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A model of this process was derived last semester and this semester we are testing this theory in the lab. We designed and had built an apparatus that can be used to simulate both the conditions in the pipe and the grit chamber.
Experimental Methods and Results
- A partial vacuum is created in the container and the effects of the vacuum on dissolved oxygen and bubble formation are observed.
DO Removal by Partial Vacuum and Aeration
- A partial vacuum is maintained in the container while the water is slightly aerated throughout each trial. The effects of the vacuum plus the aeration is observed and recorded.
The apparatus for the aeration method is mainly a segment of clear PVC pipe that is about 9.75" long and has an inner diameter of 4". One end of the pipe is connected to a base that has four evenly placed metal rods attached to it. The rods run freely along the length of the clear PVC pipe and penetrate an lid, which is held in place with butterfly screws at each rod. There are five adapters in the contraption. An adapter in the center of the lid joins the apparatus to a pump via a 3/8" tube. Water can be pumped out from this location when the container is completely full to cause a partial vacuum or air can be pumped in to pressurize the container. Two adapters are located near the base of the contraption that function as a water inlet and air inlet. The air inlet also has an air stone connected to it on the interior of the pipe. The pressure in the contraption is measured with a pressure sensor attached to an adapter near the base, and the dissolved oxygen probe is connected at the bottom of the apparatus near a magnetic stir bar to prevent bubble formation on the probe. O-rings are used to seal the contraption at each adapter location and at the interface between the pipe and the lid.
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While the water at the actual plants have dissolved oxygen in excess of the 8 mg/L saturation level at atmospheric pressure, the experiments performed have usually involved water that is originally around saturation level or slightly below. We have decided that this is acceptable, since water under negative pressure has a lower DO saturation level so the water is supersaturated with respect to the lower saturation concentration.
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.
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Experimental Methods and Results
- A partial vacuum is created in the container and the effects of the vacuum on dissolved oxygen and bubble formation are observed.
DO Removal by Partial Vacuum and Aeration
- A partial vacuum is maintained in the container while the water is slightly aerated throughout each trial. The effects of the vacuum plus the aeration is observed and recorded.
Conclusion
No conclusions have been made yet. We will be able to asses the situation better once we have test set up working properly. Current results are not promising but problems with the DO probe prevents us from drawing any definitive conclusions yet.