Thermal desorption is a process for cleaning contaminated soils in which pollutants are driven out of the soil material through targeted heat treatment and subsequently destroyed. The process is suitable for a wide range of organic and inorganic contaminants and is considered one of the most effective methods for soil remediation. The following sections answer the most important questions about how it works, its areas of application, and the relevant legal framework.
How does thermal desorption work on contaminated soils?
In thermal desorption, contaminated soil is heated in a rotary kiln to temperatures of up to approximately 600 °C, depending on the material and contaminant load. Under exclusion of oxygen, volatile and semi-volatile contaminants are driven out of the soil material, converted into a gaseous state, or directly destroyed. The process is also referred to as thermodesorption and differs fundamentally from incineration.
The process runs in several stages. First, the delivered soil is mechanically pre-treated to separate coarse components and ensure uniform grain size. The material then passes through the rotary kiln, where the heat breaks the bond between the contaminant and the soil particle. The resulting pollutant gases are treated in a downstream exhaust gas cleaning system. This typically includes dust removal, thermal post-combustion, flue gas scrubbing, and an activated carbon filter. This ensures that no pollutants are released into the atmosphere and that all statutory emission limit values are met.
Which contaminants can be removed by thermal desorption?
Thermal desorption is suitable for treating a broad spectrum of contaminants. These include mineral oil hydrocarbons (MKW), polycyclic aromatic hydrocarbons (PAH), BTEX compounds, phenols, polychlorinated biphenyls (PCB), cyanides, nitroaromatics, and per- and polyfluoroalkyl substances (PFAS/PFOS). Mercury (Hg), dioxins and furans (PCDD/PCDF), as well as a wide variety of other chlorinated hydrocarbon compounds can also be safely treated.
The treatment temperature is critical to effectiveness. More volatile compounds such as MKW or BTEX are driven off at lower temperatures. Less volatile contaminants such as PAH, PCB, or PFAS require higher temperatures and longer residence times in the kiln. The precise process management is therefore tailored to the specific combination of contaminants in order to ensure complete pollutant elimination.
For which types of waste and remediation projects is the process suitable?
Thermal soil treatment is not limited to earthen soils. The process can also be applied to construction rubble, dredged material, sludges, ashes, slags, and other mineral waste. Typical fields of application include the remediation of decommissioned industrial sites, former gasworks sites, and contaminated areas of military or chemical facilities.
The process is particularly in demand for projects where multiple contaminants occur simultaneously or where other treatment methods reach their limits. As part of a comprehensive material flow management approach, various waste fractions can be systematically captured, assigned, and directed to the most appropriate treatment method. This also includes process residues such as industrial wastewater or dusts that arise in the course of remediation measures.
What happens to the soil after thermal treatment?
After thermal treatment, the soil is present as largely contaminant-free mineral material. Due to the heat exposure, it loses organic components and changes its structure. Depending on the original quality and treatment outcome, the material may be reused as a secondary raw material in certain applications, for example as backfill material in civil engineering or in technical layers.
Whether reuse is possible depends on the analysis results after treatment and the applicable requirements of the Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV). Material that does not meet the threshold values for recovery is directed to proper disposal. Documentation of the treatment result is a central component of the quality process and provides legal certainty for clients and authorities. More information on the importance of soil as a resource worthy of protection is provided on the page on soil protection and sustainability.
How does thermal desorption differ from other soil remediation methods?
Thermal desorption differs from other soil remediation methods primarily through its ability to treat a broad spectrum of contaminants in a short time and with a high degree of safety. While biological methods rely on degradation by microorganisms and are therefore limited to readily degradable contaminants, thermal treatment operates independently of biological availability and degradability.
Comparison with biological methods
Biological soil remediation is cost-effective and gentle, but is limited to certain contaminants such as MKW and often requires months or years. Poorly degradable compounds such as PAH, PCB, or PFAS can barely or not at all be eliminated biologically. Thermal desorption is clearly superior in this regard.
Comparison with chemical-physical methods
Chemical-physical methods such as soil washing or extraction separate contaminants from the soil material but do not necessarily destroy them. They generate contaminated wash waters or concentrates that must be disposed of separately. Mechanical-physical treatment can be usefully employed as a pre-treatment stage, but does not replace thermal desorption for complex contaminations.
What legal requirements apply to thermal soil treatment facilities?
Thermal soil treatment facilities are subject to strict legal requirements in Germany. Operation requires a permit under the Federal Immission Control Act (BImSchG), which prescribes binding emission limit values for exhaust gases, dusts, and organic compounds. Additional requirements arise from the Landfill Ordinance, the Federal Soil Protection and Contaminated Sites Ordinance, and the Circular Economy Act.
Operators of such facilities must also be certified as a licensed waste management company (EfB) pursuant to § 52 of the Circular Economy Act. This certificate confirms that waste is treated properly, harmlessly, and in a manner compatible with the common good. Quality management systems in accordance with ISO 9001, environmental management systems in accordance with ISO 14001, and energy management systems in accordance with ISO 50001 complement the framework for legally compliant and responsible facility operation. Further information on quality management can be found on the corresponding quality management page.
Thermal soil treatment by ARE Deutzen GmbH
ARE Deutzen GmbH has been operating a licensed thermal soil treatment facility at its site in Deutzen in western Saxony since 1994. The company offers a complete solution for the remediation of contaminated sites, from acceptance and interim storage to certified treatment and documentation. Specific services include:
- Thermal desorption in a rotary kiln at temperatures of up to approximately 600 °C, depending on the material and contaminant load, under exclusion of oxygen
- Treatment of soils, construction rubble, dredged material, sludges, ashes, and other mineral waste
- Safe elimination of complex combinations of contaminants, including PAH, MKW, PFAS, PCB, Hg, dioxins, and more
- Multi-stage exhaust gas cleaning to comply with all statutory emission limit values
- Operation as a certified licensed waste management company under the Circular Economy Act
- Certifications in accordance with ISO 9001, 14001, and 50001
- Over 30 years of experience and more than 2.5 million tonnes of treated materials
If you wish to remediate a contaminated site or safely dispose of hazardous waste, contact ARE Deutzen directly. All information on thermal soil treatment as well as contact options can be found on the company’s website.