Role and function of protozoa in the biological treatment of polluted waters.

The activated sludge used in the biological treatment of polluted water is a typical ecosystem composed of bacteria and protozoa. There should be an indigenous picture of competition, predation, mutualism and so forth, among the microorganisms which contribute to the removal of organic matters from polluted waters. Specific protozoa have been detected in the sludge when the process proceeds satisfactorily. Therefore, a study how to control the protozoan fauna in the sludge to warrant a good quality of effluent is essential. This article presents a clue leading to the microbiological control of the biotic community in the sludge, through the studies on ecological characteristics in the monoxenic culture of ciliated protozoa isolated from the activated sludge. [ABSTRACT FROM AUTHOR]