The role of protozoa in the activated-sludge process

Abstract

Ciliates are the dominant protozoa in activated sludge, and those which either attach themselves to or crawl over the surface of the sludge are the most common. Experimental work has demonstrated that ciliated protozoa are essential for the production of a good quality effluent. Without ciliates, highly turbid, low quality effluents are obtained. Experimental evidence further suggests that the predatory activities of the ciliates upon the dispersed growths of bacteria are responsible for clarification and for the reduction of coliform numbers during the activated-sludge process. Mathematical models have been devised which take into account both the bacterial and the protozoan populations. The populations have been simulated on a computer and the results obtained in this way have helped to explain many of the observations that have been made upon the microbial populations found in full-scale activated-sludge plants. © 1973 by the American Society of Zoologists.