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Industrial SCWO for the Treatment of PFAS/AFFF Within a Water Matrix
Citation:
Sahle-Demessie, Endalkac, C. Berg, E. Shields, S. Jackson, I. George, K. Liberty, AND J. Follin. Industrial SCWO for the Treatment of PFAS/AFFF Within a Water Matrix. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-22/257, 2022.
Impact/Purpose:
Effective treatment technologies are needed for the destruction of PFAS-containing by products and wastewater streams. An industrial-scale continuous flow supercritical water oxidation (SCWO) system was tested for the destruction of high concentration foam used for fighting high-hazard flammable liquid fires obtaining 99.99% destruction with trace levels of by-products. More than 1200 gals of waste mixture was treated and study has proved that Supercritical water oxidation (SCWO) is a single step wet oxidation process that transforms organic matter including PFAS into water, carbon dioxide and, inert mineral solid residue.
Description:
General Atomics (GA) (San Diego, CA) and U.S. EPA – Office of Research and Development (EPA-ORD) entered into an agreement in November 2020 to allow for testing of the removal efficacy and destruction of per- and polyfluoroalkyl substances (PFAS) within aqueous film-forming foam (AFFF) using supercritical water oxidation (SCWO) technology currently available on the market. The intent was to conduct treatability studies of low-to-medium dilutions of AFFF and identify the destruction efficiency of PFAS per the agreed-upon quality assurance project plan (QAPP). Available information regarding the project is briefly summarized within this document. This document aims to examine the destruction of PFAS in diluted AFFF using this specific technology; this document does not represent an exhaustive review of all SCWO technologies or apply to all PFAS sources. Liquid influent feed stream and both liquid and gas effluent stream samples were collected and tested using various methods including, but not limited to EPA Method 537.1 for quantitative analysis of targeted PFAS in liquids, total organic carbon, chemical oxygen demand, total organic fluoride, non-targeted PFAS analysis, elemental analysis, and real-time measurement of stack emission flow to confirm the absence of various gases. Sorbent tubes and canisters were used to sample gas for volatile organic compounds, PFAS, and other reaction by-products. In all tests, PFAS and total organic carbon (TOC) destruction efficiencies were > 99.99%. PFAS target compounds were not detected above the background level in the gas analyses. The sorbent tubes detected many trace organic compounds but no fluorinated compounds. After appropriate caustic neutralization of the reaction products, there was no HF detected in effluent streams. After 50 hours of operation, limited corrosion was observed, since there was a slight increase in chromium concentrations in the effluent stream. Fluorine appears mainly as a fluoride ion in the liquid effluent. Trace amounts of fluorinated hydrocarbon (FH) were also found in the liquid effluent, however, it is unclear if this comes from the contaminated quench water (softened tap water) that was shown to have higher PFAS levels than the liquid effluent. This document is intended to provide an overview of the GA SCWO technology tests, a summary of the results, and discuss various opportunities for use. Note that some qualitative interpretation is provided regarding Non-Targeted Analysis (NTA), and not all NTA work is comparable. Limited data is available on the SCWO degradation pathways for the different PFAS.