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 specificall y hydro-ejectors, in the case of heterogeneous aeration. Because the transf er of oxygen only occurs in a very small part of the volume of the treatmen t basin, the transfer performance of the aerator depends on the device itse lf and on the surrounding flow characteristics. First experiments were achi eved with a 10 L mechanically agitated reactor in order to operate at a kno wn k(L)a and liquid flowrate Q. The results show that the oxygen transfer c apacity of the reactor is used to a greater or lesser extent depending on t he flowrate which passes through the bubbling region. When a hydro-ejector is concerned, the oxygen transfer occurs-inside an aerated zone of about 2 m(3): experiments carried out with an industrially scaled HE in a 120 m(3) 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 ox ygen transfer capacity of the HE as a function of the transverse liquid flo wrate. While this OC is 3 kg O-2/h under the test basin conditions, it reac hes up to 12 kg O-2/h under industrial flow conditions. This value was obta ined in the aerobic biological treatment of the washing waters of a sugar r efinery where two 33,000 m(3) basins aerated by 152 HE could degrade 35 t/d of COD. (C) 2001 Elsevier. Science Ltd. All rights reserved.