Method for controlling rapid stirrer, and rapid stirrer

A flocculating-mixing apparatus, comprising:

• a slow stirring machine comprising a slow stirring tank with a tank bottom;
• a sludge supply system configured to supply sludge;
• a flocculant supply system configured to charge flocculant into the supplied sludge;
• a rapid stirring machine on which the slow stirring machine is disposed and to which the flocculant-charged sludge is supplied, the rapid stirring machine comprising a rapid stirring tank and a rapid stirring blade disposed in the rapid stirring tank, the rapid stirring blade being configured to rotate around an axis of a drive shaft disposed in the rapid stirring tank to stir the supplied flocculant-charged sludge, the rapid stirring tank having a tank ceiling, the tank ceiling being configured to communicate with the tank bottom of the slow stirring tank through an opening having a diameter that is less than an inside diameter of the rapid stirring tank, the tank ceiling having a circular shape;
• and
• a stirrer controller configured to control a rotation speed of the rapid stirring blade, the stirrer controller being further configured to increase the rotation speed of the rapid stirring blade at a set rate with an increase in an amount of the sludge charged by the sludge supply system or an amount of a solid, and reduce the rotation speed of the rapid stirring blade at the set rate with a decrease in the amount of the sludge charged by the sludge supply system.