Activated Sludge Process Design

It is shown that if a target efficiency of BOD removal is selected in advance, the process includes seven decision variables, excluding the primary settling tank. It is possible to write five equations describing the process from which it follows that the designer is free to choose values for only two decision variables if the design is to be technologically efficient. It is shown that selection of target BOD removal specifies the amount of waste sludge produced, the required amount of sludge under aeration, and the required amount of oxygen. Equations are presented for calculating the efficiencies at which waste sludge production is a maximum and a minimum; these efficiencies are shown to be separated by only a few percentage points, which makes selection of target efficiency a difficult and important task.