Digital image analysis to assess microbubble behavior in porous media

Air sparging is a commonly implemented technology for the remediation of vo latile organic compounds from contaminated soil and groundwater. In the spa rging process, air is pressurized into the soil/groundwater matrix through injection wells. The air then travels to the ground surface through buoyanc y, acting as a collector for volatile chemicals. To date, the design and im plementation of air sparging has been largely empirical, based on the resul ts 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 spargi ng. This laboratory study compared the diameter of bubbles produced in aque ous systems with the diameters produced in uniform spherical particulate me dia (diameters of 14.5 mm and 27.0 mm) and in elliptically shaped particula te media (equivalent spherical diameters of 14.5 mm). Results showed that t he presence of a particulate media increased the average diameter and also increased the range of diameters of bubbles produced during sparging. As th e diameter of the particulate media increased, the size of the bubbles decr eased, indicating less coalescence in media with larger pore space. In addi tion, the effect of trace concentrations of surface-active agents (surfacta nts) on the diameter and coalescence behavior of bubbles was examined. In b oth aqueous and aqueous/particulate matrices, the presence of surfactants s ignificantly decreased the average diameter of the bubbles produced. Additi onally, the degree of coalescence decreased in the surfactant systems, prod ucing a very narrow range of bubble diameters in both aqueous and aqueous/p articulate media.