Nanofiltration for wastewater reuse: Counteractive effects of fouling and matrice on the rejection of pharmaceutical active compounds

• Effect of fouling and matrice on PhACs removal by NF was investigated.
• Effect of fouling layer on membrane properties was fully investigated.
• Molecule size, charge and geometry of PhACs play an important role in rejection.
• Counteractive effects govern PhACs rejection: solute–solute interactions and CECP.
• Tight NF membranes are promising alternative to RO scheme for reuse purpose.

This study investigates the influence of fouling and solute–solute interactions on the rejection of four pharmaceutical active compounds (PhACs) by two commercial nanofiltration (NF) membranes for a water reuse purpose. Membrane bioreactor effluent was filtered and modification of membrane surface was fully characterized (roughness, MWCO, contact angle, zeta potential…). It was shown that polysaccharides and humic acid were the major compounds adsorbed on the membrane which causes the flux decline. Flux decline was more severe for NF-90 than NF-270 due to a higher roughness and hydrophobicity and smaller pore size. This fouling layer modified the membrane surface properties like hydrophobicity and charge. PhACs were then filtered in Milli-Q water, using virgin and pre-fouled membranes, or in real effluent, using virgin membranes, so as to identify basic phenomena involved in their retention. It appeared that changes in membrane surface affected transport and retention of salts and PhACs in comparison with unfouled membranes, especially for NF-270. The comparison between filtration of PhACs in Milli-Q water or real effluent evidenced the effect of solute–solute interactions on retention. For all tested PhACs, rejection by NF-270 was improved when filtering spiked MBR effluent in comparison with spiked Milli-Q. The influence of the matrice was less pronounced for the NF-90. Two counteractive mechanisms appeared to be involved in the rejection of pharmaceuticals by a loose-NF like NF-270: adsorption onto macromolecules in the surrounding matrice resulting in increased rejection and the presence of a fouling layer leading to decrease in rejection. Finally, NF-90 could be a possible alternative to the systematic reverse osmosis scheme and allowed great rejection capacities and cost saving.