In the stripping column process, the nitrogen and carbon compounds are decomposed by various microorganisms. Special carrier materials are packed in the central part of the reactor, which improve the biochemical reaction processes. To ensure an optimal operating point inside the stripping column, an exact level measurement at the base of the column is required. Because the surface of the medium in the reactor is very turbulent due to air flowing in from below, the level measurement has to be carried out in a bypass tube.