Sewage sludge is the final product of sludge digestion. After the fermentation process, there are various treatment steps to which the sewage sludge can be subjected to. Most of the wet sewage sludge (about 2 - 4% DM content) are treated in a dewatering and possibly an on site sludge drying before they are either used in a thermal recovery for energy or recycled in land reclamation or even in agriculture. However, the latter will be limited in the future due to tighter regulations.
Due to the limitation of the minable phosphorus deposits, it has been tried for some time to recover the phosphorus contained in the sewage sludge.


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