Evaluation of low temperature thermal desorption as a treatment option for hydrocarbon contaminated soils

A low temperature thermal desorption (LTTD) system is to be used to treat hydrocarbon impacted soils at a 2.5ha site in southwest London. Concentrations of PAH and TPH of up to 17,400mg/kg and 38,570mg/kg respectively are present within the predominantly clay Made Ground. Japanese Knotweed is also present across the site.

It is proposed to develop the site for mixed residential and commercial use. The scheme comprises multi-storey apartment units set in open landscaping and commercial, amenity and leisure units.

The remediation will be carried out under a Mobile Plant Licence. Subject to required site levels, the soils will be either excavated or treated in-situ. The soils will be mixed with hot air at a temperature of up to 450°C to desorb hydrocarbon compounds from the soil. Fragments of Japanese Knotweed within the soil will also be destroyed in this process. Volatilised compounds will be passed through a gas treatment system prior to discharge to atmosphere. Following treatment, the moisture content of the soils will be adjusted, where appropriate, prior to placement and/or re-compaction.

The technique is relatively rapid and it is anticipated that up to 5,000m3 of soil can be treated within a 2 to 3 month period. The costs relative to other commonly used treatment techniques are discussed. The system should be capable of achieving final soil concentrations of less than 500mg/kg (PAH) and less than 800mg/kg (TPH). As the system is able to destroy all parts of the Japanese Knotweed plant, in this context, it represents a quick and efficient method of controlling its spread.

• INTRODUCTION

• DESCRIPTION OF METHODOLOGY AND APPARATUS

• APPLICATIONS AND LIMITATIONS

• COST AND TIME COMPARISON

• RE-USE OF TREATED MATERIAL

• LICENSING ISSUES

• CONCLUSIONS

• REFERENCES