Primary Treatment
After leaving the grit tanks, the wastewater flows to the Primary Settling Tanks. Some tanks are rectangular and some are circular, but they all serve the same purpose: they allow the flow of wastewater to settle so that settleable solids (sludge) may be removed from the bottom of the tanks. At the same time, floating solids (scum) are skimmed from the water's surface.

The wastewater leaving the Primary Settling Tanks (Primary Effluent) is piped to the Flow Distribution Box. From the Distribution Box, the wastewater flows to the Aeration Tank Influent Channel, or a percentage of the flow may be diverted to the Flow Equalization Tank. This tank is used to equalize the flow of wastewater through the remainder of the treatment process. During periods of high flow, the excess wastewater is sent to the Equalization Tank. Later, as the incoming wastewater flow drops off, the Equalization Tank is drained back to the Influent Channel at the beginning of the treatment process. This allows for a more consistent flow through the facility.

 
Next Step: Secondary Treatment