Concept Ex-situ soil remediation

This sheet is part of the BOSS application.


Technique 1: Physico-chemical cleaning (soil washing)

Figure: Diagram of physico-chemical cleaning


Physico-chemical cleaning of soil is a treatment process in which pollutants are removed from the soil off-site, by using a combination of techniques. Firstly, water is added to the soil, whereby a watery sludge is created through intense stirring (with scrubbers, for example).

Thereafter, organic particles and fine (mineral) particles are separated on the basis of particle size and density; the aim of this is to achieve physical separation of the pollutant.  This separation is implemented via (a combination of) separation techniques derived from mining, such as hydro-cyclones, flotation cells, jigs, spirals and shaking tables The separated content is hardened by employing a thickening process (mostly by using filter belt presses).

Further, chemicals are added to the process-water during the process to make the pollutant more soluble and to dissolve it or extract it from the mineral and organic content in the soil. These chemicals are dosed on the basis of the pollutant that needs to be treated (acids, bases, oxidation substances, detergents, complexing agents, organic solvents etc.).

The final step is to remove water from the cleaned ground. The process-water is cleaned in a separate treatment installation.


Technique 2: Biological remediation



Figure: Diagram of biological remediation: Bio-bed


Biological remediation is an on-site or off-site cleaning technique for soil polluted by biologically degradable compounds. In order to allow optimal break down to take place, a number of parameters are checked and managed. The most important parameters are the system’s oxygen content and CO2 content.  This is controlled via an aeration system, or by regularly tilling using a turning machine.

In addition, the following parameters are managed and optimised in more intensive systems:

  • The soil structure (regular homogenisation of the soil and additional substances like chalk or compost)
  • Nutrient content (mixing of artificial fertiliser)
  • Moisture content (soil moistening)
  • Temperature (heating the system)
  • Various bacteria (addition of sludge or compost)

The hops have a minimum height of 0.5 metres (in systems without active aeration and frequent homogenisation) and a maximum height of 4 metres (with an active aeration system). The average implementation time varies from a few months to 2 or 3 years, depending on the intensity of the treatment, the type of pollution and the required clean up value.


Technique 3: Thermal cleansing

Figure: Diagram of thermal cleansing (


By heating the polluted soil to a temperature of 350 to 600 °C, mainly in the rotating barrel system, pollutants are volatilised or pyrolysis of pollutants takes place.  The pollutants are transported to the gas phase and are processed in a separate gas treatment system. In this gas treatment system, the pollutants, depending on their composition, are oxidised at temperatures of 1.000 to 1.200 °C. To cool the soil and to prevent dust-forming, the soil is re-moisturised with water after the thermal desorption phase.

The structure of soil can change at temperatures above 400 to 500 °C. Thus thermally cleansed soil is not commonly re-used for civil-technical works. It can eventually be made suitable as a plant substrate after mixing with compost.


Implementation area and implementation conditions

Technique 1: Physico-chemical cleaning (soil washing)

The technique can be implemented in soil with a limited content of fine materials. Clay, sludge and peat-like soil types cannot be treated using this technique. In order to make the process economically viable, the soil that is to be treated should not contain more than 20 to 30 % clay and silt content (< 60 µm).

In principle, all pollutants can be treated. However, complete removal is not possible in many cases. Volatile and well-soluble pollutants can be removed in almost 100% of cases. Heavy metals, PAH’s and pesticides can on average be removed up to 90% (metals) to maximum 98% (PAH’s). Dioxins and PCB’s must be regarded as untreatable with this technique, unless only a low yield is required.

The capacity of mobile filters is circa 5 to 20 ton/hour. The capacity is partly determined the clay content, the type and intensity of the pollutant and the required cleaning standard. Fixed installations are able to deal with a larger input, as high as 100 ton/hour.

In principle, soil can be re-used once it has been cleaned. The content of organic substances and the share of fine mineral particles will be lower, which makes the soil suitable for use in road construction, for example.


Technique 2: Biological remediation

Biological remediation can be implemented in soil that has sufficient permeability. In principle, clay and loam soils are difficult to treat, unless the soil is intensively crumbled or mixed with something that improves its structure (‘bulking agent’).

Biological aerobically-degradable pollutants (this includes most petroleum refining products) can be treated via biological clean up. In general, these are benzene and diesel oil-like compounds with a carbon chain length up to C25, to be judged via a GC chromatogram. Heavier oil products cannot be effectively cleaned biologically.


Technique 3: Thermal cleansing

All soil polluted with organic compounds can be treated using this technique. Depending on the to-be-cleaned pollutants, the following temperatures should be used for soil purification.

  • Mineral oil: 200 to 400 °C;
  • PAH’s: Up to 600 °C;
  • Non-volatile halogenated compounds (e.g. PCB’s): Up to 600 °C.

Concentrations in the soil may not be greater than 2 or 3 percent in weight, due to the risk of pollutants spontaneously combusting.

The maximum moisture content in the soil is 35 to 40%. Higher moisture contents are not recommended due to the high energy costs for the evaporation of water.

Soil which contains mercury compounds is in principle not treated due to the high risk of mercury compound emissions via the gas phases.

The pollutants can be removed with a yield in excess of 97%. In general, all organic pollutants are removed until below the detection limit. Individual installations have capacities that vary from 5 to 40 ton/hour.

The cleansed ground is biologically free of life and is normally a dark colour. The organic substance is literally fully removed from the soil.



Technique 1: Physico-chemical cleaning (soil washing)

Investment costs for a wet soil-cleaning installation are lower than the costs for thermal techniques. Because there are many differences in the way wet remediation methods are implemented - from very simple to extensive installations with sand fraction polishing – there are also great differences in the levels of investment. In addition to this, each company employs its own investment strategy for adjustments and changes to the installation. The investment needed to realise a new installation is lower than the historically cumulative investments from existing installations. Namely, that a lot of money has been spent during the development phase of wet soil- cleaners, which is in-turn transferred to the amounts required for investment.

The writing-off of installations is partly determined by technical dating, whereby the installation and buildings must be replaced after a number of years. Parts that are subject by wear are replaced regularly. Besides technical dating, writing off is largely determined by process-related dating (new techniques, cheaper techniques, larger capacity…).

The maintenance of wet soil remediation installations is greatly determined by the complexity of the installation, and lies between € 1 to € 2.5 per tonne of treated soil.

The energy use in wet soil remediation consists predominantly of electricity used by the system’s pumps.  When intensive scrubbing takes place or when a high-pressure cleaning unit is implemented, the use of energy rises. The energy use lies between 10 to 20 kWh per tonne of treated soil. Water purification installations also use a lot of energy.

Most support aids are implemented in the separation of the finest fraction, coagulants and flocculants. An amount of € 1 to € 5 euros is allocated per tonne of separated fine fraction (dry matter).

The costs for the disposal of residue are limited by disposing as little residue as possible. The costs are determined by the fine fraction content in the soil that is to be treated.

The costs for the disposal of the cleaned product are determined by the constitution. In wet cleaning, the product can be disposed as sand.


Table: Unit costs per tonne contaminated soil, excluding transport;, fractions <63 µm and organic contents have the greatest influence on price (OVB, 2004)



Costs mob/demob

Off-site clean up

€ 30-70


On-site clean up from 15.000 ton

€ 30-50

€ 25.000-…


Technique 2: Biological remediation

The investment costs related to biological soil clean up installations are generally lower than those for other techniques. Because there are many differences in the way biological clean up methods are implemented - from very simple land farms to extensive installations with heating and aeration – there are also large differences in levels of investment. An important element is the terrain hire, because biological clean up requires a relatively large terrain surface.

The writing-off of installations is predominantly determined by technical dating, whereby under-sealing and buildings must be replaced after a number of years. The writing-off period that can be used, based on the technical dating of biological soil remediation installations, is relatively long. Whether that is also the case in practice, is determined by company strategy.

Investments in a biological soil remediation installation are, for the most part, proportionate to capacity. The financial burdens per tonne of capacity become proportionately lower as the capacity rises, but this effect is significantly less than in wet and thermal techniques.

Energy use in biological soil remediation is strongly determined by the level of intensity in the process, and the related installation of heating equipment and ventilators Because the differences are relatively large, an amount cannot be provided. The amount allocated for energy use per tonne of treated soil, is definitely less than € 5.

The quantity of used support aids - (liquid) fertilisers - is low. An amount of less than € 0.5 per tonne of treated soil is allocated to support aids.   Little use is made of the inoculation of specific (and expensive) bacteria.

When soil is cleaned to values that allow the cleaned ground to be implemented without restrictions, the quantity of residue from biological cleaning (barring sieve overflow) is zero. Costs relating to the disposal of residue are also low in such cases. In biological remediation, a conscious decision is sometimes made to not clean so intensively. When cleaning takes place up to values that make it impossible to dispose without restrictions, additional disposal costs should be taken into consideration.

The price for processing is determined by the soil type and the pollutant type. A combination of sandy soil with ‘light’ oil pollution leads to a low price, whereas a combination of clay-like soil with ‘heavy’ oil pollution leads to a high price. The most crucial determinants are the type of oil (C 30 chains), concentration of mineral oils, PAH’s and heavy metals. Market prices amount to 20 to 50 euros per tonne.


Technique 3: Thermal cleansing

The investment in thermal soil purification installations is comparable with the upper levels in other ground purifications installations. The invested amounts cannot be provided because each company employees its own strategy when investing in adjustments and changes to the installation.

The investment needed to realise a new installation is considerably lower than the historically cumulative investments in existing installations. Namely, that a lot of money was spent in the development phase of thermal soil cleaners, which is in-turn transferred to investment amounts.  The writing off of installations is not determined by technical dating. Via intensive maintenance, where important process parts are regularly replaced, installations remain in fully-operational condition. Writing off is determined by process-related dating (new techniques, cheaper techniques, larger capacity…). There is a continuous process of renewal within the installation.  The greater the capacity, the (proportionately) lower the writing off per tonne of capacity.   The total financial burden is around 20% of operational costs. The maintenance budget for each soil purification installation can amount to millions of euros per year (Van der Grun et al, 2000).

The energy use in thermal installations is high; on average, (the equivalent of) 40 to 50 litres of fuel oil per tonne of cleaned oil is used. The costs are determined by the amount of fuel used.

The costs for the disposal of residue from smoke gas are restricted by disposing of as little residue as possible.

The costs for the treatment of polluted soil are determined by the composition of the soil type, the moisture content and the composition of pollutants.  The main determining factors are the concentrations of mineral oils, heavy metals, sulphur and moisture content. Costs can vary from €65 to €85 per tonne of polluted soil in ex-site remediation and between €40-60 in on-site remediation (from 15.000 tonnes). For on-site remediation, installation costs of > € 25.000 (OVB, 2004) should be taken into consideration.


Environmental burden and measures to be implemented

In all soil cleaning installation, soil is transported, stored, treated and disposed of.

Soil drift may take place during these activities – namely in the form of the fine (dust) fraction. The drift of breathable dust (<10 µm) is central in determining the risk to the environment. An issue of concern to licence-providers is the drift of dust from un-cleaned soil, because this can lead to polluted substances being spread.

Drift can be prevented by storing the soil indoors or by coving it with a sheet, by implementing sieves, placing wind screens or by moistening the stored soil. 

All soil cleaning installations are equipped with a water-tight container which is able to capture rain water and percolation water, so that there are no emissions into the soil.

The floor construction consists of a hardening substance, normally asphalt/concrete, which is made-up of two layers, and a stone-mix layer on top of a layer of waterproof foil.  The foil is placed on a sand layer. The polluted (rain) water from the site is captured and treated in a water purification installation. As far as unpolluted rain water is concerned, please refer to the BBT study for the re-use, buffering, infiltration and evaporation of rain water. Paving also prevents polluted ground mixing with the soil.

As far as noise is concerned, a distinction can be made between so-called ‘normal noise sources’ that are present in all soil cleaning installations, and noise sources from specific installations such as thermal soil cleaning installations, sieving, wet soil cleaning installations and biological plant.

Normal noise sources are:

  • Lorries for transport and disposal
  • Lorries on the weigh-bridge.
  • Washing of lorries.


Technique 1: Physico-chemical cleaning (soil washing)

When the soil that needs treating is mixed with water - in intensive scrubbing, for example – this may lead to aerosols.  In areas of the installation where this risk is applicable, the air is sucked-in and passed through active carbon or compost filters.

In wet cleaning, odour emissions could be released during transport, storage and pre-treatment (sieving). After pre-treatment, the material that needs cleaning is put into a water phase. The result of this is that the release of odour from the to-be-cleaned material is greatly limited. The residue from wet soil cleaning installations has (when pollutants are concentrated) a strong odour potential, depending on the polluted substance.

The water environment is burdened as a result of cleaned water being discharged. Drift of substances from the location to the surface water - when it is close to the soil cleaning installation - plays a minimal role because drift is prevented by covering polluted ground with sheets and by moistening uncovered sections with water.

Finally, the following also needs to be considered. The quantity of rain water that is present in a plant is determined by the hardened surface, and in most cases forms the majority of the effluent quantity that is finally discharged. This is normally calculated on the basis of an annual net discharge quantity of 750 mm. It must be noted that this stream is not equally/consistently released and cannot be influenced. In wet years, more water will be released than in dry years. Rain water that falls on covered site areas is not polluted, thus the water that can be polluted is reduced. One should consider the fact that it is not the intention to discharge polluted rain water that is diluted by unpolluted rain water. As far as unpolluted rainwater is concerned, please refer once again to the BBT study for the re-use, buffering, infiltration and evaporation of rain water.

Process-water can also be cleaned with an active carbon filter, after which it can be re-used. Due to neutralisation, the salt content in process-water can rise and must be partly discharged.  Process-water can also be biologically purified (bacteria + active carbon filter).


Technique 2: Biological remediation

A report by VITO (report nr. 2002/MIT/R/222) established the following volatilisation percentages for polluting substances during the turning and sieving of soil.

  • During sieving of soil:
  • 80 – 83 % for benzene
  • 21 – 80 % for toluene
  • 29 – 66 % for ethylbenzene
  • 6 – 15 % for xylenes
  • In the turning process, volatilisation percentages are estimated to be greaterr than 50% for benzene, toluene and ethylbenzene and less than 40% for xylenes.

In case of intensive biological cleaning, (heated) air is passed through the soil that is to be treated. This air allows polluted substances to be transported. This concerns relatively volatile hydrocarbons. The following measures can be taken to prevent air pollution (Vito report nr. 2002/MIT/R/222).

  • The biological remediation of soils indoors, which also has an impact on the prevention of waste water pollution.
  • The placement of doors between the various halls in order to keep uncontrolled emissions to a minimum.
  • Passing air that is sucked from the halls, through an active carbon filter or compost filter.
  • Soil air extraction via air drains in static bio-piles.

In biological cleaning, odour emissions could be released during transport, storage and pre-treatment. Another source of odour can be the air that is blown through polluted soil. A compost filter (and, if this is insufficient, an active carbon filter) is also a limiting solution for odorous substances.

In biological soil remediation, a system is established for the containment of percolation water. Further discharge of waste water is the result of excess residue, which needs to be disposed of. Considering that foil is implemented in biological soil remediation to protect ground-water, excess rain water cannot run off into the soil, and is transported away via drains. The water can be re-circulated or, eventually after purification, be disposed of.  In the first instance, one should consider the possibility of re-use and re-infiltration. Thereafter, the possibility of discharging on surface water can be examined - where diluted waste water is concerned – and then the final option is to discharge into the sewer. In a closed system, where foil has been placed over the fields, no precipitation falls on the fields and gathered rain water is not polluted.

The noise sources for biological installations are:

  • Shovel(s) used for loading;
  • Transport belts and magnetic belt during pre-treatment.
  • Sieve installation pre-treatment:
  • Tilling machine(s)
  • Emission walls and roof of the hall (in intensive and very intensive land-farming).

With exception of the unnatural soil substances which are separated during pre-treatment, no waste products are formed in biological soil remediation.

The energy use in extensive biological soil remediation is very low. In more intensive biological remediation, tilling takes place at set times. In intensive methods, additional energy is needed for blowing air and heating the soil parcel. Because temperatures are low (circa 30°C), the quantity of energy needed is also relatively low.

Considering the low temperatures, it is possible to use the surplus warmth for heating. This can be surplus warmth from other processes, as well as the plant. An example of this is the combination between the supply of electricity and heating.


Technique 3: Thermal cleansing

The following subjects are of specific importance to thermal soil cleansing:

  • Dust and chimney emission
  • NOx
  • SO2
  • HCl
  • Heavy metals, including mercury
  • Dioxins
  • Other compounds

The various pollutants are examined in the paragraphs below, with regards to possible remediation techniques and attainable emission values, and are divided into mobile and stationary thermal soil purification installations, if relevant.



The emission of dust is proportionate to the quantity of smoke gases. The quantity of emitted dust is (very) low in comparison to dust that is spread as a result of transport, storage and sieving.

The de-dusting of effluent gases from thermal installations (mobile and stationary) takes place in two phases; the removal of large particles in a cyclone (prior to desorption phase) and the removal of fine particles via fabric filters that have a maximum permeability of 10 mg/Nm³.

The investment costs for a cyclone amount to 500 to 1500 euros per 1000 m³/h. The operational costs are predominantly determined by energy costs, at 160 to 970 euros per year per 1000 m³/h. In addition, there are low personnel costs and low costs for the disposal of residual substances.

Investment costs for fabric filters lie between 1000 and 13.000 euros - depending on the capacity and the design of the housing - and between 500 and 700 euros for filter material that has a capacity of 1.000 m³/h. The cost price of a fabric filter can vary depending on the type, used material etc. Operational costs amount to approximately 0.2 to 1.5 euro/m³/h. The energy use (excl. ventilator) varies between 0.2 and 2 kWh per 1000 m³. Other operational costs are for personnel, maintenance and disposal of flue dust. The main maintenance costs relate to the replacement of the filter fabric, which typically has a life-span of 5 years (, Lemmens B. et al, 2004).



When NOx is emitted, a distinction can be made between thermal, fuel and material NOx.   The former is present at high temperatures, whereby N2 undergoes certain reactions in the air.   Fuel NOx is present in the burning of oil or gas.  Further, NOx can be formed (as ‘mineral’ NOx) during the oxidation of (from polluted soil) saturated nitrogen compounds (like cyanides). Emissions derived from thermal cleaning installations amount to circa 200 mg/Nm³ (see table below).


Other compounds: SO2, HCl, heavy metals, dioxins

The emission of SO2 is almost entirely derived from the polluted ground source. When fuel with high sulphur content is used, such as waste oil, the concentration of SO2 in the gases for smoke gas (mainly injection chalk) remediation will increase. The emission of all smoke gas remediation installations on stationary thermal installations is lower than 40 mg SO2 /Nm³.

SO2 emissions originating from mobile installations are included in the table below.

In thermal soil cleansing, HCI is present in the destruction of halogenated compounds. The quantity supplied to smoke gas cleansing installations is thus entirely determined by pollution level in the treated soil. HCI is relatively easy to contain in dry smoke gas cleansing installations (injection chalk). The emission level of 10 mg/Nm³ is almost never exceeded.

The emission of heavy metals almost entirely concerns metals that are bonded to the emitted material. Because dust emission is low, (< 10 mg/Nm³), emission is also low.

Mercury may be present is smoke gases in the form of moisture. Smoke gas remediation installations must be specially adjusted for the containment of mercury. If this is the case, 50 µg/Nm³ is attainable. If this has not been done, one must set limits on the mercury content present in the to-be-treated soil.

Smoke gases from after-burning installations, in thermal soil purification installations, have a relatively low dioxin content if the soil has been cleaned with halogenated hydrocarbons. The smoke gas installations that are currently present within the company have shown that they are able to attain the norm of 0,1 ng TEQ.

Besides the already stated components, the smoke gases will also contain CO, CO2 and water. Carbon monoxide will only be encountered in quantities which exceed 50 mg/Nm³, if oxidation within the installation isn’t effective.

For the removal of harmful burning components such as mercury, heavy metals, dioxins, furanes, polyaromatic and chlorinated hydrocarbons, active carbon (in powder form) is - potentially in combination with other chemicals like lime - injected into the smoke gas.  The active carbon adsorbs these components and thus makes the smoke gases free of harmful and toxic substances.

The loaded active carbon is re-transported to the furnace. Here the active carbon or brown coal cokes are burnt along with adsorbed particles likes dioxins, dust, metals and TOC.


Mobile filters

Figure : Mobile filter for air (


These mobile filters are used for in-situ applications, temporary projects…Under normal circumstances these mobile filters are used on a rental basis and are filled with suitable active carbon - as the application requires.


Fixed Filters

These filters are used if mobile filters are not applicable, for example, in long-term projects, projects with low-level carbon replacement, projects where carbon is easy to replace…Each filter is filled with the suitable active carbon, which is selected per application.

Figure: Fixed filter for air (


Few studies are available that outline the cost framework for thermal installations. The figures that are stated below are derived from OVB (2004).

Table:  Overview of costs for use of active carbon filtration (cap. 1000 Nm³/u)





250-500 per month


1 kW (heater)

Support aids

ca. € 2.5 to 3.5 per kg active carbon


Besides adsorption with active carbon, absorption techniques can also be used to neutralise gaseous effluents. A gas washer is a remediation installation where a gas stream is brought into intensive contact with a liquid, with the aim of transferring particular gas components from the gas to liquid.

Investment costs for a scrubber vary from 2000 to 30.000 euros for 1000 Nm³/h (recirculation washer with pump). The operational costs amount to ca. 5000 euros per year. The use of support substances is determined by the in-flowing concentration and the set residue emission (Lemmens B. et al, 2004).

As a practical example of this, an emission reading can be taken by VITO in the furnace of the mobile thermal installation; during the treatment of mineral oils and with soil polluted by PCB’s. The most important measured results are contained in the table below.

Table: Measured results from emission readings at a mobile thermal installation for the treatment of soil polluted by mineral oils; per column average values over 1 day (Vito report nr.   2002/MIT/R/222)



Mobile thermal soil remediation installations

Water content in %

O2 in %

CO2 in %

NO in mg/Nm³dr

NO in mg/Nm³dr

NOx as mg NO2/Nm³dr

CO in mg/Nm³dr

SO2 in mg/Nm³dr

Hydrocarb. in mg C/Nm³dr




























Dust in mg/Nm³dr




HCI in mg/Nm³dr




HF in mg/Nm³

< 0,3

< 0,3

< 0,3



Table: Measured results from emission readings at a mobile thermal installation for the treatment of soil polluted byPCB’s; average values over 1 day (Vito report nr.   2002/MIT/R/119)




Mobile thermal soil remediation installations

Water content in %

O2 in %

CO2 in %

NO in mg/Nm³dr

NO in mg/Nm³dr

NOx as mg NO2/Nm³dr

CO in mg/Nm³dr

SO2 in mg/Nm³dr

Hydrocarb. in mg C/Nm³dr





< 2





Dust in mg/Nm³dr

measurement 1

measurement 2




HCI in mg/Nm³dr

measurement 1

measurement 2




HF in mg/Nm³

measurement 1

measurement 2


< 0,4

< 0,4

HCN in mg/Nm³

measurement 1

measurement 2





in ng/Nm³dr

in ng TEQ/Nm³dr






The added soil can be polluted in a manner that causes an odour to be released. This odour is sometimes unpleasant.  In thermal soil remediation, possible odour emissions are only caused as a result of transport, storage and pre-treatment of the soil. Once the material has been inputted into the soil remediation installation, there will be no odour emissions. The high temperature that is present, as well as the seal on the barrel(s), ensures an 'odour-free' process. At high temperatures, odour components are broken down into non-odorous components. 

Emissions via waste water rarely play a role in thermal soil remediation techniques if suitable measures are taken. Water that is released in thermal remediation can be sub-divided into precipitation, condensation water, drainage water and wash water from wet washing. Precipitation may possibly be polluted due to contact with the terrain, and pollutants may also be left behind in condensation water.  Precipitation, condensation water, drainage water and wash water can be contained in storage tanks and be purified in an internal remediation installation. This takes place with the help of an oil separator, a sand filter, a carbon filter and flotation. In hot waste water, the heat can be retained before it is cleansed. Thereafter, the water can be re-used; it can be used to cool and moisturise the soil or it can be disposed of. Infiltration of ground water can be prevented by implementing HDPE foil.

Regardless of general noise sources in soil remediation installations, the specific noise sources in thermal installations are:

  • Shovels used for loading;
  • Sieve installation pre-treatment:
  • Irradiation surfaces and roof of hall;
  • Chimney;
  • Chimney fan

Noise-reduction measures that can be implemented:

  • The use of quiet motors;
  • The use of dampers;
  • The use of noise insulation
  • The use of noise-reducing materials;;
  • The implementation of noise screens.

In thermal soil remediation, residue from the smoke gas remediation installation is released as waste. This residue consists of reaction products from acidic components with lime, active carbon with which polluted substances are adsorbed, and a small quantity of transported substance, which has not been released earlier in the process. The composition and variation make it essential for this waster product to be disposed of.

The energy use in thermal installations is relatively high; on average, (the equivalent of) 40 to 50 litres of fuel oil per tonne of cleaned oil. A large share of the energy required for heating soil to the desired temperature is required for the evaporation of water present in the soil. Further, considerable energy is also used by after-burners. The process in all soil cleansing installations is designed in such a way that efficient use is made of surplus process heat.  Besides thermal energy, there is also considerable use of electricity in thermal installations. Namely, a lot of capacity is used by ventilators required for the suction/cooling of the installation.