Evaluation of a Porous Membrane as a Mass-Transfer Efficient Structure for the Adsorption of Per- and Polyfluoroalkyl Substances from Drinking Water

With drinking water regulations forthcoming for per- and polyfluoroalkyl substances (PFAS), the need for cost-effective treatment technologies has become urgent. Adsorption is a key process for removing or concentrating PFAS from water; however, conventional adsorbents operated in packed beds suffer from mass transfer limitations. The objective of this study was to assess the mass transfer performance of a porous polyamide adsorptive membrane for removing PFAS from drinking water under varying conditions. We conducted batch equilibrium and dynamic adsorption experiments for perfluorooctanesulfonic acid, perfluorooctanoic acid, perfluorobutanesulfonic acid, and undecafluoro-2-methyl-3-oxahexanoic acid (i.e., GenX). We assessed various operating and water quality parameters, including flow rate (pore velocity), pH, ionic strength (IS), and presence of dissolved organic carbon. Outcomes revealed that the porous adsorptive membrane was a mass transfer-efficient platform capable of achieving dynamic capacities similar to equilibrium capacities at fast interstitial velocities. The adsorption mechanism of PFAS to the membrane was a mixture of electrostatic and hydrophobic interactions, with pH and IS controlling which interaction was dominant. The adsorption capacity of the membrane was limited by its surface area, but its site density was approximately five times higher than that of granular activated carbon. With advances in molecular engineering to increase the capacity, porous adsorptive membranes are well suited as alternative adsorbent platforms for removing PFAS from drinking water.