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

Procedure

While using Easy Data At the start of the experiment, both the pressure sensor and the dissolved oxygen probe were calibrated in the same manner mentioned on the Floating Floc Aeration Method page. While using EasyData to monitor the pressure and dissolved oxygen, water is was pumped out of the apparatus until the desired pressure is was attained. The A partial vacuum is was maintained while the solution is slightly aerated. The was aerated and the flow of air into the container is was regulated by a rotameter that takes either lab pressurized air or room air. Originally, lab Pressurized air was being used; however, originally used to aerate the water. However for later experiments involve detaching the air inflow tube into was detached from the rotameter and allowing to allow air to be sucked into the apparatus as it rather than being forced in; this better simulated how the air would be sucked through the holes in the actual pipesperforations in an actual pipe that had free falling water. Theoretically, the source of the air should have affect the experiment they had different partial pressures of oxygen. Since bubble formation depends on the difference in DO between the air bubbles and the water, source air with a lower partial pressure of oxygen would be able to form larger bubbles because of the greater concentration gradient. After the water is was aerated under partial vacuum for a period varied amount of time ranging from about one to four minutes, the apparatus is was again exposed to atmospheric pressure and data is was recorded in the same manner as mentioned before. The period of time can be determined by finding the approximate time the water spends under EasyData for at least two to three minutes to allow for the dissipation of erratic dissolved oxygen behavior.

The water used for this experiment was aerated under pressures ranging from 90 kPa to 100 kPa for over 10 hours in order to induce supersaturation with regards to atmospheric pressure. Aerating within the pressure range mentioned above ultimately resulted in an initial DO concentration of around 16 mg/L. Calculations using gas laws indicated that for the pressure range listed above, the concentration would be in the ballpark of 15 mg/L to 16 mg/L; however, this number may have been inaccurate due to faulty probe readings further addressed in the Results section below.

Using the Tamara Plant's design values the water entering the grit chamber is going approximately 10 m/min. This is based on using four 6 in diameter pipes to carry 740 L/day of water into the plant. Thus in a 1.5 m long vertical pipe (which is the height of the entrance tank) with free falling water the water would be exposed to a partial vacuum for only 10 seconds 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 there was results of our experiments suggested that there were many problems with using a dissolved oxygen probe in our experiments. Sharp dips in the dissolved oxygen concentration (as seen in #Figure 1) were indicative of a problem with bubbles forming on the probe. When the bubbles 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. Image Removedprobe grew large enough to float away, the dissolved oxygen concentration fluctuated significantly. We attempted to correct this problem by moving the probe closer to the stir bar but to no avail - the problem persisted. In addition to that, the DO probes proved to be unreliable after being exposed to the partial vacuum in the reactor, calling into question the accuracy of the actual numbers obtained.

The figures below represent the experiments that produced acceptable results. #Figure 1 depicts the behavior of the DO concentration while the reactor was being aerated under the negative pressure conditions profiled in #Figure 2. The pressure data stayed constant after the first minute but, as mentioned above, the DO concentration readings were very disturbed. After subjecting the reactor to about three and half minutes of negative pressure, the system was opened to the atmosphere. #Figure 3 depicts the behavior of DO levels post vacuum and under atmospheric pressure, as seen in #Figure 4. Again, even though the pressure was constant, the DO values fluctuated corresponding to bubble formation. #Figure 3 indicates that the DO concentration increased after the pressure was increased to atmospheric pressure. We believed this to be due to reincorporation of gases into the water from bubbles that were too small to float out of solution.

Click graphs to see larger images.

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[!bubbles neg pressure system DO.png|width=350px!|DO Removal by Partial Vacuum and Aeration Experiment Graphs]
h5. Figure 1: The concentration of dissolved oxygen as a function of time while the system was under negative pressure and not being aerated. 

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[!bubbles closed system pressure -.png|width=350px!|DO Removal by Partial Vacuum and Aeration Experiment Graphs]
h5. Figure 2: The pressure inside of the container while it was closed and being aerated
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[!bubbles open system DO.png|width=350px!|DO Removal by Partial Vacuum and Aeration Experiment Graphs]
h5. Figure 3: The Dissolved Oxygen inside of the container after the system had been opened

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[!bubbles open system pressure -.png|width=350px!|DO Removal by Partial Vacuum and Aeration Experiment Graphs]
h5. Figure 4: The pressure inside of the container after the system had been opened
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