*** This version of Confluence is for testing only and contains a copy of content from June 29th 2026. No changes will be preserved. ***
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Author:
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AguaClara
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Pilot
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Plant
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Spring
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'08
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Sub-Team
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Sections
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on
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Testing
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of
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the
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Tapered
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Flocculator
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were
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written
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by:
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- Rebecca
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- Thompson:
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- rnt3@cornell.edu
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- Narayana
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- Pappu:
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- nvp4@cornell.edu
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Developing
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Turbidity
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Profiles
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along
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the Flocculator
Profile Test Procedure
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Flocculator This testing procedure has two parts: finding the optimal alum dose on the day of testing and running the Profile Test. This procedure was developed and implemented in the Spring '08 semester. h4. Optimal Alum Dose Testing Because the pilot plant takes water directly from the stream, environmental conditions change all the time and affect the incoming turbidity to the plant as well as the chemical composition of the particles causing turbidity. It is therefore necessary to determine the best alum dose for each day of testing to ensure the formation of good flocs. This requirement was implemented in the following way: The Process Controller was used under the "Increment Alum" setting, which starts the Alum Dose at 0 mg/L, and increments at 5 mg/L until it reaches a maximum of 40 mg/L. Each of the alum doses ran for a 30-minute period, or for about 3 times the residence time of the tank. After the completion of the test, data processing was performed to select the data from the last 10 minutes of each individual alum increment. The first 20 minutes of data were rejected because the residence time in the flocculator was 10 minutes, and the residence time in the tube settler was also about 10 minutes. Therefore, in order to get readings from the final turbidimeter that were representative of the alum dose that we were testing, we discarded the first 20 minutes of data at each alum dose. The outgoing turbidity (from turbidimeter 4) was then analyzed for each increment, and the alum dose achieving the lowest turbidity was selected for the second part of the experiment. h4. Profile Test Procedure \\ {float} {anchor:flow path top view}[!Pilot Plant^3.jpg|width=200px!|Pilot Plant^3.jpg] h5. Picture of the Flocculator set-up. {float} \\ \\ \\ \\ \\ |
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{float}
{anchor:flow path top view}[!Pilot Plant^picture1.jpg|width=200px!|Pilot Plant^picture1.jpg]
h5. Experimental Set-up of the Tube Settler Placement.
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The
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purpose
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of
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this
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experiment
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was
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to
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develop
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a
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profile
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of
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flocculation
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at
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different
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places
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along
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the
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flocculator.
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In
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order
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to
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do
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this,
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we
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moved
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the
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tube
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settlers
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to
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different
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points
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along
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the
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length
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of
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the
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flocculator
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and
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tested
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the
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turbidities
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of
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the
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water
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after
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it
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passed
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through
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the
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tube
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settler
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and
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reached
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the
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turbidimeter.
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In
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Experimental
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Set-up
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of
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the
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Tube
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Settler
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Placement
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above,
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you
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can
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see
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a
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schematic
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of
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the
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experimental
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set-up.
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A
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photograph
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of
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the
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same
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set-up
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is
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also
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shown.
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The
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experiment
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has
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three
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parts,
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A,
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B,
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and
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C,
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each
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lasting
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for
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45
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minutes.
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During
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the
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experiment,
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the
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location
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of
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tube
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settlers
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2
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and
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3
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were
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moved
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to
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different
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places
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along
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the
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flocculator
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as
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shown
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above.
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Turbidimeter
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1
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was
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always
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testing
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the
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incoming
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water,
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and
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turbidimeter
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4
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was
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always
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testing
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the
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turbidity
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of
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the
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water
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at
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the
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end
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of
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the
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flocculator
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(location
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4
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above).
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Along
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with
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moving
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tube
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settlers
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2
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and
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3,
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we
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emptied
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tube
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settler
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4
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of
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water
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between
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parts
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A,
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B,
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and
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C
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of
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the
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experiment.
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This
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is
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because
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when
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the
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tube
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settler
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is
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filling
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with
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water,
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plug-flow
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conditions
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exist
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in
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which
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velocity
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gradients
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cannot
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develop,
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and
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flow
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up
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the
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tube
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settler
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is
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more
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even.
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So,
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by
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emptying
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tube
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settler
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4
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of
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water,
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we
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ensured
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that
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the
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potential
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effects
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of
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this
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condition
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in
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the
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tube
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settler
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were
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even
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across
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all
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the
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tube
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settlers.
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Likewise,
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when
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performing
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the
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data
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analysis
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after
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the
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experiment,
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we
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found
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an
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increase
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in
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the
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turbidity
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to
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unreasonably
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high
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levels
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(on
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the
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order
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of
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100
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NTU)
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for
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about
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10
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minutes
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after
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moving
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the
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tube
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settlers.
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This
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was
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because
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the
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air
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in
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the
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tube
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settlers
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which
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was
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being
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pumped
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through
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the
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turbidimeters.
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Therefore,
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only
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the
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data
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at
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the
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end
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of
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each
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part
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of
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the
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experiment
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was
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used
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(approximately
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after
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10
...
minutes
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of
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running). The removal of the air can be easily observed in the data when the system appears to have reached a steady-state.
Results from Profile Testing of Tapered Flocculator Set-up Spring '08
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{float}
{anchor:flow path top view}[!Pilot Plant^picture2.jpg|width=200px!|Pilot Plant^picture2.jpg]
h5. Turbidity Profile with Average Incoming Turbidity at 2 NTU.
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{float}
{anchor:flow path top view}[!Pilot Plant^picture3.jpg|width=200px!|Pilot Plant^picture3.jpg]
h5. Turbidity Profile Ratio with Average Incoming Turbidity at 2 NTU.
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{float}
{anchor:flow path top view}[!Pilot Plant^picture4.jpg|width=200px!|Pilot Plant^picture4.jpg]
h5. Turbidity Profile with Average Incoming Turbidity at 7.5 NTU.
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{float}
{anchor:flow path top view}[!Pilot Plant^picture5.jpg|width=200px!|Pilot Plant^picture5.jpg]
h5. Turbidity Profile Ratio with Average Incoming Turbidity at 7.5 NTU.
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{float}
{anchor:flow path top view}[!Pilot Plant^2.jpg|width=200px!|Pilot Plant^2.jpg]
h5. Combined Turbidity Profiles from Three Experiments.
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In figure the Combined Turbidity Profiles from Three Experiments graph, it can be seen that a general trend exists in which the turbidities taken from the end of the tube settlers first spike at the beginning of the flocculator to about 2 times what they were in the incoming water. Then, they take a rapid dive to a fraction of the original turbidity. The most likely reason for this is the formation of flocs which are not large enough to settle in the tube settlers at the beginning of the flocculator but are large enough to greatly increase the deflecton of light in the turbidity meters. Later in the flocculator, larger flocs form, and these have a settling velocity of greater than 10 m/day. Therefore, they settle in the tube settlers and do not add to the turbidity in the turbidimeters.
It appears that a trend also exists towards the peak turbidity happening earlier in the flocculator when incoming turbidity was high, and later in the flocculator when turbidity was lower. This result suggests that the flocculator is more effective when turbidities are higher. This is consistent with the expectation that the collision rate is proportional to the floc volume fraction, φ floc. However, the settled water turbidity from the end of the flocculator was lower when incoming water was lower. The outgoing turbidity was 0.9 NTU, 1.3 NTU, and 1.8 NTU for the trials where the incoming turbidity was 2.0, 2.5, and 7.5 NTU, respectively. It is important to examine the absolute turbidity at the outgoing points because this is the parameter that determines the effectiveness of chlorine and overall safety of the water produced by our system. We need to achieve water that is consistently safe to drink because the reliability of our water treatment plants affects the health of our beneficiaries on a daily basis.
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{float}
{anchor:flow path top view}[!Pilot Plant^picture6.jpg|width=200px!|Pilot Plant^picture6.jpg]
h5. Turbidity Profile vs. Gθ.
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The graph above shows the flocculation profile versus Gθ as calculated with the model developed by Leslie Campbell of the Design Team. This model is as follows:
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Where totbaffle is the number of baffles before the testing plant, Qplant is the flow rate of 100 L/min, and FlocTankwidth was the width of the flocculator sections, or 12 inches. The other parameters were set as follows: Π cell = 2, kb =3, and the viscosity of water was 1 * 10 ^-6 m ^2/s.
By examining this graph, we can see that the total Gθ of this set-up was about 5000, which similar to the Gθ of the flocculator at Ojojona, which is about 4000.