Aeration systems normally perform two functions in activated sludge wastewater treatment processes, namely, oxygen transfer and mixing. While oxygen transfer may be regarded as the primary function, mixing is also important to ensure a full utilization of the activated sludge reactor volume and a uniform dispersion of dissolved oxygen throughout the mixed liquor. However, in some applications of the activated sludge process, a mixing input is provided which is independent of the aeration system, thereby relieving the aeration system of its mixing function.
Where an independent mixing system is provided, the specific mixing power input required is dependent on the reactor configuration, being typically in the range 3 to 6 W/m3. The specific power input required for oxygen transfer is generally not less than 8 to 10 W/m3, even in high sludge age processes such as the oxidation ditch. Hence, aeration systems are generally likely to have a sufficient gross power input for their ancillary mixing function, provided that it is appropriately applied.
Aeration is used extensively for the biological (biochemical?) oxidation of both domestic and industrial organic wastes. In wastewater treatment, the function of aeration is to introduce air into the water through the most effective and least costly methods that will increase oxygen transfer (dissolved oxygen) in the wastewater.
Diffused Aeration helps maintain an aerobic condition, with a basic purpose of improving water quality for subsequent reuse. Aeration can bring about the physical removal of taste- and odor-producing substances, such as hydrogen sulfide (H2S) and other volatiles and the chemical removal of metals (iron, manganese), gases (hydrogen sulfide), and other compounds (organic and inorganic) through oxidation and settling.