The flow distribution box directs the flow to the primary clarifiers by the use of slide gates to create uniform flows and sludge settling.
The most important function of the primary clarifiers is to remove as much settleable and floatable materials as possible. The settled solids are called sludge. The floating solids are called scum. The settled raw sludge and floating scum are pumped from the primary clarifiers to the anaerobic sludge digester for treatment.