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Appl Environ Microbiol. 1965 March; 13(2): 257-261
Copyright © 1965 American Society for Microbiology. All Rights Reserved.

Microbial Ecology of Activated Sludge

II. Bacteriophages, Bdellovibrio, Coliforms, and Other Organisms

Fermentation Technology Laboratory, Indian Institute of Science, Bangalore, India

ABSTRACT

A comparative estimation of the coliform population of raw sewage, activated sludge, and the effluent derived therefrom revealed that raw sewage had a preponderance of Escherichia coli (75%), as compared with 25 and 30%, respectively, in sludge and effluent. Nitrogen-free mannitol-sucrose enrichments of activated sludge resulted in the isolation of Azotobacter agilis, Aerobacter aerogenes, Corynebacterium laevaniformans, and an Achromabacter species. Sludge had a large population of C. laevaniformans and A. aerogenes but not of Azotobacter. The bacterial parasites, Bdellovibrio and bacteriophages, were not active during activated-sludge treatment. A 10-fold reduction in phage content occurred after 2 hr of aeration, but the Bdellovibrio population was unaffected.