Granular activated carbon (GAC) adsorption is widely used to remediate sites impacted by per- and polyfluoroalkyl substances (PFAS). While GAC can effectively remove PFAS from water, PFAS are concentrated on the GAC, and strategies for managing spent GAC need to be developed. One management option is to thermally reactivate spent GAC and reuse the reactivated product. Little is currently known about factors that control the fate of PFAS during thermal reactivation of GAC. Strategies need to be developed that effectively mineralize adsorbed PFAS, prevent the release of products of incomplete combustion (PICs) and hydrogen fluoride (HF) into the air, and prevent the leaching of PICs and fluoride from reactivated GAC. The overarching objective of this project is to identify conditions that effectively mineralize PFAS during the thermal reactivation of PFAS-laden GAC. Specific objectives will be to identify the roles of (1) reactivation temperature, (2) reactivation time, (3) calcium, and (4) pretreatment with base on PFAS fate during thermal reactivation of GAC.
Laboratory experiments will be conducted at controlled conditions to evaluate the fate of PFAS under thermal conditions typically encountered during GAC reactivation. In Task 1, thermogravimetric analyses (TGA) will be conducted to understand the effects of PFAS characteristics, calcium, base (i.e. hydroxide), and natural organic matter on PFAS fate. Experiments will be conducted both in the absence and presence of GAC to determine how GAC impacts PFAS fate during thermal reactivation. In Task 2, thermal reactivation experiments using a bench-scale fluidized bed furnace will be conducted to determine the effects of reactivation time and temperature on PFAS fate. In addition, how calcium, a known catalyst of gasification reactions, and pretreatment of spent GAC with base (i.e., hydroxide ion), a known promoter of thermal dehalogenation reactions, affect PFAS mineralization will be evaluated. An overarching goal is to collect data that permit closure of the fluorine mass balance. This will start with GAC containing known PFAS loadings, and both inorganic fluoride and organofluorine in furnace exhaust and on the reactivated GAC will be evaluated. Furthermore, a suite of targeted and non-targeted approaches will be employed to identify PICs that may be present in both furnace exhaust and on reactivated GAC.
GAC adsorption is commonly implemented or considered for PFAS remediation, including at military installations. Remediation site managers need information for the appropriate management of spent GAC once GAC has lost its ability to meet treatment criteria. This project will study one management option for spent GAC, thermal reactivation. Information generated will support the development of thermal reactivation protocols and life-cycle inventory analyses for GAC treatment in the context of PFAS remediation. Such analyses are needed in decision support systems for selecting effective PFAS remediation strategies. (Anticipated Project Completion - 2023)