The use of municipal sewage sludge for the stabilization of soil contaminated by mining activities

The ability of municipal sewage sludge to immobilize Pb, Zn and Cd containe d in contaminated soil originating from a former mining area in Lavrion, Gr eece was investigated. The soil was cured with sewage sludge in various pro portions. The stabilization was evaluated primarily by applying chemical te sts and complemented by the performance of additional biological tests. App lication of the U.S. EPA Toxicity Characteristic Leaching Procedure (TCLP) on the stabilized mixtures proved that Pb, Zn and Cd solubility was reduced by 84%, 64% and 76%, respectively, at 15% w/w sludge addition, while a 10% w/w addition was sufficient to reduce Pb solubility below the U.S, EPA TCL P regulatory limit. The results of the extraction using EDTA solution showe d the same trend, resulting in 26%, 36% and 53% reduction in the Pb, Zn and Cd extractable fractions, respectively. Speciation analysis of the treated soils revealed a significant decrease in the mobile fractions of heavy met als, which was attributed to their retention in sewage sludge by adsorption and organic complexation mechanisms. For the assessment of possible phytot oxicity, experiments including growing dwarf brans in the treated soil was carried out. It was Found that sewage sludge addition had a positive effect on plant growth. Furthermore, the Pb and Zn uptake of plant leaves and roo ts was reduced, while Cd uptake was unaffected by the sludge treatment. The results of this study support the hypothesis that municipal sewage sludge is a potential effective stabilizing agent for contaminated soil containing Pb, Zn and Cd. (C) 2000 Elsevier Science B.V. All rights reserved.