Study On Organic Chemicals Removal Using Air Sparging

Air sparging (AS) is an emerging in-situ groundwater remediation technology since the early 1990's. It is mainly applied to remove volatile organic chemicals (VOCs) from saturated soils and groundwater. Its advantages of low-cost, high-efficiency and in-situ operation have been fully demonstrated in lots of field tests. However, system design has remained largely empirical during air sparging field application. Little was known about the material removal mechanism of air sparging. Hydrodynamics and contaminant mass transfer of air sparging have been studied in this paper; meanwhile, a numerical model for the axisymmetric subsurface airflow was developed.The removal efficiency of contaminants during air sparging is highly depends on the air distribution resulting in aquifer. The acetylene was used as tracer displacing air for the first time to study gas distribution during AS with different injected gas flow rates and different infiltrative aquifers. The experiments were shown that the acetylene tracing method has more sensitivity and accuracy than other methods. Moreover, it is easy to operate and suitable to generalize.In coarse sands, the acetylene tracing studies with different gas flow rates indicate that when low flow rate (0.05m3/h) was used, the gas distribution was thin and disperse. However, when injected at appropriate rate (0.15m3/h), the gas was uniformly distributed and the whole gas plume was formed with a roughly symmetrical U-shape structure. If high flow rate (0.30m3/h) was used, the gas distribution was very asymmetrical and excursive, furthermore, the gas easily traveled along a path of least resistance. As for different infiltrative sands, the acetylene tracing studies were shown that the gas was sensitive to soils' permeability. In such sands of which magnitude of permeability was close to 10-10m2, the acetylene gases were uniformly distributed and the radiuses of influence were large. But as for sands whose magnitude of permeability was near to 10-11m2, the gas distributions were uneven and there may be preferred directions of flow, or the gas would diffuse horizontally sometimes. The mass transfer of toluene in coarse sands during air sparging was investigated at appropriate gas flow rate, combined with gas distribution studies. The toluene concentrations of sampling ports were evaluated by method of sampling at different time and interposing at uniform time, in addition, those in saturated soils region were analyzed using 2D cubic interposal method, which mainly used for plotting contours in geography. An axisymmetric airflow model was put forward based on Darcy law and Bessel function transform. It was used to simulate the airflow during air sparging under experimental condition. The simulation results can be in consonance with the experimental data fairly well. Additionally, several operating effects and parameters of AS field application were forecasted in this paper using this mathematical simulation model.