Enhancing PFAS Degradation through Far-UVC Photolysis Coupled with Electrochemical Oxidation and UV-Advanced Reduction Processes

Per- and polyfluoroalkyl substances (PFAS) represent a significant and persistent threat to water quality worldwide, posing major challenges due to their chemical stability, resistance to conventional treatment methods, and documented health risks. These contaminants, once released, persist in the environment for extended periods and have been detected in drinking water, surface water, groundwater, and even human blood. Conventional remediation techniques, such as granular activated carbon (GAC) adsorption, ion-exchange resins, and reverse osmosis, often struggle with shorter-chain PFAS compounds and merely shift contamination from one medium to another. As climate change intensifies rainfall and extreme weather, PFAS transport through runoff becomes increasingly likely, heightening the need for advanced treatment solutions.

In response to this pressing need, our work investigates an innovative remediation approach employing far-UVC radiation (222 nm) delivered by krypton chloride (KrCl*) excimer lamps. Unlike conventional low-pressure UV (LPUV) systems, which typically emit at 254 nm, or vacuum UV (VUV) systems at 185 nm, far-UVC at 222 nm offers a unique balance of high photon energy and minimal absorption by water. This balance enables deeper penetration into the water matrix and provides the potential for enhanced PFAS photolysis and subsequent defluorination. Preliminary findings indicate that certain PFAS, previously resistant to direct UV photolysis, may be more susceptible under far-UVC irradiation, thereby opening a promising new pathway for their degradation.

While direct photolysis at 222 nm shows considerable promise, integrating far-UVC treatment with electrochemical oxidation (EOP) and UV-advanced reduction processes (UV-ARP) can further enhance PFAS degradation. EOP effectively removes dissolved organic matter (DOM), which often competes with PFAS for reactive species, thus reducing the overall efficiency of PFAS degradation. Meanwhile, UV-ARP generates highly reactive hydrated electrons (e_aq⁻) capable of breaking down PFAS. Although adding sulfide ions is one way to produce e_aq⁻, applying a sufficiently negative potential at a GAC cathode can also generate e_aq⁻ without introducing sulfur species. This approach requires careful consideration of competing hydrogen evolution reactions (HER), which may be thermodynamically unfavorable at a GAC cathode. By combining EOP with in situ e_aq⁻ generation in UV-ARP, PFAS can be more effectively targeted and degraded without adding extra chemicals. This integrated treatment aims to meet or surpass stringent U.S. Environmental Protection Agency (EPA) standards, ultimately facilitating the development of a portable, cost-effective, chemical-free, point-of-use water treatment system. Such a system would be especially valuable for communities experiencing environmental vulnerabilities, such as those in Puerto Rico studied by the PROTECT Center at Northeastern University, where limited infrastructure, contaminated water sources, and heightened susceptibility to adverse health outcomes underscore the urgency for sustainable PFAS remediation solutions.

By advancing the understanding of PFAS photolysis under far-UVC radiation and harnessing the combined power of EOP and UV-ARP, this work endeavors to provide an innovative solution. In doing so, it seeks not only to bridge the gap between laboratory research and practical application but also to enhance the resilience of water treatment systems against emerging contaminants and the challenges posed by a changing climate.