Abstract  Large-scale aerobic windrow composting has been used to bioremediate washout lagoon soils contaminated with the explosives TNT (2,4,6-trinitrotoluene) and RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) at several sites within the United States. We previously used 15N NMR to investigate the reduction and binding of T15NT in aerobic bench-scale reactors simulating the conditions of windrow composting. These studies have been extended to 2,4-dinitrotoluene (2,4DNT) and 2,6-dinitrotoluene (2,6DNT), which, as impurities in TNT, are usually presentwherever soils have been contaminated with TNT. Liquid-state 15N NMR analyses of laboratory reactions between 4-methyl-3-nitroaniline-15N, the major monoamine reduction product of 2,4DNT, and the Elliot soil humic acid, both in the presence and absence of horseradish peroxidase, indicated that the amine underwent covalent binding with quinone and other carbonyl groups in the soil humic acid to form both heterocyclic and non-heterocyclic condensation products. Liquid-state 15N NMR analyses of the methanol extracts of 20 day aerobic bench-scale composts of 2,4-di-15N-nitrotoluene and 2,6-di-15N-nitrotoluene revealed the presence of nitrite and monoamine, but not diamine, reduction products, indicating the occurrence of both dioxygenase enzyme and reductive degradation pathways. Solid-state CP/MAS 15N NMR analyses of the whole composts, however, suggested that reduction to monoamines followed by covalent binding of the amines to organic matter was the predominant pathway.

Abstract  The purpose of this assessment was to determine emissions from the hot gas decontaminations (HGD) system, as tested. The results will be used by the State of Nevada Bureau of Air Quality to set operational and emissions limits. The U.S. Army Environmental Center (USAEC) is investigating technologies to effectively treat explosives-contaminated components. Pilot studies have shown that decontamination of structural components is possible using a heated gas to thermally decompose or volatilize explosives with subsequent incineration in a thermal oxidizer (references 3 and 4). The pilot study conducted at HWAAP from 10 July to 21 September 1989 concluded that the HGD system is effective for treating items contaminated with TNT and ammonium picrate (reference 4). A second pilot study, from 20 June to 31 October 1994, was conducted to determine if the HGD system would successfully decontaminate items contaminated with explosives; CONP A-3, COMP B, HBX, H-6, RDX, TNT, and Yellow D (reference 5). Stack gas testing was conducted during 17-29 October to support HWAAP permitting requirements.

Abstract  The primary objective of this task was to determine the feasibility of using GAC to treat ground water contaminated by explosives at the Milan Army Ammunition Plant (MAAP) in Milan, Tennessee. Laboratory GAC isotherm studies were conducted and two carbons, Atochem, Inc. GAC 830 and Calgon Filtrasorb 300, were selected for further testing in continuous flow GAC columns. Three pilot scale continuous flow GAC column tests were performed at MAAP using the two carbons selected from the laboratory GAC isotherm studies. The results from the laboratory and pilot studies are presented in this report. They show that concurrent removal of explosives such as TNT, RDX, HMX, Tetryl, and nitrobenzenes from ground water using continuous flow granular activated carbon is feasible.

Abstract  BIOSIS COPYRIGHT: BIOL ABS. The oxidation of high explosives (HE), TNT, RDX and HMX, contaminated water has been studied under different conditions. Catalytic and advanced oxidation employing ultraviolet and hydrogen peroxide were investigated. Catalytic and non-catalytic wet oxidation of HE were carried over a 4.45 wt% PtiO2 catalyst with a particle diameter of less than 105 mum in a batch reactor at moderate pressure (|35 atm) and temperature (|200?C). Ultraviolet photolysis in combination with hydrogen peroxide oxidat mildly dependent on the amount of catalyst. The presence of catalyst resulted in about 20?C advantage in catalytic oxidation when compared to homogeneous wet oxidation. Also RDX/HMX oxidation was relatively easy without the presence of a catalyst at temperatures as low as 85?C and complete oxidation occurs at above 110?C in less than 30 min. Direct photolysis of RDX/HMX was accomplished in about 20 min whereas TNT was the most stable compound and the presence of hydrogen peroxide w

Abstract  The biotransformation of hexahydro-1,3,5-trinitro-1,3,5 triazine (RDX) has been observed in liquid culture by a consortium of bacteria found in horse manure. Five types of bacteria were found to predominate in the consortium and were isolated. The most effective of these isolates at transforming RDX was Serratia marcescens. The biotransformation of RDX by all of these bacteria was found to occur only in the anoxic stationary phase. The process of bacterial growth and RDX biotransformation was quantified for the purpose of developing a predictive type model. Cell growth was assumed to follow Monod kinetics. All of the aerobic and anoxic growth parameters were determined: micro(max), K(s), and Y(x/s). RDX was found to competitively inhibit cell growth in both atmospheres. Degradation of RDX by Serratia marcescens was found to proceed through the stepwise reduction of the three nitro groups to nitroso groups. Each of these reductions was found to be first order in both component and cell concentrations. The degradation rate constant for the first step in this reduction process by the consortium was 0.022 L/g cells . h compared to 0.033 L/g cells . h for the most efficient isolate. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 515-522, 1997.

Abstract  Biotransformation of RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) in slurry reactors was studied to determine the importance of supplementation of known biodegraders and the type of nutrient source required. Although addition of bacteria to the system increased the biotransformation rates, the increase may not justify the additional work and cost needed to grow the organisms in a laboratory and mix them into the soil. An inexpensive, rich nutrient source, corn steep liquor, was shown to provide sufficient nutrients to allow for the cometabolic biotransformation of RDX. The rate of RDX transformation was not constant throughout the course of the experiment due to the heterogeneous microbial population. Three kinetically distinct phases were observed. Regardless of the process, RDX biotransformation in slurry reactors was reaction rate limited under the test conditions. Model simulations based on experimental results demonstrate that, at cell densities of 5 g/L, bioremediation of RDX-contaminated soil is an attractive clean-up alternative.

Abstract  Phytoremediation is an emerging strategy to remediate soils contaminated with pollutants like explosives in which plants will uptake, degrade and/or accumulate pollutants. To implement this technology on a site contaminated with RDX, we chose rice, which is able to grow in lagoons, and we tested its ability to grow in soils with high levels of RDX and to decrease RDX concentrations in soil. Rice was grown for 40 days in soil contaminated with increasing [14C]RDX concentrations. Emergence and growth were not affected by RDX. Total chlorophyll content decreased with RDX concentrations of over 500 mg kg(-1). Amounts of chlorophyll were correlated with the appearance of necrosis in leaf extremities. After 40 days, rice translocated 89% of uptaken radioactivity to leaves with 90% in leaf extremities. Analyzes of leaf extracts showed that 95% of radioactivity was RDX in its parent form. Necrosis appears to be a phytotoxic symptom of RDX accumulation.

Abstract  This paper presents the results of the pilot-scale testing of these technologies conducted from December 1994 through March 1995 at the Bangor Naval Submarine Base (Silverdale, Washington). Goals of the pilot study were to provide cost and design information for the implementation of the full-scale remediation scheduled for mid-1996. Both aerobic composting and the Simplot Anaerobic Bioremediation (SABRE) process were evaluated for soils contaminated with 2,4,6-trinitrotoluene and other ordnance compounds. Cleanup goals of 33.3 mg/kg (soil D) and 33.0 mg/kg (soil F) were established for TNT. A goal of 9.1 mg/kg was additionally determined for RDX. For soil F, TNT cleanup goals were achieved within 9 days for composting (637 mg/kg to 3 mg/kg) and 40 days for anaerobic treatment (488 mg/kg to 0.7 mg/kg). For soil D, TNT goals were not statistically achieved using composting (147 mg/kg to 41 mg/kg) or anaerobic treatment (725 mg/kg to 77 mg/kg) during the treatment period. The nature of contamination in soil D (burn disposal of ordnance) may have influenced the treatment performance of both processes.

Abstract  We use the recently developed reactive force field ReaxFF with molecular dynamics to study thermal induced chemistry in RDX [cyclic-[CH(2)N(NO(2))](3)] at various temperatures and densities. We find that the time evolution of the potential energy can be described reasonably well with a single exponential function from which we obtain an overall characteristic time of decomposition that increases with decreasing density and shows an Arrhenius temperature dependence. These characteristic timescales are in reasonable quantitative agreement with experimental measurements in a similar energetic material, HMX [cyclic-[CH(2)N(NO(2))](4)]. Our simulations show that the equilibrium population of CO and CO(2) (as well as their time evolution) depend strongly of density: at low density almost all carbon atoms form CO molecules; as the density increases larger aggregates of carbon appear leading to a C deficient gas phase and the appearance of CO(2) molecules. The equilibrium populations of N(2) and H(2)O are more insensitive with respect to density and form in the early stages of the decomposition process with similar timescales.

Abstract  XplA is a cytochrome P450 that mediates the microbial metabolism of the military explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). It has an unusual structural organisation comprising a heme domain that is fused to its flavodoxin redox partner. XplA along with its partnering reductase XplB are plasmid encoded and the gene xplA has now been found in divergent genera across the globe with near sequence identity. Importantly, it has only been detected at explosives contaminated sites suggesting rapid dissemination of this novel catabolic activity, possibly within the 50-year period since the introduction of RDX into the environment. The X-ray structure of XplA-heme has been solved, providing fundamental information on the heme binding site. Interestingly, oxygen is not required for the degradation of RDX, but its presence determines the final degradation products, demonstrating that the degradation chemistry is flexible with both anaerobic and aerobic pathways resulting in the release of nitrite from the substrate. Transgenic plants expressing xplA are able to remove saturating levels of RDX from soil leachate and may provide a low cost sustainable remediation strategy for contaminated military sites.

Abstract  The widespread presence in the environment of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), one of the most widely used military explosives, has raised concern owing to its toxicity and recalcitrance to degradation. To investigate the potential of plants to remove RDX from contaminated soil and water, we engineered Arabidopsis thaliana to express a bacterial gene xplA encoding an RDX-degrading cytochrome P450 (ref. 1). We demonstrate that the P450 domain of XplA is fused to a flavodoxin redox partner and catalyzes the degradation of RDX in the absence of oxygen. Transgenic A. thaliana expressing xplA removed and detoxified RDX from liquid media. As a model system for RDX phytoremediation, A. thaliana expressing xplA was grown in RDX-contaminated soil and found to be resistant to RDX phytotoxicity, producing shoot and root biomasses greater than those of wild-type plants. Our work suggests that expression of xplA in landscape plants may provide a suitable remediation strategy for sites contaminated by this class of explosives.

Abstract  Phytoremediation is an established technology for the treatment of explosives in water and soil. This study investigated the possibility of using slurried plants (or phytoslurries) to treat explosives (TNT and RDX). The degradation of TNT in solution using intact and slurried parrotfeather (Myriophyllum aquaticum), spinach (Spinicia oleracea), and mustard greens (Brassica juncea) was evaluated. Phytoslurries of parrotfeather and spinach removed the TNT faster than the intact plant. Conversely, the removal rate constants for slurried and intact mustard greens were about the same. A study using pressurized heating to destroy enzymatic activity in the phytoslurries was also conducted to compare removal from released plant chemicals to adsorptive removal. Aqueous phase removal of TNT by autoclaved spinach phytoslurry was compared with nonautoclaved spinach phytoslurry. The autoclaved phytoslurry did remove TNT, but not as completely as nonautoclaved slurry. This suggests that some removal is due to adsorption, but not all. Phytoslurries of mustard greens and parrotfeather had higher RDX removal rates compared with intact plant removal, but the rates for parrotfeather in either case were relatively low. Phytoslurries of spinach had relatively modest increases in RDX removal rates compared with intact plant. Studies were then conducted with phytoslurry/soil mixtures at two scales: 60 ml and 1.5 l. In both cases, phytoslurries of mustard greens and spinach removed TNT and RDX at higher levels than control slurries.

Abstract  A mixed microbial culture capable of metabolizing the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) was obtained from soil enrichments under aerobic and nitrogen-limiting conditions. A bacterium, Stenotrophomonas maltophilia PB1, isolated from the culture used RDX as a sole source of nitrogen for growth. Three moles of nitrogen was used per mole of RDX, yielding a metabolite identified by mass spectroscopy and 1H nuclear magnetic resonance analysis as methylene-N-(hydroxymethyl)-hydroxylamine-N'-(hydroxymethyl)nitroamin e. The bacterium also used s-triazine as a sole source of nitrogen but not the structurally similar compounds octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, cyanuric acid, and melamine. An inducible RDX-degrading activity was present in crude cell extracts.

Abstract  A short-term study was performed to determine the feasibility of using constructed wetlands to remove explosives from groundwater, and to assess accumulation of parent explosives compounds and their known degradation compounds in wetland plants. Tolerance towards explosives in submersed and emergent plants was screened over a range of 0 to 40 mg L(-1). Tolerance varied per compound, with TNT evoking the highest, 2NT the lowest, and 24DNT, 26DNT, and RDX an intermediate growth reducing effect. Submersed plants were more sensitive to TNT than emergent ones. A small-scale 4-month field study was carried out at the Volunteer Army Ammunition Plant, Chattanooga, TN. In this surface-flow, modular system, the influent contained high levels (>2.1 mg L(-1)) of TNT, 2,4DNT, 2,6DNT, 2NT, 3NT, and 4NT, and the HRT was 7 days. The performance criteria of US EPA treatment goals for local discharge of 2,4DNT concentration <0.32 mg L(-1), and 26DNT concentration <0.55 mg L(-1) were not met at the end of the experiment, although explosives levels were greatly reduced. Low levels of 2ADNT and 4ADNT were transiently observed in the plant biomass. Results of two other, older, constructed wetlands, however, indicated that in these systems treatment goals were met most of the time, residues of explosives parent compounds and known degradation compounds in plant tissues were low and/or transient, and in substrates were low.

Abstract  BIOSIS COPYRIGHT: BIOL ABS. RRM MEETING ABSTRACT MEETING POSTER MICROORGANISM POLLUTION TOXICOLOGY BIODEGRADATION ENVIRONMENTAL CONTAMINATION TNT MINERALIZATION POLLUTANT EXPLOSIVES 2 4 6-TRINITROTOLUENE RDX HEXAHYDRO-1 3 5-TRINITRO-1 3 5-TRIAZINE PICRIC ACID NATURAL ATTENUATION BIOREMEDIATION GENETICS EXTRADIOL DIOXYGENASE TOLUENE MONOOXYGENASE CATECHOL DIOXYGENASE NITROREDUCTASE SULFITE REDUCTASE BIOPROCESS ENGINEERING SEDIMENT GROUNDWATER ARMY AMMUNITION PLANT LOUISIANA USA

Abstract  BIOSIS COPYRIGHT: BIOL ABS. An aerobic, Gram-positive bacterium was isolated from explosives-contaminated soil by enrichment culture, using the nitramine explosive, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), as the sole added N source. The organism, identified by 16S rDNA analysis as a Rhodococcus sp., strain DN22, grew exponentially with a mean generation time of 6.5 h at 25?C in minimal medium containing RDX as the sole N source. The growth medium was depleted of RDX 24 h after inoculation but growth did not cease until 20 h later. It was concluded that strain DN22 was using NO2-, released from RDX, as a growth substrate because, following inoculation of strain DN22 into RDX-containing minimal medium, the concentration of NO2- increased during the first 10 h of incubation and declined to undetectable amounts 20 h later. The ratio of the growth yields of strain DN22 grown on RDX or NO3- as N sources indicated that three of the six N atoms of RDX were being incorporated into biomass. Increased

Abstract  BIOSIS COPYRIGHT: BIOL ABS. RRM MEETING ABSTRACT MEETING POSTER BIOPROCESS ENGINEERING HEXAHYDRO-1 3 5-TRINITRO-1 3 5-TRIAZINE MINERALIZATION BIOTRANSFORMATION EXPLOSIVE RDX ANOXIC DENITRIFYING CONDITIONS HYPERION WASTEWATER TREATMENT PLANT CONTAMINATED SITE POLLUTION WASTE MANAGEMENT EL SEGUNDO CALIFORNIA USA AMARILLO TEXAS USA

Abstract  BIOSIS COPYRIGHT: BIOL ABS. A laboratory study was conducted to study the feasibility of removing explosives in contaminated soil under anaerobic conditions. Anaerobic enrichment cultures were prepared from soil samples under various electron-accepting conditions, namely, sulfate-reducing, methanogenic, and nitrate-reducing conditions. The sulfate-reducing condition was very effective in removing all of the explosive compounds from the soil. The sulfate-reducing consortium removed 100% of 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrobenzene (TNB) within 10-15 days of incubation and removed 75 to 95% of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro- 1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX), within 21 days of incubation. The consortium used explosive compounds as the nitrogen source, however, it did not use these compounds as the sole carbon source. The various metabolites obtained from TNT metabolism were 4-amino-2,6-dinitrotoluene (4-A-2,6-DNT), 2,4-diamino-6-nitrotoluene (2,4-

Abstract  BIOSIS COPYRIGHT: BIOL ABS. The successful operation of an aerobic/anoxic laboratory-scale soil slurry reactor showed that soil contaminated with 2,4,6trinitrotoluene (TNT) and hexahydro- 1,3,5-trinitro- 1,3,5-triazine (RDX) could be treated in batches or semicontinuously. Batch treatment resulted in the transformation of TNT. Semicontinuous treatment resulted in complete degradation of TNT. In addition to removing TNT, the slurry reactor also removed contaminants such as trinitrobenzene, 2,4-dinitrotoluene, RDX, and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX). Radiolabeled TNT incubated with reactor biomass showed that 23% of (14C)TNT was mineralized, 27% was converted to biomass, and 8% was adsorbed onto the soil. The rest of the (14C)TNT was accounted for as metabolites, including a ring cleavage product identified as 2,3-butanediol. Increasing the frequency of soil addition from once to two or three times weekly did not affect the TNT removal rates. The soil slurry reactor also ma

Abstract  Hexahydro-1,3,5-trinitro-1,3,5-triazine is a widely used military explosive that is more commonly known as Royal Demolition Explosive (RDX). Because of concerns with the potential toxicity of RDX, increasingly stringent regulations are anticipated for wastewater discharges from munitions manufacturing facilities. At the Holston Army Ammunition Plant (HAAP), where RDX is currently produced in the U.S., the treatment sequence includes an anoxic filter prior to aerobic filters and activated sludge reactors. The intent of the anoxic filter is to remove the high levels of nitrate that are often present in munitions wastewater. as well as RDX and other nitrated energetic compounds. However, RDX removal across the filter is typically not adequate to meet the anticipated regulatory target, and RDX tends to persist under aerobic conditions. The objective of this study was to evaluate the reason for poor RDX removal in the anoxic filter. Microcosms were set-up with HAAP wastewater and biofilm scraped from the anoxic filter. Nitrate-reducing conditions were readily established, with organics present in the wastewater as well as acetate serving as electron donors. However, as long as nitrate was present, no decrease in RDX (15 mu M) occurred. As soon as nitrate was depleted and some primary substrate was still available, RDX was rapidly biotransformed to metabolites that included mononitroso, dinitroso, and trinitroso derivatives.: The disappearance of nitrate, followed by biotransformation of RDX, coincided with a decrease in redox potential to below -200 mV. These results were confirmed with an ethanol-grown nitrate-reducing enrichment culture that was inoculated with biofilm from the HAAP anoxic filter. The presence of RDX had no apparent effect on nitrate reduction, whereas RDX biotransformation was completely inhibited until all of the nitrate was consumed. Nitrate removal was achieved by repeated additions of ethanol. Thus, in order to ensure efficient biotransformation of RDX, nitrate removal must be complete, which requires an electron donor supply that exceeds the acceptor capacity of the nitrate. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.