A mixing device for gases and liquids has a feed tube (3) open both above and below the liquid level. Below the feed tube is located a turbo-stirring member (8) driven by means of an axial shaft (4). The inner stirring blades of the stirring member (8) are surrounded by a ring (10) which turns together with them. On the outer side of the ring (10) are mounted further axial blades (9) which also convey the gases and liquids in the axial direction. In order to generate appropriately divided swirls while improving gas feed, the feed tube (3) may be provided on its outer side with flow-disturbing baffles (11) arranged in a star configuration. This mixing device, suitable for example in waste water treatment plants for aerating the water, as well as for high-pressure reactors, allows gas feed to be substantially increased with an optimum gas bubble distribution. Solids may also be fed therewith and are remarkably well suspended.
