(245b) Rate Limiting Factors for Pfas Degradation on Carbonaceous Sorbents Using UV/Sulfite Generated Hydrated Electrons

Per- and polyfluoroalkyl substances (PFAS) are a large class of persistent synthetic contaminants detected in water globally, threatening human and environmental health. Carbon-based sorbents used to remove PFAS from water can be regenerated through thermal treatments that simultaneously destroy PFAS. However, this process is energy intensive and can emit harmful byproducts back into the environment. Advanced reduction processes (ARP) can mineralize PFAS in homogeneous aqueous solutions; however, reactivity in heterogeneous systems is poorly understood. We explore an alternative regeneration treatment for carbonaceous sorbents with ARP using hydrated electrons (e_aq^-) generated by UV/sulfite. Three carbon sorbents, granular activated carbon (GAC), carbon nanotubes (CNT), and polyethyleneimine-modified lignin (Lignin), were chosen based on their varying sorption strength and surface chemistry. Reaction rates and extent of defluorination were determined by tracking the amount of parent compound perfluorooctanoic acid (PFOA) in water and on the sorbent; and measuring fluoride and target perfluorocarboxylic acid (PFCA) transformation products, respectively. Results indicate that compounds in the aqueous phase (aq) reacted rapidly compared to sorbed (s) ones. This outcome was expected due to the highly reactive and aqueous nature of e_aq^-. Once desorbed, PFCA_aq reaction rates are negatively compromised by the carbonaceous particles. Results suggest that reaction rates are hindered by the sorbents’ capabilities of scavenging e_aq^-, decreasing sulfite (SO₃^-2) sensitizer concentration, and decreasing the incident light available for the sensitizer to generate e_aq^-. Because of these limiting factors, we propose that a regeneration scheme using UV/SO₃^-2 generated e_aq^- requires a desorption step and removal of sorbents before initiating the reaction of the concentrated liquid. This study encourages using sorbents that can efficiently capture and then release PFAS on command to promote efficient degradation in a concentrated aqueous media.