The objective this study was to develop a technique that can be used to effectively degrade per- polyfluoroalkyl substances (PFAS) under specific conditions in a wastewater facility. Chitosan- or 12-amino lauricacid (ALA) modified-montmorillonite increases the sorption capacity of perfluorooctanesulfonic acid (PFOS), and potentially enhances the degradation potential, while not using or generating any toxic compounds. To maximize efficiency, 3-indole-acetic acid (IAA) was selected as the indole compound, a 254 nanometer ultraviolet monochromatic source was used, and the montmorillonite was modified using ALA and chitosan as scaffold materials. Sorption isotherms of PFOA and PFOS onto organo-clay nano-composites were determined. The rate and extent of PFOS degradation and defluorination were determined, along with identification of daughter products of PFOS degradation.
This research tested the hypothesis that a chitosan-modified montmorillonite nano-composite is an effective material for sorbing high concentrations of IAA and PFAS. The research team further hypothesized that this treatment technology is expected to operate over a large range of pH and dissolved oxygen conditions and in the presence of natural organic matter (NOM), co-occurring chemicals, and competing anions, due to spatial configuration of hydrated electrons, PFAS, co-occurring chemicals, and competing anions within the structure of the chitosan-modified montmorillonite nano-composite. These hypotheses were tested by performing three tasks:
- Synthesis of a chitosan-modified montmorillonite nano-composite and sorption experiments of IAA, PFOA and PFOS to the nano-composite;
- Experiments of PFOA and PFOS degradation by hydrated electrons generated from IAA that is intercalated into the structure of the nano-composite to determine the rate and pathway; the impacts of water chemistry (NOM, BTEX, nitrate, sulfate, and bicarbonate) on PFAS degradation;
- Degradation experiments of PFCAs and PFSAs in the presence of a wide range of PFAS under realistic environmental conditions to assess the feasibility of this novel approach for treating concentrated investigation-derived waste.
This method reported a unique green chemistry approach that achieved degradation of PFOS over the course of several hours, with similar results for PFOA. The photogenerated hydrated electrons, which were generated via 3-indole-acetic-acid hosted by an organomodified clay scaffold, induced the defluorination of the co-sorbed PFAS by utilizing the reductive power of the hydrated electrons. The near complete degradation of PFOS occurred within the first few hours of irradiation, costing less than a dollar worth of electrical power. The use of the ALA and chitosan modified montmorillonites promoted the degradation process by stabilizing the reaction during photolysis, which prolonged the half-life of the hydrated electrons.
This green chemistry approach provides the framework for the reductive remediation of PFAS using an easily made, robust, organomodified clay which does not require the application or use of hazardous chemicals either in the clay composite or as the source of the hydrated electrons.
Kugler, A., H. Dong, C. Li, C. Gu, C. Schaefer, Y. J. Choi, D. Tran, M. Spraul, C. P. Higgins. 2021. Reductive Defluorination of Perfluorooctanesulfonic acid (PFOS) by Hydrated Electrons Generated upon UV Irradiation of 3-Indole-Acetic-Acid in 12-Aminolauric-Modified Montmorillonite. Water Research, 200: 117221. https://doi.org/10.1016/j.watres.2021.117221