What type of tank is included in primary treatment?

The correct choice is a sedimentation tank. In primary treatment of wastewater, sedimentation tanks, also known as primary clarifiers, are used to remove solids from the water. These tanks allow the flow of wastewater to slow down, which enables larger solids to settle to the bottom due to gravity, forming a sludge layer. The clearer water, known as supernatant, can then overflow or be drawn off for further treatment.

Understanding the function of a sedimentation tank is crucial because it plays a key role in reducing the organic and solid load before the wastewater proceeds to secondary treatment processes. By effectively removing these solids, the tank helps improve the efficiency and operational effectiveness of subsequent treatment stages.

Other types of tanks mentioned, such as chamber tanks or separation tanks, are not standard components of the primary treatment process in wastewater treatment. Similarly, septic tanks are designed primarily for onsite wastewater treatment in households and are not considered part of the centralized wastewater treatment system like those employed in municipal plants.