Indirect Thermal desorption is a proven treatment technology that effectively removes volatile organic compounds (VOC's) from soil and several other contaminated waste streams from soil and sludge. Thermal desorption occurs when organic contaminants adsorbed into soil particles or sludge are exposed to temperatures above their respective boiling points. This heat is sufficient to effect a phase change in the contaminants, yet due to the extremely low heating value of soil or sludge, incineration of the soil does not occur. KAYAN recommends portable indirect thermal desorption plants that are designed to treat soils impacted by medium to high boiling point organic compounds at nominal throughputs of 3 to 8 tons per hour.

Usually the indirect fired thermal desorption unit (TDU) consists of an inner rotating barrel enclosed by a heating chamber (Oven). Contaminated soil is fed continuously into the rotating barrel, which is indirectly heated by burners in the surrounding heating chamber to desorb the contaminants. Heating chamber exhaust gases and off-gases from the inner rotating barrel are kept separate and never come in contact with another. There are several systems that are batch indirect thermal desorption systems that are very efficient. To select the proper technology the KAYAN checklist is utilized.

Organic contaminants amenable to treatment via an indirect TDU include essentially all regulated compounds, ranging from PCBs, PAHs and dioxins to organic solvents, including volatile and semi-volatile organic compounds, as well as oils and petroleum products. The indirect TDU system is ideal for manufactured gas plant soils and residues because high production rates can be achieved without regard to the very high contamination levels in these materials. For specific projects such as lagoon sludge or process filter cake treatment, contamination levels of 60% hydrocarbons or more can be treated. Because the system is inert and combustion of the waste is not allowed, this high level of contamination may be treated safely. Oil recovered from high hydrocarbon contamination has had the characteristics of used motor oil, i.e. low ash content and high heating value.