Understanding Bioremediation... A Guidebook for Citizens

Bioremediation--a process that uses microorganisms to transform harmful substances to nontoxic compounds--is one of the most promising new technologies for treating chemical spills and hazardous waste problems. In order to improve this technology and better understand its capabilities, the US Environmental Protection Agency (EPA) is encouraging field tests and evaluation of waste site cleanups using bioremediation

As bioremediation is considered more frequently as a cleanup alternative, citizens need information about this process to help them contribute to informed decision-making regarding the cleanup of waste sites n their communities. This brochure answers some questions about what bioremediation is, where it can be used effectively, and its advantages and disadvantages.

What is bioremediation?

Bioremediation uses naturally occuring microorganisms, such as bacteria, fungi, and yeast, to degrade harmful chemicals into less toxic or nontoxic compounds. Microorganisms, like all organisms, need nutrients (such as nitrogen, phosphate, and trace metals), carbon, and energy to survive. Microorganisms break down a wide variety of organic (carbon-containing) compounds found in nature to obtain energy for their growth. many species of soil bacteria, for example, use petroleum hydrocarbons as a food and energy source, transforming them into harmless substances consiting mainly of carbon dioxide, watter, and fatty acids. Bioremediation harnesses this natural process by promoting the growth of microorganisms that can degrade contaminants and convert them to non-toxic by-products.

When microorganisms are exposed to contaminants, they tend to develop an increases ability to degrade those substances. For example, when soil bacteria are exposed to organic contaminants, new strains of bacteria often naturally appear that can break down these substances to obtain energy. At many hazardous waste sites, microorganisms that degrade organic wastes, including some synthetic organic chemicals such as pesticides and solvents, have developed over time.

If bioremediation is a naturaly occuring process, why do some biodegradable organic chemicals persist in the environment?

A number of environmental conditions can slow down or stop the biodegradation process. For example:

• The concentration of the chemical may be so high that it is toxic to the microorganisms. The number or type of microorganisms may be inadequete for biodegradation. Conditions may be too acidic or too alkaline.
• The microorganisms may lack sufficient nutrients (such as nitrogen, phosphorous, potassium, sulfur, or trace elements), which they need to use the chemical as a food source. (Petrochemical residues, for example, are not "nutritionally balanced.")
• Moisture conditions may be unfavorable.
• The microorganisms may lack the oxygen, nitrate, or sulfate they need to use the chemical as an energy source.

In many instances, these environmental conditions can be altered to enhance the biodegradation process. To accomplish this, samples are collected at the site and analyzed to determine what types of microorganisms are present and what nutrients and climactic conditions (such as pH, moisture, temperature, and oxygen levels) can enhance microbial degradation. For example, if inadequete nitrogen or phosporus are available, the nutrients can be added to enhance the growth of the nicroorganisms. if the concentration of the waste is too high, other chemicals or uncontaminated soil can be added to reduce the toxicity so that biodegradation can occur.