Abstract
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
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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.