In primary sedimentation, how are floating solids typically removed?

In primary sedimentation, the process involves the settling of suspended solids in wastewater to reduce the load on subsequent treatment stages. Floating solids, such as grease, oil, and other less dense materials, accumulate at the surface of the sedimentation tank. These floating solids are effectively removed by skimming with a scraper, which is designed to collect and remove the scum layer from the water's surface.

This method allows for the efficient removal of materials that do not settle to the bottom, ensuring that the water leaving the primary sedimentation process is more clarified and suitable for further treatment. The skimmer continuously moves along the surface, effectively capturing the floating solids and directing them away from the treatment process.

The other methods mentioned, while useful in different contexts, do not effectively target the removal of floating solids in primary sedimentation. Mechanical pumps are more suited for transporting fluids rather than removing surface material. Chemical coagulation assists in aggregating particles for settling but does not specifically target floating substances. Filtering through media typically addresses suspended solids rather than those that float. Therefore, using a scraper for skimming is the most direct and effective technique for removing floating solids during primary sedimentation.