Abstract: The present invention relates to a device for the catalytic oxidation purification of waste water inside a reaction vessel. The vessel includes a front wall, a back wall, two side walls interconnecting the front and back wall and a bottom. The waste water is admitted into the vessel through admitting means located on the front wall and discharged through discharge means located on the back wall. The vessel is divided into a plurality of compartments each of which includes a pair of risers which are divided by a plurality of partitions to form a plurality of sub-chambers. The partitions include an oscillatable flap or, alternatively, are tilted in a direction opposite to the direction of flow of the water in the vessel. In this manner, entrapment of the catalyst particles is prevented.