Treatment of PFAS-impacted saline purge waters by the ultraviolet/boron nitride photo(cata)lytic process

Treatment of purge waters generated from monitoring wells at sites with groundwater contaminated by aqueous film-forming foams achieved degradation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) to short-chain perfluoroalkyl carboxylic acids (PFCAs) using an ultraviolet/hexagonal boron nitride (hBN + UVC/VUV) photocatalytic/photolytic process. Degradation was confirmed by detection of perfluorinated products not attributable to precursors and release of fluoride. Despite competition from dissolved organic carbon (DOC) in a saline purge water, 99% of linear and branched PFOA were degraded within 4 h, with electrical energies per order of destruction (EE/Os) of 33.0 and 55.8 kWh∙m −3 ∙order −1 , respectively. In a brackish purge water, 91% of linear PFOS was degraded within 6 h, with an EE/O of 123 kWh∙m −3 ∙order −1 , while 98% of branched PFOS was degraded within 5 h, with an EE/O of 44.8 kWh∙m −3 ∙order −1 . Results demonstrated that hBN + UVC/VUV photocatalysis can be effective at degrading long-chain PFAS to short-chain PFCA products in saline waters without perchlorate generation, and in waters with high DOC. A lag in PFOA degradation suggests that the type of DOC may determine whether hBN degrades PFOA efficiently. Finally, measurement of dissolved boron revealed that boron may be a more reliable preliminary metric for hBN stability than dissolved nitrogen or nitrate, and that hBN appeared most stable in the most complex water matrix.