A Review of PFAS Destruction Technologies

Investigation of Real-Time Gaseous Thermal Decomposition Products of Representative Per- and Polyfluoroalkyl Substances (PFAS)

The thermal decomposition of per- and poly fluoroalkyl substances (PFAS) is poorly understood. Here, we present an innovative, comprehensive analytical method to investigate their thermal decomposition, including perfluorocarboxylic acids (PFCAs), alcohol, sulfonates, and GenX (acid dimer), focusing on identifying their breakdown products. In this study, evolved gas analysis-mass spectrometry (EGA-MS) was used for fast real-time screening to determine the significant temperatures to be investigated with the thermal desorption-pyrolysis coupled with gas chromatography-mass spectrometry (TD-Py-GC-MS), which provided detailed information about evolved PFAS and their breakdown products. This approach enabled a systematic study of perfluorocarboxylic acids (PFCAs) ranging from C3 to C9 and GenX showing volatilization, followed by degradation and formation of respective perfluorinated-1-alkenes and C5F10O perfluorinated ether (from GenX). At elevated temperatures (e.g., 600 °C), the products observed included perfluorinated butene and higher molecular-weight products, likely formed by pyrolytic polymerization of perfluorinated radicals. 1H,1H,2H,2H-perfluoro-1-decanol, i.e., 8:2 FTOH, volatilized at 100 °C; however, at higher temperatures, several novel decomposition products were observed, including perfluoro-1-decene and perfluorinated compounds suggesting the presence of the hydroxylic group. Our method offers an alternative approach to studying the thermal behavior of currently regulated and emerging PFAS with a focus on application to a wide range of matrices (laboratory grade standards or environmental samples).

PFAS in landfill leachate: Practical considerations for treatment and characterization

Per- and polyfluoroalkyl substances (PFAS) are widely used in consumer products and are particularly high in landfill leachate. The practice of sending leachate to wastewater treatment plants (WWTPs) is an issue for utilities that have biosolids land application limits based on PFAS concentrations. Moreover, landfills may face their own effluent limit guidelines for PFAS. The purpose of this review is to understand the most appropriate treatment technology combinations for mitigating PFAS in landfill leachate. The first objective is to understand the unique chemical characteristics of landfill leachate. The second objective is to establish the role and importance of known and emerging analytical techniques for PFAS characterization in leachate, including quantification of precursor compounds. Next, an overview of technologies that concentrate PFAS and technologies that destroy PFAS is provided, including fundamental background content and key operating parameters. Finally, practical considerations for PFAS treatment technologies are reviewed, and recommendations for PFAS treatment trains are described. Both pros and cons of treatment trains are noted. In summary, the complex matrix of leachate requires a separation treatment step first, such as foam fractionation, for example, to concentrate the PFAS into a lower-volume stream. Then, a degradation treatment step can be applied to the concentrated PFAS stream.

Role of LiOH in Aqueous Electrocatalytic Defluorination of Perfluorooctanoic Sulfonate: Efficient Li-F Ion Pairing Prevents Anode Fouling by Produced Fluoride

Per- and polyfluoroalkyl substances (PFAS) pose a significant environmental and health threat due to their high toxicity, widespread use, and persistence in the environment. Electrochemical methods have emerged as promising approaches for PFAS destruction, offering cost-effective and energy-efficient solutions. We established recently that electrocatalysis with nonprecious materials enabled the complete defluorination of perfluorooctanesulfonate (PFOS) in aqueous 8.0 M LiOH. Here, we reveal the mechanistic role of LiOH in the efficient aqueous electrocatalytic PFOS defluorination. Our results demonstrate that synergistic effects of high lithium and high hydroxide ion concentrations are essential for complete PFOS defluorination. Two-dimensional NMR data of electrolytes post pulsed electrolysis provide experimental evidence for Li-F ion pairing, which plays a crucial role in preventing anode fouling by produced fluoride, thus enabling sustained C-F bond cleavage. This Li-F ion pairing was increased at high pH, and elevated temperatures enhanced diffusion of Li-F ion pairs into the bulk electrolyte. High hydroxide ion concentrations additionally removed fluoride from the anode surface by competitive adsorption, corroborated by XPS data. Our findings provide quantitative mechanistic insights into the electrocatalytic defluorination process and offer a general route of enhancing the efficiency of anodic PFAS defluorination.

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.

PFAS distribution in cascade derived foam at wastewater treatment plants: The role of non-linear drainage, collapse induced enrichment, and implications for removal

Per- and polyfluorinated alkyl substances (PFAS) enrichment in foam was investigated for the first time at a wastewater treatment plant cascade. A novel sampling device was utilized to allow spatial and temporal heterogeneity in PFAS concentrations and liquid content to be characterized. Concentrations of 8 PFAS compounds were normalized to liquid content and fit to a power law model revealing strong correlation (R2 = 0.91) between drainage induced enrichment and PFAS molar volume. Short chain PFAS such as perfluorobutanoate (PFBA) exhibited minor to no enrichment factors in foam (0.24-5.9) compared to effluent concentrations across the range of foam liquid contents (0.28-6.24 %), while long chain compounds such as perfluorooctane sulfonate (PFOS) became highly enriched with factors of 295-143,000. A conceptual model is proposed to explain higher than expected enrichment of more surface-active PFAS relative to liquid content, which combines continuous partitioning of PFAS to air bubbles during foam formation with additional partitioning during non-linear drainage and foam collapse, both controlled by their affinity for the air-water interface. Scoping calculations suggest the majority of PFOS and other long chain PFAS may be removed if foam is continuously collected with potential to reduce waste volume under economic barriers for current destructive technologies.

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.

Unrefined and Milled Ilmenite as a Cost-Effective Photocatalyst for UV-Assisted Destruction and Mineralization of PFAS

Per- and polyfluoroalkyl substances (PFAS) are fluorinated and refractory pollutants that are ubiquitous in industrial wastewater. Photocatalytic destruction of such pollutants with catalysts such as TiO2 and ZnO is an attractive avenue for removal of PFAS, but refined forms of such photocatalysts are expensive. This study, for the first time, utilized milled unrefined raw mineral ilmenite, coupled to UV-C irradiation to achieve mineralization of the two model PFAS compounds perfluorooctanoic acid (PFOA) and perfluoro octane sulfonic acid (PFOS). Results obtained using a bench-scale photocatalytic reactor system demonstrated rapid removal kinetics of PFAS compounds (>90% removal in less than 10 h) in environmentally-relevant concentrations (200-1000 ppb). Raw ilmenite was reused over three consecutive degradation cycles of PFAS, retaining >80% removal efficiency. Analysis of degradation products indicated defluorination and the presence of shorter-chain PFAS intermediates in the initial samples. End samples indicated the disappearance of short-chain PFAS intermediates and further accumulation of fluoride ions, suggesting that original PFAS compounds underwent mineralization due to an oxygen-radical-based photocatalytic destruction mechanism induced by TiO2 present in ilmenite and UV irradiation. The outcome of this study implies that raw ilmenite coupled to UV-C is suitable for cost-effective reactor operation and efficient photocatalytic destruction of PFAS compounds.

Rapid degradation of perfluorooctane sulfonic acid (PFOS) and perfluorononanoic acid (PFNA) through bimetallic catalyst of Fe2O3/Mn2O3 and unravelling the effect of support SiO2

Perfluoroalkyl substances (PFAS) are emerging contaminants present in various water sources. Their bioaccumulation and potential toxicity necessitate proper treatment to ensure safe water quality. Although iron-based monometallic photocatalysts have been reported to exhibit rapid and efficient PFAS degradation, the impact of bimetallic photocatalysts is unknown. In addition, the mechanistic effects of utilizing a support are poorly understood and solely based on physicochemical properties. This study investigates the efficacy of bimetallic photocatalysts (Fe2O3/Mn2O3) in inducing the photo-Fenton reaction for the degradation of perfluorooctane sulfonate (PFOS) and perfluorononanoic acid (PFNA) under various conditions. The rapid removal of both PFAS was observed within 10 min, with a maximum efficiency exceeding 97 % for PFOS under UV exposure, aided by the photocatalytic activation (photo-Fenton) of the oxidant (H2O2). Contrary to expectations, the use of the SiO2 support material did not significantly improve the removal efficiency. The efficacy of PFNA decreased despite SiO2 providing larger surface areas for Fe2O3/Mn2O3 loading. Further analysis revealed that the adsorption of PFAS onto the catalyst surfaces owing to electrostatic interactions contributed to the removal efficiency, where the degradation efficacy was worse than that of the catalyst with SiO2. This is because adsorption hindered the effective contact of H2O2 with catalytic reaction sites, thereby impeding the generation of hydroxyl (·OH) radicals. This study indicates the importance of considering chemical properties, including surface charge, in catalyst design to ensure effective degradation, focusing on physicochemical properties, such as surface area might overlook crucial factors.

Ultrasonic degradation of per-and polyfluoroalkyl substances (PFAS), aqueous film-forming foam (AFFF) and foam fractionate (FF)

The ubiquitousness of per- and polyfluoroalkyl substances (PFAS) is a big concern and PFAS remediation is urgently needed such as via degradation. While previous studies have explored ultrasonic degradation of PFAS, work evaluating the operational parameters is rare, especially concerning real wastes such as aqueous film-forming foam (AFFF) and foam fractionate (FF). This study investigates the key operational parameters affecting the degradation efficiency of PFAS, encompassing ultrasonication frequency (580-1144 kHz), power intensity (125-187.5 W), initial concentration (0.08-40 ppm), treatment duration (0.5-3 h), sample volume (100-500 mL), and PFAS structure (perfluorooctanoic acid or PFOA; perfluorooctane sulfonate or PFOS; 6:2 fluorotelomer sulfonate or 6:2 FTS). The defluorination kinetics is different from the removal/degradation kinetics due to the generation of degradation intermediates, suggesting the complex degradation mechanism, which should be evaluated to close the mass balance effectively. Notably, the optimised ultrasonic system achieves ∼125%/∼115% defluorination in AFFF/FF example wastes (compared to ∼65%/∼97% removal) despite their complex composition and the involvement of total oxidizable precursor (TOP) assay. In the meantime, a few new PFAS are detected in the post-treatments, including perfluorohexane sulfonic acid (PFHxS) and 10:2 fluorotelomer sulfonate (10:2 FTS) in the AFFF, and perfluorooctane sulfonamide (FOSA) and 8:2 fluorotelomer sulfonate (8:2 FTS) in the FF, again suggesting the complex degradation mechanism. Overall, ultrasonication is effective to degrade PFAS real example wastes, advancing its potential for scale-up applications.

Review of per- and poly-fluoroalkyl treatment in combustion-based thermal waste systems in the United States

Per- and poly-fluoroalkyl substances (PFAS) are a class of synthetic chemicals known for their widespread presence and environmental persistence. Carbon-fluorine (C-F) bonds are major components among PFAS and among the strongest organic bonds, thus destroying PFAS may present significant challenge. Thermal treatment such as incineration is an effective and approved method for destroying many halogenated organic chemicals. Here, we present the results of existing studies and testing at combustion-based thermal treatment facilities and summarize what is known regarding PFAS destruction and mineralization at such units. Available results suggest the temperature and residence times reached by some thermal treatment systems are generally favorable to the destruction of PFAS, but the possibility for PFAS or fluorinated organic byproducts to escape destruction and adequate mineralization and be released into the air cannot be ruled out. Few studies have been conducted at full-scale operating facilities, and none to date have attempted to characterize possible fluorinated organic products of incomplete combustion (PICs). Further, the ability of existing air pollution control (APC) systems, designed primarily for particulate and acid gas control, to reduce PFAS air emissions has not been determined. These data gaps remain primarily due to the previous lack of available methods to characterize PFAS destruction and PIC concentrations in facility air emissions. However, newly developed stack testing methods offer an improved understanding of the extent to which thermal waste treatment technologies successfully destroy and mineralize PFAS in these waste streams.

Low-Temperature Mineralization of Fluorotelomers with Diverse Polar Head Groups

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants linked to harmful health effects. Currently employed PFAS destruction methods are energy-intensive and often produce shorter-chain and recalcitrant partially fluorinated byproducts. We report the mineralization of five fluorotelomer compounds via a base-mediated degradation using NaOH and mild temperatures (120 °C) in a mixture of DMSO:H2O (8:1 v/v). The studied fluorotelomers have varying polar head groups-carboxylic acids, sulfonic acids, alcohols, and phosphonic acids, which are the most common polar head groups used in commercial and industrial applications. The degradation intermediates and byproducts were characterized using 1H, 13C, and 19F NMR spectroscopy. Density functional theory computations at the M06-2X/6-311 + G(2d,p)-SMD-(DMSO) level were consistent with the observed intermediates and guided an overall mechanistic hypothesis. Degradation of each fluorotelomer occurs through a similar process, in which the nonfluorinated carbons and the first fluorinated carbon are cleaved from the remaining perfluoroalkyl fragment, which degrades through previously identified pathways. These findings provide important insight into PFAS degradation processes and suggest that PFAS containing at least one C-H bond within or adjacent to its fluoroalkyl chain can be degraded under these mild conditions. Many PFAS in current use as well as recalcitrant fluorinated byproducts generated from other PFAS degradation methods are candidates for this approach.

Insights into PFAS environmental fate through computational chemistry: A review

Per- and polyfluoroalkyl substances (PFAS) are widely used chemicals that exhibit exceptional chemical and thermal stability. However, their resistance to degradation has led to their widespread environmental contamination. PFAS also negatively affect the environment and other organisms, highlighting the need for effective remediation methods to mitigate their presence and prevent further contamination. Computational chemistry methods, such as Density Functional Theory (DFT) and Molecular Dynamics (MD) offer valuable tools for studying PFAS and simulating their interactions with other molecules. This review explores how computational chemistry methods contribute to understanding and tackling PFAS in the environment. PFAS have been extensively studied using DFT and MD, each method offering unique advantages and computational limitations. MD simulates large macromolecules systems however it lacks the ability model chemical reactions, while DFT provides molecular insights however at a high computational cost. The integration of DFT with MD shows promise in predicting PFAS behavior in different environments. This work summarizes reported studies on PFAS compounds, focusing on adsorption, destruction, and bioaccumulation, highlighting contributions of computational methods while discussing the need for continued research. The findings emphasize the importance of computational chemistry in addressing PFAS contamination, guiding risk assessments, and informing future research and innovations in this field.

PFAS in Nigeria: Identifying data gaps that hinder assessments of ecotoxicological and human health impacts

This review examines the extensive use and environmental consequences of Per- and Polyfluoroalkyl Substances (PFAS) on a global scale, specifically emphasizing their potential impact in Nigeria. Recognized for their resistance to water and oil, PFAS are under increased scrutiny for their persistent nature and possible ecotoxicological risks. Here, we consolidate existing knowledge on the ecological and human health effects of PFAS in Nigeria, focusing on their neurological effects and the risks they pose to immune system health. We seek to balance the advantages of PFAS with their potential ecological and health hazards, thereby enhancing understanding of PFAS management in Nigeria and advocating for more effective policy interventions and the creation of safer alternatives. The review concludes with several recommendations: strengthening regulatory frameworks, intensifying research into the ecological and health impacts of PFAS, developing new methodologies and longitudinal studies, fostering collaborative efforts for PFAS management, and promoting public awareness and education to support sustainable environmental practices and healthier communities in Nigeria.

The role of suspended biomass in PFAS enrichment in wastewater treatment foams

Foaming in aerated bioreactors at wastewater treatment plants (WWTPs) has been identified as an operational issue for decades. However, the affinity of per- and polyfluoroalkyl substances (PFAS) for air-liquid interfaces suggests that foam harvesting has the potential to become a sustainable method for PFAS removal from sewage. Aerated bioreactors' foams are considered three-phase systems, comprising air, aqueous and solid components, the latter consisting of activated sludge biomass. To achieve a comprehensive understanding of the capability of aerated bioreactors' foams to enrich PFAS, we analysed PFAS concentrations from WWTPs in both the solid and aqueous phases of the collapsed foams (foamate) and underlying bulk mixed liquors. Our findings show that PFAS enrichment occurs not only in the aqueous phase but also in the solid phase of the foamate. This suggests that previous field studies that only analysed the aqueous phase may have underestimated the capability of the aerated bioreactors' foams to enrich PFAS. Fractions of PFOA and PFOS sorbed to the solid phase of the foamate can be as high as 60 % and 95 %, respectively. Our findings highlight the importance of implementing effective foamate management strategies that consider both the aqueous and solid phases.

Application of β-Cyclodextrin Adsorbents in the Removal of Mixed Per- and Polyfluoroalkyl Substances

The extensive use of per- and polyfluoroalkyl substances (PFASs) in industrial consumer products has led to groundwater contamination, raising concerns for human health and the environment. These persistent chemicals exist in different forms with varying properties, which makes their removal challenging. In this study, we assessed the effectiveness of three different β-cyclodextrin (β-CD) adsorbents at removing a mixture of PFASs, including anionic, neutral, and zwitterionic compounds, at neutral pH. We calculated linear partition coefficient (Kd) values to quantify the adsorption affinity of each PFAS. β-CD polymers crosslinked with hexamethylene diisocyanate (β-CD-HDI) and epichlorohydrin (β-CD-EPI) displayed some adsorption of PFASs. Benzyl chloride β-CD (β-CD-Cl), an adsorbent that had not been previously reported, was also synthesized and tested for PFAS adsorption. β-CD-Cl exhibited higher PFAS adsorption than β-CD-HDI and β-CD-EPI, with log Kd values ranging from 1.9 L·g-1 to 3.3 L·g-1. β-CD-Cl displayed no affinity for zwitterionic compounds, as opposed to β-CD-HDI and β-CD-EPI, which removed N-dimethyl ammonio propyl perfluorohexane sulfonamide (AmPr-FHxSA). A comparison between Kd values and the log Kow of PFAS confirmed the significant role of hydrophobic interactions in thee adsorption mechanism. This effect was stronger in β-CD-Cl, compared to β-CD-HDI and β-CD-EPI. While no effect of PFAS charge was observed in β-CD-Cl, some influence of charge was observed in β-CD-HDI and β-CD-EPI, with less negative compounds being more adsorbed. The adsorption of PFASs by β-CD-Cl was similar in magnitude to that of other adsorbents proposed in literature. However, it offers the advantage of not containing fluorine, unlike many commonly proposed adsorbents.

Advancing PFAS Sorbent Design: Mechanisms, Challenges, and Perspectives

Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic chemicals characterized with persistence and multisurface resistance. Their accumulation in the environment and toxicity to human beings have contributed to the rapid development of regulations worldwide since 2002. The sorption strategy, taking advantage of intermolecular interactions for PFAS capture, provides a promising and efficient solution to the treatment of PFAS contaminated sources. Hydrophobic and electrostatic interactions are the two commonly found in commercially available PFAS sorbents, with the fluorous interaction being the novel mechanism applied for sorbent selectivity. The main object of this Perspective is to provide a critical review on the current design criteria of PFAS sorbents, with particular focus on their sorption and interaction mechanisms as well as limitations. An outlook on future innovative design for efficient PFAS sorbents is also provided.

A review of foam fractionation for the removal of per- and polyfluoroalkyl substances (PFAS) from aqueous matrices

The detection of per- and polyfluoroalkyl substances (PFAS) in aqueous matrices is an emerging environmental concern due to their persistent, bioaccumulative and toxic properties. Foam fractionation has emerged as a viable method for removing and concentrating PFAS from aqueous matrices. The method exploits the surface-active nature of the PFAS to adsorb at the air-liquid interfaces of rising air bubbles, resulting in foam formation at the top of a foam fractionator. The removal of PFAS is then achieved through foam harvesting. Foam fractionation has gained increasing attention owing to its inherent advantages, including simplicity and low operational costs. The coupling of foam fractionation with destructive technologies could potentially serve as a comprehensive treatment train for future PFAS management in aqueous matrices. The PFAS-enriched foam, which has a smaller volume, can be directed to subsequent destructive treatment technologies. In this review, we delve into previous experiences with foam fractionation for PFAS removal from various aqueous matrices and critically analyse their key findings. Then, the recent industry advancements and commercial projects that utilise this technology are identified. Finally, future research needs are suggested based on the current challenges.

The use of a fluorine mass balance to demonstrate the mineralization of PFAS by high frequency and high power ultrasound

High-frequency ultrasound (sonolysis) has been shown as a practical approach for mineralizing PFAS in highly concentrated PFAS waste. However, a fluorine mass balance approach showing complete mineralization for ultrasound treatment has not been elucidated. The impact of ultrasonic power density (W/L) and the presence of co-occurring PFAS on the degradation of individual PFAS are not well understood. In this research, the performance of a 10L sonochemical reactor was assessed for treating synthetic high-concentration PFAS waste with carboxylic and sulfonic perfluoroalkyl surfactants ranging in chain length from four to eight carbons at three different initial concentrations: 6, 55, 183 μM. The mass balance for fluorine was performed using three analytical techniques: triple quadrupole liquid chromatography-mass spectrometry, a fluoride ion selective electrode, and 19F nuclear magnetic resonance. The test results showed near complete mineralization of PFAS in the waste without the formation of intermediate fluorinated by-products. The PFAS mineralization efficiency of the sonolysis treatment at two different power densities for similar initial concentrations were almost identical; the G value at 145 W/L was 9.7*10-3 g/kWh, whereas the G value at 90 W/L was 9.3*10-3 g/kWh. The results of this study highlight the implications for the scalability of the sonolytic process to treat high-concentration PFAS waste.

Adsorption of per- and polyfluoroalkyl substances (PFAS) from water with porous organic polymers

Per- and polyfluoroalkyl substances (PFAS) are man-made environmental contaminants causing increasing global concern due to their adverse effect on environmental and human health. Conventional treatment methods are ineffective in removing short-chain PFAS because they are persistent and recalcitrant to treatment. This study evaluated the performance of a structurally-tunable and chemically-stable porous organic polymer (POP) for PFAS removal under realistic environmental conditions. The POP demonstrated an exceptionally high removal efficiency (>95%) within 15 min when the initial PFAS concentration was approximately 400 ng/L. The adsorption of PFAS on the POP was not significantly affected by changes in solution pH within the range of 5-9. The common co-contaminants in water competed with short-chain PFAS for active sites during the adsorption process following the order of natural organic matter (NOM), long-chain PFAS, and Cl-. The Freundlich-type model could predict the multicomponent interactions well with a R2 value above 0.91. The spent POP was effectively regenerated using a mixture of the 10% NaCl and 30% methanol solution and the PFAS removal maintained at 90% through five adsorption and desorption cycles. The characteristics of the designed POP make it a highly promising and stable absorbent. It enables fast and effective removal of short-chain PFAS.

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.

Advanced electrocatalytic redox processes for environmental remediation of halogenated organic water pollutants

Halogenated organic compounds are widespread, and decades of heavy use have resulted in global bioaccumulation and contamination of the environment, including water sources. Here, we introduce the most common halogenated organic water pollutants, their classification by type of halogen (fluorine, chlorine, or bromine), important policies and regulations, main applications, and environmental and human health risks. Remediation techniques are outlined with particular emphasis on carbon-halogen bond strengths. Aqueous advanced redox processes are discussed, highlighting mechanistic details, including electrochemical oxidations and reductions of the water-oxygen system, and thermodynamic potentials, protonation states, and lifetimes of radicals and reactive oxygen species in aqueous electrolytes at different pH conditions. The state of the art of aqueous advanced redox processes for brominated, chlorinated, and fluorinated organic compounds is presented, along with reported mechanisms for aqueous destruction of select PFAS (per- and polyfluoroalkyl substances). Future research directions for aqueous electrocatalytic destruction of organohalogens are identified, emphasizing the crucial need for developing a quantitative mechanistic understanding of degradation pathways, the improvement of analytical detection methods for organohalogens and transient species during advanced redox processes, and the development of new catalysts and processes that are globally scalable.

A ReaxFF-based molecular dynamics study of the destruction of PFAS due to ultrasound

This work uses a computational approach to provide a mechanistic explanation for the experimentally observed destruction of per- and polyfluoroalkyl substances (PFAS) in water due to ultrasound. The PFAS compounds have caused a strong public and regulatory response due to their ubiquitous presence in the environment and toxicity to humans. In this research, ReaxFF -based Molecular Dynamics simulation under several temperatures ranging from 373 K to 5,000 K and different environments such as water vapor, O2, N2, and air were performed to understand the mechanism of PFAS destruction. The simulation results showed greater than 98% PFAS degradation was observed within 8 ns under a temperature of 5,000 K in a water vapor phase, replicating the observed micro/nano bubbles implosion and PFAS destruction during the application of ultrasound. Additionally, the manuscript discusses the reaction pathways and how PFAS degradation evolves providing a mechanistic basis for the destruction of PFAS in water due to ultrasound. The simulation showed that small chain molecules C1 and C2 fluoro-radical products are the most dominant species over the simulated period and are the impediment to an efficient degradation of PFAS. Furthermore, this research confirms the empirical findings observations that the mineralization of PFAS molecules occurs without the generation of byproducts. These findings highlight the potential of virtual experiments in complementing laboratory experiments and theoretical projections to enhance the understanding of PFAS mineralization during the application of ultrasound.

Predicting pyrolysis decomposition of PFOA using computational nanoreactors: a thermodynamic study

Per- and polyfluoroalkyl substances (PFAS) are a large, complex, environmentally persistent, and ever-expanding group of manufactured chemicals. Disposal of these compounds could produce potentially dangerous products necessitating the need to quickly predict their decomposition products. This study focuses on the thermal decomposition of perfluorooctanoic acid (PFOA) using nanoreactor simulations to find the decomposition products and their respective energies. Applying the nanoreactor method, which is novel for this system, allows for rapid prediction of thermal decomposition pathways with minimal researcher bias and it predicted PFOA to decompose at ∼650 °C, consistent with previously reported experimental studies.

Enhanced removal of perfluorooctanoic acid with sequential photocatalysis and fungal treatment

In this paper, we report the degradation of perfluorooctanoic acid (PFOA), which is a persistent contaminant in the environment that can severely impact human health, by exposing it to a photocatalyst, bismuth oxyiodide (BiOI), containing both Bi4O5I2 and Bi5O7I phases and a fungal biocatalyst (Cunninghamella elegans). Individually, the photocatalyst (after 3 h) and biocatalyst (after 48 h) degraded 35-40% of 100 ppm PFOA with 20-30% defluorination. There was a marked improvement in the degree of degradation (90%) and defluorination (60%) when PFOA was first photocatalytically treated, then exposed to the fungus. GC- and LC-MS analysis identified the products formed by the different treatments. Photocatalytic degradation of PFOA yielded short-chain perfluorocarboxylic acids, whereas fungal degradation yielded mainly 5:3 fluorotelomer carboxylic acid, which is a known inhibitor of cytochrome P450-catalysed degradation of PFAS in C. elegans. The combined treatment likely resulted in greater degradation because photocatalysis reduced the PFOA concentration without generating the inhibitory 5:3 fluorotelomer carboxylic acid, enabling the fungus to remove most of the remaining substrate. In addition, new fluorometabolites were identified that shed light on the initial catabolic steps involved in PFOA biodegradation.

Contributions of reactor geometry and ultrasound frequency on the efficieny of sonochemical reactor

An intermediate-scale reactor with 10L capacity and two transducers operating at 700 and 950 kHz frequencies was developed to study the scalability of the sonolytic destruction of Per and Polyfluoroalkyl substance (PFAS). The impact of frequency, height of liquid or power density, and transducer position on reactor performance was evaluated with the potassium iodide (KI) oxidation and calorimetric power. The dual frequency mode of operation has a synergistic effect based on the triiodide concentration, and calorimetric power. The triiodide concentration, and calorimetric power were higher in this mode compared to the combination of both frequencies operating individually. The sonochemical efficiency for an intermediate-scale reactor (10L) was similar that obtained from a bench-scale reactor (2L), showing the scalability of the sonolytic technology. The placement of the transducer at the bottom or side wall of the reactor had no significant impact on the sonochemical reactivity. The superposition of the ultrasonic field from the dual transducer mode (side and bottom) did not produce a synergistic effect compared to the single transducer mode (bottom or side). This can be attributed to a disturbance due to the interaction of ultrasonic fields of two frequencies from each transducer. With the encouraging results scaling up is in progress for site implementation.

A Path to a Reduction in Micro and Nanoplastics Pollution

Microplastics (MP) are plastic particles less than 5 mm in size. There are two categories of MP: primary and secondary. Primary or microscopic-sized MP are intentionally produced material. Fragmentation of large plastic debris through physical, chemical, and oxidative processes creates secondary MP, the most abundant type in the environment. Microplastic pollution has become a global environmental problem due to their abundance, poor biodegradability, toxicological properties, and negative impact on aquatic and terrestrial organisms including humans. Plastic debris enters the aquatic environment via direct dumping or uncontrolled land-based sources. While plastic debris slowly degrades into MP, wastewater and stormwater outlets discharge a large amount of MP directly into water bodies. Additionally, stormwater carries MP from sources such as tire wear, artificial turf, fertilizers, and land-applied biosolids. To protect the environment and human health, the entry of MP into the environment must be reduced or eliminated. Source control is one of the best methods available. The existing and growing abundance of MP in the environment requires the use of multiple strategies to combat pollution. These strategies include reducing the usage, public outreach to eliminate littering, reevaluation and use of new wastewater treatment and sludge disposal methods, regulations on macro and MP sources, and a wide implementation of appropriate stormwater management practices such as filtration, bioretention, and wetlands.

Effect of clay content on the mobilization efficiency of per- and polyfluoroalkyl substances (PFAS) from soils by electrokinetics and hydraulic flushing

The need for the efficient remediation of soils impacted by per- and polyfluoroalkyl substances (PFAS) is substantially growing because of the notable upsurge in societal and regulatory awareness of this class of chemicals. To remediate PFAS-contaminated soils using mobilization approaches, the choice of appropriate techniques highly depends on the soil's composition, particularly the clay content, which significantly affects the soil's permeability. Here, we investigated the PFAS mobilization efficiency from soils with different clay contents by using two techniques: electrokinetic (EK) remediation and hydraulic flushing. Artificial kaolinite was added to a loamy sand soil to prepare four soil blends with clay contents of 5, 25, 50, and 75%, each contaminated with perfluorooctanoic acid (PFOA) and perfulorooctanesulfonic acid (PFOA) at 10,000 μg/kg. EK remediation was conducted by applying a low voltage (30 V) with a current of 100 mA, and hydraulic flushing was carried out by applying a hydraulic gradient (HG) with a slope of 6.7%. Results show that, with a 14-day treatment duration, the EK-mobilization efficiency was enhanced substantially with the increase of clay content (removal of PFOS increased from 20% at 5% clay to 80% at 75% clay), most likely due to the increase of electroosmotic flow due to the higher content of particles having a zeta potential (i.e., clay). For HG, increasing the clay content significantly suppressed the mobilization of PFAS (removal of PFOS decreased from 40% at 5% clay to 10% at 75% clay) due to a notable decrease in the soil's permeability. Based on the results, applying hydraulic flushing and washing techniques for mobilizing PFAS would be appropriate when treating permeable soils with a maximum clay content of about 25%; otherwise, other suitable mobilization techniques such as EKs should be considered.