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1. A Review of the Applications, Environmental Release, and Remediation Technologies of Per- and Polyfluoroalkyl Substances

   https://doi.org/10.3390/ijerph17218117  

   Meegoda, Jay N. ; Kewalramani, Jitendra A. ; Li, Brian ; Marsh, Richard W. ( November 2020 , International Journal of Environmental Research and Public Health)

   null (Ed.)

   Per- and polyfluoroalkyl substances (PFAS) are pollutants that have demonstrated a high level of environmental persistence and are very difficult to remediate. As the body of literature on their environmental effects has increased, so has regulatory and research scrutiny. The widespread usage of PFAS in industrial applications and consumer products, complicated by their environmental release, mobility, fate, and transport, have resulted in multiple exposure routes for humans. Furthermore, low screening levels and stringent regulatory standards that vary by state introduce considerable uncertainty and potential costs in the environmental management of PFAS. The recalcitrant nature of PFAS render their removal difficult, but existing and emerging technologies can be leveraged to destroy or sequester PFAS in a variety of environmental matrices. Additionally, new research on PFAS remediation technologies has emerged to address the efficiency, costs, and other shortcomings of existing remediation methods. Further research on the impact of field parameters such as secondary water quality effects, the presence of co-contaminants and emerging PFAS, reaction mechanisms, defluorination yields, and the decomposition products of treatment technologies is needed to fully evaluate these emerging technologies, and industry attention should focus on treatment train approaches to improve efficiency and reduce the cost of treatment. 

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2. Molecular Tuning of Redox‐Copolymers for Selective Electrochemical Remediation

   https://doi.org/10.1002/adfm.202004635  

   Kim, Kwiyong ; Baldaguez Medina, Paola ; Elbert, Johannes ; Kayiwa, Emmanuel ; Cusick, Roland D. ; Men, Yujie ; Su, Xiao ( September 2020 , Advanced Functional Materials)

   Molecular design of redox‐materials provides a promising technique for tuning physicochemical properties which are critical for selective separations and environmental remediation. Here, the structural tuning of redox‐copolymers, 4‐methacryloyloxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TMA) and 4‐methacryloyloxy‐2,2,6,6‐tetramethylpiperidine (TMPMA), denoted as P(TMA_x‐co‐TMPMA_1−x), is investigated for the selective separation of anion contaminants ranging from perfluorinated substances to halogenated aromatic compounds. The amine functional groups provide high affinity toward anionic functionalities, while the redox‐active nitroxyl radical groups promote electrochemically‐controlled capture and release. Controlling the ratio of amines to nitroxyl radicals provides a pathway for tuning the redox‐activity, hydrophobicity, and binding affinity of the copolymer, to synergistically enhance adsorption and regeneration. P(TMA_x‐co‐TMPMA_1−x) removes a model perfluorinated compound (perfluorooctanoic acid (PFOA)) with a high uptake capacity (>1000 mg g⁻¹) and separation factors (500 vs chloride), and demonstrates exceptional removal efficiencies in diverse per‐ and polyfluoroalkyl substances (PFAS) and halogenated aromatic compounds, in various water matrices. Integration with a boron‐doped diamond electrode allows for tandem separation and destruction of pollutants within the same electrochemical cell, enabling the energy integration of the separation step with the catalytic degradation step. The study demonstrates for the first time the tuning of redox‐copolymers for selective remediation of organic anions, and integration with an advanced electrochemical oxidation process for energy‐efficient water purification.

    

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3. Managing and treating per‐ and polyfluoroalkyl substances (PFAS) in membrane concentrates

   https://doi.org/10.1002/aws2.1233  

   Tow, Emily W. ; Ersan, Mahmut Selim ; Kum, Soyoon ; Lee, Tae ; Speth, Thomas F. ; Owen, Christine ; Bellona, Christopher ; Nadagouda, Mallikarjuna N. ; Mikelonis, Anne M. ; Westerhoff, Paul ; et al ( September 2021 , AWWA Water Science)

   Per‐ and polyfluoroalkyl substances (PFAS), which are present in many waters, have detrimental impacts on human health and the environment. Reverse osmosis (RO) and nanofiltration (NF) have shown excellent PFAS separation performance in water treatment; however, these membrane systems do not destroy PFAS but produce concentrated residual streams that need to be managed. Complete destruction of PFAS in RO and NF concentrate streams is ideal, but long‐term sequestration strategies are also employed. Because no single technology is adequate for all situations, a range of processes are reviewed here that hold promise as components of treatment schemes for PFAS‐laden membrane system concentrates. Attention is also given to relevant concentration processes because it is beneficial to reduce concentrate volume prior to PFAS destruction or sequestration. Given the costs and challenges of managing PFAS in membrane concentrates, it is critical to evaluate both established and emerging technologies in selecting processes for immediate use and continued research.

   Readers will benefit from learning about established and emerging management approaches for per‐ and polyfluoroalkyl substances and the peculiarities of their application to reverse osmosis and nanofiltration concentrates.

    

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4. Adsorption as a remediation technology for short-chain per- and polyfluoroalkyl substances (PFAS) from water – a critical review

   https://doi.org/10.1039/D2EW00721E  

   Smaili, Hajar ; Ng, Carla ( February 2023 , Environmental Science: Water Research & Technology)

   Because of their ubiquitous presence in the environment and their potential toxicity to human health, per- and polyfluoroalkyl substances (PFAS) have drawn great attention over the past few years. Current conventional drinking and wastewater treatment approaches fail to effectively remove these substances from aqueous media, motivating researchers to focus on using sorption, a simple and cost-effective method, to remove PFAS from contaminated water. This work aims to summarize and critically evaluate the sorption capacities of PFAS by a variety of natural and engineered sorbents, including carbonaceous materials, ion exchange resins, polymers, different natural materials and other engineered sorbent materials. The specific focus of this review is on the performance of these different materials in removing short-chain PFAS due to their high solubility and mobility in aqueous media. A treatment train optimizing the removal of these short-chain substances from water is proposed, and challenges and future recommendations are discussed. 

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5. Efficient removal of short-chain and long-chain PFAS by cationic nanocellulose

   https://doi.org/10.1039/d3ta01851b  

   Li, Duning ; Lee, Cheng-Shiuan ; Zhang, Yi ; Das, Rasel ; Akter, Fahmida ; Venkatesan, Arjun K. ; Hsiao, Benjamin S. ( May 2023 , Journal of Materials Chemistry A)

   Although most manufacturers stopped using long-chain per- and polyfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), short-chain PFASs are still widely employed. Short-chain PFASs are less known in terms of toxicity and have different adsorption behavior from long-chain PFASs. Previous studies have shown electrostatic interaction with the adsorbent to be the dominant mechanism for the removal of short-chain PFASs. In this study, we designed a high charge density cationic quaternized nanocellulose (QNC) to enhance the removal of both short- and long-chain PFASs from contaminated water. Systematic batch adsorption tests were conducted using the QNC adsorbent to compare its efficiency against PFASs with varying chain lengths and functional groups. From the kinetic study, PFBA (perfluorobutanoic acid), PFBS (perfluorobutanesulfonic acid) and PFOS showed rapid adsorption rates, which reached near equilibrium values (>95% of removal) between 1 min to 15 min, while PFOA required a relatively longer equilibration time of 2 h (it obtained 90% of removal within 15 min). According to the isotherm results, the maximum adsorption capacity ( Q m ) of the QNC adsorbent exhibited the following trend: PFOS ( Q m = 559 mg g −1 or 1.12 mmol g −1 ) > PFOA ( Q m = 405 mg g −1 or 0.98 mmol g −1 ) > PFBS ( Q m = 319 mg g −1 or 1.06 mmol g −1 ) > PFBA ( Q m = 121 mg g −1 or 0.57 mmol g −1 ). This adsorption order generally matches the hydrophobicity trend among four PFASs associated with both PFAS chain length and functional group. In competitive studies, pre-adsorbed short-chain PFASs were quickly desorbed by long-chain PFASs, suggesting that the hydrophobicity of the molecule played an important role in the adsorption process on to QNC. Finally, the developed QNC adsorbent was tested to treat PFAS-contaminated groundwater, which showed excellent removal efficiency (>95%) for long-chain PFASs (C7–C9) even at a low adsorbent dose of 32 mg L −1 . However, short-chain PFASs ( i.e. , PFBA and perfluoropentanoic acid (PFPeA)) were poorly removed by the QNC adsorbent (0% and 10% removal, respectively) due to competing constituents in the groundwater matrix. This was further confirmed by controlled experiments that revealed a drop in the performance of QNC to remove short-chain PFASs at elevated ionic strength (NaCl), but not for long-chain PFASs, likely due to charge neutralization of the anionic functional group of PFASs by inorganic cations. Overall, the QNC adsorbent featured improved PFAS adsorption capacity at almost two-fold of PFAS removal by granular activated carbons, especially for short-chain PFASs. We believe, QNC can complement the use of common treatment methods such as activated carbon or ionic exchange resin to remove a wide range of PFAS pollutants, heading towards the complete remediation of PFAS contamination. 

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