Mixtures of 2,4- and 2,6-dinitrotoluene are produced in
large quantities as precursors of polyurethane foams and
the explosive 2,4,6-trinitrotoluene (TNT). The two
isomers
are widely distributed in contaminated groundwater and
soil.
Bacteria capable of growing with the individual
isomers
as the sole source of carbon, nitrogen, and energy have
been isolated previously. However, attempts to
degrade
2,4- and 2,6-DNT simultaneously have failed. We tested
the
hypothesis that a mixed culture could degrade an isomeric
DNT mixture if the bacteria were grown in an aerobic
biofilm at low substrate concentrations. Such
conditions
were achieved with a fluidized-bed biofilm reactor (FBBR).
The reactor was fed aqueous solutions containing 2,4-
(40
mg L-1) and 2,6-DNT (10 mg
L-1). The feed flow rate
was
gradually increased to yield surface loading rates of 36−600 mg of DNT m-2
d-1. Removal efficiencies higher
than
98% for 2,4-DNT and 94% for 2,6-DNT were achieved at
all loading rates. The nitrogen released from DNT was
found
quantitatively as nitrate that indicated the presence of
nitrite-oxidizing bacteria. COD measurements of the
reactor
effluent confirmed complete mineralization of the DNT.
The results demonstrate that mixtures of 2,4- and
2,6-DNT
can be biodegraded successfully in an aerobic
FBBR.