ATHOS: A Novel Process for Sludge Disposal

Whenever beneficial use of biosolids becomes impossible due for instance to heavy metals levels exceeding regulations, sludge becomes a waste which has to be eliminated in an effective and acceptable manner. The destruction of the organic matter of sludge is achieved either by incineration or by wet oxidation, which needs no fuel and generates minimal air pollution problems. The main features of the wet oxidation process are presented in the first section of this paper, followed by the results obtained by Anjou Recherche during the development of an improved process specifically tailored for sludge treatment. Sludge treatment at a temperature of 235 °C and a pressure of 40 bar results in 75 % COD abatement, with 70% removal of organic and ammonia nitrogen and almost total ash mineralisation. The ATHOS demonstration unit which came into operation during the 2nd quarter of 1998 is described.