Groundwater at many military factory, munition
storage and maneuver sites is contaminated by
explosives chemicals that were released into the subsurface.
The 2,4,6-trinitrotoluene (TNT) is among the most
common explosive pollutants. In this study, two TNT-degrading
strains, isolated from TNT-contaminated soils and
wastewater sludge, were applied for TNT biodegradation.
Based on the 16S rDNA sequence analyses, these two
bacterial strains were identified as
Achromobacter
sp. and
Klebsiella
sp. via biochemical and DNA analyses. Microcosm
study was conducted to evaluate the feasibility and
efficiency of TNT biodegradation under aerobic conditions.
Results indicate that TNT degradation by-products were
detected in microcosms (inoculated with
Achromobacter
sp. and
Klebsiella sp.) with cane molasses addition.
Klebsiella
sp. and
Achromobacter sp. used TNT as the nitrogen
source and caused completely removal of TNT. Two possible
TNT biodegradation routes could be derived: (1) part
of the TNT was transformed to nitrotoluene then transformed
to nitrobenzene followed by the nitro substitute
process, and trinitrobenzene, dinitrobenzene, and
nitrobenzene were detected; and (2) TNT was transformed
via the nitro substitute mechanism, and dinitrotoluene
followed by nitrotoluene isomers were detected. The initial
TNT degradation involved the reduction or removal of the
nitro substitute to an amino derivative or free nitrite.
Results show that the second route was the dominant TNT
biodegradation pathway. The produced by-products were
also degraded without significant accumulation during the
degradation process. These findings would be helpful in
designing a practical system inoculated with isolated TNT
degradation strains for the treatment of TNT-contained
groundwater.
