Experiments on the microbiology of cellulose decomposition in a municipal sewage plant

Summary

Analyses of sewage solids show cellulose to be one of the chief components. Culture counts of cellulolytic bacteria in a primary anaerobic sewage digestor show them to be present in numbers as high as 1 million per ml. The tendency of cellulolytic bacteria to cling to cellulose fibers makes it highly probable that the number of cellulolytic cells is much larger.

All 10 cellulolytic strains isolated in pure culture show better growth in solid than in liquid media, and for some of them agar possesses growth promoting properties. For some strains, phytone and trypticase can replace the agar but other strains could not be grown in media containing no agar.

Hydrogen, carbon dioxide, ethanol, formic acid, acetic acid, and lactic acid have been identified as fermentation products and glucose shown to be a product of cellulose digestion. Cellobiose, starch, dextrin, and maltose were fermented by 5 tested strains, inulin and esculin by one of them, but none of 17 other carbohydrates, including glucose, were attacked.

The rate of cellulose fermentation by a mixed culture of aClostridium sp. and a cellulose decomposer is much greater than the rate by the latter alone. The rate of fermentation by a pure culture is not affected by acetate concentrations up to 5000 parts per million. It is postulated that the rate of fermentation of cellulose may be the factor limiting the rate of sewage fermentation though more evidence regarding rates of fermentation of other constituents of sewage is needed before final conclusions can be drawn.