A spiral tube aerator for waste aeration which includes a shaft rotatably driven by a motor, the shaft carrying a mixing chamber, an air channel extending along the shaft and opening through at least one outlet of the mixing member, a blower for delivering air through the air channel, the mixing chamber being submerged in waste water at least to a depth of 50 cm below the waste water upper surface, and the blower providing a pressure in the range 0-35 mbar lower than the pressure exerted by the waste water at the outlet.