Fungi in Sludge Digesters
WILLIAM B. COOKE, Microbiologist
Basic and Applied Sciences Branch
Division of Water Supply and Pollution Control
Robert A. Taft Sanitary Engineering Center
Cincinnati, Ohio
INTRODUCTION
During the past decade several researchers (1,2,3,4,5,6,7,8,9,10,11,12)
have shown that fairly large numbers of filamentous fungus and yeast cells occur in
sewage, sewage-polluted water, and sewage treatment systems.
After sampling in the Dayton, Ohio, sewage treatment plant at monthly intervals during 1952-53, Cooke (2) found that, depending on the media used, and
possibly on the antibiotics in those media, the number of fungal cells in digested
sludge was lower than that in sludge from an Imhoff tank, but this number increased rapidly as the sludges dried out on open-air drying beds. Retention time
was about 40 days, and numbers of colonies recovered from sludges in the bottoms
of the digesters were usually in the hundreds of thousands per milliliter. Cooke
(5) pointed out that a broaa spectrum of fungal species occurs in digesting and
digested sludges, and that as some species declined in number, others increased
during the digestion process.
In a study of the fungi and algae in the slimes on the surface of high-rate and
low-rate trickling filters at Dayton, Ohio, Cooke and Hirsch (9) showed that a
high population of fungal species was present in the slimes. Such species existed
even in that portion of the slimes considered to be anaerobic, and as a result of
sloughing could be added to populations already present in digesters in the secondary sludge.
In checklists of filamentous fungi and yeasts (4,10), results of population
studies are listed from several sewage treatment plants, especially those at Dayton, Yellow Springs, Columbus, andGlendale, Ohio. In addition to the Dayton
Ohio, plant, species are listed from sludge digesters in the Yellow Springs, Columbus, and Loveland, Ohio, sewage treatment plants. Becker and Shaw (1)
studied populations recovered from effluents of various processes in the Pullman,
Washington, and Moscow, Idaho, sewage treatment plants. In effluents from
primary and secondary settling tanks successively lower numbers of viable cells
(represented by colonies on agar plates) were recovered. This is also true for reports by Cooke (2,3).
In considering the ecology of a sewage-polluted stream in southwestern Ohio
(Lytle Creek, Clinton Co.) Cooke (6) found large numbers of colonies of a lower
number of species of fungi in bottom sludges collected from the more heavily
polluted portions of the stream bed. Information on other studies of streams in
Ohio, West Virginia, Oregon, Utah, Idaho, and Colorado has not yet been published. In the more heavily polluted portions of streams larger numbers of fungal
colonies are recovered from bottom samples in spite of the low levels or absence
of dissolved oxygen in the stream water at the sampling points.
In waste stabilization ponds receiving domestic sewage large numbers of
yeasts and filamentous fungi have been recovered from sludges in the bottoms of
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