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Bioremediation - Overview of Bioremediation Methods

Overview of Bioremeditaion Methods


In situ soil treatment (aerobic)

Bioventing – Introduction of oxygen into the soil using forced air to encourage microbial activity. Nutrients such as nitrogen and phosphorus may also be added to the soil to increase the growth rate of microorganisms.

Injection or pumping of ORCs – ORCs are introduced into the soil to encourage microbial activity (similar to bioventing). This method is only used when the groundwater is already contaminated because ORCs are in liquid form.

Slurry-phase lagoon aeration – Air and soil are combined in a lagoon to encourage microbial activity.


Ex situ soil treatment (aerobic)

3 varieties of solid-phase treatment:

1. Contained or Biopiles – Soil is excavated and mixed with necessary amendments. Piles are placed in enclosed buildings and aerated using blowers and pumps.

2. Composting – Soil is excavated and combined with amendments e.g. wood chips to bulk out the soil. Organic amendments such as hay or manure are also added. The amendments help encourage microbial activity. The process takes place in enclosures called windrows. Open windrow systems stack the compost in elongated piles and aerate it by tearing down and rebuilding piles. Static windrow systems aerate the compost piles by a forced-air system (Sharma & Reddy, 2004).

Figure 3 shows a diagram of a typical composting method.


Figure 3 – Schematic of composting method (USEPA, 2001a)

3. Land Farming – Soil is excavated and spread in lined ‘treatment beds’. Amendments are sometimes added. The soil is tilled to aerate as necessary to encourage microbial activity. Treatment is enhanced from photoxidation from the sun. 

Slurry-phase treatment – An aqueous mix of soil and water is mixed with amendments and stored in tanks. The mix is continuously stirred to keep solids suspended to maximize contact area between contaminated soil and microorganisms.


In-situ groundwater treatment

Biosparging – Air is injected into the groundwater to encourage aerobic biodegradation.

Aerobic treatment – Amendments introduced by injection or water recirculating systems into groundwater. Can include ORC or H2O2. Organic contaminants are converted to carbon dioxide or water. Aerobic treatment is faster than anaerobic, and therefore preferred.

Anaerobic treatment – Carbon sources such as molasses or Hydrogen Releasing Compounds (HRC) are introduced by injection or water recirculating systems. In the case of carbon sources and HRCs the  contaminants are converted into methane, limited amounts of carbon dioxide, and traces of hydrogen.


A typical groundwater treatment setup is shown in Figure 4.


Figure 4 – Diagram of in-situ groundwater treatment (USEPA, 2001a)


Ex-situ treatment is decreasing in popularity compared to in-situ treatment. In 1991, 35% of treatment work at Superfund sites was in-situ compared to 53% in 1999 (USEPA, 2001a). This is likely to be due to increasing effectiveness of in-situ methods and a desire to avoid exposing the contaminated soil at the surface where likelihood of human contamination is increased. The most popular in-situ and ex-situ treatment methods are bioventing and land farming, respectively. 

An interesting use of bioremediation is the treatment of acid mine drainage (AMD) using passive wetlands and sulfate-reducing bacteria. This will be discussed later.

In aerobic degradation successful bioremediation can be monitored by measuring carbon dioxide and oxygen levels. Decreases in oxygen concentration and increases in carbon dioxide concentration signify increased bioactivity.

Bioremediation can be complemented with other technologies such as soil vapor extraction and soil washing.

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