High levels of dissolved organic matter (DOM) and its potential to form disinfection by-products (DBPs), such as trihalomethanes (THMs), during drinking water treatment raise challenges to management of source waters worldwide. Not all DOM is equally reactive in DBP formation during water disinfection and various physical and chemical fractionation techniques have been applied to identify the major reactive DBP components in DOM. In this review paper, we evaluate three commonly used fractionation techniques used in THM precursor research: XAD fractionation, ultrafiltration and size exclusion chromatography. Research findings from different source waters worldwide are summarized in order to understand the role of various DOM fractions in THM formation and to identify knowledge gaps. The hydrophobic fraction and the fraction with an apparent molecular weight of 1–10 kDa have been implicated as the primary source of THM precursors, but exceptions have been observed. Differences in isolation procedures, chlorination methodologies, origins of DOM and nomenclature used to describe DOM fractions may contribute to discrepancies in results among some studies. Advancement of fractionation techniques in conjunction with sensitive spectroscopic techniques (e.g. UV absorbance and fluorescence) is essential for effectively evaluating DOM quality and quantity in source waters and optimizing water treatment processes.

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