| Abstract
| - Perfluorooctane sulfonate (PFOS) is an emergent contaminant of substantial environmental concerns. In thisstudy, reverse osmosis (RO) and nanofiltration (NF) membraneswere used to remove this toxic and persistent compoundfrom PFOS-containing wastewater. Five RO membranesand three NF membranes were tested at a feed concentrationof 10 ppm PFOS over 4 days, and the PFOS rejectionand permeate flux performances were systematicallyinvestigated. PFOS rejection was well correlated to sodiumchloride rejection. The rejection efficiencies for the ROmembranes were >99%, and those for the NF membranesranged from 90−99%. Improvement in PFOS rejection,together with mild flux reduction (<16%), was observedat longer filtration time. Such shifts in rejection and fluxperformance were probably due to the increased PFOSaccumulation at longer duration, as shown by X-rayphotoelectron spectroscopy and liquid chromatographand tandem mass spectrometry results. A fraction of PFOSmolecules might be entrapped in the polyamide layer ofthe composite membranes, which hindered the furtherpassage of both water and other PFOS molecules. In a similarfashion, PFOS rejection and fouling were enhanced forgreater initial flux and/or applied pressure, where PFOSaccumulation was promoted probably due to increasedhydrodynamic permeate drag. Flux reduction was also shownto correlate to membrane roughness, with the roughermembranes tend to experience more flux reduction thanthe smoother ones.
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