Environmental Engineering Reference
In-Depth Information
Fig. 1.4 In situ bioremedi-
ation of contaminated site.
(Source: Biotechnology in
Medicine and Agriculture
Principles and Practices,
Kumar et al. 2013 )
methodology. The enhancement of microbial
degradation as a means of bringing about the in-
situ clean-up of contaminated soils has spurred
much research. The rhizosphere, in particular, is
an area of increased microbial activity that may
enhance transformation and degradation of pol-
lutants. The most common methods to stimulate
degradation rates include supplying inorganic
nutrients and oxygen, but the addition of deg-
radative microbial inocula or enzymes as well
as the use of plants should also be considered.
Approximately 750 tons of soil, which had been
contaminated by a wood preservative, was bio-
remediated in North Carolina using white rot
fungi. Primary contaminants of concern at the
site included pentachlorophenol and lindane.
The field degradation of PCDDs and PCDFs in
soil at a former wood treatment facility in North
Carolina has been demonstrated. Toxaphene-
contaminated soils present at a crop dusting
facility in northern California were bioremedi-
ated using white rot fungi. The soils were mixed
with a suitable substrate that had been inoculated
with the fungi and placed in biotreatment cells.
During operation of the project, toxaphene con-
centrations and environmental conditions (e.g.,
oxygen levels, moisture content, carbon dioxide
levels, and temperature) within the treatment
cells were monitored to track progress of fungal
bioremediation. Chlorophenols are recalcitrant
compounds that have been used for decades to
impregnate wood, and many residues can be
found in the environment long after the uses of
chlorophenols have been discontinued. Chloro-
phenols are soluble in water and may leach from
contaminated soil to groundwater. Therefore, the
contaminated sites must be cleaned up to prevent
further contamination into ground water. There
have been only very limited field trials of PCB
bioremediation. General Electric Corporation
has carried out most in efforts to clean up their
own contaminated sites. One in 1987 basically
“land farmed” the PCB contaminated soils. They
tilled the soils and added bacteria that degraded
PCBs together with appropriate nutrients. The
treatment result was less than laboratory results
had shown and may have been due to bioavail-
ability problems with the PCBs in the field
(Fig. 1.4 ).
In situ Physical/Chemical Treatment
In situ Air Sparging (IAS)
IAS was first implemented in Germany in 1985
as a saturated zone remedial strategy. It involves
the injection of pressurized air into the saturated
zone. IAS induces a transient, air-filled porosity
in which air temporarily displaces water as air
bubbles migrate laterally from the sparge point
and also vertically toward the water table. IAS
induces a separate phase flux in which air travels
in continuous, discrete air channels of relatively
smaller diameter from the sparge point to the
water table. Air movement through the saturated
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