Three denitrification filter systems tested in Roeselare by Inagro

Three different denitrification techniques have been tested on their capability for N removal from the drainage water from pilot plots at Inagro: a constructed wetland, a wood chips filter and a moving bed bioreactor.


The fields near the Godelieve ditch are used by Inagro for research for arable farming and vegetable cultivation. Because the plots had to be drained, this was an opportunity to make a practice-based comparison of the effects of various denitrification techniques.



The drainage water from 7 ha is also collected in this open well. The overflow of water from the open well flows towards the constructed wetland. The MBBR is also fed with this water. Part of the plot (1.5 ha) could not be connected to the open well. This drainage water is collected in a separate basin from where it flows through the wood chip filter before entering the ditch.


Constructed wetland

The total area of the constructed wetland is about 1500 m² (or 2% of the total drained area). The wetland itself is divided into three parts. The division was done by constructing two sandbanks (5 – 7 m width) through which the water must pass. Straw was mixed into these sandbanks. In this way, a carbon source is mixed in as carbon is necessary for the denitrification reaction. Reed was planted on top of the sandbanks. The maintained water column is about 70 cm high.

The overflow of the open well is connected to the constructed wetland. The water flows through the wetland. At the end of the wetland, drains have been installed for discharge into  the canal.


Wood chips filter

Before the drainage water passes through the wood chips, it is buffered. Both the buffer section and the section filled with wood chips are 40 m long and 4.6 m wide. The maintained water column is about 80 cm. About 150 m³ of wood chips (without bark) were placed in the wood chips section. After passing through the wood chips, the treated drainage water is discharged via an overflow.



The MBBR treats the water from the open well. The MBBR has a total volume of 10 m³, of which 8,5 to 9 m³ is filled with water. In the MBBR 3 m³ of carrier material was installed. Carbo ST is used as carbon source. The used dose of Carbo ST is 0,13 l/h. Every 2 hours the carriers are pumped around during 1 minute so that they don’t start clogging.


Discover all details, results and the conclusions about the filter systems in the field case description document (results up to 2022).

Result update May 2023