Abstract: A bubble generating aerator comprising a disc-like or tubular aerating element made of a sintered open-pore plastics material, the element being submerged in a surrounding liquid and connected to a pressure gas source for supplying gas into the element and discharging the gas from one surface of said element as gas bubbles into the liquid. The discharge surface of the element is provided with a number of mutually spaced recesses larger than the pores of the element into which recesses the gas discharging from the element first enter as small bubbles and are combined to form larger bubbles before finally discharging from the element into said surrounding liquid.