Per- and polyfluoroalkyl substances (PFAS) are chemical compounds that have been used in numerous industries, commercial applications, and extensively in aqueous film-forming foams (AFFF) for fire-fighting activities. They are environmentally persistent compounds and reported to cause adverse effects on human health. According to the USEPA, currently available industrial formulations of AFFF should be free from long-chain perfluoroalkyl acids (PFAAs) which are the most commonly found PFAS in the environment and reported to be the most problematic. This study characterized four industrially formulated and currently used AFFF samples to determine if they could be treated to remove PFAAs. PFAS precursors were pre-oxidized using various advanced oxidation processes (AOPs) (heat-activated persulfate, UV-activated persulfate, ozone, UV-ozone, peroxone and UV-peroxone) and then subjected to plasma treatment. Plasma is a mixture of highly reactive species generated from electrical discharge. PFAA degradation readily occurs during plasma treatment; therefore, by using AOPs prior to plasma treatment can oxidize PFAS precursors to PFAAs, and therefore, lifecycle costs and treatment times can be reduced. Preliminary measurements of 15 PFAAs and 10 precursors with an LC-MS/MS found high concentrations of short-chained PFAAs (30 to 3000 µg/L), traces of long-chain PFAAs (40 to 60 µg/L), and a significant amount of PFAS precursors (70 to 50000 µg/L). The AFFF samples also contained high concentrations of total oxidizable precursors (TOP) in the range of 1500 to 10000 mg/L, indicating the presence of unknown PFAS precursors at high concentrations. The TOP assay (involving heat-activated persulfate oxidation) was only partially effective at oxidizing the precursors, hence the existing TOP assay was modified by optimizing persulfate dose, sodium hydroxide concentration and dilution factors for complete oxidation of precursors to PFAAs. With optimized conditions, it was found that the concentrations of short-chain PFAAs increased by 2-3 orders of magnitude with the appearance of some long-chain PFAAs. This optimized TOP method was implemented as the pre-oxidation treatment prior to plasma treatment for complete removal of PFAS from AFFF. Among the different pre-oxidation options, plasma and plasma-persulfate followed by UV-persulfate were the most effective processes for the precursor’s oxidation.

Current use C6 aqueous film-forming foams (AFFF) containing per- and polyfluoroalkyl substances: Characterization and treatment options

ACS Spring Meeting 2021

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