Catalase activity of activated sludge

Catalase activity of mixed liquor suspended solids of aeration tank of activated sludge plants in Milwaukee, WI, was measured in sonicated samples. Catalase activity varied in the samples of mixed liquor suspended solids collected from the head and end of the aeration tanks; in return activated sludge; and in waste activated sludge. Catalase activity decreased in mixed liquor suspended solids, on prolonged aeration (8 days), in the absence of added sewage. Volatile suspended solids and catalase activity seemed to bear a relationship.