What happens to the sludge?

At first, sludge is held in the Sludge Storage Tanks. At this stage, primary sludge is about 96% water and secondary sludge is about 99% water.

In the Thickening and Dewatering Building, secondary sludge is processed in the Gravity Belt Thickeners to produce “thickened secondary sludge”. The thickened secondary sludge and the primary sludge continue to the Belt Filter Presses. When the sludge enters the Belt Presses, it looks like dirty water. After processing, the sludge is about 75% water and looks like mud.

The sludge is then processed in one of three sludge dryers. The dried sludge is then either used as a fuel, replacing coal, in a cement kiln or beneficially reused as landfill cover. Filtrate (water removed from the sludge in the Gravity Belt Thickeners and the Belt Presses) is returned to the main system at the head of the plant.