ABSTRACT
The objective of primary treatment is to remove a signi‹cant fraction of the suspended solids and €oating material from the wastewater by sedimentation. The suspended solids removed are organic in nature, and thus contribute to the BOD (biochemical oxygen demand) of the sludge. The €oating material can include oil, grease, rags, etc. that were not removed in upstream processes. These are removed as scum from the water surface in the tank. The removal of larger organic solids helps to reduce the load on the secondary biological reactors. The solids removed are further treated in digesters, or other processes, and stabilized before disposal.
