Environmental Engineering Reference
In-Depth Information
possible that this process, known as bioaugmen-
tation, could expand the range of possibilities for
future bioremediation systems (USEPA
1987
).
Regardless of whether the microbes are native
or newly introduced to the site, an understand-
ing of how they destroy contaminants is criti-
cal to understanding bioremediation. The types
of microbial processes that will be employed in
the cleanup dictate what nutritional supplements
the bioremediation system must supply. Further-
more, the byproducts of microbial processes can
provide an indication that the bioremediation is
successful. Whether microorganisms will be suc-
cessful in destroying man made contaminants in
the subsurface depends on three factors: the type
of organisms, the type of contaminant, and the
geological and chemical conditions at the con-
taminated site. Biological and nonbiological mea-
sures to remedy environmental pollution are used
the same way. All remediation techniques seek
first to prevent contaminants from spreading. In
the subsurface, contaminants spread primarily as
a result of partitioning into ground water. As the
groundwater advances, soluble components from
a concentrated contaminant pool dissolve, mov-
ing forward with the groundwater to form a con-
taminant plume. Because the plume is mobile,
it could be a financial, health, or legal liability
if allowed to migrate off-site. The concentrated
source of contamination, on the other hand, often
has settled into a fixed position and in this re-
gard is stable. However, until the source can be
removed by whatever cleanup technology, the
plume will always threaten to advance off-site.
Selection and application of a bioremediation
process for the source or the plume require the
consideration of several factors. The first factor
is the goal for managing the site, which may vary
from simple containment to meeting specific
regulatory standards for contaminant concentra-
tions in the groundwater and soil. The second
factor is the extent of contamination. Under-
standing the types of contaminants, their concen-
trations, and their locations, is critical in design-
ing in-situ bioremediation procedures. The third
factor are the types of biological processes that
are effective for transforming the contaminant.
By matching established metabolic capabilities
with the contaminants found, a strategy for en-
couraging growth of the proper organisms can be
developed. The final consideration is the site's
transport dynamics, which control contaminant
from spreading and influence the selection of
appropriate methods for stimulating microbial
growth.
1.3
Microorganisms
in Bioremediation
In microbial bioremediation, living microorgan-
isms are used to convert complex toxic com-
pounds into harmless by-products of cellular
metabolism such as CO
2
and H
2
O. However, in
phytoremediation plants are used to remove con-
tamination from the soil and water. In a nonpol-
luted environment, microorganisms are constant-
ly at work, utilizing toxic compounds; however,
most of the organisms die in contaminated sites.
A few of them due to their inherent genetic ma-
terial, grow, survive, and degrade the chemicals.
The successful use of microorganisms in biore-
mediation depends on the development of a basic
understanding of the genetics of a broad spectrum
of microorganisms and biotechnological innova-
tions. Pure, mixed, enriched, and genetically en-
gineered microorganisms have been used for deg-
radation of these compounds. Routes of degrada-
tion of the major natural compounds have been
well established. The entire spectrum of microbi-
al degradation is related to the breakdown of xe-
nobiotic chemicals, which are nondegradable and
is recalcitrant. A large number of microorganisms
have been isolated in recent years that are able
to degrade compounds that were previously con-
sidered to be nondegradable. This suggests that,
under the selective pressure of environmental
pollution, a microbial capacity for the degrada-
tion of recalcitrant xenobiotics is developing that
might be harnessed for pollutant removal by bio-
technological processes. Nevertheless, the fact
that many pollutants persist in the environment
emphasizes the current inadequacy of this cata-
bolic capacity to deal with such pollutants.
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