PFAS removal through foam harvesting during wastewater aeration

Aeration in wastewater treatment plants (WWTPs) is used for removal of organic matter and nutrients. Here we show that aeration can also lead to removal of per- and polyfluoroalkyl substances (PFAS), by foam fractionation. Rising air bubbles facilitate air-liquid interfacial adsorption of PFAS and spontaneous foaming occurrence. This suggests that some modifications to conventional treatment processes that enable foam removal may be sufficient to achieve PFAS removal at WWTPs. However, high suspended solids concentrations in the mixed liquor suspension within the aerated bioreactors may complicate PFAS removal in foam fractionation, as both air bubbles and suspended biomass retain PFAS. This study explored the feasibility of foam fractionation for PFAS removal and enrichment using actual mixed liquor suspensions with typical total suspended solids concentrations and WWTP-relevant PFAS concentrations. The mechanisms involved in PFAS removal and enrichment in both aqueous and solid phases were suggested, and a mass balance analysis was performed to show PFAS distribution between the two phases. Overall, PFAS removal from the aqueous phase ranged from 70 % to 100 % for PFAS with perfluorinated carbon numbers ≥ 6, while PFAS with perfluorinated carbon numbers < 6 showed low removal of < 20 %. PFAS removal from the solid phase ranged from 20 % to 60 %, depending on the PFAS species. This study represents an ongoing effort to advance the potential implementation of foam fractionation in aerated bioreactors at WWTPs.