UV Photooxidation Results in Efficient and Accelerated Remediation of PFAS Water Contaminants in Aerosol Microdroplets
RILEY WEATHERHOLT, Kaitlyn Chung, Bailey Bowers, Ryan Sullivan, Carnegie Mellon University
Abstract Number: 583
Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts
Abstract
Per- and Poly-fluorinated Alkyl Substances (PFAS) are a class of thousands of synthetic compounds characterized by carbon-fluorine bonds, which impart both hydrophobic and hydrophilic properties. PFAS are extremely persistent, ubiquitous, and many are known carcinogens, immunosuppressants, and endocrine disruptors. PFAS therefore pose a great challenge to sustainability and chemical remediation. Photo-oxidative remediation is a promising technology for the degradation of PFAS. The high surface activity of PFAS allows their concentration to be enhanced through aerosolization, placing them in a unique chemical environment that can accelerate degradation kinetics. The oxidation rate of 6:2 fluorotelomer carboxylic acid (FTCA) in the droplet phase and in bulk solution was measured to determine if a rate enhancement was observed in microdroplets. Aqueous 6:2 FTCA droplets and bulk solution were subjected to VUV/UVC light, which also produces gas-phase ozone and hydroxyl radical oxidants in situ. We compared substrate degradation, defluorination, and transformation products between droplets and bulk using both targeted HPLC-QQQ-MS and nontargeted UPLC-Orbitrap-MS. By using wavelengths that split water and molecular oxygen, we observed facile degradation of 6:2 FTCA in droplets and bulk solution without any added reagents. We observed fluoride production and a homologous series of perfluorocarboxylic acid (PFCA) transformation products, indicating perfluoryl chain-shortening of the 6:2 FTCA in addition to removal of the –CH2C(O)OH head group. Actinometry and radical probe experiments measured the steady-state hydroxyl radical concentration in droplets and bulk to determine when the kinetics are droplet-accelerated. More recent experiments compared the kinetics and products of 254 nm UVB to 193 nm VUV aerosol photodegradation. The Iodide CIMS method we recently developed enabled direct measurements of the degradation kinetics and gas and aerosol-phase products. These results represent an important step toward lower-cost PFAS remediation and mineralization, which can enable water treatment and reuse by removing ultrapersistent micropollutants.