While composting of separate collected bio-waste is currently undergoing a renaissance in Germany, sewage sludge composting offers as well the possibility to produce a hygienic soil conditioner and/or secondary raw material fertilizer. This alternative is increasingly interesting, especially to bring back nutrients and organic substances into soils. This paper explains the essential reasons for composting, shows the process conditions and the different composting processes used currently in Germany. The discussion about the heavy metal problem and the production of a high quality fair marketable product leads to the necessity of a quality assurance system, which has been proven to be effective for bio-waste composting in Germany. The necessary boundary conditions and demands for such a quality assurance system for sewage sludge are presented.

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