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What is bioremediation?

Bioremediation is the use of biological processes to remove contaminants from the environment. Decontamination through biological agents such as microbes, plants (phytoremediation), and fungi usually occurs naturally in the environment but is often slow. Therefore bioremediation technology seeks to catalyze this natural decontamination process by stimulating the remedial activity of these organisms.

How does bioremediation work?

The majority of bioremediation (excluding phytoremediation) invloves a redox reaction that detoxifies the contaminant. These reactions are held in check by some limiting environmental condition. However the reaction can be expedited by improving the environmental conditions in one of the following ways depending on what the limiting factor is:

1. Adding an electron acceptor

For some contaminants, electron donors are readily available but electron acceptors are needed to complete the redox reaction. This is the case with many organic compounds which can be remedied by adding electron acceptors such as oxygen or nitrate.

2. Adding an electron donor

In some cases electron acceptors are present but a donor is needed. This is often the case with contamination by nitrate or metals which readily accept electrons. Thus adding a carbon source as an electron donor can enhance bioremediation.

3. Adding a limiting nutrient

If all the necessary conditions for bioremediation are satisfied, the process can still be hindered if the organism's growth is hindered by some limiting nutrient. If so, fertelizers rich in nutrients like nitrogen or phosphorus can encourage the organism's growth and thus its ability to bioremediate.

4. Increasing the bioavailability of the contaminant

In many cases all the necessary conditions for bioremediation are met but the contaminant is unavailable to the organism. Metals and organic compounds that are bound to sediment can be made bioavailabe through the use of surfactants and chelates.

5. Stimulating the production of a specific enzyme

Sometime the bioremediation of certain organic molecules depends on bacterial enzymes that can metabolize the contaminant. By adding certain substrate to the environment, bacteria will produce an increased of amount of the necessary enzyme.

In situ vs. Ex situ

An important distinction to make among different decontamination strategies is whether the method is in situ or ex situ. In situ treatment means that remediation occurs directly at the site of the contaminant. Ex situ treatment requires that the contaminant be transported elsewhere, usually via a pump system, where it can then be treated. Bioremediation can occur both in situ, or ex situ. Currently, ex situ treatment is the better understood and developed approach to bioremediation, though recently in situ is gaining much attention. In situ is usually more advantageous than ex situ since it requires less equipment and labor and has a lower cost and environmental impact.

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