The Rôle of Protozoa in the Activated Sludge Process

years prior to the activated sludge researches which date from the work of Fowler and Mumford on the bacterial clarification of sewage employing a new iron bacterium, 1 MyQuite recently Heukelekian (1941) has reviewed the present state of our knowledge of mechanical flocculation and bioflocculation of sewage, and concluded that the flocculation is brought about both by physical and biological agencies working either independently or simultaneously. Mechanical flocculation plays a more important part during short periods; as the period is increased, bioflocculation plays an increasingly important role. It would appear from his account that, on the biological side, the protozoa are not recognized as an important factor in the clarification and flocculation of sewage. Fowler's observations (1916, 1922) suggested that the activated sludge process ' can be referred