The biodegradation of pollutants is the natural process of decomposition of contaminants under the action of microorganisms and plants.
Human activities sometimes release contaminants into the environment. It is often impossible to simply remove contaminated water or soil to clean up an environment. For that reason, biotechnological solutions have been developed to allow decontamination. Certain pollutants can be degraded, transformed, or accumulated by microorganisms as well as by certain plants. Many environmental problems can be solved thanks to the natural ability of certain species to feed on contaminants by decomposing them. Two environmental decontamination technologies have been developed: bioremediation and phytoremediation.
Bioremediation consists in using microorganisms (bacteria and fungi) to cleanse contaminated soil and water.
Many species of bacteria and fungi can decompose various organic contaminants such as hydrocarbons, pesticides, solvents, or plastics. Others can extract inorganic pollutants such as heavy metals (mercury, lead, etc.) from the environment. These contaminants are then accumulated in the body or transformed into material that is harmless to the environment, such as carbon dioxide and water.
These microorganism populations are generally too small to ensure rapid and efficient degradation of contaminants and thus prevent their spread in the environment. Two methods are therefore used to increase the efficiency of decontamination.
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Biostimulation consists of promoting the growth and activity of bacteria already present in the medium. This can be done by adding nutrients or oxygen necessary for their development. The soil can also be stirred to circulate air, moistened and fertilized to stimulate bacterial growth.
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Bioaugmentation consists of introducing microorganisms capable of decomposing a specific type of pollutant in the environment. These bacteria may have been genetically modified to increase their pollution reduction effectiveness under natural conditions. Alternatively, the contaminated material can be carried to a site which provides optimal growth conditions for the bacteria.
Addition of fertilizer to increase bacterial activity (biostimulation) for degradation of the oil accidentally spilled during the sinking of the Exxon Valdez.
Phytoremediation uses plants or algae to remove contaminants from a medium.
Many plants are able to absorb contaminants present in their environment. Some decompose these contaminants, but most accumulate them in their leaves, stems, and roots. The roots of plants thus limit the movement of heavy metals into groundwater. Plants with this ability include cabbage, pumpkin, sunflower, certain ferns, and trees such as poplars and willows.
Phytoremediation is an advantageous technique since it is natural and inexpensive. It also promotes reforestation and helps maintain soil stability. The effectiveness of this technique depends on the type of soil to decontaminate, the contaminants and their concentration as well as on the depth reached by the roots of the plants. Phytoremediation is often used to clean up industrial, agricultural, or military sites. After applying this technique, the plants must be disposed of in a safe manner so that they are not consumed, since they contain high concentrations of toxic contaminants.
