What is the primary function of a secondary clarifier?

The primary function of a secondary clarifier is to separate settled solids from treated water. In a wastewater treatment process, after biological treatment, the wastewater contains a mixture of treated water and suspended solids, which include microorganisms and other organic matter. The secondary clarifier provides a space where this mixture can settle.

In the clarifier, gravity causes the heavier solids to settle at the bottom, forming what is known as sludge. The treated water, now clarified and containing significantly reduced amounts of solids, can then be discharged or further treated as needed. This step is crucial as it enhances the overall quality of the treated effluent by ensuring that solids are removed, thereby preventing them from entering the next stage of treatment or being discharged into the environment.

While other options mentioned—like removing heavy metals, eliminating pathogens, or facilitating algae growth—may have relevance in various contexts within wastewater treatment, they do not specifically characterize the primary role of a secondary clarifier.