Thermally enhanced extraction of PAHs from soil

Polycyclic aromatic hydrocarbons, PAHs, are organic pollutants widely spread in the environment. In order to decrease the level or eliminate the PAHs from the environment, especially soil, the development and the application of adequate techniques of remediation became the most important issues. The processes of thermally enhanced extraction of contaminants from soil include injection of hot air, steam or water into contaminated zone in order to mobilize all volatile and semi-volatile organic compounds . These in situ treatments may readily remove semi-volatile PAHs in the vapor phase from the subsurface through the extraction wells. The extracted vapors are then treated, as necessary (commonly with carbon adsorption), and discharged to the atmosphere or possibly re-injected into the subsurface. In the soil vapor extraction (SVE) technology, a vacuum is applied through wells near the source of contamination in the soil. Volatile constituents of the contaminant mass evaporate and the vapors are drawn toward the extraction wells. The increased air flow through the subsurface can also stimulate biodegradation of some of the contaminants, especially those that are less volatile. Wells may be either vertical or horizontal. Radio-frequency Heating (RFH) brings controlled heating to the subsurface, enhancing the removal of contaminants by soil vapor extraction; is analogous to a microwave - generation of heat on a molecular level. Similar to enhanced soil vapor extraction, hot water treatment and steam flushing/stripping entails the injection of hot water into the subsurface to mobilize contaminants. Contaminants are mobilized by the hot water and flows to the recovery wells, where they are removed from the subsurface along with the hot water. Maintaining a cold water cap over the area can control volatilization of the lighter constituents. Any volatile organics condense once they reach the cold water.