Abstract: A process for exploiting plastic wastes arising in the production or further processing or after use of the plastic, by, in a sewage treatment plant, comminuting the plastic wastes then mixing them with a sewage sludge to which organic flocculants are added with or without the addition of further amounts of finely divided coal and/or ash, if appropriate, modifying the surface properties of the plastic with binders in such a way that it binds better into the sludge, filtering the pretreated sludge mixture, where the plastic can assume the properties of a filtration aid, i.e. the filtering residue is reduced, incinerating the resulting filter cake, where the plastic assumes the function of an additional energy source and depositing the ash for example in a sanitary landfill or exploiting it.

Abstract: Sodium sulfate-containing residues are worked up by reducing the sulfate by a process in which the sulfate or a mixture or solution of the sulfate is thermally cleaved by adding oxygen, air or oxygen-enriched air at above 1000.degree. C., in particular above 1200.degree. C., under reducing conditions to give gaseous sulfides and oxides of sulfur as well as alkaline slag. The sulfur compounds contained in the gaseous reaction products can be further processed to sulfur, sulfur dioxide and sulfuric acid.