Digital Image Analysis to Assess Microbubble Behavior in Porous Media

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Abstract
Air sparging is a commonly implemented technology for the remediation of volatile organic compounds from contaminated soil and ground water. In the sparging process, air is pressurized into the soil/ground-water matrix through injection wells. The air then travels to the ground surface through buoyancy, acting as a collector for volatile chemicals. To date, the design and implementation of air sparging has been largely empirical, based on the results of pilot studies. This paper uses digital image analysis to examine the transport and coalescence behavior of microbubbles in porous media, one of the most important control parameters for contaminant removal in air sparging. This laboratory study compared the diameter of bubbles produced in aqueous systems with the diameters produced in uniform spherical particulate media (diameters of 14.5 mm and 27.0 mm) and in elliptically shaped particulate media (equivalent spherical diameters of 14.5 mm). Results showed that the presence of a particulate media increased the average diameter and also increased the range of diameters of bubbles produced during sparging. As the diameter of the particulate media increased, the size of the bubbles decreased, indicating less coalescence in media with larger pore space. In addition, the effect of trace concentrations of surface-active agents (surfactants) on the diameter and coalescence behavior of bubbles was examined. In both aqueous and aqueous/particulate matrices, the presence of surfactants significantly decreased the average diameter of the bubbles produced. Additionally, the degree of coalescence decreased in the surfactant systems, producing a very narrow range of bubble diameters in both aqueous and aqueous/particulate media.