Diffused old contamination was found in sandy/silty soils coming from an industrial site where lubricating oils additives are now produced. The oil contained predominantly branched alkyl benzene and naphthalene derivatives, with hot spots having concentrations up to 7,000 mg/kg. The site is critical from an environmental viewpoint, because it is near a river and the groundwater level is very close to ground surface (-3 m). On the basis of laboratory and pilot scale experimental results the following scheme of an integrated treatment of heavily contaminated soils has been designed: 1. physical (multi gravity) separation of a suitable soil/water mixture, to remove the coarse fraction from a slurry, leaving the finest part of the soil (about 20 % of the total matter), containing more than 80 % of the contaminants 2. forwarding the slurry to the wastewater treatment plant of the factory where the active sludge microbial population is able to degrade the contaminants 3. bioremediation of the coarse fraction of the soil that continues to exceed regulatory limits, by landfarming.
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