Contaminant separation and contaminant destruction are two fundamentally different approaches to soil remediation. In separation, contaminants are removed from the soil material and treated separately, while in destruction, contaminants are chemically or thermally converted into harmless compounds. Which method makes sense depends on the type of contamination, the concentration of contaminants, and the requirements for the treated material. The following sections shed light on the most important questions surrounding both methods.
Which method is suitable for which contaminants?
The choice between contaminant separation and contaminant destruction depends primarily on the physicochemical properties of the contaminants. Volatile and semi-volatile organic compounds such as mineral oil hydrocarbons (TPH), BTEX, or PAHs can be both separated and destroyed using thermal processes. Heavy metals such as mercury (Hg), on the other hand, cannot be destroyed and must be separated and disposed of separately.
For complexly contaminated soils with multiple contaminants, thermal treatment offers a decisive advantage: it can treat different groups of contaminants simultaneously in a single process step. Soils containing organic contaminants such as PCBs, PFAS/PFOS, cyanides, nitroaromatics, or chlorinated hydrocarbons are particularly well suited for thermal processes, as these compounds are reliably destroyed or completely driven off at sufficiently high temperatures.
How does thermal desorption work as a separation method?
Thermal desorption is a process in which contaminated soil is heated through targeted heat input under exclusion of oxygen, causing contaminants to vaporize and separate from the soil material. The contaminants transition into the gaseous state and are then treated in a downstream exhaust gas purification system. The soil material itself is preserved and can be reused after treatment.
In the thermal soil treatment plant at ARE Deutzen, the contaminated soil passes through a rotary kiln after mechanical pre-treatment, where it is heated to temperatures of up to approximately 600 °C, depending on the material and contaminant load. The exclusion of oxygen is crucial: it prevents combustion of the material and ensures that organic contaminants are driven off in a controlled manner. The resulting pollutant gases are captured in a multi-stage exhaust gas purification system that includes dust removal, thermal post-combustion, flue gas scrubbing, and activated carbon filters.
What happens to the soil after contaminant separation?
After thermal desorption, a largely contaminant-free soil material is produced that can be directed toward recovery depending on its quality and source material. In many cases, the treated material meets the requirements for reuse in civil and underground engineering, as backfill material, or in construction material production. This transforms waste back into a usable resource.
Whether the treated material can actually be recovered depends on the contaminant characteristics prior to treatment, the cleaning performance achieved, and the applicable assignment values of the Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV). In some cases, landfilling of the treatment residue is required, for example when heavy metal content does not meet recovery criteria. Material flow management plays a central role here: it ensures that every material stream takes the regulatory and ecologically correct disposal route.
Which contaminants are destroyed rather than separated during desorption?
During thermal desorption, not all contaminants are merely separated. Many organic compounds are directly destroyed at the temperatures used — that is, their chemical structure is broken down and converted into harmless compounds. Contaminants that are destroyed during treatment include in particular highly halogenated compounds such as PCDD/PCDF (dioxins and furans), PCBs, PFAS/PFOS, and nitroaromatics.
The difference lies in the volatility and thermal stability of the respective compound. Highly volatile contaminants such as TPH or BTEX vaporize at lower temperatures and are further treated in the exhaust gas system. Less volatile or thermally less stable compounds, on the other hand, decompose into their components directly in the rotary kiln. Mercury occupies a special position: it vaporizes reliably and is captured and separated in the exhaust gas purification system by activated carbon filters, without any chemical destruction taking place.
When should contaminant destruction be preferred over separation?
Contaminant destruction should be preferred over pure separation when the compounds in question are so persistent that merely transferring them to another disposal route does not represent a permanent solution. This applies especially to contaminants that are barely broken down in the environment, such as PFAS/PFOS, PCDD/PCDF, or certain chlorinated hydrocarbons. Separation without subsequent destruction would merely shift the contamination problem.
Further criteria that favor destruction:
- The contaminants are present in very high concentrations that rule out safe landfilling or make it uneconomical.
- The compounds have a high hazard potential and are subject to strict disposal requirements.
- Recovery or utilization of the separated contaminants is technically or economically not feasible.
- The client or the competent authority requires proof of complete contaminant elimination.
In practice, thermal desorption combines both principles: contaminants are separated and thermally destroyed in the post-combustion stage. This makes the process particularly suitable for sites with complex contamination profiles, such as those found at decommissioned industrial sites, former gasworks, or military properties.
What legal requirements apply to both methods?
Both contaminant separation and contaminant destruction are subject to an extensive regulatory framework in Germany. The key legal bases are the Circular Economy Act (KrWG), the Federal Soil Protection Act (BBodSchG) together with the associated Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV), and the Federal Immission Control Act (BImSchG). Plants that thermally treat contaminated soils require an immission control permit and must comply with emission limit values for air pollutants.
The treated materials are subject to assignment values that determine whether the result of soil remediation must be directed toward recovery or landfilling. Operators of thermal treatment plants must also be recognized as a certified waste management company (EfB) pursuant to § 52 KrWG. Quality management in accordance with ISO 9001, supplemented by certifications to ISO 14001 (environmental management) and ISO 50001 (energy management), provides the foundation for documented and traceable compliance with all relevant standards and regulations.
How ARE Deutzen GmbH helps with soil remediation
ARE Deutzen GmbH specializes in the thermal treatment of contaminated mineral waste and combines contaminant separation and contaminant destruction in an integrated process. With more than 30 years of operational experience and over 2.5 million tonnes of treated material, the company offers a reliable solution for demanding remediation projects.
The range of services specifically includes:
- Thermal treatment of contaminated soils, construction rubble, and mineral waste 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 a broad spectrum of contaminants: Hg, TPH, BTEX, phenols, PAHs, PCBs, PFAS/PFOS, PCDD/PCDF, cyanides, nitroaromatics, and chlorinated hydrocarbons
- Multi-stage exhaust gas purification to ensure safe compliance with all statutory emission limit values
- Material flow management for soils, dredged material, slags, ashes, sludges, and industrial wastewater
- Individual consulting and project support from analysis through to disposal documentation
If you would like to remediate a contaminated site and need expert advice on which method is suitable for your specific contamination, contact ARE Deutzen directly. The contact persons are available for a no-obligation initial consultation.