(110a) Thermal Treatment of PFAS: Determining What Products of Incomplete Combustion (PICs) Are Present in a Pilot-Scale Combustor.

Per- and polyfluoroalkyl substances (PFAS) have been widely used and are frequently measured in various concentrations in wastes and environmental media. PFAS are now recognized as environmental pollutants, particularly perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).

Thermal treatment is commonly used for waste disposal and destruction. Thermal treatment methods aim to mineralize various media and are now commonly exposed to PFAS. However, PFAS introduce thermal treatment to new a challenge due the presence of C-F bonds which may result in issues for thermal treatments ability to mineralize PFAS into HF and CO₂.

EPA’s pilot-scale combustor, known as the ‘Rainbow furnace,’ was used to determine the thermal viability of several commercial PFAS containing aqueous film forming foams (AFFFs) and to characterize what fluorocarbon byproducts, also known as products of incomplete combustion (PICs), may form from the incineration of neat-single component aqueous solutions of PFOA and PFOS. Experimental trials atomized the PFAS solutions into the furnace at post-flame locations at temperatures between 850 and 750 °C with intent to determine what PICs may form.

Gas-phase species were measured using real-time Fourier transform infrared (FTIR) spectroscopy, chemical ionization mass spectroscopy (CIMS), and gas chromatography/mass spectroscopy (GC/MS) analysis through the extractive other test method OTM-50.

OTM-50 and FTIR results found that C₁ and C₂ PFAS such as CHF₃, and C₂F₆ were consistently detected as the main PICs suggesting that these PICs may be the last to decompose. OTM-50 also detected the presence of larger perfluoroalkanes and 1H-perfluorocarbons. CIMS results revealed emissions of perfluoro carboxylic acids (PFCAs) from both PFOA and PFOS.

The improved methods for determining the presence and concentration of PICs are intended to enhance our understanding of how temperature affects the mineralization of PFAS. This knowledge will improve the process of thermal treatment facilities and enable more monitoring the presence of PICs.