Removal Of Perfluorooctane Sulfonate Research Articles

Enhanced foam fractionation of perfluorooctane sulfonate (PFOS) from water using amphiphilic Janus SiO2 nanoparticles

Perfluorooctane sulfonate (PFOS), a persistent environmental contaminant, presents significant risks to human health and ecological balance. In response, our research introduces an innovative approach to tackle this challenge through the development of an efficient nanoparticle surfactant that enhances PFOS removal via foam fractionation. We synthesized a novel amphiphilic Janus nanoparticle (F-SNP-NH2) by chemically modifying SiO2 nanoparticles with 1H,1H,2H,2H-perfluorooctyltrimethoxysilane and aminopropyltriethoxysilane, employing an interface masking strategy. This unique particle, bearing hydrophobic fluorocarbon chains and hydrophilic amino groups, offers surface properties conducive to foam fractionation. We verified the structure and chemical composition of F-SNP-NH2 through SEM-EDX, FTIR, and XPS. Its high surface activity enabled effective adsorption at the air–water interface, thereby promoting foam stability. Correspondingly, the foam height and half-life reached 24.5 mm and 316 s, respectively. Significantly, F-SNP-NH2 reached PFOS adsorption equilibrium in a short duration of 40 min, achieving a maximum adsorption capacity of 1015.04 mg/g. Our analysis, supported by experimental data, theoretical models, and DFT calculations, pinpointed F–F and hydrophobic interactions as the primary forces driving PFOS collection. Under suitable conditions for foam fractionation, specifically at pH 5.0 and air flowrate 700 mL/min, the removal efficiency of PFOS achieved a high range of 98.8 % to 99.2 %, with corresponding enrichment ratios varying from 23.6 to 24.9. The foam fractionation process, employing F-SNP-NH2, demonstrated high selectivity and efficiency for PFOS removal, showcased the reusability of the nanoparticle surfactant. These results highlight the potential of F-SNP-NH2 in advancing foam fractionation technology for the targeted removal of PFOS and other per- and polyfluoroalkyl substances.

Mobilization of per- and poly-fluoroalkyl substances (PFAS) in soils with different organic matter contents

There is considerable interest in addressing soils contaminated with per- and polyfluoroalkyl substances (PFAS) because of the PFAS in the environment and associated health risks. The neutralization of PFAS in situ is challenging. Consequently, mobilizing the PFAS from the contaminated soils into an aqueous solution for subsequent handling has been pursued. Nonetheless, the efficiency of mobilization methods for removing PFAS can vary depending on site-specific factors, including the types and concentrations of PFAS compounds, soil characteristics. In the present study, the removal of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) from artificially contaminated soils was investigated in a 2D laboratory setup using electrokinetic (EK) remediation and hydraulic flushing by applying a hydraulic gradient (HG) for a duration of 15 days. The percent removal of PFOA by EK was consistent (∼80%) after a 15-day treatment for all soils. The removal efficiency of PFOS by EK significantly varied with the OM content, where the PFOS removal increased from 14% at 5% OM to 60% at 50% OM. With HG, the percent removal increased for both PFOA and PFOS from about 20% at 5% OM up to 80% at 75% OM. Based on the results, the mobilization of PFAS from organic soil would be appropriate using both hydraulic flushing and EK considering their applicability and advantages over each other for site-specific factors and requirements.

Investigating the degradation potential of microbial consortia for perfluorooctane sulfonate through a functional "top-down" screening approach.

Perfluorooctane sulfonate (PFOS) is a prominent perfluorinated compound commonly found in the environment, known to pose various risks to human health. However, the removal of PFOS presents significant challenges, primarily due to the limited discovery of bacteria capable of effectively degrading PFOS. Moreover, single degradation bacteria often encounter obstacles in individual cultivation and the breakdown of complex pollutants. In contrast, microbial consortia have shown promise in pollutant degradation. This study employed a continuous enrichment method, combined with multiple co-metabolic substrates, to investigate a microbial consortium with the potential for PFOS degradation. By employing this methodology, we effectively identified a microbial consortium that demonstrated the capacity to reduce PFOS when exposed to an optimal concentration of methanol. The consortium predominantly comprised of Hyphomicrobium species (46.7%) along with unclassified microorganisms (53.0%). Over a duration of 20 days, the PFOS concentration exhibited a notable decrease of 56.7% in comparison to the initial level, while considering the exclusion of adsorption effects. Furthermore, by comparing the predicted metabolic pathways of the microbial consortium with the genome of a known chloromethane-degrading bacterium, Hyphomicrobium sp. MC1, using the KEGG database, we observed distinct variations in the metabolic pathways, suggesting the potential role of the unclassified microorganisms. These findings underscore the potential effectiveness of a "top-down" functional microbial screening approach in the degradation of stubborn pollutants.

Anaerobic biodegradation of perfluorooctane sulfonate (PFOS) and microbial community composition in soil amended with a dechlorinating culture and chlorinated solvents

Perfluorooctane sulfonate (PFOS), one of the most frequently detected per- and polyfluoroalkyl substances (PFAS) occurring in soil, surface water, and groundwater near sites contaminated with aqueous film-forming foam (AFFF), has proven to be recalcitrant to many destructive remedies, including chemical oxidation. We investigated the potential to utilize microbially mediated reduction (bioreduction) to degrade PFOS and other PFAS through addition of a known dehalogenating culture, WBC-2, to soil obtained from an AFFF-contaminated site. A substantial decrease in total mass of PFOS (soil and water) was observed in microcosms amended with WBC-2 and chlorinated volatile organic compound (cVOC) co-contaminants — 46.4 ± 11.0 % removal of PFOS over the 45-day experiment. In contrast, perfluorooctanoate (PFOA) and 6:2 fluorotelomer sulfonate (6:2 FTS) concentrations did not decrease in the same microcosms. The low or non-detectable concentrations of potential metabolites in full PFAS analyses, including after application of the total oxidizable precursor assay, indicated that defluorination occurred to non-fluorinated compounds or ultrashort-chain PFAS. Nevertheless, additional research on the metabolites and degradation pathways is needed. Population abundances of known dehalorespirers did not change with PFOS removal during the experiment, making their association with PFOS removal unclear. An increased abundance of sulfate reducers in the genus Desulfosporosinus (Firmicutes) and Sulfurospirillum (Campilobacterota) was observed with PFOS removal, most likely linked to initiation of biodegradation by desulfonation. These results have important implications for development of in situ bioremediation methods for PFAS and advancing knowledge of natural attenuation processes.

Comparison of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS) removal in a combined adsorption and electrochemical oxidation process

This study focused on three of the most studied PFAS molecules, namely perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorobutane sulfonate (PFBS). They were compared in terms of their adsorption capacity onto graphite intercalated compound (GIC), a low surface area, highly conductive and cheap adsorbent. The adsorption on GIC followed a pseudo second order kinetics and the maximum adsorption capacity using Langmuir was 53.9 μg/g for PFOS, 22.3 μg/g for PFOA and 0.985 μg/g for PFBS due to electrostatic attraction and hydrophobic interactions. GIC was added into an electrochemical oxidation reactor and >100 μg/L PFOS was found to be fully degraded (<10 ng/L) leaving degradation by-products such as PFHpS, PFHxS, PFPeS, PFBS, PFOA, PFHxA and PFBA below 100 ng/L after 5 cycles of adsorption onto GIC for 20 min followed by regeneration at 28 mA/cm2 for 10 min. PFBS was completely removed due to degradation by aqueous electrons on GIC flakes. Up to 98 % PFOA was removed by the process after 3 cycles of adsorption onto GIC for 20 min followed by regeneration at 25 mA/cm2 for 10 min. When PFBS was spiked individually, only 17 % was removed due to poor adsorption on GIC. There was a drop of 3–40 % by treating PFOS, PFOA and smaller sulfonates in a real water matrix under the same electrochemical conditions (20 mA/cm2), but PFOS and PFOA removal percentage were 95 and 68 % after 20 min at 20 mA/cm2.

Removal of per- and polyfluoroalkyl substances from wastewater via aerosol capture

The widespread use of per- and polyfluoroalkyl substances (PFAS)-containing products in numerous commercial and industrial applications has resulted in their occurrence in wastewater treatment plants (WWTPs). Herein, proof-of-concept bench-scale experiments were performed to measure the extent to which PFAS could be removed from a WWTP if aerosols generated during aeration were captured. Experiments were designed to mimic the aeration rate:water volume ratio, the water volume:surface area ratio, and aeration bubble size applicable to the full-scale aeration vessel. Results showed that substantial (75%) removal of perfluorooctane sulfonate (PFOS) was observed under these operating conditions in the bench-scale system; up to 97% PFOS removal was observed if the aeration rate was increased 3-fold. PFAS removal generally increased with increasing aerosol capture and with increasing PFAS surface activity. Analysis of semi-quantified PFAS showed that the semi-quantified PFAS accounted for approximately 93% of the identified PFAS in the raw wastewater, dominated largely by the presence of 2:2 fluorotelomer carboxylic acid (2:2 FTCA). This preliminary study suggests that aerosol capture in aeration basins has potential for mitigating PFAS in WWTPs. Further testing is needed to assess the feasibility of this approach at the field scale.

Combination of separation and degradation methods after PFAS soil washing

The current study evaluated a three-stage treatment to remediate PFAS-contaminated soil. The treatment consisted of soil washing, foam fractionation (FF), and electrochemical oxidation (EO). The possibility of replacing the third stage, i.e., EO, with an adsorption process was also assessed. The contamination in the studied soils was dominated by perfluorooctane sulfonate (PFOS), with a concentration of 760 and 19 μg kg−1 in soil I and in soil II, accounting for 97 % and 70 % of all detected per-and polyfluoroalkyl substances (PFAS). Before applying a pilot treatment of soil, soil washing was performed on a laboratory scale, to evaluate the effect of soil particle size, initial pH and a liquid-to-soil ratio (L/S) on the leachability of PFAS. A pilot washing system generated soil leachate that was subsequently treated using FF and EO (or adsorption) and then reused for soil washing. The results indicated that the leaching of PFAS occurred easier in 0.063–1 mm particles than in the soil particles having a size below 0.063 mm. Both alkaline conditions and a continual replacement of the leaching solution increased the leachability of PFAS. The analysis using one-way ANOVA showed no statistical difference in means of PFOS washed out in laboratory and pilot scales. This allowed estimating twenty washing cycles using 120 L water to reach 95 % PFOS removal in 60 kg soil. The aeration process removed 95–99 % PFOS in every washing cycle. The EO and adsorption processes achieved similar results removing up to 97 % PFOS in concentrated soil leachate. The current study demonstrated a multi-stage treatment as an effective and cost-efficient method to permanently clean up PFAS-contaminated soil.

Electrochemical oxidation of perfluorooctanesulfonate (PFOS) from simulated soil leachate and landfill leachate concentrate

The near-widespread presence of poly- and perfluoroalkyl substances (PFASs) in humans has generated concerns regarding the potential negative impact of these chemicals on human health, as some PFASs are exceedingly persistent and bioaccumulative. Among the perfluorinated PFASs, which exhibit high polarity and strong carbon–fluorine bonds, perfluorooctanesulfonate (PFOS) is one of the frequently encountered species. In this study, the efficiency of electrooxidation (EO) and its application in groundwater simulation were first evaluated as a realistic approach to PFOS removal. After optimizing EO parameters including the solution pH, current density, and the effects of inlet concentration and the anode material, 83 % total organic carbon (TOC) removal was obtained. In groundwater experiments, in which the infiltration of PFOS from soil layers into groundwater was simulated, 79 % TOC removal efficiency was achieved in the more complex groundwater; moreover, an F− ion concentration of 8.78 mg/L was obtained from the decomposition of PFOS. To increase the realism of the simulation, the leachate process was repeated four times, and the EO process was applied to each sequential leachate. In addition, the process efficiency was studied in real landfill leachate wastewater to which PFOS had been added. Despite the challenging wastewater composition, 84 % TOC removal efficiency was achieved. Together, these results indicate that BDD-anodic oxidation may be a practical method to treat PFOS-contaminated groundwater and wastewater.

Important properties of anion exchange resins for efficient removal of PFOS and PFOA from groundwater

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) present in various water sources have raised a serious concern on their health risk worldwide. Anion exchange is known to be one of the effective treatment methods but the resin properties suitable for theses contaminants have not been fully understood. We examined four commercially available anion exchange resins with different properties (DIAION™ PA312, HPA25M, UBA120, and WA30) and one polymer-based adsorbent (HP20), for their PFOA and PFOS removal in the batch experiment. All or a part of the selected resins were further characterized for their functional group, surface morphology and pore size distribution. The 72 h batch experiment with the 100 mg/L PFOA or PFOS in the laboratory pure water matrix showed a superior capacity of the strong base anion exchange resins, the porous-type HPA25M and PA312, and the gel-type UBA120, for PFOA removal (92.6–97.9%). Among those resins, the high porous HPA25M was suggested most effective due to its remarkably high reaction rate and effectiveness to PFOS (99.9%). In the groundwater matrix, however, the performance of the those anion exchange resins was generally suppressed, causing up to 71% decrease in their removal rates. The least matrix impact was observed for PFOS removal by HPA25M, which indicated the resin's high selectivity to the contaminant. The physiochemical analysis indicated that the presence of relatively large pores (1 nm–10 nm) over HPA25M played an important role in the PFAS removal.

Mechanistic understanding of perfluorooctane sulfonate (PFOS) sorption by biochars

Biochar has recently emerged as a cost-effective solution to combat per- and polyfluoroalkyl substances (PFAS) pollution in water, but mechanistic understanding of which physicochemical properties of biochars dictate PFAS sorptive removal from water remains elusive. Herein, 15 biochars were pyrolyzed from five feedstocks (corn, Douglas fir, eucalyptus, poplar, and switchgrass) at three pyrolysis temperatures (500, 700, and 900 °C) to investigate their removal efficiencies and mechanisms of perfluorooctane sulfonate (PFOS) from water. A commercial biochar was also included for comparison. Biochar physiochemical properties, including elemental composition, pH, specific surface area (SSA), pore structure, hydrophobicity, surface charge, surface functional groups, and crystalline structure were systematically characterized. Batch sorption data showed that the Douglas fir 900 biochar (Douglas fir and 900 are the feedstock type and pyrolysis temperature, respectively; this naming rule applies to other biochars), poplar 900 biochar, and commercial biochar can remove over 95% of PFOS from water. Structural equation model (SEM) was used to elucidate which biochar properties affect PFOS sorption. Interestingly, biochar pore diameter was identified as the most critical factor controlling PFOS removal, but pore diameter/pore volume ratio, SSA, pyrolysis temperature, hydrophobicity, and elemental composition all played variable roles. Hypothetically, biochars with small pore diameters and large pore volumes had a narrow yet deep pore structure that traps PFOS molecules inside once already sorbed, resulting in an enhanced PFOS sorption. Biochars with small pore diameter, low nitrogen content, and high pyrolysis temperature were also favorable for enhanced PFOS sorption. Our findings advance the knowledge of using biochars with optimized properties to remove PFOS and possibly other similar PFAS compounds from water.

Synthesis and characterization of PCN-222 metal organic framework and its application for removing perfluorooctane sulfonate from water

Poly- and perfluoro alkyl substances (PFAS) are a group of man-made, notoriously persistent, and highly toxic contaminants in the environment reported worldwide. Many adsorbents including granular activated carbon, graphene, biochar, zeolites, and clay minerals have been tested for PFAS removal from water, but most of these materials suffer from high cost and/or poor removal performance. Here, we synthesized, characterized, and examined the efficiency of PCN-222(Fe), a new porous metal organic framework (MOF) with high water stability, for adsorptive removal of a frequently occurring PFAS, perfluorooctane sulfonate (PFOS), from water. The adsorption isotherm and kinetic studies revealed high PFOS adsorption capacity of PCN-222 (2257 mg/g), with rapid PFOS removal rate (within 30 min). The structure of PCN-222 was unaffected in water in the pH range of 2–10 but disintegrated and lost its PFOS removal ability at pH > 10. The PFOS adsorption on PCN-222 was an endothermic reaction. Electrostatic attraction was a dominant mechanism for PFOS adsorption at < 1694 mg/g PFOS concentration, while hydrophobic interaction accompanied with hydrogen-bonding was responsible at ≥ 1694 mg/g PFOS concentration. The interlayer morphology of PCN-222 did not change due to increasing PFOS loading. The findings of this study demonstrated superior features of PCN-222 over other conventional adsorbents for its potential application in removing PFOS from contaminated water to reduce PFOS transfer from water to living organisms.

Efficient Recognition and Removal of Persistent Organic Pollutants by a Bifunctional Molecular Material.

Persistent organic pollutants (POPs) exist widely in the environment and place significant impact on human health by bioaccumulation. Efficient recognition of POPs and their removal are highly challenging tasks because their specific structures interact often very weakly with the capture materials. Herein, a molecular nanocage (1) is studied as an efficient sensing and sorbent material for POPs, which is demonstrated by a representative and stable perfluorooctane sulfonate (PFOS) substrate containing a hydrophilic sulfonic group and a hydrophobic fluoroalkyl chain. A highly sensitive and unusual turn-on fluorescence response within 10 s and a 97% total removal of PFOS from water in 20 min have been achieved owing to the strong host-guest interactions between 1 and PFOS. The binding constant of 1 to PFOS is 2 orders of magnitude higher than state-of-the-art adsorbents for PFOS and thus represents a new benchmark material for the recognition and removal of PFOS. The host-guest interaction has been elucidated by solid-state NMR spectroscopy and single-crystal X-ray diffraction, which provide key insights at a molecular level for the design of new advanced sensing/sorbent materials for POPs.

Efficient decomposition of perfluorooctane sulfonate by electrochemical activation of peroxymonosulfate in aqueous solution: Efficacy, reaction mechanism, active sites, and application potential

The electrochemical oxidation method is a promising technology for the degradation of perfluorooctane sulfonate (PFOS). However, the elimination processes of PFOS are still unknown, including the electron transfer pathway, key reactive sites, and degradation mechanism. Here, we fabricated diatomite and cerium (Ce) co-modified Sb2O3 (D-Ce/Sb2O3) anode to realize efficient degradation of PFOS via peroxymonosulfate (PMS) activation. The transferred electron and the generated hydroxyl radical (•OH) can high-effectively decompose PFOS. The electron can be rapidly transferred from the highest occupied molecular orbital of the PFOS to the lowest unoccupied molecular orbital of the PMS via the D-Ce/Sb2O3 driven by a potential energy difference under electrochemical process. The active site of Ce-O in the D-Ce/Sb2O3 can greatly reduce the migration distance of the electron and the •OH, and thus improving the catalytic activity for degrading various organic micropollutants with high stability. In addition, the electrochemical process shows strong resistance and tolerance to the changing pH, inorganic ions, and organic matter. This study offers insights into the electron transfer pathway and PMS activation mechanism in PFOS removal via electrochemical oxidation, paving the way for its potential application in water purification.

Novel MOF-808 metal–organic framework as highly efficient adsorbent of perfluorooctane sulfonate in water

Perfluorooctane sulfonate (PFOS) is a highly persistent contaminant of emerging concern causing harmful effects to human and ecosystem health. In this study, a novel MOF-808 metal–organic framework (MOF) was prepared and evaluated for adsorptive removal of PFOS from aqueous solution. The MOF-808 had high specific surface area (SSA; 1610 m2/g) and was structurally stable in aqueous medium for 7 days under different pH conditions. The MOF-808 reached PFOS adsorption equilibrium within 30 min (at 500 mg/L initial PFOS) and attained the maximum adsorption capacity of 939 mg/g at pH 4.1 – 5.4 (with 50 – 500 mg/L initial PFOS). The PFOS adsorption capacity of MOF-808 was unaffected at pH 2 to 7, but gradually decreased at pH > 7. High SSA, favorable pore size and abundant active adsorption sites on MOF-808 triggered high PFOS adsorption onto the adsorbent. The PFOS adsorption process was endothermic and spontaneous in nature. Electrostatic interaction between the cationic central cluster ([Zr6O4(OH)4]12+) of MOF-808 and PFOS anion was identified as the key mechanism of PFOS adsorption onto MOF-808, as evident from the infrared spectroscopic investigation of the adsorbent. This study suggests that MOF-808 can be considered as a highly efficient adsorbent for PFOS removal from water and warrants future research to evaluate the application and performance of the material under wastewater conditions.

Electrochemical oxidation combined with UV irradiation for synergistic removal of perfluorooctane sulfonate (PFOS) in water

The effect of electrochemical degradation on Magnéli phase Ti4O7 anode combined with UV irradiation on the removal of PFOS was systematically evaluated in the present study. A synergistic effect of electrolysis and UV irradiation rather than a simple additive effect for PFOS degradation was demonstrated experimentally and theoretically. The short wavelength irradiation within 400 nm is the main contribution to enhance the electrochemical degradation of PFOS, while the initial pH of the solution has little effect on the PFOS degradation. The increase of current density accelerates the removal of PFOS either by electrolysis treatment or the joint process. The time-dependent density functional theory (TD-DFT) calculation indicates that the synergistic effect of the electrolysis and UV irradiation is most likely due to the involvement of the excited PFOS induced under UV irradiation in the electrochemical reaction. This study provides the first mechanistic explanation for the electrochemical degradation of PFOS enhanced by UV irradiation.

Performance testing of mesh anodes for in situ electrochemical oxidation of PFAS

Groundwater remediation technologies that can destroy per- and polyfluoroalkyl substances (PFAS) in situ are in high demand. To address this need, using flow-through electrochemical reactors we compared the performance of three mesh electrode materials that may be implemented in the subsurface as permeable reactive barriers. A Magnéli-phase titanium suboxides TinO2n-1 anode achieved higher perfluorooctane sulfonate (PFOS) oxidation rates and lower energy consumption than boron-doped ultrananocrystalline diamond and IrO2-Ta2O5 mixed metal oxides, and was thus selected for more detailed testing regarding the impacts of varying current density, flow velocity, electrolyte conductivity, and PFOS concentration. Over 99% of PFOS removal was achieved under continuous flow conditions. The fluorine mass balance showed that most PFOS-bonded F was released as fluoride, while no organic intermediates were detected in the aqueous phase. Each ∼2% of fluorine was recovered as HF and organofluorine intermediates in the gas phase. A comparison of 10 PFAS revealed a hydrophobicity-driven increase in oxidation rate with increasing perfluoroalkyl chain length as well as faster oxidation kinetics for perfluoroalkyl carboxylic acids compared to perfluoroalkane sulfonic acids, likely due to contributions from electrochemically activated sulfate. The energy consumption of PFAS treatment under simulated slow-flow groundwater conditions was substantially higher than in ex situ electrochemical systems optimized for enhanced mass transfer. Consequently, future work should focus on in situ treatment design optimization with an emphasis on power requirements. Collectively, our investigations demonstrate that among the few water treatment technologies capable of breaking the carbon-fluorine bond, electrochemical treatment is a promising approach for in situ destruction of PFAS in the subsurface.

Degradation and Defluorination of Aqueous Perfluorooctane Sulfonate by Silica-Based Granular Media Using Batch Reactors

Per- and polyfluoroalkyl substances (PFASs) are recalcitrant emerging contaminants of concern within the United States and internationally. Of the known PFASs, the sulfonates are considered among the most toxic and difficult to destroy using traditional methods. Research presented herein describes the degradation and defluorination of perfluorooctane sulfonate (PFOS) using a novel photocatalytic porous silica-based granular media (SGM) activated with ultraviolet light, and combined with a strong or weak nucleophilic attack in batch reactors. Sodium thiosulfate proved to be the most compatible and efficient nucleophile in combination with SGM media production of free radicals. Measured aqueous fluoride content accounted for 51% defluorination of PFOS, while the remainder is theorized to mineralize and reside within the porous network of the SGM, as indicated by scanning electron microscopy and energy dispersive x-ray spectroscopy. Removal of PFOS in solution is completed by 30 min with Na2S2O3, with measurable by-product production of C2F3O2− and aqueous fluoride occurring at 15 min. The rapid increase, incipient decrease, and subsequent mineralization of fluoride reveals that the degradation of PFOS is rapid and starts with cleaving of the functional sulfonate group. Amalgamated C-F chains precipitate within the SGM alongside the crystalized fluorine. Possible pathways for PFOS destruction are proposed for the combined attack results. This approach is translatable to other PFASs and organic contaminants of concern.

Electrochemical destruction and mobilization of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in saturated soil

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) have attracted attention due to their widespread distribution, recalcitrance, and substantial toxicity. In this work, high concentrations of PFOA and PFOS were degraded and mobilized through electrochemical treatments in a simulated source zone of saturated soil. Under a low constant voltage and direct current of 24 V and 467–690 mA, approximately 51.7% and 33% of PFOA and PFOS were degraded, respectively. Additionally, a total defluorination mass balance of 44.7% and 23% were detected for PFOA and PFOS, respectively, which indicates that the removal of PFOA and PFOS occurs through its destruction. Substantial electromigration causes the destruction and mobilization of solid PFOA and PFOS to shift into the water phase. Although electrochemical oxidation of PFAS (per- and polyfluoroalkyl substances) were previously reported and studied, this study is one of the few that focus on simultaneous desorption, mobilization, and destruction of PFAS in saturated soil containing a low-intensity electrical field.

Efficient sorption of perfluoroalkyl acids by ionic liquid-modified natural clay

Contamination caused by per- and polyfluoroalkyl substances (PFAS), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), is a big concern worldwide due to their persistence in the environment. Removal of PFAS represents a special challenge for water/wastewater treatment because of their diverse structures and unique physicochemical properties such as high water solubility and high stability of the C-F bond. In this study, we primarily investigated the removal of PFOA and PFOS from water through sorption with ionic liquid (IL)-modified natural clay. A series of ILs with varied alkyl chain lengths were applied for clay modification, and the successful intercalation of ILs was verified with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), zeta potential measurement, and elemental analysis. The structure and properties of IL-modified clays were strongly affected by the IL chain lengths. Specifically, long-chain IL not only changed the surface potential of clay, but also expanded the interlayers of clay, both of which greatly facilitated PFOA and PFOS sorption. Clay modified with the long-chain IL exhibited both fast kinetics for PFOA and PFOS sorption and high PFOA and PFOS removal efficiency under various water chemistry conditions. Furthermore, long-chain IL-modified clay was very effective for the removal of a suite of perfluorinated carboxylic and sulfonic acids with various chain lengths of the perfluoroalkyl moiety. IL-modified natural clay may be potentially applied for PFAS pollution control.

Energy-efficient removal of PFOA and PFOS in water using electrocoagulation with an air-cathode

Electrocoagulation (EC) with a zinc anode demonstrated promising results to remove perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) from an aqueous solution. However, the energy requirement for EC is usually very high due to water electrolysis or aeration. This study aims to reduce energy consumption using an air-cathode in EC (ACEC) to supply oxygen electron acceptor without aeration for attenuating PFOA/PFOS in this new configuration. For the high PFOA concentration (0.25 mM), ACEC with 45 min of the reaction time exhibited an excellent PFOA removal (99.8 ± 0.3% removal) comparable to an EC with aeration (EC-aeration, 100% removal) while achieving much less energy consumption (0.14 kWh/m3). For the low PFOA concentration (0.1 μM), only 41.1 ± 11.6% was removed by the ACEC due to the low concentration gradient for adsorption. EC-aeration achieved higher PFOA removal (81.9 ± 15.1%) for the low PFOA concentration, possibly because air bubbles floated PFOA to the water surface, thereby concentrating PFOA. The PFOS removals in the ACEC and EC-aeration (76.4–88.5%) at the high concentration (0.25 mM) were lower than PFOA due tentatively to its micelle formation. However, PFOS was removed better than PFOA at the low concentration (0.1 μM) due to its higher hydrophobicity.