Pre-treated wastewater is brought up from inlet trunk sewers to ground level by centrifugal pumps, where it continues on by gravity flow to subsequent treatment. To maintain a desired level in the headworks wetwell, pump speed is often varied. Pumps turn on and off automatically according to an operator selectable sequence.
A desired wetwell level reduces the drop downstream of the influent flumes to minimize turbulence and air entrainment, and eliminates frequent pump cycling associated with variable level control. Proper level control maintenance in the wells can alleviate pump surging, which disrupts settling by causing currents and eddies in the clarifier.