ABSTRACT
C OAGULATION is a chemical process that physically makes sedimentation more efficient (see Figure 5.1). Flocculation is a physical process used to enhance the effectiveness of coagulation's chemical addition. The screened influent is pumped into large settling basins (also called clarifiers or sedimentation tanks) where it is allowed to sit for a prescribed time. The settling basin allows gravity to handle many of the suspended impurities that remain in the influent. Under quiescent basin conditions, when flow and turbulence are at the minimum, sedimentation makes particles that are denser than water sink and settle to the tank bottom. Larger and heavier particles settle faster than smaller, lighter particles. The accumulation on the bottom of the tank is called sludge or water solids.
