Effects of surfactants, ion valency and solution temperature on PFAS rejection in commercial reverse osmosis (RO) and nanofiltration (NF) processes

Abstract

Per- and polyfluoroalkyl substances (PFAS) have garnered attention as a pressing environmental issue due to their enduring presence and suspected adverse health effects. This study assessed the rejection or removal efficacy of PFAS by commercial reverse osmosis (RO) and nanofiltration (NF) membranes and examined the impacts of surfactants, ion valency and solution temperature that are inadequately explored. The results reveal that the presence of cationic surfactants such as cetyltrimethylammonium bromide (CTAB) increased the rejection of two selected PFAS compounds, perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA), by binding with negatively charged PFAS and preventing them from passing through membrane pores via size exclusion, whereas the presence of anionic surfactants such as sodium dodecyl sulfate (SDS) increased the PFAS rejection because the increased electrostatic repulsion prevented PFAS from approaching and adsorbing onto the membrane surface. Moreover, aqueous ions (e.g., Al3+ and PO43−) with higher ion valency enabled higher rejection of PFOA and PFBA through increased effective molecular size and increased electronegativity. Finally, only high solution temperature at 45 °C significantly reduced PFAS rejection efficiency because of the thermally expanded membrane pores and thus the increased leakage of PFAS. Overall, this research provides valuable insights into the various factors impacting PFAS rejection in commercial RO and NF processes. These findings are crucial for developing efficient PFAS removal methods and optimizing existing treatment systems, thereby contributing significantly to the ongoing efforts to combat PFAS contamination.