Generation of stable microbubbles and their transport through porous media

Abstract

Laboratory experiments were conducted to generate stable microbubbles and to measure their transport properties in porous media in order to evaluate their possible use in subsurface remediation. A mathematic model was developed as a special case of filtration theory for predicting microbubble transport in porous media. Several physical-chemical parameters were tested, including surfactant type, surfactant concentration, generation method, and pressure. A combination of an anionic surfactant and a hydrophobic nonionic surfactant was found to yield the highest concentrations of stable microbubbles (3 × 109 bubbles mL−1) in the size range of 0.7 to 20 μm. The specific surface areas of the microbubble suspensions were in the range of 50 cm2 mL−1, and specific air volumes were >0.07 mL mL−1. For 1 pore volume of injected bubble suspension, effluent recoveries of 100, 80, and 30% were achieved from columns of coarse (415-500 μm), medium (150-212 μm), and fine (53-106 μm) sands, respectively. Effluent recovery in the fine sand column increased to 63% following a 3 pore volume injection. Microbubble generation and injection under pressure were shown to minimize microbubble loss due to gas dissolution. Results from the modeling suggest that retention of microbubbles could be adequately described by filtration theory.