Mechanical and thermal dewatering of residual sludge

The management of residual sludge is an important subject. New environmental laws require the elimination of this waste by only two ways: incineration and agricultural use. In order to reach this goal, mechanical dewatering can be used as a first step due to its low energy cost. However, the final moisture content reached through this method is not generally sufficient and drying becomes obligatory. In this work we studied the first step: mechanical dewatering. Some experiments were carried out on a laboratory filtration-compression cell and the use of the Ruth relationship approach was tested in order to characterise slurry in filtration. We also studied the second step: thermal dewatering. From laboratory convective drying experiments, a macroscopic approach in terms of kinetics curve and drying potential was developed. This criterion, which groups a set of external conditions into a unique parameter (temperature, relative humidity, air velocity), allows for easy classification of different operating strategies.