CoFe₂O₄-peroxymonosulfate based catalytic UF and NF polymeric membranes for naproxen removal: The role of residence time

Micropollutants pose a significant threat to water quality, aquatic life, and public health. A catalytic polymeric membrane, combining membrane filtration and peroxymonosulfate (PMS) activation provides an alternative option to their treatment. In this work, CoFe2O4 based catalytic particles were blended with polyethersulfone (PES) polymer and catalytic UF (ultrafiltration) membranes were fabricated by non-solvent induced phase inversion. The catalytic UF membrane with 2.0% CoFe2O4 concentration can effectively degrade 70% naproxen in a batch experiment. Additionally, a stable selective layer was built by the layer-by-layer assembly of PDADMAC (poly(diallyldimethylammonium chloride)) and PSS (poly(styrenesulfonate)) on the surface of the catalytic UF membrane. Both the catalytic UF and NF (nanofiltration) membranes were measured in full-recycling mode and single-pass mode. In the full-recycling mode, the naproxen rejection of catalytic UF and NF membranes both increased after adding PMS due to the activation of PMS and increased adsorption. Naproxen removal at different fluxes indicates that longer residence time (i.e. lower flux) can effectively decrease the naproxen concentration in the permeate. The same effect of residence time was also observed in the single-pass mode. By prolonging the residence time of UF membranes to the same level of the NF membranes, the catalytic UF membrane exhibited 87.7% naproxen rejection which is comparable to that of the NF membranes. Significantly, the pressure used in the UF membrane was only 0.1 bar, showing a great advantage of reduced energy cost. These results reveal the important role of residence time on the treatment efficiency of micropollutants by catalytic membranes. Moreover, the application of catalytic UF membranes under low pressure provides an energy-friendly way of removing micropollutants.