Granular activated carbon (GAC) adsorption is the most
common technology
applied to treat water contaminated with per- and polyfluoroalkyl
substances (PFASs), but rapid exhaustion of the media necessitates
frequent replacement and costly off-site thermal regeneration. Here,
we extend the application of hydrothermal alkaline treatment (HALT),
which uses strong alkali and near-critical temperatures and pressures
(e.g., 350 °C, 16.5 MPa, and 1 M NaOH) to degrade and mineralize
PFASs, to the regeneration of spent GAC. Mass balance experiments
wherein a known mass of perfluorooctanesulfonate (PFOS) was adsorbed
onto GAC prior to treatment showed that HALT achieved >99% destruction
of PFOS and 96 ± 4% defluorination with no observed fluoro-organic
intermediates [167 g L–1 GAC, 350 °C, 1 M NaOH, t
rxn = 400 min, and 10–15 mg of PFOS (g
of GAC)−1]. Treatment of GAC collected from a field
pilot study also showed effective destruction of the range of adsorbed
PFASs. Moreover, repeated HALT cycles did not significantly affect
the GAC specific surface area, and similar adsorption isotherms for
perfluoropentanoic acid and PFOS were recorded for virgin and HALT-treated
GAC. These findings suggest a promising strategy for on-site regeneration
of PFAS-contaminated GAC and other adsorbent media that may be an
alternative to off-site thermal regeneration practices.
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