Catalytic pre-coat on ceramic nanofiltration membranes for segregation and Fenton cleaning of high-resistance colloids in direct surface water treatment

Abstract

Ceramic nanofiltration (NF) is a promising alternative for direct surface water treatment, but is hampered for full-scale applications by fouling and a lack of eco-friendly cleaning regimes. In this work, an innovative reactive pre-coat layer, consisting of an iron oxychloride catalyst, was constructed on top of commercial ceramic NF membranes, for segregating a large-sized colloid fraction in canal water and Fenton cleaning with a hydrogen peroxide (H₂O₂) solution. The large-sized colloids (3−30 μm) were identified as dominant substances fouling the TiO₂ separation layer of the pristine membranes, leading to a fast increase in their filtration resistance, in contrast to the small-sized colloids (<0.04 μm) and natural organic matter (NOM). As a consequence, the catalyst pre-coat layer with a pore size of 0.1–0.5 μm was able to segregate the large-sized colloids from the TiO₂ separation layer during direct filtration of the raw water. Moreover, filtration under an acceptable flux of around 23 L m⁻² h⁻¹ did not cause pore clogging in the catalyst pre-coat. In addition, Fenton oxidation initiated by the catalytic pre-coat efficiently restored the filtration resistance, whereas sole H₂O₂ flush of the pristine membrane was not effective. In the meantime, the TiO₂ separation layer of the membrane exerted a high NOM rejection of approximately 90%, measured as dissolved organic carbon, while the catalyst pre-coat on the membrane remained active in Fenton cleaning, over five one-day cycles. The findings of this work may provide guidance on the structural and functional design of a catalytic pre-coat layer for a dual purpose of foulant segregation and oxidative removal, particularly in response to key fouling-causing substances, during membrane-based treatment of real water matrices.