Fractionation of natural organic matter in the Nile River: Implications for treated water quality

Recent sampling projects in greater Cairo, Egypt have indicated the presence of trihalomethanes and other chlorine disinfection by-products (DBPs) in the public water supply at levels that are periodically in excess of regulatory limits. Therefore, hydrophobic-hydrophilic fractionation of natural organic matter (NOM) was performed for raw Nile River water samples in order to identify the organic fractions that most readily react with chlorine to produce DBPs. Averages of five events over a 13-month period revealed that the hydrophilic neutral fraction made the highest contribution (35%) to the dissolved organic carbon (DOC), followed by hydrophobic (29%), transphilic (23%), and hydrophilic charged (13%) fractions. Relative contribution of NOM fractions to DBP formation was measured according to the trihalomethane formation potential (THMFP) test. Although the transphilic fraction was only the third highest contributor to DOC, on average it constituted the major contribution to THMFP (38%) followed by the hydrophobic fraction (31%). This finding was corroborated by the results of two events in which samples were collected in both Cairo and Luxor (750km upstream). The transphilic fraction also yielded the best correlation between percent contributions to THMFP versus DOC.