Biodegradation of TNT using Bacillus mycoides immobilized in PVA–sodium alginate–kaolin

• Biodegradation of TNT by Bacillus mycoides immobilized in PVA–alginate–kaolin.
• 92.63% TNT was degraded using the beads with immobilized cells.
• Removal of TNT includes both adsorption and biodegradation.
• The immobilized cells can be used to remove TNT from wastewater.

In this study, a newly isolated TNT-degrading bacterium, Bacillus mycoides, was immobilized on a carrier containing 2.5% kaolin, 10% polyvinyl alcohol (PVA), 0.3% sodium alginate (SA) and 10% cell suspension. A batch experiment demonstrated that only 20.6% TNT was removed using gel beads without immobilized cells. In contrast, 92.63% and 71.94% TNT were degraded using the beads with immobilized cells and freely suspended cells, respectively. Kinetic studies showed that adsorption of TNT on the beads followed the pseudo-second order model, while biodegradation of TNT was well fitted to the first-order degrading model where the initial concentrations of TNT ranged from 20 mg/L to 120 mg/L. These new findings suggest that removal of TNT should employ the beads with immobilized cells where adsorption and biodegradation are combined. Immobilized cells were reused 12 times and removed more than 99.5% TNT, and when stored at 4 °C for 42 days, they removed more than 91.3% TNT. This demonstrates that immobilized cells can potentially be applied in a wastewater-treatment system to remove TNT.