Bioremediation
What Is Bioremediation?
Bioremediation is the use of biological agents such as bacteria or plants to remove or neutralize contaminants in polluted soil and water.
How Does Bioremediation Work?
When microbes eat and digest contaminants they transform the toxic materials into harmless amounts of water and gases such as carbon dioxide and ethene.4
Certain environmental conditions will cause and accelerate the right microbes to grow and multiply for more effective consumption of contaminants. Favorable conditions are improved by adding “amendments” which can be something as simple as molasses or vegetable oil.4 Adding chemicals that produce oxygen and aerating the soil can also help.4 Amendments be both mixed into the soil and pumped underground through wells to treat both soil and groundwater in situ (in place).
When the proper conditions for bioremediation are not present at the contaminated site, (i.e., climate too cold for microbes or soil too dense for amendments), soil can be excavated and cleaned “ex-situ” (above ground) on a pad or in tanks.
Is Bioremediation Effective with Lead?
Not all contaminants are easily treated by bioremediation. For example, cadmium and lead are not readily absorbed or captured by microorganisms. However, one type of bioremediation (phytoremediation) is demonstrating successful results using certain plants having the potential to uptake heavy metals such as lead.1
What Are the Different Forms of Bioremediation?
There are several bioremediation methods:
Microbial Remediation:
Microbial remediation refers to the use of microbes in degrading contaminants into a less toxic form. In this process, the microbes (tiny organisms such as bacteria) feed on contaminants as their source of food and energy. The technique can be very effective in the treatment of hydrocarbons, polycyclic aromatic hydrocarbons (PAH’s), pesticides, and PCBs.2
It might seem remarkable organisms find nourishment from toxic substances. However, petroleum is the result of natural processes that degraded ancient plant and animal life under conditions of massive pressure and intense heat.
Cost for microbial remediation is relatively low, and the operational timeframe can sometimes be short. However, there is the possibility of increased toxicity when certain metals are present.3
Phytoremediation:
Phytoremediation is the process of using plants to extract contaminants or to degrade them in the soil. As with microbial remediation, the cost is low. However, the timeframe can be longer than several years. Effectiveness in bringing soil up to agricultural standard varies because one species of plant is generally used on one type of contaminant which can potentially leave a range of contaminants behind.4 The contaminated plants used for extraction must also be disposed of in a safe and appropriate manner.
Mycoremediation / Fungal Remediation:
Fungal remediation refers to the use of certain species of fungus capable of degrading contaminants. This technique is still in the development phase and is not commercially available.
When is Bioremediation Effective?
Bioremediation processes are effective when addressing pollution from pesticides, solvents, oil and other petroleum products.4
Is Bioremediation Safe?
Microbes used in bioremediation pose no threat to people at the site or to the extended community.5 The microbes typically die off once the contamination (microbe’s food) is depleted. The substances that stimulate bioremediation are also safe. For example, the nutrients use to make microbes grow are commonly used on lawns and gardens. However, samples of soil and groundwater should be tested regularly to measure progress and ensure the bioremediation treatment is working.
In the mixing process, sometimes contaminants will evaporate before the microbes have opportunity to consume them. To prevent these vapors from contaminating the air, the mixing process can be done inside a special tank or building where the vapors can be collected and properly treated.
How Long Does Bioremediation Take?
Depending on several factors, it can take a few months or even several years for microbes to clean up a contaminated site. The conditions that cause longer clean-up time include:
- When there is a higher concentration of contaminants.
- When contaminants are trapped in hard to reach areas, like rock fractures and dense soil.
- When the contaminated area is too large or too deep.
Is Bioremediation Disruptive to the Neighborhood?
Bioremediation often occurs underground and does not cause disruption to the site or surrounding community. Contaminated soil and groundwater stay onsite, reducing truck traffic, compared with some other cleanup methods. However, area residents and businesses may hear the operation of pumps, mixers, and other construction equipment used to add amendments or improve site conditions for the bioremediation process. Excavation and pumping also will occur for ex-situ bioremediation.
Why Use Bioremediation?
Bioremediation has the advantage of using natural processes to clean up sites. Because it does not usually require as much equipment, labor, or energy as some cleanup methods, it can be cheaper. Another advantage is that contaminated soil and groundwater are treated onsite without having to dig, pump, and trans¬port them elsewhere for treatment. Because microbes change harmful chemicals into small amounts of water and gases, few if any waste byproducts are created.
How Often is Bioremediation Used?
The process has successfully cleaned up many polluted sites and has been selected, or is being used over 100 Superfund sites across the country.4
References
- Introduction to Phytoremediation, U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, OH. Agency (USEPA). 2000, EPA 600/R-99/107.
- Cometabolic Aerobic and Anaerobic Bioremediation, Overview, EPA (Technology Innovation and Field Services Division), www.cluin.org, retrieved October 16, 2014.
- Practice Guide #25—Urban Agriculture & Soil Contamination, Allison Houlihan Turner, University of Louisville Center for Environmental Policy and Management, Winter 2009, retrieved October 23, 2014.
- A Citizen’s Guide to Bioremediation, www.epa.gov, retrieved October 10, 2014
