Electrochemical Oxidation for Treatment of PFAS in Contaminated Water and Fractionated Foam─A Pilot-Scale Study

Abstract

Per-and polyfluoroalkyl substances (PFAS) are persistent synthetic contaminants that are present globally in water and are exceptionally difficult to remove during conventional water treatment processes. Here, we demonstrate a practical treatment train that combines foam fractionation to concentrate PFAS from groundwater and landfill leachate, followed by an electrochemical oxidation (EO) step to degrade the PFAS. The study combined an up-scaled experimental approach with thorough characterization strategies, including target analysis, PFAS sum parameters, and toxicity testing. Additionally, the EO kinetics were successfully reproduced by a newly developed coupled numerical model. The mean total PFAS degradation over the designed treatment train reached 50%, with long-and short-chain PFAS degrading up to 86 and 31%, respectively. The treatment resulted in a decrease in the toxic potency of the water, as assessed by transthyretin binding and bacterial bioluminescence bioassays. Moreover, the extractable organofluorine concentration of the water decreased by up to 44%. Together, these findings provide an improved understanding of a promising and practical approach for on-site remediation of PFAS-contaminated water.

Hydrothermal Alkaline Treatment (HALT) of Foam Fractionation Concentrate Derived from PFAS-Contaminated Groundwater

“…The concentrations of inorganic anions generally reflect values in the source water (Table S6) since their properties do not lend themselves to accumulation during the FF process. 16 Similar to PFASs and DOC, concentrations of cations in FC2 were much higher than those in FC1 and diluted AFFF and were elevated significantly relative to the source groundwater (e.g., calcium 272 mg/L in FC2 compared to 29.1 mg/L in the source groundwater). The accumulation of cations in the foam is consistent with the need to maintain charge neutrality in the foam concentrate containing large quantities of PFASs and surface-active DOM that are predominantly anionic in nature.…”

“…The diluted AFFF had much lower inorganic anions (individual <1 mg/L) due to the fact that it was not derived from groundwater. The concentrations of inorganic anions generally reflect values in the source water (Table S6) since their properties do not lend themselves to accumulation during the FF process . Similar to PFASs and DOC, concentrations of cations in FC2 were much higher than those in FC1 and diluted AFFF and were elevated significantly relative to the source groundwater (e.g., calcium 272 mg/L in FC2 compared to 29.1 mg/L in the source groundwater).…”

“…13 To the best of our knowledge, however, there are no reports of near-complete destruction of PFASs in FF-derived concentrates. Smith and co-workers 16 recently reported that electrochemical oxidation (EO) degraded 65% of PFASs in a leachate-derived foam concentrate (total PFASs < 20 μg/L), but degradation of the more recalcitrant perfluoroalkyl sulfonic acids (PFSAs) was insignificant (e.g., no degradation after 540 min of treatment for certain PFSAs). Moreover, destructive treatment technologies that rely on surface or interfacial reactions (e.g., electrochemical and photocatalytic) are expected to be of limited utility when treating such highly concentrated matrices due to inherent mass transfer limitations.…”

“…Moreover, destructive treatment technologies that rely on surface or interfacial reactions (e.g., electrochemical and photocatalytic) are expected to be of limited utility when treating such highly concentrated matrices due to inherent mass transfer limitations. However, plasma treatment was shown to be effective for treating still bottom samples containing PFAS concentrations at ∼100 mg/L (long-chain perfluoroalkyl acids (PFAAs) were decreased by >99.9% in 2 h). ,− Compounding the challenges of treating PFAS concentrates, FF processes will also accumulate other surface-active components in the sourcewater, including hydrocarbon surfactants and hydrophobic fractions of DOM, substances that can also inhibit PFAS destructive treatment processes by competing for available reactive species (e.g., catalyst active sites, oxidizing or reducing radicals) . Thus, identifying effective methods for the destruction of complex PFAS mixtures in FF-derived concentrates remains critical to the widespread deployment of FF technologies for PFAS remediation.…”

“…While several treatment technologies have been developed to remove PFASs from contaminated water, − foam fractionation (FF) technology has emerged as a viable strategy for remediation. − FF applies fine gas bubbles to remove molecules with surfactant properties that accumulate at gas–liquid interfaces . FF, also called protein skimming, has been increasingly employed in recirculating aquaculture systems and other water treatment processes to remove particles, colloids, and dissolved substances. ,− Foaming with air or nitrogen produces microbubbles (ca.…”