Degradation Of Perfluorooctanoic Acid Research Articles

New insights into the PFAS defluorination performance and mechanism of ultrasound-enhanced electrochemistry with peroxydisulfate electrolyte

Ultrasound (US)-assisted electrochemical oxidation (EO) has previously demonstrated its ability to degrade perfluorooctanoic acid (PFOA). However, the mechanisms of direct electron transfer and indirect oxidation by reactive oxygen species (ROS), as well as the involvement of these ROS, are unclear, particularly with the peroxydisulfate (PDS) electrolyte and the added effect of US. In this study, an US/EO/PDS system was first investigated, achieving nearly 100 % and 80.01 % defluorination for PFOA and perfluorooctane sulfonate, respectively (within 3 h). This US/EO/PDS system exhibited remarkable stability, pH tolerance, and practicality. Further experimental and theoretical studies revealed that the predominant mechanism of PFOA defluorination was indirect oxidation via ROS, rather than direct oxidation at the anode. Although none of these ROS could initiate the degradation of PFOA without additional energy, both ROS (SO4∙- ＞ •OH ＞ 1O2 ＞ O2∙-) and US/EO contributed to the initial step of PFOA defluorination. Furthermore, US enhanced the generation of ROS and the direct oxidation (electron transfer) ability of EO. The electrons were transferred from PFOA to PDS via the electrode assembly. This study clarified, for the first time, the synergistic effect of US/EO/PDS and the involvement of direct and indirect ROS oxidation in defluorination of PFOA, which shows potential for developing US and EO technology for complete degradation of polyfluoroalkyl substances.

Stimulating Acidimicrobium sp. Strain A6 in iron-rich, acidic sediments from AFFF-impacted sites for PFAS defluorination

Per- and polyfluoroalkyl substances (PFAS) are persistent and bioaccumulative contaminants that are widely used in industrial applications and consumer products and pose significant risks to ecosystems and human health. Acidimicrobium sp. Strain A6 (A6), which is common in acidic, and iron rich soils and sediments is capable of both anaerobic ammonium (NH4+) oxidation under iron reduction (Feammox) and defluorination of perfluorinated alkyl substances, such as perfluoroalkyl acids (PFAAs). This study investigates the potential for biostimulating A6 via the supply of NH4+ and ferric iron (Fe(III)) with the goal of defluorinating PFAAs. Sediment samples from acidic, iron-rich, AFFF (aqueous film forming foam) impacted sites were collected and incubated with added Fe(III) and NH4+. Quantitative PCR was used to track A6 numbers as well as dehalogenase and F− ion transporter genes during these incubations; changes in the microbial community structure were tracked through 16S rRNA gene sequencing. The findings reveal that the addition of Fe(III) and NH4+ stimulated the Feammox reaction and A6 growth and enhanced the degradation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). Results also show a significant presence and activity of the above-mentioned genes in these incubations. The insights gained from this study could inform bioremediation strategies for PFAS-contaminated environments, especially in geochemical settings that favor the presence of A6.

Enhanced selective photocatalytic reduction and oxidation of perfluorooctanoic acid on Bi/Bi5O7I decorated with poly (triazine imide)

Perfluorooctanoic acid (PFOA) is detected widely in surface and groundwater globally. Its removal poses a significant challenge due to its high chemical stability. This study demonstrates efficient PFOA degradation using poly-triazine-imides-tailored defective Bi5O7I (PTI/BB). Under 300W Xe irradiation, 1µg·L-1 PFOA could be degraded to 9.86ng·L-1 after 3hours in the presence of 0.5g·L-1 25% PTI/BB. The mechanism investigation reveals that the oxygen vacancy (OV) in partially reduced Bi/Bi5O7I (BB) generates impurity states, enhancing the light-harvesting capacity. Furthermore, forming a type Ⅱ heterojunction between conjugated PTI and BB facilitates the efficient separation of photogenerated carriers. The resulting photogenerated electrons (reduction) and holes (oxidation) drive hydrogenation reduction and oxidative decarboxylation of PFOA, respectively. This synergistic effect consequently achieves significant defluorination of PFOA. The proposed PFOA degradation pathway via the PTI/BB catalyst offers new insights into the catalyst design for photocatalytic degradation of per- and polyfluoroalkyl substances (PFAS).

Application of Response Surface Methodology for the Optimization of Operating Conditions of a Self‐Pulsing Discharge (SPD) Plasma Reactor for the Degradation of Perfluorooctanoic Acid (PFOA) in Water

ABSTRACTThis study explores atmospheric plasma as a novel approach for the degradation of persistent per‐ and polyfluoroalkyl substances (PFAS) in contaminated waters. Using response surface methodology and Box–Behnken design, the performance of the self‐pulsing discharge (SPD) reactor was optimized by adjusting the following independent factors: input power, plasma area‐to‐liquid volume ratio, and argon bubbling time. Optimization was assessed using four specific indicators: kPFOA and G50, for the process velocity and energy efficiency, respectively; kPFOA/kPFHpA and ΣPFAS/C0, both for the presence of PFAS in the treated water for the process products. Under the optimized operating conditions, residual PFAS summed up to only 2.4% of the carbon initially present as PFOA, and a remarkable G50 value of (523 ± 10) mg/kWh was obtained.

Continuous Synthesis and Processing of Covalent Organic Frameworks in a Flow Reactor.

Covalent organic frameworks (COFs) are typically prepared in the form of insoluble microcrystalline powders using batch solvothermal reactions that are energy-intensive and require long annealing periods (>120 °C, >72 h). Thus, their wide-scale adoption in a variety of potential applications is impeded by complications related to synthesis, upscaling, and processing, which also compromise their commercialization. Here we report a strategy to address both the need for scalable synthesis and processing approaches through the continuous, accelerated synthesis, and processing of imine- and hydrazone-linked COFs using a flow microreactor. The flow microreactor is capable of unprecedented COF productivities, up to 61,111 kg m-3 day-1, and provides control over key stages of COF formation, including nanoparticle growth, self-assembly, and precipitation. Additionally, the technique successfully yields highly crystalline and porous COFs in versatile macroscopic structures such as monoliths, membranes, prints, and packed beds. We also show that a COF synthesized using the flow microreactor acts as an excellent photocatalyst for the photocatalytic degradation of perfluorooctanoic acid (PFOA) outperforming the degradation efficiency of its batch analogue and other classical photocatalysts such as titanium dioxide (TiO2).

Highly efficient defluorination of perfluorooctanoic acid by a BiOCl-ND photocatalyst: Enhanced charge transfer and synergistic mechanism

Considerable attention has been given to the control of perfluorooctanoic acid (PFOA) environmental pollution due to its degradation resistance and potential risks. In this study, Bismuth oxychloride based nanodiamond (BiOCl-ND) composite materials were successfully synthesized by using hydrothermal method. The complete decomposition of PFOA and a high defluorination ratio of 74.6% by BiOCl-ND 10:1 was obtained under UV light irradiation within 60 min, and the composite's degradation rate constant was nearly 3.8 times than that of pure BiOCl. It was demonstrated that critical roles played in PFOA degradation were photogenerated holes (h+) and superoxide radicals (·O2−). A synergistic effect between BiOCl and ND and the heterostructure was revealed, the differences of the energy band structure between BiOCl and ND reduced the recombination of photogenerated e−-h+ and enhanced the charge transfer. In this process, a large number of h+ with oxidizing properties and·O2− generated from both BiOCl and ND played a critical role, and oxygen vacancies (OVs) also participated in the reaction as active species and contributed to electron transfer. Additionally, the photocatalytic decomposition intermediates of PFOA and the release of fluorine ions were analyzed to verify the effective defluorination of PFOA, and the results confirmed a gradual decrease in the toxicity of the reaction matrix during PFOA degradation. Hence, these results might provide insights for the development of photocatalysts to improve the photodegradation effect of PFOA in water.

Efficient defluorination of PFOA by vacuum ultraviolet coupling with sulfite and iodide

Perfluorooctanoic acid (PFOA), as an anthropogenic persistent contaminant, is widely distributed in the natural aquatic environment and has been a considerable threat to ecological security and human health. In this work, we propose and evaluate the vacuum ultraviolet (VUV)/sulfite-iodide system under N2 saturated condition for the decomposition of PFOA. The in situ generated hydrated electrons (eaq−) were demonstrated to be the main active species responsible for the PFOA degradation. With observation of the intermediate products, two major degradation pathways of PFOA in VUV/sulfite-iodide system were proposed: H/F exchange and chains shortening. A significant enhancement of PFOA defluorination was observed with increasing pH values from 9.0 to 12.0, which can be explained by the decreasing quenching effect of eaq− and accelerated disproportionation of I2 to I− and IO3−. Meanwhile, VUV/sulfite-iodide system also exhibited satisfactory performance in degrading high concentration of PFOA (200 μM). However, the presence of Cl−, NO3−, and humic acid inhibited the removal of PFOA via various reaction mechanism. The VUV/sulfite-iodide system was effective toward the chosen PFCAs (trifluoroacetic acid (TFA) and perfluorobutyric acid (PFBA)), demonstrating a chain length independence on the degradation of PFCAs, supporting its broad applicability.

Perfluorooctanoic acid efficient chain reaction degradation in multifunctional iron-sulfur mineral augmentation geobiochemical remediation system

Serious contamination of perfluorooctanoic acid (PFOA) has aroused global concern. General biotransformation or iron-based materials did not meet efficient PFOA elimination. Here, specific green and low-carbon microorganism-biochar pellets, multi-component and multifunctional iron-sulfur (FexSy) mineral pellets, and a microbe-FexSy interaction device were developed to solve this problem. The multi-scale (molecular, interface, and column scales) research method combined with the multi-process reaction model was constructed to explore PFOA removal mechanism. Results revealed that microbe-FexSy interaction achieved excellent PFOA degradation performance and retention effect, with degradation rate λ (0.213 h−1) increased by 113 % than FexSy (0.100 h−1) device. The distribution coefficient Kd and kinetic adsorption α increased by 18.54 % and 22.61 %; the fraction of kinetic sorption increased by 63.83 % in microbe-FexSy device (77 %) than alone FexSy (47 %) device. Delftia and Pseudomonas combined with Fe2+ drove an efficient cycle chain reaction for PFOA. Quantitative structure–activity relationship (QSAR) model prediction results indicated that intermediates exhibited lower biotoxicity than PFOA. Furthermore, NO3– further increased the retention effect of microbe-FexSy device for PFOA with little reaction rate fluctuation, making it promising for eliminating PFOA contamination, especially in NO3– type of groundwater. It provided an efficient technology and device based on microbe-mineral interaction in remediating PFOA-contaminated groundwater.

Synergistic adsorption and UV degradation of perfluorooctanoic acid by amine-functionalized A-center sphalerite

Perfluorinated alkylated substances (PFAS), as a category of persistent organic pollutants, have garnered extensive concern due to their resilience against environmental degradation. Herein, we developed an amine-functionalized sphalerite (ZnS) with adjustable surface amine functional groups and Zn defects (ZnS-X%[N]) by in situ coprecipitation and simple hydrothermal method in the presence of cetyltrimethylammonium bromide (CTAB). This material demonstrated efficient PFAS adsorption and subsequent photo-induced degradation under UV irradiation. The characterization results by TEM, BET, FTIR, XPS and EPR revealed that CTAB primarily influences ZnS by modulating surface amine functionalities, zinc defect density, and enhancing its photoreductive capacity. Adsorption and kinetic degradation experiments further showed that a medium CTAB concentration in ZnS-40%[N] achieves highest PFAS adsorption capacity (Cmax: 0.201 mol kg-1), and the corresponding decomposition rate was the fastest (kde: 1.53; kdf: 1.19). This efficacy is attributed to the ZnS-40%[N]'s ideal adsorptive sites and surface shallow defects. Moreover, theoretical simulation also supports the above experimental inference. Overall, ZnS-X%[N] exhibits a synergistic effect on PFAS adsorption and degradation, showcasing its potential for environmental adaptability and practical application.

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.

Effect of electrolyte composition on electrocatalytic transformation of perfluorooctanoic acid (PFOA) in high pH medium

Recent regulatory actions aim to limit per- and polyfluoroalkyl substances (PFAS) concentrations in drinking water and wastewaters. Regenerable anion exchange resin (AER) is an effective separation process to remove PFAS from water but will require PFAS post-treatment of the regeneration wastestream. Electrocatalytic (EC) processes using chemically boron-doped diamond electrodes, stable in a wide range of chemical compositions show potential to defluorinate PFOA in drinking water and wastewater treatments. Chemical composition and concentration of mineral salts in supporting electrolytes affect AER regeneration efficiency, and play a crucial role in the EC processes. Their impact on PFAS degradation remains understudied. This study investigates the impact of 17 brine electrolytes with different compositions on perfluorooctanoic acid (PFOA) degradation in an alkaline medium and explores the correlation between the rate of PFOA degradation and the solution's conductivity. Results show that higher electrolyte concentrations and conductivity lead to faster PFOA degradation rates. The presence of chloride anions have negligible impact on the degradation rate. However, the presence of nitrate salts reduce PFOA degradation efficiency. Additionally, the use of mixed electrolytes may be a promising approach for reducing the cost of EC operations. PFOA degradation was not influenced by the pH of the bulk solution.

Electrochemical advanced oxidation of PFOA by Ti4O7 reactive electrochemical membrane anode

In recent years, per and polyfluoroalkyl substances (PFAS) have garnered significant attention due to their persistent and harmful effects on the environment and human health. Traditional treatment methods often fall short of effectively removing PFAS from water, prompting the need for innovative techniques. One promising approach is electrochemical advanced oxidation, based on highly reactive chemical species generated through electrochemical reactions to degrade organic pollutants. In this study, a specific reactive electrochemical membrane (REM) anode was used to degrade perfluorooctanoic acid (PFOA). The anode is a tubular Ti4O7-based REM (mixture of Ti4O7 and Ti5O9 Magneli phases) with a water permeability of 3300 L m−2 h−1 bar−1. The impact of various operating parameters, including current density, flux through REM, and feed concentration, on PFOA degradation efficiency was investigated. It was found that higher current densities, feed concentrations and lower flux through REM led to increased PFOA removal rates. With this type of REM, a total degradation of PFOA was observed at PFOA flux (passing throw the REM) under 0.2 g h−1 m−2 even at the lowest current density (71 A/m2). The degradation mechanism was investigated by evaluating the generated by-products after several degradation cycles, and the results confirmed that the degradation occurs via the decomposition cycle of CF2. Energy consumption has been taken into account, as it is the major limitation of advanced oxidation processes, exhibiting value under 5 kWh/g for the lowest current density and the highest PFOA flux. The originality of this study relies on the use of a specific anode; a tubular shape Ti4O7-based REM (by Saint Gobain Company). Such concentric REM reactor is optimal for the treatment of recalcitrant effluent containing PFOA as it significantly improved mass transfer leading to a very interesting energy efficient system that can easily be scale up.

Lanthanide metal-organic frameworks as ratiometric fluorescent probes for real-time monitoring of PFOA photocatalytic degradation process

The assessment of perfluorooctanoic acid (PFOA) photocatalytic degradation usually involves tedious pre-treatment and sophisticated instrumentation, making it impractical to evaluate the degradation process in real-time. Herein, we synthesized a series of lanthanide metal-organic frameworks (Ln-MOFs) with outstanding fluorescent sensing properties and applied them as luminescent probes in the photocatalytic degradation reaction of PFOA for real-time evaluation. As the catalytic reaction proceeds, the fluorescence color changes significantly from green to orange-red due to the different interaction mechanisms between the electron-deficient PFOA and smaller radius F− with the ratiometric fluorescent probe MOF-76 (Tb: Eu = 29:1). The limit of detection (LOD) was calculated to be 0.0127 mM for PFOA and 0.00746 mM for F−. In addition, the conversion rate of the catalytic reaction can be read directly based on the chromaticity value by establishing a three-dimensional relationship graph of G/R value-conversion rate-time (G/R indicates the ratio between green and red luminance values in the image.), allowing for real-time and rapid tracking of the PFOA degradation. The recoveries of PFOA and F− in the actual water samples were 99.3–102.7% (RSD = 2.2–4.4%) and 100.7–105.3% (RSD = 3.9–6.8%), respectively. Both theoretical calculations and experiments reveal that the detection mechanism was attributed to the photoinduced electron transfer and energy transfer between the analytes and the probe. This method simplifies the sample analysis process and avoids the use of bulky instruments, and thus has great potential on the design and development of quantitative time-resolved visualization methods to assess catalytic performance and reveal mechanisms.

Breakdown of PFOA in a hydrodynamic cavitation-activated persulfate system: Comparative roles of sulfate and hydroxyl radicals in degradation process and mechanistic insights

Perfluorooctanoic acid (PFOA) remains a persistent organic pollutant within aquatic ecosystems. Activated persulfate (PS) technology has been widely used because it can effectively destroy the stable structure of PFOA. However, this technology still has some restrictive problems, such as the large amount of PS required for the reaction and the high SO42- concentration in the wastewater after the reaction. In this study, we used the advantages of hydrodynamic cavitation to activate PS, such as promoting mass transfer and oxidant utilization. After 3 hours of treatment, the HC/PS system showed outstanding performance in that 93.6% of PFOA was degraded, and 31.09% of PFOA was defluorinated under optimal conditions with smaller PS dosage and lesser SO42- generation. The different inhibitory effects of coexisting substances (Cl-, CO32-, F-, NO3-, SO42-, HA) on the system were emphasized. The contribution rates of sulfate radicals (SO4•-, 84.4%) and hydroxyl radicals (·OH, 10.9%), which are the main active substances in the HC/PS system, were calculated during the degradation of PFOA. The potential degradation pathways of PFOA were proposed based on the intermediates identified through LC-MS/MS. PFOA gradually lost CF2 units, forming shorter-chain intermediates (PFHpA, PFHxA, PFPeA, PFBA) and F-, ultimately converting to H2O and CO2. Above all, this study provides valuable insights into the future wastewater treatment process for PFOA pollution and has important guiding significance for practical engineering applications.

Enhanced perfluorooctanoic acid (PFOA) degradation by electrochemical activation of peroxydisulfate (PDS) during electrooxidation for water treatment

Improved treatment of per- and polyfluoroalkyl substances (PFAS) in water is critically important in light of the proposed United States Environmental Protection Agency (USEPA) drinking water regulations at ng L−1 levels. The addition of peroxymonosulfate (PMS) during electrooxidation (EO) can remove and destroy PFAS, but ng L−1 levels have not been tested, and PMS itself can be toxic. The objective of this research was to test peroxydisulfate (PDS, an alternative to PMS) activation by boron-doped diamond (BDD) electrodes for perfluorooctanoic acid (PFOA) degradation. The influence of PDS concentration, temperature, and environmental water matrix effects, and PFOA concentration on PDS-EO performance were systematically examined. Batch reactor experiments revealed that 99 % of PFOA was degraded and 69 % defluorination was achieved, confirming PFOA mineralization. Scavenging experiments implied that sulfate radicals (SO4–) and hydroxyl radicals (HO) played a more important role for PFOA degradation than 1O2 or electrons (e−). Further identification of PFOA degradation and transformation products by liquid chromatography-mass spectrometry (LC-MS) analysis established plausible PFOA degradation pathways. The analysis corroborates that direct electron transfers at the electrode initiate PFOA oxidation and SO4– improves overall treatment by cleaving the CC bond between the C7F15 and COOH moieties in PFOA, leading to possible products such as C7F15 and F−. The perfluoroalkyl radicals can be oxidized by SO4– and HO, resulting in the formation of shorter chain perfluorocarboxylic acids (e.g., perfluorobutanoic acid [PFBA]), with eventual mineralization to CO2 and F−. At an environmentally relevant low initial concentration of 100 ng L−1 PFOA, 99 % degradation was achieved. The degradation of PFOA was slightly affected by the water matrix as less removal was observed in an environmental river water sample (91 %) compared to tests conducted in Milli-Q water (99 %). Overall, EO with PDS provided a destructive approach for the elimination of PFOA.

The activation of PMS for PFOA degradation by adjustable metal stripping Fe/Co/N@BC catalysts: Degradation performance with single-line oxygen and high-valent metal oxides as the main active substances

In this study, a modified biochar (P-Fe/Co/N@BC) catalyst was prepared with wood chips as raw material by hydrothermal method for the activation of peroxymonosulfate (PMS) and degradation of perfluorooctanoic acid (PFOA). Scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) characterization methods were used to demonstrate the presence of FeNx, CoNx, Fe-Co and CO active sites, which contribute to the improvement of the PMS activation capacity for single-line oxygen (1O2). Electron paramagnetic resonance spectroscopy (EPR), reactive oxygen species (ROS) scavenging experiments and methyl phenyl sulfoxide (PMSO) conversion experiments were performed to clarify the main mechanisms of PFOA degradation by reactive species. Further, 1O2, sulfate radical (SO4−), hydroxyl radical (OH), high-valent metal oxides (Fe(IV) and Co(IV)) were jointly involved in the degradation of PFOA, and nonradical were the main activation pathway of PMS. In particular, Fe3+ decomposed from Fe(IV) in the presence of Fe0 and Co2+ decomposed from Co(IV) are able to enhance iron cycling and cobalt cycling, respectively. Meanwhile, Co0 accelerates the conversion of Co3+ to Co2+. The findings suggested that the removal rate of the P-Fe/Co/N@BC-PMS system (99 %) was much higher than that of the P-Fe-N-C/PMS (68.9 %) over 180 min. It emphasized that the incorporation of PTFE (polytetrafluoroethylene) can regulate metal leaching significantly and improve the cycling stability of the catalysts. This study aimed to prepare efficient and stable modified biochar catalysts to activate PMS, which provided an effective solution to the problem of metal ion leaching from metal-modified biochar materials.

Enhanced mitigation of membrane fouling and degradation of perfluorooctanoic acid in the treatment of natural surface water through the application of dielectric barrier discharge/sulfite

The present study employed a dielectric barrier discharge (DBD)/sulfite system to mitigate membrane fouling and enhance the degradation of perfluorooctanoic acid (PFOA) in surface water. Results showed that the membrane flux was remarkably enhanced by 93.6%, and the degradation of PFOA showed an impressive increase of 87.9%. The synergistic redox effect of free radicals, including hydroxyl radical (•OH), sulfate radical (SO4∙-), electron (e-/eaq-), su-peroxide anion radicals (∙O2-), and other radical, played a crucial role in mitigating membrane fouling, accounting for 36.26%, 30.10%, 18.69%, 6.75%, and 8.20%, respectively. The correlation analysis revealed that effective removal of UV254 and TOC emerged as the most crucial factors positively contributing to mitigating membrane fouling. Additionally, SO4∙-, •OH, and eaq- were identified as the primary active substances responsible for attacking PFOA, accounting for 41.30%, 25.20%, and 23.70%, respectively. The degradation pathway of PFOA was proposed through analysis using density functional theory and mass spectrometry, reducing the biotoxicity of its degradation products. This study presents a suitable strategy for simultaneous mitigation of membrane fouling and enhancement of PFOA degradation, which holds great potential for advancing the field of water treatment towards practical applications.

Microbial adaptation and biodegradation mechanisms of perfluorinated compounds in different functional zones of the Yellow River Delta, China

Perfluorinated compounds (PFCs) are widespread environmental pollutants that pose risks to ecosystems. Our research in the Yellow River Delta watershed focused on two rivers, Shenxian Gou and Tiao He, representing the impacts of oil extraction and urban wastewater, respectively. The purpose of this study was to evaluate the effects of different concentrations of PFCs on the microbial community structure and to investigate the mechanisms of their degradation by microorganisms. The results suggested that the microbial communities were influenced by the combined effects of PFCs concentration and water quality (0.33), with a notable emphasis on the impact of PFCs (0.28). The 16S rDNA gene amplicon data revealed significant variations in both the structural composition and functional aspects of microbial communities across different concentrations of PFCs (p < 0.05). In particular, perfluorooctanoic acid (PFOA) was found to interfere with several microbial metabolic functions, including DNA functions, structural pathways, and the tricarboxylic acid cycle. Certain bacteria, such as Hydrogenophaga, Luteolibacter, and Pseudorhodobacter, were found to synergistically promote perfluorooctanoic acid degradation. The results improve our understanding of the mechanisms through which microbes adapt to and degrade PFCs in different environments and the complex effects PFCs have on ecosystems.

Novel enhanced defluorination of perfluorooctanoic acids by biochar-assisted ultrasound coupling ferrate: Performance and mechanism

An ultrasound (US)/biochar (BC)/ferrate (Fe (VI)) system was firstly proposed to enhance perfluorooctanoic acid (PFOA) defluorination. It achieved 93 % defluorination optimally, higher than the sum of 77 % (28 % and 49 % for US/BC and US/Fe (VI) respectively), implying synergistic effect. Besides, the mechanism study confirmed that, this system can not only increase the specific surface area of BC and the generation of reactive oxidant species (ROS), enriching the active sites and forming new oxygen-containing functional groups, but also promote the formation of intermediate iron species. The PFOA degradation in the US/BC/Fe (VI) was probably an adsorption-degradation process, both ROS and electron transfer promoted the defluorination. Additionally, its sustainability was also demonstrated with 14 % reduced defluorination percentage after five cycles of BC. Overall, the synergistic effect of the US/BC/Fe (VI) and its enhancing mechanism for PFOA defluorination were clarified firstly, which contributes to the development of biochar for assisting polyfluoroalkyl substances degradation.

Trap-n-zap: Electrocatalytic degradation of perfluorooctanoic acid (PFOA) with UiO-66 modified boron nitride electrodes at environmentally relevant concentrations

Poly- and per-fluoroalkyl substances (PFAS) are synthetic chemicals of increasing global concern due to their toxicity and environmental persistence. Hexagonal boron nitride (h-BN) is an electrochemically active semiconductor that generates a hydrophobic electron-hole with a high affinity for the fluorinated tail of perfluorooctanoic acid (PFOA), which enhances surface interactions in aqueous solutions. We demonstrate that h-BN electrocatalytically oxidizes PFOA to shorter chains. The degradation is enhanced by modifying the h-BN surface with an adsorbent, UiO-66 (UiO-66@BN), that facilitates proximal adsorption to catalytic sites (trap-and-zap). At the environmentally relevant concentration of 100 µg/L, electrochemical trap-and-zap removes 99.5% of PFOA with 70% defluorination in 3 h at a pH 4.5. Computational results show that PFOA requires an overpotential of 1.87 V vs. SCE, which is close to the experimental overpotential. The electrical energy per order (EE/O) of UiO-66@BN is 6.1 kWh/m3, indicating that it is a competitive material for PFOA electrochemical remediation.