The physiological activity of bacteria indigenous to a mid-continental domestic wastes disposal unit (lagoon) was studied over a period extending from mid-May to the beginning of December, 1965. A rigorous climate induces a layer of ice over the lagoon for approximately 5 months of the year; this study entailed the interval under ice-free conditions during the first year of operation. Samples were collected roughly at weekly intervals and the activity of the bacteria free of algae was studied against several arbitrarily selected organic substrates. The activity was found to be a function of (a) the number of bacteria, (b) the temperature of the lagoon, and (c) the nature of the test substrate. The most rapid rates of oxidation occurred with casamino acids, acetate, and palmitate. Glucose, egg albumin, and Liqui-nox, a biodegradable detergent, were oxidized in a variable manner. Maximum activity occurred at 23 °C, the highest temperature reached by the lagoon during the summer. The rates of oxidation decreased markedly when the temperature decreased as a result of the onset of fall but all activities were not affected equally by the same temperature change.
