Considering the need for easily deployable and destructive technologies for treatment of per- and polyfluoroalkyl substances (PFAS) in investigation-derived waste (IDW) and the current need of treatment train approaches, the overall objective of this project was to integrate various treatment technologies into one engineered system to synergistically remove and decompose PFAS. In doing so, the study target was set that such an integrated system should be based on practical technologies, if possible, working under ambient conditions, which was highly challenging but significant.
To decompose PFAS in IDW effectively, this work investigated the use of an engineered system that combines advanced oxidation technologies with reductive defluorination methods. Such an integrated system can synergistically harness the two complementary chemical approaches and overcome their limitations. Highly segregated nanoscale zerovalent iron (nZVI) was coupled with common oxidants such as hydrogen peroxide, persulfate, and peroxymonosulfate, where electrons, hydrogens, and superoxide radical anions generated in situ function as strong reducing species while simultaneously hydroxyl radicals and sulfate radicals serve as strong oxidizing species. The integrated system was designed to leverage various decomposition pathways and routes to reductively cleave C−F bonds, which would then undergo subsequent downstream oxidation, eventually mineralizing PFAS.
Chemical decomposition of PFAS can also be combined with physical adsorption by utilizing transition metal particles (M0/MOx) impregnated into the mesoporous structure of granular activated carbon (GAC), so-called reactive activated carbon (RAC; GAC/M). The reactivity and treatability of the integrated RAC/oxidant system was experimentally tested in a laboratory-scale batch reactor containing a variety of PFAS including perfluorooctanesulfonic acid, perfluorooctanoic acid, perfluorobutanesulfonic acid, and perfluorononanoic acid.
This proof-of-concept project tested whether the integrated system (i.e., RAC/oxidant or M/oxidant) was effective to adsorb and decompose PFAS. In particular, the modified Fenton system was quickly evaluated for its capability to decompose PFAS. Batch experiments were conducted to investigate the effects of GAC, oxidant, metal, dose, pH, and temperature on the removal of mainly six PFAS (all perfluorinated ones) listed in the United States Environmental Protection Agency’s Third Uncontrolled Contaminant Monitoring Rule. Results showed that the integrated system was effective at removing PFAS via physical adsorption and/or chemical decomposition. Chemical oxidants conjugated with transition metals (e.g., persulfate/Ag pair) were able to decompose PFAS, particularly carboxylic PFAS, under ambient conditions. Sulfonic PFAS were removed mainly via adsorption, while the remaining did not break down under the tested conditions. As a polyfluorinated one, 6:2 fluorotelomer sulfonate also decomposed significantly even by persulfate alone at room temperature. The most practical Fenton reaction and its modifications should be revisited to better address treatment of complex media impacted by PFAS.
Study objectives were not met, but much was learned to move the technology forward. Along with revealing detailed PFAS decomposition mechanisms and pathways as well as fate and transport of PFAS in IDW, future research should be set toward accelerating decomposition of PFAS in the promising Fenton system by pairing other common oxidants and transition metals at/in different oxidation states/elemental groups and introducing new approaches to tackle sulfonic PFAS such as Ag-persulfate complex utilization and catalytic substitution reaction. Knowledge obtained from this study could be expanded to treat many other halogenated chemicals (e.g., short-chain PFAS) found in various real-world complex media. The project team envisions the ultimate treatment procedure later would be mainly simple mixing of IDW with RAC/oxidant or M/oxidant. (Project Completion - 2020)
Parenky, A.C., N. Gevaerd de Souza, P. Asgari, J. Jeon, M. Nadagouda, and H. Choi. 2020. Removal of Perfluorooctanesulfonic Acid (PFOS) in Water by Combining Zerovalent Iron Particles with Common Oxidants. Environmental Engineering Science, 37:472-481. doi.org/10.1089/ees.2019.0406.
Parenky, A.C., N. Gevaerd de Souza, H. Nguyen, J. Jeon, and H. Choi. 2020. Decomposition of Carboxylic PFAS by Persulfate Activated by Silver under Ambient Conditions. Journal of Environmental Engineering, 146(10):0602003. doi.org/10.1061/(ASCE)EE.1943-7870.0001808.
Gevaerd de Souza, N. 2020. Sorption-Mediated Chemical Processes for the Versatile Treatment of Per- and Polyfluoroalkyl Substances (PFAS) in Complex Media (Ph.D. Dissertation). The University of Texas at Arlington.
Parenky, A.C. 2020. Development of Reductive/Oxidative Treatment Strategy for the Removal of Per- and Polyfluoroalkyl Substances (PFAS) in Water (Ph.D. Dissertation). The University of Texas at Arlington.