Oxidation Ditch Velocity and Resultant Oxygen Transfer Capacity for Combined Diffused Aeration and Horizontal Mixer Applications

In the design and planning of oxidation ditch systems, there is an observed effect of aeration performance with respect to the horizontal flow of water generated by mixers. This effect can be positive or negative. Reports have shown that horizontal flow of water can increase the oxygen transfer rate of the aeration system, but at the expense of additional power from the mixers (Fayolle 2011). Alternately, a high intensity aeration zone in combination with horizontal flow mixers can also create negative effects to oxygen transfer rate if not designed correctly. Exceeding a design limit on aeration intensity can result in reduced efficiency of oxygen transfer as well as create challenges to maintain a minimum horizontal water velocity by the mixers. This paper identifies some of the key variables which affect the oxygen transfer rate, and explains how these variables can be used to ensure a proper design of the diffused aeration system.