DO Removal by Partial Vacuum

Objectives

Procedure

The procedure for this experiment is relatively simple. While using Easy Data to monitor the pressure, water is pumped out until the pressure reaches -50 to -70 kPA. The apparatus is allowed to sit for a short period of time and is then opened to atmospheric pressure and the dissolved oxygen is monitored and recorded for no more than two minutes. We wish to see a drop of at least 2 mg/L in that period of time.

Results and Discussion

From our experiments, we have found that the change in dissolved oxygen that occurs over the span of a few minutes is less than desirable. We ran experiments that involved aerating water under a partial vacuum and compared the results to data obtained from experiments in which water was only subject to a partial vacuum with no aeration. We were expecting to see a greater change in the dissolved oxygen concentration; however, contrary to our initial belief, aerating the water had little affect on the change in dissolved oxygen. Because of this, we are doubtful that the aeration method will solve the floating flocs problem and have decided to consider alternate solution methods. While we search for other possible solutions, we will still continue to run quick experiments with the aeration method in order to verify our decision to move to an alternate solution.

Some of the major concerns about our data include discrepancies caused by erratic behavior of the dissolved oxygen probe under partial vacuum. We are still trying to understand what might be causing the discrepancies and to what degree the functionality of the probe is affected. We are concerned that after the probe is subject to negative pressure, data collected after pressurization may be faulty. In the mean time, we will be measuring dissolved oxygen before and after pressurization and aeration instead of during the process. Also, we were initially concerned about the gradual pressure increase in our system. So, we tested the apparatus to make sure that it was airtight by putting the container under positive pressure and holding it over night. It proved to be airtight enough for our purposes. We postulated that the change in pressure is mostly due to bubbles leaving the solution.