Munitions Formulations Research Articles

5-Amino-1,2,4-triazol-3-one Degradation by Indirect Photolysis: A Density Functional Theory Study.

Sunlight irradiation induces formation of reactive oxygen species (superoxide, hydroperoxyl radical, singlet oxygen, etc.), which readily take part in degradation of environmental pollutants. Being a primary ingredient in a suite of insensitive munition formulations, NTO (5-nitro-1,2,4-triazol-3-one) can be released onto training range soils and reduced to ATO (5-amino-1,2,4-triazol-3-one) by soil bacteria or iron-contained minerals. ATO can be dissolved in surface water and groundwater due to its good water solubility and then undergo further decomposition. A detailed investigation of possible mechanisms for ATO decomposition in water induced by superoxide, hydroperoxyl radical, and singlet oxygen as pathways for ATO environmental degradation was performed by computational study at the PCM(Pauling)/M06-2X/6-311++G(d,p) level. Hydrolysis and degradation of ATO induced by superoxide are unlikely to occur due to the high activation energy or endergonicity of the processes. The hydroperoxyl radical causes rapid and reversible hydrogen transfer from ATO, while an attachment of the hydroperoxyl radical to ATO can induce decomposition of ATO, leading to its mineralization. Singlet oxygen shows a higher reactivity toward ATO than the hydroperoxyl radical. Decomposition of ATO was found to be a multistep process that begins with singlet oxygen attachment to the carbon atom of the C═N double bond. The intermediate that is formed undergoes recyclization, cycle opening, and sequential elimination of nitrogen gas, ammonia, and carbon(IV) oxide. Isocyanic acid, which arises intermediately, hydrolyzes into ammonia and carbon(IV) oxide. Calculated activation energies and high exergonicity of the studied processes support the contribution of singlet oxygen and the hydroperoxyl radical to ATO degradation into low-weight inorganic compounds in the environment.

Carbon and Nitrogen Isotope Fractionations During Biotic and Abiotic Transformations of 2,4-Dinitroanisole (DNAN).

2,4-Dinitroanisole (DNAN) is a main constituent in various new insensitive munition formulations. Although DNAN is susceptible to biotic and abiotic transformations, in many environmental instances, transformation mechanisms are difficult to resolve, distinguish, or apportion on the basis solely of analysis of concentrations. We used compound-specific isotope analysis (CSIA) to investigate the characteristic isotope fractionations of the biotic (by three microbial consortia and three pure cultures) and abiotic (by 9,10-anthrahydroquinone-2-sulfonic acid [AHQS]) transformations of DNAN. The correlations of isotope enrichment factors (ΛN/C) for biotic transformations had a range of values from 4.93 ± 0.53 to 12.19 ± 1.23, which is entirely distinct from ΛN/C values reported previously for alkaline hydrolysis, enzymatic hydrolysis, reduction by Fe2+-bearing minerals and iron-oxide-bound Fe2+, and UV-driven phototransformations. The ΛN/C value associated with the abiotic reduction by AHQS was 38.76 ± 2.23, within the range of previously reported values for DNAN reduction by Fe2+-bearing minerals and iron-oxide-bound Fe2+, albeit the mean ΛN/C was lower. These results enhance the database of isotope effects accompanying DNAN transformations under environmentally relevant conditions, allowing better evaluation of the extents of biotic and abiotic transformations of DNAN that occur in soils, groundwaters, surface waters, and the marine environment.

Degradation of NTO induced by superoxide and hydroperoxyl radicals: a comprehensive DFT study.

Reactive oxygen species, produced in the aquatic environment under sunlight irradiation, actively take part in degradation of environmental pollutants. NTO (5-nitro-1,2,4-triazol-3-one), being a primary ingredient in a suite of insensitive munitions formulations, may be released into training range soils after incomplete detonations and dissolved in surface water and groundwater due to good water solubility. A detailed investigation of a possible mechanism for NTO decomposition in water induced by superoxide and hydroperoxyl radicals as one of the pathways for NTO environmental degradation was performed with a computational study at the PCM(Pauling)/M06-2X/6-311++G(d,p) level. Superoxide causes rapid deprotonation of NTO. Decomposition of NTO induced by hydroperoxyl radicals was found to be a multistep process leading to mineralization of the nitrocompound. The reaction process may begin with hydroperoxyl radical attachment to carbon atom of the CN double bond of NTO, then proceeds through rupture of C-N bonds and addition of water molecules leading to the formation of nitrous acid, ammonia, nitrogen gas, hydrazine, and carbon(IV) oxide. The obtained results indicate that the anionic form of NTO shows a higher reactivity towards hydroperoxyl radicals than its neutral form. Excitation of NTO by sunlight enables complete mineralization of NTO induced by superoxide. The calculated activation energies and exergonicity of the studied processes support the contribution of hydroperoxyl radicals and superoxide to the degradation of NTO in the environment into low-weight inorganic compounds.

Isolation and characterization of nitroguanidine-degrading microorganisms

Nitroguanidine (NQ) is a component of newly developed insensitive munition (IM) formulations which are more resistant to impact, friction, heat, or sparks than conventional explosives. NQ is also used to synthesize various organic compounds and herbicides, and has both human and environmental health impacts. Despite the wide application and associated health concerns, limited information is known regarding NQ biodegradation, and only one NQ-degrading pure culture identified as Variovorax strain VC1 has been characterized. Here, we present results for three new NQ-degrading bacterial strains isolated from soil, sediment, and a lab-scale aerobic membrane bioreactor (MBR), respectively. Each of these strains -utilizes NQ as a nitrogen (N) source rather than as a source of carbon or energy. The MBR strain, identified as Pseudomonas extremaustralis strain NQ5, is capable of degrading NQ at a rate of approximately 150 μmole L−1 h−1 under aerobic conditions with glucose as a sole carbon source - and NQ as a sole N source. The addition of NH4+ to strain NQ5 during active growth with NQ as a sole N source slowed the growth rate for several hours, and the strain released NH4+, presumably from NQ. When NO3− was added as an alternate N source under similar conditions, the NO3− was not consumed, but NH4+ release into the culture medium was again observed. Strain NQ5 was also able to utilize guanylurea, guanidine, and ethyl allophanate as N sources, and - tolerate salt concentrations as high as 4 % (as NaCl). The other two stains, NQ4 and NQ7, both identified as Arthrobacter spp., grew significantly slower than strain NQ5 under similar culture conditions and tolerated only ∼1 % NaCl. In addition, neither strain NQ4 nor strain NQ7 was able to degrade guanlyurea or ethyl allophanate, but each degraded guanidine. These strains, particularly strain NQ5, may have practical applications for in-situ and ex-situ NQ bioremediation.

Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents

New energetic formulations containing insensitive high explosives (IHE), such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazole-5-one (NTO), and nitroguanidine (NQ) are being developed to provide safer munitions. The addition of IHE to munitions formulations results in complex wastewaters from explosives manufacturing, load and pour operations and demilitarization activities. New technologies are required to treat those wastewaters. The core objective of this research effort was to develop and optimize a dual anaerobic-aerobic membrane bioreactor (MBR) system for treatment of wastewater containing variable mixtures of traditional energetics, IHE, and anions. The combined system proved highly effective for treatment of traditional explosives (TNT, RDX, HMX), IHE (DNAN, NTO, NQ) and anions commonly used as military oxidants (ClO4−, NO3−). The anaerobic MBR, which was operated for more than 500 d, was observed to completely degrade mg L−1 concentrations of TNT, DNAN, ClO4− and NO3− under all operational conditions, including at the lowest hydraulic residence time (HRT) tested (2.2 d). The combined system generally resulted in complete treatment of mg L−1 concentrations of RDX and HMX to <20 μg L−1, with most of the degradation occurring in the anaerobic MBR and polishing in the aerobic system. No common daughter products of DNAN, TNT, RDX, or HMX were detected in the effluent. NTO was completely transformed in the anaerobic MBR, but residual 3-amino-1,2,4-triazole-5-one (ATO) was detected in system effluent. The ATO rapidly decomposed when bleach solution was added to the final effluent. NQ was initially recalcitrant in the system, but microbial populations eventually developed that could degrade >90% of the ∼10 mg L−1 NQ entering the anaerobic MBR, with the remainder degraded to <50 μg L−1 in the aerobic system. The dual MBR system proved to be capable of complete degradation of a wide mixture of munitions constituents and was resilient to changing influent composition.

Biodegradation of the emerging contaminant 3-nitro-1,2,4-triazol-5-one and its product 3-amino-1,2,4-triazol-5-one in perlite/soil columns

3-Nitro-1,2,4-triazol-5-one (NTO) is an ingredient of new safer-to-handle military insensitive munitions formulations. NTO can be microbially reduced to 3-amino-1,2,4-triazol-5-one (ATO) under anaerobic conditions if an electron donor is available. Conversely, ATO can undergo aerobic biodegradation. Previously, our research group developed an anaerobic enrichment culture that reduces NTO to ATO. A second culture could aerobically mineralize ATO. This study aimed to combine anaerobic/aerobic conditions within a down-flow perlite/soil column for simultaneous NTO reduction and ATO oxidation. Acetate biostimulation was investigated to promote oxygen depletion and create anaerobic micro-niches for NTO reduction, whereas perlite increased soil porosity and oxygen convection, allowing ATO oxidation. Two columns packed with a perlite/soil mixture (70:30, wet wt.%) or 100% perlite were operated aerobically and inoculated with the NTO- and ATO-degrading cultures. Initially, the influent consisted of ∼280 μM ATO, and after 30 days, the feeding was switched to ∼260 μM NTO and ∼250 μM acetate. By progressively increasing acetate from 250 to 4000 μM, the NTO removal gradually improved in both columns. The perlite/soil column reached a 100% NTO removal after 4000 μM acetate was supplemented. Additionally, there was no ATO accumulation, and inorganic nitrogen was produced, indicating ATO mineralization. Although NH4+ was produced following ATO oxidation, most nitrogen was recovered as NO3− likely via nitrification reactions. Microbial community analysis revealed that phylotypes hosted in the enrichment cultures specialized in NTO reduction (e.g., Geobacter) and ATO oxidation (e.g., Hydrogenophaga, Ramlibacter, Terrimonas, and Pseudomonas) were established in the columns. Besides, the predominant genera (Azohydromonas, Zoogloea, and Azospirillum) are linked to nitrogen cycling by performing nitrogen fixation, NO3− reduction, and nitroaromatics degradation. This study applied a bulking agent (perlite) and acetate biostimulation to achieve simultaneous NTO reduction and ATO oxidation in a single column. Such a strategy can assist with real-world applications of NTO and ATO biodegradation mechanisms.

Biodegradation of insensitive munition (IM) formulations: IMX-101 and IMX-104 using aerobic granule technology

A laboratory-scale aerobic granular sludge (AGS) sequencing batch bioreactor (SBR) was initiated in this study for the biodegradation of hazardous insensitive munition (IM) formulation constituents; 2,4-dinitroanisole (DNAN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 1-nitroguanidine (NQ), and 3-nitro-1,2,4-triazol-5-one (NTO). Efficient (bio)transformation of the influent DNAN and NTO was achieved throughout reactor operation with removal efficiencies greater than 95%. An average removal efficiency of 38.4 ± 17.5% was recorded for RDX. NQ was only slightly removed (3.96 ± 4.15%) until alkalinity was provided in the influent media, which subsequently increased the NQ removal efficiency up to an average of 65.8 ± 24.4%. Batch experiments demonstrated a competitive advantage for aerobic granular biofilms over flocculated biomass for the (bio)transformation DNAN, RDX, NTO, and NQ, as aerobic granules were capable of reductively (bio)transforming each IM compound under bulk aerobic conditions while flocculated biomass could not, thus demonstrating the contribution of inner oxygen-free zones within aerobic granules. A variety of catalytic enzymes were identified in the extracellular polymeric matrix of the AGS biomass. 16 S rDNA amplicon sequencing found Proteobacteria (27.2–81.2%) to be the most abundant phyla, with many genera associated with nutrient removal as well as genera previously described in relation to the biodegradation of explosives or related compounds.

Photolysis of 3-Nitro-1,2,4-triazol-5-one: Mechanisms and Products.

Insensitive munitions formulations that include 3-nitro-1,2,4-triazol-5-one (NTO) are replacing traditional explosive compounds. While these new formulations have superior safety characteristics, the compounds have greater environmental mobility, raising concern over potential contamination and cleanup of training and manufacturing facilities. Here, we examine the mechanisms and products of NTO photolysis in simulated sunlight to further inform NTO degradation in sunlit surface waters. We demonstrate that NTO produces singlet oxygen and that dissolved oxygen increases the NTO photolysis rate in deionized water. The rate of NTO photolysis is independent of concentration and decreases slightly in the presence of Suwannee River Natural Organic Matter. The apparent quantum yield of NTO generally decreases as pH increases, ranging from 2.0 × 10-5 at pH 12 to 1.3 × 10-3 at pH 2. Bimolecular reaction rate constants for NTO with singlet oxygen and hydroxyl radical were measured to be (1.95 ± 0.15) × 106 and (3.28 ± 0.23) × 1010 M-1 s-1, respectively. Major photolysis reaction products were ammonium, nitrite, and nitrate, with nitrite produced in nearly stoichiometric yield upon the reaction of NTO with singlet oxygen. Environmental half-lives are predicted to span from 1.1 to 5.7 days. Taken together, these data enhance our understanding of NTO photolysis under environmentally relevant conditions.

Elucidating the mechanisms associated with the anaerobic biotransformation of the emerging contaminant nitroguanidine

Nitroguanidine (NQ) is a constituent of gas generators for automobile airbags, smokeless pyrotechnics, insecticides, propellants, and new insensitive munitions formulations applied by the military. During its manufacture and use, NQ can easily spread in soils, ground, and surface waters due to its high aqueous solubility. Very little is known about the microbial biotransformation of NQ. This study aimed to elucidate important mechanisms operating during NQ anaerobic biotransformation. To achieve this goal, we developed an anaerobic enrichment culture able to reduce NQ to nitrosoguanidine (NsoQ), which was further abiotically transformed to cyanamide. Effective electron donors for NQ biotransformation were lactate and, to a lesser extent, pyruvate. The results demonstrate that the enrichment process selected a sulfate-reducing culture that utilized lactate as its electron donor and sulfate as its electron acceptor while competing with NQ as an electron sink. A unique property of the culture was its requirement for exogenous nitrogen (e.g., from yeast extract or NH4Cl) for NQ biotransformation since NQ itself did not serve as a nitrogen source. The main phylogenetic groups associated with the NQ-reducing culture were sulfate-reducing and fermentative bacteria, namely Cupidesulfovibrio oxamicus (63.1% relative abundance), Dendrosporobacter spp. (12.0%), and Raoultibacter massiliens (10.9%). The molecular ecology results corresponded to measurable physiological properties of the most abundant members. The results establish the conditions for NQ anaerobic biotransformation and the microbial community associated with the process, improving our present comprehension of NQ environmental fate and assisting the development of NQ remediation strategies.

Designing bacterial consortia for the complete biodegradation of insensitive munitions compounds in waste streams.

Insensitive munitions compounds (IMCs), such as 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), are replacing conventional explosives in munitions formulations. Manufacture and use of IMCs generate waste streams in manufacturing plants and load/assemble/pack facilities. There is a lack of practical experience in executing biodegradation strategies to treat IMCs waste streams. This study establishes a proof-of-concept that bacterial consortia can be designed to mineralize IMCs and co-occurring nitroaromatics in waste streams. First, DNAN, 4-nitroanisole (4-NA), and 4-chloronitrobenzene (4-CNB) in a synthetic DNAN-manufacturing waste stream were biodegraded using an aerobic fluidized-bed reactor (FBR) inoculated with Nocardioides sp. JS 1661 (DNAN degrader), Rhodococcus sp. JS 3073 (4-NA degrader), and Comamonadaceae sp. LW1 (4-CNB degrader). No biodegradation was detected when the FBR was operated under anoxic conditions. Second, DNAN and NTO were biodegraded in a synthetic load/assemble/pack waste stream during a sequential treatment comprising: (i) aerobic DNAN biodegradation in the FBR; (ii) anaerobic NTO biotransformation to 3-amino-1,2,4-triazol-5-one (ATO) by an NTO-respiring enrichment; and (iii) aerobic ATO mineralization by an ATO-oxidizing enrichment. Complete biodegradation relied on switching redox conditions. The results provide the basis for designing consortia to treat mixtures of IMCs and related waste products by incorporating microbes with the required catabolic capabilities.

Oxidative degradation of nitroguanidine (NQ) by UV-C and oxidants: Hydrogen peroxide, persulfate and peroxymonosulfate

Nitroguanidine (NQ), a component used in insensitive munitions formulations, has high solubility which often leads to highly contaminated wastewater streams. In this work, batch experiments were conducted to investigate and compare the NQ degradation by UV-based advanced oxidation processes (AOPs); hydrogen peroxide (H2O2), persulfate (PS) and peroxymonosulfate (PMS) were selected as oxidants. A preliminary evaluation of AOPs kinetics, byproducts, and potential degradation pathways were carried out and compared to NQ degradation by direct UV-C photolysis. The effects of oxidant dosage, NQ concentrations and pH were evaluated by determining the respective kinetic constants of degradation. Among the treatments applied, UV/PS showed to be a promising and effective alternative leading to faster rates of degradation respect to both oxidant dosage (25 mM) and initial NQ concentrations (≤24 mM). Nevertheless, the degradation rate of NQ by UV/PS appeared to be affected strongly by the initial pH compared to UV/H2O2 and UV/PMS, with the lowest rate overall at pH ≥ 8.0. In addition, the main byproducts from NQ degradation, guanidine and cyanamide, showed to be involved in further degradation steps only with UV/PS and UV/PMS suggesting higher degradation effectiveness of these oxidants compared UV/H2O2 and UV alone.

Reductive Transformation of 3-Nitro-1,2,4-triazol-5-one (NTO) by Leonardite Humic Acid and Anthraquinone-2,6-disulfonate (AQDS).

3-Nitro-1,2,4-triazol-5-one (NTO) is a major and the most water-soluble constituent in the insensitive munition formulations IMX-101 and IMX-104. While NTO is known to undergo redox reactions in soils, its reaction with soil humic acid has not been evaluated. We studied NTO reduction by anthraquinone-2,6-disulfonate (AQDS) and Leonardite humic acid (LHA) reduced with dithionite. Both LHA and AQDS reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO), stoichiometrically at alkaline pH and partially (50-60%) at pH ≤ 6.5. Due to NTO and hydroquinone speciation, the pseudo-first-order rate constants (kObs) varied by 3 orders of magnitude from pH 1.5 to 12.5 but remained constant from pH 4 to 10. This distinct pH dependency of kObs suggests that NTO reactivity decreases upon deprotonation and offsets the increasing AQDS reactivity with pH. The reduction of NTO by LHA deviated continuously from first-order behavior for >600 h. The extent of reduction increased with pH and LHA electron content, likely due to greater reactivity of and/or accessibility to hydroquinone groups. Only a fraction of the electrons stored in LHA was utilized for NTO reduction. Electron balance analysis and LHA redox potential profile suggest that the physical conformation of LHA kinetically limited NTO access to hydroquinone groups. This study demonstrates the importance of carbonaceous materials in controlling the environmental fate of NTO.

Outdoor dissolution and photodegradation of insensitive munitions formulations IMX-101 and IMX-104: Photolytic transformation pathway and mechanism study

New munition compounds have been developed to replace traditional explosives to prevent unintended detonations. However, insensitive munitions (IM) can leave large proportion of unexploded charge in the field, where it is subjected to photodegradation and dissolution in precipitation. The photolytic reactions occurring on the surfaces of IMX-101 and IMX-104 formulations and the subsequent fate of photolytic products in the environment were thoroughly investigated. The constituents of IMX-101 and IMX-104 formulations dissolve sequentially under rainfall in the order of aqueous solubility: 3-nitro-1,2,4-triazol-5-one (NTO) > nitroguanidine (NQ) > 2,4-dinitroanisole (DNAN) > 1,3,5-hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). A linear relationship between DNAN dissolution and rainwater volume was observed (r2: 0.86–0.99). It was estimated that it would take 16–228 years to completely dissolve these formulation particles under natural environmental conditions in Oracle, AZ. We used LC/MS/MS and GC/MS to examine the dissolution samples from IMX-101 and 104 particles exposed to rainfall and sunlight and found six DNAN photo-transformation products including 2-methoxy-5-nitrophenol, 4-methoxy-3-nitrophenol, 4-methoxy-3-nitroaniline, 2-methoxy-5-nitroaniline, 2,4-dinitrophenol, and methoxy-dinitrophenol, which are in good agreement with computational modeling results of bond strengths. The main DNAN photodegradation pathways are therefore proposed. Predicted eco-toxicity values suggested that the parent compound DNAN, methoxy-nitrophenols, methoxy-nitroanilines and the other two products (2,4-dinitrophenol and methoxy-dinitrophenol) would be harmful to fish and daphnid. Our study provides improved insight about the rain dissolution and photochemical behavior of IM formulations under natural conditions, which helps to form target-oriented strategies to mitigate explosive contamination in military training sites.

Review on Advanced Energetic Materials for Insensitive Munition Formulations

Insensitive munitions are munitions that are chemically stable enough to withstand thermal, mechanical, or electrical stimuli during storage and transportation, and can still explode as intended to defeat their targets. Extensive programmes have evolved worldwide for the development and introduction of insensitive munitions (IMs). The use of insensitive energetic materials significantly improves the protection of modern nuclear warheads and increases the survivability of conventional munitions in hustle environment. The most basic level to obtain insensitive munitions is the use of intrinsic insensitive energetic materials, either by synthesizing new, less sensitive crystalline materials or by improving the physical properties of existing sensitive materials. In light of the growing importance of insensitive munitions, this review paper brings out some potential insensitive energetic materials and plasticizers emphasizing their significant role in the development of futuristic IM formulations. This review also concisely brings out the recent work carried out globally, including India, on the development of advanced energetic materials and their insensitive energetic formulations.

Assessment of 2,4-Dinitroanisole Transformation Using Compound-Specific Isotope Analysis after In Situ Chemical Reduction of Iron Oxides.

Ferrous iron-bearing minerals are important reductants in the contaminated subsurface, but their availability for the reduction of anthropogenic pollutants is often limited by competition with other electron acceptors including microorganisms and poor accessibility to Fe(II) in complex hydrogeologic settings. The supply of external electron donors through in situ chemical reduction (ISCR) has been proposed as one remediation approach, but the quantification of pollutant transformation is complicated by the perturbations introduced to the subsurface by ISCR. Here, we evaluate the application of compound specific isotope analysis (CSIA) for monitoring the reduction of 2,4-dinitroanisole (DNAN), a component of insensitive munitions formulations, by mineral-bound Fe(II) generated through ISCR of subsurface material from two field sites. Electron balances from laboratory experiments in batch and column reactors showed that 3.6% to 11% of the total Fe in the sediments was available for the reduction of DNAN and its partially reduced intermediates after dithionite treatment. The extent of DNAN reduction was successfully quantified from its N isotope fractionation measured in the column effluent based on the derivation of a N isotope enrichment factor, εN, derived from a comprehensive series of isotope fractionation experiments with numerous Fe(II)-bearing minerals as well as dithionite-reduced subsurface materials. Our observations illustrate the utility of CSIA as a robust approach to evaluate the success of in situ remediation through abiotic contaminant reduction.

Review on Advanced Energetic Materials for Insensitive Munition Formulations

Review on Advanced Energetic Materials for Insensitive Munition Formulations

Advanced Oxidation Process for DNAN Using UV/H2O2

Abstract 2,4-Dinitroanisole (DNAN) is an important component of insensitive munitions that is anticipated to replace 2,4,6-trinitrotoluene (TNT) in munitions formulations. Photocatalyzed hydrogen peroxide (H2O2) oxidation experiments and chemical analyses were conducted to study the effect of initial pH and H2O2 dosage on the kinetics of DNAN decomposition and the reaction pathways. The results show that DNAN degradation followed zero-order kinetics when a 250 ppm DNAN solution was treated with ultraviolet (UV) light and 1500–4500 ppm H2O2 in an initial pH range of 4–7. However, when the H2O2 concentration was 750 ppm, DNAN degradation followed pseudo-first-order kinetics. The results indicate that DNAN can easily be oxidized by UV/H2O2 treatment. When the H2O2 dosage was 1500 ppm and the initial pH was 7, DNAN was reduced from 250 ppm to less than 1 ppm in 3 h. However, the total organic carbon (TOC) and total carbon (TC) concentrations were reduced slowly from 100 to less than 70 ppm carbon (C) in 3 h, and decreased to about 5 ppm after 9 h of treatment, suggesting the formation of other organic compounds. Those reaction intermediates were oxidized to carbon dioxide (CO2) at a slower rate than the oxidation of DNAN. CO2 was emitted from the solution because the solution pH decreased rapidly to about 3 during the UV/H2O2 oxidation. Most of the nitrogen in DNAN was converted to nitrate by UV/H2O2 oxidation after 9 h of treatment. The research results indicate that UV/H2O2 oxidation is a promising technique for the treatment of DNAN in wastewater.

Photo-transformation of aqueous nitroguanidine and 3-nitro-1,2,4-triazol-5-one: Emerging munitions compounds

Two major components of insensitive munition formulations, nitroguanidine (NQ) and 3-nitro-1,2,4-triazol-5-one (NTO), are highly water soluble and therefore likely to photo-transform while in solution in the environment. The ecotoxicities of NQ and NTO solutions are known to increase with UV exposure, but a detailed accounting of aqueous degradation rates, products, and pathways under different exposure wavelengths is currently lacking. Here, we irradiated aqueous solutions of NQ and NTO over a 32-h period at three ultraviolet wavelengths (254 nm, 300 nm, and 350 nm) and analyzed their degradation rates and transformation products. NQ was completely degraded by 30 min at 254 nm and by 4 h at 300 nm, but it was only 10% degraded after 32 h at 350 nm. Mass recoveries of NQ and its transformation products were ≥80% for all three wavelengths, and consisted of large amounts of guanidine, nitrate, and nitrite, and smaller amounts of cyanamide, cyanoguanidine, urea, and ammonium. NTO degradation was greatest at 300 nm with 3% remaining after 32 h, followed by 254 nm (7% remaining) and 350 nm (20% remaining). Mass recoveries of NTO and its transformation products were high for the first 8 h but decreased to 22–48% by 32 h, with the major aqueous products identified as ammonium, nitrate, nitrite, and a urazole intermediate. Environmental half-lives of NQ and NTO in pure water were estimated as 4 and 6 days, respectively. We propose photo-degradation pathways for NQ and NTO supported by observed and quantified degradation products and changes in solution pH.

Degradation of 3-nitro-1,2,4-trizole-5-one (NTO) in wastewater with UV/H2O2 oxidation

Insensitive Munition (IM) formulations contain 3-nitro-1,2,4-trizole-5-one (NTO), an energetic compound with the highest aqueous solubility (16 g L−1) among all IM explosives, including 2,4-dinitroanisole (DNAN) and 1-nitroguanidine (NQ); as a result wastewater streams from IM processing facilities can be highly contaminated and potentially toxic. The removal of energetic compounds from wastewater streams prior to their discharge in the environment is imperative, and new technology must be developed to efficiently treat high levels of NTO and other IM compounds in these streams. In this study, the treatment of NTO wastewater by a UV/H2O2 oxidation process under acidic conditions (pH = 3.0 ± 0.1) and a hydrogen peroxide concentration of at least 1500 mg L−1 resulted in successful removal of the energetic compound. The organic carbon from the NTO ring was completely converted to inorganic carbon (CO2), as confirmed through TOC measurements and GC–MS analysis on the reactor headspace. Nitrate and ammonium ions were the major nitrogen by-products, as indicated by mass spectrometry. The results obtained in this work demonstrate that the UV/H2O2 oxidation process can effectively mineralize high concentrations of NTO in wastewater streams leading to recovery of valuable nutrients that can be used for supporting algal biomass growth for biofuel/biogas generation.

Different Mechanisms of Alkaline and Enzymatic Hydrolysis of the Insensitive Munition Component 2,4-Dinitroanisole Lead to Identical Products

The emerging use of 2,4-dinitroanisole (DNAN) in insensitive munitions formulations has caused concern about future contamination of subsurface environments, generating significant interest in understanding and identifying its transformation processes. Here we characterized the C and N isotope fractionation associated with abiotic and biological DNAN hydrolysis through alkaline hydrolysis at high pH as well as enzymatic hydrolysis by Nocardioides sp. JS1661 and partially purified DNAN O-demethylase. Whereas both reactions generated 2,4-dinitrophenol (DNP), compound-specific isotope analysis (CSIA) of DNAN and DNP revealed that these reactions occur by different mechanisms. Alkaline hydrolysis was associated with apparent 13C and 15N kinetic isotope effects (13C-AKIE and 15N-AKIE) of 1.044 ± 0.003 and 1.0027 ± 0.0004, respectively, reflecting the previously postulated nucleophilic aromatic substitution mechanism. Conversely, enzyme-catalyzed DNAN hydrolysis exhibited a 13C-AKIE of 1.027 ± 0.005 and a 15N-A...