DO Removal by Partial Vacuum and Aeration

Purpose and Principle

The purpose of this experiment is to observe and quantify the change in dissolved oxygen transfer out of supersaturated water that is subject to slight aeration under a partial vacuum. This experiment attempts to use air bubbles as a catalyst to increase the rate of dissolved oxygen out of the water. The difference in oxygen concentration between the bubbles and the supersaturated water may be used to draw excess dissolved oxygen into the bubbles and out of the solution.

Procedure

While using Easy Data to monitor the pressure and dissolved oxygen, water is pumped out of the apparatus until the desired pressure is attained. The partial vacuum is maintained while the solution is slightly aerated. The flow of air into the container is regulated by a rotameter that takes either lab air or room air. Originally, lab air was being used; however, later experiments involve detaching the air inflow tube into the rotameter and allowing air to be sucked into the apparatus as it would be through the holes in the actual pipes. After the water is aerated under partial vacuum for a period of time, the apparatus is again exposed to atmospheric pressure and data is recorded in the same manner as mentioned before. 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

The data from this experiment shows that under partial vacuum and slight aeration the dissolved oxygen content changes by about – once the apparatus is open to atmospheric conditions.