Ex Situ Bioremediation

Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

Ex-situ bioremediation describes a process where contaminated soil or water is removed from the environment by biological organisms. Ex-situ bioremediation can use bioreactors and added nutrients to speed up the breakdown of environmental pollutants.

Different Kinds of Bioremediation

You really should thank our planet's garbage men, and not just the ones that come in a big truck each week to whisk away your waste. I'm really talking about the under-the-radar organisms, things like fungi and bacteria, dedicated to breaking down organic waste and environmental pollutants. These organisms can do pretty nifty metabolic tricks. Instead of just subsisting on the standard boring fare of sugars, fats, and proteins, they break down a wide range of chemical compounds for energy. When living organisms metabolize compounds we consider environmental pollutants into chemicals that are less toxic we call that process bioremediation.

There are two options for where bioremediation can take place. If we have a contaminated environment and leave everything in place and allow bioremediation to happen, we call that in-situ bioremediation. If we have a contaminated environment and we remove the contaminated material (for example soil or water) from the environment and let bioremediation happen off-site, we call that ex-situ bioremediation. Let's take a closer look at how ex-situ bioremediation works and why it might (or might not) be a good option.

Ex-situ Bioremediation

Based on our definition it seems like we just remove the contaminated material from the environment and then (voila!) bioremediation happens. But there are a few options for how to actually carry out the process. When the material is removed from the environment, it can be put into bioreactors, large vessels where the contaminated material can be monitored and conditions for bioremediation can be controlled. Biological organisms typically have conditions where they operate best. In bioreactors we can control the mixing rate, temperature, pH, and nutrient levels to suit the organisms breaking down our contaminant.

When bioreactors aren't used, landfarming or biopiles are alternatives. Landfarming involves spreading contaminated soil into a lined bed (to prevent leaching) and periodically applying nutrients and mixing the soil to boost biological activity. Biopiling places the contaminated soil into piles that are well aerated and nutrients are added to speed up bioremediation. In all cases, the contaminant levels are monitored to verify that bioremediation is taking place and steps are taken to ensure that contaminated material stays out of contact with the environment.

Advantages of Ex-situ Bioremediation

On the face of things it would seem that in-situ bioremediation is a lot easier than ex-situ. We don't have to move around a bunch of contaminated soil or water and set up bioreactors, landfarms, or biopiles. But there are some drawbacks to just leaving everything in place and waiting for the biological organisms to break down the pollutants. Sometimes it can be very slow, the contaminant spreads, or wildlife comes into contact with it.

When it seems that in-situ bioremediation isn't going to work out, ex-situ bioremediation can be a great alternative. The biggest advantage is speed. During ex-situ bioremediation, since the material is typically well mixed, well aerated, and plenty of nutrients are added, the breakdown of the contaminant is typically much faster than what occurs in-situ. Another advantage is that the contaminant can't keep spreading; the contaminated material is contained and monitored.

If contaminants are left in the environment, rainfall can spread the contaminant down through the soil layers and into waterways.
Soil profile

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