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==Reverse Osmosis and Nanofiltration Systems for PFAS Removal==  
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==PFAS Destruction by Ultraviolet/Sulfite Treatment==  
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[[Wikipedia: Nanofiltration | Nanofiltration (NF)]] or [[Wikipedia: Reverse osmosis | reverse osmosis (RO)]] are engineered polymeric filters designed to remove solutes down to the atomic and molecular size scale<ref name="Wilf2019">Wilf, M., 2019. Basic Terms and Definitions, Chapter 3 in Desalination: Water from Water, 2nd Edition, J. Kucera, Editor. John Wiley & Sons. ISBN: 978-1-119-40774-4 [https://doi.org/10.1002/9781119407874.ch3 doi: 10.1002/9781119407874.ch3]</ref><ref name="BellonaEtAl2004">Bellona, C., Drewes, J., Xu, P., Amy, G., 2004. Factors affecting the rejection of organic solutes during NF/RO treatment—a literature review. Water Research, 38(12), p. 2795-2809. [https://doi.org/10.1016/j.watres.2004.03.034 doi: 10.1016/j.watres.2004.03.034]</ref><ref name="BazarganSalgado2018">Bazargan, A., Salgado, B., 2018. Fundamentals of Desalination Technology, in A Multidisciplinary Introduction to Desalination, A. Bazargan, Editor.  River Publishers. p. 41-66. ISBN 9788793379541. [https://doi.org/10.1201/9781003336914 doi: 10.1201/9781003336914]</ref>. RO, and to a lesser extent NF, has been implemented in a variety of water treatment applications including seawater and brackish water desalination, surface water treatment, industrial process water separation, and purification applications<ref name="Wilf2019"/><ref name="BellonaEtAl2004"/><ref name="BazarganSalgado2018"/><ref name="TurekEtAl2017">Turek, M., Mitko, K., Piotrowski, K., Dydo, P., Laskowska, E., Jakóbik-Kolon, A., 2017. Prospects for high water recovery membrane desalination. Desalination, 401, p. 180-189. [https://doi.org/10.1016/j.desal.2016.07.047 doi: 10.1016/j.desal.2016.07.047]</ref><ref name="PanagopoulosEtAl2019">Panagopoulos, A., Haralambous, K.-J., Loizidou, M., 2019. Desalination brine disposal methods and treatment technologies - A review. Science of The Total Environment, 693, Article 133545. [https://doi.org/10.1016/j.scitotenv.2019.07.351 doi: 10.1016/j.scitotenv.2019.07.351]</ref><ref name="WarsingerEtAl2018">Warsinger, D.M., Chakraborty, S., Tow, E.W., Plumlee, M.H., Bellona, C., Loutatidou, S., Karimi, L., Mikelonis, A.M., Achilli, A., Ghassemi, A., Padhye, L.P., Snyder, S.A., Curcio, S., Vecitis, C.D., Arafat, H.A., Lienhard, J.H., 2018. A review of polymeric membranes and processes for potable water reuse. Progress in Polymer Science, 81, p. 209-237. [https://doi.org/10.1016/j.progpolymsci.2018.01.004 doi: 10.1016/j.progpolymsci.2018.01.004]</ref><ref name="Yan2017">Yan, D., 2017. Membrane Desalination Technologies, Chapter 6 in A Multidisciplinary Introduction to Desalination, A. Bazargan, Editor. River Publishers, p. 155-199. ISBN: 9788793379541</ref><ref name="Bellona2019">Bellona, C., 2019. Nanofiltration - Theory and Application, Chapter 4 in Desalination: Water from Water, 2nd Edition, J. Kucera, Editor. John Wiley & Sons. ISBN: 978-1-119-40774-4. [https://doi.org/10.1002/9781118904855.ch4 doi: 10.1002/9781118904855.ch4]</ref>. RO and NF use semi-permeable membranes that limit diffusion of solutes into the product water (i.e., permeate) through [[Wikipedia: Steric effects | steric]] and electrostatic exclusion from the membrane polymer<ref name="BellonaEtAl2004"/>. Due to the molecular size and ionic character of [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | per- and polyfluoroalkyl substances (PFAS)]], past research has demonstrated that both RO and NF membranes can achieve a high degree of separation (i.e., rejection) of PFAS<ref name="ApplemanEtAl2013">Appleman, T.D., Dickenson, E.R.V., Bellona, C., Higgins, C.P., 2013. Nanofiltration and granular activated carbon treatment of perfluoroalkyl acids. Journal of Hazardous Materials, 260, p. 740-746. [https://doi.org/10.1016/j.jhazmat.2013.06.033 doi: 10.1016/j.jhazmat.2013.06.033]</ref><ref name="Steinle-DarlingReinhard2008">Steinle-Darling, E., Reinhard, M., 2008. Nanofiltration for Trace Organic Contaminant Removal: Structure, Solution, and Membrane Fouling Effects on the Rejection of Perfluorochemicals. Environmental Science and Technology, 42(14), p. 5292-5297. [https://doi.org/10.1021/es703207s doi: 10.1021/es703207s]</ref><ref name="SafulkoEtAl2023">Safulko, A., Cath, T.Y., Li, F., Tajdini, B., Boyd, M., Huehmer, R.P., Bellona, C., 2023. Rejection of perfluoroalkyl acids by nanofiltration and reverse osmosis in a high-recovery closed-circuit membrane filtration system. Separation and Purification Technology, 326, Article 124867. [https://doi.org/10.1016/j.seppur.2023.124867  doi: 10.1016/j.seppur.2023.124867]  [[Media: SafulkoEtAl2023.pdf | Open Access Manuscript]]</ref>.  
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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>
 
<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:''' Christopher Bellona, Nicole Masters, Stephen Richardson
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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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*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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*EradiFluor<sup>TM</sup><ref name="EradiFluor"/>
  
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*Interstate Technology Regulatory Council (ITRC), PFAS – Per- and Polyfluoroalkyl Substances: [https://pfas-1.itrcweb.org/12-treatment-technologies/#12_2 12.2 Field-Implemented Liquids Treatment Technologies] and [https://pfas-1.itrcweb.org/12-treatment-technologies/#12_5 12.5 Limited Application and Developing Liquids Treatment Technologies]
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==Introduction==
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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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==Introduction==
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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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Historically, pyrogenic carbonaceous matter (PCM) has been used to remove contaminants from the aqueous phase by adsorption and/or complexation, but it was not believed to facilitate their degradation. A recent [https://serdp-estcp.mil/ Strategic Environmental Research and Development Program (SERDP)] project ([https://serdp-estcp.mil/projects/details/047de8e1-0202-40ba-8bf6-cbd89bcc5b46 ER19-1239]) developed evidence that PCM not only adsorbs but also catalyzes the hydrolysis of some munition constituents, thus potentially reducing the need for regeneration or replacement of the adsorbent material and thereby reducing costs associated with management of these contaminants. This project found that PCM can facilitate MC degradation on carbon surfaces and thus free up adsorption sites, allowing PCM to remove a significantly greater mass of some MCs than would be possible by adsorption alone. Any MCs such as [[Wikipedia: Nitrotriazolone | 3-Nitro-1,2,4-triazol-5-one (NTO)]] that are not susceptible to alkaline hydrolysis can be safely sequestered within the carbon amendment, decreasing their bioavailability to the surrounding environment. Furthermore, the tested technology boosts alkaline hydrolysis at near-neutral pH conditions rather than high pH conditions required by current methods (i.e., lime treatment). Bench studies using soils collected from Department of Defense ranges demonstrated enhanced adsorption affinity (over three orders of magnitude) for highly mobile IHEs such as NTO because the PCM amendments maintained their reactivity over consecutive additions of IHE formulations. The findings suggest that PCM has the potential to be developed and deployed as a reactive amendment for environmental remediation of MCs. Future efforts are needed to demonstrate these materials at full scale in the field.
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</br>
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::<big>'''Equation 1:'''</big>&nbsp;&nbsp; [[File: XiongEq1.png | 200 px]]
  
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Using a combined experimental and computational modeling approach, the structural features of MCs and PCM that are critical for PCM-facilitated hydrolysis were identified. Employing a polymer synthesis approach, the contribution of various functional groups and pore structures in promoting MC hydrolysis were delineated. The findings of this investigation have broad implications for reactive adsorbent design and remediation. For instance, the formation of [[Wikipedia: Sigma complex | σ complexes]] between -NH<sub>2</sub> surface functional groups and nitroaromatics suggests that PCM rich in -NH<sub>2</sub> functional groups could be easily poisoned due to the irreversible binding of [[Wikipedia: TNT | 2,4,6-trinitrotoluene (TNT)]] or [[Wikipedia: 2,4-Dinitroanisole | 2,4-dinitroanisole (DNAN)]]. By contrast, [[Wikipedia: Quaternary ammonium cation | quaternary ammonium (QA)]] functional groups could accumulate TNT, DNAN and [[Wikipedia: Hydroxide | hydroxide (OH-)]] in the same spatial region, potentially enabling hydrolysis of the MCs. Therefore, efforts can be focused on populating specific functional groups on carbon amendments for groundwater and soil remediation. For example, increasing the abundance of QA groups while decreasing the presence of -NH<sub>2</sub> and -OH can reduce the need for PCM regeneration. This is because contaminants will be destroyed on PCM surfaces rather than filling up adsorption sites. Besides functional groups, the pore structures of adsorbents could also be adjusted to favor hydrolysis and specific pathways (see Figure 3).
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The hydrated electron has demonstrated excellent performance in destroying PFAS such as perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS)<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 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., decarboxylation, hydroxylation, elimination, and hydrolysis)<ref name="BentelEtAl2019"/>.
  
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A novel adsorption mechanism known as charge-assisted hydrogen bond (CAHB) formation was proposed to account for the exceptionally high affinity of PCM for MCs that do not undergo hydrolysis, such as NTO. The findings contradicted the conventional wisdom that polar organic anions (e.g., NTO) have little affinity for or are even repelled by hydrophobic carbonaceous sorbents. The results call attention to the need for new models or modification of existing models for the sorption of ionizable compounds in order to consider CAHB formation with sorbents. The findings also have potentially important implications for the use of carbons in environmental remediation more generally, particularly for strategies that enhance the retention of anionic contaminants that are otherwise highly mobile, such as nitrite, nitrate, phosphate, or some [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | per- and polyfluoroalkyl substances (PFAS)]].
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==Process Description==
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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 treatment by UV/sulfite reduction to break C-F bonds. 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. [[File: XiongFig1.png | thumb | left | 600 px | Figure 1: Conceptual Treatment Process for a Concentrated PFAS Stream]]
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<br clear="left"/>
  
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==Feasibility of PCM-facilitated Hydrolysis of MCs==
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==Advantages==
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[[File:XuFig1.png|thumb|500px|Figure 1. Proposed reaction mechanism for PCM-facilitated DNAN hydrolysis and associated transformation products<ref name="SeenthiaEtAl2024"/>]]
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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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Results of this study suggest that hydrolysis of TNT, DNAN, and [[Wikipedia: Nitroguanidine | nitroguanidine (NQ)]], can be enhanced by the presence of various PCMs. The transformation of TNT by graphite powder, a model PCM, exhibited first-order decay kinetics, with an observed rate constant (''k<sub>obs</sub>'') of 0.258 ± 0.010 day<sup>-1</sup> and a calculated half-life (''t<sub>1/2</sub>'') of 2.70 ± 0.10 days<ref name="Ding">Ding, K., Byrnes, C., Bridge, J., Grannas, A., Xu, W., 2018. Surface-promoted hydrolysis of 2,4,6-trinitrotoluene and 2,4-dinitroanisole on pyrogenic carbonaceous matter. Chemosphere, 197, pp. 603-610. [https://doi.org/10.1016/j.chemosphere.2018.01.038 doi: 10.1016/j.chemosphere.2018.01.038]</ref>. Slower degradation was observed for DNAN under the same conditions. Increasing the pH and the temperature enhanced the degradation kinetics of DNAN<ref name="SeenthiaEtAl2024"/>. More importantly, results suggest that PCM accelerated DNAN decay by lowering the activation energy of DNAN hydrolysis by 54.3 ± 3.9%. NQ is a monoprotic acid in water with a reported ''pK<sub>a</sub>'' value of 12.8. NQ undergoes significant base hydrolysis at pH values as low as 11.5. This study showed that PCM pre-equilibrated with NQ initially accelerated NQ hydrolysis at three pH conditions (pH 11.0, 11.5, and 12.5) compared to the aqueous reaction. However, after a few hours, hydrolysis in the presence of PCM slowed down, whereas aqueous hydrolysis continued apace, indicating that the physical and chemical properties of PCMs play critical roles in controlling the hydrolysis of MCs.
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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 trifluoroacetic acid (TFA) and perfluoropropionic acid (PFPrA). 
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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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*'''No harmful byproducts:'''
  
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==Key Properties of PCM for MC Hydrolysis==
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==Analysis of PFAS Concentrations in Soil and Porewater==
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[[File:XuFig2.png | thumb |400px| Figure 2: Proposed role of PCM properties in accelerating TNT hydrolysis<ref name="Li"/>]]
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{| class="wikitable mw-collapsible" style="float:left; margin-right:20px; text-align:center;"
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To investigate the effect of PCM functional group identity and pore characteristics on MC hydrolysis, a PCM-like polymer (PLP) platform was developed to allow for delineating individual PCM properties’ contributions using a reductionist approach. PLPs exhibit properties that are similar to PCM: (i) large surface area and high microporosity, (ii) highly conjugated and amorphous, and (iii) superior affinity for apolar organic contaminants. Unlike PCM, the attributes of PLP can be individually tuned and made homogeneously throughout the polymer networks. Specifically, six PLPs were synthesized via cross-coupling chemistry with specific functionality (i.e., -OH, -NH<sub>2</sub>, -N(CH<sub>3</sub>)<sub>2</sub>, and -N(CH<sub>3</sub>)<sub>3</sub><sup>+</sup>) and pore characteristics (i.e., mesopore, micropore). Different surface functional groups were incorporated into the PLPs by adapting the synthesis approach described in previous work<ref name="Li">Li, Z., Jorn, R., Samonte, P.R.V., Mao, J., Sivey, J.D., Pignatello, J.J., Xu, W., 2022. Surface-catalyzed hydrolysis by pyrogenic carbonaceous matter and model polymers: An experimental and computational study on functional group and pore characteristics. Applied Catalysis B: Environment and Energy, 319, article 121877. [https://doi.org/10.1016/j.apcatb.2022.121877 doi: 10.1016/j.apcatb.2022.121877]&nbsp; [[Media: LiEtAl2022.pdf | Open Access Manuscript]]</ref>. The pore characteristics of PLP were controlled by rigid node-strut topology, where two polymers were obtained, one with exclusively mesopores and the other with a mixture of micropores and mesopores. This showed that -OH and -NH<sub>2</sub> functional groups can serve as weak bases to facilitate TNT hydrolysis, whereas -N(CH<sub>3</sub>)<sub>3</sub><sup>+</sup> groups can increase the local pH by accumulating OH<sup>-</sup> near PCM surfaces. Moreover, the micropores of PCM seem capable of altering the chemical environment around TNT molecules (including their location and orientation) in such a way as to facilitate their hydrolysis. This study attempted to scrutinize the complex properties of PCM that promote surface hydrolysis, namely the functional group identity and pore characteristics.
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|+Table 1. Measured and Predicted PFAS Concentrations in Porewater for Select PFAS in Three Different Soils
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|-
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!Site
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!PFAS
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!Field</br>Porewater</br>Concentration</br>(&mu;g/L)
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!Lab Core</br>Porewater</br>Concentration</br>(&mu;g/L)
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!Predicted</br>Porewater</br>Concentration</br>(&mu;g/L)
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|-
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|Site A||PFOS||6.2 ± 3.4||3.0 ± 0.37||6.6 ± 3.3
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|-
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|Site B||PFOS||2.2 ± 2.0||0.78 ± 0.38||2.8
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|-
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|rowspan="3"|Site C||PFOS||13 ± 4.1||680 ± 460||164 ± 75
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|-
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|8:2 FTS||1.2 ± 0.46||52 ± 13||16 ± 6.0
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|-
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|PFHpS||0.36 ± 0.051||2.9 ± 2.0||5.9 ± 3.4
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|}
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[[File: StultsFig2.png | thumb | 600 px | Figure 2. Field Measured PFAS concentration Data (Orange) and Lab Core Measured Concentration Data (Blue) for four PFAS impacted sites<ref name="AndersonEtAl2022"/>]]  
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[[File: StultsFig3.png | thumb | 400 px | Figure 3. Measured and predicted data for PFAS concentrations from a single site field lysimeter study. Model predictions both with and without PFAS sorption to the air-water interface were considered<ref name="SchaeferEtAl2023"/>.]]
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Schaefer&nbsp;''et&nbsp;al.''<ref name="SchaeferEtAl2024"/>&nbsp;measured&nbsp;PFAS porewater concentrations with field and laboratory suction lysimeters across several sites. Intact cores from the site were collected for soil water extraction using laboratory lysimeters. The lysimeters were used to directly compare field derived measurements of PFAS concentration in the mobile porewater phase. Results from measurements are for four sites presented in Figure 2.
  
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==Enhanced Hydrolysis of TNT and DNAN with Modified PCM==
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Data from sites A and B showed reasonably good agreement (within ½ order of magnitude) for most PFAS measured in the systems. At site C, more hydrophobic constituents (> C6 PFAS) tended to have higher concentrations in the lab core than the field site while less hydrophobic constituents (< C6) had higher concentrations in the field than lab cores. Site D showed substantially greater (1 order of magnitude or more) PFAS concentrations measured in the laboratory-collected porewater sample compared to what was measured in the field lysimeters. This discrepancy for the Site D soil can likely be attributed to soil heterogeneity (as indicated by ground penetrating radar) and the fact that the soil consisted of back-filled materials rather than undisturbed native soils.
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This investigation proposes that PCMs can affect the thermodynamics and kinetics of hydrolysis reactions by confining the reaction species near PCM surfaces, thus making them less accessible to solvent molecules and creating an environment with a weaker dielectric constant that favors nucleophilic substitution reactions. The addition of QA groups on the PCM surface can further accelerate MC hydrolysis. The performance of PCM toward DNAN hydrolysis was evaluated by comparing the MC decay kinetics across various PCM types, including unmodified PCMs such as almond shell char or activated carbon (AC)), and modified PCMs with physical or chemically attached QA groups. The results suggest that QA-modified activated carbon performed the best by reducing the half-life of DNAN to 2.5 days at pH 11.5 and 25°C while maintaining its reactivity over ten consecutive additions of DNAN<ref name="SeenthiaEtAl2024"/>. TNT exhibited faster decay in samples containing QA-modified AC than unmodified AC, with an estimated half-life of 0.2 days and 1 day, respectively<ref name="Li"/>. Nitrite was observed as one of the transformation products for both DNAN and TNT, suggesting the presence of PCM favored the denitration pathway. By contrast, demethylation, the preferred pathway in homogeneous solution, produces [[Wikipedia: 2,4-Dinitrophenol | 2,4-dinitrophenol (DNP)]]. Denitration catalyzed by PCM was advantageous when compared to demethylation because nitrite is less toxic than DNAN and DNP. Overall, the results suggest that further improvement of the PCM performance could be expected by tailoring its surface to increase the abundance of QA while decreasing the presence of -NH<sub>2</sub> or -OH groups for the hydrolysis of MCs.  
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Site&nbsp;C&nbsp;showed&nbsp;elevated PFAS concentrations in the laboratory collected porewater for the more surface-active compounds. This increase was attributed to the soil wetting that occurred at the bench scale, which was reasonably described by the model shown in Equations 1 and 2 (see Table 1<ref name="AndersonEtAl2022"/>). Equations 1 and 2 were also used to predict PFAS porewater concentrations (using porous cup lysimeters) in a highly instrumented test cell<ref name="SchaeferEtAl2023"/>(Figure 3). The ability to predict soil concentrations from recurring porewater samples is critical to the practical application of lysimeters in field settings<ref name="AndersonEtAl2022"/>.
  
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==Computational Modeling==
+
Results from suction lysimeters studies and field lysimeter studies show that PFAS concentrations in porewater predicted from soil concentrations using Equations 1 and 2 generally have reasonable agreement with measured ''in situ'' porewater data when air-water interfacial partitioning is considered. Results show that for less hydrophobic components like PFOA, the impact of air-water interfacial adsorption is less significant than for highly hydrophobic components like PFOS. The soil for the field lysimeter in Figure 3 was a sandy soil with a relatively low air-water interfacial area. The effect of air-water interfacial partitioning is expected to be much more significant for a greater range of PFAS in soils with high capillary pressure (i.e. silts/clays) with higher associated air-water interfacial areas<ref name="Brusseau2023"/><ref>Peng, S., Brusseau, M.L., 2012. Air-Water Interfacial Area and Capillary Pressure: Porous-Medium Texture Effects and an Empirical Function. Journal of Hydrologic Engineering, 17(7), pp. 829-832. [https://doi.org/10.1061/(asce)he.1943-5584.0000515 doi: 10.1061/(asce)he.1943-5584.0000515]</ref><ref>Brusseau, M.L., Peng, S., Schnaar, G., Costanza-Robinson, M.S., 2006. Relationships among Air-Water Interfacial Area, Capillary Pressure, and Water Saturation for a Sandy Porous Medium. Water Resources Research, 42(3), Article W03501, 5 pages. [https://doi.org/10.1029/2005WR004058 doi: 10.1029/2005WR004058]&nbsp; [[Media: BrusseauEtAl2006.pdf | Free Access Article]]</ref>.
−
[[File:XuFig3.png | thumb |400px| Figure 3. (a) Ball-and-stick model of TNT confined between four layers of graphene with quaternary ammonium groups with a 4-nm distance, black = graphite, green = TNT, purple = ammonium groups, orange = chloride ions, blue = hydroxide oxygens<ref name="SeenthiaEtAl2024"/>. (b) (Top) Molecular snapshot from an AIMD/MM simulation: DNAN + [OH<sup>-</sup>] → DNAN-2-OH + nitrite in a nano-pore, containing DNAN, hydroxide, Na<sup>+</sup> counter-ion, and  43 H<sub>2</sub>O, at a concentration of 1.3 M. (Bottom) Reaction pathways: Nucleophilic aromatic reaction of DNAN + [OH<sup>-</sup>] → DNAN-2-OH + Nitrite in solution and within a nano-pore, investigated using PBE and PBE0 AIMD/MM free energy simulations with WHAM. Each pathway used approximately 0.5 ns of simulation time<ref name="Li"/>.]]
 
−
Further mechanistic insights were obtained by performing non-reactive molecular dynamics simulations on idealized pore structures. Upon the introduction of positively charged QA groups, the structure changed dramatically at the PCM interface. As the number of surface groups increased, the resulting density of OH<sup>-</sup> at the PCM surface increased by a factor of four relative to the density in the middle of the pore. Hence, the impact of the surface-bound cations was to attract OH<sup>-</sup> in competition with the neutralizing anions in the environment. In addition to driving the accumulation of OH<sup>-</sup>, the surface QA groups also impacted the distribution of TNT in the pore. At low QA surface coverage, TNT sought to adsorb on the exposed graphene. However, at sufficiently high QA surface coverage, TNT was blocked from lying flat on the graphene sheet and instead aggregated in the fluid away from the pore wall. The observation of TNT surface layering at intermediate charge densities was intriguing because it demonstrated the collection of TNT molecules close to the surface in the same spatial region where hydroxide was likewise accumulating relative to its concentration in the interstitial fluid. The molecular dynamics simulations provided evidence that the presence of the surface groups can play a role in accelerating TNT hydrolysis by acting to concentrate both TNT and hydroxide near the pore wall<ref name="Li"/>.
 
  
−
[[Wikipedia: Molecular dynamics#Potentials in ab initio methods | ''Ab Initio'' Molecular Dynamics/Molecular Mechanics (AIMD/MM)]] free energy simulations using expanded slabs and unit cells were also performed, focusing on the interaction of DNAN, hydroxide ions, Na<sup>+</sup>, and multiple water molecules sandwiched between two graphene layers<ref name="SeenthiaEtAl2024"/>. The upper panel of Figure 3(b)  provides a molecular snapshot from the AIMD/MM simulation, showcasing the intermediate stage of DNAN reacting with a hydroxide ion within a nano-pore structure. The lower panel depicts the reaction energy profiles for the hydrolysis of DNAN, both in bulk aqueous solution and within the nano-pore environment. The x-axis represents the reaction coordinate, a schematic representation of the progression from reactants to products through various transition states and intermediates. The y-axis corresponds to the [[Wikipedia: Gibbs free energy| Gibbs free energy]] changes (ΔG), providing insights into the thermodynamic favorability of each step in the pathway. Lower barriers corresponded to more kinetically accessible reactions. In the nano-pore environment, the energy barriers were significantly reduced, suggesting a catalytic effect due to confinement. This reduction was quantified by a decrease in ΔG of approximately 8 kcal/mol compared to the bulk solution, indicating that the reactions were not only more thermodynamically favorable but also kinetically accelerated in the nano-pore. In conclusion, the results demonstrate that nano-pore environments can significantly alter the hydrolysis mechanism of DNAN, leading to potentially less toxic products.  
+
==Summary and Recommendations==
 +
The majority of research with lysimeters for PFAS site investigations has been done using porous cup suction lysimeters<ref name="CostanzaEtAl2025"/><ref name="AndersonEtAl2022"/><ref name="SchaeferEtAl2024"/><ref name="QuinnanEtAl2021"/>. Porous cup suction lysimeters are advantageous because they can be routinely sampled or sampled after specific wetting or drying events much like groundwater wells. This sampling is easier and more efficient than routinely collecting soil samples from the same locations. Co-locating lysimeters with soil samples is important for establishing the baseline soil concentration levels at the lysimeter location and developing correlations between the soil concentrations and the mobile porewater concentration<ref name="CostanzaEtAl2025"/>. Appropriate standard operation procedures for lysimeter installation and operation have been established and have been reviewed in recent literature<ref name="CostanzaEtAl2025"/><ref name="SchaeferEtAl2024"/>. Lysimeters should typically be installed near the source area and just above the maximum groundwater level elevation to obtain accurate results of porewater concentrations year round. Depending upon the geology and vertical PFAS distribution in the soil, multilevel lysimeter installations should also be considered.
  
−
==Exceptionally Strong NTO Adsorption on PCM==
+
Results from several lysimeters studies across multiple field sites and modelling analysis has shown that lysimeters can produce reasonable results between field and laboratory studies<ref name="SchaeferEtAl2024"/><ref name="SchaeferEtAl2023"/><ref name="SchaeferEtAl2022"/>. Transient effects of wetting and drying as well as media heterogeneity affects appear to be responsible for some variability and uncertainty in lysimeter based PFAS measurements in the vadose zone. These mobile porewater concentrations can be coupled with effective recharge estimates and simplified modelling approaches to determine mass flux from the vadose zone to the underlying groundwater<ref name="Anderson2021"/><ref name="StultsEtAl2024"/><ref name="BrusseauGuo2022"/><ref>Stults, J.F., Schaefer, C.E., MacBeth, T., Fang, Y., Devon, J., Real, I., Liu, F., Kosson, D., Guelfo, J.L., 2025. Laboratory Validation of a Simplified Model for Estimating Equilibrium PFAS Mass Leaching from Unsaturated Soils. Science of The Total Environment, 970, Article 179036. [https://doi.org/10.1016/j.scitotenv.2025.179036 doi: 10.1016/j.scitotenv.2025.179036]</ref><ref>Smith, J. Brusseau, M.L., Guo, B., 2024. An Integrated Analytical Modeling Framework for Determining Site-Specific Soil Screening Levels for PFAS. Water Research, 252, Article121236. [https://doi.org/10.1016/j.watres.2024.121236 doi: 10.1016/j.watres.2024.121236]</ref>.
−
[[File:XuFig4.png | thumb |500px| Figure 4. Proposed formation of charge-assisted hydrogen bond between NTO and weak acid functional groups on the carbon surface<ref name="Abdelraheem"/>.]]
 
−
Results from this project suggest that NTO was chemically stable for up to at least a week in NaOH solution at pH 13.8<ref name="Abdelraheem">Abdelraheem, W., Meng, L., Pignatello, J.J., Seenthia, N.I., Xu, W., 2024. Participation of Strong H-Bonding to Acidic Groups Contributes to the Intense Sorption of the Anionic Munition, Nitrotriazolone (NTO) to the Carbon, Filtrasorb 400. Environmental Science and Technology, 58(46), pp. 20719-20728. [https://doi.org/10.1021/acs.est.4c07055 doi: 10.1021/acs.est.4c07055]</ref>. Despite its highly polar and anionic character (''pK<sub>a</sub>'' = 3.78), NTO exhibited unexpectedly strong sorption toward PCM at environmentally relevant pH conditions. This high affinity was partly due to the formation of an exceptionally strong negative charge-assisted hydrogen bond, or (−)CAHB, with weak acid functional groups on the carbon surface. The CAHB was identified by evaluating adsorption isotherms, pH adsorption edge plots, competitive sorption experiments, and pH drift experiments. The findings contradict the conventional view that polar organic anions have little affinity for or are even repelled by hydrophobic carbonaceous sorbents. The results call attention to the need for new models or modification of existing models for the sorption of ionizable compounds that consider CAHB formation with sorbents. The findings also have potential implications for the use of carbons in environmental remediation and catalysis, particularly for the design of strategies for the retention and degradation of highly mobile contaminants.
 
  
−
==Performance of Modified PCM as Soil Amendments for IHE Post-Detonation Residues==
+
Future research opportunities should address the current key uncertainties related to the use of lysimeters for PFAS investigations, including:
−
Batch and column tests were conducted to evaluate the adsorption and hydrolysis of post-detonation residues of [[Wikipedia: IMX-101 | IMX-101]] in three DoD range soils amended with modified PCMs<ref name="SeenthiaEtAl2025">Seenthia, N.I., Abdelraheem, W., Beal, S.A., Pignatello, J.J., Xu, W., 2025. Simultaneous adsorption and hydrolysis of insensitive munition compounds by pyrogenic carbonaceous matter (PCM) and functionalized PCM in soils. Journal of Hazardous Materials, 494, article 138501. [https://doi.org/10.1016/j.jhazmat.2025.138501 doi: 10.1016/j.jhazmat.2025.138501]</ref>. Results indicated that adding PCMs enhanced the removal of NTO, NQ, and DNAN in soils compared to the soil controls, with enhancement factors ranging from 50 to 300. Consistent with previous results, NTO exhibited the highest partition coefficients (''K<sub>d</sub>'') in PCM-amended soils compared to DNAN and NQ despite its highly polar and anionic character. Among various PCMs, QA-modified AC performed best, followed by unmodified AC and chars. The ''K<sub>d</sub>'' values of NTO, NQ, and DNAN were slightly lower in the IMX-101 mixture than individually, possibly due to the adsorption competition from other constituents in IMX-101. The treatment was evaluated at pH 8, 10, and 12. No NTO decay was observed across the investigated pH range with or without PCM. By contrast, up to 13% of NQ was removed but only at pH > 10. Up to 90% DNAN decay occurred at pH 10 and 12 over 7 days in soils amended with modified AC. The 2% amendment dose was most effective, maintaining its adsorption capacity and reactivity over three consecutive IMX-101 additions. Column tests confirmed that 2% PCM addition significantly delayed the NTO, NQ, and DNAN breakthrough. The breakthrough volume (defined as treatment volume resulting in Concentration<sub>out</sub>=0.1*Concentration<sub>in</sub>) of NTO, NQ, and DNAN correlated with their ''K<sub>d</sub>'' values obtained from the batch tests, where no retention was observed in the absence of PCM amendments. These findings highlight the feasibility of using modified PCM to simultaneously retain and transform IMX residues, providing a strategy for using reactive amendments ''in situ'' to sustain military operation and pollutant abatement.
+
#<u>Collect larger datasets of PFAS concentrations</u> to determine how transient wetting or drying periods and media type affect PFAS concentrations in the mobile porewater. Some research has shown that non-equilibrium processes can occur in the vadose zone, which can affect grab sample concentration in the porewater at specific time periods.  
 +
#<u>More work should be done with flux averaging lysimeters</u> like the drainage cup or wicking lysimeter. These lysimeters can directly measure net recharge and provide time averaged concentrations of PFAS in water over the sampling period. However, there is little work detailing their potential applications in PFAS research, or operational considerations for their use in remedial investigations for PFAS.
 +
#<u>Lysimeters should be coupled with monitoring of wetting and drying</u> in the vadose zone using ''in situ'' soil moisture sensors or tensiometers and groundwater levels. Direct measurements of soil saturation at field sites are vital to directly correlate porewater concentrations with soil concentrations. Similarly, groundwater level fluctuations can inform net recharge estimates. By collecting these data we can continue to improve partitioning and leaching models which can relate porewater concentrations to total PFAS mass in soils and PFAS leaching at field sites.
 +
#<u>Comparisons of various bench-scale leaching or desorption tests to field-based lysimeter data</u> are recommended. The ability to correlate field measurements of PFAS concentrations with estimates of leaching from laboratory studies would provide a powerful method to empirically estimate PFAS leaching from field sites.
  
 
==References==
 
==References==

Latest revision as of 19:44, 28 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 perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS)[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 treatment by UV/sulfite reduction to break C-F bonds. 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:

Analysis of PFAS Concentrations in Soil and Porewater

Table 1. Measured and Predicted PFAS Concentrations in Porewater for Select PFAS in Three Different Soils
Site PFAS Field
Porewater
Concentration
(μg/L) 		Lab Core
Porewater
Concentration
(μg/L) 		Predicted
Porewater
Concentration
(μg/L)
Site A PFOS 6.2 ± 3.4 3.0 ± 0.37 6.6 ± 3.3
Site B PFOS 2.2 ± 2.0 0.78 ± 0.38 2.8
Site C PFOS 13 ± 4.1 680 ± 460 164 ± 75
8:2 FTS 1.2 ± 0.46 52 ± 13 16 ± 6.0
PFHpS 0.36 ± 0.051 2.9 ± 2.0 5.9 ± 3.4
Figure 2. Field Measured PFAS concentration Data (Orange) and Lab Core Measured Concentration Data (Blue) for four PFAS impacted sites[11]
Figure 3. Measured and predicted data for PFAS concentrations from a single site field lysimeter study. Model predictions both with and without PFAS sorption to the air-water interface were considered[12].

Schaefer et al.[13] measured PFAS porewater concentrations with field and laboratory suction lysimeters across several sites. Intact cores from the site were collected for soil water extraction using laboratory lysimeters. The lysimeters were used to directly compare field derived measurements of PFAS concentration in the mobile porewater phase. Results from measurements are for four sites presented in Figure 2.

Data from sites A and B showed reasonably good agreement (within ½ order of magnitude) for most PFAS measured in the systems. At site C, more hydrophobic constituents (> C6 PFAS) tended to have higher concentrations in the lab core than the field site while less hydrophobic constituents (< C6) had higher concentrations in the field than lab cores. Site D showed substantially greater (1 order of magnitude or more) PFAS concentrations measured in the laboratory-collected porewater sample compared to what was measured in the field lysimeters. This discrepancy for the Site D soil can likely be attributed to soil heterogeneity (as indicated by ground penetrating radar) and the fact that the soil consisted of back-filled materials rather than undisturbed native soils.

Site C showed elevated PFAS concentrations in the laboratory collected porewater for the more surface-active compounds. This increase was attributed to the soil wetting that occurred at the bench scale, which was reasonably described by the model shown in Equations 1 and 2 (see Table 1[11]). Equations 1 and 2 were also used to predict PFAS porewater concentrations (using porous cup lysimeters) in a highly instrumented test cell[12](Figure 3). The ability to predict soil concentrations from recurring porewater samples is critical to the practical application of lysimeters in field settings[11].

Results from suction lysimeters studies and field lysimeter studies show that PFAS concentrations in porewater predicted from soil concentrations using Equations 1 and 2 generally have reasonable agreement with measured in situ porewater data when air-water interfacial partitioning is considered. Results show that for less hydrophobic components like PFOA, the impact of air-water interfacial adsorption is less significant than for highly hydrophobic components like PFOS. The soil for the field lysimeter in Figure 3 was a sandy soil with a relatively low air-water interfacial area. The effect of air-water interfacial partitioning is expected to be much more significant for a greater range of PFAS in soils with high capillary pressure (i.e. silts/clays) with higher associated air-water interfacial areas[14][15][16].

Summary and Recommendations

The majority of research with lysimeters for PFAS site investigations has been done using porous cup suction lysimeters[17][11][13][18]. Porous cup suction lysimeters are advantageous because they can be routinely sampled or sampled after specific wetting or drying events much like groundwater wells. This sampling is easier and more efficient than routinely collecting soil samples from the same locations. Co-locating lysimeters with soil samples is important for establishing the baseline soil concentration levels at the lysimeter location and developing correlations between the soil concentrations and the mobile porewater concentration[17]. Appropriate standard operation procedures for lysimeter installation and operation have been established and have been reviewed in recent literature[17][13]. Lysimeters should typically be installed near the source area and just above the maximum groundwater level elevation to obtain accurate results of porewater concentrations year round. Depending upon the geology and vertical PFAS distribution in the soil, multilevel lysimeter installations should also be considered.

Results from several lysimeters studies across multiple field sites and modelling analysis has shown that lysimeters can produce reasonable results between field and laboratory studies[13][12][19]. Transient effects of wetting and drying as well as media heterogeneity affects appear to be responsible for some variability and uncertainty in lysimeter based PFAS measurements in the vadose zone. These mobile porewater concentrations can be coupled with effective recharge estimates and simplified modelling approaches to determine mass flux from the vadose zone to the underlying groundwater[20][21][22][23][24].

Future research opportunities should address the current key uncertainties related to the use of lysimeters for PFAS investigations, including:

  1. Collect larger datasets of PFAS concentrations to determine how transient wetting or drying periods and media type affect PFAS concentrations in the mobile porewater. Some research has shown that non-equilibrium processes can occur in the vadose zone, which can affect grab sample concentration in the porewater at specific time periods.
  2. More work should be done with flux averaging lysimeters like the drainage cup or wicking lysimeter. These lysimeters can directly measure net recharge and provide time averaged concentrations of PFAS in water over the sampling period. However, there is little work detailing their potential applications in PFAS research, or operational considerations for their use in remedial investigations for PFAS.
  3. Lysimeters should be coupled with monitoring of wetting and drying in the vadose zone using in situ soil moisture sensors or tensiometers and groundwater levels. Direct measurements of soil saturation at field sites are vital to directly correlate porewater concentrations with soil concentrations. Similarly, groundwater level fluctuations can inform net recharge estimates. By collecting these data we can continue to improve partitioning and leaching models which can relate porewater concentrations to total PFAS mass in soils and PFAS leaching at field sites.
  4. Comparisons of various bench-scale leaching or desorption tests to field-based lysimeter data are recommended. The ability to correlate field measurements of PFAS concentrations with estimates of leaching from laboratory studies would provide a powerful method to empirically estimate PFAS leaching from field sites.

References

  1. ^ 1.0 1.1 1.2 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. ^ 11.0 11.1 11.2 11.3 Cite error: Invalid <ref> tag; no text was provided for refs named AndersonEtAl2022
  12. ^ 12.0 12.1 12.2 Cite error: Invalid <ref> tag; no text was provided for refs named SchaeferEtAl2023
  13. ^ 13.0 13.1 13.2 13.3 Cite error: Invalid <ref> tag; no text was provided for refs named SchaeferEtAl2024
  14. ^ Cite error: Invalid <ref> tag; no text was provided for refs named Brusseau2023
  15. ^ Peng, S., Brusseau, M.L., 2012. Air-Water Interfacial Area and Capillary Pressure: Porous-Medium Texture Effects and an Empirical Function. Journal of Hydrologic Engineering, 17(7), pp. 829-832. doi: 10.1061/(asce)he.1943-5584.0000515
  16. ^ Brusseau, M.L., Peng, S., Schnaar, G., Costanza-Robinson, M.S., 2006. Relationships among Air-Water Interfacial Area, Capillary Pressure, and Water Saturation for a Sandy Porous Medium. Water Resources Research, 42(3), Article W03501, 5 pages. doi: 10.1029/2005WR004058  Free Access Article
  17. ^ 17.0 17.1 17.2 Cite error: Invalid <ref> tag; no text was provided for refs named CostanzaEtAl2025
  18. ^ Cite error: Invalid <ref> tag; no text was provided for refs named QuinnanEtAl2021
  19. ^ Cite error: Invalid <ref> tag; no text was provided for refs named SchaeferEtAl2022
  20. ^ Cite error: Invalid <ref> tag; no text was provided for refs named Anderson2021
  21. ^ Cite error: Invalid <ref> tag; no text was provided for refs named StultsEtAl2024
  22. ^ Cite error: Invalid <ref> tag; no text was provided for refs named BrusseauGuo2022
  23. ^ Stults, J.F., Schaefer, C.E., MacBeth, T., Fang, Y., Devon, J., Real, I., Liu, F., Kosson, D., Guelfo, J.L., 2025. Laboratory Validation of a Simplified Model for Estimating Equilibrium PFAS Mass Leaching from Unsaturated Soils. Science of The Total Environment, 970, Article 179036. doi: 10.1016/j.scitotenv.2025.179036
  24. ^ Smith, J. Brusseau, M.L., Guo, B., 2024. An Integrated Analytical Modeling Framework for Determining Site-Specific Soil Screening Levels for PFAS. Water Research, 252, Article121236. doi: 10.1016/j.watres.2024.121236

See Also

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