EFFECT OF CILIATED PROTOZOA ON FATE OF ESCHERICHIA COLI IN ACTIVATED-SLUDGE PROCESS

The removal of E. coli from sewage in two bench-scale activated-sludge plants was investigated in the absence of protozoa. Ciliated protozoa were then added to one of the plants and the results were compared. With protozoa absent the half-life of E. coli in the plant was 16 hr. This was reduced to 1 · 8 hr in the presence of protozoa. It is clear that protozoa play the dominant part in the removal of E. coli from sewage. A decrease in the total viable bacteria in the effluent was also observed when protozoa were added to the activated-sludge plant, confirming earlier demonstrations of the importance of protozoa in the clarification of sewage effluent. © 1969.