Selective removal of excess sludge from difficult-to-sediment activated sludge in secondary clarification


In a secondary clarifier, quickly and easily sedimentable activated sludge settles near the inlet area. Activated sludge that is difficult or slow to sediment tends to collect near the drainage area. If only the difficult-to-sediment activated sludge is removed as excess sludge, the sedimentation performance of a secondary clarification can be improved. This increases operational safety and enables increased sewage treatment plant capacity.

As part of this study together with the University of Duisburg-Essen, this working hypothesis is being examined in operational sewage treatment plants with the help of the sludge volume index. The objective is to determine the mass flows for poor, medium and easily sedimentable activated sludge by means of a balancing process. On this basis, the position and performance of the selective excess sludge removal process can be determined.