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

Advances in PFAS electrochemical reduction: Mechanisms, materials, and future perspectives

Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic chemicals that pose significant risks to both human and environmental health due to their widespread use and stability. Traditional remediation methods, such as adsorption and filtration, concentrate PFAS without breaking them down. Alternative methods, such as pyrolysis, chemical oxidation, and photodegradation, often require costly and complex conditions. Electrochemical technology is a promising alternative for PFAS removal. In particular, electrochemical reduction has been emerging in recent years as a promising alternative to promote C-F dissociation and H/F exchange reactions, thus generating less fluorinated compounds. This review summarizes the advances in technologies for PFAS electrochemical reduction, with proposed electrochemical reduction mechanisms, the factors that influence the removal of PFAS, and the challenges and future directions associated with these methods. Novel materials, such as nanocatalysts, molecularly inspired networks, or 2D/3D materials, are stable in aqueous environments and exhibit high electrochemical activity toward C-F bond dissociation. In addition, the above materials show potential for scalable applications in PFAS treatment, although further research is needed to optimize their performance. This review also aims to understand the opportunities and challenges in PFAS electrochemical reduction, offering insights for future research and development.

Review on the sources, distribution and treatment of per- and polyfluoroalkyl substances in global groundwater

Per- and polyfluoroalkyl substances (PFAS) have garnered increasing global attention due to their widespread occurrence in groundwater and the potential health risks to humans. This review aimed to clarify the occurrence and treatment of PFAS in groundwater by summarizing literature published in the Web of Science Core Collection from January 2000 to April 2024. Information on 461 reported PFAS-contaminated groundwater sites was compiled, revealing key characteristics of pollution sources and concentrations. The data indicated that firefighting training activities were a major source of PFAS groundwater contamination, accounting for 41 % of cases, followed by other fluorinated industrial activities, landfill leachate, and wastewater leakage. Non-point sources, such as atmospheric deposition, contributed to a lesser extent. The concentrations distribution of 25 PFAS showed a chain-length dependency, with short-chain PFAS generally exhibiting higher concentrations than long-chain PFAS. Additionally, the review systematically examined the application of separation methods and destructive methods at both laboratory and pilot/field-scales for PFAS-contaminated groundwater. Resins were favored for ex-situ treatment, whereas colloidal activated carbon (CAC) was more commonly used for in-situ treatment. In-situ direct injection of CAC was considered a highly promising approach for remediating PFAS source zones and plumes, offering advantages such as minimal surface disruption, high adsorption capacity and long-term effectiveness. Finally, the research focus and development trends in categories and treatment methods for PFAS in groundwater were noted. Overall, this review identified research gaps in the occurrence and treatment of PFAS in groundwater, and suggested further optimization of CAC-based methods to address the challenges of PFAS-contaminated groundwater.

Efficient Photocatalytic Degradation of Highly Concentrated Perfluorooctanoic Acid by Bi Self-Doped Bi2MoO6

Bi self-doped Bi2MoO6 was synthesized by a solvothermal method. The introduction of Bi enhanced the absorption of visible light by the catalyst, and the Bi could act as an electron transfer site to facilitate the separation of photogenerated carriers and enhance the photocatalytic activity of the catalyst for the degradation of PFOA. The oxidation of PFOA by ·O2- as the main reactive oxygen species of degradation facilitated its degradation. Under full spectrum illumination for 40 min, the degradation rate of PFOA (100 mg/L) by Bi3MoO6 reached 88.1%, which is 3 times that of the original Bi2MoO6. The degradation amount reached 88.1 mg·gcat-1, and the degradation rate was 2.20 mg·gcat-1·min-1. This work provides new ideas for the modification of catalysts.

Critical role of pore size on perfluorooctanoic acid adsorption behaviors in carbonaceous sorbents

Per- and polyfluoroalkyl substances (PFAS) are an emergent threat to the environment due to their toxic, carcinogenic, and environmentally persistent nature. Commonly, these harmful micropollutants are removed from contaminated water sources through adsorption by porous sorbents such as activated carbon. While studies suggest a relationship between sorbent pore size and their PFAS remediation performance, the underlying mechanisms-particularly those related to sorbate morphology-have not been elucidated through direct experimental observations. This work investigates how pore size in carbonaceous sorbents impacts the morphology of adsorbed perfluorooctanoic acid (PFOA) aggregates and their sorption behavior, using microporous and mesoporous carbons as models. Contrast-matching small-angle neutron scattering (CM-SANS) is used to determine the structure of adsorbed PFOA molecules, supported by molecular dynamics simulations and physisorption experiments. Our findings reveal that the larger pore sizes in mesoporous sorbents enable the formation of PFOA assemblies during adsorption, which is hindered in microporous sorbents. Collectively, this work provides direct insights into the adsorption and assembly mechanisms of PFAS molecules within confined pores, offering important insights for the rational design of effective remediation systems.

Complete Aqueous Defluorination of GenX (Hexafluoropropylene Oxide Dimer Acid Anion) by Pulsed Electrolysis with Polarity Reversal

Per- and polyfluoroalkyl substances (PFAS) are extremely stable chemicals that are essential for modern life and decarbonization technologies. Yet PFAS are persistent pollutants that are harmful to human health. Hexafluoropropylene oxide dimer acid (GenX), a replacement for the PFAS chemical perfluorooctanoic acid, continues to pollute waterways. In this study, we report the complete defluorination of GenX through electrocatalysis in aqueous LiOH electrolytes, utilizing high surface area anodes consisting of pulsed laser in liquid synthesized [NiFe]-(OH)₂ nanocatalysts on hydrophilic carbon fiber paper. Additional experiments with industrial nickel-iron alloy demonstrated exceptional stability for >100 hours. Including a brief interval of reversed polarity in pulsed electrolysis and optimizing the pulse train sequence enabled the complete defluorination of GenX. Our facile approach employs only nonprecious materials, does not require bisulfate or other auxiliary chemical agents that are consumed, and thus provides a promising strategy for alleviating the environmental impact of PFAS pollutants.

Matrix Effects on Electrochemical Oxidation of Per- and Polyfluoroalkyl Substances in Sludge Centrate

This study investigated the electrochemical oxidation of per- and polyfluoroalkyl substances (PFAS) using a Ti4O7 anode in centrate from sludge dewatering. Synthetic solutions containing perfluorooctanoic acid (PFOA), other PFAS, and inorganic constituents (phosphate, ammonium, chloride, carbonate, and acetate salts) found in centrate were studied to assess their impact on the oxidation process. PFOA removal decreased from 95% in a stable electrolyte (NaClO4) to 81% in a Na2HPO4 electrolyte and 30% in a solution mimicking concentrated centrate. X-ray photoelectron spectroscopy detected phosphate and nitrogen species on the electrode surface. At potentials required to oxidize PFAS (>3.0 V/SHE), phosphate and ammonium were oxidized to radicals that blocked electrode sites, inhibiting PFAS removal and shifting PFOA oxidation from first-order kinetics. The kinetics were accurately modeled using a Langmuir-Hinshelwood approach with a transient inhibition term. Results suggested that phosphate, ammonium, and bicarbonate ions reduced hydroxyl radical availability, thereby limiting PFOA defluorination. In concentrated centrate, 95% of the chemical oxygen demand and 93% of total PFAS were removed after 233 s of electrolysis at 30 mA cm-2. However, partial degradation of perfluorohexanoic acid and accumulation of perfluoroheptanoic acid, attributed to inorganic electrode fouling, suggested the need for a multistage reactor system for more complete PFAS mineralization.

Iron Doping of hBN Enhances the Photocatalytic Oxidative Defluorination of Perfluorooctanoic Acid

There is a growing need to effectively eliminate perfluorooctanoic acid (PFOA) from contaminated water, which requires extensive defluorination. Photocatalysis offers potential for PFOA degradation under ambient conditions without the need for treatment chemicals. However, photocatalytic treatment generally results in limited defluorination and, thus, incomplete elimination of potential toxicity and liability. This underscores the need to advance mechanistic understanding of the factors limiting PFOA oxidative defluorination. Here, we tested the hypothesis that direct electron transfer from PFOA to transition metals enhances photocatalytic defluorination. We developed a novel, facile approach to simultaneously functionalize and dope hexagonal boron nitride (hBN) (which is known to effectively catalyze photocatalytic PFOA oxidation) with Fe(III), using deep-eutectic solvents (DES). Addition of Fe(III) to synthesize Fe-hBN created new active sites for PFOA oxidation and doubled the defluorination extent (>40% fluoride release from initial 50 mg L-1 PFOA) compared to undoped hBN in 4 h reactions under 254 nm irradiation (64.4 W m-2). The mechanism of defluorination was elucidated through scavenger experiments that show the importance of photocatalytically generated electron holes for initiating PFOA degradation. Experiments also suggest that Fe(III) played a key role in PFOA removal, contributing to the improved extent of defluorination over undoped hBN. Density functional theory indicates that Fe(III) sites enable electrostatic adsorption of PFOA to the catalyst surface, enhance charge transfer, and promote hole localization to improve charge carrier separation, which is essential for oxidative defluorination of PFOA. This mechanistic insight informs catalytic material design to enhance oxidative defluorination processes.

Thermochemical Recycling and Degradation Strategies of Halogenated Polymers (F-, Cl-, Br-): A Holistic Review Coupled with Mechanistic Insights

Handling the waste associated with halogenated polymers is a daunting task due to the well-documented emission of halogen-bearing toxicants during the disposal or recycling operation. According to the Stockholm Convention treaty, most of these products are classified as persistent organic pollutants due to their potential health hazards. This review aims to provide a holistic overview of the recent updates for treating halogenated polymeric waste through physical, chemical and biological approaches. In the line of inquiry, critical analysis of the obstacles and prospects associated with each degradation technique on the halogenated polymer has been performed, assessing based on the degradation efficiency, treatment upscaling, pollution control, and feasibility. Though many treatments show promising results, they also entail drawbacks. Thermal treatment exploiting various metal oxides, especially calcium additives, is considered the most executable technique for halogenated polymer valorization coupled with mineralization/metal extraction due to its intuitive operational feasibility and potential scalability. Strategies for combating the soaring halogenated polymeric wastes summarized herein tap into promoting a circular economy approach for their sustainable disposal and recycling.

Complete aqueous defluorination of PFAS in aqueous film-forming foam (AFFF) by pulsed electrolysis with tailored potential modulation

Per- and polyfluoroalkyl substances (PFAS) are harmful and persistent global water contaminants. AFFF, a foam-forming aqueous mixture used for firefighting, is a major source of PFAS pollution and challenging to defluorinate. We report the complete photo-assisted electrocatalytic defluorination of PFAS in AFFF with nonprecious materials. The high salt content in the aqueous LiOH electrolyte prevented foaming. Pulsed electrolysis with tailored potential modulation balanced anodic fluoride removal and the adsorption of unreacted anionic PFAS. Our findings demonstrate the effectiveness of pulsed electrocatalysis in defluorinating persistent PFAS in AFFF.

Applying a novel mechanistic framework for drinking water management to mitigate emerging contaminants

A novel framework has been developed which summarizes the efficacy of treatment technologies for emerging contaminants (ECs) based on the general mitigation mechanisms of Removal, Inactivation/Degradation, and Destruction (i.e., RIDD). The RIDD framework allows for a concise critical evaluation of the efficacy of treatment processes for their mitigation potential, and provides an efficient methodology for drinking water system managers to identify knowledge gaps related to the management of ECs in water treatment with respect to current technologies available in practice. Additionally, the RIDD framework provides an understanding of the treatment processes which provide: (1) broad spectrum treatment, (2) effective mitigation for certain categories of contaminants or under certain circumstances, or (3) little or no mitigation of ECs. In the proposed format, this information is intended to assist water managers to make more informed treatment decisions. Four categories of ECs noted in recent literature as presently concerning to drinking water utilities, including both anthropogenic and microbial contaminants, were used in this study to provide examples of RIDD framework application. In many cases, broad-spectrum treatment barriers (e.g., high-pressure membranes) are expected to provide cost-effective management of a suite of ECs, which then can be compared to the costs and practicality of additional treatment barriers for individual ECs (e.g., selective ion exchange resins or tailored biological processes). Additionally, understanding the typical performance of existing treatment processes can help assist with capital planning for alternative treatment processes or upgrades, or for developing novel treatment approaches at the watershed scale such as integrated urban water management and One Water frameworks.

Ab Initio Investigation of Per- and Poly-fluoroalkyl Substance (PFAS) Adsorption on Zerovalent Iron (Fe0)

In this study, dispersion-corrected density functional theory (DFT) calculations were employed to investigate the adsorption of per- and poly-fluoroalkyl substances (PFAS) onto zerovalent iron (Fe0). The main objective of this investigation was to shed light on the adsorption properties, including adsorption energies, geometries, and charge transfer mechanisms, for four PFAS molecules, namely, perfluorooctanesulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS), perfluorooctanoic acid (PFOA), and perfluorobutanoic acid (PFBA), on the most thermodynamically accessible Fe0 surface facets. Additionally, the DFT investigation examined the role of PFAS chain length, functional group, protonation/deprotonation state, and solvation in water in their adsorption to Fe0. Overall, the adsorption of the four PFAS molecules on various Fe0 surfaces exhibited thermodynamically favorable energetics. Nevertheless, solvation in water resulted in less exothermic adsorption energies, and the presence of preadsorbed oxygen blocked the Fe0 surface, preventing PFAS adsorption. Additionally, the inclusion of a monolayer of Ni on top of the Fe0 surface reduced the stability of PFAS adsorption compared to pristine Fe0. Results of the computational investigation were compared to experimental results from the literature for qualitative validation.

Integrating redox-electrodialysis and electrosorption for the removal of ultra-short- to long-chain PFAS

A major challenge in per- and polyfluoroalkyl substances (PFAS) remediation has been their structural and chemical diversity, ranging from ultra-short to long-chain compounds, which amplifies the operational complexity of water treatment and purification. Here, we present an electrochemical strategy to remove PFAS from ultra-short to long-chain PFAS within a single process. A redox-polymer electrodialysis (redox-polymer ED) system leverages a water-soluble redox polymer with inexpensive nanofiltration membranes, facilitating the treatment of varied chain lengths of PFAS without membrane fouling. Our approach combines both ion migration by electrodialysis (for PFAS with chain lengths ≤C4) and electrosorption strategies (for PFAS with chain lengths ≥C6) to eliminate approximately 90% of ultra-short-, short-chain, and long-chain PFAS. At the same time, we achieve continuous desalination of the source water down to potable water level. The redox-polymer ED exhibits remarkable PFAS removal in real source water scenarios, including from matrices with 10,000 times higher salt concentrations, as well as secondary effluents from wastewaters. Additionally, the removed PFAS is mineralized with a defluorination performance between 76-100% by electrochemical oxidation, highlighting the viability of integrating the separation step with a reactive degradation process.

Emerging eco-friendly technologies for remediation of Per- and poly-fluoroalkyl substances (PFAS) in water and wastewater: A pathway to environmental sustainability

Per- and polyfluoroalkyl substances (PFAS) are rampant, toxic contaminants from anthropogenic sources, called forever chemicals for their recalcitrance. Although banned in several parts of the world for public health implications, including liver, kidney, and testicular diseases, PFAS are abundant in water sources due to easy dispersion. With chemical properties resulting from strong hydrophobic bonds, they defile many physicochemical removal methods. Though adsorption processes such as granular activated carbon (GAC) are widely used, they are marred by several limitations, including cost and secondary contamination. Thus, eco-friendly methods involving a synergy of the removal principles have been preferred for ease of use, cost-effectiveness, and near-zero effect on the environment. We present novel eco-friendly methods as the solution to PFAS remediation towards environmental sustainability. Current eco-friendly methods of PFAS removal from water sources, including electrocoagulation, membrane/filtration, adsorption, and phytoremediation methods, were highlighted, although with limitations. Novel eco-friendly methods such as microbial fuel cells, photoelectrical cells, and plasma treatment offer solutions to PFAS remediation and are quite efficient in terms of cost, result, and environmental sustainability. Overall, the successful integration of eco-friendly techniques in a seamless manner ensures the desired result. We also present a balanced position on the ecosystem impact of these ecofriendly methods, noting the successes towards environmental sustainability while exposing the gaps for further research.

Cerium added corn-based biochar as particle electrode for electrochemical oxidation industrial wastewater

Three-dimensional (3D) electrochemical oxidation has become a popular advanced oxidation technology for wastewater treatment due to its various benefits. In this study, cerium (Ce) loaded biochar (Ce/BC) was used as a particle electrode to conduct the degradation of industrial wastewater released by the chemical industry. SEM, EDS, XRD, FTIR, XPS, and BET were used to characterize the properties of Ce/BC. The effects of some variables, including Ce loading (0-5%), pH (5-9), Ce/BC dosage (12.5-50.0 g/L), and working voltage (12-20 V), were evaluated with regard to COD elimination. The kinetics of COD oxidation and the energy consumption were carefully investigated. Tert-butanol significantly reduced the removal efficiency of COD, indicating that hydroxyl radicals generated during the process rather than direct electro-oxidation were the main mechanism for COD degradation. The treatment of industrial wastewater might benefit from the use of Ce/BC as particle electrode.

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.

Soluble metal porphyrins - Zero-valent zinc system for effective reductive defluorination of branched per and polyfluoroalkyl substances (PFASs)

Nano zero-valent metals (nZVMs) have been extensively utilized for decades in the reductive remediation of groundwater contaminated with chlorinated organic compounds, owing to their robust reducing capabilities, simple application, and cost-effectiveness. Nevertheless, there remains a dearth of information regarding the efficient reductive defluorination of linear or branched per- and polyfluoroalkyl substances (PFASs) using nZVMs as reductants, largely due to the absence of appropriate catalysts. In this work, various soluble porphyrin ligands [[meso‑tetra(4-carboxyphenyl)porphyrinato]cobalt(III)]Cl·7H2O (CoTCPP), [[meso‑tetra(4-sulfonatophenyl) porphyrinato]cobalt(III)]·9H2O (CoTPPS), and [[meso‑tetra(4-N-methylpyridyl) porphyrinato]cobalt(II)](I)4·4H2O (CoTMpyP) have been explored for defluorination of PFASs in the presence of the nZn0 as reductant. Among these, the cationic CoTMpyP showed best defluorination efficiencies for br-perfluorooctane sulfonate (PFOS) (94%), br-perfluorooctanoic acid (PFOA) (89%), and 3,7-Perfluorodecanoic acid (PFDA) (60%) after 1 day at 70 °C. The defluorination rate constant of this system (CoTMpyP-nZn0) is 88-164 times higher than the VB12-nZn0 system for the investigated br-PFASs. The CoTMpyP-nZn0 also performed effectively at room temperature (55% for br-PFOS, 55% for br-PFOA and 25% for 3,7-PFDA after 1day), demonstrating the great potential of in-situ application. The effect of various solubilizing substituents, electron transfer flow and corresponding PFASs defluorination pathways in the CoTMpyP-nZn0 system were investigated by both experiments and density functional theory (DFT) calculations. SYNOPSIS: Due to the unavailability of active catalysts, available information on reductive remediation of PFAS by zero-valent metals (ZVMs) is still inadequate. This study explores the effective defluorination of various branched PFASs using soluble porphyrin-ZVM systems and offers a systematic approach for designing the next generation of catalysts for PFAS remediation.

A review of electrooxidation systems treatment of poly-fluoroalkyl substances (PFAS): electrooxidation degradation mechanisms and electrode materials

The prevalence of polyfluoroalkyls and perfluoroalkyls (PFAS) represents a significant challenge, and various treatment techniques have been employed with considerable success to eliminate PFAS from water, with the ultimate goal of ensuring safe disposal of wastewater. This paper first describes the most promising electrochemical oxidation (EO) technology and then analyses its basic principles. In addition, this paper reviews and discusses the current state of research and development in the field of electrode materials and electrochemical reactors. Furthermore, the influence of electrode materials and electrolyte types on the deterioration process is also investigated. The importance of electrode materials in ethylene oxide has been widely recognised, and therefore, the focus of current research is mainly on the development of innovative electrode materials, the design of superior electrode structures, and the improvement of efficient electrode preparation methods. In order to improve the degradation efficiency of PFOS in electrochemical systems, it is essential to study the oxidation mechanism of PFOS in the presence of ethylene oxide. Furthermore, the factors influencing the efficacy of PFAS treatment, including current density, energy consumption, initial concentration, and other parameters, are clearly delineated. In conclusion, this study offers a comprehensive overview of the potential for integrating EO technology with other water treatment technologies. The continuous development of electrode materials and the integration of other water treatment processes present a promising future for the widespread application of ethylene oxide technology.

Electrochemical Reduction of Perfluorooctanoic Acid (PFOA): An Experimental and Theoretical Approach

Perfluorooctanoic acid (PFOA) is an artificial chemical of global concern due to its high environmental persistence and potential human health risk. Electrochemical methods are promising technologies for water treatment because they are efficient, cheap, and scalable. The electrochemical reduction of PFOA is one of the current methodologies. This process leads to defluorination of the carbon chain to hydrogenated products. Here, we describe a mechanistic study of the electrochemical reduction of PFOA in gold electrodes. By using linear sweep voltammetry (LSV), an E0' of -1.80 V vs Ag/AgCl was estimated. Using a scan rate diagnosis, we determined an electron-transfer coefficient (αexp) of 0.37, corresponding to a concerted mechanism. The strong adsorption of PFOA into the gold surface is confirmed by the Langmuir-like isotherm in the absence (KA = 1.89 × 1012 cm3 mol-1) and presence of a negative potential (KA = 3.94 × 107 cm3 mol-1, at -1.40 V vs Ag/AgCl). Based on Marcus-Hush's theory, calculations show a solvent reorganization energy (λ0) of 0.9 eV, suggesting a large electrostatic repulsion between the perfluorinated chain and water. The estimated free energy of the transition state of the electron transfer (ΔG‡ = 2.42 eV) suggests that it is thermodynamically the reaction-limiting step. 19F - 1H NMR, UV-vis, and mass spectrometry studies confirm the displacement of fluorine atoms by hydrogen. Density functional theory (DFT) calculations also support the concerted mechanism for the reductive defluorination of PFOA, in agreement with the experimental values.

Aqueous and solid phase photocatalytic degradation of perfluorooctane sulfonate by carbon- and Fe-modified bismuth oxychloride

In this study, we prepared and tested a carbon-modified, Fe-loaded bismuth oxychloride (Fe-BiOCl/CS) photocatalyst for photocatalytic degradation of perfluorooctane sulfonate (PFOS). Structural analyses revealed a (110) facet-dominated sheet-type BiOCl crystal structure with uniformly distributed Fe and confirmed carbon modification of the photocatalyst. The presence of d-glucose facilitated the growth control of BiOCl particles and enhanced the adsorption of PFOS via added hydrophobic interaction. Adsorption kinetic and equilibrium tests showed rapid uptake rates of PFOS and high adsorption capacity with a Langmuir Qmax of 1.51 mg/g. When used for directly treating PFOS in solution, Fe-BiOCl/CS was able to mineralize or defluorinate 83% of PFOS (C0 = 100 μgL-1) under UV (254 nm, intensity = 21 mW cm-2) in 4 h; and when tested in a two-step mode, i.e., batch adsorption and subsequent photodegradation, Fe-BiOCl/CS mineralized 65.34% of PFOS that was pre-concentrated in the solid phase under otherwise identical conditions; while the total degradation percentages of PFOS were 83.48% and 80.50%, respectively, for the two experimental modes. The photoactivated electrons and/or hydrated electrons and superoxide radicals primarily initiated the desulfonation of PFOS followed by decarboxylation and defluorination, through a stepwise chain-subsiding mechanism. The elevated photocatalytic activity can be attributed to the effective separation of e-/h+ pairs facilitated by the (110) interlayer electrostatic field, Fe doping, and the presence of oxygen vacancies. This work reveals the potential of carbon-modified and Fe-co-catalyzed BiOCl for concentrating and degrading PFOS and possibly other persistent organic pollutants.

A review of innovative approaches for onsite management of PFAS-impacted investigation derived waste

The historic use of aqueous film-forming foam (AFFF) has led to widespread detection of per- and polyfluoroalkyl substance (PFAS) in groundwater, soils, sediments, drinking water, wastewater, and receiving aquatic systems throughout the United States (U.S.). Prior to any remediation activities, in order to identify the PFAS-impacted source zones and select the optimum management approach, extensive site investigations need to be conducted. These site investigations have resulted in the generation of considerable amount of investigation-derived waste (IDW) which predominantly consists of well purging water and drill fluid, equipment washing residue, soil, drill cuttings, and residues from the destruction of asphalt and concrete surfaces. IDW is often impacted by varying levels of PFAS which poses a substantial challenge concerning disposal to prevent potential mobilization of PFAS, logistical complexities, and increasing requirement for storage as a result of accumulation of the associated wastes. The distinct features of IDW involve the intermittent generation of waste, substantial volume of waste produced, and the critical demand for onsite management. This article critically focuses on innovative technologies and approaches employed for onsite treatment and management of PFAS-impacted IDW. The overall objective of this study centers on developing and deploying end-of-life treatment technology systems capable of facilitating unrestricted disposal, discharge, and/or IDW reuse on-site, thereby reducing spatial footprints and mobilization time.

Rapid enzymatic activity model (REAM) to decipher the toxic action of per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) have been identified as emerging contaminants and human exposure to these substances is a rising public health concern. We have developed a rapid enzymatic activity model (REAM), which can serve as a cell-free screening tool that elucidates possible mechanisms of toxic action inexpensively and quickly for these and other environmentally relevant chemicals.

Impact of supporting electrolyte on electrochemical performance of borophene-functionalized graphene sponge anode and degradation of per- and polyfluoroalkyl substances (PFAS)

Graphene sponge anode functionalized with two-dimensional (2D) boron, i.e., borophene, was applied for electrochemical oxidation of C4-C8 per- and polyfluoroalkyl substances (PFASs). Borophene-doped graphene sponge outperformed boron-doped graphene sponge anode in terms of PFASs removal efficiencies and their electrochemical degradation; whereas at the boron-doped graphene sponge anode up to 35% of the removed PFASs was recovered after the current was switched off, the switch to a 2D boron enabled further degradation of the electrosorbed PFASs. Borophene-doped graphene sponge anode achieved 32-77% removal of C4-C8 PFASs in one-pass flow-through mode from a 10 mM phosphate buffer at 230 A m-2 of anodic current density. Higher molarity phosphate buffer (100 mM) resulted in lower PFASs removal efficiencies (11-60%) due to the higher resistance of the graphene sponge electrode in the presence of phosphate ions, as demonstrated by the electrochemical impedance spectroscopy (EIS) analyses. Electro-oxidation of PFASs was more efficient in landfill leachate despite its high organic loading, with up to 95% and 75% removal obtained for perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), versus 77% and 57% removal in the 10 mM phosphate buffer, respectively. Defluorination efficiencies as determined relative to the electrooxidized fraction of PFASs indicated up to 69% and 82% of defluorination of PFOS and PFOA in 10 mM phosphate buffer, which was decreased to 16 and 29% defluorination, respectively, for higher buffer molarity (100 mM) due to the worsened electrochemical performance of the sponge. In landfill leachate, relative defluorination efficiencies of PFOS and PFOA were 33% and 45%, respectively, indicating the inhibiting effect of complex organic and inorganic matrix of landfill leachate on the C-F bond breakage. This study demonstrates that electrochemical degradation of PFASs is possible to achieve in complex and brackish streams using a low-cost graphene sponge anode, without forming toxic chlorinated byproducts even in the presence of >7 g L-1 of chloride.

Management of per- and polyfluoroalkyl substances (PFAS)-laden wastewater sludge in Maine: Perspectives on a wicked problem

This article discusses the challenges and potential solutions for managing wastewater sludge that contains per- and polyfluoroalkyl substances (PFAS), using the experience in Maine as a guide toward addressing the issue nationally. Traditional wastewater treatment, designed to remove excess organic waste and nutrients, does not eliminate persistent toxic pollutants like PFAS, instead partitioning the chemicals between discharged effluent and the remaining solids in sludge. PFAS chemistry, the molecular size, the alkyl chain length, fluorine saturation, the charge of the head group, and the composition of the surrounding matrix influence PFAS partitioning between soil and water. Land application of sludge, incineration, and storage in a landfill are the traditional management options. Land application of Class B sludge on agricultural fields in Maine peaked in the 1990s, totaling over 2 × 106 cu yd over a 40-year period and has contaminated certain food crops and animal forage, posing a threat to the food supply and the environment. Additional Class A EQ (Exceptional Quality) composted sludge was also applied to Maine farmland. The State of Maine banned the land application of wastewater sludge in August 2022. Most sludge was sent to the state-owned Juniper Ridge Landfill, which accepted 94 270 tons of dewatered sludge in 2022, a 14% increase over 2019. Between 2019 and 2022, the sum of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) concentrations in sludge sent to the landfill ranged from 1.2 to 104.9 ng/g dw. In 2022, the landfill generated 71.6 × 106 l of leachate. The concentration of sum of six PFAS in the leachate increased sixfold between 2021 and 2022, reaching 2 441 ng/l. The retention of PFAS within solid-waste landfills and the potential for long-term release of PFAS through liners into groundwater require ongoing monitoring. Thermal treatment, incineration, or pyrolysis can theoretically mineralize PFAS at high temperatures, yet the strong C-F bond and reactivity of fluorine require extreme temperatures for complete mineralization. Future alternatives may include interim options such as preconditioning PFAS with nonpolar solvents prior to immobilization in landfills, removing PFAS from leachate, and interrupting the cycle of PFAS moving from landfill, via leachate, to wastewater treatment, and then back to the landfill via sludge. Long-term solutions may involve destructive technologies such as electron beam irradiation, electrochemical advanced oxidation, or hydrothermal liquefaction. The article highlights the need for innovative and sustainable solutions for managing PFAS-contaminated wastewater sludge.