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Development of mini-wetlands with biofilters enters new phase

New mini-wetlands with biofilters will be established in the course of the summer and autumn of 2017 with the aim of generating more knowledge and experience regarding this particular measure against nitrogen loss to the aquatic environment.

2017.06.02 | Janne Hansen

The sod will soon be turned for the establishment of a new full scale mini-wetland with biofilter. Photo: Colourbox

The first sod will soon be turned for the establishment of a new full-scale mini-wetland with biofilter at the estate Gyldenholm Gods in southwest Zealand. The system will help generate more knowledge and evaluation of how well mini-wetlands with biofilters are at removing nitrogen in both the short and long term and what the cost efficiency is.

Establishment of the system at Gyldenholm Gods is part of a new four-year project for which the Ministry of Environment and Food of Denmark has granted 15 million kroner. The project, which is led by senior researcher Finn Plauborg from the Department of Agroecology at Aarhus University, is a collaboration between the Department of Agroecology and the Department of Bioscience.  

Read more about the project here: Biofilters and mini-wetlands can reduce nitrogen leaching

Part of the project will be to establish one or more new mini-wetlands with biofilters at various locations in Denmark. The aim is to work with system designs in order to maximise the nitrogen removal effect for the location in question. The nitrogen removal effect is dependent on temperature and hydraulic retention times, i.e. how long time a unit of water resides inside the filter. 

The first full scale unit

The first of the new units will be located at the estate Gyldenholm Gods in an area with a system-drained catchment area. In connection with a previous project funded by the Green Development and Demonstration Programme (GUDP), there is already documentation for the relevant amount of water and nitrogen passing through the main drain at Gyldenholm Gods. 

The unit receives water from a 120 ha catchment area and its hydrodynamics are significantly different in their runoff patterns and amounts from the existing research unit in Gjern, upon which a large portion of the present knowledge about mini-wetlands with biofilters under Danish conditions is based.   

The unit at Gyldenholm Gods will reflect some of the challenges that can arise in connection with mini-wetlands with biofilters – and hopefully also lead to proposals for how these challenges can be met. Runoff at Gyldenholm Gods only occurs in the winter. This means that much less nitrogen is removed than would be the case at a higher temperatures during summer. The topography at Gyldenholm demands that the water has to be pumped up into the biofilter. This will create an extra cost to the facility, especially as the drained area is rather large.

- We are in the process of calculating what it will cost to raise the water 1-2 metres. Another task will be to reposition the main drain and place the unit on a local slope, Finn Plauborg explains.

The unit will comprise 5 basins that are significantly larger than the ones in the pilot system in Gjern due to the larger amounts of water. In order to optimise the nitrogen removal effect a semi-automatic distribution of the total water runoff to the five  basins will be developed.  

Two more units?

Later in the year a new mini-wetland with biofilter might also be established at the estate Hofmansgave in north Funen. This is a diked and pumped area that gives full control of optimisation of the nitrogen removal effect because the hydraulic retention time can be regulated in tune with seasonal drainwater variations. In this case, there is also existing data from a previous GUDP project that proves that there is a relevant amount of nitrogen in the pumped water – water that is currently pumped directly into Odense Fjord. 

- Here there is no natural retention and the requirement for action with regard to the coastal water is high. In this case, our research will focus on designing a unit including a water storage magazine so fluctuations in the nitrogen removal effect can be reduced by regulating the hydraulic retention time directly via variation of the pumped inflow to the unit, Finn Plauborg explains.    

Location of the possible third unit has not yet been decided but the aim is to establish a unit in a lateral moraine that is point drained.  The idea here is also that the unit will have water storage for equalisation of water flow through the unit and stabilisation of the hydraulic retention time. 

For more information please contact:

Senior researcher Finn Plauborg, Department of Agroecology, email: finn.plauborg@agro.au.dk, telephone: +45 8715 7714, mobile: +45 2218 1809






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