Which device is used to dewater sludge solids in wastewater treatment?

• A. Band screen
• B. Plate or frame press
• C. Micro screen
• D. Rotary drum

Answer: (B)

Dewatering sludge solids means removing as much water as possible from the sludge to reduce its weight and volume for easier handling and disposal. A plate or frame press does this by filtration under pressure. The sludge is placed between filter plates with a cloth, then the plates are pressed together so water is squeezed out and drained away, leaving a compact sludge cake with much lower moisture content. This mechanical filtration approach is specifically designed to extract liquid from sludge, unlike screening devices that only remove solids by size and do not greatly reduce water content. A rotary drum primarily acts as a screen or thickener in many systems, not a dedicated dewatering device. So, the plate or frame press is the device best suited for dewatering sludge solids.