Wastewater Operator Level 1 Practice Test

The essential job of a secondary clarifier is gravity-based sedimentation to remove suspended solids from the clarified wastewater after biological treatment. By slowing the flow, solids settle to the bottom as sludge while the clearer liquid overflows the weir at the top, leaving the clarified effluent for onward treatment. The settled sludge can be redirected back to the biological reactor as returned sludge or withdrawn for disposal, while the clarifier helps protect downstream processes from solids carryover. Disinfection, aeration/mixing, and thickening occur in different parts of the treatment train or serve different purposes, so they are not the primary function of the secondary clarifier.