The animation below, which was kindly provided by a visitor to this site, shows the operation of a belt filter press used for dewatering sludge.  The coagulant-treated, low concentration sludge is loaded into the hopper at the top and distributed onto the moving, porous belt.  The sludge is squeezed through a series of progressively tighter rollers to expel water.  The thickened sludge "cake" is collected in another hopper, while the water is generally drained to the headworks of the treatment plant.