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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.

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

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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

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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

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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

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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

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

References

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  1. ^ Fromme H, Tittlemier SA, Völkel W, Wilhelm M, Twardella D (May 2009). "Perfluorinated compounds—exposure assessment for the general population in Western countries". Int. J. Hyg. Environ. Health. 212 (3): 239–70. Bibcode:2009IJHEH.212..239F. doi:10.1016/j.ijheh.2008.04.007. PMID 18565792.
  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.
  3. ^ a b c Wanninayake, Dushanthi M. (1 April 2021). "Comparison of currently available PFAS remediation technologies in water: A review". Journal of Environmental Management. 283. doi:10.1016/j.jenvman.2021.111977. ISSN 0301-4797. PMID 33517051. S2CID 231766709.
  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.
  11. ^ Gagliano, Erica (15 June 2021). "Microwave regeneration of granular activated carbon saturated with PFAS". Water Research. 198 (117121). doi:10.1016/j.watres.2021.117121.
  12. ^ a b c 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. hdl:11250/3141527. ISSN 0960-8524. PMID 38901748.
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