PFAS destruction and near complete defluorination of undiluted aqueous film-forming foams at ambient conditions by piezoelectric ball milling

The non-thermal destruction of aqueous film-forming foam (AFFF) stockpiles, one of the major culprits responsible for water and soil contamination by per- and polyfluoroalkyl substances (PFAS), is extremely challenging because of the coexistence of mixed recalcitrant PFAS and complicated organic matrices at extremely high concentrations. To date, the complete defluorination of undiluted AFFF at ambient conditions has not been demonstrated. This study reports a novel piezoelectric ball milling (BM) approach for treating AFFF with a total organic fluorine concentration of 9,080 mg/L and total organic carbon of 234 g/L. Near-complete defluorination (> 95% conversion of organofluorine to fluoride) of undiluted AFFF was achieved by co-milling with boron nitride (BN). By carefully examining the experimental data, we identified AFFF liquid film thickness (Z) at the collision interface as a descriptor of treatment performance. We further validated that effective defluorination proceeded when Z was less than a criteria value of 2.3 μm. In light of this new understanding, the addition of SiO2 as a dispersant and the pre-evaporation solvents to reduce Z have been validated as effective strategies to promote AFFF treatment capacity.