A Cost-Effective Technology for Destruction of Per- and Polyfluoroalkyl Substances from DoD Subsurface Investigation-Derived Wastes
Dongye Zhao | Auburn University
The overall goal of this project is to develop an innovative, cost-effective and ‘green’ technology for destruction of per- and polyfluoroalkyl substances (PFASs) from Department of Defense's (DoD) subsurface investigation-derived wastes (IDWs). Because IDWs consist of wastewater, soil, and equipment cleaning fluid, the technology is aimed at degrading PFASs in both IDW water and soil phases. The specific objectives are to: 1) Develop a novel composite material based on low-cost activated charcoal/carbon (AC) and a cutting-edge photocatalyst, titanate nanotubes (TNTs), which offers both high adsorption capacity and high photochemical degradation and regeneration capability toward PFASs, 2) Test the new material for adsorption and photocatalytic degradation of PFASs in IDW water, 3) Explore a dispersant-based cost-effective approach for extracting PFASs from IDW soil and test the effectiveness of the new material for adsorption and photodegradation of PFASs in the spent extractants, and 4) Carry out a preliminary cost-benefit analysis and assess the technology transfer potential.
The technology builds upon a high-capacity and photo-regenerable composite material (TNTs@AC) developed by the research team. The new material is composed of an AC core and a photocatalyst shell (TNTs). The AC core adsorbs and concentrates PFASs from water onto the reactive surfaces of the material, whereas the photocatalyst facilitates subsequent destruction of the contaminants under ultra violet or solar light, which also regenerates the saturated material. Based on the preliminary data, the research team hypothesize that the integrated ‘concentrate-photodegrade’ technique can be further modified and optimized for efficient degradation of PFASs along with common co-contaminants in IDW water. While perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) will be used as the model PFASs in this work, four other Environmental Protection Agency (EPA) listed high priority PFASs will also be measured and tested, including perfluorononanoic acid, perfluorohexane sulfonate, perfluoroheptanoic acid, and perfluorobutanesulfonic acid). The research objectives will be achieved by carrying out the following research tasks: 1) Synthesis and characterization of the new AC-supported photocatalyst; 2) Removal and destruction of PFASs from IDW water: Batch kinetic and isotherm tests of the new material for adsorption of PFASs in IDW water; 3) Removal of PFASs from IDW soil: Extraction of PFASs from IDW soil using a low-cost surfactant or dispersant; 4) Photodegradation of PFASs concentrated on TNTs@AC and regeneration of the spent material; and 5) Cost-benefit analysis and technology transition.
Uncontrolled spills and repeated uses of aqueous film-forming foams (AFFFs) have been correlated to elevated concentrations of various PFASs in biota, surface water, and groundwater. Drinking water supplies for six million U.S. residents exceed EPA’s lifetime health advisory (70 ng/L) for PFOS and PFOA. The U.S. military accounts for 75% of all AFFF formulations used in the U.S. and the use of PFOS-based AFFFs has been a major environmental liability of DoD. As PFASs are under EPA’s close scrutiny, and intensive subsurface investigations are ongoing or more are being launched at various DoD sites, large amounts of PFASs-bearing waste water and soil are generated. This project directly addresses the Strategic Environmental Research and Development Program (SERDP) SON to develop "more cost-effective and efficient technologies for treatment of IDW from PFAS investigations". Compared to conventional technologies such as adsorption, landfill and incineration, the new technology potentially offers the following advantages: 1) it can more cost-effectively destroy PFASs and common co-contaminants from IDW, 2) the photodegradation also regenerates the material, allowing for repeated material uses, 3) the system can be easily applied on site and is easier to operate, 4) it holds the potential to achieve unrestricted disposal, discharge, and/or reuse of IDW on-site, and 5) the treatment can be made mobile and be deployed easily, minimizing the spatial footprint and mobilization time and effort. As such, the new technology will greatly aid DoD Remedial Project Managers in the management of these sites. (Anticipated Completion - March 2019)