Degradation Of Perfluorooctane Sulfonate Research Articles

Elucidating the degradation mechanisms of perfluorooctanoic acid and perfluorooctane sulfonate in various environmental matrices: a review of green degradation pathways.

Given environmental persistence, potential for bioaccumulation, and toxicity of Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), the scientific community has increasingly focused on researching their toxicology and degradation methods. This paper presents a survey of recent research advances in the toxicological effects and degradation methods of PFOA and PFOS. Their adverse effects on the liver, nervous system, male reproductive system, genetics, and development are detailed. Additionally, the degradation techniques of PFOA and PFOS, including photochemical, photocatalytic, and electrochemical methods, are analyzed and compared, highlighted the potential of these technologies for environmental remediation. The biotransformation pathways and mechanisms of PFOA and PFOS involving microorganisms, plants, and enzymes are also presented. As the primary green degradation pathway for PFOA and PFOS, Biodegradation uses specific microorganisms, plants or enzymes to remove PFOA and PFOS from the environment through redox reactions, enzyme catalysis and other pathways. Currently, there has been a paucity of research conducted on the biodegradation of PFOA and PFOS. However, this degradation technology is promising owing to its specificity, cost-effectiveness, and ease of implementation. Furthermore, novel materials/methods for PFOA and PFOS degradation are presented in this paper. These novel materials/methods effectively improve the degradation efficiency of PFOA and PFOS and provide new ideas and tools for the degradation of PFOA and PFOS. This information can assist researchers in identifying flaws and gaps in the field, which can facilitate the formulation of innovative research ideas.

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.

A Review of Treatment Technologies for Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA) in Water

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are a category of persistent, non-degradable pollutants that are widespread in the environment and in humans. They have attracted considerable attention due to their high bioaccumulation, multiple toxicities, long-term stability, and, in particular, their effects on human health. Therefore, there is an urgent need for highly efficient technologies and systematic mechanisms for the degradation of PFOS and PFOA. Therefore, we summarize four mainstream technologies for the degradation of PFOS and PFOA in water and their research progress in this review, namely adsorption, advanced oxidation processes, microbial treatment, and membrane separation. Among them, adsorption technology is the earliest and relatively mature, the advanced oxidation process has relatively high treatment efficiency, there are deep and broad development prospects for microbial treatment in the future, and membrane separation technology can recycle raw materials and help to save resources. Based on the analysis of the advantages and disadvantages of the existing technologies, the development prospect of reasonable optimization technology is prospected, with a view to providing a practical scientific reference for the research and engineering practice of PFOS and PFOA pollution control in China.

Degradation of perfluorooctanesulfonate (PFOS) by sub-bandgap irradiation of hydrogen-terminated nanodiamond

Irradiation of aqueous suspensions containing hydrogen-terminated detonation nanodiamond (HND) with sub-bandgap (λexc > 225 nm) excitation leads to the reductive degradation of perfluorooctanesulfonate (PFOS). As evidenced by nanosecond transient absorption spectroscopy (nsTA), we show that 254 nm excitation of HND in water induces the photoemission of electrons producing hydrated electrons (eaq-). A red shift in the eaq- absorption maximum relative to bulk water indicates a disruption in the hydrogen bonding network of the interfacial water layer at the HND surface. A shortening of the eaq- lifetime with the addition of PFOS and accompanying blue shift of the eaq- absorption maximum indicate PFOS reduction and HND/PFOS surface interactions, respectively. Prolonged photolysis of HND/PFOS solutions at 254 nm results in the degradation of PFOS into smaller polyfluoroalkyl derivatives consistent with other advanced reduction processes. The degradation of PFOS by this method is less sensitive to pH than the state-of-the-art UV-sulfite method.

Low power degradation of perfluorooctane sulfonate (PFOS) in water using a nanosecond pulsed atmospheric pressure plasma

The prevalence and persistence of perfluoroalkyl substances (PFAS) has led to significant concerns over the damage they can have on human health and the environment, particularly when they contaminate bodies of water. In this work, a plasma driven with high-voltage (20 kV) pulses of varying duration (50–400 ns) and frequency (0.5–10 kHz) is investigated for degrading perfluorooctane sulfonate (PFOS) in water. The concentration of PFOS in solution decreased with repeated passes through the reactor. Increasing the power consumption of the plasma, either by increasing the pulse width or the frequency, improved the rate of PFOS loss but decreased the energy efficiency. For instance, reducing the frequency of the pulse from 10 kHz to 500 Hz decreased the power consumption by over an order of magnitude while requiring about twice as much time to reduce 50% of the PFOS signal. Time-averaged emission spectroscopy showed that increasing the frequency decreased the average electron density of the plasma while infrared measurements indicate only a modest increase to the temperature of the reactor. In contrast, increasing the pulse width from 50 ns to 400 ns did not have a significant impact on the average electron density or the reactor temperature. Spectroscopy revealed the presence of photons with energies >5 eV which could contribute to PFOS loss. This work shows that the main factor determining PFOS loss is the contact time between the plasma reactor and the solution, which implies the most energy efficient operating parameters for PFOS degradation comes from minimizing the duration and frequency of the high-voltage pulses to reduce power consumption.

Quantifying Hydrated Electron Transformation Kinetics in UV-Advanced Reduction Processes Using the Re-,UV Method.

Ultraviolet advanced reduction processes (UV-ARP) have garnered significant attention recently for the degradation of several hard to treat contaminants, including recalcitrant per- and polyfluoroalkyl substances (PFAS). The rate of contaminant degradation in UV-ARP is directly related to the available hydrated electron concentration ([eaq-]). However, reports of [eaq-] and other parameters typically used to characterize photochemical systems are not widely reported in the UV-ARP literature. Deploying monochloroacetate as a probe compound, we developed a method (Re-,UV) to quantify the time-based hydrated electron concentration ([eaq]t) available for contaminant degradation relative to inputted UV fluence. Measured [eaq]t was then used to understand the impact of eaq- rate of formation and scavenging capacity on the degradation of two contaminants─nitrate and perfluorooctane sulfonate (PFOS)─in four source waters with varying background water quality. The results show that the long-term treatability of PFOS by UV-ARP is not significantly impacted by the initial eaq- scavenging conditions but rather is influenced by the presence of eaq- scavengers like dissolved organic carbon and bicarbonate. Lastly, using [eaq]t, degradation of nitrate and PFOS was modeled in the source waters. We demonstrate that the Re-,UV method provides an effective tool to assess UV-ARP treatment performance in a variety of source waters.

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.

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.

Impact of matrix diffusion on the migration of groundwater plumes for Perfluoroalkyl acids (PFAAs) and other non-degradable compounds

Groundwater fate and transport modeling results demonstrate that matrix diffusion plays a role in attenuating the expansion of groundwater plumes of “non-degrading” or highly recalcitrant compounds. This is especially significant for systems where preferred destructive attenuation processes, such as biological and abiotic degradation, are weak or ineffective for plume control. Under these conditions, models of nondestructive physical attenuation processes, traditionally dispersion or sorption, do not demonstrate sufficient plume control unless matrix diffusion is considered. Matrix diffusion has been shown to be a notable emergent impact of geological heterogeneity, typically associated with back diffusion and extending remediation timeframes through concentration tailing of the trailing edge of a plume. However, less attention has been placed on evaluating how matrix diffusion can serve as an attenuation mechanism for the leading edge of a plume of non-degrading compounds like perfluoroalkyl acids (PFAAs), including perfluorooctane sulfonate (PFOS).In this study, the REMChlor-MD model was parametrically applied to a generic unconsolidated and heterogeneous geologic site with a constant PFOS source and no degradation of PFOS in the downgradient edge of the plume. Low levels of mechanical dispersion and retardation were used in the model for three different geologic heterogeneity cases ranging from no matrix diffusion (e.g., sand only) to considerable matrix diffusion using low permeability (“low-k”) layers/lenses and/or aquitards. Our analysis shows that, in theory, many non-degrading plumes may expand for significant time periods before dispersion alone would eventually stabilize the plume; however, matrix diffusion can significantly slow the rate and degree of this migration.For one 100-year travel time scenario, consideration of matrix diffusion results in a simulated PFOS plume length that is over 80% shorter than the plume length simulated without matrix diffusion. Although many non-degrading plumes may continue to slowly expand over time, matrix diffusion resulted in lower concentrations and smaller plume footprints. Modeling multiple hydrogeologic settings showed that the effect of matrix diffusion is more significant in transmissive zones containing multiple low-k lenses/layers than transmissive zones underlain and overlain by low-k aquitards. This study found that at sites with significant matrix diffusion, groundwater plumes will be shorter, will expand more slowly, and may be amenable to a physical, retention-based, Monitored Natural Attenuation (MNA) paradigm. In this case, a small “Plume Assimilative Capacity Zone” in front of the existing plume could be reserved for slow, de minimus, future expansion of a non-degrading plume. If potential receptors are protected in this scenario, then this approach is similar to allowances for expanding plumes under some existing environmental regulatory programs. Accounting for matrix diffusion may support new strategic approaches and alternative paradigms for remediation even for sites and conditions with “non-degrading” constituents such as PFAAs, metals/metalloids, and radionuclides.

Degradation of perfluoroalkyl substances using UV/Fe0 system with and without the presence of oxygen

ABSTRACT The wide presence of per- and poly-fluoroalkyl substances (PFAS) in the environment is a global concern, thus their degradation is an imminent task. In this study, oxidative and/or reductive degradation of three representative PFAS – perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorooctane sulfonate (PFOS) was achieved using nanoscale zero-valent iron (Fe0 NPs) under ultraviolet (UV) light, both with and without the presence of oxygen. Higher degradation and defluorination rates were obtained for a longer chain PFNA compared to PFOA, and a higher removal of PFAS was achieved without the presence of O2 compared to that with O2. The degradation followed first-order reaction kinetics, and obtained the highest rates of 97.6, >99.9, and 98.5% without the presence of O2 for PFOA, PFNA, and PFOS, respectively. The degradation rates increased with an increase in the nanoparticle concentrations in the range of 1–100 mg/L. In addition to fluoride ions, shorter chain perfluorocarboxylic acids (PFCAs) were detected as the main intermediates during PFAS degradation; PFHpS and 6:2 FTS were also detected during PFOS degradation. Hydroxyl radicals (·OH) and superoxide radicals (·O2 −) were not involved in the degradation of PFOA, but likely involved in the degradation of PFOS. Emerging contaminants PFAS degradation using the UV/Fe0 system is a cost-effective technology owing to the low cost and recyclability of Fe0 nanomaterials, low energy consumption in the system, and its capability to degrade PFAS both with and without the presence of oxygen. This technology can be potentially applied to treat PFAS-contaminated waters in the environment.

Degradation of Perfluorooctanesulfonate (Pfos) by Sub-Bandgap Irradiation of Hydrogen-Terminated Nanodiamond

Degradation of Perfluorooctanesulfonate (Pfos) by Sub-Bandgap Irradiation of Hydrogen-Terminated Nanodiamond

Exploring key reaction sites and deep degradation mechanism of perfluorooctane sulfonate via peroxymonosulfate activation under electrocoagulation process

Perfluorooctane sulfonate (PFOS), normally present in groundwater and surface water, is an emerging environmental contaminants, but is extremely difficult to be degraded due to high energy of the C-F bond. Here, an electrocoagulation (EC) technique coupled with peroxymonosulfate (PMS) activation was used to deeply degrade PFOS. Results showed that approximately 100% PFOS was removed from the solution in the monopolar serial (MS) mode within 60 min and achieved a high kinetic rate of 0.074 min−1, which was significantly higher than those of reported studies (Table S3). Energy consumption (2.06 kWh/kg) in the MS mode was significantly lower than that of Al (52.30 kWh/kg) and Zn (213.50 kWh/kg) electrodes, which further confirmed the potential application prospects of EC technique. The quenching experiments, electron spin response (ESR) analysis, and DFT calculations can verify that ·OH was the main radical from the reaction of Fe2+–OH reaction site with PMS. In addition, results from fluorine balance and TOC removal also indicated the complete mineralization and degradation of PFOS in the EC process. Quantum chemical calculations can confirm the PFOS degradation mechanism and key active sites for direct electron transfer and radical attack. After five cycle operations of PFOS degradation, the EC process was still effective in degrading PFOS with a removal efficiency above 98%. Thus, this work provided a novel alternative for the high-effective treatment of PFOS from contaminated environmental water bodies.

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.

New insight into PFOS transformation pathways and the associated competitive inhibition with other perfluoroalkyl acids via photoelectrochemical processes using GOTiO2 film photoelectrodes

The global distribution and environmental persistence of perfluoroalkyl acids (PFAAs) has been considered a critical environmental concern. In this work, we successfully fabricated a graphene oxide-titanium dioxide (GOTiO2) photoelectrode for perfluorooctane sulfonate (PFOS) degradation in a photoelectrochemical (PEC) system. The results reveal that a 5 wt.% GOTiO2 anode possesses the optimal PEC performance, with a band gap (Eg) of 2.42 eV, specific surface area (SBET) of 72.6 m2 g−1 and specific capacitance (Cs) of 4.63 mF cm−2. In the PEC system, PFOS can be efficiently removed within 4 h of reaction time, with a pseudo-first-order rate constant of 0.0124 min−1, under the optimized conditions of current density = 20 mA cm−2, electrode distance = 5 mm, solution pH = 5.64, [PFOS]0= 0.5 µM and NaClO4 electrolyte concentration = 50 mM. The electron transfer pathway, hydroxyl radicals and superoxide radicals are all responsible for PFOS decomposition/transformation. New degradation pathways were identified; a total of 25 PFOS byproducts are reported in this work; and perfluoroalkane sulfonates (PFSAs), perfluorinated aldehydes (PFALs) and hydrofluorocarbons (HFCs) were identified for the first time. PFOS degradation involves the desulfonation pathway as the first step, followed by oxidation and subsequent defluorination, decarboxylation, decarbonylation, sulfonation, defluorination and hydroxylation. The results from this work also show that the reactivity of PFAAs is related to their carbon chain length, with shorter-chain PFAAs exhibiting a lower degradation rate. In a PFAA mixture, a decline in the degradation rate was observed for the shorter-chain-length PFAAs, suggesting stronger competitive inhibition and indicating stronger environmental recalcitrance during the treatment process.Novelty statement: Although many efforts have been made to identify perfluorooctane sulfonate (PFOS) degradation byproducts, previous studies were only able to identify byproducts that are related to perfluorinated carboxylic acids (PFCAs). This is the first study to elucidate the new PFOS degradation pathway; furthermore, this is the first report to identify byproducts containing sulfonate groups (perfluoroalkane sulfonates, PFSAs), aldehyde groups (perfluorinated aldehydes, PFALs), and hydrofluorocarbons (HFCs). This study further systematically explores how perfluoroalkyl acid (PFAA) degradation may be affected in the mixture system: shorter-chain-length PFAAs suffer stronger competitive inhibition in the photoelectrochemical (PEC) system. By utilizing the graphene oxide-titanium dioxide (GOTiO2) photoelectrode fabricated in this work, PFOS can be successfully decomposed during the PEC process for the first time.

UV/FeⅡNTA as a novel photoreductive system for the degradation of perfluorooctane sulfonate (PFOS) via a photoinduced intramolecular electron transfer mechanism

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that is toxic and bio-accumulative. Previously, we used hydrated electrons (eaq–) generated by the UV photolysis of nitrilotriacetic acid (NTA) to initiate the photoreductive decomposition of PFOS. However, due to the protonation of NTA and the scavenging effect of H+ on eaq–, this process relies highly on alkaline conditions. Herein, we report on an enhanced UV photoreductive system based on FeⅡNTA, which results in the decomposition of PFOS at pH 8.0 under anoxic conditions. After 10 h of photolysis, the degradation and defluorination efficiencies of PFOS in the UV/FeⅡNTA system were ~ 60% and 29.5%, respectively, with a pseudo first-order degradation rate constant of kobs = 0.081 h−1. Laser flash photolysis results combined with time-dependent density functional theory (TDDFT) calculations indicate that PFOS, Fe(H2O)62+, and NTA form a penta-coordinated metal–ligand complex that undergoes a UV-induced directional electron transfer from FeⅡNTA to PFOS. PFOS decomposes via a mechanism that proceeds through a concerted photoinduced intramolecular charge transfer instead of direct attack by eaq–. Model chelate studies show that the inherent properties of the transition metal ion and the electron-donating capabilities of the complexing ligands determine the efficiency for photoreductive electron transfer. A low apparent activation energy of 4.74 kJ/mol over a broad pH range results in higher electron transfer efficiencies for UV/FeⅡNTA photolysis compared to photolysis initiated by un-complexed NTA.

Reductive defluorination of Perfluorooctanesulfonic acid (PFOS) by hydrated electrons generated upon UV irradiation of 3-Indole-acetic-acid in 12-Aminolauric-Modified montmorillonite

Per-and poly-fluoroalkyl substances (PFASs) are a class of persistent compounds that are resistant to degradation. Here we developed an effective method of degrading perfluorooctanesulfonate (PFOS) by hydrated electrons (eaq−) that are generated from 3-indole-acetic-acid (IAA) upon UV irradiation. The method takes advantage of spatial proximity of IAA and PFOS by their co-sorption to an organic polymer, 12-aminolauric acid (ALA), which was pre-intercalated into the interlayer space of an expandable clay mineral, montmorillonite. The interlayer spacing of this clay nanocomposite is greatly expanded relative to unmodified montmorillonite. The maximum adsorption capacity of IAA and PFOS is 168 and 1550 mmol/kg, respectively. This process achieved 40–70% defluorination of a 10 ppm PFOS solution at neutral pH in a 325 mL vessel. The presence of bicarbonate and chloride ions, or natural groundwater showed a minimal impact on PFOS degradation. Based on identification of prominent degradation products, a degradation pathway is proposed, where the primary degradation process is breakage of the C-F bonds (with fluorine replaced by hydrogen), with some cleavage of the CC bond. This approach provides an alternative for treating concentrated PFAS solutions under ambient conditions.

Adsorption and solid-phase photocatalytic degradation of perfluorooctane sulfonate in water using gallium-doped carbon-modified titanate nanotubes

Perfluorooctane sulfonate (PFOS) has drawn increasing attention due to its omnipresence and adverse health effects. We prepared a new adsorptive photocatalyst, Ga/[email protected], based on activated carbon and TiO2, and tested the adsorption and subsequent solid-phase photodegradation of PFOS. Ga/[email protected] showed faster adsorption kinetics and higher affinity for PFOS than the parent AC, and could degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradiation. The efficient PFOS photodegradation also regenerates Ga/[email protected], allowing for repeated uses without invoking chemical regenerants. The superior photoactivity is attributed to the oxygen vacancies, which not only suppressed recombination of the e−/h+ pairs, but also facilitated O2− generation. Both h+ and O2− played critical roles in the PFOS degradation, which starts with cleavage of the sulfonate group and converts it into PFOA that is then decarboxylated and defluorinated following the stepwise defluorination mechanism. Ga/[email protected] holds the potential for more cost-effective PFOS degradation.

Degradation of perfluorooctane sulfonatevia in situelectro-generated ferrate and permanganate oxidants in NOM-rich source waters

The electrooxidation of PFOS can be significantly improved with the simultaneous electrosynthesis of ferrate and permanganate from low concentration ambient Fe2+and Mn2+in source waters, even in the presence of natural organic matter (NOM).

Electrochemical Oxidation of Perfluorooctanesulfonate by Magnéli Phase Ti4O7 Electrode in the Presence of Trichloroethylene

This study examined the degradation of perfluorooctanesulfonate (PFOS) in electrochemical oxidation (EO) processes in the presence of trichloroethylene (TCE). The EO experiment was performed in a gas-tight reactor using Magnéli phase titanium suboxide (Ti4O7) as the anode. The experimental data demonstrated that 75% of PFOS (2 μM) was degraded at 10 mA/cm2 current density in 30 min without TCE present in the solution, while the presence of 76 μM TCE apparently inhibited the degradation of PFOS, reducing its removal down to 53%. Defluorination ratio suggested that PFOS was significantly mineralized upon EO treatment, and it appeared to be not influenced by the presence of TCE. The respective pseudo-first order rate constants (kobs) of PFOS removal were 0.0471 and 0.0254 min-1 in the absence and presence of TCE. The degradation rates of both PFOS and TCE increased with current density rising from 2.5 to 20 mA/cm2. In the presence of TCE, chloride, chlorate, and perchlorate were formed that accounted for 79.7 %, 5.53%, and 1.51% of the total chlorine at 60 min. This work illustrates the promise of the Magnéli phase Ti4O7 electrode based electrochemical oxidation technology for degrading per- and polyfluoroalkyl substances (PFASs) and co-contaminants in groundwaters.

Reductive transformation of perfluorooctanesulfonate by nNiFe0-Activated carbon

Degradation of linear (L) and branched (Br) perfluorooctanesulfonate (PFOS) using nNiFe° particles supported on activated carbon (AC) and heat is demonstrated for the first time and with several lines of evidence. At 60 °C, PFOS degradation plateaued at 50 ± 6%, while at 50 °C, 94 ± 4.1 % PFOS transformed. The accelerated iron corrosion at the higher temperature is attributed to the lower PFOS transformation at 60 °C. However, at both temperatures, ≥ 97 % of the PFOS transformed was accounted for by the moles of fluoride generated. At 60 °C, PFOS degradation rates were estimated at 0.028 ± 0.003 h−1 and fluoride and sulfite generation rates of 0.70 ± 0.165 h−1 and 0.62 ± 0.157 h−1, respectively, with no differences between L-PFOS and total Br-PFOS. Using time-of-flight mass spectrometry, some organic products were identified in the particle extracts from the 60 °C reaction. Products included single-bonded C8 polyfluoroalkyl sulfonates (F16 to F7) and alkyl acids (PFCAs, C4-C8) and one perfluorinated C8 desulfonated product supporting both defluorination and desulfonation pathways. Most of the organic products were gone after the first 25 h. High PFOS mineralization using nNiFe°-AC technology warrants further investigation for its use in permeable reactive barriers.