A wastewater stream flowing at the rate of 600 GPM (gallons per minute) and containing 10 ppm (parts per million by weight) benzene is to be stripped with air in a packed column operating at 25°C and 2 atm absolute pressure. The water leaving the column is to contain 0.5 ppm benzene. The packing is 1-in. Berl saddles. The solubility of liquid benzene in water at 25°C is 0.180 g per 100 g of water. It has been suggested to use a flow rate of air of 1,000 SCFM (standard cubic feet per minute), at which the following values of the mass transfer coefficients are  = 0.80 s-¹ for the gas side and  = 0.067 s-¹ for the liquid side. Determine:

(a) The minimum air flow rate.

(b) The number of transfer units, , required. (c)The overall mass transfer coefficient, , in units of mol/(m³ s).

(d) Thevolume of packing required in m³.

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