- Magdeline Islands Cliffs - J. Arbique
The U.S. produces 300 million metric tons of biohazardous waste each year from households and industry: the chemical industry alone generates approximately 5 million tons of waste and more than half of these are released into the environment.
Many organic contaminants are carcinogenic, break down very slowly, and tend to accumulate in the environment posing significant health hazards to human and other living organisms. Bioremediation involves the use of plants (phytoremediation) and microorganisms to treat contaminated soil and water in an environmentally friendly manner. This article will focus on the use of microorganisms to treat contaminated sites.
Microorganisms are used in a number of ways to decontaminate polluted areas and stimulate the environment. Microbial remediation involves natural attenuation, biostimulation and/or bioaugmentation. All three processes rely on the ability of microorganisms to break down the complex molecules of chemicals in biohazardous waste and use these simpler molecules to build cell parts; thereby, maintaining their own metabolic processes.
Natural attenuation (intrinsic or natural bioremediation) is the process that occurs naturally in contaminated soil or water, as petroleum, gas and oil are broken down by oil-degrading microorganisms indigenous to the soils at contamination sites. An example is the natural process that occurs at old gas stations with leaky underground tanks: oil-degrading microorganisms found in the soil will eventually break down the contaminants. However, researchers are investigating ways to broaden the scope of contaminants that microorganisms will digest, sort of like teaching bacteria to eat new things, and perhaps even speed up the process.
Biostimulation involves the addition of nutrients and oxygen to contaminated water or soil to encourage bacterial growth and activity. Biostimulation was used following the grounding of the Exxon Valdez when fertilizer applications were applied to the contamination site to stimulate growth of indigenous oil-degrading microorganisms.
Natural attenuation and biostimulation both rely on the natural presence of microorganisms that will degrade the specific contaminant. For instance, following the grounding of the Exxon Valdez, the growth of naturally occurring oil-degrading bacteria was promoted so microbial degradation of the oil would occur faster.
Whereas natural attenuation and biostimulation rely on indigenous microorganisms, bioaugmentation is used at sites where chemical-specific degrading microorganisms are not found. Bioaugmentation involves adding specific microorganisms to contaminated soil or water at the contamination site or at a treatment facility (e.g. municipal wastewater treatment facility). Indigenous microorganisms, with a “taste” for that type of contaminant, are isolated from other contamination sites of the same “flavour”, and added to the contaminated soil or water.
Now that I have you hooked, watch for an upcoming article on the use of microorganisms for hydrocarbon degradation.
Sources:
Mehmannavaz R. A Laboratory Study on the Development and testing of a bioaugmentation system for contaminated soils. 1999.
Judy Arbique - I graduated from Medical Laboratory Technology training in 1979 and since then obtained advanced recognition in clinical microbiology from ...
