Microbial diversity and its diverse metabolic
activities are of critical importance to the
sustainability of life on our planet, including
recycling elements on which primary productivity
depends, producing and consuming gases important
for maintaining our climate, and destroying
the wastes of human civilization. Besides that,
microbes often play key roles in conservation
of higher organisms and in restoration of degraded
ecosystems. Hence, microbial diversity goes
hand in hand with goals for maintenance of higher
organism diversity and ecosystem management.
Bioremediation refers to cleaning contaminated
environments with the aid of microorganisms
that transform contaminants to harmless or less
harmful compounds. Bioremediation offers three
main approaches for treating contaminants, i.e.
natural attenuation, biostimulation, and bioaugmentation.
In natural attenuation, the naturally occurring,
i.e.indigenous microorganisms degrade the contaminants
without any additions and the rate as well as
level of degradation is carefully monitored.
In biostimulation, indigenous microorganisms
are stimulated by the addition of nutrients
and electron acceptors. In bioaugmentation,
contaminant degradation is enhanced by introducing
microorganisms into the sites via inoculation.
There is a better understanding of the benefits
of bioremediation than of other approaches,
especially about in-situ bioremediation
of contaminated soils. Technologies related
to the application of microorganisms to the
soil, release of nutrients into the soil, and
enhancement of microbial decontamination are
being tested through various additives such
as surfactants, ion exchange resins, limestone,
or dolomite. New equipments have been developed
for crushing and mixing or inject ing and sparging
the microorganisms, as have new reactor technologies
(e.g., rotating aerator reactors, biometal sludge
reactors, and special mobile containers for
simultaneous storage, transportation, and biodegradation
of contaminated soil).
Bioremediation
Approaches
As various pollution problems are addressed
worldwide, the scope and diversity of bioremediation
in general, especially in-situ bioremediation
technology continues to grow. In Europe, particularly
in Germany, The Netherlands and Denmark huge
money is being spent for soil remediation and
funding for bioremediation research and development.
In-situ bioremediation is based on
stimulating the natural breakdown of petroleum
hydrocarbons within the subsurface by enhancing
environmental conditions. Groundwater is extracted
and treated in a surface mounted bioreactor.
The effluent from the reactor, rich in microorganisms,
nutrients and oxygen, is then reinjected into
the aquifer upgradient of the extraction point.
The treated groundwater can also be recirculated
through the soil and allowed to percolate to
the groundwater to promote in-situ
biodegradation within the soil in addition to
the groundwater. Besides that, bioremediationtechnology,
especially when it can be carried out in-situ,
is a cost-effective means of removing many chemical
pollutants that adversely spoil human health
or environmental quality.
Further, when the bioremediation technology
is applied for any ecosystem restoration, the
end products such as water and carbon dioxide
are non-toxic and are harmless to the environment
and living organisms.
Development
and application of bioremediation technology
in various countries;
Germany
Germany is one of the most developed nation
and it gives due importance for both industrialization
and environment management, and has spent more
time and money compared to other countries in
identifying environmental problems. Therefore,
more companies are involved on bioremediation.
Most of these companies are located in the region
formerly known as East Germany. The list of
contaminated sites and needed remedial actions
had been dramatically increased after German
reunification. Risk sites include vehicle workshops,
airports, traffic and parking areas, waste dumps,
fuel storage and transfer points, and munitions
sites. According to the Federal Ministry of
Research and Technology (BMFT) in Germany, 28
bioremediation techniques have been developed
there. BMFT has sponsored 16 projects with a
total funding of 20 million DM ($1 2.5 million
U.S.). The German Research Association has also
conducted projects in enzymatic dehalogenation
of contaminants using Pseudomonas Streptomyces
and thermophilic microorganisms, and in biodegradation
for "dioxin-like" substances.
A number of companies conduct polyaromatic
hydrocarbon ( PA H ) decontamination using microbes.
Researchers De Ruiter Milieutechnoiogie, Halfweg,
conducted a demonstration project involving
aliphatic or aromatic hydrocarbons to study
the influence ofpH and nutrient addition (potassium,
nitrate, and others) , and inoculation of adapted
microorganisms. The German bioremediation firm,
Argus Umweltbiotechnoiogie GmbH, uses infiltration
of air and addition of nutrients to degrade
hydrocarbons in situ. Research at the
Department of Chemical Microbiology of the Fraunhofer
Institute of Interface Technology and Biotechnology
is focused on microbial and engineering aspects
of bioremoval of xenobiotic compounds from wastewaters
and exhausted air. In particular, they have
demonstrated that PAH biodegradation can be
achieved in airlift bioreactors and accelerated
using water-soluble solvents as lipophilic mediators
to facilitate mass transfer. The biological
process in airlift reactors is carried out in
an organic-aqueous mixed phase. Wilhelm University
of Muenster and the Technical University of
Munich studied the application of specially
developed, immobilized microorganisms to xenobiotically
degrade soil contaminatio n. These immobilized
microorganisms have better resistance to soil
microflora, because they are affixed to a microporous
support that provides a habitat promoting reproduction
of microbial cells yet allowing release of cells
from the support.
Work is under way in Germany to introduce nutrients
into the soil using explosive cartridges. Soil-mixing
machines expedite mixing the soil with ion exchange
resins, dolomite or limestone (to adjust pH),
and nutrients. Microorganisms and enzymes are
immobilized on wood chips, granular clay, anthracite,
and synthetic polymers to assist their establishment
in the soil matrix.
The Netherlands
The Netherland and Denmark are leaders in establishing
nation wide programs for decontaminating thousands
of sites through the processes of bioremediation.
A number of wellestablished companies are located
in the Netherlands, and a significant number
of sites have been cleaned up since 1982. Soil
pollution is an environmental problem of the
highest prioritybecause of the limited land
area and proximity to sea level. In-situ
bioreclamation is one of several methods available
for treating oily wastes and PAH in sediments.
A petroleum contaminated site at Asten was used
to evaluate the feasibility of in situ
bioremediation and showed good prospects for
remediation of the petroleum spill if hydrogen
peroxide was added as a chemical alternative
to oxygen.
A biological method for water treatment is
available that uses controlled biological oxidation
in sulfide reactors. The process treats the
groundwater, highly polluted with sulfate and
heavy metals, underneath the property. Sulfur
compounds are reduced to hydrogen sulfide using
anaerobic sulfate-reducing bacteria, and heavy
metals are precipitated as metal sulfides. The
remaining sulfide is oxidized to elemental sulfur
using aerobic sulfide-oxidizing bacteria, and
elemental sulfur is then separated from the
water.
Other Regions
Other European countries working to address
contamination issues include Italy, France,
the Spanish province of Catalonia, Switzerland,
and the United Kingdom. These countries have
made efforts to identify contaminated sites
(the United Kingdom reportedly has 50,000 to
100,000 contaminated waste sites) but have not
yet defined nationwide decontamination measures,
selected technical approaches, or planned large
decontamination projects. Meanwhile, Spain,
Portugal, Greece, and Ireland are just beginning
to assess contamination problems and sites to
be remediated.
An interesting development in France is the
use of algal cultures in aqueous solutions to
stabilize cesium and strontium in the soil.
These cultures are used primarily for shallow
surface contamination, but adaptations may be
possible to extend the technology to groundwater
and subsurface contamination. Experimental programs
are being conducted in collaborationwith the
former USSR.
The French DVM (Decontaminating Vegetal Network)
process is a biomechanical method for removing
soil contamination using
plants that create a dense root network to trap
the contaminated soil particles. Removing the
turf then removes the contaminated soil. Biosurfactant-producing
microorganisms have been used to increase the
removal of contaminants using soil washing.
In Eastern Europe, several Czech companies
offer reasonably advanced bioremediation services.
A microbial mixed population is being studied
by the University of Prague to treat surface
contamination in an abandoned site polluted
with petroleum hydrocarbons.
Although, bioremediation offers several advantages
over physical and chemical processes used to
treat contaminated water and soil, the cleanup
costs using bioremediation is cheaper. It is
also a simple technology when compared to other
remediation technologies. Besides that, in-situ
bioremediation can be carried out with minimal
space and with less health risk.
Future Prospects
The application of microorganisms to enhance
the fertility of soil conditions and removing
the soil contaminations through bioremediation
technology is extensively used in Europe and
USA. In India, progress has been made in applying
microorganisms to the restoration of polluted
soil through bioremediation processes. However,
the application of bioremediation technology
in the restoration of ecosystem and soil management
is used less compared to Europe and USA. Hence,
we need extensive research programs to increase
the capabilities of bioremediation to deep,
extensive, subsurface contamination due to chlorinated
hydrocarbons and complex mixed wastes, including
soils and groundwater. Besides that, The American
Academy ofMicrobiology (AAM) has concluded that
enough knowledge is now available for field
trials of bioremediation technology for organic
compounds and further they emphasized that research
is needed for the following classes of environmental
pollutants: metals, metalloids, radionuclides
and complex polycyclic hydrocarbons. The on-going
microbial genomics studies will deliver more
robust technologies for the bioremediation of
metal – contaminated waters and land.
Exciting developments in the use of microorganisms
for the recycling of metal waste, with the formation
of novel biominerals with unique properties
are also predicted in the near future.
Further reading:
Bioremediation Principles,
Eweis, Ergas, Chang .Schroeder., (1998)
Mc Graw Hill Inc.
Bio Remediation Field Experience,
Paul E.Flathman, Douglas E.Jerger & Jurgen
H.Exner., (1993) Lewis Publishers,
Inc.
Hydrocarbon Bioremediation,
Robert E.Hinchee,Bruce C.Alleman, Ron E. Hoeppel
& Ross N. Miller (1994)
Lewis Publishers, Inc.
Bioremediation (Applied Microbial Solutions
for Real - World Environmental Cleanup)
Ronald M.Atlas and Jim Philp., (2005)
American society for Microbiology (Asm Press).
