Islevbro Waterworks in Copenhagen. Photo: Philip J. Binning

One step closer to restoring nitrogen balance

Tuesday 11 Oct 16


Barth F. Smets
DTU Environment
+45 45 25 22 30

Rapid gravity sand filters

Rapid gravity sand filters are designed microbial systems used worldwide for the production of drinking water from surface- and groundwater. Sand filtration—often via two serial filters—is sometimes the only treatment groundwater receives before distribution through the drinking water network.


  • VILLUM FONDEN is a non-profit foundation which supports technical and scientific research, environmental, social and cultural activities in Denmark and abroad.
  • In 2015, VILLUM FONDEN donated DKK 608 million to non-profit purposes.
  • VILLUM FONDEN was founded in 1971 by Villum Kann Rasmussen, MSc Eng, who developed the modern skylight VELUX® and established the VKR Group in which VILLUM FONDEN is the majority shareholder.
The discovery of a new, previously unknown microbe opens up a host of opportunities, both in relation to restoring the nitrogen balance in nature—which has been knocked off kilter over the past century—and with regard to purification processes for drinking water and waste water.

Earlier this year, Professor Barth F. Smets from DTU Environment announced the sensational discovery of a new microbe. He has now received DKK 5 million from VILLUM FONDEN to research into what the discovery of this microbe actually means in relation to the nitrogen cycle, where ammonium and ammonia are converted into nitrates.

“Greater understanding of, and insight into, the nitrification process will redefine our opportunities to contribute to restoring the nitrogen balance in nature—an area where the current imbalance is attributable to 100 years of fertilization in agriculture. This imbalance is actually one of the greatest threats to the climate, and to our health. Excessive levels of nitrogen in the water environment boosts the growth of algae, leading to elevated fish mortality. Moreover, too many nitrates in the drinking water may have a carcinogenic effect,” explains Professor Barth F. Smets.

Rewriting the textbooks
For the past century, all textbooks have explained that the process of nitrification was largely attributable to two different and specialized groups of microorganisms, each responsible for its own share of the process. However, working closely with his colleagues at DTU, Professor Smets has now discovered a third, previously unknown microbe that may be solely responsible for the entire process of converting ammonia into nitrates.It is without doubt one of the most significant microbial discoveries of recent times.

“It opens up completely new perspectives. That said, we don’t know all that much about the new microorganism as yet, so it’s wonderful to have received DKK 5 million from VILLUM FONDEN, which will enable us to conduct additional research in the area,” continues Professor Smets. Over the coming year, he and two colleagues will perform a series of measurements and experiments designed to obtain more knowledge about the conditions under which the new microorganisms thrive— and thus how they can best be stimulated to increase their activity, to the benefit of the nitrogen balance.

Water purification

Knowledge about the new microbe can also be applied to the purification of waste water and groundwater. For example, groundwater often contains too high a level of ammonia, which has to be removed in order to produce high-quality drinking water. Today, this is performed in large sand filters at the waterworks—known as ‘rapid gravity sand filters’—where microorganisms convert ammonia and ammonium into nitrates. It was actually in a sand filter of this kind that Professor Barth F. Smets discovered the new microbe.

“Finding out more about the organic and physiological cycle of the new microbe may also improve our knowledge about how sand filters should be designed to optimize the process of purifying groundwater. And the same naturally applies with regard to the purification of waste water,” he explains.

The researches also hope that their coming work will lead to greater evolutionary and biochemical knowledge about where the newly discovered microorganism comes from, and about its unique properties. They are likewise hopeful that their work will reveal whether the new microbe can advantageously be used in processes other than water purification.

Discovery of the microbe
Professor Barth F. Smets and Professor Thomas Sicheritz-Pontén, both from DTU, published their discovery of the new microbe in the prestigious ISME Journal in an article entitled: "Metagenomic analysis of rapid gravity sand filter microbial communities suggests novel physiology of Nitrospira spp Palomo, A. et al." (2016