Study On Organic Contaminants Removal Using Air Sparging And Biosparging

Air sparging (AS) and Biosparging (BS) are the emerging in-situ groundwater remediation technologies since the early 1990's. It is mainly applied to remove organic chemicals 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 field application. Little was known about the material removal mechanism of air sparging and biosparging. In this paper, a one-dimensional experimental chamber was designed and installed for experimental study, and MTBE was used as contaminant. The content of this paper is study on the removal efficiency and mass transfer of MTBE from saturated soil and groundwater with air sparging. In the air sparging experiment, the research focuses on the effect of air flow rates, medium permeability, methods of air sparging on removal efficiency and mass transfer. In 20~40 mesh quartzes sands, a sizable portion of MTBE is removed during the initial stages of air injection. After that, remained MTBE lingered on the soil, which is difficult to be removed. Increased air flow helped to increase dissolved MTBE removal rates, but eventually a threshold removal rate was reached, above which further increases in air injection rates did not increase removal rates. The greater the soil grain size, the more extensive the channel network formed, which, in turn, led to faster removal times. No appreciable benefit was seen when pulsed air injection was used in the coarse sand. In the fine sand, however, pulsed air injection greatly increased the ability of air sparging to remove MTBE. In the biospaging experiment, the research focuses on the effect of the initial concentration of contaminants and microorganisms on removal efficiency and mass transfer. Biodegradation accounts for a substantial portion of MTBE remediation during biosparging. Under the experimental conditions, the partitioning of MTBE into the vapor phase through volatilization is the dominant removal mechanism. The rates of biodegradation that were observed during testing were independent of the initial aqueous-phase MTBE concentration selected for this study, and, for the range utilized during testing, independent of the concentration of microorganisms. From the contrast between AS and BS, we found that volatilization was the dominant removal mechanism at higher contaminant concentration, but the importance of biodegradation increased as the contaminant concentration decreases. In particular, the biodegradation becomes the significant remedial mechanism when dissolved contaminant concentrations are below 1mg/L. In this study, a radial diffusion model with an air-water mass transfer boundary condition was developed and applied for the prediction of VOC. It was used to simulate the mass transfer through bioventing under experimental conditions. The simulation results can be in consonance with the experimental data fairly well.