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- A partial vacuum is created in the container and the effects of the vacuum on dissolved oxygen and bubble formation are observed.
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.
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.
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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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