Application of oxygen microbubbles for groundwater oxygenation to enhance biodegradation of hydrocarbons in soil systems

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Virginia Tech

Aerobic decomposition of hydrocarbon contaminants in anaerobic groundwater would be enhanced by oxygenating the water. This was done by injecting oxygen microbubbles in the soil matrix packed in a 7 ft by 7 ft by 5 inches in width Vertical Slice Test Cell, VSTC, and in a 30-inch column, also packed with sand. Transfer of oxygen to water was monitored after injecting oxygen microbubbles.

Compared to sparged air and hydrogen peroxide injections documented in the literature to have transferred less than 2 percent oxygen to water, oxygen microbubbles transferred over 40 percent oxygen to the flowing groundwater. Also, after injection of microbubbles gas retentions over 70 percent were achieved. Oxygen Transfer Coefficients, KLa(s), were higher in layered soil in VSTC compared to non-layered soil when the same amounts of microbubbles were injected in the cell. The effect of cell layering, quality, stability, and the amount of microbubbles injections on transfer efficiency and gas holdup was studied.

It was concluded that high initial gas holdups, KLa values oxygen transfer per time and percent oxygen transferred were important parameters in maintaining a sustained oxygen transfer zone. These experiments demonstrated that only one of these parameters can be at a maximum, say, a high percent oxygen transfer or a high percent initial retention or a high KLa value. However, a maximum value for one parameter is usually at the expense of the other two being low. The optimum values for these parameters would be dictated by the biochemical, sediment, and chemical oxygen demands placed on the oxygen transfer system.