Citation:

Shields, E., J. Krug, W. Roberson, S. Jackson, M. Smeltz, M. Allen, R. Burnette, J. Nash, L. Virtaranta, W. Preston, H. Liberatore, A. Wallace, J. Ryan, P. Kariher, P. Lemieux, AND Bill Linak. Pilot‐Scale Thermal Destruction of Per‐ and Polyfluoroalkyl Substances in a Legacy Aqueous Film Forming Foam. ACS ES&T Engineering. American Chemical Society, Washington, DC, 3(9):1308–1317, (2023). https://doi.org/10.1021/acsestengg.3c00098

Impact/Purpose:

Per- and polyfluoroalkyl substances (PFAS) are a large class of synthetic chemicals that possess strong carbon fluorine bonds. These bonds make PFAS possess unique properties that has allowed them to be used in a wide variety of applications, from fire fighting agents to nonstick food wrappers and high temperature lubricants to refrigerants. Unfortunately, the strong carbon fluorine bonds are very difficult to destroy and allow PFAS stay in the environment and humans for very long times. Some PFAS accumulate in humans and can create a variety of health problems. Effective methods to destroy all the carbon fluorine bonds in PFAS are needed to ensure the safety and health of people and the environment. Incineration is a common technique to destroy hazardous waste and other waste streams, and may also be effective for PFAS. Common methods to evaluate the destruction of chemicals do not necessarily apply to PFAS, since the parent molecule can be altered at low temperatures without destroying the carbon fluorine bonds. These byproducts (products of incomplete combustion, PICs) can react in the environment and create perfluocarboxylic acids, compounds that can cause health problems. Here PFAS in an aqueous film forming foam (AFFF) were incinerated in a pilot-sale combustor and the parent molecules and any fluorinated PICs were analyzed for to determine if PICs can be formed when the PFAS have high destruction efficiencies. It was found that PFAS could have >99.99% destruction efficiencies, but fluorinated byproducts could still be observed. This show that looking for the presence of PICs, and not destruction efficiencies alone, is necessary to evaluate the destruction of PFAS. This information will be of interest to EPA programs, offices, states, and local communities as effective methods to treat PFAS are being investigated.  

Description:

The destruction of per- and polyfluoroalkyl substances (PFAS) is critical to ensure effective remediation of PFAS contaminated matrices. The destruction of hazardous chemicals within incinerators and other thermal treatment processes has historically been determined by calculating the destruction efficiency (DE) or the destruction and removal efficiency (DRE). While high DE values >99.99% are deemed acceptable for most hazardous compounds, many PFAS can be destroyed at low temperatures by removal of the polar functional group. The remaining fluorocarbon portions of these PFAS can be released to the environment. Many of these products of incomplete combustion (PICs) are potent greenhouse gases, most have unknown toxicity, and some can react to create new perfluorocarboxylic acids. Experiments using aqueous film forming foam (AFFF) and a pilot-scale research combustor varied the combustion environment to determine if DEs are an acceptable metric of PFAS mineralization. Several operating conditions above 1080 °C resulted in high DEs and no detectable fluorinated PIC emissions. However, several conditions below 1000 °C produced DEs >99.99% for the quantifiable PFAS and mg/m3 emission concentrations of several non-polar PFAS PICs. These results suggest that DE alone may not be the best indication of total PFAS destruction, and additional PIC characterization may be warranted.

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