Ex situ
Ex situ bioremediation involves the physical extraction of the contaminated media to another location for treatment. If the contaminants are just in the soil, the contaminated soil is excavated and transported for treatment. If the contamination has reached the groundwater, it must be pumped and any contaminated soil must also be removed. One major thing that this removal of the contaminants does right away is stop the spread of the contamination, but it is also usually alright to have a minimal amount of contaminants rermaining. If minimal contaminants do remain in the soil, they can likely be broken down by the naturally occuring microorganisms already present.
There are two main types of ex situ bioremediation. They are refered to as phases:

Solid Phase - Solid phase treatment consists of placing the excavated materials into an enclosure. Inside this enclosure, the contaminated soil is spread onto a treatment bed, which usually has some kind of built-in aeration system. Using this system, cleanup crews are able to control the nutrients, moisture, heat, oxygen and pH. Solid phase treatment is especially effective if the contaminants are fuel hydrocarbons.
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Slurry Phase - the contaminated soil is excavated and removed from the site as completely as possible. The contaminants are then put into a large tank which is known as a bioreactor. Cleanup crews use this bioreactor to mix the contaminants and the microorganisms. This mixing process keeps the microorganisms in constant contact with the contaminants. Water, oxygen, and nutrients are added. Since the cleanup crews have complete control of the conditions in the bioreactor, they can adjust things until they acheive the optimal conditions for the degradation of the contaminants. Since the degradation can be kept at or very close to optimal conditions, it does not take very long to break down the contaminants. (7.1)​
The technologies of bioremediation can be classified as either situ or ex situ.
In situ
In situ bioremediation involves the treatment of the contamination on site. In the case of soil contamination, in situ bioremediation involves the addition of mineral nutrients. These nutrients increase the degradation ability of the microorganisms that are already present in the soil. Sometimes new microorganisms are added to the contaminated area. Microorganisms can sometimes be genetically engineered to degrade specific contaminants, or fit conditions of a site.

Which approach is taken depends on the relationship between the type of contamination, and the type(s) of microorganisms already present at the contamination site.
There are two frequently used methods of supplying oxygen to the microorganisms.

Bioventing - This consists of blowing air from the atmosphere into the contaminated soil. First, injection wells must be dug into the contaminated soil. How many wells, how close together they are, and how deep they are dug all depends on the factors affecting the rate of degradation (type of contamination, type of soil, nutrient levels, concentration of contaminants, etc). Once all of the injection wells are dug, an air blower is used to control the supply of air that is given to the microorganisms. These injection wells can also be used to add nitrogen and phosphorus, maximizing the rate of degradation.
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Hydrogen Peroxide Injection - In cases in which the contamination has already reached the groundwater, bioventing will not be very successful. Instead, hydrogen peroxide is used. It functions much the same as bioventing, using the hydrogen peroxide instead of air blowers to deliver oxygen to the microorganisms. If the soil is shallow (the groundwater is fairly close to the surface) the hydrogen peroxide can be administered through sprinkler systems. If the groundwater is fairly deep beneath the surface, injection wells are used.​ (7.1)​
A flowchart outlining the strategy involved in bioremediation activities is provided in the figure below. (7.14)​
Watch this video to learn why the process of bioremediation works. (7.2)​
The Role of Microbes
Microorganisms play a large role in bioremediation along with nutrients, participating to be able to destroy harmful contaminants. Microorganisms gain energy- producing chemical reactions that involve breaking chemical reactions that involve breaking chemical bonds and transferring electrons away from the contaminant. This is why microbes such as fungi and bacteria are used in the process, because it naturally attracted to the other contaminants. Microbes are useful during bioremediation due to the microbes rapidly eliminating the harmful chemicals, it is cleaning the product. After the contaminants has been degraded it dies off, releases the final product carbon dioxide. (7.3)​
Bioremediation also has different treatments including biostimulation, bioaugmentation, and intrinsic bioremediation. All three of them are used to remove toxic substances and contaminants from the environment whether they are soils, rivers or crude oils. (7.5)​
​Intrinsic Bioremediation:​
The process of intrinsic bioremediation takes place in soil and water because these two places are always full of contaminants and toxins. This process is also called as natural attenuation. It also means use of the microorganisms to remove the harmful substances from soil and water. Especially those sites are treated with this method, which are underground, for example underground petroleum tanks. It is difficult to know if there is a leakage in the petroleum pipes. Contaminants and toxins find their way to enter in these sites and create harmful effects on the petrol. Therefore, only microorganisms can destroy the toxins and clean the tanks. Great care should be taken if some leakage occurs in the petroleum tanks or pipes because it may damage the human health.​​ (7.5)​
​Bioaugmentation:
In some processes of bioremediation, there are some special sites where microorganisms are needed to remove the contaminants for example municipal wastewater. Bioaugmentation is used for that purpose. But unfortunately this process is not very successful as it is difficult to control the growth of microorganisms to remove the particular contaminant. (7.5)​
​​Biostimulation:​
Biostimulation is the method in which bacteria are motivated to start the process of bioremediation. In this method, first the experts release nutrients and other important substances in the soil where there is need or removing the contaminants. These are in the form of gas or liquid. It increases the growth of microbes in that area. As a result bacteria and other microorganisms remove the contaminants more quickly and efficiently. (7.5)​
View the flipbook below to learn about the general steps to treating a contaminated site. Click on the upper right hand corner to turn the page.
​View the flipbook below to learn about the general steps to treating a contaminated site. Click on the upper right hand corner to turn the page.