Removal of perfluorooctane sulfonate by a gravity-driven membrane: Filtration performance and regeneration behavior

Abstract

Perfluorooctane sulfonate (PFOS) has been under the spotlight in recent decades due to its adverse environmental and ecological concerns. Existing treatment methods (such as reverse osmosis and nanofiltration) for this recalcitrant surfactant are generally energy intensive. In this study, for the first time, a gravity-driven filtration using a highly porous nanofibrous membrane was systematically investigated for PFOS removal. The membrane possesses a high water permeability of 354.9 LMH/kPa, allowing the membrane to be operated under gravity-driven conditions. PFOS removal efficiency ranging from 36% to 90% was observed under a wide range of water chemistry conditions (5–20 ppb PFOS, pH 4–10, and ionic strength 1–10 mM). The best removal efficiency was obtained at pH 4 and 10 mM ionic strength as a result of the enhanced PFOS-membrane electrostatic attraction and/or weakened electrostatic repulsion. The removal efficiency was also higher at lower membrane permeate flux due to the increased residence time of PFOS molecules in the internal pores of the membrane. Simple methanol rinsing was able to effectively regenerate the membrane, and the high PFOS removal efficiency can be maintained over 20 cycles of regeneration. The current study may provide important insights of using highly porous membranes for energy-efficient PFOS removal and recovery.