Isolation of floc-producing bacteria from activated sludge.

Although the activated sludge process for stabilizing liquid organic wastes is primarily a biological process, very little research has been conducted on the pure biological phases of this process. Until the work of Butterfield (1935), activated sludge was considered by some as a physio-chemical process and by others as a bio-chemical process. Butterfield isolated a bacterium, Zoogloea ramigera, from activated sludge which was capable of stabilizing a liquid organic substrate and of producing floc which was characteristic of activated sludge. Wattie (1942) and Heukelekian and Littman (1939) were also successful in isolating Z. ramigera from activated sludge. Although efforts were made to isolate other floc-producing bacteria, none were found. As a result of these studies, Z. ramigera was accepted as the predominant bacteria in activated sludge being responsible for both the stabilization of the organic matter and the production of floc. Isolation of floc-producing bacteria other than Z. ramigera was made by McKinney and Horwood (1952). They isolated five additional floc-producing bacteria from activated sludge. These organisms were not only capable of floc production but also of stabilizing the organic matter. It is the purpose of this paper to report on further work in the isolation of floc-producing bacteria from activated sludge.