The themal treatment plant has been specially designed and made in various parts of Europe by VSD Avenue, the contractor appointed by East Midlands Development Agency (emda) to carry out the remediation. VSD Avenue is a consortium of VolkerStevin (the UK based civil engineering company), Sita Remediation (the Dutch thermal treatment specialist) and DEC (the Belgian based environmental contractor).  The thermal plant itself will include a 30 metre high chimney, the plant will take six months to construct, and – once fully operational in October – will run 24 hours a day, seven days a week for around two and a half years in order to remediate the most heavily contaminated soil on site (around 500,000 tonnes).

"Thermal desorption is a technique that uses high levels of heat to break down the hydrocarbons in the soil," said project director Marcus Foweather. The process will treat the most heavily hydrocarbon contaminated materials on the site, which will be loaded onto a conveyor belt and transported into a gas-fired kiln which will heat the soil to over 500°C, causing hydrocarbons to vapourise. The vapour will then be heated to over 1000°C and quickly cooled, before being passed through a 'bag house' to remove airborne particles. The gases will then be treated to remove other potentially harmful contaminants. Other pieces of plant are arriving on site for the sorting of the waste tip and the site will also be using a soil washing process (and a bespoke water treatment plant).

Remediation of the 98ha site will involve the excavation of over two million cubic metres of material, including the clean up of two silt lagoons, a registered asbestos-containing waste tip and ground pollution caused by heavy metals and waste chemicals. Almost all of the treated material will be reused on the site as part of a commitment to sustainable regeneration.

emda said: "Cleaning up the site will be one of largest applications of new remediation technologies in Europe and will place the Avenue project at the leading edge of sustainable brownfield regeneration."

Foweather says "The reason why we are using specialists from Europe is that British industry hasn't built one of these thermal treatment plants before and I don't think it would be good practice on a 'flagship' site like this to employ a company to build such a complex plant that hadn't done so before. The companies we're using are used to building this kind of plant, which is a bespoke piece of machinery specifically designed to treat the contaminants that exist on this site and the levels they exist at. With the calorific value and moisture content which this material has, the thermal treatment plant specifically needed to be able to cope with a relatively high moisture content, between 45 and 50%. The plant is unusual in that it has a 23 metre long, 65 tonne rotating kiln, with the first 14 metres of it being indirectly heated, the then the remainder is direct fired by natural gas. The indirectly heated part of the kiln  is a more gentle heat, which is mainly responsible for driving off moisture, like a pre-dryer, before the rest of the kiln does its work."

While there are other contaminants present, such as heavy metals, hydrocarbons are by far the biggest problem, meaning thermal desorption was the only real option, despite its high energy use.

Foweather explains "It is a particularly energy intensive technology, and obviously we will direct as much contaminated material as we can away from this energy intensive system, and will use less energy intensive solutions where possible.  Thermal desorption is the last resort, but it is the only treatment process we are aware of for a site so highly contaminated with hydrocarbons."

Some use of bioremediation, in the form of covered windrows, will take place. Foweather said: "We're also employing bioremediation on the site, which is obviously less energy intensive and cheaper, but bioremediation only treats contaminated material at much lower contamination levels, where micro-organisms can exist to degrade the hydrocarbon chains."

Full carbon footprinting and analysis of the options available was carried out in order to minimise energy use. Foweather said: "We are recirculating heat wherever possible in the thermal treatment plant and minimising the amount of energy which is lost or wasted wherever this is economically viable.  The site also benefits from using 100% green electricity which is generated by green and sustainable technologies"

The whole project will take approximately four and a half years to clean up 98 ha site, which was previously occupied by a coke works, colliery, power station, lime works and other industrial processes at various times.

Foweather said: "We're here to clean up the historic legacy of industrial contamination of the past and will be proud to be able to provide a green and pleasant space for people to use in the future when we complete all of the remediation and landscaping works."

Marcus Foweather, CEnv MICE