Settling column

Conditions favoring efficient separation of flocculent metal precipitates in a basin include a low surface overflow rate, adequate depth, and inlet and outlet designs for a uniform velocity field with minimal short circuiting or stagnation. Solids separation is likely to limit the overall efficiency of metals removal in treatment, so pilot studies include batch and continuous flow settling column studies.18... 

Figure 5.7a shows the basic principles of removal of solids in the settling zone. A settling column (to be discussed later) is shown moving with the horizontal flow of the water at velocity from the entrance of the settling zone to the exit. As the column moves, visualize the solids inside it as settling when the column reaches... 

Consider the presedimentation basin as a prototype. In order to design this prototype properly, its performance is often simulated by a model. In environmental engineering, the model used is a settling column. Figure 5.8 shows a schematic of columns and the result of an analysis of a settling test. 

FIGURE 5,8 Settling column analysis of discrete settling. 

Example 5.8 Assnme Anne Arundel County wants to expand its softening plant. A sample from their existing softening tank is prepared and a settling column test is performed. The initial solids concentration in the colnmn is 250 mg/L. The results are as follows ... 

Depth of settling column used to calculate terminal settling velocity of any particle... 

If the percentage removal of particles is 71.58, what is the hydrauhc loading rate The settling column has a depth of 4 m. 

Example 9.8 A settling column 4 m in height is used to determine the a of a wastewater. The wastewater is to be aerated using a fine-bubble diffuser in the prototype aeration tank. The laboratory diffuser releases air at the bottom of the tank. The result of the unsteady state aeration test is shown below. Assume P = 0.926, r = 1.0 mg/F h and the plant is 304.79 m above mean sea level. For practical purposes, assume mass density of water = 1000 kg/m. Assume an ambient temperature of 25°C. Calculate a. 

Other samples of alkaline slurry were subjected to particle size analysis by sedimentation. With the —43 xm + 1.2 [im fraction this analysis was done in a 50-mm-diameter settling column of dilute slurry with a tared pan at the base to record continuously the mass of sedimented solid. The data were analyzed by the method of Oden (8), and the particle size distribution (Stokesian diameter), expressed on a mass percent basis, was calculated. 

C, the distance settled, colimm D, and the fraction settled, column E, for each of the sizes. 

Combinations of pool depth and detention time must be discovered that will give the edfied level of removal of solids and to this end a long tube settling column (up to 5 m length) is san led at various depths H and times tj, to give concentrations c of solids. The solids concentrations may be corrected for unwanted colloidal material which is often present in such sanq)les by subtracting the background concentration of unsettleable solids. 

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