Clarifiers are utilized by various chemical process plants, including the pulp and paper industry. Clarifiers are used to minimize the amount and toxicity of suspended solids in the effluent stream. The clarification process incorporates coagulation, flocculation, and sedimentation. The removal of suspended matter by settling without chemical coagulation is rarely encountered today.
There exist many designs for clarifiers; however, the emphasis of this discussion will be based on the type of clarifier depicted in Figure 1. The walls and floor are fabricated from steel reinforced concrete, while the center well, rake, and associated moving parts of the clarifier are constructed from mild steel.
Although clarifiers are the subject of this paper, much of the corrosion theory can be applied to holding and chemical mixing tanks without rake mechanisms.