Research Brief Potential PFAS Destruction Technology Supercritical Water Oxidation


Research BRIEF

INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE

POTENTIAL PFAS DESTRUCTION TECHNOLOGY:
SUPERCRITICAL WATER OXIDATION

In Spring 2020, the EPA established the PFAS Innovative
Treatment Team (PITT). The PITT was a multi-disciplinary
research team that worked full-time for 6-months on
applying their scientific efforts and expertise to a single
problem: disposal and/or destruction of PFAS-
contaminated media and waste. While the PITT formally
concluded in Fall 2020, the research efforts initiated under
the PITT continue.

As part of the PITT's efforts, EPA researchers considered
whether existing destruction technologies could be applied
to PFAS-contaminated media and waste. This series of
Research Briefs provides an overview of four technologies
that were identified by the PITT as promising technologies
for destroying PFAS and the research underway by the
EPA's Office of Research and Development to further
explore these technologies. Because research is still
needed to evaluate these technologies for PFAS
destruction, this Research Brief should not be considered
an endorsement or recommendation to use this
technology to destroy PFAS.

Background

Various industries have produced and used per- and
polyfluoroalkyl substances (PFAS) since the mid-20th
century. PFAS are found in consumer and industrial
products, including non-stick coatings, waterproofing
materials, and manufacturing additives. PFAS are stable
and resistant to natural destruction in the environment,
leading to their pervasive presence in groundwater, surface
waters, drinking water, and other environmental media
(e.g., soil) in some localities. Certain PFAS are also
bioaccumulative, and the blood of most US citizens
contains detectable levels of several PFAS (CDC, 2009). The
toxicity of PFAS is a subject of current study and enough is
known to motivate efforts to limit environmental release
and human exposure (EPA, 2020).

To protect human health and the environment, EPA
researchers are identifying technologies that can destroy
PFAS in liquid and solid waste streams, including
concentrated and spent (used) fire-fighting foam, biosolids,
soils, and landfill leachate. These technologies should be
readily available, cost effective, and produce little to no

Supercritical

Water

374°C
705°F



Temperature

Figure 1. SCWO reactions occur above the critical point of
water. Image credit: Jonathan Kamler.

hazardous residuals or byproducts. The capability to
decompose an array of complex molecular structures
simultaneously makes supercritical water oxidation
(SCWO) a promising technology for PFAS destruction that
warrants further investigation.

Supercritical Water Oxidation: Technology
Overview

SCWO is a process that can be utilized to destroy
hazardous waste compounds. Water above a
temperature of 705 °F and pressure of 221.1 bar is
considered "supercritical" (Figure 1), a special state of
water where certain chemical oxidation processes are
accelerated. Since the 1980s, SCWO has been used
successfully to treat halogenated waste materials
(containing fluorine, chlorine, bromine, or iodine),
including polychlorinated biphenyls (PCBs) (Abeln et al.,
2001; Kim et al., 2010). Organic compounds, usually
insoluble in liquid water, are highly soluble in
supercritical water. In the presence of an oxidizing agent
(such as oxygen), supercritical water dissolves and
oxidizes various hazardous organic pollutants.
Implementation of SCWO at scale has been limited by

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several technical challenges, including the buildup of
corrosive gases during the oxidation reaction, the
precipitation of salts, and the high energy requirements.

Potential for PFAS Destruction

As an alternative to disposal of PFAS-laden material in a
landfill or combustion in an incinerator, SCWO purports to
destroy PFAS by breaking the strong carbon-fluorine bonds
and decomposing the material into a non-toxic waste
stream. SCWO's previous applications to destroy chemical
warfare agents, PCBs, and halogenated compounds makes
it a potential, but currently unproven, alternative for PFAS
destruction (Marrone et al., 2004; Mitton et al., 2001).

Jama et al., (2020) reported greater than 99% destruction
of 12 PFAS, from 3.6 ng/L to <0.036 ng/L, from a landfill
leachate. These data are preliminary, and future
experiments analyzing for more PFAS will help to
understand if high destruction efficiencies can be expected
for complex liquid wastes.

Research Gaps

Technical challenges to implementation of SCWO are
presented by the high pressures and temperatures, causing
potential system degradation and maintenance issues
(Vadillo et al., 2013). In addition, the requirement for
elevated and stable temperatures demand a large and
expensive energy input. The breakdown of PFAS in
aqueous film-forming foams and other wastes produces
fluoride salts. Although fluoride salts are not toxic, they
create reactor plugging issues and reduce system
performance, requiring careful attention to system
maintenance (Voisin et al., 2017). Additionally, the
transformation of fluorine to corrosive hydrofluoric acid
(HF) may require protections for worker health, emission
controls, and reactor care. The use of chemical additives,
such as alkaline substances, to neutralize an acidic
environment could significantly mitigate these issues.

Next Steps

SCWO is one of the technologies being evaluated by EPA
researchers for treatment of PFAS-containing wastes. EPA
researchers are partnering with commercial entities to
conduct pilot-scale SCWO studies. EPA expects to publish
the results of this work in 2021.

References

Abeln, J.; Kluth, M.; Petrich, G.; Schmieder, H. 2001.

Supercritical water oxidation (SCWO): A process for the
treatment of industrial waste effluents. High Pressure
Res. 20(1-6): 537-547.

Centers for Disease Control and Prevention (CDC). 2009.
Fourth National Report on Human Exposure to
Environmental Chemicals.

https://www.cdc.Eov/exposurereport/pdf/fourthrepo
rt.pdf. Accessed Jan. 15, 2021.

US EPA (EPA). 2020. Basic Information on PFAS.

https://www.epa.Eov/pfas/basic-information-pfas.
Accessed Aug. 13, 2020.

Jama, Y.; Lindholst, S.; Andreasen, R. R.; Andersen, H. R.;
Kokkoli, A.; Svendsen, T.; Cai, Z.; Kragelund, C. 2020.
PFAS removal from percolate by super critical water
oxidation (SCWO). In 14th DWF Water Research
Conference. University of Copenhagen.

Kim, K.; Son, S. H.; Kim, K.; Kim, K.; Kim, Y. C. 2010.

Environmental effects of supercritical water oxidation
(SCWO) process for treating transformer oil
contaminated with polychlorinated biphenyls (PCBs).
Chern. Eng. J. 165(1):170-174.

Marrone, P. A.; Hodes, M.; Smith, K. A.; Tester, J. W.
2004. Salt precipitation and scale control in
supercritical water oxidation—Part B:
Commercial/full-scale applications. J. Supercrit. Fluids.
29(3):289-312.

Mitton, D. B.; Eliaz, N.; Cline, J. A.; Latanision, R. M. 2001.
An overview of the current understanding of
corrosion in SCWO systems for the destruction of
hazardous waste products. Mater. Technol. 16(1):44-
53.

Voisin, T.; Erriguible, A.; Ballenghien, D.; Mateos, D.;
Kunegel, A.; Cansell, F.; Aymonier, C. 2017. Solubility
of inorganic salts in sub- and supercritical
hydrothermal environment: Application to SCWO
processes. J. Supercrit. Fluids. 120:18-31.

Vadillo, V.; Sanchez-Oneto, J.; Portela, J. R.; Martinez de
la Ossa, E. J. 2013. Problems in supercritical water
oxidation process and proposed solutions. Ind. Eng.
Chern. Res. 52(23) :7617-7629.

Contacts

•	E. Sahle-Damesessie, PhD - sahle-
demessie.endalkachew(a)epa.sov

•	Max Krause, PhD - krause.max@epa.gov

Note: This research brief is a summary of research
conducted by EPA's Office of Research and Development
and does not necessarily reflect EPA policy.

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