The invention relates to a method and a device for the purification of wastewaters, particularly for anaerobic purification, in a receptacle (19) receiving a medium under gas generation, whereby the generating gas is collected in a gas collector (3), the constituents of the medium carried off by the gas are separated and the separated constituents are fed back to the medium downstream from the gas separator. In order to achieve improved purification in a simple constructional manner, the medium is suctioned from the upper area of the receptacle by means of a lifting effect of the ascending gas and fed back into the receptacle.