Design of a solvent extraction process for PAH-contaminated sediments: The WAU-acetone process

Solvent extraction is one of the possibilities to clean-up polluted sediments. It is especially attractive when the sediment mainly consists of clay particles polluted with contaminants which are not, or not easily, biodegradable. Using acetone as extracting agent the extraction process has been investigated at laboratory scale for treating sediment of the Petroleum Harbour in Amsterdam. This sediment is characterised by a substantial percentage of particles with diameter < 63 mu m, a high percentage of organic matter (about 12% on dry matter basis), a high concentration of PAH (500-2,000 mg total EPA-PAH per kg dry matter) and a high concentration of mineral oil (6,000-10,000 mg/kg dry matter). Based on the laboratory scale experiments a process design has been made of a complete solvent-extraction process with acetone. The main process steps in this design consist of a countercurrent flow extractor, a separator for the sediment, a post-treatment step to remove residual acetone from the sediment, a distillation column to recover the acetone for reuse and to concentrate the pollutants and a polishing step for the water to be discharged. The sediment treatment costs with this system are estimated at 115 NGL per tonne dry matter to be treated.