Gas Phase Control for Oxygen‐Activated Sludge

A dynamic model that describes gas transfer in the oxygen‐activated sludge process was used to compare four gas phase control strategies under dry and wet weather flow conditions. Typical influent flows and oxygen uptake rates for the treatment plant at Hot Springs, Arkansas, were used for simulation purposes, The conventional control scheme was shown to be sensitive to sudden changes in the reactor liquid level during wet weather flows, and it was unable to prevent dissolved oxygen (DO) depletion when operating with relatively low levels of oxygen in the exit gas. The vacuum exhaust control (VEC) strategy, which utilizes an exhaust apparatus to control the effluent mixed liquor DO, was found to provide more stable oxygen feed and effluent DO during wet weather flows. Two other control strategies, which use measurements of the effluent mixed liquor DO to control the oxygen feed, were found to have results similar to the VEC strategy, but they generally had larger pressure variations. For both dry and wet weather flows, the alternative control strategies required approximately 10% less oxygen feed than the conventional control scheme.