Degradation and Defluorination of Aqueous Perfluorooctane Sulfonate by Silica-Based Granular Media Using Batch Reactors

Abstract

Per- and polyfluoroalkyl substances (PFASs) are recalcitrant emerging contaminants of concern within the United States and internationally. Of the known PFASs, the sulfonates are considered among the most toxic and difficult to destroy using traditional methods. Research presented herein describes the degradation and defluorination of perfluorooctane sulfonate (PFOS) using a novel photocatalytic porous silica-based granular media (SGM) activated with ultraviolet light, and combined with a strong or weak nucleophilic attack in batch reactors. Sodium thiosulfate proved to be the most compatible and efficient nucleophile in combination with SGM media production of free radicals. Measured aqueous fluoride content accounted for 51% defluorination of PFOS, while the remainder is theorized to mineralize and reside within the porous network of the SGM, as indicated by scanning electron microscopy and energy dispersive x-ray spectroscopy. Removal of PFOS in solution is completed by 30 min with Na2S2O3, with measurable by-product production of C2F3O2− and aqueous fluoride occurring at 15 min. The rapid increase, incipient decrease, and subsequent mineralization of fluoride reveals that the degradation of PFOS is rapid and starts with cleaving of the functional sulfonate group. Amalgamated C-F chains precipitate within the SGM alongside the crystalized fluorine. Possible pathways for PFOS destruction are proposed for the combined attack results. This approach is translatable to other PFASs and organic contaminants of concern.