This proof-of-concept project will develop a combined thermal desorption/microwave plasma strategy for the removal of per- and polyfluoroalkyl substances (PFAS) from granular activated carbon (GAC) filter media and their subsequent destruction. A novel ‘warm’ thermal plasma, the Microwave Inductively-Coupled Atmospheric Plasma (MICAP), will be used for high-temperature plasma-mediated mineralization of PFAS. The project objectives are as follows:

• Develop, optimize, and evaluate the efficacy of the MICAP plasma as a destruction method for highly incalcitrant gaseous PFAS surrogates CF₄ and C₂F₆, measuring the efficiency of decomposition and the resulting transformation products.
• Develop, optimize, and evaluate an energy-efficient indirect thermal desorption (TD) method for removal of PFAS from GAC at reduced temperatures by optimization of sweep gas water content and acidity, measuring the rate of PFAS volatilization and identifying any PFAS remaining in the GAC by studying a group of 40 common PFAS.
• Demonstrate, optimize, and evaluate the efficacy of the combined TD-MICAP system for removal of the 40 common PFAS from GAC. The energy and decomposition efficiencies of the TD-MICAP process will be optimized and measured.

The efficacy of MICAP plasma decomposition conditions will be quantitatively studied by analyzing the effluent flow using in-line semi-quantitative Fourier transformed infrared spectroscopy and gas-sampling gas chromatography-mass spectrometry using validated measurement methods for volatile organic fluorine compounds. Mass transformation to hydrofluoric acid will be studied based on F^- content in liquid scrubber-treatment solutions via ion chromatography (IC). The thermal desorption elution profile of a mix of 40 PFAS will be studied to optimize TD volatilization conditions. Total fluorine content remaining in TD-treated GAC will be measured by combustion IC (method 1621). The identity and quantity of PFAS and transformation products remaining in the GAC will be measured via liquid chromatography-tandem mass spectrometry (EPA Method 1633). Finally, the combined TD-MICAP system will be evaluated using the same analytical methods to determine PFAS destruction efficacy.

Water treatment using GAC-type filter media is the standard and most mature and implemented technology for PFAS removal worldwide. The fate of the spent PFAS-impacted GAC filter media presents a significant waste management issue. The TD-MICAP treatment system offers a cost- and energy-effective means of cleanup and regeneration of the GAC filter media. This ‘warm’ thermal plasma provides many of the benefits of high-temperature thermal arc-type plasmas, but with improved energy efficiency, and lower operating costs. Moreover, the MICAP plasma has much higher gas temperatures (e.g., 6000K) as compared to a typical incinerator flame (e.g., 1500K). Remediation approaches developed through this technology will improve the reliability of treatment processes and expedite the cleanup and closure of impacted sites. The strategy leverages an accepted water treatment strategy, commercial off-the-shelf technology, and thus promises immediate impact, thereby contributing to the development of affordable, deployable PFAS solutions to protect critical installations and personnel, bolstering national defense capabilities. (Anticipated Project Completion - 2026)