Factors influencing the aerobic biodegradation of 2,4-dinitrotoluene in continuous packed bed reactors

Abstract

Factors affecting continuous 2,4-DNT degradation by an immobilized mixed microbial culture were investigated including the cell adaptation to this toxic substrate, 4-NT co-degradation, packing material porosity and substrate mass loading. Experiments were carried out in two packed bed reactors, with poraver (porous glass) and expanded slate as packing materials, using a concurrent water-air flow with ample oxygen. Running the system as a batch reactor with re-circulated medium showed that the immobilized cells adapted to higher 2,4-DNT concentrations yielding higher substrate biodegradation rates. The 2,4-DNT removal rate further increased, up to 180–265 mg L⁻¹d⁻¹, when the immobilized biomass cultivation was switched to a continuous mode. The type of the packing material influenced the 2,4-DNT removal rate, apparently due to the difference in biofilm development. Significant changes in the biofilm composition were observed compared to the original inoculum despite poor biofilm growth.

Keywords:

• Packed bed reactor
• mixed microbial culture
• oxygen in excess
• biodegradation rate and efficiency

Acknowledgments

The study was financially supported by the Ministry of Education of the Czech Republic, Project MSM 6046137305, Project ME10007 and by the Czech Scientific Foundation, Project P503/11/0163.

Notes

*For batch degradation with a medium recirculation.

*Average composition, manufacturer's data.

**Obtained after leaching for 18 h with distilled water of pH = 7.0.

*Assuming the 520 mL reactor volume. To calculate this value, the medium recirculation rate was converted to mL/day and then divided by the reactor volume.

**Assuming the periodically added 2,4-DNT concentration of 20 mg/L. This concentration was multiplied by the effective residence time.

***Calculated based on the slope of the plot of measured 2,4-DNT concentration in the medium vs. time.