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 evaluated the use of air bubbles as a catalyst to increase the rate of removal of dissolved oxygen out of from 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 EasyData 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 pressurized air or room air. Originally, lab pressurized 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.

Does the source of the air affect the experiment? Are the air bubbles that form influenced by the air source?

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.

How fast is the water traveling in the transmission line and thus how many seconds would the water be exposed to a partial vacuum if there were a vertical section of tubing above the entrance tank?

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 there was a problem with bubbles forming on the DO probe. This is indicated by the sharp dips in the data which corresponds to a bubble rising off of the DO probe. Overall there was not much change in the DO over time but we found the DO probe to be unreliable when it was pressurized and was further complicated by there almost constantly being bubbles on the probe.

Was there a problem with the probe when it was under vacuum? You state that there was a problem when it was pressurized.

Explain how you produced or obtained water with 16 mg/L of dissolved oxygen. In your methods section explain where the source water came from for your experiment. What was the equilibrium dissolved oxygen concentration given the absolute pressure in the reactor for the conditions shown in the Figure?