Environmental Engineering Reference
In-Depth Information
cost-effective than traditional techniques like in-
cineration of waste and carbon filtration of water.
Bioremediation technologies can be generally
classified as in situ or ex situ. In situ bioremedia-
tion involves treating the contaminated material
at the site while ex-situ involves removal of the
contaminated material to be treated elsewhere.
Some examples of bioremediation technologies
are bioventing, landfarming, bioreactor, com-
posting, bioaugmentation, rhizofiltration, and
biostimulation.
However, not all contaminants are easily
treated by bioremediation using microorganisms.
For example, heavy metals such as cadmium
and lead are not readily absorbed or captured by
organisms. The assimilation of metals such as
mercury into the food chain may worsen mat-
ters. Phytoremediation is useful in these cir-
cumstances, because natural plants or transgenic
plants are able to bioaccumulate these toxins in
their above-ground parts, which are harvested for
removal. The heavy metals in the harvested bio-
mass may be further concentrated by incineration
or even recycled for industrial use. A wide range
of bioremediation strategies is being developed
to treat contaminated soils. In bioremediation,
microorganism transform hazardous chemical
compounds to nonhazardous end products, how-
ever, in phytoremediation plants are used for this
purpose (Brar et al.
2006
). Two basic methods
are available for obtaining the microorganism to
initiate the bioremediation: bioaugmentation—in
which adapted and genetically coded toxicants
degrading microorganism are added; biostimula-
tion—which involves the injection of necessary
nutrients to stimulate the growth of the indige-
nous microorganism.
The bioremediation systems in operation today
rely on microorganisms native to the contaminat-
ed sites, encouraging them to work by supplying
them with the optimum levels of nutrients and
other chemicals essential for their metabolism.
Thus, today's bioremediation systems are limited
by the capabilities of the native microbes. How-
ever, researchers are currently investigating ways
to augment contaminated sites with nonnative
microbes, including genetically engineered mi-
croorganisms—especially suited to degrading the
contaminants of concern at particular sites. It is
possible that this process, known as bioaugmen-
tation, could expand the range of possibilities for
future bioremediation systems.
The effectiveness of bioremediation is mainly
influenced by degradability and toxicity of the
chemical compounds. Based on this the chemi-
cal may be divided into degradable and nontoxic,
degradable and toxic, nondegradable and toxic,
and nondegradable and nontoxic chemical com-
pounds. The main goal of bioremediation can be
fulfilled by enhancing the rate and extent of bio-
degradation of the pollutants, utilizing or devel-
oping microorganisms.
1.2
Current Practice
of Bioremediation
The key players in bioremediation are bacteria—
microscopic organisms that live virtually every-
where. Microorganisms are ideally suited to the
task of contaminant destruction because they pos-
sess enzymes that allow them to use environmen-
tal contaminants as food and because they are so
small that they are able to contact contaminants
easily. In situ bioremediation can be regarded as
an extension of the purpose that microorganisms
have served in nature for billions of years: the
breakdown of complex human, animal, and plant
wastes so that life can continue from one genera-
tion to the next. Without the activity of micro-
organisms, the earth would literally be buried in
wastes, and the nutrients necessary for the con-
tinuation of life would be locked up in detritus.
The goal in bioremediation is to stimulate mi-
croorganisms with nutrients and other chemicals
that will enable them to destroy the contami-
nants. The bioremediation systems in operation
today rely on microorganisms native to the con-
taminated sites, encouraging them to work by
supplying them with the optimum levels of nu-
trients and other chemicals essential for their me-
tabolism. Researchers are currently investigating
ways to augment contained sites with nonnative
microbes including genetically engineered mi-
croorganisms specially suited to degrading the
contaminants of concern at particular sites. It is
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