CLAIRE demos sustainable remediation

CLAIRE (Contaminated Land: Applications In Real Environments) is a public/private partnership, which was established in March 1999, to encourage research, practical demonstrations, and applications of remediation technologies to clean up contaminated land, including innovative methods for site characterisation and monitoring. Demonstrations are carried out on actual contaminated sites as CLAIRE Chief Executive Paul Beck explains.

A large number of researchers and technology developers have expressed an interest in participating in CLAIRE as project operators. Technologies that have been put forward as potential projects include: bioremediation; permeable barrier wall; thermal desorption; phytoremediation; wetlands; solidification and stabilisation; vitrification, electrokinesis; soil washing; natural attenuation; novel ways of characterising contaminated sites and the development of field instrumentation to measure contaminant concentrations in real time.

CLAIRE has completed its first technology demonstration project which involved a field trial in which 40 tonnes of hydrocarbon contaminated soil were treated using low temperature thermal desorption (LTTD). Technology. The CLAIRE technical report is currently being written.

CLAIRE currently has approval for its second technology demonstration project that involves soil washing at a former gas works. This project will be written up as a CLAIRE technical report shortly. CLAIRE expects to have five projects signed up by the end of 2000 and an additional ten projects by the end of year 2001.

Case study – low temperature thermal desorption

BP Amoco and British Aerospace (BAe) Systems provided CLAIRE with its first demonstration project. This involved a field scale trial of low temperature thermal desorption (LTTD) technology carried out on 40 tonnes of hydrocarbon contaminated soil. The trial examined the feasibility of applying LTTD to full scale clean-up. The redevelopment of a former storage tank site prompted the need to review the viability of remedial techniques. The soil is primarily fine to medium grained sand, and this, together with the volatile nature of the organic contaminants make an LTTD technique suitable.

The trial was designed to assess the remediation method effectiveness and costs, to help develop the necessary operational controls, and to collect initial environmental impact data to aid early discussions with the Environment Agency on licensing issues.

The most heavily contaminated area was selected for the trial. This also provided the opportunity to assess the recovery potential of the mobile portion of the hydrocarbon.

Excavation of contaminated material

The remediation trial required some 40 tonnes of contaminated material with a mean organic concentration no greater than 3% by weight. To provide this parcel, a pit measuring 4 metres x 3 metres x 2 metres depth was dug. Hand tools were used due to the presence of liquid hydrocarbons and the inherent flammability risk. An exclusion zone extending 8 metres around the excavation was created.

During the excavation aromatic contamination was encountered within 0.3 metres of the surface and liquid hydrocarbons at 1.3 metres. The liquids seeping into the excavation were removed using porous probes situated at the perimeter of the pit and a diesel driven pumping unit. The contamination material from the pit was stored in four metal skips situated in the exclusion zone. The contaminated sand was delivered to BAe System’s Chorley facility. Twelve composite samples were taken and analysed. The total hydrocarbon content varied between 1.36 and 4.33%, with a mean value of 2.17%. Four batches of contaminated material were prepared with hydrocarbon concentrations of 0.25, 0.5, 1.0 and 2.0%. Each of these were desorbed at temperatures between 200 and 300°C.

With the exception of the 2% material, they were all successfully treated at feedrates close to the LTTD unit maximum design capacity of 22/te/hour. The 2% material caused high temperatures (>950°C) in the off-gas oxidiser within operating temperature.

The removal of benzene was satisfactory at all of the trial temperatures, with residual concentrations >1mg/kg. However, to maintain a suitable operating margin, desorption temperatures in the range 250 to 300°C are recommended.

CLAIRE is looking for additional sites on which to carry out technology demonstrations and research.

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