As the Department of Defense (DoD) has been performing various related investigations, large quantities of investigation-derived wastes (IDWs) are and continue to be generated. Yet a cost-effective technology has been lacking for treatment of per- and polyfluoroalkyl substances (PFAS)-impacted soil and water including the IDWs. As such, destructive technologies are of interest to minimize potential future environmental liability and to replace current costly practices (landfill and incineration). The overall goal of this proof-of-concept project was to develop an innovative “Concentrate-&-Destroy” technology for cost-effective degradation of PFAS from IDW (including both water and soil). The specific objectives were as follows:

1. Develop a new class of adsorptive photocatalysts that can facilitate effective adsorption and subsequent in situ photocatalytic degradation of PFAS.
2. Test the effectiveness and reusability of the new materials for selective adsorption and photocatalytic degradation of PFAS in water without chemical regeneration.
3. Develop a new strategy to remove and degrade PFAS from soil.

To achieve the project objectives, the project team carried out the following research tasks:

1. Synthesized a series of novel metal-doped, carbon-modified photocatalysts based on commercially-available, low-cost activated carbon (AC) and photocatalysts.
2. Tested the adsorption rates and capacities of the materials with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) as model PFAS.
3. Tested the photodegradation rates and extents of the pre-concentrated PFAS, and the material reusability without chemical regeneration.
4. Examined the effectiveness of low-cost dispersants for “greener” and cost-effective removal of PFAS from soil.
5. Conducted a preliminary cost-benefit analysis.

The project team synthesized, characterized and tested three of the most promising adsorptive photocatalysts, including two AC-supported, metal-doped titanate nanotubes (Fe/TNTs@AC and Ga/TNTs@AC), and a composite carbon sphere (CS) modified iron oxide (FeO/CS). All three materials were able to rapidly (<10 min) and nearly completely adsorb PFOA and PFOS. Subsequently, when subjected to ultra violet (UV), Fe/TNTs@AC was able to photodegrade >90% of the pre-concentrated PFOA and >88% of PFOS within four hours, of which ~62% (PFOA) and ~46% (PFOS) were completely defluorinated (or mineralized). Even more efficient degradation was observed with Ga/TNTs@AC, which was able to pre-concentrate all PFOS within 10 minutes and mineralize 66% of the pre-concentrated PFOS under UV within four hours. FeO/CS mineralized 60% PFOA under solar light within four hours. Upon photodegradation, the materials can be reused in multiple cycles without chemical regeneration. For instance, after repeatedly used for six cycles for PFOA removal, Fe/TNTs@AC did not show significant drop in adsorption capacity and photocatalytic activity. For treatment of a PFAS-laden field soil from the Willow Grove site, the project team developed a “green” and cost-effective desorption technique to efficiently elute PFAS from the soil by using a low-cost oil dispersant (Corexit EC9500A). Subsequently, the desorbed PFOS in the spent dispersant was reloaded on the composite material and degraded under UV.

The on-site “Concentrate-&-Destroy” technique represents a significant advancement of current practices (adsorption, ion exchange, landfill and incineration) for treating PFAS in IDW 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 PFAS-laden IDW and PFAS-impacted soil and groundwater at DoD sites.

Peer reviewed journal papers

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.

• The journal’s 2019 Best Paper of the Year.

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.

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.

U.S. Patent

Zhao D. and W. Liu. Novel High-capacity and Photo-regenerable Materials for Efficient Removal of Polycyclic Aromatic Hydrocarbons and PFAS from Water. US Patent Application Number: 62/452,648

Dissertation

Li, F. 2019. A New Class of Adsorptive Photocatalysts for Enhanced Adsorption and Destruction of 4-Chlorophenol and Perfluorooctanoic Acid (PhD Dissertation). Auburn University.