*** 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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h5. Figure 1: Front of a sedimentation tank at the Cuatro Communidades plant
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h2. |
Introduction
...
and
...
Objectives
...
The
...
Four
...
Communities
...
plant
...
was
...
designed
...
with
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shallower
...
sedimentation
...
tanks
...
than
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those
...
of
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Ojojona
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and
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Tamara.
...
To
...
determine
...
the
...
effects
...
of
...
the
...
design
...
changes
...
the
...
plant
...
effluent
...
turbidity
...
was
...
compared
...
to
...
the
...
turbidity
...
coming
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out
...
of
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a
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tube
...
settler
...
at
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the
...
end
...
of
...
the
...
flocculator.
...
The
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tube
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settler
...
was
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designed
...
to
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act
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as
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a
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model
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sedimentation
...
tank.
...
If
...
the
...
sedimentation
...
tanks
...
were
...
working
...
efficiently,
...
the
...
plant
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effluent
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turbidity
...
should
...
have
...
been
...
equal
...
to
...
or
...
less
...
than
...
the
...
turbidity
...
coming
...
out
...
of
...
the
...
tube
...
settler.
...
Additionally,
...
flocs
...
were
...
observed
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to
...
be
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settling
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out
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in
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the
...
channel
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carrying
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water
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from
...
the
...
flocculator
...
to
...
the
...
sedimentation
...
tanks
...
and
...
very
...
few
...
were
...
reaching
...
the
...
second
...
tank.
...
To
...
determine
...
what
...
effect,
...
if
...
any,
...
the
...
uneven
...
distribution
...
of
...
flocs
...
had
...
on
...
the
...
two
...
tanks,
...
the
...
effluent
...
turbidities
...
from
...
both
...
tanks
...
were
...
compared.
...
Samples
...
were
...
taken
...
from
...
within
...
the
...
effluent
...
launders
...
of
...
both
...
tanks.
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{float:right|border=2px solid black|width=240px} h2. Methods To compare ideal sedimenation with actual sedimentation in the plant, a tube settler was placed at the end of the flocculation tank (Figure ##). The [tube settler design] mimicked the design of the lamella in the sedimentation tanks except that it was an isolated systems. The effluent from the tube settler was compared to the effluent from the sedimentation tanks. Turbidity measurements were taken in twenty minute or half hour intervals over the course of several hours and the average. h2. Results and Discussion The results of each test of the effluent from both the tube settler and the sedimentation tanks are shown below in figure ##. The effluent turbidity is compared to the incoming raw water turbidity. The effluent turbidity from the sedimentation tanks and the tube settlers were fairly similar at low incoming turbidities although the tube settlers generally performed better. Most of the tests began in the morning and the incoming plant turbidity was decreasing throughout the day. This decrease was measured first in the tube settlers biasing the tube settler measurements lower than the sedimentation tank measurements. When the raw water turbidity was high, about 135 NTU, there was about a one NTU difference between the sedimentation tanks and the tube settler effluent. Perhaps the sedimentation tanks do not work as well when the incoming turbidity is higher. The would support the conclusions from the ....[Cuatro Communidades Floc Blanket Research]. However, there is not enough information from the few tests above to conclusively say this.... The tests were taken when the plant was performing well- the effluent close to or below 5 NTU. The test would be more informative when the plant was not working well but flocs were forming. In this case the test could show whether the error was in the flocculator or the sedimentation tanks. -no difference between two sed tanks. ...In the lowest incoming turbidity trial sedimentation tank 2 was shut off. !tubesettler1.jpg|width=240px! h5. Figure 2: Tube settler {float} |
Methods
To compare ideal sedimenation with actual sedimentation in the plant, a tube settler was placed at the end of the flocculation tank (Figure 2). The tube settler design (See Methods Section) mimicked the design of the lamella in the sedimentation tanks except that the tube settler was a much simpler system. The effluent from the tube settler was compared to the effluent from the sedimentation tanks. Turbidity measurements were taken in twenty minute or half hour intervals over the course of several hours and averaged when the influent, effluent, and alum dose were relatively constant.
Results and Discussion
The results of each test of the effluent from both the tube settler and the sedimentation tanks are shown below in figure 3. The effluent turbidity is compared to the incoming raw water turbidity.
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h5. Figure 3
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The effluent turbidity from the sedimentation tanks and the tube settlers were fairly similar at all incoming turbidities although the tube settlers generally performed better. The largest difference, 1 NTU between the two was at a raw water turbidity of 135 NTU. Most of the tests began in the morning and the incoming plant turbidity was decreasing throughout the day. This decrease was measured first in the tube settlers biasing the tube settler measurements lower than the sedimentation tank measurements.
There was very little difference between the two sedimentation tanks. In the other trials, one tank does not perform consistently better or worse.
The tests were taken when the plant was performing well- the effluent close to or below 5 NTU. The test would be more informative when the plant was not working well but flocs were forming. In this case the test could show whether the flocculator or the sedimentation tanks were performing poorly.