What Is the Difference Between Thermal Treatment and Direct Landfilling?

The essential difference between thermal treatment and direct landfilling lies in how the contaminants themselves are handled. With thermal treatment, contaminants in the soil are destroyed or driven out, so that the treated material can subsequently be reused. Direct landfilling permanently stores contaminated material without eliminating the contaminants. The following questions shed light on the most important technical, legal, and economic aspects of these two disposal routes.

Which contaminants can be destroyed by thermal treatment?

Thermal treatment is capable of removing or destroying a broad spectrum of organic and inorganic contaminants from mineral materials. These include mineral oil hydrocarbons (TPH), BTEX compounds, polycyclic aromatic hydrocarbons (PAH), phenols, polychlorinated biphenyls (PCB), PFAS and PFOS, dioxins and furans (PCDD/PCDF), cyanides, nitroaromatics, and numerous other chlorinated hydrocarbon compounds. Mercury (Hg) can also be driven out of soil material by thermal desorption.

Organic contaminants are either directly destroyed at sufficiently high temperatures or converted to a gaseous state and subsequently treated in a multi-stage exhaust gas purification system. Particularly persistent compounds such as PFAS or PCB, which are virtually impossible to eliminate by conventional means, can be safely removed from the material through thermal contaminant treatment. Inorganic contaminants such as heavy metals, by contrast, remain in the solid material and are concentrated rather than destroyed by the process. For these substances, additional treatment steps or secured disposal of the residues is required.

How does thermal desorption in a rotary kiln work?

In thermal desorption, contaminated soil or mineral waste is heated in a rotating rotary kiln at temperatures of up to approximately 600 °C, depending on the material and contaminant load, under exclusion of oxygen. By excluding oxygen, the contaminants do not combust uncontrollably but are vaporized and transferred into the gas stream. This gas stream is then fed into a multi-stage exhaust gas purification system.

The process is divided into several successive steps:

Mechanical pre-treatment: The delivered material is screened, crushed, and homogenized to ensure uniform treatment in the kiln.
Thermal treatment in the rotary kiln: The material passes through the rotating kiln at a defined temperature and residence time. Contaminants are driven out or destroyed in the process.
Exhaust gas purification: The resulting process gas passes through dust removal, thermal post-combustion, flue gas scrubbing, and activated carbon filters before leaving the plant. This ensures that statutory emission limits are reliably met.
Quality control of the output material: The treated material is analytically tested before being sent for further recovery or disposal.

You can find out more about the exact process and plant capacities on the page for thermal soil treatment.

What happens to the soil after thermal treatment?

After thermal treatment, the soil is generally free of organic contaminants and can, depending on the analytical results, be reused as recycled material, fill material, or building material. The treated material loses its organic components through the process and takes on an altered structure, but remains fundamentally usable as a mineral material.

Whether the treated material can actually be sent for recovery depends on the analytical values after treatment. If these fall below the relevant limit values, reuse is possible, for example as sub-base material in road construction or as fill. If heavy metal contamination remains in the material that could not be removed by the thermal process, secured landfilling of the residues is required. In any case, the removal of contaminants from the material is documented and analytically verified, providing a clear basis for the subsequent decision on use.

When is direct landfilling still permissible at all?

Direct landfilling of contaminated soils is heavily restricted in Germany and is only permissible under certain conditions. The Circular Economy Act and the Landfill Ordinance (DepV) stipulate that waste must be treated as far as possible before disposal in order to reduce volume and contaminant load. Untreated landfilling is only still permitted for materials where treatment is technically not possible or economically unreasonable.

In concrete terms, this means: heavily organically contaminated soils that exceed the assignment values of the respective landfill class may not be directly landfilled. Only after treatment that reduces the contaminant content to the permissible level is disposal possible. For many types of contamination, particularly those involving organic contaminants such as TPH, PAH, or BTEX, thermal soil treatment is therefore not only a sensible alternative to landfilling but frequently the only legally permissible option. In practice, direct landfilling remains relevant primarily for lightly contaminated mineral materials or materials for which no viable treatment option exists.

What costs arise with thermal treatment compared to landfilling?

Thermal treatment is generally more expensive than direct landfilling when comparing only the immediate treatment costs. However, this comparison is misleading in many cases because it ignores the legal restrictions, the long-term risks, and the possibility of material recovery.

The following factors significantly influence the cost comparison:

Landfill capacity and acceptance prices: Suitable landfill capacities for heavily contaminated soils are limited in Germany. Acceptance prices for hazardous waste landfills can be correspondingly high and in some cases approach the costs of thermal treatment.
Transport costs: Landfills for contaminated material are often not located near the remediation site. Transport costs can significantly increase the overall cost of landfilling.
Recovery potential: Thermally treated material may under certain circumstances be recovered as a secondary raw material, which reduces the overall costs of soil remediation.
Long-term liability: With landfilling, the contaminants remain in the material. Subsequent liability risks or aftercare costs cannot be ruled out.

A blanket statement on costs is not possible, as these depend heavily on the type of contaminant, the quantity of material, the location, and the prevailing market prices. An individual cost calculation based on material characterization is advisable in every case.

Which types of waste are suitable for thermal soil treatment?

In principle, all mineral materials contaminated with volatile or thermally decomposable organic contaminants are suitable for thermal soil treatment. In addition to contaminated soils, construction rubble, dredged material, and process residues such as slags, ashes, sludges, and dusts can also be treated, provided they meet the plant’s acceptance criteria.

Typical types of waste suitable for thermal desorption:

Contaminated soils from brownfield sites, gasworks sites, and military installations
Tar-containing materials and PAH-contaminated construction rubble
TPH-contaminated soil from petrol station remediation or industrial sites
PFAS-contaminated soils from firefighting foam applications or industrial sites
Mercury-contaminated soils from chemical plants
Dredged material with organic contaminant loads

Materials with exclusively inorganic contaminant loads are not suitable — for example, purely heavy-metal-contaminated soils without organic components — as these cannot be treated by thermal desorption. For such materials, other mechanical-physical treatment processes or secured landfilling are necessary. Material flow management helps to determine the appropriate disposal route for each type of waste.

How ARE Deutzen helps with thermal treatment and disposal decisions

ARE Deutzen GmbH has specialized in the treatment of contaminated mineral waste for over 30 years and operates one of the most powerful thermal soil treatment plants in Germany at its Deutzen site in western Saxony. For civil engineering companies, remediation planners, and industrial customers, ARE Deutzen offers concrete support throughout the entire disposal process:

Analytical assessment of delivered material and verification of acceptance eligibility
Thermal treatment of contaminated soils, construction rubble, and mineral waste in a rotary kiln at up to approximately 600 °C, depending on the material and contaminant load
Multi-stage exhaust gas purification to ensure reliable compliance with statutory emission limits
Material flow management for materials that cannot be thermally treated
Interim storage and mechanical-physical pre-treatment as supplementary services
Documentation and record-keeping in accordance with the requirements of the Circular Economy Act

If you wish to dispose of contaminated soils or mineral waste safely and in compliance with the law, contact ARE Deutzen directly. On the Contact persons page you will find the right contacts for your inquiry.