h1. Experiments 1 and 2 - Replicates of the Previous Fluidized Bed Experiments

h2. Parameters:

For both Experiment 1 and Experiment 2, the [general procedure|Evaluation of Previous Experiments] had been followed using specific parameters. The parameters used in each experiment are listed and compared below:
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h5. Table 1: Comparison of Parameters Used.
||Parameters:||Experiment 1||Experiment 2||
|Sand Grain Type|Sand 40|Sand 30|
|Sand Grain Diameter|0.42 mm - 0.59 mm|0.59 mm - 0.84 mm|
|Sand Bed Depth|60 cm|60 cm|
|Sand Bed Expansion|50%|50%|
|Aerator Air Pressure|100 kPa|100 kPa|
|Flow Rate|225 mL/min|485 mL/min|
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h2. Results and Discussion:

Data from both experiments were analyzed using the method outlined below:
For each sand grain size, the experiment was run for a certain amount of time, throughout which it completed several data collection periods. Each data collection period ("run") represents a time period during which the water level in bubble collector gradually falls down from its maximum to the set minimum point. In Figure 1. and Figure 2. this period is represented on the graph when the line slants downward. Once the minimum water level is reached, the bubble collector has to refill with water in order to continue the runs. For this reason, the water outflow valve is closed until the water level reaches the set maximum point. This period is represented on the graph by the vertical lines. More detailed information on the bubble collector setup can be found [here|Floating Flocs Summer 2009 Set-up].
Once the change in water level in the bubble collector was recorded, we added a linear fit line to each of the runs to see the rate of change of the water level inside the bubble collector with respect to time. Figure 3. and Figure 4. show the linear fit line for the second data collection period in both experiments, and more detailed graphs can also can be found [here|Gas Removal Preliminary Graphs].
The value of the linear fit is very close to 1, indicating that the data can be modeled accurately using a linear relationship. Once the slope of the fitted line was known, we calculated the content of gas removed per liter of water sent through the sand filter using the formulas:
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$$
\frac{\Delta Volume}{\Delta Time} = slope * \pi * r _{collector} ^2
$$
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{latex}
$$
\frac{mL\:gas\:removed}{L\:water\:treated} = \frac{\frac{\Delta Volume}{\Delta Time}}{Q_{water}}
$$
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where the radius of the bubble column was 1.9 cm.
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The calculations for the amount of gas removed during each data collection periods gave us the results summarized in Table 2 and Table 3 below:
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h5. Table 2: Gas Removal vs. Collection Periods; Experiment 1.
||Run||Slope (cm/min)||R ^2^ value||Dissolved Gas Removed (mL/L)||
|2|0.1013|.9948|5.0909|
|3|0.0986|.9920|4.9397|
|4|0.0861|.9933|4.3348|
|5|0.0739|.9945|3.6795|
|6|0.0659|.9921|3.2763|
|7|0.0616|.9872|3.0747|
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h5. Table 3: Gas Removal vs. Collection Periods; Experiment 2.
||Run||Slope (cm/min)||R ^2^ value||Dissolved Gas Removed (mL/L)||
|2|0.0854|.9944|1.9970|
|3|0.0856|.9482|2.0017|
|4|0.0847|.9952|1.9806|
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For further reference, please click here to download the experimental data logs from [Experiment 1.|^Data and Calculations, Experiment 1.xls] and [Experiment 2.|^Data Analysis and Graphs1.xls].
The data from Experiment 1. shows that the content of the gas removed is very similar to the result from the [Fluidized Bed Experiment|Fluidized Bed after Super Saturator] done last semester, when the measured content of gas removed was 5.07 mL/L. Yet the data for each subsequent runs revealed a gradual decrease in the content of air removed, with only 3.07 mL/L of gas removed in the last run. This tendency might have resulted from a clogging problem in the sand filter. Clogging in the filter occurs because of the relatively small diameter of the sand column. Large bubbles are formed in the sand bed and push segments of sand up to the top of the filter. While we did not directly observe this problem during the experiment, sensor data collected through Process Controller indicates that clogging occurred.
The data from Experiment 2. shows consistent amount of gas removed for each run. The uniform results might indicate reliable functioning of the components of the system. However, the amount of removed gas is still a bit lower than the result from the experiment done last semester, when the measured content of gas removed was 3.23 mL/L. The cause of the difference in results might be the experimental setup, which has been modified since last semester. The modifications include replacing the aerator with a new one. Therefore, it is possible that the current aerator is less effective at producing water that is supersaturated enough. For further observation, we measured the dissolved oxygen content at three sampling points in the system. More detailed information can be found [here|FF Dissolved Oxygen Measurements].
These experimental results may be modeled as gas removal efficiency when subjected to different sand grain sizes. The data suggests that the sand with larger grain sizes might be less effective at gas removal. Larger sand grains have relatively lower surface area to volume ratio and thus provide less surface area to which the bubbles can attach to in the sand column. Although the sand grain size is just one of the factors that affect the gas removal rate, the results indicate that perhaps using filter media with higher surface area to volume ratio might help facilitate the gas removal process under certain conditions.