The most common methods of remediation have historically involved contaminant transfer. Excavating soils for deposit in a landfill, vapor extraction, soil farming, etc. All of these methods are of the 'transfer' nature. They either relocate or deposit the soils elsewhere or transfer the contaminant to the air or another media. Thermal Desorption is a long proven method of remediation, which incorporates the 'transfer' aspect while ending in a combustion or destruction manner.
Thermal desorption is made of (3) three primary steps: Volatilization, Stripping, Combustion / Destruction. In this process, the temperature of the contaminated media is elevated causing the volatiles and semi volatiles to change into a vapor phase. The vapor phase and particulate matter is then stripped with air. The air is then passed through the baghouse to eliminate airborne particulates and sent into the combustion chamber or afterburner for combustion / destruction / incineration. Since the destruction process only involves the contaminant in the vapor phase portion and not the entire soil structure, there is no ash generated (solid waste) by this process and the soils are viable for reuse.
Thermal Desorption Plants are primarily used in the remediation of soils contaminated in the range of Parts Per Billion (Ppb) to 2% by volume or 20,000 Parts Per Million (ppm). These contaminants tend to be volatiles and semi volatiles such as diesel, gasoline, jet fuels, fuel oils, etc. The results are an environmentally acceptable soil that has been decontaminated in most cases to a non-detectable level. The soils can then be used on site or directly backfilled in the cleaned excavation.
The Thermal Desorption Process can be conducted at a relatively high rate of treatment. The majority of the plants operate in ranges from 18 - 35 tons per hour. Larger plants may operate in excess of 100 tons per hour. Based on the average historical pricing, thermal desorption treatment costs range from $29 to $45 per ton for the 18 - 35 ton per hour plants. Some of the variables in the pricing include the volume to be treated, contaminants involved, soil types, moisture content and the cost associated with the type of combustion fuel used.
When determining if Thermal Desorption is the applicable remediation method for a particular location, there are several thoughts that must be kept in mind.