Removal of per- and polyfluoroalkyl substances (PFAS) from municipal wastewater by foam fractionation

Municipal wastewater has a relatively low content of per- and polyfluoroalkyl substances (PFAS), compared with other point sources such as landfill leachate and industrial effluents. Nevertheless, it is considered as one of the major point pollution sources. Foam fractionation was previously shown to effectively remove PFAS from different water matrices and to reach a high PFAS enrichment. In this study, the removal of PFAS from municipal wastewater of different origins was investigated. Despite the low foaming potential, it was possible to reach an average removal of the sum of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorohexanesulfonic acid (PFHxS) of 93 %, the removal of the sum of 21 PFAS of 56 %, and the removal of the sum of PFAS expressed as PFOA equivalents (ΣPFOAeq) of 91 %, without any surfactant addition utilizing a novel approach of foam collection. The PFAS content was reduced to below the limit values for drinking water in Sweden and the anticipated future limit values for surface water in the European Union. The addition of four commercial surfactants and an extract of extracellular polymeric substances (EPS) from waste activated sludge each enhanced the foam formation. Moreover, a cationic surfactant increased the removal of short-chain PFAS. Additionally, foam fractionation of activated sludge was performed. A considerably lower ΣPFOAeq removal of only 20 % was demonstrated, which was explained by a high proportion of PFAS sorbed to sludge. Finally, the study discusses the practical implications of the application of foam fractionation at municipal wastewater treatment plants.