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.
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