The effect of high purity oxygen on the activated sludge process

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Virginia Polytechnic Institute and State University

This study was conducted to determine the effect of using high purity oxygen as the gas of aeration on the activated sludge process. Three completely-mixed cylindrical reactors were used in the study. The working volume for two of the reactors was 10.4 liters while that for the third was 4 liters. The gas of aeration for the small reactor and one of the large reactors was high purity oxygen and that for the other large reactor was compressed air. A soluble composition of nutrient broth, glucose, yeast extract, and various mineral salts was used as the substrate. The organic loading to each reactor was the same and this loading was maintained throughout the research period. Sludge age was used as the control parameter and control was achieved by wasting a specific volume of sludge each day. This procedure provided a means of operating over a range of sludge ages.

Results of the study indicated that an activated sludge system operating at low solids and high dissolved oxygen concentration is susceptible to takeover by filamentous microorganisms. A model was proposed to explain this phenomenon. Results also suggest that it is not the use of oxygen which is responsible for differences in substrate removal rates and yield observed between air and oxygen activated sludge units. Such differences are probably the result of high solids levels which most oxygenation systems operate at. This argument is supported by the model proposed to explain the stimulation of filamentous growth by high dissolved oxygen levels.

Results also indicate that activated sludge systems, when operated under either air or oxygen aeration, will show no significant variation in the gross composition of microbial mass between the specific growth rate range employed in this study.