Upflow clarifiers

Solids-contact clarifiers (also known as "upflow" clarifiers) typically have four treatment zones ... 

These suspensions were separated with varying efficacy in the tanks investigated. Tank C, for instance, a so-called upflow clarifier, has been identified as a reactor with a relatively stable flow structure. It showed little change in dispersion number when the hydraulic surface loading was increased, but very high values of removal efficiency over the whole range of chemical conditions investigated. 

In constant plan (flat-bottom) clarifiers the upflow velocity should be uniform at all levels and the floe blanket (fluidized bed) should have a uniform concentration and uniform particle size. In expanding upflow clarifiers (conical, or hopper-bottom) the lower levels should have greater upflow velocities and, therefore, lower floe volume concentrations or particles. In practice, such expanding upflow is highly unstable and massive vertical eddies cause recirculation, with almost uniform concentrations and particle sizes throughout the fluidized bed. A definite zone of separation forms at the surface with a clean water zone above it, relatively free from primary particles and floes. 

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. 

The source of water samples was a 4-m3/h pilot plant on the Seine River located upstream from Paris, France. The background organic concentration ranged from 2 to 3 mg/L. The process, shown in Figure 1, included an upflow solids contact clarifier (Pulsator, Degremont, Rueil Malmaison, France) followed by rapid sand filtration (RSF). The effluent of the RSF was then split into four lines, which received various levels of ozonation followed by granular activated carbon (GAC) adsorption. Postchlorination (0.2 mg/L residual after 1 h) was used for bacterial control. 

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. 

The throughput of an upflow filter is limited by the danger of fluidization. This will dismpt the bed and allow a major increase of solids in the effluent liquid. On the other hand, upward flow allows depth filtration, in which particles can be removed from the brine anywhere in the bed. Upflow filters therefore have solids capacities two or three times as great as downflow filters, resulting in longer on-stream times. They also are more stable in the face of a clarifier upset. Some filters can tolerate up to 500 ppm solids in the feed brine while maintaining a 4-hr cycle [109]. 

While the normal solids content of clarified brine is in a range that often favors downflow filtration, the other considerations given above often result in the choice of upward flow. Both types are widely found in the chlor-alkali industry. Liederbach [40], Sutter [53], and the authors have at least a mild preference for the upflow type, which we adopt here as the standard for discussion. 

Common anaerobic bioreactor configurations are designed to obtain good mixing and biomass separation. This can be achieved by filtration, sedimentation and digestion before returning the clarified or treated liquid to the bioreactor use of anaerobic filters or upflow clarification or the use sequential reactors systems (Stephenson et al., 2002). Some of the most utilized anaerobic reactor configurations are briefly described below. 

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