Rejection of per- and polyfluoroalkyl substances (PFASs) in aqueous film-forming foam by high-pressure membranes

The ubiquitous use and manufacturing of per- and polyfluoroalkyl substances (PFASs) have led to the contamination of water resources worldwide. High-pressure membranes, including nanofiltration (NF) and reverse osmosis (RO), are increasingly being deployed for water treatment and may be an effective barrier to PFASs. However, the impact of membrane operating conditions, background water matrix, and solute adsorption on rejection of diverse PFASs by NF and RO remains unclear. Rejection of perfluoroalkyl acids (PFAAs) present in aqueous film-forming foam (AFFF) diluted into a laboratory electrolyte matrix by NF and RO spiral wound elements was > 98% and > 99%, respectively. Rejection of the same PFAAs present in an AFFF-impacted groundwater matrix by NF was lower, between 92-98%, and was attributed to background water matrix constituents. Operating conditions did not have a significant impact on rejection of PFASs with the exception of shorter chain perfluoroalkyl sulfonic acids (PFSAs) in the AFFF-impacted groundwater matrix, where rejection increased with increasing flux. Structure-activity analysis of 42 PFASs, including 10 PFAAs and 32 PFASs identified in AFFF through high-resolution mass spectrometry suspect screening methods, showed some correlation between rejection and compound molecular weight. Adsorptive losses of PFAAs, most notably longer-chain hydrophobic PFAAs, to the spiral wound membrane elements and the membrane system were observed. Adsorption of PFAAs to the permeate spacer was especially pronounced and may have implications of artificially high rejection values. Still, rejection of PFASs by NF remained consistently > 98% over 13 days of continuous operation. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The widespread use of PFASs has led to water contamination globally. High-pressure membranes like NF and RO are effective barriers to PFASs, with NF showing higher rejection rates for PFAAs and lower rejection rates in AFFF-impacted groundwater matrices. Operating conditions did not significantly impact the rejection of PFASs, except for shorter chain PFSAs, where rejection increased with flux. Structure-activity analysis showed some correlation between rejection rates and compound molecular weight, with adsorptive losses of PFAAs observed in membrane elements and systems. Despite this, NF consistently maintained rejection rates > 98% over 13 days.