Concentration contactor

A differential countercurrent contactor operating with a dilute solution of the consolute component C and immiscible components A and B is shown in Figure 8. Under these conditions, the superficial velocities of the A-rich and B-rich streams can be assumed not to vary significantly with position in the contactor, and are taken to be and Ug, respectively. The concentration of C in the A-rich stream is and that in the B-rich stream is C-. ... 

Rearrangement and iategration give a relationship for the contactor height ia terms of the concentration change ... 

Disinfection. Ozone is a more effective broad-spectmm disinfectant than chlorine-based compounds (105). Ozone is very effective against bacteria because even concentrations as low as 0.01 ppm are toxic to bacteria. Whereas disinfection of bacteria by chlorine involves the diffusion of HOGl through the ceU membrane, disinfection by ozone occurs with the lysing (ie, mpture) of the ceU wall. The disinfection rate depends on the type of organism and is affected by ozone concentration, temperature (106), pH, turbidity, clumping of organisms, oxidizable substances, and the type of contactor employed (107). The presence of oxidizable substances in ordinary water can retard disinfection until the initial ozone demand is satisfied, at which point rapid disinfection is observed. 

Contactor design is important in order to maximize the ozone-transfer efficiency and to minimize the net cost for treatment. The three major obstacles to efficient ozone utilization are ozone s relatively low solubility in water, the low concentrations and amounts of ozone produced from ozone generators, and the instability of ozone. Several contacting devices are currently in use including positive-pressure injectors, diffusers, and venturi units. Specific contact systems must be designed for each different application of ozone to wastewater. Further development in this area of gas-liquid contacting needs to be done despite its importance in waste treatment applications. In order to define the appropriate contactor, the following should be specified ... 

Figure 1.25. Concentration profiles for countercurrent, stagewise contactor.

Fig. 1.27 shows a differential type of contactor as in, say a countercurrent flow packed gas absorption column, together with the resulting approximate continuous concentration profiles. 

The decolorization of Reactive Red 2 (azo dye) and Reactive Blue 4 by immobilized fungus Bjerkandera sp. strain BOL 13 was studied [56]. Birch wood was used as a carrier material and circular disks were used in the continuous rotating biological contactor. The experiment results showed the fungus to be able to decolorize mixtures of both dyes efficiently. Decolorization was found to be approximately same at 50 and 100 mg/L of dye stuff (96 and 94%, respectively). When the concentration was increased to 200 mg/L, decolorization decreased to 81%. 

The simulation starts with the initial axial concentration profiles set to zero. Using arrays, the number of sections is set by the parameter Nsiabs, allowing the axial concentration profile for each phase along the contactor to be demonstrated. 

The Alfa-Laval contactor shown in Figure 13.41, has a vertical spindle and the rotor is fitted with concentric cylindrical inserts with helical wings forming a series of spiral... 

The loading characteristics of an extractant can be determined as described above. With this information and knowledge of the different types of contactors available, the metal concentration in the feed, the extraction rate of the metal, the approximate concentration of extractant in the solvent can be determined. The optimum concentration can be determined only by operating a continuous circuit. 

A single-stage extraction using the same total volume of solvent achieves only 92% extraction, and the extract concentration is only 0.23, vs. nearly 0.25 for the cross-flow extraction. The use of four cross-flow extraction stages is clearly preferable to a single extraction. Equally, of course, the use of more than four extraction stages, each with a proportionately smaller volume, would improve the performance. In the limit, one would seek a differential contacting process similar to the Soxhlet extractor employed for extraction from solid phases, but such a contactor has not found use in solvent extraction. 

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