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Rensning af jord med blandingsforureninger ved hjælp af termiske
jordbehandlingsanlæg
A facility for off-site treatment of contaminated soil by Low Temperature Thermal
Desorption (LTTD) has been tested in the period January-March 2001. The test has been
performed by the Danish EPA and the Environmental Protection Department of the City of
Copenhagen in cooperation with the company RGS90 Jordrens.
The scope of the test is three-fold:
The test has been performed on a semi-mobile treatment facility with a nominal capacity
of 15 tons pr. hour. In the process, contaminated soil is heated in a fuel-oil heated
rotary kiln to a temperature of approx. 550-600 °C. Residence time in the kiln is approx.
15 minutes. Flue gas is cleaned in a bag filter, evaporated tar and oil components are
destructed in an afterburner and the gas is cleaned in a two-step gas scrubber. Filter
dust and effluent water from the scrubbers are recycled to the treated soil.
The tests have basically been performed as 24 hrs continuous runs, where different
types of soils have been treated. Prior to the test runs, the soil has been sieved through
a 40 mm rotary screen in order to remove rocks and to create a homogenous batch of soil
for the test.
Two soil types have been tested. Batch no. 1 is a clayish fill soil with a pronounced
content of organic matter, whereas batch no. 2 is a clayish soil containing less organic
matter. Batch no. 1 is regarded to be a typical representative of surplus soil from rural
construction works, and is contaminated with heavy metals as well as tar and oil
components. Batch no. 2 is solely contaminated with tar and oil components.
Before and after treatment of the two batches, a large number of soil samples have been
taken. Soil characteristics have been measured through sieve tests and compacting testing.
The analytical programme comprises general chemical soil parameters such as TOC, carbonate
content, pH and CEC, as well as environmental screening for heavy metals, tar components
and mineral oils. Changes in the leaching of heavy metals from the soils have been studied
through batch-tests and column-test.
Economic and environmental performance of the facility has been investigated during the
test runs by monitoring the consumption of oil, electricity and water, and through
sampling and analysis of flue-gas and discharge water.
The findings of the tests can be summarized as follows:
From an environmental perspective, low temperature thermal desorption is a very
resource-consuming process, where approx. 45 kg of fuel oil is spent on each ton of
contaminated soil. The environmental benefit, on the other side, is a product with low
levels of organic contaminants and a general reduced level of heavy metal leaching. It is
therefore a suitable treatment method for non-volatile organic persistent contaminants,
given possibilities for a controlled reuse is present.
The cost of low temperature thermal desorption treatment has in the test runs been in
the magnitude of 100 EUR pr. ton, of which fuel oil consumption has been approx. 35%. It
should be noted that the oil consumption during the test has varied with up to 50%,
depending on moisture and organic contaminant contents in the treated soil.
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