Degradation Of HMX Research Articles

Development of microbial formulation to enhance the removal of high explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) from contaminated soil

Excessive use of High Melting Explosive (HMX; Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) in various industrial activities, construction, mining, military exercises, and conflicts has resulted in severe contamination of soil and water. In the present study, a water-dispersible granule (WDG) was developed using microbial strains capable of degrading HMX. The developed microbial formulation was further investigated and characterized using soil microcosms study and the degradation pathway of HMX by these microbes were elucidated. Out of 6 bacterial strains initially selected for the study, Pelomonas aquatica and Kinneretia asaccharophila were found to be the most efficient HMX degraders in soil capable of removing 65 % and 61 % HMX respectively, within 30 days. These microbial strains formulated as WDGs has shelf-life of up to 6 months at 30˚C with only 16 % loss in viability. Enhancement of 19.64 % and 19.25 % HMX degradation in soil was observed with the use of WDGs from P. aquatica and K. asaccharophila, respectively. LC-MS (Liquid chromatography-mass spectrometry) analysis revealed the presence of nitroso derivate of HMX (1-NO-HMX) at 325 m/z as an intermediate metabolite indicating the single nitrite elimination pathway for HMX degradation leading to the formation of nitrite, nitrate, and CO2 as end products during degradation. The current study provides the base for the development of efficient microbial formulations for enhanced remediation of HMX contaminated soils.

The Methods and Characteristics of the Electrochemical Oxidation Degradation of HMX

Octagon (HMX) is a typical organic pollutant of explosives in the surrounding environments of military factories, and it is widely regarded as a carcinogen which may enter the human body through wastewater and atmospheric exposure, resulting in potential health risks. Therefore, this paper studies the degradation of HMX by electrochemical oxidation. In this study, an electrochemical system was built using a copper plate as the cathode and a Ti/PbO2 electrode as the anode. The effects of various process variables, such as the initial pH value, the current density, and the distance between the electrodes, were investigated in relation to HMX degradation. Following this, performance optimization and intermediate analysis were carried out, along with an estimation of the energy consumption of HMX deterioration in various operating situations. The experimental results in this paper show that when the electrolyte concentration is 0.25 mol/L, the current density is 70 mA/cm2, the electrode spacing is 1.0 cm, and the initial pH is 5.0. Electrochemical oxidation has a better treatment efficiency for pollutants, and the removal rate reaches 81.2%. The findings of kinetic research reveal that the electrochemical oxidation degradation process of HMX follows quasi-first-order kinetics, and protein stress and Deoxyribo Nucleic Acid (DNA) loss stress are significantly different from other stress types throughout the whole degradation process. HMX degradation solution causes damage to protein transcription or expression. However, some genes of oxidative stress are continuously up-regulated, because H2O2 and OH produced by electrochemical oxidation cause a strong response to oxidative stress in cells. The research findings in this report offer crucial guidance and suggestions for the industrialization of HMX wastewater treatment.

An Overview of Treatment Approaches for Octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX) Explosive in Soil, Groundwater, and Wastewater

Octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX) is extensively exploited in the manufacturing of explosives; therefore, a significant level of HMX contamination can be encountered near explosive production plants. For instance, up to 12 ppm HMX concentrations have been observed in the wastewater effluent of a munitions manufacturing facility, while up to 45,000 mg/kg of HMX has been found in a soil sample taken from a location close to a high-explosive production site. Owing to their immense demand for a variety of applications, the large-scale production of explosives has culminated in severe environmental issues. Soil and water contaminated with HMX can pose a detrimental impact on flora and fauna and hence, remediation of HMX is paramount. There is a rising demand to establish a sustainable technology for HMX abatement. Physiochemical and bioremediation approaches have been employed to treat HMX in the soil, groundwater, and wastewater. It has been revealed that treatment methods such as photo-peroxidation and photo-Fenton oxidation can eliminate approximately 98% of HMX from wastewater. Fenton's reagents were found to be very effective at mineralizing HMX. In the photocatalytic degradation of HMX, approximately 59% TOC removal was achieved by using a TiO2 photocatalyst, and a dextrose co-substrate was used in a bioremediation approach to accomplish 98.5% HMX degradation under anaerobic conditions. However, each technology has some pros and cons which need to be taken into consideration when choosing an HMX remediation approach. In this review, various physiochemical and bioremediation approaches are considered and the mechanism of HMX degradation is discussed. Further, the advantages and disadvantages of the technologies are also discussed along with the challenges of HMX treatment technologies, thus giving an overview of the HMX remediation strategies.

Performance Optimization and Toxicity Effects of the Electrochemical Oxidation of Octogen

Octogen (HMX) is widely used as a high explosive and constituent in plastic explosives, nuclear devices, and rocket fuel. The direct discharge of wastewater generated during HMX production threatens the environment. In this study, we used the electrochemical oxidation (EO) method with a PbO2-based anode to treat HMX wastewater and investigated its degradation performance, mechanism, and toxicity evolution under different conditions. The results showed that HMX treated by EO could achieve a removal efficiency of 81.2% within 180 min at a current density of 70 mA/cm2, Na2SO4 concentration of 0.25 mol/L, interelectrode distance of 1.0 cm, and pH of 5.0. The degradation followed pseudo-first-order kinetics (R2 > 0.93). The degradation pathways of HMX in the EO system have been proposed, including cathode reduction and indirect oxidation by •OH radicals. The molecular toxicity level (expressed as the transcriptional effect level index) of HMX wastewater first increased to 1.81 and then decreased to a non-toxic level during the degradation process. Protein and oxidative stress were the dominant stress categories, possibly because of the intermediates that evolved during HMX degradation. This study provides new insights into the electrochemical degradation mechanisms and molecular-level toxicity evolution during HMX degradation. It also serves as initial evidence for the potential of the EO-enabled method as an alternative for explosive wastewater treatment with high removal performance, low cost, and low environmental impact.

In-vessel composting of HMX and RDX contaminated sludge using microbes isolated from contaminated site

Current study was carried out with an objective to remediate highly contaminated sludge with HMX and RDX obtained from an explosive manufacturing facility in North India employing indigenous microbes, Arthrobacter subterraneus (isolate no. S2-TSB-17) and Bacillus sonorensis (isolate no. S8-TSB-4) which were isolated from the same contaminated site. In-vessel composting of the explosive contaminated sludge was performed in 12 different bioreactors using cow manure and garden waste as bulking agents. 78.5% degradation of HMX was observed in reactor no. 2 with Bacillus sonorensis having combination of 10% sludge, 70% cow manure and 20% garden waste on 80th day. Two secondary metabolites Bis(hydroxymethyl)nitramine and methylene dinitramine were identified while studying the degradation pathway. Similarly, degradation of 91.2% was observed for RDX in reactor no. 11 with consortia of Arthrobacter subterraneus and Bacillus sonorensis on 80th day. During the study, release of significant nitrate and nitrite ions were observed. It has already been established that RDX and HMX degradation leads to release of nitrite/nitrate ions. The highest nitrite (reactor no. 11) and nitrate (reactor no. 2) release observed were 24.02 ± 0.05 mg/kg and 30.65 ± 0.99 mg/kg on 50th and 70th day, respectively. Scanning electron microscopic studies confirmed the attachment and presence of microbes with solid surface and no deformation in structure was observed in the microbial cells due to contamination stress. Findings of the study concluded that in-vessel composting assisted with native bacterial species can be a potential technology for the treatment of explosive contaminated sludge at the contaminated sites.

Biodegradation and physiological response mechanism of Bacillus aryabhattai to cyclotetramethylenete-tranitramine (HMX) contamination

This study aims to reveal the biodegradation and interaction mechanism of cyclotetramethylenete-tranitramine (HMX) by a newly isolated bacteria. In this study, a bacterial strain (Bacillus aryabhattai) with high efficiency for HMX degradation was used as the test organism to analyze the changes in growth status, cell function, and mineral metabolism following exposure to different stress concentrations (0 and 5 mg L−1) of HMX. Non-targeted metabonomics was used to reveal the metabolic response of this strain to HMX stress. The results showed that when the HMX concentration was 5 mg L−1, the removal rate of HMX within 24 h of inoculation with Bacillus aryabhatta was as high as 90.5%, the OD600 turbidity was 1.024, and the BOD5 was 225 mg L−1. Scanning electron microscope (SEM) images showed that the morphology of bacteria was not obvious Variety, Fourier transform infrared spectroscopy (FTIR) showed that the cell surface –OH functional groups drifted, and ICP-MS showed that the cell mineral element metabolism was disturbed. Non-targeted metabonomics showed that HMX induced the differential expression of 254 metabolites (133 upregulated and 221 downregulated). The main differentially expressed metabolites during HMX stress were lipids and lipid-like molecules, and the most significantly affected metabolic pathway was purine metabolism. At the same time, the primary metabolic network of bacteria was disordered. These results confirmed that Bacillus aryabhattai has a high tolerance to HMX and can efficiently degrade HMX. The degradation mechanism involves the extracellular decomposition of HMX and transformation of the degradation products into intracellular purines, amino sugars, and nucleoside sugars that then participate in cell metabolism.

Optimization of process parameters for degradation of HMX with Bacillus toyonensis using response surface methodology

Contamination of soil and water with explosive compounds like octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX or commonly known as high melting explosives) is increasing day by day due to their extensive use all over the world. High level of contamination has been found near military sites, explosive manufacturing facilities, war-lands, mines and exercise ranges. Remediation of such contaminants is necessary as they may have adverse impact on biotic as well as on abiotic environment. Present study was carried out with an objective to optimize the variable process parameters for the degradation of HMX in aqueous phase by indigenously isolated bacterial strain, Bacillus toyonensis from an actual HMX contaminated site in North India using response surface methodology. The relationship among varying initial concentrations of HMX, microbial inoculum size and degradation time was revealed in the current study. Results showed that 87.7% degradation was achieved at 2 mg/L initial HMX concentration with inoculum size of 4% on 15th day. High regression coefficient value (0.9878) further supported predictability of experimental data. Nitrite and nitrate concentrations estimated during the experiment indicate breakdown and degradation process of HMX. Findings of this study concluded that Bacillus toyonensis can be a potential microorganism to degrade HMX and can be used for microbial remediation of HMX contaminated sites.

Synthesis and Characterization of a Dinuclear Nitrogen‐Rich Ferrocenyl Ligand and Its Ionic Coordination Compounds and Their Catalytic Effects During Combustion

Alkylferrocene‐based burning‐rate catalysts (BRCs) exhibit distinct migration tendency and high volatility and thus result in inferior performance of composite solid propellants during their combustion processes. To deal with these drawbacks, a novel dinuclear nitrogen‐rich ferrocene derivative, 4‐amino‐3,5‐bis(4‐ferrocenyl‐1,2,3‐triazolyl‐1‐methyl)‐1,2,4‐triazole (BFcTAZ) and its twenty seven ionic coordination compounds, [M2(BFcTAZ)2(H2O)4]mXn·xH2O (M = Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2; X = polycyano anions), were synthesized and characterized by FT‐IR, UV/Vis, and elementary analysis. Crystal structure of BFcTAZ was further confirmed by single‐crystal X‐ray diffraction and a general molecular structure of the new complexes was proposed. Their high thermal stability was verified by TG technique. Cyclic voltammetry studies suggested that the new compounds are diverse redox systems. Their effects on the thermal degradation of some common oxidizers were measured by DSC technique. The results indicated that most of the new complexes exert great effects on the thermal decomposition of AP, RDX, and 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7) and some of them are more active than catocene. The Cu2+ complexes are among the excellent ones. However, only six compounds have appreciable catalytic activity in the thermal degradation of HMX.

Preliminary investigation on ultrasound frequency determination in TNT, RDX and HMX degradation

The wastewater of the munitions industry varies in terms of the recalcitrant compounds depending on the products and the manufacturing process. The most commonly encountered energetic nitro-aromatic compounds in ammunition wastewater are trinitrotoluene (TNT), nitro-heterocyclic hexahydro-trinitrotriazine (RDX), and cyclotetramethylene-tetranitramine (HMX). These compounds are known to be very toxic and resistant to biodegradation. The aim of this study was to determine the appropriate ultrasound frequency to assist the anaerobic biodegradation of TNT, RDX, and HMX Therefore, the optimum ultrasound frequencies were investigated to degrade TNT, RDX, and HMX without destroying anaerobic microorganisms. The results showed that ultrasound irradiation was effective for the degradation of all the explosive compounds used. However, the maximum removal efficiencies and minimum microorganism lysis were achieved by the frequencies of 20 and 800 kHz.

Synthesis, characterization, migration and catalytic effects of energetic ionic ferrocene compounds on thermal decomposition of main components of solid propellants

Sixteen new energetic ionic ferrocene compounds, [FcCH2N(CH3)2(CnH2n+1]+X− (Fc=ferrocenyl; X−=nitrate or picrate anion; n=3–10), were synthesized in high yields and characterized by 1H NMR, 13C NMR, UV–Vis, elementary analysis, TG and DSC methods. All the compounds show high thermal stability. Cyclic voltammetry investigations revealed that the ionic compounds exhibit redox waves for ferrocenyl groups and are considered as irreversible redox systems. Migration studies disclosed that their migration tendency increases with elongation of alkyl chain length in the cations of the compounds, and much slower than that of neutral n-butylferrocene (NBF). The sensitivities tests towards impact and friction revealed that all picrates are sensitive compounds, while the nitrates are less sensitive analogs. Their catalytic performances for thermal degradation of main components of solid propellants such as ammonium perchlorate (AP), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), 1,2,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) and hydroxyl-terminated polybutadiene (HTPB) as well as 1:1 mixture of HTPB and AP, were evaluated by DSC and/or TG techniques. All the ionic compounds can efficiently catalyze the thermal degradation of AP, HTPB and their 1:1 mixture. Compounds 1–8, 11 and 16 exhibit catalytic activity in thermal decomposition of RDX. None of them display distinct catalytic effect on the thermal degradation of HMX. These low-migration ferrocene derivatives may be used as alternatives to NBF in HTPB/AP composite solid propellants.

Biodegradation of explosives mixture in soil under different water-content conditions

Soil redox potential plays a key role in the rates and pathways of explosives degradation, and is highly influenced by water content and microbial activity. Soil redox potential can vary significantly both temporally and spatially in micro-sites. In this study, when soil water content increased, the redox potential decreased, and there was significant enhancement in the biodegradation of a mixture of three explosives. Whereas TNT degradation occurred under both aerobic and anaerobic conditions, RDX and HMX degradation occurred only when water content conditions resulted in a prolonged period of negative redox potential. Moreover, under unsaturated conditions, which are more representative of real environmental conditions, the low redox potential, even when measured for temporary periods, was sufficient to facilitate anaerobic degradation. Our results clearly indicate a negative influence of TNT on the biodegradation of RDX and HMX, but this effect was less pronounced than that found in previous slurry batch experiments: this can be explained by a masking effect of the soil in the canisters. Fully or partially saturated soils can promote the existence of micro-niches that differ considerably in their explosives concentration, microbial community and redox conditions.

Performance of mesophilic anaerobic granules for removal of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) from aqueous solution

The performance of mesophilic anaerobic granules to degrade octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) was investigated under various conditions. The results of batch experiments showed that anaerobic granules were capable of removing HMX from aqueous solution with high efficiency. Both biotic and abiotic mechanisms contributed to the removal of HMX by anaerobic granules under mesophilic conditions. Adsorption appeared to play a significant role in the abiotic process. Furthermore, HMX could be biodegraded by anaerobic granules as the sole substrate. After 16 days of incubation, 99.04% and 96.42% of total HMX could be removed by 1 g VSS/L acclimated and unacclimated granules, respectively. Vancomycin, an inhibitor of acetogenic bacteria, caused a significant inhibition of HMX biotransformation, while 2-bromoethanesulfonic acid, an inhibitor of methanogenic bacteria, only resulted in a slight decrease of metabolic activity. The presence of the glucose, as a suitable electron donor and carbon source, was found to enhance the degradation of HMX by anaerobic granules. Our study showed that sulfate had little adverse effects on biotransformation of HMX by anaerobic granules. However, nitrate had significant inhibitory effect on the extent of HMX removal especially in the initial period. This study offered good prospects of using high-rate anaerobic technology in the treatment of munition wastewater.

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) Biodegradation Kinetics Amongst Several Fe(III)-Reducing Genera

Cyclic nitramine explosives biodegradation was investigated among four Fe(III)- and quinone-reducing bacterial genera. This strategy is an attractive option for RDX and/or HMX contamination because of their ubiquity; however, the biotransformation kinetics among different microbial populations is not known. The organisms investigated included two species within the Geobacteraceae, and one species each within the genera Anaeromyxobacter, Desulfitobacterium, and Shewanella. All species directly reduced RDX; however, humic substances (HS) and the HS analog anthraquinone-2,6-disulfonate (AQDS) significantly increased the rate and extent of RDX reduction. Degradation kinetics varied amongst the species tested, but extracellular electron shuttle mediated degradation rates were the fastest for each organism. RDX reduction rates ranged from 7.4 to 269.3 nmol RDX hr − 1 mg cell protein − 1 when AQDS was present. HMX was reduced more slowly by G. metallireducens than RDX; however, electron shuttles also stimulated HMX degradation. These data suggest that electron shuttle mediated cyclic nitramine transformation is ubiquitous among the keystone Fe(III)-reducing microbial genera, and that bioremediation strategies predicated on their physiology may be a reasonable approach in situ for both Fe(III)-rich and Fe(III)-poor environments.

Halide salts accelerate degradation of high explosives by zerovalent iron

Zerovalent iron (Fe 0, ZVI) has drawn great interest as an inexpensive and effective material to promote the degradation of environmental contaminants. A focus of ZVI research is to increase degradation kinetics and overcome passivation for long-term remediation. Halide ions promote corrosion, which can increase and sustain ZVI reactivity. Adding chloride or bromide salts with Fe 0 (1% w/v) greatly enhanced TNT, RDX, and HMX degradation rates in aqueous solution. Adding Cl or Br salts after 24 h also restored ZVI reactivity, resulting in complete degradation within 8 h. These observations may be attributed to removal of the passivating oxide layer and pitting corrosion of the iron. While the relative increase in degradation rate by Cl − and Br − was similar, TNT degraded faster than RDX and HMX. HMX was most difficult to remove using ZVI alone but ZVI remained effective after five HMX reseeding cycles when Br − was present in solution.

Degradation Kinetics and Mechanism of RDX and HMX in TiO2 Photocatalysis

This study was undertaken to examine the photocatalytic degradation of explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) with a circular photocatalytic reactor, using a UV lamp as a light source and TiO2 as a photocatalyst. The effects of various parameters, such as the RDX or HMX concentration, the amount of TiO2, and the initial pH, on the photocatalytic degradation rates of explosives were examined. In the presence of both UV light and TiO2, RDX and HMX were more effectively degraded than with either UV or TiO2 alone. The degradation rates were found to obey pseudo-first-order kinetics represented by the Langmuir-Hinshelwood model. Increases in the RDX and HMX degradation rates were obtained with decreasing initial concentrations of the explosives. The RDX and HMX degradation rates were higher at pH 7 than at either pH 3 or pH 11. A dose of approximately 0.7 g l−1 of TiO2 degraded HMX more rapidly than did higher or lower TiO2 doses. RDX (20 mg l−1) photocatalysis resulted in an approximately 20% decrease in TOC, and HMX (5 mg l−1) photocatalysis resulted in a 60% decrease in TOC within 150 minutes. A trace amount of formate was produced as an intermediate that was further mineralized by RDX or HMX photocatalysis. The nitrogen byproducts from the photocatalysis of RDX and HMX were mainly NO3 − with NO2 − and NH4 +. The total nitrogen recovery was about 60% from RDX (20 mg l−1), and 70% from HMX (5 mg l−1), respectively. Finally, a mechanism for RDX/HMX photocatalysis was proposed, along with supporting qualitative and quantitative evidence.

Photocatalytic degradation of explosives contaminated water

This study was undertaken to examine the degradation of TNT, RDX and HMX in a circular photocatalytic reactor with TiO2 as a photocatalyst. We examined the impact of parameters such as the initial concentration, initial pH of solution on rates of photocatalized transformation, and the mineralization. The results showed that photocatalysis is an effective process for the degradation of TNT, RDX and HMX. They could be comoletely degraded in 150 min with 1.0 g/L TiO2 at pH 7. An increase in the photocatalytic degradation of HMX was noticed with decreasing initial HMX. The rates of RDX and HMX degradation were greater in neutral pH than in acidic and alkaline conditions. In case of TNT degradation, the rate of degradation was the fastest at pH 11. Approximately 82% TOC decrease in the TNT degradation was achieved after 150 min, whereas TOC decrease in RDX and HMX was 24% and 59%, respectively. Nitrate, nitrite, and ammonium ions were detected as the nitrogen byproducts from the photocatalysis, and more than 50% of the total nitrogen was recovered as nitrate ion in every explosives.

Enhanced biodegradation of cyclotetramethylenetetranitramine (HMX) under mixed electron-acceptor condition

The biodegradation of cyclotetramethylenetetranitramine, commonly known as `high melting explosive' (HMX), under various electron-acceptor conditions was investigated using enrichment cultures developed from the anaerobic digester sludge of Thibodaux sewage treatment plant. The results indicated that the HMX was biodegraded under sulfate reducing, nitrate reducing, fermenting, methanogenic, and mixed electron accepting conditions. However, the rates of degradation varied among the various conditions studied. The fastest removal of HMX (from 22 ppm on day 0 to <0.05 ppm on day 11) was observed under mixed electron-acceptor conditions, followed in order by sulfate reducing, fermenting, methanogenic, and nitrate reducing conditions. Under aerobic conditions, HMX was not biodegraded, which indicated that HMX degradation takes place under anaerobic conditions via reduction. HMX was converted to methanol and chloroform under mixed electron-acceptor conditions. This study showed evidence for HMX degradation under anaerobic conditions in a mixed microbial population system similar to any contaminated field sites, where a heterogeneous population exists.

Enhanced Biodegradation and Fate of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX) and Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine (HMX) in Anaerobic Soil Slurry Bioprocess

Native soil microbial populations and unadapted municipal anaerobic sludges were compared for nitramine explosive degradation in microcosm assays under various conditions. Microbial populations from an explosive-contaminated soil were only able to mineralize 12% hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) (at a concentration of 800 mg/kg slurry) or 4% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) (at a concentration of 267 mg/kg slurry). In contrast, municipal anaerobic sludges were able to mineralize them to carbon dioxide, with efficiencies of up to 65%. Reduction of RDX and HMX into their corresponding nitroso-derivatives was notably faster than their mineralization. The biodegradation of HMX was typically delayed by the presence of RDX in the microcosm, confirming RDX is used as an electron acceptor preferentially to HMX. The laboratory-scale bioslurry reactor reproduced the results of the microcosm assays, yet with much higher RDX and HMX degradation rates. A radiolabel-based mass balance in the soil slurry indicated that, besides a significant mineralization to carbon dioxide, 25% and 31% of RDX and HMX, respectively, appeared as acetonitrile-extractable metabolites, while the remaining part was incorporated into biomass and irreversibly bound to the soil matrix. About 10% of the HMX derivatives were estimated to be chemically bound to the soil matrix, while for RDX the estimation was nil.