Bench-scale experiments were performed to assess uptake of poly- and perfluoroalkyl substances (PFAS), both single compounds and mixtures, at the air–water interface. The focus was on evaluating ...uptake at field-relevant PFAS concentrations (<2 × 10–4 mol m–3 or 0.1 mg L–1), assessing the impacts of various PFAS mixtures, and quantifying the impacts of background NaCl concentrations. Both interfacial tension measurements and direct quantification of PFAS mass sorbed at the air–water interface in water films were used to evaluate PFAS interfacial partitioning. Results showed that a Freundlich-based model, rather than a Langmuir-based model, described perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) interfacial uptake. At lower and field-relevant PFOS and PFOA concentrations, the Langmuir-based model underpredicted interfacial uptake by up to several orders of magnitude. The interfacial partition coefficient, k aw, increased as PFAS concentrations decreased. Results also showed that the interfacial tension and interfacial uptake of PFAS mixtures were (within a factor of 2) predicted based on the single solute systems assuming ideal dilute behavior. Furthermore, the addition of NaCl at concentrations of up to 0.01 M increased PFOS uptake by less than a factor of 2 at field-relevant PFOS concentrations. The results presented herein have important implications for PFAS migration in unsaturated soils as well as for remedial technologies that rely on PFAS interfacial sorption, particularly at field-relevant PFAS concentrations.
Bench-scale experiments were performed on natural sediments to assess abiotic dechlorination of trichloroethene (TCE) under both aerobic and anaerobic conditions. In the absence of oxygen (<26 μM), ...TCE dechlorination proceeded via a reductive pathway generating acetylene and/or ethene. Reductive dechlorination rate constants up to 3.1 × 10–5 d–1 were measured, after scaling to in situ solid:water ratios. In the presence of oxygen greater than 120 μM, TCE dechlorination proceeded via an oxidative pathway generating formic/glyoxylic and glycolic/acetic acids, and oxidative dechlorination rate constants (again scaled to in situ conditions) up to 7.4 × 10–3 d–1 were measured. These rates correspond to half-lives of 60 and 0.25 years for abiotic TCE dechlorination under anaerobic and aerobic conditions, respectively, indicating the potentially large impact of aerobic TCE oxidation in the field. For both reductive and oxidative TCE dechlorination pathways, measured first-order rate constants increased with increasing ferrous iron content, suggesting the role of iron oxidation. Hydroxyl radical formation was measured and increased with increasing oxygen and ferrous iron content. Rate constants associated with TCE oxidation products increased with increasing hydroxyl radical generation rates, and were zero in the presence of a hydroxyl radical scavenger, suggesting that oxidative TCE dechlorination is a hydroxyl radical driven process.
•Electrochemical treatment of AFFF-impacted groundwater was demonstrated.•A divided electrochemical cell was used.•PFOS and PFOA removal was greater than that observed in previous studies using MMO ...anodes.•Defluorination was observed for both PFOS and PFOA.•Other long-chain perfluorinated compounds also were treated.
Laboratory experiments were performed to evaluate the use of electrochemical treatment for the decomposition of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), as well as other perfluoroalkyl acids (PFAAs), in aqueous film forming foam (AFFF)-impacted groundwater collected from a former firefighter training area and PFAA-spiked synthetic groundwater. Using a commercially-produced Ti/RuO2 anode in a divided electrochemical cell, PFOA and PFOS decomposition was evaluated as a function of current density (0–20mA/cm2). Decomposition of both PFOA and PFOS increased with increasing current density, although the decomposition of PFOS did not increase as the current density was increased above 2.5mA/cm2. At a current density of 10mA/cm2, the first-order rate constants, normalized for current density and treatment volume, for electrochemical treatment of both PFOA and PFOS were 46×10−5 and 70×10−5 (min−1) (mA/cm2)−1 (L), respectively. Defluorination was confirmed for both PFOA and PFOS, with 58% and 98% recovery as fluoride, respectively (based upon the mass of PFOA and PFOS degraded). Treatment of other PFAAs present in the groundwater also was observed, with shorter chain PFAAs generally being more recalcitrant. Results highlight the potential for electrochemical treatment of PFAAs, particularly PFOA and PFOS, in AFFF-impacted groundwater.
•Perfluoroalkyl acids oxidized by BDD anodes in electrolyte and groundwater matrices.•PFOA removal was faster than PFOS removal.•Direct anodic oxidation mechanism supported by radical scavenger ...experiment results.•Treatment in natural groundwater similar to synthetic electrolyte solutions.•Perchlorate oxidation byproduct treated by downstream biological reduction.
Electrochemical treatment of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) using a nanocrystalline boron-doped diamond (BDD) anode was investigated in a series of bench-scale batch experiments. Experiments focused on assessing the impacts of chloride electrolyte and of hydroxyl radical scavenger tert-butyl alcohol (TBA) on both the rates of PFOA and PFOS removal, and the corresponding rates of defluorination. Treatment of PFOA and PFOS in natural groundwater at concentrations that might be observed in the field (0.3 and 0.6mg/L PFOA and PFOS, respectively) was also evaluated and compared to results obtained in electrolyte solutions with elevated PFOA and PFOS concentrations (15 and 10mg/L, respectively). Results showed that the presence of chloride and TBA had minimal effects (decreasing rates by <20%) on PFOA/PFOS removal and defluorination for the range of applied current densities (3–50mA/cm2), at both the low and elevated PFOA/PFOS concentrations. The latter observation is consistent with direct oxidation of PFOA/PFOS at the electrode surface rather than reaction with electrochemically generated hydroxyl radicals. In addition, treatment rates of PFOA and PFOS in natural groundwater were within a factor of two of those measured in electrolyte at a current density of 15mA/cm2 (for both low and concentration experiments). These findings indicate that hydroxyl radical scavengers that may be present in natural groundwater are unlikely to have a major adverse impact on PFOA and PFOS electrochemical treatment. Finally, it was demonstrated that perchlorate produced by BDD oxidation of Cl− could be biologically treated in bioaugmented sand columns, with a 3 order-of-magnitude removal observed within a 9-day residence time.
Ultraviolet photochemical reaction of sulfite (SO
) photosensitizer generates strongly reducing hydrated electrons (e
; NHE = -2.9 V) that have been shown to effectively degrade individual per- and ...polyfluoroalkyl substances (PFASs), including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). However, treatment of complex PFAS mixtures in aqueous film-forming foam (AFFF) remains largely unknown. Here, UV-sulfite was applied to a diluted AFFF to characterize e
reactions with 15 PFASs identified by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) targeted analysis. Results show that reactivity varies widely among PFASs, but reaction rates observed for individual PFASs in AFFF are similar to rates observed in single-solute experiments. While some structures, including long-chain perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs) were readily degraded, other structures, most notably short-chain PFSAs and fluorotelomer sulfonic acids (FTSs), were more recalcitrant. This finding is consistent with results showing incomplete fluoride ion release (up to 53% of the F content in AFFF) during reactions. Furthermore, results show that selected PFSAs, PFCAs, and FTSs can form as transient intermediates or unreactive end-products via e
reactions with precursor structures in AFFF. These results indicate that while UV-sulfite treatment can be effective for treating PFOS and PFOA to meet health advisory levels, remediation of the wider range of PFASs in AFFF will prove more challenging.
•Polyacrylic AER and short-chain PFCAs and PFECAs favor electrostatic interactions•Polystyrene AER and long-chain PFAS including neutral FASAs combine interactions•AER selectivity for PFAS: PFBA < ...PFHxA < GenX < PFBS < PFOA ≈ PFHxS ≈ FOSA < PFOS•Column studies show better removal of short-chain PFAS using polystyrene/gel AER•Weak-base AER best candidate for aqueous-only regeneration and desorption of PFAS
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A key gap in the literature on the treatment of per- and polyfluoroalkyl substances (PFAS) in impacted water is the absence of a review article dedicated to anion exchange resin (AER) treatment. This gap is important because previous research has consistently shown adsorption by AER to be one of the most effective treatment processes for PFAS removal from impacted water, and AER is one of the most commonly deployed technologies in the field. Given the scope of the previous review articles on PFAS removal by various adsorbent types, the sections on AER do not explore the full depth of PFAS and AER interactions nor cover the breadth of AER testing conditions. Accordingly, the goal of this paper was to critically review the available peer-reviewed literature on PFAS removal from water by AER. The specific objectives of the review were to synthesize the previous literature results on (1) batch adsorption behavior, (2) impact of water chemistry conditions, (3) continuous-flow adsorption, (4) adsorption modeling, (5) regeneration, and (6) weak-base AER. Following from critical review of the literature, the future research priorities discussed include: (i) improving the underlying science that governs PFAS–resin interactions, (ii) improving methods for resin regeneration and management of PFAS-contaminated concentrate streams, and (iii) comparative life cycle environmental and economic analyses for ion exchange treatment systems relative to competing technologies.
•Haloacetic acid, trihalomethane, and perchlorate were measured during disinfection.•No byproduct exceedances above regulatory levels for a 5-log pathogen removal.•Disinfection and byproduct ...formation corresponded to active chlorine generation.•Energy consumption and byproducts were most limited at low current densities.
Laboratory batch experiments were performed at room temperature to evaluate the electrochemical disinfection of surface water using Ti/IrO2 anodes. Disinfection was assessed as a function of applied current density (0–8mA/cm2) and specific charge Q (A-min/L), and active chlorine generation was measured. Generation of disinfection by-products, including haloacetic acids (HAAs), total trihalomethanes (TTHMs), and perchlorate, also was monitored. Results showed that the disinfection rate corresponded to the applied current density. With respect to the applied Q, the highest current density (8mA/cm2) showed the greatest rate of disinfection and highest rate of active chlorine generation. While no perchlorate generation was observed, HAAs and TTHMs were generated at a rate of 7.7 and 5.6μgA−1min−1, respectively. However, regulatory exceedances were not observed until greater than a 5-log decrease in bacteria was observed. HAA and TTHM formation, as well as energy consumption, associated with the highest current density were greater than the lower current densities for a given level of disinfection. Overall, this study demonstrates that effective disinfection without regulatory exceedances in TTHMs, HAAs, or perchlorate can be attained using a Ti/IrO2 anode for treatment of surface water.
Per- and polyfluoroalkyl substances (PFASs) are a heterogeneous group of persistent organic pollutants that have been detected in various environmental compartments around the globe. Emerging ...research has revealed the preferential accumulation of PFASs in shallow soil horizons, particularly at sites impacted by firefighting activities, agricultural applications, and atmospheric deposition. Once in the vadose zone, PFASs can sorb to soil, accumulate at interfaces, become volatilized, be taken up in biota, or leach to the underlying aquifer. At the same time, polyfluorinated precursor species may transform into highly recalcitrant perfluoroalkyl acids, changing their chemical identity and thus transport behavior along the way. In this review, we critically discuss the current state of the knowledge and aim to interconnect the complex processes that control the fate and transport of PFASs in the vadose zone. Furthermore, we identify key challenges and future research needs. Consequently, this review may serve as an interdisciplinary guide for the risk assessment and management of PFAS-contaminated sites.
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•The vadose zone is a critical compartment at many PFAS-contaminated sites.•PFAS sources, distribution and speciation in the vadose zone are discussed.•Processes such as sorption, biotransformation, and plant uptake are covered.•The interrelations of the processes controlling PFAS fate and transport are revealed.•Current knowledge gaps, key challenges, and research needs are identified.
Bench-scale column experiments were performed to evaluate the applicability of employing rapid small-scale column tests (RSSCTs) for the removal of perfluoroalkyl acids (PFAAs) from groundwater, ...using ground and unground anion exchange resins (AERs). Specifically, experiments were designed to assess the applicability of scaling the overall rate of PFAA uptake to the AERs by r –2, where r is the AER particle radius. Two commercially available AERs were examined. Such scaling is generally assumed to be appropriate if uptake is controlled by intraparticle diffusion with a constant diffusion coefficient. Results showed that, for each AER tested, short-chained PFAAs migrated through the columns more rapidly than the long-chained PFAAs. Also, for a given perfluorinated chain length, the perfluorinated carboxylates migrated through the AERs more rapidly than the corresponding perfluorinated sulfonates. PFAA elution through the AERs was well-described by the Thomas model, which assumes rate-limited uptake and Langmuir-type sorption. Results also showed that appropriate scaling (r –2) was valid as long as PFAA adsorption to (or near) the AER particle surface was taken into account by scaling the equilibrium sorption capacity to r –0.5. Including these scaling factors resulted in excellent agreement between the ground and unground AER results. These results suggest that the RSSCT approach to expedite bench-scale testing can be applied for PFAA uptake onto AERs, although the impacts of various groundwater geochemical conditions and the presence of a broader range of polyfluoroalkyl and perfluoroalkyl substances on the appropriateness of the RSSCT approach remains unknown.
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