Laboratory Simulation Study Of Air Sparging For Remediation Of Groundwater Pollution

In recent years, with the rapid development of social and economy, soil andgroundwater organic pollution is more and more serious. Volatile organic pollutants(VOCs) are a class of important pollutants, the development of efficient techniques toremediate soils and groundwater contaminated with volatile organic compounds is ofgreat importance to sustainable development of human environment. Air sparging (AS)has proven to be the most effective means of remediating groundwater andunsaturated soils that have been contaminated with VOCs in all the polluted siteremediation technologies. Although there have a lot of in situ air sparging site, itsdesign and operation can only based on previous field experience, and there lack ofquantitative calculation method of key parameters.According to domestic and foreign researches, laboratory two-dimensionalairflow visualisation model tests were conducted to assess the changing rules of themain parameters: the minimum and maximum sparging pressure, air flow patterns,air flow rate, gas saturation; shape, size and the predictive models of the Zone ofInfluence (ZOI); airflow distribution and predictive models associated with the zoneof influence.In this Master’s thesis, the main research results are as follows:(1) The air flow patterns mainly determined by particle sizes of porous media.Chamber flow occurred when the effective grain size D10less than0.22mm,channelised flow occurred when D10was in the range of1.42~2.1mm, bubbly flowoccurred when D10greater than2.10mm.(2) The air flow rate increases linearly with the increasing of sparging pressure.And the bigger the particle size, the greater the permeability and the slope of equation.When D10increased from0.22mm to4.20mm, the slope of equation increased from0.0726to0.2089. The average air saturation increased rapidly with the increase ofsparging during the initial stage of air sparging when the sparging pressure is small. However, the growth rate of average air saturation gradually slows down with the improving of sparging pressure, and there seemed to be a maximum saturation. The maximum average air saturation range from49%to76%.(3) The shape of zone of influence(ZOI) related to air flow patterns, when the air migration in porous medium in the form of chamber flow, the shape of ZOI is irregular, which is hard to be described. When the air migration in the form of channel flow or bubbling flow, the ZOI shows cone shaped. The ZOI size increased as the rises of sparging pressure when the pressure was relatively small, however, when the sparging pressure exceeded a certain critical pressure, the ZOI changed little and there exists a "stable ZOI". The "stable ZOI" for each type of medium represents the characteristic shape and size of that medium’s ZOI, and it decreases with the increase of particle size.(4) The size of ZOI can be characterised by two aspects:the angle between the ZOI boundary and the vertical direction and the lateral expansion length of the boundary. The prediction formula of Radius of influence(ROI) can be established as follows:R=H tanθ+L. The prediction formula of the volume of Zone of influence(ZOI) can be established as follows:V=1/3πH[H tanθ(H tanθ+3L)+3L2]. Comparing the calculated results with field data demonstrated that the formula is widely applicable, except in large-scale heterogeneous aquifers.(5) The distribution of the airflow rate within the ZOI was quite uneven:the maximum airflow rate occurred at a location just above the diffuser, and with the increase of the lateral distance from the sparger, the airflow rate decreased to zero. Increasing sparging pressure or medium size will increase the inhomogeneous distribution of air flow.(6) The airflow rate distribution within the ZOI is quite uneven and obeys Gaussian distribution. Moreover, the airflow distribution is similar for a given porous medium under different sparging pressures, and it can be fitted using a unified dimensionless Gaussian function as follows: The innovations of this work as follows:(1) established the predictive models ofthe Radius of Influence and discussed the parameters and suitable conditions of thepredictive models;(2) quantitative characterized the airflow distribution in the ZOI,established the prediction formula of airflow distribution, and discusses theparameters required for the prediction formula.