the apparatus of the present invention the system preferably is land based and is located adjacent a lagoon 12 containing a body of oxygen depleted wastewater to be treated while it is preferred that the system be land based for ease of maintenance it also can be located on a float stationed in the lagoon the aeration system 10 includes a pump 14 having an inlet pipe 16 extending into the lagoon the pump has its outlet 18 connected to a treatment vessel 20 wastewater from the lagoon is pumped into the vessel treated by aeration and then is pumped back in to the lagoon thorough a distribution pipe 22 as best seen in fig2 the treatment vessel 20 is a closed generally cylindrical vessel having an inlet 24 at an upper level of the vessel and an outlet 26 at a lower level the inlet and out let are connected to the pump outlet 18 and distributor pipe 22 respectively a valved air inlet 28 allows for the controlled entry of air into the vessel a vaned rotor 30 is disposed within the vessel the rotor is arranged for rotation about a vertical axis and comprises a shaft 32 and a plurality of vertically oriented vanes 34 that are fixed to the shaft and extend outward from the shaft preferably the vanes are four in number and are equally spaced about.