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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. 

As wastewater reclamation and reuse technologies become more critical to meeting the growing demand for water, a need has emerged for separation platforms that can be tailored to accommodate the highly varied feed water compositions and treatment demands of these technologies. Nanofiltration (NF) membranes based on copolymer materials are a promising platform in this regard because they can be engineered at the molecular scale to address an array of separation process needs. Here, for example, a resilient NF membrane is developed through the design of a poly(trifluoroethyl methacrylate- co -oligo(ethylene glycol) methyl ether methacrylate- co -glycidyl methacrylate) [P(TFEMA-OEGMA-GMA)] copolymer that can be dip-coated onto hollow fiber supports. By exploiting the microphase separation of the oligomeric ethylene glycol side chains from the copolymer backbone and by elucidating the processing–structure–property relationships for the dip-coating process, membranes with pores 2 nm-in-diameter that exhibit a hydraulic permeability of 15.6 L m −2 h −1 bar −1 were generated. The GMA repeat units were functionalized post-coating with hexamethylene diamine to incorporate positively-charged moieties along the pore walls. This functionality resulted in membranes that rejected 98% of the MgCl 2 from a 1 mM feed solution. Moreover, the reaction with the diamine crosslinked the copolymer such that the membranes operated stably in ethanol, an organic solvent that damaged the unreacted parent membranes irreparably. Finally, the stability of the crosslinked P(TFEMA-OEGMA-GMA) copolymer resulted in membranes that could operate continuously for a 24 hour period in aqueous solutions containing 500 ppm chlorine without exhibiting signs of structural degradation as evidenced by consistent rejection of neutral probe solutes. These results demonstrate how resilient, charge-selective NF membranes can be fabricated from microphase separated copolymers by engineering each of the constituent repeat units for a directed purpose.