The silt, sand and other materials present in Lake Michigan waters are removed during the treatment process. These “residual solids” from the settling tanks and filters are concentrated at the Residual Solids Processing Building for ultimate disposal at a landfill. Several steps are employed to concentrate these solids.
Solids collected at the bottom of the sedimentation basin and in the backwash water are concentrated in two gravity thickeners. Thickener “decant” is recycled to the head of the plant for pre-treatment.
The concentrated solids in the thickeners are pumped into the dewatering centrifuges. These centrifuges rotate at high speeds where more than 90% of the water is removed from the thickened sludge producing a solid, non-hazardous material that is hauled from the plant for disposal in a landfill.