What is bioremediation?

It is often used to describe a variety of quite different microbial processes that occur in natural ecosystems, such as mineralization, detoxification, co-metabolism or activation.

It can be defined as breakdown of organic compounds in nature by the action of micro organisms, such as bacteria, actinomycetes and fungi.

Remediate means to solve a problem, and “bioremediate” means to use biological organisms to solve an environmental problem such as contaminated soil or groundwater.

Must read: Factors responsible for soil pollution

Why the role of bioremediation is highly significant in restoring the contaminated soils to their original health?

Since bioremediation uses naturally occurring microorganisms to transform harmful substances to non-toxic compounds, its role in restoring the contaminated soils to their original health and thus serving the
environment from pollution is highly significant.

What are the more common genera involved in bioremediation of oil products?

Some of the more common genera involved in bioremediation of oil products include Nocardia,
Pseudomonas, Acetobacter, Flavobacterium, Micrococcus and Arthrobacter.

TECHNIQUES OF BIOREMEDIATION

The microorganisms may be indigenous to a contaminated area or they may be isolated from elsewhere and brought to the contaminated site.

I. In situ bioremediation techniques

It involves treatment of the contaminated material at the site.

It can be of following types:

1. Bioventing – supply of air and nutrients through wells to contaminated soil to stimulate the growth
of indigenous bacteria. It is used for simple hydrocarbons and can be used where the contamination
is deep under the surface.https://www.frtr.gov/matrix/Bioventing/

2. Biosparging – Injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by naturally occurring
bacteria.https://www.frtr.gov/matrix/Enhanced-Aerobic-Bioremediation/

3. Bioaugmentation – Microorganisms are imported to a contaminated site to enhance degradation process.

II. Ex situ bioremediation techniques

Ex situ -involves the removal of the contaminated material to be treated elsewhere.

It can be of following types:

1. Landfarming – contaminated soil is excavated and spread over a prepared bed and periodically tilled
until pollutants are degraded.The goal is to stimulate indigenous biodegradative microorganisms and facilitate their aerobic degradation of contaminants.https://www.frtr.gov/matrix/Landfarming/

2. Biopiles – it is a hybrid of landfarming and composting. Essentially, engineered cells are constructed as
aerated composted piles. Typically used for treatment of surface contamination with petroleum hydrocarbons.https://www.frtr.gov/matrix/Biopiles/

3. Bioreactors – it involves the processing of contaminated solid material (soil, sediment, sludge) or water
through an engineered containment system.https://www.frtr.gov/matrix/Bioreactors/

4. Composting – Composting is used to treat excavated soils and dredged sediments contaminated with a variety of pollutants. The contaminated media is mixed with bulking agents and organic amendments such as mature compost, wood chips, hay, manure, and vegetative (e.g., potato) wastes.

Composting differs from technologies such as biopiles and landfarming in that a sufficient quantity of organic material is added to maintain thermophilic temperatures during the degradation process.

Phytoremediation (Bioremediation through plants)

Phytoremediation is use of plants to remove contaminants from soil and water .https://www.frtr.gov/matrix/Phytoremediation/

Phytoremediation is of following types:

1. Phytoextraction / phytoaccumulation is the process by which plants accumulate contaminants into the roots and above ground shoots or leaves.

2. Phytotransformation or phytodegradation refers to the uptake of organic contaminants from soil, sediments, or water and their transformation to more stable, less toxic, less mobile form.

3. Phytostabilization is a technique in which plants reduce the mobility and migration of contaminated soil. Leachable constituents are adsorbed and bound into the plant structure so that they form unstable mass of plant from which the contaminants will not re-enter the environment.

4. Phytodegradation or rhizodegradation is the breakdown of contaminants through the activity existing in the rhizosphere. This activity is due to the presence of proteins and enzymes produced by the plants or by soil organisms such as bacteria, yeast, and fungi.

5. Rhizofiltration is a water remediation technique that involves the uptake of contaminants by plant roots. Rhizofiltration is used to reduce contamination in natural wetlands and estuary areas.

Mycoremediation (Bioremediation through fungus)

It is a form of bioremediation in which fungi are used to decontaminate the area.

Mycofiltration is a similar process, using fungal mycelia to filter toxic waste and microorganisms from water in soil.

ADVANTAGES OF BIOREMEDIATION

1. Residues are usually harmless products.

2. Instead of merely transferring contaminants from one environmental medium to another (e.g. from water to the air or to land) bioremediation completely eliminates the target chemicals.

3. Bioremediation is far less expensive than other technologies that are often used to clean up hazardous waste.

4. An ecologically sound, natural process ; thus environment friendly.

5 . Bioremedition can often be accomplished where the problem is located (in-situ).

DISADVANTAGES OF BIOREMEDIATION

1. Bioremediation is limited to those compounds that are biodegradable. Not all compounds are susceptible to rapid and complete degradation.

2. Biological processes are often highly specific.

3. It is difficult to extrapolate from bench and pilot-scale studies to full-scale field operations.

4. Bioremediation often takes longer time than other treatment process.

EXAMPLES

1. Recent research reveals that ‘Pteris vittata’, a fern, can readily purify water poisoned with arsenic. In other words water contaminated with arsenic can be cleaned by growing ferns in it. The procedure, called
‘phytofiltration’, could provide a cheap way to remove arsenic from water supplies.

2. The bacterium Deinococcus radiodurans has been used to de toxify toluene and ionic mercury which are released from radioactive nuclear waste.

3. Using bioremediation techniques, TERI has developed a mixture of bacteria called ‘oilzapper’ which
degrades the pollutants of oil-contaminated sites, leaving behind no harmful residues. This technique
is not only environment friendly, but also highly costeffective.

PRACTICE QUESTIONS

QUES – In the context of solving pollution problems, what is/are the advantage/advantages of bioremediation technique? UPSC 2017

1 . It is a technique for cleaning up pollution by enhancing the same biodegradation process that occurs in nature.

2 . Any contaminant with heavy metals such as cadmium and lead can be readily and completely treated by bioremediation using microorganisms.

3 . Genetic engineering can be used to create microorganisms specifically designed for bioremediation.

Select the correct answer using the code given below:

(a) 1 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) 1, 2 and 3

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QUES . Consider the following statement about bioremediation: CDS 2009

I. It may be defined as any process that uses micro-organisms or their enzymes to return the environment altered by contaminants to its original condition.

II. Bioremediation may be employed in order to attack specific contaminants, such as chlorinated pesticides that are degraded by bacteria.

Which of the statements given above is/are correct?

(a) I only

(b) II only

(c) Both I and II

(d) Neither I nor II

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