Tests on drainwater by Aarhus University

Aarhus University and Copenhagen University are testing different filtration systems for the removal of P from drainwater.

The P filter system is constructed in the Fensholt catchment consisting of a sediment and a porous, reactive P filter.
Sludge from the sediment filter is regularly being pumped into a storage tank with backflow to the P filter system. The filter system is fully monitored. The construction phase of the new P filter demo site was completed in 3 months and agricultural drainage water has been let into the system starting from the 20th of February 2019.
The reactive P filter was filled out with 2.4 m3 of Diapure™, delivered by our Swedish subcontractor. The material was not sufficient, thus the filter was topped with seashells – from the height of the outflow pipe to the top, simply to prevent overflow during high runoff events.
Three ISCO-samplers for continuous automatic water sampling were positioned before the sediment filter, before and after the reactive P filter. Total P, total dissolved P, turbidity, pH and EC are measured in the lab on time proportional samples. In the start-up phase, lasting a few weeks, the flow meter and the different sensors were calibrated, and small adjustments were made to improve the system functionality.


A control board, manufactured by Etcas, allows continuous monitoring of the inflow and water levels in the different wells. Pumping duration and frequency in the sediment filter (well 3) is currently being optimized to remove sediments efficiently from the sediment filter and to avoid clogging in the reactive P filter. This will be automated later on. All the data is stored remotely in a cloud. The monitoring period stops at the end of April and commences again in autumn (drainage season).
Also a closed P-filter bucket system (filterbox) from Ghent University and filled out with ICS will be tested at the site.