The flow from the influent structure is split between two, rectangular primary clarifiers. The clarifiers provide the next treatment step by removing most of the solids that have settled.
To accomplish this, the movement of wastewater is slowed down to the point that heavier solids settle to the bottom of the tank, and lighter-than-water materials, such as oil and grease, float to the top. The floating materials are skimmed off, and the solids at the bottom are continuously scraped to a hopper and periodically drained off. The skimmings and settled solids, called sludge, are then pumped to the aerated sludge lagoon, shown below.