Mechanistic insights into the adsorption of PFOA and PFOS onto alum-based drinking water treatment residuals

Authors

• Sushma Yadav, Charles V. Schaefer, Jr. School of Engineering and Science
• Anshuman Satpathy, Charles V. Schaefer, Jr. School of Engineering and Science
• Roxana Rahmati, Charles V. Schaefer, Jr. School of Engineering and Science
• Niranjan Haridas Menon, Newark College of Engineering
• Zhiming Zhang, Henry M. Rowan College of Engineering
• Rupali Datta, Michigan Technological University
• Sagnik Basuray, Newark College of Engineering
• Steven Larson, U.S. Army Engineer Research and Development Center
• Dibyendu Sarkar, Charles V. Schaefer, Jr. School of Engineering and Science

Document Type

Article

Publication Date

10-1-2026

Abstract

Per- and polyfluoroalkyl substances (PFAS) are of increasing environmental concern owing to their persistence, bioaccumulative potential, and adverse impacts on the environment and human health. A non-hazardous industrial solid waste, drinking water treatment residuals (WTRs) have shown potential for the adsorption of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS). However, understanding the underlying mechanisms of PFAS removal is critical for optimizing WTRs in water treatment applications. This study investigated the adsorption of PFOA and PFOS on an alum-based WTR under varying environmentally relevant water chemistries, with a focus on the development of interfacial charge, surface speciation, and proton exchange processes. Potential binding mechanisms of PFOA and PFOS were evaluated by integrating a series of sorption experiments with surface complexation modeling and electrophoretic studies. The combined results indicate that the aluminol group (≡AlOH) on WTR exhibits good sorption affinity for PFOA and PFOS, with adsorption and retention governed by pH and ionic strength. Surface complexation modeling was consistent with PFOS retention through a combination of strong inner-sphere complexes on the inner Helmholtz plane (IHP) involving proton exchange and weaker outer-sphere complexes associated with Na⁺-co-adsorption, whereas PFOA retention was primarily on the outer Helmholtz plane (OHP). Electrophoretic mobility measurements supported the modeling results, showing a decrease in the isoelectric point (IEP) from ~5.5 to ~3.3 following PFOS adsorption, while no significant IEP shift was observed for PFOA. These results advance mechanistic understanding and predictive modeling of PFAS adsorption, supporting site-specific risk assessment and the use of alum-based WTRs for PFAS mitigation in complex environmental matrices.

Publication Title

Journal of Environmental Chemical Engineering

Recommended Citation

Yadav, S., Satpathy, A., Rahmati, R., Menon, N., Zhang, Z., Datta, R., Basuray, S., Larson, S., & Sarkar, D. (2026). Mechanistic insights into the adsorption of PFOA and PFOS onto alum-based drinking water treatment residuals. Journal of Environmental Chemical Engineering, 14(5). http://doi.org/10.1016/j.jece.2026.125187
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p2/2970