A sludge with a solids content of 8 -10 percent or more can be produced by this method. A blanket of sludge is maintained by controlled removal which may be continuous at a low rate. Sludge is usually pumped continuously from the settling tank to the thickener which has a low overflow rate so that the excess water overflows and the sludge solids concentrate in the bottom. The thickening tank is equipped with slowly moving vertical paddles built like a picket fence. It may also be used to concentrate sludge to primary tanks or a mixture of primary and excess activated sludge prior to high rate digestion. Its use is largely restricted to the watery excess sludge from the activated sludge process. Gravity Thickening: This process involves the concentration of thin sludges to more dense sludge in special circular tanks designed for this purpose. The type of thickening selected is usually determined by the size of a wastewater plant, its physical constraints and the downstream process.ĪES can offer gravity thickening, dissolved air flotation (DAF) thickening, centrifugal thickening, and rotary drum thickening depending upon the process application & space availability.ġ. Centrifuge thickening is also becoming more common. The most commonly used thickening processes include gravity thickening, dissolved air flotation, and rotary drum thickening.
Sludge in wastewater treatment free#
Thickening of sludge increases its solids content and reduces the volume of free water thereby minimizing the unit load on downstream processes such as digestion and dewatering. Wastewater treatment plants commonly use thickening devices to increase the solids concentration at the end of a particular process step within the activated sludge process.
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