Integrated Foam Fractionation in Activated Sludge Systems for PFAS Removal from Landfill Leachate: Effects on Biological Nitrogen Removal

Abstract Typically high levels of ammonium in landfill leachate necessitate biological nitrogen removal at wastewater treatment facilities. Biological nitrogen removal often includes anoxic denitrification and aerated nitrification (the activated sludge process). Furthermore, landfill leachate often contains elevated concentrations of per- and polyfluoroalkyl substances (PFAS), which calls for new removal methods. Since landfill leachate naturally tends to foam in the aerated reactors of the activated sludge process, integrated foam fractionation is likely a suitable method for PFAS removal. This study evaluated the impact of integrating foam fractionation by capturing naturally occurring foam from the aerated reactor on PFAS and nitrogen removal performance. A laboratory-scale continuous nitrification/denitrification system was operated. Samples were collected from the influent, effluent, waste activated sludge, and foamate, and analyzed for 26 PFAS species in both the liquid and solid phases. Additionally, ammonium, nitrate, and nitrite concentrations were measured in the influent and effluent samples to assess nitrogen removal efficiency. Integration of foam fractionation increased the sum of measured PFAS removal from 0% to 51%. For long-chain perfluoroalkyl acids (PFAAs), this removal increased from 10% to 97%, whereas for short-chain PFAAs, removal increased from −5% to 10%. The integration of foam fractionation did not result in increased ammonium, nitrate, and nitrite concentrations in the effluent. Our findings demonstrate that foam fractionation can be effectively integrated within activated sludge processes to enhance PFAS removal from landfill leachate, without compromising process performance. This approach enables significant PFAS removal without requiring a separate tank or additional aeration energy.