The research on this project contributes to the fundamental understanding of the factors controlling reductive defluorination of perfluoroalkyl acids (PFAAs) using a membrane catalyst-film reactor (MCfR) with elemental palladium (Pd0) and other precious metal catalysts. The cooperation of catalytic reductive defluorination and biodegradation achieved in the synergistic platform reveals a novel strategy for the treatment of persistent PFAAs. It also lays the foundation for developing a reliable and cost-effective synergistic platform for treating PFAAs. 

This research is being conducted in two phases. Phase I of this effort focused on expanding the understanding of the "synergistic platform," in which palladium (Pd)-based nanoparticles catalyze the removal of fluorine (F) substituents from perfluorinated compounds, such as perfluoroactanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), via reductive defluorination. This occurs in the hydrogen-based membrane catalyst-film reactor (H₂-MCfR), in which hydrogen gas (H₂) is delivered to a film of Pd-based nanoparticle catalysts that are deposited on the exterior of gas-transfer membranes. The nanoparticle film catalyzes the oxidation of H₂ and the substitution of H for F on the PFOA or PFOS. This leads to the release of the fluoride ion (F-) and the generation of a mixture of partially to totally defluorinated products derived from PFOA and PFOS. Once defluorinated, the products become biodegradable in a second-stage oxygen (O₂)-based membrane biofilm reactor (O₂-MBfR). The bacterial biofilm continues the defluorination process and ultimately mineralizes the products to harmless CO₂, H₂O, and F-. The synergistic platform of the H₂-MCfR + O₂-MBfR is uniquely capable of removing and destroying perfluorinated alkyl substances (PFAS) present at low to moderate concentrations in impacted waters. The results of the Phase I effort are available in the Phase I Final Report. 

The Phase II work will focus on the following important science and technology issues: 

1. Quantifying the role of adsorption in relation to reductive defluorination and aerobic biodegradation 
2. Developing bi-metallic catalysts (Pd + another metal) to overcome pH limitations of Pd alone in the MCfR 
3. Understanding the degree to which F must be removed in the H₂-MCfR so that biodegradation is sufficiently rapid in the O₂-MBfR 
4. Testing all of the U.S. EPA's priority perfluorinated alkyl substances 
5. Understanding interactions among different perfluorinated compounds when they are input in mixtures 
6. Evaluating the synergistic platform with impacted water from a field site 

Accomplishing all of these objectives will aim to ready the synergistic platform for field-pilot testing.

Ultimate Synergy: the Pd-MBfR for PFAS Destruction

Under Phase I, this project had three tasks of experimental work. In Task 1, the research team determined the optimal catalyst synthesis method and catalytic conditions that yielded fast PFOA/PFOS removal with least-fluorinated products. The intermediates and products of PFOA and PFOS reductive defluorination were determined to investigate the reaction mechanisms. In Task 2, the project team conducted continuous operation of the O₂-MBfR for partially fluorinated OA/OS for oxidative defluorination and mineralization using non-fluorinated counterpart as the primary substrate. The functional microbial community and genes were identified by analyzing the shallow-metagenomic sequencing results of biofilms. In Task 3, the project team operated a complete synergistic system with the two membrane-film reactors in series and successfully achieved PFOA and PFOS continuous removal. In Task 4, the project team estimated capital and annual operating costs of a 100-gpm system treating low or high concentrations of PFOA and PFOS. 

Under Phase II, in the synergistic platform, two membrane-film reactors are linked by sending the effluent of an H₂-based membrane catalyst-film reactor (MCfR) to be the influent of an O₂-based membrane biofilm reactor (MBfR). PFOA and PFOS are reductively defluorinated in the H₂-MCfR to less-fluorinated or non-fluorinated species. The less-fluorinated species are transferred to the O₂-MBfR, where they are further defluorinated and ultimately mineralized.

Phase I Results

Fast adsorption of PFOA and PFOS and the release of the fluoride ion and partially and fully defluorinated compounds verified that the H₂-MCfR catalytically removed and destroyed PFAS. Defluorination, preceded by PFOA adsorption in an orientation parallel to the Pd0 surface, enabled a fast reaction between fluorine substituents on PFOA and PFOS and activated hydrogen on the Pd0 surface. The addition of a promoter metal enabled palladium-based bimetallic catalysts to defluorinate PFOA and PFOS at neutral potential hydrogen. The MCfR was capable of sustained removal of PFOA at environmentally relevant concentrations, averaging 97% removal, to well below 70 nanograms/liter, for continuous flow for more than two months. The continuous oxidative biomineralization of partially defluorinated PFOA/PFOS in the O₂-MBfR proved the capability of MBfR biofilms for further biodegradation and mineralization of PFOA and PFOS-hydrodefluorination products from the H₂-MCfR. Continuous experiments with the synergistic platform proved that the H₂-MCfR and O₂-MBfR worked as expected when linked together in the synergistic platform; partially defluorinated products from the MCfR were further defluorinated in the MBfR. The defluorinated ratio in H₂-MCfR affected the biodegradation in O₂-MBfR, with more hydrodefluorination in the MCfR allowing more oxidative biodefluorination in the MBfR.

The synergistic platform is uniquely able to remove and destroy PFAS present at very low (ppb) to moderate (ppm) concentrations in the wide range of impacted waters.  Nanoparticle-catalyzed hydrodefluorination in the H₂-MCfR is a universal reaction mechanism of all PFAS. Current results have shown that partial defluorination converts the "forever compounds" into biodegradable species, thus making it possible for defluorination and mineralization. The synergistic platform allows PFAS removal and destruction without the need to use any extreme conditions or unfavorable reactants. Advancing this technology will safeguard mission readiness through proactive management of chemicals of concern. (Anticipated Phase II Completion - 2026)

Gao, T., Y. Luo, M. Long, C. Zhou, Y. Cai, H. Zhao, and B .E. Rittmann. 2026. Biodegradation of Fluorinated Octanoic Acids in an O2-based Membrane Biofilm Reactor. Water Research X, 30: 100462. doi.org/10.1016/j.wroa.2025.100462.

Glass, S., H. Santiago, W. Chen, T. Zhang, J. Guelfo, B .E. Rittmann, T. Senftle, P. Vikesland, D. Villigran, H. Wang, P. Westerhoff, M .S. Wong, G. Jiang, G. Lowry, and P .J. J. Alvarez. 2025. Merits, limitations, and innovation priorities for catalytic platforms to destroy PFAS. Nature Water, 3: 644-654. doi.org/10.1038/s44221-025-00433-8. 

Long, M., Y. Chen, T. P. Senftle, W. Elias, K. Heck, C. Zhou, M. S. Wong, and B. E. Rittmann. 2024. Method of H2-transfer is Vital for Catalytic Hydrodefluorination of Perfluorooctanoic Acid (PFOA). Environmental Science & Technology, 58:1390-1398. doi.org/10.1021/acs.est.3c07650.

Long, M., J. Cheng, C. Zhou, and B. E. Rittmann. 2025. Enhanced long-term reduction of high-level Au(III) with the presence of NO3- in a H2-based membrane biofilm reactor. Water Research, 274:123013. doi.org/10.1016/j.watres.2024.123013.

Long, M., J. Donoso, M. Bhati, W.C. Elias, K.N. Heck, Y.H. Luo, Y.S. Lai, H. Gu, T.P. Senftle, C, Zhou, M.S. Wong, and B.E. Rittmann. 2021. Adsorption and Reductive Defluorination of Perfluorooctanoic Acid over Palladium Nanoparticles. Environmental Science and Technology, 55(21):14836-14843. doi.org/10.1021/acs.est.1c03134.

Long, M., W.C. Elias, K.N. Heck, Y.H. Luo, Y.S. Lai, Y. Jin, H. Gu, J. Donoso, T.P. Senftle, C. Zhou, M.S. Wong, and B.E. Rittmann. 2021. Hydrodefluorination of Perfluorooctanoic Acid in the H2-Based Membrane Catalyst-Film Reactor with Platinum Group Metal Nanoparticles: Pathways and Optimal Conditions. Environmental Science and Technology, 55(24):16699-16707. doi.org/10.1021/acs.est.1c06528.

Long, M., C. Zheng, M. A. Rolda , C. Zhou, and B. E. Rittmann. 2024. Co-Removal of Perfluorooctanoic Acid and Nitrate from Water by Coupling Pd Catalysis with Enzymatic Biotransformation. Environmental Science & Technology, 58:11514-11524. doi.org/10.1021/acs.est.3c10377.

Long, M., C. Zhou, W. Elias, H. Jacobs, K. Heck, M. Wong, and B. E. Rittmann. 2024. Auto-Assembled Pd–Rh Nanoalloys Catalyzed Faster and Deeper Hydrodefluorination of Perfluorooctanoic Acid (PFOA) in Environmental Conditions. ACS ES&T Engineering, 4:1073-1080. doi.org/10.1021/acsestengg.3c00548.

Yao, G., K. Hong, T .P. Senftle, M .S. Wong, and B .E. Rittmann. 2025.  The Membrane Catalyst-film Reactor (MCfR) Extends PGM Capability for Water Purification. Johnson Matthey Technol. Rev. doi.org/10.1595/205651326X17550075510121.

Zhou, C., Y. Luo, C. Zheng, M. Long, X. Long, Y. Bi, X. Zheng, D. Zhou, and B.E. Rittmann. 2021. H2-Based Membrane Catalyst-Film Reactor (H2-MCfR) Loaded with Palladium for Removing Oxidized Contaminants in Water. Environmental Science and Technology, 55(10):7082-7093. doi.org/10.1021/acs.est.1c01189.