Gas‐Liquid Interactions in Oxygen Activated Sludge

Abstract

A dynamic model has been developed for the gas‐liquid interactions of a closed‐tank oxygen system treating carbonaceous wastes. The model describes gas transfer between phases and accounts for equilibrium changes in the carbon dioxide‐bicarbonate buffering system. The model was developed to provide a better understanding of process behavior and to provide a tool for gas phase control studies. Computer simulations of a four stage reactor were made to illustrate model predictions when using the conventional gas phase controls. Also, the effects of changing influent bicarbonate alkalinity, respiratory quotient, and gas‐liquid volume ratio were examined. The dissolved oxygen concentration in the fourth stage was shown to vary widely and result in significant oxygen losses for the conventional control method. Influent bicarbonate alkalinity was shown to have a significant effect on pH, but changing the respiratory quotient had only a small effect on pH for moderate alkalinity wastewater. The gas‐liquid volume ratio was found to have a significant influence on the response time for changing the fourth stage gas composition.