SEGES visits MBBR installations
Everywhere in Europe diffuse pollution of nutrients from agricultural activities needs to be mitigated. Denmark has already extensive experience with constructed wetlands. Runoff water and tile-drain water are collected in such wetlands which are usually located in natural depressions in the landscape. The biofilm on the roots of the plants exerts denitrification by which nitrate is biologically converted to nitrogen gas. However, bacteria are less active at cold temperatures and therefore removal efficiency drops during winter.
High nitrate concentrations during winter
Unluckily, this coincides with the moment of the biggest water volumes and the highest nitrate concentrations. Although wetlands have no cost for operation, the limited nitrate removal, being on average 25%, is a major drawback. Therefore SEGES expressed its interest to learn more about the MBBR filter setup developed by KU Leuven in Belgium.
In December, a SEGES delegation of 6 people visited the MBBR installations in Onze-Lieve-Vrouw-Waver, Sint-Katelijne-Waver and Beitem. MBBRs have shown to remove on average 75% of nitrates. Ideal settings comprise an underground setup and power supply to protect bacteria against temperature fluctuations and to enable carbon dosing and regular mixing, respectively. Operational costs are higher as compared to constructed wetlands but the removal efficiency is also considerably higher. SEGES will further explore if an MBBR can be an add on to the Danish constructed wetlands.