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Coagulation refers to the destabilization of suspended colloidal materials. This step is necessary since the particles carry a surface charge (usually negative) and their mutual repulsion is enough to prevent them from settling. Note that coagulation is different from precipitation.
is technically different from flocculation although the two terms are often used synonymously.
Flocculation refers to the bridging between particles (polymer chains can be employed) causing them to form flogs or larger aggregates. These flocs float (flotation) or sink (sedimentation), making them easier to remove from the system.
Precipitation is the insolubilization of dissolved materials; An example is the precipitation of iron by raising the pH to 8 with calcium hydroxide to form an insoluble iron hydroxide precipitate.
Sludge dewatering is the removal of water from sludge to reduce its volume, lowering hauling costs.
Moreover, dewatering improves sludge characteristics.
This process, typically accomplished with a centrifuge, press filter or belt filter, also makes the sludge better adapted for further treatment or disposal.
Clarifiers are large cylindrical or rectangular basins wich allow the separated solids to settle from the water, permitting clear water to pass over a weir.