A lake water at 15°C is low in dissolved oxygen (1.5 mg/L DO) and is aerated in a fountain aerator. Droplets averaging 0.8 cm in diameter are released. For a mass transfer coefficient in the liquid phase (kL) of 120 cm/h, and assuming that almost all of the resistance to oxygen transfer is in that phase, find the time (seconds) that a droplet would have to be in the air to increase the DO concentration to 7.25 mg/L before it re-enters the bulk solution.
