A sludge is a colloidal solution with solid particles suspended in water. For dewatering to be effective, the smaller sludge particles should join together and form larger particles.
This is done by adding sludge conditioners. Sludge conditioners work by altering the pH value of the sludge. This results in coagulation. The water and the particulate matter separate. Different sludges have different pH value for coagulation.
Once the sludge has coagulated, it can be easily dewatered using centrifuges or vacuum filters.