samples provided by Orlando Utilities from various locations and from Florida Technological University were analyzed for organohalides. Compounds tentatively identified were 0.0024 mg/l DDT, 0.003 mg/l phosdrin, 0.00036 mg/l BHC, and 0.000095 mg/l endosulfan. These concentrations are well below recommended limits for drinking water. Two water samples were mixed with 10 mg/l of 20-40 mesh granular activated carbon, agitated for 2 minutes and then allowed to settle in the flask for 45 minutes. A reduction in the organohalide concentration varied from 25 to 98 percent of the original concentration. Also, a solution of seven common pesticides of 0.1 mg/l each were mixed with 1, 5, 10, 25, and 50 mg/l of carbon. The results indicate a reduction of 99 percent or better for all pesticides with 5 ppm carbon concentration.

This study investigated the effectiveness of the magnesium coagulation process in reduction of trihalomethane (THM) precursors. The water was obtained from Lake Washington, a highly colored potable water supply which is used by the City of Melbourne, Florida. The THM concentrations in the finished water at Melbourne currently exceed the THM standard of 0.1 mg/l. For Lake Washington water, treatment varies according to seasonal changes in water quality. During the dry period, the recycle magnesium does not perform effectively as a coagulant for THM precursor removal. This is because of the high levels of magnesium in the late water at this time. During the wet period, when magnesium concentrations are very low, it is much more effective. Magnesium sulfate was found to be effective in reducing THM precursors for both types of water. There was a direct correlation observed between THMFP, TOC and color observed in treated water samples. The lack of effectiveness in THMFP, TOC and color removals by recycle magnesium was not found to be due to a lack of magnesium precipitation. Variations in rapid and slow mixing times had no effect on THM precursor removal, but did affect settling of the floc. Addition of alum as a polymer at high pH values was also very effective in reducing the THMFP, TOC and color, and increasing floc sedimentation.

A kaolin in tapwater suspension was treated either with alum or one of two cationic polymers. The resulting suspension was filtered through various configurations of felt cloth filters. The kaolin suspension was adjusted to 100 JTU. Treatment by polymer consistently lowered the filtered effluent to less than 1 JTU. Jar tests were utilized to determine optimum coagulant dose for the tests. The formulation of a complete filter cake in the filter appeared to be the determining factor in the efficiency of water clarification by the filter. The literature lacked references to this concept as applied to water supply problems. The results of this report suggest that continuous filtration should now be examined.