Stable Foams and Sludge Bulking: The Largest Remaining Problems (Abridged)

The separation of activated sludge in secondary settling tanks is the crucial step in biological wastewater treatment from the point of view of both final effluent quality and operation of the aeration plant. The sludge‐separation problems of bulking and foaming are connected with an excessive growth of filamentous micro‐organisms in the biocenosis of activated sludge. This paper (a) describes the methods which are used for the quantification of activated‐sludge separation problems, and (b) summarizes the design recommendations for bulking and foaming control.