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Soil Contamination: Treatment, Phytoremediation & Bioremediation

Instructor: Patricia Jankowski

Patricia has a BSChE. She's an experienced registered nurse who has worked in various acute care areas as well as in legal nurse consulting.

Soil is often contaminated with various pollutants such as petroleum products, heavy metals, pesticides and other toxins. This lesson is about the treatment of contaminated soil using bioremediation and phytoremediation.

Healing the Earth With Bioremediation

''Dr. Lang, I've got the latest soil boring and groundwater data from our in-situ bioremediation pumps out in Idaho. Things look pretty hopeful!''

''Really, Jameson? You're a great tech! Tell me more.''

''Well, we added plain old whey powder and sodium lactate, your standard protein diet drink, to the groundwater because the contaminants had leached into it from the dirty soil. And guess what? It's eating up the trichloroethylene, and spitting back out water and carbon dioxide!''

''Jameson, what are the latest readings? How much of the trichloroethylene is left in your samples?''

''We started out with 12,000 micrograms per liter in the groundwater. We're down to less than 1000 micrograms per liter!''

''Bravo, Jameson! Carry on!''

Bioremediation pump
In situ bioremediation pump

The Problem of Contaminated Soil

The activities of an industrial society have compromised the natural environment, including soil and the groundwater that flows through it. Mining and smelting operations create by-products of hydrocarbons and heavy metals, military operations dump fuels into the soil, and farming with pesticides leaves organophosphates and other toxins in the earth. Because these pollutants enter our drinking water and food chain, we need ways to clean them up that are cost-effective and that do not further harm the environment. Bioremediation and phytoremediation are two methods that meet this need.

Bioremediation

Bioremediation is a method by which naturally occurring microbes are used to clean up soil that is contaminated with pollutants. The microbes actually see the contaminants as food, and they use them for energy. They break the pollutants down and then produce gases or other products that are much less harmful and toxic. There are a huge variety of remarkable technologies that are used to accomplish this, depending on soil types and conditions, the amount of contamination, and the type of contaminant. The list of toxins that bioremediation can clean up is very long and includes hydrocarbons, heavy metals, pesticide compounds, and even radioactive material.

In Situ Bioremediation

When contaminated soil is treated at its original location, the bioremediation is called in situ. This method is the most cost-effective since the dirty soil does not need to be moved. For this to work, the soil must be warm enough at the site for the microbes to grow, and it must not be so dense that the bioremediation products cannot flow through it. Natural materials that are added to the soil to promote the microbe growth and contaminant cleanup are called amendments. In the introductory example, these were whey and sodium lactate. These amendments are pumped into the ground so that they interact with the soil.

Ex Situ Bioremediation

When contaminated soil is treated at a site other than its original location, the process is called ex situ. This is generally more complicated and more expensive. If the contaminated material being cleaned up is groundwater, it is pumped to a bioreactor where the microbes can interact effectively with it. If the dirty material is solid, like soil, then a biopile may be used. In this technology, the soil is excavated and then mixed with something that will make it less dense and more permeable to the microbes, like compost or wood chips. Air may then be pumped through the piles of dirt to enhance the cleanup. An ex situ process like this has to be continuously monitored since it is more complex than in situ methods. That's why it costs more.

In general, an ex situ cleanup takes longer than an in situ process. But for either process, the cleanup may take from months to years, depending on the amount of contamination, the size of the dirty area, and the soil conditions. However, the process is very effective, and when it's done, most of the contaminants are gone.

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