Factors Affecting the Adsorption of Per- and Polyfluoroalkyl Substances (PFAS) by Colloidal Activated Carbon

• Published in: Water research (Oxford) 2023-08, Vol.242, p.120212-120212, Article 120212
• Main Authors: Hakimabadi, Seyfollah Gilak, Taylor, Alannah, Pham, Anh Le-Tuan
• Format: Article
• Language: English
• Subjects: activated carbon; adsorption; in-situ remediation; per- and polyfluoroalkyl substances; PFAS
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2023.120212

•The adsorption of PFAS on colloidal activated carbon was studied.•Hydrophobic interaction was the predominant adsorption mechanism.•The adsorption of PFOA and PFOS was increased by ionic strength and Ca2+.•Suwannee River Fulvic Acid and butyl carbitol diminished PFOS and PFOA adsorption.•Benzene and TCE diminished PFOS adsorption but enhanced PFOA adsorption. The immobilization of per- and polyfluoroalkyl substances (PFAS) by colloidal activated carbon (CAC) barriers has been proposed as a potential in-situ method to mitigate the transport of plumes of PFAS in the subsurface. However, if PFAS are continuously released from a source zone, the adsorptive sites on CAC will eventually become saturated, upon which point the breakthrough of PFAS in the barrier will occur. To predict the long-term effectiveness of CAC barriers, it is important to evaluate the factors that may affect the adsorption of PFAS on CAC. In this study, the adsorption of 7 PFAS on a polymer-stabilized CAC (i.e., PlumeStop®) and on a polymer-free CAC was investigated using batch experiments. The adsorption affinity of PFAS to CAC was in the following order: PFOS > 6:2 FTS > PFHxS > PFOA > PFBS > PFPeA > PFBA. This result indicates that hydrophobic interaction was the predominant adsorption mechanism, and that hydrophilic compounds such as PFBA and PFPeA will break through CAC barriers first. The partition coefficient Kd for the adsorption of PFAS on the polymer-stabilized CAC was 1.3 - 3.5 times smaller than the Kd for the adsorption of PFAS on the polymer-free CAC, suggesting that the polymers decreased the adsorption, presumably due to competitive sorption. Thus, the PFAS adsorption capacity of PlumeStop CAC barriers is expected to increase once the polymers are biodegraded and/or washed away. The affinity of PFOS and PFOA to CAC increased when the ionic strength of the solution increased from 1 to 100 mM, or when the concentration of Ca2+ increased from 0 to 2 mM. In contrast, less PFOS and PFOA were adsorbed in the presence of 1 - 20 mgC/L Suwannee River Fulvic Acid, which represented dissolved organic carbon, or in the presence of 10 - 100 mg/L diethylene glycol butyl ether (DGBE), which is an important component in some aqueous film-forming foam (AFFF) formulations. The presence of 0.5 - 4.8 mg/L benzene or 0.5 - 8 mg/L trichloroethylene, the co-contaminants that may comingle with PFAS at AFFF-impacted sites, diminished PFOS adsorption but had no effect or even slightly enhanced PFO