New insights into the fouling mechanism of dissolved organic matter applying nanofiltration membranes with a variety of surface chemistries

• The strength of DOM fouling cannot be explained by membrane polarity alone.
• Ca2+ can increase/decrease DOM fouling depending on membrane surface chemistry.
• Fouling by DOM is due to polar and aromatic foulant–membrane interactions.
• The physicochemical properties of membranes and foulants are key to explain fouling.
• New insights into fouling mechanisms are clearly revealed in this study.

Nanofiltration (NF) membrane fouling by DOM remains a major and poorly understood issue. To acquire a better insight we studied the fouling of the DOM fractions humic acids (HAs) and fulvic acids (FAs), with and without Ca2+, on native and grafted ceramic NF membranes. Grafting with two methods and three different grafting groups allowed to create a range of membranes with a variety of surface chemistries, and a wide range of surface polarity, much broader than ever used in previous studies. A typical polymer (polyamide) NF membrane was included for comparison. All obtained results reveal that membrane fouling is not determined by membrane hydrophilicity/hydrophobicity as a general and sole criterion, but rather on the whole of the surface chemistry determining the amount and strength of the possible foulant–membrane interactions. As a consequence the effect of inorganic ions on the fouling is also dependent on the surface chemistry. Important new insight in the DOM fouling mechanism was acquired, shedding new light on the state-of-the-art knowledge.

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