Formatted Title
Thermal Decomposition of Per- and Polyfluoroalkyl Substances in Spent Media and Soil: Mechanisms and Applications
Background/Objectives
This talk will provide a thorough overview of the thermal decomposition of per- and polyfluoroalkyl substances (PFAS), drawing from a range of studies conducted by this team and other researchers. Adsorption to granular activated carbon (GAC) has been frequently used at pilot- and full-scale operations to treat water contaminated by PFAS. The predominant residual from GAC systems is spent or exhausted carbon which contains elevated levels of PFAS. In a series of studies, our group symmetrically investigated the behavior and decomposition mechanisms of PFAS laden on GAC in various thermal processes. We have five specific objectives: (1) investigate the thermal stability of PFAS; (2) determine thermal decomposition mechanisms (temperature and time requirements, thermodynamics, kinetics) of PFAS on spent GAC; (3) tailor GAC to facilitate the adsorption of hydrophobic PFAS anions from water and investigate the long-term performance of raw and tailored GAC after multiple cycles of adsorption‒thermal reactivation; (4) remove PFAS from the brine of NF/RO by GAC; and (5) remediate PFAS-contaminated soils by thermal approaches.
Approach/Activities
We extended the tools for analyzing PFAS thermal degradation behaviors by innovatively using thermal desorption−pyrolysis−gas chromatograph−mass spectrometry (TD−Pyr−GC−MS) and thermogravimetric analysis (TGA), which are traditionally used for the analysis of biomass materials. Application of these ‘new’ tools leads to the identification many novel results. We also employed HPLC coupled with QToF-MS/MS to identify ionizable decomposition products of PFAS on spent GAC heated at different temperatures and durations. We also investigated the modification of GAC and evaluated the performance of raw/tailored GAC for PFAS removal from natural waters and NF/RO brine with multiple adsorption‒reactivation‒reuse cycles.
Results/Lessons Learned
Our team has produced many novel and significant results that have significant real-world implications in addressing environmental pollution and water treatment challenges. Understanding PFAS degradation in GAC will enable more efficient and cost-effective contaminant removal methods. This knowledge will enhance water treatment processes, public health, and environmental protection. For the first time, we identified the temperature and time requirements for thermal decomposition of PFAS, elucidated PFAS decomposition mechanisms on spent GAC during thermal regeneration and reactivation, determined the kinetics of PFAS thermal decomposition in different atmospheres, identified thermal decomposition products of PFAS, Assessed the fate and behavior of PFAS and co-contaminants during the processing of residual product streams from NF/RO; developed modified sorbents with greatly enhanced adsorption of weakly hydrophobic PFAS anions.