Modeling for Volatilization and Bioremediation of Toluene-contaminated Soil by Bioventing

A two-dimensional numerical model is developed to simulate the flow, transport and biodegradation of toluene during bioventing (BV) processes in the unsaturated zones. The simulation for a single well BV system is used to illustrate the effect of air injection rate on remediation efficiency. The air is injected into the vadose zone to create a positive pressure. Simulation results show that air injection rate is a primary parameter governing the dispersal, redistribution and surface loss of contaminant. At injection rates of 81.504 m3·d−1 (Run 1) and 407.52 m3·d−1 (Run 2), the total removed mass of toluene is 169.14 kg and 170.59 kg respectively. Ratios of volatilization to biodegradation in Run 1 and Run 2 are 0.57 : 1 and 0.89 : 1, respectively, indicating that lower air injection rate enhances the biodegradation efficiency greatly. Air injection rate should be optimized to meet oxygen demand and to minimize the operational cost.