Upscaled phosphorus filter by Ghent University
The basic concept to reduce phosphorus losses is installing a filter box containing a P sorbing material (PSM) at the end of the drainage tubes. This forces the water through the filter material and allows the removal of P from it before entering the ditch. Ghent University developed filter compact boxes that have been installed at the end of single drainage tubes. This design works well for the typical discharge of individual drainage tubes, but needed to be upscaled to also efficiently treat larger volumes of water in the case of collector drains.
Season of 2021-2022
One upscaled P filter, a concentric cylindrical filter element within a cubic container, was installed in 1st March 2022. The concentric cylindrical filter element was constructed by two cylindrically shaped wire meshes, with 140 L ICS filled in between the cylinders. Water from the collector drain was pumped to the central cylindrical cavity of the filter element, and then forced to pass the concentric cylindrical filter element with a thickness of 14 cm, from the center towards the outside. The P in the water passing through the ICS is (partially) sorbed, and then discharged from the cubic container into the ditch.
Results
P removal efficiency of upscaled filter during the season 2021-2022.
At the site of Middelkerke, 18.2% of total phosphorus (TP) and 21.3% of dissolved reactive phosphorus (DRP) was removed by the filter box during the period of 01/03/2022 - 26/04/2022 with a water flow of 17-36 m3/day.
Conclusion
During the first season, the upscaled P filter showed the potential of treating a large water flow up to 36 m3 per day. However, P removal efficiency was not satisfactory (around 20 %) and considerably below the performance of the small P filters for individual drainage tubes. The high water flow of the water and thus relatively short contact time is a possible reason for the reduced P removal efficiency. Adjustments of this filter system have been made to increase the contact time and we will continue the improvement (e.g. reducing flow) until we achieve an optimal absolute P removal for the whole drainage season taking both flow and P removal efficiency into consideration.