15    BIOLOGICAL TREATABILITY OF
RDX-CONTAMINATED SOIL
W. Craig Light, Graduate Research Assistant
School of Civil and Environmental Engineering
Oklahoma State University
Gregory G. Wilber, Associate Professor
William W. Clarkson, Associate Professor
School of Civil and Environmental Engineering
Oklahoma State University
Stillwater, Oklahoma 74078
ABSTRACT
Soils from the Department of Energy's Pantex plant in Amarillo, Texas were examined for biological removal of nitroaromatic contaminants, principally RDX. Bench-scale reactors were used
to test treatability of soil slurries, water extracts of soil contaminants, and reagent nitroaromatic
solutions. Results of these and numerous control reactors were analyzed to determine: relative
differences in the rates of RDX desorption and transformation; extent and rate of biotransformation under aerobic, nitrate-reducing, sulfate-reducing, and methanogenic conditions; and effect of
TNT on RDX bioconversion.
INTRODUCTION
Hexahydro-l,3,5-trinitro-l,3,5-triazine (RDX) is used by the military in high-impact explosives. It is commonly found in wastewaters from munitions manufacturing plants and handling
facilities. These process waters generally contain appreciable concentrations of 2,4,6-trinitro-
toluene (TNT) as well. For example, RDX and TNT concentrations of 75 and 150 mg/L, respectively, have been found in process waters.1 Improper disposal of these wastewaters can result in
contamination of surface waters and soils. RDX primarily enters the soil by leaching from waste
lagoons. Due to its low affinity for soil, RDX tends to migrate through the soil where seepage
into groundwater can occur.23
Anaerobic biodegradation of RDX has been reported. McCormick et al.4 reported essentially
complete disappearance of RDX (50-100 mg/L) after 4 days using static batch reactors inoculated with anaerobic sewage sludge. Kitts et al.5 observed RDX transformation by pure cultures
isolated from explosives-contaminated soil. Funk et al.6 reported successful removal of RDX (30
mg/L) from soil slurry batch reactors within 24 days with no identifiable intermediates.
Early studies by McCormick et al.4 indicated that RDX was not amenable to microbial degradation under aerobic conditions. Similar results were also reported by Kitts et al.5 and Smith-
Simon and Goldhaber.3 However, several recent studies have indicated aerobic transformation
and/or mineralization of RDX under nitrogen-limited conditions.7,8 RDX transformation and/or
mineralization have also been reported in studies using aerobic composting techniques.9-"
RDX is one of several nitroaromatic compounds detected in soils at the Department of Energy
(DOE) Pantex plant in Amarillo, Texas. Various areas of contaminated soils including playa lake,
landfill, and ditches have been identified.12 Concentrations of RDX range from 0.18 to 15,000
mg/kg in these contaminated soils. Although RDX levels are very high in portions of the Pantex
soils, solubility in groundwater is limited to a range of about 38^12 mg/L,3-13'14 limiting availability for biological conversion.
52nd Purdue Industrial Waste Conference Proceedings, 1997, Ann Arbor Press, Chelsea. Michigan 48118. Printed in
U.S.A.
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