Filters to remove nutrients in agricultural drainage water

Drainage filters will be used to trap nutrients before they end up in inland and coastal waters, where they can trigger algal blooms and oxygen depletion.

This is the ambition of a new project where scientists from Copenhagen University and Aarhus University together with international universities and Danish and international companies will develop and test different drainage filter technologies for the removal of nutrients from drainage water. On more than half of the Danish farmland subsurface drains and ditches function as highways for the transport of nutrients from fields to water recipient. The idea is to mitigate site-specific nutrient losses. Scientist target the development and testing of a range of filter technologies that can be adapted to local conditions and loads of nitrogen and phosphorus.

One of the new filter technologies that will now be tested is drainage well filters. Drainage well filters are particularly suited to fields with a high risk of phosphorus loss through drainage. Initially, focus is on capturing particle-bound phosphorus, and later follows the testing of different filters to capture soluble phosphorus forms. Also to be investigated is the feasibility of converting nitrogen and trapping other contaminants in drainage water. The final phase involves analysis of the cost-effectiveness of drainage well filters and comparison with various types of constructed wetlands that are also being tested in the project. This will form the basis for recommendations for targeted measures adapted to local conditions.

“Today we have the tools to identify risk areas for nutrient losses and we can use this to implement targeted measures such as drainage filters”, says Charlotte Kjaergaard senior scientist from the Faculty of Agricultural Sciences, Aarhus University – “we hope with this project that we will be able to develop cost-effective drainage filter solutions that allows in the future to combine the production of foods with the protection of nature and the environment”. Read more about the project at

Head of the five-year project is Professor Hans Christian Bruun Hansen from the University of Copenhagen, while Senior Scientist Charlotte Kjærgaard, Aarhus University is project coordinator. The project has a total budget of DKK 31 million and has received DKK 19 million from the Strategic Research Council. The project is a collaboration, which besides two institutes from the Faculty of Life Sciences at Copenhagen University and the Faculty of Agricultural Sciences and the National Environmental Research Institute from Aarhus University involves universities from USA, Holland, Sweden, Norway, Austria and Switzerland and a large number of Danish and international companies.

Fore more information please contact senior scientist and project coordinator Charlotte Kjærgaard, Department of Agroecology and Environment, telephone: +45 8999 1864, e-mail: