Sludge dewatering separates sludge into liquids and solids for waste minimisation. Various technologies for sludge dewatering include plate & frame and belt filter presses, centrifuging, screw pressing and geomembranes. In addition to these, there are other options available.
It is important to note that dewatering is not intended to treat the sludge or liquid. It only separates the solid and liquid components, making it easier and more cost-effective to handle the separate phases for final disposal. Once the sludge has been dewatered, the solid and liquid components may contain contaminants that need to be treated separately.
Thickening and dewatering processes provide a concentrated, consolidated product − retaining most of the solids from the original sludge – along with a diluted stream, predominantly water. For both process types, the diluted stream is usually directed back to the inlet of the wastewater treatment works.
Thickening processes concentrate the sludge by removing part of the free water. In doing so, the finished product retains the liquid, free-flowing characteristics of the feed sludge so that it can still be conveyed by pumping. Thickening typically increases the dry solids (DS) content to 4−6 per cent.
Dewatering processes remove significantly more of the sludge water content. It produces a concentrated sludge with a DS concentration generally between 15 and 45 per cent. At this concentration, the product, referred to as a cake, is not free-flowing and instead forms lumps that can only be transported by a conveyor belt, mechanical earth-moving equipment, or spade.
Dewatering processes apply a significant mechanical force to achieve increased water removal over that possible from thickening. These processes operate by:
