Flocculation: This term is derived from the Latin word flocculare. The meaning of the word is to firm a floc'. Hence, flocculation is stimulation by mechanical means to agglomerate destabilised particles into compact, fast setteable particle (or flocs). Flocculation is a gentle agitaion causing velocity gradient in the coagulated water and forculised pariticles come together to become large and readily settable floc.

This process is carried out in a basin or tank and it is known as flocculation basin, or flocculation tank. In this tank, slow mixing is done by revolving paddles, during which the growth of floc takes place. Many patented devices are available. Most famous is Dorroco- flocculator designed by Dorr Oliver and Co, U.S.A. A typical flocculator fitted with slow moving paddles is shown in Fig. 7.7.