Biopiles are similar to landfarms in that they are both above-ground, engineered systems that use oxygen, generally from air, to stimulate the growth and reproduction of aerobic bacteria which, in turn, degrade the petroleum constituents adsorbed to soil. While landfarms are aerated by tilling or plowing, biopiles are aerated most often by forcing air to move by injection or extraction through slotted or perforated piping placed throughout the pile. Biodegradation of these petroleum products is more significant than evaporation. However, higher molecular weight petroleum constituents such as those found in heating and lubricating oils, and, to a lesser extent, in diesel fuel and kerosene, require a longer period of time to degrade than do the constituents in gasoline. Operation Principles Biopiles are designed to optimize the conditions for aerobic bacteria to biodegrade organic contaminants.
Soil texture affects the permeability, moisture content, and bulk density of the soil.
Soils with lower permeability are more difficult aerate, but tend to retain moisture better than soil with higher permeability. However, lower permeability is usually associated with soils that clump together making it difficult to evenly distribute moisture, air, and nutrients. Soil normally contains large numbers of diverse microorganisms including bacteria, algae, fungi, protozoa, and actinomycetes. In well-drained soils, which are most appropriate for biopiles, these organisms are generally aerobic. Of these organisms, bacteria are the most numerous and biochemically active group, particularly at low oxygen levels.