The overarching goal of this project is to validate the efficacy of a novel cement-based filter media (CFM ) for destroying per- and polyfluoroalkyl substances (PFAS) in concentrated liquid waste streams, through a series of lab-based batch and column tests. CFM technology combines titanium-doped calcium-enriched alkaline materials with ultraviolet (UV) activation energy to initiate catalysis and polymer unfurling followed by fluorine or sulfate liberation and subsequent mineralization as fluorite or anhydrate minerals. The CFM unit will be used to destroy PFAS present in concentrated waste streams such as legacy aqueous film-forming foam (AFFF) concentrate, source-area groundwater, and/or ion exchange (IX) resin regeneration waste. Specific project objectives include:
Bench scale studies will be conducted using a technology prototype that consists of an ex situ cartridge unit containing a titanium-doped activated high-calcium granular media packed around a ultraviolet (UV) lamp contained within a quartz sleeve and operating over a range of wavelengths. CFM will be synthesized using titanium doped photocatalytic agents, various binding agents, inert mineral fillers, and coarse lightweight aggregate to create a media with high hydraulic conductivity. Waste liquids will be passed through CFM void space, where pH increases greater than 12 standard units due to reactions with free hydroxyl radicals (OH-) and calcium release. Catalysis and degradation of PFAS appears to be initiated and sustained with self-reinforcing production of aqueous electron (eaq-), OH-, and persistent high pH. Optimization of the rates of decomposition products will be performed. Released free calcium in solution required to induce precipitation of fluorite and anhydrate minerals after fluoride and sulfate liberation will be calculated and optimized for concentrated waste streams. Mineralization has previously been verified within the pore solutions of the prototype and side-chain byproduct production has been validated; additional testing is needed to prove-out the technology for scale-up.
UV/ silica-based granular media (SGM) was developed to degrade PFAS in concentrated liquid media. Efforts within this project to date have focused on treating PFAS within ion exchange still bottoms, with early validation of treatment efficacy for both PFAS-spiked deionized water and synthetic still bottoms matrices. PFAS removal and subsequent defluorination using UV/SGM has been validated for over 20 PFAS. A robust treatability and validation study was performed on ion exchange still bottoms sourced from a former Navy facility located in the mid-Atlantic region of the United States. Still bottoms from this site had a very complex matrix, with approximately 800 ppm of PFAS, 80,000 ppm of chloride, 12,000 ppm of total organic carbon, 4,000 ppm of nitrate, and 3,000 ppm of sulfate. UV/SGM treatment was performed at 10x, 5x, and 2x dilutions from the initial still bottoms. Treatment yielded >99.9% removal of PFOS and PFOA for all dilutions. Total PFAS removal ranged from 90% to 97% and defluorination ranged from 43% to 90% over the three dilutions.
A preliminary study treating AFFF reported promising results, providing another possible application for UV/SGM treatment. Future work will focus on performing robust treatability studies on PFAS concentrated liquids (specifically foam fractionate), elucidating a better mechanistic understanding of UV/SGM treatment, reactive species, and sinks/impacts, and assessing degradation kinetics of individual PFAS.
This technology has the potential to achieve complete destruction of PFAS and AFFF in brines or other waste streams with a fairly rapid process requiring relatively low energy inputs and low-cost of materials. It produces benign transformation products and has potential application for a variety of waste streams including IX brine treatment and ex situ treatment of source area groundwater. The results of this project will benefit the DoD by reducing the risk to human health and the environment associated with PFAS and legacy AFFF (i.e., PFAS destruction). (Anticipated Project Completion - 2024)
McIntyre, H.M. and M.L. Hart. 2021. Photocatalytic Porous Silica-Based Granular Media for Organic Pollutant Degradation in Industrial Waste-Streams. Catalysts, 11(2):258. doi.org/10.3390/catal11020258.
McIntyre, H.M., V. Minda, E. Hawley, R. Debet, and M.L. Hart. 2022. Coupled Photocatalytic Alkaline Media as a Destructive Technology for Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foam Impacted Stormwater. Chemosphere, 291(1):132790. doi.org/10.1016/j.chemosphere.2021.132790.
McIntyre, H.M., V. Minda, W. Gutheil, and M.L. Hart. 2021. Degradation and Defluorination of Aqueous Perfluorooctane Sulfonate by Silica-Based Granular Media Using Batch Reactors. Journal of Environmental Engineering, 147(11):04021048. doi.org/10.1061/(ASCE)EE.1943-7870.0001922.