The Dissolved Oxygen Profile : A Valuable Tool for Control of the Activated Sludge Process

Control of activated sludge process based on measurement of the dissolved oxygen profile has the distinct advantage of using sensors of proven reliability. These measurements, when coupled with the power of an on-line computer, permit the calculation of important variables which cannot be measured directly. The features of the profile which are of major significance are the position of the maximum slope, the value of the maximum slope, the DO concentration at the reactor outlet, the slope of the profile close to the outlet, and the second derivative of the profile towards the outlet. This paper demonstrates that the above mentioned features reflect both the hydraulic and organic loading, reaction rates, and degree of completion of the reactions in the activated sludge process. Simulations are presented to show how these features may be controlled by manipulating the mass of sludge in the reactor and the overall oxygen transfer rate coefficient