Simultaneous Biodegradation of 2,4-Dinitrotoluene and 2,6-Dinitrotoluene in an Aerobic Fluidized-Bed Biofilm Reactor

Abstract

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.

Enhanced Benzaldehyde Tolerance in Zymomonas mobilis Biofilms and the Potential of Biofilm Applications in Fine-Chemical Production

“…For example, biofilms have been used as biocatalysts in bioremediation and wastewater treatment processes (21,23,27) and in fermentative vinegar (9) and ethanol (20) production from agricultural materials, as well as in biosynthesis of polymers (42). To our knowledge, the use of biofilms for transformation of fine chemicals into value-added products has not been reported previously.…”

Federal Integrated Biotreatment Research Consortium (FIBRC): Flask to Field Initiative

“…Specific strains able to degrade nitroaromatic compounds were tested in bioreactors (chemostats, airlift reactors, fixed bed, and fluidized bed reactors) for the ability to continuously degrade artificial and authentic waste streams Lendenmann et al, 1998;Reardon and Spain, 1993;. Slurry reactor systems were also tested for the degradation of nitroaromatic compounds in soils .…”

“…An artificial ground water containing 2,4-and 2,6-DNT was used to feed a mixed culture of 2,4-and 2,6-DNT degrading bacteria in a bench scale fluidized bed reactor (FBR, Fig. 7) throughout a series of experiments spanning a 6 month period (Lendenmann et al, 1998;. Sand was used as the biomass carrier so that rigorous mass balances could be determined.…”

“…A 7-day acclimation period was required before 2,4-DNT removal rates returned to >98% at a 6 hr hydraulic retention time. The hydraulic retention time was reduced to 3 hr, and after an additional 12 days, the removal of rates of the nitrotoluenes were > 98% with the exception of 2,6-DNT for which the removal rate was 62% (Lendenmann et al, 1998).…”

“…Starvation for oxygen at BAAP could not be addressed in the laboratory because only direct measurement of soil oxygen levels in the field can establish whether sufficient oxygen is present for DNT degradation. We had, however, previously established the minimum oxygen requirements for DNT degradation in bioreactor studies (Lendenmann et al, 1998) and provided that standard to Stone & Webster for monitoring purposes at the pilot study site. In addition to oxygen, bacteria require nitrogen and phosphorus as macronutrients.…”