DO Removal by Partial Vacuum

Purpose and Principle

The purpose of this experiment is to determine the degree of dissolved oxygen removal from supersaturated water subject to a partial vacuum. Dissolved oxygen removal from the water occurs because the partial pressure of oxygen in space above the water is lowered by the partial vacuum. Thus, the dissolved oxygen will transfer out to the space above the water in order to restore equilibrium as stated in Henry's Law. Measuring the dissolved oxygen in the water over a period of time will allow us to observe the amount of dissolved oxygen removed and also to calculate the approximate rate of dissolved oxygen removal.

Procedure

While using Easy Data to monitor the pressure and dissolved oxygen, water is pumped out of the apparatus until the pressure reaches -50 to -70 kPA. Once the desired pressure is attained, the pump is stopped and the apparatus is allowed to sit for a short period of time. The period of time can be determined by finding the approximate time the water spends under partial vacuum in the transmission lines that bring water to the plants. After that period of time, the clamp on the pump is released to open the system to atmospheric pressure. The dissolved oxygen is monitored and recorded for two to three minutes after the chamber is opened to atmospheric pressure.

Results and Discussion