8.5.1 Types of Flocculators
Flocculation units are often divided into two general groups: (1) hydraulic flocculators, and (2) mechanical flocculators. The hydraulic flocculators simply utilize cross-flow baffles or 180° turns to produce the required turbulence. The critical design objective in hydraulic flocculator is to achieve gentle, uniform mixing that will not shear the floc. These types of flocculators are effective only if the flow rate is relatively constant. They are rarely used in medium- and large-sized water treatment plants, because of their sensitively to flow changes.³7 In mechanical flocculators, any of the mixers described in Section 8.4.1 can also be used (at a reduced speed) for flocculation. The mixers typically used in flocculation basins are horizontal-shaft paddle-wheel flocculators (Figure 8-12(a)). The turbine type are axial- and radial-flow vertical and horizontal flocculators. In addition to mixer type, other common flocculators are the walking-beam type and the oscillating type. These flocculator types are shown in Figure 8-12 (a) and (c)38,39