Removal Of Perfluorinated Compounds Research Articles

Kinetics and mechanism analysis of advanced oxidation degradation of PFOA/PFOS by UV/Fe3+ and persulfate: A DFT study

UV/Fe3+ and persulfate are two promising advanced oxidative degradation systems for in situ remediation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), yet a lack of comprehensive understanding of the degradation mechanisms. For the first time, we used density functional theory (DFT) to calculate the entire reaction pathways of the degradation of PFOA/PFOS in water by UV/Fe3+ and persulfate. In addition, we have deeply explored the different attack pathways driven by •OH and SO4−•, and found that SO4−• determines PFOA/PFOS to obtain PFOA/PFOS free radicals through single electron transfer to initiate the degradation reaction, while •OH determines the speed of PFOA/PFOS degradation reaction. Both degradation reactions were thermodynamically advantageous and kinetically feasible under calculated conditions. Based on the thermodynamic data, persulfate was found to be more favorable for the advanced oxidative degradation of Perfluorinated compounds (PFCs). Moreover, for SO4−• and •OH co-existing in the persulfate system, pH will affect the presence and concentration of these two types of free radicals, and low pH is not necessary for the degradation of PFOA/PFOS in the persulfate system. These results can considerably advance our understanding of the PFOA/PFOS degradation process in advanced oxidation processes (AOPs), which is driven by •OH and SO4−•. This study provides a DFT calculation process for the mechanism calculation of advanced oxidation degradation of other types of PFCs pollutants, hoping to elucidate the future development of PFCs removal. Further research should focus on determining the advanced oxidation degradation pathways of other types of PFCs, to support the development of computational studies on the advanced oxidation degradation of PFCs.

A Review of the Treatment Process of Perfluorooctane Compounds in the Waters: Adsorption, Flocculation, and Advanced Oxidative Process

Perfluorinated compounds (PFCs) are recognized as a new type of refractory organic pollutants. Due to the persistent environmental pollution, bioaccumulation, and biotoxicity of PFCs, they have received extensive attention in recent years. To deal with the environmental risks caused by PFCs, the pollution and distribution of PFCs in the aquatic environment are discussed in detail, mainly for the most widely used PFCs—perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS). The latest progress in the current processing technology of PFOA and PFOS is comprehensively introduced. It includes a variety of physical techniques to remove PFCs such as adsorption and flocculation. It has been confirmed that various adsorbents can play a key role in the enrichment and removal of PFCs through high specific surface area and hydrophobic interaction. In addition, traditional degradation processes are often unsatisfactory for PFCs, prompting the search for more efficient and cost-effective methods, with great progress having been made in advanced oxidation processes (AOPs) based on radical decomposition of pollutants. This review also integrates multiple advanced oxidation processes (AOPs) such as photocatalysis, electrochemical processes, ozone, the Fenton process, and ultrasound. This paper provides an overview of the various PFCs removal techniques and discusses their efficacy. It also explores future possible developments for PFCs elimination technologies for water treatment.

The fouling layers characteristics of osmotically driven membranes affect transport behaviors of reverse salt permeation and per-fluorinated compounds

Perfluorinated compounds (PFCs) adversely affect the environment in very small amounts and are extremely stable substances. This study investigated the transport phenomenon of PFCs in terms of functional groups and membrane fouling types using 10 types of PFCs and evaluated the performance of osmotically driven membranes. The experimental results confirmed that the reverse salt flux (RSF) of organic fouled membranes significantly decreased (16.2 % and 22.3 %, respectively) and the relatively loosely deposited MP fouled membranes with many empty spaces in the fouling layers maintained RSF values similar to those of virgin membranes (2 % decreased). The rejection rates of the PFCs with SO3H functional groups increased (virgin: 96.8 %; fouled: 98.6 %), whereas PFCs with COOH functional groups decreased after organic matter fouling (virgin: 99.5 %; fouled 97.6 %). The micelles formation by PFCs with SO3H group was easily blocking fouling layers and intra-particle diffusion of other PFCs with SO3H molecules interrupt. PFCs having high Kow values tends to have increased removal efficiency after the formation of MP fouling layer. These results demonstrated that the membrane fouling layers play positive roles in the RSF and PFCs removal efficiencies in osmotically driven membrane processes, which will enable the securing of safe water resources.

Evaluation of perfluorinated compounds removal performance and automatic regeneration performance by activated carbon adsorption process

Evaluation of perfluorinated compounds removal performance and automatic regeneration performance by activated carbon adsorption process

Congener- and isomer-specific Perfluorinated compounds in textile wastewater from Southeast China

Perfluorinated compounds (PFCs) are largely used in textile auxiliaries for the water/oil repellent finishing and have been listed as substances of very high concerns globally. Quantifying the generations and emissions of PFCs from textile and dyeing enterprises is of great significance to realizing the cleaner production management. In this study, congener- and isomer-specific PFCs were measured in regulation tank influent and final effluent from 48 textile plants in the Yangtze River Delta, China. The median ∑17 PFC concentrations in influent and effluent were 428.5 and 268.0 ng/L, respectively. Short- and medium-chain homologues accounted for three-quarters of the total PFCAs in these wastewater samples. Isomeric fingerprints showed an overwhelming occurrence of linear isomers rather than branched ones for PFOA, PFOS and PFHxS. This implied that PFCs in textile wastewater might not be exclusively from a 3M electrochemical fluorination (ECF) source. Raw materials played an important role in PFCs distributions since significantly higher levels of PFHpA, PFHxA, PFNA, PFDA, PFUnDA and PFTrDA were found in wastewater from chemical fibre manufacturing than from manufacturing of other materials. There was no significant discrepancy in PFCs removal rates between different treatments techniques. Although ecological risk assessment revealed an absent health risks of PFCs from effluent in the short term, the implement of textile cleaner production warrants concern due to the high volumes of water per unit fabric for processing. The widespread PFCs occurrence in textile wastewater highlighted the urgency of PFCs removal and disposal. We also encouraged the replacement of synthetic substances with natural materials, adoptions of technical improvements, and innovations such as life cycle analysis or cluster process management in the development of the textile industry.

Preparation of fluorinated covalent organic polymers at room temperature for removal and detection of perfluorinated compounds

Covalent organic polymers (COPs) are promising adsorbents for the removal and detection of various types of pollutants. However, the preparation of COPs that exhibit uniform dispersion and good appearance at room temperature is challenging. Herein, fluorinated covalent organic polymers (F-COPs) with different morphologies were synthesized through the Schiff base reaction of 4,4-diamino-p-terphenyl (DT) and 2,3,5,6-tetrafluoroterephthalaldehyde (TFA). The as-prepared F-COPs could selectively adsorb perfluorinated compounds (PFCs) owing to their fluoro-affinity, hydrophobicity, hydrogen bonding, and electrostatic attraction. The adsorption kinetics and isotherm simulation results showed that the adsorption process conformed to the second-order kinetics and the Langmuir model. The saturated adsorption capacity calculated by the Langmuir model was found to be 323–667 mg/g. The F-COPs were applied to the treatment of simulated fluorine industrial wastewater, and the PFC removal efficiencies of 92.3–100.0% were achieved. Moreover, ultra-high-performance liquid chromatography–mass spectrometry (UPLC–MS) was conducted for the detection of trace-level PFCs using F-COPs as dispersive solid-phase extraction (DSPE) adsorbents. The limits of detection were 0.05–0.13 ng/L and the limits of quantification were 0.17–0.43 ng/L. This study facilitates the synthesis of COPs at room temperature and extends the application of COPs as pretreated materials for environmental remediation and detection.

Different Adsorption Behavior between Perfluorohexane Sulfonate (PFHxS) and Perfluorooctanoic Acid (PFOA) on Granular Activated Carbon in Full-Scale Drinking Water Treatment Plants

Perfluorinated compounds (PFCs) in water have detrimental effects on human health, and the removal rate of these compounds by conventional water treatment processes is low. Given that the levels of PFCs have been regulated in many regions, a granular activated carbon (GAC) adsorption process has been used in drinking water treatment plants to maintain concentrations of PFCs, perfluorohexyl sulfonate (PFHxS), and perfluorooctanoic acid (PFOA), below 70 ng/L. However, it was found that these concentrations in the final product water in local water utilities unexpectedly increased because of inappropriate operation and maintenance methods of GAC, such as its inefficient regeneration and replacement cycle. In this study, the changes in PFC concentration were monitored and analyzed in raw and final water of two large-scale water treatment plants for eight months. Additionally, the correlation of the GAC replacement cycle with the removal efficiency of PFHxS and PFOA was investigated in a total of 30 GAC basins of two drinking water treatment plants. A lab-scale experiment with a coconut-shell-based GAC column showed the possibly different mechanism of removal between PFHxS and PFOA, indicating that the sulfonate-based PFCs may be a limiting factor in GAC replacement cycle for PFCs removal.

Removal mechanisms of perfluorinated compounds (PFCs) by nanofiltration: Roles of membrane-contaminant interactions

Perfluorinated compounds (PFCs)-membrane interactions play important roles in the removal of PFCs by membrane separation, especially in their adsorption onto membrane interfaces and membrane rejection. In this work, a loose nanofiltration (NF) membrane and a tight NF membrane were used to remove six PFCs that have different head groups and different C-F chains. The roles of typical PFCs-membrane interactions, including electrostatic repulsion, hydrophobic interactions and hydrogen bonding, on membrane adsorption and rejection were quantitatively evaluated. The membrane adsorption capacities to the six PFCs were determined by static adsorption experiments. Influences of the PFCs-membrane interactions mentioned above were quantified with six negatively charged PFCs by comparing the adsorption and rejection at neutral pH with those at the isoelectric points (IEPs) of the two membranes. Results showed that electrostatic repulsion caused that the rejections by the loose membrane and tight membrane increased by 2.2%–36.0%, and 0.8%–7.4%, respectively. Non-electrostatic interactions (hydrophobic interactions and hydrogen bonding) decreased rejections of the tight membrane and the loose membrane by 9.5%–23.6% and 1.2%–10.3%, respectively. Interactions between the PFCs and the membranes were further calculated by density functional theory (DFT). DFT analysis and Gibbs free energy changes suggest that PFCs could interact with membranes in thermodynamics. The head groups are away from the membrane surface because of electrostatic repulsion and the tail groups close to the membrane surface due to hydrophobic interactions and hydrogen bonding.

Removal of COD, NH4-N, and perfluorinated compounds from wastewater treatment plant effluent using ZnO-coated activated carbon.

This study investigated the removal of chemical oxygen demand (COD), NH4-N, and perfluorinated compounds (PFCs) in the effluent from a wastewater treatment plant (WWTP) using ZnO coated activated carbon (ZnO/AC). Results suggested that the optimal dosage of the ZnO/AC was 0.8 g/L within 240 min of contact time, at which the maximum removal efficiency of COD was approximately 86.8%, while the removal efficiencies of PFOA and PFOS reached 86.5% and 82.1%. In comparison, the removal efficiencies of NH4-N, PFBA, and PFBS were lower, at approximately 47.9%, 44.0%, and 55.4%, respectively. In addition, COD was preferentially adsorbed before PFCs and NH4-N, when the contact time ranged from 0 to 180 min, and the order of PFCs removal showed a positive correlation with C-F chain length. The kinetic study revealed that the removal of COD, NH4-N, and PFCs could be better depicted and predicted by the Lagergren quasi-second order dynamic model with high correlation coefficients, which involved liquid membrane diffusion, intraparticle diffusion, and photocatalytic reactions. The saturated ZnO/AC was finally regenerated using ultrasound for 3 h and retained excellent performance, which proved it could be considered as an effective and alternative technology.

Calcination of hydrotalcite to enhance the removal of perfluorooctane sulfonate from water

Perfluorinated compounds (PFCs), due to their thermal and chemical stability and broad usage in industry, have been detected in surface and ground water. As emerging compounds, their fate in the environment and removal from water attracted great attention in the last 10 years. In this study, we evaluated the performance of calcinated hydrotalcite (CHT) for the removal of PFCs using perfluorooctane sulfonate (PFOS) as an example. Our results showed that CHT can sorb up to 1.4 times of its mass for PFOS and the removal was fast, with equilibrium being achieved in 30 min. The PFOS removal was less sensitive to pH in pH 4–11 range. At low loading levels, only small fractions of CHT were intercalated by PFOS and the 3R polytype of hydrotalcite (HT) was largely maintained. As the PFOS uptake increased beyond 300 mg/g, intercalation of PFOS took place. The structure of HT changed to 1 layer stacking beyond 600 mg/g. Electrostatic interaction was responsible for the PFOS uptake at low loading levels and hydrophobic interaction started to play a role among PFOS molecules as its loading level increased. Crystalline PFOS decomposed at 513 °C, but its decomposition temperature decreased to 443 °C once sorbed on CHT, due to the breakdown of HT at about 390 °C. The CHT was regeneratable after calcination of PFOS-saturated HT at 450 °C for 3 h with the full PFOS removal capacity restored. The finding from this study showed the superior feature of using CHT for the removal of PFCs over other methods.

Efficient removal of perfluorinated compounds from water using a regenerable magnetic activated carbon

Adsorption by powder activated carbon (PAC) is recognized as an efficient method for the removal of perfluorinated compounds (PFCs) in water, while the poor separation of spent PAC makes it difficult for further regeneration, increasing the treatment cost significantly. In this study, an ultrafine magnetic activated carbon (MAC) consisting of Fe3O4 and PAC was prepared by ball milling to remove PFCs from water efficiently. Increasing the percentage of Fe3O4 and balling milling time decreased its adsorption capacity for perfluoroctane sulfonate (PFOS), whereas increased the magnetic separation property to some degree. The optimized MAC was prepared with a Fe3O4 to PAC mass ratio of 1:3 after ball milling for 2 h, and the adsorption equilibriums of all the four PFCs on the optimal MAC were reached within less than 2 h, with the adsorption capacities of 1.63, 0.90, 0.33 and 0.21 mmol/g for PFOS, perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS) and perfluorobutane sulfonate (PFBS), respectively. Increasing the solution pH hindered the adsorption of PFOS significantly when the pH was less than the zero potential point (around 6) of the MAC, due to the decreased electrostatic attraction. The spent MAC could be easily separated with a magnet and regenerated by a small volume of methanol, and the regenerated MAC could be reused for more than 5 time and remain stable adsorption capacity for PFOS after 3 cycles. This study provides useful insights into the removal of PFCs by separable magnetic PAC in wastewater.

Degradation of Low Concentrated Perfluorinated Compounds (PFCs) from Water Samples Using Non-Thermal Atmospheric Plasma (NTAP)

Perfluorinated compounds (PFCs) are manmade chemicals, containing the covalent C-F bond, which is among the strongest chemical bonds known to organic chemistry. Abundant use of these chemicals contaminates air, water, and soil around the world. Despite recent initiatives and legal regulations set to reduce their omnipresence, conventional water purification processes are either inefficient or very expensive, especially for low PFC contamination levels. This research is focused on the non-thermal atmospheric plasma (NTAP) decomposition of very low concentrations (<1 µg/L) of PFCs (especially perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS)), present in the wastewater produced during the process of PFCs removal from contaminated soil. The efficiency of the decomposition process was investigated for air, oxygen, and nitrogen plasma, with exposure times of 1–10 min and different plasma nozzle- and reactor sizes. Experiments demonstrated that the NTAP treatment is an efficient alternative method for degradation of more than 50% of the initial PFC concentration in the water samples, in less than 200 s. The final concentration of PFC showed strong dependency on the tested parameters. The treatment effect showed to be strongly non-linear with time, followed by the reduction of the pH-value of the treated sample, which might present a limiting factor for further PFC decomposition.

Cabot makes carbon for PFC removal

Cabot Corp. has developed specialty activated carbons to remove perfluorinated compounds (PFCs) from public drinking water systems. Once used in the manufacture of nonstick materials, such as Chemours’s Teflon, compounds such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are turning up in drinking water. The new grades of activated carbon have pore size distributions optimized for PFOA and PFOS removal. In June, competitor Calgon Carbon got a contract for a $3.5 million activated carbon system to remove the contaminants from Newburgh, N.Y.’s water.

Electrochemically enhanced removal of perfluorinated compounds (PFCs) from aqueous solution by CNTs-graphene composite electrode

Electrochemical removal of environmentally persistent perfluorinated compounds (PFCs) from aqueous solution by Ti/activated carbon fiber (ACF), Ti/Ebonex/carbon nanotubes (CNTs), and CNTs-graphene composite electrode was investigated. The results indicated that the CNTs with 20wt% graphene (CNTs-20% graphene composite electrode) exhibited the optimal capacitive behavior and electrochemical property for the removal of perfluorooctanoate (PFOA) from aqueous solution. The removal ratio and sorption capacity of PFOA on CNTs-20% graphene electrode were 96.9% and 2421.7μgg−1 after 4h of electrosorption, respectively. The sorption equilibriums of PFOA and perfluorooctane sulfonate (PFOS) by CNTs-20% graphene electrode were approximately 4.0h and 2.0h, respectively. The electrosorption rates were 9.7 times (PFOA) and 12.7 times (PFOS) higher than those by powder CNTs-20% graphene composite material, respectively. The maximal sorption capacities of PFOA and PFOS on CNTs-20% graphene electrode were 491.9mgg−1 and 555.8mgg−1, respectively. The results indicated that the incorporation of graphene into CNTs could effectively enhance the electrochemical removal of PFCs from aqueous solution. These results provide an effective and alternative method to remove PFCs from wastewater with low energy consumption and mild experimental conditions.

Preparation of a functional silica membrane coated on Fe3O4 nanoparticle for rapid and selective removal of perfluorinated compounds from surface water sample

In this study, a novel silica membrane functionalized with amino group and octyl-perfluorinated chain was prepared on the periphery of Fe3O4 nanoparticle (NP). The obtained nanocomposite (Fe3O4@SiO2-NH2&F13) exhibited good selectivity for perfluorinated compounds (PFCs) by electrostatic and fluorine-fluorine (F-F) interaction with the addition of size exclusion effect. In ethanol, the monolayer coverage of PFCs occurred on most of the binding sites and the adsorption capacity were in the range of 13.20–111.14mgg−1. In aqueous solution, due to the hydrophobicity of perfluoroalkane chain, some PFCs (C⩾8) may also stick together on the composite surface, which made the sorption amounts of these PFCs greatly enhanced. Thereafter, Fe3O4@SiO2-NH2&F13 was used for rapid and selective removal of nine PFCs from surface water sample. In 1L of spiked water samples fortified at 0.5–50ngL−1 levels, the composite showed a better removal efficiency (86.29%) for PFCs than that (58.61%) of powdered activated carbon (PAC). In addition, high concentrations (5–50mgL−1) of humic acid (HA) had no significant influence on the removal performance of the composite for PFCs. Furthermore, Fe3O4@SiO2-NH2&F13 could be reused for several times with no obvious decrease in the removal efficiency. Thus, the magnetic nanocomposite could be used as an effective adsorbent for PFC removal from aquatic environment.

Nano-Sized Cyclodextrin-Based Molecularly Imprinted Polymer Adsorbents for Perfluorinated Compounds-A Mini-Review.

Recent efforts have been directed towards the design of efficient and contaminant selective remediation technology for the removal of perfluorinated compounds (PFCs) from soils, sediments, and aquatic environments. While there is a general consensus on adsorption-based processes as the most suitable methodology for the removal of PFCs from aquatic environments, challenges exist regarding the optimal materials design of sorbents for selective uptake of PFCs. This article reviews the sorptive uptake of PFCs using cyclodextrin (CD)-based polymer adsorbents with nano- to micron-sized structural attributes. The relationship between synthesis of adsorbent materials and their structure relate to the overall sorption properties. Hence, the adsorptive uptake properties of CD-based molecularly imprinted polymers (CD-MIPs) are reviewed and compared with conventional MIPs. Further comparison is made with non-imprinted polymers (NIPs) that are based on cross-linking of pre-polymer units such as chitosan with epichlorohydrin in the absence of a molecular template. In general, MIPs offer the advantage of selectivity, chemical tunability, high stability and mechanical strength, ease of regeneration, and overall lower cost compared to NIPs. In particular, CD-MIPs offer the added advantage of possessing multiple binding sites with unique physicochemical properties such as tunable surface properties and morphology that may vary considerably. This mini-review provides a rationale for the design of unique polymer adsorbent materials that employ an intrinsic porogen via incorporation of a macrocyclic compound in the polymer framework to afford adsorbent materials with tunable physicochemical properties and unique nanostructure properties.

Reductive degradation of perfluorinated compounds in water using Mg-aminoclay coated nanoscale zero valent iron

Perfluorinated compounds (PFCs) are extremely persistent micropollutants that are detected worldwide. We studied the removal of PFCs (perfluorooctanoic acid; PFOA, perfluorononanoic acid; PFNA, perfluorodecanoic acid; PFDA and perfluorooctane sulfonate; PFOS) from water by different types of nanoscale zero-valent iron (nZVI). Batch experiments showed that an iron dose of 1 g L−1 in the form of Mg-aminoclay (MgAC) coated nZVI, at an initial pH of 3.0 effectively removed 38–96% of individual PFCs. An increasing order of removal efficiency was observed of PFOA < PFNA < PFOS ≈ PFDA. Compared to this, PFCs removal was less than 27% using a commercial air stabilized nZVI or freshly synthesized uncoated nZVI, under the same experimental conditions. The effectiveness of PFCs removal by MgAC coated nZVI was further investigated at various initial pH, nZVI dosage, temperature and age of the nZVI. A maximum removal was observed for all PFCs with high nZVI concentration, freshly synthesized nZVI, low pH and low temperature. A mass balance experiment with PFOS in a higher concentration of nZVI revealed that the removal was due to both sorption and degradation. Fluoride production partially matched the observed degradation, while no organic byproducts were detected using LC–QTOF–MS.

Cucurbiturils as fluorophilic receptors

We report the formation of strong inclusion complexes between the macrocyclic host cucurbit[7]uril (CB7) and more than 20 perfluorinated compounds (PFCs) in aqueous solution. The binding constants and structures of the complexes were determined through a combination of dye displacement titrations, 19F as well as 1H NMR spectroscopy, and quantum chemical calculations. The high affinities, for example 1.2 × 107 M− 1 for perfluorohexane and 1.1 × 108 M− 1 for perfluoro(methylcylohexane), are driven, among others, by the low polarisability of the cucurbituril cavity, which favours the binding of non-polarisable guests such as PFCs. The complexation-induced chemical shifts of the 19F resonances are downfield in cases where a conformational flexibility allows the (partial) interconversion of gauche conformations (favoured in water) to anti conformations (favoured inside the cavity of CB7). Only for conformationally rigid substrates, for example SF6 and (CF3)3COH, upfield shifts prevail. These are attributed to the low polarisability of the inner cavity, similar to the upfield shifts observed for 19F resonances upon going from highly polarisable to less polarisable solvents. Cucurbituril homologues (CB5, CB6 and CB8) were also studied and, among those, evidence for the formation of inclusion complexes was observed for CB6 as host and CF4, SF6 and CF3CH2OH as guests. Besides contributing to the fundamental understanding of fluorophilic interactions, the results have implications for PFC separation and for the efficient removal of PFCs from and the sensing of PFCs in aqueous solution.

Perfluorinated compounds contamination in tap water and bottled water in Bangkok, Thailand

Perfluorinated compounds (PFCs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) have been detected in the environment, in biota and in humans. The exposure pathways of these chemicals to humans are unclear. Tap water and bottled water are two possible pathways of PFCs occurrence in human blood. The major objectives of the study were to identify the occurrences of PFCs in tap and bottled water and to evaluate conventional water treatment processes performance on removal of PFCs. Solid phase extraction coupled with HPLC-ESI-MS/MS were used for the analysis of ten PFCs. PFCs were detected in all tap water samples and bottled water samples. The average PFOS and PFOA concentrations in tap water were 0.17 and 3.58 ng l −1 , respectively. PFOS and PFOA were not similarly distributed in all areas in the city. PFCs concentrations were higher in bottled water than in tap water. Moreover, the current treatment processes were not effective in removing PFCs in aqueous phase. Nevertheless, PFCs in particulate phase were effectively removed by primary sedimentation and rapid sand filtration. Based on the guideline from the New Jersey Department of Environmental Protection, PFOA concentrations in tap water and bottled water found in Bangkok were not expected to cause any health risks.