On the Oxygen Transfer Simulation in an Oxidation Ditch with Aeration Devices and an Underwater Mixer

摘要

As the medium or small size wastewater treatment plants, oxidation ditches with an underwater propeller type mixer and aeration plates are usually adopted because of its high oxygen supply. This type of oxidation ditch is equipped with separated functions of oxygen supply and mixing in order to prevent the sedimentation of sludge, and is known as a highly efficient wastewater treatment plant. In this paper, new method to simulate the flow field activated by an underwater propeller type mixer and the oxygen transfer phenomena through air bubble boundaries supplied by aeration plates is explained. In order to validate the simulated results, oxygen transfer velocities were measured using the scaled model oxidation ditch and compared with the corresponding calculation results by above stated method. Moreover, oxygen transfer velocities were measured changing arrangements of the aeration plates and mixer position, and compared with the simulated results. These results show that the oxygen transfer efficiencies have close correlation to the mean velocity just above the aeration plates.