90Polyaluminium Chloride (PACl)
Some of the alternative coagulants such as polyaluminium chloride (PACl) can be advantageous
over the traditional coagulants in low temperature conditions as these coagulants are already
hydrolyzed, and therefore temperature tends to have less effect on the coagulation process.
Following flocculation, agglomerated particles enter the clarification unit where they are removed
by sedimentation by gravity or are floated and skimmed from the surface of the clarification unit.
In the sedimentation processes, the majority of the solids are removed by gravitational settling;
particles that do not settle and are still suspended are removed during the filtration process.
Sedimentation is generally accomplished in rectangular or circular basins and is often enhanced
by the addition of inclined plates or tubes which increase effectiveness of the process by effectively
increasing the surface area of the sedimentation basin.