Abstract
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, CoFe 2 O 4 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% CoFe 2 O 4 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. • Catalytic polymeric UF and NF membranes are successfully prepared incorporating CoFe 2 O 4 particles. • Naproxen removal efficacy is dependent on the filtration flux during operation. • UF membranes obtain similar removal rates as NF membranes, but at significantly lower operating pressures.
Highlights
In the past decades, small organic micropollutants (MPs) have become an urgent global issue with ever-increasing concentrations in aquatic environments and the potential risks they pose to aqueous or ganisms and humans [1]
As the detection depth of X-ray photoelectron spec troscopy (XPS) is normally lower than 10 nm, this result indicates that the CoFe2O4 particles that appeared in the surface SEM are covered by a polymer film whose thickness is higher than 10 nm
Our results show that CoFe2O4 catalysts can be suc cessfully immobilized in the membrane structure by Non-solvent induced phase separation (NIPS) and that the amount of catalyst embedded in the membranes can be influenced by the concentration of catalytic particles in the casting solution
Summary
Small organic micropollutants (MPs) have become an urgent global issue with ever-increasing concentrations in aquatic environments and the potential risks they pose to aqueous or ganisms and humans [1]. The elimination of MPs from wastewater has become a new challenge in water treatment processes. The hydroxyl radicals or sulfate radicals generated in AOPs can degrade the complex organic molecules to smaller organics or to carbon dioxide and water [9]. The high reactivity and versatile applicability of hydroxyl and sulfate radi cals are highly desired in the elimination of MPs [10,11]. The formation of byproducts [2] and the difficulty of separating and recycling the catalysts from the treated water potentially limit their use in aqueous media [12,13]
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