Results and Discussion of Initial Experiments

These are the results of the first several experiments run, with the initial experimental setup.

Figure 1 The Bubble Volume collected at 10 minute interval with a flow rate of 200 ml/min and a sand depth of 32 cm. The glass bead are used as the filter.

In Figure 1, the experiment was ran under the flow rate of 200 ml/min with a sand depth of 32 cm. We concluded that the experiment needs to be ran for at least 20 min to achieve a plateau in which the Bubble Volume did not change. Therefore, the DO concentration would level off at about 20 minutes. We concluded that after 20 minutes, we will start to record the data.

In Figure 2 (below), we could see that the change in dissolved oxygen that occurs over the span of minutes. The first experiment used a flow rate of 200 ml/min and a sand depth of 32cm. Overall, the DO concentration was lower at the inflow. While the inflow DO concentration was about 9mg/L, the outflow was roughly at 11 mg/L. After taking the difference in DO concentration in inflow and outflow and finding the average DO concentration difference, we corrected the outflow DO concentration. The corrected outflow DO concentration was about little above 9 mg/L. Overall, the Figure 2 showed that with sand depth of 32 cm at 200 ml/min with, the outflow DO concentration was higher than the inflow concentration. This was inconsistent to what was predict. This was probably due to the error in the DO probe. After running the experiment, we noticed that the DO probe was not functioning properly. We concluded that we needed to purchase a new DO probe to measure the concentration or another method to measure the DO concentration.

Figure 2 The first run with glass beads at 200 ml/min with a sand depth of 32 cm.

Since there were problems with the DO probe, we switched to measuring the bubble volume at the outflow. Using MathCad, we used the bubble volume collected to calculate the DO concentration in the outflow water.

Next, we experimented with the sand depth. At a flow rate of 200ml/min, we obtained the following result:

Figure 3 The Effect of varying the Glass Bead Depth at a flow rate of 200 ml/min

Figure 3 showed that a sand depth of 10cm is better than the larger sand depth of 32cm. Assuming there was no error in the calculations, errors may be occuring during the experiment. Logically, this result did not make sense. In addition, this result did not go according to our prediction that at a larger depth sand, the DO concentration would be higher. Furthermore, the following results in Figures 4 and 5 (below) obtained at a later date showed that a larger sand depth extracted more DO.
Figure 4 The DO Concentration versus Time. The DO Concentration is calculated from the air volume.

Figure 5 The DO Concentration versus Time. The DO Concentration is calculated from the air volume. This graph is the same as Graph 4 except that this graph excludes the results from the flow rate of 150 ml/min for 33 cm sand depth.

Figures 4 and 5 were from the same data except that the bottom graph did not have the results from the flow rate of 150 ml/min for 33 cm sand depth. The results were taken out to show a better view of the other results that overlap each others in the top graph. Moreover, the results obtained from the flow rate of 150ml/min for 33 cm sand depth was extremely different from the other results. This may be due to a error or a series of error.The data collected for Graphs 4 and 5 is given below.

Table 1 This table displays neatly displays all the results from varying flow rates (150 ml/min and 200 ml/min) and varying sand depth (10 cm and 33 cm).

Table 1 had results indicating that the outflow DO concentration was lower than the inflow DO concentration. However, there was a discrepancy in the DO concentration reading. DO concentration calculated from the air volume was very different from the reading from the DO probe at the outflow. The initial DO concentration calculated from the air volume is wrong. This was because even air volume of 0 ml, there was DO in the water. With the air volume calculation was not taken into account. To attain a more reliable results, a new DO probe was necessary.

For a better view of the difference in the outflow DO concentration from the DO probe and the outflow DO concentration calculated from air volume, the following four figures (Figures 6-9) were derived.

Figure 6 The DO Concentration either from the DO probe or the air volume calculation versus Time for a sand depth of 10 cm at a flow rate of 150 ml/min.

Figure 7 The DO Concentration either from the DO probe or the air volume calculation versus Time for a sand depth of 10 cm at a flow rate of 200 ml/min.

Figure 8 The DO Concentration either from the DO probe or the air volume calculation versus Time for a sand depth of 33 cm at a flow rate of 150 ml/min.

Figure 9 The DO Concentration either from the DO probe or the air volume calculation versus Time for a sand depth of 33 cm at a flow rate of 200 ml/min.

In Figures 6 to 9, the DO concentrations from the DO probe were completely different from the DO concentrations calculated from the air volume. The blue lines represented DO concentrations calculated from the bubble/air volume. The red lines represented the outflow DO concentrations from the DO probe. Figures 6, 7, and 9 showed the DO concentrations calculated from the air volume (blue lines) reached a plateau after 10 minutes. The blue lines in Figures 6, 7, and 9 leveled off like the corresponding DO concentration measured by the DO probe (red lines) in Figures 6, 7, and 9. Figures 6, 7, and 9 have a large distance between the DO concentration from DO probe reading and the DO concentration calculated from the air volume. In Figures 6 and 7, the distance between the red and blue lines was 7 mg/L. For Figure 9, the distance between the red and blue lines was 5 mg/L. This distance was probably due to the initial DO concentration in the water that in not incorporated into the DO concentration calculated from the air volume. Unlike Figures 6, 7, and 9, Figure 8 had the blue line (DO concentration calculated from the air volume) higher than the red line (DO concentration from the DO probe reading). The DO concentration calculated from the air volume looked unreasonable high. Furthermore, the blue line (DO concentration calculated from the air volume) in Figure 8 did not reach a plateau. Instead of reaching a plateau, the blue line in Figure 8 peaked at 10 minutes and decreased rapidly to a lower concentration. This indicated that the high DO concentration was probably caused by the unsettle disturbances in the filter from addition glass beads added to achieve a sand depth of 33 cm.

The data collected in the Table 1 displayed relatively in the same range except for Run 3 which could be partially visualized in Figure 8. The air volume collected is very different causing the calculated DO concentration to be extremely high. We thought that it was due to addition of the sand to the sand depth that cause this difference and error. After the first two runs, the sand depth was increased from 10 cm to 33 cm. During this change, the filter was open to the atmosphere and the additional sand created disturbance into the settled sand. The addition of the sand may have cause the filter to gather more bubble and we did not allow the system to have enough time to settle out before running the experiment.

From the results collected, there were conflicting data on which sand depth was the optimal. At previous runs, the data showed that the sand depth of 10cm was the optimal. However, in the most recent runs, the data indicated that the sand depth of 33 cm out performed the depth of 10cm. This may be due to how the experiments were run. In the previous runs, the larger sand depth was run first and then the shorter sand depth was run after the longer sand depth. There was a period of rest to vacuum the sand out of the column. However, between the experiments, bubbles remained on the top of sand filter from the previous run. These bubbles settlement may have contributed the error in the data collected. In the most current runs, the short depth was run before the longer sand depth. From the data collect, no concrete conclusion could be drawn and more data was needed.

Conclusion

We have not yet drawn any final conclusions. We would be able to analyze the system better when most of the problems of the system are fixed and it was improved. The current results collected were not promising and stable. This was due to many problems, such as the DO probe not reading the concentration correctly.