Influence of a transverse flowrate on the oxygen transfer performance in heterogeneous aeration: case of hydro-ejectors.

This paper deals with the scaling of aeration devices, and more specifically hydro-ejectors, in the case of heterogeneous aeration. Because the transfer of oxygen only occurs in a very small part of the volume of the treatment basin, the transfer performance of the aerator depends on the device itself and on the surrounding flow characteristics. First experiments were achieved with a 10 L mechanically agitated reactor in order to operate at a known kLa and liquid flowrate Q. The results show that the oxygen transfer capacity of the reactor is used to a greater or lesser extent depending on the flowrate which passes through the bubbling region. When a hydro-ejector is concerned, the oxygen transfer occurs inside an aerated zone of about 2 m3; experiments carried out with an industrially scaled HE in a 120 m3 test basin allowed to estimate that the kLa in this zone is about 700-800 h(-1). Applying a compartment model, it is then possible to determine the oxygen transfer capacity of the HE as a function of the transverse liquid flowrate. While this OC is 3 kg O2/h under the test basin conditions, it reaches up to 12 kg O2/h under industrial flow conditions. This value was obtained in the aerobic biological treatment of the washing waters of a sugar refinery where two 33,000 m3 basins aerated by 152 HE could degrade 35 t/d of COD.