Development and Laboratory Scalability of Ultraviolet-Activated Silica-Based Granular Media as an Engineered System for the Degradation of Per- and Polyfluoroalkyl Substances in Concentrated Liquid Waste

Abstract

Lab-based experiments were performed to develop an engineered column system for ultraviolet silica-based granular media (UV/SGM) to degrade per- and polyfluoroalkyl substances (PFAS) in concentrated liquid waste and challenge the laboratory scalability of the system and develop a field-applicable system. UV/SGM is an innovative photocatalyst developed to degrade a variety of PFAS compounds and predominantly designed to treat low-volume highly concentrated waste. Scalability is presented by increased system wattage, volume, or flow rate at the lab scale. The resulting reactor configuration presents a proportional UV wattage to treatment volume and relative flow rate as pilot-scale treatment conditions. Treatment efficiency was established by amending concentrated PFAS waste in both strong acid (pH<4) and strong base (pH 13). UV/SGM takes advantage of the high affinity of silicon and fluorine, which overcomes Coulombic interactions in a high-pH solution for most fluorotelomers and perfluoroalkyl sulfonic acids (PFSAs), whereas increased adsorption/degradation of perfluoroalkyl carboxylic acids (PFCAs) occurs under low pH. Final reactor configurations presented in the study improved the efficiency of UV/SGM to degrade fluorotelomers and PFSAs under basic conditions while taking advantage of photolysis to degrade PFCAs. The system demonstrated >90% degradation of ∼50 mg/L total PFAS in a PFAS-spiked deionized water. Electrical energy per log order reduction (EE/O) calculated by reduction of PFAS ranged from ∼75 to ∼410 kWh/m3; however, fluoride recovered increased, respectively, with EE/O for systems of equivalent flow rate. Therefore, evaluating EE/O based on complete defluorination, rather than parent PFAS removal, could aid in technology energy comparison.