Transport process of TNT from flooded highly contaminated surface soil bed

Remediation of TNT contaminated soil by phytoremediation and bioremediation in aqueous medium is often limited by TNT desorption from the soil. Understanding the desorption of TNT from the contaminated soil is needed in order to employ effective soil remediation strategies. TNT (2,4,6-Trinitrotoluene) desorption was investigated using a flat sheet flow leaching bed reactor in the laboratory. Deionized water advective flow was pumped over the contaminated soil matrix in the form of a sheet flow. Concentrations of TNT in the collected water samples was determined by HPLC. The result is presented as the flux of TNT from the soil matrix to the water phase. The results showed a decrease in TNT concentration and flux with time. The rates of leaching were compared to the prediction of a simple mathematical model that was developed for this type of the reactors. The model accurately fits the rate of removal of TNT from soil under various experimental conditions. The effective diffusivity was calculated by fitting the developed mathematical model against the experimental data and was found to be 2.33×10^-6 cm²/s. Consequently this resulted in a molecular diffusivity of 6.54×10^-6 cm²/s. Diffusion is the limiting factor in leaching of TNT from the soil, as was apparent from the experimental results of decreasing flux with time and the TNT concentration gradient profiles within the soil bed, both during and after leaching experiment. This means that the diffusion of TNT is the limiting process in the overall TNT transport from soil into water.