A recent study on per- and polyfluoroalkyl substances (PFAS) has received major media coverage in the last few months, even being hailed by The New York Times as the end of “forever chemicals.” The study by Brittany Trang et al., published in the August 2022 issue of the journal Science, incorporates both a focus on PFAS mineralization and fluorine tracking through the degradation process to understand the potential for byproduct formation. This study represents a big step forward in our collective understanding of the mechanisms of PFAS degradation and approaches to investigate these mechanisms.
The study found that PFAS could be degraded when mixed with the solvent dimethyl sulfoxide (DMSO) and heated at 120°C for several hours with high pH. This involves a much lower temperature than established PFAS destruction technologies, like high-temperature incineration, and suggests a new pathway for PFAS breakdown. Although this is an exciting discovery, it’s important to understand the limitations that must be overcome before the approach can be applied on a commercial scale.
Costs and availability of DMSO could be major challenges for scaling up this process. The study used 90% DMSO as a solvent. A commercial application treating PFAS in water would need to include a step to move PFAS from the water or solid phase into DMSO. Breaking down PFAS molecules in this manner would produce significant volumes of organic solvent and water with a very high pH, requiring downstream management to separate or dispose of the solvent and neutralize the remaining water prior to discharge. If the DMSO solvent could be reused for many iterations of the treatment, both the sourcing and waste management issues would be reduced.
Tested concentrations in this study were in the grams per liter (g/L) range, about one billion times higher than typical concentrations at groundwater remediation sites and treatment targets, which are in the range of micrograms per liter (parts per billion) and nanograms per liter (parts per trillion). Understanding whether this process has concentration dependencies (i.e., lower efficiency at environmentally relevant concentrations) will be crucial to potential future scale-up. However, the method could be useful for treating small volumes of concentrated PFAS wastes, such as foam fractionation (foamate) or stockpiles of aqueous film-forming foam.
Limited PFAS portfolio
The term “PFAS” refers to a family of more than 4,000 chemicals, which includes many different classifications. This study demonstrated the degradation of PFAS classified as perfluorocarboxylates, which includes PFOA. However, this approach (at present) does not appear to be compatible for PFAS classified as perfluorosulfonates, which includes PFOS. Since PFAS are often present as a mixture, including sulfonates, carboxylates, and other classes of PFAS, a treatment method that only removes one class is limited to select applications.
Ultrashort-chain PFAS byproduct
This study demonstrated that, after the degradation process, most (90%) of the initial fluorine atoms associated with PFAS became the anion fluoride and most of the carbon atoms became short-chain carboxylates (like formate and oxalate) and the anion carbonate. However, a small but significant amount of the fluorine and carbon remained as trifluoroacetate (TFA), which is considered an ultrashort-chain PFAS with two carbon atoms. The environmental occurrence and treatability of TFA and other ultrashort-chain PFAS are active areas of research. The implications of TFA as a byproduct are currently uncertain.
More research needed
More research is necessary to improve our collective understanding of low-temperature PFAS destruction options, such as this one, in order to move closer to a prudent destruction technology that could be feasible on a commercial scale. Research like this offers opportunities to build collaborative academic-industry partnerships to further develop promising technologies. Additional questions that could help guide future research and progress the readiness level of this approach include:
Are there cost-effective methods to transfer PFAS from concentrated waste streams (such as foamate, activated carbon, or ion exchange resin) into DMSO?
Can DMSO be reused through iterative cycles of destruction?
What is the minimum amount of DMSO that can be used to treat a given quantity of waste?
Are there other cosolvents that could be used in place of DMSO?
Are there method improvements that can target other classes of PFAS, such as perfluoroalkyl sulfonates like PFOS?
Barr has been developing and evaluating commercially available technologies to support ongoing water treatment projects related to PFAS for several years. Barr is currently working with the Minnesota Pollution Control Agency (MPCA) to evaluate PFAS technologies and their commercial viability for a variety of municipal waste streams, including wastewater, biosolids, and landfill leachate. For additional information, contact our team of PFAS experts.
About the authors
Andy McCabe, environmental engineer, has experience with civil engineering, including working on a variety of projects for industrial and municipal clients, several of which are aimed at treating per- and polyfluoroalkyl substances (PFAS). He has worked on a variety of other projects related to emerging contaminants, industrial water treatment, water reuse and alternative water sources, and analysis of environmental monitoring data.
Ali Ling, former environmental engineer and water/wastewater process engineer at Barr, specialized in connecting basic science to engineering outcomes for clients in various industries, using tools like bench and pilot testing and process modeling. Her work included helping clients solve challenging problems associated with PFAS, active pharmaceuticals, and other contaminants of emerging concern. Ali helped facilitate Barr’s involvement in applied research and university collaborations. She has an academic background in microbial ecology and applied microbiology.
PFAS stack testing services for a manufacturing client
Barr has been measuring per- and polyfluoroalkyl substances (PFAS) in stack emissions at facilities in the U.S. for two decades. Because of this experience, a confidential manufacturing client hired Barr to perform compliance testing to evaluate the performance of thermal oxidation as a best available control technology (BACT) to control PFAS emissions from its processes.
Multi-site PFAS remedial investigation and remediation
Per- and polyfluoroalkyl substances (PFAS) have been detected in public water supplies and private wells at or near active and former manufacturing facilities owned by Saint-Gobain. Barr is part of a collaborative consulting team conducting remedial investigations and feasibility studies.