Per- and poly-fluoroalkyl substances (PFAS) are a large family of synthetic fluorochemicals often present in water as complex mixtures containing up to hundreds of individual PFAS compounds. PFAS-impacted waters are commonly treated through separation techniques that sequester and concentrate PFAS. However, these techniques typically do not destroy PFAS, thus creating potential liability and exposure. PFAS destruction methods are currently hindered by the high energy cost, incomplete defluorination, and the challenge of treating mixtures of PFAS compounds, each with a wide range of physicochemical properties. To make PFAS destruction techniques more feasible, we proposed to first utilize homogeneous treatment to simplify the complexity of PFAS mixtures in concentrated streams as described in our recently accepted Perspective article. [1] In this study, we evaluate 185nm vacuum ultraviolet (VUV) irradiation as a reagent-free method to pretreat and simplify complex PFAS mixtures toward improved mineralization. VUV can excite water molecules to generate both oxidative (e.g. hydroxyl radical) and reductive (e.g. hydrated electron, hydrogen atom) species. These reactive species can be tailored by adjusting pH and supplying different gases (e.g., O2 or N2) to target oxidation or reduction amenable PFAS. We show that fluorotelomer sulfonates, which are recalcitrant towards reduction, are quickly transformed into perfluoroalkyl acids (PFAAs) and fluoride ions under reagent-free VUV oxidation. Subsequent reduction of the formed PFAAs resulted in high defluorination efficiencies. Novel insights into the role of each oxidative and reductive species were evaluated as a function of pH. Reaction mechanisms were revealed by identifying nontarget products and rate-limiting steps. Further optimization holds great promise for cost-effectively managing and defluorinating AFFF-impacted groundwater and other complex PFAS mixtures.
[1] Glass, S; Santiago-Cruz, H. et al. Nature Water. In Press.
