Eutrophication is a big word, and it represents a big problem. It occurs when rivers and lakes reach an overabundance of nutrients – most often from agricultural and water treatment practices. This overabundance of nutrients increases algae growth, setting off an ecosystem chain reaction that can have consequences for all plant and animal life.

To prevent eutrophication of freshwater systems, wastewater treatment plants must remove phosphorus from treated water. But phosphorus is a finite resource for which there is no known substitute. In fact, the United Nations predicts global demand for phosphorus will rise 70 percent by 2050. 

So instead of removing it, why not extract and reuse it? 


In 2013 the first full-scale demonstration phosphorous extraction plant was opened at Aaby Wastewater Treatment Plant in Denmark to test the viability of renewable phosphate recapture in the country.



The process is based on fluidized bed technology in which phosphorus and nitrogen are recovered from wastewater by directing the wastewater through a separate reactor. Here, magnesium salt and air are added. The resulting precipitation process refines the phosphorus, discarding heavy metals and environmentally unfriendly substances. 

The outcome is a granulate that contains phosphorus, nitrogen, and magnesium. The struvite is precipitated as a ‘ready-to-use fertilizer’ and sold to agriculture. 


In 2019, following the proven feasibility of the process, the largest phosphorus-recovery plant in the Nordic countries opened at Marselisborg Wastewater Treatment Plant in Aarhus, Denmark. The plant has the potential to utilize up to 30 percent of the phosphorus that enters the treatment plant.

An official approval of the product as commercial fertilizer has been obtained for the struvite produced at both plants under the name PhosphorCare. The phosphorus recovery and fertilizer production is an example of how the water industry can contribute to circular economy production.


Aarhus Vand worked with with pump manufacturer Grundfos, technical consultant, Norconsult, Herning Vand and Danish Agricultural Advisory Service in finding a solution for the phosphorus extraction process.