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Numerical Modeling of Phase Change During Bioventing: Influence of Injection Flow Rates and Thermal Conductivity

Author(s): Lee G. Glascoe; Steven J. Wright; Linda M. Abriola

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Keywords: Bioventing; Subsurface remediation; Phase change; Bioremediation; Multiphase flow; Soil vapor extraction

Abstract: This modeling investigation examines the influence of evaporative phase change on moisture content and temperature distributions during a bioventing gas injection operation for vadose zone remediation. Currently few soil vapor extraction or bioventing models incorporate non-isothermal effects when considering system performance. Laboratory and field measurements suggest, however, that even small changes in temperature and moisture content can enhance or impair biological activity and could thus affect the overall efficiency of a bioventing operation. The presented model is a one-dimensional simulator which describes mass and energy transport under steady, gaseous phase flow conditions. The coupled mass and energy equations are solved using a sequential iterative solver with matric potential and temperature as primary variables. A literature-derived relation is used to quantify the combined effect of moisture content and temperature change on biological growth rates. Radial flow simulations indicate that the injection of gas at temperatures and/or water vapor contents different from the initial ambient soil conditions can result in microbiologically significant changes in moisture content and local soil temperature. This investigation identifies that under typical gaseous flow conditions up to a 37% reduction in biological activity can occur at the injection well and a 20% reduction can occur up to a radius of 3. 5 meters after one year of injection. Sensitivity to thermal parameters is explored, revealing that the representation of the thermal conductivity strongly influences model predictions.


Year: 1999

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