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Recovery of Phosphorus from Sewage Sludge

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Posted by Verena Menz on 27-10-2016 - Last updated on 27-10-2016

About two million tons of dry sludge mass accumulates each year in Germany, containing about 60,000 tons of phosphorus. Sewage sludge is thus a possible source for phosphorus recycling. With the DBU’s (Deutsche Bundesstiftung Umwelt) support, the chemical factory Budenheim KG, Budenheim, has developed a process by which phosphates can be separated from sewage sludge and thereby recovered.

 

Phosphorus is an essential “building block” for all living things. As a fundamental element in plant growth it is thus a major component of mineral plant fertilizers. In the environment, phosphorus usually appears as phosphate. About 85 % of all raw phosphates extracted go to the fertilizer market. Estimates of how long conventional deposits can continue to cover the demand for phosphates range between 300 and 400 years. However, phosphates are excreted by humans and animals, so that phosphates are also contained in farm manure and sewage sludge. About two million tons of dry sludge mass accumulates each year in Germany, containing about 60,000 tons of phosphorus. Sewage sludge is thus a possible source for phosphorus recycling.

With the DBU’s support, the chemical factory Budenheim KG, Budenheim, has developed a process by which phosphates can be separated from sewage sludge and thereby recovered. Carbon dioxide under increased pressure is introduced into the water-sludge mixture, is transformed into carbonic acid, reduces the pH-value and separates the phosphates from the sludge. The phosphates are then recovered in the form of calcium phosphate. The goal is to recycle in this manner up to 50 % of the phosphorus contained in the sludge.

Continuing to build on attempts at two testing facilities, the process will be further tested in 2016 with a pilot facility at the main sewage system in Mainz-Mombach. Current plans foresee using the recovered phosphates exclusively in agriculture. In previously executed plant experiments, the fertilizing effect of recycled fertilizers has been categorized as comparable to conventional phosphate fertilizers. To this extent phosphate recycling represents an efficient method of sparing natural phosphate reserves.

This project was funded by the Deutsche Bundesstiftung Umwelt (DBU). Read more: https://www.dbu.de/123artikel36812_2430.html

 

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