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==PFAS Soil Remediation Technologies==
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==Thermal Conduction Heating for Treatment of PFAS-Impacted Soil==  
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[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] are mobile in the subsurface and highly resistant to natural degradation processes, therefore soil source areas can be ongoing sources of groundwater contamination. The United States Environmental Protection Agency (US EPA) has not promulgated soil standards for any PFAS, although a handful of states have for select compounds. Soil standards issued for protection of groundwater are in the single digit part per billion range, which is a very low threshold for soil impacts. Well developed soil treatment technologies are limited to capping, excavation with incineration or disposal, and soil stabilization with sorptive amendments. At present, no in situ destructive soil treatment technologies have been demonstrated.
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Removal of [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] compounds from impacted soils is challenging due to the modest volatility and varying properties of most PFAS compounds. Thermal treatment technologies have been developed for treatment of semi-volatile compounds in soils such as dioxins, furans, poly-aromatic hydrocarbons and poly-chlorinated biphenyls at temperatures near 325&deg;C. In controlled bench-scale testing, complete removal of targeted PFAS compounds to concentrations below reporting limits of 0.5 µg/kg was demonstrated at temperatures of 400&deg;C<ref name="CrownoverEtAl2019"> Crownover, E., Oberle, D., Heron, G., Kluger, M., 2019.  Perfluoroalkyl and polyfluoroalkyl substances thermal desorption evaluation. Remediation Journal, 29(4), pp. 77-81. [https://doi.org/10.1002/rem.21623 doi: 10.1002/rem.21623]</ref>. Three field-scale thermal PFAS treatment projects that have been completed in the US include an in-pile treatment demonstration, an ''in situ'' vadose zone treatment demonstration and a larger scale treatment demonstration with excavated PFAS-impacted soil in a constructed pile. Based on the results, thermal treatment temperatures of at least 400&deg;C and a holding time of 7-10 days are recommended for reaching local and federal PFAS soil standards. The energy requirement to treat typical wet soil ranges from 300 to 400 kWh per cubic yard, exclusive of heat losses which are scale dependent. Extracted vapors have been treated using condensation and granular activated charcoal filtration, with thermal and catalytic oxidation as another option which is currently being evaluated for field scale applications. Compared to other options such as soil washing, the ability to treat on site and to treat all soil fractions is an advantage.
 
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'''Related Article(s):'''
 
'''Related Article(s):'''
  
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* [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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* [[PFAS Transport and Fate]]
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*[[Thermal Conduction Heating (TCH)]]
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* [[PFAS Sources]]
 
  
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'''Contributor(s):''' [[Jim Hatton]] and [[Bill DiGuiseppi]]
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'''Contributors:''' Gorm Heron, Emily Crownover, Patrick Joyce, Ramona Iery
  
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'''Key Resource(s):'''
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'''Key Resource:'''
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*Perfluoroalkyl and polyfluoroalkyl substances thermal desorption evaluation<ref name="CrownoverEtAl2019"/>
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*[https://pfas-1.itrcweb.org/12-treatment-technologies/ ITRC Fact Sheet: Treatment Technologies, PFAS – Per- and Polyfluoroalkyl Substances]<ref name="ITRC2020">Interstate Technology and Regulatory Council (ITRC), 2020. PFAS Technical and Regulatory Guidance Document and Fact Sheets, PFAS-1. PFAS Team, Washington, DC.  [https://pfas-1.itrcweb.org/ Website]&nbsp;&nbsp; [[Media: ITRC_PFAS-1.pdf | Report.pdf]]</ref>. 
 
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*Persistence of Perfluoroalkyl Acid Precursors in AFFF-Impacted Groundwater and Soil<ref name="Houtz2013">Houtz, E.F., Higgins, C.P., Field, J.A., and Sedlak, D.L., 2013. Persistence of Perfluoroalkyl Acid Precursors in AFFF-Impacted Groundwater and Soil. Environmental Science and Technology, 47(15), pp. 8187−8195.  [https://doi.org/10.1021/es4018877 DOI: 10.1021/es4018877]</ref>.
 
  
 
==Introduction==
 
==Introduction==
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PFAS are a class of highly fluorinated compounds including perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and many other compounds with a variety of industrial and consumer uses. These compounds are often highly resistant to treatment<ref name="Kissa2001">Kissa, Erik, 2001. Fluorinated Surfactants and Repellents: Second Edition. Surfactant Science Series, Volume 97. Marcel Dekker, Inc., CRC Press, New York. 640 pages.  ISBN 978-0824704728</ref> and the more mobile compounds are often problematic in groundwater systems<ref name="Backe2013">Backe, W.J., Day, T.C., and Field, J.A., 2013. Zwitterionic, Cationic, and Anionic Fluorinated Chemicals in Aqueous Film Forming Foam Formulations and Groundwater from U.S. Military Bases by Nonaqueous Large-Volume Injection HPLC-MS/MS. Environmental Science and Technology, 47(10), pp. 5226-5234. [https://doi.org/10.1021/es3034999 DOI: 10.1021/es3034999]</ref>. The US EPA has published lifetime drinking water health advisories for the combined concentration of 70 nanograms per liter (ng/L) for two common and recalcitrant PFAS: PFOS, a perfluoroalkyl sulfonic acid (PFSA), and PFOA, a perfluoroalkyl carboxylic acid (PFCA)<ref name="EPApfos2016">US Environmental Protection Agency (EPA), 2016. Drinking Water Health Advisory for Perfluorooctane Sulfonate (PFOS), EPA 822-R-16-004. Office of Water, Health and Ecological Criteria Division, Washington, DC.  [https://www.epa.gov/sites/production/files/2016-05/documents/pfos_health_advisory_final-plain.pdf Free download from US EPA]&nbsp;&nbsp; [[Media: EPA822-R-16-004.pdf | Report.pdf]]</ref><ref name="EPApfoa2016">US Environmental Protection Agency (EPA), 2016. Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA), EPA 822-R-16-005. Office of Water, Health and Ecological Criteria Division, Washington, DC. [https://www.epa.gov/sites/production/files/2016-05/documents/pfoa_health_advisory_final-plain.pdf Free download from US EPA] &nbsp;&nbsp; [[Media: EPA822-R-16-005.pdf | Report]]</ref>.(See [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] for nomenclature.)
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[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] have become prominent emerging contaminants in soil and groundwater. Soil source zones have been identified at locations where the chemicals were produced, handled or used. Few effective options exist for treatments that can meet local and federal soil standards. Over the past 30 plus years, thermal remediation technologies have grown from experimental and innovative prospects to mature and accepted solutions deployed effectively at many sites. More than 600 thermal case studies have been summarized by Horst and colleagues<ref name="HorstEtAl2021">Horst, J., Munholland, J., Hegele, P., Klemmer, M., Gattenby, J., 2021. In Situ Thermal Remediation for Source Areas: Technology Advances and a Review of the Market From 1988–2020. Groundwater Monitoring & Remediation, 41(1), p. 17. [https://doi.org/10.1111/gwmr.12424 doi: 10.1111/gwmr.12424]&nbsp; [[Media: gwmr.12424.pdf | Open Access Manuscript]]</ref>. [[Thermal Conduction Heating (TCH)]] has been used for higher temperature applications such as removal of [[1,4-Dioxane]]. This article reports recent experience with TCH treatment of PFAS-impacted soil.
  
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While many of the earliest sites where these compounds were detected in groundwater were manufacturing sites, some recent detections have been attributed to fire training activities associated with aqueous film-forming foams (AFFF). AFFF is the US Department of Defense (DoD) designation for Class B firefighting foam containing PFAS, which is required for fighting fires involving petroleum liquids. Fire training areas and other source areas where AFFF was released at the surface have the potential to be ongoing sources of groundwater contamination<ref name="Houtz2013"/>. (See also [[PFAS Sources]].)
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==Target Temperature and Duration==
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PFAS behave differently from most other organics subjected to TCH treatment. While the boiling points of individual PFAS fall in the range of 150-400&deg;C, their chemical and physical behavior creates additional challenges. Some PFAS form ionic species in certain pH ranges and salts under other chemical conditions. This intricate behavior and our limited understanding of what this means for our ability to remove the PFAS from soils means that direct testing of thermal treatment options is warranted. Crownover and colleagues<ref name="CrownoverEtAl2019"/> subjected PFAS-laden soil to bench-scale heating to temperatures between 200 and 400&deg;C which showed strong reductions of PFAS concentrations at 350&deg;C and complete removal of many PFAS compounds at 400&deg;C. The soil concentrations of targeted PFAS were reduced to nearly undetectable levels in this study.
  
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No national soil cleanup standards have been promulgated by the US EPA, although Regional Screening Levels (RSLs) have been calculated and published for perfluorobutane sulfonate (PFBS)<ref name="EPA2020">US Environmental Protection Agency (EPA), 2020. Regional Screening Levels (RSLs) – User's Guide. Washington, DC.  [https://www.epa.gov/risk/regional-screening-levels-rsls-users-guide Website]</ref> and data are available to calculate RSLs for PFOA and PFOS<ref name="ITRCwNs2020">Interstate Technology Regulatory Council (ITRC), 2020. PFAS Water and Soil Values Table. PFAS – Per- and Polyfluoroalkyl Substances: PFAS Fact Sheets. [https://pfas-1.itrcweb.org/wp-content/uploads/2020/12/ITRCPFASWaterandSoilValuesTables_NOV-2020-FINAL.xlsx Free download.]&nbsp;&nbsp; [[Media: ITRCPFASWaterandSoilTables2020.xlsx | 2020 Water and Soil Tables (excel file)]]</ref>. Several states have promulgated standards<ref name="AKDEC2020">Alaska Department of Environmental Conservation (AK DEC), 2020. 18 AAC 75, Oil and Other Hazardous Substances Pollution Control. Anchorage, AK. [https://dec.alaska.gov/media/1055/18-aac-75.pdf Free download.]&nbsp;&nbsp; [[Media: AKDEC2020_18aac75.pdf | Report.pdf]]</ref> or screening levels<ref name="MEDEP2018">Maine Department of Environmental Protection (ME DEP), 2018. Maine Remedial Action Guidelines (RAGs) for Sites Contaminated with Hazardous Substances. Augusta, ME.  [https://www.maine.gov/dep/spills/publications/guidance/rags/ME-Remedial-Action-Guidelines-10-19-18cc.pdf Free download.]&nbsp;&nbsp; [[Media: MEDEP2018.pdf | Report.pdf]]</ref><ref name="EGLE2020">Michigan Department of Environment, Great Lakes, and Energy (EGLE), 2020. Cleanup Criteria Requirements for Response Activity (Formerly the Part 201 Generic Cleanup Criteria and Screening Levels). Remediation and Redevelopment Division, Lansing, MI. [https://www.michigan.gov/egle/0,9429,7-135-3311_4109_9846-251790--,00.html Website]</ref><ref name="NEDEE2018">Nebraska Department of Energy and Environment (NE DEE), 2018. Voluntary Cleanup Program Remedial Goals, Table A-1: Groundwater and Soil Remediation Goals. Lincoln, NE.  [http://www.deq.state.ne.us/Publica.nsf/xsp/.ibmmodres/domino/OpenAttachment/Publica.nsf/D243C2B56E34EA8486256F2700698997/Body/Attach%202-6%20Table%20A-1%20VCP%20LUT%20Sept%202018.pdf Free download.]&nbsp;&nbsp; [[Media: NDEE2018.pdf | Report.pdf]]</ref><ref name="NCDEQ2020">North Carolina Department of Environmental Quality (NC DEQ), 2020. Preliminary Soil Remediation Goals (PSRG) Table. Raleigh, NC.  [https://files.nc.gov/ncdeq/risk-based-remediation/1.Combined-Notes-PSRGs.pdf Free download.]&nbsp;&nbsp; [[Media: NCDEQ2020.pdf | Report.pdf]]</ref><ref name="TCEQ2021">Texas Commission on Environmental Quality (TCEQ), 2021. Texas Risk Reduction Program (TRRP), Tier 1 Protective Concentration Levels (PCL) Tables.  [http://www.tceq.texas.gov/assets/public/remediation/trrp/2021PCL%20Tables.xlsx Free Download.]&nbsp;&nbsp; [[Media: TRRP2021PCLTables.xlsx | 2021 PCL Tables (excel file)]]</ref> for soil concentrations protective of groundwater, which are several orders of magnitude lower than direct dermal exposure guidelines. These single-digit part per billion criteria will likely drive remedial actions in PFAS source areas in the future.  At present, the lack of federally promulgated standards and uncertainty about future standards causes temporary stockpiling of PFAS-impacted soils on sites with soil generated from construction or investigation activities.
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==Heating Method==
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For semi-volatile compounds such as dioxins, furans, poly-chlorinated biphenyls (PCBs) and Poly-Aromatic Hydrocarbons (PAH), thermal conduction heating has evolved as the dominant thermal technology because it is capable of achieving soil temperatures higher than the boiling point of water, which are necessary for complete removal of these organic compounds. Temperatures between 200 and 500&deg;C have been required to achieve the desired reduction in contaminant concentrations<ref name="StegemeierVinegar2001">Stegemeier, G.L., Vinegar, H.J., 2001. Thermal Conduction Heating for In-Situ Thermal Desorption of Soils. Ch. 4.6, pp. 1-37. In: Chang H. Oh (ed.), Hazardous and Radioactive Waste Treatment Technologies Handbook, CRC Press, Boca Raton, FL. ISBN 9780849395864 [[Media: StegemeierVinegar2001.pdf | Open Access Article]]</ref>. TCH has become a popular technology for PFAS treatment because temperatures in the 400&deg;C range are needed.
  
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==Soil Treatment==
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The energy source for TCH can be electricity (most commonly used), or fossil fuels (typically gas, diesel or fuel oil). Electrically powered TCH offers the largest flexibility for power input which also can be supplied by renewable and sustainable energy sources.
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Addressing recalcitrant contaminants in soil has traditionally been done through containment/capping or excavation and off-site disposal or treatment.  Containment/capping may be an acceptable solution for PFAS in some locations. However, containment/capping is not considered ideal given the history of releases from engineered landfills and restrictions on use of land containing capped soils.  Innovative treatment approaches for PFAS include stabilization with amendments and thermal treatment.
 
  
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===Excavation and Disposal===
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==Energy Usage==
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Excavation and off-site disposal or treatment of PFAS-impacted soils is the only well-developed treatment technology option and may be acceptable for small quantities of soil, such as those generated during characterization activities (i.e., investigation derived waste, IDW). Disposal in non-hazardous landfills is allowable in most states. However, some landfill operators are choosing to restrict acceptance of PFAS-containing waste and soils as a protection against future liability.  In addition, the US EPA and some states are considering or have designated PFOA and PFOS as hazardous substances,  which would reduce the number of facilities where disposal of PFAS-contaminated soil would be allowed 
 
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[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]] are a complex family of more than 3,000 manmade fluorinated organic chemicals<ref name="Wang2017">Wang, Z., DeWitt, J.C., Higgins, C.P., and Cousins, I.T., 2017. A Never-Ending Story of Per- and Poly-Fluoroalkyl Substances (PFASs)? Environmental Science and Technology, 51(5), pp. 2508-2518. [https://doi.org/10.1021/acs.est.6b04806 DOI: 10.1021/acs.est.6b04806]&nbsp;&nbsp; [[Media: Wang2017.pdf | Open access article.]]</ref> although not all of these are currently in use or production. PFAS are produced using several different processes. Fluorosurfactants, which include perfluoroalkyl acids (PFAAs) (see [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] article for nomenclature) and side-chain fluorinated polymers, have been manufactured using two major processes: [[Wikipedia: Electrochemical fluorination | electrochemical fluorination (ECF)]] and [[Wikipedia: Telomerization | telomerization]]<ref name="KEMI2015"/>. ECF was licensed by 3M in the 1940s<ref name="Banks1994">Banks, R.E., Smart, B.E. and Tatlow, J.C. eds., 1994. Organofluorine Chemistry: Principles and Commercial Applications. Springer Science and Business Media, New York, N. Y. [https://link.springer.com/book/10.1007/978-1-4899-1202-2 DOI: 10.1007/978-1-4899-1202-2]</ref> and used by 3M until 2001. ECF produces a mixture of even and odd numbered carbon chain lengths of approximately 70% linear and 30% branched substances<ref name="Concawe2016">Concawe (Conservation of Clean Air and Water in Europe), 2016. Environmental fate and effects of poly- and perfluoroalkyl substances (PFAS). Report No. 8/16. Brussels, Belgium. [[Media:Concawe2016.pdf | Report.pdf]]</ref>. Telomerization was developed in the 1970s<ref name="Benskin2012a">Benskin, J.P., Ahrens, L., Muir, D.C., Scott, B.F., Spencer, C., Rosenberg, B., Tomy, G., Kylin, H., Lohmann, R. and Martin, J.W., 2012. Manufacturing Origin of Perfluorooctanoate (PFOA) in Atlantic and Canadian Arctic Seawater. Environmental Science and Technology, 46(2), pp. 677-685. [https://doi.org/10.1021/es202958p DOI: 10.1021/es202958p]</ref>, and yields mainly even numbered, straight carbon chain isomers<ref name="Kissa2001"/><ref name="Parsons2008">Parsons, J.R., Sáez, M., Dolfing, J. and De Voogt, P., 2008. Biodegradation of Perfluorinated Compounds. Reviews of Environmental Contamination and Toxicology, 196, pp. 53-71. Springer, New York, NY. [https://doi.org/10.1007/978-0-387-78444-1_2 DOI: 10.1007/978-0-387-78444-1_2]&nbsp;&nbsp; Free download from: [https://www.researchgate.net/profile/Jan_Dolfing/publication/23489065_Biodegradation_of_Perfluorinated_Compounds/links/0912f5087a40c9d5df000000.pdf ResearchGate]</ref>.  PFAS manufacturers have provided PFAS to secondary manufacturers for production of a vast array of industrial and consumer products.  
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During&nbsp;large&nbsp;precipitation&nbsp;events the rate of water deposition exceeds the rate of water infiltration, resulting in surface runoff (also called stormwater runoff). Surface characteristics including soil texture, presence of impermeable surfaces (natural and artificial), slope, and density and type of vegetation all influence the amount of surface runoff from a given land area. The use of passive systems such as retention ponds and biofiltration cells for treatment of surface runoff is well established for urban and roadway runoff. Treatment in those cases is typically achieved by directing runoff into and through a small constructed wetland, often at the outlet of a retention basin, or via filtration by directing runoff through a more highly engineered channel or vault containing the treatment materials. Filtration based technologies have proven to be effective for the removal of metals, organics, and suspended solids<ref>Sansalone, J.J., 1999. In-situ performance of a passive treatment system for metal source control. Water Science and Technology, 39(2), pp. 193-200. [https://doi.org/10.1016/S0273-1223(99)00023-2 doi: 10.1016/S0273-1223(99)00023-2]</ref><ref>Deletic, A., Fletcher, T.D., 2006. Performance of grass filters used for stormwater treatment—A field and modelling study. Journal of Hydrology, 317(3-4), pp. 261-275. [http://dx.doi.org/10.1016/j.jhydrol.2005.05.021 doi: 10.1016/j.jhydrol.2005.05.021]</ref><ref>Grebel, J.E., Charbonnet, J.A., Sedlak, D.L., 2016. Oxidation of organic contaminants by manganese oxide geomedia for passive urban stormwater treatment systems. Water Research, 88, pp. 481-491. [http://dx.doi.org/10.1016/j.watres.2015.10.019 doi: 10.1016/j.watres.2015.10.019]</ref><ref>Seelsaen, N., McLaughlan, R., Moore, S., Ball, J.E., Stuetz, R.M., 2006. Pollutant removal efficiency of alternative filtration media in stormwater treatment. Water Science and Technology, 54(6-7), pp. 299-305. [https://doi.org/10.2166/wst.2006.617 doi: 10.2166/wst.2006.617]</ref>.
  
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During manufacturing, PFAS may be released into the atmosphere then redeposited on land where they can also affect surface water and groundwater, or PFAS may be discharged without treatment to wastewater treatment plants or landfills, and eventually be released into the environment by treatment systems that are not designed to mitigate PFAS (see also [[PFAS Transport and Fate]]). Industrial discharges of PFAS were unregulated for many years, but that has begun to change. In January 2016, New York became the first state in the nation to regulate PFOA as a hazardous substance followed by the regulation of PFOS in April 2016. Consumer and industrial uses of PFAS-containing products can also end up releasing PFAS into landfills and into municipal wastewater, where it may accumulate undetected in biosolids which are typically treated by land application.
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===Surface Runoff on Ranges===
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[[File: FullerFig2.png | thumb | 600 px | Figure 2. Conceptual illustration of munition constituent production and transport on military ranges. Mesoscale residues are qualitatively defined as being easily visible to the naked eye (e.g., from around 50 µm to multiple cm in size) and less likely to be transported by moving water.  Microscale residues are defined as <50 µm down to below 1 µm, and more likely to be entrained in, and transported by, moving water as particulates. Blue arrows represent possible water flow paths and include both dissolved and solid phase energetics. The red vertical arrow represents the predominant energetics dissolution process in close proximity to the residues due to precipitation.]]
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Surface&nbsp;runoff&nbsp;represents&nbsp;a&nbsp;major potential mechanism through which energetics residues and related materials are transported off site from range soils to groundwater and surface water receptors (Figure 2). This process is particularly important for energetics that are water soluble (e.g., [[Wikipedia: Nitrotriazolone | NTO]] and [[Wikipedia: Nitroguanidine | NQ]]) or generate soluble daughter products (e.g., [[Wikipedia: 2,4-Dinitroanisole | DNAN]] and [[Wikipedia: TNT | TNT]]). While traditional MC such as [[Wikipedia: RDX | RDX]] and [[Wikipedia: HMX | HMX]] have limited aqueous solubility, they also exhibit recalcitrance to degrade under most natural conditions. RDX and [[Wikipedia: Perchlorate | perchlorate]] are frequent groundwater contaminants on military training ranges. While actual field measurements of energetics in surface runoff are limited, laboratory experiments have been performed to predict mobile energetics contamination levels based on soil mass loadings<ref>Cubello, F., Polyakov, V., Meding, S.M., Kadoya, W., Beal, S., Dontsova, K., 2024. Movement of TNT and RDX from composition B detonation residues in solution and sediment during runoff. Chemosphere, 350, Article 141023. [https://doi.org/10.1016/j.chemosphere.2023.141023 doi: 10.1016/j.chemosphere.2023.141023]</ref><ref>Karls, B., Meding, S.M., Li, L., Polyakov, V., Kadoya, W., Beal, S., Dontsova, K., 2023. A laboratory rill study of IMX-104 transport in overland flow. Chemosphere, 310, Article 136866. [https://doi.org/10.1016/j.chemosphere.2022.136866 doi: 10.1016/j.chemosphere.2022.136866]&nbsp; [[Media: KarlsEtAl2023.pdf | Open Access Article]]</ref><ref>Polyakov, V., Beal, S., Meding, S.M., Dontsova, K., 2025. Effect of gypsum on transport of IMX-104 constituents in overland flow under simulated rainfall. Journal of Environmental Quality, 54(1), pp. 191-203. [https://doi.org/10.1002/jeq2.20652 doi: 10.1002/jeq2.20652]&nbsp; [[Media: PolyakovEtAl2025.pdf | Open Access Article.pdf]]</ref><ref>Polyakov, V., Kadoya, W., Beal, S., Morehead, H., Hunt, E., Cubello, F., Meding, S.M., Dontsova, K., 2023. Transport of insensitive munitions constituents, NTO, DNAN, RDX, and HMX in runoff and sediment under simulated rainfall. Science of the Total Environment, 866, Article 161434. [https://doi.org/10.1016/j.scitotenv.2023.161434 doi: 10.1016/j.scitotenv.2023.161434]&nbsp; [[Media: PolyakovEtAl2023.pdf | Open Access Article.pdf]]</ref><ref>Price, R.A., Bourne, M., Price, C.L., Lindsay, J., Cole, J., 2011. Transport of RDX and TNT from Composition-B Explosive During Simulated Rainfall. In: Environmental Chemistry of Explosives and Propellant Compounds in Soils and Marine Systems: Distributed Source Characterization and Remedial Technologies. American Chemical Society, pp. 229-240. [https://doi.org/10.1021/bk-2011-1069.ch013 doi: 10.1021/bk-2011-1069.ch013]</ref>. For example, in a previous small study, MC were detected in surface runoff from an active live-fire range<ref>Fuller, M.E., 2015. Fate and Transport of Colloidal Energetic Residues. Department of Defense Strategic Environmental Research and Development Program (SERDP), Project ER-1689. [https://serdp-estcp.mil/projects/details/10760fd6-fb55-4515-a629-f93c555a92f0 Project Website]&nbsp;&nbsp; [[Media: ER-1689-FR.pdf | Final Report.pdf]]</ref>, and more recent sampling has detected MC in marsh surface water adjacent to the same installation (personal communication). Another recent report from Canada also detected RDX in both surface runoff and surface water at low part per billion levels in a survey of several military demolition sites<ref>Lapointe, M.-C., Martel, R., Diaz, E., 2017. A Conceptual Model of Fate and Transport Processes for RDX Deposited to Surface Soils of North American Active Demolition Sites. Journal of Environmental Quality, 46(6), pp. 1444-1454. [https://doi.org/10.2134/jeq2017.02.0069 doi: 10.2134/jeq2017.02.0069]</ref>. However, overall, data regarding the MC contaminant profile of surface runoff from ranges is very limited, and the possible presence of non-energetic constituents (e.g., metals, binders, plasticizers) in runoff has not been examined.  Additionally, while energetics-contaminated surface runoff is an important concern, mitigation technologies specifically for surface runoff have not yet been developed and widely deployed in the field.  To effectively capture and degrade MC and associated compounds that are present in surface runoff, novel treatment media are needed to sorb a broad range of energetic materials and to transform the retained compounds through abiotic and/or microbial processes.
  
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==Industrial Sources==
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Surface runoff of organic and inorganic contaminants from live-fire ranges is a challenging issue for the Department of Defense (DoD). Potentially even more problematic is the fact that inputs to surface waters from large testing and training ranges typically originate from multiple sources, often encompassing hundreds of acres.  No available technologies are currently considered effective for controlling non-point source energetics-laden surface runoff. While numerous technologies exist to treat collected explosives residues, contaminated soil and even groundwater, the decentralized nature and sheer volume of military range runoff have precluded the use of treatment technologies at full scale in the field.
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PFAS are used in many industrial and consumer applications, which may have released PFAS into the environment and impacted drinking water supplies in many areas of the United States<ref name="EWG2017">Environmental Working Group (EWG) and Northeastern University Social Science Environmental Health Research Institute, 2017. Mapping A Contamination Crisis. [https://www.ewg.org/research/mapping-contamination-crisis Website]</ref>. Both in the United States (US) and abroad, primary manufacturing facilities produce PFAS and secondary manufacturing facilities use PFAS to produce goods. Environmental release mechanisms associated with these facilities include air emission and dispersion, spills, and disposal of manufacturing wastes and wastewater. Potential impacts to air, soil, sediment, surface water, stormwater, and groundwater are present not only at primary release points but potentially over the surrounding area<ref name="Shin2011">Shin, H.M., Vieira, V.M., Ryan, P.B., Detwiler, R., Sanders, B., Steenland, K., and Bartell, S.M., 2011. Environmental Fate and Transport Modeling for Perfluorooctanoic Acid Emitted from the Washington Works Facility in West Virginia. Environmental Science and Technology, 45(4), pp. 1435-1442.  [https://doi.org/10.1021/es102769t DOI: 10.1021/es102769t]</ref>. Some of the potential primary and secondary sources of PFAS releases to the environment are listed here<ref name="ITRC2020"/>:
 
  
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* '''Textiles and leather:''' Factory or consumer applied coating to repel water, oil, and stains. Applications include protective clothing and outerwear, umbrellas, tents, sails, architectural materials, carpets, and upholstery<ref name="Rao1994">Rao, N.S., and Baker, B.E., 1994. Textile Finishes and Fluorosurfactants. In: Organofluorine Chemistry, Banks, R.E., Smart, B.E., and Tatlow, J.C., Eds. Springer, New York.  [https://doi.org/10.1007/978-1-4899-1202-2_15 DOI: 10.1007/978-1-4899-1202-2_15]</ref><ref name="Hekster2003">Hekster, F.M., Laane, R.W. and De Voogt, P., 2003. Environmental and Toxicity Effects of Perfluoroalkylated Substances. Reviews of Environmental Contamination and Toxicology, 179, pp. 99-121. Springer, New York, NY. [https://doi.org/10.1007/0-387-21731-2_4 DOI: 10.1007/0-387-21731-2_4]</ref><ref name="Brooke2004">Brooke, D., Footitt, A., and Nwaogu, T.A., 2004. Environmental Risk Evaluation Report: Perfluorooctanesulphonate (PFOS).  Environment Agency (UK), Science Group.  Free download from: [http://chm.pops.int/Portals/0/docs/from_old_website/documents/meetings/poprc/submissions/Comments_2006/sia/pfos.uk.risk.eval.report.2004.pdf The Stockholm Convention]&nbsp;&nbsp; [[Media:Brooke2004.pdf | Report.pdf]]</ref><ref name="Poulsen2005">Poulsen, P.B., Jensen, A.A., and Wallström, E., 2005. More environmentally friendly alternatives to PFOS-compounds and PFOA. Danish Environmental Protection Agency, Environmental Project 1013.  [[Media: Poulsen2005.pdf | Report.pdf]]</ref><ref name="Prevedouros2006">Prevedouros, K., Cousins, I.T., Buck, R.C. and Korzeniowski, S.H., 2006. Sources, Fate and Transport of Perfluorocarboxylates. Environmental Science and Technology, 40(1), pp. 32-44.  [https://doi.org/10.1021/es0512475 DOI: 10.1021/es0512475]&nbsp;&nbsp; Free download from: [https://www.academia.edu/download/39945519/Sources_Fate_and_Transport_of_Perfluoroc20151112-1647-19vcvbf.pdf Academia.edu]</ref><ref name="Walters2006">Walters, A., and Santillo, D., 2006. Technical Note 06/2006: Uses of Perfluorinated Substances. Greenpeace Research Laboratories. [http://www.greenpeace.to/publications/uses-of-perfluorinated-chemicals.pdf Website]&nbsp;&nbsp; [[Media: Walters2006.pdf | Report.pdf]]</ref><ref name="Trudel2008">Trudel, D., Horowitz, L., Wormuth, M., Scheringer, M., Cousins, I.T. and Hungerbühler, K., 2008. Estimating Consumer Exposure to PFOS and PFOA. Risk Analysis: An International Journal, 28(2), pp. 251-269.  [https://doi.org/10.1111/j.1539-6924.2008.01017.x DOI: 10.1111/j.1539-6924.2008.01017.x]</ref><ref name="Guo2009">Guo, Z., Liu, X., Krebs, K.A. and Roache, N.F., 2009. Perfluorocarboxylic Acid Content in 116 Articles of Commerce, EPA/600/R-09/033. National Risk Management Research Laboratory, US Environmental Protection Agency, Washington, DC.  Available from: [https://cfpub.epa.gov/si/si_public_record_report.cfm?Lab=NRMRL&dirEntryId=206124 US EPA.]&nbsp;&nbsp; [[Media: Guo2009.pdf | Report.pdf]]</ref><ref name="USEPA2009">US Environmental Protection Agency (USEPA), 2009. Long-Chain Perfluorinated Chemicals (PFCs), Action Plan.  [https://www.epa.gov/sites/production/files/2016-01/documents/pfcs_action_plan1230_09.pdf Website]&nbsp;&nbsp; [[Media: USEPA2009.pdf | Report.pdf]]</ref><ref name="Ahrens2011a">Ahrens, L., 2011. Polyfluoroalkyl compounds in the aquatic environment: a review of their occurrence and fate. Journal of Environmental Monitoring, 13(1), pp.20-31.
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==Range Runoff Treatment Technology Components==
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[http://dx.doi.org/10.1039/C0EM00373E DOI: 10.1039/C0EM00373E]. Free download available from: [https://www.researchgate.net/profile/Lutz_Ahrens/publication/47622154_Polyfluoroalkyl_compounds_in_the_aquatic_environment_A_review_of_their_occurrence_and_fate/links/00b7d53762cfedaf12000000/Polyfluoroalkyl-compounds-in-the-aquatic-environment-A-review-of-their-occurrence-and-fate.pdf ResearchGate]</ref><ref name="Buck2011">Buck, R.C., Franklin, J., Berger, U., Conder, J.M., Cousins, I.T., De Voogt, P., Jensen, A.A., Kannan, K., Mabury, S.A. and van Leeuwen, S.P., 2011. Perfluoroalkyl and Polyfluoroalkyl Substances in the Environment: Terminology, Classification, and Origins. Integrated Environmental Assessment and Management, 7(4), pp. 513-541. [https://doi.org/10.1002/ieam.258 DOI: 10.1002/ieam.258]&nbsp;&nbsp; [[Media:Buck2011.pdf | Open access article.]]</ref><ref name="UNEP2011">United Nations Environmental Programme (UNEP), 2011. Report of the persistent organic pollutants review committee on the work of its sixth meeting, Addendum, Guidance on alternatives to perfluorooctane sulfonic acid and its derivatives, UNEP/POPS/POPRC.6/13/Add.3/Rev.1 [http://www.pops.int/TheConvention/POPsReviewCommittee/Meetings/POPRC6/POPRC6Documents/tabid/783/ctl/Download/mid/3507/Default.aspx?id=125 Website]&nbsp;&nbsp; [[Media: UNEP2011.pdf | Report.pdf]]</ref><ref name="Herzke2012">Herzke, D., Olsson, E. and Posner, S., 2012. Perfluoroalkyl and polyfluoroalkyl substances (PFASs) in consumer products in Norway – A pilot study. Chemosphere, 88(8), pp. 980-987.  [https://doi.org/10.1016/j.chemosphere.2012.03.035 DOI: 10.1016/j.chemosphere.2012.03.035]</ref><ref name="Patagonia2016">Patagonia, Inc., 2016. An Update on Our DWR Problem.  [https://www.patagonia.com/stories/our-dwr-problem-updated/story-17673.html Website]&nbsp;&nbsp; [[Media: Patagonia2016.pdf | Report.pdf]]</ref><ref name="Kotthoff2015">Kotthoff, M., Müller, J., Jürling, H., Schlummer, M., and Fiedler, D., 2015. Perfluoroalkyl and polyfluoroalkyl substances in consumer products. Environmental Science and Pollution Research, 22(19), pp. 14546-14559.  [https://doi.org/10.1007/s11356-015-4202-7 DOI: 10.1007/s11356-015-4202-7]&nbsp;&nbsp; [[Media: Kotthoff2015.pdf | Open access article.]]</ref><ref name="ATSDR2018">Agency for Toxic Substances and Disease Registry (ATSDR), 2018. Toxicological Profile for Perfluoroalkyls, Draft for Public Comment. US Department of Health and Human Services. Free download from: [http://www.atsdr.cdc.gov/toxprofiles/tp200.pdf ATSDR]&nbsp;&nbsp; [[Media: ATSDR2018.pdf | Report.pdf]]</ref>.
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Based on the conceptual foundation of previous research into surface water runoff treatment for other contaminants, with a goal to “trap and treat” the target compounds, the following components were selected for inclusion in the technology developed to address range runoff contaminated with energetic compounds.
  
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* '''Paper products:''' Surface coatings to repel grease and moisture. Uses include non-food paper packaging (for example, cardboard, carbonless forms, masking papers) and food-contact materials (for example, pizza boxes, fast food wrappers, microwave popcorn bags, baking papers, pet food bags)<ref name="Rao1994"/><ref name="Kissa2001"/><ref name="Hekster2003"/><ref name="Poulsen2005"/><ref name="Trudel2008"/><ref name="Buck2011"/><ref name="UNEP2011"/><ref name="Kotthoff2015"/><ref name="Schaider2017">Schaider, L.A., Balan, S.A., Blum, A., Andrews, D.Q., Strynar, M.J., Dickinson, M.E., Lunderberg, D.M., Lang, J.R., and Peaslee, G.F., 2017. Fluorinated Compounds in US Fast Food Packaging. Environmental Science and Technology Letters, 4(3), pp. 105-111. [https://doi.org/10.1021/acs.estlett.6b00435 DOI: 10.1021/acs.estlett.6b00435]&nbsp;&nbsp; [[Media: Schaider2017.pdf | Open access article.]]</ref>
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===Peat===
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Previous research demonstrated that a peat-based system provided a natural and sustainable sorptive medium for organic explosives such as HMX, RDX, and TNT, allowing much longer residence times than predicted from hydraulic loading alone<ref>Fuller, M.E., Hatzinger, P.B., Rungkamol, D., Schuster, R.L., Steffan, R.J., 2004. Enhancing the attenuation of explosives in surface soils at military facilities: Combined sorption and biodegradation. Environmental Toxicology and Chemistry, 23(2), pp. 313-324. [https://doi.org/10.1897/03-187 doi: 10.1897/03-187]</ref><ref>Fuller, M.E., Lowey, J.M., Schaefer, C.E., Steffan, R.J., 2005. A Peat Moss-Based Technology for Mitigating Residues of the Explosives TNT, RDX, and HMX in Soil. Soil and Sediment Contamination: An International Journal, 14(4), pp. 373-385. [https://doi.org/10.1080/15320380590954097 doi: 10.1080/15320380590954097]</ref><ref name="FullerEtAl2009">Fuller, M.E., Schaefer, C.E., Steffan, R.J., 2009. Evaluation of a peat moss plus soybean oil (PMSO) technology for reducing explosive residue transport to groundwater at military training ranges under field conditions. Chemosphere, 77(8), pp. 1076-1083. [https://doi.org/10.1016/j.chemosphere.2009.08.044 doi: 10.1016/j.chemosphere.2009.08.044]</ref><ref>Hatzinger, P.B., Fuller, M.E., Rungkamol, D., Schuster, R.L., Steffan, R.J., 2004. Enhancing the attenuation of explosives in surface soils at military facilities: Sorption-desorption isotherms. Environmental Toxicology and Chemistry, 23(2), pp. 306-312. [https://doi.org/10.1897/03-186 doi: 10.1897/03-186]</ref><ref name="SchaeferEtAl2005">Schaefer, C.E., Fuller, M.E., Lowey, J.M., Steffan, R.J., 2005. Use of Peat Moss Amended with Soybean Oil for Mitigation of Dissolved Explosive Compounds Leaching into the Subsurface: Insight into Mass Transfer Mechanisms. Environmental Engineering Science, 22(3), pp. 337-349. [https://doi.org/10.1089/ees.2005.22.337 doi: 10.1089/ees.2005.22.337]</ref>. Peat moss represents a bioactive environment for treatment of the target contaminants. While the majority of the microbial reactions are aerobic due to the presence of measurable dissolved oxygen in the bulk solution, anaerobic reactions (including methanogenesis) can occur in microsites within the peat. The peat-based substrate acts not only as a long term electron donor as it degrades but also acts as a strong sorbent. This is important in intermittently loaded systems in which a large initial pulse of MC can be temporarily retarded on the peat matrix and then slowly degraded as they desorb<ref name="FullerEtAl2009"/><ref name="SchaeferEtAl2005"/>. This increased residence time enhances the biotransformation of energetics and promotes the immobilization and further degradation of breakdown products. Abiotic degradation reactions are also likely enhanced by association with the organic-rich peat (e.g., via electron shuttling reactions of [[Wikipedia: Humic substance | humics]])<ref>Roden, E.E., Kappler, A., Bauer, I., Jiang, J., Paul, A., Stoesser, R., Konishi, H., Xu, H., 2010. Extracellular electron transfer through microbial reduction of solid-phase humic substances. Nature Geoscience, 3, pp. 417-421. [https://doi.org/10.1038/ngeo870 doi: 10.1038/ngeo870]</ref>.
  
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* '''Metal Plating & Etching:''' Corrosion prevention, mechanical wear reduction, aesthetic enhancement, surfactant, wetting agent/fume suppressant for chrome, copper, nickel and tin electroplating, and post-plating cleaner<ref name="USEPA1996">US Environmental Protection Agency (USEPA), 1996. Emission Factor Documentation for AP-42, Section 12.20. Office of Air Quality Planning and Standards, Emission Factor and Inventory Group, Research Triangle Park, NC.  [[Media: USEPA1996.pdf | Report.pdf]]</ref><ref name="Riordan1998">Riordan, B.J., Karamchandanl, R.T., Zitko, L.J., and Cushnie Jr., G.C., 1998.  Capsule Report: Hard Chrome Fume Suppressants and Control Technologies. Center for Environmental Research Information, National Risk Management Research Laboratory, Office of Research and Development. EPA/625/R-98/002  [https://cfpub.epa.gov/si/si_public_record_Report.cfm?Lab=NRMRL&dirEntryID=115419 Website]&nbsp;&nbsp; [[Media: Riordan1998.pdf | Report.pdf]]</ref><ref name="Kissa2001"/><ref name="Prevedouros2006"/><ref name="USEPA2009a">US Environmental Protection Agency (USEPA), 2009. PFOS Chromium Electroplater Study. US EPA – Region 5, Chicago, IL.  [[Media: USEPA2009a.pdf | Report.pdf]]</ref><ref name="UNEP2011"/><ref name="OSHA2013">Occupational Safety and Health Agency (OSHA), 2013. Fact Sheet: Controlling Hexavalent Chromium Exposures during Electroplating. United States Department of Labor.  [[Media: OSHA2013.pdf | Report.pdf]]</ref><ref name="KEMI2015"/><ref name="DEPA2015">Danish Environmental Protection Agency, 2015. Alternatives to perfluoroalkyl and polyfluoroalkyl substances (PFAS) in textiles. [[Media: DEPA2015.pdf | Report.pdf]]</ref>
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===Soybean Oil===
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Modeling has indicated that peat moss amended with crude soybean oil would significantly reduce the flux of dissolved TNT, RDX, and HMX through the vadose zone to groundwater compared to a non-treated soil (see [https://serdp-estcp.mil/projects/details/20e2f05c-fd50-4fd3-8451-ba73300c7531 ESTCP ER-200434]). The technology was validated in field soil plots, showing a greater than 500-fold reduction in the flux of dissolved RDX from macroscale Composition B detonation residues compared to a non-treated control plot<ref name="FullerEtAl2009"/>. Laboratory testing and modeling indicated that the addition of soybean oil increased the biotransformation rates of RDX and HMX at least 10-fold compared to rates observed with peat moss alone<ref name="SchaeferEtAl2005"/>. Subsequent experiments also demonstrated the effectiveness of the amended peat moss material for stimulating perchlorate transformation when added to a highly contaminated soil (Fuller et al., unpublished data). These previous findings clearly demonstrate the effectiveness of peat-based materials for mitigating transport of both organic and inorganic energetic compounds through soil to groundwater.  
  
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* '''Wire Manufacturing:''' Coating and insulation<ref name="Kissa2001"/><ref name="vanderPutte2010">van der Putte, I., Murin, M., van Velthoven, M., and Affourtit, F., 2010. Analysis of the risks arising from the industrial use of Perfluorooctanoic acid (PFOA) and Ammonium Perfluorooctanoate (APFO) and from their use in consumer articles. Evaluation of the risk reduction measures for potential restrictions on the manufacture, placing on the market and use of PFOA and APFO. RPS Advies, Delft, The Netherlands for European Commission Enterprise and Industry Directorate-General.   [https://ec.europa.eu/docsroom/documents/13037/attachments/1/translations/en/renditions/pdf Website]&nbsp;&nbsp; [[Media: vanderPutte2010.pdf | Report.pdf]]</ref><ref name="ASTSWMO2015">Association of State and Territorial Solid Waste Management Officials (ASTSWMO), 2015. Perfluorinated Chemicals (PFCs): Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) Information Paper. Remediation and Reuse Focus Group, Federal Facilities Research Center, Washington, D.C. Free download from: [https://clu-in.org/download/contaminantfocus/pops/POPs-ASTSWMO-PFCs-2015.pdf US EPA]&nbsp;&nbsp; [[Media:Deeb-Article_1-Table_2-L10-Provisional_Groundwater_Remediaton_Objectives_Class_I_Groundwater.pdf | Report.pdf]]</ref>  
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===Biochar===
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Recent reports have highlighted additional materials that, either alone, or in combination with electron donors such as peat moss and soybean oil, may further enhance the sorption and degradation of surface runoff contaminants, including both legacy energetics and [[Wikipedia: Insensitive_munition#Insensitive_high_explosives | insensitive high explosives (IHE)]].  For instance, [[Wikipedia: Biochar | biochar]], a type of black carbon, has been shown to not only sorb a wide range of organic and inorganic contaminants including MCs<ref>Ahmad, M., Rajapaksha, A.U., Lim, J.E., Zhang, M., Bolan, N., Mohan, D., Vithanage, M., Lee, S.S., Ok, Y.S., 2014. Biochar as a sorbent for contaminant management in soil and water: A review. Chemosphere, 99, pp. 19-33. [https://doi.org/10.1016/j.chemosphere.2013.10.071 doi: 10.1016/j.chemosphere.2013.10.071]</ref><ref>Mohan, D., Sarswat, A., Ok, Y.S., Pittman, C.U., 2014. Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent – A critical review. Bioresource Technology, 160, pp. 191-202. [https://doi.org/10.1016/j.biortech.2014.01.120 doi: 10.1016/j.biortech.2014.01.120]</ref><ref>Oh, S.-Y., Seo, Y.-D., Jeong, T.-Y., Kim, S.-D., 2018. Sorption of Nitro Explosives to Polymer/Biomass-Derived Biochar. Journal of Environmental Quality, 47(2), pp. 353-360. [https://doi.org/10.2134/jeq2017.09.0357 doi: 10.2134/jeq2017.09.0357]</ref><ref>Xie, T., Reddy, K.R., Wang, C., Yargicoglu, E., Spokas, K., 2015. Characteristics and Applications of Biochar for Environmental Remediation: A Review. Critical Reviews in Environmental Science and Technology, 45(9), pp. 939-969. [https://doi.org/10.1080/10643389.2014.924180 doi: 10.1080/10643389.2014.924180]</ref>, but also to facilitate their degradation<ref>Oh, S.-Y., Cha, D.K., Kim, B.-J., Chiu, P.C., 2002. Effect of adsorption to elemental iron on the transformation of 2,4,6-trinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine in solution. Environmental Toxicology and Chemistry, 21(7), pp. 1384-1389. [https://doi.org/10.1002/etc.5620210708 doi: 10.1002/etc.5620210708]</ref><ref>Ye, J., Chiu, P.C., 2006. Transport of Atomic Hydrogen through Graphite and its Reaction with Azoaromatic Compounds. Environmental Science and Technology, 40(12), pp. 3959-3964. [https://doi.org/10.1021/es060038x doi: 10.1021/es060038x]</ref><ref name="OhChiu2009">Oh, S.-Y., Chiu, P.C., 2009. Graphite- and Soot-Mediated Reduction of 2,4-Dinitrotoluene and Hexahydro-1,3,5-trinitro-1,3,5-triazine. Environmental Science and Technology, 43(18), pp. 6983-6988. [https://doi.org/10.1021/es901433m doi: 10.1021/es901433m]</ref><ref name="OhEtAl2013">Oh, S.-Y., Son, J.-G., Chiu, P.C., 2013. Biochar-mediated reductive transformation of nitro herbicides and explosives. Environmental Toxicology and Chemistry, 32(3), pp. 501-508. [https://doi.org/10.1002/etc.2087 doi: 10.1002/etc.2087]&nbsp;&nbsp; [[Media: OhEtAl2013.pdf | Open Access Article.pdf]]</ref><ref name="XuEtAl2010">Xu, W., Dana, K.E., Mitch, W.A., 2010. Black Carbon-Mediated Destruction of Nitroglycerin and RDX by Hydrogen Sulfide. Environmental Science and Technology, 44(16), pp. 6409-6415. [https://doi.org/10.1021/es101307n doi: 10.1021/es101307n]</ref><ref>Xu, W., Pignatello, J.J., Mitch, W.A., 2013. Role of Black Carbon Electrical Conductivity in Mediating Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) Transformation on Carbon Surfaces by Sulfides. Environmental Science and Technology, 47(13), pp. 7129-7136. [https://doi.org/10.1021/es4012367 doi: 10.1021/es4012367]</ref>. Depending on the source biomass and [[Wikipedia: Pyrolysis| pyrolysis]] conditions, biochar can possess a high [[Wikipedia: Specific surface area | specific surface area]] (on the order of several hundred m<small><sup>2</sup></small>/g)<ref>Zhang, J., You, C., 2013. Water Holding Capacity and Absorption Properties of Wood Chars. Energy and Fuels, 27(5), pp. 2643-2648. [https://doi.org/10.1021/ef4000769 doi: 10.1021/ef4000769]</ref><ref>Gray, M., Johnson, M.G., Dragila, M.I., Kleber, M., 2014. Water uptake in biochars: The roles of porosity and hydrophobicity. Biomass and Bioenergy, 61, pp. 196-205. [https://doi.org/10.1016/j.biombioe.2013.12.010 doi: 10.1016/j.biombioe.2013.12.010]</ref> and hence a high sorption capacity.  Biochar and other black carbon also exhibit especially high affinity for [[Wikipedia: Nitro compound | nitroaromatic compounds (NACs)]] including TNT and 2,4-dinitrotoluene (DNT)<ref>Sander, M., Pignatello, J.J., 2005. Characterization of Charcoal Adsorption Sites for Aromatic Compounds:  Insights Drawn from Single-Solute and Bi-Solute Competitive Experiments. Environmental Science and Technology, 39(6), pp. 1606-1615. [https://doi.org/10.1021/es049135l doi: 10.1021/es049135l]</ref><ref name="ZhuEtAl2005">Zhu, D., Kwon, S., Pignatello, J.J., 2005. Adsorption of Single-Ring Organic Compounds to Wood Charcoals Prepared Under Different Thermochemical Conditions. Environmental Science and Technology 39(11), pp. 3990-3998. [https://doi.org/10.1021/es050129e doi: 10.1021/es050129e]</ref><ref name="ZhuPignatello2005">Zhu, D., Pignatello, J.J., 2005. Characterization of Aromatic Compound Sorptive Interactions with Black Carbon (Charcoal) Assisted by Graphite as a Model. Environmental Science and Technology, 39(7), pp. 2033-2041. [https://doi.org/10.1021/es0491376 doi: 10.1021/es0491376]</ref>. This is due to the strong [[Wikipedia: Pi-interaction | ''&pi;-&pi;'' electron donor-acceptor interactions]] between electron-rich graphitic domains in black carbon and the electron-deficient aromatic ring of the NAC<ref name="ZhuEtAl2005"/><ref name="ZhuPignatello2005"/>. These characteristics make biochar a potentially effective, low cost, and sustainable sorbent for removing MC and other contaminants from surface runoff and retaining them for subsequent degradation ''in situ''.
  
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* '''Industrial Surfactants, Resins, Molds, Plastics:''' Manufacture of plastics and fluoropolymers, rubber, and compression mold release coatings; plumbing fluxing agents; fluoroplastic coatings, composite resins, and flame retardant for polycarbonate<ref name="Kissa2001"/><ref name="Renner2001">Renner, R., 2001. Growing Concern Over Perfluorinated Chemicals. Environmental Science and Technology, 35(7), pp. 154A-160A. [https://doi.org/10.1021/es012317k DOI: 10.1021/es012317k]&nbsp;&nbsp; [[Media: Renner2001.pdf | Open access article.]]</ref><ref name="Poulsen2005"/><ref name="Fricke2005">Fricke, M. and Lahl, U., 2005. Risk Evaluation of Perfluorinated Surfactants as Contribution to the current Debate on the EU Commission’s REACH Document. Umweltwissenschaften und Schadstoff-Forschung (UWSF), 17(1), pp. 36-49. [https://doi.org/10.1007/BF03038694 DOI: 10.1007/BF03038694]</ref><ref name="Prevedouros2006"/><ref name="Skutlarek2006">Skutlarek, D., Exner, M. and Färber, H., 2006. Perfluorinated Surfactants in Surface and Drinking Waters. Environmental Science and Pollution Research International, 13(5), pp. 299-307.  [https://doi.org/10.1065/espr2006.07.326 DOI: 10.1065/espr2006.07.326]&nbsp;&nbsp; Free download from: [https://www.researchgate.net/profile/Dirk_Skutlarek/publication/6729263_Perfluorinated_surfactants_in_surface_and_drinking_waters/links/0deec52049b9cba2e4000000.pdf ResearchGate]</ref><ref name="vanderPutte2010"/><ref name="Buck2011"/><ref name="Herzke2012"/><ref name="Kotthoff2015"/><ref name="Chemours2010">Chemours, 2010. The History of Teflon Fluoropolymers. [https://www.teflon.com/en/news-events/history Website]</ref>
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Furthermore, black carbon such as biochar can promote abiotic and microbial transformation reactions by facilitating electron transfer.  That is, biochar is not merely a passive sorbent for contaminants, but also a redox mediator for their degradation.  Biochar can promote contaminant degradation through two different mechanisms: electron conduction and electron storage<ref>Sun, T., Levin, B.D.A., Guzman, J.J.L., Enders, A., Muller, D.A., Angenent, L.T., Lehmann, J., 2017. Rapid electron transfer by the carbon matrix in natural pyrogenic carbon. Nature Communications, 8, Article 14873. [https://doi.org/10.1038/ncomms14873 doi: 10.1038/ncomms14873]&nbsp;&nbsp; [[Media: SunEtAl2017.pdf | Open Access Article.pdf]]</ref>.  
  
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* '''Photolithography, Semiconductor Industry:''' Photoresists, top anti-reflective coatings, bottom anti-reflective coatings, and etchants, with other uses including surfactants, wetting agents, and photo-acid generation<ref name="Choi2005">Choi, D.G., Jeong, J.H., Sim, Y.S., Lee, E.S., Kim, W.S. and Bae, B.S., 2005. Fluorinated Organic− Inorganic Hybrid Mold as a New Stamp for Nanoimprint and Soft Lithography. Langmuir, 21(21), pp. 9390-9392. [https://doi.org/10.1021/la0513205 DOI: 10.1021/la0513205]</ref><ref name="Rolland2004">Rolland, J.P., Van Dam, R.M., Schorzman, D.A., Quake, S.R., and DeSimone, J.M., 2004. Solvent-Resistant Photocurable “Liquid Teflon” for Microfluidic Device Fabrication. Journal of the American Chemical Society, 126(8), pp. 2322-2323. [https://doi.org/10.1021/ja031657y DOI: 10.1021/ja031657y]</ref><ref name="Brooke2004"/><ref name="vanderPutte2010"/><ref name="UNEP2011"/><ref name="Herzke2012"/>
+
First, the microscopic graphitic regions in biochar can adsorb contaminants like NACs strongly, as noted above, and also conduct reducing equivalents such as electrons and atomic hydrogen to the sorbed contaminants, thus promoting their reductive degradation.  This catalytic process has been demonstrated for TNT, DNT, RDX, HMX, and [[Wikipedia: Nitroglycerin | nitroglycerin]]<ref>Oh, S.-Y., Cha, D.K., Chiu, P.C., 2002. Graphite-Mediated Reduction of 2,4-Dinitrotoluene with Elemental Iron. Environmental Science and Technology, 36(10), pp. 2178-2184. [https://doi.org/10.1021/es011474g doi: 10.1021/es011474g]</ref><ref>Oh, S.-Y., Cha, D.K., Kim, B.J., Chiu, P.C., 2004. Reduction of Nitroglycerin with Elemental Iron:  Pathway, Kinetics, and Mechanisms. Environmental Science and Technology, 38(13), pp. 3723-3730. [https://doi.org/10.1021/es0354667 doi: 10.1021/es0354667]</ref><ref>Oh, S.-Y., Cha, D.K., Kim, B.J., Chiu, P.C., 2005. Reductive transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, and methylenedinitramine with elemental iron. Environmental Toxicology and Chemistry, 24(11), pp. 2812-2819. [https://doi.org/10.1897/04-662R.1 doi: 10.1897/04-662R.1]</ref><ref name="OhChiu2009"/><ref name="XuEtAl2010"/> and is expected to occur also for IHE including DNAN and NTO.
  
−
==Class B Firefighting Foams==
+
Second, biochar contains in its structure abundant redox-facile functional groups such as [[Wikipedia: Quinone | quinones]] and [[Wikipedia: Hydroquinone | hydroquinones]], which are known to accept and donate electrons reversibly.  Depending on the biomass and pyrolysis temperature, certain biochar can possess a rechargeable electron storage capacity (i.e., reversible electron accepting and donating capacity) on the order of several millimoles e<small><sup>–</sup></small>/g<ref>Klüpfel, L., Keiluweit, M., Kleber, M., Sander, M., 2014. Redox Properties of Plant Biomass-Derived Black Carbon (Biochar). Environmental Science and Technology, 48(10), pp. 5601-5611. [https://doi.org/10.1021/es500906d doi: 10.1021/es500906d]</ref><ref>Prévoteau, A., Ronsse, F., Cid, I., Boeckx, P., Rabaey, K., 2016. The electron donating capacity of biochar is dramatically underestimated. Scientific Reports, 6, Article 32870. [https://doi.org/10.1038/srep32870 doi: 10.1038/srep32870]&nbsp;&nbsp; [[Media: PrevoteauEtAl2016.pdf | Open Access Article.pdf]]</ref><ref>Xin, D., Xian, M., Chiu, P.C., 2018. Chemical methods for determining the electron storage capacity of black carbon. MethodsX, 5, pp. 1515-1520. [https://doi.org/10.1016/j.mex.2018.11.007 doi: 10.1016/j.mex.2018.11.007]&nbsp;&nbsp; [[Media: XinEtAl2018.pdf | Open Access Article.pdf]]</ref>. This means that when "charged", biochar can provide electrons for either abiotic or biotic degradation of reducible compounds such as MC. The abiotic reduction of DNT and RDX mediated by biochar has been demonstrated<ref name="OhEtAl2013"/> and similar reactions are expected to occur for DNAN and NTO as well. Recent studies have shown that the electron storage capacity of biochar is also accessible to microbes.  For example, soil bacteria such as [[Wikipedia: Geobacter | ''Geobacter'']] and [[Wikipedia: Shewanella | ''Shewanella'']] species can utilize oxidized (or "discharged") biochar as an electron acceptor for the oxidation of organic substrates such as lactate and acetate<ref>Kappler, A., Wuestner, M.L., Ruecker, A., Harter, J., Halama, M., Behrens, S., 2014. Biochar as an Electron Shuttle between Bacteria and Fe(III) Minerals. Environmental Science and Technology Letters, 1(8), pp. 339-344. [https://doi.org/10.1021/ez5002209 doi: 10.1021/ez5002209]</ref><ref name="SaquingEtAl2016">Saquing, J.M., Yu, Y.-H., Chiu, P.C., 2016. Wood-Derived Black Carbon (Biochar) as a Microbial Electron Donor and Acceptor. Environmental Science and Technology Letters, 3(2), pp. 62-66. [https://doi.org/10.1021/acs.estlett.5b00354 doi: 10.1021/acs.estlett.5b00354]</ref> and reduced (or "charged") biochar as an electron donor for the reduction of nitrate<ref name="SaquingEtAl2016"/>. This is significant because, through microbial access of stored electrons in biochar, contaminants that do not sorb strongly to biochar can still be degraded.  
−
Aqueous film forming foam (AFFF) and other fluorinated Class B firefighting foams are another important source of PFAS to the environment, especially in military and aviation settings. [[Wikipedia: Firefighting foam | Class B firefighting foams]] have been used since the 1960s to extinguish flammable liquid hydrocarbon fires and for vapor suppression. These foams contain complex and variable mixtures of PFAS that act as surfactants. Fluorinated surfactants are both hydrophobic and oleophobic (oil-repelling), as well as thermally stable, chemically stable, and highly surface active<ref name="Moody1999">Moody, C.A. and Field, J.A., 1999. Determination of Perfluorocarboxylates in Groundwater Impacted by Fire-Fighting Activity. Environmental Science and Technology, 33(16), pp. 2800-2806. [https://pubs.acs.org/doi/10.1021/es981355%2B DOI: 10.1021/es981355+]</ref>. These properties make them uniquely suited to fighting hydrocarbon fuel fires. Use of fluorinated Class B foams is prevalent and is a major source of PFAS to the environment. Release to the environment typically occurs during firefighting operations, firefighter training, apparatus testing, or leakage during storage. Research into fluorine-free alternatives is underway and Congressional pressure is leading towards banning fluorinated Class B firefighting foams in the United States.
 
  
−
[[File: ChiangSalterBlanc1w2Fig1.png | thumb | 500px | Figure 1. Types of Class B firefighting foams. Reproduced from ITRC, 2020; original figure courtesy of S. Thomas, Wood PLC, used with permission.]]
+
Similar to nitrate, perchlorate and other relatively water-soluble energetic compounds (e.g., NTO and NQ) may also be similarly transformed using reduced biochar as an electron donor. Unlike other electron donors, biochar can be recharged through biodegradation of organic substrates<ref name="SaquingEtAl2016"/> and thus can serve as a long-lasting sorbent and electron repository in soil. Similar to peat moss, the high porosity and surface area of biochar not only facilitate contaminant sorption but also create anaerobic reducing microenvironments in its inner pores, where reductive degradation of energetic compounds can take place.
−
When discussing the relationship between firefighting foams and sources of PFAS to the environment, the emphasis is typically on AFFF; however, many different types of Class B firefighting foams exist. These may or may not be fluorinated (contain PFAS). Class B foams are used to extinguish Class B fires, that is, those involving flammable liquids. Fluorinated Class B foams spread across the surface of the flammable liquid forming a thin film and extinguish fires by (1) excluding air from the flammable vapors, (2) suppressing vapor release, (3) physically separating the flames from the fuel source, and (4) cooling the fuel surface and surrounding metal surfaces<ref name="NationalFoam">National Foam, no date. A Firefighter’s Guide to Foam. [http://foamtechnology.us/Firefighters.pdf Website]&nbsp;&nbsp; [[Media: NationalFoam.pdf | Report.pdf]]</ref>. From a PFAS perspective, Class B firefighting foams can be divided into two broad categories: fluorinated foams (that contain PFAS) and fluorine-free foams (that do not contain PFAS)<ref name="ITRC2020"/>. This distinction and examples of each type are shown in Figure 1.  
 
  
−
AFFF was developed by the US Navy in the 1960s and in 1969, the US Department of Defense (DoD) issued military specification MIL-F-24385 listing firefighting performance requirements for all AFFF used within the US DoD<ref name="ITRC2020"/><ref name="Navy1969">US Navy, 1969. Military Specification MIL-F-24385(NAVY). Fire Extinguishing Agent, Aqueous Film Forming Foam (AFFF) Liquid Concentrate, Six Percent, for Fresh and Sea Water. Department of Defense, Hyattsville, Maryland. [https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=17270 Website]&nbsp;&nbsp; [[Media: milspecAFFF1969.pdf | Report.pdf]]</ref><ref name="Navy2020">US Navy, 2020. Performance Specification MIL-PRF-24385F(SH) with Amendment 4. Fire Extinguishing Agent, Aqueous Film Forming Foam (AFFF) Liquid Concentrate for Fresh and Sea Water. Department of Defense, Washington, DC. [https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=17270 Website]&nbsp;&nbsp; [[Media: milspecAFFF2020.pdf | Report.pdf]]</ref>. These performance standards are often referred to as “Mil-Spec.” Products that meet the Mil-Spec have been added to the US DoD [https://qpldocs.dla.mil/ Qualified Product Listing (QPL)]. In 2006 the US Federal Aviation Administration (FAA) also began requiring that 14-CFR-139-certified commercial airports purchase Mil-Spec compliant AFFF only. Because the US DoD and FAA have been the primary purchasers of AFFF, development of AFFF product mixtures has historically been performance-driven (to comply with the Mil-Spec) rather than formula-driven (the specific PFAS mixtures utilized have varied over time and by manufacturer). Multiple manufacturers in the US and throughout the world produce or have produced AFFF concentrate<ref name="ITRC2020"/>. AFFF concentrate is or has been available in 1%, 3%, or 6% formulations, where the percentage designates the recommended percentage of concentrate to be mixed into water during application.  
+
===Other Sorbents===
 +
Chitin and unmodified cellulose were predicted by [[Wikipedia: Density functional theory | Density Functional Theory]] methods to be favorable for absorption of NTO and NQ, as well as the legacy explosives<ref>Todde, G., Jha, S.K., Subramanian, G., Shukla, M.K., 2018. Adsorption of TNT, DNAN, NTO, FOX7, and NQ onto Cellulose, Chitin, and Cellulose Triacetate. Insights from Density Functional Theory Calculations. Surface Science, 668, pp. 54-60. [https://doi.org/10.1016/j.susc.2017.10.004 doi: 10.1016/j.susc.2017.10.004]&nbsp;&nbsp; [[Media: ToddeEtAl2018.pdf | Open Access Manuscript.pdf]]</ref>. Cationized cellulosic materials (e.g., cotton, wood shavings) have been shown to effectively remove negatively charged energetics like perchlorate and NTO from solution<ref name="FullerEtAl2022">Fuller, M.E., Farquharson, E.M., Hedman, P.C., Chiu, P., 2022. Removal of munition constituents in stormwater runoff: Screening of native and cationized cellulosic sorbents for removal of insensitive munition constituents NTO, DNAN, and NQ, and legacy munition constituents HMX, RDX, TNT, and perchlorate. Journal of Hazardous Materials, 424(C), Article 127335. [https://doi.org/10.1016/j.jhazmat.2021.127335 doi: 10.1016/j.jhazmat.2021.127335]&nbsp;&nbsp; [[Media: FullerEtAl2022.pdf | Open Access Manuscript.pdf]]</ref>. A substantial body of work has shown that modified cellulosic biopolymers can also be effective sorbents for removing metals from solution<ref>Burba, P., Willmer, P.G., 1983. Cellulose: a biopolymeric sorbent for heavy-metal traces in waters. Talanta, 30(5), pp. 381-383. [https://doi.org/10.1016/0039-9140(83)80087-3 doi: 10.1016/0039-9140(83)80087-3]</ref><ref>Brown, P.A., Gill, S.A., Allen, S.J., 2000. Metal removal from wastewater using peat. Water Research, 34(16), pp. 3907-3916. [https://doi.org/10.1016/S0043-1354(00)00152-4 doi: 10.1016/S0043-1354(00)00152-4]</ref><ref>O’Connell, D.W., Birkinshaw, C., O’Dwyer, T.F., 2008. Heavy metal adsorbents prepared from the modification of cellulose: A review. Bioresource Technology, 99(15), pp. 6709-6724. [https://doi.org/10.1016/j.biortech.2008.01.036 doi: 10.1016/j.biortech.2008.01.036]</ref><ref>Wan Ngah, W.S., Hanafiah, M.A.K.M., 2008. Removal of heavy metal ions from wastewater by chemically modified plant wastes as adsorbents: A review. Bioresource Technology, 99(10), pp. 3935-3948. [https://doi.org/10.1016/j.biortech.2007.06.011 doi: 10.1016/j.biortech.2007.06.011]</ref> and therefore will also likely be applicable for some of the metals that may be found in surface runoff at firing ranges.
  
−
The specific mixtures of PFAS found in AFFF have varied by manufacturer and over time due to differences in production processes and voluntary formula changes. AFFF formulations can generally be grouped into three categories<ref name="ITRC2020"/>:
+
==Technology Evaluation==
 +
Based on the properties of the target munition constituents, a combination of materials was expected to yield the best results to facilitate the sorption and subsequent biotic and abiotic degradation of the contaminants.
  
−
* '''Legacy Perfluorooctane Sulfonate (PFOS) AFFF''' This type of AFFF was manufactured exclusively by 3M under the brand name “Lightwater” from the late 1960s until 2002 using the ECF production process. They contain PFOS and perflouroalkane sulfonates (PFSAs) such as perfluorohexane sulfonate (PFHxS)<ref name="ITRC2020"/><ref name="Backe2013"/>. Legacy PFOS AFFF produced by ECF were voluntarily phased out in 2002, however, use of stockpiled product was permitted after that date<ref name="ITRC2020"/>.  
+
===Sorbents===
 +
{| class="wikitable" style="margin-right: 30px; margin-left: auto; float:left; text-align:center;"
 +
|+Table 1. [[Wikipedia: Freundlich equation | Freundlich]] and [[Wikipedia: Langmuir adsorption model | Langmuir]] adsorption parameters for insensitive and legacy explosives
 +
|-
 +
! rowspan="2" | Compound
 +
! colspan="5" | Freundlich
 +
! colspan="5" | Langmuir
 +
|-
 +
! <small>Parameter</small> !! Peat !! <small>CAT</small> Pine !! <small>CAT</small> Burlap !! <small>CAT</small> Cotton !! <small>Parameter</small> !! Peat !! <small>CAT</small> Pine !! <small>CAT</small> Burlap !! <small>CAT</small> Cotton
 +
|-
 +
| colspan="12" style="background-color:white;" |
 +
|-
 +
! rowspan="3" | HMX
 +
! ''K<sub>f</sub>''
 +
| 0.08 +/- 0.00 || -- || -- || --
 +
! ''q<sub>m</sub>'' <small>(mg/g)</small>
 +
| 0.29 +/- 0.04 || -- || -- || --
 +
|-
 +
! ''n''
 +
| 1.70 +/- 0.18 || -- || -- || --
 +
! ''b'' <small>(L/mg)</small>
 +
| 0.39 +/- 0.09 || -- || -- || --
 +
|-
 +
! ''r<sup><small>2</small></sup>''
 +
| 0.91 || -- || -- || --
 +
! ''r<sup><small>2</small></sup>''
 +
| 0.93 || -- || -- || --
 +
|-
 +
| colspan="12" style="background-color:white;" |
 +
|-
 +
! rowspan="3" | RDX
 +
! ''K<sub>f</sub>''
 +
| 0.11 +/- 0.02 || -- || -- || --
 +
! ''q<sub>m</sub>'' <small>(mg/g)</small>
 +
| 0.38 +/- 0.05 || -- || -- || --
 +
|-
 +
! ''n''
 +
| 2.75 +/- 0.63 || -- || -- || --
 +
! ''b'' <small>(L/mg)</small>
 +
| 0.23 +/- 0.08 || -- || -- || --
 +
|-
 +
! ''r<sup><small>2</small></sup>''
 +
| 0.69 || -- || -- || --
 +
! ''r<sup><small>2</small></sup>''
 +
| 0.69 || -- || -- || --
 +
|-
 +
| colspan="12" style="background-color:white;" |
 +
|-
 +
! rowspan="3" | TNT
 +
! ''K<sub>f</sub>''
 +
| 1.21 +/- 0.15 || 1.02 +/- 0.04 || 0.36 +/- 0.02 || --
 +
! ''q<sub>m</sub>'' <small>(mg/g)</small>
 +
| 3.63 +/- 0.18 || 1.26 +/- 0.06 || -- || --
 +
|-
 +
! ''n''
 +
| 2.78 +/- 0.67 || 4.01 +/- 0.44 || 1.59 +/- 0.09 || --
 +
! ''b'' <small>(L/mg)</small>
 +
| 0.89 +/- 0.13 || 0.76 +/- 0.10 || -- || --
 +
|-
 +
! ''r<sup><small>2</small></sup>''
 +
| 0.81 || 0.93 || 0.98 || --
 +
! ''r<sup><small>2</small></sup>''
 +
| 0.97 || 0.97 || -- || --
 +
|-
 +
| colspan="12" style="background-color:white;" |
 +
|-
 +
! rowspan="3" | NTO
 +
! ''K<sub>f</sub>''
 +
| -- || 0.94 +/- 0.05 || 0.41 +/- 0.05 || 0.26 +/- 0.06
 +
! ''q<sub>m</sub>'' <small>(mg/g)</small>
 +
| -- || 4.07 +/- 0.26 || 1.29 +/- 0.12 || 0.83 +/- .015
 +
|-
 +
! ''n''
 +
| -- || 1.61 +/- 0.11 || 2.43 +/- 0.41 || 2.53 +/- 0.76
 +
! ''b'' <small>(L/mg)</small>
 +
| -- || 0.30 +/- 0.04 || 0.36 +/- 0.08 || 0.30 +/- 0.15
 +
|-
 +
! ''r<sup><small>2</small></sup>''
 +
| -- || 0.97 || 0.82 || 0.57
 +
! ''r<sup><small>2</small></sup>''
 +
| -- || 0.99 || 0.89 || 0.58
 +
|-
 +
| colspan="12" style="background-color:white;" |
 +
|-
 +
! rowspan="3" | DNAN
 +
! ''K<sub>f</sub>''
 +
| 0.38 +/- 0.05 || 0.01 +/- 0.01 || -- || --
 +
! ''q<sub>m</sub>'' <small>(mg/g)</small>
 +
| 2.57 +/- 0.33 || -- || -- || --
 +
|-
 +
! ''n''
 +
| 1.71 +/- 0.20 || 0.70 +/- 0.13 || -- || --
 +
! ''b'' <small>(L/mg)</small>
 +
| 0.13 +/- 0.03 || -- || -- || --
 +
|-
 +
! ''r<sup><small>2</small></sup>''
 +
| 0.89 || 0.76 || -- || --
 +
! ''r<sup><small>2</small></sup>''
 +
| 0.92 || -- || -- || --
 +
|-
 +
| colspan="12" style="background-color:white;" |
 +
|-
 +
! rowspan="3" | ClO<sub>4</sup>
 +
! ''K<sub>f</sub>''
 +
| -- || 1.54 +/- 0.06 || 0.53 +/- 0.03 || --
 +
! ''q<sub>m</sub>'' <small>(mg/g)</small>
 +
| -- || 3.63 +/- 0.18 || 1.26 +/- 0.06 || --
 +
|-
 +
! ''n''
 +
| -- || 2.42 +/- 0.16 || 2.42 +/- 0.26 || --
 +
! ''b'' <small>(L/mg)</small>
 +
| -- || 0.89 +/- 0.13 || 0.76 +/- 0.10 || --
 +
|-
 +
! ''r<sup><small>2</small></sup>''
 +
| -- || 0.97 || 0.92 || --
 +
! ''r<sup><small>2</small></sup>''
 +
| -- || 0.97 || 0.97 || --
 +
|-
 +
| colspan="12" style="text-align:left; background-color:white;" |<small>Notes:</small><br /><big>'''--'''</big> <small>Indicates the algorithm failed to converge on the model fitting parameters, therefore there was no successful model fit.<br />'''CAT''' Indicates cationized material.</small>
 +
|}
  
−
* '''Legacy fluorotelomer AFFF''' This group consists of AFFF manufactured and sold in the U.S. from the 1970s until 2016 and includes all brands that were produced using a process known as fluorotelomerization (FT). The FT manufacturing process produces polyfluorinated substances that can degrade in the environment to perfluoroalkyl substances (specifically PFAAs) including Perfluorooctanoic Acid (PFOA). Polyfluoroalkyl substances that degrade to create terminal PFAAs are referred to as “precursors” <ref name="ITRC2020"/>.
+
The&nbsp;materials&nbsp;screened&nbsp;included [[Wikipedia: Sphagnum | ''Sphagnum'' peat moss]], primarily for sorption of HMX, RDX, TNT, and DNAN, as well as [[Wikipedia: Cationization of cotton | cationized cellulosics]] for removal of perchlorate and NTO.  The cationized cellulosics that were examined included: pine sawdust, pine shavings, aspen shavings, cotton linters (fine, silky fibers which adhere to cotton seeds after ginning), [[Wikipedia: Chitin | chitin]], [[Wikipedia: Chitosan |  chitosan]], burlap (landscaping grade), [[Wikipedia: Coir | coconut coir]], raw cotton, raw organic cotton, cleaned raw cotton, cotton fabric, and commercially cationized fabrics.
−
 
−
* '''Modern fluorotelomer AFFF''' This group consists of AFFF developed in response to the USEPA 2010-2015 voluntary PFOA Stewardship Program<ref name="USEPA2018">US Environmental Protection Agency (USEPA), 2018. Fact Sheet: 2010/2015 PFOA Stewardship Program. [https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/fact-sheet-20102015-pfoa-stewardship-program Website]</ref>, which asked companies to commit to first reducing and then eliminating the following: PFOA, precursors that can break down to PFOA, and related chemicals from facility emissions and products. In response, manufacturers began producing only short-chain fluorosurfactants targeting fluorotelomer PFAS with 6 carbons per chain (C6), rather than the traditional long-chain fluorosurfactants (8 or more carbons per chain). These short-chain PFAS do not breakdown in the environment to PFOS or PFOA<ref name="ITRC2020"/>. Their toxicity in comparison to long-chain fluorosurfactants is a topic of current research.
 
−
 
 
−
In the US, AFFF users including the US DoD (predominantly the Navy and Air Force), civilian airports, oil refineries, other petrochemical industries, and municipal fire departments<ref name="Darwin2011">Darwin, Robert L. 2011. Estimated Inventory of PFOS-based Aqueous Film Forming Foam (AFFF). Fire Fighting Foam Coalition, Inc., Arlington, VA. [[Media:Darwin2011.pdf | Report.pdf]]</ref>. AFFF is used, for example, in fire fighting vehicles, in fixed fire suppression systems (including sprinklers and fixed spray systems in or at aircraft hangars, flammable liquid storage areas, engine hush houses, and fuel farms), and onboard military and commercial ships. Fluorinated Class B foams may be introduced to the environment through the following practices<ref name="ITRC2020"/>:
 
  
−
* low volume releases of foam concentrate during storage, transfer or operational requirements that mandate periodic equipment calibration
+
As shown in Table 1<ref name="FullerEtAl2022"/>, batch sorption testing indicated that a combination of Sphagnum peat moss and cationized pine shavings provided good removal of both the neutral organic energetics (HMX, RDX, TNT, DNAN) as well as the negatively charged energetics (perchlorate, NTO).
−
* moderate volume discharge of foam solution for apparatus testing and episodic discharge of AFFF-containing fire suppression systems within large aircraft hangars and buildings
 
−
* occasional, high-volume, broadcast discharge of foam solution for firefighting and fire suppression/prevention for emergency response
 
−
* periodic, high volume, broadcast discharge for fire training
 
−
* accidental leaks from foam distribution piping between storage and pumping locations, and from storage tanks and railcars
 
  
−
The DoD is currently replacing legacy, long-chain AFFF with modern, short-chain fluorotelomer AFFF and disposing of the legacy foams through incineration. While the PFAS included in modern fluorotelomer AFFF formulations are currently understood to be less toxic and less bioaccumulative than those used in legacy formulations, they are also environmentally persistent and can degrade to produce other PFAS that may pose environmental concerns<ref name="ITRC2020"/>. While fluorine free alternatives exist, they do not meet the current Mil-Spec<ref name="Navy2020"/> which requires that fluorine-based compounds be used. The US DoD is working to revise the Mil-Spec to allow fluorine-free foams, and several states have passed laws prohibiting the use of fluorinated Class B foams for training and prohibiting future manufacture, sale or distribution of fluorinated foams, with limited exceptions<ref name="Denton2019">Denton, Charles, 2019. Expert Focus: US states outpace EPA on PFAS firefighting foam laws. Chemical Watch. [https://chemicalwatch.com/78075/expert-focus-us-states-outpace-epa-on-pfas-firefighting-foam-laws Website]</ref> (e.g., WA Rev Code § 70.75A.005 (2019); VA § 9.1-207.1 (2019)). Additionally, a bill passed in the US Congress in 2018 directs the FAA to allow fluorine-free foams for use at commercial airports<ref name="FAA2018">FAA Reauthorization Act of 2018. US Public Law No: 115-254 (10/05/2018). [https://www.congress.gov/bill/115th-congress/house-bill/302/text?r=1 Website]&nbsp;&nbsp; [[Media: FAA2018.pdf | Report.pdf]]</ref>. Research into the development of Mil-Spec compliant fluorine-free foams that will be compatible with existing AFFF and supporting equipment is ongoing and includes the following:
+
===Slow Release Carbon Sources===
 +
{| class="wikitable" style="margin-right: 30px; margin-left: auto; float:left; text-align:center;"
 +
|+Table 2. Slow-release Carbon Sources
 +
|-
 +
! Material !! Abbreviation !! Commercial Source !! Notes
 +
|-
 +
| polylactic acid || PLA6 || [https://www.goodfellow.com/usa?srsltid=AfmBOoqEiqIbrvWb1Hn1Bc090efBUUfg6V4N3Vrn6ytajHMJR-FG1Ez- Goodfellow] || high molecular weight thermoplastic polyester
 +
|-
 +
| polylactic acid || PLA80 || [https://www.goodfellow.com/usa?srsltid=AfmBOoqEiqIbrvWb1Hn1Bc090efBUUfg6V4N3Vrn6ytajHMJR-FG1Ez- Goodfellow] || low molecular weight thermoplastic polyester
 +
|-
 +
| polyhydroxybutyrate || PHB || [https://www.goodfellow.com/usa?srsltid=AfmBOoqEiqIbrvWb1Hn1Bc090efBUUfg6V4N3Vrn6ytajHMJR-FG1Ez- Goodfellow] || bacterial polyester
 +
|-
 +
| polycaprolactone || PCL || [https://www.sarchemlabs.com/?hsa_acc=4540346154&hsa_cam=20281343997&hsa_grp&hsa_ad&hsa_src=x&hsa_tgt&hsa_kw&hsa_mt&hsa_net=adwords&hsa_ver=3&gad_source=1&gad_campaignid=21209931835 Sarchem Labs] || biodegradable polyester
 +
|-
 +
| polybutylene succinate || BioPBS || [https://us.mitsubishi-chemical.com/company/performance-polymers/ Mitsubishi Chemical Performance Polymers] || compostable bio-based product
 +
|-
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| sucrose ester of fatty acids || SEFA SP10 || [https://www.sisterna.com/ Sisterna] || food and cosmetics additive
 +
|-
 +
| sucrose ester of fatty acids || SEFA SP70 || [https://www.sisterna.com/ Sisterna] || food and cosmetics additive
 +
|}
  
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* Novel Fluorine-Free Replacement for Aqueous Film Forming Foam (Lead investigator: Dr. Joseph Tsang, Naval Air Warfare Center Weapons Divisions) [https://serdp-estcp.org/Program-Areas/Weapons-Systems-and-Platforms/Waste-Reduction-and-Treatment-in-DoD-Operations/WP-2737 SERDP/ESTCP Project WP-2737]
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A&nbsp;range&nbsp;of&nbsp;biopolymers&nbsp;widely used in the production of biodegradable plastics were screened for their ability to support aerobic and anoxic biodegradation of the target munition constituents. These compounds and their sources are listed in Table 2.
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* Fluorine-Free Aqueous Film Forming Foam (Lead investigator: Dr. John Payne, National Foam) [https://serdp-estcp.org/Program-Areas/Weapons-Systems-and-Platforms/Waste-Reduction-and-Treatment-in-DoD-Operations/WP-2738 SERDP/ESTCP Project WP-2738]
 
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* Fluorine-Free Foams with Oleophobic Surfactants and Additives for Effective Pool fire Suppression (Lead investigator: Dr. Ramagopal Ananth, U.S. Naval Research Laboratory) [https://serdp-estcp.org/Program-Areas/Weapons-Systems-and-Platforms/Waste-Reduction-and-Treatment-in-DoD-Operations/WP-2739 SERDP/ESTCP Project WP-2739]
 
  
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==Wastewater Treatment Plants==
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[[File: FullerFig3.png | thumb | 400 px | Figure 3. Schematic of interactions between biochar and munitions constituents]]
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Consumer and/or industrial uses of PFAS-containing materials results in the discharge of PFAS to industrial and municipal wastewater treatment plants (WWTPs). Conventional WWTP treatment processes remove less than 5% of PFAAs<ref name="Ahrens2011a"/><ref name="Schultz2006">Schultz, M.M., Higgins, C.P., Huset, C.A., Luthy, R.G., Barofsky, D.F., and Field, J.A., 2006. Fluorochemical Mass Flows in a Municipal Wastewater Treatment Facility. Environmental Science and Technology, 40(23), pp. 7350-7357. [https://doi.org/10.1021/es061025m DOI: 10.1021/es061025m]&nbsp;&nbsp; [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2556954/ Author Manuscript]</ref><ref name="MWRA2019">Michigan Waste and Recycling Association (MWRA), 2019. Statewide Study on Landfill Leachate PFOA and PFOS Impact on Water Resource Recovery Facility Influent, Second Revision.  [[Media: MWRA2019.pdf | Report.pdf]]</ref>. WWTPs, particularly those that receive industrial wastewater, are possible sources of PFAS release<ref name="Bossi2008">Bossi, R., Strand, J., Sortkjær, O. and Larsen, M.M., 2008. Perfluoroalkyl compounds in Danish wastewater treatment plants and aquatic environments. Environment International, 34(4), pp. 443-450. [https://doi.org/10.1016/j.envint.2007.10.002  DOI: 10.1016/j.envint.2007.10.002] Free download from: [https://www.academia.edu/download/43968517/Perfluoroalkyl_compounds_in_Danish_waste20160321-31116-esz4d1.pdf Academia.edu]</ref><ref name="Lin2014">Lin, A.Y.C., Panchangam, S.C., Tsai, Y.T., and Yu, T.H., 2014. Occurrence of perfluorinated compounds in the aquatic environment as found in science park effluent, river water, rainwater, sediments, and biotissues. Environmental Monitoring and Assessment, 186(5), pp. 3265-3275. [https://doi.org/10.1007/s10661-014-3617-9 DOI: 10.1007/s10661-014-3617-9]</ref><ref name="Ahrens2009">Ahrens, L., Felizeter, S., Sturm, R., Xie, Z. and Ebinghaus, R., 2009. Polyfluorinated compounds in waste water treatment plant effluents and surface waters along the River Elbe, Germany. Marine Pollution Bulletin, 58(9), pp.1326-1333. [https://doi.org/10.1016/j.marpolbul.2009.04.028 DOI: 10.1016/j.marpolbul.2009.04.028]&nbsp;&nbsp; [[Media:Ahrens2009.pdf | Author’s manuscript]]</ref>.
+
Multiple pure bacterial strains and mixed cultures were screened for their ability to utilize the solid biopolymers as a carbon source to support energetic compound transformation and degradation. Pure strains included the aerobic RDX degrader [[Wikipedia: Rhodococcus | ''Rhodococcus'']] species DN22 (DN22 henceforth)<ref name="ColemanEtAl1998">Coleman, N.V., Nelson, D.R., Duxbury, T., 1998. Aerobic biodegradation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) as a nitrogen source by a Rhodococcus sp., strain DN22. Soil Biology and Biochemistry, 30(8-9), pp. 1159-1167. [https://doi.org/10.1016/S0038-0717(97)00172-7 doi: 10.1016/S0038-0717(97)00172-7]</ref> and [[Wikipedia: Gordonia (bacterium)|''Gordonia'']] species KTR9 (KTR9 henceforth)<ref name="ColemanEtAl1998"/>, the anoxic RDX degrader [[Wikipedia: Pseudomonas fluorencens | ''Pseudomonas fluorencens'']] species I-C (I-C henceforth)<ref>Pak, J.W., Knoke, K.L., Noguera, D.R., Fox, B.G., Chambliss, G.H., 2000. Transformation of 2,4,6-Trinitrotoluene by Purified Xenobiotic Reductase B from Pseudomonas fluorescens I-C. Applied and Environmental Microbiology, 66(11), pp. 4742-4750. [https://doi.org/10.1128/AEM.66.11.4742-4750.2000 doi: 10.1128/AEM.66.11.4742-4750.2000]&nbsp;&nbsp; [[Media: PakEtAl2000.pdf | Open AccessArticle.pdf]]</ref><ref>Fuller, M.E., McClay, K., Hawari, J., Paquet, L., Malone, T.E., Fox, B.G., Steffan, R.J., 2009. Transformation of RDX and other energetic compounds by xenobiotic reductases XenA and XenB. Applied Microbiology and Biotechnology, 84, pp. 535-544. [https://doi.org/10.1007/s00253-009-2024-6 doi: 10.1007/s00253-009-2024-6]&nbsp;&nbsp; [[Media: FullerEtAl2009.pdf | Open Access Manuscript]]</ref>, and the aerobic NQ degrader [[Wikipedia: Pseudomonas | ''Pseudomonas extremaustralis'']] species NQ5 (NQ5 henceforth)<ref>Kim, J., Fuller, M.E., Hatzinger, P.B., Chu, K.-H., 2024. Isolation and characterization of nitroguanidine-degrading microorganisms. Science of the Total Environment, 912, Article 169184. [https://doi.org/10.1016/j.scitotenv.2023.169184 doi: 10.1016/j.scitotenv.2023.169184]</ref>. Anaerobic mixed cultures were obtained from a membrane bioreactor (MBR) degrading a mixture of six explosives (HMX, RDX, TNT, NTO, NQ, DNAN), as well as perchlorate and nitrate<ref name="FullerEtAl2023">Fuller, M.E., Hedman, P.C., Chu, K.-H., Webster, T.S., Hatzinger, P.B., 2023. Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents. Chemosphere, 340, Article 139887. [https://doi.org/10.1016/j.chemosphere.2023.139887 doi: 10.1016/j.chemosphere.2023.139887]</ref>. The results indicated that the slow-release carbon sources [[Wikipedia: Polyhydroxybutyrate | polyhydroxybutyrate (PHB)]], [[Wikipedia: Polycaprolactone | polycaprolactone (PCL)]], and [[Wikipedia: Polybutylene succinate | polybutylene succinate (BioPBS)]] were effective for supporting the biodegradation&nbsp;of&nbsp;the&nbsp;mixture&nbsp;of&nbsp;energetics.
  
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Evaluation of full-scale WWTPs has indicated that conventional primary (sedimentation and clarification) and secondary (aerobic biodegradation of organic matter) treatment processes can result in changes in PFAS concentrations and classes. For example, higher concentrations of PFAAs have been observed in effluent than in influent, presumably due to transformation of precursor PFAS<ref name="Schultz2006"/>. Some data has indicated that the terminal PFAS compounds PFOS and PFOA were among the most frequently detected PFAS in wastewater<ref name="Hamid2016">Hamid, H. and Li, L., 2016. Role of wastewater treatment plant in environmental cycling of poly- and perfluoroalkyl substances. Ecocycles, 2(2), pp. 43-53. [https://doi.org/10.19040/ecocycles.v2i2.62 DOI: 10.19040/ecocycles.v2i2.62]&nbsp;&nbsp; [[Media: Hamid2016.pdf | Open access article.]]</ref>. A state-wide study in Michigan indicated that PFAS were detected in all of the samples from 42 WWTPs, including influent, effluent, and biosolids/sludge samples, and that the short-chain PFAS were more frequently detected in the liquid process flow (influent and effluent), while long-chain PFAS were more common in biosolids<ref name="EGLE2020">Michigan Department of Environment, Great Lakes and Energy (EGLE), 2020.  Summary Report: Initiatives to Evaluate the Presence of PFAS in Municipal Wastewater and Associated Residuals (Sludge/Biosolids) in Michigan. [[Media:EGLE2020.pdf | Report.pdf]]&nbsp;&nbsp;
+
===Biochar===
−
[https://www.michigan.gov/documents/egle/wrd-pfas-initiatives_691391_7.pdf Website]</ref>.
+
[[File: FullerFig4.png | thumb | left | 500 px | Figure 4. Composition of the columns during the sorption-biodegradation experiments]]
 +
[[File: FullerFig5.png | thumb | 500 px | Figure 5. Representative breakthrough curves of energetics during the second replication of the column sorption-biodegradation experiment]]
 +
The&nbsp;ability&nbsp;of&nbsp;biochar&nbsp;to sorb and abiotically reduce legacy and insensitive munition constituents, as well as biochar’s use as an electron donor for microbial biodegradation of energetic compounds was examined. Batch experiments indicated that biochar was a reasonable sorbent for some of the energetics (RDX, DNAN), but could also serve as both an electron acceptor and an electron donor to facilitate abiotic (RDX, DNAN, NTO) and biotic (perchlorate) degradation (Figure 3)<ref>Xin, D., Giron, J., Fuller, M.E., Chiu, P.C., 2022. Abiotic reduction of 3-nitro-1,2,4-triazol-5-one (NTO), DNAN, and RDX by wood-derived biochars through their rechargeable electron storage capacity. Environmental Science: Processes and Impacts, 24(2), pp. 316-329. [https://doi.org/10.1039/D1EM00447F doi: 10.1039/D1EM00447F]&nbsp;&nbsp; [[Media: XinEtAl2022.pdf | Open Access Manuscript.pdf]]</ref>.
  
−
Multiple studies have found PFAS in municipal sewage sludge<ref name="Higgins2005">Higgins, C.P., Field, J.A., Criddle, C.S., and Luthy, R.G., 2005. Quantitative Determination of Perfluorochemicals in Sediments and Domestic Sludge. Environmental Science and Technology, 39 (11), pp. 3946 – 3956.  [https://doi.org/10.1021/es048245p DOI: 10.1021/es048245p]</ref><ref name="EGLE2020"/>. The US EPA states that more than half of the sludge produced in the United States is applied to agricultural land as biosolids, therefore there are concerns that biosolids applications may become a potential source of PFAS to the environment<ref name="USEPA2020">US Environmental Protection Agency (USEPA), 2020. Research on Per- and Polyfluoroalkyl Substances (PFAS).  [https://www.epa.gov/chemical-research/research-and-polyfluoroalkyl-substances-pfas Website]</ref>. Application of biosolids as a soil amendment can potentially result in transfer of PFAS to soil, surface water and groundwater and can possibly allow PFAS to enter the food chain<ref name="Sepulvado2011">Sepulvado, J.G., Blaine, A.C., Hundal, L.S. and Higgins, C.P., 2011. Occurrence and Fate of Perfluorochemicals in Soil Following the Land Application of Municipal Biosolids. Environmental Science and Technology, 45(19), pp.  8106-8112.  [https://doi.org/10.1021/es103903d DOI: 10.1021/es103903d]</ref><ref name="Lindstrom2011">Lindstrom, A.B., Strynar, M.J., Delinsky, A.D., Nakayama, S.F., McMillan, L., Libelo, E.L., Neill, M. and Thomas, L., 2011. Application of WWTP Biosolids and Resulting Perfluorinated Compound Contamination of Surface and Well Water in Decatur, Alabama, USA. Environmental Science and Technology, 45(19), pp. 8015-8021.  [https://doi.org/10.1021/es1039425 DOI: 10.1021/es1039425]</ref><ref name="Blaine2013">Blaine, A.C., Rich, C.D., Hundal, L.S., Lau, C., Mills, M.A., Harris, K.M. and Higgins, C.P., 2013. Uptake of Perfluoroalkyl Acids into Edible Crops via Land Applied Biosolids: Field and Greenhouse Studies. Environmental Science and Technology, 47(24), pp.14062-14069.  [https://doi.org/10.1021/es403094q DOI: 10.1021/es403094q]&nbsp;&nbsp; Free download from: [https://www.epa.gov/sites/production/files/2019-11/documents/508_pfascropuptake.pdf US EPA]</ref><ref name="Blaine2014">Blaine, A.C., Rich, C.D., Sedlacko, E.M., Hundal, L.S., Kumar, K., Lau, C., Mills, M.A., Harris, K.M. and Higgins, C.P., 2014. Perfluoroalkyl Acid Distribution in Various Plant Compartments of Edible Crops Grown in Biosolids-Amended Soils. Environmental Science and Technology, 48(14), pp. 7858-7865.  [https://doi.org/10.1021/es500016s DOI: 10.1021/es500016s] Free download from: [https://www.researchgate.net/profile/Kuldip_Kumar2/publication/263015815_Perfluoroalkyl_Acid_Distribution_in_Various_Plant_Compartments_of_Edible_Crops_Grown_in_Biosolids-Amended_soils/links/5984cb310f7e9b6c852f4f02/Perfluoroalkyl-Acid-Distribution-in-Various-Plant-Compartments-of-Edible-Crops-Grown-in-Biosolids-Amended-soils.pdf ResearchGate]</ref><ref name="Navarro2017">Navarro, I., de la Torre, A., Sanz, P., Porcel, M.Á., Pro, J., Carbonell, G. and de los Ángeles Martínez, M., 2017. Uptake of perfluoroalkyl substances and halogenated flame retardants by crop plants grown in biosolids-amended soils. Environmental Research, 152, pp. 199-206.  [https://doi.org/10.1016/j.envres.2016.10.018 DOI: 10.1016/j.envres.2016.10.018]</ref>. Limited studies have shown that PFAS concentrations can be elevated in surface and groundwater in the vicinity of agricultural fields that received PFAS contaminated biosolids for an extended period<ref name="Washington2010">Washington, J.W., Yoo, H., Ellington, J.J., Jenkins, T.M., and Libelo, E.L., 2010. Concentrations, Distribution, and Persistence of Perfluoroalkylates in Sludge-Applied Soils near Decatur, Alabama, USA. Environmental Science and Technology, 44(22), pp. 8390-8396.  [https://doi.org/10.1021/es1003846 DOI: 10.1021/es1003846] Free download from: [https://www.researchgate.net/profile/John_Washington3/publication/47447289_Concentrations_Distribution_and_Persistence_of_Perfluoroalkylates_in_Sludge-Applied_Soils_near_Decatur_Alabama_USA/links/5e3c0184a6fdccd9658add41/Concentrations-Distribution-and-Persistence-of-Perfluoroalkylates-in-Sludge-Applied-Soils-near-Decatur-Alabama-USA.pdf ResearchGate]</ref>. The most abundant PFAS found in biosolids are the long-chain PFAS<ref name="Hamid2016"/><ref name="EGLE2020"/>. Based on the persistence and stability of long-chain PFAS and their interaction with biosolids, research is ongoing to determine PFAS leachability from biosolids and their bioavailability for uptake by plants, soil organisms, and the consumers of potentially PFAS-impacted plants and soil organisms.  
+
===Sorption-Biodegradation Column Experiments===
 +
The&nbsp;selected&nbsp;materials&nbsp;and&nbsp;cultures discussed above, along with a small amount of range soil and crushed oyster shell as a slow-release pH buffering agent, were packed into columns, and a steady flow of dissolved energetics was passed through the columns. The composition of the four columns is presented in Figure 4. The influent and effluent concentrations of the energetics was monitored over time. The column experiment was performed twice.  As seen in Figure 5, there was sustained almost complete removal of RDX and ClO<sub>4</sub><sup>-</sup>, and more removal of the other energetics in the bioactive columns compared to the sorption only columns, over the course of the experiments.  For reference, 100 PV is approximately equivalent to three months of operation.  The higher effectiveness of sorption with biodegradation compared to sorption only is further illustrated in Figure 6, where the energetics mass removal in the bioactive columns was shown to be 2-fold (TNT) to 20-fold (RDX) higher relative to that observed in the sorption only column.  The mass removal of HMX and NQ were both over 40% higher with biochar added to the sorption with biodegradation treatment, although biochar showed little added benefit for&nbsp;removal&nbsp;of&nbsp;other&nbsp;energetics&nbsp;tested.
  
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==Solid Waste Management Facilities==
+
===Trap and Treat Technology===
−
Industrial, commercial, and consumer products containing PFAS that have been disposed in municipal solid waste (MSW) landfills or other legacy disposal areas since the 1950s are potential sources of PFAS release to the environment.  Environmental and drinking water impacts from disposal of legacy PFAS-containing industrial and consumer wastes have been documented<ref name="Oliaei2010">Oliaei, F., Kriens, D. and Weber, R., 2010. Discovery and investigation of PFOS/PFCs contamination from a PFC manufacturing facility in Minnesota—environmental releases and exposure risks. Organohalogen Compd, 72, pp. 1338-1341.</ref><ref name="Shin2011"/><ref name="MDH2020">Minnesota Department of Health (MDH), 2020. Perfluoroalkyl Substances (PFAS) Sites in Minnesota. [https://www.health.state.mn.us/communities/environment/hazardous/topics/sites.html Website]</ref>.
+
[[File: FullerFig6.png | thumb | left | 400 px | Figure 6. Energetic mass removal relative to the sorption only removal during the column sorption-biodegradation experiments.  Dashed line given for reference to C1 removal = 1.]]
 +
These&nbsp;results&nbsp;provide&nbsp;a proof-of-concept for the further development of a passive and sustainable “trap-and-treat” technology for remediation of energetic compounds in stormwater runoff at military testing and training ranges. At a given site, the stormwater runoff would need to be fully characterized with respect to key parameters (e.g., pH, major anions), and site specific treatability testing would be recommended to assure there was nothing present in the runoff that would reduce performance. Effluent monitoring on a regular basis would also be needed (and would be likely be expected by state and local regulators) to assess performance decline over time.
  
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Several studies have identified a wide variety of PFAS in MSW landfill leachates<ref name="Busch2010">Busch, J., Ahrens, L., Sturm, R. and Ebinghaus, R., 2010. Polyfluoroalkyl compounds in landfill leachates. Environmental Pollution, 158(5), pp.1467-1471. [https://doi.org/10.1016/j.envpol.2009.12.031 DOI: 10.1016/j.envpol.2009.12.031]</ref><ref name="Eggen2010">Eggen, T., Moeder, M. and Arukwe, A., 2010. Municipal landfill leachates: A significant source for new and emerging pollutants. Science of the Total Environment, 408(21), pp. 5147-5157. [https://doi.org/10.1016/j.scitotenv.2010.07.049 DOI: 10.1016/j.scitotenv.2010.07.049]</ref>. PFAS composition and concentration in leachates vary depending on waste age, climate, and waste composition<ref name="Allred2015">Allred, B. M., Lang, J. R., Barlaz, M. A., and Field, J. A., 2015. Physical and Biological Release of Poly- and Perfluoroalkyl Substances (PFAS) from Municipal Solid Waste in Anaerobic Model Landfill Reactors. Environmental Science and Technology, 49(13), pp. 7648-7656. [http://pubs.acs.org/doi/abs/10.1021/acs.est.5b01040 DOI: 10.1021/acs.est.5b01040]</ref><ref name="Lang2017">Lang, J.R., Allred, B.M., Field, J.A., Levis, J.W. and Barlaz, M.A., 2017. National Estimate of Per- and Polyfluoroalkyl Substance (PFAS) Release to U.S. Municipal Landfill Leachate. Environmental Science and Technology, 51(4), pp. 2197-2205.  [https://doi.org/10.1021/acs.est.6b05005 DOI: 10.1021/acs.est.6b05005]</ref>.  The relative concentrations of various PFAS in leachate and groundwater from landfill sites is different from those found at WWTPs and AFFF-contaminated sites. In particular, 5:3 fluorotelomer carboxylic acid (FTCA) is a common and often dominant PFAS found in landfills, and has been released from carpet in model anaerobic landfill reactors. This compound could prove to be an indicator that PFAS in the environment originated from a landfill<ref name="Lang2016">Lang, J.R., Allred, B.M., Peaslee, G.F., Field, J.A., and Barlaz, M.A., 2016. Release of Per-and Polyfluoroalkyl Substances (PFASs) from Carpet and Clothing in Model Anaerobic Landfill Reactors. Environmental Science and Technology, 50(10), pp. 5024-5032.  [https://doi.org/10.1021/acs.est.5b06237 DOI: 10.1021/acs.est.5b06237]</ref><ref name="Lang2017"/>. PFAS may also be released to the air from landfills, predominantly as fluorotelomer alcohols (FTOHs) and perfluorobutanoate (PFBA). In one study, total airborne PFAS concentrations were 5 to 30 times greater at landfills than at background reference sites<ref name="Ahrens2011b">Ahrens, L., Shoeib, M., Harner, T., Lane, D.A., Guo, R. and Reiner, E.J., 2011. Comparison of Annular Diffusion Denuder and High volume Air Samplers for Measuring Per- and Polyfluoroalkyl Substances in the Atmosphere. Analytical Chemistry, 83(24), pp. 9622-9628. [https://pubs.acs.org/doi/ DOI: 10.1021/ac202414w]&nbsp;&nbsp; Free download available from: [https://www.informea.org/sites/default/files/imported-documents/UNEP-POPS-POPRC11FU-SUBM-PFOA-Canada-2-20151211.En.pdf InforMEA]</ref>. PFAS release rates within landfills vary over time for a given waste mass, with climate (for example, rainfall) serving as the apparent driving factor for the variations<ref name="Lang2017"/><ref name="Benskin2012">Benskin, J.P., Li, B., Ikonomou, M.G., Grace, J.R. and Li, L.Y., 2012. Per-and Polyfluoroalkyl Substances in Landfill Leachate: Patterns, Time Trends, and Sources. Environmental Science and Technology, 46(21), pp.11532-11540.  [https://doi.org/10.1021/es302471n DOI: 10.1021/es302471n]</ref>.
+
The components of the technology would be predominantly peat moss and cationized pine shavings, supplemented with biochar, ground oyster shell, the biopolymer carbon sources, and the bioaugmentation cultures.  The entire mix would likely be emplaced in a concrete vault at the outflow end of the stormwater runoff retention basin at the contaminated site. The deployed treatment system would have further design elements, such as a system to trap and retain suspended solids in the runoff in order to minimize clogging the matrix. the inside of the vault would be baffled to maximize the hydraulic retention time of the contaminated runoff. The biopolymer carbon sources and oyster shell may need be refreshed periodically (perhaps yearly) to maintain performance. However, a complete removal and replacement of the base media (peat moss, CAT pine) would not be advised, as that would lead to a loss&nbsp;of&nbsp;the&nbsp;acclimated&nbsp;biomass.
  
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==Commercial and Consumer Products==
+
==Summary==
−
PFAS are widely used in consumer products and household applications, with a diverse mixture of PFAS found in varying concentrations depending on the product<ref name="Clara2008">Clara, M., Scharf, S., Weiss, S., Gans, O. and Scheffknecht, C., 2008. Emissions of perfluorinated alkylated substances (PFAS) from point sources - identification of relevant branches. Water Science and Technology, 58(1), pp. 59-66. [https://doi.org/10.2166/wst.2008.641 DOI: 10.2166/wst.2008.641]&nbsp;&nbsp; [[Media:Clara2008.pdf | Open access article.]]</ref><ref name="Trier2011">Trier, X., Granby, K. and Christensen, J.H., 2011. Polyfluorinated surfactants (PFS) in paper and board coatings for food packaging. Environmental Science and Pollution Research International, 18(7), pp. 1108–1120.  [https://doi.org/10.1007/s11356-010-0439-3 DOI: 10.1007/s11356-010-0439-3]</ref><ref name="Fujii2013">Fujii, Y., Harada, K.H. and Koizumi, A., 2013. Occurrence of perfluorinated carboxylic acids (PFCAs) in personal care products and compounding agents. Chemosphere, 93(3), pp. 538-544. [https://doi.org/10.1016/j.chemosphere.2013.06.049 DOI: 10.1016/j.chemosphere.2013.06.049]</ref><ref name="OECD2013">Organisation for Economic Cooperation and Development (OECD), 2013. Synthesis paper on per‐ and polyfluorinated chemicals (PFCs). OECD Environment Directorate/UNEP Global PFC Group.  [https://www.oecd.org/env/ehs/risk-management/PFC_FINAL-Web.pdf  Website]&nbsp;&nbsp; [[Media: OECD2013.pdf | Report.pdf]]</ref><ref name="ATSDR2018"/><ref name="Kotthoff2015"/><ref name="KEMI2015"/><ref name="USEPA2016">US Environmental Protection Agency (USEPA), 2016. Drinking Water Health Advisory for Perfluorooctane Sulfonate (PFOS), EPA Document Number: 822-R-16-004.  Office of Water, Health and Ecological Criteria Division, Washington, DC.  [https://www.epa.gov/sites/production/files/2016-05/documents/pfos_health_advisory_final_508.pdf Website]&nbsp;&nbsp; [[Media: USEPA2016.pdf | Report.pdf]]</ref>.  Environmental releases associated with the commercial and consumer products are primarily related to their production.  To a much lower extent, the environmental releases may be associated with the management of solid waste (for example, disposal of used items in a MSW landfill) and wastewater disposal (for example, discharge to WWTPs, private septic systems, or other subsurface disposal systems).
+
Novel&nbsp;sorbents&nbsp;and&nbsp;slow-release carbon sources can be an effective way to promote the sorption and biodegradation of a range of legacy and insensitive munition constituents from surface runoff, and the added benefits of biochar for both sorption and biotic and abiotic degradation of these compounds was demonstrated.  These results establish a foundation for a passive, sustainable surface runoff treatment technology for both active and&nbsp;inactive&nbsp;military&nbsp;ranges.
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Studies have shown that physical degradation of some consumer products (such as PFAS-treated paper, textiles, and carpets) may release PFAS in house dust<ref name="Bjorklund2009">Björklund, J.A., Thuresson, K. and De Wit, C.A., 2009. Perfluoroalkyl Compounds (PFCs) in Indoor Dust: Concentrations, Human Exposure Estimates, and Sources. Environmental Science and Technology, 43(7), pp. 2276-2281.  [https://doi.org/10.1021/es803201a DOI: 10.1021/es803201a]</ref>. Additionally, studies have also shown that professional ski wax technicians may have significant inhalation exposures to PFAS<ref name="Nilsson2013">Nilsson, H., Kärrman, A., Rotander, A., van Bavel, B., Lindström, G., and Westberg, H., 2013. Professional ski waxers' exposure to PFAS and aerosol concentrations in gas phase and different particle size fractions. Environmental Science: Processes and Impacts, 15(4), pp. 814-822.  [https://doi.org/10.1039/C3EM30739E DOI: 10.1039/C3EM30739E]</ref> and snowmelt and surface waters near ski areas could have measurable PFAS impacts<ref name="Kwok2013">Kwok, K.Y., Yamazaki, E., Yamashita, N., Taniyasu, S., Murphy, M.B., Horii, Y., Petrick, G., Kallerborn, R., Kannan, K., Murano, K. and Lam, P.K., 2013. Transport of Perfluoroalkyl substances (PFAS) from an arctic glacier to downstream locations: Implications for sources. Science of the Total Environment, 447, pp. 46-55.  [https://doi.org/10.1016/j.scitotenv.2012.10.091 DOI: 10.1016/j.scitotenv.2012.10.091]</ref>.
 
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As increased environmental sampling for PFAS occurs, additional information will become available to further our understanding of the major and minor PFAS contributors to the environment.
 
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==References==
 
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==See Also==
 
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*[https://serdp-estcp.mil/projects/details/10760fd6-fb55-4515-a629-f93c555a92f0/er-1689-project-overview Fate and Transport of Colloidal Energetic Residues, SERDP Project ER-1689]
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*[https://serdp-estcp.mil/projects/details/20e2f05c-fd50-4fd3-8451-ba73300c7531/er-200434-project-overview In Place Soil Treatments for Prevention of Explosives Contamination, ESTCP Project ER-200434]

Latest revision as of 20:19, 4 November 2025

Thermal Conduction Heating for Treatment of PFAS-Impacted Soil

Removal of Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) compounds from impacted soils is challenging due to the modest volatility and varying properties of most PFAS compounds. Thermal treatment technologies have been developed for treatment of semi-volatile compounds in soils such as dioxins, furans, poly-aromatic hydrocarbons and poly-chlorinated biphenyls at temperatures near 325°C. In controlled bench-scale testing, complete removal of targeted PFAS compounds to concentrations below reporting limits of 0.5 µg/kg was demonstrated at temperatures of 400°C[1]. Three field-scale thermal PFAS treatment projects that have been completed in the US include an in-pile treatment demonstration, an in situ vadose zone treatment demonstration and a larger scale treatment demonstration with excavated PFAS-impacted soil in a constructed pile. Based on the results, thermal treatment temperatures of at least 400°C and a holding time of 7-10 days are recommended for reaching local and federal PFAS soil standards. The energy requirement to treat typical wet soil ranges from 300 to 400 kWh per cubic yard, exclusive of heat losses which are scale dependent. Extracted vapors have been treated using condensation and granular activated charcoal filtration, with thermal and catalytic oxidation as another option which is currently being evaluated for field scale applications. Compared to other options such as soil washing, the ability to treat on site and to treat all soil fractions is an advantage.

Related Article(s):

Contributors: Gorm Heron, Emily Crownover, Patrick Joyce, Ramona Iery

Key Resource:

  • Perfluoroalkyl and polyfluoroalkyl substances thermal desorption evaluation[1]

Introduction

Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) have become prominent emerging contaminants in soil and groundwater. Soil source zones have been identified at locations where the chemicals were produced, handled or used. Few effective options exist for treatments that can meet local and federal soil standards. Over the past 30 plus years, thermal remediation technologies have grown from experimental and innovative prospects to mature and accepted solutions deployed effectively at many sites. More than 600 thermal case studies have been summarized by Horst and colleagues[2]. Thermal Conduction Heating (TCH) has been used for higher temperature applications such as removal of 1,4-Dioxane. This article reports recent experience with TCH treatment of PFAS-impacted soil.

Target Temperature and Duration

PFAS behave differently from most other organics subjected to TCH treatment. While the boiling points of individual PFAS fall in the range of 150-400°C, their chemical and physical behavior creates additional challenges. Some PFAS form ionic species in certain pH ranges and salts under other chemical conditions. This intricate behavior and our limited understanding of what this means for our ability to remove the PFAS from soils means that direct testing of thermal treatment options is warranted. Crownover and colleagues[1] subjected PFAS-laden soil to bench-scale heating to temperatures between 200 and 400°C which showed strong reductions of PFAS concentrations at 350°C and complete removal of many PFAS compounds at 400°C. The soil concentrations of targeted PFAS were reduced to nearly undetectable levels in this study.

Heating Method

For semi-volatile compounds such as dioxins, furans, poly-chlorinated biphenyls (PCBs) and Poly-Aromatic Hydrocarbons (PAH), thermal conduction heating has evolved as the dominant thermal technology because it is capable of achieving soil temperatures higher than the boiling point of water, which are necessary for complete removal of these organic compounds. Temperatures between 200 and 500°C have been required to achieve the desired reduction in contaminant concentrations[3]. TCH has become a popular technology for PFAS treatment because temperatures in the 400°C range are needed.

The energy source for TCH can be electricity (most commonly used), or fossil fuels (typically gas, diesel or fuel oil). Electrically powered TCH offers the largest flexibility for power input which also can be supplied by renewable and sustainable energy sources.

Energy Usage

During large precipitation events the rate of water deposition exceeds the rate of water infiltration, resulting in surface runoff (also called stormwater runoff). Surface characteristics including soil texture, presence of impermeable surfaces (natural and artificial), slope, and density and type of vegetation all influence the amount of surface runoff from a given land area. The use of passive systems such as retention ponds and biofiltration cells for treatment of surface runoff is well established for urban and roadway runoff. Treatment in those cases is typically achieved by directing runoff into and through a small constructed wetland, often at the outlet of a retention basin, or via filtration by directing runoff through a more highly engineered channel or vault containing the treatment materials. Filtration based technologies have proven to be effective for the removal of metals, organics, and suspended solids[4][5][6][7].

Surface Runoff on Ranges

Figure 2. Conceptual illustration of munition constituent production and transport on military ranges. Mesoscale residues are qualitatively defined as being easily visible to the naked eye (e.g., from around 50 µm to multiple cm in size) and less likely to be transported by moving water. Microscale residues are defined as <50 µm down to below 1 µm, and more likely to be entrained in, and transported by, moving water as particulates. Blue arrows represent possible water flow paths and include both dissolved and solid phase energetics. The red vertical arrow represents the predominant energetics dissolution process in close proximity to the residues due to precipitation.

Surface runoff represents a major potential mechanism through which energetics residues and related materials are transported off site from range soils to groundwater and surface water receptors (Figure 2). This process is particularly important for energetics that are water soluble (e.g., NTO and NQ) or generate soluble daughter products (e.g., DNAN and TNT). While traditional MC such as RDX and HMX have limited aqueous solubility, they also exhibit recalcitrance to degrade under most natural conditions. RDX and perchlorate are frequent groundwater contaminants on military training ranges. While actual field measurements of energetics in surface runoff are limited, laboratory experiments have been performed to predict mobile energetics contamination levels based on soil mass loadings[8][9][10][11][12]. For example, in a previous small study, MC were detected in surface runoff from an active live-fire range[13], and more recent sampling has detected MC in marsh surface water adjacent to the same installation (personal communication). Another recent report from Canada also detected RDX in both surface runoff and surface water at low part per billion levels in a survey of several military demolition sites[14]. However, overall, data regarding the MC contaminant profile of surface runoff from ranges is very limited, and the possible presence of non-energetic constituents (e.g., metals, binders, plasticizers) in runoff has not been examined. Additionally, while energetics-contaminated surface runoff is an important concern, mitigation technologies specifically for surface runoff have not yet been developed and widely deployed in the field. To effectively capture and degrade MC and associated compounds that are present in surface runoff, novel treatment media are needed to sorb a broad range of energetic materials and to transform the retained compounds through abiotic and/or microbial processes.

Surface runoff of organic and inorganic contaminants from live-fire ranges is a challenging issue for the Department of Defense (DoD). Potentially even more problematic is the fact that inputs to surface waters from large testing and training ranges typically originate from multiple sources, often encompassing hundreds of acres. No available technologies are currently considered effective for controlling non-point source energetics-laden surface runoff. While numerous technologies exist to treat collected explosives residues, contaminated soil and even groundwater, the decentralized nature and sheer volume of military range runoff have precluded the use of treatment technologies at full scale in the field.

Range Runoff Treatment Technology Components

Based on the conceptual foundation of previous research into surface water runoff treatment for other contaminants, with a goal to “trap and treat” the target compounds, the following components were selected for inclusion in the technology developed to address range runoff contaminated with energetic compounds.

Peat

Previous research demonstrated that a peat-based system provided a natural and sustainable sorptive medium for organic explosives such as HMX, RDX, and TNT, allowing much longer residence times than predicted from hydraulic loading alone[15][16][17][18][19]. Peat moss represents a bioactive environment for treatment of the target contaminants. While the majority of the microbial reactions are aerobic due to the presence of measurable dissolved oxygen in the bulk solution, anaerobic reactions (including methanogenesis) can occur in microsites within the peat. The peat-based substrate acts not only as a long term electron donor as it degrades but also acts as a strong sorbent. This is important in intermittently loaded systems in which a large initial pulse of MC can be temporarily retarded on the peat matrix and then slowly degraded as they desorb[17][19]. This increased residence time enhances the biotransformation of energetics and promotes the immobilization and further degradation of breakdown products. Abiotic degradation reactions are also likely enhanced by association with the organic-rich peat (e.g., via electron shuttling reactions of humics)[20].

Soybean Oil

Modeling has indicated that peat moss amended with crude soybean oil would significantly reduce the flux of dissolved TNT, RDX, and HMX through the vadose zone to groundwater compared to a non-treated soil (see ESTCP ER-200434). The technology was validated in field soil plots, showing a greater than 500-fold reduction in the flux of dissolved RDX from macroscale Composition B detonation residues compared to a non-treated control plot[17]. Laboratory testing and modeling indicated that the addition of soybean oil increased the biotransformation rates of RDX and HMX at least 10-fold compared to rates observed with peat moss alone[19]. Subsequent experiments also demonstrated the effectiveness of the amended peat moss material for stimulating perchlorate transformation when added to a highly contaminated soil (Fuller et al., unpublished data). These previous findings clearly demonstrate the effectiveness of peat-based materials for mitigating transport of both organic and inorganic energetic compounds through soil to groundwater.

Biochar

Recent reports have highlighted additional materials that, either alone, or in combination with electron donors such as peat moss and soybean oil, may further enhance the sorption and degradation of surface runoff contaminants, including both legacy energetics and insensitive high explosives (IHE). For instance, biochar, a type of black carbon, has been shown to not only sorb a wide range of organic and inorganic contaminants including MCs[21][22][23][24], but also to facilitate their degradation[25][26][27][28][29][30]. Depending on the source biomass and pyrolysis conditions, biochar can possess a high specific surface area (on the order of several hundred m2/g)[31][32] and hence a high sorption capacity. Biochar and other black carbon also exhibit especially high affinity for nitroaromatic compounds (NACs) including TNT and 2,4-dinitrotoluene (DNT)[33][34][35]. This is due to the strong π-π electron donor-acceptor interactions between electron-rich graphitic domains in black carbon and the electron-deficient aromatic ring of the NAC[34][35]. These characteristics make biochar a potentially effective, low cost, and sustainable sorbent for removing MC and other contaminants from surface runoff and retaining them for subsequent degradation in situ.

Furthermore, black carbon such as biochar can promote abiotic and microbial transformation reactions by facilitating electron transfer. That is, biochar is not merely a passive sorbent for contaminants, but also a redox mediator for their degradation. Biochar can promote contaminant degradation through two different mechanisms: electron conduction and electron storage[36].

First, the microscopic graphitic regions in biochar can adsorb contaminants like NACs strongly, as noted above, and also conduct reducing equivalents such as electrons and atomic hydrogen to the sorbed contaminants, thus promoting their reductive degradation. This catalytic process has been demonstrated for TNT, DNT, RDX, HMX, and nitroglycerin[37][38][39][27][29] and is expected to occur also for IHE including DNAN and NTO.

Second, biochar contains in its structure abundant redox-facile functional groups such as quinones and hydroquinones, which are known to accept and donate electrons reversibly. Depending on the biomass and pyrolysis temperature, certain biochar can possess a rechargeable electron storage capacity (i.e., reversible electron accepting and donating capacity) on the order of several millimoles e–/g[40][41][42]. This means that when "charged", biochar can provide electrons for either abiotic or biotic degradation of reducible compounds such as MC. The abiotic reduction of DNT and RDX mediated by biochar has been demonstrated[28] and similar reactions are expected to occur for DNAN and NTO as well. Recent studies have shown that the electron storage capacity of biochar is also accessible to microbes. For example, soil bacteria such as Geobacter and Shewanella species can utilize oxidized (or "discharged") biochar as an electron acceptor for the oxidation of organic substrates such as lactate and acetate[43][44] and reduced (or "charged") biochar as an electron donor for the reduction of nitrate[44]. This is significant because, through microbial access of stored electrons in biochar, contaminants that do not sorb strongly to biochar can still be degraded.

Similar to nitrate, perchlorate and other relatively water-soluble energetic compounds (e.g., NTO and NQ) may also be similarly transformed using reduced biochar as an electron donor. Unlike other electron donors, biochar can be recharged through biodegradation of organic substrates[44] and thus can serve as a long-lasting sorbent and electron repository in soil. Similar to peat moss, the high porosity and surface area of biochar not only facilitate contaminant sorption but also create anaerobic reducing microenvironments in its inner pores, where reductive degradation of energetic compounds can take place.

Other Sorbents

Chitin and unmodified cellulose were predicted by Density Functional Theory methods to be favorable for absorption of NTO and NQ, as well as the legacy explosives[45]. Cationized cellulosic materials (e.g., cotton, wood shavings) have been shown to effectively remove negatively charged energetics like perchlorate and NTO from solution[46]. A substantial body of work has shown that modified cellulosic biopolymers can also be effective sorbents for removing metals from solution[47][48][49][50] and therefore will also likely be applicable for some of the metals that may be found in surface runoff at firing ranges.

Technology Evaluation

Based on the properties of the target munition constituents, a combination of materials was expected to yield the best results to facilitate the sorption and subsequent biotic and abiotic degradation of the contaminants.

Sorbents

Table 1. Freundlich and Langmuir adsorption parameters for insensitive and legacy explosives
Compound Freundlich Langmuir
Parameter Peat CAT Pine CAT Burlap CAT Cotton Parameter Peat CAT Pine CAT Burlap CAT Cotton
HMX Kf 0.08 +/- 0.00 -- -- -- qm (mg/g) 0.29 +/- 0.04 -- -- --
n 1.70 +/- 0.18 -- -- -- b (L/mg) 0.39 +/- 0.09 -- -- --
r2 0.91 -- -- -- r2 0.93 -- -- --
RDX Kf 0.11 +/- 0.02 -- -- -- qm (mg/g) 0.38 +/- 0.05 -- -- --
n 2.75 +/- 0.63 -- -- -- b (L/mg) 0.23 +/- 0.08 -- -- --
r2 0.69 -- -- -- r2 0.69 -- -- --
TNT Kf 1.21 +/- 0.15 1.02 +/- 0.04 0.36 +/- 0.02 -- qm (mg/g) 3.63 +/- 0.18 1.26 +/- 0.06 -- --
n 2.78 +/- 0.67 4.01 +/- 0.44 1.59 +/- 0.09 -- b (L/mg) 0.89 +/- 0.13 0.76 +/- 0.10 -- --
r2 0.81 0.93 0.98 -- r2 0.97 0.97 -- --
NTO Kf -- 0.94 +/- 0.05 0.41 +/- 0.05 0.26 +/- 0.06 qm (mg/g) -- 4.07 +/- 0.26 1.29 +/- 0.12 0.83 +/- .015
n -- 1.61 +/- 0.11 2.43 +/- 0.41 2.53 +/- 0.76 b (L/mg) -- 0.30 +/- 0.04 0.36 +/- 0.08 0.30 +/- 0.15
r2 -- 0.97 0.82 0.57 r2 -- 0.99 0.89 0.58
DNAN Kf 0.38 +/- 0.05 0.01 +/- 0.01 -- -- qm (mg/g) 2.57 +/- 0.33 -- -- --
n 1.71 +/- 0.20 0.70 +/- 0.13 -- -- b (L/mg) 0.13 +/- 0.03 -- -- --
r2 0.89 0.76 -- -- r2 0.92 -- -- --
ClO4 Kf -- 1.54 +/- 0.06 0.53 +/- 0.03 -- qm (mg/g) -- 3.63 +/- 0.18 1.26 +/- 0.06 --
n -- 2.42 +/- 0.16 2.42 +/- 0.26 -- b (L/mg) -- 0.89 +/- 0.13 0.76 +/- 0.10 --
r2 -- 0.97 0.92 -- r2 -- 0.97 0.97 --
Notes:
-- Indicates the algorithm failed to converge on the model fitting parameters, therefore there was no successful model fit.
CAT Indicates cationized material.

The materials screened included Sphagnum peat moss, primarily for sorption of HMX, RDX, TNT, and DNAN, as well as cationized cellulosics for removal of perchlorate and NTO. The cationized cellulosics that were examined included: pine sawdust, pine shavings, aspen shavings, cotton linters (fine, silky fibers which adhere to cotton seeds after ginning), chitin, chitosan, burlap (landscaping grade), coconut coir, raw cotton, raw organic cotton, cleaned raw cotton, cotton fabric, and commercially cationized fabrics.

As shown in Table 1[46], batch sorption testing indicated that a combination of Sphagnum peat moss and cationized pine shavings provided good removal of both the neutral organic energetics (HMX, RDX, TNT, DNAN) as well as the negatively charged energetics (perchlorate, NTO).

Slow Release Carbon Sources

Table 2. Slow-release Carbon Sources
Material Abbreviation Commercial Source Notes
polylactic acid PLA6 Goodfellow high molecular weight thermoplastic polyester
polylactic acid PLA80 Goodfellow low molecular weight thermoplastic polyester
polyhydroxybutyrate PHB Goodfellow bacterial polyester
polycaprolactone PCL Sarchem Labs biodegradable polyester
polybutylene succinate BioPBS Mitsubishi Chemical Performance Polymers compostable bio-based product
sucrose ester of fatty acids SEFA SP10 Sisterna food and cosmetics additive
sucrose ester of fatty acids SEFA SP70 Sisterna food and cosmetics additive

A range of biopolymers widely used in the production of biodegradable plastics were screened for their ability to support aerobic and anoxic biodegradation of the target munition constituents. These compounds and their sources are listed in Table 2.

Figure 3. Schematic of interactions between biochar and munitions constituents

Multiple pure bacterial strains and mixed cultures were screened for their ability to utilize the solid biopolymers as a carbon source to support energetic compound transformation and degradation. Pure strains included the aerobic RDX degrader Rhodococcus species DN22 (DN22 henceforth)[51] and Gordonia species KTR9 (KTR9 henceforth)[51], the anoxic RDX degrader Pseudomonas fluorencens species I-C (I-C henceforth)[52][53], and the aerobic NQ degrader Pseudomonas extremaustralis species NQ5 (NQ5 henceforth)[54]. Anaerobic mixed cultures were obtained from a membrane bioreactor (MBR) degrading a mixture of six explosives (HMX, RDX, TNT, NTO, NQ, DNAN), as well as perchlorate and nitrate[55]. The results indicated that the slow-release carbon sources polyhydroxybutyrate (PHB), polycaprolactone (PCL), and polybutylene succinate (BioPBS) were effective for supporting the biodegradation of the mixture of energetics.

Biochar

Figure 4. Composition of the columns during the sorption-biodegradation experiments
Figure 5. Representative breakthrough curves of energetics during the second replication of the column sorption-biodegradation experiment

The ability of biochar to sorb and abiotically reduce legacy and insensitive munition constituents, as well as biochar’s use as an electron donor for microbial biodegradation of energetic compounds was examined. Batch experiments indicated that biochar was a reasonable sorbent for some of the energetics (RDX, DNAN), but could also serve as both an electron acceptor and an electron donor to facilitate abiotic (RDX, DNAN, NTO) and biotic (perchlorate) degradation (Figure 3)[56].

Sorption-Biodegradation Column Experiments

The selected materials and cultures discussed above, along with a small amount of range soil and crushed oyster shell as a slow-release pH buffering agent, were packed into columns, and a steady flow of dissolved energetics was passed through the columns. The composition of the four columns is presented in Figure 4. The influent and effluent concentrations of the energetics was monitored over time. The column experiment was performed twice. As seen in Figure 5, there was sustained almost complete removal of RDX and ClO4-, and more removal of the other energetics in the bioactive columns compared to the sorption only columns, over the course of the experiments. For reference, 100 PV is approximately equivalent to three months of operation. The higher effectiveness of sorption with biodegradation compared to sorption only is further illustrated in Figure 6, where the energetics mass removal in the bioactive columns was shown to be 2-fold (TNT) to 20-fold (RDX) higher relative to that observed in the sorption only column. The mass removal of HMX and NQ were both over 40% higher with biochar added to the sorption with biodegradation treatment, although biochar showed little added benefit for removal of other energetics tested.

Trap and Treat Technology

Figure 6. Energetic mass removal relative to the sorption only removal during the column sorption-biodegradation experiments. Dashed line given for reference to C1 removal = 1.

These results provide a proof-of-concept for the further development of a passive and sustainable “trap-and-treat” technology for remediation of energetic compounds in stormwater runoff at military testing and training ranges. At a given site, the stormwater runoff would need to be fully characterized with respect to key parameters (e.g., pH, major anions), and site specific treatability testing would be recommended to assure there was nothing present in the runoff that would reduce performance. Effluent monitoring on a regular basis would also be needed (and would be likely be expected by state and local regulators) to assess performance decline over time.

The components of the technology would be predominantly peat moss and cationized pine shavings, supplemented with biochar, ground oyster shell, the biopolymer carbon sources, and the bioaugmentation cultures. The entire mix would likely be emplaced in a concrete vault at the outflow end of the stormwater runoff retention basin at the contaminated site. The deployed treatment system would have further design elements, such as a system to trap and retain suspended solids in the runoff in order to minimize clogging the matrix. the inside of the vault would be baffled to maximize the hydraulic retention time of the contaminated runoff. The biopolymer carbon sources and oyster shell may need be refreshed periodically (perhaps yearly) to maintain performance. However, a complete removal and replacement of the base media (peat moss, CAT pine) would not be advised, as that would lead to a loss of the acclimated biomass.

Summary

Novel sorbents and slow-release carbon sources can be an effective way to promote the sorption and biodegradation of a range of legacy and insensitive munition constituents from surface runoff, and the added benefits of biochar for both sorption and biotic and abiotic degradation of these compounds was demonstrated. These results establish a foundation for a passive, sustainable surface runoff treatment technology for both active and inactive military ranges.

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