Researcher: Saeed Baghoth;
Mentor: B. Petrusevski, PhD;
Promotor: Prof. G. Amy, PhD
Natural organic matter (NOM) has aroused a lot of interest in environment studies. It is of particular concern in drinking water since it causes adverse aesthetic qualities such as colour, taste and odour; it produces undesirable disinfection by-products; it impedes the performance of water treatment processes such as granular activated carbon filtration, oxidation processes, and membrane filtration; and it leads to increased bio-film growth in water distribution pipes. A thorough understanding of the physical and chemical properties of the various components of NOM would contribute greatly towards optimisation of the design and operation of drinking water treatment processes. However, because of its complex and heterogeneous nature it is currently impossible to fully describe the chemical structure for each molecular component of NOM in the natural environment. Nevertheless, an improved picture of NOM can be achieved by analysing its operationally defined organic fractions.
Many of the techniques that have been used to characterize NOM include characterization on the basis of molecular weight by small-angle X-ray scattering, gel-permeation chromatography, ultrafiltration, and vapour pressure osmometry; and characterization by spectroscopic techniques such as infrared (IR), ultraviolet-visible (UV/Vis), nuclear magnetic resonance (NMR), fluorescence, and mass spectroscopy (MS). However, many of these techniques require complicated sample pre-treatment, are time consuming, are labour intensive and are very expensive. A powerful tool that can improve characterization of NOM in terms of size, structure and functionality is the expansion of the traditional size exclusion chromatography (SEC) with single wavelength UV detection at 254 nm to include multiple detectors such as online dissolved organic carbon (DOC), dissolved organic nitrogen (DON), fluorescence and variable UV. This approach elucidates unique characteristics for different types and sources of NOM such as allochthonous, autochthonous, and wastewater effluent and its application has revealed preferential NOM removal and/ or transformations during different water and wastewater treatment processes and it has also enabled identification of problematic NOM components such as membrane foulants. One variant of this new approach that is known as SEC-DOC in North America and LC-OCD (liquid chromatography with organic carbon detection) in Germany can also be used to identify polar NOM fractions with a lower specific UV absorbance (SUVA).
The aim of the study is to quantify the different NOM fractions in drinking water so as to optimise selective removal of the problematic fractions along the treatment train. This would lead to the development of a model that could be used to quantitatively predict the removal of the problematic fractions and that could be used to optimise the design and operation of drinking water treatment plants.