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15-03-2011, 09:25 PM
Post: #1
Bioremediation
Bioremediation
Jayakrishnan U and Meria M Dan
Third semester Biotechnology and Biochemical Engineering,
Mohandas college of engineering and technology


.pdf  Bioremediation.pdf (Size: 185.2 KB / Downloads: 133)

Abstract
Bioremediation means to use a biological remedy to abate or clean up contamination. This makes it different
from remedies where contaminated soil or water is removed for chemical treatment or decontamination,
incineration, or burial in a landfill. Microbes are often used to remedy environmental problems found in soil,
water, and sediments. Plants have also been used to assist bioremediation processes. This is called
phytoremediation. Biological processes have been used for some inorganic materials, like metals, to lower
radioactivity and to remediate organic contaminants. With metal contamination the usual challenge is to
accumulate the metal into harvestable plant parts, which must then be disposed of in a hazardous waste landfill
before or after incineration to reduce the plant to ash. Two exceptions are mercury and selenium, which can be
released as volatile elements directly from plants to atmosphere. The concept and practice of using plants and
microorganisms to remediate contaminated soil have developed over the past thirty years.
KeyWord: Phytoremediation, contamination, microorganism.

Introduction
*Bioremediation is defined as the process whereby
organic wastes are biologically degraded under
controlled condition to an innocuous state, or to
levels below concentration limits established by
regulatory authorities.
*This process is mainly carried out by biological
agents like plants, microorganisms, fungi etc…
*Contaminant compounds are transformed by
living organisms through reactions that take place
as a part of their metabolic processes i.e.., detoxify
substances substances hazardous to human health
and the environment.
* Not all contaminants are easily treated by
bioremediation using microorganisms. Like heavy
metals such as cadmium and lead are not readily
absorbed or captured by organisms. The
assimilation of metals such as mercury in the food
chain may worsen matters. In such a case
‘phytoremediation’, bio accumulates these toxins in
their above ground parts, which are then harvested
for removal.
Principles of Bioremediation
°From the name itself gives the idea that this
technique uses only living organisms only not any
other modern technologies.
°The organisms absorb the contaminants, induct
them to their metabolic pathway and thereby
enzymatically transform them into harmless
substances.
°Bioremediations can be effective only where
environmental conditions permit their growth and
activity, is application often involves the
manipulation of environmental parameters to allow
their growth and degradation to proceed at a faster
rate.
°As most of the bioremediation activities are taking
places in open environment, the main type of
reaction taking place is aerobic and the rate is
dependent on it.

Types Of Bioremediation
◊Based on the site of application bioremediation is
classified as:
1.Insitu is the application of bioremediation
techniques to soil, ground water at the site.
─Lower cost and less disturbance since they
provide the treatment in place avoiding excavation
and transport of contaminants.
─The treatment is limited by the depth of the soil
that can be effectively treated. In many soils
effective oxygen diffusion for desirable rates of
bioremediation extend of a range of only a few
centimetres to about 30cm in the soil though depths
of 60cm and greater are been effectively treated in
some cases.
─The most important land treatments are -bio
venting, biodegradation, biosparging, bio
augmentation.
2 .Ex situ application of bioremediation technique
to soil, ground water at the site which have been
removed from the actual site.
─The particular region to be mediated is removed
via excavation of pumping.
─ Important exsitu technique are land farming,
composting, bio piles, bioreactors.
◊Based on the type of organisms used in
bioremediation: Microbial, Myco and Phyto.
1. Microbial bioremediation mostly occurs
naturally by the natural microbial flora which suites
with condition and perform its life activities
thereby consuming or transforming the
contaminants.
─Sometimes in order to boost the growth fertilizers
are add (bio stimulation).
─The bioremediators are boosted to break down
contaminants when matched strains are being
added.
─Deinococcus radiodurans, the most radioresistant
organism known has been modified o consume and
digest toluene and ionic mercury from highly
radioactive nuclear waste.
On the basis of how the bioremediation process
takes place microbial bioremediation is divided in:
─Natural bioremediation is the biodegradation of
dead organism. Its natural part of carbon, sulphur,
nitrogen cycles. The microbe utilizes the chemical
energy from the waste to grow. It mainly convert
contaminants to carbon and hydrogen to
carbondioxide.
─Managed bioremediation is applied by people.
Main condition is the presence of favourable
environment. R L Raymond was awarded a patent
for the bioremediation of gasoline

2. Mycoremediation is the use of fungal mycelia
to remediate biological contamination.
─One of the primary role of fungi in the ecosystem
is decomposition, which is performed by the
mycelium.
─Mycelia secretes extracellular enzymes and acids
that break down lignin and cellulose, the two main
building blocks of plant fibres.
─It has been seen that the natural microbial
community participates with the fungi to break
down contaminants, eventually into carbondioxide
and water.
─Wood degrading fungi are particularly effective in
breaking down aromatic pollutants, as well as
chlorinated compounds.
3 .Phytoremediation is the use of plants to remove
contaminants from soil and water. It is useful in the
case when there is wide spread heavy organic and
metallic pollutants. Acts a filter to filter out the
contaminants then metabolize them.
─There are five type of phytoremediation
techniques, classified based on the fate of
contaminant: phytoextraction, phytodegradation,
phytostabilixation, rhixodegradation,
ghixofiltration.
Factors Affecting Bioremediation
▪Microbial population that suites the environment
that can biodegrade all of the contaminants.
▪Oxygen: enough to support aerobic biodegration.
▪Temperature: Appropriate temperatures for
microbial growth (0-40).
▪pH: Best range is from 6.5 to 7.5
Advantage Of Bioremediation
→As it is a natural process bioremediation is
generally accepted by people.
→Theoretically, bioremediation is useful for the
complete destruction of a wide variety of
contaminants or its transformation to harmless
product


→Bioremediation can often be carried out on site,
often without causing a major disruption of normal
activities.
→Bioremediation can prove less expensive than
other technologies that are used for clean-up of
hazardous waste.
Disadvantage Of Bioremediation
→It is limited to those compounds that are
biodegradable. Not all compounds are susceptible
to rapid and complete degradation.
→There are some concerns that the products of
biodegradations may be more persistent or toxic
than the parent compound.
→Biological processes are often highly specific and
it is difficult to extrapolate from bench and pilot-
scale studies to full-scale field operations.
→Bioremediation takes longer than other treatment
options.
→There is no accepted definition of “clean”,
evaluating performance of bioremediation is
difficult, and there are no acceptable end points for
bioremediation treatments.

References
• M Vidal, Dipartmento di chimica
Inorganic, Metallorganica, e Analitica,
Universita di Padova via Loredan, Padova,
Italy, Bioremediation. An overview, 2001
• Bioremediation-Answer.com
• Bioremediation-Wikipedia
09-08-2012, 04:45 PM
Post: #2
RE: Bioremediation
BIOREMEDIATION:


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INTRODUCTION TO BIOREMEDIATION:

Since the emergence of environmental microbiology in the early 1970s, scientists have been both humbled by the devastating impact of environmentally transmitted microorganisms on human health, and awed by the wide-ranging adaptability and usefulness of microorganisms found in the environment. Today, microorganisms are being manipulated to provide a natural method for cleaning up some of the environment’s worst chemical hazards.

Hazardous waste

Every day, industrial, commercial and personal practices produce waste -- many that are hazardous to public health or the ecosystem. Improper management of wastes may lead to contaminated air, soil and water. According to the U.S. Environmental Protection Agency (USEPA), one in four persons lives within four miles of a Superfund site -- an uncontrolled or abandoned deposit of hazardous waste -- with over 90 percent of these sites posing a threat to the surrounding population or sensitive environments. Exposure to hazardous wastes may result in reproductive disorders, birth defects, chronic illness (such as cancer or respiratory illnesses), neurological effects and weakened immunity.
The Toxic Substances Control Act’s inventory of commercial chemicals alone includes approximately 72,000 substances. While a handful of these agents are actively regulated and controlled, the exposure levels, treatment options, and public health effects of many aren’t well understood. More than 5,000 chemical accidents and 15,000 oil spills are reported each year to the National Response Center and USEPA regional offices.

What is bioremediation?

Bioremediation is the breakdown (biodegradation) of contaminating compounds using microorganisms. These microbes often use contaminants as a food source, thereby completely eliminating toxic compounds by changing them into basic elements such as carbon dioxide and water, a process known as mineralization. Incomplete degradation may also occur, or the partial breakdown of the original contaminant to a less complex form. Another result may be the transformation of a compound to a different chemical structure that may affect the toxicity and mobility of the original agent. Sometimes immobilization of a compound occurs where the agent is overcome by the microbe but not eliminated or altered, which is often a potential benefit but rarely a final solution.
Typically, bioremediation provides an efficient and economical way to reduce environmental toxins, using indigenous or introduced microbes that naturally degrade contaminants. In the process of bioremediation, natural microbial populations are exploited to enhance the biodegradation process. This process may occur at the site of contamination (in situ) or in a designated area where the contaminant is removed from the original site (ex situ). Of particular concern is the carrying capacity of the microbial population, meaning the maximum toxic load that the population is able to withstand. Isolated microbes are capable of transforming or degrading a variety of organic and inorganic contaminants such as arsenic, nitrate, MTBE, perchlorate, radionuclides, lead, mercury, petroleum products, etc., at levels beyond suspected health standards.
Many known contaminants aren’t removed by conventional water treatment processes.

WRT WATER:

Perchlorate, for example, is a known groundwater contaminant resistant to conventional chemical and physical removal processes. It is, however, readily biodegradable under proper conditions to undetectable levels by microbes that are widely available in nature. In addition, salt tolerant bacteria have been found that are capable of significant reduction of perchlorate concentrations in brines from ion exchange systems. Perchlorate is associated with the manufacture of explosives including solid propellant rocket fuel. Excessive amounts of it in drinking water can interfere with thyroid function and result in adverse developmental effects in children or tumors in all age groups.

Optimum treatment conditions

Assessing conditions of the contaminated environment and/or the site of bioremediation is vital. Not all environments are well suited for the proliferation of the microbes most adapted for treatment of the particular contaminant. Thus, bioremediation may be augmented by soil additives, used to increase the growth and metabolism of specific microbes. These additives may include moisture, oxygen, chemicals, organic matter, etc. Biodegradation typically occurs more rapidly in the presence of oxygen, i.e., under aerobic conditions. Oxygen, however, isn’t always available in subsurface environments. In the absence of oxygen, biodegradation occurs under anaerobic conditions.
Often intrinsic microorganisms are available from natural environments. If tolerant microbes cannot be isolated from the test environment, they can be isolated from sites of known contamination where they’ve adapted to the presence of the target toxin. An intrinsic population is the most desirable since these microbes will be well adapted to conditions of the surrounding environment and are most likely to survive. Alternately, microbes can be genetically engineered, where their genomes are artificially enhanced to increase their ability to survive under conditions of varied exposures. Similarly, microbes may be artificially adapted to a foreign condition by a process called successive adaptation. This is accomplished in the laboratory by slowly increasing the concentration of the contaminant of interest in the microbial growth media, selecting for pure cultures of resistant populations. These developed microbes are often used in contained, controlled, and aboveground vessels (bioreactors) where conditions of temperature, pH, etc., may be optimized.

Conclusion

Bioremediation has proven to be an effective tool in the reduction of environmental contaminants but can rarely restore the affected environment back to its original condition. Residual contamination may be difficult to completely eliminate. In addition, bioremediation can be an extremely slow process, requiring manipulation of the treated environment to enhance the microbial activity. The diversity of ecosystems and the nature of living systems lead to uncertain outcomes.
Methods of water treatment, including filtration and absorptive media, can be very effective at removing contaminants from waste streams but often produce a highly concentrated waste product in the filtration media. When combined with other treatment systems such as ion exchange, bioremediation can aid in producing a cleaner waste stream, especially for persistent compounds, mixed wastes, or hard-to-reach environments such as the deep subsurface.
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