A mechanism of floc formation by Zoogloea ramigera.

In an attempt to understand the fundamental mechanism of bacterial flocculation, many speculations, hy potheses, and theories on the subject have been proposed by numerous in vestigators. In many instances, at tempts were made to isolate zoogloeal organisms in pure culture, then grow them in nutrient solutions including sterile sewage in such a way that the cells aggregated to form floes which not only had the appearance of acti vated sludge but also settled rapidly. The term bio-flocculation was in use at least three d?cades ago. Heukele kian (1) defined it as "the coalescence of finely divided suspended matter in sewage primarily under the action of biological agencies. ' ' This was believed to be favored by either agitation in the presence of biologically active slime or by long periods of quiescence. Among the most significant papers concerned with bacterial flocculation and related phenomena in the acti vated sludge process were those of Buswell and Long (2), Baly (3), Dienert (4), Butterneid (5), White head and O'Shaughnesy (6), Theri