The effect of green sorption media pretreatment on nanofiltration during water treatment for long- and short-chain per- and polyfluoroalkyl substances (PFAS) removal

Abstract

Short-chain per- and polyfluoroalkyl substances (PFAS) have higher mobility than long-chain PFAS. This study investigated the application potential of two specialty adsorbents as pretreatment media for nanofiltration (NF) to enhance the removal of both short- and long-chain PFAS from water matrices. In this hybrid process, two specialty adsorbents, known as green sorption media (GSM), were prepared using recycled and natural materials for cost-effective, scalable, and sustainable water pretreatment. These two GSM are named the clay-perlite and sand (CPS) sorption media and zero-valent iron and perlite-based green environmental media (ZIPGEM). Such pretreatment led to significant removal of long-chain PFAS (up to 100 %) in addition to natural organic matter (NOM) and Ca2+ from the source water (canal water); however, for the short-chain PFAS (Perfluorobutanoic acid and Perfluorobutanesulfonic acid), the removal rate only rose to approximately 25 %. Such a contrasting removal rate is attributable to the source water concentration of PFAS and the hydrophobic and electrostatic interactions of the compounds within the treatment media. Yet the CPS–NF and ZIPGEM–NF hybrid processes exhibited significantly higher removal of perfluorooctanesulfonic acid (long-chain PFAS; approximately 16 % higher) when compared to the control (i.e., NF only). Because the pretreatment media removed higher percentages of long-chain PFAS, NOM, and Ca2+ from the water, the performance of the subsequent NF declined due to less calcium bridging involving NOM and PFAS and less micelle/complex formation by the compounds in bulk water. However, the integration of GSM with NF significantly improved (up to approximately 25 % higher) PFAS removal efficiency via the hybrid functionality. This signifies the membrane plays a complementary role in enhancing the overall removal efficiency of PFAS. In addition to contributing to PFAS removal from the source water, GSM pretreatment can help reduce NF membrane fouling/scaling by removing NOM and cations.