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Field Demonstration of Acetone Pretreatment andComposting of Particulate-TNT-Contaminated SoilCorey W. Radtke a , Dan M. Smith a , G. Scott Owen a & Francisco F. Roberto aa Biotechnology Department , Idaho National Engineering and Environmental Laboratory ,P.O. Box 1625 Mailstop 2203, Idaho Falls, Idaho, 83415Published online: 02 May 2007.

To cite this article: Corey W. Radtke , Dan M. Smith , G. Scott Owen & Francisco F. Roberto (2002) Field Demonstration ofAcetone Pretreatment and Composting of Particulate-TNT-Contaminated Soil, Bioremediation Journal, 6:2, 191-204, DOI:10.1080/10588330208951213

To link to this article: http://dx.doi.org/10.1080/10588330208951213

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Field Demonstration of Acetone Pretreatment andComposting of Particulate-TNT-Contaminated Soil

Corey W. Radtke,* Dan M. Smith, G. Scott Owen, and Francisco F.RobertoBiotechnology Department, Idaho National Engineering and Environmental Laboratory, P.O. Box1625 Mailstop 2203, Idaho Falls, Idaho 83415

Abstract: Solid fragments of explosives in soil are common in explosives testing and training areas. In this studywe initially sieved the upper 6 in of contaminated soil through a 3-mm mesh, and found 2,4,6-trinitrotoluene (TNT)fragments. These contributed to an estimated concentration of 1.7 kg per cubic yard soil, or for 2000 ppm TNTin the soil. Most of the fragments ranged 4 mm to 10 mm diameter in size, but explosives particles weighing upto 56 g (about 4 em diameter) were frequently observed. An acetone pretreatment/composting system was thendemonstrated at field scale. The amount of acetone required for a TNT-dissolving slurry process was controlledby the viscosity of the soil/acetone mix rather than the TNT dissolution rate. The amount needed was estimatedat about 55 gallons acetone per cubic yard soil. Smaller, 5- to 10-mm-diameter fragments went into solution in lessthan 15 min at a mixer speed of 36 rpm, with a minimum of 2 g TNT going into solution per 30 min for the largerchunks. The slurries were then mixed with compost starting materials and composted in a vented 1 yd3 container.After 34 days incubation time TNT was below the site-specific regulatory threshold of 44 ppm. TNT metabolitesand acetone were also below their regulatory thresholds established for the site.

Keywords: particulate, fragment, bioremediation, compost, solvent, acetone, TNT.

Introduction

Composting of explosives contaminated soil was re­ported in the 1970s (Osmon et al., 1978). It was laterused at the Umatilla Army Depot (U.S. Army Environ­mental Center, 1993), SUBASE Bangor, Crane NavalSurface Warfare Center (U.S. Environmental Protec­tion Agency [EPA], 1998), and the Louisiana ArmyAmmunition Plant (Griest et aI., 1990) among others.The total cost of composting at Umatilla was $346 perton, where 14",800 tons of soil were treated (U.S. AEC,1996). Currently, composting is still widely used toremediate soils contaminated by explosives.

Composting is now beginning to be applied atareas contaminated from the use of explosives, ratherthan explosives manufacture and assembly, which

contaminate soil largely via contaminated wastewaterdischarge. Not surprisingly, explosive-use areas fre­quently contain explosive fragments (Jenkins et al.,1998; Radtke et aI., 2001).

Fragments of explosives in soil are more difficultto treat than soil contaminated via washwaters.Benchtop investigations showed that fragments of ex­plosives in soil larger than 2 mm in diameter cansurvive composting (Radtke et aI., 2000). Becausefield screens are usually around I-in, large amounts ofparticulate explosives 2 mm in diameter and greaterwill undoubtedly make it into composts. These frag­ments may then sort toward the bottom of the pile asit is mixed and they avoid routine sampling.

Gilcrease et aI. (1996) studied the disappearanceof TNT particles in slurry reactors. Their methods

* Corresponding author: Telephone: 208-526-5186, Fax: 208-526-0828, e-mail radtcw@inel.gov

1058-8337/02/$.50© 2002 by CRC Press LLCBioremediation Journal 6(2):191-204 (2002) 191

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employed spherical TNT beads from 0.6 to 1.0 mmdiameter in impeller-agitated aqueous batch reactors.In biotic studies, they found that the water-dissolvedTNT plateau was higher with increasing agitator speeds.Reportedly, this was due to the positive effect of agi­tation on the mass transfer coefficient, suggesting theTNT must be in solution for biodegradation to occur.This effect was then assumed in the models developedby Gilcrease et al. (1996). Therefore, the dissolutionrate of the solid TNT can limit the overall biotransfor­mation rate of particulate explosives remediation.Gilcrease et al. (1996) also experimented with Teflon"particles in the slurry reactors to mimic non-TNT sol­ids found in soils. The Teflon particles reportedly in­creased TNT particle attrition and consequently in­creased the surface area and rate of dissolution intowater. They report that degradation of TNT in suchreactors may be influenced by TNT particle attrition.In contrast to the slurries, soil composts contain muchless water, yet have greater biodegradation potentialwithin the water. The low water concentrations incomposts coupled with the relatively infrequent turn­ing make TNT particle attrition and solubilizationdoubtfully significant within windrowed composts.Overall, composts should be less efficient at solidexplosives dissolution than slurries because (1) there isless water in a compost, (2) the water in a compost isrelatively stagnant, and (3) biofilms typically fOlIDover solid explosives in composts (Radtke et aI., 1999).

To cope with problems presented by the explo­sives fragments, at the bench scale, we reported earlieron positive results from adding acetone to soil contain­ing distributed TNT chunks. This method dissolvedthe TNT, and when followed by conventionalcomposting resulted in effective TNT degradation(Radtke et al., 2000). Surprisingly, acetone was foundto delay the self-heating of the composts but did notinhibit degradation of the TNT. The success of thelaboratory studies led us to test the acetone pretreat­ment system in the field.

In this article we report the findings of a 1 yd"field study aimed at determining the minimum amountsof acetone per volume soil and mixing time necessaryfor effective TNT fragment dissolution. This studyalso served as the first field application and scale up ofthe acetone pretreatment method,

Materials and MethodsSoilThe site is located in southeastern Idaho, within theIdaho National Engineering and Environmental Labo­ratory (INEEL). The location is comprised of an ap-

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proximately 60 x 30 foot unvegetated ellipse contain­ing explosives contamination, of which is over 50years old. Two moderately contaminated areas withinthe site were selected based on visible soil discolora­tion, each roughly circular and about 5 ft in diameter.From both areas, soil was removed using hand shovelsto a depth of 6 in, placed onto two separate plastictarps, and homogenized (Jenkins et al., 1999) by hand(three people simultaneously) with shovels for 30 min.A total of 125 L soil was excavated to comprise homo­genate #1, and 42 L for homogenate #2. All soil wasused at field moisture conditions, typically less than3% dry weight moisture.

SievingInitially, soil samples were hand sieved to develop anidea of the extent and range of particulate explosives.As previous laboratory work at the INEEL has shown(Radtke et aI., 2000) that particles below 2 mm areeffectively composted, a3-mm sieve was chosen. Thelarger particles therefore were retained. on the screenfor subsequent weighing and recording, while particlesat the "compostable" boundary of2 mm passed throughthe screen and were not included in projected calcula­tions. Eight 250 mL grab samples were independentlysieved. For the final five screenings, oversized TNTpieces were weighed to 0.01 g using a portable balanceand recorded. Subsequently, these fragments were putback into the soil pile except for a subgroup that wassaved for analysis by HPLC.

High Performance LiquidChromatography (HPLC)A modified Method 8330 (U.S. EPA, 1995) HPLCanalysis was performed using a 25 em x 4.6 mm Alltech(Deerfield, IL) mixed mode C18 reversed phase-anioncolumn (Griest et aI., 1995) with a 2-cm Supelco(Bellefonte, PA) C-18 guard column. The analysis fur­ther used a mobile phase of 50% water-50% methanoland a flow rate of 0.64 rnL/min. This column and mo­bile phase regime 'was found to be effective at resolvingthe primary contaminant (TNT) and metabolites foundin the previously reported benchtop studies, 2-amino­4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene.Analytes were detected with a Waters (Milford, MA)991 photodiode array detector at 254 nm (Bourier andOehrle, 1995). TNT and TNT-metabolite standards wereobtained from Supelco and included those recommendedin Method 8330. Added to these were 2,4-diamino-6­nitrotoluene; 2,6-diamino-4-nitrotoluene; 4,4',6,6'­tetranitro-2,2'-azoxytoluene; 2,2' ,6,6'-tetranitro-4,4'­azoxytoluene; 2,2' ,6,6'-tetranitro-4,4'-azotoluene; and4,4',6,6'-tetranitro-2,2'-azotoluene.These were purchased

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from AccuStandard, Inc. (New Haven, CT). All re­agents and solvents were of HPLC grade or better andpurchased from Fisher Scientific (Pittsburgh, PA). Theaverages reported are arithmetic means of replicatesamples.

Analyses by the commercial laboratory were per­formed using Method 8330 (U.S. EPA, 1995), consist­ing of a methanol/water mobile phase with a C-18column and UV absorbance detection at 254 nm. Stan­dard procedures at the analytical laboratory includedpicking out larger solids before grinding as part of thesample preparation. Averages reported are the arith­metic mean of four replicate samples and error barsrepresent one standard deviation.

Compost PreparationChicken manure, cow manure, potatoes, wood chips,and alfalfa were obtained from local sources and storedin containers on-site for one week before use (Table 1).When needed, compost starting materials were placedon a plastic tarp and shredded and homogenized byhand (U.S. Army Corps of Engineers, 1991; U.S. ABC,1993). The compost was contained in a 36 x 36 x 36in container of O.5-in-thick polypropylene then placedwithin a 1yd"polypropylene secondary container (Fig­ure 1). Initially, 6 in of shredded and homogenizedcompost starting material were placed in the bottom ofthe compost container. Soil/acetone slurries were thenpoured onto this bed together with more starting ma­terials and blended using pitchforks and shovels. Ad­ditional slurry runs received more fresh compost starterto a final blend of 14% slurry and a total volume of justunder 1 yd"for the acetone concentration experiment.The volume was 0.5 yd" for the mixing time experi­ment. Time zero samples were taken and a Cole-Parmer(Vernon Hills, IL) SmartChek 23500 Series digital

temperature recording probe was inserted into the ap­proximate geometric center of the composts. For theexperiment determining the necessary acetone con­centration, the internal temperature probe was inserted24 h after the compost construction. A cellulose textilemembrane was finally placed on top of the fresh com­posts. Moistened finished-compost, obtained at a localnursery, was placed on the textile as a covering layerto help minimize acetone vapor escape. Initial acetoneescape was measured at 6 in above the cover by anindustrial hygienist and never exceeded 100 ppm.Ambient temperature measurements were recorded atIS-min intervals at 2 m above ground approximately2 miles due north (typically straight downwind) of thefield site. Temperatures were taken by the NationalOceanic and Atmospheric Administration (NOAA) withCampbell Scientific (Logan, UT) 107 temperatureprobes.

Compost MaturationThe compost cover was removed for each homogeni­zation and sampling event and then immediately re­placed. Following 3 days of compost maturation, thecomposts were mixed, and 13 1.5" x 3 foot perforatedPVC pipes were installed vertically through the com­post for aeration. As needed, tap water was sprayedonto the compost while mixing. The moisture concen­tration was estimated in the field visually, as the idealmoisture concentration of a compost is related to com­post-specific conditions such as bulking agents andaeration, etc.

The compost was sampled daily in quadruplicateinto new 250 mL ICHEM (New Castle, DE) samplejars. Vertical composite samples were taken randomlyfrom four separate locations within the soil compostpile. At the end of the second experiment, at day 34,

Table 1. Compost ingredients, modified from U.S. AEC(1993)

Ingredient Volume (%)

Sawdust 21

Hay 21

Chicken Manure 3

Cow Manure 28

Potatoes 12

Contaminated Soil 15

Total 100

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Compost box

Secondary containment

Figure 1. Schematic of the primary and secondary composting containers. Both were composed of 0.5" thick polypropylene.The inner dimensions of the inside box were 36" x 36" x 36", while the secondary container was 39" x 96" x 12",

four composite confirmation samples were sent to acommercial laboratory for acetone and explosivesanalyses. The compost cover was also sampled andsent for acetone analysis.

Soil/Acetone SlurriesMixing Soil and Acetone Slurries. Slurrying the soilwith acetone was carried out using a modified 4.1 ft3

Jet (Auburn, WA) portable cement mixer model PUM­35, retrofitted with butyl rubber gaskets. An aluminumplate lid was installed with a spring-release system toavoid significant pressure buildup. The mixer turned at36 rpm throughout the course of the experiments andwas electrically bonded and grounded. The existingmotor was replaced by a Class 1, Group D Series 56Frame Baldor (Fort Smith, AR) L5004A motorhardwired with a 60 ft acetone-resistant extension cord.

Effect of Acetone Concentration. To investigate theamount of acetone needed to dissolve the TNT chunkswithin the soil, sequential additions of acetone weremade to given amounts of soil within the mixer (Ex­periment A). In this experiment, four individual soilbatches were run consisting of 38, 19,38, and 30 L ofsoil. A handful of dry ice was added to blanket theacetone with an inert atmosphere. In the first run, 38 Lof soil were placed in the mixer with 3 L acetone,mixed for 15 min and then sampled in 250-mL con­tainers. These samples were split into seven aliquotslater at the laboratory and extracted and analyzed indi­vidually. Three more liters of acetone were then addedfollowed by another 15 min mixing and another sam­pling. Finally, 2 L of acetone were added, mixed an­other 15 min, and sampled. Then the slurry was incor­porated into a bed of compost starting materials byhand as described above. The second experiment (B)was aimed at finding sizes of TNT chunks that couldbe processed by slurrying. Three chunks of the field-

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TNT, weighing 19.1, 12.3, and 9.7 g were added to 19L contaminated soil with 5 L acetone and mixed for5 min followed by sampling and searching for anyremaining chunks of TNT. One liter of acetone wasthen added, followed by mixing for 10 min, with moresampling. Then 3 L more of acetone were added withmixing for 15 min, etc. Two subsequent runs (C and D)were made with single endpoints, the first by adding37.9 L soil with 14 L acetone and 20 min mixing, andthe second by adding 30 L soil with 10 L acetone andmixing for 15 min. In the final slurry run, ExperimentD, additional smaller pieces of field-TNT were addedto the slurry before mixing.

Effect of Mixing Time. To estimate the time needed fordissolution of TNT to occur, soil to acetone at a ratio of30:14 (vjv) was mixed continuously and sampled atregular intervals.The large amount of acetone was addedto negate potential effects of acetone losses due to thelong mixing times and frequent sampling. Two indi­vidual batches were run in this experiment, consisting of30 and 11L of soil, respectively. Samples were taken byhand every 15 min up to 120 min, with the omission ofthe 75-min sample. After 120 min of mixing, eight 250­mL grab samples were taken and sieved through a3-mm screen to check that adequate dissolution of theTNT fragments had occurred. The l l-L run was per­formed with the same acetone to soil ratio, with sam­pling times of 30 and 60 min.

ResultsInitial Soil CharacterizationDue to TNT particles in the soil, estimating the initialsoil TNT concentrations quickly grew complicatedand became the subject of a separate paper (Radtke etal., 2001). Following are summaries of soil sieving andHPLC analysis of homogenized soil.

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Soil Sieving. Two general types of fragments werefound, seemingly identical from the exterior, but re­vealing different consistencies when broken. One con­sisted of small crystals; the other had long, parallelneedle-like crystals. Both of these fragment types, whenanalyzed by HPLC, were found to consist almost en­tirely of TNT. These crystal forms reportedly can re­sult from various casting processes during ordnancemanufacture. For example, an addition of "seed" TNTcrystals to a TNT melt is used to produce easily castable,very fine, randomly oriented, monoclinic TNT crystals(U.S. Department of the Army, 1984).

The average number of oversized TNT particlesretained on the 3-mm sieve was 6.5 for each 250 mLsubsample from the homogenized soil pile (Table 2).The particle weight averaged 0.087 g; therefore, agiven 250-mL subsample contained an average of 0.59 gof particulate TNT over 3 mm in diameter. This con­centration projects to an average of 19,900 TNT par­ticles in 1 yd'' with a total weight of 1.7 kg (3.7 lb).

HPLC Analysis of Homogenized Soil. The most strik­ing aspect of this data set was the large TNT concen­tration (Table 3), with an even larger associated stan­dard deviation. This is because one of the grab samplescontained an approximately 7-mm-diameter fragmentof TNT. TNT concentration estimations were accom­panied by a large variance due to the presence of thesolid TNT chunks. A site characterization study at ananti-tank firing range for the primary target analytesHMX and TNT reported a large spatial heterogeneitysimilar to that found at the INEEL (Jenkins et al.,1999).

The contract laboratory HPLC analyses for explo­sives (Table 4) differed significantly from that ana-

lyzed at the lNEEL (Table 3). Due to the spatial het­erogeneity of explosives in soil (Jenkins et al., 1999),it has been reported that samples split and sent toseveral laboratories for analysis has resulted in largediscrepancies (Grant et al., 1997). This could also bean effect of the contract laboratory separating andremoving pieces of explosives in the sample prepara­tion.

The pathway for natural attenuation of TNT in thefield seems to be a combination of photodegradationand biological degradation. The first two compoundslisted in Table 3, 2-amino-4,6-dinitrotoluene and4-amino-2,6-dinitrotoluene, are biological degradationproducts (Comfort et al., 1995; Lewis et al., 1997).However, 1,3,5-trinitrobenzene is produced as aphotodegradation product (Mabey et aI., 1983). TNBis also a by-product of TNT manufacture (U.S. Depart­ment of the Army, 1984), so concentrations of TNBshould not be used to assess degradation. Regardless,photolysis is not an efficient method for natural attenu­ation because ultraviolet radiation does not penetratevery far into soil.

The large variance in the TNT concentration datais not reflected in the TNT degradation product data(Table 3). This is likely because the degradation prod­ucts occurred after aqueous TNT solubilization intothe soil matrix. The degradation products are them­selves more water soluble and should tend to furtherdisperse rather than recrystallize.

Soil SlurriesAcetone Concentration Experiment. Acetone andthe soil, at a ratio of approximately 1 L acetone to 4 Lsoil, made a mixable slurry. When the concentration ofacetone dropped much below this ratio, the mix be-

Table 2. TNT particles recovered from sieving field homogenized soil through a 3-mm mesh

Data Description Mean Sl CV2 High Low

Collected DataNumber of TNT particles per

6.50 0.90 13.8 11 5250 mL sampleWeight of TNT particles per 0.59 0.16 27.6 0.85 0.44250 mL sample (g)

Weight of individual TNT particle (g) 0.087 0.052 60.1 0.23 0.01

Projected Data

Number of TNT particles in 1 yd3 19,900 2,750 14 33,600 15,300

Weight of TNT particles in 1 yd3 (g) 1,730 477 28 2,930 1,330IS = standard deviation2CV =coefficientof variation

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Table 3. Analytical data for excavated and homogenized soil in the acetone concentrationexperiment, analyzed at the INEEL. Averages reported are the arithmetic mean of eightreplicate samples

Compound2-amino-4,6-dinitrotoluene4-amino..2,6..dinitrotoluene

2,4,6-trinitrotoluene4-nitrotoluene2-nitrotoluene

2,4-dinitrotoluene2,6-dinitrotoluene

nitrobenzene1,3,5-trinitrobenzene

IS =standard deviation2CV = coefficient of variation

[Average] (ppm)3.31.9

39,1000.51.40.70.41.0

40.6

0.40.2

110,0001.00.20.50.30.68.4

12.511.528018216.277.867.062.220.7

Table 4. Analytical data for excavated and homogenized soil in theacetone concentration experiment, analyzed at a commerciallaboratory. Averages are reported as the arithmetic mean of foursamples

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Compound [Average] (ppm)TNT 110

1,3-DNB 14.9TNB 61.8is = standard deviation2CV=coefficient of variation

67.722.92.4

61.61543.8

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came a paste of increasing viscosity with decreasingacetone concentration. The minimum acetone concen­tration needed for this technology to be technicallyfeasible, using the INEEL clayey soil, converts to beapproximately 55 gallons acetone per yd3 soil. As canbe observed by the decreasing standard deviations andoverall TNT concentrations in Experiment A (Table 5),TNT fragments dissolved readily when we addedenough acetone to produce a mixable slurry. We alsoadded larger chunks of TNT from the field and at­tempted recovering them between slurrying runs toassess dissolution of larger fragments (Table 5, Ex­periment B). After 20 min of mixing, two fragmentswere recovered, weighing 9.4 and 7.0 g, respectively.Therefore, conservatively, a total of 2.7 and 3.0 g TNTwere dissolved in 20 min mixing time. Experiments Cand D (Table 5) were performed to ensure that theabsence of TNT particles in the first two experimentswas a result of TNT dissolution during the earlier 15­min mixing intervals. Experiment D showed a highconcentration of TNT due to the preferentially addedfield contamination.

Mixing Time. At a ratio of 7 L acetone to 15 L soil,the embedded TNT particles were dissolved within thefirst 15 min (Figure 2). Therefore, the length of timefor TNT dissolution to occur should not be a limitingfactor when compared with set up and compost gen­eration times.

Assuming a soil density of 1.2 g/mL (2000 lb/yd-'), the particulate TNT contributed 2010 ppm to thesoil contamination. Many larger, bean-sized (about1 cm) pieces of TNT were observed within the soilpile, but were missed in the random sampling of thehomogenized soil pile. Therefore, the actual averageconcentration could be considerably higher and theestimate of 201a ppm is likely low.

CompostsAcetone Concentration. Overall, the remediation wascomplete in approximately 9 days. The TNT spike andhigh standard deviations in days 5 through 8 may reflecta pocket of poorly mixed sailor other increase in avail­ability (Figure 3). This could be the result of soil thatwas added to the compost. at a low enough acetone

Table 5. TNT estimates for soil mixed with varying acetone concentrations, n=7

Experiment I ConditionsAvg

[TNT](PPM)

A38 L soil + 3 L acetone, mixed 15 min, 4,450 5,560 125sample for HPLCadd 3 L acetone, mix 15 min, sample for HPLC 9,480 16,300 172add 2 L acetone, mix 15 min, sample for HPLC 326 80.5 24.7

B19 L soil, 3 chunks of TNT, (19.1 g, 12.3 g, and 9.6 g), 4 L acetone, 300 85.5 28.6mix 5 min, sample for HPLCadd lL acetone, mix 10 min, found 1 chunk (18.6 g), sample for 289 83.2 28.8HPLCAdd 3 L acetone, mix 15 min, found 2 chunks (9.4 g and 7.0 g) 1,050 242 23.0samplefor HPLC

C38 L soil + 14 L acetone, mixed 20 min, 474 78.2 16.5sample for HPLC

S - standard deviation2ev =coefficientof variation

D30 L soil + 10 L acetone, mixed 15 min, 6,630 2,980 44.9sample for HPLC

1 _

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60000

50000-[ 40000c.:::: 30000t-

~ 20000.....10000

oo 20 40 60 80 100 120 140

198

Time (minutes)

Figure 2. TNT dissolution over time with a given concentration of acetone. Data are reported as thearithmetic mean of four samples. Error bars represent one standard deviation.

4000

3500

3000

E 2500c.e

2000I='zt:. 1500

1000

500

00 5 10 15 20 25

Time (days)

Figure 3. TNT concentration time course in the 1 yd3 compost generated from soil used in the acetoneconcentration experiment. Error bars represent one standard deviation, n==4.

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concentration that the material was a viscous paste. Twobean-sized (about 1 em diameter) TNT fragments werefound in mixing this compost, both after day 10, but nosuch large fragments were reflected in the analyses.TNT concentrations after day 9 were reduced to traces,with low standard deviations. Why the observed par­ticulate TNT in this compost was not sampled is some­what puzzling. It is possible that the mixing processphysically broke up the TNT fragments, but this isunlikelydue to the finding of the two chunks afterday 10.A more likely explanation revolves around the mixingprocess itself. As described in the methods of this report,at each mixing event the compost was transferred to thesecondary container with a pitchfork and homogenizedby hand. It was then transferred back into the primarycontainer, with more homogenization inside the pri­mary container with each load from the secondary con­tainer. The primary container was never completelyemptied, and the bottom approximately 8 in were left inthe primary container and homogenized with a pitch­fork together with the return homogenate from the sec­ondary container.Therefore,TNT fragmentswould likelyreside on the bottom of the primary container, with thehand homogenization resulting in an artifact, as thesolid TNT particles were sorted to the bottom. Afterintensive homogenization, the top of the compost, downto about 6 in depth below the surface, was sampled inquadruplicate. The samples were termed composites,due to the homogenization immediately preceding sam­pling. We observed that the soil did not sort from the

compost but blended well with the agricultural compoststarting materials.

Throughout this compost, TNT metabolites wereobserved (Figure 4). The metabolites have a weaktrend with the presence of TNT, as opposed to thedisappearance of TNT, as would be expected. Forexample, the samples that showed a transient increasein TNT were mainly days 5, 6, and 7 (Figure 3).Correspondingly, 4-amino-2,6-dinitrotoluene and2-aminoA,6-dinitrotoluene showed elevated levels atdays 5 to 7. In both cases, levels of TNT and TNTmetabolites dropped to much lower concentrations fromday 9 to the end of the experimental analyses, day 20.This is atypical of what is expected in a classic parentcompound/metabolite relationship, in which the parentcompound drops in concentration due to the conver­sion into its primary metabolites. The metabolites con­currently increase in concentration. This is followedby a drop in metabolite concentrations due the furthermetabolism of the metabolites without replenishmentfrom the parent compound. The explanation for ourfindings - that metabolite concentrations parallel TNTlevels - could be the result of poor compost mixing.If so, dirt clods containing TNT would initially bepresent in the compost. As the compost progressed, aslow biodegradation process would occur within theclod, accounting for the presence of TNT and metabo­lites. As the compost matures, further mixing wouldbreak up the clods, exposing the TNT to the composttreatment. Levels of both TNT and TNT metabolites

-¥- trinitrobenzene___ 4-amino-2,6-dinitrotoluene

-.tr- 2-amino-4,6-dinitrotoluene

-a- 2,4-diamino-6-nitrotoluene.....-.fr- 2,6-diamino-4-nitrotoluene

80

70

60

e- 50e,E:

40'i';!:!

'0 30.aJ! 20(D

!.10

0

0 2 4 6 8 10 12 14 16 18 20 22

Time (days)

Figure 4. TNT metabolite time course in the Acetone Concentration experiment. Error bars representone standard deviation, n=4.

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would eventually plummet, similar to the findings af­ter day 9 of this experiment.

Initial temperature profiles exhibited diurnal cy­cling, reflecting the ambient temperature (Figure 5).After day 4, the compost temperature exceeded theexternal temperature and likely heated beyond the tem­perature probes maximum, 120°F. It is noteworthy thatTNT had appreciably disappeared by day 4, prior tothe onset of a high compost temperature or the initialtemperature rise. The acetone may have had an effecton the temperature delay, but did not affect the degra­dation of TNT. This agreed with findings of the labo­ratory study (Radtke et aI., 2000).

Mixing Time. The dissolution of TNT in acetone waseffective, as evidenced through the 3-mm screeningsof the mixed slurry. Furthermore, because the slurrywas less viscous and much more fluid, it was far easierto achieve an adequate initial homogenous blending ofthe slurry with the compost starting materials.

The degradation of TNT over time in this com­post (Figure 6) is similar to the degradation observedin soil contaminated from explosive-laden washwaters(U.S. AEC, 1993). The appearance and subsequentdisappearance of TNT metabolites in this compost(Figure 7) also resembled contamination by aqueous­deposited explosives. Because the depth of this com­post was only 1.5 ft, the compost could not reachthermophilic conditions (Figure 8). The temperatureof this compost peaked at 4 days, in contrast to thel O-day lag period ofthe first, 3-ft-deep compost (Fig­ure 5). Similar to the findings in the first compost,TNT degradation occurred before peak temperatures

were reached. The contract laboratory results are listedin Table 6.

DiscussionThe timing of TNT degradation in the second compostclosely resembled degradation of explosives contami­nated soil from washout lagoon sites, including theappearance and disappearance of TNT metabolites(U.S. AEC, 1993). Additionally, the speciation and con­centration of TNT metabolites mirrored findings fromthe composting of soils from washout at the LouisianaArmy Ammunition Plant (LAAP) (Williams et aI., 1992).In the LAAP study, the concentration of 2-amino-4,6­dinitrotoluene and 4-amino-2,6-dinitrotoluene eachpeaked at roughly 10% of the initial TNT concentra­tions. In our study, the metabolites peaked at 2% and6%, respectively. Total diaminotoluenes peaked at 0.17%of the initial TNT concentration in the LAAP studywhen compared with approximately 12% in our study.In the LAAP study, metabolite peaks appeared at ap­proximately 10days compared with 3 days in our dem­onstration. The difference may be due to degradation ofthe diaminotoluenes in transit to the contract analyticallaboratory, as we initiated sample preparation for analy­sis by our lab on the same day the samples were taken.Other compost systems have shown both monoamino­dinitrotoluenes with no observable diaminonitrotoluenes(U.S. ABC, 1993).

Potential problems posed by fragments of explo­sives in soil are difficult to assess. Because soil screen­ing to a size of around 1 in is common beforecomposting, larger fragments are screened out. With

200

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~ 100

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~ 40~ ~ ~l

20

0 I I I I

0 3 6 9 12 15 18 21 24 27

Time (days)

Figure 5. Time course of the internal compost and ambient temperatures for the first compost,containing slurry from the acetone concentration experiment. The recorder maximum temperature was120°F.

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.I

4500 -

4000 -

3500

- 3000Ec. 2500Q.-I=' 2000zI::. 1500

1000

500 "L.0 ~

T~~~

0 5 10 15 20~ I

25 30I

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Figure 6. TNT compost time course from the mixing time experiment. Error bars represent onestandard deviation, n=4.

-.,..----,---~-r-i---,

-x - trinitrobenzene___ 4-amino-2,6-dinitrotoluene

---A- 2-amino-4,6-dinitrotoluene-D- 2,4-diamino-6-nitroto!uene-&- 2,6-diamino-4-nitrotoluene

500450- 400

EDo 350Co- 300~ 2500 200.cnI.....,

150Go)

::!: 100........

50 .:1;

0 otl

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30 35 40

Figure 7. TNT metabolites over time in the compost generated with slurries from the mixing timeexperiment.

FieldDemonstration ofAcetonePretreatment and Composting of Particulate-TNT-ContaminatedSoil 201

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M M140ii:" 120-ClJ 100....a 80~ 60Co 40E(J,) 20I-

oo

M

3 6

M

9 12 15 18 21 24

Time (days)

-Compost-Ambient

Figure 8. Compost and ambient temperature time course for the second compost, containing slurryfrom the mixing time experiment. The missing data in the ambient time course represent aninstrument outage.

Table 6. Contract laboratory results for day 34 samples taken from the secondcompost, containing slurry from the mixing time experiment, n=4

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CompoundTNT

4A26DNT2A46DNT

Acetone (compost)

Acetone (compost cover)NA == not applicable1S == standard deviation2CV :::::: coefficient of variation

[Average] (ppm)0.892.950.80

<0.0910.85

0.882.170.76NA0.70

98.373.794.6NA82.3

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up-front screening, the fragment sizes of concern shouldbe between 3 mm (the compostable boundary) and justbelow 1 in in diameter (the screening boundary). Ad­ditionally in the screening process, solid explosivesmay break apart past the screen into smaller particles,gaining entry into the compost bed. Particles of explo­sives in an active compost may also break apart duringthe mixing process, the particles may be dispersed inthe compost pile, or they may sort toward the bottomof the pile. The final disposition and significance of thefragments of explosives that enter into a compostingtreatment is largely unknown.

While the acetone pretreatment method describedherein ensures effective, quantifiable explosivesremediation, it may not be necessary depending on therequirements of the final disposition of the finishedcompost. This seems to be relatively new territory, asthe long-term significance of explosives fragments ina finished compost has yet to be assessed. Early aftertreatment the compost will still be somewhat active,and so leaching of explosives and metabolites shouldbe minimal. However, eventually composts becomerelatively inert, and so leaching may present a futureproblem. The long-term stability of finished compostsused to remediate explosive-contaminated soil is stilluncertain.

The bulk acetone used should effectively kill orinactivate (Laane et aI., 1987) much of the microflora inthe soil and in the compost starting materials. Thissuppression of indigenous compost flora might assistrecolonization in a bioaugmentation strategy. For ex­ample, the white rot basidiomycete Phanerochaetechrysosporium is potentiallyeffectivefor bioremediationof contaminated soil, yet it is suppressed by several soilorganisms (Radtke, 1994) and other soil factors (Tucker,1995). Therefore, solvent pretreatment may help renderthe contaminated soil or soil/compost system amenableto recolonization by the fungi.

AcknowledgmentsWe thank Mr. Hance Clayton for guidance and over­sight and Mr. Grayson Downs for industrial hygienesupport. We also thank the National Oceanic and At­mospheric Administration (NOAA) for sharing theirtemperature data. This work was performed under DOEcontract number DE-AC07-99ID13727 and fundedunder ID-ER-108.

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