An apparatus for the treatment of liquid by aeration is provided. The apparatus has a motor, a propeller carried by a motor-driven shaft, an air flow passage to the propeller, bearings supporting the shaft at a location spaced from the motor and at least one bearing seal between a bearing and the propeller. In accordance with the present invention, a module for releasably carrying at least one of the bearing seals is detachably secured about the shaft to faciliate removal of at least the bearing seals from the apparatus.