Remediation Of MTBE By Air Sparging In Groundwater And Mathematic Simulations

Air sparging is one of emerging in situ remedial technologies that reduces concentrations of volatile organic compounds adsorbed to soils and dissolved in groundwater. The process of air spargaring is considered a hybrid technology, because air is used to physically strip the volatile and semi-volatile components out of contaminated soil and groundwater, and the oxygen in air is used to stimulate indigenous microorganisms to degrade organic compounds from contaminated soil and groundwater. This study focuses on the removal of MTBE in the saturated soil and groundwater when air sparging involved. Theoretical basis, process parameters, transport mechanism, hydromechanics and mathematical modeling for air sparging have been investigated.The adsorption isotherm of MTBE in sand soil is determined to follow Freundlich adsorption by experiments. Monod coefficients which include the maximum specific substrate utilization rate, half-saturation coefficient and the yield coefficient are measured from batch experiments and fitted by least-square method.The conditions for MTBE aerobic biodegradation are determined by experiments. Through mixed culture one strain identified as Bacillus cereus that can degrade MTBE faster are isolated by enriching, screening and culturing from Dagang Oil Field. It is called MTBE-2.The column experiments have been used in detail to investigate the mechanisms controlling MTBE removal from saturated soil during air sparging. Results show that increasing air flow is helpful to increase the removal rate of dissolved MTBE, without biodegradation. But further increasing air injection rates don't increase the removal rate, when a threshold removal rate is reached. The higher the soil penetrability, the more extensive the channel network formed, which, in turn, lead to faster removal. A tailing effect of lingering residual contaminant occurs using the lower penetrability soil, which can be improved by pulse sparging. In condition of microorganism exiting, it is found that MTBE is mainly removed by volatilization through comparing the effect of volatilization with biodegradation on MTBE removal.A one-dimension mass transfer model is presented to describe comprehensive transport, interphase mass transfer and biodegradation during air sparging. The result of simulation is in good agreement with the experimental data.Mathematical models of non-steady state and steady state flow process have been developed based on the AS momentum equation, which are solved by finite element method. The distribution of air saturation, velocity vectors and isobars are obtained, and results from simulation show that the required time to form the steady fluid field is about 5 hours. The distribution of air saturation varies with the operating time and the saturation.