Primary Treatment

Primary Clarifier

American Bottoms has four 12 foot deep, 110 foot diameter primary clarifiers.  During normal flows, American Bottoms is able to operate with two primary clarifiers in service.  When the plant is experiencing higher flows due to large amounts of precipitation, the other two primary clarifiers are put in service.

Feed Well

The feed well is located in the center of the clarifier.  It is a 14 foot diameter circular well that spans about a quarter of the depth of the clarifier.  The wastewater is pumped through a vertical pipe into the stilling well.

The speed of the incoming water is slowed, and the water evenly distributes around the tank.

Skimmer Arm & Skimmer Rake

The skimmer arm is used to remove the floating solids such as scum and grease from the primary clarifier.  The arm makes one complete revolution around the clarifier every 25 minutes.  In order to allow the sludge to settle out, the water must be kept as calm as possible.  As the skimmer arm travels around the clarifier, it pushes the scum in front of it.  Once it reaches the scum beach, the arm traveling along the edge of the clarifier weighs down a lever that opens the door to the scum hopper.  The scum is pushed over the scum beach and into the open hopper.


The rakes at the bottom of the tank span the entire diameter of the clarifier.  The tines are angled to push the settled sludge to the center of the tank where the sludge is removed.  The rakes rotate very slowly so the settled sludge is not disturbed.

V-Notched Weirs & Launder

V-notched weirs line the outer edge of the clarifier.  The weirs help to ensure that the water leaves the clarifier evenly which helps to keep the water calm.  There is also a baffle located before the weirs.  It prevents any of the floating solids from escaping over the weirs.

The wastewater flowing over the weirs flows into the launder.  The launder is a slightly sloped channel that surrounds the clarifiers.  The effluent water drains from the launder and flows into the main channel to the next process.