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\begin_layout Title
Sedimentation Tank Hydraulics Team
\end_layout

\begin_layout Abstract
A floc blanket is a dense fluidized blanket of flocs that helps to reduce
 effluent turbitidy in the sedimentation tank by trapping other flocs.
 The geometry of the sedimentation tank is crucial in determining the extent
 of floc resuspension by the jet and hence floc blanket formation.
 To improve tank bottom geometry, nine experiments were conducted, each
 testing a different tank bottom geometry.
 The experiments were run in a 1/2 inch wide tank to model a thin slice
 of the full scale sedimentation tank.
 The geometry that resulted in the least sludge accumulation and therefore
 best floc resuspension was two 60 degree inserts leading to a semicircular
 trench 10 cm in diameter.
 We also provided initial designs and calculations for a floc weir to maintain
 the height of the floc blanket.
 A preliminary experiment was also conducted to evaluate the feasibility
 of our initial floc weir design.
 
\end_layout

\begin_layout Section
Introduction
\end_layout

\begin_layout Standard
The Sedimentation Tank Hydraulics Team seeks to incorporate a floc blanket
 into the AguaClara sedimentation tank by improving the tank bottom geometry.
 A floc blanket is a dense layer of suspended flocs that acts as a filter
 to trap particles before they reach the plate settlers, and one key condition
 for floc blanket formation is that the inlet jet continually resuspends
 settling flocs.
 Previous research done by Matthew Hurst has confirmed that floc blankets
 help to reduce effluent turbidity.
 In Spring 2011, the research team conducted experiments with a single insert
 and showed that the minimum angle of repose for the tank is around 24 degrees.
 In these experiments, the asymmetrical geometry of the experimental set
 up could be modified to model the actual sedimentation tank hydraulics
 more accurately.
 This summer, our team's objectives are to build on last semester's work
 by observing the sedimentation tank hydraulics with two inserts instead
 of one, to evaluate the effectiveness of a trench-shaped bottom geometry
 as compared to a flat bottom geometry, and to design a floc weir for the
 sedimentation tank.
 
\end_layout

\begin_layout Section
Methods
\end_layout

\begin_layout Standard
We used the same experimental apparatus and procedure as with the experiment
 documented in the Sedimentation Tank Team's Research Report 1 (Spring 2011).
 A thin 1/2
\begin_inset Quotes erd
\end_inset

 wide tank was used to model a thin slice of the full scale sedimentation
 tank.
 Figure 1 in The Sedimentation Team Final Research Report shows AutoCAD
 renderings of the side view and front view setups for the one half inch
 wide sedimentation tank and light panel system.
 A flow of 2 x 228 = 456 mL/min of aerated raw water containing 45 mg/L
 of alum and an average influent turbidity of 100 NTU made from a concentrated
 kaolinite clay stock regulated by the Process Controller was run through
 a tube flocculator before being expelled through a vertical downward-pointing
 jet suspended 10 cm from the bottom of the sedimentation tank.
 Images of the tank were acquired with a camera at fixed time intervals
 and recorded using the LabVIEW data acquisition software.
 The images were then compiled to make a video using 30 images per frame,
 thereby documenting the whole experiment.
 A schematic of turbid water flow through flocculator and sedimentation
 tank and data acquisition can be found as Figure 1 in the Sedimentation
 Tank Team's Research Report 1.
 
\end_layout

\begin_layout Standard
Our team ran ten experiments with either one or two inserts, with inserts
 of different angles of incline, and different widths of the tank bottom.
 For set ups with a single insert, the tank bottom width is defined as the
 distance between the inlet jet and the insert.
 For set ups with two inserts, the tank bottom width is the distance between
 the inserts, measured at where the inlet jet opening is located.
 Magnets were used to secure the position of the inserts.
 Images were acquired every 5 seconds in all experiments except in Experiment
 2 where the rate was 30 seconds per image.
 Table 1
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reference "tab:Inserts-and-tank"

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 summarizes the number of inserts, angle of incline, tank bottom geometry
 and number of seconds per image taken for each of the five experiments
 that were run.
 Figure 1 shows diagrams of the tank in the five experimental set ups.
 
\end_layout

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Inserts and tank bottom geometries used
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Diagrams of tank in the 10 experiments
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	filename 10 diagrams.jpg

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\begin_layout Section
Results and Discussion
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\begin_layout Subsection
Experiment 1: One 60 degree insert, 10cm-wide flat bottom 
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\begin_layout Standard
We modeled the bottom geometry of half of the actual sedimentation tank
 using a 60 degree insert and a flat bottom geometry.
 Initially, there was differential settling where the jet resuspended the
 settling flocs, causing them to flow upwards to the top of the tank and
 subsequently settle down as discrete particles, where they were again resuspend
ed.
 The flocs were spread out throughout the entire tank, but were much less
 dense on the left side of the tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp1_01"

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.We observed that the jet flowed horizontally along the flat bottom before
 moving at an angle upwards along the incline.
 About 1h into the experiment, the suspended flocs became denser and began
 to trap the upward flowing flocs that were resuspended by the jet
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp1_02"

\end_inset

.
 This transition to flocculated settling marked the beginning of floc blanket
 formation.
 After about 1h 15min, a floc blanket had formed in the tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp1_03"

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.
 The floc blanket height was approximately 65cm, the same height as the
 tank insert.
 With a 60 degree angle of repose and a flat bottom, there was no sludge
 buildup either on the bottom or on the slope, which implies that 60 degrees
 is greater than the minimum angle of repose.
 
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The tank before floc blanket formation.
 Flocs are much denser on the right hand side of the tank.
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The tank close to floc blanket formation.
 Flocs immediately suspended by the jet no longer reach the top of the tank.
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The tank after floc blanket formation.
 The height of the floc blanket is approximately the same as the height
 of the insert.
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\begin_layout Standard
Previous experimnets run with a 60 degree incline and a trench bottom resulted
 in a floc blanket forming at a much lower height and growing to the height
 of our experimental floc blanket.
 We suspect that a trench bottom allows for quicker formation of a stable
 floc blanket at a lower height because it causes vertical flow of jet water,
 allowing for immediate resuspension of flocs coming off the slope.
\end_layout

\begin_layout Standard
The actual AguaClara sedimentation tank bottom contains a 60 degree angle
 of repose and a flat bottom geometry, the same conditions that were tested
 in this experiment.
 While a floc blanket formed during our our experiment, a floc blanket does
 not currently form in the AguaClara sedimentation tanks.
 This may be due to the sludge drain located at the bottom of the current
 AguaClara sedimentation tanks, which is not contained in our experimental
 setup and can drain some flocs before they become resuspended.
 The formation of a floc blanket in our experimental apparatus may have
 also been affected by the simplifications used to model the actual plant.
 The experimental tank is only 1/2 inch thick, so the close proximity of
 the walls to the jet may have affected the motion of water and flocs in
 the tank.
 In an actual AguaClara tank, the jet is located in the middle of the tank,
 but since the experimental apparatus only contains half of the full bottom
 geometry, the jet is located on the side of the tank, which may affect
 the formation of a floc blanket.
 
\end_layout

\begin_layout Subsection
Experiment 2: One 60 degree insert, 10cm-wide flat bottom, run till failure
\end_layout

\begin_layout Standard
Experiment 2 was run for an extended period of time to observe the failure
 in the sedimentation tank.
 We define failure to have occured when the floc blanket breaks due to large
 head loss through the dense blanket, or when the floc blanket reaches the
 top of the sedimentation tank, or when the accumulated sludge hinders the
 inlet jet from effectively resuspending flocs.
 It is undesirable for the floc blanket to break or to grow to the top of
 the tank as this implies that a high concentration of flocs will be present
 in the effluent water, contaminating the whole batch of clean treated water
 that was previously collected.
 On the other hand, if the inlet jet is hindered by the accumulated sludge,
 the floc blanket is unlikely to be maintained.
 
\end_layout

\begin_layout Standard
The floc blanket formed quickly in about 45 minutes at a height of 40 cm
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp2_01"

\end_inset

.
 It then grew steadily and reached the top of the tank (90 cm) about 4h
 and 15 min later
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp2_02"

\end_inset

.
 There was a significant amount of sludge accumulation at the base of the
 insert, which formed a smaller angle of repose of about 20 degrees.
 The side of the accumulated sludge that was in contact with the jet had
 formed a curved, almost vertical surface that resembled a trench bottom
 geometry, and served to redirect the horizontal jet upwards.
 The floc blanket maintained its height for about 24 hours, after which
 the alum stock was depleted and the floc blanket thinned out as flocs and
 water were continually being drained from the top of the tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp2_03"

\end_inset

.
 After the alum stock was replenished, the floc blanket reformed and started
 to grow again
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp2_04"

\end_inset

.
 
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 2_01.jpg
	scale 50

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Formation of floc blanket
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp2_01"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 2_04.jpg
	scale 50

\end_inset


\begin_inset Caption

\begin_layout Plain Layout
Floc blanket reaches top of tank 5h into the experiment
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp2_02"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 2_05.jpg
	scale 50

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Floc blanket thins out after alum stock runs out
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp2_03"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 2_06.jpg
	scale 50

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Floc blanket reforms after alum stock is replenished
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp2_04"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
In the video of Experiment 2, 1 second in the movie corresponds to 15 minutes
 of experiment time.
 We calculated the the average growth rate of the floc blanket to be about
 0.2cm per minute.
 Assuming that the height of the plate settlers above the tank bottom in
 the actual sedimentation tank is about 70cm and that the floc blanket forms
 at an initial height of 40cm, this means that without a floc weir, failure
 will occur in about 2.5h after the formation of the floc blanket, or about
 3h 15min from the start of flow into the tank.
 The floc blanket maintained its height for about 24 hours, after which
 the alum stock was depleted and the floc blanket thinned out as flocs and
 water were continually being drained from the top of the tank.
 
\end_layout

\begin_layout Standard
Although Experiments 1 and 2 were run under the same experimental conditions,
 the floc blanket in Experiment 2 formed at a lower height than that in
 Experiment 1.
 This is possibly due to errors in alum stock concentration.
 The tube flocculator was also not cleaned out after Experiment 1, which
 may have caused residue sludge to be pumped into the tank during Experiment
 2.
 
\end_layout

\begin_layout Subsection
Experiment 3: Two 60 degree inserts, 20cm-wide flat bottom 
\end_layout

\begin_layout Standard
Experiment 3 modeled the bottom of the sedimentation tank more accurately
 by placing the inlet pipe in the middle of a pair of symmetrical 60 degree
 inserts.
 Initially, flocs were more concentrated on the right side of the tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp3_01"

\end_inset

.
 They were unable to flow by the inlet pipe to the left side, which is a
 source of error in this experiment.
 About 50 minutes into the experiment, a small 30cm high floc blanket is
 formed but never really grows in height 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp3_02"

\end_inset

.
 Sludge continues to build up on the tank bottom to form a smaller angle
 of repose of about 25 degrees leading into a trench
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp3_03"

\end_inset

.
 After 5h, a circular trench is formed in the region surrounding the jet
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp3_04"

\end_inset

.
 
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 3_01.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Differential settling predominantly on right side of tank
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp3_01"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 3_02.jpg
	scale 50

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Formation of small floc blanket
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp3_02"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 3_03.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Sludge continues to build up forming a smaller angle of repose and trench
 bottom geometry
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp3_03"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 3_05.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Circular trench forms around jet
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp3_04"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Experiment 4: Two 30 degree inserts, 20cm-wide flat bottom 
\end_layout

\begin_layout Standard
No clear floc blanket was formed in this experiment and most of the sludge
 accumulated on the inserts.
 The initial flocs that were pumped into the tank were very large
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp4_01"

\end_inset

, which is probably the result of a dirty tube flocculator that was discharging
 large flocs and sludge into the tank.
 This is a significant source of error in this experiment and could be the
 cause for the absence of a floc blanket because the jet is not strong enough
 to keep large flocs in suspension.
 Flocs accumulated unevenly on both inserts, forming two separate angles
 of repose leading up to a trench
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp4_02"

\end_inset


\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp4_03"

\end_inset

.
 It was only at 5h into the experiment that there was a slight hint of a
 floc blanket forming
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp4_04"

\end_inset

.
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 4_01.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Very large initial flocs 
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp4_01"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 4_02.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Sludge accumulation but no floc blanket formed
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp4_02"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 4_03.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
No clear angle of repose after 4h
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp4_03"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 4_04.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Slight hint of a floc blanket after 5h
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp4_04"

\end_inset

 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Experiment 5: Two 60 degree inserts, 20cm-wide trench bottom
\end_layout

\begin_layout Standard
The distribution of flocs in this experiment was more even as compared to
 Experiment 3
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp5_01"

\end_inset

, and this gave rise to the formation of an even floc blanket about 45min
 into the experiment
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp5_02"

\end_inset

.
 In contrast to Experiment 3, there was little sludge accumulation at the
 bottom of the trench for the first 2h 15min because the upward flowing
 jet was able to resuspend the flocs as they reached the tip of the insert.
 However after 2h 15min, the jet was no longer able to resuspend the flocs
 that were sliding down the incline and a second smaller trench was formed
 within the larger trench
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp5_03"

\end_inset

.
 The floc blanket grew slowly at a rate of about 0.8cm per minute and had
 not reached the top of the tank after 5h.
 More sludge accumulated in the trench, and it is likely that a circular
 trench encompassing the jet (as in Experiment 3) would be observed if the
 experiment was left to run
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp5_04"

\end_inset

.
 
\end_layout

\begin_layout Standard
From our experiments with two inserts, the trench bottom geometry is more
 efficient in forming and maintaining a floc blanket as compared to a flat
 bottom geometry.
 However, sludge still accumulated within the trench, suggesting that the
 current spacing between the inserts (20cm) is too wide for the jet to resuspend
 larger flocs when the floc blanket increases in density.
  
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 5_01.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Even distribution of flocs on both sides of inlet pipe
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp5_01"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 5_03.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Even formation of floc blanket
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp5_02"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 5_04.jpg

\end_inset


\begin_inset Caption

\begin_layout Plain Layout
Slight accumulation of sludge, forming a smaller trench within the existing
 trench bottom
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp5_03"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 5_05.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
More sludge accumulation and floc blanket growth after 5h
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp5_04"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Experiment 6: Two 30 degree inserts, 20cm-wide trench bottom
\end_layout

\begin_layout Standard
A tank with 30 degree inserts resulted in the formation of a small floc
 blanket in about an hour
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp6_01"

\end_inset

.
 Similar to Experiment 5, there was significant sludge accumulation that
 formed a smaller semicircular trench within the existing rectangular trench.
 However, about 15 minutes after formation of the floc blanket, there was
 a sudden increase in the density of the floc blanket
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp6_02"

\end_inset

, followed by a violent eruption of flocs when the blanket broke
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp6_03"

\end_inset

.
 This is likely due to an error with the apparatus, such as the raw water
 tank running out of water.
 The momentary pause in the inlet jet allows the flocs to settle, and then
 when bubbles are pumped into the tank, they generate turbulence and large
 eddies cause flocs to drain out at the top of the tank.
 Even though the floc blanket reformed at about 2.5h into the experiment
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp6_04"

\end_inset

, there was minimal growth over the next 2.5h, and most of the flocs settled
 as sludge, forming an angle of repose of about 30 degree on the left insert
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp6_05"

\end_inset

.
 The results from this experiment and Experiment 4 show that an angle of
 incline of 30 degrees is less desirable than an angle of 60 degrees, because
 only a small floc blanket is formed and does not grow significantly.
 
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 6_01.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Inital formation of the floc blanket
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp6_01"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 6_02.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Sudden increase in density of the floc blanket 
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp6_02"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 6_03.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Breaking of the floc blanket
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp6_03"

\end_inset

 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 6_04.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Floc blanket reforms 1h after breaking
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp6_04"

\end_inset

 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 6_05.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
A smaller trench formed
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp6_05"

\end_inset

 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Experiment 7: Two 60 degree inserts, 10cm-wide trench bottom 
\end_layout

\begin_layout Standard
In this experiment we halved the width of the trench from 20cm to 10 cm.
 The floc blanket formed at about 40 minutes and grew steadily in height
 and density until it reached the top of the tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp7_01"

\end_inset

.
 There was less sludge accumulation in the trench as compared to Experiment
 5 where the trench was 20cm wide, and the sludge formed a slighly curved
 surface beneath the pipe
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp7_02"

\end_inset

.
 Therefore, a narrower trench bottom allows for better floc blanket formation
 because more flocs are resuspended and less end up settling on the tank
 bottom.
 
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 7_01.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Floc blanket formed in about 40 minutes
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp7_01"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 7_02.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Very thick floc blanket 5h into experiment, some sludge accumulation in
 trench
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp7_02"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Experiment 8: Two 60 degree inserts, 20cm-wide semicircular trench bottom
\end_layout

\begin_layout Standard
In this experiment, we changed the rectangular trench bottom to a semicircular
 one because this is the geometry that is consistently formed in previous
 experiments.
 We expected that a semicircular trench would result in better floc resuspension
 because less energy is lost by the jet when it changes direction.
 The floc blanket formed in about 50 minutes
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp8_01"

\end_inset

.
 For the next hour, there was minimal growth and significant sludge accumulation
 on the left side of the trench, such that the width of the trench was narrowed
 to about 10cm and the jet was essentially diverted to the right side of
 the tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp8_02"

\end_inset

.
 After that, the floc blanket started to grow steadily.
 This result suggests that the width of the tank is too wide for the current
 jet diameter and velocity.
 
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 8_01.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Floc blanket formed in about 50 minutes
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp8_01"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 8_03.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Jet was diverted to the right side of the tank
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp8_02"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Experiment 9: Two 60 degree inserts, 10cm-wide semicircular trench bottom
\end_layout

\begin_layout Standard
With a narrower semicircular trench geometry, a floc blanket formed quickly
 and steadily grew to the top of the tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp9_01"

\end_inset

.
 Throughout the experiment, there was hardly any sludge accumulation and
 flocs were continually being resuspended.
 Therefore, this was the best bottom geometry out of all the experiments
 we conducted thus far.
 
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 9_01.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Floc blanket forms within 40 minutes
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp9_01"

\end_inset

 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 9_02.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
After 5h there is hardly any sludge accumulation
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp9_02"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Section
Floc Weir and Hopper Design
\end_layout

\begin_layout Standard
The purpose of a floc weir and floc hopper is to maintain the height of
 the floc blanket in the sedimentation tank.
 Ideally, the floc blanket will be located in the lower part of the sedimentatio
n tank below the plate settlers.
 It is undesirable for the floc blanket to grow in height until it reaches
 the plate settlers, as this is likely to result in poorer effluent quality.
 
\end_layout

\begin_layout Standard
Our current design is a sharp crested weir placed at the far end of the
 sedimentation tank with an adjacent V-shaped floc hopper to collect the
 excess flocs
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Proposed-floc-weir"

\end_inset

.
 When the height of the floc blanket exceeds the height of the weir, excess
 flocs will be collected in the hopper, and the accumulated sludge can be
 removed by opening the sludge drain.
 
\end_layout

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

\begin_layout Plain Layout

\end_layout

\begin_layout Plain Layout
\begin_inset Graphics
	filename floc hopper full tank.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Proposed floc weir and floc hopper in full size sedimentation tank
\begin_inset CommandInset label
LatexCommand label
name "fig:Proposed-floc-weir"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
As we assume the floc blanket to be uniform in all directions, we have come
 up with a similar design for a floc weir in our experimental tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Experimental floc weir"

\end_inset

.The tank is set up with either one or two inserts such that there is a small
 gap next to the leftmost insert to collect excess flocs.
 The insert itself acts as the floc weir and the empty space a simplified
 floc hopper.
 Once a floc blanket has formed and grows to the height of the insert, excess
 flocs are expected to spill over into the hopper because they are denser
 than water.
 The collected flocs can be removed via an outlet pipe at a rate Qout.
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename floc hopper no gate.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Proposed floc weir and hopper in experimental set up
\begin_inset CommandInset label
LatexCommand label
name "fig:Experimental floc weir"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Experiment 10: One 60 degree insert, 10cm flat bottom
\end_layout

\begin_layout Standard
We tested the concept of using the insert as a floc weir by running an experimen
t with a single 60 degree insert spaced 5 cm apart from the left wall to
 create a floc hopper.
 No outlet pipe was used in this experiment.
 As expected, the floc blanket formed and grew to the height of the insert
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp10_01"

\end_inset

, after which the flocs spilled over the tip of the insert into the space
 behind and the height of the floc blanket remained constant
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp10_02"

\end_inset

.
 Sludge accumulated slowly in the floc hopper, but this rate of accumulation
 was slower than expected because there was also a significant loss of flocs
 to the hole in the middle of the insert
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Exp10_03"

\end_inset

.
 Nevertheless, the results show that this design for a floc weir is feasible,
 and further experiments can be conducted without having to greatly modify
 our current apparatus.
\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 10_01.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Floc blanket forms and slowly grows to the top of the insert
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp10_01"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 10_02.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Flocs spill over the top of the insert into the hopper 
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp10_02"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

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

\begin_layout Plain Layout
\begin_inset Graphics
	filename Exp 10_03.jpg

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Sludge accumulates slowly in the hopper, but mass is not conserved due to
 flocs leaking into the pole within the insert
\begin_inset CommandInset label
LatexCommand label
name "fig:Exp10_03"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Subsection
Parameters of Floc Weir and Hopper 
\end_layout

\begin_layout Subsubsection*
Height of Floc Weir
\end_layout

\begin_layout Standard
Based on previous research by Hurst et al
\begin_inset CommandInset citation
LatexCommand cite
key "Hurst et al. (2010)"

\end_inset

, the overall particle removal efficiency improves with increasing floc
 blanket depth up to 45cm.
 This can be the initial height of our floc weir, which will ensure the
 highest possible removal efficiency for the smallest floc blanket, thereby
 saving space in the sedimentation tank.
 The floc weir should also be higher than the height of the floc blanket
 when it first forms.
 
\end_layout

\begin_layout Subsubsection*
Volume of Floc Hopper
\end_layout

\begin_layout Standard
The volume of sludge collected in 1 day can be estimated by 
\begin_inset Formula $V_{sludge}=\frac{C_{flocblanket}\cdot Q_{weir}\cdot t}{\rho_{sludge}}$
\end_inset

 , where 
\begin_inset Formula $Q_{weir}$
\end_inset

 is the flow rate of flocs over the weir and can be estimated by the growth
 rate of the floc blanket, and 
\begin_inset Formula $\rho_{sludge}$
\end_inset

 is the density of sludge.
 To determine the appropriate size of the floc hopper, we impose the constraint
 that the hopper needs to be emptied at most once a day.
 Assuming that the walls of the hopper (in the full sized tank
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Proposed-floc-weir"

\end_inset

)are at an angle 
\begin_inset Formula $\theta$
\end_inset

 and runs the breadth of the sedimentation tank, and W is the width of the
 hopper, the maximum volume of sludge that can be collected in one day is
\end_layout

\begin_layout Standard
\begin_inset Formula $V_{max}=\frac{H^{2}}{tan\theta}W$
\end_inset

 or 
\begin_inset Formula $H=\sqrt{\frac{V_{max}\cdot tan\theta}{W}}$
\end_inset


\end_layout

\begin_layout Standard
Therefore, an additional height constraint on the floc weir is 
\begin_inset Formula $H=\sqrt{\frac{C_{flocblanket}\cdot Q_{weir}\cdot t\cdot tan\theta}{W\cdot\rho_{sludge}}}$
\end_inset

.
 
\end_layout

\begin_layout Section
Future Work
\end_layout

\begin_layout Itemize
Determine the effects of further reducing the diameter of the semicircular
 trench on sludge accumulation and floc blanket formation.
 
\end_layout

\begin_layout Itemize
Change the size of the inlet pipe to more accurately reflect the diameter
 of the actual drop tube, and so that flocs are able to easily pass from
 one side of the tank to the other.
 
\end_layout

\begin_layout Itemize
Come up with an empirical relationship between the ideal diameter of the
 semicircular trench to the diamter of the inlet pipe.
 
\end_layout

\begin_layout Itemize
Determine the flow rate needed to drain sludge from the floc hopper in order
 to keep the system running at steady state without any sludge accumulation
 on the tank bottom.
 
\end_layout

\begin_layout Bibliography
\labelwidthstring References
\begin_inset CommandInset bibitem
LatexCommand bibitem
key "Hurst et al. (2010)"

\end_inset

Hurst et al.
 (2010) Parameters affecting steady-state floc blanket performance.
 
\end_layout

\end_body
\end_document
