A method and apparatus for aerating a liquid, particularly for aerating water in a wastewater treatment process, by: introducing the liquid into a primary pressurizable aeration tank; pumping liquid from the primary pressurizable aeration tank into a secondary pressurizable aeration chamber via a feed path; aerating the liquid in the secondary pressurizable aeration chamber; and recirculating aerated liquid from the secondary pressurizable aeration chamber back to the primary pressurizable aeration tank via a return path. The return path has a cross-sectional area smaller than that of the feed path through which the liquid is pumped into the secondary pressurizable aeration chamber such as to pressurize the secondary pressurizable aeration chamber to a pressure greater than that in the primary pressurizable aeration tank, and thereby (a) to enhance the aeration of the liquid in the secondary pressurizable aeration chamber, and (b) to supply the energy for recirculating the aerated liquid back to the primary pressurizable aeration tank.