EVALUATION OF THE TOXIC CONTENT OF SLUDGES PRODUCED DURING THE BIOLOGICAL TREATMENT OF MUNICIPAL AND INDUSTRIAL-WASTE WATERS

Sewage sludge was periodically sampled from one municipal and one indu strial wastewater treatment plant in Thessaloniki, N. Greece, to deter mine toxic elemental content, as well as seasonal variation. Higher co ncentrations of As, Cd, Cr, Cu, Hg, Pb, Mn, Zn and Fe were found in th e municipal sludge. The application of the US EPA Extraction Procedure of Toxicity showed that both sludges can be characterized as not toxi c. Metal leachability was highest from the industrial sludge, which ha s not subjected to digestion. Leachability of most metals from both sl udge types increased under sludge codisposal with either an acidic (gy psum solid waste) or an alkaline material (dolomite). However, in all cases, sludge mixtures were not toxic according to the criteria set by the US EPA for landfilling.