What is Bioremediation?
Bioremediation is the use of biological agents to neutralize or remove contaminants. No chemicals are used in this method. Rather, plants, fungi, and microorganisms are used. These agents transform or break down the contaminants into harmless substances, which can then be safely removed. Bioremediation can be used to remove pollutants, such as oil, gasoline, sewage, and pesticides.
Types of bioremediation
There are three different types of bioremediation: microbial bioremediation, phytoremediation, and mycoremediation.
1. Microbial bioremediation: Microbial bioremediation is the use of microorganisms, such as bioremediation bacteria, to neutralize and remove the contaminants. Using the contaminants as a food source, the microbes break them down into harmless substances.
2. Phytoremediation: Phytoremediation is the use of plants to bind, extract, and remove contaminants, such as hydrocarbons, pesticides, and heavy metals.
3. Mycoremediation: Mycoremediation is the use of fungi to neutralize and remove contaminants. The digestive enzymes of fungi are strong enough to break down contaminants, such as pesticides and hydrocarbons, into harmless substances.
How bioremediation works
Bioremediation occurs naturally, without the use of any chemical catalysts, when biological agents come into contact with the contaminants. However, it is necessary to create the ideal environmental conditions to facilitate and expedite the bioremediation process. The conditions include the right temperature, pressure, pH, and moisture.
In microbial bioremediation, the microbes secrete enzymes to break the contaminants into smaller pieces, which they then consume. As a byproduct of the digestion process, they release water, carbon dioxide, and amino acids. These are then removed. Mycoremediation works in a similar way. The digestive enzymes secreted by fungi break down the contaminants.
In phytoremediation, natural chemicals present in plants react with the contaminants. They either neutralize them or bind with them to form harmless substances.
Different bioremediation techniques
Bioremediation techniques can be divided into two broad categories: ex situ bioremediation and in situ bioremediation.
Ex situ bioremediation involves excavating the contaminants from the contaminated site and transporting them to a designated treatment site. They include biopile, windrow, bioreactor, and landfarming.
1. Biopile: Biopile involves piling the polluted soil, amending the nutrients, and aerating the soil to enhance the activity of the microbes.
2. Windrow: Windrow involves turning and aerating the polluted soil periodically to increase the activities of the bacteria that feed on hydrocarbons.
3. Bioreactor: A bioreactor is a vessel that is used to convert raw materials to products after a series of biological reactions. It is used in bioremediation to treat contaminated substances.
4. Landfarming: Landfarming involves excavating or tilling the polluted soil and treating it to increase microbial activity. It is one of the simplest bioremediation techniques.
In situ bioremediation involves treating the contaminated substances at the site of contamination. It causes little or no disturbance to the soil structure. It includes natural attenuation, bioslurping, bioventing, biosparging, and permeable reactive barrier (PRB).
1. Bioventing: Bioventing involves treating the contaminated soil with a controlled flow of oxygen to increase the activities of the indigenous microbes. Nutrients and moisture may also be added during the process.
2. Bioslurping: Bioslurping involves combining bioventing, soil vapor extraction, and vacuum-enhanced pumping to increase the activities of bioremediation bacteria and other microbes. This technique is very effective in restoring sites contaminated by petroleum hydrocarbons.
3. Biosparging: Biosparging involves injecting air into the soil subsurface to increase the bioremediation activities of the microbes. It is similar to bioventing, but the air is injected into the saturated zone.
4. Permeable reactive barrier (PRB): PRB involves submerging a permanent or semi-permanent reactive barrier (made mostly of zero-valent iron) into the trajectory of polluted groundwater. As the water flows through the barrier, it traps the pollutants and subjects them to a series of reactions. The result is clean and pollution-free water.
The application of bioremediation techniques is based on several factors. These include the location, and geology of the site, the type, depth, and degree of pollution, and the cost of treatment.
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