Sludge de watering is the separation of a liquid and solid phase whereby, generally, the least possible residual moisture is required in the solid phase and the lowest possible solid particle residues are required in the separated liquid phase. Dewatering can be done either with help of pressesor centrifuges (mechanical dewatering), filtration (e.g. infilter bags) or physical (and biological) processes in drying beds. Mechanical dewatering and filtration often require the use of chemicals (coagulants and flocculants) to enhance the process.