New technology extracts nitrogen from wastewater and puts it back on the fields

13. september 2022 kl. 06:06
Lynetten renseanlæg
Biofos and partners have high expectations for a new technology that recycles nitrogen from the waste water. Illustration: Michael Rothenborg.
Nitrogen recovery at the Lynetten wastewater treatment plant in Copenhagen reduces energy consumption and nitrous oxide emissions, while increasing capacity and promoting the circular economy. And apparently, it is no more expensive than conventional biological treatment.
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This article was originally published in Danish

For many years, there has been an increasing focus on extracting and recovering phosphorous from wastewater treatment plants—of course, in a way that makes it financially viable. 

But now, a new technology for nitrogen recovery from wastewater treatment plants may overtake the research focused on phosphorous and in time become an important part of the circular economy.

It is a technology that both recovers nitrogen, creates more capacity at the treatment plant, and reduces the emissions of nitrous oxide. A pilot plant supported by the EU’s LIFE program has just been inaugurated at Lynetten, one of the three wastewater treatment plants owned by Copenhagen wastewater utility BIOFOS.

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“Our process reduces ammoniacal nitrogen to a concentration of 10 mg/l, and we keep the nitrogen we remove in a form, ammonium sulphate, which can be used as fertilizer on agricultural land,” says Anna Lundbom, project manager for the LIFE RE-Fertitilize project.

The first consignment of 17 m3 of ammonium sulphate has been delivered to a Danish and a Swedish farmer, who will now test the product on their fields.

In other words, the nitrogen’s circular path goes from field to wastewater—and back to the field again. 

Solution to three major challenges

The pilot plant, which will take the technology from laboratory scale to industrial pilot scale, was invented by the Swedish company EasyMining. The project is a collaboration between EasyMining, BIOFOS, Lantmännen, and Ragn-Sells, which has had a smaller testing site at its waste facility in Högbytorp outside Stockholm.

The technology has been developed as an attempt to solve three of the major challenges in the biological removal of nitrogen, which has been used at Lynetten and numerous other wastewater treatment plants both in Denmark and globally for more than 25 years: 

It entails high energy consumption (at Lynetten approx. 25% of the total consumption), some nitrogen is lost to the atmosphere, and nitrous oxide emissions are generated during the process. 

Increased capacity for new inhabitants

The new pilot plant recovers more than 98% of the nitrogen in reject water from the dewatering of sewage sludge. No nitrous oxide emissions are generated, and the process is expected to be more energy-, resource- and cost-efficient than current processes.

“Removing ammoniacal nitrogen from the wastewater helps to increase the capacity of our treatment plant—which is important at a time when Copenhagen is growing by thousands of inhabitants annually. At the same time, the new process will improve our climate footprint, as the process does not generate nitrous oxide emissions—and it is also well in line with our goal of recovering wastewater resources and promoting a circular economy,” says Dines Thornberg, head of development at BIOFOS.

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The plant itself is machine-based, with tanks, centrifuges, and filters, which recover the nitrogen via chemical processes. The machines are built into two containers, which are placed on top of each other.

The initial capacity is approx. 10% of the reject water, and up to 100 kg of ammonium fertilizer can be produced per day. This will provide a 1:1 saving on that type of nitrogen fertilizer on the two farmers’ fields.

The pilot plant and the technology’s capacity are to be assessed after a trial period of two years. You can follow the project on EasyMining’s website.


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