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Experiment
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1:
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Replicate
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of
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the
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Previous
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Sand
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40 Experiment
Procedure:
For this experiment, the general procedure for this set of experiments was followed using the following parameters:
Sand Grain Size: Sand 40 (.42 mm - .59 mm)
Sand Bed Depth: 60 cm
Sand Bed Expansion: 50%
Aerator Air Pressure: 100 kPa
Flow Rate, measured manually: 225 ml/min
Results and Discussion
The results from the experiment indicate that the amount of dissolved air removed in the bubble collector decreased after each of the data collection periods.
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Experiment h2. Purpose This set of experiments is designed to ensure that the the new system and taller aerator replicate results of sand bed experiments from Spring 2009. h2. Procedure For this experiment, the following parameters were used: Sand Grain Size: Sand 40 (.42 mm - .59 mm) Sand Bed Depth: 60 cm Sand Bed Expansion: 50% Aerator Air Pressure: 100 kPa Flow Rate was measured to be: 225 ml/min In Process Controller, configure the system so that the aerator air pressure is maintained at roughly 100 kPa. Fill the sand column with 60 cm of Sand 40 and adjust the flow rate on the pump forcing water through the sand filter to establish a bed expansion of 50%. For this experiment, manual measurements of flow rate were performed by unhooking the influent water tube into the sand filter and allowing the influent to fill a large graduated cylinder over the course of a minute. The flow rate was found to be 225 ml/min. (In order to minimize changes made to the system, measurements for future experiments will be taken at the system effluent tube.) Run the Process Controller method file [here|Summer09Configurationfile.pcm] on the "On" state. The "On" state regulates the air pressure in the aerator by releasing small amounts of air through a valve when the system exceeds the maximum aerator air pressure of 102 kPa. The water level in the aerator is controlled in a similar manner; however, the water wasting valve is also subject to a duty cycle in which the valve will open for a set period of time and close for a set period of time. If the "on" condition for the wasting valve is not met (that is, if the water level does not exceed the regulated height), the wasting valve will remain closed. The water entering the aerator and leaving is maintained at a constant rate throughout the experiment via manually controlled pumps. The flow entering the sand filter column was adjusted so that a 50% expansion was met. The water is allowed to flow through the sand column, where bubbles can form. When bubbles grow large enough in the filter, they can float up to the top and out through a tube into the bubble collector. Throughout the duration of the experiment, the bubble collector will go through refilling cycles. Initially, an air valve at the top of the bubble collector will open and the water effluent valve located at the bottom of the bubble collector will close, allowing the collector to fill like a sitting column of water. Once a maximum height is reached, the air valve will shut off and the water valve will open, resulting in a partial vacuum at the top of the collector. This causes the column of water in the bubble collector to be suspended. As bubbles enter the collector, gas in the bubbles fills the partial vacuum, allowing the water column to slowly leave the collector. Once the minimum water level in the collector is reached, the apparatus refills. For each emptying period of the bubble collector, data is collected via Process Controller. Analysis of the data collected can be quantified as a gas removal rate (see below). h2. Results and Discussion The results from the experiment indicate that the amount of dissolved air removed in the bubble collector decreased after each of the data collection periods. {anchor:Figure 1} {float:left|border=12px solid white}[!figure 1.14.png|width="487", height="292"!|Gas Removal Preliminary Graphs] {float} [ |
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depicts
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the
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initial
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and
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final
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water
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level
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in
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the
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bubble
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collector
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during
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each
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of
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the
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data
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collection
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period
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("runs").
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Each
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run
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represents
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a
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time
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period
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during
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which
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the
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water
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level
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in
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bubble
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collector
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gradually
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sinks
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falls down
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from
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its
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maximum
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to
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the
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set
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minimum
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point.
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This
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period
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is
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represented
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on
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the
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graph
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when
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the
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line
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slants
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downward.
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Once
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the
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minimum
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water
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level
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is
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reached,
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the
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system
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has
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to
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refill
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with
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water
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in
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order
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to
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continue
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the
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runs.
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For
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this
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reason,
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the
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water
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outflow
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valve
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is
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closed
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until
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the
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water
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level
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reaches
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the
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set
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maximum
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point.
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This
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period
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is
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represented
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on
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the
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graph
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by
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the
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vertical
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lines.
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More
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detailed
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information
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on
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the
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bubble
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collector
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setup
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can
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be
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found
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here.
The initial data collection period was omitted from the analysis since because of the setup conditions the air might have been trapped inside the system. For the subsequent data collection periods, we calculated the content of gas removed per liter of water sent through the sand filter. We added fitted a line to each of the runs to see the rate of change of the water level inside the bubble collector when water runs through the sand filter. Figure 2. and Figure 3. show the linear fit line for the second data collection period, and more detailed graphs can also can be found here.
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|Floating Flocs Summer 2009 Set-up]. The initial data collection period was omitted from the analysis since because of the setup conditions the air might have been trapped inside the system. For the subsequent data collection periods, we calculated the content of gas removed per liter of water sent through the sand filter. We added fitted a line to each of the runs to see the rate of change of the water level inside the bubble collector when water runs through the sand filter. [Figure 2.|Gas Removal Preliminary Graphs] and [Figure 3.|Gas Removal Preliminary Graphs] show the linear fit line for the second data collection period, and more detailed graphs can also can be found [here|Gas Removal Preliminary Graphs]. {anchor:Figure 2} {float:left|border=12px solid white}[!figure 2.08.png|width="485", height="310"!|Gas Removal Preliminary Graphs] {float} {anchor:Figure 3} |
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{float:left|border=7px solid white}[!figure 3.07.png|width="464", height="308"!|Gas Removal Preliminary Graphs]
{float}
\\
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The
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value
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of
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the
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linear
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fit
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is
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very
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close
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to
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1,
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indicating
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that
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the
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data
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can
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be
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modeled
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accurately
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using
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a
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linear
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relationship.
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If
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we
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multiply
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the
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slope
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of
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the
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line
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by
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the
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cross
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sectional
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area
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of
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the
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bubble
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column,
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we
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get
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the
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rate
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of
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change
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in
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the
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volume
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of
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water
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with
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respect
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to
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time:
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Then we divide the volume rate of change by the flow rate to find out how many milliliters of dissolved gas are removed per liter of water sent upwards through the sand filter:
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For these calculations we used following values:
- radius of the bubble collector = 1.9cm
- flowrate = 225 mL/min (measured manually)
The calculations for the amount of gas removed during each data collection periods gave us the results summarized in Table 1. and Figure 4.:
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\\ {latex} $$ \frac{\Delta Volume}{\Delta Time} = slope * \pi * r _{collector} ^2 $$ {latex} \\ Then we divide the volume rate of change by the flow rate to find out how many milliliters of dissolved gas are removed per liter of water sent upwards through the sand filter: \\ {latex} $$ \frac{mL\:gas\:removed}{L\:water\:treated} = \frac{\frac{\Delta Volume}{\Delta Time}}{Q_{water}} $$ {latex} \\ For these calculations we used following values: * radius of the bubble collector = 1.9cm * flowrate = 225 mL/min (measured manually) \\ The calculations for the amount of gas removed during each data collection periods gave us the results summarized in Table 1. and [Figure 4.|Gas Removal Preliminary Graphs]: {float:left|border=12px solid white|width="200"} h5. Table 1: Gas Removal vs. Collection Periods. ||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| {float} {anchor:Figure 4} |
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{float:left|border=23px solid white}[!figure 4.04.png|width="457", height="292"!|Gas Removal Preliminary Graphs]
{float}
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Data
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was
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recorded
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for
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Sand
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40
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with
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each
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of
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the
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parameters
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specified
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above.
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The
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results
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of
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the
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experiment
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can
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be
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downloaded
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in
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the
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form
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of
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the
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Excel
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sheet.
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The
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content
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of
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the
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gas
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removed
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during
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the
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second
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run,
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5.09
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mL/L,
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is
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very
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similar
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to
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the
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result
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from
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the
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done
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last
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semester,
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when
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the
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measured
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content
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of
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gas
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removed
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was
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5.07
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mL/L.
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The
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fluidized
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bed
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experiment
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involved
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the
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same
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sand
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parameters:
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Sand
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40,
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depth
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=
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60cm,
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bed
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expansion
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=
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50%,
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aerator
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air
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pressure
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=
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100kPa,
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except
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for
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the
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flow
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rate,
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which
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was
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345
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mL/min.
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While
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the
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data
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from
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the
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second
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run
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are
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comparable,
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the
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data
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for
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each
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subsequent
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runs
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show
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gradual
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decrease
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in
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the
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content
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of
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air removed. These decreasing rates of gas removal probably resulted from a clogging problem in the sand filter. Clogging in the filter occurs because of the diameter of the sand column is relatively small. Large bubbles form 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.
Additionally, the results can be compared with the bubble formation potential model, which models the theoretical bubble formation potential as a function of the air pressure that the water equilibrated with prior to returning to atmospheric pressure.
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removed. One of the possible explanations, as described below, might be the air pockets being trapped inside the sand filter. Additionally, the results can be compared with the [bubble formation potential model|Experiment 1 - Replicate of the Previous Sand 40 Experiment^Dissolved atmospheric gases.xmcd], which models the theoretical bubble formation potential as a function of the air pressure that the water equilibrated with prior to returning to atmospheric pressure. {anchor:Figure 5} {float:left|border=12px solid white}[!Theoretical bubble formation potential.png|width="372", height="289"} !|GasTheoretical Removalbubble Preliminary Graphs]formation potential.png! h6. Figure 5: Theoretical bubble formation potential {float} |
The
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model
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predicts
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the
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theoretical
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bubble
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formation
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potential
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to
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be
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around
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18mL/L
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for
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water
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that
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has
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been
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previously
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exposed
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to
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1
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atm
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gage
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pressure
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at
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temperature
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of
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25
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C.
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Since
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our
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data
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show
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the
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removal
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of
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only
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5.09
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mL/L
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of
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the
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air
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entrained
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in
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the
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system,
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it
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is
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probable
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that
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some
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of
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the
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system
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components
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might
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not
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be
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functioning
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properly.
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The
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sand
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filter
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might
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not
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be
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able
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to
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remove
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all
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the
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bubbles
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coming
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in.
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If
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the
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bubbles
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in
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the
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system
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encounter
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a
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region
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of
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lower
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pressure,
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they
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might
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become
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trapped
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and
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form
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a
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column
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of
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gas
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entrained
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inside.
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Additionally,
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bubbles
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in
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the
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sand
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filter
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may
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be
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concentrated
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on
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the
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fluid
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surface
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as
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floats,
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thus
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creating
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a
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gas-liquid
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interface.
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It
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is
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also
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possible
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that
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the
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aerator
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and
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bubble
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collector
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might
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not
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be
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working
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properly.
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It
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might
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be
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necessary
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to
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measure
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the
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oxygen
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concentration
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at
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various
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points
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in
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the
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system
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to
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see
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what
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might
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contribute
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to
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the
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lower
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content
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of
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air
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removed.
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Conclusions
While the results collected were unexpected, the initial runs indicate a gas removal very similar to that found in the Spring 2009 experiment. Since conditions in the aerator were maintained throughout the experiment, it is likely that the new aerator works as needed. However, the decreasing gas removal found for each run is cause for concern. We plan to install a webcam at the top of the filter to observe any instances of clogging during the experiment.
While we attempt to find a permanent solution to the clogging problem, we will also determine a minimum expansion for which clogging does not occur in the sand column. Although obtaining a larger diameter sand column would probably fix the clogging problem, we hope to avoid that option since a wider sand column would require higher flow rates through the system. This would probably require significant upgrades to the plumbing in the system and would be too time-costly and inefficient, since higher flow rates would also decrease the residence time of water in the new aerator, which was installed specifically for greater residence time.