Biosurfactant-induced PFAS Leaching from Aqueous Film-Forming Foam (AFFF) Impacted Soil

The development of sustainable 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 was flushed by either tap water alone or a 0.005% rhamnolipid solution. The PFAS concentrations in eluate and mass balances were 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. The flushing tests also show that there is no significant difference in flushing with a biosurfactant for PFAS compounds other than PFOS. Transport modeling confirmed that PFOS retardation (R-value) was lower with the rhamnolipid solution (R = 9.76) than with tap water (R = 22.3), which indicates that it is more efficient at removing PFOS from soil than water alone. This concept study provides insight into the release of PFAS compounds from a real contaminated saturated soil containing organic carbon, clay, and a complex mixture of PFAS. It shows promising first results for the use of biosurfactants as a sustainable flushing strategy.