Coarse and Fine Screens
Initially the sewage water arriving at the plant undergoes a mechanical step, which consists of a screen that removes larger particles as papers, hair, rags, sticks and other debris. The screens can be either Coarse screens, Fine Screens or a combination of both, the purpose is however to prevent large particles from damaging downstream equipment or interfere with further treatment. This would create unnecessary wear which could lead to process stops and higher maintenance costs. The screenings removed by the screen generally undergoes some sort of washing/dewatering procedure before being disposed or incinerated.
Hereafter the screened wastewater flows through a grit removal channel. The grit channel allows heavier sand, gravel, and other particles to settle out while the organic materials remain suspended in the wastewater and are carried on. Grit removal is necessary to protect moving mechanical equipment from abrasion and abnormal wear and to reduce the quantity of inorganic solids in the process basins.
The last activity of mechanical treatment is a presedimentation step where larger particles in the wastewater are separated by sedimentation. This removes some of the work load from the following biological step. The sludge obtained throughout the treatment is removed to the sludge treatment.