Modulating electrode area in microbial fuel cell enhanced floating beds: synergistic effects on bioelectricity generation and perfluorooctanoic acid degradation.

Efficient PFOA degradation by persulfate-assisted photocatalytic ozonation

Comparison of microcrystalline and ultrananocrystalline boron doped diamond anodes: Influence on perfluorooctanoic acid electrolysis

Photocatalytic degradation of perfluorooctanoic acid (PFOA) by metal organic framework MIL-177-HT: New insights into the role of specific surface area, charge separation and dimensionality

Improved treatment of per- and polyfluoroalkyl substances (PFAS) in water is critically important in light of the proposed United States Environmental Protection Agency (USEPA) drinking water regulations at ng L−1 levels. The addition of peroxymonosulfate (PMS) during electrooxidation (EO) can remove and destroy PFAS, but ng L−1 levels have not been tested, and PMS itself can be toxic. The objective of this research was to test peroxydisulfate (PDS, an alternative to PMS) activation by boron-doped diamond (BDD) electrodes for perfluorooctanoic acid (PFOA) degradation. The influence of PDS concentration, temperature, and environmental water matrix effects, and PFOA concentration on PDS-EO performance were systematically examined. Batch reactor experiments revealed that 99 % of PFOA was degraded and 69 % defluorination was achieved, confirming PFOA mineralization. Scavenging experiments implied that sulfate radicals (SO4–) and hydroxyl radicals (HO) played a more important role for PFOA degradation than 1O2 or electrons (e−). Further identification of PFOA degradation and transformation products by liquid chromatography-mass spectrometry (LC-MS) analysis established plausible PFOA degradation pathways. The analysis corroborates that direct electron transfers at the electrode initiate PFOA oxidation and SO4– improves overall treatment by cleaving the CC bond between the C7F15 and COOH moieties in PFOA, leading to possible products such as C7F15 and F−. The perfluoroalkyl radicals can be oxidized by SO4– and HO, resulting in the formation of shorter chain perfluorocarboxylic acids (e.g., perfluorobutanoic acid [PFBA]), with eventual mineralization to CO2 and F−. At an environmentally relevant low initial concentration of 100 ng L−1 PFOA, 99 % degradation was achieved. The degradation of PFOA was slightly affected by the water matrix as less removal was observed in an environmental river water sample (91 %) compared to tests conducted in Milli-Q water (99 %). Overall, EO with PDS provided a destructive approach for the elimination of PFOA.

Efficient degradation of perfluorooctanoic acid by UV–Fenton process

Perfluorooctanoic acid (PFOA) is a toxic yet persistent organic pollutant which has contaminated the environment since it was first introduced in manufacturing decades ago. Many PFOA treatment processes leave a concentrated waste stream, the potential for secondary pollution, or financial and logistical challenges when considering scale-up. Electrochemical oxidation with a granular activated carbon cathode and titanium mixed-metal oxide anode provides an opportunity to degrade PFOA while circumventing these other issues. The current work studied adsorption and electrochemical degradation of PFOA in a flow-through reactor while optimizing the treatment configuration by considering cathode composition, initial contaminant concentration, limiting current, and the addition of persulfates. PFOA concentration and hydrogen peroxide concentration were measured while the presence of fluoride and other perfluorocarboxylic acid intermediates was investigated. The optimal configuration featured 2 g of granular activated carbon in stainless-steel mesh as the cathode, a 400 mA limiting current, and a 5 mg/L initial PFOA concentration. This configuration without persulfate addition (81.9% PFOA removal) performed similarly to this configuration with 5 mM persulfate addition (80.9% PFOA removal), while producing maximum hydrogen peroxide concentrations of 1.98 ppm and 2.37 ppm respectively. These configurations performed better than experiments which relied on adsorption only or which used only stainless-steel as a cathode (no granular activated carbon). This work demonstrates the possibility for degradation of PFOA in an electrochemical flow-through reactor with inexpensive electrode materials, representing an improvement in applicability from studies which focused on batch configurations. There was no measurable fluoride mineralization and only trace amounts of perfluorocarboxylic acid degradation intermediates were detected, though those were likely impurities in the initial reaction solution. Further experimentation is recommended to refine a method for fluoride detection and assess the potential for complete or partial mineralization. It is also recommended to perform further testing to confirm or deny the presence of intermediates and determine the oxidation mechanism which prevails in this work, such as confirming the role of sulfate radicals, hydroxyl radicals, and/or direct electron transfer to the anode. This work contributes to the current understanding of adsorption and electrochemical oxidation of PFOA while presenting additional questions for future research.--Author's abstract

Removal of perfluorooctanoic acid and perfluorooctane sulfonate via ozonation under alkaline condition

Visible and UV photocatalysis of aqueous perfluorooctanoic acid by TiO2 and peroxymonosulfate: Process kinetics and mechanistic insights.

This study aimed to probe the interactions of hydrated electrons (eaq–) and perfluorooctanoic acid (PFOA)-laden ion-exchange (IX) resins in the presence of natural organic matter (NOM). PFOA and Suwannee River NOM-loaded resins were prepared through the removal of PFOA in simulated natural water with weak-base anion (WBA) resins (IRA67). Adsorption tests reveal that sorbed NOM was much more abundant than cosorbed PFOA, highlighting the role of NOM in resin saturation. Ensuing UV/SO32– treatment of PFOA/NOM-laden resins (pH 10.0) under a dissolved oxygen-free condition indicates that eaq– generated could effectively degrade sorbed and aqueous PFOA, the latter of which derived from desorption of PFOA due to pH increase. Finally, cyclic adsorption-UV/SO32– treatment tests demonstrate that the PFOA sorbed on the WBA resins could be mostly degraded over six cycles. However, eaq– could not effectively decompose cosorbed NOM, resulting in a gradual decrease in the recovered PFOA adsorption capability with the cycle number. This study spotlights that eaq– can decompose PFOA sorbed on the WBA resins in the presence of NOM. The UV/SO32– process, when jointly used with appropriate strategies for mitigating cosorbed NOM, can enable a promising on-site resin regeneration process with PFOA degradation while producing a relatively small volume of regenerant waste.

Removal of perfluorooctanoic acid (PFOA) in the liquid culture of Phanerochaete chrysosporium

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.

Application of electric potential and Fe(Ⅲ) to stimulate perfluorooctanoic acid (PFOA) degradation using mixed culture anammox granules

Photochemical degradation of perfluorooctanoic acid under UV irradiation in the presence of Fe (III)-saturated montmorillonite

Thermal assisted heterogeneous activation of peroxymonosulfate by activated carbon to degrade perfluorooctanoic acid in soil

Mechanism insight of PFOA degradation by ZnO assisted-photocatalytic ozonation: Efficiency and intermediates