Unit Operations in Ozonation

In its simplest form, the unit operations of ozonation involve the production of ozone and the mechanics of dissolving and mixing the ozone in the water or wastewater. The unit operations of dissolving and mixing have already been discussed in Part II of this book. The design of the contact tank is similar to that of chlorination, the contact time and dosage being best determined by a pilot plant study. As mentioned before, a contact time of 20 min is not unreasonable, and a residual of 0.4 mg/L of ozone has been found to be effective. The equation for ozone disinfection follows the universal law of disinfection given by Equation (17.2).

Example 17.20 A total flow of 1000 m /d is to be disinfected using ozone. What should be the cross-sectional area of the serpentine channel in order to maintain self-cleaning velocity? What would be the total combined length of the channel if the contact time has been determined by a pilot study to be 20 min?

Solution: Cross-sectional area = 1000/24(60)(2.0) = 0.34 m , assuming a self-cleaning velocity of 2.0 m/min. Ans

Length of channel = 20(2) = 40 m. The flow in the tank will not be exactly plug flow, so increase channel length by 10%. Thus, length of channel = 40(1.10) = 44 m. Ans

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