Simultaneous biodegradation of 2,4-dinitrotoluene and 2,6-dinitrotoluene in an aerobic fluidized-bed biofilm reactor

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.