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==Hydrothermal Alkaline Treatment (HALT)==  
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==PFAS Destruction by Ultraviolet/Sulfite Treatment==  
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Hydrothermal alkaline treatment (HALT) is a thermochemical processing technology effective at destroying and defluorinating [[Wikipedia: Halogenation | halogenated]] organic compounds such as [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | per- and polyfluoroalkyl substances (PFAS)]]. HALT is highly effective at destroying and defluorinating all types of PFAS that have been evaluated. The HALT technology enables end-to-end treatment and destruction of PFAS from a variety of matrices when integrated into a suitable treatment train.  
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The ultraviolet (UV)/sulfite based reductive defluorination process has emerged as an effective and practical option for generating hydrated electrons (''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'' ) which can destroy [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] in water. It offers significant advantages for PFAS destruction, including significant defluorination, high treatment efficiency for long-, short-, and ultra-short chain PFAS without mass transfer limitations, selective reactivity by hydrated electrons, low energy consumption, low capital and operation costs, and no production of harmful byproducts. A UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor">Haley and Aldrich, Inc. (commercial business), 2024. EradiFluor. [https://www.haleyaldrich.com/about-us/applied-research-program/eradifluor/ Comercial Website]</ref>) has been demonstrated in two field demonstrations in which it achieved near-complete defluorination and greater than 99% destruction of 40 PFAS analytes measured by EPA method 1633.
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
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*[[PFAS Ex Situ Water Treatment]]
 
*[[PFAS Ex Situ Water Treatment]]
 
*[[PFAS Sources]]
 
*[[PFAS Sources]]
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*[[PFAS Transport and Fate]]
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*[[PFAS Treatment by Electrical Discharge Plasma]]
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*[[Supercritical Water Oxidation (SCWO)]]
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*[[Photoactivated Reductive Defluorination - PFAS Destruction]]
  
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'''Contributors:''' Dr. Brian Pinkard, [[Dr. Timothy J. Strathmann | Dr. Timothy Strathmann]], Dr. Shilai Hao
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'''Contributors:''' John Xiong, Yida Fang, Raul Tenorio, Isobel Li, and Jinyong Liu
  
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'''Key Resource(s):'''
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'''Key Resources:'''
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*Defluorination of Per- and Polyfluoroalkyl Substances (PFAS) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management<ref name="BentelEtAl2019">Bentel, M.J., Yu, Y., Xu, L., Li, Z., Wong, B.M., Men, Y., Liu, J., 2019. Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management. Environmental Science and Technology, 53(7), pp. 3718-28. [https://doi.org/10.1021/acs.est.8b06648 doi: 10.1021/acs.est.8b06648]&nbsp; [[Media: BentelEtAl2019.pdf | Open Access Article]]</ref>
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*Hydrothermal Technologies for On-Site Destruction of Site Investigation Wastes Contaminated with Per- and Polyfluoroalkyl Substances (PFAS), Phase I<ref name="Strathmann2023">Strathmann, T.J., Higgins, C., Deeb, R., 2020. Final Report: Hydrothermal Technologies for On-Site Destruction of Site Investigation Wastes Contaminated with Per- and Polyfluoroalkyl Substances (PFAS), Phase I. Strategic Environmental Research and Development Program (SERDP) Project number ER18-1501. [[Media: ER18-1501.pdf | Final Report.pdf]]&nbsp; [https://serdp-estcp.mil/projects/details/b34d6396-6b6d-44d0-a89e-6b22522e6e9c Project Website]</ref>
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*Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies<ref>Liu, Z., Chen, Z., Gao, J., Yu, Y., Men, Y., Gu, C., Liu, J., 2022. Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies. Environmental Science and Technology, 56(6), pp. 3699-3709. [https://doi.org/10.1021/acs.est.1c07608 doi: 10.1021/acs.est.1c07608]&nbsp; [[Media: LiuZEtAl2022.pdf | Open Access Article]]</ref>
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*Destruction of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment<ref>Tenorio, R., Liu, J., Xiao, X., Maizel, A., Higgins, C.P., Schaefer, C.E., Strathmann, T.J., 2020. Destruction of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment. Environmental Science and Technology, 54(11), pp. 6957-67. [https://doi.org/10.1021/acs.est.0c00961 doi: 10.1021/acs.est.0c00961]</ref>
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*Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foam<ref name="HaoEtAl2021">Hao, S., Choi, Y.J., Wu, B., Higgins, C.P., Deeb, R., Strathmann, T.J., 2021. Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Aqueous Film-Forming Foam. Environmental Science and Technology, 55(5), pp. 3283-3295.&nbsp; [https://doi.org/10.1021/acs.est.0c06906 doi: 10.1021/acs.est.0c06906]</ref>
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*EradiFluor<sup>TM</sup><ref name="EradiFluor"/>
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*[[Media: PinkardEtAl-2024a.pdf | Degradation and Defluorination of Ultra Short-, Short-, and Long-Chain PFASs in High Total Dissolved Solids Solutions by Hydrothermal Alkaline Treatment ─ Closing the Fluorine Mass Balance]]<ref name="PinkardEtAl2024a">Pinkard, B., Smith, S.M., Vorarath, P., Smrz, T., Schmick, S., Dressel, L., Bryan, C., Czerski, M., de Marne, A., Halevi, A., Thomsen, C., Woodruff, C., 2024. Degradation and Defluorination of Ultra Short-, Short-, and Long-Chain PFASs in High Total Dissolved Solids Solutions by Hydrothermal Alkaline Treatment─Closing the Fluorine Mass Balance. ACS ES&T Engineering, 4(11), pp. 2810-2818.&nbsp; [https://doi.org/10.1021/acsestengg.4c00378 doi: 10.1021/acsestengg.4c00378]&nbsp; [[Media: PinkardEtAl-2024a.pdf | Open Access Report.pdf]]</ref>
 
  
 
==Introduction==
 
==Introduction==
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[[File:PinkardFig1.png|thumb|400px|Figure 1. HALT refers to the [[Wikipedia: Critical_point_(thermodynamics)#Liquid–vapor critical point | subcritical]] water region on the pressure–temperature phase diagram of water]]
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The hydrated electron (''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'' ) can be described as an electron in solution surrounded by a small number of water molecules<ref name="BuxtonEtAl1988">Buxton, G.V., Greenstock, C.L., Phillips Helman, W., Ross, A.B., 1988. Critical Review of Rate Constants for Reactions of Hydrated Electrons, Hydrogen Atoms and Hydroxyl Radicals (⋅OH/⋅O-) in Aqueous Solution. Journal of Physical and Chemical Reference Data, 17(2), pp. 513-886. [https://doi.org/10.1063/1.555805 doi: 10.1063/1.555805]</ref>. Hydrated electrons can be produced by photoirradiation of solutes, including sulfite, iodide, dithionite, and ferrocyanide, and have been reported in literature to effectively decompose per- and polyfluoroalkyl substances (PFAS) in water. The hydrated electron is one of the most reactive reducing species, with a standard reduction potential of about −2.9 volts. Though short-lived, hydrated electrons react rapidly with many species having more positive reduction potentials<ref name="BuxtonEtAl1988"/>.  
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Hydrothermal alkaline treatment (HALT) is a thermochemical processing technology effective at destroying and defluorinating halogenated organic compounds such as per- and polyfluoroalkyl substances (PFAS). HALT is also known as “[[Wikipedia: Hydrolysis#Alkaline_hydrolysis |alkaline hydrolysis]],” and is very similar to processing technologies such as [[Wikipedia: Hydrothermal liquefaction | hydrothermal liquefaction (HTL)]] which have been developed and investigated for organic waste-to-energy applications.
 
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HALT processing subjects PFAS in an aqueous solution to high pressure, high temperature, and high pH conditions. The required operating conditions are dependent on the specific target PFAS being destroyed, as [[Wikipedia: Perfluoroalkyl carboxylic acids | perfluorocarboxylic acids (PFCAs)]] such as [[Wikipedia: Trifluoroacetic acid |trifluoroacetic acid (TFA)]] can be destroyed under mild conditions (e.g., P ~ 2 MPa, T ~ 200 °C, pH ~ 13)<ref name="AustinEtAl2024">Austin, C., Purohit, A., Thomsen, C., Pinkard, B.R., Strathmann, T.J., Novosselov, I.V., 2024. Hydrothermal Destruction and Defluorination of Trifluoroacetic Acid (TFA). Environmental Science and Technology, 58(18), pp. 8076-8085.&nbsp; [https://doi.org/10.1021/acs.est.3c09404 doi: 10.1021/acs.est.3c09404]</ref>, whereas [[Wikipedia: Perfluorosulfonic acids | perfluorosulfonic acids (PFSAs)]] such as [[Wikipedia: Perfluorobutanesulfonic acid | perfluorobutanesulfonic acid (PFBS)]] require more aggressive processing conditions (e.g., P ~ 25 MPa, T ~ 350 °C, pH ~ 14.7) [5] (Figure 1) . HALT is capable of facilitating complete “mineralization” of PFAS, defined as the conversion of organic fluorine to dissolved inorganic fluoride. The treatment time for HALT is relatively shorter (<2 hours) compared to most other PFAS destructive technologies. For instance, treatment of two-fold diluted [[Wikipedia: Firefighting foam | aqueous film-forming foams (AFFFs)]] using HALT in batch mode achieved nearly complete defluorination in just 30 minutes under conditions of 350 °C and 5 M NaOH<ref name="HaoEtAl2021"/>. PFCAs can be destroyed with even faster kinetics at milder conditions; for example, >90% destruction and defluorination of [[Wikipedia: Trifluoroacetic acid | trifluoroacetic acid (TFA)]] was achieved within 40 min at 200 °C<ref name="AustinEtAl2024"/>. Kinetic rate constants for individual PFAS compounds in HALT environments have been proposed in several studies<ref name="AustinEtAl2024"/><ref name="WuEtAl2019">Wu, B., Hao, S., Choi, Y.J., Higgins, C.P., Deeb, R., Strathmann, T.J., 2019. Rapid Destruction and Defluorination of Perfluorooctanesulfonate by Alkaline Hydrothermal Reaction. Environmental Science and Technology Letters, 6(10), pp. 630-636.&nbsp; [https://doi.org/10.1021/acs.estlett.9b00506 doi: 10.1021/acs.estlett.9b00506]</ref>. The fluorine mass balance during HALT processing has also been investigated, showing near-stoichiometric conversion of organic fluorine to inorganic fluoride under optimal conditions<ref name="PinkardEtAl2024a"/>.
 
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From a practical perspective, HALT is best suited for destroying PFAS in concentrated liquids such as liquid concentrate streams produced as byproducts of other water treatment processes (e.g., [[PFAS Treatment by Anion Exchange | regenerable ion exchange]], foam fractionation). Previous publications demonstrate that complex sample matrices, including high concentrations of inorganic salts (e.g., 83 g/L chloride) and dissolved organic carbon (e.g., 13 g/L), do not inhibit the degradation rate of PFAS compared to a clean matrix, such as groundwater<ref name="HaoEtAl2022">Hao, S., Choi, Y.J,. Deeb, R.A., Strathmann, T.J., Higgins, C.P., 2022. Application of Hydrothermal Alkaline Treatment for Destruction of Per- and Polyfluoroalkyl Substances in Contaminated Groundwater and Soil. Environmental Science and Technology, 56(10), pp. 6647-6657.&nbsp; [https://doi.org/10.1021/acs.est.2c00654 doi: 10.1021/acs.est.2c00654]</ref><ref name="HaoEtAl2023">Hao, S., Reardon, P.N., Choi, Y.J., Zhang, C., Sanchez, J.M., Higgins, C.P., Strathmann, T.J., 2023. Hydrothermal Alkaline Treatment (HALT) of Foam Fractionation Concentrate Derived from PFAS-Contaminated Groundwater. Environmental Science and Technology 57(44), pp. 17154-17165.&nbsp; [https://doi.org/10.1021/acs.est.3c05140 doi: 10.1021/acs.est.3c05140]</ref>. Moreover, several field demonstrations of HALT have been performed successfully, and the technology is scalable for commercialization.
 
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==Reaction Mechanisms and Treatment Efficacy==
 
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[[File:PinkardFig2.png|thumb|400px|Figure 2. Representative classes of PFAS structures among 148 PFASs demonstrated complete degradation during HALT<ref name="HaoEtAl2021"/>]]
 
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[[File:PinkardFig3.png|thumb|400px|Figure 3. The degradation of representative classes of PFAS during HALT of 1-to-1000 diluted AFFF under conditions of 1 M NaOH, 350 °C, and a reaction time of 60 minutes<ref name="HaoEtAl2021"/>.]]
 
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Laboratory scale batch experiments have shown that the full suite of PFAS detected in aqueous film-forming foams (AFFFs) through targeted [[Wikipedia: Liquid chromatography–mass spectrometry | LC-MS/MS and LC-HRMS]] suspect screening analysis are degraded and defluorinated by HALT<ref name="HaoEtAl2021"/>. Figure 2 presents representative classes of PFAS structures among 148 PFAS demonstrating complete degradation during HALT. Figure 3 illustrates the degradation during HALT of representative classes of PFAS detected in an AFFF. The extent of destruction for all PFAS is highly temperature dependent, but results show that some subclasses of PFAS degrade in the absence of alkali amendments (e.g., PFCAs)<ref name="AustinEtAl2024"/>, whereas other subclasses require strong alkali in addition to near-critical reaction temperatures (e.g., PFSAs)<ref name="Strathmann2023"/><ref name="HaoEtAl2021"/><ref name="WuEtAl2019"/>. This is attributed to different mechanisms that initiate the destruction of the individual PFAS subclasses. Degradation of PFCAs is initiated by thermally driven [[Wikipedia: Decarboxylation | decarboxylation reactions]]<ref name="AustinEtAl2024"/>, whereas PFSA degradation, in the temperature range of HALT reactors, is proposed to be initiated via attack by the strong nucleophile [[Wikipedia: Hydroxide | OH<sup>-</sup>]].<ref name="HaoEtAl2021"/> 
 
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A mechanistic understanding of the HALT process for PFAS destruction needs further evaluation to optimize the process and reduce the consumption of chemicals and energy. While the studies of neat compounds are relatively straightforward, one of the major challenges is to address the effect of co-contaminants and apply the process to real-world operating scenarios. Recent laboratory studies with batch reactors conducted at the Colorado School of Mines (CSM) have extended the application of HALT for the destruction of PFAS in a variety of contaminated matrices, including groundwater and soils<ref name="HaoEtAl2022"/> and foam fractionation-derived liquid concentrate<ref name="HaoEtAl2023"/>. Apparent rates for the transformation of individual PFAS have been found to be largely insensitive to the type of media<ref name="HaoEtAl2023"/>, but there is a need to account for any reactions with the media that consume OH· (e.g., OH· reactions with silica-containing soil minerals)<ref name="HaoEtAl2022"/> Notably, while alkali is not required to degrade PFCAs, it is still necessary to convert the organically bound fluorine to inorganic F<sup>-</sup>. Austin ''et. al.''<ref name="AustinEtAl2024"/> showed that TFA, a C<sub>1</sub> PFCA, degrades at similar rates in the absence and presence of NaOH, but mineralization to F<sup>-</sup> and CO<sub>3</sub><sup>2-</sup> only occurs when NaOH is added; otherwise [[Wikipedia:Fluoroform | fluoroform (CHF<sub>3</sub>)]] is the terminal product when no NaOH is added to the reaction solution.
 
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HALT can also be applied to destroy other fluorinated compounds, for example, [[Wikipedia:Hydrofluorocarbon | hydrofluorocarbon (HFC)]] refrigerants. HFC refrigerants are known to decompose into PFAS such as TFA in the atmosphere and thereby subsequently appear in concerning concentrations in rainwater. By themselves, HFCs are resistant to thermal degradation; however, in the presence of alkali (e.g., NaOH), alkaline hydrolysis can occur at T < 150˚C<ref name="AustinEtAl2024"/>.
 
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==State of the Art==
 
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[[File:PinkardFig4.png | thumb |400px| Figure 4: HALT field demonstration at Fairbanks International Airport (FAI) in August 2023]]
 
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Recently, several field demonstrations of pilot-scale HALT systems were performed by commercial HALT provider Aquagga, Inc. These have focused on treating PFAS-rich liquids, including industrial wastewater at a 3M Company facility (April 2024)<ref name="PinkardEtAl2024b">Pinkard, B.R., Smith, S.M., Bryan, C., 2024. PFAS Degradation and Defluorination of High TDS Wastewater via Continuous Hydrothermal Alkaline Treatment (HALT). In: (Proceedings of the) 85th Annual International Water Conference (IWC 2024), Volume 1, pp. 359-374. Engineers Society of Western Pennsylvania. ISBN: 979-8-3313-1299-2</ref>, foam fractionate from a fire training pit in Fairbanks, AK (August 2023), foam fractionate from groundwater at Beale Air Force Base, CA (May 2024), and AFFF (May 2024). For all field demonstrations, a containerized HALT system was mobilized to the site and operated for up to several weeks. The systems were typically operated at a throughput between 5 and 10 gallons per hour (gph). Since 2019, HALT has progressed from small-scale batch reactors to successful field demonstration of pilot-scale systems. This technology maturation attests to strong technical and regulatory tailwinds. Effort is still needed to demonstrate the technology at full scale and in complex treatment scenarios. Long-term operation of the systems will allow for further optimization of the systems and provide data on the applicability of HALT for the treatment of industrial and environmental PFAS-contaminated waste streams.
 
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Pilot-scale HALT systems are typically continuous flow tubular reactor systems, consisting of a single high-temperature, high-pressure fluid path. In commercial HALT systems offered by Aquagga, Inc., chemical dosing for pH adjustment is achieved via an automated chemical dosing and mixing system. The high pH feedstock is then introduced to the high-pressure reactor via a high-pressure metering pump. Pressure is controlled via a back-pressure device downstream of the high-temperature reactor zone. The pressurized reactants are brought to reaction temperatures via a recuperative heat exchanger followed by electric resistive heaters. The reactor vessel contains the reactants at the necessary temperature and pressure and for a sufficient residence time to facilitate the destruction reactions. The product stream is then cooled through a recuperative heat exchanger, before being throttled to ambient pressure through the back-pressure device. Pressure transducers, flow meters, and thermocouples are used to monitor the reactor operations at various points in the system. All reactor components are typically housed within a shipping container, for ease of system transport and to provide secondary chemical containment.
 
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==Practical Applications==
 
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[[File:PinkardFig5.png | thumb |400px| Figure 5: An on-site HALT pilot demonstration at a 3M Company wastewater treatment facility]]
 
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The ideal use case for HALT is treating PFAS-rich liquid matrices. PFAS concentrations are high enough for HALT to be directly applicable primarily in the cases of AFFF treatment or industrial process water treatment. In the majority of use cases, it is more practical to apply a separation and concentration technology prior to HALT, to reduce the volume of liquid requiring HALT treatment while increasing PFAS concentrations in that liquid. These concentration technologies may include regenerable sorbents, membranes, or foam fractionation, all of which produce a liquid byproduct amenable for HALT.
 
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===Destruction of PFAS in Ion Exchange Regeneration Brine===
 
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One of the most promising applications of HALT is for treating PFAS-rich ion exchange (IX) regeneration brines, either in site remediation applications (e.g., groundwater treatment<ref name="Pinkard2024">Pinkard, B.R., 2024. Hydrothermal Alkaline Treatment for a Closed-Loop, On-Site PFAS Treatment Solution. Project Number ER23-8400, Environmental Security Technology Certification Program (ESTCP).&nbsp; [https://serdp-estcp.mil/projects/details/a4c6918a-fe3b-43d2-95cb-fa3dfa3a50a2 Project Website]</ref>) or industrial wastewater treatment applications<ref name="PinkardEtAl2024a"/>. IX capture and regeneration involve sorbing PFAS to an IX resin, followed by chemical desorption of PFAS from the resin, typically with a solvent and/or salt wash solution. The IX regeneration technology is commercially mature and available from several vendors.
 
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A treatment train of IX followed by HALT shows promise for several reasons. One reason is that the HALT process is highly compatible with the liquid matrix produced through the IX regeneration. Typically, IX regeneration brine (a.k.a. “still bottoms”) contains high levels of dissolved solids such as sodium chloride, which can cause practical processing challenges with other liquid treatment technologies. However, high levels of TDS do not appear to cause processing challenges with HALT<ref name="PinkardEtAl2024a"/>. Another reason is that IX regeneration brines often contain ultra short- and short-chain PFAS, which are amenable to destructive treatment with HALT.
 
  
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In 2022, commercial HALT provider Aquagga performed a bench study in partnership with the 3M Company, demonstrating PFAS destruction performance for HALT processing of a synthetic IX regeneration brine<ref name="PinkardEtAl2024a"/>. Seven treatment conditions were tested, and fluorine mass balance closure was demonstrated for most conditions using a range of analytical techniques. In 2024, Aquagga performed an on-site demonstration in partnership with the 3M Company treating IX regeneration brine produced from active wastewater treatment activities<ref name="PinkardEtAl2024b"/>.
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Among the electron source chemicals, sulfite (SO<sub>3</sub><sup>2−</sup>) has emerged as one of the most effective and practical options for generating hydrated electrons to destroy PFAS in water. The mechanism of hydrated electron production in a sulfite solution under ultraviolet is shown in Equation 1 (UV is denoted as ''hv, SO<sub>3</sub><sup><big>'''•-'''</big></sup>'' is the sulfur trioxide radical anion):
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</br>
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::<big>'''Equation 1:'''</big>&nbsp;&nbsp; [[File: XiongEq1.png | 200 px]]
  
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===Foam Fractionate Treatment===
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The hydrated electron has demonstrated excellent performance in destroying PFAS such as [[Wikipedia:Perfluorooctanesulfonic acid | perfluorooctanesulfonic acid (PFOS)]], [[Wikipedia:Perfluorooctanoic acid|perfluorooctanoic acid (PFOA)]]<ref>Gu, Y., Liu, T., Wang, H., Han, H., Dong, W., 2017. Hydrated Electron Based Decomposition of Perfluorooctane Sulfonate (PFOS) in the VUV/Sulfite System. Science of The Total Environment, 607-608, pp. 541-48. [https://doi.org/10.1016/j.scitotenv.2017.06.197 doi: 10.1016/j.scitotenv.2017.06.197]</ref> and [[Wikipedia: GenX|GenX]]<ref>Bao, Y., Deng, S., Jiang, X., Qu, Y., He, Y., Liu, L., Chai, Q., Mumtaz, M., Huang, J., Cagnetta, G., Yu, G., 2018. Degradation of PFOA Substitute: GenX (HFPO–DA Ammonium Salt): Oxidation with UV/Persulfate or Reduction with UV/Sulfite? Environmental Science and Technology, 52(20), pp. 11728-34. [https://doi.org/10.1021/acs.est.8b02172 doi: 10.1021/acs.est.8b02172]</ref>. Mechanisms include cleaving carbon-to-fluorine (C-F) bonds (i.e., hydrogen/fluorine atom exchange) and chain shortening (i.e., [[Wikipedia: Decarboxylation | decarboxylation]], [[Wikipedia: Hydroxylation | hydroxylation]], [[Wikipedia: Elimination reaction | elimination]], and [[Wikipedia: Hydrolysis | hydrolysis]])<ref name="BentelEtAl2019"/>.
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Foam fractionation is a technology that concentrates PFAS in liquids by taking advantage of the hydrophobic/interface-partitioning behavior exhibited by many types of PFAS. Foam fractionation is seeing broad adoption for challenging liquid matrices such as landfill leachate and groundwater. Long-chain PFAS are known to partition to interfaces much more readily than short-chain PFAS, and foam fractionation is correspondingly much more effective at removing long-chain PFAS from liquids. When coupled with HALT, foam fractionation can remove and destroy a high fraction of PFAS from challenging liquid matrices<ref name="HaoEtAl2023"/>.
 
  
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===Destruction of PFAS in AFFF===
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==Process Description==
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Legacy AFFF contains high levels of PFAS (typically 0.1 to 6 wt%) in a liquid matrix. Several studies at lab and pilot scales have demonstrated that HALT can destroy PFAS in AFFF with minimal dilution<ref name="HaoEtAl2021"/>. While the treatment is effective, the wide variety of AFFF formulations make this a challenging application.
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A commercial UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>) includes an optional pre-oxidation step to transform PFAS precursors (when present) and a main treatment step to break C-F bonds by UV/sulfite reduction. The effluent from the treatment process can be sent back to the influent of a pre-treatment separation system (such as a [[Wikipedia: Foam fractionation | foam fractionation]], [[PFAS Treatment by Anion Exchange | regenerable ion exchange]], or a [[Reverse Osmosis and Nanofiltration Membrane Filtration Systems for PFAS Removal | membrane filtration system]]) for further concentration or sent for off-site disposal in accordance with relevant disposal regulations. A conceptual treatment process diagram is shown in Figure 1. [[File: XiongFig1.png | thumb | left | 600 px | Figure 1: Conceptual Treatment Process for a Concentrated PFAS Stream]]<br clear="left"/>
  
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==Advantages and Drawbacks==
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==Advantages==
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===Advantages of HALT include:===
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A UV/sulfite treatment system offers significant advantages for PFAS destruction compared to other technologies, including high defluorination percentage, high treatment efficiency for short-chain PFAS without mass transfer limitation, selective reactivity by ''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'', low energy consumption, and the production of no harmful byproducts. A summary of these advantages is provided below:
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*Ability to achieve >99% destruction of all PFAS chain lengths and subtypes
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*'''High efficiency for short- and ultrashort-chain PFAS:''' While the degradation efficiency for short-chain PFAS is challenging for some treatment technologies<ref>Singh, R.K., Brown, E., Mededovic Thagard, S., Holson, T.M., 2021. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. Journal of Hazardous Materials, 408, Article 124452. [https://doi.org/10.1016/j.jhazmat.2020.124452 doi: 10.1016/j.jhazmat.2020.124452]</ref><ref>Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S., Holson, 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. 13973-80. [https://doi.org/10.1021/acs.est.0c02158 doi: 10.1021/acs.est.0c02158]</ref><ref>Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M., Mededovic Thagard S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly- and Perfluoroalkyl Substances in Groundwater. American Chemical Society’s Environmental Science and Technology (ES&T) Water, 1(3), pp. 680-87. [https://doi.org/10.1021/acsestwater.0c00170 doi: 10.1021/acsestwater.0c00170]</ref>, the UV/sulfite process demonstrates excellent defluorination efficiency for both short- and ultrashort-chain PFAS, including [[Wikipedia: Trifluoroacetic acid | trifluoroacetic acid (TFA)]] and [[Wikipedia: Perfluoropropionic acid | perfluoropropionic acid (PFPrA)]]. 
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*Ability to fully mineralize or defluorinate PFAS to dissolved inorganic fluoride as an end product
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*'''High defluorination ratio:''' As shown in Figure 3, the UV/sulfite treatment system has demonstrated near 100% defluorination for various PFAS under both laboratory and field conditions.
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*Commercial systems are compact and simple to operate
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*'''No harmful byproducts:''' While some oxidative technologies, such as electrochemical oxidation, generate toxic byproducts, including perchlorate, bromate, and chlorate, the UV/sulfite system employs a reductive mechanism and does not generate these byproducts.
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*Commercial systems do not have an air emission point
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*'''Ambient pressure and low temperature:''' The system operates under ambient pressure and low temperature (<60°C), as it utilizes UV light and common chemicals to degrade PFAS. 
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*Ability to treat wastes with high TDS
+
*'''Low energy consumption:''' The electrical energy per order values for the degradation of [[Wikipedia: Perfluoroalkyl carboxylic acids | perfluorocarboxylic acids (PFCAs)]] by UV/sulfite have been reduced to less than 1.5 kilowatt-hours (kWh) per cubic meter under laboratory conditions. The energy consumption is orders of magnitude lower than that for many other destructive PFAS treatment technologies (e.g., [[Supercritical Water Oxidation (SCWO) | supercritical water oxidation]])<ref>Nzeribe, B.N., Crimi, M., Mededovic Thagard, S., 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>.
−
*Ability to treat wastes with high TOC
+
*'''Co-contaminant destruction:''' The UV/sulfite system has also been reported effective in destroying certain co-contaminants in wastewater. For example, UV/sulfite is reported to be effective in reductive dechlorination of chlorinated volatile organic compounds, such as trichloroethene, 1,2-dichloroethane, and vinyl chloride<ref>Jung, B., Farzaneh, H., Khodary, A., Abdel-Wahab, A., 2015. Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation. Journal of Environmental Chemical Engineering, 3(3), pp. 2194-2202. [https://doi.org/10.1016/j.jece.2015.07.026 doi: 10.1016/j.jece.2015.07.026]</ref><ref>Liu, X., Yoon, S., Batchelor, B., Abdel-Wahab, A., 2013. Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) – Effects of reagents and pH. Chemical Engineering Journal, 215-216, pp. 868-875. [https://doi.org/10.1016/j.cej.2012.11.086 doi: 10.1016/j.cej.2012.11.086]</ref><ref>Li, X., Ma, J., Liu, G., Fang, J., Yue, S., Guan, Y., Chen, L., Liu, X., 2012. Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process. Environmental Science and Technology, 46(13), pp. 7342-49. [https://doi.org/10.1021/es3008535 doi: 10.1021/es3008535]</ref><ref>Li, X., Fang, J., Liu, G., Zhang, S., Pan, B., Ma, J., 2014. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Research, 62, pp. 220-228. [https://doi.org/10.1016/j.watres.2014.05.051 doi: 10.1016/j.watres.2014.05.051]</ref>.
−
*Low overall energy usage (<0.9 kWh/gal-treated)
 
  
−
===Drawbacks or challenges associated with HALT include:===
+
==Limitations==
−
*Not well-suited for directly processing solid materials or slurries
+
Several environmental factors and potential issues have been identified that may impact the performance of the UV/sulfite treatment system, as listed below. Solutions to address these issues are also proposed.
−
*Treated effluent brine contains high TDS and must be managed accordingly
+
*Environmental factors, such as the presence of elevated concentrations of natural organic matter (NOM), dissolved oxygen, or nitrate, can inhibit the efficacy of UV/sulfite treatment systems by scavenging available hydrated electrons. Those interferences are commonly managed through chemical additions, reaction optimization, and/or dilution, and are therefore not considered likely to hinder treatment success.
−
*Hard minerals (e.g., Ca<sup>2+</sup>) may precipitate and require periodic cleaning
+
*Coloration in waste streams may also impact the effectiveness of the UV/sulfite treatment system by blocking the transmission of UV light, thus reducing the UV lamp's effective path length. To address this, pre-treatment may be necessary to enable UV/sulfite destruction of PFAS in the waste stream. Pre-treatment may include the use of strong oxidants or coagulants to consume or remove UV-absorbing constituents.
 +
*The degradation efficiency is strongly influenced by PFAS molecular structure, with fluorotelomer sulfonates (FTS) and [[Wikipedia: Perfluorobutanesulfonic acid | perfluorobutanesulfonate (PFBS)]] exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.
  
−
===Safety considerations related to HALT include:===
+
==State of the Practice==
−
*The use of strong bases and conjugate acids require safe chemical handling practices external to the HALT system and appropriate operator precautions
+
[[File: XiongFig2.png | thumb | 500 px | Figure 2. Field demonstration of EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> for PFAS destruction in a concentrated waste stream in a Mid-Atlantic Naval Air Station: a) Target PFAS at each step of the treatment shows that about 99% of PFAS were destroyed; meanwhile, the final degradation product, i.e., fluoride, increased to 15 mg/L in concentration, demonstrating effective PFAS destruction; b) AOF concentrations at each step of the treatment provided additional evidence to show near-complete mineralization of PFAS. Average results from multiple batches of treatment are shown here.]]
−
*High-pressure, high-temperature, and high-pH operating conditions are harsh and corrosive on processing equipment, and appropriate material selection, metallurgy, and corrosion control methods must be applied to ensure reactor vessel reliability
+
[[File: XiongFig3.png | thumb | 500 px | Figure 3. Field demonstration of a treatment train (SAFF + EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>) for groundwater PFAS separation and destruction at an Air Force base in California: a) Two main components of the treatment train, i.e. SAFF and EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>; b) Results showed the effective destruction of various PFAS in the foam fractionate. The target PFAS at each step of the treatment shows that about 99.9% of PFAS were destroyed. Meanwhile, the final degradation product, i.e., fluoride, increased to 30 mg/L in concentration, demonstrating effective destruction of PFAS in a foam fractionate concentrate. After a polishing treatment step (GAC) via the onsite groundwater extraction and treatment system, all PFAS were removed to concentrations below their MCLs.]] 
 +
The effectiveness of UV/sulfite technology for treating PFAS has been evaluated in two field demonstrations using the EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> system. Aqueous samples collected from the system were analyzed using EPA Method 1633, the [[Wikipedia: TOP Assay | total oxidizable precursor (TOP) assay]], adsorbable organic fluorine (AOF) method, and non-target analysis. A summary of each demonstration and their corresponding PFAS treatment efficiency is provided below.
 +
*Under the [https://serdp-estcp.mil/ Environmental Security Technology Certification Program (ESTCP)] [https://serdp-estcp.mil/projects/details/4c073623-e73e-4f07-a36d-e35c7acc75b6/er21-5152-project-overview Project ER21-5152], a field demonstration of EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was conducted at a Navy site on the east coast, and results showed that the technology was highly effective in destroying various PFAS in a liquid concentrate produced from an ''in situ'' foam fractionation groundwater treatment system. As shown in Figure 2a, total PFAS concentrations were reduced from 17,366 micrograms per liter (µg/L) to 195 µg/L at the end of the UV/sulfite reaction, representing 99% destruction. After the ion exchange resin polishing step, all residual PFAS had been removed to the non-detect level, except one compound (PFOS) reported as 1.5 nanograms per liter (ng/L), which is below the current Maximum Contaminant Level (MCL) of 4 ng/L. Meanwhile, the fluoride concentration increased up to 15 milligrams per liter (mg/L), confirming near complete defluorination. Figure 2b shows the adsorbable organic fluorine results from the same treatment test, which similarly demonstrates destruction of 99% of PFAS.
 +
*Another field demonstration was completed at an Air Force base in California, where a treatment train combining [https://serdp-estcp.mil/projects/details/263f9b50-8665-4ecc-81bd-d96b74445ca2 Surface Active Foam Fractionation (SAFF)] and EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was used to treat PFAS in groundwater. As shown in Figure 3, PFAS analytical data and fluoride results demonstrated near-complete destruction of various PFAS. In addition, this demonstration showed: a) high PFAS destruction ratio was achieved in the foam fractionate, even in very high concentration (up to 1,700 mg/L of booster), and b) the effluent from EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was sent back to the influent of the SAFF system for further concentration and treatment, resulting in a closed-loop treatment system and no waste discharge from EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>. This field demonstration was conducted with the approval of three regulatory agencies (United States Environmental Protection Agency, California Regional Water Quality Control Board, and California Department of Toxic Substances Control).
  
 
==References==
 
==References==
Line 83: Line 58:
  
 
==See Also==
 
==See Also==
−
*[https://www.aquagga.com/ourtech Aquagga (company) website]
 
−
*[https://strathmanngroup.com/research/ Strathmann Research Group]
 
−
*[https://www.youtube.com/watch?v=UANEiMIDcZM&t=2696s SERDP Webinar Series: PFAS Fate, Transport and Treatment]
 
−
*[https://www.youtube.com/watch?v=KRVJ2S9F9qU&t=3261s SERDP Webinar Series: Developing and Demonstrating Technologies for Destruction of PFAS in Concentrated Liquid Waste Streams]
 

Latest revision as of 11:33, 29 January 2026

PFAS Destruction by Ultraviolet/Sulfite Treatment

The ultraviolet (UV)/sulfite based reductive defluorination process has emerged as an effective and practical option for generating hydrated electrons (eaq- ) which can destroy PFAS in water. It offers significant advantages for PFAS destruction, including significant defluorination, high treatment efficiency for long-, short-, and ultra-short chain PFAS without mass transfer limitations, selective reactivity by hydrated electrons, low energy consumption, low capital and operation costs, and no production of harmful byproducts. A UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluorTM[1]) has been demonstrated in two field demonstrations in which it achieved near-complete defluorination and greater than 99% destruction of 40 PFAS analytes measured by EPA method 1633.

Related Article(s):

Contributors: John Xiong, Yida Fang, Raul Tenorio, Isobel Li, and Jinyong Liu

Key Resources:

  • Defluorination of Per- and Polyfluoroalkyl Substances (PFAS) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management[2]
  • Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies[3]
  • Destruction of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment[4]
  • EradiFluorTM[1]

Introduction

The hydrated electron (eaq- ) can be described as an electron in solution surrounded by a small number of water molecules[5]. Hydrated electrons can be produced by photoirradiation of solutes, including sulfite, iodide, dithionite, and ferrocyanide, and have been reported in literature to effectively decompose per- and polyfluoroalkyl substances (PFAS) in water. The hydrated electron is one of the most reactive reducing species, with a standard reduction potential of about −2.9 volts. Though short-lived, hydrated electrons react rapidly with many species having more positive reduction potentials[5].

Among the electron source chemicals, sulfite (SO32−) has emerged as one of the most effective and practical options for generating hydrated electrons to destroy PFAS in water. The mechanism of hydrated electron production in a sulfite solution under ultraviolet is shown in Equation 1 (UV is denoted as hv, SO3•- is the sulfur trioxide radical anion):

Equation 1:   XiongEq1.png

The hydrated electron has demonstrated excellent performance in destroying PFAS such as perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA)[6] and GenX[7]. Mechanisms include cleaving carbon-to-fluorine (C-F) bonds (i.e., hydrogen/fluorine atom exchange) and chain shortening (i.e., decarboxylation, hydroxylation, elimination, and hydrolysis)[2].

Process Description

A commercial UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluorTM[1]) includes an optional pre-oxidation step to transform PFAS precursors (when present) and a main treatment step to break C-F bonds by UV/sulfite reduction. The effluent from the treatment process can be sent back to the influent of a pre-treatment separation system (such as a foam fractionation, regenerable ion exchange, or a membrane filtration system) for further concentration or sent for off-site disposal in accordance with relevant disposal regulations. A conceptual treatment process diagram is shown in Figure 1.

Figure 1: Conceptual Treatment Process for a Concentrated PFAS Stream


Advantages

A UV/sulfite treatment system offers significant advantages for PFAS destruction compared to other technologies, including high defluorination percentage, high treatment efficiency for short-chain PFAS without mass transfer limitation, selective reactivity by eaq-, low energy consumption, and the production of no harmful byproducts. A summary of these advantages is provided below:

  • High efficiency for short- and ultrashort-chain PFAS: While the degradation efficiency for short-chain PFAS is challenging for some treatment technologies[8][9][10], the UV/sulfite process demonstrates excellent defluorination efficiency for both short- and ultrashort-chain PFAS, including trifluoroacetic acid (TFA) and perfluoropropionic acid (PFPrA).
  • High defluorination ratio: As shown in Figure 3, the UV/sulfite treatment system has demonstrated near 100% defluorination for various PFAS under both laboratory and field conditions.
  • No harmful byproducts: While some oxidative technologies, such as electrochemical oxidation, generate toxic byproducts, including perchlorate, bromate, and chlorate, the UV/sulfite system employs a reductive mechanism and does not generate these byproducts.
  • Ambient pressure and low temperature: The system operates under ambient pressure and low temperature (<60°C), as it utilizes UV light and common chemicals to degrade PFAS.
  • Low energy consumption: The electrical energy per order values for the degradation of perfluorocarboxylic acids (PFCAs) by UV/sulfite have been reduced to less than 1.5 kilowatt-hours (kWh) per cubic meter under laboratory conditions. The energy consumption is orders of magnitude lower than that for many other destructive PFAS treatment technologies (e.g., supercritical water oxidation)[11].
  • Co-contaminant destruction: The UV/sulfite system has also been reported effective in destroying certain co-contaminants in wastewater. For example, UV/sulfite is reported to be effective in reductive dechlorination of chlorinated volatile organic compounds, such as trichloroethene, 1,2-dichloroethane, and vinyl chloride[12][13][14][15].

Limitations

Several environmental factors and potential issues have been identified that may impact the performance of the UV/sulfite treatment system, as listed below. Solutions to address these issues are also proposed.

  • Environmental factors, such as the presence of elevated concentrations of natural organic matter (NOM), dissolved oxygen, or nitrate, can inhibit the efficacy of UV/sulfite treatment systems by scavenging available hydrated electrons. Those interferences are commonly managed through chemical additions, reaction optimization, and/or dilution, and are therefore not considered likely to hinder treatment success.
  • Coloration in waste streams may also impact the effectiveness of the UV/sulfite treatment system by blocking the transmission of UV light, thus reducing the UV lamp's effective path length. To address this, pre-treatment may be necessary to enable UV/sulfite destruction of PFAS in the waste stream. Pre-treatment may include the use of strong oxidants or coagulants to consume or remove UV-absorbing constituents.
  • The degradation efficiency is strongly influenced by PFAS molecular structure, with fluorotelomer sulfonates (FTS) and perfluorobutanesulfonate (PFBS) exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.

State of the Practice

Figure 2. Field demonstration of EradiFluorTM[1] for PFAS destruction in a concentrated waste stream in a Mid-Atlantic Naval Air Station: a) Target PFAS at each step of the treatment shows that about 99% of PFAS were destroyed; meanwhile, the final degradation product, i.e., fluoride, increased to 15 mg/L in concentration, demonstrating effective PFAS destruction; b) AOF concentrations at each step of the treatment provided additional evidence to show near-complete mineralization of PFAS. Average results from multiple batches of treatment are shown here.
Figure 3. Field demonstration of a treatment train (SAFF + EradiFluorTM[1]) for groundwater PFAS separation and destruction at an Air Force base in California: a) Two main components of the treatment train, i.e. SAFF and EradiFluorTM[1]; b) Results showed the effective destruction of various PFAS in the foam fractionate. The target PFAS at each step of the treatment shows that about 99.9% of PFAS were destroyed. Meanwhile, the final degradation product, i.e., fluoride, increased to 30 mg/L in concentration, demonstrating effective destruction of PFAS in a foam fractionate concentrate. After a polishing treatment step (GAC) via the onsite groundwater extraction and treatment system, all PFAS were removed to concentrations below their MCLs.

The effectiveness of UV/sulfite technology for treating PFAS has been evaluated in two field demonstrations using the EradiFluorTM[1] system. Aqueous samples collected from the system were analyzed using EPA Method 1633, the total oxidizable precursor (TOP) assay, adsorbable organic fluorine (AOF) method, and non-target analysis. A summary of each demonstration and their corresponding PFAS treatment efficiency is provided below.

  • Under the Environmental Security Technology Certification Program (ESTCP) Project ER21-5152, a field demonstration of EradiFluorTM[1] was conducted at a Navy site on the east coast, and results showed that the technology was highly effective in destroying various PFAS in a liquid concentrate produced from an in situ foam fractionation groundwater treatment system. As shown in Figure 2a, total PFAS concentrations were reduced from 17,366 micrograms per liter (µg/L) to 195 µg/L at the end of the UV/sulfite reaction, representing 99% destruction. After the ion exchange resin polishing step, all residual PFAS had been removed to the non-detect level, except one compound (PFOS) reported as 1.5 nanograms per liter (ng/L), which is below the current Maximum Contaminant Level (MCL) of 4 ng/L. Meanwhile, the fluoride concentration increased up to 15 milligrams per liter (mg/L), confirming near complete defluorination. Figure 2b shows the adsorbable organic fluorine results from the same treatment test, which similarly demonstrates destruction of 99% of PFAS.
  • Another field demonstration was completed at an Air Force base in California, where a treatment train combining Surface Active Foam Fractionation (SAFF) and EradiFluorTM[1] was used to treat PFAS in groundwater. As shown in Figure 3, PFAS analytical data and fluoride results demonstrated near-complete destruction of various PFAS. In addition, this demonstration showed: a) high PFAS destruction ratio was achieved in the foam fractionate, even in very high concentration (up to 1,700 mg/L of booster), and b) the effluent from EradiFluorTM[1] was sent back to the influent of the SAFF system for further concentration and treatment, resulting in a closed-loop treatment system and no waste discharge from EradiFluorTM[1]. This field demonstration was conducted with the approval of three regulatory agencies (United States Environmental Protection Agency, California Regional Water Quality Control Board, and California Department of Toxic Substances Control).

References

  1. ^ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Haley and Aldrich, Inc. (commercial business), 2024. EradiFluor. Comercial Website
  2. ^ 2.0 2.1 Bentel, M.J., Yu, Y., Xu, L., Li, Z., Wong, B.M., Men, Y., Liu, J., 2019. Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management. Environmental Science and Technology, 53(7), pp. 3718-28. doi: 10.1021/acs.est.8b06648  Open Access Article
  3. ^ Liu, Z., Chen, Z., Gao, J., Yu, Y., Men, Y., Gu, C., Liu, J., 2022. Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies. Environmental Science and Technology, 56(6), pp. 3699-3709. doi: 10.1021/acs.est.1c07608  Open Access Article
  4. ^ Tenorio, R., Liu, J., Xiao, X., Maizel, A., Higgins, C.P., Schaefer, C.E., Strathmann, T.J., 2020. Destruction of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment. Environmental Science and Technology, 54(11), pp. 6957-67. doi: 10.1021/acs.est.0c00961
  5. ^ 5.0 5.1 Buxton, G.V., Greenstock, C.L., Phillips Helman, W., Ross, A.B., 1988. Critical Review of Rate Constants for Reactions of Hydrated Electrons, Hydrogen Atoms and Hydroxyl Radicals (⋅OH/⋅O-) in Aqueous Solution. Journal of Physical and Chemical Reference Data, 17(2), pp. 513-886. doi: 10.1063/1.555805
  6. ^ Gu, Y., Liu, T., Wang, H., Han, H., Dong, W., 2017. Hydrated Electron Based Decomposition of Perfluorooctane Sulfonate (PFOS) in the VUV/Sulfite System. Science of The Total Environment, 607-608, pp. 541-48. doi: 10.1016/j.scitotenv.2017.06.197
  7. ^ Bao, Y., Deng, S., Jiang, X., Qu, Y., He, Y., Liu, L., Chai, Q., Mumtaz, M., Huang, J., Cagnetta, G., Yu, G., 2018. Degradation of PFOA Substitute: GenX (HFPO–DA Ammonium Salt): Oxidation with UV/Persulfate or Reduction with UV/Sulfite? Environmental Science and Technology, 52(20), pp. 11728-34. doi: 10.1021/acs.est.8b02172
  8. ^ Singh, R.K., Brown, E., Mededovic Thagard, S., Holson, T.M., 2021. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. Journal of Hazardous Materials, 408, Article 124452. doi: 10.1016/j.jhazmat.2020.124452
  9. ^ Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S., Holson, 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. 13973-80. doi: 10.1021/acs.est.0c02158
  10. ^ Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M., Mededovic Thagard S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly- and Perfluoroalkyl Substances in Groundwater. American Chemical Society’s Environmental Science and Technology (ES&T) Water, 1(3), pp. 680-87. doi: 10.1021/acsestwater.0c00170
  11. ^ Nzeribe, B.N., Crimi, M., Mededovic Thagard, S., 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. doi: 10.1080/10643389.2018.1542916
  12. ^ Jung, B., Farzaneh, H., Khodary, A., Abdel-Wahab, A., 2015. Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation. Journal of Environmental Chemical Engineering, 3(3), pp. 2194-2202. doi: 10.1016/j.jece.2015.07.026
  13. ^ Liu, X., Yoon, S., Batchelor, B., Abdel-Wahab, A., 2013. Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) – Effects of reagents and pH. Chemical Engineering Journal, 215-216, pp. 868-875. doi: 10.1016/j.cej.2012.11.086
  14. ^ Li, X., Ma, J., Liu, G., Fang, J., Yue, S., Guan, Y., Chen, L., Liu, X., 2012. Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process. Environmental Science and Technology, 46(13), pp. 7342-49. doi: 10.1021/es3008535
  15. ^ Li, X., Fang, J., Liu, G., Zhang, S., Pan, B., Ma, J., 2014. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Research, 62, pp. 220-228. doi: 10.1016/j.watres.2014.05.051

See Also

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