What does primary treatment in sewage treatment involve?

Primary treatment in sewage treatment is focused on the separation of solids from liquids. This initial phase typically involves the physical processes of sedimentation and flotation. During primary treatment, raw sewage is directed into a large tank where heavier solids settle to the bottom as sludge, while lighter materials, such as grease and oils, float to the surface. This process effectively reduces the amount of suspended solids and organic matter in the wastewater.

By removing a significant portion of the solids during this stage, primary treatment prepares the sewage for further treatment processes, which can include biological methods or advanced filtration techniques, depending on the treatment facility’s design and treatment goals. This step is crucial for improving the quality of effluent before it undergoes secondary treatment, where biological processes further break down the remaining organic matter.

Other processes listed, such as biological degradation, filtration, and chlorination, are part of secondary and tertiary treatments and play different roles in the overall sewage treatment process.