Per- and polyfluoroalkyl substances (PFAS) have been detected in groundwater, surface water, and operation- or investigation-derived wastewater at hundreds of sites. In particular, the use of PFAS-laden aqueous film-forming foam (AFFF) has been a major environmental liability. As the pertinent environmental regulations are rapidly evolving, there is an urgent need for “more cost-effective and efficient technologies” to treat PFAS at impacted sites. This project was conducted in two phases, with a proof-of-concept tested in the first phase and further optimization of the technology conducted in the second phase.
In Phase I, preliminarily testing of an innovative “Concentrate-&-Destroy” strategy was conducted. The technology is based on a new class of adsorptive photocatalysts that can effectively adsorb (or trap) and then photodegrade (zap) perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Three of the most promising adsorptive photocatalysts were preliminarily synthesized, characterized and tested under controlled conditions. While bench-scale data unveiled great promise of these materials for both adsorption and photocatalytic destruction of pre-sorbed PFOA and PFOS, there was a need to further polish the material preparation and optimize the subsequent photocatalytic degradation conditions for treating more DoD-relevant PFAS under DoD field conditions.
The overall goal of Phase II of this project is to further polish and optimize the technology for destruction of aqueous PFAS under relevant field conditions. The specific objectives of this follow-on research are to:
The following key hypotheses will be tested: 1) the carbon-photocatalyst composite materials can be further tailored to more selectively adsorb PFAS under relevant field conditions by enhancing concurrent hydrophobic, Lewis acid-base, and anion-π interactions; 2) the selective adsorption will mitigate potential interfering effects of co-solutes and dissolved organic matter on the subsequent photodegradation; and 3) the photodegradation/mineralization rates of pre-concentrated PFAS can be further improved through low-cost engineered means.
The ‘Trap-&-Zap’ technology is based on a new class of adsorptive photocatalysts that are prepared by integrating low-cost carbonaceous materials and metal-doped titanate nanotubes (Me/TNTs) or other photocatalysts. The composite materials act as both an adsorbent and a photocatalyst. As an adsorbent, the materials offer not only rapid adsorption rate, but also high adsorption selectivity towards PFAS, thanks to the concurrent hydrophobic interactions (between carbons and PFAS tail groups) and Lewis acid-base interactions (between metals and PFAS head groups). As a photocatalyst, the materials provide superior photocatalytic activity over conventional photocatalysts (e.g., TiO2) owing to the carbon-mediated side-on adsorption mode, carbon-mediated electron transfer, and enhanced generation of reactive species.
During Phase II of the study, treating PFAS in groundwater will be tested. As such, groundwater from the Naval Air Station Joint Reserve Base Willow Grove will be used as a representative PFAS-impacted groundwater. While PFOS will be used as a probe compound in the material screening tests, 10 other relevant priority PFAS also will be targeted in assessing the overall material performances. The research objectives will be achieved by carrying out the following tasks:
The key findings from Phase I are summarized as follows and are available in the Phase I Final Report:
The on-site “Concentrate-&-Destroy” technique represents a significant advancement of current practices (adsorption, ion exchange, landfill and incineration) for treating PFAS in investigation-derived waste or PFAS-impacted water and soil at large. Upon further testing and polishing (especially under field conditions), the technology will provide DoD remedial project managers with a more cost-effective technology for handling and disposal of these PFAS-impacted materials. (Anticipated Phase II Completion - 2026)
Duan, J., H. Ji, T. Xu, F. Pan, X. Liu, W. Liu, and D. Zhao. 2021. Simultaneous Adsorption of Uranium(VI) and 2-Chlorophenol by Activated Carbon Fiber Supported/Modified Titanate Nanotubes (TNTs@ACF): Effectiveness and Synergistic Effects. Chemical Engineering Journal, 406:126752.
Li, F., J. Duan, S. Tian, H. Ji, Y. Zhu, Z. Wei, and D. Zhao. 2020. Short-chain Per- and Polyfluoroalkyl Substances in Aquatic Systems: Occurrence, Impacts and Treatment. Chemical Engineering Journal, 380(1):122506.
Li, F., W. Liu, X. Cheng, M. Boersma, Z. Wei, K. He, L. Blaney, and D. Zhao. 2020. A Concentrate-&-destroy Technique for Degradation of Perfluorooctanoic Acid in Water using a New Adsorptive Photocatalyst. Water Research, 185:116219.
Wei, Z., T. Xu, and D. Zhao. 2019. Treatment of Per- and Polyfluoroalkyl Substances in Landfill Leachate: Status, Chemistry and Prospects. Environmental Science: Water Research & Technology, 5:1814–1835.
Xu, J., B. Xu, D. Zhao. 2019. Enhanced Adsorption of Perfluorooctanoic Acid (PFOA) from Water by Granular Activated Carbon Supported Magnetite Nanoparticles. Science of The Total Environment, 723:137757. (The journal’s 2019 Best Paper of the Year)
Xu, T., Y. Zhu, J. Duan, Y. Xia, T. Tong, L. Zhang, and D. Zhao. 2020. Enhanced Photocatalytic Degradation of Perfluorooctanoic Acid using Carbon-modified Bismuth Phosphate Composite: Effectiveness, Material Synergy and Roles of Carbon. Chemical Engineering Journal, 395:124991.
Zu, T., H. Ji, Y. Gu, T. Tong, Y. Xia, L. Zhang, and D. Zhao. 2019. Enhanced Adsorption and Photo-degradation of Perfluorooctanoic Acid in Water using Iron Oxide/Carbon Sphere Composite. Chemical Engineering Journal, 388:124230.
Zhao, D. and W. Liu. 2017. Novel High-capacity and Photo-regenerable Materials for Efficient Removal of Polycyclic Aromatic Hydrocarbons and PFAS from Water. U.S. Patent 62/452,648.
Li, F. 2019. A New Class of Adsorptive Photocatalysts for Enhanced Adsorption and Destruction of 4-Chlorophenol and Perfluorooctanoic Acid (Ph.D. Dissertation). Auburn University.