When planning thermal soil treatment, the most common mistakes occur in three areas: incomplete preliminary investigations, incorrect material characterization, and involving specialists too late. These errors regularly lead to delays, unexpected additional costs, and, in the worst case, rejection of the material by the treatment facility. The following questions and answers show what planners and clients need to pay specific attention to when it comes to thermal soil treatment.
Which types of waste are suitable for thermal desorption?
Suitable for thermal desorption are mineral wastes such as contaminated soils, construction rubble, dredged material, and process residues such as slags, ashes, sludges, and dusts that contain organic or volatile pollutants. The process is particularly effective for contamination with TPH, BTEX, PAH, PCB, phenols, PFAS/PFOS, cyanides, nitroaromatics, mercury, and chlorinated hydrocarbons.
The key factor is that the pollutants can be vaporized or destroyed at temperatures between 250 and 600 °C, depending on the material and contaminant load. Not suitable, however, are wastes with high water content without pre-treatment, heavily organically contaminated materials such as sewage sludge with high loss on ignition, or wastes that contain exclusively inorganically bound heavy metals, as these cannot be mobilized by thermal desorption.
Mechanical pre-treatment for homogenization and particle size reduction is generally a prerequisite for efficient treatment in a rotary kiln. Materials containing foreign matter such as metal, wood, or plastic must be appropriately processed before delivery.
Why do many projects fail at the preliminary investigation stage?
Many projects fail at the preliminary investigation stage because the contaminant spectrum is incompletely recorded or the sampling is not representative. A preliminary investigation that targets only the suspected primary contaminants frequently overlooks accompanying pollutants that complicate the treatment process or trigger additional regulatory requirements.
Typical mistakes in preliminary investigations include:
- Too low a sampling density, which does not reflect the actual contaminant distribution
- Missing analysis for relevant parameters such as PFAS, PCDD/PCDF, or cyanides at sites with a corresponding history of use
- Insufficient information on particle size distribution, water content, and organic fraction
- No comparison of analytical results with the approval parameters of the intended treatment facility
Particularly at decommissioned industrial and gasworks sites or former military installations, the contaminant profile is often complex and heterogeneous. Here, a systematic historical site investigation as the basis for sampling planning is indispensable.
Which permits and documentation must be in place before delivery?
Before delivering contaminated material to a soil treatment facility, a valid disposal declaration from the facility operator, current analytical certificates from the responsible laboratories, and a declaration analysis in accordance with the facility’s requirements must generally be in place. For hazardous waste, an accompanying document in accordance with the waste tracking regulations is also required.
The following documents are typically required:
- Analytical characterization of the material with all relevant contaminant parameters
- Waste code according to AVV (Abfallverzeichnis-Verordnung)
- Disposal verification or collective disposal verification for hazardous waste
- Accompanying document for each transport operation
- Where applicable, official transport permits for cross-border shipments
Anyone who does not prepare these documents in time risks delivery stoppages and construction delays. The facility is approved under the Federal Immission Control Act and is bound by strict acceptance criteria that cannot be circumvented on a case-by-case basis.
How does incorrect material characterization affect treatment costs?
Incorrect material characterization significantly increases treatment costs because adjustments to the process, additional analyses, and in the worst case a rejection of the material become necessary. If the actual contaminant content is underestimated, treatment parameters must be adjusted retrospectively or the material must be sent for a more complex disposal route.
Specific cost consequences of incorrect characterization include:
- Re-declaration and repeat laboratory analysis at the client’s expense
- Longer dwell times in the rotary kiln due to higher contaminant loads than declared
- Additional transport costs due to rejection and rerouting to alternative disposal routes
- Delays on the construction site due to unplanned downtime
- Possible regulatory consequences for incorrect information on accompanying documents
A careful and complete declaration analysis prior to delivery is therefore not a bureaucratic obligation but a direct cost-control measure. Anyone who cuts corners on analytics typically pays more elsewhere.
When should a specialized waste management company be involved in the planning?
A certified waste management company should be involved in the planning as early as possible, ideally already during the site investigation phase. At this point, sampling concepts, analysis programs, and logistical requirements can still be coordinated without time pressure.
In practice, the waste management company is often not contacted until shortly before construction begins, when excavation volumes and contaminant findings are already established. This limits the available options and increases the coordination effort. Early involvement, on the other hand, enables:
- Alignment of the sampling scope with the acceptance criteria of the treatment facility
- Early capacity planning and scheduling
- Clarification of logistical questions such as container placement, transport routes, and interim storage
- Optimization of material flows through targeted material flow management
Particularly for larger remediation projects with multiple waste fractions and varying contamination levels, early collaboration with an experienced disposal partner pays off.
What happens to the treated material after thermal desorption?
After thermal desorption, a largely contaminant-free mineral material is produced that can be reused as a construction material or deposited at a landfill, depending on its quality. The decision regarding further use depends on the analytical results of the treated material and the applicable assignment values.
In the rotary kiln, the organic pollutants are vaporized or destroyed at up to approximately 600 °C under exclusion of oxygen, with the exact temperature depending on the material and contaminant load. The resulting exhaust gas then passes through a multi-stage purification system with dust removal, thermal post-combustion, flue gas scrubbing, and activated carbon filtration before leaving the facility. The treated solid material is sampled and analyzed after treatment.
Possible recovery routes for the treated material include:
- Use as backfill material in earthworks and road construction, provided the assignment values of the Federal Soil Protection and Contaminated Sites Ordinance are met
- Return to the material cycle as a mineral construction material
- Disposal at a suitable landfill if the limit values for recovery are not achieved
The goal of soil remediation is in every case to recover the treated material at the highest possible quality and to conserve landfill capacities. How well this is achieved depends substantially on the quality of the preliminary investigation and the process management at the facility.
How ARE Deutzen GmbH supports thermal soil treatment
ARE Deutzen GmbH has specialized in the thermal treatment of contaminated mineral waste since 1994 and offers civil engineering companies, project developers, and industrial clients comprehensive support from planning through to the recovery of the treated material. The most common planning mistakes can be avoided from the outset with the right advice.
ARE Deutzen provides specific support through:
- Expert advice on the suitability of materials for thermal desorption already during the preliminary investigation phase
- Clear acceptance criteria and support in compiling the required documentation and accompanying documents
- Operation of an approved soil treatment facility with a rotary kiln for a broad spectrum of contaminants, including TPH, PAH, PCB, PFAS, cyanides, and mercury
- Material flow management for various waste fractions including interim storage and mechanical-physical pre-treatment
- Certified waste management company in accordance with § 52 KrWG with over 30 years of experience and more than 2.5 million tonnes of treated mineral materials
Get in touch early to plan your remediation project together. Through the contact persons at ARE Deutzen, you can reach the specialist team directly for an initial assessment of your project.