Sludge blanket clarifier

The design of the sludge-blanket clarifiers used primarily in the water industry is based on the jar test and a simple measurement of the blanket expansion and settling rate (12). Different versions of the jar test exist, but essentially it consists of a bank of stirred beakers used as a series flocculator to optimize the flocculant addition that produces the maximum floc-setfling rate. Visual floc-size evaluation is usually included. 

Design and operation of recirculation systems can be compHcated. Problems are avoided by using a sludge-blanket clarifier, in which feed enters below a blanket of accumulated and flocculated soflds which become fluidized in the zone-settling regime by the upflowing feed. Feed soflds are trapped in the blanket. The soflds content of the blanket continuously increases and part must be bled off in order to maintain the mass balance. 

Sludge-blanket clarifiers are difficult to start up because the first blanket must be estabUshed, and large-scale units require extensive excavation. Sizes range from 600 x 600 mm to 50 x 50 m. Precipitation and crystallization can be carried out in similar hopper-designed units, having overflow rates of 80 m/h or higher. 

Hopper-tank sludge-blanket clarifier, 22 61-62 Hops, 3 569-572... 

Sludge-blanket clarifiers, 22 56, 61-62 Sludge control, crude tank, 26 708-711 Sludge dewatering... 

Figure 8.4 Spiracone sludge-blanket clarifier. Courtesy and registered trademark of Siemens Water Technologies Corp., Warrendale, PA.

Steam is used to heat the process. Figure 8.19 shows the cross section of a sludge-blanket (upflow) hot process softener. The operations of the sludge blanket hot process unit is similar to that for sludge-blanket clarifiers (see Chapter 8.1.1.1). Figure 8.20 shows the cross section of a downflow hot process softener. The downflow units rely on recirulation pumps to provide sludge contact. 

Ives, K. J., Theory of operation of sludge blanket clarifiers . Proc. Inst. Civ. Engrs, 39, 243-260 (1968)... 

Ide, T. and Kataoka, K., A technical innovation in sludge blanket clarifiers . 

Two American thickener designs are based on feeding the slurry under the settling sohds interface in a way similar to the sludge blanket clarifiers described in the previous section. They also have other features, all designed to accelerate the flocculation and increase the capacity. 

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