a method for the separation of components of solid waste which has been treated by thermal explosive decompression followed by biodegradation is presented . the explosive decompression and composting pretreatment before separation presents a granular and inoffensive finely - divided product mixed with less - fragmented non - biodegradable materials such as plastic , metals and other substances . the method first separates the finely - divided product from the waste to leave a first residue , then magnetically separates any magnetic components from the first residue to leave a second residue , and then separates by gravity flotation any plastic components from the second residue , each step being carried out successively without interruption for further treatment of the waste . a system is described which separates the biodegradable and fine residues first , followed by the separation of other , more valuable components from each other at later stages of separation .