Landfarming is a bioremediation technique that is performed in the upper soil zone or in excavated stockpiled cells. Contaminated soils, sediments and sludges can be spread on the ground and periodically tilled to aerate and encourage bacterial growth. Nutrients, minerals, and/or moisture may be added to speed degradation. Sometimes bacteria which have been selected for their success in breaking down hydrocarbons are added. Contaminants are degraded, transformed, and immobilized by microbiological processes and by oxidation. Contaminated material is usually treated in lifts that are up to 50 cm thick. When the desired level of treatment is achieved, the lift is removed and a new lift is constructed. It may be desirable to only remove the top of the remediated lift, then construct the new lift by adding more contaminated media to the remaining material and mixing. This serves to inoculate the freshly added material with an actively degrading microbial culture, and can reduce treatment times. Please note, a Landfarm treatment area must be managed properly to prevent both on-site and off-site migration/cross contamination problems with ground, ground water, surface water contamination.
Land farming has been proven most successful in treating petroleum hyrdrocarbons and other less volatile, biodegradable contaminants. As a rule of thumb, the higher the molecular weight (i.e., the more rings within a hydrocarbon), the slower the degradation rate. Landfarming will not usually work when hydrocarbon parametres are greater than 50,000 ppm and heavy metals parametres are greater than 2,500 ppm.
Factors that may limit the applicability and effectiveness of the process include:
- Conditions affecting biological degradation of contaminants (e.g., temperature, rain fall) are largely uncontrolled, which increases the length of time to complete remediation.
- Inorganic contaminants will not be biodegraded.
- Dust control is an important consideration, especially during tilling and other material handling operations.
- Runoff collection facilities must be constructed and monitored.
- Topography, erosion, climate, soil stratigraphy, and permeability of the soil at the site must be evaluated to determine the optimum design of facility.
The more chlorinated or nitrated the compound, the more difficult it is to degrade.
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