1. Definition
   1. Sludge thickening
      1. the separation of solid particles from the liquid phase by gravity into higher conc of solids
   2. Sludge stabilisation
      1. to reduce biological activity by chemical, biological or thermal treatment
   3. Sludge dewatering
      1. to reduce the weight/volume of sludge requiring disposal involves the removal of water entrapped in the sludge
2. Typical sludge handling system
3. Types of thickening
   1. Gravity
      1. Clarifiers
   2. Flotation
      1. Dissolved air flotation (DAF)
   3. Gravity belt
   4. Centrifugation
   5. Rotary drum