Pilot-Scale Thermal Destruction of Per- and Polyfluoroalkyl Substances in a Legacy Aqueous Film Forming Foam

Abstract

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 DEs, >99.99%, are deemed acceptable for most hazardous compounds, many PFAS can be converted to other PFAS at low temperatures resulting in high DEs without full mineralization and the potential release of the remaining fluorocarbon portions to the environment. Many of these products of incomplete combustion (PICs) are 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 indicate PFAS mineralization. Several operating conditions above 1090 °C resulted in high DEs and few 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.

Keywords: AFFF; PFAS; destruction efficiency; incineration; products of incomplete combustion.

Figure 1:

EPA refractory-lined natural gas-fired furnace showing the AFFF injection locations, through the flame with the natural gas and at ports 4 and 8 and the stack sampling locations indicated. Measurements are made prior to the facility air pollution control system (APCS).

Figure 2:

The sums of the peak areas of fluorinated features observed with nontargeted analyses of the OTM-45 extracts. Each fraction of the sampling train is shown for each temperature. The darkened portion of each bar is the sum of the targeted compounds’ peak areas, included to show how well the targeted list covers the observed PFAS.