Fact sheet: Biopile—biological process—in situ

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• Description
• Recommended analyses for detailed characterization
• Recommended trials for detailed characterization
• Other information recommended for detailed characterization
• Applications
• Treatment type
• State of technology
• Target contaminants
• Treatment time
• Secondary by-products and/or metabolites
• Limitations and Undesirable Effects of the Technology
• Complementary technologies that improve treatment effectiveness
• Required secondary treatments
• Performance
• References
• Author and update

Description

The in situ biopile is a remediation technology used for the treatment of contaminated surface soils (less than 4 meters from soil surface). This technology is only applicable in the unsaturated zone and is for the treatment of soils contaminated with organic compounds.

The in situ biopile technique consists of periodic mixing of the soil to improve oxygenation which enhances the aerobic biodegradation of petroleum hydrocarbons. During the mixing process, there can be volatilization of volatile and/or semi-volatile contaminants, although this is not the objective of the technology. The addition of fertilizers to stimulate microbial activity and/or the addition of agents to improve the soil structure and to control soil water content are also options. It is important to monitor and control the ammoniacal nitrogen concentration, potential of hydrogen (pH), and soil water content in the contaminated biopile to avoid a reduction or an inhibition of microbial activity. A monitoring system, including down gradient observation wells, must be integral to an in situ biopile system to ensure that no contamination is leaching toward the groundwater or other sensitive receptors.

Sources:

• Alternative Cleanup Technologies for Underground StorageTanks-Biopile pdf- US EPA

Recommended analyses for detailed characterization

Recommended trials for detailed characterization

Other information recommended for detailed characterization

Applications

• Applies to the treatment of residual contamination in soils to a depth of 4 meters from the surface
• Principally applies to petroleum hydrocarbon contamination
• Water content must be maintained between 50% and 80% of the total soil water holding capacity
• The number of microorganisms should be maintained above 10³ CFU/g (Colony Forming Units / gram soil)
• The potential of hydrogen (pH) must be maintained between 6 and 8 to facilitate bacterial growth and activity

Treatment type

State of technology

Target contaminants

Notes:

Chlorobenzenes: suitable for chlorobenzene, dichlorobenzene and trichlorobenzene Phenolic compounds: suitable for cresol, pentachlorophenol and tetrachlorophenol Monocyclic Aromatic Hydrocarbons: applies with restrictions because these compounds are generally volatilized before being biodegraded.

Treatment time

Secondary by-products and/or metabolites

Generally, biodegradation of petroleum hydrocarbons does not generate any deleterious secondary by-products or metabolites.

Limitations and Undesirable Effects of the Technology

• Requires accessible soil
• Only applies to surface soil contamination (less than 4 meters from soil surface)
• Climate influences the treatment conditions
• Volatile organic compounds may impact air quality
• A dust control system may be required during the soil mixing procedures
• It is difficult to reduce petroleum hydrocarbon concentrations more than 95%, and/or obtain residual concentrations below 0.1 ppm
• High contaminant concentrations can be toxic for the microorganisms
• Soils must be well drained and able to maintain a water content between 50% and 80% of the total water holding capacity

Complementary technologies that improve treatment effectiveness

• Air injection system
• Thermal treatment such as hot air injection
• Irrigation system to maintain water content
• Run-off water and/or leachate collection to control the migration of the contaminants

Required secondary treatments

• Gas emission collection system

Performance

The treatment time required for site remediation with the in situ biopile varies according to the concentration and characteristics of the contaminants, the natural microbial populations, and the physical and chemical properties of the soil.

References

• Center for Public Environmental Oversight. 2002. Landfarming. U.S.A.
• Federal Remediation Technology Roundtable. 2002. Remediation Technologies Screening Matrix, version 4.0. U.S.A.
• How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers. (EPA 510-B-94-003; EPA 510-B-95-007; and EPA 510-R-04-002).

Author and update

Composed by : Magalie Turgeon, National Research Council

Latest update provided by : Karine Drouin, M.Sc., National Research Council

Updated Date : April 1, 2008