Granular activated carbon (GAC) is a commonly used treatment technology for the removal of per- and polyfluoroalkyl substances (PFAS) from impacted waters. Once saturated, the GAC can be thermally regenerated to desorb and destroy contaminants. However, little is known about the reaction byproducts and remaining residuals resulting from thermal reactivation of spent GAC loaded with PFAS. Thus, it is difficult to evaluate their impacts on the environment and human health. In addition, high energy consumption for thermal regeneration of GAC is generally undesirable, which needs a timely investigation to improve and optimize the treatment processes to allow for a more cost-effective solution for remediation. This proof-of-concept project aims to acquire necessary data to:
- evaluate the sorption capability of regenerated GAC at different temperature settings;
- provide a better understanding of the chemical fate and transport of PFAS during thermal reactivation of PFAS-laden GAC; and
- offer a rapid and effective evaluation of possible reaction pathways for thermal decomposition of PFAS using quantum chemical calculations.
The research combines experimental and theoretical approaches to characterize the physicochemical properties of regenerated GAC and to examine chemical residuals remaining in the reactivated carbon materials and degradation products produced and subsequently released into the atmosphere after incineration. This project involves three major components.
First, to understand the temperature requirements for the thermal destruction of PFAS, laboratory-scale pyrolysis experiments for PFAS-laden carbon sorbent will be performed in a tube furnace operated at different temperature settings (300 to 900°C). Carbon materials will be characterized, and the sorption capability of the reactivated GAC will be evaluated in comparison to fresh GAC.
Second, to achieve a thorough product characterization and the full fluorine (F) mass balance to prevent the release of potential toxic byproducts, thermal degradation products and residuals of PFAS in both gas and condensed phases will be identified using complementary mass spectrometric and spectroscopic techniques in conjunction with thermogravimetric analysis.
Third, to provide an improved understanding of potential reaction mechanisms, theoretical calculations will be performed to determine the dominant reaction pathways and their thermodynamic and kinetic parameters to construct a mechanistic model for prediction of the PFAS thermal decomposition.
This project focuses on the demonstration of the proof-of-concept to facilitate the development of mechanistic understanding and improved remediation approaches that will benefit the Department of Defense’s engineering application. Data collected will be able to be used to optimize the thermal treatment of GAC at desired temperature settings to reduce energy consumption, extend the life cycle of GAC, and achieve a sustainable waste management plan. Understanding the chemical fate and transport of PFAS-derived thermal degradation products is fundamental to the remediation of contaminated sites. The development of a mechanistic model offers a rapid evaluation and prediction for the in situ degradation of PFAS in GAC. Overall, the expected results from this research will enhance current knowledge and understanding toward the better design and application of GAC treatment systems for PFAS removal. (Anticipated Project Completion - 2022)