Assessing Continued Electrochemical Treatment of Groundwater Impacted by Aqueous Film-Forming Foams.
By Charles E. Schaefer; Christina Andaya; Andrew Maizel; and Christopher P. Higgins
Jour. of Envir. Eng.
October 1, 2019
Although electrochemical treatment has received increased attention with respect to treating poly- and perfluoroalkyl substances (PFAS), studies assessing treatment longevity for the wide range of PFAS present in water impacted by aqueous film-forming foam (AFFF) are lacking. A 21-day study was performed in which electrochemical treatment using boron-doped diamond (BDD) anodes was performed in successive 24-h batch cycles on groundwater impacted with AFFF. Results showed substantial defluorination of both the perfluoroalkyl acids (PFAAs) and defluorination of polyfluoroalkyl compounds (based on fluoride generation). Substantial perchlorate generation was observed throughout the study. PFAS treatment effectiveness diminished over time due to scaling, resulting in decreased removal of the PFAAs and generation of perfluorobutanoic acid (PFBA). Based on measured generation of fluoride relative to the concentrations of the PFAAs, defluorination of the polyfluoroalkyl acids decreased 2–3 times more than the PFAAs due to this scaling. This suggests that defluorination of the polyfluoroalkyl acids occurred via a mechanism different from that of the PFAAs. Acid cleaning to remove the accumulated scale resulted in restoration of PFAS treatment. Together, these results suggest that electrochemical treatment of AFFF-impacted waters shows promise. Polyfluorinated compounds and PFBA showed greater adverse impacts from the mass transfer and/or residence time decreases associated with the scaling than what was observed for the other PFAAs. This implies that these compounds may prove to be the greater challenge in long-term full-scale applications.
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