Which equipment is used to dewater sludge?

• A. Gravity thickener or DAF
• B. Grit separator
• C. Aerobic or anaerobic digester
• D. Belt press or plate press

Answer: (D)

Dewatering sludge means removing more water to leave a drier, more manageable solids cake. This is done with mechanical press systems that apply pressure to the sludge to squeeze out water. Belt presses use belts and rollers to filter and compress the sludge, pulling water out as it moves through the system. Plate presses stack filter plates and use tight pressure to force water out of the sludge inside the plates. These methods reduce the water content far more than simple settling or flotation.

In contrast, a gravity thickener relies on gravity to settle solids and remove some water, while a DAF unit floats and removes clarified water and lightweight solids—these are thickening, not dewatering steps. A grit separator removes inert grit, and a digester treats sludge biologically, not for water removal.