Groundwater impacted by aqueous film-forming foams is often encountered with high concentrations of per- and polyfluoroalkyl substances (PFASs) such as 6:2 fluorotelomer sulfonate (6:2 FTS), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS). Sulfate radicals generated by UV or heat-activated persulfate have been reported to degrade PFOA with shorter chain perfluorocarboxylic acids as intermediates and fluoride and carbon dioxide as the end products. But the low pH required for efficient transformation limits the application of persulfate as an in situ chemical oxidation agent in PFAS-contaminated groundwater. In this study, we assessed the transformation potential of sulfate radicals generated from activated peroxymonosulfate (PMS) towards FTS, PFOA, and PFOS. PMS can generate sulfate radicals in the presence of transition metals; among them, Co(II) is considered to be the most effective and can activate PMS at neutral pH and room temperature. Thus PMS is a more feasible oxidant for in situ removal of PFAS from groundwater. We found that Co(II)-activated PMS (5 mM) completely transformed 5 µM FTS at pH 2.1 within 4 hours and 80% of the FTS at pH 6.5 in 1 hour under room temperature. PFOA can be transformed at higher PMS concentrations (100 mM). The reaction conditions were further optimized with respect to temperature, pH, and ratio of PMS/Co(II) for different PFASs. The transformation products, reaction pathways and mechanisms, and defluorination efficiency were determined and compared with those of heat-activated persulfate. We also tested the influence on reactivity from groundwater ions, natural organic matter, and the presence of sediment. In addition, other transition metals that could potentially activate PMS were also tested especially Fe(II) on their reactivity towards the target PFASs.

Degradation of per- and polyfluoroalkyl substances (PFASs) by sulfate radicals generated from activation of peroxymonosulfate

256th National Meeting (2018)

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