TERTIARY CLARIFIER DESIGN CONCEPTS AND CONSIDERATIONS

Tertiary clarification is a unit process that can be used after conventional biological treatment to provide effluent water quality that is better than secondary standards. Common applications for tertiary clarification are enhanced removal of phosphorus, suspended solids, metals, and pathogens. Information is presented on the scientific basis for tertiary clarification processes including characterization of suspended solids, settling velocities and overflow rates, chemical coagulation, precipitation of metals, and chemical phosphorus removal. Material from a large number of sources has been summarized and referenced to provide the practicing engineer detailed information to support the design of tertiary clarification processes on a rational basis. Clarifiers for two- and three-sludge processes are considered to be a form of secondary sedimentation associated with an activated sludge process, and are not considered here.