This research focused on membrane flux decline trends observed during ultrafiltration (UF) of solutions of NOM fractions isolated from surface waters. All filtration experiments were performed with a non-stirred dead-end cell unit equipped with flat sheet polyethersulfone PES UF membrane coupons under a constant transmembrane pressure of 1 bar. Results showed that the most significant flux decline was due to the organic colloid fraction, a hydrophilic fraction consisting mostly of bacterial cell wall residues. This research demonstrated that these colloids which incorporate 2/3 of dissolved organic structures (<0.45 μm) and 1/3 of particulate organics exert strong fouling properties due to both rejection phenomena and the adsorption mechanism. The fouling contribution by humic-like materials depends on their origin and nature. Aromaticity appears to be a secondary parameter which influences membrane fouling. Polysaccharides, proteins and amino sugars also largely present in humic-like structures (supramolecular structure) play an important role in UF membrane fouling. The perspective of NOM as a biopolymer mixture can contribute to an understanding of membrane fouling.

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