Use of colloidal gas aphron in subsurface treatment of soil

Colloidal gas aphrons (CGAs) are microbubbles stabilized by surfactant multilayers. Their unique characteristics (i.e., large interfacial area to adsorb charged and/or hydrophobic molecules, excellent flow properties compared to that of conventional foam and good blocking mechanisms that allows for a good solvent/solute contact) make them a potential alternative for soil subsurface treatment fluids. The gaseous core inside CGAs also decreases their overall specific gravity and enables their separation from bulk fluid by enhanced buoyancy. A new method that utilizes the use of Coulter Multisizer was successfully applied for characterizing CGA bubble size distribution.;Parameters influencing CGA bubble size distribution and stability are reported. Surfactant concentration below critical micelle concentration (CMC) was found to be a key player in influencing both. As the surfactant concentration increases, the average bubble size decreases at the same quality (gas holdup), giving rise to higher interfacial area per unit volume. It was also found that increased surfactant concentration below CMC stabilizes the surfactant-liquid film surrounding the gas core. These two observations were explained by the reduction of interfacial tension of the film encapsulating the microbubbles and the realization that the pressure inside a bubble is directly proportional to the interfacial tension and inversely proportional to bubble size. Other factors like quality, shear rate and surfactant type were also investigated.;Experiments were conducted to remove entrapped tetrachloroethylene (PCE), nonaqueous phase liquid (NAPL) from the soil column. CGA, surfactant solution, water, conventional foam and air sparging were used to remove PCE from the soil column. CGA and surfactant solution flushing experiments were conducted at two SDS concentrations, 50mM and 100mM. In all experiments, CGA was found to be more effective in removing the entrapped PCE. At 50mM SDS concentration, 89.1% of the entrapped PCE was removed by the CGA suspension compared to 72.9% by surfactant solution and 37.7% by conventional foam. At 100mM, 91.4% of the PCE was removed in the case of CGA compared to 78.9% for the surfactant solution. It should be noted, however, the treatment time dropped from 640 minutes to 380 minutes when the surfactant concentration was doubled for CGA. The effect of adding 15mM NaCl to the surfactant mixture was also studied. The addition of this electrolyte enhanced the removal of PCE. PCE removal increased from 89.1% to 92.6% for CGA and 72.9% to 77.2% for surfactant solution. Results of the effect of soil heterogeneity were also reported.;PCE transport in porous media was modeled using the convection dispersion equation (CDE). The removal of PCE was modeled using micellar solubilization as the main removal mechanism. A linear source depletion was added to the CDE. Parameters in the CDE, dispersion and mass transfer coefficient were determined by fitting the model to the experimental data. The model equations were solved numerically using the finite difference method.