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==PFAS Treatment by Electrical Discharge Plasma==
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==Photoactivated Reductive Defluorination PFAS Destruction==  
Plasma-based water treatment is a technology that, using only electricity, converts water into a mixture of highly reactive species including OH•, O, H•, HO<sub>2</sub>•, O<sub>2</sub>•<sup>‒</sup>, H<sub>2</sub>, O<sub>2</sub>, H<sub>2</sub>O<sub>2</sub> and aqueous electrons (e<sup>‒</sup><sub>aq</sub>), called a plasma<ref name="Sunka1999">Sunka, P., Babický, V., Clupek, M., Lukes, P., Simek, M., Schmidt, J., and Cernak, M., 1999. Generation of Chemically Active Species by Electrical Discharges in Water. Plasma Sources Science and Technology, 8(2), pp. 258-265. [https://doi.org/10.1088/0963-0252/8/2/006 DOI: 10.1088/0963-0252/8/2/006]</ref><ref name="MededovicThagard2009">Mededovic Thagard, S., Takashima, K., and Mizuno, A., 2009. Chemistry of the Positive and Negative Electrical Discharges Formed in Liquid Water and Above a Gas-Liquid Surface. Plasma Chemistry and Plasma Processing, 29(6), pp.455-473. [https://doi.org/10.1007/s11090-009-9195-x DOI: 10.1007/s11090-009-9195-x]</ref>. These highly reactive species rapidly and non-selectively degrade [[Wikipedia: Volatile organic compound |volatile organic compounds (VOCs)]]<ref name="Du2019">Du, C., Gong, X., and Lin, Y., 2019. Decomposition of volatile organic compounds using corona discharge plasma technology. Journal of the Air and Waste Management Association, 69(8), pp.879-899.  [https://doi.org/10.1080/10962247.2019.1582441 DOI: 10.1080/10962247.2019.1582441]  [https://www.tandfonline.com/doi/full/10.1080/10962247.2019.1582441 Open access article.]</ref>, [[1,4-Dioxane | 1,4-dioxane]]<ref name="Xiong2019">Xiong, Y., Zhang, Q., Wandell, R., Bresch, S., Wang, H., Locke, B.R. and Tang, Y., 2019. Synergistic 1,4-Dioxane Removal by Non-Thermal Plasma Followed by Biodegradation. Chemical Engineering Journal, 361, pp.519-527. [https://doi.org/10.1016/J.CEJ.2018.12.094 DOI: 10.1016/J.CEJ.2018.12.094]</ref><ref name="Ni2013">Ni, G.H., Zhao, Y., Meng, Y.D., Wang, X.K., and Toyoda, H., 2013. Steam plasma jet for treatment of contaminated water with high-concentration 1,4-dioxane organic pollutants. Europhysics Letters, 101(4), p.45001. [https://doi.org/10.1209/0295-5075/101/45001 DOI: 10.1209/0295-5075/101/45001]</ref>, and a broad spectrum of [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | per- and polyfluoroalkyl substances (PFAS)]] including perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), and short-chain PFAS<ref name="Stratton2015">Stratton, G.R., Bellona, C.L., Dai, F., Holsen, T.M. and Mededovic Thagard, S., 2015. Plasma-Based Water Treatment: Conception and Application of a New General Principle for Reactor Design. Chemical Engineering Journal, 273, pp.543-550. [https://doi.org/10.1016/j.cej.2015.03.059 DOI: 10.1016/j.cej.2015.03.059]</ref><ref name="Singh2019a">Singh, R.K., Multari, N., Nau-Hix, C., Anderson, R.H., Richardson, S.D., Holsen, T.M. and Mededovic Thagard, S., 2019. Rapid Removal of Poly- and Perfluorinated Compounds from Investigation-Derived Waste (IDW) in a Pilot-Scale Plasma Reactor. Environmental Science and Technology, 53(19), pp.11375-11382. [https://doi.org/10.1021/acs.est.9b02964 DOI: 10.1021/acs.est.9b02964]</ref><ref name="Singh2019b">Singh, R.K., Fernando, S., Baygi, S.F., Multari, N., Mededovic Thagard, S., and Holsen, T.M., 2019. Breakdown Products from Perfluorinated Alkyl Substances (PFAS) Degradation in a Plasma-Based Water Treatment Process. Environmental Science and Technology, 53(5), pp.2731-2738. [https://doi.org/10.1021/acs.est.8b07031 DOI: 10.1021/acs.est.8b07031]</ref>. A plasma reactor can simultaneously oxidize and reduce organics by producing a mixture of hydroxyl radicals and aqueous electrons, the latter of which act as strong reducing agents and could be the key species in removing PFAS and other non-oxidizable compounds. Additionally, the plasma process produces no residual waste and requires no chemical additions, although adding surfactants or injecting inert gas into the liquid phase can increase interfacial PFAS concentrations, exposing more of the PFAS to the plasma and therefore increasing removal efficiency.  
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Photoactivated Reductive Defluorination (PRD) is a [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] destruction technology predicated on [[Wikipedia: Ultraviolet | ultraviolet (UV)]] light-activated photochemical reactions. The destruction efficiency of this process is enhanced by the use of a [[Wikipedia: Surfactant | surfactant]] to confine PFAS molecules in self-assembled [[Wikipedia: Micelle | micelles]]. The photochemical reaction produces [[Wikipedia: Solvated electron | hydrated electrons]] from an electron donor that associates with the micelle. The hydrated electrons have sufficient energy to rapidly cleave fluorine-carbon and other molecular bonds of PFAS molecules due to the association of the electron donor with the micelle. Micelle-accelerated PRD is a highly efficient method to destroy PFAS in a wide variety of water matrices.
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
 
*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]  
 
*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]  
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*[[PFAS Sources]]
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*[[PFAS Transport and Fate]]
 
*[[PFAS Ex Situ Water Treatment]]
 
*[[PFAS Ex Situ Water Treatment]]
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*[[Supercritical Water Oxidation (SCWO)]]
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*[[PFAS Treatment by Electrical Discharge Plasma]]
  
 
'''Contributor(s):'''  
 
'''Contributor(s):'''  
*Dr. Selma Mededovic Thagard
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*Dr. Suzanne Witt
*Dr. Thomas Holsen
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*Dr. Meng Wang
*Dr. Stephen Richardson, P.E
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*Dr. Denise Kay
*Poonam Kulkarni, P.E.
 
*Dr. Blossom Nzeribe
 
  
 
'''Key Resource(s):'''
 
'''Key Resource(s):'''
* [https://pfas-1.itrcweb.org/12-treatment-technologies/#12_2  PFAS – Per- and Polyfluoroalkyl Substances: 12.2 Field-Implemented Liquids Treatment Technologies. Interstate Technology Regulatory Council (ITRC).] See also: [https://pfas-1.itrcweb.org/12-treatment-technologies/#12_5 12.5 Limited Application and Developing Liquids Treatment Technologies].
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*Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement<ref name="ChenEtAl2020">Chen, Z., Li, C., Gao, J., Dong, H., Chen, Y., Wu, B., Gu, C., 2020. Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement. Environmental Science and Technology, 54(8), pp. 5178–5185. [https://doi.org/10.1021/acs.est.9b06599 doi: 10.1021/acs.est.9b06599]</ref>
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*Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-Acetic-Acid in Organomodified Montmorillonite<ref name="TianEtAl2016">Tian, H., Gao, J., Li, H., Boyd, S.A., Gu, C., 2016. Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-Acetic-Acid in Organomodified Montmorillonite. Scientific Reports, 6(1), Article 32949. [https://doi.org/10.1038/srep32949 doi: 10.1038/srep32949]&nbsp;&nbsp; [[Media: TianEtAl2016.pdf | Open Access Article]]</ref>
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*Application of Surfactant Modified Montmorillonite with Different Conformation for Photo-Treatment of Perfluorooctanoic Acid by Hydrated Electrons<ref name="ChenEtAl2019">Chen, Z., Tian, H., Li, H., Li, J. S., Hong, R., Sheng, F., Wang, C., Gu, C., 2019Application of Surfactant Modified Montmorillonite with Different Conformation for Photo-Treatment of Perfluorooctanoic Acid by Hydrated Electrons. Chemosphere, 235, pp. 1180–1188. [https://doi.org/10.1016/j.chemosphere.2019.07.032 doi: 10.1016/j.chemosphere.2019.07.032]</ref>
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*[https://serdp-estcp.mil/projects/details/c4e21fa2-c7e2-4699-83a9-3427dd484a1a ER21-7569: Photoactivated Reductive Defluorination PFAS Destruction]<ref name="WittEtAl2023">Kay, D., Witt, S., Wang, M., 2023. Photoactivated Reductive Defluorination PFAS Destruction: Final Report. ESTCP Project ER21-7569. [https://serdp-estcp.mil/projects/details/c4e21fa2-c7e2-4699-83a9-3427dd484a1a Project Website]&nbsp;&nbsp; [[Media: ER21-7569_Final_Report.pdf | Final Report.pdf]]</ref>
  
* Physico-Chemical Processes for the Treatment of Per- And Polyfluoroalkyl Substances (PFAS): A review28<ref name="Nzeribe2019">Nzeribe, B.N., Crimi, M., Mededovic Thagard, S. and Holsen, T.M., 2019. Physico-Chemical Processes for the Treatment of Per- And Polyfluoroalkyl Substances (PFAS): A review. Critical Reviews in Environmental Science and Technology, 49(10), pp.866-915. [https://doi.org/10.1080/10643389.2018.1542916 DOI: 10.1080/10643389.2018.1542916]</ref>
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==Introduction==
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[[File:WittFig1.png | thumb |600px|Figure 1. Schematic of PRD mechanism<ref name="WittEtAl2023"/>]]
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The&nbsp;Photoactivated&nbsp;Reductive Defluorination (PRD) process is based on a patented chemical reaction that breaks fluorine-carbon bonds and disassembles PFAS molecules in a linear fashion beginning with the [[Wikipedia: Hydrophile | hydrophilic]] functional groups and proceeding through shorter molecules to complete mineralization. Figure 1 shows how PRD is facilitated by adding [[Wikipedia: Cetrimonium bromide | cetyltrimethylammonium bromide (CTAB)]] to form a surfactant micelle cage that traps PFAS. A non-toxic proprietary chemical is added to solution to associate with the micelle surface and produce hydrated electrons via stimulation with UV light. These highly reactive hydrated electrons have the energy required to cleave fluorine-carbon and other molecular bonds resulting in the final products of fluoride, water, and simple carbon molecules (e.g., formic acid and acetic acid). The methods, mechanisms, theory, and reactions described herein have been published in peer reviewed literature<ref name="ChenEtAl2020"/><ref name="TianEtAl2016"/><ref name="ChenEtAl2019"/><ref name="WittEtAl2023"/>.
  
* Low Temperature Plasma for Biology, Hygiene, and Medicine: Perspective and Roadmap<ref name="Laroussi2021">Laroussi, M., Bekeschus, S., Keidar, M., Bogaerts, A., Fridman, A., Lu, X.P., Ostrikov, K.K., Hori, M., Stapelmann, K., Miller, V., Reuter, S., Laux, C., Mesbah, A., Walsh, J., Jiang, C., Mededovic Thagard, S., Tanaka, H., Liu, D.W., Yan, D., and Yusupov, M., 2021. Low Temperature Plasma for Biology, Hygiene, and Medicine: Perspective and Roadmap. IEEE Transactions on Radiation and Plasma Medical Sciences. [https://doi.org/10.1109/TRPMS.2021.3135118 DOI: 10.1109/TRPMS.2021.3135118]  [https://ieeexplore.ieee.org/abstract/document/9650590 Open access article.]</ref>
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==Advantages and Disadvantages==
  
==Introduction==
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===Advantages===
[[File:Plasma4PFASFig1.png | thumb |left|700px|Figure 1. Plasmas generated within liquids (Courtesy of Plasma Research Laboratory, Clarkson University)]]
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In comparison to other reported PFAS destruction techniques, PRD offers several advantages:  
Plasma processing plays an essential role in various industrial applications such as semiconductor fabrication, polymer functionalization, chemical synthesis, agriculture and food safety, health industry, and hazardous waste management<ref name="VanVeldhuizen2002">Van Veldhuizen, E.M., and Rutgers, W.R., 2002. Pulsed Positive Corona Streamer Propagation and Branching. Journal of Physics D: Applied Physics, 35(17), p.2169. [https://doi.org/10.1088/0022-3727/35/17/313 DOI: 10.1088/0022-3727/35/17/313]</ref><ref name="Yang">Yang, Y., Cho, Y.I. and Fridman, A., 2012. Plasma Discharge in Liquid: Water Treatment and Applications. CRC press. ISBN: 978-1-4398-6623-8  [https://doi.org/10.1201/b11650 DOI: 10.1201/b11650]</ref><ref name="Rezaei2019">Rezaei, F., Vanraes, P., Nikiforov, A., Morent, R., and De Geyter, N., 2019. Applications of Plasma-Liquid Systems: A Review. Materials, 12(17), article 2751, 69 pp. [https://doi.org/10.3390/ma12172751 DOI: 10.3390/ma12172751]&nbsp;&nbsp;  [https://www.mdpi.com/1996-1944/12/17/2751 Open access article].</ref><ref name="Herianto2021">Herianto, S., Hou, C.Y., Lin, C.M., and Chen, H.L., 2021. Nonthermal plasma-activated water: A comprehensive review of this new tool for enhanced food safety and quality. Comprehensive Reviews in Food Science and Food Safety, 20(1), pp. 583-626. [https://doi.org/10.1111/1541-4337.12667 DOI: 10.1111/1541-4337.12667]</ref>. Plasma is a gaseous state of matter consisting of charged particles, metastable-state molecules or atoms, and free radicals. Depending on the energy or temperature of the electrons, compared with the temperature of the background gas, plasmas can be classified as thermal or non-thermal. In thermal plasma, an example of which is an electrical arc, individual species’ temperatures typically exceed several thousand kelvins (K). Non-thermal plasmas are formed using less power with temperatures ranging from ambient to approximately 1000 K<ref name="Jiang2014">Jiang, B., Zheng, J., Qiu, S., Wu, M., Zhang, Q., Yan, Z. and Xue, Q., 2014. Review on Electrical Discharge Plasma Technology for Wastewater Remediation. Chemical Engineering Journal, 236, pp. 348–368. [https://doi.org/10.1016/j.cej.2013.09.090 DOI: 10.1016/j.cej.2013.09.090]</ref>. An example of a non-thermal plasma is a dielectric barrier discharge used for commercial ozone generation.  
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*Relative to UV/sodium sulfite and UV/sodium iodide systems, the fitted degradation rates in the micelle-accelerated PRD reaction system were ~18 and ~36 times higher, indicating the key role of the self-assembled micelle in creating a confined space for rapid PFAS destruction<ref name="ChenEtAl2020"/>. The negatively charged hydrated electron associated with the positively charged cetyltrimethylammonium ion (CTA<sup>+</sup>) forms the surfactant micelle to trap molecules with similar structures, selectively mineralizing compounds with both hydrophobic and hydrophilic groups (e.g., PFAS).
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*The PRD reaction does not require solid catalysts or electrodes, which can be expensive to acquire and difficult to regenerate or dispose.  
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*The aqueous solution is not heated or pressurized, and the UV wavelength used does not cause direct water [[Wikipedia: Photodissociation | photolysis]], therefore the energy input to the system is more directly employed to destroy PFAS, resulting in greater energy efficiency.  
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*Since the reaction is performed at ambient temperature and pressure, there are limited concerns regarding environmental health and safety or volatilization of PFAS compared to heated and pressurized systems.  
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*Due to the reductive nature of the reaction, there is no formation of unwanted byproducts resulting from oxidative processes, such as [[Wikipedia: Perchlorate | perchlorate]] generation during electrochemical oxidation<ref>Veciana, M., Bräunig, J., Farhat, A., Pype, M. L., Freguia, S., Carvalho, G., Keller, J., Ledezma, P., 2022. Electrochemical Oxidation Processes for PFAS Removal from Contaminated Water and Wastewater: Fundamentals, Gaps and Opportunities towards Practical Implementation. Journal of Hazardous Materials, 434, Article 128886. [https://doi.org/10.1016/j.jhazmat.2022.128886 doi: 10.1016/j.jhazmat.2022.128886]</ref><ref>Trojanowicz, M., Bojanowska-Czajka, A., Bartosiewicz, I., Kulisa, K., 2018. Advanced Oxidation/Reduction Processes Treatment for Aqueous Perfluorooctanoate (PFOA) and Perfluorooctanesulfonate (PFOS) – A Review of Recent Advances. Chemical Engineering Journal, 336, pp. 170–199. [https://doi.org/10.1016/j.cej.2017.10.153 doi: 10.1016/j.cej.2017.10.153]</ref><ref>Wanninayake, D.M., 2021. Comparison of Currently Available PFAS Remediation Technologies in Water: A Review. Journal of Environmental Management, 283, Article 111977. [https://doi.org/10.1016/j.jenvman.2021.111977 doi: 10.1016/j.jenvman.2021.111977]</ref>.
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*Aqueous fluoride ions are the primary end products of PRD, enabling real-time reaction monitoring with a fluoride [[Wikipedia: Ion-selective electrode | ion selective electrode (ISE)]], which is far less expensive and faster than relying on PFAS analytical data alone to monitor system performance.
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===Disadvantages===
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*The CTAB additive is only partially consumed during the reaction, and although CTAB is not problematic when discharged to downstream treatment processes that incorporate aerobic digestors, CTAB can be toxic to surface waters and anaerobic digestors. Therefore, disposal options for treated solutions will need to be evaluated on a site-specific basis. Possible options include removal of CTAB from solution for reuse in subsequent PRD treatments, or implementation of an oxidation reaction to degrade CTAB.
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*The PRD reaction rate decreases in water matrices with high levels of total dissolved solids (TDS). It is hypothesized that in high TDS solutions (e.g., ion exchange still bottoms with TDS of 200,000 ppm), the presence of ionic species inhibits the association of the electron donor with the micelle, thus decreasing the reaction rate.
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*The PRD reaction rate decreases in water matrices with very low UV transmissivity. Low UV transmissivity (i.e., < 1 %) prevents the penetration of UV light into the solution, such that the utilization efficiency of UV light decreases.  
  
Plasma that is applied in water treatment (Figure 1) is typically non-thermal, which offers high-energy process efficiency and selectivity<ref name="Jiang2014"/><ref name="Magureanu2018">Magureanu, M., Bradu, C., and Parvulescu, V.I., 2018. Plasma Processes for the Treatment of Water Contaminated with Harmful Organic Compounds. Journal of Physics D: Applied Physics, 51(31), p. 313002. [https://doi.org/10.1088/1361-6463/aacd9c DOI:    10.1088/1361-6463/aacd9c]</ref>. Since the 1980s when the first plasma reactor was utilized to oxidize a dye<ref name="Clements1987">Clements, J.S., Sato, M., and Davis, R.H., 1987. Preliminary Investigation of Prebreakdown Phenomena and Chemical Reactions Using a Pulsed High-Voltage Discharge in Water. IEEE Transactions on Industry Applications, IA-23(2), pp. 224-235.  [https://doi.org/10.1109/TIA.1987.4504897 DOI: 10.1109/TIA.1987.4504897]</ref>, over a hundred different plasma reactors have been developed to treat a range of contaminants of environmental importance including biological species. Examples include treatment of pharmaceuticals, volatile organic compounds (VOCs), 1,4-dioxane, herbicides, pesticides, warfare agents, bacteria, yeasts and viruses using direct-in-liquid discharges with and without bubbles and discharges in a gas over and contacting the surface of a liquid. Different excitation sources including AC, nanosecond pulsed and DC voltages have been utilized to produce pulsed corona, corona-like, spark, arc, and glow discharges, among other discharge types. Many reviews of plasma processing for water treatment applications have recently been published<ref name="Zeghioud2020">Zeghioud, H., Nguyen-Tri, P., Khezami, L., Amrane, A., and Assadi, A.A., 2020. Review on Discharge Plasma for Water Treatment: Mechanism, Reactor Geometries, Active Species and Combined Processes. Journal of Water Process Engineering, 38, p.101664. [https://doi.org/10.1016/j.jwpe.2020.101664 DOI: 10.1016/j.jwpe.2020.101664]</ref><ref name="Murugesan2020">Murugesan, P., Evanjalin Monica, V., Moses, J.A., and Anandharamakrishnan, C., 2020. Water Decontamination Using Non-Thermal Plasma: Concepts, Applications, and Prospects. Journal of Environmental Chemical Engineering, 8(5), p. 104377. [https://doi.org/10.1016/j.jece.2020.104377 DOI: 10.1016/j.jece.2020.104377]</ref>.
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==State of the Art==
[[File: Plasma4PFASFig2.png | thumb |500px|Figure 2. Continuous flow enhanced contact plasma treatment system (Courtesy of Plasma Research Laboratory, Clarkson University).]]
 
Plasma-based water treatment (PWT) owes its strong oxidation and disinfection capabilities to the production of reactive oxidative species (ROS), primarily OH radicals, atomic oxygen, singlet oxygen and hydrogen peroxide. The process also produces reductive species such as solvated electrons and reactive nitrogen species (RNS) when nitrogen and oxygen are present in the discharge. This process has the advantage of synergistic effects of high electric fields, UV/VUV light emissions and in some cases shockwave formation in a liquid. It requires no chemical additions, and can be optimized for batch or continuous processing.
 
  
==Application of Plasma for the Treatment of PFAS-Contaminated Water==
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===Technical Performance===
Several research groups have investigated the use of plasma to treat and remove PFAS from contaminated water<ref name="Hayashi2015">Hayashi, R., Obo, H., Takeuchi, N., and Yasuoka, K., 2015. Decomposition of Perfluorinated Compounds in Water by DC Plasma within Oxygen Bubbles. Electrical Engineering in Japan, 190(3), pp.9-16. [https://doi.org/10.1002/eej.22499 DOI: 10.1002/eej.22499]&nbsp;&nbsp;  [https://onlinelibrary.wiley.com/doi/full/10.1002/eej.22499 Open access article].</ref><ref name="Matsuya2014">Matsuya, Y., Takeuchi, N., Yasuoka, K., 2014. Relationship Between Reaction Rate of Perfluorocarboxylic Acid Decomposition at a Plasma-Liquid Interface and Adsorbed Amount. Electrical Engineering in Japan, 188(2), pp.1-8. [https://doi.org/10.1002/eej.22526 DOI:  10.1002/eej.22526]&nbsp;&nbsp; [https://onlinelibrary.wiley.com/doi/full/10.1002/eej.22526 Open access article].</ref><ref name="Stratton2017">Stratton, G.R., Dai, F., Bellona, C.L., Holsen, T.M., Dickenson, E.R., and Mededovic Thagard, S., 2017. Plasma-Based Water Treatment: Efficient Transformation of Perfluoroalkyl Substances in Prepared Solutions and Contaminated Groundwater. Environmental Science and Technology, 51(3), pp.1643-1648. [https://doi.org/10.1021/acs.est.6b04215 DOI: 10.1021/acs.est.6b04215]</ref><ref name="Takeuchi2013">Takeuchi, N., Kitagawa, Y., Kosugi, A., Tachibana, K., Obo, H., and Yasuoka, K., 2013. Plasma-Liquid Interfacial Reaction in Decomposition of Perfluoro Surfactants. Journal of Physics D: Applied Physics, 47(4), p.045203. [https://doi.org/10.1088/0022-3727/47/4/045203 DOI: 10.1088/0022-3727/47/4/045203]</ref><ref name="Yasuoka2011">Yasuoka, K., Sasaki, K., and Hayashi, R., 2011. An Energy-Efficient Process for Decomposing Perfluorooctanoic and Perfluorooctane Sulfonic Acids Using DC Plasmas Generated within Gas Bubbles. Plasma Sources Science and Technology, 20(3), p. 034009. [https://doi.org/10.1088/0963-0252/20/3/034009 DOI: 10.1088/0963-0252/20/3/034009]</ref><ref name="Yasuoka2010">Yasuoka, K., Sasaki, K., Hayashi, R., Kosugi, A., and Takeuchi, N., 2010. Degradation of Perfluoro Compounds and F<sup>-</sup> Recovery in Water Using Discharge Plasmas Generated within Gas Bubbles. International Journal of Plasma Environmental Science and Technology, 4(2), 113–117.  [http://ijpest.com/Contents/04/2/PDF/04-02-113.pdf Open access article].</ref><ref name="Lewis2020">Lewis, A.J., Joyce, T., Hadaya, M., Ebrahimi, F., Dragiev, I., Giardetti, N., Yang, J., Fridman, G., Rabinovich, A., Fridman, A.A., McKenzie, E.R., and Sales, C.M., 2020. Rapid Degradation of PFAS in Aqueous Solutions by Reverse Vortex Flow Gliding Arc Plasma. Environmental Science: Water Research and Technology, 6(4), pp.1044-1057. [https://doi.org/10.1039/c9ew01050e DOI: 10.1039/c9ew01050e]</ref><ref name="Saleem2020">Saleem, M., Biondo, O., Sretenović, G., Tomei, G., Magarotto, M., Pavarin, D., Marotta, E. and Paradisi, C., 2020. Comparative Performance Assessment of Plasma Reactors for the Treatment of PFOA; Reactor Design, Kinetics, Mineralization and Energy Yield. Chemical Engineering Journal, 382, p.123031. [https://doi.org/10.1016/j.cej.2019.123031 DOI: 10.1016/j.cej.2019.123031]</ref><ref name="Palma2021">Palma, D., Papagiannaki, D., Lai, M., Binetti, R., Sleiman, M., Minella, M. and Richard, C., 2021. PFAS Degradation in Ultrapure and Groundwater Using Non-Thermal Plasma. Molecules, 26(4), p. 924. [https://doi.org/10.3390/molecules26040924 DOI: 10.3390/molecules26040924]&nbsp;&nbsp; [https://www.mdpi.com/1420-3049/26/4/924/htm Open access article].</ref>.  Of those studies, the Enhanced Contact (EC) plasma reactor developed by researchers at Clarkson University is one of the most promising in terms of treatment time, cost, the range of PFAS treated and scale up/throughput. Their process has been shown to degrade PFOA, PFOS, and other PFAS in a variety of PFAS-impacted water sources.
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[[File:WittFig2.png | thumb |400px| Figure 2. Enspired Solutions<small><sup>TM</sup></small> commercial PRD PFAS destruction equipment, the PFASigator<small><sup>TM</sup></small>. Dimensions are 8 feet long by 4 feet wide by 9 feet tall.]]
  
[[File: Plasma4PFASFig3.png | thumb |left|350px|Figure 3. Degradation profiles of combined PFOA and PFOS concentrations in investigation derived waste (IDW) obtained from nine different Air Force site investigations. In all the IDW samples, both PFOS and PFOA were removed to below EPA’s lifetime health advisory level concentrations (70 ng/L) in < 1 minute of treatment, demonstrating the lack of sensitivity of the plasma-based process to the effects of co-contaminants<ref name="Singh2019a"/>.]]
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{| class="wikitable mw-collapsible" style="float:left; margin-right:20px; text-align:center;"
[[File: Plasma4PFASFig4.png | thumb |600px|Figure 4. (a) Mobile plasma treatment trailer depicting the (b) plasma side of the trailer featuring two plasma reactors and the plasma-generating network; and (c) control and plumbing side of the plasma trailer featuring multiple rotameters, storage tanks and plumbing.]]
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|+Table 1. Percent decreases from initial PFAS concentrations during benchtop testing of PRD treatment in different water matrices
In the EC plasma reactor (Figure 2), argon gas is continuously pumped through the solution to form a layer of foam and thus concentrate PFAS at the gas-liquid interface where plasma is formed. The process is able to lower the concentrations of PFOA and PFOS in groundwater obtained from multiple DoD sites to below Environmental Protection Agency’s (EPA’s) lifetime health advisory level (HAL) of 70 parts per trillion (70 nanogram per liter, ng/L)<ref name="USEPA2016">US Environmental Protection Agency (EPA), 2016. Lifetime Health Advisories and Health Effects Support Documents for Perfluorooctanoic Acid and Perfluorooctane Sulfonate. Federal Register, Notices, 81(101), p. 33250-33251.  [https://www.epa.gov/sites/production/files/2016-05/documents/2016-12361.pdf Free download].</ref> within 1 minute of treatment (Figure 3) with energy requirements much lower than those of alternative technologies (~2-6 kWh/m3 for plasma vs. 5000 kWh/m3 for persulfate, photochemical oxidation and sonolytic processes and 132 kWh/m3 for electrochemical oxidation)<ref name="Singh2019a"/><ref name="Nzeribe2019"/>. The EC plasma reactor owes its high efficacy to the plasma reactor design, in particular to the gas bubbling through submerged diffusers to transport PFAS to the plasma-liquid interface and thus minimize bulk liquid limitations.
+
|-
[[File: Plasma4PFASFig5.png | thumb |left|500px|Figure 5. Plasma destruction of PFAS-impacted groundwater at the fire-training area at Wright-Patterson Air Force Base<ref name="Nau-Hix2021"/>. One cycle = 18 gallons.]]
+
! Analytes
In 2019, a mobile plasma treatment system (Figure 4) was successfully demonstrated for the treatment of PFAS-contaminated groundwater at the fire-training area at Wright-Patterson Air Force Base<ref name="Nau-Hix2021">Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M. and Mededovic Thagard, S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly-and Perfluoroalkyl Substances in Groundwater. ACS ES&T Water, 1(3), pp. 680-687. [https://doi.org/10.1021/acsestwater.0c00170 DOI: 10.1021/acsestwater.0c00170]</ref>.
+
!
 +
! GW
 +
! FF
 +
! AFFF<br>Rinsate
 +
! AFF<br>(diluted 10X)
 +
! IDW NF
 +
|-
 +
| &Sigma; Total PFAS<small><sup>a</sup></small> (ND=0)
 +
| rowspan="9" style="background-color:white;" | <p style="writing-mode: vertical-rl">% Decrease<br>(Initial Concentration, &mu;g/L)</p>
 +
| 93%<br>(370) || 96%<br>(32,000) || 89%<br>(57,000) || 86 %<br>(770,000) || 84%<br>(82)
 +
|-
 +
| &Sigma; Total PFAS (ND=MDL) || 93%<br>(400) || 86%<br>(32,000) || 90%<br>(59,000) || 71%<br>(770,000) || 88%<br>(110)
 +
|-
 +
| &Sigma; Total PFAS (ND=RL) || 94%<br>(460) || 96%<br>(32,000) || 91%<br>(66,000) || 34%<br>(770,000) || 92%<br>(170)
 +
|-
 +
| &Sigma; Highly Regulated PFAS<small><sup>b</sup></small> (ND=0) || >99%<br>(180) || >99%<br>(20,000) || 95%<br>(20,000) || 92%<br>(390,000) || 95%<br>(50)
 +
|-
 +
| &Sigma; Highly Regulated PFAS (ND=MDL) || >99%<br>(180) || 98%<br>(20,000) || 95%<br>(20,000) || 88%<br>(390,000) || 95%<br> (52)
 +
|-
 +
| &Sigma; Highly Regulated PFAS (ND=RL) || >99%<br>(190) || 93%<br>(20,000) || 95%<br>(20,000) || 79%<br>(390,000) || 95%<br>(55)
 +
|-
 +
| &Sigma; High Priority PFAS<small><sup>c</sup></small> (ND=0) || 91%<br>(180) || 98%<br>(20,000) || 85%<br>(20,000) || 82%<br>(400,000) || 94%<br>(53)
 +
|-
 +
| &Sigma; High Priority PFAS (ND=MDL) || 91%<br>(190) || 94%<br>(20,000) || 85%<br>(20,000) || 79%<br>(400,000) || 86%<br>(58)
 +
|-
 +
| &Sigma; High Priority PFAS (ND=RL) || 92%<br>(200) || 87%<br>(20,000) || 86%<br>(21,000) || 70%<br>(400,000) || 87%<br>(65)
 +
|-
 +
| Fluorine mass balance<small><sup>d</sup></small> || ||106% || 109% || 110% || 65% || 98%
 +
|-
 +
| Sorbed organic fluorine<small><sup>e</sup></small> || || 4% || 4% || 33% || N/A || 31%
 +
|-
 +
| colspan="7" style="background-color:white; text-align:left" | <small>Notes:<br>GW = groundwater<br>GW FF = groundwater foam fractionate<br>AFFF rinsate = rinsate collected from fire system decontamination<br>AFFF (diluted 10x) = 3M Lightwater AFFF diluted 10x<br>IDW NF = investigation derived waste nanofiltrate<br>ND = non-detect<br>MDL = Method Detection Limit<br>RL = Reporting Limit<br><small><sup>a</sup></small>Total PFAS = 40 analytes + unidentified PFCA precursors<br><small><sup>b</sup></small>Highly regulated PFAS = PFNA, PFOA, PFOS, PFHxS, PFBS, HFPO-DA<br><small><sup>c</sup></small>High priority PFAS = PFNA, PFOA, PFHxA, PFBA, PFOS, PFHxS, PFBS, HFPO-DA<br><small><sup>d</sup></small>Ratio of the final to the initial organic fluorine plus inorganic fluoride concentrations<br><small><sup>e</sup></small>Percent of organic fluorine that sorbed to the reactor walls during treatment<br></small>
 +
|}
 +
</br>
 +
The&nbsp;PRD&nbsp;reaction&nbsp;has&nbsp;been validated at the bench scale for the destruction of PFAS in a variety of environmental samples from Department of Defense sites (Table 1). Enspired Solutions<small><sup>TM</sup></small> has designed and manufactured a fully automatic commercial-scale piece of equipment called PFASigator<small><sup>TM</sup></small>, specializing in PRD PFAS destruction (Figure 2). This equipment is modular and scalable, has a small footprint, and can be used alone or in series with existing water treatment trains. The PFASigator<small><sup>TM</sup></small> employs commercially available UV reactors and monitoring meters that have been used in the water industry for decades. The system has been tested on PRD efficiency operational parameters, and key metrics were proven to be consistent with benchtop studies.  
  
Over 300 gallons of PFAS-impacted groundwater were treated at a maximum flowrate of 1.1  gallon per minute (gpm) resulting in ≥90% reduction (mean percent removal of 99.7%) of long-chain PFAAs (fluorocarbon chain ≥ 6) and PFAS precursors in a single pass through the reactor (Figure 5) at a treatment cost of $7.30/1000 gallons<ref name="Nau-Hix2021"/>. As expected, the removal of short-chain PFAS was slower due to their lower potential for interfacial adsorption compared to long-chain PFAS. However, post-field laboratory studies revealed that the addition of a cationic surfactant such as CTAB (cetrimonium bromide) minimizes bulk liquid transport limitations for short-chain PFAS by electrostatically interacting with these compounds and transporting them to the plasma-liquid interface where they are degraded.26 Both bench and pilot-scale EC plasma-based process have been extended for the treatment of PFAS in membrane concentrate, ion exchange brine, and landfill leachate<ref name="Singh2020">Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S. and Holsen, T.M., 2020. Removal of Poly- And Per-Fluorinated Compounds from Ion Exchange Regenerant Still Bottom Samples in a Plasma Reactor. Environmental Science and Technology, 54(21), pp.13973-13980. [https://doi.org/10.1021/acs.est.0c02158 DOI: 10.1021/acs.est.0c02158]</ref><ref name="Singh2021">Singh, R.K., Brown, E., Mededovic Thagard, S., and Holsen, T.M., 2021. Treatment of PFAS-Containing Landfill Leachate Using an Enhanced Contact Plasma Reactor. Journal of Hazardous Materials, 408, p.124452. [https://doi.org/10.1016/j.jhazmat.2020.124452 DOI: 10.1016/j.jhazmat.2020.124452]</ref>.  
+
Bench scale PRD tests were performed for the following samples collected from Department of Defense sites: groundwater (GW), groundwater foam fractionate (FF), firefighting truck rinsate ([[Wikipedia: Firefighting foam | AFFF]] Rinsate), 3M Lightwater AFFF, investigation derived waste nanofiltrate (IDW NF), [[Wikipedia: Ion exchange | ion exchange]] still bottom (IX SB), and Ansulite AFFF. The PRD treatment was more effective in low conductivity/TDS solutions. Generally, PRD reaction rates decrease for solutions with a TDS > 10,000 ppm, with an upper limit of 30,000 ppm. Ansulite AFFF and IX SB samples showed low destruction efficiencies during initial screening tests, which was primarily attributed to their high TDS concentrations. Benchtop testing data are shown in Table 1 for the remaining five sample matrices.
  
As a part of a currently-funded ESTCP project (ESTCP ER20-5535)<ref name="Mededovic2020">Mededovic, S., 2020. An Innovative Plasma Technology for Treatment of AFFF Rinsate from Firefighting Delivery Systems. Environmental Security Technology Certification Program (ESTCP), Project ER20-5355. [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/ER20-5355  Project Overview]</ref>, the Clarkson University team with the support of GSI Environmental Inc. is evaluating the effectiveness of their plasma process in treating diluted aqueous film-forming foams (AFFFs) as well as the benefits of pre-oxidation of PFAS precursors in high concentration AFFF solutions in terms of post-oxidation plasma treatment time, destruction efficiency and cost.
+
During treatment, PFOS and PFOA concentrations decreased 96% to >99% and 77% to 97%, respectively. For the PFAS with proposed drinking water Maximum Contaminant Levels (MCLs) recently established by the USEPA (PFNA, PFOA, PFOS, PFHxS, PFBS, and HFPO-DA), concentrations decreased >99% for GW, 93% for FF, 95% for AFFF Rinsate and IDW NF, and 79% for AFFF (diluted 10x) during the treatment time allotted. Meanwhile, the total PFAS concentrations, including all 40 known PFAS analytes and unidentified perfluorocarboxylic acid (PFCA) precursors, decreased from 34% to 96% following treatment. All of these concentration reduction values were calculated by using reporting limits (RL) as the concentrations for non-detects.  
  
==Advantages and Limitations of the Technology for PFAS Treatment==
+
Excellent fluorine/fluoride mass balance was achieved. There was nearly a 1:1 conversion of organic fluorine to free inorganic fluoride ion during treatment of GW, FF and AFFF Rinsate. The 3M Lightwater AFFF (diluted 10x) achieved only 65% fluorine mass balance, but this was likely due to high adsorption of PFAS to the reactor.
===Advantages:===
 
* High removal rates of long-chain PFAS (C5-C8) due to the production of versatile reactive species
 
* Requires no chemical additions and produces no residual waste
 
* Total organic carbon (TOC) concentration and other non-surfactant co-contaminants do not influence the process efficiency
 
* The process is mobile and scalable
 
* Versatile: can be used in batch and continuous systems
 
  
===Limitations:===
+
===Application===
* Removal of short-chain PFAS due to their inability to concentrate at plasma-liquid interfaces. Addition of surfactants such as CTAB improves their removal and degradation rates.
+
Due to the first-order kinetics of PRD, destruction of PFAS is most energy efficient when paired with a pre-concentration technology, such as foam fractionation (FF), nanofiltration, reverse osmosis, or resin/carbon adsorption, that remove PFAS from water. Application of the PFASigator<small><sup>TM</sup></small> is therefore proposed as a part of a PFAS treatment train that includes a pre-concentration step.
* Excessive foaming caused by bubbling argon gas through a solution containing high (>10 mg/L) concentrations of long-chain (surfactant) PFAS may interfere with the formation of plasma.
 
  
==Summary==
+
The first pilot study with the PFASigator<small><sup>TM</sup></small> was conducted in late 2023 at an industrial facility in Michigan with PFAS-impacted groundwater. The goal of the pilot study was to treat the groundwater to below the limits for regulatory discharge permits. For the pilot demonstration, the PFASigator<small><sup>TM</sup></small> was paired with an FF unit, which pre-concentrated the PFAS into a foamate that was pumped into the PFASigator<small><sup>TM</sup></small> for batch PFAS destruction. Residual PFAS remaining after the destruction batch was treated by looping back the PFASigator<small><sup>TM</sup></small> effluent to the FF system influent. During the one-month field pilot duration, site-specific discharge limits were met, and steady state operation between the FF unit and PFASigator<small><sup>TM</sup></small> was achieved such that the PFASigator<small><sup>TM</sup></small> destroyed the required concentrated PFAS mass and no off-site disposal of PFAS contaminated waste was required.
PFAS are susceptible to plasma treatment because the hydrophobic PFAS accumulates at the gas-liquid interface, exposing more of the PFAS to the plasma. Plasma-based treatment of PFAS contaminated water successfully degrades PFOA and PFOS to below the EPA health advisory level of 70 ppt and accomplishes the near complete destruction of other PFAS within a short treatment time. PFAS concentration reductions of ≥90% and post-treatment concentrations below laboratory detection levels are common for long chain PFAS and precursors.
 
The lack of sensitivity of plasma to co-contaminants, coupled with high PFAS removal and defluorination efficiencies, makes plasma-based water treatment a promising technology for the remediation of PFAS-contaminated water. The plasma treatment process is currently developed for ex situ application and can also be integrated into a treatment train<ref name="Richardson2021">Richardson, S., 2021. Nanofiltration Followed by Electrical Discharge Plasma for Destruction of PFAS and Co-occurring Chemicals in Groundwater: A Treatment Train Approach. Environmental Security Technology Certification Program (ESTCP), Project Number ER21-5136.  [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/ER21-5136  Project Overview]</ref>.
 
  
 
==References==
 
==References==

Revision as of 18:43, 8 May 2024

Photoactivated Reductive Defluorination PFAS Destruction

Photoactivated Reductive Defluorination (PRD) is a PFAS destruction technology predicated on ultraviolet (UV) light-activated photochemical reactions. The destruction efficiency of this process is enhanced by the use of a surfactant to confine PFAS molecules in self-assembled micelles. The photochemical reaction produces hydrated electrons from an electron donor that associates with the micelle. The hydrated electrons have sufficient energy to rapidly cleave fluorine-carbon and other molecular bonds of PFAS molecules due to the association of the electron donor with the micelle. Micelle-accelerated PRD is a highly efficient method to destroy PFAS in a wide variety of water matrices.

Related Article(s):

Contributor(s):

  • Dr. Suzanne Witt
  • Dr. Meng Wang
  • Dr. Denise Kay

Key Resource(s):

  • Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement[1]
  • Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-Acetic-Acid in Organomodified Montmorillonite[2]
  • Application of Surfactant Modified Montmorillonite with Different Conformation for Photo-Treatment of Perfluorooctanoic Acid by Hydrated Electrons[3]
  • ER21-7569: Photoactivated Reductive Defluorination PFAS Destruction[4]

Introduction

Figure 1. Schematic of PRD mechanism[4]

The Photoactivated Reductive Defluorination (PRD) process is based on a patented chemical reaction that breaks fluorine-carbon bonds and disassembles PFAS molecules in a linear fashion beginning with the hydrophilic functional groups and proceeding through shorter molecules to complete mineralization. Figure 1 shows how PRD is facilitated by adding cetyltrimethylammonium bromide (CTAB) to form a surfactant micelle cage that traps PFAS. A non-toxic proprietary chemical is added to solution to associate with the micelle surface and produce hydrated electrons via stimulation with UV light. These highly reactive hydrated electrons have the energy required to cleave fluorine-carbon and other molecular bonds resulting in the final products of fluoride, water, and simple carbon molecules (e.g., formic acid and acetic acid). The methods, mechanisms, theory, and reactions described herein have been published in peer reviewed literature[1][2][3][4].

Advantages and Disadvantages

Advantages

In comparison to other reported PFAS destruction techniques, PRD offers several advantages:

  • Relative to UV/sodium sulfite and UV/sodium iodide systems, the fitted degradation rates in the micelle-accelerated PRD reaction system were ~18 and ~36 times higher, indicating the key role of the self-assembled micelle in creating a confined space for rapid PFAS destruction[1]. The negatively charged hydrated electron associated with the positively charged cetyltrimethylammonium ion (CTA+) forms the surfactant micelle to trap molecules with similar structures, selectively mineralizing compounds with both hydrophobic and hydrophilic groups (e.g., PFAS).
  • The PRD reaction does not require solid catalysts or electrodes, which can be expensive to acquire and difficult to regenerate or dispose.
  • The aqueous solution is not heated or pressurized, and the UV wavelength used does not cause direct water photolysis, therefore the energy input to the system is more directly employed to destroy PFAS, resulting in greater energy efficiency.
  • Since the reaction is performed at ambient temperature and pressure, there are limited concerns regarding environmental health and safety or volatilization of PFAS compared to heated and pressurized systems.
  • Due to the reductive nature of the reaction, there is no formation of unwanted byproducts resulting from oxidative processes, such as perchlorate generation during electrochemical oxidation[5][6][7].
  • Aqueous fluoride ions are the primary end products of PRD, enabling real-time reaction monitoring with a fluoride ion selective electrode (ISE), which is far less expensive and faster than relying on PFAS analytical data alone to monitor system performance.

Disadvantages

  • The CTAB additive is only partially consumed during the reaction, and although CTAB is not problematic when discharged to downstream treatment processes that incorporate aerobic digestors, CTAB can be toxic to surface waters and anaerobic digestors. Therefore, disposal options for treated solutions will need to be evaluated on a site-specific basis. Possible options include removal of CTAB from solution for reuse in subsequent PRD treatments, or implementation of an oxidation reaction to degrade CTAB.
  • The PRD reaction rate decreases in water matrices with high levels of total dissolved solids (TDS). It is hypothesized that in high TDS solutions (e.g., ion exchange still bottoms with TDS of 200,000 ppm), the presence of ionic species inhibits the association of the electron donor with the micelle, thus decreasing the reaction rate.
  • The PRD reaction rate decreases in water matrices with very low UV transmissivity. Low UV transmissivity (i.e., < 1 %) prevents the penetration of UV light into the solution, such that the utilization efficiency of UV light decreases.

State of the Art

Technical Performance

Figure 2. Enspired SolutionsTM commercial PRD PFAS destruction equipment, the PFASigatorTM. Dimensions are 8 feet long by 4 feet wide by 9 feet tall.
Table 1. Percent decreases from initial PFAS concentrations during benchtop testing of PRD treatment in different water matrices
Analytes GW FF AFFF
Rinsate
AFF
(diluted 10X)
IDW NF
Σ Total PFASa (ND=0)

% Decrease
(Initial Concentration, μg/L)

93%
(370)
96%
(32,000)
89%
(57,000)
86 %
(770,000)
84%
(82)
Σ Total PFAS (ND=MDL) 93%
(400)
86%
(32,000)
90%
(59,000)
71%
(770,000)
88%
(110)
Σ Total PFAS (ND=RL) 94%
(460)
96%
(32,000)
91%
(66,000)
34%
(770,000)
92%
(170)
Σ Highly Regulated PFASb (ND=0) >99%
(180)
>99%
(20,000)
95%
(20,000)
92%
(390,000)
95%
(50)
Σ Highly Regulated PFAS (ND=MDL) >99%
(180)
98%
(20,000)
95%
(20,000)
88%
(390,000)
95%
(52)
Σ Highly Regulated PFAS (ND=RL) >99%
(190)
93%
(20,000)
95%
(20,000)
79%
(390,000)
95%
(55)
Σ High Priority PFASc (ND=0) 91%
(180)
98%
(20,000)
85%
(20,000)
82%
(400,000)
94%
(53)
Σ High Priority PFAS (ND=MDL) 91%
(190)
94%
(20,000)
85%
(20,000)
79%
(400,000)
86%
(58)
Σ High Priority PFAS (ND=RL) 92%
(200)
87%
(20,000)
86%
(21,000)
70%
(400,000)
87%
(65)
Fluorine mass balanced 106% 109% 110% 65% 98%
Sorbed organic fluorinee 4% 4% 33% N/A 31%
Notes:
GW = groundwater
GW FF = groundwater foam fractionate
AFFF rinsate = rinsate collected from fire system decontamination
AFFF (diluted 10x) = 3M Lightwater AFFF diluted 10x
IDW NF = investigation derived waste nanofiltrate
ND = non-detect
MDL = Method Detection Limit
RL = Reporting Limit
aTotal PFAS = 40 analytes + unidentified PFCA precursors
bHighly regulated PFAS = PFNA, PFOA, PFOS, PFHxS, PFBS, HFPO-DA
cHigh priority PFAS = PFNA, PFOA, PFHxA, PFBA, PFOS, PFHxS, PFBS, HFPO-DA
dRatio of the final to the initial organic fluorine plus inorganic fluoride concentrations
ePercent of organic fluorine that sorbed to the reactor walls during treatment


The PRD reaction has been validated at the bench scale for the destruction of PFAS in a variety of environmental samples from Department of Defense sites (Table 1). Enspired SolutionsTM has designed and manufactured a fully automatic commercial-scale piece of equipment called PFASigatorTM, specializing in PRD PFAS destruction (Figure 2). This equipment is modular and scalable, has a small footprint, and can be used alone or in series with existing water treatment trains. The PFASigatorTM employs commercially available UV reactors and monitoring meters that have been used in the water industry for decades. The system has been tested on PRD efficiency operational parameters, and key metrics were proven to be consistent with benchtop studies.

Bench scale PRD tests were performed for the following samples collected from Department of Defense sites: groundwater (GW), groundwater foam fractionate (FF), firefighting truck rinsate ( AFFF Rinsate), 3M Lightwater AFFF, investigation derived waste nanofiltrate (IDW NF), ion exchange still bottom (IX SB), and Ansulite AFFF. The PRD treatment was more effective in low conductivity/TDS solutions. Generally, PRD reaction rates decrease for solutions with a TDS > 10,000 ppm, with an upper limit of 30,000 ppm. Ansulite AFFF and IX SB samples showed low destruction efficiencies during initial screening tests, which was primarily attributed to their high TDS concentrations. Benchtop testing data are shown in Table 1 for the remaining five sample matrices.

During treatment, PFOS and PFOA concentrations decreased 96% to >99% and 77% to 97%, respectively. For the PFAS with proposed drinking water Maximum Contaminant Levels (MCLs) recently established by the USEPA (PFNA, PFOA, PFOS, PFHxS, PFBS, and HFPO-DA), concentrations decreased >99% for GW, 93% for FF, 95% for AFFF Rinsate and IDW NF, and 79% for AFFF (diluted 10x) during the treatment time allotted. Meanwhile, the total PFAS concentrations, including all 40 known PFAS analytes and unidentified perfluorocarboxylic acid (PFCA) precursors, decreased from 34% to 96% following treatment. All of these concentration reduction values were calculated by using reporting limits (RL) as the concentrations for non-detects.

Excellent fluorine/fluoride mass balance was achieved. There was nearly a 1:1 conversion of organic fluorine to free inorganic fluoride ion during treatment of GW, FF and AFFF Rinsate. The 3M Lightwater AFFF (diluted 10x) achieved only 65% fluorine mass balance, but this was likely due to high adsorption of PFAS to the reactor.

Application

Due to the first-order kinetics of PRD, destruction of PFAS is most energy efficient when paired with a pre-concentration technology, such as foam fractionation (FF), nanofiltration, reverse osmosis, or resin/carbon adsorption, that remove PFAS from water. Application of the PFASigatorTM is therefore proposed as a part of a PFAS treatment train that includes a pre-concentration step.

The first pilot study with the PFASigatorTM was conducted in late 2023 at an industrial facility in Michigan with PFAS-impacted groundwater. The goal of the pilot study was to treat the groundwater to below the limits for regulatory discharge permits. For the pilot demonstration, the PFASigatorTM was paired with an FF unit, which pre-concentrated the PFAS into a foamate that was pumped into the PFASigatorTM for batch PFAS destruction. Residual PFAS remaining after the destruction batch was treated by looping back the PFASigatorTM effluent to the FF system influent. During the one-month field pilot duration, site-specific discharge limits were met, and steady state operation between the FF unit and PFASigatorTM was achieved such that the PFASigatorTM destroyed the required concentrated PFAS mass and no off-site disposal of PFAS contaminated waste was required.

References

  1. ^ 1.0 1.1 1.2 Chen, Z., Li, C., Gao, J., Dong, H., Chen, Y., Wu, B., Gu, C., 2020. Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement. Environmental Science and Technology, 54(8), pp. 5178–5185. doi: 10.1021/acs.est.9b06599
  2. ^ 2.0 2.1 Tian, H., Gao, J., Li, H., Boyd, S.A., Gu, C., 2016. Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-Acetic-Acid in Organomodified Montmorillonite. Scientific Reports, 6(1), Article 32949. doi: 10.1038/srep32949   Open Access Article
  3. ^ 3.0 3.1 Chen, Z., Tian, H., Li, H., Li, J. S., Hong, R., Sheng, F., Wang, C., Gu, C., 2019. Application of Surfactant Modified Montmorillonite with Different Conformation for Photo-Treatment of Perfluorooctanoic Acid by Hydrated Electrons. Chemosphere, 235, pp. 1180–1188. doi: 10.1016/j.chemosphere.2019.07.032
  4. ^ 4.0 4.1 4.2 Kay, D., Witt, S., Wang, M., 2023. Photoactivated Reductive Defluorination PFAS Destruction: Final Report. ESTCP Project ER21-7569. Project Website   Final Report.pdf
  5. ^ Veciana, M., Bräunig, J., Farhat, A., Pype, M. L., Freguia, S., Carvalho, G., Keller, J., Ledezma, P., 2022. Electrochemical Oxidation Processes for PFAS Removal from Contaminated Water and Wastewater: Fundamentals, Gaps and Opportunities towards Practical Implementation. Journal of Hazardous Materials, 434, Article 128886. doi: 10.1016/j.jhazmat.2022.128886
  6. ^ Trojanowicz, M., Bojanowska-Czajka, A., Bartosiewicz, I., Kulisa, K., 2018. Advanced Oxidation/Reduction Processes Treatment for Aqueous Perfluorooctanoate (PFOA) and Perfluorooctanesulfonate (PFOS) – A Review of Recent Advances. Chemical Engineering Journal, 336, pp. 170–199. doi: 10.1016/j.cej.2017.10.153
  7. ^ Wanninayake, D.M., 2021. Comparison of Currently Available PFAS Remediation Technologies in Water: A Review. Journal of Environmental Management, 283, Article 111977. doi: 10.1016/j.jenvman.2021.111977

See Also