Commercial-scale removal of short-chain PFAS in a batch-wise adsorptive bubble separation process by dosing with cationic co-surfactant

Abstract

Studies performed by Burns et al. in 2021 and 2022 demonstrated that a three-stage batch-wise adsorptive bubble separation process, surface active foam fractionation (SAFF), is effective at removing most per- and polyfluoroalkyl substances (PFASs) from contaminated groundwaters and landfill leachates. However, PFAS species with very low adsorption coefficients to bubble surfaces are difficult to remove, which is parallel to the difficulties in removing short-chain PFAS in granulated activated carbon beds and other solid media. It is well known that the adsorption coefficient to bubble surfaces improves in the presence of electrolytes in solution and it has previously been shown that this improves the removal of PFAS. By developing a correlation for the removal percentage of one species or another of PFAS due to SAFF in commercial-scale processes as a function of the adsorption coefficient, it is possible to generally estimate the removal percentage of any PFAS. The addition of a cationic co-surfactant, cetrimonium bromide, to the feed can significantly further improve the adsorption coefficient and, as a consequence, materially improve the removal of short-chain PFAS due to SAFF. A method for estimating this improved performance is in qualitative agreement with plant trials of SAFF at a North American site with a history of groundwater contamination due to the use of aqueous film forming foams firefighting foams, but the precise improvements appear to be dependent upon the concentration of the added co-surfactant. The required concentration of co-surfactant is significantly larger than might be expected on charge equivalence considerations, and this may be due to its consumption by other species in the feed, including PFAS that have not been accounted for. It is noted that the SAFF process may not be true foam fractionation and may, instead, be a bubble fractionator, both of which can be collectively described by the term “adsorptive bubble separation processes.”.