Remediation of per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS or PFASs) are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. They are highly stable, lipophobic, and hydrophobic, and are used in applications such as non-stick cookware and aqueous film forming foams. Most sources of PFAS pollution are from firefighting, industry wastewater discharge, and landfills, and humans are generally exposed to PFAS through diet and drinking water. PFAS are associated with adverse health effects, such as cancer, decreased fertility, and impact on child development.

Adsorption

Through the process of adsorption, PFAS molecules can be made to accumulate on an adsorbent and removed. Adsorption is generally more efficient in an acidic environment and with large 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 then be regenerated through incineration. 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 to be treated.

Regeneration

Activated carbon granules or particles can be incinerated to regenerate 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.

Reverse osmosis

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

Destruction

Destruction methods include the use of sonolysis, electrochemical oxidation, and advanced oxidation processes, all of which promote the formation of hydroxyl radicals which can oxidize PFAS and break its C-C bonds.