Occurrence of zoogloea colonies and protozoans at different stages of sewage purification.

The presence of fingered branch-bearing Zoogloea has been noted on a number of occasions in the Baroda Sewage Disposal Works. Samples of raw sewage, the effluent from the continuous flow settling basin, the raw sludge, the floating scum in the settling basin, the final secondary digested sludge, and the supernatant liquid from the secondary digester were kept without any disturbance in 1-liter Pyrex glass beakers, which were loosely covered with petri dishes. Scum was formed on the surface within 48 hr in all the samples, and fingered Zoogloea colonies resembling the pure culture of Zoogloea ramigera reported by Crabtree et al. (5) were found in all except the final secondary digested sludge and the supernatant liquid from the secondary digester. It is not known whether the Zoogloea colonies discovered in the above cases are the same as or different from the typical Zoogloea ramigera of activated sludge, and whether they are slime-forming or flocculent types of bacteria. In any case, they seem to be different in their ecological status and in the nature of the accompanying protozoans from the typical Zoogloea ramigera. The reasons for the absence of zoogloeas in two of the samples are unknown.