Phosphorus removal in agricultural drainage water
The 324 km² catchment area of lake Dümmer is characterized by intensive agricultural use (approximately 526 farms). The embankment of lake Dümmer, including regulation of the inflows and drainage of the swamps, increased the diffuse nutrient input into lake Dümmer. This is mainly attributed to erosion and runoff and to a smaller extent to drainage water discharge. The chamber of agriculture of Niedersachsen wants to test filter technology able to reduce P concentrations at the outlet of the tile drainage. As such, algae blooms in the Dümmer lake can be reduced. 
This field demonstration comprises a remote filter system installed inline with the tile drain. The tile drain is gathering drainage water from a plot of 8,2 ha. Current P concentration at the outlet of the tile drain is about 4 mg/l of total P.
The filter shaft has been filled with iron coated sand received from a local drinking water company. Prior to installation, iron coated sand was sieved to withhold grains with a mesh size bigger than 3,15 mm. Smaller particles hamper the water flow. Initially, a good P adsorption on the material was attained but the filter system suffered from clogging due the presence of ochre fluffs in the drainage water.
Therefore a pre-filter will be installed to prevent the entry of amorphous organic substances into the filter system. The next drainage season will reveal if this filter configuration is suitable for the inline treatment of drainage water.