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==Hydrothermal Alkaline Treatment==  
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==Remediation of Stormwater Runoff Contaminated by Munition Constituents==  
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Hydrothermal alkaline treatment (HALT) is a  
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Past and ongoing military operations have resulted in contamination of surface soil with [[Munitions Constituents | munition constituents (MC)]], which have human and environmental health impacts.  These compounds can be transported off site via stormwater runoff during precipitation events.  Technologies to “trap and treat” surface runoff before it enters downstream receiving bodies (e.g., streams, rivers, ponds) (see Figure 1), and which are compatible with ongoing range activities are needed.  This article describes a passive and sustainable approach for effective management of munition constituents in stormwater runoff. 
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<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
  
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*[[Contaminated Sediments - Introduction]]
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*[[Munitions Constituents]]
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*[[Contaminated Sediment Risk Assessment]]
 
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*[[In Situ Treatment of Contaminated Sediments with Activated Carbon]]
 
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*[[Passive Sampling of Munitions Constituents]]
 
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*[[Sediment Capping]]
 
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*[[Mercury in Sediments]]
 
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*[[Passive Sampling of Sediments]]
 
  
  
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'''Contributor(s):'''  
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'''Contributor:''' Mark E. Fuller
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*Florent Risacher, M.Sc.
 
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*Jason Conder, Ph.D.
 
  
 
'''Key Resource(s):'''
 
'''Key Resource(s):'''
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*SERDP Project ER19-1106: Development of Innovative Passive and Sustainable Treatment Technologies for Energetic Compounds in Surface Runoff on Active Ranges
  
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*A review of peeper passive sampling approaches to measure the availability of inorganics in sediment porewater<ref>Risacher, F.F., Schneider, H., Drygiannaki, I., Conder, J., Pautler, B.G., and Jackson, A.W., 2023. A Review of Peeper Passive Sampling Approaches to Measure the Availability of Inorganics in Sediment Porewater. Environmental Pollution, 328, Article 121581. [https://doi.org/10.1016/j.envpol.2023.121581 doi: 10.1016/j.envpol.2023.121581]&nbsp;&nbsp;[[Media: RisacherEtAl2023a.pdf | Open Access Manuscript]]</ref>
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==Background==
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===Surface Runoff Characteristics and Treatment Approaches===
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[[File: FullerFig1.png | thumb | 400 px | left | Figure 1. Conceptual model of passive trap and treat approach for MC removal from stormwater runoff]]
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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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*Best Practices User’s Guide: Standardizing Sediment Porewater Passive Samplers for Inorganic Constituents of Concern<ref name="RisacherEtAl2023">Risacher, F.F., Nichols, E., Schneider, H., Lawrence, M., Conder, J., Sweett, A., Pautler, B.G., Jackson, W.A., Rosen, G., 2023b. Best Practices User’s Guide: Standardizing Sediment Porewater Passive Samplers for Inorganic Constituents of Concern, ESTCP ER20-5261. [https://serdp-estcp.mil/projects/details/db871313-fbc0-4432-b536-40c64af3627f Project Website]&nbsp;&nbsp;[[Media: ER20-5261BPUG.pdf | Report.pdf]]</ref>
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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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*[https://serdp-estcp.mil/projects/details/db871313-fbc0-4432-b536-40c64af3627f/er20-5261-project-overview Standardizing Sediment Porewater Passive Samplers for Inorganic Constituents of Concern, ESTCP Project ER20-5261]
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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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==Introduction==
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==Range Runoff Treatment Technology Components==
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Biologically available inorganic constituents associated with sediment toxicity can be quantified by measuring the freely-dissolved fraction of contaminants in the porewater<ref>Conder, J.M., Fuchsman, P.C., Grover, M.M., Magar, V.S., Henning, M.H., 2015. Critical review of mercury SQVs for the protection of benthic invertebrates. Environmental Toxicology and Chemistry, 34(1), pp. 6-21. [https://doi.org/10.1002/etc.2769 doi: 10.1002/etc.2769]&nbsp;&nbsp; [[Media: ConderEtAl2015.pdf | Open Access Article]]</ref><ref name="ClevelandEtAl2017">Cleveland, D., Brumbaugh, W.G., MacDonald, D.D., 2017. A comparison of four porewater sampling methods for metal mixtures and dissolved organic carbon and the implications for sediment toxicity evaluations. Environmental Toxicology and Chemistry, 36(11), pp. 2906-2915. [https://doi.org/10.1002/etc.3884 doi: 10.1002/etc.3884]</ref>. Classical sediment porewater analysis usually consists of collecting large volumes of bulk sediments which are then mechanically squeezed or centrifuged to produce a supernatant, or suction of porewater from intact sediment, followed by filtration and collection<ref name="GruzalskiEtAl2016">Gruzalski, J.G., Markwiese, J.T., Carriker, N.E., Rogers, W.J., Vitale, R.J.,  Thal, D.I., 2016. Pore Water Collection, Analysis and Evolution: The Need for Standardization. In: Reviews of Environmental Contamination and Toxicology, Vol. 237, pp. 37–51. Springer. [https://doi.org/10.1007/978-3-319-23573-8_2 doi: 10.1007/978-3-319-23573-8_2]</ref>. The extraction and measurement processes present challenges due to the heterogeneity of sediments, physical disturbance, high reactivity of some complexes, and interaction between the solid and dissolved phases, which can impact the measured concentration of dissolved inorganics<ref>Peijnenburg, W.J.G.M., Teasdale, P.R., Reible, D., Mondon, J., Bennett, W.W., Campbell, P.G.C., 2014. Passive Sampling Methods for Contaminated Sediments: State of the Science for Metals. Integrated Environmental Assessment and Management, 10(2), pp. 179–196. [https://doi.org/10.1002/ieam.1502 doi: 10.1002/ieam.1502]&nbsp;&nbsp; [[Media: PeijnenburgEtAl2014.pdf | Open Access Article]]</ref>. For example, sampling disturbance can affect redox conditions<ref name="TeasdaleEtAl1995">Teasdale, P.R., Batley, G.E., Apte, S.C., Webster, I.T., 1995. Pore water sampling with sediment peepers. Trends in Analytical Chemistry, 14(6), pp. 250–256. [https://doi.org/10.1016/0165-9936(95)91617-2 doi: 10.1016/0165-9936(95)91617-2]</ref><ref>Schroeder, H., Duester, L., Fabricius, A.L., Ecker, D., Breitung, V., Ternes, T.A., 2020. Sediment water (interface) mobility of metal(loid)s and nutrients under undisturbed conditions and during resuspension. Journal of Hazardous Materials, 394, Article 122543. [https://doi.org/10.1016/j.jhazmat.2020.122543 doi: 10.1016/j.jhazmat.2020.122543]&nbsp;&nbsp; [[Media: SchroederEtAl2020.pdf | Open Access Article]]</ref>, which can lead to under or over representation of inorganic chemical concentrations relative to the true dissolved phase concentration in the sediment porewater<ref>Wise, D.E., 2009. Sampling techniques for sediment pore water in evaluation of reactive capping efficacy. Master of Science Thesis. University of New Hampshire Scholars’ Repository. 178 pages. [https://scholars.unh.edu/thesis/502 Website]&nbsp;&nbsp; [[Media: Wise2009.pdf | Report.pdf]]</ref><ref name="GruzalskiEtAl2016"/>.  
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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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To address the complications with mechanical porewater sampling, passive sampling approaches for inorganics have been developed to provide a method that has a low impact on the surrounding geochemistry of sediments and sediment porewater, thus enabling more precise measurements of inorganics<ref name="ClevelandEtAl2017"/>. Sediment porewater dialysis passive samplers, also known as “peepers,” were developed more than 45 years ago<ref name="Hesslein1976">Hesslein, R.H., 1976. An in situ sampler for close interval pore water studies. Limnology and Oceanography, 21(6), pp. 912-914. [https://doi.org/10.4319/lo.1976.21.6.0912 doi: 10.4319/lo.1976.21.6.0912]&nbsp;&nbsp; [[Media: Hesslein1976.pdf | Open Access Article]]</ref> and refinements to the method such as the use of reverse tracers have been made, improving the acceptance of the technology as decision making tool.
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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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==Peeper Designs==
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===Soybean Oil===  
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[[File:RisacherFig1.png|thumb|300px|Figure 1. Conceptual illustration of peeper construction showing (top, left to right) the peeper cap (optional), peeper membrane and peeper chamber, and (bottom) an assembled peeper containing peeper water]]
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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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[[File:RisacherFig2.png | thumb |400px| Figure 2. Example of Hesslein<ref name="Hesslein1976"/> general peeper design (42 peeper chambers), from [https://www.usgs.gov/media/images/peeper-samplers USGS]]]
 
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[[File:RisacherFig3.png | thumb |400px| Figure 3. Peeper deployment structure to allow the measurement of metal availability in different sediment layers using five single-chamber peepers (Photo: Geosyntec Consultants)]]
 
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Peepers (Figure 1) are inert containers with a small volume (typically 1-100 mL) of purified water (“peeper water”) capped with a semi-permeable membrane. Peepers can be manufactured in a wide variety of formats (Figure 2, Figure 3) and deployed in in various ways.  
 
  
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Two designs are commonly used for peepers. Frequently, the designs are close adaptations of the original multi-chamber Hesslein design<ref name="Hesslein1976"/> (Figure 2), which consists of an acrylic sampler body with multiple sample chambers machined into it. Peeper water inside the chambers is separated from the outside environment by a semi-permeable membrane, which is held in place by a top plate fixed to the sampler body using bolts or screws. An alternative design consists of single-chamber peepers constructed using a single sample vial with a membrane secured over the mouth of the vial, as shown in Figure 3, and applied in Teasdale ''et al.''<ref name="TeasdaleEtAl1995"/>, Serbst ''et al.''<ref>Serbst, J.R., Burgess, R.M., Kuhn, A., Edwards, P.A., Cantwell, M.G., Pelletier, M.C., Berry, W.J., 2003. Precision of dialysis (peeper) sampling of cadmium in marine sediment interstitial water. Archives of Environmental Contamination and Toxicology, 45(3), pp. 297–305. [https://doi.org/10.1007/s00244-003-0114-5 doi: 10.1007/s00244-003-0114-5]</ref>, Thomas and Arthur<ref name="ThomasArthur2010">Thomas, B., Arthur, M.A., 2010. Correcting porewater concentration measurements from peepers: Application of a reverse tracer. Limnology and Oceanography: Methods, 8(8), pp. 403–413. [https://doi.org/10.4319/lom.2010.8.403 doi: 10.4319/lom.2010.8.403]&nbsp;&nbsp; [[Media: ThomasArthur2010.pdf | Open Access Article]]</ref>, Passeport ''et al.''<ref>Passeport, E., Landis, R., Lacrampe-Couloume, G., Lutz, E.J., Erin Mack, E., West, K., Morgan, S., Lollar, B.S., 2016. Sediment Monitored Natural Recovery Evidenced by Compound Specific Isotope Analysis and High-Resolution Pore Water Sampling. Environmental Science and Technology, 50(22), pp. 12197–12204. [https://doi.org/10.1021/acs.est.6b02961 doi: 10.1021/acs.est.6b02961]</ref>, and Risacher ''et al.''<ref name="RisacherEtAl2023"/>. The vial is filled with deionized water, and the membrane is held in place using the vial cap or an o-ring. Individual vials are either directly inserted into sediment or are incorporated into a support structure to allow multiple single-chamber peepers to be deployed at once over a given depth profile (Figure 3).
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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''.
  
−
==Peepers Preparation, Deployment and Retrieval==
+
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>.  
−
[[File:RisacherFig4.png | thumb |300px| Figure 4: Conceptual illustration of peeper passive sampling in a sediment matrix, showing peeper immediately after deployment (top) and after equilibration between the porewater and peeper chamber water (bottom)]]
 
−
Peepers are often prepared in laboratories but are also commercially available in a variety of designs from several suppliers. Peepers are prepared by first cleaning all materials to remove even trace levels of metals before assembly. The water contained inside the peeper is sometimes deoxygenated, and in some cases the peeper is maintained in a deoxygenated atmosphere until deployment<ref>Carignan, R., St‐Pierre, S., Gachter, R., 1994. Use of diffusion samplers in oligotrophic lake sediments: Effects of free oxygen in sampler material. Limnology and Oceanography, 39(2), pp. 468-474. [https://doi.org/10.4319/lo.1994.39.2.0468 doi: 10.4319/lo.1994.39.2.0468]&nbsp;&nbsp; [[Media: CarignanEtAl1994.pdf | Open Access Article]]</ref>. However, recent studies<ref name="RisacherEtAl2023"/> have shown that deoxygenation prior to deployment does not significantly impact sampling results due to oxygen rapidly diffusing out of the peeper during deployment. Once assembled, peepers are usually shipped in a protective bag inside a hard-case cooler for protection.
 
  
−
Peepers are deployed by insertion into sediment for a period of a few days to a few weeks. Insertion into the sediment can be achieved by wading to the location when the water depth is shallow, by using push poles for deeper deployments<ref name="RisacherEtAl2023"/>, or by professional divers for the deepest sites.  If divers are used, an appropriate boat or ship will be required to accommodate the diver and their equipment. Whichever method is used, peepers should be attached to an anchor or a small buoy to facilitate retrieval at the end of the deployment period.
+
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.  
  
−
During deployment, passive sampling is achieved via diffusion of inorganics through the peeper’s semi-permeable membrane, as the enclosed volume of peeper water equilibrates with the surrounding sediment porewater (Figure 4). It is assumed that the peeper insertion does not greatly alter geochemical conditions that affect freely-dissolved inorganics. Additionally, it is assumed that the peeper water equilibrates with freely-dissolved inorganics in sediment in such a way that the concentration of inorganics in the peeper water would be equal to that of the concentration of inorganics in the sediment porewater.  
+
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.  
  
−
After retrieval, the peepers are brought to the surface and usually preserved until they can be processed. This can be achieved by storing the peepers inside a sealable, airtight bag with either inert gas or oxygen absorbing packets<ref name="RisacherEtAl2023"/>. The peeper water can then be processed by quickly pipetting it into an appropriate sample bottle which usually contains a preservative (e.g., nitric acid for metals). This step is generally conducted in the field. Samples are stored on ice to maintain a temperature of less than 4°C and shipped to an analytical laboratory. The samples are then analyzed for inorganics by standard methods (i.e., USEPA SW-846). The results obtained from the analytical laboratory are then used directly or assessed using the equations below if a reverse tracer is used because deployment time is insufficient for all analytes to reach equilibrium.
+
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.
  
−
==Equilibrium Determination (Tracers)==
+
===Other Sorbents===
−
The equilibration period of peepers can last several weeks and depends on deployment conditions, analyte of interest, and peeper design. In many cases, it is advantageous to use pre-equilibrium methods that can use measurements in peepers deployed for shorter periods to predict concentrations at equilibrium<ref name="USEPA2017">USEPA, 2017. Laboratory, Field, and Analytical Procedures for Using Passive Sampling in the Evaluation of Contaminated Sediments: User’s Manual. EPA/600/R-16/357.&nbsp;&nbsp; [[Media: EPA_600_R-16_357.pdf | Report.pdf]]</ref>.  
+
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.
  
−
Although the equilibrium concentration of an analyte in sediment can be evaluated by examining analyte results for peepers deployed for several different amounts of time (i.e., a time series), this is impractical for typical field investigations because it would require several mobilizations to the site to retrieve samplers. Alternately, reverse tracers (referred to as a performance reference compound when used with organic compound passive sampling) can be used to evaluate the percentage of equilibrium reached by a passive sampler.
+
==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.
  
−
Thomas and Arthur<ref name="ThomasArthur2010"/> studied the use of a reverse tracer to estimate percent equilibrium in lab experiments and a field application. They concluded that bromide can be used to estimate concentrations in porewater using measurements obtained before equilibrium is reached. Further studies were also conducted by Risacher ''et al.''<ref name="RisacherEtAl2023"/> showed that lithium can also be used as a tracer for brackish and saline environments. Both studies included a mathematical model for estimating concentrations of ions in external media (''C<small><sub>0</sub></small>'') based on measured concentrations in the peeper chamber (''C<small><sub>p,t</sub></small>''), the elimination rate of the target analyte (''K'') and the deployment time (''t''):
+
===Sorbents===
−
</br>
+
{| 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
−
| || '''Equation&nbsp;1:'''  
+
|-
−
|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation1r.png]]
+
! 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;" |
 
|-
 
|-
−
| Where: || ||
+
! 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 || -- || --
 
|-
 
|-
−
| || ''C<small><sub>0</sub></small>''|| is the freely dissolved concentration of the analyte in the sediment (mg/L or &mu;g/L), sometimes referred to as ''C<small><sub>free</sub></small>  
+
! ''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 || -- || --
 
|-
 
|-
−
| || ''C<small><sub>p,t</sub></small>'' || is the measured concentration of the analyte in the peeper at time of retrieval (mg/L or &mu;g/L)
+
| colspan="12" style="background-color:white;" |
 
|-
 
|-
−
| || ''K'' || is the elimination rate of the target analyte
+
! 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
 
|-
 
|-
−
| || ''t'' || is the deployment time (days)
+
! ''n''
−
|}
+
| -- || 1.61 +/- 0.11 || 2.43 +/- 0.41 || 2.53 +/- 0.76
−
 
+
! ''b'' <small>(L/mg)</small>
−
The elimination rate of the target analyte (''K'') is calculated using Equation 2:
+
| -- || 0.30 +/- 0.04 || 0.36 +/- 0.08 || 0.30 +/- 0.15
−
</br>
+
|-
−
{|  
+
! ''r<sup><small>2</small></sup>''
−
| || '''Equation&nbsp;2:'''  
+
| -- || 0.97 || 0.82 || 0.57
−
|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation2r.png]]
+
! ''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 || -- || -- || --
 
|-
 
|-
−
| Where: || ||
+
! ''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 || -- || -- || --
 
|-
 
|-
−
| || ''K''|| is the elimination rate of the target analyte
+
| colspan="12" style="background-color:white;" |
 
|-
 
|-
−
| || ''K<small><sub>tracer</sub></small>'' || is the elimination rate of the tracer
+
! 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 || --
 
|-
 
|-
−
| || ''D'' || is the free water diffusivity of the analyte (cm<sup>2</sup>/s)
+
! ''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 || --
 
|-
 
|-
−
| || ''D<small><sub>tracer</sub></small>'' || is the free water diffusivity of the tracer (cm<sup>2</sup>/s)
+
| 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>
 
|}
 
|}
  
−
The elimination rate of the tracer (''K<small><sub>tracer</sub></small>'') is calculated using Equation 3:
+
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.
−
</br>
+
 
−
{|  
+
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).
−
| || '''Equation&nbsp;3:'''
+
 
−
|&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[[File: Equation3r2.png]]
+
===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
 
|-
 
|-
−
| Where: || ||
+
| polyhydroxybutyrate || PHB || [https://www.goodfellow.com/usa?srsltid=AfmBOoqEiqIbrvWb1Hn1Bc090efBUUfg6V4N3Vrn6ytajHMJR-FG1Ez- Goodfellow] || bacterial polyester
 
|-
 
|-
−
| || ''K<small><sub>tracer</sub></small>'' || is the elimination rate of the tracer
+
| 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
 
|-
 
|-
−
| || ''C<small><sub>tracer,i</sub></small>''|| is the measured initial concentration of the tracer in the peeper prior to deployment (mg/L or &mu;g/L)
+
| polybutylene succinate || BioPBS || [https://us.mitsubishi-chemical.com/company/performance-polymers/ Mitsubishi Chemical Performance Polymers] || compostable bio-based product
 
|-
 
|-
−
| || ''C<small><sub>tracer,t</sub></small>'' || is the measured final concentration of the tracer in the peeper at time of retrieval (mg/L or &mu;g/L)
+
| sucrose ester of fatty acids || SEFA SP10 || [https://www.sisterna.com/ Sisterna] || food and cosmetics additive
 
|-
 
|-
−
| || ''t'' || is the deployment time (days)
+
| sucrose ester of fatty acids || SEFA SP70 || [https://www.sisterna.com/ Sisterna] || food and cosmetics additive
 
|}
 
|}
  
−
Using this set of equations allows the calculation of the porewater concentration of the analyte prior to its equilibrium with the peeper water. A template for these calculations can be found in the appendix of Risacher ''et al.''<ref name="RisacherEtAl2023"/>.
+
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.
  
−
==Using Peeper Data at a Sediment Site==
+
[[File: FullerFig3.png | thumb | 400 px | Figure 3. Schematic of interactions between biochar and munitions constituents]]
−
Peeper data can be used to enable site specific decision making in a variety of ways. Some of the most common uses for peepers and peeper data are discussed below.
+
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.
  
−
'''Nature and Extent:''' Multiple peepers deployed in sediment can help delineate areas of increased metal availability. Peepers are especially helpful for sites that are comprised of coarse, relatively inert materials that may not be conducive to traditional bulk sediment sampling. Because much of the inorganics present in these types of sediments may be associated with the porewater phase rather than the solid phase, peepers can provide a more representative measurement of C<small><sub>0</sub></small>. Additionally, at sites where tidal pumping or groundwater flux may be influencing the nature and extent of inorganics, peepers can provide a distinct advantage to bulk sediment sampling or other point-in-time measurements, as peepers can provide an average measurement that integrates the variability in the hydrodynamic and chemical conditions over time.
+
===Biochar===
 +
[[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>.
  
−
'''Sources and Fate:''' A considerable advantage to using peepers is that C<small><sub>0</sub></small> results are expressed as concentration in units of mass per volume (e.g., mg/L), providing a common unit of measurement to compare across multiple media. For example, synchronous measurements of C<small><sub>0</sub></small> using peepers deployed in both surface water and sediment can elucidate the potential flux of inorganics from sediment to surface water. Paired measurements of both C<small><sub>0</sub></small> and bulk metals in sediment can also allow site specific sediment-porewater partition coefficients to be calculated. These values can be useful in understanding and predicting contaminant fate, especially in situations where the potential dissolution of metals from sediment are critical to predict, such as when sediment is dredged.
+
===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.
  
−
'''Direct Toxicity to Aquatic Life:''' Peepers are frequently used to understand the potential direct toxicity to aquatic life, such as benthic invertebrates and fish. A C<small><sub>0</sub></small> measurement obtained from a peeper deployed in sediment (''in situ'') or surface water (''ex situ''), can be compared to toxicological benchmarks for aquatic life to understand the potential toxicity to aquatic life and to set remediation goals<ref name="USEPA2017"/>. C<small><sub>0</sub></small> measurements can also be incorporated in more sophisticated approaches, such as the Biotic Ligand Model<ref>Santore, C.R., Toll, E.J., DeForest, K.D., Croteau, K., Baldwin, A., Bergquist, B., McPeek, K., Tobiason, K., and Judd, L.N., 2022. Refining our understanding of metal bioavailability in sediments using information from porewater: Application of a multi-metal BLM as an extension of the Equilibrium Partitioning Sediment Benchmarks. Integrated Environmental Assessment and Management, 18(5), pp. 1335–1347. [https://doi.org/10.1002/ieam.4572 doi: 10.1002/ieam.4572]</ref> to understand the potential for toxicity or the need to conduct toxicological testing or ecological evaluations.
+
===Trap and Treat Technology===
 +
[[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.
  
−
'''Bioaccumulation of Inorganics by Aquatic Life:''' Peepers can also be used to understand site specific relationship between C<small><sub>0</sub></small> and concentrations of inorganics in aquatic life. For example, measuring C<small><sub>0</sub></small> in sediment from which organisms are collected and analyzed can enable the estimation of a site-specific uptake factor. This C<small><sub>0</sub></small>-to-organism uptake factor (or model) can then be applied for a variety of uses, including predicting the concentration of inorganics in other organisms, or estimating a sediment C<small><sub>0</sub></small> value that would be safe for consumption by wildlife or humans. Because several decades of research have found that the correlation between C<small><sub>0</sub></small> measurements and bioavailability is usually better than the correlation between measurements of chemicals in bulk sediment and bioavailability, C<small><sub>0</sub></small>-to-organism uptake factors are likely to be more accurate than uptake factors based on bulk sediment testing.
+
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.
  
−
'''Evaluating Sediment Remediation Efficacy:''' Passive sampling has been used widely to evaluate the efficacy of remedial actions such as active amendments, thin layer placements, and capping to reduce the availability of contaminants at sediment sites. A particularly powerful approach is to compare baseline (pre-remedy) C<small><sub>0</sub></small> in sediment to C<small><sub>0</sub></small> in sediment after the sediment remedy has been applied. Peepers can be used in this context for inorganics, allowing the sediment remedy’s success to be evaluated and monitored in laboratory benchtop remedy evaluations, pilot scale remedy evaluations, and full-scale remediation monitoring.
+
==Summary==
 +
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.
  
 
==References==
 
==References==
Line 126: Line 222:
  
 
==See Also==
 
==See Also==
−
*[https://vimeo.com/809180171/c276c1873a Peeper Deployment Video]
+
*[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]
−
*[https://vimeo.com/811073634/303edf2693 Peeper Retrieval Video]
+
*[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]
−
*[https://vimeo.com/811328715/aea3073540 Peeper Processing Video]
 
−
*[https://sepub-prod-0001-124733793621-us-gov-west-1.s3.us-gov-west-1.amazonaws.com/s3fs-public/2024-09/ER20-5261%20Fact%20Sheet.pdf?VersionId=malAixSQQM3mWCRiaVaxY8wLdI0jE1PX Fact Sheet]
 

Latest revision as of 14:16, 30 October 2025

Remediation of Stormwater Runoff Contaminated by Munition Constituents

Past and ongoing military operations have resulted in contamination of surface soil with munition constituents (MC), which have human and environmental health impacts. These compounds can be transported off site via stormwater runoff during precipitation events. Technologies to “trap and treat” surface runoff before it enters downstream receiving bodies (e.g., streams, rivers, ponds) (see Figure 1), and which are compatible with ongoing range activities are needed. This article describes a passive and sustainable approach for effective management of munition constituents in stormwater runoff.

Related Article(s):


Contributor: Mark E. Fuller

Key Resource(s):

  • SERDP Project ER19-1106: Development of Innovative Passive and Sustainable Treatment Technologies for Energetic Compounds in Surface Runoff on Active Ranges

Background

Surface Runoff Characteristics and Treatment Approaches

Figure 1. Conceptual model of passive trap and treat approach for MC removal from stormwater runoff

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[1][2][3][4].

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[5][6][7][8][9]. For example, in a previous small study, MC were detected in surface runoff from an active live-fire range[10], 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[11]. 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[12][13][14][15][16]. 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[14][16]. 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)[17].

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[14]. 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[16]. 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[18][19][20][21], but also to facilitate their degradation[22][23][24][25][26][27]. Depending on the source biomass and pyrolysis conditions, biochar can possess a high specific surface area (on the order of several hundred m2/g)[28][29] 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)[30][31][32]. 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[31][32]. 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[33].

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[34][35][36][24][26] 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[37][38][39]. 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[25] 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[40][41] and reduced (or "charged") biochar as an electron donor for the reduction of nitrate[41]. 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[41] 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[42]. Cationized cellulosic materials (e.g., cotton, wood shavings) have been shown to effectively remove negatively charged energetics like perchlorate and NTO from solution[43]. A substantial body of work has shown that modified cellulosic biopolymers can also be effective sorbents for removing metals from solution[44][45][46][47] 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[43], 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)[48] and Gordonia species KTR9 (KTR9 henceforth)[48], the anoxic RDX degrader Pseudomonas fluorencens species I-C (I-C henceforth)[49][50], and the aerobic NQ degrader Pseudomonas extremaustralis species NQ5 (NQ5 henceforth)[51]. 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[52]. 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)[53].

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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See Also

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