A comparative study of coagulation, granular- and powdered-activated carbon for the removal of perfluorooctane sulfonate and perfluorooctanoate in drinking water treatment

Per- and polyfluoroalkyl substance (PFAS) removal from soil washing water by coagulation and flocculation

Soil washing is currently attracting attention as a promising remediation strategy for land contaminated with per- and polyfluoroalkyl substances (PFAS). In the soil washing process, the contaminant is transferred from the soil into the liquid phase, producing a PFAS contaminated process water. One way to treat such process water is to use coagulation and flocculation; however, few studies are available on the performance of coagulation and flocculation for removing PFAS from such process water. This study evaluated 6 coagulants and flocculants (polyaluminium chloride (PACl), zirconium oxychloride octahydrate, cationic and anionic polyacrylamide, Polyclay 685 and Perfluor Ad®), for the treatment of a proxy PFAS contaminated washing water, spiked with PFAS concentrations found at typical Aqueous Film Forming Foam (AFFF) contaminated sites. PFAS removal efficiencies (at constant pH) varied greatly depending on the coagulants and flocculants, as well as the dosage used and the targeted PFAS. All tested coagulants and flocculants reduced the turbidity by >95%, depending on the dosage. Perfluor Ad®, a specially designed coagulant, showed the highest removal efficiency for all longer chain (>99%) and shorter chain PFAS (>68%). The cationic polyacrylamide polymer removed longer chain PFAS up to an average of 80%, whereas average shorter chain PFAS removal was lower (<30%). The two metal-based coagulants tested, PACl and zirconium, removed longer chain PFAS by up to an average of 61% and shorter chain PFAS up to 48%. Polyclay 685, a mixture of powdered activated carbon (PAC) and aluminium sulphate, removed longer chain PFAS by 90% and shorter chain PFAS on average by 76%, when very high dosages of the coagulant were used (2,000 mg/L). PFAS removal efficiencies correlated with chain length and headgroup. Shorter chain PFAS removal was dependent on electrostatic interaction with the precipitating flocs, whereas for longer chain PFAS, hydrophobic interactions between apolar functional groups and flocs created by the coagulant/flocculant, dissolved organic matter and suspended solids played a major role. The results of this study showed that by selecting the most efficient coagulant and aqueous conditions, a greater amount of PFAS can be removed from process waters in soil washing facilities, and thus included as part of various treatment trains.

Toward systematic understanding of adsorptive removal of legacy and emerging per-and polyfluoroalkyl substances (PFASs) by various activated carbons (ACs)

Per-and polyfluoroalkyl substances (PFASs) have received great attention due to their persistence, bioaccumulation and toxicity. Various activated carbons (ACs) exhibit wide variability in adsorptive performance towards PFASs. In order to gain a systematic understanding of adsorptive removal of legacy and emerging PFASs by ACs, the adsorption of ten PFASs on various ACs was comprehensively investigated. Results showed that granular activated carbon-1 (GAC-1) and powdered activated carbon-1 (PAC-1) removed more than 90% of all target PFASs. Particle size, surface charge, and micropores quantity of ACs were closely related to their performance for PFASs removal. Electrostatic interaction, hydrophobic interaction, surface complexation and hydrogen bonding were the adsorption mechanisms, with hydrophobic interaction being the predominant adsorptive force. Physical and chemical adsorption were both involved in PFAS adsorption. The removal rates of PFASs by GAC-1 decreased from 93%-100% to 15%-66% in the presence of 5 mg/L fulvic acid (FA). GAC was able to remove more PFASs under acidic medium, whereas PAC removed hydrophobic PFASs better under the neutral medium. The removal rates of PFASs by GAC-3 increased significantly from 0%-21% to 52%-97% after being impregnated with benzalkonium chlorides (BACs), demonstrating the superiority of this modification method. Overall, this study provided theoretical support for removing PFASs from water phase with ACs.

Effective PFAS degradation by electrochemical oxidation methods-recent progress and requirement

The presence of per- and poly-fluoroalkyl substances (PFASs) in water is of global concern due to their high stability and toxicity even at very low concentrations. There are several technologies for the remediation of PFASs, but most of them are inadequate either due to limited effectiveness, high cost, or production of a large amount of sludge. Electrochemical oxidation (EO) technology shows great potential for large-scale application in the degradation of PFASs due to its simple procedure, low loading of chemicals, and least amount of waste. Here, we have reviewed the recent progress in EO methods for PFAS degradation, focusing on the last 10 years, to explore an efficient, cost-effective, and environmentally benign remediation technology. The effects of important parameters (e.g., anode material, current density, solution pH, electrolyte, plate distance, and electrical connector type) are summarized and evaluated. Also, the energy consumption, the consequence of different PFASs functional groups, and water matrices are discussed to provide an insight that is pivotal for developing new EO materials and technologies. The proposed degradation pathways of shorter-chain PFAS by-products during EO of PFAS are also discussed.

Separation of Low-Molecular-Weight Organics by Water-Soluble Macrocyclic Arenes

In this study, we fabricate a series of water-soluble anionic macrocyclic arenes, including pillar[5]arene (WP5), pillar[6]arene (WP6), leaning pillar[6]arene (WLT6), and biphenyl-extended pillar[6]arene (WBpP6), which show different separation capabilities toward low-molecular-weight organics, such as short chain haloalkanes, cyclic aliphatics, and aromatics, in water. The liquid-liquid distribution experiments are carried out at room temperature. The separation factor for low-molecular-weight organics is evaluated in the extraction of equimolar mixtures. WP6 demonstrates a high extraction efficiency of up to 89% in separating toluene/methylcyclohexane mixtures. These adsorbents also have the advantages of rapid adsorption, high separation efficiency, remarkable selectivity, and good recyclability. This work not only expands the application scope of macrocyclic chemistry, but also has practical research value for organics separation and water purification.

XGBoost model as an efficient machine learning approach for PFAS removal: Effects of material characteristics and operation conditions

Due to the implications of poly- and perfluoroalkyl substances (PFAS) on the environment and public health, great attention has been recently made to finding innovative materials and methods for PFAS removal. In this work, PFAS is considered universal contamination which can be found in many wastewater streams. Conventional materials and processes used to remove and degrade PFAS do not have enough competence to address the issue particularly when it comes to eliminating short-chain PFAS. This is mainly due to the large number of complex parameters that are involved in both material and process designs. Here, we took the advantage of artificial intelligence to introduce a model (XGBoost) in which material and process factors are considered simultaneously. This research applies a machine learning approach using data collected from reported articles to predict the PFAS removal factors. The XGBoost modeling provided accurate adsorption capacity, equilibrium, and removal estimates with the ability to predict the adsorption mechanisms. The performance comparison of adsorbents and the role of AI in one dominant are studied and reviewed for the first time, even though many studies have been carried out to develop PFAS removal through various adsorption methods such as ion exchange, nanofiltration, and activated carbon (AC). The model showed that pH is the most effective parameter to predict PFAS removal. The proposed model in this work can be extended for other micropollutants and can be used as a basic framework for future adsorbent design and process optimization.

A Review on Removal and Destruction of Per- and Polyfluoroalkyl Substances (PFAS) by Novel Membranes

Per- and Polyfluoroalkyl Substances (PFAS) are anthropogenic chemicals consisting of thousands of individual species. PFAS consists of a fully or partly fluorinated carbon–fluorine bond, which is hard to break and requires a high amount of energy (536 kJ/mole). Resulting from their unique hydrophobic/oleophobic nature and their chemical and mechanical stability, they are highly resistant to thermal, chemical, and biological degradation. PFAS have been used extensively worldwide since the 1940s in various products such as non-stick household items, food-packaging, cosmetics, electronics, and firefighting foams. Exposure to PFAS may lead to health issues such as hormonal imbalances, a compromised immune system, cancer, fertility disorders, and adverse effects on fetal growth and learning ability in children. To date, very few novel membrane approaches have been reported effective in removing and destroying PFAS. Therefore, this article provides a critical review of PFAS treatment and removal approaches by membrane separation systems. We discuss recently reported novel and effective membrane techniques for PFAS separation and include a detailed discussion of parameters affecting PFAS membrane separation and destruction. Moreover, an estimation of cost analysis is also included for each treatment technology. Additionally, since the PFAS treatment technology is still growing, we have incorporated several future directions for efficient PFAS treatment.

A review on per- and polyfluorinated alkyl substances (PFASs) in microplastic and food-contact materials

Plastic, paper and cardboard are widely used as food contact materials (FCMs), due to its numerous favourable characteristics. However, they are usually coated with hazardous substances, such as per- and polyfluorinated alkyl substances (PFASs). PFASs, with its functional properties of oil- and water-repellency, can migrate from FCMs into the food and cause potential risk to human health. There are also increasing concerns about the harm that FCMs can cause to the environment. These concerns include accumulation of non-degradable plastics in the environment, generation of microplastics (MPs) and nanoplastics, and release of PFASs from FCMs. While many reviews have been conducted on PFASs in the environment, including their occurrence, fate, toxicity, biodegradation, migration in ecosystems and remediation technologies, a systematic review of PFASs in FCMs and MPs is currently lacking. In addition, our knowledge of the PFAS sorption processes on MPs is rather limited, and in particular their desorption processes. Thus, this review aims to (1) review the presence of various classes of PFASs in FCMs and their migration into food, (2) review the PFASs in MPs and summarize the sorption mechanisms, and factors that influence their sorption behaviour on MPs in the aquatic environment, and (3) identify the current research gaps and future research directions to predict the risks associated with the presence and sorption of PFASs in FCMs and MPs.

Persistent organic pollutants: The trade-off between potential risks and sustainable remediation methods

Persistent Organic Pollutants (POPs) have become a very serious issue for the environment because of their toxicity, resistance to conventional degradation mechanisms, and capacity to bioconcentrate, bioaccumulate and biomagnify. In this review article, the safety, regulatory, and remediation aspects of POPs including aromatic, chlorinated, pesticides, brominated, and fluorinated compounds, are discussed. Industrial and agricultural activities are identified as the main sources of these harmful chemicals, which are released to air, soil and water, impacting on social and economic development of society at a global scale. The main types of POPs are presented, illustrating their effects on wildlife and human beings, as well as the ways in which they contaminate the food chain. Some of the most promising and innovative technologies developed for the removal of POPs from water are discussed, contrasting their advantages and disadvantages with those of more conventional treatment processes. The promising methods presented in this work include bioremediation, advanced oxidation, ionizing radiation, and nanotechnology. Finally, some alternatives to define more efficient approaches to overcome the impacts that POPs cause in the hydric sources are pointed out. These alternatives include the formulation of policies, regulations and custom-made legislation for controlling the use of these pollutants.

Membrane-based technologies for per- and poly-fluoroalkyl substances (PFASs) removal from water: Removal mechanisms, applications, challenges and perspectives

Water purification from per- and poly-fluoroalkyl substances (PFASs), as a group of persistent and mobile fluoro-organic contaminants, is receiving increasing attention worldwide due to the ubiquitous presence of these highly toxic compounds. To reduce the risk of exposure of human life to PFASs and their dispersion in the environment, various techniques, primarily based on membrane technologies, have been rapidly developed. Here we critically review and analyze the current state-of-the-art of membrane-based techniques for PFASs removal, including direct membrane filtrations, adsorption-based membranes, and hybrid membrane processes. Membranes performance, treatment efficiencies, characteristic parameters and mechanisms for PFASs removal are discussed in detail. We highlight and discuss advantages and limitations, as well as challenges and prospects of individual membrane-based PFASs treatments, pointing towards the practical and sustainable application of these technologies.

GenX is not always a better fluorinated organic compound than PFOA: A critical review on aqueous phase treatability by adsorption and its associated cost

Hexafluoropropylene oxide dimer acid (GenX) has been marketed as a substitute for perfluorooctanoic acid (PFOA) to reduce environmental and health risks. GenX and PFOA have been detected in various natural water sources, and adsorption is recognized as a typical treatment process for PFOA removal. In this paper, comparisons of GenX and PFOA adsorption are evaluated, including adsorption potential, adsorption mechanisms, and associated costs. A detailed literature review suggests that anion-exchange resins are more effective in removing GenX than activated carbon. GenX removal efficiency through activated carbon (30%) is lower than that of PFOA (80-95%), while GenX and PFOA removal efficiencies by anion exchange resins are similar (99%). Unconventional adsorbents, such as ionic fluorogels and covalent organic frameworks can effectively remove GenX from water. The review reveals that GenX adsorption is more challenging, requiring almost 4 times the treatment cost of its predecessor, PFOA. Annual operation and maintenance costs for GenX adsorption (initial concentration of GenX and PFOA = 0.2 µg.L^-1) by GAC for treating 10,000 m³ per day is almost US$1,000,000 per year, but only around US$240,000 per year for PFOA. Desorption of GenX in the presence of PFOA highlights GenX's inferior treatability by adsorption. It is believed that GenX is a more environmentally friendly compound than PFOA, but this environmental friendliness comes with the price.

Sequestration and potential release of PFAS from spent engineered sorbents

Per- and poly-fluoroalkyl substances (PFAS) have contaminated land and water at numerous sites worldwide that now require remediation. The most common approach for treating contaminated water currently relies on removal of PFAS by sorption. The spent sorbents loaded with PFAS can potentially be disposed of at landfills, provided the sorbed contaminants remain sequestered and certain risk criteria are met. Hence, it is essential that remediation sorbents (i) rapidly adsorb a large variety of PFAS under varying water chemistry conditions, and (ii) do not release the adsorbed PFAS in due course. This review aims at establishing the current state of knowledge about the potential release of PFAS that may occur during and after treatment. The scientific literature currently provides data for a very restricted range of long-chain PFAS. Our knowledge of the dynamics of PFAS adsorption processes on engineered sorbents is limited, and even less is known about their desorption processes. The sorption of PFAS can be strongly affected by changes in the solution pH, ionic strength and dissolved organic matter content, and the process is also subject to complex competition mechanisms in the presence of other PFAS as well as organic contaminants and inorganic salts. Several studies suggest that changes in one or several of these factors may trigger the release of PFAS from engineered sorbents. This phenomenon is more likely to occur for PFAS with shorter carbon chain lengths (<C8), at high pH and in the presence of other PFAS or other anionic sorbates. The release of PFAS from spent sorbent materials, stored or deposited under conditions that vary over time, is highly undesirable, as they can potentially become a secondary source of PFAS in the environment. Our analysis identifies a number of knowledge-gaps that should be urgently addressed in order to design sustainable remediation solutions, including an improved management of spent sorbent materials.

Removal of per- and polyfluoroalkyl substances (PFAS) from water by ceric(iv) ammonium nitrate

Removing per- and polyfluoroalkyl substances (PFASs) from water by ceric ammonium nitrate (CAN).

The Adsorption Selectivity of Short and Long Per- and Polyfluoroalkyl Substances (PFASs) from Surface Water Using Powder-Activated Carbon

Nine per- and polyfluoroalkyl substances (PFASs), including six perfluoroalkyl carboxylic acids (PFCAs) and three perfluoroalkyl sulfonic acids (PFSAs), were tested to find their adsorption selectivity from surface water and the feasibility of the powder activated carbon (PAC) process between the perchlorination and coagulation processes by operating parameters such as mixing intensity, dosage, contact time, initial pH, and concentration of perchlorination. The removal efficiency of four types of PAC revealed that the coal-based activated carbon was clearly advanced for all of the PFASs, and the thermal regenerated PAC did not exhibit a significant reduction in adsorption capacity. The longer carbon chain or the higher molecular weight (MW) obtained a higher adsorption capacity and the MW exhibited a more proportional relationship with the removal efficiency than the carbon chain number, regardless of the PFCA and PFSA species. Approximately 80% and 90% equilibria were accomplished within 60 and 120 min for the long chain carbon PFAS, respectively, while for the short chain PFAS, 240 min was required to reach 85% equilibrium. The effect of mixing intensity (rpm) was not considered for the removal of the PFAS, although it was relatively influenced in the short PFAS species. Due to the surface charge of the PAC and the properties of protonation of the PFASs, the acid condition increased the PFASs’ adsorption capacity. The prechlorination decreased the removal efficiency, and the reduction rate was more significantly influenced for the short chain PFAS than for the long chain PFAS.

Long-term investigation on the removal of perfluoroalkyl substances in a full-scale drinking water treatment plant in the Veneto Region, Italy

Drinking water contamination by perfluoroalkyl and polyfluoroalkyl substances (PFASs) is an issue of relatively recent concern. The literature indicates that anion exchange resins and granular activated carbon (GAC) are suitable technologies for removing these compounds. While several laboratory-scale and pilot-scale experiments have been conducted to study activated carbon adsorption/desorption mechanisms of a number of PFASs, little data on full-scale plants are available. This work examines a real case of groundwater contamination by PFASs in an area of approximately 200 km². The performance of the main drinking water treatment plant in the area (flowrate = 30,000 m³/d; 100,000 people served), which is equipped with GAC filters, was analysed. Approximately 17,000 analytical data points from a working period of five years were processed. Perfluorobutyric acid (PFBA) was the first compound to attain breakthrough, followed by perfluoropentanoic acid, perfluorohexanoic acid, perfluorobutanesulfonic acid, and perfluorooctanoic acid (PFOA). The adsorption capacity and treated bed volumes at complete breakthrough (saturation) were calculated, and ranged from 1.71 g/t and 7100 (PFBA) to 24.6 g/t and 50,900 (PFOA), with the total organic carbon concentration in the groundwater ranging from <0.1 to 0.5 mg/L. The overall adsorption capacity was approximately 40 g of total PFASs/t. The breakthrough behaviour of PFASs was correlated with the CF chain length, the type of hydrophilic head (either carboxyl or sulfonic), and the n-octanol/water partition coefficients logP and logD. The results corroborate the findings of previously published bench-scale and pilot-scale experiments.

Removal of poly- and perfluoroalkyl substances (PFAS) from water by adsorption: Role of PFAS chain length, effect of organic matter and challenges in adsorbent regeneration

Poly- and perfluoroalkyl substances (PFAS) are a wide group of environmentally persistent organic compounds of industrial origin, which are of great concern due to their harmful impact on human health and ecosystems. Amongst long-chain PFAS, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are the most detected in the aquatic environment, even though their use has been limited by recent regulations. Recently, more attention has been posed on the short-chain compounds, due to their use as an alternative to long-chain ones, and to their high mobility in the water bodies. Therefore, short-chain PFAS have been increasingly detected in the environmental compartments. The main process investigated and implemented for PFAS removal is adsorption. However, to date, most adsorption studies have focused on synthetic water. The main objective of this article is to provide a critical review of the recent peer-reviewed studies on the removal of long- and short-chain PFAS by adsorption. Specific objectives are to review 1) the performance of different adsorbents for both long- and short-chain PFAS, 2) the effect of organic matter, and 3) the adsorbent regeneration techniques. Strong anion-exchange resins seem to better remove both long- and short-chain PFAS. However, the adsorption capacity of short-chain PFAS is lower than that observed for long-chain PFAS. Therefore, short-chain PFAS removal is more challenging. Furthermore, the effect of organic matter on PFAS adsorption in water or wastewater under real environmental conditions is overlooked. In most studies high PFAS levels have been often investigated without organic matter presence. The rapid breakthrough of PFAS is also a limiting factor and the regeneration of PFAS exhausted adsorbents is very challenging and needs more research.

Treatment train approaches for the remediation of per- and polyfluoroalkyl substances (PFAS): A critical review

Per- and polyfluoroalkyl substances (PFAS) have recently drawn great attention due to their ubiquitous presence in aquatic environments and potential toxicity to human health and the environment. A number of recent studies have demonstrated that "passive" removal approaches, such as adsorption, filtration, and reverse osmosis or "active" degradation technologies, such as enhanced photolysis, electrochemical oxidation, and sonochemical destruction, are all able to individually conduct remedial measures for PFAS contamination at some level. However, drawbacks, specifically high energy consumption, low cost-efficiency, and extreme operating conditions, are commonly observed from these studies which significantly suppress the future for commercialization of these innovative technologies. Since 2015, a new trend of PFAS remediation has emerged that uses multiple synergetic technologies simultaneously (known as treatment train processes) to effectively achieve in-situ remediation of PFAS. This paper provides new insight of the recently reported treatment train studies selected from approximately 150 different publications with regards to the remediation of PFAS and discusses their innovative designs, remediation performances, present limits, and possible improvements. Based on a comprehensive review of the current treatment train studies, this review work proposes a new design that consists of three individual technologies, namely, nanofiltration, electrochemical anodic oxidation, and electro-Fenton degradation, to maximize economic and environmental benefits of PFAS remedial measures.

A case study of organic micropollutants in a major Swedish water source - Removal efficiency in seven drinking water treatment plants and influence of operational age of granulated active carbon filters

A wide range of organic micropollutants (n = 163) representing several compound categories (pharmaceuticals, pesticides, per- and polyfluorinated alkyl substances, flame retardants, phthalates, food additives, drugs and benzos) were analysed in water samples from the Göta Älv river (Sweden's second largest source water). The sampling also included raw water and finished drinking water from seven drinking water treatment plants and in addition a more detailed sampling at one of the treatment plants after six granulated active carbon filters of varying operational ages. In total, 27 organic micropollutants were detected, with individual concentrations ranging from sub ng L^-1 levels to 54 ng L^-1. The impact of human activities along the flow path was reflected by increased concentrations downstream the river, with total concentrations ranging from 65 ng L^-1 at the start of the river to 120 ng L^-1 at the last sampling point. The removal efficiency was significantly (p = 0.014; one-sided t-test) higher in treatment plants that employed granulated active carbon filters (n = 4; average 60%) or artificial infiltration (n = 1; 65%) compared with those that used a more conventional treatment strategy (n = 2; 38%). The removal was also strongly affected by the operational age of the carbon filters. A filter with an operational age of 12 months with recent addition of ~10% new material showed an average removal efficiency of 92%, while a 25-month old filter had an average of 76%, and an even lower 34% was observed for a 71-month old filter. The breakthrough in the carbon filters occurred in the order of dissolved organic carbon, per- and polyfluorinated alkyl substances and then other organic micropollutants. The addition of fresh granulated active carbon seemed to improve the removal of hydrophobic organic compounds, particularly dissolved organic carbon and per- and polyfluorinated alkyl substances.

Enhanced degradation of perfluorooctanoic acid by a genome shuffling-modified Pseudomonas parafulva YAB-1

Perfluorooctanoic acid (PFOA) as an emerging persistent organic pollutant is hard to be degraded by conventional methods because of its stable physical and chemical properties. Microbial transformation is an attractive remediation approach to prevent and clean up PFOA contamination. To date, several strains of wild microbes have been reported to have limited capacity to degrade PFOA, selection of superior strains degrading PFOA become urgently necessary. Here, we report the application of genome shuffling to improve the PFOA-degrading bacterium Pseudomonas Parafulva YAB-1. The initial mutant populations of strain YAB1 were generated by nitrosoguanidine and ultraviolet irradiation mutagenesis respectively, resulting in mutants YM-9 and YM-19 with slightly improved PFOA-degrading ability. YM-9 and YM-19 were used as the starting strains for three rounds of recursive protoplast fusion. The positive mutants were screened on inorganic salt medium plates containing different concentrations of PFOA and selected based on their PFOA degradability in shake-flask fermentation test. The best performing recombinant F3-52 was isolated after three rounds of genome shuffling. In batch fermentation, the PFOA degradation rate of mutant F3-52 was up to 58.6%, which was 1.8-fold higher than that of the parent strain YAB1, and 1.6-fold higher than the initial mutants YM-9 and YM-19. Pass-generation test indicated that the heredity character of F3-52 was stable. The results demonstrated that genome shuffling was an efficient method for improving PFOA degradation of Pseudomonas Parafulva YAB1. The bred mutant F3-52 with 58.6% PFOA-degrading rate could be used for the environmental control of PFOA pollutant.

Regulation of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonic Acid (PFOS) in Drinking Water: A Comprehensive Review

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are receiving global attention due to their persistence in the environment through wastewater effluent discharges and past improper industrial waste disposal. They are resistant to biological degradation and if present in wastewater are discharged into the environment. The US Environmental Protection Agency (USEPA) issued drinking water Health Advisories for PFOA and PFOS at 70 ng/L each and for the sum of the two. The need for an enforceable primary drinking water regulation under the Safe Drinking Water Act (SDWA) is currently being assessed. The USEPA faces stringent legal constraints and technical barriers to develop a primary drinking water regulation for PFOA and PFOS. This review synthesizes current knowledge providing a publicly available, comprehensive point of reference for researchers, water utilities, industry, and regulatory agencies to better understand and address cross-cutting issues associated with regulation of PFOA and PFOS contamination of drinking water.

Occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in Source Water and Their Treatment in Drinking Water

Per-and polyfluoroalkyl substances (PFAS) occurrence in drinking water and treatment methods for their removal are reviewed. PFAS are fluorinated substances whose unique properties make them effective surface-active agents with uses ranging from stain repellants to fire-fighting foams. In response to concerns about drinking water contamination and health risks from PFAS exposure, the United States Environmental Protection Agency published Health Advisories (HAs) for perfluorooctanoic acid and perfluorooctane sulfonic acid. The occurrence of six PFAS in drinking water has been reported in the Third Unregulated Contaminant Monitoring Rule (UCMR3), and subsequent analysis of the dataset suggested that four percent of water systems reported at least one detectable PFAS compound and 1.3 percent of water systems reported results above the HAs. Many treatment technologies have been evaluated in the literature, with the most promising and readily applied treatment technologies being activated carbon, anion exchange resins, and high-pressure membrane systems. From these data and literature reports, research and data gaps were identified and suggestions for future research are provided.

Per- and polyfluoroalkyl substances in source and treated drinking waters of the United States

Contaminants of emerging concern (CECs), including per- and polyfluoroalkyl substances (PFAS), are of interest to regulators, water treatment utilities, the general public and scientists. This study measured 17 PFAS in source and treated water from 25 drinking water treatment plants (DWTPs) as part of a broader study of CECs in drinking water across the United States. PFAS were quantitatively detected in all 50 samples, with summed concentrations of the 17 PFAS ranging from <1 ng/L to 1102 ng/L. The median total PFAS concentration was 21.4 ng/L in the source water and 19.5 ng/L in the treated drinking water. Comparing the total PFAS concentration in source and treated water at each location, only five locations demonstrated statistically significant differences (i.e. P < 0.05) between the source and treated water. When the perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) concentrations in the treated drinking water are compared to the existing US Environmental Protection Agency's PFOA and PFOS drinking water heath advisory of 70 ng/L for each chemical or their sum one DWTP exceeded the threshold. Six of the 25 DWTPs were along two large rivers. The DWTPs within each of the river systems had specific PFAS profiles, with the three DWTPs from one river being dominated by PFOA, while three DWTPs on the second river were dominated by perfluorobutyric acid (PFBA).

Photodegradation of perfluorooctanoic acid by graphene oxide-deposited TiO2 nanotube arrays in aqueous phase

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant in the environment with serious health risks including endocrine-disrupting characteristics, immunotoxicity, and causing developmental defects. The photocatalytic deposition has proven to be an inexpensive, effective, and sustainable technology for the removal of PFOA in the aqueous phase. Most investigations are conducted in ultrapure water at concentrations higher than those detected in actual water systems. A few studies deal with the toxicity of treated water. In this research, the photocatalytic degradation of PFOA, including photo-oxidative and photo-reductive degradation, is reviewed comprehensively. Compared to photo-oxidation, photo-reduction is more suitable for PFOA removal since it favors defluorination of PFOA and complete mineralization. We used graphene oxide/TiO₂ nanotubes array for photocatalytic degradation of PFOA. The effects of key parameters on the photocatalytic degradation and defluorination processes of PFOA, such as initial PFOA concentration, initial pH of the solution, an initial temperature of the solution, and external bias constant potential, are addressed. We observed that at pH 3 the PFOA degradation was around 83% in 4 h, and at 75 °C almost complete PFOA degradation was observed in 2.5 h. In photoelectrocatalytic process at 2.0 V external bias 97% of PFOA was degraded in 4 h. The mechanisms of the PFOA photodegradation process are also discussed in detail.

Metal nanoparticles by doping carbon nanotubes improved the sorption of perfluorooctanoic acid

Due to considerable application of perfluorooctanoic acid (PFOA) and its refractory degradation, the widespread distribution of PFOA has already resulted in its' risks to environment and organisms. However, the intrinsic characteristic of pristine multi-walled carbon nanotubes (MWCNTs) limited their application for removing PFOA from aqueous medium. Therefore, three nano-metals (nano-crystalline iron, copper and zinc) grafted MWCNTs were synthesized and characterized by BET-N₂, TEM, FTIR, XPS and XRD as well as MWCNTs (as the control treatment) in this study. The results showed that nano metals were well grafted on the surface of MWCNTs. Adsorption were investigated by using radioactive labeled PFOA (¹⁴C-PFOA) to quantify the trace PFOA. Adsorption kinetics showed the adsorption of PFOA on the metal doped MWCNTs (MDCNTs) was controlled by intra-particle diffusion. Adsorption isotherms showed the sorption amounts on the MDCNTs were higher than the control. This attributed much to the hydrophobic interaction, electrostatic interaction and the formation of the inner sphere complexes. Ionic strength (0-100 mM) and ionic species (Ca²⁺) had little effects on the sorption of MDCNTs. PFOA adsorption on MDCNTs strongly depended on pH value in the medium. These results provide an innovative approach for removing trace PFOA from liquid medium.

Improved sorption of perfluorooctanoic acid on carbon nanotubes hybridized by metal oxide nanoparticles

Multi-walled carbon nanotubes (MWCNTs) are often used as adsorbent because of their strong adsorption capacity. However, due to the nature of MWCNTs, their ability to adsorb perfluorooctanoic acid (PFOA), a highly hydrophobic pollutant, is low. In this study, MWCNTs were modified by three nano metal oxides (nano iron oxide, copper oxide, and zinc oxide). The pristine (as the control) and modified MWCNTs were characterized by BET-N₂, TEM, FTIR, XPS, and XRD, which showed that nano metal oxides were well hybridized on the surface of MWCNTs. Radioactive-labeled PFOA (¹⁴C-PFOA) was used to quantify it at trace level. Adsorption kinetics showed that intra-particle diffusion was the control step of PFOA adsorbing on metal oxides hybridized MWCNTs (MOHCNTs). Adsorption capacity of PFOA on the MOHCNTs was higher than that on the control due to electrostatic and hydrophobic interactions. In addition, PFOA formed inner-sphere complexes with metal oxide nanoparticles via ligand exchange. The alteration of PFOA adsorption capacity by increasing ionic strength was attributed to the aggregation degree of MWCNTs, electrostatic shielding, and/or salting out effect. The presence of Ca²⁺ increased the adsorption, owing to not only its higher electrostatic shielding ability than Na⁺ but also its formation of bridge between PFOA and MOHCNTs. PFOA adsorption on MOHCNTs strongly depended on medium pH value. These results provide an innovative approach for removing trace PFOA from liquid medium.

Impact of biological filtrations for organic micropollutants and polyfluoroalkyl substances removal from secondary effluent

The impact of biological activated carbon (BAC), sand filtration (SF) and biological aerated filter (BAF) for removal of the selected organic micropollutants and polyfluoroalkyl substances (PFASs) from secondary effluent was studied. BAC led to greater removal of dissolved organic carbon (43%) than BAF (30%) which in turn was greater than SF (24%). All biological filtration systems could effectively remove most of the selected organic micropollutants, and there was a greater removal of these micropollutants by BAC (76-98%) than BAF (70-92%) or SF (68-90%). It was found that all treatment was effective for removal of the hydrophobic (log D > 3.2) and readily biodegradable organic micropollutants. The major mechanism for the removal of these molecules was biodegradation by the micro-organism and sorption by the biofilm. Compared to organic micropollutants removal, there was a lower removal of PFASs by all treatments, and BAF and SF had a considerably lower removal than BAC treatment. The better removal for all molecule types by BAC was due to additional adsorption capacity by the activated carbon. This study demonstrated that the BAC process was most effective in removing organic micropollutants present in the secondary effluent.