General
- Bioremediation can
be defined as any process that uses microorganisms, fungi, green
plants or their enzymes to return the environment altered by
contaminants to its original condition. Bioremediation may be employed
to attack specific soil contaminants, such as degradation of
chlorinated hydrocarbons by bacteria.
-
Bioremediation
is an option that offers the possibility to destroy or render harmless
various contaminants using natural biological activity. As such, it
uses relatively low-cost, low-technology techniques, which generally
have a high public acceptance and can often be carried out on site.
Process
- There are two main
avenues of bioremediation operation: In situ can be used where
excavation is impractical - under highways, buildings, runways, etc.
This process can simultaneously treat soil and groundwater in one
step, without the generation of hazardous waste products. Using an
engineered treatment setup where contamination is placed for
bioremediation is called an ex situ process (bioslurry, bioreactor,
landfarming, etc.)
-
The
anaerobic reductive de-chlorination process is a biodegradation
mechanism that relies on the growth of bacteria as a result of the
reduction of PCE and its daughter products under anaerobic conditions.
As one or more chlorine atoms on the CAH are replaced with hydrogen,
the bacteria gain energy. The CAH serves as the electron acceptor in
this anaerobic process and the hydrogen is the electron donor. The
hydrogen necessary for this reaction is delivered by direct infusion.
Applications
-
In-situ
groundwater bioremediation is a technology that encourages growth and
reproduction of indigenous microorganisms to enhance biodegradation of
organic constituents in the saturated zone. In-situ groundwater
bioremediation can effectively degrade organic constituents which are
dissolved in groundwater and adsorbed onto the aquifer matrix.
-
In-situ
groundwater bioremediation can be effective for the full range of
petroleum hydrocarbons. While there are some notable exceptions
the short-chain, low-molecular-weight, more water soluble constituents
are degraded more rapidly and to lower residual levels than are
long-chain, high-molecular-weight, less soluble constituents.
Recoverable free product should be removed from the subsurface prior
to operation of the in-situ groundwater bioremediation system. This
will mitigate the major source of contaminants as well as reduce the
potential for smearing or spreading high concentrations of
contaminants. In-situ bioremediation of groundwater can be combined
with other saturated zone remedial technologies (e.g., air sparging)
and vadose zone remedial operations (e.g., soil vapor extraction,
bioventing).
Technology
-
The
J.R. Simplot Ex-Situ Bioremediation Technology is designed to
anaerobically degrade nitroaromatic and energetic compounds in soils
and liquids without forming identifiable toxic intermediate compounds
produced by other biotreatment methods. This technology was evaluated
under the Superfund Innovative Technology Evaluation (SITE) Program on
soils contaminated with 2-sec-butyl-4,6-dinitrophenol (dinoseb), a
RCRA-listed herbicide (P020).
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Enhanced
aerobic bioremediation technologies are used to accelerate naturally
occurring in-situ bioremediation of petroleum hydrocarbons, and some
fuel oxygenates such as methyl tertiary-butyl ether (MTBE), by
indigenous microorganisms in the subsurface. Enhanced aerobic
bioremediation technologies include biosparging; bioventing; use of
oxygen releasing compounds; pure oxygen injection; hydrogen peroxide
infiltration; and ozone injection. These technologies work by
providing a supplemental supply of oxygen to the subsurface, which
becomes available to aerobic, hydrocarbon-degrading bacteria.
Market
and Report
-
The
current technology-based land remediation market is worth in the
region of £120 – £130 million. Technologies such as soil washing,
bioremediation and other extractive methods have developed to a stage
where they are both commercially viable and compete head-to-head with
excavate and landfill options. Over the next 5 years, this is expected
to grow to £320 – £350 million per annum. Major sites will
increasingly use soil washing, bio-remediation and other
technology-based remediation. Funding will be a mixture of public
sector (UK and European) and private sector with increasing use of
public/private partnership.
-
Although
bioremediation holds great promise for dealing with intractable
environmental problems, it is important to recognize that much of this
promise has yet to be realized. Specifically, much needs to be learned
about how microorganisms interact with different hydrologic
environments. As this under-standing increases, the efficiency and
applicability of bioremediation will grow rapidly. Because of its
unique interdisciplinary expertise in microbiology, hydrogeology, and
geochemistry, the USGS will continue to be at the forefront of this
exciting and rapidly evolving technology.
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