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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.
Procedures
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.
This contraption is used to simulate the interface between the distribution pipe exit and the grit chamber at the AguaClara plants. The container is filled with water and sealed off and water is pumped out of the lid causing a partial vacuum. The environment created is similar to that in segments of the distribution pipes of actual plants. After the water is put under negative pressure, the pump clamp is released to open the container to atmospheric pressure, which simulates the grit chamber conditions.
Two types of experiments have been run, thus far. The first involves creating a partial vacuum in the container without aeration and observing the effects of the vacuum on dissolved oxygen and bubble formation. 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. At that point, 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. The second involves maintaining a partial vacuum in the container with slight aeration. The flow of air into the container is regulated by a rotameter
Results and Discussion
Conclusion
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