Abstract: Disclosed is an agitator assembly which comprises an agitator and means for mounting the agitator assembly on top of a tank. The agitator comprises a shaft, a propeller fixed to one end of the shaft, and means for rotating the shaft to provide an axial discharge from the propeller of at least 4.0 m/sec with a flow equivalent of at least 0.2 tank volumes/minute. The agitator is mounted on top of the tank so that the shaft enters the tank at an angle &agr; to the longitudinal axis of the tank of between about 30 and about 60 degrees and at an angle &bgr; to the transverse vertical axis of the tank of less than about 50 degrees.