Removal of natural organic matter by ultrafiltration with TiO₂-coated membrane under UV irradiation

This study investigates the performance of ultrafiltration (UF) by membranes coated with titanium dioxide (TiO₂) photocatalyst under ultraviolet (UV) illumination in removing natural organic matter (NOM) and possibly in reducing membrane fouling. Experiments were carried out using heat-resistant ceramic disc UF membranes and humic acids as model substances representing naturally occurring organic matter. Membrane sizes of 1, 15, and 50 kDa were used to examine the effects of coating under ultraviolet irradiation. A commercial humic solution was subjected to UF fractionation (batch process); gel filtration chromatography was applied to study the effects of molecular weight distribution of NOM on UF membrane fouling. When compared to naked membranes, UV₂₅₄ (ultraviolet light of λ = 254   nm) illumination of TiO₂-coated membranes exhibits more flux decline with similar effluent quality. Although the UF membrane is able to remove a significant amount of humic materials, the incorporated photocatalysis results in poor performance in terms of permeate flux. The TiO₂-coated membrane under UV₂₅₄ irradiation alters the molecular weight (MW) distribution of humic materials, reducing them to <1 kDa, which is smaller than the smallest (1-kDa) membrane in this study. Thus, TiO₂-coated membranes under UV₂₅₄ irradiation do not perform any better in removing natural organic matter and reducing membrane fouling.