Aaby Wastewater Treatment Plant in Aarhus extracts phosphorus from the wastewater.

In 2014, Aarhus Vand opened the first full scale demonstration plant to test the viability of renewable phosphate production in Denmark. In the long term, the plant will be able to extract 60 percent of the amount of phosphorus in the wastewater.

Aaby Wastewater Treatment Plant uses a simple technique to extract phosphorus from the wastewater and turn it into a valuable fertiliser. With it comes the added bonus that the challenges of clogged-up pipes in the sewage works have been considerably minimised. This, in turn, reduces the expenses of maintaining the sewage works.

In 2015, the water utility Herning Vand opened the largest phosphorus-recovery plant in Denmark, which recovers phosphorus from a concentrated side stream in the wastewater treatment plant.

At both plants, the struvite is precipitated as a ‘ready-to-use fertiliser’ and sold to a fertiliser company. An official approval of the product as commercial fertiliser has been obtained for the struvite produced at both the Aarhus and Herning plants under the name PhosphorCare™. The operational savings at the treatment plants and the expected revenue from sale of struvite is expected to result in a payback time of seven years.

Both plants are the result of a collaboration between a number of private and public partners. The partnership behind the project includes three Danish water utilities (Aarhus Vand, Herning Vand and Horsens Vand), Grundfos, Norconsult and the Danish Agricultural Advisory Service.

Recovering phosphorus has great potential
If similar systems were established at the 50 largest plants in Denmark, the country would be more or less self-sufficient in phosphorus. Phosphate is a finite resource with few global suppliers. With the world facing twin crises of excessive energy use and diminishing resources, the project is consistent with the Aarhus Vand corporate focus on sustainability.

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