Abstract: A process and apparatus for treating dried sludge comprising organic material, inorganic material and heavy mertals. The process comprises indirectly heating the sludge in the absence of oxygen to a temperature of from 300.degree. to 550.degree. C. for volatilization of organic material and heating the residual char in the absence of oxygen to a temperature of from 750.degree. C. to 1000.degree. C. together with injecting steam for gasifying non volatile organic carbons in theresidual char, whereby the organic material in the sluge is converted into energy-containing products. The heavy metals remain in the ash as metal-sulfide complexes which are not soluble in acdidic water.