Application of oxygen microbubbles for in situ biodegradation of p-xylene contaminated ground water in a soil column

In situ biodegradation of p-xylene was studied in a 2.75 inch diameter column using oxygen microbubbles to supply the electron acceptor. One objective was to demonstrate that pxylene can be biodegraded in the soil column and to follow the degradation and pressure drops as a function of time.

The next objective was to demonstrate the potential for biodegradation of p-xylene in the presence of ferrous iron and to follow bioremediation and anticipated pressure drops as a function of time. Then, an air sparging section was added prior to the biodegradation section to determine if the ferrous iron could be removed in this section. The air sparging section would then be flushed with air and/or water to determine if the ferrous could be removed from the sand matrix and alleviate the expected plugging.

The bacteria degraded p-xylene to below detectable limits until the oxygen supply was exhausted. The pressure drops over this time showed a slight increase over the first few days and then a gradual decline, which shows promise for in situ biodegradation as the microorganisms were thought to cause plugging.

The next run which studied the simultaneous biodegradation of xylene and ferrous oxidation showed no interference from the ferrous iron. The microorganisms seemed to store the oxygen that they needed before the ferrous could oxidize. The pressure drops showed no general trend, therefore the ferric precipitate did not cause an appreciable amount of plugging as expected.

The air sparging section resulted in volatilization of xylene with very little ferrous oxidation. To flush the ferric precipitate from this zone, either a combination of air sparging and backwashing or backwashing at the fluidization velocity was needed to remove the ferric iron.