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\begin_layout Title
Sedimentation Tank Hydraulics
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status open

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This team has potential for the EPA P3 competition and should consider a
 submission in the fall of 2011
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\begin_layout Abstract
The goal of this research is to evaluate sedimentation tank bottom geometry,
 jet location, and the design requirements for a floc hopper in an AguaClara
 sedimentation tank.
 Inlet jet geometry along the bottom of the sedimentation tank is critical
 in the resuspension of flocs.
 The inlet end of the sedimentation tank needs to be redesigned to re suspend
 flocs.
 A floc weir will be needed to set the upper limit of the floc blanket level
 and a floc hopper will be needed to consolidate the wasted flocs.
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students 3 MT
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\begin_layout Labeling
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skills fabrication, experimentation, fluids, process controller
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\begin_layout Section
Sedimentation tank geometry
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\begin_layout Standard
AguaClara sedimentation tanks have evolved rapidly from 
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\begin_layout Enumerate
flat bottom with 3 large pipe inlets (Ojojona) 
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\begin_layout Enumerate
sloped bottom with 3 large pipe inlets (Marcala 1 and Tamara)
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\begin_layout Enumerate
sloped bottom with inlet ducts under the sloped bottom (Cuatro Comunidades)
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\begin_layout Enumerate
sloped bottom with simple inlet manifold (Agalteca)
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\begin_layout Enumerate
sloped bottom with inlet manifold with diffuser drop tubes (Marcala 2)
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\begin_layout Standard
The evolution of the sedimentation tank design continues as we learn more
 about what is required to produce floc blankets and as we improve how we
 handle the sludge.
 The focus of our current research is to carefully design the interaction
 between the flocs that settle on the bottom slopes as they return to the
 central valley of the sedimentation tank and the jets produced by the diffuser
 drop tubes.
 The design of the interaction between the settled flocs and the inlet jets
 is critical because it is the jets that re-suspend the settled flocs and
 thus create the floc blanket.
 As we improve tank geometry to reliably create floc blankets it will necessary
 to also control the depth of the floc blanket (with a floc blanket weir)
 and use a floc hopper to provide time for the wasted flocs to consolidate
 or dewater to reduce the amount of water that must be wasted with the resulting
 sludge.
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\begin_layout Standard
The manifold currently doesn't have diffuser drop tubes below and behind
 the elbow in the inlet manifold.
 It may be critical for rapid floc blanket formation to develop a method
 of fabricating an inlet manifold with diffuser pipes that extend all the
 way to the end of the tank or it may be possible to add a slope to return
 flocs to the first drop tube.
 We need a method to assess which approach should be used and we should
 implement these changes in the design tool as soon as possible.
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\begin_layout Standard
We have preliminary evidence that floc blanket formation and performance
 is negatively influenced by any consolidation of the flocs before resuspension
 by the jet.
 It would be useful to confirm this observation with overall performance
 data for a sedimentation tank including residual turbidity after plate
 (or tube) settlers.
 This will require setting up the tube settlers on the 2D sedimentation
 tank apparatus (Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:2D-sedimentation-tank"

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 and 
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LatexCommand ref
reference "fig:Schematic-of-apparatus"

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).
 The tube settler effluent turbidity should be compared for different bottom
 and jet geometries to see if tank geometry has a significant influence
 on overall performance.
 We are particularly interested in comparing bottom geometries that cause
 floc consolidation prior to resuspension and bottom geometries that resuspended
 flocs without floc consolidation.
 If floc consolidation is shown to negatively influence performance then
 the AguaClara sedimentation tank bottom geometry should be redesigned.
 The experimental conditions could be 100 NTU raw water and 1 mm/s up flow
 velocity in the sedimentation tank.
 The coagulant should be PACl and the appropriate dose can be supplied by
 the Tube Floc team.
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wide false
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status open

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\begin_inset Graphics
	filename 2D sed tank front view.png

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\begin_inset Caption

\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:2D-sedimentation-tank"

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2D sedimentation tank apparatus
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wide false
sideways false
status open

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\begin_inset Graphics
	filename 2d Sed tank complete schematic.png

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\begin_layout Plain Layout
\begin_inset CommandInset label
LatexCommand label
name "fig:Schematic-of-apparatus"

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Schematic of apparatus including turbidimeters, camera, source water, flocculato
r, and sedimentation tank.
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\begin_layout Section
Floc hopper geometry
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\begin_layout Standard
The parameters of interest are the ratio of the plan view area of the floc
 hopper to the plan view area of the rest of the sedimentation tank, the
 volume of the floc hopper, and possible the angle of the bottom of the
 hopper.
 We are also interested in knowing how the geometry of the floc hopper influence
s the required sludge flow rate.
 The depth of flow and flow rate over the floc hopper weir is also of interest.
 The depth of flow over the floc hopper weir is not expected to be significant
 design constraint.
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\begin_layout Standard
The critical design constraint is expected to be during high turbidity events
 when the floc volume fraction is high and hence the flow of flocs into
 the floc hopper will be the greatest.
 The fractal flocculation model predicts that at 500 NTU the floc volume
 fraction is 0.08.
 Thus the flow over the weir would be 
\begin_inset Formula $0.08Q_{SedBay}$
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.
 The floc volume fraction is proportional to the turbidity for high turbidities
 and thus at 1000 NTU the floc volume fraction is 0.16.
 Without consolidation of the flocs it would be necessary to waste 16% of
 the flow during a 1000 NTU event.
 AguaClara plants have already treated water in excess of 700 NTU and so
 it would be reasonable to design the floc hopper to handle a 1000 NTU event.
 
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\begin_inset Float figure
wide false
sideways false
status open

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\begin_inset Graphics
	filename floc weir double slope.png
	width 12cm

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\begin_layout Plain Layout
\begin_inset Caption

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Preliminary sketch of a floc hopper with a double bottom slope.
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\begin_inset CommandInset label
LatexCommand label
name "double bottom slope"

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\begin_layout Standard
A floc hopper can be installed in the 2d sedimentation apparatus (Figure
 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Schematic-of-apparatus"

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).
 You could start with a floc hopper that occupies 15% of the plan view area
 of the sedimentation tank.
 The bottom slope could be very steep so that the sludge hopper extends
 all the way to the bottom of the sedimentation tank.
 A peristaltic pump can be used to remove sludge from the very bottom of
 the floc hopper.
 The flow rate of the pump can be slowly varied and the depth of the flocs
 in the floc hopper can be measured.
 This will give a relationship between the required plan view area of the
 floc hopper and the corresponding required sludge wasting rate.
 The steady state depth of sludge in the floc hopper will increase as the
 sludge wasting rate decreases.
 There may be problems with this experimental method because the sludge
 may consolidate so well that the pump won't be able to remove it.
 
\end_layout

\begin_layout Standard
The plan view area and time required for floc consolidation is not easily
 estimated.
 The fractal flocculation model predicts that at 1000 NTU the floc volume
 fraction is 0.16.
 Thus the flow over the weir would be 
\begin_inset Formula $0.16Q_{SedBay}$
\end_inset

.
 Does this mean that the area of the floc hopper should be about 16% of
 the sedimentation tank area? We need some modeling work here to understand
 what controls this consolidation process.
 A literature review would be useful and experimental work may be needed.
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\begin_layout Standard
The goal is to develop an understanding of how floc consolidation works
 and to determine the top width of the floc hopper.
 
\end_layout

\begin_layout Enumerate
Z.SedFlochopperWeir - The height of the top of the floc hopper weir that
 will then set the depth of the floc blanket.
 It is probably best if the floc blanket doesn't reach the bottom of the
 plate settlers and thus we may want to set the top of the floc hopper weir
 to be approximately 10 cm below the bottom of the plate settlers.
\end_layout

\begin_layout Enumerate
AN.SedFlochopper - The angle of the floc hopper could be 60º or perhaps as
 low as 45º.
 The goal is to be able to have the sludge slide down the incline easily.
 It may be best to make this 60º to reduce the risk that sludge will accumulate
 and not slide into the drain.
\end_layout

\begin_layout Enumerate
ND.SedFlochopperValve - Ten state standards suggests that the minimum diameter
 for any sludge valve should be 3 inches.
 That seems rather large given what this valve has to handle.
 I believe we have used 2 inch valves on sedimentation tanks and they performed
 well.
 The flow rate for this valve will be very low.
 We should estimate the sludge flow rate.
 My intuition is that the valve should be at least 1 inch in diameter so
 that it won't clog too easily.
 In normal operation the plant operator may leave the valve open slightly
 with a low continuous flow rate discharging the sludge as it accumulates
 and consolidates in the floc hopper.
\end_layout

\begin_layout Enumerate
L.SedFlochopper - distance between the drain end wall of the sedimentation
 tank and the floc hopper weir.
 This would be estimated based on the floc hopper plan view area required
 to consolidate the flocs.
\end_layout

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