In continuation to our previous studies and to get a better understanding of PFAS decomposition, we studied five perfluoroalkyl carboxylic acids (PFCAs), and one perfluoroalkyl ether carboxylic acid (PFECA) in three different conditions (only PFAS (T1), PFAS with GAC (T2) and PFAS pre-adsorbed on GAC (T3)) in a closed system. We found that the destabilization of studied compounds during thermal treatment in general followed first-order kinetics. The temperature needed for thermally destabilizing PFCAs increased with the number of perfluorinated carbons (nCF2) when PFAS were adsorbed on to GAC. Decomposition of PFCAs such as perfluorooctanoic acid (PFOA) on GAC initiated at temperatures as low as 200 °C. The PFECA was even more readily decomposed than PFCA with the same nCF2. The presence of GAC has accelerated PFAS degradation at low and moderate temperatures (&lt;400 °C). In addition to the volatile organofluorine species identified in previous studies we noticed the formation and then decomposition of short-chain compounds during thermal degradation of four PFCAs. Efficient mineralization to fluoride ions (&gt;80%) of PFOA and PFOS on GAC occurred at 700 °C or higher, accompanied by near complete PFOA and PFOS decomposition (&gt;99.9%). A few possible thermal decomposition pathways of PFOA were proposed. Based on the data, GAC reactivation is a practical, sustainable and effective approach to treat PFAS without needing to incineration or landfilling the spent media. Organofluorine and short-chain compounds generated from thermal decomposition of PFAS at low to moderate temperatures (≤600 °C) warrant studies on the exposure to these compounds during cooking, baking, firefighting, and other relevant thermal processes involving PFAS.

Thermal degradation of poly- and perfluoroalkyl substances (PFAS)

ACS Spring Meeting 2021

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