Recovery of phosphorus from sewage sludge is desirable from a sustainability point of view, but there are important questions around cost, especially if it is to be applied on a wide scale. Keith Hayward heard from Erik Bundgaard, Vice President and Director of Technology at Veolia group company Krüger, about the new Struvia process and how it has been designed as a practical option with the cost of phosphorus recovery in mind.
The current growing interest in Denmark in recovering phosphorus from sewage sludge is driven mainly by a desire to move towards resource recovery and achieve a circular economy. ‘It is done for being the right thing for the environment and for us [the people]. That is the driver here in our country,’ says Erik Bundgaard, Vice President and Director of Technology at Veolia group company Krüger.
Denmark has regulations relating, for example, to use of sewage sludge on land, but there are not currently specific requirements to recover phosphorus. Municipalities are however increasingly aware that phosphorus is a limited resource and that recovering it provides an opportunity to better control its reuse in agriculture. ‘So some municipalities in Denmark have looked into phosphorus recovery because they want to be involved in this resource recovery and show that the community is working towards something that is to the benefit of everybody,’ says Bundgaard.
The Struvia solution for Helsingor
Against this backdrop, the first full scale municipal installation of Veolia’s new Struvia process was commissioned last year at the main wastewater treatment plant of the Danish city of Helsingor.
Building on pilot work at Brussels North wastewater plant in Belgium and the Braunschweig plant in Germany, the process provides a means of recovering phosphorus in the form of struvite, which can in turn be used as a fertiliser in agriculture. Struvite is formed by increasing the pH and adding a magnesium salt to the reject water from sludge digestion, converting dissolved phosphate into struvite – magnesium ammonium phosphate. The Struvia process combines a Turbomix reactor with a lamellar settler, and the precipitated struvite prills are separated off and drained in bags.
- Denmark, Veolia, Kruger, municipal wastewater, resource recovery, phosphates