Formatted Title
Non-Extractable PFAS in Solid Matrices Using Draft 1633 Method: How to Improve Your Understanding?
Background/Objectives
Single-use anion exchange resin (AER) has been successfully demonstrated to remove PFAS from water sources. AER technology does not destroy PFAS but generates spent AER requiring waste management. Growing concerns and public awareness of PFAS and PFAS-containing wastes returning to the environment through air emissions, atmospheric deposition, and groundwater contamination has increased scrutiny over the handling of PFAS-laden waste streams. No PFOS and PFOA were detected in spent AER generated during 2 years of pump and treat (P&T) operation using draft Method 1633. The calculated PFOS and PFOA mass loading to the spent AER was approximately 50.9 and 36.8 milligrams per kilogram, respectively. Our work highlights how the current analytical method (i.e., draft USEPA Method 1633) has its limitation and is not efficient at extracting PFAS from spent AER for PFAS characterization. The inefficient waste characterization results by Method 1633 can lead to acceptance of spent AER by local landfills and underestimates of the PFAS mass in spent AER that can affect destruction and removal efficiency (DRE) when a destruction technology is applied. Our project developed more robust PFAS extraction techniques by testing multiple brine-solvent solutions and by testing physical milling to increase the surface area of the spent AER with the objective to improve PFAS extractability. We also used novel total fluorine (TF) and inorganic fluorine (IF) analytical methods to provide enhanced mass balance and DRE of the total PFAS load to better characterize PFAS in the solid media.
Approach/Activities
Our novel approach to characterize PFAS in the spent AER includes multiple steps to determine PFAS in the solid phase spent AER. Direct combustion ion chromatography (CIC) was used to analyze TF in the spent AER without chemical extraction procedures. A unique wash was then applied to further remove IF and allow characterization of total organic fluorine (TOF). This TOF approach includes nontarget PFAS typically not assessed by other methods (e.g., adsorbable organo-fluorine [AOF]). PFAS extractability was evaluated using four different organic solvent-salt solutions. Target PFAS (draft 1633 Method) as well as TF/IF/TOF were then used to analyze the extractant solutions and the solid media. The PFAS extractability and mass balance are estimated by comparing TF results in raw spent AER to TF results from the solid-phase and solvents. The study also evaluated the impact of cryomilling on improving PFAS extractability assuming grinded AER would offer greater AER contact with the extraction solutions. The study verified procedure repeatability, data usability and included precision testing.
Results/Lessons Learned
This is the first study that confirms the limitation of draft Method 1633 on quantifying PFAS in single use spent AER. A comprehensive assessment was conducted using multiple procedures and analytical methods to improve the understanding of PFAS mass in the spent AER. The TF concentrations of solid-phase spent AER was determined to be approximately 60% higher than the sorbed target analysis PFAS concentrations calculated based on the P&T operational and monitoring data. The low level precision offered by target PFAS analysis compliment the TF approach. The PFAS extraction study will be completed using four different solvents in 2023. This presented will shed light on the limitations of current PFAS analytical method to extract PFAS from solid matrices and how to establish an analytical framework to better characterize PFAS in difficult matrices (e.g., single use AER) for your project via more robust extraction methods and by using TF measurements.