After the inorganic grit is removed from the wastewater, the next step is to remove the organic solids. The organic solids are material that can be processed at the treatment facility through the anaerobic digestion process. To separate these solids from the rest of the wastewater we use simple gravity.
The wastewater is split into four long tanks that allow the water to slow down to less than 0.5 feet per second. At this speed, floatable material will separate from the water to the top, and the heavier solid material will sink to the bottom. The floatable material (also called "scum") is skimmed off the surface of the water and also sent to the digester.