Flocculation
Flocculation is a water treatment process that coagulate or combine smaller particles into larger particles, which settle out of the water as sediment. Iron salts and alum or synthetic organic polymers are commonly used to increase coagulation. The salts and alum can be used either alone or in combination with metal salts. Sedimentation or settling occurs naturally as flocculated particles settle out of the water.
Flocculation can be achieved in two ways, by mechanical devices or hydraulic methods. Hydraulic methods are used in small plants while mechanical flocculators are used in bigger plants.
- Mechanical Flocculators: Mechanical
flocculators are used widely due to their greater flexibility in
varying G values and also due to low head loss. They are of
different types. One is horizontal shaft flocculator, which
oscillates with a back-and-forth motion. One of its benefit is that
it prevents water from rotating continuously in the same direction
around the shaft.
The shape of flocculation compartments is affected by the type of mechanical flocculator. Vertical flocculators are associated with square compartments of varying dimensions. Vertical flocculators are higher speed devices than horizontal shaft flocculators. They are more applicable to high energy flocculation situations like direct filtration.
- Hydraulic Flocculators: Hydraulic flocculating methods are effective and simple, specially in the case of relatively constant flow. The total volume of each compartment is the assumed flocculation volume. In some cases there may be decreased turbulence in portions of the compartments. The main disadvantage with it is that G values are a function of flow that can't be easily adjusted.