Methods
In this experiment, we seek to determine what direct impact the diameter of the tube settler has on sedimentation efficiency. From the experiment detailed on the previous page, we were able to identify a range of capture velocities that produce low turbidity effluent regardless of tube diameter. For this experiment, we chose three capture velocities within this range and adjusted the length of the tube settlers to satisfy this velocity. Upflow velocity through the tubes was held constant. Recall that
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h2. Methods In this experiment, we seek to determine what direct impact the diameter of the tube settler has on sedimentation efficiency. From the experiment detailed on the previous page, we were able to identify a range of capture velocities that produce low turbidity effluent regardless of tube diameter. For this experiment, we chose three capture velocities within this range and adjusted the length of the tube settlers to satisfy this velocity. Upflow velocity through the tubes was held constant. Recall that {latex}\large\[V_c = \frac{{dV_{up} }}{{L_{tube} \sin (\alpha )\cos (\alpha ) + d}}\]{latex} |
is
...
the
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capture
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velocity
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equation.
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As
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the
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capture
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velocity
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equation
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above
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indicates,
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holding
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the
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capture
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velocity
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constant
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and
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varying
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the
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length
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to
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satisfy
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this
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velocity,
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allows
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isolation
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of
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the
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diameter
...
of
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the
...
tube
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as
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the
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parameter
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that
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should
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most
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directly
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impact
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settling
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efficiency.
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Results
To this point (5/7/09), we have tested four different diameter tube settlers with a capture velocity of 8 m/day.
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Unfortunately,
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the
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data
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for
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the
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9.5
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mm
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inner
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diameter
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tube
...
settlers
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are
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not
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convincing.
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As
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is
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evident
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from
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Figure
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1
...
below,
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these
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data
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do
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not
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follow
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the
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trend
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of
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the
...
other
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diameter
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tubes
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and
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the
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effluent
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turbidity
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is
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quite
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low.
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We
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will
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rerun
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the
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9.5
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mm
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tubes
...
and
...
be
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sure
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that
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water
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is
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flowing
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at
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all
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times.
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However,
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the
...
other
...
data
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gathered
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so
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far
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are
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quite
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interesting.
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The
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graph
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below
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shows
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the
...
average
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effluent
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turbidity
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over
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a
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six
...
hour
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period
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for
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the
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four
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tube
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settler
...
diameters.
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Figure 1. Average effluent turbidity for various tube settler diameters with capture velocity of 8 m/day.
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As
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Figure
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1
...
above
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reveals,
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there
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is
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a
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correlation
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between
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tube
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settler
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diameter
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and
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effluent
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turbidity.
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In
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fact,
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the
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average
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effluent
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turbidity
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jumps
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0.8
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NTU
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when
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the
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inner
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diameter
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of
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the
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tube
...
settler
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changes
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from
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17
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mm
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to
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15
...
mm!
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This
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may
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indicate
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that
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there
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is
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a
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critical
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diameter,
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below
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which
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the
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sedimentation
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efficacy
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drops
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significantly.
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Another
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preliminary
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observation
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of
...
note
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is
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the
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consistency
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of
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the
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tube
...
settler
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performance.
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For
...
example,
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Figure
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2
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below
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shows
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the
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effluent
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turbidity
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of
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the
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23
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mm
...
inner
...
diameter
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tube
...
settlers
...
over
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several
...
hours.
...
Figure 2. Effluent turbidity over time for 23 mm inner diameter tube settlers with capture velocity of 8 m/day.
This graph shows consistently low effluent turbidity over six hours for the 23 mm tubes. Conversely, the 15 mm and 17 mm diameter tubes showed a steady increase in effluent turbidity over time. Figure 3 below shows the effluent turbidity of the 17 mm inner diameter tube settlers over several hours. Although only the 17 mm effluent turbidities are shown below, the 15 mm tubes showed a similarly sloped linear increase.
Figure 3. Effluent turbidity over time for 17 mm inner diameter tube settlers with capture velocity of 8 m/day.
Future work
There is not information to draw any conclusions at this point, however, it is clear that there is a difference in performance in the tubes with the largest diameter and the smaller tubes. These experiments should be re-run at longer time intervals. The additional experiments will be added as a post-mortem addendum.