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h1. DO Removal by Partial Vacuum

h2. Purpose and Principle

The purpose of this experiment iswas 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 iswas lowered by the partial vacuum. Thus, the dissolved oxygen willwould 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 allowallowed us to observe the amount of dissolved oxygen removed and also to calculate the approximate rate of dissolved oxygen removal.

h2. Procedure
{panel} Water source? Water temperature? Same text here with multiple references to a period of time that isn't specified. Was the reactor stirred? How was the dissolved oxygen probe calibrated?{panel}

While using EasyData to monitor the pressure and dissolved oxygen, water originating from the large container above the sink filled with tap water iswas pumped out of the apparatus until the desired pressure iswas reached. The water was at around 20 degrees centigrade and constantly stirred. Once the desired pressure iswas attained, the pump iswas stopped and the apparatus iswas 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, This time was varied to determine, after being converted from time to distance based on a influent water velocity of 700 m/day, what the optimal vertical pipe length would be using our system. These values varied from seconds to a few minutes representing a pipe length of a fraction of a meter to a few meters. The system was then opened to the atmosphere by releasing the clamp on the pump isthat releasedconstricted tothe opentube theleading systemout toof atmosphericthe pressureapparatus. The dissolved oxygen iswas monitored and recorded for two to three minutes after the chamber is opened to atmospheric pressurethis. 


h2. Results and Discussion

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[!Ex1T1.jpg|width=400px!|Experiment 1 Test 1 Results]
*Experiment 1 Test 1:* DO behavior under negative pressure change (gradual decrease to -70kpa70 kpa) and under atmospheric conditions. Click to see larger.
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[!Ex1T2.jpg|width=400px!|Experiment 1 Test 2 Results]
*Experiment 1 Test 2:* DO under negative pressure (held at -37kPa37 kPa and gradually decreased to -70kPa70 kPa) and under atmospheric conditions. Click to see larger.
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The graphs above indicate a change in dissolved oxygen of about 0.3 mg/L {panel} numbers never start with a decimal point. {panel} over a minute to two minutes for water subject solely to partial vacuum. For the first test, the water was subject to a pressure drop from atmospheric to approximately -70kPa {panel} always a space between numbers and their units. {panel}70 kPa. A total pressure drop of -70kPa70 kPa was also used in the second test also; however, during the experimentthough the water was kept at approximately -37kPa37 kPa for about a period of timeminute in order to observe the effect of this pressure on the dissolved oxygen. It can be seen by juxtaposing the two curves on the same plot that the behavior of dissolved oxygen before and after vacuum are fairly similar. The first test was performed with a higher initial dissolved oxygen content in the water, so the graph is positioned slightly higher than the second test curve. 
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!E1T1T2Comparison.PNG|width=600px!
*Figure:*Graph comparing DO curves from Test 1 and Test 2.
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The change in dissolved oxygen under a range of pressure iswas fairly consistent. Using this data as a baseline, a second experiment was run in which the water was aerated under partial vacuum and is described in [DO Removal by Partial Vacuum and Aeration|DO Removal by Partial Vacuum and Aeration]

{panel} Show the pressure trace too since you emphasize that you changed the pressure part way through the experiment. Eliminate the negative time values on the x axis. The spikes that occurred after allowing the reactor to return to atmospheric pressure could have been due to bubbles that were on the dissolved oxygen probe membranes. When the pressure increases the oxygen in these bubbles began to go back into solution and some of the molecules were detected by the dissolved oxygen probe. {panel}