Process Flow Diagrams

In addition to the conventional extended-aeration process shown in Figure 7.21.4, a variation known as the oxidation ditch (see Figure 7.21.10) is also widely used. The aeration rotor provides the dual function of aeration and flow velocity. An alternating anoxic or oxic environment occurs in the oxidation ditch depending on the distance from the aeration rotor. As a result, an oxidation ditch achieves good nitrogen removal via nitrification and denitrification.

The process separates sludge from the treated effluent by using either an external secondary clarifier or an intrachannel clarifier. Primary clarification is usually not provided.

Several manufactured extended-aeration units are available (Viessman and Hammer 1993).

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