Bacterial transport in gas-sparged porous medium

To improve the feasibility of soil-acquifer remediation using bioaugmentation, more efficient methods are needed to widely disperse pollutant-degrading bacteria in porous media. Under water-saturated conditions, bacteria readily adhere to soil particles, but under unsaturated conditions, bacteria preferentially accumulate at the air-water interface. Air sparging a saturated porous medium produces a mobile water interface that was hypothesized to facilitate bacterial transport. To investigate whether gas sparging increased bacterial transport relative to saturated-water conditions, the transport of three strains of bacteria and negatively charged microspheres of different relative hydrophobicities R(H) was measured in saturated and gas-sparged quartz-packed columns. Gas sparging increased (>60%) the bacterial transport in only one case (Pseudomonas fluorescens P17; R(H) = 27%). Transport of the other two strains were either unaffected by gas sparging (Mycobacterium vaccae JOB5; R(H) = 33%), or was reduced (Pseudomonas aeruginosa; R(H) = 75%) relative to water-saturated conditions. Microspheres were the most hydrophobic (R(H) = 98%) and the most retained of all particles under saturated conditions, but microsphere transport was unaffected by gas sparging. These preliminary results suggest that the effect of gas sparging on colloid transport is particle specific and not predictable from measurement of relative hydrophobicity.