For a treatment of sewage sludge which contains high levels of chromium, direct melting method of dried sludge has been generally used. The direct melting treatment is usually operated under strong reduction atmosphere not to generate hexavalent chromium. However, hexavalent chromium is not stable under high temperature conditions, so high temperature melting is expected to result in preventing hexavalent chromium generation even not under reduction atmosphere. Heating experiments of sewage sludge were conducted to confirm influences of melting temperature on chromium behavior in slag under oxidation atmosphere. It was confirmed that hexavalent chromium elution from molten slag could be depressed with heating treatment at 1,400°C even under oxidation atmosphere.
