Enhanced removal of perfluorooctane sulfonic acid and perfluorooctanoic acid via polyelectrolyte functionalized ultrafiltration membrane: Effects of membrane modification and water matrix

Abstract

This study investigated the mechanisms of removal of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) using polyelectrolyte (PE) functionalized ultrafiltration (UF) membranes, performed through a fluidic method of layer-by-layer (LbL) deposition of polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) multilayer coatings. The effects of source water composition (humic acids [HA] and cations [Ca²⁺ and Mg²⁺]) on PFOS and PFOA removal efficiency by the functionalized membrane were determined. PAH/PAA modification resulted in approximately 38 % and 9.2 % reduction in membrane molecular weight cut-off (MWCO) and porosity, respectively, leading to approximately 30 % increase in the removal of PFOS and PFOA primarily due to size exclusion. The presence of only HA led to 10–12 % higher removal of PFOS/A when compared to DI water; however, an increase in HA concentration did not further influence their removal efficiency. The coexistence of cations and HA resulted in significantly higher removal of PFOS and PFOA (up to 23 % higher for PFOS). Further enhancement of PFOS removal (14 % higher) was observed when cation concentrations were doubled, attributable to the interactions of PFOS/A with the source water components and the functionalized membrane, resulting in enhanced size and charge exclusion of macromolecular complexes including PFOS-cation-PFOS, PFOS-cation-HA, and PFOA-cation-HA.