It is a process used to increase the amount of solids by removing the excess water contained in the biological or chemical sludge taken from the settling pools. Increasing the solids in the sludge condensation allows for smaller selection of systems for the dewatering steps. Fixed Bridge Central Shaft Concentrators are suitable for use in sedimentation pools up to 16 m in diameter. It is not economically suitable for larger diameters. In such cases, rotary bridge concentrators should be preferred.