Initially, putrescent waste is deposited on a surface of a disposal volume which is partially composed of putrescent waste. A living system bio-converts at least a portion of the putrescent waste in the disposal volume, transforming the putrescent waste into waste residue. While bio-conversion is occurring on a portion of the putrescent waste in the disposal volume, waste residue is excavated from the disposal volume below the surface of the disposal volume. Because the excavation takes place below the surface area, the bio-conversion process is not affected by excavating the waste residue. A device for continuous bio-conversion of putrescent waste comprises a disposal track having lateral side walls and floor for containing the disposal volume. An excavation gap is associated with at least one of the lateral side walls for excavating waste material from the disposal volume. The excavation gap is positioned substantially below the living system so waste can be excavated simultaneously with bio-conversion. The device further employs a scraper for excavating at least a portion of the waste residue. The scraper has a plurality of blades attached to a chain for excavating the waste and interposed between the blades are backplates which clean the blades as the chain rounds a sprocket. The scraper is moved along the floor of the disposal track as it excavates the waste material. The floor both supports the disposal volume and the scraper, and has a filter screen to filter water from the disposal volume.