PURPOSE: To cut or destroy flocks and microbes in activated slurry precipitated and returned to an aeration tank by means of a slurry pump.

CONSTITUTION: An impeller 5 supported by a rotational shaft 4 is housed in a pump casing 1 having a suction port 2 and discharge port 3 of activated slurry. A slitted or porous plate 7 is fixed to the tip of the shaft 4 and another slitted or porous plate 8 is fixed to the casing 1, keeping a distance of 0.9W0.5mm between both plates 7, 8 for cutting or destroying flocks and microbes. As the shaft drives the impeller 5, the activated slurry is taken in from the suction port 2, passes through the cutting and destroying mechanism 7, 8 and is discharged from the discharge port 3.