M.Sc. / The prevalence of natural organic matter (NOM) in water remains a huge challenge for water treatment companies and municipalities. NOM, however, is not a stand-alone problem as it affects water quality in many ways. NOM is largely responsible for the formation of disinfection by-products (DBPs) via its interaction with disinfectants during water disinfection. It is implicated for the undesirable colour, taste and odour of water and NOM even inhibits precipitation precursors which form the backbone of drinking water treatment. There is therefore no question that NOM, which is either a precursor to or direct cause of the problems highlighted above, should be considered as one of the critical design parameters to be considered for drinking water treatment. In our laboratories, research that involves the use of cyclodextrin (CD) polyurethanes for the removal of organic pollutants from water has been extensively investigated, and the CD polyurethanes have demonstrated the ability to effectively remove the organic species from water at low (ppb) concentrations. CDs, which are cyclic oligomers consisting of glucopyranosyl units linked together through α-1,4 glycosidic linkages, behave like molecular hosts. They are capable of forming inclusion complexes with guest molecules and hence can be utilised for the removal of organic contaminants from water. Their solubility in water, however, limits their application in the removal of organic contaminants from water. This limitation is easily resolved by polymerising the CDs into water-insoluble polymers with bifunctional linkers such as hexamethylene diisocyanate (HMDI). In this study, CD polyurethanes and ion exchange resins were used for the removal of NOM and possibly its DBPs from water. This study first investigated the local NOM source to establish its type and character, hence the study involved the characterization of the bulk water samples and fractionating the NOM using ion exchange resins for further characterization. The water samples were found to consist mainly of humic substances in the form of hydrophobic NOM, with the hydrophilic basic (HpiB) fraction being the most abundant NOM fraction in all samples. Trihalomethanes (THMs) were used as a representative of DBPs in this vii study. THMs formation studies of the individual NOM fractions indicated that all six NOM fractions were found to form THMs but in varying proportions. The HpiB fraction was found to be the most reactive precursor fraction for THMs formation. The ozonation process was also independently evaluated for its ability to remove the NOM fractions from water. Ozonation was found not to be very effective at NOM removal since it only resulted in a 12% overall decrease of the NOM in the water samples. The CD polyurethanes, when used alone, were also not very effective at removing the NOM fractions from water (maximum of 33% NOM removal). On the other hand, the combination method (i.e. the use of CD polyurethanes and ozonation for NOM removal) resulted in a good capability of the CD polyurethanes at decreasing some NOM fractions in water as evidenced by a 73% and 88% decrease of the HpiB and hydrophilic acid (HpiA) fractions, respectively. The 73% reduction of the HpiB fraction demonstrates a great success of the combination approach employed herein, as this study reports this fraction as the most reactive precursor fraction for THM formation.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:6765 |
| Date | 08 April 2010 |
| Creators | Nkambule, Thabo Innocent |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
Page generated in 0.002 seconds