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Ex-Situ Thermal Desorption

Ex-situ thermal desorption is used to treat recalcitrant compounds such as Persistent Organic Pollutants that have impacted soil or heavy end hydrocarbons that are not susceptible to biological processes. The process works by heating soil in a rotating kiln.

Ex-situ thermal desorption is used to treat recalcitrant compounds such as POP’s that have impacted soil or on occasion heavy end hydrocarbon contamination that is not susceptible to biological process treatment. The process works by heating soil in a rotating kiln to temperatures between 350oC (low temperature thermal desorption) to 850oC (high temperature thermal desorption). The temperature of the desorber is dependent on what contaminants are being targeted, but the preference due to fuel and capital costs is to use the lower temperature systems where possible.

Essentially, at elevated temperatures contaminants that are adsorbed to soils are driven into the vapour phase. The vapours are subsequently drawn through a filter under vacuum prior to being combusted in a thermal oxidiser unit prior to exhaust to atmosphere. Cleaned soils are quenched for cooling and lost moisture added prior to re-use.

There are limitations with thermal desorption, specifically with the quality of the feedstock. Soil that is too clayey or silty will reduce the process efficiency as will over saturated soil. Soil that has a high contaminant load will also need to be carefully considered prior to treatment. However if the feedstock can be properly managed through appropriate pre-treatment steps thermal desorption can be an effective treatment method, often resulting in a very high standard of clean-up.