Abstract: An aerator has a housing which contains a fluid inlet nozzle and a fluid discharge nozzle positioned on either side of an air inlet formed in a T-pipe. The fluid inlet nozzle has a bore with a flared inlet, and a cylindrical outlet, in which a spiral groove or rifling is formed which extends to the end of the inlet nozzle, allowing the infed contaminated water to pass through, being swirled by the spiral groove, and then exit into an expansion chamber in communication with the air inlet, where air is entrained within the swirling water. Banks of the aerators are used in a wastewater treatment system, having a rectangular tank with a serpentine flow path. Dissolved oxygen meters provide data to a Programmable Logic Controller to control the pumps recirculating liquid within the tank. Pumps are turned on and off to achieve target minimum levels of dissolved oxygen.