Abstract: A device for aerobic purification of industrial and/or household waste water, which device comprises a trough-like container for receiving the water for treating, at least two rotatably mounted contactors introduced into the container and having filler elements such as rings arranged loosely therein, feed means for feeding the contaminated water in doses into the container and a sludge collection space for settling the aerobically treated waste water lying behind the container and connected thereto via an overflow, which device is distinguished in that a seal is arranged between the contactors to prevent a direct flow from the one contactor to the other, wherein resistance means are arranged for transporting therebetween of waste water with increased resistance in order to aerobically treat the waste water in each contactor to a sufficient extent.