A new device has been developed in order to achieve urban or industrial wastewater biological treatment. It has been designed specially for lagoon applications to oxygenate and mix with the same apparatus. The goal is both to achieve a high gas flooding rate and to reach a maximal depth with the bubble plume. Mass transfer measurements have allowed us to choose the most appropriate geometry. Considering the application of the device and the possible use of low-pressure 02 produced on-site, the agitation system is located close to the liquid surface and is composed of a gas-inducing turbine. The role of propellers in addition to the gas-inducing turbine, as well as the use of baffles and a shell, have been experimentally studied. Numerical simulations (CFD) of the whole apparatus in single-phase flow have been used to study the influence of the stator part of the geometry.