Which of the following describes a primary settling unit?

A primary settling unit is designed to clarify wastewater primarily through the process of sedimentation. During this phase of wastewater treatment, heavier solids in the wastewater settle at the bottom of the tank due to gravity, leading to the separation of suspended solids from the liquid. This process effectively reduces the load of solids that will need further treatment and helps to improve the overall quality of the effluent.

The function of a primary settling unit is critical in the treatment process as it prepares the influent for subsequent stages such as biological treatment. While it does not involve biological treatment or promote the breakdown of organic matter, its primary role is focused on physical separation and clarification. Additionally, it does not stabilize sludge, as that process typically occurs further along in the treatment process.