Separation of Selected Organic Micropollutants Using the Ultrafiltration Membrane Modified with Carbon Nanotubes

This study compares retention characteristics and retention potential as well as antifouling properties of three ultrafiltration membranes. The commercial membrane UE50 and two membranes produced under laboratory conditions - polyethersulfone membrane (PES) and polyethersulfone membrane modified with hydroxyl-functionalized carbon nanotubes (PES-SWCNT-OH) - were selected for the research. Retention potential was determined for selected organic micropollutants, i.e. caffeine, bisphenol A and pentachlorobenzene. It was determined that removal degree of micropollutants depended mainly on their physicochemical properties. Removal efficacy of highly hydrophobic substances, i.e. bisphenol A and pentachlorobenzene was significantly higher than of hydrophilic caffeine. Furthermore, it was found that adsorption played a key role in the micropollutant removal and the process was more intense on the modified membrane as nanotubes enhanced sorption capacity of the membrane. For all the ultrafiltration membranes studied, the retention of micropollutants decreased with an increase of the transmembrane pressure. At higher pressures, mass transport through the membrane was faster and resulted in shorter contact time between the micropollutants and membrane. Moreover, the modified ultrafiltration membrane had better antifouling properties compared to the commercial membrane UE50. It was an effect of its rougher surface with multiple protrusions, which interfered with even sediment layer formation. Importantly, the membrane was modified with hydroxyl-functionalized carbon nanotubes, which added to its hydrophilic character. The same it improved the antifouling properties of the membrane by weakening the hydrophobic interactions between the membrane surface and target pollutants.