EFFECTS OF THERMAL AND ACID TREATMENT ON THE DISTRIBUTION OF HEAVY-METALS IN SEWAGE-SLUDGE

Anaerobically treated sludge from a wastewater treatment plant (Psitta lia) was found to contain significant amounts of metals (Cr, Cu, Fe, N i, Pb and Zn). The sludge samples were subjected to thermal drying at 105 degrees C and acid treatment was applied before and after thermal drying. Different acid concentrations and contact times were used in o rder to find the combination that caused the highest metal removal. Th e metal distribution in raw sewage and in thermally dried sludge as we ll as the chemical forms of the remaining metal load after acid treatm ent were determined by the application of a sequential chemical extrac tion procedure. It was found that thermal drying causes a shift of the metal content to more stable phases. A sufficient metal amount was re moved by acid treatment and the remaining metal content was further st abilized.