With increasing legislative and public interest in per-and polyfluoroalkyl substances (PFAS), the quest for PFAS remediation technologies is advancing quickly. While currently limited, the number of tools available to manage these substances is growing as associated research gains momentum.
In case you forgot: PFAS chemicals 101
PFAS are recalcitrant chemicals linked to potential toxicity and bioaccumulation in humans and ecological receptors. Perceived PFAS toxicity is indicated by the extremely low Environmental Protection Agency (EPA) Health Advisory (HA) levels of 70 parts per trillion (ppt) for two PFAS compounds combined, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). PFAS are found in everyday items including food packaging, nonstick pans, and waterproof fabric, as well as industrial products such as aqueous film-forming foams (AFFFs) used to extinguish fuel fires.
So, is PFAS remediation possible?
PFAS are known for being difficult to remediate – particularly due to their strong carbon-fluorine bond – and researchers are moving to develop and test novel treatment approaches. For field-scale PFAS treatment, extracted groundwater is typically treated using activated carbon or ion exchange. While these methods can effectively reduce PFOA and PFOS concentrations to the EPA’s HA levels, they do not destroy PFAS. Instead, they produce a concentrated waste stream that must subsequently be treated (e.g., through incineration).
While current field-scale options for PFAS destruction are limited, recent research and development holds promise. For example, biological and abiotic PFAS degradation may offer a more straightforward remediation pathway, and the U.S. Department of Defense is funding several research projects. Other treatment options continue to develop, and a selection of these is highlighted below.
Electrochemical oxidation uses charged electrodes placed in contaminated water to oxidize PFAS into free fluoride (F-) and carbon dioxide. Electrochemical oxidation has proved promising as a PFAS remediation technology in laboratory settings, as evidenced through research conducted by Colorado State University and others, and efforts to bring this technology to pilot- and field-scale applications are underway.
Plasma reactors use electricity to generate plasma, an ionized gas consisting of positive ions and free electrons. Plasma produces highly reactive conditions that can achieve complete degradation of PFAS in water. A recent study demonstrated efficient removal of PFOA and PFOS. To improve the feasibility of this treatment option, various plasma reactor designs are being evaluated.
Hydrothermal reactors use high temperature and pressure conditions to achieve rapid and complete degradation of PFOA and PFOS. For example, a recent study employed temperatures of 200 to 374°C (400 to 660°F) and pressures up to 2 to 22 megapascal (MPa) (20 to 220 atmosphere (atm)) to remediate PFAS. As with other novel technologies, evaluation for pilot- or field-scale applications is warranted.
Biodegradation has generally been classified as not applicable to PFAS. While select precursors may biotransform into PFOA, PFOS, or similar end-products, complete PFAS biodegradation has remained elusive. However, recent research suggests PFAS may not be immune to this remediation method after all. History has witnessed other groundwater contaminants (e.g., MTBE, 1,4-dioxane, and even chlorinated solvents) once thought to be recalcitrant become treatable through biodegradation. Therefore, although in its infancy, biodegradation by bacteria or fungi as a possible PFAS treatment option should not be overlooked. The Department of Defense is funding PFAS biodegradation research, and study results are likely to become publicly available over the next couple years.
In laboratory settings, each of these approaches has provided evidence of F- production, which demonstrates breaking of the carbon-fluorine bond in PFAS. The next steps for promising PFAS degradation technologies will involve larger-scale applications to assess cost-effectiveness and feasibility of field-scale implementation.
Combining remedies into “treatment trains”
Depending on the scenario, a remediation technology can serve as a standalone solution or can be combined with others into a “treatment train.” Treatment trains combine any number of remedies to achieve synergistic interaction benefits, and they can be advantageous in their ability to amplify the strengths of standalone technologies and promote cost-efficiencies.
In an example treatment train, a pre-treatment filtration step could separate a PFAS-impacted water stream into a “clean” stream to meet drinking water standards, and a concentrated waste stream. The clean water stream would be acceptable for community use while the waste stream would be isolated for treatment using PFAS-destructive reactors discussed above, which have been found to be generally more effective and cost-efficient when treating high-concentration streams.
Interested in PFAS remediation strategies? Ask us your PFAS questions!
Trihydro’s team of emerging contaminants experts are involved in research projects to help advance PFAS management solutions. Reach out to one of our subject matter experts to discuss the current state of PFAS remediation technologies.
Mitch Olson, Ph.D., P.E.
PFAS Subject Matter Expert
Andrew Pawlisz, D.A.B.T.
Toxicologist & Risk Assessor