A bio-pile is a bioremediation technology in which excavated soils are mixed with soil amendments, formed into compost piles, and enclosed for treatment. The basic bio-pile system includes a treatment bed, an aeration system, an irrigation/nutrient system and a leachate collection system. Moisture, heat, nutrients, oxygen, and pH are controlled to enhance biodegradation. An irrigation/nutrient system is buried under the soil to pass air and nutrients through the soil. Soil piles can be up to 20 feet high. They may be covered with plastic to control runoff, evaporation, and volatilization, as well as to promote solar heating. If volatile organic compounds (VOCs) in the soil volatilize into the air stream, the air leaving the soil may be treated to remove or destroy the VOCs before they are discharged into the atmosphere. Treatment time is typically 3 to 6 months, after which the excavated material is either returned to its original location or disposed.
Limitations and Concerns
Contaminated soils must be excavated, and dust and noise must be controlled.
It is difficult to reduce concentrations by more than 95 percent, or reduce contaminant levels to less than 1 part per million.
This process has questionable effectiveness for treating chlorinated compounds and may not be effective in degrading the transformation products of explosives. If there are volatile organic compounds (VOCs) in the soil that will volatilize into the air stream, the air leaving the soil may require treatment to prevent discharge of VOCs to the atmosphere.
Static treatment processes may result in less uniform treatment than processes that involve periodic mixing.
Laboratory or field treatability studies are needed to identify the best amendments that promote microbial activity, as well as to determine potential degradation byproducts and the potential degradation rate.
The treatment area is generally covered or contained with an impermeable liner to minimize the risk of contaminants leaching into an uncontaminated soil. This should be considered in the design.
For small volumes of contamination (less than 250 cubic yards), off-site disposal may be more economical.
A large amount of relatively flat space is required to build a bio-pile system.
Biopile treatment has been applied to the treatment of non-chlorinated VOCs and fuel-contaminated soil. Chlorinated VOCs, semi-volatile organic compounds (SVOCs), and pesticides can also be treated, but process effectiveness varies.
Technology Development Status
The technology is commercially available for treating fuel contamination. It is in the pilot stage for other contaminants.
Other Resources and Demonstrations
See http://cedb.asce.org/cgi/WWWdisplay.cgi?9700073 for a description of remediation of diesel contamination at Kennedy Space Center.