Rectangular Clarifiers

Primary clarifier rectangular basin, concrete excluding the earthwork and mechanism. Installed cost 160000 at surface area = 400 m with n = 0.56 for the range 60-400 and n = 1.45 for the range 400-800. 

Blanket clarifier Circular clarifier inclined plate clarifier Rectangular clarifier Vertical flow clarifier... 

Clarifiers. The largest user of clarifiers is probably the water-treatment industry. The conventional one-pass clarifier uses horizontal flow in circular or rectangular vessels (Eig. 2) with feed at one end and overflow at the other. The feed is preflocculated in an orthokinetic (paddle) flocculator... 

Fig. 2. Schematic diagram of a rectangular basin clarifier having an orthokinetic flocculator where the feed is mixed with a flocculant.

Suspended Solids Removal. Depending on the concentration and characteristics of the suspended soflds, they can be removed by filtration, flotation, or sedimentation. Coarse soflds are removed by screening. Settleable suspended soflds are removed in a clarifier, which may be circular or rectangular. The efficiency of soflds removal is a function of the overflow rate (m /-d (gal/ft -d) as shown in Figure 5. 

Plate pr esses. Sometimes called sheet filters, these are assemblies of plates, sheets of filter media, and sometimes screens or frames. Thev are essentially modified filter presses with practically no cakeholding capacity. A press may consist of many plates or of a single filter sheet between two plates, the plates may be rectangular or circular, and the sheets may lie in a horizontal or vertical plane. The operation is similar to that of a filter press, and the flow rates are about the same as for disk filters. The operating pressure usually does not exceed 138 kPa (20 psig). The presses are used most frequently for low-viscosity liqmds, but an ordinaiy filter press with thin frames is commonly used as a clarifier for 100-Pa s (1000-P) rayon-spinning solution. Here the filtration pressure may be 6900 kPa (1000 psig). 

There are commercially available clarifier simulation software for comprehensive (2D) analyzes of wastewater treatment processes in circular and rectangular clarifiers. With these software, you can predict processes like ... 

All DAFs are similar to each other in terms of theory, principles, design, operation, and secondary flotation performance. The authors select the circular DAF process equipment manufactured by KEC for the purpose of feasibility studies. The users should contact more than one major DAF and DAFF manufacturers for appropriate pilot plant demonstrations and cost comparisons. Rectangular DAF and DAFF clarifiers are as good as circular DAF and DAFF clarifiers. 

The mechanism for sedimentation (clarification) is based on the density difference between SS and liquid. In addition, SS with larger particle sizes can settle down more easily. Rectangular tanks, circular tanks, combination flocculator-clarifiers, and stacked multilevel clarifiers can be used.14 Oliveira et al.15 reported that flocculation and sedimentation were conducted in the cassava meal industry and reduced the effluent concentration of organics from 14,000 to 2000 mg/L in the bench-scale reactor, with a hydraulic retention time (HRT) of 37 min. 

Figure 8.3 Actiflo rectangular recirculation clarifier. Courtesy and registered trademark ofVeolia Water North America, Chicago, JL.

Sedimentation clarifiers may be circular or rectangular in configuration. In a circular sedimentation clarifier, the influent enters into the center or the perimeter ("peripheral feed") of the unit. In a center-fed unit, the effluent water is collected in the perimeter. It is difficult to control the recirculation in a perimeter-fed unit, and hence, is not common. In a rectangular sedimentation unit, the flow is linear. Rise rate is about 1 gpm/ft2 with a residence time of two to six hours. 

Selection of Type of Thickener or Clarifier Selection of the type of unit thickener or clarifier depends primarily on the optimization of performance requirements, installation cost and operating cost. For example, the inclined-plate type of clarifier provides for less solids-holding capacity than a circular or rectangular clarifier, but at a lower installation cost. The high-density thickener maximizes underflow solids concentration, requiring a higher torque rating than conventional thickeners. 

FIGURE 5.6 Elevation sections of a circular clarifier (a) and a rectangular clarifier (b). 

Flow-through velocity—The horizontal velocity in a rectangular clarifier. 

Vi Flow-through velocity in a rectangular clarifier v Terminal settling velocity of particle removed 100%... 

The prototype detention time and overflow rate were calculated to be 1.5 h and 28 m/d, respectively. The peaking factor is 3.0 and the minimizing factor is 0.3. Assuming the particles are flocculent, calculate the width of the rectangular clarifier. The average daily flow rate is 20,000 ml A. 

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