What is it about?

Superphosphate fertilisers, which are necessary for agricultural production, are made by mixing mined rock phosphate with sulfuric acid. As rock phosphate reserves are depleting, it is necessary to find other substrates for the prodcution of fertilisers. These can be found in human settlements, where phosphate is recovered in waste water streams. When sewage sludge is incinerated, phosphate-rich ash remains. This ash might be added to the fertiliser production stream, thereby reducing the need for rock phosphate.

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Why is it important?

It is necessary to close the human nutrient cycle by returning nutrients from human settlements to agricultural productions systems as effectively as possible!

Perspectives

There remains some work to be done. Other than phsophate, sewage sludge ash also contains other elements, such as heavy metals, which may be harmful to the agricultural enviroment when certain threshhold values are exceeded. The accumulation of these elements in sewage sludge ash therefore needs to be decreased.

Tobias Edward Hartmann
Universitat Hohenheim

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This page is a summary of: Partial replacement of rock phosphate by sewage sludge ash for the production of superphosphate fertilizers, Journal of Plant Nutrition and Soil Science, February 2020, Wiley, DOI: 10.1002/jpln.201900085.
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