Combining nanofiltration and adsorbents to achieve effective PFAS removal in wastewater effluent

Adsorption of per- and polyfluoroalkyl substances (PFAS) by granular activated carbon (GAC) and ion exchange resins (IX) is negatively impacted by elevated concentrations of effluent organic matter (EfOM) and other background water constituents (e.g., co-adsorbing inorganic ions) in complex matrices such as wastewater effluent. Here, we evaluated a hybrid system comprised of nanofiltration (NF) as an initial treatment step to reduce concentrations of PFAS, EfOM, and select inorganic ions followed by either GAC or IX treatment of membrane permeate. A pilot membrane system utilizing a loose nanofilter (NF270) was operated continuously for >45 days treating wastewater effluent with PFAS periodically added to the feed to evaluate rejection in high recovery (90%) batch experiments. Experimental results demonstrated >92% rejection of C≥4 perfluoroalkyl acids (PFAAs), >98% rejection of hexafluoropropylene oxide dimer acid (Gen-X), and lower rejection (63-92%) of ultrashort-chain PFAS and perfluorobutane sulfonamide (FBSA). Without NF pretreatment of wastewater effluent, rapid small scale column tests (RSSCTs) of adsorbents showed that PFAS maximum contaminant level (MCL) criteria were exceeded within 81 bed volumes (BVs) for GAC and 9,000 BVs for IX. In comparison, GAC treated >5,000 BVs of permeate from the NF experiments before exceeding MCLs, while IX-treated NF permeate never exceeded MCLs for the duration of the experiment (450,000 BVs). The proposed NF-adsorbent treatment train represents a promising strategy for PFAS removal from complex wastewater matrices, preventing point source discharges into the environment.