Theoretical evaluation of dissolution and biochemical reduction of TNT for phytoremediation of contaminated sediments

In this study the removal of 2,4,6-trinitrotoluene (TNT) in the subsurface was theoretically simulated using a steady-state one-dimensional form of the advection-dispersion-reaction (ADR) equation, also accounting for TNT dissolution. The system studied consists of equal-sized spherical TNT particles uniformly distributed in an anaerobic saturated sediment. Water is assumed to flow steadily and uniformly through the sediment. The TNT removal is accomplished by biochemical catalysts (enzymes) released by plants. A sensitivity analysis was performed by varying TNT particle diameter, soil TNT content, Darcy velocity and a first-order biochemical reduction rate constant, and studying their effect on the TNT aqueous-phase concentration and TNT removal rate from the exposure zone. With zero or low biochemical reduction rate constants, it was found that the rate of removal of TNT from the exposure zone improved with higher flushing rates. On the other hand, higher biochemical reduction rate constants resulted in significant reduction of the aqueous TNT concentration at all flushing rates and in higher TNT removal rates from the exposure zone. A biochemical reduction rate constant of 14.25 day−1 was measured for reduction of dissolved TNT by sediments containing biochemical catalysts under anaerobic conditions. A simulation using this rate constant suggested the feasibility of in situ phytoremediation of TNT-contaminated sediments.