Device for dewatering sludge or the like

A device for dewatering sludge comprising:

• means for supplying sludge to be dewatered;
• A first gravity pressure dewatering stage having a plurality of endlessly rotating perforated filter pockets for receiving sludge from said means for supplying and for straining water therethrough;
• a second dewatering stage located below and coupled to the output of said first dewatering stage, said second stage including a plurality of sequentially arranged horizontal dewatering zones and a pair of perforated horizontal filter belts each associated with a respective horizontal dewatering zone, the output of one horizontal zone feeding the input of another for further straining water from sludge exiting from said first stage, said horizontal dewatering zones being provided one above another with a first such horizontal dewatering zone receiving output sludge from said first stage, each of said horizontal filter belts sliding across a respective horizontal dewatering zone on a flat surface permeable to fluid and cooperating with the other filter belt to form a wedge shaped compartment in each horizontal zone which tapers in the direction of sludge movement through the associated horizontal dewatering zone, said wedge shaped compartment applying greater than gravity pressure to the sludge as it passes therethrough;
• a third dewatering stage located below said first and second dewatering stages and coupled to receive the output sludge of said second dewatering stage, said third stage receiving said pair of horizontal filter belts from the last horizontal dewatering zone of said second dewatering stage and including at least two drums against which said pair of filter belts is pressed, the pressure applied to sludge by the pressing contact of said pair of filter belts with said drums being higher than pressure applied to sludge by said pair of filter belts defining said wedge shaped compartment;
• and,
• a fourth dewatering stage for receiving said pair of filter belts from said third stage and applying pressure to sludge greater than that applied by said third dewatering stage and for discharging dewatered sludge, said fourth stage comprising two endless rotating platen belts pressurized towards one another, said pair of filter belts passing through the nip defined by said platen belts.