Combined biological-chemical detoxification of organics

Abstract

A method is disclosed for the combined biological-chemical detoxification of municipal sewage sludge. A slurry of thickened primary sludge and secondary waste-activated sludge is fed to an enclosed insulated reactor vessel. The slurry is aerated with ambient air by a self-aspirating aerator to achieve autoheating of the slurry to thermophilic temperatures by the conservation of the metabolic heat of microbiological oxidation of the biodegradable organic material present in the slurry. The slurry is retained in the reactor for a period of time sufficient to destroy pathogenic bacteria and to increase the oxidation reduction potential of the biological reactor contents for the conversion of heavy metals to their desired oxidation state, following which the autoheated slurry is acidified to pH 1.0-3.0 for 6 to 12 hours to solubilize the heavy metals. Conventional dewatering techniques are used to separate the detoxified, acidic sludge and the acidic, heavy-metal-containing water. The sludge may be neutralized and reconditioned for safe land application and the metals can be recovered from the water using existing conventional techniques.