Clarifiers designs

Fig. 6. A reactor clarifier designed for both coagulation and settling.

TABLE 18-7 Typical Thickener and Clarifier Design Criteria and Operating Conditions... 

Rising sludge can also be caused by internal solids overloading and hydraulic overloading to the secondary sedimentation. Poor sedimentation clarifier design and operation in terms of flow-through velocity, weir design, and so on are also possible causes. 

Objective Tree clarify design objectives and sub-objectives, and their relationships... 

Solids flux method. The design of the thickener area considers zone C. (Note you do not consider zone D.) As indicated, the concentration of the solids in this zone is variable. Thus, the behavior of the solids is modeled by making several dilutions of the sludge to conform to the several concentrations possible in the zone. The ultimate aim of the experiment is to be able to determine the solids loading into the thickener. The experiment is similar to that of the clarifier design, except that several concentrations are modeled in this instance. Also, it is the relation between subsidence velocity and concentration that is sought. The reason is that if velocity is multiplied by the concentration, the result is the solids loading called the solids flux, the parameter that is used to size the thickener portion. 

Table 3 Typical Surface Overflow Rates for Clarifier Design...

Clarifier Design. Design methods for dilate sedimoitation are based on the prin(%le of providing enough residence time for tiie separation to take place. Estimates can be made using Stokes law or Newton s law as described in Chapter 3, e ecially for well-defiaed homogeneous systems, but due allowance must be nude for deleterious effects due to convection, air-induced surface waves, inlet and outlet turbulence etc. 

When agglomerates form in brine as a result of the addition of a flocculant, they tend to trap liquid within their structure and in the irregularities on their surfaces. While clarification is enhanced, therefore, thickening may suffer. The concentration of the sludge produced in the clarifier may be reduced. The same will be true with some of the modified clarifier designs discussed in Section 7.S.3.3. 

Many clarifier designs include scum boxes that are placed at one spot along the periphery. Thin, low-speed rakes gather the scum from the surface and deliver it to the box for removal. 

Clarifier design has traditionally been based on the principle of dilute sedimentation. The design calculations of a clarifier include feed well design, sedimentation basin design (providing enough residence time for the separation), and solid flux (G). The other design parameters, such as the torque requirement and clarifier area, are similar to those of the thickeners, which have been discussed in the previous section (3.2.1). 

Many clarifier designs, such as the solids contact unit, combine mixing, flocculation, and coagulation in one basin. This may have economic advantages and may produce better-quality effluent with shorter overall detention time than the approach using separate treatment units. 

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