CAREER: Interfacial Behavior of Microbubbles During Contaminant Stripping in Saturated Soils: Multiscale Investigations in Research and Education

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9984206- BurnsThis Faculty Early Career Development (CAREER) research and education project addresses the physical factors that govern the formation and movement of discrete air bubbles through otherwise saturated soils. In geoenvironmental applications, the transport and distribution of injected air bubbles is critical to the effectiveness of the air sparging process -- an in-situ stripping technique designed to mobilize volatile organic compounds to the vapor phase. The project involves an experimental, multi-scale investigation into the dynamics of air bubble transport through pore, pore network, and continuum scale soil models.The rate and pattern of air transport is quantified as a function of injection pressure/velocity, injection orifice, and interfacial tension in a model soil pore. Etched glass micromodels are used to simulate air transport through soil pore networks, and the air saturation, bubble volume, and transport heterogeneity are quantified as a function of the controlling parameters identified at the pore scale. The microscale investigations manipulates the system parameters, such as injection velocity and interfacial tension, in order to identify the conditions that lead to decreased bubble diameter, increased bubble residence time, and increased bubble surface area. Stripping bubbles with these characteristics significantly enhances the air sparging process at the global scale. The data obtained at the pore and pore network scales is used as inputs for column tests performed at the continuum scale. The column tests quantifies contaminant removal efficiency, degree of bubble coalescence, and mass transfer effects, based on the enhanced system control parameters identified in the pore and pore network scale investigations.The data obtained in this multiscale investigation will significantly enhance the state of knowledge by developing a rigorous, fundamental understanding of the variables that control bubble movement through otherwise saturated soil systems. While the objectives proposed are set within the framework of air sparging, the results of the multiscale, fundamental investigation are equally applicable to similar processes, such as petroleum recovery.Parallel to the developments in the research project, the influence of microscale physical and chemical phenomena is interwoven into undergraduate Civil Engineering courses, undergraduate research, and a workshop targeted to attract middle school girls to pursue the study of science and engineering. Consideration of multiscale physical and chemical behavior is integrated into classroom lectures and a series of five-minute classroom demonstration experiments. These "change-up" experiments are carefully designed to illustrate the macroscale effects of microscale phenomena in engineering practice. An undergraduate remediation case studies course that incorporates microscale physical and chemical considerations into remedial design is being developed. Additionally, an outreach workshop designed to encourage middle school girls in the study of science and engineering is being developed and implemented.