1,4-Dioxane and per- and polyfluoroalkyl substances (PFAS) co-occur in mixed plumes at several sites and are resistant to many natural and engineered degradation processes. Costly ex situ treatment technologies are often required to break them down. More cost-efficient destructive treatment approaches are urgently needed that can (1) generate synergistic effects and (2) optionally be applied in situ. Previous work has shown that electrochemical water treatment, one of the few processes that can break the C-F bond in PFAS, can be installed in situ. Building on this work, the objective of this project was to advance the efficacy of combining electrochemical with biological oxidation for the in situ remediation of groundwater contaminated by mixed contaminants of concern.

The bioelectrochemical treatment train approach is based on creating synergistic effects between two processes: (1) rapid electrochemical oxidation on dimensionally stable electrodes and (2) enhancement of aerobic biodegradation processes via electrochemically generated oxygen with concurrent removal of inhibiting co-occurring chemicals of concern. Here, the project team tested various mesh electrode materials in both commercial and custom-fabricated flow-through electrochemical reactors and investigated the coupling with 1,4-dioxane biodegradation by Pseudonocardia dioxanivorans CB1190 and aqueous film-forming foam (AFFF) pretreatment by the laccase-producing fungus Trametes versicolor.

Bioelectrochemical treatment rapidly reduced concentrations of 1,4-dioxane by several orders of magnitude even in the presence of biologically inhibitory chlorinated solvents, demonstrating the technology’s viability for both source zone and plume treatment. Coupling electrochemical with biological oxidation reduced energy consumption, material usage, and treatment costs by about one order of magnitude while mitigating oxidation byproduct formation. Several mesh anode materials were shown to be effective for flow-through PFAS mineralization, Magnéli-phase titanium suboxides being the most efficient. Over 99% of PFAS removal was achieved, demonstrating fluoride generation without aqueous organofluorine intermediate formation. Fungal AFFF pretreatment did not conclusively lead to PFAS transformation, possibly due to time limitations, but aerobic degradation of non-fluorinated AFFF components decreased the energy consumption of subsequent electrochemical treatment by 20%. The energy consumption of in situ electrochemical PFAS treatment under mass transfer-limitations is high, however, and further efforts on process configuration, material development, and implementation should be explored.

At many sites, remediation of groundwater impacted with 1,4-dioxane, chlorinated solvents, and PFAS requires costly ex situ treatment. This project provided DoD site managers with a new technology to treat mixed persistent chemicals of concern in situ. Bioelectrochemical treatment is sufficiently developed and understood to move ahead with field application, and is currently being tested at the pilot scale. More work is needed to establish in situ (bio)electrochemical PFAS treatment, but this research provides a solid foundation and critical early insights. (Project Completion - 2022)

Fenti, A., J. Yukun, A. J. Hanson Rhoades, G. P. Dooley, P. Iovino, S. Salvestrini, D. Musmarra, S. Mahendra, G. F. Peaslee, and J. Blotevogel. 2022. Performance Testing of Mesh Anodes for in situ Electrochemical Oxidation of PFAS. Chemical Engineering Journal Advances, 9:100205. 

Luo, Q., J. Lu, H. Zhang, Z. Wang, M. Feng, S. D. Chiang, D. Woodward, and Q. Huang. 2015. Laccase-Catalyzed Degradation of Perfluorooctanoic Acid. Environmental Science & Technology Letters, 2(7):198-203. 

Luo, Q. X. Yan, J. Lu, and Q. Huang. 2018. Perfluorooctanesulfonate Degrades in a Laccase-Mediator System. Environmental Science & Technology, 52(18):10617-10626.

Pica, N.E., N.W. Johnson, Y. Miao, P. Ramos, S. Mahendra, J. Blotevogel. 2021. Bioelectrochemical Treatment of 1,4-Dioxane in the Presence of Chlorinated Solvents: Design, Process, and Sustainability Considerations. ACS Sustainable Chemistry & Engineering, 9:3172-3182.

Sharifan, H., M. Bagheri, D. Wang, J.G. Burken, C.P. Higgins, Y. Liang, J. Liu, C.E. Schaefer, and J. Blotevogel. 2021. Fate and Transport of Per- and Polyfluoroalkyl substances (PFASs) in the Vadose Zone. Science of the Total Environment, 771:145427.