Charlotte-Mecklenburg Utilities uses a very common process in treating and purifying water for Charlotte and Mecklenburg County. The process is broken into five steps: coagulation, flocculation, sedimentation, filtration and disinfection.
During coagulation, liquid aluminum sulfate (alum) is added to untreated water (raw water). When mixed with the water, this causes the tiny particles of dirt in the water to stick together or coagulate.
Paddles in these large tanks stir the alum and water mixture, causing them to stick together and form large, heavier particles called floc.
As the water and the floc particles progress through the treatment process, they move into sedimentation basins where the water moves slowly, causing the heavy floc particles to settle to the bottom. Floc which collects on the bottom of the basin is removed from the water.
From the sedimentation basin, the water flows through a filter designed to move any remaining particles left in the water. The filters are made of layers of sand and gravel.