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Pilot‐Scale Thermal Destruction of Per‐ and Polyfluoroalkyl Substances (PFAS) in a Legacy Aqueous Film Forming Foam (AFFF)
Citation:
Krug, J., W. Roberson, E. Shields, P. Lemieux, J. Ryan, P. Kariher, S. Jackson, L. Wickersham, Bill Linak, P. Burnette, J. Nash, L. Virtaranta, AND W. Preston. Pilot‐Scale Thermal Destruction of Per‐ and Polyfluoroalkyl Substances (PFAS) in a Legacy Aqueous Film Forming Foam (AFFF). The Science of PFAS: Transforming Research into Action A&WMA Specialty Conference, Durham, NC, November 08 - 10, 2022.
Impact/Purpose:
This paper reflects work performed on the Rainbow Furnace in EPA’s RTP facilities, where an Aqueous Film Forming Foam (AFFF) was introduced into the furnace through the flame as well as through several post-flame locations at various firing rates, temperatures, and residence times. Various samples were collected for targeted and non-targeted analysis, with the intention of reporting PFAS Destruction Efficiencies (DEs) and Products of Incomplete Combustion (PICs). The presentation's first author is Jonathan Krug (CEMM, AMCD), other authors include several researchers from CEMM, Paul Lemieux (CESER, HSSMD), Lindsay Wickersham (Region 9, formerly CEMM, AMCD), Jacobs and CSS contractors. This work represents several unique applications of applied combustion science where, 1) PFAS containing liquid was injected into an incinerator under controlled conditions, and targeted and non-targeted samples were collected for analysis of PFAS thermal destruction (DEs) and formation of products of incomplete combustion. This represents a significant potential enhancement in knowledge regarding the thermal treatment of PFAS-containing waste and in developing sampling methodologies. DEs are a traditional indicator of hazardous waste incinerator performance. However, it is believed that due to the uniquely electronegative nature and stability of C-F bonds and the relative fragility of the non-fluorinated polar functional groups commonly associated with PFAS, that DEs may not be an adequate indicator of full defluorination (mineralization). This abstract was internally reviewed by an ORD researcher and will be presented at The Science of PFAS: Transforming Research into Action, A&WMA Specialty Conference being held in Durham, NC on Nov 8-10, 2022.
Description:
Per/polyfluorinated alkyl substances (PFAS) are a group of anthropogenic chemicals used for their hydrophobic and lipophobic properties, as well as their chemical and thermal stability. PFAS can be present in multiple waste streams, some of which are treated by thermal destruction processes. However, as the C-F bond is one of the strongest in organic chemistry, it is unclear how effectively different thermal destruction processes can fully transform fluorocarbon chains in PFAS to produce only CO2 and HF. We present results from an experimental study of the thermal destruction of PFAS in a pilot-scale down-fired natural gas combustor. Experiments were completed for an aqueous film forming foam (AFFF) containing known concentrations of 10 PFAS, primarily perfluorooctane sulfonic acid (PFOS). Variations in combustion conditions, furnace load, stoichiometry, and PFAS injection location help evaluate the effectiveness of thermal destruction processes under different thermal environments, including those in the flame and the post-flame. For this study, developing source sampling methods include coated stainless-steel canisters and Other Test Method 45 (OTM-45), followed by either gas chromatography or liquid chromatography coupled with triple quad mass spectroscopy analyses for targeted and non-targeted PFAS and PFAS products of incomplete combustion (PICs). Canister results for the AFFF experiments indicate mostly non-detects for 30 targeted volatile non-polar PFAS PICs when the AFFF was introduced through the flame or at post-flame locations >1090 °C. However, as injection location temperatures fell below 1000 °C, concentrations of PFAS PICs (and CO) increased notably. This compares to the OTM-45 samples that indicate destruction efficiencies (DEs) of the 10 PFAS mostly >99.99% when the AFFF was introduced through flame and post-flame locations >970 °C, and DEs mostly >99.9% when AFFF was introduced at 870 °C. Even at the lowest injection location (810 °C), DEs >99.9% were measured for all five of the perfluorinated sulfonic acids. This suggests that DE calculations may not be the best indicator of total PFAS destruction. PFAS may contain structures that are both fragile and stable that allow partial molecular transformations at temperatures unable to achieve full destruction (mineralization) of the fluorinated alkyl chain.