Leaching of heavy metals from municipal sewage sludge

Municipal sewage sludge from the wastewater treatment plant of Thessaloniki was examined for leaching of heavy metals using a standard leaching test and various extracting solutions. The parameters which affect leaching are: liquid to solid (L/S) ratio, contact time, pH, type of leaching agents, and particle size. For most values of L/S tested, the percentage of leached amounts for the examined metals followed the order Cd > Zn > Pb > Fe > Mn. As pH decreased, metal concentrations measured in the leachate increased. In general, EDTA showed the greatest mobilization ability, followed by NaOH, acid solutions (HCl, H3PO4), and water. Particle size distribution had negligible effect on Cd, Mn, and Pb leaching from sewage sludge. However, a decrease in the amount of Fe, Zn, and Cu leached was observed with increasing particle size. (C) 1998 Elsevier science Ltd.