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==Sediment Capping==
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==Photoactivated Reductive Defluorination PFAS Destruction==  
Capping is an ''in situ'' remedial technology that involves placement of a clean substrate on the surface of [[Contaminated Sediments - Introduction | contaminated sediments]] to reduce contaminant uptake by benthic organisms and contaminant flux to surface water. Simple sand caps can be effective in reducing exposure of benthic organisms and by limiting oxygen transport, resulting in precipitation of metal sulfides. Amendments are sometimes included in caps to reduce permeability and water flow, to increase contaminant sorption or biodegradation, or to improve habitat.
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Photoactivated Reductive Defluorination (PRD) is a [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] destruction technology predicated on [[Wikipedia: Ultraviolet | ultraviolet (UV)]] light-activated photochemical reactions. The destruction efficiency of this process is enhanced by the use of a [[Wikipedia: Surfactant | surfactant]] to confine PFAS molecules in self-assembled [[Wikipedia: Micelle | micelles]]. The photochemical reaction produces [[Wikipedia: Solvated electron | hydrated electrons]] from an electron donor that associates with the micelle. The hydrated electrons have sufficient energy to rapidly cleave fluorine-carbon and other molecular bonds of PFAS molecules due to the association of the electron donor with the micelle. Micelle-accelerated PRD is a highly efficient method to destroy PFAS in a wide variety of water matrices.
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
*[[Contaminated Sediments - Introduction]]
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]  
*[[In Situ Treatment of Contaminated Sediments with Activated Carbon]]
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*[[PFAS Sources]]
*Sediment Risk Assessment
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*[[PFAS Transport and Fate]]
*[[Passive Sampling of Sediments]]
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*[[PFAS Ex Situ Water Treatment]]
 +
*[[Supercritical Water Oxidation (SCWO)]]
 +
*[[PFAS Treatment by Electrical Discharge Plasma]]
  
 
'''Contributor(s):'''  
 
'''Contributor(s):'''  
*Danny Reible
+
*Dr. Suzanne Witt
 +
*Dr. Meng Wang
 +
*Dr. Denise Kay
  
 
'''Key Resource(s):'''
 
'''Key Resource(s):'''
*Processes, Assessment and Remediation of Contaminated Sediments<ref name="Reible2014">Reible, D. D., Editor, 2014. Processes, Assessment and Remediation of Contaminated Sediments. Springer, New York, NY. 462 pp. ISBN: 978-1-4614-6725-0</ref>
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*Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement<ref name="ChenEtAl2020">Chen, Z., Li, C., Gao, J., Dong, H., Chen, Y., Wu, B., Gu, C., 2020. Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement. Environmental Science and Technology, 54(8), pp. 5178–5185. [https://doi.org/10.1021/acs.est.9b06599 doi: 10.1021/acs.est.9b06599]</ref>
 
+
*Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-Acetic-Acid in Organomodified Montmorillonite<ref name="TianEtAl2016">Tian, H., Gao, J., Li, H., Boyd, S.A., Gu, C., 2016. Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-Acetic-Acid in Organomodified Montmorillonite. Scientific Reports, 6(1), Article 32949. [https://doi.org/10.1038/srep32949 doi: 10.1038/srep32949]&nbsp;&nbsp; [[Media: TianEtAl2016.pdf | Open Access Article]]</ref>
* Guidance for In-Situ Subaqueous Capping of Contaminated Sediments<ref name="Palermo1998">Palermo, M., Maynord, S., Miller, J. and Reible, D., 1998. Guidance for In-Situ Subaqueous Capping of Contaminated Sediments. Assessment and Remediation of Contaminated Sediments (ARCS) Program, Great Lakes National Program Office, US EPA 905-B96-004. 147 pp.</ref>
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*Application of Surfactant Modified Montmorillonite with Different Conformation for Photo-Treatment of Perfluorooctanoic Acid by Hydrated Electrons<ref name="ChenEtAl2019">Chen, Z., Tian, H., Li, H., Li, J. S., Hong, R., Sheng, F., Wang, C., Gu, C., 2019. Application of Surfactant Modified Montmorillonite with Different Conformation for Photo-Treatment of Perfluorooctanoic Acid by Hydrated Electrons. Chemosphere, 235, pp. 1180–1188. [https://doi.org/10.1016/j.chemosphere.2019.07.032 doi: 10.1016/j.chemosphere.2019.07.032]</ref>
 +
*[https://serdp-estcp.mil/projects/details/c4e21fa2-c7e2-4699-83a9-3427dd484a1a ER21-7569: Photoactivated Reductive Defluorination PFAS Destruction]<ref name="WittEtAl2023">Kay, D., Witt, S., Wang, M., 2023. Photoactivated Reductive Defluorination PFAS Destruction: Final Report. ESTCP Project ER21-7569. [https://serdp-estcp.mil/projects/details/c4e21fa2-c7e2-4699-83a9-3427dd484a1a Project Website]&nbsp;&nbsp; [[Media: ER21-7569_Final_Report.pdf | Final Report.pdf]]</ref>
  
 
==Introduction==
 
==Introduction==
[[File:SedCapFig1.png|thumb|left|Figure 1. Conceptual sketch of a cap configuration]]
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[[File:WittFig1.png | thumb |600px|Figure 1. Schematic of PRD mechanism<ref name="WittEtAl2023"/>]]
Capping is an ''in situ'' remedial technology for contaminated sediments that involves placement of a clean substrate on the sediment surface. Capping contaminated sediments following [[Wikipedia: Dredging | dredging operations]] and capping of dredged material to stabilize contaminants has been a common practice by the United States Army Corps of Engineers since the 1970s.  Beginning in the 1980s, in Japan and subsequently elsewhere, capping has been used more widely as a remedial approach to improve the quality of the bottom substrate and reduce contaminant exposures to benthic organisms and fish. The USEPA published a capping guidance document in 1998 that summarizes past uses of sediment capping and outlines its basic design<ref name="Palermo1998"/>.    Although capping technology has developed substantially in the past 20 years, this early reference still provides useful information on the approach and its applications.  A more recent summary of capping is described in Reible 2014<ref name="Reible2014"/>.
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The&nbsp;Photoactivated&nbsp;Reductive Defluorination (PRD) process is based on a patented chemical reaction that breaks fluorine-carbon bonds and disassembles PFAS molecules in a linear fashion beginning with the [[Wikipedia: Hydrophile | hydrophilic]] functional groups and proceeding through shorter molecules to complete mineralization. Figure 1 shows how PRD is facilitated by adding [[Wikipedia: Cetrimonium bromide | cetyltrimethylammonium bromide (CTAB)]] to form a surfactant micelle cage that traps PFAS. A non-toxic proprietary chemical is added to solution to associate with the micelle surface and produce hydrated electrons via stimulation with UV light. These highly reactive hydrated electrons have the energy required to cleave fluorine-carbon and other molecular bonds resulting in the final products of fluoride, water, and simple carbon molecules (e.g., formic acid and acetic acid). The methods, mechanisms, theory, and reactions described herein have been published in peer reviewed literature<ref name="ChenEtAl2020"/><ref name="TianEtAl2016"/><ref name="ChenEtAl2019"/><ref name="WittEtAl2023"/>.
 
 
Capping serves to contain contaminated sediment solids, isolate contaminants from benthic organisms and reduce contaminant transport to the sediment surface and overlying water.  The clean substrate may be an inert material such as sand, a natural sorbing material such as other sediments or clays, or be amended with an active/reactive material to enhance the isolation of the contaminants.  Amendments to enhance contaminant isolation include permeability reduction agents to divert groundwater flow, sorbents to retard contaminant migration through the capping layer or provide greater accumulation capacity, or reagents to encourage degradation or transformation of the contaminants.  
 
  
The basic concept of a cap is illustrated in Figure 1.  The Figure also illustrates that a cap is often a thin layer or layers relative to water depth and generally causes little disturbance to the underlying sediments or body of water in which it is placed.  Depending upon the erosive forces to which the cap may be subjected, the surface layer may be composed of relatively coarse material to withstand those erosive forces.
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==Advantages and Disadvantages==
  
Although a cap is typically thin compared to the water depth, it generally must be thicker than the biologically active zone (BAZ) of the sediments. The biologically active zone is that zone in which benthic organisms live and interact with the sediment. Their activities tend to mix the BAZ (known as [[Wikipedia: Bioturbation | bioturbation]]) over the course of a few years and thus a cap that is thinner than the BAZ will tend to become intermixed with the underlying contaminated sediments.   Processes other than bioturbation including diffusion, advection or groundwater upwelling, hyporheic exchange near the interface, biogenic gas production and migration and underlying sediment consolidation can all lead to contaminant migration into and through a capThese occur at different rates and intensities and their assessment and evaluation ultimately governs the effectiveness of a cap and the feasibility of its use as a sediment remediation technology for a particular site.
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===Advantages===
 +
In comparison to other reported PFAS destruction techniques, PRD offers several advantages:
 +
*Relative to UV/sodium sulfite and UV/sodium iodide systems, the fitted degradation rates in the micelle-accelerated PRD reaction system were ~18 and ~36 times higher, indicating the key role of the self-assembled micelle in creating a confined space for rapid PFAS destruction<ref name="ChenEtAl2020"/>. The negatively charged hydrated electron associated with the positively charged cetyltrimethylammonium ion (CTA<sup>+</sup>) forms the surfactant micelle to trap molecules with similar structures, selectively mineralizing compounds with both hydrophobic and hydrophilic groups (e.g., PFAS).
 +
*The PRD reaction does not require solid catalysts or electrodes, which can be expensive to acquire and difficult to regenerate or dispose.  
 +
*The aqueous solution is not heated or pressurized, and the UV wavelength used does not cause direct water [[Wikipedia: Photodissociation | photolysis]], therefore the energy input to the system is more directly employed to destroy PFAS, resulting in greater energy efficiency.  
 +
*Since the reaction is performed at ambient temperature and pressure, there are limited concerns regarding environmental health and safety or volatilization of PFAS compared to heated and pressurized systems.  
 +
*Due to the reductive nature of the reaction, there is no formation of unwanted byproducts resulting from oxidative processes, such as [[Wikipedia: Perchlorate | perchlorate]] generation during electrochemical oxidation<ref>Veciana, M., Bräunig, J., Farhat, A., Pype, M. L., Freguia, S., Carvalho, G., Keller, J., Ledezma, P., 2022. Electrochemical Oxidation Processes for PFAS Removal from Contaminated Water and Wastewater: Fundamentals, Gaps and Opportunities towards Practical Implementation. Journal of Hazardous Materials, 434, Article 128886. [https://doi.org/10.1016/j.jhazmat.2022.128886 doi: 10.1016/j.jhazmat.2022.128886]</ref><ref>Trojanowicz, M., Bojanowska-Czajka, A., Bartosiewicz, I., Kulisa, K., 2018. Advanced Oxidation/Reduction Processes Treatment for Aqueous Perfluorooctanoate (PFOA) and Perfluorooctanesulfonate (PFOS) – A Review of Recent Advances. Chemical Engineering Journal, 336, pp. 170–199. [https://doi.org/10.1016/j.cej.2017.10.153 doi: 10.1016/j.cej.2017.10.153]</ref><ref>Wanninayake, D.M., 2021. Comparison of Currently Available PFAS Remediation Technologies in Water: A Review. Journal of Environmental Management, 283, Article 111977. [https://doi.org/10.1016/j.jenvman.2021.111977 doi: 10.1016/j.jenvman.2021.111977]</ref>.
 +
*Aqueous fluoride ions are the primary end products of PRD, enabling real-time reaction monitoring with a fluoride [[Wikipedia: Ion-selective electrode | ion selective electrode (ISE)]], which is far less expensive and faster than relying on PFAS analytical data alone to monitor system performance.
  
In general, capping is an effective remedial technology for contaminants that are strongly associated with the sediment solids including hydrophobic organic compounds such as high molecular weight [[Polycyclic Aromatic Hydrocarbons (PAHs) | polycyclic aromatic hydrocarbons (PAHs)]], [[Wikipedia: Polychlorinated biphenyl | polychlorinated biphenyls (PCBs)]], [[Wikipedia: Dioxins and dioxin-like compounds | dioxins]] and [[Wikipedia: DDT | DDTx]], but also [[Metal and Metalloid Contaminants | heavy metals]]. Hydrophobic organic compounds tend to strongly associate with the organic fraction of sediments so organic rich sediments or the addition of organic phases to the capping material can be very effective at containing these contaminants. Many of the common heavy metals of concern, including cadmium, copper, nickel, zinc, lead and mercury, tend to be associated with insoluble sulfides under strongly reducing conditions.  Since oxygen penetration into a capping layer is typically limited to a few cm or less at the surface, a cap serves to drive the underlying contaminated sediment toward strongly reducing conditions and, particularly in marine and estuarine sediments, encourage sulfate reduction leading to the formation of these insoluble sulfides.  The low solubility of these sulfides encourages retention by a capping layer and makes the cap extremely effective as a remedial approach for sediments with elevated concentrations of heavy metals.
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===Disadvantages===
 +
*The CTAB additive is only partially consumed during the reaction, and although CTAB is not problematic when discharged to downstream treatment processes that incorporate aerobic digestors, CTAB can be toxic to surface waters and anaerobic digestors. Therefore, disposal options for treated solutions will need to be evaluated on a site-specific basis. Possible options include removal of CTAB from solution for reuse in subsequent PRD treatments, or implementation of an oxidation reaction to degrade CTAB.  
 +
*The PRD reaction rate decreases in water matrices with high levels of total dissolved solids (TDS). It is hypothesized that in high TDS solutions (e.g., ion exchange still bottoms with TDS of 200,000 ppm), the presence of ionic species inhibits the association of the electron donor with the micelle, thus decreasing the reaction rate.
 +
*The PRD reaction rate decreases in water matrices with very low UV transmissivity. Low UV transmissivity (i.e., < 1 %) prevents the penetration of UV light into the solution, such that the utilization efficiency of UV light decreases.  
  
A variety of tools have been developed to evaluate the processes leading to sorption and retardation of contaminants as well as processes leading to contaminant migration and release. The original references quantifying contaminant behavior in a sediment cap were explored in a series of papers in the early 1990s<ref name="Wang1991">Wang, X.Q., Thibodeaux, L.J., Valsaraj, K.T. and Reible, D.D., 1991. Efficiency of Capping Contaminated Bed Sediments in Situ. 1. Laboratory-Scale Experiments on Diffusion-Adsorption in the Capping Layer. Environmental Science and Technology, 25(9), pp.1578-1584.  [https://doi.org/10.1021/es00021a008 DOI: 10.1021/es00021a008]</ref><ref name="Thoma1993">Thoma, G.J., Reible, D.D., Valsaraj, K.T. and Thibodeaux, L.J., 1993. Efficiency of Capping Contaminated Bed Sediments in Situ 2. Mathematics of Diffusion-Adsorption in the Capping Layer. Environmental Science and Technology, 27(12), pp.2412-2419.  [https://doi.org/10.1021/es00048a015 DOI: 10.1021/es00048a015]</ref>.  Since that time, design tools have been continuously improved. [https://www.depts.ttu.edu/ceweb/research/reiblesgroup/downloads.php CapSim] is a commonly used and current tool developed by Dr. Reible and collaborators. This tool can evaluate contaminant release from uncapped, capped, and treated sediments for purposes of design and evaluation.  The model formulation and structure is described in Shen et al. 2018<ref name="Shin2018">Shen, X., Lampert, D., Ogle, S. and Reible, D., 2018. A software tool for simulating contaminant transport and remedial effectiveness in sediment environments. Environmental Modelling and Software, 109, pp. 104-113.  [https://doi.org/10.1016/j.envsoft.2018.08.014 DOI: 10.1016/j.envsoft.2018.08.014]</ref>. One common use of such a tool is to evaluate the effect of various cap materials and thicknesses on the performance of a cap.
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==State of the Art==
  
==Environmental Fate==
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===Technical Performance===
TCP’s fate in the environment is governed by its physical and chemical properties (Table 1). TCP does not adsorb strongly to soil, making it likely to leach into groundwater and exhibit high mobility. In addition, TCP is moderately volatile and can partition from surface water and moist soil into the atmosphere. Because TCP is only slightly soluble and denser than water, it can form a [[Wikipedia: Dense non-aqueous phase liquid | dense non-aqueous phase liquid (DNAPL)]] as observed at the Tyson’s Dump Superfund Site<ref name="USEPA2019"> United States Environmental Protection Agency (USEPA), 2019. Fifth Five-year Review Report, Tyson’s Dump Superfund Site, Upper Merion Township, Montgomery County, Pennsylvania. Free download from: [https://semspub.epa.gov/work/03/2282817.pdf USEPA]&nbsp;&nbsp; [[Media: USEPA2019.pdf | Report.pdf]]</ref>. TCP is generally resistant to aerobic biodegradation, hydrolysis, oxidation, and reduction under naturally occurring conditions making it persistent in the environment<ref name="Tratnyek2010"/>.
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[[File:WittFig2.png | thumb |400px| Figure 2. Enspired Solutions<small><sup>TM</sup></small> commercial PRD PFAS destruction equipment, the PFASigator<small><sup>TM</sup></small>. Dimensions are 8 feet long by 4 feet wide by 9 feet tall.]]
  
{| class="wikitable" style="float:right; margin-left:10px;text-align:center;"
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{| class="wikitable mw-collapsible" style="float:left; margin-right:20px; text-align:center;"
|+Table 1. Physical and chemical properties of TCP<ref name="USEPA2017">United States Environmental Protection Agency (USEPA), 2017. Technical Fact Sheet—1,2,3-Trichloropropane (TCP). EPA Project 505-F-17-007. 6 pp.  Free download from: [https://www.epa.gov/sites/production/files/2017-10/documents/ffrrofactsheet_contaminants_tcp_9-15-17_508.pdf  USEPA]&nbsp;&nbsp; [[Media: epa_tcp_2017.pdf | Report.pdf]]</ref>
+
|+Table 1. Percent decreases from initial PFAS concentrations during benchtop testing of PRD treatment in different water matrices
 
|-
 
|-
!Property
+
! Analytes
!Value
+
!
 +
! GW
 +
! FF
 +
! AFFF<br>Rinsate
 +
! AFF<br>(diluted 10X)
 +
! IDW NF
 
|-
 
|-
| Chemical Abstracts Service (CAS) Number || 96-18-4
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| &Sigma; Total PFAS<small><sup>a</sup></small> (ND=0)
 +
| rowspan="9" style="background-color:white;" | <p style="writing-mode: vertical-rl">% Decrease<br>(Initial Concentration, &mu;g/L)</p>
 +
| 93%<br>(370) || 96%<br>(32,000) || 89%<br>(57,000) || 86 %<br>(770,000) || 84%<br>(82)
 
|-
 
|-
| Physical Description</br>(at room temperature) || Colorless to straw-colored liquid
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| &Sigma; Total PFAS (ND=MDL) || 93%<br>(400) || 86%<br>(32,000) || 90%<br>(59,000) || 71%<br>(770,000) || 88%<br>(110)
 +
|-  
 +
| &Sigma; Total PFAS (ND=RL) || 94%<br>(460) || 96%<br>(32,000) || 91%<br>(66,000) || 34%<br>(770,000) || 92%<br>(170)
 
|-
 
|-
| Molecular weight  (g/mol) || 147.43
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| &Sigma; Highly Regulated PFAS<small><sup>b</sup></small> (ND=0) || >99%<br>(180) || >99%<br>(20,000) || 95%<br>(20,000) || 92%<br>(390,000) || 95%<br>(50)
 
|-
 
|-
| Water solubility at 25°C  (mg/L)|| 1,750 (slightly soluble)
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| &Sigma; Highly Regulated PFAS (ND=MDL) || >99%<br>(180) || 98%<br>(20,000) || 95%<br>(20,000) || 88%<br>(390,000) || 95%<br> (52)
 
|-
 
|-
| Melting point  (°C)|| -14.7
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| &Sigma; Highly Regulated PFAS (ND=RL) || >99%<br>(190) || 93%<br>(20,000) || 95%<br>(20,000) || 79%<br>(390,000) || 95%<br>(55)
 
|-
 
|-
| Boiling point  (°C) || 156.8
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| &Sigma; High Priority PFAS<small><sup>c</sup></small> (ND=0) || 91%<br>(180) || 98%<br>(20,000) || 85%<br>(20,000) || 82%<br>(400,000) || 94%<br>(53)
 
|-
 
|-
| Vapor pressure at 25°C  (mm Hg) || 3.10 to 3.69
+
| &Sigma; High Priority PFAS (ND=MDL) || 91%<br>(190) || 94%<br>(20,000) || 85%<br>(20,000) || 79%<br>(400,000) || 86%<br>(58)
 
|-
 
|-
| Density at 20°C (g/cm<sup>3</sup>) || 1.3889
+
| &Sigma; High Priority PFAS (ND=RL) || 92%<br>(200) || 87%<br>(20,000) || 86%<br>(21,000) || 70%<br>(400,000) || 87%<br>(65)
 
|-
 
|-
| Octanol-water partition coefficient</br>(log''K<sub>ow</sub>'') || 1.98 to 2.27</br>(temperature dependent)
+
| Fluorine mass balance<small><sup>d</sup></small> || ||106% || 109% || 110% || 65% || 98%
 
|-
 
|-
| Organic carbon-water partition coefficient</br>(log''K<sub>oc</sub>'') || 1.70 to 1.99</br>(temperature dependent)
+
| Sorbed organic fluorine<small><sup>e</sup></small> || || 4% || 4% || 33% || N/A || 31%
 
|-
 
|-
| Henry’s Law constant at 25°C</br>(atm-m<sup>3</sup>/mol) || 3.17x10<sup>-4</sup><ref name="ATSDR2021"/> to 3.43x10<sup>-4</sup><ref name="LeightonCalo1981">Leighton Jr, D.T. and Calo, J.M., 1981. Distribution Coefficients of Chlorinated Hydrocarbons in Dilute Air-Water Systems for Groundwater Contamination Applications. Journal of Chemical and Engineering Data, 26(4), pp. 382-385.  [https://doi.org/10.1021/je00026a010 DOI: 10.1021/je00026a010]</ref>
+
| colspan="7" style="background-color:white; text-align:left" | <small>Notes:<br>GW = groundwater<br>GW FF = groundwater foam fractionate<br>AFFF rinsate = rinsate collected from fire system decontamination<br>AFFF (diluted 10x) = 3M Lightwater AFFF diluted 10x<br>IDW NF = investigation derived waste nanofiltrate<br>ND = non-detect<br>MDL = Method Detection Limit<br>RL = Reporting Limit<br><small><sup>a</sup></small>Total PFAS = 40 analytes + unidentified PFCA precursors<br><small><sup>b</sup></small>Highly regulated PFAS = PFNA, PFOA, PFOS, PFHxS, PFBS, HFPO-DA<br><small><sup>c</sup></small>High priority PFAS = PFNA, PFOA, PFHxA, PFBA, PFOS, PFHxS, PFBS, HFPO-DA<br><small><sup>d</sup></small>Ratio of the final to the initial organic fluorine plus inorganic fluoride concentrations<br><small><sup>e</sup></small>Percent of organic fluorine that sorbed to the reactor walls during treatment<br></small>
 
|}
 
|}
 +
</br>
 +
The&nbsp;PRD&nbsp;reaction&nbsp;has&nbsp;been validated at the bench scale for the destruction of PFAS in a variety of environmental samples from Department of Defense sites (Table 1). Enspired Solutions<small><sup>TM</sup></small> has designed and manufactured a fully automatic commercial-scale piece of equipment called PFASigator<small><sup>TM</sup></small>, specializing in PRD PFAS destruction (Figure 2). This equipment is modular and scalable, has a small footprint, and can be used alone or in series with existing water treatment trains. The PFASigator<small><sup>TM</sup></small> employs commercially available UV reactors and monitoring meters that have been used in the water industry for decades. The system has been tested on PRD efficiency operational parameters, and key metrics were proven to be consistent with benchtop studies.
  
==Occurrence==
+
Bench scale PRD tests were performed for the following samples collected from Department of Defense sites: groundwater (GW), groundwater foam fractionate (FF), firefighting truck rinsate ([[Wikipedia: Firefighting foam | AFFF]] Rinsate), 3M Lightwater AFFF, investigation derived waste nanofiltrate (IDW NF), [[Wikipedia: Ion exchange | ion exchange]] still bottom (IX SB), and Ansulite AFFF. The PRD treatment was more effective in low conductivity/TDS solutions. Generally, PRD reaction rates decrease for solutions with a TDS > 10,000 ppm, with an upper limit of 30,000 ppm. Ansulite AFFF and IX SB samples showed low destruction efficiencies during initial screening tests, which was primarily attributed to their high TDS concentrations. Benchtop testing data are shown in Table 1 for the remaining five sample matrices.
TCP has been detected in approximately 1% of public water supply and domestic well samples tested by the United States Geological Survey. More specifically, TCP was detected in 1.2% of public supply well samples collected between 1993 and 2007 by Toccalino and Hopple<ref name="ToccalinoHopple2010">Toccalino, P.L., Norman, J.E., Hitt, K.J., 2010. Quality of Source Water from Public-Supply Wells in the United States, 1993–2007. Scientific Investigations Report 2010-5024. U.S. Geological Survey. [https://doi.org/10.3133/sir20105024 DOI: 10.3133/sir20105024]  Free download from: [https://pubs.er.usgs.gov/publication/sir20105024 USGS]&nbsp;&nbsp; [[Media: Quality_of_source_water_from_public-supply_wells_in_the_United_States%2C_1993-2007.pdf | Report.pdf]]</ref> and 0.66% of domestic supply well samples collected between 1991 and 2004 by DeSimone<ref name="DeSimone2009">DeSimone, L.A., 2009. Quality of Water from Domestic Wells in Principal Aquifers of the United States, 1991–2004. U.S. Geological Survey, Scientific Investigations Report 2008–5227. 139 pp. Free download from: [http://pubs.usgs.gov/sir/2008/5227 USGS]&nbsp;&nbsp; [[Media: DeSimone2009.pdf | Report.pdf]]</ref>. TCP was detected at a higher rate in domestic supply well samples associated with agricultural land-use studies than samples associated with studies comparing primary aquifers (3.5% versus 0.2%)<ref name="DeSimone2009"/>.
 
 
 
==Regulation==
 
The United States Environmental Protection Agency (USEPA) has not established an MCL for TCP, although guidelines and health standards are in place<ref name="USEPA2017"/>. TCP was included in the Contaminant Candidate List 3<ref name="USEPA2009">United States Environmental Protection Agency (US EPA), 2009. Drinking Water Contaminant Candidate List 3-Final. Federal Register 74(194), pp. 51850–51862, Document E9-24287. [https://www.federalregister.gov/documents/2009/10/08/E9-24287/drinking-water-contaminant-candidate-list-3-final Website]&nbsp;&nbsp; [[Media: FR74-194DWCCL3.pdf | Report.pdf]]</ref> and the Unregulated Contaminant Monitoring Rule 3 (UCMR 3)<ref name="USEPA2012">United States Environmental Protection Agency (US EPA), 2012. Revisions to the Unregulated Contaminant Mentoring Regulation (UCMR 3) for Public Water Systems. Federal Register 77(85) pp. 26072-26101. [https://www.federalregister.gov/documents/2012/05/02/2012-9978/revisions-to-the-unregulated-contaminant-monitoring-regulation-ucmr-3-for-public-water-systems  Website]&nbsp;&nbsp; [[Media: FR77-85UCMR3.pdf | Report.pdf]]</ref>. The UCMR 3 specified that data be collected on TCP occurrence in public water systems over the period of January 2013 through December 2015 against a reference concentration range of 0.0004 to 0.04 μg/L<ref name="USEPA2017a">United States Environmental Protection Agency (USEPA), 2017. The Third Unregulated Contaminant Monitoring Rule (UCMR 3): Data Summary. EPA 815-S-17-001. [https://www.epa.gov/dwucmr/data-summary-third-unregulated-contaminant-monitoring-rule  Website]&nbsp;&nbsp; [[Media: ucmr3-data-summary-january-2017.pdf | Report.pdf]]</ref>. The reference concentration range was determined based on a cancer risk of 10-6 to 10-4 and derived from an oral slope factor of 30 mg/kg-day, which was determined by the EPA’s Integrated Risk Information System<ref name="IRIS2009">USEPA Integrated Risk Information System (IRIS), 2009. 1,2,3-Trichloropropane (CASRN 96-18-4). [https://cfpub.epa.gov/ncea/iris2/chemicalLanding.cfm?substance_nmbr=200 Website]&nbsp;&nbsp; [[Media: TCPsummaryIRIS.pdf | Summary.pdf]]</ref>. Of 36,848 samples collected during UCMR 3, 0.67% exceeded the minimum reporting level of 0.03 µg/L. 1.4% of public water systems had at least one detection over the minimum reporting level, corresponding to 2.5% of the population<ref name="USEPA2017a"/>. While these occurrence percentages are relatively low, the minimum reporting level of 0.03 µg/L is more than 75 times the USEPA-calculated Health Reference Level of 0.0004 µg/L. Because of this, TCP may occur in public water systems at concentrations that exceed the Health Reference Level but are below the minimum reporting level used during UCMR 3 data collection. These analytical limitations and lack of lower-level occurrence data have prevented the USEPA from making a preliminary regulatory determination for TCP<ref name="USEPA2021">USEPA, 2021. Announcement of Final Regulatory Determinations for Contaminants on the Fourth Drinking Water Contaminant Candidate List. Free download from: [https://www.epa.gov/sites/default/files/2021-01/documents/10019.70.ow_ccl_reg_det_4.final_web.pdf USEPA]&nbsp;&nbsp; [[Media: CCL4.pdf | Report.pdf]]</ref>.
 
 
 
Some US states have established their own standards including Hawaii which has established an MCL of 0.6 μg/L<ref name="HDOH2013">Hawaii Department of Health, 2013. Amendment and Compilation of Chapter 11-20 Hawaii Administrative Rules. Free download from: [http://health.hawaii.gov/sdwb/files/2016/06/combodOPPPD.pdf Hawaii Department of Health]&nbsp;&nbsp; [[Media: Amendment_and_Compilation_of_Chapter_11-20_Hawaii_Administrative_Rules.pdf | Report.pdf]]</ref>. California has established an MCL of 0.005 μg/L<ref name="CCR2021">California Code of Regulations, 2021. Section 64444 Maximum Contaminant Levels – Organic Chemicals (22 CA ADC § 64444). [https://govt.westlaw.com/calregs/Document/IA7B3800D18654ABD9E2D24A445A66CB9 Website]</ref>,  a notification level of 0.005 μg/L, and a public health goal of 0.0007 μg/L<ref name="OEHHA2009">Office of Environmental Health Hazard Assessment (OEHHA), California Environmental Protection Agency, 2009. Final Public Health Goal for 1,2,3-Trichloropropane in Drinking Water. [https://oehha.ca.gov/water/public-health-goal/final-public-health-goal-123-trichloropropane-drinking-water Website]</ref>, and New Jersey has established an MCL of 0.03 μg/L<ref name="NJAC2020">New Jersey Administrative Code 7:10, 2020. Safe Drinking Water Act Rules. Free download from: [https://www.nj.gov/dep/rules/rules/njac7_10.pdf  New Jersey Department of Environmental Protection]</ref>.
 
 
 
==Transformation Processes==
 
[[File:123TCPFig2.png|thumb|600px|left|Figure 2. Figure 2. Summary of anticipated primary reaction pathways for degradation of TCP. Oxidation, hydrolysis, and hydrogenolysis are represented by the horizontal arrows. Elimination (dehydrochlorination) and reductive elimination are shown with vertical arrows. [O] represents oxygenation (by oxidation or hydrolysis), [H] represents reduction. Gray indicates products that appear to be of lesser significance<ref name="Tratnyek2010"/>.]]
 
Potential TCP degradation pathways include hydrolysis, oxidation, and reduction (Figure 2). These pathways are expected to be similar overall for abiotic and biotic reactions<ref name="Sarathy2010">Sarathy, V., Salter, A.J., Nurmi, J.T., O’Brien Johnson, G., Johnson, R.L., and Tratnyek, P.G., 2010. Degradation of 1, 2, 3-Trichloropropane (TCP): Hydrolysis, Elimination, and Reduction by Iron and Zinc. Environmental Science and Technology, 44(2), pp.787-793.  [https://doi.org/10.1021/es902595j DOI: 10.1021/es902595j]</ref>, but the rates of the reactions (and their resulting significance for remediation) depend on natural and engineered conditions.
 
 
 
The rate of hydrolysis of TCP is negligible under typical ambient pH and temperature conditions but is favorable at high pH and/or temperature<ref name="Tratnyek2010"/><ref name="Sarathy2010"/>. For example, ammonia gas can be used to raise soil pH and stimulate alkaline hydrolysis of chlorinated propanes including TCP<ref name="Medina2016">Medina, V.F., Waisner, S.A., Griggs, C.S., Coyle, C., and Maxwell, M., 2016. Laboratory-Scale Demonstration Using Dilute Ammonia Gas-Induced Alkaline Hydrolysis of Soil Contaminants (Chlorinated Propanes and Explosives). US Army Engineer Research and Development Center, Environmental Laboratory (ERDC/EL), Report TR-16-10. [http://hdl.handle.net/11681/20312 Website]&nbsp;&nbsp; [[Media: ERDC_EL_TR_16_10.pdf  | Report.pdf]]</ref>. [[Thermal Conduction Heating (TCH)]] may also produce favorable conditions for TCP hydrolysis<ref name="Tratnyek2010"/><ref name="Sarathy2010"/>.
 
 
 
==Treatment Approaches==
 
Compared to more frequently encountered CVOCs such as [[Wikipedia: Trichloroethylene | trichloroethene (TCE)]] and [[Wikipedia: Tetrachloroethylene | tetrachloroethene (PCE)]], TCP is relatively recalcitrant<ref name="Merrill2019">Merrill, J.P., Suchomel, E.J., Varadhan, S., Asher, M., Kane, L.Z., Hawley, E.L., and Deeb, R.A., 2019. Development and Validation of Technologies for Remediation of 1,2,3-Trichloropropane in Groundwater. Current Pollution Reports, 5(4), pp. 228–237.  [https://doi.org/10.1007/s40726-019-00122-7 | DOI: 10.1007/s40726-019-00122-7]</ref><ref name="Tratnyek2010"/>. TCP is generally resistant to hydrolysis, bioremediation, oxidation, and reduction under natural conditions<ref name="Tratnyek2010"/>.  The moderate volatility of TCP makes air stripping, air sparging, and soil vapor extraction (SVE) less effective compared to other VOCs<ref name="Merrill2019"/>. Despite these challenges, both ''ex situ'' and ''in situ'' treatment technologies exist. ''Ex situ'' treatment processes are relatively well established and understood but can be cost prohibitive. ''In situ'' treatment methods are comparatively limited and less-well developed, though promising field-scale demonstrations of some ''in situ'' treatment technologies have been conducted.
 
 
 
===''Ex Situ'' Treatment===
 
The most common ''ex situ'' treatment technology for groundwater contaminated with TCP is groundwater extraction and treatment<ref name="SaminJanssen2012">Samin, G. and Janssen, D.B., 2012. Transformation and biodegradation of 1,2,3-trichloropropane (TCP). Environmental Science and Pollution Research International, 19(8), pp. 3067-3078. [https://doi.org/10.1007/s11356-012-0859-3 DOI: 10.1007/s11356-012-0859-3]&nbsp;&nbsp; [[Media:  SaminJanssen2012.pdf | Report.pdf]]</ref>. Extraction of TCP is generally effective given its relatively high solubility in water and low degree of partitioning to soil. After extraction, TCP is typically removed by adsorption to granular activated carbon (GAC)<ref name="Merrill2019"/><ref name="CalEPA2017">California Environmental Protection Agency, 2017. Groundwater Information Sheet, 1,2,3-Trichloropropane (TCP). State Water Resources Control Board, Division of Water Quality, Groundwater Ambient Monitoring and Assessment (GAMA) Program, 8 pp. Free download from: [http://www.waterboards.ca.gov/gama/docs/coc_tcp123.pdf California Waterboards]&nbsp;&nbsp; [[Media: CalEPA2017tcp123.pdf | Report.pdf]]</ref>.
 
 
 
TCP contamination in drinking water sources is typically treated using granular activated carbon (GAC)<ref name="Hooker2012">Hooker, E.P., Fulcher, K.G. and Gibb, H.J., 2012. Report to the Hawaii Department of Health, Safe Drinking Water Branch, Regarding the Human Health Risks of 1, 2, 3-Trichloropropane in Tap Water. [https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.269.2485&rep=rep1&type=pdf Free Download]&nbsp;&nbsp; [[Media: Hooker2012.pdf | Report.pdf]]</ref>.
 
 
 
In California, GAC is considered the best available technology (BAT) for treating TCP, and as of 2017 seven full-scale treatment facilities were using GAC to treat groundwater contaminated with TCP<ref name="CalEPA2017a">California Environmental Protection Agency, 2017.  Initial Statement of Reasons 1,2,3-Trichloropropane Maximum Contaminant Level Regulations. Water Resources Control Board, Title 22, California Code of Regulations (SBDDW-17-001). 36 pp.  [https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/123-tcp/sbddw17_001/isor.pdf  Free download]</ref>. Additionally, GAC has been used for over 30 years to treat 60 million gallons per day of TCP-contaminated groundwater in Hawaii<ref name="Babcock2018">Babcock Jr, R.W., Harada, B.K., Lamichhane, K.M., and Tsubota, K.T., 2018. Adsorption of 1, 2, 3-Trichloropropane (TCP) to meet a MCL of 5 ppt. Environmental Pollution, 233, 910-915. [https://doi.org/10.1016/j.envpol.2017.09.085  DOI: 10.1016/j.envpol.2017.09.085]</ref>.
 
 
 
GAC has a low to moderate adsorption capacity for TCP, which can necessitate larger treatment systems and result in higher treatment costs relative to other organic contaminants<ref name="USEPA2017"/>.  Published Freundlich adsorption isotherm parameters<ref name="SnoeyinkSummers1999">Snoeyink, V.L. and Summers, R.S, 1999. Adsorption of Organic Compounds (Chapter 13), In: Water Quality and Treatment, 5th ed., Letterman, R.D., editor.  McGraw-Hill, New York, NY. ISBN 0-07-001659-3</ref> indicate that less TCP mass is adsorbed per gram of carbon compared to other volatile organic compounds (VOCs), resulting in increased carbon usage rate and treatment cost.  Recent bench-scale studies indicate that subbituminous coal-based GAC and coconut shell-based GAC are the most effective types of GAC for treatment of TCP in groundwater<ref name="Babcock2018"/><ref name="Knappe2017">Knappe, D.R.U., Ingham, R.S., Moreno-Barbosa, J.J., Sun, M., Summers, R.S., and Dougherty, T., 2017. Evaluation of Henry’s Law Constants and Freundlich Adsorption Constants for VOCs. Water Research Foundation Project 4462 Final Report. [https://www.waterrf.org/research/projects/evaluation-henrys-law -constant-and-freundlich-adsorption-constant-vocs  Website]</ref>. To develop more economical and effective treatment approaches, further treatability studies with site groundwater (e.g., rapid small-scale column tests) may be needed.
 
 
 
===''In Situ'' Treatment===
 
''In situ'' treatment of TCP to concentrations below current regulatory or advisory levels is difficult to achieve in both natural and engineered systems. However, several ''in situ'' treatment technologies have demonstrated promise for TCP remediation, including chemical reduction by zero-valent metals (ZVMs), chemical oxidation with strong oxidizers, and anaerobic bioremediation<ref name="Merrill2019"/><ref name="Tratnyek2010"/>.
 
 
 
===''In Situ'' Chemical Reduction (ISCR)===
 
Reduction of TCP under conditions relevant to natural attenuation has been observed to be negligible. Achieving significant degradation rates of TCP requires the addition of a chemical reductant to the contaminated zone<ref name="Merrill2019"/><ref name="Tratnyek2010"/>.  Under reducing environmental conditions, some ZVMs have demonstrated the ability to reduce TCP all the way to [[wikipedia:Propene | propene]]. As shown in Figure 2, the desirable pathway for reduction of TCP is the formation of [[Wikipedia: Allyl_chloride | 3-chloro-1-propene (also known as allyl chloride)]] via [[Biodegradation_-_Reductive_Processes#Dihaloelimination | dihaloelimination]], which is then rapidly reduced to propene through [[Wikipedia:Hydrogenolysis |  hydrogenolysis]] <ref name="Merrill2019"/><ref name="Tratnyek2010"/><ref name="Torralba-Sanchez2020">Torralba-Sanchez, T.L., Bylaska, E.J., Salter-Blanc, A.J., Meisenheimer, D.E., Lyon, M.A., and Tratnyek, P.G., 2020. Reduction of 1, 2, 3-trichloropropane (TCP): pathways and mechanisms from computational chemistry calculations. Environmental Science: Processes and Impacts, 22(3), 606-616. [https://doi.org/10.1039/C9EM00557A DOI: 10.1039/C9EM00557A]&nbsp;&nbsp; [[Media: Torralba-Sanchez2020.pdf | Open Access Article]]</ref>.  ZVMs including granular zero-valent iron (ZVI), nano ZVI, [[wikipedia: In_situ_chemical_reduction#Bimetallic%20materials | palladized nano ZVI]], and [[wikipedia: In_situ_chemical_reduction#Zero_valent_metals_%28ZVMs%29 | zero-valent zinc (ZVZ)]] have been evaluated by researchers<ref name="Merrill2019"/><ref name="Tratnyek2010"/>.
 
 
 
ZVI is a common reductant used for ISCR and, depending on the form used, has shown variable levels of success for TCP treatment. The Strategic Environmental Research and Development Program (SERDP) Project ER-1457 measured the TCP degradation rates for various forms of ZVI and ZVZ.  Nano-scale ZVI and palladized ZVI increased the TCP reduction rate over that of natural attenuation, but the reaction is not anticipated to be fast enough to be useful in typical remediation applications<ref name="Sarathy2010"/>.
 
 
 
Commercial-grade zerovalent zinc (ZVZ) on the other hand is a strong reductant that reduces TCP relatively quickly under a range of laboratory and field conditions to produce propene without significant accumulation of intermediates<ref name="Sarathy2010"/><ref name="Salter-BlancTratnyek2011">Salter-Blanc, A.J. and Tratnyek, P.G., 2011. Effects of Solution Chemistry on the Dechlorination of 1,2,3-Trichloropropane by Zero-Valent Zinc. Environmental Science and Technology, 45(9), pp 4073–4079. [https://doi.org/10.1021/es104081p DOI: 10.1021/es104081p]&nbsp;&nbsp; [[Media: Salter-BlancTratnyek2011.pdf | Open access article]]</ref><ref name="Salter-Blanc2012">Salter-Blanc, A.J., Suchomel, E.J., Fortuna, J.H., Nurmi, J.T., Walker, C., Krug, T., O'Hara, S., Ruiz, N., Morley, T. and Tratnyek, P.G., 2012. Evaluation of Zerovalent Zinc for Treatment of 1,2,3-Trichloropropane‐Contaminated Groundwater: Laboratory and Field Assessment. Groundwater Monitoring and Remediation, 32(4), pp.42-52. [https://doi.org/10.1111/j.1745-6592.2012.01402.x DOI: 10.1111/j.1745-6592.2012.01402.x]</ref><ref name="Merrill2019"/>. Of the ZVMs tested as part of SERDP Project ER-1457, ZVZ had the fastest degradation rates for TCP<ref name="Tratnyek2010"/>. In bench-scale studies, TCP was reduced by ZVZ to propene with 3-chloro-1-propene as the only detectable chlorinated intermediate, which was short-lived and detected only at trace concentrations<ref name="Torralba-Sanchez2020"/>.
 
 
 
Navy Environmental Sustainability Development to Integration (NESDI) Project 434 conducted bench-scale testing which demonstrated that commercially available ZVZ was effective for treating TCP. Additionally, this project evaluated field-scale ZVZ column treatment of groundwater impacted with TCP at Marine Corps Base Camp Pendleton (MCBCP) in Oceanside, California. This study reported reductions of TCP concentrations by up to 95% which was maintained for at least twelve weeks with influent concentrations ranging from 3.5 to 10 µg/L, without any significant secondary water quality impacts detected<ref name="Salter-Blanc2012"/>.
 
 
 
Following the column study, a 2014 pilot study at MCBCP evaluated direct injection of ZVZ with subsequent monitoring. Direct injection of ZVZ was reportedly effective for TCP treatment, with TCP reductions ranging from 90% to 99% in the injection area. Concentration reduction downgradient of the injection area ranged from 50 to 80%. TCP concentrations have continued to decrease, and reducing conditions have been maintained in the aquifer since injection, demonstrating the long-term efficacy of ZVZ for TCP reduction<ref name="Kane2020"/>.
 
 
 
Potential ''in situ'' applications of ZVZ include direct injection, as demonstrated by the MCBCP pilot study, and permeable reactive barriers (PRBs). Additionally, ZVZ could potentially be deployed in an ''ex situ'' flow-through reactor, but the economic feasibility of this approach would depend in part on the permeability of the aquifer and in part on the cost of the reactor volumes of ZVZ media necessary for complete treatment.
 
 
 
===''In Situ'' Chemical Oxidation (ISCO)===
 
Chemical oxidation of TCP with mild oxidants such as permanganate or ozone is ineffective. However, stronger oxidants (e.g. activated peroxide and persulfate) can effectively treat TCP, although the rates are slower than observed for most other organic contaminants<ref name="Tratnyek2010"/><ref name="CalEPA2017"/>. [[Wikipedia: Fenton's reagent | Fenton-like chemistry]] (i.e., Fe(II) activated hydrogen peroxide) has been shown to degrade TCP in the laboratory with half-lives ranging from 5 to 10 hours<ref name="Tratnyek2010"/>, but field-scale demonstrations of this process have not been reported. Treatment of TCP with heat-activated or base-activated persulfate is effective but secondary water quality impacts from high sulfate may be a concern at some locations.
 
 
 
===Aerobic Bioremediation===
 
No naturally occurring microorganisms have been identified that degrade TCP under aerobic conditions<ref name="SaminJanssen2012"/>. Relatively slow aerobic cometabolism by the ammonia oxidizing bacterium [[Wikipedia: Nitrosomonas europaea | Nitrosomonas europaea]] and other populations has been reported<ref name="Vanelli1990">Vannelli, T., Logan, M., Arciero, D.M., and Hooper, A.B., 1990. Degradation of Halogenated Aliphatic Compounds by the Ammonia-Oxidizing Bacterium Nitrosomonas europaea. Applied and Environmental Microbiology, 56(4), pp. 1169–1171. [https://doi.org/10.1128/aem.56.4.1169-1171.1990 DOI: 10.1128/aem.56.4.1169-1171.1990] Free download from: [https://journals.asm.org/doi/epdf/10.1128/aem.56.4.1169-1171.1990 American Society of Microbiology]&nbsp;&nbsp; [[Media: Vannelli1990.pdf | Report.pdf]]</ref><ref name="SaminJanssen2012"/>, and genetic engineering has been used to develop organisms capable of utilizing TCP as a sole carbon source under aerobic conditions<ref name="Bosma2002">Bosma, T., Damborsky, J., Stucki, G., and Janssen, D.B., 2002. Biodegradation of 1,2,3-Trichloropropane through Directed Evolution and Heterologous Expression of a Haloalkane Dehalogenase Gene. Applied and Environmental Microbiology, 68(7), pp. 3582–3587. [https://doi.org/10.1128/AEM.68.7.3582-3587.2002 DOI: 10.1128/AEM.68.7.3582-3587.2002] Free download from: [https://journals.asm.org/doi/epub/10.1128/AEM.68.7.3582-3587.2002 American Society for Microbiology]&nbsp;&nbsp; [[Media: Bosma2002.pdf | Report.pdf]]</ref><ref name="SaminJanssen2012"/><ref name="JanssenStucki2020">Janssen, D. B., and Stucki, G., 2020. Perspectives of genetically engineered microbes for groundwater bioremediation. Environmental Science: Processes and Impacts, 22(3), pp. 487-499. [https://doi.org/10.1039/C9EM00601J DOI: 10.1039/C9EM00601J] Open access article from: [https://pubs.rsc.org/en/content/articlehtml/2020/em/c9em00601j Royal Society of Chemistry]&nbsp;&nbsp; [[Media: JanssenStucki2020.pdf | Report.pdf]]</ref>.
 
 
 
===Anaerobic Bioremediation===
 
Like other CVOCs, TCP has been shown to undergo biodegradation under anaerobic conditions via reductive dechlorination by [[Wikipedia:Dehalogenimonas | Dehalogenimonas (Dhg)]] species<ref name="Merrill2019"/><ref name="Yan2009">Yan, J., B.A. Rash, F.A. Rainey, and W.M. Moe, 2009. Isolation of novel bacteria within the Chloroflexi capable of reductive dechlorination of 1,2,3-trichloropropane. Environmental Microbiology, 11(4), pp. 833–843. [https://doi.org/10.1111/j.1462-2920.2008.01804.x DOI: 10.1111/j.1462-2920.2008.01804.x]</ref><ref name="Bowman2013">Bowman, K.S., Nobre, M.F., da Costa, M.S., Rainey, F.A., and Moe, W.M., 2013. Dehalogenimonas alkenigignens sp. nov., a chlorinated-alkane-dehalogenating bacterium isolated from groundwater. International Journal of Systematic and Evolutionary Microbiology, 63(Pt_4), pp. 1492-1498. [https://doi.org/10.1099/ijs.0.045054-0 DOI: 10.1099/ijs.0.045054-0]  Free access article from: [https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.045054-0?crawler=true Microbiology Society]&nbsp;&nbsp; [[Media: Bowman2013.pdf | Report.pdf]]</ref><ref name="Loffler1997">Loffler, F.E., Champine, J.E., Ritalahti, K.M., Sprague, S.J. and Tiedje, J.M., 1997. Complete Reductive Dechlorination of 1, 2-Dichloropropane by Anaerobic Bacteria. Applied and Environmental Microbiology, 63(7), pp.2870-2875. Free download from: [https://journals.asm.org/doi/pdf/10.1128/aem.63.7.2870-2875.1997 American Society for Micrebiology]&nbsp;&nbsp; [[Media: Loffler1997.pdf | Report.pdf]]</ref><ref name="Moe2019">Moe, W.M., Yan, J., Nobre, M.F., da Costa, M.S. and Rainey, F.A., 2009. Dehalogenimonas lykanthroporepellens gen. nov., sp. nov., a reductively dehalogenating bacterium isolated from chlorinated solvent-contaminated groundwater. International Journal of Systematic and Evolutionary Microbiology, 59(11), pp.2692-2697. [https://doi.org/10.1099/ijs.0.011502-0 DOI: 10.1099/ijs.0.011502-0] Free download from: [https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/ijs.0.011502-0?crawler=true Microbiology Society]&nbsp;&nbsp; [[Media: Moe2009.pdf | Report.pdf]]</ref><ref name="SaminJanssen2012"/>. However, the kinetics are slower than for other CVOCs.  Bioaugmentation cultures containing Dehalogenimonas (KB-1 Plus, SiREM) are commercially available and have been implemented for remediation of TCP-contaminated groundwater<ref name="Schmitt2017">Schmitt, M., Varadhan, S., Dworatzek, S., Webb, J. and Suchomel, E., 2017. Optimization and validation of enhanced biological reduction of 1,2,3-trichloropropane in groundwater. Remediation Journal, 28(1), pp.17-25. [https://doi.org/10.1002/rem.21539 DOI: 10.1002/rem.21539]</ref>. One laboratory study examined the effect of pH on biotransformation of TCP over a wide range of TCP concentrations (10 to 10,000 µg/L) and demonstrated that successful reduction occurred from a pH of 5 to 9, though optimal conditions were from pH 7 to 9<ref name="Schmitt2017"/>. 
 
 
 
As with other microbial cultures capable of reductive dechlorination, coordinated amendment with a fermentable organic substrate (e.g. lactate or vegetable oil), also known as biostimulation,  creates reducing conditions in the aquifer and provides a source of hydrogen which is required as the primary electron donor for reductive dechlorination.  
 
  
A 2016 field demonstration of ''in situ'' bioremediation (ISB) was performed in California’s Central Valley at a former agricultural chemical site with relatively low TCP concentrations (2 µg/L). The site was first biostimulated by injecting amendments of emulsified vegetable oil (EVO) and lactate, which was followed by bioaugmentation with a microbial consortium containing Dhg. After an initial lag period of six months, TCP concentrations decreased to below laboratory detection limits (<0.005 µg/L)<ref name="Schmitt2017"/>.
+
During treatment, PFOS and PFOA concentrations decreased 96% to >99% and 77% to 97%, respectively. For the PFAS with proposed drinking water Maximum Contaminant Levels (MCLs) recently established by the USEPA (PFNA, PFOA, PFOS, PFHxS, PFBS, and HFPO-DA), concentrations decreased >99% for GW, 93% for FF, 95% for AFFF Rinsate and IDW NF, and 79% for AFFF (diluted 10x) during the treatment time allotted. Meanwhile, the total PFAS concentrations, including all 40 known PFAS analytes and unidentified perfluorocarboxylic acid (PFCA) precursors, decreased from 34% to 96% following treatment. All of these concentration reduction values were calculated by using reporting limits (RL) as the concentrations for non-detects.  
  
{| class="wikitable" style="float:right; margin-left:10px;text-align:center;"
+
Excellent fluorine/fluoride mass balance was achieved. There was nearly a 1:1 conversion of organic fluorine to free inorganic fluoride ion during treatment of GW, FF and AFFF Rinsate. The 3M Lightwater AFFF (diluted 10x) achieved only 65% fluorine mass balance, but this was likely due to high adsorption of PFAS to the reactor.
|+Table 2. Advantages and limitations of TCP treatment technologies<ref name="Kane2020"/>
 
|-
 
! Technology
 
! Advantages
 
! Limitations
 
|-
 
| ZVZ
 
| style="text-align:left;" |
 
* Can degrade TCP at relatively high and low concentrations
 
* Faster reaction rates than ZVI
 
* Material is commercially available
 
| style="text-align:left;" |
 
* Higher cost than ZVI
 
* Difficult to distribute in subsurface ''in situ'' applications
 
|-
 
| Groundwater</br>Extraction and</br>Treatment
 
| style="text-align:left;" |
 
* Can cost-effectively capture and treat larger, more dilute</br>groundwater plumes than ''in situ'' technologies
 
* Well understood and widely applied technology
 
| style="text-align:left;" |
 
* Requires construction, operation and maintenance of</br>aboveground treatment infrastructure
 
* Typical technologies (e.g. GAC) may be expensive due</br>to treatment inefficiencies
 
|-
 
| ZVI
 
| style="text-align:left;" |
 
* Can degrade TCP at relatively high and low concentrations
 
* Lower cost than ZVZ
 
* Material is commercially available
 
| style="text-align:left;" |
 
* Lower reactivity than ZVZ, therefore may require higher</br>ZVI volumes or thicker PRBs
 
* Difficult to distribute in subsurface ''in situ'' applications
 
|-
 
| ISCO
 
| style="text-align:left;" |
 
* Can degrade TCP at relatively high and low concentrations
 
* Strategies to distribute amendments ''in situ'' are well established
 
* Material is commercially available
 
| style="text-align:left;" |
 
* Most effective oxidants (e.g., base-activated or heat-activated</br>persulfate) are complex to implement
 
* Secondary water quality impacts (e.g., high pH, sulfate, </br>hexavalent chromium) may limit ability to implement
 
|-
 
| ''In Situ''</br>Bioremediation
 
| style="text-align:left;" |
 
* Can degrade TCP at moderate to high concentrations
 
* Strategies to distribute amendments ''in situ'' are well established
 
* Materials are commercially available and inexpensive
 
| style="text-align:left;" |
 
* Slower reaction rates than ZVZ or ISCO
 
|}
 
The 2016 field demonstration was expanded to full-scale treatment in 2018 with biostimulation and bioaugmentation occurring over several months. The initial TCP concentration in performance monitoring wells ranged from 0.008 to 1.7 µg/L. As with the field demonstration, a lag period of approximately 6 to 8 months was observed before TCP was degraded, after which concentrations declined over fifteen months to non-detectable levels (less than 0.005 µg/L). TCP degradation was associated with increases in Dhg population and propene concentration. Long term monitoring showed that TCP remained at non-detectable levels for at least three years following treatment implementation<ref name="Merrill2019"/>.
 
  
==Treatment Comparisons and Considerations==  
+
===Application===
When selecting a technology for TCP treatment, considerations include technical feasibility, ability to treat to regulated levels, potential secondary water quality impacts and relative costs. A comparison of some TCP treatment technologies is provided in Table 2.  
+
Due to the first-order kinetics of PRD, destruction of PFAS is most energy efficient when paired with a pre-concentration technology, such as foam fractionation (FF), nanofiltration, reverse osmosis, or resin/carbon adsorption, that remove PFAS from water. Application of the PFASigator<small><sup>TM</sup></small> is therefore proposed as a part of a PFAS treatment train that includes a pre-concentration step.
  
==Summary==
+
The first pilot study with the PFASigator<small><sup>TM</sup></small> was conducted in late 2023 at an industrial facility in Michigan with PFAS-impacted groundwater. The goal of the pilot study was to treat the groundwater to below the limits for regulatory discharge permits. For the pilot demonstration, the PFASigator<small><sup>TM</sup></small> was paired with an FF unit, which pre-concentrated the PFAS into a foamate that was pumped into the PFASigator<small><sup>TM</sup></small> for batch PFAS destruction. Residual PFAS remaining after the destruction batch was treated by looping back the PFASigator<small><sup>TM</sup></small> effluent to the FF system influent. During the one-month field pilot duration, site-specific discharge limits were met, and steady state operation between the FF unit and PFASigator<small><sup>TM</sup></small> was achieved such that the PFASigator<small><sup>TM</sup></small> destroyed the required concentrated PFAS mass and no off-site disposal of PFAS contaminated waste was required.
The relatively high toxicity of TCP has led to the development of health-based drinking water concentration values that are very low. TCP is sometimes present in groundwater and in public water systems at concentrations that exceed these health-based goals. While a handful of states have established MCLs for TCP, US federal regulatory determination is hindered by the lack of low-concentration occurrence data. Because TCP is persistent in groundwater and resistant to typical remediation methods (or costly to treat), specialized strategies may be needed to meet drinking-water-based treatment goals.  ''In situ'' chemical reduction (ISCR) with zero valent zinc (ZVZ) and ''in situ'' bioremediation have been demonstrated to be effective for TCP remediation.
 
  
 
==References==
 
==References==
Line 180: Line 102:
  
 
==See Also==
 
==See Also==
ATSDR Toxicological Profile: https://www.atsdr.cdc.gov/ToxProfiles/TP.asp?id=912&tid=186
 
 
EPA Technical Fact Sheet: https://www.epa.gov/sites/production/files/2014-03/documents/ffrrofactsheet_contaminant_tcp_january2014_final.pdf
 
 
Cal/EPA State Water Resources Control Board Groundwater Information Sheet: http://www.waterboards.ca.gov/gama/docs/coc_tcp123.pdf
 
 
California Water Boards Fact Sheet: http://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/123-tcp/123tcp_factsheet.pdf
 

Revision as of 18:43, 8 May 2024

Photoactivated Reductive Defluorination PFAS Destruction

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

Related Article(s):

Contributor(s):

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

Key Resource(s):

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

Introduction

Figure 1. Schematic of PRD mechanism[4]

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

Advantages and Disadvantages

Advantages

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

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

Disadvantages

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

State of the Art

Technical Performance

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

% Decrease
(Initial Concentration, μg/L)

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


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

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

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

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

Application

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

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

References

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

See Also