Purpose
A major operating cost for water purification is the sludge disposal cost. The lower the dry matter content of this sludge, the more ons is paying for the disposal of water. To significantly lower the costs for sludge disposal dewatering is often recommended. Sludge dewatering means that the free water between the solid materials is removed so that a semi-solid mass is obtained.
Concentration of solids, sludge dewatering
Separation of manure and digestate into a thick fraction and fine fraction
Dewatering biological or physicochemical sludge
Dewatering mineral slurries
Principle
Centrifugation is widely used in various industrial sectors. A decanter centrifuge separates the sludge and water by means of the centrifugal force. Here, the heavier sludge particles are flung against the inner wall of a rotating cylinder. The centrifugal force subsequently causes a further compaction and dewatering of the sludge. The sludge is finally removed from the centrifuge along one side via a screw, while the centrate exits the decanter along the other side.
The efficiency of the sludge dewatering is evaluated on the basis of the final dry matter content of the separated pasty sludge and the quality of the centrifugate. Process variables which influence the performance of the centrifuge are, i.a. the feed rate, drum volume, speed of rotation of the screw, rotational speed difference between the screw and the drum, the depth of sedimentatie zone, chemicals usage and physicochemical properties of the sludge-water mixture. Vibration and sound effects should be taken into account in the construction of the plant. Pilot tests are recommended before the final design should be chosen.
Scheme
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Applications
A decanter centrifuge and a belt press require little supervision, which is an advantage with respect to a chamber filter press. A decanter centrifuge is easily adjusted for various types of sludge, though this is more difficult with a sieve belt press and the chamber filter press (other screen cloths). A chamber filter press has generally a higher dry matter content than a decanter centrifuge, which, in turn, performs better than a sieve belt press.
Approach Trevi
Trevi aims to initially minimize the sludge production by means of process oriented interventions. For this we look both to a reduction of the pollution load from the production as well as optimization of the water treatment plant (load, chemical use). We then investigate in function of the amount and type of sludge if there's an economic advantage to be gained by sludge dewatering and what technique is beneficial in case.With the degree of sludge dewatering the cost of dewatering increases. The balance between intensity of dewatering and sludge disposal costs has to be found.