3D Numerical Simulation of Air Sparging Remediation Process

Air sparging(AS) is an important in situ remedial technology which was widely used in groundwater remediation for volatile organic compounds(VOCs).However,lack of standards,the field design of air sparging system was mainly based on experience.In order to further explore the process of contaminant removal by AS and provide principles for field design,numerical simulation of air sparging process was conducted.In the process of water-air two phase flow,Darcy's law and mass conservation law were employed to get the control equations of water and air transport.The relationship between permeability-saturation-suction(K-S-P) was described by the Van Genuchten(VG) model and Mualem formula.Based on the water-air two phase flow,numerical simulation of contaminant removal was performed regarding the solute transport,inter-phase mass transfer and biodegradation model.3D FEM model was developed to simulate the air sparging process and compared with the 2D simulation results.As shown in the simulation results,the zone of influence(ZOI) calculated by the 3D model is much smaller,and the lowest water saturation occurs near the sparging point while above the point the water saturation goes higher then lower.Either considering buoyant force or neglecting the air compressibility makes the ZOI smaller.The contaminant removal zone fits well with sparging influence zone.Within the ZOI,solute transfer enhances removal process while biodegradation which is the main removal factor outside the ZOI makes the removal process slow.The results suggest a better remediation effect is achieved when the contaminant zone is covered by the air sparging ZOI.It is shown that two phase flow model combined with contaminant removal could be applied to well simulate the whole process of air sparging,instructive and meaningful to the in-situ air sparging design,application and effectiveness evaluation.