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The decanter centrifuge is an important piece of equipment for sludge volume reduction prior to thermal drying. Understanding centrifuge operation helps manage drying energy costs Consecutive mechanical dewatering and thermal drying are integral parts of sludge management, lowering the sludge volume that needs to be disposed of or further treated. Because drying is an energy-intensive unit operation, the mechanical pre-concentration of the solids is a prerequisite. The economic necessity for sludge-volume reduction in the chemical process industries (CPI) as a way to manage downstream sludge-handling costs was discussed previously (Chem. Eng., Sept. 2014, pp. 51–54 [1]). Because dewatering prior to drying is such an important stage in the sludge-volume-reduction process — the drier the sludge solids, the less costly the next drying stage — this article discusses sludge dewatering with a solid-bowl decanter centrifuge, one of the most frequently used types of equipment for mechanical dewatering of sludge. The high energy consumption of sludge dryers is primarily due to the latent heat of evaporation of water, which is equal to 2,260 kJ/kg at 100°C. To first raise the water temperature from, for instance, 25°C to 100°C, an…