Effects of Flow Rate and Gas Species on Microbubble and Nanobubble Transport in Porous Media

Transport of microbubbles and nanobubbles (MNBs) in porous media has drawn increasing attention as a promising technology for soil and groundwater remediation. Understanding the transport mechanisms of MNBs in soils is essential to optimize MNB-based remediation techniques. In this study, effects of flow rates and bubble gas species on transport characteristics of MNBs were investigated in columns packed with glass beads. Microbubbles and nanobubbles were created by either air or oxygen injection to the columns at different flow rates. All results showed marked entrapment of MNBs inside the columns and relatively higher retardation of MNBs with smaller bubble size. The entrapment was enhanced for air-based MNBs under lower flow rate. A convection-dispersion model including bubble attachment could well capture the obtained effluent curves for MNB transport at high flow conditions. For low flow conditions, a model including bubble attachment-detachment and straining terms best described the data. The fitted model parameters suggested that irreversible straining is an important deposition mechanism for MNB transport in porous media.