Difference between revisions of "User:Jhurley/sandbox"

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The persistent release of residual contaminants from low hydraulic conductivity (low ''k'') zones prevents many chlorinated solvent sites from reaching groundwater cleanup goals. Low ''k'' aquifer settings limit the effectiveness of many conventional remediation technologies that rely on extraction, recirculation, or amendment delivery and distribution to achieve contact between the residual contaminants and the reagents, contact which is necessary for subsequent contaminant transformation or destruction. Alternative methods are needed to effectively distribute remedial amendments, to control contaminants leaving low ''k'' source zones, and to enhance natural attenuation processes. Two innovative remediation technologies for the treatment of chlorinated solvents and other contaminants in low ''k'' media are introduced, along with operational and performance results from recent field demonstrations.
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==PFAS Destruction by Ultraviolet/Sulfite Treatment==
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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>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
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* [[Bioremediation - Anaerobic | Anaerobic Bioremediation]]
 
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* [[Chemical Oxidation (In Situ - ISCO) | In Situ Chemical Oxidation]]
 
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* [[Chemical Reduction (In Situ - ISCR) | In Situ Chemical Reduction]]
 
  
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'''CONTRIBUTOR(S): '''
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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* [[Stephen D. Richardson, Ph.D., PE]]
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*[[PFAS Ex Situ Water Treatment]]
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* [[Craig E. Divine, Ph.D., PG]]
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*[[PFAS Sources]]
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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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'''Key Resource(s):'''
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'''Contributors:''' John Xiong, Yida Fang, Raul Tenorio, Isobel Li, and Jinyong Liu
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* The Horizontal Reactive Media Treatment Well (HRX Well<sup>&reg;</sup>) for Passive In-Situ Remediation<ref name="Divine2018a">Divine, C. E., Roth, T, Crimi, M., DiMarco, A.C., Spurlin, M., Gillow, J., and Leone, G., 2018. The Horizontal Reactive Media Treatment Well (HRX Well<sup>&reg;</sup>) for Passive In-Situ Remediation. Groundwater Monitoring & Remediation, 38(1), pp. 56–65.  [https://doi.org/10.1111/gwmr.12252 DOI: 10.1111/gwmr.12252]</ref>
 
  
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* The Horizontal Reactive Media Treatment Well (HRX Well<sup>&reg;</sup>) for Passive In Situ Remediation: Design, Implementation, and Sustainability Considerations<ref name="Divine2018">Divine, C.E., Wright, J., Wang, J., McDonough, J., Kladias, M., Crimi, M., Nzeribe, B.N., Devlin, J.F., Lubrecht, M., Ombalski, D., Hodge, B., Voscott, H., and Gerber, K., 2018. The Horizontal Reactive Media Treatment Well (HRX Well<sup>&reg;</sup>) for Passive In Situ Remediation: Design, Implementation, and Sustainability Considerations. Remediation, 28(4), pp. 5-16. [https://doi.org/10.1002/rem.21571 DOI: 10.1002/rem.21571]&nbsp;&nbsp; Also available from: [https://www.researchgate.net/publication/327487096_The_horizontal_reactive_media_treatment_well_HRX_WellR_for_passive_in_situ_remediation_Design_implementation_and_sustainability_considerations ResearchGate]</ref>
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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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* New Application of A Geotechnical Technology to Remediate Low-Permeability Contaminated Media – Final Technical Report<ref name="Richardson2020">Richardson, S.D., Hart, D.M., Long, J.A., and Newell, C.J., 2020. New Application of A Geotechnical Technology to Remediate Low-Permeability Contaminated Media – Final Technical Report. ER-201627, Environmental Security Technology Certification Program (ESTCP). [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Groundwater/Persistent-Contamination/ER-201627/ Project Overview]</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"/>
  
 
==Introduction==
 
==Introduction==
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[[File:Richardson1w2Fig1.png | thumb | 400px | Figure 1. Examples of low ''k'' geology. Upper left: bay muds, Oakland, California; lower left: weathered siltstone, Denver, Colorado; right: tailings slimes, central New Mexico<ref name="Horst2019"/>.]]
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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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[[File:Richardson1w2Fig2.png | thumb | 400px | Figure 2. Contaminant back diffusion (“Matrix Diffusion”) from low ''k'' zones<ref name="NRC2005">National Research Council, 2005. Contaminants in the Subsurface: Source Zone Assessment and Remediation. National Academies Press, Washington, DC, pp. 372. [https://doi.org/10.17226/11146 DOI: 10.17226/11146]&nbsp;&nbsp; [[Media: NRC2005.pdf | Book.pdf]]</ref>.]]
 
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A critical challenge preventing many chlorinated solvent sites from achieving groundwater cleanup goals is the long term release of residual contaminants from low hydraulic conductivity (low ''k'') zones such as silts, clays, glacial till, over-bank deposits, marine deposits, tailings “slimes”, saprolite and bedrock (see Figure 1)<ref name ="Horst2019">Horst, J., Divine, C., Schnobrich, M., Oesterreich, R., and Munholland, J., 2019. Groundwater Remediation in Low-Permeability Settings: The Evolving Spectrum of Proven and Potential. Groundwater Monitoring & Remediation, 39(1), pp. 11-19. [https://doi.org/10.1111/gwmr.12316 DOI: 10.1111/gwmr.12316]</ref><ref name ="Sale2008">Sale, T., C. Newell, H. Stroo, R. Hinchee, and Johnson, P., 2008. Frequently Asked Questions Regarding Management of Chlorinated Solvents in Soils and Groundwater. Environmental Security Technology Certification Program (ESTCP) Project ER-0530, 38 pp. [[Media:2008-Sale-Frequently_Asked_Questions_Regarding_Management_of_Chlorinated_Solvent_in_Soils_and_Groundwater.pdf  | Report.pdf]]&nbsp;&nbsp; [https://serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Groundwater/Persistent-Contamination/ER-200530/(language)/eng-US Project overview]</ref>. Such sites may be dominated by matrix diffusion processes (see Figure 2) which can significantly prolong restoration and site management timeframes. Residual contaminants residing in low permeability zones slowly diffuse from the low ''k'' matrix back into higher permeability zones, becoming a persistent source that is very difficult to remediate. One of the side effects of matrix diffusion is concentration rebound after an ''in situ'' treatment is applied. This is commonly observed at sites treated with chemical oxidation<ref name="McGuire2006">McGuire, T.M., McDade, J.M., and Newell, C.J., 2006. Performance of DNAPL Source Depletion Technologies at 59 Chlorinated Solvent-Impacted Sites. Groundwater Monitoring & Remediation. Volume 26, Issue 1, pp. 73-84.  [https://doi.org/10.1111/j.1745-6592.2006.00054.x DOI: 10.1111/j.1745-6592.2006.00054.x]&nbsp;&nbsp; [https://www.provectusenvironmental.com/marketing/p-ox1/McGuire%20et%20al%202006.pdf  Free download.pdf]</ref><ref name="Krembs2010">Krembs, F., Siegrist, R., Crimi, M., Furrer, R., and Petri, B., 2010. ISCO for Groundwater Remediation: Analysis of Field Applications and Performance. Groundwater Monitoring & Remediation, 30(4), pp. 42-53.  [https://doi.org/10.1111/j.1745-6592.2010.01312.x DOI: 10.1111/j.1745-6592.2010.01312.x]</ref> and has the potential to occur at ''in situ'' bioremediation sites after the depletion of electron donors<ref name="Adamson2011">Adamson, D., McGuire, T., Newell, C., and Stroo, H., 2011. Sustained Treatment: Implications for Treatment Timescales Associated with Source-Depletion Technologies. Remediation, 21(2), pp. 27-50. [https://doi.org/10.1002/rem.20280 DOI: 10.1002/rem.20280]</ref>.
 
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Currently, there are limited remediation options available to treat residual contamination trapped in low ''k'' zones. Low ''k'' settings limit the applicability and effectiveness of conventional remediation technologies due to the constraint on fluid introduction and recovery. As such, methods relying on extraction, recirculation, or reagent delivery and distribution are often limited in their effectiveness. For the long lived, difficult to treat sites, innovative technologies are needed that will reliably address mass flux limitations of contaminants leaving low ''k'' source zones, and also increase the actual treatment of the contaminants leaving these low ''k'' zones by enhancing natural attenuation processes. Two innovative technologies investigated by ESTCP are summarized below.
 
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==“Grout Bomber”==
 
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===Technology Description===
 
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[[File:Richardson1w2Fig3.png | thumb | 400px | Figure 3. a) Grout Bomber equipment; b) hopper for mixing and delivery of grout to the “stitcher”; and c) grout exiting the mandrel]]
 
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[[File:Richardson1w2Fig4.png | thumb | 400px | Figure 4. Application of the Bomber technology for contaminated sites in low ''k'' materials.]]
 
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[[File:Richardson1w2Fig5.png | thumb | 400px | Figure 5. Chlorinated ethene concentrations at well pair (CMT-1 and IS17MW04).]]
 
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The geotechnical industry offers a variety of well-established techniques for quickly and efficiently accessing the subsurface for the purposes of ground stabilization, foundation rehabilitation, porewater drainage, and structural support. The speed and efficiency of these techniques can also be a major advantage for emplacement of remedial amendments into the subsurface. One promising approach is the Grout Bomber, a larger adaptation of conventional cement or compaction grouting techniques for subsurface stabilization. The technology uses an excavator equipped with specialized equipment (a “stitcher”) to quickly push a mandrel (3.5 in. diameter hollow cylindrical rod) into the subsurface and subsequently fill the hole and subsurface voids with cement grout (from bottom to top) using an in-line grout delivery system. The typical arrangement of the Grout Bomber technology includes the installation rig (excavator with the “stitcher” mast; see Figure 3a) and an on-site grout mixing and delivery unit consisting of mixing hopper, pumps, hosing, and power supply. Raw materials are loaded into the mixing hopper (see Figure 3b) where it is mixed to the appropriate consistency, then pumped to the Bomber rig at a rate of approximately 0.25 cubic feet per pump stroke. At the exit end of the Bomber mandrel (see Figure 3c), the grout flows in a continuous and uniform manner, allowing the columns to be emplaced with grout while the mandrel (which was pushed into the subsurface) is lifted to the surface.  Hundreds of closely spaced vertical grout columns can be installed per day using this technology.
 
  
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For environmental applications, the Grout Bomber approach can be “repurposed” as a means to improve delivery of remediation amendments into contaminated treatment zones in low ''k'' materials. The remedial amendment (e.g., mixture of zero-valent iron (ZVI), sand, neat oil) can replace the grout and be directly placed into the subsurface from bottom to top (not injected into the surrounding formation), creating hundreds of reaction columns. The Bomber technology offers the following benefits:
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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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* '''Reduces uncertainty: '''  
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</br>
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The Bomber technology circumvents the “delivery problem” associated with conventional injection-based remediation approaches, particularly in low ''k'' zones. The closely spaced nature of the reaction columns (2-3 ft spacing) reduces the diffusion lengths out of low ''k'' zones and also the uncertainty associated with amendment delivery because contaminants are always < 1 - 1.5 ft from an active treatment zone (see Figure 4).  
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::<big>'''Equation 1:'''</big>&nbsp;&nbsp; [[File: XiongEq1.png | 200 px]]
  
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* '''Rapid installation of reaction columns: '''
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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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The Grout Bomber can install 100+ reaction columns per day to depths of 40-50 ft below ground surface (bgs) to encourage contaminant degradation in source zones. Since the Grout Bomber is a direct push technique, it is better suited to silts and clays with blow counts < 35. Consolidated materials with higher blow counts will require additional equipment to pre-drill the columns prior to amendment emplacement. In general, this technology represents a much simpler, less intensive, and easier to install version of complete soil mixing.  
 
  
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* '''Accommodates various amendment types: '''
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==Process Description==
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In one example<ref name="Richardson2020"/>, vertical reaction columns containing a mixture of ZVI, vegetable oil, sand and minor amounts of water were installed to a depth of 30 ft bgs in a low ''k'' treatment area consisting primarily of silts, sandy clays, and lean clays<ref name="Divine2018"/>.  The ZVI-sand-oil mixture was designed to have a similar consistency (or viscosity) to cement grout, thus requiring no major alterations to the existing Bomber equipment for the project.  Recommended practices to ensure uninterrupted flow of amendments to the Bomber mandrel include:  
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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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** Conduct simple pumping pilot studies with amendments of varying consistencies,  
 
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** Consult with a well trained pump operator, and  
 
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** Minimize the length of hosing between mixing hopper pump and Bomber mandrel.  
 
  
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* '''Cost effective source zone treatment: '''
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==Advantages==
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Estimated treatment costs associated with emplacement of amendments with the Grout Bomber are ~$35 per cubic yard of source zone treated (including contractor labor, equipment, and materials). This is generally less than the reported unit cost for ''in situ'' biodegradation ($20-$80/yd<sup>3</sup>) and significantly less than chemical oxidation ($125/yd<sup>3</sup>) and thermal remediation (median $200/yd<sup>3</sup>)<ref name="McDade2005">McDade, J.M., T.M. McGuire, and Newell, C.J., 2005. Analysis of DNAPL Source Depletion Costs at 36 Field Sites, Remediation, 15(2), pp. 9-18. [https://doi.org/10.1002/rem.20039 DOI: 10.1002/rem.20039]</ref>.
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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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*'''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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*'''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:''' 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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*'''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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*'''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>.
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*'''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>.
  
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===Operational Approach & Results===
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==Limitations==
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A field demonstration was conducted at Site 17, Naval Support Facility Indian Head, Maryland. The treatment area consists primarily of silts, sandy clays, and lean clays with TCE concentrations in soil and groundwater of up to 250 mg/kg and 400 mg/L, respectively. Eight hundred reaction columns (consisting of ZVI/sand or oil/sand), were installed 2-3 ft apart, to a depth of 30 ft bgs at the site. Approximately 100 reaction columns were installed per day, with the most productive day totaling 180 columns. During operation, installation time for each reaction column was on the order of 1-2 minutes. Overall, 77,000 lbs of ZVI and 650 gallons of vegetable oil were emplaced within the source area of ~5,000 ft<sup>2</sup>.  
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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.
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*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.
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*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.
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*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.
  
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===Performance Results===
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==State of the Practice==
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Ongoing post installation monitoring of treatment area groundwater has found moderate reductions in TCE in site monitoring wells and that key degradation products that serve as indicators for both abiotic and biotic mechanisms (i.e., acetylene, ethene/ethane) are present. Samples from Continuous Multilevel Tubing (CMT) wells installed within reaction columns (anulus filled with ZVI amendment) have demonstrated 1-3 orders of magnitude reductions in TCE relative to the surrounding formation water (see Figure 5). These results provide evidence that the reaction columns are creating steep concentration gradients that could drive contaminants out of low permeability zones. Further, gaseous products (e.g., propane, propene, i-butane, n-butane, n-pentane, n-hexane) were detected in the unsaturated zone of several reaction columns further supporting abiotic TCE degradation. Results of this full scale project were very promising and, although several operational improvements were identified (e.g., improved pumpability of ZVI/sand mixture; minor equipment modifications; improved site prep practices), the Bomber technology has the potential to be an important remediation alternative for hard-to-treat chlorinated source zones, particularly ones with large, persistent matrix diffusion sources over large areas.
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[[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.]]
 +
[[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).
  
 
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==See Also==

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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