A 500-gallon tank 8 feet deep is to be saturated with air using a small sparger 2 inches in diameter with a flow of 1 ft³/min. The sparger produces 0.3 cm bubbles that rise through a dilute aqueous solution at a velocity of 10 cm/s. How long does it take to reach 50% saturation? Hints: (1) Mass transfer is a lot faster in gases than it is in liquids. (2) You may assume that this small sparger provides minimal agitation to the liquid. (3) See Tables 8.3-2 and 8.3-3 in Cussler's book.

(Answer: 8.7 minutes)