The anaerobic sludge digester is used for the sludge treatment when it is necessary to obtain the anaerobic biological decomposition of the organic matters contained in the sludge, according to a mineralization, humidification and gasification process. The digester consists of a cylindrical concrete tank; on request, the digesters can be of small size, prefabricated in steel, for which the supply includes the piping for sludge inflow, extraction and handling, excess water and biological gas, moisture separator, grit filter and ceramic filter, sludge extraction telescopic valves, overflow and extraction of excess water valves, biogas compressor and any measuring and control equipment required for the good digester operation.