Biosurfactant-induced PFAS leaching from aqueous film-forming foam (AFFF) impacted soil

The development of novel per- and polyfluoroalkyl (PFAS) remediation techniques is critical for the removal of contaminants from soil and water at sites impacted by aqueous film-forming foam (AFFF). This study is the first to explore the feasibility of flushing PFAS with a rhamnolipid biosurfactant solution using column testing and soil from an AFFF-contaminated site. Soil is flushed by tap water alone and a 0.005% rhamnolipid solution. PFAS concentrations in eluate and mass balances are compared for each test. In the first 12 pore volumes, 91% of the total perfluorooctane sulfonic acid (PFOS) flushed by the rhamnolipid solution was removed, while only 64% of PFOS was flushed in that time by tap water alone. Phosphate leached from soil and PFOS measured in the same eluate had similar concentration patterns, suggesting competitive sorption occurs with negatively charged phosphate, PFOS, and the anionic biosurfactant rhamnolipid. A one-dimensional groundwater transport model confirmed that PFOS retardation (R-values) was lower with the rhamnolipid solution (9.76) than with tap water as the eluent (22.3 ± 0.9). The flushing tests and model both confirm that there is no significant difference in flushing PFAS with a biosurfactant for PFAS compounds other than PFOS. The decreased retardation and the faster elution of PFOS by the rhamnolipid solution indicate that it is more efficient at removing PFOS from soil than water alone.