Land Contamination: Technical Guidance on Special Sites: Acid Tar ...

Box 6.1 Example of Remediation of Acid Tar Sludge by DCR Treatment(Grajczak, 1995)Acid tar sludge from the former Sinclair refinery site in Texas (a Superfundsite) was treated by the DCR process using a specially commissionedtransportable treatment unit handling 180 US tons/hour. 137,000 cubic yardsof waste (about 100,000 cubic yards of which was classified as acid tar) wastreated in total. The stabilised waste was then disposed of in a landfillconstructed on site to legislative standards. The treatment technology initiallyspecified was incineration unless it could be proven that a solidificationtechnology would be as effective. As site characterisation showed thatneutralisation would be required to reduce sulphur dioxide emissions, thisprompted detailed study of solidification/stabilisation technologies as analternative to incineration.Most of the waste, particularly that deeper in the pits, was in the form of slowflowing, viscous tar. Bench scale trials were conducted by vendors againstestablished treatment goals (expressed in terms of parameters such ascompressive strength, liquid release, and leach testing). Followingexamination of these and evaluation of tenders, a tender based on the DCRprocess was selected. The treatment unit comprised a waste crusher/feedsystem, a reagent feed system, an emissions control system and two paralleltreatment trains (hoppers, mixer, reaction chamber). Emission control wasrequired as the initial reaction is exothermic and dust and VOCs needed to becaptured and treated for a minimum of 30 minutes following waste-reagentmixing. This comprised a hydrostatic precipitator for dust, a packed spraytower and activated carbon for organic vapours.The material produced was described as homogeneous, dry, free-flowing, easyto transport and readily compacted in the landfill. It is similar to natural claysbut without the affinity for water. The period from conceptual engineering tostart-up was 12 months and the treatment period was 13 months. The projectwas reported by the above author to have been concluded successfully.Other Processes• Other processes include several involving solidification, similar to those used for thesolidification of sewage sludge;• two processes have been piloted in Germany with some success, one of whichproduced a solid concrete-like material and another produced a powder. However,certain problems were encountered, most notably the need for large quantities ofbulking material (580 kg were needed to solidify 25 kg of acid tar). This could lead todisposal problems due to the large amount of space required.R&D <strong>Technical</strong> Report P5-042/TR/04 37