Remediation of per- and polyfluoroalkyl substances

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Remediation of per- and polyfluoroalkyl substances refers to the destruction or removal of per- and polyfluoroalkyl substances (PFASs) from the environment. PFASs are a group of synthetic organofluorine compounds, used in diverse products such as non-stick cookware and firefighting foams, that have attracted great concern as persistent organic pollutants. Because they are pervasive and have adverse effects, much interest has focused on their removal.

Contents

PFASs are by design highly stable. They often occur as extremely dilute (ppm to ppb) solutions. [1] These factors - resilience and diluteness - make remediation extremely challenging. Nonetheless, diverse methods are being tested including sonolysis, electrochemical oxidation, advanced oxidation processes, as well as the use of oxidative enzymes (such as peroxidase and laccase). [2] All of these methods promote the formation of hydroxyl radicals or other oxidizing agents that can oxidize PFAS and break its C−C bonds. [3] [4] However, the remediation of PFAS depends on the environmental medium where the these compounds reside. For example, the treatment of contaminated soil, biosolids and water is not the same, and risk-based approach may be recommended for the remediation. [5] [6]

Destruction

Both oxidative and reductive approaches can be taken to destroy PFASs. The oxidation of perfluorooctane sulfonic acid (PFOS), as one prominent example, is described as follows:

C8F17SO3H + 8 H2O + 4 O2 → 17 HF + 8 CO2 + SO3

The challenge implicit in this approach is that PFASs have been used in aqueous film forming foam (AFFF) because they both make foams and they resist oxidation. [7]

For the perfluorocarboxylic acids, such as perfluorooctanoic acid (PFOA), decarboxylation has been identified as a possible route to their eventual degradation. [8]

C8F17CO−2 → C6F13CF=CF2 + F− + CO2

No remediation technology is applicable to real-world concentrations and media.

Adsorption

Through the process of adsorption, PFASs can in principle be concentrated to facilitate their physical removal from the environment.

Adsorption is generally more efficient in an acidic environment and with mesopores. Carbons such as activated carbon and biochar have a very high specific surface area and are nonpolar, allowing them to interact with the hydrophobic tail of PFAS molecules. They can also be regenerated through different methods like heat treatment, microwave assisted regeneration and with different solvents [9] [10] [11] .Anion exchange resins, metal–organic frameworks, and layered double hydroxides may also be used for the adsorption of PFAS (PFAS can become an anion through losing a hydrogen from its head). In situ, adsorption is less effective due to the presence of other pollutants in the water. [12] Hence, this area provides more opportunities for potential research.

Hybrid methodologies

Several "hybrid" methodologies have been described for the treatment of PFAS, [13] such as nanofiltration combined with electrochemical oxidation, biochar with zero valent ion, GAC adsorption and thermal mineralization. [14]

Of several biological hybrid methods thermophilic anaerobic digestion can be combined by adsorption by activated carbon to remove up to 61% of PFAS from sewage sludge. [15]

Regeneration

Activated carbon granules or particles can undergo thermal regeneration and reuse the surface while breaking down PFAS at the same time. However, various harmful products can be produced as a result, such as tetrafluoromethane, a strong greenhouse gas, and the heating process is expensive. Meanwhile, regeneration with a solvent does not break down PFAS, so further waste treatment is required. [3] [12]

Reverse osmosis

Reverse osmosis and nanofiltration effectively separate PFAS but are typically too expensive to be viable solutions. [3] [12]

Related Research Articles

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Trinitrotoluene, more commonly known as TNT (and more specifically 2,4,6-trinitrotoluene, and by its preferred IUPAC name 2-methyl-1,3,5-trinitrobenzene), is a chemical compound with the formula C6H2(NO2)3CH3. TNT is occasionally used as a reagent in chemical synthesis, but it is best known as an explosive material with convenient handling properties. The explosive yield of TNT is considered to be the standard comparative convention of bombs and asteroid impacts. In chemistry, TNT is used to generate charge transfer salts.

<span class="mw-page-title-main">Water treatment</span> Process that improves the quality of water

Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. This treatment is crucial to human health and allows humans to benefit from both drinking and irrigation use.

<span class="mw-page-title-main">Activated carbon</span> Form of carbon with an extremely high surface area

Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that greatly increase the surface area available for adsorption or chemical reactions that can be thought of as a microscopic "sponge" structure. Activation is analogous to making popcorn from dried corn kernels: popcorn is light, fluffy, and its kernels have a high surface-area-to-volume ratio. Activated is sometimes replaced by active.

<span class="mw-page-title-main">Environmental remediation</span> Removal of pollution from soil, groundwater etc.

Environmental remediation is the cleanup of hazardous substances dealing with the removal, treatment and containment of pollution or contaminants from environmental media such as soil, groundwater, sediment. Remediation may be required by regulations before development of land revitalization projects. Developers who agree to voluntary cleanup may be offered incentives under state or municipal programs like New York State's Brownfield Cleanup Program. If remediation is done by removal the waste materials are simply transported off-site for disposal at another location. The waste material can also be contained by physical barriers like slurry walls. The use of slurry walls is well-established in the construction industry. The application of (low) pressure grouting, used to mitigate soil liquefaction risks in San Francisco and other earthquake zones, has achieved mixed results in field tests to create barriers, and site-specific results depend upon many variable conditions that can greatly impact outcomes.

<span class="mw-page-title-main">Perfluorooctanesulfonic acid</span> Fluorosurfactant and persistent organic pollutant

Perfluorooctanesulfonic acid (PFOS) is a chemical compound having an eight-carbon fluorocarbon chain and a sulfonic acid functional group, and thus it is a perfluorosulfonic acid and a perfluoroalkyl substance (PFAS). It is an anthropogenic (man-made) fluorosurfactant, now regarded as a global pollutant. PFOS was the key ingredient in Scotchgard, a fabric protector made by 3M, and related stain repellents. The acronym "PFOS" refers to the parent sulfonic acid and to various salts of perfluorooctanesulfonate. These are all colorless or white, water-soluble solids. Although of low acute toxicity, PFOS has attracted much attention for its pervasiveness and environmental impact. It was added to Annex B of the Stockholm Convention on Persistent Organic Pollutants in May 2009.

<span class="mw-page-title-main">Industrial wastewater treatment</span> Processes used for treating wastewater that is produced by industries as an undesirable by-product

Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.

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<span class="mw-page-title-main">Perfluorinated compound</span> Type of organic chemical

A perfluorinated compound (PFC) or perfluoro compound is an organofluorine compound that lacks C-H bonds. Many perfluorinated compounds have properties that are quite different from their C-H containing analogues. Common functional groups in PFCs are OH, CO2H, chlorine, O, and SO3H. Electrofluorination is the predominant method for PFC production. Due to their chemical stability, some of these perfluorinated compounds bioaccumulate.

Perfluoroalkyl carboxylic acids (PFCAs), or perfluorocarboxylic acids are compounds of the formula CnF(2n+1)CO2H that belong to the class of per- and polyfluoroalkyl substances. The simplest example is trifluoroacetic acid. These compounds are organofluorine analogues of ordinary carboxylic acids, but they are stronger by several pKa units and they exhibit great hydrophobic character. Perfluoroalkyl dicarboxylic acids (PFdiCAs) are also known, e.g. C2F4(CO2H)2.

The electrochemical regeneration of activated carbon based adsorbents involves the removal of molecules adsorbed onto the surface of the adsorbent with the use of an electric current in an electrochemical cell restoring the carbon's adsorptive capacity. Electrochemical regeneration represents an alternative to thermal regeneration commonly used in waste water treatment applications. Common adsorbents include powdered activated carbon (PAC), granular activated carbon (GAC) and activated carbon fibre.

Electrochemical regeneration of activated carbon adsorbents such as granular activated carbon present an alternative to thermal regeneration or land filling at the end of useful adsorbent life. Continuous adsorption-electrochemical regeneration encompasses the adsorption and regeneration steps, typically separated in the bulk of industrial processes due to long adsorption equilibrium times, into one continuous system. This is possible using a non-porous, electrically conducting carbon derivative called Nyex. The non-porosity of Nyex allows it to achieve its full adsorptive capacity within a few minutes and its electrical conductivity allows it to form part of the electrode in an electrochemical cell. As a result of its properties Nyex can undergo quick adsorption and fast electrochemical regeneration in a combined adsorption-electrochemical regeneration cell achieving 100% regeneration efficiency.

Nanoremediation is the use of nanoparticles for environmental remediation. It is being explored to treat ground water, wastewater, soil, sediment, or other contaminated environmental materials. Nanoremediation is an emerging industry; by 2009, nanoremediation technologies had been documented in at least 44 cleanup sites around the world, predominantly in the United States. In Europe, nanoremediation is being investigated by the EC funded NanoRem Project. A report produced by the NanoRem consortium has identified around 70 nanoremediation projects worldwide at pilot or full scale. During nanoremediation, a nanoparticle agent must be brought into contact with the target contaminant under conditions that allow a detoxifying or immobilizing reaction. This process typically involves a pump-and-treat process or in situ application.

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Perfluorodecanoic acid (PFDA) is a fluorosurfactant and has been used in industry.

<span class="mw-page-title-main">Perfluorohexanesulfonic acid</span> Chemical compound

Perfluorohexanesulfonic acid (PFHxS) is a synthetic chemical compound. It is one of many compounds collectively known as per- and polyfluoroalkyl substances (PFASs). It is an anionic fluorosurfactant and a persistent organic pollutant with bioaccumulative properties. Although the use of products containing PFHxS and other PFASs have been banned or are being phased out in many jurisdictions, it remains ubiquitous in many environments and within the general population, and is one of the most commonly detected PFASs.

<span class="mw-page-title-main">TOP Assay</span> Laboratory analysis method

The TOP Assay is a laboratory method developed in 2012 that oxidatively converts (unknown) precursor compounds of perfluorocarboxylic acids (PFCAs) into the latter. This makes quantification possible. Potassium peroxodisulfate is used. This sum parameter can be used to determine the concentration of precursor compounds present by comparing the sample before and after the application of the TOP Assay.

References

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  2. ↑ Hu M, Scott C (April 2024). "Toward the development of a molecular toolkit for the microbial remediation of per-and polyfluoroalkyl substances". Appl. Environ. Microbiol. 90 (4): e0015724. doi:10.1128/aem.00157-24. PMC   11022551 . PMID   38477530.
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  4. ↑ Kucharzyk, Katarzyna H.; Darlington, Ramona; Benotti, Mark; Deeb, Rula; Hawley, Elisabeth (15 December 2017). "Novel treatment technologies for PFAS compounds: A critical review". Journal of Environmental Management. 204 (Pt 2): 757–764. doi:10.1016/j.jenvman.2017.08.016. ISSN   0301-4797. PMID   28818342.
  5. ↑ Australian Defence. "Defence approach to PFAS management" . Retrieved 26 September 2024.
  6. ↑ Heads of EPAs of Australia and New Zealand. "PFAS National Environmental Management Plan 2.0" . Retrieved 26 September 2024.
  7. ↑ Darlington, R.; Barth, E.; McKernan, J. (2018). "The Challenges of PFAS Remediation". The Military Engineer. 110 (712): 58–60. PMC   5954436 . PMID   29780177.
  8. ↑ Trang, Brittany; Li, Yuli; Xue, Xiao-Song; Ateia, Mohamed; Houk, K. N.; Dichtel, William R. (2022). "Low-temperature mineralization of perfluorocarboxylic acids". Science. 377 (6608): 839–845. Bibcode:2022Sci...377..839T. doi:10.1126/science.abm8868. PMID   35981038.
  9. ↑ Siriwardena, Dinusha (2 April 2021). "Regeneration of per- and polyfluoroalkyl substance-laden granular activated carbon using a solvent based technology". Journal of Environmental Management. 289 (112439). doi:10.1016/j.jenvman.2021.112439. PMID   33819657.
  10. ↑ Baghirzade, Busra (April 21, 2021). "Thermal Regeneration of Spent Granular Activated Carbon Presents an Opportunity to Break the Forever PFAS Cycle". Environmental Science & Technology. 55 (5608−5619): 5608–5619. doi:10.1021/acs.est.0c08224. PMID   33881842.
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  12. 1 2 3 Lei, Xiaobo; Lian, Qiyu; Zhang, Xu; Karsili, Tolga K.; Holmes, William; Chen, Yushun; Zappi, Mark E.; Gang, Daniel Dianchen (15 March 2023). "A review of PFAS adsorption from aqueous solutions: Current approaches, engineering applications, challenges, and opportunities". Environmental Pollution. 321. doi: 10.1016/j.envpol.2023.121138 . ISSN   0269-7491. PMID   36702432.
  13. ↑ Loganathan, Paripurnanda (19 March 2024). "Treatment Trends and Hybrid Methods for the Removal of Polyand Perfluoroalkyl Substances from Water—A Review". Applied Sciences. 14 (2574): 2574. doi: 10.3390/app14062574 .
  14. ↑ Lu, Dingnan (15 March 2020). "Treatment train approaches for the remediation of per- and polyfluoroalkyl substances (PFAS): A critical review". Journal of Hazardous Materials. 386 (121963). doi:10.1016/j.jhazmat.2019.121963.
  15. ↑ Deligiannis, Michalis; Gkalipidou, Evdokia; Gatidou, Georgia; Kostakis, Marios G.; Triantafyllos Gerokonstantis, Dimitrios; Arvaniti, Olga S.; Thomaidis, Nikolaos S.; Vyrides, Ioannis; Hale, Sarah E. (August 2024). "Study on the fate of per- and polyfluoroalkyl substances during thermophilic anaerobic digestion of sewage sludge and the role of granular activated carbon addition". Bioresource Technology. 406: 131013. doi: 10.1016/j.biortech.2024.131013 . ISSN   0960-8524. PMID   38901748.
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