The role of colloidal particles on the migration of air bubbles in porous media

摘要

The contamination of groundwater and soils has been a big issue of great interest and importance to human health. When organic compounds from leaking underground storage tanks or accidental spills on the surface infiltrate into the subsurface environment, they migrate downward through the unsaturated zone. These contaminants are dissolved into groundwater and move with groundwater flow. Thus, there is a need for remediation technologies. Air sparging is relatively cost-effective, as well as an efficient and safe technique for recovering organic contaminants in the subsurface. This technique introduces air into the subsurface system to enhance the volatilization and bioremediation of the contaminant in the groundwater system. In this operating system, the movement of air phase can take place either as a continuous air phase or as discrete air bubbles. However, the present research focused on continuous air phase assumption and mass balance equations of individual phases rather than taking into account the movement of air bubbles and colloidal particle capture on discrete air-water interface. Generally colloidal particles are treated as suspended particles in the water, so the hypothesis is that the rising air bubble can collect the particles and transport them up to the water table where the pump extracts the dirty bubbles from the groundwater system to the processing unit on the ground surface. This dissertation developed a pore-scale study to model the migration of discrete air phase in the presence of colloidal particles captured on the air-water interface. The model was based on the pore-scale balance equation for forces acting on a bubble rising in a porous medium in the presence of colloids. A dimensional analysis of the phenomenon was also conducted to provide a more generalized methodology to evaluate the effect of individual forces acting on an air bubble. The results indicate that the proposed model can predict the terminal velocity of a rising bubble without or with colloidal particles and provide the effect of numbers of colloidal particles, properties of colloidal particles, and solid grain size. The results showed that the terminal velocity of a discrete bubble was affected by the attachment of particles on a bubble, and then the volatile organic compound (VOC) removal rate was changed by the various radii of a bubble and the number of colloidal particles on a bubble.