System Approaches

The choice of a bioremediation approach, whether it be in situ, on-site, or off-site, depends a great deal on the specifics of the site and the media being decontaminated:

In Situ Bioremediation

Bioremediation is frequently applied in situ, without resorting to excavation. The desirability of this approach is often dictated by the site itself, such as contamination that may stretch under a road or building. Frequently, the appeal of bioremediation is directly related to the viability of in situ treatment, contrasted with traditional "dig and haul" remediation, such as incineration and landfilling. Groundwater and soil treatment are the leading applications for in situ bioremediation. The issue is of major concern, with groundwater and soil contamination at an estimated 300,000 to 400,000 sites in the United States alone. Some cost estimates for a general cleanup of these sites are as high as $1 trillion over the next 30 years.

On-Site Bioremediation

Some sites cannot be effectively or economically treated in situ. Fortunately, there are numerous bioremediation systems for on-site remediation, including:

- Engineered treatment cells reduce very high contaminant levels in soils and sludges with a method similar to composting. The media is aerated with piping, and nutrients, water, and oxygen are administered. Volatile vapors are automatically displaced by the air. This approach is distinctly more economical than alternatives such as disposal through landfilling.

- Composting is another bioremediation alternative that may be done on site, usually for pretreatment of very highly contaminated soil. Aerated piles using leachate circulating systems accelerate natural degradation.

- Landfarming employs cultivation methods, such as frequent turning, to mix liquid or solid residues with soil, providing a uniform zone for natural bioremediation. The equipment used is often modified agricultural machinery. Landfarming is most frequently applied to soils contaminated by petroleum hydrocarbons.

- Bioreactors are contained environments that enhance the biodegradative capabilities of microorganisms coming in contact with contaminated soil, sludge, sediment, water, or air. In a bioreactor, variables such as pH, temperature, and nutrient and oxygen delivery can be precisely controlled, optimizing the environment for bioremediation. Bioreactors can use naturally occurring, cultured or genetically engineered microorganisms to treat such contaminants as PCBs, TCE, hydrocarbons, and industrial process wastewater streams. Bioreactors, along with biofilters, represent the chief area of application for genetically modified bacteria in the bioremediation industry.

Off-Site Bioremediation

The effectiveness and popularity of in situ and on-site bioremediation leaves relatively little to cover in the offsite treatment category. When a site does not provide ample space for remediation work, or when site conditions are too severe for bioremediation to work, the contaminated soils may be excavated and transported to central processing facilities, where technologies such as engineered treatment cells, composting, land farming, and bioreaction/biofiltration can be performed on a large scale under controlled conditions.