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\begin_body

\begin_layout Title
Floc Hopper
\end_layout

\begin_layout Abstract
We have evidence that floc blankets are forming in the sedimentation tanks
 at Marcala, Honduras.
 The floc blankets grow too deep and flocs begin to rise through the plate
 settlers.
 We need a method to control the height of the floc blankets.
 The proposed solution is a floc hopper at the drain end of the sedimentation
 tank.
 The floc hopper has two functions.
 It sets the depth of the floc blanket in the sedimentation tank and it
 consolidates the flocs prior to wasting with the floc hopper valve.
 Floc consolidation is important because this reduces the volume of water
 that is wasted.
 The design of the AguaClara sedimentation tank must be revised to incorporate
 a floc weir.
\end_layout

\begin_layout Labeling
\labelwidthstring 00.00.0000
students 2 FT (This is a design team)
\end_layout

\begin_layout Section
Introduction
\end_layout

\begin_layout Standard
The floc hopper (see Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "floc hopper sketch"

\end_inset

) must be placed at the end of the sedimentation tank that is closest to
 the drain channel so the floc hopper drain can also discharge into the
 drain channel.
 The floc hopper design choices are:
\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

\begin_layout Standard
The plan view area required for floc consolidation is not yet known (by
 AguaClara...).
 The sedimentation tank hydraulics research team will be investigating this
 parameter using laboratory experiments.
 The consolidation process is sufficiently complex that this may not be
 an easy parameter to obtain by modeling.
 The best approach may be to build a floc hopper either in the plate settler
 spacing apparatus or in Matt Hurst's sedimentation tank slice.
 The required area will be proportional to the floc blanket production rate.
\end_layout

\begin_layout Standard
It is important that the design be checked to ensure that it is constructable
 and that a human can clean out the floc hopper from inside the sedimentation
 tank if necessary.
 
\end_layout

\begin_layout Standard
The sedimentation tank design parameter V.UpBod should probably be increased
 to closer to 1 mm/s and then the effective area of the bottom of the sedimentat
ion tank should NOT include the area designated for the floc hopper.
 This will require modification of the sedimentation tank design algorithm.
\end_layout

\begin_layout Standard
The maximum distance between the drain end wall of the sedimentation tank
 and the floc hopper weir is the distance to the first plate settler.
 This space up to the first plate settler is currently poorly utilized and
 thus could easily all be used by the floc hopper.
 If the floc hopper length causes the angle of the floc hopper to become
 too shallow, then the floc hopper could have a bottom that slopes in all
 four directions.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename floc weir.png
	width 16cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Preliminary sketch of a floc hopper with a bottom sloping to the drain end
 wall.
\end_layout

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "floc hopper sketch"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
The double bottom slope (see Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "double bottom slope"

\end_inset

) is used to extend the length of the floc hopper without using a bottom
 slope that is too shallow.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\begin_inset Graphics
	filename floc weir double slope.png
	width 16cm

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Preliminary sketch of a floc hopper with a double bottom slope.
\end_layout

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "double bottom slope"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
There may be other geometries for the design of the floc hopper.
 For example, the floc hopper weir could be a thin vertical wall made from
 removable ferrocement 
\begin_inset Quotes eld
\end_inset

boards
\begin_inset Quotes erd
\end_inset

.
 The bottom slope could be longest on the drain wall end of the floc hopper.
 
\end_layout

\begin_layout Standard
The two drain valves (sedimentation tank drain and floc hopper drain) need
 to be positioned so that both are easy to use.
 They can't be aligned vertically because we may want to have valve control
 rods extending through the platform to each of these valves.
 Thus the valves must be offset.
 
\end_layout

\begin_layout Standard
It would be great if the operator could see the depth of sludge in the floc
 hopper and the depth of the floc blanket in the bottom of the sedimentation
 tank.
 A submersible LED could be lowered into the sedimentation tank and the
 depth of light extinction could be used to estimate the location of the
 top of the sludge in the floc hopper.
 It may be possible to cut out a small opening in the first plate settler
 to provide a space to lower a light into the floc hopper.
\end_layout

\begin_layout Section
L.SedFlochopper considerations
\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.
\end_layout

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\end_document
