Dynamics in flocculation and settling properties studied at a full scale activated sludge plant

A comprehensive study of the dynamics in settling and flocculation properties at a full scale activated sludge treatment plant with secondary settlers operated at their maximum capacity is presented. An extensive set of process data was analysed to assess physical parameters affecting the capacity and performance of the secondary settlers. There was a large variation in the settling and compaction properties and they changed quickly due to the short sludge age. Even though the flocculation properties changed throughout the year they were generally improved during the summer with lower values of effluent turbidity and effluent suspended solids concentration. The shear sensitivity, which is a measure of floc stability, was higher during the winter when the water temperatures were lower. The sludge floc morphology had in general a different internal structure with more round microbial colonies during the warmer summer months and a more net-like open structure during the winter