Effect of nanofiltration membrane surface fouling on organic micro-pollutants rejection: The roles of aqueous transport and solid transport

• The effect of NF membrane fouling on the transport of EDCs was differentiated.
• Aqueous transport of EDCs was not affected by fouling due to the thin fouling layer.
• Solid transport of EDCs was promoted by fouling (i.e., reduced real rejection).
• The reduction of real rejection was dependent on steric hindrance.

This paper provides a thorough understanding of the effect of nanofiltration (NF) membrane surface fouling on the two-stage transport of organic micro-pollutants (aqueous transport across the concentration polarization boundary layer and solid transport across the surface fouling layer and membrane), given that the role of each stage has been scarcely explored. The mass transfer coefficient (k), real rejection (Rr), and observed rejection (Robs), were applied to represent the aqueous, solid, and overall transport, respectively. Rejection experiments were conducted with five representative endocrine disrupting compounds (EDCs), subjected to alginate fouling layers with varying properties modulated by Ca2 +. Robs and Rr of EDCs decreased substantially after fouling at high Ca2 + concentrations (> 2 mM), while k changed little, revealing that fouling mainly altered solid transport rather than aqueous transport of EDCs. The reduction in Rr correlated well with the molecular weight of EDCs and the specific resistance of fouling layer, suggesting that steric hindrance of fouling layer was the predominant mechanism affecting solid transport. Additionally, the susceptibility of Rr of EDCs to membrane surface fouling depended on their rejection levels by the virgin membrane.

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