Abstract: The invention relates to a device for stirring a liquid in a reactor and for injecting a gas into the said liquid in order to form a gas-liquid dispersion, comprising a) a drive device (1) positioned above the reactor, provided with a vertical output shaft (2) fitted at its lower end with at least one axial flow rotor (4) immersed in the liquid, b) means for introducing gas (3 and 7) above the axial flow rotor (4), c) a deflector (5) placed above the axial flow rotor (4) preventing the gas-liquid dispersion from rising, and d) a deflector (6) placed below the axial flow rotor (4) converting the axial flow of the said axial flow rotor into a radial flow. This device may be used in shallow basins.