The wastewater treatment process typically includes three stages: primary, secondary and tertiary treatment. A pretreatment stage is also present that removes objects and materials that can be easily collected from the wastewater.
Primary treatment consists of removing floating and settleable solids through sedimentation. Sedimentation is a physical water treatment process that uses gravity to remove suspended solids from water. In the primary sedimentation stage, wastewater flows through large tanks, commonly called “pre-settling basins”, “primary sedimentation tanks” or “primary clarifiers”. The tanks are used to settle sludge while grease and oils rise to the surface and are skimmed off.
Primary settling tanks are usually equipped with mechanically-driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank where it is pumped to sludge treatment facilities.
In addition to reducing the content of suspended solids, primary clarifiers also reduce the pollutants embedded in the suspended solids.
For any additional information on primary treatment, please visit the Wikipedia article that was used for this webpage.